lake devlin and pinedale glacial history front range colorado abstract glacial lake devlin was an ice margin lake that formed during pinedale time when the north boulder creek valley glacier blocked the mouth of a tributary near the downvalley limit of glaciation the lake was about 2 km long and as much as 60 m deep and was fed by meltwater from small valley glaciers it accumulated sediment apparently without interruption for about 10 000 yr the inception of lake devlin between 23 500 and 21 000 yr b p provides a limiting date for the maximum expansion of pinedale ice because the lake could not form until the north boulder creek glacier had advanced to within 2 km of its downvalley limit the maximum lowering of timberline which occurred about 19 000 yr b p is assumed to coincide with the pinedale glacial maximum apparent timberline elevations determined from picea pinus pollen ratios suggest that ice front positions during the time between 23 000 and 19 000 yr b p may have been only slightly less extensive than at the pinedale maximum lake devlin drained catastrophically about 13 000 yr b p which was after ice had receded from the outlet area pinedale glaciation in the front range began about or after 30 000 yr b p and final deglaciation occurred between 15 000 and 12 000 yr b p

holocene lake level trends in the rocky mountains u s a abstract the availability of water shapes life in the western united states and much of the water in the region originates in the rocky mountains few studies however have explicitly examined the history of water levels in the rocky mountains during the holocene here we examine the past levels of three lakes near the continental divide in montana and colorado to reconstruct holocene moisture trends using transects of sediment cores and sub surface geophysical profiles from each lake we find that mid holocene shorelines in the small lakes 4 110 ha were as much as 10 m below the modern lake surfaces our results are consistent with existing evidence from other lakes and show that a wide range of settings in the region were much drier than today before 3000 2000 years ago we also discuss evidence for millennial scale moisture variation including an abruptly initiated and terminated wet period in colorado from 4400 to 3700 cal yr bp and find only limited evidence for low lake stands during the past millennium the extent of low water levels during the mid holocene which were most severe and widespread ca 7000 4500 cal yr bp is consistent with the extent of insolation induced aridity in previously published regional climate model simulations like the simulations the lake data provide no evidence for enhanced zonal flow during the mid holocene which has been invoked to explain enhanced mid continent aridity at the time the data including widespread evidence for large changes on orbital time scales and for more limited changes during the last millennium confirm the ability of large boundary condition changes to push western water supplies beyond the range of recent natural variability

investigations regarding alpine talus slopes using ground penetrating radar gpr in the bavarian alps germany the applicability of ground penetrating radar gpr for the investigation of loose debris was tested at two sites viererkar and zugspitzplatt a pulseekko 100 gpr system equipped with 25 mhz antennae was utilized the aim of the investigation was to record the base of the debris layer and thereby acquire an estimation of the backweathering rates of the adjacent rockwalls the study areas are situated in the northern alps near the german austrian border the sites are characterized by steep limestone rockwalls and extensive talus accumulations a total of six profiles was surveyed the method is suitable and effective for a quick survey in this dry high ohmic substrate the gpr system was able to deliver information about the subsurface stratigraphy to c 70 m depth the boundary line to the bedrock was discovered depending upon the profile surveyed 5 to 25 m below the surface the base of the debris material sometimes shows no distinct reflection buried features v shaped furrows zones overdeepened by ice action geological structures could be detected arched structures well below the talus bedrock interface can be interpreted as drainage systems in the karstic bedrock a thick scree layer of late glacial age was separated from a thinner layer on the talus surface which was related to the holocene the backweathering rates were fixed by a calculation of talus volume to c 100 mm 103 a during the holocene viererkar and 150 300 mm 103 a zugspitzplatt the detrital formation in north exposed sites is twice as intense as in south exposed sites these results match the rates of recent rockfall in the same area of investigation the calculated backweathering for the late glacial period is 150 730 mm 103 a the magnitude of the calculated rockwall retreat lies well within the range of previous measurements the discrepancy between some weathering rates highlights the fact that recent and past relief formation must be differentiated otherwise recent removal rates may be overestimated copyright 2001 john wiley sons ltd

