| Summary: | Molecular nitrogen (N2) is the most abundant form of nitrogen, however only a limited number of organisms can use this reservoir through a process named nitrogen fixation. Therefore, nitrogen is the main limiting nutrient in both marine and terrestrial ecosystems. Nitrogen fixation was initially considered a minor source in the ocean, mainly attributed to organisms of the genus Trichodesmium that inhabit regions where surface temperature is above 20°C, and the stability of the water column is high. The discovery of other groups of marine diazotrophs has evidenced that the range of environments where nitrogen fixation may be relevant is more extensive than it was originally thought. Recent studies demonstrate the activity of nitrogen-fixing organisms in relatively rich nitrogen regions, as for example the Canadian Arctic, the English Channel, the Mekong River plume in the China Sea, the equatorial Atlantic, and the NE coast of the United States. In addition, a study carried out in Cabo Silleiro in summer 2009 described nitrogen fixation rates similar in magnitude to the ones reported for subtropical regions. In this project we propose to determine the seasonal variability in nitrogen fixation rates, and also its biogeochemical relevance as a source for new nitrogen into the shelf of the Galician upwelling system. We propose a multidisciplinary approach that combines experiments of nitrogen fixation rates and microstructure turbulence observations. Although, nowadays biological nitrogen fixation probably represents a minor input of nitrogen into the system, its quantification is crucial to understand the functioning of the global nitrogen cycle. At the local scale, under an ocean threatened by global change, this study will provide a basis to determine changes in the relative importance of the different mechanisms controlling the input of new nitrogen into the system, a process that determines the productivity of fisheries in this region. Aunque el nitrógeno molecular es la forma más abundante de nitrógeno, sólo ...
|
|---|