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ARCSS/OAII
Western Arctic Shelf-Basin Interactions (SBI) Science Plan

ARCSS/OAII Report Number 7
February 1998

      Edited by J.M. Grebmeier and T.E. Whitledge (co-chairs),
L.A. Codispoti, K.H. Dunton, J.J. Walsh, T.J. Weingartner, and P.A. Wheeler,
with contributions from the SBI  Workshop I and II Participants.
With support from the National Science Foundation Grants OPP-9416103 and OPP-9612784  

(contact the ARCSS/OAII SMO for copies)

To review the 1998 SBI Phase I Announcement for Opportunity, click here.

Acknowledgments
    The SBI Science Steering Committee wishes to thank the many colleagues who made important contributions to the development of this plan.  In particular, we thank all participants in the two SBI workshops for their input. The lists of attendees may be found in Appendices C1 and C2.  We also thank those who sent in comments after  reviewing an initial copy of this plan that was posted on the OAII Web page. Financial support for the workshops, publications of this report, and associated expenses was provided by the National Science Foundation by ARCSS program grants OPP-9416103 and OPP-9612784. We are particularly grateful to Dr. M. Ledbetter of NSF/OPP for his support and advice.

This report may be cited as:
Grebmeier, J.M. et al. (eds.), 1998, Arctic System Science  Ocean-Atmosphere-Ice Interactions Western Arctic Shelf-Basin Interactions Science Plan, ARCSS/OAII Report Number 7, Old Dominion University, Norfolk, VA, 65 pgs.
 
Additional copies of this report may be obtained from:
ARCSS/OAII Science Management Office
Center for Coastal Physical Oceanography
Crittenton Hall, Old Dominion University
Norfolk, VA  23529, USA

  TABLE OF CONTENTS  
 

• 1.  EXECUTIVE SUMMARY
   
• 2.  INTRODUCTION
   
• 3.  RELEVANCE TO GLOBAL CHANGE
   
• 4.  BACKGROUND
   
• 5.  CORE WESTERN ARCTIC SBI SCIENCE PLAN
• 5.1  Shelf/Basin Physical Processes
• 5.2  Biogeochemical Fluxes and Transformations
• 5.3  Biological Standing Stocks, Processes and Trophic Structure
• 5.3.1  Lower Trophic Levels
• 5.3.2  Higher Trophic Levels
• 5.4  Modeling: Pan-Arctic
• 6.  SBI IMPLEMENTATION PLAN
• 6.1  Sampling Program and Platforms
• 6.1.1  Sampling Program
• 6.1.2  Required Platforms
• 6.1.3  Instrumentation
• 6.1.4  Remote Sensing
• 6.1.5 Upcoming Opportunistic Field Opportunities (1997-2002)
• 6.2  Collaboration and Integration with Other U.S. and International Programs
• 6.2.1 U.S. Programs
• a.  Arctic System Science (ARCSS) Program
• b.  Other NSF Programs
• c.  Other Federal Programs
• 6.2.2 International Programs
• 6.3  Western Arctic SBI Program Outline
• 6.4  Program and Data Management
• 7.  RECOMMENDATIONS
   
• REFERENCES
   
• APPENDIX A: Workshop Agendas: 1. SBI I (1995) and 2. SBI II (1996)
   
• APPENDIX B: Abstract Authors and Titles: SBI Workshops I and II
   
• APPENDIX C: Particpant Lists: 1. SBI Workshop I and 2. SBI Workshop II

1.  EXECUTIVE SUMMARY  
         The Arctic Ocean system is strongly influenced by processes occurring on its adjacent continental shelves. Portions of the Arctic shelf/slope region have extremely high biological productivity and are rich in living resources. Despite this ecological importance, the outer shelves and slopes of the Arctic remain one of the most under-sampled environments in the global ocean.  Consequently, many shelf processes and impacts are poorly understood. It is, for example, not clear  how variability on the shelves affects the interior basins. Even the inner portions of the shelves lack adequate seasonal coverage, and have not benefited sufficiently from advances in technology and analytical techniques.  This document outlines the Western Arctic Shelf-Basin Interactions (SBI) program, which will significantly improve our knowledge and understanding of shelf-basin exchange processes, and will lead to an enhanced predictive capability for global change impacts in the Arctic.
 
         The largely landlocked Arctic Ocean bears the distinct imprint of waters from the Pacific and Atlantic Oceans and from the rivers draining the surrounding continents. These inflows are important sources of salt, heat, nutrients, carbon, sediments, and organisms to the central basin. However, with the exception of a portion of the Atlantic contribution, all of these inflows must cross continental shelves where they are modified by benthic and water-column biological processes and by exchanges with the atmosphere, sea ice, and bottom sediments. The modified shelf waters eventually feed the polar mixed layer and/or ventilate the subsurface layers of the interior basin. In this manner, the shelves profoundly influence the thermohaline structure and maintenance of the ice cover of the Arctic Ocean. These same processes must markedly affect biogeochemical cycles and the biological productivity that support the living marine resources of the Arctic Ocean. However, a mechanistic understanding of the processes that affect the magnitude and rates of biological production, physical and chemical modification of shelf and slope water masses, and water mass exchange with the central basin is virtually lacking.
 
         We hypothesize that interactions between Arctic shelves and basins have a major influence on the Arctic Ocean system. What will be the likely impact of global change on this sentinel Arctic ecosystem, where future thermal changes may be the largest?  We propose to examine the postulated effects of global change and the subsequent feedback of such altered climate signals to lower latitudes.  For example, the extent and thickness of sea ice has a direct impact on global change, with general circulation models (GCMs) indicating that the Arctic will be a focal region for observing early effects of global change. Warming will decrease ice and alter the annual cycle of melting and freezing, thereby affecting the nature and rates of exchange between the shelf and the basin. Global change would also affect freshwater runoff of Arctic rivers, influencing sea ice production and stratification of the Arctic Ocean. Presently, shelf nutrients and dissolved organic matter (DOM) that are not assimilated by animals and plants in the western Arctic are exported to the basin. Reduced export and increased light availability on the shelves should lead to larger primary production, based on enhanced nutrient uptake and recycling of the DOM. Increased photosynthesis may then lead to: 1) larger fish yields, with diversion of food away from the benthos and the higher trophic levels they support, 2) greater sequestration of atmospheric carbon dioxide in the shelf/basin sediments, and 3) more denitrification losses of fixed nitrogen. The former will impact adjacent human populations of the Arctic, while the latter two could have global consequences.
 
         These issues must be resolved to achieve the Arctic System Science (ARCSS) goal of understanding the present day Arctic Ocean and predicting its influence on global change and how it may be affected by global change. The overarching goal of the SBI program is to provide a major step forward in this understanding so that predictive capabilities related to global change can be developed.  The SBI program will include field and modeling studies directed at elucidating the underlying  physical and biological shelf and slope processes that influence the structure and functioning of the Arctic Ocean.  The SBI program will have a regional focus in the Chukchi and Beaufort Seas for several reasons. First, within the Arctic halocline, the clearest physical and biogeochemical signals are caused by Pacific Ocean waters that are modified on these shelves before passing into the interior ocean. Second, these shelf seas are ideal for comparative studies of shelf-basin interaction due to substantial differences in their geomorphic characteristics, physical forcing, and source waters (riverine versus marine). Third, the existing oceanographic (physical, chemical and biological) data are easily  accessible and possibly more comprehensive than for most other Arctic shelves. This data base allows for retrospective analysis and hypothesis development. Fourth, there are important regional human dimension concerns, such as marine resource use issues (hunting and food availability) associated with these shelves. Fifth, both seas are readily accessible (logistically and politically) thereby permitting year-round studies for several years. Sixth, our European colleagues are proposing to the European Union to conduct a multinational, multidisciplinary oceanographic study of the influence of climate change in the eastern Arctic Ocean. The European initiative also includes a shelf/basin component that  would complement the western Arctic initiative, resulting in a pan-Arctic study (P. Wassman, 1997, pers. comm.).
 
         Over its 7-10 year lifetime, the SBI program will combine modeling with observations made to take advantage of the naturally occurring large interannual variability of this western shelf region. In addition, studies of the present-day environment could aid in interpreting the paleoclimatological record. An understanding of past and present variations should, in turn, contribute to the development of models capable of predicting possible future responses to global change.
 
         The SBI program will go forward in three phases. Phase I involves regional historical data analysis, opportunistic field investigations, and modeling. Phase II constitutes the core regional field investigations in the Chukchi and Beaufort Seas, along with continued regional modeling efforts. Phase III will investigate global change ramifications on the ecosystems of the Arctic shelves and basin. This phase will involve development of a Pan-Arctic model (including embedded regional submodels) suitable for exploring "what-if scenario" studies related to global change. Such studies will be particularly useful in understanding the potential impact of such changes on mankind.

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  2.  INTRODUCTION  
         This document describes the Western Arctic Shelf-Basin Interactions (SBI) program, the motivation behind it, its scientific objectives, and the plan for achieving these objectives. The intended audience includes prospective SBI investigators, agency personnel, operations and logistics managers, and others interested in Arctic Ocean processes. This document is an outgrowth of two scientific workshops held in March, 1995 in Townsend, Tennessee and in September, 1996 in Virginia Beach, Virginia.
 
         The SBI program will contribute toward the National Science Foundation (NSF) Arctic System Science (ARCSS) program goal of understanding the role of the Arctic Ocean in the global climate system and the response of this ocean to global change (Moritz et al., 1990; ARCUS, 1997a). These issues are unresolved for two reasons. First, many Arctic processes that potentially affect global climate are not well studied and associated mechanisms are not well understood. Second, observational climatologies for the Arctic are incomplete in comparison to other parts of the global ocean. Certain regions of the Arctic Ocean, including its shelves, have a minimal description of the circulation, hydrography, and seasonal variability. Likewise, the few data pertaining to biological productivity and  the fate of this production are so broadly distributed in time and space that it is difficult to distinguish temporal from spatial variability.
 
         The Western Arctic Shelf-Basin Interactions (SBI) program is a contribution to the Ocean-Atmosphere-Ice Interactions (OAII) component of ARCSS which investigates the Arctic marine ecosystem in an effort to improve our capacity to predict environmental change (OAII, 1992). The SBI program will focus on shelf/slope water mass modification and exchange processes and biogeochemical cycles in the Chukchi and Beaufort Seas. While the program is geographically restricted, the focus is on understanding processes that occur in many Arctic shelf seas. These topics are particularly important because they profoundly influence the thermohaline and biogeochemical structure of the Arctic Ocean.
 
         Waters modified on the shelves of both the western and eastern Arctic ventilate the Canada Basin (Aagaard et al., 1981; Schauer et al., 1997). Eventually the blended shelf and basin water is discharged into the North Atlantic Ocean through Fram Strait and the Canadian Archipelago. Understanding regional and basin scale issues and how the Arctic Ocean will respond to and effect global change are important because at present the Arctic Ocean is only coarsely represented in climate models. Consequently, conclusions drawn from these models on the role of the Arctic Ocean in global climate are equivocal. Indeed these issues motivate much of the ARCSS program (Moritz et al., 1990).
 
         In spite of these uncertainties, there are compelling indications that the Arctic Ocean exerts substantial influence on climate over a range of spatial and temporal scales. This influence is largely mediated by the effects of the permanent ice pack on the surface heat balance and the global hydrologic cycle. Ice properties affect the surface albedo and the magnitude of the ocean-atmosphere heat flux. Apparently even synoptic scale changes in ice properties rapidly propagate into mid-latitudes (Grumbine, 1994).
 
