Collaborative Research: Submarine Melting of Greenland's Glaciers: What are the relevant ocean dynamics?

知识价值：格陵兰冰川的海底融化已经成为冰盖的一个关键术语？格陵兰岛的质量平衡，并作为一个合理的触发器，为他们最近的加速，这有助于加倍格陵兰岛的贡献，海平面上升。尽管它的重要性，我们对海底融化的理解是有限的，它是目前缺乏或粗略参数化的冰川，冰盖和气候模型。格陵兰岛的冰川以600到800米深的峡湾结束，这些峡湾连接着冰盖的边缘和冰架。冰川终端通常位于海平面以下数百米处，因此暴露在峡湾水柱的厚部分中。最近由两名研究人员从格陵兰东南部的两个大型冰川峡湾收集的独特数据表明，这些峡湾全年充满了来自北极的寒冷、新鲜的沃茨和来自亚热带的温暖、咸的沃茨，它们的不同性质影响着冰缘的环流。此外，船基和停泊的速度测量表明，峡湾的特点是快速，高度可变，剪切流和一个有力的峡湾/大陆架交换，很可能发挥作用，在运输热量的冰川终端。这意味着，海底融化率取决于一套海洋过程，包括外部强迫峡湾环流，峡湾/大陆架交换和大陆架上的属性分布。然而，这些过程如何影响潜艇的融化速率或影响其可变性的细节目前还不清楚，该项目将通过将来自两个峡湾的船基数据和系泊数据的分析与一系列模型相结合来填补这一空白（实验室和数值），以确定控制峡湾特性和环流以及海洋海底融化速率的参数和机制。冰川界面在确定了海底融化速度的控制因素之后，项目调查人员将利用历史海洋学和大气数据，在没有峡湾数据的情况下，确定冰川加速之前的峡湾条件和海底融化速度。气候模式预测将用于估计未来海洋变化对格陵兰岛海底融化的潜在影响？的冰川。与出口冰川动力学、冰-海边界物理学和峡湾环流方面的专家合作，将为这一本质上多学科的问题提供相关学科的专门知识和双向信息交流。这项工作旨在了解新发现的气候系统的线路：海洋的变化可以对格陵兰冰盖的质量平衡产生快速和直接的影响。它是及时的，因为格陵兰正在发生巨大的和不可预测的变化，并且相关，因为冰盖/海洋相互作用目前在气候和冰盖/冰川模型中不存在。它是对南极洲周围冰盖/海洋相互作用研究的补充（两者中研究得较多的），因为格陵兰岛的大规模海洋环流和狭长峡湾的存在都促成了一套独特的相关动力机制。这项工作旨在增加我们对以前被忽视的，这是我们气候系统中的一个重要联系，对我们准确预测海平面上升的能力有着深远的影响，这是一个严重和紧迫的社会问题。预计这项工作的结果将有助于在今后的模型中纳入相关动态（即使是参数化形式），从而改进今后的海平面预测。该工作计划涉及来自互补领域的若干国际专家，因此将有助于促进所涉多学科之间的互动和超越国界。它涉及两名研究生和一名博士后，他们将接触前沿问题和多学科研究团队。该项目的结果将广泛传播给各学科的科学家，正如项目研究所长期组织暑期学校和工作组所证明的那样，并通过不同的媒体渠道向公众传播，正如最近在波士顿科学博物馆、纽约时报、天气频道和意大利国家电视台等场所对调查人员在格陵兰的工作进行的报道所证明的那样。

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.