optical chronology and climatic implication of glacial advances from the southern ladakh range nw himalaya india abstract morphological sedimentological and chronological evidence suggests the preservation of three glacial advances of decreasing magnitude in the puche valley near leh southern ladakh ranges the oldest moraine of puche glacier advance 1 pga 1 is optically dated to the early marine isotopic stage mis 2 31 5 3 3 ka that persisted until around the global last glacial maxima lgm 22 7 1 6 ka the pga 2 is optically dated to the post lgm 14 4 1 0 ka and perhaps was triggered by meltwater pulse 1a cooling the youngest pga 3 remains undated and could be of holocene age the optically stimulated luminescence osl ages suggest a greater role of westerlies in driving the glacier advances during the mis 2 in the southern ladakh ranges and are at variance with the previous suggestions that recommended monsoon driven glacier advances the osl ages compared to the previously obtained 10be surface exposure ages are younger by a magnitude the study explores probable causes for the variance in two chronologies and suggests employing multiple dating methods to minimize the uncertainty both in terms of age and climatic interpretation

surface exposure dating of moraines in the kromer valley silvretta mountains austria evidence for glacial response to the 8 2 ka event in the eastern alps 10 be dating of a pronounced glacier advance kromer stadial in the western part of the silvretta mountains western austria yielded ages ranging from 8010 360 to 8690 410 years with a mean age for moraine stabilization of 8410 690 years hence the kromer stadial which was previously considered as early preboreal may represent the glacier response to the early phase of the 8 2 ka event as it is recorded in the greenland ice cores the glacier advanced to a position beyond its little ice age lia limit the end moraines are situated 750 1000 m downvalley from the glacier ends in 1850 the corresponding drop of the equilibrium line altitude relative to the lia datum was 75 m the glacier advance was followed by a period of glacier recession and rock glacier development in total the climatic fluctuation may have lasted for about 500 200 years the age and duration of the climatic fluctuation is in good accordance with the misox cold phase and ce 3 climatic fluctuation as recorded in switzerland climate during the kromer stadial was characterized by more humid conditions than today along the northern fringe of the alps and slightly negative to moderately positive changes in precipitation in the central part of the austrian alps summer temperatures changes were most likely in the order of i to 0k mean annual temperature was 1 5k to 2k lower than today at least during the second phase of the climatic fluctuation

relationship among o mg isotopes and the petrography of two spinel bearing compound chondrules the petrological properties and o and al mg isotopic compositions of two spinel bearing chondrules from the allende cv chondrite were investigated using scanning electron microscopy and secondary ion mass spectrometry a coarse spinel grain in a barred olivine bo chondrule is less enriched in 16o 17o 5 17o 17o 0 52 18o whereas smaller spinel grains in a plagioclase rich chondrule member of a compound chondrule are extremely 16o rich 17o 17 and the spinels have a strongly serrated character the petrological features and 16o enrichments of the spinels in the plagioclase rich chondrule indicate that spinels originating in coarse grained ca al rich inclusions cais were incorporated into chondrule precursors and survived the chondrule forming event the degree of 16o excesses among minerals within each chondrule is correlated to the crystallization sequences this evidence suggests that the o isotopic variation among minerals may have resulted from incomplete exchange of o isotopes between 16o rich chondrule melt and 16o poor nebular gas aqueous alteration also has changed the o isotope compositions in the mesostasis the feldspathic mesostasis in the bo chondrule shows a disturbed mg al isochron indicating that the bo chondrule experienced secondary alteration while plagioclase in the plagioclase rich chondrule member of the compound chondrule shows slight 26mg excesses corresponding to 26al 27al 0 4 6 4 0 2 10 6 nepheline formed by secondary alteration shows no detectable excess the al mg isotopic system of these chondrules was disturbed by aqueous alteration and thermal metamorphism on the allende parent body

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

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

last glacial interglacial environments in the southern rocky mountains usa and implications for younger dryas age human occupation abstract the last glacial interglacial transition lgit 19 9 ka was characterized by rapid climate changes and significant ecosystem reorganizations worldwide in western colorado one of the coldest locations in the continental us today mountain environments during the late glacial period are poorly known yet archaeological evidence from the mountaineer site 2625 m elev indicates that folsom age paleoindians were over wintering in the gunnison basin during the younger dryas chronozone ydc 12 9 11 7 ka to determine the vegetation and fire history during the lgit and possible explanations for occupation during a period thought to be harsher than today a 17 ka old sediment core from lily pond 3208 m elev was analyzed for pollen and charcoal and compared with other high resolution records from the southern rocky mountains widespread tundra and picea parkland and low fire activity in the cold wet late glacial period transitioned to open subalpine forest and increased fire activity in the bolling allerod period as conditions became warmer and drier during the ydc greater winter snowpack than today and prolonged wet springs likely expanded subalpine forest to lower elevations than today providing construction material and fuel for the early inhabitants in the early to middle holocene arid conditions resulted in xerophytic vegetation and frequent fire

