Spatial variability in the sink for atmospheric carbon dioxide in the North Atlantic

Abstract

DIRECT calculation of the air-sea flux of CO₂ requires detailed knowledge of the partial pressure of carbon dioxide ($P_{{\text{CO}}_{\text{2}}}$) and gas-transfer velocities at the surface of the global ocean¹, with the available observations of surface $P_{{\text{CO}}_{\text{2}}}$ suggesting that it varies in a smooth manner with season and position over the major ocean regions^2-5. In spring 1989 we mapped surface $P_{{\text{CO}}_{\text{2}}}$, total inorganic carbon (TIC), chlorophyll, temperature and salinity at several locations between 47° N and 60° N in the northeast Atlantic near 20° W, observing large variations in $P_{{\text{CO}}_{\text{2}}}$ on spatial scales of ≪100 km, Correlated with plankton chlorophyll, surface temperature and TIC. The variation of $P_{{\text{CO}}_{\text{2}}}$ with latitude was in the opposite sense to that previously reported for this region^3-5. Thus, in this ocean area and season at least, the air-sea flux is strongly modulated by biological activity and variable on short spatial scales. The inhomogeneity observed suggests that estimates of the oceanic sink for fossil fuel inferred from existing data (relatively sparse even in the North Atlantic) will be subject to significant error.