Antarctic weathering and hydrologic cycling through the Paleogene greenhouse to icehouse transition (IODP Expedition 318, Wilkes Land)

在过去6500万年的地质时间里，地球的气候发生了戏剧性的变化--从一个海洋温暖、极地冰川有限的世界过渡到一个两极地区寒冷、大陆大冰盖的世界。这种全球气候的长期变化被称为“温室”到“冰屋”的转变，主要发生在始新世和渐新世地质时期(5500万年前到2300万年前)。研究这一引人注目的古代气候变化事件，可以为理解促成这种转变的机制以及洞察过去不同地球系统过程的运行提供宝贵的信息。对这些过程的进一步了解，包括全球碳循环和不同的气候反馈机制，可以用来为未来对人为温室气体排放到大气中造成的气候变化的预测提供信息。为了获得关于温室到冰屋过渡期间高纬度气候条件的更多信息，综合海洋钻探计划(IODP)最近在威尔克斯陆地海岸(澳大利亚正南部)外的南极边缘采集了海洋沉积物。钻探岩芯是使用船基钻井平台发现的，为了解南极海岸和边缘海的始新世和渐新世气候史提供了一个窗口。拟议的研究重点是保存在威尔克斯陆地海岸岩心中的粘土矿物组合。由于粘土矿物是从陆地环境中剥落下来的主要沉积风化产物，整个岩心中粘土矿物类型的变化将提供有关普遍风化制度变化的重要信息。具体地说，粘土矿物可以用来确定在始新世-渐新世期间从化学风化状态(在温暖、潮湿条件下)向物理风化状态(受冰川活动影响)转换的时间。通过合作，粘土矿物记录将与目前正在使用各种方法开发的其他气候替代记录相结合。这项研究产生的新的南极气候重建将提供关键的高纬度气候信息，这些信息可用于：(1)确定始新世高峰期和渐新世冰川开始期间南极气候条件的性质，以及(2)通过“温室”到“冰屋”的转变，评估全球气候变化和大气二氧化碳变异性之间的联系。

Over the past 65 million years of geologic time, Earth's climate has changed dramatically--transitioning from a world with warm oceans and limited polar glaciation to a world with cold polar regions and large continental ice sheets. This long-term change in global climate is known as the 'Greenhouse' to 'Icehouse' transition and primarily occurred during the Eocene and Oligocene geological epochs (between 55 and 23 million years ago). Study of this remarkable episode of ancient climate change can provide valuable information for understanding the mechanisms that precipitated this shift, as well as insight into the operation of different Earth system processes in the past. Further knowledge of these processes, involving the global carbon cycle and different climate feedback mechanisms, can be used to inform future predictions of climate change resulting from anthropogenic greenhouse gas emissions to the atmosphere.In an effort to gain further information on high-latitude climate conditions during the 'Greenhouse' to 'Icehouse' transition, the Integrated Ocean Drilling Program (IODP) recently cored marine sediments on the Antarctic margin off the Wilkes Land coast (directly south of Australia). The drillcores were recovered using a ship-based drilling platform and provide a window into Eocene and Oligocene climate history of the Antarctic coast and marginal seas. The proposed study is focused on clay mineral assemblages preserved in cores obtained from the Wilkes Land coast. Since clay minerals are a primary sedimentary weathering product shed from the terrestrial environment, variation in the types of clay mineral present throughout cores will provide important information on changes in the prevailing weathering regime. Specifically, clay minerals can be used to determine the timing of the switch from a chemical weathering regime (under warm, humid conditions) to physical weathering regime (influenced by glacial activity) during the Eocene-Oligocene time interval. Through collaborative work, the clay mineral records will be integrated with other climate proxy records currently being developed using a variety of approaches. The new Antarctic climate reconstructions that result from this research will provide critical high-latitude climate information that can be used to: (1) determine the nature of Antarctic climate conditions during peak Eocene warmth and during the onset of Oligocene glaciation, and (2) assess links between global climate change and atmospheric pCO2 variability through the 'Greenhouse' to 'Icehouse' transition.