Multi-scale study of the air-sea exchanges of CO2 and the ocean acidification in the western English Channel

• Main Author: Gac, Jean-Philippe
• Other Authors: Adaptation et diversité en milieu marin (AD2M), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Station biologique de Roscoff (SBR), Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Sorbonne Université, Yann Bozec, Pascal Morin
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2021
• Subjects: Air-sea CO2 exchanges; Carbon dioxide; Acidification; High frequency; Decadale trends; Coast of the North-Western Europe; Estuary-coast gradient; Echanges air-mer de CO2; Dioxyde de carbone; Haute fréquence; Tendance décennale; Côtes du nord-ouest de l'Europe; Gradient rivière-estuaire-côtier; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Ocean acidification; sami
• Online Access: https://tel.archives-ouvertes.fr/tel-03511012; https://tel.archives-ouvertes.fr/tel-03511012/document; https://tel.archives-ouvertes.fr/tel-03511012/file/GAC_Jean_Philippe_2021.pdf

The anthropogenic impact of the raise of atmospheric CO2 has been observed on the global oceanic scale, resulting in the Ocean Acidification (OA). Largely present in the coastal ecosystems, a decrease of their population could have significant socio-economic consequences. Coastal ecosystems represent only 7% of the global ocean but host a third of the total primary production of the oceans, playing a key role in the global carbon cycle. They are highly diversified and influenced by continental inputs, which complexifies the study of the CO2 cycle. This PhD thesis investigated at different spatial and temporal scales the variability of the carbon cycle in megatidal environments of the North Western European Shelves. From 2015 to 2019, we installed an autonomous sensor of pCO2 (Sunburst SAMI-CO2) on a cardinal buoy located off Roscoff, in the south of the English Channel. Coupled with additional proximal and offshore observations of the carbon cycle and biogeochemical parameters, we were able to describe precisely this ecosystem and assess the tidal, diurnal and interannual variability. Secondly, we followed the variability of these parameters at the decadal scale, based on regular sampling from 2008 to 2018 in two coastal environments very close geographically (Brest and Roscoff, NWES), but with different freshwater influence. Finally, since methane is increasingly considered as a key player in the understanding of the coastal ecosystem functioning and Climatically-Actives Gas cycles, we quantified the driving processes of CO2 and CH4 air-sea exchanges in two mega-tidal estuaries influencing our study region. L’impact anthropique lié à l’augmentation du CO2 atmosphérique a été observé à l’échelle globale océanique, avec comme conséquence l’acidification des océans (AO). Comme l’océan ouvert, les écosystèmes côtiers sont soumis à l’AO. Ces écosystèmes ne représentent que 7% de la surface océanique mais ils sont responsables d’un tiers de la production primaire océanique mondiale, jouant ainsi un rôle clé dans le ...