responses of ocean circulation and carbon cycle to changes in the position of the southern hemisphere westerlies at last glacial maximum 1 we explore the impact of a latitudinal shift in the westerly wind belt over the southern ocean on the atlantic meridional overturning circulation amoc and on the carbon cycle for last glacial maximum background conditions using a state of the art ocean general circulation model we find that a southward northward shift in the westerly winds leads to an intensification weakening of no more than 10 of the amoc this response of the ocean physics to shifting winds agrees with other studies starting from preindustrial background climate but the responsible processes are different in our setup changes in amoc seemed to be more pulled by upwelling in the south than pushed by downwelling in the north opposite to what previous studies with different background climate are suggesting the net effects of the changes in ocean circulation lead to a rise in atmospheric pco2 of less than 10 atm for both northward and southward shift in the winds for northward shifted winds the zone of upwelling of carbon and nutrient rich waters in the southern ocean is expanded leading to more co2outgassing to the atmosphere but also to an enhanced biological pump in the subpolar region for southward shifted winds the upwelling region contracts around antarctica leading to less nutrient export northward and thus a weakening of the biological pump these model results do not support the idea that shifts in the westerly wind belt play a dominant role in coupling atmospheric co2 rise and antarctic temperature during deglaciation suggested by the ice core data

late miocene environmental change in nepal and the northern indian subcontinent stable isotopic evidence from paleosols neogene sediments belonging to the siwalik group crop out in the himalayan foothills along the length of southern nepal carbon and oxygen isotopic analyses of siwalik paleosols from four long siwalik sections record major ecological changes over the past 11 m y the carbon isotopic composition of both soil carbonate and organic matter shifts dramatically starting ca 7 0 ma marking the displacement of largely c3 vegetation probably semi deciduous forest by c4 grasslands by the beginning of the pliocene all the flood plains of major rivers in this region were dominated by monsoonal grasslands the floral shift away from woody plants is also reflected by the decline and final disappearance of fossil leaves and the decrease in coal logs in the latest miocene a similar carbon isotopic shift has been documented in the paleosol and fossil tooth record of pakistan and in terrigenous organic matter from the bengal fan showing that the floral shift was probably continentwide the latest miocene also witnessed an average change of 4 in the oxygen isotopic composition of soil carbonate as observed previously in pakistan the reasons for this are unclear if not diagenetic a major environmental change is indicated perhaps related to that driving the carbon isotopic shift recently described pollen and leaf fossils from the surai khola section show that evergreen forest was gradually displaced by semi deciduous and dry deciduous forest between 11 and 6 ma the gradual nature of this floral shift which culminated in the rapid expansion of c4 grasses starting 7 0 m y ago is difficult to explain by a decrease in atmospheric pco2 alone cerling et al 1993 but fits well with a gradual onset of monsoonal conditions in the late miocene in the northern indian subcontinent himalayan uplift driving both monsoonal intensification and consumption of co2 through weathering may be the common cause behind major late miocene environmental change globally however the decline of effective moisture associated with monsoon development has probably slowed not increased the rate of consumption of co2 by chemical weathering of himalayan sediments

middle miocene ocean climate transition high resolution oxygen and carbon isotopic records from deep sea drilling project site 588a southwest pacific high resolution stable isotopic records are presented for the epi benthic foraminifer cibicidoides the inferred shallow dwelling planktonic globigerinoides quadrilobatus and the inferred deep dwelling planktonic globoquadrina dehiscens from the middle miocene 16 12 ma of deep sea drilling project site 588a lord howe rise southwest pacific high resolution multiple species oxygen and carbon isotopic data define the timing and character of the well known middle miocene climatic oceanographic transition with a resolution comparable to quaternary records the benthic foraminiferal 18o record is marked by several large fluctuations from 16 to 14 8 ma followed by a series of rapid 50 kyr 18o increases that suggest a new state of the ocean climate system after 14 8 ma the total middle miocene benthic oxygen isotopic increase of 1 2 is largely incorporated in two steps an increase of 0 8 from 14 5 to 14 0 ma and a second increase of 0 7 from 13 45 to 12 45 ma each step is comprised of a series of marked 18o increases indicative of rapid east antarctic ice sheet growth and contemporaneous deepwater cooling a strong covariance of 0 7 between the benthic and deep dwelling planktonic species from 14 5 to 14 0 ma including a rapid increase from 14 1 to 14 05 ma suggests a 0 7 increase in the 18o composition of seawater 18osw because of east antarctic ice sheet growth comparison of the 18o record of gs quadrilobatus suggests that surface waters warmed at this site by 3 c from 14 1 to 13 6 ma carbon isotopic time series for each species generally covary throughout the early to middle miocene interval 16 12 ma confirming that 13c variations in this interval largely represent reservoir changes high resolution 13c data allow improved resolution of the latter five of six 13c maxima within the well known early to middle miocene carbon isotopic excursion the monterey carbon isotopic excursion from 17 0 to 13 5 ma this is useful for global correlation the last of these maxima ends with a 1 decrease centered from 13 9 to 13 7 ma 300 kyr after the 18o increase considered to reflect east antarctic ice growth covariance between benthic 18o and 13c from 16 to 13 8 ma suggests a sensitive relation between global carbon cycling and the ocean climate system prior to 13 8 ma episodic increases in organic carbon burial may have contributed to deep sea benthic 13c maxima and synchronous global cooling the positive relationship ended at 13 8 ma indicative of changing relations between global carbon cycling and the ocean climate system brought on by the increased stability of the east antarctic ice sheet after a major growth phase from 14 5 to 14 0 ma

a higher order method for determining quasi brittle tensile fracture parameters governing the release of slab avalanches and a new tool for in situ indexing 1 the tensile fracture of heterogeneous earth materials such as snow ice and rocks can be characterized by two fracture parameters the fracture toughness and the fracture process zone length the latter length scale characterizes the zone of microcracking surrounding a crack tip in a heterogeneous material for alpine snow these two fracture parameters influence the release dimensions and thus destructive potential of slab avalanches in general it is difficult to determine these parameters concurrently and most experimental methods are based on first order scaling laws that have considerable errors unless very large test specimens are used here we introduce a simple experimental method based on a higher order quasi brittle scaling law that has never been applied to snow nor any other geophysical material we conducted hundreds of beam bending experiments using natural cohesive snow samples to produce the most comprehensive measurements to date of the tensile fracture toughness and effective process zone length of snow we also adopt a new penetration resistance gauge to index the fracture toughness data addressing a longstanding need for better proxy measurements to characterize snow structure the peak penetration resistance met by a thin blade proved better than the bulk snow density for predicting fracture toughness a finding that will improve field predictions and facilitate comparisons of results across studies the tensile fracture process zone previously a highly uncertain length scale related to avalanche fractures is shown to be about 5 10 times the snow grain size implying nonlinear fracture scaling for the majority of avalanches

complementary constraints from carbon 13c and nitrogen 15n isotopes on the glacial ocean s soft tissue biological pump a three dimensional process based model of the ocean s carbon and nitrogen cycles including 13c and 15n isotopes is used to explore effects of idealized changes in the soft tissue biological pump results are presented from one preindustrial control run pictrl and six simulations of the last glacial maximum lgm with increasing values of the spatially constant maximum phytoplankton growth rate max which accelerates biological nutrient utilization mimicking iron fertilization the default lgm simulation without increasing max and with a shallower and weaker atlantic meridional overturning circulation and increased sea ice cover leads to 280 pg more respired organic carbon corg storage in the deep ocean with respect to pictrl dissolved oxygen concentrations in the colder glacial thermocline increase which reduces water column denitrification and with delay nitrogen fixation thus increasing the ocean s fixed nitrogen inventory and decreasing 15nno3 almost everywhere this simulation already fits sediment reconstructions of carbon and nitrogen isotopes relatively well but it overestimates deep ocean 13cdic and underestimates 15nno3 at high latitudes increasing max enhances corg and lowers deep ocean 13cdic improving the agreement with sediment data in the model s antarctic and north pacific oceans modest increases in max result in higher 15nno3 due to enhanced local nutrient utilization improving the agreement with reconstructions there models with moderately increased max fit both isotope data best whereas large increases in nutrient utilization are inconsistent with nitrogen isotopes although they still fit the carbon isotopes reasonably well the best fitting models reproduce major features of the glacial 13cdic 15n and oxygen reconstructions while simulating increased corg by 510 670 pg compared with the preindustrial ocean these results are consistent with the idea that the soft tissue pump was more efficient during the lgm both circulation and biological nutrient utilization could contribute however these conclusions are preliminary given our idealized experiments which do not consider changes in benthic denitrification and spatially inhomogenous changes in aeolian iron fluxes the analysis illustrates interactions between the carbon and nitrogen cycles as well as the complementary constraints provided by their isotopes whereas carbon isotopes are sensitive to circulation changes and indicate well the three dimensional corg distribution nitrogen isotopes are more sensitive to biological nutrient utilization

permafrost carbon as a missing link to explain co 2 changes during the last deglaciation the atmospheric concentration of co2 increased from 190 to 280 ppm between the last glacial maximum 21 000 years ago and the pre industrial era1 2 this co2 rise and its timing have been linked to changes in the earth s orbit ice sheet configuration and volume and ocean carbon storage2 3 the ice core record of 13co2 refs 2 4 in the atmosphere can help to constrain the source of carbon but previous modelling studies have failed to capture the evolution of 13co2 over this period5 here we show that simulations of the last deglaciation that include a permafrost carbon component can reproduce the ice core records between 21 000 and 10 000 years ago we suggest that thawing permafrost due to increasing summer insolation in the northern hemisphere is the main source of co2 rise between 17 500 and 15 000 years ago a period sometimes referred to as the mystery interval6 together with a fresh water release into the north atlantic much of the co2 variability associated with the bolling allerod younger dryas period 15 000 to 12 000 years ago can also be explained in simulations of future warming we find that the permafrost carbon feedback increases global mean temperature by 10 40 relative to simulations without this feedback with the magnitude of the increase dependent on the evolution of anthropogenic carbon emissions

global mean marine δ13c and its uncertainty in a glacial state estimate 2015 elsevier ltd a paleo data compilation with 492 13c and 18o observations provides the opportunity to better sample the last glacial maximum lgm and infer its global properties such as the mean 13c of dissolved inorganic carbon here the paleo compilation is used to reconstruct a steady state water mass distribution for the lgm that in turn is used to map the data onto a 3d global grid a global mean marine 13c value and a self consistent uncertainty estimate are derived using the framework of state estimation i e combining a numerical model and observations the lgm global mean 13c is estimated to be 0 14 0 20 at the two standard error level giving a glacial to modern change of 0 32 0 20 the magnitude of the error bar is attributed to the uncertain glacial ocean circulation and the lack of observational constraints in the pacific indian and southern oceans to halve the error bar roughly four times more observations are needed although strategic sampling may reduce this number if dynamical constraints can be used to better characterize the lgm circulation the error bar can also be reduced to 0 05 to 0 1 emphasizing that knowledge of the circulation is vital to accurately map 13c in three dimensions

