tectonic control on 10 be derived erosion rates in the garhwal himalaya india erosion in the himalaya is responsible for one of the greatest mass redistributions on earth and has fueled models of feedback loops between climate and tectonics although the general trends of erosion across the himalaya are reasonably well known the relative importance of factors controlling erosion is less well constrained here we present 25 10 be derived catchment averaged erosion rates from the yamuna catchment in the garhwal himalaya northern india tributary erosion rates range between 0 1 and 0 5 mm yr 1 in the lesser himalaya and 1 and 2 mm yr 1 in the high himalaya despite uniform hillslope angles the erosion rate data correlate with catchment averaged values of 5 km radius relief channel steepness indices and specific stream power but to varying degrees of nonlinearity similar nonlinear relationships and coefficients of determination suggest that topographic steepness is the major control on the spatial variability of erosion and that twofold to threefold differences in annual runoff are of minor importance in this area instead the spatial distribution of erosion in the study area is consistent with a tectonic model in which the rock uplift pattern is largely controlled by the shortening rate and the geometry of the main himalayan thrust fault mht our data support a shallow dip of the mht underneath the lesser himalaya followed by a midcrustal ramp underneath the high himalaya as indicated by geophysical data finally analysis of sample results from larger main stem rivers indicates significant variability of 10 be derived erosion rates possibly related to nonproportional sediment supply from different tributaries and incomplete mixing in main stem channels

grain size dependent concentration of cosmogenic 10be and erosion dynamics in a landslide dominated himalayan watershed for documenting recent or late quaternary erosion rates at the scale of a small watershed or even an entire mountain range the use of in situ terrestrial cosmogenic nuclides tcn such as 10be in river sediments has become widespread over the last decade in mountainous settings however landslides may induce a two fold complication in the cosmogenic nuclide budget first they may episodically deliver large amounts of sediment with low tcn concentrations to the river channel second they may generate a grain size concentration dependence in these sediments however studies that have explored grain size dependence in landslide dominated areas have reached differing conclusions and the underlying mechanisms remain poorly understood the present study focuses on the khudi khola river basin a small drainage basin in the central himalayas the area is characterized by steep slopes heavy rainfall and high sediment production rates importantly the watershed contains a large area of active landsliding in situ 10be was analyzed in sediments of grain sizes ranging from 75 m to 4 cm collected from five locations upstream downstream and in the small tributaries which drain the landslides in all sampling locations including those situated upstream of the landslides the finest grains 75 250 m are two to four times more concentrated in 10be than the largest clasts 4 7 mm we developed a numerical slope model which includes a low level of background soil erosion and episodic denudation from large mass wasting events we then introduced a coarsening of average grain size with soil depth to the model our simulation shows that the data available for this valley are compatible with a scenario in which landslides deliver coarse grains to the channel that are less concentrated in tcn and have deeper provenance best fit estimates of the model parameters suggest recurrence times of 3000 to 9000 years for a major landslide on the same slope and mean long term landslide denudation rates of 1 7 to 4 7 mm yr 1 a negative correlation between tcn concentration and grain size is also observed directly upstream and 5 km downstream of the landsliding area suggesting that nearly all of the sediment carried by the river is derived from ancient landslides while almost no sediment is supplied by erosion of soil mantled slopes despite these complications apparent denudation rates directly derived from the tcn concentrations and from previously published data in the region are all on the same order of magnitude around 2 mm yr 1 however a factor of three variability remains between the different studies depending on the location the year of sampling and the analyzed grain size fraction thus although tcn derived average denudation rates provide a useful first order estimate even in fast eroding terrains dominated by landslides caution should be applied when using quantitative results in such settings

temporally and spatially uniform rates of erosion in the southern appalachian great smoky mountains we measured 1 0 be in fluvial sediment samples n 27 from eight great smoky mountain drainages 1 330 km 2 results suggest spatially homogeneous sediment generation on the 10 4 10 5 yr time scale and 100 km 2 spatial scale at 73 11 t km 2 yr 1 equivalent to 27 4 m m y of bedrock erosion this rate is consistent with rates derived from fission track long term sediment budget and sediment yield data all of which indicate that the great smoky mountains and the southern appalachians eroded during the mesozoic and cenozoic at 30 m m y in contrast unroofing rates during the paleozoic orogenic events that formed the appalachian mountains were higher 10 2 m m y erosion rates decreased after termination of tectonically driven uplift enabling the survival of this ancient mountain belt with its deep crustal root as an isostatically maintained feature in the contemporary landscape

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

southeast greenland high accumulation rates derived from firn cores and ground penetrating radar despite containing only 14 of the greenland ice sheet by area the southeastern sector has the highest accumulation rates and hence receives 30 of the total snow accumulation we present accumulation rates obtained during our 2010 arctic circle traverse derived from three 50 m firn cores dated using geochemical analysis we tracked continuous internal reflection horizons between the firn cores using a 400 mhz ground penetrating radar gpr gpr data combined with depth age scales from the firn cores provide accumulation rates along a 70 km transect we followed an elevation gradient from 2350 to 1830m to understand how progressive surface melt may affect the ability to chemically date the firn cores and trace the internal layers with gpr from the firn cores we find a 52 0 43 m w e a 1 increase in average snow accumulation and greater interannual variability at the lower site than the upper site the gpr profiling reveals that accumulation rates are influenced by topographic undulations on the surface with up to 23 variability over 7 km these measurements confirm the presence of high accumulation rates in the southeast as predicted by the calibrated regional climate model polar mm5

hybrid inventory gravimetry and altimetry higa mass balance product for greenland and the canadian arctic abstract we present a novel inversion algorithm that generates a mass balance field that is simultaneously consistent with independent observations of glacier inventory derived from optical imagery cryosphere attributed mass trends derived from satellite gravimetry and ice surface elevation trends derived from airborne and satellite altimetry we use this algorithm to assess mass balance across greenland and the canadian arctic over the sep 2003 to oct 2009 period at 26 km resolution we evaluate local algorithm inferred mass balance against forty in situ point observations this evaluation yields an rmse of 0 15 mwe a and highlights a paucity of in situ observations from regions of high dynamic mass loss and peripheral glaciers we assess mass losses of 212 67 gt a to the greenland ice sheet proper 38 11 gt a to peripheral glaciers in greenland and 42 11 gt a to glaciers in the canadian arctic these magnitudes of mass loss are dependent on the gravimetry derived spherical harmonic mass trend we invert we spatially partition the transient glacier continuity equation by differencing algorithm inferred mass balance from modeled surface mass balance in order to solve the horizontal divergence of ice flux as a residual this residual ice dynamic field infers flux divergence or submergent flow in the ice sheet accumulation area and at tidewater margins and flux convergence or emergent flow in land terminating ablation areas which is consistent with continuum mechanics theory

accumulation over the greenland ice sheet from historical and recent records water accumulation defined as precipitation minus evaporation was estimated over all of greenland as part of a program to understand changes in ice sheet mass and elevation over 360 historical and recent point accumulation estimates on the greenland ice sheet were evaluated and 276 estimates that were judged to be high quality were used to develop the accumulation map the data set includes 99 points developed as part of four investigations of the past 5 15 years these are judged to have the greatest accuracy using kriging the average accumulation over greenland is estimated to be 30 g cm 2 yr 1 for the interior part of the ice sheet above 1800 m elevation where most of the data were acquired the average accumulation is also estimated to be 30 g cm 2 yr 1 there are still many areas on the ice sheet including northwest southeast and southern greenland where accumulation is highly uncertain exceeding the mean ice sheet uncertainty at a point of 20 25 in these regions further sampling will be required to reduce uncertainty in both regional and ice sheet wide accumulation

