29 Mar 2021

29 Mar 2021

Review status: this preprint is currently under review for the journal ESSD.

Harmonization of global surface ocean pCO2 mapped products and their flux calculations; an improved estimate of the ocean carbon sink

Amanda R. Fay1, Luke Gregor2, Peter Landschützer3, Galen A. McKinley1, Nicolas Gruber2, Marion Gehlen4, Yosuke Iida5, Goulven G. Laruelle6, Christian Rödenbeck7, and Jiye Zeng8 Amanda R. Fay et al.
  • 1Columbia University and Lamont Doherty Earth Observatory, Palisades NY, USA
  • 2Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, Zürich, Switzerland
  • 3Max Planck Institute for Meteorology, 20146 Hamburg, Germany
  • 4Laboratoire des Sciences du Climat et de l'Environnement, Institut Pierre Simon Laplace, Gif‐Sur‐Yvette, France
  • 5Atmosphere and Ocean Department, Japan Meteorological Agency, 1-3-4 Otemachi, Chiyoda-Ku, Tokyo 100-8122, Japan
  • 6Dept. - Geoscience, Environment & Society (DGES), Université Libre de Bruxelles, Bruxelles, CP16002, Belgium
  • 7Biogeochemical Signals, Max Planck Institute for Biogeochemistry, P.O. Box 600164, Hans-Knöll-Str. 10, 07745 Jena, Germany
  • 8National Institute for Environmental Studies (NIES), 16-2 Onogawa, Tsukuba, Ibaraki, 305-8506, Japan

Abstract. Air-sea flux of carbon dioxide (CO2) is a critical component of the global carbon cycle and the climate system with the ocean removing about a quarter of the CO2 emitted into the atmosphere by human activities over the last decade. A common approach to estimate this net flux of CO2 across the air-sea interface is the use of surface ocean CO2 observations and the computation of the flux through a bulk parameterization approach. Yet, the details for how this is done in order to arrive at a global ocean CO2 uptake estimate varies greatly, unnecessarily enhancing the uncertainties. Here we reduce some of these uncertainties by harmonizing an ensemble of products that interpolate surface ocean CO2 observations to near global coverage. We propose a common methodology to fill in missing areas in the products and to calculate fluxes and present a new estimate of the net flux. The ensemble data product, SeaFlux (Fay et al. (2021),,, accounts for the diversity of the underlying mapping methodologies. Utilizing six global observation-based mapping products (CMEMS-FFNN, CSIR-ML6, JENA-MLS, JMA-MLR, MPI-SOMFFN, NIES-FNN), the SeaFlux ensemble approach adjusts for methodological inconsistencies in flux calculations that can result in an average error of 15 % in global mean flux estimates. We address differences in spatial coverage of the surface ocean CO2 between the mapping products which ultimately yields an increase in CO2 uptake of up to 19 % for some products. Fluxes are calculated using three wind products (CCMPv2, ERA5, and JRA55). Application of an appropriately scaled gas exchange coefficient has a greater impact on the resulting flux than solely the choice of wind product. With these adjustments, we derive an improved ensemble of surface ocean pCO2 and air-sea carbon flux estimates. The SeaFlux ensemble suggests a global mean uptake of CO2 from the atmosphere of 1.92 +/- 0.35 PgC yr-1. This work aims to support the community effort to perform model-data intercomparisons which will help to identify missing fluxes as we strive to close the global carbon budget.

Amanda R. Fay et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on essd-2021-16', Rik Wanninkhof, 29 Apr 2021
    • AC1: 'Reply on RC1', Luke Gregor, 21 Jun 2021
  • RC2: 'Comment on essd-2021-16', Timothy DeVries, 01 May 2021
    • AC2: 'Reply on RC2', Luke Gregor, 21 Jun 2021
  • RC3: 'Comment on essd-2021-16', Andrea Fassbender, 10 May 2021
    • AC3: 'Reply on RC3', Luke Gregor, 21 Jun 2021

Amanda R. Fay et al.

Data sets

SeaFlux data set: Air-sea CO2 fluxes for surface pCO2 data products using a standardised approach Luke Gregor and Amanda Fay

Amanda R. Fay et al.


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Short summary
The movement of carbon dioxide from the atmosphere to the ocean is estimated using surface ocean carbon (pCO2) measurements and an equation including variables such as temperature and wind speed; the choices of these variables lead to uncertainties. Introducing the SeaFlux ensemble which provides carbon flux maps calculated in a consistent manner, thus reducing uncertainty by using common choices for wind speed and a set definition of "global" coverage.