the role of carbon dioxide during the onset of antarctic glaciation earth s modern climate characterized by polar ice sheets and large equator to pole temperature gradients is rooted in environmental changes that promoted antarctic glaciation 33 7 million years ago onset of antarctic glaciation reflects a critical tipping point for earth s climate and provides a framework for investigating the role of atmospheric carbon dioxide co2 during major climatic change previously published records of alkenone based co2 from high and low latitude ocean localities suggested that co2 increased during glaciation in contradiction to theory here we further investigate alkenone records and demonstrate that antarctic and subantarctic data overestimate atmospheric co2 levels biasing long term trends our results show that co2 declined before and during antarctic glaciation and support a substantial co2 decrease as the primary agent forcing antarctic glaciation consistent with model derived co2 thresholds

preservation of miocene glacier ice in east antarctica antarctic climate during the pliocene has been the subject of considerable debate one view holds that during part of the pliocene east antarctica was largely free of glacier ice and that vegetation survived on the coastal mountains1a 4 an alternative viewpoint argues for the development of a stable polar ice sheet by the middle miocene which has persisted since then5a 10 here we report the discovery of buried glacier ice in beacon valley east antarctica which appears to have survived for at least 8 1 million years we have dated the ice by 40ar 39ar analysis of volcanic ash in the thin overlying glacial till which we argue has undergone little if any reworking isotope and crystal fabric analyses of the ice show that it was derived from an ice sheet we suggest that stable polar conditions must have persisted in this region for at least 8 1 million years for this ice to have avoided sublimation

water isotopes in precipitation data model comparison for present day and past climates abstract variations of hdo and h2 18 o concentrations are observed in precipitation both on a geographical and on a temporal basis these variations resulting from successive isotopic fractionation processes at each phase change of water during its atmospheric cycle are well documented through the iaea wmo network isotope concentrations are in middle and high latitudes linearly related to the annual mean temperature at the precipitation site paleoclimatologists have used this relationship to infer paleotemperatures from isotope paleodata extractable from ice cores deep groundwater and other such sources for this application to be valid however the spatial relationship must also hold in time at a given location as the location undergoes a series of climatic changes progress in water isotope modeling aimed at examining and evaluating this assumption has been recently reviewed jouzel et al 1997 with a focus on polar regions and more specifically on greenland we extend this review in comparing the results of two different isotopic agcms nasa giss and echam and in examining with a more global perspective the validity of the above assumption i e the equivalence of the spatial and temporal isotope temperature relationships these results confirm the dominating role of local temperature changes on the paleo isotope signal in most regions however the exact calibration of this valuable paleothermometer is biased by for example the seasonality of precipitation and other factors we forced the two models by the climatic boundary conditions of the mild holocene at 6 kyr bp which only slightly differs from today s climate the isotope response on this weak forcing is quite heterogeneous the only robust common response is the intensification of the hydrological cycle in low latitudes and therefore isotopically more depleted precipitation in the tropics and subtropics we also examine recent progress made in modeling the relationship between the conditions prevailing in moisture source regions for precipitation and the deuterium excess of that precipitation

reply to comment by p olivier on preorogenic exhumation of the north pyrenean agly massif eastern pyrenees france we make this reply to philippe oliver s comments on the deformation of the mesozoic cover of the northern agly massif

recent antarctic ice mass loss from radar interferometry and regional climate modelling observed estimates of ice losses in antarctica combined with regional modelling of ice accumulation in the interior suggest that east antarctica is close to a balanced mass budget but large losses of ice occur in the narrow outlet channels of west antarctic glaciers and at the northern tip of the antarctic peninsula

hydrologic cycling over antarctica during the middle miocene warming global warmth 20 15 million years ago allowed vegetation to grow on formerly ice covered areas of antarctica leaf wax and pollen data show that this growth was supported by increased hydrologic activity over the antarctic coast derived from a local moisture source

ion probe u th pb zircon dating of polymetamorphic orthogneisses from northern labrador canada rounded zircons included within igneous zircons from the uivak i gneisses northern labrador have ages of up to 3863 12 ma 2 showing the former existence of rocks that predate the uivak gneisses by more than 100 ma the igneous zircons themselves have experienced varying amounts of early pb loss but age estimates based on maximum 207pb 206pb from three separate gneiss samples agree to within error at 3732 6 ma 2 which is taken as the age of emplacement of the igneous precursor to the dominant component of the uivak gneisses a new generation of zircons was formed during migmatization at ca 3620 ma the volumetrically less important lister gneiss was emplaced at 3235 8 ma 2 in the late archaean different parts of the gneiss complex were subjected to different grades of metamorphic overprinting the zircon chronology of gneisses affected by granulite facies metamorphism suggests a rapid sequence of events with simultaneous recrystallization of old zircons and growth of new u poor zi

