Antarctica Slope Front bifurcation eddy: A stationary feature influencing CO2 dynamics in the northern Antarctic Peninsula

The Southern Ocean is a key region for analyzing environmental drivers that regulate sea-air CO2 exchanges. These CO2 fluxes are influenced by several mesoscale structures, such as meanders, eddies and other mechanisms responsible for energy dissipation. Aiming to better understand sea-air CO2 dynamics in the northern Antarctica Peninsula, we investigated an anticyclonic stationary eddy located south of Clarence Island, in the eastern basin of Bransfield Strait - named the Antarctica Slope Front bifurcation (ASFb) eddy. Physical, chemical and biological data were sampled, and remote sensing measurements taken, in the region during late summer conditions in February 2020. The eddy's core consisted of cold (0.31 degrees C), salty (34.38) and carbon-rich (2247 mu mol kg-1) waters with dissolved oxygen depletion (337 mu mol kg- 1). The core retains a mixture of local surface waters with waters derived from Circumpolar Deep Water (i.e., Warm Deep Water from the Weddell Sea and modified Circumpolar Deep Water from the Bransfield Strait) and Dense Shelf Water. The ASFb eddy acts as a CO2 outgassing structure that reaches a CO2 emission to the atmosphere of -1.5 mmol m- 2 d-1 in the eddy's core, mostly due to enhanced dissolved inorganic carbon (DIC). The results suggest that surface variation in DIC in the eddy's core is modulated by (i) the entrainment of CO2-rich intermediate waters at -500 m, (ii) low primary productivity, associated with small phytoplankton cells such as cryptophytes and green flagellates, and (iii) respiration processes caused by heterotrophic organisms (i.e., zooplankton community). By providing a comprehensive view of these physical and biogeochemical properties of this stationary eddy, our results are key to adding new insights to a better understanding of the behavior of mesoscale features influencing sea-air CO2 exchanges in polar environments.

Automated summary

The study investigated the characteristics of sea-air CO2 dynamics through the investigation of an anticyclonic stationary eddy called the Antarctica Slope Front bifurcation (ASFb) eddy, located south of Clarence Island in the eastern basin of Bransfield Strait. The results revealed that the ASFb eddy acts as a CO2 outgassing structure with a core consisting of carbon-rich waters. These findings provide important insights into the behavior of mesoscale features influencing sea-air CO2 exchanges in polar environments.