did the last sea level lowstand always lead to cross shelf valley formation and source to sink sediment flux 1 it is commonly believed that the efficiency of sediment flux from continents to oceans is maximized during relative sea level rsl lowstands by means of cross shelf valleys that are directly connected to the continental slope and deep marine environment while such conditions have been documented for the last rsl lowstand along several continental margins there is increasing evidence that radically different conditions persisted during the last glacial maximum lgm elsewhere with lowstand shorelines that remained on the continental shelf here we analyze the relationship between the lgm 21 ka shoreline and the shelf edge for the gulf of mexico off the united states and the bay of biscay off france a geophysical model is used to compute shoreline positions corrected for isostatic movements and the shelf edge position is quantified by means of curvature the conditions in the two study areas differed markedly throughout the gulf of mexico study area lgm sea level dropped to a point commonly 40 m below the shelf edge consistent with conventional sequence stratigraphic models while in the bay of biscay the modeled lgm shoreline remained well landward of the shelf edge in places separated by hundreds of kilometers these observations hint at potentially significant implications for 1 the source to sink sediment flux from continents to oceans and its variation in time and space 2 sequence stratigraphic models that predict deep marine sedimentation as being particularly prominent during rsl lowstands and 3 the occurrence of paleovalleys and related features on the continental shelf in addition our findings raise fundamental questions about the mechanics of shelf edge formation

sedimentary characteristics and origin of the late pleistocene ice complex on north east siberian arctic coastal lowlands and islands a review abstract the origin of late pleistocene ice rich fine grained permafrost sequences ice complex deposits in arctic and subarctic siberia has been in dispute for a long time corresponding permafrost sequences are frequently exposed along seacoasts and river banks in yedoma hills which are considered to be erosional remnants of late pleistocene accumulation plains detailed cryolithological sedimentological geochronological and stratigraphical results from 14 study sites along the laptev and east siberian seacoasts were summarized for the first time in order to compare and correlate the local datasets on a large regional scale the sediments of the ice complex are characterized by poorly sorted silt to fine sand buried cryosols toc contents of 1 2 4 8 wt and very high ground ice content 40 60 wt absolute a second large constituent of the ice complex are large syngenetic ice wedges resulting in a total ice content of the ice complex of up to 80 vol ice complex deposits were mostly formed during the middle weichselian interstadial and or during the late weichselian stadial periods a conceptual model of nival lithogenesis of ice complex deposits was developed that integrates various other formation hypotheses a combination of various local and regional paleogeographical geological and paleoclimate conditions controlled the formation of ice complex sequences during the late pleistocene in northern east siberia they are chronologically and stratigraphically but not genetically equivalent to eurasian and alaskan loess deposits

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

character of hearwaters adjustment to base level drop investigated by digital modeling using a computer model written for dynamic river profile modeling snow and slingerland 1987 long term profile adjustments to constant rate base level lowering tectonic block uplift have been simulated with varied conditions of outflow discharge 10 and 100 m3 s sediment diameter 0 1 0 4 and 2 0 mm and sediment load concentrations of 1200 and 400 ppm by weight tweleve sets of initially graded profile data cover all possible combinations of the variables each modeled stream has been subjected to each of three base level drop rates 0 1 1 0 and 10 0 mm yr for 10 000 years of model time modeled histories of headwaters erosional response differ in two ways the first is length of lag time of response characterized by a period of quiescence in erosion at the headwaters prior to the channel steepening sufficiently for erosion to commence at this upstream point variations in discharge and sediment concentration affect the lag time of response in all cases the second variable aspect of response is the relative magnitude of eventual headwaters erosion the main control is the drop rate a high drop rate yields a low relative magnitude whereas a low drop rate yields a high relative magnitude of response the rate of base level drop also controls to what degree the other controlling variables of discharge sediment concentration and sediment diameter affect the eventual magnitude of headwaters erosion rates of trunk stream and headwaters erosion indicate that 21 out of 36 of the modeled stream systems attain a condition approximating parallel profile erosion after 10 000 years some examples notably those with low power to erode and high imposed drop rates exhibit headwaters erosion rates that continue to be well below rates of base level lowering creating profile steepening with no apparent time limit

in situ x ray observations of phase assemblages in peridotite and basalt compositions at lower mantle conditions implications for density of subducted oceanic plate 1 phase relationships in klb 1 peridotite normal type mid oceanic ridge basalt nmorb and k rich basalt compositions were investigated experimentally from 28 to 143 gpa and 2050 to 3000 k a laser heated diamond anvil cell with the synchrotron x ray diffraction was developed to perform in situ observations of samples at simultaneous high pressures and temperatures we confirmed that the peridotite composition crystallized into an assemblage of mg perovskite ca perovskite magnesiowustite at pressures below 97 gpa and that nmorb and k rich basalt compositions both crystallized as mg perovskite ca perovskite stishovite an aluminous phase with a cafe2o4 type structure at pressures below 68 gpa the orthorhombic mg perovskite is stable in natural rock compositions at pressures less than 97 gpa corresponding to about 2200 km depth phase transition of silica phase from stishovite to cacl2 type phase was observed at 78 gpa in nmorb composition moreover we observed that nmorb crystallized in to an assemblage of cairo3 type mg fe sio3 ca perovskite pbo2 type silica an aluminous phase with a calcium cati2o4 type structure at 143 gpa corresponding to the core mantle boundary depth we measured the unit cell volumes of minerals in the nmorb composition at high p t and thereby estimated the density of subducted morb to a depth of 1800 km in the lower mantle in this depth regime morb is denser than model mantle densities e g prem and ak135 the estimated density of morb may contribute to an understanding of dynamics of the subducted slab in the deep lower mantle

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

correlation and interpretation of paleosols and loess across european russia and asia over the last interglacial glacial cycle abstract loess paleosol sequences of the last interglacial glacial cycle are correlated from european russia to central siberia and the chinese loess plateau during cold periods represented by marine oxygen isotope stages ois 2 and 4 loess deposition dominated in the russian plain and the loess plateau in central siberia loess deposition took place also but five to seven thin weakly developed paleosols are identified in both stages ois 3 in the chinese loess plateau near yangchang consists of a loess bed that is flanked by two weakly developed paleosols at kurtak siberia ois 3 is represented by two distinct stacked paleosols with no loess bed separating the paleosols in the russian plain ois 3 consists of a single possibly welded paleosol representing upper and lower stage 3 climates brunisols and chernozems dominate the profiles in china and siberia whereas regosols luvisols and chernozems are evident in the northern and southern russian plain respectively ois 5 is represented in china and the russian plain by pedo complexes in a series of welded soils whereas in contrast the kurtak site consists of six paleosols with interbedded loess the paleosols consist largely of brunisols and chernozems although the three areas examined have different climates geographical settings and loess source areas they all had similar climate changes during the last interglacial glacial cycle

slope sediment yield in arid lowland continuous permafrost environments canadian arctic archipelago abstract surface wash erosion was measured at runoff plots on low to moderate slopes in clayey and sandy silts underlain by continuous permafrost on the fosheim peninsula ellesmere island due to snow redistribution in winter total precipitation on the plots varied from 34 to 150 mm with corresponding surface runoff values of 0 to 102 mm where runoff occurred at least 80 of it was derived from snowmelt suspended sediment removal was plot data precipitation vegetation and surface grain size from the fosheim peninsula and banks island were used to develop a statistical model of suspended sediment removal by surface wash on undisturbed slopes for any given grain size the model predicts a rise in erosion from zero precipitation because of an absence of runoff to a peak at about 50 mm a decline as precipitation increases to 300 mm and a further increase in erosion beyond this inflection point this non linear response is due to the complex interaction of moisture primarily snow and vegetation cover erosion at any given precipitation value varies through three orders of magnitude depending on surface grain size the maximum erosion predicted is 1 kg m 2 a 1 for a runoff plot with 1100 mm of precipitation a corresponding vegetation cover of 77 and a median surface grain size of 7

possible closed system pingo and ice wedge thermokarst complexes at the mid latitudes of utopia planitia mars abstract on earth hydrostatic or closed system pingos csps are perennial ice cored mounds formed by the freeze thaw cycling of water when or as thermokarst lakes lose their water by drainage or evaporation the mounds vary in shape from circular or sub circular to elongate are sub kilometre in their long axes and may reach decametres in height often the mounds show summit depressions radial fractures and single tiers or benches as the csps degrade small scale debris flows or slumps occur end stage degradation typically exhibits debris laden ramparts elevated metres above the surrounding terrain typically the csps originate and develop where deep and continuous permafrost is ice rich i e infused with excess ice as it is in the tuktoyaktuk coastlands of northern canada mid to northern alaska and northeast russia in these areas or regions the terrain often is populated by a thermokarst lakes and alases thermokarst lake basins absent of water b fields of small scale ice wedge polygons either low centred or high centred relative to the polygon margins and c melt water filled or emptied polygon margin troughs or corner pits individual troughs and pits connected by means of the local topographical gradient comprises beaded stream systems or networks here we report describe and discuss a suite of candidate csps at the mid latitudes of utopia planitia up 35 50 n 80 115 e the morphologies scale and height of the martian mounds as well as the surface textures and characteristics landscape features and spatially associated landforms are consistent with the csps observed in ice rich regions on earth the up mounds are nested in or reside adjacent to flat floored possibly thermokarstic depressions small scale polygons some of which exhibit low or high centres relative to their margins and connected polygon margin depressions or pits that mirror beaded stream systems in ice rich terrain on earth the size frequency distribution of craters in our study region precludes a surface younger than 100 ma thus the csp like mounds in up and the pre mound periglacial revisions of the landscape presented by us may be markers of freeze thaw cycling that occurred much earlier in the amazonian epoch than most of the current discussions about periglaciation in up suggest

