eocene bipolar glaciation associated with global carbon cycle changes the transition from the extreme global warmth of the early eocene greenhouse climate 55 million years ago to the present glaciated state is one of the most prominent changes in earth s climatic evolution it is widely accepted that large ice sheets first appeared on antarctica 34 million years ago coincident with decreasing atmospheric carbon dioxide concentrations and a deepening of the calcite compensation depth in the world s oceans and that glaciation in the northern hemisphere began much later between 10 and 6 million years ago here we present records of sediment and foraminiferal geochemistry covering the greenhouse icehouse climate transition we report evidence for synchronous deepening and subsequent oscillations in the calcite compensation depth in the tropical pacific and south atlantic oceans from 42 million years ago with a permanent deepening 34 million years ago the most prominent variations in the calcite compensation depth coincide with changes in seawater oxygen isotope ratios of up to 1 5 per mil suggesting a lowering of global sea level through significant storage of ice in both hemispheres by at least 100 to 125 metres variations in benthic carbon isotope ratios of up to 1 4 per mil occurred at the same time indicating large changes in carbon cycling we suggest that the greenhouse icehouse transition was closely coupled to the evolution of atmospheric carbon dioxide and that negative carbon cycle feedbacks may have prevented the permanent establishment of large ice sheets earlier than 34 million years ago between 55 and 34 million years ago earth switched from a warm greenhouse ocean climate system to the icehouse that we now enjoy frustratingly the few oceanographic datasets that exist for this key period are of low resolution tripati et al now present measurements of sediment and foraminiferal geochemistry that provide the first continuous high resolution records for this period the data suggest that northern hemisphere glaciation started 34 million years ago rather than between 10 and 8 million years ago as previously thought

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

rapid stepwise onset of antarctic glaciation and deeper calcite compensation in the pacific ocean the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution is termed the calcite compensation depth at present this depth is 4 500 m with some variation between and within ocean basins the calcite compensation depth is linked to ocean acidity which is in turn linked to atmospheric carbon dioxide concentrations and hence global climate1 geological records of changes in the calcite compensation depth show a prominent deepening of more than 1 km near the eocene oligocene boundary 34 million years ago 2 when significant permanent ice sheets first appeared on antarctica3 4 5 6 but the relationship between these two events is poorly understood here we present ocean sediment records of calcium carbonate content as well as carbon and oxygen isotopic compositions from the tropical pacific ocean that cover the eocene oligocene boundary we find that the deepening of the calcite compensation depth was more rapid than previously documented and occurred in two jumps of about 40 000 years each synchronous with the stepwise onset of antarctic ice sheet growth the glaciation was initiated after climatic preconditioning7 by an interval when the earth s orbit of the sun favoured cool summers the changes in oxygen isotope composition across the eocene oligocene boundary are too large to be explained by antarctic ice sheet growth alone and must therefore also indicate contemporaneous global cooling and or northern hemisphere glaciation

simulation of heterogeneity creep damage and lifetime for loaded brittle rocks abstract a grain based heterogeneous numerical model originated from the discrete element method is developed and applied for lac du bonnet granite basing on voronoi cells the modelled microstructure considers different mineral components and grain size the model takes into account elastic grain and elasto plastic contact deformation inter and intra granular fracturing and lifetime prediction on basis of subcritical crack growth the procedure is successfully applied to simulate uniaxial compression tests brazilian tests and uniaxial creep tests the damage processes are studied in detail and mode i and mode ii fracture toughness were determined the proposed modelling allows the simulation of time dependent behaviour in terms of the damage process during primary secondary and tertiary creeps until the final failure characterized by macroscopic fracturing shear band and or macroscopic tensile fracture all simulations have shown reasonable agreement with macroscopic results obtained from lab tests on granite but have in addition delivered deeper insight into the microscopic damage process the proposed modelling approach is recommended for brittle rocks

marked decline in atmospheric carbon dioxide concentrations during the paleogene the relation between the partial pressure of atmospheric carbon dioxide pco2 and paleogene climate is poorly resolved we used stable carbon isotopic values of di unsaturated alkenones extracted from deep sea cores to reconstruct pco2 from the middle eocene to the late oligocene approximately 45 to 25 million years ago our results demonstrate that pco2 ranged between 1000 to 1500 parts per million by volume in the middle to late eocene then decreased in several steps during the oligocene and reached modern levels by the latest oligocene the fall in pco2 likely allowed for a critical expansion of ice sheets on antarctica and promoted conditions that forced the onset of terrestrial c4 photosynthesis

the influence of temperature ph and growth rate on the δ18o composition of inorganically precipitated calcite abstract the oxygen isotope composition of carbonate minerals varies with temperature as well as other environmental variables for carbonates that precipitate slowly under conditions that approach thermodynamic equilibrium the temperature dependence of 18 o uptake is the dominant signal and the measured 18 o content can be used as a paleotemperature proxy in the more common case where carbonate minerals grow in a regime where they are not in isotopic equilibrium with their host solution their oxygen isotope compositions are a convolution of multiple environmental variables here we present results from calcite growth experiments demonstrating the occurrence of large 2 non equilibrium oxygen isotope effects under conditions relevant to biogenic calcite growth and many natural inorganic systems we show that these non equilibrium effects vary systematically with ph and crystal growth rate an isotopic ion by ion crystal growth model quantifies the competing roles of temperature ph and growth rate and provides a general description of calcite water oxygen isotope fractionation under non equilibrium conditions the crystal growth model results show that 1 there are both equilibrium and kinetic contributions to calcite oxygen isotopes at biogenic growth rates 2 calcite does not directly inherit the oxygen isotope composition of dic even at fast growth rates 3 there is a kinetically controlled variation of about 1 per ph unit between ph 7 7 and 9 3 at constant growth rate for inorganic calcite as well as biogenic calcite and 4 extreme light isotope enrichments in calcite in alkaline environments are likely due to disequilibrium among dic species in aqueous solution the model can be extended to 13 c uptake into carbonates as well as clumped isotopes but additional data are needed to constrain the kinetic fractionation factors for carbon isotopes the experimental and model results constitute an important step in separating the relative influence of inorganic and biologic processes on isotopic fractionation and may aid the development of new paleoproxies based on non equilibrium effects

digital image based numerical modeling method for prediction of inhomogeneous rock failure abstract this paper presents a two dimensional digital image based numerical modeling method for prediction of inhomogeneous rock failure behavior under loadings actual inhomogeneities of granitic rocks are extracted from color images of the granite cross sections they are represented as the internal spatial distribution of three main granite minerals quartz feldspar and biotite the actual mineral spatial distribution on granite cross section is then incorporated into conventional numerical software packages to examine the rock failures under loading some digital image processing algorithms are presented to isolate and identify the main internal minerals and their distribution from color digital images a simple method is proposed to transform the actual image data into vector data for generation of finite meshes or grids the vector data are used directly as uniform square element meshes or grids that can be inputted into the existing software packages the finite difference software package flac is used as an example for the present investigation the conventional mohr coulomb and tensile stress failure criteria are used to examine the failure behavior of a circular granite cross section under the conventional brazilian indirect tensile test loading conditions the numerical results indicate that the vertical tensile crack initiates in a biotite located near the geometrical center of the granite cross section and the actual spatial distribution of the three minerals plays an important role in modifying the propagation pattern of the tensile crack from its theoretical position at the central vertical diameter of a homogeneous circular cross section the numerically predicted failure load and tensile strength values for inhomogeneous granite are much lower than the expected values

temperature dependence of oxygen isotope fractionation in coccolith calcite a culture and core top calibration of the genus calcidiscus abstract reconstructions of seawater temperature based on measurement of oxygen isotopes in carbonates mostly derive from analyses of bulk sediment samples or manually picked foraminifera the temperature dependence of 18 o fractionation in biogenic calcite was first established in the 1950s and the objective of the present study is to re evaluate this temperature dependence in coccolith calcite with a view to developing a robust proxy for reconstructing vital effect free 18 o values coccoliths the micron sized calcite scales produced by haptophyte algae that inhabit surface mixed layer waters are a dominant component of pelagic sediments despite their small size recent methodological developments allow species specific separation and thus isotopic analysis of coccoliths from bulk sediments this is especially the case for calcidiscus spp coccoliths that are relatively easy to separate out from other sedimentary carbonate grains including other coccolith taxa three strains of coccolithophores belonging to the genus calcidiscus and characterised by distinct cell and coccolith diameters were grown in the laboratory under controlled temperature conditions over a range from 15 to 26 c the linear relationship that relates 18 o fractionation to the temperature of calcification is here calibrated by the equation t c 5 83 18 o calcidiscus 18 o medium 4 83 r 0 98 the slope of the regression is offset of 1 1 from that of equilibrium calcite this offset corresponds to the physiologically induced isotopic effect or vital effect the direction of fractionation towards light isotopic values is coherent with previous reports but the intensity of fractionation in our dilute batch cultures was significantly closer to equilibrium compared to previously reported offset values no significant isotopic difference was found between the three calcidiscus coccolithophores ruling out a control of the cell geometry on oxygen isotope fractionation within species of this genus this also indicates that our culture calibration may be applied to all calcidiscus coccoliths found in the sediment we compared the culture calibration to 18 o measured from near monogeneric calcidiscus fractions separated out from core top sediments we found concordant 18 o fractionation factors for the core top calibration with a good linear coefficient r 0 94 the near monogeneric calcidiscus assemblages seem however to record slightly heaviest 18 o values compared to the data of culture study this discrepancy may be due to a possible seasonality effect on the production of calcidiscus coccoliths the uncertainty of the calibration is of similar magnitude to those of other proxies used for sst reconstruction such as foraminiferal 18 o or the alkenone undersaturation index this confirms that coccoliths can be used as a complementary or alternative substrate to foraminiferal shells for isotopic analyses comparing 18 o of coccoliths to these other sst proxies or developing an interspecific comparison of coccolith geochemistry may give insights into the carbonate chemistry of seawater through key periods of the geological record

