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ortheast FISheries Science Center

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sciences.
NOAA Technical Report NMFS 139

A Technical Report of the Fishery Bulletin

Seasonal, Horizontal, and Vertical

Distribution ofPhytoplankton

Chlorophyll a in the Northeast

U.S. Continental ShelfEcosystenl

John E. O'Reilly

Christine Zctlin

November 1998

U.S. DepartInent ofConunerce

Seattle, Washington
Suggested reference

O'Reilly,]ohn E., and Christine Zetlin. Seasonal, horizontal, and vertical

distribution of phytoplankton chlorophyll a in the northeast U.S. continental

shelf ecosystem. U.S. Dep. Commer., NOAA Tech. Rep. NMFS 139, 119 p.

Purchasing additional copies

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or microfiche from the National Technical Information Service, 5285

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recommend, or endorse any proprietary product or proprietary material

mentioned in this publication. No reference shall be made to NMFS, or

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recommends, or endorses any proprietary product or proprietary

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directly or indirectly the advertised product to be used or purchased

because of this NMFS publication.
Contents

Introduction

Description of Study Area

Gulf ofMaine

Georges Bank

Middle Atlantic Bight

Methods

Data Sources

Sampling

Measurement ofChlorophyll a

Computations

Contouring

Standard Sampling Stations (Tiles)

Statistical Subareas

Results and Discussion

Range ofChlorophyll Concentrations

Size Composition of Phytoplankton

Horizontal Distribution ofChlorophyll

Horizontal Distribution ofNetplankton/Nanoplankton

Percent Phaeopigment

Recurring Patterns in Phytoplankton Biomass

Cross-ShelfChlw Gradient

Recurring Patterns in Phytoplankton Size Composition

Annual Cycle ofChlw

Vertical Distribution ofChlorophyll

Middle Atlantic Bight

Georges Bank

Gulf ofMaine

Winter-Spring Bloom

The Fate ofWS-bloom

Stratified Season: Subsurface Chlorophyll Maxima

Seasonal Changes in Subsurface Maxima

Spatial Distribution of Subsurface/Surface Ratio

Fall Bloom

Sununary

Ackno1Nledgnnents

Citations

III

2

4

4

6

7

8

8

10

10

11

11

12

12

16

16

16

17

21

23

25

26

28

28

32

37

40

42

44

44

46

47

47

54

55

57

57
APPENDIX A

Figure A 1. Locations ofstations sampled during the 78 surveys

considered in this report. 64

Figure A2. Temporal distribution of chlorophyll sampling in subareas

of the Middle Atlantic Bight, Georges Bank, and Gulf ofMaine, 1977-1988. 68

APPENDIXB

Figures B1-38. Chlorophyll distribution from 38 MARMAP surveys. 71-108

APPENDIXC

Table C 1. Chronological listing ofsurveys, dates ofsampling, number of

vertical profiles, number ofsamples, number ofsamples taken 3 m below

surface while underway, and summary by field program. 109

Table C2. Coordinates ofstandard MARMAP stations used in the

Dirichlet tesselation to define tiles. 111

Table C3. Mean water column concentration of chlorophyll a and

associated statistics by tile and by two-month periods. 115

IV
Seasonal, Horizontal, and Vertical Distribution of

Phytoplankton Chlorophyll a in the

Northeast U.S. Continental Shelf Ecosystem

JOHN E. O'REILLY

Northeast Fisheries Science Center

National Marine Fisheries Service, NOAA

28 Tarzwell Drive

Narragansett, Rhode Island 02882-1199

CHRISTINE ZETLIN

Northeast Fisheries Science Center

National Marine Fisheries Service, NOAA

Bldg. 74 McGruder Road

Highlands, Newfersey 07732

ABSTRACT

The broad scale features in the horizontal, vertical, and seasonal distribution of phytoplankton chlorophyll a on the northeast U.S. continental shelf are described based on

57,088 measurements made during 78 oceanographic surveys from 1977 through 1988.

Highest mean water column chlorophyll concentration (ChI,) is usually observed in

nearshore areas adjacent to the mouths of the estuaries in the Middle Atlantic Bight (MAB),

over the shallow water on Georges Bank, and a small area sampled along the southeast edge

of Nantucket Shoals. Lowest Chlw «0.125 Jlg I-I) is usually restricted to the most seaward

stations sampled along the shelf-break and the central deep waters in the Gulf of Maine.

There is at least a twofold seasonal variation in phytoplankton biomass in all areas, with

highest phytoplankton concentrations (m3) and highest integrated standing stocks (m2)

occurring during the winter-spring (WS) bloom, and the lowest during summer, when

vertical density stratification is maximal. In most regions, a secondary phytoplankton biomass pulse is evident during convective destratification in fall, usually in October. Fall bloom

in some areas of Georges Bank approaches the magnitude of the WS-bloom, but Georges

Bank and Middle Atlantic Bight fall blooms are clearly subordinate to WS-blooms.

Measurements of chlorophyll in two size-fractions of the phytoplankton, netplankton

(>20 Jlm) and nanoplankton «20 Jlm), revealed that the smaller nanoplankton are responsible for most of the phytoplankton biomass on the northeast U.S. shelf. Netplankton tend

to be more abundant in nearshore areas of the MAB and shallow water on Georges Bank,

where chlorophyll a is usually high; nanoplankton dominate deeper water at the shelf-break

and deep water in the Gulf of Maine, where Chlw is usually low. As a general rule, the

percent of phytoplankton in the netplankton size-fraction increases with increasing depth

below surface and decreases proceeding offshore.

There are distinct seasonal and regional patterns in the vertical distribution of chlorophyll a and percent netplankton, as revealed in composite vertical profiles of chlorophyll a

constructed for 11 layers of the water column. Subsurface chlorophyll a maxima are

ubiquitous during summer in stratified water. Chlorophyll a in the subsurface maximum

layer is generally 2-8 times the concentration in the overlying and underlying water and

approaches 50 to 75% of the levels observed in surface water during WS-bloom. The

distribution of the ratio of the subsurface maximum chlorophyll a to surface chlorophyll a

(SSR) during summer parallels the shelfWide pattern for stability, indexed as the difference

in density (sigma-t) between 40 m and surface (stabilitY4o)' The weakest stability and lowest

SSR's are found in shallow tidally-mixed water on Georges Bank; the greatest stability and
2 NOAA Technical Report NMFS 139

highest SSR's (8-12:1) are along the mid and outer MAB shelf, over the winter residual

water known as the "cold band." On Georges Bank, the distribution of SSR and the

stabilitY40 are roughly congruent with the pattern for maximum surface tidal current

velocity, with values above 50 cms-1 defining SSR's less than 2: 1 and the well-mixed area.

Physical factors (bathymetry, vertical mixing by strong tidal currents, and seasonal and

regional differences in the intensity and duration of vertical stratification) appear to

explain much of the variability in phytoplankton chlorophyll a throughout this ecosystem.

Introduction

Continental shelves are a disproportionately important

part of the marine realm, occupying only 10% of the

world's oceans but supporting a rich fishery where 99%

of the global fish harvest is taken (Walsh, 1981). This

rich fishery is nourished by high rates of phytoplankton

productivity and high concen trations of phytoplankton

(Raymont, 1949; Esaias et aI., 1986; Nixon, 1992; Hooker

et aI., 1993) characteristic of shallow coastal environments having ample supply of nutrients and light for

photosyn thesis.

This report focuses on seasonal and spatial variations

in phytoplankton biomass over the northeast U.S. continental shelf. One of the most productive shelf ecosystems in the world, it encompasses the Middle Atlantic

Bight, Georges Bank, and the Gulf of Maine (Fig. 1).

Annual phytoplankton production in the tidally-mixed

shallow waters on Georges Bank and in the shallow

nearshore waters of the Middle Atlantic Bight is three

times the mean for world continental shelves (O'Reilly

et aI., 1987). However there are large seasonal and

regional differences in primary productivity. These are

mainly related to variations in phytoplankton biomass,

as well as the rate oflight absorption by phytoplankton,

and seasonal changes in incident light and efficiency of

light utilization (Campbell and O'Reilly, 1988).

There is great in terest in the abundance and distribution of phytoplankton because they playa pivotal

role in the trophodynamics of aquatic ecosystems

(Lasker, 1978; Smith and Eppley, 1982). Most marine

fish larvae feed on young stages of copepods (Hunter,

1981), and copepods feed on phytoplankton. Reports

of the significance of phytoplankton to the nutrition

and survival of higher trophic levels are numerous. As

early as 1941, Hjort proposed a relationship between

the timing of the spring phytoplankton bloom, the

spawning of Norwegian spring-spawning herring, and

the success of the year-class recruitment (May, 1974).

A strong association exists between landings of finfish and shellfish, annual phytoplankton primary production, and the input of nitrogen to estuarine and

marine ecosystems, with the fisheries yield approaching

1% of the phytoplankton carbon production in the

most productive systems (Nixon, 1988, 1992). In some

areas the ratio of phytoplankton production to fish

production is used to estimate size of fish stock, which

in turn can be related to fish catch, to determine the

percentage of the community taken through fishing

(Steven, 1975). Iverson (1990) developed convincing

arguments that carnivorous fish production in coastal

and open ocean environments (including the Gulf of

Maine) is controlled by the amount of new nitrogen

entering the euphotic layer and consequent new phytoplankton production, and not by systemic differences

in trophic transfer efficiency or number of steps in the

food chain. On Georges Bank, a high level of fish

production is, in part, traceable to the high level of

primary production (Cohen and Grosslein, 1987). The

phytoplankton requirements of scallop populations in

the eastern half of Georges Bank could potentially be

met from the flux of nitrate across the tidal front and

consequent phytoplankton production (Horne et aI.,

1989).

There is also keen interest in the role played by

phytoplankton, presumably responding to nutrients

from agriculture and sewage wastes, in -the eutrophication of many coastal environments worldwide (Walsh,

1981; Larsson et aI., 1985; Rosenberg, 1985; Stoddard

et aI., 1986; Smith et aI., 1987; Mahoney et aI., 1990;

Smayda, 1990, 1991; Hinga et aI., 1991). Additionally,

concerns over the buildup of atmospheric carbon dioxide and global climate change have led to renewed

interest in phytoplankton as principal intermediaries

in the flux of carbon from the atmosphere to the marine biosphere and sediments (Keeling et aI., 1976;

Broeker et aI., 1979; Walsh et aI., 1981; Malone et aI.,

1983b). For example, in the central North Pacific Ocean

since 1968, there has been a doubling in phytoplankton biomass (vertically integrated chlorophyll) which is

believed to be caused by climate change: increased

winter winds and decreased sea surface temperature

(Venrick et aI., 1987).

Measurements of phytoplankton chlorophyll throughout the euphotic and upper mixed layers are essential

for the calibration (Gordon et a!., 1980; Smith, 1981;

Gordon, 1987) and interpretation (Collins, 1989) of

pigment distributions derived from satellite spectral
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 3

44°

77°

76°

75°

74° 72°

71°

.}.. ..... ...

69°

.... '., ···200 m "

70°

67°

I I I I I

o 50 100 150 200 Ian

68°

65°

66°

40°

38°

36°

Figure 1

The northeast U,S. continental shelf and its major oceanographic regions: Gulf of Maine, Georges Bank, and Middle Atlantic

Bight; major estuaries: Penobscot Bay (P. Bay), Narragansett Bay (1 . Bay), Hudson-Raritan Bay (H-R. Bay), Delaware Bay (D.

Bay), Chesapeake Bay (C. Bay); and coastal points ofreference: ova Scotia, Maine (ME), ew Hampshire ( H), Massachusetts

(MA), Cape Cod, Connecticut (CT), Long Island, New Jersey (NJ), Delaware (DE), Maryland (MD), Virginia (VA), North

Carolina (NC), Cape Hatteras.

radiometers such as the Coastal Zone Color Scanner

(CZCS) and the Sea-viewing Wide Field-of-view Sensor

(SeaWiFS) (Hooker and Esaias, 1993). Since the launch

of the CZCS in 1978, synoptic descriptions offine scale
4 NOAA Technical Report NMFS 139

features (1-4 km) in the distribution of phytoplankton

pigments have been generated for large areas of the

ocean (Yoder et aI., 1988; Hooker et aI., 1993). However, radiometers such as the CZCS indirectly detect

plant pigments in just the upper one-fifth of the euphotic layer (Campbell and O'Reilly, 1988). Their accuracy, using a general algorithm relating ocean color

to chlorophyll, is only 0.3-0.5 log chlorophyll (Gordon

et aI., 1980; Balch et aI., 1992) but may improve to

±40% using ship data from the study region to optimize

the chlorophyll algorithm (Smith and Baker, 1982).

Thus it is becoming widely recognized that direct measurements of chlorophyll and remote measurements

are complementary; both are required to generate accurate assessments of phytoplankton standing stocks

and phytoplankton production at a number of spatial

scales for large areas of the ocean (Sathyendranath and

Platt 1989; Kuring et aI., 1990; Platt et aI., 1991; Sathyendranath et aI., 1991; Antoine et aI., 1996).

Therefore, it is important to understand the abundance and distribution of phytoplankton, to delineate

regional and seasonal and long-term patterns in their

abundance, and to determine the oceanographic and

ecological factors responsible for such distributions (e.g.

Walsh et aI., 1978; Marra et aI., 1982; Malone et aI., 1983a;

Campbell and Esais, 1985; Eslinger and Iverson, 1986).

Some of the major features in the horizontal and seasonal distribution of chlorophyll a have been described

for portions of the northeast U.S. continental shelf

based on relatively short studies: New York Bight (e.g.

Ryther and Yentsch, 1958; Mandelli et aI., 1970; Malone,

1976; Yentsch, 1977; Falkowski et aI., 1983; Malone et

al. 1983b; Falkowski et aI., 1988); Georges Bank (e.g.

Riley, 1941; Colton et aI., 1968; Yentsch et aI., 1994;

Thomas et al. l ); and Gulf of Maine (e.g. Bigelow, 1926;

Bigelow et aI., 1940; Cohen, 1976; Yentsch and Garfield,

1981). Only the New York Bight has been comprehensively described at a high level (monthly) of temporal

resolution (Malone, 1976; Malone et aI., 1983b).

The purpose of this report is to illustrate and characterize typical (mean) coarse-scale features in the horizontal, seasonal, and vertical distribution ofphytoplankton chlorophyll a over the northeast U.S. continental

shelf. Our characterizations are derived from an extensive series of shipboard surveys conducted from 1977

through 1988. Previous studies did not routinely survey

the entire ecosystem. Our report establishes ecological

baselines, defines the annual cycle of phytoplankton

abundance, and identifies similarities and differences

I Thomas,]. P., H. Mustafa, A. A. Tvirbutas, C. A. McPherson. and].

B. Suomala. 1982. Seasonal patterns of surface temperature and

phytoplankton pigments in the Georges Bank region. Int. Coun.

Explor. Sea, BioI. Oceanogr. Comm. Doc. Council Meeting 1982/

L:14 (poster).

among the Middle Atlantic Bight, Georges Bank, and

the Gulf of Maine. Baselines such as these may prove

useful in understanding regional differences in fishery

productivity (e.g. Sherman et aI., 1984) and in assessments of long term ecological change (e.g. Venrick et

aI., 1987; Radach et aI., 1990).

Description of Study Area

Our study area includes the northeast U.S. continental

shelf and adjacent continental slope (Fig. 1). It spans

10 degrees latitude and longitude, from Cape Hatteras

in the southwest to Nova Scotia in the northeast, and

encompasses approximately 275,000 km2• The Gulf of

Maine, Georges Bank, and the Middle Atlantic Bight

constitute the three major subdivisions of the shelf,

based on diverse bottom topography (Fig. 2); differences in fresh water sources and inputs, water mass

characteristics, circulation, and tidal mixing; and zoogeographic provinces (Sherman et aI., 1988). The following brief description of the oceanography of the

study area provides background and perspective for

subsequent discussion of seasonal and spatial patterns

in phytoplankton biomass.

Gulf of Maine-The Gulf of Maine, a semi-enclosed

continental shelfsea, is bounded landward by the northeast U.S. and ova Scotia coasts and includes waters

west of longitude _660 between Georges Bank and the

entrance to the Bay of Fundy (Fig. 1). Bottom depth

throughout much of the Gulf of Maine is greater than

100 m, and averages 150 m (Uchupi and Austin, 1987).

Three large basins (Georges Basin, 377 m; Wilkinson

Basin, 295 m; and Jordan Basin, 311 ni) and a number

of smaller basins (Uchupi, 1965; Uchupi and Austin,

1987) are deeper than 200 m (Fig. 2). Shallow water

<60 m is mostly confined to a relatively narrow band

along the coast and on Stellwagen Bank, which is west

of the Jordan Basin and north of Cape Cod (Fig. 2).

Seawater exchange between the Gulf of Maine and

the North Atlantic is fairly restricted, occurring mostly

through the deep Northeast Channel (Ramp et aI.,

1985; Mountain and Jessen, 1987) located between

Georges and Browns Banks (Fig. 2). Georges Bank limits the flow of water such that only the upper 20 m of

Gulf of Maine water can pass over it, while flow in the

Great South Channel is limited to the upper 70 m

(Butman and Beardsley, 1987). Waters deeper than 70

m communicate with the gulf only through the Northeast Channel, the principal entry point for slope water

into the region. Freshwater enters the Gulf of Maine

from rivers in Maine, the Bay ofFundy (St.Johns River),

and the Scotian Shelf where the freshwater originates

from the Gulf of St. Lawrence. Maine rivers, principally
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 5

77° 75° 73° 71 ° 69° 67" 65°

38°

44°

36°

Northeast U.S. Continental Shelf

36°

38°

44°

42° Depth m 42°

<20

20-40

40-60

60-80

80-100

100-200

200-1000

1000-2000

2000-3000

3000-4000

>4000

40° • 40°

Figure 2

Major bathymetric features of the northeast U.S. continental shelf: Browns Bank (BB), Scotian Shelf (SS), Northeast Channel

(NEC), Georges Basin (GBas), Wilkinson Basin (WB), Jordan Basin UB), Georges Bank (GB), Great South Channel (GSC) ,

Nantucket Shoals ( S), Hudson Shelf Valley (HSV), Continental Slope (S).

the Androskogen, Penobscott, Merrimak, and Kennebeck, flow into the gulf and, during spring, form a

plume ofrelativeIy brackish stratified waters in the western gulf (Franks and Anderson, 1992a, 1992b). Most of

the land drainage (-90%) occurs north of Cape Elizabeth (TRIGOM, 1974) and, in response to snow melt,

maximum river runoff occurs in the south earlier than

in the north. In the northern Gulf of Maine, a cold

buoyan t coastal current (Townsend et aI., 1987) may

extend from the Bay of Fundy to Penobscott Bay where

it may split into a nearshore and offshore limb (Bisagni

et aI., 1996b). Local rivers have a significant contribu-
6 NOAA Technical Report NMFS 139

tion to the upper 40 m of the water column (Brown and

Irish, 1993). Along with the outflow of the Bay of Fundy

and the east-to-west flow of slope water, they maintain

the gulfs counterclockwise circulation, which seems

stron?;est in sprin?; (Sherman et. a!., 1988). The most

significant input of fresh water to the ?;ulf comes from

the Scotian Shelf. Based on the total volume of water in

the Gulf of Maine, most of the fresh-water input derives

from cold, low-salinity Scotian Shelf water (Hopkins

and Garfield, ] 979) that enters throu?;h the Northeast

Channel and through passages formed between Cape

Sable and Browns Bank (Brown and Irish, 1993).

Upwelling is common along the coastal areas in the

western Gulf of Maine, off Nova Scotia, and on the

Scotian Shelf (Garrett and Loucks, ] 976). In comparison with deep waters of the central basin, northwestern

coastal waters are turbid with reduced transparency

due to river runoff (TRIGOM, 1974). During warmer

months, stratification occurs where bottom depth exceeds 20 m. At shallower depths, tidal mixin?; and coastal

currents prevent stratification (TRIGOM, 1974). Waters along the Scotian Shelf, at the mouth of the Bay of

Fundy, and nearshore, north of Penobscott Bay, are

only weakly stratified during summer as a consequence

of strong tidal currents (Moody et a!., 1984).

Based on hydrographic features, Gulf of Maine waters are divided vertically into three layers: Maine surface water (MSW), water less than 50 m; Maine intermediate water (MIW), water between 50-100 m; and Maine

bottom water (MBW), water greater than 100 m

(Hopkins and Garfield, 1979). During summer, the

temperature minimum is found in MIW that is isolated

from the warmer layers above and below. Durin?; spring

the relatively fresh MSW is warmed through solar heating. Maine bottom water is warmer because it is derived

from warmer and saltier continental slope water that

enters the Northeast Channel. During this time the

isolation ofthis water is similar to the isolation ofGeorges

Bank-Middle Atlantic Bi?;ht cold band water described

below. During winter months the water column is mixed

to about 100 m and only two layers are present.

Georges Bank-Georges Bank is generally delineated

by the 200 m isobath except in the west and northwest

(Fig. 2). Along the northern flank, sharp bathymetric

?;radients between Georges Basin and Geor?;es Bank

define the bank. Here water shoals quickly from 200 m

to 60 m within a relatively short distance « 30 km). The

eastern and southern extent, where shoaling from the

200 m isobath is more gradual, is defined by the Northeast Channel and the shelf-break, respectively (Fig. 2).

Georges Bank is defined in the west by the western edge

of the Great South Channel, which separates Georges

Bank from antucket Shoals, and in the northwest by

the 100 m isobath (Fig. 2). The shallowest watersGeorges, Cultivator, and some unnamed shoals-are

found on the northwestern part of the bank within the

60 m isobath, where shifting medium-to-coarse sand

ridges cover most of the bottom and contribute to the

turbulence (Uchupi and Austin, ]987) and turbidity of

overlying waters (Butman, 1987; Twichell et. a!., 1987).

Diurnal and semidiurnal tides interacting with the shallow bottom topography of the bank generate exceptionally strong currents (Butman and Beardsley, 1987)

that maintain a vertically well-mixed water column within

the 60 m isobath throughout the year (Yentsch and

Garfield, 1981; Bisagni and Sano, 1993). The maximum

tidal current speed near surface on the bank increases

gradually from 10-20 cm 5.1 at the 200 m isobath along the

southern flank, to 60-70 cm 5-1 over the shallow area (Fig.

3). Maximum tidal current speeds decrease sharply from

the northern edge of the bank into Georges Basin.

During spring and summer, a clockwise recirculation

pattern sets up around the shallow water on the bank

(Limeburner and Beardsley, ] 996). This recirculation

prolon?;s mean residence time (-60 days) of shallow

water (Colton and Anderson, 1983) and limits exchange

with surrounding waters. During winter, recirculation

is minimal, prevailing northwest winds drive surface

water offshore (Bumpus, ] 976), and generally more

exchange occurs between the shallow Georges Bank

water and Gulf ofMaine and Scotian Shelfwater (Flagg,

19157). In the deeper areas of the bank, the water column is vertically mixed during winter but thermally

stratified during summer, and subject to variations from

advection of slope water onto the bank (Bisagni and

Sano, 1993). During summer, a tidally-induced front,

found around the 60 m isobath and often extending

across the Great South Channel toward Nantucket Shoals,

separates the vertically-mixed shallow water from deeper

stratified water on the bank (Butman and Beardsley, ] 987).

The mean flow ofwater beyond the 60 m isobath is to

the southwest, and is strongest in late summer and

weakest in winter (Butman and Beardsley, 1987). Physical properties of deeper Georges Bank waters are influenced by the advection of slope water onto the bank

(Bisagni and Sano, 1993) and by entrainment of bank

water by warm core rings passing along the southern

flank (Bisagni, 1983; Evans et a!., ] 985). During spring,

cold, low salinity water from the Scotian Shelf may

move onto the southern flank ofGeorges Bank (Bisagni

et aI., 1996a). From spring through fall turnover, cold,

winter-residual water, known as the "cold band" or "cold

pool," occurs beneath the seasonal thermocline, within

the 60-100 m isobaths from the Northeast Peak of

Geor?;es Bank south to near Cape Hatteras (Butman

and Beardsley, 1987; Flagg, 1987). The axis of the cold

band is along the 80 m isobath on Georges Bank (Flagg,

1987), the 65 m isobath off Long Island, and the 55-60

m isobath in the Middle Atlantic Bight offshore of
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 7

: .. ..\.' .

/

f f ! :

200m .....

Maximum Tidal (M2)

Surface Current (cm/s)

Figure 3

Maximum tidal current velocity (M2 current, cm/s) of surface water. Redrawn from Moody et al. (1984).

Chesapeake Bay (Ketchum and Corwin, 1964; Colton

et a\., 1968; Houghton et a\., 1982; Flagg, 1987).

Middle Atlantic Bight-The Middle Atlantic Bight includes the shelf area between Cape Hatteras and the

Great South Channel. The shelf in the Middle Atlantic

Bight slopes gently offshore and is shallow compared

with the Gulf of Maine and Georges Bank; much of the

bight from Long Island south is less than 60 m deep

(Fig. 2).
8 NOAA Technical Report NMFS 139

A retrograde shelf-slope front, delineated by the 34.5

salinity isohaline (Wright, 1976; Mooers et aI., 1979), is

located along the shelf-break in the Middle Atlantic

Bight and on Georges Bank. It is generally centered

near the 200 m isobath, however since it is angled and

not vertical the location of the surface and bottom of

the front is not the same. The bottom of the front is

anchored closely to the 80-100 m isobath year round,

but the front in surface water undergoes seasonal onshore-offshore excursions, reaching its maximum seaward extension during June-August when it is approximately 100 km seaward of the shelf-break, over the

-2000 m isobath.

Waters in the Middle Atlantic Bight are well mixed

during winter and strongly stratified during summer

with the exception of shallow coastal areas which experience episodes of vertical mixing from storms, upwelling, and downwelling (Ingham and Eberwine, 1984).

Nearshore waters are more turbid than offshore because of their shallowness, resuspension of sediment,

and from estuarine outflow they receive. Fresh water

enters the Middle Atlantic Bight at the mouth of the

Hudson-Raritan, Delaware, and Chesapeake bays. These

local sources are responsible for approximately 70% of

the large interannual variation in salinity in the bight

(Manning, 1991). Runoff peaks in spring, when about

half the annual runoff occurs (Bigelow and Sears, 1935).

While the inflow of freshwater is predictable, removal

of shelf water is not. Shelf water predictably travels

from Georges Bank in a southwesterly direction with

some loss at Cape Hatteras; however, loss ofshelf water

can also occur erratically around the shelf-break.

Though the shelf-slope front is coherent from Georges

Bank to the Cape Hatteras; warm core rings drifting

southwest between the northern edge ofthe GulfStream

current and the continental shelf-break, and intrusions

of Gulf Stream water along the southern portion of the

Middle Atlantic Bight, may entrain and displace significant amounts of shelf water (Churchill and Cornillon,

1991) .

The cold band is present throughout the summer in

the Middle Atlantic Bight and disappears during fall

overturn. The inshore edge of the cold band is at shallower depths in the Middle Atlantic Bight (30-40 m)

than on Georges Bank (70-80 m). Presumably this is a

consequence of the relatively greater surface and bottom tidal current mixing (at comparable depths) along

the southern flank of Georges Bank, relative to the

outer Middle Atlantic Bight (Moody et aI., 1984). In the

New York Bight the cold band is typically 6°C during

the early summer and warms to about 1O-12°C just

before convective overturn in fall. The coldest part of

the cold band is usually between the 40 and 80 m

isobaths (Ketchum and Corwin, 1964), whereas on the

southern flank of Georges Bank, it is centered along

the 80 m isobath and spans between the 65 and 95 m

depths. In the Middle Atlantic Bight the greatest thermal contrast appears during June, when the cold band

is 6-7°C and surface water temperature is 22°C (Benway

et aI., 1993). At that time the inshore edge of the cold

band is 80 km offshore, at about the 40 m isobath.

During fall overturn, when the water column becomes

nearly vertically isothermal, the winter residual water

disappears first in the shallow nearshore area (early

September) and last in the outer shelf area in early

December (Benway et aI., 1993). The annual maximum

bottom water temperature (16°C nearshore, 13°C offshore to the shelf-slope front) occurs during the fall

overturn (Benway et aI., 1993). In nearshore waters off

the Raritan Estuary the annual minimum surface water

salinity occurs during March-April, with a secondary

minimum in August (Benway et aI., 1993). Along the

outer Middle Atlantic Bight the minimum appears during July-August (31.5-32%0), when tern perature is at

its annual maximum across the shelf (22-24°C; Benway

et aI., 1993), reinforcing density stratification.

Methods _

Data Sources

Data presented in this monograph were collected during several multidisciplinary field programs conducted

by the National Oceanographic and Atmospheric Administration, Northeast Fisheries Science Center, between 1977 and 1987 (Append. Table C1). Major field

programs included the Marine Resources Monitoring,

Assessment, and Prediction Program (MARMAP) described by Sherman (1980); the Northeast Monitoring

Program (NEMP) described by Pearce (1981); and the

Warm Core Ring (WCR) Program (Evans et aI., 1985).

The objectives and sampling areas of these programs

differed but phytoplankton chlorophyll sampling and

measurement protocols were consistent.

During MARMAP surveys, vertical profiles of temperature, salinity, chlorophyll, and primary productivity were routinely measured from hydrocasts and by

using expendable bathythermographs (XBT's) (temperature). Mountain and Holzwarth (1989) and Mountain and Manning (1994) summarized hydrographic

data from MARMAP surveys. Major plant nutrients were

also measured on some surveys (Draxler et aI., 1985;

Sibunka and Silverman, 1989). Double oblique net tows

were made to 200 m to determine the abundance and

species composition of zooplankton and ichthyoplankton (Morse et aI., 1987; Sherman, 1988; Sibunka

and Silverman, 1989). MARMAP surveys occupied up

to 193 standard sites (Fig. 4). Usually surveys progressed

from south to north and lasted four weeks. Stations
_____ O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 9

44°

42°

40°

38°

77°

76°

75°

A

74°

73°

.-..'

o

o

o·200m

72°

71 °

70°

69°

E

F

68°

67" 65°

66°

44°

40°

38°

36°

Figure 4

Locations of Standard 193 MARMAP sampling sites, onshore-offshore transects (A, B, C, D, E, F, G), and the 60 m and 200 m

isobaths (only the 200 m isobath is shown north of Cape Cod).

along transects A, B, C, D; those portions of transects E,

F, and G on Georges Bank; and transects E, F, and G in

the Gulf of Maine, were usually sampled sequen tially to

obtain synoptic data (Fig. 4).

NEMP surveys involved collection of water samples

from hydrocasts, demersal fish using trawls, and benthic

invertebrate community and sediment contaminants

using grab samplers. Surveys took two weeks to com-
10 NOAA Technical Report NMFS 139

plete. The stations were sparsely distributed throughout the study area since the objective of the program

was to sample key sites that represented the range of

conditions in the ecosystem. The distribution of stations during a typical NEMP survey is illustrated in

Append. Fig. Al (survey AL8009). There was some

overlap between NEMP and MARMAP sites.

Warm core ring surveys were conducted in deeper

water near and beyond the shelf and focused on the

entrainment of filaments of shelf water and associated

biota (Colton and Anderson, 1983). Both underway

and hydrocast sampling were conducted (Append. Table

Cl). Surveys labeled "Other" (Append. Table Cl) had

various objectives, areas ofinterest, and sampling intensities (e.g. Append. Fig. AI: AD7701, EV8002).

Of the 78 oceanographic surveys considered in this

analysis, only a few covered the entire study area (Append. Fig. AI). The combined data set consists of61,533

discrete measurements of phytoplankton chlorophyll

(Append. Table Cl). The majority of chlorophyll measurements were made during MARMAP surveys (Append. Table Cl, bottom). Most of the measurements

were taken from 6,686 hydrocast profiles of the upper

100 m of the water column. Some of the surveys obtained samples inside the mouths of estuaries and seaward of the continental slope; those samples are not

considered here (Append. Fig. AI). The focus of this

report is on the 57,088 samples from the upper -100 m

of the water column on the continental shelf and adjacent slope.

Sampling

Generally, water samples were collected using 5-1 opaque

PVC Niskin bottles suspended within the water column

from a hydrowire at standard depths, i.e. 1,5,10,15,20,

25, 30, 35, 50, and 75 m below sea surface. Prior to

being sequentially tripped, Niskin bottles were equilibrated (flushed) with water at the desired depth for at

least five minutes. At stations where bottom depth was

less than 75 m, an additional sample was collected

within -2-3 m of bottom. Beginning in October 1979, a

bottom-trip bottle (rigged to close when a tripping

device contacted the seabed) collected near-bottom

water within 1 m of the seabed. Mter spring 1980, the

sampling protocol included samples from 100 m and

from within 1 m of bottom, when bottom depths were

approximately 100 m or less. Additional nonstandard

depths were sampled to coincide with depths sampled

for measurements of simulated in situ primary production (O'Reilly and Thomas, 1983; O'Reilly et aI., 1987).

On all surveys, samples were collected from the

hydrocast except DL8510, DL8601, DL8603, DL8607,

Dl8610, Dl8701, and DL8704 (Append. Fig. AI) during

which water for chlorophyll analyses was obtained only

from the vessel's saltwater intake (-3 m) while the ship

was underway. During warm core ring surveys, samples

were collected from hydrocasts and the vessel's saltwater intake (Append. Table Cl).

Measurement of Chlorophyll a

The concentration of chlorophyll a, the dominant photosynthetic pigment in phytoplankton, is widely used by

biological oceanographers as a proxy for phytoplankton carbon biomass. However, the relationship between

chlorophyll a and phytoplankton biomass is not constant, but varies widely in space and time with the

species composition and physiological state of the phytoplankton (Banse, 1977; Cullen, 1982). Because it is

operationally difficult to distinguish routinely organic

carbon in autotrophic phytoplankton from that in

microheterotrophs and detritus, measurements of chlorophyll a remain the best chemical index of the biomass of natural assemblages of autotrophic phytoplankton (Cullen, 1982). In this report, the expressions "phytoplankton biomass," or "biomass," are used frequently

as shorthand notation for "the concentration of chlorophyll a in a liter ofseawater," but the distinction should

be remembered.

Immediately following retrieval of Niskin bottles,

subsamples were drawn through silicon tubing into

opaque 1-1 polyethylene bottles. During subsampling,

zooplankton >300 Jlm were removed by an in-line, I-in

diameter, 300 Jlm mesh nylon filter. Water samples

were size-fractionated immediately after collection by

serial filtration, using 25-mm diameter Nitex Nylon

filters (20 Jlm mesh) in the upper stage and 25-mm

diameter Whatman GFIF glass fiber filters (-0.7 Jlm

mesh) in the lower stage of a filtration manifold, which

allowed up to 10 samples to be processed simultaneously.

Vacuum pressure on the lower filter stage was regulated

by a manostat and did not exceed 55 mm Hg. Usually

from 200 to 900 ml ofseawater were filtered, the amoun t

chosen to avoid filter clogging and yet achieve a

fluorescence measurement significantly above blanks

and within the accurate range of a Turner Designs

fluorometer.

Phytoplankton retained on the upper 20 Jlm mesh

are defined operationally as netplankton, while phytoplankton passing the 20 Jlm and retained on -0.7 Jlm

GFIF filters are defined as nanoplankton. This sizefractionation scheme follows that established by Malone

(1976).

Phytoplankton chlorophyll a concentration was determined following the methods ofYentsch and Menzel

(1963) and Holm-Hansen et al. (1965) where the in

vitro fluorescence of pigments extracted into 90% ac-
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 11

etone is measured. Through August 1985, pigments

were extracted by grinding filters and retained particulate matter in a glass grinding vessel (Arthur H. Thomas) with a teflon-tip rod driven by an electric hand

drill at -500 rpm for <1 minute. Prior to grinding,

samples were covered with 3-4 ml 90% acetone and

chilled in a refrigerator. A Whatman GFF glass fiber

filter was added to the Nitex nylon filter to facilitate

grinding. Following grinding, additional 90% acetone

was added to the vessel to obtain 10 ml. Samples were

mixed and allowed to extract in dark for 5 minutes,

then this was repeated. Extracts, while in the grinding

vessels, were centrifuged at 4000 r/min for 2 minutes,

and a 5-6 ml aliquot was decanted into a fluorometer

cuvette (13 x 100 mm).

Due to loss of equipment in a fire, after September

1985 the extraction procedure was modified. Following

Parsons et al. (1984), pigments were extracted by submerging filters and phytoplankton in 90% acetone and

refrigerating for 12-24 hours. Following extraction,

samples were mixed and particulates allowed to settle

through centrifugation or gravity. The supernatant liquid was decanted into a fluorometer cuvette.

Following extraction, sample fluorescence was measured using a Turner Designs fluorometer equipped

with a 10-045 blue lamp, a red-sensitive photomultiplier tube, and Corning filters 10-050,10-051, and 10-

052 for excitation, emission, and reference light paths,

respectively. Fluorescence of the extract was measured

before and after the addition oftwo drops of5% HCI to

the cuvette to determine corrected chlorophyll a concentration as well as phaeophytin a concentration

(Holm-Hansen and Riemann, 1978).

Fluorometers were calibrated immediately before and

after each survey using a 90% acetone solution of pure

chlorophyll a (Sigma Chemical Company). The fluorescence of individual (not serial) dilutions (1, 0.1,

0.04, 0.02, 0.01, 0.002, and 0.001) of this calibration

solution (approx. 1 mg/l) were measured to check

linearity of the fluorometer over the working range of

the instrument. Additionally, the fluorescence of

aliquots of the calibration solution (kept in dark in a

freezer) was recorded approximately each night at sea

to detect any drift or change in the calibration during

the survey.

The concentration of chlorophyll a in the calibration

solution was determined using the method outlined by

Holm-Hansen and Riemann (1978). The absorption of

the pure chlorophyll a stock solution at 480, 630, 645,

663, 665, and 750 nm, before and after acidification (2

drops of 5% HCI per 10 ml aliquot), was determined

using a dual-beam Perkin-Elmer #550 spectrophotometer and a 5 cm cuvette. A specific absorption coefficient of 89.31 l/g cm for chlorophyll a (UNESCO,

1966) was applied. The accuracy of the calibration was

routinely checked against the chlorophyll a calibration

standard obtained from U.S. EPA, Quality Assurance

Branch, Cincinnati, Ohio. The coefficient of variation

(standard error x 100/average) among 10 replicate

size-fractionated seawater subsamples is usually 6-7% at

1 llg chlorophyll/I. Evans et al. (1987) describes additional details of our method.

Computations

Chlorophyll a concentrations measured in the netplankton and nanoplankton size-fractions are added to

generate an estimate of total chlorophyll a concentration at each sampling depth. Standing stocks of water

column chlorophyll a (llg m-2) in the upper 75 m (or

bottom depth if < 75 m) is computed by arithmetically

integrating values over depth using the trapezoidal rule.

In the integration, the measured value at 1 m below

surface is used as the estimate for 0 m. In water deeper

than 75 m, when sampling did not exactly coincide with

75 m, the chlorophyll a concentration at 75 m was

estimated by linear interpolation, using measurements

from the two adjacent sampling depths. Water column

concentration of chlorophyll a (llg 1-1), abbreviated as

Chlw ' is computed by dividing the water column integral (llg chlorophyll a m-2 ) by the depth of integration

(m). The percent netplankton in the water column is

calculated as 100 times water column netplankton chlorophyll a, divided by water column total chlorophyll a.

Similarly, percent phaeopigment in the water column

is calculated as 100 times phaeophytin a, divided by

(phaeophytin a + chlorophyll a). Venrick (1978) provides an indication of the statistical precision of estimated Chlw based on the systematic sampling used

during our study.

Contouring

Contoured distributions of chlorophyll a were generated using Surface III (Sampson, 1988). Latitude and

longitude coordinates of each station were transformed

into map coordinates using Lambert's conic conformal

map projection (Uchupi, 1965; Snyder, 1987). The grid

resolution used for contoured horizontal distribution

maps is 10.2 km/grid. That used for cross sections is 2

km and 2 m per grid. Grid values were estimated from a

distance-weighted average (1/d2) of the nearest eight

data values. Prior to generating contoured cross sections, original data were linearly interpolated, first vertically (1 m), then horizontally (1 km) between transect

stations. This provided the "control points" (Sampson,

1988) necessary to avoid artifacts in the contouring of

vertically clustered transect data.
12 NOAA Technical Report NMFS 139

Statistical Subareas

Table I

Two-way analysis of variance in Chlw among subareas

and months.