decadal scale sensitivity of northeast greenland ice flow to errors in surface mass balance using issm the behavior of the greenland ice sheet which is considered a major contributor to sea level changes is best understood on century and longer time scales however on decadal time scales its response is less predictable due to the difficulty of modeling surface climate as well as incomplete understanding of the dynamic processes responsible for ice flow therefore it is imperative to understand how modeling advancements such as increased spatial resolution or more comprehensive ice flow equations might improve projections of ice sheet response to climatic trends here we examine how a finely resolved climate forcing influences a high resolution ice stream model that considers longitudinal stresses we simulate ice flow using a two dimensional shelfy stream approximation implemented within the ice sheet system model issm and use uncertainty quantification tools embedded within the model to calculate the sensitivity of ice flow within the northeast greenland ice stream to errors in surface mass balance smb forcing our results suggest that the model tends to smooth ice velocities even when forced with extreme errors in smb indeed errors propagate linearly through the model resulting in discharge uncertainty of 16 or 1 9 gt yr we find that mass flux is most sensitive to local errors but is also affected by errors hundreds of kilometers away thus an accurate smb map of the entire basin is critical for realistic simulation furthermore sensitivity analyses indicate that smb forcing needs to be provided at a resolution of at least 40 km

greenland ice sheet mass balance reconstruction part i net snow accumulation 1600 2009 ice core data are combined with regional atmospheric climate model version 2 racmo2 output 1958 2010 to develop a reconstruction of greenland ice sheet net snow accumulation rate at g spanning the years 1600 2009 regression parameters from regional climate model rcm output regressed on 86 ice cores are used with available cores in a given year resulting in the reconstructed values each core site s residual variance is used to inversely weight the cores respective contributions the interannual amplitude of the reconstructed accumulation rate is damped by the regressions and is thus calibrated to match that of the rcm data uncertainty and significance of changes is measured using statistical models a 12 or 86 gt yr 21 increase in ice sheet accumulation rate is found from the end of the little ice age in 1840 to the last decade of the reconstruction this 1840 1996 trend is 30 higher than that of 1600 2009 suggesting an accelerating accumulation rate the correlation of at g with the average surface air temperature in the northern hemisphere satnht remains positive through time while the correlation of at g with local near surface air temperatures or north atlantic sea surface temperatures is inconsistent suggestinga hemispheric scale climateconnection an annualsensitivityof at g to satnhtof 6 8 k 21 or 51 gt k 21 is found the reconstuction at g correlates consistently highly with the north atlantic oscillation index however at the 11 yr time scale the sign of this correlation flips four times in the 1870 2005 period

deciphering the driving forces of erosion rates on millennial to million year timescales in glacially impacted landscapes an example from the western alps in many regions tectonic uplift is the main driver of erosion over million year myr timescales but climate changes can markedly affect the link between tectonics and erosion causing transient variations in erosion rates here we study the driving forces of millennial to myr scale erosion rates in the french western alps as estimated from in situ produced cosmogenic 10be and a newly developed approach integrating detrital and bedrock apatite fission track thermochronology millennial erosion rates from 10be analyses vary between 0 27 and 1 33 m kyr similar to rates measured in adjacent areas of the alps significant positive correlations of millennial erosion rates with geomorphic measures in particular with the lgm ice thickness reveal a strong transient morphological and erosional perturbation caused by repeated quaternary glaciations the perturbation appears independent of myr scale uplift and erosion gradients with the effect that millennial erosion rates exceed myr scale erosion rates only in the internal alps where the latter are low 0 4 km myr these areas moreover exhibit channels that clearly plot above a general linear positive relation between myr scale erosion rates and normalized steepness index glacial erosion acts irrespective of rock uplift and thus not only leads to an overall increase in erosion rates but also regulates landscape morphology and erosion rates in regions with considerable spatial gradients in myr scale tectonic uplift our study demonstrates that climate change e g through occurrence of major glaciations can markedly perturb landscape morphology and related millennial erosion rate patterns even in regions where myr scale erosion rates are dominantly controlled by tectonics

climatic signals in multiple highly resolved stable isotope records from greenland abstract twenty ice cores drilled in medium to high accumulation areas of the greenland ice sheet have been used to extract seasonally resolved stable isotope records relationships between the seasonal stable isotope data and greenland and icelandic temperatures as well as atmospheric flow are investigated for the past 150 200 years the winter season stable isotope data are found to be influenced by the north atlantic oscillation nao and very closely related to sw greenland temperatures the linear correlation between the first principal component of the winter season stable isotope data and greenland winter temperatures is 0 71 for seasonally resolved data and 0 83 for decadally filtered data the summer season stable isotope data display higher correlations with stykkisholmur summer temperatures and north atlantic sst conditions than with sw greenland temperatures the linear correlation between stykkisholmur summer temperatures and the first principal component of the summer season stable isotope data is 0 56 increasing to 0 66 for decadally filtered data winter season stable isotope data from ice core records that reach more than 1400 years back in time suggest that the warm period that began in the 1920s raised southern greenland temperatures to the same level as those that prevailed during the warmest intervals of the medieval warm period some 900 1300 years ago this observation is supported by a southern greenland ice core borehole temperature inversion as greenland borehole temperature inversions are found to correspond better with winter stable isotope data than with summer or annual average stable isotope data it is suggested that a strong local greenland temperature signal can be extracted from the winter stable isotope data even on centennial to millennial time scales

reconstructing climate variability from greenland ice sheet accumulation an era40 study 1 re analysis data covering the period 1958 2001 are used to investigate the relationship between regional inter annual snow accumulation variability over the greenland ice sheet gris and large scale circulation patterns cyclone frequency and strength four regions of the gris have been identified that are highly independent with respect to accumulation variability accumulation indices of three of these regions are associated with distinct large scale circulation patterns central western gris reveals an inverse relationship with a nao like pattern the south west a positive correlation with a high pressure bridge from central north atlantic to scandinavia and the south eastern gris a positive correlation with a high pressure anomaly over the greenland sea these large scale patterns also impact european climate in different ways accumulation variability in north eastern gris however is dominated by cyclones originating from the greenland sea thus greenland ice core accumulation records offer the potential to reconstruct various large scale circulation patterns and regional storm activity

recent accumulation variability in northwest greenland from ground penetrating radar and shallow cores along the greenland inland traverse accumulation is a key parameter governing the mass balance of the greenland ice sheet several studies have documented the spatial variability of accumulation over wide spatial scales primarily using point data remote sensing or modeling direct measurements of spatially extensive detailed profiles of accumulation in greenland however are rare we used 400mhz ground penetrating radar along the 1009 km route of the greenland inland traverse from thule to summit during april and may of 2011 to image continuous internal reflecting horizons we dated these horizons using ice core chemistry at each end of the traverse using density profiles measured along the traverse we determined the depth to the horizons and the corresponding water equivalent accumulation rates the measured accumulation rates vary from 0 1mw e a in the interior to 0 7mw e a near the coast and correspond broadly with existing published model results though there are some excursions comparison of our recent accumulation rates with those collected along a similar route in the 1950s shows a 10 increase in accumulation rates over the past 52 years along most of the traverse route this implies that the increased water vapor capacity of warmer air is increasing accumulation in the interior of greenland

