On the importance of atmospheric inputs of inorganic nitrogen species on the productivity of the eastern Mediterranean Sea

To assess the importance of the atmospheric deposition of nitrogen (N) on the productivity of the eastern Mediterranean Sea, measurements of both wet and dry deposition of dissolved inorganic nitrogen (DIN) have been performed at a remote coastal area in the island of Crete (Finokalia) during a 3-year period (1996-1999). The estimation of dry deposition of DIN is based on measurements of both gaseous (HNO3 and NH3) and particulate phase (NO3- and NH4+) nitrogen compounds. The results of the wet and dry deposition obtained at Finokalia have been compared with data of particulate organic nitrogen (PON) obtained during two yearly (1994-1995 and 1997-1998) surveys (CINCS and MATER) in the Cretan Sea by using sediment traps deployed at 200 and 500 in depths. Our results show that the atmospheric deposition of DINT can account for up to 370% of the measured PON in the sediment traps, indicating that atmospheric pathway alone can sufficiently account for the measured new nitrogen production. On the basis of the primary productivity induced by the imported DIN and the productivity of the southeastern Mediterranean derived from in situ measurements a mean f ratio of 0.24 is calculated indicating that from the N point of view, the eastern Mediterranean can no longer be considered as among the most oligotrophic seas of the world. Other elements, most probably phosphorus (P), can account for the oligotrophic character of the eastern Mediterranean Sea. To our knowledge this is the first attempt to understand the role of the atmospheric input of nitrogen on the productivity of the eastern Mediterranean Sea.