Northern Adriatic Sea
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The separation line of the semi-enclosed northern basin from the rest of the Adriatic Sea is conventionally defined at the 100 m isobath, at about 43 20 N, from where the bottom depth moderately decreases up to the northern coast reaching the smallest average depth in the northernmost protrusion of the basin, the Gulf of Trieste (surface are 600 km2, volume 9.5 km3, maximal depth approx. 25 m).
The oceanographic properties of Gulf of Trieste are affected by water mass exchange with the northern Adriatic at the open western boundary, by local meteorological conditions that induce a pronounced seasonal cycle of seawater temperature (from 6 C in February to summer peaks of about 28 C) (Malačič et al., 2006) and by the largest freshwater input, the Soča (Isonzo) River. The latter enters the Gulf on the shallower northern coastline with an average flow of 123 m3 s-1 and represents the major source of land-borne nutrients in this coastal zone, in particular of nitrate, whereas inputs along the south-eastern coast are comparatively small (contributing less than 10% to the freshwater balance in the Gulf) (Cozzi et al., 2012). The circulation pattern is variable, however the prevailing ENE wind is the most efficient for the water exchange (Solidoro et al., 2009), especially during winter. These physical features, in addition to freshwater inputs, are ultimately reflected in the distribution of nutrients and in the seasonal and inter-annual variability of plankton communities (Fonda µmani et al., 1992; Malej et al., 1995; Mozetič et al., 2010; Mozetič et al., 2012) but also in events of hypoxia/anoxia (Malej and Malačič, 1995) and mucous macroaggregates (Kovač et al., 2008), which have characterised the whole northern Adriatic basin in the recent past.
The waters of the Gulf of Trieste have been monitored for several physical-chemical and biological variables since 70s but the longest and most continuous data set of biological variables is represented by the phytoplankton time series, which started in 1990 when the national monitoring programme has become operational (set by Slovenian Environmental Agency). From 2007onwards, the monitoring programme complies with the regulations of the EU Water Framework Directive (2000/60/EC). The relatively unimpacted (by anthropogenic pressures) station 000F (22 m deep, about 1 NM off the coast) is sampled monthly. Sampling and analyses are carried out by the National Institute of Biology, Marine Biology Station Piran.
Cozzi, S., Falconi, C.F., Comici, C., Cermelj, B., Kovac, N., Turk, V., Giani, M., 2012. Recent evolution of river discharges in the Northeastern Adriatic Sea and their potential response to climate changes and anthropogenic pressure. Estuarine, Coastal and Shelf Science, 115, 14 24.
Fonda Umani, S., Franco, P., Ghirardelli, E., Malej, A., 1992. Outline of oceanography and the plankton of the Adriatic Sea. In: Colombo, G., Ferrari, I., Ceccherelli, V.U., Rossi, R. (Eds.), Marine Eutrophication and Population Dynamics. Proceedings of the 25th EMBS. Olsen & Olsen, Fredensborg, pp. 347-365.
Kovac, N., Faganeli, J., Bajt, O., 2008. Mucous macroaggregates in the northern Adriatic. In: Stefansson, O. (Ed.), Geochemistry research Advances. Nova Science Publishers, Inc., pp. 119-141.
Malej, A., Malacic, V., 1995. Factors affecting bottom layer oxygen depletion in the Gulf of Trieste (Adriatic Sea). Annales, Series historia naturalis 7, 33-42.
Malej, A., Mozetic, P., Malacic, V., Terzic, S., Ahel, M., 1995. Phytoplankton response to freshwater inputs in a small semi-enclosed gulf (Gulf of Trieste, Adriatic Sea). Marine Ecology Progress Series 120, 111-121.
Mozetic, P., France, J., Kogovsek, T., Talaber, I., Malej, A., 2012. Plankton trends and community changes in a coastal sea (northern Adriatic): Bottom-up vs. top-down control in relation to environmental drivers. Estuarine, Coastal and Shelf Science 115, 138-148.
Mozetic, P., Solidoro, C., Cossarini, G., Socal, G., Precali, R., France, J., Bianchi, F., De Vittor, C., Smodlaka, N., Fonda Umani, S., 2010. Recent trends towards oligotrophication of the Northern Adriatic: Evidence from Chlorophyll a time series. Estuaries and Coasts 33, 362-375.
Solidoro, C., Bastianini, M., Bandelj, V., Codermatz, R., Cossarini, G., Melaku Canu, D., Ravagnan, E., Salon, S., Trevisani, S., 2009. Current state, scales of variability, and trends of biogeochemical properties in the northern Adriatic Sea. Journal of Geophysical Research 114, C07S91.