Sensitivity of airborne geophysical data to sublacustrine and near-surface permafrost thaw (original) (raw)
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Sensitivity of airborne geophysical data to sublacustrine permafrost thaw
The Cryosphere Discussions, 2014
ABSTRACT A coupled hydrogeophysical forward and inverse modeling approach is developed to illustrate the ability of frequency-domain airborne electromagnetic (AEM) data to characterize subsurface physical properties associated with sublacustrine permafrost thaw during lake talik formation. Several scenarios are evaluated that consider the response to variable hydrologic forcing from different lake depths and hydrologic gradients. The model includes a physical property relationship that connects the dynamic distribution of subsurface electrical resistivity based on lithology as well as ice-saturation and temperature outputs from the SUTRA groundwater simulator with freeze/thaw physics. Electrical resistivity models are used to simulate AEM data in order to explore the sensitivity of geophysical observations to permafrost thaw. Simulations of sublacustrine talik formation over a 1000 year period modeled after conditions found in the Yukon Flats, Alaska, are evaluated. Synthetic geophysical data are analyzed with a Bayesian Markov chain Monte Carlo algorithm that provides a probabilistic assessment of geophysical model uncertainty and resolution. Major lithological and permafrost features are well resolved in the examples considered. The subtle geometry of partial ice-saturation beneath lakes during talik formation cannot be resolved using AEM data, but the gross characteristics of sub-lake resistivity models reflect bulk changes in ice content and can be used to determine the presence of a talik. A final example compares AEM and ground-based electromagnetic responses for their ability to resolve shallow permafrost and thaw features in the upper 1-2 m below ground.
Environmental Research Letters
Lakes in boreal lowlands cycle carbon and supply an important source of freshwater for wildlife and migratory waterfowl. The abundance and distribution of these lakes are supported, in part, by permafrost distribution, which is subject to change. Relationships between permafrost thaw and lake dynamics remain poorly known in most boreal regions. Here, new airborne electromagnetic (AEM) data collected during June 2010 and February 2016 were used to constrain deep permafrost distribution. AEM data were coupled with Landsat-derived lake surface-area data from 1979 through 2011 to inform temporal lake behavior changes in the 35 500-km 2 Yukon Flats ecoregion of Alaska. Together, over 1500 km of AEM data, and roughly 30 years of Landsat data were used to explore processes that drive lake dynamics across a variety of permafrost thaw states not possible in studies conducted with satellite imagery or field measurements alone. Clustered time-series data identified lakes with similar temporal dynamics. Clusters possessed similarities in lake permanence (i.e. ephemeral versus perennial), subsurface permafrost distribution, and proximity to rivers and streams. Of the clustered lakes, ∼66% are inferred to have at least intermittent connectivity with other surfacewater features, ∼19% are inferred to have shallow subsurface connectivity to other surface water features that served as a low-pass filter for hydroclimatic fluctuations, and ∼15% appear to be isolated by surrounding permafrost (i.e. no connectivity). Integrated analysis of AEM and Landsat data reveals a progression from relatively synchronous lake dynamics among disconnected lakes in the most spatially continuous, thick permafrost to quite high spatiotemporal heterogeneity in lake behavior among variably-connected lakes in regions with notably less continuous permafrost. Variability can be explained by the preferential development of thawed permeable gravel pathways for lateral water redistribution in this area. The general spatial progression in permafrost thaw state and lake area behavior may be extended to the temporal dimension. However, extensive permafrost thaw, beyond what is currently observed, is expected to promote ubiquitous subsurface connectivity, eventually evolving to a state of increased lake synchronicity.