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

constraint of the co2 rise by new atmospheric carbon isotopic measurements during the last deglaciation 1 the causes of the 80 ppmv increase of atmospheric carbon dioxide co2 during the last glacial interglacial climatic transition remain debated we analyzed the parallel evolution of co2 and its stable carbon isotopic ratio 13co2 in the european project for ice coring in antarctica epica dome c ice core to bring additional constraints agreeing well but largely improving the taylor dome ice core record of lower resolution our 13co2 record is characterized by a w shape with two negative 13co2 excursions of 0 5 during heinrich 1 and younger dryas events bracketing a positive 13co2 peak during the bolling allerod warm period the comparison with marine records and the outputs of two c cycle box models suggest that changes in southern ocean ventilation drove most of the co2 increase with additional contributions from marine productivity changes on the initial co2 rise and 13co2 decline and from rapid vegetation buildup during the co2 plateau of the bolling allerod

simulating soil organic carbon in yedoma deposits during the last glacial maximum in a land surface model substantial quantities of organic carbon oc are stored in the thick ice rich and organic rich sediments called yedoma deposits distributed in eastern siberia and alaska today quantifying yedoma carbon stocks during the glacial period is important for understanding how much carbon could have been decomposed during the last deglaciation yet processes that yield the formation of thick frozen oc in yedoma deposits are missing in global carbon cycle models here we incorporate sedimentation parameterizations into the organizing carbon and hydrology in dynamic ecosystems orchidee mict land surface model which leads to reasonable results in oc vertical distribution and regional budgets compared with site specific observations and inventories for today s nondegraded yedoma region simulated total soil oc stock for the northern permafrost region during the last glacial maximum lgm is 1536 1592 pg c of which 390 446 pg c is within today s yedoma region this result is an underestimation since we did not account for the potentially much larger yedoma area during the lgm than the present day

oxygen and carbon isotope ratios of lampsilis cardium unionidae from two streams in agricultural watersheds of iowa usa abstract climate archives preserved as seasonal variation in oxygen and carbon isotope ratios 18o and 13c in unionid shells potentially provide records of pre instrumental environmental conditions in mid to high latitude continental regions this study measured 18o and 13c values of biogenic carbonate and 18owater to investigate the timing of growth line formation and to examine the utility of lampsilis cardium as an environmental archive we tested the hypotheses that 1 l cardium precipitates its shell in isotopic equilibrium with the environment during biomineralization and 2 growth lines form seasonally during winter months these questions were addressed by monitoring water chemistry by tagging l cardium to record growth and by combining sclerochronology and stable isotope geochemistry temperature and 18owater were measured fortnightly from september 2002 to july 2004 with a break in sampling from december 2003 to february 2004 in two iowa rivers boone river and buffalo creek these data were used to calculate expected 18o values to compare to measured shell values one hundred fifty four individuals were marked at the postero dorsal margin in september 2002 and june 2003 to monitor growth seven recaptured shells collected in july 2004 were analyzed for shell 18o and 13c across three growth lines including growth lines prior to the initial marking period from the growing edge toward the umbo comparison of shell 18o with expected values revealed precipitation of 18o in equilibrium with the ambient environment from early spring to early fall winter values were not recorded due to winter growth cessation change in temperature or reaching a threshold temperature appeared to control the onset and cessation of growth moreover the locations of seasonal growth lines corresponded to winter growth cessation allowing the assignment of calendar years to growth lines seasonal growth lines were distinguished from non seasonal disturbance lines by their seasonal location inferred from the 18o time series recorded in shell growth thus we can faithfully reconstruct ontogeny through time and environmental and climate conditions from mid to high latitudes using l cardium variation in 13cshell followed a more or less sinusoidal trend similar to the seasonal profiles of 18oshell suggesting that seasonal processes influenced the variation in carbon isotopes reduced amplitudes and more negative 13cshell values with increasing age suggest that kinetic and or metabolic isotope effects become important through ontogeny as observed in other bivalves the profiles of 13cshell potentially record local differences in landscape vegetation however specific factors influencing 13cshell are unknown and further study of water quality are required to fully assess the variation of 13cshell as an environmental proxy

structural petrological and thermal evolution of a tertiary ductile strike slip shear zone diancang shan yunnan the diancang shan a horst massif within the red river fault zone in yunnan people s republic of china preserves a structural petrological and thermal record of two distinct phases of tectonic activity a left lateral ductile shear that terminated between 20 and 17 ma and a ductile to brittle phase of normal faulting which began at 4 7 ma and remains active mylonitic rocks in the core of the range display an early steep high temperature ht schistosity and a horizontal stretching lineation that are both parallel to the trend of the belt kinematic indicators indicate that shear was left lateral the complex shape of the ht schistosity at the southern termination of the massif likely results from a large scale oblique left lateral c shear plane that dismembered the shear zone and separated the ailao shan and the diancang shan as left lateral deformation terminated thermochronological and thermobarometric results suggest that the gneisses were partially unroofed during this event along the eastern edge of the diancang shan the ht fabrics were overprinted by low temperature structures during activation of east dipping normal faults cooling associated with this normal right lateral faulting along the diancang shan and perhaps activation of the right lateral normal movement on the range front fault farther south along the ailao shan began at 4 7 0 1 ma these results tend to support the view that extrusion of indochina occurred along the left lateral red river shear zone between 35 and 19 17 ma initiation of right lateral normal slip during the late miocene may relate to eastward extensional collapse of the thickened tibetan crust or more probably to initiation of the second phase of extrusion

oxygen isotope records of the australian flat oyster ostrea angasi as a potential temperature archive abstract the response of the oxygen isotope ratio 18o in shells of the australian native flat oyster ostrea angasi to changes in water temperature has been assessed using growth experiments conducted for one year at two locations on the east coast of australia the analysed 18o of the oyster shells 18oshell closely follows the predicted oyster shell 18o constructed from measured 18o in the water 18owater and water temperature influxes of freshwater that occur in the estuarine habitats of o angasi can modify the 18owater and consequently 18oshell salinity fluctuations can also cause interruptions to shell growth in this species this can cause overestimated temperatures in o angasi 18oshell temperature reconstructions a 18oshell temperature calibration was established for o angasi yielding the relationship t c 13 97 3 57 18oshell 18owater 0 17 18oshell 18owater 2 n 79 r2 0 79 which within the experimental uncertainties of the data is similar to other published biogenic carbonate paleotemperature equations

ice age terrestrial carbon changes revisited n shackleton 1977 first proposed that changes in the marine 13 c record 13 c could be used to infer ice age changes in carbon storage on land the previously published best estimate from the marine record is equivalent to about 490 gt 0 32 13 c however adams et al 1990 utilized a pollen database to estimate a 1350 gt change in carbon storage which would cause a 13 c of about 0 90 the nearly trillion ton difference in estimates amounts to almost half of the total carbon stored on land to address the nature of this discrepancy i have reexamined the terrestrial carbon record based on a new pollen database compiled by r webb and the cooperative holocene mapping project cohmap group i estimate about 750 1050 gt glacial interglacial change in terrestrial carbon storage with the range reflecting uncertainties in carbon storage values for different biomes additional uncertainties apply to rainforest and wetland extent and presence of c4 plants which have a significantly different isotopic signature than c3 plants although some scenarios overlap a new estimate of carbon storage based on the oceanic 13 c record revised to 0 40 and 610 gt most estimates seem to fall outside the envelope of uncertainty in the marine record several possible explanations for this gap involve 1 a missing sink may be involved in land sea carbon exchange e g continental slopes 2 the geochemistry of the exchange process is not understood 3 carbon storage by biome may have changed under ice age boundary conditions or 4 the standard interpretation of whole ocean changes in the marine 13 c record requires reevaluation this latter conclusion receives some support from comparison of the 13 c records for 18 o stages 2 and 6 for the stage 6 glacial the 13 c changes are 50 60 larger than for the stage 2 glacial yet implications of increased aridity are not supported by longterm trends in atmospheric dust loading to summarize the above analysis implies that despite the uncertainties remaining in estimates of terrestrial carbon storage changes a case can be made that our understanding of the transfer process is incomplete and that the eventual explanation may require clarification of factors affecting the marine 13 c record

automatic determination of 3d orientations of fossilized oyster shells from a densely packed miocene shell bed shell beds represent a useful source of information on various physical processes that cause the depositional condition we present an automated method to calculate the 3d orientations of a large number of elongate and platy objects fossilized oyster shells on a sedimentary bedding plane developed to support the interpretation of possible depositional patterns imbrications or impact of local faults the study focusses on more than 1900 fossil oyster shells exposed in a densely packed miocene shell bed 3d data were acquired by terrestrial laser scanning on an area of 459 m2 with a resolution of 1 mm bivalve shells were manually defined as 3d point clouds of a digital surface model and stored in an arcgis database an individual shell coordinate system iscs was virtually embedded into each shell and its orientation was determined relative to the coordinate system of the entire tectonically tilted shell bed orientation is described by the rotation angles roll pitch and yaw in a cartesian coordinate system this method allows an efficient measurement and analysis of the orientation of thousands of specimens and is a major advantage compared to the traditional 2d approach which measures only the azimuth yaw angles the resulting data can variously be utilized for taphonomic analyses and the reconstruction of prevailing hydrodynamic regimes and depositional environments for the first time the influence of possible post sedimentary vertical displacements can be quantified with high accuracy here the effect of nearby fault lines present in the reef was tested on strongly tilted oyster shells but it was found out that the fault lines did not have a statistically significant effect on the large tilt angles aside from the high reproducibility a further advantage of the method is its non destructive nature which is especially suitable for geoparks and protected sites such as the studied shell bed

fracture energy applicable to dry snow slab avalanche release 1 dry slab avalanches release by a sequence of propagating fractures first by shear fracture mode ii and mode iii in a weak layer at the base of the slab and second by tensile fracture through the crown after which release of the slab is imminent the fracture energy is the energy which must be provided to produce a unit area of fracture surface it is a key parameter in determining how and when fractures will propagate and important slab characteristics such as length and width that are necessary in order to estimate slab mass and volume in relation to destructive potential in this paper approximate estimates of fracture energy are calculated from field measurements of slab properties laboratory measurements and in situ strength tests in alpine snow estimates of fracture energy are given for both tensile fracture mode i through the crown as well as for shear fracture mode ii in fragile weak layers of slab avalanches the results when compared with other values from ice rock and engineering materials suggest that snow has the lowest values

dust impact on marine biota and atmospheric co2 during glacial periods 1 we assess the impact of high dust deposition rates on marine biota and atmospheric co2 using a state of the art ocean biogeochemistry model and observations our model includes an explicit representation of two groups of phytoplankton and colimitation by iron silicate and phosphate when high dust deposition rates from the last glacial maximum lgm are used as input our model shows an increase in the relative abundance of diatoms in today s iron limited regions causing a global increase in export production by 6 and an atmospheric co2 drawdown of 15 ppm when the combined effects of changes in dust temperature ice cover and circulation are included the model reproduces roughly our reconstruction of regional changes in export production during the lgm based on several paleoceanographic indicators in particular the model reproduces the latitudinal dipole in the southern ocean driven in our simulations by the conjunction of dust sea ice and circulation changes in the north pacific the limited open ocean data suggest that we correctly simulate the east west gradient in the open ocean but more data are needed to confirm this result from our model data comparison and from the timing of the dust record at vostok we argue that our model estimate of the role of dust is realistic and that the maximum impact of high dust deposition on atmospheric co2 must be 30 ppm