the deglaciation of the americas during the last glacial termination this paper reviews current understanding of deglaciation in north central and south america from the last glacial maximum to the beginning of the holocene together with paleoclimatic and paleoceanographic data we compare and contrast the pace of deglaciation and the response of glaciers to major climate events during the global last glacial maximum glgm 26 5 19 ka average temperatures decreased 4 to 8 c in the americas but precipitation varied strongly throughout this large region many glaciers in north and central america achieved their maximum extent during the glgm whereas others advanced even farther during the subsequent heinrich stadial 1 hs 1 glaciers in the andes also expanded during the glgm but that advance was not the largest except on tierra del fuego hs 1 17 5 14 6 ka was a time of general glacier thickening and advance throughout most of north and central america and in the tropical andes however glaciers in the temperate and subpolar andes thinned and retreated during this period during the bolling allerod interstadial b a 14 6 12 9 ka glaciers retreated throughout north and central america and in some cases completely disappeared many glaciers advanced during the antarctic cold reversal acr 14 6 12 9 ka in the tropical andes and patagonia there were small advances of glaciers in north america central america and in northern

bipolar changes in atmospheric circulation during the little ice age annually dated ice cores from siple dome west antarctica and central greenland indicate that meridional atmospheric circulation intensity increased in the polar south pacific and north atlantic at the beginning 1400 a d of the most recent holocene rapid climate change event the little ice age lia as deduced from chemical concentrations at these core sites the lia was characterized by substantial meridional circulation strength variability and this variability persists today despite strong evidence for an end to lia cooling thus increased late 20th century storm variability may be in part a result of the continuation of these climatic fluctuations

an early advance of glaciers on mount akdag sw turkey before the global last glacial maximum insights from cosmogenic nuclides and glacier modeling abstract for the first time in turkey we report an early advance of glaciers before the broadly defined global last glacial maximum lgm forty one moraine boulders from three glacial valleys on mount akdag 36 54 n 29 57 e 3016 m southwest coast of turkey were dated with cosmogenic 36 cl valleys on the north side of the mountain were filled with few km long glaciers that terminated at elevations of about 2000 m above sea level a s l the pre lgm glaciations reached their maximum positions 2150 m a s l by 35 1 2 5 ka ago 1 ka 1000 calendar years the glaciers readvanced during the global lgm and reached their farthest locations 2050 m a s l by around 21 7 1 2 ka ago later glaciers retreated and shortly stabilized during the lateglacial at around 15 1 0 9 ka ago using the glacier modeling and paleoclimate proxies from the eastern mediterranean we estimated that if temperatures during the lgm were 8 11 c colder than modern which is suggested by paleotemperature proxies from the region precipitation was up to two times more than that of today previous estimates on southwest coast of turkey indicate a similar precipitation value while central turkey requires drier conditions implying regional heterogeneity on lgm climates in turkey

surface exposure ages of front range moraines that may have formed during the younger dryas 8 2 cal ka and little ice age events abstract surface exposure 10 be ages have been obtained on boulders from three post pinedale end moraine complexes in the front range colorado boulder rounding appears related to the cirque to moraine transport distance at each site with subrounded boulders being typical of the 2 km long chicago lakes glacier subangular boulders being typical of the 1 km long butler gulch glacier and angular boulders being typical of the few hundred m long isabelle glacier surface exposure ages of angular boulders from the isabelle glacier moraine which formed during the little ice age lia according to previous lichenometric dating indicate cosmogenic inheritance values ranging from 0 to 3 0 10 be ka 1 subangular boulders from the butler gulch end moraine yielded surface exposure ages ranging from 5 to 10 2 10 be ka we suggest that this moraine was deposited during the 8 2 cal ka event which has been associated with outburst floods from lake agassiz and lake ojibway and that the large age range associated with the butler gulch end moraine is caused by cosmogenic shielding of and or spalling from boulders that have ages in the younger part of the range and by cosmogenic inheritance in boulders that have ages in the older part of the range the surface exposure ages of eight of nine subrounded boulders from the chicago lakes area fall within the 13 0 11 7 10 be ka age range and appear to have been deposited during the younger dryas interval the general lack of inheritance in the eight samples probably stems from the fact that only a few thousand years intervened between the retreat of the pinedale glacier and the advance of the chicago lakes glacier in addition bedrock in the chicago lakes cirque area may have remained covered with snow and ice during that interval thus partially shielding the bedrock from cosmogenic radiation

