Office of Naval Research (ONR) sponsored a program of manned ice camps in the late 1940’s where scientists worked

and lived for long periods of time. Initially the camps were situated on thick pieces of glacial ice (100 or more feet thick) which

were stable and lasted for decades. Such ice islands were rare because very few glaciers drift into the Arctic Ocean.

Starting in the 1970’s, ONR shifted to manned camps on thinner mobile sea ice. Logistic and support techniques have

been perfected to the point that such camps are now routine for Arctic research and are used to support under-ice naval

operations. Ice camps are the research and equipment platforms for studying large scale sea ice in its environment.

Up-to-date information on the extent, position, thickness and break up characteristics of sea ice are vital for Arctic naval

missions. An understanding of the large scale response of sea ice to its environment is needed for solving many important

practical and theoretical problems ranging from the interaction between the ice cover and global circulation to navigation on

and under the ice-covered sea.

Picture courtesy of A. Heiberg.
One/1998 1

Naval Research Reviews publishes articles about research conducted by the laboratories and contractors of the

Office of Naval Research and describes important naval experimental activities. Manuscripts submitted for

publication, correspondence concerning prospective articles, and changes of address, should be directed to Code

00PA, Office Naval Research, Arlington, VA 22217-5660. Requests for subscriptions should be directed to the

Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20403. Naval Research

Reviews is published from appropriated funds by authority of the Office of Naval Research in accordance with

Navy Publications and Printing Regulations. NAVSOP-35.

CHIEF OF NAVAL RESEARCH

RADM Paul G. Gaffney, II, USN

DEPUTY CHIEF OF NAVAL RESEARCH

TECHNICAL DIRECTOR

Dr. Fred Saalfeld

CHIEF WRITER/EDITOR

William J. Lescure

SCIENTIFIC EDITOR

Dr. Robert H. Bourke

Dr. Thomas B. Curtin

MANAGING EDITOR

Norma Gerbozy

ART DIRECTION

Cynthia Nishikawa

Jorge Scientific Corporation

Office of Naval Research

One/1998

Vol L

About the cover

Finger rafting is a common phenomenon in ice covered regions. Individual fingers range in scale

from centimeters to hundreds of meters, and usually occur in regular patterns. The finger shown here

is about three meters long. The precise mechanism for finger rafting is not well understood.

Articles

Departments

2

History of the ONR Chair in

Arctic Marine Science

R. H. Bourke

6

Historical Perspectives on

the Arctic Program at the

Office of Naval Research

T. B. Curtin

9

Arctic Climate Variability:

Observations and Model

Simulations

J. E. Walsh

13

Bottom Water Formation and

Distribution in the Weddell

Sea

A. L. Gordon

17

Sea Ice Growth in Antarctic

Leads: Top Freezing vs.

Bottom Melting

S. F. Ackley

19

Modeling Sea Ice Behavior

R. S. Pritchard

23

Sea Ice Thickness

Distribution as a State

Variable

A. Thorndike

25

Project SPINNAKER;

ICESHELF 1988 -1996 and

Beyond

J. L. Newton

29

Interdisciplinary Interaction

in Arctic Research

H. J. Niebauer

12

Profiles in Science

32

List of papers from the

American Geophysical Union

Meeting dedicated to the

ONR Arctic Marine Science

Chair 20th Anniversary
2 Naval Research Reviews

The polar marine science community is a small segment of the much larger and broader U.S. and international

marine science community. It is a close knit community as

attested that most of us gathered in this room this afternoon

know a considerable number of the attendees. We may be

small in numbers but we are truly global in our interests as

many of us study phenomena and processes associated with

both the Arctic and Antarctic polar regions. The polar oceanography community is truly international in its make up with

most U.S., Canadian and European scientists having worked

together over the years. In the past 15 years this international cooperation has flourished with meetings and workshops being held in the U.S. and Europe and attended by

members from many countries including colleagues from

Asia. As an example, think back and recall how many different countries were represented on the Polarstern during

the MIZEX experiments. Another example is to note that

over 15 countries had scientists present at the Nansen Centennial Symposium in Bergen in 1993.

Today this diverse group, encompassing members from

a broad spectrum of the geophysical sciences, is gathered to

honor both the U.S. Navy, in particular the Office of Naval

Research, for having the wisdom and foresight to establish a

research Chair in Arctic Marine Science and the scientists

who have occupied the Chair. In 1976, 20 years ago, the

Chair was founded through the efforts of Warren Denner and

Ron McGregor. Twenty years later the occupants of the Chair

read like a who’s who in polar marine science with representatives from universities, government and research laboratories, a variety disciplines and five different countries

(Table 1). Today we will hear from 13 of these Chair alumni.

Before I introduce our honored colleagues and speakers, let me digress and tell you of the early history of the

Chair, its formation and evolution.

In the years after WWII during the 1950s and 1960s,

the U.S. Navy exhibited little interest in the Arctic region,

i.e., the Navy didn’t expect to conduct war fighting operations there. However, scientists from various universities

History of the ONR

Chair in Arctic Marine

Science

Robert H. Bourke, Department of Oceanography, Naval Postgraduate School, Monterey, CA
One/1998 3

were interested in studying a broad range of topics related to

the Arctic environment. In 1947 the Naval Arctic Research

Laboratory (NARL) was established at Pt Barrow in Alaska

to provide a base of operations for these scientists. When

Warren Denner joined the faculty of NPS in 1963, he inherited and expanded a course in Polar Oceanography based

mainly on the venerable Russian work of Zubov. Warren

recognized the need to get these naval officer students into

the field to experience the harsh realities of the polar environment so he arranged to have the class taught at NARL in

1964/65. The class continued to be offered twice a year at

NARL until the lab closed in 1978.

During the late 60s, early 70s, when the ARLIS and

T-3 ice camps were in operation, Warren got to know Ron

McGregor who was the Polar Program Manager at ONR. In

1973 Warren was selected to be the Director of NARL where

he remained until 1976. It was during these years that Warren and Ron recognized the need to increase the Navy’s

awareness of polar science. The reluctance to consider polar operations as a potential warfare theater was one mainly

borne of ignorance, with the important exception of the submarine force who recognized its significance after the successful trans-Arctic voyage of NAUTILUS in 1958.

When Warren Denner returned to NPS in 1976, he

convinced the NPS administration to establish a research

Chair supported by ONR. This was no easy task as Chairs

were a new entity to NPS at that time. Warren was the first

Chairholder and worked to establish its foundations of providing a means to make the civilian polar science community aware of the Navy’s needs and capability to conduct

operations in, above and beneath ice-covered waters. The

objectives of the Chair, as defined 20 years ago, are still valid

today: (1) the Chairholders are to conduct polar research

and assist in translating basic knowledge into operational

products and (2) to inculcate a love of polar science in NPS

students and students from their own institutions in order to

provide the Navy with a cadre of officer and civilian polar

experts.

In 1977-78 Alan Beal held the Chair. Alan had a long,

illustrious career at the Arctic Submarine Laboratory working with its founder, Waldo Lyon. He served as Chief Scientist on many of the icebreaker cruises that my colleague, Bob

Paquette, and I participated in. Alan passed away several

years ago, the only deceased Chairholder among the Chair

alumni.

In 1978, when Warren left NPS, Bob Paquette took

1976-77: PROFESSOR WARREN W. DENNER

Naval Postgraduate School

(Ice Dynamics/Mechanics)

1977-78: PROFESSOR ALLAN M. BEAL

Arctic Sub Lab

(Sea Floor Bathymetry)

1978-79: PROFESSOR WILFORD F. WEEKS

CRREL

(Ice Mechanics)

1979-80: PROFESSOR ALLAN R. MILNE

IOS (CANADA)

(Ambient Noise)

1980-81: PROFESSOR PETER WADHAMS

Scott Polar Research Institute

(Ice-Wave Interaction)

1981-82: PROFESSOR OLA M. JOHANNESSEN

University of Bergen

(Marginal Ice Zone)

1982-83: PROFESSOR MILES G. MCPHEE

Private Consultant

(Ice-Water Boundary Layer)

1983-84: PROFESSOR WALKER O. SMITH

University of Tennessee

(Ice Edge Biology)

1984-85: PROFESSOR H. JOSEPH NIEBAUER

University of Alaska

(Ice Dynamics)

1985-86: PROFESSOR STEPHEN A. ACKLEY

CRREL

(Ice Mechanics)

1986-87: PROFESSOR JOHN E. WALSH

University of Illinois

(Sea Ice Variability)

1987-88: PROFESSOR ROBERT S. PRITCHARD

Consulting Scientist

(Arctic Sea-Ice Dynamics)

1988-89: PROFESSOR ARNE FOLDVIK

University of Bergen

(Ocean-Ice Shelf Interaction)

1989-90: PROFESSOR JAMES H. MORISON

University of Washington

(Under-Ice Boundary Layer Dynamics)

Table 1:

Occupants of the ONR Arctic Marine Sciences Chair

1990-91: PROFESSOR JOHN L. NEWTON

Consulting Scientist

(Arctic ASW)

1991-92: PROFESSOR ALAN S. THORNDIKE

University of Puget Sound

(Sea Ice Physics)

1992-94: PROFESSOR JAMES H. WILSON

Consulting Scientist

(Arctic Ambient Noise and ASW)

1994-95: PROFESSOR ARNOLD L. GORDON

Lamont-Doherty Earth Observatory

(Antarctic Circulation)

1996-97: PROFESSOR LAWSON W. BRIGHAM

Cambridge University, USCG (Ret)

(Remote Sensing, Ice Operations)
4 Naval Research Reviews

over the duties of Chair Administrator during which time he

recruited Willy Weeks, Allen Milne, Peter Wadhams, Ola

Johannessen and Miles McPhee to the Chair. I took over as

the Chair Administrator in 1983/4 upon the retirement of

Bob Paquette and have had the good fortune to recruit and

work with 12 more Chairholders since then.

As I said earlier, the Chairholders represent a broad

spectrum of countries, universities and labs and disciplines.

Four have come from other countries: Allen Milne from

Canada, Peter Wadhams from England, Ola Johannessen and

Arne Foldvik from Norway. Government labs are represented

by Alan Beal from ASL, Willy Weeks and Steve Ackley from

CRREL, and John Newton from NRAD. Private consulting

companies are represented by Miles McPhee, Bob Pritchard

and Jim Wilson.