new insights into the weichselian environment and climate of the east siberian arctic derived from fossil insects plants and mammals multidisciplinary study of a key section on the laptev sea coast bykovsky peninsula east lena delta in 1998 2001 provides the most complete record of middle and late weichselian environments in the east siberian arctic the 40 m high mamontovy khayata cliff is a typical ice complex section built of icy silts with a network of large syngenetic polygonal ice wedges and is richly fossiliferous in combination with pollen plant macrofossil and mammal fossils a sequence of ca 70 insect samples provides a new interpretation of the environment and climate of the area between ca 50 and 12 ka the large number of radiocarbon dates from the section together with an extensive 14c database on mammal bones allows chronological correlation of the various proxies the bykovsky record shows how climate change and the last glacial maximum in particular affected terrestrial organisms such as insects and large grazing mammals both during the presumed karginsky interstadial mis 3 and the sartanian glacial mis 2 the vegetation remained a mosaic arctic grassland with relatively high diversity of grasses and herbs and dominance of xeric habitats the tundra steppe type this biome was supported by a constantly very continental climate caused by low sea level and enormous extension of shelf land variations within the broad pattern were caused mainly by fluctuations in summer temperature related to global trends but overprinted by the effect of continentality no major changes in humidity were observed nor were advances of modern type forest or forest tundra recorded suggesting a major revision of the karginsky interstadial paradigm the changing subtypes of the tundra steppe environment were persistently favourable for mammalian grazers which inhabited the shelf lowlands throughout the studied period mammal population numbers were lowered during the lgm especially toward its end and then flourished in a short but impressive peak in the latest weichselian just before the collapse of the tundra steppe biome throughout mis 3 and mis 2 the climate remained very favourable for the aggradation of permafrost no events of regional permafrost degradation were observed in the continuous bykovsky sequence until the very end of the pleistocene

eemian and late glacial holocene palaeoenvironmental records from permafrost sequences at the dmitry laptev strait ne siberia russia abstract terrestrial permafrost sections from the southern and northern coasts of dmitry laptev strait have preserved records of landscape transition from glacial to interglacial periods they allow geomorphologic and environmental changes to be traced from pre eemian time to the eemian and from the late glacial to the holocene the transition from one period to another induced extensive thawing of permafrost thermokarst evolving thermokarst depressions transformed formerly frozen ground into taberal unfrozen deposits with accumulating overlying lacustrine deposits lacustrine horizons rich in palaeontological remains retain evidence of changes in environmental conditions the pollen records reflect changes from grass sedge dominated vegetation during the early eemian to shrub dominated spectra during the middle eemian thermal optimum followed by late eemian grass sedge dominated tundra vegetation abundant larix pollen have been found in middle eemian deposits from the south coast of the dmitry laptev strait oyogos yar but are absent in similar deposits from the north coast bol shoy lyakhovsky island likely indicating that the northern tree line was located near the oyogos yar region during the eemian thermal optimum grass sedge dominated tundra vegetation occurred during the late glacial holocene transition which was replaced by shrub tundra during the early holocene rich fossil ostracod records from eemian and late glacial holocene lacustrine deposits could be correlated with the eemian thermal optimum and the late glacial allerod warm period for both periods the stable oxygen isotope data from the fossil ostracods suggest an approximate mean summer water temperature range between about 10 and 19 c in the palaeo lakes

phase transformations in subducted oceanic crust and buoyancy relationships at depths of 600 800 km in the mantle abstract phase transformations in a representative oceanic crust composition morb have been studied at pressures up to 28 gpa at 1200 c and 1500 c using a multi anvil apparatus the assemblage of majorite casio 3 rich perovskite stishovite which is displayed by the morb composition at pressures above 20 gpa was found to transform further into an assemblage containing a new aluminous phase at pressures above 25 gpa this al phase has a complex composition and is also relatively sodium rich its x ray diffraction pattern is similar to that observed for mgal 2 o 4 calcium ferrite type and is tentatively indexed on the basis of an orthorhombic cell yielding a zero pressure density of 3 87 2 g cm 3 majorite garnet was found to remain as the most abundant phase at the highest pressure studied 28 gpa and does not appear likely to transform to perovskite until pressures exceed 29 30 gpa these results imply that the basaltic crust component of subducted oceanic lithosphere would be 0 1 0 2 g cm 3 less dense than surrounding mantle pyrolite between the depths of 660 800 km thereby confirming an earlier hypothesis of anderson moreover the underlying layer of harzburgite would be 0 05 g cm 3 less dense than pyrolite throughout most of this depth interval these buoyancy relationships contribute to a barrier which impedes and may sometimes prevent the entry of slabs into the lower mantle

climate changes in east europe and siberia at the late glacial holocene transition abstract the main climatic oscillations of the lateglacial early holocene allerod younger dryas and preboreal can be distinguished all over eastern europe and siberia distribution of the main climatic indices in the lateglacial early holocene from west to east in northern eurasia shows that variations of the mean january temperature t jan o were larger than those of july temperature t july o as at present t jan o decreased to the east while the deviations from the present day values were greater in the west during the younger dryas the seasonality of climate increased considerably especially in the western european part of the studied area the greatest negative temperature deviations from the present day values up to 14 c occurred in the northwestern part of the east european plain near the scandinavian ice sheet it can be explained by a cooling influence from the remaining large ice body accordingly with degradation of the ice sheet at the warmer intervals of the lateglacial and early holocene the regional differences in temperature deviations became smaller up to 8 c on the whole precipitation p decreased in an easterly direction though its deviations from the modern level varied for different time intervals during the younger dryas p amounted to 60 65 of the present day values in the east european plain 80 in central west siberia and only 50 in central yakutia for the entire northern eurasia p did not exceed 300 350 mm yr in yakutia it was only 100 mm yr levels typical for present day dry steppe and semidesert zones nevertheless the reconstructed changes of the main climatic indexes were proportional to the present day climatic characteristics so that the general tendencies of their contemporary distribution in the mid latitudes were preserved during the entire lateglacial early holocene interval this shows that the general circulation of the atmosphere and geographical distribution of the main highs and lows in the studied time interval were in essence similar to the present day ones boundaries of permafrost in lateglacial and early holocene migrated in response to climate changes the southern limit of permafrost during the allerod was at 60 n in east europe and 55 n in west siberia during the younger dryas it moved south to 50 52 n in east europe and parabolic sand dunes were formed

methane oxidation following submarine permafrost degradation measurements from a central laptev sea shelf borehole submarine permafrost degradation has been invoked as a cause for recent observations of methane emissions from the seabed to the water column and atmosphere of the east siberian shelf sediment drilled 52 m down from the sea ice in buor khaya bay central laptev sea revealed unfrozen sediment overlying ice bonded permafrost methane concentrations in the overlying unfrozen sediment were low mean 20 m but higher in the underlying ice bonded submarine permafrost mean 380 m in contrast sulfate concentrations were substantially higher in the unfrozen sediment mean 2 5 mm than in the underlying submarine permafrost mean 0 1 mm using deduced permafrost degradation rates we calculate potential mean methane efflux from degrading permafrost of 120 mg m 2 yr 1 at this site however a drop of methane concentrations from 190 m to 19 m and a concomitant increase of methane 13c from 63 to 35 directly above the ice bonded permafrost suggest that methane is effectively oxidized within the overlying unfrozen sediment before it reaches the water column high rates of methane ebullition into the water column observed elsewhere are thus unlikely to have ice bonded permafrost as their source

thermokarst in siberian ice rich permafrost comparison to asymmetric scalloped depressions on mars 1 on earth the thawing of permafrost deposits with high ground ice content results in massive surface subsidence and the formation of characteristic large thermokarst depressions slope asymmetries within thermokarst depressions suggest lateral growth which occurs due to thermoerosion and gravimetric mass wasting along these slopes it has been proposed that rimless asymmetrically shaped depressions called scalloped depressions on mars were formed by insolation driven ground ice sublimation we investigated a large thermokarst depression in ice complex deposits in the siberian arctic as a terrestrial analogue for scalloped depressions in martian volatile rich mantle deposits our results from field studies insolation modeling and geomorphometric analyses suggest lateral thermokarst development in a northern direction this conclusion is obvious due to steeper slope angles of the south facing slopes insolation and surface temperatures are crucial factors directly influencing thermokarst slope stability and steepness comparative analyses of martian scalloped depressions in utopia planitia were conducted using high resolution high resolution imaging science experiment context camera and thermal infrared thermal emission imaging system satellite data by direct analogy we propose that the lateral scalloped depression development on mars was primarily forced on the steep pole facing slopes in the equator ward direction insolation modeling confirms that this must have happened in the last 10 ma during an orbital configuration of higher obliquity than today development would have been maximized if the orbit was both highly oblique and highly eccentric and or the martian summer coincided with perihelion relatively short events of increasing sublimation or even thawing of ground ice led to fast slumping processes on the steep pole facing slopes

cryostratigraphy of late pleistocene syngenetic permafrost yedoma in northern alaska itkillik river exposure abstract extremely ice rich syngenetic permafrost or yedoma developed extensively under the cold climate of the pleistocene in unglaciated regions of eurasia and north america in alaska yedoma occurs in the arctic foothills the northern part of the seward peninsula and in interior alaska a remarkable 33 m high exposure along the lower itkillik river in northern alaska opened an opportunity to study the unmodified yedoma including stratigraphy particle size distribution soil carbon contents morphology and quantity of segregated wedge and thermokarst cave ice the exposed permafrost sequence comprised seven cryostratigraphic units which formed over a period from 48 000 to 5 000 14c yr bp including 1 active layer 2 intermediate layer of the upper permafrost 3 4 two yedoma silt units with different thicknesses of syngenetic ice wedges 5 buried peat layer 6 buried intermediate layer beneath the peat and 7 silt layer with short ice wedges this exposure is comparable to the well known mus khaya and duvanny yar yedoma exposures in russia based on our field observations literature sources and interpretation of satellite images and aerial photography we have developed a preliminary map of yedoma distribution in alaska

