Linking Water Turbidity and

Total Suspended Solids Loading to Kelp

Productivity within the Stefansson Sound

Boulder Patch

ANIMIDA Task 6 (Boulder Patch)

Final Report to

Minerals Management Service

Contract 1435-01-99-CT-30998, TO 10906

Linking Water Turbidity and

Total Suspended Solids Loading to Kelp

Productivity within the Stefansson Sound

Boulder Patch

ANIMIDA Task 6 (Boulder Patch)

Final Report to

Minerals Management Service

Contract 1435-01-99-CT-30998, TO 10906

Ken Dunton, Adrian Burd, Dale Funk, and Robert Maffione, PI’s

Report Prepared by Craig Aumack

Ken Dunton, Adrian Burd, Dale Funk, and Robert Maffione, PI’s

Report Prepared by Craig Aumack

March 2004

OCS Report MMS 2005-011

U.S. Department of the Interior 

Minerals Management Service 

Alaska Outer Continental Shelf Region
ii 

The Department of the Interior Mission 

As the Nation's principal conservation agency, the Department of the Interior has responsibility for most of our 

nationally owned public lands and natural resources. This includes fostering sound use of our land and water 

resources; protecting our fish, wildlife, and biological diversity; preserving the environmental and cultural values of 

our national parks and historical places; and providing for the enjoyment of life through outdoor recreation. The 

Department assesses our energy and mineral resources and works to ensure that their development is in the best 

interests of all our people by encouraging stewardship and citizen participation in their care. The Department also 

has a major responsibility for American Indian reservation communities and for people who live in island territories 

under U.S. administration. 

The Minerals Management Service Mission 

As a bureau of the Department of the Interior, the Minerals Management Service's (MMS) primary responsibilities 

are to manage the mineral resources located on the Nation's Outer Continental Shelf (OCS), collect revenue from 

the Federal OCS and onshore Federal and Indian lands, and distribute those revenues. 

Moreover, in working to meet its responsibilities, the Offshore Minerals Management Program administers the 

OCS competitive leasing program and oversees the safe and environmentally sound exploration and production of 

our Nation's offshore natural gas, oil and other mineral resources. The MMS Royalty Management Program

meets its responsibilities by ensuring the efficient, timely and accurate collection and disbursement of revenue from 

mineral leasing and production due to Indian tribes and allottees, States and the U.S. Treasury. 

The MMS strives to fulfill its responsibilities through the general guiding principles of: (1) being responsive to the 

public's concerns and interests by maintaining a dialogue with all potentially affected parties and (2) carrying out its 

programs with an emphasis on working to enhance the quality of life for all Americans by lending MMS assistance 

and expertise to economic development and environmental protection. 
iii 

LINKING WATER TURBIDITY AND TOTAL SUSPENDED SOLIDS 

LOADING TO KELP PRODUCTIVITY WITHIN THE STEFANSSON SOUND 

BOULDER PATCH 

ANIMIDA Task 6 (Boulder Patch) 

March 2003 

Ken Dunton1

, Adrian Burd2, Dale Funk3, and Robert Maffione4, PI’s 

Report Prepared by Craig Aumack1

 

1

The University of Texas Marine Science Institute, 750 Channel View Drive, Port Aransas, TX 78373 

(361) 749-6728, FAX (361) 749-6777, E-mail: dunton@utmsi.utexas.edu; 

2

Department of Marine Science, University of Georgia, Athens, GA 30602-3636 

(706) 542-1604, FAX (704) 542-5888, E-mail: adrianb@arches.uga.edu; 

3

LGL Alaska Research Associates, Inc. 1101 East 76th Ave. Suite B, Anchorage, AK 99518 

(907) 562-3339; FAX (907) 562-7223; E-mail: dfunk@lgl.com

4

HOBI-Laboratories, 8987 E. Tanque Verde #309-366, Tucson, AZ 85749 

(520) 299-2598, FAX (520) 299-2598, E-mail: maffione@hobilabs.com;

This study was funded by the U.S. Department of the Interior, Minerals 

Management Service (MMS), Alaska Outer Continental Shelf Region, Anchorage 

Alaska, under Contract No. 1435-01-99-CT-30998, TO 10906, as part of the 

MMS Alaska Environmental Studies Program. 

The opinions, findings, conclusions, or recommendations expressed in this report or product are 

those of the authors and do not necessarily reflect the views of the U.S. Department of the Interior, 

nor does mention of trade names or commercial products constitute endorsement or 

recommendation for use by the Federal Government.
Project Organization Page

Responsibilities IOP Collection TSS Chl a Nutrients Physiochem

Data 

Field Collection

Ken Dunton, 

Craig Aumack, 

Dale Funk, 

Robert Maffione 

Ken Dunton, 

Craig Aumack, 

Dale Funk 

Ken Dunton, 

Craig Aumack, 

Dale Funk 

Ken Dunton, 

Craig Aumack, 

Dale Funk 

Ken Dunto

Craig Auma

Dale Funk

Robert Maffi

Laboratory 

Analyses -- 

Craig Aumack, 

Dale Funk, 

Ken Dunton 

Craig Aumack Craig Aumack -- 

Data Entry Craig Aumack Craig Aumack Craig Aumack Craig Aumack Craig Auma

Model Design 

and Analysis

Adrian Burd, 

Robert Maffione 

Craig Aumack 

Adrian Burd, 

Robert Maffione 

Craig Aumack 

-- -- -- 

Statistics Craig Aumack Craig Aumack Craig Aumack Craig Aumack -- 

Report 

Generation

Ken Dunton, 

Craig Aumack, 

Dale Funk, 

Adrian Burd 

Ken Dunton, 

Craig Aumack, 

Dale Funk, 

Adrian Burd 

Ken Dunton, 

Craig Aumack, 

Dale Funk, 

Adrian Burd 

Ken Dunton, 

Craig Aumack, 

Dale Funk, 

Adrian Burd 

Ken Dunto

Craig Auma

Dale Funk

Adrian Bur
v 

Table of Contents

Executive Summary............................................................................................... 1 

Introduction ........................................................................................................... 4 

Methods and Materials .......................................................................................... 8 

Study Area ................................................................................................. 8 

Light Measurements .................................................................................. 9 

Total Suspended Solids (TSS)................................................................. 10 

Chlorophyll Concentrations .................................................................... 10 

Radiative Transfer Equation and Productivity Model ............................ 11 

Nutrient Concentrations .......................................................................... 16 

Physiochemical Parameters .................................................................... 16 

Kelp Growth ............................................................................................ 17 

Statistics and GIS .................................................................................... 17 

Results ................................................................................................................. 19 

Light Measurements ................................................................................ 19 

Total Suspended Solids (TSS).................................................................. 21 

Chlorophyll Concentrations .................................................................... 22 

Radiative Transfer Equation (RTE) and Productivity Model.................. 23 

Nutrient Concentrations .......................................................................... 25 

Physiochemical Parameters.................................................................... 25 

Kelp Growth ............................................................................................ 27 

Discussion............................................................................................................ 30 

Light Measurements ................................................................................ 30 

Total Suspended Solids (TSS).................................................................. 31 

Chlorophyll Concentrations .................................................................... 32 

Radiative Transfer Equation (RTE) and Productivity Model.................. 34 

Nutrient Concentrations.......................................................................... 36 

Physiochemical Parameters.................................................................... 37 

Kelp Growth ............................................................................................ 39 

Model Verification Based on Kelp Growth, TSS, and Irradiance........... 40 

Acknowledgements ............................................................................................. 44 

Literature Cited.................................................................................................... 45 
1

Executive Summary

The Stefansson Sound Boulder Patch, located 20 km northeast of Prudhoe 

Bay in the Alaskan Beaufort Sea, supports the only known kelp bed on the 

Alaskan arctic coast that is characterized by high benthic diversity associated with 

an abundance of boulders, cobbles, and pebbles. Growth and production of the 

endemic arctic kelp Laminaria solidungula, which is abundant throughout the 

area, is regulated primarily by PAR (photosynthetically active radiation) 

availability during the summer open-water period. Variation in underwater PAR, 

caused by changes in water transparency, can have significant effects on the 

annual productivity of this species (Dunton, 1990). Although the physiological 

responses of L. solidungula to changes in PAR are well described, the relationship 

between PAR and water turbidity (measured in terms of total suspended solids 

[TSS]) is poorly understood. Consequently, our ability to assess the effects of 

changes in water transparency, whether caused by natural or anthropogenic 

events, is significantly compromised. 

In an attempt to further our understanding of the relationship between TSS 

and light availability, we measured the inherent optical properties (IOPs) of 

Stefansson Sound waters, including absorption, scattering, and attenuation, in 

conjunction with TSS concentrations for a two-week period in summers 2001 and 

2002. These data were used in a radiative transfer equation (RTE), and a TSS 

concentration specific attenuation coefficient [K*

d(λ,H)] was determined. The 

attenuation coefficient was inserted into a productivity model to estimate daily 

kelp production throughout the Boulder Patch. Our model output agreed well 

with previously published measurements of annual kelp production based on the 

number of hours of saturating irradiance available to the kelp under average water 

transparency conditions. 
2

The highest TSS levels (23.0 – 24.2 mg L-1) occurred in nearshore areas 

during summer 2001 and were coincident with increased light attenuation (11.4 – 

14.0 m-1). In both years, lower TSS concentrations and lower light attenuations 

were measured in areas furthest from the coast within the Boulder Patch kelp 

community. Although light attenuation through the water column decreased in 

summer 2002, attenuation and TSS were significantly correlated (p < 0.01). 

Our results clearly demonstrate that suspended sediment concentrations 

have varying but substantial affects on light availability, and subsequent kelp 

production, during the summer open-water period. Increasing average TSS 

concentrations from 1 to 10 mg L-1, within ranges measured in situ, decreased 

annual production by an order of magnitude. Even under an array of surface 

irradiance budgets, production estimates and rates changed substantially under 

different TSS concentrations. Production, modeled under a variety of summer 

surface light regimes, was always higher at lower TSS concentrations and 

estimated kelp production was higher in offshore locations, despite deeper depths, 

because they are characterized by lower TSS. 

The accuracy of the model was tested using previously recorded surface 

irradiance data from 1990 and 1991. In both years, model estimated production 

coincided well with annual production calculated from blade length data. Similar 

accuracy was demonstrated when the model was used to estimate annual 

production for 2001. Although previous years’ estimates coincided with those 

calculated using blade length data, estimates for 2002 production were distinctly 

different. This was most likely the result of temporal sampling bias. Low TSS 

concentrations recorded during a two-week period in summer 2002 were probably 

not representative of water conditions for the entire summer open water season in 

2002. Consequently, reasonable estimates of kelp production using this model are 
3

dependent on TSS, IOP, and surface light measurements reflective of overall 

summer conditions. 
4

Introduction

Unconsolidated sediments composed of silty clays and mud generally 

characterize the nearshore Alaskan Beaufort Sea, but areas of hard rock 

substratum also occur along portions of the coast (Dunton et al., 1982). In 

Stefansson Sound, these deposits are incorporated into the Gubik formation and 

support abundant kelp and diverse epilithic fauna. The boulders, cobbles, and 

pebbles contain mineral types that are clearly extrinsic to northern Alaska 

(MacCarthy, 1958; Hopkins, 1979; Dunton et al., 1982) and suggest that rocks 

were transported from arctic Canada during the last glaciation (MacCarthy, 1958; 

Hopkins, 1979). These rocks provide a solid substratum needed for kelp 

colonization (Dunton et al., 1982; Busdosh et al., 1985). Consequently, kelp beds 

occupy areas of rocky substratum within Stefansson Sound and support a diverse 

community of kelp and epilithic invertebrates collectively known as the Boulder 

Patch. 

Similar to other kelp dominated ecosystems, sunlight, nutrient availability, 

and temperature are important abiotic factors regulating primary production. 

Among these, light displays the largest variation. In polar regions, solar 

irradiance changes dramatically with season (Lüning and Dring, 1979; Chapman 

and Lindley, 1980; Dunton, 1990; Kirst and Wiencke, 1995) and at 70o

 N, annual 

solar radiation is 30 to 50% less than temperate and equatorial regions 

(Kondratyev, 1954). The Arctic’s already restricted light availability is 

compounded in the Boulder Patch by formation of 2-m thick fast ice in the 

nearshore Beaufort Sea during the long seven-month winter season. These factors 

contribute to poor light availability for kelp growing within Stefansson Sound. 

Marine flora have a variety of adaptive responses that help compensate for 

lower irradiances at high latitudes. For example, the endemic arctic kelp 

Laminaria solidungula completes over 90% of its annual linear growth during the 
5

dark nine-month ice covered winter period (Dunton and Schell, 1986). Kelp 

utilize carbon reserves accumulated during the previous summer when waters are 

predominantly free of ice and light is available (Chapman and Lindley, 1980; 

Hooper, 1984; Dunton, 1985; Dunton and Schell, 1986; Henley and Dunton, 

1995). Photosynthetic production during the open-water period is usually 

sufficient to compensate for respiratory demands and allow accumulation of 

carbon storage compounds. However, large variations in underwater irradiance 

can occur during summer depending on sediment concentrations in the water 

column. Suspended sediments decrease water transparency and may significantly 

reduce annual kelp productivity (Dunton, 1990; Best et al., 2001). 

