meteoric sphaerosiderite lines and their use for paleohydrology and paleoclimatology sphaerosiderite a morphologically distinct millimeter scale spherulitic siderite feco 3 forms predominantly in wetland soils and sediments and is common in the geologic record ancient sphaerosiderites are found in paleosol horizons within coal bearing stratigraphic intervals and like their modern counterparts are interpreted as having formed in water saturated environments here we report on sphaerosiderites from four different stratigraphic units each of which has highly variable 13 c and relatively stable 18 o compositions the unique isotopic trends are analogous to well documented meteoric calcite lines which we define here as meteoric sphaerosiderite lines meteoric sphaerosiderite lines provide a new means of constraining ground water 18 o and thus allow evaluation of paleohydrology and paleoclimate in humid

an oxygen isotope record from the foscagno rock glacier ice core upper valtellina italian central alps new high resolution isotopic records 18o d and deuterium excess from an ice core drilled in the foscagno rock glacier italian central alps are presented the 18o data suggest a clear division between an upper part 2 5 and 4 m showing relatively homogeneous values and a middle part 4 7 65 m showing seasonal variations of this parameter the isotopic analyses confirm previous results crystallographic and chemical analyses suggesting a division of this relict glacier ice body into an upper part between 2 5 and 4 m where melting and refreezing processes occur and a middle part between 4 and 7 65 m where the isotopic signal is preserved larger deuterium excess variations d d 8 18o are found in the massive ice below 4 m depth rather than in the overlying ice these are in antiphase with the 18o but without any clear correspondence with the presence of the debris layers postdepositional processes could have affected at least partially the isotopic content of the original pre

paleobotanical evidence for near present day levels of atmospheric co2 during part of the tertiary understanding the link between the greenhouse gas carbon dioxide co 2 and earth9s temperature underpins much of paleoclimatology and our predictions of future global warming here we use the inverse relationship between leaf stomatal indices and the partial pressure of co 2 in modern ginkgo biloba and metasequoia glyptostroboides to develop a co 2 reconstruction based on fossil ginkgo and metasequoia cuticles for the middle paleocene to early eocene and middle miocene our reconstruction indicates that co 2 remained between 300 and 450 parts per million by volume for these intervals with the exception of a single high estimate near the paleocene eocene boundary these results suggest that factors in addition to co 2 are required to explain these past intervals of global warmth

late holocene terrestrial glacial history of miki and i c jacobsen fjords east greenland we present a late holocene glacial and environmental history of three valleys within miki and i c jacobsen fjords east greenland 68 n the fjords have no direct connection with the main ice sheet and are presently glacierized by a series of local ice caps and glaciers little sediment has been deposited within the study area but bedrock is distinctly glacially striated which suggests that extensive valley glaciers reached the present coastline in the past moraines are the prominent morphological features including distinct end and lateral moraines most of the moraines are related to the existing glaciers in the area apparent moraines extend as far as 2 to 2 5 km in front of present day glaciers based on morphological and stratigraphical studies of the sediments in these valleys five glacier advances during the late holocene are implied stabilization of the oldest moraines is lichenometrically dated to c 1450 to 1650 years ago younger moraines in both miki and i c jacobsen fjords are lichenometrically dated to c 1050 1100 years ago c 750 950 years ago and c 600 700 years ago the youngest moraines containing measurable lichens stabilized c 300 400 years ago the timing of this moraine formation correlates to marine records from previous research on the inner part of miki fjord where apparent intensification in sediment stratification is related to a glacier advance into the fjord c 290 years ago this glacial advance may correlate to the little ice age cooling observed in many records from the north atlantic region our glacial record from miki and i c jacobsen fjords also shows good correlation with temperature proxies within the grip ice core in greenland and foraminifera records from nansen fjord east greenland less pronounced correlation is observed with the icelandic sea ice index and records of glacier fluctuation in iceland during the last 1000 years these results suggest that widespread climatic cooling was the direct cause of many of the late holocene glacier variations documented in this study although the glacial advance at c 1050 1100 years ago coincides with the so called medieval warm period and could reflect the response of glaciers to increased precipitation within the area

evidence for an earliest oligocene ice sheet on the antarctic peninsula there is growing consensus that development of a semipermanent ice sheet on antarctica began at or near the eocene oligocene e o boundary beyond ice rafted debris in oceanic settings however direct evidence for a substantial ice sheet at this time has been limited and thus far restricted to east antarctica it is unclear where glacier ice first accumulated and how extensive it was on the antarctic continent in the earliest oligocene sediments at the top of the eocene marine shelf section on seymour island antarctic peninsula include glacial marine deposits and a lodgment till with clasts derived from a variety of rock units on the peninsula dinoflagellate biostratigraphy and strontium isotope stratigraphy indicate an age at or very close to the e o boundary glacier ice extending to sea level in the northern peninsula at this time suggests the presence of a regionally extensive west antarctica ice sheet and thus an even more dramatic response to the forcing factors that facilitated high latitude ice expansion in the earliest oligocene

atmospheric oxygenation caused by a change in volcanic degassing pressure around two and a half billion years ago following the end of the archaean eon the atmosphere turned from anoxic to weakly oxic in what is known as the great oxidation event using a model of volcanic degassing gaillard et al demonstrate that a preceding period of continental crust formation may have been the trigger they propose that as continents emerged and volcanoes became increasingly subaerial rather than submarine magmatic volatiles were degassed at lower pressures leading to a progressive oxidation of the gases released this shift to a release of sulphur as sulphur dioxide rather than as hydrogen sulphide could then have fed marine sulphate reduction and the eventual oxygenation of earth s atmosphere the precambrian history of our planet is marked by two major events a pulse of continental crust formation at the end of the archaean eon and a weak oxygenation of the atmosphere the great oxidation event that followed at 2 45 billion years ago this oxygenation has been linked to the emergence of oxygenic cyanobacteria1 2 and to changes in the compositions of volcanic gases3 4 but not to the composition of erupting lavas geochemical constraints indicate that the oxidation state of basalts and their mantle sources has remained constant since 3 5 billion years ago5 6 here we propose that a decrease in the average pressure of volcanic degassing changed the oxidation state of sulphur in volcanic gases initiating the modern biogeochemical sulphur cycle and triggering atmospheric oxygenation using thermodynamic calculations simulating gas melt equilibria in erupting magmas we suggest that mostly submarine archaean volcanoes produced gases with so2 h2s 1 and low sulphur content emergence of the continents due to a global decrease in sea level and growth of the continental crust in the late archaean then led to widespread subaerial volcanism which in turn yielded gases much richer in sulphur and dominated by so2 dissolution of sulphur in sea water and the onset of sulphate reduction processes could then oxidize the atmosphere

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

a paleogene flora from the upper bonnet plume formation of northeast yukon territory canada palaeontological exploration of the bonnet plume basin in northwestern yukon territory canada has revealed a late paleocene to early eocene macrofloral assemblage from a channel fill deposit the flora is typified by cosmopolitan taxa and dominated by deciduous angiosperms with the notable presence of zizyphoides ettingshausenia and corylites floras with a similar composition are known from late cretaceous through early eocene deposits in alaska and the canadian arctic archipelago where they have been interpreted as evidence for warm equable temperatures this collection represents the most diverse known paleogene plant macrofossil assemblage from the yukon territory and helps to expand our knowledge of ancient high latitude floras

paleosols spanning the cretaceous paleogene transition eastern montana and western north dakota paleosols occur in exposures of the latest cretaceous hell creek and paleocene tullock ludlow formations in montana and western north dakota these units are composed mainly of interbedded siltstones and sandstones of meandering fluvial origin the paleosols indicate that changes in ancient soil development occurred concomitantly with the better known faunal transition in order of decreasing abundance silty soils sandy soils organic soils and volcanic soils are preserved pedogenic features present in these soils include roots microscopic segregations of amorphous material birefringence fabric and soil structures the features suggest that throughout the cretaceous paleogene transition pedogenic processes in the region produced immature profiles an observation consistent with the unstable fluvial setting in which the ancient soils formed gleization was a dominant process in this setting and podzolization modified some sandy soils the association of the features enables recognition of o a e btg bhs bg bc cg and c horizons during middle hell creek time soils formed in a poorly drained setting that was only stable enough to permit incipient pedogenesis the bulk of the pedogenesis occurred in levee and flood plain deposits soils also occurred on point bar and crevasse splay deposits in topographically depressed regions organic accumulations formed with minimal soil development matted plant debris is the product of this environment gley features and segregations of iron oxides around voids suggest fluctuation of the water table by latest hell creek time the mean level of the water table rose and in the lowest tullock ludlow exposures extensive ponded deposits are preserved vegetation accumulated at a rate sufficient for coal formation the amount of fluctuation apparently was reduced and pedogenesis was further inhibited as indicated by the virtual absence of illuviated clays in the sediments

