early jurassic late pliensbachian co2 concentrations based on stomatal analysis of fossil conifer leaves from eastern australia the stomatal index a measure of stomatal density of an extinct australian early jurassic araucariacean conifer species allocladus helgei jansson is used to reconstruct the atmospheric carbon dioxide concentration pco 2 in the early jurassic the fossil leaves are preserved in a single bed palynologically dated to late pliensbachian similar to 185 183 mya atmospheric pco 2 is estimated from the ratios between the stomatal index of a helgei and the stomatal indices of three modern analogs nearest living equivalent plants co2 concentration in the range of similar to 750 975 ppm was calibrated from the fossil material with a best estimated mean of similar to 900 ppm the new average pco 2 determined for the late pliensbachian is thus similar to although similar to 10 lower than previously inferred minimum concentrations of similar to 1000 based on data from the northern hemisphere but may help constrain pco 2 during this period our results are the first pco 2 estimates produced using jurassic leaves from the southern hemisphere and show that i paleo atmospheric pco 2 estimates are consistent at a global scale though more investigations of southern hemisphere material are required and ii the stomatal proxy method can now be used without the context of relative change in pco 2 when applying the correct methodology c 2014 the authors published by elsevier b v on behalf of international association for gondwana research less

biomarker and carbon isotope variation in coal and fossil wood of central europe through the cenozoic abstract carbon isotope analyses of terrigenous organic matter are often used to reconstruct changes in the isotopic composition of upper ocean and atmospheric carbon reservoirs carbon isotope values from tree rings fossil wood and coal matrices have been related to climatic change e g temperature humidity via water use efficiency of land plants in this study we report on carbon isotope analyses on low rank coal deposits of the alpine realm and middle german lignite district covering the early eocene to pliocene time interval fossil wood and extracted wood cellulose from gymnosperms and angiosperms respectively are used for paleoenvironmental reconstructions the trend in 13c is parallel to the carbon isotope record obtained from benthic foraminifera because both data sets sample a common reservoir in the atmosphere the evaluation of the magnitudes of 13c variations of coal caused by environmental change requires the correction of the 13c data due to the effects of different contents of lipids in the organic matter differences in biogeochemical carbon cycling varying contributions of gymnosperms versus angiosperms to peat formation and differences in 13c of atmospheric co2 the resulting carbon isotope record of coal generally co varies with the estimated variability in mean annual temperatures during the tertiary based on paleobotanical data changes in humidity and pco2 may be responsible for deviations between the isotopic trend and the paleotemperature curve during the miocene the obtained temperature coefficient for 13c of c3 plants of about 0 3 c is in agreement with the results of previous studies

oak leaves as biosensors of late neogene and early pleistocene paleoatmospheric co2 concentrations abstract complementary to the interpretation of 13 c values of biogenic carbonate and sedimentary organic carbon in marine sediments paleoatmospheric co 2 levels can be estimated by considering the inverse relationship between atmospheric co 2 concentration and stomatal parameters frequency size on leaves of land plants in woody plants the significance of this species specific physiological response to changing co 2 regimes is now repeatedly confirmed both experimentally and from historical sequences of leaves collected since the onset of industrialization a corollary of this relationship is that analysis of stomatal parameters on fossil leaves has the potential of determining changes in paleoatmospheric co 2 levels at different time scales well preserved cuticle remains of oak leaves from late miocene pliocene and early pleistocene sediments of the lower rhine embayment germany the netherlands give promise of extending the record of stomatal frequency response to the last 10 ma during intervals with warm temperate to subtropical climatic conditions oak leaves are characterized by a high stomatal resistance or low conductance to co 2 diffusion and low stomatal frequencies during cooler intervals we observe an opposite picture comparison with historical relations between co 2 concentration and stomatal properties suggests that paleoatmospheric co 2 concentrations were not significantly higher than during the last 200 years and fluctuated several times between 280 and 370 ppmv in covariation with contrasting regional climatic conditions on a global scale intervals with reduced co 2 levels match glacial pulses characterized by the occurrence of ice rafted detritus in high latitude oceanic sediments

δ13c and stomatal number variability in the cretaceous conifer frenelopsis abstract the 13 c 12 c ratios of leaves of the conifer morphotype frenelopsis were measured to decipher the influences of water and salt stress on stomatal density sd epidermal cell density ecd and stomatal index si three morphospecies were analyzed f ugnaensis from freshwater fluvio lacustrine deposits upper barremian f turolensis and alata from coastal deposits lower middle albian and upper albian respectively the cuticle 13 c values show a large variation from 28 to 21 comparison with previously published marine carbonate 13 c records indicate that the difference in cuticle 13 c between the different deposits are mainly due to difference in co 2 plant isotope fractionation rather than to change in isotopic composition of inorganic carbon in the atmosphere and ocean the less negative 13 c and wide range in 13 c of f turolensis and alata 27 5 to 21 compared to f ugnaensis 28 to 25 are interpreted as a result of salt and or water stress the data as a whole yield a good relationship between the 13 c 12 c ratio and sd r 0 67 n 42 p r 0 53 n 41 p f ugnaensis decreases with increasing 13 c value r 0 57 n 15 p 0 026 as well as a decrease of si r 0 62 n 15 p 0 013 possibly reflecting warmer and drier conditions average si of f alata does not significantly change with 13 c and inferred soil salinity in contrast to sd p

oxygen isotope calibration of the onset of ice rafting and history of glaciation in the north atlantic region we report here that dsdp site 552a cored with the hydraulic piston corer on the west flank of rockall bank recovered an undisturbed sequence of alternating white deep sea carbonate oozes and dark coloured layers that are rich in glacial debris oxygen isotope analysis of the sequence together with detailed nannofossil and palaeomagnetic stratigraphy shows that the first major horizon of ice rafting occurred at about 2 4 myr and was preceded by a minor pulse of ice rafting at about 2 5 myr the carbon isotope record shows that the site has been bathed by a water mass of similar characteristics to present day north atlantic deep water at least since 3 5 myr

new constraints on atmospheric co2 concentration for the phanerozoic earth s atmospheric co2 concentration ca for the phanerozoic eon is estimated from proxies and geochemical carbon cycle models most estimates come with large sometimes unbounded uncertainty here we calculate tightly constrained estimates of ca using a universal equation for leaf gas exchange with key variables obtained directly from the carbon isotope composition and stomatal anatomy of fossil leaves our new estimates validated against ice cores and direct measurements of ca are less than 1000 ppm for most of the phanerozoic from the devonian to the present coincident with the appearance and global proliferation of forests uncertainties obtained from monte carlo simulations are typically less than for ca estimates from other approaches these results provide critical new empirical support for the emerging view that large 2000 3000 ppm long term swings in ca do not characterize the post devonian and that earth s long term climate sensitivity to ca is greater than originally thought key points a novel co2 proxy calculates past atmospheric co2 with improved certainty co2 is unlikely to have exceeded 1000 ppm for extended periods post devonian earth s long term climate sensitivity to co2 is greater than originally thought

introduction pliocene climate processes and problems climate predictions produced by numerical climate models often referred to as general circulation models gcms suggest that by the end of the twenty first century global mean annual surface air temperatures will increase by 1 1 6 4 c trace gas records from ice cores indicate that atmospheric concentrations of co 2 are already higher than at any time during the last 650 000 years in the next 50 years atmospheric co 2 concentrations are expected to reach a level not encountered since an epoch of time known as the pliocene uniformitarianism is a key principle of geological science but can the past also be a guide to the future to what extent does an examination of the pliocene geological record enable us to successfully understand and interpret this guide how reliable are the retrodictions of pliocene climates produced by gcms and what does this tell us about the accuracy of model predictions for the future these questions provide the scientific rationale for this theme issue

late neogene continental stages in nw europe revisited pollen records from fluvial deposits in the netherlands have traditionally been used to establish continental stages for the neogene in nw europe these stages are still widely used across europe for stratigraphic correlations and palaeoclimatic studies despite their extensive use the validity of this continental correlation scheme for the plio and pleistocene has never been tested in the area where they were originally proposed the roer valley graben rvg the fluvial and deltaic depositional setting in this area is controlled by a complex pattern of tectonic and climatic processes which strongly complicates the definition of stages and sub stages of regional or supra regional significance here the original palynological data used to define the praetiglian reuverian brunssumian susterian and linne sub stages are assessed and compared to new borehole data with a multivariate correspondence analysis approach we show that most of these stages cannot be distinguished by numerical analysis of the pollen assemblages a tripartition of pollen assemblages is possible which results in a cooler pleistocene cluster warm temperate to sub tropical pliocene cluster and a warm and relatively dry late miocene to early pliocene cluster however no further stages sub stages or clear climatic phases can be consistently recognized in these data a detailed lithostratigraphic framework of the study area allows a correlation of the sections independent of the pollen data results confirm the numerical analyses and furthermore point to a strong lithological depositional bias on the pollen assemblages variations in the abundance of sequoia and taxodium originally used to define the brunssumian reuverian transition and brunssumian a c sub stages are shown to represent mostly local changes the number and absolute percentage of the fluctuations in sequoia and taxodium abundances depend largely on the sample resolution and the site location within the rvg our data assessment indicates that long distance chronostratigraphic correlations based on the original continental neogene stages likely are invalid furthermore the palaeoclimatic reconstructions that have been based on the rvg successions are largely over interpreted the present palaeoclimate reconstructions from the rvg reflect variations in the highly dynamic fluvial depositional setting taphonomic effects and environmental conditions including climate a sequence stratigraphic approach combined with the analysis of interfingering marine sediments is potentially better suited to establish absolute ages and associated climatic conditions of the neogene deposits within the rvg 2007 elsevier b v all rights reserved

global trends of pco2 across the cretaceous paleogene boundary supported by the first southern hemisphere stomatal proxy based pco2 reconstruction reliable reconstructions of atmospheric carbon dioxide concentrations pco2 are required at higher resolution than currently available to help resolve the relationship between mass extinctions and changes in palaeo pco2 levels such reconstructions are needed 1 at a high temporal resolution for constraining the pre and post extinction atmospheres and 2 at a sufficient spatial resolution to constrain potential inter hemispheric differences here we estimate pco2 based on fossil lauraceae leaf cuticle specimens derived from three localities with strata spanning the latest cretaceous to the mid paleocene including a new cretaceous paleogene boundary k pg locality in new zealand we use two independent methods of stomatal density based pco2 reconstructions a transfer function calibrated using herbarium material and the stomatal ratio method producing three calibration sets our results based on the mean values of each of the three calibration methods indicate pco2 ranging between ca 460 and 650 ppm during the latest cretaceous falling precipitously to average values between ca 360 and 430 ppm across the k pg boundary and further to ca 305 320 ppm in the mid paleocene a spike of extremely high pco2 at the k pg could not be confirmed but our results are nonetheless consistent with previously published pco2 records from the northern hemisphere and show that stomatal density worldwide was responding to significant changes in pco2 across the k pg

