Western Arctic Shelf-Basin Interactions (SBI) Project

LIST OF SBI PHASE I PROJECT ABSTRACTS



BERING STRAIT: A VITAL AND VARIABLE FORCING OF THE WESTERN ARCTIC SHELVES, SLOPES, AND BASINS

Knut Aagaard
Polar Science Center – APL, University of Washington , 1013 NE 40th St., Seattle , WA 98105-6698

The variable influx of Pacific waters through Bering Strait provides a key forcing for the Western Arctic shelf-slope-basin system. As a contribution to Phase I of the SBI initiative, we therefore propose to measure the Bering Strait flow and its water properties during 1999-2001. In conjunction with earlier and present measurements, this will provide near-continuity in the record of flow and water properties in the strait over a decade. The proposed extension of measurements in Bering Strait will specifically contribute to the SBI initiative by addressing:
1) The variability of transport and water properties of the Pacific inflow to the Chukchi Sea
2) The flux and processing of freshwater on the Western Arctic shelves
3) The variability of Western Arctic shelf sources for the interior ocean and the causes of that variability
4) The needs of a variety of Arctic simulations for accurate long-term boundary conditions and forcing in the Pacific sector.
Finally, the proposed data set will be placed in the public domain in accord with the ARCSS/OAII data management plan.

A SYNTHESIS OF OCEANIC TIME SERIES FROM THE CHUKCHI AND BEAUFORT SEAS AND THE ARCTIC OCEAN, WITH APPLICATION TO SHELF-BASIN EXCHANGE

Knut Aagaard
Polar Science Center – APL, University of Washington , 1013 NE 40th St., Seattle , WA 98105-6698
Tom Weingartner
Institute of Marine Science , University of Alaska Fairbanks , Fairbanks, AK 99775-7220

In support of the SBI initiative we propose a two-year analysis and synthesis of over 150 instrument years of time series measurements (primarily of velocity, temperature, and salinity) from selected portions of the arctic shelves, slopes, and adjacent deep basins. Our intent is to:
1) Provide an observationally based indication of the variability of the shelf-basin system, with an emphasis on the Western Arctic;
2) Contribute to focusing and refining the field programs planned under Phase II of SBI, particularly as these depend upon an understanding of the mechanisms of shelf-basin exchange, and upon the climatology and variability of the shelf-slope-basin system; and
3) Promote further improvements in the rapidly growing array of models of arctic circulation and hydrographic structures and their variability, and provide patterns and statistics against which to test the fidelity of these models. While the emphasis is on time series, we will also take advantage of the large hydrographic data base now available.

The geographic coverage of the already assembled data set includes the Western Arctic shelves, the continental slope and ridges in both the Eurasian and Canadian basins, and the Canada Basin abyssal plain. The intended synthesis will cover the circulation and its variability, with an emphasis on the statistics of the measured flows and their temperature and salinity, together with the dynamics that these statistics imply. We will also make this data set widely available through the National Snow and Ice Data Center, Boulder, likely via CD ROM.

The proposed retrospective study takes advantage of a large data set, the coordinated analysis of which will substantially improve our understanding of the circulation and hydrographic structures of the Arctic shelf-slope-basin system, including their links and variability. The effort will specifically contribute to the SBI initiative by addressing:
1) The variability of Western Arctic shelf sources for the interior ocean and the causes of that variability;
2) The principal mechanisms of exchange across the shelf and slope, likely together with bounds on the effective rates;
3) The background circulation over the shelf, slope, and adjacent abyssal plain and their relation to shelf-basin exchanges;
4) Secondary circulation over the outer shelf and slope and their variability; and
5) Freshwater processing and transport on the shelf.

The synthesis will further contribute to the development of improved models; it will constrain tracer interpretations and dynamical hypotheses; it will aid in the analysis of other data sets, including portions of the SHEBA data; and it will help provide a Pan-Arctic perspective for the SBI initiative.



