|Importance of nitrogen fixation in the surface primary production process near the Azores Front, North Atlantic Ocean|
Roukaerts, A. (2012). Importance of nitrogen fixation in the surface primary production process near the Azores Front, North Atlantic Ocean. MSc Thesis. Vrije Universiteit Brussel, Faculty of sciences, Department of Analytical and Environmental Chemistry: Brussel. 55 + appendix pp.
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VLIZ: Non-open access 266319
|Document type: Dissertation|
Most ocean surfaces are depleted in fixed nitrogen due to the removal of nutrients by the biological carbon pump. Diazotrophs however, are capable of fixing atmospheric nitrogen gas (N2) and can be an important supply of ‘New’ nitrogen to the surface. Previous studies imply a substantial role for biological nitrogen fixation at the Azores Current (AC), though absolute rates measurements are scarce. In summer 2011, the DIAPICNA expedition was conducted, sampling five stations across the Azores Current at 34°W. The goal was to study actors and activity of nitrogen fixation in this region and quantify the uptake rates. The present thesis presents the results for the measurements of nutrients and isotopic signatures of nitrate (?15N18O3-) and particulate matter, as well as 15N2 and H13CO3- uptake experiments. For the enrichment experiments, a new method proposed by Mohr et al. was tested and used. The results all suggest that there is fixation of N2 at all sampled stations, with a high importance on both sides of the current. The highest relative importance was found south of the Azores Current. On average, up to 50% of the new nitrogen at these stations came from N2-fixation with station 2 (south of the AC) apparently obtaining 83% of the fixed nitrogen from N2-fixation.