from greenhouse to icehouse organic walled dinoflagellate cysts as paleoenvironmental indicators in the paleogene abstract dinoflagellates are an important component of the extant eukaryotic plankton their organic walled hypnozygotic cysts dinocysts provide a rich albeit incomplete history of the group in ancient sediments building on pioneering studies of the late 1970s and 1980s recent drilling in the southern ocean has provided a wealth of new dinocyst data spanning the entire paleogene such multidisciplinary studies have been instrumental in refining existing and furnishing new concepts of paleogene paleoenvironmental and paleoclimatic reconstructions by means of dinocysts because dinocysts notably exhibit high abundances in neritic settings dinocyst based environmental and paleoclimatic information is important and complementary to the data derived from typically more offshore groups as planktonic foraminifera coccolithophorids diatoms and radiolaria by presenting case studies from around the globe this contribution provides a concise review of our present understanding of the paleoenvironmental significance of dinocysts in the paleogene 65 25 ma representing earth s greenhouse icehouse transition this episode holds the key to the understanding of extreme transient climatic change we discuss the potential of dinocysts for the reconstruction of paleogene sea surface productivity temperature salinity stratification and paleo oxygenation along with their application in sequence stratigraphy oceanic circulation and general watermass reconstructions

cenozoic ice rafting history of the central arctic ocean terrigenous sands on the lomonosov ridge the cenozoic ice rafted debris ird history of the central arctic is reconstructed utilizing the terrigenous coarse sand fraction in iodp 302 cores from 0 to 273 meters composite depth this holocene middle eocene quantitative record of terrigenous sand accumulation on the lomonosov ridge along with qualitative information on grain texture and composition confirms the interpretation that ice initiation sea ice and glacial ice occurred 46 ma in the arctic and provides a long term pattern of arctic ice expansion and decay since the middle eocene ird mass accumulation rates range from 0 to 0 13 g cm2 ka in the middle eocene and from 0 to 0 36 g cm2 ka in the neogene ird mass accumulation rate mar maxima in the miocene and pliocene cooccur with either glacial initiation or intensification in the sub arctic the 46 25 ma ird onset in the central arctic slightly precedes the earliest evidence of ice in the antarctic and compares in timing with a 1000 ppm decrease in atmospheric concentrations of co2 the decline of pco2 in the middle eocene may have driven both poles across the temperature threshold that enabled the nucleation of glaciers on land and partial freezing of the surface arctic ocean especially during times of low insolation

past glacial and interglacial conditions in the arctic ocean and marginal seas a review past changes in the arctic ocean and its marginal seas have been profound even during the last 10 000 years understanding these changes such as those occurring during the transition from glacial to interglacial climates are important for research on modern processes because this knowledge provides a framework and unique perspective in which to view the modern physical and biological processes this paper discusses our current understanding of past environmental change and processes relative to those currently in progress special emphasis is placed on the most recent transition from a glacial state to the modern interglacial conditions

seismic detection of a subglacial lake near the south pole antarctica 1 seismic reflection data are analyzed to verify radar identification of a subglaical lake near the geographic south pole the seismic amplitude variation with offset avo technique is applied to confirm the presence of extensive free water and seismic imaging of the subsurface constrains lake depth and deeper subglacial structure in the region this lake is at least 4 2 km wide and likely as much as 10 km in diameter is up to 32 10 m deep and occupies a basin of thick sedimentary strata these results imply that extensive water storage is occurring in the south pole region the proximity of this lake to the amundsen scott south pole station makes research drilling to sample the lake and underlying sediments feasible and supportable

clean subglacial access prospects for future deep hot water drilling accessing and sampling subglacial environments deep beneath the antarctic ice sheet presents several challenges to existing drilling technologies with over half of the ice sheet believed to be resting on a wet bed drilling down to this environment must conform to international agreements on environmental stewardship and protection making clean hot water drilling the most viable option such a drill and its water recovery system must be capable of accessing significantly greater ice depths than previous hot water drills and remain fully operational after connecting with the basal hydrological system the subglacial lake ellsworth sle project developed a comprehensive plan for deep greater than 3000 m subglacial lake research involving the design and development of a clean deep ice hot water drill however during fieldwork in december 2012 drilling was halted after a succession of equipment issues culminated in a failure to link with a subsurface cavity and abandonment of the access holes the lessons learned from this experience are presented here combining knowledge gained from these lessons with experience from other hot water drilling programmes and recent field testing we describe the most viable technical options and operational procedures for future clean entry into sle and other deep subglacial access targets

late eocene southern ocean cooling and invigoration of circulation preconditioned antarctica for full scale glaciation during the eocene oligocene transition eot 34 33 5 ma antarctic ice sheets relatively rapidly expanded leading to the first continent scale glaciation of the cenozoic declining atmospheric co2 concentrations and associated feedbacks have been invoked as underlying mechanisms but the role of the quasi coeval opening of southern ocean gateways tasman gateway and drake passage and resulting changes in ocean circulation is as yet poorly understood definitive field evidence from eot sedimentary successions from the antarctic margin and the southern ocean is lacking also because the few available sequences are often incomplete and poorly dated hampering detailed paleoceanographic and paleoclimatic analysis here we use organic dinoflagellate cysts dinocysts to date and correlate critical southern ocean eot successions we demonstrate that widespread winnowed glauconite rich lithological units were deposited ubiquitously and simultaneously in relatively shallow marine environments at various southern ocean localities starting in the late eocene 35 7 ma based on organic biomarker paleothermometry and quantitative dinocyst distribution patterns we analyze southern ocean paleoceanographic change across the eot we obtain strong indications for invigorated surface and bottom water circulation at sites affected by polar westward flowing wind driven currents including a westward flowing antarctic countercurrent starting at about 35 7 ma the mechanism for this oceanographic invigoration remains poorly understood the circum antarctic expression of the phenomenon suggests that rather than triggered by tectonic deepening of the tasman gateway progressive pre eot atmospheric cooling played an important role at localities affected by the antarctic countercurrent sea surface productivity increased and simultaneously circum antarctic surface waters cooled we surmise that combined these processes contributed to preconditioning the antarctic continent for glaciation

evidence for warmer interglacials in east antarctic ice cores reconstructions of temperature variations from antarctic ice cores rely on the assumption that the relationship between hydrogen and oxygen isotopic ratios and temperature are stable in space and time sime et al analyse three 340 000 year old ice cores from east antarctica and use an isotope enabled general circulation model to show that instead the relationship is nonlinear during warm periods the ratios are less sensitive to temperature so previous estimates of interglacial temperatures are likely to be about 3 c too low this is consistent with peak antarctic interglacial temperatures at least 6 c higher than today this work suggests that there are serious deficiencies in our understanding of climates that are warmer than today s reconstructions of temperature variations from antarctic ice cores rely on the assumption that the relationship between hydrogen and oxygen isotope ratios and temperature are stable in space and time three east antarctic ice core records are now analysed alongside input from general circulation models to reveal that during warmer interglacial periods the isotope ratios are less sensitive to temperature than during colder interglacials consequently previous estimates of interglacial temperatures are probably too cold stable isotope ratios of oxygen and hydrogen in the antarctic ice core record have revolutionized our understanding of pleistocene climate variations and have allowed reconstructions of antarctic temperature over the past 800 000 years 800 kyr refs 1 2 the relationship between the d h ratio of mean annual precipitation and mean annual surface air temperature is said to be uniform 10 over east antarctica3 and constant with time 20 refs 3 5 in the absence of strong independent temperature proxy evidence allowing us to calibrate individual ice cores prior general circulation model gcm studies have supported the assumption of constant uniform conversion for climates cooler than that of the present day3 5 here we analyse the three available 340 kyr east antarctic ice core records alongside input from gcm modelling we show that for warmer interglacial periods the relationship between temperature and the isotopic signature varies among ice core sites and that therefore the conversions must be nonlinear for at least some sites model results indicate that the isotopic composition of east antarctic ice is less sensitive to temperature changes during warmer climates we conclude that previous temperature estimates from interglacial climates are likely to be too low the available evidence is consistent with a peak antarctic interglacial temperature that was at least 6 k higher than that of the present day approximately double the widely quoted 3 1 5 k refs 5 6

late eocene to early oligocene dinoflagellate cysts from the priabonian type area northeast italy biostratigraphy and paleoenvironmental interpretation abstract marginal marine late eocene through early oligocene dinoflagellate cyst successions have been studied from the type area of the priabonian stage northeast italy the results allow the recognition of dinoflagellate zones previously defined in bio and magnetostratigraphically well calibrated pelagic sequences from central italy thus providing a first order correlation of the priabonian stage to the standard chronostratigraphic scale with unprecedented precision within this detailed biostratigraphic framework successive shifts in the composition of the dinoflagellate cyst assemblages are interpreted in terms of sea level and sea surface temperature sst fluctuations the evaluation of ecologically and sedimentary controlled changes in the composition of dinoflagellate cyst assemblages in combination with sequence stratigraphic analysis allows the reconstruction of third and fourth order sea level fluctuations the third order sea level fluctuations appear to correspond to exxon cycles ta4 1 4 5 the stratigraphically and palaeoenvironmentally important late eocene dinoflagellate cyst species glaphyrocysta priabonensis sp nov is formally described

