quaternary tectonic response to intensified glacial erosion in an orogenic wedge active orogens are thought to behave as internally deforming critical taper wedges that are in rough long term equilibrium with tectonic influx and erosional outflux spatial and temporal variations in climate are therefore hypothesized to have a significant influence on denudation topography and deformation of orogens thereby affecting wedge taper however the impact of the most severe transition in northern hemisphere climate during the cenozoic era the onset of glaciation has hitherto not been empirically documented here we analyse the spatial patterns of denudation and deformation and their temporal variations in the heavily glaciated st elias orogen in southern alaska low temperature thermochronometry thermokinematic modelling and offshore seismic reflection and borehole data suggest that the global scale intensification of glaciation in the middle pleistocene epoch enhanced glacier growth and caused ice streams to advance to the edge of the continental shelf this led to focused denudation across the subaerial reaches of the orogen and burial of the actively deforming wedge toe by the eroded sediment we propose that this climatically driven mass redistribution forced a structural reorganization of the orogen to maintain critical taper our empirical results thus support decades of numerical model predictions of orogenesis and provide compelling field evidence for the significant impact of climate change on tectonics intense glaciation during the middle pleistocene epoch led to focused denudation and mass redistribution within the st elias orogen in southern alaska and resulted in structural reorganization of the orogen the tectonic response of this orogen to climate change is consistent with predictions of numerical models

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

glacier response to climatic change during the loch lomond stadial and early flandrian geomorphological and palynological evidence from the isle of skye scotland the deglaciation of skye at the close of the loch lomond stadial is assessed on the basis of detailed geomorphological mapping and pollen stratigraphic correlations it is concluded that deglaciation proceeded in two distinct stages the first was marked by numerous glacier stillstands and readvances while uninterrupted retreat and local glacier stagnation occurred during the second and final stage the pollen evidence indicates that the first stage was well advanced before the marked thermal improvement at the start of the flandrian and it is inferred that initial glacier retreat occurred in response to a decline in precipitation in the later part of the loch lomond stadial the first stage of glacier retreat continued into the early flandrian during which climatic amelioration was interrupted briefly final deglaciation appears to have occurred rapidly in response to sustained temperature increases the collective evidence also indicates spatial variations in the timing of deglaciation which appear to reflect differences in glacier morphology

exposure dating and validation of periglacial weathering limits northwest scotland periglacial weathering limits on two mountains in northwest scotland separate zones of contrasting exposure history exposure dating of bedrock below the weathering limits gives ages consistent with late devensian deglaciation but six out of seven samples from above the weathering limits give minimum exposure ages older than late devensian ice expansion these results suggest that mountain summits stood as nunataks above the last ice sheet surface and rule out formation of weathering limits by periglacial rock breakdown since deglaciation trimming of frost debris during an ice sheet readvance or enhanced weathering prior to climatic warming during ice sheet downwastage the dating results do not preclude the possibility that weathering limits mark a former englacial boundary between passive cold based ice on mountain summits and erosive warm based ice at lower elevations although 26 al 10 be ratios for high level bedrock surfaces provide no evidence of prolonged static ice cover

a lateglacial 10be production rate from glacial lake shorelines in scotland the identification of tephra within varved deposits of a former ice dammed lake that existed in scotland during the younger dryas provides an opportunity to calibrate 10be production rates using previously published 10be concentrations from the lake shoreline and independently derived ages for the tephras derived from the greenland ice core records the best estimate ages of the tephras yield indistinguishable 10be production rate values for spallation with an average value of 4 26 0 21 atoms g 1 a 1 using the lm scaling scheme these values are in best agreement with the most proximal reference 10be production rate from norway

late glacial and holocene 10be production rates for western norway we present a new regional calibration of the 10be production rate from two well dated surfaces insouthern norway a rock avalanche with 14c dated wood and a precisely dated younger dryas moraine c

