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Western Arctic Shelf-Basin Interactions (SBI) Project
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SBI III PROJECT ABSTRACTS
The Arctic is now undergoing significant change. Arctic surface air temperatures are increasing at a faster rate than most anywhere else on Earth. The multi-year ice pack that covers the central Arctic Ocean has thinned from 3.1 m in the 1960's to 1.8 m in the 1990's. Over this time period, the long-term areal extent of sea ice has decreased by 14%. Although these changes could represent a component in a natural cycle, this trend could also be a harbinger of the "meltdown" of the Arctic in response to anthropogenic climate warming. Whether man-made or natural, the observed fluctuations in sea-ice extent dramatically affect the unique and fragile arctic marine ecology. Assessing the effects of present variability in sea-ice cover and hydrography on arctic marine ecosystems and regional climate (and a fortiori that of a potential net reduction of arctic sea ice in response to climate change) requires a substantial improvement in our understanding of the links between, among other components, freshwater and sea ice, sea ice and climate, and sea ice and biogeochemical fluxes. The extensive arctic shelves (25% of global shelf area) are of central importance in any arctic change scenario. The shelves themselves are strongly influenced by widely differing physical and environmental processes. The waters on some shelves are influenced by extra-Arctic import of ocean waters, for example, the Alaskan shelf is influenced by the North Pacific Ocean waters via transport through the Bering Strait, while other shelves are principally influenced by riverine input, such as the Mackenzie shelf which is greatly affected by the seasonal inflow of the Mackenzie River. The sea-ice cover can also vary greatly between shelves, with individual shelves having differing amounts of landfast ice cover, lead polynya, and stamukhi zones. The peculiarities of sea-ice cover over individual shelves, in turn, determines the air-sea exchange of heat and moisture over the shelf and constrains the strongly pulsed annual cycle of biological productivity. The differences in ice-cover character also affect the export of carbon to the pelagic and benthic food webs, and to the deep Arctic basins where it is ultimately sequestered. Given the
importance of the shelves, the need for observational data has
been particularly strong for these shallow, coastal regions (30%
of the Arctic basin) where variability in the extent, thickness
and duration of sea ice has been most pronounced and where Arctic
marine food webs are most vulnerable to change. In recent years,
two major observational programs have been launched and have
garnished significant physical, geochemical, and biological data
over specific Arctic shelves. The successful Shelf-Basin
Interaction (SBI) project over the Alaskan Shelf and Canadian
Arctic Shelf Exchange Study (CASES) over the Mackenzie shelf
represents a major step forward in quality and quantity of
observational data upon which a model of the present and future
behavior of the Arctic shelf systems can be constructed. This
project will construct a robust, coupled physical and biological
model of the Alaskan and Mackenzie shelf ecosystems and their
interaction with the Arctic basin, based on the observational
data sets of the SBI and CASES programs. A thorough analysis and
intercomparison of these two physical, chemical, and biological
oceanographic data sets will be performed, allowing for an
improved understanding of the universal and non-universal
properties of polar shelf ecosystems. A coupled physical,
chemical, and biological model of the two specific Arctic shelves
and their nesting inside a pan-Arctic computer model will allow
us to better understand the present function of these shelves, as
well as their future behavior in the larger changing Arctic
environment. Carin Ashjian, (Woods Hole
Oceanographic Institution), Robert Campbell (University of Rhode
Island), Changsheng Chen, (University of Massachusetts,
Dartmouth) Copepods of the genus Calanus are the keystone pelagic species in Arctic pelagic ecosystems. Ecosystem structure in the Arctic Ocean and marginal seas is significantly influenced by Calanus population dynamics and production that in turn determines the amount of primary production available either for benthic or pelagic food webs. Calanus are an important food source for pelagic fish species such as capelin, herring, pollock, and larval cod. Therefore, it is not surprising that ecosystems that support a high biomass of these large-bodied, lipid-rich copepods also have rich fisheries (e.g. Bering and Barents Seas). Ongoing warming of the Arctic seas due to climate change will have dramatic impacts on the shelf and basin ecosystems, potentially leading to regime shifts or shifts of biogeographic boundaries of the Calanus spp. Such shifts can have dramatic impacts both to the shelf ecosystems and to the exchange of carbon between Arctic shelves and basins. Furthermore, changes in Arctic shelf ecosystem structure and function can cascade up to upper trophic levels including commercially important fish species and marine mammals that in turn can significantly impact both indigenous and world human populations. Biological-physical coupled
models and numerical experimentation will be used to explore the
physical and biological factors that control Calanus population
dynamics and biogeographic boundaries in the Arctic Ocean and
marginal seas, and to investigate the impacts of various climate
warming scenarios on the potential for Calanus mediated regime
shifts in these systems. The Arctic Ocean Finite Volume Coastal
Ocean Model integrated physical model system will be coupled to
an individually-based Calanus model and a 4-stage Calanus
concentration model. The physical model incorporates the
atmosphere, ice, and ocean components of the system and
establishes the environmental framework in which the Calanus
population dynamics operate. The Chukchi and Barents Seas are
similar in many ways yet different in others. The analyses will
focus on these two shelf-seas and adjacent basins, however, the
results of the analyses will be applicable to Calanus dynamics on
all Arctic shelves. Data will be integrated from a wide range of
physical and biological data sets, including the SBI program.
