"South Pacific Paleogene Climate" IODP Expedition 378: Stratigraphy, Chronology and Provenance of late Eocene-early Oligocene South Pacific sediments

在过去的6600万年里，地球的气候已经从一个几乎没有冰的“温室”世界变成了一个“冰屋”世界，在那里，巨大的冰盖覆盖了北方和南半球的大片土地。虽然这种变化是渐进的，但南极洲第一次被大冰盖覆盖发生在大约3390万年前。这种过渡被称为始新世-渐新世过渡。大气中二氧化碳浓度的大幅下降被认为是第一次南极冰川作用的主要原因。然而，在南极洲形成冰盖的另一个关键条件是，这片大陆需要与从地球赤道蔓延过来的温暖沃茨隔热。今天，一个巨大的寒冷的深水洋流环绕着南极洲，从而提供了一个温度屏障。这股洋流被称为南极绕极洋流，一些研究表明，第一次南极冰川作用发生在这股深水洋流开始时。然而，这一主张是有争议的。目前很难解决这一争论，因为没有足够的记录可以准确地追踪南极绕极流的开始。像国际海洋发现计划（IODP）及其前身这样的科学海洋钻探计划是恢复存储在我们海底深海沉积物中的过去气候变化档案的唯一途径。南太平洋是南极绕极流占主导地位的一个关键区域，然而，它仍然完全没有进行科学的海洋钻探。这将随着IODP远征378而改变，该远征将前往南太平洋并恢复关键的沉积物，使我们能够回顾南极洲首次形成大型冰盖时的气候动态。在这里，我们建议使用这些沉积物来调查南极绕极流首次出现在南太平洋的化学和矿物学的过去的沉积物跨越始新世-渐新世过渡。我们还将利用生活在海底的微观化石（称为底栖有孔虫）的化学性质，对同一时间间隔内冰量在较长时间尺度上的变化进行初步评估。将这些初步的冰量记录与化学和矿物学记录相结合，应该可以提高我们对南极绕极流在南极洲第一次主要冰川作用中的作用的理解。

Over the last 66 million years, Earth's climate has changed from a near ice-free "Greenhouse" world to an "Icehouse" world, where large ice sheets cover huge areas of land in both the northern and southern hemispheres. Although some of this change has been gradual, the first time Antarctica was covered with a large ice sheet occurred approximately 33.9 Million years ago. This transition is referred to as the Eocene-Oligocene Transition. A large drop in atmospheric carbon dioxide concentrations has been proposed as the main cause of the first major Antarctic glaciation. However, another key condition for ice sheets forming on Antarctica is that this continent needed to be thermally isolated from warm waters that spread from the Earth's equator. In the present day, a large, cold deep-water current circles Antarctica, thereby providing a temperature barrier. This current is called the Antarctic Circumpolar Current, and some research suggests that the first Antarctic glaciation occurred when this deep-water current first started. However, this claim is debated. It is currently difficult to solve this debate as there are insufficient records that can trace the start of the Antarctic Circumpolar Current accurately. Scientific ocean drilling programmes like the International Ocean Discovery Program (IODP) and its predecessors are the only way to recover the archives of past climate change locked away in deep-sea sediments stored on our ocean floor. The south Pacific Ocean is a key area that is dominated by the Antarctic Circumpolar Current, however, it remains entirely unexplored by scientific ocean drilling. This will change with IODP Expedition 378, which will go to the South Pacific and recover key sediments and enable us to look back at climate dynamics when large ice sheets first formed on Antarctica. Here, we propose to use these sediments to investigate when the Antarctic Circumpolar Current first appeared in the South Pacific by looking at the chemistry and mineralogy of the past sediments across the Eocene-Oligocene Transition. We will also make an initial assessment of how the ice volume changed over longer timescales during the same time interval, using the chemistry of microscopic fossils that live on the ocean floor, called benthic foraminifera. Combining these preliminary ice volume records with the chemistry and mineralogy records should improve our understanding of the role of the Antarctic Circumpolar Current in the first major glaciation of Antarctica.