Impacts of a Warm Core Ring on the Biogeochemistry and Food web in the Ross Sea

Eddies are common mesoscale features known to impact regional ocean biogeochemistry and water mass exchange. In 2022-2023, we deployed two gliders in the southern Ross Sea, Antarctica, carrying sensors to measure temperature, salinity, chlorophyll fluorescence, dissolved oxygen, optical backscatter, and acoustic backscatter for biomass.  The glider survey revealed five sub- to mesoscale features, likely eddies, during the spring season: three cold core rings and two warm core rings with radii of approximately 1-2 km. Most noteworthy of these was a shallow, warm core ring that caused isopycnal doming, bringing in cold, salty water to the surface (upper 100 m) ocean from depth. This feature substantially altered the biogeochemistry of the surface waters, inducing declines in concentrations of carbon (derived from optical backscatter) and krill (derived from acoustic backscatter), with chlorophyll exhibiting the most dramatic decline within the ring. Chlorophyll concentrations of ring waters averaged <1 – 2% of deployment average concentrations. The biogeochemical impacts of the ring may in turn impact carbon export, penguin foraging, and energy transfer to higher trophic levels. This feature serves as a characteristic example of warm core rings in the Ross Sea and illustrates the important role of mesoscale, physical features on regional biogeochemistry and foodweb dynamics.