Paleoclimate evolution of the NW-Pacific over the past 25Ma

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The subtropical Kuroshio Current (KC) is an important western boundary current of the Northwest (NW) Pacific Ocean, which transports warm and saline water masses from the Western Pacific Warm Pool to northern mid-latitudes. At present the KC and the polar Oyashio Current (OC) converge at ~36°N off Japan, but the KC-OC interfrontal zone is known to have shifted to more southerly latitudes during glacial periods, thereby allowing the OC to transport cold surface water masses to more southerly latitudes. Therefore, the interplay of both ocean currents plays an important role in the meridional advection of moisture and heat to northern latitudes and exerts a major control on the climate and terrestrial evolution of the NW Pacific and the East Asian continent. The aim of this study is to establish deep-time high-resolution records of sea surface temperature (SST) and terrestrial vegetation change in order to study the paleoceanography and paleoclimate evolution of the NW Pacific and associated shifts in terrestrial floral communities from the early Miocene to the present. For this, deep-sea sediments recovered at Sites C0011/C0012 during IODP Expeditions 322 and 333 as well as Site U1437, which was drilled during IODP Expedition 350, are currently investigated using bulk-geochemical and lipid biomarker techniques. Extraction of sediments from Sites C0011/C0012 yielded a continuous record of SST change off the coast of Japan over the last 14.3 Ma using the TEXH86, UK´37 and LDI lipid paleothermometers. Although absolute SST values for the different proxies vary in magnitude, all three records show a long-term cooling trend from the late Miocene to the present with temperatures decreasing by some 5-10 °C. At Site U1437, a sedimentary sequence spanning a time interval from the early Miocene to Holocene was drilled with excellent core recovery. Preliminary lipid biomarker data indicates that the application of organic temperature proxies is feasible at Site U1437 with TEXH86 and LDI-based SST records showing similar trends as observed for Sites C0011/C0012. Difference in absolute temperatures may, however, provide valuable information on the meander flow pattern of the KC and thus on the meridional transport of heat to northern mid-latitudes. In the framework of the 2nd phase of the project, we plan to extend our existing records of paleoclimate and paleoceanographic change in the NW Pacific to the early Miocene and study the variability and strength of the OC by including deep-sea sediments recovered from Site 436 during DSDP Expedition 56 in our lipid biomarker analysis. The final synthesis of our data will allow reconstructing the paleoclimate and paleoceanographic evolution of the NW Pacific in an unprecedented spatiotemporal resolution and will provide the first deep-time record of SST change from the NW Pacific that dates back to the early Miocene (~25 Ma BP).