Research studies have clearly documented that growth and productivity of 

kelp within Stefansson Sound are regulated by light availability 

(photosynthetically active radiation [PAR]) during the summer open-water season 

(Henley and Dunton, 1997). Results from a variety of experimental studies, 

including the linear growth response of kelp to natural changes in the underwater 

light field (Dunton, 1984; Dunton and Schell, 1986; Dunton, 1990), carbon 

radioisotope tracer experiments (Dunton and Jodwalis, 1988), and laboratory and 

field physiological work (Henley and Dunton, 1995; 1997), have been used 

successfully to develop models relating kelp productivity to PAR. 

However, PAR availability in the summer open-water period is not 

constant and is largely a function of water transparency, measured by the amount 

of total suspended solids (TSS; Table 1) in the local area (Henley and Dunton, 

1995). TSS are particles in the water column that diminish sub-surface irradiance. 

These particles include clay, silt, sand, decaying vegetation and animals, or any 

inanimate particulate matter (Kirk, 1983). TSS originates from erosion, industrial 

or natural discharge, run-off, dredging, and flocculation. As these suspended 

particulates move through the water column, they reflect, refract, and absorb 
6

sunlight, thereby reducing light availability for macroalgal photosynthesis and 

biomass production. Ultimately, reduced kelp production means less food and 

habitat for organisms dependent on the kelp forest. 

Spatial and temporal TSS variations alter the number of hours kelp are 

exposed to levels of saturating irradiance (Hsat). Hsat for Laminaria solidungula in 

the Boulder Patch has ranged from as low as 39 hours to as high as 171 hours in a 

single summer (Dunton, 1990). Despite known variations in irradiance levels 

reaching the kelp canopy during summer and the impact of reduced summer light 

on annual kelp production, the relationship between TSS and PAR is poorly 

understood. Consequently, it has been difficult, if not impossible, to accurately 

estimate productivity on the basis of TSS data alone. 

TSS concentrations should be linearly related to light attenuation by 

particles in the water column (Di Toro, 1978; Kirk, 1984b; Van Duin et al., 2001; 

Maffione et al., 2003). Attenuation (k), or the fraction of radiant energy removed 

from light per unit distance through a given media, is quantified by two important 

optical parameters, absorption and scattering (Van De Hulst, 1957; Kirk, 1983; 

1984a; 1984b; Maffione, 1998; Van Duin et al., 2001). Absorption (a) occurs 

when photons are absorbed throughout the water column by colored dissolved 

organic matter (CDOM), biological organisms, suspended sediment, and the water 

itself (Kirk, 1983; Van Duin et al., 2001). Scattering (b) does not remove a 

significant fraction of photons but increases the effective length of photon travel, 

thereby increasing the probability of being absorbed (Kirk, 1983; Van Duin et al., 

2001). High ratios of scattering coefficient to absorption coefficient (b:a) are 

typically affiliated with areas of increased turbidities (Kirk, 1994). Coastal 

regions receiving high river discharge or shallow waters with unconsolidated 

sediments often have high b:a ratios (> 30), a direct result of increased TSS, 

which are typically correlated with photon scattering rather than absorption (Van 
7

De Hulst, 1957). Connections between PAR and TSS concentrations in 

Stefansson Sound can be quantified through measurement of these two inherent 

optical properties (IOPs). Once determined, the IOPs in Stefansson Sound can be 

used to develop attenuation coefficients for PAR penetration to the seabed. With 

this information, we can determine potential changes in primary production in 

response to varying water transparency, caused by changes in TSS concentration, 

throughout Stefansson Sound. 

The objective of this study was to determine the influence of suspended 

sediments during the summer season on the productivity of Laminaria 

solidungula in Stefansson Sound. We did this by quantifying the inherent optical 

properties and their relationship to suspended particulates in the water column. 

Once accomplished, we developed an attenuation coefficient based on specific 

TSS concentrations [K*

d(λ,H)]. This coefficient allowed us to estimate benthic 

irradiance levels based on surface PAR measurements and water depth. Published 

photosynthesis versus irradiance curves were used in conjunction with calculated 

benthic irradiance levels to attain a reasonable production estimate for the coming 

growth year (GWYR). Proximity of the Sagavanirktok River Delta outflow, 

along with the shallow depths, silty bottoms, and high turbidities that characterize 

Stefansson Sound indicate that light attenuation should be heavily influenced by 

suspended sediment concentrations. Kelp production, directly related to summer 

irradiance, will be indirectly impacted by TSS concentrations. We hypothesize 

that kelp beds located further offshore should be characterized by relatively 

higher rates of annual productivity, despite the deeper depths, because lower 

concentrations of TSS permit significantly higher light penetration to the seabed.
8

Materials and Methods

Study Area 

 This study was conducted within Stefansson Sound (70o

25’ N; 147o80’ 

W), which lies 20 km northeast of Prudhoe Bay in the Alaskan Beaufort Sea 

(Figure 1). Stefansson Sound extends from the Midway Islands in the west to 

Tigvariak Island in the east and is enclosed by a barrier island chain to the north. 

Holocene marine deposits of silts and mud generally characterize the Stefansson 

Sound seabed, boulders and cobbles cover various areas. These areas of solid 

benthos are collectively referred to as the Stefansson Sound Boulder Patch. The 

Boulder Patch covers over 20 km2 (Dunton, 1984) and provides the substratum 

necessary for a diverse assemblage of invertebrates and macroalgae. The most 

dominant organism is the kelp Laminaria solidungula, which constitutes over 

90% of phaeophyte biomass in the Boulder Patch (Dunton et al., 1982). 

Fieldwork for this study was conducted from Endicott Island, a British 

Petroleum Exploration (Alaska) owned and operated facility near the mouth of the 

Sagavanirktok River Delta during summers 2001 through 2003. Samples and 

measurements were obtained in the field using the R/V Proteus, a 7.6 m (25 foot) 

Boston Whaler equipped for arctic coastal work. Terminology and units for 

parameters measured or calculated as part of this study are listed in Table 1. 

The National Climatic Data Center (www.ncdc.noaa.gov), using a 30-yr 

record, characterized the following average summer weather conditions along the 

North Slope; temperature (39.6°C), wind speed (19.3 km hr-1), and cloud cover 

(70.5 d summer-1). Based on personal observations from Stefansson Sound, 

weather patterns are difficult to predict and changes are periodic and sudden. 

Wind speed, precipitation, and sea surface conditions are all highly variable and 

dependent on changing wind directions (NW, E, SE, SW). 
9

Light Measurements 

In situ water column absorbance and attenuation were measured using an 

ac-9 (WET Labs Inc., Philomath, Oregon, USA), which simultaneously 

determines the spectral transmittance and spectral absorbance over nine 

wavelengths (412, 440, 488, 510, 532, 555, 630, 676, and 715 nm) and calculates 

the absorption (a) and attenuation (k) of the water at those frequencies 

(www.wetlabs.com). The instrument was towed at a constant speed, 4.0 – 6.5 km 

hr-1, behind the R/V Proteus at 0.10 and 0.50 m. depths. Measurements were 

made along predetermined transects in and around Stefansson Sound and the 

Boulder Patch during summers 2001 and 2002 (Figure 2). Daily tracklines 

included transects both inside and outside the Boulder Patch for comparison. 

Most transects outside the Boulder Patch were in coastal waters between the 

Boulder Patch and shoreline. Measurements were downloaded, averaged over 1-

min intervals, and corrected by subtracting the specific wavelength’s pure water 

correction value. Once completed, absorption was scatter-corrected 

(www.wetlabs.com) and matched to its congruent geographic location. Similarly, 

the ac-9 was used to conduct vertical profiles at 11 different locations (Figure 3). 

Profiles at routine sampling locations were taken at different times of the day to 

examine diel changes in light transmittance. 

 PAR was measured continuously at DS-11 from 28 July to 8 August 2002. 

DS-11, the site of highest kelp biomass, was chosen because of its historical 

relevance. Data were collected using four underwater light sensors, two LI193SA spherical quantum sensors and two LI-190SA underwater cosine sensors, 

connected to two LI-1000 dataloggers (LI-COR Inc., Lincoln, Nebraska, USA). 

Sensors were mounted on PVC poles and positioned just above the kelp canopy to 

prevent fouling or shading by kelp fronds. Instantaneous PAR measurements 

were taken at 1-min intervals and integrated over 1-hr periods. Subsequent 
10

surface PAR measurements were taken with two LI-190SA terrestrial cosine 

sensors connected to two LI-1000 dataloggers located at nearby Endicott Island. 

Sensors were placed on the roofs of two stationary storage containers to eliminate 

shading. Data from both sets of paired dataloggers were graphed and compared 

statistically to ensure similar results. 

Total Suspended Solids (TSS) 

 To determine in situ TSS during summers 2001 and 2002, three replicate 

water samples were sampled at collection sites along transects and at several 

depths during vertical profiles (Figure 4). Water was forced to the surface 

through plastic tubing from the ac-9’s internal water pump and collected on the 

surface in 1-L plastic bottles. Bottles were labeled and sampling point geographic 

coordinates (Lat/Long) recorded using a handheld Garmin Global Positioning 

System, GPSMap 76S (Garmin International Inc., Olathe, Kansas, USA). 

Samples were stored in a cooler and transported to a lab on Endicott Island for 

processing. 

 A known volume of water from each sample was filtered through preweighed, pre-combusted 4-mm glass fiber filters (Pall Corporation, Ann Arbor, 

Michigan, USA). Filters were oven dried to constant weight at 65o

C. The net 

weight of particles collected in each sample was calculated by subtracting the 

filter’s initial weight from the total weight following filtration. Weights were 

determined with a microbalance (Denver Instruments APX-60, Arvada, Colorado, 

USA). 

Chlorophyll Concentrations 

 At each collection site (Figure 4), water for chlorophyll measurements was 

sampled in triplicate using 1-L plastic bottles. Water was collected from depths 
11

(0 – 8 m) using the ac-9. Bottles were stored in a dark cooler and transported to 

Endicott Island. In the dark, 100 ml of water from each replicate sample was 

filtered through a 0.45 μm cellulose nitrate membrane filter (Whatman, 

Maidstone, England). After filtration, the filters and residue were placed in prelabeled 10 ml Crio-Vials and frozen in liquid nitrogen. The frozen filters were 

transported to The University of Texas Marine Science Institute (UTMSI) in Port 

Aransas, Texas for subsequent chlorophyll analysis. 

At UTMSI, filters were removed from the vials and placed in pre-labeled 

test tubes containing 10 ml of methanol for overnight extraction (Parsons et al., 

1984). Chlorophyll a concentration, in μg L-1, was determined using a Turner 

Designs 10-AU fluorometer (Turner Design, Sunnyvale, California, USA). Nonacidification techniques were used to account for the presence of chlorophyll b 

and phaeopigments (Welschmeyer, 1994). 

Radiative Transfer Equation and Productivity Model 

 IOPs obtained in the field were used in a Radiative Transfer Equation 

(RTE; Maffione, 2003; Maffione et al., 2003): 

 Kd(λ,H) = ln[Ed(λ,0+)/Ed(λ,H)] (1.1) 

 H 

where Kd(λ,H) is the bulk downwelling irradiance attenuation coefficient at depth 

(H), Ed(λ,0+

) denotes the downwelling spectral irradiance incident on the water’s 

surface (0+

), and Ed(λ,H) is the downwelling spectral irradiance incident at depth 

H. Kd(λ,H) was computed for a range of TSS concentrations (CTSS), and a linear 

regression of Kd(λ,H) vs. CTSS was performed. The slope of this regression 
12

denotes the sediment concentration specific attenuation coefficient [K*

d(λ,H)] 

(Van Duin et al., 2001). Once K*

d(λ,H) was established, Ed(λ,H) or the 

downwelling spectral irradiance incident at depth H, was easily computed for any 

TSS concentration: 

 Ed(λ,H) = Ed(λ,0+

) exp[-K*

d(λ,H)

.

CTSS.H]. (1.2) 

Accurate Kd(λ,H) for Stefansson Sound is crucial for calculating 

reasonable productivity estimates. Since Kd(λ,H) is a function of the relationship 

between the IOPs and TSS, annual comparisons between these two parameters 

were statistically verified prior to insertion into the RTE. Additionally, accuracy 

of the final Kd(λ,H) was determined through in situ irradiance measurements 

taken in 2002 (refer to Light Measurements section). Input of the calculated 

K*

d(λ,H) into equation (1.2) along with known surface spectral irradiance 

(Ed(λ,0+)), TSS concentration (CTSS), and depth (H) yielded bottom irradiance 

measurements (Ed(λ,H)) comparable to in situ measurements. 

Results from the RTE were coupled with a clear-sky irradiance model 

(Gregg and Carder, 1990). The model computes spectral irradiance as well as 

PAR at the surface and applies the resulting K*

d(λ,H) based on measured TSS 

concentrations from the local area. Irradiance reaching the kelp canopy is 

calculated based on the effects of K*

d(λ,H) on surface irradiance and depth. 

The model was designed specifically for marine atmospheres and includes 

factors for oxygen concentration, ozone and water absorption, aerosols, and seasurface reflectance (Burd, 2003). Meteorological data required for the irradiance 

model, including air temperature (°C), relative humidity (%), and wind speed (m 

s

-1), were taken from NOAA National Data Center for the airport at Deadhorse, 
13

Alaska (70o 11’N, 148o 29’W). This data center was chosen for its proximity to 

Stefansson Sound. 

