Circulation-driven variability of Atlantic anthropogenic carbon transports and uptake

The ocean absorbs approximately a quarter of the carbon dioxide currently released to the atmosphere by human activities (C anth ). A disproportionately large fraction accumulates in the North Atlantic due to the combined effects of transport by the Atlantic Meridional Overturning Circulation (AMOC) and air–sea exchange. However, discrepancies exist between modelled and observed estimates of the air–sea exchange due to unresolved ocean transport variability. Here we quantify the strength and variability of C anth transports across 26.5° N in the North Atlantic between 2004 and 2012 using circulation measurements from the RAPID mooring array and hydrographic observations. Over this period, decreasing circulation strength tended to decrease northward C anth transport, while increasing C anth concentrations (preferentially in the upper limb of the overturning circulation) tended to increase northward C anth transport. These two processes compensated each other over the 8.5-year period. While ocean transport and air–sea C anth fluxes are approximately equal in magnitude, the increasing accumulation rate of C anth in the North Atlantic combined with a stable ocean transport supply means we infer a growing contribution from air–sea C anth fluxes over the period. North Atlantic C anth accumulation is thus sensitive to AMOC strength, but growing atmospheric C anth uptake continues to significantly impact C anth transports.