Record-breaking salinities in the middle Adriatic during summer 2017 and concurrent changes in the microbial food web

Observation, Preconditioning and Recurrence of Exceptionally High Salinities in the Adriatic Sea

“…The temperature and salinity observations taken at the Palagruža Sill transect (Figure 2) indicate high salinity conditions throughout 2017, in respect to values/data presented in previous Adriatic climatologies and literature (Buljan and Zore-Armanda, 1976;Artegiani et al, 1997;Lipizer et al, 2014;Beg Paklar et al, 2020). The bilinear interpolation (e.g., Kirkland, 2010) was used to plot these transects from available CTD casts, still likely resulting in some artifacts due to small number of CTD profiles along the transect, such as somewhat peculiar salinity vertical structures between the first three CTD casts on the right, which are likely generated by not accounting for the seamount in our interpolation.…”

“…These data were collected with monthly to seasonal resolution, using different sampling techniques (reversing thermometers and various CTD probes for temperature; titration with AgNO 3 , portable induction salinometers and various CTD probes for salinity). The series were homogenized and used in different studies (e.g., Beg Paklar et al, 2020), in which more details on the measurements procedures can be found. We focused on episodes 1 www.seabird.com with surface salinity values higher than 38.8 observed on at least one station along the transect, between 0 and 20 m (considering them as high surface salinity events).…”

“…We focused on episodes 1 www.seabird.com with surface salinity values higher than 38.8 observed on at least one station along the transect, between 0 and 20 m (considering them as high surface salinity events). This threshold was based on long-term monthly measurements at the Stončica station (CJ009), as it is at least one standard deviation above long-term average for any month of the year (Beg Paklar et al, 2020).…”

“…Additionally, a large freshwater load through rivers and precipitation, that created haline-driven stratification, was documented during 2014 (Mihanović et al, 2018;Kokkini et al, 2020). The surface inflow of high salinity waters from the Eastern Mediterranean continued in early 2017, preconditioning the record-breaking salinities observed in summer and autumn at the coastal Stončica station (CJ009 -see Figure 1 for the location of the station) off the eastern Middle Adriatic coast, characterized by unusual "inverse" salinity vertical structure (with the highest salinities observed in the surface and near-surface layers, Beg Paklar et al, 2020). Such a vertical structure is uncommon in the Adriatic, but it regularly appears in the Levantine basin, preconditioning (among other) the LIW formation (Kubin et al, 2019).…”

“…An interesting consequence of the unusual salinity conditions, hypothesized to be governed by local (heat and water fluxes) and remote (BiOS) drivers, documented in the eastern Middle Adriatic in 2017, was their effect on the microbial food web (Beg Paklar et al, 2020), in particular to the substantially lower bacterial production and abundance. In this manuscript we intend to provide a wider basin-scale picture of the airsea interactions and circulation in the Adriatic-Ionian basin during the appearance of surface and near-surface high salinity maxima.…”