Concentration and isotopic composition of marine nitrous oxide, in particular the oxygen-17 isotope excess

Grefe, Imke (2013) Concentration and isotopic composition of marine nitrous oxide, in particular the oxygen-17 isotope excess. Doctoral thesis, University of East Anglia.

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The oxygen isotope excess Δ(17O) is a potential tracer of biological nitrous oxide (N2O) cycling.
This study presents the first measurements of Δ(17O) in marine N2O together with details about
the design and development of a custom-built Gas Chromatography-Isotope Ratio Mass
Spectrometry (GC-IRMS) analytical system for δ(15N), δ(18O) and Δ(17O) of N2O.
Δ(17O) values between 0.1 and 4.6 ‰ (relative to VSMOW) were observed during three field
campaigns in the temperate, subtropical and tropical Atlantic Ocean, the Scotia Sea and the
Weddell Sea. This indicates a biological source for oxygen isotope excess in N2O, as oceanic
N2O was not in equilibrium with the atmosphere (0.9 ‰).
δ(15N) values ranged from 2.3 to 25.1 ‰ (relative to Air-N2). δ(18O) measured in the Weddell
Sea ranged from 44.9 to 48.8 ‰ (relative to VSMOW). The dataset from the Atlantic Ocean
and the Atlantic sector of the Southern Ocean suggest nitrification and nitrifier-denitrification as
the main N2O production pathway in the oxic, deep ocean. High δ(15N) values in the south
Atlantic Gyre are presumably associated with a denitrification source.
A novel off-the-shelf N2O analyser was tested in combination with an equilibrator for semiautonomous
concentration measurements in the surface ocean. The subtropical gyres in the
Atlantic Ocean were confirmed to be weak sinks ((-0.14±0.31) μmol m-2 d-1 N2O flux to the
ocean in the northern, and (-0.16±0.33) μmol m-2 d-1 in the southern gyre) and the equatorial
region was a source of N2O to the atmosphere (flux of 0.53 μmol m-2 d-1). New data from the
Scotia Sea identified a strong source region ((2.9±2.7) μmol m-2 d-1), while the Weddell Sea was
closer to equilibrium with the atmosphere ((0.9±1.0) μmol m-2 d-1).

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Environmental Sciences
Depositing User: Users 2259 not found.
Date Deposited: 13 Jun 2014 09:05
Last Modified: 13 Jun 2014 09:05


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