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

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

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

climatic controls of western u s glaciers at the last glacial maximum abstract we use a nested atmospheric modeling strategy to simulate precipitation and temperature of the western united states 18 000 years ago 18 ka the high resolution of the nested model allows us to isolate the regional structure of summer temperature and winter precipitation that is crucial to determination of the net mass balance of late pleistocene mountain glaciers in this region of diverse topography and climate modeling results suggest that climatic controls of these glaciers varied significantly over the western u s glaciers in the northern rocky mountains existed under relatively cold july temperatures and low winter accumulation reflecting anticyclonic easterly wind flow off the laurentide ice sheet in contrast glaciers that existed under relatively warmer and wetter conditions are located along the pacific coast south of oregon where enhanced westerlies delivered higher precipitation than at present between these two groupings lie glaciers that were controlled by a mix of cold and wet conditions attributed to the convergence of cold air from the ice sheet and moisture derived from the westerlies sensitivity tests suggest that for our simulated 18 ka climate many of the glaciers exhibit a variable response to climate but were generally more sensitive to changes in temperature than to changes in precipitation particularly those glaciers in central idaho and the yellowstone plateau our results support arguments that temperature depression generally played a larger role in lowering equilibrium line altitudes in the western u s during the last glacial maximum than did increased precipitation although the magnitude of temperature depression required for steady state mass balance varied from 8 18 c only the sierra nevada glaciers required a substantial increase in precipitation to achieve steady state mass balance while glaciers in the cascade range existed with decreased precipitation

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

remarkably extensive glaciation and fast deglaciation and climate change in turkey near the pleistocene holocene boundary moraines in the taurus mountains of south central turkey dated to latest pleistocene or earliest holocene show that glaciers were extraordinarily large typical of the last glacial maximum 21 ka and that rates of glacier retreat and temperature rise exceeded those of the past century surface exposure ages of 7 moraines in a valley at altitudes between 1100 m and 3100 m above sea level range from 10 2 0 2 ka to 8 6 0 3 ka computed using our own production rates and spatiotemporal scaling factors hitherto unresolved differences in cosmogenic 36 cl production rate estimates can make these ages signifi cantly older and therefore the analysis presented here focuses on the rate of change and not on the absolute chronology during deglaciation the equilibrium line altitude ascended 1430 m and the air temperature rose by 9 c deglaciation occurred in two phases during the second faster phase which lasted 500 yr the glacier length decreased at an average rate of 1700 m 100 yr implying a warming rate of 1 44 c 100 yr indicating a rapid climate shift marking the onset of the holocene in turkey

diel changes in metal concentrations in a geogenically acidic river rio agrio argentina abstract rio agrio in patagonia argentina is a geogenically acidic stream that derives its low ph waters from condensation of acidic gases near its headwaters on the flanks of the active copahue volcano this study reports the results of three diel 24 h water samplings in three different ph regimes 3 2 4 4 and 6 3 along the river changes in the concentration and speciation of fe dominated the diel chemical changes at all three sites although the timing and intensity of these cycles were different in each reach at the two acidic sampling sites total dissolved fe and dissolved fe iii concentrations decreased during the day and increased at night whereas dissolved fe ii showed the reverse pattern these cycles are explained by fe iii photoreduction as well as enhanced rates of precipitation of hydrous ferric oxide hfo during the warm afternoon hours a strong correlation was observed between fe iii and as at the furthest upstream ph 3 2 site most likely due to co precipitation of as with hfo at the downstream ph 6 3 location fe ii concentrations increased at night as did concentrations of rare earth elements and dissolved al photoreduction does not appear to be an important process at ph 6 3 although it may be indirectly responsible for the observed diel cycle of fe ii due to advection of photochemically produced fe ii from acidic upstream waters the results of this study of a naturally acidic river are very similar to diel trends recently obtained from mining impacted streams receiving acid rock drainage the results are also used to explore the link between geochemistry and microbiology in acidic eco systems for example fe iii photoreduction produces chemical potential energy in the form of metastable fe 2 that helps support the bacterial community in this unique extreme environment