Additional required parameters include atmospheric pressure, some 

relative degree of aerosol (1 for open-ocean to 10 for continental atmosphere) 

based on Junge distributions that have been fitted to the Navy Aerosol Model 

(Gregg and Carder, 1990), and total amount of water precipitate in a 1-cm2

 area in 

a vertical path from the top of the atmosphere to the surface (h). Here, h was 

calculated using the expression (Butler, 1998): 

h = 

P0

3.T0

 (1.3)

where h is in millimeters, T0 is the surface temperature in Kelvin, and P0 is the 

surface water vapor partial pressure. P0 must be calculated from the equation: 

 P0 = (2.409×1012)

.

R.θ4.e

-22.64θ (1.4) 

where R is relative humidity and θ = 300/ T0 is inverse temperature. 

Photosynthetic rates (hourly, diel, or annual) in response to changing 

irradiance and respiration rates for Laminaria solidungula were obtained from 

published literature (Dunton and Jodwalis, 1988). Although a variety of formulas 

exist for estimating photosynthetic production as a function of incident irradiance, 

the following equation was chosen for its simplicity (Jassby and Platt, 1976): 

 P = Pmax.

tan h. 











I 

Ik (1.5) 
14

where P is calculated production, Pmax is maximum photosynthetic production 

sustained assuming no photoinhibition, Ik is saturation irradiance, and I is 

irradiance available to algae. Although equation (1.5) was first developed for 

phytoplankton, it is valid for kelp because photosynthetic response to changing 

light concentrations is similar for many protists. Only basal blade biomass was 

modeled, as this is where the bulk of photosynthetic production occurs during 

summer (Dunton and Jodwalis, 1988). 

Several assumptions and caveats exist that need consideration prior to 

interpreting results. The base model uses clear-sky irradiance without cloud cover 

influence. Although an arbitrary reduction factor (≤ 1) was applied to simulate 

cloud cover and reduce atmospheric irradiance concentrations, the simulation 

cannot accurately mimic overhead cloud effects (Burd, 2003). Alternatively, 

specific hourly surface or bottom irradiances can be entered into the model to 

provide productivity estimates for explicit conditions. Another limitation of the 

model is its inability to account for photoinhibition, or reduced photosynthetic 

production at high irradiances. Entering data in the equation (Platt et al., 1980): 

 P = Ps

.

(1-e-a)

.

e

-b (1.6) 

where Ps = Pmax, a = α.

I/Ps and b = β.I/Ps represents the effects of photoinhibition. 

Here, α is the initial slope of photosynthetic production per unit irradiance and β

is the slope of photosynthetic production per unit irradiance once any increase in 

irradiance causes a decline in photosynthetic yield. This revealed no evidence of 

photoinhibition in basal blades and little evidence in secondary blades. Thus, the 

difference between using equation (1.5) and equation (1.6), including 

photoinhibition, proved minimal (≈ 2%; Burd, 2003). This test was conducted 

with published data (Dunton and Jodwalis, 1988), and the results could vary 
15

between years. Model results were all calculated using Matlab 6.1 (The 

Mathworks Inc., Natick, Massachusetts, USA). 

 Model reasonability was determined through various artificial simulations 

throughout Stefansson Sound. At each of the 11 sampling sites, the model was 

used to generate daily production, in g C gdw-1 d-1, based on a 60-d summer 

period and three fixed TSS concentrations (1, 10 , and 20 mg L-1). Surface 

irradiance for any production estimate was model-generated and remained 

constant for all tests at all sites. Between fixed TSS concentrations, any 

difference in production could only be attributed to a change in site depth. 

Similarly, production differences between specific sites could only be attributed 

to varying TSS concentrations. These artificial production values were used to 

check model accuracy and determine potential effects of varying TSS 

concentrations on kelp production. 

 The influence of TSS on kelp production was examined over a range of 

insolation values to simulate changes in cloud cover based on in situ light 

measurements recorded in 1990 and 1991 by Dunton et al. Hourly irradiance 

values in 1990 and 1991 were increased or reduced by 10, 20, 30, 40, and 50% to 

create a variety of summer light conditions. Steady increments of TSS (1, 3, 5, 7, 

9, 11, and 13 mg L-1) were entered into the model under each of the light budgets. 

Productivity was then calculated throughout the summer season for all light 

budgets at each turbidity level. These were compared to determine the TSS 

influence on annual production under a variety of seasonal light levels. 

Subsequently, production percent increase over common ranges of increasing 

light levels (50 – 60%, 75 – 85%, 115 – 120%, and 140 – 150% incident 

irradiance for summers 1990 and 1991) was examined under three different TSS 

concentrations (1, 7, and 13 mg L-1). Comparison allowed us to examine the 
16

influence of TSS on set irradiance increases (10%) at various magnitudes of light 

in terms of production percentage. 

 Annual production estimates, in g C m-2 yr

-1, were calculated for each of 

the 11 sites for both 2001 and 2002. This was accomplished using TSS and IOP 

data measured in situ during their respective years. Modeled surface irradiance 

along with average annual site specific TSS concentrations were used as input to 

the production model. Estimated production, g C gdw-1 d-1, was then extrapolated 

to a 60-d summer growth period. Based on previous calculations, assumed 

biomass of 39.3 gdw m-2 for boulder cover 25% or greater and 10.0 gdw m-2 for 

boulder cover between 10-25% were used to convert production units to g C m-2

yr

-1 (Dunton et al., 1982). 

Nutrient Concentrations 

 At six water collection sites (W-1, W-3, DS-11, E-1, Brower-1, and 

Narwhal Island), water for nutrient measurements was sampled in triplicate using 

100 ml plastic bottles during summer 2002 (Figure 3). Water was collected from 

2-m depth using the ac-9. At the offshore site, Narwhal Island, water samples for 

nutrients were collected at 2 and 8 m depth for comparison. Bottles were stored 

in a dark cooler and transported to Endicott Island where they were frozen. Water 

samples were then transferred to UTMSI for nutrient analysis. Nutrient 

concentrations (μM) for NH4

+

, NO2

-

 + NO3

-

, and PO4

3- were determined by 

continuous flow injection analysis using colorimetric techniques described in 

QuikChem Methods manual on a Lachat QuikChem 8000 (Zellweger Analytics 

Inc., Milwaukee, Wisconsin, USA) with a minimum detection level of 0.03 μM. 

Physiochemical Parameters 

 Salinity (psu), depth (m), temperature (oC), and water density (kg m-3) 

were measured using a Seabird 911plus CTD (Sea-Bird Electronics Inc., 
17

Bellevue, Washington, USA). The instrument was towed behind the R/V Proteus 

at a constant speed (4.0 – 6.5 km hr-1) along predetermined transects throughout 

Stefansson Sound (Figure 2). Depths ranged between 0.14 - 0.50 m. 

Measurements were recorded every 0.5 seconds. Data were imported to 

Microsoft Excel and averaged over 1-minute intervals. Mean values were 

assigned to their known geographic coordinates and interpolated across 

Stefansson Sound. 

The CTD was also used to conduct vertical profiles in both 2001 and 

2002. Vertical profiles were generally at 11-preset sampling stations throughout 

the Boulder Patch (Figure 3). These locations included seven dive sites (DS-11, 

E-1, E-2, E-3, L-1, L-2, Brower-1), three western sites (W-1, W-2, W-3), and one 

site located offshore near the barrier islands (Narwhal Island). Data were graphed 

and used to visually trace the vertical distribution of different water mass types. 

Kelp Growth 

 At each of the seven dive sites within the Boulder Patch (DS-11, Brower1, E-1, E-2, E-3, L-1, and L-2), SCUBA divers collected 15-30 individual 

specimens of Laminaria solidungula attached to large cobbles and boulders 

during summers 2001 through 2003 (Figure 3). Samples were placed in prelabeled black bags, transported to Endicott, and processed. Blade lengths from 

every specimen, each corresponding to a different year’s growth (Dunton, 1985), 

were measured and recorded to produce a recent (3-4 yr) growth record of linear 

expansion at each site. A growth year (GWYR) is defined as the period 

beginning 15 November one year and ending 15 November the following year. 

Statistics and GIS 

 IOPs, final PAR measurements, TSS concentrations, chlorophyll a 

concentrations, and annual production estimates were matched with their 
18

respective geographic coordinates and plotted using GIS software ArcView 3.2 

(ERSI, Redlands, California, 1999). ArcView 3.2 allowed point data collected in 

the field to be represented in a media aiding spatial contrast (Alexander and 

Dunton, 2002). Data were interpolated across a polygon of Stefansson Sound, 

including the Boulder Patch, using Spatial Analyst 3.0 extension and Inverse 

Distance Weighting function in ArcView 3.2. Using this technique, entered data 

acts as a reference point with a local influence that diminishes with distance. The 

interpolated values are more similar to data points closest to the respective value 

than those more distant.

All data were analyzed using standard parametric models. Spatial and 

inter-annual significance among IOP, TSS, and chlorophyll measurements were 

determined using a two-way analysis of variance (ANOVA) and Tukey multiplecomparison tests to examine significant differences (p < 0.05) among treatment 

variables using SPSS 10.0 (SPSS Inc., Chicago, Illinois, USA). Variation among 

measured light wavelengths was tested using a Principle Component Analysis 

(Primer-E Ltd, Plymouth Marine Laboratory, Plymouth, UK). 
19

Results

Light Measurements

 Distinct geographic differences in the IOPs occurred throughout 

Stefansson Sound in 2001 and 2002. Similar trends were noted at all quantified 

wavelengths. Furthermore, a principle component analysis indicated variance 

among measured wavelengths to be < 0.001. We chose to display coefficients 

collected at the 676 nm wavelength since this wavelength is most sensitive to 

changes in chlorophyll a (absorption peak is 670 nm) and TSS (Figures 5 – 10). 

Absorption (a) coefficients ranged between 0.096 – 0.153 m-1 and were 

highest along coastal zones between Endicott Island and Satellite Drilling Island 

(SDI), 0.153 and 0.144 m-1, respectively, in 2001 (Figure 5). Increased a values 

were also present in offshore waters overlying the Boulder Patch, particularly in 

areas of greater kelp abundance (>25% rock cover). Site DS-11, historically a site 

with high kelp biomass, had an average a of 0.137 m-1. In 2002, a values were 

lower and ranged between 0.076 – 0.138 m-1. The highest values occurred along 

the coastline between SDI and Pt. Brower, 0.129 m-1 and 0.136 m-1, respectively 

(Figure 6). However, absorption measurements in the Boulder Patch were 

noticeably lower in 2002. The largest value was 0.125 m-1 near E-3, and DS-11 

had an average value of 0.092 m-1, one of the lowest in the entire Boulder Patch. 

 Trends in scattering (b) coefficients were more consistent between years. 

Higher b measurements were always seen in coastal zones near Endicott Island, 

SDI, and Pt. Brower and gradually decreased with distance from the shoreline 

(Figures 7 and 8). In 2001, b values varied between 1.1 – 13.7 m-1 throughout 

Stefansson Sound. High coastal values ranged from 13.7 m-1 off Endicott Island 

to 6.6 m-1 off Pt. Brower. Scattering values in 2002 decreased, ranging between 

0.1 – 7.0 m-1. Coastal values varied between 7.0 m-1 near Endicott Island and 5.1 
20

m

-1 off Pt. Brower. Lowest b values in both 2001 (1.1 m-1) and 2002 (0.1 m-1) 

were found offshore near Narwhal Island. 

Although water transparency varied between the two sampling periods, 

greater light attenuation (k) consistently occurred in coastal zones near Endicott 

Island, SDI, and Pt. Brower, while lower k values were recorded offshore along 

the eastern and northeastern sides of Stefansson Sound (Figures 9 and 10). In 

2001, attenuation ranged from 1.0 - 13.8 m-1 throughout Stefansson Sound (Figure 

9). Measurements were significantly lower in waters overlying the Boulder Patch 

(p = 0.002) than k values from nearshore waters south of the Boulder Patch. 

Values were lowest in offshore waters (1.0 – 2.7 m-1) and increased with 

proximity to the coastline, indicating more turbid water closer to shore. The 

majority of Boulder Patch, including areas with dense kelp populations (> 25% 

rock cover), is found predominantly in offshore waters where attenuation 

measurements were consistently less than 3.6 m-1. 

Much lower attenuation coefficients were recorded in summer 2002 than 

in summer 2001 (Figure 10). The highest values (7.1 – 8.3 m-1) were again 

recorded near Endicott Island, SDI, and Pt. Brower, but most of Stefansson Sound 

had measured attenuations less than 6.0 m-1. Similar to 2001, the Boulder Patch 

was generally characterized by low attenuation measurements (< 2.0 m-1) and had 

significantly lower k values (p < 0.001) than nearshore waters. 