significant southern ocean warming event in the late middle eocene a prominent middle eocene warming event is identified in southern ocean deep sea cores indicating that long term cooling through the middle and late eocene was not monotonic at sites on maud rise and the kerguelen plateau a distinct negative shift in 1 8 o values 1 0 is observed ca 41 5 ma this excursion is interpreted as primarily a temperature signal with a transient warming of 4 c over 600 k y affecting both surface and middle bathyal deep waters in the indian atlantic region of the southern ocean this isotopic event is designated as the middle eocene climatic optimum and is interpreted to represent a significant climatic reversal in the midst of middle to late eocene deep sea cooling the lack of a significant negative carbon isotope excursion as observed during the paleocene eocene thermal maximum and the gradual rate of high latitude warming suggest that this event was not triggered by methane hydrate dissociation rather a transient rise in pco 2 levels is suspected possibly as a result of metamorphic decarbonation in the himalayan orogen or increased ridge arc volcanism during the late middle eocene

global cooling during the eocene oligocene climate transition about 34 million years ago earth s climate shifted from a relatively ice free world to one with glacial conditions on antarctica characterized by substantial ice sheets how earth s temperature changed during this climate transition remains poorly understood and evidence for northern hemisphere polar ice is controversial here we report proxy records of sea surface temperatures from multiple ocean localities and show that the high latitude temperature decrease was substantial and heterogeneous high latitude 45 degrees to 70 degrees in both hemispheres temperatures before the climate transition were 20 c and cooled an average of 5 c our results combined with ocean and ice sheet model simulations and benthic oxygen isotope records indicate that northern hemisphere glaciation was not required to accommodate the magnitude of continental ice growth during this time

effect of heterogeneity of brittle rock on micromechanical extensile behavior during compression loading a grain based universal distinct element code model was developed to generate a deformable polygonal grain like structure to simulate the microstructure of brittle rock it takes into account grain scale heterogeneity including microgeometric heterogeneity grain scale elastic heterogeneity and microcontact heterogeneity the microgeometric heterogeneity can be used to match the grain size distribution of the rock the discrete element approach is able to simulate the microheterogeneity caused by elastic variation and contact stiffness anisotropy the modeling approach was evaluated using lac du bonnet granite and a aspo diorite the microheterogeneity played an important role in controlling both the micromechanical behavior and the macroscopic response when subjected to uniaxial compression loading the crack initiation stress was found to be controlled primarily by the microscale geometric heterogeneity while the microcontact heterogeneity controlled the strength characteristics the effect of heterogeneity on the distribution and evolution of tensile stresses and associated extension cracks was also examined

microstructural and geochemical perspectives on planktic foraminiferal preservation glassy versus frosty in recent years it has become apparent that the cool tropic paradox of paleogene and cretaceous greenhouse climates arises because of the diagenetic alteration of tropical planktic foraminiferal calcite near the seafloor yielding artificially high 18o values because the mg ca compositions of foraminiferal and inorganic calcite are thought to be quite different mg ca measurements should be a sensitive way of monitoring diagenetic alteration here we examine the extent of diagenetic alteration of eocene planktic foraminiferal calcite using scanning electron microscope imaging of foraminiferal test microstructures and geochemical 18o and mg ca analyses we compare microstructural and geochemical characteristics between given species exhibiting two contrasting states of preservation those that appear frosty under reflected light and those that appear glassy microstructural evidence reveals extensive diagenetic alteration of frosty foraminiferal tests at the micron scale while 18o analyses document consistently higher 18o and therefore lower paleotemperatures in this material yet we find that 18o offsets between species in these frosty foraminiferal assemblages appear to be generally preserved suggesting that frosty foraminifera remain valuable for generating relatively short approximately 1 myr paleoceanographic time series that do not demand absolute estimates of paleotemperature we also find that the observed increase in mg ca for planktic foraminifera exhibiting diagenetic alteration compared to glassy taphonomies is far smaller than would be expected from the addition of inorganic calcite based on laboratory derived mg2 partition coefficients our findings imply that a much lower mg2 partition coefficient controls inorganic calcite formation in deep sea sedimentary sections in accordance with the findings of baker et al 1982

opening the gateways for diatoms primes earth for antarctic glaciation the abrupt onset of antarctic glaciation during the eocene oligocene transition 33 7 ma oi1 is linked to declining atmospheric pco2 levels yet the mechanisms that forced pco2 decline remain elusive biogenic silicon cycling is inextricably linked to both long and short term carbon cycling through the diatoms siliceous walled autotrophs which today account for up to 40 of primary production it is hypothesised that during the late eocene a sharp rise in diatom abundance could have contributed to pco2 drawdown and global cooling by increasing the proportion of organic carbon buried in marine sediment diatom and sponge silicon isotope ratios 30si are here combined for the first time to reconstruct the late eocene early oligocene ocean silicon cycle and provide new insight into the role of diatom productivity in antarctic glaciation at odp site 1090 in the southern ocean a 0 6 rise in diatom 30si through the late eocene documents increasing diatom silicic acid utilisation with high near modern values attained by the earliest oligocene a concomitant 1 5 decline in sponge 30si at odp site 689 on the maud rise tracks an approximate doubling of intermediate depth silicic acid concentration in the high southern latitudes intermediate depth silicic acid concentration peaked at 31 5 ma coincident with the final establishment of a deepwater pathway through the tasman gateway and drake passage these results suggest that upwelling intensification related to the spin up of a circum antarctic current may have driven late eocene diatom proliferation organic carbon burial associated with higher diatom abundance and export provides a mechanism that can account for pco2 drawdown not only at but also prior to antarctic glaciation as required by a pco2 threshold mechanism for ice sheet growth

surface features of uniaxial tensile fractures and their relation to rock anisotropy in inada granite abstract uniaxial tensile fractures parallel to the rift grain and hardway planes were formed in inada granite most of the fractures split the rock forming mineral grains as transgranular paths under microscopic observations the surface topography of the fractures was measured by the stereo photogrammetric technique and is different in different orientations the rift parallel uniaxial fracture has the smoothest surface and the grain parallel fractures are smoother than hardway parallel fractures the mineral compositions are also different on the failed surfaces of different directions the rift parallel fractures have almost the same constituent mineral ratio as the parent rock however the grain parallel fractures pass preferentially through feldspar grains and contain less quartz grains as compared to the bulk composition of the parent rock in addition it is remarkable on hardway parallel fractures it is considered that the differences of surface topography and mineral compositions are caused by preferred orientations and spatial distributions of pre existing microcracks in inada granite

atmospheric carbon dioxide through the eocene oligocene climate transition geological and geochemical evidence1 2 3 indicates that the antarctic ice sheet formed during the eocene oligocene transition4 33 5 34 0 million years ago modelling studies5 6 suggest that such ice sheet formation might have been triggered when atmospheric carbon dioxide levels fell below a critical threshold of 750 p p m v but the timing and magnitude of relative to the evolution of the ice sheet has remained unclear here we use the boron isotope ph proxy7 8 on exceptionally well preserved carbonate microfossils from a recently discovered geological section in tanzania9 10 to estimate before during and after the climate transition our data suggest that a reduction in occurred before the main phase of ice growth followed by a sharp recovery to pre transition values and then a more gradual decline during maximum ice sheet growth was between 450 and 1 500 p p m v with a central estimate of 760 p p m v the ice cap survived the period of recovery although possibly with some reduction in its volume implying as models predict11 a nonlinear response to climate forcing during melting overall our results confirm the central role of declining in the development of the antarctic ice sheet in broad agreement with carbon cycle modelling12 and help to constrain mechanisms and feedbacks associated with the earth s biggest climate switch of the past 65 myr