Subareas 25 184.9 123.5 <0.0001

Months II 54.7 36.5 <0.0001

Interaction 275 10.6 7.1 <0.0001

Residual 6,252 1.5

Maine (tiles 168,169,171,172,173,181,189,190) were

sampled infrequently because many of the surveys abbreviated by inclement weather began offCape Hatteras

and proceeded northward.

Degrees of Mean

Source freedom square Frequency Probability

Data were grouped into subareas to construct generalized mon thly represen tations of chlorophyll over broad

but relatively homogeneous areas of the shelf. Clustering techniques (Fastclus, SAS Inst., 1990) were employed as an exploratory tool to aid the definition of

subareas. Two expressions of the chlorophyll data were

used in separate clustering analyses: two-month mean

water column chlorophyll and pt>rcent netplankton,

averaged by tile; and chlorophyll concentration averaged by tile (193), depth strata (11), and month (12).

The first expression emphasizes areas having similar

annual cycles in the magnitude and size composition of

Chlw' while the second expression groups tiles with

similar annual cycles in the magnitude and shape ofthe

vertical profile of chlorophyll a. We also examined

monthly composite profiles constructed for each of the

193 tiles. These provided anumber offeatures useful in

identifying tiles which were similar and therefore could

be grouped into subareas: the magnitude of chlorophyll, the occurrence and timing of a distinct winterspring bloom and fall bloom, the shapes of the vertical

profiles of chlorophyll concentration and percent

netplankton throughout the annual cycle, and the presence/ absence of a distinct subsurface chlorophyll maximum layer during the summer (indicative of physical

and biological vertical stratification). Thus, these composite profiles, recurring patterns in contoured distributions of Chlw from surveys, and results from clustering explorations were considered in the development

of subareas shown in Fig. 8. An analysis of varianc~ of

mean water column chlorophyll a concentration indicates the efficacy ofour partitioning scheme, with highly

significan t differences among subareas as well as signifiThe sampling density and coverage of the continental shelf during MARMAP surveys permitted contouring. The distance between stations along the seven

MARMAP cross-shelf transects is approximately 25 km

(Fig. 4). Stations on these transects were usually sampled

sequentially over a 24-48 hr period. This spatial resolution and synopticity permitted the construction of cross

section portrayals. Inter-station distances during NEMP

surveys were judged too large to generate representative contours. Contoured distributions of chlorophyll

from WCR surveys are also not portrayed here since the

focus of WCR surveys was the outer shelf-slope region

under the influence ofseveral specific warm core rings.

Contoured distributional maps of mean water column chlorophyll concentration (chlw) and contoured

cross-shelf sections of chlorophyll a are presented for

38 MARMAP surveys in Append. B. Contoured maps of

data, composited and averaged by tile, used the standard station location coordinate to represent data (see

below).

To unify data from several field programs, each with

different spatial sampling patterns, all data were assigned to standard locations. This enabled the construction of composite horizontal, vertical, and temporal portrayals. The coordinates of the 193 MARMAP

stations (Fig. 4, Append. Table C2) were used to define

the standard locations since these sites were repeatedly

sampled during MARMAP surveys, where most of the

chlorophyll observations were measured (Append. Table

CI). Dirichlet cells (Ripley, 1981) or tiles (Green and

Sibson, 1978) were constructed around each standard

location (Fig. 5). The northeast U.S. continental shelf

was thus subdivided into 193 areas or tiles such that all

samples within a tile were closer to the standard coordinate used to generate the polygon tile than to any other

standard coordinate. Additional artificial sites were

employed to constrain the offshore extent of tiles along

the outer continental shelf-break (Fig. 5). The median

distance between standard MARMAP coordinates defining the 193 tiles is 42 km (Fig. 6). Using this partitioning scheme, 84% of the 6,344 stations occupied in

the study area were within 10 km of the standard site,

and 96% were within 20 km (Fig. 7).

The resulting temporal sampling intensity for each

tile, grouped by subarea and region, is depicted in

Append. Fig. A2. Sampling intensity was highest in

1978 through 1980. Tiles surrounding stations at the

offshore terminus of MARMAP transects (18, 36, 63,84,

116,152) were sampled infrequently as were tiles along

the eastern edge of Georges Bank (180, 191, 192).

Similarly, northern and eastern areas of the Gulf of

Standard Sampling Stations (Tiles)
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 13

Figure 5

Tiles (polygons) surrounding each of the 193 MARMAP station coordinates. Tile numbers are centered on MARMAP station

coordinates except for tiles 184, 140, and 148, which were adjusted to enhance legibility.

cant variability among months and interaction effects

between subareas and mon ths (Table 1).

Our partitioning of Georges Bank approximates the

physical regimes defined by Butman and Beardsley

(1987) and Flagg (1987), which are based primarily on

tidal current velocity, water properties, locations of hydrographic fronts, bottom topography, and bottom type.

The partitioning between Georges Bank and Gulf of
14 NOAA Technical Report NMFS 139 _

80 r--~---;---~---:-------,---------====-- 100

o

40

-10

- 80

..- 20

... - 90

the relatively restricted cross-bank transport during summer (Perry et al., 1993).

In the Gulf of Maine, as will be

discussed later, recurring Chlw distribution patterns are not as obvious

as in the Middle Atlantic Bight and

Georges Bank, partly because sampling in the gulf was sparser than in

other areas. Nevertheless, the westeast distinction between the Scotian

Shelf, Georges Basin, Wilkinson Basin, and the coastal water in the western Gulf of Maine is similar to the

partitioning based on cluster analysis of standardized anomalies of sea

surface temperature and salinity data

collected along a transect-swath between Massachusetts Bay and the

southern tip of Nova Scotia (Benway

etal.,1993).

Subareas in the Middle Atlantic

Bight are bathymetrically defined

into nearshore «30 m), midshelf

(30-60 m), outer shelf (60-100 m),

and shelf-break (>100 m). The

nearshore region is influenced by

brackish, nutrient-enriched plumes

from the Hudson-Raritan, Delaware,

and Chesapeake bays. These plumes

tend to hug the coasts south of the

estuarine mouths (Bowman and

Wunderlich, 1976; Fedosh and

Munday, I9S2). During summer, the

nearshore is also subject to episodes

of wind-forced destratification, upwelling, and downwelling (Ingham

and Eberwine, I9S4). The nearshore

region is separated into several subareas: one adjacent to each of the

three estuaries and others that include remaining nearshore tiles

which are not as obviously influenced

by estuarine plumes. Analyses of

chlorophyll data (chlw) variances in

the New York Bight by Malone et al.

(l 9S3b) indicated statistically insignifican t variation among stations

within bathymetric regions relative to

the high variability among regions and

monthly variability within a region.

Our depth-based subareas differsomewhat from those used by Malone et

al., (19S3b) «= 40 m, 41-S0 m, SI1000 m). We partition the shelf into

four subareas, nearshore «=30 m),

35

.....- 70

--------c---------- 30

30

i::

-----f----------+--------- 60

.,

>

.~

]

=' U

.. , c 50

. .. . .. . .. . .. ------,---------- 20

15 20 25

Distance (kIn)

II

- .....II .. -....-- ..... -----~------------~---------- 40

5 10

. . . ........ - -- ~- , .

40~ Th" .. o

-----------:-----;[~- .~. ... ... ... ... . . -Rhjl-- 0

o 10 20 30 40 50 60 70 80

Distance (kIn)

1,600

1,200

800

2,000 ..

24 ----------------------- ...

16 -----------~----------- 'Ii .

· . · . 72 -----------~-----------+----------+----------..;.. --------,---------- -,------------"---------- 90 .. . · .

64 -----------~------------;----------_+----------+.-------+-- --------~------------"---------- 80

56 .i.. ~__ . --- -,------------~------------~---------- 70

g 48 -----------:------------;------------j II

iI.l 40 __ ..

,~- 32

4,000 n·I---:----:-----;----;-----=::::;::::;=---:---~-___, 100

3,600 .1 : ./:/.,-<: .

3,200 -l :/<J.-"C.. , .

2,800 ·I~:· .. >-. 2,400 . . : g

iI.l

!

Figure 7

The frequency and cumulative percent distribution of distance between sampling coordinates and MARMAP standard station coordinates for all 193 tiles.

Figure 6

The frequency and cumulative percent distribution of average distance

hetween each MARMAP standard station and its neighboring stations.

Maine, along the northern flank, corresponds with the

100 m isobath and follows the Chlw patterns as well as
_____ O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 15

Middle Atlantic Bight -Depth (m)

C Chesapeake Plume 14

D Delaware Plume 20

H Hudson-Rariton Plume 23

X Southern Nearshore 15-20

• Central Nearshore 15-30

+ Southern Midshelf 20-40

D Central Midshelf 30-60

¢ Northern Midshelf 30-60

o Southern Outer Shelf 60-200

<> Northern Outer Shelf 60-200

II Southern Slope 200-2000

Georges Bank -Depth (m)

.. Northern Shoals 30-40

• Central Shoals 35-55

N Nantucket Shoals 37

11 Western Outer Shoals 50-60

4 Eastern Outer Shoals 60-80

Great South Channel 60-100

* Northeast Peak 80-200

l:1 Southern Flank 60-200

I Northern Slope 200-2000

44'

42'

38'

36'

77'

76'

75"

74'

73'

72'

71'

70'

69"

68'

67' 65'

66'

400

38'

36'

Figure 8

Subareas in the Gulf of Maine, Georges Bank, and Middle Atlantic Bight. Symbols indicate locations of standard MARMAP

stations used to define tiles.

rnidshelf (>30<= 60 m), outer shelf (60-200 m), and slope

adjacent to Middle Atlantic Bight and Georges Bank

(>200<2,000 m) to accommodate the distribution ofstandard sampling stations during MARMAP surveys.

The shelf-break subarea includes waters seaward of

the 100 m isobath, on Georges Bank and in the Middle

Atlantic Bight. This is a region of transition between

continental shelf and continental slope waters (Colton
16 NOAA Technical Report NMFS 139

respectively, while concentrations below 0.13,0.06, and

0.03Ilg/1 occur at frequencies of 5.3%, 2.1 %, and 0.6%,

respectively.

When considering all samples without regard to sampling depth, season, or geographic region, nanoplankton «20 11m) dominate the phytoplankton. The

frequency distribution is strongly skewed toward low

percent netplankton, with a median value of -29%

netplankton (Fig. 10). Chlorophyll a in the netplankton

(>20 11m) exceeds 50% of the total chlorophyll in only

30% of the 57,019 paired measurements; the remainder of the time (70%), nanoplankton dominate (Fig.

10). Strong dominance (>90%) by netplankton is rare

(only -2% of the samples), but strong dominance

by nanoplankton is common (25% of the samples).

When the samples are grouped by depth strata, a vertical progression emerges in the median percent

netplankton value. Percent netplankton increases with

increasing depth, to -50 m below surface. In subsequent sections we illustrate that phytoplankton size

composition varies not only with depth, but also seasonally and regionally.

Size Composition of Phytoplankton

Figure 9

Frequency and cumulative percent distributions of chlorophyll concentration measured during 78 surveys of the northeast U.S. continental shelf

(57,088 discrete samples).

:::r;rr; .•••.······y1J,:i".,:i,;N_

s

l:,088 '7:0:

2,800 -------i-······j-------f---··--f------;--·---· . iii iii l i i E

2,400 ------!-------j------·r-------r------l·- . . ---+-----i-------f-------!------ 60

s:: : i ] i ": iii i J2,000--!:,-------!:,----...!:,-------:::,----- '. . . - - . --·i-------i-------~-------~----- 50 .~

;: i ! i i

1,600 -----i-------r------i------r----- - - ··-(----i-----i-------(-- 40 §

1,200 -------i---···-i------L--f-- - -... ------ i------j-----r------.!------ 30 u

800 ------r-----j------r-f- '" .----j----r-----(-···- 20

40: ~~-----i-------~- ... -...--------.... -t--[---j~-l~ ~O

.008 .016 .031 .063 .125 .25 .5 1 2 4 8 16 32 64

Chlorophyll a (ug/l)

Range of Chlorophyll Concentrations

The frequency distribution of phytoplankton chlorophyll a in 57,088 water samples collected throughout

the study area from 1977-1988 is depicted in Fig. 9.

Data were log2-transformed prior to generating the

frequency histogram to normalize the wide distribution

«.01 and 57.81lg 1-]) encompassed by all samples, from

varying regions, depths, and seasons. The resulting distribution is still platykurtic and skewed toward lower

values. A broad mode, centered at - 11lg I-I, is evident.

The median value is 0.87 Ilg/1 and the geometric mean

(mean) is 0.84Ilg/1. Chlorophyll a exceeding 4, 8, and

161lg/1 are observed 6.7%, 1.1 %, and 0.1 % of the time,

Results and Discussion

et aI., 1985). Along the shelf-break,

a coherent shelf water-slope front is

present throughout the year (Butman and Beardsley, 1987). Its mean

position varies seasonally, moving

seaward during summer and landward during winter (Wright, 1976;

Flagg, 1987; Benway et aI., 1993).

During summer, in the lower water

column, a cold band (winter residual

water) extends offshore to -95 m

along the southern flank ofGeorges

Bank (Flagg, 1987) and to -100 m

in the Middle Atlantic Bight (Bowman and Wunderlich, 1977). This

cold band serves to further delineate the outer shelf from the shelfbreak region. Near surface, the shelfslope front, defined by the 34.5 ps

isohal, is found landward of the 100

m isobath only a small fraction of

the time (Flagg, 1987; Benway et aI.,

1993). Therefore, the shelf-break region includes shelf water the majority of the time but is likely to be

overrun by surface slope water from

October through March.

It should be kept in mind that no

single partitioning scheme will be the best fit throughout all seasons, given the diversity and complexity in

the distribution of water masses, circulation, degree of

mixing by tides and winds, and stratification by seasonal heating and brackish plumes from estuaries. Nevertheless, the partitioning scheme employed here does

embody the major coarse-scale differences among regions of the shelf.
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 17

4,000 rr-r----,------,-----,----,----,--------,-----,-------,------:=;:?----, 100

N=5?,632

100

80

C<l.l

II

... 60 <l.l

0..

<l.l

>

"" 40 "3

E

:::l

U

20

0

100

---- 80

------ 40

<=ll.l

II

----- 60

ll.l

.::

'iii

:;

E

:::l

U

90

rhh1,- :0

90 100

80

80

--------

-_ .... !.. - ----:- ----"'r--

30 40 50 60 70

Percent netplankton

30 40 50 60 70

Percent netplankton

20

20

and Penobscot Bay. Here, mean chlorophyll concentrations are modest, between 1 and 41lg/l, but nevertheless

represent a doubling over mean values in NovemberDecember. Along the outer shelf, Chlwis approximately

0.5-1 Ilg/1 on Georges Bank and increases to -1-2 Ilg1

I in the southern end of the Middle Atlantic Bight. The

lowest values (0.25-0.5Ilg/l) during January-February

occur in the northern Gulf of Maine and at some of the

most seaward stations sampled along the shelf-break.

The distributional pattern and magnitude ofChlwalong

II

10

10

A

B

o

o

o

800

1,600

3,200

Figure 10

(A) Frequency and cumulative percent distributions of the percent of

chloroplyll a in netplankton size-fraction (>20 ~m) in 56,632 discrete water

samples. (Samples having total chlorophyll concentrations less than 0.04 ~g/I

are not included since the estimates of percent netplankton would be

imprecise.) (B) Cumulative percent distributions of percent of chlorophyll a

in netplankton for five depth strata: 1 (0<3 m); 5 (3<8 m); 15 (13<18 m); 25

(23<28 m); 50 (38<63 m)_

G 2,400 1:=

Q)

;:l

0'

£

Horizontal Distribution of Chlorophyll

A wide range in mean water column chlorophyll concentration (ChI,) is obvious in each of the two-month

composite distributions (Fig. 11) and in most of the

distributions based on individual surveys (Append. B).

The contoured two-month distributions are generated

from Chlwaveraged by tile. The range, mean, and coefficient of variation of ChI", for each of the 193 tiles,

tabulated by two-mon th periods, is provided in Table

C3. The precision (coefficient of

variation or CV) of the Chlw estimates is depicted in Fig. 12. The

sampling frequency per tile was

judged insufficient for constructing

representative contours of the

monthly distribution of Chlw' The

two-month composites will obscure,

in the mean, shorter-period chlorophyll events or pulses such as those

obvious from survey to survey (Append. B). For the climatological intent of this monograph, the twomonth portrayals adequately represent the major broadscale and seasonal features ofinterest, except perhaps in portions of the GulfofMaine

which were sampled infrequently

duringJanuary-February and MarchApril (Fig. 13).

High levels ofChlw' between 4 and

16 Ilg/l, occur in the shallow

nearshore waters (-<30 m) of the

Middle Atlantic Bight during the

January-February period. These

concentrations are about double

those observed in November-December, and indicate that the WSbloom commences relatively early

in nearshore water. The 2 Ilg/1

isochlor parallels the 60 m isobath

from Nantucket Shoals to Cape

Hatteras, but not on Georges Bank

(Fig. 11). Water column chlorophyll

concentration exceeding 2 Ilg/1 is

restricted to a small area in the shallow water on Georges Bank, and

Chlw during January-February is

generally lower than the proceeding November-December period.

This suggests that the WS-bloom has

not yet begun on Georges Bank. An

early WS-bloom also occurs in isolated nearshore areas ofthe western

Gulf of Maine, between Cape Cod
18 NOAA Technical Report NMFS 139 _

CWorophyll a

mean, upper 75 m

1977-1988

Jan-Feb

May-Jun

Sep-Oct

Mar-Apr

Jul-Aug

Nov-Dec

Figure II

Contoured distribution of chlorophyll a in the upper 75 m ofthe water column duringJan-Feb, Ylarch-Apr, May-June,July-Aug, SeptOct, and ov-Dec. Depth-weighted means (Chi) were composited by tIle and 2-mo periods before contouring.
_____ O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 19

40

160

80

20

·0

Jul-Aug

Mar-Apr

Nov-Dec

mean, upper 75 m

1977-1988

Coefficient of variation

Figure 12

Contoured distribution of percent coefficient of variation (C.V.) of average concentration of chlorophyll a in the upper 75 m of

the water column duringJan-Feb, March-Apr, May-June,July-Aug, Sept-Oct, and Nov-Dec. Depth-weighted means (Chi) were

composited by tile and 2-mo periods before contouring.
20 NOAA Technical Report NMFS 139

Number of profiles

upper 75 m

1977-1988

....

"

o

o

a ./ ,. - - • 0

.,; . o 'iI." o ,,0 -. :-.... o ur._~..o··

o 0

0 00

a 0

o a 0 0

o

'. a

a

9. ...a---·· g '. o 0 0 o ,8" 0 0

a a 0 0 DoDo

o 0 0 O· 0 ,ri

08 00 ° 0 ._

o 0 0

o 0 0 o"-~',b--"'"

o .0'-"'"

N

2

3

4

6 0 8 0 11

0 16

0 22

0 32

o

o 0

o

po .

o 0

a a 00 t;J..,.······D···· o P 0

o ..

o~·:·o

0 .....0

o ,

[] ~._.D

[] ,.0

o

o 0

o .,'

p'

o •

00

~o 0 ...... "'0'" .·..... ..A ••• 'h- ,0···· 0

0 0 \ c:

o ..0

a ..

Jul-Aug

Nov-Dec

Mar-Apr

r{'

;\..- 0' o·

~'D

[] i

0;

.'

...-: '

o

9· ." .. ,. .0

.~;

0 0 0 0 0 0 0 0 .,

0

0 0

o 0

o 0

00

.0

a., ,_'" ~"".".

:r ....

D 0

!" ."

o ./

.ri

, ,O"'~

o co:. J

o ,0

o

o 0 O.....0"-

Sep-Oct

May-Jun

Jan-Feb

O'

~.

'l:'

... .. o~.

0'

..---

Figure 13

~umber of vertical profiles (stations) used in calculation of ChI" and related calculations, during jan-Feb, March-Apr, Mayjune,july-Aug, Sept-Oct, and Nov-Dec.
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 21

the shelf-break and in offshore areas of the Gulf of

Maine in January-February are essentially unchanged

from November-December.

In March-April, Chlwover the shallows on Georges

Bank and flanking Nantucket Shoals reaches WS-bloom

levels (2-8 J.lg/I). In the Middle Atlantic Bight, between

Long Island and north of Chesapeake Bay, the WSbloom extends from the coast to the shelf-break (Fig.

11). High Chlwis also observed adjacent to the mouths

of estuaries in the Middle Atlantic Bight, but Chlw in

the nearshore bight has generally decreased from the

January-February period. Some exceptionally low values (0.13-0.25 J.lg/I) are present in the central region

of the Gulf of Maine. (Note, however, that the composite distribution in March-April for the northern half of

the Gulf of Maine is based on very few observations

(Fig. 13) and may not represent true mean conditions).

In May-June, the highest Chlw values (-2-4 J.lg/l)

occur near the Middle Atlantic Bight estuaries and over

shallow areas on Georges Bank. In both areas values are

lower than in the preceding period. The lowest Chlw (0.25-0.5 J.lg 1-1) is found along the shelf-break in the

Middle Atlantic Bight.

Overall, the July-August period represents the annual minimum in mean water column concentrations

of chlorophyll a. On Georges Bank, Chlwhas decreased

progressively since the annual peak in March-April. In

the Middle Atlantic Bight, the 2 J.lg 1-1 isochlor has

receded from the 60 m to the -40 m isobath since the

May-June period. Water column chlorophyll concentration is again highest in the nearshore Middle Atlantic Bight and the shallow water on Georges Bank.

The pattern ofChlwdistribution in the Middle Atlantic Bight during September-October is similar to the

distribution during July-August, except that in the

nearshore area (-<30 m) levels during September-October are higher (Fig. II). Similar increases are evident

in the shallow water on Georges Bank, Western Gulf of

Maine, and off the coast of Nova Scotia. These relative

increases constitute the fall bloom, an event of lesser

magnitude than the WS-bloom.

During November-December, phytoplankton distribution on Georges Bank is similar to the pattern in

September-October. In the nearshore Middle Atlantic

Bight, Chlw ranges between 2 and 5 J.lg 1-1, a slight

increase over the September-October period. Mean

values exceeding 2 J.lg 1-1 occur nearshore, between

Narragansett Bay and the southern flank of Nantucket

Shoals (Fig. 11). In the Middle Atlantic Bight, the 2 J.lg 1-1

and 1 J.lg 1-1 isochlors extend farther offshore in November-December than during the preceding period, indicating a seaward extension of the fall bloom. Throughout

much of the northern GulfofMaine, chlorophyll concentrations are below 0.5 J.lg 1-1, much less than values on

Georges Bank and the nearshore Middle Atlantic Bight.

Horizontal Distribution of

Netplankton/Nanoplankton

There is considerable horizontal and temporal variation in the size composition of the phytoplankton community, indexed as percent netplankton (Fig. 14).

Throughout most ofthe year, percent netplankton generally decreases from the nearshore to offshore Middle

Atlantic Bight. Similarly, an annular, bathymetric pattern in phytoplankton size composition is evident on

Georges Bank, where percent netplankton usually decreases from the shallow to deeper water.

In the nearshore areas of the Middle Atlantic Bight,

the shallow water on Georges Bank, and in western Gulf

of Maine, 40-80% of the chlorophyll is bound in the

netplankton size-fraction during January-February. Elevated percent netplankton occurs in areas with elevated Chlw (cf. Figs. 11 and 14) and reflects the initiation of a WS-bloom, presumably comprised of large

diatoms and chains or colonies of smaller diatoms retained on a 20 m mesh. The areas with lowest Chi also w

have the lowest percent netplankton (cf. Figs. 11 and

14). The spatial contrasts in the size composition of the

phytoplankton at this time are extreme: netplankton

predominate in nearshore areas of the Middle Atlantic

Bight and shallow water on Georges Bank, while

nanoplankton predominate in deeper water on Georges

Bank, along the shelf-break, and surrounding the Jordan Basin in the Gulf of Maine.

The advance of the WS-bloom across the Middle

Atlantic Bight and deeper areas on Georges Bank during March-April is evident in the distribution of percent netplankton (Fig. 14). The initiation of the WSbloom in the western Gulf of Maine and easterly sweep

across the gulf, noted by Curra (1987), is also evident.

March-April is the peak period of netplankton dominance on the northeast U.S. continental shelf.

Netplankton exceeds 60% ofthe total biomass throughout a large portion of the Middle Atlantic Bight and

Georges Bank. Although chlorophyll concentrations

are still elevated in the nearshore region of the Middle

Atlantic Bight, there is an overall decrease in percent

netplankton from the January-February period. This

may indicate a successional change toward post-WSbloom phytoplankton assemblages.

The composite distributions for May-June and JulyAugust periods indicate that nanoplankton generally

dominate the phytoplankton (Fig. 14). However, in the

Middle Atlantic Bight, south of Long Island, a broad

band exists where netplankton and nanoplankton are

approximately equal. A similar phytoplankton size composition is evident in the shallow water on Georges

Bank. Percent netplankton is relatively high in patches

in the western Gulf of Maine, off Casco Bay and Penobscott Bay. July-August is the only period when mean
22 NOAA Technical Report NMFS 139 _

Percent netptankton

mean, upper 75 m

1977-1988

Jan-Feb

May-lun

Sep-Oct

Mar-Apr

Jut-Aug

Nov-Dec

Percent

100

95

80

60

40

20

.5

·0

Figure 14

Distribution of percent netplankton chlorophyll a in the upper 75 m ofthe water column duringJan-Feb, March-Apr, May-June,

July-Aug, Sept-Oct, and ov-Dec. Depth-weighted means (ChI,) were composited by tile and 2-mo periods before contouring.
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 23

6

6

1

j

6

,

•

5

5

4

4

3

2 3

• •• fill ... 80 .!'- ~.

M -t.i.F'''1.- ..... •• - 60 • .~ •• I. • ..... . 40 :,~J .,

'" • ,_ e.

t

I •

20 I..'. \. • Mar-Apr o •

12 o I 2 3 4 5

•

•

10

•

4 S 6 0 I 2

Chlorophyll a (ug/l)

8

.

'" .

Jan-Feb

3

6

2

4

•.

2

.: '" .. :~-:: . ~."J, ,,- . 'h.••,." • • &:-.... . . •

20~ o~_~_~_~_-"-----_--'--------..J

o

40

l00 ,----.-~-~--.---~-----, l00 ,---~-----,-.----,------.---,

80

60~

100 r~~-~---~---, 100 ,----.-~-~---,--~----,

.§ 80 .. 80 . 5 •• • _. • ., '~60 ~. 60· • •• • '0. .~. ~.. • )••• Q) ..!i..r...., ••• ~. \ = 40 ..~... • • 40 f-.. "',. ... '5 .~~ ••• : f

t

OO :.....

20 Ii 20· ••• ..- May-Jull •• • Jul-Aug

0.. O· , 0 .f"

012345601

100 ]OO~ , , ,

=r ~~n ...•.. : \.~~:....~ : 40

f

S";;:.:J ... .. j- 40 .f!'~~~;1:·'·..·: ...:.,

O • 4 20 ,.. •••

2 ". .' .... 0 :ff Nov-Dec ••• ~ep- ct • o ,••~._~,_~,__~_ OL·_·_·--'---_~_~_~~_~._J

Figure 15

Relationship between mean percent of water column chlorophyll in netplankton

and mean water column chlorophyll (l concentration for Jan-Feb, March-Apr,

May--June, July-Aug, Sept-Oct, and Nov-Dec. Data points represent means for

each tile.

percent netplankton values do

not exceed 60% in the shallow

areas of Georges Bank. During

September-October and continuing through November-December, percent netplankton increases on Georges Bank, reaching 60-80%. In contrast, ~xcept

for patches off Narragansett Bay,

only modest changes in percent

netplankton are seen in the

Middle Atlantic Bight fromJulyAugust to November-December.

There is a direct relationship

between mean Chlw and mean

percent netplankton throughout

the annual cycle (Fig. 15) and

increases in Chlw' particularly

above 1 Ilg 1-1, are more related

to netplankton increases than to

nanoplankton increases. During

many of the two-month periods,

elevated levels of Chlw are observed in areas adjacent to the

three Middle Atlantic Bight estuaries. Malone et al. (1980) suggested that during winter-spring

periods of netplankton abundance in coastal water, the coastal

water acts as a source and the

estuary as a sink for netplankton.

In the stratified season, the

nanoplankton and fl3.gellate

blooms in the estuarine surface

water represent a source of new

phytoplankton and the coastal

water a sink.

Percent Phaeopigment

The percent phaeopigment index provides additional

diagnostic information on the plankton community.

Very low values indicate rapid phytoplankton growth

combined with minimal grazing by zooplankton. High

values are not as unambiguously in terpreted. They would

indicate either a senescent phytoplankton community

or extensive grazing by copepods (Downs and Lorenzen,

1985; Falkowski et aI., 1988), or methodological error

due to chlorophyll band c (Trees et aI., 1985).

Despite this ambiguity, regular, distinct patterns of

increasing percen t phaeopigmen t from shallow to deep

water are evident in the two-month composite distributions (Fig. 16). Percent phaeophytin is relatively low in

Middle Atlantic Bight shelf water and shallow water

over Georges Bank and relatively high in the offshore

Gulf ofMaine and along the shelf-break. In many of the

subareas, seasonal variation in median percent phaeopigment is modest or not apparent. Over the annual

cycle the range of median values is -20% and in some

areas only 10%. The largest sea~onal variation appears

in subareas where WS-bloom is intense or prolonged.

During January-February, the lowest percen t phaeopigment occurs in regions with highest Chlw and highest percent netplankton (cf. Figs. 11, 14, and 16). Values below 20% are evident nearshore, in large patches

adjacent to the Hudson-Raritan and Delaware estuaries, arragansett Bay, and the western Gulf of Maine

(Fig. 16). Over most of Georges Bank and the eastern

half of the Gulf of Maine, values exceed 30%, whereas
24 NOAA Technical Report NMFS 139 _

Percent phaeopigment

mean, upper 75 m

1977-1988

lan-Feb

May-lun

Sep-Oct

Mar-Apr

luI-Aug

Nov-Dec

Percent

100

80

70

60

50

40

30

20

10

o

Figure 16

Distribution of average percent phaeopigment in the upper 75 m of the water column during Jan-Feb, March-Apr, May-June,JulyAug, Sept-Oct, and Nov-Dec. Depth-weighted means (ChU were composited by tile and 2-mo periods before contouring.
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 25

100

100

100

80

80

80

60

60

60

40

40

20 40

20

Jul-Aug

10 Mar-Apr

oL--_~_~__~_~_ ____'

100 0

60 "'--~---'--~-~n-:1-89-

SO :. i: 46.54 s: -0.43 r: -0.58

80

40

30

20

10 Nov-Dec

OL--_~_~__~_~_--.J

80 100 0 20

Percent netplankton

60

60

Recurring Patterns in Phytoplankton Biomass

There are recurring patterns in the distribution ofphytoplankton chlorophyll on the northeast U.S. shelf that

are evident throughout most of the year (Append. Fig.

B1-B38). In general, chlorophyll concentrations decrease with increasing bottom depth and distance from

shore. On Georges Bank, relatively high concentrations

of Chlw are consistently found within the shallow, tidally well-mixed waters approximately delineated by the

60 m isobath. Chloropleths which decrease from shallow to deep (e.g. Append. Figs. Bll, B15, B20, B22,

B33, B34, and B35) are roughly concentric (annular)

n: 185 60 n: 174

i: 45.04 50 , I·· i: 51.39 .. s: -0.37 s: -0.46 r: -0.77 r: -0.80

40 . •

30

20

40

40

• •

20

20

Jan-Feb

Sep-Oct

...

40

10

oL--__~_~__~_~_ ___'

o

20

20

60 ,---~-~-~--.-----,

50

30

10

oL--_~_~__~_~_ ___'

o

60 ,---~-~-~-~n-:-19-0--'

50 i: 40.73 s: -0.32 r: -0.62

....

c

8 10 May-Jun 10 ..... 0 L--_~_~__~_~_ ___' 0 L--_~_~__~_~_ ____'

o 20 40 60 80 I 00 0

60 n: 192 60,--~--~----r--~n-:-1-83---'

50 i: 44.67 50 i: 42.95 s: -0.36 s: -0.32 r: -0.58 r: -0.72

....

c

(1)

E

Of}

'5. 40

o

30

..c

0.. 20

Figure 17

Relationship between mean percent phaeopigment and mean percent

netplankton in the upper 75 m of the water column duringJan-Feb, March-Apr,

May-June, July-Aug, Sept-Oct, and Nov-Dec. Data points represent means for

each tile. Line represents functional regression (n=number of observations,

r=correlation coefficient, s=functional slope, i=functional intercept).

throughout most ofthe Middle

Atlantic Bight shelf water, values are less. The percen t

phaeopigment index reinforces

the generalization, based on increases in Chlw and increases

in percent netplankton, that

the W5-bloom commences in

January-February in the nearshore areas of the Middle Atlantic Bight and the western

Gulf of Maine, and extends

throughout the Middle Atlantic Bight and over Georges Bank

during March-April.

Overall, the percent phaeopigment index is highest during the July-August and September-October periods. In

November-December, percent

phaeophytin is high (>30%)

throughout most of the Gulf of

Maine, when compared with

the band of relatively lower values extending throughout most

of the Middle Atlantic Bight

and onto the shallow water on

Georges Bank.

Throughout the annual

cycle, percent phaeopigment

generally decreases as the percent netplankton and Chlw increase (Fig. 17). Since the increases in Chlw above 1 g I-I are

primarily due to the netplankton (Fig. 15), low percent

phaeopigment values probably

reflect relatively rapid (netplankton) growth. Alternatively, actively dividing chain

and colonial forms of phytoplankton and larger dinoflagellates are likely to be retained in the netplankton

pigment fraction, whereas chlorophyll degradation

products such as phaeophytin a would tend to be decimated and more likely recovered in the particulate

fraction passing the 20 m mesh (nanoplankton). These

percent phaeopigment patterns reported may also reflect temporal and spatial variation in phytoplankton

species composition and pigment composition (the relative amounts chlorophylls a, b, and c), because the

fluorometric method used here to derive chlorophyll a

and phaeophytin a is known to be influenced adversely

by moderate concentrations of chlorophyll b and chlorophyll c (Trees et aI., 1985; Welschmeyer, 1994).
26 NOAA Technical Report NMFS 139 _

Table 2

Ranking of tiles with Chi" exceeding 8 llg I-I two or

more times.

around the epicenter which is generally found toward

the middle of the southern half of the shallows (Fig. 5:

Tiles 123, 147, 148, 156). Similarly, in the MAB,

chloropleths frequently parallel isobaths. Water column chlorophyll concentration is usually highest in

shallow water and decreases offshore with increasing

bottom depth until minima are reached along the shelfbreak. Exceptionally high (>8 /lg 1-1) Chlw ' when present

in the Middle Atlantic Bight (Table 2), usually occurs

near the mouths of the Hudson-Raritan, Delaware, and

Chesapeake bays, areas receiving high concentrations

of river-borne nutrients (e.g. Malone, 1976; Malone,

1984). Occasionally, high Chlw concentrations are found

in Middle Atlantic Bight coastal waters not in close

proximity to estuaries, and may reflect upwelling episodes. High Chlw are also found in a small area along

the southeast edge of Nantucket Shoals (Table 2). In

the Gulf of Maine, Chlw is usually greatest near the

coast in pockets near Cape Cod Bay, Massachusetts Bay,

Casco Bay, and Penobscott Bay. Highest concentrations

are generally found between Penobscot and Casco bays.

Lowest values are generally found in the deeper water

over the offshore basins.

Tile

55

187

12

185

29

184

28

23

93

13

56

53

41

42

68

21

11

76

123

148

126

Subarea

MABI Hudson-Raritan plume

MAB Hudson-Raritan plume

MAB Chesapeake plume

MAB central nearshore

MAB Delaware plume

MAB Delaware plume

MAB southern nearshore

MAB southern nearshore

GB2 Nantucket shoals

MAB southern midsherf

MAB central nearshore

MAB central nearshore

MAB central nearshore

MAB cen tral nearshore

MAB central nearshore

MAB southern nearshore

MAB southern nearshore

MAB northern midshelf

GB central shoals

GB central shoals

GOM3 Wilkinson Basin

Frequency

28.0

17.0

11.0

9.0

9.0

7.0

7.0

5.0

4.0

3.0

3.0

3.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

Cross-Shelf Chlw Gradients

A significant portion of the spatial variation in phytoplankton biomass is related to bottom depth. When

considering the entire dataset, there is nearly an eightfold decrease in Chlw from the shallowest to the deepest water column sampled (Fig. 18). The correlation

coefficient between log2(Chlw' /lg I-I) and log2 (bottom

depth, meters) is -0.53 and the linear regression (leastsquares-y) is highly significant at <0.00001 P. The regression line in Fig. 18 does not represent well those

areas deeper than -250 m, because sampling was usually limited to the upper 100 m and chlorophyll concentrations below 100 m are less than those above.

Therefore, values in the deep water overestimate Chlw

and are above the regression line. The independence

between Chlw and bottom depths greater than -250 m

suggests that the depth of the permanent thermocline

over slope water (and the relevant vertical mixing depth

for plankton in these areas) may express the relationship more appropriately.

When we examine the data by region and season we

find significant exceptions to the above-generalized

cross-shelf Chlw gradient. In fact, there is a distinct

seasonality in the magnitude of the cross-shelf chlorophyll gradient and notable differences among shelf

regions (Fig. 19). The steepest cross-shelf Chlw gradients on Georges Bank occur during February and March.

Water column chlorophyll concentration in the shallowest water sampled is approximately 25-38 times Chlw

1 MAB=Middle Atlantic Bight.

2 GB=Georges Bank.

3 GOM=Gulf of Maine.

ID the deepest water. This is a significant departure

from the mean cross-shelf gradient of 8: 1 shown in Fig.

18, and reflects the initiation of the WS-bloom in shallow central Georges Bank. Similarly, the steepest gradients in the Middle Atlantic Bight reflect the appearance of the WS-bloom nearshore in January-February.

As the WS-bloom spreads offshore in the Middle Atlantic Bight during March-April and into deeper water on

Georges Bank during April, cross-shelf Chlw gradients

drop precipitously, approaching the annual minimum.

In a number of surveys that captured WS-bloom conditions, cross-shelf gradients in chlorophyll are not obvious (Append. Figs. B16, B17, B22, B23, and B26).

On Georges Bank, Chlw gradients are low from June

through August when the central tidally-mixed area

reaches its annual Chlw minimum (Fig. 11; Append.

Figs. B6 and B19). During summer the presence of a

pronounced subsurface chlorophyll maximum layer in

the seasonal thermocline in deeper, stratified waters

also tends to diminish the magnitude of the cross-bank

Chlw gradient (see section "Subsurface Chlorophyll

Maximum" below).

In the Gulf of Maine, Chlw gradients are muted relative to the Middle Atlantic Bight and Georges Bank.

Many of the estimated gradien ts (linear regression
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 27

40 4

35 3.5

Gulf of Maine

30 3

25 • Gradient 2.5

20 .... Chlw @ Gradient (n.s.) 2

15 1.5

10 .....................•.

". ..........

5 0.5

0 0

40 4

C 35 3.5 eu 30 Georges Bank

:a 3 (OJ

....

0.0 25 2.5

::c 20 2 ::a

U U ...... 15 1.5 a:i

..c

'1 10 on

on

0

.... 5 0.5

U

0 0

40 4

35 3.5

30

Middle Atlantic Bight 3

25 2.5

20 2

15 1.5

10

5 0.5

0 0

J FMAMJ J A S ON D

32 5

Log2(Chl) =3.94 - 0.644(Log2 (bottom depth)) r=-0.54

16 4

8 3

4 2

,-.. 2

OJ) 0 ::: -=. ::a

::: .5 -I U

::a N

U .25 OJ)

-2 0

.....l

.13 -3

.063 -4

.03 -5

.016 -6

.008 -7

(Log2) 3 4 5 6 7 8 9 10 II 12

(m) 8 16 32 64 128 256 512 1024 2048 4096

Bottom depth (m)

Figure 19

(Right) Cross-shelf (bathymetric) gradient in Chlw and mean Chlw versus month for

Gulf of Maine, Georges Bank, and Middle Atlantic Bight regions. Cross-shelf gradients were computed as the product of the slopes from least-squares-y regressions of

log2 (water column chlorophyll a) on log2 (bottom depth) times the depth range for

each region (Gulf of Maine: 32-256 m, Georges Bank: 22.6-256 m, Middle Atlantic

Bight: 8-256 m). Bottom depths greater than 256 m were ignored in the regression.

