TY - JOUR T1 - Key Uncertainties in the Recent Air‐Sea Flux of CO2 A1 - Woolf,D.K. A1 - Shutler,J.D. A1 - Goddijn‐murphy,L. A1 - Watson,A.J. A1 - Chapron,Bertrand A1 - Nightingale,P.D. A1 - Donlon,C.J. A1 - Piskozub,J. A1 - Yelland,M.J. A1 - Ashton,Ian A1 - Holding,T. A1 - Schuster,U. A1 - Girard-Ardhuin,Fanny A1 - Grouazel,Antoine A1 - Piolle,Jean-Francois A1 - Warren,M. A1 - Wrobel‐niedzwiecka,I. A1 - Land,P.E. A1 - Torres,R. A1 - Prytherch,J. A1 - Moat,B. A1 - Hanafin,J. A1 - Ardhuin,Fabrice A1 - Paul,Frederic AD - International Centre for Island Technology, Heriot‐Watt University, UK AD - College of Life and Environmental Sciences, University of Exeter, UK AD - University of the Highlands and Islands ,UK AD - Ifremer, Univ. Brest, CNRS, IRD, Laboratoire d’Oceanographie Physique et Spatiale (LOPS), IUEM Brest, France AD - Plymouth Marine Laboratory, UK AD - European Space Agency ,The Netherlands AD - Institute of Oceanology, Polish Academy of Sciences Sopot ,Poland AD - National Oceanography Centre Southampton ,UK AD - College of Engineering, Mathematics and Physical Sciences, University of Exeter ,UK AD - Ifremer, Univ. Brest, CNRS, IRD, Laboratoire d’Oceanographie Physique et Spatiale (LOPS), IUEM Brest, France UR - https://archimer.ifremer.fr/doc/00513/62450/ DO - 10.1029/2018GB006041 KW - Carbon dioxide KW - air-sea flux KW - uncertainty KW - transfer velocity KW - sampling N2 - 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. Y1 - 2019/12 PB - American Geophysical Union (AGU) JF - Global Biogeochemical Cycles SN - 0886-6236 VL - 33 IS - 12 SP - 1548 EP - 1563 ID - 62450 ER -