Increase of dissolved inorganic carbon and decrease in pH in near-surface waters in the Mediterranean Sea during the past two decades

Merlivat, Liliane; Boutin, Jacqueline; Antoine, David; Beaumont, Laurence; Golbol, Melek; Vellucci, Vincenzo

Two 3-year time series of hourly measurements of the fugacity of inline-formulaCO2 (inline-formulafCO2) in the upper 10 m of the surface layer of the northwestern Mediterranean Sea have been recorded by CARIOCA sensors almost two decades apart, in 1995–1997 and 2013–2015. By combining them with the alkalinity derived from measured temperature and salinity, we calculate changes in pH and dissolved inorganic carbon (DIC). DIC increased in surface seawater by inline-formula∼25inline-formulaµmol kginline-formula−1 and inline-formulafCO2 by 40 inline-formulaµatm, whereas seawater pH decreased by inline-formula∼0.04 (0.0022 yrinline-formula−1). The DIC increase is about 15 % larger than expected from the equilibrium with atmospheric inline-formulaCO2. This could result from natural variability, e.g. the increase between the two periods in the frequency and intensity of winter convection events. Likewise, it could be the signature of the contribution of the Atlantic Ocean as a source of anthropogenic carbon to the Mediterranean Sea through the Strait of Gibraltar. We then estimate that the part of DIC accumulated over the last 18 years represents inline-formula∼30 % of the total inventory of anthropogenic carbon in the Mediterranean Sea.

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Merlivat, Liliane / Boutin, Jacqueline / Antoine, David / et al: Increase of dissolved inorganic carbon and decrease in pH in near-surface waters in the Mediterranean Sea during the past two decades. 2018. Copernicus Publications.

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