collapse of polar ice sheets during the stage 11 interglacial the magnitude of sea level rise during marine isotope stage 11 about 400 000 years ago is shown to have been probably only 6 to 13 metres in contrast to some earlier estimates of up to 20 metres the ice sheets in greenland and west antarctica are known to be susceptible to climate warming and both are losing mass how the east antarctic ice sheet will respond to warming is less clear recent evidence from shoreline features in bermuda and the bahamas suggested that during marine isotope stage 11 a period of warming that occurred about 400 000 years ago the sea level was 20 metres higher than it is today which pointed to significant melting of the east antarctic ice sheet now an estimate that takes into account post glacial crustal subsidence of the shoreline sites during an anomalously long interglacial period puts the sea level during stage 11 at 6 13 metres higher than today that can be explained by the collapse of the greenland and west antarctic ice sheets with only a small contribution from the east antarctic ice sheet contentious observations of pleistocene shoreline features on the tectonically stable islands of bermuda and the bahamas have suggested that sea level about 400 000 years ago was more than 20 metres higher than it is today1 2 3 4 geochronologic and geomorphic evidence indicates that these features formed during interglacial marine isotope stage mis 11 an unusually long interval of warmth during the ice age1 2 3 4 previous work has advanced two divergent hypotheses for these shoreline features first significant melting of the east antarctic ice sheet in addition to the collapse of the west antarctic ice sheet and the greenland ice sheet1 2 3 or second emplacement by a mega tsunami during mis 11 ref 4 5 here we show that the elevations of these features are corrected downwards by 10 metres when we account for post glacial crustal subsidence of these sites over the course of the anomalously long interglacial on the basis of this correction we estimate that eustatic sea level rose to 6 13 m above the present day value in the second half of mis 11 this suggests that both the greenland ice sheet and the west antarctic ice sheet collapsed during the protracted warm period while changes in the volume of the east antarctic ice sheet were relatively minor thereby resolving the long standing controversy over the stability of the east antarctic ice sheet during mis 11

the bas ice shelf hot water drill design methods and tools the 2011 12 antarctic field season saw the first use of a new british antarctic survey bas ice shelf hot water drill system on the larsen c and george vi ice shelves delivering 90 l min 1 at 80 c a total of five holes 30cm in diameter at three locations were successfully drilled through almost 400m of ice to provide access to the underlying ocean including the first access beneath the larsen c ice shelf these access holes enabled the deployment of instruments to measure sea water conductivity temperature depth and microstructure the collection of water samples and up to 2 9m long sediment cores before long term oceanographic moorings were deployed the simple modular design allowed for twin otter aircraft deployment rapid assembly and commissioning of the system which proved highly reliable with minimal supervision a number of novel solutions to various operational sub ice shelf profiling and mooring deployment issues were successfully employed through the hot water drilled access holes to aid the positioning recovery and deployment of instruments with future activities now focusing on the filchner ronne ice shelf the drill has been upgraded from its current 500m capability to 1000m with additional drill hose and further generator pumping and heating modules

a novel proxy for terrestrial organic matter in sediments based on branched and isoprenoid tetraether lipids we propose a novel tracer for terrestrial organic carbon in sediments based on the analysis of tetraether lipids using high performance liquid chromatography mass spectrometry hplc ms analysis of terrestrial soil and peats shows that branched tetraether lipids are predominant in terrestrial environments in contrast to crenarchaeol the characteristic membrane lipid of non thermophilic crenarchaeota which is especially abundant in the marine and lacustrine environment based on these findings an index was developed the so called branched and isoprenoid tetraether bit index based on the relative abundance of terrestrially derived tetraether lipids versus crenarchaeol this bit index was applied to surface sediments from the angola basin where it was shown to trace the outflow of the congo river furthermore analyses of particulate organic matter from the north sea showed relatively higher bit indices in water column particulate organic matter near large river inputs a survey of globally distributed marine and lacustrine surface sediments shows that the bit index in these environments correlates with the relative fluvial input of terrestrial organic material making this index generally applicable the new proxy allows the rapid assessment of the fluvial input of terrestrial organic material in immature sediments up to 100 ma old

sandstone reservoir quality prediction the state of the art joanna ajdukiewicz joined exxon production research company in 1980 she was reservoir quality assessment and prediction team lead there from 1991 to 1995 and at imperial oil research centre in calgary from 1995 to 1997 subsequently she has worked a variety of exploration company assignments in the north sea gulf of mexico and middle east her current interests are in predicting the distribution of early diagenetic controls on deep reservoir quality rob lander develops diagenetic models for geocosm llc he obtained his ph d in geology from the university of illinois in 1991 was a research geologist at exxon production research from 1991 to 1993 and worked for rogaland research and geologica as from 1993 to 2000 he is also a research fellow at the bureau of economic geology to guess is cheap to guess wrongly is expensive chinese proverb reservoir quality predictive models will be a useful element of risk analysis until remote sensing tools are invented that accurately measure effective porosity and permeability ahead of the bit this issue of the aapg bulletin highlights recent advances in a new generation of reservoir quality models that have successfully predicted porosity and permeability in diverse siliclastic reservoirs under many different burial conditions most previous attempts at predrill reservoir quality prediction have relied on empirical correlations or on first principle geochemical simulations that incorporate laboratory derived input parameters wood and byrnes 1994 the new reservoir quality models differ from previous approaches in that although incorporating theory inspired algorithms they include terms with values that are explicitly designed to be calibrated by and tested against data sets of high quality petrographic analyses that are linked to thermal and effective stress histories petrographic observations therefore provide essential constraints in these models on the types timing and rates of key geologic processes affecting sandstone pore systems this approach avoids the pitfalls inherent

driftwood dropstones in middle miocene climate optimum shallow marine strata calvert cliffs maryland coastal plain erratic pebbles no certain proxy for cold climate abstract sparse lithic erratics pebbles to cobbles sampled from three shallow marine strata deposited during the middle miocene climate optimum mmco ca 16 14 ma along the western atlantic margin exposed in the calvert cliffs maryland suggest transport and deposition not from ice but from the roots of trees uprooted during floods and carried out to sea evidence for driftwood transport includes carbonized wood in the same strata more than half the ca 225 erratics were quarried in the largely metamorphic piedmont province including a few from the port deposit gneiss still outcropping on the lower susquehanna river the lowest sampled bed parker creek bone bed is assigned to the ca 15 7 15 5 ma peak warmth of the mmco which we attribute in part to co2 from the coevally erupted grande ronde flood basalts grfb the peak effusiveness episode of the columbia river flood basalts crfb the three sampled beds predate the ca 13 9 ma antarctic cryosphere expansion which may be recorded in the calvert cliffs by a unique buried channel

stable warm tropical climate through the eocene epoch earth s climate cooled from a period of extreme warmth in the early eocene epoch ca 50 ma to the early oligocene ca 33 ma when a large ice cap first appeared on antarctica evidence from the planktonic foraminifer oxygen isotope record in deep sea cores has suggested that tropical sea surface temperatures declined by 5 10 degrees over this interval eventually becoming much cooler than modern temperatures here we present paleotemperature estimates from foraminifer isotopes and the membrane lipids of marine crenarcheota from new drill cores in tanzania that indicate a warm and generally stable tropical climate over this period we reinterpret the previously published isotope records in the light of comparative textural analysis of the deep sea foraminifer shells which shows that in contrast to the tanzanian material they have been diagenetically recrystallized we suggest that increasingly severe alteration of the deep sea plankton shells through the eocene produced a diagenetic overprint on their oxygen isotope ratios that imparts the false appearance of a tropical sea surface cooling trend this implies that the long term eocene climatic cooling trend occurred mainly at the poles and had little effect at lower latitudes

variability in the length of the sea ice season in the middle eocene arctic finely laminated middle eocene sediments from the central arctic contain high abundances of the delicate sea ice dwelling fossil diatoms synedropsis spp and sea ice rafted debris sea ice ird establishing an offshore seasonal sea ice regime ca 47 ma synedropsis spp co occur with other diatom taxa and microfossils requiring open water this strongly indicates seasonality nonetheless seasonal reconstruction of the flux cycle cannot be resolved by standard bulk sediment analysis which destroys sedimentary fabrics and averages data within samples here we resolve and reconstruct seasonal scale flux events from these sediments using backscattered electron imagery bsei of resin embedded sediment a nondestructive technique that preserves the integrity of sedimentary microfabrics thus revealing discrete productivity flux events at ultrahigh e g 30 m resolution seasonality is expressed at the submillimeter scale by successions of discrete mono specific laminae and micro lenses of synedropsis spp terrigenous material sea ice ird and open water taxa indicating that first year ice existed in the central arctic further bsei reveals millimeter scale alternation of bundles of laminae and microlenses of two distinct types one characterized by synedropsis spp and terrigenous material the other by mainly open water taxa and little terrigenous material the sedimentation rate and preliminary assessment of annual cycles indicate suborbital variability on the order of multi decadal to centennial duration we argue that this reflects variations in the sea ice season length

freshwater balance and the sources of deep and bottom waters in the arctic ocean inferred from the distribution of h218o data from sections across the eurasian basin of the arctic ocean occupied in 1987 and 1991 are used to derive information on the freshwater balance of the arctic ocean and on sources of the deep waters of the nansen amundsen and makarov basins using salinity h218o and mass balances we estimate the river runoff and the sea ice melt water fractions contained in the upper waters of the arctic ocean and infer pathways of the river runoff signal from the shelf seas across the central arctic ocean to fram strait the average mean residence time of the river runoff fraction contained in the arctic ocean halocline is determined to be about 11 to 14 years pacific water entering through bering strait is traced using silicate and its influence on the halocline waters of the canadian basin is estimated water column inventories of river runoff and sea ice melt water are calculated for a section just north of fram strait and implications of these inventories for sea ice export through fram strait are discussed comparison of the 18o 16o ratios of shelf water atlantic water and the deep waters of the arctic ocean indicate that the sources of the deep and bottom waters of the eurasian basin are located in the barents and kara seas

