RAPID: Fate of freshwater and heat in the West Greenland Current

过去二十年来，北冰洋的淡水量一直在大幅增加，气候预测表明，这将导致这些水更多地向南输送到北大西洋。与此同时，格陵兰冰盖的融水排放在过去30年里一直在加速。这两个淡水来源最终都进入了环绕格陵兰岛的边界流。确定这一水的最终命运是当务之急。如果它被输送到边界洋流的近海，可能会影响有助于维持地球气候的大规模全球颠覆环流。此外，在淡水之下，边界流携带着源自亚热带的暖水。这种高温被认为是导致格陵兰冰川底部融化的原因之一--这反过来又会导致更多的淡水释放。因此，我们需要了解温暖的亚热带水是如何进入冰川的。拟议的项目旨在解决西格陵兰岛边界流中携带的淡水和热量的路径和命运。我们将在巴芬湾进行一次详细的船上调查，包括沿着通往格陵兰西部冰川峡湾的一些航道进行测量。这之所以成为可能，是因为美国破冰船希利号正在执行一项罕见的任务，前往北极东部，进行这组独特的测量。合作者将进行两项有贡献的研究，该项目不承担任何费用。第一个将使用化学测量解决不同的淡水来源，第二个将使用远程操作工具揭示峡湾附近的循环。一名博士后和三名研究生将参加这次巡航。将在USCGC Healy从戴维斯海峡到巴芬湾北部进行广泛的水文/流速测量，以确定由西格陵兰流(WGC)平流进入该地区的热量和淡水的路径和命运。该项目利用了这样一个事实，即Healy将于2021年夏/秋在北极东部运行，并可在9月中旬至10月中旬进行科学巡航。已经设计了一套高分辨率的战略剖面，以(1)估计淡水从世界GC流入内陆的通量；(2)处理世界GC与峡湾的双向交换，这些峡湾通过大陆架上的深槽排出几个西格陵兰冰川；以及(3)量化世界GC的结构和演变，以及巴芬湾的环流，以评估其体积、淡水和热量收支。在研究区域，从来没有在足够小的站距来解决所有重要洋流的情况下进行过这样的调查，包括直接速度测量，同时提供解决整个盆地问题所需的广泛覆盖范围。我们将使用Healy的电导率-温度-深度(CTD)系统及其外壳安装的声学多普勒海流剖面仪(ADCP)以及消耗性CTD来填补空白。该项目将免费开展两个合作项目。第一个将测量营养物质和氧同位素，以帮助区分淡水来源，第二个将部署一架Seaglider，以绘制雅各布港冰川附近的温暖水路径和混合。一名博士后和三名研究生将参加这次巡航。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。

The amount of freshwater in the Arctic Ocean has been increasing substantially over the past two decades, and climate projections indicate that this will lead to enhanced transfer of this water southward to the North Atlantic Ocean. At the same time, the meltwater discharge from the Greenland ice sheet has been accelerating over the last 30 years. Both of these sources of freshwater end up in the boundary current that encircles Greenland. It is imperative to determine the ultimate fate of this water. If it gets fluxed offshore of the boundary current it could impact the large-scale global overturning circulation that helps maintain Earth’s climate. Furthermore, underneath this freshwater, the boundary current carries warm water that originated from the subtropics. This heat has been implicated in causing basal melt in Greenland’s glaciers – which in turn would lead to more freshwater release. As such, we need to understand how the warm subtropical-origin water makes it to the glaciers. The proposed project is designed to address the pathways and fate of both the freshwater and heat carried in the boundary current along West Greenland. We will conduct a detailed shipboard survey in Baffin Bay, including measurements along some of the channels leading to west Greenland’s glacial fjords. This is made possible because the US icebreaker Healy is undertaking a rare mission to the eastern sector of the Arctic, allowing for this unique set of measurements. Two contributing studies will be undertaken by collaborators, at no cost to the project. The first will address the different sources of freshwater using chemical measurements, and the second will shed light the circulation near the fjords using a remotely operated vehicle. A post-doc and three graduate students will participate on the cruise.An extensive hydrographic/velocity survey will be conducted on the USCGC Healy, from Davis Strait to the northern part of Baffin Bay, to determine the pathways and fate of heat and freshwater that are advected into the region by the West Greenland Current (WGC). The project takes advantage of the fact that Healy will be operating in the eastern Arctic in summer/fall 2021 and is available for a scientific cruise from mid-September to mid-October. A strategic set of high-resolution sections has been designed to (1) estimate the flux of freshwater from the WGC into the interior; (2) address the two-way exchange of the WGC with the fjords draining several West Greenland glaciers via deep troughs on the shelf; and (3) quantify the structure and evolution of the WGC, as well as the circulation of Baffin Bay to assess its volume, freshwater, and heat budgets. Such a survey has never been done in the study region at small enough station spacing to resolve all of the important currents, with the inclusion of direct velocity measurements, while simultaneously providing the broad coverage necessary to address basin-wide issues. We will use Healy’s conductivity-temperature-depth (CTD) system, and its hullmounted acoustic Doppler current profilers (ADCPs), along with expendable CTDs to fill in gaps. Two collaborative programs will be carried out at no-cost to the project. The first will measure nutrients and oxygen isotopes to help distinguish the freshwater sources, and the second will deploy a Seaglider to map out warm water pathways and mixing near Jakobshavn glacier. A post-doc and three graduate students will participate on the cruise.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.