Page 14 - ebsaws-2014-03

Page 13

Fig. 2-6. Chlorophyll climatological annual mean (SeaWIfs data, 1998-2003, courtesy of V. Barale, JRC).

Compared to average oceanic productivity in temperate latitudes, Mediterranean waters are mostly
oligotrophic, particularly in the eastern portion of the basin, except in the vicinity of large rivers, in
areas where geomorphological, meteorological and oceanographic features cause localised
upwellings and consequent higher levels of primary production (e.g., Jacques 1989, Bakun and
Agostini 2001), and through gravity-induced sediment transport in underwater canyons (Canals et
al. 2007). High Seas areas where primary productivity is above average include the Alborán Sea,
the Gulf of Lion and Ligurian-Provencal Basin, the waters offshore the Kerkenna Islands shallows,
the Northern Adriatic, the Northern Aegean and the waters offshore the Nile Delta (Fig. 2-6).
Sediments have in general low organic carbon content due to the low biological productivity of the
waters and the presence of high oxygen concentrations in deep waters. Local oxygen deficiencies
are always connected with eutrophication sources, mostly discharges of raw or treated urban or
agricultural effluents. Their distribution around the region is uneven, with a maximum in the
northwest and in the Adriatic Sea and a minimum on the southern shores. Owing to the strong
stratification of surface waters, eutrophication is more acute in summer when ambient nutrient
concentrations are low and oxygen transport through the thermocline is strongly reduced. Winter
mixing allows for the required vertical transport of oxygen to keep the deep waters and the
sediments oxidized all over the Mediterranean Sea (Cruzado 1985).
The Mediterranean High Seas also contain ecologically significant features such as slopes,
seamounts, canyons, and undersea volcanoes. Clark et al. (2006) predicted the existence of 59
large seamounts in the Mediterranean and Black Seas, based on GIS technology. Such
rudimentary information on the location and condition of some of these undersea features could be
improved through a combination between observed features and GIS-based predicted locations of
seamounts. This, together with information on frontal systems and other ecological significant
features of the water column, can be used to identify priority conservation areas.