Consumption of CH3Cl, CH3Br and CH3I and emission of CHCl3, CHBr3 and CH2Br2 from a retreating Arctic glacier's forefield [post]

Moya L. Macdonald, Jemma L. Wadham, Dickon Young, Chris R. Lunder, Ove Hermansen, Guillaume Lamarche-Gagnon, Simon O'Doherty
2019 unpublished
<p><strong>Abstract.</strong> The Arctic is one of the most rapidly warming regions of the Earth, with predicted temperature increases of 5–7 °C and the accompanying extensive retreat of Arctic glacial systems by 2100. This will reveal new proglacial 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
more » ... umption of halogenated organic compounds (halocarbons) from proglacial land surfaces. 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 from proglacial land surfaces spanning recently-exposed sediments (< 10 years), to approximately 1950 year old tundra in front of a High Arctic glacier. Proglacial land surfaces were found to consume methyl chloride (CH<sub>3</sub>Cl) and methyl bromide (CH<sub>3</sub>Br), with both consumption and emission of methyl iodide (CH<sub>3</sub>I) observed. The largest consumption rates of these compounds occurred at the oldest, vegetated, tundra sites (−126 ± 4, −1.8 ± 0.04 and −0.13 ± 0.03 nmol m<sup>−2</sup> d<sup>−1</sup>, respectively for CH<sub>3</sub>Cl, CH<sub>3</sub>Br and CH<sub>3</sub>I). However, similar consumption rates were recorded at much younger sites with little soil development, but with the presence of extensive cyanobacterial mats (means of −106 ± 7, −1.7 ± 0.1, −0.01 ± 0.03 nmol m<sup>−2</sup> d<sup>−1</sup> for CH<sub>3</sub>Cl, CH<sub>3</sub>Br and CH<sub>3</sub>I). Emission of chloroform (CHCl<sub>3</sub>), bromoform (CHBr<sub>3</sub>) and dibromomethane (CH<sub>2</sub>Br<sub>2</sub>) was detected across the forefield, with the highest emission of CHCl<sub>3</sub> from cyanobacterial mats (106 ± 42 nmol m<sup>−2</sup> d<sup>−1</sup>), CHBr<sub>3</sub> from bare sediment adjacent to the mats (0.7 ± 0.3 nmol CHBr<sub>3</sub> m<sup>−2</sup> d<sup>−1</sup>) and CH<sub>2</sub>Br<sub>2</sub> from the vegetated tundra (mean 0.8 ± 0.3 nmol m<sup>−2</sup> d<sup>−1</sup>). We have demonstrated that proglacial surfaces can consume and emit halocarbons despite their young age and low soil development. With future glacial retreat and the expansion of these surfaces, these fluxes may become more important in the future.</p>
doi:10.5194/acp-2019-943 fatcat:jphcr7barnello2sczc6mk76ru