phanerozoic atmospheric co2 change evaluating geochemical and paleobiological approaches abstract the theory and use of geochemical modeling of the long term carbon cycle and four paleo pco 2 proxies are reviewed and discussed in order to discern the best applications for each method geochemical models provide pco 2 predictions for the entire phanerozoic but most existing models present 5 10 m y means and so often do not resolve short term excursions error estimates based on sensitivity analyses range from 75 200 ppmv for the tertiary to as much as 3000 ppmv during the early paleozoic the 13 c of pedogenic carbonates provide the best proxy based pco 2 estimates for the pre tertiary with error estimates ranging from 500 1000 ppmv pre devonian estimates should be treated cautiously error estimates for tertiary reconstructions via this proxy are higher than other proxies and models 400 500 ppmv and should not be solely relied upon we also show the importance of measuring the 13 c of coexisting organic matter instead of inferring its value from marine carbonates the 13 c of the organic remains of phytoplankton from sediment cores provide high temporal resolution up to 10 3 10 4 year high precision 25 100 ppmv for the tertiary to 150 200 ppmv for the cretaceous pco 2 estimates that can be near continuous for most of the tertiary its high temporal resolution and availability of continuous sequences is advantageous for studies aiming to discern short term excursions this method however must correct for changes in growth rate and oxygen level at elevated pco 2 750 1250 ppmv this proxy loses its sensitivity and is not useful the stomatal density and stomatal index of land plants also provide high temporal resolution 2 year high precision 10 40 ppmv for the tertiary and possibly cretaceous pco 2 estimates and so also is ideal for discerning short term excursions unfortunately this proxy also loses sensitivity at some level of pco 2 above 350 ppmv which currently is largely undetermined our analysis of the recently developed 11 b technique shows that it currently is not yet well constrained most importantly it requires the assumption that the boron isotopic composition of the ocean remains nearly constant through time in addition it assumes that there are no biological or temperature effects and that diagenetic alteration of the boron isotopic composition does not occur a fifth co 2 proxy based on the redox chemistry of marine cerium has several fundamental flaws and is not discussed in detail here

could bacteria have formed the precambrian banded iron formations banded iron formations bifs are prominent sedimentary deposits of the precambrian but despite a century of endeavor the mechanisms of their deposition are still unresolved interactions between microorganisms and dissolved ferrous iron in the ancient oceans offer one plausible means of mineral precipitation in which bacteria directly generate ferric iron either by chemolithoautotrophic iron oxidation or by photoferrotrophy on the basis of chemical analyses from bif units of the 2 5 ga hamersley group western australia we show here that even during periods of maximum iron precipitation most if not all of the iron in bifs could be precipitated by iron oxidizing bacteria in cell densities considerably less than those found in modern fe rich aqueous environments those ancient microorganisms would also have been easily supported by the concentrations of nutrients p and trace metals v mn co zn and mo found within the same iron rich bands these calculations highlight the potential importance of early microbial activity on ancient metal cycling

late holocene climate in central west greenland meteorological data and rock glacier isotope evidence the central west greenland climate during the instrumental period since ad 1873 is analysed con cerning interannual and seasonal variations a marked temperature rise was experienced from ad 1920 to 1930 especially affecting the winter season after which the mean annual air temperature for ten years was about 3 5 c higher than during the previous period effectively changing coastal central west greenland from having the climatological character of a continuous permafrost region to a discontinuous permafrost region since then temperatures have gradually decreased and are now approaching the little ice age level experienced in the late nineteenth century and early twentieth century interannual twentieth century temperature variations since ad 1923 have been substantial 5 15 c for the winter season intermediate 2 7 c for the spring season and smaller 1 2 c regarding summer and autumn seasons during the instrumental period the overall atmospheric circulation rather than air temperature appear

environmental memory and a possible seasonal bias in the stable isotope composition of u th he dated goethite from the canadian arctic abstract goethite ax 2 from axel heiberg island 80 n on the margin of the arctic ocean is the dominant mineral in a sample of petrified eocene wood but u th and he measurements suggest that the goethite feooh crystallized in the latest miocene pliocene ca 5 5 to 2 8 ma measured d and 18 o values of ax 2 are 221 6 and 9 6 0 5 respectively the inferred d and 18 o values of the ancient water were about 139 and 18 6 respectively with a calculated temperature of crystallization of 3 5 c which compares with the modern summer j j a temperature of 3 c and contrasts with a modern mat of 19 c published results from various biological proxies on nearby ellesmere island indicate a pliocene 4 ma mat of either 6 or 0 4 c and corresponding seasonal amplitudes of about 18 or 13 c a conductive heat flow model suggests that a temperature of 3 c could represent goethite crystallization at depths of 100 200 cm for mat 6 c or 250 450 cm for mat 0 4 c over seasonally restricted intervals of time the 18 o value of the ax 2 water 18 6 is more positive than the modern j j a precipitation 22 in combination the paleotemperatures and 18 o values of ancient waters from ax 2 and published results from three eocene or pliocene proxy sites on axel heiberg and ellesmere islands are consistent with a warm season bias in those isotopic proxies the results are also consistent with higher proportions of j j a precipitation in the annual total if so this emphasizes the importance of seasonality at high latitudes even in times of warmer global climates and suggests that the arctic hydrologic cycle as expressed in the seasonal distribution and isotopic composition of precipitation perhaps modified by a warmer arctic ocean differed from modern the 13 c value of the fe co 3 oh component in the ax 2 goethite is 6 6 which is much more positive than expected if crystallizing goethite incorporated co 2 derived primarily from oxidation of relict eocene wood with 13 c values of about 24 this apparent paradox may be resolved if the goethite is a product of oxidation of 13 c rich siderite which had previously replaced wood in an eocene methanogenic burial environment thus the goethite retains a carbon isotope memory of a diagenetic eocene event but a d and 18 o record of the latest miocene pliocene arctic climate

is that a relict rock glacier abstract the distribution of rock glaciers is often used to investigate the occurrence of permafrost in mountain areas and to understand their climate and paleoclimate evolution this requires the creation of regional and global inventories capable of discriminating active and relict landforms in order to forecast the presence or absence of ice in the ground in this paper geomorphological geophysical and microclimatic surveys are performed on a rock glacier of the carnic alps eastern european alps in the classification currently used for implementing regional inventories of permafrost evidence in the alps this rock glacier would be defined as relict however the geophysical climatological and geomorphological results indicate that internal ice is widespread in large portions of the rock glacier these are generally interpreted as ice in pore spaces and local ice lenses probably without layers of massive ice moreover the occurrence of ice during the maximum thawing season at depths

the mid cretaceous water bearer isotope mass balance quantification of the albian hydrologic cycle a latitudinal gradient in meteoric n 18 o compositions compiled from paleosol sphaerosiderites throughout the cretaceous western interior basin kwib 34 75 n paleolatitude exhibits a steeper more depleted trend than modern predicted values 3 0x 34 n latitude to 9 7x 75 n lighter furthermore the sphaerosiderite meteoric n 18 o latitudinal gradient is significantly steeper and more depleted 5 8x 34 n to 13 8x 75 n lighter than a predicted gradient for the warm mid cretaceous using modern empirical temperature n 18 o precipitation relationships we have suggested that the steeper and more depleted relative to the modern theoretical gradient meteoric sphaerosiderite n 18 o latitudinal gradient resulted from increased air mass rainout effects in coastal areas of the kwib during the mid cretaceous the sphaerosiderite isotopic data have been used to constrain a mass balance model of the hydrologic cycle in the northern hemisphere and to quantify precipitation rates of the equable greenhouse albian stage in the kwib the mass balance model tracks the evolving isotopic composition of an air mass and its precipitation and is driven by latitudinal temperature gradients our simulations indicate that significant increases in albian precipitation 34 52 and evaporation fluxes 76 96 are required to reproduce the difference between modern and albian meteoric siderite n 18 o latitudinal gradients calculations of precipitation rates from model outputs suggest mid high latitude precipitation rates greatly exceeded modern rates 156 220 greater in mid latitudes 2600 3300 mm yr 99 greater at high latitudes 550 mm yr the calculated precipitation rates are significantly different from the precipitation rates predicted by some recent general circulation models gcms for the warm cretaceous particularly in the mid to high latitudes our mass balance model by no means replaces gcms however it is a simple and effective means of obtaining quantitative data regarding the mid cretaceous hydrologic cycle in the kwib our goal is to encourage the incorporation of isotopic tracers into gcm simulations of the midcretaceous and to show how our empirical data and mass balance model estimates help constrain the boundary conditions

methanogenesis in eocene arctic soils inferred from δ13c of tree fossil carbonates we report on the carbon and oxygen stable isotope composition of fossil tree material collected at the white mountain locality of the buchanan lake formation on axel heiberg island in the high arctic of canada the fossils are middle eocene in age and have been permineralized with carbonate microscopic examination of fossils revealed them to be the remains of metasequoia stems composed of secondary carbonate calcite and original wood intermingled at the cellular level because the specimens show little compression crushing or tissue degradation we believe that carbonate permineralization occurred soon after burial and therefore provides insight into eocene carbon cycling at the locality the carbon isotope signature of the carbonate suggests that methanogenesis resulted in a 13 c enriched co2 pool that equilibrated with soil water and gave rise to unusually 13 c enriched caco3 tree fossil carbonate exhibited strikingly high d 13 c values 4 0 to 7 4x compared to published phanerozoic pedogenic carbonate d 13 c values these d 13 c values in conjunction with fractionation factors a previously determined for carbonate precipitation and methanogenic pathways indicate an eocene soil co2 pool containing 80 95 co2 produced as a by product of acetate fermentation methanogenesis because methane in the atmosphere is a powerful greenhouse gas we suggest that methane emissions from axel heiberg soils contributed to the relatively warm arctic climate during the middle eocene d 2004 elsevier b v all rights reserved

