Collaborative Research: Pathways and fate of freshwater near the southern tip of Greenland

这个项目将调查格陵兰冰盖的淡水融化是如何从格陵兰岛最南端的弗莱尔角附近的沿海海洋流出的。当运送大陆架上大部分淡水的沿海洋流到达好望角时，强风的力量加上它与海岸线曲率和复杂的水深测量有关的方向，可能会把海水冲到那里的近海。该项目将部署漂浮物和剖面漂浮物，在模拟环流的背景下进行解释，以研究大量淡水如何进入公海。先前的研究表明，这种输出的陆架水可能对大西洋经向翻转环流（AMOC）产生潜在影响，从而对全球气候产生影响。该项目将支持一名年轻的观察研究者的职业发展，一个专门的项目网站将被开发，一名本科生暑期研究员将帮助分析数据，一名本科生志愿者将参加一次研究巡航。这项工作将阐明高纬度地区陆架衍生的淡水如何影响大规模的海洋环流，并应适用于其他地区，这些地区的浮力沿海洋流会绕过尖锐的水深线。更广泛的相关性将包括解决融水通过提供微量营养素和北大西洋次极地分层可能在何处以及如何影响北大西洋春季水华。目前北极和格陵兰冰盖的融化为北大西洋的亚极地带来了足够的淡水，从而显著地改变了大西洋经向翻转环流，但是这些水在哪里以及如何离开大陆架海洋，与北大西洋亚极地的边界流和深盆地相互作用，却很少受到限制。该项目将使用联合观测和建模研究来探索永别角周围淡水的路径和命运，并确定驱动通量的强迫机制。2021年和2022年将沿格陵兰岛东南部大陆架部署水面漂浮器和快速剖面Argo漂浮器，以评估沿海洋流的顺流、横流和垂直一致性。建模组件将提供一个高分辨率（约2公里的横向网格间距）长达一年的MITgcm运行数据，沿海洋流中的虚拟浮子沿着它们在永别角周围的路径运行，辅以对模式环流对内部不稳定性和外部强迫的响应的检查，以及由此产生的模拟陆架-盆地交换的量化。这项工作将首次全面研究永别角周围的陆架-盆地交换，这一过程经常被用来解释北大西洋的变化。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。

This project will investigate how freshwater melt from the Greenland ice sheet exits the coastal ocean near Cape Farewell, the southernmost tip of Greenland. As the coastal current transporting much of the fresh water on the shelf reaches the Cape, the strong wind forcing combined with its orientation with respect to the coastline curvature and complex bathymetry may flush water offshore there. The project will deploy drifters and profiling floats, interpreted in the context of modeled circulation to investigate how this high volume freshwater may enter the open ocean. Prior studies have indicated the potential influence this exported shelf water may have on the Atlantic Meridional Overturning Circulation (AMOC), and hence global climate. The project will support the career development of an observational young investigator, a project-specific website will be developed, an undergraduate summer student fellow will help analyze the data, and a volunteer undergraduate student will participate in a research cruise. This work will clarify how shelf-derived fresh water at high latitudes can influence the large-scale ocean circulation, and should be applicable to other regions where buoyant coastal currents veer around sharp bathymetry. Broader relevance will include addressing where and how meltwater may affect the North Atlantic spring bloom through its supply of micronutrients and stratification of the subpolar North Atlantic.The current melting of the Arctic and the Greenland Ice Sheet introduces enough fresh water into the subpolar North Atlantic to significantly alter the Atlantic Meridional Overturning Circulation, but where and how this water leaves the shelf ocean to interact with the boundary currents and deep basins of the subpolar North Atlantic is poorly constrained. This project will use a joint observational and modeling study to explore the pathways and fate of fresh water around Cape Farewell, and to determine the forcing mechanisms that drive the fluxes. Surface drifters and rapidly-profiling Argo floats will be deployed along the southeast Greenland shelf in 2021 and 2022 to assess the along-stream, cross-stream, and vertical coherency of the coastal current. The modeling component will seed a high-resolution (~2 km lateral grid spacing) year-long run of the MITgcm with virtual floats in the coastal current to follow their pathways around Cape Farewell, complemented by an examination of model circulation response to internal instabilities and external forcing, and quantification of the resulting modeled shelf-basin exchange. This work will provide the first comprehensive study of the shelf-basin exchange around Cape Farewell, a process often invoked to explain North Atlantic variability.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.