Investigating the exchange flow in glacial fjords through an estuarine lens

通过河口透镜研究冰川峡湾的交换流

• 批准号: 2023415
• 负责人: Rebecca Jackson
• 金额: $ 61.75万
• 依托单位: Rutgers University New Brunswick
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2023415&HistoricalAwards=false
• 关键词: Investigating; exchange; flow; glacial; fjords

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.

随着格陵兰冰层以加速率损失质量，对海洋冰川相互作用的了解不足会导致海平面上升项目的不确定性。尽管在全球气候模型中无法解决峡湾，但必须了解峡湾过程并最终被参数化，以研究两种海洋变暖对冰川静修的全球影响，并增加冰川淡水对海洋循环的影响。峡湾将格陵兰岛的海洋末端冰川连接到连续的架子海洋，形成长而狭窄的导管，以出口冰川淡水，并进口海洋热量以融化冰。因此，峡湾动力学调节了海洋和冰川之间的热量和淡水的交换，气候相关性的过程都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，格陵兰冰盖以加速的速度失去了质量，并且已经实施了海洋变暖，以触发最近通过峡湾的海底熔化近期变化的诱因。在另一个方向上，绿地的淡水增加可能会影响海洋动力学和生态系统 - 在峡湾内，沿海水流区域，并可能通过改变北大西洋鲈鱼的深度交流，从而影响全球。尽管峡湾循环对海洋冰川相互作用的重要性很重要，但我们对在架子海洋和冰川之间运输热，盐和淡水的峡湾过程有限。最近的观察结果表明，两种主要循环模式的重要性：冰川下冰川排放的淡水浮力强迫，以及架子上风和沿海捕获的波的天气外部强迫。利用这些观察结果，研究人员将对峡湾及其相邻的架子进行数值模拟，以用于准现实的峡湾和一组理想化的模拟。该项目的目的是研究峡湾尺度上繁殖驱动流动流的动力学，以及该循环如何与概要外部强迫相互作用，以驱动热，盐和淡水的净运输。这些循环模式对混合和总交换流的相对贡献将在峡湾中经常评估，其特征代表了格陵兰的主要峡湾。该项目将与Rutgers的两位教育专家密切合作，支持K-12教育外展。 PI将有助于开发具有公平观察结果和理想化模型输出的极地数据套件，以供学生在Rutgers的数据JAM计划中使用，这是学生获得与数据合作并发展科学技能的动手经验的机会。该项目将涉及参与Rutgers的4-H STEM大使计划的数据JAM活动，PIS将与来自服务不足学校的9年级学生互动，并开发着侧重于冰川融化，海平面上升和气候变化的教育成分。此外，该项目汇集了各种职业阶段的科学家，将培训博士生并支持早期的职业研究员。近距离调查的新观察和峡湾下游系泊设备对了解峡湾的交流流动。最近已经为外部（架子和风）强迫开发了动态框架，但是没有理论来描述浮力驱动的流，该流通过峡湾传递示踪剂或外部强迫对这种交换的影响。现实的峡湾模型可以解开这些相互交织的动力学，并为推动海洋界面交换的过程提供新的见解。尽管冰川峡湾从根本上是河口（沿海植物植物，陆地淡水都会混合到海水中 - 它们并不容易适合传统的河口范式。但是，有许多有用的框架可以从沿海和河口世界建立。该项目将通过河口晶状体研究峡湾动力学，利用标准河口的培养过程，并将试图扩大河口范式以包括冰川峡湾。这些问题将由一个调查员团队解决，该团队在峡湾动态和海洋冰上互动，河口动力学以及沿海建模和货架过程方面具有完整的专业知识。该奖项反映了NSF的法定任务，并被认为是通过基金会的知识分子优点和更广泛的影响审查标准来通过评估来获得的支持。