rates and timing of earth surface processes from in situ produced cosmogenic be 10 beryllium 10 is the longest lived of the seven known unstable isotopes of be it results mostly from the interaction of cosmic radiation primarily neutrons with a variety of target atoms by spallation the splitting of nuclei lal 1988 it can also be produced at very low levels by radio disintegration of u and th sharma and middleton 1989 although all radioactive be isotopes are produced in the atmosphere via cosmic ray reactions arnold 1956 lal and peters 1967 morris et al chapter 5 this volume in this paper we are most interested in 10be produced in rock which we refer to as in situ produced such in situ produced 10be is a cosmic ray dosimeter functioning as a quantitative monitor of near surface residence time in some geologic situations 10be can be used as a chronometer allowing one to estimate the duration of surface exposure in other settings 10be can be used as a tracer allowing one to estimate the rate distribution and behavior of earth surface processes rates of 10be production are very low in rocks exposed at earth s surface 102 atoms g 1 y 1 resulting in typical in situ produced 10be concentrations termed activities of 103 to 107 atoms g 1 the development of accelerator mass spectrometry ams in the 1980s allowed routine measurement of 10be at levels typical of rocks exposed near earth s surface elmore and phillips 1987 analytical refinements in the 1990s lowered detection limits by an order of magnitude allowing dating of exposure periods 103 years in favorable geologic and geographic situations simple exposure histories at high altitude and latitude most in situ 10be is measured in quartz mineral separates where the primary spallation target is o lal and arnold 1985

exhumation along the fairweather fault southeastern alaska based on low temperature thermochronometry 1 the southern alaskan syntaxis marks the spectacular junction between the 1000 km long pacific north america transform margin and the chugach st elias belt where subduction and terrane accretion drive rapid convergent deformation and rock uplift new low temperature thermochronometry reveals that intense orogenic deformation is not restricted to one side of the syntaxis but extends nearly 300 km south along the dextral fairweather fault apatite and zircon u th he ages as young as 0 9 and 2 0 ma suggest maximum exhumation rates of nearly 2 mm a in close proximity 0 5 mm a along the entire plate margin we estimate that long term rock uplift accommodates 3 mm a of fault normal convergence in this area this suggests that the fairweather fault is slightly transpressive and highly partitioned analogous to the central san andreas fault this convergence only accounts for 1 5 of the obliquity between pacific plate motion and the continental margin however implying the deficit is taken up by 1 2 cm a thrust sinistral motion along the offshore transition fault additionally thermochronometry shows a marked increase in bedrock cooling coincident with onset of heavy glaciation similar to what has been observed in other parts of the pacific northwest the tectonically active fairweather corridor is distinguished however by the magnitude of the acceleration and the depth of exhumation since pliocene climate change

evaluation of a numerical model of the british irish ice sheet using relative sea level data implications for the interpretation of trimline observations the glacial isostatic adjustment gia of the british isles is complex due to the interplay between local and non local signals a number of recent studies have modelled the gia response of the british isles using relative sea level data this study extends these previous analyses by using output from a numerical glaciological model as input to a gia model this is a necessary step towards more realistic gia models and although there have been similar studies for the major late pleistocene ice sheets this is the first study to do so for the british isles we test three reconstructions classed as minimal median and maximal in terms of their volume at maximum extent and find it is possible to obtain good data model fits the minimal reconstruction is clearly preferred by the sea level data the ice reconstructions tested were not constrained by geomorphological information of past ice extent lateral and vertical as a consequence the reconstructions extend further than much of this information suggests particularly in terms of ice thickness it is notable however that the reconstructions produce good fits to many sea level data from central mountainous regions e g scottish highlands which lends support to the suggestion that trimlines often used as an constraint on the palaeo ice surface location are in fact features formed at the transition from warm to cold based ice and so mark a minimum constraint on the ice surface altitude based on data model misfits suggestions are made for improving the ice model reconstructions however in many locations the cause of the misfit could be due to non local predominantly fennoscandian ice and so interpretation is not straightforward as a result we suggest that future analyses of this type consider models and observations for both fennoscandia and the british isles copyright 2012 john wiley sons ltd

pliocene quaternary transpressional evolution of the anzi calvello and northern s arcangelo basins basilicata southern apennines italy as a consequence of deep seated fault reactivation abstract in this paper we report the results of a study of the plio pleistocene anzi calvello basin and the northern sector of the s arcangelo basin southern apennines italy our work suggests that the evolution of the anzi calvello basin is related to the activity of a deep seated roughly nne trending dextral transpressional fault zone camastra transcurrent fault zone ctfz structural control of sedimentation by this structure is indicated by the geometry of the unconformity bounded stratigraphic units as well as by the deformation of the basin fill en echelon n s trending thrusts n to ne trending dextral transpressional faults and nw to nnw striking folds affecting the substratum constitute the surface response to lateral displacement along the ctfz the s arcangelo basin is bounded to the north by a deep seated roughly wnw nw trending sinistral transpressional structure valsinni lateral ramp vlr that terminates northwestward against the ctfz at the surface the vlr is dominated by back thrusts and by transpressional fault zones the vlr has been interpreted as the sinistral lateral ramp of the large scale valsinni thrust anticline and it is inferred to have strongly controlled local deposition within the s arcangelo basin the deep seated structures ctfz and vlr probably represent reactivated pre existing normal and transfer faults affecting the rigid apulian platform that were generated during passive margin evolution as well as during the flexural bending of the apulian lithosphere during the pliocene pleistocene these structures were reactivated as lateral ramps accommodating the thrusting within the apulian platform transpression along the lateral ramps in the apulian platform propagated upwards through the nappe pile giving rise to a complex surface structural pattern and the local development of flower like structures

