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JOURNAL OF GEOPHYSICAL RESEARCH,
VOL. 109,
C08S02,
doi:10.1029/2003JC002256,
2004
Air-sea CO2 exchange in the equatorial Pacific
Wade R. McGillis
Lamont-Doherty Earth Observatory, Palisades, New York, USA
James B. Edson
Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA
Christopher J. Zappa
Lamont-Doherty Earth Observatory, Palisades, New York, USA
Jonathan D. Ware
Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA
Sean P. McKenna
Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA
Eugene A. Terray
Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA
Jeffrey E. Hare
Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA
Christopher W. Fairall
NOAA Environmental Technology Laboratory, Boulder, Colorado, USA
William Drennan
Division of Applied Marine Physics, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida,
USA
Mark Donelan
Division of Applied Marine Physics, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida,
USA
Michael D. DeGrandpre
Department of Chemistry, University of Montana, Missoula, Montana, USA
Rik Wanninkhof
NOAA Atlantic Oceanographic and Meteorological Laboratory, Miami, Florida, USA
Richard A. Feely
NOAA Pacific Marine and Environmental Laboratory, Seattle, Washington, USA
Abstract
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°W, 3°S 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.
Received 17
December
2003;
accepted 21
July
2004;
published 28
August
2004.
Keywords: air-sea carbon dioxide fluxes;
equatorial Pacific;
direct covariance technique;
profile flux technique;
diurnal surface layer.
Index Terms: 0312 Atmospheric Composition and Structure: Air/sea constituent fluxes (3339, 4504); 3307 Meteorology and Atmospheric Dynamics: Boundary layer processes; 3339 Meteorology and Atmospheric Dynamics: Ocean/atmosphere interactions (0312, 4504); 4231 Oceanography: General: Equatorial oceanography; 4227 Oceanography: General: Diurnal, seasonal, and annual cycles.
Read Full Article (file size: 962559 bytes) Cited by
Citation: McGillis, W. R., et al.
(2004),
Air-sea CO2 exchange in the equatorial Pacific,
J. Geophys. Res.,
109,
C08S02,
doi:10.1029/2003JC002256.
Copyright 2004 by the American Geophysical Union.
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