ice sheet sources of sea level rise and freshwater discharge during the last deglaciation we review and synthesize the geologic record that constrains the sources of sea level rise and freshwater discharge to the global oceans associated with retreat of ice sheets during the last deglaciation the last glacial maximum 26 19 ka was terminated by a rapid 5 10 m sea level rise at 19 0 19 5 ka sourced largely from northern hemisphere ice sheet retreat in response to high northern latitude insolation forcing sea level rise of 8 20 m from 19 to 14 5 ka can be attributed to continued retreat of the laurentide and eurasian ice sheets with an additional freshwater forcing of uncertain amount delivered by heinrich event 1 the source of the abrupt acceleration in sea level rise at 14 6 ka meltwater pulse 1a 14 15 m includes contributions of 6 5 10 m from northern hemisphere ice sheets of which 2 7 m represents an excess contribution above that derived from ongoing ice sheet retreat widespread retreat of antarctic ice sheets began at 14 0 15 0 ka which together with geophysical modeling of far field sea level records suggests an antarctic contribution to this meltwater pulse as well the cause of the subsequent younger dryas cold event can be attributed to eastward freshwater runoff from the lake agassiz basin to the st lawrence estuary that agrees with existing lake agassiz outlet radiocarbon dates much of the early holocene sea level rise can be explained by laurentide and scandinavian ice sheet retreat with collapse of laurentide ice over hudson bay and drainage of lake agassiz basin runoff at 8 4 8 2 ka to the labrador sea causing the 8 2 ka event

retreat history of the east antarctic ice sheet since the last glacial maximum the east antarctic ice sheet eais is the largest continental ice mass on earth and documenting its evolution since the last glacial maximum lgm is important for understanding its present day and future behaviour as part of a community effort we review geological evidence from east antarctica that constrains the ice sheet history throughout this period 30 000 years ago to present this includes terrestrial cosmogenic nuclide dates from previously glaciated regions 14c chronologies from glacial and post glacial deposits onshore and on the continental shelf and ice sheet thickness changes inferred from ice cores and continental scale ice sheet models we also include new 14c dates from the george v land terre adelie coast shelf we show that the eais advanced to the continental shelf margin in some parts of east antarctica and that the ice sheet characteristically thickened by 300 400 m near the present day coastline at these sites this advance was associated with the formation of low gradient ice streams that grounded at depths of 1 km below sea level on the inner continental shelf the lambert amery system thickened by a greater amount 800 m near its present day grounding zone but did not advance beyond the inner continental shelf at other sites in coastal east antarctica e g bunger hills larsemann hills very little change in the ice sheet margin occurred at the lgm perhaps because ice streams accommodated any excess ice build up leaving adjacent ice free areas relatively unaffected evidence from nunataks indicates that the amount of ice sheet thickening diminished inland at the lgm an observation supported by ice cores which suggest that interior ice sheet domes were 100 m lower than present at this time ice sheet recession may have started 18 000 years ago in the lambert amery glacial system and by 14 000 years ago in mac robertson land these early pulses of deglaciation may have been responses to abrupt sea level rise events such as meltwater pulse 1a destabilising the margins of the ice sheet it is unlikely however that east antarctica contributed more than 1 m of eustatic sea level equivalent to post glacial meltwater pulses the majority of ice sheet recession occurred after meltwater pulse 1a between 12 000 and 6000 years ago during a period when the adjacent ocean warmed significantly large tracts of east antarctica remain poorly studied and further work is required to develop a robust understanding of the lgm ice sheet expansion and its subsequent contraction further work will also allow the contribution of the eais to post glacial sea level rise and present day estimates of glacio isostatic adjustment to be refined

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

glacial interglacial ice stream stability in the weddell sea embayment antarctica the resilience of the antarctic ice sheet and its effect on global sea level depends on the dynamics of ice streams antarctic ice streams are known to be responsive to changes at the ocean interface and as expected most have thinned in response to ocean warming and sea level rise since the last glacial maximum lgm here we provide direct and unexpected evidence that points toward the glacial interglacial stability of the slessor and recovery glaciers ice streams of the east antarctic ice sheet eais which merge with the west antarctic ice sheet wais to form the filchner ice shelf in the weddell sea embayment cosmogenic nuclide measurements in the shackleton range suggest that the slessor and recovery ice streams were not significantly thicker than today during the lgm we hypothesise that the glaciers did not thicken because the grounding line was not able to migrate seaward beyond the deep thiel crary trough beneath the filchner ice shelf immediately offshore this discovery reveals how a topographic threshold can affect the dynamics of ice streams it also reduces uncertainties on the thickness extent and volume of the antarctic ice sheet in a large but unknown sector of the antarctic ice sheet it constrains the potential sea level rise from antarctica it helps explain observed anomalies in glacio isostatic adjustment above all it suggests that the behaviour of the atlantic facing weddell sea sector of the wais contrasts with that of the pacific facing ross and amundsen sea sectors

dating of sirius group tillites in the antarctic dry valleys with cosmogenic3he and21ne we measured in situ produced cosmogenic3he and21ne in boulder and bedrock surface samples in and near sirius group tillites from two localities in southern victoria land antarctica pyroxene quantitatively retains cosmogenic3he for millions of years the deposit at mt fleming has a minimum exposure age of 6 5 ma while 6 ma is a probable minimum age for the table mountain tillite these lower limits not taking into account erosion of the sampled surfaces are based on the samples with the highest concentrations of cosmogenic noble gases and currently accepted production rates since the plagioclase bearing mt fleming samples almost certainly lost part of their cosmogenic ne the minimum exposure age at this location is presumably even 50 higher than the stated value the concentrations of cosmogenic ne in our samples constrain uplift rates of the transantarctic mountains to 170 m ma these data contradict the hypothesis of a collapse of the east antarctic ice sheet in the pliocene coupled with high uplift rates and support the model of a stable ice sheet since the middle miocene

