Canyons Influence on Cross-shelf Exchange - When Dense Water Goes Down, Warm Water Comes Up

这个项目将研究斜坡峡谷中由稠密的陆架水下降到峡谷中引起的跨陆架交换的动力学。南极洲地区的情况具有全球意义，因为近海流动的致密水形成南极底水，从而影响全球经向环流，而回流引起的陆上热量输送驱动冰川融化，从而导致海平面上升。这些重要的过程将通过实验室和数值相结合的方法进行研究。该项目将探索控制密水从峡谷下降时跨陆架交换动量、热量和示踪剂的主导顺序动力学。将确定衡量密集陆架水、近海运输和近海岸上运输的关键地点，为今后的实地行动提供指导。这项提案将支持一名研究生的博士研究，其他学生将通过私人投资机构的积极实验室小组参与进来。实验工作将利用世界卫生组织的地球物理流体动力学实验室。在第一年和第三年，地球物理流体动力学实验室开放周活动将针对本科生和研究生、博士后和K-12学生。本次活动将举办10场动手演示和展示。该项目的材料将用于合作伙伴的教育活动。初步的数值模拟显示，南极沿海地区出现了两股意想不到的流动。第一种是峡谷以东大陆架上的水流，它将三分之一的致密水输送到峡谷上游的陆架断裂处(从开尔文波传播的角度来看)，从而促进了跨陆架交换。第二个是深水峡谷的岸上入侵，其中一些能够到达海岸。该项目将结合数值模拟和实验室水槽实验来验证两个假设：第一，在峡谷顶部的陆架上产生的相当大一部分致密水流入上游陆架，最终进入峡谷上游一侧的斜坡海；第二，沿着峡谷向下下降的致密水导致峡谷深水在岸上回流。它还假设，这种陆上水流起源于峡谷下游的大陆坡，从峡谷出来，进入峡谷上游的大陆架。区域海洋模拟系统(ROMS)将用于模拟在沿海地区产生的致密陆架水(DSW)的形成和随后的输送，以及环境水在理想的大陆架和斜坡系统中的运动。将使用与数值模拟非常相似的设置的旋转玻璃槽进行理想化的实验室实验。这些实验将测试数值模型中使用的假设和参数是否影响感兴趣的动力学。此外，实验室和数值结果之间的一致将使人们有信心在实验室中正确地捕捉到相关的动态。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 examine the dynamics of the cross-shelf exchange in a slope canyon induced by dense shelf water descending into the canyon. The case to be examined in the Antarctica region is of global significance because the offshore flowing dense water forms Antarctic Bottom Water and thus affects the global meridional circulation, while the onshore heat transport induced by the return flow drives glacial ice melt and therefore contributes to sea level rise. These important processes will be investigated through a combined laboratory and numerical approach. The project will explore the leading order dynamics controlling the cross-shelf exchange of momentum, heat and tracers when dense water descends a canyon. Key locations to measure dense shelf water offshore transport and offshore water onshore transport will be identified to provide guidance to future field campaigns. This proposal will support the Ph.D. research of a graduate student, and other students will be involved through the PIs’ active lab-groups. The experimental work will utilize the Geophysical Fluid Dynamics Laboratory at WHOI. In Years 1 and 3, the Geophysical Fluid Dynamics Laboratory Open Week event will target undergraduate and graduate students, postdocs, K-12 students. This event will host 10 hands-on demonstrations and displays. Material from this project will be used in educational activities by the Co-PIs. Preliminary numerical modeling revealed two unexpected flows in the Antarctic coastal region. The first is a current on the continental shelf east of the canyon, which contributes to the cross-shelf exchange by transporting a third of dense water across the shelf-break upstream (from the perspective of the Kelvin wave propagation) of the canyon. The second is the onshore intrusion into the canyon of deep offshore water, some of which is able to reach the coast. The project will combine numerical modeling with laboratory tank experiments to test two hypotheses: first, that a substantial fraction of dense water generated on the shelf over the head of a canyon flows onto the upstream shelf and eventually moves offshore into the slope sea on the upstream side of the canyon; and second, dense water descending down a canyon induces an onshore return flow of deep offshore water in the canyon. It is also hypothesized that this onshore flow originates on the continental slope downstream of the canyon and exits the canyon onto the continental shelf upstream of the canyon. The Regional Ocean Modeling System (ROMS) will be used to simulate the formation and subsequent transport of Dense Shelf Water (DSW) generated in a coastal region, as well as the motion of ambient water, in an idealized continental shelf and slope system. Idealized laboratory experiments using a rotating glass tank with a very similar set up as the numerical simulations will be used. These experiments will test whether the assumptions and parameterizations used in the numerical model are influencing the dynamics of interest. In addition, agreement between the laboratory and numerical results will provide confidence that the relevant dynamics are correctly captured in the laboratory.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.