MODELING THE FORMATION AND OFFSHORE TRANSPORT OF DENSE SHELF WATER FROM HIGH-LATITUDE COASTAL POLYNYAS

David C. Chapman and Glen Gawarkiewicz
Woods Hole Oceanographic Institution, Woods Hole, MA 02543

We propose to study the processes involved in the formation and offshore transport of dense water formed in high-latitude coastal polynyas. Our hypothesis is that dense water, formed in coastal polynyas, is transported across the shelf via small-scale (15-25 km) eddies. These dense-water eddies are potentially capable of moving offshore across the shelf break and into the deep basins where they contribute to the maintenance of the observed thermohaline structure. This hypothesis is based on our previous process modeling in which we developed simple formulas for water mass characteristics formed within a coastal polynya as a function of polynya geometry (essentially open water area) and the negative surface buoyancy flux (ice production).

We propose to test our hypothesis with:

1. Process-oriented numerical modeling: We will extend our idealized models to include ambient alongshelf currents and wind forcing. This will improve our understanding of the dynamical processes and our ability to model realistic situations.

2. Realistic numerical modeling: We will use the results from ongoing field programs to test our ability to model realistic coastal polynyas in the Bering, Okhotsk and Chukchi Seas.

The combination of process-oriented and realistic modeling will allow us to refine our dynamical ideas in the context of observed forcing and environmental factors, and thereby progress toward an ability to make accurate estimates of dense-water production and shelf-basin exchange.



ARCTIC SHELF AND BASIN PRODUCTIVITY

Glenn F. Cota
Center for Coastal Physical Oceanography, Old Dominion University, Norfolk, VA 23529
Lawrence R. Pomeroy
Department of Zoology and Institute of Ecology, University of Georgia, Athens, GA 30602

The NSF/ONR Western Arctic Shelf Basin Interactions (SBI) program has identified biological production and biogeochemical cycling as priorities for improving our ability to predict environmental change in the Arctic. Primary producers play a central role in marine food webs and biogeochemical cycles, but their response to environmental changes can only be assumed because in many regions we have little or no direct knowledge of historical productivity. Our principal goal is to determine regional patterns of primary productivity on Arctic shelves, slopes and basins. Although we will focus on the Chukchi and Beaufort Seas, our efforts will encompass most of the Arctic Ocean and its marginal seas. Our main objectives are to: 1) better understand the mechanisms responsible for regional differences in productivity, 2) determine the net trophic status of regions to evaluate the potential for shelf-basin exchange of organic materials, 3) focus hypotheses and research efforts in subsequent phases, 4) provide validation data for coupled biophysical models in all phases (e.g. J.J. Walsh and others), and 5) establish benchmarks to assess environmental change. With climatologies and simple models of physical forcing and biogenic activities we propose to constrain estimates of primary production with two different approaches: 1) a "top down" irradiance forced model, and 2) a "bottom up" water column biogeochemical model. The irradiance-based model utilizes climatologies of clouds, radiation, and ice and snow cover to define the light available for photosynthesis by phytoplankton and ice algae. The biogeochemical model utilizes oxygen and nutrient profiles to estimate seasonal primary production (total and new) and net community trophic status from late summer property distributions. Whenever possible we will compare direct photosynthetic measurements and oxygen fluxes with modeled productivity estimates.

We have already accumulated ca. 4500 oxygen profiles and 2000 nitrate profiles from Arctic shelves and basins to estimate regional patterns. More data are also being collected. Although some data are from other seasons, most profiles are from the late summer "navigable" season and represent post-bloom conditions. The data sets span most of this century and a few locations have multiple revisits within and between years, which may help assess seasonal and interannual variability. Large databases with both biogeochemical and physical observations are necessary to validate models of primary productivity, and carbon, nitrogen and silicon fluxes. This project complements current and planned research to study the Arctic Ocean and its marginal seas.



COLLABORATIVE RESEARCH: PALEOCEANOGRAPHIC RECORDS OF WESTERN ARCTIC SHELF-BASIN INTERACTIONS

Dennis Darby, Jens Bischof, and Greg Cutter, Dept. of Ocean, Earth, & Atmospheric Sciences, Old Dominion University, Norfolk, VA 23529
Anne de Vernal, GEOTOP and Claude Hillaire-Marcel, Universite du Quebec a Montreal, C.P. 8888 Succursale Centre Ville. Montreal, Quebec, Canada H3C 3P8
Gary Dwyer, Division of Earth and Ocean Sciences, Old Chemistry Building, Duke University, Durham, NC 27708
Leonid Polyak, Byrd Polar Research Center (Office Of Research), 274 Scott Hall, 1090 Carmack Road, Columbus, Oh 43210
Richard Poore and Lisa Ostermann, USGS, MS 955 National Center, 12201 Sunrise Valley Drive, MS 955, Reston, VA 20192
James McManus, Large Lakes Observatory, University of Minnesota, 109 RLB, 10 University Dr., Duluth, MN 55812