pleistocene deglaciation chronology of the amery oasis and radok lake northern prince charles mountains antarctica abstract the east antarctic ice sheet is the largest ice mass on earth with a capacity to raise global sea level by up to 65 m as the lambert glacier amery ice shelf drainage system is the largest to reach the coast of antarctica quantifying its evolution over the quaternary is a vital component in developing an understanding of the antarctic response to future climate change here we present a deglaciation chronology based on 10 be and 26 al in situ cosmogenic exposure ages of the northern prince charles mountains which flank the lambert glacier amery system and that records the progressive emergence of mcleod massif and radok lake basin from beneath the mac robertson land lobe of the east antarctic ice sheet the exposure ages monotonically decrease with both decreasing altitude and increasing proximity to the amery ice shelf at the antarctic coast exposure ages from the crests of mcleod massif near the edge the amery ice shelf and from fisher massif 75 km further inland each at 1200 m above sea level are 2 2 0 3 and 1 9 0 2 ma respectively suggesting their continuous exposure above the ice sheet at least since close to the plio pleistocene boundary an extensive plateau at 800 m altitude on mcleod massif above battye glacier records the massif s increased emergence above the ice sheet surface at about between 880 and 930 ka ago indicating 400 m of ice volume reduction in the mid pleistocene correcting these apparent ages for a reasonable choice in erosion rate would extend this event to 1 15 ma a period identified from prydz bay odp core 1167 when sedimentation composition alters and rates decrease 10 fold exposure ages from boulder mantled erosional surfaces above and beyond the northern end of radok lake at 220 m range from 28 to 121 ka independent of choice of model interpretation to explain this age spread the most recent major reoccupation of radok lake by battye glacier ice occurred during the last glacial cycle moraine ridges at the lower altitude of 70 125 m were deposited during the final withdrawal of battye glacier ice from the lake basin between 11 and 20 ka ago this new chronology indicates that the highest amery oasis peaks have not been overridden by the mac robertson land lobe of the east antarctic ice sheet for at least the past 2 ma since this time we document 3 major periods of regional reduction in ice sheet volume at 1 1 ma during the last glacial cycle 120 to 30 ka and through the last glacial maximum 20 to 10 ka that resulted in an overall 1000 m of ice lowering in the battye glacier radok lake region

dipoles of the south east madagascar current from an analysis using almost 20 years of satellite altimetry data and in situ observations we have shown thatat the southern tip of madagascar the semc breaks up in a series of nearly symmetric dipolar vortex pairs of approximately zero net relative vorticity they appear at a frequency of about 4 6 per year most vortex pairs break up shortly after their formation and interact with previously formed cyclones and anticyclones the velocity shear across the semc is so large that the dynamics of the evolution of the dipole is dominantly nonlinear a surprising consequence is that there is no retroflection of the semc nor does it continue as an unstable westward jet instead the lobes develop symmetrically and the dynamics appear more similar to that of modon formation flierl et al 1983 the eke south of madagascar was shown to correlate with the strength of the semc prior to separation such a relationship could not be found by palastanga et al 2006 probably because they used a more upstream satellite transect to determine the surface velocity of the semc within the semc there is a short decorrelation length scale also observed in the gulf stream sturges and hong 2001 and the velocity at our transect does not significantly correlate with the velocity at locations further than 450 km upstream the very early retroflection of the ac in 2001 was an exceptional one only one more appeared in the 18 year period in 2008 in both cases it needed a concerted action of cyclonic meanders of the ac and the arc to shortcut the retroflection loop with an active role of the madagascar dipoles in generating the agulhas cyclones interannual variability in the separation region appeared related with the enso cycle but not significantly with the iod significant correlations were found between the nino3 4 index and both the strength of the semc and the eke southwest of madagascar positive and negative lags are between 250 and 500 days preceding a positive negative enso phase stronger weaker velocities in the semc were observed following a positive negative phase weaker stronger velocities in the semc were observed we are presently investigating the possible explanations of these relations and their impact

investigating absolute chronologies of glacial advances in the nw sector of the cordilleran ice sheet with terrestrial in situ cosmogenic nuclides abstract geologic mapping in yukon territory canada over the past 100 years has revealed a consistent pattern of diminishing cordilleran ice sheet cis extent during successively younger glaciations although this pattern is generally accepted there is still much uncertainty about the number of glaciations their ages and the dynamics of the different lobes that constituted the digitate ice sheet margin their subglacial thermal regimes and ice thicknesses we address uncertainties in the timing of glaciation using cosmogenic nuclide exposure dating at key localities that straddle several major lobes of the cis in west central yukon territory differences in exposure duration within what are thought to be the same map units are perhaps due to inheritance older than expected but more likely result from postglacial shielding younger than expected or surface erosion despite a significant spread in exposure durations on moraines and within map units and tending to rely on longest exposure durations on moraines due to postglacial degradation and shielding our results indicate that the mcconnell glacial advance occurred during marine oxygen isotope stage mis 2 judging from oldest minimum apparent exposure ages of 15 7 1 5 and 17 7 1 6 ka a gladstone glacial advance occurred before 51 8 4 7 ka mis 4 and reid glacial advances before 79 8 7 3 and 82 8 7 5 ka consistent with mis 6 traces of even older glacial advances predate 100 ka 107 5 9 9 154 3 14 2 ka

errata neogene fjordal sedimentation on the western margin of the lambert graben east antarctica the lambert graben is occupied by the world s largest fjord system through which flows the lambert glacier the amery ice shelf and their tributaries along the western margin of the graben in the northern prince charles mountains remnants of uplifted miocene and pliocene strata of the glacigenic fjordal pagodroma group total more than 800 m in thickness these sediments provide evidence for a dynamic east antarctic ice sheet during the neogene period each of the four pagodroma group formations defined from this region rests unconformably on either proterozoic or permo triassic rocks the unconformity surfaces represent parts of the walls and floors of neogene fjords for these surfaces to have been eroded the ice must have been grounded out as far as the continental shelf in prydz bay the pagodroma group was deposited by wet based glaciers discharging into a fjordal setting and includes lithofacies that are quite different from those produced by modern antarctic ice masses the principal lithofacies are massive diamicts and soulder gravels deposited both close to a calving grounded glacier terminus and from icebergs the few stratified diamicts are the product of more distal iceberg sedimentation an ice transported gravel lithofacies includes rockfall debris derived from palaeofjord walls and mixed with subglacially derived diamicts some lithofacies contain evidence of subaquatic slumping and gravity flowage volumetrically minor lithofacies include laminites with some exposures exhibiting large ice rafted clasts the laminites represent less proximal mainly ice free fjordal sediments resulting either from tidal current sorting of suspended sediment originating from subaquatic glaciofluvial discharge or from turbidity currents derived from unstable subaquatically deposited glacigenic sediment the pagodroma group provides a record of multiple glaciation by dynamic sliding glaciers carrying large amounts of both basal and supraglacial debris the closest modern analogues in terms of the thermal and dynamic characteristics of the neogene lambert glacier appear to be the fast flowing tidewater glaciers of east greenland these glaciers originate from the interior ice sheet and discharge large volumes of icebergs the resulting lithofacies are predominantly diamicts

history of ice sheet elevation in east antarctica paleoclimatic implications abstract the multi disciplinary study of past ice surface elevations in the grove mountains of interior east antarctica provides direct land based data on the behavior of the east antarctic ice sheet since the pliocene the glacial geology the ages of cold desert soils the depositional environment of younger moraine sedimentary boulders and their spore pollen assemblages combine to imply a possible significant shrinkage of the ice sheet before the middle pliocene epoch with the ice sheet margin retreating south of the grove mountains 450 km south from its present coastal position exposure age measurements of bedrock indicate that the elevation of the ice surface in the grove mountains region subsequently rose at about mid pliocene to at least 200 m higher than today s levels the ice surface then progressively lowered with some minor fluctuations middle to late pleistocene exposure ages found on the lowest samples at the ice bedrock contact line indicate a long period with ice surface elevations kept at the current level or complex fluctuation history during the quaternary epoch