hydrologic changes in colorado during the mid holocene and younger dryas abstract the stratigraphy of upper big creek lake ubc an overflowing lake in northern colorado indicates that the lake responded to a series of hydroclimatic changes over the past 13 000 years modern sediments in eight comparator lakes from across wyoming and colorado facilitate the stratigraphic interpretation by showing that littoral sediments have exponentially higher sand content lower loss on ignition loi and lower net accumulation rates than off shore sediments sand layers in two near shore cores from ubc share the characteristics of the modern littoral sediments 80 sand 1 9 m below its outlet from 12 500 to 11 300 and from 7500 to 2100 cal yr bp ground penetrating radar gpr profiles consistent with the low water episodes show correlative sand layers and submerged wave cut scarps around the lake margin the stratigraphic features correlate with those formed in the comparator lakes during extensive droughts at 11 300 6900 6000 and 4800 3400 cal yr bp as well as a series of north south anti phased droughts between 5800 and 1200 cal yr bp lake closure at ubc amplified the local changes and demonstrates that climate changes can increase the extent of intermittent streamflow in the rocky mountains relative to today

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

surface and deep ocean interactions during the cold climate event 8200 years ago evidence from a north atlantic deep sea sediment core reveals that the largest climatic perturbation in our present interglacial the 8200 year event is marked by two distinct cooling events in the subpolar north atlantic at 8490 and 8290 years ago an associated reduction in deep flow speed provides evidence of a significant change to a major downwelling limb of the atlantic meridional overturning circulation the existence of a distinct surface freshening signal during these events strongly suggests that the sequenced surface and deep ocean changes were forced by pulsed meltwater outbursts from a multistep final drainage of the proglacial lakes associated with the decaying laurentide ice sheet margin

cosmogenic 10be and 26al ages of holocene moraines in southern norway ii evidence for individualistic responses of high altitude glaciers to millennial scale climatic fluctuations abstract 10be and 26al exposure ages are reported for boulder moraine ridges in front of two high altitude cirque glaciers austanbotnbreen jotunheimen and ostre tundradalskyrkjabre breheimen in southern norway ages and 1 external uncertainties for austanbotnbreen moraines range from 7 4 0 75 ka to 8 7 0 9 ka when no adjustment for snow shielding is made with the maximum conceivable snow cover effect 2 m thick a density of 0 2 g cm3 6 months duration at the exposed site the resulting adjusted 7 7 0 8 to 10 9 1 3 ka as well as unadjusted ages suggest moraine formation possibly during both the 8 2 ka event finse event in southern norway and the erdalen event c 10 0 ka in contrast ages obtained for the outer ridges of the large moraine complex in front of ostre tundradalskyrkjabre range from 1 1 0 3 ka to 1 9 0 4 ka assuming no snow shielding assuming extreme snow lie conditions 4 m thick 0 2 g cm3 density 6 months duration at this more sheltered site the adjusted ages

contributions and unrealized potential contributions of cosmogenic nuclide exposure dating to glacier chronology 1990 2010 abstract this paper reviews the application of cosmogenic nuclide exposure dating to glacier chronology exposure dating of glacial landforms has made an outsize impact on this field because the technique filled an obvious need that had already been recognized by glacial geologists by now hundreds of studies have used cosmogenic nuclide exposure dating to date glacial deposits and in fact it is rare to find a study of glacial geology or glacier chronology or any paleoclimate synthesis that makes use of such studies that does not involve exposure dating these developments have resulted in major contributions to glacier chronology and paleoclimate in particular i reconstructing antarctic ice sheet change ii establishing the chronology of late pleistocene and holocene glacier change in mountain regions where it was previously unknown iii establishing the broad chronological outlines of mountain glaciations prior to the last glacial maximum and iv gaining insight into subglacial erosional processes through the observation that many glaciated surfaces preserve cosmogenic nuclide inventories from long past ice free periods as well as the present one an important potential future contribution will be the application of the large data set of exposure dated glacier chronologies to better understand global and regional climate dynamics during lateglacial and holocene millennial scale climate changes however this contribution cannot be realized without significant progress in two areas i understanding and accounting for geologic processes that cause apparent exposure ages on glacial landforms to differ from the true age of the landform and ii minimizing systematic uncertainties in exposure ages that stem from cosmogenic nuclide production rate estimates and scaling schemes at present there exists an enormous data set of exposure ages on glacial deposits but these data cannot be used to their full potential in paleoclimate syntheses due to an inadequate understanding of geologic scatter and production rate uncertainties the intent of this paper is to highlight this situation and suggest some strategies for realizing this potential

