C21A-0050
Cryogenic Structure of Perennially Frozen Lacustrine Sediments
The existing data on cryogenic structure of lacustrine sediments in various permafrost regions of Eurasia and North America show that these sediments can vary from ice-poor to extremely ice-rich. Complicated cryogenic structure of lacustrine sediments can indicate the conditions of freezing; its study helps to reconstruct the history of permafrost development. There are four mechanisms of lacustrine sediments freezing and formation of their cryogenic structure: 1) epigenetic; 2) syngenetic; 3) para-syngenetic; 4) quasi-syngenetic. Para-syngenetic type of freezing is the most widespread for the lacustrine sediments accumulating in the taliks surrounded by permafrost. The freezing of such sediments goes in various directions (from the surface, from the bottom, from the sides). The ice layers and lenses in para-syngenetic sediments are usually inclined, and the ice content is relatively small in the central parts of the lens-like geological bodies of lacustrine origin. Ice content increases towards top, bottom, and marginal parts of these geological bodies. Such distribution of the ice content is connected with water migration to the multidirectional fronts of freezing. Our study includes the data from several field sites located in Russia and Alaska. One of the most interesting sections was studied in the Kular mining region, Northern Yakutia, where the big lens of lacustrine silts, whose thickness reaches 18-20 m, was observed. This lens was enclosed in the ice-rich syngenetic Late Pleistocene "Yedoma" sediments containing huge ice wedges. The cryogenic structure of the most part of the observed geological body is typical for para-syngenetic sediments. Gravimetric moisture content of lacustrine silts varies in wide range: from 35% up to 130%. At the upper part of the section the ice lenses up to 10-15 cm thick were observed. Ice wedge pseudomorphs were found at the boundary between lacustrine sediments and underlying alluvial gravels. Para-syngenetic part of this section includes lens of syngenetically frozen lacustrine sediments with small ice wedges, which was presumably formed during the period of lowering of the water level in the lake.
C21A-0051
TSP NORWAY – Thermal Monitoring and Modelling of Permafrost in Northern Norway
The Norwegian funded IPY project ‘Permafrost Observatory Project: A Contribution to the Thermal State of Permafrost in Norway and Svalbard', (TSP NORWAY) is a part of the international IPY full project ‘Permafrost Observatory Project: A Contribution to the Thermal State of Permafrost (TSP)'. TSP will obtain a "snapshot" of the permafrost environments as a benchmark against which to assess past and future changes by making standardized temperature measurements in existing and new boreholes throughout the World's permafrost regions. The ultimate payoff is long-term and will serve as validation of current models and understanding of how permafrost conditions are reacting to climate change. Permafrost distribution in the north Atlantic area is strongly climatically controlled, mainly by the North Atlantic Drift, providing much less permafrost than in any other high latitude terrestrial region on the Northern Hemisphere. The extent of permafrost in the north Atlantic area is, however, not mapped, and it is therefore important to delaminate and assess the thermal state of permafrost. The main objective of TSP NORWAY is to measure and model the permafrost distribution in northern Norway and Svalbard, including its thermal state, thickness and influence on periglacial landscape-forming processes. The current knowledge on the extent and the thermal conditions of permafrost in northern Norway is scarce. Thawing of permafrost in Norway may lead to subsidence of the ground surface, having a substantial impact on e.g. infrastructure and on the stability of mountain slopes. Nine 7-31 m deep boreholes were drilled in bedrock in northern Norway in August and September 2007. In three of the boreholes, a measurement setup with 15-20 thermistors connected to dataloggers, with data recording every six hours, were installed. The other six boreholes were instrumented with miniature temperature dataloggers at selected depths. All boreholes were cased. Periodic recalibration of the installed thermistors is possible and the holes remain accessible for other probes in future. Furthermore, some deep boreholes (> 100 m) drilled for mining purposes were logged for gamma, temperature and electrical conductivity. In addition, a series of miniature temperature data loggers were installed for monitoring surface and air temperatures at selected sites. This presentation summarises first results of this activity and shows a first quantitative picture of permafrost distribution in northern Norway. http://www.tspnorway.com/
C21A-0052
Permafrost Observatory Project: A Contribution to the Thermal State of Permafrost in Norway and Svalbard, TSP NORWAY
