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| Titel |
High-resolution measurements of atmospheric molecular hydrogen and its isotopic composition at the West African coast of Mauritania |
| VerfasserIn |
S. Walter, A. Kock, T. Röckmann |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 10, no. 5 ; Nr. 10, no. 5 (2013-05-23), S.3391-3403 |
| Datensatznummer |
250018258
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| Publikation (Nr.) |
 copernicus.org/bg-10-3391-2013.pdf |
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| Zusammenfassung |
Oceans are a net source of molecular hydrogen (H2) to the atmosphere,
where nitrogen (N2) fixation is assumed to be the main biological
production pathway followed by photochemical production from organic
material. The sources can be distinguished using isotope measurements
because of clearly differing isotopic signatures of the produced hydrogen.
Here we present the first ship-borne measurements of atmospheric molecular
H2 mixing ratio and isotopic composition at the West African coast of
Mauritania (16–25° W, 17–24° N). This area is one of the biologically most active regions of the world's
oceans with seasonal upwelling events and characterized by strongly
differing hydrographical/biological properties and phytoplankton community
structures. The aim of this study was to identify areas of H2
production and distinguish H2 sources by isotopic signatures of
atmospheric H2. For this more than 100 air samples were taken during
two cruises in February 2007 and 2008. During both cruises a
transect from the Cape Verde Islands towards the Mauritanian Coast was
sampled to cover differing oceanic regions such as upwelling and
oligotrophic regimes. In 2007, additionally, four days were sampled at high
resolution of one sample per hour to investigate a possible diurnal cycle of
atmospheric H2.
Our results indicate the influence of local sources and suggest the Banc
d'Arguin as a pool for precursors for photochemical H2 production,
whereas oceanic N2 fixation could not be identified as a source for
atmospheric H2 during these two cruises. The variability in diurnal
cycles is probably influenced by released precursors for photochemical
H2 production and also affected by a varying origin of air masses. This
means for future investigations that only measuring the mixing ratio of
H2 is insufficient to explain the variability of an atmospheric diurnal
cycle and support is needed, e.g. by isotopic measurements. Nevertheless,
measurements of atmospheric H2 mixing ratios, which are easy to conduct
online during ship cruises, could be a useful indicator of production areas of
biological precursors such as volatile organic compounds (VOCs) for further
investigations. |
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