Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 15, issue 6
Biogeosciences, 15, 1701-1720, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Biogeosciences, 15, 1701-1720, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 22 Mar 2018

Research article | 22 Mar 2018

Uncertainty in the global oceanic CO2 uptake induced by wind forcing: quantification and spatial analysis

Alizée Roobaert1, Goulven G. Laruelle1,2,3, Peter Landschützer4, and Pierre Regnier1 Alizée Roobaert et al.
  • 1Department Geoscience, Environment & Society (DGES), Université Libre de Bruxelles, Brussels, CP160/02, Belgium
  • 2UMR 7619 Metis, Sorbonne Universités, UPMC, Univ Paris 06, CNRS, EPHE, IPSL, Paris, France
  • 3FR636 IPSL, Sorbonne Universités, UPMC, Univ Paris 06, CNRS, Paris, France
  • 4Max Planck Institute for Meteorology, Bundesstr. 53, Hamburg, 20146, Germany

Abstract. The calculation of the air–water CO2 exchange (FCO2) in the ocean not only depends on the gradient in CO2 partial pressure at the air–water interface but also on the parameterization of the gas exchange transfer velocity (k) and the choice of wind product. Here, we present regional and global-scale quantifications of the uncertainty in FCO2 induced by several widely used k formulations and four wind speed data products (CCMP, ERA, NCEP1 and NCEP2). The analysis is performed at a 1° × 1° resolution using the sea surface pCO2 climatology generated by Landschützer et al. (2015a) for the 1991–2011 period, while the regional assessment relies on the segmentation proposed by the Regional Carbon Cycle Assessment and Processes (RECCAP) project. First, we use k formulations derived from the global 14C inventory relying on a quadratic relationship between k and wind speed (k = c ⋅ U102; Sweeney et al., 2007; Takahashi et al., 2009; Wanninkhof, 2014), where c is a calibration coefficient and U10 is the wind speed measured 10m above the surface. Our results show that the range of global FCO2, calculated with these k relationships, diverge by 12% when using CCMP, ERA or NCEP1. Due to differences in the regional wind patterns, regional discrepancies in FCO2 are more pronounced than global. These global and regional differences significantly increase when using NCEP2 or other k formulations which include earlier relationships (i.e., Wanninkhof, 1992; Wanninkhof et al., 2009) as well as numerous local and regional parameterizations derived experimentally. To minimize uncertainties associated with the choice of wind product, it is possible to recalculate the coefficient c globally (hereafter called c) for a given wind product and its spatio-temporal resolution, in order to match the last evaluation of the global k value. We thus performed these recalculations for each wind product at the resolution and time period of our study but the resulting global FCO2 estimates still diverge by 10%. These results also reveal that the Equatorial Pacific, the North Atlantic and the Southern Ocean are the regions in which the choice of wind product will most strongly affect the estimation of the FCO2, even when using c.

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