Concomitant ocean acidification and increasing total alkalinity at a coastal site in the NW Mediterranean Sea (2007-2015)
Lydia Kapsenberg1, Samir Alliouane1, Frédéric Gazeau1, Laure Mousseau1, and Jean-Pierre Gattuso1,21Sorbonne Universités, Université Pierre et Marie Curie-Paris 6, CNRS-INSU, Laboratoire d'Océanographie de Villefranche, 06230, Villefranche-sur-Mer, France 2Institute for Sustainable Development and International Relations, Sciences Po, 27 rue Saint Guillaume, F-75007 Paris, France
Received: 30 Aug 2016 – Accepted for review: 09 Sep 2016 – Discussion started: 13 Sep 2016
Abstract. Monitoring of global ocean change is necessary in coastal zones due to their physical and biological complexity. Here, we document changes in coastal carbonate chemistry at the coastal time-series station, Point B, in the NW Mediterranean Sea from 2007 through 2015 at 1 and 50 m. The rate of surface ocean acidification (−0.0028 ± 0.0003 units pHT yr−1) was faster-than-expected based on atmospheric carbon dioxide forcing alone. Changes in carbonate chemistry were predominantly driven by an increase in total dissolved inorganic carbon (CT, +2.97 ± 0.20 μmol kg−1 yr−1), > 50 % of which was buffered by a synchronous increase in total alkalinity (AT, +2.08 ± 0.19 μmol kg−1 yr−1). The increase in AT was unrelated to salinity and its cause remains to be identified. Interestingly, concurrent increases in AT and CT were most rapid from May to July. Changes at 50 m were slower compared to 1 m. It seems therefore likely that changes in coastal AT cycling via a shallow coastal process gave rise to these observations. This study exemplifies the importance of understanding coastal ocean acidification through localized biogeochemical cycling that extends beyond simple air-sea gas exchange dynamics, in order to make relevant predictions about future coastal ocean change and ecosystem function.
Kapsenberg, L., Alliouane, S., Gazeau, F., Mousseau, L., and Gattuso, J.-P.: Concomitant ocean acidification and increasing total alkalinity at a coastal site in the NW Mediterranean Sea (2007-2015), Ocean Sci. Discuss., doi:10.5194/os-2016-71, in review, 2016.