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doi:10.2204/iodp.sp.323.2009

Introduction

Over the last 5 m.y., global climate has evolved from being warm with only small Northern Hemisphere glaciers and ice sheets (~5–3 Ma) to being cold with major Northern Hemisphere glaciations every 100 to 40 k.y. The reasons for this major transition are unknown. Although there are data to show that the Pacific experienced oceanographic reorganizations that were just as dramatic as those in the Atlantic, the scarcity of data in critical regions of the Pacific (the largest ocean with arguably the largest potential to influence global climate) has prevented a comprehensive evaluation of the role of North Pacific processes in global climate evolution.

Over the last hundreds of thousands of years, glacial–interglacial and millennial-scale climate oscillations have also occurred because of mechanisms that are unknown, although several studies from the North Pacific subtropical and mid-latitude regions indicate that the generation and/or transmission of climate oscillations around the globe might involve intermediate water ventilation of the North Pacific. Drilling in the Bering Sea to recover comprehensive records of environmental conditions during periods of time with different climate boundary conditions can help answer questions about the global extent of climate oscillations and the mechanisms that produce them.

This expedition will obtain sedimentary sequences to study the Pliocene–Pleistocene evolution of millennial- to Milankovitch-scale climatic oscillations in the Bering Sea, the marginal sea connecting the Pacific and Arctic Oceans. Paleoclimatic indicators will be used to generate complete and detailed records of changes in the biological, chemical, and physical oceanographic conditions in the Bering Sea, as well as those of the adjacent continental climate. In addition to being sensitive to regional and potentially global climate change, the Bering Sea is one of the source regions of North Pacific Intermediate Water (NPIW). Because the production of NPIW is thought to be tied to global climate change and to Pacific Ocean circulation and nutrient distributions, investigating the evolution of conditions in regions of NPIW formation is critical for understanding Pacific paleoceanography.

Drilling in the Bering Sea will also document the effect of changes in the Bering Strait Gateway region. The Bering Strait is the main gateway through which communication (flux of heat, salt, and nutrients) between the Atlantic and Pacific, via the Arctic Ocean, occurs today. Investigating the evolution of the Bering Strait is critical to an understanding of transitions in global ocean heat and nutrient budgets.

Detailed high-resolution paleoenvironmental reconstructions from the Bering Sea have not been achieved in the past, although there was some reconnaissance work during Deep Sea Drilling Project (DSDP) Leg 19 (Scholl and Creager, 1973), as well as shallow-penetration piston core work that focused on generating paleoceanographic records from the latest Pleistocene (e.g., Cook et al., 2005; Takahashi et al., 2005). Planned drilling (Fig. F1; Table T1), including triple coring with the advanced piston corer (APC) at all sites, will provide the first continuous sedimentary records that can be used to reconstruct the history of this important marginal sea and its role in global climate and oceanographic changes over the past 5 m.y.

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