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| Titel |
Photooxidation of dimethylsulfide (DMS) in the Canadian Arctic |
| VerfasserIn |
A. Taalba, H. Xie, M. G. Scarratt, S. Bélanger, M. Levasseur |
| 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. 11 ; Nr. 10, no. 11 (2013-11-01), S.6793-6806 |
| Datensatznummer |
250085383
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| Publikation (Nr.) |
 copernicus.org/bg-10-6793-2013.pdf |
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| Zusammenfassung |
| Photolysis of dimethylsulfide (DMS), a secondary photochemical process
mediated by chromophoric dissolved organic matter (CDOM), has previously
been demonstrated to be an important loss term of DMS in the surface layer
of warm seas and the Southern Ocean. The role of photolysis in regulating
the DMS dynamics in northern polar seas remains, however, less clear. This
study for the first time determined the apparent quantum yield (AQY) spectra
of DMS photooxidation in Canadian Arctic seas covering Baffin Bay, the
Mackenzie estuary and shelf, and the Canada Basin. The DMS AQY was fairly
invariant at salinities < 25 but rose rapidly with further
increasing salinity in an exponential manner. Salinity can therefore be used
as a quantitative indicator of the DMS AQY. The DMS AQY in the ultraviolet
(UV) wavelengths was linearly and positively correlated with the spectral
slope coefficient (275–295 nm) of the CDOM absorption spectrum, suggesting
that marine CDOM photosensitizes the degradation of DMS more efficiently
than does terrestrial CDOM or that coastal waters contain higher
concentrations of substrates (most likely dissolved organic matter and redox
metals) that compete for DMS-oxidizing radical intermediates. High
concentrations of nitrate (~ 12 μmol L−1) in deep water
samples boosted DMS photooxidation by 70–80%, due likely to radical
chemistry of nitrate photolysis. Coupled optical-photochemical modeling,
based on the obtained DMS AQY spectra, shows that UV-A (320–400 nm)
accounted for 60–75% of the DMS photolysis in the sunlit surface layer
and that photochemistry degraded DMS on an e-folding time from 9 to 100 d
(mean: 29 d). The photooxidation term on average accounted for 21% of the
DMS gross loss rate and was comparable to the atmospheric DMS ventilation
rate estimated for the same geographic regions. The methodology adopted here
to study the relationship between CDOM quality/origin and DMS AQYs, if
applicable to other ocean areas, may bring results of global significance
for DMS cycling and might have implications for probing other CDOM-driven
photochemical processes. |
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