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: 1434149
• 负责人: Patrick Heimbach
• 金额: $ 47.12万
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-11-01 至 2017-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1434149&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.

格陵兰冰川的潜艇融化增加已成为它们最近加速质量损失的合理触发因素，以及格陵兰岛对1992 - 2000年至2001 - 2011年海平面上升的四倍贡献。尽管它的重要性，但目前对海底熔化的理解是有限的，目前在冰川，冰盖和气候模型中没有或粗鲁代表。海洋模型开始包括从格陵兰岛的淡水排放，但是在淡水进入大陆货架的何时何地，在很大程度上尚不清楚。了解管理海洋水平融化和淡水出口到开阔海洋的动态和空间分布是预测海平面上升的关键步骤以及格陵兰引起的海洋新鲜趋势的后果。 一种多方面的方法，包括分析现有观察结果，一系列实验室实验和高分辨率数值模拟将寻求量化潜艇熔融和淡水出口分布的敏感性与主导控制的敏感性，并得出基本参数，以将海底融化速率和淡水出口与大型级别的列表相关联，i.门槛），以及大陆架水文和分层。该项目涉及与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与国家边界之外的互动。一名学生和一名博士后研究员将面临一个尖端的问题，并在多学科研究人员团队中工作。该项目的结果将被广泛传播给跨学科的科学家，如项目团队的组织暑期学校和工作组的长期记录所证明，并通过不同的媒体（包括Polar Science的博客）向公众提供。该项目团队最近与格陵兰的工作相关的工作在《纽约时报》，《天气频道》和《意大利国家电视台》中以及其他媒体中都有介绍。海洋和格陵兰岛的出口冰川之间的热量和淡水交换，通常在海平面以下数百米，这是在长长的高处，在冰上牌片和大规模的杂物范围内，发生在大型冰上板块上。项目团队和其他人的最新工作表明，对于几种理想化或特定情况，峡湾的温度和分层以及冰川底部的表面熔体（冰川下放电）的夏季排放对海底熔化的大小，分布和时间影响。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化，海底熔化和相关的淡水出口分布作为大规模控制的函数。将执行两个特定的任务：1）建立海底熔化之间的动态联系，与冰川相关的淡水导出及其主要控制剂，其中包括：亚冰块排放的大小和空间分布；大陆架上的水文特性和分层；以及峡湾的大小和地形，特别是门槛的存在和高度。 2）制定两个互补的参数化：一个用于海底熔化的大小和空间分布作为峡湾的地形和大小的函数，架子分层和冰川下放电，用于冰川和冰盖模型；其中一个是从峡湾出口淡水的大小和垂直分布，该峡湾用于大规模的海洋和气候模型，这些模型无法解决峡湾。该项目涉及对现有数据，实验室实验和高分辨率数值模拟的分析。它将与两位国际专家合作进行：冰川水文学家（牛津大学的Ian Hewitt）和峡湾海洋学家（哥德堡大学的Lars Arneborg）。这项工作旨在理解我们气候系统的新发现的“接线”，并且由于格陵兰岛边缘发生了巨大而意外的变化而及时。这是对南极周围的冰盖/海洋相互作用的研究（两者中研究越多），因为大规模的海洋循环和格陵兰岛中狭窄的长峡湾的存在都造成了一套独特的相关动力学机制。