The sediment record in the western Arctic Ocean has been shown to contain valuable information on the past climatic and oceanographic changes such as variations in sea ice coverage, iceberg and sea ice rafting, nutrient and metal contents, and faunal/floral abundances. The interactions between the Chukcki Shelf with its Pacific water component and the deep adjacent basins is the focus of the Western Arctic Shelf-Basin Interactions Program (SBI). This collaborative research proposal addresses some of the critical questions raised by SBI and will meet some of its basic goals and establish critical data for Phase II of SBI. Recognizing the temporal variability of sediment proxies for productivity, different water masses, riverine influx, sources of ice-rafted detritus (IRD), different water current regimes, and sea ice extent and thickness is critical to understand the processes that cause these changes. We propose a coordinated study of the important sediment proxies in three to five piston cores currently in cold storage at the U.S.G.S. At least one of these cores is suspected to extend back to oxygen isotope stage 5 at a core depth of about 650 cm. All of these cores from the slope and Northwind Basin appear to have sufficiently high sedimentation rates to permit century to millennium scale resolution. Our focus will be on the last 50-100 kyrs with emphasis on the changes recorded during the Holocene. Detrital Fe oxide grains will be matched to previously characterized circum-arctic source areas by discriminate function analysis using electron microprobe geochemical compositions of individual grains. Similarly, coarse lithic grain assemblages will be matched to sources using the clast petrology and mineralogy. These independent source determinations will provide information on changes in IRD sources and thus details on water mass circulation and climatic conditions. Microfaunal data will provide spacial and temporal data on: 1) benthic biodiversity and abundance, 2) shelf-to-basin sediment fluxes, 3) deep and intermediate water mass distribution and circulation, and 4) sea ice distribution and general thickness. Chemical analyses of foraminifer and ostracode tests (including stable isotopes) will provide similar data on: 1) the thermal structure of the western Arctic Ocean, 2) Arctic deep and intermediate water mass distribution and circulation (especially the strength of the warm Atlantic layer), and 3) the depth and extent of the halocline. Cd in benthic foraminifers has proven to be a valuable surrogate for phosphate, and thus is a quantitative indicator of upwelling intensity. Measurements of the sediment organic carbon, nitrogen, sulfur, and carbonate carbon, along with sedimentation rate determinations by AMS radiocarbon analyses will provide information of the biogenic flux rates from the surface waters. A combination of elements accumulating in marine sediments including Ba, U, Cd, and Mo provide a powerful tool for quantifying the export of organic carbon from the surface ocean to the sea floor. These proxies are critical for determining paleoproductivity and to improve quantitative reconstruction of past conditions. The records of past global change in the Arctic Ocean, when compared to other records from the global ocean, are the only means we have to assess if the Arctic is a harbinger of global change. Records of paleo-upwelling and productivity, for example, allow us to quantitatively assess the frequency and driving mechanisms of change in this environment, and hence to better understand and predict current and future changes.


BENTHIC COMMUNITY STRUCTURE AND BIOMASS IN THE WESTERN ARCTIC: LINKAGE TO BIOLOGICAL AND PHYSICAL PROCESSES

Ken Dunton, University of Texas at Austin, Marine Science Institute, Port Aransas, TX 78373
David Maidment, University of Texas at Austin, Austin, TX 78712
Jackie Grebmeier, Department of Ecology and Evolutionary Biology, The University of Tennessee, Knoxville, TN 37996

Spatial and temporal patterns in the flux of sinking matter are critical to the development and productivity of the benthos, particularly at high latitudes where environmental controls are extreme. The input of this energy, in the form of highly reduced organic matter, ultimately links production in the water column with the abundance and diversity of the benthos. The goal of our proposed research is to utilize the benthos as a spatial and temporal integrator of oceanographic processes that could provide a valuable indicator of potential global change impacts.