         Arctic sea-ice represents a large reservoir of freshwater and the Arctic Ocean is an important path for interhemispheric freshwater transport. Indeed Wijffels et al. (1992) found that nearly all the freshwater gained by the North Pacific Ocean (through an excess of precipitation over evaporation) is returned to the North Atlantic via Bering Strait and the Arctic Ocean. Perturbations in the flux of freshwater from the Arctic Ocean could alter the stability and internal variability of the ocean's thermohaline circulation on decadal-century time scales (Bryan, 1986; Weaver et al., 1993) and may be the dominant climate signal in the upper portion of the North Atlantic (Reverdin et al., 1997). On even longer time scales fluctuations in sea ice distribution may be one of several factors, including Milankovitch factors and vegetation content, that may combine to trigger Ice Ages (Imbrie et al., 1993).
 
         Low-frequency climate perturbations are likely initiated by variations in the freshwater flux from the Arctic Ocean into the North Atlantic Ocean where changes in upper ocean salinity will enhance or inhibit convection in the Labrador Sea and the Greenland-Iceland-Norwegian (GIN) Sea. Aagaard et al. (1985) argue that under present day conditions deep convection in the GIN Sea (and therefore the formation rate of North Atlantic Deep Water) depends critically on the buoyancy flux from the Arctic Ocean. In recent years, the anomalous increase in the freshwater efflux from the Arctic Ocean created the so-called Great Salinity Anomaly (Dickson, 1988; Hakkinen, 1993) and led to decreases in deep water production rates in the GIN Sea (Schlosser et al., 1991).
 
         Collectively, these studies imply that changes in sea ice properties could lead to broad scale changes in climate. However, the present day distribution of the permanent ice pack is due to the Arctic Ocean s halocline, a strongly stratified layer that inhibits the vertical flux of heat into the surface layer from the vast pool of warm water found at mid-depths in the Arctic Ocean. Stratification also affects biological production by hindering the upward flux of nutrients into the polar mixed layer.
 
         The maintenance of the halocline depends upon lateral advection of source waters from the adjacent shelves into the interior of the Arctic Ocean. The shelves occupy ~35% of the Arctic Ocean s area and they are the primary sites for processing waters received from the Pacific and Atlantic Oceans and the numerous large rivers that drain the circumpolar continents. These inflows affect the formation of halocline source waters which are cold, salty waters formed when salt is  rejected during the seasonal growth of sea ice on the shelves.
 
         Hence, the thermohaline structure of the Arctic Ocean relies upon ventilation via a horizontal, cross-slope transport of shelf waters whose density is determined by the salt distillation effects of freezing and thawing. Ventilation also depends on mixing between shelf outflows and ambient shelf and slope waters. In contrast, ventilation of mid-latitude oceans is primarily accomplished in the interior of the basin by the subsidence of surface waters whose density depends upon the heating and cooling cycle.
 
         Since marine productivity and biogeochemical cycles are intimately linked to the physical environment, fundamental uncertainties surround the role of the Arctic Ocean in global biogeochemistry cycles. The timing of physical transport processes relative to biological rate processes is still relatively unknown in the Arctic. During earlier interglacial periods when the climate was warmer and the ice cover reduced or absent, the Arctic Ocean had relatively high biological  productivity and was an apparent sink for atmospheric CO2 (Lundberg and Haugan, 1996). Today it appears that the Arctic Ocean has very recently, once again, become a sink for atmospheric CO2 (Walsh and Dieterle, 1994; Lundberg and Haugan, 1996). The sediment record contains information that should help us to understand shelf basin interactions during the past, particularly processes or events that occurred at very slow or infrequent rates. Proxies for these processes, such as fossil and geochemical records, would provide valuable information for coupling paleoclimate and modern observational records to improve quantitative reconstructions of past conditions. High resolution and good stratigraphic control on archived or sediment cores collected as part of the SBI program would provide valuable insight on these processes recorded in the sediment record.
 
         The fate of recently sequestered carbon produced on the shelves or in situ over the slope region is unknown as is an understanding of the relative forms of carbon being advected off slope vs. that being recycled in situ over the shelves and slope. There are questions concerning the direction of the air-sea carbon flux in a hypothetically ice-free Arctic Ocean (Walsh, 1989). Similar uncertainties exist concerning the present amounts of N2 lost through denitrification in Arctic shelf sediments (Devol et al., 1997) and of dimethysulfide (DMS) released from polar seas after prymnesiophyte and diatom growth (Levasseur et al., 1994; Turner et al., 1995).
 
         There are also indications that the present day climate of the Arctic is delicately poised, such that small perturbations to the present day climate system could be dramatically amplified in the Arctic. For example, several general circulation model (GCM) studies predict a "polar amplified" warming response (involving an increase in both air temperature and precipitation) to elevated greenhouse gas concentrations (Sarmiento and Toggweiler, 1984; Broecker and Peng, 1989; Manabe et al., 1992; Miller and Russell, 1992; Intergovernmental Panel on Climate Change, 1996).
 
         If true, these results imply that the Arctic might serve as a harbinger of global change. Indeed, a consensus is emerging in the scientific community that a change has recently occurred in the Arctic Ocean circulation (Macdonald, 1996). Warming and shallowing of the Atlantic layer were first reported by Aagaard and Carmack (1994) and Carmack et al. (1995). The warming was confirmed by Mikhalevsky et al. (1995) during the Transarctic Acoustic Propagation experiment conducted in April 1994. Other analyses suggest decreasing trends over the past 20-30 years in sea ice extent (Maslanik et al., 1997) which coincides with warming trends (Martin et al., 1997). Thus, the characteristics of the boundary currents along the continental slope regions might also be experiencing changes in density and velocity structure which could affect the mechanics of shelf-basin exchange and influence the biological and physical processes. Preliminary data collected during the OAII Arctic Ocean Section (AOS) and NSF/Office of Naval Research (ONR) Submarine Science Experiment (SCICEX) cruises indicate the transfer of western Arctic shelf-derived carbon to the Canada Basin (Sambrotto, 1996). High total CO2 water was seen to extend from the shelf edge and enter the upper halocline at about 100 m, suggesting that the Canada Basin could be an important reservoir for oceanic carbon.
 
         Large scale variations in wind and ice fields along the nearshore Arctic shelf that are associated with  global change could also have significant effects on the sedimentation of organic matter onto the shelf. These wind and ice changes could also initiate a possible climate threat from destabilizing methane from sediment-clathrate deposits, although studies of these deposits are beyond the biological focus of the SBI program.
 
         On a regional scale, climate changes could have a number of important consequences for the people living in northern regions. For example, alterations in cloud cover and/or ice distribution could profoundly alter the spatial and temporal patterns of primary production given the sensitive dependency of high-latitude primary production on surface irradiance (Platt and Sathyendranath, 1995). Arctic trophic systems are relatively simple compared to those of lower latitudes and changes in productivity patterns and/or rates could therefore be rapidly reflected in the structure of Arctic marine ecosystems.

         Most of the primary and secondary production in the Arctic takes place over continental shelves, directly influencing water column and benthic faunal populations. In addition, benthic fauna in certain large shelf regions of the Arctic, such as the Chukchi Sea, directly consume a large proportion of the carbon fixed by microalgae and these benthic organisms sustain huge herds of several marine mammal species that are culturally and economically important to the endemic peoples of the Arctic. Thus, changes in primary productivity over Arctic shelves could impact marine mammal populations through modification of prey populations.
 
         Recent studies indicate increased levels of anthropogenic contaminants (persistent organic contaminants, heavy metals, and radionuclides), along with significant resource development impacts in the Arctic (Arctic Monitoring and Assessment Programme, 1997; Jensen et al., 1997; Nilsson, 1997; Strand, 1997). Changes in trophic pathways and flux rates due to global change may affect the bioamplification and delivery of pollutants to consumers of Arctic fish, mammals, and bird populations that may, in turn, jeopardize the health and/or economic future of traditional indigenous populations. A comprehensive understanding of shelf-basin exchange, including physical and biogeochemical interactions, would assist in analyses of global change impacts on contaminant transport, transformation, and fate in the polar north.
 
         In summary, the 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 s interior, and the biological structure and function of Arctic shelf and slope ecosystems. As such, SBI is a multi- and inter-disciplinary effort that will involve several field and modeling phases. Phase I will analyze existing data sets and include a hierarchy of modeling studies designed to understand the fundamentals of particular processes.
 
         Phase II will include the major field effort in the Chukchi and Beaufort Seas and modeling. The halocline of the western Arctic Ocean has distinct physical and chemical signatures associated with Pacific Ocean waters modified on the Chukchi and Beaufort shelves. Important comparisons can be made between these shelves because they differ so significantly in terms of their geomorphic characteristics and the advective inflows which dominate their water masses (Pacific Ocean water in the Chukchi Sea and Mackenzie River water in the eastern Beaufort Sea). Both of these shelves are among the more abundantly sampled regions of the Arctic Ocean and provide a basis for historical analysis, model building and hindcasting, and comparison with the other Arctic shelves.
 
         Phase III will involve modeling global change effects and synthesizing of the data sets obtained during SBI. This final phase will be pan-Arctic in approach and will involve colleagues from abroad working on similar programs in the eastern Arctic under the aegis of the World Meteorological Organization's Arctic Climate System Study (ACSYS).

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3.  RELEVANCE TO GLOBAL CHANGE
         We expect that global change influences on the Arctic Ocean will have greatest magnitude, at least initially, on the continental shelves. These changes might occur as alterations in the properties of the source waters (Atlantic or Pacific Oceans, rivers), the magnitudes of these inflows, or their seasonal phasing. They might also occur as changes in atmospheric forcing (winds, heat fluxes, radiation properties). Insofar as shelf processes influence the thermohaline structure of the Arctic Ocean they also affect the sea ice distribution and the properties of the waters exported into the North Atlantic Ocean. Changes in sea ice and/or freshwater export into the North Atlantic would likely have repercussions on the climate of lower latitudes.
 
         As a further example, global warming will likely alter the annual cycle of ice formation and advance and ice ablation and retreat over Arctic shelves. The biology and physics of these shelves are intimately linked to this annual cycle. Warming will thin the ice cover and expand the area of seasonally open water and the length of this season. With a reduction in sea ice coverage, we expect diminished cloud cover (less cold condensation) and a decrease in albedo (with a positive feedback on sea ice coverage). This scenario could possibly lead to an increase in primary production, resulting in removal of atmospheric CO2 and increased sequestration of carbon on the world's largest continental shelves.
 
         In the western Arctic, unutilized shelf nutrients and dissolved organic matter (DOM) are exported to the basin (Walsh et al., 1997). Hence, reduced export and/or increased light availability on the shelves should lead to larger primary production through enhanced nutrient uptake and recycling of the DOM. Increased photosynthesis may then lead to larger fish yields, thus positively influencing pelagic prey availability for certain higher trophic populations while diverting food away from the benthos and associated higher trophic level species they support. Moreover, alteration in the ice cover will likely affect marine mammal migration patterns and habitat availability for seals, walruses, and polar bears, all of which will impact subsistence use of marine resources by Arctic peoples. Global change is also likely to have more widespread economic impacts in the Arctic. Increased photosynthesis might also lead to greater sequestration of atmospheric carbon dioxide in the shelf/basin sediments and more denitrification losses of fixed nitrogen. These latter two effects could have global consequences.

4.  BACKGROUND  
         Fridtjof Nansen (1902) postulated that the Arctic Ocean plays an important role in global climate and that alterations in its circulation and/or thermohaline structure would lead to extensive climatic change. While Nansen's claims remain to be proven conclusively, there are two mechanisms by which the Arctic Ocean affects climate.  The first mechanism is through its control on the strength of the thermohaline component of the global ocean circulation, which critically depends on the freshwater flux from the Arctic Ocean into the convective gyres of the Greenland and Iceland Seas (Aagaard and Carmack, 1989).
 