stable isotopes reveal high southeast tibetan plateau margin since the paleogene abstract the evolution of the topography of eastern tibet reflects the dynamic interaction between processes at earth s surface and the lower crust reconstruction of its spatio temporal development provides constraints for our understanding of the geodynamics of continental deformation this study examines the topographic evolution of the southeast margin of the tibetan plateau throughout the cenozoic using stable isotope paleoaltimetry of pedogenic carbonates preserved in cenozoic basins extending from the northern to the southern portions of the se margin of the tibetan plateau yunnan province china paleoelevations are calculated using a monte carlo simulation of the normally distributed uncertainties in each parameter used to calculate elevations from the isotopic value of pedogenic carbonate isotope elevation relationships are determined from a modern sampling transect along the modern lancang mekong river and an estimated eocene rayleigh fractionation model that was randomly resampled calculated elevations indicate the se margin of tibet was at its present elevation as early as the late eocene with elevations of 3 3 km as far south as the northern third of china s yunnan province this result expands the extent of the eocene tibetan plateau more than 1000 km east of that previously known and precludes surface uplift via lower crustal flow in the area of sw sichuan and northern yunnan as a driver for drainage reorganization and an observed middle to late miocene pulse of rapid exhumation elevation estimates from the southern two thirds of the study area parallel to the red river fault suggest approximately 1 km of post late miocene surface uplift consistent with estimates from previous studies

palaeoclimate hidden glacial carbon atmospheric co2 levels were much lower during the last glacial maximum than in the pre industrial period ice core data and biogeochemical modelling suggest that difference is partly due to the greater mass of inert carbon in glacial terrestrial biomes

mio pliocene monsoonal record from himalayan foreland basin indian siwalik and its relation to vegetational change carbon and oxygen isotope ratios of soil carbonate nodules and carbon isotope ratio of associated organic matter were measured from three indian siwalik stratigraphic successions in order to reconstruct vegetational history and change in contemporaneous precipitation 13c values of soil carbonates show that from 10 5 to 6 ma the vegetation was c3 type and around 6 ma c4 grasses appeared the 18o variations of soil carbonates suggest that the monsoon system intensified with one probable peak at around 10 5 ma and a clear onset at 6 ma with peak at 5 5 ma after 5 5 ma monsoon strength decreased and attained the modern day condition with minor fluctuations which is supported by marine proxy of upwelling in the arabian sea and sedimentary morphology in siwalik the covariation between 18o and 13c data suggests that a change in precipitation pattern was partly responsible for expansion of c4 grasses in a mixed c3 c4 environment estimation of abundance of c3 and c4 plants using soil carbonate in one case and residual soil organic matter in another may differ this can be explained by assuming that the plant respired co2 is the main contributor of carbon in soil carbonate and may have different isotopic composition from that of the residual organic matter in the soil in addition the abundance estimate of c3 c4 plants also shows variation with time probably caused by change in growing season conditions through time

late miocene decoupling of oceanic warmth and atmospheric carbon dioxide forcing measurements from several ocean cores reveal that ocean warmth persisted throughout the late miocene epoch despite co2 levels of only 200 350 p p m v probably driven by a deep thermocline that isolated climate responses from co2 variations geological records of past climate provide the only opportunity to investigate earth s response to large variations in atmospheric carbon dioxide concentrations during the late miocene between 12 million and 5 million years ago atmospheric co2 levels of only 200 to 350 parts per million by volume were accompanied by almost ice free conditions in the northern hemisphere and the continents were warmer than they are at present raising questions about the persistence of co2 climate couplings using measurements from several ocean cores lariviere et al show that ocean warmth persisted throughout the late miocene probably driven by a thick thermocline that isolated climate responses from co2 variations as the depth of the thermocline declined during the late miocene the more familiar relationship between co2 and climate was established deep time palaeoclimate studies are vitally important for developing a complete understanding of climate responses to changes in the atmospheric carbon dioxide concentration that is the atmospheric partial pressure of co2 1 although past studies have explored these responses during portions of the cenozoic era the most recent 65 5 million years myr of earth history comparatively little is known about the climate of the late miocene 12 5 myr ago an interval with values of only 200 350 parts per million by volume but nearly ice free conditions in the northern hemisphere2 3 and warmer than modern temperatures on the continents4 here we present quantitative geochemical sea surface temperature estimates from the miocene mid latitude north pacific ocean and show that oceanic warmth persisted throughout the interval of low 12 5 myr ago we also present new stable isotope measurements from the western equatorial pacific that in conjunction with previously published data5 6 7 8 9 10 reveal a long term trend of thermocline shoaling in the equatorial pacific since 13 myr ago we propose that a relatively deep global thermocline reductions in low latitude gradients in sea surface temperature and cloud and water vapour feedbacks may help to explain the warmth of the late miocene additional shoaling of the thermocline after 5 myr ago probably explains the stronger coupling between sea surface temperatures and climate that is characteristic of the more recent pliocene and pleistocene epochs11 12

impacts of uplift of northern tibetan plateau and formation of asian inland deserts on regional climate and environment abstract based on the geological evidence that the northern tibetan plateau ntp had an uplift of a finite magnitude since the miocene and the major asian inland deserts formed in the early pliocene a regional climate model regcm4 1 with a horizontal resolution of 50 km was used to explore the effects of the ntp uplift and the related aridification of inland asia on regional climate we designed three numerical experiments including the control experiment representing the present day condition the high mountain experiment representing the early pliocene condition with uplifted ntp but absence of the asian inland deserts and the low mountain experiment representing the mid miocene condition with reduced topography in the ntp by as much as 2400 m and also absence of the deserts our simulation results indicated that the ntp uplift caused significant reductions in annual precipitation in a broad region of inland asia north of the tibetan plateau tp mainly due to the enhanced rain shadow effect of the mountains and changes in the regional circulations however four mountainous regions located in the uplift showed significant increases in precipitation stretching from the pamir plateau in the west to the qilian mountains in the east these mountainous areas also experienced different changes in the rainfall seasonality with the greatest increases occurring during the respective rainy seasons predominantly resulted from the enhanced orographically forced upwind ascents the appearance of the major deserts in the inland asia further reduced precipitation in the region and led to increased dust emission and deposition fluxes while the spatial patterns of dust deposition were also changed not only in the regions of uplift impacted topography but also in the downwind regions one major contribution from this study is the comparison of the simulation results with 11 existing geological records representing the moisture conditions from miocene to pliocene the comparisons revealed good matches between the simulation results and the published geological records therefore we conclude that the ntp uplift and the related formation of the major deserts played a controlling role in the evolution of regional climatic conditions in a broad region in inland asia since the miocene

what have we learnt from palaeoclimate simulations there has been a gradual evolution in the way that palaeoclimate modelling and palaeoenvironmental data are used together to understand how the earth system works from an initial and largely descriptive phase through explicit hypothesis testing to diagnosis of underlying mechanisms analyses of past climate states are now regarded as integral to the evaluation of climate models and have become part of the toolkit used to assess the likely realism of future projections palaeoclimate assessment has demonstrated that changes in large scale features of climate that are governed by the energy and water balance show consistent responses to changes in forcing in different climate states and these consistent responses are reproduced by climate models however state of the art models are still largely unable to reproduce observed changes in climate at a regional scale reliably while palaeoclimate analyses of state of the art climate models suggest an urgent need for model improvement much work is also needed on extending and improving palaeoclimate reconstructions and quantifying and reducing both numerical and interpretative uncertainties

the deep permafrost carbon pool of the yedoma region in siberia and alaska estimates for circumpolar permafrost organic carbon oc storage suggest that this pool contains twice the amount of current atmospheric carbon the yedoma region sequestered substantial quantities of oc and is unique because its deep oc was incorporated into permafrost during ice age conditions rapid inclusion of labile organic matter into permafrost halted decomposition and resulted in a deep long term sink we show that the deep frozen oc in the yedoma region consists of two distinct major sub reservoirs yedoma deposits late pleistocene ice and organic rich silty sediments and deposits formed in thaw lake basins generalized as thermokarst deposits we quantified the oc pool based on field data and extrapolation using geospatial datasets to 83 61 57 gt for yedoma deposits and to 128 99 96 gt for thermokarst deposits the total yedoma region 211 160 153 gt is a substantial amount of thaw vulnerable oc that must be accounted for in global models

poorly ventilated deep ocean at the last glacial maximum inferred from carbon isotopes a data model comparison study atmospheric co was 90 ppmv lower at the last glacial maximum lgm compared to the late holocene but the mechanisms responsible for this change remain elusive here we employ a carbon isotope enabled earth system model to investigate the role of ocean circulation in setting the lgm oceanic c distribution thereby improving our understanding of glacial interglacial atmospheric co variations we find that the mean ocean c change can be explained by a 378 88 gt c 2 smaller lgm terrestrial carbon reservoir compared to the holocene critically in this model differences in the oceanic c spatial pattern can only be reconciled with a lgm ocean circulation state characterized by a weak 10 15 sv and relatively shallow 2000 2500 m north atlantic deep water cell reduced antarctic bottom water transport 10 sv globally integrated and relatively weak 6 8 sv and shallow 1000 1500 m north pacific intermediate water formation this oceanic circulation state is corroborated by results from the isotope enabled bern3d ocean model and further confirmed by high lgm ventilation ages in the deep ocean particularly in the deep south atlantic and south pacific this suggests a poorly ventilated glacial deep ocean which would have facilitated the sequestration of carbon lost from the terrestrial biosphere and atmosphere

a fracture arrest model for unconfined dry slab avalanches a simplified model of an unconfined dry snow slab is used to derive expressions for the rate at which elastic strain energy is released and for the fracture resistance during the propagation of the rapid brittle fractures that result in slab avalanches a relatively constant energy release rate is derived based on arguments that associate most of the released energy with the crown fracture in contrast advancing basal and crown fractures result in increasing fracture resistance by assuming fracture propagation will stop when the strain energy release rate is just greater than the fracture resistance the width of a slab avalanche is found to be proportional to an arrest parameter this parameter includes the slab thickness slab tensile strength and basal shear strength each of which can be measured prior to avalanching it is argued that compared to the three variables which can be measured the remaining variables have limited influence on the width of unconfined slab avalanches these less influen

recent and historical discharge of a large european river system oxygen isotopic composition of river water and skeletal aragonite of unionidae in the rhine abstract seasonal variations in the oxygen isotopic composition of rhine river water were analyzed in detail and compared with the oxygen isotopic record from recent and historical specimens of freshwater bivalves unionidae the purpose of this study was to investigate the potential use of these aragonitic bivalves as proxy recorders for varying amounts and sources of discharge and thereby infer climate change seasonal variations in the river water 18 o are on the order of 1 2 during summer alpine melt water contributes significantly to the total discharge resulting in average values of 10 to 10 5 whereas the non alpine contribution is higher during winter as indicated by mean 18 o values of 8 5 to 9 the basic pattern of the modern seasonal variation of 18 o of river water can be described by a numerical mass balance approximation of the various contributions from the alpine and non alpine catchments with their average 18 o composition the 18 o of growth increments in the prismatic shell layer of anodonta corresponds perfectly to what is predicted by known fractionation of 18 o between water and aragonite shell growth is restricted to water temperatures above 8 10 c so variations in 18 o and the river water temperature are faithfully recorded by relatively large growth increments during summer the distinctive isotopic signatures of individual flood events during summer and autumn are also recorded in the shells

carbon isotope constraints on the deglacial co2 rise from ice cores the stable carbon isotope ratio of atmospheric co2 13catm is a key parameter in deciphering past carbon cycle changes here we present 13catm data for the past 24 000 years derived from three independent records from two antarctic ice cores we conclude that a pronounced 0 3 per mil decrease in 13catm during the early deglaciation can be best explained by upwelling of old carbon enriched waters in the southern ocean later in the deglaciation regrowth of the terrestrial biosphere changes in sea surface temperature and ocean circulation governed the 13catm evolution during the last glacial maximum 13catm and atmospheric co2 concentration were essentially constant which suggests that the carbon cycle was in dynamic equilibrium and that the net transfer of carbon to the deep ocean had occurred before then

