Climate impacts on multidecadal pCO₂ variability in the North Atlantic: 1948–2009

Abstract. The North Atlantic is the most intense region of ocean CO₂ uptake in term of units per area. Here, we investigate multidecadal timescale variability of the partial pressure of CO₂ (pCO₂) that is due to the natural carbon cycle, using a regional model forced with realistic climate and preindustrial atmospheric pCO₂ for 1948–2009. Large-scale patterns of natural pCO₂ variability are primarily associated with basin-averaged sea surface temperature (SST) that, in turn, is composed of two parts: the Atlantic Multidecadal Oscillation (AMO) and a long-term positive SST trend. The North Atlantic Oscillation (NAO) drives a secondary mode of variability. For the primary mode, positive AMO and the SST trend modify pCO₂ with different mechanisms and spatial patterns. Positive AMO is also associated with a significant reduction in dissolved inorganic carbon (DIC) in the subpolar gyre, due primarily to reduced vertical mixing; the net impact of positive AMO is to reduce pCO₂ in the subpolar gyre. Through direct impacts on SST, the net effect of positive AMO is to increase pCO₂ in the subtropical gyre. From 1980 to present, long-term SST warming has amplified AMO impacts on pCO₂.