a diffusion adsorption model of uranium uptake by archaeological bone abstract an argument for the possibility of uranium uptake by buried bone taking place through the adsorption of uranyl species on bone mineral is advanced in the light of this a diffusion adsorption model for uranium uptake by buried bone is developed the necessary constants are evaluated from the literature and from laboratory measurements of the partition coefficient between solution and bone mineral the geochemical and hydrological parameters which control uptake are discussed the predictions of the model are shown to be in general accordance with the timescale magnitude and distribution of uranium uptake in archaeological bone using the model specific predictions of the variation of apparent uranium series ages in bone can be made and bone is shown clearly not to conform to the closed system assumption when the model is extended to tooth enamel it is found to be incompatible with the early uptake model used for esr dating but to fall between the early uptake and linear uptake models similarly it suggests that uranium series dates on enamel assuming a closed system are liable to underestimate the true age by at least one third

asian origin of interannual variations of summer climate over the extratropical north atlantic ocean abstractthe authors have identified an interannual relationship between asian tropospheric temperature and the north atlantic ocean sea surface temperature sst during summer may september and discussed the associated features of atmospheric circulation over the atlantic eurasian region when tropospheric temperature is high low over asia positive negative sst anomalies appear in the extratropical north atlantic this relationship is well supported by the changes in background atmospheric circulation and ocean atmosphere land thermodynamic processes when heat transfer from the land surface to the atmosphere over asia strengthens local tropospheric temperature increases and positive temperature anomalies propagate westward from asia to the north atlantic leading to an increase in summer tropospheric temperature over the atlantic eurasian region accordingly a deep anomalous ridge occurs over the extratropical north atlantic ocean with low level southerly anomalies over the western portion of t

palaeoclimatic implications of the occurrence of the arcoid bivalve anadara trapezia deshayes in the quaternary of australasia abstract the arcoid bivalve anadara trapezia deshayes 1840 is a eurythermal estuarine mollusc that flourishes at present in eastern australia between port phillip bay victoria and townsville in northern queensland a trapezia first appeared in the australian quaternary fossil record during oxygen isotope stage ois 7 in new zealand where it is now extinct the earliest known occurrences are in the rangitawa fossil beds and in uppermost castlecliffian strata west of wanganui north island ois 11 ca 400 ka the species had an extensive distribution during the last interglacial maximum ois 5e in both australia and new zealand and appears to have had a slightly wider than present geographic range in southeastern australia during the middle holocene as shown by records from tasmania and western victoria where it no longer lives apart from an isolated population inhabiting oyster harbour western australia a trapezia has not been confirmed living in coastal waters west of port phillip bay victoria it became extinct in new zealand sometime after ois 5e the extensive distribution and abundance of a trapezia and other fauna of subtropical affinity during the last interglacial maximum in areas where both are now extinct appears to be associated with an enhanced leeuwin current at that time coinciding with higher less seasonally concentrated levels of precipitation and river discharge the arrival of a trapezia in australasian coastal waters may have been a consequence of planktonic dispersal from southern south america a bravardi del rio from the middle miocene puerto madryn formation on the valdes peninsula argentina may be a possible ancestor for a trapezia

uranium 234 anomalies in corals older than 150 000 years we present new precise u th ages of well preserved coral specimens collected from the island of barbados west indies and the atoll of mururoa french polynesia our new data confirm the ages attributed to oxygen isotope stage 7 in the framework of the milankovitch theory berger 1978 mar tinson et al 1987 by using thermal ionization mass spectrometry tims it is also possible to quantify precisely the 234u238u ratios in corals samples older than 150 kyr b p are shown to be characterized by significant excesses of 234u relative to the uranium isotopic composition expected if the corals grew in present day sea water assuming that the 230th ingrowth ages are accurate these anomalies translate into high initial 234u238u ratios about 1 2 at 200 kyr and up to 1 5 at about 450 kyr b p we propose that the anomalies result from both diagenetic addition and replacement of u and possibly from global changes in the 234u238u composition of sea water through time the 234u anomalies cast doubt on the accuracy of the classical 230th ingrowth dating method in old corals and in particular for the use of measured 234u238u ratios alone to date corals older than 150 kyr