controls on subaerial erosion rates in antarctica erosion rates offer insight on landscape development and the relative importance of chemical and physical processes of weathering minimal chemical weathering makes antarctica an ideal location in which to compare the physical weathering of carbonate rocks to other lithologies here we report the first cosmogenic nuclide derived erosion rates for carbonate rocks in antarctica carbonate samples collected in the southernmost ellsworth mountains reflect a 36cl erosion rate of 0 22 0 02 mm ka this erosion rate is consistent with other reported antarctic erosion rates but is lower than 36cl erosion rates derived from other arid regions in the world these results are integrated with a continent wide reanalysis of 28 erosion rate studies 200 measurements which comprise numerous rock types and other cosmogenic nuclides by combining cosmogenic nuclide derived erosion rates across studies the larger trends provide insight into factors e g lithology glacial history and availability of abrasive material affecting subaerial erosion rates in antarctica statistical analysis of the compiled data set shows differences based on lithology with sandstone having the largest range of erosion rates the compiled data also reveals higher erosion rates in areas with a large potential sediment supply like the dry valleys samples collected from boulders yield lower erosion rates than those collected from bedrock likely due to a combination of physical processes that affect boulders and bedrock differently and glacial history which can affect the apparent cosmogenic nuclide derived erosion rate

cosmogenic nuclides 10be and 26al imply limited antarctic ice sheet thickening and low erosion in the shackleton range for 1 m y concentrations of the cosmogenic nuclides 1 0 be and 2 6 al on bedrock surfaces in the shackleton range antarctica indicate minimum exposure ages between 3 0 03 and 1 16 0 10 ma the isotope data indicate that the maximum long term erosion rate is 0 10 0 35 m m y and the ratios suggest no prolonged periods of burial by cold based ice the findings are important because of the location of the massif close to the junction of the east antarctic ice sheet and the landward extent of the filchner ice shelf these results point to three conclusions first the massif has not been overridden by the east antarctic ice sheet during the late quaternary rather moraines 200 340 m above outlet glaciers are likely to represent the maximum thickening of the filchner ronne ice shelf during the quaternary second the high radionuclide concentrations on bedrock surfaces one of which is striated suggest that some glacial landforms were created in at least pliocene or more likely miocene time third the exceptionally low erosion rates imply that the modern cold arid climate has persisted for millions of years these findings provide evidence of old stable landscapes over a wider area of antarctica than the mc murdo dry valleys

variation in glacial erosion near the southern margin of the laurentide ice sheet south central wisconsin usa implications for cosmogenic dating of glacial terrains we measured the abundance of cosmo genic 10 be and 26 al in 22 samples collected from five striated granite metarhyolite and quartzite outcrops in south central wiscon sin that were covered by the late wisconsin laurentide ice sheet in two outcrops mea sured nuclide abundances are consistent with the existing radiocarbon chronology of ice retreat in three outcrops nuclide abun dances were up to eight times higher than predicted by the radiocarbon chronology at these three sites several thousand years of ice flow eroded only centimeters to deci meters of rock allowing a significant quan tity of nuclides 10 5 two samples carry the equivalent of 150 000 yr of surface exposure even though they were covered by ice during the last glacial maximum advance samples highest on the landscape or in plucked ar eas have less inheritance than those from the lee sides of large hills or lower in the landscape three quartzite samples collect ed 10 km up ice from the margin contain three to four times the expected nuclide abundance 10 5 to 10 6 atoms per gram of quartz in contrast eight other quartzite and granite samples from two outcrops 50 km up ice from the former margin contain only 10 5 atoms of 10 be per gram of quartz consistent with late pleistocene ex posure and little if any nuclide inheri tance this relationship between glacial erosion and distance from the former ter minus is consistent with a marginal zone of minimal subglacial erosion the ice was ei ther frozen to its bed there or the ice thick ness and duration of ice cover were less near the terminus these data together with simple model ing of nuclide production by deeply pene trating muons suggest that many meters of rock must be removed to reduce inheri tance to negligible levels 1000 yr in con tinental terrains with low long term erosion rates our results indicate that cosmogenic dating of exposed bedrock surfaces near former ice margins or in areas where ice was frozen to the bed may be uncertain and in some cases impossible because nu clides are inherited from prior periods of cosmic ray exposure unfortunately striat ed glacial outcrops that can be used to dem onstrate most easily the assumption of no postglacial erosion are also the most likely to have undergone little glacial erosion this finding suggests that cosmogenic nuclide production rates based on glacially striated surfaces may include cosmogenic nuclides inherited from prior exposure

east antarctic deglaciation and the link to global cooling during the quaternary evidence from glacial geomorphology and 10be surface exposure dating of the sor rondane mountains dronning maud land abstract reconstructing past variability of the antarctic ice sheets is essential to understand their stability and to anticipate their contribution to sea level change as a result of future climate change recent studies have reported a significant decrease in thickness of the east antarctic ice sheet eais during the last several million years however the geographical extent of this decrease and subsequent isostatic rebound remain uncertain in this study we reconstruct the magnitude and timing of ice sheet retreat at the sor rondane mountains in dronning maud land east antarctica based on detailed geomorphological survey cosmogenic exposure dating and glacial isostatic adjustment modeling three distinct deglaciation phases are identified for this sector during the quaternary based on rock weathering and 10 be surface exposure data we estimate that the ice sheet thinned by at least 500 m during the pleistocene this thinning is attributed to the reorganization of southern ocean circulation associated with global cooling into the pleistocene which reduced the transport of moisture from the southern ocean to the interior of eais the data also show that since the last glacial maximum the ice surface has lowered less than ca 50 m and that this lowering probably started after ca 14 ka this suggests that the eais in dronning maud land is unlikely to have been a major contributor to postglacial sea level rise and meltwater pulse 1a

minimum 10be exposure ages of early pliocene for the table mountain plateau and the sirius group at mount fleming dry valleys antarctica using accelerator mass spectrometry ams we have measured 10be and 26al in quartz from granites and sandstones from table mountain and mount fleming antarctica our data show that the plateau surface at table mountain had formed by early pliocene time at the latest granites fringing but within the sirius group at table mountain give a minimum exposure age of 2 6 ma for this deposit a sandstone clast on the ferrar dolerite surface just outside and below and thus postdating the sirius group has a minimum age of 2 9 ma two samples from the sirius group at mount fleming have 10be concentrations that have reached secular equilibrium this deposit is at least 4 8 m y old the sirius group at mount fleming cannot have been deposited after 3 0 2 5 ma as implied by biostratigraphic data our dates contradict the hypothesis that in the pliocene east antarctica was deglaciated and the climate was significantly warmer and wetter the preservation of these surfaces indicates a continuous cold desert in the dry valleys since the beginning of the pliocene the high 10be concentrations we have measured cannot be reconciled with uplift of the transantarctic mountains at a rate of 1 km m y during the past 3 m y

