IODP Expedition 323 Scientific Prospectus

doi:10.2204/iodp.sp.323.2009

Abstract

Over the last 5 m.y., global climate has evolved from being warm with only small Northern Hemisphere glaciers to being cold with major Northern Hemisphere glaciations every 100–40 k.y. The ultimate reasons for this major transition are unknown. Over the last hundreds of thousands of years, Milankovitch- and millennial-scale climate oscillations have occurred; although processes responsible for these oscillations are known in some regions, the global nature of these oscillations are due to unknown mechanisms. Possible mechanisms responsible for both the long-term evolution of global climate as well as the generation of high-frequency climate oscillations involve intermediate water ventilation of the North Pacific. However, the paucity of data in critical regions of the Pacific, such as the Bering Sea, has prevented an evaluation of the role of North Pacific processes in global climate change. The Bering Sea is a marginal sea in the North Pacific that has experienced major climate changes. Because North Pacific Intermediate Water (NPIW) is known to form in the Bering Sea, the basin does not only record, but it is potentially critically involved in causing major climate changes. Thus, drilling in the Bering Sea can help to answer questions not only about the global extent of climate trends and oscillations but also about the mechanisms that produce them.

We plan to core sediments to study the Pliocene–Pleistocene evolution of millennial- to Milankovitch-scale climatic oscillations in the Bering Sea. Biological, chemical, and physical oceanography, as well as the adjacent continental climate of the Bering Sea, are highly sensitive to global climate conditions and are recorded by variations in the sedimentary composition of diatoms and other microfossil groups, as well as many other paleoclimatic indicators. Intermediate water formation in these regions can be tracked using paleoceanographic proxies of subsurface water that can be related to open Pacific records. Sediments can not only be used to produce records of climate and intermediate water ventilation in these critical marginal seas but can also be applied to testing the effect of changes in the Bering Strait Gateway and its influence (via the Arctic) on heat and nutrient partitioning between the Atlantic and Pacific. Planned coring will provide continuous and high-resolution paleoenvironmental records from these critical marginal seas for the first time. These new records can then be used to understand the processes that influence intermediate water ventilation and its role in global climate change over the last 5 m.y.

Major objectives of planned drilling in the Bering Sea are as follows:

To elucidate a detailed evolutionary history of climate and surface ocean conditions since the earliest Pliocene in the Bering Sea where amplified high-resolution changes of climatic signals are recorded;
To shed light on temporal changes in the origin and intensity of NPIW and possibly deeper water mass formation in the Bering Sea;
To characterize the history of continental glaciation, river discharges, and sea ice formation, in order to investigate the link between continental and oceanic conditions of the Bering Sea and adjacent land areas; and
To investigate linkages, through comparison to pelagic records, between ocean/climate processes that occur in the more sensitive marginal sea environment and processes that occur in the North Pacific and/or globally. This objective includes an evaluation of how the history of ocean/climate of the Bering Strait gateway region may have had an effect on North Pacific and global conditions.

All of these scientific objectives will focus on the long-term ocean and climate trends, as well as the evolution of higher frequency glacial–interglacial to millennial-scale oscillations through the Pliocene–Pleistocene.

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