CONTRASTS IN ARCTIC SHELF SEA-ICE REGIMES AND SOME IMPLICATIONS - BEAUFORT SEA VERSUS LAPTEV SEA

The winter ice-regime of the < 80 km wide Alaskan Beaufort Sea shelf i s characterized by compression and shearing, resulting in the formatio n of major grounded pressure ridge systems stabilizing the fast ice on the mid-shelf, and essentially no open-water areas. In contrast, the winter ice-regime of the 500-km wide Laptev Sea shelf is controlled by winds blowing from land to sea, and is therefore dilational. A perenn ial polynya borders the hundreds of kilometers-wide and very smooth fa st ice offshore. In this body of open water, rapidly forming ice is co ntinuously advected offshore by the mean wind field, making the Laptev Sea the single major ice factory for the Arctic Ocean and Transpolar Drift. Conversely, with summer warming this dark polynya turns into an area of high heat gain, which results in the retreat of the ice edge to a much higher latitude and greater distance (>500 km) from the main land than in the Beaufort Sea. As a result, the annual freeze-up does not incorporate old, deep-draft ice, and with a lack of compression, s uch deep-draft ice is not generated in situ, as on the Beaufort Sea sh elf. The Laptev Sea has as much as 1000 km of fetch at the end of summ er, when freezing storms move in and large (6 m) waves can form. Also, for the first three winter months, the polynya lies inshore at a wate r depth of only 10 m. Turbulence and freezing are excellent conditions for sediment entrainment by fraziI and anchor ice, when compared to c onditions in the short-fetched Beaufort Sea. We expect entrainment to occur yearly. Different from the intensely ice-gouged Beaufort Sea she lf, hydraulic bedforms probably dominate in the Laptev Sea. Correspond ing with the large volume of ice produced, more dense water is generat ed in the Laptev Sea, possibly accompanied by downslope sediment trans port. Thermohaline convection at the midshelf polynya, together with t he reduced rate of bottom disruption by ice keels, may enhance benthic productivity and permit establishment of open shelf benthic communiti es which in the Beaufort Sea can thrive only in the protection of barr ier islands. Indirect evidence for high benthic productivity is found in the presence of walrus, who also require year-round open water. By contrast, lack of a suitable environment restricts walrus from the Bea ufort Sea, although over 700 km farther to the south. We could specula te on other consequences of the different ice regimes in the Beaufort and Laptev Seas, but these few examples serve to point out the dangers of exptrapolating from knowledge gained in the North American Arctic to other shallow Arctic shelf settings.