Methyl bromide degradation in Southern Ocean sea ice
Mass, Alexandra Quinn
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Methyl bromide utilization in sea ice, brine, and under-ice seawater was measured from four stations in the Amundsen Sea using a 14-C isotope technique during the Icebreaker Oden’s 2008-09 austral summer route through the Pacific sector of the Southern Ocean. Increases in 14-C measured on 0.2 μm filter membranes and CO2-trapping wicks are attributed to microbial incorporation and respiration due to the dehalogenating activity of cold-adapted bacteria. Respiration rate constants were >50-fold higher than incorporation constants, reaching 0.51/day in sea ice samples, 0.23/day in brine samples, and 0.15/day in under-ice seawater. These rate constants did not correlate with overall bacterial abundance and suggest that dehalogenating populations are not proportional to the overall microbial communities in the sample types examined. These data show evidence of microbial degradation of methyl bromide in sea ice, brine, and under-ice seawater of the Amundsen Sea, and may help to explain the under-saturation of methyl bromide in the Southern Ocean.