Investigating the exchange flow in glacial fjords through an estuarine lens

随着格陵兰冰盖质量的加速丧失，对海洋-冰川相互作用的不了解导致了海平面上升预测的不确定性。虽然在全球气候模式中无法解决峡湾问题，但为了研究海洋变暖对冰川退缩和冰川淡水增加对海洋环流的全球影响，必须了解峡湾过程，并最终将其参数化。峡湾将格陵兰岛的海洋冰川与大陆架海洋连接起来，形成了长而窄的管道，用于输出冰川淡水和输入海洋热量来融化冰。因此，峡湾动态调节了海洋和冰川之间的热量和淡水交换，而气候相关过程受到这种海洋-冰相互作用的两个方向的影响。就冰冻圈对海洋的影响而言，格陵兰冰盖正在加速失去质量，海洋变暖被认为是引发最近峡湾海底融化的冰川变化的一个因素。在另一个方向上，格陵兰岛淡水的增加可以影响海洋动力学和生态系统——局部在峡湾内，局部在沿海洋流中，并可能通过改变北大西洋盆地的深层对流而影响全球。尽管峡湾环流对海洋-冰川相互作用很重要，但我们对在大陆架海洋和冰川之间运输热、盐和淡水的峡湾过程的了解有限。最近的观测已经证明了两种主要环流模式的重要性：冰川冰下流量的淡水浮力强迫，以及风和大陆架上海岸困波的天气性外部强迫。根据这些观察结果，研究人员将对一个峡湾及其邻近的大陆架进行数值模拟，包括一个准现实的峡湾和一组理想的模拟。该项目的目标是研究峡湾尺度上浮力驱动的流动动力学，以及这种环流如何与天气外部强迫相互作用，从而驱动热、盐和淡水的净输送。这些循环模式对混合和总交换流量的相对贡献将在具有格陵兰主要峡湾特征的峡湾内进行空间评估。该项目将与罗格斯大学的两位教育专家密切合作，支持K-12教育的推广。pi将帮助学生开发带有峡湾观测和理想模型输出的极地数据工具包，供学生在罗格斯大学的数据堵塞项目中使用，这是学生获得数据处理和发展科学技能的实践经验的机会。该项目将包括参与Data Jam活动，以及罗格斯大学的4-H STEM大使项目，在该项目中，pi将与来自服务不足学校的9年级学生接触，并开发一个专注于冰川融化、海平面上升和气候变化的教育内容。此外，该项目汇集了不同职业阶段的科学家，将培养一名博士生，并支持一名早期职业研究人员。来自近冰川调查和峡湾下游系泊的新观测结果有助于了解峡湾交换流。最近已经开发了孤立的外部（陆架和风）强迫的动力框架，但没有理论来描述通过峡湾运输示踪剂的浮力驱动流或外部强迫对这种交换的影响。一个现实的峡湾模型可以解开这些纠缠在一起的动力学，并为推动海洋-冰冻圈交换的过程提供新的见解。虽然冰川峡湾基本上是河口——陆地淡水与海水混合的沿海海湾——但它们不容易符合传统的河口范例。然而，沿海和河口世界有许多有用的框架可供构建。该项目将通过河口透镜研究峡湾动力学，借鉴标准河口中研究得更好的过程，并将尝试扩大河口范例以包括冰川峡湾。这些问题将由一组在峡湾动力学和海洋-冰相互作用、河口动力学、海岸建模和大陆架过程方面具有互补专业知识的调查人员来解决。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

With the Greenland Ice Sheet losing mass at an accelerating rate, a poor understanding of ocean-glacier interactions contributes to the uncertainties in sea level rise projections. Although fjords cannot be resolved in global climate models, fjord processes must be understood – and eventually parameterized – in order to study the global impacts of both ocean warming on glacier retreat and increased glacial freshwater on ocean circulation. Fjords connect Greenland’s marine-terminating glaciers to the continental shelf ocean, forming long, narrow conduits for the export of glacial freshwater and the import of oceanic heat to melt ice. As such, fjord dynamics modulate the exchange of heat and freshwater between the ocean and glaciers, and processes of climatic relevance are affected by both directions of this ocean-ice interaction. In terms of the cryosphere’s impact on the ocean, the Greenland Ice Sheet is losing mass at an accelerating pace, and ocean warming has been implicated as a trigger for recent glacier changes via submarine melting in fjords. In the other direction, increased freshwater from Greenland can impact ocean dynamics and ecosystems – locally within fjords, regionally in coastal currents, and potentially globally by altering the deep-convection in basins of the North Atlantic. Despite the importance of fjord circulation to ocean-glacier interactions, we have a limited understanding of the fjord processes that transport heat, salt and freshwater between the shelf ocean and glaciers. Recent observations have demonstrated the importance of two primary modes of circulation: freshwater buoyancy forcing from subglacial discharge at the glacier, and synoptic external forcing from winds and coastal trapped waves on the shelf. Drawing on these observations, the investigators will carry out numerical simulations of a fjord and its adjacent shelf, for both a quasi-realistic fjord and an idealized set of simulations. The goal of the project is to investigate the dynamics of the buoyancy-driven flow at the fjord-scale, and how this circulation interacts with synoptic external forcing to drive a net transport of heat, salt and freshwater. The relative contributions of these modes of circulation to mixing and the total exchange flow will be assessed spatially within fjords with characteristics representative of Greenland’s major fjords. This project will support K-12 education outreach, in close collaboration with two educational specialists at Rutgers. The PIs will help develop polar data kits with fjord observations and idealized model output for students to use in the Rutgers’ Data Jam Program, an opportunity for students to get hands-on experience working with data and developing scientific skills. The project will involve participation in Data Jam activities and also the 4-H STEM Ambassador program at Rutgers, where the PIs will engage with 9th graders from underserved schools and develop an educational component focused on melting of glaciers, sea level rise, and climate change. Additionally, this project, which brings together scientists across a wide range of career stages, will train a PhD student and support an early career researcher.New observations from near-glacier surveys and downstream moorings in fjords have been instrumental for understanding fjord exchange flow. Dynamical frameworks have recently been developed for external (shelf and wind) forcing in isolation, but no theory exists to describe the buoyancy-driven flow that transports tracers through the fjord or the impact of external forcing on this exchange. A realistic fjord model could untangle these intertwined dynamics and provide new insights into processes driving ocean-cryosphere exchange. While glacial fjords are fundamentally estuaries – coastal embayments where terrestrial freshwater mixes into seawater – they do not fit easily into traditional estuarine paradigms. However, there are many useful frameworks to build on from the coastal and estuarine world. This project will investigate fjord dynamics through an estuarine lens, drawing on better-studied processes in standard estuaries, and will attempt to expand estuarine paradigms to include glacial fjords. These questions will be addressed by a team of investigators with complementary expertise in fjord dynamics and ocean-ice interactions, estuarine dynamics, and coastal modeling and shelf processes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.