instantaneous end moraine and sediment wedge formation during the 1890 glacier surge of bruarjokull iceland abstract contemporary understanding of the behaviour of surging glaciers and ice streams is hampered by the lack of data on landsystem evolution and sedimentary environments this study concerns the ice marginal environment of the surge type bruarjokull in iceland the sediment distribution in the glacier forefield as well as the morphology sedimentology and tectonic architecture of the 1890 end moraine is investigated for highlighting the interaction between very dynamic ice and sediment landform associations as a result of substrate bedrock decoupling during the 1890 surge subglacial sediment was dislocated across the bedrock surface and deformed compressively leading to gradual substrate thickening and the formation of a sediment wedge in the marginal zone a drop in subglacial porewater pressure at the very end of the surge led to substrate bedrock coupling and a stress transfer up into the sediment sequence causing brittle deformation of the substrate simultaneously the glacier toe ploughed into the topmost part of the marginal sediment wedge initiating the moraine ridge construction fine grained and incompetent sediment deformed in ductile manner resulting in a narrow moraine dominated by rooted folds while coarse grained and competent sediment deformed in brittle fashion resulting in a wider moraine dominated by thrust blocks a new sequential model of subglacial and ice marginal processes operating during a glacier surge is proposed illustrating the stepwise formation of a marginal sediment wedge and an end moraine a twofold inseparable marginal end product that formed during the last days of the 1890 surge

soil weathering and accumulation rates of oxalate extractable phases derived from alpine chronosequences of up to 1 ma in age abstract in this study we compare newly developed chemical weathering data with previously published data from soils developed along two chronosequences of glacial deposits in the european alps and the rocky mountains wind river range usa by combining these chronosequences we are able to present a comprehensive dataset that represents a time period of 1 ma we describe weathering trends of important elements using a number of weathering indices e g k ca ti ratio the weathering index b of kronberg and nesbitt 1981 and the open mass transport function further we describe the accumulation of al fe si and mn oxyhydroxides including partially organic phases as a function of time and derive the corresponding accumulation rates we calculated pedogenetically formed oxyhydroxides using an approach based on immobile elements our study represents one of only a few studies that describe rates of soil chemical weathering over a period as long as 1 ma results show that rates of chemical weathering clearly decrease along the chronosequences with increasing age of the soils we find weathering rates are nearly four orders of magnitude lower in the 1 ma old soils than in the young soils our results suggest that the older soils may be reaching a steady state for these chemical properties in their present environments a power function best explains the measured time trends of the index b and k ca ti ratios in the soils the best time trend model for pedogenic weakly to poorly crystalline phases and the relative losses gains based on the open system mass transport function were obtained with an exponential decay model function in terms of the soil system the decreases in the accumulation rate of the oxyhydroxides appears to be influenced not only by the factor of time but by climate as well increased precipitation at higher altitudes slows the decrease in weathering rate over time thus our 1 ma chronosequences also become pedogenic gradients since we describe variations in soil properties along biogenic gradients

a limited area model of the gulf stream design initial experiments and model data intercomparison abstract a primitive equation n layer eddy resolving creation model has been applied to the gulf stream system from cape hatteras to cast of the grand banks 78 45 w 30 48 n within the limitations of the model realistic coastlines bottom topography and forcing functions have been used a two layer version of the model was driven by observed mean climatological wind forcing and mass transport prescribed at inflow outflow was determined by a radiation boundary condition and an integral constraint on the mass field in each layer specification of a deep western boundary current dwbc was included in some model runs six numerical experiments from a series of over fifty integrated to statistical equilibrium were selected for detailed description and intercomparison with observations the basic case consisted of a flat bottom regime driven by wind forcing only realistic inflow transport in the upper layer was then prescribed and two different outflow specifications at the eastern boundary were s

eddy resolution versus eddy diffusion in a double gyre gcm part ii mixing of passive tracers abstract the parameterization of the effect of the unresolved scales of motion on a passive tracer field in large scale numerical ocean models is analyzed through a combination of lagrangian and eulerian velocities the primitive equation isopycnal model discussed by bleck and boudra is used in part i to simulate the trajectory of particles in an eddy resolving double gyre circulation from these trajectories and from the associated eulerian velocity field a lagrangian isopycnal diffusivity field and a deformation dependent diffusivity distribution were estimated part i here part ii the same velocity field is used to simulate the evolution of idealized passive tracer fields in fine 20 km and coarse 200 km resolution models the main goal of this work is to test the limitations that coarse horizontal resolution imposes on the advective diffusive equation by comparing the evolution of a passive tracer field in a high resolution version of the model and in an off line version this off line vel

application of an inverse method to interpret 231pa 230th observations from marine sediments constraints then sediment 231 pa 230 th data for each time interval are combined with an advection scavenging model in order to determine their in consistency with the modern circulation estimate we find that the majority of sediment 231 pa 230 th data for the holocene lgm or h1 can be brought into consistency with the modern circulation if plausible assumptions are made about the large scale distribution of 231 pa and about model uncertainties moreover the adjustments in the data needed to reach compatibility with a hypothetical state of no flow no advection are positively biased for each time interval suggesting that the 231 pa 230 th data including that for h1 are more consistent with a persistence of some circulation than with no circulation our study does not imply that earlier claims of a circulation change during the lgm or h1 are inaccurate but that these claims cannot be given a rigorous basis given the current uncertainties involved in the analysis of the 231 pa 230 th data

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

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

weathering and evolution of soils formed on granitic glacial deposits results from chronosequences of swiss alpine environments abstract two soil chronosequences of mountainous ecosystems in switzerland served as the basis to calculate the accumulation of soil organic matter transformation of pedogenic fe and al and net losses of the main elements ca mg k na fe al mn and si by means of mass balance calculations elemental losses due to deglaciation and exposure to the weathering environment were calculated these mass balance calculations indicate that extensive mineral weathering resulted in significant leaching losses of si major base cations and al particularly from the upper horizons the losses are especially pronounced in the early stages of soil formation in most cases the exponential decay model incorporating an asymptotic or logarithmic regression model seems to provide a good description of weathering the greatest changes in the soil chemistry of these alpine soils on granitic host material occurred within the first 3000 4000 years of soil development later the weathering rates decreased rapidly and the overall depletion of elements nearly reached an asymptote we also found that the mean ratio of al t fe d al d fe t of the fine earth of the a e and b horizons is closely linked to the duration of soil development a very rapid decrease of this ratio also occurred at the beginning of soil evolution in order to reach asymptotic values after about 3000 years consequently this ratio could be a good indicator of the age of alpine soils furthermore there is a close relationship between the mass of organic c or n in the whole profile and the soil age the older the soil the higher the corresponding mass per unit area the chronofunctions presented give a first attempt of the chemical soil evolution in the alps however only little data has been available up until now regarding alpine soils and this fact inhibits a more detailed observation of the changes that have occurred over a period of 2000 8000 years of soil formation under similar climatic conditions

determining the strength of the deep western boundary current using the chlorofluoromethane ratio abstract the dilution of a passive tracer during deep water formation and the subsequent advection mixing in a deep boundary current is modeled with application to chlorofluoromethanes cfms in the north atlantic two different types of boundary currents are considered a uniform flow and a simple shear flow in each case the core of the flow mixes with surrounding water which continually accumulates cfms in an extreme case the coupled systems predicts that the cfm ratio in the current is unaltered from the ratio of its source water save for a time lag more realistic cases however suggests that the ratio is not a conserved quantity but is substantially altered in both the overflow basin and boundary current matching the model results to cfm data collected near the grand banks gives a predicted average core speed of 5 10 cm s 1 for the deep western boundary current and provides a constraint on the transport and diffusivity of the flow as well

discovery of early holocene wood and peat on the forefield of the pasterze glacier eastern alps austria during recent years a number of fragments of pinus cembra and larix decidua as well as peat were found in front of the tongue of the pasterze glacier in the eastern alps these were washed out by the stream from under the present ice the wood originates from trees which reached ages of upto 400 years or more radiocarbon dating shows them to come from the early holocene they indicate that between cal bc 8100 and cal bc 6900 the pasterze glacier was smaller than at present the pasterze glacier advanced around cal bc 6900 a lump of peat shows that around cal bc 6300 at the latest the pasterze glacier was again smaller than today the radiocarbon age of the fulvic acid fraction of thepeat suggests that growth could have continued until cal bc 5430 5080 further wood samples dated to around cal bc 4800 and cal bc 3800 show that at these times the pasterze glacier was smaller than at present the pasterze glacier had a relatively limited extent over long periods inthe early holocene thus mostly favou