paleogene record of elemental concentrations in sediments from the arctic ocean obtained by xrf analyses we present a high resolution x ray fluorescence xrf core scanner record for the expanded middle eocene section from integrated ocean drilling program iodp expedition 302 acex drilled on the lomonosov ridge central arctic ocean the division of the middle eocene into two units subunit 1 6 and unit 2 is seen in the cyclical behavior of the elements as well as the changing interelemental correlations and their relationship to physical property measurements of bulk sediment al ti and k strongly correlate throughout the record while the behavior of fe mn and si is more complex utilizing sediment geochemistry calibration to ground truth the xrf data we suggest the middle eocene arctic ocean was predominately euxinic although periodic oxygenation of bottom waters must have occurred during unit 2 49 7 45 4 ma initially the sediments are rich in biogenic silica unit 2 but there is a pronounced shift to terrigenous dominated sediment accumulation in subunit 1 6 we report changes in the elemental concentrations of these elements and investigate the relationship between fe content and pyrite additionally we explore the potential change in paleoenvironmental conditions across the unit boundary

ephemeral formation of perennial sea ice in the arctic ocean during the middle eocene arctic sea ice is a key component of the modern climate system marine sediment analyses suggest that perennial sea ice in the arctic ocean first formed transiently about 44 million years ago

new 3d bathymetry and sediment distribution in lake vostok implication for pre glacial origin and numerical modeling of the internal processes within the lake abstract a new distribution of water and unconsolidated sediments in subglacial lake vostok east antarctica was developed via inversion of airborne gravity data constrained by 60 seismic soundings a model was developed for host rock with a density of 2550 kg m 3 that was inferred from prior 2d modeling our 3d bathymetry model of lake vostok corresponds better with seismic data rms of 125 m than two previous models based on the same gravity dataset the good match in both water and sediment thicknesses between the gravity model and seismic measurements confirms two major facts about lake vostok 1 the lake is hosted by sedimentary rocks and 2 the bottom of the lake is covered with a layer of unconsolidated sediments that does not exceed 300 m in the southern basin and thickens almost to 400 m in the northern basin our new bathymetry model suggests much shallower water thicknesses up to twice the previous estimates in the middle and northern parts of the lake while the water layer is thicker in the southern basin numerical modeling of the internal processes in the lake reveals the relevance of our new bathymetry model to the basal mass balance a significant decrease in transport is observed in the shallower northern basin as well as a decrease of 33 in the turbulent kinetic energy however only minor differences were observed in the distribution of the calculated freezing and melting zones compared to previous models estimates for the sedimentation rates for six possible mechanisms were made possible sedimentation mechanisms are 1 fluvial and periglacial i e those that are active prior to the establishment of a large subglacial lake 2 deposition due to overlying ice sheet including melting out of the ice as well as bulldozering by the overriding ice and 3 suspended sediments from subglacial water flow including those deposited by periodical subglacial outbursts the estimates for these mechanisms show that unconsolidated sediments of the observed thickness are most consistent with a lake that existed before glaciation

introduction to special section on cenozoic paleoceanography of the central arctic ocean 1 in late summer 2004 the integrated ocean drilling program iodp conducted one of the most transformational missions in the almost 40 year history of scientific ocean drilling the arctic coring expedition acex backman et al 2006 moran et al 2006a this technically challenging expedition moran et al 2006b to the lomonosov ridge near 88 n recovered the first long term cenozoic sediment record from the arctic ocean extending previous records from 1 5 ma to an unprecedented 56 ma glimpses of the breadth of this transformation were seen during the acex cruise when the massulae from freshwater ferns azolla were found in 49 ma old sediments brinkhuis et al 2006 and the presence of apectodinium augustum confirmed that the paleocene eocene thermal maximum petm 55 ma was unexpectedly recovered sluijs et al 2006 2 soon after the expedition when the cores were opened and analyzed ice rafted debris was found in surprisingly old 46 ma sediments moran et al 2006a these middle eocene sediments are characterized also by their high organic carbon content stein et al 2006 the exciting early results attracted other investigators that expanded the scientific investigating team to more than 40 people analyses were extended to include studies that revealed surprisingly high arctic ocean surface water temperatures sluijs et al 2006 and an amplified hydrological system pagani et al 2006 during the petm initial analyses revealed an extensive hiatus encompassing about 26 million years that occurred below a short interval showing starkly alternating black and white layers that is now dubbed the zebra interval thus the time interval from the late early miocene 18 ma to the middle middle eocene 44 ma is missing although the hiatus is a lost window in time for the arctic paleoclimate record it spawned other studies that integrated the regional tectonic history with acex results revealing a major oceanographic reorganization at 17 5 ma ventilation of the arctic ocean to the north atlantic through the fram strait jakobsson et al 2007 in terms of ventilation and water mass history neogene neodymium isotope data reveal that arctic intermediate waters originate from brine formation on eurasian shelf areas between 15 and 2 ma and during glacial periods throughout pleistocene times haley et al 2008a they conclude that this mode of arctic circulation differs markedly from today s situation showing relatively high contributions of north atlantic intermediate water and minor input from brine formation 3 in this special section the transformation continues results from the large acex scientific family include a robust age model detailed analyses of the middle eocene that document a unique brackish water environment sea ice and iceberg history reconstructions as well as the provenance of ice rafted debris from the eocene to present evolution of depositional environments times of isolation and connection to the global ocean geochemical analyses of the organic carbon rich sediments and unique applications of high resolution proxies and cyclostratigraphy highlights from this special section are presented here

salinity of the eocene arctic ocean from oxygen isotope analysis of fish bone carbonate stable isotope analysis was performed on the structural carbonate of fish bone apatite from early and early middle eocene samples 55 to 45 ma recently recovered from the lomonosov ridge by integrated ocean drilling program expedition 302 the arctic coring expedition the 18o values of the eocene samples ranged from 6 84 to 2 96 vienna peedee belemnite with a mean value of 4 89 compared to 2 77 for a miocene sample in the overlying section an average salinity of 21 to 25 was calculated for the eocene arctic compared to 35 for the miocene with lower salinities during the paleocene eocene thermal maximum the azolla event at 48 7 ma and a third previously unidentified event at 47 6 ma at the azolla event where the organic carbon content of the sediment reaches a maximum a positive 13c excursion was observed indicating unusually high productivity in the surface waters

potential seaways across west antarctica the west antarctic ice sheet wais has long been considered vulnerable to rapid retreat and today parts are rapidly losing ice projection of future change in wais is however hampered by our poor understanding of past changes especially during interglacial periods that could be analogs for the future but which undoubtedly provide an opportunity for testing predictive models we consider how ice loss would open seaways across wais these would likely alter southern ocean circulation and climate and would broadly define the de glacial state but they may also have left evidence of their existence in the coastal seas they once connected we show the most likely routes for such seaways and that a direct seaway between weddell and ross seas which did not pass through the amundsen sea sector is unlikely continued ice loss at present rates would open seaways between amundsen and weddell seas a w and amundsen and bellingshausen seas a b in around one thousand years this timescale indicates potential future vulnerability but also suggests seaways may have opened in recent interglacial periods we attempt to test this hypothesis using contemporary bryozoan species assemblages around antarctica concluding that anomalously high similarity in assemblages in the weddell and amundsen seas supports recent migration through a w other authors have suggested opening of seaways last occurred during marine isotope stage 7a 209 ka bp but we conclude that opening could have occurred in mis 5e 100 ka bp when antarctica was warmer than present and likely contributed to global sea levels higher than today

humidity estimate for the middle eocene arctic rain forest the exquisite preservation of fossilized metasequoia trees that grew near 808n latitude during the middle eocene ca 45 ma in nunavut canada allowed for dd and d 18 o analyses of cellulose techniques previously restricted to wood 30 000 yr old from the isotopic results we determined that the middle eocene arctic atmosphere contained 23 the water found in the region s atmosphere today this water vapor contributed to a middle eocene greenhouse effect that insulated the polar region during dark polar winters

pleistocene collapse of the west antarctic ice sheet some glacial sediment samples recovered from beneath the west antarctic ice sheet at ice stream b contain quaternary diatoms and up to 108 atoms of beryllium 10 per gram other samples contain no quaternary diatoms and only background levels of beryllium 10 less than 10 6 atoms per gram the occurrence of young diatoms and high concentrations of beryllium 10 beneath grounded ice indicates that the ross embayment was an open marine environment after a late pleistocene collapse of the marine ice sheet

physical processes in subglacial lake whillans west antarctica inferences from sediment cores abstract the hydrologic system beneath the antarctic ice sheet is thought to influence both the dynamics and distribution of fast flowing ice streams which discharge most of the ice lost by the ice sheet despite considerable interest in understanding this subglacial network and its affect on ice flow in situ observations from the ice sheet bed are exceedingly rare here we describe the first sediment cores recovered from an active subglacial lake the lake known as subglacial lake whillans is part of a broader dynamic hydrologic network beneath the whillans ice stream in west antarctica even though floods pass through the lake the lake floor shows no evidence of erosion or deposition by flowing water by inference these floods must have insufficient energy to erode or transport significant volumes of sediment coarser than silt consequently water flow beneath the region is probably incapable of incising continuous channels into the bed and instead follows preexisting subglacial topography and surface slope sediment on the lake floor consists of till deposited during intermittent grounding of the ice stream following flood events the fabrics within the till are weaker than those thought to develop in thick deforming beds suggesting subglacial sediment fluxes across the ice plain are currently low and unlikely to have a large stabilizing effect on the ice stream s grounding zone

