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.
Located in the Pacific subarctic, the Bering Sea is a key basin for global oceanic circulation and a region where climatically important sea ice and dense oxygenated deep waters form. The Bering Sea hosts some of the most productive ecosystems in the world, all of which are very sensitive to climate change. This study investigates deep-sea core sediments that were collected in the ocean margins and ocean basins of the Bering Sea during a scientific drilling cruise by the Integrated Ocean Drilling Program (IODP), Expedition 323 (2009). This was the first time that the sub-seafloor of the Bering Sea was extensively cored to reconstruct the basin’s oceanographic history through geologic time during the last ~ 5 millions of years (Ma). Using the geologic principle of uniformitarianism and modern sedimentological techniques, we have analyzed the Exp. 323 core record to understand how oceanography has changed in the Bering Sea in response to the major climatic events of the past 5 Ma. For this project we have developed methods that combine optical and electronic (SEM) microscopy together with high-resolution laser grain size analysis. The analysis of sediments from the core tops reveal deposition on the modern Bering Sea seafloors, which reflects the oceanographic conditions that exist at the surface. There are two main types of sediment sources: plankton productivity and sea ice delivery. Plankton productivity in the Bering Sea is the highest in the world and results in the deposition of vast quantities of siliceous microorganism remains (mainly diatoms). Sea ice delivers very fine minerals (mainly clay) and rock particles. For the last 5 Ma, sedimentation across the Bering Sea has been essentially dominated by two components: diatoms and clay. The relative abundance of these two components has alternated at different scales of climate variability, including glacial-interglacial and millennial scale cycles. In the sediments deposited during cold times (for instance the Last Glacial Maximum), the diatom tests are much less preserved; therefore, the fine mineral fraction increases suggesting lower primary productivity and increased contribution of sea ice. Conversely, in sediments deposited during warm times, a higher abundance of diatom remains and higher preservation suggest very high surface productivity and ice-free conditions. In conclusion, the sedimentologic data produced by the analysis of the Bering Sea cores show that this important subarctic basin has been subjected to dramatic changes in oceanography, primary productivity and sea-ice extent at both ‘short’ (centennial-millennial) and longer time scales. Our data show that the Bering Sea was characterized by partially or completely ice-free conditions and diatom proliferation during warmer times. These conditions are similar to what some of the most recent models suggest that will happen before the middle of the 21st century.
