The Mediterranean Sea is an oligotrophic basin characterized by low nutrient levels and productivity. This research provides an unprecedented and high-quality nutrients dataset from the Strait of Sicily and Gulf of Sirt, gateway from Eastern and Western Mediterranean basin, and argue on the main mechanisms driving the unbalanced Redfieldian biogeochemistry of the studied area. In particular, in order to investigate the biogeochemistry of the Sicily Channel, a sampling plan from Sicilian to Libyan coasts and Gulf of Sirt was performed in July 2008. The θ-S diagrams highlight the presence of three main water masses: Modified Atlantic Water (MAW), Levantine Intermediate Water (LIW) and Eastern Mediterranean Deep Water (EMDW) with different chemical-physical features. MAW were identified by an intrusion of low-salinity water near the Sicilian and Libyan coasts, which are Atlantic Ionian Stream (AIS) and Atlantic Tunisian Current (ATC) jet, respectively. Analysis of nutrients reveal the oligotrophic character of the area with strong reduction of concentration in surface layers due to the assimilation of phytoplankton in the euphotic zone and evident increase below 200 m caused by organisms' re-mineralization. In the eastern Mediterranean, the nitrate to phosphate (N:P) ratio in the deep water is ~28:1, far in excess of the normal Redfield ratio (N:P=16:1) found in the oceans' deep water. Our dataset shows N:P ratios of ~10 ~30 and Si:N ~3.8 ~1.1 in surface waters and deep waters, respectively. Moreover, macronutrients from the Libyan coast shown no enrichment due to the potential effect of the Sahara desert as source of phosphorus for the Mediterranean system. Estimation of fluxes demonstrated that the eastern basin is a "nutrient source" for the western one. Effects of anthropogenic contamination from industrial activities present on the surrounding areas of the Strait of Sicily and the Gulf of Sirt waters were clearly detected by investigation of selecetd trace metals such as Pb and Cd, that evidence impact of Pb-rich fuel and of many steel mills from the northern Africa, especially in the area of the urban-industrial complex of Misurata. Distribution patterns of trace metals in the dissolved phase, some of which (Cd, Cu, Ni), show a clear Mediterranean specificity with clear lack of nutrient-like oceanic type behavior. The trace metals in the particulate show a strong contribution of impulsive inputs of Saharan dust, confirmed by the high levels of concentration and abundance of Ca, Al and Fe demonstrating a clear signal of crustal origin.
Biogeochimica del Canale di Sicilia e del Golfo della Sirte (macro e micronutrienti) / Placenti, Francesco. - (2011 Apr 19).
Biogeochimica del Canale di Sicilia e del Golfo della Sirte (macro e micronutrienti)
Placenti, Francesco
2011-04-19
Abstract
The Mediterranean Sea is an oligotrophic basin characterized by low nutrient levels and productivity. This research provides an unprecedented and high-quality nutrients dataset from the Strait of Sicily and Gulf of Sirt, gateway from Eastern and Western Mediterranean basin, and argue on the main mechanisms driving the unbalanced Redfieldian biogeochemistry of the studied area. In particular, in order to investigate the biogeochemistry of the Sicily Channel, a sampling plan from Sicilian to Libyan coasts and Gulf of Sirt was performed in July 2008. The θ-S diagrams highlight the presence of three main water masses: Modified Atlantic Water (MAW), Levantine Intermediate Water (LIW) and Eastern Mediterranean Deep Water (EMDW) with different chemical-physical features. MAW were identified by an intrusion of low-salinity water near the Sicilian and Libyan coasts, which are Atlantic Ionian Stream (AIS) and Atlantic Tunisian Current (ATC) jet, respectively. Analysis of nutrients reveal the oligotrophic character of the area with strong reduction of concentration in surface layers due to the assimilation of phytoplankton in the euphotic zone and evident increase below 200 m caused by organisms' re-mineralization. In the eastern Mediterranean, the nitrate to phosphate (N:P) ratio in the deep water is ~28:1, far in excess of the normal Redfield ratio (N:P=16:1) found in the oceans' deep water. Our dataset shows N:P ratios of ~10 ~30 and Si:N ~3.8 ~1.1 in surface waters and deep waters, respectively. Moreover, macronutrients from the Libyan coast shown no enrichment due to the potential effect of the Sahara desert as source of phosphorus for the Mediterranean system. Estimation of fluxes demonstrated that the eastern basin is a "nutrient source" for the western one. Effects of anthropogenic contamination from industrial activities present on the surrounding areas of the Strait of Sicily and the Gulf of Sirt waters were clearly detected by investigation of selecetd trace metals such as Pb and Cd, that evidence impact of Pb-rich fuel and of many steel mills from the northern Africa, especially in the area of the urban-industrial complex of Misurata. Distribution patterns of trace metals in the dissolved phase, some of which (Cd, Cu, Ni), show a clear Mediterranean specificity with clear lack of nutrient-like oceanic type behavior. The trace metals in the particulate show a strong contribution of impulsive inputs of Saharan dust, confirmed by the high levels of concentration and abundance of Ca, Al and Fe demonstrating a clear signal of crustal origin.File | Dimensione | Formato | |
---|---|---|---|
tesi dottorato Francesco Placenti_matr_955530.pdf
accesso aperto
Tipologia:
Tesi di dottorato
Dimensione
12.95 MB
Formato
Adobe PDF
|
12.95 MB | Adobe PDF | Visualizza/Apri |
I documenti in ARCA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.