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

the environmental water of the middle eocene arctic evidence from δd δ18o and δ13c within specific compounds abstract the extensive vertical exposure 150 m of terrestrial sediments on axel heiberg island which contain thick fossiliferous lignites presents an exceptional opportunity to follow the establishment and re establishment of arctic metasequoia forests during the middle eocene we compared d values in n alkanes of chain length 23 25 27 and 29 with 18 o values in phenylglucosazone p g derived from cellulose we also analyzed abundance of ferns gymnosperms and angiosperms using pollen and spores isolated from each lignite our results showed that forest composition was altered upon uplift as gymnosperms became more abundant within the relatively well drained upland sediments this was also reflected in the small 1 but significant increase in the 13 c value of tom from lowland to upland environments however neither the d values of n alkanes nor the 18 o in p g were statistically different in the upland sediments as compared to the lowland sediments from this we inferred that the oxygen isotope signature of environmental water available to the forests for plant growth was relatively uniform throughout the time of the fossil forests the d value of environmental water implied by both n alkanes and p g ranged from 168 to 131 and was considerably enriched compared to all environmental water samples available from the modern arctic region

declining moisture availability on the antarctic peninsula during the late eocene paleobotanical data have indicated that the antarctic landscape shifted from a beech nothofagus dominated forest to a more sparsely vegetated taiga like woodland and tundra during the late eocene coincident with progressive cooling and glacial growth reduced moisture availability may have contributed to this vegetation change but there is limited evidence for assessing the late eocene hydrologic regime we evaluated the relationship between nothofagus 13c and moisture availability by determining 13c of modern nothofagus pollen sporopollenin and leaves and comparing these results to precipitation data to assess plant moisture availability and vegetation composition just prior to the eocene oligocene boundary we measured 13c of fossil nothofagus sporopollenin nothofagidites from the shaldril 3c cores which date to 35 9 my and evaluated these results in the context of temporal variation in pollen assemblages from the same sediments values of carbon isotope discrimination for modern nothofagus sporopollenin range between 18 1 and 22 4 these values are positively correlated with precipitation amount as well as pollen and leaf which suggests that fossil sporopollenin records the level of plant moisture availability values obtained from nothofagidites sporopollenin from the shaldril 3c sediments range between 17 9 and 20 2 and generally decline through time these results suggest a decrease in plant moisture availability on the antarctic peninsula during the late eocene perhaps as a result of declining precipitation and or soil moisture therefore moisture stress experienced by nothofagus likely contributed to the shift to a more sparsely vegetated late eocene landscape our results show that carbon isotopic analysis of pollen from c3 plants may aid understanding how variations in moisture availability contribute to shifts in plant community composition in the paleorecord

temperature and leaf wax δ2h records demonstrate seasonal and regional controls on asian monsoon proxies orbital scale precipitation isotope records can elucidate climate forcing mechanisms and provide benchmarks for climate model validation the ability to differentiate the influence of temperature seasonality and vapor transport history on precipitation isotope proxies is critical to both objectives we present a 300 k y leaf wax hydrogen isotope record from the south china sea with the effects of local condensation temperature removed 2 h wax t 2 h wax t reflects annually integrated precipitation 2 h in the pearl river catchment of southeast china depleted 2 h wax t lags minimum precession p min by 1 0 0 7 k y reflecting the influence of maximum summer insolation and minimum winter insolation with a minor influence of global ice volume which lags p min by 3 3 0 4 k y in contrast annually integrated cave 18 o minima in central china 1000 km north of our site lag p min by 2 7 0 3 k y in phase with ice volume minima this phase indicates that precipitation 18 o in central china is more strongly influenced by ice volume forcing at the precession band with a lesser influence of northern hemisphere insolation our new 2 h wax t data demonstrate that precipitation isotopes in asia have strong regional variability interpreting water isotope records within the context of regionally varying temperature seasonality and sensitivity to changing glacial boundary conditions is imperative to understanding asian hydroclimatic change