When categorized by scientific discipline, the largest

preponderance is, perhaps not surprisingly, associated with

sea ice, the all pervasive medium that defines the polar regime. In this category I have included Warren Denner, Willy

Weeks, Peter Wadhams, Steve Ackley, Bob Pritchard and

Alan Thorndike. Their studies mainly concern ice mechanics, its properties, strength, thickness and temporal and spatial distribution. The study of the ocean underlying the ice

cover, i.e., its physical oceanography has been conducted on

micro to macro scales by Arnold Gordon, Arne Foldvik, Joe

Niebauer, Jamie Morison, Miles McPhee and, if we fold in

the specialty of remote sensing, we include Ola Johannessen

and Lawson Brigham. The Navy has long had an interest in

acoustic propagation and noise generation in the polar seas

tied to submarine operations in ice-covered waters and the

conduct of ASW missions to counter the submarine threat.

This group of applied scientists includes John Newton (who

has ridden on most of the SUBICEX boats and participated

in many ice camps), Jim Wilson, Allen Milne, Alan Beal and

Warren Denner.

We have two remaining Chairholders whose specialty

is not in either of these three preceding groups. Walker Smith

is the lone biological oceanographer but is well known for

his interaction with the physical oceanographers. Indeed,

he and Joe Niebauer have teamed up over the years in large

part because their tenure in the Chair overlapped and opened

the door for a shared view of the oceanography near the ice

edge. Our lone mid-westerner and atmospheric scientist, John

Walsh, has shown how climate variability affects the ice distribution on seasonal, annual and longer time scales.

Although the Chair was initially set up to further our

knowledge and understanding of the processes affecting the

Arctic Ocean and its peripheral seas, it soon broadened to

polar seas in general. Like many of you in the room today,

many of our Chairholders have conducted research in Antarctic waters, notably Arnold Gordon, Steve Ackley, Willy

Weeks, Arne Foldvik, Peter Wadhams, Walker Smith, Jamie

Morison, and Miles McPhee. In their talks this afternoon

you will hear of the similarities and differences between these

two ice-covered oceans.

My initial intent was to include some anecdotal remarks for each Chairholder relative to their stay in Monterey.

However, the compacted schedule prevents me from doing

this. I can say that all have enthusiastically enjoyed their

time at NPS and found it highly productive. Most finally

found time to complete long over due manuscripts, thoughtfully examine old and recent data sets or participate in planning for future field projects. In this latter regard, ONR

actively involved the Chairholders in much of the early planning for the MIZEX series of experiments and follow on

experiments such as CEAREX and LEADEX. Many acted

as thesis advisors for our Naval Officer students; their expertise was highly sought after by both our faculty and students. One of the side benefits of the Chair has been the

continued interaction with NPS faculty long after their departure from the Chair. The collegial relationships developed at NPS have lead to joint partnerships on research

projects and scholarly papers. I am also appreciative of the

Table 2

Technological Advances

GPS

- provides precise navigational accuracy

Satellites

- visual, infrared, microwave, radar

- frequent, wide area remotely sensed observation

Arctic Buoy Program

- surface pressure/winds and temperature throughout Arctic basin

SUBICEX/SCICEX

- submarine science measurement programs

Icebreakers

- deep penetration into Arctic Ocean

- North Pole and Trans-Arctic voyages “routine”

CTD

- continuous observations in the vertical, increased speed and

accuracy

ADCP

- ship/moored current observations over large segments of the

water column

Computer Power

- in situ data processing/analysis

- high resolution forecast/simulation models developed

Acoustic Sensors

- horizontal and vertical directionality

- upward looking sonars for ice draft observations

Data Sets

- longer records, higher quality
One/1998 5

Circulation

- improved knowledge of surface, intermediate, deep waters

- seasonal, interannual and decadal variability

- role of continental shelves, convective cells, canyons

Ice Rheology

- improved models relating to ice deformation processes

Ice Concentration/Thickness

- temporal and spatial distribution

- long term trends

Heat Flux

- albedo, leads/polynyas, cloud cover, boundary layer

Geochemistry

- water mass, circulation tracers

Acoustic Propagation

- underice scattering models

- signal processing to reduce reverberation, improve target recognition

Russian Data/Collaboration

 - access to Russian arctic

- historical data bases of many parameters

Climate Models

- dominant role of arctic region in global circulation, climate studies

help they gave me in providing lectures in the Polar Oceanography course.

An important and integral part of the Arctic Chair team

are the ONR Polar/High Latitude Program Managers who

have provided guidance and financial support for the Chair.

Leonard Johnson took over from Ron McGregor in the late

1970s and he and Tom Curtin have since been the mainstays

of program support for the Chair, and Arctic marine science

in general, for the past two decades. To them we owe a debt

of gratitude for steering numerous field programs from inception to successful completion. Tom Curtin, in the next

talk, will highlight the purpose and scientific advances of

some of these major programs. Today Mike Van Woert heads

up the ONR High Latitude program. He sends his regards to

our honored alumni. Unfortunately, he is unable to join us

this afternoon as he is on a long awaited trip to Antarctica at

this moment.

We have chosen the theme of this anniversary session

to look back upon the advances we have made in the past

twenty years, and they are indeed impressive, and to suggest

where we might focus our attention, resources and effort for

the next 5 to 10 years. Each of our Chairholders will address the accomplishments and potential future direction for

the various disciplines they represent. It is our intention to

publish their talks as a collection of extended abstracts.

In order to kick off this theme I have prepared the two

following tables which illustrate some of the technological

advances (Table 2) of the past 25 years and the scientific

advances (Table 3) that have resulted from this improved

technology. The lists are by no means complete but do serve

to illustrate how far we have pushed the scope of our understanding of Arctic processes.

As we look back over the past 20 years, I think we

would all agree that indeed we have made substantial progress

in our understanding of the processes that drive the Arctic

atmosphere ice-ocean environment. They have been years

filled with challenging and exciting field programs, mostly

conducted in the Alaskan-Canadian-Greenland sector of the

Arctic. We can look forward to increased mutual cooperation with our Russian colleagues and perhaps joint observational programs conducted in the Siberian Arctic. Much data

exchange has recently take place with Russian scientists and

even more is anticipated. Instead of field programs conducted mainly in the spring and summer seasons, we can

anticipate data collection efforts year ‘round as remote or

autonomous instruments will relay their data via satellite or

internet back to our labs. This may be the route that we will

take if we are to set up a continuous monitoring program to

observe the remarkable changes that have been taking place

in the Arctic Ocean since the start of this decade.

I think we can say that the goals of the Chair have

been met. The Navy has developed a pool of officers who

have a strong appreciation for the impact of the Arctic environment on all aspects of naval operations. These officers

occupy positions of technical and strategic importance at the

Table 3

Scientific Advances

National/Naval Ice Center, ONR, the Naval Research Lab

and other commands. On the other hand, the operational

forecasts they routinely produce and interpret were for the

most part developed and continuously improved by the collective efforts of many of you sitting in the audience this

afternoon.

Because of the breadth and visibility that the Chair

brings to the study of polar marine science, I am pleased to

report that ONR will continue to support the Chair for the

foreseeable future. Announcements and advertisements in

EOS have gone out for next year’s Chair. So, if you are

interested in spending a year at Monterey, starting next fall,

or perhaps sometime in the next few years, please contact

me.

Now as we commence our program to celebrate the

Arctic Chair’s 20th anniversary, I salute our former

Chairholders and ONR program sponsors. I look forward to

welcoming many more of you to the Chair in the coming

years.
6 Naval Research Reviews

“In the history of exploration of the North country, the

United States Navy has played a most significant and exciting role. The names of Admiral Robert E. Perry, Admiral

Richard E Byrd, Commander Donald B. MacMillan, Commander Richard Cruzen, Commander Lincoln Elllsworth and

of Dr. Elisha Kent Kane, a naval medical officer who led his

expedition in search of a lost Sir John Franklin expedition,

immediately make one realize how great has been the role

that the United States Navy has played in searching the mysteries of the North.” (Shelesnyak, M.C. and V. Stefansson,

1947)

For more than fifty years, the Office of Naval Research

has continued the tradition of scientific inquiry by maintaining an active, multi-disciplinary, Arctic basic research program. The tenets of the program, set forth in 1947, remain

valid today:

“Specifically, however, the Office of Naval Research

is interested in precise information regarding the meteorology, geology, and environmental influences of the North

country on man and to that end is getting underway a program for the scientific information of Arctic conditions in

the United States’ own Arctic territory, the northern slopes

of Alaska. With this basis of information and the possibility

of exchange of information from other sources, the Navy

should have a complete picture of the true north and therefore be able to use it to its fullest possible extent.

“This last frontier of exploration presents an exciting

field not alone in terms of the old geographical exploration,

but more in terms of the utilization of our finest and newest

techniques in geophysical and biological science applied to

a large and vast area of relatively unknown territory. It is a

true challenge to the research-minded youth of our country.”

(ibid., 1947)

In addition to high quality investigations across a range

of scientific disciplines, key elements of the program, established at inception and maintained for over a half century,

Historical

Perspectives on the

Arctic Program at the

Office of Naval

Research

Thomas B. Curtin, Office of Naval Research, Arlington, VA
One/1998 7

are international collaboration, bold field experiments, development and use of innovative technology, and support of

graduate students.

Singular among federal research programs in any field,

the Arctic Program at the Office of Naval Research has been

managed by just seven people spanning over fifty years (Figure 1). The tradition of proactive, involved managers was

established early as documented in one of the program’s first

publications:

The Office of Naval Research has many Arctic experts

working on various phases of its Arctic research program.

Several of these men have contributed to this pamphlet. Sir

Hubert Wilkins has written a valuable introduction and Dr.

Vilhjalmur Stefansson has compiled a useful bibliography

on Arctic literature. The main article of the pamphlet was

written by Dr. M.C. Shelesnyak, Head of the Environmental

Physiology Branch, Office of Naval Research.

“Dr. Shelesnyak gathered material about the Arctic as

United States Naval Observer with the Moving Forces, Canadian Army Winter Arctic Expedition, Operation Musk-Ox,

in 1945. The expedition traveled by motorized, tracked vehicles 3100 miles across the Canadian Arctic prairies, Queen

Maude Gulf, Coronation Gulf and southward from

Coppermine to Port Radium, across Great Bear Lake and

down through the bush country along the Alaskan-Canadian

Highway to Edmonton. Dr. Shelesnyak’s first-hand knowledge of the Arctic was further broadened by his experiences

in traveling by dog sled from Coppermine N.W.T. to Cambridge Bay, Victoria Island, having left the Moving Forces

to rejoin them later.” (ibid., 1947)

Measures of the fifty years of research supported by

the program are the associated cumulative scientific literature and the strategy and tactical procedures, both military

and commercial, influenced by that knowledge. A comprehensive bibliography has not been compiled. To do so would

be a major task, and no doubt the result would be impressive. A few of of the major insights achieved over the years

are highlighted in Figure 2. Atmospheric circulation patterns and pollutant (haze) pathways are now well established.

