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

该项目将调查格陵兰冰盖融化的淡水是如何从格陵兰最南端法雷韦尔角附近的沿海海洋流出的。随着输送大陆架上的大部分淡水的海岸洋流到达海角，强风强迫，加上其相对于海岸线曲率的方向和复杂的水深测量，可能会将海水冲到那里的近海。该项目将部署漂浮物和剖面浮标，在模拟环流的背景下进行解释，以调查这些高流量的淡水可能如何进入公海。先前的研究已经表明，这些输出的陆架水可能会对大西洋子午线翻转环流(AMOC)产生潜在影响，从而影响全球气候。该项目将支持一名观察型青年调查员的职业发展，将开发一个特定于项目的网站，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游。这项工作将阐明高纬度陆架来源的淡水如何影响大规模海洋环流，并应适用于沿海漂浮洋流绕过急剧水深测量的其他地区。更广泛的相关性将包括解决融化水可能影响北大西洋春季水华的地方和如何通过其供应的微量营养素和北大西洋次极地的分层。目前北极和格陵兰冰盖的融化向北大西洋次极地引入了足够的淡水，从而显著改变了大西洋子午线翻转环流，但这些水从哪里以及如何离开大陆架海洋与北大西洋次极地的边界洋流和深盆地相互作用的限制很差。该项目将使用一项联合观测和模型研究来探索法雷韦尔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，格陵兰东南部陆架将部署水面漂浮器和快速剖面ARGO浮标，以评估沿岸流的顺流、横流和垂直连贯性。模拟部分将为MITgcm的一年高分辨率(约2公里横向网格间距)播种，使沿海洋流中的虚拟漂浮物沿着其在Farewell角周围的路径行驶，并辅之以检查模型环流对内部不稳定和外部强迫的反应，并对由此产生的陆架-盆地交换进行量化。这项工作将提供对Farewell角周围陆架-盆地交换的第一次全面研究，这一过程经常被用来解释北大西洋的变化。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.