What did we do?     We analyzed a suite of Earth System Models (ESMs) used in the IPCC’s Fifth Assessment Report to examine the response of the Southern Ocean’s carbon storage in this century. We explained the average behavior of the ESMs using a simpler ocean model.

What did we find?     We found that the Southern Ocean gets warmer and fresher, and its the formation of bottom water weakens in the warming climate. As a result it tends to better traps deeply sequestered carbon. This mechanism helps the Southern Ocean to hold onto its carbon stock even though the global ocean carbon uptake is declining in the warming climate.

Why is this important?     We are worried about the ocean’s ability to absorb carbon dioxide in the future – Models predict that the oceans will not be as effective as absorbing fossil fuel CO2 in the warming climate. As a part of OCB-CLIVAR working group, we analyzed this effect in the Southern Ocean, which is the major carbon sink. To our surprise, this region’s carbon stock is somewhat resilient due to internally compensating changes. However, the global carbon uptake, which is what really matters for the GHGs and climate warming, is still declining in the warming climate.

Reference: Ito T., A. Bracco, C. Deutsch, H. Frenzel, M. Long and Y. Takano, (2015), Sustained growth of the Southern Ocean carbon storage in a warming climate, Geophysical Research Letters, 42, doi:10.1002/2015GL064320