EMC Experiment: Examining the Fate of the East Madagascar Current

该奖项全部或部分由《2021年美国救援计划法案》（公法117-2）资助。形成全球经向翻转环流（GMOC）的洋流系统在调节地球气候方面发挥着核心作用。南印度洋东马达加斯加海流（EMC）的上层环流是该系统最不为人所知但却至关重要的方面之一。该项目将在该地区的数值模型中使用表面漂浮物、地下RAFOS漂浮物和粒子跟踪来检查EMC从马达加斯加南端附近的大陆架分离后的路径：它是向东转向马达加斯加盆地还是向西转向莫桑比克盆地，还是两者兼而有之。该项目将利用与已经资助的马达加斯加盆地深水项目（NSF/OCE/PO #1924431）相关的几个RAFOS声源，增加一个额外的声源，以促进新项目中深水RAFOS浮子的三角测量。该项目将在一个取样不足的海洋区域进行观测，帮助确定印度尼西亚通流（ITF）水域的命运，并可能有助于了解尚未解释的马达加斯加东南部水华——一个全球“热点”，在一个其他营养不良的亚热带地区进行初级生产。该项目将支持PI，一位早期职业研究者，并资助六位早期职业马达加斯加科学家（包括一位合作者）参加研究巡航。该项目还将在马达加斯加组织一个为期两周的暑期学校。每年夏天将支持本科WHOI暑期实习生，包括资助他们参加科学会议。拟议的研究将是美国对第二次国际印度洋考察的贡献。为了观察分离EMC的流体包裹路径，该项目将在一年内四次同时在EMC内释放地面漂浮器和地下声学跟踪的等环流RAFOS漂浮器。这个拉格朗日实验是EMC中第一个此类实验，将与粒子跟踪模拟相结合，以研究与分离的EMC相关的表面和地下路径，其与阿古拉斯流和南印度逆流的连通性，以及各自的传输时间。研究将评估电磁兼容强度、下游传播涡流和海底地形对分离电磁兼容路径的影响。具体目标是：1)确定地面和斜斜水平的电磁辐射平流路径和穿越时间，并研究控制这些路径的物理机制；2)描述任何电磁辐射产生的向西移动的涡流的演变特征；3)评估潜在的电磁辐射反射模式，并研究对它们的控制；4)确定电磁辐射产生的包裹在测量和模拟的潜在路径后的命运和平流穿越时间。这些知识将有助于了解南印度洋内的ITF水之旅、马达加斯加东南部水华发展、马达加斯加南部沿海上升流单元以及对阿古拉斯海流和GMOC的影响。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。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).The system of ocean currents that forms the global Meridional Overturning Circulation (GMOC) plays a central role in regulating Earth's climate. One of the least understood yet critical aspects of this system is the upper-layer circulation within the East Madagascar Current (EMC) in the South Indian Ocean. This project will use surface drifters, subsurface RAFOS floats and particle tracking in a numerical model of the region to examine pathways after the EMC separates from the continental shelf near the southern tip of Madagascar: whether it turns east into the Madagascar Basin or west into the Mozambique Basin, or both. The project will take advantage of several RAFOS sound sources associated with the already-funded Deep Madagascar Basin project (NSF/OCE/PO #1924431), adding one additional sound source to facilitate triangulation of the mid-depth RAFOS floats of the new project. The project will provide observations in an under sampled ocean region, help define the fate of Indonesian Throughflow (ITF) waters, and may inform understanding of the as yet unexplained Southeast Madagascar Bloom -- a global 'hotspot' for primary production in an otherwise oligotrophic subtropical region. The project will support the PI, an early career investigator, and fund the participation of six early-career Malagasy scientists (including a collaborator) in the research cruises. The project will also organize a 2-week summer school in Madagascar. Undergraduate WHOI summer interns will be supported each summer, including funding for their participation in scientific meetings. The proposed research will be a US contribution to the 2nd International Indian Ocean Expedition. To observe fluid parcel pathways of the detached EMC, the project will simultaneously release surface drifters and subsurface acoustically-tracked isopycnal RAFOS floats within the EMC four times over a year. This Lagrangian experiment, the first of its kind in the EMC, will be paired with particle tracking simulations to investigate surface and subsurface pathways associated with the detached EMC, its connectivity with the Agulhas Current and the South Indian Countercurrent, and respective transit times. The research will assess the impacts of EMC strength, downstream propagating eddies, and seafloor topography on the detached EMC pathways. The specific objectives are to 1) determine the advective pathways and transit times of the EMC extension at surface and pycnocline levels and investigate the physical mechanisms that control those pathways, 2) characterize the evolution of any EMC-originated eddies that transit westward, 3) evaluate potential EMC retroflection modes and investigate controls on them, and 4) determine the fates and advective transit times of EMC originated parcels following measured and modeled potential paths. This knowledge will inform understanding the ITF water journey within the South Indian Ocean, the Southeast Madagascar Bloom development, southern Madagascar coastal upwelling cells, and impacts on the Agulhas Current and the GMOC.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.