Assessing the sensitivity of major East Antarctic outlet glaciers to recent and future changes in the ocean-climate system

由于温室气体浓度的增加，地球的大气和海洋正在变暖。当地球变暖时，冰川融化，储存在陆地上的冰流入海洋，导致海平面上升。在过去的几十年里，测量表明海平面每年上升约3毫米，这是由于温暖的海水和冰川径流的扩张。在20世纪，冰川融化对海平面的贡献主要是小的山地冰川和冰帽，但现在人们知道，格陵兰岛和南极洲的巨大冰盖对海平面的贡献也同样大，而且这种贡献正在加速。冰盖对海平面产生影响的主要方式之一（尤其是在南极洲，但也包括格陵兰岛）是通过快速流动的出口冰川将冰从内部转移到边缘，在那里断裂成冰山。最近的测量（主要是利用卫星观测）表明，许多出水口冰川正在变薄和退缩，在某些情况下，它们的流动也在加速。这有助于解释为什么它们的冰流量在增加。冰川出口的这些变化是复杂的，但科学家们认为，它们是由海洋温度升高引起的，在某些情况下，是由冰川出口下面的景观引起的，特别是当它们流经海平面以下的深谷，并在冰下深入内陆时。最显著的变化发生在格陵兰岛和南极洲西部，这两个地区分别储存了相当于6米和4米的海平面。因此，与较小的山地冰川不同，出口冰川的变化可能会在很短的时间尺度内（根据一些预测，只有几个世纪）使全球海平面上升几米。正是由于这个原因，许多研究的目标是监测格陵兰岛和南极洲西部的出口冰川。然而，南极洲的大部分冰都储存在南极洲东部，那里的海平面约为53米。因此，对南极东部冰盖（EAIS）出口冰川的测量如此之少，这可能令人惊讶，但这可能是因为传统上认为它比南极洲西部稳定得多。然而，最近发现的证据表明，当过去气候稍微变暖时，EAIS的某些部分，特别是那些位于深谷和盆地之上的部分，可能会急剧退缩。此外，对这些地区的一两个冰川的观测表明，它们也在变薄和退缩，类似于格陵兰岛和南极洲西部的冰川。因此，虽然数量不多，但越来越多的证据表明，东亚的某些地区可能也容易受到全球变暖的影响。不幸的是，我们没有足够的观测来确切地知道东南极洲不同地区正在发生什么，而且它的出口冰川是否对海洋和/或大气的变化敏感还有很大的不确定性。该项目旨在专门解决这种不确定性。我们将使用卫星测量来确定来自东南极洲不同地区的一些最大和最重要的出口冰川最近的变化。这将告诉我们哪里发生了最剧烈的变化，哪些地区更稳定。然后，我们将使用计算机模型来观察如果未来空气或海洋温度升高会发生什么样的变化。这将告诉我们哪些冰川是最敏感的，以及它们在未来几个世纪对海平面的影响。即使在冰川目前稳定的地方，重要的是要知道在它们做出反应之前气候需要发生多大的变化。这一新发现对于帮助政府规划未来海平面的变化至关重要。

The Earth's atmosphere and oceans are warming as a result of increased concentrations of greenhouse gases. Glaciers melt when the Earth warms and water that was stored as ice on land runs off into the ocean and increases sea-level. Over the last few decades, measurements have shown that sea-level is increasing by around 3 millimetres per year, and that this is due to the expansion of the warmer ocean water and the runoff from glaciers. In the 20th century, the sea-level contribution from melting ice was dominated by small mountain glaciers and ice caps, but it is now known that the vast ice sheets in Greenland and Antarctica are contributing an equally large amount to sea level and that their contribution is accelerating. One of the main ways in which ice sheets contribute to sea-level (especially in Antarctica, but also in Greenland) is through rapidly-flowing outlet glaciers that transfer ice from the interior to the margins, where it breaks off as icebergs. Recent measurements, mostly using observations from satellites, have shown that many outlet glaciers are thinning and retreating and, in some cases, their flow is also accelerating. This helps explain why their ice discharge is increasing. These changes in outlet glaciers are complex, but scientists think that they are caused by warmer ocean temperatures and, in some cases, by the landscapes underneath the outlet glaciers, especially if they flow through deep valleys that are below sea level and get deeper inland under the ice. The most dramatic changes have been observed in Greenland and West Antarctica, which store around 6 and 4 m of sea-level equivalent, respectively. Thus, unlike smaller mountain glaciers, changes in outlet glaciers could contribute several metres to global sea-level, possibly over quite short time-scales (just a few centuries according to some predictions). It is for this reason that a lot of research is aimed at monitoring outlet glaciers in Greenland and West Antarctica. Most of the ice in Antarctica is, however, stored in East Antarctica, which holds a sea-level equivalent of around 53 m. It is perhaps surprising, therefore, that there are so few measurements of outlet glaciers in the East Antarctic Ice Sheet (EAIS), but this is probably because it was traditionally thought to be much more stable than West Antarctica. Recently, however, evidence has been uncovered which indicates that parts of the EAIS, especially those parts that that overlie deep valleys and basins, might have retreated quite dramatically when climate was slightly warmer in the past. Moreover, observations of just one or two glaciers in these same regions indicates that they are also thinning and retreating, similar to those in Greenland and West Antarctica. Thus, there is a small but growing body of evidence suggesting that some parts of the EAIS might also be vulnerable to global warming. Unfortunately, we do not have enough observations to know exactly what is happening in different parts of East Antarctica and there is a large amount of uncertainty about whether its outlet glaciers are sensitive to changes in the ocean and/or atmosphere. This project has been designed to specifically address this uncertainty. We will use satellite measurements to determine recent changes on some of the largest and most important outlet glaciers from different regions of East Antarctica. This will tell us where the most dramatic changes have taken place and which areas are more stable. We will then use a computer model to see what kind of changes would take place if air or ocean temperatures increase in the future. This will tell us which glaciers are most sensitive and what their contribution to sea level might be over the next few centuries. Even where glaciers are currently stable, it is important to know by how much climate would need to change before they might react. This new knowledge is vitally important to help governments plan for future changes in sea-level.