a microbial ecosystem beneath the west antarctic ice sheet liquid water has been known to occur beneath the antarctic ice sheet for more than 40 years but only recently have these subglacial aqueous environments been recognized as microbial ecosystems that may influence biogeochemical transformations on a global scale here we present the first geomicrobiological description of water and surficial sediments obtained from direct sampling of a subglacial antarctic lake subglacial lake whillans slw lies beneath approximately 800 m of ice on the lower portion of the whillans ice stream wis in west antarctica and is part of an extensive and evolving subglacial drainage network the water column of slw contained metabolically active microorganisms and was derived primarily from glacial ice melt with solute sources from lithogenic weathering and a minor seawater component heterotrophic and autotrophic production data together with small subunit ribosomal rna gene sequencing and biogeochemical data indicate that slw is a chemosynthetically driven ecosystem inhabited by a diverse assemblage of bacteria and archaea our results confirm that aquatic environments beneath the antarctic ice sheet support viable microbial ecosystems corroborating previous reports suggesting that they contain globally relevant pools of carbon and microbes that can mobilize elements from the lithosphere and influence southern ocean geochemical and biological systems

quasi quadrennial and quasi biennial variability in the equatorial pacific evaluation of competing el nino southern oscillation enso theories requires one to identify separate spectral peaks in equatorial wind and sea surface temperature sst time series to sharpen this identification we examine the seasonal to interannual variability of these fields by the data adaptive method of multi channel singular spectrum analysis m ssa m ssa is applied to the equatorial band 4 n 4 s using 1950 1990 data from the comprehensive ocean and atmosphere data set two major interannual oscillations are found in the equatorial sst and surface zonal wind fields u the main peak is centered at about 52 months we refer to it as the quasi quadrennial qq mode quasi biennial qb variability is split between two modes with periods near 28 months and 24 months a faster 15 month oscillation has smaller amplitude the qq mode dominates the variance and has the most distinct spectral peak in time longitude reconstructions of this mode the sst has the form of a standing oscillation in the eastern equatorial pacific while the u field is dominated by a standing oscillation pattern in the western pacific and exhibits also slight eastward propagation in the central and western pacific the locations of maximum anomalies in both qb modes are similar to those of the qq mode slight westward migration in sst across the eastern and central and eastward propagation of u across the western and central pacific are found the significant wind anomaly covers a smaller region than for the qq the qq and qb modes together represent the enso variability well and interfere constructively during major events the sharper definition of the qq spectral peak and its dominance are consistent with the devil s staircase interaction mechanism between the annual cycle and enso

eocene continental climates and latitudinal temperature gradients global climate during the mesozoic and early cenozoic is thought to have been warmer than at present but there is debate about winter temperatures paleontological data indicate mild temperatures even at high latitudes and in mid latitude continental interiors whereas computer simulations of continental paleoclimates produce winter temperatures closer to modern levels foliar physiognomy and floristic composition of 23 eocene floras from the interior of north america and australia indicate cold month means generally 2 c even where the mean annual temperature mat was

late paleocene arctic coastal climate inferred from molluscan stable and radiogenic isotope ratios abstract characterizing polar climates during past warm intervals is important for understanding greenhouse climate dynamics because high latitude surface temperatures and precipitation patterns are extremely sensitive to global climatic conditions model data comparisons of high latitude climates during past warm intervals cretaceous eocene pliocene are currently at odds specifically simulations of past warm climates produce polar regions characterized by sub freezing temperatures and significant seasonality whereas limited fossil proxy data indicate higher mean annual temperatures and low seasonality i e an equable climate we have constructed a data set to infer northern hemisphere polar marine temperatures during the late paleocene seasonal and mean annual temperature and the oxygen isotopic composition of precipitation are reconstructed for an arctic coastal setting during the thanetian 57 58 ma using fossil shell stable isotope profiles we estimate that coastal water temperatures varied between 10 and 15 c during the seasons of growth presumably spring summer and fall these findings support paleontological evidence implying northern hemisphere polar climates were seasonally warm during the late paleocene in addition estuarine fossil oxygen isotope profiles show periodic excursions to low values as low as 19 vpdb which indicate seasonal pulses of isotopically depleted freshwater

a siliceous microfossil view of middle eocene arctic paleoenvironments a window of biosilica production and preservation integrated ocean drilling program iodp expedition 302 the arctic coring expedition acex unearthed the most significant find of paleogene siliceous microfossils in nearly 2 decades 100 m of early middle eocene organic rich finely laminated sediments contain abundant marine and freshwater siliceous microfossils allowing intriguing insights into central arctic paleoenvironments during the start of cenozoic cooling largely endemic assemblages of marine diatoms and ebridians are preserved along with very high abundances of chrysophyte cysts the endogenously formed resting stage of freshwater algae an overall brackish environment is invoked but variations in group dominance suggest episodic changes in salinity stratification and trophic status with the backing of inorganic geochemistry we synthesize the sediment characteristics by hypothesizing an environmental model for the cooccurrence of these diverse siliceous microfossil groups we also report on initial insights into the composition of some of the laminations which may help explain the formation of this rich sediment archive

orbital forcing of arctic climate mechanisms of climate response and implications for continental glaciation progress in understanding how terrestrial ice volume is linked to earths orbital configuration has been impeded by the cost of simulating climate system processes relevant to glaciation over orbital time scales 10 3 10 5 years a compromise is usually made to rep resent the climate system by models that are averaged over one or more spatial dimensions or by three dimensional models that are limited to simulating par ticular snapshots in time we take advantage of the short equilibration time 310 years of a climate model consisting of a three dimensional atmosphere coupled to a simple slab ocean to derive the equilibrium climate response to accelerated variations in earths orbital configuration over the past 165 000 years prominent decreases in ice melt and increases in snowfall are sim ulated during three time intervals near 26 73 and 117 thousand years ago ka when aphelion was in late spring and obliquity was low there were also significant decreases in ice melt and increases in snowfall near 97 and 142 ka when eccentricity was relatively large aph elion was in late spring and obliquity was high or near its long term mean these glaciation friendly time intervals correspond to prominent and secondary phases of terrestrial ice growth seen within the marine d 18 o record both dynamical and thermal effects contribute to the increases in snowfall during these periods through increases in storm activity and the fraction of precipi tation falling as snow the majority of the mid to high latitude response to orbital forcing is organized by the properties of sea ice through its influence on radiative feedbacks that nearly double the size of the orbital forcing as well as its influence on the seasonal evolution of the latitudinal temperature gradient

dinosaur bones fossils or pseudomorphs the pitfalls of physiology reconstruction from apatitic fossils abstract a prerequisite to any attempt to reconstruct thermophysiology of ancient animals through analysis of stable isotopes of oxygen is the assumption that apatitic fossils are isotopically unaltered parts of their original skeletons we suggest that sufficient evidence is available to seriously question this assumption because living bones contain about 1 3 by weight of organic matrix mass balance considerations show that at least half of an apatitic fossil must be new material added post mortem furthermore living apatitic skeletons contain almost no rare earth elements and uranium whereas apatitic fossils bear high concentrations of these elements additionally we found that while in living fish correlation between 18o of oxygen in the phosphate and that in the carbonate of apatite is poor these two values are linearly correlated in fossil fish this suggests diagenetic recrystallization has taken place perfect preservation of micro textures such as haversian canals does not prove the pristine condition of a fossil some of the most beautifully preserved fossils are highly silicified most apatitic fossils probably are pseudomorphs replacing original skeletal elements whereas distribution of stable isotopes of oxygen in fossils might provide information about their burial environment it could be misleading in attempts to interpret the organisms physiology this cautionary note is supported by the similarity of 18op in bones of coexisting fossil fish dinosaurs and various other reptiles at different latitudes the overlap of predicted 18op values in fish and mammals living in contact with the same environmental water also weakens the hope that ectotherms can be distinguished from endotherms by the isotopic composition of oxygen in their bones and teeth

anoxia and high primary production in the paleogene central arctic ocean first detailed records from lomonosov ridge 1 except for a few discontinuous fragments of the late cretaceous early cenozoic climate history and depositional environment the paleoenvironmental evolution of the pre neogene central arctic ocean was virtually unknown prior to the iodp expedition 302 arctic ocean coring expedition acex drilling campaign on lomonosov ridge in 2004 here we present detailed organic carbon oc records from the entire ca 200 m thick paleogene oc rich section of the acex drill sites these records indicate euxinic black sea type conditions favorable for the preservation of labile aquatic marine algae type oc occur throughout the upper part of the early eocene and the middle eocene explained by salinity stratification due to freshwater discharge the superimposed short term milankovitch type variability in amount and composition of oc is related to changes in primary production and terrigenous input prominent early eocene events of algae type oc preservation coincide with global 13c events such as the petm and elmo events the elmo 13c event has been identified in the arctic ocean for the first time

climate sensitivity to arctic seaway restriction during the early paleogene abstract the opening and closing of ocean gateways affects the global distribution of heat salt and moisture potentially driving climatic change on regional to global scales between 65 and 45 million years ago ma during the early paleogene exchange between the arctic and global oceans occurred through two narrow and shallow seaways the greenland norway seaway and the turgai strait sediments from the arctic ocean suggest that during this interval the surface ocean was warm brackish and episodically enabled the freshwater fern azolla to bloom the precise mechanisms responsible for the development of these conditions in the paleogene arctic remain uncertain here we show results from an isotope enabled atmosphere ocean general circulation model which indicate that northern hemisphere climate would have been very sensitive to the degree of oceanic exchange through the arctic seaways we also present modelled estimates of seawater and calcite 18o for the paleogene by restricting these seaways we simulate freshening of the surface arctic ocean to 6 psu and warming of sea surface temperatures by 2 c in the north atlantic and 5 10 c in the labrador sea our results may help explain the occurrence of low salinity tolerant taxa in the arctic ocean during the eocene and provide a mechanism for enhanced warmth in the north western atlantic we propose that the formation of a volcanic land bridge between greenland and europe could have caused increased ocean convection and warming of intermediate waters in the atlantic if true this result is consistent with the theory that bathymetry changes may have caused thermal destabilisation of methane clathrates and supports a tectonic trigger hypothesis for the paleocene eocene thermal maximum petm

