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

摘要

Two 3-year time series of hourly measurements of the fugacity of COsub2/sub (fCOsub2/sub) 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 ～?25 μmol kgsup?1/sup and fCOsub2/sub by 40 μatm, whereas seawater pH decreased by ～?0.04 (0.0022 yrsup?1/sup). The DIC increase is about 15 % larger than expected from the equilibrium with atmospheric COsub2/sub. 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 ～?30 % of the total inventory of anthropogenic carbon in the Mediterranean Sea.