Episodic subduction patches in the western North Pacific identified from BGC-Argo float Data
Abstract. Subduction associated with mesoscale eddies is an important but difficult to observe process that can efficiently export carbon and oxygen to the mesopelagic zone (100–1000 db). Using a novel BGC-Argo dataset covering the western North Pacific (20–50° N, 120–180° E), we identified imprints of episodic subduction using anomalies in dissolved oxygen and spicity, a water mass marker. These subduction patches were present in 4.0 % (288) of the total profiles (7,120) between 2008 and 2019, situated mainly in the Kuroshio Extension region between March and August (70.6 %). Unlike eddy subduction processes observed at higher latitudes, roughly half (52 %) of these episodic events injected carbon- and oxygen-enriched waters below the annual permanent thermocline depth (450 db), with > 20 % occurring deeper than 600 db. Export rates within these subductions are estimated to be on the order of 85–159 mg C m−2 day−1 and 175 to 417 mg O2 m−2 day−1. These mesoscale events would markedly increase carbon removal above that due to biological gravitational settling as well as oxygen ventilation in the region, both helping to support the nutritional and metabolic demands of mesopelagic organisms. Climate-driven patterns of increasing eddy kinetic energies in this region imply that the magnitude of these processes will grow in the future, meaning that these unexpectedly effective small-scale subduction processes need to be better constrained in global climate and biogeochemical models.