extractable fe and al in late pleistocene and holocene paleosols on niwot ridge colorado front range summary surface and buried paleosols on niwot ridge in the front range of colorado were analyzed for extractable fe and al to determine if their distributions would assist in the interpretation of past and present soil forming environments extractable fe and al distributions in surface and buried paleosols suggest that leaching is more pronounced in the older paleosols with a considerable difference in soil forming environment between pleistocene interstadial later pleistocene and postglacial paleosols using radiocarbon dated buried a horizons it appears that little pyrophosphate extractable fe and al have been translocated downward into these middle latitude alpine buried paleosols there is no evidence that the na pyrophosphate extractable fe and al were affected by degradation of organic matter following burial however the data suggest that some amorphous fe and al might have been affected by soil water movement over permafrost and by redistribution of preweathered sediments

cosmogenic 10be and 36cl ages from late pleistocene terminal moraine complexes in the taylor river drainage basin central colorado usa abstract cosmogenic surface exposure ages from boulders on a terminal moraine complex establish the timing of the local last glacial maximum lgm in the taylor river drainage basin central colorado five zero erosion 10 be ages have a mean of 19 5 1 8 ka while that for three 36 cl ages is 20 7 2 3 ka corrections for modest rates 1 mm ka 1 of boulder surface erosion result in individual and mean ages that are generally within 2 of their zero erosion values both the means and the range in ages of individual boulders are consistent with those reported for late pleistocene moraines elsewhere in the southern and middle rocky mountains and thus suggest local lgm glacier activity was regionally synchronous two anomalously young zero erosion 10 be ages mean 14 4 0 8 ka from a second terminal moraine are tentatively attributed to the boulders having been melted out during a late phase of ice stagnation

latest pleistocene glacial chronology of the uinta mountains support for moisture driven asynchrony of the last deglaciation abstract recent estimates of the timing of the last glaciation in the southern and western uinta mountains of northeastern utah suggest that the start of ice retreat and the climate driven regression of pluvial lake bonneville both occurred at approximately 16 cal ka to further explore the possible climatic relationship of uinta mountain glaciers and the lake and to add to the glacial chronology of the rocky mountains we assembled a range wide chronology of latest pleistocene terminal moraines based on seventy four cosmogenic 10be surface exposure ages from seven glacial valleys new cosmogenic exposure ages from moraines in three northern and eastern valleys of the uinta mountains indicate that glaciers in these parts of the range began retreating at 22 20 ka whereas previously reported cosmogenic exposure ages from four southern and western valleys indicate that ice retreat began there between 18 and 16 5 ka this spatial asynchrony in the start of the last deglaciation was accompanied by a 400 m east to west decline in glacier equilibrium line altitudes across the uinta mountains when considered together these two lines of evidence support the hypothesis that lake bonneville influenced the mass balance of glaciers in southern and western valleys of the range but had a lesser impact on glaciers located farther east regional scale variability in the timing of latest pleistocene deglaciation in the rocky mountains may also reflect changing precipitation patterns thereby highlighting the importance of precipitation controls on the mass balance of pleistocene mountain glaciers

morphology and paleoclimatic significance of pleistocene lake bonneville spits abstract pleistocene lake bonneville of western utah contains a variety of spits associated with shorelines and other features that formed between 21 000 and 12 000 14 c yr bp field studies in the low lying mountain ranges of the central portion of lake bonneville identified 17 spits of various types the spits are connected to small mountain ranges and islands vary in size from 0 02 to 0 5 km 2 and are composed of coarse grained well rounded poorly sorted sedimentary material sixteen of the 17 spits have a northeasterly to southwesterly orientation implying that winds were from the northwest to northeast approximately 180 out of phase with modern winds in the eastern great basin lake bonneville spit orientation is best explained as the result of persistent northerly winds caused by the high atmospheric pressure cell of the continental ice sheet and passage of low pressure extratropical storms south of the lake similar strong persistent winds are a common feature of modern continental ice sheets and passing low pressure systems if so the north american jet stream tracked south of lake bonneville as recently as 12 000 14 c yr bp well past the height of the last glacial maximum

last glacial maximum equilibrium line altitudes and paleoclimate northern uinta mountains utah u s a nineteen former valley glaciers were reconstructed for their last glacial maximum lgm extents in the northern uinta mountains utah u s a mean equilibrium line altitudes elas calculated by four methods accumulation area ratio toe headwall altitude ratio lateral moraines and cirque floors range from 3050 to 3300 m a s l modern mean summer temperatures t s at the elas range from 8 7 to 11 2 c while modern winter precipitation p ranges from 354 to 590 mm snow water equivalent swe based on the difference in elevation of mean elas across the range lgm p values must have ranged from 940 to 3040 mm swe assuming the modern summer lapse rate was the same during the lgm a t s depression of 5 5 c is required for these precipitation values to plot in the range of modern ela values the reconstructed increase in p at the western end of the range is 10 times the modern increase reflecting the influence of pluvial lake bonneville assuming ela depression ela resulted from this p increase and a uniform 5 5 c t s decrease the regional lgm ela was approximately 900 m

new evidence for an extended occupation of the provo shoreline and implications for regional climate change pleistocene lake bonneville utah usa abstract lake bonneville was a climatically sensitive closed basin lake that occupied the eastern great basin during the late pleistocene ongoing efforts to refine the record of lake level history are important for deciphering climate conditions in the bonneville basin and for facilitating correlations with regional and global records of climate change radiocarbon data from this and other studies suggest that the lake oscillated at or near the provo level much longer than depicted by current models of lake level change radiocarbon data also suggest that the lake dropped from threshold control much more rapidly than previously supposed these revisions to the lake bonneville hydrograph coupled with independent evidence of climate change from vegetation and glacial records have important implications for conditions in the bonneville basin and during the pleistocene to holocene transition

cosmogenic 3he exposure ages of pleistocene debris flows and desert pavements in capitol reef national park utah abstract the quaternary history of the capitol reef area utah is closely linked to the basaltic andesite boulder deposits that cover much of the landscape understanding the age and mode of emplacement of these deposits is crucial to deciphering the quaternary evolution of this part of the colorado plateau using cosmogenic 3 he exposure age dating we obtained apparent exposure ages for several key deposits in the capitol reef area coarse boulder diamicts capping the johnson mesa and carcass creek terraces are not associated with the bull lake glaciation as previously thought but were deposited 180 15 to 205 17 ka minimum age and are the result of debris flow deposition desert pavements on the johnson mesa surface give exposure ranging from 97 8 to 159 14 ka and are 34 96 kyears younger than the boulder exposure ages the offset between the boulder and pavement exposure ages appears to be related to a delay in pavement formation until the penultimate glacial interglacial transition or periodic burial and exposure of pavement clasts since debris flow deposition incision rates for the capitol reef reach of the fremont river calculated from the boulder exposure ages range from 0 40 to 0 43 m kyear 1 maximum rates and are some of the highest on the colorado plateau

pacing the post last glacial maximum demise of the animas valley glacier and the san juan mountain ice cap colorado during the last glacial maximum lgm a 5000 km 2 ice cap covered the san juan mountains of southwest colorado the largest valley glacier draining this ice cap occupied the animas valley and flowed 91 km to the south to characterize the post lgm demise of the animas valley glacier we employ cosmogenic 10 be to date the lgm terrace outside the terminal moraines and a suite of seven glacially polished bedrock samples the 10 be depth profile within the terrace sediments suggests abandonment at 19 4 1 5 ka as deglaciation began the ponding of glacial lake durango behind the terminal moraines shut off fluvial sediment supply and caused terrace abandonment the age of the terrace therefore records the initiation of lgm retreat negligible 10 be inheritance in the terrace profile suggests that glacial erosion of the bedrock valley floor from which sediments were derived erased all cosmogenic inventory glacial polish exposure ages monotonically decrease up valley from 17 1 to 12 3 ka with the single exception of a sample collected from a quartzite rib yielding an average retreat rate of 15 4 m yr this trend and the lack of inherited cosmogenic nuclides in the terrace sediments imply that polish ages accurately record the glacial retreat history retreat of the animas lobe began at a time of regional drying recorded in sediments and shoreline elevations of large lakes deglaciation lasted for 7 2 k y and was complete by 12 3 1 0 ka the retreat history followed the pattern of increasing insolation and was perhaps fastest during a time of regional drying