The Norwegian funded IPY project ‘Permafrost Observatory Project: A Contribution to the Thermal State of Permafrost in Norway and Svalbard', (TSP NORWAY) is part of the TSP cluster. The main goal of TSP NORWAY is to measure and model the permafrost distribution in Norway and Svalbard, focussing on its thermal state, thickness and associated periglacial processes, including increased knowledge of the mountain permafrost distribution related to geohazard studies on rockslides. TSP NORWAY will contribute to IPY by providing a spatially distributed set of observations on the present status of permafrost temperatures and active layer thicknesses, and periglacial processes in Svalbard and Norway. Special focus is given to empirical and numerical modelling of permafrost distribution and thermal ground heat fluxes to address future climate variability on permafrost distribution and associated geomorphic activity. Permafrost distribution in the North Atlantic area is strongly climatically controlled, mainly by the North Atlantic Drift, providing much less permafrost than in any other high latitude terrestrial region on the Northern Hemisphere. Hopefully a first Nordic permafrost map will be based on Nordic permafrost collaboration during IPY. The TSP NORWAY project has established two permafrost observatories with intensive permafrost and periglacial monitoring sites in maritime and continental areas. One in Troms, northern Norway, which will be part of the north Scandinavian Permafrost Observatory extending into northernmost Sweden and Finland, and the Svalbard Nordenskiöld Land Permafrost Observatory also with both maritime and continental sites. The first Norwegian permafrost database, NORPERM, with all permafrost data from Norway and Svalbard, collected before and during IPY, has been established at the Norwegian Geological Survey. NORPERM shall contribute data as requested in the IPY data protocol and the TSP cluster to the international Global Terrestrial Network on Permafrost (GTN-P). During the first half year of the IPY we have carried out significant installations in both permafrost observatories. Four new 30 m boreholes located in the mountains of the Troms area have been drilled and instrumented. A borehole logging campaign of 5 existing boreholes have been carried out. Also remote sensing of large areas in the Troms observatory has been done, locating significant periglacial slope activity, which has been field verified. To study when permafrost has been present at lower latitudes in the Troms observatory, some sample for cosmogenic isotope dating has been collected from fossil rock glaciers. In Svalbard we have established a new solifluction monitoring station, a network of fix points for surveying rock glacier and solifluction movement in the Kapp Linne area and performed geophysical measurements do determine new borehole localities. Several new boreholes are planned in Svalbard to be drilled during the 2007-2008 winter, one in thin permafrost close to sea level in Kapp Linne. http://www.tspnorway.com
C21A-0053
Impacts of tundra fire on active layer condition and estimation of true resistivity value of soil in Seward Peninsula, Alaska
In Seward Peninsula, southwest Alaska, large tundra fires were occurred in 1997 and 2002, and a discontinuous permafrost area burned widely near the Kougarok River. After fires, a vegetation condition was destroyed and a ground surface thermal condition was changed. Then, field observations were conducted at burned and unburned sites in summer 2005, 2006 and 2007, in order to clarify impacts of the tundra fire on thermal and water conditions of active layer. From pit surveys, ground temperatures at burned sites showed 4-5 °C higher values than those at unburned sites. Soil water contents at burned sites showed relative high values in 2005, but low in 2006. Active layer thicknesses were significantly different between burned and unburned sites, about 60cm and 40cm, respectively. There is no significant increasing of the thickness between 2005 and 2006, however, the thickness in 2007 at north-facing sites increased to 80cm at the burned site and 50cm at the unburned site, respectively. Apparent electrical resistivity values up to 1m deep were obtained from electrical soundings in 2006, and values at burned sites were lower than those at unburned sites due to the thick active layer whose resistivity value is relatively low. As an apparent resistivity value is generally produced from the combination of a true resistivity value and a thickness of a layer, a simple calculation was carried out in order to estimate a true resistivity value of unfrozen mineral soil in the active layer. The calculated results showed that the true resistivity at burned sites was higher than that at unburned sites, which was seemed to correspond to a relative low water condition. This result is in agreement with the measured result of water content in 2006. Using this method, the apparent resistivity may show a soil water condition.