The mechanical, electrical and chemical properties of sea

ice as well as its dynamics and thermodynamics over a hierarchy of scales are known well enough to enable predictive

models with some skill. The statistics of sea ice extent, variability, drift, and to some degree its thickness have been determined. Propagation of sound, both at low and high

frequencies, including scattering and transformation into a

rich class of plate waves some of which were discovered

initially in the Arctic, can now be modeled accurately. Ambient noise mechanisms have been established. The Ekman

spiral, derived theoretically, was first observed in the Arctic, as was thermal microstructure. The ocean circulation,

including water mass residence times and mesoscale eddy

distributions, is now generally known. Unique aspects of

the internal wave spectrum have been documented. The high

primary productivity in the marginal ice zone has been quantified and its mechanisms elucidated. The Nordic Seas have

been determined to be carbonate vice silicate dominated

oceans, leading to a role in global carbon sequestration. Near

surface bacterial abundance at high latitude is far greater than

previously thought. The properties of permafrost are known

and were used to great advantage in pipeline construction.

Bathymetric, magnetic and gravity fields have been mapped

to useful, but not high, resolution. Understanding how much

there is yet to be understood is always sobering. However,

contrasting man’s knowledge of the Arctic marine environment from a view in 1945 to one in 1998 gives an appreciation of how much has been accomplished.

Logistics has always been inextricable from science

in the Arctic. Ice stations or camps have been central ways

of doing business since Nansen pioneered the method with

the Fram. A relative ice station activity index for the program is plotted at the bottom of Figure 2. During peak years,

logistics costs typically consumed 20-40% of the program

budget. The locations of ice stations since 1971 are shown

in the inside front cover of this issue. From the mid sixties

to the late seventies, many expeditions in the western Arctic

were staged from the Naval Arctic Research Laboratory

(NARL) at Point Barrow, Alaska. Eastern Arctic stations

were staged from Greenland or Norway. Since the Navy’s

divestiture of NARL to the North Slope Borough in the late

seventies, there has been a slow but steady trend toward autonomous instrumentation. That trend is expected to accelerate in the coming years with advances in microprocessors,

navigation and communication technology. Considering the

number and diversity of people involved, the variability and

extremes of nature, the remote and Spartan accommodations

on the ice, and the invariably tight budgets, it is a notable

tribute to the operations managers over the years that all have

returned safely to analyze their data.

From a historical perspective, there have been three

stages of United States Naval interest in the Arctic. The first

stage was marked by exploration, driven by personalities like

Figure 1

Program managers of the Arctic Program since its inception

at the Office of Naval Research.

1947 - 1954 M.C. Shelesnyak

1954 - 1970 M.E. Britton

1970 - 1975 R. McGregor

1975 - 1984 G.L. Johnson

1984 - 1994 T.B. Curtin

1994 - 1996 M. Van Woert

1998 - Dennis Conlon
8 Naval Research Reviews

Figure 2

A few of the major insights by discipline achieved over the years of the Arctic Program at the Office of Naval Research.

Perry, Byrd, Ellsworth and Kane. The second stage was characterized by more calculated investigations and classified

operations, framed by the cold war and the advent of the

nuclear submarine. The Office of Naval Research was established at the beginning of this second stage, and the Arctic program has existed only in this context until recently.

The third stage began with the end of the cold war. The

investment strategy and method of operation for the current

stage are evolving now. This evolution is in many ways unprecedented.

Acknowledgments

The collective principal investigators spanning fifty

years are the essence of the ONR Arctic Program. The complete history of the Program lies in their accomplishments

reflected both in the scientific literature and in numerous

unrecorded, successful naval missions accomplished. Art

Baggeroer, Andy Heiberg, Ken Hunkins, Leonard Johnson,

Ned Ostenso, Norbert Untersteiner and Willy Weeks contributed significantly to this article.

REFERENCES

Shelesnyak, M.C. and V. Stefansson, 1947. Across the Top

of the World, A Discussion of the Arctic. Office of

Naval Research, Navy Department, NAVEXOS P489, Washington, D.C., 71 p.
One/1998 9

It is well-known that global climate models show a

polar amplification of the near-surface warming of the atmosphere in response to increased concentrations of greenhouse gases. While the Arctic warming is diminished

somewhat when the climate models include sulfate aerosol

effects and coupling to a deep ocean, the polar amplification

is a pervasive feature of model-projected greenhouse warming, especially in the Northern Hemisphere. The model-projected warming is associated with a retreat of sea ice and is

generally accompanied by an increase of precipitation in high

latitudes (IPCC, 1996, p. 307-309). If the models are correct about the amplification of greenhouse effects in the polar regions, then the recent build-up of greenhouse gas

concentrations (an increase of equivalent CO2

 by approximately 50% since the mid-eighteenth century) should be producing a detectable response in the polar regions.

Unfortunately, detection of such signals is hampered by the

short record lengths of datasets describing the polar atmospheres in a systematic way. Many polar datasets are not

only limited to the past several decades, but are often extremely limited in spatial coverage over the Arctic Ocean,

the subpolar seas, and most of Antarctica. In the present

summary, we examine several datasets depicting Arctic variability over short climatic timescales: the most recent several decades. Such timescales are likely inadequate for

unambiguous detection of greenhouse effects in the Arctic.

Nevertheless, these datasets illustrate the magnitudes of the

Arctic’s multidecadal variability (natural or otherwise), and

they will point to several regions, seasons, and variables that

may merit close monitoring in the coming decades. In addition, an examination of data-derived variations in the context of climate model simulations will point to several

observational issues relevant to climate signal detection in

the polar regions.

In general, station data show a near-surface warming

in the Arctic over the past several decades (Chapman and

Walsh, 1993). This warming is apparent even when stations

suspected of having urban influence are removed from the

Arctic Climate

Variability:

Observations and

Model Simulations

John E. Walsh, Department of Atmospheric Science, University of Illinois, Urbana, IL
10 Naval Research Reviews

dataset (e.g., Jones, 1994). The warming is most apparent

over northwestern North America and northern Eurasia.

Although the absence of permanent stations over the Arctic

Ocean makes it difficult to map the recent temperature variations poleward of the northern continental margins, an analysis by Martin et al. (1997) of temperatures from drifting ice

stations suggests that the Arctic Ocean’s surface air temperatures have indeed increased since 1960 during the winter

and spring (Fig. la). This seasonality is consistent with the

warming over the northern continents. However, this seasonality does not match the seasonality of climate models’

greenhouse warming, which is generally strongest in autumn.

There is a general compatibility in the spatial patterns of the

annual mean warming obtained from models and observational data, although the tendency for the northern continental areas to warm the most is also consistent with the natural

variability found in climate model simulations. The observed

warming over northern high latitudes also appears to be at

least partially attributable to recent shifts in the atmospheric

circulation and its temperature advection pattern (e.g.,

Trenberth, 1990). In addition, the associated sea ice trends

are different in the observational data and in the model

simulations of climate change. Thus any attribution of the

recent multidecadal warming to the greenhouse effect of increased CO2

 is open to question.

Figure 2 is a monthly time series of Northern Hemisphere sea ice extent for the years 1953 1995, inclusive. The

wintertime maximum of sea ice extent has remained remarkably constant through the period. However, there is a noticeable tendency for more frequent extreme summer minima

in recent years. The three lowest values of summer ice extent in the period of record occurred during the 1990s, in

agreement with the recent findings of Maslanik et al. (1996).

The linear trends of sea ice extent (Fig. lb) are consistent

with the time series of Fig. 2: negative trends are largest in

the summer and essentially nonexistent in the winter. The

extent to which this seasonality disagrees with all the greenhouse projections of climate models will likely depend on

the rapidity of the recovery of the extent of sea ice, perhaps

only of small thickness, to its “historical” winter maximum

after an extreme summer melt. Regionally, the decrease of

summer sea ice has been largest in the Asian Arctic; there

has been no decrease (and even a slight increase) in the Labrador and Greenland Seas.

Observational data (IPCC, 1996, p. 152-155) also suggest that precipitation has increased over northern land areas in recent decades, although the spatial scatter of

precipitation reduces the statistical significance of these increases. Correspondence with the increases projected by

models must be tempered by the apparent biases in the model

simulations of present-day precipitation, as well as by the

considerable uncertainty in observational measurements of

precipitation in cold windy environments. There is a definite tendency for the climate models to oversimulate Arctic

precipitation. The model biases are typically 25-75%. This

Figure 1

Linear trends (1961-1990) of (a) Arctic Ocean surface air

temperature, °C per decade, from POLES data (S. Martin,

Univ. of Washington); (b) Arctic sea ice extent, % per decade

(from Chapman and Walsh, 1993). In both (a) and (b), data

are pooled into three-month periods centered on indicated

months.

Figure 2

Time series of end-of-month sea ice extent, 1953-1995, for

the Northern Hemisphere. Data are from Chapman and

Walsh (1993), updated through 1995 using data from National

Ice Center.
One/1998 11

bias extends to the northern terrestrial regions and to P-E

(precipitation minus evaporation), based on comparisons of

observed river discharge and the areally-integrated P-E from

climate model simulations (Walsh, et al., 1997).

In summary, recent decadal-scale variations of Arctic

climate are generally consistent across variables, at least in

the annual mean: the Arctic has become warmer, wetter, and

more likely to experience extreme summer minima of sea

ice extent. An exception appears to be the North Atlantic,

including the Labrador and Greenland Seas. However, given

that the warming has been relatively strong in winter, it is

unclear why there has not been a more notable decrease of

wintertime sea ice extent. Claims of compatibility between

the recent variations and model-derived greenhouse projections appear to be premature for several reasons. First, the

seasonally of key features such as the polar warming is different in the data (winter/spring warming) and the models

(autumn/winter warming). Second, there are large differences among models in their simulations of variables such

as precipitation and cloudiness for the present climate. For

those variables for which direct observational comparisons

can be made, there are often substantial biases of the simulated quantities relative to their observational counterparts.

Explanations of the scatter and elimination of the polar biases will require systematic mode experiments.

The next 5-10 years will likely provide unprecedented

opportunities for the detection of the climate-change signals

in the Arctic. Not only are such changes anticipated (and

arguably, overdue), but there are likely to be observational

and modeling opportunities that significantly enhance our

knowledge of the Arctic climate system’s temporal evolution. The availability of a nuclear submarine dedicated to

science missions (SCICEX) will permit the measurement of

sea ice thickness in a more systematic manner than has heretofore been possible. Given the ambiguities in the recent

record of sea ice extent, ice thickness may well be the variable of choice for sea ice monitoring. In addition, the length

of the Arctic buoy network’s database is now approaching

20 years, permitting meaningful determination of trends in

the basin-wide fields of atmospheric pressure (circulation),

ice motion/deformation, and air temperature. Improved sensors of temperature will allow the mapping of this key variable with much greater confidence than in the past.

