charcoal records from thermokarst deposits in central yakutia eastern siberia implications for forest fire history and thermokarst development abstract macroscopic charcoal records from a thermokarst lake deposit in central yakutia eastern siberia were used to reconstruct the history of forest fires and investigate its relationship to thermokarst initiation high accumulation rates of charcoal and pollen were coincident in the basal deposits of the thermokarst lake which suggests that both were initially deposited on the forest floor and subsequently reworked and accumulated in the thermokarst depression high charcoal and pollen accumulation rates in the basal deposits dating to 11 000 9000 cal yr bp also indicate that the thermokarst topography developed during the early holocene a lower charcoal accumulation rate after ca 9000 cal yr bp suggests that thermokarst development has been inhibited since this time it also indicates that a surface fire regime has been predominant at least since ca 9000 cal yr bp in central yakutia

influence of water density on the water retention curve of expansive clays there is increasing evidence from researchers on clay mineralogy that the density of water attached to clay minerals may be greater than 1 0 mg m3 this fact becomes especially evident in compacted highly expansive clays close to water saturation this kind of material is being considered in the design of engineered barriers for radioactive waste disposal because of its sealing and retention properties from a geotechnical point of view most of the analyses required to check the performance of the barrier are sensitive to the value considered for the water density this is the case for the unsaturated flow calculations which depend on the water retention properties of the soil this paper presents first a review of measurements performed at microscopic level a description of the hydration process of expansive clay considering the micro and macrostructure is included then a method to obtain an average water density as a function of suction for sodium and calcium bentonites is proposed the method is

postglacial flooding and vegetation history on the ob river terrace central western siberia based on the palaeoecological record from lake svetlenkoye the hemispheric scale climatic fluctuations during the holocene have probably influenced the large siberian rivers however detailed studies of the west siberian plain postglacial environmental ch

contrasting patterns of early twenty first century glacier mass change in the himalayas glaciers are among the best terrestrial climate indicators an important water resource in mountains1 2 and a major contributor to global sea level rise3 4 in the hindu kush karakoram himalaya region hkkh a paucity of appropriate glacier data has prevented a comprehensive assessment of current regional mass balance5 however there are indirect evidences of a complex pattern of glacial responses5 8 in reaction to heterogeneous climate change signals9 here we provide the first coherent data set of detailed glacier thickness changes over the hkkh during 2003 2009 by combining satellite laser altimetry and a global elevation model in the eastern central and south western parts of the hkkh glacier wastage is widespread with regional thinning rates up to 0 66 0 09 m a 1 in the jammu kashmir region conversely in the karakoram glaciers are close to balance with only a slight thinning of 0 07 0 04 m a 1 regionally averaged thinning rates under debris mantled ice are similar to those of clean ice despite insulation by debris covers the 2003 2008 specific mass balance for our hkkh study region is 0 21 0 05 m a 1 water equivalent we significantly less negative than the global average of 0 7 m a 1 we for glaciers and ice caps4 10 this difference is mainly an effect of the balanced glacier mass budget in the karakoram the corresponding hkkh sea level contribution is 0 035 0 009 mm a 1 amounting to 1 of the present day sea level rise11 our 2003 2008 mass budget of 12 8 3 5 gt a 1 is more negative than recent satellite gravimetry based estimates of 5 6 gt a 1 over 2003 2010 ref 12 for the mountain catchments of the indus and ganges basins13 the glacier imbalance contributes 3 5 and 2 0 respectively to the annual average river discharge13 and up to 10 for the upper indus basin14

