Characteristics and Origins of Eddies beneath Antarctic Sea Ice

The world ocean is continuously in motion, and a large fraction of this motion takes the form of "eddies", nearly-horizontal swirls of water spanning tens to hundreds of kilometers. These eddies affect the ocean by mediating large-scale currents, redistributing heat, and supplying nutrients to oceanic ecosystems. Consequently, the ocean science community has historically invested substantial effort in characterizing the properties and impact of these eddies. In polar regions, the sea ice cover inhibits observations of eddies, and the relatively small horizontal size of the eddies hampers computer simulations of their behavior. Nonetheless, previous studies have identified an active population of eddies beneath the Arctic sea ice and shown that these eddies play a crucial role in maintaining the large-scale circulation in the Arctic seas. However, there has been no systematic attempt to study such eddies under Antarctic sea ice, leaving a significant gap in our understanding of eddies and their contribution to the large-scale ocean circulation around Antarctica.

The proposed research combines multiple approaches to improve our understanding of the eddy dynamics. Statistical characterizations of the sub-sea ice eddy field will be derived using hydrographic observations under Antarctic sea ice from Argo floats and instrumented seals. High-resolution global ocean and sea ice models will be used to track the simulated eddies back to their formation sites to identify the eddy formation mechanisms. Theoretical calculations will be conducted to test the hypothesis that the eddies primarily originate from hydrodynamic instabilities associated with subsurface density gradients. These theoretical, modeling, and data analysis approaches will be combined to estimate the eddies' contribution to lateral tracer transports and their impact on mean circulations of the near-Antarctic ocean. The proposed work will facilitate future scientific endeavors by providing publicly-available databases of detected eddy properties. This project will support the research of several junior scientists: an undergraduate student, two graduate students, and an early-career faculty member.

This work is supported by the National Science Foundation, grant number ANT-2220968.

The central image shows a snapshot of sea ice cover around Antartica, as simulated by a global ocean/sea ice model simulation run at NASA Ames by D. Menemenlis (NASA JPL). The surrounding panels show snapshot of relative vorticity (a measure of the fluid's rotation about the vertical axis) at 230m below the ocean surface in different selected areas aroun Antarctica. The quasi-circular patches of positive and negative relative vorticity correspond to eddies.