Coordinated field programs such as SHEBA, ARM and FIRE

will provide not only their suites of intensive measurements,

but also process studies that will enhance our understanding

and modeling capabilities with regard to key Arctic processes

(especially those involving the surface energy budget and

clouds). The resulting model improvements should add credibility to model-based data assimilation efforts, e.g., reanalyses, which will likely emerge as useful tools for the

documentation of changes in the Arctic climate system.

REFERENCES

Chapman, W. L., and J. E. Walsh, 1993: Recent variations

of sea ice and air temperature in high latitudes. Bull.

Amer. Meteor. Soc., 74, 33-47.

IPCC, 1996: Climate Change 1995: The Science of

Climate Change (J. T. Houghton- L. G. Meira Filho,

B. A. Callander, N. Harris, A. Kattenberg, and K.

Maskell, Eds.), Intergovernmental Panel on Climate

Change, Cambridge Univ. Press, 572 pp.

Jones, P. D., 1994: Hemispheric surface air temperature

variations: A reanalysis and an update to 1993. J.

Clim., 7, 1794-1802.

Martin, S., E. Muñoz, and R. Drucker, 1997: Recent

observations of a spring-summer warming over the

Arctic Ocean. Nature, submitted.

Maslanik, J. A., M. C. Serreze, and R. . Barry, 16: Recent

decreases in Arctic summer ice cover and linkages to

atmospheric circulation anomalies. Geophys. Res.

Lett., 23, 1677-1680.

Trenberth, K. E., 1990: Recent observed inter-decadal

climate changes in the Northern Hemisphere. Bull.

Amer. Meteor. Soc., 71, 988-993.

Walsh, J. E., V. Kattsov, D. Portis, and V. Meleshko, 1997:

Arctic precipitation and evapotranspiration: Model

results and observational estimates. J. Clim., submitted.
12 Naval Research Reviews

Dr. Wilford “Willy” Weeks has been a Principal Investigator of the Office of Naval Research (ONR) for many

years focusing his research efforts on the iced covers of the

world’s polar oceans. He retired in 1996 from the University of Alaska but remains active as a consultant to the Federal Government on ice problems associated with the Polar

Regions. His career in snow and ice began in 1955 when he

was an Air Force Research and Development Officer leading a field operation along the Labrador coast studying the

properties and behavior of sea ice.

After teaching geology for five years at Washington

University, he joined the staff of the Snow and Ice Branch of

the Army Cold Regions Research and Engineering Laboratory in Hanover, New Hampshire. He was at the Laboratory

for 26 years and was also an Adjunct Professor of Earth Sciences at Dartmouth College. In 1986, he became Chief Scientist at the Alaska Synthetic Aperture Radar Facility and

Professor of Geophysics at the Geophysical Institute of the

University of Alaska in Fairbanks.

Dr. Weeks has participated in 35 field operations in

the Arctic, three in the Antarctic, and five winter operations

in more temperate regions. Colleagues recognized his outstanding work by electing him to the National Academy of

Engineering and to the Presidency of the International Glaciological Society. He was also honored as the ONR Chair

in Arctic Marine Science at the Naval Postgraduate School,

Monterey, California. Recently, he was named an honorary

member of the American Polar Society, a Fellow of the

American Geophysical Union, and a Fellow of the Arctic

Institute of North America. He was awarded the U.S. Army

Research and Development Achievement Award on two occasions, the Army award for Meritorious Civilian Service,

and the Navy Meritorious Unit Commendation for his part

in field operations in the Arctic Ocean.

Profiles

in Science

Wilford “Willy” Weeks
One/1998 13

As we collect more observational data it is becoming

increasingly evident that the ocean varies both spatially and

temporally far more energetically than previously thought.

So is the case in the Weddell Sea, where detailed observations within its western rim from the Ice Station Weddell

(ISW Group, 1993) exposed the co-existence of two types

of bottom water, one relatively fresh, the other more saline.

Often these two types are observed within a single station,

forming a highly stratified benthic layer (Gordon, et al.,

1993). Using the ISW data and that of other recent data in

the Weddell Sea a more detailed map of bottom potential

temperature and salinity is constructed (Fig. 1, 2).

Within the deeper central part of the Weddell Sea

the bottom potential temperature pattern (Fig. 1) reveals the

presence of relatively warm bottom water, above -0.8°C. This

broad feature forms as >-0.8°C water shifts towards the

deeper center of the basin upon encountering the outflow of

very cold and dense Ice Shelf Water from the Weddell Sea

Shelf, channeled within the Filchner Depression (Foldvik,

et al., 1985). The warm bottom water approaching from the

east at depths below the mouth of the Filchner Depression

(between 600 to 650 m; map 567 from the AWI bathymetry

series, in prep) is pushed towards the central basin, while

the warmer bottom water of the upper slope, first undercut

by the colder water, reappears along the upper slope to the

west of the cold water plume, which drops to deeper levels

while advecting westward.

A major export of cold shelf water appears to occur

just west of General Belgrano Bank (72.5 to 73.5°S and 47°

to 50°W). From that point the areal extent of the sea floor

deeper than 1000 m covered with cold bottom water

(<-1.0°C) grows progressively larger along the general flow

path of the Weddell Gyre towards the west and north (Muench

and Gordon, 1995). Most of the Ice Station Weddell bottom

temperatures in the western Weddell Sea at depths of 2500

to 3000 m, south of 67°S is well below -1.2°C. North of

67°S the width of the <-1.4°C bottom layer abruptly narrows, which may be a product of increased vertical mixing

Bottom Water

Formation and

Distribution in the

Weddell Sea

Arnold L. Gordon, Lamont-Doherty Earth Observatory, Palisades, NY
14 Naval Research Reviews

with slightly warmer overlying water (Gordon, et al., 1993).

In the northwestern Weddell Sea cold bottom water turns

towards the east as <-1.0°C water near 64°S and continues

eastward as <-0.9°C water between 64° and 66 °S.

The bottom salinity distribution (Fig. 2) in the western Weddell Sea reveals the spatial distribution of the two

types of bottom waters. A plume of <34.62 bottom water

emanates from just west of General Belgrano Bank, winding itself along a path of 700 km towards the north, ending

near 65°S and 50°W. The saline shelf water of the western

Weddell Sea (Western Shelf Water, Foldvik, et al., 1985),

migrates northward, escaping from the shelf near 69°S, forming a saline plume just landward of the <34.62 plume. The

Ice Station Weddell stations (Gordon, et al., 1993) shows

that this salty bottom water lifts the lower salinity bottom

water off the sea floor, inducing a very stratified double layer

slope plume. It is suspected that slope canyon near 70°S

directs the saline shelf water into the deep ocean.

Figure 1

Bottom potential temperature pattern of the Weddell Sea.
One/1998 15

Seaward of the elongated <34.62 plume, there is a

suggestion of a plume of >34.65 water. It is expected that

the Filchner Depression outflow of Ice Shelf Water entrains

some of the older more saline bottom water advected in from

the east. This mixture is still colder than the -0.8°C water of

the central Weddell Basin.

In summary: bottom water characteristics reveal

major export of low salinity shelf water near 72°S 51°W

immediately west of General Belgrano Bank. It is joined

downstream by high salinity bottom water just north of 70°S.

The low salinity bottom water is expected to be derived from

Ice Shelf Water, similar to the export from Filchner Depression; the high salinity bottom water is derived from the mass

of Western Shelf Water, a product of sea ice formation. Only

in the western Weddell Sea do these two types of bottom

stratify to occupy the same water column. One wonders if

the ratio of low to high salinity bottom water changes with

time, perhaps in response to sea ice changes.

Figure 2

Bottom salinity distribution in the western Weddell Sea.
16 Naval Research Reviews

Acknowledgment

The Ice Station Weddell research is supported by a

grant from NSF’s Office of Polar Programs, OPP-93-13700.

REFERENCES:

Foldvik, A., T. Gammelsrod and T. Torresen 1985:

Circulation and water masses on the southern

Weddell Sea shelf. In Antarctic Res. Series Volume

43 ed. S.S. Jacobs, Am Geop Union, Wash DC, pages

5-20.

Gordon, A.L., B.A. Huber, H.H. Hellmer, and A. Ffield,

1993: Deep and bottom water of the Weddell Sea’s

western rim. Science, 262, 95-97.

ISW Group, 1993: Weddell Sea exploration from ice

station. EOS, 74, 121 & 124-126.

Muench, R.D. and A.L. Gordon (1995) Circulation and

Transport of Water Along the Western Weddell Sea

Margin. J. Geophs. Res. 100: 18,503-18,515.
One/1998 17

Ocean heat flux values, as observed in many regions

of the Southern Ocean, often exceed 25 W/m2 and will melt

ice, from below at a rate of 1 cm/day at this level. Models of

the ice-ocean processes (e.g. Martinson, 1990) have estimated

a leads fraction, or open water percentage, of 5% or greater

is necessary to provide adequate ventilation for this level of

ocean heat to the atmosphere, otherwise the ice cover may

be destroyed prematurely from below. Ice growth in leads

(covered with thin ice) is typically treated as a one-dimensional heat transfer problem, with the energy balance at the

bottom ice surface balanced between three terms: conduction of heat upward through the overlying ice (Fc

), upward

ocean heat flux (Fw) and the latent heat of the phase change

from water to ice at the ice bottom (ρiLdH/dt).

Observations, however, show a radically different behavior for ice growth in Antarctic sea ice leads than is currently used in models. During the winter Antarctic Zone

Flux Experiment (AnzFlux), we installed thermistor strings

and ice thickness gauges into leads and sea ice at the beginning of two drift experiments (Ackley, et al., 1995). The

sites were measured at 15 minute intervals for temperature,

twice daily for ice thickness changes and periodically for ice

structure during the experiment. For a narrow (3-5 m width)

lead, we observed bottom ice accretion (16 cm) for the first

1.5 days during a calm cold period. During the following

two days, however, a storm caused two effects. One was a

strong increase in oceanic heat flux as vertical mixing was

enhanced (McPhee, et al., 1996), which resulted in bottom

melting of several cm of the newly accreted sea ice at this

site. The second storm effect, caused by surface winds in

excess of 20 m/s, was to deposit drifting snow on the originally bare ice surface to a depth of 20 cm. Flooding of the

full depth of the snow by sea water then took place through

pores in the ice. The surface slush subsequently froze as sea

ice from the top snow surface downward. At the end of five

days, the original lead was covered with 20 cm of sea ice, all

Sea Ice Growth in

Antarctic Leads: Top

Freezing vs. Bottom

Melting

Stephen F. Ackley, Cold Regions Research and Engineering Laboratory, Hanover, NH
18 Naval Research Reviews

of it converted from the flooding of the snow cover, while

the original sea ice that had formed had been ablated from

below by the high ocean heat flux.