PAR measurements collected during summer 2002 followed a typical 

cyclical pattern with terrestrial surface irradiances peaking between 1200 – 1400 

μmoles photons m-2 s-1 (Figure 11). Surface irradiance maximums were always 

around 14:00 hr. Starting 5 August, surface irradiance dropped dramatically in 

conjunction with a series of overcast days. Maximum PAR reached only about 

600 μmoles photons m-2

 s

-1 during this period. Decreased PAR concentrations 

continued through 8 August when dataloggers were removed. Underwater 
21

sensors also recorded a strong cyclical pattern (Figure 12). The highest PAR 

values measured by the spherical quantum sensors normally occurred around 

14:00 h. and ranged from 100 – 140 μmoles photons m-2 s

-1. Corresponding to the 

sudden change in surface irradiance, a large decrease in underwater PAR occurred 

starting 5 August. Underwater cosine sensors routinely measured downward 

irradiance between 60 – 80 μmoles photons m-2 s

-1 until 5 August when 

downward irradiance declined to levels of 20 – 30 μmoles photons m-2 s

-1. 

Apparent increased measurements in underwater PAR levels occurred on all 

sensors 8 August because dataloggers were removed. Values recorded from both 

surface and underwater PAR sensors are similar to irradiance measurements made 

in Stefansson Sound during previous studies (Dunton, 1990). 

Total Suspended Solids 

Total suspended solids varied greatly throughout Stefansson Sound during 

summer 2001 (2.6 – 24.2 mg L-1). Lower TSS values (2.6 – 2.8 mg L-1) were 

consistently measured in the northeastern sections offshore, near Narwhal Island. 

Higher values (23.0 – 24.2 mg L-1) were located nearshore, adjacent to Endicott 

Island and SDI, respectively. TSS measurements were significantly lower 

throughout the Boulder Patch than nearshore waters (p < 0.001). We observed a 

gradual reduction in TSS seaward of the coast toward the northern reaches of 

Stefansson Sound (Figure 13). Within the Boulder Patch, TSS ranged from 4.2 - 

14.3 mg L-1, with a mean of 6.8 mg L-1. 

Although TSS concentrations were dramatically lower in summer 2002, 

the same trends were observed (Figure 14). Highest concentrations (17.5 – 18.5 

mg L-1) were found near Endicott Island, SDI, and Pt. Brower while lower 

concentrations ( < 1.0 mg L-1) were found offshore near Narwhal Island. Most of 

the Boulder Patch was located in low turbidity water (i.e., TSS < 4.0 mg L-1), 
22

which was significantly lower than coastal waters south of the Boulder Patch (p = 

0.001). In both 2001 and 2002, TSS concentrations were significantly correlated 

with attenuation at 676 nm (R2 ≈ 0.90, p < 0.005; Figure 15). An analysis of 

covariance revealed a significant difference between the two years’ slopes (p < 

0.05) indicating different relationships between TSS concentrations and k values 

measured in Stefansson Sound between years. 

Chlorophyll Concentrations 

Chlorophyll a concentrations ranged from 9.0 to 26.4 μg L-1 in summer 

2001. The highest concentrations were measured near SDI (24.0 – 26.4 μg L-1). 

Interpolated chlorophyll data revealed higher concentrations in nearshore areas 

between Endicott Island and Pt. Brower (Figure 16). Similar chl a concentrations 

were measured in the Boulder Patch at site DS-11 and the surrounding area (19.5 

- 20.8 μg L-1). Other sites in Stefansson Sound exhibited relatively lower 

concentrations (13.0 – 15.0 μg L-1). During summer 2001 there was no 

significant difference between chlorophyll concentrations taken in nearshore areas 

versus the Boulder Patch offshore (p > 0.05). However, a comparison between 

chlorophyll a concentrations and light attenuation in summer 2001 revealed a 

significant relationship (p < .01). 

Chlorophyll a concentrations measured in summer 2002 were 

considerably lower than those measured in 2001. Concentrations ranged from 

0.80 – 7.11 μg L-1 with the highest concentration occurring near SDI (Figure 17). 

An interpolation of chlorophyll data revealed that all other sites within Stefansson 

Sound, including nearshore sampling close to SDI and Endicott Island, exhibited 

chlorophyll a concentrations less than 5.0 μg L-1. Chlorophyll a concentrations 

over the Boulder Patch varied between 2.0 – 4.0 μg L-1. Although Stefansson 

Sound exhibited lower concentrations in summer 2002, a significant difference (p 
23

< 0.01) was discovered between chlorophyll measurements in the Boulder Patch 

and those taken in nearshore waters. In summer 2002, there was no significant (p 

> .05) relationship between chlorophyll a concentrations and light attenuation 

measured in Stefansson Sound. 

Radiative Transfer Equation (RTE) and Productivity Model 

IOP data from summers 2001 and 2002 were entered into the RTE to 

calculate a TSS concentration specific attenuation coefficient [K*

d(λ,H)]. Using 

the K*

d(λ,H), reasonable irradiance estimates for varying TSS concentrations were 

determined. Once incorporated into the productivity model, kelp production was 

estimated at fixed TSS concentrations (1, 10, and 20 mg L-1) for the 11 sampling 

sites over the 60-d open-water period (Table 2). At all sites, greater estimated 

productivity occurred at lower suspended sediment concentrations (1.0 mg L-1). 

The lowest estimated productivities at common TSS concentrations occurred at 

the deepest sites, W-3, W-2, and L-2 (Narwhal Island does not have kelp but was 

included in Table 2 for comparison), while the largest estimated production 

occurred at shallower sites, E-1 and E-2. Average estimated production values 

decreased by an order of magnitude as TSS concentration changed from 1 mg L-1

(0.0205 g C gdw-1 day-1) to 10 mg L-1 (0.0031 g C gdw-1 day-1). Assuming a 60-d 

summer season, this would translate into a change in production from 48.3 g C m2

 yr

-1 to 7.3 g C m-2

 yr

-1 in an area of the Boulder Patch where substratum is 

greater than 25% boulder cover and biomass is equal to 39.3 gdw m-2 (Dunton et 

al, 1982). With exception of the two shallowest sites (E-1 and E-2), increasing 

TSS concentrations to 20 mg L-1 throughout the 60-d summer season would result 

in negative production values as the metabolic costs of respiration exceed 

photosynthetic production. 
24

Using the data from the interpolated TSS contours for summers 2001 and 

2002 (Figures 13 and 14), production values (g C gdw-1 yr

-1) were calculated 

across the Boulder Patch using the unique depths, in situ TSS concentrations from 

the 11 fixed sites (Figure 3), and an arbitrary cloud cover factor of 0.15, chosen to 

match bottom irradiance values measured in 2002. Estimated production values 

(g C m-2

 yr

-1) were calculated using biomass numbers reported in Dunton et al. 

(1982). Biomass was 39.3 gdw m-2 for areas with rock cover greater than 25% 

and 10.0 gdw m-2 for areas with rock cover of 10-25%. Production estimates for 

these sites were then interpolated across the Boulder Patch for summers 2001 and 

2002 (Figures 18 and 19). During 2001, estimated production ranged from 1.2 to 

13.9 g C m-2 yr

-1 (sites E-1 and W-3, respectively). Average production 

throughout the Boulder Patch was 7.2 g C m-2 yr

-1. Highest production values 

were usually in areas with a substratum of > 25% boulder cover. Offshore areas 

tended to have larger productivity estimates despite increased depths. In 2002, 

average production increased to 19.5 g C m-2 yr

-1. Throughout the Boulder Patch, 

estimated production increased and ranged from 2.4 to 33.3 g C m-2

 yr

-1 (sites E-1 

and W-1, respectively). Again, productivity was always highest where boulder 

cover exceeded 25%. The higher estimated production values for 2002 are a 

direct result of the lower TSS concentrations measured during summer 2002. 

Estimated daily production over a range of light regimes and TSS 

concentrations showed that water transparency has a profound effect on kelp 

productivity (Figure 20). At a TSS concentration of 13 mg L-1, production was 

0.0012 g C gdw-1 d-1 at half the measured irradiance of 1990; it steadily increased 

nearly six-fold to 0.0070 g C gdw-1 d-1 at 1.5 times the measured irradiance. In 

contrast, production only doubled (0.033 to 0.07 g C gdw-1 d-1) between the same 

irradiance extremes at a TSS of 1 mg L-1. Similarly, modeled production was 

consistently more sensitive to changes in TSS at lower irradiances. For example, 
25

small (10%) increases in irradiance resulted in a 25 – 30% rise in production at 13 

mg L-1 TSS (Figure 21) at one-half measured insolation. However, at normal or 

above average insolation values, the percent increase in production was only 10 – 

12%. These analyses indicate that kelp production is most sensitive to changes in 

TSS levels, especially during periods of low summer insolation (i.e. high cloud 

cover). 

Nutrient Concentrations 

 Ammonium concentrations varied slightly throughout Stefansson Sound in 

summer 2002. The highest concentrations, 0.26 - 0.29 μM, were measured at DS11 and E-1, respectively (Table 3). Lower NH4

+

 concentrations (≤ 0.10 μM) were 

found in northern Stefansson Sound. 

Nitrite + nitrate (NO2

-

 + NO3

-

) concentrations were slightly higher than 

NH4

+

 concentrations, but were all < 1.0 μM (Table 3). There was little variability 

in NO2

-

 + NO3

-

 measurements throughout Stefansson Sound, with concentrations 

ranging from 0.40 μM at Narwhal Island to 0.59 μM at E-1. With exception of E1, all sites had measured NO2

-

 + NO3

-

 concentrations between 0.40 – 0.48 μM. 

Ortho-phosphate (PO4

3-) displayed the greatest variation of all nutrients. 

Concentrations ranged from 1.42 – 5.11 μM (Table 3). The lowest concentration 

(1.42 μM) was measured at Brower-1, closest to shore. The highest 

concentrations (4.92 and 5.11 μM) were at sites furthest offshore (W-1 and 

Narwhal Island, respectively). 

Physiochemical Parameters 

In summer 2001, surface salinity generally varied between 12.0 – 17.0 

psu. Although day-to-day variability was sometimes considerable, mean surface 

salinity was 12.3 psu with highest values (21.0 – 24.0 psu) recorded off Endicott 
26

Island on 1 August 2001 and the lowest values (7.0 – 7.2 psu) recorded on 3 

August 2001 along the coast between SDI and Pt. Brower. Surface salinity within 

the Boulder Patch was relatively constant (11.0 – 13.0 psu) in 2001, with the most 

northern areas having slightly higher salinities (14.0 – 15.0 psu). Salinity was 

slightly elevated in summer 2002 compared to summer 2001; average surface 

salinity was 16.7 psu and ranged between 16.0 – 19.1 psu throughout the Boulder 

Patch. Generally, surface salinity in Stefansson Sound varied between date rather 

than site. At all sites except Narwhal Island, surface salinity was highest on 2 

August 2002 and lowest on 23 July 2002. 

In summer 2001, the average bottom salinity was 22.3 psu and ranged 

between 18.1 – 30.6 psu. Similar readings were taken in summer 2002; average 

bottom salinity was 23.3 psu and ranged between 16.7 – 30.0 psu. In both years, 

highest benthic salinities were recorded at offshore sites (Narwhal Island and W3), which were also the deepest sites (8.2 and 6.6 m, respectively). Lowest 

average bottom salinities were measured further inshore, near or at sites E-3 and 

E-2. Daily fluctuations (2 - 3 psu) occurred mainly in nearshore sites, while 

deeper, offshore sites remained relatively constant over the study’s duration. This 

trend was observed in both summer 2001 and 2002. 

Generally, surface water temperature was elevated close to shore and 

consistently decreased with increasing distance seaward. In both years, 

temperatures nearshore were highest, approximately 6.9o

C in 2001 and 7.2°C in 

2002. Water temperatures were lower in northern Stefansson Sound, about 1.2o

C, 

in both 2001 and 2002. Average sea surface temperature increased throughout the 

Boulder Patch from 4.0°C in 2001 to 4.8°C in 2002. Though spatial trends were 

seen in both years, daily fluctuations were also observed both summers, as much 

as 3.0°C throughout the Boulder Patch in 2002. Average sea surface temperature 
27

was warmest on 3 August 2002 (average 7.3°C) and coldest on 26 July 2002 

(3.0°C). 

 In 2001, bottom temperatures varied between -0.9 – 2.7°C. The average 

benthic temperature was 0.8°C. Bottom temperatures were elevated in 2002, 

ranging between -1.2 – 4.4°C and averaging 1.6°C. In both years, coldest bottom 

temperatures were always measured at Narwhal Island but otherwise did not show 

any geographic trends. Daily fluctuations between bottom temperatures were 

prominent. In direct contrast with 2002 surface temperatures, coldest bottom 

temperatures were generally measured on 3 August 2002 (0.2°C) and warmest on 

26 July 2002 (3.2°C). 

Vertical profiles conducted in 2001 and 2002 revealed the dynamic nature 

of Stefansson Sound. Daily changes in both temperature (°C) and salinity (psu) 

were evident throughout the water column, both at shallow inshore sites (E-1; 

Figure 22) and at deeper offshore sites (Narwhal Island; Figure 24). Most vertical 

profiles showed a water column predominantly stratified into two distinct layers 

(Figures 22 - 24). Despite these tendencies, atmospheric conditions and water 

current dramatically affect water column properties in the area. Comparisons 

between dates with heavy stratification at similar sites revealed daily temperature 

changes between 0.0 and 5.0°C and salinity changes between 0.0 and 10.0 psu. 

On other dates (eg. 26 July 2002) the water column is mixed with little 

temperature or salinity variation. Daily variations in water column properties are 

a likely indication of turbidity change, ultimately affecting daily kelp production 

values. 