deglacial climate carbon cycle and ocean chemistry changes in response to a terrestrial carbon release researchers have proposed that a significant portion of the post glacial rise in atmospheric co2 could be due to the respiration of permafrost carbon stocks that formed over the course of glaciation in this paper we used the university of victoria earth system climate model v 2 9 to simulate the deglacial and interglacial carbon cycle from the last glacial maximum to the present the model s sensitivity to mid and high latitude terrestrial carbon storage is evaluated by including a 600 pg c carbon pool parameterized to respire in concert with decreases in ice sheet surface area the respiration of this stored carbon during the early stages of deglaciation had a large effect on the carbon cycle in these simulations allowing atmospheric co2 to increase by 40 ppmv in the model with an additional 20 ppmv increase occurring in the case of a more realistic prescribed co2 radiative warming these increases occurred prior to large scale carbon uptake due to the reestablishment of boreal forests and peatlands in the proxy record beginning in the early holocene surprisingly the large external carbon input to the atmosphere and oceans did not increase sediment dissolution and mean ocean alkalinity relative to a control simulation without the high latitude carbon reservoir in addition our simulations suggest that an early deglacial terrestrial carbon release may come closer to explaining some observed deglacial changes in deep ocean carbonate concentrations than simulations without such a release we conclude that the respiration of glacial soil carbon stores may have been an important contributor to the deglacial co2 rise particularly in the early stages of deglaciation

uvigerina proboscidea abundances and paleoceanography of the northern indian ocean dsdp site 214 during the late neogene abstract this study attempts to understand the significance of uvigerina proboscidea in paleoceanographic reconstructions at the northern tropical indian ocean dsdp site 214 from the late miocene through the pleistocene in this interval at this site u proboscidea is the most abundant species of the benthic assemblage and shows abrupt frequency changes about 1 74 based on relative percentages of u proboscidea calibrated with oxygen and carbon isotope record and the sediment accumulation rates the modern distribution of the species in the indian ocean and other evidence the peaks of abundance of u proboscidea are inferred to represent times of high surface productivity this productivity is related to intensified trade winds during strong southwest sw indian monsoons causing widespread upwelling along equatorial divergence in the indian ocean the sudden increase of u proboscidea abundance at approximately 8 5 7 5 ma reflects significant upwelling at the equatorial divergence this event corresponds to the permanent build up of west antarctic ice sheets and a major increase in sw indian monsoons related upwelling in the northwestern indian ocean the chron 6 carbon shift at approximately 6 2 ma is marked by another peak of abundance reflecting widespread ocean fertility the highest abundances of u proboscidea and highest sediment accumulation rates occur between 5 8 and 5 1 ma which coincides with the greatest development of antarctic ice sheets and strong southwest monsoons the higher percentages at 3 2 3 1 ma approximately 2 4 ma and 1 6 ma all represent phases of high productivity at the equatorial divergence

deglacial whole ocean δ13c change estimated from 480 benthic foraminiferal records terrestrial carbon storage is dramatically decreased during glacial periods due to cold temperatures increased aridity and the presence of large ice sheets on land most of the carbon released by the terrestrial biosphere is stored in the ocean where the light isotopic signature of terrestrial carbon is observed as a 0 32 0 7 depletion in benthic foraminiferal 13c the wide range in estimated 13c change results from the use of different subsets of benthic 13c data and different methods of weighting the mean 13c by volume we present a more precise estimate of glacial interglacial 13c change of marine dissolved inorganic carbon using benthic cibicidoides spp 13c records from 480 core sites more than 3 times as many sites as previous studies we divide the ocean into eight regions to generate linear regressions of regional 13c versus depth for the late holocene 0 6 ka and last glacial maximum 19 23 ka and estimate a mean 13c decrease of 0 38 0 08 2 for 0 5 5 km estimating large uncertainty ranges for 13c change in the top 0 5 km below 5 km and in the southern ocean we calculate a whole ocean change of 0 34 0 19 this implies a terrestrial carbon change that is consistent with recent vegetation model estimates of 330 694 gt c additionally we find that a well constrained surface ocean 13c change is essential for narrowing the uncertainty range of estimated whole ocean 13c change

soil organic carbon pools in the northern circumpolar permafrost region of all soils in the northern permafrost region is approximately 18 782 10 3 km 2 o r approximately 16 of the global soil area in the northern permafrost region organic soils peatlands and cryoturbated permafrost affected mineral soils have the highest mean soil organic carbon contents 32 2 69 6 kg m 2 here we report a new estimate of the carbon pools in soils of the northern permafrost region including deeper layers and pools not accounted for in previous analyses carbon pools were estimated to be 191 29 pg for the 0 30 cm depth 495 80 pg for the 0 100 cm depth and 1024 00 pg for the 0 300 cm depth our estimate for the first meter of soil alone is about double that reported for this region in previous analyses carbon pools in layers deeper than 300 cm were estimated to be 407 pg in yedoma deposits and 241 pg in deltaic deposits in total the northern permafrost region contains approximately 1672 pg of organic carbon of which approximately 1466 pg or 88 occurs in perennially frozen soils and deposits this 1672 pg of organic carbon would account for approximately 50 of the estimated global belowground organic carbon pool

the dole effect and its variations during the last 130 000 years as measured in the vostok ice core we review the current understanding of the dole effect the observed difference between the delta sup 18 o of atmospheric o sub 2 and that of seawater and its causes extended the record of variations in the dole effect back to 130 kyr before present using data on the delta sup 18 o of o sub 2 obtained from studying the vostok ice core and discuss the significance of temporal variations the dole effect reflects oxygen isotope fractionation during photosynthesis respiration and hydrologic processes evaporation precipitation and evapotranspiration our best prediction of the present day dole effect 20 8 per thousand is considerably lower than the observed value 23 5 per thousand and we discuss possible causes of this discrepancy during the past 130 kyr the dole effect has been 0 05 per thousand lower than the present value on average the standard deviation of the dole effect from the mean has been only per thousand and the dole effect is nearly unchanged between glacial maxima and interglacial periods the small variability in the dole effect suggests that relative rates of primary production in the land and marine realms have been relatively constant most periodic variability in the dole effect is in the precession band suggesting that changes in this global biogeochemical termmore reflects variations in low latitude land hydrology and productivity or possibly variability in low latitude oceanic productivity 65 refs 4 figs 3 tabs less

analysis of critical length measurements for dry snow slab weak layer shear fracture snow slab avalanches primarily release by propagation of shear fractures within thin weak layers under much thicker slabs in some cases the weak layer is on the order of 1 mm thick and such fractures may be considered to be a mode ii shear fracture at initiation in the cases analysed in this paper the weak layer has finite thickness and slope normal effects may be present field data from 500 snow shear fracture tests are analysed and applied to the problem of weak layer fracture the paper contains a detailed analysis using a simple analytical model to estimate the critical length prior to an unstable shear fracture the model contains the assumption of a finite fracture process zone which may be a significant fraction of the slab depth d or the critical length l for weak layer shear fracture the field results show that the l d ratio varies from 0 1 to just over 2 and the model results are close to the same range the analysis also shows that both the field and model results for l d follow a gumbel probability density function since the experimental field data contain rate dependent viscoelastic and slope normal effects it is imperative to account for these in the model and for snow slab instability evaluation when using test data detailed evaluations considering both these effects are given the applicability of the test data to avalanche release is discussed

dominant control of the south asian monsoon by orographic insulation versus plateau heating heat emitted from the tibetan plateau as dry heat and water vapour has long been assumed to be the main driver of the south asian summer monsoon but new work suggests that in fact it is the neighbouring mountains that are the major influence william boos and zhiming kuang use an atmospheric model to show that flattening the tibetan plateau has little effect on the monsoon so long as the himalayas and surrounding mountain ranges remain the plateau does boost rainfall locally along its southern edge but it is the build up of hot moist air over india insulated from colder drier air by the himalayas that drives large scale monsoon circulation the elevation of the tibetan plateau is thought to cause its surface to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales here however an atmospheric model is used to show that flattening of the tibetan plateau has little effect on the monsoon provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved the tibetan plateau like any landmass emits energy into the atmosphere in the form of dry heat and water vapour but its mean surface elevation is more than 5 km above sea level this elevation is widely held to cause the plateau to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales1 2 3 4 5 observations of the present climate however do not clearly establish the tibetan plateau as the dominant thermal forcing in the region peak upper tropospheric temperatures during boreal summer are located over continental india south of the plateau here we show that although tibetan plateau heating locally enhances rainfall along its southern edge in an atmospheric model the large scale south asian summer monsoon circulation is otherwise unaffected by removal of the plateau provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved additional observational and model results suggest that these mountains produce a strong monsoon by insulating warm moist air over continental india from the cold and dry extratropics these results call for both a reinterpretation of how south asian climate may have responded to orographic uplift and a re evaluation of how this climate may respond to modified land surface and radiative forcings in coming decades

on the fracture toughness of snow the release of a dry snow slab avalanche involves brittle fracture it is therefore essentially a non linear fracture mechanics problem traditional snow stability evaluation has mainly focused on snow strength measurements fracture toughness describes how well a material can withstand failure the fracture toughness of snow is therefore a key parameter to assess fracture propagation propensity and hence snow slope stability fracture toughness in tension kic and shear kiic was determined with notched cantilever beam experiments in a cold laboratory measurements were performed at different temperatures and with different snow types of density 100 300 kg m 3 corresponding to typical dry snow slab properties the fracture toughness in tensionkic was found to be larger by about a factor of 1 4 than in shear kiic typical values of the fracture toughness were 500 1000 pa m 1 2 for the snow types tested this suggests that snow is one of the most brittle materials known to man a power law relation of toughness kic on relative density was found with an exponent of about 2 the fracture toughness in tensionkic decreased with increasing temperature following an arrhenius relation below about 8 c with an apparent activation energy of about 0 16 ev above 6 c the fracture toughness increased with increasing temperature towards the melting point i e the ar rhenius relation broke down the key property in dry snow slab avalanche release the critical crack size under shear at failure was estimated to be about 1m

biological oxygen productivity during the last 60 000 years from triple oxygen isotope measurements during isotope exchange between o2 and co2 in the stratosphere the relative rates of biologic o2 production and stratospheric processing determine the relationship between d 17 o and d 18 oo f o2 in the atmosphere variations of this relationship thus allow us to estimate changes in the rate of mass dependent o2 production by photosynthesis versus the rate of o2 co2 exchange in the stratosphere with about equal fractionations of d 17 o and d 18 o in this study we reconstruct total oxygen productivity for the last glacial the last glacial termination and the early holocene from the triple isotope composition of atmospheric oxygen trapped in ice cores with a box model we estimate that total biogenic productivity was only 76 83 of today for the glacial and was probably lower than today during the glacial interglacial transition and the early holocene depending on how reduced the oxygen flux from the land biosphere was during the glacial the oxygen flux from the glacial ocean biosphere was 88 140 of its present value index terms 3344 meteorology and atmospheric dynamics paleoclimatology 4870 oceanography biological and chemical stable isotopes 1615 global change biogeochemical processes 4805 0315 atmospheric composition and structure biosphere atmosphere interactions keywords gisp2 siple ice cores oxygen isotopes past oxygen productivity stratospheric isotope exchange respiration