subtropical anticyclones and summer monsoons the summer subtropical circulation in the lower troposphere is characterized by continental monsoon rains and anticyclones over the oceans in winter the subtropical circulation is more strongly dominated by the zonally averaged flow and its interactions with orography here the mechanics of the summer and winter lowertropospheric subtropical circulation are explored through the use of a primitive equation model and comparison with observations by prescribing in the model the heatings associated with several of the world s monsoons it is confirmed that the equatorward portion of each subtropical anticyclone may be viewed as the kelvin wave response to the monsoon heating over the continent to the west a poleward flowing low level jet into a monsoon such as the great plains jet is required for sverdrup vorticity balance this jet effectively closes off the subtropical anticyclone to the east and also transports moisture into the monsoon region the low level jet into north america induced by its monsoon heating is augmented by a remote response to the asian monsoon heating the rossby wave response to the west of subtropical monsoon heating interacting with the midlatitude westerlies produces a region of adiabatic descent it is demonstrated here that a local diabatic enhancement can lead to a strengthening of the descent longitudinal mountain chains act to block the westerly flow and also tend to produce descent in this region below the descent sverdrup vorticity balance implies equatorward flow that closes off the subtropical anticyclone to the west and induces cool upwelling in the ocean through ekman transport feedbacks involving for example sea surface temperatures may further enhance the descent in these regions the conclusion is that the mediterranean type climates of regions such as california and chile may be induced remotely by the monsoon to the east hence it can be argued that the subtropical circulation in summer comprises a set of weakly interacting monsoon systems each involving monsoon rains a low level poleward jet a subtropical anticyclone to the east and descent and equatorward flow to the west in winter it is demonstrated how the nonlinear interaction between the strong zonal mean circulation associated with the winter hadley cell and the mountains can define many of the large scale features of the subtropical circulation the blocking effect of the longitudinal mountain chains is shown to be very important subsequent diabatic effects such as a local diabatic enhancement would appear to be essential for producing the observed amplitude of these features

reply to the comments by mauz b and antonioli f on sea level and climate changes during ois 5e in the western mediterranean we really appreciate the comments by mauz and antonioli on our paper bardaji et al 2009geomorphologic maps are often lacking in studies related to the reconstruction of past sea level changes in most cases these maps would be the only way of reconstructing past sea level oscillations see for example but here we respond to the erroneous statements made in their critical reading of our work we agree with the authors historic review of the problems raised when effects of tectonics and sea level oscillations are observed in the record of relative sea level changes in western mediterranean we should not forget that the mediterranean itself constitutes a collision plate boundary with few stable areas within it therefore the study of the last interglacial shorelines cannot be simply analysed according to altitude as they say what we do not share with mauz and antonioli is that the only solution to this seemed to be determining the age of a coastal deposit using radiometric dosimetric and chemical dating techniques it is obvious that we need a chronological approach to be as accurate as possible first of all however an exhaustive field analysis is needed and this is overlooked by mauz and antonioli at least in the spanish mediterranean sector to begin with field analysis would yield a deeper wider geological knowledge not only of the precise sections but also on a regional scope second a geomorphologic understanding of the selected sections is necessary geomorphology is the best tool that enables us to understand how many different sea level highstands or intervals we are dealing with in terms of their relation to former and younger sea level indicators i e 3d stratigraphic architecture sampling for dating purposes can only be done when the sedimentary sequence is clear and after detailed geomorphologic mapping unfortunately radtke and schellmann 2004

role of atlantic air sea interaction in modulating the effect of tibetan plateau heating on the upstream climate over afro eurasia atlantic regions previous studies have demonstrated that atmospheric diabatic heating over the tibetan plateau tp exerts significant influences on the upstream climate of the atlantic african european sector in boreal summer using the ncar community earth system model this study demonstrates that the tp induced change in north atlantic sea surface temperature sst including evident warming over the mid latitude north atlantic and cooling over the south can in turn modulate the above tp impact compared with the tp heating experiment without atlantic sst variation anomalous wave train pattern appears with north northeastward downstream influences when the change in atlantic sst is considered the wave train pattern is characterized by three positive centers over the north atlantic the arctic ocean and east of japan and four negative centers over northeastern north america north europe the mid atlantic and the northwestern pacific it intensifies the northern portions of the tp induced tropospheric anticyclones over the extratropical north atlantic and the cyclones over northeastern north america and north europe correspondingly precipitation decreases over the northwestern atlantic but increases over northeastern north america and north europe due to the easterly anomalies on the southern side of the weakened thermal low over subtropical africa precipitation over the sahel decreases indicating a weakening of tp induced precipitation dipole over the tropical eastern atlantic and west africa when the atlantic sst influence is considered overall the modulation of atlantic sst variation accounts for above 20 percent of the upstream climate signals induced by the tp thermal effect