The linear regression model explained a significant portion of the chlorophyll

variation (probability of a larger F-value<O.OOl) and computed regression slopes

were significantly different from zero (p<O.OOl) for all gradient values except those

circled (not significant, n.s.).

Figure 18

(Above) Relationship between Chlw and bottom depth (all data). Line represents

least-squares linear regression (r=correlation coefficien t).

slopes) are not significantly different from zero. Still,

the annual maximum gradient occurs during March,

the time of the WS-bloom in the western gulf.

The cross-shelf, depth-related decrease in the mean

water column chlorophyll a reported here has also

been observed during oceanographic surveys of other

shelf ecosystems, such as the Southern California Bight

(Eppley et aI., 1978), the Southeast Atlantic Bight

(Haines and Dunstan, 1975), and in coastal waters off

Washington and Oregon (Anderson, 1964). The general cross-shelfgradient in phytoplankton pigment concentrations in near surface water on the northeast U.S.

continental shelf is also evident in monthly composites

of satellite images remotely sensed using the CZCS

(Feldman et aI., 1989). Off the coast of Georgia, in the

Southeast Atlantic Bight, Bishop et aI. (1980) found

high concentrations of chlorophyll in nearshore surface water (1.9-8.0 Ilg/l), and lower concentrations at

midshelf, 20-30 km offshore (<1.0 Ilg/l). Along the

shelf-break, 100 km offshore, they observed even lower

values (0.1-0.2 Ilg) in surface water throughout the

year, except during upwelling episodes when concentrations reached -2-6 Ilg/I. Occasionally our surveys

detected small patches of high Chlw along the shelfbreak (Append. B), where low concentrations are usually observed. Phytoplankton in these areas may be

responding to localized nutrient enrichment due to

upwelling along the shelf-break, although this process

is not as obvious or recurrent in our data as in other

studies of the area (Marra et aI., 1990) or along the
28 NOAA Technical Report NMFS 139 _

shelf-break south of Cape Hatteras (Yoder et aL, 1983,

1985).

A somewhat different pattern from water column

average chlorophyll emerges when the chlorophyll data

are integrated to 75 m (Chi) and expressed as standing

stocks per m2 (Fig. 20). Integrated chlorophyll will

naturally underestimate standing stocks in water deeper

than 75 m, and more so during the unstratified season

than the stratified season, when concentrations are

modest below 75 m. As is the case for Chlw' bathymetric

gradients in Chli are present on Georges Bank during

each of the two-mon th periods, the most pronounced

during the March-April WS-bloom. However, the crossshelf gradient in Chli in the Middle Atlantic Bight differs from the cross-shelf decreases in Chlw (cf. Fig. 11,

20). During the March-April WS-bloom, Chli is higher

at mid- and outer shelf and shelf-break areas than

nearshore, except for small patches near the estuaries.

These observations agree with those reported for the

New York Bight (Malone et aI., 1983b). Off Chesapeake

Bay, Chli increases from the coast to the shelf-break

(March-April, May-June) or is relatively uniform across

the shelf (remaining periods). In this area, there is no

strong onshore-offshore bathymetric gradient as found

to the north (Fig. 20); the 60 m isobath converges

offshore with the 200 m isobath, resulting in a narrow,

uniformly shallow shelf.

Recurring Patterns in

Phytoplankton Size Composition

Recurring onshore-offshore patterns in the size composition of the phytoplankton on the northeast U.S. shelf

are also evident in the two-month composite maps of

size-fractionated Chlw (Fig. 14) and in the distributions

from individual surveys (Append. B). However, the sizestructure pattern varies more by season and region

than does biomass. Generally netplankton dominate

phytoplankton in areas where Chlw is consistently high,

such as the nearshore Middle Atlantic Bight and the

shallow water on Georges Bank, while nanoplankton

dominate in areas that have low Chlw , such as deeper

water along the slope and in deep offshore water in the

Gulf of Maine. These general gradients in size composition reflect the shift from a predominantly diatom flora

nearshore to a phytoflagellate flora offshore (Marshall,

1976, 1984; Malone et aI., 1983b). Curra (1987) reported that total phytoplankton cell abundance (primarily diatoms) during early spring and summer in the

shallow waters on Georges Bank is at least ten times that

observed in the surrounding deeper water (primarily

dinoflagellates). The prolonged presence of diatoms following the WS-bloom seems to be a characteristic feature

ofshallow, vertically well-mixed waters on Georges Bank.

In contrast, diatoms are particularly sparse in the central Gulf of Maine during summer (Curra, 1987).

Onshore-offshore gradients in the size composition

of the phytoplankton have been observed on other

continental shelves. Bishop et al. (1980) reported a

seaward decrease in percent netplankton (>10 11m) in

the South Atlantic Bight off the coast of Georgia.

Annual Cycle of Chlw

Water column chlorophyll concentration generally folIowan annual cycle typical of temperate shelf ecosystems. In most shelf areas, Chlw is low from late spring

through late summer, the period of strongest vertical

density stratification of the water column, and relatively

high during the unstratified season, with highest values

observed during spring and fall blooms (Fig. 21). Fall

bloom is generally subordinate in magnitude to spring

bloom. Minor blooms or "bursts" occur outside ofspring

and fall bloom time periods but their duration is short

and their occurrence unpredictable from year to year

as they result from conditions temporarily favorable for

phytoplankton growth or accumulation.

This general cycle is most recognizable in the central

and northern midshelf areas of the Middle Atlantic

Bight (Fig. 21). However, it is also obvious that there is

considerable variation among shelf areas in the timing

and duration of winter-spring and fall blooms, and in

the overall magnitude ofChlw' WS-bloom begins earlier

(january-February) and persists longer in southern and/

or shallow waters than in northern and/or deeper waters. By March, WS-bloom is in progress over most of

the shelf between Long Island and north of Chesapeake Bay. By April, WS-bloom is past throughout most

of the shelf except deeper northern.waters which have

Chlw peaks in April (Gulf of Maine Wilkinson Basin,

Georges Bank southern flank, and Georges Bank Great

South Channel) and April-May (Georges Bank northern slope).

With the exception of areas in the Middle Atlantic

Bight influenced by river plumes, Chlw over the entire

shelf are at or near annual minima during July and

August (Figs. 11 and 22). Only during this period are

most stratified shelf areas at the same stage of the

annual cycle, when cross-shelf gradients in Chlw are

weakest (Fig. 19). Water column chlorophyll concentration is low from May through September throughout

the Middle Atlantic Bight, and in subareas-Georges

Bank southern flank, Georges Bank northern slope,

and Gulf of Maine western, Wilkinson Basin, and

Georges Basin. Like spring bloom, fall bloom progresses

from shallow to deeper water, beginning early in southern shallow water in October and starting in deeper

water in October- ovember.
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 29

Chlorophyll a

Integrated, upper 75 m

1977-1988

Jan-Feb

May-Jun

Sep-Oct

Mar-Apr

Jul-Aug

Nov-Dec

a (mg/m2

)

>640

640

320

160

80

40

20

o

Figure 20

Contoured distribution of integrated chlorophyll a in the upper 75 m of the water column during Jan-Feb, March-Apr, May-June,

July-Aug, Sept-Oct, and ov-Dec. Integrated chlorophyll a data were composited by tile and 2-mo periods before contouring.
30 NOAA Technical Report NMFS 139

l_:~~ti1l.~r~~~~s~n _:_ tIl I I I 1 I I I I

I I I , 1 I I I I 1 I

1 _1_ L J _1_ L 1 _1_ L 1 _I_

I I I I I 1 I I I 1 I

I I I I 1 I I I I I I

..I. _,_ L .1 _1_ L .1 _I _ L .1 _,_

I t 1 •• I I I I I I

I 1 I • '. I I It.' I

-t -1- I- -t • .-- I- -t -1- I- 5 -1-

: : : I.: : : : 1

j-I-r ri-I- -tJ FMAMJ J ASOND

: yBI N,an~u~k~t ~h~al~ :

I -,- I 1 -.- II -1- I I -.-

f

:_:~~ • I I

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I :.: 1 ;.:. ::.:

~-:-~~~~-~ :-~.~-~-

I I 1 I 'I ., I , I

MA~ :Northern Outer Shelf 1-'.1- I" -I-II -1- II -II ,- I I I I I I I I I

1 _1_ '-.1 _1_ L .! _1_ L 1 _'_ • I I I I t I I I I I

I 1.1 I I I I It. I 'I

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•• ~I I I I I I I I '.

-+ ~"'.".I- r-.-+ -1- 1-.-+- '- 1'1 I I- I I I I I

r!;~••~"'I. I. I~4_ 1'1·

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1-'-11-'-11-'-11-1-

I 1 I , I I , , , , 1

1_1_ L 1._'_ L J _,_ L J _'_ , 1 , , , I , I I I 1

1 I I I I , 1 1 , , •

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-t - I- -t <'-I- -t -1- I- -t -II .1.' I I I I • I

I I I I 1 I 1 I

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. I I "I I I· I I I I '- t.

I .MAB Delaware Plume.I_- I I I I I T I I t I I

I I. I I I I • I

,e;. -:- I !.I- - • I i",-

I I I I I I·:I 1-'

J_"_LJ_I_ ..I _L .... _I_

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-I-I- -l-,r -f 1- f- -f -I..

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I I I I J 1.1 I • I I

I I I I I I I I I I I

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, t , I.' , , , 1 1 ,

.1 _'_ L...! _'_ L.1 _'_ L J _'_ , I I I I I I I I I ,

I , , I I , I , 1 I '.

.1 _,_ .... ...J _I!. L. .1 _,_ l.. .J _' .....

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• ..1'.1" -

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GB Great South Channel 'I -,"'-, ,,-,- II -,- II -,-

I • I I I I I I Itt

I t I I I I I I I I I '-1-' '';'-11-'-11-'- I J , I '. I I I I I I

J _1_ _1_ L .J _1_ L J _I_

I '. .11 I I I I I r 1 I -'I I. I I .-1

-+- I--t-I.I-'-.-I-

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6 1 , , , I I I It' ,

I GOM Scotian Shelf I

5 I -,- II -,- II -1- II -,-

, I , 1 , I 1 I I , I

4 ~-:-~~-:;~~-:-~~-:- 1 1 1 I I I I I lit

3 -:- -:~ -:- -:- I , I , " I , , , I 1

2 -:- ..:- ..:.- ~; -:- , 1 I' , • , 1 1 1 i,l-r - ...

f1: - o J FMAMJ J ASOND

;:l

......

o

u

l-;

Q)

....

ro

Figure 21

Mean water column concentration of chlorophyll a versus month for 26 subareas of the northeast U.S. continental shelf.

Individual observations are represented as dots. The solid line connects monthly means.
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 31

80

60

40

20

o L---'----'------'-----=----'------'---_---'------'

100

80

60

40

20

o JFMAMJJ ASOND

JFMAMJJ ASOND JFMAMJJ ASOND

Figure 22

Mean water column percent netplankton versus month for 26 subareas of the northeast U.S. continental shelf. Individual

observations are represented as dots. The solid line connects monthly means.
32 NOAA Technical Report NMFS 139

A regular seasonal progression of netplankton/

nanoplankton is evident, with percent netplankton

maxima usually coinciding with Chlw maxima during

spring and fall blooms (Fig. 22). However, even though

percent netplankton is at its annual maximum, the

phytoplankton community is not necessarily strongly

dominated everywhere by netplankton as might be expected based on the spring bloom paradigm. In deeper

areas of the Middle Atlantic Bight, on Georges Bank,

and in the Gulf of Maine, the annual cycle of percent

netplankton generally follows that of chlorophyll (cf.

Figs. 21 and 22). In shallow waters less than 60 m

during stratification, neither netplankton nor nanoplankton strongly dominate (percent netplankton -40-

60%). In the outer shelf and slope, nanoplankton generally are strongly dominant through September (percent netplankton-lO-30%) and become less dominant

in October when Chlw begins to increase.

The summer pattern in the southern part of the Gulf

of Maine (western Gulf of Maine, Wilkinson Basin, and

Georges Basin) is similar to that of the Middle Atlantic

Bight. Following the WS-bloom, Chlw is low (-.75-1.0)

and in the western Gulf of Maine increases in October.

The percent netplankton in the southern Gulf of Maine

follows the pattern ofouter shelf (Middle Atlantic Bight)

waters. It ranges from -10-20% and increases during

October (Georges Basin) and November (western Gulf

of Maine and Wilkinson Basin).

Vertical Distribution of Chlorophyll

Some extremely interesting and regular features in the

vertical distribution of phytoplankton are obscured in

portrayals of average water column concentrations previously described. The vertical distribution of chlorophyll a across the continental shelf is illustrated as

cross-sections for individual MARMAP surveys in Append. B. To characterize typical regional and seasonal

patterns in vertical distribution of phytoplankton biomass and size composition, monthly mean profiles were

constructed for subareas of the Middle Atlantic Bight,

Georges Bank, and the Gulf of Maine (Figs. 23-25).

Depending on bottom depth, up to 11 layers of the

water column are represented in a mean chlorophyll a

profile. Layers (depth strata) are approximately centered on standard sampling depths: 1,5,10,15,20,25,

30, 35, 50, 75, and 100 m. These composite profiles

complemen t two-month shelfwide distributional contours

described earlier (Figs. 11 and 14) by providing greater

temporal and vertical resolution but less horizontal resolution of trends, since many tiles are grouped into each

subarea. To enhance legibility and enable seasonal and

regional comparisons, estimates of data dispersion about

the mean values forming each profile are not graphed.

There are large seasonal changes in the vertical distribution of phytoplankton which are mostly related to

seasonal changes in density stratification (Figs. 23-25).

Four general profile shapes are evident: uniform, declining, bell, and inverted. Vertically uniform chlorophyll a profiles are most obvious from November

through February, the period of minimal density stratification (e.g. January-April, outer Middle Atlantic

Bight), and year-round in the tidally well-mixed shallow

water on Georges Bank (e.g. Georges Bank northern

and central shoals). Declining vertical profiles occur

during the winter-spring and fall blooms, where highest biomass appears in the upper 20-30 m of the column (e.g. September-November, nearshore Middle

Atlantic Bight). Inverted profiles occur infrequently.

They are most obvious following the WS-bloom, when

elevated concentrations of chlorophyll a appear near

the bottom of the water column in the midshelf region

of the Middle Atlantic Bight, but they are not found on

Georges Bank and in the Gulf of Maine. Bell-shaped

profiles characterize periods of vertical density stratification. Chlorophyll a is relatively low near surface, progressively increases forming a subsurface chlorophyll

maximum layer generally in the pycnocline (20-35 m

below surface), and then progressively decreases over

the remaining deeper portion of the profile. Subsurface chlorophyll a maxima are ubiquitous during summer in stratified water. Chlorophyll a in the subsurface

maximum layer is generally 2-8 times the concentration in the overlying and underlying water and approaches 50-75% of the levels observed throughout

the upper mixed layer during WS-bloom.

The composite profiles of chlorophyll a also reveal

large vertical gradients in the size composition of phytoplankton during the stratified season. Usually, percent netplankton increases with increasing depth below surface. In some areas, such as the midshelf and

outer shelf Middle Atlantic Bight (Fig. 23), percent

netplankton increases from -10-20% at surface to 40-

70% at 50 m below surface, suggesting substantial vertical differences in the species composition of phytoplankton. Similar but less sharp gradients are observed during summer in the deeper stratified water on Georges

Bank and in the Gulf of Maine.

In general, during late fall and winter the water column is well-mixed and chlorophyll a is evenly distributed throughout the water column in shallower areas

and to -35-50 or 100 m in some of the deepest areas

sampled (Figs. 23-25). The transition between summer

stratification and well-mixed conditions begins as the

upper mixed layer deepens, the water column chlorophyll a maximum is found near surface, and the distributional pattern changes to declining. Subsequent deepening of this upper mixed layer leads to the uniform

chlorophyll a distribution observed during winter. This
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 33

pattern is clear in the Gulf of Maine, deeper waters of

Georges Bank, and in the Middle Atlantic Bight from

midshelf to the slope. In general, the bell shape disappears during September Uordan Basin, Georges Basin,

and the northern Gulf of Maine) or October (remaining areas where summer stratification is observed). By

November, chlorophyll a is vertically uniform in the

upper 35-50 m and remains so until February-March

when the transition to stratified conditions begins. In

the Gulf of Maine (except the western gulf) and the

::..::::.. ::::::::::::..:MAR:DeIaware:Phiine: 20 riL :.. .. ····fe· H ----_.~ . 11

10

9

8

1j JZ;&<i~~J . ··~k····<1\; . nf-''-'...,....'-'.-'. '-'.=''-'-'.'-' '-'-'.'-'--..'',---'-'.'-'......". '.---' .-'.-'.'--.''.-"-.----,.. ,,'.-'.-'.'----,' .;;-' .-'.-'.'-'.-;;-' .-'.-..",.---...,,-------;;;;----1 .)'•••• ?.···.~·· •••·?'•.:;••:.d.•• ;·::·:4'•• ·.:$:•••••f-.:•••;':•••3'•••:r!

.. .::.:::.:::' .j :/...MARChesapeake'Phiriie'14 rill.·····::··::::.:.. ...:::: .. 6 ········l····· ~. 1 •...... j...\J ~J;;t

or----,-J----:;:22,-------;108-----;018----:;:32,-------;7,-------;20;;;---;;;;22------;;15.--------;1<5---1;L6-------,-,U--l ..............::( sgo _

::~:::::::::7:::::::1!::::::::~::::::::<:::::::~::::::::(:::::::~::::::::j:::::::~::::::::;:::::::~ ~g

J F M A M J J A SON D

Figure 23

Monthly composite profiles of chlorophyll a and percent netplankton for subareas in the Middle Atlantic Bight.

(See Fig. 8 for location of subareas.) The profiles were generated by averaging all observations within each of II

depth strata by month. Depth strata bracketed standard sampling depths; I m (0<3); 5 m (3dl); 10 m (8<13); 15 m

(13<18); 20 m () 8<23); 25 m (23<28); 30 m (28<::13); 35 m (33<38); 50 m (38<63); 75 m (63<88); 100 m (88<113).

Four strata are marked: 1 m (large open circle), 20 m (small open circle), 50 m (small solid circle), and 100 m (large

open triangle). The number of water samples in the monthly composite is shown below each chlorophyll a profile.
5

34 NOAA Technical Report NMFS 139 _

5 MAB Northern Midshelf 30-60 m

J: 0~Zj·· ..............> ..•......... ..~. U 1 r/-. A .~ A·cA . of---~-......-;----=>---;;;:,----.;;u---=--........-------..-.------;;:;;----.;;;;-------,w;----,;;;----1

::7:~1t:0<2~;';:;0;.z=2 r!

MAB Central Midshelf 30-60 m

~:: : : r.····::.:::.::..::.::::::.··:::::::: : :..: ::::::.::..::: :..: .

2 .""'\..;rj\f\j\ j\j\.~~ . o1--~---=-----=----=,__ ..____-;;;;;;---__.=_-_____=>-_____.n;;~______...._-;;n----;;;;;;----1

?2~Z:;Jjt£.!ftr:+:22- r!

: ~t;;!~sOUt!leIT1Mi~helf~0-40m~;)I. •.

a1 •••.••••...................... ;!fI·;f···J"····iil /t <?Y .

O"':;2?'!?;;JlA';~/?;:' r!

J F M A M J J A SON D

Figure 23 (continued)
3

2 ..:!.

Q

tJ 1

o

O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 35

MAB Northern Outer Shelf 60-200mOO • t::.

