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

副热带黑潮（KC）是西北太平洋重要的西边界流，它将西太平洋暖池的暖盐水团输送到北方中纬度地区。目前，KC和极地亲潮海流（OC）在日本近海约36°N处汇合，但已知KC-OC锋间带在冰期期间已向更南的纬度移动，从而允许OC将冷的地表水团输送到更南的纬度。因此，两种洋流的相互作用在水汽和热量向北方纬度的纬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变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记录的海表温度（SST）和陆地植被的变化，以研究古海洋学和古气候演变的西北太平洋和相关的变化陆地植物群落从中新世早期到现在。为此，目前正在使用整体地球化学和脂质生物标志物技术调查在IODP第322和333次考察期间在C 0011/C 0012站点以及在IODP第350次考察期间钻探的U1437站点回收的深海沉积物。从C 0011/C 0012站点提取沉积物，使用TEXH 86、UK ′ 37和LDI脂质古温度计获得了过去14.3 Ma日本海岸SST变化的连续记录。尽管不同替代物的绝对SST值在幅度上有所不同，但所有三个记录都显示出从中新世晚期到现在的长期冷却趋势，温度降低了约5-10 °C。在U1437现场，钻取了一个从早中新世到全新世的沉积层序，岩心回收率很好。初步脂质生物标志物数据表明，在研究中心U1437应用有机温度代用指标是可行的，TEXH 86和基于LDI的SST记录显示与研究中心C 0011/C 0012观察到的趋势相似。然而，绝对温度的差异可能提供有价值的信息，KC的曲流模式，从而对热量的纬向输送到北方中纬度地区。在该项目的第二阶段的框架内，我们计划将我们现有的西北太平洋的古气候和古海洋学变化的记录扩展到中新世早期，并通过在我们的脂质生物标志物分析中包括DSDP Expedition 56期间从Site 436恢复的深海沉积物来研究OC的变化和强度。我们的数据的最终合成将允许重建的古气候和古海洋学的西北太平洋的演变在一个前所未有的时空分辨率，并将提供第一个深时记录的SST变化从西北太平洋，可以追溯到早中新世（约25马BP）。

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).