glacial valley cross profile morphology tian shan mountains china abstract the morphology of glacial valley cross sections can be described in terms of power law y ax b or quadratic equations y a bx cx 2 fitted to empirical data the quadratic solution provides a more robust way of describing the morphology of glacial valley cross sections whereas the power law has more potential in understanding the cross sectional shapes and their evolution these two functions are used to study the cross sectional morphology of glacial valleys in the middle and western tian shan mountains and to discuss the comparison with fluvial channels the major conclusions are 1 power law equation parameters a and b are sensitive to the origin selection with larger sensitivity in vertical and a a ln a values conversely c values of the quadratic equation are more stable regardless of different origins selected 2 hirano and aniya earth surf processes landforms 13 1988 707 716 suggested two characteristic patterns in the relationship between the power law exponent b and the valley form ratio fr however glacial valleys in these areas do not fit the rocky mountain model for b fr values described by hirano and aniya for alpine glacial valleys this indicates that this rocky mountain model cannot be applied to all alpine glacial areas 3 the c values of the quadratic equation represent a curvi linear trend with its corresponding fr s at the same time power law parameters a and b fit a closed linear relationship both from these areas and others in the published literature 4 the cross sectional shapes of glacial valleys show clear differences with fluvial channels by comparing a b values of glacial valleys with the hydraulic geometry of fluvial channels this implies that the a b relationship and the variation range of b values commonly with 1 5 2 5 may be helpful to differentiate valleys formed by different processes

quaternary glaciation of the himalayan tibetan orogen glacial geological evidence from throughout the himalayan tibetan orogen is examined to determine the timing and extent of late quaternary glaciation in this region and its relation to similar changes on a global scale the evidence summarised here supports the existence of expanded ice caps and extensive valley glacier systems throughout the region during the late quaternary however it cannot yet be determined whether the timing of the extent of maximum glaciation was synchronous throughout the entire region or whether the response was more varied the lack of organic material needed for radiocarbon dating has hindered past progress in glacial reconstruction however application of optically stimulated luminescence and terrestrial cosmogenic radionuclide methods has recently expanded the number of chronologies throughout the region limits to the precision and accuracy available with these methods and more importantly geological uncertainty imposed by processes of moraine formation and alteration both conspire to limit the time resolution on which correlations can be made to milankovitch timescales several ka in order to put all studies on a common scale well dated sites have been re evaluated and all the published terrestrial cosmogenic nuclide ages for moraine boulders and glacially eroded surfaces in the himalayan tibetan orogen have been recalculated locally detailed studies indicate that there are considerable variations in the extent of glaciation from one region to the next during a glaciation glaciers throughout monsoon influenced tibet the himalaya and the transhimalaya are likely synchronous both with climate change resulting from oscillations in the south asian monsoon and with northern hemisphere cooling cycles in contrast glaciers in pamir in the far western regions of the himalayan tibet orogen advanced asynchronously relative to the other regions that are monsoon influenced regions and appear to be mainly in phase with the northern hemisphere cooling cycles broad patterns of local and regional variability based on equilibrium line altitudes have yet to be fully assessed but have the potential to help define changes in climatic gradients over time copyright 2008 john wiley sons ltd

multi scale curvature for automated identification of glaciated mountain landscapes erosion by glacial and fluvial processes shapes mountain landscapes in a long recognized and characteristic way upland valleys incised by fluvial processes typically have a v shaped cross section with uniform and moderately steep slopes whereas glacial valleys tend to have a u shaped profile with a changing slope gradient we present a novel regional approach to automatically differentiate between fluvial and glacial mountain landscapes based on the relation of multi scale curvature and drainage area sample catchments are delineated and multiple moving window sizes are used to calculate per cell curvature over a variety of scales ranging from the vicinity of the flow path at the valley bottom to catchment sections fully including valley sides single scale curvature can take similar values for glaciated and non glaciated catchments but a comparison of multi scale curvature leads to different results according to the typical cross sectional shapes to adapt these differences for automated classification of mountain landscapes into areas with v and u shaped valleys curvature values are correlated with drainage area and a new and simple morphometric parameter the difference of minimum curvature dmc is developed at three study sites in the western united states the dmc thresholds determined from catchment analysis are used to automatically identify 5 5 km quadrats of glaciated and non glaciated landscapes and the distinctions are validated by field based geological and geomorphological maps our results demonstrate that dmc is a good predictor of glacial imprint allowing automated delineation of glacially and fluvially incised mountain landscapes

the paleoclimatic record provided by eolian deposition in the deep sea the geologic history of wind the mineral component of pelagic sediment is brought to the deep sea by transport in the wind extraction and analysis of this dust allows estimation of the past aridity of the eolian source region via flux determinations and of the intensity of the transporting winds from grain size data these two parameters the grain size and mass flux of dust vary independently there are three significant sources of modern dust eastern and central asia northwest africa and arabia all in the northern hemisphere as the rainfall associated with the intertropical convergence zone is an effective barrier to southerly transport of dust the northern hemisphere is an order of magnitude more dusty than is the southern an asymmetry that has characterized most of the cenozoic eolian flux data show that most of the northern hemisphere was more arid during glacial maxima with 3 to 5 times as much dust transported during glacial stages than during interglacials only northwestern south america varied in the opposite sense the periodicity of quaternary variation in both eolian flux and eolian grain size data is strongly influenced by the milankovitch cycles of orbital variability wind intensities vary on a shorter time scale than the general 100 kyr cycles of glaciation and general aridity eolian grain sizes display forcing at precessional 19 and 23 kyr tilt 41 kyr and at approximately 30 kyr periodicities as a result the generalization that winds are uniformly stronger during glacial times is not valid whole cenozoic records show that the largest change in dust flux an order of magnitude increase occurred in the northern hemisphere and reflects continental drying associated with the late pliocene onset of northern hemisphere glaciation southern hemisphere eolian records show no sign of paleoclimatic changes in the late pliocene the most important change in cenozoic atmospheric circulation was a severalfold reduction in wind intensity that occurred at the time of the paleocene eocene boundary before then latest cretaceous and paleocene winds were essentially as strong as those of the late cenozoic this shift appears to be one of several climatic responses to a change in the nature and amount of global heat transport at about 55 ma

volume size distribution of microparticles in ice cores from the tibetan plateau the volume distribution of atmospheric dust particles microparticles of 1 30 mm diameter in muztagata dunde dasuopu and everest ice cores from the tibetan plateau was measured and fitted as a log normal function in order to characterize their basic size properties our results reveal that whether the volume distribution fits the log normal function or not largely depends on the dust concentration and the specific dust storm event but is independent of physiographical location and season our results show only high concentration samples obey the log normal distribution in volume with mode sizes ranging from 3 to 16 mm the log normal distribution was largely attributed to the mid sized particles between 3 and 15 mm which contribute most 70 of the total volume the volume size distribution characteristics for mineral dust particles from ice cores reveal that the coarse particles might be common in the upper level troposphere over the tibetan plateau these dust size features are useful to advance our understanding of dust effects on climate and provide clues to better characterize atmospheric dynamics over the tibetan plateau that will help to improve the current models

