Subantarctic Eastern South Pacific surface Ocean Dynamics since the Late Miocene (IODP Expedition 383)

南极绕极流（ACC）是世界上最强的纬向流系统，连接全球海洋的所有三个主要海洋盆地，因此整合并应对全球气候变化。ACC的太平洋部分显然缺乏来自深海钻探记录的新生代古海洋学信息。为了加深对太平洋中新世至全新世大气-海洋-冰冻圈动力学及其对区域和全球气候以及大气CO2的影响的理解，我们的目标是研究北方ACC系统的表层海洋变化。我们将提供一个轨道到亚轨道时间尺度的海表温度（SST）变化的独特参考记录，以（i）评估横跨亚南极南太平洋和沿南太平洋东部沿着向热带的大尺度SST梯度的发展，以（ii）捕获通过德雷克海峡输送并进入大西洋纬向翻转环流的ACC水的长期变化，以及（iii）评估南太平洋东部的热历史与南极西部和巴塔哥尼亚冰盖的动态之间的联系。我们的SST重建将基于对IODP站点U1543样本的生物标志物分析，该站点位于智利南部德雷克通道入口以西约3850 m水深处。更新世SST记录表明，在这一太平洋亚南极地区，基于UK 37古温度计的古SST是一种高度可靠的方法。该站点的船载年龄模型表明，在过去的~8 Ma期间，持续沉积（~5 cm/ka）。精确的年龄控制是通过结合众多的生物地层标志物，一个特殊的古地磁记录，和一个有前途的地层调整的物理性质和XRF数据回到中新世的最高部分，这是我们的知识前所未有的南大洋。除了亚南极大西洋ODP站点1090和新西兰海域ODP站点（例如站点593和594），目前没有连续的SST记录超过3.5 Ma，太平洋作为南大洋最大的部分的长期热历史仅受到很差的限制。我们将记录晚中新世和上新世相对稳定的温暖时期的海洋表面条件，大气CO2与今天相似，并将分析亚南极洲ACC的轨道尺度SST变化如何响应于比现在更温暖的气候下不同模式的轨道强迫。此外，我们将了解南太平洋东部的SST如何与上新世-更新世的总体冷却趋势和主要北方半球冰川的开始有关，以及轨道尺度的变化如何在主要的更新世气候转变（如中更新世革命）中发生变化。最后，我们将确定东南太平洋SST的发展和西南极和巴塔哥尼亚冰盖的动态的相关性。

The Antarctic Circumpolar Current (ACC), the world’s strongest zonal current system, connects all three major ocean basins of the global ocean and therefore integrates and responds to global climate variability. The Pacific sector of the ACC clearly lacks information on its Cenozoic paleoceanography from deep-sea drilling records. To advance our understanding of Miocene to Holocene atmosphere- ocean-cryosphere dynamics in the Pacific and their implications for regional and global climate and atmospheric CO2, we aim to investigate surface ocean changes in the northern ACC system. We will provide a unique reference record of sea surface temperature (SST) changes at orbital to suborbital time-scales to (i) evaluate the development of the large scale SST gradients across the subantarctic South Pacific and meridionally along the eastern South Pacific into the tropics, to (ii) capture long-term changes in the ACC water transported through the Drake Passage and entering the Atlantic meridional overturning circulation, and to (iii) assess the links between the thermal history of the eastern South Pacific and the dynamics of the West Antarctic and Patagonian Ice sheets. Our SST reconstructions will be based on biomarker analyses on samples from IODP Site U1543 located at ~3850 m water depth west of southern Chile at the entrance of the Drake Passage. Pleistocene SST records showed that paleo-SSTs based on UK37 paleothermometry is a highly reliable method in this subantarctic region of the Pacific. The ship-board age model for this site suggests continuous sedimentation (~5 cm/ka) throughout the past ~8 Ma. Precise age control is provided through a combination of numerous biostratigraphic markers, an exceptional paleomagnetic record, and a promising stratigraphic tuning of physical property and XRF data back to the uppermost part of the Miocene, which is to our knowledge unprecedented for the Southern Ocean. Except for subantarctic Atlantic ODP Site 1090 and ODP Sites off New Zealand (e.g. Sites 593 and 594), no continuous SST record presently extends beyond 3.5 Ma and the long-term thermal history of the Pacific as the largest Southern Ocean sector is only poorly constrained. We will document surface ocean conditions during the relatively stable warm periods of the late Miocene and Pliocene with atmospheric CO2 similar to today and will analyze how orbital-scale SST variations in the subantarctic ACC responded to different modes of orbital forcing under warmer- than-present climates. Moreover, we will learn how SSTs in the eastern South Pacific relate to the general Plio-Pleistocene cooling trend and the onset of major northern hemisphere glaciation and how orbital-scale variability changed across major Pleistocene climate transitions such as the Mid-Pleistocene Revolution. Finally, we will identify the relevance of eastern South Pacific SSTs for the development and the dynamics of the West Antarctic and Patagonian Ice Sheets.