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

late cenozoic deposits at reedy glacier transantarctic mountains implications for former thickness of the west antarctic ice sheet abstract deposits corresponding to multiple periods of glaciation are preserved in ice free areas adjacent to reedy glacier southern transantarctic mountains glacial geologic mapping supported by 10be surface exposure dating shows that reedy glacier was significantly thicker than today multiple times during the mid to late cenozoic longitudinal surface profiles reconstructed from the upper limits of deposits indicate greater thickening at the glacier mouth than at the head during these episodes indicating that reedy glacier responded primarily to changes in the thickness of the west antarctic ice sheet surface exposure ages suggest this relationship has been in place since at least 5 ma the last period of thickening of reedy glacier occurred during marine isotope stage 2 at which time the glacier surface near its confluence with the west antarctic ice sheet was at least 500 m higher than today

fragment of an ancient outlet glacier system near the top of the transantarctic mountains sirius group tillite near the summit of mount feather transantarctic mountains is critically located for reconstructing past behavior of the east antarctic ice sheet new ice direction indicators and tillite geometry show that the tillite accumulated beneath wet based ice on a transverse paleovalley floor a hanging remnant of a landscape largely removed by erosion we conclude that the mount feather tillite formed primarily by lodgment as part of an ancient wet based outlet glacier system when the transantarctic mountains were at least 1500 m lower than today till deposition took place before 20 ma on the basis of estimated past uplift rates

on marine microfossil transport and pathways in antarctica during the late neogene evidence from the sirius group at mount fleming there are two extreme views of the evolution of the pliocene antarctic ice sheet dynamicists argue for ice sheet reduction and reexpansion on the basis of pliocene marine diatoms in a glacial deposit the sirius group that is widespread in the transantarctic mountains stabilists argue from other evidence that the antarctic cryosphere remained essentially constant in area and volume they propose marine diatom transport by eolian processes and emplacement into terrestrial glacial strata hence the inferred source area and transport mechanism of marine diatoms are of critical importance we tested the reduction hypothesis on an important outcrop of the sirius group at mount fleming south victoria land we observed very few unidentifiable marine diatom fragments in sirius group strata in contrast marine diatoms enclosed in a surface diamicton covering the sirius group were more abundant and identifiable our study further indicates that the sirius group at mount fleming was not deposited by the east antarctic ice sheet but rather by alpine ice originating on the transantarctic mountains on the basis of both data sets we infer that marine diatoms postdate sirius group deposition at mount fleming and that transport was by wind and we advance alternative scenarios for their source and transport pathways

ross sea paleo ice sheet drainage and deglacial history during and since the lgm onshore and offshore studies show that an expanded grounded ice sheet occupied the ross sea embayment during the last glacial maximum lgm results from studies of till provenance and the orienta

the timing of the last glacial maximum in australia abstract late pleistocene glaciation of australia was restricted to the snowy mountains and the tasmanian highlands glaciers were most extensive in tasmania where ice caps formed on the central plateau and west coast ranges and systems of valley and cirque glaciers formed on surrounding mountains to investigate the timing of maximum glacier advance during the last glacial maximum lgm we dated boulders on 18 moraines in 8 glaciated areas using cosmogenic 36cl and 10be we sampled moraines deposited by cirque and valley glaciers in a range of climate types and lithologies over a 7 latitudinal and a 1430 m altitudinal transect exposure ages for lgm moraine boulders group tightly in the range 17 20 ka boulders from the hamilton moraine often treated as the lgm type moraine range in age from 190 350 ka indicating that it was deposited well before the last glaciation collectively the exposure ages show that southeastern australia was glaciated briefly during and after the lgm and deglaciated well before the holocene ice retreated from the terminal moraines after the period of coldest sea surface temperatures in the southwest pacific ocean no evidence was found for readvance of glaciers during the antarctic cold reversal or the younger dryas period