post 10 ma uplift and exhumation of the northern coast mountains british columbia apatite u th he ages reveal three distinct periods in the exhumation history of the northern coast mountains 54 n a well developed helium partial retention zone indicates little or no exhumation between ca 30 and 10 ma beginning at 10 ma and extending to at least 4 ma the range underwent steady but slow exhumation of 0 22 mm yr after which the exhumation rate increased by at least 70 an 85 km long he age traverse across the orogen at sea level shows that vertical offsets on post 10 ma faults are minor furthermore the sea level he ages 14 2 8 ma inversely correlate with local mean elevation along the traverse these data suggest that the coast mountains first appeared as a significant topographic feature only within the past few million years this history is not consistent with suggestions that uplift of the range resulted from formation of the queen charlotte basin in early middle miocene time we speculate that intense erosion by alpine and continental glaciation after 2 5 ma triggered isostatic uplift and creation of the modern topography of the coast mountains

glaciation as a destructive and constructive control on mountain building glacial erosion is thought to have an important role in controlling mountain height a common perception is that glaciers are powerful erosive agents inhibiting the ability of active mountains to rise significantly above the elevation of permanent glaciation through a process known as the glacial buzzsaw but now a study of erosion patterns and climate data from the late cenozoic in the glaciated patagonian andes suggests that glaciation can also have the reverse effect in effect making mountains higher at these polar latitudes glaciation acts as a protective layer preserving the uplifting mountains from erosion and allowing them to reach heights well above those predicted had a glacial buzzsaw been active it has been suggested that glacial erosion has an important role in controlling mountain height here spatial and temporal patterns of erosion in the glaciated patagonian andes have been assessed with the help of a low temperature thermochronologic data set the results show that between 38 s and 49 s accelerated erosion at the onset of widespread glaciation limits mountain height but at higher latitudes glaciation protects the landscape from erosion and leads to growth in mountain height and width theoretical analysis predicts that enhanced erosion related to late cenozoic global cooling can act as a first order influence on the internal dynamics of mountain building leading to a reduction in orogen width and height1 2 3 the strongest response is predicted in orogens dominated by highly efficient alpine glacial erosion producing a characteristic pattern of enhanced erosion on the windward flank of the orogen and maximum elevation controlled by glacier equilibrium line altitude3 4 where long term glacier mass gain equals mass loss however acquiring definitive field evidence of an active tectonic response to global climate cooling has been elusive5 here we present an extensive new low temperature thermochronologic data set from the patagonian andes a high latitude active orogen with a well documented late cenozoic tectonic climatic and glacial history data from 38 s to 49 s record a marked acceleration in erosion 7 to 5 myr ago coeval with the onset of major patagonian glaciation6 and retreat of deformation from the easternmost thrust front7 the highest rates and magnitudes of erosion are restricted to the glacial equilibrium line altitude on the windward western flank of the orogen as predicted in models of glaciated critical taper orogens where erosion rate is a function of ice sliding velocity3 8 in contrast towards higher latitudes 49 s to 56 s a transition to older bedrock cooling ages signifies much reduced late cenozoic erosion despite dominantly glacial conditions here since the latest miocene6 the increased height of the orogenic divide at these latitudes well above the equilibrium line altitude leads us to conclude that the southernmost patagonian andes represent the first recognized example of regional glacial protection of an active orogen from erosion leading to constructive growth in orogen height and width

