Ocean Forcing of Ice Sheet Evolution in the Marine Basins of East Antarctica

目前，世界各地的海平面都在上升，洪水和海岸侵蚀加剧威胁着居住在海岸附近的人口。评估未来的威胁需要更好地了解驱动地球冰盖变化的物理过程。最近的观测表明，在冰盖边缘附近的一些关键地点，迅速变薄目前正使全球海平面每年上升1.3毫米，而且这一数字近年来急剧上升。大部分注意力都集中在格陵兰岛和南极西部冰盖上，那里的冰盖变薄范围最广，速度最快。人们普遍认为，罪魁祸首是与冰盖接触的海水变暖。浮冰架和潮汐冰川的融化加剧，导致它们变薄，迫使接地线或产冰前沿后退，使内陆冰更快地流向海岸。虽然目前南极东部冰盖（EAIS）变薄的范围和剧烈程度远低于在南极西部观测到的情况，但东部冰盖的很大一部分位于海平面以下，因此可能容易受到冰架变薄、接地线退缩和冰流加速的相同过程的影响。此外，与南极洲西部类似的海洋强迫可能影响东亚系统的海洋部分。在这两个地区，南极环极流将温暖的环极深水（CDW）带到靠近大陆斜坡的地方。虽然CDW可能已经影响了Totten冰川，该冰川现在在整个EAIS上显示出最强烈的变薄特征，但该地区的其他冰川，最明显的是Mertz冰川，可能受到当地冰融区密集的冷架水形成的保护。然而，我们对大陆架的海洋学知识，以及在浮冰架下循环并与之相互作用的水域的知识，目前还不足以理解是什么过程推动了托滕冰川的变化，以及它的近邻，如默茨冰川可能有多脆弱。因此，我们预测这些出口冰川系统未来行为的能力受到严重限制。为了解决这一缺陷，该项目将对浮冰架下发生的关键过程进行观测，以确定冰下地形和空洞外的海洋学强迫如何控制冰架融化的速度。进行必要观测的关键工具是一个自主水下航行器（Autosub3），其配置和运行方式类似于之前一次非常成功的活动，在那次活动中，它在南极洲西部松树岛冰川60公里长的浮舌下完成了500公里的跟踪观测。我们将使用这些数据来验证冰架下海洋环流的数值模型，并使用计算的融化速率来强迫冰流的数值模型，以便研究冰川对一系列气候强迫的响应。对Totten和Mertz冰川下的海洋环流和融化的详细了解将有助于深入了解与格陵兰岛和南极洲许多其他地点相关的海洋-冰相互作用，并将推进我们对冰盖排放及其未来对海平面上升的影响的不断发展的知识。这项工作是集中研究东南极洲海洋与冰架相互作用的密集观测活动的一部分。澳大利亚、法国、英国和美国机构的研究小组协调进行了海洋和冰川的跨学科合作研究。

Sea levels around the world are currently rising, threatening populations living near the coast with flooding and increased coastal erosion. Evaluating the future threat requires a better understanding of the physical processes responsible for driving changes in the Earth's ice sheets. Recent observations show that in some key locations around the ice sheets' margins, rapid thinning is currently contributing 1.3 mm/yr to global sea level rise, and that that number has risen dramatically in recent years. Most of the attention has been focussed on the Greenland and West Antarctic ice sheets, where the thinning is most widespread and rapid. It is generally assumed that the culprit is a warming of the ocean waters that come into contact with the ice sheet. Increased melting of the floating ice shelves and tidewater glaciers has caused them to thin, forcing the grounding line or calving front to retreat and allowing the inland ice to flow faster towards the coast.Although thinning of the East Antarctic Ice Sheet (EAIS) is currently much less widespread and dramatic than that observed in West Antarctica, a large sector of the EAIS is grounded below sea level and is thus potentially vulnerable to the same process of ice shelf thinning, grounding line retreat and ice stream acceleration. In addition, analogous ocean forcing to that in West Antarctica could influence the marine-based sector of the EAIS. In both regions the Antarctic Circumpolar Current brings warm Circumpolar Deep Water (CDW) close to the continental slope. While CDW may already be influencing Totten Glacier, which now shows the strongest thinning signature over the entire EAIS, other glaciers in the region, most notably Mertz Glacier, may be protected by the formation of dense, cold Shelf Water in local polynyas. However, our knowledge of the oceanography of the continental shelf and of the waters that circulate beneath and interact with the floating ice shelves is presently insufficient to understand what processes are driving the change on Totten Glacier and how vulnerable its near neighbours such as Mertz Glacier might be. Our ability to project the future behaviour of these outlet glacier systems is severely limited as a result.To address this deficiency, this project will make observations of the critical processes that take place beneath the floating ice shelves, to determine how the topography beneath the ice and the oceanographic forcing from beyond the cavity control the rate at which the ice shelves melt. The key tool with which the necessary observations will be made is an Autonomous Underwater Vehicle (Autosub3), configured and run in a manner analogous to that used for an earlier, highly successful campaign in which it completed 500 km of along-track observations beneath the 60-km long floating tongue of Pine Island Glacier in West Antarctica. We will use these data to validate a numerical model of ocean circulation beneath the ice shelves and use the computed melt rates to force a numerical model of ice flow, in order to investigate the response of the glaciers to a range of climate forcing. A detailed understanding of ocean circulation and melting beneath Totten and Mertz glaciers will generate insight into ocean-ice interactions that will be relevant to many other sites in Greenland and Antarctica, and will advance our developing knowledge of ice sheet discharge and its future effect on sea-level rise.This work forms part of an intensive observational campaign focused on ocean-ice shelf interactions in East Antarctica. The collaborative, interdisciplinary effort consists of coordinated ocean and glacier studies conducted by groups at Australian, French, UK and US institutions.