quantifiable effectiveness of experimental scaling of river and delta morphodynamics and stratigraphy laboratory experiments to simulate landscapes and stratigraphy often suffer from scale effects because reducing length and time scales leads to different behaviour of water and sediment classically scaling proceeded from dimensional analysis of the equations of motion and sediment transport and minor concessions such as vertical length scale distortion led to acceptable results in the past decade many experiments were done that seriously violated these scaling rules but nevertheless produced significant and insightful results that resemble the real world in quantifiable ways here we focus on self formed fluvial channels and channel patterns in experiments the objectives of this paper are 1 to identify what aspects of scaling considerations are most important for experiments that simulate morphodynamics and stratigraphy of rivers and deltas 2 to establish a design strategy for experiments based on a combination of relaxed classical scale rules theory of bars and meanders and small scale experiments focussed at specific processes we present a number of small laboratory setups and protocols that we use to rapidly quantify erosional and depositional types of forms and dynamics that develop in the landscape experiments as a function of detailed properties such as effective material strength and to assess potential scale effects most importantly the width to depth ratio of channels determines the bar pattern and meandering tendency the strength of floodplain material determines these channel dimensions and theory predicts that laboratory rivers should have 1 5 times larger width to depth ratios for the same bar pattern we show how floodplain formation can be controlled by adding silt sized silicaflour bentonite medicago sativa alfalfa or partially hydrolyzed polyacrylamide a synthetic polymer to poorly sorted sediment the experiments demonstrate that there is a narrow range of conditions between no mobility of bed or banks and too much mobility the density of vegetation and the volume proportion of silt allow well controllable channel dimensions whereas the polymer proved difficult to control the theory detailed methods of quantification and experimental setups presented here show that the rivers and deltas created in the laboratory seem to behave as natural rivers when the experimental conditions adhere to the relaxed scaling rules identified herein and that required types of fluvio deltaic morphodynamics can be reproduced based on conditions and sediments selected on the basis of a series of small scale experiments

late quaternary ice sheet history of northern eurasia the maximum limits of the eurasian ice sheets during four glaciations have been reconstructed 1 the late saalian 140 ka 2 the early weichselian 100 80 ka 3 the middle weichselian 60 50 ka and 4 the late weichselian 25 15 ka the reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in russia and siberia and with marine seismic and sediment core data the barents kara ice sheet got progressively smaller during each glaciation whereas the dimensions of the scandinavian ice sheet increased during the last ice age the barents kara ice sheet attained its maximum size as early as 90 80 000 years ago when the ice front reached far onto the continent a regrowth of the ice sheets occurred during the early middle weichselian culminating about 60 50 000 years ago during the late weichselian the barents kara ice sheet did not reach the mainland east of the kanin peninsula with the exception of the nw fringe of taimyr a numerical ice sheet model forced by global sea level and solar changes was run through the full weichselian glacial cycle the modeling results are roughly compatible with the geological record of ice growth but the model underpredicts the glaciations in the eurasian arctic during the early and middle weichselian one reason for this is that the climate in the eurasian arctic was not as dry then as during the late weichselian glacial maximum

geological and geomorphological evolution of a sedimentary periglacial landscape in northeast siberia during the late quaternary a wide variety of environmental records is necessary for analysing and understanding the complex late quaternary dynamics of permafrost dominated arctic landscapes a ne siberian periglacial key region was studied in detail using sediment records remote sensing data and terrain modelling all incorporated in a geographical information system gis the study area consists of the bykovsky peninsula and the adjacent khorogor valley in the kharaulakh ridge situated a few kilometres southeast of the lena delta in this study a comprehensive cryolithological database containing information from 176 sites was compiled the information from these sites is based on the review of previously published borehole data outcrop profiles surface samples and our own field data these archives cover depositional records of three periods from pliocene to early pleistocene the late pleistocene and the holocene the main sediment sequences on the bykovsky peninsula consist of up to 50 m thick ice rich permafrost deposits ice complex that were accumulated during the late pleistocene they were formed as a result of nival processes around extensive snowfields in the kharaulakh ridge slope processes in these mountains such as in the khorogor valley and alluvial proluvial sedimentation in a flat accumulation plain dominated by polygonal tundra in the mountain foreland bykovsky peninsula during the early to middle holocene warming a general landscape transformation occurred from an extensive late pleistocene accumulation plain to a strongly thermokarst dominated relief dissected by numerous depressions thermokarst subsidence had an enormous influence on the periglacial hydrological patterns the sediment deposition and on the composition and distribution of habitats climate deterioration lake drainage and talik refreezing occurred during the middle to late holocene the investigated region was reached by the post glacial sea level rise during the middle holocene triggering thermo abrasion of ice rich coasts and the marine inundation of thermokarst depressions

knickpoint initiation and distribution within fluvial networks 236 waterfalls in the waipaoa river north island new zealand if knickpoints transmit signals of base level fall in river networks then improvements in our understanding of their retreat rate and basin wide distribution helps constrain the transient response following perturbation many studies of knickpoint retreat focus on the response of trunk streams to base level fall here we examine the response of an entire fluvial network as recorded by 236 active knickpoints distributed within the waipaoa river on the north island of new zealand base level fall within the waipaoa catchment initiated 18 000 years ago in response to a climatically triggered and tectonically exacerbated pulse of incision using observations from field work aerial photo analysis and a digital elevation model dem we study the knickpoint positions within the network we find that 70 of the knickpoints are located at drainage areas between 1 10 5 m 2 and 1 10 6 m 2 and more than half are b1 km upstream of a large change in drainage area for the knickpoints b1 km upstream of large tributary junctions we find that the retreat distances were well correlated with the tributaries drainage areas in order to determine how a pulse of incision distributes itself throughout a fluvial network we develop two simple end member models and compare their behavior to the observed knickpoint distribution in the waipaoa in the first model we propose that a knickpoint initiated at the basin outlet retreats upstream and distributes the signal throughout the network at a rate that is a power law function of drainage area in the second model we propose that knickpoints form near a threshold drainage area below which channels cannot incise with the same efficiency as possible in downstream reaches though neither model addresses the along stream variability in substrate or knickpoint form the misfit between the modeled and the observed knickpoints along stream positions are surprisingly low b1 km 1 25 of the total stream length for knickpoints with drainage areas b1 10 6 m 2 large misfits up to 3 5 km are observed for knickpoints with present day drainage areas greater than 1 10 6 m 2 the large single step in channel elevation that characterizes knickpoints presently observed in tributaries of the waipaoa river may not characterize the base level fall signal that propagated through the trunk streams evidence for progressive rather than instantaneous incision in the trunk streams the knickpoints vicinities to tributary junctions and the equivalent success of the two end member models lead us to conclude that the present positions of the 236 observed knickpoints are largely a consequence of thresholds in channel incision at low drainage areas

late quaternary paleoenvironmental records from the western lena delta arctic siberia abstract the three main lena delta terraces were formed during different stages of the late quaternary while only the first floodplain terrace is connected with active deltaic processes the second and third terraces which dominate the western part of the delta are erosional remnants of arctic paleolandscapes affected by periglacial processes the landscape dynamics of the second and the third terraces and their relationship to each other are of particular importance in any effort to elucidate the late quaternary paleoenvironment of western beringia multidisciplinary studies of permafrost deposits on the second terrace were carried out at several sites of the arga complex named after the largest delta island arga muora sise the frozen sediments predominantly consist of fluvial sands several tens of meters thick radiocarbon dated from 52 to 16 kyr bp these sands were deposited under changing fluvial conditions in a dynamic system of shifting river channels and have been additionally modified by synsedimentary and postsedimentary cryogenesis later thermokarst processes affected this late pleistocene fluvial landscape during the lateglacial and the holocene in addition eolian activity reworked the fluvial sands on exposed surfaces at least since the lateglacial resulting in dune formation in some areas contrary to the arga complex the third terrace is mainly composed of polygenetic alluvial and proluvial ice rich permafrost sequences ice complex deposits radiocarbon dated from 50 to 17 kyr bp which cover older fluvial sand units luminescence dated to about 100 50 kyr bp paleoecological records reflect tundra steppe conditions that varied locally depending on landscape dynamics during the marine isotope stage mis 4 and 3 periods and a persistent change to shrub and arctic tundra during lateglacial and holocene periods the study results indicate a continuous fluvial sedimentation environment for the laptev sea shelf in the region of the second lena delta terrace during the late pleistocene and confirm the presence of a dynamic channel system of the paleo lena river that flowed at the same time as the nearby subaerial ice complex deposits were being formed

the periglacial climate and environment in northern eurasia during the last glaciation this paper summarizes the results of studies of the late weichselian periglacial environments carried out in key areas of northern eurasia by several queen teams european science foundation esf programme quaternary environment of the eurasian north the palaeoglaciological boundary conditions are defined by geological data on timing and extent of the last glaciation obtained in the course of the eu funded project eurasian ice sheets these data prove beyond any doubt that with the exception of the northwestern fringe of the taymyr peninsula the rest of the eurasian mainland and severnaya zemlya were not affected by the barents kara sea ice sheet during the last glacial maximum lgm inversed modelling based on these results shows that a progressive cooling which started around 30 ka bp caused ice growth in scandinavia and the northwestern areas of the barents kara sea shelf due to a maritime climate with relatively high precipitation along the western flank of the developing ice sheets in the rest of the eurasian arctic extremely low precipitation rates less than 50 mm yr 1 did not allow ice sheet growth in spite of the very cold temperatures palaeoclimatic and palaeoenvironmental conditions for the time prior to during and after the lgm have been reconstructed for the non glaciated areas around the lgm ice sheet with the use of faunal and vegetation records permafrost eolian sediments alluvial deposits and other evidences the changing environment from interstadial conditions around 30 ka bp to a much colder and drier environment at the culmination of the lgm at 20 15 ka bp and the beginning of warming around 15 ka bp have been elaborated from the field data which fits well with the modelling results

fossil organic matter characteristics in permafrost deposits of the northeast siberian arctic 1 permafrost deposits constitute a large organic carbon pool highly vulnerable to degradation and potential carbon release due to global warming permafrost sections along coastal and river bank exposures in ne siberia were studied for organic matter om characteristics and ice content om stored in quaternary permafrost grew accumulated froze partly decomposed and refroze under different periglacial environments reflected in specific biogeochemical and cryolithological features om in permafrost is represented by twigs leaves peat grass roots and plant detritus the vertical distribution of total organic carbon toc in exposures varies from 0 1 wt of the dry sediment in fluvial deposits to 45 wt in holocene peats variations in om parameters are related to changes in vegetation bioproductivity pedogenic processes decomposition and sedimentation rates during past climate variations high toc high c n and low 13c reflect less decomposed om accumulated under wet anaerobic soil conditions characteristic of interglacial and interstadial periods glacial and stadial periods are characterized by less variable low toc low c n and high 13c values indicating stable environments with reduced bioproductivity and stronger om decomposition under dryer aerobic soil conditions based on toc data and updated information on bulk densities we estimate average organic carbon inventories for ten different stratigraphic units in northeast siberia ranging from 7 2 kg c m 3 for early weichselian fluvial deposits to 33 2 kg c m 3 for middle weichselian ice complex deposits to 74 7 kg c m 3 for holocene peaty deposits the resulting landscape average is likely about 25 lower than previously published permafrost carbon inventories