using meteoric 10be to track fluvial sand through the waipaoa river basin new zealand we use meteoric 10 be measured in 24 fluvial sand samples collected along the mainstem and from prominent tributaries within the tectonically active waipaoa river basin new zealand to identify sediment sources and monitor the mixing of sediment as it travels from headwater basins to the sea deforestation for agriculture beginning in the early 1900s resulted in severe but nonuniformly distributed erosion tributaries in the northern headwaters where large amphitheater gullies that continually feed prodigious amounts of deeply sourced sediment to the mainstem are prevalent yield exceptionally low concentrations of meteoric 10 be 1 5 10 6 atoms g 1 in the more stable eastern and western tributaries concentrations of meteoric 10 be are nearly an order of magnitude greater 14 10 6 atoms g 1 meteoric 10 be concentrations in samples collected along the mainstem above and below tributary confluences steadily and regularly increase downstream r 2 0 92 as large amounts of low concentration gully derived sediments are augmented with higher concentration sediment from more stable tributaries providing strong evidence that meteoric 10 be concentrations reflect sediment sourcing in this fluvial network a two component mixing model indicates that the gullied northern region of the waipaoa basin produces sediment at a rate 20 times that of the eastern and western regions these results suggest that meteoric 10 be in contrast to the widely applied in situ technique that is limited by the availability and distribution of quartz is an effective tool for the rapid assessment of sediment dynamics and movement within a wide range of fluvial networks

cosmogenic nuclide budgeting of floodplain sediment transfer abstract cosmogenic nuclides produced in quartz may either decay or accumulate while sediment is moved through a river basin a change in nuclide concentration resulting from storage in a floodplain is potentially important in large drainage basins in which sediment is prone to repeated burial and remobilization as a river migrates through its floodplain we have modeled depth and time dependent cosmogenic nuclide concentration changes for 10 be 26 al and 14 c during sediment storage and mixing in various active floodplain settings ranging from confined shallow rivers with small floodplains to foreland basin scale floodplains traversed by deep rivers floodplain storage time estimated from channel migration rates ranges from 0 4 kyr for the beni river basin bolivia to 7 kyr for the amazon river basin while floodplain storage depth estimated from channel depth ranges from 1 to 25 m for all modeled active floodplain settings the long lived nuclides 10 be and 26 al show neither significant increase in nuclide concentration from irradiation nor decrease from decay we predict a hypothetical response time after which changes in 10 be or 26 al concentrations become analytically resolvable this interval ranges from 0 07 to 2 myr and exceeds in all cases the typical residence time of sediment in a floodplain due to the much shorter half life of 14 c nuclide concentrations modeled for the in situ produced variety of this nuclide are however sensitive to floodplain storage on residence times of the cosmogenic nuclide composition of old deposits in currently inactive floodplains that have been isolated for periods of millions of years from the river that once deposited them is predicted to either increase or decrease in 10 be and 26 al concentration depending on the depositional depth these conditions can be evaluated using the 26 al 10 be ratio that readily discloses the depth and duration of storage we illustrate these models with examples from the amazon basin as predicted modern bedload collected from an amazon tributary the bolivian beni river shows no systematic change in nuclide concentration as sediment is moved through 500 km of floodplain by river meandering in contrast in the central amazon floodplain currently untouched by the modern river system low 26 al 10 be ratios account for minimum burial depths of 5 to 10 m for a duration of 5 myr the important result of this analysis is that in all likely cases of active floodplains cosmogenic 10 be and 26 al concentrations remain virtually unchanged over the interval sediment usually spends in the basin thus spatially averaged denudation rates of the sediment producing area can be inferred throughout the entire basin provided that nuclide production rates are scaled for the altitudes of the sediment producing area only because floodplain storage does not modify nuclide concentrations introduced from the sediment source area

felsenmeer persistence under non erosive ice in the torngat and kaumajet mountains quebec and labrador as determined by soil weathering and cosmogenic nuclide exposure dating soil analyses and terrestrial cosmogenic nuclide exposure dating are combined and a conceptual model proposed to explain altitudinal weathering contrasts in high latitude highlands we show that summits in the torngat and kaumajet mountains were covered by ice during the last glacial maximum and that their felsenmeer cover probably survived multiple glaciation events for similar lithologies soils on felsenmeer covered summits are signigicantly more weathered than those below the felsenmeer limit displaying higher concentrations of crystalline iron amorphous aluminium and silicium extracted with oxalate secondary minerals such as gibbsite and kaolinite occur in felsenmeer soils whereas those formed in till lacked these secondary minerals 10be and 26al exposure ages for nine of ten samples from high elevation tors and autochthonous felsenmeer blocks range from 73 6 to 157 15 ka by contrast ages of 11 4 1 0 and 11 7 1 0 ka are measured for bedrock in the much lower saglek zone indicating extensive 3 m glacial erosion of this zone during late wisconsinan glaciation 26al 10be ratios demonstrate that exposure of the high elevation surfaces was interrupted during at least one cosmic ray shielding event by either ice or till cover in either case late wisconsinan glaciers could not have extensively eroded these surfaces five erratics dated above the saglek zone including one in the felsenmeer zone have exposure ages ranging from 11 6 1 0 to 13 6 0 7 ka this indicates that valley and high elevation ice persisted through the younger dryas chron and provides further evidence that the highlands were not nunataks during the late wisconsinan period

