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

南极冰盖（东南极洲和西南极洲）拥有足够的淡水，使全球海平面上升60米以上。即使是南极西部冰盖的部分崩溃，也可能使海平面上升2-3米，使数百万人流离失所，迫使他们在内陆寻找新的居住地。众所周知，南极冰盖正在以更快的速度失去质量，这意味着它们正在走向比现在更小的配置。要了解这样的配置是如何达到的，了解冰盖的行为在过去的时候，他们比现在小是至关重要的。冰盖行为的计算机模型能够做出预测，但需要观察验证和改进。其中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。南极洲有限的未被冰层覆盖的地区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的信息。为了了解比现在更小的构造，这项提议将访问现在被冰覆盖的岩石。这块岩石保留了可测量的属性，记录了它最后一次被冰盖覆盖的时间，从而可以确定这些事件的时间和持续时间。该项目将从南极洲西部的一个关键地区威德尔海收集冰下样本。在这一领域，最近的工作使用雷达确定了冰盖内部的结构，这表明它最近经历了变化。具体来说，这些数据与冰盖在过去几百年中扩大的情况是一致的，在过去的一段时间里，冰盖比现在小。了解冰盖的当前状态以及控制其行为的过程是预测它将如何应对人类引起的全球变暖的关键。我将使用一个便携式钻机系统钻穿冰接近今天的山脉突出以上的冰盖。在两个南极野外季节的过程中，钻头将被用来收集一系列冰下岩石核心，这些核心将被送回实验室，在那里将采用一种新的地质年代学方法组合，以确定岩石是否先前由于冰盖较小而暴露。通过结合不同的技术，我将改进可以获得的约束条件;因此，不仅可以确定过去冰盖是否较小，而且还可以确定何时以及持续多久。然后，我将使用新的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，以模拟冰盖随时间的行为。通过探索不同参数值的范围，大量的模拟（集合）定义了一系列可能的冰盖模拟，这些模拟可能会或可能不会密切反映现实。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重大变化。此外，本项目中确定的精确冰盖历史和模型参数范围将改进未来的建模工作，并对未来冰盖行为和相关的海平面上升进行更精确的预测。

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.