late quaternary vegetation and lake system dynamics in north eastern siberia implications for seasonal climate variability although the climate development over the holocene in the northern hemisphere is well known palaeolimnological climate reconstructions reveal spatiotemporal variability in northern eurasia here we present a multi proxy study from north eastern siberia combining sediment geochemistry and diatom and pollen data from lake sediment cores covering the last 38 000 cal years our results show major changes in pyrite content and fragilarioid diatom species distributions indicating prolonged seasonal lake ice cover between 13 500 and 8900 cal years bp and possibly during the 8200 cal years bp cold event a pollen based climate reconstruction generated a mean july temperature of 17 8 c during the holocene thermal maximum htm between 8900 and 4500 cal years bp naviculoid diatoms appear in the late holocene indicating a shortening of the seasonal ice cover that continues today our results reveal a strong correlation between the applied terrestrial and aquatic indicators and natural seasonal climate dynamics in the holocene planktonic diatoms show a strong response to changes in the lake ecosystem due to recent climate warming in the anthropocene we assess other palaeolimnological studies to infer the spatiotemporal pattern of the htm and affirm that the timing of its onset a difference of up to 3000 years from north to south can be well explained by climatic teleconnections the westerlies brought cold air to this part of siberia until the laurentide ice sheet vanished 7000 years ago the apparent delayed ending of the htm in the central siberian record can be ascribed to the exceedance of ecological thresholds trailing behind increases in winter temperatures and decreases in contrast in insolation between seasons during the mid to late holocene as well as lacking differentiation between summer and winter trends in paleolimnological reconstructions

satellite radar interferometry for monitoring ice sheet motion application to an antarctic ice stream satellite radar interferometry sri provides a sensitive means of monitoring the flow velocities and grounding line positions of ice streams which are indicators of response of the ice sheets to climatic change or internal instability the detection limit is about 1 5 millimeters for vertical motions and about 4 millimeters for horizontal motions in the radar beam direction the grounding line detected by tidal motions where the ice goes afloat can be mapped at a resolution of 0 5 kilometer the sri velocities and grounding line of the rutford ice stream antarctica agree fairly well with earlier ground based data the combined use of sri and other satellite methods is expected to provide data that will enhance the understanding of ice stream mechanics and help make possible the prediction of ice sheet behavior

holocene land cover changes on the tibetan plateau information on changes in land surface features on the tibetan plateau tp during the holocene may help our understanding of the forcing of monsoonal circulation we analyse vegetation changes during the last 9000 years from pollen records of four lakes hurleg lake in the qaidam basin qinghai lake on the northeastern tp zigetang lake on the central tp and koucha lake on the eastern tp which represent different regions and vegetation types on the plateau today a set of modern pollen assemblages from 111 lake sediment samples originating from different vegetation types is used for the interpretation of the holocene pollen records four types of numerical analyses are used to infer different aspects of pollen stratigraphical and inferred vegetation changes biome reconstruction ordination to infer palynological compositional turnover rate of assemblage change analysis and a pollen lai leaf area index transfer function our results show strong regional differences in inferred vegetation change in

flow of glaciar moreno argentina from repeat pass shuttle imaging radar images comparison of the phase correlation method with radar interferometry high resolution radar images of glaciar moreno argentina acquired by the shuttle imaging radar c sir c on 9 and 10 october 1994 at 24 cm wavelength l band are utilized to map the glacier velocity both interferometrically and using the phase correlation method the precision of the interferometric ice velocities is 1 8 cm d 1 6 m a 1 1 the phase correlation method measures ice velocity with a precision of 14 cm d 1 50 m a 1 with image data at a 6 m sample spacing acquired 1 day apart averaged strain rates are measured with a precision of 10 4 d 1 at a 240 m sample spacing with the phase correlation method and 10 5 d 1 with radar interferometry the phase correlation method is less precise than radar interferometry but it performs better in areas of rapid flow is more robust to temporal changes in glacier scattering and measures the glacier velocity in two dimensions with only one image pair using this technique we find that glaciar moreno flows at 400 m a 1 in the terminal valley and 800 m a 1 at the calving front in agreement with velocities recorded a decade ago assuming steady state flow conditions the vertical strain rates measured by sir c are combined with prior data on mass ablation to estimate the glacier thickness and ice discharge the calculated discharge is 0 6 0 2 km3 ice a 1 at 300 m elevation and 1 1 0 2 km3 ice a 1 at the equilibrium line elevation 1150 m which yields a balance accumulation of 6 1m ice a 1

