This research provides the first Pliocene paleo-oceanographic observations from the Bering Sea and supports the objectives of IODP expedition 323 for understanding the associated factors influencing climate change during the Pliocene and Pleistocene, including a warm period of the early Pliocene, when pCO2 levels were similar to today¡¦s levels. The flow of water masses between the Bering Sea and the Arctic and Pacific oceans, changes in Arctic ice volume, and whether dense intermediate waters formed in the Pacific during this time will be investigated as some of the possible triggers of past climate change. The high resolution sediment records obtained from this cruise, with relatively large-amplitude signals, provide a unique opportunity to understand how insulation changes in the upper atmosphere propagate through the climate system and to further test if the orbital cycles of climate change primarily operate on 23ky versus 40 ky timescales. This study utilizes K % logging data from the cruise with paleomagnetic, sedimentological (eg., grain size analysis) and paleontological (eg., analysis of microfossil assemblages; d18O and d13C measurements of benthic and planktonic forams) measurements from the drill cores. The information expected from this study is critical for understanding the fundamental drivers and feedbacks between ice sheets, oceanic and atmospheric circulation and the global carbon cycle.
Broader Impacts: This project significantly advances large investments previously made in an important IODP expedition. The data derived from this investigation can provide important information for paleoclimate/ocean models, and is relevant towards projections of future climate under IPCC AR4 scenarios. The project includes a team of early and mid-career scientists, and includes international collaborations with other scientists of the IODP community. Support is also provided for undergraduate and graduate education, and for public outreach and education.
During times of climate warming, the oceanic oxygen minimum zone in the Bering Sea strengths and expands, resulting in intervals of hypoxia (low oxygen sufficient to impact the biota) or anoxia (no oxygen). Evidence for this finding is based on the distribution of laminated sediments (i.e., those that have not been disturbed by benthic organisms due to low oxygen) and stable oxygen isotope stratigraphy. Particularly large expansions of hypoxia occur during deglacial and early interglacial intervals, as sealevel is rising. A plausible local cause of these events is the role of the flooding of the Bering Shelf during sealevel rise, as the shelf systems are highly productive, and the organic matter produced here is exported to the deep sea, where it remineralizes and consumes oxygen. However, other studies have found similar events outside the Bering Sea. It is not yet clear if these distal events are mechanistically linked; if they are, the role of local sealevel is likely an amplifier rather than a cause. Other likely mechanisms involve changes in deep-sea circulation, and input of nutrients from continental runoff and/or volcanism. The primarly contribution of this study was to develop detailed chronologies of these events within the Bering Sea, which will facilitate comparison with results outside of the Bering Sea as the mechanisms of these changes are constrained.