C21A-0054
The Permafrost Young Researchers Network (PYRN): Contribution to IPY's "Thermal State of Permafrost"
The Permafrost Young Researchers Network (PYRN, www.pyrn.org) is a unique resource for students, young scientists, and engineers studying permafrost. It is an international organization fostering innovative collaboration, seeking to recruit, retain, and promote future generations of permafrost scientists and engineers. Initiated for and during IPY, PYRN directs the multi-disciplinary talents of its membership toward global awareness, knowledge, and response to permafrost-related challenges in a changing climate. Created as an education and outreach component of the International Permafrost Association (IPA), PYRN is a central database of permafrost information and science for more than 350 young researchers from 33 countries. PYRN distributes a newsletter, recognizes outstanding permafrost research by its members through an annual awards program, organizes training workshops (2007 in Abisko, Sweden and St. Petersburg, Russia), and contributes to the growth and future of the permafrost community. While networking forms the basis of PYRN's activities, the organization also seeks to establish itself as a driver of permafrost research for the IPY and beyond. We recently launched a series of initiatives on several continents aimed at providing young scientists and engineers with the means to conduct ground temperature monitoring in under-investigated permafrost regions. Focusing on sites not currently covered by the IPA's "Thermal State of Permafrost" project, the young investigators of PYRN will provide and use lightweight drills and temperature sensors to instrument shallow boreholes in those regions. The data and results will be incorporated in the global database on permafrost temperatures and made freely available to the scientific community, thereby contributing to the advance of permafrost science and the strengthening of the next generation of permafrost researchers.
C21A-0055
Increased Active Layer Development Associated with Thermokarst Activity in Continuous Permafrost Region in the Brook Range foothills, Alaska
We documented the distribution of hill slope thermokarst features in tundra landscapes across the western Brooks Range of Alaska. Previously we observed that thermokarst features in the Noatak River basin were often associated with the presence of a zero-order stream (water track). During the 2007 field season, fourteen thermokarst features within the southwest Noatak River drainage in north western Alaska were characterized. The thermokarst features were located on a variety of lithologies, but mainly on non-carbonate sedimentary slopes. We measured the depth of thaw along multiple transects through each thermokarst feature and found thaw depth to be deeper by an average of 10 to 30 cm within features compared to the surrounding hill slopes. The relative deepening of the thaw was more pronounced further down slope within each thermokarst feature. This increased thaw beneath thermokarst features creates an exaggerated upper surface of the permafrost compared to the ground surface. This exaggeration is especially pronounced where up to three meters of material has been removed by erosion within thermokarst features, and could lead to increased geomorphic incision in these locations. The presence of a hill slope thermokarst feature is associated with a loss of vegetation, reduction in surface albedo, and potential for erosion of mineral soil. All of these affect hill slope's hydrologic function, likely leading to extension of stream networks and may contribute to the further deepening of the upper surface of the permafrost these areas.