quartz grain surface microtextures of dam break flood deposits from a landslide dammed lake a case study abstract a landslide dam break flood can cause great damage to the downstream area in a mountainous watershed the analysis of quartz sand surface textures is a valid microscale method by which to study the genetic mechanisms of flood deposits however previous studies have not considered the microstructures of dam break outburst deposits in this research samples from 24 sites along the diexi dam break flood deposits in southwestern china were examined and analyzed using scanning electron microscopy sem photomicrographs in addition the frequency statistical results of quartz sand microtextures were also compared in different sedimentary environments on one hand the upstream end of dam break flood deposits contained quartz grains with breakage blocks and inherited microtextural characteristics while the downstream quartz sands are characterized by v shaped and small conchoidal fractures the different combinations of quartz sand surface textures indicate the transformation process changing from high energy collisions to low energy collisions over a short distance on the other hand the results exhibit the difference between dam break flood deposits and other sediments such as debris flow deposits or normal flood deposits which reveals the potential of this microscopy method for recognition of dam break flood deposits the features of quartz sand microtextures also indicate that channel topography sediment concentration and other factors may play important roles in routing of dam break flood events thus we suggest that the quartz sand microtextures can be used as a complementary method rather than the only identification criterion of dam break flood deposits

polynomial and power functions for glacial valley cross section morphology an empirical evaluation of glacial trough cross section shape is performed on seven vertical cross sections in three sierra nevada valleys glaciated during the late quaternary power and second order polynomial functions are fitted by statistical regression power functions are very sensitive to subtle valley bottom topographic features and require precise specification of the valley bottom centre location this dependency is problematic given under representation of valley bottoms by conventional contour sampling methods and the common alteration of valley bottom morphology by non glacial processes power function exponents vary greatly in response to these and other non genetic factors and are not found to be reliable indicators of overall valley morphology second order polynomials express overall valley shape in a single robust function they are applied to both bedrock and sediment floored glacial valleys with negligible statistical bias except where side slopes are stepped or convex upward or where valley form is asymmetrical they can describe alluviated or severely eroded valleys and can objectively identify indi vidual components of polymorphic valleys because valley bottom and centre locations need not be specified mathematical expressions of parameters useful for geomorphic measurements and glaciological modelling are analytically derived from the polynomials as functions of the three polynomial coefficients these parameter equations provide estimates of valley side slopes mean and maximum depth midpoint location width area boundary length form ratio and symmetry

distribution of rare earth elements and other high field strength elements in glacial meltwaters and sediments from the western greenland ice sheet evidence for different sources of particles and nanoparticles although global warming increases meltwater input into the oceans rather little is known about the distribution of high field strength elements such as the rare earths and y rey zr hf th and u in arctic glacial meltwaters and glacial fed rivers we studied glacial meltwater and glacial fed rivers from the kangerlussuaq area and a glacial fed lake and its meltwater inflow in the isua area both in the western part of the greenland ice sheet gris trace element concentrations were determined in 0 2 m filtered water samples dissolved fraction in the respective filter residues particulate fraction and in ambient sediments including cryoconite from a meltwater pond on the surface of the gris we also measured truly dissolved rey concentrations in a 10 kda ultrafiltered sample from glacial fed watson river shale normalized sn rey patterns of the particulate fraction and ambient sediments including cryoconite are rather similar to those of local archean gneisses and show positive eusn anomalies this rules out asian dust which does not show positive eusn anomalies as a possible source of these aluminosilicate particles but suggests that local archean basement is eroded and currently transported by ice water and wind to the depositional sites in front of and onto the gris all 0 2 m filtered glacial fed rivers show very unusual reysn patterns in comparison to tropical temperate and boreal rivers and are significantly enriched in light relative to heavy rey for glacial fed watson river the 99 of la and 78 of yb in the latter are associated with nanoparticles and colloids although the reysn patterns of the 0 2 m filtrates are rather similar to those of the particulate fraction and ambient sediments they lack any eusn anomalies whereas the 0 2 m filtrates from a meltwater pond on the surface of the gris show positive eusn anomalies similar to but somewhat smaller than the cryoconite while the water from the meltwater pond carries nanoparticles derived from local archean sources the lack of eusn anomalies in the glacial fed rivers suggests that their nanoparticle and colloid load represents atmospheric dust that is remobilized from greater depth in the gris most of this dust probably originated from eastern asia and shows a rey distribution similar to post archean upper continental crust i e lacks any eusn anomaly hence rey geochemistry suggests that the particulates and the nanoparticles colloids in these arctic meltwaters are derived from different sources

spatial distribution of sediment storage types and quantification of valley fill deposits in an alpine basin reintal bavarian alps germany spatial patterns of sediment storage types and associated volumes using a novel approach for quantifying valley fill deposits are presented for a small alpine catchment 17 km 2 in the bavarian alps the different sediment storage types were analysed with respect to geomorphic coupling and sediment flux activity the dominant landforms in the valley in terms of surface area were found to be talus slopes sheets and cones followed by rockfall deposits and alluvial fans and plains more than two thirds of the talus slopes are relict landforms completely decoupled from the geomorphic system notable sediment transport is limited to avalanche tracks debris flows and along floodplains sediment volumes were calculated using a combination of polynomial functions of cross sections seismic refraction and gis modelling a total of 66 seismic refraction profiles were carried out throughout the valley for a more precise determination of sediment thicknesses and to check the bedrock data generated from geomorphometric analysis we calculated the overall sediment volume of the valley fill deposits to be 0 07 km 3 this corresponds to a mean sediment thickness of 23 3 m the seismic refraction data showed that large floodplains and sedimentation areas which have been developed through damming effects from large rockfalls are in general characterised by shallow sediment thicknesses 20 m by contrast the thickness of several talus slopes is more than twice as much for some locations e g narrow sections of valley the polynomial generated cross sections resulted in overestimations of up to one order of magnitude whereas in sections with a moderate valley shape the modelled cross sections are in good accordance with the obtained seismic data for the quantification of valley fill deposits a combined application of bedrock data derived from polynomials and geophysical prospecting is highly recommended d 2003 elsevier b v all rights reserved

valley formation by fluvial and glacial erosion cross valley profiles from the west slope of the olympic peninsula washington are used to investigate the relative effects of fluvial and glacial erosion on valley formation unlike most ranges where glaciers and rivers sequentially occupied the same valleys neighboring valleys in the olympic mountains developed in similar lithologies but were subject to different degrees of glaciation allowing comparison of the net effect of glacial and fluvial processes integrated over many glacial cycles upslope drainage area was used to normalize comparisons of valley width ridge crest to valley bottom relief and valley cross sectional area as measures of net differences in the mass of rock excavated from below ridgelines for 131 valley spanning transects valley width relief and cross sectional areas are similar for glaciated partly glaciated and unglaciated fluvial valleys with drainage areas of 10 km 2 but diverge downslope glaciated valleys draining 50 km 2 reach two to four times the cross sectional area and have to 500 m greater relief than comparable fluvial valleys partly glaciated valleys have intermediate dimensions at distances of 5 km from valley heads the cumulative upstream volume of rock removed to form valleys is two to four times greater in glacially incised valleys than in fluvial valleys the finding of strong differences in the net result of valley excavation by fluvial and glacial erosion supports the interpretation that alpine glaciers are more effective erosional agents than are rivers and implies that large alpine valleys deepened and enlarged in response to pleistocene glaciation

using parabolas to describe the cross sections of glaciated valleys it is widely accepted that the simple power curve y axb can be used to describe the cross section of glaciated valleys there are however good reasons to suppose that this particular form of equation is inappropriate for this purpose

