Nitrogen fixation from diel surveys by stable-isotope mass spectrometry on UKSOLAS cruise D325.

Nitrogen fixation was determined from near surface waters using ¹⁵N methodology at 5 different oceanographic stations in the vicinity of the Cape Verde Islands (north-east Atlantic) between 13 November and 18 December 2007 onboard RRS Discovery. Stations were selected from remotely sensed information on surface chlorophyll concentrations to give a gradient of conditions between 0.06 and 0.38 µg L^-1. High rates (>13.8 nmol L^-1h^-1) were determined at Station A coincident with maximum iron concentration (1.51 nM). At all other stations rates were between 0.03 and 0.54 nmol L^-1h^-1.