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，连接着全球海洋的所有三个主要洋盆，因此整合并响应了全球气候变化。行政协调会太平洋部门显然缺乏深海钻探记录中有关其新生代古海洋学的信息。为了促进我们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和大气CO2的影响的理解，我们旨在研究ACC系统北部的表层海洋变化。我们将提供一个独特的从轨道到亚轨道时间尺度的海表面温度变化的参考记录，以(1)评估跨越亚南极南太平洋和沿南太平洋东部经向进入热带的大尺度SST梯度的发展，(2)捕捉通过德雷克海峡输送并进入大西洋经向翻转环流的ACC水的长期变化，以及(3)评估南太平洋东部的热历史与西南极和巴塔哥尼亚冰盖动态之间的联系。我们的SST重建将基于对位于智利南部德雷克海峡入口处智利南部以西约3850米水深的IODP站点U1543的样品进行的生物标志物分析。更新世海温记录表明，以UK37古测温为基础的古海温测量方法在这一太平洋亚南极地区是一种高度可靠的方法。该地点的船板年龄模型表明，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组合众多的生物地层标志、特殊的古地磁记录以及回到中新世最上部的物理性质和XRF数据的有希望的地层学调整来提供的，据我们所知，这在南大洋是前所未有的。除了亚南极大西洋ODP1090站和新西兰近海的ODP站(如593和594站)外，目前没有连续的SST记录超过3.5 Ma，太平洋作为最大的南大洋部分的长期热历史仅受到很少的限制。我们将记录晚中新世和上新世相对稳定的温暖时期的表层海洋条件，大气中的二氧化碳与今天类似，并将分析在比现在更温暖的气候下，亚南极ACC的轨道尺度SST变化如何对不同的轨道强迫模式做出反应。此外，我们还将了解南太平洋东部的海温如何与上更新世-更新世的总体降温趋势和北半球主要冰川的开始有关，以及在主要的更新世气候转变期间，如中更新世革命，轨道尺度变异性是如何变化的。最后，我们将确定东南太平洋海温与西南极和巴塔哥尼亚冰盖的发展和动态的相关性。

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.