hypsometry and relief analysis of the southern termination of the calabrian arc ne sicily southern italy abstract tectonic forcing causes the relief building of mountain chains and enforces the surficial processes in a persistent dismantling of rock volumes continuously modelling earth s surface actually we observe transient landscapes that have temporarily recorded tectonic forcing as a codified signal the late quaternary tectonic evolution of northeastern sicily located along the nubia eurasia plate boundary at the southern termination of the calabrian arc has been dominated by intense plio pleistocene dynamics that severely modified the late miocene landscape the present work aims to investigate geomorphically northeastern sicily essentially focusing on the hypsometric and relief analyses of the region in order to define how the topography responds to the post pliocene tectonic deformation we apply different relief morphometric indices hypsometric integral topographic relief and topographic dissection measured for each differently sized moving window and we use different swath topographic profiles as well our analysis evidences differential morphological responses between distinct morphotectonic domains of the studied area led by the combination of earlier morphological background and late quaternary tectonic deformation stages of the region in addition in the context of a constant and uniform tectonic uplift the results define the general space and time relating pathways of the landscape geomorphic metrics this enables us to bring out the controls of the vertical scale of landscape on hypsometry exploring their mutual relationships finally we reconstruct the late quaternary morphotectonic evolution of the region defining the role played by the main tectonic alignments on the present geomorphic setting

paleoecological studies of a holocene lacustrine record from the kangerlussuaq sondre stromfjord region of west greenland abstract a lacustrine sediment record from the kangerlussuaq region west greenland has resulted in a pollen macrofossil and sediment stratigraphy that encompasses the last 5000 14 c yr deglaciation of the area and subsequent development of a nearby floodplain occurred before 5000 yr b p since that time eolian sand and silt deposition appear to have been continuous with a significant increase ca 1000 14 c yr b p pollen analysis shows little change in the character of the vegetation throughout the record fluctuations in herb pollen taxa indicate changes in the extent and development of eolian sand sheets the oldest pollen zone records relatively little pollen accumulation and low taxa diversity this is followed by a zone of high pollen accumulation presumably a phase of highest vegetation density from 4400 to 3400 14 c yr b p thereafter declining pollen accumulation rates reveal a gradual environmental deterioration macrofossil analyses record significant limnological changes with an early eutrophic phase followed by a masotrophic phase and a reversal to more eutrophic conditions in the final phase the preserved record illustrates the interactions of deglaciation eolian activity regional vegetation and limnological change

evidence for restricted ice extent during the last glacial maximum in the koryak mountains of chukotka far eastern russia field evidence in the koryak mountains lake mainitz region of far eastern russia supports three pleistocene glacial advances the early wisconsinan and pre wisconsinan glaciations are represented by broad lobate moraines extending as much as 30 km north of the koryak mountains field evidence demonstrates that the terminal lateral and medial moraines as well as meltwater channels dead ice topography kettles and outwash plains mark the extent of ice during the last glacial maximum lgm during which glaciers reached no more than 20 km beyond their present limits those emanating from the southern koryak mountains may have reached the bering sea numerical and relative dating techniques support these results and test the theoretical models of the lgm in western beringia erratics on moraines and glaciofluvial terraces common to all valleys at 13 13 8 m above river level yield 36 cl exposure ages ranging from 10 08 to 25 78 ka the koryak mountains lake mainitz record of glaciation is spatially and temporally consistent with the glaciation pattern across central beringia found in other terrestrial and marine records glacier growth in the koryak mountains was sustained by possible increased summer sea surface temperatures and precipitation in the northwest pacific region evidence from the northern koryak mountains lat 64 n long 177 e indicates that the extent of ice in western beringia was limited to mountain and valley glaciers during the lgm this fieldbased research contradicts m g grosswald s theoretical beringian ice sheet hypothesis

the recession of the inland ice margin during the holocene climatic optimum in the jakobshavn isfjord area of west greenland recent subsurface mapping of parts of the greenland inland ice margin in the region of jakobshavn isbrae indicates that the fjord system in the period of at least 2700 4700 calendar yr b p was more ice free than at present and that the front of the glacier was at least 15 km behind the present position the 14c datings of subfossils brought to the present ice margin fit with the climatic records from ice cores and confirm the favourable conditions for greenland s first settlers the sarqaq people who arrived in the region about 4000 yr ago to find hunting grounds 10 20 larger than the present

the russian component of an arctic ice sheet during the last glacial maximum abstract the extent of late weichselian glaciation in arctic russia remains a problem our model of 1995 1998 suggests a continuous and long lived ice sheet centered on the kara sea other reconstructions suggest a smaller and diachronous glaciation the vast majority of dates support the model of restricted glaciation we show that these dates are inconsistent with the geologic record of ice flow across the kara barents divide with second order glacial geology of kola peninsula and with evidence for glacial surges they are also inconsistent with late weichselian climate of the arctic with eurasian continental paleohydrology including meltwater drainage systems cataclysmic megafloods major transgressions of the caspian sea and with the entire paleogeographic context of northern eurasia we believe that due to impeded ventilation of the pleistocene arctic ocean these dates are often too old and that recycling and contamination of the samples would also contribute to the dating errors destructive impacts of late glacial ice sheet surges and megafloods upon the arctic glacial sequences would also aggravate the situation by ignoring the dates until these problems are addressed we find that the field evidence supports continuous glaciation of arctic russia at the lgm and that the resulting ice sheet was part of an arctic ice sheet that included an ice shelf in the arctic ocean and ice sheets in greenland and north america we present 3 d reconstructions of the arctic ice sheet and with an enlarged antarctic ice sheet we show that the ice volume is equivalent to an lgm sea level that was 130 135 m lower than at present the reconstructions depict the arctic ice sheet before and after massive thawing of the bed that allows partial gravitational collapse of the overlying ice with a minimal change in ice volume

relative size of fluvial and glaciated valleys in central idaho quantitative comparisons of the morphometry of glaciated and fluvial valleys in central idaho were used to investigate the differences in valley relief and width in otherwise similar geologic and geomorphic settings the local relief width and cross sectional area of valleys were measured using gis software to extract information from usgs digital elevation models hillslope gradients were also measured using gis software power law relationships for local valley relief width and cross sectional area as a function of drainage area were developed local valley relief in glaciated valleys relates to drainage area with a power law exponent similar to fluvial valleys but glaciated valleys are deeper for a given drainage area local valley width in glaciated valleys is greater than in fluvial valleys but the exponent of the power law relationship to drainage area is similar in both valley types local valley cross sectional area in glaciated valleys increases with drainage area with a power law exponent similar to fluvial valleys however glacial valleys have roughly 80 greater cross sectional area steep valley walls in glaciated basins increase the potential for bedrock landsliding relative to fluvial basins both the olympic mountains of washington and valleys in central idaho show relationships in which glaciated valleys are up to 30 deeper than fluvial valleys despite differences in lithology tectonic setting and climate

frost weathering versus glacial grinding in the micromorphology of quartz sand grains processes and geological implications abstract micromorphology of quartz sand grains is used to reconstruct processes occurring in the glacial environment and to distinguish the latter from other environments two processes dominate in the glacial environment i e crushing and abrasion or a combination thereof their effect is a wide range of microstructures on the surface of quartz grains e g chattermarks conchoidal fractures and multiple grooves however the periglacial environment also effectively modifies the surface of quartz grains the active layer of permafrost is considered to have a significantly higher contribution to the formation of crushed grains and the number of microstructures resulting from mechanical destruction e g breakage blocks or conchoidal fractures as compared to deposits which are not affected by freeze thaw cycles however only a few microstructures are found in both environments at the same time there are several processes in subglacial environments related to freeze thaw cycles e g regelation congelation basal adfreezing and glaciohydraulic supercooling most likely therefore the role of the glacial environment in the destruction of quartz grains has been misinterpreted and consequently the conclusions regarding environmental processes drawn on the basis of the number of crushed grains and edge to edge contacts are erroneous