C21A-0056
Ground Truth Observations of the Interior of a Rockglacier as Validation for Geophysical Monitoring Data Sets
Monitoring the permafrost evolution in mountain regions is currently one of the important tasks in cryospheric studies as little data on past and present changes of the ground thermal regime and its material properties are available. In addition to recently established borehole temperature monitoring networks, techniques to determine and monitor the ground ice content have to be developed. A reliable quantification of ground ice is especially important for modelling the thermal evolution of frozen ground and for assessing the hazard potential due to thawing permafrost induced slope instability. Near surface geophysical methods are increasingly applied to detect and monitor ground ice occurrences in permafrost areas. Commonly, characteristic values of electrical resistivity and seismic velocity are used as indicators for the presence of frozen material. However, validation of the correct interpretation of the geophysical parameters can only be obtained through boreholes, and only regarding vertical temperature profiles. Ground truth of the internal structure and the ice content is usually not available. In this contribution we will present a unique data set from a recently excavated rockglacier near Zermatt/Valais in the Swiss Alps, where an approximately 5 m deep trench was cut across the rockglacier body for the construction of a ski track. Longitudinal electrical resistivity tomography (ERT) and refraction seismic tomography profiles were conducted prior to the excavation, yielding data sets for cross validation of commonly applied geophysical interpretation approaches in the context of ground ice detection. A recently developed 4-phase model was applied to calculate ice-, air- and unfrozen water contents from the geophysical data sets, which were compared to the ground truth data from the excavated trench. The obtained data sets will be discussed in the context of currently established geophysical monitoring networks in permafrost areas. In addition to the unique validation opportunity for electric and seismic data sets on rockglaciers, photographs of several trenches through different rockglaciers along the construction site of the ski track provide images of the internal structure and material composition of the uppermost 5 to 8 m of the rockglaciers. By analysing these data it is hoped to gain new insights into geomorphic processes involved in the formation and kinematics of rockglaciers.
C21A-0057
Accuracy of precipitation measurements in the Arctic, Barrow, Alaska
To improve the accuracy of precipitation measurements in the Arctic, the daily solid precipitation in Barrow, Alaska, was measured using a Double Fence Intercomparison Reference (DFIR) as the WMO reference standard for solid precipitation measurements. Further, a new approach using a snow particle counter (SPC) that outputs the number flux of snow particles without directly catching them is introduced. The correction procedures for wind, wetting losses, and trace amounts are applied on a daily basis to the DFIR precipitation. Using the precipitable water vapor estimates obtained from GPS observations (RINEX data) and NCEP/NCAR reanalysis data (NOAA- CIRES CDC), a precipitation pattern was investigated. On the whole, the corrected DFIR precipitation was 1.32 times the non-corrected one. The SPC-estimated precipitation exhibited a better performance than the corrected DFIR one. Gauges using an optical sensor may be effective in low precipitation areas such as the polar regions. The daily mean diameter of snow particles ranging from 0.05 to 0.5 mm with an average of 0.16 mm was smaller than that in the mid-latitudes. The particle diameter distribution was not sufficiently shaped compared to that without snowfall. In particular, relatively small snow particles were blown during mid-winter due to a cold polar air mass and lack of water vapor.
C21A-0058
Snow Cover Mapping at the Continental to Global Scale Using Combined Visible and Passive Microwave Satellite Data
