DEEP SEA BENTHIC FORAMINIFERA FROM IODP SITE U1344, BERING SEA, OVER THE LAST ~2MA

Integrated Ocean Drilling Program Site U1344 was cored during Expedition 323 to the Bering Sea (July-September 2009) to investigate Pliocene-Pleistocene paleoceanography. This site is the deepest site from the expedition (3200mbsl) and is in a located proximal to the Arctic Ocean, near the maximum extent of present-day seasonal sea ice cover, and under an area of high biological productivity called the “Green Belt”. Benthic foraminifera are used in this study as paleoceanographic proxies. Data collected is anticipated to shed light on mechanisms responsible for the global transition from Pliocene warm to Pleistocene glacial climate and to help understand the evolution of higher frequency glacial cycles. Considerable amounts of terrigenous material are observed during both glacial and interglacial times. In addition, intervals with high diatom concentration reflect periodic blooms in surface productivity. Benthic foraminiferal abundance increases markedly through the Mid-Pleistocene Transition (MPT), though it is unclear whether or not this may reflect a bias in preservation. A significant increase across the MPT and the first common appearance of some low oxygen tolerant groups may reflect intensification in climatic variability and seasonality throughout the Bering Sea. The benthic foraminifera assemblage at Site U1344 is dominated by low-oxygen tolerant species, indicating cycles of low to poorly oxygenated bottom water during the last ~2My. The low oxygen-tolerant genera Elphidium and Valvulineria are used to constrain bottom water δ¹⁸O and δ¹³C, which are interpreted to represent changes in deep water ventilation and help define glacial/interglacial intervals. Elphidium and Valvulineria, which are known to occupy similar microhabitats, appear to alternate in dominance (by absolute abundance), but Valvulineria has a higher tolerance for low oxygen conditions. Therefore the pattern likely reflects changes in bottom water oxygenation and/or competition for a food source (i.e. diatoms). The variable flux of diatoms to the Bering Sea is likely controlled by sea-ice. Statistical analysis of living populations of benthic foraminifera from the nearby analogue, the Okhotsk Sea, suggests that sea-ice is the main control on their overall distribution in this region.