classification of lithology from seismic tomography a case study from the messum igneous complex namibia 1 combined analysis of seismic p and s velocity information provides a reasonable and efficient basis for the petrologic interpretation of seismic cross sections in this paper a methodology is presented which allows extraction of prominent features related to well defined p velocities and poisson s ratios from a tomographic velocity model using a classification approach we used first arrival travel time data from a near vertical seismic experiment and independently determined p and s velocities by forward and inverse modeling resolution and uncertainties were estimated from inverting synthetic data the classification procedure was carried out in two subsequent steps first prominent classes were identified in the parameter space spanned by poisson s ratios and p wave velocities for this purpose a probability density function was calculated from the tomograms a function measuring the topography of the probability density was then determined and a histogram analysis was carried out to detect significant classes in the second step the results from principal component analysis for the identified classes were used to map their distribution along the seismic profile we applied the method to the messum intrusive complex of namibia and identified three prominent classes on the basis of the integration of petrophysical data and comparison with surface geology we conclude that quartz syenite composition dominates the upper 800 m of the crust under the complex outside of the intrusion the upper crust has properties corresponding to felsic metasediments and granites which are abundant in the local basement this material shows strong depth dependent changes of seismic properties which are ascribed to decreasing porosity and fluid saturation with depth

a century of geometry and velocity evolution at eqip sermia west greenland rapid dynamic changes of ocean terminating outlet glaciers of the greenland ice sheet are related to atmospheric and oceanic warming but the detailed link to external forcing is not well understood observations show high variability in dynamic changes and are mainly limited to the past three decades with dense satellite observations here we compile a long term record of dynamic changes of eqip sermia glacier west greenland starting in 1912 we combine historical measurements of terminus positions ice surface elevation and flow velocity together with more recent in situ and remote sensing observations in the 20th century the glacier underwent small variations in terminus position and flow speed between 2000 and 2003 the terminus retreated substantially but stabilized thereafter in 2009 the northern terminus lobe started to retreat very rapidly the southern lobe collapsed in 2013 the present terminus position which has retreated by 4 km since 1920 is unprecedented in the historical record flow velocities were relatively stable until 2010 the recent acceleration reached threefold velocities in 2014 and rapidly affected the whole terminus region up to 15 km inland comparison with forcings from the atmosphere and the ocean over the past century shows that no dominant cause can be identified and that local effects of bed geometry modulate the glacier response

precipitation over greenland retrieved by a dynamic method and its relation to cyclonic activity abstract in order to calculate the vertical motion over some high mountain regions such as greenland an equation without the quasigeostrophic approximation in coordinates has been developed a dynamic method for retrieving precipitation over greenland is based on this equation the retrieved annual mean precipitation distribution for 1987 and 1988 is in very good agreement with the observed annual accumulation pattern over the greenland ice sheet the major weather system producing precipitation over greenland is the frontal cyclone based on the precipitation characteristics greenland can be divided into five subregions precipitation over the north coastal and central interior regions primarily occurs in summer for the three other subregions if the composite monthly mean sea level pressure charts for high and low monthly precipitation amounts are constructed a clear relationship between precipitation and cyclonic activity emerges if a mean cyclone exists in the labrador sea heavy precipita

bedrock composition regulates mountain ecosystems and landscape evolution earth s land surface teems with life although the distribution of ecosystems is largely explained by temperature and precipitation vegetation can vary markedly with little variation in climate here we explore the role of bedrock in governing the distribution of forest cover across the sierra nevada batholith california our sites span a narrow range of elevations and thus a narrow range in climate however land cover varies from giant sequoia sequoiadendron giganteum the largest trees on earth to vegetation free swaths that are visible from space meanwhile underlying bedrock spans nearly the entire compositional range of granitic bedrock in the western north american cordillera we explored connections between lithology and vegetation using measurements of bedrock geochemistry and forest productivity tree canopy cover a proxy for forest productivity varies by more than an order of magnitude across our sites changing abruptly at mapped contacts between plutons and correlating with bedrock concentrations of major and minor elements including the plant essential nutrient phosphorus nutrient poor areas that lack vegetation and soil are eroding more than two times slower on average than surrounding more nutrient rich soil mantled bedrock this suggests that bedrock geochemistry can influence landscape evolution through an intrinsic limitation on primary productivity our results are consistent with widespread bottom up lithologic control on the distribution and diversity of vegetation in mountainous terrain

application of promice q transect in situ accumulation and ablation measurements 2000 2017 to constrain mass balance at the southern tip of the greenland ice sheet

twentieth century global mean sea level rise is the whole greater than the sum of the parts confidence in projections of global mean sea level rise gmslr depends on an ability to account for gmslr during the twentieth century there are contributions from ocean thermal expansion mass loss from glaciers and ice sheets groundwater extraction and reservoir impoundment progress has been made toward solving the enigma of twentieth century gmslr which is that the observed gmslr has previously been found to exceed the sum of estimated contributions especially for the earlier decades the authors propose the following thermal expansion simulated by climate models may previously have been underestimated because of their not including volcanic forcing in their control state the rate of glacier mass loss was larger than previously estimated and was not smaller in the first half than in the second half of the century the greenland ice sheet could have made a positive contribution throughout the century and groundwater depletion and reservoir impoundment which are of opposite sign may have been approximately equal in magnitude it is possible to reconstruct the time series of gmslr from the quantified contributions apart from a constant residual term which is small enough to be explained as a long term contribution from the antarctic ice sheet the reconstructions account for the observation that the rate of gmslr was not much larger during the last 50 years than during the twentieth century as a whole despite the increasing anthropogenic forcing semiempirical methods for projecting gmslr depend on the existence of a relationship between global climate change and the rate of gmslr but the implication of the authors closure of the budget is that such a relationship is weak or absent during the twentieth century

understanding erosion rates in the himalayan orogen a case study from the arun valley understanding the rates and pattern of erosion is a key aspect of deciphering the impacts of climate and tectonics on landscape evolution denudation rates derived from terrestrial cosmogenic nuclides tcns are commonly used to quantify erosion and bridge tectonic myr and climatic up to several kiloyears time scales however how the processes of erosion in active orogens are ultimately reflected in 10be tcn samples remains a topic of discussion we investigate this problem in the arun valley of eastern nepal with 34 new 10be derived catchment mean denudation rates the arun valley is characterized by steep north south gradients in topography and climate locally denudation rates increase northward from 0 2 mm yr 1 to 1 5 mm yr 1 in tributary samples while main stem samples appear to increase downstream from 0 2 mm yr 1 at the border with tibet to 0 91 mm yr 1 in the foreland denudation rates most strongly correlate with normalized channel steepness r2 0 67 which has been commonly interpreted to indicate tectonic activity significant downstream decrease of 10be concentration in the main stem arun suggests that upstream sediment grains are fining to the point that they are operationally excluded from the processed sample this results in 10be concentrations and denudation rates that do not uniformly represent the upstream catchment area we observe strong impacts on 10be concentrations from local nonfluvial geomorphic processes such as glaciation and landsliding coinciding with areas of peak rainfall rates pointing toward climatic modulation of predominantly tectonically driven denudation rates

