Collaborative Research: Submarine Melting and Freshwater Export in Greenland's Glacial Fjords: The Role of Subglacial Discharge, Fjord Topography and Shelf Properties

格陵兰冰川海底融化的增加似乎是最近加速质量损失的一个合理触发因素，并使格陵兰对海平面上升的贡献从1992-2000年到2001-2011年翻了两番。尽管它的重要性，目前对海底融化的理解是有限的，它是目前缺乏或粗略地表示在冰川，冰盖和气候模型。海洋模型开始包括来自格陵兰岛的淡水排放，但这些淡水何时何地进入大陆架基本上是未知的。了解海底融化和淡水输出到公海的规模和空间分布的动态是预测海平面上升和格陵兰岛引起的海洋淡化后果的关键一步。 一个多方面的方法，包括分析现有的观测结果、一系列实验室实验和高分辨率数值模拟，将力求量化海底融化和淡水输出分布对主要控制因素的敏感性，并得出基本参数，将海底融化率和淡水输出与大规模参数联系起来，包括冰下流量、峡湾大小和地形（即岩床）和大陆架水文地理和分层。该项目涉及与互补领域的国际专家合作，并将有助于促进所涉多学科之间的互动和超越国界。一名学生和一名博士后研究员将接触到一个前沿问题，并在一个多学科的研究团队中工作。该项目的成果将广泛传播给各学科的科学家，项目小组组织暑期学校和工作组的长期记录证明了这一点，并通过不同的媒体渠道，包括关于极地科学的博客，向公众传播。该项目小组最近的格陵兰相关工作已在纽约时报、天气频道和意大利国家电视台等媒体上进行了专题报道。海洋和格陵兰出口冰川之间的热量和淡水交换通常发生在海平面以下数百米处，连接冰盖边缘与大陆架和大规模北大西洋环流的深峡湾。项目小组和其他人最近的工作表明，在几个理想化或具体的情况下，峡湾的温度和分层，以及夏季冰川底部表面融化的排放（冰下排放）对海底融化的规模、分布和时间有一级影响。这些结果将通过制定参数化，适用于大规模的冰盖和气候模型，海底融化和相关的淡水输出分布作为一个功能的大规模控制。将执行两项具体任务：1）在海底融化和冰川的相关淡水输出及其主要控制因素之间建立动态联系，其中包括：冰下排放的规模和空间分布;水文特性和大陆架分层;峡湾的大小和地形，特别是岩床的存在和高度。2)制定两个互补的参数化：一个是海底融化的幅度和空间分布，作为峡湾地形和大小、大陆架分层和冰下流量的函数，用于冰川和冰盖模型;另一个是峡湾淡水输出的幅度和垂直分布，用于无法解决峡湾问题的大规模海洋和气候模型。该项目涉及现有数据分析、实验室实验和高分辨率数值模拟。这项工作将与两名国际专家合作进行：一名冰川水文学家（牛津大学的Ian休伊特）和一名峡湾海洋学家（哥德堡大学的Lars Arneborg）。这项工作旨在了解我们气候系统的新发现的“布线”，并且由于格陵兰岛边缘正在发生的巨大和意外的变化而及时。这是对南极洲周围冰盖/海洋相互作用研究的补充（两者中研究较多的），因为大规模海洋环流和格陵兰狭长峡湾的存在提供了一套独特的相关动力机制。

Increased submarine melting of Greenland's glaciers has emerged as a plausible trigger for their recent acceleration in mass loss and for quadrupling Greenland's contribution to sea-level rise from 1992-2000 to 2001-2011. Notwithstanding its importance, current understanding of submarine melting is limited and it is presently absent or crudely represented in glacier, ice sheet and climate models. Ocean models are beginning to include freshwater discharge from Greenland, but where and when this freshwater enters the continental shelves is largely unknown. Understanding the dynamics that govern the magnitude and spatial distribution of both submarine melt and freshwater export to the open ocean is a key step in projecting sea level rise and the consequences of the Greenland-induced ocean freshening. A multifaceted approach that includes the analysis of existing observations, a series of laboratory experiments and high-resolution numerical simulations will seek to quantify the sensitivity of submarine melting and freshwater export distribution to the dominant controls, and to derive basic parameterizations that relate submarine melt rates and freshwater export to large-scale parameters including subglacial discharge, fjord size and topography (i.e. sill), and continental shelf hydrography and stratification. The project involves collaborations with international experts from complementary fields and will contribute to fostering interactions between the multiple disciplines involved and beyond national boundaries. One student and one post-doctoral fellow will be exposed to a cutting-edge problem and work within a multidisciplinary team of researchers. Results from this project will be widely disseminated to scientists across disciplines, as demonstrated by the project team's long track record of organizing summer schools and working groups, and to the public through different media outlets, including a blog on polar science. Recent Greenland related work by the project team has been featured in the New York Times, the Weather Channel and Italian National Television, amongst other media.The exchange of heat and freshwater between the ocean and Greenland's outlet glaciers, typically grounded hundreds of meters below sea level, occurs at the head of long, deep fjords that connect the ice sheet margins to the continental shelves and the large-scale North Atlantic circulation. Recent work by the project team, and others, has shown, for several idealized or specific cases, that the fjord's temperature and stratification, as well as the summer discharge of surface melt at the base of the glacier (subglacial discharge) have a first order impact on the magnitude, distribution and timing of submarine melting. These results will be generalized by formulating parameterizations, suitable for large-scale ice sheet and climate models, of submarine melting and associated freshwater export distributions as a function of large-scale controls. Two specific tasks will be carried out: 1) Establishing dynamical links between submarine melting, and the associated freshwater export from the glacier, and its dominant controls, which include: the magnitude and spatial distribution of subglacial discharge; hydrographic properties and stratification on the continental shelf; and fjord size and topography, in particular the presence and height of a sill. 2) Formulating two complementary parameterizations: one for the magnitude and spatial distribution of submarine melting as a function of the fjord's topography and size, the shelf stratification and the subglacial discharge, to be used in glacier and ice sheet models; and one for the magnitude and vertical distribution of the freshwater export from the fjords to be used in large scale ocean and climate models which do not resolve the fjords. This project involves the analysis of existing data, laboratory experiments and high-resolution numerical simulations. It will be carried out in collaboration with two international experts: a glacial hydrologist (Ian Hewitt at the University of Oxford) and a fjord oceanographer (Lars Arneborg at the University of Goteborg). The work is aimed at understanding a newly discovered "wiring" of our climate system and is timely because of the large and unanticipated changes that are occurring at Greenland's margins. It is complementary to the study of ice sheet/ocean interactions around Antarctica (the more studied of the two) since both the large-scale ocean circulation and the presence of narrow, long fjords in Greenland contribute a unique set of relevant dynamical mechanisms.