Suppression of air-sea CO2 transfer by surfactants – direct evidence from the Southern Ocean
<p>Uncertainty in the CO<sub>2</sub> gas transfer velocity (K<sub>660</sub>) severely limits the accuracy of air-sea CO<sub>2</sub> flux calculations and hence hinders our ability to produce realistic climate projections.&#160; Recent field observations have suggested substantial variability in K<sub>660</sub>, especially at low and high wind speeds.&#160; Laboratory experiments have shown that naturally occurring surface active organic materials, or surfactants, can suppress gas transfer.&#160; Here we provide direct open ocean evidence of gas transfer suppression due to surfactants from a ~11,000 km long research expedition by making measurements of the gas transfer efficiency (GTE) along with direct observation of K<sub>660</sub>.&#160; GTE varied by 20% during the Southern Ocean transect and was distinct in different watermasses.&#160; Furthermore GTE correlated with and can explain about 9% of the scatter in K<sub>660</sub>, suggesting that surfactants exert a measurable influence on air-sea CO<sub>2</sub> flux.&#160; Relative gas transfer suppression due to surfactants was ~30% at a global mean wind speed of 7 m s<sup>-1</sup> and was more important at lower wind speeds.&#160; Neglecting surfactant suppression may result in substantial spatial and temporal biases in the computed air-sea CO<sub>2</sub> fluxes.</p>