Air-sea CO2 exchange in the equatorial Pacific

Publication Type  Journal Article
Year of Publication  2004
Authors  McGillis, W. R.; Edson, J. B.; Zappa, C. J.; Ware, J. D.; McKenna, S. P.; Terray, E. A.; Hare, J. E.; Fairall, C. W.; Drennan, W.; Donelan, M.; DeGrandpre, M. D.; Wanninkhof, R.; Feely, R. A.
Journal Title  Journal of Geophysical Research-Oceans
Volume  109
Issue  C8
Pages  -
Journal Date  Aug 28
ISBN Number  0148-0227
Accession Number  ISI:000223616500001
Key Words  air-sea carbon dioxide fluxes; equatorial pacific; direct covariance technique; profile flux technique; diurnal surface layer; water gas-exchange; mixed-layer; interannual variability; surface temperature; carbon-dioxide; wind-speed; cool-skin; ocean; flu
Abstract  

[ 1] GasEx-2001, a 15-day air-sea carbon dioxide (CO2) exchange study conducted in the equatorial Pacific, used a combination of ships, buoys, and drifters equipped with ocean and atmospheric sensors to assess variability and surface mechanisms controlling air-sea CO2 fluxes. Direct covariance and profile method air-sea CO2 fluxes were measured together with the surface ocean and marine boundary layer processes. The study took place in February 2001 near 125 degreesW, 3 degreesS in a region of high CO2. The diurnal variation in the air-sea CO2 difference was 2.5%, driven predominantly by temperature effects on surface solubility. The wind speed was 6.0 +/- 1.3 m s(-1), and the atmospheric boundary layer was unstable with conditions over the range - 1 < z/L < 0. Diurnal heat fluxes generated daytime surface ocean stratification and subsequent large nighttime buoyancy fluxes. The average CO2 flux from the ocean to the atmosphere was determined to be 3.9 mol m(-2) yr(-1), with nighttime CO2 fluxes increasing by 40% over daytime values because of a strong nighttime increase in ( vertical) convective velocities. The 15 days of air-sea flux measurements taken during GasEx-2001 demonstrate some of the systematic environmental trends of the eastern equatorial Pacific Ocean. The fact that other physical processes, in addition to wind, were observed to control the rate of CO2 transfer from the ocean to the atmosphere indicates that these processes need to be taken into account in local and global biogeochemical models. These local processes can vary on regional and global scales. The GasEx-2001 results show a weak wind dependence but a strong variability in processes governed by the diurnal heating cycle. This implies that any changes in the incident radiation, including atmospheric cloud dynamics, phytoplankton biomass, and surface ocean stratification may have significant feedbacks on the amount and variability of air-sea gas exchange. This is in sharp contrast with previous field studies of air-sea gas exchange, which showed that wind was the dominating forcing function. The results suggest that gas transfer parameterizations that rely solely on wind will be insufficient for regions with low to intermediate winds and strong insolation.

Notes  

850MRTimes Cited:7Cited References Count:71

URL  <Go to ISI>://000223616500001
DOI  Doi 10.1029/2003jc002256