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

high resolution geological record of historic earthquakes in the dead sea basin a 2000 year paleoseismic record of the dead sea area was recovered from a lacustrine sedimentary section the section is being exposed at the ze elim terrace on the shores of the dead sea due to the fast retreat of the lake the section consists of laminated detrital and chemical mainly aragonite sediments that were deposited in the holocene paleo dead sea eight layers in the section show deformed sedimentary structures and are identified as seismites their chronology was determined by radiocarbon dating on organic remains the seismite ages are well correlated with the historically documented earthquakes of 64 and 31 b c and 33 363 1212 1293 1834 and 1927 a d the few historically documented earthquakes that have no correlatives in the ze elim seismite record occurred in times of sedimentary hiatuses at this site e g 749 a d based on modern analogues and the association of similar disturbed layers with syndepositional faults the ze elim terrace seismites indicate m 5 5 earthquakes the average recurrence interval is estimated as 100 300 years and represents slip events on different faults in the dead sea area the ze elim section provides a unique opportunity to correlate two independent and extensive data sets the historical and sedimentary records this study opens the way for better understanding of spatial and temporal distribution of earthquakes along the dead sea transform and elsewhere

late quaternary ice rich permafrost sequences as a paleoenvironmental archive for the laptev sea region in northern siberia ice rich permafrost sequences with large polygonal ice wedges represent excellent archives for paleoenvironmental reconstruction such deposits contain numerous well preserved records ground ice paleosols peat beds different types of fossils which permit characterization of environmental conditions during a clearly defined period of the past 60 ka based on field investigations carried out within framework of the german russian project laptev sea system 2000 on the bykovsky peninsula se of the lena delta results from cryolithological studies sedimentological analyses as well as new radiocarbon data are presented for the first time it is shown that the ice complex accumulated without significant interruptions from approximately 60 k y b p until the end of the pleistocene geochemical data total organic carbon c n 13corg and the mass specific magnetic susceptibility clearly show changing environmental conditions from stadial to interstadial times in the late pleistocene and during the transition to the holocene these results permit us to reconstruct the development of an arctic periglacial landscape in the coastal lowland during ice complex formation in the late quaternary this evolution coincided generally with the global environmental trend up to marine isotope stage 4

permafrost of the east siberian arctic shelf and coastal lowlands in the past decade within the framework of joint russian german marine and terrestrial studies on the arctic shelf new siberian islands and coastal lowlands of the laptev and east siberian seas fundamentally new data have been obtained on terrestrial and offshore permafrost in this area field and laboratory investigations supplemented with numerical modeling and generalization of the results of numerous geological surveys exploratory works and scientific researches performed in previous years have made it possible to revise existing knowledge about the distribution thickness physical state and history of development of terrestrial and offshore permafrost in the east siberian part of the arctic the main results of these studies and their interpretation are discussed in this paper

paleoenvironmental and paleoclimatic records from permafrost deposits in the arctic region of northern siberia ice complexes extremely ice rich permafrost deposits with large ice wedges are widely distributed in the arctic region of northeast siberia they present excellent archives for the reconstruction of late quaternary paleoenvironmental conditions in nonglaciated areas in 1998 1999 and 2000 russian and german scientists worked together on the bykovsky peninsula southeast of the lena delta in order to investigate the ice complex and its associated sediments intensive cryolithological and sedimentological studies radiocarbon age determinations paleobotanical studies micropaleontological investigations studies of mammal and insect fossils and stable isotope analyses of ground ice were performed radiocarbon data have been obtained from the entire exposed sequence coveringapproximately the last 60 000 years the results indicate that compared with modern time the investig ated ice complex sequence was formed duringtwo cooler and more arid stages of the late pleistocene with relatively uniform environmental conditions separated by a stage with environmental variations and more intensive soil formation caused by climate amelioration the late pleistocene environmental changes were not as strong as those occurring during the pleistocene holocene transition where a sharp break is evident r 2002 elsevier science ltd and inqua all rights reserved

vegetation and climate history in the laptev sea region arctic siberia during late quaternary inferred from pollen records abstract paleoenvironmental records from a number of permafrost sections and lacustrine cores from the laptev sea region dated by several methods 14 c ams tl irsl osl and 230 th u were analyzed for pollen and palynomorphs the records reveal the environmental history for the last ca 200 kyr for interglacial pollen spectra quantitative temperature values were estimated using the best modern analogue method sparse grass sedge vegetation indicating arctic desert environmental conditions existed prior to 200 kyr ago dense wet grass sedge tundra habitats dominated during an interstadial ca 200 190 kyr ago reflecting warmer and wetter summers than before sparser vegetation communities point to much more severe stadial conditions ca 190 130 kyr ago open grass and artemisia communities with shrub stands alnus fruticosa salix betula nana in more protected and moister places characterized the beginning of the last interglacial indicate climate conditions similar to present shrub tundra alnus fruticosa and betula nana dominated during the middle eemian climatic optimum when summer temperatures were 4 5 c higher than today early weichselian sparse grass sedge dominated vegetation indicates climate conditions colder and dryer than in the previous interval middle weichselian interstadial records indicate moister and warmer climate conditions for example in the interval 40 32 kyr bp salix was present within dense grass sedge dominated vegetation sedge grass artemisia communities indicate that climate became cooler and drier after 30 kyr bp and cold dry conditions characterized the late weichselian ca 26 16 kyr bp when grass dominated communities with caryophyllaceae asteraceae cichoriaceae selaginella rupestris were present from 16 to 12 kyr bp grass sedge communities with caryophyllaceae asteraceae and cichoriaceae indicate climate was significantly warmer and moister than during the previous interval the presence of salix and betula reflect temperatures about 4 c higher than present at about 12 11 kyr bp during the allerod interval but shrubs were absent in the younger dryas interval pointing to a deterioration of climate conditions alnus fruticosa betula nana poaceae and cyperaceae dominate early holocene spectra reconstructed absolute temperature values were substantially warmer than present up to 12 c shrubs gradually disappeared from coastal areas after 7 6 kyr bp when vegetation cover became similar to modern a comparison of proxy based paleoenvironmental reconstructions with the simulations performed by an earth system model of intermediate complexity climber 2 show good accordance between the regional paleodata and model simulations especially for the warmer intervals

late quaternary environmental and landscape dynamics revealed by a pingo sequence on the northern seward peninsula alaska a terrestrial sediment sequence exposed in an eroding pingo provides insights into the late quaternary environmental history of the northern seward peninsula alaska we have obtained the first radiocarbondated evidence for a mid wisconsin thermokarst lake demonstrating that complex landscape dynamics involving cyclic permafrost aggradation and thermokarst lake formation occurred over stadiale interstadial as well as glacialeinterglacial time periods high values of picea pollen and the presence of larix pollen in sediments dated to 50e40 ka bp strongly suggest the presence of forest or woodland early in mis 3 the trees grew within a vegetation matrix dominated by grass and sedge and there is indirect evidence of grazing animals thus the interstadial ecosystem was different in structure and composition from the holocene or from the preceding last interglacial period an early holocene warm period is indicated by renewed thermokarst lake formation and a range of fossil taxa multiple extralimital plant taxa suggest mean july temperatures above modern values the local presence of spruce during the early holocene warm interval is evident from a radiocarbon dated spruce macrofossil remain and indicates significant range extension far beyond the modern tree line the first direct evidence of spruce in northwest alaska during the early holocene has implications for the presence of forest refugia in central beringia and previously assumed routes and timing of post glacial forest expansion in alaska

floodplains permafrost cottonwood trees and peat what happened the last time climate warmed suddenly in arctic alaska abstract we use the stratigraphy of floodplains on alaska s north slope to describe how tundra watersheds responded to climate changes over the last 15 000 calibrated years bp 15 cal ka bp two episodes of extremely rapid floodplain alluviation occurred during the pleistocene holocene transition one between 14 and 12 8 cal ka bp and the other between 11 5 and 9 5 cal ka bp these aggradation episodes coincided with periods of warming in summer when cottonwood populus balsamifera l expanded its range peatlands became established and widespread thermokarst occurred the two aggradation episodes were separated by a period of floodplain incision during the younger dryas under cooler and possibly drier conditions at times of increasing summer warmth melting permafrost and enhanced precipitation probably triggered widespread mass wasting on hillslopes that overwhelmed the capacity of streams to transport sediment downstream and rapid floodplain aggradation resulted after peatlands became widespread in the early holocene rivers slowly incised their valley fills because major pulses of sediment input were limited to times of rapid thaw and increasing moisture many floodplains on the north slope have been effectively decoupled from upstream hillslopes for much of the past 15 000 years our findings a confirm the sensitivity of arctic watersheds to rapid warming in summer b emphasize the importance of hillslope mass wasting in landscape scale responses to climate change and c suggest that the presence of peatland on this arctic landscape today has raised its geomorphic response threshold to climate warming compared to what it was 14 000 years ago