u series dating of the late pleistocene mammalian fauna from wood quarry steetley nottinghamshire uk we present the u series dating of bones from wood quarry steetley quarry cave using the diffusion adsorption model to account for uranium uptake the results give a weighted mean date of 66 8 3 0 kyr placing this assemblage within or just before marine oxygen isotope stage 4 the fauna is thought to correlate with the banwell bone cave mammal assemblage zone of the early devensian in britain our results support the idea that this assemblage zone immediately precedes the assemblage represented nearby at pin hole in creswell crags which is contemporary with the mid devensian and correlates with mis 3 our dates and dates for the banwell bone cave mammal assemblage zone from stump cross cavern and evidence from other sites may indicate a longevity for this fauna copyright 2005 john wiley sons ltd

start of the last interglacial period at 135 ka evidence from a high alpine speleothem a detailed study of growth periods of a flowstone from spannagel cave in the zillertal alps austria at 2500 m above sea level a site highly sensitive to climate changes offers unprecedented new insights into pleistocene climate change in central europe flowstone sample spa 52 has a high u content to 116 ppm analyses of this sample reveal that episodes of calcite deposition started at 204 3 ka 135 1 2 ka and 122 ka suggesting that at these times the mean air temperature at this high alpine site was within 1 5 c of the present day condition the beginning of growth at 135 ka corresponds to the ending of the last glaciation and is concordant with a midpoint age for the penultimate deglaciation at 135 2 5 ka as deduced from the absolutely dated oxygen isotope curve in sediments from the bahamas as well as with recent coral evidence from barbados indicating a high sea level already by 135 8 0 8 ka this set of data supports evidence against northern hemisphere forcing of termination ii because the insolation maximum is at 127 ka

zircon u pb o and hf isotopic constraints on mesozoic magmatism in the cyclades aegean sea greece compared to the well documented cenozoic magmatic and metamorphic rocks of the cyclades aegean sea greece the geodynamic context of older meta igneous rocks occurring in the marble schist sequences and melanges of the cycladic blueschist unit is as yet not fully understood here we report o hf isotopic compositions of zircons ranging in age from ca 320 ma to ca 80 ma from metamorphic rocks exposed on the islands of andros ios sifnos and syros with special emphasis on triassic source rocks ion microprobe shrimp ii single spot oxygen isotope analysis of pre cretaceous zircons from various felsic gneisses and meta gabbros representing both the marble schist sequences and the melanges of the study area yielded a large range in 18o values varying from 2 7 to 10 1 vsmow with one outlier at 0 4 initial ehf values 12 5 to 15 7 suggest diverse sources for melts formed between late carboniferous to late cretaceous time that record derivation from mantle and reworked older continental crust in particular variable 18o and ehf t values for triassic igneous zircons suggest that magmatism of this age is more likely rift than subduction related the significant crustal component in 160 ma meta gabbros from andros implies that some jurassic gabbroic rocks of the hellenides are not part of ssz type supra subduction zone ophiolites that are common elsewhere along the margin of the pelagonian zone

the transient atmospheric circulation response to north atlantic sst and sea ice anomalies abstract the objective of this study is to investigate the transient evolution of the wintertime atmospheric circulation response to imposed patterns of sst and sea ice extent anomalies in the north atlantic sector using a large ensemble of experiments with the ncar community climate model version 3 ccm3 the initial adjustment of the atmospheric circulation is characterized by an out of phase relationship between geopotential height anomalies in the lower and upper troposphere localized to the vicinity of the forcing this initial baroclinic response reaches a maximum amplitude in 5 10 days and persists for 2 3 weeks diagnostic results with a linear primitive equation model indicate that this initial response is forced by diabatic heating anomalies in the lower troposphere associated with surface heat flux anomalies generated by the imposed thermal forcing following the initial baroclinic stage of adjustment the response becomes progressively more barotropic and increases in both spatial extent an