cosmogenic nuclide measurements in southernmost south america and implications for landscape change we measured in situ 10be 26al and 36cl on glacial deposits as old as 1 1 myr in the southernmost part of patagonia and on northern tierra del fuego to understand boulder and moraine and by inference landscape changes nuclide concentrations indicate that surface boulders have been exposed for far less time than the ages of moraines they sit upon the moraine ages are themselves constrained by previously obtained 40ar 39ar ages on interbedded lava flows or u series and amino acid measurements on related non glacial marine deposits we suggest that a combination of boulder erosion and their exhumation from the moraine matrix could cause the erratics to have a large age variance and often short exposure histories despite the fact that some moraine landforms are demonstrably 1 myr old we hypothesize that fast or episodic rates of landscape change occurred during glacial times or near the sea during interglacials comparison with boulder erosion rates and exhumation histories derived for the middle latitudes of semi arid patagonia imply different geomorphic processes operating in southernmost south america we infer a faster rate of landscape degradation towards the higher latitudes where conditions have been colder and wetter

late cenozoic glacial history of the ross embayment antarctica abstract knowledge of the cenozoic terrestrial and marine glacial history of antarctica has been developed through studies of on land surface outcrops and subsurface drillcores and through examination of drillcores and piston cores obtained from a variety of offshore marine geological settings these field and laboratory endeavors have been a major target of the antarctic earth science community for more than thirty years the ross sea sedimentary basins including the byrd basin west antarctica wilkes and pensacola basins east antarctica and the transantarctic mountains provide significant data on the cenozoic glacial record a record that has been traced back to at least 38 ma close to the eocene oligocene boundary this paper reviews the late cenozoic history of the transantarctic mountains and flanking sedimentary basins with emphasis on the debate between the stabilist view of antarctic ice sheet history see clapperton and sugden 1990 and our favored multi glacial dynamic ice sheet model

topographic controls on post oligocene changes in ice sheet dynamics prydz bay region east antarctica within the general trend of post eocene cooling the largest and oldest outlet of the east antarctic ice sheet underwent a change from ice cliff to ice stream and or ice shelf dynamics with an associated switch from line source to fan sedimentation available geological data reveal little about the causes of these changes in ice dynamics during the miocene epoch or the subsequent effects on pliocene pleistocene ice sheet history icesheet numerical modeling reveals that bed morphology was probably responsible for driving changes in both ice sheet extent and dynamics in the lambert amery system at prydz bay the modeling shows how the topography and bathymetry of the lambert graben and prydz bay control ice sheet extent and flow the changes in bathymetric volume required for shelf edge glaciation correlate well with the prydz channel fan sedimentation history this suggests a negative feedback between erosion and glaciation whereby the current graben is overdeepened to such an extent that shelf edge glaciation is now not possible even if a last glacial maximum environment recurs we conclude that the erosional history of the lambert graben and prydz bay in combination with the uplift histories of the surrounding mountains are responsible for the evolution of this section of the east antarctic ice sheet once the necessary initial climatic conditions for glaciation were achieved at the start of the oligocene epoch

cosmic ray produced 10be and 26al in antarctic rocks exposure and erosion history we have measured cosmic ray produced t1 2 1 5 million years 10be and t1 2 0 705 million years 26al in purified quartz fractions of selected rock samples from antarctic mountains from these data we calculate 1 mean erosion rates for the limiting case of steady state surface exposure to cosmic rays and 2 minimum exposure ages for the limiting case of no erosion calculated mean erosion rates are very low on the order of a few times 10 5 cm yr we believe the sampling to be sufficient to generalize this result to exposed bedrock in antarctica in favorable cases it is possible to distinguish between the limiting cases steady state erosion seems a better description in such cases most samples including some taken a few meters above the present ice level seem to have been exposed for millions of years without major episodes of burial or abrasion by ice

last glacial maximum ice sheet dynamics in arctic canada inferred from young erratics perched on ancient tors along standing debate regarding the reconstruction of former ice sheets revolves around the use of relative weathering of landscapes i e the assumption that highly weathered landscapes have not been recently glaciated new cosmogenic isotope measurements from upland bedrock surfaces and erratics along the northeastern margin of the laurentide ice sheet lis shed light on this debate 10 be and 26 al concentrations from three perched erratics yielding cosmogenic exposure ages of 17 11 ka are much lower than those measured in two unmodified highly weathered tors upon which they lie which yield cosmogenic exposure ages of 60 ka these findings suggest that non erosive ice covered weathered upland surfaces along the northeastern margin of the lis during the last glacial maximum these data challenge the use of relative weathering to define the margins of pleistocene ice sheets the juxtaposition of non erosive ice over upland plateaus and erosive ice in adjacent fiords requires strong gradients in basal thermal regimes suggestive of an ice stream mode of glaciation r 2003 elsevier science ltd all rights reserved

the probable importance of snow and sediment shielding on cosmogenic ages of north central colorado pinedale and pre pinedale moraines abstract eight uncorrected 36 cl ages for pinedale boulders in north central colorado fall in the range 16 5 to 20 9 kyr 10 be age determinations on four of five boulders are in close agreement 6 difference with 36 cl determinations hypothetical corrections for snow shielding increased the 36 cl ages of pinedale boulder surfaces by an average of 12 most ages for pre pinedale bull lake boulders fall within marine isotope stage mis 5 a time when continental and sierran ice accumulations were small or nonexistent under the assumption that these boulders were deposited on moraines that formed before the end of mis 6 140 kyr bp calculations indicated that rock surface erosion rates would have had to range from 5 9 to 10 7 mm kyr 1 to produce the observed 36 cl values when compared to rates that have been documented for the past 20 kyr these erosion rates are extremely high snow shielding accounts for 0 48 of the additional years needed to shift pre pinedale dates to mis 6 this suggests that some combination of snow shielding sediment shielding or 36 cl leakage has greatly decreased the apparent ages of most pre pinedale boulders inability to account for the effects of these processes seriously hinders the use of cosmogenic ages of pre pinedale boulders as estimators of the timing of alpine glaciation

a 2 million year glacial chronology of the hatherton glacier antarctica and implications for the size of the east antarctic ice sheet at the last glacial maximum abstract a series of distinct glacial deposits flanking the margins of the upper hatherton glacier an outlet glacier in the central transantarctic mountains are used to constrain the behaviour of the antarctic ice sheets cosmogenic exposure ages of 18 erratics from four glacial drifts covering the ice free dubris and bibra valleys range in age from 5 to 1997 ka our results document four glacial advance and retreat events superimposed on an overall long term ice thickness reduction of about 500 m since the mid pleistocene the lack of field evidence and absence of lgm exposure ages in the glacial deposits of the hatherton glacier supports our conclusion that at the lgm the east antarctic ice sheet was of similar size or may have been slightly smaller than present minimum exposure ages from the oldest two glacial events represented by the isca and danum drifts are 1 2 ma and 0 5 ma respectively the britannia ii drift previously assumed to mark the maximum extent of the last glacial maximum advance has a mean 10 be age of 126 3 2 ka n 5 ages from the younger britannia i drift suggest that since the mid holocene 6 5 1 2 ka n 5 approximately 200 m of additional ice has been lost