~~5./\. ....;',""~'~

~~~j20;~5.~..IU~?\2? r!

3

2 S.~.~~J:1.€?~. ~~~P~. ~~9.~?Q~9 .~ . ..:!.

al~~"""""""""'" 0I-__=.......::;::....-.......,,...---=;----=,........l!'---=,..-3'.....::::...-=,--""~_=:_"'~=_=~c.=_=--'!!'--_=~~__=,___r."--_=,..J04

~22~:gC0:C2Jb:-.C2~C;S~ r!

J F M A M J J A SON D

Figure 23 (continued)

southern slope of the Middle Atlantic Bight, the depth

of uniform chlorophyll distribution deepens to 100 m

in January and/or February.

Unlike the fall transition, when water column distribution patterns are similar among all areas that are

stratified, the distributional pattern in the water column during spring transition varies among areas. By

February or March in nearshore and midshelf Middle

Atlantic Bight, chlorophyll a is distributed in the water

column in an inverted pattern and remains so until the

appearance of the bell-shaped distribution. In slope

waters, outer shelf Middle Atlantic Bight, and the Gulf

of Maine, the spring profile is declining. Generally the

transition starts in March in southern waters and in

April in northern gulf and Georges Bank waters. Regardless of area, it generally takes two months for the

bell-shaped distribution and subsurface maximum to

appear, occurring in May in the south and June in the

north. Once formed, the bell shape is most distinct in

the Middle Atlantic Bight (central nearshore, northern

and central midshelf, outer shelf and slope); Georges

Bank southern flank and northern slope; and Gulf of

Maine, all regions except Scotian Shelf. In other areas,

subsurface maxima are present but the bell shape is

missing (Middle Atlantic Bight southern nearshore;

Scotian Shelf) or weakly defined (Middle Atlantic Bight

southern midshelf; Georges Bank Great South Channel, eastern outer shoals, and southern flank).

In shallow areas influenced by estuarine plumes and

in the shoal areas of Georges Bank (Figs. 23- 25), the

vertical distribution of chlorophyll a does not fit the

seasonal cycle described above. Vertical profiles for

subareas adjacent to the Hudson-Raritan, Delaware,

and Chesapeake estuaries are "noisier" than comparable nearshore areas remote from the estuaries. This is

expected, given the high temporal variability, sharp

horizontal gradients associated with estuarine plumes,

the small size of these subareas, and our infrequent

sampling. In the Hudson-Raritan Plume, for instance,

the chlorophyll profile shape is declining within the

water column throughout the year except during February, March, July, and December, when a subsurface

maximum is present (Fig. 23).

The following sections characterize monthly variation in the vertical distribution of chlorophyll a by

region and subarea, beginning with the Middle Atlantic
4

36 NOAA Technical Report NMFS 139 _

18sm.;J.·······:·····GBCeiitiaIShoals··3.5-5S···················· . . 7 .. . . . .

6 . .

tl 5 . .

a !~..........••.. .• •••.. ~;..j~?.~ •• .•

•••••·•••••• ¢':••• •••_2••• ;;.~.~0.4v. •• •• ~. ~!

Ji~~~~,~iV1~G:7;:et:ls~m~

·;,.··S••••~.·.·;:\··.~ •. ·.J'.••••;i••••:;;.·.2••• 4··•• i·•••·~ ••

5

.. OB.Western OuterShQals 50-:-60 m

I: boft'rfr;;r~~~~~ 1~ ..

0f---..---,.----....,----;;;;-----,=-----,,,,-------;co-------=c,------=--~--~-- _ ____l

::;.~~~:::::::o::::::±:::~::::~::::~:::~:::/S::::S::::~:::~~~::::=:: W! .. ··?P

::r ··~··M .:········:··GBEastern"Diifer·Shoals 60:'.80 IIi . :::... .:

a1;;.:;..... .........~~~ ~~<Y"'-\~ ..

~-.7~~±i??0-;;.~?±? r!

J F M A M J J A s o N D

Figure 24

Monthly composite profiles of chlorophyll a and percent netplanklOn for subareas on Georges Bank. See Fig. 8 for

location of subareas and Fig. 23 caption for additional details.
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 37

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Figure 24 (continued)

Bight. Once basic patterns in the annual cycle are familiar, only noteworthy similarities and differences between previously described subareas are presented to

avoid repetitious descriptions.

Middle Atlantic Bight-A number of temporal and spatial distributional features evident in the water column

average concentrations discussed earlier are also evident in the composite vertical profiles for the Middle

Atlantic Bight (Fig. 23). The general trend of decreasing phytoplankton biomass from nearshore to slope

water is readily discerned. With some exceptions, this

onshore-offshore gradient is present at each depth stratum year-round; however, the gradient is steeper in

surface water than at mid-depths in the column. The

general trend of decreasing netplankton dominance

from nearshore to the slope is also illustrated in the

composite profiles and is particularly evident during

summer (Fig. 23).

Hudson-Raritan Plume-In the Hudson-Raritan

Plume subarea, highest chlorophyll a is usually observed

in the surface; chlorophyll a generally decreases toward

the bottom of the water column. The WS-bloom appears during January-February as an increase in both

chlorophyll a and percent netplankton from November-December. Winter-spring bloom is strongly dominated by netplankton, presumably diatoms. The annual

maximum biomass in surface water appears in August

when brackish water from the estuary generates the

annual minimum surface salinity (Benway et aI., 1993).
38 NOAA Technical Report NMFS 139 _

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Figure 25

Monthly composite profiles of chlorophyll a and percent netplankton subareas of the Gulf of Maine. See Fig. 8 for

location of subareas and Fig. 23 caption for additional details.
______ O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 39

Over the annual cycle, netplankton prevail over nanoplankton, except during May-June when nanoplankton dominate in the upper layer. During the remaining

months, vertical gradients in size composition are weak.

Delaware Plume-Despite the small sample size used

to form composite profiles, an annual chlorophyll a

cycle is evident (Fig. 23). A vigorous WS-bloom, strongly

dominated by netplankton with chlorophyll a exceeding 10 J..Lg/I, is observed in February (in January there is

insufficientsampling). Following WS-bloom, chlorophyll

a declines, reaching minima during the stratified season as netplankton are replaced by nanoplankton. Vertical size composition gradients are weak except perhaps during May-August when percent netplankton

increases with depth.

Chesapeake Plume-Sampling frequency is inadequate to characterize well the general vertical and

seasonal trends in the Chesapeake Plume subarea, except to note that chlorophyll a is generally elevated and

in the same range as observed for the Hudson-Raritan

and Delaware Plume subareas. In August, a speciessuccession favoring netplankton occurs here, as well as

in the Delaware and Hudson-Raritan subareas.

Nearshore-In the central and southern nearshore,

mean chlorophyll a is elevated above 1 J..Lg I-I throughout the year in nearly all depth strata (Fig. 23). The

annual cycle is well defined, with minima during the

stratified season and maxima during the unstratified

season. Chlorophyll a and netplankton increase progressively from September to the WS-bloom maxima.

Thus, WS-bloom is defined more by the timing of the

annual peak than by abrupt changes in either biomass

or phytoplankton size composition. Winter-spring bloom

in the southern nearshore occurs duringJanuary-February but in the central nearshore it persists from January

through March, and netplankton are more abundant.

During October, a fall bloom is indicated by chlorophyll a and netplankton increases over September values. The fall bloom in the southern nearshore is marked

by more abrupt increases in chlorophyll a and percent

netplankton than that in the central nearshore. Furthermore, the fall bloom does not constitute the secondary annual maximum since biomass following the

bloom, in November-December, is higher.

Subsurface chlorophyll a maxima (SSM) emerge 15-

20 m below surface duringJune-August. Chlorophyll a

in these maxima is more than half the concentration

observed during WS-bloom. Subsurface maxima tend

to be near bottom in the relatively shallow southern

nearshore water column; in the central nearshore, profiles take on a bell shape with lower chlorophyll a above

and below the SSM. Bell shape profiles weaken in September and are replaced by more vertically uniform

chlorophyll a and percent netplankton profiles during

October. Presumably this is the result of destratification

of nearshore water which can begin, with significant

interannual variation, throughout September and is

usually complete by mid October (Ingham et aI., 1982).

From October through March, the period when vertical density stratification is weak and intermittent in

the nearshore Middle Atlantic Bight, there are shifts in

the size composition of the phytoplankton and in the

magnitude of chlorophyll a, but the percent netplankton

profiles are essentially vertically uniform (Fig. 23). In

contrast, during the stratified season, there are vertical

gradients in phytoplankton size composition. For instance, duringJuly percent netplankton increases from

-10% near surface to -60% at the bottom of the

southern nearshore profile (Fig. 23). The percent

netplankton profile for August presents an exception

to this pattern; netplankton prevail throughout the

water column. Perhaps this netplankton shift from the

preceding month reflects the appearance of large motile dinoflagellates? Alternatively, nonmotile netplankton may be responsible. Benway et al. (1993) report

relatively large temperature variations nearshore during August, which they attributed to wind-forced mixing of the shallow water column and upwelling/

downwelling events. Presumably these interruptions of

stratification enrich the surface waters with subpycnocline nutrients as well as reinject netplankton species,

already abundant near the bottom of the column, into

the upper layer.

In the nearshore Middle Atlantic Bight, netplankton

are an important component of the plankton from

October through April, and during August (Fig. 23). In

fact, this sustained contribution by netplankton throughout much of the year is a characteristic feature of the

nearshore bight.

Midshelf-As in the nearshore, a clear annual chlorophyll a cycle is eviden t in the three midshelf subareas

(Fig. 23). Netplankton increase during a prolonged

WS-bloom beginning in January, achieving maximum

dominance in March. The precipitous netplankton decline in April, particularly in the upper column, signifies the end of the WS-bloom.

A secondary biomass peak, half that achieved during

WS-bloom, appears during the October fall bloom.

There are important differences between WS-bloom

and fall bloom. During the WS-bloom, biomass is elevated throughout the water column and netplankton

clearly dominate, but during fall bloom biomass increases are restricted to the upper 20 m and netplankton

and nanoplankton are approximately equal.

There is indication that WS-bloom diatoms are settling out of the water column in March and April; the

shape of the composite chlorophyll a profile (inverse)

is very different from the vertically uniform profiles in

January and February and from those constructed for

the rest of the year. April biomass progressively in-
40 NOAA Technical Report NMFS 139

creases fourfold from surface to near boltom in the

northern midshelf, and twofold in the central midshelf

and southern midshelf. Additionally, large vertical gradients in phytoplankton size composition and presumably species composition are established in April following WS-bloom; nanoplankton replace netplankton in

the upper column and netplankton continue their prevalence in the lower column.

The annual minimum surface chlorophyll a is during

June-August when pronounced SSM appear in the seasonal thermocline 20-25 m below surface. Biomass in

the central midshelf SSM approaches values observed

during WS-bloom. Steep vertical gradients in phytoplankton size composition appear from April through

September, the steepest in the central midshelf. Similar

to the nearshore, there is an August netplankton pulse

in the southern midshelf and an increase in percent

netplankton without concomitant increase in biomass

in the northern midshelf.

Outer Shelf-The basic features of the annual cycle

in the outershelfregions are similar to those for midshelf

and nearshore areas, but there are notable differences

in the shapes of the composite vertical profiles, the

magnitude and timing of maxima, and in the size composition of the phytoplankton. In the midshelf region,

WS-bloom is prolonged from January through March;

in the outer shelf WS-bloom appears distinctly during

March.

In the southern outer shelf, netplankton achieve their

maximum dominance during March, as biomass triples

over values during February. etplankton in the northern outer shelf are dominant as early as January, but

increases in biomass also do not occur until March. The

WS-bloom in the southern outer shelf is twice as intense

as the northern outer shelf. A marked shift from

netplankton to nanoplankton dominance from March

to April signals the conclusion ofWS-bloom. Netplankton are still relatively abundant toward boltom following WS-bloom, but phytoplankton do not appear to

accumulate in the lower water column in April, as in

the midshelf bight.

Phytoplankton size composition is vertically uniform,

or percent netplankton increases slightly with increasing depth from October through March. Exceptionally

large vertical gradients in phytoplankton size composition are established in the southern outer shelf during

April-July. For example percent netplankton grades

from -10% in surface waters to -60% near boltom in

June. Presumably, this reflects major vertical gradients

in the species-composition of the phytoplankton. Vertical gradients in phytoplankton size composition are

less sharp in the northern outer shelf.

During the October fall bloom, biomass increases in

the upper 30-35 m of the column but not below.

Nanoplankton dominate the fall bloom, in sharp contrast to the strong netplankton dominance during WSbloom. The fall bloom, though modest compared with

the WS-bloom, nevertheless represents a four- to fivefold increase in biomass over levels in the upper surface

layer during stratified conditions. Moreover, as in the

nearshore Middle Atlantic Bight, biomass throughout

the column in November-December exceeds that of

the fall bloom.

Southern Slope-The annual biomass cycle in the

southern slope is similar to that observed in adjacent

outer shelf areas of the Middle Atlantic Bight, but biomass is generally lower in slope water. A distinct and

intense WS-bloom occurs in March. The WS-bloom represen ts a fivefold increase in chlorophyll a over values

during February and a shift from 20% to 70%

netplankton. The WS-bloom collapse in April is marked

by a decrease in chlorophyll a and a shift to strong

dominance by nanoplankton in the upper column. Note

that netplankton are still relatively abundant toward

the boltom of the April profile, possibly indicating a

residual WS-bloom community which is subsequently

replaced by nanoplankton in May.

Over the annual cycle, netplankton are not as abundant in the southern slope as in the adjacent southern

outer shelf. Netplankton dominate only during March

and near the boltom of the water column during April.

The remainder of the time, including the October fall

bloom, nanoplankton predominate.

Beginning in May and continuing through September, SSM develop in the seasonal thermocline 25-35 m

below surface. Vertical gradients in percent netplankton

are much less pronounced at this time than in the

adjacent southern outer shelf. Percent netplankton is

quite low in the SSM layer, suggesting that floristic

composition ofthe thermocline community in the southern slope differs greatly from that of the outer and

midshelf Middle Atlantic Bight.

Following the modest October fall bloom in the upper 40 m, biomass becomes more vertically uniform,

with increasing destratification from November through

January. By February the most vertically homogeneous

conditions are established in the slope water.

Georges Bank

Northern and Central Shoals-Phytoplankton biomass in the northern and central shoals is comparable

to the high levels observed in central nearshore and

southern nearshore areas of the Middle Atlantic Bight

but less than nearshore areas ofthe bight influenced by

estuarine plumes (d. Figs. 23 and 24; also see Table 3).

The annual chlorophyll a maximum (-5-7 /J.g/l) is

observed in March. There are no observations in February. However, biomass is exceptionally high throughout the water column during March, as percent netplankton exceeds 70% and biomass declines markedly
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 41

Table 3

Water column chlorophyll a concentration (Ilg I-I) by subarea and month. Underlined entries indicate W5-bloom period;

bold font indicates the probable peak in WS-bloom.

Region Subarea JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Mean Rank

Middle Atlantic Hudson-Raritan plume 7.63 8.14 6.23 4.87 2.99 4.36 3.38 6.09 6.83 2.77 3.63 4.11 5.09 1

Bight Delaware plume 3.99 11.25 5.59 5.06 3.67 3.76 2.95 2.13 4.89 3.98 4.11 4.31 4.64 2

Chesapeake plume 1.91 4.06 3.35 8.36 4.15 1.47 3.82 3.03 6.78 2.69 4.06 5.73 4.12 3

Central nearshore 5.32 5.25 3.88 1.72 1.67 2.13 1.84 2.28 1.98 2.42 3.49 4.00 3.00 6

Southern nearshore 6.69 5.37 2.62 1.11 1.93 1.77 1.72 2.38 1.95 3.08 4.01 3.76 3.03 5

Northern midshelf 3.08 2.53 3.08 2.11 1.19 1.03 1.14 1.02 1.06 1.23 2.06 1.96 1.79 11

Central midshelf l1.l 2.55 3.67 1.28 1.24 1.30 1.09 1.45 0.81 1.44 2.13 1.45 1.72 12

Southern midshelf 2.36 3.04 2.32 1.00 1.24 0.74 0.64 1.12 0.96 1.45 1.99 2.21 1.59 13

Northern outer shelf .ill 1.07 1.40 0.93 0.85 0.66 0.55 0.48 0.53 0.78 0.93 1.12 0.87 18

Southern outer shelf 1.36 1.25 2.81 1.16 0.92 0.68 0.63 0.65 0.56 0.79 1.09 0.90 1.07 16

Southern slope 0.85 0.42 1.98 1.01 0.61 0.48 0.40 0.47 0.48 0.48 0.85 0.71 0.73 24

Georges Bank Northern shoals 0.99 4.93 1.36 3.18 2.58 1.62 1.64 3.68 2.44 2.18 1.36 2.50 7

Central shoals 1.90 7.29 2.70 2.49 2.50 1.77 1.45 2.52 3.14 3.30 3.30 3.05 4

Nantucket shoals 1.37 4.43 6.39 2.06 1.23 3.43 1.54 0.48 2.48 1.80 2.04 2.31 2.46 8

Western outer shoals 1.15 2.98 2.47 2.41 2.51 1.30 0.65 1.67 1.61 1.67 2.22 1.95 10

Eastern outer shoals 0.70 3.62 4.38 3.43 2.64 2.27 2.13 1.20 1.38 1.64 1.51 0.90 2.15 9

Great South Channel 0.58 .L..U 1.76 3.47 1.65 1.98 0.97 0.89 0.91 1.13 1.06 1.04 1.38 14

Northeast peak 0.50 0.93 2.28 0.91 1.21 0.80 0.63 0.26 0.72 0.60 0.57 0.53 0.83 22

Southern flank 0.94 0.96 1.18 1.63 1.27 1.14 0.76 0.68 0.66 1.08 0.79 1.06 1.01 17

Northern slope 0.50 0.61 0.57 0.81 0.96 0.60 0.37 0.39 0.41 0.45 0.51 0.67 0.57 26

Gulf of Maine Western 0.86 2.01 .L1.2 1.91 0.79 0.82 0.78 1.07 0.80 1.57 0.95 1.50 1.23 15

Northern 0.41 1.24 0.29 1.31 1.38 0.38 0.55 0.67 1.52 0.45 0.57 0.85 20

Wilkinson Basin 0.43 0.89 0.75 2.51 1.07 0.86 0.63 0.53 0.59 0.72 0.74 0.71 0.87 19

Georges Basin 0.43 0.60 .!.:i! 1.13 0.98 0.84 0.55 0.52 0.75 0.81 0.36 0.55 0.74 23

Jordan Basin 0.39 0.48 0.21 0.63 1.00 1.07 0.21 0.38 0.68 1.07 0.43 0.61 0.60 25

Scotian Shelf 0.31 0.46 0.88 0.80 1.64 0.89 0.68 1.19 0.85 0.27 0.46 0.85 21

from March to April. Taken together, this suggests the

WS-bloom probably begins in February, peaks during

March, and is over by April. This is supported by Curra

(1987) who examined phytoplankton counts and

changes in species-composition. The magnitude ofWSbloom is comparable but it does not persist as long as

the nearshore Middle Atlantic Bight WS-bloom.

Following WS-bloom, chlorophyll a is sustained at

high levels (-2 f.,lg 1-1) throughout the water column

through June. Annual chlorophyll a minima are during

July-August and in January. The January minimum is

lower than January biomass in comparably deep areas

of the midshe1fMiddle Atlantic Bight where WS-bloom

is already underway (cf. Figs. 23 and 24).

Fall bloom appears during September, with chlorophyll a increases above the summer minimum and

netplankton more dominant. But fall bloom in the

northern shoals appears greater than in the central

shoals. Following fall bloom, chlorophyll a increases

through December in the central shoals but decreases

in the northern shoals.

A strong seasonality in the phytoplankton size composition is present in the central shoals. Netplankton

dominate standing stocks from October through March

when peak dominance (75% netplankton) occurs,

whereas nanoplankton achieve only weak dominance

(40% netplankton) from June through August. The

abundance of netplankton throughout the year is a

characteristic feature of the shallow water on Georges

Bank.

The vertical distribution of chlorophyll a is essentially uniform throughout the year, as are composite

profiles of phytoplankton size composition. There is no

well-defined SSM layer characteristically found in areas

that undergo vertical density stratification during summer. Temperature and salinity are also vertically uniform throughout the year (Bisagni and Sano, 1993).

This vertical uniformity is the consequence of vigorous

mixing, primarily by tidal currents which reach magnitudes of 70-80 cm s-1 over the shoals (Fig. 3). Perhaps

only during December is the estimated critical depth

(O'Reilly et aI., 1987) below the seafloor in the shallow

water on the Bank.

Nantucket Shoals-Even though sampling in this subarea is suboptimal, the annual phytoplankton cycle resembles that of the northern and central shoals. Similarities include the magnitude and timing ofWS-bloom

and fall bloom, the occurrence of annual minima in
42 NOAA Technical Report NMFS 139 _

January and August, and the size composition of the

phytoplankton throughout the year.

Western and Eastern Outer Shoals-The annual chlorophyll a cycle in the western and eastern outer shoals

(Fig. 8) has many features in common with the northern and central shoals: Winter-spring bloom peaks in

March, there is a modest fall bloom in September, and

there are annual chlorophyll a minima in January and

August. Chlorophyll a and percent netplankton are

also vertically uniform but biomass profile is more variable, and well-defined SSM do not persist during summer. The major difference is that biomass is generally

lower in the western and eastern outer shoals than in

the northern and central shoals (also see Table 3).

Following WS-bloom, netplankton persist in the eastern outer shoals in April but are replaced by

nanoplankton (the usual successional pattern) in the

western outer shoals. There is also a trend of higher

chlorophyll a during December and January in the

western outer shoals.

Great South Channel-This subarea is sligh tly deeper

than the adjacent western outer shoals (Fig. 8). Following the annual biomass minimum in January,

netplankton steadily accrue until the March-April WSbloom. From May through September, netplankton are

replaced by nanoplankton in the upper column but

continue to prevail in the lower column, and weak SSM

are present in the seasonal thermocline. As in the western outer shoals, high chlorophyll a persists untilJune,

followed by a secondary annual biomass minimum during July-August.

Fall bloom in September is modest, limited to the

upper column, and dominated by nanoplankton. From

October to January, netplankton become as abundant

as nanoplankton, chlorophyll a decreases near surface

but increases at the bottom of the column, and chlorophyll a and percent netplankton profiles become increasingly more vertically uniform, as expected with

increasing wind mixing.

Northeast Peak-Chlorophyll a and netplankton

steadily increase fromJanuary to WS-bloom climax during March. Sharp vertical gradients in size composition

appear during May, and perhapsJune-July, but not the

remainder of the year. Nanoplankton are responsible

for a greater share of biomass during summer here

than in the shallower areas of Georges Bank.

Southern Flank-Perhaps the most interesting feature in the biomass cycle in the southern flank is the

relatively weak netplankton dominance and low biomass achieved during WS-bloom. The bloom is not easily

discerned; based on phytoplankton size composition,

the peak may be in March, but biomass levels are higher

in April (upper 15 m) and even higher in May when

nanoplankton species prevail. This pattern contrasts

sharply with the intense, distinct WS-bloom in the comparably deep southern outer Middle Atlantic Bight shelf

(cf. Figs. 23 and 24).

A weak SSM is present in the thermocline and relatively steep vertical gradients in the size composition of

the phytoplankton occur from May throughout September, but not during the remainder of the year when

the water column is not well-stratified. The October fall

bloom occurs one month later than the bloom in other

areas of Georges Bank and is not dominated by

nanoplankton. There is a trend of increasing vertical

homogeneity in chlorophyll a and percent netplankton

profiles from October to January, presumably the consequence of increased wind mixing of the column during winter. This is also evident in individual synoptic

cross-bank sections (Append. B).

Northern Slope-The overall annual cycle is similar

to the cycle in the southern slope, except WS-bloom in

the northern slope is much weaker, appears later (in

April), and is comprised ofnanoplankton (cf. Figs. 23 and

24). Low chlorophyll a «0.5 !lg 1-1), typically observed in

stratified surface waters, appears during May in the southern slope but not untilJuly in the northern slope.

Nanoplankton dominate the community throughout

the water column during all months. During summer,

netplankton do not increase toward the bottom of the

column in the northern slope as they do in the adjacent

southern flank of Georges Bank. This is a major difference between these two areas, and matches the floristic

transition from the southern outer Middle Atlantic Bight

shelf to the adjacent southern slope.

Gulf of Maine

Western Gulf of Maine-The annual minimum surface chlorophyll a occurs during January. Netplankton

become strongly dominant as chlorophyll a doubles to

2 !lg I-I during February, and persist at this level through

March (Fig. 25). The February-March bloom is weak

relative to WS-blooms in the Middle Atlantic Bight and

the shallow area on Georges Bank. Like most other WSblooms in the study area, it is strongly dominated (80%)

by species in the netplankton, presumably diatoms.

During April, a second, more intense nanoplanktondominated WS-bloom appears. Tentatively, we suggest

that this is a second WS-bloom because its size composition, and presumably species composition, is very different from the February-March bloom. (The composite

profile for April is based on few observations so it must be

considered with caution.) Biomass is greatest 25-35 m

below surface. The size composition of the community is

vertically uniform, without indication that netplankton

from the preceding bloom are accumulating in the lower

column, as is the case in midshelfMiddle Atlantic Bight.

Biomass again increases in the upper column during

June, but there are no obvious changes in phytoplankton size composition. Subsurface chlorophyll maxima
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 43

(-2 Ilg 1-1) emerge 15-20 m below surface from June

through September. Biomass in the SSM is similar to

the high levels in the thermocline community in central Middle Atlantic Bight. Note that vertical gradients

in size composition during summer are weak when

contrasted with stratified areas of Georges Bank and

the Middle Atlantic Bight. The bell-shaped profiles are

not as symmetrical as those for stratified waters in the

Middle Atlantic Bight and Georges Bank. In part this is

because chlorophyll a in the upper mixed layer during

summer is greater than that observed in stratified areas

of the Middle Atlantic Bight and Georges Bank. Also,

biomass is quite low at the bottom of the column during summer: at 50 m below surface, chlorophyll a is

roughly one-third the values observed at comparable

depths along the southern flank of Georges Bank and

outer shelf areas of the Middle Atlantic Bight.

The annual surface biomass maximum is during the

October fall bloom. The bloom is largely confined to

the upper 25 m and represents a fivefold biomass increase above September levels. This peak is strongly

dominated by the nanoplankton and surpasses fall

blooms in all other subareas except the nearshore

Middle Atlantic Bight and the shallow water on Georges

Bank (cf. Figs. 23, 24, and 25). Moreover, this annual

cycle differs greatly from those constructed for the Middle

Atlantic Bight, Georges Bank, and slope areas, in which

fall bloom is clearly subordinate to the WS-bloom.

Northern Gulf of Maine-Annual minima surface

chlorophyll a occur in January and March, just before

and after the weak WS-bloom in February (Fig. 25).

Netplankton are exceptionally low (<10%) duringJanuary. This is a characteristic feature of deep regions

within the study area, such as the entire Gulf of Maine

(except western gulf), northeast peak on Georges Bank,

and northern and southern slope subareas.

Biomass in the upper 30 m during May-June is high

relative to levels achieved during the WS-bloom, and

consists of equal proportions of netplankton and

nanoplankton. Moderate vertical gradients in size composition are established from June through September

and netplankton are relatively more abundant during

summer here than in the western gulf. As in the western

gulf, a fall bloom which exceeds the WS-bloom is evident in surface water during October.

Wilkinson Basin-During February, biomass increases

above the annual minimum inJanuary and netplankton

begin to prevail, but maximum biomass is not reached

until April (Fig. 25). This slowly developing WS-bloom

surpasses those in other areas of the Gulf of Maine. The

bloom is over by April as indicated in the nanoplankton

dominance in the upper layer. An SSM is present in the

general vicinity of the seasonal thermocline fromJuneSeptember. Biomass in the SSM is generally less than in

the western gulf.

Georges Basin-The essential features of the annual

phytoplankton cycle are similar to those of Wilkinson

Basin. The biggest difference involves the progression

and makeup of the WS-bloom (s). From February

through March, netplankton dominance and biomass

increase. But biomass does not peak until April, when

the community shifts to nanoplankton. Our tentative

interpretation is that the March and April peaks represent two distinct but modest WS-blooms comprised of

different species of phytoplankton. Perhaps what is lacking in the annual progression is the usual precipitous

decline in biomass that punctuates the conclusion of

the WS-bloom and the start of nanoplankton prevalence as seasonal stratification intensifies.

Biomass doubles in surface water in September and

nanoplankton achieve maximal dominance. Fall bloom

starts one month earlier here than in the Wilkinson

Basin, perhaps resulting from lower water column stability (see below) and earlier destratification. Only during April do netplankton achieve weak dominance over

nanoplankton; the rest of the year nanoplankton

strongly dominate.

Jordan Basin-It appears that a netplankton WSbloom does not occur in the Jordan Basin until April and

it is weak relative to WS-blooms in Wilkinson and Georges

Basin. Biomass during April barely exceeds 1 Ilg 1-1. This

conclusion must be tentative since sampling frequency

in March and April was poor.

A nanoplankton increase in the upper layer appears

in May and is sustained through June, as is the case in

the Wilkinson and Georges Basins and northern gulf

subarea. The steepest vertical gradients in size composition in the Gulf of Maine appear over Jordan Basin

during May, June, and July. Fall bloom appears during

October; netplankton playa larger role in the bloom

than in any other subareas in the gulf where the fall

bloom is strongly dominated by nanoplankton.

Scotian Shelf-Surface concentrations decline from

October to January, the annual minimum. Except for

the vertically uniform chlorophyll a profile duringJanuary and February, most of the chlorophyll a decreases

with increasing depth. Subsurface chlorophyll a maxima

are weak and very near surface from May through September. The relatively high chlorophyll a and percent

netplankton during April, and the abrupt shift to

nanoplankton in May, suggest that the WS-bloom may

peak during April. This conclusion is tentative since

data are lacking for March.

There is a suggestion of a trend ofincreasing percent

netplankton from May through June, followed by a

return to strong dominance by nanoplankton in August. This pattern is not evident in other areas of the

Gulf of Maine. The contribution by netplankton to

annual standing phytoplankton stocks is generally

greater in the Scotian Shelf and other northerly subar-
44 NOAA Technical Report NMFS 139

eas of the Gulf of Maine (Jordan Basin and northern

gulf), than in southerly gulf areas.

Winter-Spring Bloom

Sverdrup (1955) in troduced the concept of critical

depth to explain increases in phytoplankton biomass

such as spring bloom. The critical depth is the depth in

the water column at which phytoplankton respiration,

vertically integrated from surface, equals integrated

photosynthesis. The upper mixed layer must be less

than critical depth for a net increase in phytoplankton

biomass to occur, assuming nutrients are not limiting

growth, and grazing and other biomass losses are held

constant. Riley (1957) expanded on this and reported a

mean radiation of about 0.03 g-cal cm-2 min-lor about

40 Iy d- 1 was critical to the onset of flowering. In support, Riley (1957) cited the occurrence of increases in

phytoplankton biomass between December and March

in Cape Cod Bay (Bigelow, 1926), Long Island Sound

(Riley, 1956), coastal waters of Woods Hole (Lillick,

1937), Block Island Sound (Riley, 1952), and Georges

Bank (Riley, 1941). More recent observations by

Townsend and Spinrad (1986) of the W5-bloom in the

Gulf of Maine support Riley's work. Surveys of nearshore

shallow water over the past several decades have also

revealed that the bloom may commence and even culminate during winter, as early as january or December

(Hitchcock and Smayda, 1977). Therefore, ''winter-spring

bloom" seems a more accurate label than "spring bloom"

for this pulse in the annual cycle.

Thus, a strong pulse of phytoplankton growth and

increase in biomass occurs during late winter-early spring

following increases in incident solar radiation, water

temperature and stratification, and reductions in wind

velocity and turbulence (Riley, 1957; Yentsch, 1977;

Eslinger and Iverson, 1986; Mann, 1993). In shallow

water, suitable conditions for the bloom may be met

through seasonal increase in incident solar radiation

and concomitant increase in mean radiation in the

mixed column. In deeper waters, bloom conditions are

met through a combination of increased solar radiation and shoaling of the upper mixed layer that occurs

with increased stability within the water column. This

stability can be accomplished in several ways: by fresh

water forming a low salinity surface layer, such as in

coastal areas where there is river runoff; by vernal heating of the upper water column and formation of the

pycnocline; and by "doming," whereby water from below pushes the mixed layer higher into the water column. Combining with the above is the winter to summer reduction in the average number of wind events

that mix the water column (Walsh et. aI., 1978; Eslinger

and Iverson, 1986).

In a broad temporal sense the above classical picture

ofWS-bloom is correct. However, recent intensive studies by Falkowski (1991) and others suggest that the WSbloom paradigm needs reexamination. They found that

the WS-bloom does not continuously build, but instead

develops as a series of short (3-5 day) pulses of phytoplankton increases. Therefore, our characterizations of

W5-bloom based on composited data (multi-year means)

at a monthly temporal resolution do not represent well

the actual dynamics which proceed at short time scales.

On the northeast U.S. shelf, there are differences

among and within regions in the timing, magnitude,

duration, and size composition of the WS-bloom. In

Table 3 we summarize these differences based on Figs.

23-25 by highlighting (underlining) the WS-bloom period when netplankton biomass increases, and defining

peaks (bold entries) for each of the subareas. Winterspring bloom is prolonged, from january through

March, in nearshore, midshelf, and northern outer

shelf areas of the Middle Atlantic Bight. The peak occurs earlier in shallow water in the nearshore and

midshelf areas, as might be expected based on the

critical depth concept. In fact, in the nearshore shallow

column, biomass is elevated during November and December, such that additional biomass increases of the

WS-bloom seem less dramatic when compared with

deeper areas of the shelf. This contrasts with the relatively rapid change in mean photic light levels resulting

from spring stratification in the outer shelf and slope

regions of the Middle Atlantic Bight (where a distinct

pulse is evident in surface waters during spring and fall).

A relatively prolonged WS-bloom also occurs in Great

South Channel, Wilkinson Basin, and the Scotian Shelf,

with peaks achieved in April. In contrast, more distinct

WS-bloom occurs during March in the deep water over

the southern slope, April in the northern slope, and

March in the northern Gulf of Maine. WS-blooms in

subareas of Georges Bank and the Gulf of Maine start

later and are generally not as prolonged as those in the

Middle Atlantic Bight. Some areas of the shelf appear

to have very weak (or ill-defined in our data set) WSblooms (e.g. southern flank of Georges Bank).

The end of the WS-bloom is most easily discerned by

rapid decreases in biomass and a shift to nanoplankton

in the upper layer. In some areas (Western Gulf of

Maine, Georges Basin,jordan Basin), the shift to nanoplankton occurs but biomass persists at high levels,

leading to the question: Are there two distinct WSblooms in these areas?

The Fate of WS-bloom

In addition to differences among subareas with respect

to the course and magnitude of WS-bloom, there are
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 45

also differences among areas following the bloom which

have potentially significant consequences to shelf ecosystem trophodynamics. The composite vertical profiles (Figs. 23-25) provide insight into regional differences in the amount and vertical distribution of phytoplankton biomass following WS-bloom, and suggest

differences in the fate of the WS-bloom. The inverted

profiles provide insight into the near-term fate of the

WS-bloom. They are easily identified in March and

April profiles for the midshelf Middle Atlantic Bight

and perhaps in the central nearshore bight, but are not

obvious in mean portrayals for Georges Bank and the

Gulf of Maine (Figs. 23-25). The most remarkable inverted profile occurs in the northern midshelf Middle

Atlantic Bight in April, and marks the conclusion of the

WS-bloom. Here, surface concen trations average -lllg 1-1

and bottom concentrations average 41lg 1-1 (Fig. 23).

Accumulations of phytoplankton biomass near bottom during March and April 1984 have been reported

by Falkowski et al. (1988) and Falkowski (1991), with

the largest buildup in the midshelf Middle Atlantic

Bight. They observed highest chlorophyll a accumulations (10-25 Ilg I-I) in April in the Middle Atlan tic

Bight midshelfbetween the 30-60 m isobath. The mean

values we report are less than this, but values exceeding

10 Ilg I-I were observed during several surveys (Append.

B). These inverted profiles are not an artifact of

compositing very diverse vertical distributions, since

the preponderance of phytoplankton biomass in near

bottom water at this time is seen midshelfin most of the

vertical cross-sections along transects A, B, and C (Append. B). These inverted chlorophyll a profiles, plus

the progressive relative increase in netplankton (presumably diatoms) with depth, indicate the near-term

fate of the WS-bloom in these waters: sinking and accumulating in the lower water column and on the seafloor.

Evidence is mounting that much of the WS-bloom is

not assimilated in the water column by zooplankton but

instead sinks to the lower column (e.g. LignelI et aI.,

1993) where its subsequent fate (1-4 months) is uncertain. It may be advected off the shelf to the continental

slope (Walsh, 1981; Dagg and Turner, 1982), consumed

by the benthic community (Townsend and Cammen,

1988), or be remineralized on the shelf (Rowe et al.,

1986; Falkowski et aI., 1988). Malone et al. (1983b)

indicate that between wind events, the netplankton

diatom blooms sink and accumulate near bottom but

that 90% of the biomass produced during the diatom

bloom period is exported to the continental slope.

Falkowski et al. (1988) and Falkowski (1991) estimate

that 51 % ofthe 1984 spring bloom off the coast ofLong

Island sank, forming a near-bottom nepheloid layer

which was subsequently oxidized. Falkowski et al. (1988)

further reported that along-shelf transport of particles

in the Middle Atlantic Bight dominates cross-shelf transport during spring and that 50-60% of the along-shelf

transport leaves the shelf at Cape Hatteras.

Our composite profiles suggest yet an additional fate

for a portion of the WS-bloom phytoplankton. Following WS-bloom, sharp vertical gradients in size composition become established in shelf areas undergoing seasonal density stratification. Nanoplankton prevail in

the upper column and netplankton in the lower. For

example, in the central midshelfMiddle Atlantic Bight,

biomass in the lower column steadily declines following

the WS-bloom through July, yet netplankton continue

to prevail over nanoplankton in the lower column. This

leaves open the possibility that residual WS-bloom species may be influencing the floristic composition of

phytoplankton below the thermocline during the ensuing summer months, and acting as a seed stock for the

fall bloom. Alternatively, the netplankton in the lower

column may be comprised of dinoflagellates. Evaluation of this hypothesis will require vertically detailed

examinations ofthe successional patterns of phytoplankton species from spring through summer. To our knowledge, such examinations are lacking.

Despite the manifold trajectories available to WSblooms on continental shelves, evidence is accumulating that a large portion of the WS-bloom is not grazed

by pelagic herbivores but sinks to the bottom of the

water column, where it is more likely to enter demersal

fishery food webs than pelagic webs. Townsend and

Cammen (1988) suggest that benthic production may

be enhanced in years with early WS-blooms. In their

paradigm, early blooms would persist longer because

the relatively cold water present earlier in the annual

cycle would retard zooplankton development, growth,

and grazing pressure. Conversely, WS-blooms arriving

late would be expected to enhance zooplankton production and survival of pelagic fish larvae. They suggest

further that variations in the onset and duration ofWSbloom are potentially relevant to understanding variability in recruitment success for some coastal fisheries.

Sampling frequency during our study is insufficient

to resolve conclusively interannual variability. However,

the concept may be useful in understanding the potential ecological significance of the systematic differences

in mean conditions among regions of the continental

shelf during and following WS-bloom. For instance,

greatest near bottom accumulations of biomass occur

during the final stage of prolonged and intense WSbloom in the midshelf Middle Atlantic Bight. In the

portrayals of mean vertical distribution of chlorophyll

a, inverted profiles characterize the vertical distribution of phytoplankton, where chlorophylI a increases

from surface to bottom and netplankton are disproportionately more abundant near bottom. The prolonged

WS-bloom, characteristic of this area, may explain why

these near bottom accumulations are observed here
46 NOAA Technical Report NMFS 139 _

but not in the Gulf of Maine or on Georges Bank. It

seems reasonable to speculate that the benthic community here would benefit more from this pulse than

benthos in deep waters of the Gulf of Maine, where

netplankton do not appear (on average) to accumulate

in the lower column we sampled following WS-bloom.

However, since our sampling was limited to the upper

100 m, this conclusion must be tentative for the deep

basins in the Gulf of Maine.

Our composite profiles indicate the disappearance

in May of the high levels of netplankton chlorophyll

observed near bottom during the preceding two months.

We suggest that a potentially significant fraction of the

spring diatom bloom remains on the shelf in the cold

band, influencing the floristic composition of phytoplankton in and below the thermocline during the

ensuing summer months. The biomass and percent

netplankton profiles in May and June suggest that a

fraction of the netplankton WS-bloom persists near

bottom. To examine this hypothesis, a detailed knowledge is needed of phytoplankton species successional

patterns near bottom following the WS-bloom and into

summer.

Stratified Season: Subsurface CWorophyll Maxima

A pronounced subsurface chlorophyll maximum

emerges 20-35 m below surface from May through

September in those regions of the continental shelf

which undergo and sustain vertical density stratification (Figs. 23-25). Thus, the vertical chlorophyll profile takes a characteristic bell-shape; mean chlorophyll

a increases from surface to 20-35 m below surface, then

decreases progressively toward bottom. The position of

the SSM layer during the stratified season is generally

coincident with the mean depth of the thermocline

and tends to track the thermocline's seasonal and onshore-offshore deepening.

Phytoplankton biomass in the SSM layer may be substantial, between 50-70% of the levels attained during

the WS-bloom. Consequently, the amplitude of the seasonal fluctuation in biomass is greatly reduced by these

subsurface maxima. For instance, in the southern outer

shelf Middle Atlantic Bight, mean surface chlorophyll a

during July (-0.3 Ilg 1-1) is approximately one-tenth

the March value (-3 Ilg 1-1), whereas 30 m below surface, in the SSM layer, chlorophyll a (1.81lg 1-1) is more

than one-half the WS-bloom chlorophyll a maximum

(Fig. 23).

Typically, strong vertical gradients in phytoplankton

size composition also begin to appear in April-May and

persist through the stratified season. These gradients

represent a large change from relatively vertically uniform profiles of percent netplankton in March, to profiles which show nanoplankton dominance in the upper layer and increasing netplankton contribution with

depth (Figs. 23-25).

Based on extensive hydrographic surveys of shelf water from Cape Sable to Long Island, from 1964-66,

Colton (1972) reported that whenever marked vertical

density gradients were present: "chlorophyll was concentrated within the thermocline, the maximum depth

limit of which seldom exceeded 40 m." Moreover, a

series of 2-hour profiles made in June 1966 over a 42-

hour period off Cape Cod (41.5°N, 69°W; 100 m) revealed a pronounced SSM layer at an average depth of

30 m (Colton, 1972). In the outer Middle Atlantic Bight

during June-July 1979, vertical sections portrayed by

Cosper and Stepien (1984) show an SSM layer at 20-40

m. In deeper slope water seaward of the 200 m isobath

in the Middle Atlantic Bight (67 profiles), the median

depth of SSM during June-September is -40 m below

surface, and 75 m in northern Sargasso Sea water (Cox

et a!., 1981).

The SSM is generally in the lower half (10-1 % of

surface light) of the euphotic zone. Though light is

suboptimal, the SSM has relatively greater access to

higher concentrations of inorganic nitrogen present in

and below the thermocline during summer; whereas

phytoplankton in the upper euphotic layer depend

more upon nutrients made available through heterotrophic recycling. Thus, with ample light and nutrients for growth, the SSM layer contributes significantly

to the overall primary productivity ofthe water column.

In the deeper waters on Georges Bank which stratify

during summer, the SSM layer is responsible for 37% of

the daily integral primary production (O'Reilly et a!.,

1987). Similarly, 37% of primary productivity takes place

below the seasonal pycnocline in the New York Bight

shelf (Malone et aI., 1983b). Holligan (1978) estimated

phytoplankton in the thermocline in the western English Channel were responsible for 30-80% of daily

summer production and may contribute as much as the

WS-bloom to annual primary production. In stratified

waters surrounding the Dogger Bank in the North Sea,

the SSM layer was responsible for up to 70% of the

in tegral primary production in May 1990 (Nielsen et

aI., 1993). In the southern Kattegat, the SSM layer is

responsible for 30% of the annual primary production,

whereas the spring bloom is responsible for only 19%

(Richardson and Christoffersen, 1991).

A number ofinvestigators have reported associations

Uuxtapositions) between the depth of the SSM layer,

the thermocline, and nitroclines (Anderson, 1964;

Herbland and Voiturez, 1979; Cox et aI., 1981; Cullen

and Eppley, 1981; Kiefer and Kremer, 1981; Cullen et

aI., 1982; Holligan et aI., 1984; Townsend et aI., 1984;

Nielsen et aI., 1993). Cullen (1982) reviewed a number

of processes potentially responsible for the persistence
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 47

of the SSM layer. These include sinking; physiological

changes (decreases in the sinking rate from increased

phytoplankton buoyancy, in response to increased nutrient concentrations and decreased photosynthetically

active radiation (PAR) at the thermocline); behavioral

aggregation at the thermocline by motile phytoplankton; greater stability; residence times which are much

greater than phytoplankton generation time in the thermocline relative to waters above and below; and depthdifferential grazing.

Our purpose here is not to choose among these

mechanisms but to underscore the trophodynamic significance of this layer. The SSM is ubiquitous, persists

throughout the stratified season, is a productive layer,

and therefore represents a concentrated and renewable source of organic matter for herbivores.

Relatively little is known about the species composition of the SSM in the study area. The magnitude,

species composition, and temporal variability of the

SSM have been shown to be key determinants in the

success ofthe northern anchovy on the west coast ofthe

United States. The dinoflagellate Gymnodinium splendens

is a nutritionally important food source for first-feeding

northern anchovy larvae, and the success of the year

class may be partly dependent upon the availability of

this organism or other nutritionally comparable dinoflagellates (Lasker, 1975, 1978, 1981).

Seasonal Changes in Subsurface Maxima

To better understand temporal changes in SSM, and its

relationship to surface chlorophyll concentrations, the

SSR is computed for each vertical profile and portrayed

for each subarea (Fig. 26). Subsurface/surface chlorophyll ratios of 1 indicate that the maximum chlorophyll

concentration is at the surface; a value of 2 means that

chlorophyll a concentration at some depth below surface

is twice the concentration observed in surface water.

The monthly geometric mean (meang) SSR is less

than 2 from October through March in nearly all 26

subareas (Fig. 26). These low SSR's indicate that vertical variation in phytoplankton biomass is relatively low

during the period of minimal vertical density stratification in the upper 40 m (Fig. 27). In the nearshore

Middle Atlantic Bight, meang SSR drops below 2 in

September when destratification may begin during some

years (Fig. 26). One month later during destratification

in October, mean SSR drops below 2 throughout most

of the study area (Fig. 26). SSR's below 2 correspond to

density differences between 40 m and surface which are

less than 1 sigma-t unit (cf. Figs. 26 and 27).

Subsurface/surface ratios increase markedly during

the stratified season. Peaks in the monthly meang SSR

occur from June through September (Fig. 26). These

high SSR's result mostly from bell-shaped profiles where

the maximum chlorophyll a is in the seasonal thermocline at -20-35 m. In the Middle Atlantic Bight,

individual SSR's above 16 are present in all subareas

except those near estuaries; on Georges Bank, values

exceed 16 only along the southern flank and adjacent

northern slope; and in the Gulf of Maine, values above

16 are found only in Wilkinson Basin, and western and

northern subareas. Subsurface/surface ratios above 32

are present only in the Middle Atlantic Bight and meang

adjacent southern slope.

Highest SSR's usually occur in the Middle Atlantic

Bight central midshelf. The meang SSR during July is

-10. Note that the relatively high meang SSR during

April in this area is due to near-bottom, not midwater,

chlorophyll maxima (Fig. 23). Lowest SSR's occur in

the weakly stratified water on Georges Bank (central

shoals, northern shoals, western outer shoals, eastern

outer shoals), Nantucket Shoals, and Scotian Shelf.

Individual SSR's exceeding 2 are present in these areas

but the monthly meang SSR persists at very low values

from May through September.

In the deeper water on Georges Bank which stratify

during summer (Fig. 27), SSR's exceeding 2 are common but SSR's above 8 are rare. In the Gulf of Maine,

the monthly meang SSR does not surpass 2 untilJune,

two months later than in the outer shelf Middle Atlantic Bight, although a number ofindividual values above

2 occur in May.

Spatial Distribution of Subsurface/Surface Ratio

Some striking spatial patterns are evident in the

shelfwide distribution of SSR during summer (Fig. 28).

This is the period of greatest density stratification (Fig.

27), when vertical profiles of phytoplankton chlorophyll a are generally bell-shaped in stratified water (e.g.

Fig. 23).

Relatively low SSR's are presen t off the mouths ofthe

Raritan, Delaware, and Chesapeake bays, over the shallow region on Georges Bank, and in the eastern Gulf of

Maine (Fig. 28). In the Gulf of Maine, summer SSR is

aligned in east to west bands. Values between 2-2.8

characterize the western region of the gulf while values

below 2 characterize the eastern region. In between, a

band of moderately high SSR's stretches northward,

from Wilkinson Basin to the area nearshore, between

Casco Bay and Penobscot Bay (Fig. 28). In the Wilkinson

Basin (Fig. 5: tiles 106, 107) SSR's are 2.8-4. In the

nearshore northern Gulf of Maine (Fig. 5: tile 104),

SSR's are 5.6--8 and match well the observations by

Holligan eta!' (1984) of SSM (-3Ilg I-I) 10-20 m below

surface and SSR of - 6 during June 1979 surveys across

the 100 m isobath. The chlorophyll a and phytoplank-
48 NOAA Technical Report NMFS 139

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Figure 26

Ratio of the subsurface/surface chlorophyll a versus month for 26 subareas of the northeast U.S. continental shelf. Individual

observations are represented as open circles. The solid line connects monthly geometric mean ratios.
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 49

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I I I -, A~ I _L I

GB Western Outer Shoalsl ...l _1_ L.J _1_ L.J _1_ L.J _I_

I I I r I I r r I t I

t I I I I t I I I I ,

1 -'-'I -,- II -1- II -,-

I I I I I I I I I I 1

-t -1- I- .... -1- I-- .... -1- I- -I -It I I I I I I I I I I

J _,_!... J _1_ !- J _1_ !- J _,_ , 1 , I I I I I I I I

I I 1 I I I I I , I I

i -1- r , -,- r , -1- r ., -,-

I I , I t I I _, I I I

.1 _1_ L .J -''-ihL.1_1_ L .J _It , , I -, I I I I

I I 'I- I _I

GB Eastern OUler ShoalsI

.1. _1_ L .J _,_ L .1. _I _ L .J _I_

I 1 1 I I I I 1 I , I

I , I I , I 1 I I , I

'1 -,- ,- '1 -,- 1- '1 -,-. I -,-

I , 1 , 1 , , , , , ,

-'-I- -,- I- -+ -1- I- -+ -II , tit t , , , I I

.! _1_ L.! _,_ L .! _,_ L.! _I_

I I 1 I I I I I , 1 I

I , , I , I ,_, I I I

i -1- r i -1- r i -1- r , -,-

I I I I I ,-I I I , I

..1 _1_ L .1. _1_ L .1 -'r L .J _T_ I I I I ,_ It' I

I I _ I I 1 I

, GB Nantucket ShuaJs I

...I-_I_L...1_I_L _'_L.J_I_

I 1 I I , , I I I 1 ,

, I 1 I , , I I 1 I I

'1 -,- 1- I -I-II -,-. I -,- , I , 1 , I , , I I ,

-1- I- -,- I- -+ -,- t- -+ -II I , , I I I I 1 I I

.! _1_ L ..! _1_ L 1 _1_ L J _,_ I I , I I I 1 I I I I

I 1 I I I I I 1 I I 1

, -,- r , -,- r "1 -1- r , -IIt' It' _I 1 I , I

.1 _I _ L .1. _1_ L ...1 _I _ L ..1 _I_

I 1 II! I- I I I , I

I I I I 'I '" I

Figure 27

Stability (Sigma-t 40 m-O m) versus month for 26 subareas of the northeast U.S. continental shelf. Individual observations are

represented as open circles. The solid line connects monthly means.
50 NOAA Technical Report NMFS 139 _

ton biomass maxima were present at the base of the

seasonal thermocline, at the top of the nitracline, and

in the lower euphotic layer at between 1% and 5% of

surface light intensity (Holligan et aI., 1984).

A general onshore-offshore or bathymetric gradient

in mean SSR is evident in the Middle Atlantic Bight

and on teorges Bank (Fig. 28). A gradient is also evident proceeding south along the outer continental shelf:

Subsurface/surface CW a

lune-August

1977-1988

Number of profiles

lune-August

1977-1988

o·

o

o

o

o

N

2

3

4

6

8

II

16

22

32

Coefficient of variation

lune-August

1977-1988

Percent

>140

140

120

100

80

·60

··40

20

o

Figure 28

Contoured distribution of the ratio of subsurface/surface chlorophyll concentration, coefficient of variation percentage in the

ratio of subsurface/surface chlorophyll concentration, and number of vertical profiles, during the period June-August.

Subsurface/surface ratios were log2-transformed and composited by tile before contouring. The coefficient of variation was

based on log2-transformed ratios.
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 51

Figure 29

(A) Relationship between coefficient of variability and

ratio ofsubsurface/surface chlorophyll concentration.

(B) Depth of maximum chlorophyll versus subsurface/

surface chlorophyll concentration. (C) Log2 (surface

chlorophyll a) versus log2 (subsurface chlorophyll a).

(N=number of observations, r=correlation coefficient,

s=functional slope, i=functional intercept.)

4

32

16

8

•

8 16 32

n= 188

i= 113.9

s= -31.99 r= -0.69

•

•

• 4

<:l 2::a

U

................/.:.-- / sm;i j r = 0.58

-5 +------1'--1---+---+-+--+----1-+--+-1---+.031

-6 -5 -4 -3 -2 -I 0 I 2 3 4 5

Log2 (surface ChI a)

C Surface CW a ?16 .031 .063.125 .25 0.5 1 2 4

20

• 0

I 2 4 8 16 32

B Subsurface/surface ChI a 80

•

g 60

S

;:l

S

.~ • S 40

4-<

0

oS

0-

0 •

Cl 20 n= 189

i= 6.69

s= 8.68

r =0.62

0

1 2 4 8 16 32

Subsurface/surface ChI a

,........

t:i

e2

8 I

<t;:l 0

.g'" -1

......... '" -2

tin .3 -3

-4

AI60

• 140

~120 c

0

.~ 100

.~

;>

4-< 80 0

1::

0 60

'G

..::

4-< 40 0

0

U

SSR is 2-2.8 at the southeast flank of Georges Bank;

2.8-4 near Great South Channel; 4-5.6 near the Hudson

Shelf Valley; and 5.6-8 offshore of Delaware Bay.

Variability in mean SSR is lowest in tiles with highest

SSR's and greatest in 1iles which, on average, have little

vertical structure in chlorophyll concentration (Fig. 29A).

This follows the pattern expected: low temporal persistence of vertical structure in areas with weak or intermittent density stratification and high persistence where

density stratification is high and continuous during

summer. Variance in the composite summer meang

SSR's includes inter- and intra-annual sources, so high

CV's may mean either or both sources are responsible,

while low CV's indicate both sources of variation are

small. Subsurface/surface ratios also tend to increase

with increasing depth below surface (Fig. 29B), following the general onshore-offshore tilt (deepening) of

the seasonal thermocline with increasing water column

depth. Chlorophyll a in the SSM and near surface layers begin to converge (vertical uniformity) at surface chlorophyll a concentrations greater than 1 J.Lg/1 (Fig. 29C).

There is a distinct band within the Middle Atlantic

Bight with elevated SSR's (8-16), roughly between the

30 and 60 m isobaths offshore of Chesapeake Bay,

Delaware Bay, and the southern half of NewJersey (Fig.

5: tiles 50, 4~ 40, 31, 32, 27, 24, 20,14,45,39,33,19).

This is a relatively stable feature during the stratified

season as the CV's in SSR's are low (Fig. 28). This

midshelf band coincides with the location of cold winter residual water known as the "cold pool" (Ketchum

and Corwin, 1964) or "cold band" (Houghton et aI.,

1982). The cold band is approximately bounded between the 30 and 100 m isobaths in the Middle Atlantic

Bight (Ketchum and Corwin, 1964; Bowman and

Wunderlich, 1977), and extends uninterrupted onto

Georges Bank at 65-96 m where it is further offshore

than in the bight (Flagg, 1987; Bisagni, 1992).

Overall, the shelfwide pattern in mean summer SSR

is similar to the shelfwide pattern in upper water column stability (d. Figs. 28 and 30), where stability is

indexed (stability40) as the difference between density

(sigma-t) at 40 m and surface. The greatest SSR's occur

where density stratification is greatest, in the Middle

Atlantic Bight midshelf. The Middle Atlantic Bight is

among the most stratified coastal regions in the world;

density gradients across the summer pycnocline are

0.3-0.4sigma-tunitsm-1 (Falkowskietal., 1983). Thisis

reflected in the distribution of the stability40 (Fig. 30).

The thermal contrast between the cold band below the

seasonal thermocline and the warmest brackish surface

water, found in the southern halfofthe Middle Atlantic

Bight (Mountain and Manning, 1994), endows this area

with the highest vertical density stratification.

Conversely, lowest summer SSR's are found where

stability is lowest (d. Figs. 28 and 30)-shallow areas on
52 NOAA Technical Report NMFS 139

Georges Bank, Nantucket Shoals, Browns Bank, and

eastern Gulf of Maine. The low stability in these areas is

the consequence of vigorous tidal currents (Fig. 3)

interacting with shallow topography (Fig. 2) to vertically mix the water column and dissipate density stratification. Despite the spatial coarseness of our observations, there is good agreement between the distribution of meang

SSR's below 2, stability40 below 1, and

maximum tidal surface currents exceeding -50 cm s-l

(Fig. 3). These parameters roughly define the mixing

front separating well-mixed from surrounding stratified water on Georges Bank. Strong currents and mixSigma-t (40 m-O m)

June-August

1977-1988

Number of profiles

June-August

1977-1988

N

2

3

4

6 0 8 0 11

0 16

0 22

D 32

Ratio

6

5

4

3

2

1

.5

..25

o

";'0/ . oo'oV o

Coefficient of variation

June-August

1977-1988

Percent

>140

140

120

100

80

60

40

20

o

Figure 30

Contoured distribution of mean stability (Sigma-t 40 m-O m), coefficient of variation percentage ofstability, and the number of

vertical profiles, during the period June-August. Data were composited by tile before contouring.
______ O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 53

ing on Georges Bank during summer are dominated by

the M2 tidal component. With mixing by summertime

wind included, Loder and Greenberg (1986) predict

that the position of the mixing front generally parallels

the 50 m isobath, except it is shoaler than 50 m along

the north and southern edges on Georges Bank and

deeper than 50 m along the northeast peak.

On a very coarse scale, the west-east banding ofSSR's

in the western gulf follows the general west-east banding in stability (d. Figs. 28 and 30). The pattern for

stability probably reflects the greater density differences

in the western gulf that result from warm stratified

surface water overlying a relatively thick lens of winter

residual Maine Intermediate Water (Brown and Irish,

1993). The relatively low SSR's in the extreme western

Gulf of Maine are less than would be expected based on

stability, and point out the limitations of this simple

SSR index. The reason for this departure is that, unlike

other well-stratified waters in the study area, chlorophyll a is high in the surface layer (Fig. 25). Low SSR's

are also found in subareas influenced by plumes from

Hudson-Raritan, Delaware, and Chesapeake bays, where

stability is quite high (Fig. 31). Highest chlorophyll a is

not in the thermocline but in the nutrient-enriched

surface water entering the coastal zone (Fig. 23).

The SSR is a useful simple index of the degree of

vertical stratification of phytoplankton. This index, with

the above noted but understandable exceptions, parallels indices of vertical density stratification. The importance of physical stability to the establishment of subsurface chlorophyll maxima during summer has been

known for some time (Pingree et aI., 1976; Pingree,

1978). Thermoclines and pycnoclines generate sharp

biological gradients. These gradients structure the column into approximately three layers. Phytoplankton in

the upper mixed layer have optimal light, but nutrient

demands must be met largely through recycling processes. Phytoplankton forming SSM in the thermocline

layer are exposed to suboptimal light and reduced turbulence, and have relatively greater access to new nutri32 All Regions Gulf of Maine

3 4 5

Georges Bank

•

•

o

12

•

•

45012

Sigma-t (40 m - 0 m)

3

•

•

•

•

2

I

•• .' ,. . . . .- .. .. .. .. ..,..... ....... • y • • e •• e. ••

• •

Middle Atlantic Bight

4 •

2

16

16 n =185

i = 0.252

s=0.672

r =0.79

Figure 31

Relationship between the geometric mean ratio of subsurface/surface chlorophyll (SSR)

and stability (Sigma-t 40 m-O m) during the period June-August. The line in each panel

represents the functional regression slope for all data except tiles adjacent to Middle

Atlantic Bight estuaries (labeled 184, 29, 55, 187, 12). (N=number of observations,

r=correlation coefficient, s=functional slope, i=functional intercepL)
54 NOAA Technical Report NMFS 139 _

ents present in the nitrocline. Below the thermocline

community, light intensity decreases to levels which

permit only very modest growth above respiratory demands. The SSR may provide an index of the relative

importance of new versus recycled nutrients during

stratified conditions. It seems reasonable to infer that

the supply of new nitrogen to the upper mixed layer

would be minimal in areas with high SSR's and maximal in areas with relatively lower SSR's, providing that

the reservoir of nutrients below the pycnocline is ample.

Shallow water on Georges Bank would be an exception,

since nutrients are low through the water column during summer (Draxler et aI., 1985; O'Reilly et aI., 1987;

Walsh et aI., 1987; Bisagni, 1992) and new nitrogen

must come into the well-mixed region laterally across

the mixing front at approximately 50-60 m isobath.

Fall Bloom

During late summer and early fall in stratified water,

the shallow upper mixed layer begins to deepen due to

seasonal decreases in solar radiation and seasonal increases in wind and convective mixing. The pycnocline

begins to erode and the euphotic layer gains access to

fresh supplies of nutrients previously trapped below.

The ensuing increase in phytoplankton biomass is

termed the "fall bloom."

Conditions leading to fall bloom are quite different

from those leading to WS-bloom. The critical mixed

depth model, described above, helps to understand

these differences. During WS-bloom in deep water, the

mixed layer is shoaling, incident radiation is seasonally

increasing, and consequently the mean level of light

available to phytoplankton in the mixed layer is increasing; during fall bloom the opposite trend occurs. Phytoplankton are exposed to decreasing mean light levels

in the mixed layer with seasonal decreases in solar

radiation compounded by the mixed layer becoming

deeper as destratification proceeds. Thus, the extent of

the fall bloom will depend upon the extent to which

nutrient enhancement of growth is offset by decreases

in light and by deepening of the mixed layer below the

critical depth (Yentsch, 1981).

It is these basic differences outlined above which

appear to explain why fall bloom is usually subordinate

in magnitude to WS-bloom. This is the general case for

the Middle Atlantic Bank, Georges Bank, and Wilkinson

and Georges basins, where chlorophyll a is roughly

one-half the W5-bloom values. Fall bloom in other subareas of the Gulf of Maine, such as the Scotian Shelf,

Jordan Basin, and northern and western Gulf of Maine,

may surpass WS-bloom. Because sampling during spring

was not always adequate, this conclusion must be tentative. The significance of fall blooms in the Gulf of

Maine is underscored by the observation that chlorophyll a near surface during October is greater in the

western gulf than in any other area of the shelf except

the southern nearshore Middle Atlantic Bight (cf. Figs.

23, 24, and 25).

Unlike the WS-bloom where chlorophyll a becomes

elevated throughout most of the water column, biomass increases during fall bloom are largely restricted

to the upper -20-30 m of the column. Fall bloom is

thus identified as a disappearance of bell-shaped vertical biomass profiles characteristically seen during the

stratified season (Figs. 23-25). Moreover, because surface chlorophyll a is low in stratified water prior to the

bloom, the relative biomass increase near surface during the fall bloom is generally greater than during the

W5-bloom. Conversely, prior to W5-bloom, biomass near

bottom is generally quite low, but during and following

the W5-bloom peak, phytoplankton biomass reaches annual maxima in the lower portion of the water column.

The emergence offall bloom is temporally associated

with decreases in the stability40 below 1 sigma-t (Fig.

27). In the Gulf of Maine, fall bloom appears in September in weakly stratified eastern subareas which

destratify early (Jordan Basin, Georges Basin, Scotian

Shelf). Later, during October, it appears in the relatively more stratified western portion (Wilkinson Basin,

western Gulf of Maine; see Fig. 27 and Mountain and

Manning, 1994). In the northern Gulf of Maine subarea, near surface biomass increases during September

but does not peak until October. In the Middle Atlantic

Bight, the fall bloom occurs during October, and perhaps begins during September in the central nearshore,

as indicated by the disappearance of the summer bellshaped profile and the noisy composite profile for September (Fig. 23).

The fall bloom is not strongly dominated by

netplankton as is the W5-bloom, and there are differences among areas in the mean size composition offall

blooms. In the Middle Atlantic Bight and Georges Bank,

and the northern Gulf of Maine and Jordan Basin,

netplankton and nanoplankton are approximately

equal; throughout the rest of the gulf and the northern

and southern slope areas, nanoplankton tend to dominate fall bloom.

Moderate increases in biomass are evident in September (Fig. 24) in tidally-mixed unstratified areas of

Georges Bank, where stability40 is usually less than 1

sigma-t unit throughout summer (Fig. 27). If these

pulses signify fall bloom and are responses to nutrient

enrichment, then the critical mixed depth-stratification model does not directly apply. Nutrients in the

well-mixed water are uniformly low during summer but

abundant below seasonal pycnoclines in the surrounding water (Draxler et aI., 1985; O'Reilly et aI., 1987).

The new nutrients presumed needed for these biomass
______ O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 55

increases might be derived by advection and subsequent tidal mixing of nutrient-enriched surface water

from surrounding water undergoing destratification.

Alternatively, the additional nutrients, ifrequired, could

potentially be supplied from enhanced nutrient recycling which would be expected to peak during September when temperature of the well-mixed water (Bisagni

and Sano, 1993) reaches its annual peak. Other hypotheses meriting examination concern whether the sharp

drop in zooplankton biomass (Sherman et aI., 1987)

and abundance of herbivorous copepods (Davis, 1987;

Meise and O'Reilly, 1996) represent a relaxation in

grazing pressure during fall and early winter. We also

note that the photosyn thetic efficiency of phytoplankton is highest not during summer solstice, when photosynthetically active radiation is highest, but during fall

(O'Reilly et aI., 1987). This may be due to the species

composition or to environmental factors.

Summary _

The broad scale features in the horizontal, vertical, and

seasonal distribution of chlorophyll a on the northeast

U.S. continental shelf are described based on 57,088

measurements made during 78 oceanographic surveys

from 1977 through 1988. The meangfor all observations is 0.84 llg/1. The distribution of chlorophyll a,

considered here as an index of autotrophic phytoplankton biomass, is strongly influenced by physical factors.

Bathymetry, vertical mixing by strong tidal currents,

and seasonal and regional differences in the intensity

and duration of vertical stratification appear to explain

a large fraction of the variability in chlorophyll a. Vertical density stratification ranges widely; areas of the

Middle Atlantic Bight are among the most stratified in

the world and the shallow water on Georges Bank (where

vigorous tidal mixing occurs) is essentially vertically

homogeneous year-round. The wide range in measured

chlorophyll a «0.01-57.8 llg I-I) reflects wide seasonal

and regional variations in hydrographic conditions

throughout this ecosystem.

Highest mean Chlw is usually observed in nearshore

areas adjacent to the mouths of the Hudson-Raritan,

Delaware, and Chesapeake estuaries, over the shallow

water on Georges Bank, and in a small area along the

southeast edge of Nantucket Shoals. Occasionally, high

Chlw concentrations are found in Middle Atlantic Bight

coastal waters not in close proximity to estuaries, and

may reflect upwelling episodes. Lowest Chlw «0.125 llg

I-I) is usually restricted to the most seaward stations

sampled along the shelf-break and the central deep

waters in the Gulf of Maine. When relatively high Chlw

occurs in the Gulf of Maine, it is in the nearshore

western portion, between Penobscot and Casco bays.

The annual cycle of phytoplankton biomass follows

the paradigm for temperate continental shelf ecosystems. There is at least a twofold seasonal variation in all

areas. The highest phytoplankton concentrations (m3)

and highest integrated standing stocks (m2) occur during the WS-bloom; the lowest occur during summer,

when vertical density stratification is maximal. In most

regions, a secondary phytoplankton biomass pulse is

evident during convective destratification in fall, usually in October.

The timing, duration, and intensity ofW5-bloom vary

by region. In the Middle Atlantic Bight the W5-bloom

progresses from nearshore to the slope, occurring during January-March in the nearshore and midshelf regions, and March in outer shelf and adjacent southern

slope water. On Georges Bank, WS-bloom peaks during

March, except in the Great South Channel along the

southern flank and in the northern slope waters, where

the peak is reached during April. Winter-spring bloom

appears during February-March in the nearshore western gulf and during April throughout the gulfs deeper

waters. Greatest concentrations of biomass near surface

appear in the Wilkinson Basin during April.

In shallow nearshore Middle Atlantic Bight, fall bloom

appears during September-October. In the midshelf

and outer shelf regions and along the Middle Atlantic

Bight shelf-break, fall bloom occurs one month later in

October and follows the expected delay in destratification of deeper water. In the shallow water on

Georges Bank, chlorophyll a increases above the summer minimum during September, but continues

through November. In the deeper water, fall bloom appears during October, followed by decreases in Chlw during November and December. Fall bloom in some areas

of the Gulf of Maine approaches the magnitude of the

W5-bloom, but Georges Bank and Middle Atlantic Bight

fall blooms are clearly subordinate to WS-blooms.

Generally, mean Chlw decreases from nearshore to

the shelf-break. These cross-shelf gradients are usually

present in the Middle Atlantic Bight. On Georges Bank,

an annular pattern is usually evident, where Chlw decreases from shallow to deep water surrounding the

shoals. In the Gulf of Maine, Chlw is not well correlated

with water column depth and bathymetric gradients are

much weaker than those for the Middle Atlantic Bight

and Georges Bank, where there is a regular seasonal

progression. Cross-shelf gradients are steeper during

the unstratified season than during the stratified season. They are most pronounced duringJanuary-Februarywhen the W5-bloom appears in the nearshore Middle

Atlantic Bight and in the shallow water on Georges

Bank, and least pronounced during April when the W5-

bloom appears in deeper water.

Measurements of chlorophyll in two size-fractions of

the phytoplankton, netplankton (>20 11m) and nano-
56 NOAA Technical Report NMFS 139 _

plankton «20 j.l.m), reveal that the smaller nanoplankton are responsible for most of the phytoplankton biomass on the northeast U.S. shelf. Considering

all samples, the median size composition is 70%

nanoplankton, 30% netplankton. Strong dominance

(>90%) by nanoplankton was common while strong

dominance by netplankton was rare. Most of the annual phytoplankton primary production on the shelf is

also by the nanoplankton (O'Reilly et aI., 1987).

There are distinct patterns in seasonal, regional, and

vertical variation in size composition, which presumably reflect variations in the species-composition of the

phytoplankton. Cross-shelf gradients in phytoplankton

size composition are frequently observed in contour

maps of individual surveys and in the two-month composite contours. Netplankton dominate nearshore areas of the Middle Atlantic Bight and shallow water on

Georges Bank, where chlorophyll a is usually high;

nanoplankton «20 Ilm) dominate deeper water at the

shelf-break and deep water in the Gulf of Maine, where

Chlw is usually low. As a general rule, the percent of

phytoplankton in the netplankton size-fraction increases

with increasing depth below surface and decreases proceeding offshore.

Size-fractionated measurements of chlorophyll into

netplankton (>20 j.l.m) and nanoplankton «20 Ilm)

also provide a useful rough index of major changes in

the phytoplankton composition that occur during spring

and fall blooms and between stratified and unstratified

conditions. Overall, netplankton dominate standing

stocks during the WS-bloom, whereas the fall bloom is

strongly dominated by nanoplankton offshore and

weakly dominated by nanoplankton nearshore. Our

findings support the emerging ecological paradigm

(Malone et aI., 1983b) that netplankton (presumably

large diatoms or chain and colonial small diatoms)

prevail during the unstratified period when turbulence,

vertical mixing, and nutrients are high and photosynthetically active radiation (PAR) in the upper mixed

layer is variable; and that smaller nanoplankton and

motile species prevail during density stratification, when

turbulence is low and average PAR is high in the upper

mixed layer.

Composite vertical profiles of mean chlorophyll a

concentration in 11 layers of the water column constructed for 26 subareas provide additional insight on

regional and seasonal differences in the vertical distribution of chlorophyll a and percent netplankton. Four

basic profile shapes are evident: uniform, declining,

bell, and inverted.

Vertically uniform chlorophyll a profiles are most

obvious from November through February, the period

of minimal density stratification, and year-round in the

tidally well-mixed shallow water on Georges Bank. Declining vertical profiles occur during the winter-spring

and fall blooms, when highest biomass is in the upper

20-30 m of the column. Inverted profiles occur relatively infrequently. They are most obvious following the

WS-bloom, when elevated concentrations of chlorophyll

a appear near the bottom of the water column in the

midshelf region of the Middle Atlantic Bight, but not

on Georges Bank and in the Gulf of Maine. The inverted profiles indicate that the near-term fate of the

WS-bloom in some areas ofthe shelfis sedimentation and

accumulation near bottom. Thus there are significant

differences among regions with respect to the fate of the

WS-bloom and the extent of its potential availability to

benthic animals. The intense and prolonged WS-bloom

throughout the water column in midshelf and outer shelf

MAB is followed by a major diatom sinking event, as

indicated by increases in chlorophyll a from surface to

bottom and by disproportionally more netplankton at the

bottom of the water column than near surface.

Bell-shaped profiles characterize periods of vertical

density stratification. Chlorophyll a is relatively low near

surface, progressively increases to the subsurface chlorophyll maximum layer (generally in the pycnocline

20-35 m below surface), and then progressively decreases over the remaining deeper portion of the profile. Subsurface chlorophyll a maxima are ubiquitous during summer in stratified water. Chlorophyll a in the subsurface maximum layer is generally 2-8 times the concentration in the overlying and underlying water and approaches 50-75% of the levels observed in surface water

during WS-bloom. This concentration of phytoplankton

biomass in and just below the seasonal pycnocline makes

this layer a highly localized and potentially important

source of organic carbon for herbivorouscopepods.

The SSR during summer parallels the shelfWide pattern for stability, indexed as the difference in density

(sigma-t) between 40 m and surface. The weakest stability and lowest SSR's are found in shallow tidally-mixed

water on Georges Bank; the greatest stability and highest SSR's (8-12:1) are along the mid and outer MAB

shelf, over the winter residual water known as the "cold

pool." On Georges Bank, the distribution of SSR and

the stabilitY40 are roughly congruent with the pattern

for maximum surface tidal current velocity, with values

above 50 cms-1 defining SSR's less than 2:1 and the

well-mixed area.

A strong seasonality is evident in the magnitude of

chlorophyll, the size composition of the phytoplankton

chlorophyll, and in the shape of the vertical profile of

chlorophyll. In areas that stratify during summer, chlorophyll a concentrations at depths between 20-35 m

below surface are less variable over an annual cycle

than those in surface and bottom waters. Surface water

exhibits the most pronounced seasonal change. Chlorophyll concentrations are generally lowest during the

period of vertical density stratification and highest dur-
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 57

ing the WS-bloom. Chlorophyll concentrations 20-35

m below surface are less variable over the annual cycle

as a consequence of the establishment of a seasonal

thermocline. At this depth there is approximately a 2: 1

range in chlorophyll concen tration over the annual

cycle, whereas in surface, the range is 8: 1.

The composite profiles of chlorophyll a also reveal

large vertical gradients in the size composition of phytoplankton during the stratified season. Usually, percent netplankton increases with increasing depth below surface. In some areas, such as the midshelf and

outer shelf Middle Atlantic Bight, percent netplankton

increases from -10-20% near surface to 40-70% 50 m

below surface, suggesting large differences in phytoplankton species composition. Similar but less sharp

gradients are observed in the deeper stratified water on

Georges Bank and in the Gulf of Maine.

Although size composition of the phytoplankton varies throughout the annual cycle and throughout the

water column in regular patterns in many shelf areas,

there remains much uncertainty about the precise species composition of the phytoplankton, particularly during the stratified period when largest vertical gradients

in size composition are observed. This is a neglected

area and warrants further field studies.

These characterizations of the seasonal and regional

differences in the magnitude of Chlw' annual cycles,

and the shape of the mean chlorophyll a profile should

prove useful in understanding regional differences in

fisheries productivity. They will also help increase the

precision of ecosystem-wide estimates of euphotic standing stocks and primary productivity, when combined

with synoptic satellite measurements of the surficial

layer of the ocean.

Acknowledgments _

In any extensive endeavor spanning a decade, a number of individuals are responsible. We would like to

acknowledge]. Pearce, K. Sherman, and R. Murchelano

for providing sustained support and guidance, and W.

Smith for his efficient coordination of MARMAP field

surveys. We thank]. Sibunka, F. Steimle, P. Berrien,

and D. Mountain for serving as Chief Scientist during

many of the field surveys. Their wise decisions at sea led

to the most comprehensive sampling possible.

We are fortunate to have worked with many highly

competent technicians involved in data collection and

analysis:]. Anderson, S. Barker, R. Bruno,]. Cain,]. Duggan,

T. Finneran, A. Fischer, P. Forunier, S. Fromm, S. Fromm,

B. Hogelin, C. Ingham, B. Lamp, C. Muchant Cain, ].

Nickels, A. Pratt,]. Prezioso, S. Ward, and K Workman.

We thank]. Thomas for his assistance with the initial

sampling design and methods; P. Fournier, S. Fromm,

and R. Pikanowski for their assistance in developing

computer routines and database management; D. Mountain,]. Manning, and T. Holzworth for providing hydrographic data; E. Escowitz for providing bathymetric

data; R. Armstrong,]. Bisagni, and]. Landry for their

suggestions on data analyses; and S. Arenas for many

helpful editorial suggestions.

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APPENDIX A

'---,

'---,

.,

May 07-May 07 May Og-May 10 May 12-May 13 totoy 17-Moy 18 May 19-Moy 28

Moy 22-May 26 May 24-Moy 25

o Dec 08-0ec 09 E Nov 13-08C 02 F Nov 15-Nov 30

G Nov 16-Nov 17

.. '\.. . ,

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•

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Jon

:..'.'

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Nov OS-Noy 06

~~: ~~:~~: ~g i F Nov 19-NoY 21 I

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---,L_

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:Wo .-.: A ~~g9 U::~~99 n .I~: r AU9 27-Au9 2B i --='-- ---ll. -'

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1979

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Appendix Figure Al

Locations of stations sampled during the 78 surveys considered in this report. Surveys are presented in chronological

order. The survey period and the survey name are shown in the upper left area of each panel. The dates of occupations of

standard transects (A, B, C, D, E, F, G) are shown in the lower right area for MARMAP surveys. Stations east ofthe map area

are not shown for survey AL 80 II.
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 65

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66 NOAA Technical Report NMFS 139

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Appendix Figure Al (continued)
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 67

~oy 09-Jun 02.

AL8403

Nov 07-08C 10. 1985

DL8510

\~ "\" :i~i;' ""~~..~_~~_~-Y·~~~G .&4 :. •• e,' C .... :: c

i /. e.~.. A Nov OS-Nov 05 i 1 ""e· .' A Jan 24-Jan 24

I -, • B Nov 07-NoY 08 fll/'.~. B Jon 25-Jon 27 ';e .e:: B C Nov 09-Nov 17 I" 0 ••~. B C Jan 30-Jan 30 I =""tIo.'' A 0 Nov 19-Nov 20 "\.=""tIo A [ Nov 23-Nov 24

'I' : •• r Oec 02-0ec 08 :1' .•. ;}.,.,•

'

e., G aec 09-0ec 10 '."" < .: L_--''-- ---JL _'I·

Appendix Figure Al (continued)

A reb 07-reb 07 B reb os-reb 06 c reb 02-reb 02 o Jan 25-Jan 26 E Jan l'-Jon 24 F Jan 14-Jan 22 G Jon 16-Jon 17

A ~oy 23-Moy 23 B ~oy 21-~oy 21 C ~oy la-May 19 o May 1S-~oy 16 £ ~oy 09-~oy 14

r ~oy 09-~oy 12 G ~oy 1O-~oy 11

,.------,

A Aug 20-Aug 20 B Aug 22-Aug 23 C AU9 25-Aug 2S o Sep Ol-Sep 02 £ Sep 03-Sep 18 r Sep 05-Sep 16 G Ssp 07-Ssp OB
68 NOAA Technical Report NMFS 139

1988

,-

, 1_1_1_1_1_

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r 1 I I 1

1986 1987

:-,~H

lei••

t- t- to. to

II 1.,

LLLLL

: ,: I i- I-I r 'r 1.1 I I

t-err.,..

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r • r r. Ttl•• e l -, -I I II lit I 1 I I I I I 111

1-1-1-1-+ +-1-+-+-1 -1-1-1-1-1-

I I I e I 1.1 •••1

,

1983 1984 1985

1 I I I

~~I-~ l- ~-+---l

I 1.1 I re e: I I

1979 1980 1981 1982

-,-,..- 11 I , I

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~!J.L.~- __:-:-:-: ~." " I • j I I I

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,'~ " ..'" 1 ..-: -: -.~:-:-: el., 1 .rel 11 ·~"HI-·"'''_II'''·_ --..'-,-, ..e' elll

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I

.1•• 1 ••1"1

--••H...._...... ' I I , I I I I I I I

-: -: -:-:-:-:-:-

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.1 el I .1 I e I ~...J~ _.1.... 1_1