a comparison of two surface wind stress analyses over the tropical atlantic during 1980 1987 abstract two sets of monthly sea surface wind stress over the tropical atlantic ocean are compared the datasets are based on the ecmwf analyses during 1980 87 the e winds and the monthly pseudo wind stress from ship observations for the same period the s winds our examination shows that both datasets give qualitatively similar mean fields and annual cycles quantitatively the zonal component of the e winds is larger than that of the s winds especially in the winter hemisphere the strongest southeast trades of the e winds are also shifted to the east of the strongest southeast trades of the s winds in the vicinity of the itcz the e winds are more zonally oriented so that the convergence zone is not as clearly defined interannually both datasets show that the northeast trades were gradually strengthening from 1980 to 1986 the southeast trade winds on the other hand were anomalously strong during 1981 83 but weak during 1984 86 with the e winds the southeast trades decreased gradually duri

circumglobal teleconnections the jet stream waveguide and the north atlantic oscillation abstract monthly and seasonally averaged upper tropospheric northern hemisphere winter fields are examined to determine whether the waveguiding effect of the time averaged tropospheric jets on low frequency disturbances that is predicted by theory does affect the behavior of these disturbances it is found that indeed disturbances in the vicinity of the mean jets particularly the jet that stretches across south asia are fundamentally different from those that reside in regions where the mean winds have weaker meridional gradients like the mid pacific patterns of variability in the jets tend to be smaller scale and to consist of zonally oriented chains of anomalies while variability in the mid pacific is composed of patterns with distinct meridional orientation because they are meridionally trapped and zonally elongated patterns associated with the jet stream waveguide connect activity at points that are much farther apart than do patterns in other regions of the globe within the south asian waveg

u series dating of bone using the diffusion adsorption model abstract u series dating of bone has suffered problems of reliability since its inception because bone remains an open system with respect to uranium commonly applied a priori assumptions of u uptake such as early uptake or linear uptake are inadequate because they have no physical or chemical bases no means of demonstrating which model is suitable for a particular bone and no intrinsic tests of reliability despite this and numerous examples of anomalous u series dates such assumptions are still routinely applied we address this problem using the diffusion adsorption d a model of u uptake millard and hedges 1996 which incorporates a physicochemical description of u uptake using this model we show how the u uptake of a bone responds to geochemical changes in the burial environment which can lead to phenomena such as the removal of u from bones leaching or u uptake late in their burial history recent uptake and we show how the overall uptake history is reflected in distributions profiles of u and u series isotopes across a bone section we present measurements of u concentration profiles and 230 th 234 u profiles on archeological bone from a number of different sites and burial environments and compare the results to profiles predicted by the d a model bones that have undergone complex uptake histories which include u leaching or recent uptake are identified on the basis of these profiles and rejected as unsuitable for dating for bones that appear to have undergone uptake under constant geochemical conditions the d a model is applied to calculate u series dates with much improved reliability

u series measurements in tyrrhenian deposits from mallorca further evidence for two last interglacial high sea levels in the balearic islands the campo de tiro type section for the tyrrhenian ecostratigraphic beds of the balearic islands shows four indurated littoral conglomerates and beach rocks unconformably superimposed the lower two units 1 and 2 are separated by a thin layer of reddish continental silts both contain a typical eutyrrhenian fauna whereas a neotyrrhenian fauna characterizes the overlying units 3 and 4 thu measurements by thermal ionisation mass spectrometry on mollusk shells from these deposits yielded ages of 135 ka unit 1 117 ka units 2 and 3 and a scatter of ages around 100 ka unit 4 the stratigraphic relationships and thu data indicate i that uranium was uptaken by mollusks shells but arca sp each time during a relatively short early diagenetic interval before cementation ensured a fair closure of the radioactive system ii two high sea stands characterized the last interglacial isotopic substage 5e of the balearic islands area iii the duration of this episode was 17 ka and iv the change in faunal assemblages and disconformity observed between units 2 and 3 are due to fluctuations in sea level and surface water conditions which occurred during the second high sea level episode of the last interglacial

