Articles | Volume 11, issue 3
Biogeosciences, 11, 709–734, 2014

Special issue: REgional Carbon Cycle Assessment and Processes (RECCAP)

Biogeosciences, 11, 709–734, 2014

Research article 06 Feb 2014

Research article | 06 Feb 2014

Air–sea CO2 flux in the Pacific Ocean for the period 1990–2009

M. Ishii1,2, R. A. Feely3, K. B. Rodgers4, G.-H. Park5,6,*, R. Wanninkhof5, D. Sasano1,2, H. Sugimoto2, C. E. Cosca3, S. Nakaoka7, M. Telszewski7,**, Y. Nojiri7, S. E. Mikaloff Fletcher8, Y. Niwa1, P. K. Patra9, V. Valsala7,***, H. Nakano1, I. Lima10, S. C. Doney10, E. T. Buitenhuis11, O. Aumont12, J. P. Dunne13, A. Lenton14, and T. Takahashi15 M. Ishii et al.
  • 1Oceanography and Geochemistry Research Department, Meteorological Research Institute, Japan Meteorological Agency, Tsukuba, 305-0052, Japan
  • 2Global Environment and Marine Department, Japan Meteorological Agency, Tokyo, 100-8122, Japan
  • 3Ocean Climate Research Division, Pacific Marine Environmental Laboratory, NOAA, Seattle, WA 98115, USA
  • 4Program in Atmospheric and Oceanic Sciences, Princeton University, Princeton, NJ 08544, USA
  • 5Ocean Chemistry Division, Atlantic Oceanographic and Meteorological Laboratory, NOAA, Miami, FL 33149, USA
  • 6Cooperative Institute for Marine and Atmospheric Studies, University of Miami, Miami, FL 33149-1098, USA
  • 7Center for Global Environmental Research, National Institute for Environmental Studies, Tsukuba, 305-8506, Japan
  • 8National Institute of Water and Atmospheric Research, Wellington, 6021, New Zealand
  • 9Research Institute for Global Change, Japan Agency for Marine Science and Technology, Yokohama, 236-0001 Japan
  • 10Marine Chemistry and Geochemistry Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
  • 11School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK
  • 12Laboratoire de Physique des Océans, Centre IRD de Bretagne, 29280 Plouzané, France
  • 13Geophysical Fluid Dynamics Laboratory, NOAA, Princeton, NJ, 08540-6649, USA
  • 14Centre for Australian Weather and Climate Research, CSIRO Marine and Atmospheric Research, Hobart, Tasmania, 7000, Australia
  • 15Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA
  • *now at: East Sea Research Institute, Korea Institute of Ocean Science & Technology, Uljin, 767-813 Korea
  • **now at: International Ocean Carbon Coordination Project, Institute of Oceanology of Polish Academy of Sciences, ul. Powstancow Warszawy, 81-712 Sopot, Poland
  • ***now at: Indian Institute of Tropical Meteorology, Pune, Maharashtra, India

Abstract. Air–sea CO2 fluxes over the Pacific Ocean are known to be characterized by coherent large-scale structures that reflect not only ocean subduction and upwelling patterns, but also the combined effects of wind-driven gas exchange and biology. On the largest scales, a large net CO2 influx into the extratropics is associated with a robust seasonal cycle, and a large net CO2 efflux from the tropics is associated with substantial interannual variability. In this work, we have synthesized estimates of the net air–sea CO2 flux from a variety of products, drawing upon a variety of approaches in three sub-basins of the Pacific Ocean, i.e., the North Pacific extratropics (18–66° N), the tropical Pacific (18° S–18° N), and the South Pacific extratropics (44.5–18° S). These approaches include those based on the measurements of CO2 partial pressure in surface seawater (pCO2sw), inversions of ocean-interior CO2 data, forward ocean biogeochemistry models embedded in the ocean general circulation models (OBGCMs), a model with assimilation of pCO2sw data, and inversions of atmospheric CO2 measurements. Long-term means, interannual variations and mean seasonal variations of the regionally integrated fluxes were compared in each of the sub-basins over the last two decades, spanning the period from 1990 through 2009. A simple average of the long-term mean fluxes obtained with surface water pCO2 diagnostics and those obtained with ocean-interior CO2 inversions are −0.47 ± 0.13 Pg C yr−1 in the North Pacific extratropics, +0.44 ± 0.14 Pg C yr−1 in the tropical Pacific, and −0.37 ± 0.08 Pg C yr−1 in the South Pacific extratropics, where positive fluxes are into the atmosphere. This suggests that approximately half of the CO2 taken up over the North and South Pacific extratropics is released back to the atmosphere from the tropical Pacific. These estimates of the regional fluxes are also supported by the estimates from OBGCMs after adding the riverine CO2 flux, i.e., −0.49 ± 0.02 Pg C yr−1 in the North Pacific extratropics, +0.41 ± 0.05 Pg C yr−1 in the tropical Pacific, and −0.39 ± 0.11 Pg C yr−1 in the South Pacific extratropics. The estimates from the atmospheric CO2 inversions show large variations amongst different inversion systems, but their median fluxes are consistent with the estimates from climatological pCO2sw data and pCO2sw diagnostics. In the South Pacific extratropics, where CO2 variations in the surface and ocean interior are severely undersampled, the difference in the air–sea CO2 flux estimates between the diagnostic models and ocean-interior CO2 inversions is larger (0.18 Pg C yr−1). The range of estimates from forward OBGCMs is also large (−0.19 to −0.72 Pg C yr−1). Regarding interannual variability of air–sea CO2 fluxes, positive and negative anomalies are evident in the tropical Pacific during the cold and warm events of the El Niño–Southern Oscillation in the estimates from pCO2sw diagnostic models and from OBGCMs. They are consistent in phase with the Southern Oscillation Index, but the peak-to-peak amplitudes tend to be higher in OBGCMs (0.40 ± 0.09 Pg C yr−1) than in the diagnostic models (0.27 ± 0.07 Pg C yr−1).

Final-revised paper