Over the past several decades both visible and passive microwave satellite data have been utilized for snow mapping at the continental to global scale. Snow mapping using visible data has been based primarily on the magnitude of the surface reflectance, and in more recent cases on specific spectral signatures, while microwave data can be used to identify snow cover because the microwave energy emitted by the underlying soil is scattered by the snow grains resulting in a sharp decrease in brightness temperature and a characteristic negative spectral gradient. Both passive microwave and visible data sets indicate a similar pattern of inter-annual variability, although the maximum snow extents derived from the microwave data are consistently less than those provided by the visible satellite data and the visible data typically show higher monthly variability. We describe the respective problems as well as the advantages and disadvantages of these two types of satellite data for snow cover mapping and demonstrate how a multi-sensor approach is optimal. For the period 1978 to present we combine data from the NOAA weekly snow charts with snow cover derived from the SMMR and SSM/I brightness temperature data. For the period since 2002 we blend NASA EOS MODIS and AMSR-E data sets. Our current product incorporates MODIS data from the Climate Modelers Grid (CMG) at approximately 5 km (0.05 deg.) with microwave-derived snow water equivalent (SWE) at 25 km, resulting in a blended product that includes percent snow cover in the larger grid cell whenever the microwave SWE signal is absent. Validation of AMSR-E at the brightness temperature level is provided through the comparison with data from the well-calibrated heritage SSM/I sensor over large homogeneous snow-covered surfaces (e.g. Dome C region, Antarctica). We also describe how the application of the higher frequency microwave channels (85 and 89 GHz)enhances accurate mapping of shallow and intermittent snow cover. http://nsidc.org
C21A-0059
Recent Advances in Low-Power, Low-Cost, Real Time, Global, Sensor Communication: Using New Irdium's Data Capabilities
Recent advances in low-power communications using the new Iridium data capabilities now available (SBD, SMS) has allowed the development of systems that can stream transmit data (and receive commands) reliably in real time from very remote locations. This has allowed the development of sites or systems where one can put up instruments (cameras, gps, weather monitors, etc.) to collect data and not need to return to the site for data download. This has then expanded the possibilities where sites can be located by either removing the logistical costs of returning or being able to put sites where it would be too dangerous to return (tip of surging glaciers, crevasse locations, moulins, volcanoes, etc.). http://eis.jpl.nasa.gov/~behar
C21A-0060
Ground ice formed after underground thermo-erosion of the permafrost in Alaska
Cryostratigraphic studies realized in the CRREL permafrost tunnel (ˇÖ 64 57 N, 147 37 W) located near Fairbanks, Alaska revealed the presence of multi-directional reticulate ice veins and massive ice bodies in the permafrost. We propose that this reticulate-chaotic cryostructure and the massive ice bodies were formed by inward closed-system freezing of pools of water and saturated sediments trapped in underground tunnels cut in the permafrost by thermo-erosion. The massive ice and the multi-directional reticulate ice veins were likely formed after the cessation of the underground flow, either by tunnel blockage or collapse, or cessation of runoff infiltration in the permafrost. The observed tunnels were slightly inclined and could often be traced for several meters. The properties of the sediments filling these tunnels differed from the enclosing original syngenetic Pleistocene permafrost. The latter was made of ice-rich loess with abundant rootlets and was characterized by a well developed micro-lenticular cryostructure whereas the tunnels were filled with massive ice and/or organic- poor, stratified silts, sands and gravels sediments. The water content of the original syngenetic loess was about twice the water content of the sediments in the underground tunnels. The contact between the original syngenetic loess and the sediments in the tunnels was manifestly discordant and outlined by erosion lag. Release of latent heat from the poll of water and water of the saturated sediments created thaw unconformities at the tunnel boundary. Similar types of massive ice and reticulate-chaotic cryostructures were observed in Holocene to Pleistocene permafrost exposures along the Beaufort Sea Coast, on the Seward Peninsula, on the North Slope and in the Alaskan interior. The massive ice bodies and reticulate-chaotic cryostructures were always associated with, or incorporated within, ice wedges that showed signs of thermo-erosion. This indicates that the process of underground thermo-erosion has occurred widely in Alaska. On Bylot Island in the Canadian Arctic archipelago, Fortier et al. (2007) observed that extensive gullying of the permafrost resulted from the process of underground thermo-erosion. More studies are needed to determine the role of this process in the evolution of ice-wedge polygons landscape in Alaska. Fortier, D., Allard, M., Shur, Y. 2007. Observation of rapid drainage system development by thermal erosion of ice wedges on Bylot Island, Canadian Arctic Archipelago. Permafrost and Periglacial Processes 18 (3): 229-243.
