Geophysical and biogeochemical observations using BGC Argo floats in the western North Pacific during late winter and early spring. Part 1: Restratification processes of the surface mixed layer

Abstract. To understand oceanic restratification in the subtropical northwestern Pacific and its influence on biogeochemical (BGC) processes, we examined post-storm restratification events observed from February to April 2018 by BGC-Argo floats, the BGC data from which were stoichiometrically analyzed by Sukigara et al. (2021; this issue). We found that during these events, restratification of the mixed layer (ML) was driven by geostrophic adjustment or ML eddy formation related to surface cooling during February to March. At the end of March, high surface chlorophyll a concentrations were observed within submesoscale eddies and at the edge of a mesoscale cyclonic feature observed from satellite data. Our results indicate that primary production in the subtropical northwestern Pacific is enhanced by the combined effects of mesoscale upwelling, storm-driven formation of a deep ML, subsequent formation of ML eddies, weak cooling, and the length of intervals between storms.