Ocean carbonate system variability in the North Atlantic Subpolar surface water (1993-2017)

• Published in: Biogeosciences
• Main Authors: Leseurre, Coraline, Lo Monaco, Claire, Reverdin, Gilles, Metzl, Nicolas, Fin, Jonathan, Ólafsdóttir, Sólveig R., Racapé, Virginie
• Other Authors: Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-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)-École polytechnique (X)-Centre National d'Études Spatiales Toulouse (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-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)-École polytechnique (X)-Centre National d'Études Spatiales Toulouse (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Cycles biogéochimiques marins : processus et perturbations (CYBIOM), 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)-École polytechnique (X)-Centre National d'Études Spatiales Toulouse (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Processus et interactions de fine échelle océanique (PROTEO), Marine and Freshwater Research Institute, Laboratoire d'Océanographie Physique et Spatiale (LOPS), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), European Project: 30029,CARBOOCEAN, European Project: 264879,EC:FP7:ENV,FP7-ENV-2010,CARBOCHANGE(2011)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2020
• Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDE.MCG]Environmental Sciences/Global Changes; North Atlantic; Ocean acidification
• Online Access: https://hal.science/hal-02573889; https://hal.science/hal-02573889/document; https://hal.science/hal-02573889/file/Leseurre-bg-17-2553-2020.pdf; https://doi.org/10.5194/bg-17-2553-2020

The North Atlantic is one of the major ocean sinks for natural and anthropogenic atmospheric CO 2. Given the variability of the circulation, convective processes or warming-cooling recognized in the high latitudes in this region , a better understanding of the CO 2 sink temporal variability and associated acidification needs a close inspection of seasonal, interannual to multidecadal observations. In this study, we investigate the evolution of CO 2 uptake and ocean acidification in the North Atlantic Subpolar Gyre (50-64 • N) using repeated observations collected over the last 3 decades in the framework of the long-term monitoring program SURATLANT (SURveillance de l'ATLANTique). Over the full period (1993-2017) pH decreases (−0.0017 yr −1) and fugacity of CO 2 (f CO 2) increases (+1.70 µatm yr −1). The trend of f CO 2 in surface water is slightly less than the atmospheric rate (+1.96 µatm yr −1). This is mainly due to dissolved inorganic carbon (DIC) increase associated with the anthropogenic signal. However, over shorter periods (4-10 years) and depending on the season, we detect significant variability investigated in more detail in this study. Data obtained between 1993 and 1997 suggest a rapid increase in f CO 2 in summer (up to +14 µatm yr −1) that was driven by a significant warming and an increase in DIC for a short period. Similar f CO 2 trends are observed between 2001 and 2007 during both summer and winter, but, without significant warming detected, these trends are mainly explained by an increase in DIC and a decrease in alkalinity. This also leads to a pH decrease but with contrasting trends depending on the region and season (between −0.006 and −0.013 yr −1). Conversely , data obtained during the last decade (2008-2017) in summer show a cooling of surface waters and an increase in alkalinity, leading to a strong decrease in surface f CO 2 (between −4.4 and −2.3 µatm yr −1 i.e., the ocean CO 2 sink increases). Surprisingly, during summer, pH increases up to +0.0052 yr −1 in the southern subpolar ...