holocene glacier fluctuations in the american cordillera abstract in many areas of the american rocky mountains colorado wyoming utah idaho montana cascade range washington oregon and the sierra nevada california radiocarbon ages suggest that ice receded to near present limits before 10 ka bp a pre altithermal readvance or stillstand left moraines ca 1 3 km beyond and ca 50 300 m below present glacier margins at one locality on glacier peak in washington these deposits are perhaps dated to the early holocene but in general these deposits are probably at least 10 ka old glacial advances during the altithermal ca 8 to 5 ka bp elsewhere are rare radiocarbon evidence for altithermal glacial advances in the colorado front range is questionable the earliest radiocarbon dated neoglacial advances occurred about 5 ka bp in the washington cascades moraines and related deposits believed to be of early neoglacial age i e 5 to 3 ka bp elsewhere are poorly dated for example moraines believed to date to the early neoglacial in colorado triple lakes and wyoming temple lake are actually late pleistocene age based on radiocarbon ages derived from lake sediments at the type localities although relative age data i e lichens rock weathering soils from many areas suggest a three fold neoglacial sequence little supporting radiocarbon evidence is available however tephrochronology distinguishes three neoglacial advances near mount rainier in washington in most mountain ranges of the western united states fresh unweathered sharp crested moraines usually adjacent to present ice margins or near headwalls in empty cirques date to the little ice age of the last several centuries however detailed photographic or other historical records of glacial fluctuations during the last century are rare and detailed mass balance studies rarer still whether or not pre little ice age glacial fluctuations in the american cordillera are synchronous must await better radiometric dating of local moraine sequences

precise cosmogenic 10be measurements in western north america support for a global younger dryas cooling event the inner titcomb lakes moraine in the wind river mountains wyoming has been dated with a precision of 5 using accelerator mass spectrometric measurements of cosmogenic 10be in surface samples from nine boulders resting on its crest the age of this moraine is 11 4 0 5 to 13 8 0 6 ka the range in age is due to the uncertainty in the 10be production rate and uncertainties in rock erosion rate and shielding of cosmic rays by snow additional exposure ages on bedrock and boulder surfaces that are stratigraphically younger and older than the inner titcomb lakes moraine conform with this age the exposure ages of the inner titcomb lakes moraine overlap the north atlantic younger dryas event 12 8 0 2 to 11 5 0 3 ka

evidence for cirque glaciation in the colorado front range during the younger dryas chronozone abstract late pleistocene glacial chronologies developed for the front range mountains of colorado include two or more cirque glacier advances locally known as the satanta peak advances sediment cores were recovered from sky pond an alpine lake 3320 m located less than 100 m downvalley from a moraine that exhibits late pleistocene to early holocene relative age features and appears to correlate to the satanta peak deposits one of the cores penetrated 0 5 m of basal diamict and recovered 3 3 m of overlying sediments that are predominantly gyttja an accelerator mass spectrometry ams age of 12 040 60 yr14c b p was obtained from directly above the basal diamict and is similar to other reported ages for cirque deglaciation in the front range mountains the lower portion of the gyttja contains an interval of clastic sediments that show characteristics consistent with glacial activity in alpine catchments radiocarbon ages obtained from below and near the upper contact of this clastic interval are 11 070 50 and 9970 8014c yr b p respectively an additional ams age of 10 410 9014c yr b p was obtained from within the clastic interval in a second core the most likely source for this interval of clastic sediments is a moraine situated directly upvalley from sky pond and consequently it appears that the deposition of this moraine was coeval with the european younger dryas event 11 000 10 00014c yr b p similarities in soil development weathering features and altitude between this moraine and the type satanta peak moraines suggest that the moraines are correlative these findings are in agreement with a growing body of evidence that suggests a relatively minor advance of alpine glaciers occurred in the north american rockies during the younger dryas chron

