Permafrost Thaw Dynamics and Methane Release in Arctic Tundra Ecosystems
DOI:
https://doi.org/10.5281/zenodo.22810997Keywords:
permafrost thaw, active layer thickness, thermokarst, methane flux, eddy covariance, Arctic tundra, carbon-climate feedback, ice-wedge degradationAbstract
Warming of the Arctic at roughly three to four times the global rate is driving progressive deepening of the
seasonally thawed active layer and, in ice-rich lowland tundra, localized collapse of the ground surface as massive
ground ice melts, a process known as thermokarst. Both pathways expose previously frozen soil organic carbon to
decomposition, but their consequences for methane emission are expected to differ because thermokarst
additionally saturates and often inundates the collapsed ground, creating the anoxic conditions methanogens
require. We report an eight-year (2016-2023) record from a lowland ice-wedge polygon tundra catchment,
combining two eddy covariance towers, one over largely intact polygonal tundra and one over an actively degrading
thermokarst basin, with a static chamber network stratified across four microforms (intact polygon centers,
degrading polygon rims, collapsed thermokarst pits, and thermokarst ponds) and a monitoring grid of active layer
thaw probes and boreholes instrumented with thermistor strings to 15 m depth. Active layer thickness increased
from a catchment mean of 46.3 cm in 2016 to 61.4 cm in 2023, a trend of 2.06 cm per year, while mean annual
ground temperature at 10 m depth warmed from -3.8 degrees C to -2.9 degrees C over the same interval.
Thermokarst pond and pit cover expanded from 4.2% to 7.8% of the catchment area. Growing-season chamber
fluxes scaled strongly with thaw stage, rising from a mean of 3.1 mg CH4 m-2 d-1 in intact polygon centers to 41.8
mg CH4 m-2 d-1 in thermokarst ponds, and catchment-scale eddy covariance fluxes tracked this shift, increasing by
58% over the study period even after accounting for interannual variability in growing-season temperature and
precipitation. Cold-season and shoulder-season emissions, captured by the towers but largely missed by chamber
campaigns, contributed a mean of 27% of the annual methane budget, with a disproportionate share from the
thermokarst basin tower. These results indicate that thermokarst expansion, rather than active layer deepening
alone, is emerging as the dominant control on methane flux from this landscape, with implications for how
permafrost-region methane emissions are represented in Earth system models that resolve gradual thickening but
not abrupt thaw.
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