SEA ICE CHARACTERISTICS IN BERING SEA

Sea ice samples collected from the NORTHWIND icebreaker cruise Jan.-Feb. 1970 extending from Cape Newenham to the Russian coast were studied onboard ship. Large blocks of sea ice were obtained for their section petrofabric examination and the collection of ice-sediments. The Bering Sea ice consisted of three layers: a thick horizontal C axis layer bounded by thin vertical C axis layers at the top and the bottom. The maximum sediment concentration in Bering sea ice was observed near the lower boundary of horizontal C axis layer. The unusual bottom vertical C axis ice layer in Bering Sea may be due to several sea ice forming phenomena. However, extreme cold weather accompanied by severe storm in this area is suggested for this ice-layer. Bering Sea throughout the region displayed a consistent crystallographic structure. Sea ice was layered, with a bubbly, milky, fine-grained layer on the top and a layer of clear, dense, bubble-free ice near the bottom. The ice near the top contained a layer with vertically oriented crystals. This layer underlain by a thick layer of clear, dense ice consisting of long, tapered crystals with horizontal C-axis. This particular crystal fabric is quite common in lake ice and stream ice. A layer of clear, very fine grained dense, bubbly milky ice was observed at the bottom. Beside crystal orientation the vertical layering of the Bering sea ice can also be differentiated on the basis of crystallinity. Maximum of five layers were observed in some samples. These layers were characterized by primarily the crystal orientation, size and shape of individual crystal, air bubbles, salt pockets and sediment or phytoplankton content in the ice. The freezing of seawater and the resulting sea is a complex process in which the rate of cooling, salinity and the rate of loading play a significant role. Theoretical as well as experimental work to elucidate the formation of sea ice has been conducted by Anderson and Weeks (1958), and Weeks (1962). Field observations on sea ice have been made by several investigators and these studies were conducted primarily to evaluate the mechanical properties of sea ice, better icebreaker design, sea ice landing strips, offshore drilling platforms, dredging facilities and other related structures. The petrofabric studies of sea ice have been made and described insofar as to explain the mechanical properties such as strength of sea ice etc.