paleotemperatures and ice volume of the past 27 myr revisited with paired mg ca and 18o 16o measurements on benthic foraminifera 1 we explore the applicability of paired mg ca and 18o 16o measurements on benthic foraminifera from southern ocean site 747 to paleoceanographic reconstructions on pre pleistocene timescales we focus on the late oligocene through pleistocene 27 0 ma history of paleotemperatures and the evolution of the 18o values of seawater 18osw at a temporal resolution of 100 200 kyr absolute paleotemperature estimates depend on assumptions of how mg ca ratios of seawater have changed over the past 27 myr but relative changes that occur on geologically brief timescales are robust results indicate that at the oligocene to miocene boundary 23 8 ma temperatures lag the increase in global ice volume deduced from benthic foraminiferal 18o values but the smaller scale miocene glaciations are accompanied by ocean cooling of 1 c during the mid miocene phase of antarctic ice sheet growth 15 13 ma water temperatures cool by 3 c unlike the benthic foraminiferal 18o values which remain relatively constant thereafter temperatures vary by 3 c and reach maxima at 12 and 8 5 ma the onset of significant northern hemisphere glaciation during the late pliocene is synchronous with an 4 c cooling at site 747 a comparison of our 18osw curve to the haq et al 1987 sea level curve yields excellent agreement between sequence boundaries and times of increasing seawater 18o 16o ratios at 12 11 ma in particular when benthic foraminiferal 18o values do not support a further increase in ice volume the 18osw curve comes to a maximum that corresponds to a major mid miocene sea level regression the agreement between the character of our mg ca based 18osw curve and sequence stratigraphy demonstrates that benthic foramaniferal mg ca ratios can be used to trace the 18osw on pre pleistocene timescales despite a number of uncertainties related to poorly constrained temperature calibrations and paleoseawater mg ca ratios the mg ca record also highlights that deep ocean temperatures can vary independently and unexpectedly from ice volume changes which can lead to misinterpretations of the 18o record

mid miocene paleoproductivity in the atlantic ocean and implications for the global carbon cycle 1 a prominent middle miocene 17 5 13 5 ma carbon isotope excursion ubiquitously recorded in carbonate sediments has been attributed to enhanced marine productivity and sequestration of 13c depleted organic carbon in marine sediments or enhanced carbon burial in peat lignite deposits on land here we test the hypothesis that the marine 13c record reflects a change in productivity with proxy records from three atlantic ocean sites deep sea drilling program site 608 and ocean drilling program sites 925 and 1265 our multiproxy approach is based on benthic foraminiferal accumulation rates elemental ratios ba al and p al the 13c of bulk sedimentary organic matter and dissolution indices we compare these proxies to benthic foraminiferal 13c values measured on the same samples our results indicate that marine paleoproductivity in the atlantic ocean is not related to the benthic foraminiferal 13c excursion a numerical box model confirms that marine productivity cannot account for the 13c maximum the model shows that sequestration of 1 5 1018 mol c in the terrestrial realm over a period of 3 ma leads to a 0 9 13c increase in the deep ocean which is near the observed records therefore an increase in continental organic carbon sequestration is the most plausible way to enrich the ocean s carbon pool with 13c which is consistent with coeval lignite deposits worldwide the 13c values of bulk sedimentary organic matter parallel the 13c of dissolved inorganic carbon as reflected by benthic foraminiferal 13c values suggesting no significant change in atmospheric pco2 levels over the investigated period

middle to late miocene stepwise climate cooling evidence from a high resolution deep water isotope curve spanning 8 million years 1 we present high resolution 2 3 kyr benthic foraminiferal stable isotopes in a continuous well preserved sedimentary archive from the west pacific ocean ocean drilling program site 1146 which track climate evolution in unprecedented resolution over the period 12 9 to 8 4 ma we developed an astronomically tuned chronology over this interval and integrated our new records with published isotope data from the same location to reconstruct long term climate and ocean circulation development between 16 4 and 8 4 ma this extended perspective reveals that the long eccentricity 400 kyr cycle is prominently encoded in the 13c signal over most of the record reflecting long term fluctuations in the carbon cycle the 18o signal closely follows variations in short eccentricity 100 kyr and obliquity 41 kyr in particular the obliquity cycle is prominent from 14 6 to 14 1 ma and from 9 8 to 9 2 ma when high amplitude variability in obliquity is congruent with low amplitude variability in short eccentricity the 18o curve is additionally characterized by a series of incremental steps at 14 6 13 9 13 1 10 6 9 9 and 9 0 ma which we attribute to progressive deep water cooling and or glaciation episodes following the end of the miocene climatic optimum on the basis of 18o amplitudes we find that climate variability decreased substantially after 13 ma except for a remarkable warming episode at 10 8 10 7 ma at peak insolation during eccentricity maxima 100 and 400 kyr this transient warming associated with a massive negative carbon isotope shift is reminiscent of intense global warming events at eccentricity maxima during the miocene climatic optimum