Kelp Growth 

 Annual Laminaria solidungula blade elongation displayed large spatial 

and temporal variability. Kelp collected in 2001 at DS-11 had an annual blade 
28

elongation of 23.0 – 37.0 cm, values comparable to previous studies (Dunton, 

1990; Martin and Gallaway, 1994). A mean blade elongation of 23.5 cm 

characterized the most recent period of growth (GWYR 2000; November 2000 to 

August 2001) at all sites (Figure 25). During GWYR 2000, five of seven sites 

had an average increase blade length of 20.0 – 26.0 cm. The other two sites, E-2 

and DS-11, grew an average of 12.1 and 37.0 cm, respectively. Specimens at DS11 consistently had the highest annual elongation. An interannual comparison 

showed that growth was lowest during the 1999-2000 (GWYR 1999) growth year. 

With exception of DS-11, blade elongation did not exceed 10.0 cm during this 

year, suggesting very poor water transparency conditions in summer 1999. 

 Kelp blade length measurements from specimens collected in summer 

2002 confirmed observations from summer 2001 (Figure 26). For example, mean 

blade elongation for GWYR 2000 was 23.8 cm (compared to 23.5 cm in 2001). 

In addition, average blade elongation ranged from 20.0 to 26.0 cm at four sites in 

2001; at sites E-2, L-2, and DS-11, blade growth for GWYR 2000 was 12.4, 27.9, 

and 34.3 cm, respectively. We again noted low linear growth during the 1999-

2000 growth period, with only specimens collected from DS-11 having an 

average blade elongation greater than 14.0 cm. The mean blade elongation 

measured at all sites in GWYR 2001 was 33.8 cm. Additionally, average linear 

growth was greatest at all sites during GWYR 2001 compared to previous years, 

and ranged from 39.4 cm at Brower-1 to 23.7 cm at L-2. 

 Summer 2003 specimens exhibited similar trends as those from summers 

2001 and 2002. Blade elongation for GWYR 2002 ranged from 20.0 – 35.2 cm 

and had an average 28.1 cm (Figure 27). Highest annual linear growth occurred 

at sites DS-11 and E-1 (35.2 and 33.2 cm, respectively). Unlike other years, sites 

L-1, L-2, and Brower-1 had reduced elongation compared to other sites. Average 

elongation for GWYR 2002 (28.8 cm.) was second only to GWYR 2001 (38.8 
29

cm.). Only specimens from DS-11 and E-2 had higher average growth rates in 

GWYR 2002 than GWYR 2001. Once again GWYR 1999 exhibited reduced 

elongation compared to other years, and only kelp from DS-11 had elongation 

measurements greater than 14.0 cm. Average elongation for GWYR 2000 was 

21.0 cm, compared to 23.8 cm in GWYR 2002 and 2003. 
30

Discussion

Light Measurements

 Each inherent optical property measured demonstrated unique trends in 

Stefansson Sound. Absorption (a), typically affiliated with phytoplankton or 

dissolved organics (Van Duin et al., 2001; Pegau, 2002), was elevated in waters 

surrounding Endicott Island and the Boulder Patch in 2001 (Figure 5). Relatively 

uniform chlorophyll concentrations throughout Stefansson Sound suggest that 

colored dissolved organic matter (CDOM) may serve an important role. Pegau 

(2002) found that CDOM could increase arctic nearshore water’s absorption 

properties by 30% in the top 10 m. Highest absorptions were located in areas of 

the Boulder Patch with greater percentages of rock cover. In previous studies, 

kelp biomass was routinely higher in areas with the most rock cover (Dunton et 

al., 1982; Busdosh et al., 1985). This may cause higher humic substance 

concentrations, which are also affiliated with CDOM (Van Duin et al., 2001). In 

2002, a was highest in nearshore waters between Pt. Brower and SDI (Figure 6). 

Increased values occurred over the Boulder Patch as well, but predominantly in 

areas of low rock cover (E-1, E-2, and E-3). 

 Typically, scattering (b) is affiliated with suspended sediments and 

organic debris (Van Duin et al., 2001). In 2001, b was greatest nearshore and 

gradually decreased with increasing distance from the shoreline (Figure 7). A 

similar trend was observed in 2002, although values were substantially lower 

(Figure 8). Increased b near the coast probably results from greater TSS 

concentrations. As seen in Figures 13 and 14, TSS concentrations are typically 

highest nearshore. Shallow depths, erosion, and terrestrial runoff are probable 

causes of elevated suspended sediment and higher subsequent b values. 

Scattering values were substantially greater than absorption values throughout 

Stefansson Sound (b:a > 30), indicating that the system is optically dominated by 
31

unconsolidated sediments suspended in the water (Kirk, 1981; 1994). Beam 

attenuation (k) interpolations were similar to those for b (Figures 9 and 10), and 

are indicative of high b:a ratios. 

Total Suspended Solids

 TSS interpolations throughout Stefansson Sound may reflect higher water 

turbidity characteristic of eroding coastlines. TSS levels measured in 2001 (22.0 

– 24.2 mg L-1) along SDI and Endicott Island shorelines were often three to four 

times higher than those at more seaward locations. TSS concentrations were 

dramatically lower in 2002, but nearshore concentrations were still significantly 

higher than offshore waters. The Boulder Patch resides predominately in areas 

offshore with significantly lower suspended sediment concentrations. 

 Results show a strong relationship between water column TSS and light 

attenuation at all measured wavelengths. In both years, high attenuation 

coefficients and consequent low light penetration were found near SDI and 

Endicott Island. These appear to correlate with elevated TSS concentrations 

(compare Figures 9, 10, 13, and 14). Low attenuation (< 3.0 m-1), or high light 

penetration, corresponded directly to low TSS levels in northern and eastern 

Stefansson Sound. Offshore waters, typically affiliated with lower TSS values, 

had higher light penetration through the water column. 

Although there was a strong correlation between TSS and attenuation in 

both years (R2

 = 0.89, p < 0.05), an ANCOVA revealed that the two slopes were 

not statistically similar. This indicates a different, albeit strong, relationship 

between TSS and the IOPs between summers 2001 and 2002. There are several 

possible explanations. Suspended solids include both inorganic and organic 

detritus that contribute mainly to light scattering but have different optical 

properties. Zimmerman and Maffione (2000) calculated absorption by inorganic 
32

particles in coastal zones to be an order of magnitude lower than values reported 

for organic detritus (Roessler et al., 1989). Any change in the (in)organic 

composition of suspended material could alter the relationship between IOPs and 

suspended material. Several studies have demonstrated the impacts of particle 

characteristics on optical properties (Blom et al., 1994; Best et al., 2001; Van 

Duin et al., 2001). Particle size and shape affect fall velocity and the subsequent 

time particles spend attenuating light in the water column. According to Stoke’s 

law, the fall velocity of any sediment particle is proportional to its square 

diameter and relative density. Absorption and scattering coefficients are also 

proportional to the square diameter (Van De Hulst, 1981; Kirk, 1983), and 

relative density is related to the internal ratio of organic to inorganic material, 

which influences optical properties as well (Zimmerman and Maffione, 2000). 

Therefore, significant changes to the amounts of various sized particles may alter 

IOPs and their relationship to TSS concentrations. Van Duin et al. (2001) noted 

that underwater light conditions in shallow water bodies are predominantly 

controlled by sedimentation and wind driven resuspension, with changes in wind 

direction and/or speed causing the majority of temporal variability. Considering 

the varying and abrupt weather patterns in Stefansson Sound, annual change in 

suspended sediments’ optical properties is expected. 

Chlorophyll Concentrations

 Chlorophyll a concentrations changed dramatically between summers 

2001 and 2002 even though measurements remained relatively constant 

throughout the Boulder Patch during their respective years. In 2001, elevated 

concentrations (16.0 – 26.4 μg L-1) typical of summer open water conditions in 

Stefansson Sound were measured in nearshore waters (Schell et al., 1982). 

Measurements throughout the Boulder Patch and further offshore were reduced 
33

although not significantly (p > 0.05) different from chlorophyll concentrations 

along the coast. Although chlorophyll a concentrations never reached spring 

bloom conditions common in arctic coastal areas (Alexander, 1974), August 

sampling occurred well after initial ice cover melt in spring and subsequent 

nutrient depletion by phytoplankton. Phytoplankton populations likely increase 

rapidly following ice cover melt in late spring to early summer and gradually 

decrease throughout summer with nutrient depletion (Schell et al., 1982). 

 In 2002, chlorophyll a concentrations were considerably lower than 2001. 

Values never exceeded 7.2 μg L-1, and most of Stefansson Sound had 

concentrations between 2.0 – 4.0 μg L-1, which were lower than those previously 

recorded (Schell et al., 1982). Chlorophyll a concentrations within the Boulder 

Patch and surrounding offshore waters were significantly (p < 0.01) less than 

those nearshore. Low phytoplankton abundance in summer 2002 may be 

attributed to reduced freshwater surge from the Sagavanirktok River Delta (Figure 

1; Trefry, 2003). Annual outflow from the delta could be a primary source of 

nutrient enrichment to Stefansson Sound, and reduction of outflow may 

substantially affect spring and summer phytoplankton populations. 

 Chlorophyll a and light attenuation (k) were significantly correlated (p < 

0.01) in summer 2001 but not in summer 2002 (p > 0.05). These results suggest 

that greater phytoplankton biomass throughout Stefansson Sound in summer 2001 

had a significant impact on underwater light conditions while lower 

phytoplankton biomass in summer 2002 had little impact. Although 

phytoplankton contribute to absorption and scattering (Van Duin et al., 2001), 

their cumulative effect on light attenuation may vary with biomass and irradiance 

(i.e. higher biomass may have more effect at lower irradiances). Future 

chlorophyll measurements in conjunction with optical monitoring may be useful 
34

in determining relative importance of phytoplankton to underwater light 

conditions in the Boulder Patch. 

Radiative Transfer Equation (RTE) and Productivity Model

A concentration specific attenuation coefficient [K*

d(λ,H)] was developed 

utilizing IOP and TSS data measured in situ. The coefficient allowed reliable 

estimation of benthic irradiance in systems where suspended sediments are the 

dominant attenuation source (Maffione et al., 2003). Once K*

d(λ,H) was 

incorporated into the productivity model, production was estimated using 

previously published photosynthesis vs. irradiance curves (Dunton and Jodwalis, 

1988) and calculated PAR levels reaching the canopy. To ensure reasonable 

estimates, production was calculated at 11 sampling sites (Table 2) under 

matching abiotic conditions throughout Stefansson Sound. Constant TSS 

concentrations and surface PAR ensured that the only variable affecting light 

attenuation between sites is depth (i.e. volume of water absorbing photons 

between the surface and bottom). 

The model results showed that shallower sites always had greater daily 

productivities. Additionally, daily production measurements at all sites decreased 

as TSS was increased. These results verified model reasonability and indicate the 

tremendous influence TSS can have on annual kelp production throughout the 

Boulder Patch. Under similar photic conditions, an increase in TSS from 1.0 mg 

L-1 to 10.0 mg L-1 (TSS values within ranges measured during summers 2001 and 

2002) decreased estimated daily production an order of magnitude. At deeper 

sites, an increase in TSS to 20.0 mg L-1 resulted in negative daily production 

estimates as respiration exceeded photosynthetic production. 

Our results clearly demonstrate the important roles of TSS and incident 

solar irradiance in regulating kelp production. Based on hourly PAR data 
35

collected in 1990 – 1991 under a range of TSS levels, we found that increases in 

modeled daily production coincided with increased surface irradiance, but 

changes were greatest at lower TSS concentrations. Under higher TSS levels, 

there was little change in actual production even under intense surface light 

regimes (Figure 20). These results suggest that changes in surface irradiance, will 

be most important when TSS concentrations are less than 5 mg L-1 (Figure 20). 

At lower TSS concentrations, the photosynthetic maximum in adult kelp, 

Pmax (42 μmols m-2 s

-1; Dunton and Jodwalis, 1988), can be attained at lower 

surface irradiance levels. As surface light levels continuously rise, hours of 

saturating irradiance (Hsat) climb steadily as well. Any increase in surface 

irradiance beyond Pmax has no added effects on production; the excess photons are 

unused. Our productivity model does not account for photoinhibition (reduced 

photosynthetic production at higher PAR levels). According to Dunton and 

Jodwalis (1988), daily production could be inhibited beyond 80 μmols m-2 s

-1. 

Therefore, kelp production at lower TSS values would continually increase, albeit 

at reduced amounts, under elevating irradiance conditions until there is an 

eventual production loss from photoinhibition. However, photoinhibition is 

unlikely to occur very often, since high TSS loads normally prevent light from 

reaching levels above 80 μmols photons m-2 s-1 for extended periods. These 

results suggest that changes in TSS concentrations will significantly affect annual 

kelp production in the Boulder Patch over a broad range of summer light regimes. 

