GEO ICE - Benchmark Geological Records for the Response of the West Antarctic Ice Sheet to Near Future Temperature

《巴黎协定》向人类提出了一个雄心勃勃的关键目标：将全球变暖幅度控制在远高于工业化前水平2摄氏度以下。所有197个国家都签署了协议，其中189个国家已经正式批准。但毫无疑问，这些目标提出了一个巨大的挑战，一定程度的环境变化已经是不可避免的。我们知道，在未来几十年里，海平面将上升几十厘米，数百万生活在低洼沿海地区的人将流离失所。但我们还不知道在接下来的几个世纪里，海平面还会上升多少。我们控制排放的努力能阻止南极冰架的崩塌和南极西部冰盖的消失吗？崩溃发生在什么条件下？冰盖的哪一部分会首先发生反应呢？计算机模型在这些问题上得出了相互矛盾的结果，部分原因是它们使用不同的环境条件和模型物理来模拟过去（和我们的未来）。为了弄清楚哪一个是正确的，我们需要从过去的地质中获得观测数据来测试这些模型。我们的项目将从一个侦探故事开始，提供一些长期寻找的证据。我们将利用两个地质记录，在温度仅略高于现代水平（即晚更新世间冰期）的条件下，重建南极西部冰盖的历史。这些记录中的第一个来自于最近的一次船基钻探活动（国际海洋探索计划远征374），该活动从罗斯海（紧邻南极西部冰盖的地区）回收了泥土和沙子。第二个记录将从一个基于冰架的钻井平台上获取，该钻井平台将从罗斯冰架下方很远的地方恢复海底泥土和沙子的第一个扩展记录，在南极西部冰盖从海底分离并开始漂浮到罗斯海的位置（简单海岸钻探）。在我们的第一个工作包中，我们将分析泥浆、沙子和有机颗粒的化学成分，以重建关键的环境条件。首先，泥土和沙子将揭示大陆上的岩石碎片来自哪里。对侵蚀位置的了解可以反过来告诉我们，南极西部冰盖在过去的温度只比现在高一点的时候是否融化了。其次，同一样品中有机颗粒的化学成分将揭示沉积时的普遍海洋温度。第三，某些类型的海洋藻类的存在或不存在将告诉我们浮冰是否存在。三组不同数据的结合将帮助我们解开西南极洲冰川融化的地理位置。对于我们的第二个工作包，我们将利用我们的新数据来测试耦合的冰盖-气候模型，这些模型也用于预测未来的海平面。评估这些模型在模拟地质过去方面的表现如何，是确定它们对未来的预测有多准确的关键方法。我们将详细测试两个这样的模型，称为PSUICE3D和BISICLES。我们将分析在过去温暖时期导致南极西部冰盖崩塌的现有模型模拟，并在新数据的约束下使用更现实的环境框架进行新的模拟。以前从未实现过对预测的冰退缩地点和模拟的冰退缩地点的比较，这将使我们能够查明南极洲的哪些地区最容易受到中等程度的全球变暖的影响，为全球沿海地区的住区减缓和适应海平面上升提供重要信息。

The Paris Agreement presents humanity with an ambitious and critical goal: to keep global warming well below 2 degrees above pre-industrial levels. All 197 countries have signed up, and 189 have formally approved it. But there is no doubt that these targets present a massive challenge, and a certain amount of environmental change is already inevitable. We know that sea level will rise 10s of centimetres over the next several decades, displacing many millions of people living in low lying coastal areas. But we don't yet know just how much more our seas will rise through the coming centuries. Will our efforts to curb emissions stop the collapse of Antarctica's ice shelves and loss of the West Antarctic Ice Sheet? Under which conditions does collapse occur? And which part of the ice sheet will react first? Computer models yield conflicting results on these questions, partly because they simulate the past (and our future) using different environmental conditions and model physics. To figure out which of these are right, we need to obtain observational data from the geological past to test the models. Our project will embark in a detective story to provide some long-searched for evidence. We will exploit two geological records to reconstruct West Antarctic Ice Sheet history under temperatures only slightly elevated above modern levels (i.e. late Pleistocene interglacials). The first of these records comes from a recent ship-based drilling campaign (International Ocean Discovery Program Expedition 374) that recovered mud and sand from the Ross Sea, an area right next to the West Antarctic Ice Sheet. The second record will be retrieved from an ice shelf-based drilling rig that will recover the first extended record of sub-seafloor mud and sand from far beneath the Ross Ice Shelf, at a location where the West Antarctic ice sheet detaches from the seafloor and starts to float into the Ross Sea (Siple Coast drilling). For our first work package, we will analyse the chemical composition of mud, sand and organic particles to reconstruct critical environmental conditions. Firstly, the mud and sand will uncover where on the continent the pieces of rocks came from. Knowledge of the location of erosion can then tell us in turn whether the West Antarctic Ice Sheet melted during past times when temperatures were just a little bit warmer than today, or not. Secondly, the chemical composition of organic particles in the same samples will reveal prevailing ocean temperatures at the time of deposition. Thirdly, the presence/absence of certain types of marine algae will tell us whether floating ice was present or not. The combination of the three different sets of data will help us unravel where geographically ice melting started in West Antarctica.For our second work package, we will utilise our new data to test coupled ice sheet-climate models, which are also used to predict future sea level. Assessing how well these models perform in simulating the geological past is a key way of determining how accurate their projections of the future are. In detail we will test two such models, called PSUICE3D and BISICLES. We will analyse existing model simulations that led to collapse of the West Antarctic Ice Sheet during past warm times, and perform new simulations using a more realistic environmental framework constrained by our new data. The comparison of predicted places of ice retreat and modelled places of ice retreat has never been realised before and will allow us to pinpoint which parts of Antarctica are most vulnerable to moderate levels of global warming, providing vital information towards mitigation and adaptation of sea level rise for settlements in coastal areas around the globe.