epigenetic salt accumulation and water movement in the active layer of central yakutia in eastern siberia observations of soil moisture and salt content were conducted from may to august at neleger station in eastern siberia seasonal changes of salt and soil moisture distribution in the active layer of larch forest undisturbed and a thermokarst depression known as an alas disturbed were studied electric conductivity ece of the intact forest revealed higher concentrations that increased with depth from the soil surface into the active layer and the underlying permafrost 1 ms cm 1 at 1 1 m to 2 6 ms cm 1 at 160 cm depth in the permafrost however a maximum value of 5 4 ms cm 1 at 0 6 m depth was found in the dry area of the alas the concentration of ions especially na mg2 ca2 so42 and hco3 in the upper layers of this long term disturbed site indicates the upward movement of ions together with water a higher concentration of solutes was found in profiles with deeper seasonal thawing the accumulation of salts in the alas occurs from spring through into the growing season the low concentration of salt in the surface soil layers appears to be linked to leaching of salts by rainfall there are substantial differences between water content and electric conductivity of soil in the forest and alas modern salinization of the active layer in the alas is epigenetic and it happens in summer as a result of spring water collection and high summer evaporation the gradual salt accumulation in the alas in comparison with the forest is controlled by the annual balance of water and salts in the active layer present climatic trends point to continuous permafrost degradation in eastern siberia increasing the risk of surface salinization which has already contributed to changing the landscape by hindering the growth of forest copyright 2006 john wiley sons ltd

influence of temperature on the water retention properties of compacted gmz01 bentonite investigation of the temperature effects on the water retention properties of compacted bentonite is of great importance in the context of geological disposal of high level radioactive waste hlw based on the multi barrier concept gaomiaozi gmz bentonite collected from the inner mongolia autonomous region of china has been selected as a potential buffer backfill material for the construction of chinese hlw deep geological repository in this study soil water retention curves swrcs of both confined and unconfined compacted gmz01 bentonite specimens with an initial dry density of 1 70 g cm3 were investigated at temperatures 20 40 60 and 80 c results indicate that the water content decreases as temperature rises even though the temperature effects on the water retention capacity of compacted gmz01 bentonite depend on constraint conditions the influence of constraint conditions is more significant at relatively low suctions under unconfined conditions the temperature effect is insignificant however under confined conditions the influence on the water retention capacity is found to be significantly suction dependent the hysteresis behavior of unconfined compacted bentonite becomes less significant as temperature increases based on the corresponding results obtained a modified model was developed for describing the swrcs of confined compacted gmz01 bentonite with consideration of temperature effects it appears that the calculated swrcs agree well with the experimental ones indicating that the modified model can satisfactorily describe the effect of temperature on the water retention properties of confined compacted gmz01 bentonite

measurement of ice sheet topography using satellite radar interferometry detailed digital elevation models dems do not exist for much of the greenland and antarctic ice sheets radar altimetry is at present the primary in many cases the only source of topographic data over the ice sheets but the horizontal resolution of such data is coarse satellite radar interferometry uses the phase difference between pairs of synthetic aperture radar sar images to measure both ice sheet topography and surface displacement we have applied this technique using ers 1 sar data to make detailed i e 80 m horizontal resolution maps of surface topography in a 100 km by 300 km strip in west greenland extending northward from just above jakobshavns isbrae comparison with a 76 km long line of airborne laser altimeter data shows that we have achieved a relative accuracy of 2 5m along the profile these observations provide a detailed view of dynamically supported topography near the margin of an ice sheet in the final section we compare our estimate of topography with phase contours due to motion and confirm our earlier analysis concerning vertical ice sheet motion and complexity in ers 1 sar interferograms

