What does chlorophyll variability tell us about export and air‐sea CO2 flux variability in the North Atlantic?

Abstract

The importance of biology to the ocean carbon sink is often quantified in terms of export, the removal of carbon from the ocean surface layer. Satellite images of sea surface chlorophyll indicate variability in biological production, but how these variations affect export and air‐sea carbon fluxes is poorly understood. We investigate this in the North Atlantic using an ocean general circulation model coupled to a medium‐complexity ecosystem model. We find that biological CO2 drawdown is significant on the mean and dominates the seasonal cycle of pCO2, but variations in the annual air‐sea CO2 flux and export are not significantly correlated. Large year‐to‐year variability in summertime pCO2 occurs, because of changing bloom timing, but integrated bloom strength and associated carbon uptake and export do not vary substantially. The model indicates that small biological variability, quantitatively consistent with SeaWiFS (1998–2006), is not sufficient to be a first‐order control on annual subpolar air‐sea CO2 flux variability.