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

constraints on the vital effect in coccolithophore and dinoflagellate calcite by oxygen isotopic modification of seawater in this study we show that there are independent controls of 18o 16o and 13c 12c fractionation in coccolithophore and dinoflagellate calcite due to the contrasting kinetics of each isotope system we demonstrate that the direction and magnitude of the oxygen isotope fractionation with respect to equilibrium is related to the balance between calcification rate and the replenishment of the internal pool of dissolved inorganic carbon dic as such in fast growing cells such as those of emiliania huxleyi and gephyrocapsa oceanica forming the so called heavy group calcification of the internal carbon pool occurs faster than complete isotopic re adjustment of the internal dic pool with h2o molecules hence coccoliths reflect the heavy oxygen isotope signature of the co2 overprinting the whole dic pool conversely in large and slow growing cells such as coccolithus pelagicus ssp braarudii complete re equilibration is achieved due to limited influx of co2 leading to coccoliths that are precipitated in conditions close to isotopic equilibrium equilibrium group species exhibiting the most negative oxygen isotope composition such as calcidiscus leptoporus light group precipitate coccolith under increased ph in the coccolith vesicle as previously documented by the carbonate ion effect we suggest that for the carbon isotope system any observed deviation from isotopic equilibrium is only apparent as the carbon isotopic composition in coccolith calcite is controlled by a rayleigh fractionation originating from preferential incorporation of 12c into organic matter therefore species with low pic poc ratios as e huxleyi and g oceanica are shifted towards positive carbon isotope values as a result of predominant carbon fixation into the organic matter by contrast cells with higher pic poc as c braarudii and c leptoporus maintain to some extent the original negative isotopic composition of the co2 the calcareous dinoflagellate thoracosphaera heimii exhibits different behaviour for both isotopic systems in particular with respect to its very negative carbon isotope composition owing to coeval intra and extracellular biomineralisation in this group in this study we also investigate the sensitivity of 18o 16o fractionation to varying ambient oxygen isotope composition of the medium for inorganic coccolithophore and dinoflagellate calcite precipitated under controlled laboratory conditions the varying responses of different taxa to increased oxygen isotope composition of the growth medium may point to a potential bias in sea surface temperature reconstructions that are based on the oxygen isotopic compositions of sedimentary calcite especially during times of changing seawater oxygen isotopic composition overall this study represents an important step towards establishing a mechanistic understanding of the vital effect in coccolith and dinoflagellate calcite and provides valuable information for interpreting the geochemistry of the calcareous nannofossils in the sedimentary record at both monospecific and interspecies levels

a comparison of volcanic eruption processes on earth moon mars io and venus the silicate planets and satellites display a wide range of physical chemical and atmospheric characteristics which may influence the nature of volcanism a major geological process common to the evolution of the surfaces of these bodies consideration of the process of magma ascent and eruption from first principles allows predictions to be made concerning volcanic eruption styles and expected landforms and deposits on each planetary body examination of actual land forms and deposits in light of these predictions leads to a better understanding of the nature of volcanic eruption processes and outlines outstanding problems

novel grain based model for simulation of brittle failure of alxa porphyritic granite abstract a grain based model gbm is generally employed by many researchers to simulate the microcracking process of crystalline brittle rock by the distinct element method in this study a novel grain based model ngbm in two dimensional particle flow code 5 0 pfc2d 5 0 is proposed to emulate the brittle failure of crystalline rock first the ngbm scheme is introduced in which the flat joint model is employed to model the contacts in mineral grains and the smooth joint model is assigned to the grain interface contacts then compressive tests are performed using alxa porphyritic granite and the strength values are fitted with the hoek brown failure criterion third a ngbm was generated based on the petrographic texture of realistic rock such as mineral constituents grain size and distribution the input microscale parameters are carefully calibrated according the experimental results finally this model is applied to study the microcracking process of alxa porphyritic granite and the influence of spatial distribution of minerals it is found that a relatively high ratio of uniaxial compressive strength to tensile strength of each mineral or synthetic samples can be reproduced by the ngbm moreover the simulated results show this model can capture the nonlinear characteristic of the hoek brown failure criterion after modeling numerous mineral grains were cut across which is consistent with the actual experimental observation the tensile crack is over the shear crack in the models while the number of intra grain shear crack increases dramatically with increasing confining pressure in addition the numerical results indicate that the effect of spatial distribution of minerals has limited influence on the evolution of microcracks but has great impact on microcrack distribution in summary the proposed ngbm in pfc2d can well reproduce the realistic failure process of granitic rocks under different loading conditions

discrete element modeling on fracture coalescence behavior of red sandstone containing two unparallel fissures under uniaxial compression abstract particle flow code pfc2d was adopted to carry out a discrete element modeling dem for the fracture coalescence behavior of red sandstone specimens containing two unparallel fissures under uniaxial compression the numerical micro parameters of red sandstone were firstly validated from the experimental results of intact specimen and were then checked with the experimental results for red sandstone containing two unparallel fissures under uniaxial compression four key factors i e the axial stress axial strain curve the peak strength and elastic modulus the ultimate failure mode and the crack coalescence process were put forward to discriminate the rightness and reasonability of numerical simulated results a systematic simulation for red sandstone specimens was performed to compare quantitatively the numerical results with the experimental results which showed that the numerical simulated results were in good agreement with the experimental results numerical simulated results showed that the peak strength and elastic modulus of red sandstone containing two unparallel fissures were increased at the fissure angle 2 90 before decreasing up to our maximum fissure angle of 180 however the ratio of lateral stiffness of red sandstone containing two unparallel fissures firstly decreased and then increased with the increase of 2 and had a lowest value at 2 90 the shear and tensile crack numbers of red sandstone reaching the peak strength with respect to 2 were also discussed through the numerical simulation we made a detailed summarization for the crack initiation propagation and coalescence in the entire deformation process of red sandstone which was found to be dependent to 2 the simulated cracks replicated most of the phenomena observed during the experiment finally the stress field in the red sandstone specimens containing two unparallel fissures was obtained which revealed the fracture coalescence mechanism of flawed red sandstone under uniaxial compression

mars mapping with delay doppler radar mars radar imaging results from arecibo 12 6 cm observations are presented the images were derived from delay doppler mapping using a coded long pulse technique to mitigate the effects of echo overspreading images of the depolarized echo are used to identify regions of high decimeter scale roughness some of the strongest echo features are located on the major shield volcanoes or on relatively young off shield flows such as the olympus and pavonis lava aprons the shields themselves have highly irregular radar signatures suggesting complex volcanic histories some mars radar features have twice the depolarized brightness of the roughest terrestrial lava flows apparently due to higher levels of multiple scattering from surfaces of spectacular roughness or from volume scattering low brightness smooth areas are associated with older surfaces such as fractured and highland terra as well as with terrain interpreted to be debris lobes ash flows and aureoles in particular a close connection was found between the 12 6 cm counterpart of the stealth feature and the medusae fossae formation postulated to be deep ignimbrite deposits marte valus is anomalous in being the only outflow channel showing strongly enhanced echoes which supports the idea that this channel and the elysium basin that it drained are filled with lava flows a weak radar feature was found for the south polar residual ice cap comparisons with goldstone 3 5 cm data show that the south polar enhancement is much weaker at 12 6 cm than at 3 5 cm indicating that the southern ice cap becomes optically thin at the longer wavelength a north polar enhancement has also been found which is comparable in strength to the 12 6 cm south polar feature

thresholds for cenozoic bipolar glaciation the long standing view of earth s cenozoic glacial history calls for the first continental scale glaciation of antarctica in the earliest oligocene epoch 33 6 million years ago1 followed by the onset of northern hemispheric glacial cycles in the late pliocene epoch about 31 million years later2 the pivotal early oligocene event is characterized by a rapid shift of 1 5 parts per thousand in deep sea benthic oxygen isotope values3 oi 1 within a few hundred thousand years4 reflecting a combination of terrestrial ice growth and deep sea cooling the apparent absence of contemporaneous cooling in deep sea mg ca records4 5 6 however has been argued to reflect the growth of more ice than can be accommodated on antarctica this combined with new evidence of continental cooling7 and ice rafted debris8 9 in the northern hemisphere during this period raises the possibility that oi 1 represents a precursory bipolar glaciation here we test this hypothesis using an isotope capable global climate ice sheet model that accommodates both the long term decline of cenozoic atmospheric co2 levels10 11 and the effects of orbital forcing12 we show that the co2 threshold below which glaciation occurs in the northern hemisphere 280 p p m v is much lower than that for antarctica 750 p p m v therefore the growth of ice sheets in the northern hemisphere immediately following antarctic glaciation would have required rapid co2 drawdown within the oi 1 timeframe to levels lower than those estimated by geochemical proxies10 11 and carbon cycle models13 14 instead of bipolar glaciation we find that oi 1 is best explained by antarctic glaciation alone combined with deep sea cooling of up to 4 c and antarctic ice that is less isotopically depleted 30 to 35 than previously suggested15 16 proxy co2 estimates remain above our model s northern hemispheric glaciation threshold of 280 p p m v until 25 myr ago but have been near or below that level ever since10 11 this implies that episodic northern hemispheric ice sheets have been possible some 20 million years earlier than currently assumed although still much later than oi 1 and could explain some of the variability in miocene sea level records