         The second mechanism is mediated by the surface heat budget of the polar ice cap.  At present, the largest rates of heat loss from the Arctic Ocean to the atmosphere occur over its shelves and slopes where, seasonally, the ice retreats and the ocean stratification erodes.  In contrast, the ice cap of the central basin is insulated from the vast pool of warm water found at depth by the permanent halocline.  This salt-stratified layer, with temperatures close to freezing, inhibits the vertical flux of heat from the interior.  By so doing, the halocline maintains the present day distribution of sea ice.  As much of the freshwater in the Arctic Ocean is stored in sea ice, changes in the heat budget of the ice cap would presumably cause changes in the rate of freshwater export.
 
         Although the Arctic Ocean is largely landlocked, it has a number of crucial connections with the oceans to the south (Figure 1).  Much of the ice and water exported from the Arctic Ocean enters the North Atlantic via the Greenland Sea through the ~3000 m deep Fram Strait. The straits permeating the Canadian Archipelago are the other main path by which waters from the upper 300 m of the Arctic Ocean flow into the North Atlantic Ocean via the Labrador Sea. The Atlantic Ocean is the primary source of oceanic heat to the Arctic Ocean and Atlantic waters enter along two paths. One branch crosses the Barents and Kara shelf seas (200 to 300 m deep), whereupon it is cooled and freshened (Steele et al., 1995; Schauer et al., 1997), and contributes the bulk of the lower halocline waters. A second branch consists of warmer and saltier water and enters the Arctic Ocean through the ~3000 m deep Fram Strait that connects the Greenland sea with the Arctic Ocean (Boyd and D'Asaro, 1994; Rudels et al., 1996; Schauer et al., 1997).

         The Arctic Ocean receives approximately 10% of the global river runoff (Aagaard and Carmack, 1989).  This immense discharge, along with the advective contributions from the Pacific and Atlantic Oceans, establish the Arctic Ocean s halocline (Aagaard et al., 1981; Steele et al., 1994; Rudels et al., 1996; Schauer et al., 1997; Figure 2). These various inflows are physically modified by cooling, the salt distillation effects associated with ice ablation and formation, and mixing before entering the interior.

Figure 1. Surface and subsurface circulation in the Arctic Ocean. NSI: New Siberian Islands; FJL: Franz Josef Land; CAP: Canadian Archipelago; BI: Bathurst Island (modified from Aagaard, 1989 and Dunton, 1992).

Figure 2.  Schematic drawing of the circulation and stratification patterns associated with
river inflow and halocline ventilation in the Arctic Ocean (modified from Carmack, 1990).

         A great variety of evidence supports the position that lateral advection from the shelves maintains much of the Arctic Ocean structure, perhaps even including parts of the eddy field (Aagaard et al., 1981; Killworth and Smith, 1984; Jones and Anderson, 1986; Moore and Smith, 1986; Wallace et al., 1987; D Asaro, 1988a,b; Aagaard and Carmack, 1994; Schlosser et al., 1994a,b; Steele et al., 1995).

        The majority of the attention has centered on the maintenance of the halocline, but there is also evidence for a deeper influence of shelf processes on the interior Arctic Ocean, even if regional and temporal variability have made unequivocal interpretation of some of the data difficult (Aagaard et al., 1985; Ostlund et al., 1987; Anderson et al., 1989; Schlosser et al., 1991; Macdonald et al., 1993). An important point is that each shelf sea appears to be unique in its links to the Arctic Ocean, with differing contributions to the interior structure, probably depending both on the underlying shelf water mass climatology and on which processes of modification and exchange dominate.
 
        With the exception of the deep flows through Fram Strait, the inflows to the Arctic Ocean from the oceans and rivers to the south include transport across extensive continental shelf seas. The shelves comprise 35% of the total surface area of the Arctic Ocean and represent about 25% of the global shelf area.  All of these inflows are substantially altered on the shelves by mixing and by interactions with the atmosphere, the seabed, the ice cover, and the biota.  The effects of these interactions are reflected in the water mass properties and the circulation of the Arctic Ocean (Aagaard et al., 1981, 1985; Jones and Anderson, 1986; Wallace et al., 1987; D'Asaro, 1988a,b;  Melling and Moore, 1995).  In winter, shelf water densities increase due to cooling and the addition of salt as sea ice forms.  Some of this dense water enters the halocline and maintains the distinct temperature and salinity properties of this layer (Aagaard et al., 1981). These same outflows also contribute to the deep waters of the Arctic Ocean.  Accordingly, ventilation of the Arctic Ocean is largely accomplished by lateral transport from adjoining shelves.
 
        Arctic Ocean processes also influence a number of important global biogeochemical cycles. Outflows produced through physical processes described above effectively transfer biogeochemical products from the shelves into the subsurface layers of the Arctic Ocean (Björk, 1989). In the western Arctic, the Pacific Ocean is an important source of nutrient-rich, low-salinity water that flows northward through Bering Strait into the Arctic Ocean, ultimately influencing the nutrient maximum in the upper halocline (Cooper et al., 1997 and references therein).  Sarmiento et al. (1989) specifically identified biological processes in high-latitude oceans as central in the control of atmospheric pCO2. The large continental shelves of the Arctic are important for transporting atmospheric CO2 to deeper regions of the ocean (Anderson, 1995).
 
        Denitrification, which is enhanced in shelf and slope sediments (Christensen et al., 1987), is a major marine sink for combined nitrogen and is important in the nitrous oxide cycle.  Present estimates suggest that Arctic-shelf denitrification accounts for about 12% of the total oceanic rate, but small redistributions of carbon (whether in the water or sediments) can cause large changes (Codispoti, 1989).  Arctic waters can be a significant source of dimethyl sulfide (DMS), a gas that affects the radiative properties of the Arctic atmosphere (Charlson et al., 1987).  These properties may be enhanced by the frequent occurrence of Phaeocystis spp. blooms (Smith et al., 1991).
 
        Codispoti (1979) suggests that changes in the northward transport of Pacific Ocean waters through Bering Strait could substantially affect global silica distributions and perhaps the cycles for other chemical constituents as well (Walsh et al., 1989). Although biogenic silica preservation is a complex process, the sedimentary silica record could contain information related to paleoproductivity during past ice ages when Bering Strait was closed; this technique has been explored in the Ross Sea, Antarctica (DeMaster et al., 1996). Arctic shelf and slope sediments also contain a significant reservoir of methane, primarily tied up in clathrate deposits.  Like CO2, methane is a greenhouse gas, and any increase in global warming in the Arctic may release methane to the atmosphere and subsequently contribute to the greenhouse effect. The goals of SBI are however, focused on biogeochemical and biological processes whose changes would have a direct impact on human populations of North America. An in-depth assessment of destabilizing methane stored in sediment-clathrate deposits will require more of a geophysical focus and is outside the scope of the SBI
 program.
 
        Variables controlling biological production in the Arctic, such as ice coverage, seasonal irradiance, and nutrient inputs, change over space and time, resulting in patchiness of biological phenomena. Some of the highest global levels of primary and secondary production (both water column and benthic) occur on the wide shelves of the Arctic Ocean, particularly in the western portions of the northern Bering and Chukchi Seas (Codispoti et al., 1991; Springer and McRoy, 1993; Grebmeier et al., 1995). By comparison, other Arctic shelf regions and the deep basin have low to medium production which influences variability in ecosystem structure. In addition, some of the components of the "biological pump" are unique to the Arctic, resulting in variance in chemical and regenerative signals, such as C/N ratios of autotrophs (Smith et al., 1995).
 
        Walsh (1995) and Walsh et al. (1989, 1997) speculate that there is significant offshore transport of particulate organic carbon (POC) and dissolved organic carbon (DOC) from highly productive areas of the Bering and Chukchi shelves/slope due to a decoupling between water column production and consumption. However, other studies indicate that in situ recycling of POC/DOC in upper surface waters over less productive shelves and basin areas of the Arctic Ocean have a significant coupling to surface water production (Pomeroy et al., 1990; Cota et al., 1996; Wheeler et al., 1996). Therefore, a key unknown in the Arctic is the transformation and fate of variable levels of production and forms of particulate and dissolved organic carbon in the Arctic marine system. The role of riverine input versus marine production on the balance of POC and DOC in the Arctic is also unknown.
 
        Most of the primary production and secondary production (including living resource production) in the Arctic takes place over continental shelves. A large fraction of this production, up to 78%, ultimately finds its way to the underlying sediments (Walsh and McRoy, 1986).  Furthermore, if the Arctic is similar to other oceans, something on the order of 50% of the easily oxidizable sedimentary carbon is found in these sediments (Emerson and Hedges, 1988) and most of the contemporary carbon and nutrient burial (storage) in the Arctic takes place in shelf sediments (Hedges and Keil, 1995). Thus, to understand the carbon and nutrient element budgets of the Arctic Ocean and how shelves interact with the Arctic Ocean interior, we need to study the rates of cycling and loss within the sediments.  This is true not only for the contemporary situation, but also with respect to how the Arctic Ocean system operated in the past and to how it might react to future global change.
 
        Current studies of basin cores are successfully identifying changes in shelf-basin sedimentation patterns on the geologic time scale and include identification of sediment source areas during different parts of the alternating sea ice (non-glacial) and iceberg (glacial) depositional cycle (e.g., Reimnitz and Barnes, 1974; Reimnitz et al., 1994; Darby and Bischof, 1996; Bischof et al., 1996; Phillips and Grantz, 1997). However, knowledge of the exact timing of ice cover and ice free periods in the Arctic Ocean is basically unknown. Recent studies on surface sediment cores in the east Chukchi Sea determined the mass sediment accumulation rates to be an order of magnitude lower than the yearly particle flux obtained from sediment traps (Baskaran and Naidu, 1995). This difference was attributed to the resuspension of fine particles in the continental shelf regions and subsequent advective transport of these particles to sites other than their initial depositions. The changes in sediment types and sources during the past ~2.5 Ma should be a useful guide in interpreting various types of Arctic shelf-basin biological and chemical exchanges that operated in the past.  The sediment record in the deeper basin cores serves as a proxy for former source areas and provides data that suggest which parts of the broad Arctic shelves were principle contributors to the Arctic Basin during particular intervals of the Pleistocene. Biogeochemical imprints in the sediments should reflect preexisting source areas and conditions, and provide a background for understanding modern conditions. In addition, the rise and fall of sea level during the past ~2.5 Ma may be reflected in lateral migration of geologically significant organisms such as benthic foraminifera and ostracods.  Plio-Pleistocene forms living on the shelves are different from those living in the basins (Joy and Clark, 1977; Cronin, 1988; Briggs, unpublished manuscript). Ecologic shifts should be reflected in changing biogeography.
 
        The halocline controls many of the physical, chemical, and biological processes in the Arctic; changes in water mass and transport conditions forming the halocline may, for example, be translated into biological changes in the lower trophic level food web. Such changes could, in turn, influence higher trophic populations (fish, birds, and marine mammals) that ultimately affect resource availability for human populations in the polar north. For example, past studies in the northern Bering Sea and southern Chukchi Seas also suggest that exclusion of bottom fish populations is likely due to low bottom water temperatures on the shelf (Nieman, 1963; Jewett and Feder, 1980). Such a situation would represent a direct effect of halocline formation waters on higher trophic levels.
 
