THERMAL SKIN EFFECT OF THE SURFACE OCEAN AND ITS IMPLICATIONS FOR CO2 UPTAKE

AN understanding of the natural sources and sinks of atmospheric carbon dioxide is necessary for predictions of future atmospheric loading and its consequences for global climate. Present estimates of emissions and uptake do not balance1, and although some have attributed the imbalance to a terrestrial sink2, the magnitude of the oceanic sink remains unresolved2-4. It is known5-8 that the upper 1 mm or so of the oceans represents a cool 'skin', with a temperature gradient such that the surface is generally cooler than the bulk mixed layer by about 0.3-degrees-C as a result of the upward heat flux. Here we discuss the consequences of the 'skin effect' for the global air-sea flux of CO2. We show that it produces an increased oceanic global uptake of about 0.7 Gt C yr-1, when the flux from the atmosphere to the oceans is calculated on the basis of measured surface-ocean partial pressures of CO2. This correction helps to bring into closer agreement the oceanic CO2 uptake calculated by different methods2-4.