high precision u series dating of corals from western australia and implications for the timing and duration of the last interglacial abstract u series ages using methods of thermal ionisation mass spectrometry tims are reported for last interglacial fossil reefs along the stable coastal margin of western australia thorium isotope ratios were measured with superior precision using methods of charge collection high levels of precision in the measurement of both uranium and thorium isotopes has reduced the age uncertainty due to analytical errors excluding the uncertainty in the decay constants by a factor of four over the precisions reported by many earlier tims workers uncertainties in 234u t determined from both 230th 238u and 234u 238u are also significantly smaller than previously reported allowing samples which have undergone diagenetic exchange of uranium and thorium to be more easily identified strict criteria were adopted to screen the new western australian data reliable ages range from 127 to 122 ka published tims observations from other localities have been assessed using the same strict criteria when these are combined with glacio hydro isostatic sea level models they indicate that the last interglacial period occurred from at least 130 to 117 ka however these age constraints are largely determined from single data points and need to be verified with additional ages before considering them to be robust estimates for the timing of onset and termination of the last interglacial globally the main episode of reef growth appears to be confined to a narrow interval occurring from 127 to 122 ka in direct agreement with the narrow range in ages obtained from the western australian sites this may indicate that the last interglacial was of short duration extending from 127 to 122 ka only alternatively this interval may reflect a major reef building event in the middle of a longer duration 130 117 ka interglacial interval

north atlantic oscillation response to anomalous indian ocean sst in a coupled gcm the dominant pattern of atmospheric variability in the north atlantic sector is the north atlantic oscillation nao since the 1970s the nao has been well characterized by a trend toward its positive phase recent atmospheric general circulation model studies have linked this trend to a progressive warming of the indian ocean unfortunately a clear mechanism responsible for the change of the nao could not be given this study provides further details of the nao response to indian ocean sea surface temperature sst anomalies this is done by conducting experiments with a coupled ocean atmosphere general circulation model oagcm the authors develop a hypothesis of how the indian ocean impacts the nao

the modeled atmospheric response to midlatitude sst anomalies and its dependence on background circulation states abstract the atmospheric response to a midlatitude sst anomaly in the north pacific and its dependence on background flow are examined in a gcm experiments are conducted using the same warm sst anomalies but two different model states perpetual january and perpetual february the atmospheric responses to the sst anomalies are statistically significant in both january and february but are completely different the anomalous circulation in january is characterized by a trough decaying with height immediately downstream of the sst anomalies in february the anomalous circulation is dominated by a downstream ridge growing with height the patterns of the anomalous heights in the two months are nearly orthogonal vorticity and thermodynamic budgets are diagnosed to illustrate how the anomalous circulations are maintained over the sst anomalies low level convergence and ascent are observed in both months in january the anomalous convergence is balanced by a residual due primarily to the forcing by submont

u series dating and human evolution some of the major events in human evolution occurred during the middle pleistocene these include the evolutionary rise of the neanderthals in eurasia and of anatomically modern humans either in africa or on a broader geographical front in addition to major biogeographic changes among mammals including the hominine colonization of europe prior to the middle pleistocene the application of potassium argon and argon argon dating has yielded a relatively detailed chronological picture for the earlier phases of hominid evolution and from c 50 ky radiocarbon dating provides the backbone of our chronology for the extinction of the neanderthals colonization of europe by anatomically modern humans and all subsequent events between these however the middle pleistocene has only been amenable to precise chronometric dating for the past few decades before the advent of radiometric dating as glynn isaac 1975 famously observed the middle pleistocene was the muddle in the middle u series dating is one of a range of dating methods employed by archaeologists to provide a chronology for human evolution fig 1 other applicable methods include optically stimulated luminescence osl which can be used to date sediments perhaps back to about 0 5 my measuring the time since the last exposure to sunlight it is increasingly employed as a dating method especially since suitable sediments are common on archaeological sites e g aitken 1992 a related technique thermoluminescence tl can be used to date burnt flint artifacts e g aitken 1985 which provide a more direct date for specific human activity on a site although material that is suitably burnt is relatively rare potassium argon and argon argon dating have been the most useful techniques for calibrating early hominid evolution because its limit for dating extends considerably beyond the origins of the earliest hominids at around 5 my e g curtis and hay 1972 their application however is