        If a shift in fish population structure were to occur on the shelves of the northern Bering and Chukchi Seas, due to an increase in seawater temperature and associated change in plankton species composition with global change, this trophic shift could influence the highly productive benthic faunal populations that maintain benthic-feeding whales, walruses, seals, and diving seabirds in the region. The timing and geographic extent of marine mammal migrations may also be altered by changes in ice cover, producing shifts in the seasonal and regional roles of marine mammals in structuring pelagic and benthic communities of the Arctic shelf-basin ecosystem. Dyke et al. (1996) utilized the bones of the bowhead whale (a planktivorous animal that lives in the edges of the north polar ice) as a proxy for sea-ice history.
 
        It is possible that the predicted and observed changes in the extent and concentration of sea ice may alter distributions and relative abundances of cetaceans and pinnipeds primarily through fluctuations in prey availability (Tynan and DeMaster, 1996a,b; DeMaster and Davis, 1995; International Whaling Commission, 1997; Harwood and Stirling, 1992). For example, the presence of ice cover dominates primary productivity regimes which provide supportive habitats for the Bering Sea population of bowhead whales (Niebauer and Schell, 1993). The impact of the non-uniform, areal reduction of marginal ice edge zones will depend, in part, on the comparative productivity of open water versus marginal ice edge zones (Tynan and DeMaster, 1996a).
 
        Thus, Arctic shelf and slope processes play a critical role in regulating many of the physical and biogeochemical balances that maintain today s Arctic ecosystem.  Evaluating these processes and the interactions between the deep basin and the adjoining shelves is therefore a prerequisite to an understanding of the present day structure of the Arctic Ocean and its evolution in a changing global environment.

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  5. CORE WESTERN ARCTIC SBI SCIENCE PLAN  
        The overarching rationale for the Western Arctic SBI program is based on the premise that the major global changes that influence biological and physical linkages between the shelf and basin will have amplified effects in the Arctic ecosystem, specifically to maintenance of water column stratification, sea ice distribution, renewable resources, and human habitability of the Arctic. The Western Arctic SBI program focuses on processes crucial to understanding exchange and interaction between Arctic shelves and the basin.  This focus encompasses the critical zone comprised of the shelf, shelf break, and slope regions where many important biological, chemical, and physical processes undergo significant changes and modifications.  The exchange between the shelves and basin in the Arctic is a key element in determining the current extent of global change and prediction of further changes in the future in this important segment of the world ocean. The focus on the shelf-basin zone targets the area in the Arctic seas where the least is known about transport processes and fluxes, biological activity, chemical modifications, and the paleo-sedimentary environment.
 
        An array of shelf-basin interactions (including cross shelf transport of fresh water and ice, halocline renewal via brine drainage and cooling, on shelf upwelling) have been shown to be responsible for maintenance of the stratification and ice cover of the upper Arctic Ocean (Figure 3). These characteristics are, in turn, key determinants in the existence of the unique ecosystem that supports the valuable living marine resources of the Arctic.  To predict the impacts of global change on this ecosystem the links between shelf-basin interactions and productivity need to be established.  The combination of observations and modeling of the response of these links to sizable natural variability over the seven-ten year lifespan of this program will enhance development of societally-relevant predictive capabilities.

Figure 3.  Relationship of physical forcing functions to shelf-basin exchange processes in the Arctic.

       Major goals for SBI will include studies of: 1) the interactions of physical mechanisms (including ice) on advective processes and shelf-basin exchange, including the timing of physical movement relative to biological rate processes, 2) the fate of fixed carbon as it is advected, consumed (by pelagic and benthic consumers), or transformed, with particular emphasis on the relative importance of different types of primary producers to total annual production, and 3) the overall effects of global change on various taxa and trophic structure. These processes are the result of a series of physical, chemical, and biological interactions whose history is recorded in the sediments, suggesting that a knowledge of the natural variability in the system is also recorded in sediments. Therefore, the SBI program will include studies of the sediments with emphasis on those components that can produce proxy records for processes of interest to SBI.

      The overarching goal of the Western Arctic SBI program is to predict the effects of global change on shelf productivity, fluxes, and shelf-basin interactions in the Arctic by defining the magnitude and variability of:
                   1) physical processes (exchanges of water, heat, salt, and ice)
                   2) biogeochemical cycling, and
                   3) biological production and processes.
 
 
5.1  Shelf/Basin Physical Processes
 
        The flux of shelf waters into the Arctic Ocean is of paramount importance in establishing the potential vorticity distribution of the central basin. This influence is effected through controls on basin stratification, circulation along the continental slope, and perhaps even portions of the Arctic Ocean's eddy field (Killworth and Smith, 1984; D'Asaro, 1988a,b). This exchange also involves a cross-shelf transport of dissolved and suspended material, including sediment, that affects the vertical distribution of these materials in the Arctic Ocean (Moore and Smith, 1986; Jones and Anderson, 1986; Björk, 1989; Schlosser et al., 1994b; Jones et al., 1995). The water masses involved in these exchanges have their origin in the enormous freshwater discharge from the surrounding continents (Aagaard et al., 1989; Schlosser et al., 1994a) as well as inflows from the Atlantic and Pacific Oceans (Coachman and Aagaard, 1974). However, the shelves are important sites wherein the freshwater and the inflows from the oceans to the south are substantially modified before entering the central basin.  The extent to which these various water masses are modified depends upon many factors, including the seasonally varying extent of sea ice formation and melting, the source, phasing, and delivery rate of imported waters (be these from other oceans, other shelves or rivers), the atmospheric forcing, and the geomorphology and stratification of the shelf and slope. These features differ considerably among the Arctic shelf seas and suggest that each shelf has a unique link to the Arctic Ocean and its interior structure. Exchange dynamics are also very sensitive to the velocity and/or density gradients at the shelfbreak.
 
        One of the clearest signals of shelf processes within the Arctic Ocean is the halocline of the Canada Basin which bears the physical, chemical, and biological signatures of Pacific Ocean waters (Coachman and Barnes, 1961). Here ventilation of the halocline depends upon formation of dense water in winter by brine drainage from growing sea ice on the shelves of the Chukchi and Bering Seas (Aagaard et al., 1981).
 
        Recent findings indicate that the halocline structure has a remarkable large-scale variability (Carmack et al., 1995; McLaughlin et al., 1996), although the causes of this variability are unknown. There are, however, considerable interannual differences in both the volume transport through Bering Strait and the properties of the Pacific Ocean waters involved in this throughflow (Roach et al., 1995) and in the production of dense water on the shelves of the Chukchi (Aagaard and Roach, 1990) and Beaufort Seas (Melling, 1993). While some of this interannual variability must be due to differences in the rates of winter sea ice production (Martin and Cavalieri, 1989; Cavalieri and Martin, 1994), other evidence suggests that the volume and salinity of the dense water produced depends upon the character of the shelf circulation during the fall preceding ice formation (Melling, 1993).
 
        The structure of Arctic shelf ecosystems also depends upon the underlying physics. For example, biological production on the shelf and slope depends upon the dispersal of freshwater from rivers and ice melt, the production and transport of dense water during ice formation, the three-dimensional circulation field on the shelf and slope including shelfbreak upwelling, and exchanges of heat and momentum with the atmosphere. By controlling nutrient fluxes, stratification, zooplankton transport and aggregation, light penetration, and sea-ice distribution, these physical processes affect the sites and rates of carbon (and other biochemical element) production, deposition, consumption and the trophic structure of Arctic shelves.
 
        We lack a detailed understanding of the physical processes affecting shelf water mass modification, biological production, and exchange with the deep basin. Further, we lack quantitative information on the rates and the variability of these physical processes, both with respect to their physics as well as their relationship to biological production.  A mechanistic understanding of these issues would constitute a major advance toward developing a predictive capability for the Arctic marine system and its relation to the global ocean.
 
To achieve such a capability we need to know:

• the seasonal, interannual and longer term variability of the shelf sources of the halocline and what determines that variability;
• the predominant mechanisms of exchange across the shelf and slope (e.g., plumes, frontal instabilities, eddies, upwelling, intrusions,  sea ice drift) and the rates of these exchanges;
• how control over these mechanisms of halocline source water formation and shelf/slope exchange is exercised (e.g., through topography, stratification, atmospheric forcing);
• how the circulation on the shelf and over the slope modifies the offshore exchange and passes shelf products into the basin interior, including the depth of this exchange;
• what secondary circulations are induced near the continental margin and what their variability is; and
• how freshwater (ice, river discharge, and ice melt) is processed and transported on the shelves.

    With this understanding several specific physical oceanographic hypotheses to be addressed within the SBI program are:
 
1. Changes in the physical processes that affect dense shelf water production (e.g., shelf  ice extent and thickness, river discharge, atmospheric fluxes, transport through Bering Strait, shelfbreak upwelling) initiate changes in the hydrographic structure and ice cover of the Arctic Ocean and possibly even the global thermohaline circulation.
 
2. Changes in the physical processes that affect dense shelf water production directly influence shelf and basin biogeochemical cycles: a cessation of dense water production will lead to increased nutrient concentrations on the shelf and/or a larger nutrient flux into the surface layers of the Arctic Ocean. As a result, alterations in rates of biological production and the Arctic food chain will occur.
 
3. Present-day natural variability could be used to aid the interpretation of high resolution paleorecords thereby affording an understanding of conditions that existed in the past. In conjunction with the paleorecord, the extreme seasonal and interannual variability on the Arctic shelves will provide a paradigm for the possibilities of a changing world.
 
 
5.2  Biogeochemical Fluxes and Transformations
 
        Arctic Ocean processes influence a number of important global biogeochemical cycles. Physical outflows effectively transfer biogeochemical products from the shelves into the surface and subsurface layers of the Arctic Ocean (Anderson, 1995).  Sarmiento et al. (1995) and Lundberg and Haugen (1996) argue that fluxes of carbon through the Arctic Ocean may be a key factor in balancing the Atlantic Ocean carbon budget. The extensive Arctic shelves may contribute significantly to global rates of denitrification (Christensen et al., 1987), which is a major marine sink for combined nitrogen. High latitude precipitation, river flow, subpolar sea circulation and Arctic ice cover affect the complex cycling of nutrients and energy through the biogeochemical pathways of the Arctic shelves and basins. Global change (e.g., polar amplification of global warming and human patterns of activity) could alter biogeochemical  pathways that  determine the in situ recycling and/or exchange of material between the Arctic shelves and basins.
 
        The formation and movement of the halocline waters may be the major mechanism that removes organic material and anthropogenic pollution from the shelf to the slope and ocean basin (Jones et al., 1990; Figure 4).  Halocline formation and shelf-basin exchange of biogeochemical products are intimately connected to the Arctic s hydrological cycle (Avakyan et al., 1994). In addition, the freshwater volume entrained in Bering Strait is roughly equivalent to the sum of freshwater inflows of all Arctic rivers draining directly into the Arctic Ocean  (Macdonald et al., 1989) and is a  major point source for nutrient input to the Arctic Ocean (Codispoti and Owens, 1975; Cooper et al., 1997). Ice transport can play a significant role in nutrient and material transport in the Arctic.

Figure 4.  Fluxes and transformations of carbon on the shelves and slopes of the Arctic Ocean.
Variations in sea ice extent with global change will impact oceanic current transport conditions
and associated nutrient and biogeochemical fluxes over the shelf and slope regions of the Arctic.

        Many Arctic shelves are relatively unproductive, being limited by low temperatures and seasonal changes in light,  nutrient availability, freshwater runoff, and ice cover (Dayton, 1990). However, a few Arctic shelves are host to levels of primary and secondary production that are among the highest reported for any area, e.g., the northern Bering and Chukchi Seas in the western Arctic and portions of the Barents Sea shelf in the eastern Arctic (Grebmeier and Barry, 1991 and references therein).  There are significant biogeochemical exchanges between the shelves and basins, but we currently lack the information necessary to quantify these exchanges, assess their seasonal and interannual variability, and predict their susceptibility to global change.  Important research questions related to the outer shelf and continental slope zones of both the Russian and North American Arctic include the transport and sequestering of carbon (both particulate and dissolved phases).
 
