Testing smaller-than-present configurations of the Antarctic Ice Sheet using a novel integration of geochronology

南极冰盖(东南极和西南极)容纳的淡水足以使全球海平面上升60米以上。即使是西南极冰盖的部分崩溃，也可能使海平面上升2-3米，导致数百万人流离失所，迫使他们在内陆寻找新的栖息地。众所周知，南极冰盖正在以更快的速度失去质量，这意味着它们正朝着比现在更小的形状前进。要了解这样的结构是如何实现的，关键是要了解过去冰盖在小于现在的时候的行为。冰盖行为的计算机模型能够做出预测，但需要观察以进行验证和改进。要做到这一点，一种方法是测试模型是否准确地再现了现实中观察到的行为。南极洲没有冰覆盖的有限区域提供了关于过去冰盖范围的重要信息，但只能提供比现在更大的冰盖结构信息。为了了解比目前更小的结构，这项提议将接近现在被冰覆盖的岩石。这块岩石保留了可测量的属性，这些属性记录了它最后一次被冰盖发现的时间，从而可以确定这些事件的时间和持续时间。该项目将从西南极洲的关键区域威德尔海采集冰下样本。在这一领域，最近使用雷达的工作已经确定了冰盖内的内部结构，这表明它最近经历了变化。具体地说，这些数据与冰盖在过去数百年里经历了一段时间的扩张是一致的，在这段时间里，冰盖比现在小。了解冰盖的当前状态和控制其行为的过程，对于预测冰盖将如何应对人类引发的全球变暖至关重要。我将使用便携式钻探系统钻穿今天突出在冰盖上方的山脉附近的冰层。在南极的两个野外季节中，钻探将被用来收集一系列冰下岩芯，这些岩芯将被送回实验室，在那里将使用一种新的地质年代学方法组合来确定岩石是否以前因冰盖较小而裸露。通过结合不同的技术，我将改进可以获得的约束；因此，不仅可以确定过去的冰盖是否较小，而且可以确定何时和多久会出现这种情况。然后，我将使用新数据来评估冰盖行为的计算机模型。这些模型使用参数值的组合，代表现实中发生的过程，来模拟冰盖随时间变化的行为。通过探索一个不同参数值的范围，大量的模拟(集合)定义了一系列潜在的冰盖模拟，这些模拟可能会也可能不会紧密地反映现实。新的地质数据是实际冰盖行为的产物，可以用来筛选出与现实相去甚远的模型模拟。剩余的模拟可以根据它们与地质数据的匹配程度进行评分。通过这种方式，我将确定哪些参数(即哪些过程)是控制冰盖行为的关键。通过这种方式，我的项目将使我们对在短地质时间尺度上控制冰盖行为的过程的理解发生阶段性变化。此外，该项目确定的改进的冰盖历史和模型参数范围将改进未来的建模工作，并导致对未来冰盖行为和相关海平面上升的更准确预测。

The Antarctic Ice Sheets (East Antarctica and West Antarctica) hold enough fresh water to raise global sea levels by over 60 m. Even a partial collapse of the West Antarctic Ice Sheet, by far the smaller of the two, could raise sea level by 2-3 m displacing many millions of people and forcing them to find new places to live inland. It is known that the Antarctic Ice Sheets are losing mass at an increased rate meaning they are heading to a configuration that is smaller than present. To understand how such a configuration is reached it is vital to understand ice sheet behavior at times in the past when they were smaller than present.Computer models of ice sheet behaviour are capable of making predictions but require observations for validation and improvement. One way of doing this is to test whether the models accurately reproduce behaviours observed in reality. The limited areas of Antarctica that are not ice covered have yielded vital information on past ice sheet extents but can only inform on larger than present ice sheet configurations. To understand smaller than present configurations this proposal will access rock that is now covered by ice. This rock retains measureable properties that record when it was last uncovered by the ice sheet allowing the timing and duration of these events to be determined. This project will collect sub-glacial samples from a key region of West Antarctica, the Weddell Sea. In this area recent work using radar has identified internal structures within the ice sheet that suggests it has undergone recent change. Specifically, the data is consistent with the ice sheet having expanded over the last few hundreds of years following a period of time where it was smaller than present. Understanding the current state of the ice sheet and the process that control its behaviour is key to making predictions about how it will respond to human induced global warming. I will use a portable drill system to drill through ice close to present day mountains that protrude above the ice sheet. Over the course of two Antarctic field seasons the drill will be used to collect a series of sub-glacial rock cores that will be returned to laboratories where a novel combination of geochronological methods will be employed to establish if the rock has previously been exposed due to the ice sheet being smaller. By combining different techniques I will improve the constraints that can be obtained; thus not only can it be established if the ice sheet was smaller in the past but also when, and for how long, this was the case. I will then use the new data to evaluate computer models of ice sheet behaviour. These models use combinations of parameter values, representing processes that occur in reality, to produce simulations of ice sheet behaviour through time. By exploring a range a different parameter values large collections of simulations (ensembles) define a range of potential ice sheet simulations that may or may not closely reflect reality. The new geological data is a product of the actual ice sheets behaviour and can be used to sieve out model simulations that are far from reality. Remaining simulations can be scored according to how closely they match the geological data. In this way I will determine what parameters (i.e. what processes) are key to controlling ice sheet behaviour. In this way my project will bring about a step-change in our understanding of processes that control ice sheet behaviour on short geological timescales. Furthermore, the refined ice sheet history and model parameter ranges identified in this project will improve future modelling efforts and lead to more precise predictions of future ice sheet behaviour and associated sea level rise.