In the laboratory and using geophysical well logs in the field, gas hydrate saturation S h is often determined by two petrophysical measurements: compressional-wave velocity V p measurements and electrical resistivity or its inverse, conductivity. Almost twenty years ago, Dvorkin established four models for linking S h to V p. Each model assumed gas hydrate was homogeneously distributed in one of four idealized morphologies, and choosing the proper model required knowing which morphology was present.
Research has increasingly pointed gas hydrate existing as a separate, connected phase in the pores when formed from dissolved-phase methane. This formation process is the most common in marine environments, and the resulting trend of V p with S h follows the predictions of the 'load-bearing' model. Moreover, we show recent work that indicates ice can be an accurate 'load-bearing' hydrate analog for V p measurements to determine gas hydrate saturation, significantly lowering the time required for laboratory studies and eliminating the need for high pore pressures. Electrical resistivity measurements of gas hydrate and ice-bearing sediments, however, do not yield the same results in the field as they do in the laboratory, suggesting ice is probably not a reasonable analog for gas hydrate in this case.
Here, we discuss possible reasons for differences between resistivity measured using downhole logging tools and resistivity measured in the laboratory. Furthermore, we share a newly-developed field-based technique that uses a combination of V p and electrical resistivity to solve for a crucial petrophysical parameter, Archie's saturation exponent commonly referred to as n.
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Exploring the interactions between thermal hydrology, soil structure, and dynamic topography in warming polygonal tundra [abstr. Observations of warming Arctic polygonal tundra suggest significant changes in hydrology and geomorphology at multiple scales. The magnitude and pattern of these changes are fundamentally affected by ground ice and thermal and hydrologic properties of the landscape, potentially affecting both the water and energy balances.
Answering seemingly simple questions like, "will a warmer Arctic be wetter or dryer than current conditions? Such basic understanding is critical to predict the fate of carbon stored in thawing soils, infrastructure stability, and water fowl habitat. In coastal regions like Barrow, Alaska, systematic geomorphic change has been observed, including both subsidence across scales of ss of meters and local polygon degradation at scales of 1ss of meters. As soils warm, ground ice thaws and soils subside and compact.
The active layer gains new soil, but porosity decreases, changing where and how much water is stored in the soil column. As polygons degrade, poorly connected low centers that store significant snowmelt become well-connected high centers, resulting in significant increase in runoff and less potential for infiltration. The tradeoffs between these and other considerations are difficult to understand. We present a mechanistic model coupling permafrost thermal hydrology to a simple soil subsidence representation based upon grain consolidation.
This model is parameterized by data derived from entire cross-polygon profiles 3m deep at Barrow reconstructed from analyses of soil horizons sampled via trenching and coring. A multi-decade regional subsidence record at Barrow is used to evaluate one-dimensional, regional subsidence simulations, and year projections are explored. Finally, a first-of-a-kind, multiscale model integrates these columns through a dynamic parameterization capturing the impacts of polygon degradation on lateral flow.
Predictions are made of how these processes interact to determine the fate of polygonal tundra under a warming climate. Trends in bedfast lake ice extent on the Arctic Coastal Plain of Alaska [abstr. Arctic landscapes are susceptible to stronger and earlier impacts from climate change than are the mid-latitudes. Thermokarst lakes are abundant landforms and ecosystems throughout the Arctic Coastal Plain of Alaska that play an important role in hydrology, ecology, and biogeochemical cycling.
Whether lake ice freezes to the lake bottom or not is an important environmental parameter that has garnered extensive study. Changes in lake ice extent and depth through time have important implications for regional hydrology as well as potential sub-lake permafrost thaw and associated changes in the permafrost-carbon system. Previous studies have addressed the question of ordinal lake ice classification change through time bedfast, floating, transitional, intermittent , but due to high levels of interannual variability in the short time window of data availability, have found no significant trends in lake ice regime in some areas.
Lake depth and ice thickness are the determining factors for ice regime. Shallow lakes that are always bedfast do not respond to thinning lake ice; however, lakes and portions of lakes that are between meters deep will show a response to ice that is thinning. Simple linear regression analysis revealed statistically significant slopes and good model performance in the vulnerable sub-population of lakes that are mostly floating ice. The results of this study elucidates the smaller scale changes occurring in the areal bedfast ice extents that could be indicative of future larger-scale changes.
Constraining ages of glacial deposits recorded in a Victoria Valley permafrost core [abstr. Here, a meter ice-cemented permafrost core collected in Victoria Valley is analyzed using cosmogenic nuclides to provide quantitative constraints on the timing of the EAIS glacial history in the Dry Valleys. Based on the presence of oxidized layers from apparent paleosols, the core appears to have recorded four depositional events that are believed to represent different periods of glaciation. Each depositional unit was deposited and exposed to cosmic rays at the surface until subsequently buried during the next glacial event that then shielded the sediment from further cosmic ray exposure.
