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.
This study is part of a collaborative research program devised by the U.S. shipboard scientists from Integrated Ocean Drilling Program (IODP) Expedition 323 to the Bering Sea (2009) to construct age models and produce primary paleoceanographic records for the sites drilled during the expedition. The primary goal of Expedition 323 was to examine processes responsible for Pliocene and Pleistocene climate change. Members of the international science party have examined the sediment cores recovered to address changes in flow in and out of the Bering Sea and its role in climate change, the role of sea ice in amplifying climate changes, possible dense water formation and its impact on Pacific-wide climate, and past ocean productivity and biogeochemical cycles. U.S. contributions are a key component of the international effort to meet the expedition’s scientific objectives. Our research focused on the study of benthic foraminifers at the deepest site drilled during Expedition 323 (Site U1344 at 3200 m water depth) to reconstruct changes in bottom water conditions (physico-chemical characteristics) over the last 2 million years. In addition, the study is also producing a millennial-scale record of glacial-interglacial bottom water variability during Marine Isotopes Stages 9 to 11 (~300-500 ky). Benthic foraminifers are a major component of marine communities, highly sensitive to environmental factors, and the most abundant benthic organisms preserved in the deep-sea fossil record. Changes in their faunal assemblage composition are controlled by a number of closely interrelated environmental parameters. At Site U1344, they show their highest variability through the period when glacial-interglacial cycles changed from 41 ky to 100 ky cyclicity due to the cooling trend of the Earth from the greenhouse world of the Pliocene to the icehouse world of the late Pleistocene. This interval is known as the Mid-Pleistocene Transition or MPT. The period after the MPT is characterized by a marked increase in the amplitude and magnitude of benthic foraminifer communities and the expansion of seasonal sea ice cover in the Bering Sea. A significant increase across the MPT and the first common appearance of some low oxygen tolerant groups may reflect intensification in climate variability and seasonality throughout the Bering Sea. The benthic foraminifer assemblage at Site U1344 is dominated by low-oxygen tolerant species. Their temporal variability indicates phases of low to poorly oxygenated bottom water during the last ~2My. Although research is still ongoing, current results of this project combined with the results of the other members of the shipboard scientific party significantly advances large investments previously made in an important IODP expedition. The data derived from this investigation provides important paleoceanographic information. The project included a team of early and mid-career scientists and a student, and it included international collaborations with other scientists of the IODP community. This NSF award has directly contributed financial support, and to the research training and laboratory and analytical skills for an undergraduate and a graduate student from the Department of Geology at Texas A&M University. The main part of the project which aimed to reconstruct the long term (2 Ma) history of deep water variability in the Bering Sea was made into the Master’s thesis of the graduate student, who later earned a merit-based fellowship from the ODASES (Ocean Drilling and Sustainable Earth Science) program at Texas A&M. The fellowship included a $25,000 award for one academic year. The results of this project were presented at the 2012 GSA Annual Meeting and the Master thesis defense is anticipated for Spring 2013 academic semester. Two manuscripts are currently being prepared for publication.