russell fault early strike slip fault of california coast ranges the subsurface russell fault is a controlling structure for oil fields in the cuyama basin in the southern salinian block of coastal california movement on the russell fault began at about 23 ma following deposition of the oligocene simmler formation in extensional basins bounded on the south by normal fault ancestors of the la panza and ozena reverse faults right lateral strike slip on the russell fault began with deposition of the soda lake shale member of the vaqueros formation the soda lake shale member and painted rock sandstone member of the vaqueros formation were deposited in west trending right stepping troughs while most of the right slip on the russell fault accumulated 23 19 ma pre vaqueros strata are offset 26 29 km but vaqueros isopachs are offset onl 3 7 km the whiterock bluff shale member of the monterey formation is dated as 16 5 14 ma the facies boundary between the whiterock bluff shale member and the branch canyon sandstone is offset 3 3 4 km coeval subsidiary faults near the russell fault in miocene strata at least as young as 11 ma also support distributed right lateral shear the russell fault is overlain unconformably by the morales formation which includes strata as old as 4 ma 1 m y north of russell ranch oil field the russell fault bifurcates into a western strand that joins the chimeneas fault and an eastern strand that is overridden by the big spring reverse fault the russell fault may continue to the southeast as the ozena fault and be offset across the big pine fault right slip began 6 7 m y after the predicted time of first contact of the pacific and north american plates slip rates were 6 5 7 mm yr during 23 19 ma 0 1 0 3 mm yr during 19 14 ma and 0 3 1 1 mm yr during 14 4 ma the sudden decrease in slip rate occurred as the basin deepened at the time of monterey formation deposition which began about 19 ma the relation of development of vaqueros basins containing soda lake shale member to strike slip on the russell fault suggests that a reconstruction of the early miocene strike slip tectonics of the southeastern coast ranges may permit exploration for other hidden vaqueros basins elsewhere in the salinian block

global vegetation dynamics and latitudinal temperature gradients during the mid to late miocene 15 97 5 33 ma a 617 site palaeobotanical dataset for the mid to late miocene is presented this dataset is internally consistent and provides a comprehensive overview of vegetational change from 15 97 to 5 33 ma the palaeobotanical dataset has been translated into the biome4 classification scheme to enable direct comparison with climate model outputs the vegetation change throughout the langhian seravallian tortonian and messinian is discussed the data shows that the langhian which includes the end of the mid miocene climatic optimum represents a world significantly warmer than today the high northern latitudes were characterised by cool temperate forests the mid latitudes by warm temperate mixed forests the tropics by tropical evergreen broadleaf forests and antarctica by tundra shrub vegetation cool temperate mixed forest existed during the seravallian in the high northern latitudes a reduction in warm temperate mixed forests in the mid latitudes and a loss of tundra on antarctica was noted tortonian vegetation distribution indicates that further cooling had occurred since the seravallian the major changes in vegetation include the first evidence for cold taiga forest in the high northern latitudes and a further reduction of warm temperate mixed forests by the messinian this cooling trend had eliminated warm temperate mixed forests from the western usa and australia and had formed mid latitude deserts despite the cooling trend throughout the mid to late miocene the vegetation distribution of all four reconstructed stages reflect the vegetation of a world warmer than the pre industrial conditions the latitudinal distribution of bioclimatic zones suggests that the latitudinal temperature gradient for the langhian would have been significantly shallower than at present and has gradually but asymmetrically become more modern towards the end of the miocene first the southern hemisphere distribution of bioclimatic zones became more modern probably due to the climatic effects of a fully glaciated antarctica the northern hemisphere bioclimatic zone gradient continued to be shallower than modern throughout the miocene and slowly became more modern by the messinian

withdrawn neogene palaeovegetation reconstruction based on the isotopic composition of pedogenic carbonates from siwalik palaeosols india

advent of strong south asian monsoon by 20 million years ago abstractthe monsoonal paleoclimate of india has been critical for understanding the tectonic history of himalayan and tibetan uplift over the past 60 my monsoonal circulation in deep time has been inferred from variation in stable isotopes of tooth enamel diatom blooms and dust influx in the indian ocean and the advent of c4 grasses but these proxies are compromised by temperature biotic and source effects our study uses a proxy of carbonate distribution within paleosol profiles to infer appearance of monsoonal circulation of modern strength in the himachal pradesh segment of the himalayan foreland by at least 20 my ago cued to high himalayan deformation and ongoing tibetan plateau uplift and retreat of the paratethys sea paleosol records also demonstrate declining chemical weathering with himalayan and tibetan uplift which was a force for global warming rather than cooling over the past 20 my

changes in graminoid stomatal morphology over the last glacial interglacial transition evidence from mount kenya east africa abstract stomatal size and density were measured from graminoid cuticular fragments extracted from dated sediments in two tropical montane crater lakes on mount kenya the sediments had been dated in other studies and spanned 1500 37 000 calibrated years bp changes in the mean size and density of the graminoid stomata were found using a coarse signal analysis the two lakes gave fairly similar results although there was some divergence at the start and end of the time period analyzed there is some correspondence between the atmospheric co 2 concentration and graminoid stomatal density during the transition from the lgm to the start of the holocene where stomatal density decreased while co 2 concentrations increased all the changes observed may have been plastic responses within existing species at the site or competitive replacements of grass floras we argue that higher stomatal density may have been a response to falling co 2 levels during the last glaciation accompanying the replacement of a c 3 flora by c 4 species the stomatal size changes exhibited over this time period may have adapted plants to changes in soil water availability that stomatal morphology changes in a sample flora not a single taxon over millennia is a novel finding and one that may have implications for paleoecological interpretation and the prediction of grass behavior in the future

the late miocene to early pliocene climate transition in the southern ocean abstract we have constructed a relatively high resolution 5 10 kyr globigerina bulloides stable isotope record from ocean drilling program site 1088 south atlantic sector of the southern ocean together with the two published records from the high latitudes of the southern hemisphere that each span at least a portion of this interval of time we begin to assemble a spatial picture of sea surface hydrography during the late miocene early pliocene climate transition 8 3 ma we hypothesize that meridional movements in the frontal zones polar front and subtropical convergence with their impact on hydrographic gradients would be evident in temporal changes in the planktonic foraminiferal stable isotopic gradients among the sites our results indicate that there were no large changes in 18o gradients during the interval of study relatively small changes such as a gradual warming of about 3 4 c at site 1088 during the late miocene fall well within the realm of modern ocean seasonality in this region the early pliocene 18o records largely parallel the global decrease defined by benthic foraminifera in the deep pacific suggesting no amplified warming of surface waters in the southern ocean the planktic 13c records vary positively with the 18o records both in the long term trend as well as on the scale of individual data points we believe that this association reflects primarily reduced nutrient utilization during warmer intervals although a small component of the signal would also be consistent with reduced carbon isotope fractionation during air sea gas exchange during relatively warmer conditions if correct this argument would have implications for carbon cycling during the early pliocene and would support scenarios of elevated co2 levels

disentangling the roles of late miocene palaeogeography and vegetation implications for climate sensitivity the impact of rising co2 on future climate remains uncertain but the evidence for high co2 in the palaeorecord suggests that past climates could provide a potentially quantifiable indication of climate in a high co2 world one such past time period is the late miocene 11 6 5 3 ma for which co2 reconstructions indicate higher levels than those of preindustrial and similar to the present atmospheric level 400 ppm the late miocene palaeorecord suggests a much warmer and wetter northern hemisphere than preindustrial however vegetation feedbacks are an important component of the climate system and vegetation distribution reconstructions from the palaeorecord have been shown to be very different to the present vegetation distribution we examine the roles that different vegetation and palaeogeography play in climate sensitivity for the late miocene and consider the implications for potential future climate change to do this we use coupled atmosphere ocean vegetation simulations of late miocene and potential modern climates forced by three different co2 concentrations with vegetation perturbation experiments and make quantitative comparisons to the palaeorecord optimal regions to target late miocene palaeodata acquisition for the purposes of informing about future climate include north america northern africa australia paraguay and southern brazil and northeastern asia these regions are those which the model results predict to be most sensitive to co2 forcing but where the local temperature response to co2 forcing is similar between the simulated potential modern and late miocene climates the model results suggest that climate sensitivity to co2 forcing is directly affected by the palaeogeographic configuration and that the inferred climate sensitivity for doubled co2 is 0 5 0 8 c higher for the late miocene than we might expect for future climate because of differences in synergy the greater land mass at high northern latitudes during the late miocene and the differences in vegetation distribution predictions that result combined with differences in ocean circulation and the effect of sea ice make the late miocene boundary conditions more sensitive to co2 forcing than the modern boundary conditions

variability of stomatal density and index in the upper permian conifer quadrocladus madler a taphonomical case study abstract changes in atmospheric co 2 concentrations over the geological past have attracted a considerable amount of scientific interest during the last decade many authors have demonstrated that for some extant plants stomatal densities and indices are negatively correlated with atmospheric co 2 concentrations similarly changes in stomatal densities and indices in fossil plants are considered to be reliable proxies for changes of atmospheric co 2 concentrations in the geological past not only in the cenozoic but also in the mesozoic and palaeozoic however systematic investigations on the variability of these parameters in most mesozoic and palaeozoic plants are still lacking in this study we investigate the inherent variability of both parameters in the conifer genus quadrocladus madler from the upper permian of europe conifers are generally not considered to be valuable taxa for determining sd and si as palaeoatmospheric co 2 proxies because of their regular arrangement of stomata in rows quadrocladus is one of the few late palaeozoic conifers which shows a more uniform distribution of stomata on both surfaces and no such distribution patterns as exhibited by other conifer taxa within an individual needle of this taxon variations of sd and si increased almost consistently from the base 100 to the apex 169 of the needle both surfaces in cuticles of quadrocladus from fluvial deposits from culmitzsch thuringia e germany the overall range of both parameters was smaller than in cuticles from marginal marine beds of frankenberg geismar nw hesse w germany this difference is probably due to the wider variety of micro climatic and edaphic conditions experienced by material from the latter locality cuticles from upper permian deposits of northern italy showed no significant changes in sd whereas si showed a significant excursion towards higher values within the investigated profile mean values from northern italy were slightly lower than values from the german deposits which could be interpreted as an elevated atmospheric p co 2 however our data suggest that taphonomic distortions fragmentation of individual needles mixing of material from different micro habitats time averaging of the data have to be taken into account when sd and si of fossil plants with no closely related living relatives i e same genus or even species are used as palaeoatmospheric or climatic proxies especially when only a small number of cuticles is available for investigation