dry snow slab quasi brittle fracture initiation and verification from field tests 1 dry snow slab avalanches initiate from shear fracture in a thin weak layer underneath a planar slab of cohesive snow in this paper field data from more than 400 snow shear fracture tests are analysed and applied to the problem of snow slab release and snow pack instability evaluation the paper contains a new but simple analytical model to estimate the critical length for fracture the model contains the assumption of a finite fracture process zone which may be a significant fraction of the slab depth d or the critical length l for weak layer shear fracture the results suggest that the ratio l d is of order 1 for both the data and the model as previously predicted for the snow slab using a combination of experimental results from laboratory tests two sets of field data and the new model suggests that previous theoretical arguments about snow slab release over almost 30 years are congruent with the field data simple extension to explain viscoelastic temperature effects and slope normal weak layer deformation on snow slab instability evaluation is included in the analysis since the experimental field data contain viscoelastic effects and slope normal effects it is imperative to account for these in the model and for snow slab instability evaluation

can shells of freshwater mussels unionidae be used to estimate low summer discharge of rivers and associated droughts this paper examines if shell oxygen isotope ratios 18oar of unio sp can be used as a proxy of past discharge of the river meuse the proxy was developed from a modern dataset for the reference time interval 1997 2007 which showed a logarithmic relationship between discharge and measured water oxygen isotope ratios 18ow to test this relationship for past time intervals 18oar values were measured in the aragonite of the growth increments of four unio sp shells two from a relatively wet period and two from a very dry time interval 1910 1918 and 1969 1977 respectively shell 18oar records were converted into 18ow values using existing water temperature records summer 18ow values reconstructed from 18oar of 1910 1918 showed a similar range as the summer 18ow values for the reference time interval 1997 2007 whilst summer reconstructed 18ow values for the time interval 1969 1977 were anomalously high these high 18ow values suggest that the river meuse experienced severe summer droughts during the latter time interval 18ow values were then applied to calculate discharge values it was attempted to estimate discharge from the reconstructed 18ow values using the logarithmic relationship between 18ow and discharge a comparison of the calculated summer discharge results with observed discharge data showed that meuse low discharge events below a threshold value of 6 m3 s can be detected in the reconstructed 18ow records but true quantification remains problematic

probabilistic size effect law for mode ii fracture from critical lengths in snow slab avalanche weak layers from field observations dry snow slab avalanche initiation is associated with fracture within relatively thin weak layers under stronger cohesive slabs for risk based avalanche prediction it is important to understand the fracture properties of alpine snow alpine snow is a quasi brittle material with a fracture mechanical size effect on nominal shear strength meaning that strength decreases with increasing specimen size a related size effect is the critical length required for rapid propagation of a shear fracture in that case the probability of fracture increases with increasing crack length in this paper 45 sets of field measured critical lengths are presented based on 591 individual tests from analysis a probabilistic size effect law based on critical lengths is derived analogous to the deterministic size effect law for nominal shear strength related to fracture mechanics the new size effect law may be useful in applications particularly since the critical length is easily measured in the field and it is a principal component of weak layer fracture toughness

c and o isotope compositions of modern fresh water mollusc shells and river waters from the himalaya and ganga plain the aim of this paper is to unfold the relationship between the o and c isotope compositions of modern fresh water mollusc shells and water in order to refine the basis of interpretation for paleoenvironnemental reconstruction in the sub himalayan river basins large number of mollusc shells and associated host water from both running water and closed body of water were analysed including intra shell variability in a few cases the o isotopic compositions of river waters in the himalaya and ganga plain have a large range from 18 in the north of the high range up to 8 to 4 in the ganga plain 18o of rivers are also seasonally variable especially in foothills rivers whereas the seasonal contrast is smoothed out for the main himalayan rivers having large catchments o isotopic compositions of bulk shells aragonite vary between 15 and 5 average 18oara values are consistent with precipitation at equilibrium with host waters at a temperature range of 20 25 c suggesting that shell growth may be favoured during non monsoon conditions shells collected along the main himalayan rivers have 18o values uniformly distributed within 11 and 6 reflecting the minimal seasonal contrast shown by these rivers in contrast o isotopic compositions of shells from foothills rivers vary only by 4 this shows that depending on the type of river where the molluscs grow the information in term of 18o amplitude will be different for identical climatic conditions in closed or pond water bodies significant enrichment in 18o due to evaporation is observed the c isotopic compositions of river dissolved inorganic carbon dic decrease downstream from 0 to 10 reflecting input of soil derived alkalinity and plant productivity in the river 13c of shells are systematically lower than compositions calculated for equilibrium with river dic indicating that in addition to dic a significant fraction of carbon is derived from metabolic sources intra shell 13c are stable compared to the seasonal variability of dic suggesting that the pool of organic carbon changes throughout year

large scale hydrological change drove the late miocene c4 plant expansion in the himalayan foreland and arabian peninsula carbon isotope changes in paleosols from siwalik pakistan and marine sediments from the bengal fan indicate a major c 4 plant expansion in the himalayan foreland during the late miocene however the timing and mechanisms behind the c 4 plant expansion remain enigmatic here we present high resolution 60 k y biomarker and compound specific isotope data spanning the past 11 m y from ocean drilling program site 722 in the arabian sea an 5 6 increase in leaf wax 13 c values indicates a marked rise of c 4 plants from 10 to 5 5 ma with accelerated expansion from 7 9 to 5 5 ma a concurrent 50 rise in leaf wax d values is attributed to a combined effect of changes in precipitation amount and evaporation indicating that source regions for the plant waxes became progressively drier from 10 to 5 5 ma in contrast to earlier reports our isotope records biomarker abundances alkenone u k 37 and globigerina bulloides abundance data do not suggest enhanced summer monsoon circulation during this time interval rather our results suggest that large scale hydrological changes drove the late miocene expansion of c 4 plants in the himalayan foreland and arabian peninsula

large inert carbon pool in the terrestrial biosphere during the last glacial maximum during each of the late pleistocene glacial interglacial transitions atmospheric carbon dioxide concentrations rose by almost 100 ppm the sources of this carbon are unclear and efforts to identify them are hampered by uncertainties in the magnitude of carbon reservoirs and fluxes under glacial conditions here we use oxygen isotope measurements from air trapped in ice cores and ocean carbon cycle modelling to estimate terrestrial and oceanic gross primary productivity during the last glacial maximum we find that the rate of gross terrestrial primary production during the last glacial maximum was about 40 10 pg c yr 1 half that of the pre industrial holocene despite the low levels of photosynthesis we estimate that the late glacial terrestrial biosphere contained only 330 pg less carbon than pre industrial levels we infer that the area covered by carbon rich but unproductive biomes such as tundra and cold steppes was significantly larger during the last glacial maximum consistent with palaeoecological data our data also indicate the presence of an inert carbon pool of 2 300 pg c about 700 pg larger than the inert carbon locked in permafrost today we suggest that the disappearance of this carbon pool at the end of the last glacial maximum may have contributed to the deglacial rise in atmospheric carbon dioxide concentrations

comparative carbon cycle dynamics of the present and last interglacial changes in temperature and carbon dioxide during glacial cycles recorded in antarctic ice cores are tightly coupled however this relationship does not hold for interglacials while climate cooled towards the end of both the last eemian and present holocene interglacials co2 remained stable during the eemian while rising in the holocene we identify and review twelve biogeochemical mechanisms of terrestrial vegetation dynamics and co2 fertilization land use wildfire accumulation of peat changes in permafrost carbon subaerial volcanic outgassing and marine origin changes in sea surface temperature carbonate compensation to deglaciation and terrestrial biosphere regrowth shallow water carbonate sedimentation changes in the soft tissue pump and methane hydrates which potentially may have contributed to the co2 dynamics during interglacials but which remain not well quantified we use three earth system models esms of intermediate complexity to compare effects of selected mechanisms on the interglacial co2 and 13co2 changes focusing on those with substantial potential impacts namely carbonate sedimentation in shallow waters peat growth and in the case of the holocene human land use a set of specified carbon cycle forcings could qualitatively explain atmospheric co2 dynamics from 8 ka bp to the pre industrial however when applied to eemian boundary conditions from 126 to 115 ka bp the same set of forcings led to disagreement with the observed direction of co2 changes after 122 ka bp this failure to simulate late eemian co2 dynamics could be a result of the imposed forcings such as prescribed caco3 accumulation and or an incorrect response of simulated terrestrial carbon to the surface cooling at the end of the interglacial these experiments also reveal that key natural processes of interglacial co2 dynamics shallow water caco3 accumulation peat and permafrost carbon dynamics are not well represented in the current esms global scale modeling of these long term carbon cycle components started only in the last decade and uncertainty in parameterization of these mechanisms is a main limitation in the successful modeling of interglacial co2 dynamics

seasonal stable isotope variations of the modern amazonian freshwater bivalve anodontites trapesialis in a floodplain lake of the amazon river near the city of iquitos northeastern peru a one year monitoring experiment was conducted during which water samples and living bivalves anodontites trapesialis were collected with the aim to investigate seasonal 18o variation in and fractionation between bivalve aragonite and host water both host water and molluscan growth increments show more than 8 seasonal variation in 18o in the floodplain lake under study the 18o variation of the water is controlled by contrasting dry and wet season evaporation precipitation regimes molluscan 18o appears to be in equilibrium with the host water although an approximately 4 0 offset occurs 13c records of water and bivalves are in good agreement suggesting that both 18o and 13c of the shells of freshwater bivalve a trapesialis are good recorders of palaeo environmental conditions the 13c of dissolved inorganic carbon dic is governed by plant growth and or by changes in aquatic chemistry affecting the dic pool

the 13c record for atmospheric co2 what is it trying to tell us abstract records of the 13c to 12c ratio of atmospheric co2 13catm trapped in antarctic ice may offer important insights into past changes in the carbon cycle and drivers of past fluctuations in atmospheric pco2 a recently published record offers the highest resolution 13catm record to date covering the last deglaciation schmitt et al 2012 two features are of particular interest one is the small magnitude 0 15 0 05 of the 13catm difference between the last glacial maximum lgm and the holocene the other is the abrupt drop 0 30 0 05 in 13catm between 17 5 and 16 0 ka this drop is coincident with that of dust deposition on the antarctic ice cap and into the ocean off south australia consistent with the hypothesis that increased efficiency of southern ocean nutrient utilization during the last glacial period and the consequent reduction in atmospheric pco2 was driven in part by dust related iron fertilization however in order to further explore either the small lgm holocene difference or the rapid drop during the early deglaciation 13catm changes related to the lgm cooling the lgm upper ocean 13c change ocean circulation changes and the lgm change in the photosynthetic fractionation factor must be known as each is currently the subject of a sizable uncertainty we present only a roadmap regarding what must be done in order to interpret the schmitt et al 2012 record

late cenozoic eolian deposition in the north pacific asian drying tibetan uplift and cooling of the northern hemisphere a newly constructed record of eolian dust accumulation from the central north pacific shows that dust deposition increased by an order of magnitude quite rapidly at 3 6 ma we associate this sudden drying with the uplift of at least the northern portion of the tibetan plateau shutting off the indian ocean moisture source to central and western china this ten fold increase in atmospheric dust loading appears to be associated with the 1 m y long shift toward heavy 18o values that occurred at 3 6 2 6 ma the dust grain size record of wind intensity begins its late cenozoic coarsening a million years before the drying event at 4 5 ma the northern hemisphere cooling that results in intensification of the subpolar westerly winds may have as its ultimate cause the drawdown of atmospheric co2 in the latest miocene and the early pliocene closing of the panamanian seaway