reconstruction of atmospheric co2 during the early middle eocene by application of a gas exchange model to fossil plants from the messel formation germany abstract in this study atmospheric co 2 during the early middle eocene 47 ma is reconstructed using fossil plants from the messel formation close to darmstadt germany co 2 concentration is calculated using a mechanistic model of gas exchange which optimizes co 2 uptake by photosynthesis against water vapor loss by transpiration a strategy that is commonly realized in land plants input data for the model are stomatal data density and pore length paleoclimate data obtained by two different approaches and biochemical parameters of photosynthesis leaves from three taxa belonging to two different families were studied laurophyllum lanigeroides daphnogene crebrigranosa both lauraceae and rhodomyrtophyllum sinuatum myrtaceae the results suggest that co 2 was between 853 and 1033 ppm during the development of the messel formation stomatal data therefore indicate a co 2 concentration that was substantially higher than today the reconstructed range of co 2 concentration is close to data provided by geochemical modeling results and conforms to various data that indicate a warm and ice free climate during this time interval

the transitional climate of the late miocene arctic winter dominated precipitation with high seasonal variability the late miocene 11 6 5 3 ma was an important transitional period following the greenhouse conditions of the eocene in order to gain insight into the arctic paleoclimate of the time we performed high resolution intraring 13 c analyses on fossil wood collected from the late miocene khapchansky sediments of northeastern siberia 69 n from these data we quantified the ratio of summer to winter precipitation ps pw and compared it to current values for the region determined from modern wood samples and instrumental records we observed much greater frequency of winter dominated precipitation ps pw 1 and much greater variability in ps pw during the miocene than today specifically years with ps pw 1 occurred three times more often and years with at least three times as much precipitation in summer or winter 0 33 ps pw 3 0 occurred approximately twice as often during the miocene than today we attribute the high interannual variability in precipitation to an inconsistent moisture source associated with the relatively unstable and incomplete ice cover in the arctic ocean during the late miocene our result highlights the potential for enhanced variability in arctic precipitation in response to arctic sea ice decline caused by anthropogenic co 2 induced warming

pollen analysis and 14c age of moss remains in a permafrost core recovered from the active rock glacier murtel corvatsch swiss alps geomorphological and glaciological implications within the framework of core drilling through the permafrost of the active rock glacier murtel corvatsch in the swiss alps subfossil stem remains of seven different bryophyte species were found at a depth of 6 m below surface and about 3 m below the permafrost table in samples from massive ice the composition of the moss species points to the former growth of the recovered mosses in the nearest surroundings of the drill site a total of 127 pollen and spores captured by the mosses and representing 23 taxa were determined the local vegetation during deposition time must be characterized as a moss rich alpine grassland meadow rich in cyperaceae poaceae chenopodiaceae and asteraceae comparable to today s flora present around the study site for l4 c analysis accelerator mass spectrometry had to be used due to the small sample mass about 0 5 mg carbon content the mean conventional 14 c age of 2250 100 years 1 variability corresponds to ranges in the calibrated calendar age of 470 170 bc and 800 bc to ad 0 at statistical probabilities of 68 and 95 respectively this result is compared with the present day flow field as determined by high precision photogrammetry and with information about the thickness vertical structure and flow of the permafrost from borehole measurements total age of the rock glacier as a landform is on the order of 10 4 years the development of the rock glacier most probably started around the onset of the holocene when the area it now occupies became definitely deglaciated the bulk of the ice rock mixture within the creeping permafrost must be several thousand years old characteristic average values are estimated for 1 surface velocities through time cm a 1 2 long term ice and sediment accretion rates mm a 1 on the debris cone from which the rock glacier develops 3 retreat rates 1 2 mm a 1 of the cliff which supplies the debris to the debris cone and rock glacier and 4 ice content of the creeping ice rock mixture 50 90 by volume the pronounced supersaturation of the permafrost explains the steady state creep mode of the rock glacier

digital isochrons of the world s ocean floor we have created a digital age grid of the ocean floor with a grid node interval of 6 arc min using a self consistent set of global isochrons and associated plate reconstruction poles the age at each grid node was determined by linear interpolation between adjacent isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust were interpolated by estimating the ages of passive continental margin segments from geological data and published plate models we have constructed an age grid with error estimates for each grid cell as a function of 1 the error of ocean floor ages identified from magnetic anomalies along ship tracks and the age of the corresponding grid cells in our age grid 2 the distance of a given grid cell to the nearest magnetic anomaly identification and 3 the gradient of the age grid i e larger errors are associated with high age gradients at fracture zones or other age discontinuities future applications of this digital grid include studies of the thermal and elastic structure of the lithosphere the heat loss of the earth ridge push forces through time asymmetry of spreading and providing constraints for seismic tomography and mantle convection models

micro and nanobands in late archean and palaeoproterozoic banded iron formations as possible mineral records of annual and diurnal depositions abstract the microbands in precambrian banded iron formations bifs have been conjectured to record annual or even diurnal depositions however these bands have rarely been observed in high resolution at their true micro scale here i suggest that nanobands of fine grained hematite represent possible diurnal depositions and that microbands of chert jasper represent possible annual depositions in three sets of bifs 2460 myr bifs from the kuruman iron formation transvaal supergroup of south africa 2480 myr bifs from the dales gorge member of the brockman iron formation western australia and 2728 myr bifs from the hunter mine group abitibi greenstone belt canada observations made using scanning electron microscopy indicate that hematite and chert were syngenetic and that there was a hiatus between their precipitation and the genesis of the remainder of the minerals containing structural fe ii spindle like grains of hematite monocrystals of magnetite and ferro dolomite formed microbands of 30 70 m in thickness which appear cyclically in the matrix of the chert neither the band bound magnetite and dolomite nor the linear formations of the hematite spindles represent annual depositions due to their diagenetic features the thinnest microbands 3 12 m were observed in the chert and jasper and indicate depositional rates of 6 6 22 2 m myr in the bifs these rates are consistent with the integrated deposition rates calculated by geochronologic methods for the bifs if annual deposition is assumed the 26 nm nanobands observed only in hematite grains reflect an annual deposition of 18 6 m or 18 6 m myr which is also consistent with the depositional rate calculated by geochronologic methods it is tentatively suggested that these 26 nm nanobands were formed from the diurnal precipitation of fe iii resulting from the circadian metabolism of fe ii oxidizing or oxygen evolving photosynthetic microorganisms which slowed down the rise of atmospheric oxygen the diurnal precipitation of fe iii as hematite and the annual deposition of silica as chert jasper in the bifs provide internal clocks that may facilitate the examination of short term processes such as ecological oceanographic and climatic cycles that are recorded by the mineral or chemical compositions of bifs

high latitude meteoric δ18o compositions paleosol siderite in the middle cretaceous nanushuk formation north slope alaska siderite bearing pedogenic horizons of the nanushuk formation of the north slope alaska provide a critical high paleolatitude oxygen isotopic proxy record of paleoprecipitation supplying important empirical data needed for paleoclimatic reconstructions and models of greenhouse world precipitation rates siderite 18 o values were determined from four paleosol horizons in the national petroleum reserve alaska npr a grandstand 1 core and the values range between 17 6 and 14 3 peedee belemnite pdb with standard deviations generally less than 0 6 within individual horizons the 13 c values are much more variable ranging from 4 6 to 10 8 pdb a covariant 18 o versus 13 c trend in one horizon probably resulted from mixing between modified marine and meteoric phreatic fluids during siderite precipitation groundwater values calculated from siderite oxygen isotopic values and paleobotanical temperature estimates range from 23 0 to 19 5 standard mean ocean water smow minor element analyses show that the siderites are impure having enrichments in ca mg mn and sr minor element substitutions and mg fe and mg ca mg ratios also suggest the influence of marine fluids upon siderite precipitation the pedogenic horizons are characterized by gleyed colors rare root traces abundant siderite abundant organic matter rare clay and silty clay coatings and infillings some preservation of primary sedimentary stratification and a lack of ferruginous oxides and mottles the pedogenic features suggest that these were poorly drained reducing hydromorphic soils that developed in coal bearing delta plain facies and are similar to modern inceptisols model derived estimates of precipitation rates for the late albian of the north slope alaska 485 626 mm yr are consistent with precipitation rates necessary to maintain modern peat forming environments this information reinforces the mutual consistency between empirical paleotemperature estimates and isotope mass balance models of the hydrologic cycle and can be used in future global circulation modeling gcm experiments of greenhouse world climates to constrain high latitude precipitation rates in simulations of ancient worlds with decreased equator to pole temperature gradients