The ice thickness measurements from the other sites,

located on sea ice up to 0.8 m thickness, showed bottom

ablation rates (>1 cm/day) commensurate with the lead site

and also in agreement with turbulent heat flux measurements

in the ocean mixed layer (McPhee, et al., 1996). Two other

regional observations showed that the formation of snow ice

on the surface by flooding and refreezing were common occurrences. First, we found the ice structure was dominated

by granular ice (>80%) of primarily snow ice origin, in the

ice cores that were taken throughout the region. Second, ice

thickness, snow depth and surface elevation measurement

profiles taken concurrently with the ice cores showed widespread areas where the ice surface was below sea level, and

approximately one-third of the measured profiles were

flooded at the snow cover base at the time of measurement.

Results from a one-dimensional thermodynamic model

(e.g. Maykut, 1986), showed however, that in the absence of

a snow slush freezing mechanism, that ice less than 40 cm

thickness (the mean thickness observed) would be melted

prematurely for this region.

Two dilemmas therefore summarize the conflict of the

observations with some models: 1) the direct melting of sea

ice by the ocean heat flux is observed rather than ventilation

through leads and, 2) ice of observed mean thickness or thinner is predicted to melt prematurely when typical heat flux

models are used.

These are resolved however by the additional observation of widespread and relatively continuous freezing of

surface snow slush onto the ice top surface. The sea ice

cover acts as a vertical conveyor belt, with ice added on the

top surface by snow slush freezing, at a similar rate that it is

melted from below by the high ocean heat flux A continuous lead fraction is therefore not necessary to ventilate the

ocean heat flux, and the ice cover may therefore be sustained

by this process, freezing from above while melting from

below for the period of its observed lifetime of several months

rather than melting prematurely.

References

Ackley, S.F., V.I. Lytle, K.M. Golden, M.N. Darling, G.A.

Kuehn, 1995, Sea Ice Measurements during AnzFlux,

Ant. Jl. of the U.S.

McPhee, M., S.F. Ackley, P. Guest, B.A. Huber, D.G.

Martinson, J.H. Morison, R.D. Meunch, L. Padman,

T.P. Stanton, 1996, The Antarctic Zone Flux Experiment, Bull. of the AMS, v. 77, p. 1221-1232.

Martinson, D.G., 1990, Evolution of the Southern Ocean

winter mixed layer and sea ice: open ocean

deepwater formation and ventilation, Jl. of Geophys.

Res., 95(C7), p. 11641-54.

Maykut, G.A., 1986, The Surface Heat and Mass Balance,

in the Geophysics of Sea Ice (N. Untersteiner, ed.),

NATO ASI Series v. 146, Plenum Press, New York.
One/1998 19

Modern Beginning

A brief history of sea ice dynamics modeling is presented. It leans heavily toward studies in which I was involved. The story begins in the early 1970s with the Aidjex

elastic plastic constitutive law [Coon, et al., 1974].

Thorndike, et al. [1975] described ice condition by its thickness distribution. Equating the power dissipated by stress

during plastic stretching to the rate of work done by changing gravitational potential energy and sliding friction provided an estimate of the compressive strength [Rothrock,

1975]. This strength estimate was too low.

Idealized problems and simulations using ideal plasticity showed that isotropic compressive strength must be of

order 100 kN/m [Pritchard, 1976] for typical Beaufort and

Chukchi Sea ice conditions. The energy dissipated by shear

ridging was added to rate of work done by small scale sinks,

and parameters were adjusted to increase strength [Pritchard,

1981]. Unconfined compressive strength of order 100 kN/m

for typical Chukchi Sea winter ice conditions is necessary to

support arching across the Bering Strait. By comparing model

motions with buoy motions, the model was found to have

errors of order 3 km/day for a wide range of conditions [Kollé

and Pritchard, 1983].

Hibler [1979] introduced a viscous plastic constitutive law. The geophysics community warmly embraced this

model, and it has been widely used for large scale simulations. Scientists have made hundreds of simulations, mostly

using versions of Hibler model with two-component ice description. It is the ice model used in the PIPS system developed by the Navy and used by the Joint Ice Center. This

two-component description of ice conditions, while quick

and easy to implement because it uses only the fraction of

open water and the mean thickness, cannot accurately describe strength because the amount and thickness of the thinnest ice controls strength. Recently, Flato and Hibler [1995]

improved this model by returning to a complete thickness

Modeling Sea Ice

Behavior

Robert S. Pritchard, IceCasting, Inc., San Rafael, CA
20 Naval Research Reviews

distribution, with separate categories for ridged and

undeformed ice.

Ice dynamics models were coupled to ocean dynamics models in the early 1980s [e.g., Hibler and Bryan, 1987;

Pritchard, et al., 1990, and many more recent studies], so

that currents, thermal and salt fluxes become part of the solution. These models have developed into sophisticated climate dynamics tools [e.g., Maslovski, 1997], but most retain

the viscous plastic ice model with a two-component description of ice conditions.

Coon and Pritchard [1979] introduced the mechanical energy balance of the ice cover as a simple diagnostic

tool for understanding the essential processes that control

ice behavior. These scalar fields clearly described the transfer of mechanical energy from the atmosphere, through the

ice, and into the ocean. A simulation of Beaufort Sea ice

behavior showed that the rate of dissipation of energy as

measured by the product of stress and plastic stretching, is

an order of magnitude larger in the nearshore region where

extensive ridging occurs [Thomas and Pritchard, 1980]. The

energy balance equation is a natural extension of the Aidjex

model because we define the strength in terms of small scale

energy sinks that we equate to this rate of dissipation of energy.

Pritchard [1984] developed a model to simulate and

forecast under-ice ambient noise. The noise at any location

is assumed to be generated at all locations in the ice cover by

different processes. Four different processes were considered: pressure and shear ridging, microcracking, and mixed

layer shearing [Pritchard, 1990]. Each source propagates

outward, and propagation loss is estimated. We assume that

the source level related to variables that appear in the ice

dynamics model. For example, ridging noise is assumed to

be proportional to the energy dissipated in ridging. This

model attempts to use basic acoustic principles wherever

possible. The acoustic intensities of the different source processes are summed, rather than the logarithmic magnitudes

that are more common in the acoustics community. Therefore, it is natural to assume that each noise source is proportional to an energy measure, rather than to the force [Makris

and Dyer, 1986] or deformation [Lewis and Denner, 1988]

measures used by other investigators.

Present

During the 1990s, an anisotropic elastic plastic constitutive law was introduced to describe lead formation and

evolution directly [Coon, et al., 1992]. We are still developing it. Coon, et al., [1998a] describe the physical basis for

introducing an anisotropic elastic plastic constitutive law.

Small scale processes that affect leading, rafting, and ridging are taken into account directly. The idea is that the largescale stress state must lie within all of the yield surfaces that

describe failure of individual ice features. Coordinate rotations provide the technique for bringing together the differently oriented surfaces and their flow rules. The new anisotropic model allows our research attention to focus on the

individual small scale processes that contribute to leading,

rafting and ridging.

In the new anisotropic plasticity model, Coon, et

al.[1998b] describe ice conditions in terms of a thickness

distribution for each lead and ridge system. A system here

may mean an individual or a set of parallel leads or ridges.

Pritchard [1998] describes ice conditions using a three-dimensional thickness distribution, which is the fraction of area

covered by ice having each thickness and each orientation.

Isotropic ice conditions resulting from equal fractions of ice

having all orientations.

Much of the mathematical formalism of the plasticity

model follows from the Aidjex numerical model, with several crucial exceptions [Pritchard, 1996, 1998]. First, the

stress state in the isotropic Aidjex model had its principal

directions aligned with principal directions of stretching, but

in the new anisotropic model they are not necessarily aligned.

Thus, we must obtain solutions for three stress components

(σxx ,

 

σyy ,σxy ) in a general coordinate system, rather than the

stress invariants. Second, the yield surface of the isotropic

model was constructed from one tensile cutoff cone and a

compression cap with strength dependent on the ice thickness distribution. The anisotropic yield surface is defined

by the region in stress component space lying within the isotropic surface plus additional yield surfaces for each lead or

ridge system. The numerical integration will be more complex because of the piecewise definition of this combined

yield surface.

Assume that a set of m features exist. These features

might include new deforming leads, ridges that have formed

from older leads, or velocity discontinuities that have been

generated along a mathematical characteristic but have not

yet opened. The stress state cannot violate the yield criterion of any feature φj

(σ,κj) ≤ 0, where σ is the stress tensor,

κj represents variables such as strength of the feature that

depends on its thickness distribution, and j ranges from 1 to

m, where m is the number of branches undergoing plastic

deformation. For a normal flow rule the plastic stretching is

orthogonal to the yield surface

D p = 

m 

3 

j = 1 

λ j n j 

where

n j = 

∂φ j 

∂σ 

is orthogonal to the yield surface φj, and the multiplier λj

must be nonnegative. We also define Dj = λjnj as the plastic

stretching of each lead system. The plasticity model shows

that deformations from multiple active leads combine by addition.
One/1998 21

For an elastic plastic material, the stress rate satisfies

a linear elastic law

σ  ̇ = M e  ̇ 

where M is the elastic modulus tensor and e is the elastic

strain. The kinematic expression relates the elastic strain

rate and plastic stretching [Pritchard, 1975]

e  ̇ − We + eW = D − Dp 

where D is stretching and W is spin, which are the symmetric and antisymmetric parts of the velocity gradient L, respectively

L = 

∂v 

∂x 

A 

Here v is ice velocity and x is position.

The anisotropic plasticity model is better. It can identify lead formation and evolution directly. Leads are oriented, and their strength along the lead direction may be large.

The older isotropic models averaged the strengths along and

across the leads by assuming that a range of ice thicknesses

affected the strength. We expect that the more accurate description of a lead system will allow for more accurate estimates of open water fractions. This last variable is essential

for determining the effect of sea ice on climate dynamics.

We expect that the anisotropic plasticity model can

resolve behavior of individual lead systems, which might be

as small as a few kilometers.

Future

The new anisotropic plasticity model is not yet tested.

We have devised a numerical method to integrate the constitutive equations. The method has been implemented into a

computer program [Pritchard, 1996], but the material model

has not yet been incorporated into a finite element or finite

difference code to allow simulations. Output from this model

will include motion, deformation, stress, lead size and orientation. The last two variables will be observable in satellite images, and allow direct testing of model performance.

The Sea Ice Mechanics Initiative (SIMI) had a goal of

including micro mechanical physical behavior such as fracture and damage modeling in the large scale constitutive laws.

The basic question remains: How do these processes affect

the large scale behavior where leading, rafting, and ridging

dominate the essential processes? It appears now that these

smaller scale effects are small compared with the uncertainty

in large scale parameters. We now assume that tensile

strength is zero. Perhaps fracture affects the initiation of

large scale processes.

