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

合作研究：格陵兰岛冰川峡湾的海底融化和淡水输出：冰下排放、峡湾地形和陆架特性的作用

• 批准号: 1737759
• 负责人: Patrick Heimbach
• 金额: $ 32.65万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-02-01 至 2018-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1737759&HistoricalAwards=false
• 关键词: Collaborative; Research; Submarine; Melting; Freshwater

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.

格陵兰冰川海底融化的加剧似乎是最近冰川质量损失加速的诱因，也是格陵兰在1992-2000年至2001-2011年期间对海平面上升的贡献翻了两番的原因。尽管它很重要，但目前对海底融化的了解有限，目前冰川、冰盖和气候模型中没有或粗略地反映了这一点。海洋模型开始包括格陵兰岛的淡水排放，但这些淡水何时何地进入大陆架在很大程度上是未知的。在预测海平面上升和格陵兰引起的海洋清新的后果方面，了解控制海底融化和向公海输出淡水的规模和空间分布的动态是关键的一步。一个多层面的办法，包括对现有观测结果的分析、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出口分布对主要控制因素的敏感性，并得出将海底融化速度和淡水出口与大尺度参数之间的关系的基本参数，这些参数包括冰下流量、峡湾大小和地形(即海床)以及大陆架水文和分层。该项目涉及与来自互补领域的国际专家的合作，并将有助于促进所涉及的多学科之间以及超越国界的互动。一名学生和一名博士后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，正如项目组组织暑期学校和工作组的长期记录所表明的那样，并将通过不同的媒体渠道向公众传播，包括极地科学博客。该项目团队最近在格陵兰开展的相关工作被《纽约时报》、天气频道和意大利国家电视台等媒体报道。海洋和格陵兰出口冰川之间的热量和淡水交换发生在连接冰盖边缘与大陆架和大规模北大西洋环流的又长又深的峡湾的顶部，这些冰川通常位于海平面以下数百米处。项目组和其他人最近的工作表明，对于几个理想化或具体的情况，峡湾的温度和层化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、分布和时间具有一级影响。这些结果将通过制定适用于大规模冰盖和气候模型的参数来推广，作为大规模控制的函数，海底融化和相关的淡水出口分布。将执行两项具体任务：1)建立海底融化与相关的淡水从冰川输出及其主要控制之间的动态联系，其中包括：冰下流量的大小和空间分布；大陆架的水文特性和分层；以及峡湾的大小和地形，特别是基床的存在和高度。2)制定了两个互补的参数：一个是海底融化的规模和空间分布与峡湾的地形和大小、陆架分层和冰下流量的函数，将用于冰川和冰盖模型；另一个是来自峡湾的淡水输出的规模和垂直分布，将用于不分解峡湾的大规模海洋和气候模型。该项目包括对现有数据的分析、实验室实验和高分辨率数值模拟。它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 Hewitt)和一名峡湾海洋学家(哥德堡大学的Lars Arneborg)。这项工作的目的是了解新发现的气候系统的“连线”，由于格陵兰边缘正在发生意想不到的大变化，这项工作是及时的。它是对南极洲周围冰盖/海洋相互作用研究(两者中研究较多的)的补充，因为大规模海洋环流和格陵兰狭长峡湾的存在都提供了一套独特的相关动力学机制。