climatic interpretation of alpine snowline variations on millennial time scales abstract the depression of snowlines or equilibrium line altitudes of alpine glaciers is often used by glacial geologists to infer variations in mass balance the climatic interpretation of snowline depression however is complicated by the number of factors that control glacier mass balance the simple lapse rate method of temperature interpretation ignores the effects of changes in radiation and snow accumulation the statistical approach to temperature interpretation which regresses precipitation and temperature against snowline altitude neglects the effect of radiation the most comprehensive approach for the climatic interpretation of snowline depression couples the heat and mass balances of a glacier surface a sensitivity analysis that utilizes the coupled heat and mass balance approach indicates that the 1000 m variation in snowline of alpine glaciers on glacial to interglacial time scales could be a result of significant changes in temperature and to a lesser extent changes in insolation snowline variations are sensitive only to relatively large changes in annual accumulation which should also be evident in other proxy records of moisture change the approaches outlined here provide glacial geologists with a summary of how various climatic forcings associated with glaciation may be quantified from snowline data

latest pleistocene glacial and climate history of the wasatch range utah abstract the geologic record of mountain glaciation is one of the most sensitive archives of terrestrial climate change during the late quaternary period pleistocene glacial deposits are exceptionally well preserved in the great basin of north america where they are found in close proximity to shoreline deposits of coeval paleo lakes representing a unique opportunity to investigate paleoclimate change using both hydrologic systems mountain glaciers advanced across much of the wasatch range utah during the same general time interval when lake bonneville expanded in the adjacent bonneville basin here we present a range wide latest pleistocene glacial history for the wasatch range based on 22 new and 41 recalculated cosmogenic 10be surface exposure ages and reconstruct glaciers and climate for the last glacial maximum lgm and lateglacial periods our results indicate three distinct range wide phases of glaciation in the wasatch including the pinedale 1 ca 21 20 ka pinedale 2 ca 17 5 ka and pinedale 3 ca 15 ka our modeling results indicate that the pinedale 1 advance near the end of the global lgm was primarily driven by decreased annual temperatures with little to no change in precipitation as compared to modern wasatch glaciers appear to have reoccupied near maximum positions after the end of the lgm during the pinedale 2 responding to increased precipitation in concert with rising lake levels across western north america and then retreated from ice distal positions near ca 17 5 ka wasatch glaciers occupied recessional positions at approximately half their maximum lengths during pinedale 3 until ca 15 ka followed by rapid i e several millennia deglaciation our glacial chronologies establish that wasatch glaciers responded synchronously across the range to global and regional climate forcings during the latest pleistocene the new wasatch glacial chronology combined with global glacial chronologies and paleoclimate proxies from western north america suggest glacier change was driven by a combination of long term global temperature forcing as well as regional to local modifications in precipitation

temporal correspondence between pluvial lake highstands in the southwestern us and heinrich event 1 pluvial lakes were abundant in the southwestern united states during pleistocene glaciations particu larly in the great basin many of these lakes occupied closed basins therefore fluctuations of their water surface elevations are valuable sources of paleoclimate information histories of the largest lakes are well constrained whereas dozens of smaller lakes that were present in this region have received relatively little scientific attention given their dimensions these smaller lakes were climatically sensitive and can offer important information about quaternary climate variability here we present new ages for the highstands of three previously undated small lakes based on radiocarbon dating of gastropod shells recovered from beach ridges these results are combined with other published and unpublished 14 c ages to yield an extensive compilation of highstand shoreline ages for lakes of all sizes throughout the southwestern us the results indicate that although some lakes reached highstands during the last glacial maximum the strongest temporal correspondence is between highstands and heinrich event h1 these results are consistent with speleothem based reconstructions of effective moisture in the southwestern us which show increased precipitation during stadials of the last glacial cycle copyright 2012 john wiley sons ltd

the rise and fall of lake bonneville between 45 and 10 5 ka a sediment core taken from the western edge of the bonneville basin has provided high resolution proxy records of relative lake size change for the period 45 1e10 5 calendar ka hereafter ka age control was provided by a paleomagnetic secular variation psv based age model for blue lake core bl04 4 continuous records of d 18 o and total inorganic carbon tic generally match an earlier lake level envelope based on outcrops and geomorphic features but with differences in the timing of some hydrologic events states the stansbury oscillation was found to consist of two oscillations centered on 25 and 24 ka lake bonneville appears to have reached its geomorphic highstand and began spilling at 18 5 ka the fall from the highstand to the provo level occurred at 17 0 ka and the lake intermittently overflowed at the provo level until 15 2 ka at which time the lake fell again bottoming out at w14 7 ka the lake also fell briefly below the provo level at w15 9 ka carbonate and d

