Stationary Rossby waves dominate subduction of anthropogenic carbon in the Southern Ocean

Abstract

The Southern Ocean has taken up more than 40% of the total anthropogenic carbon (C_ant) stored in the oceans since the preindustrial era, mainly in subantarctic mode and intermediate waters (SAMW-AAIW). However, the physical mechanisms responsible for the transfer of C_ant into the ocean interior remain poorly understood. Here, we use high resolution (1/10°) ocean simulations to investigate these mechanisms at the SAMW-AAIW subduction hotspots. Mesoscale Stationary Rossby Waves (SRWs), generated where the Antarctic Circumpolar Current interacts with topography, make the dominant contribution to the C_ant transfer in SAMW-AAIW in the Indian and Pacific sectors (66% and 95% respectively). Eddy-resolving simulations reproduce the observed C_ant sequestration in these layers, while lower spatial resolution models, that do not reproduce SRWs, underestimate the inventory of C_ant in these layers by 40% and overestimate the storage in denser layers. A key implication is that climate model simulations, that lack sufficient resolution to represent sequestration by SRWs, are therefore likely to overestimate the residence time of C_ant in the ocean, with implications for simulated rates of climate change.