new data for late pleistocene pinedale alpine glaciation from southwestern colorado abstract new cosmogenic surface exposure ages of moraine crest boulders from southwestern colorado are compared with published surface exposure ages of boulders from moraine complexes in north central colorado and in west central fremont lake basin wyoming 10be data sets from the three areas were scaled to a single 10be production rate of 5 4 at g yr at sea level and high latitude slhl which represents the average 10be production rate for two high altitude mid latitude sites in the western united states us and austria multiple nuclide ages on single boulders indicate that this 10be production rate yields ages comparable to those calculated with a commonly used 36cl production scheme the average age and age range of moraine crest boulders on terminal moraines at the southwestern colorado and wyoming sites are similar indicating a retreat from their positions 16 8 36cl ka cosmogenic ages in this paper are labeled 10be or 36cl ka or just ka when both 10be or 36cl ages are being discussed radiocarbon ages are labeled 14c ka calibrated radiocarbon are labeled cal ka and calendar ages are labeled calendar ka errors 1 associated with ages are shown in tables radiocarbon ages were calibrated using the data of hughen et al science 303 2004 202 this suggests a near synchronous retreat of pinedale glaciers across a 470 km latitudinal range in the middle and southern rocky mountains hypothetical corrections for snow shielding and rock surface erosion shifts the time of retreat to between 17 2 and 17 5 10be ka at pinedale wyoming and between 16 3 and 17 3 36cl ka at hogback mountain colorado

pedogenic gradients for iron and aluminum accumulation and phosphorus depletion in arctic and alpine soils as a function of time and climate pedogenically significant chemical extracts of iron aluminum and phosphorus are related mainly to time in chronosequences from baffin island canadian arctic the alpine sierra nevada and wind river range western united states the alpine khumbu glacier area himalaya nepal and the alpine southern alps new zealand based on the accumulation index for fe and al and the depletion index for p in each region the following ranking of chemical pedogenic development is obtained southern alps khumbu glacier area wind river range sierra nevada coastal baffin island inland baffin island the ranking mainly follows regional climate with the greatest accumulation and depletion to the warmest and wettest environment and the least accumulation and depletion in the coldest and driest environment

a glacial chronology for the fish creek drainage of boulder mountain utah usa abstract boulder mountain located in south central utah is one of several mountain ranges on the colorado plateau that was glaciated during the late pleistocene using 3he exposure age dating corrected for non cosmogenic 3he with shielded samples we determined 3he exposure ages for boulders from the most well preserved moraines in the fish creek drainage of boulder mountain 3he exposure ages indicate a last glacial maximum lgm advance 23 100 1300 to 20 000 1400 yr ago and a later and smaller advance 16 800 500 to 15 200 500 yr ago this chronology is very similar to other cosmogenic glacial chronologies from the western u s and suggests that the timing of glacial advance and retreat on the colorado plateau was generally in phase with the rest of the western u s during the late pleistocene

neoglacial chronology and floristics in the middle teton area central teton range western wyoming the relative ages of neogfacial deposits above 2900m near cloudveil dome middle teton and teepe glaciers central teton range western wyoming were determined using topographic position weathering features lichenometry vegetation characteristics and soils a three fold deposit sequence is identified and correlated with the gannett peak audubon and indian basin neoglacial advances described elsewhere in the teton and nearby wind river ranges while soil profile morphology proved very useful in distinguishing deposits of different age other age indicators such as clay mineralogy and soil chemistry proved of only marginal value in age discrimination this chronosequence emplaced over the last 5000yr provides an excellent setting upon which to test changes in plant species composition and its use as a relative dating method vascular plant species composition cannot be used to discriminate deposits of the different advances possibly because of random colonisation and establishment combined with extensive mass wasting during the neoglacial however certain vegetation features such as total cover and species densities appear useful as relative dating methods

extractable fe and al as an indicator for buried soil horizons summary reddish brown and associated horizons from several buried soils were analyzed for dithionite oxalate and pyrophosphate extractable fe and al although these methods can be used with surficial soils they are not necessarily applicable to buried soils however on the basis of morphology and the fact that dithionite and oxalate extractable fe and al were always highest for the reddish brown horizon in each profile sequence it was concluded that these horizons were zones of pedogenic accumulation since pyrophosphate extractable fe and al essentially measures only the organic forms of pedogenic fe and al and organic compounds are usually subjected to further degradation after burial it is suggested that for buried soils dithionite and oxalate extractable fe and al are more meaningful comparisons with data in the literature giving typical ranges for the main types of soil horizons allowed both the classification of the profiles sampled and the recognition of past processes such as gleying which are not identifiable morphologically today

modelling of icecap glaciation of the northern rocky mountains of montana abstract the extent of the lastglacial icecap over the northern rocky mountains of montana has been inferred only from cursory correlation of its marginal deposits which leaves several significant unresolved controversies those controversies all involve the maximum altitude and shape of that interconnected ice mass and include 1 the source of the two medicine piedmont lobe local or cordilleran ice 2 correlation of terminal deposits of the flathead lobe late lastglacial early lastglacial or prelastglacial and 3 regional paleoclimate at last glacial maximum dominant westerlies or local easterlies theoretical reconstructions of the glacial surface along major flowlines constrained by ice marginal features nunataks and breached divides throughout the region tentatively resolve those issues the two medicine lobe was dominantly composed of northeast flowing local ice not ice of northwestern canadian cordillera origin flathead lobe deposits include lastglacial deposits both supported by and without a component from the swan valley there is evidence of only a regional westerly flow of moisture across the region in addition a proglacial lake 60 km long occupied the swan valley during the early stages of deglaciation although subject to revision from fieldwork glacial process modelling remains one of the few geological arenas in which rigorous process modelling can be used to predict the evolution of form

synoptic gulf stream velocity profiles through simultaneous inversion of hydrographic and acoustic doppler data data from a shipborne acoustic profiling device have been combined with conductivity temperature depth o 2 sections across the gulf stream to form estimates of the absolute flow fields the procedure for the combination was a form of inverse method the results suggest that at the time of the observations june 1982 the net gulf stream transport off hatteras was 107 11 sv and that across a section near 72 5ow it had increased to 125 6 sv subject to further uncertainty from the definition of the stream the transport of the deep western boundary current was 9 3 sv these and other transport estimates are plausibly close to previous calculations but we do not claim that they represent the temporal mean for comparison purposes we have done an inversion using the hydrographic o 2 data alone as in previously published results and obtained qualitative agreement with the combined inversion inversion of the acoustic measurements alone when corrected for instrument biases leaves unacceptably large mass transport residuals in the deep water our conclusion is that the inversion of the combined data sets produces results much improved over those from using either acoustic or hydrographic chemical constraints in isolation the procedures are close analogues to those which can be used with satellite altimeters and are a procedure for obtaining very accurate geoid slope measurements

how does the deep western boundary current cross the gulf stream abstract the manner in which the deep western boundary current dwbc crosses the gulf stream is investigated using data from a hydrographic survey conducted in 1990 absolute geostrophic velocity vectors are computed using in situ float data to obtain the reference level three density layers are considered in detail two mid depth layers which together make up the shallowest water mass component of the dwbc 500 1200 m and a deep layer consisting of the norwegian greenland overflow water 2500 3500 m the shallowest layer does not make it through the crossover and is completely entrained by the gulf stream however the resulting drop in equatorward transport is almost completely replenished by offshore entrainment just south of the crossover in the intermediate layer which is denser than the gulf stream coming off the shelf part of the dwbc recirculates to the northeast while the onshoremost portion continues equatorward in the deep layer only a small amount of recirculation occurs the lateral