biomechanics dinosaur locomotion from a new trackway ardley quarry in oxfordshire uk contains one of the most extensive dinosaur trackway sites in the world with individual trackways extending for up to 180 metres we have discovered a unique dual gauge trackway from a bipedal theropod dinosaur from the middle jurassic in this locality which indicates that these large theropods were able to run and that they used different hindlimb postures for walking and running our findings have implications for the biomechanics and evolution of theropod locomotion

the role of oceanic heat advection in the evolution of tropical north and south atlantic sst anomalies abstract the role of horizontal oceanic heat advection in the generation of tropical north and south atlantic sea surface temperature sst anomalies is investigated through an analysis of the oceanic mixed layer heat balance it is found that sst anomalies poleward of 10 are driven primarily by a combination of wind induced latent heat loss and shortwave radiation away from the eastern boundary horizontal advection damps surface flux forced sst anomalies due to a combination of mean meridional ekman currents acting on anomalous meridional sst gradients and anomalous meridional currents acting on the mean meridional sst gradient horizontal advection is likely to have the most significant effect on the interhemispheric sst gradient mode through its impact in the 10 20 latitude bands of each hemisphere where the variability in advection is strongest and its negative correlation with the surface heat flux is highest in addition to the damping effect of horizontal advection in these latitude bands e

an open system model for u series age determinations of fossil corals the source of excess 234u in fossil corals and its relationship to u series age determinations has been an outstanding problem in geochronology for more than 20 years with increasing numbers of u series isotope measurements in corals and significant improvements in analytical precision through mass spectrometry it is increasingly apparent that a substantial fraction of observed isotope ratios cannot be reasonably explained by closed system decay moreover observations of a positive correlation between 234u 238u and 230th 238u ratios in corals from the same terrace are difficult to explain however the decay of dissolved uranium and recoil mobilization of uranium daughters produce particle reactive 234th and 230th and the coupled addition of these th isotopes could simultaneously increase coral 234u 238u and 230th 238u here we present a quantitative model based on decay dependent redistribution of 234th and 230th permitting calculation of open system coral ages these equations provide a general solution to the recoil redistribution problem applicable to any alpha decay series while measured isotope ratios of corals from the three youngest stratigraphically defined barbados terraces are inconsistent with closed system decay they fall in broadly linear arrays agreeing with model predictions isotopic arrays of older barbados corals and corals from terraces around the world are also consistent with model predictions suggesting the open system model is generally applicable corals with extreme isotopic compositions that are impossible to produce by closed system decay are consistent with the limited range of isotopic compositions predicted by the model at ages older than 600 ka for corals from a single terrace 234th and 230th redistribution appears to be a source of systematic conventional age error even for corals with slightly elevated 234u however open system ages are consistent even for corals with extremely elevated 234u for the youngest three barbados terraces mean open system terrace ages are consistent with mean conventional terrace ages calculated from pristine samples if the most accurate conventional ages are from corals with an initial 234u 238u identical to modern seawater then the open system model will improve the accuracy of coral u series age determinations and dramatically increase the number of reliable ages