the structure and origin of prydz bay and macrobertson shelf east antarctica abstract a marine geophysical survey in early 1982 conducted by the australian bureau of mineral resources indicated that much of prydz bay is underlain by a sedimentary basin severe seismic multiples preclude an accurate estimate of total sediment thickness but interpretation of the seismic and magnetic data suggest that it is probably at least 5 km the trends of the southeast basin margin and of mild faulting and folding in the southwest indicate an overall nne trend roughly orthogonal to the continental margin in the south of prydz bay two series of seismic sequences are evident separated by a mildly erosional unconformity the lower series ranges from poorly to well stratified has minor folding and faulting and probably derives from continental and perhaps shallow marine pre breakup sediments the upper series is generally well stratified and prograded near the shelf edge it probably represents shallow marine post breakup sediments the seabed is distinctly unconformable with the underlying sediments implying both that much of the upper series sediments and some of the lower series sediments have been bulldozed off by advances of the amery ice shelf and that present sedimentation rates are very low possible thin moraines or tillites in the northeast part of the prydz bay are also attributed to these glacial advances the continental slope and rise sedimentary section ranges from at least 3 km thick off prydz bay to thin off the macrobertson shelf to the west reflecting the more prolific sediment source in prydz bay the deep water section includes several seismic sequences the most distinctive being interpreted as sheet volcanics and turbidite fans the deepest visible unconformity is locally strongly faulted and may separate the pre breakup and post breakup sediments indo antarctic breakup has been tentatively dated as early neocomian 130 ma and the e w orientation of the resultant antarctic coast invites interpretation of the lambert glacier prydz bay structure as a possible failed rift arm of a triple junction direct information on the age and nature of the sediments under prydz bay is lacking but permian continental sediments cropping out at beaver lake to the south may correspond to the lower pre breakup series this interpretation gains some support from analogies with fault bounded intracratonic basins in india which contain permian to triassic continental strata and which may have been juxtaposed prior to breakup the upper series probably consists of upper cretaceous and cainozoic sands and shales with moraines or tillites at the top of the section

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

the last deglacial history of lutzow holm bay east antarctica past fluctuations of the antarctic ice sheet are poorly understood because of a lack of datable materials radiocarbon reservoir ages and severe environments direct evidence of the timing of ice retreat is important in order to understand the antarctic contribution to global sea level rise since the last glacial maximum here we report the first exposure ages constraining the timing of the last deglaciation from lutzow holm bay east antarctica our data suggest that the final retreat of the ice sheet in the region occurred rapidly in the early holocene and the reduction of the ice thickness in the region was at least 350 m this occurred after the major northern hemisphere deglaciation copyright 2011 john wiley sons ltd

mid late pleistocene glacial evolution in the grove mountains east antarctica constraints from cosmogenic 10be surface exposure dating of glacial erratic cobbles abstract glacial histories from the east antarctic ice sheet eais provide keys to understanding correlations between the eais and global climate they are especially helpful in the assessment of global sea level change and as a means of quantifying the magnitude of past glacial activity and the rate at which ice responded to climate change given the significance of eais glacial histories it is imperative that more glacial chronologic data for this region be obtained especially for the mid to late pleistocene we report cosmogenic 10 be surface exposure dating results from glacially transported cobbles embedded in blue ice moraine material at mount harding the grove mountains eais forty exotic cobbles sampled along two profiles a and b on this blue ice moraine present apparent exposure ages ranging from 7 2 to 542 2 ka we explore this scattered dataset by using principal component analysis pca to identify statistically significant trends in the data we identify a correlation between exposure age and distance of the cobbles from mount harding in profile a cobbles further from mount harding yield older exposure ages than those that are relatively close in profile b cobbles closer to mount harding are found to have relatively older exposure ages in term of glacial history we suggest that the direction of ice flow changed during the period from 60 to 200 ka and that multiple glacial fluctuations occurred in the mid late pleistocene

cosmogenic nuclide ages for new england coastal moraines martha s vineyard and cape cod massachusetts usa abstract cosmogenic nuclide exposure ages for 13 glacially transported boulders atop the martha s vineyard moraine ma usa indicate that the southeastern margin of the laurentide ice sheet reached its maximum extent during the last glaciation 23 200 500 yr ago another 10 age determinations from the younger buzzards bay moraine near woods hole ma indicate that this moraine complex was formed 18 800 400 yr ago these ages correlate approximately with the terminations of cooling cycles recorded in greenland ice cores and coeval ice rafting events suggesting that the marginal position of this sector of the ice sheet was tightly coupled to north atlantic climate during the last glacial maximum

cosmogenic noble gas studies in the oldest landscape on earth surface exposure ages of the dry valleys antarctica extraordinarily high surface exposure ages have been determined for sirius group tillites of mt fleming and mt feather as well as at localities in the inner dry valleys using cosmogenic helium and neon ages of 10 ma at mt fleming 5 3 ma at mt feather and 6 5 ma at insel mountain are among the highest nominal exposure ages published so far these values are minimal ages as they are based on the assumption of zero erosion and uplift the mt feather sample independently confirms the pre pliocene age of the sirius group sediments in the dry valleys as previously determined at mt fleming the insel mountain samples provide evidence for a landscape formation of the inner dry valleys not later than late miocene time assuming conservatively low values of 2 5 cm ma 1 for erosion rate and 50 m ma 1 for uplift rate we infer that the sirius group tillites at mt fleming were deposited earlier than 20 ma ago this indicates that the overriding of the dry valleys block of the transantarctic mountains by the east antarctic ice sheet occurred not later than the early miocene maximum long term erosion rates in the inner dry valleys must be 15 cm ma 1 down to altitudes 1000 m since such low erosion rates require permanently cold and hyperarid conditions the response of antarctica to the pliocene warm climatic episode must have been small cosmogenic nuclide data from both the inner dry valleys and the sirius group sediment localities support the hypothesis of a stable east antarctic ice sheet since at least late miocene time implying that the climate of antarctica was decoupled from that of lower southern latitudes we present also new elemental 21ne production rates of p21 mg 196 atoms g 1 yr 1 and p21 al 55 atoms g 1 yr 1 at sea level and high geomagnetic latitude these figures are consistent with a 3he production rate of p3 110 atoms g 1 yr 1 similar to previously published values this consistency provides evidence that pyroxene is retentive for both helium and neon over at least 10 ma cosmogenic ne in quartz and pyroxene has a 22ne 21ne cos ratio of 1 266 0 040 and 1 159 0 040 respectively