late pliocene greenland glaciation controlled by a decline in atmospheric co2 levels it is thought that the northern hemisphere experienced only ephemeral glaciations from the late eocene to the early pliocene epochs about 38 to 4 million years ago and that the onset of extensive glaciations did not occur until about 3 million years ago several hypotheses have been proposed to explain this increase in northern hemisphere glaciation during the late pliocene here we use a fully coupled atmosphere ocean general circulation model and an ice sheet model to assess the impact of the proposed driving mechanisms for glaciation and the influence of orbital variations on the development of the greenland ice sheet in particular we find that greenland glaciation is mainly controlled by a decrease in atmospheric carbon dioxide during the late pliocene by contrast our model results suggest that climatic shifts associated with the tectonically driven closure of the panama seaway with the termination of a permanent el nino state or with tectonic uplift are not large enough to contribute significantly to the growth of the greenland ice sheet moreover we find that none of these processes acted as a priming mechanism for glacial inception triggered by variations in the earth s orbit

winter spring precipitation as the principal control on predominance of c3 plants in central asia over the past 1 77 myr evidence from δ13c of loess organic matter in tajikistan abstract although changes in atmospheric co2 levels are thought to be the major factor driving long term c3 c4 vegetation evolution recent studies tend to emphasize the effect of regional climate conditions on c3 c4 variations the middle latitudes 30 45 in which c3 c4 plants are highly sensitive to environmental changes provide an optimal basis for the investigation of the relative impacts of climate and pco2 on shifts in c3 c4 cover in order to assess the factors controlling these shifts as well as the complex interactions between environmental factors the carbon isotopic composition of bulk organic matter from the chashmanigar loess section southern tajikistan was measured for the past 1 77 myr in general the 13c record shows mostly negative values throughout the sequence almost all 13c values falling between 23 and 26 indicating a predominance of c3 plants in central asia over this time period despite the presence of numerous glacial interglacial cycles from 0 85 myr to the present the 13c values become increasingly positive reflecting a growing c4 signal however this c4 component is not detectable prior to 0 25 myr after which minor peaks are evident at 228 171 and 18 kyr the 13c record from chashmanigar indicates that winter spring precipitation i e mediterranean climatic conditions have characterized central asia throughout the past 1 77 myr leading to the predominance of c3 vegetation in the context of glacial interglacial scale changes in atmospheric co2 therefore it is climate rather than pco2 that controls c3 c4 variations in asia s middle latitudes the gradual increase in the c4 component since 0 85 myr especially the notable peaks after 0 25 myr may have been caused by an increase in summer precipitation due to an enhanced southward shift of the climate zones

comparative sclerochronology of modern and mid pliocene c 3 5 ma aequipecten opercularis mollusca bivalvia an insight into past and future climate change in the north east atlantic region records of environment contained within the accretionarily deposited tissues of fossil organisms afford a means of detailed reconstruction of past climates and hence of rigorous testing of numerical climate models we identify the environmental factors controlling oxygen and carbon stable isotopic composition and microgrowth increment size in the shell of modern examples of the queen scallop aequipecten opercularis this understanding is then applied in interpretation of data from mid pliocene a opercularis from eastern england on the basis of oxygen isotope evidence we conclude that winter minimum seafloor temperature was similar to present values typically 6 7 c in the adjacent southern north sea and that summer maximum seafloor temperature was a few degrees lower than present values typically 16 17 c this contrasts with evidence from other proxies that winter and summer temperatures were higher than present the pattern of seasonal variation in microgrowth increment size suggests the existence of intense thermal stratification in summer we therefore conclude that summer surface temperatures were much higher maxima well over 20 c than those recorded isotopically on the seafloor and that the annual range of surface temperature probably over 14 c was greater than now at the times in the mid pliocene when the investigated a opercularis were alive taken in conjunction with other proxy evidence of warmer winters as well as summers the data point to substantial fluctuation up to 10 c in winter minimum temperatures during the mid pliocene in the north east atlantic region this fluctuation may be attributable to variation in the strength of the gulf stream north atlantic drift since the pliocene has been widely used as a test bed for numerical models of a greenhouse earth the results have implications for prediction of future climate in the north east atlantic region under the influence of anthropogenic global warming

a multi proxy study of pliocene sediments from ile de france north east greenland abstract a multi technique approach has been used to study a pliocene shallow water marine deposit designated the ile de france formation in north east greenland the sequence is correlated on the basis of 87sr 86sr ratios in shells and palaeomagnetic studies with the gauss normal polarity chron which is dated to between 2 60 and 3 58 ma years bp this dating is in accordance with amino acid epimerisation and evidence from dinoflagellates foraminifers and molluscs sediments marine molluscs and foraminifers show that the sequence was deposited on the inner shelf below storm wave base seawater temperatures were much higher than today as demonstrated by the occurrence of a number of southern extra limital species the same applies to air temperature and the few remains of land plants may indicate a forested upland with picea and thuja a number of extinct taxa are present including nucula jensenii that is erected as a new species

atmospheric paleo co2 estimates based on taxodium distichum cupressaceae fossils from the miocene and pliocene of eastern north america abstract neogene atmospheric paleo co2 estimates based on fossils of the extant cupressaceous conifer species taxodium distichum from the brandywine formation of maryland and the citronelle formation of southern alabama are presented these are important as the first such estimates from eastern north american paleofloras and provide new evidence from a time for which the role of co2 in climate change is controversial comparisons of the stomatal density sd of the fossil leaf cuticles to a calibration curve constructed from modern leaves of the same species collected over the last century of anthropogenic co2 increase produces miocene and pliocene atmospheric paleo co2 mean estimates of 360 and 351 ppmv respectively although the temporal resolution of the fossil sites is low these results are in agreement with multiple independent proxies that indicate near modern co2 levels during this interval and demonstrate the utility of t distichum leaves as instruments for stomatal frequency analysis

alkenone and boron based pliocene pco2 records abstract the pliocene period is the most recent time when the earth was globally significantly 3 c warmer than today however the existing pco2 data for the pliocene are sparse and there is little agreement between the various techniques used to reconstruct palaeo pco2 this disagreement coupled with the general low temporal resolution of the published records does not allow a robust assessment of the role of declining pco2 in the intensification of the northern hemisphere glaciation inhg and a direct comparison to other proxy records are lacking for the first time we use a combination of foraminiferal 11b and organic biomarker alkenone derived carbon isotopes proxies to determine the concentration of atmospheric co2 over the past 5 ma both proxy records show that during the warm pliocene pco2 was between 330 and 400 ppm i e similar to today the decrease to values similar to pre industrial times 275 285 ppm occurred between 3 2 ma and 2 8 ma coincident with the inhg and affirming the link between global climate the cryosphere and pco2

el nino southern oscillation pliocene climate and equifinality it has been suggested that during the pliocene ca 5 1 8ma an el nino state existed as a permanent rather than an intermittent feature that is the tropical pacific ocean was characterized by a much weaker east west gradient than today one line of inquiry used to investigate this idea relates modern el nino teleconnections to pliocene proxy data by comparing regional differences in precipitation and surface temperature with climate patterns associated with present day el nino events assuming that agreement between pliocene data and observations of modern el nino events supports this interpretation here we examine this assumption by comparing outputs from a suite of mid pliocene climate simulations carried out with the uk met office climate model regional patterns of climate change associated with changes in model boundary conditions are compared with observed el nino southern oscillation teleconnection patterns our results indicate that many of the proposed permanent el nino surface temperature and precipitation patterns are observable in mid pliocene climate simulations even when they display variability in tropical pacific sea surface temperatures ssts or when forced with a modern east west sst gradient our experiments highlight the possibility that the same outcome may be achieved through different initial conditions equifinality an important consideration for reconstructed patterns of regional mid pliocene climate

use of carbon isotopes in paleosols as an indicator of the p co2 of the paleoatmosphere measurements of carbon isotopic composition of coexisting paleosol organic matter and carbonate results in improved estimates of the paleo p co2 content of the paleoatmosphere measurements from tertiary paleosols indicate that the levels of co2 in the early eocene middle and late miocene and pliocene were less than 1000 ppmv early cretaceous levels of p co2 were significantly higher of the order of 1500 to 3000 ppmv

tectonics or climate what drove the miocene global expansion of c4 grasslands investigations into the most plausible causes which triggered the late miocene global expansion of c4 grasslands have reached no consensus and are still being debated the global decline in co2 levels in the late miocene has been thought to be the most common driver although c4 grassland expansion was largely confined to the late miocene their first appearance varied significantly in different parts of the old and new world and therefore emphasizes role of local and or regional factors may or may not be in combination with one or more global factors the dynamic himalayan orogen constitutes a significant global tectonic event that is believed to have affected global climate hence a study of the himalayan foreland basin sediments could help in gleaning out possible causes behind this major paleoecologic event which could perhaps be directly or indirectly related stable carbon isotope analyses of a total of 141 pedogenic carbonates in the mio pleistocene siwalik paleosols of the ramnagar sub basin are coherent providing a better insight into paleovegetational changes across the sub basin on temporal and spatial scales furthermore paleovegetational history during oligocene is reconstructed from dagshai paleosols exposed in the subathu sub basin the isotopic results show dominance of c3 vegetation pre 7 ma and dominance of c4 vegetation post 5 ma percentage abundance of c4 vegetation was less than 20 pre 7 ma but increased to more than 40 post 5 ma reaching up to 100 in the youngest analyzed sediments there is exclusive dominance of c3 vegetation during oligocene these results conform to the pattern of change in vegetation documented in other parts of the himalayan belt the global expansion of c4 grasslands largely during late miocene have long been linked with then climate changes particularly brought by declining atmospheric co2 level large scale fires intensification of monsoon seasonality and aridity as demonstrated by various researchers these major hypotheses explaining expansion of c4 grasslands during late miocene are not very convincing due to significant shortcomings associated with them for example expansion of c4 grasslands in non monsoonal regions put serious constraints on the monsoonal intensification hypothesis likewise aridity as being the primary driver of c4 grassland expansion seems hard to support since there is no substantial evidence that could suggest global onset of arid conditions at about same geologic time and some most arid periods like the triassic show no evidence of c4 plants we suggest that the initial lowering of co2 below 450 ppmv created an environment for the beginning of c4 vegetation but the persistence of this threshold value for a considerable time during late miocene appears to be the probable cause of the late miocene global expansion of c4 grasslands irrespective of their time of first appearance it has been deduced through the correlation of himalayan tectonic events with atmospheric co2 levels and paleovegetational changes since upper miocene times that it was indeed the late miocene continuous intense tectonic instability of the himalayas that significantly decreased atmospheric co2 levels and which perhaps played a key role in changing the nature of photosynthetic pathways

