| Abstract |
Atmospheric deposition is recognized as a potential source of trace elements of continental origin to oceanic areas. Of particular interest are the inputs of elements such as N, P, and Fe, which are essential for the biological growth of oceanic biota. The potential role of atmospheric deposition on the oceans productivity is expected to be particularly important for oligotrophic oceanic areas, such as the Mediterranean Sea and especially its eastern basin. Atmospheric deposition of inorganic phosphorus in the Levantine Basin, eastern Mediterranean was examined in order to estimate it s spatial and temporal variability and its role in seawater productivity. Total and dissolved inorganic phosphorus (IP) was measured in both rainwater and aerosol samples collected from a remote coastal area on the island of Crete (Greece). Particle size distributions of P, as well as total deposition were also measured. Wet and dry deposition data of dissolved inorganic phosphorus (DIP) from Crete are compared with phosphorus data from vicinal areas, as well as with simultaneously obtained dissolved inorganic nitrogen (DIN) and with productivity data from the literature. Our results indicate that in both wet and dry deposition, the DIN/DIP molar ratio ranges between 63 and 349, exceeding by a factor of up to 22 the N/P ratio observed in seawater (ranging from 25 to 28). An observation which is also verified from other studies focused on the Mediterranean sea. So phosphorous could be responsible for the oligotrophic status of the eastern Mediterranean. At Finokalia, both DIP and TIP present a significant seasonal variation, with higher values being observed during the summer. The origin of the air mass is of particular importance for phosphorus solubility. Interesting is the fact that the lowest values for the DIP/TIP ratio are associated with the SE and SW sectors, and the highest with the N sectors. Moreover it was found that the atmospheric deposition of DIP could reasonably account for a significant part of the new production (up to 38%) observed during the summer and autumn period (i.e., when water stratification is at its maximum). The next step towards the better understanding of phosphoruss role in East Mediterranean seawater productivity is the successful determination of the various atmospheric and liquid phosphorous forms. The results given in the present study are a first attempt to estimate total and organic phosphorous in rainwater and dry deposition samples. The organic part of the total phosphorous content of the samples was quite small (0-25%). Even though the number of samples was relatively small in order to estimate the temporal variability of these species, it is characteristic that the highest values of total and organic phosphorous were measured during the dry season.
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Προσδιορισμός και εποχική διακύμανση μορφών φωσφόρου στην ατμόσφαιρα της Ανατολικής Μεσογείου