valencia gorge possible messinian refill channel for the western mediterranean sea a deeply incised gorge is buried nearly 800 m beneath the floor of the valencia trough in the western mediterranean sea the gorge is steeply cut more than 200m into messinian evaporite deposits and has been mapped for more than 40 km published and unpublished seismic profiles show the total length to be nearly 300 km the gorge is not aligned with any known large fluvial systems and its orientation indicates that it may have been connected near valencia with the betic strait the portal in southern spain proposed to link the atlantic and the western mediterranean the betic strait was probably open at least through early messinian time conservative estimates show that sea water flowing through the valencia gorge at rates of 0 5 to 2 m s could have refilled the western mediterranean basins below 2000 m in less than 50 yr

implications of increased greenland surface melt under global warming scenarios ice sheet simulations abstract the greenland ice sheet is likely to make a faster contribution to sea level rise in a warming world than previously believed based on numerical modelling using a parameterization of recent results showing surface meltwater lubrication of ice flow zwally et al science 297 557 2002 218 documented correlation between increased ice velocity and increased surface melt as parameterized by positive degree days they argued that surface water is piped directly to the bed with little delay causing increased basal water pressures and basal sliding velocities an effect not included in recent greenland ice sheet models known to the authors using the pennsylvania state university university of chicago thermomechanical flowline model numerous simulations were conducted to test a wide range of parameter space linking surface melt with a new sliding law based on the zwally et al data under three different global warming scenarios 2 co2 4 co2 and 8 co2 comparisons to reconstructions generated with a traditional sliding parameterization illustrate an enhanced sensitivity of the ice sheet to surface warming resulting in higher ablation rates additional thinning and retreat of the margin and a reduction in ice volume leading to an increased contribution to global sea level rise

minimal pliocene pleistocene uplift of the dry valleys sector of the transantarctic mountains a key parameter in ice sheet reconstructions we propose that there has been little or no pliocene pleistocene uplift of the dry valleys sector of the transantarctic mountains on the basis of isotopic dating and mapping of in situ cinder cone deposits on the walls of taylor valley twenty seven 40ar 39ar incremental heating analyses on whole rock samples from subaerially erupted olivine basanite volcanic outcrops of known elevations define 14 eruptions ranging in age from 3 89 to 1 50 ma because taylor valley opens directly onto the ross sea these results show that any surface uplift during the past 2 57 m y was 300 m our conclusion of minimal uplift contradicts previous models of dramatic uplift up to 3000 m since 3 ma and associated hypotheses that uplift caused climatic cooling and growth of a polar east antarctic ice sheet

40ar 39ar and k ar chronology of pleistocene glaciations in patagonia during the pleistocene east of lago buenos aires argentina at 46 5 s at least 19 terminal moraines were deposited as piedmont glaciers from the patagonian ice cap advanced onto the semi arid high plains adjacent to the southern andes exceptional preservation of these deposits offers a rare opportunity to document ice cap fluctuations during the last 1 2 m y 4 0 ar 3 9 ar incremental heating and unspiked k ar experiments on four basaltic lava flows interbedded with the moraines provide a chronologic framework for the entire glacial sequence the 4 0 ar 3 9 ar isochron ages of three lavas that overlie till 90 km east of the cordillera at lago buenos aires and another 120 km from the andes along rio gallegos at 51 8 s that underlies till strongly suggest that the ice cap reached its greatest eastward extent ca 1100 ka at least six moraines were deposited within the 256 k y period bracketed by basaltic eruptions at 1016 10 ka and 760 14 ka similarly six younger more proximal moraines were deposited during an 651 k y period bracketed by an underlying 760 14 ka basalt and the 109 3 ka cerro volcan basalt flow that buried all six moraines coupled with in situ cosmogenic surface exposure ages of moraine boulders the 109 ka age of cerro volcan implies that moraines deposited during the penultimate local glaciation correspond to marine oxygen isotope stage 6 further westward toward lago buenos aires six additional moraines younger than the cerro volcan basalt flow occur surface exposure dating of boulders on these moraines combined with the 1 4 c age of overlying varved lacustrine sediment indicates deposition during the last glacial maximum lgm 23 16 ka although antarctic dust records signal an important patagonian glaciation at 60 40 ka moraines corresponding to marine oxygen isotope stage 4 are not preserved at lago buenos aires apparently these were overrun and obliterated by the younger ice advance at 23 ka notwithstanding the overall pattern of glaciation in patagonia is one of diminishing eastward extent of ice during successive glacial advances over the past 1 m y we hypothesize that tectonically driven uplift of the patagonian andes which began in the pliocene yet continued into the quaternary in part due to subduction of the chile rise spreading center during the past 2 m y maximized the ice accumulation area and ice extent by 1 1 ma subsequent deep glacial erosion has reduced the accumulation area resulting in less extensive glaciers over time