Using a fixed TSS concentration, daily production can vary substantially 

based on a combination of surface irradiance and site depth. However, 

interpolations suggest that TSS concentrations are rarely similar between 

nearshore and offshore locations. Offshore sites, although located at greater 

depths, routinely had lower suspended sediment concentrations and higher 

estimated annual productivities. For instance, estimated production for both 
36

summer periods was greater at DS-11, 0.19 g C gdw-1 (summer 2001) and 0.78 g 

C gdw-1 (summer 2002), than E-2, 0.16 g C gdw-1 (summer 2001) and 0.27 gdw-1

(summer 2002), despite DS-11’s deeper location. Greater water transparencies, as 

a result of lower TSS concentrations, facilitate higher irradiance to the bottom at 

DS-11. Site E-2, although shallower, receives less light due to higher TSS 

concentrations, which results in less production. This indicates the importance of 

TSS concentrations during the summer open-water period in determining total 

annual production throughout the Stefansson Sound Boulder Patch. 

Interpolations of biomass dependent production (g C m-2 yr

-1) indicate 

greater kelp bed production in offshore areas of the Boulder Patch that are 

characterized by >25% boulder cover. Regions of 10% and 25% benthic rock 

cover have less solid substratum needed for kelp establishment, which has 

significant effects on production per unit area. As a result, the interpolated 

productivity estimates (Figures 18 and 19) were higher in areas of greater boulder 

cover. This demonstrates the importance of biomass measurements in providing 

accurate kelp production estimates. Productivity interpolations completed for this 

study are based on one-time estimates of biomass reported by Dunton et al. 

(1982). Therefore, the accuracy of these production estimates is difficult to 

assess. Although estimated production values are slightly higher than those 

measured in previous studies (Dunton and Schell, 1986), the lack of TSS or 

canopy light measurements for years of measured in situ production makes direct 

comparison impossible. 

Nutrient Concentrations

 Kelp growth in arctic nearshore environments has been directly linked to 

seasonal nutrient fluxes (Chapman and Lindley, 1980; Dunton et al., 1982; 

Dunton and Schell, 1986; Henley and Dunton, 1997). In many arctic kelp beds, 
37

including the Boulder Patch, nutrients are readily available in the winter but are 

low to undetectable in the summer (Dunton et al., 1982; Schell et al., 1982; 

Dunton and Schell, 1986; Henley and Dunton, 1997). Nutrient concentrations in 

summer 2002 were very low and agreed with previously published results from 

Stefansson Sound (Schell et al., 1982; Dunton and Schell, 1986). Schell et al. 

(1982) found that most available form of inorganic nitrogen, NO2

-

 + NO3

-

 , was 

usually undetectable but was measured as high as 0.50 μM. Inorganic nitrogen 

concentrations usually begin to rise in early November following the summer 

open water period (Chapman and Lindley, 1980). Ortho-phosphate 

concentrations measured in 1980 ranged from undetectable to 0.60 μM (Schell et 

al., 1982), dramatically lower than ortho-phosphate concentrations measured in 

summer 2002. 

Physiochemical Parameters

 Salinity throughout Stefansson Sound was comparable to values 

previously recorded (Schell et al., 1982). In 1980, surface salinity in the Beaufort 

Sea ranged between 13.8 – 29.2‰ and averaged 23.3‰. Salinity further inshore 

and in the Boulder Patch, was less than 20.0‰. Similar measurements were 

recorded in Stefansson Sound in 1981 (Schell et al., 1982). Surface salinity in 

2001, between 11.0 – 15.0 psu, corresponded to previously published 

measurements (Barnes et al., 1977; Schell et al., 1982; Dunton, 1990). In 2002, 

surface salinity in the Boulder Patch increased to 16.0 – 19.1 psu. Higher 

salinities could be attributed to the reduced outflow of the Sagavanirtok River 

Delta in spring 2002 (Trefry, 2003), less freshwater to dilute surface salt 

concentrations in Stefansson Sound. 

 Bottom salinities varied little between 2001 and 2002 and coincided with 

values recorded in 1980 and 1981 (Schell et al., 1982). In previous years, salinity 
38

in Stefansson Sound was consistently measured at a depth of 6.0 m, and all values 

were between 26.0 – 30.8‰. Although there was a broader range of bottom 

salinities in 2001 and 2002 (16.7 – 30.6 psu), this difference could be attributed to 

depth and measurement location. Many sites in 2001 and 2002 were located near 

the coast (i.e. E-3, E-2, etc.) and did not exceed 6 m in depth. Shallower depths 

and proximity to shore likely reduced benthic salinities at deeper, offshore sites 

(DS-11, Narwhal Island). 

 Both surface and bottom temperatures from 2001 and 2002 coincided with 

previous studies. During the summer open-water period, temperatures have been 

reported between 0.0 – 7.0°C on the surface (Dunton, 1984; Dunton, 1985) and -

1.0 – 1.5°C on the bottom (Dunton and Jodwalis, 1988; Dunton, 1990). 

Vertical profiles results demonstrate the dynamic nature of Stefansson 

Sound. Relatively shallow waters in Stefansson Sound are heavily influenced by 

local weather patterns, and several studies have implicated local weather 

conditions to changes in subsurface conditions (Dunton et al., 1982; Schell et al., 

1982; Busdosh et al., 1985; Dunton and Jodwalis, 1988; Dunton, 1990; Martin 

and Gallaway, 1994). When stratified, the water column in Stefansson Sound 

appears to form two distinct layers (Figures 22 – 24). Comparison between 

previous studies’ salinity and temperature data at several depths indicates a 

similar trend (Dunton et al., 1982; Schell et al., 1982). Vertical structure of the 

water column in Stefansson Sound should be an emphasis of further study. 

Optical properties of water in the Boulder Patch may change with various density 

layers. Additionally, reduction of downward irradiance from either reflection or 

refraction as light passes through two distinct water masses is still unknown. 
39

Kelp Growth

Linear growth data from Boulder Patch kelp beds provide a valuable 

baseline for monitoring yearly changes in Laminaria solidungula productivity. 

Current growth data are comparable to previous studies (Dunton, 1990; Martin 

and Gallaway, 1994) and indicate that the Boulder Patch has maintained kelp bed 

populations since the construction of the Endicott facility in 1985 (Martin and 

Galloway, 1994). The substantial decrease, at all sites except DS-11 in kelp blade 

elongation in the 1999 growth year may reflect reduced water transparency during 

summer 1999, especially near the shoreline. High light attenuation from elevated 

TSS levels was most likely the result of a series of major storm events that 

occurred 18 - 24 August 1999 and again on 2 - 6 October 1999 (Weingartner and 

Okkonen, 2001; www.wunderground.com). Consistently high blade elongation 

rates recorded in L. solidungula plants collected from DS-11 reflect both the 

offshore location of this site relative to the other sites and its higher percentage of 

rock cover (Martin and Gallaway, 1994). Greater rock cover minimizes sediment 

resuspension. Despite apparently poor water transparency conditions in summer 

1999, plant growth rebounded to pre-1999 rates in the 2000 growth year. 

Blade elongation data from 2000 to 2002 reflect lower TSS levels and 

higher water transparency at offshore sites. Almost all sites, except L-2, had an 

increase in annual linear growth during the 2001 GWYR compared to previous 

years (Figures 26 and 27). Decreased sediment concentrations measured 

predominantly offshore during summer 2002, which increased productivity 

estimates for 2002, agreed with annual linear growth measurements taken from 

offshore sites (DS-11, E-3, and E-2) in 2003. Other sites maintained similar blade 

elongations in GWYR 2002 and GWYR 2001 except sites L-1 and Brower-1 and 

may reflect the sites nearshore locations, shallow depths, and reduced boulder 

cover. Increased blade elongation from GWYR 2002 and 2001 suggest that a 
40

combination of high surface irradiance and/or low average TSS concentrations 

were present during those two summer seasons. 

Model Verification Based on Kelp Growth, TSS, and Irradiance Measurements

A large record, encompassing five years (1980 – 1984) and over 800 

observations, was used to determine the quadratic relationship between basal 

blade length and basal blade dry weight (Figure 28). Using this relationship, 

basal blade lengths from DS-11 for 1990 and 1991 (22.9 and 23.6 cm 

respectively; Dunton et al., 1992), were converted to dry weights (2.03 and 2.13 

g). Assuming 30% of dry weight is carbon (Dunton and Schell, 1986), total 

carbon produced in summers 1990 and 1991 would be 0.61 and 0.64 g for an 

averaged sized specimen, respectively. For kelp at DS-11, calculated productivity 

from the model using hourly surface irradiance measurements from summers 

1990/1991 and modeled TSS concentrations from 2001 was 0.0055 and 0.0054 g 

C gdw-1 d-1 for 1 g dry weight, respectively. Over the 120-d summer growth 

season, the model predicts summer production estimates of 0.64 and 0.66 g C, 

very similar to calculated production based on blade elongation data (Figure 29). 

Although in situ TSS data was not measured in summers 1990 and 1991, the 

proximity of production estimates, using modeled TSS from 2001, indicates the 

potential accuracy of the productivity model using in situ hourly irradiance values 

collected within 7 km of the study site (Dunton et al., 1992). 

Subsequently, we compared modeled summer production (g C) with blade 

elongation data for 2001 and 2002 using the same approach. Integrated values of 

surface insolation during the same summer periods in 1990, 1991, and 2002 (28 

July to 8 August) produced daily averages of 28.90, 24.61, and 28.87 mol photons 

m

-2 d-1 respectively. Based on the excellent agreement between the measured 

insolation values in 1990 and 2002, we chose to use the 1990 surface insolation 
41

values to estimate kelp production in GWYR 2001 and 2002. For GWYR 2001, 

mean blade elongation at DS-11 was 34.8 cm based on measurements collected in 

2002 and 2003. Using the quadratic relationship between frond length and dry 

weight, along with 30% carbon content of dry weight (Dunton and Schell, 1986) 

1.21 g C was produced during GWYR 2001. Using TSS concentrations measured 

at DS-11 during summer 2001 and hourly surface irradiance measurements from 

1990, modeled production was 1.38 g C (Figure 29). Summer 2002 production 

estimations were not as accurate. Average blade length for DS-11 was 35.2 cm, 

which equates to 1.24 g C produced over GWYR 2002. However, model 

estimates of production for GWYR 2002 were 5.18 g C (Figure 29). 

The large discrepancy between measured and modeled productivity for 

GWYR 2002 is likely related to low TSS values that are not representative of the 

entire summer. TSS concentrations measured during a two-week period in 

summer 2002 (≈ 3.0 mg L-1 average at DS-11) were three times lower than those 

measured over the same period in summer 2001 (≈ 9.5 mg L-1 average at DS-11; 

Figures 13 and 14). However, average blade lengths at DS-11 for GWYR 2002 

(35.2 cm; Figure 27) were nearly the same as blades lengths for GWYR 2001 

(34.8 cm; Figure 26 and 27). This implies that overall light conditions at DS-11 

between summers 2001 and 2002 were not significantly different. TSS 

concentrations may have risen dramatically in summer 2002 following the 

conclusion of sampling in early August. River discharge studies indicate that 

some rivers in 2002 refroze after initial ice breakup, a rare event. This 

phenomenon decreased river discharge rates, affecting normal TSS loads, during 

our sampling regime in summer 2002 (Trefry, 2003). Photoinhibition may have 

also played a role since resulting bottom irradiance may have been above the 

photoinhibition point, 80 μmoles photons m-2 s-1 (Dunton and Jodwalis, 1988), 

much of the time. Our model does not account for the losses in production due to 
42

photoinhibition. Finally, production equivalent to over 5 g C for an average-sized 

plant would translate into an average basal blade length of over 60 cm (Figure 

28). Kelp of such size were not observed at DS-11 in 2003, indicating that 

average TSS values for summer 2002 were probably underestimated. 

In conclusion, TSS can have variable influences on annual productivity in 

the Stefansson Sound Boulder Patch. Low summer TSS concentrations will 

usually result in high annual kelp productivity by increasing the number of hours 

Laminaria solidungula can sustain Pmax. Any increase in TSS will result in 

decreased production. Under certain conditions, substantial TSS concentrations 

and/or low surface irradiance may result in negative production rates, where the 

metabolic costs of respiration exceed photosynthesis. Comparison of model 

output with in situ blade elongation data indicates that the model does provide 

reasonable estimates of productivity, but is extremely sensitive to accurate 

measurements of TSS. Although blade elongation data is subject to less 

discrepancy than model derived production estimates, using a model precludes 

extra logistical efforts needed for specimen collection (i.e. SCUBA needs, trained 

personnel). Time spent, costs, and effort are likely comparable between the two 

methods. Resources spent for underwater collection would be replaced by efforts 

filtering water and adjusting model calculations. Overall, future monitoring 

should probably incorporate both methods; collecting kelp periodically (every 2-3 

years) and using blade elongation data to verify model derived production 

estimates for previous years’ production. 

Future monitoring efforts should continue to focus on the critical linkages 

between light attenuation (based on the IOP’s of the water column), continuous 

surface irradiance, TSS, and site specific kelp biomass and annual growth. Using 

these measurements, we can provide nearly instantaneous estimates of kelp 

productivity using the model we have developed. Site specific biomass would 
43

contribute to more accurate estimates of kelp production per unit area across 

Stefansson Sound and allow more precise comparisons of kelp production in 

response to both natural and anthropogenic events. 
44

Acknowledgements

We thank the MMS Scientific Review Board, whose constructive criticism 

of earlier drafts of this report has been very helpful. We also express our sincere 

appreciation to the following BP employees for their logistical support and for 

maintaining a safe working environment at BP Endicott: Bill Streever, Stan Gates, 

Troy Weiss, Henry Harrington, Jerry Ferguson, Rocky Jones, Royce O’Brien, and 

Vince Volpe. We thank Steve Schreiber and Brian Stevens for the continuous use 

of their water treatment lab and Ted Dunton and John Dunton for their 

mechanical expertise. We especially appreciate the kindness and hospitality 

extended to us by the entire Endicott facility of BP Exploration, Alaska. Without 

the joint financial and logistical support provided by BP and MMS, this study 

would not have been possible. 
45

Literature Cited

Alexander, V. 1974. Primary productivity regimes of the nearshore Beaufort Sea, 

with reference to potential roles of ice biota. pgs. 609-635. In: J.C. Reed 

and J.E. Sater (eds.), The Coast of Shelf of the Beaufort Sea. Arctic Inst. 

