Collaborative Research: A Modeling Comparison of the Alaskan and Mackenzie Shelves

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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.