Seasonal variability and Po River plume influence on biochemical properties along western Adriatic coast

Abstract

[1] The influence of the Po plume on the northern Adriatic Sea was observed during two seasons in 2003 under distinct physical forcing regimes. During the winter, the plume was cool, low in both salinity and chlorophyll, but with higher chlorophyll concentrations occurring along the plume boundary. The plume mixed deeply in the water column in response to the strong wind forcing. The northern Adriatic and the Po plume cooled significantly during the observational period, and therefore salinity alone was the best discriminator of water mass variability. In contrast to the strong forcing of the winter period, the late spring was characterized by weak wind forcing, and below-average Po River discharge ($600 m 3 /s) which was about one third of the typical discharge for this period. As in winter, salinity was again the best discriminator of water mass variability. The Po plume advected southward along the Italian coast and in some locations portions of the coastal plume were transferred offshore in filament-like features. However, the one observed filament was quite low in chlorophyll and was quite thin vertically, extending downward less than 5 m from the surface. The spring observations provide a distinct contrast in the effects of the physical forcings of river flow and wind stress from two different seasons. The strong winter forcing resulted in deep mixing of the plume despite its low salinity and buoyancy, whereas the weak summer flow under weak winds resulted in a very shallow plume (<5 m) that was high in chlorophyll.

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

“…Numberger et al (2009) showed that along the African coast where the surface waters are oligotrophic during summer the species G. ruber type platys show a trend to deeper habitats (50 m). Along the southern Italian coast the nutrient content decreases offshore (Marini et al, 2008;Morović et al, 2006), which causes the species further away from the coast to live deeper in the water column. Fig.…”

“…The Adriatic Sea behaves like a dilution basin in all seasons (Artegiani et al, 1997b). Besides the less saline water masses the river discharge brings large fluxes of nutrients into the basin (Marini et al, 2008).…”

“…In the shallow areas along the coast the higher nutrient supply may provide the foraminifera the possibility to live until late summer or early fall, thus recording higher temperatures. Satellite images (Marini et al, 2008;Morović et al, 2006) show a narrow band of nutrient-rich, freshwater during all seasons along the coast which corresponds to higher temperature and lower salinity conditions in the coastal regions during summer and early autumn (Marini et al, 2008) …”

“…In a pattern similar to that of δ 13 C of G. ruber (white) the chlorophyll a concentration during summer around the southern Italian coast (Zonneveld et al, 2008) shows a decrease towards the open sea. Satellite images (Marini et al, 2008) reveal that the nutrient supply is not constant in the area between the Gargano Peninsula and the Gulf of Taranto and show that chlorophyll a is mainly found in the plume of river-influenced WAC, thereby illustrating the separation of the nutrient-rich waters along the Italian coast from the more oligotrophic offshore regions in the central and southern Adriatic basins (Marini et al, 2008). The extended algal blooma documented by these satellite images also corresponds to higher temperature and lower salinity conditions in the coastal regions (Marini et al, 2008).…”

“…Satellite images (Marini et al, 2008) reveal that the nutrient supply is not constant in the area between the Gargano Peninsula and the Gulf of Taranto and show that chlorophyll a is mainly found in the plume of river-influenced WAC, thereby illustrating the separation of the nutrient-rich waters along the Italian coast from the more oligotrophic offshore regions in the central and southern Adriatic basins (Marini et al, 2008). The extended algal blooma documented by these satellite images also corresponds to higher temperature and lower salinity conditions in the coastal regions (Marini et al, 2008). The southward extension of the Po river plume within the WAC could allow G. ruber (white) to thrive in the upper 0-5 m of the water column in the coastal areas while the G. ruber (white) would have to dwell in the subsurface waters (0-30 m and up to 50 m) in the more oligotrophic offshore regions as well.…”