Antarctic Deep Water Circulation and Continental Weathering from the Eocene Greenhouse to the Oligocene Icehouse (IODP Expedition 318, Wilkes Land).

我们目前生活在一个气候变化的世界里。全球大气中二氧化碳浓度正在以地球历史上前所未有的速度上升，毫无疑问，这种上升在很大程度上是由于人类的活动。我们预测大气中二氧化碳浓度增加和相关变暖的影响的能力，在很大程度上取决于对地球系统中物理、化学和生物过程之间的关系的理解，这些过程通过所谓的“反馈机制”与温度和大气二氧化碳内在地耦合。但我们如何研究这种机制呢？一个重要的方面是通过直接观测来研究现代气候系统是如何运行的。然而，这样的观察只能涵盖相对较短的时间跨度。要想看到气候系统的完全波动，我们需要超越人类的观察，看看过去的气候档案，比如从海底发现的沉积物岩芯。经过30多年的国际协调海洋钻探，已经从大洋盆地的数百个地点取回了包含气候记录的钻芯，时间追溯到1亿多年前。根据这些核心重建气候系统的各种参数，如海洋温度、大陆风化强度或过去的海洋环流模式，为了解气候系统、现有的反馈机制及其过去的运作方式提供了宝贵的见解。过去6500万年来最显著的(自然)气候转变是从温室世界向我们现在生活的冰库世界的过渡，温室世界的特点是即使在高纬度(北极和南极；约5000万年前)也是以亚热带条件为特征的(即，低纬度温暖的温度，高纬度的寒冷温度；开始于约3300万年前)。为了理解这种气候转变，我们必须研究在高纬度地区实际发生了什么。综合海洋钻探方案(IODP)的318探险队接受了这一挑战，目标是10年来首次在南极大陆附近钻探沉积物岩心。由于天气和冰层条件，在南极洲附近钻探是一项具有技术挑战性的任务，但也因为海底往往是粗粒沉积物的性质。318次探险发生在2010年1月至3月，我们带回的是一份壮观的沉积物记录，告诉我们一个关于温室气体峰值条件的故事，冰库世界的最早时刻，以及从大约3000万年前到今天的南极冰盖的历史。虽然这份材料将使我们能够解决气候变化方面的许多长期问题，但特别值得注意的是，这是首次在南极东部海岸附近地区发现温室沉积物峰值。这些沉积物，加上冰库世界最初时刻的特征，构成了我们拟议研究的中心。我们制定了一项研究计划，在新的岩芯中研究大陆风化和海洋环流，这两个关键气候变量。我们的结果将为更全面地了解气候系统中的驱动因素、放大器和反馈奠定关键的一步。

We are currently living in a world of climate change. Global atmospheric concentrations of carbon dioxide are rising at a rate unprecedented in the history of the Earth, and there is no doubt that a large part of this rise is due to human acitivity. Our ability to predict the effects of increased CO2 concentrations in the atmosphere and associated warming, heavily depends on understanding the relationship between physical, chemical, and biological processes in the Earth system, which are intrinsically coupled to temperature and atmospheric CO2 through so called 'feedback mechanisms'. But how can we study such mechanisms? One important aspect is to study how the modern climate system operates, by direct observations. However, such observations can only cover time spans, which are relatively short. To see the full swings of the climate system, we need to go beyond human observations and look at climate archives of the past, such as sediment cores recovered from the bottom of the ocean. More than 30 years of internationally coordinated ocean drilling has retrieved drillcores containing climate records from hundreds of locations all across the ocean basins, reaching back in time more than 100 million years. Reconstruction of various parameters of the climate system from such cores, such as ocean temperatures, intensity of continental weathering, or past ocean circulation patterns, has provided valuable insights into the climate system, existing feedback mechanisms and how they operated in the past. The most significant (natural) climate swing of the past 65 million years was the transition from the Greenhouse world, characterised by subtropical conditions even at high latitudes (Arctic and Antarctic; ~50 million years ago) to the icehouse world we are currently living in (i.e., warm temperature at low latitudes, cold temperatures at high latitudes; started ~33 million years ago). To understand this climate transition, we have to study what actually happened at high latitudes. Expedition 318 of the Integrated Ocean Drilling Program (IODP) took on this challenge and aimed to drill for the first time in 10 years sediment cores close to the Antarctic continent. Drilling in the vicinity of Antarctica is a technically challenging task due to weather and ice conditions, but also due to the nature of the often coarse-grained sediments at the seafloor. Expedition 318 took place in January to March 2010, and what we came back with is a spectacular record of sediments that tells us a story about peak greenhouse conditions, the earliest moments of the icehouse world, and the history of the Antarctic ice sheet all the way from ~30 million years ago to today. While this material will enable us to address many longstanding questions in climate change, it is especially noteworthy that this is the first time peak greenhouse sediments have been recovered from an area proximal to the East Antarctic coast. These sediments, together with the ones characteristic of the first moments of the icehouse world, build the center of our proposed study. We developed a research plan to study continental weathering and ocean circulation, two of the key climate variables, in the new cores. Our results will build a critical step in developing a more comprehensive understanding of drivers, amplifiers, and feedbacks in the climate system.