extent of the last ice sheet in northern scotland tested with cosmogenic 10be exposure ages the extent of the last british irish ice sheet biis in northern scotland is disputed a restricted ice sheet model holds that at the global last glacial maximum lgm ca 23 19 ka the biis terminated on land in northern scotland leaving buchan caithness and the orkney islands ice free an alternative model implies that these three areas were ice covered at the lgm with the biis extending offshore onto the adjacent shelves we test the two models using cosmogenic 10be surface exposure dating of erratic boulders and glacially eroded bedrock from the three areas our results indicate that the last biis covered all of northern scotland during the lgm but that widespread deglaciation of caithness and orkney occurred prior to rapid warming at ca 14 5 ka copyright 2008 john wiley sons ltd

using in situ cosmogenic 10be to identify the source of sediment leaving greenland we use the concentration of in situ 10be in quartz isolated from fluvial and morainal sand to trace sediment sources and to determine the relative contribution of glacerized and deglaciated terrain to greenland s sediment budget we sampled along the western eastern and southern margins of the greenland ice sheet and collected sediment sourced from glacerized n 19 and non glacerized terrain n 10 from channels where sediment from glacerized and non glacerized terrain is mixed n 28 from holocene glacial fluvial terraces n 4 and from one sand dune in situ 10be concentrations in sediment range from 1600 to 34 000 atoms g 1 the concentration of in situ 10be in sediment sourced from non glacerized terrain is significantly higher than in sediment sourced from glacerized areas in mixed channel sediment and in terrace sediment that was deposited during the holocene to constrain the timing of landscape exposure for the deglaciated portion of the narsarsuaq field area in southern greenland we measured in situ 10be concentration in bedrock n 5 and boulder n 6 samples paired bedrock and boulder ages are indistinguishable at 1 uncertainty and indicate rapid exposure of the upland slopes at 10 5 ka the isotope concentration in sediment sourced from non glacerized terrain is higher than in sediment sourced from glacerized terrain because the non glacerized landscape has been exposed to cosmic radiation since early holocene deglaciation sediment from glacerized areas contains a low but measurable concentration of 10be that probably accumulated at depth during a prolonged period of exposure probably before the establishment of the greenland ice sheet the concentration of 10be in mixed fluvial sediment and in terrace sediment is low and similar to the concentration in sediment from glacerized areas which indicates that the greenland ice sheet is the dominant source of sediment moving through the landscape outside the glacial margin in the areas we sampled copyright 2014 john wiley sons ltd

effect of alpine glaciation on thermochronometer age elevation profiles 1 low temperature thermochronometers are widely used to quantify exhumation histories typically by interpreting sample cooling age elevation relationships however the effects of specific geomorphic processes on age elevation profiles are seldom considered we integrate apatite u th he ahe apatite fission track and zircon u th he thermochronometry with numerical modeling to determine the effect of glacial erosion on an age elevation profile from the heavily glaciated southern coast mountains british columbia ahe data show a distinct break in slope in ageelevation between 1900 2100 m we interpret this break in slope as an acceleration of erosion associated with the onset ofalpineglaciation weusea3 dthermo kinematic modelto constrain pre and synglacial erosion rates results indicate a preglacial erosion rate of 0 4 mm yr that accelerated by a factor of 2 since 6 ma we propose that glacial valley widening and deepening are responsible for the observed nonlinear ahe age elevation profile citation densmore m s t a ehlers and g j woodsworth 2007 effect of alpine glaciation on thermochronometer age elevation profiles geophys res lett 34 l02502 doi 10 1029 2006gl028371

high resolution numerical simulation of younger dryas glaciation in scotland golledge n r hubbard a sugden d e 2008 high resolution numerical simulation of younger dryas glaciation in scotland quaternary science reviews 27 9 10 888 904 sponsorship nerc