scaling factors for the rates of production of cosmogenic nuclides for geometric shielding and attenuation at depth on sloped surfaces abstract the decrease in rates of production of cosmogenic nuclides occurs because of shielding of cosmic rays by mountains sloped surfaces and local rock formations that block them when a large part of the sky is blocked this correction is large and requires detailed model calculations this paper considers three geometries a rectangular obstruction a triangular obstruction and a sloped surface other geometries can be considered as a combination of these the results are presented in terms of formulas and graphs so that the reader can easily apply them to common field situations any use of cosmogenic nuclides in the study of geomorphic processes or forms must consider factors that introduce variations in the production of nuclides

geomagnetic effects on time integrated cosmogenic nuclide production with emphasis on in situ 14c and 10be abstract production of cosmogenic nuclides cns in geologic material is a function of the cosmic ray flux at the earth s surface which in turn is a function of the intensity and orientation of the earth s geomagnetic field temporal variations in the intensity of the geomagnetic field and the position of the geomagnetic dipole axis i e polar wander must be considered when calculating production rates that are integrated through time we have developed a model based in part on protocols set forth by desilets and zreda earth planet sci lett 206 2003 21 42 that accounts for these variations in an effort to systematically determine their impact on time integrated production of short lived in situ 14c t1 2 5 73 ka and long lived in situ 10be t1 2 1 5 ma cns our modeling results show that for samples exposed for the last 3 ka integrated in situ 14c and 10be production rates that account for temporal variations in the intensity of the earth s geomagnetic field are up to 13 lower than modern rates at the same location modern rates are referenced to the 1945 0 definitive geomagnetic reference field dgrf in contrast intensity corrected 10be rates are up to 30 higher than modern for samples exposed for 25 30 ka intensity variations have little effect our modeling results also show that the impact of polar wander on integrated cn production is secondary compared to intensity variations accounting for polar wander is critical however when determining modern production rates at midlatitudes 30 40 because of the current offset between the geomagnetic and geographic poles at sea level integrated in situ 14c production rates that account for both intensity variations and polar wander range from 27 higher to 24 lower than modern rates at the same location and integrated in situ 10be rates range from 48 higher to 26 lower than modern differences between integrated and modern rates increase significantly at higher altitudes based on these results we recommend correcting the modern production rate referenced to the 1945 0 dgrf or another specific geomagnetic reference field at site latitudes

late quaternary eolian sand depositional record for southwestern kansas landscape sensitivity to droughts abstract eolian deposits and landforms are ubiquitous in western kansas particularly south of the arkansas river with the presence of a stabilized dune field stratigraphic studies and associated optical dating reveal a complex depositional history for this dune field spanning the late quaternary the oldest eolian deposits from ca 16 to 12 ka completely or partially bury high terraces with ages of ca 16 and 33 ka it is unknown whether these eolian deposits reflect regional aridity and or a change in sediment availability with the transition of the arkansas river from a single channel to a braided system there is pervasive evidence for episodic eolian erosion and deposition ca 9 8 to 6 3 ka generally coincident with loess deposition on upland surfaces olson c g nettleton w d porter d a brasher b r 1997 middle holocene aeolian activity on the high plains of west central kansas holocene 7 3 255 261 and thus it is inferred to reflect regional aridity sites within the dune field show a sequence of eolian sands and weak buried soils reflecting either dune migration or sand sheet accretion at ca 1490 430 380 320 180 and 70 yr ago which correspond well with continental scale droughts in the tree ring record eolian sand in the arkansas river dune field may be derived principally with variability in fluvial activity and in climate during the late pleistocene to the middle holocene with substantial reactivation of eolian systems during decadal scale drought variability in the past 2000 yr

the schmidt hammer as a holocene calibrated age dating technique testing the form of the r value age relationship and defining the predicted age errors most recent developments of schmidt hammer exposure age dating shd as a calibrated age dating tool have been limited by the use of locations at two age control points this has necessitated 1 making assumptions about a linear r value age relationship and 2 basing predictions of age errors only on r value variance at the two age control points this paper analyses 9900 r values obtained from multiple age control points on a sequence of glacio isostatically raised shorelines with well constrained ages skuleskogen high coast world heritage site and environs gulf of bothnia northern sweden ranging from modern to 10 5 ka in age the sampling design involved 30 measurements on granite beach boulders from 30 sites at 11 age control points the r value age relationship is best described by a linear function ordinary least squares ols with an r 2 of 0 89 p 0 0001 predicted age errors are calculated using two approaches 1 ols regression which takes account of the uncertainties associated with the regression line and the age control points and 2 weighted total least squares wtls regression which in addition takes account of possible shoreline age errors and the heteroscedasticity of r value residuals with increasing age with both approaches 95 predicted age errors are relatively modest 355 455 years and 300 515 years respectively with larger r value variance and hence uncertainty for older surfaces and the possibility of further improvement from a more selective field sampling scheme that differentiates between age related and non age related rock surface variability our results also indicate that for certain lithologies and weathering environments it is possible to construct reliable calibrated age curves from relatively few age control points

