Inland Migration of Crevasses on the Greenland Ice Sheet

格陵兰冰原裂缝向内迁移

• 批准号: 1339465
• 负责人: Gordon Hamilton
• 金额: $ 7.73万
• 依托单位: University of Maine
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-05-01 至 2015-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1339465&HistoricalAwards=false
• 关键词: Inland; Migration; Crevasses; Greenland; Ice

The surface of the Greenland Ice Sheet experienced unprecedented melting during the 2012 summer, capping a decade of summers with above average melt extent and duration. Melting covered ~97% of the ice sheet during its 2012 peak and lasted almost two months longer than the 1979-2011 average. This sustained intensified melt has led to down-wasting of the surface, and has also played a role in accelerated ice flow by supplying runoff to enhance subglacial sliding. Altogether, melting has accounted for about half of the ice sheet's increased contribution to sea level rise in the last decade. Reports of surface cracks appearing at hitherto crevasse-free locations on the ice sheet have coincided with the intensified melt. These cracks can act as nascent pathways for the delivery of surface meltwater to the ice sheet bed, which might promote the inland propagation of accelerated ice flow and may lead to additional surface cracking. Their occurrence also constitutes a potential hazard to safe logistic operations (aircraft landing, surface traversing). Cracks appeared at Raven Camp, Greenland, during the peak melt event in 2012 and led to a temporary halt in U.S. military aircraft training activities. New cracks also appeared on the route used by the Greenland Inland Traverse (GrIT) in northwest Greenland and may severely impact future traversing activities. Two hypotheses have been proposed to explain the occurrence of the cracks: one invokes the sudden drainage of a firn aquifer beneath Raven and the resulting subsidence of the overlying firn to form the cracks; the other hypothesis involves the downstream acceleration of ice flow leading to an increase in strain rates and the formation of true crevasses. If the second hypothesis is correct, crack sizes and their frequency of occurrence are likely to increase in the future. This proposal will test those hypotheses by carrying out global positioning system (GPS) surveys of ice motion and strain rate, and a detailed assessment of crevasse distributions through time using very high-resolution satellite imagery. Improved predictions of the ice sheet's response to future climate forcings as well as the ability to make informed long-term planning decisions about logistic activities in Greenland require an understanding of the processes responsible for the appearance of new surface cracks and an assessment of the likelihood that their distribution will increase with time.

格陵兰冰盖表面在 2012 年夏季经历了前所未有的融化，结束了十年来融化程度和持续时间高于平均水平的夏季。在 2012 年高峰期，融化覆盖了约 97% 的冰盖，持续时间比 1979-2011 年平均水平长了近两个月。这种持续加剧的融化导致了地表的向下消耗，并且还通过提供径流来增强冰下滑动，从而起到了加速冰流的作用。总的来说，过去十年冰盖对海平面上升的贡献大约有一半是由融化造成的。有关冰原上迄今为止无裂缝位置出现表面裂缝的报告与加剧的融化同时发生。这些裂缝可以作为将表面融水输送到冰盖床的新生通道，这可能会促进加速冰流向内陆传播，并可能导致额外的表面裂缝。它们的出现也对安全物流操作（飞机着陆、地面穿越）构成潜在危险。 2012年融化高峰期间，格陵兰岛乌鸦营出现裂缝，导致美国军用飞机训练活动暂时停止。格陵兰岛西北部的格陵兰内陆穿越（GrIT）所使用的路线也出现了新的裂缝，可能会严重影响未来的穿越活动。人们提出了两种假设来解释裂缝的出现：一种是由于雷文下方的冷杉含水层突然排水，导致上覆的冷杉下沉而形成裂缝；另一种是由于雷文地下的冷杉含水层突然排水，导致上覆的冷杉下沉而形成裂缝；另一种是由于雷文地下的冷杉含水层突然排水，导致上覆的冷杉下沉而形成裂缝。另一种假设涉及冰流的下游加速，导致应变率增加并形成真正的裂缝。如果第二个假设是正确的，裂纹尺寸及其发生频率在未来可能会增加。该提案将通过对冰运动和应变率进行全球定位系统（GPS）调查，以及使用极高分辨率卫星图像对裂缝分布随时间的详细评估来测试这些假设。为了更好地预测冰盖对未来气候强迫的反应，以及就格陵兰岛的物流活动做出明智的长期规划决策，需要了解导致新表面裂缝出现的过程，并评估其分布随时间增加的可能性。