Nick
Bates (Bermuda Biological Station), Dennis
Hansell (University of Miami, Rosenstiel
School
of Marine and Atmospheric Science), and Bradley Moran (University
of Rhode Island) As a contribution to SBI phase III efforts, it is critical to improve both our understanding of the Arctic Ocean carbon cycle and predictive capabilities for future responses to environ-mental changes. This requires data integration, synthesis, and modeling activities that lead to new system-level understanding of present and future carbon cycling in the Arctic Ocean. A central hypothesis to be tested in this research is that: H. The physical forcing (e.g., sea-ice, nutrient supply) and biological responses exert fundamentally different controls on the carbon cycle and the rates air-sea CO2 exchange, NCP and export production in the Chukchi Sea compared to other shelves. This project will compile organic and inorganic carbon data, and rate measurements (e.g., 234Th/238U export) collected during SBI phase II with other hydrographic, biogeochemical and carbon datasets from across the Arctic. Incorporation of these datasets provides a pan-Arctic context for understanding carbon dynamics in the present and under climate change scenarios (e.g., changes in sea-ice melt, river input, stratification, and biological responses). Specific objectives that will test the central hypothesis, include: Objective 1: Determine stocks of inorganic and organic carbon in the Chukchi Sea and pan-Arctic (including anthropogenic CO2); Objective 2: Determine rates, including air-sea CO2 gas exchange, net community production, and export production on the Chukchi and other shelves, and in the adjacent Arctic Ocean basin; Objective 3: Synthesize rates and stocks using carbon mass balance approaches. This effort includes comparative analyses of the Chukchi shelf with other shelves (carbon cycling on inflow versus interior shelves) and anticipated changes in the Arctic carbon cycle. These analyses will advance understanding through collaborative synthesis and modeling efforts, and, national and international coordination through workshop meetings in 2008 and 2010.
James
Moore (University Corporation for Atmospheric Research, UCAR) The National Center for Atmospheric Research (NCAR) Earth Observing Laboratory (EOL) will develop and implement a comprehensive data management strategy for Phase III of the Western Arctic Shelf Basin Interactions (SBI) Project in cooperation with the SBI Project Office (SBI-PO), the investigators who will provide datasets and information, as well as other collaborating projects. An integrated data management activity will ensure that a complete database is provided with easy access by all project investigators and the science community in general. The SBI Project continues to focus on the understanding of physical and biogeochemical modifications of the ecosystem overlying North Pacific, Chukchi, and Beaufort Sea shelf and slope. This follows a very successful field campaign over the past 5 years. The project was designed as a multidisciplinary, multi-year project with many investigators and varied instrumentation to address the aforementioned objectives. Activities in SBI Phase III will focus on the integration and synthesis of Phase II measurements using models and additional data. A key objective will be to scale-up SBI observations to regional and Pan-arctic coverage. SBI data management support from EOL will help assure that data are accurate, accessible, well documented and disseminated in a timely fashion. The approach will be responsive to the needs of the investigators, but also make it clear that the participants understand what is expected of them in providing data to the archive as the synthesis and modeling phase begins. Such a collaborative effort will assure the integrity and completeness of this rich dataset. EOL will work with the investigators to gather research datasets and documentation for submission to the SBI interim archive.
Robert
Pickart, Principal Investigator (Woods Hole Oceanographic
Institution) It is predicted that one of the consequences of a warmer climate will be an increase in the intensity and frequency of cyclones that influence the arctic domain. This carries with it strong ramifications, including increased precipitation, more severe coastal flooding and erosion, and enhanced transfer of momentum to the pack-ice and the water beneath it. At present it is not well understood how such changing atmospheric conditions would influence the communication between the shelves and the interior Arctic Ocean. There is increasing evidence that wind-forcing is a dominant driver of such exchange, and that the impacts of this forcing involve multiple aspects of the food web. However, wind-forced shelf-basin exchange is not simply a regional phenomenon, but one that involves a mix of time and space scales, including understanding the behavior and evolution of storm systems centered thousands of kilometers away from the areas in question. In addition, the pack-ice significantly modulates the oceanic response. Therefore, it is necessary to address simultaneously different aspects the of the atmosphere-ice ocean system -over a myriad of scale- to understand fully the causes and effects of storm-driven shelf-basin exchange. This project brings together multiple fields (meteorology, oceanography), disciplines (physics, biochemistry), and tools (atmospheric and oceanic modeling, data analysis) to enhance the understanding of the system-wide nature of wind-driven exchange and its impact on the ecosystem of the interior and coastal Arctic. The oceanic scope is the Chukchi/Beaufort Sea region, but the atmospheric connections extend into the North Pacific, which in this context clearly needs to be considered as part of the arctic system. The project will unfold in three phases. In phase I NCEP reanalysis fields, AMSR-E ice concentration data, and SBI mooring data will be used to investigate the present storm climate, elucidating the conditions (e.g. upper-level atmospheric currents, orography of Alaska, configuration of pack-ice) leading to the strongest upwelling and downwelling. In Phase II detailed case studies of three storm events will be performed using the MIT ocean/ice model, driven by output from the high-resolution WRF atmospheric model, and analyzed in tandem with the SBI physical mooring data and biochemical shipboard data. This will enable the understanding of how regional variations in the wind and ice fields, together with the topography, influence the shelf-basin exchange. Net fluxes of biochemically important properties for each of the storms will be computed, and scaled up to obtain annual fluxes. In Phase III automated cyclone tracking applied to the full NCEP data set, together with historical ice concentration data, will be used to investigate the storm climate and associated upwelling/downwelling over several decades that encompass different climatic regimes. This will allow an assessment of possible impacts of a future warmer climate. This research will strive to determine what factors dictate the development and evolution of storms that lead to strong shelf-basin exchange, how the distribution of pack-ice modulates this, and the detailed dynamics that accomplish the exchange. Obtaining quantitative estimates of the associated biochemical fluxes will enable us to address the ramifications on the ecosystems of the shelves and central Arctic. |