New observations of CO₂-induced acidification in the northern Adriatic Sea over the last quarter century

Abstract

Current global trends will lead to large-scale changes in climate patterns, ocean circulation and stratification; increased atmospheric CO₂ levels will cause acidification of the oceans, with significant impacts on marine biogeochemical cycles and calcareous organisms. In the Mediterranean area, the northern Adriatic Sea is one of the most suitable sites for studying the responses of marine pH to such occurrences because it is the northernmost basin affected by dense water formation during winter, and is also one of the most productive areas in the Mediterranean. The first comparison between two sets of data relating to the dense cold waters of the northern Adriatic, formed in the winters of 1982–1983 and 2007–2008, is presented here. pH values on the Nation Bureau Standard scale from the old dataset have been converted to the ‘total hydrogen ion concentration scale’ adopted for the new dataset, and are expressed as μmol H. Results at 25 °C show acidification (−0.063 pH_T units) and a decrease in carbonate ion concentration (−19.6 μmol H) in the dense water mass between 1983 and 2008, whereas total alkalinity, carbonate alkalinity, dissolved inorganic carbon and CO₂ fugacity exhibit net increases of 74.4, 77.8 and 110.3 μmol H, and 108.3 μatm, respectively, over the same period.

Keywords:

• ocean acidification
• seawater pH
• alkalinity
• north Adriatic Sea
• marine carbonate buffer system
• atmospheric CO₂ dissolution
• inorganic carbon chemistry
• carbon dioxide

Acknowledgements

The authors thank the captains and crews of R.V. Bannock and Urania for their helpful work. We are grateful to Vedrana Kovacevic (OGS Trieste), to Stefano Cozzi (ISMAR Trieste) for the use of CTD and inorganic nutrient data collected during the VECSES 1 cruise, and to Salvi and Schirone (ENEA) for atmospheric pCO₂ values. We are grateful to the ASCOP Project carried out with changing fortune from 1979 to 1989 in the frame of an agreement, drawn up between Italy and the former Yugoslavia, for the monitoring of the Adriatic Sea. This study was supported by the VECTOR Project of the Italian Ministry for University and Scientific Research.