environmental variability in northeastern siberia during the last 13 300 yr inferred from lake diatoms and sediment geochemical parameters abstract in northeastern siberia russia a 1 2 m sediment core was retrieved and radiocarbon dated from a small and shallow lake located at the western side of the lower lena river n 69 24 e 123 50 81 m a s l the objective of this paper is to reconstruct the palaeoenvironmental variability and to infer major palaeoclimate trends that have occurred since 13 3 cal kyr bp we analysed the diatom assemblages sedimentology grain size total organic carbon toc total nitrogen tn and the elemental and mineralogical composition using x ray fluorescence xrf and x ray diffractometry xrd of the sediment core our results show parallel changes in the diatom species composition and sediment characteristics enhanced minerogenic sediment input and the occurrence of pyrite is indicative of a cold period between 12 7 and 11 6 cal kyr bp the diatom data enable a qualitative inference about the local ecological conditions to be made and reveal an oligotrophic lake system with alkaline and cold conditions during the earliest holocene moderately warmer climates are inferred for the period from 9 1 to 5 7 cal kyr bp the major shift in the diatom assemblage from dominance of small benthic fragilarioid taxa to a more complex diatom flora with an influx of several achnanthoid and naviculoid diatom species occurred after a transitional period of about 1400 yr 7 1 to 5 7 cal kyr bp at 5 7 cal kyr bp indicating a circumneutral and warmer hydrological regime during the holocene thermal maximum htm diatom valve concentrations declined starting 2 8 cal kyr bp but have been rising again since 600 cal yr bp this has occurred in parallel to the increased presence of acidophilous diatom taxa e g eunotia spp and decreased presence of small benthic fragilarioid species in the most recent sediments which is interpreted as the result of neoglacial cooling and subsequent recent climate warming our findings are compared to other lake inferred climate reconstructions along the lena river we conclude that the timing and spatial variability of the htm in the lower lena river area reveal a temporal delay from north to south

ice velocity determined using conventional and multiple aperture insar abstract we combine conventional interferometric synthetic aperture radar insar and multiple aperture insar mai to determine the ice surface velocity on the langjokull and hofsjokull ice caps in iceland in 1994 this approach allows the velocity of the 20 principal ice cap outlet glaciers to be fully resolved we show that mai leads to displacement estimates of finer resolution 15 versus 150 m and superior precision 5 versus 15 cm to those afforded by the alternative technique of speckle tracking using sar data acquired in ascending and descending orbits we show that ice flows within 15 of the direction of maximum surface slope across 66 of the ice caps it is therefore possible to determine ice displacement over the majority of the ice caps using a single sar image pair thereby reducing errors associated with temporal fluctuations in ice flow

rapid thermokarst evolution during the mid holocene in central yakutia russia the reconstruction of holocene thermokarst landform evolution is important to understand the potential impact of current global climate change on permafrost regions a multi proxy approach was applied to analyse the sedimentological and biogeochemical characteristics as well as pollen and lacustrine microfossils of a core profile drilled in a small pingo within a large central yakutian thermokarst basin alas age depth modelling with macrofossil 14c ages reveals high thermokarst deposit sedimentation rates and a complete thermokarst sequence spanning about 900 years during the mid holocene between 6750 and 5870 cal yr bp in total three stages of thermokarst landscape evolution have been identified thermokarst processes were initiated at 6750 to 6500 cal yr bp terrestrial conditions changed quickly to lacustrine conditions and a thermokarst lake rapidly emerged and grew to an estimated size of 120 600 m diameter and 7 5 15 m depth during only 150 years between 6500 and 6350 cal yr bp the dec

holocene climate conditions in central yakutia eastern siberia inferred from sediment composition and fossil chironomids of lake temje abstract a 380 cm long sediment core from lake temje central yakutia eastern siberia was studied to infer holocene palaeoenvironmental change in the extreme periglacial setting of eastern siberia during the last 10 000 years data on sediment composition were used to characterize changes in the depositional environment during the ontogenetic development of the lake temje the analysis of fossil chironomid remains and statistical treatment of chironomid data by the application of a newly developed regional russian transfer functions provided inferences of mean july air temperatures tjuly and water depths wd reconstructed wds show minor changes throughout the core and range between 80 and 120 cm all the fluctuations in reconstructed water depth lie within the mean error of prediction of the inference model rmsep 0 35 so it is not possible to draw conclusions from the reconstructions a qualitative and quantitative reconstruction of holocene climate in central yakutia recognized three stages of palaeoenvironmental changes the early holocene between 10 and 8 ka bp was characterized by colder than today and moist summer conditions cryotextures in the lake sediments document full freezing of the lake water during the winter time a general warming trend started around 8 0 ka bp in concert with enhanced biological productivity reconstructed mean tjuly were equal or up to 1 5 c higher than today between 6 0 ka and 5 0 ka bp during the entire late holocene after 4 8 ka bp reconstructed mean tjuly remained below modern value limnological conditions did not change significantly the inference of a mid holocene climate optimum supports scenarios of holocene climatic changes in the subpolar part of eastern siberia and indicates climate teleconnections to the north atlantic realm