thermokarst lake to lagoon transitions in eastern siberia do submerged taliks refreeze as the arctic coast erodes it drains thermokarst lakes transforming them into lagoons and eventually integrates them into subsea permafrost lagoons represent the first stage of a thermokarst lake transition to a marine setting and possibly more saline and colder upper boundary conditions in this research borehole data electrical resistivity surveying and modelling of heat and salt diffusion were carried out at polar fox lagoon on the bykovsky peninsula siberia polar fox lagoon is a seasonally isolated water body connected to tiksi bay through a channel leading to hypersaline waters under the ice cover the boreholes in the centre of the lagoon revealed floating ice and a saline cryotic bed underlain by a saline cryotic talik a thin ice bearing permafrost layer and unfrozen ground the bathymetry showed that most of the lagoon was ice grounded in spring in bedfast ice areas the electrical resistivity profiles suggest that an unfrozen saline layer was underlain by a thick layer of refrozen talik the modelling suggests thermokarst lake taliks refreeze when submerged in saltwater with mean annual bottom water temperatures below or slightly above 0 c this occurs because the top down chemical degradation of newly formed ice bearing permafrost is slower than the cooling of the talik hence lagoons may pre condition taliks with a layer of ice bearing permafrost before encroachment by the sea and this frozen layer may act as a cap on gas migration out of the underlying talik

the laptev sea rift abstract in north eastern siberia the active mid ocean gakkel ridge interacts with the continental shelf of the laptev sea extension has affected the shelf since at least the early tertiary and has resulted in the formation of a complex horst and graben system we present new seismic data from the laptev sea including deep seismic soundings the most prominent rift basin is the ust lena rift with a minimum e w width of 300 km at latitude 75 n and a cenozoic infill up to 13 km in thickness the asymmetric shape of the basin and conclusive evidence for a detachment imply a simple shear geometry the suggested rift model combines a ramp and flat geometry for the detachment with ductile stretching beneath the detachment a major west dipping hingeline listric fault separates the ust lena rift from the laptev horst the 100 150 km wide laptev horst is subdivided into three units by narrow rift grabens another prominent rift graben is the anisin basin which is located in the northern shelf area though the laptev sea rift formed in interaction with an active mid oceanic ridge there are indications that the laptev sea rift is of the passive rift type the rift was developed east of a sw ne trending transfer zone which links the gakkel ridge to the laptev sea rift

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

the mystery of bunge land new siberian archipelago implications for its formation based on palaeoenvironmental records geomorphology and remote sensing abstract multiproxy datasets geocryology geochronology sedimentology palaeo ecology from permafrost exposures were used together with land surface information based on satellite imagery and thematic maps in order to reconstruct the lateglacial to holocene landscape and environmental dynamics of bunge land zemlya bunge this area of little relief situated in the new siberian archipelago connects the geomorphologically well structured islands of kotel ny and fadeevsky a buried thermokarst landscape was found in the northwest region of the bunge land low terrace sand plain whereas the bunge land high terrace seems to be an exposed residue of a similar late quaternary thermokarst landscape that is confirmed especially by radiocarbon accelerator mass spectrometry and optically stimulated luminescence age determinations and by pollen analyses palaeogeographically the late pleistocene periglacial landscape and sedimentation of bunge land was closely connected to kotel ny and fadeevsky only later on seismotectonical block movements resulted in reshaping parts of bunge land the bunge land low terrace area first subsided and the original landscape there was destroyed by marine inundation followed by marine sedimentation subsequent block heave of the low terrace region exposed a vast sheet of marine sands which is continuously surficially reworked by aeolian processes while the original alluvial plain landscape in the high terrace area was preserved and started degrading only by early holocene thermokarst development the studied exposures contain one of the northernmost 74 88 n environmental records for the late pleistocene holocene transition in the eurasian arctic

circular cryogenic structures from the hirnantian deglaciation sequence anti atlas morocco abstract more than a hundred circular structures are observed at the topmost part of the late ordovician glaciogenic record in the central anti atlas southern morocco the structures were formed in the outer glaciated platform and characterize the hirnantian deglaciation sequence they are distributed within a 20 meter thick stratal interval and at present relicts of them still occupy several square kilometers in map view the circular to ovoidal structures which comprise fluvial sandstone beds and are sealed by shallow marine strata occur in closely spaced clusters they are 13 320 m in diameter with half of them in the 40 90 m range stratal wedging and bending as well as extensional and reverse centimeter to meter scale soft sediment fractures demonstrate that formation processes initially involved synsedimentary uplifts subsequent subsidence and collapse resulted in the formation of circular structures which essentially correspond to localized depocenters in the form of small scale sag basins regarding the overall deglaciation context the circular structures are interpreted as periglacial in origin with vertical movements ascribed to cryogenic processes involving the growth and then decay of bodies of segregation ice the size and diameter distributions which are comparable to the recent younger dryas and current lithalsa structures suggest that hirnantian circular features relate to similar genetic processes and can be referred to as lithalsa like structures a conceptual emplacement model is proposed which considers that a long term sedimentary aggradation over the fluvial plain prevented any significant landforms either a bump or a depression from being expressed at the depositional surface at the time of the circular structure formation the hirnantian lithalsa like structures constitute firm evidence for a late ordovician discontinuous permafrost during the deglaciation stage assuming that the late quaternary meridional zonation is valid it suggests the anti atlas was at latitudes in the 55 65 interval if combined with the rare pingo structures described in the literature which attest that coeval continuous permafrost conditions occurred at higher paleo latitudes the moroccan circular structures provide evidence for an alternate south pole position during the hirnantian 444 ma

deposition and degradation of a volatile rich layer in utopia planitia and implications for climate history on mars 1 we investigate the surface morphology of a study area in western utopia planitia mars which is characterized by a variety of landforms that resemble those of terrestrial periglacial landscapes polygonally fractured ground and thermokarst like depressions are found to be located in a young mantling deposit with a thickness of several tens of meters we observe a latitudinal dependence of the degradation of this mantling deposit larger depressions whose floors reveal the underlying basement rocks cover a higher fraction of the total terrain in the southern part of the study area than in the northern part indicating a more intense degradation of the mantle in the south all depressions have an asymmetric cross section in north south direction interpreted to be the result of the different solar radiation on differently oriented slopes on the basis of our morphological observations we develop a conceptual model for landscape evolution in western utopia planitia it involves subaerial deposition of a layered ice rich mantle and its subsequent degradation by polygon formation and sublimation a terrestrial analog to the polygonally fractured mantling deposit and its thermokarst like depressions is the siberian ice complex or yedoma which consists of subaerial ice rich deposits and is connected to nonglaciated landscapes with highly continental cold climatic environmental conditions our comparison suggests that no unusual or exotic processes need to be invoked to explain the current morphology of western utopia however the young age of the deposition and degradation implies climatic excursions in the very recent past on mars

fluvial adjustment of the lower jordan river to a drop in the dead sea level water utilization in the upper part of the jordan basin has led to a significant reduction in inflow to the dead sea over the last 70 years a drop of about 22 m in mean sea level has occurred and has resulted in a continual adjustment of the lower jordan river the impacts of this lowering on the channel morphology of the lower jordan river were examined using aerial photographs until the late 1970s the drop in the sea level was small but still led to channel extension since the early 1980s a rapid drop in sea level took place leading to major changes in channel morphology and deep incisions the greatest change in channel width was recorded near the river mouth between 1850 and 1980 there were only insignificant changes in channel sinuosity but subsequently a 25 increase of channel sinuosity has been recorded most of changes in the channel sinuosity were recorded in the newly exposed area over the last 30 years the active channel width has narrowed by almost four times until the late 1980s the channel was relatively stable with minor bank collapses and only one bar detected near the jisr abdallah during the 1990s a number of bars developed along the channel the downcutting is in parallel with the sea level drop resulting in the development of terraces along the lower part of the study reach in 1983 the channel incision reached 8 km upstream and by 1993 it was about 11 km

casio3 perovskite may cause electrical conductivity jump in the topmost lower mantle the electrical conductivity of casio3 perovskite was measured in situ between 17 24 gpa and 1300 2000 k using a multi anvil apparatus and solartron 1260 impedance gain phase analyzer in the frequency range of 107 1 hz the activation energies are 95 100 and 100 120 kj mol and the activation volumes are 0 06 0 08 and 0 46 0 03 cm3 mol at 1300 1800 and 1800 2000 k respectively conduction under lower mantle conditions may be dominated by the ionic diffusion of oxygen the electrical conductivity of casio3 perovskite is higher than that of bridgmanite majoritic garnet and ferropericlase the main constituents of the topmost lower mantle therefore casio3 perovsktie may significantly contribute to the electrical structure of the topmost lower mantle in spite of its relatively small volume proportion

heat and salt flow in subsea permafrost modeled with cryogrid2 thawing of subsea permafrost can impact offshore infrastructure affect coastal erosion and release permafrost organic matter thawing is usually modeled as the result of heat transfer although salt diffusion may play an important role in marine settings to better quantify nearshore subsea permafrost thawing we applied the cryogrid2 heat diffusion model and coupled it to a salt diffusion model we simulated coastline retreat and subsea permafrost evolution as it develops through successive stages of a thawing sequence at the bykovsky peninsula siberia sensitivity analyses for seawater salinity were performed to compare the results for the bykovsky peninsula with those of typical arctic seawater for the bykovsky peninsula the modeled ice bearing permafrost table ibpt for ice rich sand and an erosion rate of 0 25 m year was 16 7 m below the seabed 350 m offshore the model outputs were compared to the ibpt depth estimated from coastline retreat and electrical resistivity surveys perpendicular to and crossing the shoreline of the bykovsky peninsula the interpreted geoelectric data suggest that the ibpt dipped to 15 20 m below the seabed at 350 m offshore both results suggest that cold saline water forms beneath grounded ice and floating sea ice in shallow water causing cryotic benthic temperatures the freezing point depression produced by salt diffusion can delay or prevent ice formation in the sediment and enhance the ibpt degradation rate therefore salt diffusion may facilitate the release of greenhouse gasses to the atmosphere and considerably affect the design of offshore and coastal infrastructure in subsea permafrost areas