the influence of kinetics on the oxygen isotope composition of calcium carbonate paleotemperature reconstructions rely on knowledge of the equilibrium separation of oxygen isotopes between aqueous solution and calcium carbonate although oxygen isotope separation is expected on theoretical grounds the temperature dependence remains uncertain because other factors such as slow exchange of isotopes between dissolved co2 species and water can obscure the temperature signal this is problematic for crystal growth experiments on laboratory timescales and for interpreting the oxygen isotope composition of crystals formed in natural settings we present results from experiments in which inorganic calcite is precipitated in the presence of 0 25 m dissolved bovine carbonic anhydrase ca the presence of dissolved ca accelerates oxygen isotope equilibration between the dissolved carbon species co2 h2co3 hco3 co32 and water thereby eliminating this source of isotopic disequilibrium during calcite growth the experimental results allow us to isolate for the first time kinetic oxygen isotope effects occurring at the calcite water interface we present a framework of ion by ion growth of calcite that reconciles our new measurements with measurements of natural cave calcites that are the best candidate for having precipitated under near equilibrium conditions our findings suggest that isotopic equilibrium between calcite and water is unlikely to have been established in laboratory experiments or in many natural settings the use of ca in carbonate precipitation experiments offers new opportunities to refine oxygen isotope based geothermometers and to interrogate environmental variables other than temperature that influence calcite growth rates

changes in sea surface conditions in the equatorial pacific during the middle miocene pliocene as inferred from coccolith geochemistry abstract this study presents a new alkenone derived sea surface temperature sst record and 18onoelaerhabdaceae data of the 2 5 m carbonate fractions from the iodp site u1338 located in the eastern equatorial pacific eep over the miocene pliocene our data and those available from other sites of the same area show the establishment of a cold tongue during the early pliocene 4 4 3 6 ma sst and 18onoelaerhabdaceae time series indicate periods of significant salinity variations comparison with the 18obenthic curve from sediment cores of the equatorial pacific ocean allows us to distinguish between global changes and local surface salinity variations in the eep ice sheet growth and evaporation precipitation are then discussed as possible drivers of such changes along with the role of central american and the indonesian seaway restriction our data suggest a shallowing of the thermocline in the eep between 6 8 and 6 ma and its shoaling between 4 8 and 4 0 ma suggesting the appearance of the cold tongue steph et al 2010 the pliocene climate transition would therefore not be primarily driven by northern hemisphere glaciation

ancient and modern slopes in the tharsis region of mars the directions of lava flows in the tharsis region of mars are used to identify regional palaeo slopes vent areas and local topography a comparison is made between these flow directions and the present day radar measured topography good agreement between these data sets indicates that little infra regional tectonic deformation has occurred following the emplacement of the preserved lavas

the olympus mons aureole formation by gravitational spreading new observations of the aureole deposits of olympus mons are in agreement with previous suggestions that the aureole lobes could have been formed by movement under gravity away from the observed scarps the characteristic corrugated morphology of the aureole is probably secondary formed by erosion along structural inhomogeneities geometries of the corrugations and translational faults in the aureole deposits favor a mechanism of emplacement that involves material with substantial shear strength rather than viscous flow estimates of the aspect ratios of terrestrial landslides nappes and ash flows suggest that the aureole deposits are more similar in overall shape to slide emplaced bodies than to pyroclastic flows although martian physical conditions permit the formation of ash flows there is no positive evidence for their existence a gravitational spreading mechanism is proposed that involves imbricate thrusting in distal regions analogous with terrestrial thrust sheets corrugations in the aureole developed by erosion along imbricate or listric faults basal shear stresses on the decoupling surface may have been of the order of 106 pa 10 bars the nature of the decoupling surfaces in the proximal regions is uncertain but is likely to have been the topographic surface in distal parts the aureole deposits were probably emplaced as a series of sheets by spreading under gravity from an ancestral olympus mons which extended farther to the northwest than does the present volcano as a result of the accumulation of lavas under the then prevailing stress conditions recent lava eruptions from the volcano have been concentrated in northeast and southwest sectors indicating a changed stress regime since aureole emplacement

rapid cenozoic glaciation of antarctica induced by declining atmospheric co2 the sudden widespread glaciation of antarctica and the associated shift towards colder temperatures at the eocene oligocene boundary 34 million years ago refs 1 4 is one of the most fundamental reorganizations of global climate known in the geologic record the glaciation of antarctica has hitherto been thought to result from the tectonic opening of southern ocean gateways which enabled the formation of the antarctic circumpolar current and the subsequent thermal isolation of the antarctic continent5 here we simulate the glacial inception and early growth of the east antarctic ice sheet using a general circulation model with coupled components for atmosphere ocean ice sheet and sediment and which incorporates palaeogeography greenhouse gas changing orbital parameters and varying ocean heat transport in our model declining cenozoic co2 first leads to the formation of small highly dynamic ice caps on high antarctic plateaux at a later time a co2 threshold is crossed initiating ice sheet height mass balance feedbacks that cause the ice caps to expand rapidly with large orbital variations eventually coalescing into a continental scale east antarctic ice sheet according to our simulation the opening of southern ocean gateways plays a secondary role in this transition relative to co2 concentration

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

paleogene opening of drake passage the timing of events leading to the earliest connection between the pacific and atlantic oceans at drake passage is controversial but important because gateway opening probably had a profound effect on global circulation and climate a rigorous new analysis of marine geophysical data demonstrates a major change in the motion of the south american and antarctic plates at about 50 ma from n s to wnw ese accompanied by an eightfold increase in separation rate this would have led to crustal extension and thinning and perhaps the opening of small oceanic basins with the probable formation of a shallow b1000 m gateway during the middle eocene no change in south american antarctic motion is observed near the eocene oligocene boundary but a deep water connection developed between 34 and 30 ma when continued extension led to the initiation of seafloor spreading at the west scotia ridge these timings correlate with events seen in the oxygen isotope record from benthic foraminera and support the view that drake passage opening was the trigger for abrupt eocene oligocene climate deterioration and the growth of extensive antarctic ice sheets d 2005 elsevier b v all rights reserved

the ascraeus mons fan shaped deposit volcano ice interactions and the climatic implications of cold based tropical mountain glaciation abstract amazonian aged fan shaped deposits extending to the northwest of each of the tharsis montes in the tharsis region on mars have been interpreted to have originated from mass wasting volcanic tectonic and or glacial processes we use new data from mro mgs and odyssey to characterize these deposits building on recent evidence for cold based glacial activity at pavonis mons and arsia mons we interpret the smaller ascraeus fan shaped deposit to be of glacial origin our geomorphological assessment reveals a number of characteristics indicative of glacial growth and retreat including 1 a ridged facies interpreted to be composed of drop moraines emplaced during episodic glacial advance and retreat 2 a knobby facies interpreted to represent vertical downwasting of the ice sheet and 3 complex ridges showing a cusp like structure we also see evidence of volcano ice interactions in the form of 1 an arcuate inward facing scarp interpreted to have formed by the chilling of lava flows against the glacial margin 2 a plateau feature interpreted to represent a subglacial eruption and 3 knobby facies superimposed on flat topped flows with leveed channels interpreted to be subglacial inflated lava flows that subsequently drained and are covered by glacial till we discuss the formation mechanisms of these morphologies during cold based glacial activity and concurrent volcanism on the basis of a mid to late amazonian age 250 380 ma established from crater size frequency distribution data we explore the climatic implications of recent glaciation at low latitudes on mars gcm results show that increased insolation to the poles at high obliquities 45 forces sublimation of polar ice which is transported to lower latitudes and deposited on the flanks of the tharsis montes we assess how local orographic effects the mass balance of the glacier and the position of equilibrium line altitudes all played a role in producing the observed geomorphologies in doing so we outline a glacial history for the evolution of the ascraeus mons fan shaped deposit and compare its initiation growth and demise with those of arsia mons and pavonis mons

martian tharsis bulge insight to mantle related processes abstract when examining the tectonics of the one plate planet mars it is possible to test and even to develop further some ideas with respect to earth s plate tectonic paradigm the definition of terrestrial plate movements does not unambiguously identify the actual mantle processes involved one way to leam more about the endogenous development of planets is to undertake comparative studies the main tectonic structures of mars are interpreted here to give information concerning mantle processes which may relate to those processes driving earth s plate tectonics but which in the case of mars have been insufficient to break martian lithosphere into plates but which have been sufficient to cause rift block tectonics and to build the tharsis bulge