asynchronous behavior of the antarctic ice sheet and local glaciers during and since termination 1 salmon valley antarctica abstract the stability of the antarctic ice sheet under future warming remains an open question with broad implications for sea level prediction and adaptation in particular knowledge of whether the ice sheet has the capacity for rapid drawdown or collapse or whether it can remain stable during periods of warming is essential for predicting its future behavior here we use 55 radiocarbon dates coupled with geomorphologic mapping to reconstruct the timing of changes in ice extent and elevation during the last ice age termination in salmon valley adjacent to mcmurdo sound in the western ross sea embayment results indicate that a grounded ice sheet in the ross sea embayment achieved its maximum elevation and extent along the headlands of salmon valley at 18 000 yr bp during a period of increasing temperatures and accumulation over the antarctic continent this ice remained at or near its maximum on the headlands near the valley mouth until after 14 000 yr bp removal of grounded ross sea ice from salmon valley was complete shortly after 7900 yr bp indicating that the grounding line had retreated through southern mcmurdo sound by that time we suggest the primary driver of ross sea ice removal from mcmurdo sound was marine based either through basal melting or calving due to sea level rise when combined with regional data the salmon valley record suggests that this sector of the antarctic ice sheet did not contribute in a significant way to deglacial meltwater pulses such as meltwater pulse 1a in contrast to the ross sea ice our work also shows that local independent alpine glaciers in salmon valley have advanced through the holocene land terminating glaciers such as these elsewhere in the region show a similar pattern and may reflect the continued influence of increased accumulation following the termination of the last ice age

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

dynamics of the last glacial maximum antarctic ice sheet and its response to ocean forcing retreat of the last glacial maximum lgm antarctic ice sheet is thought to have been initiated by changes in ocean heat and eustatic sea level propagated from the northern hemisphere nh as northern ice sheets melted under rising atmospheric temperatures the extent to which spatial variability in ice dynamics may have modulated the resultant pattern and timing of decay of the antarctic ice sheet has so far received little attention however despite the growing recognition that dynamic effects account for a sizeable proportion of mass balance changes observed in modern ice sheets here we use a 5 km resolution whole continent numerical ice sheet model to assess whether differences in the mechanisms governing ice sheet flow could account for discrepancies between geochronological studies in different parts of the continent we first simulate the geometry and flow characteristics of an equilibrium lgm ice sheet using pan antarctic terrestrial and marine geological data for constraint then perturb the system with sea level and ocean heat flux increases to investigate ice sheet vulnerability our results identify that fast flowing glaciers in the eastern weddell sea the amundsen sea central ross sea and in the amery trough respond most rapidly to ocean forcings in agreement with empirical data most significantly we find that although ocean warming and sea level rise bring about mainly localized glacier acceleration concomitant drawdown of ice from neighboring areas leads to widespread thinning of entire glacier catchments a discovery that has important ramifications for the dynamic changes presently being observed in modern ice sheets

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

decoding the dipstick thickness of siple dome west antarctica at the last glacial maximum ice thickness in west antarctica at the last glacial maximum lgm is poorly known yet is key information for understanding ice streams and interpreting ice cores although trim lines moraine limits and exposure age dating provide geologic constraints on ice thickness near the transantarctic mountains and in marie byrd land lack of exposed bedrock hampers traditional geologic methods in a central 2 3 10 6 km 2 region here we infer ice sheet thickness changes in the central ross sea embayment by using a tran sient ice flow model to find combinations of accumulation rate and ice sheet thickness histories that match the depth age relationship and the measured layer thickness pattern in the siple dome ice core after we reject unreasonable accumulation rate histories the remaining history pairs indicate thinning of 200 400 m since the lgm our estimate is lower than previous reconstructions that were constrained by geologic evidence from the transantarctic mountains and by marine data from the ross sea floor which indicate that a grounded ice sheet extended to the continental shelf margin during the last glacial period low surface elevations in the central ross sea embayment during the lgm do not preclude thicker ice along its boundaries however if this grounded ice sheet came over 1000 km from interior west antarctica as is usually assumed then it had very low surface slope requiring a very slippery bed alternatively the grounded ross sea ice might have flowed from the transantarctic mountains and western marie byrd land