        If projected global and regional climate changes occur, how will the biological pump over the large Arctic continental shelves be affected? If sea ice cover varies with climate change, will there be an increase or decrease in shelf-basin water exchange and subsequent changes in water column production? Any changes in the physical forcing functions in the Arctic Ocean and its marginal seas may dramatically influence biogeochemical cycling over the wide Arctic shelves as well as overall ecosystem function with potentially significant consequences for living resources and the human populations that are dependent on these resources.
 
        Determining the rates of processes that effect the fate of biogeochemically important chemicals, i.e., C, N, P, and S, in Arctic shelf sediments is especially important because, with the exception of the deepwater input through Fram Strait, essentially all of the input of these elements into the Arctic Ocean must cross the shelves before being incorporated into the interior basin. Since the Arctic Ocean and its marginal seas represent only 2% of the total volume of water in the global oceans, but contain 25% of the global shelf area, the shelf area to basin volume ratio is anomalously high (Sverdrup et al., 1942; Menard and Smith, 1966).
 
          Sediments play an important role in nutrient cycling, especially with respect to nitrogen. Regeneration of nitrate and ammonium from sedimented organic material is an important mechanism by which nutrients are returned to the water column (Walsh and McRoy, 1986; Rowe and Phoel, 1992).  Arctic sediments may play a globally important role through the process of denitrification (Codispoti, 1995; Devol et al., 1997).  This is because the largest marine sink for fixed nitrogen appears to be denitrification in continental shelf and hemipelagic sediments.  Given the large fraction of shallow sediments, the Arctic Ocean might be a large sink.  Only a few denitrification rate estimates exist for Arctic shelf sediments and most of these were made in a rather limited area of the Chukchi Sea (Lomstein et al., 1989; Henriksen et al., 1993; Devol et al., 1997).  However, all of these estimates suggest that denitrification in Arctic shelf sediments is comparable to other shelf regions and that it is globally significant.
 
        This removal of biologically usable fixed nitrogen is a negative feedback to primary production. The magnitude of this loss within the Arctic may be significant as a long-term control on global marine primary production (Codispoti et al., 1991), and denitrification in Arctic shelf sediments may represent about 12% of the global total.  Minor redistributions of carbon can cause this rate to change significantly (by factors of 2-3; Codispoti, 1989).  It is clear that this process significantly reduces the potential productivity of water in the Chukchi, Bering, and East Siberian Seas (Codispoti et al., 1991).  Thus, to understand nitrogen cycling and its feedback on productivity in the Arctic in general, and to better quantify the global nitrogen budget, a thorough understanding of sedimentary nitrogen cycling is necessary.  This includes a need for representative coverage both areally and seasonally.
 
        Arctic Ocean margin sediments should play an important role with respect to carbon cycling and carbon burial.  Permanent burial in marine sediments is the ultimate long term sink in the global carbon cycle, and although there is debate over how to determine the amount of C buried in any given sediment, nearly all contemporary C burial is taking place in continental margin sediments (Berner, 1982).  Because of the high proportion of shelf sediments in the Arctic, understanding carbon burial (and oxidation) in Arctic margin sediments is necessary to understand not only shelf basin carbon exchange, but also global carbon burial. In addition, Arctic shelves are the major source of Arctic Basin sediment during interglacial climate periods, and the adjacent Arctic continents are the major source of Arctic Basin sediment during glacial and deglacial intervals (Clark and Hanson, 1983). Sediment fluxes from the shelves into the basins are accompanied by biogeochemical fluxes, and study of the sediment characteristics can illustrate how and when these fluxes occurred.  A correlation of basin sediment types with climate events is important background for understanding shelf-basin processes today and in the future.
 
        Since factors such as precipitation, river flow, circulation, and ice cover influence the cycling of nutrients and energy through the biogeochemical pathways of the Arctic shelves and basin, global change could alter biogeochemical pathways that determine the fate of shelf production. Because of the markedly different summer and winter regimes in the Arctic, strong physiochemical interactions occur between the continental shelves and the basins which could be influenced by global change. For example, organic matter that accumulates over the shelves during the spring and summer could be "swept" into the basin by offshore currents associated with ice and brine formation during winter (Honjo, 1990; Cavalieri and Martin, 1994; Melling and Moore, 1995; Steele et al., 1995), and global warming could alter this process.  Features that may change are outlined in Figure 5 (Arctic Shelf-Basin Exchange Model) and they include:

• annual biogeochemical cycles
• budgets of C, N, P, Si, O2, Fe, Ba and S
• spatial and temporal scales of ice algal blooms
• phytoplankton effects on climate via DMS, etc.
• remineralization in water column vs. benthic regeneration
• transport of allochthanous organic matter
• deposition on slope vs shelf
• zooplankton distributions
• hydrologic cycle which affects ice cover, sea level, and currents

Figure 5.  Western Arctic Shelf-Basin Exchange Model with associated forcing functions, biological pools,
biogeochemical processes and potential impact path- ways with global change.  Although only the input
and output are indicated as global change impact points, the effects of global change are hypothesized
in the SBI program to cascade through the trophic food web.

         Important physical controls on the above mentioned topics are addressed in the hypotheses outlined in the preceding physical section and shown in Figures 3 and 4. Some of the most important physical and biogeochemical relationships are those between halocline formation and: 1) the fate of biological production,  2) the source terms for nutrients on annual time and space scales, 3) the way physical processes may alter storage of carbon in shelf/slope sediments, and 4) the effect that a reduced ice cover would have on zooplankton distribution, which in turn would affect vertical particle transport.
 
        Processes influencing transport of materials between the shelf and basin systems in the Arctic vary dramatically in time and space, and these variations greatly influence the total, new and export production (see Berger et al., 1989 for definitions of these terms) for various portions of the Arctic (Figure 6).  The slopes of the relationship between total and export production may vary with changes in climate. Three production lines (with patterned envelopes suggesting plausible export/total production "envelopes" in  different  regimes)  show different values that are useful for hypothesis testing for the Bering/Chukchi Sea (high production), the Eurasian shelf (medium production), and the Polar Ocean (low production).

Figure 6.  Schematic of processes influencing transport of materials between the shelf and basin systems
of the Arctic. The downward pointing arrows indicate the increasing distance from the one-to-one line
where total production = new production = export production.  This hypothetical one-to-one line is a
situation that is never achieved, but which tends to be more closely approximated in regions where the
nutrient supply and/or total production rates are highest.  This type of model could provide a basis for a set
of testable hypotheses for an interdisciplinary program.

        Table 1 outlines possible, testable hypotheses with an expected climate warming trend that could influence the amounts and fates of total and new production and the ratio between total and new production.  Basically high export production arises mainly from "pulsed" diatom and phaeocystis blooms (e.g., Berger et al., 1989) which require abundant nutrients (including Fe) and light, and any change that detracts from the occurrence of such conditions will lower export production. Other scenarios include a reduction in export production with global warming due to an increase in microbial recycling of organic matter and/or a decrease in ice coverage.  Each region of the Arctic would be affected to a different extent depending on the existing trophic interactions scheme.
 
Table 1.  Some possible factors influencing the level and fate of Arctic shelf export production under a global warming scenario.

 
       Because of the markedly different summer and winter regimes in the Arctic, strong physiochemical interactions occur between the continental shelves and the basins which will be influenced by global change, including seasonal ice production, halocline formation and associated nutrient transfer between the shelf and basin, and changes in freshwater input. With this understanding several specific biogeochemical hypotheses to be addressed within the SBI program are:

1. Ice formation and dense shelf water production contribute to a highly stratified upper layer in the Arctic Ocean. Therefore, changes in the physical processes that affect dense shelf water production directly influence shelf and basin biogeochemical cycles: a cessation of dense water production will lead to increased nutrient concentrations on the shelf and/or a larger nutrient flux into the surface layers of the Arctic Ocean.  As a result, alterations in the rates and timing of biological production, and the associated Arctic food chain, will occur.
2. Increased river runoff will lead to a significant increase in terrestrial inputs of POC/DOC to the shelves and basin.
3. Reduced ice cover will lead to a decreased carbon efflux from the shelves to the basin (including zooplankton), because offshore bottom currents that arise from ice and brine formation will be reduced.
4. Reduced ice cover in the Arctic will significantly increase Arctic shelf/slope (and global) rates of denitrification.
5. Reduced ice cover with global change will result in increased carbon sedimentation and carbon storage in the Arctic shelf and slope sediments, thus providing an increased sink for global CO2.

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5.3  Biological Standing Stocks, Processes and Trophic Structure
 
        The continental shelves of the Arctic Ocean and the surrounding marginal seas comprise an extensive area that is important to biological activity and potential carbon deposition or export. As shown in studies conducted in the Bering and Chukchi Seas (Dunton et al., 1989; Grebmeier, 1993), the export of carbon from the shelves is largely dependent on in situ rates of primary production, pelagic food web structure, and a variety of physical conditions, including current fields, frontal systems, depth, and vertical stratification (Grebmeier and Barry, 1991).  Of all these factors, the degree of pelagic-benthic coupling of photosynthetically produced carbon on Arctic shelves is probably most poorly understood, yet can play a major role in the sequestering of carbon on the shelves (Dunton et al., 1989; Hobson et al., 1995).
 
        Since a greater proportion of biogenic material may reach the bottom in the Arctic compared to lower latitudes (Peterson and Curtis, 1980; Welch et al., 1997), changes in primary productivity, most of which is concentrated on Arctic shelves, could have dramatic effects on benthic productivity and consequently the transport of carbon to the Arctic basin. Large scale variations in wind and ice fields along the nearshore Arctic shelf that are associated with global climate change could also have significant effects on the sedimentation of organic matter onto the shelf.  In Norwegian fjords, wind stress plays a critical role in the advection of both phytoplankton and zooplankton, controlling the fate of vernal blooms, and ultimately, the degree of pelagic-benthic coupling (Reigstad and Wassman, 1996).  In the high Arctic, we have relatively little information on the significance of large scale meteorological events on primary production and the advection of organic biomass onto the Arctic shelf or basin.
 
        Arctic marine mammals have undergone large population fluctuations due to human hunting and climatic fluctuations (Vibe, 1967).   For example, bowhead and gray whales were hunted commercially throughout the Arctic and on their migration routes during the 19th century (Henderson, 1984; Woodby and Botkin, 1993), although populations of both species have experienced a recognizable degree of recovery during the 20th century (Buckland et al., 1993; Zeh et al., 1993). Due to the lack of suitable time-series, it is impossible to identify with certainty the influence of climatic change amid past population declines and recoveries.  However, the role of marine mammals in the Arctic ecosystems can be modeled from diet studies, estimates of population size, habitat selection studies (e.g., Moore and DeMaster, 1997), migration patterns and seasonal movements, and process-oriented field studies which examine fronts, eddies, marginal ice zones, and other productive mesoscale features utilized by marine mammals.
 
         Biological research issues important to the SBI program are outlined in Figure 5 and specifically include:

• the magnitude and seasonal variability of total and new primary production
• the spatial variations in the abundance and diversity of benthic and epibenthic fauna
• the causes and consequences of variations in abundance (space/time distributions) of higher trophic organisms (fish, seabirds, marine mammals)
• the export of carbon to higher trophic levels and sedimentary burial
• the geological record of cyclical changes in production and carbon burial

          It is clear that new and more extensive sampling is needed to describe and understand the effects of global change on biological processes and exchanges between the shelves, slope and basins. Coordinated observational studies, process studies, and modeling efforts will permit the testing of important hypotheses about the effects of global change on both lower and higher trophic levels.
 
