DOI: 10.1594/pangaea.928664
title: Dissolved nitrous oxide distribution in the central South Pacific

description: Nitrous oxide (N2O) is an important atmospheric trace gas involved in tropospheric warming and stratospheric ozone depletion. The ocean is a net source of this gas, contributing around 25% of global N2O sources, although this emission is highly variable. It is the case of eastern South Pacific, a region with marked zonal gradients, ranging from highly productive and suboxic conditions in coastal upwelling systems to oligotrophic and oxygenated conditions in the subtropical gyre. Indeed, South Pacific Ocean has the largest permanent anticyclonic oceanic gyre which has been described as the most oligotrophic zone in the world ocean. Nitrous oxide concentration in the water column was measured on a transect crossing the Subtropical South Pacific Gyre during the BIOSOPE cruise (austral spring, 2004). This dataset includes nitrous oxide and nutrient concentrations at different depths from French program BIOSOPE, funded by the Centre National de la Recherche Scientifique (CNRS), the Institut des Sciences de l'Univers (INSU), the Centre National d'Etudes Spatiales (CNES), the European Space Agency (ESA), The National Aeronautics and Space Administration (NASA) and the Natural Sciences and Engineering Research Council of Canada (NSERC). Nitrous oxide measurements belong to Concepción University.
description: &lt;0.00 = NaNContinuously sampled variables: Temperature and salinity profiles were obtained with a Seabird SBE 911 + CTD. Oxygen was obtained with a Seabird SBE43 oxygen sensor mounted in a rosette system and calibrated with Winkler titration.Discretely sampled variables: Water samples were collected using Niskin bottles attached to rosette sampler, in order to obtain discrete measurements of dissolver oxygen (O2) and nutrients (NO3, NO2, SiO4 and PO43). Discrete samples of DO (in triplicate) were analyzed using manual Winkler method. Concentrations of nitrate, nitrite, phosphate and silicate have been analysed using a Technicon Autoanalyser II (Treguer and Le Corre, 1975). All the measurements have been done onboard, except for the silicate samples, which were poisoned (mercuric chloride 1µg ml−1 ) and analyzed on land. Measurements in the nanomolar range (lower detection limit=3 nmoles l−1 ) were obtained from the sensitive method described by Raimbault et al. (1990; doi:10.1007/BF01313277). Nitrate at submicromolar levels (detection limit: 0.05µmoles l−1 ) and phosphate (detection limit: 0.02µ moles l−1 ) were measured according to Armstrong et al. (1967; doi:10.1016/0011-7471(67)90082-4).The samples for N2O analyses were transferred directly into 125‐mL glass flasks (duplicate), preserved with HgCl2, and sealed with butyl rubber stoppers. The N2O was extracted from the sample by sparging with helium and then carried to a pre‐concentration loop, which is a stainless steel tube (4.35 mm internal diameter) packed with glass beads (Flushing GH, 60/80 mesh). The N2O was determined with an HP 6890 gas chromatograph equipped with a Pora PLOT‐Q capillary column and attached to a Finnigan MAT252 mass spectrometer. A detailed description of the analytical procedure is given by Yamagishi et al. (2005; doi:10.1029/2004GL021458). The analytical accuracy of the N2O concentration analyses was better than 1%.