Air-sea gas transfer velocity for oxygen derived from float data

We estimated the air-sea gas transfer velocity for oxygen using 3 consecutive years (September 2003 to August 2006) of high-quality oxygen measurements from profiling floats in the central Labrador Sea. Mixed layer oxygen concentrations exhibit strong seasonality characterized by biologically and thermally driven evasion during spring/summer and invasion during fall/winter caused by cooling and ventilation of oxygen deficient subsurface waters. Mixed layer oxygen budgets entirely excluding the spring bloom period are employed to estimate the air-sea transfer velocity for oxygen. By using colocated wind speed data acquired by scatterometry from the QuikSCAT satellite, wind speed-dependent parameterizations for the air-sea gas transfer velocity k(660) (CO2 at 20 degrees C and salinity 35) are established and compared with prominent parameterizations from the literature. Quadratic, cubic, and quartic functions are fitted to the data for short-term and long-term wind speed averages separately. In both cases, the quadratic functions yield the poorest fit to the observations. Overall, the stronger curvature of the cubic functions provides the best fit, while the quartic function also fits the data less well. Our results generally confirm the stronger wind speed dependencies among the suite of published parameterizations. Also, the better fits found for cubic function point at the strong importance of very high wind speed for air-sea gas exchange of O-2.