planetary radar astronomy planetary radar research reported during 1979 1982 was highlighted by radar observations of venus by the pioneer venus spacecraft earth based high resolution imaging of venus and the moon construction of accurate topographic profiles for martian tropical regions observational and theoretical advances in relating the radar signatures of mars and the moon to surface characteristics and the initial radar detections of echoes from a comet and a mainbelt asteroid this review begins with a brief synopsis of radar definitions and technical terminology and then summarizes recent results for individual targets readers interested in radar astronomy prior to the current quadrennium are directed to excellent reviews by jurgens 1982a pettengill 1978 evans 1969 muhleman 1966 and pettengill and shapiro 1965 detailed descriptions of planetary radar techniques include pettengill 1970 and evans and hagfors 1968

early paleogene temperature history of the southwest pacific ocean reconciling proxies and models we present a new multiproxy tex86 18o and mg ca marine temperature history for canterbury basin eastern new zealand that extends from middle paleocene to middle eocene including the paleocene eocene thermal maximum petm and early eocene climatic optimum eeco in light of concerns that proxy based sea surface temperature sst estimates are untenably warm for the southwest pacific during the eocene we review the assumptions that underlie the proxies and develop a preliminary paleo calibration for tex86 that is based on four multiproxy eocene records that represent an sst range of 15 34 c for the southwest pacific paleogene we show that tex86l exhibits the best fit with the eocene paleo calibration ssts derived from related proxies tex86h 1 tex86 exhibit a systematic warm bias that increases as tex86 values decrease a warm bias of 4 7 c where tex86 0 7 the tex86l proxy indicates that southwest pacific sst increased by 10 c from middle paleocene to early eocene with sst maxima of 26 28 c tropical during the petm and eeco and an sst minimum of 13 16 c cool warm temperate at the middle late paleocene transition 58 7 ma the base of the eeco is poorly defined in these records but the top is well defined in canterbury basin by a 2 5 c decrease in sst and bottom water temperature bwt in the latest early eocene 49 3 ma bwt falls from a maximum of 18 20 c in the eeco to 12 14 c in the middle eocene overall cooler temperatures are recorded in the mid waipara section which may reflect a deeper 500 m water depth and less neritic depositional setting compared with hampden and odp 1172 200 m water depth the high ssts and bwts inferred for the petm and eeco can be reconciled with eocene coupled climate model results if the proxies are biased towards seasonal maxima and the likely effect of a proto east australian current is taken into account

arecibo radar imagery of mars the major volcanic provinces abstract we present earth based radar images of mars obtained with the upgraded arecibo s band 12 6 cm radar during the 2005 2012 oppositions the imaging was done using the same long code delay doppler technique as for the earlier pre upgrade imaging but at a much higher resolution 3 km and for some regions a more favorable sub earth latitude this has enabled us to make a more detailed and complete mapping of depolarized radar reflectivity a proxy for small scale surface roughness over the major volcanic provinces of tharsis elysium and amazonis we find that vast portions of these regions are covered by radar bright lava flows exhibiting circular polarization ratios close to unity a characteristic that is uncommon for terrestrial lavas and that is a likely indicator of multiple scattering from extremely blocky or otherwise highly disrupted flow surfaces all of the major volcanoes have radar bright features on their shields although the brightness distribution on olympus mons is very patchy and the summit plateau of pavonis mons is entirely radar dark the older minor shields paterae and tholi are largely or entirely radar dark which is consistent with mantling by dust or pyroclastic material other prominent radar dark features include the fan shaped deposits possibly glacial associated with the three major tharsis montes shields various units of the medusae fossae formation a region south and west of biblis patera where stealth deposits appear to obscure tharsis flows and a number of dark halo craters with radar absorbing ejecta blankets deposited atop surrounding bright flows several major bright features in tharsis are associated with off shield lava flows these include the olympus mons basal plains volcanic fields east and south of pavonis mons the daedalia planum flows south of arsia mons and a broad expanse of flows extending east from the tharsis montes to echus chasma the radar bright lava plains in elysium are concentrated mainly in cerberus and include the fluvio volcanic channels of athabasca valles grjota valles and marte valles as well as an enigmatic region at the southern tip of the cerberus basin some of the cerberus bright features correspond to the distinctive platy ridged flows identified in orbiter images the radar bright terrain in amazonis planitia comprises two distinct but contiguous sections a northern section formed of lavas and sediments debouched from marte valles and a southern section whose volcanics may derive in part from local sources this south amazonis region shows perhaps the most complex radar bright structure on mars and includes features that correspond to platy ridged flows similar to those in cerberus

multi peak deformation behavior of jointed rock mass under uniaxial compression insight from particle flow modeling abstract evaluation of mechanical properties of jointed rock mass is very important for geological engineering problems related to underground opening slope stability dam foundation and hydraulic fracturing etc it is generally known that both strength and deformability of rock mass may change with joint geometry and arrangement by pfc particle flow code modeling this paper aims at understanding the damage mechanism of the multi peak deformation behavior of jointed rock mass with different joint orientations and continuity factors under uniaxial compression observed in the physical model tests with the smooth joint contact model not only has the inherent roughness in conventional joint model been avoided but also we can monitor the joint aperture number of closed joints and forces acting on the joints during the damage process it is shown that mobilization of joint strength plays an important role in the multi peak deformation behavior of rock mass if the joint strength is slightly mobilized or immobilized i e most joints keep open during the test strain softening occurs however if the joint strength is significantly or fully mobilized yielding platform or strain hardening may happen

numerical methods in rock mechanics the purpose of this civilzone review paper is to present the techniques advances problems and likely future development directions in numerical modelling for rock mechanics and rock engineering

control of ambient ph on growth and stable isotopes in phytoplanktonic calcifying algae the present work examines the relationship between ph induced changes in growth and stable isotopic composition of coccolith calcite in two coccolithophore species with a geological perspective these species gephyrocapsa oceanica and coccolithus pelagicus with differing physiologies and vital effects possess a growth optimum corresponding to average ph of surface seawater in the geological period during their first known occurrence the ancestral c pelagicus has much wider ph tolerance in terms of growth rates than the more recently evolved g oceanica diminished growth rates are explained by the challenge of proton translocation into the extracellular environment at low ph and enhanced aqueous co2 limitation at high ph reducing the cell dynamics in this way leads to a lower degree of oxygen isotopic disequilibrium in g oceanica in contrast the slower growing species c pelagicus which typically precipitates near equilibrium calcite does not show any modulation of oxygen isotope signals with changing ph overall carbon and oxygen isotope compositions are best explained by the degree of utilization of the internal dissolved inorganic carbon dic pool and the dynamics of isotopic reequilibration inside the cell thus the carbonate ion effect may not apply to coccolithophores this difference with foraminifera can be traced to different modes of dic incorporation into these two distinct biomineralizing organisms from a geological perspective these findings have implications for refining the use of oxygen isotopes to infer more reliable sea surface temperatures ssts from fossil carbonates and contribute to a better understanding of how climate relevant parameters are recorded in the sedimentary archive

mars paleostratigraphic restoration of buried surfaces in tharsis montes volcanism in the tharsis province of mars occurred in several different areas and was generally continuous without large time intervals between eruptive episodes major lava flow units are numerous and extensive but relatively thin in many places impact craters on buried surfaces project above younger flows that overlie them a new application of crater dating methods has been developed to aid in the identification of these buried surfaces and to determine their lateral extent the technique is especially adaptable to the tharsis region where the stratigraphic succession of major flow units has been established by detailed geologic mapping knowledge of the overall stratigraphy allows correlations to be made between known and unknown surfaces by comparing their crater frequencies at diameters large enough to insure their recognition on the buried unit the method has been applied to aid in the restoration of buried rock units and to construct a series of paleostratigraphic maps showing the sequence of major eruptive events in the tharsis region

vital effects in coccolith calcite cenozoic climate pco2 drove the diversity of carbon acquisition strategies in coccolithophores 1 coccoliths calcite plates produced by the marine phytoplankton coccolithophores have previously shown a large array of carbon and oxygen stable isotope fractionations termed vital effects correlated to cell size and hypothesized to reflect the varying importance of active carbon acquisition strategies culture studies show a reduced range of vital effects between large and small coccolithophores under high co2 consistent with previous observations of a smaller range of interspecific vital effects in paleocene coccoliths we present new fossil data examining coccolithophore vital effects over three key cenozoic intervals reflecting changing climate and atmospheric partial pressure of co2 pco2 oxygen and carbon stable isotopes of size separated coccolith fractions dominated by different species from well preserved paleocene eocene thermal maximum petm 56 ma samples show reduced interspecific differences within the greenhouse boundary conditions of the petm conversely isotope data from the plio pleistocene transition ppt 3 5 2 ma and the last glacial maximum lgm 22 ka show persistent vital effects of 2 ppt and lgm data show a clear positive trend between coccolith cell size and isotopic enrichment in coccolith carbonate as seen in laboratory cultures on geological timescales the degree of expression of vital effects in coccoliths appears to be insensitive topco2 changes over the range 350 ppm pliocene to 180 ppm lgm the modern array of coccolith vital effects arose after the petm but before the late pliocene and may reflect the operation of more diverse carbon acquisition strategies in coccolithophores in response to decreasing cenozoic pco2