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

decoupling photochemical fe ii oxidation from shallow water bif deposition abstract oxidized fe minerals in archean paleoproterozoic banded iron formations bifs are commonly taken to indicate the presence of biogenic o 2 or photosynthetic fe ii oxidizing bacteria in the oceans photic zone however at least one viable abiogenic oxidation mechanism has been proposed prior to the rise of atmospheric oxygen and the development of a protective ozone layer the earth s surface was subjected to high levels of ultraviolet radiation bulk ocean waters that were anoxic at this time could have supported high concentrations of dissolved fe ii under such conditions dissolved ferrous iron species such as fe 2 and fe oh would have absorbed radiation in the 200 400 nm range leading to the formation of dissolved ferric iron fe iii which in turn would have hydrolyzed to form ferric hydroxide fe oh 3 at circumneutral ph cairns smith a g 1978 precambrian solution photochemistry inverse segregation and banded iron formations nature 76 807 808 braterman p s cairns smith a g and sloper r w 1983 photo oxidation of hydrated fe 2 significance for banded iron formations nature 303 163 164 this process has been invoked to account for bif deposition without need for biology francois l m 1986 extensive deposition of banded iron formations was possible without photosynthesis nature 320 352 354 here we evaluate the potential importance of photochemical oxidation using a combination of experiments and thermodynamic models the experiments simulate the chemistry of ambient precambrian seawater mixing with fe ii rich hydrothermal fluids with and without uv irradiation we find that if fe ii was effused from relatively shallow seamount type vent systems directly into an anoxic photic zone the photochemical contribution to solid phase precipitation would have been negligible instead most of the fe ii would have precipitated rapidly as an amorphous precursor phase to the ferrous silicate mineral greenalite fe 3 si 2 o 5 oh 4 and or the ferrous carbonate siderite feco 3 depending on different simulated atmospheric pco 2 levels conversely in experiments where fe ii was exposed either to phototrophic fe ii oxidizing bacteria or to o 2 ferric hydroxide formed rapidly and the precipitation of ferrous iron phases was not observed if as suggested on mass balance grounds bif deposition requires that fe be sourced from shallow seamount type systems then we are driven to conclude that oxide facies bif are the product of a rapid non photochemical oxidative process the most likely candidates being direct or indirect biological oxidation and that a significant fraction of bif could have initially been deposited as ferrous minerals

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

co2 forced climate thresholds during the phanerozoic abstract the correspondence between atmospheric co2 concentrations and globally averaged surface temperatures in the recent past suggests that this coupling may be of great antiquity here i compare 490 published proxy records of co2 spanning the ordovician to neogene with records of global cool events to evaluate the strength of co2 temperature coupling over the phanerozoic last 542 my for periods with sufficient co2 coverage all cool events are associated with co2 levels below 1000 ppm a co2 threshold of below 500 ppm is suggested for the initiation of widespread continental glaciations although this threshold was likely higher during the paleozoic due to a lower solar luminosity at that time also based on data from the jurassic and cretaceous a co2 threshold of below 1000 ppm is proposed for the initiation of cool non glacial conditions a pervasive tight correlation between co2 and temperature is found both at coarse 10 my timescales and fine resolutions up to the temporal limits of the data set million year timescales indicating that co2 operating in combination with many other factors such as solar luminosity and paleogeography has imparted strong control over global temperatures for much of the phanerozoic

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

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

on the isotopic composition in δd and δ18o of water and ice during freezing experiments on progressive unidirectional freezing are coi1 ducted to determine rhe evol ution in 00 and 51 bo of successive water samples and ice layers ta ken during the course of freezing r es ults indicate t hal lhi s evoluti on takes pl ace in a bd bibo diagram a long a strai ght line wi th a characteri sti c slope this slope different from that due to the precip itation effec t gives a finger print of the occurrence of a freezing or of a melt ing refreez ing process in the stud ied reservoir residual water was sampled at the beginning of the experiment after 40 80 85 90 and 95 of the material had frozen when the freezing process was complete the ice core was recovered and sectioned the samples covered the freezing ranges from 0 to 10 10 to 20 20 to 50 50 to 60 60 to 70 70 to 80

princess margaret arch re evaluation of an element of the eurekan orogen axel heiberg island arctic archipelago it is argued on the basis of structural stratigraphic and sedimentologic criteria that princess margaret arch developed during the principal phase of eurekan thrusting and folding and therefore is no older than middle eocene sub eureka sound group unconformities on eastern axel heiberg island are not associated with uplift on the eastern flank of this arch but are related to erosion of mesozoic sverdrup basin strata over local evaporite diapir domes and ridges considerable disparity exists between levels of erosion on the flanks of the arch and the level of erosion along its axis which cannot be explained by pre eocene uplift sedimentary facies and textural and petrographic characterisitics of eureka sound group strata do not reflect proximity to an arch palynomorph assemblages in the west derived syntectonic buchanan lake formation middle eocene contain reworked latest cretaceous spores and pollen that were derived from eureka sound group strata originally located on or close to the arch axis e

stratigraphy and floristics of eocene swamp forests from axel heiberg island canadian arctic archipelago a record of polar eocene forests is preserved as in situ tree stump fields and leaf litter mats in buchanan lake formation sediments on axel heiberg island in the canadian arctic archipelago stratigraphic examination at the centimetre to metre scale of peat coal lithology and macrofossil floristics in two levels of these fossil forests reflects small scale changes in forest composition and swamp hydrology horizontally and temporal variation vertically root system structure and tree base stratigraphy suggest that exposed tree stumps may not include only coeval individuals of a single forest stand but rather also individuals representing different phases of the forest through one cycle of the hydrological development of this eocene polar forest community earlier calculations of stand density and biomass based upon the assumption that all stumps represent coeval trees may therefore be greatly overestimated a mosaic of alnus fern bog mixed coniferous community and taxodiaceous metasequoia glyptos

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

glacier and lake level variations in west central europe over the last 3500 years on the basis of glacier and lake level records this paper attempts for the first time a comparison between high resolution palaeohydrological and palaeoglaciological data in west central europe over the past 3500 years a data set of tree ring width radiocarbon and archaeological data in addition to historical sources were used to reconstruct fluctuations of the great aletsch the gorner and the lower grindelwald glaciers in the swiss alps the three ice streams experienced nearly synchronous advances at c 1000 600 bc and ad 500 600 800 900 1100 1200 and 1300 1860 these glacier fluctuations show strong correspondence with lake level variations reconstructed in eastern france jura mountains and pre alps and on the swiss plateau this supports the hypothesis of climatically driven fluctuations historical data available for the period since ad 1550 reveal in detail various meteorological conditions behind the successive glacier advances however in agreement with the general trend shown by th

very high18o enrichment in archean cherts from south india implications for archean ocean temperature stable carbon and oxygen isotopic compositions of essentially unmetamorphosed archean 2 6 gyr old cherts and carbonates of the dharwar sequence of southern india from the northernmost part of the dharwar shimoga supracrustal belt kalche and nagargali have been determined the cherts from the nagargali area which preserve oolitic texture and cryptocrystalline silica show highly enriched 18 o values ranging from 28 to 31 4 o relative to smow such values are the highest yet reported from archean nondetrital sediments but are similar to those of modern marine cherts on the assumption of a seawater 18 o of 0 0 calculation of temperature based on the maximum 18 o value of 31 4 0 yields a value of 40 c this is significantly less than 70 80 c reported for the archean oceans based on cherts and chert phosphate pairs diagenetically recrystallized microcrystalline chert dolomite pairs of kalche area exhibit a range of oxygen isotopic ratios similar to those reported for archean cherts and carbonates from other parts of the world the temperature of diagenesis is estimated to be about 68 c

shrimp u pb zircon ages for the palaeoproterozoic kuruman iron formation northern cape province south africa evidence for simultaneous bif deposition on kaapvaal and pilbara cratons abstract stilpnomelane rich tuffaceous mudrocks are an important component of the palaeoproterozoic kuruman and griquatown iron formations in the northern cape province they document volcanic activity during the deposition of these iron formations and the zircon populations that they contain record syn depositional volcanism resedimentation and post depositional isotopic disturbance the trace element signatures of tuffaceous samples suggest that although zircons are felsic volcanogenic in origin mixing of felsic ash with basaltic ash and or muds in the water column was also likely in addition these rocks record minor terrigenous input and some samples indicate mixing with iron rich clays oxides and smectites moreover they reflect a shift from mafic volcanism e g mafic tuffs in the underlying gamohaan formation towards more felsic volcanism that is a trend also recorded for tuffaceous rocks in the brockman iron formation the best estimate of the depositional age for the top of the riries member and hence the kuruman iron formation is 2460 ma where most of the zircon populations were derived from volcanism coeval with bif deposition ages obtained in this study that are older than the 2465 5 ma age for the lower riries member probably represent resedimented pyroclastic deposits i e give eruptive ages from earlier eruptions that contain an unimodal zircon population and as such only provide maximum depositional ages although a compacted sedimentation rate csr for the entire kuruman iron formation is 3 4 m per million years a csr of about 22 m per million years is deduced for the riries member suggesting that there are cryptic gaps within the kuruman stratigraphic record the latter is comparable to the csr of 33 m per million years calculated for hamersley province bifs ages of the tuffaceous horizons in the kuruman iron formation are comparable to those from the brockman iron formation of the hamersley province the 2460 5 ma age for the top of the riries member corresponds to the 2459 3 ma age for the base of the joffre member and the 2463 5 ma whaleback shale member of the brockman iron formation although ca 2468 2478 ma ages reflect detrital or syn depositional zircon populations they are comparable to the 2470 4 ma s13 and the 2479 3 ma s9 macrobands of the dales gorge member brockman iron formation moreover the zircon age spectra and pb loss histories of both the kuruman and brockman iron formation tuffaceous sediments are strikingly similar without doubt the kuruman and brockman iron formations were deposited synchronously whether they were a response to global magmatic events or were deposited in the same basin are questions still being debated

