Offshore Export of Glacial Water and Ice in an Eddying Ocean

气候学中一个流行的假设是，大陆冰川和冰盖的大量水（“冰川水”）排入北大西洋可能会破坏海洋环流并引起气候变化。这一假设隐含的意思是，冰川水会以浮力（轻）表面层的形式从海岸向外扩散，并降低高纬度开阔海域表层水的密度。反过来，深密水域的形成和随之而来的向北的热量通量将会减少。在这个项目中，海洋环流的计算机模型将以前所未有的空间分辨率，用于研究冰川水沿北美东部排放到不同海洋区域的途径。该模型将模拟小规模的漩涡，并将与冰山模型相结合，这样就可以测试各种海洋过程将融水和冰山向海输送的能力。该项目将通过阐明各种海洋现象对液态和固态冰川水的离岸输出的贡献来促进科学的进步。这对科学界将是有益的，因为：(1)为设计冰川水扰动实验提供信息，这些实验是用不能明确表示海洋中小规模涡流的粗分辨率气候模式进行的；（ii）限制对海底和沉积物岩心观测的解释，这些观测表明，在过去3万年中，深龙骨冰山沿着北大西洋西部边缘向南移动，冰川融水经常侵入大陆架以外；（iii）通过开放获取的网站分享实验结果。该项目将通过一名研究生和三名本科生来支持教育。研究生将接触到现代海洋环流模式的能力，以研究与气候相关的动力现象。三名本科生将利用旋转转盘进行淡水排放实验，并将实验录像放到网上。将编写一份操作手册，并将其链接到视频中，以便科学家、教师和学生可以重复实验。最后，该项目将通过(i)更好地评估过去和未来冰川水排放导致气候变化的潜力，以及（ii）作为未来冰山对海上航运活动和高纬度水域石油/天然气勘探影响的模型研究的模板，造福社会。用更专业的术语来说，在这个项目的过程中，一个具有亚中尺度分辨率的海洋环流-冰山耦合模型将被开发出来，并用于详细模拟沿北美东部以液体和固体形式进入海洋的冰川水的演变。该项目的具体目标是：(i)测试不同动力现象在劳伦泰德冰盖（LIS）冰川水离岸输出中的作用，该冰盖在最后（去）冰期占据北美，（ii）开发冰川水输出的参数化，用于粗分辨率气候模型。（iii）根据美国冰川水的排放，对来自北美东部边缘的海底观测和沉积物记录进行解释。为了实现这些目标，将在区域域应用千米尺度或更高分辨率的模式。本项目的工作计划包括三个任务。(1)将配置一个海洋环流的数值模式来代表北大西洋西部的两个海洋区域：纽芬兰大浅滩和包括哈特拉斯角附近的海洋区域在内的大西洋中部海湾。(2)环流模式将与冰山模式耦合。(3)耦合模式实验将阐明三个过程在冰川水向海输出中的作用：大浅滩附近的海岸流分离、大西洋中部湾的大陆架断裂涡流输送和哈特拉斯角附近的墨西哥湾流夹带。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。

A popular hypothesis in climatology posits that the discharge of large amounts of water from continental glaciers and ice sheets ("glacial water") into the North Atlantic may disrupt ocean circulation and cause climate change. Implicit in this hypothesis is that the glacial water would spread away from the coast, as a buoyant (light) surface layer, and decrease the density of surface waters in the open ocean at high latitudes. In turn, the formation of deep dense waters and the attendant northward flux of heat would be reduced. In this project, a computer model of ocean circulation, with unprecedented spatial resolution, will be used to study the pathways of glacial water discharged into different oceanic regions along eastern North America. The model will simulate small-scale eddies and will be coupled to an iceberg model, so that the ability of various oceanic processes to transport meltwater and icebergs seaward could be tested. This project will promote the progress of science by elucidating the contribution of various oceanic phenomena to the offshore export of glacial water in both liquid and solid forms. It will be profitable to the scientific community by (i) informing the design of glacial water perturbation experiments performed with coarse-resolution climate models which cannot explicitly represent small-scale eddies in the ocean, (ii) constraining the interpretation of seafloor and sediment core observations which suggest that deep-keeled icebergs moved southward along the western North Atlantic margin and that glacial meltwater intruded recurrently beyond the continental shelf during the last 30,000 years, and (iii) sharing experimental results via open-access web sites. This project will support education by engaging a Graduate Student and three Undergraduate Students. The Graduate Student will be exposed to the capability of modern ocean circulation models to study dynamical phenomena of climatic relevance. The three Undergraduate Students will conduct laboratory experiments of freshwater discharge with rotating turntables and make the video footage of the experiments available on-line. A how-to manual will be written and linked to the footage, so scientists, teachers, and students could repeat the experiments. Finally, this project will benefit society by (i) providing a better assessment of the potential of both past and future glacial water discharges to cause climate change, and (ii) serving as a template for future model studies on the impact of icebergs on offshore shipping activities and oil/gas exploration in high-latitude waters.In more technical terms, over the course of this project, a coupled ocean circulation-iceberg model with submesoscale resolution will be developed and used to produce detailed simulations of the evolution of glacial water entering the ocean along eastern North America in liquid and solid forms. The specific objectives of this project are (i) to test the role of different dynamical phenomena in the offshore export of glacial water from the Laurentide Ice Sheet (LIS), which occupied North America the last (de)glacial periods, (ii) to develop a parameterization of glacial water export for use in coarse-resolution climate models, and (iii) to yield constraints on the interpretation of seafloor observations and sediment records from the eastern North American margin in terms of glacial water discharges from the LIS. To meet these objectives, a model with kilometer-scale or higher resolution will be applied in regional domains. The work plan of this project includes three tasks. (1) A numerical model of ocean circulation will be configured to represent two oceanic regions in the western North Atlantic: the Grand Banks of Newfoundland, and the Middle Atlantic Bight including the oceanic region near Cape Hatteras. (2) The circulation model will be coupled to an iceberg model. (3) Experiments with the coupled model will be conducted to elucidate the roles of three processes in the seaward export of glacial water: coastal current separation near the Grand Banks, transport by shelfbreak eddies in the Middle Atlantic Bight, and entrainment with the Gulf Stream near Cape Hatteras.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.