cosmogenic 36cl accumulation in unstable landforms 2 simulations and measurements on eroding moraines cosmogenic 36cl surface exposure ages obtained for multiple boulders from single landforms are usually characterized by a variance larger than that of the analytical methods employed this excessive boulder to boulder variability progressively more profound with increasing age of landforms is due to removal of soil and gradual exposure of boulders at the surface in our gradual exposure model boulders are initially buried in moraine matrix with time erosion lowers the moraine surface and the boulders are gradually exposed to cosmic rays because the cosmic ray intensity changes with depth the boulders are subjected to variable production rates of the cosmogenic 36cl initial depth of boulders and their chemical composition are variable which results in different amounts of the accumulated cosmogenic 36cl and thus different apparent ages of boulders the shape of the resulting distribution of the apparent ages and the coefficient of variation depend on the erosion depth while the first moment is a function of the true surface age and the erosion depth these properties of the apparent age distributions permit calculation of the surface age the erosion depth and also the average erosion rate we tested the model calculations using 26 boulders from a late pleistocene moraine at bishop creek sierra nevada california the set exhibited a bimodal distribution of the 36cl surface exposure ages we interpreted the older mode as the result of gradual exposure and the younger one as the result of surficial processes other than soil removal the 10 samples that constitute the older mode produced a distribution which closely matches the modeled distribution calculated using an age of 85 kyr and erosion depth of 570 g cm 2 this age is the same as an independent estimate obtained from cation ratio studies and the calculated erosion depth is very close to the erosion depth of 600 g cm 2 based on a simple analytical model of soil erosion these results indicate that our statistical model adequately describes effects of soil erosion on accumulation of cosmogenic 36cl the approach can be used to simultaneously obtain the true landform age and the erosion rate from apparent 36cl ages and thereifore may help in evaluation of surface exposure ages of eroding landforms

cosmogenic exposure dating of late pleistocene moraine stabilization in alaska seventy three new 1 0 be 2 6 al ages from 57 moraine boulders and 2 tors together with 43 previously published cosmogenic exposure ages from 41 moraine boulders allow us to critique the use of cosmogenic exposure ce dating of moraine boulders in alaska boulder exhumation during moraine degradation likely gives rise to the largest uncertainty in constraining the timing of initial moraine stabilization following ice retreat isotopic inheritance appears to be most important for moraines deposited close to their cirque headwalls boulder surface bedrock erosion rate can be roughly constrained and leads to a range in moraine stabilization ages snow cover history is difficult to constrain but its effect is thought to be minor for the tall boulders sampled despite these complications the ce ages provide important new information regarding the timing of the last and penultimate glaciations in alaska three penultimate moraines yielded ce ages that overlap with marine isotope stage mis 4 early mis 3 45 65 ka rather than mis 6 ca 140 ka based on a combination of our new ce chronologies and existing 1 4 c ages from six study areas glaciers retreated from their local late wisconsin maxima ca 24 27 ka kokrines hills west interior alaska ca 24 26 ka northeastern brooks range ne alaska ca 21 23 ka yukon tanana upland east interior alaska ca 22 ka ahklun mountains sw alaska ca 20 ka western alaska range central alaska ca 16 18 ka chuilnuk mountains sw alaska overall glacier retreat was concurrent with the peak of the last global glacial maximum probably in response to limited moisture availability

holocene deglaciation of marie byrd land west antarctica surface exposure ages of glacial deposits in the ford ranges of western marie byrd land indicate continuous thinning of the west antarctic ice sheet by more than 700 meters near the coast throughout the past 10 000 years deglaciation lagged the disappearance of ice sheets in the northern hemisphere by thousands of years and may still be under way these results provide further evidence that parts of the west antarctic ice sheet are on a long term trajectory of decline west antarctic melting contributed water to the oceans in the late holocene and may continue to do so in the future

lower pliocene hominid remains from sterkfontein cosmogenic aluminum 26 and beryllium 10 burial dates of low lying fossiliferous breccia in the caves at sterkfontein south africa show that associated hominid fossils accumulated in the lower pliocene these dates indicate that the skeleton stw 573 and newly discovered specimens from jacovec cavern have much the same age approximately 4 million years these specimens are thus of an age similar to australopithecus anamensis from east africa

the neogene east antarctic ice sheet a dynamic or stable feature abstract this paper is a review of the history and behaviour of the east antarctic ice sheet during the late neogene and is a response to the publication of sugden et al 1993a the case for a stable east antarctic ice sheet in geografiska annaler 75a 4 the antarctic ice sheet is a critical factor in the global climate and oceanographic system knowledge of its historical development is critical to understanding global palaeoceanographic and palaeoclimatic systems and their development the webb harwood hypothesis proposes that the ice sheet while being present in antarctica for more than 40 ma was until recently ca 2 5 ma a dynamic feature waxing and waning under a more temperate climatic and glaciologic regime the stabilistic hypothesis proposes that the current ice sheet has existed in its present cold and polar form for at least the last 14 ma the case for a stable east antarctic ice sheet is the clearest statement of the stabilistic argument to date the authors find support for their viewpoint by presenting evidence from several geologic data bases that does not support their own null meltdown hypothesisr which they deem to be equivalent to the webb harwood hypothesis thereby they conclude supporting the stabilistic hypothesis however their conclusions are weakened by failure to reject their null hypothesis conflict between the meltdown and webb harwood hypotheses infraction of geological laws and poor application of stratigraphic principles several issues are highlighted here as important for direction of future research and discussion concerning late cenozoic antarctic glacio climatic history

quaternary relief generation by polythermal glacier ice the juxtaposition of wet based erosive ice in valleys and cold based non erosive ice atop felsenmeer covered interfluve plateaus has generated relief in the torngat mountains of northeastern canada measurements of in situ terrestrial cosmogenic nuclide tcn concentrations from 31 bedrock sites coupled with soils and geomorphology indicate that erosion of the valleys has been 2 m during a single glacial interglacial cycle however on summit plateaus the long term over several glacial interglacial cycles erosion rate is 1 4 m ma 1 tcn ratios reveal that the exposure plus ice cover history retained on some summit surfaces probably spans more than 800 ka despite complete ice cover as recently as 11 ka a thermodynamic ice sheet model with a basal water calculation is used to calculate the sliding distance normalized by the duration of ice cover for the region we formulate a general glacial erosion rule for the torngat mountains which correlates tcn derived erosion rates for terrain once partially covered by cold based ice with modelled average ice basal sliding velocities erosion rates vary linearly with average sliding velocity by a glacial erosion coefficient of 5 10 7 due to the significant distribution of cold based ice cover in this high latitude region our estimates of net regional glacial erosion and glacial erosion coefficient are orders of magnitude lower than a previously published value copyright 2005 john wiley sons ltd

neogene fjordal sedimentation on the western margin of the lambert graben east antarctica neogene glacial sedimentation east antarctica

geomorphology and glacial history of rauer group east antarctica abstract the presence of glacial sediments across the rauer group indicates that the east antarctic ice sheet formerly covered the entire archipelago and has since retreated at least 15 km from its maximum extent the degree of weathering of these glacial sediments suggests that ice retreat from this maximum position occurred sometime during the latter half of the last glacial cycle following this phase of retreat the ice sheet margin has not expanded more than 1 km seaward of its present position this pattern of ice sheet change matches that recorded in vestfold hills providing further evidence that the diminutive marine isotope stage 2 ice sheet advance in the nearby larsemann hills may have been influenced by local factors rather than a regional ice sheet response to climate and sea level change

