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.

格陵兰岛冰川海底融化的增加似乎是其最近质量损失加速以及格陵兰岛对海平面上升的贡献从1992-2000年到2001-2011年翻了两番的一个合理触发因素。尽管它很重要，但目前对海底融化的了解仍然有限，而且目前在冰川、冰盖和气候模型中还没有或粗略地体现了这一点。海洋模型开始包括格陵兰岛的淡水排放，但这些淡水在何时何地进入大陆架的情况在很大程度上尚不清楚。了解控制海底融化和淡水向公海输出的幅度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水化后果的关键一步。 包括现有观测分析、一系列实验室实验和高分辨率数值模拟在内的多方面方法将寻求量化海底融化和淡水出口分布对主导控制的敏感性，并得出与海底融化速率相关的基本参数化淡水输出到大尺度参数，包括冰下流量、峡湾大小和地形（即窗台）以及大陆架水文学和分层。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个学科之间和跨国界之间的互动。一名学生和一名博士后将接触前沿问题，并在多学科研究团队中工作。该项目的结果将广泛传播给跨学科的科学家，正如项目团队组织暑期学校和工作组的长期记录所证明的那样，并通过不同的媒体渠道（包括极地科学博客）向公众传播。该项目团队最近与格陵兰岛相关的工作已在《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。海洋与格陵兰岛出口冰川之间的热量和淡水交换，这些冰川通常位于海下数百米处水平，发生在长而深的峡湾的顶部，将冰盖边缘与大陆架和大规模的北大西洋环流连接起来。项目团队和其他人最近的工作表明，对于几个理想化或具体的情况，峡湾的温度和分层，以及冰川底部表面融化的夏季排放（冰下排放）具有一阶对海底融化的程度、分布和时间的影响。这些结果将通过制定适合大规模冰盖和气候模型的参数化、海底融化和相关淡水出口分布作为大规模控制的函数来推广。将执行两项具体任务： 1）建立海底融化和相关的冰川淡水输出及其主要控制之间的动态联系，其中包括：冰下排放的大小和空间分布；大陆架的水文特性和分层；峡湾的大小和地形，特别是窗台的存在和高度。 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、陆架分层和冰下流量的函数，用于冰川和冰盖模型；另一项是关于峡湾淡水出口的大小和垂直分布，用于大型海洋和气候模型，但不能解决峡湾问题。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。该项目将与两位国际专家合作进行：一位冰川水文学家（牛津大学的伊恩·休伊特）和一位峡湾海洋学家（哥德堡大学的拉斯·阿内堡）。这项工作旨在了解我们气候系统新发现的“线路”，并且由于格陵兰岛边缘正在发生巨大且意想不到的变化，因此是及时的。它是对南极洲周围冰盖/海洋相互作用的研究（两者中研究较多的一个）的补充，因为大规模的海洋环流和格陵兰岛狭窄而长的峡湾的存在都贡献了一套独特的相关动力机制。