diatom records and tephra mineralogy in pingo deposits of seward peninsula alaska vast areas of the terrestrial subarctic and arctic are underlain by permafrost landscape evolution is therefore largely controlled by climate driven periglacial processes the response of the frozen ground to late quaternary warm and cold stages is preserved in permafrost sequences and deducible by multi proxy palaeoenvironmental approaches here we analyse radiocarbon dated mid wisconsin interstadial and holocene lacustrine deposits preserved in the kit 1 pingo permafrost sequence combined with water and surface sediment samples from nine modern water bodies on seward peninsula nw alaska to reconstruct thermokarst dynamics and determine major abiotic factors that controlled the aquatic ecosystem variability our methods comprise taxonomical diatom analyses as well as detrended correspondence analysis dca and redundancy analysis rda our results show that the fossil diatom record reflects thermokarst lake succession since about 42 14c kyr bp different thermokarst lake stages during the mid wisconsin interstadial the late wisconsin and the early holocene are mirrored by changes in diatom abundance diversity and ecology we interpret the taxonomical changes in the fossil diatom assemblages in combination with both modern diatom data from surrounding ponds and existing micropalaeontological sedimentological and mineralogical data from the pingo sequence a diatom based quantitative reconstruction of lake water indicates changing lake environments during mid wisconsin to early holocene stages mineralogical analyses indicate presence of tephra fallout and its impact on fossil diatom communities our comparison of modern and fossil diatom communities shows the highest floristic similarity of modern polygon ponds to the corresponding initial shallow water development stages of thermokarst lakes we conclude that mid wisconsin thermokarst processes in the study area could establish during relatively warm interstadial climate conditions accompanied by increased precipitation due to approaching coasts while still high continentality and hence high seasonal temperature gradients led to warm summers in the central part of beringia

ageing effects in a compacted bentonite a microstructure approach it is suspected that the as compacted state of heavily compacted clays used as possible engineered barriers for nuclear waste disposal is time dependent and that further change may occur in the material even at constant water content and density this paper presents an investigation of the time dependent microstructure changes of an mx80 clay bentonite compacted at various dry densities and water contents microstructure investigation is based on mercury intrusion pore size distribution measurements and scanning electron microscopy sem results obtained by other researchers by using x ray diffraction at low angles are also used statically compacted samples of mx80 were kept at constant volume and water content for various periods of time 1 30 and 90 days prior to mercury intrusion and sem micro structure investigation a significant change in micro structure with time was observed characterised by a decrease in the inter aggregate porosity and an increase in the very thin porosity not intruded by

oedometric and water retention behaviour of highly compacted unsaturated smectites this paper summarizes the findings from an experimental program concerning the hydromechanical behavior of two smectite clays tested under high stresses increasing axial stress on the smectite sam

three dimensional glacial flow and surface elevation measured with radar interferometry outlet glaciers which serve to drain ice from ice sheets seem to be dynamically less stable in north greenland than in south greenland1 2 3 storstrommen a large outlet glacier in northeastern greenland which surged between 1978 and 1984 ref 2 has been well studied in general neither glacier surge mechanisms nor the geographical distribution of the surges are well known conventional satellite radar interferometry can provide large scale topography models with high resolution4 and can measure the radar line of sight component of ice flow vectors5 but cannot map full vector flow fields here we present an interferometry method that combines observations from descending and ascending satellite orbits which assuming ice flow parallel to the topographic surface allows us to use the differing view angles to estimate full three dimensional surface flow patterns the accuracy of our technique is confirmed by the good agreement between our radar based flow model and in situ global positioning system gps reference data at storstrommen radar measurements such as these made regularly and at high spatial density have the potential to substantially enhance our understanding of glacier dynamics and ice sheet flow as well as improve the accuracy of glacier mass balance estimates