Within the Western Arctic Shelf-Basin Interactions (SBI) program, Phase I was designed to undertake a retrospective studies of data sets in the Chukchi and Beaufort Seas that would help focus research efforts on the impacts of global change on arctic ecosystems. There exist large and potentially invaluable historical databases from the Arctic region that have not been synthesized, including thousands of records on the biomass, density and composition of benthic organisms from the Chukchi and Beaufort, mostly unpublished. A wide variety of information on physical and geochemical parameters, including the seasonal extent of ice cover, circulation patterns, water column characteristics and sediment parameter, are also available from both published and unpublished sources. Together, these sources of information represent a substantial collection of baseleind data, most of which was collected 20-30 years ago.

The purpose of the work proposed here is to retrieve benthic biological data from NODC and other published and unpublished data sets from western and Russian sources and use Geographic Information Systems (GIS) software to examine and graphically display relationships between predominant physical forcing processes (e.g. freshwater inflows, ice cover, circulation) and ecosystem productivity. Preliminary development of coupled biological and physical models based on historical data would provide an opportunity to identify specific research needs and refine hypotheses with respect to the processes regulating biogeochemical cycles and biological
productivity on Arctic shelves.



TRACER BASED EXAMINATION OF HALOCLINE AND FRESH WATER EXCHANGE IN THE WESTERN ARCTIC

Kelly K. Falkner,.College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis , OR 97311

This proposal is a contribution to Phase I (retrospective data synthesis and modeling) of the Western Arctic Shelf-Basin Interactions (SBI) program. The main goals of the SBI program are to understand quantitatively and mechanistically the major processes involved in shelf water mass modification, including biogeochemical transformations, exchange with the Arctic Ocean interior and the biological structure and function of Arctic shelf and slope ecosystems. Achievement of these goals is prerequisite to development of a predictive capability regarding the Arctic system response to and role in global change.

Four main objectives are to be addressed in this proposal which are aimed at improving the knowledge base from which to design an effective field strategy for SBI. They are concerned with the application of tracers, primarily Ba, to questions of water mass origin and transformations occurring both for the whole Arctic shelf-basin system and specifically in Beaufort and Chukchi regions. Work to date by our laboratory group suggests that Ba may be a particularly useful dye of Mackenzie River and the Bering Sea inputs, which play a dominant role in the Beaufort and Chukchi seas respectively and enhance stratification in the western Arctic.

The first objective is to add the Ba data base to an inverse box-model of Arctic shelf-basin exchange recently developed by others. This model has demonstrated through the use of temperature, salinity and del-18O fields that tracer constraints significantly reduce uncertainties in the magnitudes of the exchanges required to achieve heat, salt and mass balances consistent with known boundary flows. It is hypothesized that inclusion of the Ba data base, which is an order of magnitude larger than the del-18O data base and inherently contains information orthogonal to that tracer, would reduce errors even further and so improve the integrated estimate of the relative contribution of processes involved in shelf-basin exchange. This exercise requires characterization of all boundary flows for the system. A ship-of-opportunity transect in the Fram Strait for Ba is presently being collected as part of the European VEINS program. The proposed analyses of these samples would complete a first order characterization of advective boundary flows for the Arctic system. The non-advective flux terms are to be addressed as part of the second objective.

The second objective is to obtain a first order estimate of the vertical flux of particulate Ba under the ice cover via the analysis of existing sediment trap samples available to us via collaboration with Canadian colleagues at the Institute of Ocean Sciences, Sidney BC. The samples span the time frame from 1987 to the present and include transects of the Canadian Beaufort Shelf in the Mackenzie region, a long time series at a climate station in the deep Beaufort and a time series from the drifting SHEBA site. Additional information on currents, light transmission, particle transmissometry and hydrography complement this sample suite. Our collaborative arrangement involves provision of training in state-of-the-art analytical methodology at COAS facilities to a Canadian student and colleagues.

The third objective involves completion of the analyses of an extensive suite of samples in the Chukchi and Beaufort region (1992-1997) and examination of that data set for clues regarding modification of shelf source waters and their variability. This project will involve collaboration with several colleagues who kindly provided us with samples from their expeditions and possess a range of complementary measurements. While some findings have already been reported from these missions, they were not funded for the topics discussed here and so the data have yet to be fully explored in these respects.