temporal evolution of mechanisms controlling ocean carbon uptake during the last glacial cycle many mechanisms have been proposed to explain the 85 90 ppm decrease in atmospheric carbon dioxide co2 during the last glacial cycle between 127 000 and 18 000 yrs ago when taken together these mechanisms can in some models account for the full glacial interglacial co2 drawdown most proxy based evaluations focus on the peak of the last glacial maximum 24 000 18 000 yrs ago and little has been done to determine the sequential timing of processes affecting co2 during the last glacial cycle here we use a new compilation of sea surface temperature records together with time sequenced records of carbon and nd isotopes and other proxies to determine when the most commonly proposed mechanisms could have been important for co2 drawdown we find that the initial major drawdown of 35 ppm 115 000 yrs ago was most likely a result of antarctic sea ice expansion importantly changes in deep ocean circulation and mixing did not play a major role until at least 30 000 yrs after the first co2 drawdown the second phase of co2 drawdown occurred 70 000 yrs ago and was also coincident with the first significant influences of enhanced ocean productivity due to dust finally minimum concentrations of atmospheric co2 during the last glacial maximum resulted from the combination of physical and biological factors including the barrier effect of expanded southern ocean sea ice slower ventilation of the deep sea and ocean biological feedbacks

the owen ridge uplift in the arabian sea implications for the sedimentary record of indian monsoon in late miocene abstract the pelagic cover of the owen ridge in the arabian sea recorded the evolution of the indian monsoon since the middle miocene the uplift of the owen ridge resulted from tectonic processes along the previously unidentified miocene india arabia plate boundary based on seismic reflection data tied with deep sea drilling to track the miocene india arabia plate boundary we propose a new timing for the uplift of the owen ridge and highlight its impact on the record of climate changes in pelagic sediments the new dataset reveals a fracture zone east of the owen ridge corresponding to the fossil plate boundary and documents that the main uplift of the owen ridge occurred close to 8 5 ma and is coeval with a major uplift of the east oman margin late miocene deformation at the india arabia plate boundary is also coeval with the onset of intra plate deformation in the central indian ocean suggesting a kinematic change of india and surrounding plates in the late miocene the uplift of the owen ridge above the lysocline at 8 5 ma accounts for a better preservation of globigerina bulloides in the pelagic cover previously misinterpreted as the result of a monsoon intensification event

the critical size of macroscopic imperfections in dry snow slab avalanche initiation 1 dry snow slab avalanches initiate after mode ii fracture propagation within a thin weak layer under a planar slab dry alpine snow in which avalanches form is a porous material typically with volume fraction filled by solids of between 10 and 50 if snow slab avalanches were caused by small scale flaws there would be continuous avalanches and alpine snow would not survive on steep slopes instead snow slab avalanches initiate from macroscopic imperfections or weak zones within the weak layer these are called sweet spots by practitioners and deficit zones in the pioneering work by conway and abrahamson in the 1980s in this paper the results of 750 in situ shear fracture tests from 68 slab weak layer combinations are summarized in relation to the critical sweet spot length and weak layer crystal form the results show that the critical sweet spot lengths follow a gamma probability density function with a range from 0 14 to 1 3 m and most probable value 0 5 m the results also imply that critical sweet spot length depends on weak layer grain type with significantly larger values for persistent forms surface hoar and facets than for nonpersistent forms decomposing and fragmented grains

stable and clumped isotope sclerochronologies of mussels from the brazos river texas usa environmental and ecologic proxy abstract oxygen isotope sclerochronology with mollusk shells can provide vital environmental and ecologic information but is complicated in regulated subtropical rivers by irregular river water 18o and consequently irregular shell 18o patterns we performed multi proxy analyses 18o 13c clumped isotopes from serially sampled freshwater mussels in two specimens each of amblema plicata and cyrtonaias tampicoensis from the brazos river texas to age specimens and test whether they accurately record environmental conditions such as river discharge and water source oxygen isotopic measurements are similar to predicted aragonite 18o values based on temperature and water 18o but the record is complex and irregular to better resolve the chronologies we performed clumped isotope analyses on select shell intervals clumped isotope temperatures t 47 ranged from 19 to 36 c summer t 47 values were 3 5 c higher than measured temperatures suggesting an offset in paleothermometer calibration chronologies based on 47 and 18o reveal specimen ages of 3 4 years and winter growth cessation or dramatic slowing in both c tampicoensis and a plicata highlighting thermal limitations on growth and potential biases in environmental reconstructions compared with modern shells historical shells collected before intensive damming showed lower 18o values yet similar clumped temperatures suggesting enhanced evaporation in modern river water due to impoundment and or the 2011 12 drought carbon isotope trends were similar between conspecific shells but differed between species with substantially higher average values for a plicata shells 9 than c tampicoensis shells 12 the correlation between shell 13c values and the release of 13c enriched waters from upstream reservoirs demonstrates that 13c can be used as a proxy for dam release in regulated rivers

the use of oxygen isotope variation in shells of estuarine mollusks as a quantitative record of seasonal and annual colorado river discharge abstract we describe a new method for the calculation of river flow that uses the oxygen isotope composition of bivalve mollusk shells that grew in the river water seawater mixing zone of the colorado river estuary sclerochronological techniques are used to identify tidally induced fortnight scale bundles of daily growth increments within shell cross sections these fortnightly markers are used to establish a chronology for samples taken for 18 o analysis a composite seasonal 18 o profile derived from five shells that grew in the absence of river water flow is used as a baseline against which profiles of river influenced shells are compared because this comparison is between matched fortnights within a year the temperature of shell growth is likely to be very similar the difference in 18 o between the river influenced shell and the no flow composite shell therefore represents the change in the 18 o of the water due to the presence of river water in the mixing zone the river water end member is also determined within a fortnightly context so that the change in the 18 o of mixing zone water can be used to calculate the relative proportions of seawater and fresh water the fresh water end member is calculated from the 18 o of bivalves alive prior to the emplacement of dams and water diversions on the colorado river the marine end member is based on direct measurements of the 18 o of northern gulf of california water during times of no colorado river flow the system has been calibrated to absolute flow amounts using recent releases of known volume and rate

clay mineral assemblages in the zhaotong basin of southwestern china implications for the late miocene and pliocene evolution of the south asian monsoon abstract the characteristics of the evolution of the south asian monsoon during the late miocene through the pliocene are highly debated to obtain a better understanding we studied the clay mineral assemblages and the clay fraction content of a high quality sedimentary sequence borehole core zk1 spanning the interval of 8 8 2 62 ma in the zhaotong basin southwestern yunnan province on the southeastern margin of the tibetan plateau smectite kaolinite illite and vermiculite were the four main clay minerals identified and changes in their relative abundance reveal a distinct pattern of climate change during the study interval until the very late miocene kaolinite and smectite with a small amount of illite were dominant suggesting a relatively warm and humid climate from 6 2 to 2 8 ma smectite was dominant with a minor amount of kaolinite and illite indicating a relatively cool and humid climate and from 2 8 to 2 62 ma vermiculite hiv and illite were dominant with a minor amount of kaolinite indicating a relatively cold and humid climate the variation in clay mineral assemblages indicate substantial changes in the south asian monsoon in the zhaotong basin that promoted a change from a warm and humid climate in the late micoene to cool and humid climate in the very late miocene through pliocene followed by a gradual trend towards a cold and humid climate in the very late pliocene comparison with records from elsewhere indicates that the observed variations in the south asian monsoon were mainly controlled by global cooling rather than by tibetan plateau uplift

late cenozoic uplift of southeastern tibet the age of surface uplift in southeastern tibet is currently unknown but the initiation of major river incision can be used as a proxy for the timing of initial uplift the topographically high eastern plateau and gently dipping southeastern plateau margin are mantled by an elevated low relief relict landscape that formed at a time of slow erosion at low elevation and low tectonic uplift rates prior to uplift of the eastern tibetan plateau thermochronology from deep river gorges that are cut into the relict landscape shows slow cooling between ca 100 and ca 10 20 ma and a change to rapid cooling after ca 13 ma with initiation of rapid river incision at 0 25 0 5 mm yr between 9 and 13 ma a rapid increase in mean elevation of eastern tibet beginning at this time supports tectonic climate models that correlate the lateral eastern expansion of high topography in tibet with the late miocene intensification of the indian and east asian monsoons

dimensions of dry snow slab avalanches from field measurements 1 dry slab avalanches release by a sequence of propagating fractures in this paper i provide field measurements of the important length parameters resulting from fractures for hundreds fallen slabs including depth length and width the field data show wide variations in these parameters probability plots of all dimensions length width and depth suggest they approximately obey log normal probability density functions given slab dimensions two applications are considered on the basis of the field data these applications are 1 estimates of total fracture energy consumed around the perimeter of the slab are given where it is presumed fracture is mostly mode i and along the base weak layer of the slab where shear fracture mode ii and iii is expected for average characteristic dimensions the analysis suggests that energy consumed on the perimeter is somewhat less than in the weak layer even though fracture energy around the perimeter is expected to be higher than in the weak layer the larger area fractured in shear at the base of the slab compared to area fractured in tension around the perimeter results in a comparable amount of total energy needed around the perimeter 2 approximate estimates of avalanche mass for average characteristic dimensions based on slab depth d the only length possibly known prior to avalanching are made the mass is considered related to destructive potential and simple guidelines are given to estimate mass in relation to d with validation by considering concurrent size and estimates of d by mountain guides

fracture mechanical models of dry slab avalanche release experimental evidence shows that snow is a pressure sensitive dilatant strain softening material in slow constant rate shear deformation when strain softening initiates in a weak layer underneath a snow slab avalanche release is hypothesized to be possible with or without additional loading specifically two cases are discussed 1 a shear crack like disturbance can initiate after formation of a slip surface in the weak layer and traverse the layer by a self propagating progressive failure with or even without loading and 2 a self propagating shear instability can develop when a region of the weak layer is driven past peak shear strength by loading for these cases the implied fracture sequence fracture geometry time scale of release and temperature effects are discussed and shown to be consistent with the known facts of dry slab avalanche release

responses of the deep ocean carbonate system to carbon reorganization during the last glacial interglacial cycle we present new deep water carbonate ion concentration co 3 2 records reconstructed using cibicidoides wuellerstorfi b ca for one core from caribbean basin water depth 3623 m sill depth 1 8 km and three cores located at 2 3 4 3 km water depth from the equatorial pacific ocean during the last glacial interglacial cycle the pattern of deep water co 3 2 in the caribbean basin roughly mirrors that of atmospheric co 2 reflecting a dominant influence from preformed co 3 2 in the north atlantic ocean compared to the amplitude of 65 mol kg in the deep caribbean basin deep water co 3 2 in the equatorial pacific ocean has varied by no more than 15 mol kg due to effective buffering of caco 3 on deep sea ph in the pacific ocean our results suggest little change in the global mean deep ocean co 3 2 between the last glacial maximum lgm and the late holocene the three records from the pacific ocean show long term increases in co 3 2 by 7 mol kg from marine isotope stage mis 5c to mid mis 3 consistent with the response of the deep ocean carbonate system to a decline in neritic carbonate production associated with 60 m drop in sea level the coral reef hypothesis superimposed upon the long term trend deep water co 3 2 in the pacific ocean displays transient changes which decouple with 13 c in the same cores at the start and end of mis 4 these changes in co 3 2 and 13 c are consistent with what would be expected from vertical nutrient fractionation and carbonate compensation the observed 4 mol kg co 3 2 decline in the two pacific cores at 3 4 km water depth from mis 3 to the lgm indicate further strengthening of deep ocean stratification which contributed to the final step of atmospheric co 2 drawdown during the last glaciation the striking similarity between deep water co 3 2 and 230 th normalized caco 3 flux at two adjacent sites from the central equatorial pacific ocean provides convincing evidence that deep sea carbonate dissolution dominantly controlled caco 3 preservation at these sites in the past our results offer new and quantitative constraints from deep ocean carbonate chemistry to understand roles of various mechanisms in atmospheric co 2 changes over the last glacial interglacial cycle