orbitally forced azolla blooms and middle eocene arctic hydrology clues from palynology the high abundances and cyclic distribution of remains of the freshwater fern azolla in early middle eocene sediments from the arctic ocean have previously been related to episodic surface water freshening which was speculated to be orbitally modulated our integrated palynological and cyclostratigraphical analysis of the recovered azolla interval in integrated ocean drilling program iodp core 302 m0004a 11x resulted in the recognition of two clear periodicities a dominant 1 2 m cyclicity which we relate to changes in obliquity 40 k y and a weaker 0 7 m cyclicity which we link to precession 21 k y cycles in the abundances of azolla cysts of freshwater tolerant dinoflagellates and swamp vegetation pollen show covariability in the obliquity domain this strong correlation suggests periods of enhanced rainfall and runoff during azolla blooms presumably linked to increased local summer temperatures during obliquity maxima larix and bisaccate conifer pollen covary at the precession frequency with peak occurrences corresponding to precession minima possibly as a result of enhanced continental runoff from a more remote source area and a stronger seasonal contrast following the sudden demise of azolla ca 48 1 ma runoff cycles continued to influence the central arctic at decreased intensity this and a concomitant decline in swamp vegetation pollen suggest edaphically drier conditions on land and decreased runoff into the arctic ocean causing salinity changes which might have been fatal for azolla moreover a sea level rise inferred from overall decreasing total terrestrial palynomorph concentrations possibly facilitated oceanic connections 2011 geological society of america

retreat history of the ross ice sheet shelf since the last glacial maximum from deep basin sediment cores around ross island abstract radiocarbon dated sediment cores from deep basins beneath the mcmurdo ice shelf and seasonally open water north of ross island mcmurdo sound display a characteristic succession of sedimentary facies that document the retreat of the ross ice sheet at the last glacial maximum to its present ice shelf configuration the facies succession records a transition from a nearly grounded ice sheet to open marine environments north of ross island that comprises in ascending stratigraphic order 1 slightly consolidated clast rich muddy diamict dominated by basement clasts from the transantarctic mountains and interpreted as melt out from the basal layer debris proximal to a retreating grounding zone 2 sparsely fossiliferous reworked diatom frustules and non bioturbated mud lacking lonestones interpreted as a sub ice shelf facies and 3 diatom mud and diatom ooze indicative of open marine conditions with evidence of iceberg rafting the succession in the open marine lewis basin north of ross island is similar though the diamict is much sandier and sedimentation rates 1 2 orders of magnitude higher we present a radiocarbon chronology from total organic carbon which implies that lift off of grounded ice in the 900 m deep marine basins surrounding ross island occurred by 10 100 14c years bp following lift off an ice shelf was maintained to the north of ross island until 8900 14c years bp we identify a phase of accelerated retreat at that time between the drygalski trough and ross island immediately preceding the timing of meltwater pulse 1b at 8900 14c years bp the calving line became pinned to ross island significantly decoupling from the grounding line and marking the transition from a retreating ice sheet to the development of the present ice shelf

eocene silicoflagellate and ebridian paleoceanography in the central arctic ocean the silicoflagellate and ebridian assemblages in early middle eocene arctic cores obtained by iodp expedition 302 acex were studied in order to decipher the paleoceanography of the upper water column the assemblages in lithologic unit 2 49 7 45 1 ma one of the biosiliceous intervals were usually endemic as compared to the assemblages that occurred outside of the arctic ocean the presence of these endemic assemblages is probably due to a unique environmental setting controlled by the degree of mixing between the low salinity arctic waters and relatively high salinity waters supplied from outside the arctic ocean such as the atlantic and possibly the western siberian sea using the basin to basin fractionation model the early middle eocene arctic ocean corresponds to an estuarine circulation type which includes the modern day black sea the abundant down core occurrence of ebridians strongly suggests the past presence of low salinity waters and may indicate that low oxygen concentrations prevailed in the euphotic layer on the basis of the ecology of the modern ebridian hermesinum adriaticum

cyclicity in the middle eocene central arctic ocean sediment record orbital forcing and environmental response 1 continuous x ray fluorescence scanning of middle eocene 46 ma core m0002a 55x 236 241 m composite depth recovered during integrated ocean drilling program expedition 302 revealed a strong cyclical signal in some major and trace geochemical elements we performed a multiproxy study of the same core which included organic geochemical sedimentological and biological parameters and integrated our results with available geochemical and physical properties data the target was to look for cyclicity in the several proxies investigate their frequency and understand the environmental response to the potential forcing results indicate that a higher terrigenous component corresponds to lower organic carbon concentration smaller contributions by angiosperm pollen and spores organic walled dinoflagellate cysts and chrysophyte cysts lower productivity shorter growing season for flowering plants and lower stratification but higher contributions by bisaccate pollen and diatoms drier conditions on land more marine conditions and higher terrigenous sand ice rafted debris ird our investigation shows that physical proxy parameters hold cyclicity with periods of about 50 and 100 cm and that these frequency components are compatible with a milankovitchtype orbital forcing representing precession and obliquity respectively the longer 100 cm cyclicity is also present in the biological pollen dinoflagellate cysts and siliceous microfossils and in the sedimentological ird proxies the environmental signal derived from the integrated multiproxy analysis suggests that in an enclosed arctic ocean at time of ice sea ice and glacial ice initiation the biological proxies responded more strongly to growing season length darkness whereas the terrigenous components directly driven by sea ice and or glacial ice formation and extent responded more directly to seasonal insolation

technologies for retrieving sediment cores in antarctic subglacial settings accumulations of sediment beneath the antarctic ice sheet contain a range of physical and chemical proxies with the potential to document changes in ice sheet history and to identify and characterize life in subglacial settings retrieving subglacial sediments and sediment cores presents several unique challenges to existing technologies this paper briefly reviews the history of sediment sampling in subglacial environments it then outlines some of the technological challenges and constraints in developing the corers being used in sub ice shelf settings e g george vi ice shelf and larsen ice shelf under ice streams e g rutford ice stream at or close to the grounding line e g whillans ice stream and in subglacial lakes deep under the ice sheet e g lake ellsworth the key features of the corers designed to operate in each of these subglacial settings are described and illustrated together with comments on their deployment procedures

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

exploring former subglacial hodgson lake antarctica paper ii palaeolimnology direct exploration of subglacial lakes buried deep under the antarctic ice sheet has yet to be achieved however at retreating margins of the ice sheet there are a number of locations where former subglacial lakes are emerging from under the ice but remain perennially ice covered one of these lakes hodgson lake 72 00 549 s 068 27 708 w has emerged from under more than 297 465 m of glacial ice during the last few thousand years this paper presents data from a multidisciplinary investigation of the palaeolimnology of this lake through a study of a 3 8 m sediment core extracted at a depth of 93 4 m below the ice surface the core was dated using a combination of radiocarbon optically stimulated luminescence and relative palaeomagnetic intensity dating incorporated into a chronological model stratigraphic analyses included magnetic susceptibility clast provenance organic content carbonate composition siliceous microfossils isotope and biogeochemical markers based on the chronological model we provisionally assign a well defined magnetic polarity reversal event at ca 165 cm in the lake sediments to the mono lake excursion ca 30 34 ka whilst osl measurements suggest that material incorporated into the basal sediments might date to 93 9 ka four stratigraphic zones a d were identified in the sedimentological data the chronological model suggests that zones a c were deposited between marine isotope stages 5 2 and zone a during stage 1 the holocene the palaeolimnological record tracks changes in the subglacial depositional environment linked principally to changing glacier dynamics and mass transport and indirectly to climate change the sediment composition in zones a c consists of fine grained sediments together with sands gravels and small clasts there is no evidence of overriding glaciers being in contact with the bed reworking the stratigraphy or removing this sediment this suggests that the lake existed in a subglacial cavity beneath overriding lgm ice in zone d there is a transition to finer grained sediments characteristic of lower energy delivery coupled with a minor increase in the organic content attributed either to increases in allochthonous organic material being delivered from the deglaciating catchment a minor increase in within lake production or to an analytical artefact associated with an increase in the clay fraction evidence of biological activity is sparse total organic carbon varies from 0 2 to 0 6 and cannot be unequivocally linked to in situ biological activity as comparisons of 13c and c n values with local reference data suggest that much of it is derived from the incorporation of carbon in catchment soils and gravels and possibly old co2 in meteoric ice we use the data from this study to provide guidelines for the study of deep continental subglacial lakes including establishing sediment geochronologies determining the extent to which subglacial sediments might provide a record of glaciological and environmental change and a brief review of methods to use in the search for life

high tide of the warm pliocene implications of global sea level for antarctic deglaciation we obtained global sea level eustatic estimates with a peak of 22 m higher than present for the pliocene interval 2 7 3 2 ma from backstripping in virginia united states new zealand and enewetak atoll north pacifi c ocean benthic foraminiferal 18 o values and mg ca 18 o estimates statistical analysis indicates that it is likely 68 confi dence interval that peak sea level was 22 5 m higher than modern and extremely likely 95 that it was 22 10 m higher than modern benthic foraminiferal 18 o values appear to require that the peak was 20 21 m our estimates imply loss of the equivalent of the greenland and west antarctic ice sheets and some volume loss from the east antarctic ice sheet and address the longstanding controversy concerning the pliocene stability of the east antarctic ice sheet

