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doi:10.2204/iodp.proc.323.101.2011

Introduction

The rate and regional expression of recent global warming is difficult to understand and even more difficult to predict because of the complex nature of the climate system, whose components interact nonlinearly with various time lags. Paleoclimate and paleoceanographic studies present opportunities to study climate system dynamics by examining how they respond to external forcing (e.g., greenhouse gas and solar radiation changes) and how they generate internal variability due to interacting Earth-system processes. Of note is the amplified recent warming of the high latitudes in the Northern Hemisphere (Solomon et al., 2007), which is presumably related to sea ice albedo feedback and teleconnections to other regions; both the behavior of sea ice–climate interactions and the role of large-scale atmospheric and oceanic circulation in climate change can be studied with geologic records of past climate changes in the Bering Sea.

Prior to Integrated Ocean Drilling Program (IODP) Expedition 323, little was known about the sedimentology and climate history of the Bering Sea outside of a few piston core studies (e.g., Cook et al., 2005; Okazaki et al., 2005; Tanaka and Takahashi, 2005; Takahashi et al., 2005) and Deep Sea Drilling Project (DSDP) Sites 188 and 185 (Scholl and Creager, 1973), which were drilled in 1971 with old drilling technology and poor recovery. Past studies using piston cores in the Bering Sea indicate that although current conditions in the Bering Sea promote seasonal sea ice formation, during the Last Glacial Maximum (LGM), conditions sustained perennial or nearly perennial sea ice cover (Katsuki and Takahashi, 2005), attesting to the potential usefulness of sedimentary records in the Bering Sea in examining sea ice distribution. In paleoceanographic studies in the North Pacific, the Bering and Okhotsk seas have been implicated as sources of dense, oxygenated intermediate water that possibly impacted oceanic and climate conditions throughout the Pacific on glacial–interglacial (e.g., Gorbarenko, 1996; Matsumoto et al., 2002) and millennial (e.g., Hendy and Kennett, 2003) timescales. In addition, changes in Bering Sea conditions could be related to sea level and circulation changes, which alter flow through small straits that connect the Bering Sea to the Arctic Ocean to the north and to the Pacific Ocean to the south. The lack of Bering Sea material has so far prevented the evaluation of these and other ideas.

Seven sites whose terrigenous and biogenic components capture the spatial and temporal evolution of the Bering Sea through the Pliocene and Pleistocene were successfully drilled during Expedition 323 (Fig. F1; Tables T1, T2). Additionally, a rich archive of information was collected regarding the role of microbes on biogeochemical cycles in ultra-high-productivity environments; the postdepositional processes that impact the geochemical, lithologic, and physical properties of sediment; and the chemistry of pore waters. This expedition summary presents background on the environmental setting and important scientific questions in the Bering Sea, followed by highlights of the scientific findings of Expedition 323.

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