rock glaciers protalus ramparts and pronival ramparts in the south eastern alps abstract rock glaciers and protalus ramparts are characteristic landforms of the periglacial domain often used as markers for the occurrence of permafrost in mountain terrains as such relict rock glaciers can be used for paleoclimate reconstructions we present here the first previously unreported rock glacier inventory of the south eastern alps including the north eastern most region of italy and slovenia interpreted from high resolution orthophotos and a high resolution digital terrain model interpolated from airborne laser scanning lidar we mapped 53 rock glaciers covering a total area of 3 45 km 2 the majority of rock glaciers are classified as relict and distributed between 1708 and 1846 m a s l with slope ranging between 19 and 27 in addition to rock glaciers we observed 66 protalus pronival ramparts having median elevation of 1913 m a s l and covering 0 48 km 2 more than half of the inventoried protalus ramparts are located in the more maritime area of the alps with higher precipitation compared to the location of rock glaciers using paleoclimate reconstruction based on the 1981 2010 climatological record of the area we infer that the rock glaciers formed during one of the dry and cold periods of the late pleistocene and early holocene possible evolution of the active pronival forms observed in the most maritime area of this alpine sector is also discussed

volatiles in basaltic glasses from the east pacific rise at 21 n implications for morb sources and submarine lava flow morphology pillow rim glasses from a suite of moderately evolved lavas erupted along the axis of the east pacific rise epr at 21 n were analyzed by high temperature mass spectrometry for volatile content concentrations of h2o f and cl in the 21 n glasses are low and correlate inversely with mg yielding well defined trends these and other geochemical data indicate derivation of the 21 n glasses from similar parental magmas produced from a highly depleted nearly homogeneous source 1 total volatile h2o f and s contents are lower and co2 content is somewhat higher in these samples than in previously analyzed mid atlantic ridge mar glasses 21 n glasses are similar in volatile content to glasses from the galapagos spreading center gsc at 95 w except in cl lower and co2 higher unlike most mar and gsc glasses co2 is the dominant volatile in all of the 21 n glasses with mg 62 all of the epr and gsc glasses contain reduced carbon species co and ch4 unlike most previously analyzed mar samples these data indicate that sources for mid ocean ridge basalts are extremely volatile poor 0 10 wt and are probably dominantly reduced below quartz fayalite magnetite buffer sheet flow and pillow basalts contain identical volatile contents thus volatile abundance is not a factor controlling flow morphology extrusion rate and or surface topography are probably the most important factors influencing flow morphology in submarine basalts h2o release patterns are however related to flow morphology mass pyrograms for sheet flow and pillow basalt glasses both show bimodal h2o release behavior at the same temperatures 800 c and1000 c 50 c however the dominant h2o release peak for sheet flow glasses is at the lower temperature for pillow rim glasses it is at the higher temperature infrared spectroscopic studies indicate that h2o in these glasses is present only as hydroxyl groups thus the cause of differences in the bimodal h2o release and how it is related to flow morphology is unclear

radiocarbon dating of palaeosol components in moraines in lapland northern sweden abstract accurate geochronologies are the key for comparison of palaeoclimate records in order to clarify problems concerning the geochronology of glacier fluctuations we dated palaeosols in moraines in the kebnekaise mountain region of swedish lapland these palaeosols already have been dated several years ago using bulk samples of the palaeosols and yielded ages of 6180 5790 and 2750 2100 cal yr bp in an attempt to evaluate the sources of contamination associated with bulk samples these soils were re dated by using coleoptera fragments cenococcum geophilum spores humic acids and woody plant tissues the new dates reveal that the two palaeosols found within the moraines represent much longer periods of time than was previously assumed soil formation periods can be distinguished for periods 7800 7580 6300 4080 2450 2000 and 1170 740 cal yr bp these age groups point to differentiated soil formation processes resedimentation bioturbation and or cryoturbation the results show that dated terrestrial macrofossils from glacial moraines indicate climate changes that are in accordance with other proxy records in northern and central scandinavia and in certain times off phase with glacier fluctuations in southern maritime norway this throws light on possible changing interaction of forcing factors during the holocene

iron silicate microgranules as precursor sediments to 2 5 billion year old banded iron formations banded iron formations bifs are chemical sedimentary rocks comprising alternating layers of iron rich and silica rich minerals that have been used to infer the composition of the early precambrian ocean and ancient microbial processes however the identity of the original sediments and their formation is a contentious issue due to postdepositional overprinting and the absence of modern analogues petrographic examination of the ca 2 5 ga dales gorge member of the brockman iron formation hamersley group western australia reveals the presence of abundant silt sized microgranules composed of stilpnomelane the microgranules are most common in the least altered bif where they define sedimentary laminations implying a depositional origin we suggest that the precursor mineral was an iron rich silicate that formed either in the water column or on the seafloor the microgranular texture may have developed due to clumping of amorphous mud forming silt sized floccules the microgranules were resedimented by dilute density currents and deposited in lamina sets comprising a basal microgranular rich lamina overlain by amorphous mud with dispersed microgranules the lamina sets collectively define plane lamination structure probably of the lower flow regime the microgranular textures are preserved only where early diagenetic silica prevented the compaction of lamina sets episodic resedimentation of iron silicates alternating with periods of nondeposition and seafloor silicification provides an explanation for some of the characteristic banding in bif we propose that for most of the early precambrian the persistence of ferruginous oceans with elevated silica concentrations favored the widespread growth of iron silicate minerals which in environments starved of continental sediments formed extensive deposits of the precursor sediment to iron formation

beyond methane towards a theory for the paleocene eocene thermal maximum abstract extreme global warmth and an abrupt negative carbon isotope excursion during the paleocene eocene thermal maximum petm have been attributed to a massive release of methane hydrate from sediments on the continental slope 1 however the magnitude of the warming 5 to 6 c 2 3 and rise in the depth of the ccd 2 km 4 indicate that the size of the carbon addition was larger than can be accounted for by the methane hydrate hypothesis additional carbon sources associated with methane hydrate release e g pore water venting and turbidite oxidation are also insufficient we find that the oxidation of at least 5000 gt c of organic carbon is the most likely explanation for the observed geochemical and climatic changes during the petm for which there are several potential mechanisms production of thermogenic ch4 and co2 during contact metamorphism associated with the intrusion of a large igneous province into organic rich sediments 5 is capable of supplying large amounts of carbon but is inconsistent with the lack of extensive carbon loss in metamorphosed sediments as well as the abrupt onset and termination of carbon release during the petm a global conflagration of paleocene peatlands 6 highlights a large terrestrial carbon source but massive carbon release by fire seems unlikely as it would require that all peatlands burn at once and then for only 10 to 30 ky in addition this hypothesis requires an order of magnitude increase in the amount of carbon stored in peat the isolation of a large epicontinental seaway by tectonic uplift associated with volcanism or continental collision followed by desiccation and bacterial respiration of the aerated organic matter is another potential mechanism for the rapid release of large amounts of co2 in addition to the oxidation of the underlying marine sediments the desiccation of a major epicontinental seaway would remove a large source of moisture for the continental interior resulting in the desiccation and bacterial oxidation of adjacent terrestrial wetlands

permafrost conditions in the mediterranean region since the last glaciation the relatively warm climate conditions prevailing today in the mediterranean region limit cold geomorphological processes only to the highest mountain environments however climate variability during the late pleistocene and holocene has led to significant spatio temporal variations of the glacial and periglacial domain in these mountains including permafrost conditions here we examine the distribution and evolution of permafrost in the mediterranean region considering five time periods last glaciation deglaciation holocene little ice age lia and present day the distribution of inactive permafrost derived features as well as sedimentary records indicates that the elevation limit of permafrost during the last glaciation was between 1000 m and even 2000 m lower than present permafrost was also widespread in non glaciated slopes above the snowline forming rock glaciers and block streams as well as meter sized stone circles in relatively flat summit areas as in most of the northern hemisphere the onset of deglaciation in the mediterranean region started around 19 20 ka the ice free terrain left by retreating glaciers was subject to paraglacial activity and intense periglacial processes under permafrost conditions many rock glaciers protalus lobes and block streams formed in these recently deglaciated environments though most of them became gradually inactive as temperatures kept rising especially those at lower altitudes following the younger dryas glacial advance the early holocene saw the last massive deglaciation in mediterranean mountains accompanied by a progressive shift of permafrost conditions to higher elevations it is unlikely that air temperatures recorded in mediterranean mountains during the holocene favoured the existence of widespread permafrost regimes with the only exception of the highest massifs exceeding 2500 3000 m lia colder climate promoted a minor glacial advance and the spatial expansion of permafrost with the development of new protalus lobes and rock glaciers in the highest massifs finally post lia warming has led to glacial retreat disappearance enhanced paraglacial activity shift of periglacial processes to higher elevations degradation of alpine permafrost along with geoecological changes