northern hemisphere controls on tropical southeast african climate during the past 60 000 years the processes that control climate in the tropics are poorly understood we applied compound specific hydrogen isotopes d and the tex86 tetraether index of 86 carbon atoms temperature proxy to sediment cores from lake tanganyika to independently reconstruct precipitation and temperature variations during the past 60 000 years tanganyika temperatures follow northern hemisphere insolation and indicate that warming in tropical southeast africa during the last glacial termination began to increase 3000 years before atmospheric carbon dioxide concentrations d data show that this region experienced abrupt changes in hydrology coeval with orbital and millennial scale events recorded in northern hemisphere monsoonal climate records this implies that precipitation in tropical southeast africa is more strongly controlled by changes in indian ocean sea surface temperatures and the winter indian monsoon than by migration of the intertropical convergence zone

palynomorph evidence for tropical climate stability in the gulf of papua papua new guinea over the latest marine transgression and highstand 14 500 years bp to today abstract three sediment cores mv 41 mv 46 and md 50 from the gulf of papua gop papua new guinea were analyzed to assess changes in climatic oceanographic and sedimentological conditions over the last 14 5 kyr palynomorphs which were isolated from sediment core samples were collected at approximately 0 5 m intervals using a strong acid and oxidant md 50 non oxidant mv 41 mv 46 procedure radiocarbon 14c stable isotope geochronology magnetic susceptibility stable isotope analysis md 50 only oxygen 18 18o and carbon 13 13c and clay mineral maturity analysis were also completed for each core palynological data indicate that climatic conditions at sea level have remained warm wet and stable for the past 14 5 kyr with sea surface temperatures in the gop above 14 c potential decreases in vegetative cover marked the younger dryas interval 12 5 11 5 kyr bp as indicated by reduced pollen and spore recovery the end of the latest marine transgression and the subsequent return to eustatic sea level highstand is clearly delineated by increases in marine palynomorph recovery and decreases in mangrove pollen at approximately 5 kyr bp an increase in seasonality and potential el nino southern oscillation variability is observed in md 50 s oxygen isotope results at 5 kyr bp this is not supported by the palynomorph record likely because of the sampling interval and dilution by tropical pollen flora which indicates stable climatic conditions throughout the last 14 5 kyr sediment transport pathways in the gop remained fairly constant throughout the time interval which is supported by the lack of major changes in palynomorph assemblage composition

late cretaceous climate in the canadian arctic multi proxy constraints from devon island abstract arctic climate in the late cretaceous has long been recognized to have been warm and wet relative to the present but quantitative assessments of paleoclimate have been challenging due in part to disagreements between proxies in marine and terrestrial environments this study provides a first multiproxy evaluation of late cretaceous 93 90 ma to 73 72 ma paleoclimate and paleohydrology from devon island in the canadian high arctic modern location 76 17 n 91 12 w late cretaceous location 71 30 n 24 30 w surface temperatures are reconstructed at 12 6 to 20 6 c for the ocean and 11 7 to 16 9 c over land using glycerol dialkyl glycerol tetraether gdgt based proxies measured from marine tex86 and terrestrial samples mbt 5me these proxies are likely skewed toward warm month temperatures based on novel analysis and interpretation of biomarkers in sediment and co occurring marine vertebrate coprolites the hydrogen isotopic composition 2h of precipitation is constrained to have varied from 123 to 82 vsmow using evidence from n alkanes likely derived from higher plants 18o of shelfal marine surface water is constrained to have been between 10 5 to 3 4 using phosphate oxygen isotopes of marine vertebrate teeth and coprolites from these marine salinity is modeled to have varied from 10 psu and 30 psu indicative of periodic freshwater influx these estimates indicate that large marine vertebrates lived and fed at least intermittently in near shore brackish waters finally the arctic was similarly warm in both the late cretaceous and paleocene eocene but the late cretaceous isotopic composition of precipitation at devon island was enriched in the heavy isotope of hydrogen by up to 60 to 70 relative to arctic eocene sites the combination of techniques used here reduces uncertainties related to the application of proxies to an environment without a modern analogue providing novel paleoclimatic constraints on the late cretaceous arctic region