N. Am., Arlington, VA. 

Alexander, H.D. and K.H. Dunton. 2002. Freshwater inundation effects on 

emergent vegetation of a hypersaline salt marsh. Estuaries 25: 1426-1435. 

Barnes, P.W., E. Reimnitz, and D. McDowell. 1977. Current meter and water 

level observations in Stefansson Sound, Summer, 1976. In: Miscellaneous 

Hydrologic and Geologic Observations on the Beaufort Seas Shelf, 

Alaska. U.S. Geological Survey open file report 77-477. B1-B7. 

Best, E.P.H., C.P. Buzzelli, S.M. Bartell, R.L. Wetzel, W.A. Boyd, R.D. Doyle, 

and K.R. Campell. 2001. Modeling submersed macrophyte growth in 

relation to underwater light climate: modeling approaches and application 

potential. Hydrobiologia 444: 43-70. 

Blom G., E.H.S. Van Duin, and L. Lijklema. 1994. Sediment resuspension and 

light conditions in some shallow Dutch lakes. Water Science and 

Technology 30: 243-252. 

Burd, A.B. 2003. Boulder Patch kelp model: draft report. Technical report, 

Department of Marine Sciences, University of Georgia. 

Busdosh, M., C.L. Beehler, G.A. Robilliard, and K.R. Tarbox. 1985. Distribution 

and abundance of kelp in the Alaskan Beaufort Sea near Prudhoe Bay. 

Arctic 38(1): 18-22. 

Butler, B. 1998. “Precipitable water at kp – 1993-1998”. MMA Memo No. 238, 

1998. 

Chapman, A.R. and J.E. Lindley. 1980. Seasonal growth of Laminaria 

solidungula in the Canadian High Arctic in relation to irradiance and 

dissolved nutrient concentrations. Marine Biology. 57: 1-5. 
46

Di Toro, D.M. 1978. Optics of turbid estuarine waters: approximations and 

applications. Water Research 12: 1059-1068. 

Dunton, K.H., E. Reimnitz, and S. Schonberg. 1982. An arctic kelp community in 

the Alaskan Beaufort Sea. Arctic 35(4): 465-484. 

Dunton, K.H. 1984. An annual carbon budget for an arctic kelp community. In: P. 

Barnes, D. Schell, and E. Reimnitz (eds.). The Alaskan Beaufort Sea –

Ecosystems and Environment. Orlando: Academic Press. 311-326. 

Dunton, K.H. 1985. Growth of dark-exposed Laminaria saccharina (L.) Lamour 

and Laminaria solidungula (J.) Ag. (Laminariales, Phaeophyta) in the 

Alaskan Beaufort Sea. Journal of Experimental Marine Biology and 

Ecology 94: 181-189. 

Dunton, K.H. 1990. Growth and production in Laminaria solidungula: relation to 

continuous underwater light levels in the Alaskan High Arctic. Marine 

Biology 106: 297-304. 

Dunton, K.H. and D.M. Schell. 1986. A seasonal carbon budget for the kelp 

Laminaria solidungula. Limnology and Oceanography 42(2): 209-216. 

Dunton, K.H. and C.M. Jodwalis. 1988. Photosynthetic performance of Laminaria 

solidungula measured in situ in the Alaskan High Arctic. Marine Biology

98:277-285. 

Dunton, K.H., S.V. Schonberg, and L.R. Martin. 1992. Linear growth, tissue 

density, and carbon content in Laminaria solidungula. In: Endicott

Beaufort Sea Boulder Patch Monitoring Program (1984 – 1991). Final 

Report: LGL Ecological Research Associates, Inc. 3-1. 

ESRI, Inc. 1999. ArcView 3.2. Redlands, California. 

Gregg W.W. and K.L. Carder. 1990. A simple spectral solar irradiance model for 

cloudless marine atmospheres. Limnology and Oceanography 35: 1657-

1675. 
47

Henley, W.J. and K.H. Dunton. 1995. A seasonal comparison of carbon, nitrogen, 

and pigment content in Laminaria solidungula and L. saccharina

(Laminariales, Phaeophyta) in the Alaskan Arctic. Journal of Phycology

31: 325-331. 

Henley, W.J. and K.H. Dunton. 1997. Effects of nitrogen supply and seven 

months of continuous darkness on growth and photosynthesis of the arctic 

kelp, Laminaria solidungula. Limnology and Oceanography 42(2): 209-

216. 

Hooper, R.G. 1984. Functional adaptations to the polar environment by the arctic 

kelp, Laminaria solidungula. British Phycological Journal 19: 194. 

Hopkins, D.M. 1979. The Flaxman formation on northern Alaska: record of early 

Wisconsinan shelf glaciation in the High Arctic? “XIVth Pacific Science 

Congress, Khabarovsk”. Abstracts volume: 15-16. 

Jassby, A. and T. Platt. 1976. Mathematical formulation of the relationship 

between photosynthesis and light for phytoplankton. Limnology and 

Oceanography 21: 540-547. 

Kirk, J.T.O. 1981. Monte Carlo study of the nature of the underwater light field 

in, and the relationships between optical properties of, turbid yellow 

waters. Australian Journal of Marine Freshwater Research 32(4): 517-

532. 

Kirk, J.T.O. 1983. Light and Photosynthesis in Aquatic Ecosystems. Cambridge 

University Press, Cambridge. 12-13. 

Kirk, J.T.O. 1984a. Dependence of relationship between inherent and apparent 

optical properties of water on solar altitude. Limnology and Oceanography

29(2): 350-356. 

Kirk, J.T.O. 1984b. Attenuation of solar radiation in scattering-absorbing waters: 

a simplified procedure for its calculation. Applied Optics 23(21): 3737-

3739. 

Kirk, J.T.O. 1994. Characteristics of the light field in highly turbid waters; A 

Monte Carlo study. Limnology and Oceanography 39(3): 702-706. 
48

Kirst, G.O. and C. Wiencke. 1995. Ecophysiology of polar algae. Journal of 

Phycology 31: 181-199. 

Kondratyev, K.Y. 1954. Radiant solar energy [In Russ.]. Leningrad. [cited after 

Kirk (1983)]. 

Lüning, K. and M.J. Dring. 1979. Continuous underwater light measurement near 

Helgoland (North Sea) and its significance for characteristic light limits in 

the sublittoral region. Helgolander wiss. Meeresunters. 32: 403-424. 

MacCarthy, G.R. 1958. Glacial boulder on the arctic coast of Alaska. Arctic 11: 

71-86. 

Maffione, R.A., 1998. Theoretical developments on the optical properties of 

highly turbid waters and sea ice. Limnology and Oceanography 43: 29-

33. 

Maffione, R.A. 2003. Boulder Patch Optical Model: Preliminary Model. 

Technical report, HOBI Laboratories. 

Maffione, R.A., J. Kaldy, and L. Cifuentes. 2003. Semi-empirical model of the 

benthic spectral-downwelling irradiance in high suspended sediment 

environments. Estuaries. in press. 

Martin, L.R. and B.J. Gallaway. 1994. The effects of the Endicott Development 

Project on the Boulder Patch, an arctic kelp community in Stefansson 

Sound, Alaska. Arctic 47(1): 54-64. 

The Mathworks, Inc. 2000. Matlab 6.1. Natick, Massachusetts. 

Parsons, T.R., Y. Maita, and C.M. Lalli. 1984. In: A Manual of Chemical and 

Biological Methods for Seawater Analysis. Oxford: Pergamon Press. 107-

109. 

Pegau, W.S. 2002. Inherent optical properties of the central arctic surface waters. 

Journal of Geophysical Research 107(C10): 1995-1999. 
49

Platt, T., C.L. Gallegos, and W.G. Harrison. 1980. Photoinhibition of 

photosynthesis in natural assemblages of marine phytoplankton. Journal 

of Marine Research 38: 687-701. 

Primer-E Ltd. 2001. Primer v5. Plymouth Marine Laboratory, Plymouth, UK. 

Roessler, C.S., M.J. Perry, and K.L. Carder. 1989. Modeling in situ phytoplankton 

absorption from total absorption spectra in productive inland marine 

waters. Limnology and Oceanography 34: 1510-1523. 

Schell D.M., P.J. Ziemann, D.M. Parrish, K.H. Dunton, and E.J. Brown. 1982. 

“Foodweb and nutrient dynamics in nearshore Alaska Beaufort Sea 

waters”. Draft final report, Institute of Water Resources, University of 

Alaska Fairbanks. 

SPSS Inc. 2000. SPSS 10.0. Chicago, Illinois. 

Trefry, J.H. 2003. “River loading and the bifurcated breakup”. ANIMIDA task 5 

final report, Minerals Management Service. Anchorage, Ak. 

Van Duin, E.H., G. Blom, F.J. Los, R. Maffione, R. Zimmerman, C.F. Cerco, M. 

Dortch, and E.P Best. 2001. Modeling underwater light climate in relation 

to sedimentation, resuspension, water quality and autotrophic growth. 

Hydrobiologica 444: 25-42. 

Van De Hulst, H.C. 1957. Light Scattering by Small Particles. New York. John 

Wiley & Sons, Inc. 3-5. 

Weingartner, T.J. and S.R. Okkonen. 2001. “Beaufort Sea nearshore under-ice 

currents: Science, analysis and logistics”. OCS Study MMS 2001-068. 

Welschmeyer, N.A. 1994. Fluorometric analysis of chlorophyll a in the presence 

of chlorophyll b and pheopigments. Limnology and Oceanography 39(8): 

1985-1992. 

Zimmerman, R.C. and R.A. Maffione. 2000. Radiative transfer and 

photosynthesis of aquatic vegetation in turbid coastal waters. 

Hydrobiologia: in press. 
50

Table 1. Terminology and Units. 

Term Description Units 

IOPs 

Inherent Optical Properties; a term characterizing the 

absorption, scattering, and attenuation of a particular area --- 

PAR Photosynthetically Active Radiation; total radiation in the 

400 to 700 nm wavelength interval 

μmols photons

 m

-2

 s

-1

TSS Total Suspended Solids; measure of the amount of nondissolved material in water column mg L-1

RTE Radiative Transfer Equation; equation used to determine 

spectral irradiance at any given depth --- 

Absorption 

(a) 

Fraction of radiant energy absorbed from light per unit 

distance passed through water column m

-1

Scattering 

(b) 

Fraction of radiant energy reflected from light per unit 

distance passed through the water column m

-1

Light 

Attenuation 

(k) 

Fraction of radiant energy removed from light per unit 

distance passed through the water column by either 

absorption or scattering 

m-1

Kd(λ,H) 

Bulk Downwelling Irradiance Attenuation Coefficient; 

Fraction of irradiance removed per unit distance passed 

through the water column by depth H

m

-1

Hsat

Number of hours that L. solidungula is exposed to PAR that 

meets or exceeds the minimum irradiance to produce 

maximum photosynthetic production 

hrs 

H Depth of measurement m 

Ed(λ,0+) or 

Ed(λ,H)

Downwelling Spectral Irradiance Incident; Likely amount of 

spectral irradiance occurring on the water’s surface (0+

). An 

H denotes spectral irradiance reaching depth H

W m-2

CTSS Total beam attenuation at a specific TSS m-1

K*

d(λ,H)

Concentration Specific Attenuation Coefficient; Fraction of 

radiant energy removed per unit distance by depth H (by 

either absorption or scattering) based on the concentration of 

suspended solids 

m-1

GWYR Growth Year; Period beginning 15th November one year and 

ending 15th November the following year yr 
51

Table 2. Productivity model estimates of daily production at eleven 

locations within Stefansson Sound Boulder Patch over a 60-d. 

summer period at fixed TSS concentrations of 1, 10, and 20 mg 

L-1. Note: negative production denotes respiration costs 

exceeding photosynthetic production. 

Production (g C gdw-1 day-1) 

Site Depth 

(m) 1.0 mg L1

 of TSS 

10.0 mg L1

 of TSS 

20.0 mg L1

 of TSS 

% decrease from 

1.0 to 20.0 mg L-1 

Narwhal 

Island 8.2 0.0177 0.0005 -0.0005 103 

W-3 6.6 0.0196 0.0018 -0.0004 102 

W-2 6.2 0.0200 0.0022 -0.0003 102 

L-2 6.2 0.0200 0.0022 -0.0003 102 

DS-11 6.1 0.0202 0.0023 -0.0003 101 

W-1 6.0 0.0203 0.0025 -0.0003 101 

L-1 5.5 0.0210 0.0033 -0.0001 100 

E-3 5.5 0.0210 0.0033 -0.0001 100 

Brower-1 5.4 0.0211 0.0035 -0.0001 100 

E-1 4.4 0.0222 0.0061 0.0006 97 

E-2 4.3 0.0223 0.0064 0.0006 97 
52

Table 3: Average NH4

+

, NO2

-

 + NO3

-

, and PO4

3- concentrations (μM) measured at six 

sites within Stefansson Sound during summer 2002. 