Models should combine the best statistical and the best

deterministic components. Some method of blending observations (historical and local) with statistical relationships

and physics-based models is desirable. There are random

components to behavior that deterministic models alone cannot describe. However, we now have only a poor idea how

large are these random components. We are still trying to

understand the errors in deterministic modeling of ice motions and open water fractions. We have only begun to compare the deformations or ice conditions.

The stream of high resolution SAR imagery that now

exists could be used to initialize and correct calculated fields

of ice motion and ice condition data. This will require that

sophisticated data assimilation techniques be available for

these systems. Future simulations and forecasts should use

these satellite data more actively.

Ice forecasting techniques are still not very reliable.

Errors often exceed the 3 km/day found during extensive

simulations with careful tuning. Ice models provide little

information on ice conditions or stresses.

Shipping offers an operational need for understanding

sea ice behavior and its forecasting. However, this must move

far from our research approach into a practical industrial

approach. Satellite imagery is now available to ship masters, and they are far more comfortable with accurate pictures of the present than they are with uncertain forecasts of

the future. The new anisotropic model might help here because it provides a measure of lead formation and evolution,

which is one of the ice condition measures needed specifically for navigation.

Something is wrong with the large scale models. I

showed that compressive strengths (both isotropic and unconfined) must be greater than 100 kN/m to avoid movement under certain conditions. Yet large scale models use

strengths of order 10 kN/m, and simulations show their best

comparisons with this lower strength. I do not know what

the problem is. It could be that isotropic plasticity is not

adequate. It could be that we do not characterize strength

formulations adequately in terms of thickness distribution.

Specifically, strengths must vary more rapidly with changes

in ice condition. It could be that we must characterize ice

condition differently, although similar low strengths are

needed by both Hibler 2-level models and a 6-level model

[e.g., Polyakov, et al., 1997]. We must understand this contradiction.

We must identify known sea ice properties and avoid

redoing the same calculations. For example, we know that

a yield surface cannot have an arbitrary shape because nonzero unconfined compressive strength implies that the tensile cutoff cone must lie within or on the yield surface. Yet

present-day studies ignore this fact while attempting to learn

the effects of varying the yield surface shape. I believe that

these properties should be fixed, and our limited funding

should address other essential questions.

High resolution coupled ice-ocean models now use the

best ocean models at ever smaller resolution, but they use

simplified ice models (e.g., two component ice conditions).

These global climate models must begin to use the best ice
22 Naval Research Reviews

models if they are to ensure accurate estimates of open water fractions and heat transfer rates.

We do know the essential physical processes that affect ice behavior on scales of 1-100 km. They are leading,

rafting, and ridging. We can describe some smaller scale

processes that contribute to rafting and ridging forces: gravitational potential energy changes and sliding friction. These

small scale processes control the forces needed to continue

the large scale processes after they begin. We know little

about the loads needed to initiate these large scale processes,

however. Some guidance might come from the micro mechanics community, including fracture mechanics.

Except for questions about climate dynamics, the study

of Arctic sea ice is fading away. The U. S. Navy has reduced

interest because it no longer perceives an enemy across the

Arctic Ocean. The petroleum companies have all but quit

the Alaskan Arctic for cheaper international finds. This includes the Russian Arctic, where Russian scientists have difficulty finding work. Arctic acoustics, which was once an

essential field of study to the military, is now far less important. We can use our acoustic knowledge as a tool for acoustic oceanography, and we can use acoustic techniques to

identify and measure sea ice deformations. Thus for the near

term future, interest in sea ice must arise from its basic scientific interest, from its ability to provide insight into other

scientific areas such as material science, or from a need to

study climate dynamics.

REFERENCES

Coon, M.D., and Pritchard, R. S. (1979) “Mechanical

Energy Considerations in Sea Ice Dynamics,” J.

Glaciol., 24(90), 377-389.

Coon, M.D., Maykut, G. A., Pritchard, R. S., Rothrock, D.

A., and Thorndike, A. S., (1974) Modeling the Pack

Ice as an Elastic-Plastic Material, Aidjex Bulletin No.

25, University of Washington, Seattle, WA, pp. 1-

105.

Coon, M.D., Echert, D. C., and Knoke, G. S. (1992) “Pack

Ice Anisotropic Constitutive Law,” in IAHR 92,

Proceedings of the 11th International Symposium on

Ice, Banff, Alberta.

Coon, M.D., Knoke, G. S., and Echert, D. C., and

Pritchard, R. S. (1997a) “An Oriented Thickness

Distribution for Sea Ice,” J. Geophys. Res., to be

submitted.

Coon, M.D., Knoke, G. S., and Echert, D. C., and

Pritchard, R. S. (1997) “The Architecture of a New

Sea Ice Mechanics Model,” J. Geophys. Res., to be

submitted.

Flato, G.M., and Hibler, W. D., III. (1995) “Ridging and

strength in modeling the thickness distribution of

Arctic sea ice,” J. Geophys. Res., 100(C9), 18,611-

18,626.

Hibler, W.D., III. (1979) “A dynamic thermodynamic sea

ice model,” J. Phys. Oceanogr., 9, pp. 817-846.

Hibler, W.D., III, and Bryan, K. (1987) “A diagnostic iceocean model,” J. Phys. Oceanogr., 17, pp. 987-1015.

Kollé, J. J., and Pritchard, R. S. (1983) “A Comparison of

Two Sea Ice Trajectory Models with AIDJEX

Observations,” J. Energy Res. Tech, 105(3), pp. 346-

351.

Lewis, J.K. and Denner, W. W. (1988) “Arctic Ambient

Noise in the Beaufort Sea: Seasonal Relationships to

Seasonal Kinematics,” J. Acoust. Soc. Am., 83, pp.

549-565.

Makris, N.C. and Dyer, I. (1986) “Environmental Correlates of Pack Ice Noise,” J. Acoust. Soc. Am., 79, pp.

1434-1440.

Maslowski, W. (1997) “Advanced Modeling of the Arctic

Ocean and Sea Ice in Support of Global Climate

Studies,” Bull. Meteorol. Soc., in press.

Polyakov, I.V., Kulakov, I. Yu., Kolesov, S. E., Dmitriev,

N. Eu., Pritchard, R. S., Driver, D., and Naumov, A.

K. (1997) “A coupled Sea Ice-Ocean Dynamical

Thermodynamical Model of the Arctic Ocean,” J.

Offshore Mech. and Arctic Engrg., submitted.

Pritchard, R.S. (1975) “An Elastic-Plastic Constitutive

Law for Sea Ice,” J. Appl. Mech., 42(E2): pp. 379-

384.

Pritchard, R.S. (1976) “An Estimate of the Strength of

Arctic Pack Ice,” AIDJEX Bulletin No. 34, University of Washington, Seattle, WA, pp. 94-113.

Pritchard, R.S. (1981) “Mechanical Behavior of Pack Ice,”

In A.P.S. Selvadurai, Ed. Mechanics of Structured

Media, Part A, pp. 371-405. Elsevier, Amsterdam.

Pritchard, R.S., (1984) “Arctic Ocean Background Noise

Caused by Ridging of Sea Ice,” J. Acoust. Soc. Am.,

75(2), 419-427.

Pritchard, R.S. (1990) “Sea Ice Noise-Generating Processes,” J. Acoust. Soc. Am., 88(6), 2830-2842.

Pritchard, R.S. (1996) “Sea Ice as a Pathway for the

Transport of Radionuclides,” IceCasting, Inc.,

Seattle, WA.

Pritchard, R.S., Mueller, A. C., Hanzlick, D. J., and Yang,

Y.- S. (1990) “Forecasting Ice Edge Motion in the

Bering Sea,” J. Geophys. Res., 95(1), pp. 775-788.

Rothrock, D.A. (1975) “The Energetics of the Plastic

Deformation of Pack Ice by Ridging,” J. Geophys.

Res., 80(33), 4514-4519.

Thomas, D.R., and Pritchard, R. S. (1980) “Beaufort Sea

Ice Mechanical Energy Budget 1975-76,” Flow

Research Company, Kent, WA.

Thorndike, A.S., Rothrock, D. A., Maykut, G. A., and

Colony, R. (1975) “The Thickness Distribution of

Sea Ice,” J. Geophys. Res., 80(33), 4501-4513.
One/1998 23

Statistical representations of the sea ice pack are used

in climate models, the most common representation being a

distribution function for ice thickness. This practice can be

defended using two arguments. First, observed ice thickness distributions, from different regions, different seasons,

and different years, have enough similarity — and enough

variation — to suggest that the thickness distribution can

serve as a state variable. The idea is that bulk properties of

the ice pack, such as its strength, might be expressed in terms

of the thickness distribution. If a local property, p, depends

on ice thickness, then there is a corresponding bulk property, P, constructed as a weighted average of p, weighted by

the thickness distribution, g(h).

The thickness distribution therefore provides a way to

model bulk properties of the ice pack. Because observations show variation in g(h), it is likely that there are variations in bulk ice properties. Successful models of the ice

pack will probably need to account for these variations.

The second reason why thickness distributions appear

in models is that theory exists for how the thickness distribution adjusts to other climate variables. Thus it is possible,

in models, to study interactions between the statistical ice

pack and the modeled climate.

At the same time, the practice can be challenged on

two grounds. First, we do not know enough about the present

spatial and temporal variations in thickness distribution to

evaluate the theory. Second, the theory involves free parameters that represent certain thermal and mechanical processes. It is not likely that these parameters can be determined

uniquely from observations.

Ongoing measurement programs using moored upward

looking sonar and submarines and data from the Surface Heat

Balance experiment will address these challenges. Within a

few years we will have improved our documentation of the

current ice state. We should also be able to say how much of

the observed space and time variation in thickness distribution is explained by variation in the thermal and mechanical

forcing, while holding the free model parameters constant.

Sea Ice Thickness

Distribution as a

State Variable

Alan Thorndike, Department of Physics, University of Puget Sound, Tacoma, WA
24 Naval Research Reviews

It is important to know the magnitude of the unexplained

variance, because this sets a threshold for detection of climate change.

While a prodigious quantity of data is accumulating,

it is important not to underestimate the difficulty involved in

assembling a useful data set from it. Take as one goal, for

example, maps of the climatological mean and variance of

thickness at the times of minimum and maximum ice extent.

The interannual departures from climatology are equally

important. The existing data seem to justify a careful effort

to estimate these fields. Until this is done, it won’t be possible to make more than a qualitative assessment of the ability of the thickness distribution theory to simulate the ice

climate.

