Collaborative Research: Shelf-Basin Exchange South of Denmark Strait: Forcing, Dynamics, and Large-Scale Impact

伊尔明格海位于格陵兰岛南部和雷克扬斯海脊之间，是北冰洋首次汇入北大西洋的重要区域。在丹麦海峡南部，寒冷而新鲜的北极水与温暖的亚热带咸水相遇，形成了一股锋利的锋面。这股锋面及其相关的急流--东格陵兰岛/伊尔明格流--是亚热带地区的北极水输出到北大西洋的主要途径。由于邻近格陵兰高原的下锋阻挡风的作用，加上锋面和伊尔明格流的不稳定性和时变性，该地区与开阔的大西洋发生了强烈的陆架-盆地交换。作为这一交换过程的一部分，稠密的陆架水从陆架断裂处倾泻而出，形成一个位于东格陵兰岛/伊明格洋流下方的“喷流”。这导致了拉布拉多海下游的大量下沉，并影响了亚极地涡旋和向北部淡水水源的经向翻转环流。目前，科学家们对这一复杂的陆架断裂洋流系统知之甚少，因此不确定它的输送、淡水通量、季节演变以及导致质量和性质跨河流交换的中尺度变率的性质和动力学。通过一项联合观测/模拟研究，来自伍兹霍尔海洋研究所和约翰霍普金斯大学的海洋学家建议量化水动力不稳定性和大气强迫在格陵兰岛以东发生的陆架-盆地交换。通过研究东格陵兰/伊尔明格洋流系统的平均和季节性变化的输送、结构和运动学，并确定导致陆架-盆地交换的中尺度变化的性质和动力学，他们将能够探索陆架-盆地交换在过去几十年对亚极地北大西洋的影响如何变化，以及这种影响在未来可能如何演变。这项研究的更广泛影响解决了人们对北大西洋经向翻转环流对北部淡水水源的敏感性的关切。北极淡水出口总量的大约一半经过格陵兰岛以东，在拟议的研究区域与开放的大西洋相接，因此，了解该区域陆架-盆地交换的动态对于潜在预测北大西洋对未来气候变化的反应至关重要。这项研究包括资助教育推广活动，包括在格陵兰岛南部偏远地区的活动，以及在美国的科学中心展览。资金还包括用于支持研究生和本科生的教育和培训。

The Irminger Sea, situated between southern Greenland and the Reykjanes Ridge, is a critically important area where the Arctic Sea first meets the North Atlantic Ocean. South of the Denmark Strait, a sharp front is formed where cold, fresh outflowing Arctic water meets the warm, salty subtropical-origin water. This front and its associated jet, the East Greenland/Irminger Current, act as the main pathway that recirculating subtropical-origin Arctic water is exported to the North Atlantic. With the stress of the down-front barrier winds adjacent to the Greenland plateau in addition to the instability and time-variability of both the front and the Irminger Current, intense shelf-basin exchange with the open Atlantic occurs in this region. As part of this exchange process, dense shelf water cascades over the shelf-break to form a "Spill Jet" which resides below the East Greenland/Irminger Current. This results in substantial sinking, which occurs downstream in the Labrador Sea and impacts the sub-polar gyre and the meridional overturning circulation to northern freshwater sources. Currently, scientists have a poor understanding of this complex shelf-break current system, and thus are unsure of its transport, freshwater flux, seasonal evolution, and the nature and dynamics of the mesoscale variability that lead to the cross-stream exchange of mass and properties. Through a joint observational/modeling study, oceanographers from Woods Hole Oceanographic Institution and Johns Hopkins University propose to quantify the hydrodynamic instability and atmospheric forcing that drive shelf-basin exchange to occur east of Greenland. By examining the mean and seasonally varying transport, structure, and kinematics of the East Greenland/Irminger Current system and determining the nature and dynamics of the mesoscale variability that leads to shelf-basin exchange, they will be able to explore how the impact of shelf-basin exchange on the sub-polar North Atlantic has changed in the last few decades and how it may evolve in the future. The broader impacts of this study address the concern about the sensitivity of the North Atlantic meridional overturning circulation with respect to northern freshwater sources. Approximately one half of the total Arctic export of freshwater passes east of Greenland and meets the open Atlantic in the proposed study area, therefore understanding the dynamics of the shelf-basin exchange in this region is essential to potentially predict the response of the North Atlantic to future changes in climate. This research includes funding to support educational outreach including activities in a remote location in southern Greenland, as well as science center exhibits in the United States. Funding is also included to support education and training at both the graduate and undergraduate level.