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Monitoring the role of subsurface physical processes in carbon flux from a degraded permafrost site using novel multidisciplinary observations
Stephanie
R.
James, U.S. Geological Survey, Denver CO, sjames@usgs.gov
(Presenter)
Understanding the impact of permafrost thaw and thermokarst formation on the global carbon budget remains incomplete due to the complex relationships between above and below ground processes, dramatic seasonal changes, and limitations in subsurface measurement capabilities. To address some of these uncertainties and better the understanding of the subsurface physical controls on carbon fluxes at the site scale, we will be conducting a multidisciplinary field experiment using novel combinations of geophysical and biogeochemical methods. This work will take place from 04/2018 to 07/2019 at the Alaskan Peatland Experiment (APEX) thermokarst research site near Fairbanks, AK. Passive seismic, nuclear magnetic resonance (NMR), temperature, soil moisture, and both surficial and subsurface carbon gas measurements will be recorded along a transect between forested permafrost and two collapse-scar bogs of different age. The unique combination of complementary geophysical methods (passive seismic + NMR) and in situ biogeochemical data will characterize the relationships between subsurface physical properties and surface carbon fluxes. Of particular interest is the potential role of unfrozen water within permafrost and frozen soils in sustaining microbial activity, which may be significant in enhancing carbon export but has been poorly characterized in situ. An array of seismic stations will continuously monitor subsurface freeze/thaw and water saturation changes along the thermokarst gradient and periodic borehole NMR profiles will provide direct measurements of unfrozen water content. These geophysical recordings will be collocated with in situ measurements of subsurface gas concentrations and temperature. Other key variables such as organic layer thickness, surface gas fluxes, and active layer thickness will also be measured at select locations. Initial work has begun using SUTRA-ICE to generate 1-D numerical simulations of water and energy transport for representative vertical profiles along the planned transect to provide a conceptual framework and help clarify the complex relationships between surface conditions and subsurface properties. We plan to integrate simulations with empirical data from the field experiment to aid interpretations, as well as combine with forward modeling of seismic velocity variations to quantify the sensitivity of the passive seismic technique to subtle changes in ice and water saturation. This multifaceted, interdisciplinary approach will serve as a proof-of-concept for the integration of geophysical and biogeochemical measurements for better understanding the impacts of thermokarst development on ecosystem-scale carbon fluxes in a lowland boreal forest. Associated Project(s): Poster Location ID: 97 Session Assigned: Carbon Dynamics
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