Decadal Dynamics of the CO2 System and Associated Ocean Acidification in Coastal Ecosystems of the North East Atlantic Ocean

• Published in: Frontiers in Marine Science
• Main Authors: Gac, Jean-Philippe, Marrec, Pierre, Cariou, Thierry, Grosstefan, Emilie, Macé, Éric, Rimmelin-Maury, Peggy, Vernet, Marc, Bozec, Yann
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Frontiers Media SA 2021
• Subjects: North East Atlantic; Ocean acidification
• Online Access: http://dx.doi.org/10.3389/fmars.2021.688008; https://www.frontiersin.org/articles/10.3389/fmars.2021.688008/full

Weekly and bi-monthly carbonate system parameters and ancillary data were collected from 2008 to 2020 in three coastal ecosystems of the southern Western English Channel (sWEC) (SOMLIT-pier and SOMLIT-offshore) and Bay of Brest (SOMLIT-Brest) located in the North East Atlantic Ocean. The main drivers of seasonal and interannual partial pressure of CO 2 (pCO 2 ) and dissolved inorganic carbon (DIC) variabilities were the net ecosystem production (NEP) and thermodynamics. Differences were observed between stations, with a higher biological influence on pCO 2 and DIC in the near-shore ecosystems, driven by both benthic and pelagic communities. The impact of riverine inputs on DIC dynamics was more pronounced at SOMLIT-Brest (7%) than at SOMLIT-pier (3%) and SOMLIT-offshore (<1%). These three ecosystems acted as a weak source of CO 2 to the atmosphere of 0.18 ± 0.10, 0.11 ± 0.12, and 0.39 ± 0.08 mol m –2 year –1 , respectively. Interannually, air-sea CO 2 fluxes (FCO 2 ) variability was low at SOMLIT-offshore and SOMLIT-pier, whereas SOMLIT-Brest occasionally switched to weak annual sinks of atmospheric CO 2 , driven by enhanced spring NEP compared to annual means. Over the 2008–2018 period, monthly total alkalinity (TA) and DIC anomalies were characterized by significant positive trends ( p -values < 0.001), from 0.49 ± 0.20 to 2.21 ± 0.39 μmol kg −1 year −1 for TA, and from 1.93 ± 0.28 to 2.98 ± 0.39 μmol kg –1 year –1 for DIC. These trends were associated with significant increases of calculated seawater pCO 2 , ranging from +2.95 ± 1.04 to 3.52 ± 0.47 μatm year –1 , and strong reductions of calculated pH in situ , with a mean pH in situ decrease of 0.0028 year –1 . This ocean acidification (OA) was driven by atmospheric CO 2 forcing (57–66%), Sea surface temperature (SST) increase (31–37%), and changes in salinity (2–5%). Additional pH in situ data extended these observed trends to the 2008–2020 period and indicated an acceleration of OA, reflected by a mean pH in situ decrease of 0.0046 year –1 in ...