Nitrogen fixation from vertical profiles from CTD rosette samples by mass spectrometry on RRS Discovery Cruise D369.

D369 was the last of three National Oceanography Centre process study research cruises to be run by the Ocean Biogeochemistry and Ecosystems research group under the NERC Ocean 2025 research programme. The cruise was aimed at studying effect of ubiquitous eddies on links between microbial carbon, nitrogen and phosphorus cycling (LINK) in the North Atlantic subtropical gyre. This data was collected during August/September 2011. Rates of nitrogen fixation were measured via a series of simulated in-situ incubations using both on-deck incubators and plant growth chambers using standard stable isotope techniques. In a typical sampling strategy, water samples were collected every other day from five light depths from the early morning CTD cast. The depths sampled corresponded to irradiance depths of 97, 55, 33, 14 and 1 percent of surface irradiance. Incubations for N2 fixation lasted 24 hours. The Nitrogen fixation rates were measured using the bubble technique of Montoya et al., (1996). Further details on the methodology and results are described in Painter et al., (2013).