global warming and the end permian extinction event proxy and modeling perspectives abstract the mass extinction event that occurred at the close of the permian period 252 million years ago represents the most severe biodiversity loss in the ocean of the phanerozoic the links between the global carbon cycle climate change and mass extinction are complex and involve a whole range of often inter related geochemical biological ecologic and climatic factors it has become widely accepted that the end permian mass extinction was associated with a global warming event because the age of the siberian trap eruption a potentially massive source of carbon dioxide coincides within error with the extinction event however geologic data that are in support of this global warming event are relatively sparse the chain of events and the causal relationship between the eruption of siberian traps and mass extinction is not well established global warming in particular has only been reported from limited proxy data and climate models for which the pco2 in the atmosphere just before and during the end permian extinction event is poorly known this study critically assesses both the proxy climate data and the existing paleoclimate simulations with the goals of assessing our current understanding of the link between mass extinction and climate change and providing some guidance for future studies proxies indicate that prior to the end permian extinction event tropical sea surface temperatures ranged from 22 to 25 c and possible pco2 values ranged from 500 to 4000 ppm before the extinction event during the peak extinction tropical temperatures rose up to 30 c while pco2 perhaps increased up to 8000 ppm climate models that use different pre event pco2 values show similar amount of co2 doubling to replicate the observed carbon isotope excursions we find that the temperature anomaly during the end permian extinction is consistent with 1 5 doublings of atmospheric pco2 and that the implied climate sensitivity is 5 6 c within the upper range of values produced by climate models

history of atmospheric co2 constraints from the deep sea record the carbon chemistry of deep ocean water is quantitatively reflected in carbonate preservation and in the 13c values of foraminifera by using benthic 13c ranges to estimate total dissolved co2 and correcting for the aging effect of deep water back aging the pco2 of the atmosphere can be reconstructed data at hand are insufficient for detailed studies but allow the calculation of an upper limit of pco2 for selected periods within the last 100 million years the limit is probably near a factor of 2 5 times present atmospheric co2 for post eocene time and below a factor of 10 for the late cretaceous

results from a detailed aeromagnetic survey across the northeast newfoundland margin part ii early opening of the north atlantic between the british isles and newfoundland abstract poles of rotation for the north atlantic have been derived from the results of a new aeromagnetic survey northeast of newfoundland reconstruction of the north atlantic at anomaly 34 time shows a band of large amplitude magnetic anomalies which parallels anomaly 34 on both sides of the atlantic from flemish cap and goban spur to the azores gibraltar fracture zone a group of similar anomalies has also been identified in the bay of biscay north of goban spur and flemish cap these anomalies follow the ocean continent boundary poles of rotation derived for this anomaly show that it forms an isochron 100 110 m y during the long cretaceous normal polarity interval the cause of this anomaly is not definite but it may represent an increase in the magnetization of the crust during a limited time within the cretaceous magnetic quiet zone by a process such as replacement of thermoremanent magnetization by chemical remanent magnetization as proposed by raymond and labrecque the north atlantic has also been reconstructed at the time of the initial opening in the region between flemish cap and the charlie gibbs fracture zone using inferred ocean continent boundaries on the west and east sides it has been shown that the entire region could not have saparated at one time but that spreading between the british isles and newfoundland had to progress from south to north consequently when active sea floor spreading was taking place between goban spur and flemish cap about 110 m y the region to the north was still being stretched the calculated amount of stretching as derived from the reconstructions about 25 agrees well with the extension of the lithosphere obtained from modelling the subsidence history of this region and with the results of deep seismic studies active spreading in the north started about 100 m y ago

closure of the panama seaway during the pliocene implications for climate and northern hemisphere glaciation the panama hypothesis states that the gradual closure of the panama seaway between 13 million years ago 13 ma and 2 6 ma led to decreased mixing of atlantic and pacific water masses the formation of north atlantic deep water and strengthening of the atlantic thermohaline circulation increased temperatures and evaporation in the north atlantic increased precipitation in northern hemisphere nh high latitudes culminating in the intensification of northern hemisphere glaciation nhg during the pliocene 3 2 2 7 ma here we test this hypothesis using a fully coupled fully dynamic ocean atmosphere general circulation model gcm with boundary conditions specific to the pliocene and a high resolution dynamic ice sheet model we carry out two gcm simulations with closed and open panama seaways and use the simulated climatologies to force the ice sheet model we find that the models support the panama hypothesis in as much as the closure of the seaway results in a more intense atlantic thermohaline circulation enhanced precipitation over greenland and north america and ultimately larger ice sheets however the volume difference between the ice sheets in the closed and open configurations is small equivalent to about 5 cm of sea level we conclude that although the closure of the panama seaway may have slightly enhanced or advanced the onset of nhg it was not a major forcing mechanism future work must fully couple the ice sheet model and gcm and investigate the role of orbital and co2 effects in controlling nhg

changing co2 conditions during the end triassic inferred from stomatal frequency analysis on lepidopteris ottonis goeppert schimper and ginkgoites taeniatus braun harris abstract end triassic fluctuations in atmospheric carbon dioxide co2 concentration were reconstructed by the use of stomatal frequency analysis on a single plant species the seedfern lepidopteris ottonis goeppert schimper stomatal index showed no distinct intra and interpinnule variation which makes it a suitable proxy for past relative co2 changes records of decreasing stomatal index and density from the bottom to the top of the rhaetian hettangian wustenwelsberg section bavaria germany indicate rising co2 levels during the triassic jurassic transition additionally stomatal frequency data of fossil ginkgoalean leaves ginkgoites taeniatus braun harris suggest a maximum palaeoatmospheric co2 concentration of 2750 ppmv for the latest triassic

modelling pliocene warmth contribution of atmosphere oceans and cryosphere the relative role of the atmosphere oceans and cryosphere in contributing towards middle pliocene warmth ca 3 ma bp is investigated using the hadcm3 coupled ocean atmosphere general circulation model the model was initialised with boundary conditions from the usgs prism2 data set and a pliocene atmospheric co2 level of 400 ppmv and run for 300 simulated years the simulation resulted in a global surface temperature warming of 3degreesc compared to present day in contrast to earlier modelling experiments for the pliocene surface temperatures warmed in most areas including the tropics 1 5degreesc compared with present day the model predicts a general pattern of ocean warming 1 5degreesc in both hemispheres to a depth of 2000 m below which no significant differences are noted sea ice coverage is massively reduced up to 90 the flow of the gulf stream north atlantic drift is up to 100 mm s 1 greater in the pliocene case analysis of the model predicted meridional streamfunction suggests a global pattern of reduced outflow of antarctic bottom water aabw up to 5 sv a shallower depth for north atlantic deep water formation and weaker thermohaline circulation 3 sv the decrease in aabw occurs mainly in the pacific rather than atlantic ocean model diagnostics for heat transports indicate that neither the oceans nor the atmosphere are transporting significantly more heat in the pliocene scenario rather these results indicate that the major contributing mechanism to global pliocene warmth was the reduced extent of high latitude terrestrial ice sheets 50 reduction on greenland 33 reduction on antarctica and sea ice cover resulting in a strong ice albedo feedback these results highlight the need for further studies designed to improve our knowledge regarding pliocene terrestrial ice configurations

warmer tropics during the mid pliocene evidence from alkenone paleothermometry and a fully coupled ocean atmosphere gcm 1 traditional reconstructions of sea surface temperatures ssts produced by the pliocene research interpretations and synoptic mapping prism group indicate that mid pliocene surface ocean temperatures were unchanged or slightly cooler than modern at the tropics and low latitudes and significantly warmer at higher latitudes particularly in the north atlantic this change in the latitudinal pattern of ssts has been attributed to enhanced meridional ocean heat transport generated by more vigorous surface ocean gyres and or thermohaline circulation thc this study derives new sst estimates using the alkenone paleothermometer in the pacific ocean these estimates combined with published alkenone sst data from two atlantic sites are located in tropical and subtropical regions where the distribution of prism sites is sparse a fully coupled ocean atmosphere general circulation model oagcm running for the mid pliocene was also used to predict sst significant differences are noted between absolute prism ssts interpolated to our core locations and alkenone derived ssts these differences may be related to errors in the prism and alkenone paleothermometry estimates or to regional differences between localities where data was collected however the available alkenone and model based sst estimates are consistent in the sign of temperature change they predict and provide the first indication of warmer ssts during the mid pliocene in the tropics and subtropics this contrasts with prism s estimates of unchanged or slightly cooler ssts for the same geographical regions the pattern of ssts produced by alkenone estimates and modeling is not characteristic of that produced by enhanced meridional ocean heat transport or thc instead the pattern is similar to that which might be expected as a result of higher concentrations of atmospheric co2 which would act to warm the oceans at the tropics and other latitudes furthermore model diagnostics indicate that reduced sea ice and terrestrial ice sheet extents and a strong ice albedo feedback played a major role in forcing mid pliocene warmth further work aimed at validating these conclusions should concentrate on expanding the mid pliocene sst data set particularly at low latitudes as well as undertaking model model comparisons to assess model dependency of the results

pliocene aridification of australia caused by tectonically induced weakening of the indonesian throughflow tectonic changes of the early to mid pliocene largely modified the indonesian passages by constricting and uplifting the passages between today s new guinea and sulawesi the associated changes in strength and water mass properties of the indonesian throughflow itf might have influenced the amount of heat transported from the pacific to the indian ocean and thus contributed to pliocene climate change of the indo pacific we study the climate response to changes in the geometry of the indonesian passages in an atmosphere ocean general circulation model aogcm we compare climate simulations with present day topography and with a topography resembling the early pliocene situation in the indo pacific i e passages east of sulawesi deepened and widened to the south we find that transport through the indonesian archipelago is weakened in the constricted passage by 1 7 sv and in the unchanged makassar strait west of sulawesi by 3 5 sv while transport weighted temperature of the outflow into the indian ocean increases by 1 c consistent with recent proxy evidence the reduction in itf transport causes a decrease in subsurface temperatures in the indian ocean while surface waters of the equatorial pacific exhibit an increase by up to 0 9 c centred in the warm pool as a local response to the sea surface temperature anomalies we observe an anomalous precipitation dipole across the indonesian passages with increased rainfall over the pacific warm pool and decreased precipitation in the eastern indian ocean the australian continent experiences a pronounced aridification with mean annual precipitation rates dropping by 30 over most parts of the continent using an uncoupled vegetation model we demonstrate that the simulated climate change might partly explain the observed late pliocene desertification of australia