~~~-: .'11 " -,.: .'t",-:. ~Ie: I I ~J 1 I

..., • ..,., "'1.'-1

• '. I' .1 I.' ~"I_l"

~~~-: ~.' ..~~:-:-:- '.' , 1 I I. I I I 1 I , , • ..,.., ., 1-.

, '. I I ••1 I I .-..-' --... e'.11 "'11

!J-'." ~'

.:~:-I ~;. ; ,~...,..--t.,~ _,.-, ele. _I' ,1----...-1-. _-, .I I I '. ''1...I I , I , ', -~::-:-: -:-: :-:-:- ..",., -.,-,.,-.- I I , " I' I'

....... -'1. I_ I I 1 I' I'.'

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.,~-,-, -.,.,,-,-, 11' '1 I I. 11

-+ -+ -+ -f --l -1-1"1_1_

'-1 I ••1 I I

1978

tl tl .. -: ------:.;-

.

•••• "".,.,- .'"~~er- .... ' . ...~- _'-

1111:11 tlt! tl-:-' *=.':- ..... "" ,- -_.,.- ..........

..... .....---.. .·ht!"-ff~

1977

.... ,..,....,.. I It r I

LLl.l..1

I I I I I

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.,. IrTI.- ,. ere ~.,.

I I I I I

L L l .1.. I I I '. f- rTtt - I I I I I

r- r r"'. I I I I I

L- L.L.J..l

.r. ~~H:T•••••• :h!iiI - ..__

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L 1- .1-.1.••••••_ _

.'." ,'.' .. :: : ;~:~:- -m;:- ~~~. : :=:-.~H1.~..~.~~ l-- l- L.1. J. ••1 .... -1-< _I •• _'_1_1_1_1-

I I I III

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: : : :~ r r r T T

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ere + +

e'. 'e L L L J J.

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75 r- r r r

76 I I I ••

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78 : : : : r

79 I I "I T 86 , , , ,..- 87 t'- r r t"e

8

9

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1

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9 I I I 'e 25 L L L .1. •

26 : : : :~ 34 1111 7

378 ",," 3 r r r Te

47 I I I 1. 9 .1-.-1.-.

59 leI. I I

60 Hd"

I I I I I 65 .,.T.

70 ' , , ,

71 "'-.L.

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80

1 I I I I I 8 r r T T

85 I I 1 I

90 l91 ""..- !...LLll 8 I I I I I

17-~~~~~ 18 I I I I.

35 .. .. ~.

36 ' , , , I

46 L L L L~

48 : : : :~ 61 rrrTT

62 "" 63 I- 1- .. + +

64 I I I Ie

ORTHERN

OUTER

SHELF

SVBAREA,TI.FiLr;E'-r-rTT"""'-r-rTT""...,,,-r-rr-T-rTTT-r-rT-T-TT-.,.::,~-r-,::...;:..n--rr.,...,-rrr--rr"""-r-T-r--rrTT""n-r.,..,,--n'-r-r-'--' CH. PLUME 12

DE. PLUME 29

18

H-R. PLUME 55

18

SOUTHERN 4

NEARSHORE I

22

23

28

CE TRAL 30

NEARSHORE ~1

43

52

53

18

54

56

67

68

I

2

5

6

7

10

13

14

15

20

24

27

31

32

iz

44

45

50

51

18

57

58

SOUTHERN

SLOPE

CENTRAL

MlDSHELF

SOUTHERN

MlDSHELF

ORTHERN

MIDSHELF

SOUTHERN

OUTER

SHELF
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 69

1988

1 I I I I

_1_1_1_1_1_

I I I I I

_1_1 ~I_I_I_

r I I I I

I 111 I

-1-'-'-1-1-

1 I 1 1 1

_1_1_1_1_1_

11111

11111

-1-1-1-1-1-

I •• 1 1

-'-1-1-1-1-

11I11

_1_1_1_1_1-

11111

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1 I 1 1 1

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II I 1 1

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II I 1 1

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11111

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11111

1978 1979 1980 1981 1982

;~~=-:~. .eM" r I I I r ;4'---1-_

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of -i -t .-1- -I-I-I-I-~

I I I I t I I I I I

Jj.J-.J_I __1_1_1_1_1_ LLL11

H,~ H"~ ....:~

~ff~ ~~~, .. -:-Itm

,~"....... ~~,. ;-t.,.,-'--I-I-I-I-r-- r-r r-.,-.,. "

I el. I I.I I. .' I I. J-.l.J.-1 __I_.'_l ~ll..

:::,: :~: :·:-Itflt 1 "I -I -I -I - -I -)-1-\- 1- - I ! r T T

•••• I 1).1 I I I I I I

..._----_. 1\1-'-1--1-1-1-1-1-

;;;~t=t

...-.'- --

=~

...----.- ...-..- '.... '.- :-=:= -:-= ,-, --, ..,.--1-..... I el" 1.1 I. -1-1-1-1 __1_I_l_I_lI t I. I I Ie' I.

..!...! J ;_1 __1_1..1_1 I I I I 1'-1 I

I I I t I ~I I

, -, -,.., -, - -I-I-I-I-r

1 I I I I I I I ••

.lJ.J.J..J __I_I_t_l_L

1977

NORTHEAST

PEAK

GREAT

SOUTH

CHANNEL

WESTERN

O. SHOALS

EASTERN

O. SHOALS

SUBAREA, TFi IL::.:;:E::"-'-T"TT"TT"T"T"1rTT"T"T""rrT""T"T""rrT"T"G.,...E.,...0rrR.,.G.,...E.,...S,....,B..,.A"T"N.,...Kr-rr"""""""TT"T"'T""1rTT.,..,..-r--,-r"""""'''''''''''''''''''rrT''''''''''''''''''

CENTRAL 123

SHOALS 147 148

156

NORTHERN 124

SHOALS 146 160

120

121

157

158

159

92

III

112

113

122

SOUTHERN 114

FLANK ll~

149

150

153

155

177

178

179

191

192

NORTHERN 82

SLOPE ~~

115

116

118

151

152

154

NANTUCKE)~~ SHOALS 93

Appendix Figure A2 (facing page and above)

Temporal distribution of chlorophyll sampling in subareas ofthe Middle Atlantic Bight, Georges Bank, and Gulf of Maine,

1977-88. Values in the left column are standard tile numbers (see Figs. 5, 8).
WESTERN

JORDAN

BASIN

70 NOAA Technical Report NMFS 139

94 I I I I. I •• • I I rei.. I 1 1 I I

9

9

7

5 1-1-....... I-•• -I-.-1-l _1_1_1_1_1_

• Ill. I lei I I I lei I I I I I I I

998 l..-!..Ll.. '-teL.1 .!.!J....!J _1_1_1_1_1_ 9 I I I I I I I I I I I I I I I I I I I

188 T ~.~ _: _: _:_:_:_

I I I I I tIl I I I I I I I I NORTHERN 101 ~~+-+. + .... _ -<-O-H-'-

1,82 I I I I. I tel Itt 1 I I I

I~~ IL~~~; ~~~~ -:-:-:-:-:- I~ ~~~~. :~~-: :::::

11 1-1-t-1". +.,;4-; -1-1-1-1-1-

135 I I I I. I I t I I t I

136 LLLLe .1.lJJ-l _I_I_I_I_L

137 I I I I. 11 I I I I r I I ,

138 T r' + _: _:_:_:_:_:_ I I 1 I I I I I I I I I I I I WlLKINSON 96 ,..,..,..,. ''''44 _,_,_,_,_,_

BASlN 182 1111. ~~.~J.~ ~_:_:_:_:_.

Ii87 ::::! ::-: :: ::::: IO~ :-:::. :r::: -:-:-:-:-:-

110 r r r r •• -1-1-'-1-1-

125 .,.'. • , '. '. , , 126 L L L.l- ..l. -e-J..l....J _1_1_1_1_1_

127 I t I I it I I I I I I I I I I

128 "'" +H~ -:-:-:-;-:- 129 ::::~ 1111111111

r r r r T T,., 1.., -I -'-'-1-1-

GEORGES 130 "". , , , " "'" BASIN 143 ••+. + ....... --<-,-,-,-,- 144 I I I I • I lei. 1 I I I I I

145 L L L 1 .1 .1 J _I _I _1_1_1_

161 :.:,: I_ : : :.: :;::: 162 rrrT-' T.,.' • ., -1-'-1-1-1-

163 I I I I. I I I.' I I I I I

174 1-1- ... +-. -+- -1".-1 --1-1-1-1-1- 175 I I I I • I I 1.1 I I I I I

176 ~} I ~,~ -:-:-:-:-:-

13 2 • _: _: _:.: : 133 I I I I. I I. I I I I

134 I- t- +- +. + .... -t -i _ • I_

142 I I I I. 1 t.' I I 'I I I I

167 L L l 1. • .1 -leI.--.J _1_1_1 I I

182 ::::: : :.: :: ;:::: IIlfl 1111-1 -1-1-1-1-1-

139 I I I I I I I I I I I I I , I

140 t-+-t-t-e "1"1"1;-; _1_1_1_1_1_

141 I I I I. I lei I I I I I I I

164 LLL1. .l.leJ • ...J _ •• 1_1,1_1

165 I I I I; I I , l I I I , I I

I I I I I lit I l' I I I

19~ :::: ::.: ~-: I I I I I

169 ,rr r. T-ret • ..., -1"-1-1-1-

170 I I t I. I I 1.1 I I I I I

181 L L L.L j. ..l...l- -l • ..J _1_1_1_1_1_

171 I I I I" I I I I I I I I I I

190 !...!.. I. .!..!... ! ._1 I I I I I

172 :::: .: :.: .: -;-; :-;-;- 189 rrrTT • .., ,-1-1-1-1-

i73 w'-:-,'",'"*-,',;.·...l...-'-;'";t*"c-.J~7r~~.l....t-T.;t;;~..L+-t""*'~.....J. ......~-rt¢-L--<.7;~-;:;-.L'-t*"~...l...-'-;'"*~,c...J~7r:rrT.L .......~'.c:'<i.~'..L.' -;'""*,''¢'~' 1977 1978 1985 1987 1988

Appendix Figure A2 (continued)
APPENDIXB

Chi aug/I

%Net 0-.13

0-5 ••••••• ,13-.25

5-20 .25-.5 .~

20-40 : .5-1

!!~!t I'; II

>16

0' /'--

.'. "

'"

, , ,

km 60

105

1900 Net 1900

60-

BOA: Chi a

o

o ,/

o

Q o

o

o

,~" 0 t. 0 •.. 0 0

o

o 0

o

A Ocl 19-0cl 19

B Oct 21-0cl 21

C Del 24-0cl 26

o Ocl 28-0cl 28

E Nov 01-Nov 02

f Nov 05-Nov 06

Oct 17-NoY 09, 1977

AR7701

Appendix Figure Bl

The distribution of chlorophyll a (Chi a) and percent netplankton (% Net) during survey AR7701,
72 NOAA Technical Report NMFS 139 _

Nov 12-Dec 13, 1977

MM7711

201 ISZB

128 2861097 Net 128 2861097

Net

BO0: Chi a

o

,: G

o

o

o

o " ?"

o

Chi aug/I

%Net 0-,13

0-5 ,13-,25

5-20 ,25-,5

20-40) ,5-1

i!~!tI H: o Dec DB-Dec 09

E Nov 13-0ec 02

F Nov IS-Nov 30

G Nov IB-Nov 17

.~'

Appendix Figure B2

The distribution of chlorophyll a and percent netplankton during survey MM7711,
O'Reilly &: Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 73

:r;"1 - . . . .

126 mQ 18B4

12071972

110 160

BO80-

A: % Net 12011972

BO60-

B: Chi a

80-

A: Chi a

0 0

0 0

0

0 0

" " 0 0

0 ,6'

Chi aug/I 40-

%Net 0-,13

0-5 ".13-.25

5- 20 •••••••. 25 - , 5

20-40) .5-1

li~!l. i l~1: Feb 17-Feb 16

Feb 19-Feb 20

Feb 27-Feb 26

Mar 09-Mar 10

Mar 13-Mar 14

Feb 16-Mar 16, 1978

DL7802

Appendix Figure B3

The distribution of chlorophyll a and percent netplankton during survey DL7802,
74 NOAA Technical Report NMFS 139 _

gOO 25

12002000

135

Net

IJJ 2J5

III

lei

1B5

12002000

O-~: (' ..

I::~"~\II~I' BO-

'F: % Net BO :.''!5

/V O-!;;

20-:·;

. 40-·:-

SO--:··

BOF: Chi a 110 225

Chi aug/I

%Net 0-.13

0-5 .13-.25 - 5-20 ._.25-.5

20-40 :i; .5-1

il~!tIU II

) 16

c

Apr 20-Apr 20

Apr 22-Apr 23

May OB-May 10

May ll-May 12

May IS-May 17

May 20-May 22

Apr 18-May 22, 1978

AR78D4

Appendix Figure B4

The distribution of chlorophyll a and percent netplankton during survey AR7804.
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 75

106 234117

1915

k m 60

15002156 Net

20-'

40-

60-

BO15002156 A:%

o o 0

o

Chi aug/I

%Net 0-.13

0-5 ........ 13-.25

5- 20 ••••••• _25 - _5

20-40) .5-1

!!~!lo I n:

c

o 0 0

o 0 ..6'

-;_ o.~~.~ 0 0 0 : F)":

o 0 0 0 0 0 ,.".,

o 0 0 ;.0, .... :.··

00 00''''''_' ~_""~?_'_ ,..:.9-"-"

\t/ D E

Jun 25-Jun 25

Jun 26-Jun 27

Jun 29-Jun 30

Jul 07-Jul 07

Jul 10-Jul 11

Jul 15-Jul 16

Chlorophyll a

(1 m]

Jun 23-Jul 16, 1978

Al7807

Appendix Figure B5

The distribution of chlorophyll a and percent netplankton during survey AL7807.
76 NOAA Technical Report NMFS 139

, , ,

km 60

105 1400 2000

2004

8152070

,

.... , ..... ,

'.: :-'."-:.:-:-:-:-:.'

.~

200 204 217 181

HIS 2070

Netm

60-

80-

A: Chi a

2~:~~~

:~~~ 80-;<~- E: Chi a ZIS 192 216 no

G

o 0 ,:

o

0 0 0 0

0 0 Q

0

0 0

8 0

o~-o'\~~o 0

00~00;0 °9_:"--\'_~"~~_'" ~~.).~' o "., 0 o 0 0.. Chi aug/I

o<~)~I C X:i~ I"~; ~l} 00 00/ B 40 - 60 !,,,,,,,,,,...: 1- 2

A Aug 13-Aug 14 60-80 12- 4 o 0 0.:' A Be Aug IS-Aug 16 80 - 95 4- 8

Aug 18-Aug 19

o 0 0 0 Aug 21-Aug 22 95 -100 8-16 o E Sep 02-Sep 04 ) 16 F Aug 31-Sep 02

G Aug 27-Aug 28

Aug ll-Sep 04, 1978

BE7801

Appendix Figure B6

The distribution of chlorophyll a and percent netplankton during survey BE7801.
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 77

245 !JOD

60-

BOC: % Net

215 190 205

60-

BOC: Chi a

0-'

/V~~;··60-

BOE:·Chl

o

F

o 0

o - 0

. ,,?-'\-"

o 0 -,~_ .. _---

o ,({

o 0

o

Chi a ug/I

%Net 0-_ 13

0-5 ... .13-.25 60-

- BO- 5- 20 _25 - _5 .- B: % Net

20 -40 t?~(f .5-1

40 - 60 I

1-2 B Ocl 31-ocl 31 60 - 80 2-4

C Oct 23-ocl 24 : D Oct 20-oct 21 80 -95 4-8

E Oct DB-Oct 17 95 -100 8-16

F Oct 13-oct 15 >16

Oct 06-Nov 01, 1976

BE7603

Appendix Figure B7

The distribution of chlorophyll a and percent netplankton during survey BE7803.
78 NOAA Technical Report NMFS 139 _

157 800

Net

... ,;'

0- /V20:. 40-

50'

BO0: Chi a " .•..•...l.- ~"'~32!'...O--"16!!!EOO!.f2J!!!!OO~L ..!E....1,l!-,~,tlliJ

.'-". " km 60

I':-~'" ~f;(o 0

o

o 00

o 0

o 0

o

. :"

Chi aug/I

%Net 0-.13

0-5 .13-.25

5-20 =.25-.5

20 - 40 ;:;~ . i

!!~!tl~" H>16

o 00

00 0 .i

- .1lII~·0 ":rr

o

:,,"", 00 \,',if

._./" _ ?... F

" E \-" 0

Nov 27-Nov 29

Nov 15-Nov 23

Nov 19-Nov 21

...

Nov 16-Nov 29, 1978

8[7804

Appendix Figure B8

The distribution of chlorophyll a and percent netplankton during survey BE7804.
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 79

Feb 24-Mar 14, 1979

DL79D3

A feb 26-feb 26

B feb 2B-feb 2B

C Mar 03-Mar 03

o Mar OB-Mar OB

E Mar 10-Mar 10

, , .-- --- -~- ..

." ..",

;

.:'

Chi aug/I

%Net 0-,13

0-5 ,13-,25 - 5-20 ••••••• ,25-,5

milo irl: 60-

BO,

A: Chi a Net

Appendix Figure B9

The distribution of chlorophyll a and percent netplankton during survey DL7903,
80 NOAA Technical Report NMFS 139

May 06-May 29, 1979

DL7905

F

Chi a ug/I

%Net 0-.13

0-5 - 13 -.25

5- 20 .;,,;..;.;,.:.;. 25 -.5

20 -40 f?ff .5-1 126 1244

, , ,

40 - 60 I

1-2 km 50

A May 07-May 07 60 - 60 2-4 B May 09-May 10 60-95 4-6 c May 12-May 13

0 May 17-May lB 95 -100 6-16 E May 19-May 2B ) 16

F May 22-May 25 Net

G May 24-May 25 12BO 12BO

Appendix Figure BI 0

The distribution of chlorophyll a and percent netplankton during survey DL7905.

I"

106 228
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 81

Jun 17-Jul 13, 1979

Al7906

/( _? O-y' ~20···

. :~~~>

BO-

,/ F: Chi a 2JO

Chi a ug/I

%Net 0-.13

0-5 .13-.25 60-

5-20 - BO- ....... .25 -.5 B: Chi Net

20 -40 .5-1 a

::::::::::::::: 101 1278

40 - 60 1-2 , , ,

I km 60

A Jun lB-Jun lB 60 - 80 2-4

B Jul 02-Jul 02

C Jul 05-Jul 05 80 - 95 4- 8

0 Jul 07-Jul 07 95 -100 8-16 60-

E Jul Og-Jul 10 ) 16 BO- F Jul 12-Jul 13 A:% Net 1097 1097

Appendix Figure B 11

The distribution of chlorophyll a and percent netplankton during survey AL7906.
82 NOAA Technical Report NMFS 139

eoo

60

J05

0-

20

40-

60-

BO0: % Net 130 310

0-'

20

40-

60-

BOC:% Net 1061(6

60- o.

- BOA: Chi a Net 1200 1200

BOC: Chi a

BOE: % Net 160 ISO 2011 ll!l ISJ

/v}~ BO0: Chi a

Chi aug/I

%Net 0-.13

0-5 ···.13-.25

5-20 •••••••. 25-.5

20-40 ? .5-1

illl r!: A Aug 13-Aug 13

B Aug IS-Aug 15

C Aug IB-Aug 19

o Aug 21-Aug 22

E Aug 24-Aug 31

F Aug 27-Aug 2B

Aug ll-Sep 02, 1979

BE7901

Appendix Figure B12

The distribution of chlorophyll a and percent netplankton during survey BE7901.
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 83

Oct 04-0ct 28, 1979

AL 7911

'" '"

Chi a ug/I

%Net 0-.13

0-5 .13-.25

5- 20 •••••••. 25 -.5

20 -40 //UU .5-1 1:l40 ::::: I 1-2 , ,

km 6'0

A Oct 05-0ct 06 2-4 B Oct 07-0ct OB

c Oct 11-0ct 11 80 - 95 4-8

0 Oct 17-0ct 17 95 -100 8-16 E Oct 20-0ct 27 >16 F Oct 23-0ct 26 Net G Oct 24-0ct 26 "I 14l

Appendix Figure B13

The distribution of chlorophyll a and percent netplankton during survey AL7911.
84 NOAA Technical Report NMFS 139

Nov IS-Dec 2D, 1979

AL7913

Chi a ug/I

%Net 0-.13 : ;:,' 0-5 .13-.25

5- 20 .......

... 25 -. 5 - 20 -40 p~ .5-1

... 40 - 60 I

1-2

0 Dec 09-0ec 10 60 - 80 2-4 F Dec 02-0ec 15

G Dec 06-0ec 16 80 - 95 4-8

95 -100 8-16

>16 :

Net 216

'" '68 194 230 402

km 6'0

Appendix Figure B14

The distribution of chlorophyll a and percent netplankton during survey AL7913.
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 85

500

.. 135 270 Net

F: % Net

BO-·

F: Chi a

o

o

F=rf~~~~~~5~E~~~~~~~=:C~=;==7"l--;-..lI~B~ I

km 60

o o 0

o

Chi aug/I

%Net 0-.13

0-5.·.·.·.. 13-.25

5- 20 •••••••. 25 - . 5

20-40\ .5-1

40-60 : ";": 1-2

60-80 12-4

80-95 4-8

95-100 8-16

>16

Mar DB-Mar 09

Feb 21-Mar 07

Feb 20-Mar 02

Feb 20-Mar 10, 1980

WI8002

Appendix Figure Bl5

The distribution of chlorophyll a and percent netplankton during survey W18002.
86 NOAA Technical Report NMFS 139 _

Feb 2B-Apr 04, 19BO

ALB002

"7

Net 109 I" 109 I"

%Net

Chi a

0-.13

ug/I 40-,:~•

0-5 _13-.25 60-

5-20 ....... .25 -.5 BO-

.- B: % Net 20 - 40 11(((: .5-1 102

40 - 60 i::i::.,;;:;:! 1-2 2~~g\. , , km 6'0

A Feb 29-Mar 01 60 - 80 I

2-4 B Mar 04-Mar 05

C Mar OB-Mar 09 80 - 95 4-8 40- 40-

0 Mar 17-Mar 19 95 -100 8-16 60- 60-

E Mar 24-Mar 25 ) 16 BO- BO- F Mar 27-Mar 2B

G Apr 02-Apr 03 A: Chi a A:% Net 1134 11J4

Appendix Figure B16

The distribution of chlorophyll a and percent netplankton during survey AL8002.
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 87

Apr 16-May 12, 1980

EV8001

A Apr 18-Apr 18

B Apr 20-Apr 20

C Apr 23-Apr 24

o Apr 26-Apr 27

E May 03-May 11

F May OS-May 07

.- -..,

',.'

,

.:'

F

Chi a ug/I

%Net 0-.13

0-5 .13-.25 60'

5- 20 - 80· ....... .25 -.5 B: Chi Net 20 -40 .5-1 a 105 '50

40 - 60 I1-2 km 60

60 - BO 2-4

BO - 95 4-B 40-

95 -100 B-16 60- 60·

) 16 80· 80·

A: Chi a A:% Net \400 1400

175

180

115 1200

Appendix Figure B17

The distribution of chlorophyll a and percent netplankton during survey EV8001.
88 NOAA Technical Report NMFS 139 _

May 23-Jun 29, 1980

DL8003

0'

A May 24-May 25

B May 25-May 27

C Jun 03-Jun 04

D Jun 05-Jun 05

E Jun OB-Jun 29

F Jun 25-Jun 27

%Net

0-5

5- 20

20 -40

40 - 60

60 - 80

80 -95

95-100

Chi 3 ug/I

0-. 13

.13-.25

.25 -.5

.5-1

1-2

2-4

4-8

8-16

>16

50·

BO·

A: Chi 3 1235 Net 1235

1041267

, ,

km 50

170

110 236

Appendix Figure BI8

The distribution of chlorophyll a and percent netplankton during survey DL8003.
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 89

/v;~.~ D: Chi a

Chi aug/I

%Net 0-.13

0-5 _13 - _25

5- 20 _25 - . 5

20-40/ .5-1

l!~!lo Il~l:

Jul 16-Aug OB, 19BO

EVB006

0/- C

A Jul 17-Jul 16

6 Jul 19-Jul 20

C Jul 23-Jul 23

o Jul 26-Jul 26

E Aug 01-Aug 07

F AU9 03-Aug 05

,'AY'"

:' ~b 0

o

o 0

o 0

o o 0

o

o

60-·

E: % Net192 1~8 lIS 200 218

0-: ..

20-"

40-

60-

60-

B: Chi a

:~~ BOA: Chi a 1400 1400

1141100

118 28!>

1320

Appendix Figure B19

The distribution of chlorophyll a and percent netplankton during survey EV8006.
90 NOAA Technical Report NMFS 139

100

101 207

km 60

102 1200

lI7a Net

60-

BO·

B: % Net

,,"

102 126lJ

:~¥;~i

BOmil A:%