5.3.1  Lower Trophic Levels
 
        Regional patterns of primary and secondary productivity on the shelves, slopes, and basins of the Chukchi and Beaufort Seas may be altered by global change.  For example, global warming and sea ice retreat may change the relative contributions of sea ice algae and phytoplankton, the species and/or size composition of producers, and the total and new production, impacting trophic structure, and the abundance of secondary producers in the benthos and water column. Year-to-year variations in ice cover provide a natural experiment for evaluating qualitative and quantitative effects on lower trophic level dynamics.  These results will also provide insights into the most extreme situation predicted by the GCMs, i.e., that disproportionate warming in the Arctic will greatly reduce, if not eliminate, the ice over the broad Arctic shelves.
 
        With this understanding several specific lower trophic level hypotheses to be addressed within the SBI program are:

1. Reduction in ice cover and stratification, which may already be occurring and which are the plausible result of any warming trend, will increase total/new production in the Arctic Ocean and its marginal seas.
2. Even without changes in overall total/new production, a change in ice cover will cause a major shift in the relative contributions of ice algae and phytoplankton to shelf and slope primary production.
3. The degree of ice cover will have no effect on total secondary production, but it will instead cause a major shift in the relative importance of the benthic fauna and pelagic zooplankton.
4. If ice algae and ice-edge blooms of phytoplankton are drastically reduced on the broad Arctic shelves due to reduced ice cover, then the role of zooplankton in structuring food webs by preferentially consuming either protozoans (microbial loop) or diatoms (classical loop) would become more important (particularly among contrasting food webs of continental shelves and continental slopes).  Changes in the composition of zooplankton grazers will have distinct impacts on food web structure and dynamics, and will ultimately be reflected in the composition and abundance of both pelagic and benthic fauna.

5.3.2  Higher Trophic Levels
 
        Higher trophic levels in the Arctic (fish, marine mammals, and seabirds) may be especially vulnerable to global change, and serve as indicators of the health of the Arctic system (i.e., in the bioamplification of contaminants) or changes in the species composition and biomass of lower trophic levels.  To predict the direct and indirect effects of a warmer Arctic (primarily loss of suitable ice habitat and shifts in prey availability) on resident and migratory marine mammals, models which provide regional predictions of the extent and concentration of sea ice, productivity, and the cascade of trophic dynamics are critical. In addition, analysis of past and current natural history data on how higher trophic organisms modify their distribution under existing ice changes would provide valuable insight into understanding the distribution patterns of ice-associated marine mammals.
 
        Whereas lower trophic hypotheses interact with broad-scale oceanographic processes, the spatial and temporal links between large oceanographic processes and the distribution and abundance of upper trophic level organisms is not nearly as clear. Some of the following higher trophic level hypotheses are species or technique specific, and therefore they are provided only as suggestions of possible hypotheses that could be tested during the SBI program:

1. The reduction of ice cover and increased seawater temperatures will increase both pelagic and benthic fish production through migration, reduced predation by ice-associated seal populations, and increased levels of benthic productivity.
2. Alternatively, increased fish predation will change the benthic community structure, resulting in reduced ampeliscid amphipod and bivalve populations, and a subsequent reduction in benthic-feeding marine mammals (e.g., gray whales and walruses).
3. At least four species of marine mammals (ringed seal, ribbon seal, bearded seal, polar bear) are obligately ice-associated.  Changes in the extent of ice cover will control where these mammals are located and where higher trophic levels will have the most significant impact on lower trophic levels.
4. The extent of bowhead whale migrations is strictly governed by sea ice cover. In addition, paleo-ranges of the Bering Sea bowhead whale stock can be determined through  radiocarbon dating of bowhead whale subfossils. Thus, the extent of ice cover and associated ecosystem structure in the past can be described and time recorded by various measurements of these whale subfossils.

  5.4  Modeling: Pan-Arctic
 
        General circulation models (GCMs) suggest that greenhouse warming may be amplified in the Arctic (Stouffer et al., 1989), resulting in large temperature increases ranging from 2-12°C (Hansen et al., 1983; Houghton et al., 1996). Other model estimates of the consequent changes of: 1) the local ice albedo feedback and surface heat fluxes (Moritz and Perovich, 1996), and 2) the far-field formation of North Atlantic Deep Water (Manabe and Stouffer, 1993) indicate profound impacts on both polar and global climate. What might be the biogeochemical implications of such an altered physical habitat of the Arctic shelves and basins?
 
        Prior box models of pre-Holocene nutrient cycles (Knox and McElroy, 1984; Sarmiento and Toggweiler, 1984) suggested that higher productivities prevailed in ancient polar regions of warmer habitats than present, and could have been responsible for the low concentrations of atmospheric CO2 found in ice cores. Now the Arctic Ocean may again be a sink for atmospheric carbon dioxide (Lundberg and Haugan, 1996). Such a sink may be less than 250 years old, however, as a consequence of anthropogenic releases of CO2 at lower latitudes (Walsh and Dieterle, 1994). The fates of this recently sequestered CO2, whether as: 1) DOC and DIC storage pools in the halocline (Walsh et al., 1997),  2) burial of POC in the sediments, or 3) harvest by sea mammals and man, are unknown.
 
        Similar uncertainties exist about the present amounts of N2 lost from polar sediments after denitrification (Henriksen et al., 1993; Devol et al., 1997) and of dimethylsulfide (DMS) evaded from polar waters after prymnesiophyte and diatom growth (Levasseur et al., 1994;  Turner et al., 1995). Indeed, there is some question about the future sign of air-sea carbon exchange in a hypothetically ice-free Arctic Ocean (Walsh, 1989), which now receives about 10% of the terrestrial effluxes of river-borne DIC and DOC (Anderson et al., 1990). As part of the NSF-ARCSS Western Arctic Shelf-Basin Interactions program, a set of biochemical models of C/N/S cycling and subsequent yield to humans in the Arctic system is thus required to assess the consequences of global change on this sentinel system of high latitude shelves and basins.
 
        These ecological models must be nested in a series of ice (Mellor and Hakkinen, 1994)  and ocean circulation submodels at varying scales from local entrainment of sinking dense water (Jiang and Garwood, 1995; 1996) to regional and basin-wide flows (Semtner, 1987; Riedlinger and Preller, 1991; Hakkinen, 1993; Maslowski, 1996; Maslowski et al., 1997; Zhang et al., 1997), and their feedbacks to larger climatic features of GCMs at lower latitudes (Semtner and Chervin, 1988).  The first objectives of such three dimensional models would be to define why certain shelf regions of the Arctic appear to be more productive, e.g., as much as 250 g C m-2 yr-1 in the southern Chukchi Sea compared to perhaps 25 g C m-2 yr-1 in the Beaufort Sea, and how these regions communicate with others in terms of changing population dynamics, in likely response to alteration of polar and global climates - different ice cover, salt budgets, and wind forcing.
 
        Several fundamental issues can most easily be addressed through the use of relatively simple process models designed to isolate dominant physical mechanisms and their space and time scales. The goal of these models is to guide field efforts and to aid in the parameterizing of complicated processes for GCMs. Many of these effects occur at spatial scales smaller than those typically resolved by GCMs (Gawarkiewicz and Chapman, 1995; Jiang and Garwood, 1995; 1996; Chapman and Gawarkiewicz, 1996). Among the issues to be addressed by such modeling studies are spreading and mixing of positively and negatively buoyant water masses across the shelf and slope, the along slope ramifications of this cross-shelf transport and the means by which these shelf water masses ultimately penetrate into the interior.
 
        With application of such validated models to the other East Siberian, Laptev, Kara, and Barents Seas, a second set of objectives would be an analysis of the future coupled Pan-Arctic perturbations of both C/N/S cycling and of yields to humans and other apex predators. As an integral part of a multidisciplinary field program, such objectives would guide the original synthesis of historical data, selection of sample sites and designs, and modification of subsequent field experiments.  A third and final product of such a theoretical component of an SBI program would be specification of the possible feedbacks of polar change to those at lower latitudes.

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  6.  SBI IMPLEMENTATION PLAN  
        The Western Arctic SBI program will be undertaken using analysis of historical data, modeling, sampling programs (with required platforms) and integration with both national and international programs. The core program will include regional investigations, regional models, Pan-Arctic data synthesis and international comparison of regional models, and development of a "Pan-Arctic" model (with embedded regional submodels) suitable for "what-if" global change scenario studies. The purpose of the SBI science plan is to summarize the goals and disciplinary objectives of the program and to propose a broad outline for an implementation plan. Development of a detailed implementation plan, with priority measurements and appropriate time and space scales for coordinating projected results of physical and biogeochemical process studies, will be developed during Phase I by the SBI Executive Committee, with input from Phase I PI s. In addition, this committee will work to develop linkages with the other ARCSS components, specifically HARC and LAII. A finalized implementation plan will result from a workshop to be held after the first year of retrospective data analysis and will consist of both Phase I and prospective Phase II PI's.

6.1  Sampling Program and Platforms
 
        Recent reports by the National Research Council entitled "Arctic Ocean Research and Supporting Facilities" (National Research Council, 1995) and the U.S. Arctic Research Commission entitled "Logistics Recommendations for an Improved U.S. Arctic Research Capability" (Schlosser et al., 1997) provide comprehensive evaluations of the current status and future needs of the U.S. scientific community for Arctic research. The following categories outline the major topics for Phase I and will be expanded and refined as a detailed implementation plan is developed for the Phase II field program.
 
6.1.1  Sampling Program
 
        The initial phase of the SBI program will mainly gather data that are needed for preliminary modeling efforts and for enhancing planning for the full field seasons that will follow.  This phase could utilize the sea trials of the new icebreaker, HEALY,  and/or join with other funded ongoing projects occurring in the proposed study area.  Arrays of moored instruments may also be installed in critical areas to provide an early assessment of flow fields and water mass characteristics through multiple seasons.
 
        The main phase of the SBI program will require major field efforts over multiple years to determine seasonal and interannual variability.  While the specific requirements of the field program will depend on the requirements of the research funded, a major expedition is expected in each of the years.  Given the limitations of the available icebreakers, early season cruises will focus on the shelves with later sampling occurring over the shelf break and upper slope.  When ice conditions will not allow studies from surface vessels, a combination of aircraft, submarines, ice camps and remote sensing will be used to collect necessary measurements during the fall, winter and spring.  Since the seasonal changes are virtually unknown for most processes, major new understanding will accrue from measurements collected during the cold seasons.  The nature of the main field operations are likely to change during the 5-10 year study period as some studies are phased out and replaced with new projects.  An initial estimation of surface vessel logistic support needed for the major field years is 3-4 months/year.
 
        The final phase of the SBI program will primarily focus on data synthesis and modeling, but continued measurements of some long term data collections may be advisable.
 
6.1.2  Required Platforms
 
        The field program envisioned for SBI will include a combination of platforms, such as surface vessels, submarines, air craft, ice camps, moored instrument arrays and remote sensing that are deployed depending on the spatial and temporal scales of the studies undertaken. There is a need for year-round logistic access to the high Arctic, with support by ice breakers and ice-strengthened ships, shore-based marine stations, aircraft (fixed wing, helicopter), over-ice and nearshore surface vessels, as well as clothing and specialty equipment as is provided by NSF in the Antarctic.
 
        Ice-breaker support (surface vessels March-November) is required for the SBI program and should include U.S. Coast Guard vessels, specifically the upcoming USCGC HEALY. Foreign vessels that may also be leased include Canadian (LOUIS ST. LARENT, LARSEN), Russian (FEDEROV), and Swedish (ODIN) icebreakers. Ice-strengthened vessels of potential use include the UNOLS vessel RV ALPHA HELIX, along with Japanese, Canadian, and Russian ice-strengthened vessels.
 
