Plio-Pleistocene paleoceanography of the northern and western Pacific

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The NeogeneQuaternary (Pliocene-Pleistocene) transition around 2.8 to 2.45 million years ago represents a fundamental shift in Earth's climate system. The extreme glacial-interglacial oscillations that characterize our more recent climate emerged at this time, although the causes remain uncertain. Deep-ocean sediments offer clues to climate history owing to their continuous and well-dated character, and because the oceans themselves are crucial heat and CO2 sources / sinks as well as being suppliers of moisture for ice sheet growth. Extensive research on North Atlantic sediments has revealed that large ice sheets covered the high northern latitudes around 2.74 and 2.6 million years ago. While research has focused mostly on the North Atlantic, plausible evidence holds that the northern Pacific Ocean supplied moisture to northern North America allowing the growth of ice sheets 2.74 million years ago. The proposed research targets five deep-sea cores along a transect from the Bering Sea to the South China Sea, and aims to elucidate the Pacific Ocean's role in climate evolution during the NeogeneQuaternary transition. It specifically addresses ice sheet expansion 2.74 and 2.6 million years ago, and explores the associated surface current patterns. It also examines teleconnections between high northern latitude ice sheets and the East Asian winter monsoon system, as reflected in sediments of the marginal Sea of Japan and South China Sea. The intensification of this monsoon is seen in Chinese loess sequences and is driven by cooling in northern Asia. The examination of well-dated ocean sediments may therefore resolve uncertainties in the timing of Chinese loess deposition. The tools used primarily in the proposed research are the fossilized cysts of dinoflagellates: single-celled microplankton known to be sensitive to environmental change, and as a group tolerant of a wide range in salinities. The cysts (“dinocysts”) are acid-insoluble and resistant to dissolution, and are used as tracers of water masses and indicators of sea-ice extent. Acritarchs, also to be studied, occur in the same preparations as dinocysts but are of unknown biological affinity. They are abundant and relatively diverse in high northern latitudes, and have strong potential for paleoenvironmental analysis over the selected time interval. Dinocysts and acritarchs have been studied extensively in Pliocene and lower Pleistocene deposits of the North Atlantic, but have been largely neglected for the Pacific. Results will be of particular importance to the paleoclimate and paleoceanography communities, and to climate modelers who test models of future climate against evidence-based paleoclimate reconstructions. The detailed study of dinocysts and acritarchs in tandem with other paleoenvironmental proxies will enhance the utility of this microfossil group for future applications in the Pacific and elsewhere.