14c dating and palaeoenvironment of the historic little ice age glacier advance of nigardsbreen southwest norway moss and grass remains associated with a well developed in situ palaeosol buried beneath a moraine ridge in front of nigardsbreen jostedalsbreen ice cap southern norway have been 14c dated pollen preserved with the plant remains suggests the existence of an agricultural landscape prior to the deposition of the moraine the calibrated dates and the pollen spectra are in close accord with historically documented evidence for the timing and palaeoenvironment of the little ice age advance of the glacier considerable potential is indicated for estimating the maximum ages of moraine ridges and for palaeoenvironmental reconstruction where such documentary evidence does not exist

younger dryas glacial landsystems in north west scotland an assessment of modern analogues and palaeoclimatic implications abstract by explicitly linking process to form landsystem models developed in modern environments provide powerful tools for the reconstruction of past environments from the sedimentological and geomorphological record some landform characteristics however may originate by more than one process equifinality so although a particular depositional model may fit the data it is not necessarily the correct one here we critically examine the use of modern analogues to interpret glacial landforms focusing on hummocky moraine a distinctive landform association consisting of numerous sharp crested moraine mounds and ridge fragments which occurs on many valley floors in upland britain detailed studies of examples of younger dryas age in the north west highlands of scotland show that they represent ice contact fans which have been affected to varying degrees by ice push and subglacial deformation and that they formed at active oscillating ice margins the sedimentological data are inconsistent with an origin by englacial thrusting as has been proposed for similar moraines elsewhere in upland britain on the basis of morphological criteria comparison with modern glacial landsystems shows that although aspects of hummocky moraines in the study area have close modern counterparts none provides an exact analogue in all respects this may reflect the distinctive climate of western scotland during the younger dryas estimates of mean july temperatures in the younger dryas in scotland based on chironomid assemblages are c 8 c at sea level when combined with reconstructed equilibrium line altitudes for contemporaneous glaciers these estimates indicate mean annual precipitation totals in the range of 2358 337 mm yr 1 at sea level in nw scotland c 26 higher than present day values the implied heavy snowfall suggests that glaciers in western scotland during the younger dryas were of high activity type unlike modern glaciers in svalbard for example high glacier velocities and high winter precipitation would suppress permafrost development despite low mean annual temperatures the climatic environment also favoured rapid oscillations of glacier margins during both glacier build up and retreat phases climatic factors combined with the availability of large quantities of subglacial debris led to the development of distinctive glacial landsystems which may have no direct modern analogue

accuracy of cosmogenic ages for moraines analyses of all published cosmogenic exposure ages for moraine boulders show an average age range of 38 between the oldest and youngest boulders from each moraine this range conflicts with the common assumption that ages of surface boulders are the same as the age of the landform the wide spread in boulder ages is caused by erosion of the moraine surface and consequent exhumation of fresh boulders a diffusion model of surface degradation explains the age range and shows that a randomly sampled small set of boulders n 3 7 will always yield a lower age limit for the moraine the model indicates that for identical dating accuracy six to seven boulders are needed from old and tall moraines 40 000 100 000 yr 50 100 m initial height but only one to four boulders from small moraines 20 000 100 000 yr 10 20 m by following these guidelines the oldest obtained boulder age will be 90 of the moraine age 95 probability this result is only weakly sensitive to a broad range of soil erosion rates our analysis of published boulder ages indicates that 3 of all moraine boulders have prior exposure and 85 of these boulders predate the dated moraine

cosmogenic 36cl and 10be ages of quaternary glacial and fluvial deposits of the wind river range wyoming we measured cosmogenic 36 cl in 56 samples from boulders on moraines and fluvial terraces in the vicinity of the wind river range wyoming we also measured 10 be in 10 of the same samples most of the 10 be ages were in good agreement with the 36 cl ages indicating that rock surface erosion rates were very low the oldest moraine investigated the type sacagewea ridge site yielded only a limiting minimum age of 232 ka the oldest moraines in the type bull lake complex also could be constrained only to 130 ka the main sequence of type bull lake moraines yielded age distributions indicating deposition within the intervals 130 to 100 ka and 120 to 100 ka the best estimates are closer to the upper limits of these ranges and associated uncertainties are in the range of 10 to 15 these uncertainties could permit deposition in either marine isotope stage 6 or stage 5d we found no evidence of glacial deposits dating to marine isotope stage 4 both bull lake age moraines from fremont lake on the opposite side of the wind river range and boulders on a fluvial terrace above the wind river gave age distributions very similar to that of the second oldest bull lake advance ca 130 to 100 ka the distribution of boulder ages for pinedale moraines at bull lake indicated deposition between 23 and 16 ka nearly identical to the distribution of 10 be ages previously reported for the type pinedale moraines at fremont lake

potential vorticity dynamics of boundary currents in a quasi geostrophic ocean abstract boundary layer potential vorticity dynamics for a quasi geostrophic eddy resolving general circulation ocean model are studied using both lagrangian and eulerian analyses active western boundary layers are found not only in the upper wind driven layer but also in the lower layers despite the lack of a direct vorticity input to the deep ocean at the western wall dissipative and inertial boundary regimes are exclusively controlled by the time mean dynamics except for the deepest layer where eddy fluxes drive the mean flow across mean potential vorticity contours boundary layers formed at the southern wall in this model are dynamically distinct from the western boundary layers they are controlled solely by the eddy flux of potential vorticity found in this region of active baroclinic instability basin integrated vorticity balances reveal a strong contribution to the vorticity cycle by the lateral boundaries with such input overshadowed by the vorticity exchange across the midbasin gyre bounda

timing of glaciation and last glacial maximum paleoclimate estimates from the fish lake plateau utah abstract the high plateaus of utah include seven separate mountain ranges that supported glaciers during the pleistocene the fish lake plateau located on the eastern edge of the high plateaus preserves evidence of at least two glacial advances four cosmogenic 3 he exposure ages of boulders in an older moraine range from 79 to 159 ka with a mean age of 129 39 ka and oldest ages of 152 3 and 159 5 ka these ages suggest deposition during the type bull lake glaciation and marine oxygen isotope stage mis 6 twenty boulder exposure ages from four different younger moraines indicate a local last glacial maximum lgm of 21 1 ka coincident with the type pinedale glaciation and mis 2 reconstructed pinedale age glaciers from the fish lake plateau have equilibrium line altitudes ranging from 2950 to 3190 m lgm summer temperature depressions for the fish lake plateau range from 10 7 to 8 2 c assuming no change in precipitation comparison of the fish lake summer temperature depressions to a regional dataset suggests that the fish lake plateau may have had a slight increase 1 5 modern in precipitation during the lgm a series of submerged ridges in fish lake were identified during a bathymetric survey and are likely bull lake age moraines

dynamics of the gulf stream deep western boundary current crossover part i entrainment and recirculation abstract a regional primitive equation model is applied to the study of the interaction between the gulf stream and the deep western boundary current dwbc where they cross at cape hatteras it is found that for a wide range of forcing parameters the upper core of the dwbc is split into two mean paths at the crossover one flowing toward the south along the western boundary and the other flowing toward the cast under the gulf stream the eastward branch is entrained into the southern recirculation gyre and after being diverted into the interior for up to 1500 km eventually returns to the western boundary current and continues to flow southward this recirculation and mixing is shown to have a significant impact on the separation point and mean path of the gulf stream the basin scale stratification and the properties of the dwbc south of the crossover for most configurations the lower dwbc remains largely on the western boundary and interacts only weakly with the interior the entrainment of the upp

cosmogenic exposure age chronologies of pinedale and bull lake glaciations in greater yellowstone and the teton range usa abstract we have obtained 69 new cosmogenic 10be surface exposure ages from boulders on moraines deposited by glaciers of the greater yellowstone glacial system and teton range during the middle and late pleistocene these new data combined with 43 previously obtained 3he and 10be ages from deposits of the northern yellowstone outlet glacier establish a high resolution chronology for the yellowstone teton mountain glacier complexes boulders deposited at the southern limit of the penultimate ice advance of the yellowstone glacial system yield a mean age of 136 13 10be ka and oldest ages of 151 157 10be ka these ages support a correlation with the bull lake of west yellowstone with the type bull lake of the wind river range and with marine isotope stage mis 6 end moraines marking the maximum pinedale positions of outlet glaciers around the periphery of the yellowstone glacial system range in age from 18 8 0 9 to 16 5 1 4 10be ka and possibly as young as 14 6 0 7 10be ka suggesting differences in response times of the various ice cap source regions moreover all dated pinedale terminal moraines in the greater yellowstone glacial system post date the pinedale maximum in the wind river range by 4 6 kyr indicating a significant phase relationship between glacial maxima in these adjacent ranges boulders on the outermost set and an inner set of pinedale end moraines enclosing jenny lake on the eastern teton front yield mean ages of 14 6 0 7 and 13 5 1 1 10be ka respectively the outer jenny lake moraines are partially buried by outwash from ice on the yellowstone plateau hence their age indicates a major standstill of an expanded valley glacier in the teton range prior to the younger dryas followed closely by deglaciation of the yellowstone plateau these new glacial chronologies are indicative of spatially variable regional climate forcing and temporally complex patterns of glacier responses in this region of the rocky mountains during the pleistocene