        Submarines, helicopters, ice camps, and deliberate setting of a vessel into the ice for Lagrangian-type studies are also possible. Current land-based facilities need to be upgraded and made more available to support transportation to and from research sites, equipment storage, and communication. Possible field station programs could be staged from Barrow, Alaska for work in the western Arctic region.
 
6.1.3  Instrumentation
 
        Instrumentation for seasonal studies, both pelagic and benthic, is needed, including automation for DMS sensing and other biogeochemical sampling.  Evidence is needed to address the effects of warmer, shorter winters on food web dynamics. These include deployment of sediment traps and instrumental moorings on the outer shelves and down the continental slopes.
 
6.1.4  Remote Sensing
 
        Remote-sensing platforms will be important for understanding both physical and biogeochemical processes. They will be helpful in providing regional and basin scale spatial coverage as well as year-round measurements. Data collected during the SBI program, in conjunction with archived satellite data sets, will help quantify ocean and ice variability. That information will be particularly helpful for placing in a historical context the environmental conditions encountered during the SBI field program. Satellite sensors such as the Synthetic Aperture Radar (SAR), the Defense Meteorological Satellite Program Special Sensor Microwave/Imager (DMSP-SSM/I) and the NOAA Advance Very High Resolution Radiometer (AVHRR) can measure ice type, concentration, and displacement, thereby contributing to quantifying freshwater transport and ice production rates. The SAR and AVHRR sensors can provide information on fronts, circulation, and weather.  Western Arctic data from these sensors are downloaded to the SAR facility at the University of Alaska, Fairbanks. The recently launched NASA SeaWiFs satellite detects chlorophyll pigments and will therefore be useful in ocean production studies. NASA P3 aircraft could also be equipped with an array of specialized sensors geared for use in conjunction with local field experiments. Under-ice observations, from submersibles, remotely operated vehicles (ROVs), autonomous underwater vehicles (AUVs), and divers are also feasible measurement approaches.
 
6.1.5 Upcoming Opportunistic Field Opportunities (1997-2002)
 
        The following opportunities could provide "platforms of opportunity" for the Western Arctic SBI program during Phase I and II:

• SHEBA icebreaker freeze in (1997/1998)
• SCICEX submarine program (NSF/ONR; 1997-2000 and beyond?)
• USCGC HEALY ice trial opportunities in the western Arctic (1999)
• USCGC Polar class ships of opportunity (POLAR SEA AND STAR) in the western Arctic (1997-2002)
• ice camps.

        Access to these platforms of opportunity will be investigated through the SBI Science Management Office, NSF, and research scientists.
 
6.2  Collaboration and Integration with Other U.S. and International Programs
 
6.2.1 U.S. Programs
 
a.  Arctic System Science (ARCSS) Program
 
OAII (Ocean-Atmosphere-Ice Interactions) - The Western Arctic SBI program would be a component of the OAII program which currently consists of the SHEBA (Surface HEat Budget of the Arctic) and numerous individual projects.  Close collaboration would be mandated for all SBI projects through an annual PI meeting. Crossover analyses between pertinent individual and group OAII projects and SBI studies would be stimulated as part of the OAII biennial meeting and through informal arrangements.  In particular, the SHEBA project will provide some very important ice/energy dynamics and preliminary sampling opportunities that will be useful to SBI. Likewise, the Western Arctic SBI may provide SHEBA some opportunities for follow up field measurements. The Western Arctic SBI program will provide the initial framework for three proposed OAII programs (presently in the initial stages of development) to study the hydrography and biogeochemical components of the Arctic Ocean's Canada Basin (J. Swift et al., 1997, pers. comm.), the characteristics and variability of outflow dynamics of Arctic Ocean water exiting through the Canadian Archipelago and downwelling in the North Atlantic (M. Johnson et al., 1997, pers. comm.), and global change impacts on observed temperature and salinity regimes in the interior Arctic Ocean (J. Morison et al., 1997, pers. comm.). Each program will make important ontributions to our understanding of regional and basin scale issues and how the Arctic Ocean will respond to the effects of global change.
 
LAII (Land-Atmosphere-Ice Interactions) - The LAII program shares a common interface with OAII at the shorelines of the Arctic Ocean (ARCSS, 1997).  The export of materials from the land to the ocean crosses the boundary of these two ARCSS programs and represents an important interface that has heretofore been minimally studied except for relatively large riverine effluxes. Both programs also have similar close ties to atmospheric processes that may transport materials and energy across the common boundary.  The Western Arctic SBI program will appoint a set of Principal Investigators to link to specific LAII projects that will enhance joint goals of OAII/LAII integration and synthesis of scientific results. The proposed RAISE (Russian-American Initiative on Shelf-Land Environments in the Arctic) project will be particularly useful and informative with regard to the export of materials from the tundra and several Russian rivers onto the East Siberian shelf (Forman and Johnson, RAISE Science Plan, in prep.).
 
HARC (The Human Dimensions of the Arctic System) - There are many potential linkage areas between SBI and HARC programs, including studies of contaminants being transported though the Arctic Ocean ecosystem, anthropogenic impacts resulting from change in the freshwater balance of the Arctic, and evaluating how global change will affect the size, distribution, and condition of higher trophic organisms used by human populations (outlined as OAII/HARC linkages in the HARC science plan; ARCUS, 1997b). More specifically, studies are needed of anthropogenic impacts, including river modifications, that influence Arctic shelves and basins and which may lead to modification of natural cycles of global change. Issues of importance to human use and exploitation of the Arctic include whether shelf-basin interactions, such as those influencing sea ice and nutrient conditions, control the availability of harvestable and/or subsistence resources (e.g., fish, marine mammals, and seabirds). We need to know the control mechanisms governing resource population levels and how climate change and human-produced impacts would affect these renewable resources. Investigations developed within the SBI framework for linkage to the HARC program may include: 1) possible changes in the abundance and distribution of fish, marine mammals, and seabirds that may result from global change, and in turn affect resource availability to Arctic human communities, 2) changes in trophic pathways and flux rates that may affect the bioamplification and delivery of pollutants to consumers of Arctic higher trophic organisms, and 3) studies of prior climate change including bioarchaeology, evaluation of marine resource use records, and oral history of marine mammal resource use and sea ice conditions.
 
        During Phase I, the SBI Executive Committee will strive to develop a working relationship with local communities, governments, educational institutions or people living near or reliant on the resources of the Chukchi and Beaufort seas. Incorporation of ethical principles for Arctic research (e.g., currently under review by the International Arctic Science Committee) will be pursued. As such, the SBI Executive Committee, in collaboration with a HARC PI or SSC member on the committee, could pursue public and educational opportunities to present the goals, objectives, implementation plan, and results of SBI work to local communities in the Arctic. In addition, potential logistical support may arise from partnerships with local government entities, such as the Barrow Arctic Science Consortium.
 
GISP2 (Greenland Ice Sheet Project 2) - The GISP2 program has obtained highly significant long term climate records from Greenland ice sheet cones. The paleorecords in the sediments of the Western Arctic SBI study area are very poorly sampled, but there will be a strong impetus to attempt a correlation with the GISP2 horizons in order to assess the uniformity of processes within the Arctic.
 
PALE (Paleoclimates of Arctic Lakes and Estuaries) - The PALE program has focused on records of changes that are contained in Arctic lake sediments. These records are relatively recent compared to GISP2, but they yield important information on regional and local history. The Western Arctic SBI program would utilize PALE results in retrospective modeling to provide specific event markers during the past few thousand years.
 
b.  Other NSF Programs
 
        There are numerous small and individual projects within the Office of Polar Programs and Oceanography/Geosciences Sections that relate to SBI issues. Communications with large programs, such as WOCE, JGOFS and GLOBEC, will be fostered both for the intellectual synergisms that should result and the need to harmonize data collection protocols.
 
c. Other Federal Programs
 
        Several federal agencies (e.g., ONR, NOAA, NASA, DOI, DOD) support research that is related to the goals of SBI. Direct relations with such agencies will be facilitated by the SBI management office whenever appropriate. We will also keep the Arctic Research Commission informed of SBI activities.  This Presidentially-appointed commission coordinates the overall federal research efforts in the Arctic region. In summary, the Western Arctic SBI program will strive to establish a working relationship with all relevant U.S. programs in the Arctic and to provide information/data to related scientific programs such as global change and global climate models.
 
6.2.2 International Programs
 
        There was strong consensus at the workshops that successful implementation of the Western Arctic SBI program requires best use of all existing and future data, including international sources. The overall success of the Western Arctic SBI program will depend on coordination and collaboration with international Arctic research programs, such as ACSYS. Bilateral and multilateral international agreements with Arctic rim nations supporting free access to marine waters within national boundaries are needed as well as collaborative scientific exchanges in joint cruises and at existing field stations.  Proposed or ongoing international programs should be integrated into the U.S. scientific planning process to make best use of current or future data and to provide a broad representation of pan-Arctic shelf-basin interactions.  This is especially true for Canadian and Russian programs that border on the Western Arctic SBI study area. Key SBI principal investigators will be appointed by the SBI Executive Committee to act as liaisons to international partners.
 
        A sound plan for collaboration between the various proposed or on-going projects would foster valid comparative analyses of data sampled in different Arctic regions. To achieve this goal, it would be desirable to establish the use of standardized methodologies, possibly compiled in a "handbook of methods". The broader spatial (and possibly also temporal) coverage would allow for drawing more general conclusions about the shelf-basin processes and their significance for the Arctic Ocean as a whole.  The following summaries describe some of the current and planned international programs.
 
        The interrelationships between Eurasian shelf productivity and the central Arctic Ocean deep-sea ecosystem are being used as the basis for future research by our European colleagues.  A major European effort that focuses on the Eurasian fringe of the Arctic Ocean is  "The  Arctic Ocean System in the Global Environment" program (AOSGE) proposed to the MAST III program in fall 1996. This program is designed to investigate all aspects of shelf-basin exchange in the northern Barents Sea and probably the northern Kara Sea and will involve investigators from Norway, Europe and Russia.
 
        Another significant suite of studies is represented by the on-going Russian-German "System Laptev Sea" project. This program should provide important comparative data to the SBI program.
 
        Canadian researchers will study the physics and biology of the North Water Polynya in Northern Baffin Bay in 1998. The North Water Polynya Project (NOW) is part of the International Arctic Polynya Programme (IAPP) of the Arctic Ocean Science Board (AOSB). The general hypothesis underlying much of the proposed research is that the very same physical processes that open the North Water polynya are responsible for its unusual productivity.
 
        A proposal to study the physics and the biology of Labrador Sea will be submitted to NSERC in September 1997. This project is part of phase 3 of the Canadian Joint Global Flux Study Program (CJGOFS). It is aimed at characterizing the factors regulating biological and physical pumping in a region which has a strong annual cycle of primary production and temperature, and which experiences episodic deep convective mixing in winter.

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6.3  Western Arctic SBI Program Outline
 
        The Western Arctic Shelf-Basin Interactions (SBI) program will develop via a phased approach in which initial synthesis, including modeling, of present knowledge will be used to develop the field studies and regional comparisons which, in turn, will evolve into the final stages of assessment of the interactions between global change and biological processes in the Arctic (Figure 7).

Figure 7.  Phases and associated interconnections to major tasks within the SBI program.