Sites NH4

+

 (μM) NO2

-

 + NO3

-

 (μM) PO4

3- (μM) 

W-1 0.05 ± 0.01 0.44 ± 0.04 4.92 ± 0.54 

W-3 0.10 ± 0.01 0.45 ± 0.01 2.40 ± 1.07 

Narwhal 

(2 meters) 

0.11 ± 0.01 0.42 ± 0.01 3.99 ± 2.25 

Narwhal 

(8 meters) 

0.12 ± 0.11 0.40 ± 0.04 5.11 ± 1.31 

DS-11 0.26 ± 0.24 0.48 ± 0.12 3.03 ± 2.01 

E-1 0.29 ± 0.04 0.59 ± 0.11 3.11 ± 0.18 

Brower-1 0.18 ± 0.18 0.44 ± 0.11 1.42 ± 0.89 
53

Figure 1. Location of Stefansson Sound, Alaska (adapted from 

Weingartner and Okkonen, 2001). 

Cross 

Island

Narwhal 

Island

Pt.

Cross 

Island

Narwhal 

Island

Pt.

Brower Tigvariak 

Island 

Beaufort Sea 
54

 Figure 2. Tracklines for ac-9 and CTD tows conducted during August 2001 and July 

2002. Grey shaded areas represent seabed boulder and cobble distribution 

based on geologic surveys conducted in 1980 and 1999 (Hopkins, 1979; 

Dunton et al., 1982). Dark grey represents areas of boulder cover > 25%. 

Light grey represents areas of boulder cover between 10% - 25%. 

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

= 01 August 2001

= 03 August 2001

= 06 August 2001

= 07 August 2001

= 24 July 2002

= 27 July 2002

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

= 01 August 2001

= 03 August 2001

= 06 August 2001

= 07 August 2001

= 24 July 2002

= 27 July 2002
55

 Figure 3. Sites where vertical profiles were measured in summer 2001 and 2002. 

Grey shaded areas represent Boulder Patch extent based on geologic 

surveys conducted in 1980 and 1999 (Hopkins, 1979; Dunton et al., 

1982). Dark grey represents areas of boulder cover > 25%. Light grey 

represents areas of boulder cover between 10% - 25%. 

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

DS-11

L-2

L-1

Brower-1

E-1

E-2

E-3

W-1

W-2

W-3

Narwhal

Station

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

DS-11

L-2

L-1

Brower-1

E-1

E-2

E-3

W-1

W-2

W-3

Narwhal

Station
56

 

Figure 4. Locations of Summer 2001 and 2002 water collection sites for TSS 

and chlorophyll a measurement. Grey shaded areas represent extent of 

Boulder Patch based on geologic surveys conducted in 1980 and 1999. 

Dark grey represents areas of boulder cover > 25%. Light grey 

represents areas of boulder cover between 10% - 25%. 

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

= Summer 2001 collection site

= Summer 2002 collection site

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

= Summer 2001 collection site

= Summer 2002 collection site
57

Figure 5. Interpolated absorption coefficients (m-1) at 676 nm for summer 2001. 

Areas of > 10% boulder cover are outlined in black. 

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower
58

Figure 6. Interpolated absorption coefficients (m-1) at 676 nm for summer 2002. 

Areas of > 10% boulder cover are outlined in black. 

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower
59

Figure 7. Interpolated scattering coefficients (m-1) at 676 nm for summer 2001. 

Areas of > 10% boulder cover are outlined in black. 

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower
60

Figure 8. Interpolated scattering coefficients (m-1) at 676 nm for summer 2002. 

Areas of > 10% boulder cover are outlined in black. 

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower
61

Figure 9. Interpolated beam attenuations (m-1) at 676 nm for summer 2001. 

Areas of > 10% boulder cover are outlined in black. 

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower
62

Figure 10. Interpolated beam attenuations (m-1) at 676 nm for summer 2002. 

Areas of > 10% boulder cover are outlined in black

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower
0

200400600800

100012001400

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200 0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200 0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200 0

200

400

600

800

1000

Irradiance (μmoles photons m-2s-1)

0

200400600800

100012001400

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200 0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200 0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200 0

200

400

600

800

1000

0

200400600800

100012001400

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200 0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200 0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200 0

200

400

600

800

1000

Solar Time (hrs)

Figure 11. Daily surface irradiance measurements from 28 July to 8 August 2002.

28-July-02 29-July-02 30-July-02 31-

01-August-02 02-August-02 03-August-02 04

05-August-02 06-August-02 07-August-02 0

= Terrestrial Sensor 1 = Terrestrial Sensor 
0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200 0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200 0

200

400

600

800

1000

0

20406080

100120140

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

Irradiance (μmoles photons m-2s-1)

0

20406080

100120140

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200 0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200 0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200 0

200

400

600

800

1000

0

20406080

100120140

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200 0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200 0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200 0

200

400

600

800

28-July-02 29-July-02 30-July-02 31-Ju

01-August-02 02-August-02 03-August-02 04-A

05-August-02 06-August-02 07-August-02 08

Solar Time (hrs)

Figure 12. Daily underwater irradiance measurements from 28 July to 8 August 2002.

= Underwater Cosine Sensor 1 X = Underwater Cosine Sensor 2 = Spherical Sensor 1 = Sph
65 

Figure 13. Interpolated TSS concentrations (mg L-1) for summer 2001. Areas of > 

10% boulder cover are outlined in black. 

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower
66

Figure 14. Interpolated TSS concentrations (mg L-1) for summer 2002. Areas of > 

10% boulder cover are outlined in black. 

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower
Summer 200

y = 0.371x + 1.0

R2 = 0.8894

p = 0.005

Summer 2001

y = 0.5062x + 0.4235

R2 = 0.8908

p = 0.002

0.002.004.006.008.00

10.0012.0014.0016.00

0.00 3.00 6.00 9.00 12.00 15.00 18.00 21.00 2

20022001

Figure 15. Correlations between light attenuation at 676 nm and TSS concentrations across Stefan

summers 2001 and 2002. 

Total Suspended Solids (mg L-1) 

Light Attenuation (m-1) 
68 

Figure 16. Chl a concentrations (μg L-1) interpolated across Stefansson Sound 

during summer 2001. Areas of > 10% boulder cover are outlined in 

black. 

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower
69

Figure 17. Chl a concentrations (μg L-1) interpolated across Stefansson Sound 

during summer 2002. Areas of > 10% boulder cover are outlined in 

black. 

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower
70

 Figure 18. Interpolated production estimates (g C m-2

 yr

-1) for a 60 day summer 

period within Stefansson Sound Boulder Patch for 2001 based on in situ

measurements of TSS and IOPs. We assumed a biomass of 39.3 gdw m-2

for boulder cover 25% or greater and 10.0 gdw m-2 for boulder cover 

between 10-25% based on previous calculations (Dunton et al., 1982). 

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

DS-11

L-2

L-1

Brower-1

E-1

E-2

E-3

W-1

W-2

W-3

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

DS-11

L-2

L-1

Brower-1

E-1

E-2

E-3

W-1

W-2

W-3
71

Figure 19. Interpolated production estimates (g C m-2 yr-1) for a 60 day summer period 

within Stefansson Sound Boulder Patch for 2002 based on in situ

measurements of TSS and IOPs. We assumed a biomass of 39.3 gdw m-2

for boulder cover 25% or greater and 10.0 gdw m-2 for boulder cover 

between 10-25% based on previous calculations (Dunton et al., 1982). 

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

DS-11

L-2

L-1

Brower-1

E-1

E-2

E-3

W-1

W-2

W-3

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

DS-11

L-2

L-1

Brower-1

E-1

E-2

E-3

W-1

W-2

W-3

North Slope,

Alaska

Endicott

Island

Cross

Island

Narwhal

Island

SDI

Pt. Brower

DS-11

L-2

L-1

Brower-1

E-1

E-2

E-3

W-1

W-2

W-3
72

Summer 1990

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

-50% -40% -30% -20% -10% 1990 +10% +20% +30% +40% +50%

1.0 mg/L

3.0 mg/L

5.0 mg/L

7.0 mg/L

9.0 mg/L

11.0 mg/L

13.0 mg/L

Summer 1991

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

-50% -40% -30% -20% -10% 1991 +10% +20% +30% +40% +50%

1.0 mg/L

3.0 mg/L

5.0 mg/L

7.0 mg/L

9.0 mg/L

11.0 mg/L

13.0 mg/L

 Figure 20. Estimated daily production as a function of percent summer surface 

irradiance based on hourly PAR measurements (μmols photons m

-2

 s

-1) 

collected in 1990 and 1991 by Dunton et al. (1992). 

Production g C gdw-1 d-1

Change in Irradiance (%)
73

Summer 1990

0

5

10

15

20

25

30

35

50 - 60% 100 - 110% 140 - 150%

1.0 mg/L

7.0 mg/L

13.0 mg/L

Summer 1991

0

5

10

15

20

25

30

35

50 - 60% 100 -110% 140 - 150%

1.0 mg/L

7.0 mg/L

13.0 mg/L

 Figure 21. Percent increase in daily production as a function of modest (10%) 

increases in summer irradiance under three different TSS levles (1, 

7, and 13 mg L-1). Modeled production estimates are based on 

extremes in summer insolation derived from hourly surface PAR 

(μmols photons m-2 s

-1) recorded in summers 1990 and 1991 

(Dunton et al., 1992). 

Dail

y Production Increase (%)

Change in Irradiance (%) 
74

Figure 22. Vertical profiles of salinity and temperature at site E1 in summers 2001 and 2002. 
75

Figure 23. Vertical profiles of salinity and temperature at site 

DS-11 in summers 2001 and 2002. 
76

Figure 24. Vertical profiles of salinity and temperature at site 

Narwhal Island in summers 2001 and 2002. 
77

Annual Linear Growth of L. solidungula in 2001

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

50.0

StipeBlade 1

(2000)

Blade 2

(1999)

Blade 3

(1998)

Blade 4

(1997)

Blade 5

(1996)

GWYR

Length (cm)

E-1

E-2

E-3

DS-11

L-1

L-2

Brower-1

Figure 25. Annual linear growth of Laminaria solidungula blades at seven sites within 

Stefansson Sound Boulder Patch in summer 2001. Growth year (GWYR) for 

each blade is a defined period beginning 15 November one year and ending 15 

November the following year. No specimens collected at DS-11 or L-2 possessed 

a 5th blade. Values are mean ± SE (n = 15 to 30). 
78

Annual Linear Growth of L. solidungulai in 2002

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

50.0

StipeBlade 1

(2001)

Blade 2

(2000)

Blade 3

(1999)

Blade 4

(1998)

Blade 5

(1997)

Blade 6

(1996)

GWYR

Length (cm)

E-1

E-2

E-3

DS-11

L-1

L-2

Brower-1

Figure 26. Annual linear growth of Laminaria solidungula blades at seven sites within 

Stefansson Sound Boulder Patch in 2002. Growth year (GWYR) for each blade is a 

defined period beginning 15 November one year and ending 15 November the 

following year. No specimens collected at E-1, DS-11 or L-2 possessed a 5th blade. 

Only sites E-2, L-1, and Brower-1 possessed a 6th blade. Values are mean ± SE (n = 

15 to 30). 
79

Annual Linear Growth of L. solidungula Measured in 2003

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

50.0

StipeBlade 1

(2002)

Blade 2

(2001)

Blade 3

(2000)

Blade 4

(1999)

Blade 5

(1998)

GWYR

Length (cm)

E-1

E-2

E-3

DS-11

L-1

L-2

Brower-1

Figure 27. Annual linear growth of Laminaria solidungula blades at seven sites within the 

Stefansson Sound Boulder Patch measured in 2003. Growth year (GWYR) for each 

blade is a defined period beginning 15 November one year and ending 15 November 

the following year. No specimens collected at E-1, E-3, DS-11, or L-1 possessed a 

5th blade. No specimens collected possessed a 6th blade. Values are mean ± SE (n = 

15 to 30). 
80

Figure 28. Correlation between basal blade dry weight (g) and basal blade length 

(cm) of Laminaria solidungula in Stefansson Sound Boulder Patch. 

Specimens were collected between 1980 – 1984 (n=820; Dunton et al., 1982; 

Dunton and Schell, 1986). 
81

0.0

1.0

2.0

3.0

4.0

5.0

6.0

1990 1991 2001 2002

Calculated based on blade lengths

Calculated from production model

Figure 29. Comparison of actual production (g C) for an averaged sized kelp specimen 

at DS-11 based on basal blade lengths and model predictions over four 

different GWYRs.. Linear growth measurements were converted to carbon 

production based on analysis of published data (see Figure 28; Dunton and 

Schell, 1986). Production estimates for 1990 and 1991 used in situ

measurements of modeled TSS from 2001 and measured values of 

irradiance collected in each respective year; surface light data from 1990 

was used in model calculations for 2001 and 2002. 

GWYR

Estimated Production (g C)