near synchronous interhemispheric termination of the last glacial maximum in mid latitudes isotopic records from polar ice cores imply globally asynchronous warming at the end of the last glaciation however 10be exposure dates show that large scale retreat of mid latitude last glacial maximum glaciers commenced at about the same time in both hemispheres the timing of retreat is consistent with the onset of temperature and atmospheric co2 increases in antarctic ice cores we suggest that a global trend of rising summer temperatures at the end of the last glacial maximum was obscured in north atlantic regions by hypercold winters associated with unusually extensive winter sea ice

climate during the last glacial maximum in the wasatch and southern uinta mountains inferred from glacier modeling abstract recent improvements in understanding glacial extents and chronologies in the wasatch and uinta mountains and other mountain ranges in the western u s call for a more detailed approach to using glacier reconstructions to infer paleoclimates than commonly applied aar ela at methods a coupled 2 d mass balance and ice flow numerical modeling approach developed by plummer m a phillips f m 2003 a 2 d numerical model of snow ice energy balance and ice flow for paleoclimatic interpretation of glacial geomorphic features quaternary science reviews 22 1389 1406 allows exploration of the combined effects of temperature precipitation shortwave radiation and many secondary parameters on past ice extents in alpine settings we apply this approach to the little cottonwood canyon in the wasatch mountains and the lake fork and yellowstone canyons in the south central uinta mountains results of modeling experiments indicate that the little cottonwood glacier required more precipitation during the local last glacial maximum lgm than glaciers in the uinta mountains assuming lapse rates were similar to modern model results suggest that if temperatures in the wasatch mountains and uinta mountains were 6 c to 7 c colder than modern corresponding precipitation changes were 3 to 2 modern in little cottonwood canyon and 2 to 1 modern in lake fork and yellowstone canyons greater amounts of precipitation in the little cottonwood canyon likely reflect moisture derived from the surface of lake bonneville and the lake may have also affected the mass balance of glaciers in the uinta mountains

ventilation of the deep western boundary current and abyssal western north atlantic estimates from tritium and 3he distributions abstract the tritium and excess 3he data from the 1981 tto nas program are used to study the time scales for the ventilation of the deep western basin by recently formed north atlantic deep water nadw the large scale distributions of tritium and 3he in the deep north atlantic are presented and tracer inventories are computed for individual deep water basins the bulk of the bomb tritium and thus new nadw resided in 1981 in the deep labrador sea and western subpolar gyre with a slightly smaller amount in the deep western subtropical gyre the maximum excess 3he values were located south of the overflows in the labrador sea the result of competition between ventilation and in situ tritium decay the subpolar gyre was also the site of the strongest increase in decay corrected tritium 120 and excess 3he 100 between the 1972 geosecs survey and the 1981 tto nas program the observed deep water tritium inventory is in reasonable agreement with model tracer inputs computed for the combined overflow

ages and significance of glacial and mass movement deposits on the west side of boulder mountain utah usa abstract using air photos satellite images and field observations we mapped quaternary glacial and mass movement deposits on the west side of boulder mountain in south central utah usa prominent glacial moraines were deposited by outlet glaciers that emanated from an ice cap that existed atop boulder mountain cosmogenic 3 he exposure ages of these deposits range from 20 2 1 5 to 22 5 2 5 ka and indicate maximum ice advance during the global last glacial maximum lgm three 3 he exposure ages of boulders from the pine creek slump deposit indicate that the slumping likely occurred at or before 125 ka eight 3 he exposure ages of boulders from the miller creek potholes debris flow deposit range from 20 2 2 0 to 50 4 3 0 ka five of those boulders yielded ages in the range of 26 33 ka and suggest emplacement of the debris flow deposit during that time both of these mass movement features cover prominent fault traces related to the thousand lakes fault but do not appear to be offset suggesting that major faulting has not occurred since 125 kyr ago in this area

particle dispersion and mixing of conservative properties in an eddy resolving model we examine the diffusive behavior of the flow field in an eddy resolving primitive equation circulation model analysis of fluid particle trajectories illustrates the transport mechanisms which are leading to uniform tracer and potential vorticity distributions in the interior of the subtropical thermocline in contrast to the assumption of weak mixing in recent analytical theories the numerical model indicates the alternative of tracer and potential vorticity homogenization on isopycnal surfaces taking place in a nonideal fluid with strong along isopycnal eddy mixing the eastern ventilated portion of the gyre appears to be sufficiently homogeneous to allow the concept of an eddy diffusivity to apply a break in a random walk behavior of particle statistics occurs after about 100 days when along flow dispersion sharply increases indicative of mean shear effects during the first months of particle spreading eddy dispersal and mean advection are of similar magnitude eddy kinetic energy is of o 60 80 cm2 s 2 in the model thermocline comparable to the pool of weak eddy intensity found in the eastern parts of the subtropical oceans eddy diffusivity in the model thermocline kxx 8 107 kyy 3 107 cm2 s 1 seems to be higher by a factor of about 3 than oceanic values estimated for these area below the thermocline model diffusivity decreases substantially and becomes much more anisotropic with particle dispersal preferentially in the zonal direction the strong nonisotropic behavior prominent also in all other areas of water eddy intensity appears as the major discrepancy when compared with the observed behavior of sofar floats and surface drifters in the ocean

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

the wind driven circulation quasi geostrophic simulations and theory for nonsymmetric winds abstract simulations of the wind driven ocean circulation carded out with an eddy resolving quasi geostrophic numerical model and symmetric idealized wind forcing have a large scale structure that is predicted wen by the steady nonlinear theory of rhines and young the sharp jet and inertial recirculation am often confined weft inside the region of closed hyperbolic characteristics defined by that theory and hence do not affect the sverdrup dynamics part of the gyre the characteristics make possible simple predictions about the development of the circulation including time dependence and eddy stirring by tilting the line of vanishing ekman pumping away from the east west orientation as it is tilted in the north atlantic and less so the north pacific we explore a family of circulations as the tilt of the wind held is increased characteristics originating at the eastern boundary begin to thread through the energetic region occupied by the free jet then extensive new branches of eddy driven f

late pleistocene glacial equilibrium line altitudes in the colorado front range a comparison of methods abstract six methods for approximating late pleistocene pinedale equilibrium line altitudes elas are compared for rapidity of data collection and error rmse from first order trend surfaces using the colorado front range trend surfaces computed from rapidly applied techniques such as glaciation threshold median altitude of small reconstructed glaciers and altitude of lowest cirque floors have relatively high rmses 97 186 m because they are subjectively derived and are based on small glaciers sensitive to microclimatic variability surfaces computed for accumulation area ratios aars and toe to headwall altitude ratios thars of large reconstructed glaciers show that an aar of 0 65 and a thar of 0 40 have the lowest rmses about 80 m and provide the same mean ela estimate about 3160 m as that of the more subjectively derived maximum altitudes of pinedale lateral moraines rmse 149 m second order trend surfaces demonstrate low elas in the latitudinal center of the front range perhaps due to higher winter accumulation there the mountains do not presently reach the ela for large glaciers and small front range cirque glaciers are not comparable to small glaciers existing during pinedale time therefore pleistocene ela depression and consequent temperature depression cannot reliably be ascertained from the calculated ela surfaces

beryllium 10 dating of the duration and retreat of the last pinedale glacial sequence accurate terrestrial glacial chronologies are needed for comparison with the marine record to establish the dynamics of global climate change during transitions from glacial to interglacial regimes cosmogenic beryllium 10 measurements in the wind river range indicate that the last glacial maximum marine oxygen isotope stage 2 was achieved there by 21 700 700 beryllium 10 years and lasted 5900 years ages of a sequence of recessional moraines and striated bedrock surfaces show that the initial deglaciation was rapid and that the entire glacial system retreated 33 kilometers to the cirque basin by 12 100 500 beryllium 10 years

