Interannual variability in atmospheric CO2 uptake on the northeast U.S. continental shelf

Abstract

Continental shelf systems are thought to play an important role in the exchange of carbon dioxide (CO2) between the atmosphere and ocean. Currently, our ability to quantify the air‐sea flux of CO2 on continental shelves is limited due to large spatial and temporal variability coupled with historically sparse oceanographic measurements (e.g., of surface water pCO2). Here we use the Regional Ocean Modeling System (ROMS) to quantify the air‐sea flux of CO2 and its interannual variability on the northeast U.S. continental shelf, which includes the Middle Atlantic Bight (MAB) and Gulf of Maine (GOM). Two years marked by opposite phases of the North Atlantic Oscillation (NAO) are considered in the study. A novel analysis method, second‐order Taylor series decomposition, is used to identify the important processes responsible for producing NAO‐related changes in the CO2 air‐sea flux. On the northeast U.S. shelf, atmospheric CO2 uptake as simulated by ROMS decreases from 2.4 Mt C yr−1 in 1985 (low NAO) to 1.8 Mt C yr−1 in 1990 (high NAO), with most of this decrease (0.5 Mt C yr−1) occurring in the MAB. In the MAB the difference in annual air‐sea flux of CO2 is due mainly to changes in near‐surface wind speed, while the flux difference in the GOM is controlled primarily by surface water pCO2 (CO2 partial pressure) changes resulting from changes in sea surface temperature and new production. The large magnitude of interannual variability in the air‐sea flux of CO2 simulated here suggests the potential for even more significant flux changes in the future as climate change accelerates.