Effects Of Pacific Inflow On Arctic Sea Ice

Sea ice is a crucial element in climate system. Significant change in arctic sea ice has been observed in the past half a century, and pacific inflow region (the Bering Sea and Chukchi Sea) is found to be one of places where the most intense sea ice concentration reduction occurred. The warm water entering Chukchi Sea through the Bering Strait from Pacific Ocean plays an important role in the process of sea ice melting and freezing not only in Chukchi Sea, but also in the Arctic Ocean. To study the influence of pacific inflow to the arctic sea ice will improve our understanding of Arctic sea ice variation, and so do the research of Northern hemisphere and global climate change.First, the seasonal cycle of arctic sea ice is simulated and studied with Oberhuber's ice-ocean coupled model from Deutsches Klimarechezentrum GmbH. The model's novel feature is that the ocean component uses potential density surfaces as its vertical coordinate. Coordinate rotation is employed to remove the Arctic Ocean's spherical coordinate singularity at the North Pole. The model domain includes the northern part of Bering Sea, the whole Arctic Ocean, Hudson Bay, Baffin Bay, the Greenland-Iceland-Norwegian (GIN) Sea and part of North Atlantic Ocean. The horizontal resolution is about 0.2o in the focus region. The simulated sea ice area reaches a maximum of 1.46×107km2 in winter and a minimum of in summer. This is, by and large, close to the results calculated with data from Met Office Hadley Center and National Snow and Ice Data Center. The model also can capture the basic feature, the space distributions of ice thickness and ice motion. The influence of pacific inflow to arctic sea ice is analysed from the results of a numerical study case, in which the Bering Strait is closed. Lacking the heat content from pacific inflow, the ice concentration north of Alaska coast will increase and sea ice in Canada basin can be thicker as much as 0.4m. Nevertheless, the dynamic feature of sea ice seems less sensitive to that change.Bering Sea and Chukchi Sea, the transient region between Pacific Ocean and Arctic Ocean, is the only way for pacific inflow to enter the Arctic Ocean. The air-sea-ice interactions are particularly intense where ice edge is located in. Sea ice in the two seas shows distinct seasonal, interannal and decadal variations.From the results of our study, we can conclude that: 1) The ice extent in the two regions decreased sharply during the past half century, especially in Bering Sea, the trend was 3693km2/year, that of Chukchi Sea was 2846km2/year. 2) With the methods of moving-t abrupt test and wavelet analysis, abrupt changes of the ice extent (1953-2004) in Bering and Chukchi Sea are found separately in the late of 1970s──an abrupt change of the mean value in Bering Sea and a frequency shift in Chukchi Sea. 3) The distributions of SLP, wind field and SAT changed significantly before and after the regime shift, and Aleutian Low became much stronger--core pressure decreased, area with pressure lower than 1005hPa enlarged, and its core position moved to the southeast of Bering Sea, and the wind field changed in accordance, especially during the winter months. As a result, more heat flux is transported to ice-covered seas from mid-latitude region and resulted in the significant reduction of ice extent in Bering Sea. 4) In thermodynamics, the frequency shift that occurred in the sea ice extent of Chukchi Sea may be response to the signal conveyed by warm pacific inflow from winter Pacific Decadal Oscillation (PDO). In dynamics, the advection of arctic sea ice, result of surface wind, in pacific section such as Beaufort Sea and East Siberian Sea, is also closely related to the frequency shift.