peat accumulation in drained thermokarst lake basins in continuous ice rich permafrost northern seward peninsula alaska thermokarst lakes and peat accumulating drained lake basins cover a substantial portion of arctic lowland landscapes yet the role of thermokarst lake drainage and ensuing peat formation in landscape scale carbon c budgets remains understudied here we use measurements of terrestrial peat thickness bulk density organic matter content and basal radiocarbon age from permafrost cores soil pits and exposures in vegetated drained lake basins to characterize regional lake drainage chronology c accumulation rates and the role of thermokarst lake cycling in carbon dynamics throughout the holocene on the northern seward peninsula alaska most detectable lake drainage events occurred within the last 4 000 years with the highest drainage frequency during the medieval climate anomaly peat accumulation rates were highest in young 50 500 years drained lake basins 35 2 g c m 2 yr 1 and decreased exponentially with time since drainage to 9 g c m 2 yr 1 in the oldest basins spatial analyses of terrestrial peat depth basal peat radiocarbon ages basin geomorphology and satellite derived land surface properties normalized difference vegetation index ndvi minimum noise fraction mnf from landsat satellite data revealed significant relationships between peat thickness and mean basin ndvi or mnf by upscaling observed relationships we infer that drained thermokarst lake basins covering 391 km2 76 of the 515 km2 study region store 6 4 6 6 tg organic c in drained lake basin terrestrial peat peat accumulation in drained lake basins likely serves to offset greenhouse gas release from thermokarst impacted landscapes and should be incorporated in landscape scale c budgets

ratio of 36cl cl in ground ice of east siberia and its application for chronometry abundance of the cosmogenic nuclide chlorine 36 36cl was measured together with the chloride cl concentration in different horizons of quaternary permafrost samples collected from various types of ground ice in the northeastern part of siberia the 36cl cl in 32 samples ranged in value from 2 4 10 14 to 1 4 10 12 nonetheless after a few extreme values were excluded these 36cl cl ratios provided a local permafrost chronometry the general concordance of the modeled ages with geological expectations and other chronological methods supports the potential power of the proposed dating method however the large observed change in ratios from higher to lower values during the transition from last glacial maximum to holocene climatic conditions remains unexplained an attempt to make use of the corresponding beryllium 10 10be absolute concentrations in the same samples failed because input of 10be attached to particulate matter into permafrost is unknown further 36cl cl serial measurements of modern precipitation and fossil ground ice are needed to refine this dating method into a practical tool with a clear protocol

an experimental investigation of the pyroxene garnet transformation in a pyrolite composition and its bearing on the constitution of the mantle abstract the pyroxene garnet transformation in a model pyrolite composition has been investigated over the pressure interval 4 0 to 17 5 gpa at temperatures of 1200 1400 c the transformation is largely completed in the pressure interval 14 16 gpa and a single phase aluminum deficient garnet majorite becomes stable above 16 gpa the mineral assemblages and the density and seismic velocity distributions for pyrolite are calculated as a function of depth on the basis of this and other recent experimental data density and seismic velocity profiles calculated for pyrolite are consistent with models based on seismic observations to a depth of 550 km if the existence of a high density velocity gradient between 550 km and 650 km is confirmed the presence of further phase transformations in majorite and or some degree of chemical heterogeneity in this depth interval would be indicated

vegetation climate and lake changes over the last 7000 years at the boreal treeline in north central siberia abstract palaeoecological investigations in the larch forest tundra ecotone in northern siberia have the potential to reveal holocene environmental variations which likely have consequences for global climate change because of the strong high latitude feedback mechanisms a sediment core collected from a small lake radius 100 m was used to reconstruct the development of the lake and its catchment as well as vegetation and summer temperatures over the last 7100 calibrated years a multi proxy approach was taken including pollen and sedimentological analyses our data indicate a gradual replacement of open larch forests by tundra with scattered single trees as found today in the vicinity of the lake an overall trend of cooling summer temperature from a 2 c warmer than present mid holocene summer temperatures until the establishment of modern conditions around 3000 years ago is reconstructed based on a regional pollen climate transfer function the inference of regional vegetation changes was compared to local changes in the lake s catchment an initial small water depression occurred from 7100 to 6500 cal years bp afterwards a small lake formed and deepened probably due to thermokarst processes although the general trends of local and regional environmental change match the lake catchment changes show higher variability furthermore changes in the lake catchment slightly precede those in the regional vegetation both proxies highlight that marked environmental changes occurred in the siberian forest tundra ecotone over the course of the holocene

floodplain width adjustments in response to rapid base level fall and knickpoint migration abstract geomorphology has long been engaged in characterizing the form and understanding the evolution of floodplains this study primarily examines floodplain width in four tributaries to the minnesota river in southern minnesota namely the maple le sueur and blue earth rivers and seven mile creek the tributary systems are relatively young having formed after retreat of the wisconsinan ice sheet and are rapidly evolving in response to a base level fall of nearly 70 m 13 400 ybp as a result the lower reaches of all four river channels are aggressively incising this study applies a new freely available open code plug in for arcgis to measure floodplain width as a function of elevation above the geomorphic top of bank systematic changes are observed in all four systems above the steep incising knickzone reaches of each of the tributaries relatively wide and mostly unconfined floodplains are observed within the knickzone floodplains progressively narrow to between 25 60 of their width above the knickzone despite the fact that sediment loads increase significantly in the downstream direction a power law relationship is consistently observed between floodplain width and the ratio of local channel slope to contributing drainage area to about the negative one third power in all four rivers this same power law relationship is observed for two other rivers that differ significantly from our study systems in climatic and tectonic environment as well as base level history

palaeoenvironmental dynamics inferred from late quaternary permafrost deposits on kurungnakh island lena delta northeast siberia russia abstract late quaternary palaeoenvironments of the siberian arctic were reconstructed by combining data from several fossil bioindicators pollen plant macro fossils ostracods insects and mammal bones with sedimentological and cryolithological data from permafrost deposits the record mirrors the environmental history of beringia and covers glacial interglacial and stadial interstadial climate variations with a focus on the middle weichselian interstadial 50 32 kyr bp the late pleistocene to holocene sequence on kurungnakh island reflects the development of periglacial landscapes under changing sedimentation regimes which were meandering fluvial during the early weichselian colluvial or proluvial on gently inclined plaines during the middle and late weichselian and thermokarst affected during the holocene palaeoecological records indicate the existence of tundra steppe vegetation under cold continental climate conditions during the middle weichselian interstadial due to sedimentation gaps in the sequence between 32 and 17 kyr bp and 17 and 8 kyr bp the late weichselian stadial is incompletely represented in the studied outcrops nevertheless by several palaeoecological indications arctic tundra steppe vegetation under extremely cold arid conditions prevailed during the late pleistocene the tundra steppe disappeared completely due to lasting paludification during the holocene initially subarctic shrub tundra formed which later retreated in course of the late holocene cooling

development of longitudinal profiles of alluvial channels in response to base level lowering degradation of alluvial channels in cohesive sediments was studied in 15 m and 20 m long flumes with a slope of 0 01 cm cm degradation was initiated by lowering base level to a fixed position and the development of the longitudinal profile of the channel is analysed through a model formulated as a heat diffusion equation it is based on the equation of sediment continuity combined with an assumption regarding sediment transport namely that sediment discharge is linearly proportional to the channel slope in accordance with the boundary and initial conditions imposed by the experimental setup and procedure the basic equation is amenable to an analytical solution which defines bed elevation at any distance and time as a function of the amount of base level lowering and a diffusion coefficient additional problems arising from bank erosion and channel armouring are also treated successfully within the framework of the same model the results show that in homogeneous alluvial sediments not subject to armouring the ultimate result of base level lowering by a certain amount is degradation all along the channel by the same amount the main impact of erosion is felt in the early stages after initiation of the process and mainly near the mouth the rate of degradation at any station along the channel reaches a peak and then slowly decreases with time and the peak rate is attenuated with distance from the outlet the model permits the prediction of intermediate stages of profile development at any distance from the outlet and at different times

testate amoebae protozoa testacealobosea and testaceafilosea as bioindicators in the late quaternary deposits of the bykovsky peninsula laptev sea russia testate amoebae protozoa testacea were studied in the late quaternary permafrost deposits in the siberian arctic bykovsky peninsula of the laptev sea coast 71 40 71 80 n and 129 129 30 e the testacea associations studied reflect specific environmental conditions in paleocryosols which were controlled by the local micro relief as well as by regional climate conditions in total 86 species varieties and forms of testate amoebae were found in 38 pleistocene and holocene samples the rhizopods indicate that soil conditions at ca 53 000 14c years bp were probably rather similar to the modern cold and wet arctic tundra environment more moisture and warmer soil conditions were relatively favorable for rhizopods ca 45 300 43 000 14c years bp but it was significantly drier at about 42 000 14c years bp drier and colder environmental conditions were also present about 39 300 35 000 14c years bp the late pleistocene samples radiocarbon dated to 33 000 12 000 years bp are characterized by a low species diversity and density indicating that this period may have been extremely cold and dry this conjecture is also supported by the polymorphism of some species hydrophilic difflugia species mostly obligate hydrobiotes are broadly represented in the studied holocene samples the species composition and density of rhizopods in the majority of holocene samples suggest wet and relatively warm conditions changes in rhizopod assemblages during the last 53 000 years were not very dramatic mostly consisting of rare species and changes in the dominant species complexes during the pleistocene and holocene however these changes were more drastic during the pleistocene they were probably at least partly responsible for the disappearance of some rare testacean species such as argynnia sp