annual accumulation over recent centuries at four sites in central greenland 1 accurate accumulation records are fundamental to understanding mass balance of the greenland ice sheet ice cores can provide multicentury high resolution ground based point estimates of water accumulation in 2003 and 2004 four new ice cores were collected in the central western d4 and d5 and summit sandy and katie regions of greenland annual layer counting based on multiple glaciochemical parameters primarily hydrogen peroxide sea salt and dust proxies was used to date the ice cores resulting in annual dating the bottom depth ages for d4 d5 sandy and katie were estimated at 1738 1673 1844 and 1934 a d with mean annual accumulation rates of 41 4 35 2 22 4 and 22 4 cmweq yr 1 respectively these new records were in good agreement with previous accumulation maps and four previously published records from nearby multicentury ice cores spatial variability was quantified through an analysis of variance thereby allowing for more meaningful comparisons to atmospheric processes more regionally representative accumulation records were constructed for the central western and summit regions spanning recent centuries using a principle component analysis of both the new and previously reported ice core measurements these regional records exhibited 6 7 interannual variability 1 standard deviation of the mean and had lower spatial variability uncertainties than individual accumulation records correlations indicate that 20 of the variance in the central western region was explained by the north atlantic oscillation nao and suggests that an array of more northern ice cores may correlate more closely with nao

local to regional scale variability of annual net accumulation on the greenland ice sheet from parca cores a suite of spatially distributed cores collected under the program for arctic regional climate assessment parca provides an unprecedented opportunity to assess local to regional variability of annual accumulation rates over the greenland ice sheet parca cores are unique in their broad spatial distribution and accurate dating of annual layers using multiple seasonally varying indicators the core data provide 1 a more rigorous evaluation of spatial and temporal variations in accumulation rates 2 critical input to ice sheet mass balance estimates 3 ground truth measurements for satellite observations and climate model based precipitation estimates and 4 important constraints on paleoclimatic interpretations from ice cores multiple closely spaced cores demonstrate that signals of high frequency annual to possibly decadal scale climate variability preserved in the ice sheet are partially masked by glaciological noise two 350 year accumulation histories one from northwest greenland and one from the summit area reveal significant multidecadal variability the regional trends show long periods 60 90 years of strong positive correlation and an equally long period of strong negative correlation since 1940 the trends have been decoupled this spatial variability reflects the strong modulation of greenland precipitation and the climate information it contains by changes in north atlantic atmospheric circulation patterns proxy records from the parca cores document that climate reconstructions from a single core must be interpreted cautiously with application of appropriate filters to reduce local noise and careful extrapolations from local to regional scales richer more robust ice core derived data sets should result from combining multiple more widely spaced cores to produce regional stacked records

physically based model of downstream fining in bedrock streams with lateral input 1 bed load particles in bedrock streams receiving lateral input from hillslopes may or may not show a clear monotonic pattern of size reduction in the downstream direction both abrasion and selective sorting may play important roles in generating downstream fining the objective of this study is to develop a physically based model of downstream fining in bedrock streams with lateral input based on both processes a surface based gravel transport relation for the size mixture is employed to account for the effect of selective sorting differential transport while the model produces silt and sand by abrasion it is also assumed to loosely capture particle fracturing via a lumped abrasion coefficient embodied in sternberg s law the model is here tested against field data from vieux habitants river in guadeloupe island which is located in the caribbean sea the river shows clear downstream fining and this pattern is captured reasonably well by the model the model results indicate that abrasion including fracturing is solely responsible for the downstream fining pattern for most of the study reach of the vieux habitants river sensitivity analysis of the model has also been performed the model results suggest that in general selective sorting by differential transport can play a role in downstream fining only in cases of streams with relatively fine gravel sizes and lower slopes the results also indicate that abrasion including fracturing and selective sorting can be equally important for downstream fining in bedrock rivers the results also suggest that future work should explicitly consider fracturing comminution separately from abrasion wear rather than lumping them in a sternberg type coefficient

a new framework for modeling sediment fining during transport with fragmentation and abrasion 1 a new framework for modeling sediment fining during transport is proposed the model is based on a physical description of both abrasion and fragmentation processes it attempts to describe and explain the changes in the grain size distribution of sediments during their transport in a water flow abrasion and fragmentation are modeled through the use of breakage frequency functions and daughter size distributions these functions are determined experimentally for the specific case study which is presented comparison between the predictions from the model and experimental data from the case study show that 1 both abrasion and fragmentation are involved in the degradation 2 fragmentation efficiency decreases during the experiment and 3 the shape of the pebbles provides feedback between abrasion and fragmentation this type of model is therefore appropriate for explaining degradation mechanisms which is promising for a future application to rivers

momentum budget of the atmospheric boundary layer over the greenland ice sheet and its surrounding seas 1 the atmospheric circulation patterns over the greenland ice sheet and its surrounding seas are studied by explicitly calculating the momentum budget components using data of a high resolution regional atmospheric climate model in winter djf the katabatic pressure gradient force pgf dominates the momentum budget of the atmospheric boundary layer abl over the ice sheet over the western slopes of the ice sheet the large scale pgf acts in the same direction as the katabatic pgf resulting in a strong southerly jet of up to 12 m s 1 in winter the accumulation of cold air over the sea ice along the northeast coast leads to a thermally induced northerly flow this circulation facilitates southward sea ice transport in this area and is enhanced by the large scale circulation along the west coast a similar west east temperature gradient also forces a northerly flow in the summer months sea ice is absent and thermal wind forcing is largely reduced over the ocean summer insolation also reduces katabatic forcing the large scale forcing dominates the abl momentum budget over the ice sheet heating of the abl over the snow free tundra induces thermal contrasts with the ice sheet and ocean forcing barrier winds in the coastal regions throughout the year strong surface layer winds along the southeast coast of greenland are forced by the large scale pgf

cosmogenic 21ne analysis of individual detrital grains opportunities and limitations we use a numerical model describing cosmogenic nuclide acquisition in sediment moving through the upper gaub river catchment to evaluate the extent to which aspects of source area geomorphology and geomorphological processes can be inferred from frequency distributions of cosmogenic 21ne 21nec concentrations in individual detrital grains the numerical model predicts the pathways of sediment grains from their source to the outlet of the catchment and calculates the total 21nec concentration that each grain acquires along its pathway the model fully accounts for variations in nuclide production due to changes in latitude altitude and topographic shielding and allows for spatially variable erosion and sediment transport rates model results show that the form of the frequency distribution of 21nec concentrations in exported sediment is sensitive to the range and spatial distribution of processes operating in the sediment s source areas and that this distribution can be used to infer the range and spatial distribution of erosion rates that characterise the catchment the results also show that lithology can affect the form of the 21nec concentration distribution indirectly by exerting control on the spatial pattern of denudation in a catchment model results further indicate that the form of the distribution of 21nec concentrations in the exported sediment can also be affected by the acquisition of 21nec after detachment from bedrock in the diffusive hillslope and or advective fluvial domains however for such post detachment nuclide acquisition to be important this effect needs to at least equal the nuclide acquisition prior to detachment from bedrock copyright 2009 john wiley and sons ltd

numerical and analytical models of cosmogenic radionuclide dynamics in landslide dominated drainage basins 1 in many tectonically active regions on earth landslides dominate sediment delivery to channels while cosmogenic radionuclides crn represent a valuable tool to document basin averaged erosion rates a better understanding of crn dynamics in these systems is required before erosion rates can be reliably inferred from crn concentrations the stochastic nature of landslides results in variability of crn concentrations in both alluvial and hillslope samples that is both difficult to document and poorly understood to guide sampling strategies we developed a 2 d plan view model to simulate the influence of landslides on crn dynamics we employ a sediment mixing model in which concentrations of crns from material eroded by both landslides and steady processes are combined to evaluate how best to infer erosion rates from crn concentrations this model is further used to test a new analytical solution for the distribution of crn concentrations on hillslopes in a landslide prone system results suggest that for landscapes dominated by deep 5 m landslides only large drainage basins 100 km2 provide consistently reliable estimates of erosion rates from crn concentrations for landscapes dominated by shallow landslides 0 7 2 m smaller basins can produce reliable estimates results further suggest that the distribution of concentrations from hillslope samples could be used to deduce the relative contribution of material derived from landslide and steady processes these findings underscore the need to consider carefully the sources of natural variability in sampling and analyzing crns if properly done the variability can reveal useful information about geomorphic processes in landslide prone areas

