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

副热带黑潮流（KC）是西北太平洋重要的西部边界流，将西太平洋暖池的暖盐水团输送到中纬度北部地区。目前，KC和极流在日本外海~36°N交汇，但已知KC-OC锋面间区在冰期向更南的纬度移动，从而使OC向更南的纬度输送冷地表水团。因此，两股洋流的相互作用在水汽和热量向北纬的经向平流中起着重要作用，并对西北太平洋和东亚大陆的气候和陆地演化起着重要的控制作用。本研究的目的是建立深时高分辨率的海温和陆地植被变化记录，以研究中新世早期至今西北太平洋的古海洋学和古气候演变及其相关陆生植物群落的变化。为此，目前正在使用体积地球化学和脂质生物标志物技术对IODP探险322和333期间在C0011/C0012地点以及IODP探险350期间钻探的U1437地点回收的深海沉积物进行研究。利用TEXH86、UK´37和LDI脂质古温度计提取C0011/C0012站点的沉积物，获得了过去14.3 Ma日本海岸海温变化的连续记录。虽然不同代用物的绝对海表温度在量级上存在差异，但从晚中新世到现在，所有三个记录都显示出长期的降温趋势，温度下降了约5-10°C。U1437遗址钻取了早中新世至全新世的沉积层序，岩心恢复良好。初步的脂质生物标志物数据表明，有机温度替代指标在U1437位点的应用是可行的，基于TEXH86和ldi的海温记录显示了与C0011/C0012位点相似的趋势。然而，绝对温度的差异可能提供有关KC蜿蜒流动模式的宝贵信息，从而提供热量向中纬度北部经向输送的宝贵信息。在项目第二阶段的框架内，我们计划将现有的西北太平洋古气候和古海洋变化记录扩展到早中新世，并通过将DSDP第56次远征期间从436站点恢复的深海沉积物纳入我们的脂质生物标志物分析，研究OC的变率和强度。数据的最终合成将使我们能够以前所未有的时空分辨率重建西北太平洋的古气候和古海洋演化，并将提供西北太平洋早中新世（~25 Ma BP）以来海温变化的第一个深度记录。

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).