response of deep ocean circulation to initiation of northern hemisphere glaciation 3 2 ma carbon isotopic records from benthic foraminifera are used to map patterns of deep ocean circulation between 3 and 2 million years ago the interval when significant northern hemisphere glaciation began the 18o and 13c data from four atlantic sites 552 607 610 and 704 and one pacific site 677 show that global cooling over this interval was associated with increased suppression of north atlantic deep water nadw formation however the relative strength of nadw production was always greater than is observed during late pleistocene glaciations when extreme decreases in nadw are observed in the deep north atlantic our data indicate that an increase in the equator to pole temperature gradient associated with the onset of northern hemisphere glaciation did not intensify deepwater production in the north atlantic but rather the opposite occurred this is not unexpected as it is the warm high salinity characteristic rather than the low temperature of thermocline waters that is critical to the deepwater formation process in this region today

changes in atmospheric co2 concentrations and climate from the late eocene to early miocene palaeobotanical reconstruction based on fossil floras from saxony germany abstract in the present study proxy data concerning changes in atmospheric co2 and climatic conditions from the late eocene to the early miocene were acquired by applying palaeobotanical methods fossil floras from 10 well documented locations in saxony germany were investigated with respect to 1 stomatal density index of fossil leaves from three different taxa eotrigonobalanus furcinervis laurophyllum pseudoprinceps and laurophyllum acutimontanum 2 the coexistence approach ca based on nearest living relatives nlr and 3 leaf margin analysis lma whereas the results of approach 1 indicate changes in atmospheric co2 concentration approaches 2 and 3 provide climate data the results of the analysis of stomatal parameters indicate that the atmospheric co2 concentration was higher during the late eocene than during the early oligocene and increased towards the late oligocene a lower atmospheric pco2 level after the late eocene is also suggested by an increase in marine palaeoproductivity at this time from the late oligocene onwards no changes in atmospheric co2 concentration can be detected with the present data for the considered sites the results of the coexistence approach and of the leaf margin analysis document a significant cooling event from the late eocene to the early oligocene the pco2 decrease from the late eocene to the early oligocene indicated by the stomatal data raised in this study was thus coupled to a temperature decrease which is reflected by the present datasets from the early oligocene onwards however no further fundamental climate change can be inferred for the considered locations the pco2 increase from the early oligocene to the late oligocene which is indicated by the present data is thus not accompanied by a climate change at the considered sites a warming event during the late oligocene is however recorded by marine climate archives according to the present data no change in pco2 occurred during the cooling event at the oligocene miocene boundary which is also indicated by marine data the quality and validity of stomatal parameters as sensors for atmospheric co2 concentration are discussed

extension of the astronomically calibrated polarity time scale to the miocene pliocene boundary the early pleistocene to late pliocene astronomically calibrated time scale of shackleton et al 1 and hilgen 2 is extended to the miocene pliocene boundary this is done by correlating the detailed record of caco3 cycles in the trubi and the lower part of the overlying narbone formation rossello composite section sicily to the astronomical record using 1 inferred phase relations between these caco3 cycles and the corresponding orbital cycles of precession and eccentricity and 2 calibration points provided by the previously established astronomical calibration of sapropelitic layers which occur in the topmost part of the caco3 record 2 this correlation allows all small scale caco3 cycles in the rossello composite section to be coded after the correlative precession peak and to be dated astronomically with an accuracy of 1 ky in combination with the available high resolution magnetostratigraphy it further allows the construction of an astronomically calibrated geomagnetic polarity time scale for the major part of the gilbert and gauss chrons this new time scale gives ages for the reversal boundaries of the kaena 3 04 3 11 ma and mammoth 3 22 3 33 ma the gilbert gauss chron boundary 3 58 ma and the reversal boundaries of the cochiti 4 18 4 29 ma nunivak 4 48 4 62 ma sidufjall 4 80 4 89 ma and thvera 4 98 5 23 ma these ages are significantly older than the ages given by conventional time scales age discrepancies gradually increase with increasing age the age of 5 32 ma for the miocene pliocene boundary as defined by the base of the trubi on sicily is almost 0 5 m y 9 5 older than the presently accepted age of 4 86 ma 3 these considerable discrepancies with the conventional time scale can either be explained by an consistent error in the decay constants used in k ar radiometric dating or more likely by diffusional loss of radiogenic argon

seven million years of glaciation in greenland glacial till glaciomarine diamictites and ice rafted detritus found in marine cores collected off the shore of southeast greenland record multiple late cenozoic glaciations beginning in the late miocene distinct rock assemblages and seismic stratigraphic control correlate the diamictites with glaciation of the southeast greenland margin glaciers advanced to the sea during several intervals in the pliocene and pleistocene north atlantic glaciation may have nucleated in southern greenland rather than further north because of the high mountains and the high levels of precipitation in this region

modelling the phanerozoic carbon cycle and climate constraints from the 87sr 86sr isotopic ratio of seawater a numerical model describing the coupled evolution of the biogeochemical cycles of carbon sulfur calcium magnesium phosphorus and strontium has been developed to describe the long term changes of atmospheric carbon dioxide and climate during the phanerozoic the emphasis is on the effects of coupling the cycles of carbon and strontium various interpretations of the observed phanerozoic history of the seawater 87sr 86sr ratio are investigated with the model more specifically the abilities of continental weathering volcanism and surface lithology in generating that signal are tested and compared it is suggested that the observed fluctuations are mostly due to a changing weatherability over time it is shown that such a conclusion is very important for the modelling of the carbon cycle indeed it implies that the conventional belief that the evolution of atmospheric carbon dioxide and climate on a long time scale is governed by the balance between the volcanic input of co2 and the rate of silicate weathering is not true rather carbon exchanges between the mantle and the exogenic system are likely to have played a key role too further the increase of the global weathering rates with increasing surface temperature and or atmospheric co2 pressure usually postulated in long term carbon cycle and climate modelling is also inconsistent with the new model other factors appear to have modulated the weatherability of the continents through time such as mountain building and the existence of glaciers and ice sheets based on these observations a history of atmospheric carbon dioxide and climate during phanerozoic time consistent with the strontium isotopic data is reconstructed with the model and is shown to be compatible with paleoclimatic indicators such as the timing of glaciation and the estimates of cretaceous paleotemperatures

late miocene climate and life on land in oregon within a context of neogene global change abstract clarendonian 12 ma fossil soils plants molluscs fish and mammals of eastern oregon allow reconstruction of late miocene paleogeography paleoclimate and paleoecology on land between the global thermal maximum of the middle miocene 16 ma and global cooling and drying of the late miocene 7 ma six different pedotypes of paleosols recognized near unity and juntura allow reinterpretation of local mammalian paleoecology fossil beavers dominated gleyed entisols of riparian forest abundant camels and common hipparionine horses dominated alfisols of wooded grassland and grassy woodland diatomites overlying mammal bearing beds have bullhead catfish ictalurus ameiurus vespertinus as well as fossil leaves dominated by live oak quercus pollardiana fossil plants and soils of unity and juntura are most like those of grassy live oak woodland and savanna on the western slopes of the sierra nevada in northern california today fossil plants and soils indicate mean annual temperature of 12 9 7 7 17 7 c and mean annual precipitation of 879 604 1098 mm miocene paleoclimatic changes in eastern oregon show no relationship to changes in oxygen isotopic composition of marine foraminifera usually taken as an index of global paleoclimatic change mismatch between land and sea paleoclimatic records is most likely an artefact of global ice volume perturbation of oxygen isotopic values instead miocene paleoclimatic change in eastern oregon parallels changes in carbon isotopic composition of marine foraminifera presumably through fluctuations in greenhouse gases

early pliocene climate a perspective from the western equatorial atlantic warm pool high resolution 3 4 kyr planktonic stable isotope stratigraphies from site 925 drilled on ceara rise ocean drilling program leg 154 are used to investigate the role of the western equatorial atlantic sea surface hydrography in early pliocene 3 2 4 7 ma climate change oxygen isotope results from globigerinoides sacculifer a mixed layer dweller suggest that equatorial sea surface temperatures were cooler than today by 2 3 c consistent with relatively strong northward advection of heat away from the equator oxygen isotope results from neogloboquadrina dutertrei suggest that over the long term this thermocline dweller tracks global ice volume fluctuations stable isotope gradients between the two planktonic species throughout the entire interval imply a stable warm pool in the western equatorial atlantic we observe a rapid 3 4 kyr decrease in g sacculifer and the n dutertrei 18o values at 4 36 ma that may reflect a freshening of the sea surface a direct response to a southward displacement of the intertropical convergence zone and perhaps an indirect response to restricted flow through the central american seaway

palaeoclimate global warmth with little extra co 2 most climate models consider only short term processes such as cloud and sea ice formation when assessing earth s sensitivity to greenhouse gas forcing mounting evidence indicates that the response could be stronger if boundary conditions change drastically

synchronous records of pco2 and δ14c suggest rapid ocean derived pco2 fluctuations at the onset of younger dryas just before the onset of the younger dryas yd cold event several stomatal proxy based pco2 records have shown a sharp increase in atmospheric co2 concentration pco2 of between ca 50 and 100 ppm followed by a rapid decrease of similar or even larger magnitude here we compare one of these records a high resolution pco2 record from southern sweden with the intcal13 record of radiocarbon d 14 c the two records show broadly synchronous fluctuations at the yd onset specifically the intcal13 record documents decreasing d 14 c just before the yd onset when pco2 peaks consistent with a source of old co2 from the deep ocean we propose that this fluctuation occurred due to a major ocean flushing event the cause of the flushing event remains speculative but could be related to the hypothesis of the glacial ocean as a thermobaric capacitor we confirm that the earth system can produce such large multidecadal timescale fluctuations in pco2 through simulating an artificial ocean flushing event with the genie earth system model we suggest that sharp transitions of pco2 may have remained undetected so far in ice cores due to inter firn gas exchange and time averaging the stomatal proxy record is a powerful complement to the ice core records for the study of rapid climate change

north atlantic climate evolution through the plio pleistocene climate transitions during the plio pleistocene the earth witnessed the growth of large northern hemisphere ice sheets and profound changes in both north atlantic and global climate here we present a 3 2 myr long orbitally resolved alkenone sea surface temperature sst record from deep sea drilling project dsdp site 607 41 n 33 w water depth 3427 m in the north atlantic ocean we employ a multi proxy approach comparing these new observations with existing bottom water temperature bwt and stable isotope time series from the same site and sst time series from other sites shedding new light on plio pleistocene climate change north atlantic temperature records show a long term cooling with two major steps occurring during the late pliocene 3 1 to 2 4 ma and the mid pleistocene 1 5 to 0 8 ma closely timed with intervals of major change in northern hemisphere ice sheets existing evidence suggests that the late pliocene cooling may have been caused by a thresholded response to secular changes in atmospheric carbon dioxide co2 while an explanation for the mid pleistocene cooling may involve glacial interglacial changes in atmospheric co2 it seems to also require a change in the behavior of the ice sheets themselves north atlantic climate responses were closely phased with benthic oxygen isotope 18o changes during the 41 kyr world indicating a strong common northern hemisphere high latitude imprint on north atlantic climate signals after the mid pleistocene transition mpt north atlantic sst records and the site 607 benthic carbon isotope 13c record are more closely phased with 18o whereas bwt significantly leads 18o in the 100 kyr band suggesting a shift from a northern to a southern hemisphere influence on north atlantic bwt we propose that the expansion of the west antarctic ice sheet wais across the mpt increased the production and export of antarctic bottom water from the southern ocean and subsequently controlled its incursion into the north atlantic especially during glacial intervals it follows that the early 100 kyr response of bwt implies an early response of the wais relative to the northern hemisphere deglaciation thus in the 100 kyr world both northern hemisphere and southern hemisphere processes affect climate conditions in the north atlantic ocean