reconstructing the antarctic ice sheet at the last glacial maximum abstract a reconstruction of the antarctic ice sheet at the last glacial maximum lgm constrained by geologic data shows expansion across continental shelves accompanied by little inland change this added peripheral ice volume contributed 14 m to the lowering of eustatic sea level at the lgm of the total expansion one third took place in east antarctica and two thirds in west antarctica

measurements of past ice sheet elevations in interior west antarctica a lateral moraine band on mount waesche a volcanic nunatak in marie byrd land provides estimates of past ice sheet surface elevations in west antarctica helium 3 and chlorine 36 surface exposure ages indicate that the proximal part of the moraine up to 45 meters above the present ice surface was deposited about 10 000 years ago substantially later than the maximum ice extent in the ross embayment the upper distal part of the moraine may record multiple earlier ice sheet high stands a nonequilibrium ice sheet model predicts a delay of several thousand years in maximum ice levels at mount waesche relative to the maximum ice extent in the ross sea the glacial geologic evidence coupled with the ice sheet model indicates that the contribution of the ross sea sector of the west antarctic ice sheet to holocene sea level rise was only about 3 meters these results eliminate west antarctic ice as the principle source of the large meltwater pulse during the early holocene

geometry and dynamics of an east antarctic ice sheet outlet glacier under past and present climates 1 the behavior of east antarctic ice sheet eais outlet glaciers both at present and during the recent geological past is of considerable interest both from the point of view of understanding the mechanics of contemporary glacier dynamics and also with regard to epoch scale ice sheet stability during plio pleistocene climate transitions here we use a glacier flowline model that incorporates the effects of longitudinal stresses to numerically simulate ferrar glacier first under present day environmental conditions and subsequently under both colder and warmer climate regimes representing the last glacial maximum lgm and mid pliocene peak warmth respectively using airborne radar profiles insar derived surface velocities ice core and geological data for empirical constraint we present a diagnostic simulation that uses an iterative method to closely reproduce observed dynamics our model suggests that the glacier is largely cold based under present conditions flows predominantly by way of internal deformation and cascades over bedrock ridges due to the combined action of changes in cross sectional valley geometry local steepening of the glacier surface and the non local effects of longitudinal coupling time dependent evolutionary simulation of a lower profile glacier under a colder drier lgm climate predicts flow velocities lower than present with minimal bedrock erosion or basal till flux conversely the warmer than present mid pliocene climate produces a more dynamic glacier that is warm based and sliding along much of its bed we propose that eais outlet glaciers such as the ferrar respond dynamically along their length in response to changing environmental forcings with most significant changes taking place in their lower reaches adjustment to perturbations in upper catchments is more muted

late quaternary ice surface fluctuations of hatherton glacier transantarctic mountains abstract former longitudinal profiles of hatherton glacier an outlet through the transantarctic mountains constrain nearby polar plateau elevations and ice shelf grounding in the southwestern ross embayment four gravel drift sheets of late quaternary age beside hatherton glacier are from youngest to oldest hatherton britannia i britannia ii and danum the hatherton drift limit is uniformly 20 to 70 m above the present ice surface the britannia ii drift limit is within 100 m of the present surface of uppermost hatherton glacier but is 450 m above middle hatherton glacier extrapolation of this profile downglacier indicates a surface elevation 1100 m above the present ross ice shelf the britannia i drift limit is parallel to but 50 100 m below britannia ii drift the danum drift limit is parallel to but 50 100 m above the britannia ii profile from correlation with drifts near mcmurdo sound and from local 14 c dates we assign an early holocene age to hatherton drift a late wisconsin age to britannia drifts and an age of marine isotope stage 6 to danum drift by our age model the upper reaches of hatherton glacier and presumably the adjacent polar plateau have not exceeded their current elevations by more than 100 150 m during the last two complete global glacial interglacial cycles whereas the middle and lower reaches of hatherton glacier have thickened considerably during the last two global glaciations late wisconsin and marine isotope stage 6 the effect of ice shelf grounding probably was the major control of these changes of hatherton glacier holocene ice surface lowering probably represents the last pulse of grounding line recession in the southwestern ross embayment