towards radiocarbon dating of ice cores a recently developed dating method for glacier ice based on the analysis of radiocarbon in carbonaceous aerosol particles is thoroughly investigated we discuss the potential of this method to achieve a reliable dating using examples from a mid and a low latitude ice core two series of samples from colle gnifetti 4450 m a s l swiss alps and nevado illimani 6300 m a s l bolivian andes demonstrate that the 14c ages deduced from the water insoluble organic carbon fraction represent the age of the ice sample sizes ranged between 7 and 100 g carbon for validation we compare our results with those from independent dating this new method is thought to have major implications for dating non polar ice cores in the future as it provides complementary age information for time periods not accessible with common dating techniques

long range transport of giant aeolian quartz grains linkage with discrete sedimentary sources and implications for protective particle transfer abstract several articles have documented the presence of large particles 62 5 m that have been transported great distances 1000 km through the atmosphere at present we do not understand the mechanisms that lead to mineral grains being carried aloft far beyond the limits imposed by conventional gravitational settling models typically marine geologists refer to ice rafting and or advective transport by ocean currents as the dominant transport processes that deliver large mineral grains to deep sea sediments textural analyses of giant quartz grains from six sedimentary deposition events collected from various sources including a single site in the north pacific ocean and sites in the british isles and france strongly support the idea that in each case all of the grains were initially eroded from a discrete sediment type and often a discrete point source and subsequently transported via the atmosphere to our sampling sites up to 10 000 km away these findings suggest that at least at times erosional events fuelling long distance atmospheric transport are exceedingly specific and operate upon geologically distinctive assemblages and are able to effect long distance transfer of large grains with no grain to grain collisions this work also suggests that atmospheric transport should be included as a possible means of delivery for significant quantities of giant sedimentary particles to remote marine sites such as the lord howe rise

characterisation of two fluvio lacustrine loessoid deposits on the island of gran canaria canary islands abstract the canary islands are close to the largest desert in the world the sahara and as a result the influence of air transported dust in the area is of great significance the present analysis consists of a study of two deposits in the ne and nw respectively of the island of gran canaria considered as fluvio lacustrine loessoids they exhibit the characteristics of aeolian deposits re worked by fluvial processes at the mouth of gullies and later edaphized in the nw profile galdar formed from 400 ka to present there are four different levels with abundant manganese stains over each and separated by dense calcrete laminations this sequence may be associated with cyclical processes of deposits in humid conditions and drying mn mobility plus the formation of arid soil carbonate precipitation the formation of the galdar profile took place between the upper pliocene and the upper pleistocene holocene the ne profile jinamar reveals a similar cyclic profile the jinamar fluvio loess deposit was formed between the upper pliocene and the upper pleistocene 1 96 0 1 ma the high percentage of the silt fraction 60 90 and the high percentage of quartz a mineral which is totally imported from the sahara desert are the main arguments in favour of the definition of these loess like deposits

environmental discrimination based on quartz grain surface textures a statistical investigation the relative abundance of thirty two surface features identified on the surfaces of quartz sand grains from eight coded samples was noted independently by five scanning electron microscopists these data reduced to binary form were the subject of canonical variate analyses which discriminated clearly between all samples thirteen variables were important in distinguishing between the eight samples this indicates that there are no single key surface features which on their own would allow rapid environmental discrimination the contention that a multiplicity of surface features should be recorded for the purpose of environmental discrimination is therefore upheld operator variance although considerable in the recognition of individual surface features is negligible in discrimination of samples based on binary data the sem technique of analysis of quartz grain surface textures is a reliable and statistically valid means of discriminating between samples from different environments

gas records from the west greenland ice margin covering the last glacial termination a horizontal ice core abstract certain sites along ice sheet margins provide an easily accessible and almost unlimited supply of ancient ice at the surface measurements of gases in trapped air from ice outcropping at pakitsoq west greenland demonstrate that ancient air is mostly well preserved no alterations in 18 o atm and 15 n of n 2 are apparent and alterations in methane are found in only a few ice sections using measurements of these gases we have unambiguously identified a stratigraphic section containing ice from the end of last glacial period as well as bolling allerod younger dryas and preboreal intervals extensive sections of ice from the holocene and most ages within the last glacial period are probably also present very accurate dating has been possible in the ice section containing the younger dryas preboreal abrupt climate transition signal the ice at pakitsoq is folded and non uniformly thinned with many cross cutting bands of bubble free ice and dust the cross cutting features are associated with anomalies in both the gas and the ice records with careful sampling to avoid these the ice at pakitsoq is suitable for recovery of large volume samples of the ancient atmosphere for analysis of trace constituents such as 14 ch 4

comparison between greenland ice margin an ice core oxygen 18 records old ice for paleoenvironmental studies retrieved by deep core drilling in the central regions of the big ice sheets can also be retrieved from the ice sheet margins the d18o content of the surface ice was studied at 15 different greenland ice margin locations at some locations two or more records were obtained along closely spaced parallel sampling profiles showing good reproducibility of the records we present ice margin d18o records reaching back into the pleistocene many of the characteristic d18o variations known from greenland deep ice cores can be recognized allowing an approximate time scale to be established along the ice margin records a flow line model is used to determine the location on the ice sheet where the margin ice was originally deposited as snow the pleistocene holocene d18o change at the deposition sites is determined by comparing the d18o values in the ice margin record to the present 18o values of the surface snow at the deposition sites on the northern slope of the greenland ice sheet the pleistocene holocene d18o change is c 10 per mil in contrast to a change of 6 7 per mil at locations near the central ice divide this is in accordance with deep ice core results we conclude that d18o records measured on ice from the greenland ice sheet margin provide useful information about past climate and dynamics of the ice sheet and thus are important and cheap supplements to deep ice core records

multivariate geostatistical modeling of the spatial sediment distribution in a large scale drainage basin upper rhone switzerland abstract there is a notable discrepancy between detailed sediment budget studies in small headwater catchments 103 km2 in higher order catchments applying modeling and or remote sensing based approaches for major sediment storage delineation to bridge the gap between these scales we compiled an inventory of sediment and bedrock coverage from field mapping remote sensing analysis and published data for five key sites in the upper rhone basin val d illiez val de la liene turtmanntal lotschental goms 360 3 km2 equivalent to 6 7 of the upper rhone basin this inventory was used as training and testing data for the classification of sediment and bedrock cover from a digital elevation model 2 2 m ground resolution and landsat imagery we derived 22 parameters characterizing local morphometry topography and position contributing area and climatic and biotic factors on different spatial scales which were used as inputs for different statistical models logistic regression principal component logistic regression generalized additive model best prediction results with an excellent performance mean auroc 0 8721 0 0012 and both a high spatial and non spatial transferability were achieved applying a generalized additive model since the model has a high thematic consistency the independent input variables chosen based on their geomorphic relevance are suitable to model the spatial distribution of sediment our high resolution classification shows that 53 5 21 7 of the upper rhone basin are covered with sediment these are by no means evenly distributed small headwaters

implications for deglaciation chronology from new ams age determinations in central west greenland abstract new evidence has been obtained for the age of the umivit keglen and orkendalen moraine systems close to the present ice sheet margin in central west greenland the umivit keglen moraine system is dated at 7500 to 6500 14 c yr b p which is older than the previously assumed date of 7300 to 6000 14 c yr b p the orkendalen system is now dated at 6200 to 5600 14 c yr b p against earlier estimates of 300 to 700 14 c yr b p the new age is based on ams radiocarbon dated organic material within depressions between morainic ridges belonging to the orkendalen system a major implication of the new age is that ice margin positions prevailed for about 6000 years behind the present ice sheet margin the retreat behind the present margin could be substantial and in the light of deglaciation rates prior to the orkendalen phase may be ca 10 s of kilometers rather than kilometers circumstantial evidence is found for the retreat of the ice sheet margin behind its present position during the holocene climatic optimum the results placed into a time frame of deglaciation since the last glacial maximum enable comparison with greenland ice sheet models and ice core records

