The observed evolution of oceanic pCO 2 and its drivers over the last two decades

• Published in: Global Biogeochemical Cycles
• Main Authors: Lenton, Andrew, Metzl, Nicolas, Takahashi, Taro, Kuchinke, Mareva, Matear, Richard J., Roy, Tilla, Sutherland, Stewart C., Sweeney, Colm, Tilbrook, Bronte
• Other Authors: Couplage physique-biogéochimie-carbone (PHYBIOCAR), Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS-PSL), Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales Toulouse (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS-PSL), Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales Toulouse (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales Toulouse (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2012
• Subjects: [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph]; [PHYS.PHYS.PHYS-GEO-PH]Physics [physics]/Physics [physics]/Geophysics [physics.geo-ph]; [SDE.MCG]Environmental Sciences/Global Changes; Southern Ocean
• Online Access: https://hal.science/hal-00753350; https://hal.science/hal-00753350/document; https://hal.science/hal-00753350/file/2011GB004095.pdf; https://doi.org/10.1029/2011GB004095

International audience We use a database of more than 4.4 million observations of ocean pCO 2 to investigate oceanic pCO 2 growth rates. We use pCO 2 measurements, with corresponding sea surface temperature and salinity measurements, to reconstruct alkalinity and dissolved inorganic carbon to understand what is driving these growth rates in different ocean regions. If the oceanic pCO 2 growth rate is faster (slower) than the atmospheric CO 2 growth rate, the region can be interpreted as having a decreasing (increasing) atmospheric CO 2 uptake. Only the Western subpolar and subtropical North Pacific, and the Southern Ocean are found to have sufficient spatial and temporal observations to calculate the growth rates of oceanic pCO 2 in different seasons. Based on these regions, we find the strength of the ocean carbon sink has declined over the last two decades due to a combination of regional drivers (physical and biological). In the subpolar North Pacific reduced atmospheric CO 2 uptake in the summer is associated with changes in the biological production, while in the subtropical North Pacific enhanced uptake in winter is associated with enhanced biological production. In the Indian and Pacific sectors of the Southern Ocean a reduced winter atmospheric CO 2 uptake is associated with a positive SAM response. Conversely in the more stratified Atlantic Ocean sector enhanced summer uptake is associated with increased biological production and reduced vertical supply. We are not able to separate climate variability and change as the calculated growth rates are at the limit of detection and are associated with large uncertainties. Ongoing sustained observations of global oceanic pCO 2 and its drivers, including dissolved inorganic carbon and alkalinity, are key to detecting and understanding how the ocean carbon sink will evolve in future and what processes are driving this change.