Climate impacts on multidecadal <i>p</i>CO₂ variability in the North Atlantic: 1948–2009

Abstract

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.