Biogeochemical evolution of mesoscale subsurface eddies off central Chile

Mesoscale subsurface eddies (MSSE) that mainly form and move in the thermocline region play an important role in the eastern boundary upwelling systems. They transport intermediate waters from coastal productive zones to oligotrophic regions in the open ocean. Off central Chile there is a great activity of MSSEs that show in their interior suboxic conditions where biogeochemical processes such as denitrification, anammox, and increased production of N₂O may occur, but little is known about how these processes change during the lifetime of MSSEs. In this work, we use a coupled physical/biogeochemical model (ROMS-AGRIF/BioEBUS) to study the evolution of the biogeochemical reactions in MSSEs (primary production, grazing, metabolism, mortality, excretion, hydrolysis, remineralization, nitrification, denitrification, anammox) that move from the coastal oxygen minimum zone to the open ocean hundreds of kilometers away. We identify and track different MSSEs and calculate the rates of the different biogeochemical processes in their interior. These processes are directly impacted by the oxygen concentration in the eddy interior and the availability of nutrients, which are modified by both, the dynamics of themselves and the exchange with the surrounding waters controlled by physical processes.