stratigraphy of the younger dryas chronozone and paleoenvironmental implications central and southern great plains abstract the great plains of the united states was the setting for some of the earliest research in north america into patterns and changes in the character of late pleistocene environments and their effects on contemporary human populations many localities in the region have well stratified records of terminal pleistocene and early holocene human paleoindian activity and past environments these have proven important in debates over the character of the younger dryas chronozone ydc 11 000 10 000 14c bp 12 900 11 700 cal bp in the continental interior this paper reviews the lithostratigraphic record of the ydc on the central and southern great plains and summarizes paleobiological records largely isotopic the goal is to determine if there is any uniformity in the timing character direction and or magnitude of changes in depositional environments or broader geomorphic systems before during or after the ydc in order to address the question of the character of environments through this time the stratigraphic records of the late pleistocene to early holocene transition and in particular the stratigraphic records of the ydc vary through time and space the data clearly show that a host of geomorphic processes produced the terminal pleistocene and early holocene stratigraphic records of the great plains moreover the ydc is not necessarily manifest as a distinct lithostratigraphic or biostratigraphic entity in these different types of deposits and soils the various geomorphic systems of the great plains did not behave synchronously in response to any common climate driver these stratigraphic records reflect local environmental conditions and probably a complex response to the reorganization of mid latitude climates in the terminal pleistocene and early holocene

cosmic ray production rates of 10be and 26al in quartz from glacially polished rocks we have studied the concentrations of 10be and 26al in quartz crystals extracted from glacially polished granitic surfaces from the sierra nevada range these surfaces were identified with the glacial advance during the tioga period 11 000 years ago our measurements yield the most accurate estimates to date for the absolute production rates of these nuclides in sio2 due to cosmic ray nucleons and muons for geomagnetic latitudes 43 8 44 6 n and altitudes 2 1 3 6 km the estimates are relatively free from uncertainties in snow cover since we studied a suite of rock surfaces inclined 0 75 with respect to the horizontal the principal uncertainty arises due to the lack of a precise date for the glacial retreat event about 10 the 26al 10be ratio at production 6 0 is determined more accurately since the exposure age of the samples is 2 orders of magnitude smaller than the mean lives of the two nuclides production rates of 10be and 26al in quartz at other latitudes and altitudes in the troposphere can be determined from the present measurements by scaling using the known altitude and latitude dependence of cosmic ray fluxes of nucleons and negative muons knowledge of the production rates of these nuclides is a prerequisite for their application in erosion and geomorphological studies

late pleistocene piedmont glaciations in the eastern mediterranean insights from cosmogenic 36cl dating of hummocky moraines in southern turkey abstract we report the presence of late pleistocene piedmont glaciers represented by the largest hummocky moraine field observed in the eastern mediterranean the piedmont glaciers originated from the geyikdag ice cap 40 km 2 situated between 2350 and 2650 m above sea level a s l central tauride mountains of turkey and deeply carved the north facing hillslopes before reaching the namaras valley 2000 2050 m a s l the hummocky moraines resulted from in situ deposition of stagnant glacier ice where debris cover was heterogeneously distributed on the glacier surface thirty four boulders from hummocky disintegration lateral and terminal moraines from the namaras valley and the tributary susam valley 2100 2200 m a s l were dated by cosmogenic 36 cl surface exposure dating the moraine ages indicate three phases of deglaciation during the late pleistocene the oldest deglaciation occurred in the namaras valley at 18 0 1 1 ka ka thousand years ago towards the end of the last glacial maximum lgm and is recorded entirely by hummocky moraines we speculate that hummocky moraine forming processes with cycles of relief inversion gave rise to boulder apparent ages up to a few thousand years younger in our study area therefore 18 0 1 1 ka should be regarded as a minimum age with a probable true age much closer to the local lgm values 20 ka as observed in the surrounding mountains paleo piedmont glaciers also deposited several lateral moraines that are 50 m higher than the hummocky moraines although the lateral moraines probably represent the build up and the hummocky moraines the final phase of the same local lgm pulse both lateral moraines started to retreat from the late glacial 14 0 2 7 ka and gradually disappeared by mid holocene 5 2 1 0 ka encompassing the younger dryas yd stadial in the susam valley the late glacial is represented by a terminal moraine 13 4 1 5 ka the glacier retreat was very fast as indicated by an almost instantaneous disappearance of 5 km long susam valley glacier represented by disintegration and hummocky moraines 14 0 1 3 ka alternatively in case the oldest boulder age is taken into account the susam valley glacier can be also attributed to the late lgm 17 ka to late glacial 14 ka transition near the exit of the susam valley a right lateral moraine was deposited 11 6 1 3 ka ago confirming the presence of the yd in geyikdag comparable glacial chronologies were obtained from other turkish and mediterranean mountains

