Field Campaign august 9-18, 2011
Scientists: Lisa Pratt, Jeff White, Kevin Webster, Jacob Rebholz
Results from First-Year Summer Campaign
In August of 2011, we deployed a Boreal Open-Path Laser at multiple transects across a major shear zone that extends for tens of kilometers from the margin of the ice sheet to the head of Sondre Stromfjord near Kangerlussuaq, Greenland. Bedrock adjacent to the shear zone is Archaean gneisses with numerous cross-cutting mafic dykes. One principal sinistral strike-slip fault and numerous ancillary faults are visible in satellite images of the narrow valley that defines our study site.
The infrared laser was positioned at a height of about 2 meters above the ground surface and was run for durations of 1.0 to 4.5 hours along nine transects across the shear-zone valley. The transect length varied from 22.6 to 77.0 meters, reflecting the distance between the steep valley walls. Raw data was transformed by removing readings of 0 ppm, removing data taken before a stable light level was obtained, and narrowly defining the range of light levels for optimal performance.
The average concentration of CH4 measured across the shear-zone valley varied from 1.4 to 2.3 ppm. Substantial variation in concentration is inferred to result from the presence of open-water lakes and vegetated peatlands for high values and rocky outcrops for low values. Background concentrations of atmospheric CH4 from ice-margin environments in Greenland are about 1.8 ppm. Previous studies of methanogenic arctic environments have reported atmospheric CH4 concentrations of 1.7-2.3 ppm. Data obtained in 2011 by open-path laser measurements suggest that the study site is a significant net emitter of CH4 in late summer.
Future studies in western Greenland will allow determination of diurnal and seasonal fluxes of CH4 allowing for comparison with fluxes at other permafrost sites in the northern and southern hemispheres. Starting in summer of 2012, a suite of field instruments will allow in situ determination of carbon and hydrogen isotopic compositions for CH4 sampled in soil-pipe wells and in bedrock boreholes. The combination of concentration and isotopic signatures for CH4 will help unravel biotic from abiotic influences on methane cycling along a major shear intersection of a deep permafrost profile in western Greenland.