evidence for late pleistocene thinning of siple dome west antarctica 1 we use a two dimensional full stress thermomechanical flow band model to investigate late pleistocene and holocene histories of ice thickness and ice flow at siple dome in west antarctica measurements obtained from an ice core and borehole near the ice divide and measurements of radar detected internal stratigraphy are used as targets for modeling models that account for the climate history accumulation rate and temperature alone yield a poor match to observations histories of ice dynamics ice thickness ice divide location and ice flow enhancement also need to be included our favored model includes 350 m of thinning at siple dome between 15 000 and 14 000 years ago onset of divide flow 3000 years ago ongoing divide migration starting 2500 years ago and evolution of ice fabric over the past 30 000 years the timing of thinning is earlier than that inferred from geologic evidence from the margins but is coincident with a 20 m rise in global sea level about 14 500 years ago meltwater pulse 1a this opens the possibility that thinning was a result of increased activity of the ice streams in the late pleistocene forced by meltwater pulse 1a the contribution to meltwater pulse 1a as a result of this thinning was likely small

ice elevation near the west antarctic ice sheet divide during the last glaciation 1 interior ice elevations of the west antarctic ice sheet wais during the last glaciation which can serve as benchmarks for ice sheet models are largely unconstrained here we report past ice elevation data from the ohio range located near the wais divide and the onset region of the mercer ice stream cosmogenic exposure ages of glacial erratics that record a wais highstand 125 m above the present surface date to 11 5 ka the deglacial chronology prohibits an interior wais contribution to meltwater pulse 1a our observational data of ice elevation changes compare well with predictions of a thermomechanical icesheet model that incorporates very low basal shear stress downstream of the present day grounding line we conclude that ice streams in the ross sea embayment had thin lowslope profiles during the last glaciation and interior wais ice elevations during this period were several hundred meters lower than previous reconstructions citation ackert r p jr s mukhopadhyay b r parizek and h w borns 2007 ice elevation near the west antarctic ice sheet divide during the last glaciation geophys res lett 34 l21506 doi 10 1029 2007gl031412

holocene ice recession at polygon spur reedy glacier antarctica the holocene history of outlet glaciers affords information on the behavior and mechanisms controlling the extent of the east antarctic ice sheet here we present both new radiocarbon and recalcul

late wisconsin and early holocene glacial history inner ross embayment antarctica abstract lateral drift sheets of outlet glaciers that pass through the transantarctic mountains constrain past changes of the huge ross ice drainage system of the antarctic ice sheet drift stratigraphy suggests correlation of reedy iii reedy glacier beardmore beardmore glacier britannia hatherton darwin glaciers ross sea mcmurdo sound and younger terra nova bay drifts radiocarbon dates place the outer limits of ross sea drift in late wisconsin time at 24 000 13 000 yr b p outlet glacier profiles from these drifts constrain late wisconsin ice sheet surface elevations within these constraints we give two extreme late wisconsin reconstructions of the ross ice drainage system both show little elevation change of the polar plateau coincident with extensive ice shelf grounding along the inner ross embayment however in the central ross embayment one reconstruction shows floating shelf ice whereas the other shows a grounded ice sheet massive late wisconsin holocene recession of grounded ice from the western ross embayment which was underway at 13 040 yr b p and completed by 6600 6020 yr b p was accompanied by little change in plateau ice levels inland of the transantarctic mountains sea level and basal melting probably controlled the extent of grounded ice in the ross embayment the interplay between the precipitation low late wisconsin and high holocene values and the influence of grounding on outlet glaciers late wisconsin thickening and late wisconsin holocene thinning with effects dying out inland probably controlled minor elevation changes of the polar plateau

