THE WARM OCEANIC SURFACE-LAYER - IMPLICATIONS FOR CO2 FLUXES AND SURFACE GAS MEASUREMENTS

The ocean and air-sea interface are important for the exchange of heat , momentum, water vapour and carbon-dioxide. The details of the exchan ge mechanisms, which are often coupled and complex, have to be underst ood in order to assess the future role of the global oceans in climate change. Recently; much attention has focused on the 'thermal skin eff ect', cooling or warming of the uppermost millimeters of the sea Surfa ce, and its global implications for enhancing CO2 uptake [Robertson an d Watson, 1992; Van Scoy et al., 1995]. Routinely, air-sea flux estima tes derived from oceanic pCO(2) measurements are corrected for the usu ally cooler thermal Skin by applying a correction factor [Sarmiento an d Sundquist, 1992; Wong et al,, 1995]. Here we describe how near surfa ce warming of the upper few meters of the ocean by solar radiation, ro utinely observed but not fully appreciated in this context, can signif icantly affect the net daily exchange of CO2 over and above the skin e ffect, and can even lead to a reversal of the direction of the air-sea flux calculated from pCO(2) measurements and wind speed alone. The wa rming and cooling cycle produces a net asymmetry between CO2 invasion and evasion, having the effect of decreasing CO2 invasion:and increasi ng CO2 evasion.