modeled patterns of late pleistocene glacier inception and growth in the southern and central rocky mountains usa sensitivity to climate change and paleoclimatic implications abstract high resolution modern climate data for the southern and central rocky mountains provide a starting point for analysis of climate changes necessary to produce regional late pleistocene glaciation a gis based model was used to assess the sensitivity of glaciation in different ranges to climatic change and the combinations of temperature and precipitation change necessary to sustain the last glacial maximum lgm extent of glaciation in each range extensive glaciation initiates first in the wind river range of wyoming under every climate change scenario tested in absence of precipitation change a summer temperature depression of 6 8 c would be necessary to maintain lgm ice extents in colorado and wyoming if precipitation was halved necessary summer temperature depression would be 8 10 c if precipitation was doubled a depression of 3 5 5 5 c would suffice given model uncertainties these values may underestimate necessary temperature depression by as much as 2 c under all scenarios tested lgm glaciation in utah particularly the wasatch range requires either more temperature depression for given precipitation change or more precipitation for a given temperature depression than is required in the colorado wyoming rockies a summer temperature depression of 7 c which would suffice to sustain lgm ice extent with little change from modern precipitation in the colorado wyoming rockies would need to be coupled with a near doubling of precipitation to maintain lgm ice extent in the wasatch range this difference appears to reflect lgm precipitation enhancement in the wasatch range and to a lesser degree the uinta mountains resulting from the presence of lake bonneville immediately upwind of these ranges

latest pleistocene and holocene glacier variations in the european alps in the alps climatic conditions reflected in glacier and rock glacier activity in the earliest holocene show a strong affinity to conditions in the latest pleistocene younger dryas glacier advances in the alps related to younger dryas cooling led to the deposition of egesen stadial moraines egesen stadial moraines can be divided into three or in some cases even more phases sub stadials moraines of the earliest and most extended advance the egesen maximum stabilized at 12 2 1 0 ka based on 10be exposure dating at the schonferwall tyrol austria and the julier pass outer moraine switzerland final stabilization of moraines at the end of the egesen stadial was at 11 3 0 9 ka as shown by 10be data from four sites across the alps from west to east the sites are piano del praiet northwestern italy grosser aletschgletscher central switzerland julier pass inner moraine eastern switzerland and val viola northeastern italy there is excellent agreement of the 10be ages from the four sites in the earliest holocene glaciers in the northernmost mountain ranges advanced at around 10 8 1 1 ka as shown by 10be data from the kartell site northern tyrol austria in more sheltered drier regions rock glacier activity dominated as shown for example at julier pass and larstig valley tyrol austria new 10be dates presented here for two rock glaciers in larstig valley indicate final stabilization no later than 10 5 0 8 ka based on this data we conclude the earliest holocene between 11 6 and about 10 5 ka was still strongly affected by the cold climatic conditions of the younger dryas and the preboreal oscillation with the intervening warming phase having had the effect of rapid downwasting of egesen glaciers at or slightly before 10 5 ka rapid shrinkage of glaciers to a size smaller than their late 20th century size reflects markedly warmer and possibly also drier climate between about 10 5 ka and 3 3 ka conditions in the alps were not conducive to significant glacier expansion except possibly during rare brief intervals past tree line data from kaunertal tyrol austria in concert with radiocarbon and dendrochronologically dated wood fragments found recently in the glacier forefields in both the swiss and austrian alps points to long periods during the holocene when glaciers were smaller than they were during the late 20th century equilibrium line altitudes ela were about 200 m higher than they are today and about 300 m higher in comparison to little ice age lia elas the larstig rock glacier site we dated with 10be is the type area for a postulated mid holocene cold period called the larstig oscillation presumed age about 7 0 ka our data point to final stabilization of those rock glaciers in the earliest holocene and not in the middle holocene the combined data indicate there was no time window in the middle holocene long enough for rock glaciers of the size and at the elevation of the larstig site to have formed during the short infrequent cold oscillations between 10 5 and 3 3 ka small glaciers less than several km2 may have advanced to close to their lia dimensions overall the cold periods were just too short for large glaciers to advance after 3 3 ka climate conditions became generally colder and warm periods were brief and less frequent large glaciers for example grosser aletschgletscher advanced markedly at 3 0 2 6 ka around 600 ad and during the lia glaciers in the alps attained their lia maximum extents in the 14th 17th and 19th centuries with most reaching their greatest lia extent in the final 1850 1860 ad advance

climate at the equilibrium line of glaciers the relationships between temperature precipitation and radiation on glacier equilibrium lines are investigated using 70 glaciers for which the mass balance and meteorological observations have been carried out for sufficiently long periods it is found that the characteristic climate at glacier equilibrium lines can be described using the summer 3 months temperature in a free atmosphere annual total precipitation and the sum of global and long wave net radiation all of these are measured at or very near the equilibrium line altitudes then it is shown how the shift of the equilibriumline will occur as a result of a climatic change finally the effect of the shift of the equilibrium line on the annualmean specific mass balance is analytically derived and compared with observations the present results make it possible to identify the altitudes in climate models where glacierization should begin and to evaluate the mass balance changes as a result of possible future changes in the climate

timing and nature of late quaternary mountain glaciation compilations of regional to subcontinental scale mountain glacier chronologies from five continents plus hawaii examine the temporal and spatial patterns of mountain glaciation the compilations yield key insights into the nature of past fluctuations in temperature and precipitation in mountains and adjacent regions and provide baseline data for examining the dynamics of glacier responses to climate change key insights from these compilations include the wide variability of glacier responses to fluctuations in insolation temperature and precipitation and the regionally specific variations in climatic variables through late quaternary time the compilations highlight the need to improve the density and quality of geochronological data and to enhance the understanding of the links between climate and glaciation copyright 2008 john wiley sons ltd

soils as indicators of the pleistocene and holocene landscape evolution in the alay range kyrgystan abstract soils derived from quaternary glacial glaciofluvial and aeolian deposits in the alay range kyrgystan were studied to reconstruct the pleistocene and holocene landscape evolution geomorphologic studies radiocarbon dating of a horizons in palaeosols and iron fractionation were undertaken during the last glacial maximum lgm the abramov glacier in the alay range advanced down the koksu valley to an altitude of 2500 m asl about 50 km from the modern snout ela lowering about 600 m in addition several frontal moraine complexes could be identified at the valley bottom of the koksu river between 3100 m asl and the modern glacier snout at 3650 m asl the complexes can be assigned to the following glacier advances late glacial ela lowering 200 300 m early holocene to end of late glacial younger dryas ela lowering about 110 m neoglacial ela lowering about 50 m and little ice age ela lowering about 50 m similar glacier advances could be reconstructed according to the soil development on the lateral moraines near the abramov glacier at 3600 4000 m asl determination of pedogenic iron oxides corroborated the morphologic and radiocarbon results

moisture variability in the southwestern united states linked to abrupt glacial climate change the atmospheric response to millennial scale circulation changes in the north atlantic ocean during the last glacial period has been difficult to constrain cave deposits from southwestern north america reveal that atmospheric moisture in this region increased in response to slowdowns of the atlantic meridional overturning circulation

the influence of eddies on tracer transport in the abyssal ocean abstract tracer transport mechanisms in a deep western boundary current dwbc are explored using a three layer eddy resolving quasigeostrophic model the model is forced with a steady sinusoidal wind stress the effects of the wind stress coupled with instabilities create an unsteady zonal surface jet at the boundary between the model subtropical and subpolar gyres the bottom layer includes a dwbc created by specifying a mass inflow at the northern boundary and a mass outflow at the southern boundary a numerical tracer is introduced into the dwbc with the mass source at the northern boundary the surface jet creates an effective boundary to tracer transport in the dwbc this barrier to meridional tracer transport causes approximately 70 of the tracer moved out of the northern part of the dwbc to be transported zonally into the interior with only 30 continuing southward in the dwbc in model runs with a flat bottom approximately 20 of the total meridional tracer flux is due to the eddy field w

eddy resolution versus eddy diffusion in a double gyre gcm part i the lagrangian and eulerian description abstract the lagrangian and eulerian descriptions of the flow in a double gyre eddy resolving numerical simulation are compared in the context of exploring the use of drifter arrays to describe ocean circulation the parameterization of the unresolved scales of motion in large scale numerical ocean models is analyzed through a combination of lagrangian and eulerian simulated fields here in part i the lagrangian and eulerian description of the flow is presented with special emphasis on the description of the eddy diffusivity field in part ii the limitations that coarse spatial resolution imposes on the advective diffusive equation are tested by comparing the evolution of a passive tracer field in high and low resolution numerical models the number of buoy days used in the numerical experiment is similar to what is expected to be launched in the atlantic ocean during woce toga surface velocity program the parameters that determine the model ocean circulation were chosen such that the mean and edd

