Observational Evidence of Ventilation Hotspots in the Southern Ocean

Standing meanders are a key component of the Antarctic Circumpolar Current (ACC) circulation system, and numerical studies have shown that these features may locally enhance subduction, upwelling, as well as lateral and vertical tracer transport. Yet, observational data from these regions remain sparse. Here, we present results based on measurements made by a group of autonomous platforms sampling an ACC standing meander formed due to the interaction of the Polar Front with the Southwest Indian Ridge. Two Seagliders were deployed alongside a Biogeochemical-Argo float that was advected through the standing meander. In the high eddy kinetic energy region of the standing meander, the glider observations reveal enhanced submesoscale frontal gradients as well as heightened tracer variability at depth, as compared to the more quiescent region further downstream. Vertical gradients in spice and apparent oxygen utilization are reduced in the standing meander despite similarities in the large-scale vertical stratification, suggesting greater ventilation of the surface ocean. These observations are consistent with numerical studies that highlight standing meanders as hotspots for ventilation and subduction due to enhanced mesoscale stirring and submesoscale vertical velocities. Our results emphasize the need to account for spatial heterogeneity in processes influencing air-sea exchange, carbon export, and biogeochemical cycling in the Southern Ocean.

Automated summary

Standing meanders in the Antarctic Circumpolar Current (ACC) play a key role in enhancing subduction, upwelling, and tracer transport. Observations in a high eddy kinetic energy region of a standing meander show increased submesoscale frontal gradients and heightened tracer variability at depth compared to downstream regions. Despite similar large-scale vertical stratification, vertical gradients in spice and apparent oxygen utilization are reduced in standing meanders, indicating greater ventilation of the surface ocean.