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| Titel |
A mechanism for biologically induced iodine emissions from sea ice |
| VerfasserIn |
A. Saiz-Lopez, C. S. Blaszczak-Boxe, L. J. Carpenter |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 17 ; Nr. 15, no. 17 (2015-09-01), S.9731-9746 |
| Datensatznummer |
250120004
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| Publikation (Nr.) |
 copernicus.org/acp-15-9731-2015.pdf |
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| Zusammenfassung |
| Ground- and satellite-based measurements have reported high concentrations of
iodine monoxide (IO) in coastal Antarctica. The sources of such a large
iodine burden in the coastal Antarctic atmosphere remain unknown. We propose
a mechanism for iodine release from sea ice based on the premise that
micro-algae are the primary source of iodine emissions in this environment.
The emissions are triggered by the biological production of iodide (I−)
and hypoiodous acid (HOI) from micro-algae (contained within and underneath
sea ice) and their diffusion through sea-ice brine channels, ultimately accumulating in a thin
brine layer (BL) on the surface of sea ice. Prior to reaching the BL, the
diffusion timescale of iodine within sea ice is depth-dependent. The BL is
also a vital component of the proposed mechanism as it enhances the chemical
kinetics of iodine-related reactions, which allows for the efficient release
of iodine to the polar boundary layer. We suggest that iodine is released to
the atmosphere via three possible pathways: (1) emitted from the BL and then
transported throughout snow atop sea ice, from where it is released to the
atmosphere; (2) released directly from the BL to the atmosphere in regions of
sea ice that are not covered with snowpack; or (3) emitted to the atmosphere
directly through fractures in the sea-ice pack. To investigate the proposed
biology–ice–atmosphere coupling at coastal Antarctica we use a multiphase
model that incorporates the transport of iodine species, via diffusion, at
variable depths, within brine channels of sea ice. Model simulations were
conducted to interpret observations of elevated springtime IO in the coastal
Antarctic, around the Weddell Sea. While a lack of experimental and
observational data adds uncertainty to the model predictions, the results
nevertheless show that the levels of inorganic iodine (i.e. I2, IBr,
ICl) released from sea ice through this mechanism could account for the
observed IO concentrations during this timeframe. The model results also
indicate that iodine may trigger the catalytic release of bromine from sea
ice through phase equilibration of IBr. Considering the extent of sea ice
around the Antarctic continent, we suggest that the resulting high levels of
iodine may have widespread impacts on catalytic ozone destruction and aerosol
formation in the Antarctic lower troposphere. |
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