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

glacier readvance during the late glacial younger dryas in the ahklun mountains southwestern alaska an expansion of alpine glaciers during the latest pleistocene produced an extraordinarily well defined end moraine system in the ahklun mountains southwestern alaska these moraines deposited during the mount waskey advance are several kilometers beyond modern glacier termini and 80 km upvalley of the late wisconsin ahklun mountains ice cap terminal moraine eleven cosmogenic 10 be and 26 al exposure ages on moraine boulders combined with radiocarbon ages from a lake core upvalley of a moraine deposited during the mount waskey advance suggest that the advance culminated between 12 4 and 11 0 ka sometime during or shortly following the younger dryas event ca 12 9 11 6 ka we believe that the mount waskey advance was a consequence of cooling during the younger dryas these data further strengthen emerging evidence for younger dryas age cooling of the north pacific region

deglacial environments in eastern prydz bay east antarctica abstract a high resolution continuous record of diatom census counts and diatom specific biomarkers in sediment core nbp0101 jpc24 allows assessment of oceanographic and environmental conditions in eastern prydz bay during the deglaciation 11 100 9000 cal yr bp at decadal timescale our study improves previous snapshots investigations based on resin embedded thin sections and presents a new proxy that compliments the diatom census counts our results suggest that the ice sheet retreat over the core site is dated at 11 100 cal yr bp setting the onset of local deglaciation and subsequent open marine conditions the glacial retreat in prydz bay is due to global warming initiated at 18 cal ka bp and the regional development of the prydz bay cyclonic gyre our results further demonstrate that the deglaciation in eastern prydz bay can be separated in four phases the first between 11 100 and 10 900 cal yr bp when the ice shelf was proximal and sea ice was almost perennial the second and the third phases between 10 900 10 400 cal yr bp and 10 400 9900 cal yr bp respectively when the ice shelf retreated and seasonal sea ice cycle consequently developed promoting warmer water to pump into the bay within the gyre which in turn forced the ice shelf recession and the yearly sea ice cycle establishment and the fourth between 9900 and 9000 cal yr bp when holocene condition were set with a recurrent seasonal sea ice cycle and a well established prydz bay gyre

do blue ice moraines in the heritage range show the west antarctic ice sheet survived the last interglacial abstract we present a hypothesis that best explains cosmogenic isotope data on blue ice moraines in the heritage range west antarctica the age of the moraines implies that they and the related ice sheet surface with which they are associated have persisted on the flanks of nunataks throughout at least the last interglacial glacial cycle the implication is that although the west antarctic ice sheet wais may have fluctuated in thickness during glacial cycles the central dome has remained intact for at least 200 kyr and possibly even for 400 kyr such a finding if substantiated would contribute to our understanding of the sensitivity of the wais to climate change further it would be a powerful geomorphic constraint on models of the past behaviour of the ice sheet during glacial cycles and thus those predicting the future of the ice sheet in a warming world

chronology of taylor glacier advances in arena valley antarctica using in situ cosmogenic 3he and 10be abstract in situ produced cosmogenic nuclides provide a new technique for constraining exposure ages of glacial deposits in situ3he and 10be in quartz sandstone boulders from arena valley southern victoria land antarctica provide chronological constraints for a sequence of moraines taylor ii ivb moraines related to expansions of taylor glacier and the east antarctic ice sheet mean 3he ages are 113 000 45 000 yr 208 000 67 000 yr 335 000 187 000 yr and 1 2 0 2 myr for taylor ii iii iva and ivb moraines respectively mean 1 corresponding mean 10be ages for taylor ii and ivb moraines are 117 000 51 000 yr and 2 1 0 1 myr for the older deposits the 3he ages are probably lower limits due to diffusive loss although the exposure ages appear consistent with the few previous age estimates particularly with an isotope stage 5 age for taylor ii each moraine exhibits a broad age distribution the distribution probably results from a variety of factors which may include prior exposure to cosmic rays 3he loss erosion postdepositional boulder movement and radiogenic production of 3he nonetheless the exposure ages provide direct chronological constraints for the moraine sequence and suggest a maximum thickening of taylor glacier relative to the present ice surface of 500 m since the late pliocene early pleistocene

quantification of subaerial and episodic subglacial erosion rates on high latitude upland plateaus cumberland peninsula baffin island arctic canada abstract long term rates of subaerial and episodic subglacial erosion by predominately cold based ice cover are determined for tors on weathered plateaus on cumberland peninsula by measuring terrestrial cosmogenic nuclide concentrations in differentially weathered surfaces on a given tor we reconstruct the complex exposure and erosion history involving recurring cold based ice cover the style and rate of subaerial and subglacial erosion at multiple tor sites on cumberland peninsula are assessed with a monte carlo approach that computes plausible exposure histories based on a proxy record of global ice volume constant subaerial erosion rates by weathering are low

major neogene fluctuations of the east antarctic ice sheet stratigraphic evidence from the lambert glacier region stratigraphic and sedimentological data are presented from a region likely to directly record the evolution of the east antarctic ice sheet along the western margin of the lambert graben which now drains 1 106 km2 or one eighth of the total area of the east antarctic ice sheet extensive remnants of cenozoic glaciomarine fjordal sediment known as the pagodroma group are preserved as far as several hundred kilometers inland from the open coast the sediments resemble those produced by tidewater glaciers in the arctic rather than those of modern antarctica four separate formations of the pagodroma group spanning the interval from early miocene or older to pliocene or early pleistocene are preserved the oldest and highest crop out at nearly 1500 m above sea level each formation was deposited in close proximity to an ice margin grounded on the fjord bottom during major recessional phases of the lambert glacier underlying each formation is a glacially cut erosion surface each surface records a separate stage of fjord excavation when ice expanded onto the continental shelf in prydz bay evidence from offshore drilling in prydz bay and these data indicate fluctuations of the lambert glacier terminus in excess of 500 km in neogene time thereby reflecting large changes in the volume of the ice sheet depositional episodes were succeeded by phases of uplift totalling more than 1500 m

evidence for long lasting landform surface instability on hummocky moraines in the pamir mountains tajikistan from 10be surface exposure dating abstract surface exposure dating is a new but already widely used tool in geomorphological studies aiming e g at the establishment of glacial chronologies sometimes however results from samples taken from one and the same moraine scatter widely and thus interpretation turns out to be difficult here we assess sample specific effects topographic shielding sample geometry and erosion on 17 surface exposure ages obtained by analysis of in situ produced cosmogenic 10be in boulders from moraines in the pamir mountains tajikistan a wide scatter of exposure ages is observed only for hummocky moraines 45 to 10 ka bp but not for distinct lateral moraines 20 and 60 ka bp respectively it is hypothesized that inheritance prior exposure and moraine degradation may be responsible for the wide scatter of exposure ages on the hummocky moraines to proof this hypothesis a data set of 72 boulders from the pamir mountains is used we conclude that most likely hummocky moraines experienced long lasting landform surface instability probably due to buried glacier ice that is protected from melting several ten thousand years by a thick debris cover