a permanent el nino like state during the pliocene the pliocene may have been characterized by permanent el nino like conditions initial modeling studies suggest that this may have contributed to pliocene warmth the termination of this state may have influenced northern hemisphere glaciation nhg we use the hadley centre coupled model version 3 to examine the role of the oceans and ocean structure on pliocene warmth a permanent el nino like state is not predicted annual mean sea surface temperatures in the eastern equatorial pacific at ocean drilling program sites 847 and 851 increase by 1 71 c and 1 15 c respectively however el nino southern oscillation events are clearly expressed by the model sensitivity tests indicate that a prescribed permanent el nino like condition increases annual global mean surface temperatures by a maximum of 0 6 c if the pliocene was characterized by such a condition it is questionable that it provided a major contribution to global warmth and therefore unlikely that the termination of this state contributed significantly to the onset of nhg

a 20 million year record of planktic foraminiferal b ca ratios systematics and uncertainties in pco2 reconstructions we use new and published data representing a 20 million long record to discuss the systematics of interpreting planktic foraminiferal b ca ratios b ca based reconstructions of seawater carbonate chemistry and atmospheric pco 2 assume that the incorporation of boron into foraminiferal tests can be empirically described by an apparent partition coefficient k d b ca caco 3 b oh 4 hco 3 seawater hemming and hanson 1992 it has also been proposed that there is a species specific relationship between k d and temperature yu et al 2007 as we discuss although these relationships may be robust there remain significant uncertainties over the controls on boron incorporation into foraminifera it is difficult to be certain that the empirically defined correlation between temperature and k d is not simply a result of covariance of temperature and other hydrographic variables in the ocean including carbonate system parameters there is also some evidence that k d may be affected by solution hco 3 co 2 3 ratios i e ph or by co 2 3 in addition the theoretical basis for the definition of kd and for a temperature control on k d is of debate we also discuss the sensitivity of pco 2 reconstructions to different k d temperature calibrations and seawater b ca if a k d temperature calibration is estimated using ice core pco 2 values between 0 and 200 ka b ca ratios can be used to reasonably approximate atmospheric pco 2 between 200 and 800 ka however the absolute values of pco 2 calculated are sensitive to the choice of k d temperature relationship for older time periods the absolute values of pco 2 are also dependent on the evolution of seawater b concentrations however we find that over the last 20 ma reconstructed changes in declining pco 2 across the mid pleistocene transition pliocene glacial intensification and the middle miocene climate transition are supported by the b ca record even if a constant coretop k d is used or different k d temperature calibrations and models of seawater b evolution are applied to the data the inferred influence of temperature on k d from coretop data therefore cannot itself explain the structure of a published pco 2 reconstruction tripati et al 2009 we conclude the raw b ca data supports a coupling between pco 2 and climate over the past 20 ma finally we explore possible implications of b ca based pco 2 estimates for the interpretation of other marine pco 2 proxies

late pliocene to pleistocene sensitivity of the greenland ice sheet in response to external forcing and internal feedbacks the timing and nature of ice sheet variations on greenland over the last 5 million years remain largely uncertain here we use a coupled climate vegetation ice sheet model to determine the climatic sensitivity of greenland to combined sets of external forcings and internal feedbacks operating on glacial interglacial timescales in particular we assess the role of atmospheric pco2 orbital forcing and vegetation dynamics in modifying thresholds for the onset of glaciation in late pliocene and pleistocene the response of circum arctic vegetation to declining levels of pco2 from 400 to 200 ppmv and decreasing summer insolation includes a shift from boreal forest to tundra biomes with implications for the surface energy balance the expansion of tundra amplifies summer surface cooling and heat loss from the ground leading to an expanded summer snow cover over greenland atmospheric and land surface fields respond to forcing most prominently in late spring summer and are more sensitive at lower pleistocene like levels of pco2 we find cold boreal summer orbits produce favorable conditions for ice sheet growth however simulated ice sheet extents are highly dependent on both background pco2 levels and land surface characteristics as a result late pliocene ice sheet configurations on greenland differ considerably from late pleistocene with smaller ice caps on high elevations of southern and eastern greenland even when orbital forcing is favorable for ice sheet growth

micropaleontological evidence for increased meridional heat transport in the north atlantic ocean during the pliocene the middle pliocene approximately 3 million years ago has been identified as the last time the earth was significantly warmer than it was during the last interglacial and holocene a quantitative micropaleontological paleotemperature transect from equator to high latitudes in the north atlantic indicates that middle pliocene warmth involved increased meridional oceanic heat transport

late miocene atmospheric co2 concentrations and the expansion of c4 grasses the global expansion of c4 grasslands in the late miocene has been attributed to a large scale decrease in atmospheric carbon dioxide co2 concentrations this triggering mechanism is controversial in part because of a lack of direct evidence for change in the partial pressure of co2 pco2 and because other factors are also important determinants in controlling plant type distributions alkenone based pco2 estimates for the late miocene indicate that pco2 increased from 14 to 9 million years ago and stabilized at preindustrial values by 9 million years ago the estimates presented here provide no evidence for major changes in pco2 during the late miocene thus c4 plant expansion was likely driven by additional factors possibly a tectonically related episode of enhanced low latitude aridity or changes in seasonal precipitation patterns on a global scale or both

mid pliocene deep sea bottom water temperatures based on ostracode mg ca ratios abstract we studied magnesium calcium mg ca ratios in shells of the deep sea ostracode genus krithe from a short interval in the middle pliocene between 3 29 and 2 97 ma using deep sea drilling sites in the north and south atlantic in order to estimate bottom water temperatures bwt during a period of climatic warmth results from dsdp and odp sites 552a 610a 607 658a 659a 661a and 704 for the period ma reveal both depth and latitudinal gradients of mean mg ca values shallower sites 552a 610a and 607 have higher mean mg ca ratios 10 3 9 7 10 1 mmol mol than deeper sites 661a 6 3 mmol mol and high latitude north atlantic sites 552a 610a 607 have higher mg ca ratios than low latitude 658a 9 8 mmol mol 659a 7 7 mmol mol 661a 6 3 mmol mol and southern ocean 704 8 0 mmol mol sites converting mg ca ratios into estimated temperatures using the calibration of dwyer et al 1995 dwyer g s cronin t m baker p a raymo m e buzas j s correge t 1995 north atlantic deepwater temperature change during late pliocene and late quaternary climatic cycles science 270 1347 1351 suggests that mean middle pliocene bottom water temperatures at the study sites in the deep atlantic were about the same as modern temperatures however brief pulses of elevated bwt occurred several times between 3 29 and 2 97 ma in both the north and south atlantic ocean suggesting short term changes in deep ocean circulation

the initiation of northern hemisphere glaciation for well over a century scientists have speculated that variations in the atmospheric concentration of radiatively important trace gases such as carbon dioxide could control the earth s climate e g arrhenius 1 896 recent observations of significant glacial interglacial variation in atmo spheric co2 in ice cores put this idea on a firm observational as well as theoretical footing e g barnola et ai1 987 in this century as atmospheric co2 levels creep steadily upwards in response to the burning of fossil fuels and forests the specter of manmade global climate change looms before us ipcc 1990 a possibility that has heightened interest in the natural variability of climate in the past in particular the 3 c warming pre dicted for the next century has stimulated interest in past warm climates such as the middle pliocene around 3 0 million years ma ago an interval that has often been invoked as a greenhouse world budyko et al 1985 in this paper the climate transition from the warm mid pliocene around 3 2 ma to the onset of northern hemisphere ice ages around 2 4 ma is examined evidence for the initiation of significant northern hemisphere glaciation is examined as well as how this event affected climate around the globe while the cause of individual glacial interglacial oscillations is tied to milankovitch variations in the earth s orbit around the sun e g imbrie et ai 1 992 these insolation changes cannot account for the long term cooling trend which culminated in northern hemisphere glaciation in the final section of this paper mechanisms of long term climate change

a model for atmospheric co 2 over phanerozoic time a new model has been constructed for calculating the level of atmospheric co sub 2 over phanerozoic time which is much simpler mathematically than the blag model but more complex geologically and biologically results suggest that there has been a notable pattern of varying atmospheric co sub 2 level over the past 570 my with high levels during the mesozoic and early paleozoic and low levels during the permo carboniferous and late cenozoic sensitivity analysis shows that within reasonable limits of the principal governing parameters this qualitative trend of varying co sub 2 is relatively insensitive to the actual values chosen for these parameters causes of the co sub 2 variation are multiple and no single geological or biological process can be called upon to explain all co sub 2 variation for all time the calculated trend of co sub 2 over time agrees well with independent estimations of paleoclimates thus the greenhouse theory of paleoclimate on a long geological time scale is supported by the results of the present study

vegetation cover in a warmer world simulated using a dynamic global vegetation model for the mid pliocene in this study we employ the triffid top down representation of interactive flora and foliage including dynamics dynamic global vegetation model dgvm and the hadley centre atmospheric general circulation model version 3 hadam3 gcm to investigate vegetation distributions and climate vegetation feedbacks during the mid pliocene and examine the implications of these results for the origins of hominid bipedalism the triffid model outputs support extant palaeoenvironmental reconstructions for the mid pliocene provided by the prism group pliocene research interpretations and synoptic mapping compared to the pre industrial triffid simulates a significant increase in forest cover during the mid pliocene composed of needle leaf trees in the higher latitudes of the northern hemisphere and broad leaf trees in other regions needle leaf trees extend from the arctic coast into the northern mid latitudes the fractional coverage of bare soil declines in north africa the arabian peninsula australia and southern south america a pattern that is consistent with prism s assertion of less extensive arid deserts a significant increase in the fractional coverage of both broad leaf trees in africa and south america in the mid pliocene scenario is not indicative of a major expansion of tropical rainforests rather it represents an expansion of general woodland type habitats the principal impact of using a dgvm on the gcm predicted climatology for the mid pliocene is to reduce minimum and maximum temperature extremes thus reducing the seasonality of temperature over wide regions the predicted pliocene expansion in broad leaf trees in africa is difficult to reconcile with the savannah hypothesis for the evolution of hominid bipedalism rather the results lend credence to an alternative hypothesis which suggests that bipedalism evolved in wooded to forested ecosystems and was for several million years linked to arborealism