regional uplift gas hydrate dissociation and the origins of the paleocene eocene thermal maximum much of the north atlantic region experienced hundreds of metres of transient uplift during the latest paleocene regional uplift should cause dissociation of gas hydrates stored in marine sedimentary strata and the subsequent release of carbon to the atmosphere should enhance warming through the greenhouse effect we have developed models of the spatial distribution of uplift to match observational constraints from sedimentary basins fringing the north atlantic in order to provide quantitative estimates of the carbon released upon uplift these models are coupled to a simple parameterisation of carbon storage in sub seafloor gas hydrates results of modelling indicate that large quantities of carbon can be released by uplift with some models generating over 2000 gt of carbon release the possibility that latest paleocene regional uplift occurred over the same time interval as onset of the paleocene eocene thermal maximum petm around 30 kyr cannot be ruled out using current stratigraphical observations or mantle convection models in this case the uplift mechanism alone can account for the magnitude and timing of the carbon isotope excursion associated with the petm alternatively if the duration of latest paleocene uplift was closer to the upper bound of around 1 myr or if other paleocene uplift events were equally significant then gas hydrate dissociation upon uplift could have contributed to longer term changes in ocean temperature and carbon isotope composition through the late paleocene these temperature changes in combination with development of the north atlantic land bridge during the latest paleocene culmination of uplift may be able to force rapid changes in ocean circulation and cause phenomena such as the petm

cross bedded woody debris from a pliocene forested river system in the high arctic beaufort formation meighen island canada abstract cross bedding the inclined internal stratification that records the migration of certain transverse sedimentary bedforms is nearly ubiquitous in current transported bedload sediments although examples of the structure are known from inorganic clastic sediments and sedimentary rocks from practically all depositional environments and intervals of geologic history here we report cross bedded lenses that are composed wholly or significantly of woody debris in pliocene alluvium of the beaufort formation in the canadian high arctic the uniqueness of cross bedded woody debris has hitherto been overlooked but we demonstrate that in the entire phanerozoic record it is apparently restricted to alluvium deposited during a warm climatic interval that permitted the growth of boreal type forests within 10 latitude of the north pole the marked spatiotemporal restriction of cross bedded woody debris implies that there may be environmental factors unique to polar forests which promote the subaqueous transport of large amounts of fine woody debris as fluvial bedload we propose a non uniformitarian conceptual model for the formation of cross bedded woody debris in forested polar rivers whereby an exceptional abundance of woody debris could accumulate and become saturated and denser than water due to reduced decomposition on forest floors that were subject to prolonged periods of darkness and subzero temperatures

reconstruction of temperature in the central alps during the past 2000 yr from a δ18o stalagmite record the precisely dated isotopic composition of a stalagmite from spannagel cave in the central alps is translated into a highly resolved record of temperature at high elevation during the past 2000 yr temperature maxima during the medieval warm period between 800 and 1300 ad are in average about 1 7 8c higher than the minima in the little ice age and similar to present day values the high correlation of this record to d 14 c suggests that solar variability was a major driver of climate in central europe during the past 2 millennia d 2005 elsevier b v all rights reserved

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

high arctic forests during the middle eocene supported by moderate levels of atmospheric co2 fossils from paleogene high arctic deposits provide some of the clearest evidence for greenhouse climates in the past and offer the potential to improve our understanding of earth system dynamics in a largely ice free world one of the most well known and stunningly preserved polar forest sites napartulik crops out of middle eocene 47 9 37 8 ma sediments on eastern axel heiberg island nunavut canada 78 n paleolatitude an abundance of data from napartulik suggests mean annual temperatures at least 30 c warmer than today and atmospheric water loads 2 current levels despite this wealth of paleontological and paleoclimatological data there are currently no direct constraints on atmospheric co 2 levels for napartulik or any other polar forest site here we apply a new plant gas exchange model to metasequoia dawn redwood leaves to reconstruct atmospheric co 2 from six fossil forest horizons at napartulik individual reconstructions vary between 392 ppm and 474 ppm with a site median of 424 ppm 351 523 ppm at 95 confidence these estimates represent the first direct constraints on co 2 for a high arctic forest and suggest that the temperate conditions present at napartulik during the middle eocene were maintained under co 2 concentrations 1 5 pre industrial levels our results support the case that long term climate sensitivity to co 2 in the past was sometimes high even during largely ice free periods highlighting the need to better understand the climate forcings and feedbacks responsible for this amplification

reactive oxygen species at the oxide water interface formation mechanisms and implications for prebiotic chemistry and the origin of life the goal of our study is to identify free radical formation pathways on mineral surfaces organic molecules on early earth might have been modified or decomposed by such pathways thus affecting the total organic inventory for prebiotic synthesis reactions specifically we evaluated several common oxide minerals under a range of environmental conditions and combinations of conditions ph o2 level uv wavelength and particle loading for formation of highly reactive oxygen species ros at the oxide surfaces by quantifying the generated oh and h2o2 we identified anatase rutile tio2 tio2 and hematite fe2o3 as active in ros production and importantly found different dominant pathways for ros formation on anatase rutile versus hematite hydroxyl radicals oh in anatase and rutile suspensions were generated mainly through the oxidation of oh by photo generated holes and h2o2 was generated through the combination of an oh radical with an oh and a hole this pathway for the tio2 phases did not require the presence of o2 and was not shut down under anaerobic conditions in contrast formation of h2o2 and oh in hematite suspensions involved reduction of o2 by electrons which was inhibited under anaerobic conditions the surface ros as well as free radicals formed by reactions with other gases on early earth atmosphere were capable of destroying molecules such as lipids and pre rna or rna essential to assembly of protocells and survival of the earliest cells at the same time surface associated ros and other free radicals may also have promoted aminoamide formation thus the surface ros would have affected prebiotic organic compound inventory and protocell early life evolution

alternating si and fe deposition caused by temperature fluctuations in precambrian oceans precambrian banded iron formations contain thin alternating layers of iron and silica rich minerals microbial culture experiments show that these alternations could be caused by changes in the relative dominance of microbial iron oxidation and abiotic silica precipitation driven by fluctuating ocean temperature

cenozoic global plate motions cenozoic global plate motions relative to the hot spots are investigated and compared to plate motions in a mean lithosphere reference frame plate motions were analyzed over six time intervals divided by ages 10 25 43 48 and 56 ma chosen as much as possible to coincide with key plate reorganizations alternative motion circuits and rotational parameters were considered and evaluated with paleomagnetic data from the pacific and north american plates the circuit found to be in best agreement with the paleomagnetic data is one in which the hot spots in the atlantic region are assumed to be fixed relative to the hot spots in the pacific region throughout the cenozoic the hot spot and mean lithosphere reference frames have been in continual slow relative motion the rate of motion is nonuniform however most of the motion having occurred during the middle cenozoic the net cenozoic rotation of the lithosphere relative to the hot spots is described by a right handed rotation of 7 about a euler pole at 46 s 87 e which yields a 5 displacement of the north poles of the two reference frames this motion is small enough that inferences drawn about plate speeds in one reference frame should be valid in the other analysis of the global motions resulting from our preferred model showed that many characteristics of current plate motions have persisted throughout the cenozoic plate speeds correlate with latitude plates moving faster near the equator than near the poles throughout the cenozoic as at present continental plates except for the indian plate moved slower than oceanic plates throughout the cenozoic even the structure of the velocity fields as revealed in a contour of root mean square velocities in equatorial bands persists throughout the cenozoic the migration of the paleomagnetic axis over time is also compared to the hot spot and mean lithosphere reference frames the paleomagnetic axis has shifted 5 10 relative to the hot spot frame and a lesser amount relative to the mean lithosphere frame

expansion of alpine glaciers in pacific north america in the first millennium a d radiocarbon ages and lichen dated moraines from 17 glaciers in coastal and near coastal british columbia and alaska document a widespread glacier advance during the first millennium a d glaciers at several sites began advancing ca a d 200 300 based on radiocarbon dated overridden forests the advance is centered on a d 400 700 when glaciers along an 2000 km transect of the pacific north american cordillera overrode forests impounded lakes and deposited moraines the synchroneity of this glacier ad vance and inferred cooling over a large area suggest a regional climate forcing and to gether with other proxy evidence for late holocene environmental change during the me dieval warm period and little ice age provide support for millennial scale climate variability in the north pacific region