trimlines blockfields mountain top erratics and the vertical dimensions of the last british irish ice sheet in nw scotland periglacial trimlines separating glacially eroded lower slopes from blockfield covered plateaus on british and irish mountains have been interpreted either 1 in terms of representing the maximum altitude of the last ice sheet during the last glacial maximum lgm or 2 as a thermal boundary separating wet based ice at pressure melting point from cold based ice on summit plateaus we test these competing hypotheses through 10be exposure dating of high level erratic boulders above trimlines on five mountains in nw scotland nine out of 14 erratics yielded post lgm exposure ages ranging from 14 0 0 7 ka to 16 5 0 9 ka or from 14 9 0 9 ka to 17 6 1 1 ka depending on the 10be production rate employed in exposure age calculation these ages refute hypothesis 1 as they imply that the last ice sheet overtopped the mountains preservation of apparently intact blockfields on the summits implies cold based ice cover supporting hypothesis 2 as altitudinally consistent high level trimlines extend from our sampled sites across much of nw scotland and the hebrides our conclusions apply to all trimlines in this broader area and probably to all high level trimlines elsewhere in the british isles preservation of blockfields under cold based ice is consistent with blockfield evolution on plateaus throughout much or all of the quaternary averaged exposure ages of 15 16 ka for plateau top erratics implies nunatak emergence from the downwasting ice sheet prior to a regional readvance of the ice margin the wester ross readvance and before rapid warming at 14 7 ka at the onset of the lateglacial interstade but after the timing of ice sheet thinning as retrodicted by recent proxy climate driven thermo mechanical coupled models our findings provide an additional constraint on the future development of such models by implying that high level trimlines represent the altitude of a former transition zone between ice at pressure melting point and ice below pressure melting point

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

evidence from apatite fission track analysis for the post devonian burial and exhumation history of the northern highlands scotland abstract devonian and older rock samples from outcrops in the northern scottish highlands have undergone protracted cooling since they reached palaeotemperatures of 110 c or more in the late palaeozoic to early mesozoic the results not only suggest that the northern highlands region has experienced kilometre scale exhumation since the late palaeozoic but also that devonian and possibly permo carboniferous sedimentation was probably more extensive than current outcrop patterns would imply a permian outcrop sample from the minches basin reached a maximum palaeotemperature of 70 90 c prior to the onset of cooling in the early tertiary while data from devonian and older samples suggest an acceleration in the rate of cooling in the early tertiary the magnitude of early tertiary palaeotemperatures on the mainland adjacent to the inner moray firth imf indicate similar amounts of tertiary exhumation to those derived from compaction analyses for the imf however to the west the magnitude of tertiary cooling cannot be solely ascribed to exhumation and a contribution of heating due to hydrothermal effects and or elevated heat flow associated with the tertiary igneous complex may also need to be invoked

extent and deglacial chronology of the last british irish ice sheet implications of exposure dating using cosmogenic isotopes over 160 10be and 36cl exposure ages pertaining to the extent and chronology of the last british irish ice sheet biis are critically reviewed despite uncertainties inherent in the use of exposure ages this approach has demonstrated that at the last glacial maximum lgm ca 26 21 ka the biis extended over all low ground in scotland and all or almost all of ireland consistent with recent models depicting extension of the last biis to the atlantic shelf edge all exposure ages obtained for high level sites above trimlines on the mountains of northwestern scotland and ireland pre date the lgm this finding confirms that high plateaux in these areas escaped significant glacial erosion probably under a protective cover of cold based glacier ice that remained frozen to the underlying substrate in terms of deglaciation chronology the southern irish sea basin was probably deglaciated by 19 18 ka with extensive deglaciation of low ground in ireland and northeastern scotland prior to ca 14 5 ka ice cover on low ground in northwestern scotland apparently persisted after 14 0 ka suggesting survival of ice in favourable locations during the lateglacial interstade ca 14 5 12 9 ka attempts to date readvances have had mixed success the wester ross readvance in northwestern scotland was initially dated to ca 16 3 ka but more recent research implies a much younger age ca 14 0 13 5 ka exposure ages indicating a prolonged stillstand during ice sheet retreat in the cairngorms at ca 14 5 14 0 ka conflict with ages obtained on postglacial rockslides and basal radiocarbon dates which indicate deglaciation before ca 15 5 15 0 ka exposure dating has been successfully employed to confirm a loch lomond stadial ca 12 9 11 5 ka age for moraines in several mountain areas and to constrain the minimum altitude of the ice cap that extended over the western grampians at that time copyright 2009 john wiley sons ltd