refining our estimate of atmospheric co2 across the eocene oligocene climatic transition abstract the eocene oligocene transition eot followed by oligocene isotope event 1 oi 1 is a dramatic global switch in climate characterized by deep sea cooling and the first formation of permanent antarctic ice models and proxy evidence suggest that declining partial pressure of atmospheric carbon dioxide co 2 atm below a threshold may explain the onset of global cooling and associated ice formation at oi 1 however significant uncertainty remains in the estimated values and salient features of reconstructed co 2 atm across this interval in this study we present novel carbon isotope records from size separated diatom associated organic matter 13 c diatom preserved in silica frustules physical preservation of this material allows concurrent investigation of isotopic and cell size information providing two input parameters for biogeochemical models and the reconstruction of co 2 atm we estimate co 2 atm in two ways first we use size and reaction diffusion kinetics of a cell to calculate a co 2 atm threshold second we use the calibrated relationship between e p diatom and carbon dioxide from culture and field studies to create a record of co 2 atm prior to and across the transition our study from site 1090 in the atlantic sector of the southern ocean shows co 2 atm values fluctuating between 900 and 1700 100 p p m v across the eot followed by a drop to values in the order of 700 to 800 100 p p m v just prior to the onset of oi 1 our values and magnitude of co 2 atm change differ from previous estimates but confirm the overall trends inferred from boron isotopes and alkenones including a marked rebound following oi 1 due to the intricate nature of the climate system and complexities in constraining paleo proxies this work emphasizes the importance of a multi proxy approach to estimating of co 2 atm in order to elucidate its role in the emplacement of antarctic ice sheets at the eot

morphometric properties of martian volcanoes 1 mars orbiter laser altimeter mola data have been used to construct digital elevation models dem of the martian volcanoes in order to determine height flank slope caldera depth and volumes summit elevations range from 21 1 km to 0 5 km and relief varies from 1 0 km to almost 22 km average flank slopes are in the range of 1 to 10 consistent with basaltic shield volcanism the very low slopes of highland patera are also consistent with pyroclastic volcanism minimum volumes range from 1012 to 1015 m3 estimates of the time required to build these volcanoes on the basis of long term terrestrial eruption rates range from hundreds of thousands to tens of millions of years

distinct element method simulations of rock concrete interfaces under different boundary conditions abstract the shear behaviour of concrete rock interfaces has been the aim of extensive research in geotechnical engineering applications such as rock socketed piles rock bolts and concrete dam arch bridge foundations several experimental studies through direct shear tests have been conducted to evaluate the shear behaviour of rock concrete interfaces under cnl constant normal load and cns constant normal stiffness conditions in this paper pfc2d numerical simulations of unbonded rock concrete planar and saw tooth triangular joints under cnl and cns boundary conditions are conducted using the shear box genesis sbg approach proposed by bahaaddini et al 2013b the numerical simulation results are compared with experimental data published by gutierrez 2013 and gu et al 2003 results indicate that the sbg approach reproduces suitably the shear behaviour failure mode and asperity damage of unbonded planar and triangular rock concrete interfaces specially under cnl conditions

water isotopologues as a quantitative paleosalinity proxy 1 paleosalinity reconstructions are a goal of paleoceanographic study because of their potential to provide insight into past ocean circulation while temperature reconstructions have been assessed by using multiple independent proxies the skill of existing salinity reconstructions remains poorly quantified we examine the applicability of two different approaches using a set of coupled water isotope enabled general circulation model experiments as a numerical analog for the real climate system these simulations for the holocene at roughly 1000 year time steps explicitly track variability in both the water isotopologues and salinity our simulations suggest that quantitative reconstructions of past salinity variability based solely on inferred 18osw variability have very large errors and uncertainties however we find that paired 18osw and d variability from combining biomarker and calcite proxies holds promise for providing better quantitative estimates of salinity variability

modelling the oxygen isotope distribution of ancient seawater using a coupled ocean atmosphere gcm implications for reconstructing early eocene climate one of the motivations for studying warm climates of the past such as the early eocene is the enhanced understanding this brings of possible future greenhouse conditions traditionally climate information deduced from biological or chemical proxies have been used to test computer model simulations of past climatic conditions and hence establish some of the uncertainties associated with model based predictions however extracting climate information from proxies is itself an interpretative process and discrepancies between climate information inferred from different types of proxy undermines the assumption that model data conflicts automatically mean that the model is inherently flawed a new approach which both acknowledges and reduces the uncertainties associated with both model and data is required although the oxygen isotopic ratio 18o preserved in calcareous marine fossils has been used to reconstruct past seawater temperature for several decades significant uncertainties associated with this method persist these include assumptions about past seawater 18o for which no proxy exists and which is a key control on the temperature inferred from fossil carbonate here we present the results of an early eocene simulation made using a state of the art general circulation model gcm hadcm3 with co2 set at six times pre industrial values and which has oxygen isotopes incorporated into the full hydrological cycle and hence simulates the 18o of past seawater this allows us to explore the implications of the different seawater 18o correction factors commonly used for 18o based temperature reconstruction it also allows us to focus model data comparison on 18o rather than interpret ocean temperature an approach that reduces uncertainties in model data comparison since the effects of both the temperature and the isotopic composition of ocean water on 18o of carbonate are accounted for the good agreement between model and data for both modern and well preserved early eocene carbonate increases confidence in climate reconstructions of this time

role of membrane stresses in the support of planetary topography the principal purpose of this paper is to examine whether membrane stresses can support topographic loads on planetary elastic lithospheres it is found that the ability of a spherical shell to support loads through membrane stresses is determined by the nondimensional parameter ed gr2 where d is the thickness of the elastic lithosphere is the density difference between the mantle and crust and r is the radius of the planetary body when this parameter is large membrane stresses can fully support topographic loads without flexure and when it is small the influence of membrane stresses can be neglected solutions of the equation governing the behavior of a spherical shell are obtained for a topographic load expressed in terms of spherical harmonics spherical harmonic expansions of the measured gravity and topography for mars and the moon are compared with the theory it is found that for mars the support of topography is primarily due to membrane stresses for n 8 and for the moon for n 17 for mars the data for 4 n 7 give 0 5 for the moon the data have considerable scatter that is attributed to the mascons but generally correlate with 0 5 if bending stresses are neglected the governing equation for the deflection of the spherical shell is legendre s equation a general solution is obtained for an axisymmetric load this solution is applied to the tharsis region on mars the 60 65 compensation of this region requires that 0 6 the well defined fracture pattern surrounding the tharsis region is attributed to tensional membrane stresses

empirical ratio of dynamic to static stiffness for propped artificial fractures under variable normal stress abstract the stiffness coefficient is a key parameter of rock fractures that controls the properties and behavior of a rock mass according to the displacement discontinuity theory the dynamic stiffness of rock fractures can be back analyzed using stress wave propagation this study aims to measure the dynamic stiffness of rock fractures then develop an empirical ratio to describe the relationship between dynamic and static stiffness propped artificially fractured shale and granitic rock samples are employed mechanical and ultrasonic tests are conducted on two artificial rock fractures during uniaxial loading and unloading as normal stress changes from 1 mpa to 50 mpa the average dynamic normal stiffness of shale and granitic rock fractures changes from 330 gpa m to 1960 gpa m and from 90 gpa m to 2320 gpa m respectively for both artificial fractures the dynamic stiffness is higher than the static stiffness but approaches the static stiffness with increasing normal stress the ratio of dynamic to static normal stiffness is approximately 2 0 at a normal stress of 15 mpa this ratio approaches 1 0 with increasing normal stress and varies widely under low normal stress this study provides a method for evaluating the static or dynamic stiffness of rock fractures which has important applications for seismic surveys or acoustic logs in the field of geological engineering

stable isotope vital effects in coccolith calcite uncertainties about the origin of the many disequilibrium or vital effects in a variety of calcifying organisms and whether these effects are constant or variable have hampered paleoceanographic application of carbon and oxygen isotopic ratios unraveling the source of these effects will improve paleoceanographic applications and may provide new information on changes in cell physiology and ecology culture of eight species of coccolithophorids a dominant marine phytoplankton group reveals a 5 array of disequilibrium or vital effects in both the carbon and oxygen isotopic composition of coccolith calcite in moderate light and nutrient replete cultures oxygen isotopic fractionation and carbon isotopic fractionation correlates directly with cell division rates and correlates inversely with cell size across a range of species however when growth rates of a single species are increased or decreased by higher or lower light levels 18o is relatively invariant likewise growth rate variations as a function of temperature do not influence coccolith 18o the slope of the 18o vs temperature relation in cultures of both gephyrocapsa oceanica and helicosphaera carteri is the same as for abiogenic carbonates this suggests a constant species specific isotopic fractionation which does not vary with cell physiology the constancy of vital effects suggests that coccolith stable isotopes will provide reliable phase for paleoceanographic reconstruction of temperature and seawater chemistry as long as monospecific fractions are analyzed or changes in nannofossil assemblages are accounted for with species specific correction factors we suspect that the cell size and its constraints on the rate of co2 diffusion relative to c fixation may be the first order influence on coccolith stable isotope vital effects a quantitative model of this process may provide important constraints on mechanisms of carbon acquisition of coccolithophorids in both modern and extinct species