a precisely dated climate record for the last 9 kyr from three high alpine stalagmites spannagel cave austria 1 here we use the 18o time series of three stalagmites from the high alpine spannagel cave austria which grew in small distance from each other to construct a precisely dated continuous 18o curve for the last 9 kyr comnispa this speleothem record is not influenced by effects of kinetic isotope fractionation due to the low temperatures in the cave thus the variations in 18o can be interpreted in terms of past climate change comnispa exhibits several oscillations within the holocene and their timing and duration is in agreement with that documented by other alpine archives

rock glacier dynamics and paleoclimatic implications many rock glaciers contain massive ice that may be useful in paleoclimate studies interpreting geochemical ice core records from rock glaciers requires a thorough understanding of rock glacier structure and dynamics high precision surface velocity data were obtained for the galena creek rock glacier absaroka mountains wyoming surface velocities range from 0 to 1 00 m yr and vary across the rock glacier in a manner similar to true glaciers we used glen s flow law to calculate the thickness of the deforming ice layer the modeled ice thickness ranges from 0 to 50 m and is confirmed by direct observations this agreement shows that rock glacier movement can be entirely explained by deformation of massive ice within the rock glacier neither basal sliding nor deformation of basal debris is necessary recovered ice cores to depths of 25 m contain thin debris layers associated with summer ablation in the accumulation zone the ages of four samples of organic material removed from several debris layers inthe southern half of the rock glacier range from 200 40 to 2250 35 14c yr b p demonstrating that the rock glacier formed well before the little ice age and may contain ice dating to the middle holocene or earlier

a new method to estimate accumulation rates of lignites in the eocene buchanan lake formation canadian arctic abstract exceptionally well preserved eocene plant fossils occurring in leafy litter mats from the buchanan lake formation canadian arctic make it possible to estimate the accumulation rate of the lignite this method is based on the assumption that the projected leaf surface area of individual tree species per unit of ground surface area leaf area index is more or less constant the calculated accumulation rate of 1 6 mm year has been corrected to the minimum accumulation rate of 0 8 mm year by considering the effects of organic decomposition since the compaction ratio of the leaf lignite is difficult to estimate correct comparison with accumulation rates of modern and quaternary peats that have been determined by using 14c ages is impossible however the accumulation rate calibrated in the peat stage of coalification by using the compaction ratio of woods embedded in the leaf lignite is within the range of accumulation rates determined for modern and quaternary peats

generation of reactive oxygen species on pyrite surfaces a likely oxidation mechanism for near vent hydrothermal fluid dominated bifs abstract the key to understand the origin of banded iron formations bifs formed in 3 8 2 5 ga is to identify the oxidation mechanism of fe2 in anoxic oceans in this study we proposed a likely pyrite induced fe2 oxidation mechanism for near vent hydrothermal fluid dominated bifs a series of important environmental conditions including light intensity wavelength and ph were considered and monitored to check their effects on the production of reactive oxygen species ros in anaerobic pyrite suspensions by quantifying the concentration of oh and h2o2 we observed a stable ros production as induced by pyrite in both dark and light under a wide ph range interestingly light significantly promoted the producing rate of ros which increased with the light intensity but was poorly correlated with the light wavelength in addition the producing rate of ros remarkably increased as the ph decreased from 6 0 to 3 0 suggesting the acidic conditions were more beneficial for ros generation the production of ros could be attributed to the semiconducting photocatalysis of pyrite and the sulfur deficient defect on its surface based on the sulfur content of volatiles in modern submarine basalts and black smokers we assumed that the concentration of h2s in archean hydrothermal fluids ranged from 0 5 to 55 mmol kg combined with the experimental results of h2o2 producing rates under 150 mw cm2 irradiation at ph 3 0 and under dark at ph 6 0 the h2o2 flux of 6 9 105 1 1 109 mol yr could be estimated in a thermal flow this value covered the amount of h2o2 required for fe2 oxidation in archean oceans to form the near vent hydrothermal fluid dominated bifs 1 7 106 1 3 107 mol yr the reaction kinetics revealed that the conversion of amorphous fes into pyrite under hydrothermal conditions was very quick while the consumption of h2o2 during the back reaction with pyrite was quite limited this view can explain why this type of bifs typically occurs as intercalated layers in volcanic rocks and is associated with volcanogenic massive sulfide ore vms type deposits

the late eocene 187os 188os excursion chemostratigraphy cosmic dust flux and the early oligocene glaciation abstract high resolution records ca 100 kyr of os isotope composition 187os 188os in bulk sediments from two tropical pacific sites odp sites 1218 and 1219 capture the complete late eocene 187os 188os excursion and confirm that the late eocene 187os 188os minimum earlier reported by ravizza and peucker ehrenbrink earth planet sci lett 210 2003 151 165 is a global feature using the astronomically tuned age models available for these sites it is suggested that the late eocene 187os 188os minimum can be placed at 34 5 0 1 ma in the marine records in addition two other distinct features of the 187os 188os excursion that are correlatable among sections are proposed as chemostratigraphic markers which can serve as age control points with a precision of ca 0 1 myr we propose a speculative hypothesis that higher cosmic dust flux in the late eocene may have contributed to global cooling and early oligocene glaciation oi 1 by supplying bio essential trace elements to the oceans and thereby resulting in higher ocean productivity enhanced burial of organic carbon and draw down of atmospheric co2 to determine if the hypothesis that enhanced cosmic dust flux in the late eocene was a cause for the 187os 188os excursion can be tested by using the paired bulk sediment and leachate os isotope composition 187os 188os were also measured in sediment leachates results of analyses of leachates are inconsistent between the south atlantic and the pacific sites and therefore do not yield a robust test of this hypothesis comparison of 187os 188os records with high resolution benthic foraminiferal 18o records across the eocene oligocene transition suggests that 187os flux to the oceans decreased during cooling and ice growth leading to the oi 1 glaciation whereas subsequent decay of ice sheets and deglacial weathering drove seawater 187os 188os to higher values although the precise timing and magnitude of these changes in weathering fluxes and their effects on the marine 187os 188os records are obscured by recovery from the late eocene 187os 188os excursion evidence of the global influence of glaciation on supply of os to the ocean is robust as it has now been documented in both pacific and atlantic records

the temperature of europe during the holocene reconstructed from pollen data we present the first area average time series reconstructions of warmest month coldest month and mean annual surface air temperatures across europe during the last 12 000 years these series are based on quantitative pollen climate reconstructions from over 500 pollen sites assimilated using an innovative four dimensional gridding procedure this approach combines three dimensional spatial gridding with a fourth dimension represented by time allowing data from irregular time series to be focussed onto a regular time step we provide six regional reconstructed temperature time series as well as summary time series for the whole of europe the results suggest major spatial and seasonal differences in holocene temperature trends within a remarkably balanced regional and annual energy budget the traditional mid holocene thermal maximum is observed only over northern europe and principally during the summer this warming was balanced by a mid holocene cooling over southern europe whilst central europe occupied an intermediary position changes in annual mean temperatures for europe as a whole suggest an almost linear increase in thermal budget up to 7800 bp followed by stable conditions for the remainder of the holocene this early holocene warming and later equilibrium has been mainly modulated by increasing winter temperatures in the west which have continued to rise at a progressively decreasing rate up to the present day

the arctic forest of the middle eocene abstractlush forests dominated by deciduous conifers existed well north of the arctic circle during the middle eocene 45 ma the fossil forest site located on axel heiberg island canada has yielded a particularly rich assemblage of plant macro and microfossils as well as paleosols all exquisitely preserved methods ranging from classical paleobotany to stable isotope geochemistry have been applied to materials excavated from the fossil forest and have revealed layers of diverse conifer forests with a rich angiosperm understory that successfully endured three months of continuous light and three months of continuous darkness paleoenvironmental reconstructions suggest a warm ice free environment with high growing season relative humidity and high rates of soil methanogenesis methods to evaluate intraseasonal variability highlight the switchover from stored to actively fixed carbon during the short annual growing season

global reconstructions of cenozoic seafloor ages implications for bathymetry and sea level abstract although accurate estimates of cenozoic seafloor ages will serve to further our understanding of the relationship between mantle dynamics plate tectonics and a variety of surficial geological processes it is difficult to estimate ages of subducted seafloor however given the near constancy of surface velocities within a tectonic stage we can estimate cenozoic plate ages even for subducted lithosphere we reconstruct seafloor ages based on the cenozoic plate reconstructions and absolute rotation poles of gordon and jurdy r g gordon and d m jurdy cenozoic global plate motions j geophys res 91 1986 12389 12406 for the western pacific we explore alternative models based on the reconstructions of hall r hall cenozoic geological and plate tectonic evolution of se asia and the sw pacific computer based reconstructions model and animations j asian earth sci 20 2002 353 434 both reconstructions indicate an increase in average seafloor age since the early cenozoic resulting in an increase in the volume of ocean basins and a decreased sea level since the early cenozoic these trends are more pronounced for the gordon and jurdy r g gordon and d m jurdy cenozoic global plate motions j geophys res 91 1986 12 389 12 406 reconstruction because the hall r hall cenozoic geological and plate tectonic evolution of se asia and the sw pacific computer based reconstructions model and animations j asian earth sci 20 2002 353 434 reconstruction retains older seafloor in the western pacific which approximately halves the predicted sea level decrease since the early cenozoic 250 vs 125 m compared to geologic estimates of 150 m these changes in sea level occur despite decreases in oceanic lithosphere production rates of only about 20 in both models thus the changing distribution of seafloor age has a larger effect on sea level than changes in spreading rates or ridge lengths these reconstructions can also be used to estimate past heat flow the volume of subducted buoyancy and changes in the bathymetry of the cenozoic ocean basins

