Carbonate system distribution, anthropogenic carbon and acidification in the western tropical South Pacific (OUTPACE 2015 transect)

International audience The western tropical South Pacific was sampled along a longitudinal 4000 km transect (OUTPACE cruise, 18 February, 3 April 2015) for the measurement of car-bonate parameters (total alkalinity and total inorganic carbon) between the Melanesian Archipelago (MA) and the western p...

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Published in:Biogeosciences
Main Authors: Wagener, Thibaut, Metzl, Nicolas, Caffin, Mathieu, Fin, Jonathan, Helias Nunige, Sandra, Lefèvre, Dominique, Lo Monaco, Claire, Rougier, Gilles, Moutin, Thierry
Other Authors: Institut méditerranéen d'océanologie (MIO), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Toulon (UTLN)-Centre National de la Recherche Scientifique (CNRS), Cycles biogéochimiques marins : processus et perturbations (CYBIOM), 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)-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)), 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), Laboratoire d'océanographie et de biogéochimie (LOB), Université de la Méditerranée - Aix-Marseille 2-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), LEFE-CyBER program (CNRS-INSU)GOPS program (IRD) CNES (BC T23, ZBC 4500048836), OUTPACE (Oligotrophy from Ultra-oligoTrophy PACific Experiment) project, ANR-14-CE01-0007,OUTPACE,Sequestration océanique du CO2 et fixation d'azote atmosphérique dans l'océan oligotrophe (campagne océanographique OUTPACE).(2014)
Format: Article in Journal/Newspaper
Language:English
Published: HAL CCSD 2018
Subjects:
Online Access:https://hal.science/hal-01868023
https://hal.science/hal-01868023/document
https://hal.science/hal-01868023/file/bg-15-5221-2018.pdf
https://doi.org/10.5194/bg-15-5221-2018
Description
Summary:International audience The western tropical South Pacific was sampled along a longitudinal 4000 km transect (OUTPACE cruise, 18 February, 3 April 2015) for the measurement of car-bonate parameters (total alkalinity and total inorganic carbon) between the Melanesian Archipelago (MA) and the western part of the South Pacific gyre (WGY). This paper reports this new dataset and derived properties: pH on the total scale (pH T ) and the CaCO 3 saturation state with respect to aragonite (Ω ara ). We also estimate anthro-pogenic carbon (C ANT ) distribution in the water column using the TrOCA method (Tracer combining Oxygen, inorganic Carbon and total Alkalinity). Along the OUTPACE transect a deeper penetration of C ANT in the intermediate waters was observed in the MA, whereas highest C ANT concentrations were detected in the subsurface waters of the WGY. By combining our OUTPACE dataset with data available in GLODAPv2 (1974–2009), temporal changes in oceanic inorganic carbon were evaluated. An increase of 1.3 to 1.6 µmol kg −1 a −1 for total inorganic carbon in the upper thermocline waters is estimated, whereas C ANT increases by 1.1 to 1.2 µmol kg −1 a −1 . In the MA intermediate waters (27 kg m −3 < σ θ < 27.2 kg m −3 ) an increase of 0.4 µmol kg −1 a −1 C ANT is detected. Our results suggest a clear progression of ocean acidification in the western tropical South Pacific with a decrease in the oceanic pH T of up to −0.0027 a −1 and a shoaling of the saturation depth for aragonite of up to 200 m since the pre-industrial period.