climate pco2 and terrestrial carbon cycle linkages during late palaeozoic glacial interglacial cycles the late palaeozoic was marked by a series of glacial interglacial cycles geochemical and fossil data suggest a role for terrestrial vegetation carbon cycle feedbacks in the climate response to orbital forcing

pliocene climate variability northern annular mode in models and tree ring data the northern annular mode nam and its regional expression the north atlantic oscillation nao are the primary interannual oscillatory systems in the northern hemisphere in the modern climate nam has been linked with a number of weather extremes including large terrestrial temperature increases and extreme snowfalls its connection to climate is more controversial although a change in its behaviour between 1970 and 2000 coincided with rapid temperature increases in the northern hemisphere the north atlantic and nordic seas are a key component in pliocene climate showing the largest increases from modern sea surface temperature to understand these changes and the ability of climate models to reproduce them we must consider simulations of the nam here we show that existing mid pliocene simulations exhibit large changes to the mean state and variability in the north atlantic and a significant dampening of the nao through sensitivity experiments this change is primarily attributed to the impact of the lowering of the rocky mountains as the timing of rocky mountains uplift is still disputed simulations of the north atlantic region contain significant uncertainty particularly relating to interannual variability and its climate feedbacks new high temporal resolution climate proxy data is required to test these model reconstructions here we report new annual resolution data and an analysis of climate variability from fossil tree rings these fossils from sites in the canadian arctic provide support for a strong north atlantic oscillation during the pliocene

new grounds for reassessing palaeoclimate of the sirius group antarctica fossil nothofagus leaves from the meyer desert formation of the sirius group in the central transantarctic mountains have been found with recycled marine diatoms indicating that they are no older than 4 1 3 1 ma they have been interpreted as evidence for pliocene warming and diminution of the east antarctic ice cap in contrast plio pleistocene ice cap stability and sustained polar palaeoclimate has been argued from landforms in victoria land and isotopic data from the southern ocean new evidence on this question comes from fossil soils in the meyer desert formation one of these the siesta palaeosol has a gypsic horizon at a depth of 85 cm as in soils of polar deserts with a mean annual precipitation map of 120 220 mm clastic dykes from a 60 80 cm thick permafrost active layer in the palaeosols are evidence of a mean annual temperature mat of 3 to 11 c this is warmer and wetter than the dominion range today map 36 mm mat 39 c but still a periglacial climate cooler and drier than southern chilean moorland and krummholz map 600 7500 mm mat 5 8 c or subantarctic tundra map 400 2500 mm mat 5 to 5 c a pliocene age for the nothofagus fossils and siesta palaeosol is compatible with soil development on surfaces that bracket their enclosing deposits the dominion range was significantly warmer and wetter than it is today during pliocene c 3 5 ma growth of nothofagus and formation of the siesta palaeosol but the beardmore glacier was still large at that time surface soils and palaeosols of the meyer desert formation are evidence of another warmer and wetter episode earlier during the pliocene c 5 ma both warm intervals were separated by intervening times of glacial expansion and frigid palaeoclimate

the beginning of the ice age in europe and its major subdivisions abstract the time range of the quaternary is discussed in terms of the view that this period is essentially the one in the earth s history in which during certain intervals inland ice developed in the northern hemisphere this process first became evident about 2 3 ma bp since then the quaternary thus defined has witnessed many climatic variations although for practical reasons it is not feasible to assign the status of stage to each distinclty warm or cold phase climatic change is nevertheless the most appropriate basis for world wide correlation it seems possible to use both climatic change and other correlation parameters to arrive at a practicable subdivision of the quaternary period into stages before about 1 ma vegetational succession during interglacials in western europe differed from that seen in later times a possible cause for this divergence is discussed in the later part of the quaternary after about 1 ma two distinct types of warm temperate intervals occurred one associated with high sea levels and an oceanic climate the other showing lower sea levels and a cooler and more continental climate the difference between these two types is shown by comparison of the distribution of abies during these time intervals

temperature and precipitation history of the arctic as the planet cooled from peak warmth in the early cenozoic extensive northern hemisphere ice sheets developed by 2 6 ma ago leading to changes in the circulation of both the atmosphere and oceans from not vert similar2 6 to not vert similar1 0 ma ago ice sheets came and went about every 41 ka in pace with cycles in the tilt of earth s axis but for the past 700 ka glacial cycles have been longer lasting not vert similar100 ka separated by brief warm interglaciations when sea level and ice volumes were close to present the cause of the shift from 41 ka to 100 ka glacial cycles is still debated during the penultimate interglaciation not vert similar130 to not vert similar120 ka ago solar energy in summer in the arctic was greater than at any time subsequently as a consequence arctic summers were not vert similar5 c warmer than at present and almost all glaciers melted completely except for the greenland ice sheet and even it was reduced in size substantially from its present extent with the loss of land ice sea level was about 5 m higher than present with the extra melt coming from both greenland and antarctica as well as small glaciers the last glacial maximum lgm peaked not vert similar21 ka ago when mean annual temperatures over parts of the arctic were as much as 20 c lower than at present ice recession was well underway 16 ka ago and most of the northern hemisphere ice sheets had melted by 6 ka ago solar energy reached a summer maximum 9 higher than at present not vert similar11 ka ago and has been decreasing since then primarily in response to the precession of the equinoxes the extra energy elevated early holocene summer temperatures throughout the arctic 1 3 c above 20th century averages enough to completely melt many small glaciers throughout the arctic although the greenland ice sheet was only slightly smaller than at present early holocene summer sea ice limits were substantially smaller than their 20th century average and the flow of atlantic water into the arctic ocean was substantially greater as summer solar energy decreased in the second half of the holocene glaciers re established or advanced sea ice expanded and the flow of warm atlantic water into the arctic ocean diminished late holocene cooling reached its nadir during the little ice age about 1250 1850 ad when sun blocking volcanic eruptions and perhaps other causes added to the orbital cooling allowing most arctic glaciers to reach their maximum holocene extent during the warming of the past century glaciers have receded throughout the arctic terrestrial ecosystems have advanced northward and perennial arctic ocean sea ice has diminished here we review the proxies that allow reconstruction of quaternary climates and the feedbacks that amplify climate change across the arctic we provide an overview of the evolution of climate from the hot house of the early cenozoic through its transition to the ice house of the quaternary with special emphasis on the anomalous warmth of the middle pliocene early quaternary warm times the mid pleistocene transition warm interglaciations of marine isotope stages 11 5e and 1 the stage 3 interstadial and the peak cold of the last glacial maximum

modeling pliocene warmth modeling studies relevant to the question of pliocene warmth are reviewed although significant regional climate variations may be due to pliocene changes in orography and ocean circulation these changes do not appear sufficient to explain inferred globally increased warmth climate modeling studies for a doubling of co2 suggest high latitude temperature increases approximately comparable to inferred warming during the pliocene i suggest that such a co2 increase may be primarily responsible for the pliocene temperature increase downdraw of co2 since the pliocene is consistent with some geochemical indications of enhanced weathering in the pleistocene however additional proxy testing of this hypothesis is required the co2 models also predict tropical sea surface warming of 2 3 c and winter temperature warming in central eurasia 50 70 n of 4 10 c predictions that distinguish co2 from some other mechanisms enhanced scrutiny of pliocene records from the above regions may prove a valuable test of the co2 hypothesis finally although a co2 increase may be responsible for pliocene warmth this time interval should not be cited as a direct analog for a future greenhouse warming as the future climate will have a significant nonequilibrium response because of the rapid rate of change of forcing despite these limitations enhanced study of pliocene climates may be very valuable as an independent source of validation of co2 doubling simulations

extremely elevated co2 concentrations at the triassic jurassic boundary abstract although progress has been made in recent years in reconstructing the environmental conditions at the triassic jurassic boundary tjb published records of atmospheric co 2 concentrations have been of low resolution and or based on multi taxon estimates this is addressed here by reconstructing co 2 concentrations across the tjb using stomatal frequencies of four phylogenetically and ecologically distinct plant groups from two depositionally geographically and taphonomically separate boundary sections in east greenland and northern ireland with stomatal proxy methods and regression analysis the resulting co 2 records then are compared with an additional existing tjb record from a geological section in sweden the final results indicate that pre tjb rhaetian the co 2 concentration was approximately 1000 ppm that it started to rise steeply pre boundary and had doubled to around 2000 2500 ppm at the tjb the co 2 concentration then remained elevated for some time post boundary before returning to pre tjb levels in the hettangian these results are in very good accordance with published c isotope fire and leaf dissection records and clearly indicate steeply rising and lingering co 2 concentration at the tjb

interpreting environmental and biological signals from the stable carbon isotope composition of fossilized organic and inorganic carbon stable carbon isotope studies on marine and terrestrial organic and inorganic carbon provide a means for detecting global climate change and for reconstructing past concentrations of atmospheric co 2 comparison between the co 2 estimates reconstructed from carbon isotope studies for the past 150ma show good agreement with the predictions of a long term carbon cycle model based on mass balance studies further the co 2 estimates from these sources over the entire phanerozoic show agreement with the fossil record of leaf stomatal density change a feature inversely related to the concentration of atmospheric co 2 isotopic studies on temporal sequences of fossilized terrestrial organic matter have contributed to palaeoecological studies on shifts in the dominance of plants with the c 4 photosynthetic pathway in ecosystems and historical changes in the metabolic processes of leaves of individual species the long term perspective offered by these studies provides critical information for assessing the responses of biological systems to future global environmental change

vegetation change in the baringo basin east africa across the onset of northern hemisphere glaciation 3 3 2 6 ma abstract vegetation in east africa is generally thought to have shifted from forests to more open grasslands and savannas as global climate cooled and high latitude ice sheets expanded during the plio pleistocene such a shift would have greatly influenced landscape resources and potentially hominin evolution as well existing records of african vegetation spanning these time scales are generally derived from offshore marine records that record continental scale changes or paleosol carbonate records that record very local vegetation changes during the short time intervals of soil carbonate formation here we present a new record of basin scale vegetation change from the late pliocene 3 3 2 6 ma derived from a drill core from the chemeron formation located in the baringo basin tugen hills region of the kenya rift valley specifically we present a new record of the relative abundance of c4 grasses and c3 vegetation based on the carbon isotopic composition of leaf wax biomarkers 13cwax which captures a signal of regional vegetation change these data demonstrate that vegetation in the baringo basin varied greatly between c3 forests and c4 grasslands and that vegetation exhibits both long term secular trends and orbital scale variations the contribution of c3 plants was lower than estimates based on low resolution carbon isotope data from paleosol carbonates and organic matter in the basin c3 plants averaged 53 of the vegetation during the late pliocene from 3 3 to 3 04 ma after which time 13cwax indicates more open vegetation and 41 c3 plants this transition may have been driven by changes in basin geomorphology but also possibly occurred as part of larger scale drying and expansion of c4 vegetation in east africa in addition to this secular change we observe high amplitude variability in the 13cwax record including oscillations between 80 and 0 c3 plants these vegetation changes are correlated with changes in precipitation inferred from 2hwax and lake level oscillations inferred from sedimentary facies implying that high amplitude orbital scale variations in precipitation drove significant changes in vegetation resources during the late pliocene in the baringo basin these variations have important implications for changes in terrestrial resources in light of the evolutionary innovations in the hominin fossil record related to changes in foraging strategies