the blast in the past the rapidity and amount of carbon being released through human agency have been thought to be unprecedented not so it emerges from the evidence of anomalies in the ratios of carbon isotopes in an ocean core it seems that around 55 million years ago there was an equivalently swift and massive blast of carbon into the ocean and atmosphere the source was probably methane hydrates that are usually locked up in huge deposits on continental shelves

note on the importance of hydrocarbon fill for reservoir quality prediction in sandstones oil emplacement retarded the rate of quartz cementation in the brae formation deep water sandstone reservoirs of the miller and kingfisher fields united kingdom north sea thus preserving porosity despite the rocks being buried to depths of 4 km and 120 degreesc quartz precipitation rates were reduced by at least two orders of magnitude in the oil legs relative to the water legs important contrasts in quartz cement abundances and porosities have emerged between the oil and water legs where reservoirs have filled with hydrocarbons gradually over a prolonged period of time 15 m y the earlier the hydrocarbon fill the greater is the degree of porosity preservation failure to consider this phenomenon during field development could lead to overestimation of porosity and permeability in the water leg potentially leading in turn to poor decisions about the need for and placement of downflank water injectors during exploration the retarding effect of oil on quartz cementation could lead to the presence of viable reservoirs situated deeper than the perceived regional economic basement

visions of ice sheets in a greenhouse world abstract backstripped eustatic estimates from new jersey and the russian platform show large 25 m and rapid 18 o record highlights the enigma this was the warmest interval of the past 200 my yet it was bracketed by two inferred eustatic falls of 25 m that were associated with two large 0 75 deep sea 18 o increases 92 93 ma mid turonian and 96 ma mid cenomanian we reconcile records of warm high latitudes with glacioeustasy by proposing that late cretaceous early eocene ice sheets generally reached maximum volumes of 8 12 10 6 km 3 20 30 m glacioeustatic equivalent but did not reach the antarctic coast hence coastal antarctica hence deep water remained relatively warm even though there were significant changes in sea level as the result of glaciation unlike the oligocene and younger icehouse world these ice sheets only existed during short intervals of peak milankovitch insolation leaving antarctica ice free during much of the greenhouse late cretaceous to middle eocene these results highlight the need to re evaluate the paradigm that polar ice sheets did not exist during times of warm high latitude climates

antarctic cenozoic climate history from sedimentary records andrill and beyond mounting evidence from models and geological data implies that the antarctic ice sheet may behave in an unstable manner and retreat rapidly in response to a warming climate which is a key factor motivating efforts to improve estimates of antarctic ice volume contributions to future sea level rise here we review antarctic cooling history since peak temperatures of the middle eocene climatic optimum approx 50 ma to provide a framework for future initiatives to recover sediment cores from subglacial lakes and sedimentary basins in antarctica9s continental interior while the existing inventory of cores has yielded important insights into the biotic and climatic evolution of antarctica strata have numerous and often lengthy time breaks providing a framework of snapshots through time further cores and more work on existing cores are needed to reconcile antarctic records with the more continuous far field records documenting the evolution of global ice volume and deep sea temperature to achieve this we argue for an integrated portfolio of drilling and coring missions that encompasses existing methodologies using ship and sea ice ice shelf based drilling platforms as well as recently developed seafloor based drilling and subglacial access systems we conclude by reviewing key technological issues that will need to be overcome

exploring former subglacial hodgson lake antarctica paper i site description geomorphology and limnology at retreating margins of the antarctic ice sheet there are a number of locations where former subglacial lakes are emerging from under the ice but remain perennially ice covered this paper presents a site description of one of these lakes hodgson lake situated on southern alexander island west of the antarctic peninsula 72 00 549 s 68 27 708 w first we describe the physical setting of the lake using topographic and geomorphological maps second we determine local ice sheet deglaciation history and the emergence of the lake using cosmogenic isotope dating of glacial erratics cross referenced to optically stimulated luminescence dating of raised lake shoreline deltas formed during ice recession third we describe the physical and chemical limnology including the biological and biogeochemical evidence for life results show that the ice mass over hodgson lake was at least 295 m thick at 13 5 ka and has progressively thinned through the holocene with the lake ice cover reaching an altitude of c 6 5 m above the present lake ice sometime after 4 6 ka thick perennial ice cover persists over the lake today and the waters have remained isolated from the atmosphere with a chemical composition consistent with subglacial melting of catchment ice the lake is ultra oligotrophic with nutrient concentrations within the ranges of those found in the accreted lake ice of subglacial lake vostok total organic carbon and dissolved organic carbon are present but at lower concentrations than typically recorded in continental rain no organisms and no pigments associated with photosynthetic or bacterial activity were detected in the water column using light microscopy and high performance liquid chromatography increases in so4 and cation concentrations at depth and declines in o2 provide some evidence for sulphide oxidation and very minor bacterial demand upon o2 that result in small perhaps undetectable changes in the carbon biogeochemistry however in general the chemical markers of life are inconclusive and abiotic processes such as the diffusion of pore waters into the lake from its benthic sediments are far more likely to be responsible for the increased concentrations of ions at depth the next phases of this research will be to carry out a palaeolimnological study of the lake sediments to see what they can reveal about the history of the lake in its subglacial state and a detailed molecular analysis of the lake water and benthos to determine what forms of life are present combined these studies will test some of the methodologies that will be used to explore deep continental subglacial lakes

ice stream subglacial access for ice sheet history and fast ice flow the beamish project on rutford ice stream west antarctica and initial results on basal conditions

spells of low frequency oscillations and weather regimes in the northern hemisphere abstract the low frequency variability in the midlatitudes is described through an analysis of the oscillatory phenomena in order to isolate nearly periodic components of the atmospheric flow the multichannel version of the singular spectrum analysis m ssa is developed and applied to an nmc 32 year long set of 700 hpa geopotential heights in the same way that principal component analysis identifies the spatial patterns dominating the variability m ssa identifies dynamically relevant space time patterns and provides an adaptive filtering technique three major low frequency oscillations lfos are found with periods of 70 days 40 45 days and 30 35 days the 70 day oscillation consists of fluctuations in both position and amplitude of the atlantic jet with a poleward propagating anomaly pattern the 40 45 day oscillation is specific to the pacific sector and has a pronounced pacific north american pna structure in its high amplitude phase the 30 35 day mode is confined over the atlantic region

wissard at subglacial lake whillans west antarctica scientific operations and initial observations a clean hot water drill was used to gain access to subglacial lake whillans slw in late january 2013 as part of the whillans ice stream subglacial access research drilling wissard project over 3 days we deployed an array of scientific tools through the slw borehole a downhole camera a conductivity temperature depth ctd probe a niskin water sampler an in situ filtration unit three different sediment corers a geothermal probe and a geophysical sensor string our observations confirm the existence of a subglacial water reservoir whose presence was previously inferred from satellite altimetry and surface geophysics subglacial water is about two orders of magnitude less saline than sea water 0 37 0 41 psu vs 35 psu and two orders of magnitude more saline than pure drill meltwater 0 002 psu it reaches a minimum temperature of 0 558c consistent with depression of the freezing point by 7 019 mpa of water pressure subglacial water was turbid and remained turbid following filtration through 0 45 mm filters the recovered sediment cores which sampled down to 0 8 m below the lake bottom contained a macroscopically structureless diamicton with shear strength between 2 and 6 kpa our main operational recommendation for future subglacial access through water filled boreholes is to supply enough heat to the top of the borehole to keep it from freezing

the early miocene onset of a ventilated circulation regime in the arctic ocean deep water formation in the northern north atlantic ocean and the arctic ocean is a key driver of the global thermohaline circulation and hence also of global climate1 deciphering the history of the circulation regime in the arctic ocean has long been prevented by the lack of data from cores of cenozoic sediments from the arctic s deep sea floor similarly the timing of the opening of a connection between the northern north atlantic and the arctic ocean permitting deep water exchange has been poorly constrained this situation changed when the first drill cores were recovered from the central arctic ocean2 here we use these cores to show that the transition from poorly oxygenated to fully oxygenated ventilated conditions in the arctic ocean occurred during the later part of early miocene times we attribute this pronounced change in ventilation regime to the opening of the fram strait a palaeo geographic and palaeo bathymetric reconstruction of the arctic ocean together with a physical oceanographic analysis of the evolving strait and sill conditions in the fram strait suggests that the arctic ocean went from an oxygen poor lake stage to a transitional estuarine sea phase with variable ventilation and finally to the fully ventilated ocean phase 17 5 myr ago the timing of this palaeo oceanographic change coincides with the onset of the middle miocene climatic optimum3 although it remains unclear if there is a causal relationship between these two events

probe technologies for clean sampling and measurement of subglacial lakes it is 4 years since the subglacial lake community published its plans for accessing sampling measuring and studying the pristine and hitherto enigmatic and very different antarctic subglacial lakes vostok whillans and ellsworth this paper summarizes the contrasting probe technologies designed for each of these subglacial environments and briefly updates how these designs changed or were used differently when compared to previously published plans a detailed update on the final engineering design and technical aspects of the probe for subglacial lake ellsworth is presented this probe is designed for clean access is negatively buoyant 350 kg 5 2 m long 200 mm in diameter approximately cylindrical and consists of five major units i an upper power and communications unit attached to an optical and electrical conducting tether ii iv three water and particle samplers and v a sensors imaging and instrumentation pack tipped with a miniature sediment corer to date only in subglacial lake whillans have instruments been successfully deployed probe technologies for subglacial lake vostok 2014 15 and lake ellsworth 2012 13 were not deployed for technical reasons in the case of lake ellsworth because hot water drilling was unable to access the lake during the field season window lessons learned and opportunities for probe technologies in future subglacial access missions are discussed