late quaternary ice surface fluctuations of beardmore glacier transantarctic mountains abstract former longitudinal profiles of beardmore glacier an outlet through the transantarctic mountains constrain polar plateau elevations near the center of antarctica and ice shelf grouding in the southern ross embayment three gravel drift sheets of late quaternary age occur alongside beardmore glacier plunket drift the youngest is parallel to and 7 30 m above the present ice surface the upper limit of beardmore drift intermediate in age is within 35 40 m of the present ice surface near the polar plateau but about 1100 m above the present ice surface near the glacier mouth the upper limit of meyer drift the oldest is parallel to and 30 50 m above beardmore drift from correlation with numerically dated drifts farther north we assign an early holocene age to plunket drift a late wisconsin age to beardmore drift and an age of marine isotope stage 6 to meyer drift by our age model beardmore glacier was close to current elevations in its upper reaches and thickened considerably in its middle and lower reaches during the last two global glaciations represented by beardmore and meyer drifts most likely grounded ice in the southern ross embayment caused such thickening of beardmore glacier almost to the polar plateau a concomitant decline in precipitation is implied by ice cap retreat on the nearby dominion range and is consistent with little change of upper beardmore glacier ice shelf grounding most likely resulted from lowered sea level and or basal melting lower than present precipitation was probably caused by colder air temperatures and more distant open water the plunket profile records holocene ice surface lowering from increased surface ablation decreased ice flow or grounding line recession

late neogene sirius group strata in reedy valley antarctica a multiple resolution record of climate ice sheet and sea level events late neogene sirius group strata from tillite spur and quartz hills in the reedy glacier area antarctica demonstrate the variability in sirius group facies and contrasts sirius group strata deposited at high and low paleo elevation respectively the tillite spur and quartz hills formations pliocene are formally defined here the tillite spur formation type section crops out on the edge of the wisconsin plateau overlooking tillite spur it comprises 32 m of alternating coarse gray conglomerate and muddy olive brown diamictites the quartz hills formation type section crops out above the western margin of reedy glacier in a pre existing cirque towards the southern end of the quartz hills it comprises c 100 m of alternating massive diamictites and rhythmically interbedded sandstone and laminated mudstones which were deposited close to sea level and subsequently rapidly uplifted 500 m myr 1 to their present elevation at c 1500 m three orders of paleoclimatic variability are recorded in the sirius group strata from reedy valley 1 recycled marine microfloras in glacial diamictites indicate intervals of marine incursion into the antarctic cratonic interior co occurring with reductions in the east antarctic ice sheet 2 an advancing and retreating paleo reedy glacier deposited a glacial interglacial sequence alternating on a 10 100 kyr scale 3 centimeter and millimeter stratification in strata of the quartz hills formation record annual kyr scale variability

cenozoic deep sea temperatures and global ice volumes from mg ca in benthic foraminiferal calcite a deep sea temperature record for the past 50 million years has been produced from the magnesium calcium ratio mg ca in benthic foraminiferal calcite the record is strikingly similar in form to the corresponding benthic oxygen isotope 18o record and defines an overall cooling of about 12 c in the deep oceans with four main cooling periods used in conjunction with the benthic 18o record the magnesium temperature record indicates that the first major accumulation of antarctic ice occurred rapidly in the earliest oligocene 34 million years ago and was not accompanied by a decrease in deep sea temperatures

cosmogenic chlorine 36 chronology for glacial deposits at bloody canyon eastern sierra nevada deposits from mountain glaciers provide an important record of quaternary climatic fluctuations but have proved difficult to date directly a chronology has been obtained for glacial deposits at bloody canyon california by measurement ofthe accumulation of chlorine 36 produced by cosmic rays in boulders exposed on moraine crests the accumulation ofchlorine 36 indicates that episodes of glaciation occurred at about 21 24 65 115 145 and 200 ka thousand years ago although the timing of the glaciations correlates well with peaks of global ice volume inferred from the marine oxygen isotope record the relative magnitudes differ markedly the lengths of the moraines dating from 115 ka and 65 ka show that the early glacial episodes were more extensive than those during the later wisconsin and indicate that the transition from interglacial to full glacial conditions was rapid