Another way to test the theory is to attempt to simulate the actual space and time variations in the thickness distribution, rather than the climatology. Work on this problem,

by Rothrock and Zhang, uses the observed time varying forcing fields, since 1979, to determine the thickness distribution at all subsequent times and locations. From these

calculations they extract distributions for comparison with

distributions observed along submarine tracks or at fixed

locations. It is too early to tell if the calculations explain

any of the variance in the observations.

There has been no challenge to the 1975 theory, partly

because the data demands for testing the theory are so formidable, and also because the theory itself depends on several free or poorly constrained parameterizations. First, there

is the growth rate function dh/dt = f(h,x,y,t). Second is the

redistribution process ψ(h). It is tempting to think that the

theory would be exact, if we knew these functions, but this

is not true. The theory supposes that these functions exist,

whereas, in fact, even in a particular location and time, dh/dt

may depend on other variables than thickness (snow thickness, for example). So there is room for an examination of

the theory. In particular, someone should look into the effect

of random fluctuations in f and ψ. It is also interesting to ask

whether a simpler theory might yield insights into the behavior of the natural system, insights that are hard to extract

from the full theory.

This latter possibility motivated my attempt to examine steady state solutions. Similar features of the thickness

distribution appear in all observations: a strong maximum

between 2 and 4 meters, and a thick end that drops off exponentially. The thin end shows more variation since it is more

sensitive to the recent thermal and mechanical history. A

linear, steady state argument helps to explain these features.

Taking D as the mean divergence, E as the rms shear strain

rate, k as the ridging multiplier (h-->kh), H as the equilibrium thickness, and f(h) as the annual growth function, one

finds that g(h) depends on two dimensionless numbers:

DH/f(0) and E/kD. Solutions have the form in the sketch,

provided D is not too small.

There are a few conclusions to be drawn from this argument. First, a plausible thickness distribution has been

produced based only on a statistical representation of the

deformation, and annual average thermodynamics. Second,

the importance of the slope of the growth function f(0)/H, is

highlighted. Third, the failure of this approximation to the

theory at small D should be examined carefully. How can

we recast the theory in some simple way that remains valid

when D=0?

Much work remains to be done. We have an idea that

has been useful in developing a conceptual model of the ice

pack. But it is not yet known how successful this idea is in 

ccounting for the natural phenomenon, or whether simpler

ideas might be just as successful. There is reason to expect

progress on these issues during the next few years.

Figure 1

Results of a linear, steady state thickness distribution model.

The singularity at the equilibrium thickness diverges as |h-H|

raised to the power DH/f(0)-1. The area of ice thicker than

equilibrium is E/kD. The value of g at h=0 is (D+E)/f(0).
One/1998 25

1. Introduction

Project SPINNAKER was an ambitious technology

demonstration project combining long range fiber optic

cables, Autonomous Underwater Vehicle (AUV) operations

under the ice, low power, lightweight array technology and

real time data processing and recording. Significant engineering and environmental challenges were resolved during

a series of field experiments called ICESHELF. In addition,

the project was been able to assemble an important set of

environmental and oceanographic observations from the

sparsely measured Lincoln Sea.

As SPINNAKER was essentially completed this year

it seems an appropriate time to review the project, highlight

some of its major accomplishments and present some of the

significant oceanographic contributions of the project.

2. Brief Overview of

Project SPINNAKER

SPINNAKER is a joint United States/Canadian program whose objective was to install a large, bottom-mounted,

multi-aperture array of acoustic and engineering sensors

under the ice on the continental shelf break of the Lincoln

Sea. The array system would be cabled to shore for data

processing and recording.

The project focused on an area of the Lincoln Sea continental slope about 170 km north of Ellesmere Island, NWT,

Canada in water depths of 500 to 700 m. The field work and

array installation was staged and supported logistically from

the Canadian forces station at Alert.

Joint field work for SPINNAKER started in 1988. A

Project SPINNAKER;

ICESHELF 1988 -1996

and Beyond

John L. Newton, Polar Associates, Inc., Goleta, CA
26 Naval Research Reviews

memorandum of understanding was signed between the US

and Canada in 1992. While most of the work was joint, the

US focused on acoustic array technology and deployment,

and the Canadians had primary responsibility for the development and testing of the large AUV which would lay the

fiber optic cable to the shore.

3. ICESHELF Objectives

and Accomplishments

ICESHELF experiments were conducted annually

during the springtime to collect information to support the

final installation. These field efforts tested aspects of the

array technology and the developed and practiced array deployment techniques.

A critical part of the ICESHELF experiments were the

navigation tests and Arctic trials of the Theseus AUV.

Theseus, developed by International Submarine Engineering of Vancouver, Canada, had the formidable task of laying

the fiber optic cable from Alert to the array site. Theseus is

about 11 m (35 ft) in length, 1.3 m (50 in) in diameter and

displaces about 8900 kgs (10 tons, 19,500 lbs). The cargo

bay (2.4 m x 1.1 m, 96 in x 44 in) was modified to hold

220 km of 1.8 mm (0.07 in) fiber optic cable. The vehicle is

capable of about 4 knots and was batteried (silver-zinc) for a

minimum of a 50 hour mission. Navigation was accomplished by a combination of an inertial navigation unit for

heading, a Doppler sonar for velocity, with a provision for

position updates at transponders along the route.

4. SPINNAKER 1996

Deployment

The deployment of the SPINNAKER array required a

rather large ice floe, about 4 km across, which, of course had

to be conveniently located in the desired area. Because a

shear zone between moving ice to the north and more stationary ice near land exists in the ice cover along the

shelfbreak, this can be a difficult requirement. After an

icecamp was established, a series of large holes were melted,

tents set up, and the deployment equipment was installed.

Lines were run under the ice between the deployment

holes using a small AUV developed and operated by the

Applied Physics Laboratory/University of Washington. This

vehicle has a nominal range of about 1 km and strings a light

(80 lb test) line between the holes. Using the light line, a

series of stronger working lines were then passed under the

ice for array deployment. The array was lowered and held

under the ice off of the ocean bottom, just in case the ice

decided to start to move.

Theseus then began the deployment of the small fiber

optic trunk cable from Alert to the camp. When Theseus

was about half way on its 24 hour journey, the array was

lowered to the seafloor and tensioned so that the horizontal

part of the array was straight. The Theseus AUV successfully completed the deployment of the 180 km fiber optic

data link from shore by passing through a triangular saddle

with 200 m sides at the camp. This was quite a feat; the

overall cross track error in navigation was less than 0.05%

of the distance traveled. The fiber optic cable was recovered, fusion spliced to the array and released. Good data

immediately appeared on the shore processing and recording system.

In its final deployed configuration the primary SPINNAKER array consists of a long horizontal bottom array

(2400 m), a short, perpendicular horizontal bottom array

(213 m) and two vertical arrays (468 m). 120 acoustic and

39 engineering sensors are distributed in the array.

The SPINNAKER array is batteried for a lifetime of 3

to 5 years. The acoustic sensors have a design spacing of

30.2 m (50 Hz wavelength spacing) in both the horizontal

and vertical arrays. The system has a design frequency range

from below 2 Hz to just above 60 Hz. Engineering sensors

include a variety of test signals and the receivers/controllers

necessary to navigate the vertical arrays.

Each acoustic sensor is sampled at 256 Hz. Engineering and test sensors are sampled at various, usually slower

rates. Analog signals are converted to digital in the array

Node and output with synch and status words into a serial

bit stream. Data is transmitted optically through the nonrepeatered trunk cable to the shore processing site.

5. Preliminary Acoustic

Results

Acoustic and engineering data was continuously collected for 8 weeks. A problem with the array electronics or

the fiber optic data link terminated data collection.

On a positive note the two month data record seems

quite good. Several groups including ARL, University of

Texas, Naval Research Laboratory, APL, University of Washington, Institute of Ocean Sciences in Victoria, and the

Scripps Institution of Oceanography have started analysis. I

would like to briefly show some of the physical characteristics of the installation and examples of the data.

Figure 1 is a view looking down on the array. A

north/south east/west grid in meters is superimposed and the

local bathymetric contours are shown. Each element of the

horizontal array, shown as the - symbols, was located acoustically by popping lightbulbs at several locations around the

array. These locations were referenced to a careful theodolite survey of the camp and high accuracy GPS position recordings. The acoustic elements are located with a relative

accuracy of 1 to 2 m. On a geographic scale the location of

the array is known to about 10 to 20 m. The long horizontal

array is oriented at 119/299 Deg T, roughly along the bathymetric contours; the short horizontal array lays almost ex-
One/1998 27

actly north/south. Because the vertical arrays are very lightweight they move significant distances with the currents and

must be navigated using a set of transponders on the ocean

floor and receivers on the array.

6. Environmental

Measurements

Environmental measurements collected during the

ICESHELF included: Conductivity and Temperature versus

Depth (CTD) profiles, current profiles, winter-over moorings, ice drift, meteorological information, geoacoustic studies, bottom samples, bottom photographs.

CTD sections were obtained by helicopter in 1991,

1992, and 1993. Year long current meter moorings were

deployed in 1992-93 and 1993-94. Oceanographic moorings with CTDs and current meters were set out in 1994 in

cooperation with Dr. Knut Aagaard of APL, University of

Washington. All moorings were recovered with good data

with the exception of one of the 1994 moorings.

A paper discussing the major results from the 1988

through 1994 experiments has been accepted by JGR Oceans.

These results are presented adding some CTD data from the

1996 experiment. Two oceanographic features of the Lincoln Sea are of particular importance. First is the presence

of a boundary undercurrent along the slope; the second is

the inter annual changes in the temperature and salinity structure of the upper 200 m.

Geostrophic currents were computed from the three

CTD cross sections using the ocean surface as the level of

no motion. Measured currents suggest motion at the surface

is less than at depth in this area. Each section displayed an

under current directed toward the east along continental slope.

Figure 2 is a simplified view of the geostrophic current structure over the slope. The 5 cm s-1 iso tach and shaded region

is the area of relative high geostrophic currents of 5 to 9 cm s-1.

The shaded region defines a persistent current core, along

the slope, which is interpreted as a boundary undercurrent.

Outside the shaded region currents were less than 5 cm s-1

and usually less than 2 cm s-1. The positions of the recording

current meters from the 1992-3 and 1993-4 moorings are

shown.

Daily averages from the current moorings are shown

in Figure 3. To better display the vectors, north is to the

right rather than up. In the core of the under current, currents are persistently directed toward the east. The mean

currents are easterly at 5 to 6 cm s-1 at both meters in the

current core. Above the current, core currents are variable

in direction and except for a couple of events are relatively

Figure 1

Orientation of the Spinnaker array.

Figure 2

Simplified view of geostrophic current structure over the

continental slope of the Lincoln Sea.

Figure 3

Daily average currents from winter-over current moorings on

the continental slope.
28 Naval Research Reviews

low with a mean value near zero. Near the southern edge of

the current, currents are typically directed toward the east

but there are a fair number of reversals. Here the mean current was about 2 cm s-1 toward the east.

