Air-sea CO2 exchange in the equatorial Pacific

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Read Full Article (file size: 962559 bytes) Cited by 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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