late pleistocene climate inferred from the reconstruction of the taylor river glacier complex southern sawatch range colorado abstract ice surface topography of a late pleistocene glacier complex herein named the taylor river glacier complex trgc was reconstructed on the basis of detailed mapping of glacial landforms combined with analyses of aerial photos and topographic maps during the last glacial maximum lgm the trgc covered an area of 215 km 2 and consisted of five valley or outlet glaciers that were nourished by accumulation in cirques basins and or upland ice fields equilibrium line altitudes elas for the glaciers of the trgc were estimated using the accumulation area ratio method assuming that ratio to be 0 65 0 05 elas thus derived ranged from about 3275 to 3400 m with a mean of 3340 60 m a degree day model ddm was used to infer the climatic significance of the lgm ela with no appreciable differences in precipitation with respect to modern climate the ela implies that mean summer temperatures during the lgm were 7 6 c cooler than today the ddm was also used to determine the temperatures required to maintain steady state mass balances for each of the reconstructed glaciers the required reductions in summer temperature vary little about a mean of 7 1 c the sensitivity of these results to slight 25 changes assumed for lgm precipitation are less than 0 5 c even under an lgm climate in which precipitation is assumed to be substantially different 50 than the present mean summer temperatures must be on the order of 7 0 to 8 5 c lower to depress equilibrium lines to lgm altitudes the greater sensitivity of the ela to changes in temperature suggests that glaciation in the region was driven more by decreases in summer temperature rather than increases in precipitation

geochemistry and extractable fe and al in cold temperature soils of northwestern siberia the concentrations of major minor and trace elements in three cryosols from north western siberia were analysed to determine profiles of geochemical uniformity element mobility and the release and build up of extractable fe and al the scope of this study involves weathering processes over all or part of the lateglacial to the holocene epoch 10 ka bp q1 in a cold environment the variability of hf content in the horizons is likely silica induced and accounts for much of the concentration variation in the other elements the slight increases of mobile to immobile elements in the b horizons indicate trivial downward movement within the profiles iron and al extracts were investigated to elicit information regarding profile age and palaeoclimate extractable fe and al show slight increases relative to the total concentrations in the soil sola ah bw horizons lattice fe decreases in the ah bw horizons as a result of weathering and production of sesquioxides over time increases of ferrihydrite in the ah horizons and in the parent material of some profiles may indicate perched water tables at some time in the past possibly as sustained yearly water levels in the active layer free iron fed relative to total fe increases in the ah bw horizons compared with the lower horizons where the oxidation potential is weaker low total fe reflects reworked felsic rich deltaic and shallow marine deposits from the permian to the early tertiary thereafter emplaced by episodic flooding of glacial meltwater from the arctic urals and or the kara sea ice sheet organically complexed al alp uniformly low in all soils nevertheless shows trends indicating some downward movement a rather unique occurrence in arctic tundra soils as indicated by the slow increase of oxihydrites it may not be realistic to estimate the age of a profile by its physical characteristics however it appears possible to determine broad age ranges from the isotopic composition of water in soils organic carbon concentrations between and within soil profiles indicate it may be more prevalent in tundra soil than previously thought and may also play a significant role in uploading co2 to the atmosphere as warming and microbial activity q2 progresses copyright 2009 john wiley sons ltd

weathering rinds archives of paleoenvironments on mount kenya east africa abstractweathering rind thicknesses on pebble and cobble size sediment have been used for the past half century at least as an age indicator of postdepositional time following a geologic event in mountainous terrain rind thickness is taken as a measurement of weathering over time frames of 0 5 m yr variable thicknesses are used to discriminate relative ages of glacial deposits the effects of chemical and physical weathering that together produce rinds are only rarely considered and most research objectives have centered on lichen alteration of clast surfaces recent microscopic analyses of weathering rinds on volcanic clasts of 70 0 ka to 2 0 m yr age produced new data on weathering products as well as unexpected incorporated biotic materials undergoing diagenesis the question as to how much physical mineral chemical biotic paleoenvironmental data might be archived in rinds is discussed the character and classification of organic materials undergoing diagenesis are also discussed

surface exposure dating of the great aletsch glacier egesen moraine system western swiss alps using the cosmogenic nuclide 10be egesen moraines throughout the alps mark a glacial advance that has been correlated with the younger dryas cold period using the surface exposure dating method in particular the measurement of the cosmogenic nuclide 10 be in rock surfaces we attained four ages for boulders on a prominent egesen moraine of great aletsch glacier in the western swiss alps the 10 be dates range from 10 460 1100 to 9040 1020 yr ago three 10 be dates between 9630 810 and 9040 1020 yr ago are based upon samples from the surfaces of granite boulders two 10 be dates 10 460 1100 and 9910 970 yr ago are based upon a sample from a quartz vein at the surface of a schist boulder in consideration of the numerous factors that can influence apparently young 10 be dates and the scatter within the data we interpret the weighted mean of four boulder ages 9640 430 yr including the weighted mean of two 10 be dates of the quartz vein as a minimum age of deposition of the moraine all 10 be dates from the great aletsch glacier egesen moraine are consistent with radiocarbon dates of nearby bog bottom organic sediments which provide minimum ages of deglaciation from the moraine the 10 be dates from boulders on the great aletsch glacier egesen moraine also are similar to 10 be dates from egesen moraines of vadret lagrev glacier on julier pass in the eastern swiss alps both the morphology of the great aletsch glacier egesen moraine and the comparison with 10 be dates from the inner vadret lagrev egesen moraine support the hypothesis that the climatic cooling that occurred during the younger dryas cold episode influenced the glacial advance that deposited the great aletsch glacier egesen moraine because of the large size and slow response time of great aletsch glacier we suggest that the great aletsch glacier egesen moraine was formed during the last glacial advance of the multiphased egesen cold period the kromer stage during the preboreal chron copyright 2004 john wiley sons ltd

spatial patterns of holocene glacier advance and retreat in central asia glaciers in the southern himalayas advanced in the early holocene despite an increase in incoming summer solar insolation at the top of the atmosphere these glacier advances are in contrast to the smaller alpine glaciers in the western and northern regions of central asia two different glacier mass balance models are used to reconcile this holocene glacier history with climate by quantifying the change in equilibrium line altitudes ela for simulated changes in holocene climate both ela models clearly show that the lowering of elas in the southern himalayas is largely due to a decrease in summer temperatures and that an increase in monsoonal precipitation accounts for less than 30 of the total ela changes the decrease in summer temperatures is a dynamic response to the changes in solar insolation resulting in both a decrease in incoming shortwave radiation at the surface due to an increase in cloudiness and an increase in evaporative cooling in the western and northern zones of central asia both ela models show a rise in elas in response to a general increase in summer temperatures this increase in temperatures in the more northern regions is a direct radiative response to the increase in summer solar insolation

reconstructing the transport history of glacigenic sediments a new approach based on the co variance of clast form indices abstract two indices are used to describe the aggregate shape and roundness characteristics of glacially transported clasts the c40 index the percentage of clasts with c a ratios 0 4 and the ra index the percentage of very angular and angular clasts in a sample analysis of the between and within sample co variance of these indices provides a powerful tool for discriminating actively and passively transported clasts in glacigenic deposits use of these indices is illustrated in an analysis of the form characteristics of clasts from lateral and frontal moraines at storbreen jotunheimen these fall between those of actively transported clasts in basal till low c40 and ra values and those of unmodified frost weathered clasts high c40 and ra values both indices decline down moraine within sample analyses of clast shape demonstrates that these aggregate clast form gradients reflect changes in the relative proportions of actively and passively transported debris on the moraines rather than progressive modification of actively transported clasts these analyses also indicate that actively transported clasts form the dominant component of the moraines particularly near the former glacier terminus further applications of the approach developed here are suggested