The fourth objective is to assure the development of an on-board and perhaps in-situ technique for Ba analysis in a time-frame suitable for application during SBI. An on-board technique offers the improvement of being able to make informed decisions regarding sampling in the field. Continuous methodology can overcome resolution limitations inherent to bottle sampling based measurements but its development is far more challenging. ONR funds, awarded to undertake these developments, are limited and so funding is requested here to support the second year of a graduate student's related research.

FATE OF PRIMARY PRODUCTION IN THE WESTERN ARCTIC OCEAN

Rodger Harvey
Chesapeake Biological Laboratory, UMCES, 1 Williams Street, Box 38, Solomons, MD 20688

This proposal represents a collaborative effort to address the fate of primary production in the complex system of the western Arctic Ocean. Recent work in the region has observed some of the highest global levels of primary production measured, yet the fate of this material and the fraction which is preserved in the sedimentary record is unknown. This project will take advantage of the specificity that multiple molecular markers of organisms and their processes can provide to define the fate organic matter produced and its sedimentary fate in a system where ice plays a dominant role in regulating the timing and magnitude of its production. These organic tracers are particularly useful in helping to understand how systems process, metabolize and sequester carbon, a question central for the SBI program.

Our specific objectives include:

- To determine the suite of molecular organic markers that are most useful for tracking the fate of primary production through food webs and into sediments.

- To compare the fraction of primary production that escapes recycling and is buried in sediments underlying the high productivity waters of the Chukchi shelf versus the more varied inputs to the Beaufort shelf.

- To explore the historical record of cyclical changes in productivity and community structure of phytoplankton and other members of the pelagic community using molecular organic markers preserved in sediments.

- To adopt the molecular organic markers most characteristic of primary production to construct preliminary budgets for the export of marine carbon from the Beaufort and Chukchi Shelves.

Using a combination of established and recently developed methods at the interface of organic geochemistry and biogeochemistry, we will extend recent work in the Beaufort Sea to the more productive Chukchi, allowing a comparative measure of the multiple forms of carbon which are incorporated into these broad continental shelves. Using both archived samples and samples of opportunity, our first goal is a focused assessment of the molecular organic markers most suitable for tracking the fate of marine production through the Arctic food web and into sediments. Multivariate analysis both within and between shelves will provide a rigorous evaluation of those molecular tracers most effective at reflecting inputs and preservation. Once accomplished, we can begin to examine the historical record of primary production, its consumers, and changes in community structure which may be preserved in the sedimentary record.

INVESTIGATION OF THE RATE OF SHELF-BASIN INTERACTION IN THE WESTERN ARCTIC OCEAN USING RADIUM ISOTOPES

David Kadko and Mark Stevens
University of Miami, Rosensteil Schl. of Mar. and Atm. Sciences, 4600 Rickenbacker Causeway, Miami FL,33149

The largely landlocked Arctic Ocean receives input from the Pacific and Atlantic Ocean, and from rivers draining the surrounding continents. These inflows are important sources of salt, heat, nutrients, sediment and organisms to the central basin. With the exception of a portion of the Atlantic contribution, these inputs must cross continental shelves where they are significantly modified by benthic, water column, air/sea and sea/ice interactions. There are therefore significant biogeochemical exchanges between the shelves and basins, but we currently lack the information necessary to quantify these exchanges. A better understanding of the processes and rate of exchange with the central basin is clearly needed. To address this issue, we propose as part of the Western Shelf-Basin Interaction (SBI) program, a PHASE I pilot program to examine the use of an isotopic tracer technique that will be applied to investigation of the rate of exchange between the Arctic shelves and the Arctic Ocean interior. The technique utilizes the measurement of the water column ratio of two naturally occurring radium isotopes 228Ra/226Ra. Because these species are derived from input from the shelf sediments, their relative distribution in the shelf and basin water are very valuable in assessing the degree of shelf-basin interaction. This technique is mature, having been utilized in shelf-basin exchange investigations elsewhere, but will be applied here for the first time to a dedicated western Arctic Ocean study.