greenland ice sheet surface mass balance variability 1991 2003 the polar mm5 mesoscale atmospheric model was run for 13 years 1991 2003 over greenland at 24 km horizontal resolution box and others 2004 the model physics were driven by satellite station and weather balloon observational data assimilation i e european centre for medium range weather forecasts ecmwf operational analysis the analysis in this study focuses on the response of the surface mass balance to its primary controls temperature and precipitation the results indicate coherent spatial patterns of variability and statistically significant links with temperature and precipitation and the north atlantic oscillation precipitation trends have the same spatial pattern and sign as temperature suggesting an association of precipitation and temperature variability increasing temperatures contribute to an increasing ablation trend and expansion of the ablation zone despite increasing accumulation trends the pinatubo philippines volcanic cooling in the early 1990s enhances this apparent warming trend only in the northeast does precipitation appear to dominate the surface mass balance where both temperature and precipitation have decreased there is little evidence for a total ice sheet surface mass balance trend although the meltwater runoff has a positive trend and combined with iceberg discharge and basal melting estimates suggests the ice sheet as a whole is in a state of net mass loss over this period

hillslope response to tectonic forcing in threshold landscapes hillslopes are thought to poorly record tectonic signals in threshold landscapes numerous previous studies of steep landscapes suggest that large changes in long term erosion rate lead to little change in mean hillslope angle measured at coarse resolution new lidar derived topography data enables a finer examination of threshold hillslopes here we quantify hillslope response to tectonic forcing in a threshold landscape to do so we use an extensive cosmogenic beryllium 10 10 be based dataset of catchment averaged erosion rates combined with a 500 km 2 lidar derived 1 m digital elevation model to exploit a gradient of tectonic forcing and topographic relief in the san gabriel mountains california we also calibrate a new method of quantifying rock exposure from lidar derived slope measurements using high resolution panoramic photographs two distinct trends in hillslope behavior emerge below catchment mean slopes of 30 modal slopes increase with mean slopes slope distribution skewness decreases with increasing mean slope and bedrock exposure is limited above mean slopes of 30 our rock exposure index increases strongly with mean slope and the prevalence of angle of repose debris wedges keeps modal slopes near 37 resulting in a positive relationship between slope distribution skewness and mean slope we find that both mean slopes and rock exposure increase with erosion rate up to 1 mm a in contrast to previous work based on coarser topographic data we also find that as erosion rates increase the extent of the fluvial network decreases while colluvial channels extend downstream keeping the total drainage density similar across the range our results reveal important textural details lost in 10 or 30 m resolution digital elevation models of steep landscapes and highlight the need for process based studies of threshold hillslopes and colluvial channels

ice sheet in peril earth s large ice sheets in greenland and antarctica are major contributors to sea level change at present the greenland ice sheet see the photo is losing mass in response to climate warming in greenland 1 but the present changes also include a long term response to past climate transitions on page 590 of this issue macgregor et al 2 estimate the mean rates of snow accumulation and ice flow of the greenland ice sheet over the past 9000 years based on an ice sheet wide dated radar stratigraphy 3 they show that the present changes of the greenland ice sheet are partly an ongoing response to the last deglaciation the results help to clarify how sensitive the ice sheet is to climate changes

defining rates of landscape evolution in a south tibetan graben with in situ produced cosmogenic 10be the tangra yum co graben is one of the active structures that accommodate the east west extension of the southern tibetan plateau and hosts one of the largest tibetan lakes which experienced lake level changes of 200 m during the holocene in this study cosmogenic 10be is employed to 1 quantify catchment wide denudation rates in fault bounded mountain ranges adjacent to the tangra yum co graben 2 date palaeo shorelines related to the holocene lake level decline and 3 determine the age of glacial advances in this region the fault bounded non glaciated mountain range north of tangra yum co and presumably most other areas around the lake erode at low rates of 10 70 mm ka owing to the slow erosion of the landscape the sediments delivered to tangra yum co have high 10be concentrations as a consequence accurate exposure dating of sediment covered terraces and beach ridges is difficult because the pre depositional 10be concentration may exceed the post depositional 10be concentration from which exposure ages are calculated this difficulty is illustrated by a rather inaccurate 10be exposure age of 2 3 1 4 ka i e an error of 60 for a terrace that is located 67 m above the lake nevertheless the age is consistent with luminescence ages for a series of beach ridges and provides further evidence for the decline of the lake level in the late holocene at tangra yum co exposure dating of beach ridges via 10be depth profiles is not feasible because the pre depositional 10be component in these landforms varies with depth which violates a basic assumption of this approach 10be ages for boulders from two moraines are much older than the early holocene lake level highstand indicating that melting of glaciers in the mountain ranges adjacent to tangra yum co has not contributed significantly to the lake level highstand in the early holocene copyright 2015 john wiley sons ltd

glaciological investigations in the crete area central greenland a search for a new deep drilling site the results of the 1984 85 post gisp campaigns in central greenland are presented eight ice cores were obtained some spanning up to 360 years we present i geographical positions and elevations at the drill sites

control of geomorphic processes on 10be concentrations in individual clasts complexity of the exposure history in gobi altay range mongolia the dating of alluvial landforms by cosmogenic nuclides requires distinguishing the pre deposition inheritance from the post deposition history of the clasts in the studied marker moreover estimating catchment scale erosion rates from the concentrations of cosmogenic nuclides in active alluvia requires a good knowledge of the local regional relationships between rock exhumation and transport through space and time this is still poorly known for timescales of tens of thousand years in order to document the evolution of clast exhumation and transport rates through time we analyze in situ 10be concentrations in boulders and cobbles from hillslopes to outlet of an arid mountainous catchment located in gobi altay mongolia strongly affected by global climatic changes during the pleistocene holocene period samples were collected on bedrock abandoned alluvial deposits active colluvia and alluvia our results show a large 10be scattering in the active river bed consistent with a low and discontinuous catchment erosion rate dominated by mass wasting and fluvial incision on the contrary pre exposure signal within abandoned terraces is much more homogeneous consistent with climatic pulses responsible of strong erosional events on hillslopes and rapid fluvial transport these results show that exhumation transport processes at the catchment scale vary in style and intensity through time as a consequence of climatic oscillations the occurrence of abrupt climatic changes during short periods of time recorded by 10be concentrations in abandoned alluvia raise questions about the temporal applicability of catchment erosion rates derived from cosmogenic nuclide concentrations measured in sediments of active rivers on the other hand strong and short erosion events limit and homogenize the pre exposure 10be signal in associated deposits like debris flows making them particularly suitable markers for dating in active tectonic and paleoclimatic studies

greenland high elevation mass balance inference and implication of reference period 1961 90 imbalance we revisit the input output mass budget of the high elevation region of the greenland ice sheet evaluated by the program for arctic regional climate assessment parca our revised reference period 1961 90 mass balance of 54 48gt a is substantially greater than the 0 21gt a assessed by parca but consistent with a recent fully independent input output estimate of high elevation mass balance 41 61gt a together these estimates infer a reference period high elevation specific mass balance of 4 8 5 4 cmw e a the probability density function pdf associated with this combined input output estimate infers an 81 likelihood of high elevation specific mass balance being positive 0 cmw e a during the reference period and a 70 likelihood that specific balance was 2 cmw e a given that reference period accumulation is characteristic of centurial and millennial means and that in situ mass balance observations exhibit a dependence on surface slope rather than surface mass balance we suggest that millennial scale ice dynamics are the primary driver of subtle reference period high elevation mass gain failure to acknowledge subtle reference period dynamic mass gain can result in underestimating recent dynamic mass loss by 17 and recent total greenland

