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。这似乎是它们最近加速的一个诱因，而加速导致格陵兰岛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了解有限，目前在冰川、冰盖和气候模式中缺乏或粗略地参数化了它。格陵兰的潮汐冰川在600到800米深的峡湾中结束，这些峡湾连接着冰盖的边缘和冰架。冰川的终点站通常位于海平面以下几百米的地方，因此暴露在峡湾的一层厚厚的水柱中。两位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表明，这些峡湾全年都充满了来自北极的寒冷淡水和来自亚热带的温暖咸水，它们的不同性质影响着冰缘的环流。此外，基于船只和系泊的速度测量表明，峡湾的特点是快速、高度可变、剪切流动和峡湾/大陆架的强烈交换，这可能在将热量输送到冰川末端方面发挥作用。这意味着海底融化速度取决于一系列海洋过程，包括外部强迫峡湾环流、峡湾/大陆架交换和大陆架上的性质分布。然而，这些过程如何促进海底融化速度或影响其变异性的细节目前尚不清楚。该项目将通过对两个峡湾的船舶和系泊数据的分析与模型层次（实验室和数值）相结合来填补这一空白，以确定控制峡湾特性和环流以及海洋/冰川界面海底融化速度的参数和机制。在确定了对海底融化速度的控制之后，项目调查人员将使用历史海洋学和大气数据来确定冰川加速之前（没有峡湾数据可用）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。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业知识和双向信息交流。这项研究的目的是了解气候系统的一个新发现：海洋的变化会对格陵兰岛冰盖的质量平衡产生迅速而直接的影响。这是及时的，因为格陵兰岛正在发生巨大的、不可预测的变化，也是相关的，因为目前在气候和冰盖/冰川模式中不存在冰盖/海洋的相互作用。它是对南极洲周围冰盖/海洋相互作用研究的补充（两者中研究较多），因为大尺度海洋环流和格陵兰岛狭长的峡湾的存在都提供了一套独特的相关动力机制。更广泛的影响：这项工作旨在增加我们对气候系统中一个以前被忽视的重要联系的理解，这个联系对我们准确预测海平面上升的能力有着深远的影响——海平面上升是一个严重而紧迫的社会问题。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力学（即使是以参数化的形式），并因此导致未来海平面预测的改进。这项工作计划涉及来自互补领域的几位国际专家，因此将有助于促进所涉及的多个学科之间和超越国界的相互作用。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研究团队。该项目的成果将广泛传播给各学科的科学家，如ppi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，如最近调查人员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格陵兰工作的报道所表明的那样。

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.