PHYSICAL MODELING OF THE ARCTIC MARINE RESPONSE TO GLOBAL CHANGE

W. Maslowski and R.W. Garwood
Oceanography Department, 833 Dyer Road , Naval Postgraduate School, Monterey , CA 93943-5122

Under the new circumstances for this proposal, which is to be funded for its physical oceanography part only (i.e. coupled sea ice and ocean modeling of the Pan-Arctic region communicating results to small scale turbulence (LES) models but excluding the biogeochemical modeling part of the proposal by J. Walsh) in addition to modeling physical environment of interest to the SBI program we propose to do the following:

1. Provide results from this work to all interested and funded by the SBI program investigators as requested (both raw model output as well as processed results such as animation of various fields, time- and space-averaged fields, etc).

2. Establish a web site where description of model output and some results will be available and updated for viewing and downloading to all SBI PI's and other interested scientists.

3. Concentrate on the main area of interest extending from the Bering and Chukchi shelves across the shelf break into the Beaufort Sea; other regions of the Arctic Ocean might be included if needed.

4. Collaborate with other PIs in Phase I of this program in order to provide quidance and to establish communication and understanding of future requirements during the field project (i.e. Phase II) of this program.

EDDIES IN THE BEAUFORT GYRE

Albert J. Plueddemann
Woods Hole Oceanographic Inst., MS-29, 360 Woods Hole Road, Woods Hole, MA, USA 02543-1541

New observations of upper ocean velocity in the Beaufort Gyre will be used to investigate the distribution and properties of subsurface eddies. The observations come from autonomous drifting buoys outfitted with Acoustic Doppler Current Profilers (ADCPs). The buoy drifts include two broad, anticyclonic arcs at the periphery of the Beaufort Gyre and an east-west transect of the southern Canadian Basin. The ADCP data span the upper pycnocline (25--300~m) with vertical and temporal resolution sufficient to resolve eddies which are encountered during the buoy drifts. Three ADCP deployments have been made during the last six years, resulting in a combined four buoy-years of data.

The fact that eddies contribute a significant fraction of the total upper-ocean kinetic energy the Beaufort Sea and Canada Basin was demonstrated by the comprehensive survey of Manley and Hunkins [1985]. However, since the time of their review, only a few additional eddy observations have been reported. The new ADCP observations are of interest in that they: (1)~Significantly extend the sampling region relative to previous observations and can provide updated statistics for the eddy population, (2)~Include sampling near possible source regions at the perimeter of the Beaufort Sea and Canada Basin, and (3)~Contain several transects across the continental slope from the basin to the shelves of the Beaufort and Chukchi Seas.

Preliminary analysis of two buoy-years of data has shown that eddies with the same general character as those reported by previous investigators are abundant. The properties of these eddies have not been analyzed in detail, and the remaining two buoy-years of data have yet to be examined. Support is requested for further investigation of the eddy population, consisting of three primary tasks. First, time series analysis will be used to describe the general character of upper ocean velocity variability. Near-inertial waves and tides as well as eddies will be included in this portion of the analysis. Second, individual eddies will be identified and some of their fundamental properties determined (radius, vertical extent, sense of rotation, rotation rate, kinetic energy, relative vorticity, and Rossby number). These properties, along with the rate of encounter of eddies and their depth distribution will be compared with previous observations. Finally, the drift tracks which cross the basin boundaries will be used to determine whether eddy properties differ near the source region, whether bottom trapped currents are found on the slope, and whether eddies are found on the shelf.

DISSOLVED ORGANIC MATERIAL (DOM) IN THE ARCTIC OCEAN

Annelie Skoog
Department of Marine Sciences, University of Connecticut at Avery Point, 1084 Shennecossett Road, Groton, CT 06340

Dissolved organic material (DOM) in the Arctic ocean has the highest concentration in any ocean basin but is mostly unknown on the molecular level. DOM is potentially an important factor in supporting the net hetrotrohic open ocean in the Arctic. An increased riverine inflow has been suggested as a consequence of global warming and points to the importance of determining the role of riverine DOM in the Arctic carbon cycle. The Shelf-Basin Interaction model suggests a possible transport mechanism for DOM from the shelf to the open Arctic Ocean. I suggest to begin molecular level studies of DOM in the Arctic Ocean to:

* determine whether the high DOC concentrations in the Arctic Ocean include a higher concentration of biologically labile components than are found in other oceans.
* determine the relative biological lability of DOM from riverine inputs to the Arctic Ocean and compare that to relative lability of DOM formed in situ.
* determine which biologically labile compounds in the Arctic have detectable concentrations, in order to carry out flux studies on a molecular level to calculate a reasonable heterotrophic incorporation efficiency for the Arctic Ocean during phase II of the SBI effort.