Airborne electromagnetic imaging of discontinuous permafrost
Geophysical Research Letters, 2012
1] The evolution of permafrost in cold regions is inextricably connected to hydrogeologic processes, climate, and ecosystems. Permafrost thawing has been linked to changes in wetland and lake areas, alteration of the groundwater contribution to streamflow, carbon release, and increased fire frequency. But detailed knowledge about the dynamic state of permafrost in relation to surface and groundwater systems remains an enigma. Here, we present the results of a pioneering 1,800line−kilometerairborneelectromagneticsurveythatshowssedimentsdepositedoverthepast1,800 line-kilometer airborne electromagnetic survey that shows sediments deposited over the past 1,800line−kilometerairborneelectromagneticsurveythatshowssedimentsdepositedoverthepast4 million years and the configuration of permafrost to depths of 100metersintheYukonFlatsareanearFortYukon,Alaska.TheYukonFlatsisneartheboundarybetweencontinuouspermafrosttothenorthanddiscontinuouspermafrosttothesouth,makingitanimportantlocationforexaminingpermafrostdynamics.Ourresultsnotonlyprovideadetailedsnapshotofthepresent−dayconfigurationofpermafrost,buttheyalsoexposepreviouslyunseendetailsaboutpotentialsurfacegroundwaterconnectionsandthethermallegacyofsurfacewaterfeaturesthathasbeenrecordedinthepermafrostoverthepast100 meters in the Yukon Flats area near Fort Yukon, Alaska. The Yukon Flats is near the boundary between continuous permafrost to the north and discontinuous permafrost to the south, making it an important location for examining permafrost dynamics. Our results not only provide a detailed snapshot of the present-day configuration of permafrost, but they also expose previously unseen details about potential surfacegroundwater connections and the thermal legacy of surface water features that has been recorded in the permafrost over the past 100metersintheYukonFlatsareanearFortYukon,Alaska.TheYukonFlatsisneartheboundarybetweencontinuouspermafrosttothenorthanddiscontinuouspermafrosttothesouth,makingitanimportantlocationforexaminingpermafrostdynamics.Ourresultsnotonlyprovideadetailedsnapshotofthepresent−dayconfigurationofpermafrost,buttheyalsoexposepreviouslyunseendetailsaboutpotentialsurfacegroundwaterconnectionsandthethermallegacyofsurfacewaterfeaturesthathasbeenrecordedinthepermafrostoverthepast1,000 years. This work will be a critical baseline for future permafrost studies aimed at exploring the connections between hydrogeologic, climatic, and ecological processes, and has significant implications for the stewardship of Arctic environments.
The time-domain electromagnetic (TDEM) method provides virtually the only surface geophysical technique suitable for interpreting deep permafrost conditions. This report describes profiles collected in early spring in a transitional area of the Mackenzie Delta, Arctic Canada, with differing permafrost conditions and surficial geology. These data augment previously published profiles and allow the construction of a 30 km-long TDEM transect from Holocene-age Mackenzie Delta in the southwest to Pleistocene-age Tuktoyaktuk Coastlands in the northeast.
The paper is dedicated to the topical problem of examining permafrost state and the processes of its geocryological changes by means of geophysical methods. To monitor the cryolithozone, we propose and scientifically substantiate a new technique of pulsed electromagnetic cross-well sounding. Based on the vector finite-element method, we created a mathematical model of the cross-well sounding process with a pulsed source in a three-dimensional spatially heterogeneous medium. A high-performance parallel computing algorithm was developed and verified. Through realistic geoelectric models of permafrost with a talik under a highway, constructed following the results of electrotomography field data interpretation, we numerically simulated the pulsed sounding on the computing resources of the Siberian Supercomputer Center of SB RAS. The simulation results suggest the proposed system of pulsed electromagnetic cross-well monitoring to be characterized by a high sensitivity to the presence an...
Frequency Domain Electromagnetic Soundings of Canadian Deep Permafrost
Geophysica
Frequency domain electromagnetic soundings were carried out at the Lupin gold mine and Ulu gold prospect in Northern Canada by the Geological Survey of Finland to investigate the lateral and vertical conditions of deep permafrost. The results indicate a deep seated electrical conductor in approximately half of the soundings. The detected conductor is interpreted as unfrozen and porous rock underneath the permafrost base saturated with saline groundwater. The mean depth of the permafrost base is 589 m and 476 m at the Lupin mine and Ulu prospect, respectively. The permafrost base, as deep as few hundreds of meters, can be detected using frequency domain electromagnetic soundings.
