"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近乎无冰的“温室”世界变成了一个“冰屋”世界，在这个世界里，巨大的冰盖覆盖了南北半球的大片土地。虽然其中一些变化是渐进的，但南极洲第一次被大冰盖覆盖是在大约3390万年前。这种转变被称为始新世-渐新世转变。大气中二氧化碳浓度的大幅下降被认为是第一次南极大冰期的主要原因。然而，在南极洲形成冰盖的另一个关键条件是，这块大陆需要与从地球赤道传播过来的温暖海水在热上隔离。在今天，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。这种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种深水洋流开始的时候。然而，这种说法是有争议的。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）这样的科学海洋钻探计划及其前身是恢复过去气候变化档案的唯一途径，这些档案被锁在海底的深海沉积物中。南太平洋是由南极绕极流主导的一个关键区域，然而，它仍然完全没有被科学的海洋钻探所探索。这将随着IODP探险队378的到来而改变，它将前往南太平洋，恢复关键的沉积物，使我们能够回顾大冰盖首次在南极洲形成时的气候动态。在这里，我们建议通过观察始新世-渐新世过渡时期过去沉积物的化学和矿物学，利用这些沉积物来研究南极环极流在南太平洋首次出现的时间。我们还将利用生活在海底的被称为底栖有孔虫的微小化石的化学成分，初步评估在同一时间间隔内，冰量在更长时间尺度上是如何变化的。将这些初步冰量记录与化学和矿物学记录结合起来，应该能提高我们对南极环极流在南极第一次大冰川作用的认识。

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.