cosmogenic nuclide evidence for minimal erosion across two subglacial sliding boundaries of the late glacial fennoscandian ice sheet abstract the existence of sliding and frozen bed areas under ice sheets is significant in understanding basal thermal regimes patterns of erosion and landform development and in constraining boundary conditions for the reconstructions of ice sheets recognition of subglacial boundaries between sliding and frozen bed areas for former ice sheets is typically based on distinct morphological contrasts between areas with glacial landform assemblages and relict areas showing little alteration of pre existing features some of these boundaries especially on continental shield areas however are clearly visible from air photos but have minimal topographic expression understanding the chronology and erosional development of such boundaries is important to provide insight into the pattern and persistence of basal conditions under ice sheets geomorphic evidence and cosmogenic radionuclide concentrations of bedrock outcrops on either side of two sliding boundaries on ultevis and arvestuottar low relief upland plateaus in northern sweden are consistent with negligible erosion in relict landscape frozen bed areas due to the last glaciation but also indicate insignificant erosion in the sliding areas such a pattern and magnitude of landscape modification indicates that sliding was short lived in these areas likely as a transient phase during deglaciation these sites demonstrate that short periods of sliding are in some cases sufficient to produce landscapes that are recognized as glacial from air photos thus regions of sliding identified on shield areas must be viewed as the cumulative total area that has experienced sliding at any time during a glaciation the actual extent of sliding areas during any single ice sheet phase is presumably considerably less than this cumulative total which has important implications for establishing appropriate basal boundary conditions for ice sheet reconstructions

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

scaling factors for production rates of in situ produced cosmogenic nuclides a critical reevaluation abstract new scaling factors are presented describing the altitude and latitudinal dependence of production rates for in situ produced cosmogenic nuclides the new factors incorporate the influence of the non dipole contributions to the geomagnetic field on the cosmic ray flux the currently used scaling factors of lal earth planet sci lett 104 1991 424 439 are based on the assumption of a dipole field the overall strategy used in deriving the new scaling factors is however very similar to that of lal and relies on the same and or similar nuclear data in this reevaluation data are only used if the effective geomagnetic parameters inclination horizontal field strength can be reconstructed for the time of measurement the absorption free pathlengths for cosmic rays selected for this study are based on observational data at altitudes relevant for exposure age dating sea level to 7000 m at sea level and latitudes between 20 and 40 the new factors are up to 18 lower and at high altitudes more than 30 higher than those of lal in addition to accounting for the influence of the effective geomagnetic field and providing more applicable estimates of the new factors also allow for correction for the significant deviations from the standard pressure altitude relationship that exist in the atmosphere 10

reconstruction of ice sheet changes in the antarctic peninsula since the last glacial maximum this paper compiles and reviews marine and terrestrial data constraining the dimensions and configuration of the antarctic peninsula ice sheet apis from the last glacial maximum lgm through deglaciation to the present day these data are used to reconstruct grounding line retreat in 5 ka time steps from 25 ka bp to present glacial landforms and subglacial tills on the eastern and western antarctic peninsula ap shelf indicate that the apis was grounded to the outer shelf shelf edge at the lgm and contained a series of fast flowing ice streams that drained along cross shelf bathymetric troughs the ice sheet was grounded at the shelf edge until 20 cal ka bp chronological control on retreat is provided by radiocarbon dates on glacimarine sediments from the shelf troughs and on lacustrine and terrestrial organic remains as well as cosmogenic nuclide dates on erratics and ice moulded bedrock retreat in the east was underway by about 18 cal ka bp the earliest dates on recession in the west are from bransfield basin where recession was underway by 17 5 cal ka bp ice streams were active during deglaciation at least until the ice sheet had pulled back to the mid shelf the timing of initial retreat decreased progressively southwards along the western ap shelf the large ice stream in marguerite trough may have remained grounded at the shelf edge until about 14 cal ka bp although terrestrial cosmogenic nuclide ages indicate that thinning had commenced by 18 ka bp between 15 and 10 cal ka bp the apis underwent significant recession along the western ap margin although retreat between individual troughs was asynchronous ice in marguerite trough may have still been grounded on the mid shelf at 10 cal ka bp in the larsen a region the transition from grounded to floating ice was established by 10 7 10 6 cal ka bp the apis had retreated towards its present configuration in the western ap by the mid holocene but on the eastern peninsula may have approached its present configuration several thousand years earlier by the start of the holocene mid to late holocene retreat was diachronous with stillstands re advances and changes in ice shelf configuration being recorded in most places subglacial topography exerted a major control on grounding line retreat with grounding zone wedges and thus by inference slow downs or stillstands in the retreat of the grounding line occurring in some cases on reverse bed slopes

constraints on age erosion and uplift of neogene glacial deposits in the transantarctic mountains determined from in situ cosmogenic 10be and 26al 10 be and 26 al data from sandstone boulders in three neogene glacial deposits in the mcmurdo sound dry valleys region of southern victoria land antarctica indicate minimum exposure ages of approx 3 ma and maximum long term erosion rates of approx 5 12 cm m y supporting the suggestion that polar desert conditions have persisted in the dry valleys since at least late pliocene time variation of cosmogenic nuclide production rate with altitude also allows constraints on past uplift rates model calculations employing 10 be data indicate little or no uplift in the dry valleys region in the past 3 m y precluding rapid 1 km m y late pliocene uplift previously suggested for some parts of the transantarctic mountains

extensive glaciation in transbaikalia siberia at the last glacial maximum abstract successively smaller glacial extents have been proposed for continental eurasia during the stadials of the last glacial period leading up to the last glacial maximum lgm at the same time the large mountainous region east of lake baikal transbaikalia has remained unexplored in terms of glacial chronology despite clear geomorphological evidence of substantial past glaciations we have applied cosmogenic 10be exposure dating and optically stimulated luminescence to establish the first quantitative glacial chronology for this region based on eighteen exposure ages from five moraine complexes we propose that large mountain ice fields existed in the kodar and udokan mountains during oxygen isotope stage 2 commensurate with the global lgm these ice fields fed valley glaciers 100 km in length reaching down to the chara depression between the kodar and udokan mountains and to the valley of the vitim river northwest of the kodar mountains two of the investigated moraines date to the late glacial but indications of incomplete exposure among some of the sampled boulders obscure the specific details of the post lgm glacial history in addition to the lgm ice fields in the highest mountains of transbaikalia we report geomorphological evidence of a much more extensive ice cap type glaciation at a time that is yet to be firmly resolved