monsoons and the dynamics of deserts the existence of subtropical deserts such as the sahara has often been attributed to the annual mean zonal mean hadley circulation which shows strong descent in the subtropics however the zonal mean hadley circulation shows considerable evolution over the course of the year with very strong subtropical descent during winter but practically no zonal mean subtropical descent during summer when rainfall over the eastern sahara and the mediterranean is least charney 1975 proposed a biosphere albedo feedback mechanism whereby local anthropogenic effects related to over grazing could affect the radiative balance enhancing summertime diabatic descent and leading to desertification of the subtropics in general the present study which uses an idealized model suggests a monsoon desert mechanism for desertification whereby remote diabatic heating in the asian monsoon region can induce a rossby wave pattern to the west integral with the rossby wave solution is a warm thermal structure that interacts with air on the southern flank of the mid latitude westerlies causing it to descend this adiabatic descent is localized over the eastern sahara and mediterranean and over the kyzylkum desert to the south east of the aral sea by the mountains of north africa and south west asia trajectories indicate that the monsoon desert mechanism does not represent a simple walker type overturning cell instead the descending air is seen to be mainly of mid latitude origin it is speculated that the monsoon forced adiabatic descent may result in clear air and therefore a local diabatic enhancement which effectively doubles the strength of descent with this mechanism desertification can be forced by remote changes in monsoon strength rather than by local effects this conclusion is supported by the observed dramatic strengthening of descent over the mediterranean and east sahara during the onset of the asian monsoon and on the longer timescale by relating prehistoric lake levels to milankovitch monsoon forcing the latter may help to explain the perceived discrepancies between the palaeoclimate of the eastern sahara and the strength of a tropic wide monsoon the monsoon desert mechanism may not be confined to the asian monsoon alone and the existence of other monsoon climate regions over the globe may in a similar way explain the observed summertime strengthening of the oceanic sub tropical anticyclones and the existence of western continental deserts and mediterranean type climate regions

a wide gauge large mammal trackway from the upper paleocene of alberta canada a very rare 11 2 m long wide gauge trackway made by an as yet undetermined large mammal is described from the lacombe member late paleocene of the paskapoo formation paleocene the exposure of the trackway was connected with the record setting floods of 2013 in the province of alberta as the tracks were exposed close to the base of the brazeau dam in west central alberta the tracks are preserved on the top surface of a siltstone but extensive erosion of the tracks resulted in the removal of details such as claw and digit traces as well as any heel or palm impressions the tracks are all circular to subcircular in outline and it is not possible to determine the direction of travel of the trackmaker sequences of distinct pairings of adjacent tracks on both the left and right set of traces are present and these are interpreted to represent manus pes couples the tracks do not show any overprinting the mean pace angulations of the two best preserved sections range from 113 to 125 while their mean stride lengths range from 95 to 96 cm the lack of any distinctive anatomical details being preserved in the tracks prevents a precise identification of the trackmaker but the sizes shapes and age of the tracks suggest that they could have been made by a large pantodont

precise th u dating of small and heavily coated samples of deep sea corals marine carbonate skeletons like deep sea corals are frequently coated with iron and manganese oxides hydroxides which adsorb additional thorium and uranium out of the sea water a new cleaning procedure has been developed to reduce this contamination in this further cleaning step a solution of na2edta na2h2tb and ascorbic acid is used which composition is optimised especially for samples of 20 mg of weight it was first tested on aliquots of a reef building coral which had been artificially contaminated with powdered ferromanganese nodule applied on heavily contaminated deep sea corals scleractinia it reduced excess 230th by another order of magnitude in addition to usual cleaning procedures the measurement of at least three fractions of different contamination together with an additional standard correction for contaminated carbonates results in th u ages corrected for the authigenic component a good agreement between th u and 14c ages can be achieved even for extremely coated corals

interdecadal variations in north atlantic sea surface temperature and associated atmospheric conditions abstract evidence is presented for a distinct pattern of ocean atmosphere relationship associated with interdecadal variability in the north atlantic region using a century of surface marine observations it is shown that middle and high latitude sea surface temperature sst display a long term fluctuation with negative anomalies before 1920 and during the 1970s and 1980s positive sst conditions prevailed from about 1930 to 1960 the pattern of interdecadal sst variability is constructed by subtracting the average field during 15 cold years from that during a similar interval of warm years the early century warming and the more recent cooling display a similar spatial pattern in both cases the pattern is basin scale and largely of one polarity with maxima in the vicinity of iceland in the labrador sea and northeast of bermuda the corresponding differences in surface atmospheric conditions are determined by averaging and subtracting in the same manner fields of sea level pressure slp and surf