sediment production and delivery in the amazon river basin quantified by in situ produced cosmogenic nuclides and recent river loads we use cosmogenic nuclide derived denudation rates from in situ produced 10 be in river sediment to determine sediment production rates for the central amazon river and its major tributaries recent developments have shown that this method allows calculating denudation rates in large depositional basins despite intermediate sediment storage with the result that fluxes of the sediment producing hinterland can now be linked to those discharged at the basins outlet in rivers of the central amazonian plain sediment of finer grain sizes 125 500 m yields a weighted cosmogenic nuclide derived denudation rate of 0 24 0 02 mm yr that is comparable to the integrated rate of all main andean draining rivers 0 37 0 06 mm yr which are the beni napo mamore ucayali and maranon rivers coarser grained sediment 500 m of central amazonian rivers is indicative of a source from the tectonically stable cratonic headwaters of the guyana and brazilian shields for which the denudation rate is 0 01 0 02 mm yr respective sediment loads can be calculated by converting these cosmogenic nuclide derived rates using their sediment producing areas for the amazon river at obidos a sediment production rate of 610 mt yr results non andean source areas contribute only 45 mt yr a comparison with published modern sediment fluxes shows similarities within a factor of 2 with an average gauging derived sediment load of 1000 mt yr at obidos for example we attribute this similar trend in cosmogenic versus modern sediment loads first to the absence of long term deposition within the basin and second to the buffering capability of the large amazon floodplain the buffering capability dampens short term high amplitude fluctuations climatic variability in source areas and anthropogenic soil erosion by the time the denudation rate signal of the hinterland is transmitted to the outlet of the basin

a new estimate of the holocene lowstand level of lake titicaca central andes and implications for tropical palaeohydrology new evidence from piston cores and high resolution seismic reflection data shows that water levels in lake titicaca were as much as 100 m below the present level during the early to mid holocene between 6 and 3 8 14c kyr bp climatological and modelling studies indicate that lake titicaca rainfall depends on convective activity in upwind amazonia the lake level data therefore suggest a drier amazon basin during this time this view is bolstered by an excellent match between the titicaca lake level curve and decreased methane concentrations in greenland ice previously ascribed to drying of low latitude wetlands blunier et al 1995 the postglacial history of lake titicaca fits a global pattern of lake level change in the tropics characterized by opposite phasing between the southern and northern hemispheres this pattern is most likely the result of orbital controls over the intensity of summer insolation

in situ cosmogenic exposure ages from the isle of skye northwest scotland implications for the timing of deglaciation and readvance from 15 to 11 ka we present 10 in situ cosmogenic exposure ages from two moraines on the isle of skye the strollamus medial moraine was deposited during deglaciation of the devensian ice sheet and yields a mean exposure age from five samples of 14 3 0 9 ka the moraine age indicates that a significant ice mass existed on skye at the time of a regional readvance recorded in wester ross northwest scotland taken at face value the ages suggest that deglaciation did not occur until well into greenland interstade 1 the slapin moraine represents the local limit of the loch lomond readvance llr and yields a mean exposure age from five samples of 11 5 0 7 ka which is consistent with deposition relating to the llr these ages suggest that the maximum extent may have been reached late in the stadial and that some glaciers may have remained active until after the climatic amelioration that marks its end this scenario is considered unlikely given the nature of the climate during this period which leads us to call for a locally calibrated production rate copyright 2011 john wiley sons ltd

landscape preservation under fennoscandian ice sheets determined from in situ produced 10be and 26al some areas within ice sheet boundaries retain pre existing landforms and thus either remained as ice free islands nunataks during glaciation or were preserved under ice differentiating between these alternatives has significant implications for paleoenvironment ice sheet surface elevation and ice volume reconstructions in the northern swedish mountains in situ cosmogenic 10be and 26al concentrations from glacial erratics on relict surfaces as well as glacially eroded bedrock adjacent to these surfaces provide consistent last deglaciation exposure ages 8 13 kyr confirming ice sheet overriding as opposed to ice free conditions however these ages contrast with exposure ages of 34 61 kyr on bedrock surfaces in these same relict areas demonstrating that relict areas were preserved with little erosion through multiple glacial cycles based on the difference in radioactive decay between 26al and 10be the measured nuclide concentration in one of these bedrock surfaces suggests that it remained largely unmodified for a minimum period of 845 418 461 kyr these results indicate that relict areas need to be accounted for as frozen bed patches in basal boundary conditions for ice sheet models and in landscape development models subglacial preservation also implies that source areas for glacial sediments in ocean cores are considerably smaller than the total area covered by ice sheets these relict areas also have significance as potential long term subglacial biologic refugia