quantifying effects of deep and near surface chemical erosion on cosmogenic nuclides in soils saprolite and sediment cosmogenic nuclides in rock soil and sediment are routinely used to measure denudation rates of catchments and hillslopes although it has been shown that these measurements are prone to biases due to chemical erosion in regolith most studies of cosmogenic nuclides have ignored this potential source of error here we quantify the extent to which overlooking effects of chemical erosion introduces bias in interpreting denudation rates from cosmogenic nuclides we consider two end member effects one due to weathering near the surface and the other due to weathering at depth near the surface chemical erosion influences nuclide concentrations in host minerals by enriching or depleting them relative to other more or less soluble minerals this increases or decreases their residence times relative to the regolith as a whole at depth where minerals are shielded from cosmic radiation chemical erosion causes denudation without influencing cosmogenic nuclide buildup if this effect is ignored denudation rates inferred from cosmogenic nuclides will be too low we derive a general expression termed the chemical erosion factor or cef which corrects for biases introduced by both deep and near surface chemical erosion in regolith the cef differs from the quartz enrichment factor of previous work in that it can also be applied to relatively soluble minerals such as olivine using data from diverse climatic settings we calculate cefs ranging from 1 03 to 1 87 for cosmogenic nuclides in quartz this implies that ignoring chemical erosion can lead to errors of close to 100 in intensely weathered regolith cef is strongly correlated with mean annual precipitation across our sites reflecting climatic influence on chemical weathering our results indicate that quantifying cefs is crucial in cosmogenic nuclide studies of landscapes where chemical erosion accounts for a significant fraction of the overall denudation copyright 2012 john wiley sons ltd

terminus driven retreat of a major southwest greenland tidewater glacier during the early 19th century insights from glacier reconstructions and numerical modelling tidewater glaciers in greenland experienced widespread retreat during the last century information on their behaviour prior to this is often poorly constrained due to lack of observations while determining the drivers prior to instrumental records is also problematic here we present a record of the dynamics of kangiata nunaata sermia kns southwest greenland from its little ice age maximum liamax to 1859 the period before continuous air temperature observations began at nuuk in 1866 using glacial geomorphology historical accounts photographs and gis analyses we provide evidence kns was at its liamax by 1761 had retreated by 5 km by 1808 and a further 7 km by 1859 this predates retreat at jakobshavn isbrae by 43 113 years demonstrating the asynchroneity of tidewater glacier terminus response following the lia we use a one dimensional flowband model to determine the relative sensitivity of kns to atmospheric and oceanic climate forcing results demonstrate that terminus forcing rather than surface mass balance drove the retreat modelled glacier sensitivity to submarine melt rates is also insufficient to explain the retreat observed however moderate increases in crevasse water depth driving an increase in calving are capable of causing terminus retreat of the observed magnitude and timing

dynamic equilibrium among erosion river incision and coastal uplift in the northern and central apennines italy erosion river incision and uplift rates in the northern and central apennines italy since 0 9 ma are determined from new cosmogenic nuclide data beryllium 10 concentrations in modern and middle pleistocene sediments indicate erosion rates from 0 20 to 0 58 mm yr these rates are similar to estimates of sediment yield 0 12 0 44 mm yr river incision 0 35 mm yr and uplift 0 01 1 0 mm yr rates inferred from other methods that integrate landscape process rates since the early pleistocene these rates of landscape change are significantly lower than long term exhumation rates of 1 2 mm yr since ca 4 5 ma inferred from thermochronometry collectively these data suggest that hillslope erosion and river incision rates in the northern and central apennines have balanced local uplift rates for 1 my but that exhumation rates have slowed significantly since emergence of the mountain chain in the pliocene this condition of dynamic equilibrium was potentially achieved within ca 3 ma similar to some model predictions of hillslope and fluvial system adjustment

delineation of carbonate dust aluminous dust and sea salt deposition in a greenland glaciochemical array using positive matrix factorization 1 high resolution trace element records from polar ice cores are fundamental to identifying spatial and temporal variability in dust and sea salt aerosols here we developed high temporal resolution glaciochemical records over recent centuries from an array of seven recently collected greenland ice cores positive matrix factorization pmf was used to assess apportionment of trace elements between three unique sources which were identified as proxies of carbonate dust aluminous dust and sea salt the three pmf factors agree well with literature values and represent the first time carbonate and aluminous dust sources have been quantifiably differentiated using high resolution glaciochemistry the concentrations of all three sources varied with ice core site however the large array of ice cores provided a regional scale understanding of the sources and magnitude of dust and sea salt impurities deposited on the greenland ice sheet at the regional level all three sources varied on seasonal annual and multiyear timescales the seasonal deposition of sea salt impurities reached a maximum in the winter followed by spring peaks of carbonate and aluminous dust over the 331 year composite record only aluminous dust exhibited a long term increasing trend that peaked in the 1930s and was followed by a 20 decline in recent decades

retrieving a common accumulation record from greenland ice cores for the past 1800 years 1 in the accumulation zone of the greenland ice sheet the annual accumulation rate may be determined through identification of the annual cycle in the isotopic climate signal and other parameters that exhibit seasonal variations on an annual basis the accumulation rate in different greenland ice cores is highly variable and the degree of correlation between accumulation series from different ice cores is low however when using multiyear averages of the different accumulation records the correlation increases significantly a statistical model has been developed to estimate the common climate signal in the different accumulation records through optimization of the ratio between the variance of the common signal and of the residual using this model a common greenland accumulation record for the past 1800 years has been extracted the record shows significant 11 9 years periodicity a sharp transition to very dry conditions is found just before a d 1200 and very dry conditions during the 13th century together with dry and cold spells during the 14th century may have put extra strain on the norse population in greenland and may have contributed to their extinction accumulation rates gradually decrease from a distinct maximum in a d 1394 to very dry conditions in the late 17th century and thus reflect the little ice age

atmospheric circulation and cyclone frequency variations linked to the primary modes of greenland snow accumulation 1 data from 34 greenland firn cores extending from 1982 to 1996 are used to identify spatial accumulation variability patterns and their associated atmospheric circulation and cyclone frequencies the first principal component representing west central greenland accumulation is correlated to nao variability having increased southwesterly northeasterly flow over that area during high low accumulation winters the flow is linked to a relative increase in cyclone activity on the west central region of the ice sheet during high accumulation periods the second principal component represents accumulation over southeastern greenland where strong westerly flow leads to high accumulation and an increase in lee cyclones on the east and southeast coast the study provides evidence that increased cyclone activity occurs over or immediately adjacent to areas experiencing anomalously high accumulation and it is important to distinguish lee cyclones from icelandic cyclones as they produce opposite precipitation effects over the ice sheet