Sediment was subsampled in the core at the upper, middle, and lower limits of each depositional unit and analyzed for 10 Be and 26 Al, as well as texture, soluble salts, and other parameters. Several possible models of the burial history, accounting for exposure time, burial time, and inherited nuclides, are tested using inverse modeling techniques to provide a timeline for EAIS history in Victoria Valley. Modeling surface water and soil freezing processes using WaSiM [abstr.
Hydro-thermal soil processes drive surface and permafrost temperatures in northern regions.
We are developing WaSiM to be a state of the art permafrost hydrology model that can simulate the thermal regime of permafrost in addition to the hydrological response of the landscape to variably frozen conditions. WaSiM is a capable hydrological model for the simulation of dynamic glaciers, snow and permafrost. We are currently interested in developing better surface hydrology interaction with thermal processes.
Especially in ice wedge degradation regions the presence of surface water ponds can significantly change the thermal behavior of the ground.
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In this study we show strong delay, due to latent heat release from surface ponding, on the freezing of the active layer in the fall. WaSiM has a surface routing module that we use to simulate standing water on the frozen tundra in the summer. We take that amount of standing water that is in equilibrium with other hydrological fluxes and use it to simulate freezing ponds. Rather than simulating the surface processes separately we choose to include the standing water column in the soil column in order to simulate the freezing process of the standing water integrated with the freezing of the underlying active layer.
We show that including the process of freezing surface water in the thermal regime of a high resolution simulation of an ice-wedge polygon landscape in Barrow Alaska, improves soil temperatures significantly especially during fall when surface water in these ponds freezes. Development and use of a distributed temperature profiling DTP system to estimate arctic soil thermohydrology and depth to permafrost, and their relationships with geomorphological and vegetation properties [abstr.
A substantial improvement in our ability to quantify and monitor soil and permafrost thermohydrology is important for improving our prediction of Arctic ecosystem feedbacks to climate under warming temperatures. In particular, understanding the relationships between soil thermal and hydrological behaviors, soil physical properties incl. However, obtaining such information is extremely challenging using conventional measurement approaches. The DTP system has been developed with an extraordinarily low production and assembly cost; uses automated data acquisition, management and transfer; and leverages open source software and hardware to encourage community-based development and deployment.
Here, we describe the new DTP system and its joint use with electrical resistivity tomography ERT datasets, soil sample analysis, soil moisture data, and UAV-inferred vegetation indexes, digital surface elevation models and snow thickness to investigate the characteristics of and controls on permafrost processes in a watershed on the Alaskan Seward Peninsula.
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Together, the various datasets allowed us to distinguish shallow permafrost from deep permafrost with an overlying perennially thawed layer i. Understanding controls on Arctic soil moisture using in-situ soil moisture and thaw depth observations and airborne SAR data at Barrow and Seward Peninsulas, Alaska [abstr. By co-analyzing in-situ and remote sensing data at multiple sites, we aim to extend local observations to regional scales. In particular, we examine how local geomorphology, topography, climate and vegetation properties interact with thaw depth and soil moisture across a range of field sites and settings near Utqiagvik, AK and Nome, AK.
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In Utqiagvik, in-situ data were collected at high-center, flat-center, and low-center polygons during the June SAR P-band and September L-band overflights. At all sites on the Seward Peninsula, in-situ data were collected in May and August, coincident with P-band overflights. At each field site the same measurement techniques were used including the establishment of multiple m by m plots designated for SAR ground-truthing.
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Within each "SAR plot" two 60 meter transects were established along which both soil moisture and thaw depth measurements were taken. This configuration is consistent with the ABoVE protocols which enables proper averaging of multiple pixels for airborne or spaceborne SAR data. Moisture data was collected using a Hydrosense-II soil-water sensor and data logger which relies on the dielectric properties of the soil to estimate volumetric moisture content VMC. Soil moisture and thaw depth are key factors controlling subsurface biogeochemistry and surface ecosystem type and function.
Our observations and analysis provides a unique benchmark dataset with which to test predictions of spatial variation and temporal evolution of soil moisture in local and regional permafrost models. Dataset DOI Modeling the response of permafrost affected mesoscale watersheds to long term warming [abstr.
Recently observed increase in the Arctic river runoff and subannual reshaping of the hydrographs demand an explanation of processes responsible for these changes. Theoretical models of heat and water dynamics in the ground material suggest a non-linear response of permafrost to increase in air temperature.