ocean and climate response to north atlantic seaway changes at the onset of long term eocene cooling abstract around the early middle eocene boundary the first occurrence of contourite drift sediments and widespread deep ocean erosion indicate changes in the north atlantic ocean circulation interestingly these changes coincide with the first steps of cenozoic cooling from the paleogene greenhouse climate towards the modern icehouse the cause for this ocean circulation reorganization is poorly understood since modern water mass tracers may have worked fundamentally different in the past and the paleoceanographic proxy record is limited in both time and space as a result it is challenging to reliably reconstruct the climatic and tectonic boundary conditions e g atmospheric greenhouse gas concentration and the depth and geometry of developing and closing passages between ocean basins in this study we attempt to identify thresholds in tectonic gateway passages and atmospheric co2 concentration using the fully coupled earth system model cosmos indeed the simulation of earth s past climates can unravel the physical processes driving deep water formation in a greenhouse world specifically we use cosmos to evaluate the impact of changes in the north atlantic gateways at the early middle eocene boundary on the north atlantic deep western boundary currents under low obliquity configuration we find that northern component waters start to form when the greenland scotland ridge reaches a threshold depth of deeper than 200 m while the arctic ocean is still shut off from the north atlantic in this scenario the relatively deep greenland scotland ridge allows for sufficient inflow of warm salty atlantic surface waters into the nordic seas to initiate convection during winter cooling opening the seaway towards the arctic leads to a cessation of northern component water formation as it allows for inflow of brackish surface waters into the northern nordic seas hindering northern component water formation

early to middle eocene history of the arctic ocean from nd sr isotopes in fossil fish debris lomonosov ridge strontium and neodymium radiogenic isotope ratios in early to middle eocene fossil fish debris ichthyoliths from lomonosov ridge integrated ocean drilling program expedition 302 help constrain water mass compositions in the eocene arctic ocean between 55 and 45 ma the inferred paleodepositional setting was a shallow offshore marine to marginal marine environment with limited connections to surrounding ocean basins the new data demonstrate that sources of nd and sr in fish debris were distinct from each other consistent with a salinity stratified water column above lomonosov ridge in the eocene the 87sr 86sr values of ichthyoliths 0 7079 0 7087 are more radiogenic than eocene seawater requiring brackish to fresh water conditions in the environment where fish metabolized sr the 87sr 86sr variations probably record changes in the overall balance of river sr flux to the eocene arctic ocean between 55 and 45 ma and are used here to reconstruct surface water salinity values the nd values of ichthyoliths vary between 5 7 and 7 8 compatible with periodic or intermittent supply of nd to eocene arctic intermediate water aiw from adjacent seas although the norwegian greenland sea and north atlantic ocean were the most likely sources of eocene aiw nd input from the tethys sea via the turgay strait in early eocene time and the north pacific ocean via a proto bering strait also contributed

subglacial lake whillans seismic observations of a shallow active reservoir beneath a west antarctic ice stream abstract active subglacial lakes concentrate the distribution of water beneath ice sheets in both space and time seismic and surface observations from subglacial lake whillans slw west antarctica reveal that this active lake forms a persistent albeit fluctuating reservoir beneath whillans ice stream imaging and phase observations using active source seismic data show that slw is a perpetually shallow feature when surveyed near its low stand a water column was resolvable by seismic techniques along only 5 km of the 45 km profiled with a maximum depth of less than 8 m satellite altimetry shows that the high stand adds no more than 3 4 m to this this water column presents a suitable drill site at s 84 240 w 153 694 elsewhere the majority of the bed appears wet with soft sediment or water thicknesses of less than the imaging resolution of our data of approximately 2 m the surface expression of the active lake previously revealed by icesat elevation data and image differencing generally corresponds to the seismic estimate of soft sediment or water with notable exceptions occurring at the upstream and downstream ends of the lake these exceptions indicate that slw s water column is very shallow or absent in places at low stands or has disconnected or transiently active and inactive portions

cortex a shipboard xrf scanner for element analyses in split sediment cores abstract the cortex corescanner texel is a non destructive xrf system for the logging of split sediment cores it is a seaworthy instrument that remains active during heavy weather conditions the scanner produces reliable counts for k to sr highly correlated with concentrations measured with atomic absorption spectrometry aas the option to scan al si and elements heavier than sr is in preparation a core section of 1 m can be scanned at 2 cm intervals within an hour a maximum resolution of 1 mm can be achieved at present each region and sedimentary environment requires separate calibration in the nearby future the generator settings will be standardized which may result in the development of a standard calibration procedure because of the high resolution of its semi quantitative records the cortex is a useful tool for detailed time series analysis inter core correlation and shipboard analysis

orbital scale variations and timescales from the arctic ocean we investigate geochemical measurements from the arctic coring expedition to derive sedimentation rates for selected intervals in the early and middle eocene this analysis is performed by quantifying cyclical variations in physical property data and elemental concentrations derived with an x ray fluorescence xrf core scanner our results show that physical properties and xrf derived elemental concentrations are coherent and correlated to each other changes in elemental concentrations occur on depth scales from decimeters to meters and correspond to varying contributions of detrital minerals and biogenic silica we confirm and refine sedimentation rates of the order of 10 to 25 m ma 1 these rates were obtained independently through biostratigraphic and magnetostratigraphic methods we observe a strong imprint of astronomically sourced cycles particularly through climatic precession this observation allows us to test recently proposed theoretical calculations of insolation

paleoceanographic and paleoclimatic constraints on the global eocene diatom and silicoflagellate record abstract eocene diatom and silicoflagellate biostratigraphy are summarized and correlated with the most recent geologic time scale as well as with the global oxygen isotope and eustatic sea level curves the global distribution of eocene diatom silicoflagellate bearing sediments varies considerably reflecting changing oceanic gateways and paleoceanography with changing patterns that are punctuated by four major depositional events event 1 49 million years ago ma at the end of the early eocene climatic optimum eeco saw the cessation of diatom silicoflagellate deposition in epicontinental regions of the north sea region and in the northern russia and the onset of biosilica deposition in the arctic event 2 46 ma which coincided with intensification of the middle eocene cooling trend marked the widespread expansion of diatom silicoflagellate deposition in both the north and south atlantic a shift of diatom silicoflagellate deposition from the atlantic to the pacific began at event 3 at the end of the middle eocene climatic optimum meco 40 ma that was likely tied to the initial opening of the drake passage between antarctica and south america event 4 39 ma coincided with a major sea level fall and a widespread deep sea hiatus in the latest middle eocene late eocene diatom silicoflagellate deposition became more concentrated in middle to high latitude regions and coastal upwelling regions particularly in the pacific ocean tabulation of the first and last occurrences of 132 biostratigraphically important diatoms suggests increased species turnover during the latest paleocene to earliest eocene that may be in part due to a monographic effect an increasing rate of evolution of new diatom species between 46 and 43 ma and after 40 ma coincides respectively with the widespread expansion of diatom deposition in the atlantic and with an increased pole to equator thermal gradient that witnessed the expansion of diatoms in high latitude oceans and coastal upwelling settings

distributional variations in marine crenarchaeotal membrane lipids a new tool for reconstructing ancient sea water temperatures it has recently been shown that membrane lipids of marine crenarchaeota a ubiquitous and abundant component of plankton occur in relatively high concentrations in recent and ancient sediments in this study we investigated the environmental controls on the relative distribution of these lipids in surface sediments we especially focussed on temperature as it is known from the thermophilic genetic relatives of marine crenarchaetoa that the composition of their membrane strongly depends on growth temperature indeed a significant linear correlation r2 0 92 is found between the number of cyclopentane rings in sedimentary membrane lipids derived from marine crenarchaeota and the annual mean sea surface temperatures this suggests that the mechanism of physical adaptation of their membrane compositions to temperature is identical to that of their thermophilic relatives in turn archaeal lipid distributions in sediments may thus allow the reconstruction of sea water temperatures of ancient marine environments

diagenetic modeling to assess the relative timing of quartz cementation and brittle grain processes during compaction this study describes porosity reduction by brittle deformation and the application of touchstone sandstone diagenesis modeling software to assess the relative timing and interactions between grain fracturing and cement formation during burial compaction two examples from a previous study of compactional fracturing are used the oligocene frio formation gulf of mexico basin and the cambrian mount simon formation illinois basin united states grain fracturing during compaction creates intragranular fracture surfaces that are favorable sites for quartz nucleation compared to external grain surfaces that may bear coatings that inhibit the nucleation and growth of quartz cement thus the progress of brittle fracture processes during diagenesis affects quartz cementation in turn modeling of the quartz cementation process can serve to place fracturing into its proper context in burial history in the mount simon formation the extent of brittle deformation of quartz grains correlates with reconstructed effective stress at the onset of quartz cementation for frio formation samples however the extent of brittle deformation does not correlate well with reconstructed effective stress obtained using a one dimensional basin model that uses compaction disequilibrium as the dominant mechanism for overpressure generation judging from the observed degree of grain fracturing significant fluid overpressures in the frio may not have developed at the shallow depths indicated by our basin models the degree of compactional fracturing in sandstones constitutes observable evidence that can be used to decipher the complexities of pressure history

