Key Uncertainties in the Recent Air‐Sea Flux of CO2

Type Article
Date 2019-12
Language English
Author(s) Woolf D.K.1, Shutler J.D.2, Goddijn‐murphy L.3, Watson A.J.2, Chapron BertrandORCID4, Nightingale P.D.5, Donlon C.J.6, Piskozub J.7, Yelland M.J.8, Ashton Ian9, Holding T.2, Schuster U.2, Girard-Ardhuin FannyORCID4, Grouazel AntoineORCID4, Piolle Jean-Francois4, Warren M.5, Wrobel‐niedzwiecka I.7, Land P.E.5, Torres R.5, Prytherch J.8, Moat B.8, Hanafin J.10, Ardhuin FabriceORCID10, Paul Frederic4
Affiliation(s) 1 : International Centre for Island Technology, Heriot‐Watt University, UK
2 : College of Life and Environmental Sciences, University of Exeter, UK
3 : University of the Highlands and Islands ,UK
4 : Ifremer, Univ. Brest, CNRS, IRD, Laboratoire d’Oceanographie Physique et Spatiale (LOPS), IUEM Brest, France
5 : Plymouth Marine Laboratory, UK
6 : European Space Agency ,The Netherlands
7 : Institute of Oceanology, Polish Academy of Sciences Sopot ,Poland
8 : National Oceanography Centre Southampton ,UK
9 : College of Engineering, Mathematics and Physical Sciences, University of Exeter ,UK
10 : Ifremer, Univ. Brest, CNRS, IRD, Laboratoire d’Oceanographie Physique et Spatiale (LOPS), IUEM Brest, France
Source Global Biogeochemical Cycles (0886-6236) (American Geophysical Union (AGU)), 2019-12 , Vol. 33 , N. 12 , P. 1548-1563
DOI 10.1029/2018GB006041
WOS© Times Cited 41
Keyword(s) Carbon dioxide, air-sea flux, uncertainty, transfer velocity, sampling

The contemporary air‐sea flux of CO2 is investigated by the use of an air‐sea flux equation, with particular attention to the uncertainties in global values and their origin with respect to that equation. In particular, uncertainties deriving from the transfer velocity and from sparse upper ocean sampling are investigated. Eight formulations of air‐sea gas transfer velocity are used to evaluate the combined standard uncertainty resulting from several sources of error. Depending on expert opinion, a standard uncertainty in transfer velocity of either ~5% or ~10% can be argued and that will contribute a proportional error in air‐sea flux. The limited sampling of upper ocean fCO2 is readily apparent in the Surface Ocean CO2 Atlas (SOCAT) databases. The effect of sparse sampling on the calculated fluxes was investigated by a bootstrap method; i.e. treating each ship cruise to an oceanic region as a random episode and creating 10 synthetic datasets by randomly selecting episodes with replacement. Convincing values of global net air‐sea flux can only be achieved using upper ocean data collected over several decades, but referenced to a standard year. The global annual referenced values are robust to sparse sampling, but seasonal and regional values exhibit more sampling uncertainty. Additional uncertainties are related to thermal and haline effects and to aspects of air‐sea gas exchange not captured by standard models. An estimate of global net CO2 exchange referenced to 2010 of ‐3.0 ± 0.6 Pg C yr‐1 is proposed, where the uncertainty derives primarily from uncertainty in the transfer velocity.

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Woolf D.K., Shutler J.D., Goddijn‐murphy L., Watson A.J., Chapron Bertrand, Nightingale P.D., Donlon C.J., Piskozub J., Yelland M.J., Ashton Ian, Holding T., Schuster U., Girard-Ardhuin Fanny, Grouazel Antoine, Piolle Jean-Francois, Warren M., Wrobel‐niedzwiecka I., Land P.E., Torres R., Prytherch J., Moat B., Hanafin J., Ardhuin Fabrice, Paul Frederic (2019). Key Uncertainties in the Recent Air‐Sea Flux of CO2. Global Biogeochemical Cycles, 33(12), 1548-1563. Publisher's official version : , Open Access version :