Microbial Respiration Across Subtropical Eddies: Submesoscale Variability and Biogeochemical Drivers

Abstract

Island‐induced eddies from the Canary Islands region propagate southwestward along the Canary Eddy Corridor, exporting biological and biogeochemical properties to the oligotrophic open ocean. However, their contribution to organic matter remineralization, and consequently to the biological carbon pump, throughout their life cycle remains poorly understood. Using respiratory electron transport system (ETS) activity as a proxy for microbial respiration, we investigated two cyclonic and two anticyclonic eddies at different stages of development and found distinct respiration patterns. Epipelagic respiration peaked in the most intense cyclonic eddy, whereas mesopelagic respiration showed localized maxima beneath most eddies and tended to be higher in cyclonic than in anticyclonic eddies. At submesoscale resolution, plume‐like ETS structures emerged within the mesopelagic layer, modulating respiration variability across eddies. Mesopelagic respiration variability was driven primarily by suspended particulate organic matter, whereas dissolved organic matter and its chromophoric and fluorescent protein‐like fractions contributing less. This contrasts with the greater contribution of dissolved organic matter to apparent oxygen utilization. Notably, fluorescent humic‐like substances were negatively correlated with respiration, indicating reduced microbial activity in older water masses. These findings demonstrate that mesoscale eddies can strongly regulate microbial organic matter remineralization and, consequently, influence ocean carbon cycling.