Collaborative Research: Submarine Melting of Greenland's Glaciers: What are the Relevant Ocean Dynamics?

学术价值：格陵兰冰川的海底融化已经成为冰盖-S物质平衡中的一个关键术语，并似乎是它们最近加速的触发因素，这使得格陵兰对海平面上升的贡献翻了一番。尽管它很重要，但我们对海底融化的理解是有限的，目前在冰川、冰盖和气候模型中没有它或被粗略地参数化。格陵兰岛的潮水冰川末端大约600到800米深，连接冰盖边缘和大陆架的长峡湾。冰川末端通常在海平面以下几百米处搁浅，因此暴露在峡湾水柱的厚厚部分中。两名研究人员最近从格陵兰岛东南部的两个大型冰川峡湾收集的独特数据显示，这些峡湾常年充满源于北极的寒冷淡水和源于亚热带的温暖咸水，它们的不同性质影响着冰缘的循环。此外，基于船舶和系泊的速度测量表明，峡湾的特点是水流快速、高度可变、剪切，峡湾/陆架交换强烈，这可能在将热量输送到冰川终端方面发挥作用。这意味着海底融化速率取决于一系列海洋过程，包括外部强迫峡湾环流、峡湾/陆架交换和陆架上属性的分布。然而，这些过程如何影响海底融化速率或其可变性的细节目前尚不清楚。该项目将通过将对两个峡湾的船舶和系泊数据的分析与一系列模型(实验室和数值)相结合来填补这一空白，以确定控制峡湾中的特性和环流以及海洋/冰川界面上的海底融化速度的参数和机制。在确定了海底融化速度的控制之后，项目调查人员将使用历史的海洋和大气数据来确定没有峡湾数据时冰川加速之前一段时间的峡湾条件和海底融化速度。气候模型预测将被用来估计未来海洋变化对格陵兰-S冰川海底融化的潜在影响。与出口冰川动力学、冰-海边界物理和峡湾环流方面的专家合作，将为这一本质上的多学科问题提供相关学科的专门知识和双向信息交流。这项拟议的工作旨在理解一个新发现的气候系统的联系：海洋的可变性可以对格陵兰的冰盖质量平衡产生快速而直接的影响。这是及时的，因为格陵兰正在发生的巨大和不可预测的变化，以及相关的，因为目前气候和冰盖/冰川模型中没有冰盖/海洋相互作用。它是对南极洲周围冰盖/海洋相互作用研究(两者中研究较多的一个)的补充，因为大规模海洋环流和格陵兰狭长峡湾的存在都贡献了一套独特的相关动力学机制。更广泛的影响：这项工作旨在增加我们对气候系统中以前被忽视的重要联系的理解，这种联系对我们准确预测海平面上升的能力具有深远的影响--这是一个严重而紧迫的社会关切问题。预计这项工作的结果将有助于在未来的模式中纳入相关的动态(即使是参数形式)，并因此有助于改进未来的海平面预测。该工作计划涉及来自互补领域的几名国际专家，因此将有助于促进所涉多学科之间以及超越国界的互动。它涉及两名研究生和一名博士后，他们将接触到一个前沿问题和多学科的研究团队。该项目的成果将广泛传播给不同学科的科学家，如私人投资机构组织暑期学校和工作组的长期轨迹所表明的那样，并通过不同的媒体向公众传播，如最近对调查人员在格陵兰的工作的报道所表明的那样，这些场所包括波士顿的科学博物馆、纽约时报、天气频道和意大利国家电视台。

Intellectual Merit: Submarine melting of Greenland's glaciers has emerged as a key term in the ice sheet?s mass balance and as a plausible trigger for their recent acceleration, which contributed to doubling Greenland's contribution to sea-level rise. Notwithstanding its importance, our understanding of submarine melting is limited and it is presently absent or crudely parameterized in glacier, ice sheet and climate models. Greenland's tidewater glaciers end in about 600 to 800 m deep, long fjords that connect the margins of the ice sheet to the shelf. The glaciers termini are typically grounded several hundreds of meters below sea-level and, as such, are exposed to a thick portion of the fjord's water column. Unique data, recently collected by two of the investigators, from two large glacial fjords in south-east Greenland show that these are filled year-round with cold, fresh waters of Arctic origin and warm, salty waters of subtropical origin whose different properties influence the circulation at the ice-edge. Furthermore, ship-based and moored velocity measurements show that the fjords are characterized by fast, highly variable, sheared flows and a vigorous fjord/shelf exchange which, likely, play a role in transporting heat to the glaciers termini. The implication is that submarine melt rates depend on a suite of oceanic processes including externally forced fjord circulations, fjord/shelf exchange and the distribution of properties on the shelf. Yet, the details of how these processes may contribute to the submarine melt rate or affect its variability are presently unknown.This project will fill this gap by combining the analysis of ship-based and moored data from the two fjords with a hierarchy of models (laboratory and numerical) to identify the parameters and mechanisms which control the properties and circulation in the fjords and the rate of submarine melting at the ocean/glacier interface. Having identified the controls on the submarine melt rate, the project investigators will then use historical oceanographic and atmospheric data to determine fjord conditions and submarine melt rates for the period preceding the acceleration of the glaciers when no fjord data are available. Climate model predictions will be used to estimate the potential impact of future oceanic variability on submarine melting of Greenland?s glaciers. Collaborations with experts in outlet glacier dynamics, the physics of the ice-ocean boundary and fjord circulations will provide expertise in related disciplines and a two-way exchange of information for this intrinsically multidisciplinary problem. The work proposed is aimed at understanding a newly discovered wiring of the climate system: that ocean variability can have a rapid and direct impact on the Greenland's ice sheet mass balance. It is timely because of the large and unpredicted changes that are occurring in Greenland and relevant because ice sheet/ocean interactions are presently absent from climate and ice sheet/glacier models. 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.Broader Impacts: This work seeks to increase our understanding of a previously overlooked, important connection in our climate system which has profound implications for our ability to accurately predict sea-level rise - an issue of grave and immediate societal concern. It is expected that results from this work will contribute to the inclusion of the relevant dynamics (even if in parameterized form) in future models and, as such, lead to the improvement of future sea level predictions. The work plan involves several international experts from complementary fields and, as such, will contribute to fostering interactions between the multiple disciplines involved and beyond national boundaries. It involves two graduate students and one post-doc who will be exposed to a cutting-edge problem and multidisciplinary team of researchers. Results from this project will be widely disseminated to scientists across disciplines, as demonstrated by the PIs long-track of organizing summer schools and working groups, and to the public through different media outlets, as shown by the recent coverage of the investigators' Greenland work in venues that include the Museum of Science in Boston, the New York Times, the Weather Channel and Italian National Television.