Cardinal Buoys: An Opportunity for the Study of Air-Sea CO 2 Fluxes in Coastal Ecosystems

• Published in: Frontiers in Marine Science
• Main Authors: Gac, Jean-Philippe, Marrec, Pierre, Cariou, Thierry, Guillerm, Christophe, Macé, Éric, Vernet, Marc, Bozec, Yann
• Other Authors: Adaptation et diversité en milieu marin (ADMM), Institut national des sciences de l'Univers (INSU - 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), Graduate School of Oceanography Narragansett, University of Rhode Island (URI), Fédération de recherche de Roscoff (FR2424), Station biologique de Roscoff (SBR), Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Division technique INSU/SDU (DTI), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2020
• Subjects: buoy of opportunity; high-frequency; tidal cycle; multi-annual; air-sea CO 2 exchanges; ocean acidification; coastal ecosystems; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; Ocean acidification
• Online Access: https://hal.sorbonne-universite.fr/hal-02944673; https://hal.sorbonne-universite.fr/hal-02944673/document; https://hal.sorbonne-universite.fr/hal-02944673/file/fmars-07-00712.pdf; https://doi.org/10.3389/fmars.2020.00712

International audience From 2015 to 2019 we installed high-frequency (HF) sea surface temperature (SST), salinity, fluorescence, dissolved oxygen (DO) and partial pressure of CO 2 (pCO 2) sensors on a cardinal buoy of opportunity (ASTAN) at a coastal site in the southern Western English Channel (sWEC) highly influenced by tidal cycles. The sensors were calibrated against bimonthly discrete measurements performed at two long-term time series stations near the buoy, thus providing a robust multi-annual HF dataset. The tidal transport of a previously unidentified coastal water mass and an offshore water mass strongly impacted the daily and seasonal variability of pCO 2 and pH. The maximum tidal variability associated to spring tides (>7 m) during phytoplankton blooms represented up to 40% of the pCO 2 annual signal at ASTAN. At the same time, the daily variability of 0.12 pH units associated to this tidal transport was 6 times larger than the annual acidification trend observed in the area. A frequency/time analysis of the HF signal revealed the presence of a day/night cycle in the tidal signal. The diel biological cycle accounted for 9% of the annual pCO 2 amplitude during spring phytoplankton blooms. The duration and intensity of the biologically productive periods, characterized by large inter-annual variability, were the main drivers of pCO 2 dynamics. HF monitoring enabled us to accurately constrain, for the first-time, annual estimates of air-sea CO 2 exchanges in the nearshore tidally-influenced waters of the sWEC, which were a weak source to the atmosphere at 0.51 mol CO 2 m −2 yr −1. This estimate, combined with previous studies, provided a full latitudinal representation of the WEC (from 48 • 75 N to 50 • 25 N) over multiple years for air-sea CO 2 fluxes in contrasted coastal ecosystems. The latitudinal comparison showed a clear gradient from a weak source of CO 2 in the tidal mixing region toward sinks of CO 2 in the stratified region with a seasonal thermal front separating these hydrographical ...