swelling phenomena and effective stress in compacted expansive clays the central aim of this paper is to discuss the applicability of the effective stress principle as defined by terzaghi total stress minus pore water pressure to predict the behaviour of expansive

estimation and analysis of the surface velocity field of mountain glaciers in muztag ata using satellite sar data muztag ata is a mountain known as the father of glaciers in the west of china however its glacier flow pattern has never been studied in this paper the velocity of mountain glaciers on muztag ata is mapped by two methods insar and offset tacking using sar data this map provides a detailed view of the features of glacier motion on muztag ata a special effort was also made to assess the accuracy of the glacier velocity estimates to ensure the accuracy of the derived results the validation of the results was conducted over two glaciers saliymek glacier and kuksay glacier the two methods yielded similar results that agree well with each other the patterns of glacier velocity on muztag ata suggest that mountain topography westerly winds and the monsoon have a strong influence our results show that motion of glaciers in the southern and western regions of muztag ata is faster than that in the northern and eastern regions eleven glaciers were identified along which glacier velocities exhibited distinctive behavior in terms of the spatial variability of the glacier motion the occurrence of the local flow maxima and minima at consistent locations over different parts of different glaciers suggests that the subglacial topography glacier size and glacier orientation affect the overall flow patterns the velocities are very low in the surface debris cover of some glaciers which suggests debris cover has an impact on glacier motion

holocene thermokarst dynamics in central yakutia a multi core and robust grain size endmember modeling approach abstract differentiating thermokarst basin sediments with respect to the involved processes and environmental conditions is an important tool to understand permafrost landscape dynamics and scenarios and future trajectories in a warming arctic and subarctic thermokarst basin deposits have complex sedimentary structures due to the variability of yedoma source sediments reworking during the late glacial to holocene climate changes and different stages of thermokarst history here we reconstruct the dynamic growth of thermokarst lakes and basins and related changes of depositional conditions preserved in sediment sequences using a combination of biogeochemical data and robust grain size endmember analysis remma this multi proxy approach is used on 10 sediment cores each 300 400 cm deep from two key thermokarst sites to distinguish four time slices that describe the holocene thermokarst lake basin evolution in central yakutia cy biogeochemical proxies and remma reveal fine grained sedimentation with rather high lake levels and or reducing conditions and coarse grained sedimentation with rather shallow lake levels and or oxidizing i e terrestrial conditions in relation to distal and proximal depositional and post sedimentary conditions statistical analysis suggests that the biogeochemical parameters are almost independent of thermokarst deposit sedimentology thus the biogeochemical parameters are considered as signals of secondary post sedimentary reworking the remma results are clearly reflecting grain size variations and depositional conditions this indicates small scale varying depositional environments frequently changing lake levels and predominantly lateral expansion at the edges of rapidly growing small thermokarst lakes and basins these small bodies finally coalesced forming the large thermokarst basins we see today in cy considering previous paleoenvironmental reconstructions in siberia we show the initiation of thaw and subsidence during the late glacial to holocene transition between about 11 and 9 cal kyrs bp intensive and extensive thermokarst activity for the holocene thermal maximum htm at about 7 to 5 cal kyrs bp severely fluctuating water levels and further lateral basin growth between 3 5 cal kyrs bp and 1 5 cal kyrs bp and the cessation of thermokarst activity and extensive frost induced processes i e permafrost aggradation after about 1 5 cal kyrs bp however gradual permafrost warming over recent decades in addition to human impacts has led to renewed high rates of subsidence and abrupt rapid cy thermokarst processes

