Qualified temperature, salinity and dissolved oxygen climatologies in a changing Adriatic Sea

An updated climatology, based on a comprehensive data set (1911-2009) of temperature, salinity and dissolved oxygen, has been produced for the whole Adriatic Sea with the variational inverse method using the DIVA (Data-Interpolating Variational Analysis) software. Climatological maps were produced at 26 levels and validated with ordinary cross-validation and with a real vs. synthetic temperature-salinity diagram intercomparison. The concept of climatology-observation misfit (COM) has been introduced as an estimate of the physical variability associated with the climatological structures. In order to verify the temporal stability of the climatology, long-term variability has been investigated in the Middle Adriatic and the South Adriatic pits, regarded as the most suitable records of possible long-term changes. Compared with previous climatologies, this study allows a clear identification of the seasonal dynamic of the southern Adriatic, where a clear oxygen minimum is typically observed in the centre of the South Adriatic Gyre. New and better resolved features emerged from this analysis: (1) below 100 m all properties profoundly differ between the central and the southern Adriatic and seem characterized by different biogeochemical dynamics; (2) the South Adriatic Pit clearly shows the remote effects of the Eastern Mediterranean Transient, while no effect is observed in the Middle Adriatic Pit; (3) the deepest part of the southern Adriatic seems now to be significantly saltier (+0.18 psu since the period 1910-1914, with an increase of +0.018 decade(-1) since the late 1940s) and warmer (+0.54 degrees C since 1910-1914) even though a long-term temperature trend could not be statistically demonstrated; (4) the Middle Adriatic Pit shows a long-term increase in apparent oxygen utilization (+0.77 mL L-1 since 1910-1914, with a constant increase of +0.2 mL L-1 decade(-1) after the 1970s).