quantitative reconstruction of the late miocene monsoon climates of southwest china a case study of the lincang flora from yunnan province the miocene lincang leaf assemblage is used in this paper as proxy data to reconstruct the palaeoclimate of southwestern yunnan sw china and the evolution of monsoon intensity three quantitative methods were chosen for this reconstruction i e leaf margin analysis lma climate leaf analysis multivariate program clamp and the coexistence approach ca these methods however yield inconsistent results particularly for the precipitation as also shown in european and other east asian cenozoic floras the wide range of the reconstructed climatic parameters includes the mean annual temperature mat of 18 5 24 7 degrees c and the mean annual precipitation map of 1213 3711 mm compared with the modem lincang climate mat 17 3 degrees c map 1178 7 mm the miocene climate is slightly warmer wetter and has a higher temperature seasonality a detailed comparison on the palaeoclimatic variables with the coeval late miocene xiaolongtan flora from the eastern part of yunnan allows us to investigate the development and interactions of both south asian and east asian monsoons during the late miocene in southwest china now under strong influence of these monsoon systems our results suggest that the monsoon climate has already been established in southwest yunnan during the late miocene furthermore our results support that both southeast asian and east asian monsoons co occurred in yunnan during the late miocene c 2010 elsevier b v all rights reserved

widespread global peatland establishment and persistence over the last 130 000 y glacial interglacial variations in co2 and methane in polar ice cores have been attributed in part to changes in global wetland extent but the wetland distribution before the last glacial maximum lgm 21 ka to 18 ka remains virtually unknown we present a study of global peatland extent and carbon c stocks through the last glacial cycle 130 ka to present using a newly compiled database of 1 063 detailed stratigraphic records of peat deposits buried by mineral sediments as well as a global peatland model quantitative agreement between modeling and observations shows extensive peat accumulation before the lgm in northern latitudes 40 n particularly during warmer periods including the last interglacial 130 ka to 116 ka mis 5e and the interstadial 57 ka to 29 ka mis 3 during cooling periods of glacial advance and permafrost formation the burial of northern peatlands by glaciers and mineral sediments decreased active peatland extent thickness and modeled c stocks by 70 to 90 from warmer times tropical peatland extent and c stocks show little temporal variation throughout the study period while the increased burial of northern peats was correlated with cooling periods the burial of tropical peat was predominately driven by changes in sea level and regional hydrology peat burial by mineral sediments represents a mechanism for long term terrestrial c storage in the earth system these results show that northern peatlands accumulate significant c stocks during warmer times indicating their potential for c sequestration during the warming anthropocene

development of asian monsoon revealed by marked ecological shift during the latest miocene in northern pakistan carbon isotopes from soil carbonate1 4 and soil organic matter5 6 yield palaeoecological information because the carbon in the soil carbonate forms in isotopic equilibrium with local soil co2 refs 1 7 the isotopic composition of which is in turn determined by local plant cover siwalik group sediments in northern pakistan contain a well exposed palaeosol record spanning the past 18 myr here we report on stable carbon isotope results from associated pedogenic carbonate which indicate a dramatic ecological shift from to dominated floodplain biomass beginning 7 4 7 0 myr ago the earlier c3 floodplain biomasses were probably mainly composed of trees and shrubs whereas c4 grasslands dominated in the plio pleistocene oxygen isotopes also exhibit a shift in the latest miocene probably corresponding to a major climate change which may have induced the forest to grassland transition this dramatic ecological shift in the latest miocene may mark the inception or a marked strengthening of the asian monsoon system

clay mineral sedimentation in high northern latitude deep sea basins since the middle miocene odp leg 151 naag high resolution clay mineralogical investigations and their comparison with other sedimentological data from odp sites 908 and 909 central fram strait were used to reconstruct the paleoclimate and paleoceanography in the high northern latitudes since the middle miocene ice rafting has probably occurred since 15 ma the comparison of sand sized components and clay mineral distribution demonstrate that both were not delivered by the same transport process the input of the clay fraction is related to transport through sea ice and or oceanic currents a provenance change at 11 2 ma is indicated by variations within clay mineral distribution and increased accumulation rates this is interpreted as a result of an increase in water mass exchange through the fram strait decreases of the smectite to illite and chlorite ratio at site 909 suggest a middle miocene cooling phase between 14 8 and 14 6 ma and a further cooling phase between 10 and 9 ma the intensification of glaciation in the northern hemisphere is documented by an increase of illite and chlorite from 3 4 to 3 3 ma which is synchronous to the onset of major northern hemisphere glaciation as indicated by oxygen isotope data

climate change and arctic ecosystems 1 vegetation changes north of 55 n between the last glacial maximum mid holocene and present a unified scheme to assign pollen samples to vegetation types was used to reconstruct vegetation patterns north of 55 n at the last glacial maximum lgm and mid holocene 6000 years b p the pollen data set assembled for this purpose represents a comprehensive compilation based on the work of many projects and research groups five tundra types cushion forb tundra graminoid and forb tundra prostrate dwarf shrub tundra erect dwarf shrub tundra and low and high shrub tundra were distinguished and mapped on the basis of modern pollen surface samples the tundra forest boundary and the distributions of boreal and temperate forest types today were realistically reconstructed during the mid holocene the tundra forest boundary was north of its present position in some regions but the pattern of this shift was strongly asymmetrical around the pole with the largest northward shift in central siberia 200 km little change in beringia and a southward shift in keewatin and labrador 200 km low and high shrub tundra extended farther north than today at the lgm forests were absent from high latitudes graminoid and forb tundra abutted on temperate steppe in northwestern eurasia while prostrate dwarf shrub erect dwarf shrub and graminoid and forb tundra formed a mosaic in beringia graminoid and forb tundra is restricted today and does not form a large continuous biome but the pollen data show that it was far more extensive at the lgm while low and high shrub tundra were greatly reduced illustrating the potential for climate change to dramatically alter the relative areas occupied by different vegetation types

pollen evidence of the palaeoenvironments of lufengpithecus lufengensis in the zhaotong basin southeastern margin of the tibetan plateau evolutionary processes in hominoid primates were closely related to global and or regional environmental changes and therefore palaeoenvironmental reconstruction is fundamental for understanding how environmental changes shaped their evolution here we present pollen data from the 16 m thick shuitangba stb section yunnan province southwestern china bearing remains of the hominoid lufengpithecus lufengensis of the terminal miocene and use principal component analysis to reconstruct the palaeovegetation and palaeodimate during the key period when the hominoid lived our results show that before the stb hominoid appeared zone a the vegetation was dominated by subtropical evergreen broad leaved taxa with a few temperate deciduous taxa e g quercus castanea castanopsis alnus the development of aquatic plants commencing at the similar to 12 m depth is a prominent feature indicating a warm and humid climate during the time when the hominoid lived zone b evergreen broad leaved forests with evergreen quercus were predominant while grasses including poaceae began to expand and simultaneously conifers decreased indicating a warm climate the significant presence of aquatic pollen taxa in subzone a 2 and zone b suggests the occurrence of lacustrine or swampy environments in contrast in zone c the vegetation changed to coniferous forest indicating cooler and drier conditions these results provide substantive evidence of the vegetation conditions when the hominoid lived suggesting that the greater diversity of vegetation and the warm humid climate compared to the present day would have favoured its survival c 2015 elsevier b v all rights reserved

field experiments and numerical modeling of mass entrainment in snow avalanches 1 snow entrainment alters the speed and hence the run out distance of avalanches yet little is known about this significant process we studied entrainment in snow avalanches using observations from 1 the swiss vallee de la sionne test site 2 the italian pizzac site 3 catastrophic avalanches that occurred during the winter 1998 1999 in switzerland and 4 a medium sized spontaneous avalanche that occurred in 2000 in davos switzerland we determined mass and energy balances for 18 avalanche events on average the mass increased by a factor of 4 the primary mode of entrainment appeared to be frontal ploughing although entrainment behind the avalanche front was also observed step entrainment where a snow cover layer fractures and is entirely consumed by the avalanche also occurred basal erosion was negligible mass availability and snow cover structure were the limiting factors governing entrainment other factors such as track topography and avalanche dimension played a secondary role using the experimental results we introduced an entrainment model into a saint venant type flow model where the internal shear deformation of the avalanche is governed by a bagnold law and the shear stress at the basal layer is treated as a voellmy fluid the model with entrainment not only improves the prediction of the velocities and flow heights in comparison to measurements but also reproduces the variations in run out distances which characterize avalanches with similar terminal velocities but different masses

lowering of glacial atmospheric co2 in response to changes in oceanic circulation and marine biogeochemistry 1 we use an earth system model of intermediate complexity climber 2 to investigate what recent improvements in the representation of the physics and biology of the glacial ocean imply for the atmospheric concentration the coupled atmosphere ocean model under the glacial boundary conditions is able to reproduce the deep salty stagnant water mass inferred from antarctic deep pore water data and the changing temperature of the entire deep ocean when carbonate compensation is included in the model we find a co2 drawdown of 43 ppmv associated mainly with the shoaling of the atlantic thermohaline circulation and an increased fraction of water masses of southern origin in the deep atlantic fertilizing the atlantic and indian sectors of the southern ocean north of the polar front leads to a further drawdown of 37 ppmv other changes to the glacial carbon cycle include a decrease in the amount of carbon stored in the terrestrial biosphere 540 pg c which increases atmospheric co2 by 15 ppmv and a change in ocean salinity resulting from a drop in sea level which elevates co2 by another 12 ppmv a decrease in shallow water caco3 deposition draws down co2 by 12 ppmv in total the model is able to explain more than two thirds 65 ppmv of the glacial to interglacial co2 change based only on mechanisms that are clearly documented in the proxy data a good match between simulated and reconstructed distribution of 13c changes in the deep atlantic suggests that the model captures the mechanisms of reorganization of biogeochemistry in the atlantic ocean reasonably well additional poorly constrained mechanisms to explain the rest of the observed drawdown include changes in the organic carbon caco3 ratio of sediment rain reaching the seafloor iron fertilization in the subantarctic pacific ocean and changes in terrestrial weathering