water isotopes during the last glacial maximum new general circulation model calculations 1 the application of water isotopes to estimate the glacial interglacial cycle of temperature t assumes the validity of the present day spatial relationship between ta and 18o in precipitation 18op to estimate temporal changes of the temperature at a fixed location we explored how and why the spatial relationship between annual mean ta 18op is different from the temporal relationship at one location our general circulation isotope model exhibits a spatial slope of 1 22 c between annual mean temperature at the top of the inversion layer ti and 18op over antarctica comparable to the observed value of 1 25 c from dahe et al 1999 and using the phillpot and zillman 1970 relationship between surface temperature and the temperature of the inversion layer over the southern ocean 45 60 s local evaporation accounts for 50 of precipitation and this evaporative flux mean 18oe of 1 increases the 18o of vapor mean 18ov of 16 during the last glacial maximum lgm 21 000 years ago the isotopic composition of the vapor near the ice edge 60 s is calculated to be similar to the present values because evaporative recharge also accounts for 50 of the precipitation over the southern ocean as a result the isotopic composition of vapor during the lgm is close to the present values at the ice edge the apparent temporal slope over eastern antarctica is half of the observed spatial slope our lgm experiment estimates an antarctic mean annual temperature decrease of 13 c at vostok much larger than previous estimates our experiments with two specifications of lgm sea surface temperatures suggest that the value of the temporal slope is related to the temperature decrease over the southern ocean

middle miocene ice sheet dynamics deep sea temperatures and carbon cycling a southern ocean perspective 1 relative contributions of ice volume and temperature change to the global 1 18o increase at 14 ma are required for understanding feedbacks involved in this major cenozoic climate transition a 3 ma benthic foraminifer mg ca record of southern ocean temperatures across the middle miocene climate transition reveals 2 2 c cooling 14 2 13 8 ma indicating that 70 of the increase relates to ice growth seawater 18o calculated from mg ca and 18o suggests that at 15 ma antarctica s cryosphere entered an interval of apparent eccentricity paced expansion glaciations increased in intensity revealing a central role for internal climate feedbacks comparison of ice volume and ocean temperature records with inferred pco2 levels indicates that middle miocene cryosphere expansion commenced during an interval of southern ocean warmth and low atmospheric pco2 the antarctic system appears sensitive to changes in heat moisture supply when atmospheric pco2 was low suggesting the importance of internal feedbacks in this climate transition

dynamic antarctic ice sheet during the early to mid miocene geological data indicate that there were major variations in antarctic ice sheet volume and extent during the early to mid miocene simulating such large scale changes is problematic because of a strong hysteresis effect which results in stability once the ice sheets have reached continental size a relatively narrow range of atmospheric co2 concentrations indicated by proxy records exacerbates this problem here we are able to simulate large scale variability of the early to mid miocene antarctic ice sheet because of three developments in our modeling approach i we use a climate ice sheet coupling method utilizing a high resolution atmospheric component to account for ice sheet climate feedbacks ii the ice sheet model includes recently proposed mechanisms for retreat into deep subglacial basins caused by ice cliff failure and ice shelf hydrofracture iii we account for changes in the oxygen isotopic composition of the ice sheet by using isotope enabled climate and ice sheet models we compare our modeling results with ice proximal records emerging from a sedimentological drill core from the ross sea andrill 2a that is presented in a companion article the variability in antarctic ice volume that we simulate is equivalent to a seawater oxygen isotope signal of 0 52 0 66 or a sea level equivalent change of 30 36 m for a range of atmospheric co2 between 280 and 500 ppm and a changing astronomical configuration this result represents a substantial advance in resolving the long standing model data conflict of miocene antarctic ice sheet and sea level variability

progressive cenozoic cooling and the demise of antarctica s last refugium the antarctic peninsula is considered to be the last region of antarctica to have been fully glaciated as a result of cenozoic climatic cooling as such it was likely the last refugium for plants and animals that had inhabited the continent since it separated from the gondwana supercontinent drill cores and seismic data acquired during two cruises shaldril i and ii in the northernmost peninsula region yield a record that when combined with existing data indicates progressive cooling and associated changes in terrestrial vegetation over the course of the past 37 million years mountain glaciation began in the latest eocene approximately 37 34 ma contemporaneous with glaciation elsewhere on the continent and a reduction in atmospheric co2 concentrations this climate cooling was accompanied by a decrease in diversity of the angiosperm dominated vegetation that inhabited the northern peninsula during the eocene a mosaic of southern beech and conifer dominated woodlands and tundra continued to occupy the region during the oligocene approximately 34 23 ma by the middle miocene approximately 16 11 6 ma localized pockets of limited tundra still existed at least until 12 8 ma the transition from temperate alpine glaciation to a dynamic polythermal ice sheet took place during the middle miocene the northernmost peninsula was overridden by an ice sheet in the early pliocene approximately 5 3 3 6 ma the long cooling history of the peninsula is consistent with the extended timescales of tectonic evolution of the antarctic margin involving the opening of ocean passageways and associated establishment of circumpolar circulation