statistics of mars topography from the mars orbiter laser altimeter slopes correlations and physical models data obtained recently by the mars orbiter laser altimeter mola were used to study the statistical properties of the topography and slopes on mars we find that the hemispheric dichotomy manifested as an elevation difference can be described by long baseline tilts but in places is expressed as steeper slopes the bimodal hypsometry of elevations on mars becomes unimodal when referenced to the center of figure contrary to the earth for which the bimodality is retained however ruling out a model in which the elevation difference is expressed in a narrow equatorial topographic step cannot be done by the hypsometry alone mars slope distribution is longer tailed than those of earth and venus indicating a lower efficiency of planation processes relative to relief building tectonics and volcanics we define and compute global maps of statistical estimators including the interquartile scale rms and median slope and characteristic decorrelation length of the surface a correspondence between these parameters and geologic units on mars is inferred surface smoothness is distinctive in the vast northern hemisphere plains where slopes are typically 0 5 amazonis planitia exhibits a variation in topography of 1 m over 35 km baselines the region of hematite mineralization in sinus meridiani is also smooth with median slopes lower than 0 4 but does not form a closed basin the shallower long wavelength portion of the lowlands topographic power spectrum relative to the highlands can be accounted for by a simple model of sedimentation such as might be expected at an ocean s floor the addition of another process such as cratering is necessary to explain the spectral slope in short wavelengths among their application these mola derived roughness measurements can help characterize sites for landing missions

the mars observer laser altimeter investigation the primary objective of the mars observer laser altimeter mola investigation is to determine globally the topography of mars at a level suitable for addressing problems in geology and geophysics secondary objectives are to characterize the 1064 nm wavelength surface reflectivity of mars to contribute to analyses of global surface mineralogy and seasonal albedo changes to assist in addressing problems in atmospheric circulation and to provide geodetic control and topographic context for the assessment of possible future mars landing sites the principal components of mola are a diode pumped neodymium doped yttrium aluminum garnet laser transmitter that emits 1064 nm wavelength laser pulses a 0 5 m diameter telescope a silicon avalanche photodiode detector and a time interval unit with 10 ns resolution mola will provide measurements of the topography of mars within approximately 160 m footprints and a center to center along track foot print spacing of 300 m along the mars observer subspacecraft ground track the elevation measurements will be quantized with 1 5 m vertical resolution before correction for orbit and pointing induced errors mola profiles will be assembled into a global 0 2 deg x 0 2 deg grid that will be referenced to mars center of mass with an absolute accuracy of approximately 30 m other data products will include a global grid of topographic gradients corrected individual profiles and a global 0 2 deg x 0 2 deg grid of 1064 nm surface reflectivity

new radar derived topography for the northern hemisphere of mars earth based radar altimetry data for the northern equatorial belt of mars 6 s 23 n have recently been reduced to a common basis corresponding to the 6 1 mbar reference surface a first look at these data indicates that the elevations of tharsis elysium and lunae planum are lower by 2 5 km than has been suggested by previous estimates these differences show that the required amount of tectonic uplift or constructional volcanism for each area is less than has been previously envisioned atmospheric or surficial conditions are suggested which may explain the discrepancies between the radar topography and elevations measured by other techniques the topographies of chryse planitia syrtis major and valles marineris are also described

coupled greenhouse warming and deep sea acidification in the middle eocene 1 the middle eocene climatic optimum meco is an enigmatic warming event that represents an abrupt reversal in long term cooling through the eocene in order to further assess the timing and nature of this event we have assembled stable isotope and calcium carbonate concentration records from multiple deep sea drilling project and ocean drilling program sites for the time interval between 43 and 38 ma revised stratigraphy at several sites and compilation of 18o records place peak warming during the meco event at 40 0 ma chron c18n 2n the identification of the 18o excursion at sites in different geographic regions indicates that the climatic effects of this event were globally extensive the total duration of the meco event is estimated at 500 ka with peak warming lasting 100 ka assuming minimal glaciation in the late middle eocene 4 6 c total warming of both surface and deep waters is estimated during the meco at the study sites the interval of peak warming at 40 0 ma also coincided with a worldwide decline in carbonate accumulation at sites below 3000 m depth reflecting a temporary shoaling of the calcite compensation depth the synchroneity of deep water acidification and globally extensive warming makes a persuasive argument that the meco event was linked to a transient increase in atmospheric pco2 the results of this study confirm previous reports of significant climatic instability during the middle eocene furthermore the direct link between warming and changes in the carbonate chemistry of the deep ocean provides strong evidence that changes in greenhouse gas concentrations exerted a primary control on short term climate variability during this critical period of eocene climate evolution

productivity and sea surface temperature changes recorded during the late eocene early oligocene at dsdp site 511 south atlantic this study investigates paleoenvironmental changes during the eocene oligocene transition eot at deep sea drilling project dsdp site 511 south atlantic as inferred from lipid biomarker long chain diols alkenones and calcareous nannofossil accumulation rates as well as changes in sedimentation regime i e relative contributions of total organic carbon toc calcium carbonate and biogenic silica sea surface temperatures ssts reconstructed from the alkenone unsaturation index uk 37 indicate a progressive but significant cooling 8 c from 34 5 ma to 33 6 ma consistent with estimates derived from other temperature proxies tex86 18o at the same site and for the same time interval this cooling is associated with a marked increase in primary productivity as indicated by high accumulation rates of biogenic silica toc alkenones long chain diols and calcareous nannofossils together these results are consistent with an enhancement of upwelling conditions favorable to the development of siliceous organisms at dsdp site 511 possibly induced by the oi 1 glaciation in antarctica that occurred during this period

late stage intrusive activity at olympus mons mars summit inflation and giant dike formation by mapping the distribution of 351 lava flows at the summit area of olympus mons volcano on mars and correlating these flows with the current topography from the mars orbiter laser altimeter mola we have identified numerous flows which appear to have moved uphill this disparity is most clearly seen to the south of the caldera rim where the elevation increases by 200 m along the apparent path of the flow additional present day topographic anomalies have been identified including the tilting down towards the north of the floors of apollo and hermes paterae within the caldera and an elevation difference of 400 m between the northern and southern portions of the floor of zeus patera we conclude that inflation of the southern flank after the eruption of the youngest lava flows is the most plausible explanation which implies that intrusive activity at olympus mons continued towards the present beyond the age of the youngest paterae 200 300 myr neukum et al 2004 robbins et al 2011 we propose that intrusion of lateral dikes to radial distances 2 000 km is linked to the formation of the individual paterae at olympus mons two specific dikes to the se of the volcano are inferred to have volumes of 4 400 km3 and 6 100 km3 greater than the volumes of individual calderas and implying triggering of both caldera collapse and lateral dike injection by the arrival of large inputs of magma from the mantle a comparable disparity between lava flow direction and current topography together with a tilted part of the caldera floor has been identified at ascraeus mons

limited range of interspecific vital effects in coccolith stable isotopic records during the paleocene eocene thermal maximum 1 small but significant differences exist among stable carbon and oxygen isotopic excursions measured in coccolith dominated bulk carbonate and planktic foraminifera during the paleocene eocene thermal maximum petm one hypothesis suggests that the bulk carbonate isotopic record is compromised by changing nannofossil assemblages since modern nannofossils show a large 5 permil range of interspecific vital effects new techniques are employed here to separate different size fractions of coccoliths from petm sediments at odp site 690 for isotopic analysis removing a major portion of the variation in nannofossil assemblages isotopic compositions of coarse and fine coccolith fractions dominated by coccoliths of genus chiasmolithus and toweius respectively differ by less than 0 5 permil for both oxygen and carbon the near monogeneric toweius record closely parallels the main trends in the bulk carbonate isotope records including multiple steps in the negative carbon isotopic excursion suggesting that the trends in the bulk carbonate record are not artifacts of changing species assemblages because both coccolithophorids and symbiont bearing foraminifera like acarinina must inhabit the photic zone it is unlikely that the 103 year lags in isotope event onset between coccoliths and acarinina reflect true time transgressive invasion of isotopically depleted co2 into the water column the small range of vital effects among paleocene coccoliths is unlikely to result from diagenetic homogenization and instead may reflect more similar carbon acquisition strategies of paleocene coccolithophorid algae due to larger and or more similar cell sizes and higher atmospheric carbon dioxide the small range of vital effects suggests that bulk carbonate records are likely reliable for other early and pre cenozoic sediments where foraminifera are often scarce