last glacial maximum records in permafrost of the east siberian arctic palaeontological proxy data and cryolithological information from siberian arctic permafrost preserves records of late quaternary climate and environmental conditions in west beringia and their variability which results from interglacial glacial and interstadial stadial dynamics to date the last glacial maximum lgm period has been rather poorly represented in east siberian permafrost records here we present pollen sediment and ground ice stable water isotope data obtained from coastal exposures on bol shoy lyakhovsky island new siberian archipelago arctic ocean that mirror the coldest conditions during the sartan period between about 26 and 22 ka bp using pollen and sediment data for summer conditions and stable water isotope data for winter conditions the pollen record revealed a cold tundra steppe vegetation with characteristic predominance of grass pollen over sedge pollen while the stable isotope ice wedges data indicate extremely cold winter temperatures with mean values of d 18 oo f about 37 dd of about 290 combined with available regional lgm permafrost records that extend from the taymyr peninsula in the west to the yana river lowland in the east the new data set from bol shoy lyakhovsky island indicate that the regional appearance of lgm conditions depended on atmospheric circulation patterns that were influenced by the extent of the northern hemisphere glaciation

evolution of vertical knickpoints waterfalls with resistant caprock insights from numerical modeling 1 vertical knickpoints waterfalls mark a prominent process transition zone whose governing mechanics is not represented by conventional stream power incision models we examine the evolution of vertical knickpoints with resistant caprock utilizing numerical simulations that explicitly represent 1 face failure mechanisms 2 flow acceleration and amplified erosion above a knickpoint lip 3 deposition and removal of coarse debris below the knickpoint and 4 base level lowering or tectonic uplift rates our model demonstrates that knickpoint retreat rate where the subcaprock is weak or vertically jointed and base level fall rates are steady is likely to become tied to downstream conditions and equal to the downstream incision rate divided by channel gradient mechanically this coupling occurs where the subcaprock reaches a threshold height for failure in shear or buckling or where the weathering rate of the subcaprock is higher than the downstream incision wave velocity vi ds the height of the subcaprock face can influence its gravitational stability and the knickpoint lateral erosion rate and lead to a feedback between downstream incision and retreat rate retreat rate can be lower than vi ds during transients which could be long 106 years and set by the weathering rate of the subcaprock or influenced by lag debris evacuation key variables other than discharge can be important in setting retreat rates these include base level lowering rate the rock strength of stratigraphic units downstream of the knickpoint and the size and flux of sediment contributed from above the knickpoint or from the canyon walls two types of oversteepened reaches can form in association with a vertical knickpoint 1 an upstream free fall induced oversteepened reach whose length is longer than the flow acceleration zone and 2 a downstream coarse debris induced oversteepened reach although the model was constructed with caprock type knickpoints in mind some of its elements and insights are also relevant to homogenous substrates

lowstand rivers need not incise the shelf an example from the great barrier reef australia with implications for sequence stratigraphic models a key tenet of many sequence stratigraphic models is that sea level lowering causes widespread fluvial incision of the subaerially exposed continental shelf and that river borne terrigenoclastic sediments bypass the lowstand shoreline via canyons to the continental slope and basin floor consequently the occurrence of incised channels is considered a fundamental criterion for the recognition of sequence boundaries in ancient shelf successions contrary to this we argue that rivers may not necessarily incise during glacio eustatic lowstands if they flow out onto a coastal plain flanked by a broad low angle shelf on the great barrier reef shelf fluvial incision did not occur during the last glacial maximum lgm but instead subaerial accommodation was created and infilled as contemporary rivers graded to the lgm bayline incision was restricted to the lowstand shelf break where canyons of limited extent formed by nickpoint retreat

late quaternary sedimentation history of the lena delta abstract core and outcrop analysis from lena mouth deposits have been used to reconstruct the late quaternary sedimentation history of the lena delta sediment properties heavy mineral composition grain size characteristics organic carbon content and age determinations 14c ams and ir osl are applied to discriminate the main sedimentary units of the three major geomorphic terraces which form the delta the development of the terraces is controlled by complex interactions among the following four factors 1 channel migration according to the distribution of 14c and ir osl age determinations of lena mouth sediments the major river runoff direction shifted from the west during marine isotope stages 5 3 third terrace deposits towards the northwest during marine isotope stage 2 and transition to stage 1 second terrace to the northeast and east during the holocene first terrace deposits 2 eustasy sea level rise from last glacial lowstand to the modern sea level position reached at 6 5 ka bp resulted in back filling and flooding of the palaeovalleys 3 neotectonics the extension of the arctic mid ocean ridge into the laptev sea shelf acted as a halfgraben showing dilatation movements with different subsidence rates from the continent side differential neotectonics with uplift and transpression in the siberian coast ridges are active both likely have influenced river behavior by providing sites for preservation with uplift in particular allowing accumulation of deposits in the second terrace in the western sector the actual delta setting comprises only the eastern sector of the lena delta 4 peat formation polygenetic formation of ice rich peaty sand ice complex was most extensive 7 11 m in thickness in the southern part of the delta area between 43 and 14 ka bp third terrace deposits in recent times alluvial peat 5 6 m in thickness is accumulated on top of the deltaic sequences in the eastern sector first terrace

palaeobotanical evidence for warm summers in the east siberian arctic during the last cold stage plant macrofossils from the mamontovy khayata permafrost sequence 71 60 n 129 25 e on the bykovsky peninsula reflect climate and plant biodiversity in west beringia during the last cold stage 70 ams and 20 conventional 14c dates suggest sediment accumulation between about 60 000 and 7500 14c yr b p the plant remains prove that during the last cold stage arctic species minuartia arctica draba spp kobresia myosuroides coexisted with aquatic potamogeton vaginatus callitriche hermaphroditica littoral ranunculus reptans rumex maritimus meadow hordeum brevisubulatum puccinellia tenuiflora and steppe taxa alyssum obovatum silene repens koeleria cristata linum perenne the reconstructed vegetation composition is similar to modern vegetation mosaics in central and northeast yakutian relict steppe areas thus productive meadow and steppe communities played an important role in the siberian arctic vegetation during the late pleistocene and could have served as food resource for large populations of herbivores the floristic composition reflects an extremely continental arid climate with winters colder and summers distinctly warmer than at present holocene macrofossil assemblages indicate a successive paludification possibly connected with marine transgression increased oceanic influence and atmospheric humidity although some steppe taxa were still present in the early holocene they disappeared completely before 2900 14c yr b p

water bearing high pressure ca silicates abstract water bearing minerals provide fundamental knowledge regarding the water budget of the mantle and are geophysically significant through their influence on the rheological and seismic properties of earth s interior here we investigate the cao sio 2 h 2 o system at 17 gpa and 1773 k corresponding to mantle transition zone condition report new high pressure hp water bearing ca silicates and reveal the structural complexity of these phases we document the hp polymorph of hartrurite ca 3 sio 5 post hartrurite which is tetragonal with space group p 4 ncc a 6 820 5 c 10 243 8 a v 476 4 8 a 3 and z 4 and is isostructural with sr 3 sio 5 post hartrurite occurs in hydrous and anhydrous forms and coexists with larnite ca 2 sio 4 which we find also has a hydrous counterpart si is 4 coordinated in both post hartrurite and larnite in their hydrous forms h substitutes for si 4h for each si hydrogrossular substitution fourier transform infrared ftir spectroscopy shows broad hydroxyl absorption bands at 3550 cm 1 and at 3500 3550 cm 1 for hydrous post hartrurite and hydrous larnite respectively hydrous post hartrurite has a defect composition of ca 2 663 si 0 826 o 5 h 1 370 5 84 weight h 2 o according to electron probe microanalysis epma and the si deficiency relative to ca is also observed in the single crystal data hydrous larnite has average composition of ca 1 924 si 0 851 o 4 h 0 748 4 06 weight h 2 o according to epma and it is in agreement with the si occupancy obtained using x ray data collected on a single crystal superlattice reflections occur in electron diffraction patterns of the hydrous larnite and could indicate crystallographic ordering of the hydroxyl groups and their associated cation defects although textural and epma based compositional evidence suggests that hydrous perovskite may occur in high ca containing or low silica activity systems the ftir measurement does not show a well defined hydroxyl absorption band for this phase implying the water content at least in the quenched glass is below the limit of detection 100 1000 ppm we conclude that at high pressure as at ambient pressure some calcium silicates have a high affinity for h 2 o and high dehydration temperatures the thermal stability of these hydrous phases suggests that they could exist along a typical mantle geotherm and thus they might be relevant for understanding the mineralogy and water content of earth s mantle

geoelectric observations of the degradation of nearshore submarine permafrost at barrow alaskan beaufort sea 1 submarine permafrost degradation rates may be determined by a number of interacting processes including rates of sea level rise and coastal erosion sea bottom temperature and salinity regimes geothermal heat flux and heat and mass diffusion within the sediment column observations of ice bearing permafrost in shelf sediments are necessary in order to determine its spatial distribution and to quantify its degradation rate we tested the use of direct current electrical resistivity to ice bearing permafrost in elson lagoon northeast of barrow alaska beaufort sea a sharp increase in electrical resistivity was observed in profiles collected perpendicular to and along the coastline and is interpreted to be the boundary between ice free sediment and underlying ice bearing submarine permafrost the depth to the interpreted ice bearing permafrost increases from 2 m below sea level to over 12 m below sea level with increasing distance from the coastline the dependence of the saline sediment electrical resistivity on temperature and freezing was measured in the laboratory to provide validation for the field measurements electrical resistivity was shown to be effective for detection of shallow ice bearing permafrost in the coastal zone historical coastal retreat rates were combined with the inclination of the top of the ice bearing permafrost to calculate mean vertical permafrost degradation rates of 1 to 4 cm yr 1

late quaternary glaciations in northeastern russia a summary of the extent and chronology of quaternary glaciations in ne russia is presented in this paper the complex timing and style of glaciations include asynchronous development of alpine glaciers in the western and eastern part of the area while in the eastern part of ne russia well preserved moraines have been dated to the global last glacial maximum 18 24 ka in the westernmost part of the area no glacial advance took place at this time in general glacial advances were more extensive earlier rather than later in the last glacial cycle although only a handful of studies with reliable absolute ages in the vast area of ne russia exist it is clear that the number of advances throughout the region varies variable glacial response to global climate patterns is attributable to contrasting sources of precipitation an atlantic moisture source dominates in the western part of ne russia while a pacific source influences the eastern part of the region the glacial advances in the interior of ne russia are largely unexplored and further research is needed in order to understand quaternary climate change in the region copyright 2008 john wiley sons ltd