hypsometric analysis to identify spatially variable glacial erosion 1 relatively little research has been undertaken on the use of digital elevation models to recognize the spatially variable glacial imprint of a landscape using theoretical topographies and a landscape evolution model we investigate to what extent the hypsometric analysis of digital elevation models may be used to recognize the glacial signature of mountain ranges a new morphometric parameter which we term the hypsokyrtome from the greek ipsos elevation kyrtoma curvature is derived from the gradient of the hypsometric curve the efficacy of the hypsometric integral and hypsokyrtome is tested through the study of the ben ohau range new zealand whose glacial imprint has been described previously with a numerical model we further test the geomorphic parameters in describing the morphologies of regions subject to diverse climatic and tectonic conditions the hypsokyrtome is highly sensitive to glacial erosion and the maps produced provide insights into the spatial distribution of glacial erosion we use srtm data and focus on two alternative geomorphic settings the european alps and the apennines the former has been affected by both fluvial and glacial erosion while the latter mainly exhibits a fluvially dominated morphology the correlation between elevations with increased glacial erosion and last glacial maximum lgm equilibrium line altitudes elas suggests the prevalence of a glacial buzz saw in the alps indicating that climate may put a limit on alpine topography

hillslope to valley transition morphology new opportunities from high resolution dtms abstract the search for the optimal spatial scale for observing landforms to understand physical processes is a fundamental issue in geomorphology topographic attributes derived from digital terrain models dtms such as slope curvature and drainage area provide a basis for topographic analyses the slope area relationship has been used to distinguish diffusive hillslope from linear valley processes and to infer dominant sediment transport processes in addition curvature is also useful in distinguishing the dominant landform process recent topographic survey techniques such as lidar have permitted detailed topographic analysis by providing high quality dtms this study uses lidar derived dtms with a spatial scale between 1 and 30 m in order to find the optimal scale for observation of dominant landform processes in a headwater basin in the eastern italian alps where shallow landsliding and debris flows are dominant the analysis considered the scaling regimes of local slope versus drainage area the spatial distribution of curvature and field observations of channel head locations the results indicate that i hillslope to valley transitions in slope area diagrams become clearer as the dtm grid size decreases due to the better representation of hillslope morphology and the topographic signature of valley incision by debris flows and landslides is also best displayed with finer dtms ii regarding the channel head distribution in the slope area diagrams the scaling regimes of local slope versus drainage area obtained with grid sizes of 1 3 and 5 m are more consistent with field data and iii the use of thresholds of standard deviation of curvature particularly at the finest grid size were proven as a useful and objective methodology for recognizing hollows and related channel heads

a simple analytical model for pressure on obstacles induced by snow avalanches the forces snow avalanches are able to exert on protection dams or buildings are of crucial interest in order to improve avalanche mitigation measures and to quantify the mechanical vulnerability of structures likely to be damaged by snow avalanches this paper presents an analytical model that is able to calculate these forces taking into account dead zone mechanisms first we present a 2 d analytical hydrodynamic model describing the forces on a wall overflown by gravity driven flows down an inclined plane second the 2 d model is successfully validated on discrete simulations of granular flows third we provide ingredients to extend the 2 d model to flows of dry and cold snow fourth we propose a simplified 3 d analytical model taking into account lateral fluxes finally the predictions from the simplified 3 d analytical model are successfully compared to recent measurements on two full scale snow avalanches released at the lautaret site in france

the evolution of saharan dust input on lanzarote canary islands influenced by human activity in the northwest sahara during the early holocene an overall holocene increase of saharan dust input to the canary islands and to the north canary basin is accompanied by a strong coarsening of saharan dust in loess like sediments deposited on lanzarote from 7 8 ka no similar coarsening events are indicated in investigations of the sedimentological record for the last 180 ka a period showing several dramatic climate changes therefore a mobilisation of holocene dust by anthropogenic activity in the northwest sahara east of the canary islands is assumed although scarce archaeological data from the coastal area of that region does not point to strong anthropogenic activity during the early holocene a high density of unexplored archaeological remains is reported from the coastal hinterlands in the western sahara thus the hypothesis of early anthropogenic activity cannot be excluded

loess in italy genesis characteristics and occurrence abstract there is currently a renewed interest in loess genesis and occurrence in italy well known loess profiles in northern italy have been re examined and previously unknown loess deposits in central and southern italy have been reported this work combines a meta analysis of published data with new data presented here for the first time to provide the state of the art on the spatial distribution characteristics genesis and deposition ages of loess in italy a database of 98 soil horizons from 91 soil profiles was created and made available it stores information on soils formed from loess or containing layers that show admixture of loess soil data include the source of information the topographic geomorphological and geological setting kind of parent material and land use main soil horizon properties as described in the field soil classification particle size distribution and chemical data loess is reported from almost all regions of italy it is generally pedogenized throughout the entire loess body and forms the parent material of deep and complex soil profiles the thickness of the loess deposits varies from a few decimeters to a few meters pedogenesis and local reworking partially change the original loess characteristics in this study we propose a set of parameters that help recognizing loess in soils particle size distribution and sorting geomorphological setting pedostratigraphic position shape of the grains under optical and scanning electron microscope sem and soil micromorphological characteristics the ages of the loess deposits range between 70 ka bp and 18 ka bp there are also a number of samples that have been dated to the holocene the meta analysis suggests that climate is not the only driver of loess deposition in italy geomorphological instability and human disturbance as well as the influence of saharan dust most likely played major roles too this study demonstrates that loess is much more widespread in italy than previously estimated yet further research on the spatial and temporal distribution of loess deposition across the mediterranean region is needed to better understand its genesis sources and trajectories periods of enhanced loess formation and the role of loess deposits in ecosystem functioning and resilience

foraminiferal evidence of major environmental changes driven by the sun climate coupling in the western portuguese coast 14th century to present abstract new paleoclimatic data from the casa branca salt marsh in the southwest coast of portugal are compared with records previously published on the northwest coast caminha salt marsh to offer a more comprehensive overview of the environmental evolution of the west iberian margin over the last six centuries these reconstructions are based on the foraminiferal records of two dated sediment cores retrieved from the high marsh settings and supported by geochemical sedimentological data both marshes were originally formed in the ad 1300s between the medieval climatic anomaly mca and the little ice age lia highlighting a major episode of increased sediment supply in lower estuaries linked to climate driven changes in continental runoff afterwards the two marshes evolved under different climatic regimes as reflected by their foraminiferal assemblages the environmental conditions are characterized by higher salinity in casa branca southwest with jadammina macrescens and trochammina inflata as dominant species than in caminha northwest where haplophragmoides spp dominates we suggest that a long term trend of a net gain in evapotranspiration at casa branca inducing a higher marsh salinity baseline may explain this microfaunal contrast trochammina inflata seems to be a good indicator of drier periods in the studied area connected to key events of aeolian large dust input to the southwest coast of portugal the influence of the most important climate drivers was assessed namely external solar and internal north atlantic oscillation nao forcings spectral and wavelet transform coherence analyses were used to detect solar footprints on foraminiferal and climate related time series a main significant quasi periodicity was identified within the range of the secular gleissberg cycle of solar activity modulating the annual nao and regional spring summer simulated temperatures after ad 1700 this stronger solar climate coupling may be related to the known upward secular trend in the total solar irradiance after the maunder minimum