cosmogenic 3he and 10be chronologies of the late pinedale northern yellowstone ice cap montana usa cosmogenic 3 he and 10 be ages measured on surface boulders from the moraine sequence deposited by the northern outlet glacier of the yellowstone ice cap indicate that the outlet glacier reached its terminal position at 16 5 6 0 4 3 he ka and 16 2 6 0 3 10 be ka respectively concordance of these ages supports the scaled production rates used for 3 he 118 6 6 6 6 atoms g 21 y r 21 and 10 be 5 1 6 0 3 atoms g 21 y r 21 62s at high latitudes at sea level two recessional moraines upvalley from the terminal moraine have mean ages of 15 7 6 0 5 10 be ka and 14 0 6 0 4 10 be ka respectively and a late glacial flood bar was deposited at 13 7 6 0 5 10 be ka these cosmogenic chronologies identify a late pinedale glacial maximum in northern yellowstone that is significantly younger than previously thought and they suggest deglaciation of the yellowstone plateau by 14 10 be ka

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

last glacial maximum climate inferences from cosmogenic dating and glacier modeling of the western uinta ice field uinta mountains utah abstract during the last glacial maximum lgm the western uinta mountains of northeastern utah were occupied by the western uinta ice field cosmogenic 10 be surface exposure ages from the terminal moraine in the north fork provo valley and paired 26 al and 10 be ages from striated bedrock at bald mountain pass set limits on the timing of the local lgm moraine boulder ages suggest that ice reached its maximum extent by 17 4 0 5 ka 2 10 be and 26 al measurements on striated bedrock from bald mountain pass situated near the former center of the ice field yield a mean 26 al 10 be ratio of 5 7 0 8 and a mean exposure age of 14 0 0 5 ka which places a minimum limiting age on when the ice field melted completely we also applied a mass energy balance and ice flow model to investigate the lgm climate of the western uinta mountains results suggest that temperatures were likely 5 to 7 c cooler than present and precipitation was 2 to 3 5 times greater than modern and the western most glaciers in the range generally received more precipitation when expanding to their maximum extent than glaciers farther east this scenario is consistent with the hypothesis that precipitation in the western uintas was enhanced by pluvial lake bonneville during the last glaciation

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

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

vein type tungsten deposits of china and adjoining regions abstract taking the south china tungsten province as representative this paper deals systematically with the geological setting geometry paragenesis wallrock alteration and geochemical characteristics of asian vein type tungsten deposits on the basis of data acquired since the 1970 s the regional metallogenic conditions and the genesis of the deposits are discussed the large scale distribution of vein type tungsten deposits in asia is inferred to be controlled by tungsten enriched formations multi period and multi stage granitic activity and favourable tectonic environment the deposits are not only controlled by magmatic differentiation but also by the overall evolution of the continental crust

stratigraphy and chronology of offshore to nearshore deposits associated with the provo shoreline pleistocene lake bonneville utah abstract stratigraphic descriptions and radiocarbon data from eleven field locations are presented in this paper to establish a chronostratigraphic framework for offshore to nearshore deposits of lake bonneville based on key marker beds and geomorphic position the deposits are interpreted to have accumulated during the period from the late transgressive phase through the overflowing phase into the regressive phase of the lake radiocarbon ages of sediments associated with the provo shoreline indicate that lake bonneville dropped rapidly from the provo shoreline at about 12 600 14c yr bp 15 000 cal yr b p the presence of one or more sand beds in the upper part of the provo aged marl indicates rapid lowering of lake level or storm events at the end of the provo episode an accurate understanding of the timing and nature of lake bonneville s climate driven regression from the provo shoreline is critical to correlations with records of regional and hemispheric climate change the rapid descent of the lake from the provo shoreline correlates with the decline of lakes lahontan and estancia and with the onset of the b o lling aller o d warming event