C21A-0061
Soil Temperatures Under a Range of Organic and Snow Covers
Snow can insulate the soil from cold winter air temperatures. The timing of first snow fall, its thickness during the coldest months of the winter and the structure of the snowpack are important factors in determining the soil temperature drop over the winter. Although snow cover is often assesed late in the season, prior to melt, daily observations yield a basis for analyzing the effect of snowfall timing on soil temperature. Multiyear records are required to compare the effect of snowpack thickness. We present snow depths and soil temperature observation records up to 9 years in length and include sites on the North Slope of Alaska, at Ny Alesund, Spitsbergen and on Samoylov Island in the Lena Delta, Siberia. Vertical arrays of sensors were installed in and below the seasonally thawing layer of soil, from near the ground surface into the upper permafrost. Snow depth was measured using either a snow probe, snow pit excavation or an automatically logged ultrasonic snow depth sensor. The observations cover a wide range of snow depths and soil temperatures: maximum annual snow depth at all sites ranged from less than 0.2 m to over 1.5 m in depth; the earliest soil freezing following snow fall (below 0.1 m) began on August 30 and some soil horizons unremained unfrozen until mid-December. The effect of an intermediate snow cover, under normal winter conditions, can be to delay freeze-back by at least 1 month at most depths. The combined effects of the exposed frost boil mineral soil, shallow snow depth and cold winter temperatures lead to extremely cold soil temperatures in the soil.
C21A-0062
Micrometeorological conditions under different soil frost depths
Eastern Hokkaido, where is one of the largest agricultural production regions in Japan, is characterized by low air temperature and relatively thin snow covers resulting in soil frost over the winter. However, the soil frost depth has been significantly decreasing since late 1980's due to an insulation from the cold air by a thick snow cover developing in early winter. In the current study, soil water movement, soil temperature, and surface heat balance under different soil frost conditions were monitored to obtain a knowledge of changes in micrometeorological condition of the agricultural production systems in the Eastern Hokkaido associated with the decreasing soil frost depth in the region. A paired soil plot experiment was conducted from Nov. 2005 to May 2006, where the frost depth was artificially enhanced by removing snow for 24 days in the retreatment plot and the natural condition was maintained in the control plot. The soil in the experimental field was classified as Andisol with much porosity and high drainability. In each plot, water content and soil temperature were measured by TDR and thermocouple, respectively. The maximum soil-frost depth in the treatment and control plots resulted in 43.8 and 13.6\.cm, respectively. Changes in snow water equivalent volume SWE) and snow depth were manually recorded. The difference of SWE just before melting snow was same. The day of snow disappearing was 18th April 2006 for both plots. The control plot with a thin frozen layer allowed infiltration of snow melt water, and water content at the lower subsoil increased accordance in snowmelting, whereas a thick frozen layer in the treatment plot impeded the infiltration resulting in waterlogging being observed on the soil surface. These differences in profile of water content and in developing soil frost depth results in more delay in increasing soil temperature at the deeper depth. At the surface, however, the difference in soil temperature was quickly disappeared, and the differences in elements of heat balance in each plot were small. Consequently, the result suggests that the recent decreasing soil frost depth in the Eastern Hokkaido changes hydraulic and thermal soil conditions extensively below the surface, but has no feedback effect to the atmosphere after snow disappearing.
C21A-0063
Spatial and Temporal Variation of Soil Temperatures and Snow Cover in the Kuparuk River Basin, Alaska
A series of environmental studies have been carried out in the northern foothills of the Brooks Range and the Arctic Coastal Plain in the Kuparuk River Basin, Alaska to develop a better understanding of the physical and climatic dynamics of an arctic ecosystem. As part of these studies, soil temperature and snow depth measurements along a transect from near the Beaufort Sea coast across the coastal plain to the Brooks Range foothills were made continuously at eight locations. Summarized here are trends observed in soil temperature spanning the last 21 years in this area. Soil temperatures measurements were made in the active layer and permafrost to depths exceeding 10 meters. Data collection began at three of these sites in 1986, with other sites being added until 1994. These data sets are of sufficient length to begin showing long-term trends in arctic soil temperature and the relationship between snow depth and winter soil temperature. All locations show a trend to warming soils over the period, especially in the deeper permafrost soils. Soil temperatures at all sites indicate warming of the permafrost. Summertime soil temperatures within the active layer do not indicate warmer soils.
C21A-0064
Measurements of Turbulent Fluxes over Sea Ice Region in the Sea of Okhotsk.