slope process change and colluvium deposition in swaziland an sem analysis electron microscope analysis of sixty samples taken from six colluvium sites in swaziland has shown that the quartz grains exhibit marked edge abrasion in the uppermost beds of exposures this edge abrasion is lacking in the lower beds in all sections examined and indicates slope process change during colluvium deposition a model of slope evolution is provided in which slope erosion progressively brings about more channelling and causes greater surface roughness because of the exhumation of more core stones and differentially weathered rock this roughness causes increased edge abrasion

assessing glacial modification of bedrock valleys using a novel approach abstract analysis of valley cross sections is an established technique for evaluating the effects of glacial erosion here we present a semiautomated approach for assessing glacial modification of bedrock valleys by quantifying morphological variability in valley cross sections extracted in bulk from digital elevation models dems this method can be tailored to derive cross sections of user specified width and spacing and can generate cross sectional data sets of multiple orders of magnitude we demonstrate the technique by extracting 27 000 cross sections from the sierra nevada california and computing measures of valley morphology including a form ratio a quadratic curve fit and a power law curve fit for each cross section in addition we introduce a novel metric the v index which is calculated by comparing valley cross sectional area to that of an ideal v shaped cross section and is thus an expression of the deviation from an ideal v shaped form statistical comparisons of the different measures suggest that the v index is a robust alternative to traditional morphological measures because it can accommodate irregular valley cross sections and discriminate between glacial and nonglacial forms we document the distribution of valley forms throughout the sierra nevada using the v index to identify range scale patterns in cross sectional morphology and to investigate the role of lithology on glacial modification of bedrock valleys

scaling regimes of local slope versus contributing area in digital elevation models four scaling regimes are observed in digital elevation models dems when the average local slope is calculated for pixels grouped according to the values of the contributing area threshold criteria proposed by various researchers to identify the extent of the channel network are examined relative to the slope area scaling diagram the scaling response observed in dems is reproduced with a landscape evolution and channel network growth model originally developed by willgoose et al 1989 the threshold criterion proposed in this model is a useful tool to separate two different slope area scaling regimes observed in dem data

latest pleistocene alpine glacier advances in the sawtooth mountains idaho usa reflections of midlatitude moisture transport at the close of the last glaciation mountain glaciers in the sawtooth mountains responded strongly to reinvigorated atmospheric moisture transport following the last ice sheet maximum the glaciers constructed an extensive moraine belt in the southeastern sawtooth mountains allowing determination of a detailed radiocarbon chronology from lake and marsh cores moraine morphometry and soil data indicate construction of seven to nine moraines in each of four valleys during two main late pleistocene ice advances a basal radiocarbon date from marsh cores in the alturas valley documents that the maximum advance during marine oxygen isotope stage 2 occurred shortly before ca 16 900 calibrated cal yr b p minimum limiting dates on glacial lacustrine sediment in lake and marsh cores from three valleys clustered around 13 950 cal yr b p document the maintenance or reestablishment of extensive ice volume during early late glacial time the ca 16 900 cal yr b p advance postdates the last ice sheet maximum by 4000 yr and is broadly correlative with maximum advances of the north yellowstone outlet glacier and the puget lobe of the cordilleran ice sheet and a near maximum advance of wallowa mountain glaciers these synchronous advances indicate response of a variety of ice systems to reinvigorated moisture transport following the ice sheet maximum as does the subsequent sawtooth advance during early late glacial time together these responses indicate strong sensitivity of certain ice systems to moisture delivery fluctuations

extensive early and middle wisconsin glaciation on the western olympic peninsula washington and the variability of pacific moisture delivery to the northwestern united states abstract large glaciers descended western valleys of the olympic mountains six times during the last wisconsin glaciation terminating in the pacific coastal lowlands the glaciers constructed extensive landforms and thick stratigraphic sequences which commonly contain wood and other organic detritus the organic material coupled with stratigraphic data provides a detailed radiocarbon chronology of late pleistocene ice margin fluctuations the early wisconsin lyman rapids advance which terminated prior to ca 54 000 14c yr b p represented the most extensive ice cover subsequent glacier expansions included the hoh oxbow 1 advance which commenced between ca 42 000 and 35 000 14c yr b p the hoh oxbow 2 advance ca 30 800 to 26 300 14c yr b p the hoh oxbow 3 advance ca 22 000 19 300 14c yr b p the twin creeks 1 advance 19 100 18 300 14c yr b p and the subsequent undated twin creeks 2 advance the hoh oxbow 2 advance represents the greatest ice extent of the last 50 000 yr with the glacier extending 22 km further downvalley than during the twin creeks 1 advance which is correlative with the global last glacial maximum local pollen data indicate intensified summer cooling during successive stadial events because ice extent was diminished during colder stadial events precipitation not summer temperature influenced the magnitude of glaciation most strongly regional aridity independently documented by extensive pollen evidence limited ice extent during the last glacial maximum the timing of glacier advances suggests causal links with north atlantic bond cycles and heinrich events

the glacially overdeepened trough of the salzach valley austria bedrock geometry and sedimentary fill of a major alpine subglacial basin abstract overdeepened valleys are unambiguous features of glacially sculpted landscapes they result from erosion at the bed of the glacier and their size and shape is determined by ice dynamics and the characteristics of the underlying bedrock major overdeepened valleys representing vertical bedrock erosion of several hundreds of meters are characteristic features of many trunk valleys in the formerly glaciated parts of the alpine mountain belt the thick sedimentary fill usually hinders attempts to unravel bedrock geometry formation history and fill characteristics based on reflection seismic data and core logs from multiple deep drillings we construct a detailed bedrock model of the lower salzach valley trough one of the largest overdeepened valleys in the european alps the analysed overdeepened structure characterized by a strongly undulating topography two reaches of enhanced erosion can be identified and are suggested to be related to variations in bedrock erodibility and a triple glacier confluence the sedimentary fill shows clear characteristics of rapid infilling and subaqueous fan delta deposits indicate a strong influence of tributary streams associated surface lowering of the valley floor had a major impact on tributary stream incision but also on the available ice accumulation area at subsequent glaciations the extent to which fills of earlier glaciations have been preserved from erosion during the last glacial maximum remains ambiguous and demands further exploration to our knowledge the presented bedrock model is one of the best defined of any major overdeepened trunk valley

ice core record of dust sources in the western united states over the last 300 years over the past 5000 years amplified dust generation and deposition in the american west has been linked to human activity in recent decades intensified rates of agriculture and livestock grazing have been correlated with greater dust production detected on seasonal to annual timescales the combination of land use intensification and climate change i e increased drought frequency in north america highlights the importance of characterizing the sources of dust both before and after the influence of anthropogenic activity we apply high precision geochemical and isotopic sr and nd isotopes techniques to an ice core from the upper fremont glacier wyoming usa to produce the first glacial dataset from the american west our sr nd isotopic composition data indicates the evolving dust provenance to the upper fremont glacier ufg from a long range transport of mineral dust to a local source this increasing input of dust from a local source is supported by a rise in average dust particle diameter combined with greater average dust concentration throughout the record the greater presence of dust particles smaller than 2 5 m in the most recent samples from ufg ice core record support existing satellite and sediment core data regarding the effects of anthropogenic activity upon dust sources and pathways in the american west although the sr nd isotope database in north america needs be expanded our results provide a survey of windborne dust through the past 270 years

