Consumption of CH<sub>3</sub>Cl, CH<sub>3</sub>Br, and CH<sub>3</sub>I and emission of CHCl<sub>3</sub>, CHBr<sub>3</sub>, and CH<sub>2</sub>Br<sub>2</sub> from the forefield of a retreating Arctic glacier
<p>The Arctic is one of the most rapidly warming regions of the Earth, with predicted temperature increases of 5–7 <span class="inline-formula"><sup>∘</sup></span>C and the accompanying extensive retreat of Arctic glacial systems by 2100. Retreating...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-06-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/20/7243/2020/acp-20-7243-2020.pdf |
| Summary: | <p>The Arctic is one of the most rapidly warming regions of the Earth, with
predicted temperature increases of 5–7 <span class="inline-formula"><sup>∘</sup></span>C and the accompanying
extensive retreat of Arctic glacial systems by 2100. Retreating glaciers
will reveal new land surfaces for microbial colonisation, ultimately
succeeding to tundra over decades to centuries. An unexplored dimension to
these changes is the impact upon the emission and consumption of halogenated
organic compounds (halocarbons). Halocarbons are involved in several
important atmospheric processes, including ozone destruction, and despite
considerable research, uncertainties remain in the natural cycles of some of
these compounds. Using flux chambers, we measured halocarbon fluxes across
the glacier forefield (the area between the present-day position of a
glacier's ice-front and that at the last glacial maximum) of a high-Arctic
glacier in Svalbard, spanning recently exposed sediments (<span class="inline-formula"><10</span> years) to approximately 1950-year-old tundra. Forefield land surfaces were
found to consume methyl chloride (<span class="inline-formula">CH<sub>3</sub>Cl</span>) and methyl bromide
(<span class="inline-formula">CH<sub>3</sub>Br</span>), with both consumption and emission of methyl iodide
(<span class="inline-formula">CH<sub>3</sub>I</span>) observed. Bromoform (<span class="inline-formula">CHBr<sub>3</sub></span>) and dibromomethane
(<span class="inline-formula">CH<sub>2</sub>Br<sub>2</sub></span>) have rarely been measured from terrestrial sources but
were here found to be emitted across the forefield. Novel measurements
conducted on terrestrial cyanobacterial mats covering relatively young
surfaces showed similar measured fluxes to the oldest, vegetated tundra
sites for <span class="inline-formula">CH<sub>3</sub>Cl</span>, <span class="inline-formula">CH<sub>3</sub>Br</span>, and <span class="inline-formula">CH<sub>3</sub>I</span> (which were consumed) and for
<span class="inline-formula">CHCl<sub>3</sub></span> and <span class="inline-formula">CHBr<sub>3</sub></span> (which were emitted). Consumption rates of
<span class="inline-formula">CH<sub>3</sub>Cl</span> and <span class="inline-formula">CH<sub>3</sub>Br</span> and emission rates of <span class="inline-formula">CHCl<sub>3</sub></span> from tundra and
cyanobacterial mat sites were within the ranges reported from older and more
established Arctic tundra elsewhere. Rough calculations showed total
emissions and consumptions of these gases across the Arctic were small
relative to other sources and sinks due to the small surface area
represented by glacier forefields. We have demonstrated that glacier
forefields can consume and emit halocarbons despite their young age and low
soil development, particularly when cyanobacterial mats are present.</p> |
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| ISSN: | 1680-7316 1680-7324 |