Variability of Adriatic Sea coastal turbid waters from SeaWiFS imagery

Abstract

The objective of this work is to gain new insight on the variability and offshore export of turbid coastal waters in the Adriatic Sea, which are optically classified as Case 2 waters. This is done by means of the 1998–2004 SeaWiFS ocean color products (chlorophyll, Case 2 flags and light attenuation coefficient at 490 nm, k490) and NOAA AVHRR sea surface temperature. The role of wind‐driven circulation in the redistribution of the above ocean color features is also analyzed both at seasonal and interannual time scales and in the light of particular wind and current situations occurring in 2003, via scatterometer wind data as well as atmospheric and marine circulation medium and high resolution model output. Results indicate that turbid (Case 2) waters are exported offshore at the Po delta and Ancona headland during the colder months, in concomitance of Bora wind events and when the 2003 daily Po river discharge is above about 500 m3 s−1 and 1000 m3 s−1, respectively. Southeasterly Sirocco events do not to originate extensive offshore transport, but only locally modify the shape of the WAC front. Mistral episodes enhance the WAC flow into the Ionian Sea. Finally, estimates of coastal current width and length from Case 2 flag distribution follow the Po discharge pattern, confirming this forcing to be the main responsible for WAC width seasonal modulation. Experimental WAC widths agree reasonably with theoretical analyses, while underestimation of WAC length suggests the necessity to include the other Italian rivers in the freshwater discharge evaluation.

Core-top calibration of δ18O and δ13C of G. ruber (white) and U. mediterranea along the southern Adriatic coast of Italy

“…Part of the entering water turns westward and recirculates towards the Italian coast. In addition, the discharge of the Po River has a significant influence on the circulation (Artegiani et al, 1997a;Turchetto et al, 2007) leading to the formation of the Western Adriatic Current (WAC) which is colder and less saline than the ISW and flows southward along the western Adriatic coast (Bignami et al, 2007). The Adriatic Sea behaves like a dilution basin in all seasons (Artegiani et al, 1997b).…”

“…The lower salinity water coming from the north, however, is limited to a narrow belt near the Italian coast (Turchetto et al, 2007). According to Poulain (2001) the WAC has similar characteristics during fall, winter and summer but is characterized by a strongly reduced offshore transport during the warm season (April-September) (Bignami et al, 2007).…”

“…1) (Borzelli et al, 1999). From late spring to early fall the hydrographic conditions in the southern Adriatic are characterized by a thermohaline stratification due to surface warming and the gyres and coastal currents are prevailing (Turchetto et al, 2007;Bignami et al, 2007;Poulain, 2001). As a result, G. ruber (white) further away from the coast could be influenced by the nutrient-poor, more saline water masses from the eastern Mediterranean.…”

Seasonal phytoplankton dynamics in the coastal waters of the north-eastern Adriatic Sea

“…Otherwise, it can extend into the northern Adriatic interior. There it forms the Po River plume, either as a tongue of fresh water or it spreads as a thin surface layer over the entire northern Adriatic basin during stable, stratified conditions (Bignami et al, 2007;Cushman-Roisin et al, 2001). Additionally, the eastern part of the northern Adriatic Sea is under influence of highly saline, oligotrophic waters by advection of the Eastern Adriatic Current (EAC) from the central Adriatic.…”

On the use of a simple primary productivity model to assess the skill of a physical ocean model

“…For instance, the possibility of tracking coastal waters by means of satellite ocean color products, including SeaWiFS -derived chlorophyll and Case 2 turbid waters, was demonstrated by Bignami et al (2007) for the Adriatic Sea. They were able to show a qualitative correlation between satellite observed structures and dynamic (physical) circulation features reproduced by the Regional Ocean Modeling System (ROMS, www.myroms.org) ocean model.…”