Trends in the North Atlantic carbon sink: 1992–2006

Abstract

A biogeochemical general circulation model is used to assess the impact of climate variability from 1992 to 2006 on air‐sea CO2 fluxes and ocean surface pCO2 in the North Atlantic and to understand trends in the North Atlantic carbon sink over this time period. The model indicates that the North Atlantic carbon sink increased from the mid‐1990s to the mid‐2000s. Consistent with observations, the model output indicates large changes in the physical and chemical systems of the basin. An analysis of the changes in dissolved inorganic carbon (DIC), alkalinity (ALK), and sea‐surface temperature (SST), combined with model‐derived DIC tendency terms, allow for an investigation of the mechanisms that dominate the spatial variability and magnitude of the trends in the air‐sea fluxes and pCO2. Modeled parameters compare favorably with available data from the Bermuda Atlantic Time Series in the subtropical gyre and the SURATLANT volunteer observation ship data in the subpolar gyre. Subtropical changes are controlled primarily by changes in sea‐surface temperature. Subpolar changes in pCO2 are instead driven dynamically, primarily through changing vertical supply of DIC. The amplitude of the ocean pCO2 and air‐sea flux trends are largely related to the increase in atmospheric CO2, but changes to the forcing and circulation of the North Atlantic during this period set the spatial patterns. Model changes are consistent with variation in the North Atlantic Oscillation over the period of study.