interannual variations of snow accumulation on the greenland ice sheet 1985 1996 new observations versus model predictions newly measured time series of net water equivalent accumulation from ice cores are reported for 11 sites located near the 2000 m contour of the greenland ice sheet many of these sites are located in regions where accumulation has not been previously measured we compared these new time series of annual accumulation with previously reported modeled precipitation covering the same time range because ice core accumulation records include both regional and local accumulation components we used adjacent ice core records at six multiple core sites to estimate the local component and extrapolated these results to the five single core sites we investigated the impact of this short scale spatial variability in accumulation on statistical comparisons between the observed accumulation and model precipitation although sealers were required to match the 12 year mean modeled precipitation to the mean observed accumulation a high degree of correspondence between observed interannual accumulation and scaled modeled precipitation was found at 7 of 11 locations the need for scaling and the low correspondence between model simulations and observations at some sites clearly indicate that model improvements are needed although very encouraging a more spatially distributed array of ice core accumulation measurements spanning the same time period as the precipitation modeling is necessary for continued model improvement and validation in agreement with earlier studies the large temporal variability in snow accumulation predicted by modeling and confirmed by ice cores indicates that the ice sheet elevation varies by tens of centimeters from year to year simply because of changing accumulation

denudation rates determined from the accumulation of in situ produced 10be in the luquillo experimental forest puerto rico we present a simple method for estimation of long term mean denudation rates using in situ produced cosmogenic 10be in fluvial sediments procedures are discussed to account for the effects of soil bioturbation mass wasting and attenuation of cosmic rays by biomass and by local topography our analyses of 10be in quartz from bedrock outcrops soils mass wasting sites and riverine sediment from the icacos river basin in the luquillo experimental forest puerto rico are used to characterize denudation for major landform elements in that basin the 10be concentration of a discharge weighted average of size classes of river sediment corresponds to a long term average denudation of 43 m ma 1 consistent with mass balance results

surface mass balance changes of the greenland ice sheet since 1866 mass loss from the greenland ice sheet over the past decade has caused the impression that the ice sheet has been behaving anomalously to the warming of the 1990s we have reconstructed the recent 1866 2005 surface mass balance smb history of the greenland ice sheet on a 5 5 km grid using a runoff retention model based on the positive degree day method the model is forced with new datasets of temperature and precipitation patterns dating back to 1866 we use an innovative method to account for the influence of year on year surface elevation changes on smb estimates and have found this effect to be minor all smb estimates are made relative to the 1961 90 average smb and we compare annual smb estimates from the period 1995 2005 to a similar period in the past 1923 33 where smb was comparable and conclude that the present day changes are not exceptional within the last 140 years peripheral thinning has dominated the smb response during the past decade as in 1923 33 but we also show that thinning was not restricted to the margins during this earlier period

observed and modeled greenland ice sheet snow accumulation 1958 2003 and links with regional climate forcing abstract annual and monthly snow accumulation for the greenland ice sheet was derived from ecmwf forecasts mainly 40 yr ecmwr re analysis era 40 and further meteorological modeling modeled accumulation was validated using 58 ice core accumulation datasets across the ice sheet and was found to be 95 of the observed accumulation on average with a mean correlation of 0 53 between modeled and observed many of the ice core datasets are new and are presented here for the first time central and northern interior parts of the ice sheet were found to be 10 30 too dry in era 40 in line with earlier ecmwf analysis although too much 50 locally snow accumulation was modeled for interior southern parts of greenland nevertheless 47 of 58 sites show significant correlation in temporal variability of modeled with observed accumulation the model also captures the absolute amount of snow accumulation at several sites most notably das1 and das2 in southeast greenland mean modeled accumulation over the

high resolution 1 km positive degree day modelling of greenland ice sheet surface mass balance 1870 2012 using reanalysis data we show results from a positive degree day pdd model of greenland ice sheet gris surface mass balance smb 1870 2012 forced with reanalysis data the model includes an improved daily temperature parameterization as compared with a previous version and is run at 1 km rather than 5 km resolution the improvements lead overall to higher smb with the same forcing data we also compare our model with results from two regional climate models rcms while there is good qualitative agreement between our pdd model and the rcms it usually results in lower precipitation and lower runoff but approximately equivalent smb mean 1979 2012 smb standard deviation in gt a 1 is 382 78 in the pdd model compared with 379 101 and 425 90 for the rcms comparison with in situ smb observations suggests that the rcms may be more accurate than pdd at local level in some areas although the latter generally compares well dividing the gris into seven drainage basins we show that smb has decreased sharply in all regions since 2000 finally we show correlation between runoff close to two calving glaciers and either calving front retreat or calving flux this being most noticeable from the mid 1990s the author s 2016

recent greenland accumulation estimated from regional climate model simulations and ice core analysis the accumulation defined as precipitation minus evaporation over greenland has been simulated with the high resolution limited area regional climate model hirham4 applied over an arctic integration domain this simulation is compared with a revised estimate of annual accumulation rate distribution over greenland taking into account information from a new set of ice core analyses based on surface sample collections from the north greenland traverse the region with accumulation rates below 150 mm yr21 in central northwest greenland is much larger than previously assumed and extends about 500 km farther to the south it is demonstrated that good agreement between modeled and observed regional precipitation and accumulation patterns exists particularly concerning the location and the values of very low accumulation in the middle of greenland the accumulation rates in the northern part of greenland are reduced in comparison to previous estimates these minima are connected with a prevailing blocking high over the greenland ice sheet and katabatic wind systems preventing humidity transports to central greenland the model reasonably represents the synoptic situations that lead to precipitation maxima of precipitation and accumulation occur at the southwestern and southeastern coasts of greenland and are connected with cyclonic activity and the main storm tracks around greenland the central region of the greenland ice sheet acts as a blocking barrier on moving weather systems and prohibits cyclones moving from west to east across this region and thus prevents moisture transports

climatic control of denudation in the deglaciated landscape of the washington cascades erosion in the washington cascades mountains was dominated by glacier activity until the end of the last glacial maximum when fluvial incision and mass wasting became the dominant drivers an analysis of millennial scale rates of denudation in the range suggest erosion is sensitive both to spatial variations in precipitation and inherited topography

strong tectonic and weak climatic control of long term chemical weathering rates the relationships among climate physical erosion and chemical weathering have remained uncertain because long term chemical weathering rates have been difficult to measure here we show that long term chemical weathering rates can be measured by combining physical erosion rates inferred from cosmogenic nuclides with dissolution losses inferred from the rock to soil enrichment of insoluble elements we used this method to measure chemical weathering rates across 22 mountainous granitic catchments that span a wide range of erosion rates and climates chemical weathering rates correlate strongly with physical erosion rates but only weakly with climate implying that by regulating erosion rates tectonic uplift may significantly accelerate chemical weathering rates in granitic landscapes

uplift history of the sila massif southern italy deciphered from cosmogenic 10be erosion rates and river longitudinal profile analysis 1 the sila massif in the calabrian arc southern italy is a key site to study the response of a landscape to rock uplift here an uplift rate of 1 mm yr has imparted a deep imprint on the sila landscape recorded by a high standing low relief surface on top of the massif deeply incised fluvial valleys along its flanks and flights of marine terraces in the coastal belt in this framework we combined river longitudinal profile analysis with hillslope erosion rates calculated by 10be content in modern fluvial sediments to reconstruct the long term uplift history of the massif cosmogenic data show a large variation in erosion rates marking two main domains the samples collected in the high standing low relief surface atop sila provide low erosion rates from 0 09 0 01 to 0 13 0 01 mm yr conversely high values of erosion rate up to 0 92 0 08 mm yr characterize the incised fluvial valleys on the massif flanks the analyzed river profiles exhibit a wide range of shapes diverging from the commonly accepted equilibrium concave up form generally the studied river profiles show two or more frequently three concave up segments bounded by knickpoints and characterized by different values of concavity and steepness indices the wide variation in cosmogenic erosion rates and the non equilibrated river profiles indicate that the sila landscape is in a transient state of disequilibrium in response to a strong and unsteady uplift not yet counterbalanced by erosion

