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

Abstract

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 °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).