long term experimental evidences of saturation of compacted bentonite under repository conditions abstract this paper summarises the information gathered in the last 15 years on the saturation of compacted bentonite obtained from different laboratory scale tests a large scale mock up test and a real scale in situ test that were performed to simulate the conditions of the bentonite barrier in a high level radioactive waste repository and to better understand the hydration heating processes in all the tests the bentonite used was the spanish febex bentonite the maximum temperature in the system was 100 c and the water used was of the granitic type with low salinity some of the tests were running for more than thirteen years the migration of water vapour in areas affected by the high temperature induced by the radioactive waste decay is very rapid its extent depending on the actual temperature and bentonite porosity the water vapour condensates in cooler areas and this causes water content increases in internal zones of the barrier where the liquid water coming from the host rock has not yet arrived the hydration kinetics is initially quicker when the temperature is high provided no vapour phase is formed nevertheless the major effect of the thermal gradient on saturation is a delaying of it in the inner parts of the barrier which can be very persistent and depends on the actual thermal gradient and consequently on the barrier thickness and boundary conditions during the transient period in which the barrier is saturating important changes in the water content and dry density of the bentonite are generated which induce bentonite density and water content gradients along its thickness these gradients could eventually disappear once the barrier is fully saturated depending on the irreversibility of the deformations the average density of the water in the saturated barrier will be higher than 1 g cm3 due to the predominance of high density interlayer water in the compacted bentonite and consequently more water than expected according to calculations made considering the density of free water would fit in the bentonite pores the rate of hydration of the barrier depends on the bentonite and surrounding media hydraulic properties that is water availability waste temperature and buffer thickness and geometry

a typology of pleistocene cold based rivers abstract a classification of periglacial rivers is proposed it is based on the generally valid laws relating the ratio of stream power to bed load with fluvial processes and morphology however river patterns may be modified by the special characteristics of the periglacial environment snowmelt especially in areas of continuous permafrost and river ice especially in zones of discontinuous permafrost determine the respective hydrological regimes the frozen state of the subsoil as well as the density of the vegetation cover contributes significantly to the bank cohesion and the sediment load of the rivers these specific periglacial characteristics have a complex influence on the thresholds in river activity resulting in a high diversity of periglacial river types

present day variability and holocene dynamics of permafrost affected lakes in central yakutia eastern siberia inferred from diatom records thermokarst lakes are assumed to develop cyclically driven by processes that are triggered by climate and maintained by internal feedbacks that may trigger lake drainage however the duration of these cycles remains uncertain as well as whether or not they affect the stabilization of lake ecosystems in permafrost regions over millennial time scales our research has combined investigations into modern lake to lake variability with a study of the long term development of individual lakes we have investigated the physico chemical and diatom compositions of a set of 101 lakes with a variety of different origins in central yakutia eastern siberia including thermokarst lakes fluvial erosion thermokarst lakes fluvial erosion lakes and dune lakes we found a significant relationship between lake genesis and the present day variability in environmental and diatom characteristics as revealed by multi response permutation procedures indicator species analyses and redundancy analyses environmental parameters also exhibit a significant correlation with variations in the diatom data for which they may have been to a substantial extent responsible mg and so4 concentrations together with ph and water depth were identified as the most important parameters influencing the variations in the diatom data almost as much as the entire environmental parameter set we were therefore able to establish a robust mg diatom transfer function which was then applied to three holocene lake records from these reconstructions together with a general interpretation of the diatom record including e g the ratio between benthic epiphytic and planktonic taxa we have been able to infer that all three of these lakes show 1 a continuous record with no desiccation events 2 high lake water levels during the early holocene 3 centennial to millennial scale variability and 4 high levels of variability during the early holocene but rather stable conditions during the late holocene a feature that is also known from other sites around the world we therefore concluded that the development of these three lakes was mainly driven directly by the climate rather than by thaw lake cycling

role of debris cover in the thermal physics of glaciers modele de fonte de la glace en presence de debris morainiques on en deduit une technique de noircissement de la surface des glaciers en vue d augmenter le debit d eau

