Microbial Greenhouse Gas Dynamics Associated With Warming Coastal Permafrost, Western Canadian Arctic

Abstract

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 12 m permafrost 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.

Source, Migration Pathways, and Atmospheric Release of Geologic Methane Associated With the Complex Permafrost Regimes of the Outer Mackenzie River Delta, Northwest Territories, Canada

“…Methane could have accumulated during past interglacial warm periods when the sediments were thawed and then trapped in place as permafrost formed during glacial periods. In addition, as documented by Lapham et al (2021) in similar Quaternary sediments occurring to the east of our study site, active methane formation can also occur as a result of microbial activity at negative temperatures within the ice bonded permafrost body itself. Both processes could be operative in the permafrost setting that we describe.…”

Mapping subsea permafrost around Tuktoyaktuk Island (NWT, Canada) using electrical resistivity tomography

“…Assessment of the terrestrial and nearshore geology and of the nearshore bathymetry benefited by previous studies led by the Geological Survey of Canada (Boike and Dallimore, 2019) and completion of two terrestrial boreholes on Tuktoyaktuk Island and two nearshore boreholes was conducted in 2018 (Lapham et al, 2020).…”

“…4 to 6 m high cliff. Sediments making up the island consist of Quaternary-aged, ice bonded sands and silt with some random massive ice bodies which are deformed indicating glacial overriding (Lapham et al, 2020). On top of the cliff, the island is mostly flat and covered by lowland and highland tundra with active layer depths around 60 cm.…”

“…Since the onset of Arctic amplification in 1970, air temperatures in the region are rising twice as fast as the global average (Hansen et al, 2010;Lenssen et al, 2019): 0.052 °C per year on average in the past 50 years to a current mean annual temperature of -8 °C (Lenssen et al, 2019;Lapham et al, 2020;GRID-Arendal, 2020). Rising temperatures lead to an extension of the open water period, which accelerates coastal retreat due to thermoerosion (Berry et al, 2021).…”