summer temperatures of late eocene to early oligocene freshwaters the marine foraminiferal isotope record displays a positive 18o shift early in the oligocene which has been identified as the onset of the antarctic oi 1 glaciation reported here are the first oxygen isotope derived summer paleotemperatures for continental freshwater in the northern hemisphere hampshire basin isle of wight uk leading up to and across this event these paleotemperatures are derived from multiple paleoproxies rodent tooth enamel gastropod shells charophyte gyrogonites and fish otoliths and are independent of freshwater evaporation effects and changes in ice volume we conclude that a fluctuating mesothermal climate existed but that there was no significant decrease in summer temperatures across the oi 1 glaciation this result is concordant with several other studies in suggesting that the majority of the isotopic shift in the marine realm across the oi 1 glaciation is linked to changes in antarctic ice volume and not to global temperature change our new approach has allowed us to derive numerical values for summer temperatures as well as to reconstruct relative temperature change across this key interval of the eocene oligocene transition

deuterium excess record in a southern tibetan ice core and its potential climatic implications a 55 m long ice core drilled close to bedrock from mt noijin kangsang on the southern tibetan plateau in summer 2007 was annually dated covering the period of 1864 2006 ad the stable isotope ratios 18o and d of the ice core were measured and thereby the deuterium excess d was calculated by d d 8 18o for the individual ice samples results show that the d values of the ice samples were predominantly controlled by the moisture sources the significant increasing trend of annual mean d values along the ice core is mainly related to the rapid warming of the tropical indian ocean although the tendency is subjected to the modulation by the western derived moisture the decreasing indian monsoon precipitation on the southern tibetan plateau physically linked with the increasing tropical indian ocean sst reduced the share of monsoon precipitation in the annual total accumulation making an additional contribution to the significant increase of annual mean d in the noijin kangsang ice core with high values during the past 143 years

late holocene glacier growth in svalbard documented by subglacial relict vegetation and living soil microbes much renewed research interest in arctic regions stems from the increasing concentration of atmospheric greenhouse gases and the alleged climatic sensitivity of high latitude areas glacier and permafrost changes are among a number of proxies used for monitoring past and present arctic climate change here we present observations on frozen in situ soil and vegetation found below cold based glacier longyearbreen 78813 n 2 km upstream from the present glacier terminus dating of the relict vegetation indicates that the glacier has increased in length from about 3 km to its present size of about 5 km during the last c 1100 years the meteorological setting of non surging longyearbreen suggests this example of late holocene glacier growth represents a widespread phenomenon in svalbard and in adjoining arctic regions in addition we use the subglacial permafrozen soil system to evaluate microbial survival capacity over considerable time periods and we present evidence for microbes having survived more than 1100 years in a subglacial permafrozen state

sensitivity of seawater oxygen isotopes to climatic and tectonic boundary conditions in an early paleogene simulation with giss modele r 1 an isotope enabled ocean atmosphere general circulation model giss modele r is used to estimate the spatial gradients of the oxygen isotopic composition of seawater 18osw where is the deviation from a known reference material in per mil during the early paleogene 45 65 ma understanding the response of 18osw to changes in climatic and tectonic boundary conditions is important because records of carbonate 18o document changes in hydrology as well as changes in temperature and global ice volume we present results from an early paleogene configuration of modele r which indicate that spatial gradients of surface ocean 18osw during this period could have been significantly different to those in the modern ocean the differences inferred from modele r are sufficient to change early paleogene sea surface temperature estimates derived from primary carbonate 18o signatures by more than 2 c in large areas of the ocean in the north atlantic indian and southern oceans the differences in 18osw inferred from our simulation with modele r are in direct contrast with those from another 18o tracing model study which used different but equally plausible early paleogene boundary conditions the large differences in 18osw between preindustrial and early paleogene simulations and between models emphasizes the sensitivity of 18osw to climatic and tectonic boundary conditions for this reason absolute estimates of eocene paleocene temperature derived from carbonate 18o alone are likely to have larger uncertainties than are usually assumed

isotopic composition of precipitation in italy a first overall map abstract composite monthly samples of atmospheric precipitation were collected over different periods of time ranging from one to seven years at 77 different locations throughout italy these samples were measured for their oxygen and hydrogen isotopic composition to obtain basic information for hydrological and meteorological studies in this area on the basis of the results obtained a first map of the isotopic composition of precipitations in italy has been drawn up the main features of this map are the following 1 no isotopic latitudinal gradient has been found along the tyrrhenian coast from sicily to the italian french border despite the considerable range of latitude 2 a minor latitudinal gradient is found in the southeasternmost section of the country apulia partially favored by the local morphology 3 a marked shadow effect of the apennines is apparent along the southern section of the po valley and along the central section of the adriatic coast 4 the contribution of water vapor from the northernmost section of the adriatic sea affects the eastern and central sections of the po plain 5 the shadow effect of the alps is considerably smaller than expected 6 the isotopic vertical gradients calculated in nine different areas and based on groups of two to five different stations vary but are essentially close to about 0 2 100 m 7 when mean monthly temperature values were available their relationship with the isotopic composition of precipitation was found to be on average very poor 8 the relationship between mean 18o and mean d calculated for the collection locations shows shifts of both the slope and the deuterium excess when compared to the global meteoric water line these shifts are different for northern central and southern italy 9 in a few cases anomalously low monthly values suggest the existence of pronounced amount effects

the internal structure of rock glaciers and recently deglaciated slopes as revealed by geoelectrical tomography insights on permafrost and recent glacial evolution in the central and western alps italy france abstract ground ice of permafrost origin and sedimentary ice of glacial origin can coexist in locations where rock glaciers and glaciers interacted as well as in glacigenic sediments abandoned by a retreating glacier and subsequently exposed again to atmospheric cooling some of these geomorphological settings in the central foscagno rock glacier and western alps marinet and schiantala rock glaciers schiantala debris covered glacier maledia glacier were explored by means of geoelectrical tomographies the aim was that of inferring the presence of ice and cryologically interpreting electrical stratigraphies in order to test whether or not the internal structure of these landforms can be used for the reconstruction of recent permafrost and glacier evolution geomorphological data assisted these reconstructions and available borehole stratigraphies were used to calibrate the resistivities along with the ice debris mixture massive ice has also been found as lenses both at the apex and the front of the studied rock glaciers these lenses of sedimentary origin are thought to be transferred from a glacier snout to sectors of rock glacier and eventually embedded into the permafrost creep the scarcity of frozen debris in the mid upper part of the rock glaciers as revealed by low resistivity values can be due to the disruptive effect of the over riding glacier over the permafrost the near surface sedimentary ice masses detected along the slopes of the studied glacial cirques are interpreted as or debris covered terminations of the glaciers still visible upward or as fragments of it detached by the main bodies these ice masses are locally associated to medium high resistive sediments consistent with permafrost occurrence this indicates that the non glacial environment established during the deglaciation allowed the onset of frozen sediments formation overall the results indicate that internal structure of rock glaciers and recent deglaciated slopes can store the different climate related episodes occurred in a specific area such as those linked to the shifting between glacial to criotic condition and vice versa

silicon isotopes in 3 8 ga west greenland rocks as clues to the eoarchaean supracrustal si cycle we report mc icp ms si isotopic measurements 29si recalculated as 30si on micro subsamples at 500 m scale from several major rock types of the 3 8 ga old isua greenstone belt igb southern west greenland and surrounding eoarchaean terrains with a large overall range of variations 2 80 30si 0 68 they demonstrate strong involvement of surface fluids enriched with dissolved si the resistance of si isotopes to metamorphic resettings and metasomatic overprints is also established metabasaltic pillows and metasediments display similar 30si enriched signatures suggesting that emergent surfaces of the eoarchaean protocrust were composed of slightly weathered hydrothermally altered mafic ultramafic bodies isua magnetite quartz banded iron formation bif is strongly depleted in 30si relative to all coeval rocks this depletion supports rayleigh controlled precipitation from seafloor vented hydrothermal fluids in contrast banded quartz pyroxene rocks from akilia island some 150 km southwest of the igb which some authors have identified as bif related yield quartz with si isotopic composition 30si 0 36 similar to metamorphic derived quartz 30si 0 50 this supports their derivation from tectonic reworking of ultramafic protoliths penetrated by metamorphic silica and is at variance with their proposed role as harboring earliest biogenic tracers