greenland ice sheet mass balance reconstruction part ii surface mass balance 1840 2010 abstractmeteorological station records ice cores and regional climate model output are combined to develop a continuous 171 yr 1840 2010 reconstruction of greenland ice sheet climatic surface mass balance bclim and its subcomponents including near surface air temperature sat since the end of the little ice age independent observations are used to assess and compensate errors melt water production is computed using separate degree day factors for snow and bare ice surfaces a simple meltwater retention scheme yields the time variation of internal accumulation runoff and bare ice area at decadal time scales over the 1840 2010 time span summer june august sat increased by 1 6 c driving a 59 surface meltwater production increase winter warming was 2 0 c substantial interdecadal variability linked with episodic volcanism and atmospheric circulation anomalies is also evident increasing accumulation and melt rates bare ice area and meltwater retention are driven by increasing sat as a con

gopher bioturbation field evidence for non linear hillslope diffusion it has generally been assumed that diffusive sediment transport on soil mantled hillslopes is linearly dependent on hillslope gradient fieldwork was done near santa barbara california to develop a sediment transport equation for bioturbation by the pocket gopher thomomys bottae and to determine whether it supports linear diffusion the route taken by the sediment is divided into two parts a subsurface path followed by a surface path the first is the transport of soil through the burrow to the burrow opening the second is the discharge of sediment from the burrow opening onto the hillslope surface the total volumetric sediment flux as a function of hillslope gradient is found to be qs cm3 cm 1 a 1 176 dz dx 3 189 dz dx 2 68 dz dx 34 dz dx 0 4 this result does not support the use of linear diffusion for hillslopes where gopher bioturbation is the dominant mode of sediment transport a one dimensional hillslope evolution program was used to evolve hillslope profiles according to non linear and linear diffusion and to compare them to a typical hillslope the non linear case more closely resembles the actual profile with a convex cap at the divide leading into a straight midslope section copyright 2000 john wiley sons ltd

variability of accumulation in northwest greenland over the past 250 years during summer 1996 a 120 m firn and ice core was drilled to determine annual accumulation rates at a northwest greenland site gits 77 1392 n 61 0422 w 1910 m elevation annual layers were identified in the core using multiple parameters 18o and concentrations of dust hydrogen peroxide ammonium calcium and nitrate using all parameters together to define annual layers resulted in a 251 year record with a dating uncertainty of one year within that period annual accumulation over the period of record averaged about 0 37 m water equivalent comparing this record with four other multi century long records from the west central and northwest portion of the ice sheet shows many periods when decadal scale fluctuations in accumulation at the different sites are in phase overall variations in accumulation in this portion of the ice sheet were 8 9 per decade versus 25 for individual cores annual accumulation at gits showed a significant correlation with a 12 month north atlantic oscillation index pearson s r 0 32 with a significance level of 99 though the correlation was slightly lower than for two cores roughly 350 and 700 km south

greenland accumulation an error model 1 total surface accumulation total snowfall minus total sublimation on the greenland ice sheet is estimated as 299 23 kg m 2 yr 1 for an assumed 30 year span the uncertainty being quoted as twice the standard error the estimate is very similar to earlier estimates because it relies largely on the same compiled observations but it is the first to be accompanied by formal error bars an error model was developed for this purpose it incorporates uncertainties due to measurement error record length or span and spatial bias in the distribution and density of the observations measurement errors although dominant over large parts of the interior make only a small contribution to uncertainty in the accumulation of the whole ice sheet time series of accumulation are shown to be stationary and independent which means that the date of any given observation is of no importance when evaluating its uncertainty as an estimate of accumulation at any other date however as found earlier the span of the observation is a leading contributor to uncertainty and a means of placing short and long span measurements on an equal footing is developed spatial bias is the other leading contributor to judge from modeling of the standard error of averages of pairs of observations as a function of their separation and from a map of the standard error of accumulation the standard error of interpolated point estimates of accumulation is small where measurements are dense and well distributed in the interior but grows rapidly where measurements are more thinly or unevenly distributed estimates of accumulation are therefore most uncertain in the peripheral ablation zone it is suggested that uncertainty in accumulation needs to be reduced by a factor of two or more if the measurements are to contribute reliably to explaining the observed sea level rise

new precipitation and accumulation maps for greenland annual total precipitation and the annual accumulation on the greenland ice sheet are evaluated and presented in two maps the maps are based on accumulation measurements of 25 1 pits and cores obtained from the upper accumulation zone and precipitation measurements made at 35 meteorological stations in the coastal region to construct the accumulation map the annual precipitation was split into solid and liquid precipitation components annual total precipitation exceeding 2500 mm w e occurs on the southeastern tip of greenland while the minimum precipitation is estimated to occur on the northeastern slope of the ice sheet the mean annual precipitation for all of greenland is 340 mm w e the largest annual accumulation of about 1500 mm w e is found on the glaciers in the southeastern corner of greenland while the smallest accumulation is found on the northeastern slope of the ice sheet west of danmarkshavn the mean accumulation on the greenland ice sheet is estimated at 310 mm w e the regional difference in accumulation is examined with respect to the 850 hpa m bar level circulation the present surface topography is found to play an important role in determining regional accumulation on the ice sheet

greenland ice sheet mass balance reconstruction part iii marine ice loss and total mass balance 1840 2010 abstractgreenland ice sheet mass loss to the marine environment occurs by some combination of iceberg calving and underwater melting referred to here as marine ice loss lm this study quantifies the relation between lm and meltwater runoff r at the ice sheet scale a theoretical basis is presented explaining how variability in r can be expected to govern much of the lm variability over annual to decadal time scales it is found that r enhances lm through three processes 1 increased glacier discharge by ice warming softening and basal lubrication sliding 2 increased calving susceptibility through undercutting glacier front geometry and reducing ice integrity and 3 increased underwater melting from forcing marine convection applying a semiempirical lm f r parameterization to a surface mass balance reconstruction enables total ice sheet mass budget closure over the 1840 2010 period the estimated cumulative 171 yr net ice sheet sea level contribution is 25 10 mm the rise punctuated by periods

annual accumulation for greenland updated using ice core data developed during 2000 2006 and analysis of daily coastal meteorological data an updated accumulation map for greenland is presented on the basis of 39 new ice core estimates of accumulation 256 ice sheet estimates from ice cores and snow pits used in previous maps and reanalysis of time series data from 20 coastal weather stations the period 1950 2000 is better represented by the data than are earlier periods ice sheetwide accumulation was estimated based on kriging the average accumulation 95 confidence interval or 2 times standard error over the greenland ice sheet is 30 0 2 4 g cm 2 a 1 with the average accumulation above 2000 m elevation being essentially the same 29 9 2 2 g cm 2 a 1 at higher elevations the new accumulation map maintains the main features shown in previous maps however there are five coastal areas with obvious differences southwest northwest and eastern regions where the accumulation values are 20 50 lower than previously estimated and southeast and northeast regions where the accumulation values are 20 50 higher than previously estimated these differences are almost entirely due to new coastal data the much lower accumulation in the southwest and the much higher accumulation in the southeast indicated by the current map mean that long term mass balance in both catchments is closer to steady state than previously estimated however uncertainty in these areas remains high owing to strong gradients in precipitation from the coast inland a significant and sustained precipitation measurement program will be needed to resolve this uncertainty copyright 2009 by the american geophysical union