convergent cenozoic co2 history reconstructions of atmospheric carbon dioxide concentrations over the past 65 million years are heading towards consensus it is time for systematic testing of the proxies against measurements and against each other

gradients in seasonality and seawater oxygen isotopic composition along the early permian gondwanan coast se australia abstract oxygen isotope compositions of marine carbonates are commonly employed for understanding ancient temperatures but this approach is complicated in the very distant past due to uncertainties about the effects of diagenesis and the isotopic composition of seawater both locally and globally microsampled accretionary calcite from two species of the fossil bivalve eurydesma sowerby and morris 1845 collected from sediments of cisuralian age in high latitude marine sediments along the se coast of australia records cyclic seasonal fluctuations in shell 18 o values during growth demonstrating the primary nature of the isotope signal and thus allowing investigation of early permian seawater isotopic composition and water temperature in the high southern latitudes the mean and seasonal range of 18 o carb decreases poleward across about 10 of paleolatitude 67 s 77 s the presence of co occurring dropstones and stratigraphically associated glendonites constrains winter temperatures across the region to near freezing thus permitting calculation of realistic estimates of water composition and summer temperatures summer 18 o carb values indicate water temperatures between 5 c and 12 c with warmer values at lower latitudes the decrease in both mean sea surface temperature and seasonal amplitude with increasing latitude on the gondwanan coast is much like that observed along high latitude coastlines today calculated 18 o water decreases toward the pole likely associated with an increasing contribution of isotopically light fresh water derived from summer snow melt the gradient in 18 o water is similar to that documented over a similar span of latitude on the modern se greenland coast we infer the presence of a north flowing coastal current of cold o 18 depleted water that entrains progressively greater amounts of more typical seawater as it moves away from the pole 18 o values in se australia however are about 3 lower than those off greenland suggesting comparatively lower salinity water or more o 18 depleted glacial ice runoff in the permian gondwanan high latitudes perhaps augmented by more depleted negative global average seawater conditions in southeastern australia during the largest of the permian deglaciations were warmer than present day antarctica at similar latitudes but may approximate those of early mid miocene antarctica with frozen winters but summers closer to 10 c

an early to middle miocene record of ice sheet and landscape evolution from the friis hills antarctica the friis hills 77 45 s 161 30 e in the mcmurdo dry valleys region antarctica is a 1 km high inselberg with early to middle miocene aged glacial deposits preserved on its upper surface lithology sedimentology and ice flow direction define three units within a 34 m thick sequence the friis i friis ii and cavendish drifts tills in friis i drift were deposited from alpine glaciers flowing to the sw an extensive tephra bed in the drift is 19 76 0 11 ma in age based on 40 ar 39 ar dating tills in friis ii drift were deposited from alpine glaciers flowing to the se fossiliferous fluvial and lacustrine beds in the drift indicate that vegetation and insects repeatedly recolonized the friis hills during periods of reduced ice the geographic distribution of modern descendants of the fossils specifies mean summer temperatures of 6 7 c and precipitation as much as 3000 mm during these interglacial periods the presence of fossils also indicates deposition of friis ii drift occurred before the mid miocene climate transition ca 14 1 ma after this eastward flowing ice partially eroded the friis i and ii drifts the ice also cut parallel troughs to the n and s topographically isolating the friis hills the cavendish drift represents renewed deposition but from eastward flowing outlet glaciers within the newly established troughs together the friis hills drifts register multiple stages in the evolution of the east antarctic cryosphere including the general growth of the system reorganizations of glacial drainage patterns and periods of major downcutting importantly they also provide constraints on terrestrial climate conditions during these stages the friis hills record is the first that can be directly compared with shallow marine records from the ross sea the record also provides new constraints for paleoglaciological models of the early east antarctic ice sheet based on lithologic and geomorphic arguments the friis hills drifts are younger than nearby sirius group tillites which predicates that the sirius group in the dry valleys region is at least early miocene or more probably oligocene in age