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

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

mid pleistocene cosmogenic minimum age limits for pre wisconsinan glacial surfaces in southwestern minnesota and southern baffin island a multiple nuclide approach abstract paired 10 be and 26 al analyses n 14 indicate that pre wisconsinan glaciated bedrock surfaces near the northern baffin island and southern minnesota paleo margins of the laurentide ice sheet have long and complex histories of cosmic ray exposure including significant periods of partial or complete shielding from cosmic rays using the ratio 26 al 10 be we calculate that striated outcrops of sioux quartzite in southwestern minnesota southern margin were last overrun by ice at least 500 000 years ago weathered bedrock tors on the once glaciated uplands of baffin island northern margin are eroding no faster than 1 1 m myr 1 the equivalent of at least 450 000 years of surface and near surface exposure our data demonstrate that exposure ages and erosion rates calculated from single nuclides can underestimate surface stability dramatically because any intermittent burial and the resultant lowering of nuclide production rates and nuclide abundances will remain undetected

latest pleistocene advance of alpine glaciers in the southwestern uinta mountains utah usa evidence for the influence of local moisture sources cosmogenic surface exposure 10 be dating of last glacial maximum lgm moraines indicates that glaciers in the southwestern uinta mountains remained at their maximum positions until ca 16 8 0 7 ka 2 k y after glaciers in the neighboring wind river range and colorado rockies began to retreat the timing of the local lgm in the south western uintas overlaps with both the hydrologic maximum of lake bonneville and pre liminary estimates of the local lgm in the western wasatch mountains this broad syn chroneity indicates that lake bonneville and glaciers in northern utah were responding to similar climate forcing furthermore equilibrium line altitudes elas for reconstruct ed lgm alpine glaciers increase with distance from the lake bonneville shoreline rising from 2600 m to 3200 m over the 120 km length of the glaciated uintas this pro nounced ela gradient suggests that the magnitude of the latest pleistocene glacial advance in the western uintas was due at least in part to enhanced precipitation derived from lake bonneville thus the lake acted as a local amplifier of regional climate forcing this relationship underscores the sensitivity of alpine glaciers to moisture availability during the latest pleistocene and further demonstrates the importance of local moisture sources on glacier mass balance

lake bonneville fluctuations and global climate change lake bonneville the largest late pleistocene closed basin lake in the north american great basin fluctuated widely in response to changes in climate the geochemistry and mineralogy of endogenic calcium carbonate deposited in deep water and stratigraphic studies of shore zone deposits provide evidence of millennial scale lake level fluctuations that had amplitudes of about 50 m between 30 and 10 ka falling lake events occurred at 21 18 5 19 17 5 16 15 5 14 13 and 10 ka radiocarbon years synchronously with the terminations of heinrich events h1 and h2 and other smaller scale iceberg rafting events a b c and younger dryas in the north atlantic ocean the lake bonneville results thus support other climate records that suggest that late pleistocene millennial scale climate change was global in extent the size and shape of the northern hemisphere ice sheets which determined the mean positions of storm tracks may have been the primary control on late pleistocene water budgets of great basin lakes

slip rate variations on faults in the basin and range province caused by regression of late pleistocene lake bonneville and lake lahontan late pleistocene regression of two large pluvial lakes lake bonneville and lake lahontan caused considerable lithospheric rebound in the basin and range province usa here we use finite element models to show how lake growth and regression affect the temporal and spatial slip evolution on faults near the former lakes our results show that fluctuations in the volume of lake bonneville caused along strike slip variations on the wasatch normal fault with a pronounced slip rate increase on its northern and central parts during lake regression the response of normal and strike slip faults near the ring shaped lake lahontan depends on their location within the rebound area faults located in the centre of rebound show a slip rate increase during lake regression whereas strike slip faults at the periphery decelerate all slip rate variations are caused by differential stress changes owing to changing lake levels regardless of the individual fault response

variable responses of western u s glaciers during the last deglaciation cosmogenic 10 be exposure ages from moraines in the wallowa mountains oregon identify two maximal late pleistocene glaciations at 21 1 6 0 4 ka and 17 0 6 0 3 ka and a minor glacial event at 10 2 6 0 6 ka our new high resolution chronology integrated with other well dated glacial records from the western united states demonstrates sub stantial differences in the synoptic responses of western u s glaciers to climate forcing associated with the global last glacial maximum and subsequent millennial scale events originating in the north atlantic region these variable synoptic glacier responses identify large changes in the relative contributions of regional to global controls on the climate of the western united states that accompanied the deglaciation