Specifically, amino acids, neutral aldoses and low-molecular-weight organic acids will be studied. Analysis will be carried out with IC-PAD for neutral aldoses, with CE-LIF for amino acids and with CE-indirect Abs for organic acids. The presently available methods for organic acid analysis suffer from high practical detection limits due to poor sensitivity and contamination problems, therefore the initial work will be focused on developing a new method. The method will have very high sensitivity, minimal sample preparation and contamination, and be compact enough to be suitable for shipboard analysis.

In order to determine the background concentrations of biologically labile compounds in the Arctic Ocean, samples from the Arctic will be collected with ships of opportunity and these concentrations will be compared with values found in the Atlantic and Pacific Oceans. In order to answer the question of biological lability of riverine organic matter, samples from the McKenzie River will be obtained. The relative concentrations of biologically degradable components (normalized to DOC) will be compared with Arctic Basin water. The values for biological lability of DOM in different locations in the Arctic will be very valuable information for modeling studies of the Arctic ecosystem.

The biologically labile components that have concentrations above the detection limits of the employed methods will be targeted for experimental studies of microbial flux during phase II of the SBI effort. If combined with classic radiotracer studies, the molecular level determinations will make possible the estimation of heterotrophic carbon flux for an unprecedented fraction of labile components of DOC. This will make possible an estimate of heterotrophic incorporation efficiency in the Arctic Basin and will give a unique picture of heterotrophic carbon demand and utilization.

ADVECTION AND FOOD WEBS IN THE WESTERN ARCTIC: RETROSPECTIVE SAMPLE AND DATA ANALYSIS AND MODELLING

Sharon Smith
University University of Miami RSMAS - MBF , 4600 Rickenbacker Cswy, Miami , FL 33149-1098

This project will initiate a study of the advection of large copepods onto continental shelves from the deep Arctic basin as a vital source of carbon for the planktonic ecosystem on the shelf. Without this source of carbon, the planktonic biota would have little food supply and the benthic fauna would dominate the food web. This fundamental process of transferring carbon from basin to upper waters of the shelf has not been studied in the Arctic ecosystem. The process is very important due to the possible overwintering of the copepods in the deep basin where they can serve as an annual source of food for zooplankton and fish when advected to the shelf during the short
Arctic summer. The investigator will use retrospective analysis of data collected in the Chukchi and Beaufort Seas to develop a biological model of the advection of copepods to test hypotheses about the migration of plankton as well as the effects of ocean circulation on the process. The model will allow testing of global change impacts on the availability of this important food source on the shelf. The results of this project will provide input for planning a large Phase 2 field program of the Shelf Basin Interactions project in 2002 in the same geographic area.

LIGHT AND LIFE IN THE WESTERN ARCTIC OCEAN: A CONTRIBUTION TO THE SHELF-BASIN-INTERACTIONS (SBI) PROGRAM

Knut Stamnes and Bingquan Chen
Department of Physics and Engineering Physics, Stevens Institute of Technology, Castle Point on Hudson, Hoboken, New Jersey 07030