reconstruction of altitudinal transportation range of leaves based on stomatal evidence an example of the early pleistocene fagus leaf fossils from central japan abstract fossil plant assemblages play a critical role in paleoenvironment estimation especially for the cenozoic however the extent that the fossil assemblage reflects the source forest is difficult to estimate the comparison between modern assemblages and their subfossil assemblages shows a significant difference indicating that the transportation of plant organs can affect the accuracy of paleoenvironment analysis in this study we aim to detect leaf transport based on stomatal frequency stomatal index and stomatal density variation of 30 fossilized fagus crenata leaves from the sayama formation 1 54 1 66 ma we distinguished the sun and shade morphotype of fossil leaves by using undulation index and calculated stomatal frequency variation of only sun fossil leaves considering the stomatal index variation of fossil fagus crenata leaves the paleo pco2 variation in a warm period between 1 54 ma and 1 66 ma was estimated as ca 35 0 to 39 6 pa based on this paleo pco2 variation altitudinal transportation range of the early pleistocene fossil fagus crenata leaves was estimated at over 1000 m we presume that leaves of fagus crenata in the fossil assemblage possibly had come from a wide range of altitudes near the fossil site during the early pleistocene this provides an example of altitudinal transportation of plants before their deposition which suggests a consideration when reconstructing the palaeovegetation and palaeoclimate from fossil assemblages

reconstruction of glaciation over the past 6 myr from ice borne deposits in the norwegian sea it is well known that a significant intensification of northern hemisphere glaciation occurred 2 5 myr ago in contrast to the much earlier onset 35 myr of glaciation in antarctica1 3 much less is known about the behaviour of the climate before 2 5 myr and it has remained unclear when sizeable glaciers first started to develop in the northern hemisphere here we deduce the history of high northern latitude glaciation over the past 6 myr from records of ice borne deposits in deep sea sediments of the norwegian sea we find that glaciers large enough to reach sea level were present in the norwegian sea area as early as 5 5 myr three million years before the intensification of glaciation at 2 5 myr fluctuations in ice volume can be deduced from the oxygen isotope record but this provides only a global average which may not reflect the history of ice sheet growth in specific regions from a comparison of the oxygen isotope records with the record of ice rafted material we derive an estimate of the relative contributions of southern and northern hemisphere glaciation to global variations in ice volume

correlation of plio pleistocene deposits of the lower rhine basin north west germany and the valle ricca pits central italy abstract biostratigraphic and palaeomagnetic research has been carried out on selected profiles in north western germany and central italy in order to correlate plio pleistocene sections around the reunion subchronozone vegetation in the valle ricca was dominated by a mountain forest type pointing to cool climatic conditions in the lower rhine basin vegetation had a slightly warmer character but was also dominated strongly by a mountain type of forest vegetation characteristic of cooler summers and higher precipitation than at present two warmer periods have been determined in the central italian profiles the youngest around the olduvai reversal should correspond to the youngest tiglian beds of the lower rhine basin deposits older than the reunion subzone have not been found in the valle ricca in the lower rhine basin on the other hand the gauss matuyama boundary is located between the uppermost pliocene the reuverian c and the praetiglian

environmental history of the german lower rhine embayment during the middle miocene as reflected by carbon isotopes in brown coal stable carbon isotope investigations have been carried out on miocene brown coal from the garzweiler seam of the german lower rhine embayment material studied included fossil wood from seven different taxa and brown coal matrix isotope results from macrofossil analysis show variations of more than 6 within individual samples and reveal a general isotopic difference between angiosperm and gymnosperm wood specimens according to mean carbon isotope values found for gymnosperms angiosperms and brown coal matrix 23 3 26 0 and 25 8 the peat forming vegetation of the garzweiler seam was dominated by angiosperm taxa results from brown coal matrix establish a continuous high resolution depth profile of carbon isotope variations during the late middle miocene they show a significant and characteristic isotope pattern with distinct medium and short term cycles high frequency variations in the two main units of garzweiler seam locally split into three units the medium term 13c variations are most likely caused by varying proportions of gymnosperms within the peat forming vegetation while high frequency oscillations seem to be a direct signal of environmental changes a long term decline of carbon isotope values observed within the complete garzweiler seam from base to top is presumably due to a cooling trend in the miocene

plio pleistocene climate sensitivity evaluated using high resolution co2 records theory and climate modelling suggest that the sensitivity of earth s climate to changes in radiative forcing could depend on the background climate however palaeoclimate data have thus far been insufficient to provide a conclusive test of this prediction here we present atmospheric carbon dioxide co2 reconstructions based on multi site boron isotope records from the late pliocene epoch 3 3 to 2 3 million years ago we find that earth s climate sensitivity to co2 based radiative forcing earth system sensitivity was half as strong during the warm pliocene as during the cold late pleistocene epoch 0 8 to 0 01 million years ago we attribute this difference to the radiative impacts of continental ice volume changes the ice albedo feedback during the late pleistocene because equilibrium climate sensitivity is identical for the two intervals when we account for such impacts using sea level reconstructions we conclude that on a global scale no unexpected climate feedbacks operated during the warm pliocene and that predictions of equilibrium climate sensitivity excluding long term ice albedo feedbacks for our pliocene like future with co2 levels up to maximum pliocene levels of 450 parts per million are well described by the currently accepted range of an increase of 1 5 k to 4 5 k per doubling of co2

declining atmospheric co2 during the late middle eocene climate transition the transition from the extreme greenhouse of the early paleogene 52 ma to the present day icehouse is the most prominent change in earth s cenozoic climate history during the late middle eocene climate transition 42 38 ma which preceded the onset of long lived continental scale ice sheets there is concor dant evidence for brief pulses 1 m y in length of global warmth and ice sheet growth but few constraints on atmospheric co 2 here we estimate the concentration of atmospheric co 2 during this critical interval using stomatal indices of fossil metasequoia needles from ten levels in an exceptionally well preserved core from the giraffe kimberlite locality in northwestern canada reconstructed co 2 concentra tions are mainly between 700 to 1000 ppm but include a secular decline to 450 ppm towards the top of the investigated section because the co 2 threshold for nucleating continental ice sheets at this time was 500 to 750 ppm the co 2 decline is compatible with a rapid 10 4 yrs transition from warm largely ice free conditions to cooler climates with ice sheets these fossils provide direct evidence that high latitude deciduous forests thrived in the geological past under co 2 concentrations that will likely be reached within the 21 st century 500 1000 ppm

early holocene atmospheric co2 concentrations wagner et al 1 1 present a high resolution record of leaf stomatal index si from which they reconstruct the concentration of atmospheric co2 in the early holocene 10 070 to 9 38014c yr bp 11 300 to 10 600 cal yr bp 1 1 2 2 the resulting record shows a co2 concentration of

sensitivity of pliocene ice sheets to orbital forcing the stability of the earth s major ice sheets is a critical uncertainty in predictions of future climate and sea level change one method of investigating the behaviour of the greenland and the antarctic ice sheets in a warmer than modern climate is to look back at past warm periods of earth history for example the pliocene this paper presents climate and ice sheet modelling results for the mid pliocene warm period mpwp 3 3 to 3 0 million years ago which has been identified as a key interval for understanding warmer than modern climates jansen et al 2007 using boundary conditions supplied by the united states geological survey prism group pliocene research interpretation and synoptic mapping the hadley centre coupled ocean atmosphere climate model hadcm3 and the british antarctic survey ice sheet model basism we show large reductions in the greenland and east antarctic ice sheets gris and eais compared to modern in standard mpwp experiments we also present the first results illustrating the variability of the ice sheets due to realistic orbital forcing during the mid pliocene while gris volumes are lower than modern under even the most extreme cold mid pliocene orbit losing at least 35 of its ice mass the eais can both grow and shrink losing up to 20 or gaining up to 10 of its present day volume the changes in ice sheet volume incurred by altering orbital forcing alone means that global sea level can vary by more than 25 m during the mid pliocene however we have also shown that the response of the ice sheets to mpwp orbital hemispheric forcing can be in anti phase whereby the greatest reductions in eais volume are concurrent with the smallest reductions of the gris if this anti phase relationship is in operation throughout the mpwp then the total eustatic sea level response would be dampened compared to the ice sheet fluctuations that are theoretically possible this suggests that maximum eustatic sea level rise does not correspond to orbital maxima but occurs at times where the anti phasing of northern and southern hemisphere ice sheet retreat is minimised

changes in co2 during ocean anoxic event 1d indicate similarities to other carbon cycle perturbations past greenhouse intervals of the mesozoic were repeatedly punctuated by ocean anoxic events oaes major perturbations to the global carbon cycle and abrupt climate changes that may serve as relevant analogs for earth s greenhouse gas forced climate future the key to better understanding these transient climate disruptions and possible co2 forced tipping points resides in high resolution precise and accurate estimates of atmospheric co2 for individual oaes here we present a high temporal resolution multi proxy pco2 reconstruction for the onset of mid cretaceous albian cenomanian boundary oae1d coupling of pco2 estimates with carbon isotopic compositions 13c of charcoal vitrain and cuticle from the rose creek pit rcp nebraska reveals complex phasing including a lag between the well documented negative 13c excursion defining the onset of oae1d and the co2 increase this lag indicates that increased co2 or other c based greenhouse gases may not have been the primary cause of the negative excursion our study reveals a pco2 increase within the interval of the negative 13c excursion reaching a maximum of up to 840 ppm 95 confidence interval 307 ppm 167 ppm toward its end the reconstructed magnitude of co2 increase 357 ppm is similar to that of late cretaceous oae2 but of smaller magnitude than that of other major carbon cycle perturbations of the mesozoic assessed via stomatal methods e g the toarcian oae toae triassic jurassic boundary event cretaceous paleogene boundary event furthermore our results indicate a possible shared causal or developmental mechanism with oae1a and the toae