isolating the role of mesoscale eddies in mixing of a passive tracer in an eddy resolving model 1 this study examines the role of mesoscale eddies in distribution of chlorofluorocarbon cfc in a numerical model of the north atlantic our main conclusions are based on a comparison of two eddy resolving experiments one with and one without eddy advection of cfc the cfc distributions in these two experiments exhibit substantial differences within the subpolar gyre in particular in the presence of eddies the horizontal distribution of cfc in the upper 1000 m is more uniform and the cfc concentration is lower in the lower 1500 m our analysis demonstrates that these basin wide differences are caused by the interactions of eddy advection with convection and mean advection in several isolated locations the corresponding eddy flux divergence terms are spatially non uniform in magnitude their effects are often nonlocal and sometimes work against the spreading of cfc being carried out by the mean advection these conclusions are further confirmed by a third experiment in which the eddy advection was replaced by a down gradient diffusive parameterization our results demonstrate that advection by mesoscale eddies is crucial to the mixing of atmospheric gasses into the ocean and outline difficulties in representing eddies by the down gradient diffusion

lgm and late glacial fluctuations in the eastern alps abstract studies of glacier development in the eastern alps around the last glacial maximum lgm for more than a hundred years have created a reasonably well based knowledge of glacier extent sedimentation and palaeoclimate as well as chronology this was obtained from broad and detailed mapping palynological investigations and radiocarbon dating despite a very cold climate between 31 and 21 ka bp topographical constraints meant that glacier extent was limited to tributary valleys of the main trenches until about 24 ka bp then rapid ice build up in the main longitudinal valleys led to extended ice streams and to piedmont glaciers in the foreland this build up virtually ended at ca 21 ka bp according to radiocarbon dates obtained from organic matter embedded in the outwash and periglacial gravels niederterrasse the lgm possibly lasted 3000 4000 years and shows a short maximalstand and a more prolonged hochstand both connected with outwash deposits the ice decay was apparently very fast and the glaciers vanished from the longitudinal valleys probably within some hundreds of years this retreat was interrupted by two short oscillations of active glaciers in contact with huge masses of inactive ice occupying the main valley floors before these became totally ice free these events at the beginning of the oldest dryas ca 16 ka bp were followed by a distinct glacier readvance gschnitz marked by end moraines and outwash fans according to some radiocarbon dates this occurred around 14 ka bp during the bolling interstade the valleys became almost ice free the next two glacier readvances daun and egesen were limited to cirques and the higher parts of the valleys and are dated to the older and younger dryas stades respectively

the role of seasonality in abrupt climate change abstract a case is made that seasonality switches dominated by wintertime were instrumental in abrupt climate changes in the north atlantic region during the last glaciation and into the holocene the primary evidence comes from mismatches between mean annual temperatures from greenland ice cores in comparison with snowline changes in east greenland northern europe and north america the most likely explanation is a shutdown or reduction in strength of the conveyor this allows the spread of winter sea ice across the north atlantic thus causing the northern region to experience much colder winters because they mimic the greenland temperature rather than the snowline signal changes in the atlantic intertropical convergence zone and the asian monsoon may also share a winter linkage with greenland thus the paleoclimate record is consistent with the notion that a huge continental sector of the northern hemisphere stretching from greenland to asia was close to an extreme winter threshold during much of the last glaciation winter climate crossed this threshold repeatedly with marked changes in seasonality that may well have amplified and propagated a signal of abrupt change throughout the hemisphere and into the tropics

cosmogenic 3he in igneous and fossil tooth enamel fluorapatite igneous fluorapatite samples from a suite of six granitic rocks from the transantarctic mountains have high 3he concentrations to 5 10 9 atoms g 1 and high 3he 4he ratios to 9 10 7 these values are far higher than those found in several hundred igneous apatites from elsewhere around the world and are higher than can be attributed to nuclear reactions on 6li this 3he is almost certainly derived from cosmic ray reactions in rocks with high exposure ages at high latitude and elevation several samples of fossil tooth enamel fluorapatite from the turkana basin of kenya are similarly rich in 3he with up to 1 10 7 atoms 3he g 1 and 3he 4he ratios up to 4 10 6 again this 3he is most logically attributed to cosmic ray reactions provided that cosmogenic 3he like radiogenic 4he is quantitatively retained in fluorapatite under earth surface conditions routine 3he exposure dating of this common phase may be possible based on its chemical composition the 3he production rate in fluorapatite is about 100 atoms g 1 yr 1 at sea level and high latitude using this rate the apatites from the transantarctic mountains have apparent exposure ages of 0 5 6 2 myr in agreement with values elsewhere in the range the fossil tooth enamel samples have apparent exposure ages ranging from a few up to 130 kyr such high exposure ages suggest some of these fossils may be lag deposits with a very long residence time at or near the earth s surface 3he exposure ages can provide insights to the depositional and reworking history of enamel bearing fossils at present the major limitations to 3he exposure dating of fluorapatite are purification of sufficient amounts of material and measurement of small amounts of 3he in the presence of large quantities of 4he in addition further work is necessary to establish the nucleogenic 3he background in fluorapatite

extreme southwestern margin of late quaternary glaciation in north america timing and controls well preserved latero frontal moraines in the eastern san bernardino mountains of southern california provide evidence for several glacial advances during the late quaternary and mark the southwesternmost limit of glaciation in the western cordillera using geomorphology and 10be cosmogenic radionuclide dating a succession of moraines from three glaciated valleys is dated to 18 20 ka last glacial maximum 15 16 ka heinrich event 1 12 13 ka younger dryas stade and 5 9 ka early middle holocene these ages substantiate the view that glaciation throughout the american cordilleras was synchronous during the late quaternary furthermore these data show that glacial advances in southern california occur when a significant decrease in summer temperature is coupled with an increase in moisture flux producing high winter snowfall this allows for perennial snow accumulation that may under appropriate conditions persist to form glacial ice

surface dating of dynamic landforms young boulders on aging moraines the dating of landforms is crucial to understanding the evolution history and stability of landscapes cosmogenic isotope analysis has recently been used to determine quantitative exposure ages for previously undatable landform surfaces a pioneering application of this technique to date moraines illustrated its considerable potential but suggested a chronology partially inconsistent with existing geological data consideration of the dynamic nature of landforms and of the ever present processes of erosion deposition and weathering leads to a resolution of this inconsistency and more generally offers guidance for realistic interpretation of exposure ages

debris covered glaciers in the sierra nevada california and their implications for snowline reconstructions abstract ice walled melt ponds on the surfaces of active valley floor rock glaciers and matthes little ice age moraines in the southern sierra nevada indicate that most of these landforms consist of glacier ice under thin ca 1 10 m but continuous covers of rock fall generated debris these debris blankets effectively insulate the underlying ice and greatly reduce rates of ablation relative to that of uncovered ice such insulation explains the observations that ice cored rock glaciers in the sierra actually debris covered glaciers are apparently less sensitive to climatic warming and commonly advance to lower altitudes than do adjacent bare ice glaciers accumulation area ratios and toe to headwall altitude ratios used to estimate equilibrium line altitudes elas of former glaciers may therefore yield incorrect results for cirque glaciers subject to abundant rockfall inadvertent lumping of deposits from former debris covered and bare ice glaciers partially explains an apparently anomalous regional ela gradient reported for the pre matthes recess peak neoglacial advance distinguishing such deposits may be important to studies that rely on paleo ela estimates moreover matthes and recess peak ela gradients along the crest evidently depend strongly on local orographic effects rather than latitudinal climatic trends indicating that simple linear projections and regional climatic interpretations of ela gradients of small glaciers may be unreliable

late glacial retreat and neoglacial advance sequences in the zillertal alps austria abstract late glacial terrain in the schwarzensteinkees hornkees and waxeckkees forelands of the zillertal alps is dominated by sediments deposited by readvancing ice emplaced in the little ice age starting approximately 550 70 cal 14 c yr bp late glacial ice scoured the massif with remnants of late glacial end moraines fronting lia end moraines and buried paleosols underlying lia end moraines providing scattered evidence of compositional change and weathering since the later dryas the amount of recovered wood from lia moraines indicates that the massif was forested for at least part of mid holocene times most likely during the atlantic chronozone when presumably soil morphogenesis was accelerated details of till composition and weathering history provide a pedostratigraphic reconstruction which includes mid lia readvances between 400 70 cal 14 c yr bp and 350 70 cal 14 c yr bp the heavily convoluted character of underlying early lia or older tills suggests either pre existing strongly active cryoturbation in a thin entisol regosol or active push moraine dynamics of advancing warm ice sem analysis documents differences in glacial dynamics that may be related to ice thickness stick slip motion or clastic load in the ice coupled with rate of movement