lithology landscape dissection and glaciation controls on catchment erosion as determined by cosmogenic nuclides in river sediment the wutach gorge black forest cosmogenic nuclides measured in quartz from recent river bedload provide a novel tool to quantify catchment wide erosion rates at geologically meaningful time scales here we present an analysis of the geomorphological evolution of the 350 km2 wutach catchment in the uplands of the south west german black forest the robustness of the method is demonstrated by the fact that although the area was affected by river capture at 18 kyr bp the formed gorge is so narrow that spatially averaged erosion rates were not resolvably perturbed however because cosmogenic nuclides preserve an erosion memory of several thousand years the only perturbation introduced was detected in the minor areas that have been subject to the last maximum glaciation in unglaciated areas an important relationship between lithology and erosion can by quantified sandstone lithologies erode at 12 18 mm kyr 1 granite lithologies at 35 47 mm kyr 1 and limestone lithologies as deduced from river load gauging at 70 90 mm kyr 1

timing and significance of late glacial and holocene cirque glaciation in the sierra nevada california mapping and radiocarbon dates of cirque moraines in the sierra nevada demonstrate that the last significant pre little ice age glacier advance in the range the recess peak resulted from snowline lowering roughly twice that of the matthes little ice age advance and that the recess peak advance is late pleistocene in age we mapped recess peak and matthes deposits in 64 cirques along a profile of the main sierran crest that spans the north south limits of neoglacial deposits in the range equilibrium line altitudes for the reconstructed recess peak glaciers vary greatly but coherently with those of the matthes advance the variability of both sets of deposits reflects strong topographic influences on snow accumulation and ablation patterns in their deep cirques tephrochronology and radiocarbon dates from lake sediment cores provide limits on the timing of the two advances previous work documenting the absence of a young regionally extensive tephra on matthes moraines in the central sierra demonstrates that they formed after 700 14c years bp 650 cal years bp the age of the recess peak advance has been less certain we therefore collected and dated sediment cores from lakes dammed behind terminal moraines correlating to the recess peak advance in four widely separated drainages along the sierran crest north to south south fork american river lee vining creek middle fork san joaquin river and bishop creek twenty three high precision ams radiocarbon dates on gyttja peat and macrofossils from the cores are internally consistent and demonstrate that the recess peak advance previously thought to be of late holocene age 2500 years bp ended before 11 190 70 14c years bp 13 100 85 cal years bp recess peak is therefore late pleistocene in age and probably predates the north atlantic younger dryas climatic reversal the absence of any glacial deposits on the bedrock between the recess peak and matthes deposits indicates that 1 any advance related to the younger dryas event in central california was smaller than the matthes advance 2 the matthes advance was the most extensive and possibly the only neoglacial event in the range and 3 climate in the sierra between 13 000 cal years bp and 650 cal years bp was apparently too warm and or dry to support glaciers larger than those of the little ice age other mapping indicates that the recess peak is the first significant glacier advance after retreat of tioga local late wisconsin maximum glaciers these results suggest a regionally variable climate in western north america during the younger dryas event because glaciers appear to have expanded in the canadian rockies at that time the new recess peak age limits combined with other dated lake cores indicate that the sierra was essentially deglaciated by 14 000 15 000 cal years bp 12 000 13 000 14c years bp substantially earlier than previously estimated this finding indicates that current production rates of some in situ cosmogenic nuclides calibrated on an assumed deglaciation of the range at 11 000 cal years bp 10 000 14c years bp may be systematically too high by as much as 20