Jones, Benjamin
(Ed.)
Permafrost sediments contain one of the largest reservoirs of organic carbon on Earth that
is relatively stable when it remains frozen. As air temperatures increase, the shallow
permafrost thaws which allows this organic matter to be converted into potent greenhouse
gases such as methane (CH4) and carbon dioxide (CO2) through microbial processes.
Along the Beaufort Sea coast in the vicinity of the Tuktoyaktuk Peninsula, Northwest
Territories, Canada, warming air temperatures are causing the active layer above
permafrost to deepen, and a number of active periglacial processes are causing rapid
erosion of previously frozen permafrost. In this paper, we consider the biogeochemical
consequences of these processes on the permafrost sediments found at Tuktoyaktuk
Island. Our goals were to document the in situ carbon characteristics which can support
microbial activity, and then consider rates of such activity if the permafrost material were to
warm even further. Samples were collected from a 12mpermafrost core positioned on the
top of the island adjacent to an eroding coastal bluff. Downcore CH4, total organic carbon
and dissolved organic carbon (DOC) concentrations and stable carbon isotopes revealed
variable in situ CH4 concentrations down core with a sub-surface peak just below the
current active layer. The highest DOC concentrations were observed in the active layer.
Controlled incubations of sediment from various depths were carried out from several
depths anaerobically under thawed (5°C and 15°C) and under frozen (−20°C and −5°C)
conditions. These incubations resulted in gross production rates of CH4 and CO2 that
increased upon thawing, as expected, but also showed appreciable production rates
under frozen conditions. This dataset presents the potential for sediments below the active
layer to produce potent greenhouse gases, even under frozen conditions, which could be
an important atmospheric source in the actively eroding coastal zone even prior to thawing.
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