IODP Expedition 323: Pliocene-Pleistocene paleoceanography and climate history of the Bering Sea

The primary objective of drilling at Site U1340 (Site BOW-12B) was to study highresolution Pliocene and Pleistocene paleoceanography in the southernmost part of Bering Sea at a topographic high location on the Bowers Ridge where relatively good calcium carbonate preservation is expected. The Bowers Ridge is well situated to study the past extent of water mass exchange with the Pacific Ocean through the adjacent Aleutian passes such as Amukta, Amchikta and Buldir Passes. Of particular interest is the ability to examine the influence of the warm Alaskan Stream water mass entry into this region, which influenced the distribution of the past sea-ice coverage. While the productivity in the Bering Sea in general is very high with respect to the other parts of the global oceans, the expected productivity at this site is lower than at Site U1339, which has substantially greater influence from the nearby Bering Shelf and was exposed during the glacial low stands. Drilling at this site with relatively shallow water depth should provide us with the ability to study physical and chemical changes in upper water mass conditions. A good example is the low dissolved oxygen concentration conditions which caused the formation of laminated sediments at a site on the Bering Shelf at similar water depths. The vertical structure of past water masses can be made by comparing results at this site with the other planned drilling sites on Bowers Ridge (U1341, w.d. = 2177 m; U1342, w.d. = 837 m).