The year long current measurements confirm the presence of an easterly flow at depth along the slope suggested

by the geostrophic calculations. Similar under currents in

the Beaufort Sea and the Barents Sea are described by

Aagaard in several papers. In the Lincoln Sea the under

current has a width of about 50 km and mean speeds of

5-8 cm s-1 and daily average speeds up to 20 cm s-1. Transport would be about 2 Sverdrups.

The waters within the undercurrent evidenced temperature-salinity (TS) characteristics similar to Canadian Basin

waters, suggesting a boundary current system, which is continuous along the continental slope north of Alaska and

Canada.

Temperature and salinity profiles over the slope during 1989 through 1994 reflected significant inter-annual

variations which may be related to variations in the large

scale circulation of the Arctic. In 1989 and 1990 the upper

pycnocline waters over the slope did not indicate a significant contribution of waters with Bering Sea characteristics.

Starting in 1991 and continuing through the most recent

measurements in 1994 the TS correlation evidenced a relative temperature maximum overlying a relative temperature

minimum in the upper part of the pycnocline. The TS characteristics of these features were similar to waters attributed

to Bering Sea origin typically found in the Canadian Basin.

Figure 4

Temperature variations over the Lincoln Sea continental slope

from 1989 through 1996.

7. Summary

The Spinnaker project successful deployed a large

acoustic array on the continental slope of the Lincoln Sea.

The array is cabled to shore via a long (180 km) nonrepeatered fiber optic cable. The system collected a valuable set of acoustic data which is being used to study ambient

noise and seismic events such as earthquakes. Oceanographic

data collected by the project defined a boundary undercurrent along the continental slope and quantified significant

inter annual temperature changes in the upper 200 m.
One/1998 29

I started out my career as a physical scientist; a physical oceanographer. However, a thread that has woven its

way throughout my career is interdisciplinary interactive

research with biological and chemical oceanographers and

other physical scientists such as meteorologists and computer modelers. In particular, I have concentrated on Arctic

air-ice-ocean interaction at marginal ice edge zones (MIZ)

where melting ice lays down stratification leading to intense

phytoplankton blooms. This work involves both oceanographic cruises into the ice as well as constructing numerical models of these phenomena. This has led into the topic

of vertical flux of carbon out of the photic zone into the deep

ocean. In order to make progress in understanding these

phenomena it became necessary to interact with scientists

outside my discipline.

The Arctic Chair/ONR experience came along for me

at just the right time. My tenure in the Arctic Chair in 1985

crossed for about 2 weeks with the only Biological Oceanographer, Professor Walker O. Smith, Jr., to occupy the Arctic Chair. It was a very productive time in which we sat and

discussed bio-physical-nutrient interactions in the MIZ. This

lead to collaborative biophysical numerical modeling and

field work in the Greenland Sea supported by ONR. The

modeling was supported primarily by ONR (Initially through

Dr. Leonard Johnson and then by Drs. Thomas Curtin and

Lou Codispoti). This work had its genesis in joining a physical ocean circulation model with an ice model and with a

nutrient-phytoplankton-zooplankton (N-P-Z) model applied

to the MIZ in both Arctic and Antarctic. We are continuing

this work and have recently we added particle aggregation

in studying the ‘biological pump’ and particle scavenging

(through the Arctic Nuclear Waste Assessment Program,

ANWAP) and flux of carbon to the deeper ocean as shown

in Figures 1 and 2.

Figure 1 is model output showing modeled chlorophyll

distribution over time and over aggregate size class (30-300

cells/particle or 45-123 μm diameter), and through 2 depths

(52 m and 250 m). This model is for conditions similar to

Interdisciplinary

Interaction in Arctic

Research

H. J. Niebauer, School of Fisheries and Ocean Science, University of Alaska, Fairbanks, AK
30 Naval Research Reviews

spring in the Greenland Sea. Maximum surface primary productivity is about 1000 mg C m-2 day-l. The sharp increase

in chlorophyll at about 14 days is penetrative convection of

~0.08 ms-1 (~7000 m day-1) with vertical transort of about

600 mg C m-2 day-l, or about 60% of the surface productivity.

This convection is caused by first preconditioning the

surface water through upwelling (by cyclonic eddy and cyclonic wind) warmer but saltier water from deeper in the

water column. At the beginning of the second week, the

wind and eddy are turned off and the cooling turned on. The

cooling not only cools the surface water but generates ice

which generates cold salty brine which aids in the convection. Even then, the advective penetrative convection will

not occur without including Coriolis effects and without making density a function not only of temperature and salinity,

but also pressure.

The other mode of transport of carbon is through the

slower sinking of the aggregating material from the bloom.

This is seen first in the smaller particles at about 35 days at

52 m, and then in progressively larger particles which reach

a peak at about 50 days at 52 m and about 80 days at 250 m.

The vertical flux associated with the sinking bloom (note,

this is not sinking water) is about 150 mg C m-2 day-l, or

about 15% of the surface productivity and 25% of the convective flux.

Figure 2 shows the mean winter sea level pressure

patterns over the Greenland Sea for 1994-1996. Recent observations (Dr. Kim Van Scoy, pers. comm.) suggested that

there was little deep convection around the Odin region of

the Greenland Sea in winters of 1993-94 and 1994-95, but

that there seemed to be much more deep convection in winter 1995-96. Figure 2 shows that the winter of 1994-95 (also

the previous winter 1993-94, not shown) was a period of

deeper than normal Icelandic low (992 mb). This cyclonic

flow is conducive to wet, windy, warmer conditions with

upwelling to bring warmer salty water closer to the surface

(i.e., preconditioning) .

The next panel shows that during the next winter,

1995-96, the Icelandic low does not occupy the Greenland

Sea. Instead, the Asian high has reached all across Europe

out over the Greenland Sea (~1012 mb). These high pressure conditions tend to be clear and cold and conducive to

deep convection by producing cold, salty water from the previous “preconditioned” warm salty water. The third panel

shows the difference between the two winters with a rise of

22 mb within one year.

Two points here

1. Obviously, it takes true interdisciplinary interaction to solve these problems. It appears that quite a lot science and science funding is going in that direction now (e.g.,

Global Ocean Ecosystems Dynamics, or GLOBEC) and I

certainly see interdisciplinary science as continuing and increasing.

2. A somewhat peripheral point is that the availability

and accessibility of large, high quality, collated data sets is

greatly increasing. This is especially true for the internet

(e.g., the Northern Hemisphere sea level pressure data for

Figure 2). I expect to see this trend continue and expand

into biological, chemical, geological, physical oceanographic

etc. realms. I think that the availability of these data sets

combined with better numerical models on better and faster

computer systems will allow greatly increased understanding of these complicated interdisciplinary ecosystem problems such as e.g., global ecosystem change.

Figure 1

Modeled chlorophyll distribution over aggregate size class

(30-300 cells/particle or 45-123 μm diameter) and over time.
One/1998 31

Figure 2

Mean winter sea level pressure patterns over the Greenland Sea for 1994-1996.
32 Naval Research Reviews

History of the ONR Chair in Arctic Marine Science

Robert H. Bourke (Department of Oceanography, Naval Postgraduate School, Monterey, CA 93943: ph. 408-656-

2373).

History of the Arctic Program at the Office of Naval Research

Thomas B. Curtin (Office of Naval Research, 800

North Quincy Street, Arlington, VA 22217: ph. 703-696-

4119). G. Leonard Johnson (7708 Lake Glen Drive, Glen

Dale, MD 20769: ph. 301-464-6724). Michael VanWoert

(Office of Naval Research, 800 North Quincy Street, Arlington, VA 22217: ph. 703-696-4720).

Two Decades of Upper Ocean Physics from Sea Ice: a

Tribute to ONR Arctic Sciences

M. G. McPhee (McPhee Research Co., Nachea WA

98937: ph. 509-658-2575).

Sounds from the Ice: Past and Future

Warren W. Denner (EOS Research Associates,200

Camino Aguajito #202, Monterey, CA 93940: ph. 408-373-

1567).

A Summary of Progress in Understanding Low Frequency Arctic Ambient Noise

James H. Wilson (Neptune Sciences, Inc., 4711

Viewridge Ave. # 150, San Diego, CA 92123; ph. 619-167-

1146).

Interdisciplinary Interaction in Arctic Research

Henry J. Niebauer (Institute of Marine Science, University of Alaska, Fairbanks, AK 99775-7220; ph. 907-174-

7832).

Project SPINNAKER: Iceshelf 1988-1996 and Beyond

John L. Newton (Polar Associates, Inc., 100 Burns

Place, Goleta, CA 93117; ph. 619-553-3007).

On Modeling Sea Ice Dynamics in Numerical Investigations of Climate

W. D. Hibler III (Dartmouth College, Hanover, NH

03755; ph. 603-646-3172).

Satellite Passive Microwave Remote Sensing of Sea Ice

in the Laptev Sea

L. W. Brigham (ONR Arctic Chair, Department of

Oceanography, Naval Postgraduate School, Monterey, CA

93943-5122; ph. 408-656-2226).

Modeling Sea Ice Behavior

R. S. Prichard (IceCasting Inc., 11042 Sand Point Way

NE, Seattle WA 98125; ph. 206-363-3394).

Weddel Sea Plumes and Bottom Water

A. L. Gordon (Lamont-Doherty Earth Observatory,

Palisades, NY 10964-8000).

Arctic Sea Ice: Properties and Processes

Stephen F. Ackley (CRREL-SI, 72 Lyme Road,

Hanover NH 03755; ph. 803-464-4258).

Spatial Variability in the Arctic Ocean Measured at Large

Scales and Small by Underwater Vehicles, Manned and

Unmanned

James M. Morison (Polar Science Center, APL University of Washington, 1013 NE 40th St. Seattle, WA 98105;

ph. 206-543-1394).

Sea Ice Thickness Distribution as a State Variable

Alan S. Thorndike (University of Puget Sound,

Tacoma, WA 98105; ph. 206-756-3817).

Recent Climate Change in the Arctic

John E. Walsh (University of Illinois, Urbana, IL

61801; ph. 217-333-7521).

Biological Oceanography in the Arctic: Past Experiments

and Future Challenges

Walker O. Smith (University of Tennessee, Knoxville,

TN 37996; ph. 615-974-3065).

FALL MEETING AMERICAN GEOPHYSICAL UNION

OFFICE OF NAVAL RESEARCH ARCTIC MARINE SCIENCE CHAIR

20TH ANNIVERSARY SESSION

DECEMBER 16, 1996

Presiding: R. H. Bourke, Naval Postgraduate School
Sea Ice Mechanics Initiative (SIMI)

Ice Camp in 1992