the surface albedo of the greenland ice sheet satellite derived and in situ measurements in the sondre stromfjord area during the 1991 melt season the temporal and spatial variation in the surface albedo of the greenland ice sheet during the ablation season of 1991 is investigated the study focuses on an area east of sondre stromfjord measuring 200 km by 200 km and centred at 67 5 n 48 13 w the analysis is based on satellite radiance measurements carried out by the advanced very high resolution radiometer avhrr the broad band albedo is estimated from the albedos in channel 1 visible and channel 2 near infrared the results are calibrated with the surface albedo of sea and dry snow satellite derived albedos are compared with gimex ground measurements at three stations there is a high degree of consistency in temporal variation at two of the three stations large systematic differences are attributed to albedo variations on subpixel scale in the course of the ablation season four zones appear each parallel to the ice edge it is proposed that these are in order of increasing altitude i clean and dry ice ii ice with surface water iii superimposed ice and iv snow an extensive description of these zones is given on the basis of the situation on 25 july 1991 zones i iii and iv reveal fairly constant albedos 0 46 0 65 and 0 75 on average whereas zone ii is characterised by an albedo minimum 0 34 survey of the western margin of the greenland ice sheet up to 71 n shows that the zonation occurs between 66 and 70 n

soil abrasion and eolian dust production implications for iron partitioning and solubility 1 eolian dust is a source of iron for phytoplankton in many ocean areas and there are complex pathways of atmospheric processing from soil to ocean overlooked parts of the pathways are the impact of large 10 m grains including a role as proxies for the behavior of smaller grains and the effect of multiple cycles of uplift and abrasion in the dust source region partitioning readily released acid leachable and refractory and dissolution rates of iron were determined for an artificial dust produced by abrading an australian soil untreated soil abraded soil after production of the artificial dust and a natural australian eolian dust sample taken during a dust storm readily released iron is not created during abrasion and therefore the amount of readily released iron in a dust or dust derived soil depends on processing events since the dust or soil last experienced an abrasion event our study develops a method for the partitioning of iron within airborne dusts and appears to be the first to consider the effect of multiple uplift events on iron partitioning

the influence of rock mass strength on glacial valley cross profile morphometry a case study from the southern alps new zealand the erosional morphology in the vicinity of the main divide of the southern alps and fiordland new zealand appears to be a product of the interaction between alpine fault induced tectonic processes rock mass strength of the uplifted and eroded bedrock and the processes acting to denude the developing mountain landscape the magnitude of the effects of glacial erosion on the landscape is directly controlled by the size and physical properties of the glaciers whilst the form of the trough is a direct consequence of the rock mass strength rms properties of the slope rock realistic models of development of the cross profile shape of glacial valleys must take into consideration the rms properties of the eroded substrate

glacial erosion evolution of river long profiles and the organization of process domains in mountain drainage basins of coastal british columbia 1 in glaciated british columbia canada quaternary climate changes are responsible for profound spatial reorganization of earth surface processes these changes have left a landscape characterized by topographic anisotropy associated with a hierarchy of glacial troughs the evolution of glaciated landscapes is examined by analyzing the structure of geomorphic process domains and channel long profiles to identify process domains we use channel surveys and gis analysis to construct slope area transects of the channel network this analysis reveals generalized process form disequilibrium with a mismatch between topographic signatures and currently active geomorphic process domains at the landscape scale of source colluvial channels contributing area 1 km2 the glacial paraglacial signature commonly overrides that produced by contemporary debris flows along the axis of former ice flows relict glacial cirques introduce a hanging fluvial domain at contributing areas as small as 8 10 2 km2 and produce complex channel long profiles similar to those observed for rivers responding to tectonic forcing slope area relations typical of unglaciated equilibrium environments do not apply here the concept of process domains appears to hold however some major glacially forced modifications in the alluvial colluvial transition are observed and the definition of a depositional colluvial subdomain is proposed comparison between field and gis measured slopes reveals that gis associated error is not uniform between process domains and that gis based plots do not successfully discriminate field based process domains the combination of glacial and post glacial fingerprints and the effects of ongoing earth surface processes generate a complex landscape whose glacial signatures may persist until the onset of the next ice age

northern mid latitude glaciation in the late amazonian period of mars criteria for the recognition of debris covered glacier and valley glacier landsystem deposits lobate debris aprons lda and lineated valley fill lvf have been known to characterize the mid latitude regions of mars since documented by viking their flow like character suggested that deposition of ice in talus pile pore space caused lubrication and flow during an earlier climatic regime a number of factors have remained uncertain however including the detailed structure and texture of lda lvf the relationships between them their direction of flow the origin and abundance of the lubricating agent and their exact mode of origin e g ice assisted rock creep ice rich landslides rock glaciers debris covered glaciers we use new high resolution stereo camera hrsc image and topography data in conjunction with a range of other post viking data sets and new insights provided by cold based terrestrial glacial analogs to assess the characteristics of lda lvf in the northern mid latitudes of mars we find evidence that the characteristics and flow patterns of the lda and lvf are most consistent with late amazonian debris covered glacial valley landsystems the broad distribution and integrated characteristics of the lda lvf systems suggest that earlier in the amazonian climatic conditions were such that significant snow and ice accumulated on mid latitude plateaus and in valleys producing integrated glacial landsystems the remnants of which are preserved today beneath residual sublimation till derived from adjacent valley walls atmospheric general circulation models suggest that these climatic conditions occurred when mars was at a spin axis obliquity of 35 and the atmosphere was relatively dusty glacial flow modeling under these conditions produces patterns similar to those documented in the lda lvf and sharad radar data suggests that significant amounts of ice remain sequestered below the sublimation lag today

terrigenous sedimentation processes along the continental margin off nw africa implications from grain size analysis of seabed sediments the terrigenous fraction of seabed sediments recovered along the north west african continental margin illustrates spatial variability in grain size attributed to different transport mechanisms three subpopulations are determined from the grain size analyses n 78 of the carbonate free silt fraction applying an end member modelling algorithm g j weltje 1997 the two coarsest endmembers are interpreted as representing aeolian dust and the fine grained end member is related to fluvial supply the end member model thus allows aeolian fallout to be distinguished from fluvial sourced mud in this area the relative contributions of the end members show distinct regional variations that can be related to different transport processes and pathways understanding present day sediment dispersal and mixing is important for a better understanding of older sedimentary records and palaeoclimate reconstructions in the region

a continuous record of holocene eolian activity in west greenland eolian landforms are widespread alongside proglacial valley sandurs in west greenland and comprise low relief sand sheets climbing dunes and upland loess sedimentary facies mainly reflect distance to outwash source zones and the influence of vegetation cover the sediments show stratification types typical for poorly to moderately vegetated sand sheets alternately laminated silt peat sequences and unstratified loess twenty five accelerator mass spectrometry 14c dates provide the basis for the chronostratigraphy of the inland eolian deposits 14c dates from interstratified sand sheets suggest that the bulk of eolian sands were deposited prior to 3400 cal yr b p and after 550 cal yr b p this two phase formation for the inland dunes most likely reflects local changes in proglacial floodplain development and meltwater rerouting associated with a significant recession of the greenland ice sheet during the mid holocene climate optimum subsequent floodplain regeneration and renewed sand sheet formation after 550 cal yr b p followed when the ice margin readvanced to its present position in contrast atmospheric deposition of regionally derived silt in upland peat mires has been continuous since at least 4750 cal yr b p silt influx data demonstrate a strongly episodic history of the intensity of eolian activity over the past five millennia which tentatively reflects alternating periods of winter aridity associated with the variable incursion of maritime air masses over the interior ice free areas of west greenland