~~~ 60- "'-'

BO·

A: Chi a

BOB: Chi a

Chi aug/I

%Net 0-.13

0-5 """ .13-.25

5- 20 =. 25 - . 5

20 - 40 ;i .5- 1

!l~!!o I H: A Sep 27-Sep 2B

B Sep 29-Sep 29

C Ocl 06-0cl 06

o Ocl OB-Ocl 09

E Del 16-0cl 2B

fOci 19-0cl 24

G Del 21-0cl 22

Sap 26-0ct 29. 1980

AL8010

Appendix Figure B20

The distribution of chlorophyll a and percent netplankton during survey AL8010.
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 91

Nov 19-Dec 21, 1980

AL8012

208

Chi a ug/I

%Net 0-.13

0-5 ... .13-.25

5- 20 -

...... .25 -.5

20 -40 ~tt)~ .5-1

40 - 60 1-2 ,

I 60

A Nov 20-Nov 21 60 -80 2-4

B Nov 22-Nov 23

C Dec 04-0ec 05 80 - 95 4-8

0 Dec 06-0ec 07 95 -100 8-16

E Dec 09-0ec 10 >16 F Dec IB·Oec IB

G Dec 20-0ec 21 a Net ID?!'! ID7!l

Appendix Figure B21

The distribution of chlorophyll a and percent netplankton during survey AL8012.
92 NOAA Technical Report NMFS 139

700

1280 Net 1280

156

0 00

0

0

0

-.'().'---

0 0

0

0

: G

o?,.

'"

106 190

, , km 60

Chi aug/I

%Net 0-.13

0-5 13-.25

5-20 •• •••••. 25-.5

20-40 « .5-1

1!~!1.1 H: B M., 23-M., 24

C Mar 19-M., 20

o Mar 1B-Mar 19

E Feb 19-M.r 10

f Feb 21-M., 07

G Feb 23-Feb 24

Feb 17-Mar 24, 1961

AL6101

Appendix Figure B22

The distribution of chlorophyll a and percent netplankton during survey AL810l.
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 93

Mar 18-Apr 08, 1981

KE8103

A Mar 21-Mar 21

B Mar 23-Mar 24

C Mar 31-Apr 01

D Apr 02-Apr 02

E Apr 03-Apr 04

F Apr 04-Apr 05

G Apr D6-Apr 06

860

860

'.,. I,

'..

\1 "

, ,

\" 0 i o 0 ~,.:

o .: G 60-

o 0 0"" BOo 0, ..,.-

,.9-"-' F C: Chi a

"'C' I" 141

'IIIIIIIIIIII Chi ug/I 20 a

%Net 0-_13 40:

0-5 " ' .13-.25 60-

5-20 _25 -,5 80-

20 -40 !~>(}~ ,5-1 B: Chi a Net log

40 - 60 I

1-2 , km 60

60 - 80 2-4

80 -95 4-8

95 -100 8-16

>16

i006

Appendix Figure B23

The distribution of chlorophyll a and percent netplankton during survey KE81 03.
94 NOAA Technical Report NMFS 139

Nov 18-Dec 21, 1981

AL8114

Chi a ug/I

%Nat 0-.13

0-5 . 13 - . 25 - 5- 20 .25 -.5 .- 20 -40 :\~<?! .5-1

./ 40 - 60

-

1-2

0 Dec 20-0ec 21 60 - 80 2-4

E Dec 16-0ec 19

F Nov 24-0ec DB 80 - 95 4-8 G Dec 03-0ec 04 95 -100 8-16

) 16

Appendix Figure B24

The distribution of chlorophyll a and percent netplankton during survey DL8103.

60
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 95

May 21-Jun 17, 19B1

DLB1D3

Chi a ug/I

%Net 0-.13

0-5 .... .13-.25

5- 20 .-.25 -.5 Net 20-40 :]<><~ .5-1

40 - 60 I

1-2 B Jun 15-Jun 16 60 - 80 2-4 c Jun 12-Jun 13 : 0 Jun 10-Jun II BO-95 4-B

E May 24-Jun DB 95 -100 B-16 f May 25-Jun 06 ) 16 G May 25-Jun 04

128

18J

113 240

km' 60

Appendix Figure 825

The distribution of chlorophyll a and percent netplankton during survey AL8114.
96 NOAA Technical Report NMFS 139 _

Feb 16-Mar 23, 1982

Al8202

Chi a ug/I

%Net 0-.13

0-5 ... .13-.25 - 5- 20 - .25 -.5

20 -40 ~~t(r~ .5-1

40 - 60 a,;,,,: ' :•....:::,,=;;:; 1-2

A Mar 22-Mar 23 60 -80 I

2-4 B Mar 20-Mar 21 80 -95 4-8 c Mar 17-Mar 1B

0 Mar 10-Mar 10 95 -100 8-16 60-

E Feb 1B-Mar 09 ) 16 BOF Feb 23-Mar 06 A: Chi Net G Feb 22-Mar 04 a

Appendix Figure B26

The distribution of chlorophyll a and percent netplankton during survey AL8202.

766
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 97

'"

km 60

60-

BOC: % Net 106

:;~ BOC: Chi a

G o o o

o 0

o 0 Q':'.~'

, ,? ,-c:" F

Chi a ug/I

%Net 0-.13

';,' 0-5 .. .13-,25

.' 5- 20 ....... , 25 - . 5

20 -40 j)j(h! .5-1 .- 40 - 60 1-2 .~' I c May 27·May 27 60 - 80 2-4

0 May 24·May 25

E May 22·Jun 10 80 - 95 4-8

f May 20·Jun 06 95 -100 8-16

G May 1B·Jun 04 >16

May 18-Jun 10, 1982

Dl8203

Appendix Figure B27

The distribution of chlorophyll a and percent netplankton during survey DL8203.
98 NOAA Technical Report NMFS 139

km 60

227 196 212

22J 196

E.

o 0

Chi 3 ug/I

%Net 0-.13

0-5 .13-.25

5- 20 . 25 - . 5

20-40<) .5-1

l!~!lo I H:

o 0 "' -.0--- -

o -' 0 0 .,0

o 0 0

000

o

o

o

o

o 0

o

o .: G

° 0 "- o .0 'F'"

--0 ~. ' ..~?_,)~.. ;,9-'~'-'" o

o

E Feb OHeb 04

F Jan 19-Jan 25

G Jan 22-Jan 23

Jan 17-Feb 10, 1963

DL6301

Appendix Figure B28

The distribution of chlorophyll a and percent netplankton during survey DL8301.
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 99

May 26-Jun 21, 1983

AL8304

Chi a ug/I

%Net 0-.13

0-5 .. .13-.25

5- 20 ....... . 25 -.5

20 -40 ,~.5-1

40 - 60 l~~><~~:i 1-2 A M,y 27-M,y 28 60 - 80 I

2-4 8 M,y 29-M,y 30

c Jun 01-Jun 02 80-95 4-8

0 Jun OB-Jun DB 95 -100 8-16 60-

E Jun 09-Jun 19 ) 16 BOF Jun 12-Jun 17 A: Chi Net G Jun 13-Jun 15 a \\4

Appendix Figure B29

The distribution of chlorophyll a and percent netplankton during survey AL8304.

\60
100 NOAA Technical Report NMFS 139

Nov 16-0ec 20, 1983

OL8309

182 201

0

0 Q 0

0 -.0"---

0 0 0

Chi a ug/I

%Net 0-.13

0-5 .13-.25

5 - 20 .25 -.5

20 -40 rrrm .5-1

40 - 60 ~:... ... 1-2 , , ,

km 60

A Nov I7-Nov 18

"-50 I 2-4

8 Nov 19-Nov 20 60 -95 4-6 c Nov 29-Nov 30

0 Dec 01-0ec 02 95 -100 6 -16 60-

E Dec 03-0ec 19 ) 16 80- f Dec 05-0ec 17

G Oec 15-0ec 16 A: Chi a Net 11119 1189

Appendix Figure B30

The distribution of chlorophyll a and percent netplankton during survey DL8309.
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 101

o 0 00'

o .0 ,,,,,

" _; .9-'~'-"

E

Chi a U9/1

%Nat 0-.13

0-5< .13-.25

5 - 20 •••••••. 25 - . 5

20-40i .5-1

40 - 60 .'••"H::Hii: 1- 2

60-80 12-4

80-95 4-8

95-100 8-16

) 16

Jan 09-Feb 08, 1984

DL8401

A feb 07-feb 07

B feb 05-feb 06

C feb 02-feb 02

D Jan 25-Jan 26

E Jan ll-Jan 24

f Jan 14-Jan 22

G Jan 16-Jan 17

0

0 _,6

0 0

0 0

o 0

o .: G

60-

BOA: Chi a Nat lZ50

, ,

km ,60

Appendix Figure B31

The distribution of chlorophyll a and percent netplankton during survey DL8401.
102 NOAA Technical Report NMFS 139

1500

, , , km 50

1109 Net 1109

o q. ...

Chi aug/I

0-.13

........ 13-.25

•••••••. 25 -.5

.5-1

1-2

2-4

4-8

8-16

>16

o 0

o .0

.9-...." F

%Net

0-5

5- 20

20 -40 .--. 40 - 60 !" .·!;;!i.,l

i!:!:,I

o ,.,

o ,.6 o 0

o 0 8

A May 10-May 11

B May 12-May 12

C May IS-May 15

o May 17-May 17

E May 22-Jun 01

f May 24-May 29

G May 25-May 27

May 09-Jun 02, 1984

AL8403

Appendix Figure B32

The distribution of chlorophyll a and percent netplankton during survey AL8403.
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 103

Nov 01-0ec 05, 1984

DL8409

A Nay 02-NoY 02

B Nay 04-NoY 04

C Nay 07-NoY 07

o Nay IS-Nay IS

E Nay 19-NoY 19

F Nay 2B-NoY 29

G Dec Ol-Oec 02

<V:~· ..... 60

BO'.

-:~~__ E: Chi a .68

<@W?\W,V..··· i=;;=;==,=,;===;===e==c===!~

E: % Net

Chi aug/I

%Net 0-.13

0-5.·.·.·•. 13-.25

5- 20 •••••••. 25 - . 5

20-40 ?: .5-1

!!~!1.1 H:

730

Appendix Figure B33

The distribution of chlorophyll a and percent netplankton during survey DL8409.
104 NOAA Technical Report NMFS 139 _

Jan 07-Feb 06. 1985

DL8501

110

2~:?~'Ti> .". . ......••..

40-)" . ::,' ::':'::::::

60:>::/

- .

BO<:::: ~~~~~)::

G:% Net Z4D181

.,0

Chi a ug/I

%Net 0-.13

0-5 - _13 - . 25

5- 20 ....... .25 -.5

20 -40 ~rr:r .5-1

40 - 60 ~_ J 1-2

A Feb OS-Feb OS 60 -80 I

2-4 B Feb 04-Feb 04 80 - 95 4-8 c Feb 01-Feb 02

0 Jan 2B-Jan 29 95 -100 8-16 60-

E Jan 2S-Jan 28 ) 16 Bo- F Jan 13-Jan 14 A:% Net G Jan II-Jan 12 1I~2

Appendix Figure B34

The distribution of chlorophyll a and percent netplanklOn during survey DL8501.
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 105

°0:b;;:~ ::.~ •.•.•.•:.':':'•.•'••.di

1128

Net 110 2~O

, ,60

lD1~

,

k

..•••LQG

Net

•. 0:::::::::::

.~

Net

40-

60'

BO·

B: %

Ill8

60·

BO·

A: Chi 3

60'

BOC: Chi 3

Chi 3 ug/I

%Net 0-.13

0-5 ::::::: .13 -.25

5-20 .25-.5 .~

20-40(( .5-1

!!~!rl' II

>16

A May 23-May 23

B May 2l-May 21

C May lB-May 19

o May IS-May 16

f May 09-May 14

F May 09-May 12

G May 10-May 11

May 08-Jun 04, 1985

Al8504

Appendix Figure B35

The distribution of chlorophyll a and percent netplankton during survey AL8504.
106 NOAA Technical Report NMFS 139 _

,

60

, ,

km

'"

Net

::~~I;lJI 28S

Net

.. ~._".

40'~' 20:: '.%t\~~ ..~::::~•.

60-

BO·

B: % Net lIDIl96

O-~.'ij

~~t~~~

'"

60-

BO·

A: Chi a

: G o ,.ff

....p.

F

o

o Q.

-.{)--- -- o 0

o 0

o 0/

o

o 00

o

o

o

o o

o ..

.'"o

do

t~ "" . :' ,,-

o o 0

o 0 0

o

Chi a ug/I

%Net 0-.13

0-5 .13-.25

5- 20 .25 -.5 .~

20 -40 :=:f:::::::; .5-1

40 - 60 ~:........::;

1-2 A Aug 20-Aug 20 60 - 80 I

2-4

B Aug 22-Aug 23 80-95 4-8 c Aug 2S-Aug 2S

0 Sop 01-Sop 02 95 -100 8 -16 E Sop 03-Sop IB >16 F Sop OS-Sop 16

G Sop Oi-Sop OB

Aug 19-5ep 19. 1987

Dl8708

Appendix Figure B36

The distribution of chlorophyll a and percent netplankton during survey DL8708.
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 107

Nov 04-Dec 10, 1987

Dl8710

A Nov OS-Nov OS

B Nov 07-Nov OB

C Nov 09-Nov 17

o Nov 19-Nov 20

E Nov 23-Nov 24

F Dec 02-0ec OB

G Dec 09-0ec 10

Chi aug/I

%Net 0-.13

0-5 .... 13-.25 - 5-20 ::::.25-.5

20 - 40 ,n: .5-1

i!~!!o IC~ II

) 16

60-

BOA: ChI a 1175

Appendix Figure B37

The distribution of chlorophyll a and percent netplankton during survey DL8710.
108 NOAA Technical Report NMFS 139

..-..... _-_.-- ...'

,.:'

}....,.':......

;

.:'

"-" .....

~" .

.. '~ -..-

':Iff,'" ,..

'..

~fIi5'" /i'lf'i< ••

).,--

~fIi5'" 'i'lfi< ••

.:....,'.':..... ~.".: .' ...- ,. __ .

Chi a ug/I

%Nat 0-.13

0-5 , , .13-.25

5 - 20 - .25 -.5

20 -40 mrrr .5-1

40 - 60 ;,.-,:~

?==_:l§ 1-2 60

A Jan 24 ·Jan 24 60 - 80 I

2-4 B Jan 25-Jan 27

C Jan 30-Jan 30 80-95 4-8

95 -100 8 -16 60-

>16 BOA: Chi a Nat 109

Chlorophyll a

(1 m)

Jan 09-Jan 3D, 1988

DL8801

Appendix Figure B38

The distribution of chlorophyll a and percent netplankton durin~ survey DL8801.
APPENDIXC

Table CI

Chronological listing of surveys, dates of sampling, number of vertical profiles, number of samples, number of samples

taken 3 m below surface while underway, and summary by field program.

Cruise l Program Start Finish Profiles Samples Underway

AD7701 Other Mar 16,77 Apr 01,77 29 179

AL7705 Other Jun 22,77 Jul 13,77 45 304

AR7701 MARMAp2 Oct 17,77 Nov 09,77 116 807

MM7711 MARMAP Nov 12,77 Dec 13,77 90 677

DL7802 MARMAP Feb 16,78 Mar 16,78 131 1,073

AR7804 MARMAP Apr 18,78 May 22,78 156 1,322

AL7807 MARMAP Jun 23,78 Ju116,78 146 1,230

BE7801 MARMAP Aug 11,78 Sep 04,78 154 1,358

AL7812 NEMp3 Sep 20,78 Oct 04,78 23 210

BE7803 MARMAP Oct 06,78 Nov 01,78 129 1,169

BE7804 MARMAP Nov 16,78 Nov 29,78 77 720

DL7901 NEMP Jan 23,79 Jan 31,79 10 73

DL7902 NEMP Feb 15,79 Feb 15,79 2 19

DL7903 MARMAP Feb 24,79 Mar 14,79 111 849

AD7901 Other Apr 18,79 Apr 26,79 48 347

DL7905 MARMAP May 06,79 May 29,79 168 1,390

AL7906 MARMAP Jun 17,79 Ju113,79 131 1,140

AL7907 NEMP Ju117,79 Ju126,79 50 449

BE7901 MARMAP Aug 11,79 Sep 02,79 149 1,351

BE7903 Other Sep 12,79 Oct 09,79 54 498

AL7910 NEMP Sep 12,79 Sep 27,79 55 486

AL7911 MARMAP Oct 04,79 Oct 28,79 155 1,342

AL7913 MARMAP Nov 15,79 Dec 20,79 82 785

BE7905 Other Nov 22,79 Nov 27,79 16 151

DL7911 NEMP Dec 04,79 Dec 17,79 50 375

W18002 MARMAP Feb 20,80 Mar 10,80 87 806

AL8002 MARMAP Feb 28,80 Apr 04,80 154 1,361

KE8004 NEMP Mar 24,80 Mar 30,80 29 198

EV8001 MARMAP Apr 16,80 May 12,80 153 1,413

EV8002 Other May 18,80 May 28,80 48 453

DL8003 MARMAP May 23,80 Jun 29,80 149 1,332

AL8007 NEMP Jull0,80 Ju123,80 56 475

EV8006 MARMAP Jul 16,80 Aug 08,80 159 1,445

EG8002 Other Aug 05,80 Aug 06,80 5 20

AL8009 NEMP Sep 03,80 Sep 17,80 69 557

AL8010 MARMAP Sep 26,80 Oct 29,80 175 1,601

KE8011 NEMP Oct 28,80 Nov 05,80 34 260

AL8012 MARMAP Nov 19,80 Dec 21,80 137 1,2]]

DL8009 NEMP Dec 02,80 Dec 18,80 66 516

AL8101 MARMAP Feb 17,81 Mar 24,81 150 1,374

KE8103 MARMAP Mar 18,81 Apr 08,81 93 773

KE8104 NEMP Apr 24,81 May 08,81 54 431

DL8103 MARMAP May 21,81 Jun 17,81 148 1,428

AL8107 NEMP Ju107,81 Ju121,81 65 542

AL8lJO NEMP Aug 27,81 Sep 16,81 67 583

AL81l1 WCR4 Sep 23,81 Oct 05,81 62 552 25

AL8112 WCR Oct 12,81 Oct 22,81 73 530

AL8114 MARMAP Nov 18,81 Dec 21,81 88 917

AL8201 NEMP Jan 26,82 Feb 10,82 49 421

AL8202 MARMAP Feb 16,82 Mar 23,82 145 1,356

AL8203 NEMP Mar 30,82 Apr 06,82 23 178

AL8204 WCR Apr 19,82 May 03,82 64 7Y2 8

DL8203 MARMAP May 18,82 Jun 10,82 110 1,104

continued on next page

109
110 NOAA Technical Report NMFS 139

Table Cl (continued)

Cruise I Program Start Finish Profiles Samples

AL8207 WCR Jun 18,82 Ju101,82 88 874

AL8209 WCR Aug 09,82 Aug 19,82 53 420

AL8210 NEMP Aug 23,82 Sep 02,82 44 397

DL8206 WCR Sep 22,82 Sep 27,82 33 284

DL8209 WCR Nov 17,82 Dec 20,82 161 1,559

DL8301 MARMAP Jan 17,83 Feb 10,83 103 1,039

AL8303 Other May 13,83 May 17,83 30 199

AL8304 MARMAP May 26,83 Jun 21,83 176 1,640

AL8305 NEMP Ju104,83 Jul 13,83 24 254

DL8309 MARMAP Nov 16,83 Dec 20,83 152 1,387

DL8401 MARMAP Jan 09,84 Feb 08,84 160 1,491

AL8403 MARMAP May 09,84 Jun 02,84 177 1,655

DL8409 MARMAP Nov 01,84 Dec 05,84 141 1,273

DL8501 MARMAP Jan 07,85 Feb 06,85 130 1,187

AL8504 MARMAP May 08,85 Jun 04,85 167 1,403

DL8510' MARMAP Nov 07,85 Dec 10,85 0 338

DL8601 MARMAP Jan 10,86 Feb 11,86 0 297

DL8603 MARMAP May 08,86 Jun 05,86 0 277

DL8607 MARMAP Aug 27,86 Sep 22,86 0 283

DL8610 MARMAP Nov 05,86 Dec 10,86 0 256

DL8701 MARMAP Jan 07,87 Feb 08,87 0 188

DL8704 MARMAP May 07,87 Jun 06,87 0 415

DL8708 MARMAP Aug 19,87 Sep 19,87 170 1,738

DL8710 MARMAP Nov 04,87 Dec 10,87 125 1,212

DL8801 MARMAP Jan 09,88 Jan 30,88 63 534

Program Profiles Samples

MARMAP 5,107 47,947

NEMP 770 6,424

WCR 534 5,011

Other 275 2,151

Grand total 6,686 61,533

Underway

82

54

12

338

297

277

283

256

188

415

1

67

27

Underway

2,149

o

181

o

2,330

1 Vessel Codes: AD~Advance IV, AL~Albatross IV, AR~Argus, BE~Belogorsk, DL~Delaware, EG~Evergreen, EV~Evrika, KE~Kelez,

MM~Mount Mitchel, WI~Wieczno.

2 MARMAP~Marine Resource Monitoring and Prediction.

3 NEMP~Northeast Monitoring Program.

4 WCR~Warm Core Ring Studies.
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 111

Table C2

Coordinates ofstandard MARMAP stations used in the Dirichlet tesselation to define tiles.

Region/Subarea Tile Lat. N Long. W Depth (m) Area (km2 )

MAW Chesapeake plume 12 36°57' 75°48' 13.7 966

MAE Delaware plume 29 38°45' 74°57' 19.8 649

184 38°34' 74°53' 19.3 544

MAE Hudson-Raritan plume 55 40°26' 73°50' 23.7 718

187 40°15' 73°54' 22.8 342

MAE southern nearshore 4 35°51' 75°29' 21.1 1,197

11 36°33' 75°47' 17.1 1,055

21 37°15' 75°40' 13.5 1,163

22 37°37' 75°19' 20.3 1,195

23 37°48' 75°17' 17.5 1,041

28 38°10' 74°54' 20.4 1,522

MAE central nearshore 30 38°35' 74°48' 24.7 562

41 38°55' 74°33' 20.9 1,282

42 39°14' 74°26' 17.7 934

43 39°21 ' 74°06' 25.8 1,307

52 39°34' 73°49' 24.0 1,176

53 39°43' 74°03' 15.3 565

185 39°55' 73°56' 21.6 684

54 40°07' 73°48' 29.3 620

56 40°16' 73°36' 27.2 829

67 40°28' 73°13' 31.4 1,681

68 40°44' 72°40' 26.4 836

MAE southern midshelf 1 35°16' 75°14' 31.0 1152

2 35°28' 75°15' 27.5 1,193

5 36°15' 75°32' 24.9 1,348

6 36°23' 75°15' 33.7 1,224

7 36°09' 75°06' 35.7 1,499

10 36°43' 75°22' 20.2 1,020

13 36°55' 75°33' 20.0 853

14 36°53' 75°19' 27.7 729

15 36°51 ' 75°04' 33.8 899

20 37°18' 75°09' 26.9 1,454

24 37°31 ' 74°57' 30.9 969

MAB central midshelf 27 37°48' 74°46' 38.8 1,465

31 38°25' 74°39' 32.6 868

32 38°14' 74°31' 40.5 874

33 38°04' 74°22' 48.7 1,107

39 38°25' 74°07' 53.9 1,535

40 38°40' 74°19' 42.6 1,260

44 38°57' 74°07' 41.8 1,460

45 38°45' 73°45' 55.3 1,991

50 39°12' 73°39' 42.7 2,143

51 39°39' 73°23' 34.2 1,667

186 39°52' 73°33' 34.1 971

57 40°06' 73°23' 46.6 1,188

58 39°52' 73°05' 68.4 1,618

MAE northern midshelf 66 40°19' 72°43' 50.0 2,225

69 40°34' 72°28' 44.6 1,476

74 40°49' 72°08' 37.9 1,696

75 41 °04' 71°42' 43.1 1,179

76 41 °20' 71 °21' 30.0 765

77 4P09' 71 °15' 40.2 653

78 40°58' 71°10' 50.6 1,252

79 40°41 ' 71°02' 62.3 1,651

86 40°42' 70°35' 57.5 1,521

87 4PI0' 71 °00' 33.8 966

88 41 °03' 70°33' 44.4 1,400

continued on next page
112 NOAA Technical Report NMFS 139

Table C2 (continued)

Region/Subarea Tile Lal. N Long. W Depth (m) Area (km2 )

MAB northern midshelf (continued) 89 40°41 ' 70°11' 49.6 2,348

MAB southern outer shelf 3 35°41 ' 74°58' 50.8 1,570

9 36°39' 74°52' 56.9 1,120

16 36°49' 74°50' 53.9 711

19 3T13' 74°45' 65.0 1,773

25 37°31' 74°39' 62.2 1,087

26 37°38' 74°21 ' 145.5 1,279

34 37°51' 74°11' 105.8 714

37 37°59' 73°58' 215.2 1,428

38 38°21' 73°39' 186.5 1,894

47 38°59' 73°08' 78.7 1,676

49 39° 17' 72°51 ' 77.6 1,721

59 39°39' 72°46' 70.2 1,310

60 39°28' 72°33' 106.0 982

MAB norhern outer shelf 65 39°51' 72°27' 72.8 2,119

70 40°14' 71 °57' 66.1 2,265

71 39°52' 71 °49' 145.5 2,209

72 40°04' 71 °30' 137.3 2,633

73 40°31 ' 71 °36' 70.1 2,503

80 40°21 ' 70°51 ' 96.9 1,595

81 40°10' 70°46' 133.4 1,061

85 40°13' 70°25' 114.9 2,204

90 40°24' 69°42' 70.1 2,095

91 40°08' 69°34' 91.7 1,735

Southern slope 8 36°16' 74°46' 318.0 1,380

17 36°46' 74°35' 1059.0 1,082

18 36°44' 74°20' 2055.0 1,314

35 3T41' 74°03' 1217.7 1,036

36 37°26' 73°50' 2044.9 1,675

46 38°39' 73°09' 198.5 1,773

48 38°58' 72°48' 735.1 1,535

61 39°18' 72°19' 239.3 1,071

62 39°10' 72°07' 1275.0 1,149

63 39°02' 71 °57' 2250.0 1,174

64 39°33' 72°07' 307.0 1,785

GB2 central shoals 123 41 °11' 68°08' 37.5 1,933

147 41 °30' 67°41 ' 38.1 1,211

148 41 °16' 67°41 ' 37.2 822

156 41°18' 67°33' 54.7 1,196

GB northern shoals 124 41°37' 68°06' 37.1 1,633

146 41 °48' 67°42' 35.4 1,479

160 41°59' 67°24' 35.7 1,450

GB western outer shoals 120 40°48' 68°17' 54.1 1,786

121 40°51 ' 68°44' 61.9 1,519

GB eastern outer shoals 157 41 °33' 67°01' 60.8 2,084

158 4)036' 66°31' 78.8 1,263

159 42°02' 66°50' 69.8 2,119

GB Great South Channel 92 40°37' 69°14' 62.0 996

111 41°04' 69°06' 79.9 1,093

112 40°55' 69°06' 73.1 793

113 40°39' 69°05' 72.6 710

122 41 °20' 68°42' 86.9 1,857

GB southern flank 114 40°25' 69°03' 80.5 1,275

117 40°29' 68°37' 82.2 1,419

119 40°31 ' 67°56' 126.7 1,240

149 40°56' 67°41 ' 60.5 1,559

150 40°37' 67°41' 84.9 1,022

153 40°46' 67° 19' 91.2 1,399

continued on next page
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 113

Table C2 (continued)

Region/Subarea Tile Lat. N Long. W Depth (m) Area (km~)

GB southern flank (continued) 155 41°13' 66°56' 69.3 2,161

GB northeast peak 177 41 °52' 66°20' 81.7 1,331

178 41 °30' 66°20' 88.0 1,213

179 41°10' 66°19' 152.5 1,759

191 41 °39' 65°55' 123.5 1,472

192 41°54' 65°49' 130.8 1,570

GB northern slope 82 39°59' 70°40' 311.5 1,237

83 39°48' 70°35' 1,224.3 1,361

84 39°37' 70°30' 2,261.7 1,334

115 40°05' 69°01' 275.1 1,585

116 39°52' 69°00' 1,812.9 1,666

118 40°20' 68°21' 162.3 1,643

151 40°22' 67°40' 820.0 1,415

152 40°04' 67°41' 2,116.8 1,799

154 40°40' 67°05' 267.0 1,974

180 40°53' 66°19' 1,932.8 1,069

193 40°52' 66°37' 542.3 1,619

GB antucket shoals 93 40°53' 69°34' 37.2 1,967

GOM3 western 94 41 °32' 69°26' 68.4 1,392

95 41°58' 69°50' 98.0 1,588

97 42°06' 70°20' 59.7 1,103

98 42°26' 70°38' 71.1 1,267

99 42°48' 70°32' 88.5 1,848

188 42°26' 70°09' 78.0 1,752

GaM northern 101 43°08' 69°58' 145.0 1,554

102 43°24' 70°12' 91.9 1,616

103 43°20' 69°41 ' 177.8 1,533

104 43°40' 69°22' 96.5 1,426

183 43°17' 69°20' 165.3 1,240

105 42°58' 69°17' 163.3 1,717

131 42°45' 68°46' 183.7 1,791

135 43°22' 68°41 ' 135.2 1,841

136 43°08' 69°01 ' 161.8 1,344

137 43°37' 68°56' 116.5 1,661

138 43°58' 68°35' 81.5 951

GaM Wilkinson Basin 96 42°15' 69°43' 228.8 1,846

100 42°50' 70°00' 184.0 2,119

106 42°35' 69°14' 217.6 2,231

107 42°11' 69°12' 195.3 1,463

108 41 °54' 69°]0' 207.0 1,400

109 41 °39' 69°09' 168.5 792

110 41 °20' 69°07' 151.4 1,190

125 41 °5~' 68°11' 161.2 1,789

126 41 °37' 68°53' 127.3 1,352

127 41°59' 68°39' 165.5 1,398

128 42°10' 68°48' 187.1 1,231

129 42°19' 68°27' 197.5 1,982

GaM Georges Basin 130 42°40' 68°19' 202.9 1,612

143 42°59' 67°42' 182.8 1,989

144 42°36' 67°42' 198.4 1,434

145 42°18' 67°42' 228.5 2,014

161 42°11' 67°15' 188.3 1,803

162 42°43' 67°28' 210.7 1,519

163 42°46' 66°58' 180.0 2,658

174 42°28' 66°20' 250.7 1,217

175 42°17' 66°20' 243.5 1,046

176 42°09' 66°20' 173.9 1,122

GaM Jordan Basin 132 42°55' 68°22' 163.6 1,700

continued on next page
114 NOAA Technical Report NMFS 139

Region/Subarea

GOMJordan Basin (continued)

GOM Scotian Shelf

I MAB=Middle Atlantic Bight.

2 GB=Georges Bank.

3 GOM=Gulf of Maine.

Table C2 (continued)

Tile Lat. N Long. W Depth (m) Area (km2)

133 43°12' 67°59' 200.6 1,113

134 43°23' 68°08' 206.3 1,790

142 43°49' 67°43' 220.6 1,751

167 43°42' 67°26' 208.8 1,415

182 43°24' 67°43' 251.0 1,779

139 44°01 ' 68°17' 88.3 646

140 43°58' 68°11 ' 135.8 1,452

141 44°20' 67°43' 83.4 1,804

164 43°12' 66°48' 142.3 2,027

165 43°35' 66°44' 118.0 1,673

166 43°30' 67°00' 204.1 1,612

168 44°02' 67°10' 139.9 1,957

169 44°16' 67°07' 140.8 1,449

170 44°16' 66°36' 197.1 1,570

181 44°00' 66°12' 23.0 1,093

171 43°32' 66°20' 71.4 1,490

190 43°17' 66°20' 74.6 1,241

172 43°01' 66°20' 127.6 1,210

189 42°49' 66°20' 61.5 1,020

173 42°39' 66°20' 105.2 1,006

Total Area = 272,807 km2
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 115

Table C3

Mean water column concentration of chlorophyll a and associated statistics by tile and by two-month periods.

January-February March-April May-June

Min. Max. Mean C.V.3 Min. Max. Mean C.V. Min. Max. Mean C.V.

V' pi Chi a Chi a Chi a Chi a Nel.' Pha.' V P Chi a Chi a Chi a Chi a Nel. Pha. V P Chi a Chi a Chi a Chi a Nel. Pha.

