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Significant advances have been made over the last decade in estimating air-sea CO2 fluxes over the ocean by the bulk formulation that expresses the flux as the product of the gas transfer velocity and the concentration difference of aqueous CO2 over the liquid boundary layer. This has resulted in a believable global monthly climatology of air-sea CO2 fluxes over the ocean on a 4o by 5o grid [38]. It is shown here that the global air-sea CO2 fluxes are very sensitive to estimates of gas transfer velocity and the parameterization of gas transfer with wind. Wind speeds can now be resolved at sufficient temporal and spatial resolution that they should not limit the estimates, but the absolute magnitudes of winds for different wind products differ significantly. It is recommended to use satellite-derived wind products that have the appropriate resolution instead of assimilated products that often do not appropriately resolve variability on sub-daily and sub-25-km space scales. Parameterizations of gas exchange with wind differ in functional form and magnitude but the difference between the most-used quadratic relationships is about 15%. Based on current estimates of uncertainty of the air-water CO2 concentration differences, the winds, and the gas exchange-wind speed parameterization, each parameter contributes similarly to the overall uncertainty in the flux that is estimated at 25%. [ABSTRACT FROM AUTHOR]

Studies deploying atmospheric flux-profile techniques in laboratory wind-wave tanks have been performed to demonstrate and verify the use of airside turbulent transport models and micrometeorological approaches to accurately determine air-water gas transfer velocities. Air-water gas transfer velocities have been estimated using the CO2 atmospheric flux-profile technique in laboratory wind-wave tanks both at the NASA Wallops Flight Facility, USA and Kyoto University, Japan. Gas fluxes using the flux-profile and the waterside mass balance techniques have been reconciled. Air-water fluxes of H2O and momentum were also measured simultaneously in a linear wind-wave tank. The waterside mass balances used the evasion of SF6. The CO2, H2O, and momentum fluxes were calculated using the atmospheric flux-profile technique over a wind speed range of 1 to 14 m s−1. The CO2 and H2O atmospheric profile model uses airside turbulent diffusivities derived from momentum fluxes. These studies demonstrate that the quantification of air-water CO2 fluxes using the atmospheric flux-profile technique can be implemented in the laboratory. The profile technique can be used to measure an air-water flux in much less time than a mass balance. Effects of surfactants, wind speed, and wind stress on air-water transfer are also explored using the flux-profile technique. Validation of the air-water CO2 gas exchange in laboratory wind-wave tanks provides evidence and support that this technique may be used in field studies. [ABSTRACT FROM AUTHOR]

Measurements of partial pressure of CO2 in surface waters (pCO2sw) and overlying air (pCO2air) were made intermittently in the central and western equatorial Pacific from January 1987 to January 2003. We estimated the long-term trend of the pCO2sw in the high nutrient low chlorophyll (HNLC) region and the western Pacific warm pool. The spatial distribution of pCO2sw in the HNLC region could be expressed as a linear function of sea surface temperature (SST) and concentration of macronutrients ([NO2-]+[NO3-]), and in the western Pacific warm pool as a function of SST and sea surface salinity (SSS). By using an average SST (27.4 °C) and concentration of nitrate and nitrite (3.9 μmol/kg) in the HNLC region and the average SST (29.6 1C) and SSS (34.29) in the western Pacific warm pool between 1987 and 2003, we obtained pCO2sw values for respective cruises. The growth rate of pCO2sw due to increases in atmospheric CO2 was calculated to be 1.4±0.5 μatm/yr in the HNLC region and 1.3±0.3 μatm/yr in the western Pacific warm pool. The sea—air CO2 flux in the equatorial Pacific since 1998 was evaluated by using underway pCO2sw data measured by Japan Meteorological Agency, Meteorological Research Institute (JMA/MRI), National Oceanic and Atmospheric Administration, Pacific Marine Environmental Laboratory (NOAA/PMEL), and NOAA, Atlantic Oceanographic and Meteorological Laboratory (NOAA/AOML). From 1998 to 2003 the sea—air CO2 flux in the equatorial Pacific (5°N-10°S, 140°E-90°W) showed lowest flux in January/February 1998 (0.1±0.1 Pg C/yr, 1997/98 El Niño), and highest (0.9±0.4 Pg C/yr) in January/February 2001, suggesting significant interannual variations in sea—air CO2 flux in the equatorial Pacific. In October 2002—January 2003, which was within a weak El Niño period, the CO2 flux in the equatorial Pacific was 0.5±0.3 Pg C/yr, almost same as that of the non-El Niño period. In this period, sea—air CO2 flux in the central and western equatorial Pacific decreased considerably to the same level of January/February 1998, but that in the eastern equatorial Pacific remained fairly constant. [ABSTRACT FROM AUTHOR]