The measurements of turbulent fluxes over sea ice area were done in the southern part of the Sea of Okhotsk, during the cruises of the ice-breaker P/V 'Soya' in 2000-2005. The air-ice drag coefficients CDN were 3.57×10-3 over small floes \left(diameter:φ=20- 100m\right), 3.38×10-3 over medium floes \left(φ=100-500m\right), and 2.12×10-3 over big floes \left( φ=500m-2km\right), which showed a decrease with the increase of floe size. This is because the smaller floes contribue to the roughness of sea-ice area by their edges more than the larger ones. The average CDN values showed a gradual upslope with ice concentration, which is simply due to the rougher surface of sea ice than that of open water, while they showed a slight decline at ice concentration 100%, which is possibly due to the lack of freeboard effect of lateral side of floes. We also compared the relation between the roughness length zM and the friction velocity u* with the model developed in the previous study. The zM-u* relation well corresponded with the model results, while the range of zM we obtained was larger than those obtained at the Ice Station Weddell and during the Surface Heat Budget of the Arctic Ocean project. The sensible heat transfer coefficients CHN were 1.35×10-3 at 80-90% ice concentration, and 0.95×10-3 at 100% ice concentration, which are comparable with the results of the past reaserches. On the other hand, we obtained a maximum CHN value of 2.39×10-3at 20-50% ice concentration, and 2.35×10-3 over open water, which are more than twice as the typical value of 1.0×10-3 over open water. These large CHN values are due to the significant upward sensible heat flux during the measurements.
C21A-0065
Temperate Ice Depth Sounding Radar (TIDSoR)
Glaciers in several parts of the world are reported to be retreating and thinning rapidly over the last few years. A key variable in the study of glacier dynamics is ice thickness. A few attempts have been made to develop airborne sounding radars for temperate-ice thickness measurements [Arcone et al., 2000]. There is an urgent need for compact radar for routine ice thickness measurements from ground-based and airborne platforms. Radars (Radio Detection and Ranging) have been widely used to measure ice thickness in Greenland and Antarctica. However, the radars used in these areas operate in the VHF and UHF part of the electromagnetic spectrum. Due to the composition of temperate ice, the attenuation and back-scatter from large pockets of water makes UHF and VHF ineffective in sounding of its thickness. Radars operating in lower part of the HF spectrum are required for sounding temperate ice. We are designing and developing a Temperate Ice Depth-Sounding Radar (TIDSoR) that can penetrate through the water pockets and provide a more accurate measurement of the ice thickness. TIDSoR is a light-weight system for ground-based operations in mountainous terrain or aerial surveys in which weight is an important factor, such as in an UAV. TIDSoR operates on two channels in the HF spectrum using two-linear, frequency-modulated chirp waveforms. The two chirp frequency ranges are 7 to 8 MHz and 13.5 to 14.5 MHz. The radar will operate from a 12-V battery and is designed to weigh less than 2 kg, excluding the battery. The radar consists of three main sections: Digital, RF and antenna. The digital-section generates the transmitter waveforms, timing and control signals, and digitizes processes and stores the received signal. The RF-section consists of a transmitter with a 20-W peak-power amplifier, band-pass filters, and a switching system for a shared antenna. The receiver consists of a blanking switch, a limiter, a low-noise amplifier, a band-pass filter and a data acquisition system to store the acquired data. At HF, a physically large-antenna is needed. TIDSoR takes advantage of the helix antenna concept to minimize its physical dimensions and weight. Moreover, the ability to achieve different polarizations (linear, circular and elliptical) was considered to maximize the performance of the radar system. Arcone, S. A., Lawson, D. E., Moran, M. and Delaney, A. J., 2000, 12-100-MHz profiles of ice depth and stratigraphy of three temperate glaciers. In: Proc. GPR 2000, Eighth Intl. Conf. Ground-Penetrating Radar, Gold Coast, Austral., 23-26 May, 2000.