Tile # # ~gl" ~g 1.1 ~g I·' % % % # # ~gl·1 ~gl·1 ~gl" % % % # # ~g 1.1 ~g ,., ~g 1.1 % % %

MAB Chesa~ake Plume 14 m 12 6 1.53 9.37 3.75 64.7 62.4 22.3 5 10 0.28 22.60 5.85 109.4 58.5 21.8 9 0.64 19.16 3.55 156.2 34.1 22.3

MAB Delaware Plume 20 m

29 6 6 3.92 18.55 10.74 43.8 70.4 19.6 4 9 0.76 9.70 5.54 57.8 58.4 20.4 7 8 0.46 6.32 3.72 49.1 43.1 26.6

184 5 5 4.05 12.03 8.97 31.0 66.7 19.1 3 5 2.36 7.97 5.16 42.6 50.8 15.5 6 7 1.25 6.52 3.65 51.1 49.0 23.8

MAB Hudson-Raritan Plume 23 m

55 5 6 2.72 13.90 8.03 46.6 82.1 15.4 5 17 0.13 15.37 5.79 71.7 64.1 17.5 9 12 0.77 6.87 3.44 54.7 28.6 24.7

187 3 3 5.94 9.78 8.01 19.8 68.1 15.9 5 10 1.05 12.30 5.75 67.7 55.5 19.2 7 8 1.35 10.63 4.20 65.4 37.0 25.1

MAB Southern Nearshore 15-20 m

4 4 4 2.29 5.75 4.04 32.6 64.3 24.0 4 4 1.02 2.13 1.58 26.8 34.1 31.0 7 8 0.37 3.88 1.31 77.3 28.9 29.9

11 6 6 2.38 15.01 5.71 74.9 68.6 20.6 4 5 0.90 3.42 1.92 48.2 43.4 22.3 7 8 0.65 6.00 2.27 70.9 29.3 22.3

21 5 6 1.61 8.71 4.93 46.3 50.3 30.7 4 6 0.36 7.16 1.93 122.9 42.0 28.2 6 7 0.48 7.58 2.54 86.9 28.6 19.4

22 5 5 1.99 9.59 5.29 48.2 53.4 20.2 4 6 0.67 3.52 1.90 58.1 38.8 29.6 7 8 0.37 2.85 1.55 52.4 42.9 24.8

23 6 7 2.58 10.67 6.88 33.5 56.5 21.1 4 7 0.39 5.20 2.31 67.5 47.8 29.1 7 9 0.63 4.12 2.04 51.2 55.0 27.6

28 6 8 3.63 9.51 6.49 33.8 60.7 16.3 4 7 1.29 3.38 2.20 37.6 46.3 25.4 7 7 0.67 3.53 1.61 53.5 38.5 26.4

MAB Central Nearshore 15-30 m

30 5 5 2.72 8.92 5.40 38.9 64.9 19.2 5 7 0.70 9.52 3.85 79.1 61.9 23.1 6 6 0.90 4.55 2.16 53.8 52.6 23.9

41 5 5 3.20 5.88 4.25 25.3 59.8 22.0 5 7 0.65 7.37 3.40 76.8 71.6 22.7 7 7 1.45 5.02 2.53 45.3 55.7 22.9

42 4 4 4.32 7.27 5.21 23.0 65.6 28.6 5 7 0.61 10.21 3.95 87.8 68.6 26.1 7 7 0.30 2.43 1.46 46.1 19.4 30.2

43 4 5 1.61 6.00 3.90 39.8 61.0 28.4 6 11 0.33 6.06 2.84 65.4 53.2 24.4 6 6 0.78 4.50 2.05 57.2 52.0 22.9

52 5 5 1.14 4.79 3.28 40.7 60.5 19.4 5 II 0.24 7.24 2.41 88.2 59.0 20.8 6 7 0.92 3.66 1.74 53.8 50.3 24.0

53 4 4 4.94 15.29 10.36 35.5 81.7 18.3 5 7 1.26 9.72 4.18 63.4 56.0 24.0 7 7 0.96 5.79 3.27 56.7 49.7 28.3

185 3 3 3.01 11.10 7.80 44.4 66.5 13.7 5 10 1.30 9.30 4.92 54.5 58.7 20.0 8 II 0.62 4.60 1.75 60.9 38.5 31.3

54 4 4 2.28 7.29 4.19 44.7 64.4 18.5 5 8 1.27 5.48 3.08 50.1 57.4 20.4 7 7 0.75 3.56 1.76 52.5 55.1 25.7

56 4 4 2.30 .11.67 7.63 46.0 71.5 16.3 4 8 0.57 7.44 3.37 69.8 64.7 16.0 8 9 0.58 3.64 1.51 57.6 45.5 27.4

67 6 6 2.74 8.19 4.82 35.6 67.8 20.3 4 II 0.83 4.53 1.77 53.6 68.0 19.1 9 9 0.41 1.97 1.27 48.9 36.0 27.4

68 6 6 1.84 7.21 3.80 44.8 73.4 22.0 4 10 0.96 6.41 2.37 79.6 72.2 17.4 8 9 0.29 3.03 1.34 60.4 30.2 30.2

MAB Southern Midshelf 20-40 m

I 4 4 0.71 3.85 2.46 46.2 67.0 25.9 2 2 1.08 1.24 1.16 6.9 52.2 36.3 6 9 0.20 1.60 0.60 68.2 18.1 33.5

2 4 4 0.59 5.70 2.66 70.3 60.7 24.6 3 3 0.54 2.39 1.47 51.4 51.0 44.3 6 8 0.15 1.11 0.60 49.5 30.3 34.1

5 4 4 0.97 3.13 2.36 36.1 68.8 21.6 3 4 0.66 3.40 1.73 65.3 43.9 24.8 7 8 0.27 1.43 0.83 50.0 24.5 33.6

6 5 5 1.51 3.86 2.46 33.0 54.4 21.9 3 3 0.32 3.61 1.74 79.3 64.2 20.9 6 8 0.30 1.84 0.94 53.5 43.7 26.5

7 4 4 1.87 2.83 2.36 17.0 65.7 23.4 3 3 0.43 5.66 2.30 103.5 74.4 14.8 6 7 0.30 1.58 0.93 40.7 32.1 31.1

10 6 6 1.17 4.57 2.83 44.9 54.1 21.8 3 3 0.72 1.78 1.17 38.2 30.5 26.9 5 6 0.61 2.65 1.26 60.7 32.5 20.3

13 5 5 1.73 5.00 3.59 31.8 50.1 23.6 6 0.33 1.94 1.14 60.5 27.6 30.1 6 7 0.19 8.06 1.89 135.9 31.9 20.6

14 5 5 0.54 3.26 2.30 43.0 45.9 25.8 5 0.02 2.45 1.04 80.3 58.1 18.1 6 7 0.28 3.85 1.67 73.1 41.9 25.4

15 6 6 1.14 5.04 3.22 42.4 56.2 19.1 5 8 0.03 4.10 2.12 69.0 69.2 20.6 7 8 0.33 2.54 1.24 55.6 40.1 27.0

20 6 1.74 5.13 2.77 40.9 51.8 26.5 4 5 0.26 2.42 1.16 74.9 54.0 21.1 6 7 0.21 1.74 1.03 50.0 31.1 30.0

24 5 1.68 7.66 4.36 50.0 58.2 20.1 4 6 0.67 5.28 2.38 64.5 68.5 18.2 8 9 0.51 2.43 1.25 49.1 40.9 23.8

MAB Central Midshelf 30-60 m

27 6 8 1.65 6.78 3.62 47.7 55.0 18.3 5 8 0.96 5.00 2.11 67.9 71.6 19.8 7 8 0.71 3.06 1.27 58.1 53.3 22.6

31 5 5 1.80 6.55 2.93 62.2 58.1 20.6 4 6 0.44 5.10 2.47 67.4 69.1 19.3 7 8 0.39 2.36 1.27 49.0 51.0 25.7

32 5 5 1.40 7.35 2.78 82.8 62.0 23.2 4 6 0.43 7.30 3.18 79.9 78.4 13.8 7 7 0.65 1.98 1.29 36.6 57.7 25.9

33 6 6 0.78 3.94 2.03 55.1 62.7 22.5 4 7 0.67 7.37 3.47 70.6 82.1 13.0 7 8 0.45 1.80 1.21 41.0 60.6 23.4

39 5 6 0.77 2.86 1.63 48.8 47.4 24.9 5 10 0.68 7.54 3.19 74.6 78.0 16.9 8 10 0.47 2.73 1.36 56.5 65.8 23.6

40 4 4 1.52 2.47 1.95 17.5 45.8 29.1 5 8 0.80 6.16 3.09 58.7 79.5 19.3 7 7 0.60 2.27 1.40 46.1 58.0 25.2

44 5 5 1.65 4.48 2.72 36.9 49.5 24.2 5 9 0.62 7.63 2.77 80.3 75.9 17.1 8 8 0.33 3.18 1.24 70.1 61.7 25.8

45 5 5 0.51 2.59 1.46 48.8 49.4 25.2 5 10 0.85 6.49 3.28 58.3 75.1 15.2 7 10 0.44 2.00 1.18 49.0 54.3 23.4

50 3 3 2.13 2.97 2.54 13.5 24.8 26.4 6 8 0.85 6.94 2.55 73.4 74.2 15.0 8 8 0.48 2.10 1.23 52.1 54.5 25.5

51 4 4 1.26 3.01 2.21 28.3 52.6 23.0 5 6 1.14 5.13 2.77 52.8 60.8 16.3 8 8 0.67 2.43 1.39 43.1 49.6 24.8

186 4 4 2.14 3.73 3.10 20.8 56.6 23.8 4 8 0.98 6.12 2.89 57.6 70.9 17.9 6 6 0.54 2.26 1.45 43.5 55.6 22.8

57 2.19 4.17 3.32 22.5 63.2 18.4 5 8 0.52 4.51 2.15 67.6 71.7 17.3 9 11 0.46 2.96 1.34 57.9 60.1 23.5

58 5 5 0.83 2.21 1.52 36.7 56.2 24.4 5 10 0.72 6.22 2.89 57.3 76.7 15.5 8 11 0.62 1.32 0.96 21.2 51.7 28.9

MAB Nonhern Midshelf 30-60 m

66 4 4 0.82 4.13 2.35 50.5 62.9 23.7 4 6 0.77 3.71 2.52 35.3 77.7 15.4 8 9 0.44 2.33 1.32 47.0 50.4 19.5

69 4 4 2.25 3.37 2.96 15.2 71.7 18.4 3 7 0.56 2.99 1.53 50.2 73.8 21.2 9 10 0.45 2.68 1.05 64.9 51.9 26.6

74 5 5 2.12 4.58 3.35 23.4 70.9 20.4 4 7 0.48 3.89 1.89 52.7 73.7 22.2 8 8 0.18 2.94 1.18 64.4 37.9 30.6

75 3 3 3.99 4.89 4.40 8.5 75.2 25.8 5 8 1.22 5.57 3.13 51.6 78.6 21.2 8 8 0.43 3.12 1.42 64.0 36.8 30.0

76 3 3 1.25 2.72 2.15 29.9 73.8 18.6 5 11 0.67 8.04 3.60 69.0 70.2 20.3 8 8 0.44 2.58 1.09 61.6 25.6 29.7

77 2 2 3.24 3.65 3.44 6.0 85.9 14.2 5 8 1.49 3.99 2.95 28.0 82.2 21.6 8 8 0.27 3.54 1.17 79.7 42.3 29.5

78 2 2 2.12 3.21 2.67 20.5 71.7 23.1 5 8 0.20 5.43 2.27 67.5 63.4 22.3 8 8 0.31 1.64 0.79 49.8 38.2 35.7

79 3 3 0.85 4.12 2.03 73.2 74.0 23.1 5 9 0.33 8.88 2.45 100.7 77.0 19.7 8 9 0.24 0.87 0.62 32.1 19.3 38.1

86 3 4 0.67 4.45 2.40 62.4 73.8 23.3 5 7 0.82 5.22 2.84 55.3 81.5 18.6 8 8 0.19 3.37 1.19 83.3 46.7 30.4

87 3 4 2.86 5.55 4.19 29.8 79.6 21.8 5 9 0.42 4.58 2.38 61.5 75.8 23.5 7 7 0.55 1.92 1.03 44.6 23.6 29.5

88 4 5 1.74 5.47 3.60 36.7 69.3 26.4 5 6 0.99 12.04 5.09 75.4 85.6 18.2 8 8 0.20 4.53 1.10 120.7 42.8 27.7

89 5 6 0.83 3.72 1.76 53.9 63.1 26.9 5 14 1.21 8.41 3.40 62.5 72.4 24.8 7 7 0.44 4.48 1.73 71.1 53.2 27.0

MAB Southern Outer Shelf 60-200 m

3 4 5 1.00 2.52 1.74 27.7 71.0 24.3 3 3 0.47 4.51 2.02 87.8 73.0 22.6 6 7 0.21 0.98 0.48 59.3 33.8 41.4

9 7 7 0.55 4.72 1.87 71.8 55.0 23.7 4 5 0.52 5.83 2.15 90.4 72.3 19.8 7 9 0.11 2.22 1.17 52.8 35.6 26.9

16 5 5 0.51 4.22 2.00 65.0 59.0 24.0 3 4 0.08 4.62 1.75 98.7 31.5 16.3 6 8 0.30 2.22 0.86 68.1 45.2 28.8

19 5 6 0.47 2.13 1.07 48.7 41.4 31.4 4 6 0.21 4.57 1.82 84.3 69.7 17.2 6 7 0.41 1.85 0.98 44.5 50.4 28.9

25 4 4 0.71 1.74 1.04 40.1 46.0 32.4 4 4 0.62 6.77 3.57 70.4 80.0 16.0 7 10 0.35 2.42 1.01 68.2 58.0 25.8

26 4 4 0.49 1.30 0.73 45.8 34.7 36.0 4 6 0.63 4.55 1.62 84.9 75.8 19.8 8 12 0.31 1.82 0.86 56.1 44.4 25.2

34 5 5 0.27 1.40 0.73 63.0 29.4 32.9 5 6 0.81 4.27 2.17 60.4 73.1 22.5 6 9 0.14 2.24 0.86 68.6 46.4 25.3

37 5 5 0.36 0.94 0.58 34.2 14.1 39.5 4 6 0.81 3.45 1.80 57.1 66.3 21.4 8 10 0.15 1.59 0.70 55.1 32.1 29.3

38 4 4 0.29 0.86 0.54 38.0 12.4 39.2 5 8 0.79 2.88 1.90 34.8 74.2 20.8 8 14 0.25 0.90 0.50 41.7 14.5 34.9

47 4 4 0.39 5.98 2.12 106.7 28.2 41.9 5 6 0.28 5.03 2.59 69.2 83.2 17.8 7 7 0.33 2.54 0.95 73.4 33.2 31.6

49 5 5 0.47 2.81 1.31 66.2 55.3 23.8 6 9 0.61 5.22 2.17 77.1 71.1 15.6 8 9 0.24 1.24 0.78 38.9 38.0 33.4

59 5 6 0.84 2.39 1.52 38.0 56.0 25.1 9 0.69 6.70 2.82 71.1 71.6 14.3 9 10 0.23 1.53 0.85 45.9 41.1 30.8

60 4 4 0.58 0.83 0.71 13.6 28.3 34.1 6 0.59 3.76 1.89 58.6 69.4 17.1 8 9 0.36 1.15 0.68 36.8 16.6 32.0

continued on next page
116 NOAA Technical Report NMFS 139

Julv-Augusl

Table C3 (continued)

September-OClober November-December

Tile

\"' p2

# #

\1in. Max.

Chi a Chi a ~g 1.1 ~g 1.1

~e.n c.\'.' Chi a Chi a 'el.' Ph•.'

~gl" % % %

y

#

Min. Max.

P Chi a Chi a # ~g 1.1 ~g 1.1

\Ie.n C.\'.

Chi a Chi a Xel. Ph•.

~gl" '1, % %

Min.

Y P Chi a # ~g 1.1

Max.

Chi a

~gl"

\1e.n S.\'.

Chi a Chi a ~el. ?h•.

~gl·1 % % %

5 .:>

6 8

5 1.91

5 .:>

:> 5

7 11

7 10

MAB Chesapeake Plume 14 m

12 6 8 1.38 6.99 3042 49.2 46.0 23.6

MAB Delaware Plume 20 m

29 6 0.~2 4.94 2.93 ~O. 7 40.4 29.2

184 4 6 0.83 6.69 2.42 81.2 32.6 27.3

MAB Hudson-Raritan Plume 23 m

~~ 4 8 1.20 16.12 ~.39 87.1 42.~ 2~.7

I 7 10 1.3~ ~A3 3.13 42.~ 47.8 27.4

~IAB Southern Nearshore 1~-20 III

4 4 4 1.10 2.21 1.64 32.7 47.9 24.1

II 6 7 0.40 4.08 2.02 66.8 41.8 30.4

21 1.03 3.~3 2.38 40.~ 42.3 29.2

22 4 4 0.74 4.61 2.~4 ~8.3 7~.6 18.6

23 7 8 0.93 6.69 2.61 67.9 ~1.9 24.1

28 7 0.~3 3.29 1.40 ~9.6 4~.9 21.8

~IAB Central \'earshore 1~-30 m

30 4 6 0.77 3.78 1.79 ~9.0 ~9.4 21.5

41 4 8 0.40 4.71 2.26 62.8 64.~ 20.7

42 7 0.97 ~.23 2.67 61.2 49.0 21.9

43 8 0.41 2.72 1.61 ~2.8 ~0.4 24.~

~2 6 10 0.44 4.~9 1.64 73.3 48.~ 28.1

~3 6 2.73 ~.~3 3.9~ 26.~ ~9.8 23.6

18~ 4 8 0.72 9.99 2.~2 114.6 63.0 20.8

~4 3 4 0.67 2.00 1.33 37.8 ~2.~ 23.6

~6 8 0.6~ 4.81 2.07 66.9 ~0.7 28.6

67 10 0.~4 2042 1.3~ 43.~ 36.6 2~.9

68 6 10 0.48 2.82 1.62 49.1 28.6 29.2

~I.-\B Soulhern ~1idshelf20-40 m

I 4 4 0.20 1.17 0.66 ~7.0 33.3 34.7

2 4 4 0.:>8 1.2~ 0.91 3~A 47.8 30.1

6 0.27 2.38 1.10 62.4 ~2. 7 27.1

6 4 O.~I 1.19 0.91 29.8 ~4.1 26.7

7 3 3 0.3~ 0.87 0.69 34.9 45.4 26.6

10 4 4 0.30 2.67 1.06 89.~ 46.3 24.3

13 4 0.51 2.~3 1.20 61.1 61.~ 24.~

14 4 4 O.~I 2048 1.17 67.3 67.2 32.1

1~ 6 7 0.22 1.42 0.88 47.~ 38.8 28.~

20 4 0.30 1.71 0.9~ 48.9 ~3.9 24.~

24 4 4 0.39 1.38 1.03 36.8 42.3 26.~

MAB Central ~lidshelf 30-60 m

27 6 7 0.81 3.9~ 1.66 60.2 ~~.3 23.2

31 4 0.87 2.~9 1.7~ 3~A 48.0 21.1

32 6 0.63 5.~4 1.86 91.9 2~.2 23.~

33 6 8 0.61 1.94 1.21 36.9 43.1 24.9

39 5 7 0.7~ 1.~3 1.02 28.9 ~~.7 24.9

40 4 0.28 1.66 1.09 41.8 46.3 26.8

44 6 9 0.~7 1.99 1.29 32.8 ~2.8 24.1

4~ 7 0.34 2.33 1.03 63.2 39.~ 2~3

~O 4 6 0.6.5 2.48 1.41 40.9 ~6.2 27.3

51 4 6 0.~1 1.71 1.04 41.2 49.0 28.8

186 3 0.75 1.9~ 1.2~ 34.5 47.9 26.0

~7 7 0.64 1.27 0.98 2~.8 49.6 27.4

~8 4 6 0.4~ 1. 71 0.93 50. 7 ~8.0 23.1

~IAB :\onhern ~Iidshelf 30-60 m

66 4 6 0.41 1.12 0.78 28.7 45.4 37.0

69 7 0.4~ 0.96 0.73 23.2 29.9 31.9

74 4 6 0.~3 2.87 1.32 62.7 ~4.5 28.2

7~ 9 0.62 3.1 1.70 43.0 39.2 29.~

76 4 7 0.76 4.19 1.8~ 62.7 2~.2 31.0

77 3 0.49 1.19 0.8~ 33.3 36.2 33.7

78 3 o.~~ 1.30 0.7~ 38.2 33.9 33.0

79 4 4 0.41 1.23 0.84 43.7 40.6 28.9

86 3 :> 0.09 1.06 O.~ 7 6004 5404 31.2

87 5 6 0.64 1.90 1.11 3904 27.0 31.5

88 4 0.52 1.59 0.95 40.0 39.3 29.1

9 6 14 0.37 3.74 1.10 i7.4 20.1 33.3

~IAB Soulhern OUler Shelf 60-200 III

3 4 5 0.31 1.09 0.61 44.4 40.0 37.1

9 6 7 0.20 1.18 0.71 45.5 34.3 33.1

16 4 4 0.22 0.87 0.58 40.9 28.8 32.1

19 6 0.51 1.01 0.76 25.9 34.1 31.4

25 3 0.72 1.32 0.93 30.0 48.9 25.1

26 6 7 0.34 1.06 0.65 41.0 20.2 31.5

34 4 5 0.29 O. 78 0.~3 33.9 35.9 32.9

37 4 6 0.17 1.10 0.59 62.7 23.2 3104

38 4 0.27 0.64 0042 3~.6 13.~ 33.5

47 8 0.27 0.86 0.57 31.~ 26.~ 35.9

49 7 11 0.37 1.09 0.64 27.9 16.4 3~,4

~9 6 11 0.3~ 1.26 0.74 34.9 39.6 30.3

60 4 5 0.33 0.7~ 0.~4 2~.6 10.7 34.1

1.33 12.40

6 2.83 8.89

4 6 0.49 6.81

14 0.5~ 18.61

4 :> 0.98 12.33

3 3 0.64 1.57

4 6 0.5~ 6.92

4 0.28 6.30

2 2 0.80 4.92

4 6 0.68 6.30

3 0.37 5.12

6 1.7~ 4.88

7 1.04 8.64

5 1.26 10.74

6 0.17 3.95

4 7 0.60 4040

4 4 0.89 ~.O~

4 6 0.61 ~.97

4 4 0.81 3.34

4 9 0.31 3.2~

6 8 0.37 2.00

6 7 0.~8 2.92

3 3 0.70 1.17

3 3 0.83 1.43

3 4 0.17 1.54

3 3 0.60 2.27

3 3 0.62 1.99

3 3 0.99 2.12

2 2 1.14 1.83

3 3 1.13 2.13

3 0046 2.92

3 3 0.74 2.31

3 3 0.~3 l.i~

4 6 0.23 1.29

3 3 0.96 1.10

4 0.47 1.82

3 4 0.63 2.3~

5 9 0.44 2.93

4 4 1.0~ ~.37

3 6 0.42 2.98

8 0.27 2.29

4 4 0.7~ 4.03

4 4 0.75 2.50

3 1.00 1.42

7 0.32 1.61

10 0.30 0.96

4 6 0.33 2.31

4 6 0.16 3.10

4 4 0.48 2.61

6 0.42 3.1~

5 7 0.62 2.86

3 4 0.67 1.80

4 4 0.~3 0.90

6 12 0049 :1.48

6 8 0.72 1.12

4 4 0.46 1.84

4 8 0.39 2.24

6 I 1 0.50 3.~3

3 3 0.26 0.63

4 6 0.~2 1.1 7

4 4 0.30 1.98

3 4 0.46 0.78

6 O~O 2.67

3 3 0.14 1.43

2 3 0042 0.66

3 3 0.46 1.60

4 5 0.31 1.11

4 4 0.~9 1.38

5 8 0.2~ 0.83

4 8 0.29 1.~2

4 0.30 0.84

4.74 84.3 21.~ 32.4

~.36 46.2 45.4 3~.3

3.97 5~.7 26.9 29.7

~.36 102.9 47.6 22.3

~.24 833 49.1 22.1

1.03 38.~ 39.3 39.1

2.16 100.2 22.8 35.2

3.36 76.6 1.8 26.3

2.86 720 64.0 30.2

2.46 84.3 41.8 3~.4

2.33 69.~ 3~.4 27.4

2.88 3~.0 42.4 25.8

2.96 88.4 47.4 26.7

3.~2 103.0 49.7 28.6

2.09 61.6 60.4 27.9

2.11 73.1 ~O.~ 24.6

2.70 ~~.4 38.2 3~.7

2049 86.0 47.8 2~.~

1.87 ~4.6 ~O. 7 31.2

1.34 63.6 40.2 34.7

1.44 39.9 ~2.1 32.6

2.01 39.8 36.8 31.4

0.98 20.6 29.4 47.4

1.1 21.6 22.3 43.0

0.70 81.0 27.9 37.~

1.3~ ~1.3 44,4 3~.1

1.4 I 41.1 ~~.9 34.2

1.45 3304 43.9 32.2

1.49 23.2 ~I.~ 33.9

U9 2~. 41.0 34.3

1.1 79.1 46.9 30.3

U9 10.8 33.6 3~.1

1.2~ 41.7 2~.~ 43.6

0.78 ~0.9 27.0 366

1.0 I 61 38.8 36.8

1.03 H.~ 46.2 32.6

1.32 50.~ ~7.2 21.4

1.06 66.6 7.0 28.8

2040 72.0 64.6 23.3

1.42 73.1 62.9 21.5

0.94 67.3 49.4 29.3

2.14 ~~.6 ~6.3 28.2

1.60 42.9 ~0.7 29.8

1.14 13.2 49.7 30.0

1.08 4~.6 41.6 3~.4

0.54 34.6 39.8 39.3

0.94 71.8 ~7.9 30.~

1.27 72.7 ~8.8 33.8

1.16 74.9 24.4 ~0.3

1.50 61.0 4~.2 31.7

1.41 ~6.3 21.4 34.4

1.1 42.3 39.4 3~.8

072 18.6 30.~ 36.7

1.02 77.3 38.7 31.9

0.96 14.2 28.6 33.4

1.10 44.~ 29.5 39.2

1.23 44.7 32.0 30.8

1.38 61.~ 43,4 31.0

0.51 3404 21.7 48.6

0.84 27.0 36.7 32.7

0.84 1.0 37.~ 3~.9

O.~9 23.3 43.9 37.1

0.97 78.8 31.9 29.7

0.77 68.~ 43.7 36.4

0.50 22.0 23.8 34.1

0.90 5~.6 38.2 2~.0

0.64 46.8 4~.~ 3~.9

0.87 3~.3 39.2 36.1

0048 36.3 31.2 36.9

O. 76 ~6.4 29.4 33.3

0047 44.2 131 41.9

6 8 0.93

6 8 1.90

6 12 2.00

6 8 2.69

5 0.80

5 6 1.36

6 2.29

4 4 0.15

6 7 1.26

6 7 1.84

2.2~

1.86

5 2046

6 8 2.13

6 7 2.64

4 4 2.23

6 8 2.12

2.2~

2.13

1.27

1.26

3 3 0.68

3 3 0.82

4 0.92

4 6 1.26

5 0.97

4 4 1.03

4 4 1.~0

4 4 1.35

5 7 0.92

4 4 1.36

1.17

6 0.~8

1.93

5 1.16

0.78

6 7 0.36

5 5 1.40

7 8 0.85

6 7 0.78

6 6 1.18

5 1.66

6 1.88

6 7 0.75

0.64

7 7 0.60

7 II 0.~4

7 7 1.00

8 0.73

8 II 1.00

9 9 0.92

9 9 0.6~

9 9 0,4:>

8 8 0.51

8 9 1.29

7 8 1.29

9 13 0.74

0.33

6 0.3~

4 4 0.88

4 4 0.90

0.70

0.34

5 5 0.47

0.26

0.22

6 O.~I

6 7 0.42

6 0.52

0.65

8.37

6.29

7.12

~.13

6.32

7.81

7.26

9.37

4.88

7.40

4.61

~.22

6.81

3.62

~.I~

4.46

~.92

6.~~

4.84

3.98

5.23

10.93

2.96

4.~7

2.92

3.12

3.63

2.65

4.29

2.14

2.97

2.72

3.17

2.84

2.69

2.61

2.56

2.81

3.38

3.59

2.78

2.37

3.28

3.86

2.06

2.38

2.49

2.9~

3.09

3.96

4.10

3.4~

3.80

3.24

1.92

6.42

2.88

2.72

1.46

1.86

1.79

1.63

2.90

1.81

1.91

1.61

1.24

1.34

1.70

1.86

1.86

4.78 40.8 44.7 27.3

3.~2 46.4 ~8.2 33.2

4.84 29.8 49.6 23.2

3.~7 32.7 50.6 23.9

4.38 28. I 42.8 21.8

3.82 67.1 60.0 22.2

4.61 39.~ ~3.1 2~.8

4.87 49.1 40.4 24.5

2.~7 6~.1 41.3 34.4

4.12 60.5 ~0.8 26.7

3.22 30.3 39.4 30.9

3.93 24.8 ~1.4 23.4

3.63 39.9 ~8.8 23.4

3.07 13.7 37.9 31.3

3.62 28.7 33.9 24.8

3.39 18.7 43.9 26.6

4.77 31.0 49.6 28.~

4.28 36.1 38.0 22.7

3.73 2~.6 22.4 22.9

2.99 20.2 23.6 27.4

2.98 43.3 4~.~ 29.~

4.4~ 73.0 ~4.0 30.3

1.70 ~~.~ 3~.4 3~.1

2.10 82.9 42.2 25.0

2.18 33.6 39.7 32.~

2.16 3~.~ 34.6 26.8

1.96 46.2 ~2.4 28.5

1.84 35.0 38.7 28.2

2. 7~ 40.9 40.7 23.4

1.60 19.8 26.9 27.3

1.92 34.0 34.9 27.0

1.96 28.9 32.3 28.5

1.92 37.9 26.0 29.1

1.67 48.7 38.1 28.0

2.35 11.9 4U 25.9

1.84 26.1 43.6 29.5

1.29 50.1 47.9 29.4

1.49 ~2.2 42.8 28.7

2.33 3~.0 47.9 2~.4

2.16 42.9 43.0 26.8

1.68 41.2 39.0 27.9

1.79 2~.1 30.3 30.1

2.43 26.9 18.9 29.2

2.76 31.2 41.5 2~.0

1.53 30.~ 31.~ 27.8

1.44 46.9 33.8 28.0

I. 76 37.~ 50.2 24.8

1.73 44.7 46.4 29.7 1.6~ 37.5 46.7 30.3

1.73 ~8.9 60.0 34.2

2.54 40.9 ~9.4 23.3

2.41 37.3 68.9 21.8

2.24 49.7 66.8 23.0

1.~9 ~6.1 6~.1 25.4

1.27 32.6 ~3.9 26.6

3.2~ 46.6 67.4 21.9

2.05 29.9 64.2 22.0

1.~9 30.9 ~6.0 29.6

0.85 4~.2 28.4 3~.2

1.06 45.2 24.1 31.6

1.19 29.8 31.7 31.6

1.1 24.8 24.8 33.6

1.47 53.5 42.9 30.0

0.92 56.4 40.2 30.9

1.08 48.0 42.4 29.9

0.82 ~7.9 41.9 31.8

0.72 48.2 23.6 31.4

0.90 39.2 33.2 32.4

1.13 44.5 44.8 30.7

1.18 43.3 42.8 2~.8

1.0~ 44.1 42.8 26.~

continued on next page
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 117

Table C3 (continued)

January-february ~1arch-April .~Iay-June

Tile

Vi p2

# #

Min. Max.

Chi a Chi a

~gl'l ~g 1.1

Mean C.V'

Chi a Chi a Net.' Pha'

~gl·1 % % %

V

#

Min. \1.x,

P Chi a Chi a

# ~g 1.1 ~g i·1

Mean c.V

Chi a Chi a

~gi'l % ·el. Pha.

% %

Min.

V P Chi a

# # ~g 1.1

\Iax.

Chi a

~g 1'1

Me.n c.v.

Chi a Chi a Nel. Pha.

~gl·1 % % %

1.53 37.0 67.6 32.6

1.72 6.9 54.0 35.1

2.44 27.5 73.6 38.5

2.70 67.0 59.6 27.1

3.15 50.8 54.9 21.2

3.06 23.9 63.8 18.4

2.40 60.9 52.0 26.4

2.48 52.0 58.7 26.6

1.99 39.7 63.9 29.4

2.41 58.4 60.2 21.8

2.91 44.6 64.7 19.6

1.04 67.1 30.3 32.4

0.74 35.2 18.9 33.9

0.65 29.6 13.1 35.0

0.69 54.5 8.6 35.9

0.53 45.2 22.0 43.1

0.80 36.2 6.9 37.1

0.71 30.4 5.5 38.4

0.76 45.0 4.7 36.7

0.96 35.4 26.2 34.7

0.86 54.8 6.8 32.8

0.66 48.5 39.5 31.9

0.59 54.2 28.4 32.0

0.21 14.3 51.2

0.60 41.0 23.6 29.6

0.50 20.1 5.6 38.1

0.67 51.8 22.6 28.7

0.34 8.8 44.3

0.49 42.3 17.3 34.5

0.44 44.8 4.6 46.6

0.39 22.1 3.9 43.8

0.49 44.9 17.6 37.4

2.46 71.8 54.6 27.9

2.88 44.3 60.2 25.2

2.33 69.6 54.8 27.2

1.96 68.2 44.6 24.6

2.52 63.5 62.2 21.5

1.50 39.5 58.0 28.2

1.20 61.4 50.9 26.4

1.13 34.5 36.5

2.05 119.0 50.3 26.7

0.96 42.9 18.4 37.3

0.88 37.1 10.4 35.8

0.71 64.1 19,4 33.6

1.54 144.7 30.3 32.1

0.80 50.5 20.7 32.7

1.12 37.4 7.7 33.3

1.29 63.9 43.4 3!.i

1.40 38.0 64.6 30.0

0.97 66.1 40.0 32.1

0.97 52.9 21.5 30.6

0.94 41.8 20.6 36.8

1.07 15.0 17.3 35.2

0.60 35.8 5.6 40.0

0.55 7.3 45.5

1.31 51.8 12.9 29.9

0.91 56.4 3.2 33.2

1.08 99.9 5.4 29.9

O. ii 60.0 10.8 35.2

0.40 2.5 49.4

0.76 54.9 9.7 33.9

0.83 42.5 16.1 34.7

0.70 45.8 21.5 43.4

0.90 61.0 22.6 36.2

1.02 67.0 14.8 37.4

0.83 79.8 9.0 39.5

0.53 52.5 7.6 38.6

continued on next page

2.98

4.95

5.18

4.90

4.81

4.87

5.69

2.52

2.74

2.55

1.07

0.94

1.41

0.94

1.28

1.04

1.38

1.70

1.85

1.37

1.23

0.21

1.06

0.66

1.40

0.34

0.72

0.63

0.47

1.00

6.41

4.86

5.68

7.23

5.90

3.87

2.08

2.38

1.81

1.34

1.23

0.86

0.55

1.98

!.i0

4.13

J.i5

0.40

1.64

1.13

8.17

1.22

1.48

1.94

2.18

2.11

1.15

1.50

1.44

1.78

16.60

1.81

1.81

3.11

9 9 0.37

6 6 0.25

9 11 0.27

8 12 0,19

8 8 0.17

8 8 0.37

7 7 0.40

8 9 0.34

8 8 0.60

8 8 0.32

6 7 0,34

6 7 0,14

1 1 0,21

8 11 0.16

2 6 0.33

7 7 0.25

1 1 0.34

7 8 0.18

1 2 0.24

1 2 0.30

8 11 0.16

8 13 0.58

8 9 0.73

8 20 0.34

8 9 0.45

8 9 1.01

7 7 1.98

8 9 0.33

8 10 0.37

7 0.68

5 5 0.67

7 9 0.79

7 9 0.50

7 9 0.52

8 9 0.41

8 9 0.23

8 10 0.47

8 9 0.35

8 9 0.16

8 59 0.15

8 10 0,43

6 17 0,53

7 8 0,20

6 6 0.68

6 6 0.52

6 6 0.38

2 2 0.55

2 2 0.91

8 8 0.15 I 1 0.55

2 3 0.38

7 8 0.34

8 10 0.25

8 9 0.35

1 1 0.40

8 10 0.26

1.13

8 8 0.49

8 8 0.18

8 8 0.39

6 7 0.25

6 8 0.18

5 5 0.34

5 7 0.20

6.41 60.9 71.6 21.5

6.27 49.3 72.0 17.6

6.62 43.8 68.5 21.4

4.06 36.0 71.5 24.2

3.35 82.2 59.2 20.4

6.62 50.9 79.4 14.6

1.43 38.4 52.3 19.6

1.57 113.6 71.2 18.7

1.17 82.2 62.2 21.,5

1.23 55.7 63.5 21.7

1.30 82.1 59.3 18.3

1.99 75.5 65.1 16.7

0.92 33.2 34.1 30.4

1.05 49.6 59.3 29.5

1.41 59.5 64.1 28.8

0.69 46.1 44.3 33.8

0.96 21.1 43.9 31.0

1.43 91.4 51.3 25.1

0.62 43.5 26.6 36.7

1.07 14.3 52.2 26.7

1.08 66,7 23.9

1.69 67.2 56.4 23.5

1.25 56.2 62.8 21.8

1.62 85.4 57.1 23.2

1.00 35.0 32.9

1.06 45,3 29.8

2.18 50.7 68.1 20.1

5.63 44.2 78.2 20.7

1.89 63.9 83.0 16.4

2.94 75.1 65.0 14.3

42.7 34.4

1.65 46.9 77.9 24.3

2.27 61.2 78.2 20.9

2.67 57.3 79.9 22.0

1.58 80.2 64.5 22.2

2.09 90.3 75.7 30.1

3.16 57.3 59.8 22.0

2.02 128.6 55.1 24.6

0.97 49.5 54,9 33,0

0,67 43.2 27,8 32,9

1.57 55.0 60.7 30,0

0.83 62.7 45.4 29.6

0.69 44.7 43.0 26.6

1.98 43.1 7!.i 28.0

2.07 59.1 79.1 17.2

1.24 70.9 59.5 17.9

0.84 50.1 40.3 23.7

1.15 66.1 24.3

3.70 84.9 8.6

0.74 58.6 35.2 28.2

0.51 78.8 14.7 39.3

0.36 11.1 46.3

0.83 39.6 23.8 30.2

0.24 8.3 52.0

0.54 58.6 25.8 35.6

0.74 38.6 20.9 30.3

0.58 40.4 30.9 32.6

0.68 8.8 10.3 33.3

0.76 6.6 39.7

5.67 82.6 80.6 17.6

2.58 65.5 65.2 22.7

1.22 37.0 68.1 25.2

1.63 41.4 65.1 23.1

2.09 87.6 24.9 22.9

0.57 16.5 36.5 32.7

2.39 83.7 22.1

6 1.22 15.13

I 0.82 0.82 0.82

5 7 0.23 2.66

5 7 0.26 4.40

5 7 0.40 4.91

3 5 0.39 3.92

4 5 0.72 2.~4

4 5 0.53 5.13

4 6 0.29 2.87

4 5 0.30 2.17

5 7 0.43 3.38

5 10 0.49 4.82

5 8 0.47 1.44

5 11 0.39 2.00

5 8 0.28 2.91

5 6 0.38 1.30

3 0.79 1.24

4 5 0.39 3,97

2 2 0.35 0.89

4 4 0.89 1.29

1 1 1.08 1.08

5 9 0.22 4.05

3 3 0.51 2.20

4 7 0.46 4.59

1 1 1.00 1.00

1 1 1.06 1.06

4 5 0.46 3.41

2 4 0.49 5.20

4 8 0.79 6.43

4 6 2.07 9.14

2 2 0.68 3.09

4 5 1.04 7.03

4 5 3.11 6.95

3 5 1.24 8.29

3 3 2.57 10.82

4 6 0.94 11.91

3 5 2.87 11.54

3 5 3.27 11.00

5 7 0.23 5.43

5 6 0.81 2.08

4 4 1.08 2.79

3 3 0.70 4.67

2 2 0.48 0.67

I 1 2.39 2.39

6 8 0.48 8.74

5 6 0.44 1.75

4 8 0.40 1.36

4 8 0.35 3.06

3 6 0.37 1.93

2 3 0.34 1.09

4 6 0.96 3.49

3 3 0.51 3.50

2 2 0.36 2.11

3 4 0.42 1.48

1 I 1.15 1.15

1 1 3.70 3.70

4 10 0.24 1.82

3 4 0.16 1.18

1 I 0.36 0.36

3 6 0.41 1.33

1 1 0.24 0.24

3 6 0.15 1.19

3 7 0.34 1.03

4 0.31 1.05

1 0.62 0.74

1 0.76 0.76

32.0

34.9

41.6

39,8

46.8

42.2

52.8

39.2

50.6

52.2

37.0

28.5

35.7

31.2

26.7

34.4

27.4

28.9

34.1

33.2

36.1

35.3

35.3

29.4

17.3

19.7

15.2

24.5

20.1

7.1 40.8

30,0

18.5

46,2

10,9

44.1

20.4

8.0

14.8

10.3

12,5

8.7

38.8

35.3

19.4

4.6

3.0

56.0

30.7

32.7

68.1

19.2

25.3

59.6

38.6

75.7

76.9

67.7

57.6

68.4

44.8

79.3

45.3

41.7

31.8

38.8

3.5 36.4 50.2

87.3 67.9 23.7

25.4 28.7 36.8

22,3

23.5

21.6

78.0

43.6

43.4

55.0

38.3

37.5

19.8

37.7

i1.8

44.4

74.5

35.1

66.3

0.66

0.49

0,52

0,53

0.59

0.47

0,25

0.57

0.39

0.32

0,55

0.71

0.60

0.48

0.44

0.66

C.98

0.68

0,75

1.64

0.59

0.58

1.01

0.55

1.58

2.69

1.90

0.86

1.27

MAR Northern Outer Shelf 60-200 m

65 4 4 0.51 2.20 1.41 42.9 61.6 22.1

70 3 3 1.68 2.28 2.03 12.6 68.9 21.3

71 3 3 0.35 0.70 0.57 27.4 17.0 38.7

72 3 3 0.40 0.80 0.56 30.9 32.7 29.1

73 4 4 0.81 3.70 1.81 62.0 63.8 23.9

80 3 3 0.28 2.74 1.33 78.2 75.6 20.4

81 3 3 0.31 0.84 0.61 36.4 44.6 27.3

85 3 4 0.58 2.79 1.30 66.6 61.3 27.3

90 4 4 0.33 1.33 0.84 45.0 55.8 23.0

91 4 5 0.29 1.76 0.85 58.3 49.8 29.8 Southern Slope 200-2,000 m

8 4 4 0.31 1.04

17 5 5 0.02 1.19

18 1 1 0,52 0.52

35 4 4 0,29 0.77

36 1 1 0.59 0.59

46 4 4 0.21 0.71

48 1 1 0.25 0.25

61 4 4 0.44 0.89

62 1 1 0.39 0,39

63 1 1 0,32 0,32

64 4 4 0,25 0,93

GB Central Shoals 35-55 m

123 3 3 0,74 2,03

147 3 3 1.55 1.81

148 3 3 1.59 3,23

156

GB Northern Shoals 30-40 m

124 3 3 1.24 1.37 1.30 4,2 55.8 36.9

146 3 3 0.48 1.35 0.85 43.2 39.2 38.8

160 3 3 0.64 1.03 0.81 19.9 28.7 38.1 GB Western Outer Shoals 50-60 m

120 3 3 0.53 1.33 1.03 34.5 49.7 36.1

121 3 3 0.90 !.i0 1.27 26.1 62.9 33.2 GB Eastern Outer Shoals 60-80 m

157 2 2 0.69 0.74 0.71

158 4 4 0.57 3.62 1.45

159 4 4 0.51 0.95 0.67 GB Great South Channel 60-100 111

92 1 1 0.33 0.33 0.33 15.2 47.6 I

III 3 3 0.23 0,46 0.37 27.3 25.0 38.1

112 3 3 0.37 0.82 0.60 30.8 36.9 42.4

113 3 3 0.63 1.52 1.19 33.5 53.6 32.3

122 3 3 0.24 0.77 0.53 41.3 28.8 34.4 GB Southern Flank 60-200 m

114 4 4 0.63 1.21

117 3 3 0.57 0.91

119 4 4 0.59 1.02

149 4 5 0.35 4.10

150 3 3 0,24 0,85

153 4 4 0.27 0.94

155 5 6 0.45 1.88 GB Northeast Peak 80-200 111

177 4 4 0.44 1.17

178 4 4 0.42 0.99

179 4 4 0.37 0.63

191 I I 0.44 0.44

192 1 J 0.66 0.66 Northern Slope 200-2,000 m

82 3 3 0.28 1.01 0.68 44.5 41.9 25.4

83

84

115 2 2 0.38 0.72 0.55 30.9 37.3 28.6

116

118 3 3 0.28 0.47 0.40 21.0 19.3 31.2

151 2 2 0.52 0.53 0.53 1.0 6.7 36.4

152

154 5 5 0.32 0.78 0.50 31.6 12.9 34.4

180

193 1 1 0.42 0.42 0.42 GB 1\antucket Shoals 37 m

93 4 4 0.96 6.32 2.90 70.9 78.3 20.8 GOM Western 60-100 m

94 5 6 0.29 0.92

95 5 6 0.45 3.26

97 6 7 0.85 4.23

98 5 6 0.50 4.03

99 5 6 0.51 1.42

J88 6 6 0.38 2.86
118 NOAA Technical Report NMFS 139

Table C3 (continued)

July-August September-October November-December

Tile

Vi P'

# #

Min. Max.

