Nitrogen and oxygen isotope measurements of nitrate from CTD bottles during cruise AMT16 (D294).

These data originate from analyses on samples collected from CTD bottles between 20 May and 29 June 2005. Samples were taken from a meridional cross section from the Northen Gyre through the equatorial upwelling zone to the Northen Gyre. Samples were also taken from the euphotic zone. The 15N/14N and 18O/16O isotope ratios were analysed using the denitrifier method (see Casciotti et al., 2002 and Sigman et al., 2001 for detailed methods). The method of measurement of the isotopic composition of nitrate is based on the isotopic analysis of nitrous oxide (N2O) generated from nitrate in denitrifying bacteria that lack N2O reductase activity.