Shifting winds weakened the recent Southern Ocean CO2 absorption

Similar to a fizzy drink, the ocean can hold dissolved gases. The global ocean absorbs about one quarter of the annually emitted CO₂ by humans. Half of this uptake occurs in the ocean surrounding Antarctica, i.e. the Southern Ocean making it one of the most important marine sinks for anthropogenic CO₂.

However, the amount of CO₂ absorbed by the Southern Ocean changes over the years. In the 1980^s and 1990^s, the Southern Ocean carbon sink stalled, while in the 2000^s, the sink regained its expected uptake strength. Researchers at MPI-M have investigated what happened since then.

The Southern Ocean is extremely harsh, cold, and very remote. Hence, ship measurements are rare in this region. Therefore, Keppler and Landschützer used a machine learning algorithm to fill data gaps in the measurements.

They found that the Southern Ocean carbon sink has weakened again since 2012, despite a continued increase in atmospheric CO₂. The authors explain this by shifts in regional wind pattern resulting in enhanced regional upwelling of carbon rich deep water. Like a fizzy drink losing its bubbles, some carbon at the surface returned to the air. This loss meant that overall less carbon was absorbed in the Southern Ocean.