C21A-0066
Compositional Change of Meltwater Infiltrating Frozen Ground
Frozen ground underneath a melting snowpack may constrain infiltration and meltwater reaching the base of the snowpack will either infiltrate the underlying stratum, runoff, or refreeze, forming a basal ice layer. Compositional changes in chemistry will take place for each of these flow paths as a result of contact between meltwater and soil and mixing between meltwater and soil water. It is assumed that chemical alteration takes place soon after contact with a soil layer occurs. Three major flow paths were hypothesized distinguishable based on alterations in ion concentrations: overland flow, organic interflow, and mineral interflow. Laboratory experiments were carried out to identify compositional changes in meltwater, which had sustained contact with a basal ice layer, a forest organic layer, or a forest mineral soil layer. The experimental setup consisted of melting a snowpack in a large insulated box in a temperature-controlled environment. A cooling system at the chemically inert base ensured frozen substrate conditions during snowmelt. Throughout melt, samples of meltwater were collected from within the snowpack using an extraction tube; runoff or interflow samples were collected from the surface or soil along the base of the box. All samples were filtered and analyzed for major anions and cations. Runoff and interflow concentrations were normalized using meltwater concentrations. Results showed an overall enrichment in ion concentrations for overland flow that had sustained contact with a basal ice layer. Organic interflow showed significant increases in H+ and K+ and depletion in Mg2+. Mineral interflow showed an increase in Ca2+ and slight decrease in H+. Repeated flushes of meltwater through each interflow path caused a washout of ions. Similarly, ion concentrations were generally highest the first time meltwater was in contact with the soil. Generally, changes in ion concentrations were most significant for H+, K+, Mg2+, and Ca2+.
C21A-0067
How lake morphometry reflects environmental conditions in the permafrost-dominated Lena Delta
Numerous lakes characterize the landscape of the northeast Siberian Lena Delta, which is situated in the zone of continuous permafrost. We provide a detailed lake inventory of this largest Arctic delta. The inventory is based on Landsat-7 ETM+ image data and spatial analysis in ArcGIS. Several morphometric lake attributes were determined from the resulting data set and statistically analysed regarding the lakes' association with one of the three geomorphological main units of the Lena delta. Significant differences in the morphometric lake characteristics allowed the distinction of a mean lake type for each main unit. The lake types reflect the special lithological and cryolithological conditions and geomorphologic processes prevailing on each terrace. The first main unit, which represents the modern active delta, is characterized by small lakes of irregular shape, like meander scrolls and oxbow lakes. Large oriented lakes dominate on the second terrace that consists of Late Pleistocene to Early Holocene sands. On the third terrace, which is represented by relics of a Late Pleistocene accumulation plain with fine-grained and ice-rich deposits, typical thermokarst lakes with regular, circular shorelines prevail. Most studied lakes are thermokarst lakes by their nature, as they have been or still are expanding by thermoabrasion of shore banks and deepening of the lake basin. However, a distinction between primary and secondary thermokarst lakes can be made. Primary lakes are those initially formed by thaw subsidence, i.e. the third terrace lakes. Secondary thermokarst lakes are typically formed by other processes, e.g. the change of the fluvial channel network on the first terrace. The role of lakes on the second terrace is still debated. They appear to be typical thermokarst lakes by morphometry, but their primary initiation might have been related to inter-dune or old fluvial water bodies.
C21A-0068
Topoclimatic Influences on Active-Layer Development in Northern Alaska
Although many recent studies of active layer development address spatial variations in soil thermal properties and moisture conditions, few have attempted to isolate topoclimatic influences over thaw depth. The n-factor, the ratio of ground surface to air degree-day sums, is widely used in conjunction with analytic solutions for thaw depth in geotechnical work. In an analogous manner, the ratio of potential radiation received on a slope to that incident on a horizontal surface at the same latitude can be incorporated into formulations such as the Berggren or Stefan equations. Observed patterns of thaw depth on various facets of an anthropogenic thermokarst landform near Prudhoe Bay, Alaska show systematic variation with slope aspect. Use of the "r-factor" with the Berggren solution accurately reproduces these patterns, demonstrating the importance of differential radiation loading, even in high-latitude regions.