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

fluvial response to an historic lowstand of the great salt lake utah understanding fluvial adjustments to base level changes benefits the fields of sequence stratigraphy geomorphology and petroleum geology this investigation is a modern case study of the channel dynamics of lee creek and the goggin drain two streams that are part of the jordan river drainage into the endorheic great salt lake of northern utah a lacustrine system that has experienced multiple decadal scale base level changes since 1965 the lake level has fluctuated in elevation more than 6 m transitioning from an historic lowstand 1284 m a s l and in 2009 2010 approaching an historic lowstand this study uses detailed aerial images fieldwork and lidar data to link the modern geomorphology and channel hydraulics to specific variations in sediment transport channel form and avulsion behavior although lee creek and the goggin drain are situated only a few kilometers apart and share similar shore zone gradients substrates and vegetation patterns and have been subjected to the same changes in lake level their channel forms have evolved very differently differences in discharge patterns are likely the most influential factor causing the meandering form of lee creek and the braiding channel of the goggin drain despite the differences in discharge total sediment eroded from the two streams is comparable and can be attributed to similar stream power unit stream width in the two streams although lee creek has not recently been avulsive three major avulsions of the goggin drain have taken place since 1965 two possible styles of avulsion are interpreted an allogenic response to changing base level and an autogenic response dictated by channel morphology and hydraulics despite a wealth of available information avulsions cannot be unequivocally attributed to one style or another caution should be used when attempting to link the complex process of avulsion to causal mechanisms copyright 2011 john wiley sons ltd

thermodynamics of water solubility and partitioning when it was realized that nominally anhydrous minerals could be a major storage site of water in the mantle smyth 1987 bell and rossman 1992 it also became rather obvious that many mantle samples probably have lost most of their water during ascent e g ingrin and skogby 2000 while analyses of natural samples therefore in many circumstances only provide a lower limit of the actual water content in the mantle measurements of water solubility give an upper limit of the amount of water that might be stored in a mineral experimental measurements of water solubility have therefore naturally evolved in the last decades as a major tool for understanding the water storage capacity of the mantle closely related to studies of water solubility are studies of water partitioning among minerals if the water solubility in two minerals is known under given conditions the partition coefficient is just the ratio of the water solubilities under the same conditions provided that the composition of the fluid coexisting with the two minerals is the same since the pioneering work of bai and kohlstedt 1992 and of kohlstedt et al 1996 the water solubility in all major upper mantle minerals has been studied as well as the partitioning of water between the minerals of the lower mantle and the transition zone solubility studies by themselves do not directly give the water content in the mantle they constrain the storage capacity of the mantle i e the maximum amount of water that may be stored if the mantle were water saturated however as most of the mantle is very likely water undersaturated the actual water content is probably far below the storage capacity estimates of the actual abundance and distribution of water in the mantle may be obtained by combining solubility and partitioning data with direct

ice rich periglacial vs icy glacial depressions in the argyre region mars a proposed cold climate dichotomy of landforms on mars so called scalloped depressions are widely observed in utopia planitia up and malea planum mp typically they are rimless metres to decametres deep incised sharply tiered inwardly polygonised and sometimes pitted the depressions seemingly incise terrain that is icy and possibly thermokarstic i e produced by the thermal destabilisation of the icy terrain agewise the depressions are thought to be relatively youthful originating in the late amazonian epoch here we report the presence of similar depressions in the argyre region ar 30 60 s 290 355 e more importantly we separate and differentiate these landforms into two groups ice rich periglacial depressions type 1 and icy glacial depressions type 2a c this differentiation is presented to the mars community for the first time based on a suite of morphological and geological characteristics synonymous with ice complexes in the lena peninsula eastern russia and the tuktoyaktuk coastlands northwest territories canada we propose that the type 1 depressions are ice rich periglacial basins that have undergone volatile depletion largely by sublimation and as the result of thermal destabilisation in keeping with the terms and associated definitions derived of terrestrial periglacial geomorphology ice rich refers to permanently frozen ground in which ice lenses or segregation ice collectively referenced as excess ice have formed we suggest that the depressions are the product of a multi step cold climate geochronology 1 atmospheric precipitation and surface accumulation of an icy mantle during recent high obliquities 2 regional or local triple point conditions and thaw evaporation of the mantle either by exogenic forcing i e obliquity driven rises of aerial and sub aerial temperatures or endogenic forcing i e along argyre impact related basement structures 3 meltwater migration into the regolith at least to the full depth of the depressions 4 freeze thaw cycling and the formation of excess ice 5 sublimation of the excess ice and depression formation as high obliquity dissipates and near surface ice becomes unstable the type 2 depressions exhibit characteristics suggestive of supra glacial dead ice basins and snow ice suncups observed in high alpine landscapes on earth e g the swiss alps and the himalayas like the type 1 depressions the type 2 depressions could be the work of sublimation however the latter differ from the former in that they seem to develop within a glacial like icy mantle that blankets the surface rather than within an ice rich and periglacially revised regolith at near the surface interestingly the type 2 depressions overlie the type 1 depressions at some locations if the periglacial glacial morphological and stratigraphical dichotomy of depressions is valid then this points to recent glaciation at some locations within the ar being precursed by at least one episode of periglaciation this also suggests that periglaciation has a deeper history in the region than has been thought hitherto moreover if the hypothesised differences amongst the argyre based depressions are mirrored in utopia planitia and malea planum then perhaps this periglacial glacial dichotomy and its associated geochronology are as relevant to understanding late period landscape evolution in these two regions as it is in the ar

the postglacial pleistocene of the northern russian mainland abstract the paper summarizes the results of recent studies of late pleistocene postglacial geological events which occurred in the flatlands of northern russia stretching from the timan ridge to the laptev sea coast the available sedimentary record includes thawed and perennially frozen subaerial sediments and in places lacustrine and fluvial formations hundreds of geochronometric measurements by radiocarbon and luminescence techniques place this record within the time span of 50 11 ka bp which confirms an early mid weichselian age of the underlying glacial complex first established by the queen programme the spectrum of proxies includes sedimentary facies pollen data plant macrofossils oxygen isotope values megafauna remains insect assemblages traces of dna paleosols and permafrost properties together they indicate a continental progressively deteriorating climate with very cold winters and warmer than present summers through the second half of the late pleistocene minor climatic fluctuations are largely due to slightly changing humidity during mis 3 these changes are more pronounced in periglacial european russia in the vicinity of the barents kara ice sheet where the mid weichselian biotic maximum contrasts with conditions in the late weichselian polar desert in siberia the periglacial environments were more stable and beneficial for biota inspite of the increased continentality the recent data accumulated by various researchers are incompatible with the conventional correlation of the karginsky interglacial strata of siberia with mis 3 or any part of the european pleniglacial

the evolution of a thermokarst lake landscape late quaternary permafrost degradation and stabilization in interior alaska thermokarst processes characterize a variety of ice rich permafrost terrains and often lead to lake formation the long term evolution of thermokarst landscapes and the stability and longevity of lakes depend upon climate vegetation and ground conditions including the volume of excess ground ice and its distribution the current lake status of thermokarst lake landscapes and their future trajectories under climatewarming are better understood in the light of their long term development we studied the lake rich southern marginal upland of the yukon flats northern interior alaska using dated lake sediment cores observations of river cut exposures and remotely sensed data the region features thick up to 40 m quaternary deposits mainly loess that contain massive ground ice two of three studied lakes formed 11 000 12 000 cal yr bp through inferred thermokarst processes and fire may have played a role in initiating thermokarst development from 9000 cal yr bp all lakes exhibited steady sedimentation and pollen stratigraphies are consistentwith regional patterns the current lake expansion rates are low 0 to b7 cmyr 1 shoreline retreat compared with other regions 30 cm yr 1 or more this thermokarst lake rich region does not showevidence of extensive landscape lowering by lake drainage nor of multiple lake generations within a basin however lidar images reveal linear corrugations n5 m amplitude deep thermo erosional gullies and features resembling lake drainage channels suggesting that highly dynamic surface processes have previously shaped the landscape evidently widespread early holocene permafrost degradation and thermokarst lake initiation were followed by lake longevity and landscape stabilization the latter possibly related to establishment of dense forest cover partial or complete drainage of three lakes in 2013 reveals that there is some contemporary landscape dynamism holocene landscape evolution in the study area differs from that described from other thermokarst affected regions regional responses to future environmental change may be equally individualistic

pereletki and the initiation of glaciation in siberia abstract modern glaciers present in northern siberia adjacent to the arctic ocean littoral develop through the gradual accumulation of windblown snow and firn in river valleys and other depressions such snow glaciers pereletki are largely ephemeral in nature and produce landscapes dominated by nivation hollows and other snow related landforms deposits associated with pereletki include nival nival solifluctionary and fluvio nival units the modern pereletki are considered to represent an initial form of glaciation and their development can be regarded as an analogue for the formation of nival deposits commonly attributed to a more extensive sartanian glacial event late quaternary glacial events in siberia involved both alpine and piedmont glaciation and widespread development of pereletki in lowland areas distinguishing between features and sediments produced by glacial ice and those attributable to ephemeral pereletki is necessary for accurate assessment of late quaternary glaciation in siberia