Istituto di Scienze Marine     
Ibello V., Cantoni C., Cozzi S., Civitarese G., Ribera D'Alcalą M. Nitrogen fixation in the Mediterranean Sea. In: ASLO 2008 - ASLO Ocean Sciences Meeting: From the Watershed to the Global Ocean. (Orlando, Florida, 2-7/03 2008). Abstract, pp. NP - NP. American Society of Limnology and Oceanography, the American Geophysical Union, The Oceanography Society, and the Estuarine Research Federation, 2008.
The Mediterranean Sea is an oligotrophic basin characterized by low nutrient levels and unusually high NO3/PO4 molar ratios in the deeper layers, that reach the maximum (N/P = 28) in the Eastern Mediterranean. An external nitrogen source needs to be claimed in order to explain the nitrogen excess. Pantoja et al. (2002) found that the 15N/14N natural abundance in particulate and in dissolved inorganic nitrogen display low values, suggesting an important role of a "light" nitrogen source. Two hypotheses can be invoked: (i) nitrogen compounds from atmospheric deposition and/or(ii)atmospheric molecular nitrogen throughout nitrogen fixation . During TRANSMED oceanographic cruise carried out in the framework of Italian project VECTOR(June 2007), N2 fixation experiments have been carried out all over the Mediterranean Sea and outside the Gibraltar Strait. Surprisingly, very low rates (< 0.10 nmol N2*l-1*d-1) have been observed in different areas of the basin, while higher values have been observed in Atlantic Ocean according with literature data. These preliminary results suggest a major role for nitrogen atmospheric deposition in shaping the NO3/PO4 anomaly of the basin. Pantoja, S., D. J. Repeta, J. P. Sachs, and D. M. Sigman (2002). Stable isotope constraints on the nitrogen cycle of the Mediterranean Sea water column, Deep Sea Res., Part I, 4, 1609- 1621.
URL: http://www.aslo.org/orlando2008/
Subject nitrogen fixation

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