carbon stocks and isotopic budgets of the terrestrial biosphere at mid holocene and last glacial maximum times abstract the carbon fluxes stocks and isotopic budgets of the land biosphere at mid holocene 6 ka bp and last glacial maximum 21 ka bp times are reconstructed with the carbon assimilation in the biosphere caraib model forced with two different sets of climates simulated by the european centre hamburg echam and lmd general circulation models it is found that the trends predicted on the basis of both sets of gcm climatic fields are generally consistent with each other although substantial discrepancies in the magnitude of the changes may be observed actually these discrepancies in the biospheric results associated with the use of different gcm climatic fields are usually smaller than the differences between biospheric runs performed while considering or neglecting the co2 fertilization effect which might however be overestimated by the model due to uncertainties concerning changes in nutrient availability the calculated changes with respect to the present of the biosphere carbon stock range from 132 to 92 gt c for the mid holocene and from 710 to 70 gt c for the last glacial maximum it is also shown that the relative contribution of the material synthesized by c4 plants to the total biomass of vegetation litter and soils was substantially larger at mid holocene and last glacial maximum times than today this change in the relative importance of the c3 and c4 photosynthetic pathways induced changes in the 13 c fractionation of the land biosphere these changes in the average biospheric fractionation resulting from the redistribution of c3 and c4 plants were partly compensated for by changes of opposite sign in the fractionation of c3 plants due to the modification of the intercellular co2 pressure within their leaves with respect to present times the combination of both processes reduced the 13 c discrimination i e less negative fractionation of the land biosphere by 0 03 to 0 32 during the mid holocene and by 0 30 to 1 86 at the last glacial maximum

paleoenvironmental reconstruction using stable isotopes and trace elements from archaeological freshwater bivalve shell fragments in northwest patagonia argentina abstract stable oxygen and carbon isotopes 18o and 13c and the trace elements manganese mn and strontium sr were analyzed in archaeological bivalve diplodon chilensis shell fragments recovered from parque diana cave patagonia argentina to analyze the temporal trends of human occupation of the north patagonia forest with climatic conditions recorded at regional scale but poorly known at local scale for this site we established a stratigraphic sequence of thirteen 10 cm thick layers spanning the period c 2370 bp to c 580 bp and grouped these layers into three cultural components according to this region s climate with rain and snow concentrated in winter and dry summers our data suggest that these components are contemporary with three climatic periods a dry period indicated by high values of 18oshell 13cshell and sr ca ratio mn ca ratio does not show any significant trend in the lower component is associated with brief incursions of hunter gatherers from the eastern steppe in the middle component low 18oshell 13cshell and sr ca ratios suggest a humid climate with increased supply of meteoric and or melt water along with terrestrial plants organic matter and soil carbonates to the river according to the archaeological evidence in this period hunter gatherers from the pacific coast and forest started to colonize the area across the andes cordillera at the beginning of the upper component which is mostly contemporary with the expression of the medieval climatic anomaly mca the proxies are not totally coincident but a tendency to progressively drier conditions could be inferred except for layer 4 for 18oshell and layer 5 for sr ca ratio 18oshell 13cshell and sr ca ratio show consistently high levels in the upper than in the middle component in layer 5 18oshell and 13cshell are elevated with respect to the middle component while sr ca ratio remains low in layer 4 13cshell and sr ca ratio are high while 18oshell shows a negative peak in layers 3 to 1 18oshell 13cshell and sr ca ratio remain at high levels indicating an arid warm climate with high aquatic plant productivity in coincidence with the expression of the mca reported for this region in a partially contemporaneous period 1080 1250 ad at this time the occupation of the site by groups of the same origin as those present in the middle component became permanent extensive and intensive use of local resources in this period can be inferred from the quality and quantity of artifacts recovered

quantifying the global carbon cycle response to volcanic stratospheric aerosol radiative forcing using earth system models 1 large volcanic eruptions can have a significant cooling effect on climate which is evident in both modern and palaeo data however due to the difficulty of disentangling volcanic and other influences in the modern atmospheric co2 record and uncertainties associated with palaeo reconstructions of atmospheric co2 the magnitude of the carbon cycle response to volcanically induced climatic changes is difficult to quantify in this study three earth system models simearth climber 2 and climber lpj are used to simulate the effects of different magnitudes of volcanic eruption from relatively small e g mount pelee 1902 to very large e g the 1258 ice core event on the coupled global climate carbon cycle system these models each use different but justifiable parameterizations to simulate the global carbon cycle and climate key differences include how soil respiration and net primary productivity respond to temperature and atmospheric co2 all models simulate global surface cooling in response to volcanic events in response to a mount pinatubo equivalent eruption the modelled temperature decrease is 0 3 c to 0 4 c and atmospheric co2 decreases by 1 1 ppm to 3 4 ppm the initial response time of climate to volcanic forcing and subsequent recovery time vary little with changes in the size of the forcing response times for vegetation and soil carbon are relatively consistent across forcings for each model however results indicate that there is significant uncertainty concerning the response of the carbon cycle to volcanic eruptions suggestions for future research directed at reducing this uncertainty are given

climatic and ecological implications of late pliocene palynoflora from longling yunnan china abstract the longling coal mine w yunnan is situated in an area of substantial geotectonic activity its late pliocene palynoflora is of considerable interest since the area represents a centre of biodiversity eighty two palynomorphs belonging to 61 families were recovered from the lignite the palynoflora is dominated by angiosperms 68 3 with ferns 24 4 gymnosperms 4 9 and algae 2 4 comparisons indicate that most of the palynoflora was derived from the montane humid evergreen broad leaved forest with lesser contributions from the tsuga dumosa forest and evergreen coniferous broad leaved mixed forest as well as the montane mossy evergreen broad leaved forest this indicates that the late pliocene climate was cooler than that of the present in the course of the accumulation of the lignite the climate underwent five major phases of warming and cooling

last glacial maximum permafrost in china from cmip5 simulations abstract the distributions of frozen ground and active layer thickness alt during the last glacial maximum lgm and pre industrial periods in china were investigated using coupled model intercomparison project phase 5 cmip5 model experiments compared to the pre industrial period the lgm climate was 5 c colder and featured significantly higher freezing indices on the tibetan plateau and in northeast china frozen ground expanded widely in the lgm the extents of permafrost and seasonally frozen ground in china were 4 11 106 km2 and 4 97 106 km2 respectively which are 2 42 106 km2 larger and 1 45 106 km2 smaller respectively than the pre industrial levels moreover the colder climate and longer duration also resulted in lgm alt values that were 1 3 m less than the pre industrial values in the permafrost areas common to both periods altitudinal permafrost was present mainly on the tibetan plateau and adjacent mountains in west china between 28 n and 41 30 n and covered an area of 2 63 106 km2 latitudinal permafrost was present mainly in northeast china and occupied an area of 1 48 106 km2 the southern limit of latitudinal permafrost was located 10 of latitude farther south during the lgm than during the pre industrial period the lgm simulation results agree reasonably well with previous reconstructions with the exception of an underestimation in the permafrost extent although relatively high level disagreement exists between the models in terms of the exact locations of the southern limits the ensemble average is still able to represent the large scale spatial pattern of frozen ground remarkably well

long term storage and age biased export of fluvial organic carbon field evidence from west iceland terrestrial organic carbon oc plays an important role in the carbon cycle but questions remain regarding the controls and timescale s over which atmospheric co remains sequestered as particulate oc poc motivated by observations that terrestrial poc is physically stored within soils and other shallow sedimentary deposits we examined the role that sediment storage plays in the terrestrial oc cycle specifically we tested the hypothesis that sediment storage impacts the age of terrestrial poc we focused on the efri haukadalsa river catchment in iceland as it lacks ancient sedimentary bedrock that would otherwise bias radiocarbon based determinations of poc storage duration by supplying pre aged petrogenic poc our radiocarbon measurements of riverine suspended sediments and deposits implicated millennial scale storage times comparison between the sample types suspended and deposits suggested an age offset between transported suspended sediments and stored deposits poc at the time of sampling which is predicted by theory for the sediment age distribution in floodplains we also observed that poc in suspended sediments is younger than the predicted mean storage duration generated from independent geomorphological data which suggested an additional role for oc cycling consistent with this we observed interparticle heterogeneity in the composition of poc by imaging our samples at the microscale using x ray absorption spectroscopy specifically we found that particles within individual samples differed in their sulfur oxidation state which is indicative of multiple origins and or diagenetic histories altogether our results support recent coupled sediment storage and oc cycling models and indicate that the physical drivers of sediment storage are important factors controlling the cadence of carbon cycling

quantifying landscape differences across the tibetan plateau implications for topographic relief evolution 1 we quantify the bulk topographic characteristics of the tibet qinghai plateau with specific focus on three representative regions northern central and southeastern tibet quantitative landscape information is extracted from shuttle radar topography mission digital elevation models we find that the morphology of the tibetan plateau is nonuniform with systematic regional differences the northern and central parts of the plateau are characterized by what we suggest to call positive topography i e a topography in which elevation is positively correlated with relief and mean slope a major change from the internally drained central part of tibet to the externally drained part of eastern tibet is accompanied by a transition from low to high relief and from positive to negative topography i e a topography where there is an inverse or negative correlation between elevation and relief and between elevation and mean slope relief in eastern tibet is largest along rivers as they cross an ancient eroded plateau margin at high angle to the major strike slip faults the yalong yulong thrust belt implying strong structural control of regional topography we propose that the evolution of river systems and drainage efficiency the ability of rivers to transport sediments out of the orogen coupled with tectonic uplift is the simplest mechanism to explain systematic regional differences in tibetan landscapes basin filling due to inefficient drainage played a major role in smoothing out the tectonically generated structural relief this mode of smoothing started concurrently with tectonic construction of the relief as most clearly illustrated today in the qilian shan qaidam region of the northeastern plateau in the interior of tibet further passive filling due to internal drainage only continued to smooth the local relief millions of years after the cessation of major phases of surface uplift due to crustal shortening thus diachronous beveling at high elevation produced the low relief surface of the high plateau in southeast tibet headward retreat of external drainages brought back in the global ocean base level first disrupting then interrupting the relief reduction process it produced a transitional topography by dissecting the old remnant plateau surface which introduced younger and steeper incision of this hitherto preserved high base level this provides a unifying mechanism for the formation of the low relief plateau interior and for the origin of the high elevation low relief relict surface in southeastern tibet our analysis brings forth the importance of surface processes in particular drainage efficiency in shaping plateau morphology and landscape relief such key processes appear to have been mostly ignored in numerical models of plateau deformation our results also cast doubt on and provide a more realistic alternative to the fashionable contention that a continuous preuplift low relief surface first formed at low elevation extending all the way to the south china sea shore before being warped upward in the late miocene pliocene by lower crustal channel flow

vegetation and climatic changes of sw china in response to the uplift of tibetan plateau abstract to understand the vegetation succession and climatic changes at the southeastern margin of the tibetan plateau in the neogene we reconstructed the middle miocene vegetation and climate based on palynological data from four localities which are at different latitudes along the ailao mountains in yunnan southwest china the palynological assemblages suggest that the vegetation there was composed of mixed evergreen and deciduous broad leaved forests growing under subtropical conditions based on the palynological data the palaeoclimatic parameters from the four localities are established the new parameters were compared with those of the late miocene of the late pliocene and of today the comparison revealed that the temperatures were obviously lower in the middle miocene than they are today this suggested that the ailao mountains were not high enough to block the asian winter monsoon in the middle miocene the middle miocene vegetation at the southeastern edge of the tibetan plateau was also compared to that of central tibet it would appear that the palaeoclimate at the southeastern edge of the tibetan plateau was warmer and wetter than in central tibet in contrast to the neogene cooling in central europe the climate at the southeastern edge of the tibetan plateau has gradually warmed since the middle miocene this phenomenon was most likely caused by the uplift of the tibetan plateau which has succeeded in blocking the asian winter monsoon since the middle miocene