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| Titel |
Halocarbon emissions and sources in the equatorial Atlantic Cold Tongue |
| VerfasserIn |
H. Hepach, B. Quack, S. Raimund, T. Fischer, E. L. Atlas, A. Bracher |
| 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 ; 12, no. 21 ; Nr. 12, no. 21 (2015-11-09), S.6369-6387 |
| Datensatznummer |
250118156
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| Publikation (Nr.) |
 copernicus.org/bg-12-6369-2015.pdf |
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| Zusammenfassung |
| Halocarbons from oceanic sources contribute to halogens in the troposphere,
and can be transported into the stratosphere where they take part in ozone
depletion. This paper presents distribution and sources in the equatorial
Atlantic from June and July 2011 of the four compounds bromoform
(CHBr3), dibromomethane (CH2Br2), methyl iodide (CH3I)
and diiodomethane (CH2I2). Enhanced biological production during
the Atlantic Cold Tongue (ACT) season, indicated by phytoplankton pigment
concentrations, led to elevated concentrations of CHBr3 of up to
44.7 and up to 9.2 pmol L−1 for CH2Br2 in
surface water, which is comparable to other tropical upwelling systems.
While both compounds correlated very well with each other in the surface
water, CH2Br2 was often more elevated in greater depth than
CHBr3, which showed maxima in the vicinity of the deep chlorophyll
maximum. The deeper maximum of CH2Br2 indicates an additional
source in comparison to CHBr3 or a slower degradation of
CH2Br2. Concentrations of CH3I of up to 12.8 pmol L−1 in the surface water were measured. In contrary to expectations of a
predominantly photochemical source in the tropical ocean, its distribution
was mostly in agreement with biological parameters, indicating a biological
source. CH2I2 was very low in the near surface water with maximum
concentrations of only 3.7 pmol L−1. CH2I2 showed distinct
maxima in deeper waters similar to CH2Br2. For the first time,
diapycnal fluxes of the four halocarbons from the upper thermocline into and
out of the mixed layer were determined. These fluxes were low in comparison
to the halocarbon sea-to-air fluxes. This indicates that despite the
observed maximum concentrations at depth, production in the surface mixed
layer is the main oceanic source for all four compounds and one of the main
driving factors of their emissions into the atmosphere in the ACT-region.
The calculated production rates of the compounds in the mixed layer are 34 ± 65 pmol m−3 h−1
for CHBr3, 10 ± 12 pmol m−3 h−1 for CH2Br2, 21 ± 24 pmol m−3 h−1 for CH3I and 384 ± 318 pmol m−3 h−1 for
CH2I2 determined from 13 depth profiles. |
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