The EPREX consisted of a transect cruise with six stations
spanning a range of biogeochemical conditions. At each station
we collected water samples at depths ranging from the surface
to 2000 meters. Oxygen was measured using Winkler titration
(Grasshoff et al., 1983); nitrite was measured using colorimetry
(Grasshoff et al., 1983); ammonium was measured using the
fluorescence method of Jones (1991); and N2O was measured by
headspace equilibration in a gas tight syringe, followed by
packed-column gas chromatography using an electron capture
detctor (Cohen, 1977). Nutrient samples, including nitrate,
nitrite, and ammonium were collected in acid-washed plastic
bottles and frozen for later analysis. Additional water samples
were collected in glass serum bottles, preserved with mercuric
chloride and sealed with gas tight septa for stable isotopic
analysis of N2O in the mass spectrometry laboratory at the
University of Hawaii.
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source of atmospheric nitrous oxide from subtropical North Pacific
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