controls on stable strontium isotope fractionation in coccolithophores with implications for the marine sr cycle abstract the controls on stable sr isotope fractionation into the calcite produced by the coccolithophore species emiliania huxleyi coccolithus pelagicus spp braarudii and gephyrocapsa oceanica are investigated each species has been cultured under controlled laboratory conditions at a range of temperatures 10 25 c to test the potential of 88 86 sr as a proxy for growth rate and or sea surface temperature coccolithophores are one of the most abundant pelagic calcifiers since sr substitutes to some degree for ca in their calcite coccoliths coccolithophores represent a significant output of sr from seawater potentially influencing the 88 86 sr mass balance in the modern oceans the coccoliths are investigated for their 88 86 sr sr ca and 18 o measured as function of temperature as temperature is increased all species show a negative stable sr isotopic fractionation related to a temperature controlled growth rate we infer the shift of 88 86 sr to lighter values as indicative of a kinetic control on the isotope fractionation revealing the potential of 88 86 sr as a proxy for growth rate which in these experiments is primarily dictated by temperature the results from these experiments indicate that coccolithophore calcite incorporates sr with a very light 88 86 sr isotope composition as low as 0

equatorial heat accumulation as a long term trigger of permanent antarctic ice sheets during the cenozoic abstract growth of the first permanent antarctic ice sheets at the eocene oligocene transition eot 33 7 million years ago indicates a major climate shift within long term cenozoic cooling the driving mechanisms that set the stage for this glaciation event are not well constrained however owing to large uncertainties in temperature reconstructions during the eocene especially at lower latitudes to address this deficiency we used recent developments in coccolith biogeochemistry to reconstruct equatorial atlantic sea surface temperature sst and atmospheric pco2 values from pelagic sequences preceding and spanning the eot we found significantly more variability in equatorial ssts than previously reported with pronounced cooling from the early to middle eocene and subsequent warming during the late eocene thus we show that the antarctic glaciation at the eocene oligocene boundary was preceded by a period of heat accumulation in the low latitudes likely focused in a progressively contracting south atlantic gyre which contributed to cooling high latitude austral regions this prominent redistribution of heat corresponds to the emplacement of a strong meridional temperature gradient that typifies icehouse climate conditions our equatorial coccolith derived geochemical record thus highlights an important period of global climatic and oceanic upheaval which began 4 million years before the eot and superimposed on a long term pco2 decline drove the earth system toward a glacial tipping point in the cenozoic

unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on antarctica since the earliest oligocene circa 35 ma the growth and decay of ice sheets during the oligocene to modern ice house world caused glacioeustatic sea level changes the early eocene was an ice free greenhouse world but it is not clear if ice sheets existed during the middle to late eocene doubt house world benthic foraminiferal 18o records place limits on the history of glaciation suggesting the presence of ice sheets at least intermittently since the earliest oligocene the best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic 18o records although planktonic isotope records from the western equatorial regions are limited subtropical planktonic foraminifera may also record such ice volume changes it is difficult to apply these established principles to the cenozoic 18o record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events we improved oligocene to miocene correlations of 18o records and erected eight oxygen isotope zones oi1 oi2 mi1 mi6 benthic foraminiferal 18o increases which are associated with the bases of zones oil circa 35 8 ma oi2 circa 32 5 ma and mil circa 23 5 ma can be linked with 18o increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near antarctica our new correlations of middle miocene benthic and western equatorial planktonic 18o records show remarkable agreement in timing and amplitude we interpret benthic planktonic covariance to reflect substantial ice volume increases near the bases of zones mi2 circa 16 1 ma mi3 circa 13 6 ma and possibly mi5 circa 11 3 ma possible glacioeustatic lowerings are associated with the 18o increases which culminated with the bases of zone mi4 circa 12 6 ma and mi6 circa 9 6 ma although low latitude planktonic 18o records are required to test this these inferred glacioeustatic lowerings can be linked to seismic and rock disconformities for example we link 12 oligocene early late miocene inferred glacioeustatic lowerings with 12 of the sequence boundaries inferred eustatic lowerings of haq et al 1987

bipolar atlantic deepwater circulation in the middle late eocene effects of southern ocean gateway openings we present evidence for antarctic circumpolar current acc like effects on atlantic deepwater circulation beginning in the late middle eocene modern ocean circulation is characterized by a thermal differentiation between southern ocean and north atlantic deepwater formation regions in order to better constrain the timing and nature of the initial thermal differentiation between northern component water ncw and southern component water scw we analyze benthic foraminiferal stable isotope 18obf and 13cbf records from ocean drilling program site 1053 upper deep water western north atlantic our data compared with published records and interpreted in the context of ocean circulation models indicate that progressive opening of southern ocean gateways and initiation of a circum antarctic current caused a transition to a modern like deep ocean circulation characterized by thermal differentiation between scw and ncw beginning 38 5 ma in the initial stages of drake passage opening in addition the relatively low 18obf values recorded at site 1053 show that the cooling trend of the middle late eocene was not global because it was not recorded in the north atlantic the timing of thermal differentiation shows that ncw contributed to ocean circulation by the late middle eocene 1 4 myr earlier than previously thought we propose that early ncw originated in the labrador sea based on tectonic reconstructions and changes in foraminiferal assemblages in this basin finally we link further development of meridional isotopic gradients in the atlantic and pacific in the late eocene with the tasman gateway deepening 34 ma and the consequent development of a circumpolar proto acc

timing and climatic consequences of the opening of drake passage age estimates for the opening of drake passage range from 49 to 17 million years ago ma complicating interpretations of the relationship between ocean circulation and global cooling secular variations of neodymium isotope ratios at agulhas ridge southern ocean atlantic sector suggest an influx of shallow pacific seawater approximately 41 ma the timing of this connection and the subsequent deepening of the passage coincide with increased biological productivity and abrupt climate reversals circulation productivity linkages are proposed as a mechanism for declining atmospheric carbon dioxide these results also indicate that drake passage opened before the tasmanian gateway implying the late eocene establishment of a complete circum antarctic pathway

ocean overturning since the late cretaceous inferences from a new benthic foraminiferal isotope compilation 1 benthic foraminiferal oxygen isotopic d 18 o and carbon isotopic d 13 c trends constructed from compilations of data series from multiple ocean sites provide one of the primary means of reconstructing changes in the ocean interior these records are also widely used as a general climate indicator for comparison with local and more specific marine and terrestrial climate proxy records we present new benthic foraminiferal d 18 o and d 13 c compilations for individual ocean basins that provide a robust estimate of benthic foraminiferal stable isotopic variations to 80ma andtentatively to 110ma first order variations ininterbasinal isotopicgradients delineate transitions from interior ocean heterogeneity during the late cretaceous 65 ma to early paleogene 35 65 ma homogeneity and a return to heterogeneity in the late paleogene early neogene 35 0 ma we propose that these transitions reflect alterations in a first order characteristic of ocean circulation the ability of winds to make water in the deep ocean circulate we document the initiation of large interbasinal d 18 o gradients in the early oligocene and link the variations in interbasinal d 18 o gradients from the middle eocene to oligocene with the increasing influence of wind driven mixing due to the gradual tectonic opening of southern ocean passages and initiation and strengthening of the antarctic circumpolar current the role of wind driven upwelling possibly associated with a tethyan circumequatorial current in controlling late cretaceous interior ocean heterogeneity should be the subject of further research

trace metal mg ca and sr ca analyses of single coccoliths by secondary ion mass spectrometry here we present the first multi species comparison of modern and fossil coccolith trace metal data obtained from single liths we present both trace metal analyses sr ca mg and al and distribution maps of individual paleogene fossil coccoliths obtained by secondary ion mass spectrometry sims we use this data to determine the effects of variable coccolith preservation and diagenetic calcite overgrowths on the recorded concentrations of strontium and magnesium in coccolith calcite the analysis of coccoliths from deep ocean sediments spanning the eocene oligocene transition demonstrates that primary coccolith calcite is resistant to the neomorphism that is common in planktonic foraminifera from similar depositional environments instead where present diagenetic calcite forms distinct overgrowths over primary coccolith calcite rather than replacing this calcite diagenetic overgrowths on coccoliths are easily distinguished in sims analyses on the basis of relatively higher mg and lower sr concentrations than co occurring primary coccolith calcite this interpretation is confirmed by the comparable sims analyses of modern cultured coccoliths of coccolithus braarudii further with diagenetic calcite overgrowth being the principle source of bias in coccolith based geochemical records we infer that lithologies with lower carbonate content deposited below the palaeo lysocline are more likely to produce geochemical records dominated by primary coccolith calcite than carbonate rich sediments where overgrowth is ubiquitous the preservation of primary coccolith carbonate in low carbonate lithologies thus provides a reliable geochemical archive where planktonic foraminifera are absent or have undergone neomorphism