Large contribution of the sea-ice zone to Southern Ocean carbon export revealed by BGC-Argo floats

Abstract

Abstract The Southern Ocean (south of 30°S) contributes significantly to global ocean carbon uptake through the solubility pump and phytoplankton productivity. Many studies have estimated carbon export to the deep ocean, but very few have attempted a basin-scale perspective. In this study, we use an extensive array of BGC-Argo floats to improve previous estimates of carbon export across basins and frontal zones, with a focus on the seasonal ice zone (SIZ). We find that the SIZ contributes 33% of the total circumpolar carbon export of 5.08 PgC y− 1. We also show that subsurface carbon respiration, not flux out of the surface ocean, contributes most strongly to the temporal and spatial variability of subsurface particulate organic carbon. Our work highlights the importance of closely monitoring the SIZ, because it is an area prone to extreme events and strong interannual variability, but also for more accurately quantifying the total Southern Ocean carbon sink. Tightening these estimates and their drivers ultimately impacts our understanding of climate variability at the global ocean scale.