968 / 2024-09-19 22:44:12

Observational insight into the mechanisms of submesoscale fronts modulating the carbon export to the mesopelagic oceans

submesoscale fronts, carbon export, mesopelagic ocean

This study examines the mechanisms by which submesoscale fronts modulate carbon export to the mesopelagic ocean. While physical subduction has been proposed as a rapid pathway for particulate organic carbon (POC) export, BGC-Argo observations indicate that such events are infrequent, suggesting limited direct contribution to carbon export. However, we hypothesize that submesoscale fronts may enhance carbon export indirectly by modulating the biological carbon pump within the euphotic zone. Utilizing BGC-Argo data, we captured particle export events within fronts and anticyclonic eddies. Comparison of chlorophyll-a, dissolved oxygen, and POC distributions revealed significantly higher concentrations on fronts, accompanied by a pronounced high-ratio zone of chlorophyll-a to particulate backscattering coefficient (b_bp), indicative of front-induced stimulation of phytoplankton biomass and modulation of particle size. By segregating b_bp into large and small particle signals following Briggs et al. (2020), we found that fronts hosted a larger proportion of large particles and faster sinking speeds compared to eddies. These findings align with the hypothesis that submesoscale fronts enhance POC export through modulation of the biological carbon pump, facilitating deeper penetration of larger particles. Our results emphasize the importance of submesoscale fronts in regulating carbon export via biological processes, even when physical subduction is infrequent, highlighting their pervasive role in shaping oceanic carbon sequestration.