The polar regions are the places on Earth where potential climate changes are likely to be first observed. Expected changes due to stratospheric ozone depletion are increased levels of ultraviolet-B (UV-B) radiation, large enough to have harmful effects on aquatic and terrestrial ecosystems. Potential changes in cloudiness due to climate changes will also strongly affect both UV and photosynthetically active radiation (PAR). In spite of the significant changes recently observed in the ozone layer over the Arctic, little has been done to measure and model the corresponding changes in the underwater UV and PAR
radiation environment and their impact on marine arctic ecosystems. On this background, one of the objectives of the proposed research is to develop a computationally-efficient radiative transfer model specifically tailored for the tightly coupled atmosphere-sea ice-ocean environment, test it against spectral irradiance measurements, integrate it with an existing phytoplankton model designed to interpret field measurements, and perform sensitivity studies of the impact of changes in atmospheric and oceanic parameters on primary production, taxonomic structure, and biological diversity in arctic waters. Another
objective is to measure and theoretically predict underwater spectral irradiance and its variation with depth in arctic waters as a function of changes in atmospheric ozone concentrations, meteorological conditions, ice/snow cover, and sea water type. A third objective is to use the measurements to establish a data base that can be used in future studies (including the phase 2 and phase 3 in the SBI program as well as other related studies) and monitoring of the arctic environment by satellite remote sensing. The last objective is to carry out remote-sensing study to derive cloud and surface parameters (albedo) that can be used to characterize the radiation budget in the Western Arctic, modify and improve previous approaches for retrieving the chlorophyll pigments, and establish data sets of cloud and surface parameters (albedo) as well as chlorophyll pigments for high latitudes and coastal waters in the Western Arctic for the SBI program.

CIRCULATION AND THERMOHALINE STRUCTURE ALONG THE CHUKCHI-BEAUFORT CONTINENTAL SLOPE.

Thomas Weingartner
Institute of Marine Science, University of Alaska Fairbanks, Fairbanks, AK 99775

This program will investigate the circulation and thermohaline structure of the Chukchi-Beaufort continental slope during SCICEX99. This project seeks to better understand the poorly sampled circumpolar boundary currents of the Arctic Ocean. These flows are important in the distribution and exchange of mass, heat, and materials around the basin and between the shelves and the interior ocean. The measurements, collected from sail-mounted CTDs and submarine launched expendable CTDs (SSXCTD), will determine the correlation length scale of the along slope thermohaline fields, the magnitude and structure of the alongshore baroclinic pressure gradient, and alongslope variations in the cross-slope baroclinic pressure gradient. The data should shed light on the scales of cross-slope exchanges and forcing mechanisms for the eastward-flowing boundary current. The temperature and salinity measurements will complement ADCP and chemical data sets being collected by other investigators. In aggregate the data sets will help characterize the mesoscale circulation and establish the mixing history of the regional waters. This proposal complements a mooring program (supported by the MMS) that will provide concurrent time series of velocity, temperature, and salinity at several locations along the Alaskan Beaufort slope and within the sampling grid of the SCICEX-99 expedition.

CONFIGURATION OF AN ECOSYSTEM MODEL FOR THE CHUKCHI SEA USING DATA FROM 1994-1996.

P. A. Wheeler and Y. H. Spitz
Ocean Administration Bldg 104, College of Ocean & Atmospheric Sciences, Oregon State University, Corvallis, OR 97331-5503

Past ecosystem models for the Chukchi Sea have lacked critical verification data. We propose to use a data assimilation scheme, results from the 1994 AOS Arctic Ocean Section, and additional chemical and biomass data from two 1996 cruises to adapt a recent improvement of an Atlantic Time Series ecosystem model to the Chukchi Sea ecosystem. Initial development of the ecosystem model will focus on the lower trophic level pelagic system. Subsequent versions will be expanded to include specific parameters for benthic process and remineralization and for the seasonal activity of the sea ice biological communities.

The model will be used to evaluate the sources and sinks of organic carbon and nitrogen in the Chukchi Sea, and the export of inorganic nutrients, particulate and dissolved organic material from the shelf sea into the Canadian Basin. By understanding the factors that regulate biological processes on the shelf, we will be able to predict the effects of changes in physical parameters (including climate and ice cover) on the magnitude and fate of shelf production and the exchange of nutrients between the shelf and the basin.

Major gaps or uncertainties of model parameters will be identified at each stage of development. Ship of opportunity cruises will be used in 1999-2001 to expand data coverage, to test predictions of the model, and to lead to model refinement. At each stage in the proposed work we will prepare and update the list of minimum core measurements that will be needed in future field studies to address the key questions about the influence of global change on the amounts and fates of primary production in the Chukchi Sea. As platforms for sampling and appropriate data become available we will extend the proposed ecosystem model to the Beaufort Sea.