Sustained growth of the Southern Ocean carbon storage in a warming climate

We investigate the mechanisms controlling the evolution of Southern Ocean carbon uptake and storage under a climate warming scenario. A subset of CMIP-5 models predicts that the inventory of biologically sequestered carbon south of 40ºS increases about 18-34PgC by 2100 relative to the preindustrial condition. To put this in a context, this is 9 to 17 years equivalent of additional carbon sink relative to the current rate of ~2PgC/year. We perform sensitivity experiments using an ocean circulation and biogeochemistry model to diagnose the mechanism behind this increased carbon storage. While ocean heat uptake reduces the solubility of CO₂, intensified and poleward-shifted westerly wind strengthens the upper overturning circulation, leading to an increased uptake of anthropogenic CO₂. Increased ventilation also releases biologically regenerated carbon to the atmosphere. Freshening of Antarctic Surface Water causes a slowdown of the lower overturning circulation, leading to an increased retention of biologically sequestered carbon in the deep water. The combination of these processes leads to the sustained growth of the carbon storage in the Southern Ocean, even under the warming climate with a weaker global ocean carbon uptake.