      Phase I would be comprised of several small projects associated with collection and analysis of historical data coupled to preliminary modeling.  This period would be primarily intended to refine and focus the later field programs.  Several modest field sampling programs may be implemented to take advantage of sampling opportunities and logistics during this initial phase, especially if there are strong couplings to later phases of the SBI program. Preliminary development of coupled biochemical and physical models of the Arctic marine response to global change would include a synthesis of historical data to refine hypotheses of SBI studies in order to specify sites and logistics of field experiments in the Western Arctic.
 
        Phase II of the Western Arctic SBI consists of the main field program and of simultaneous and interactive development of a Pan-Arctic modeling component with linked regional submodels.  The main  field program must occupy a major portion of the 7-10 year SBI program in order to sample a sufficient range of climate and oceanographic conditions to significally enhance predictive capabilities.  As the field program progresses, coupling to developing progress in Pan-Arctic synthesis and understanding of other Arctic shelf-basin areas must be included.  This would best be accomplished by a series of workshops sponsored by the Western Arctic SBI program that would be focused on specific topics of general interest to the Arctic science community. Within the modeling portion of the program, priority projects would place the Western Arctic ecosystems in the context of basin-wide circulation, element cycling and population dynamics of biota, thus enabling mid-course correction to experimental design after initial data assimilation.
 
        Phase III of the Western Arctic SBI program would be focused on assessments of: (1) global change effects on the biological, chemical and physical processes in the Arctic, and (2) the delineation of global change on the overall carbon/nitrogen cycles and the combined effects on the yield and structure of the higher trophic levels, including human populations in the Arctic. Within the modeling portion of the program, there would be an expanded synthesis of Western Arctic analyses to Pan-Arctic assessment of other shelves and basins to indicate positive and negative feedbacks of polar change to processes at lower latitudes. Special efforts will be made to interact with prominent general circulation modeling efforts.

6.4  Program and Data Management

        The Western Arctic SBI program is planned as a 7-10 yr. program consisting of the three phases outlined in the previous section and presented as a timeline in Figure 8. Upon NSF approval of the SBI science plan, an announcement of opportunity (AO) for the Western Arctic SBI program will be presented to the scientific community. An SBI Science Management Office (SMO) will be initiated at the start of Phase I in order to coordinate the historical, modeling, field, and workshop components of the program. An SBI/SMO will coordinate specific data protocols between the SBI PI s, the SBI SMO and the ARCSS NSIDC. The SBI SMO will also coordinate liaisons between the OAII SMO and NSF management, other U.S. government agencies, and the international forum. Annual SBI Principal Investigator (PI) meetings will be organized through the SBI SMO.
 
        Upon initiation of the SBI SMO and determination of the SBI Phase I individual projects, SBI PI s representing the major disciplines in the SBI program will be chosen to participate in a SBI Executive Committee which will include the Director of the SBI SMO. The purpose of this committee is to provide guidance to SBI PI s and the SBI SMO, along with NSF, in field preparations and logistical coordination, and to act as a scientific liaison body with other national and international programs. A workshop will be organized at the end of the first year after funding is awarded for Phase I projects in order to synthesize existing data and to develop field planning efforts for Phase II. The workshop will be open to both Phase I PI's and prospective Phase II PI's.

Figure 8.  SBI Program Management Timeline, 1997-2007.

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  7.  RECOMMENDATIONS  
 
        The overarching rationale for the Western Arctic Shelf-Basin Interactions (SBI) program is based on the premise that the major global changes that influence biological and physical linkages between the shelf and basin will have amplified effects in the Arctic ecosystem, specifically to maintenance of water column stratification, sea ice distribution, renewable resources, and human habitability of the Arctic.
 
        In order to address the influence of shelf-basin interactions on, and in response to, global change, the Western Arctic SBI program will:

1. focus on shelf/slope water mass modification and exchange processes and biogeochemical cycles in the Chukchi and Beaufort seas, processes that profoundly influence the thermohaline and biogeochemical structure of the Arctic Ocean and which are intimately tied to global climate and ecosystem response;
2. study potential changes in productivity patterns and rates that could be rapidly reflected in the structure of Arctic marine ecosystems up to human populations;
3. develop a set of biochemical models of C/N/S cycling and subsequent yield to humans in the Arctic system, nested in a series of ice and circulation submodels, in order to assess the consequences of global change that would guide the synthesis of historical data, selection of sample sites and designs, and modification of subsequent field experiments; and
4. develop a Pan-Arctic model, comprised of embedded regional submodels, suitable for "what-if" global change scenario studies that can provide specification of the possible feedbacks of polar change to to larger climatic features of GCMs at lower latitudes.

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APPENDIX A: SBI I AND II WORKSHOP AGENDAS

1.  SBI WORKSHOP I (TOWNSEND, TN, 23-25 MARCH 1995)
 
Wednesday: evening: 22 March
                      1800 -    Steering Committee Meeting
                      1900 -    2100 Registration/Social Hour
 
Thursday: Day 1 - 23 March
morning:     0800 -    Registration
                  0830 -    General Session: Introduction-Jackie Grebmeier and Terry Whitledge
                  0845 -    ARCSS and the OAII Program-Mike Ledbetter
                  0900 -    UNOLS Arctic Research Vessel-Gary Brass
                  0915 -    Seasonal Organic Loading of the Canadian Basin from Source Waters South of
                                       Bering Strait-John J. Walsh et al.
                  0945 -    Arctic Shelf/Slope Exchange: Physical Processes-Tom Weingartner
                  1015 -    BREAK
                  1030 -    The Northeast Water Polynya Project, A Multidisciplinary ARCSS
                                        Project: Results, Status and Future Goals-Walker O. Smith, Jr and Jody
                                        Deming
                  1100 -    Another Look at Arctic Ocean Primary and Secondary Production-
                                        Larry and Glenn Cota
                  1130 -    Freshwater, Terrestrial and Oceanic Systems-Larry Hinzman
                  1200 -    LUNCH
 
 afternoon:  1300 -    Shelf Processes and Their Importance in the Chemical Modification of Water
                                       Masses in the Deep Arctic Ocean-Leif Anderson
                  1330 -    Some Results of Russian Research on the Arctic Phyto- and Zoo-
                                        plankton Carried Out During the Last Few Years-Mikhail Flint
                  1400 -    Dynamics of Vertical Flux in the Coastal Zone of Northern Norway-
                                       Paul Wassman
                  1430 -    Potential Influence of Pelagic Ecosystems on the Fluxes of Biogenic
                                       Carbon on Arctic Ocean Shelves-Louis Legendre
                  1500 -    BREAK
                  1515 -    Shelf-to-Basin Transport by Sea Ice-Erk Reimnitz
                  1600 -    Exchange of Dissolved and Particulate Substances Between Shelf and
                                       Open Ocean in the Eurasian Arctic-Victor Smetacek, and Benthos in
                                        the Eurasian Arctic-An Indicator of Shelf-Basin Relations-Eike Rachor
                  1630 -    Progress in Study of Bottom Fauna and Communities in Eurasian
                                       Arctic Shelf Seas-Boris Sirenko
                  1700 -    BREAK
                  1730 -    Social hour/poster session
                  1900 -    Shuttle to restaurant/DINNER
 
Friday:Day 2 - 24 March
morning:     0830 -    The ARCSS Ocean-Atmosphere-Ice Interactions Component-Dick Moritz
                  0900 -    LAII PI Workshop-Lou Codispoti
                  0915 -    GISP2 Overview-Debra Meese
                  0930 -    The Russian Arctic Shelf Land Environmental System (RASE): A
                                        report of an ARCSS Workshop, January 12-14, 1995 -Steve Forman
                  0945 -    Sea Ice Dynamics-Debra Meese, CRREL
                  1000 -    BREAK
                  1015 -    General meeting-tasks for Working Group Phase I
                  1030 -    Phase I Working Groups-development of strategy
                  1200 -    LUNCH
 
afternoon:   1300 -    Cross-fertilize Phase I Working Groups
                  1515 -    BREAK
                  1530 -    General Meeting-Chair Reports on Status of Working Groups I;
                                        discussion
                  1700 -    BREAK
                  1730 -    Social hour/poster session
                  1900 -    Shuttle to restaurant/DINNER
 
Saturday: Day 3 - 25 March
morning:     0830 -    General meeting/tasks Phase II
                  0845 -    Phase II-Working groups-development of strategy/write up
                  1015 -    BREAK
                  1030 -    Phase II Working groups reconvene
                  1200 -    LUNCH
 
afternoon:  1300 -    General Meeting-Final Reports of Working group II
                  1500 -    ADJOURN WORKSHOP
                  1600 -    Steering Committee Meeting
 
evening:     1900 -     Shuttle to restaurant/DINNER
 
Voluntary poster presentations were set up in the main meeting room for discussion during the social hour and breaks.  A table was also available for reprints and other information.

2. SBI WORKSHOP II (VIRGINIA BEACH, VA, 19-21 SEPTEMBER  1996)
 
Day 0: evening (Wednesday, Sept. 18)
 
    1800-2000     Social (with registration)
    2000-2200     Steering committee dinner meeting
 
Day 1 (Thursday, Sept. 19)
 
    Session Chair: Grebmeier
    0800-0830     Registration/Continental breakfast
    0830-0845     Welcome/Grebmeier
    0845-0900     Introduction & Review of SBI Report/Whitledge
    0900-0930     General discussion of "focus" for proposed Science Plan
    0930-0945     Workshop Charge/Grebmeier & Whitledge
    0945-1000     Presentation-SBI issues: David Chapman
    1000-1030     Break
    1030-1200     Working Group Sessions on Topic 1: Shelf/Slope Physical Processes
                               (Weingartner & Whitledge)
    1200-1330     Lunch (on own)
 
    Session Chair: Whitledge
    1330-1500     Plenary Session for Topic 1 Discussion
    1500-1530     Break
    1530-1700     Working Group Sessions on Topic 2: Biogeochemical Fluxes and
                               Transformations of Major Constituents in Ice, Water and Sediments (Walsh &
                               Codispoti)
   1830-1900      Social on deck
   1900-2100      Deck dinner for participants and guests
 
Day 2 (Friday, Sept. 20)
 
    Session Chair: Codispoti
    0830-0945     Plenary Session for Topic 2 Discussion
    0945-1000     ARCSS-OAII Program Perspective/Ledbetter
    1000-1030     Break
    1030-1200     Working Group Sessions on Topic 3: Characterization of Carbon Pools and
                               Trophic Structure (Dunton &  Wheeler)
    1200-1330     Lunch (on own)
 
    Session Chair: Whitledge
    1330-1500     Continue Session on Topic 3
    1500-1530     Break
    1530-1600     Plenary Session for Topic 3 Discussion
    1600-1730     Writing and Compiling
    1730-              Dinner (on own)
 
Day 3 (Saturday, Sept. 21)
 
    Session Chair: Grebmeier
    0830-1000     Open Discussion of Scientific Plan including:
                               -integration of 3 main topics
                               -integration with other ARCSS programs
                               -international collaboration
    1000-1030     Break
    1030-1200     -special logistics considerations
                               -special temporal/spatial considerations
                               -funding/ program costs
    1200-1330     Lunch (on own)
 
    Session Chair: Whitledge
    1330-1500     Adoption of draft scientific plan based on integration of 3 topics with other
                               ARCSS initiatives; discussion of time line of SBI/collaborators major events;
                               wrap-up to end meeting
    1600-1730     Steering Committee meeting (Whitledge suite)

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APPENDIX B: ABSTRACT AUTHORS AND TITLES FOR SBI WORKSHOPS I AND II (abstract books for both workshops available from J. Grebmeier)  

1. SBI WORKSHOP I

2. SBI WORKSHOP II

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APPENDIX C: PARTICIPANT ADDRESS LIST FOR SBI WORKSHOPS I AND II  
 
 1. SBI WORKSHOP I

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2. SBI WORKSHOP II

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