The Carbon Cycle from North to South along the Galathea 3 Route

Air-sea exchange of CO2 is parameterized along the cruise track of Galathea 3 – a worldwide research expedition. A key parameter is the gas transfer velocity, which varies with wind speed. Wind speeds are measured continuously on board the research vessel. For selected areas, winds are also retrieved from Envisat ASAR images, as the ASAR senses small-scale waves at the sea surface generated by the local wind. A demonstration from the coastal up-welling zone of Peru shows that CO2 fluxes are numerically smaller when satellite winds, rather than ship measurements of the wind speed, are used to determine the gas transfer velocity. This difference is likely related to the presence of algae films at the sea surface of the cold and nutrient rich up-welling waters. Algae films have a damping effect on small-scale surface waves and are also believed to hamper air-sea CO2 transfers. Satellite wind maps may thus be better indicators of the gas transfer velocity than the wind speed at 10 m measured from ships or masts. The relationship between the wind and the CO2 transfer velocity will be investigated further from a combination of ship and satellite data obtained along the Galathea 3 route.