North Pacific Climate, Ocean Circulation, And Productivity Over Millennial And Orbital Timescales
Due to processes that are poorly understood, the arctic/subarctic region is currently warming at approximately twice the rate of the rest of the globe, and these regional changes may in turn have important consequences on global climate. The Bering Sea is an ideal location to study the relationship between sea ice distribution, ocean circulation, and biological productivity, which are all thought to be components of important interactions that both respond to and influence climate changes on regional (North Pacific) to global scales. Geologic records are essential for understanding and predicting future oceanic and climatic changes, but most previous studies of Bering Sea and North Pacific climate and oceanic conditions were limited by short records that only spanned one glacial-interglacial climate cycle (~100 kyr). This dissertation presents new geochemical and sedimentological records of oceanic and climatic conditions over the past 1.2 Myr using sediment cores from Integrated Ocean Drilling Program Site U1342 (54.83N, 176.92E, 818 m water depth) in the Bering Sea, providing an unprecedented opportunity to examine trends over multiple glacial-interglacial cycles. Long benthic foraminiferal stable isotope records from Site U1342 provide the first evidence of an important recurring relationship in which extremely cold glacial conditions lead to enhanced Bering Sea ice extent and enhanced local formation of North Pacific Intermediate Water (NPIW), the water mass primarily associated with large-scale North Pacific circulation and heat transport. These results contradict model predictions for weaker NPIW formation during extreme glacial conditions and show that North Pacific and North Atlantic circulation acted in phase on glacial-interglacial timescales. Furthermore, new records of nitrate utilization based on nitrogen isotopes demonstrate that glacial climates were consistently associated with enhanced physical stratification in the Bering Sea, which resulted in increased utilization of nutrients by phytoplankton and a reduction in the carbon dioxide released from the ocean to the atmosphere. Finally, multiple new records that demonstrate high productivity during intervals of laminated sediments, which represent brief anoxic events, indicate that interglacial climates precondition the Bering Sea for rapid oceanic and biological change.