Chi a Chi a ~g ,., ~g ,.1

Mean C.V.'

Chi a Chi a Net.' Pha.' ~gl·1 % % %

V

#

Min. Max.

P Chi a Chi a # ~g 1.1 ~g 1.1

Mean C.V.

Chi a Chi a Net. Pha. ~gl·1 % % %

Min.

V P Chi a

# # ~g 1.1

Max.

Chi a

~gl·1

Mean C.V.

Chi a Chi a Net. Pha.

~gl·' % % %

1.39 22.2 45.2 29.4

1.84 48.8 36.6 28.1

1.74 47.1 51.2 26.6

1.44 46.5 30.9 37.9

1.05 0.66 38.1 38.6 34.0

0.86 0.49 41.3 34.7 32.7

0.69 0.44 29.8 17.1 38.7

0.69 0.50 39.4 13.1 31.7

0.66 0.60 10.0 5.8 38.8

2.16 0.99 61.2 37.8 24.5

9.88 3.46 68.0 77.0 21.7

5.27 3.00 44.5 64.7 27.3

5.88 3.88 35.9 70.1 24.2

2.01 l.50 33.6 70.8 25.3

5.26 2.18 61.5 58.6 24.6

3.39 1.83 42.7 57.7 29.0

2.20 1.34 47.6 50.2 27.2

3.34 1.98 42.0 65.8 29.8

3.72 1.70 51.2 66.2 27.7

4.78 1.70 66.5 72.9 28.3

1.80 0.77 63.3 54.9 32.5

1.60 0.82 46.8 45.9 29.8

2.46 1.03 53.8 40.4 30.3

1.69 1.01 39.6 45.1 31.8

2.87 1.27 60.4 52.8 27.9

1.34 0.88 37.4 45.2 31.8

2.01 0.80 65.0 51.8 29.2

2.27 1.10 54.8 52.9 31.3

0.77 0.62 18.3 39.1 32.6

3.27 1.77 50.1 69.3 28.1

0.92 0.61 33.3 42.9 34.4

1.14 0.60 39.9 39.8 32.5

1.36 0.76 44.5 56.1 35.0

2.31 1.38 39.6 54.7 23.8

2.90 1.32 50.2 67.1 22.9

2.23 1.07 52.0 53.8 27.6

3.54 1.38 77.1 64.4 22.4

2.95 1.31 51.4 56.2 25.6

2.45 1.06 58.1 56.8 26.4

1.42 0.84 38.7 41.9 28.2

1.51 0.69 57.8 47.8 28.9

2.00 1.16 50.4 54.5 25.7

1.94 0.75 71.4 48.8 31.1

1.02 0.90 8.2 24.9 33.7

1.29 0.93 23.1 23.5 32.2

1.96 0.86 54.5 30.6 31.7

0.77 0.54 33.6 17.7 34.8

0.88 0.60 25.9 17.9 32.7

1.47 0.75 54.4 41.1 28.5

0.62 0.46 25.0 36.6 35.5

0.29 0.29 10.3 42.0

1.12 0.68 43.2 26.4 32.0

0.31 0.22 40.1 6.0 46.0

1.17 0.68 36.3 40.7 32.7

0.69 0.48 34.9 19.3 35.9

0.74 0.56 20.7 30.4 34.8

1.08 0.79 37.6 7.6 34.9

3.79 2.22 49.8 37.4 27.7

1.80 1.03 44.7 27.3 31.3

1.65 0.89 54.7 45.3 25.9

3.46 2.03 51.2 60.3 21.3

2.21 1.10 61.1 50.2 25.7

3.45 1.42 65.8 39.2 24.8

1.47 0.86 36.8 49.8 26.0

continued on next page

5 6 0.38

6 7 0.60

7 8 0.49

6 8 0.34

6 6 0.34

6 8 0.56

9 II 0.38

9 13 0.30

9 12 0.22

9 10 0.35

8 8 0.27

4 4 0.82

4 4 0.75

6 8 0.21

5 5 0.31

8 10 0.69

7 7 0.17

7 12 0.39

6 6 0.51

7 8 0.49

6 8 0.02

7 9 0.01

7 8 0.02

7 8 0.31

0.62

8 9 0.46

8 8 0.47

9 9 0.51

8 9 0.24

8 8 0.29

8 9 0.52

8 9 0.45

9 II 0.78

9 10 0.17

8 8 0.25

7 8 0.22

8 8 0.36

8 8 0.13

7 7 0.30

2 2 0.30

2 2 0.54

8 9 0.27

4 6 0.33

I I 0.29

8 10 0.19

2 3 0.10

8 9 0.38

9 II 0.22

8 9 0.32

2 2 0.49

6 6 0.31

9 10 1.20

9 II 0.78

9 9 1.53

2 2 1.00

9 9 0.59

9 9 0.99

8 8 0.53

7 8 0.75

8 9 0.50

l.51 41.9 52.3 28.1

1.80 3l.5 61.5 23.7

1.41 41.6 60.3 23.0

1.29 2.9 54.0 27.9

1.73 18.1 50.3 26.4

2.84 31.2 62.6 22.0

2.71 21.4 59.4 23.9

2.95 21.8 64.9 20.1

2.06 48.0 35.5 30.7

1.09 74.6 9.7 33.9

1.29 58.7 17.2 26.3

1.50 38.4 19.6 21.9

1.48 80.6 15.1 24.9

1.24 84.3 10.8 28.3

0.94 60.3 19.4 29.8

1.06 20.8 44.2

0.93 37.6 29.1 32.2

1.09 38.9 37.1 31.9

1.09 54.9 42.7 30.1

1.11 51.4 58.4 27.9

0.51 35.4 21.6 39.3

0.45 27.1 14.1 36.6

0.35 47.6 11.8 37.4

0.42 19.1 40.8

0.42 14.3 41.7

0.47 12.7 10.6 45.3

2.61 26.9 65.6 24.1

3.04 42.6 6l.5 24.5

3.16 31.3 55.6 25.0

1.07 22.4 50.5 31.8

0.62 49.0 21.8 35.9

0.49 37.3 25.3 37.1

0.56 49.0 35.4 33.5

0.57 50.9 28.0 39.9

0.63 51.1 18.0 39.5

1.00 88.1 32.6 31.5

0.49 42.4 14.3 33.8

0.79 41.9 36.4 30.7

1.02 82.4 47.7 3l.5

1.01 100.8 41.4 29.4

0.64 46.9 36.7 33.3

0.37 5.4 9.5 43.1

0.75 16.0 49.3

0.62 65.7 31.9 31.9

1.00 81.2 37.9 28.1

0.66 52.9 30.7 34.8

0.64 51.0 28.1 32.8

0.95 49.8 34.7 30.6

0.86 43.7 21.4 31.8

0.85 56.2 47.8 32.1

1.06 60.3 57.3 29.8

0.88 18.5 43.0 38.1

0.77 18.4 35.5 37.9

0.47 19.0 27.5 36.3

0.51 35.8 25.0 31.1

0.72 1.4 32.7

0.46 27.4 14.9 40.3

0.46 28.7 13.8 36.8

0.40 8.9 20.3 43.2

0.41 42.4 9.4 38.0

0.39 27.6 4.8 42.8

0.35 52.9 12.8 38.4

0.52 65.7 25.6 35.8

0.41 49.7 19.9 36.6

0.48 25.5 18.2 35.3

0.34 17.6 5.9 42.4

0.46 9.4 8.7 37.0

4 6 1.53 3.85

4 4 1.94 3.33

3 3 2.40 3.85

5 6 0.60 2.19

4 4 1.25 2.75

5 5 0.14 2.59

5 8 0.29 2.60

4 6 1.04 2.70

4 6 0.33 3.88

4 6 0.29 3.26

3 4 0.29 1.85

3 3 0.65 2.08

3 3 1.24 1.33

3 1.19 2.15

I I 1.06 1.06

5 9 0.54 l.55

4 8 0.53 1.85

6 9 0.41 2.16

4 4 0.50 2.05

6 12 0.25 2.87

5 7 0.27 1.20

6 13 0.22 1.60

6 10 0.37 2.13

5 13 0.33 1.96

4 4 0.42 1.62

0.40 2.27

3 3 0.72 1.10

3 3 0.57 0.87

3 3 0.36 0.58

3 4 0.25 0.73 I 1 0.72 0.72

6 0.28 0.61

4 5 0.29 0.68

2 2 0.36 0.43

6 12 0.13 0.69

3 7 0.22 0.56

6 10 0.06 0.66

6 10 0.16 1.47

3 4 0.21 0.75

4 6 0.25 0.62

1 2 0.28 0.40

2 3 0.42 0.52

6 8 0.75 3.49

4 6 1.71 3.40

4 9 1.05 5.54

4 5 1.81 4.54

1 2 0.83 1.31

4 5 0.28 1.04

4 7 0.33 0.89

4 7 0.19 1.02

4 5 0.32 1.12

5 7 0.28 1.14

5 5 0.41 2.75

5 9 0.25 1.01

6 12 0.24 1.36

6 8 0.33 2.93

6 7 0.31 3.44

2 2 0.34 0.94

2 2 0.35 0.39

I I 0.75 0.75

4 5 0.22 1.40

4 5 0.32 0.80

2 3 0.28 0.56

3 7 0.17 0.59

I I 0.42 0.42

I I 0.42 0.42

4 4 0.42 0.57

38.5

50.0

46.4

34.4

44.7

39.6

41.4

47.7

40.2

40.2

33.6

31.1

30.2

32.8

55.6

35.8

37.4

39.1

39.8

35.1

35.0

35.0

37.3

59.5

35.2

41.5

32.7

42.9

37.4

53.7

43.9

38.8

30.5

36.2

33.1

25.8

30.1

31.4

33.6

36.1

31.3

6.7

10.2

3.5

11.2

33.3

23.4

10.8

20.8

3.1

8.1

9.6

17.5

7.9

17.8

27.6

6.0

3.7

3.1

25.0

22.3

12.5

5.9

10.3

21.1

25.9

15.0

7.5

5.3

4.4

5.3

33.1

29.7

24.6

43.4

35.2

44.5

27.8

29.6

80.7

47.8

28.2

38.2

23.3

33.3

32.8

17.2

30.0

54.3

59.4

33.0

55.9 53.2 27.4

14.4 42.1 30.2

33.2 38.6 26.0

59.9

29.0

49.2

41.0

57.1

5l.5

11.1

27.0

28.0

32.8

52.5

35.6

59.5

94.3

52.9

53.2

10.8

60.0

0.41

0.16

0.30

0.55

0.57

0.63

0.72

0.87

0.98

1.24

0.65

0.32

0.28

0.28

0.36

0.36

0.38

0.42

0.35

0.45

0.04

0.70

0.42

0.58

1.29

0.58

0.61

0.81

0.59

0.42

0.34

0.46

0.38

0.54

0.40

0.40

0.19

0.23

0.41

MAB Northern Outer Shelf 60-200 m 65 4 6 0.29 0.71 0.51 31.8 24.2 37.0

70 5 7 0.21 0.92 0.60 45.2 19.0 33.3

71 7 9 0.17 0.79 0.41 41.9 8.3 35.8

72 4 7 0.28 0.56 0.42 20.2 11.9 36.4

73 4 8 0.41 1.22 0.69 38.7 19.8 32.9

80 4 7 0.36 1.04 0.53 45.5 22.3 36.8

81 5 7 0.29 0.80 0.51 40.3 1l.5 33.7

85 4 14 0.20 1.26 0.45 65.2 19.6 34.8

90 4 6 0.20 1.92 0.82 67.1 31.7 31.5

91 3 5 0.22 0.61 0.38 46.7 20.4 34.4

Southern Slope 200-2,000 m 8 4 4 0.32 0.72

17 4 4 0.28 0.56

18 I I 0.34 0.34

35 5 7 0.14 0.87

36 1 I 0.38 0.38

46 4 6 0.23 1.13

48 3 3 0.34 0.44

61 4 7 0.12 0.86

62 I 1 0.19 0.19

63 2 2 0.12 0.34

64 5 6 0.25 0.54

GB Central Shoals 35-55 m 123 4 7 0.91 1.73

147 7 II 0.74 3.08

148 4 5 0.63 2.82

156 2 2 0.77 2.11

GB Northern Shoals 30-40 m 124 4 5 0.82 2.49 1.44 48.2 48.1 29.8

146 3 4 0.78 2.26 l.55 44.6 49.4 30.2

160 2 3 1.77 2.42 2.05 13.2 39.3 28.5

GB Western Outer Shoals 50-60 m

120 3 4 0.49 1.22 0.92 29.0 49.3 34.3

121 4 5 0.23 2.57 1.21 65.6 47.1 25.3

GB Eastern Outer Shoals 60-80 m

157 3 3 0.85 2.56 1.43

158 3 3 1.08 l.50 1.25

159 5 8 1.07 2.73 1.80

GB Great South Channel 60-100 m 92 2 3 0.48 0.94 0.77 26.6 30.4 28.8

III 3 5 0.49 2.35 1.27 53.5 30.0 29.9

112 4 6 0.55 1.73 1.08 42.1 49.5 27.1

113 3 0.47 0.73 0.60 13.9 44.2 32.7

122 4 6 0.24 1.58 0.92 49.6 38.3 33.3

GB Southern Flank 60-200 m 114 5 II 0.31 1.69

117 4 7 0.27 0.63

119 6 II 0.25 1.21

149 5 10 0.55 2.56

150 5 10 0.14 1.28

153 3 4 0.34 1.15

155 2 2 0.72 0.90

GB Northeast Peak 80-200 m 177 2 2 0.08 0.75

178 I I 0.16 0.16

179 1 I 0.30 0.30

191 2 3 0.40 0.78

192 I I 0.57 0.57

Northern Slope 200-2,000 m 82 3 5 0.18 0.49

83 3 7 0.17 0.39

84 1 2 0.19 0.38

115 3 6 0.11 0.45

116 3 3 0.28 0.43

118 4 8 0.16 0.53

151 3 15 0.10 1.01

152 3 7 0.14 0.82

154 4 25 0.09 0.70

180 1 I 0.04 0.04

193

GB Nantucket Shoals 37 m 93 3 6 0.35 1.90 1.19 45.2 35.1 29.6

GOM Western 60-100 m 94 3 3 0.36 0.86

95 4 4 0.29 1.21

97 4 5 0.64 1.47

98 4 6 0.29 2.17

99 4 0.32 3.46

188 1 0.65 0.65
O'Reilly & Zetlin: Seasonal, Horizontal, and Vertical Distribution of Phytoplankton Chlorophyll a 119

Table C3 (continued)

January-February March-April May-June

Min. Max. Mean C.V.! Min. Max. Mean C.V. Min. Max. Mean C.V.

VI pi Chi a Chi a Chi a Chi a Net' Pha.; V P Chi a Chi a Chi a Chi a Nel. Pha. V P Chi a Chi a Chi a Chi a Nel. Pha.

Tile # # ~gl·1 ~gl·1 ~g 1.1 % % % # # ~g 1.1 ~gl·1 ~g 1.1 % % % # # ~gl·1 ~g 1.1 ~gl·1 % % %

GOM Northern 80-200 m

101 5 5 0.40 4.19 1.47 97.1 75.0 13.6 0.23 0.23 0.23 17.4 53.1 6 6 0.40 1.43 0.79 46.2 10.8 34.8

102 5 5 0.51 3.25 1.30 79.7 75.9 17.2 0.54 0.54 0.54 42.6 36.5 5 5 0.26 4.05 1.45 92.1 66.3 35.2

103 3 3 0.53 3.62 1.84 71.1 83.5 13.2 0.24 0.24 0.24 33.3 38.5 5 6 0.52 3.87 1.39 82.5 25.0 26.8

104 5 5 0.37 2.47 1.12 76.4 72.6 18.3 6 7 0.21 2.95 1.65 51.6 64.3 34.2

183 5 6 0.21 3.14 0.93 109.2 66.8 18.4 5 6 0.58 1.53 1.01 34.5 42.2 33.9

105 4 5 0.16 1.30 0.57 71.6 46.5 23.0 0.28 0.28 0.28 21.4 49.1 7 8 0.29 0.98 0.63 38.1 15.0 32.9

131 4 4 0.40 0.68 0.55 23.3 18.6 31.1 0.18 0.18 0.18 16.7 51.4 6 7 0.30 1.25 0.74 43.7 18.8 30.2

135 4 4 0.21 0.57 0.41 31.5 16.5 30.5 0.34 0.34 0.34 41.2 41.4 7 8 0.18 4.14 1.60 85.2 57.7 28.3

136 5 5 0.20 1.14 0.54 61.6 41.6 24.0 0.24 0.24 0.24 33.3 45.5 5 6 0.48 2.02 1.24 43.3 46.8 30.8

137 4 4 0.34 0.53 0.41 17.9 26.1 30.4 6 7 0.50 4.45 1.91 68.7 58.6 28.0

138 3 3 0.41 4.16 1.69 103.0 81.1 15.5 6 7 0.12 5.88 2.26 95.0 75.7 23.6

GOM Wilkinson Basin 100-250 m

96 5 5 0.40 2.85 0.94 101.7 60.4 21.7 4 5 0.28 6.16 1.83 119.\ 71.8 20.7 7 8 0.26 0.92 0.65 34.1 5.6 33.7

100 5 6 0.42 l.l5 0.70 45.5 51.9 24.0 I 1 0.26 0.26 0.26 15.4 49.0 6 6 0.24 1.23 0.66 56.3 10.1 33.9

106 4 4 0.29 1.17 0.66 51.1 45.4 25.1 1 1 0.22 0.22 0.22 9.1 5l.l 7 9 0.23 2.28 0.87 66.4 26.6 30.4

107 3 3 0.46 1.26 0.74 50.3 40.7 24.6 4 5 0.23 1.01 • 0.74 39.8 47.8 28.8 7 8 0.19 1.12 0.66 44.3 18.8 30.6

108 3 3 0.45 1.17 0.70 47.5 35.2 27.1 4 5 0.19 1.28 0.70 52.8 38.3 29.3 8 9 0.34 1.12 0.76 38.4 21.2 31.4

109 4 4 0.33 1.17 0.61 54.2 32.9 33.0 4 6 0.21 1.36 0.79 42.4 49.7 28.1 7 8 0.14 5.00 1.45 96.2 29.6 24.1

110 2 2 0.30 0.39 0.34 13.0 10.1 36.7 5 6 0.18 3.55 1.46 74.6 66.3 21.5 8 9 0.18 2.14 1.07 52.0 12.2 31.9

125 3 3 0.21 0.48 0.38 32.0 11.3 38.5 6 9 0.25 2.22 1.04 63.7 48.1 25.7 8 9 0.15 1.79 0.84 59.1 17.8 31.8

126 4 4 0.46 1.15 0.66 43.4 35.4 29.9 4 7 0.16 1.22 0.67 52.0 33.1 28.6 6 7 0.38 5.01 1.37 II 1.5 48.9 26.0

127 3 3 0.46 1.00 0.65 38.7 23.7 27.9 4 5 0.18 l.l5 0.65 48.1 39.1 30.9 8 9 0.23 2.49 1.21 63.6 22.1 26.7

128 2 2 0.51 0.85 0.68 25.0 39.0 26.9 4 5 0.13 0.88 0.62 45.8 37.9 29.6 5 6 0.58 4.34 1.65 86.5 36.4 25.4

129 3 3 0.36 1.64 0.81 73.1 52.9 23.7 4 5 0.22 0.84 0.58 35.9 31.9 31.9 7 8 0.22 2.06 0.90 59.6 23.5 30.8

GOM Georges Basin. 150-250 m

130 4 4 0.45 0.62 0.52 12.4 28.2 29.6 I 0.26 0.26 0.26 19.2 50.0 6 7 0.17 2.09 0.84 66.6 32.5 28.8

143 5 5 0.19 0.49 0.35 33.4 14.4 36.5 7 8 0.37 1.41 0.85 41.2 10.2 33.1

144 5 5 0.24 1.10 0.55 52.9 26.6 31.3 7 8 0.36 1.78 0.82 54.8 10.5 31.1

145 4 5 0.30 1.43 0.64 63.7 45.0 25.7 2 3 0.50 0.87 0.67 22.8 19.4 29.5 8 9 0.36 1.42 0.78 41.5 22.6 31.5

161 3 3 0.40 0.49 0.46 8.8 5.8 35.4 4 4 1.06 4.69 2.86 47.5 54.4 18.8 7 7 0.70 2.24 1.07 49.2 11.2 26.1

162 2 2 0.53 0.53 0.53 00 5.7 32.9 I I 0.45 0.45 0.45 57.8 32.8 4 4 0.85 1.43 1.07 22.0 15.4 28.1

163 3 3 0.32 0.62 0.42 32.9 5,5 34.2 I I 0.66 0.66 0.66 63.6 27.5 5 5 0.47 1.49 1.00 39.7 2.4 30.1

174 4 4 0.27 0.41 0.35 14.8 12.1 35.0 I I 0.43 0.43 0.43 44.2 34.8 6 7 0.69 2.03 1.09 38.8 5.1 28.7

175 5 0.24 1.02 0.51 52.2 26.1 32.7 2 2 0.44 1.11 0.78 43.2 45.8 29.2 6 7 0.50 0.86 0.64 18.6 6.5 32.0

176 4 4 0.48 0.88 0.60 26.8 22.4 32.5 3 3 0.57 1.50 1.07 35.8 54.5 20.7 5 5 0.52 2.95 1.29 69.0 44.2 20.9

GOM Jordan Basin 150-250 m

132 4 4 0.39 0.58 0.50 15.2 16.7 33.6 0.17 0.17 0.17 11.8 57.5 7 8 0.21 2.09 0.95 61.3 22.0 32.6

133 3 3 0.45 0.57 0.49 11.0 13.5 32.7 0.19 0.19 0.19 15.8 48.6 3 4 0.45 1.23 0.83 43.1 25.2 38.0

134 3 3 0.20 0.47 0.36 32.3 9.2 33.1 0.27 0.27 0.27 22.2 40.0 7 9 0.31 5.04 1.37 100.5 47.5 29.3

142 5 6 0.37 0.64 0.45 20.2 17.0 30.7 7 8 0.32 1.36 0.86 42.7 26.0 35.4

167 3 3 0.19 0.51 0.38 36.1 11.4 33.3 0.63 0.63 0.63 36.5 30.0 4 4 0.65 2.26 1.31 45.3 35.6 28.4

182 4 4 0.24 0.50 0.41 24.9 15.2 33.7 6 7 0.26 1.43 0.80 49.2 25.7 29.3

GOM Scotian Shelf 60--200 m

139 I 1 0.50 0.50 0.50 8.0 39.8

140 4 4 0.14 0.43 0.26 46.8 25.7 34.7 6 7 0.30 2.06 1.21 52.1 38.1 26.7

l41 4 4 0.13 0.40 0.30 34.2 25.2 46.6 6 6 0.22 0.97 0.60 38.0 39.7 34.8

164 3 3 0.18 0.47 0.36 35.6 6.5 40.0 0.45 0.45 0.45 44.4 31.8 5 5 0.38 2.55 1.26 60.2 28.3 25.9

165 3 3 0.16 0.48 0.34 39.3 8.8 39.3 4 4 0.50 3.11 1.35 77.1 44.7 25.4

166 2 2 0.39 0.47 0.43 9.3 12.8 34.8 0.49 0.49 0.49 49.0 35.5 5 5 0.47 1.98 1.17 44.7 15.3 25.1

168 3 3 0.33 0.45 0.41 13.8 9.8 37.9 4 4 1.35 1.73 1.55 8.8 19.4 26.2

169 2 2 0.32 0.41 0.36 12.3 13.7 37.6 3 3 0.44 2.49 1.52 55.3 27.9 24.8

170 2 2 0.28 0.38 0.33 15.2 19.7 38.9 3 3 0.35 1.70 1.00 55.2 32.0 31.5

181 4 5 0.18 0.85 0.52 49.9 49.4 48.4 3.16 3.16 3.16 93.4 19.0 4 4 1.18 1.97 1.41 23.0 40.7 30.5

171 4 4 0.20 0.49 0.36 29.6 22.9 40.0 5 5 0.43 4.19 1.56 88.8 47.0 32.2

190 2 2 0.26 0.44 0.35 25.7 8.6 43.5 0.55 0.55 0.55 63.6 32.9 2 2 0.34 2.41 1.38 75.3 73.8 27.8

172 4 4 0.28 0.52 0.38 24.8 11.1 37.5 0.29 0.29 0.29 55.2 34.1 5 7 0.39 3.76 1.36 78.6 32.1 23.2

189 2 2 0.28 0.39 0.34 16.4 6.0 40.7 3 3 1.04 1.67 1.38 18.8 26.1 23.8

173 4 4 0.19 0.47 0.35 32.1 15.7 36.4 1 0.32 0.32 0.32 46.9 37.3 4 0.42 1.05 0.71 36.1 7.6 32.3

continued on next page
120 NOAA Technical Report NMFS 139

Table C3 (continued)

July-:\ugusl September-Orlober ~ovel1lber-Decernber

~'lill. \lax. Meall c.\':\ Mill. \Iax. Mt"3n U· ~Iill. Max. ~ean C.\'

Y' P' Chi" Chi" Chi a Chi a ;\let.' Pha.' Y Chi a Chi a Chi a Chi" :-iel. Pha. Y Chi a Chi a Chi a Chi a . elo Pha.

Tile # # ~g I" ~g I' ~g I" % '( 'It # ~g I" ~g I" ~g I" (,~ % % # ~g I" ~g I" ~g I' % % %

CO\I :'\onherJI ~0-200 m

101 4 I 0.20 0.62 0.33 46.6 10.1 43.7 4 0.38 1.83 0.83 58.6 39.:; 29.6 7 8 0.21 1.14 0.58 55.1 38.6 30.0

102 3 3 0.21 0.36 0.2R 22.0 31.0 54.1 4 0.37 2.77 UO 62.7 20.9 26.3 7 8 0.39 1.30 0.80 36.0 47.1 28.6

103 3 3 0.21 0.69 0.16 42.5 36.0 41.4 4 5 0.74 2.36 1.12 51.2 28.H 26.1 6 6 0.29 0.82 0.52 335 19.9 350

104 2 0.28 0.35 0.32 11.1 31.9 50.1 2 2 1.00 2.27 1.61 38.8 41.3 26.8 6 6 0.16 067 0.47 37.2 21.8 38.7

183 3 4 0.31 0.59 0.45 20.7 28.9 39.2 3 4 0.57 3.16 1.66 69.8 60.1 23.9 4 4 0.27 0.62 0.48 27.1 28.4 33.1

105 4 4 0.34 0.97 0.65 31.6 16.2 34.3 3 4 0.47 1.55 0.93 49.7 38.3 2X.0 5 6 0.21 0.70 0.46 32.8 25.5 38.5

131 3 5 0.19 0.91 0.42 61.4 327 33.2 3 3 0.19 2.7R 1.17 63.3 50.5 23.8 5 6 0.32 0.86 0.47 38.6 18.7 39.6

13:; 3 4 0.31 0.55 0.44 19.4 27.1 42.7 2 2 1.19 1.29 1.24 1.0 55.2 23.0 6 7 0.25 073 0.44 341 23.6 35.2

136 3 4 0.34 070 0.:;1 32.5 24.0 3H.6 3 3 0.50 3.13 1.82 59.0 51.:; IX.4 4 1 0.00 0.55 0.34 600 31.9 31.7

137 3 3 0.31 0.62 0.31 28.0 44.2 52.6 2 3 0.39 2.92 1.16 73.2 52.7 23.6 7 9 0.21 0.77 0.45 396 28.3 34.9

1% 3 3 0.91 1.73 1.25 27.9 68.R 29.8 2 2 1.16 1.97 1.36 2,'.9 56.6 22.3 7 7 0.34 0.68 0.50 26.0 37.4 352

COM Wilkinson Basin 100-250 III

96 3 ~l 0.30 0.60 0.40 34.5 23.1 3D 4 6 O.IR 2.21 0.76 91.8 16.2 33.3 6 6 0.29 1.54 0.72 56.7 34.8 32.1

100 3 3 023 1.14 0.39 67.0 27.1 37.2 4 6 0.34 1.19 0.80 39.7 30.X 31.1 6 6 0.00 091 0.51 65.0 22.R 34.0

106 5 7 0.18 0.97 063 44.4 59 411 3 6 0.23 1.67 080 636 37.7 27.4 5 5 0.38 0.63 0.51 18.2 18.8 36.3

107 4 5 0.16 1.02 0.43 75.0 4.7 34.8 3 5 0.26 1.03 0.53 51.6 4.5 36.8 6 7 0.03 1.74 0.75 69.2 26.6 31.3

108 4 7 0.06 0.77 0.51 43.4 5.h 34.6 3 9 0.24 0.86 0:;3 32.2 18.1 31.9 7 9 0.37 1.16 0.65 433 44.9 30.2

109 3 4 O.I~ 0.64 0.35 53.2 4.2 38.3 4 7 0.35 0.X3 0.52 28.5 14.4 39.0 5 8 0.23 1.51 0.68 58.7 28.8 34.6

110 3 4 0.33 050 0.44 15.3 14.7 36.1 4 6 0.40 0.89 0.64 2H.4 19.4 33.5 9 10 0.42 1.90 0.88 48.7 28.2 29.0

125 6 9 0.65 2.99 1.21 57.1 3X.3 27.5 4 4 0.R3 1.55 116 22.2 26.3 29.7 9 10 0.57 1.53 0.96 30.6 39.9 28.8

126 4 5 0.15 OR6 0.48 65.8 8.8 37.0 4 6 0.13 0.83 0.57 11:1 11.4 36.0 6 6 0.48 1.34 0.X4 35.5 33.5 28.3

127 3 4 0.20 0.47 0.34 30.8 7.3 13.0 2 2 0.46 0.68 0.-,7 19.:1 Y.7 40.0 4 5 0.45 0.79 0.60 21.5 23.0 333

128 3 5 0.14 0.72 0.35 56.9 6.8 39.4 3 3 0.43 0.78 0.61 2~.5 8.2 39.6 3 3 0.36 0.91 0.62 367 30. 280

129 3 6 O.IX 1.24 0.61 52.6 :;2 34.2 3 6 0.:;3 1.12 0.7X 27.7 10.9 29.6 6 7 0.40 0.86 0.64 24.7 24.8 30.4

COM Ceorges Basin 150-250 III

130 2 3 0.19 0.68 0.43 47.0 39.8 38.7 2 2 0.76 1.16 1.11 31.5 31.1 27.9 5 5 0.01 0.86 0.45 63.9 30.4 34.9

143 3 3 0.22 0.45 0.35 27.6 10.4 38.4 3 4 027 118 0.7h 12.9 17.6 30.4 5 5 0.18 0.84 0.50 37.0 2R.X 35.1

111 3 4 0.18 0.78 0.39 61.7 IY:1 36.2 3 4 0.44 1.21 0.82 33.8 6.'l 338 6 7 0.27 0.88 0.47 42.2 22.6 37.1

115 4 6 0.08 1.02 0.56 62.9 IR3 33.2 3 12 0.24 1.26 0.60 52.2 14.3 32.0 7 10 0.24 0.68 0.55 23.4 20.0 35.5

161 2 3 0.83 1.30 1.01 20.3 3.3 35.6 3 3 0.73 1.4 l.i'I 27.2 IR.7 29.6 7 7 0.16 0.69 0.44 41.5 25.6 32.5

162 I I 0.62 0.62 0.62 29.0 31.9 2 2 0.28 0.91 0.59 52.9 39.5 31.2 3 3 0.00 0.92 0.42 90.4 45.2 23.6

163 I I 0.73 0.73 0.73 12.3 38.1 2 2 0.79 1.00 0.90 11.7 15.1 32.5 4 5 0.00 0.67 0.39 62.3 13.9 37.2

174 2 2 0.44 062 0.53 17.0 1.9 36.9 3 3 0.32 0.61 0.47 25.4 12.1 33.0 6 7 0.08 1.41 0.58 71.4 17.9 30.0

175 3 3 0.13 0.80 0.52 54.7 2.6 38.1 2 2 0.65 0.7X 0.71 9.1 4.2 29.6 6 7 0.3 0.88 0.51 32.8 15.6 34.5

176 I I 0.04 0.01 0.04 20.0 50.0 3 3 0.35 2.2, I.U9 7X.1 61 36.3 8 8 0.29 0.66 0.44 25.9 15.2 40.8

GOMJordan Basin 1~)0-230 III

132 3 4 0.20 0.65 0.40 42.5 16.4 45.3 3 4 0.43 0.89 0.09 30.8 22.6 34.5 6 0.35 1.19 0.61 54.0 35.6 32.1

133 3 3 0.22 0.'17 0.31 36.6 17.2 13.6 3 6 0.44 1.86 0.86 36. 2•.0 31.7 5 0.28 1.16 0.58 52.4 43.5 31.8

134 3 4 0.19 034 0.28 20.2 13.2 16.7 2 2 0.45 2.10 1.27 64.7 55.3 24.8 5 6 0.00 0.99 0.46 65.8 32.4 32.4

142 3 4 0.19 0.75 0.38 59.6 8.7 10.9 2 2 1.31 2.37 I.XI 2X.8 52.5 22.4 6 7 0.00 0.70 0.42 535 19.9 35.2

167 2 2 0.45 1..,2 0.98 54.3 41.6 27.8 4 4 0.30 0.89 0.57 37.6 32.2 36.7

IX2 2 2 0.18 0.13 0.30 41.0 13.1 33.0 2 2 0.50 1.03 0.77 34.6 41.8 34.3 5 5 0.34 1.00 O.5R 39.8 28.2 31.7

GOM Scolian Shelf 6U-2011 III

139 I I 0.7R 0.78 078 70.5 44.7 I I 1.37 1.37 1.37 74.5 222

140 3 5 0.00 0.99 0.76 24.2 36.4 39.1 2 2 0.60 0.83 0.71 Ih.1 39.2 353 7 7 0.16 0.90 0.43 49.3 19.1 32.6

141 3 0.21 0.89 0.47 47.9 31.H 3X.1 2 2 0.50 0.53 0.52 2.9 30.1 33.5 5 5 0.23 0.44 0.30 24.9 36.9 40.2

164 I 0.57 057 0.57 12.3 36.7 2 2 05:; 0.79 0.67 17.9 39.6 30.9 4 4 0.11 0.40 0.33 33.3 8.4 40.1

165 1 021 0.21 0.21 23.8 48.8 I I 088 088 0.H8 15.9 31.8 3 3 0.36 0.41 039 5.5 9.4 44.3

166 I 0.77 0.77 0.77 6.5 44.2 I 1 2.13 213 2.13 59.2 23.4 4 1 0.23 0.95 0.46 61.9 28.7 33.2

16R I 0.02 0.62 0.62 1.8 39.8 2 2 0.73 0.77 0.71i 1.3 309 28.3 4 4 0.24 0.71 0.39 49.5 9.7 39.4

169 I 0.09 0.09 0.09 11.1 4:1.8 2 2 1.09 1.17 1.13 3.5 252 28.5 3 3 0.23 070 0.44 43.8 15.0 39.6

170 I 0.16 0.16 0.16 68.8 27.3 2 2 0.% 1.2R I.I~ 14.8 18.4 31.0 3 3 0.25 0.:;4 0.35 374 15.1 46.8

181 2 2 1.03 1.31 1.17 120 35.9 350 4 4 0.37 1.05 066 37.9 47.0 63.5

171 0.50 050 0.50 22.0 46.2 1 1 0.65 0.65 0.65 33.9 37.5 6 6 0.00 0.55 0.34 53.7 133 39.4

190 I 2 0.66 1.19 0.93 28.1i 12.4 3R.9 2 2 0.26 0.55 0.41 35.8 8.6 43.4

172 2 3 0.50 1.93 114 520 10.:, 26.0 3 3 08~ 1.37 1.11 203 274 27.5 7 9 0.00 0.60 0.33 52.9 10.1 41.0

189 I 1 1.44 1.44 1.14 10.4 22.6 I I 0.93 0.93 0.9~ II.X 32.1 3 3 0.40 0.47 0.42 7.8 7.9 37.1

173 2 2 0.35 1.89 112 6R.X 6.7 26.8 0 3 0.58 I.RI 0.99 ;8.6 13.5 29.8 6 6 0.21 0.73 0.39 53.9 18.2 38.9

1 Y: Number of years with observatiuns.

P: Number of stations per two-month periocl.

:, C.V.: Coefficient of variation.

" ]\'et.: Netplankton.

:, Pha.: Phaeopigment.