Geosciences
Subsea permafrost stability is the key to whether pre-performed methane sequestered in hydrate deposits escapes to the overlying strata. By making use of the 1D numerical modeling and field data, we analyze the capabilities of the time-domain (transient) electromagnetic method (TDEM) when being applied for subsea permafrost mapping, and study the effect of the background resistivity structure on the inversion models’ accuracy for a series of settings typical for the East Siberian Arctic Shelf—the broadest and shallowest shelf in the world ocean, which represents more than 70% of the subsea permafrost. The synthetic response analysis included the construction of a series of resistivity models corresponding to different settings (presence/absence of ice-bonded permafrost layer, different position of its top and bottom boundaries, different width and thickness of thawed bodies or taliks, variable seawater depth and its resistivity), and calculation of synthetic apparent resistivity res...
Permafrost and Periglacial Processes, 2013
Machine-learning regression tree models were used to extrapolate airborne electromagnetic resistivity data collected along flight lines in the Yukon Flats Ecoregion, central Alaska, for regional mapping of permafrost. This method of extrapolation (r = 0.86) used subsurface resistivity, Landsat Thematic Mapper (TM) at-sensor reflectance, thermal, TM-derived spectral indices, digital elevation models and other relevant spatial data to estimate near-surface (0-2.6-m depth) resistivity at 30-m resolution. A piecewise regression model (r = 0.82) and a presence/absence decision tree classification (accuracy of 87%) were used to estimate active-layer thickness (ALT) (< 101 cm) and the probability of near-surface (up to 123-cm depth) permafrost occurrence from field data, modelled near-surface (0-2.6 m) resistivity, and other relevant remote sensing and map data. At site scale, the predicted ALTs were similar to those previously observed for different vegetation types. At the landscape scale, the predicted ALTs tended to be thinner on higher-elevation loess deposits than on low-lying alluvial and sand sheet deposits of the Yukon Flats. The ALT and permafrost maps provide a baseline for future permafrost monitoring, serve as inputs for modelling hydrological and carbon cycles at local to regional scales, and offer insight into the ALT response to fire and thaw processes. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.
Advances in geophysical methods for permafrost investigations
Permafrost and Periglacial Processes, 2008
Geophysical techniques can be used to examine the spatial distribution of subsurface geophysical properties to delineate horizontally and vertically the active layer, permafrost and taliks. Spatial and temporal changes in subsurface geophysical properties due to permafrost cooling, warming, aggradation or degradation can also be assessed through geophysical monitoring. This paper reviews the geophysical methods most frequently applied in mountain and arctic/subarctic lowland permafrost investigations. Key results and recommendations based on the analysis of the applicability and reliability of different geophysical techniques for permafrost studies are summarised. Emphasis is put on the tomographic capabilities of geophysical methods. Recent advances in application and data interpretation are shown in relation to five case studies, and future perspectives are highlighted. Electrical resistivity and refraction seismic tomograms along a vegetated scree slope with isolated permafrost lenses at relatively low elevation in the Bever Valley, Switzerland.
2018
13 This paper presents the results of two-dimensional electrical resistivity tomography (ERT) of 14 permafrost developed in coastal zone of Hornsund, SW Spitsbergen. Using the ERT inversion results, 15 we studied the ‘sea influence’ on deeper parts of the frozen ground. The study builds on previous 16 ground temperature measurements conducted in several boreholes located in study area, which 17 captured the propagation of ground heat waves from the base of permafrost. Our resistivity models 18 indicate a major differentiation in terms of resistivity of permafrost in the coastal zone. The resistivity 19 measures obtained reveal exceptionally low resistivity in deepest layers of permafrost at the coast and 20 continuing further inland. We interpret this inversion as the result of seawater temperature and salinity 21 influences affecting the basal layers of permafrost. Based on repeat ERT surveys, two years apart, 22 we detect significant changes in the distribution of resistivity, wit...