organic matter content and quality in supraglacial debris across the ablation zone of the greenland ice sheet quantifying the biogeochemical cycling of carbon in glacial ecosystems is of great significance for regional and potentially global carbon flow estimations the concentration and quality of organic carbon oc is an important indicator of biogeochemical and physical processes that prevail in an ice sheet ecosystem here we determine the content and quality of oc in debris from the surface of the greenland ice sheet gris using microscopic chromatographic spectrophotometric and high temperature combustion techniques the total oc content in the debris increased with distance from the edge of the ice sheet from virtually zero to 6 dry weight at 50 km inland and there was a peak in the carbohydrate proportion and the microbial abundance at 6 km inland the highest galactose mannose arabinose xylose ratios indicating maximum autochthonous microbial production were found at 10 km inland we propose that three key processes influence the carbon cycling on the gris aeolian input of microbial inoculum and nutrients in situ biological c transformation and the wash away of supraglacial debris by meltwaters we show that all these processes have significant spatial variability while the total oc content of the debris on the ice sheet is probably controlled by the physical processes of wind transport and wash away by meltwater the microbial abundance and the quantity of the labile cell contained oc within the debris is likely to be driven by the balance between the wash away and the microbial productivity

long range transport of volcanic ash to the greenland ice sheet betzer et al 1 reported the surprising discovery of giant 75 m mineral particles transported more than 10 000 km from their source we have found volcanic ash containing glass shards as large as 300 m in a section of wisconsinian ice from the dye 3 core in greenland which is similarly unexpected and raises interesting questions concerning the long range aeolian transport of particulate matter as the volcanic ash correlates well with similar ash in deep sea sediment cores from the atlantic it also allows us to date the ice with some confidence

the greenland ice sheet margin a mine of ice for paleo environmental studies abstract stable isotope analysis of surface ice samples from three locations on the margin of the greenland ice sheet have provided 18 o records dating back into the wisconsinan the samples were collected in profiles transverse to the ice margin on a location about 40 km northeast of jakobshavn west greenland and at two locations in warming land north greenland the holocene wisconsinan transition as detected by a large aburpt shift was found between 470 and more than 850 m from the ice edge the magnitude of the shift was about 8 and 12 in the west and north greenland records respectively the west greenland record which is the more detailed documents that some variations in the wisconsinan are apparently preserved in the ice margin isotopic records by linking locations in the accumulation and ablation zones with the same observed value the surface ice of the ablation zone can be dated back to at least the wisconsinan holocene transition if the velocity of the ice motion is measured or estimated by ice flow modelling this means that dated records of ice constituents gas composition chemistry content of microparticles micro meteorites etc can be established by mining the easily accessible surface ice of the ablation zone

on the mathematical description of glaciated valley cross sections morphometric analyses of glaciated valleys typically involve attempts to fit empirical data from valley cross profiles to quadratic parabolic or power law equations with the choice of equation depending on the goal of the analysis in assessing the relative merits of these two types of equations some confusion has arisen because of apparent variations in coordinate system datums between studies which have made use of the power law equation however we show that this confusion relates to a simple mathematical error rather than any true difference in methodology of more significance however is the fact that in fitting a power law equation to observed profiles significant bias is introduced by the use of a logarithmic data transformation because of this implicit bias power law equation parameters are influenced most strongly by data points close in elevation to the centre of the valley and so failure to account for the depositional elements which frequently occur in these areas can lead to significant errors if the aim of the analysis is to characterize the form of the erosional profile

eolian input into the late ordovician postglacial soom shale south africa the soom shale member of the cedarberg formation south africa is a key early paleozoic lagerstatte that directly overlies glacigenic deposits of the late ordovician glacial maximum it was deposited on the gondwanan craton during deglacial transgression we show that it contains a substantial coarse silt to fine sand component that occurs in discrete laminae intimately associated with plankton derived organic material we interpret this component as loess sourced from glacially derived debris and blown into the sea either directly or across seasonal sea ice as happens today on the mcmurdo ice shelf antarctica falling through the water column this material likely stimulated production of phytoplankton which then sank as sediment loaded aggregates in marked sedimentary partitioning these silt and or organic laminae alternate with fine organic poor mud laminae that likely represent river derived nepheloid plumes and that sporadically thicken into centimeter scale mud turbidites sustained eolian input directly into the surface water may have been key to maintaining the high productivity of the soom sea and then via eutrophication and anoxia to the exceptional preservation of its biota

a novel radiocarbon dating technique applied to an ice core from the alps indicating late pleistocene ages ice cores retrieved from high altitude glaciers are important archives of past climatic and atmospheric conditions in midlatitude and tropical regions because of the specific flow behavior of ice their age depth relationship is nonlinear preventing the application of common dating methods such as annual layer counting in the deepest and oldest part here we present a new approach and technique allowing dating of any such ice core at arbitrary depth for the age range between 500 years b p and the late pleistocene this new complementary dating tool has great potential for numerous ice core related paleoclimate studies since it allows improvement and extension of existing and future chronologies using small to ultrasmall sample size 100 g carbon content 5 g accelerator mass spectrometry we take advantage of the ice included water insoluble organic carbon fraction of carbonaceous aerosols for radiocarbon 14c dating analysis and dating of the bottom ice of the colle gnifetti glacier swiss italian alps 45 55 50 n 7 52 33 e 4455 m asl has been successful in a first application and the results revealed the core to cover most of the holocene at the least with indication for late pleistocene ice present at the very bottom

quantitative analysis of land surface topography land surface topography significantly affects the processes of runoff and erosion a system which determines slope aspect and curvature in both the down slope and across slope directions is developed for an altitude matrix also the upslope drainage area and maximum drainage distance are determined for every point within the altitude matrix a fortran 66 program performs the analysis

carbonaceous particles reveal that late holocene dust causes the dark region in the western ablation zone of the greenland ice sheet a dark region in the western ablation zone of the greenland ice sheet is caused by outcropping ice layers that contain more dust than the surrounding brighter ice these higher amounts of dust were deposited in the accumulation zone of the ice sheet and travelled with the ice to the ablation zone to deduce the period and the causes of this higher dust deposition carbonaceous particles in ice samples from the dark region and from brighter reference ice were analysed and used for dating samples including ice from directly below the surface contain high amounts of modern organic carbon probably from microorganisms on the ice surface deeper samples reveal low amounts of carbonaceous particles which are originally deposited in the accumulation zone the amount of outcropping carbonaceous particles in the dark region seems significantly higher than in the reference ice one of the samples that contained material initially deposited in the accumulation zone was dated and revealed late holocene ages coinciding with a period of enhanced eolian activity in the nearby tundra therefore variable eolian activity during the holocene effected dust fluxes towards the ice and hence leads to albedo variations in the present ablation zone of the ice sheet

sem analysis of quartz sand grain surface textures indicates alluvial colluvial origin of the quaternary glacial boulder clays at huangshan yellow mountain east central china abstract geomorphic features and pleistocene deposits on huangshan have been attributed to glaciation recent reassessment questions this interpretation as part of the reassessment quartz sand grains from deposits identified as glacial boulder clays till composed of boulders in a clay or silt matrix were analyzed by scanning electron microscope for evidence of their sedimentary history surface textures found on the boulder clay grains were compared with those on grains with known sedimentary histories including glacial grus colluvial and alluvial grains the analysis shows that the grains lack typical glacial textures the surface textures present indicate a complex history nonuniformly weathered grain surfaces point to chemical weathering of the source rock this is supported by the deep weathering of the nonquartz clasts in the sand sized fraction as well as in boulders at the outcrops the close correspondence in surface texture frequencies with those of the alluvial grains indicates an alluvial component to the grains history the similarity with the colluvial grains and the outcrops structures suggest an alluvial colluvial origin for the deposits the history indicated by the surface textures agrees with the recent reassessment of the geomorphic features and points to warm climatic conditions in east central china for at least part of the pleistocene