ice sheet velocity mapping a combined interferometric and speckle tracking approach the first and second radarsat antarctic mapping missions amm 1 and 2 have now acquired interferometric synthetic aperture radar sar overmuch of the ice sheet the radarsat 24 day repeat cycle is nearly ideal for measuring slow ice motion e g 1 but application of sar interferometry is limited in faster moving areas with a 1day repeat period ers 1 2 tandem sar data are much better matched to fast motion but are not always available fortunately several authors have demonstrated the ability to measure velocity in fast moving areas by tracking sar speckle from image to image which works well even in the absence of visible features while these estimates have intrinsically lower resolution and poorer accuracy than direct phase measurements they serve well in areas where there are no data suitable for conventional interferometry this paper describes algorithms i have developed for merging interferometric and speckle tracking data from multiple swaths to form a single seamless mosaic of velocity at each point in the mosaic all the available data are combined to produce estimates of the velocity and the associated error this technique is demonstrated using radarsat data collected over lambert glacier antarctica during amm 1 and 2

glacier surface velocities in alpine terrain from optical satellite imagery accuracy improvement and quality assessment the worldwide retreat of mountain glaciers has important consequences for the water food and power supply of large and densely populated areas in south and central asia successful mitigation of the hydrological impacts on societies as well as assessing glacier related hazards require large scale monitoring of glacier dynamics however detailed glaciological data from the asian highlands are lacking due to its size and difficult accessibility we have applied a novel technique for precise orthorectification co registration and sub pixel correlation of advanced spaceborne thermal emission and reflection radiometer aster satellite imagery to derive surface velocities of himalayan glaciers our approach allows for the correction of offsets due to attitude effects and sensor distortions as well as elevation errors if a digital elevation model dem from the shuttle radar topography mission srtm was used for orthorectification after post processing the error on the displacements is on the order of 2 4 m per correlation translated into annual velocities this error is reduced increased when the correlated images are more less than a year apart through application of a filtering procedure and several quality tests the consistency of the results is validated to provide confidence in the remotely sensed velocity measurements despite the lack of ground control this novel approach allows fast easy and economically viable acquisition of detailed glaciological data in areas of difficult access and provides a means for large scale monitoring of glaciers in high mountainous terrain

interferometric radar observations of glaciar san rafael chile interferometric radar observations of glaciar san rafael chile were collected in october 1994 by nasa s spaceborne imaging radar c sir c at both l 24 cm and c band frequency 5 6 cm with vertical transmit and receive polarization the c band data did not yield good geophysical products because the temporal coherence of the signal was significantly reduced after 24 h the l band data were however successfully employed to map the surface topography of the icefield with a 10 m uncertainty in height and measure ice velocity with a precision of 4 mm d 1 or 1 4 ma 1 the corresponding error in strain rates is 0 05 a 1 at a 30 m horizontal spacing the one dimensional interferometric velocities were subsequently converted to horizontal displacements by assuming a flow direction and complemented by feature tracking results near the calving front the results provide a comprehensive view of the ice flow dynamics of glaciar san rafael the glacier has a core of rapid flow 4 5 km in width and 3 5 in average slope surrounded by slowermoving ice not by rock ice velocity is 2 6 m d 1 or 0 95 km a 1 near the equilibrium line altitude 1200 m increasing rapidly before the glacier enters the narrower terminal valley to reach 17 5 m d 1 or 6 4 km a 1 at the calving front strain rates are dominated by lateral shearing at the glacier margins 0 4 0 7 a 1 except for the terminal valley section where longitudinal strain rates average close to 1 a 1 this spectacular longitudinal increase in ice velocity in the last few kilometers may be a fundamental feature of tidewater glaciers

estimation of ice sheet motion using satellite radar interferometry method and error analysis with application to humboldt glacier greenland satellite radar interferometry provides glaciologists with an important new tool for determining the motion and topography of large ice sheets we examine the sources of error in interferometrically derived ice motion measurements including those errors due to inaccurate estimates of the interferometric baseline several simulations are used to assess baseline accuracy in terms of tie point error and the number and distribution of tie points these results give insight into how best to select tie points and also demonstrate the level of accuracy that can be achieved examination of two representative cases likely to occur in mapping ice sheet motion leads to the conclusion that with adequate tie point information ice velocity can be measured accurately to within a few meters per year a method to correct horizontal velocity estimates for the effect of vertical displacement using surface slopes is also developed finally we estimate the single component velocity field for an area on humboldt glacier northern greenland using interferograms formed from ers i sar images we estimate that these velocity measurements are accurate to within 2 3 m year 1