episodic fresh surface waters in the eocene arctic ocean it has been suggested on the basis of modern hydrology and fully coupled palaeoclimate simulations that the warm greenhouse conditions that characterized the early palaeogene period 55 45 myr ago probably induced an intensified hydrological cycle with precipitation exceeding evaporation at high latitudes little field evidence however has been available to constrain oceanic conditions in the arctic during this period here we analyse palaeogene sediments obtained during the arctic coring expedition showing that large quantities of the free floating fern azolla grew and reproduced in the arctic ocean by the onset of the middle eocene epoch approximately 50 myr ago the azolla and accompanying abundant freshwater organic and siliceous microfossils indicate an episodic freshening of arctic surface waters during an approximately 800 000 year interval the abundant remains of azolla that characterize basal middle eocene marine deposits of all nordic seas probably represent transported assemblages resulting from freshwater spills from the arctic ocean that reached as far south as the north sea the termination of the azolla phase in the arctic coincides with a local sea surface temperature rise from approximately 10 degrees c to 13 degrees c pointing to simultaneous increases in salt and heat supply owing to the influx of waters from adjacent oceans we suggest that onset and termination of the azolla phase depended on the degree of oceanic exchange between arctic ocean and adjacent seas

sediment core from beneath the amery ice shelf east antarctica suggests mid holocene ice shelf retreat the stability of floating ice shelves is an important indicator of ocean circulation and ice shelf mass balance a sub ice shelf sediment core collected during the austral summer of 2000 2001 from site am02 69 42 8 s 72 38 4 e on the amery ice shelf east antarctica contains a full and continuous record of glacial retreat the am02 core site is 80 km south of the floating ice shelf edge and contains a 0 5 m thick holocene surface layer of siliceous mud and diatom ooze of marine origin core data are supportive of sub ice shelf circulation models that predict the landward flow of oceanic water and prove that the landward transport of hemipelagic sediments occurs beneath floating ice shelves over distances of at least 80 km an increase in sea ice associated diatom deposition in the upper part of the holocene suggests that a major retreat of the amery ice shelf to at least 80 km landward of its present location may have occurred during the mid holocene climatic optimum

could changing ocean circulation have destabilized methane hydrate at the paleocene eocene boundary 1 during the paleocene eocene thermal maximum petm 55 ma marine and terrestrial carbon isotope values exhibit a negative shift of at least 2 5 indicative of massive destabilization of marine methane hydrates releasing 2000 gigatons of methane carbon the cause of the hydrate destabilization is unknown but has been speculated to be warming due to a change from high latitude to low latitude deepwater formation here we present results from a numerical ocean model indicating that a sudden switch of deepwater formation from southern to northern high latitudes caused middepth and deep ocean warming of 3 5 c the switch is caused by a slow increase in the intensity of the atmospheric hydrologic cycle as expected under increasing temperatures and consistent with petm sedimentary evidence deepened subtropical subduction prior to the thermohaline circulation switch causes warming of 1 4 c in limited areas at thermocline through upper intermediate depths which could destabilize methane hydrates gradually and at progressively greater depths warming accompanying a south to north switch in deepwater formation would produce sufficient warming to destabilize seafloor gas hydrates over most of the world ocean to a water depth of at least 1900 m

multiple miocene marine productivity events in west antarctica as recorded in upper miocene sediments beneath the ross ice shelf site j 9 abstract considerable debate surrounds the age and origin of sediments recovered from underneath the ross ice shelf antarctica at site j 9 although diatom biostratigraphy provides the best means of dating these sediments diatom fragmentation sediment reworking and microfossil assemblage mixing have led to conflicting interpretations regarding the age and depositional history of sediments collected as part of the ross ice shelf project r i s p our biostratigraphic approach differs from previous analyses of r i s p sediments by differentiating between microfossil assemblages recovered from the sediment matrix and from within abundant semi indurated sediment clasts diatomaceous clasts that were eroded and transported to site j 9 by glacier ice reveal the age and composition of unknown marine deposits in west antarctic interior basins in addition to rare reworked paleogene and cretaceous microfossils three distinct miocene diatom assemblages are recognized two from sediment clasts middle lower miocene and early middle miocene and a third restricted to matrix sediments middle upper miocene contrary to some published reports no microfossils unequivocally younger than middle late miocene are present other than modern subice shelf benthic foraminifera and ostracodes found in the uppermost sediments whether r i s p sediments are an in situ glacimarine deposit or a basal till is still uncertain however new data presented here support deposition by glacial marine processes during the middle late miocene an age indicated by foraminifera and the youngest diatom assemblage in r i s p pliocene and pleistocene marine sediments were probably stripped off by subsequent ice grounding events most likely in association with the ross sea unconformity reworked sedimentary clasts of diatomite suggest a highly productive open marine environment in west antarctica with intense productivity and limited glacial ice at sea level in the ross sea embayment during the middle early miocene

paleoenvironmental implications of cenozoic sediments from the central arctic ocean iodp expedition 302 using inorganic geochemistry 1 integrated ocean drilling program iodp expedition 302 arctic coring expedition acex recovered a unique sediment record from the central arctic ocean revealing that this region underwent major environmental fluctuations since the late cretaceous major and trace element composition of 1 300 samples were determined using x ray fluorescence xrf the results show significant compositional variability of the sediments with depth that can be attributed to changes in a provenance and pathways of detrital material b paleoenvironmental conditions and depositional processes and c diagenetic overprint of the primary record in addition to existing lithological units we introduce new geochemical units for a more process related approach interpreting the acex record in detail via the geochemical signature of siberian flood basalts we are able to reconstruct the discontinuous rifting and deepening of the central lomonosov ridge during the paleogene accompanied by changing current regimes and the onset of sea ice eocene biosiliceous sedimentation took place in a relatively shallow setting under predominantly anoxic bottom water conditions causing a positive anoxia productivity feedback although water column stratification was repeatedly interrupted by ventilation events anoxic to sulfidic conditions were even more extreme after biosilica production ceased and significant amounts of pyrite were deposited on the lomonosov ridge especially in organic matter rich paleogene deposits diagenetic processes obscured the paleoenvironmental signals fundamental environmental changes occurred in the middle eocene but geochemical and micropaleontological proxies point not to the identical sediment depth after approximately 26 ma of non deposition or erosion the middle miocene record shows the transition to dominantly oxic bottom water conditions although suboxic diagenesis seemingly affected these deposits

evidence for the long term sedimentary environment in an antarctic subglacial lake lakes beneath the antarctic ice sheet are of fundamental scientific interest for their ability to contain unique records of ice sheet history and microbial life in their sediments however no records of subglacial lake sedimentation have yet been acquired from beneath the interior of the ice sheet and understanding of sediment pathways processes and structure in subglacial lake environments remains uncertain here we present an analysis of seismic data from subglacial lake ellsworth showing that the lake bed comprises very fine grained sediments deposited in a low energy environment with low water and sediment fluxes minimum sediment thickness is 6 m the result of prolonged low sedimentation rates based on the few available analogues we speculate this sediment age range is a minimum of 150 ka and possibly 1 ma sediment mass movements have occurred but they are rare and have been buried by subsequent sedimentation we present a new conceptual model of subglacial lake sedimentation allowing a framework for evaluating processes in subglacial lake environments and for determining future lake access locations and interpreting subglacial lake samples

sedimentary processes at the base of a west antarctic ice stream constraints from textural and compositional properties of subglacial debris samples of sediments from beneath ice stream b at camp upb west antarctica provide the first opportunity to study the relationship between sediment properties and physical conditions in a sub ice stream environment piston coring in holes bored by hot water drilling yielded five 1 3 m long undisturbed subglacial sediment cores we analyzed granulometry composition and particle morphology in these cores the upb cores are composed of a clay rich unsorted diamicton containing rare marine diatoms sedimentary particles in these cores bear no evidence of the recent crushing or abrasion that is common in other subglacial sedimentary environments the presence of reworked diatoms and their state of preservation as well as the relative spatial homogeneity of this diamicton suggest that the upb cores sampled a several meter thick till layer and not in situ glacimarine sediments the till does incorporate material recycled from the subjacent poorly indurated tertiary glacimarine sediments of the ross sea sedimentary basin which extends beneath this part of the west antarctic ice sheet we propose that the lack of significant comminution in the upb till is ultimately due to its setting over these easily erodible clay rich source sediments the resulting fine grained till matrix inhibits glacial comminution because it facilitates buildup of high pore water pressures and hinders interparticle stress concentrations our observations are consistent with the conjecture that subglacial deformation of weak fine grained tills does not produce significant comminution of till debris elson 1988 based on our findings we hypothesize that extensive layers of weak till may develop preferentially where ice overrides preexisting poorly indurated fine grained sediments since such weak till layers create a permissive condition for ice streaming sub glacial geology may have an indirect but strong control over the location extent and basal mechanics of ice streams

continental ice in greenland during the eocene and oligocene the eocene and oligocene epochs approximately 55 to 23 million years ago comprise a critical phase in earth history an array of geological records supported by climate modelling indicates a profound shift in global climate during this interval from a state that was largely free of polar ice caps to one in which ice sheets on antarctica approached their modern size however the early glaciation history of the northern hemisphere is a subject of controversy here we report stratigraphically extensive ice rafted debris including macroscopic dropstones in late eocene to early oligocene sediments from the norwegian greenland sea that were deposited between about 38 and 30 million years ago our data indicate sediment rafting by glacial ice rather than sea ice and point to east greenland as the likely source records of this type from one site alone cannot be used to determine the extent of ice involved however our data suggest the existence of at least isolated glaciers on greenland about 20 million years earlier than previously documented at a time when temperatures and atmospheric carbon dioxide concentrations were substantially higher