asymmetrical erosion and morphological development of the central ladakh range northern india abstract variations in erosion were quantified across the topographically and morphometrically asymmetrical central ladakh range in nw india to elucidate erosion and sediment transfer processes across space and time and to gain insight into how mountains erode and evolve morphometric analysis and 10 be cosmogenic nuclide analysis of 14 fluvial sediment samples from active channels in six catchments conducted across the mountain range constrains 100 ka timescale erosion rates for catchments on the northern side of the mountain range and are between 56 12 and 74 11 m ma while catchments on the southern side of the mountain range to between 20 3 and 39 8 m ma for the last 300 ka maximum elevation from swath analysis across the range shows a strong correlation with the elas of 382 contemporary glaciers the higher erosion rate to the north likely relates to tectonic tilting of the central ladakh range and to active rock uplift on the northern side of the range along the karakoram fault morphometric analysis shows that the maximum and average elevations increase at nearly the same rate on a catchment scale across the central ladakh range with higher elevation on the northern side this suggests that greater erosion on the northern side of the range is not keeping pace with rock uplift moreover long term denudational unloading does not play a significant role in the tectonic tilting of the central ladakh range

retreating ice research in pro glacial areas matters glacier forefields are landscapes in transition from glacial to non glacial conditions this implies intense geomorphic hydrological and ecological dynamics with important on and off site effects this special issue collects 13 papers covering recent research in both sub polar and alpine proglacial environments that focus on i proglacial sediment sources ii proglacial rivers iii proglacial lakes iv ground water and ice and v the development of soil and vegetation in its interplay with morphodynamics advances in mapping surveying and geophysical techniques form the basis for research perspectives related to the historical evolution of proglacial areas the understanding of complex interactions of multiple processes and the effects of continued glacier recession

tracking paraglacial sediment with cosmogenic 10 be using an example from the northwest scottish highlands abstract beryllium 10 concentrations in samples of sediment and bedrock from five study sites across the scottish highlands trace paraglacial sediment sources and define the nature of glacial erosion for the late quaternary exposure ages derived from 10 be concentrations in ridge and lower elevation bedrock range from 10 to 33 ka which suggest that polythermal ice and warm based ice were primarily responsible for producing glacial sediment comparisons of 10 be concentrations between catchment wide sediment 2 06 0 34 10 4 to 11 24 1 54 10 4 atoms g 1 sio 2 n 33 near surface deposits 2 71 0 33 10 4 to 3 48 0 49 10 4 atoms g 1 sio 2 n 6 4 m thick deep till 0 68 10 4 10 be atoms g 1 sio 2 n 1 ridge bedrock 8 93 0 47 10 4 to 34 05 1 66 10 4 atoms g 1 sio 2 n 20 and lower elevation polished bedrock 6 74 0 67 10 4 to 12 65 0 7 10 4 atoms g 1 sio 2 n 5 indicate that most sand fluxing through catchments in the scottish highlands is sourced from the remobilization and vertical mixing of near surface deposits these findings indicate that glaciogenic material continues to dominate paraglacial sediment budgets more than 11 ka after deglaciation

did large ice caps persist on low ground in north west scotland during the lateglacial interstade recent research based primarily on exposure ages of boulders on moraines has suggested that extensive ice masses persisted in fjords and across low ground in north west scotland throughout the lateglacial interstade greenland interstade 1 ca 14 7 12 9 ka and that glacier ice was much more extensive in this area during the older dryas chronozone ca 14 0 ka than during the younger dryas stade ca 12 9 11 7 ka we have recalibrated the same exposure age data using locally derived 10be production rates this increases the original mean ages by 6 5 12 implying moraine deposition between ca 14 3 and ca 15 1 ka and we infer a most probable age of ca 14 7 ka based on palaeoclimatic considerations the internal consistency of the ages implies that the dated moraines represent a single readvance of the ice margin the wester ross readvance pollen stratigraphic evidence from a lateglacial site at loch droma on the present drainage divide demonstrates deglaciation before ca 14 0 ka and therefore implies extensive deglaciation of all low ground and fjords in this area during the first half of the interstade ca 14 7 14 0 ka this inference appears consistent with lateglacial radiocarbon dates for shells recovered from glacimarine sediments and a dated tephra layer our revised chronology conflicts with earlier proposals that substantial dynamic ice caps persisted in scotland between 14 and 13 ka that large active glaciers probably survived throughout the lateglacial interstade and that ice extent was greater during the older dryas period than during the younger dryas stade copyright 2011 john wiley sons ltd