reinterpretation of palmate and semi palmate webbed fossil tracks insights from finite element modelling abstract a track from the late cretaceous previously described as being generated by a semi palmate bird was studied with the aid of high resolution laser scanning substrate conditions at the time of track formation were diagnosed fine grained soft waterlogged sediment and used to constrain a finite element track simulator the indentation of a non webbed virtual tridactyl foot in such conditions created a resultant track with features analogous to webbing between digits this webbing was a function of sediment deformation and subsequent failure in 3d specific to rheology variation of substrate conditions and interdigital angle was incrementally stepped apparent webbing impressions were clearly developed only within a limited range of sediment conditions and pedal geometry the implications of this work are that descriptions of webbed tracks should account for the possibility that webbing was indirectly formed through sediment failure and not necessarily the direct impression of a webbed foot additionally dating the earliest occurrence of webbed feet in the fossil record and potentially extending phylogenetic ranges should be treated with caution when based upon evidence from tracks

uranium concentration and isotope ratio profiles within mercenaria shells geochronological implications shells of nineteen specimens of mercenaria from unconsolidated sediments of the southeastern usa coast ranging in age from alive to pliocene were each separated into three to six sections parallel to the shell surface the uranium concentration and isotope ratio of each subsample was determined the results confirm those of previous studies that whole fossil shells have about 8 times as much uranium 300 vs 40 ppb and considerably higher 234u 238u ratios than do whole live collected shells however it was also found that uranium concentrations fall very steeply by factors of 300 and 15 in live and fossil shells respectively from the exterior of the shell to about two thirds of the shell thickness between this depth and the interior surface the uranium concentrations of live shells increase by about a factor of 5 while fossils have gradients which vary from moderately positive to moderately negative the most surprising finding of the study is that the interior portions of the shells become closed chemical systems by no more than about 15 ka after their death this is known from the observation that these portions of late pleistocene shells still have oceanic uranium isotope ratios while the exterior portions of the same shells have ratios which reflect an uptake of uranium from continental groundwaters the water the shells have been in contact with for the vast majority of their existence thus the u series ages of the interior portions of mercenaria shells may be valid after a small correction though shells older than about 200 ka seem less promising firm conclusions cannot be drawn regarding them because of the great scatter in the data

deep sea coral evidence for rapid change in ventilation of the deep north atlantic 15 400 years ago coupled radiocarbon and thorium 230 dates from benthic coral species reveal that the ventilation rate of the north atlantic upper deep water varied greatly during the last deglaciation radiocarbon ages in several corals of the same age 15 41 0 17 thousand years and nearly the same depth 1800 meters in the western north atlantic ocean increased by as much as 670 years during the 30 to 160 year life spans of the samples cadmium calcium ratios in one coral imply that the nutrient content of these deep waters also increased our data show that the deep ocean changed on decadal centennial time scales during rapid changes in the surface ocean and the atmosphere

u series dating of diagenetically altered fossil reef corals initial 234u 238u activity ratios higher than those expected from closed system evolution of seawater are an outstanding problem in u series dating of fossil reef corals the increased activity ratios are ascribed to post depositional diagenesis we analysed six last interglacial and one holocene coral of the genus porites collected near the northern end of the gulf of aqaba northern red sea together with three recent corals from this location as a modern reference while the values measured on the recent samples show no deviation from expected values the holocene and last interglacial corals display highly elevated 234u 238u activity ratios as well as increased 238u and 232th concentrations 234u 238u activity ratios are strongly correlated with 230th 238u and total uranium content a model assuming different degrees of uranium addition and subsequent loss in different sub samples of one coral produces straight lines isochrons on a 234u 238u 230th 238u plot and predicts that the true age of the coral can be calculated by intersecting this isochron with the seawater evolution curve we used the strong correlation detected in the aqaba corals to calculate isochron ages the isochron age of the holocene coral 3116 167 156 yr is concordant with its calibrated 14c age 2963 92 103 yr the ages of the last interglacial corals are between 121 6 7 5 3 and 121 9 7 0 6 3 kyr for a higher terrace 7 10 m asl and 106 4 8 9 8 1 and 117 1 19 7 15 3 kyr for a lower terrace 4 5 m asl one last interglacial coral with an aragonite content of 85 could not be dated the elevation and ages of the fossil terraces are consistent with existing sea level reconstructions from the red sea

circumglobal teleconnection in the northern hemisphere summer analysis of the 56 yr ncep ncar reanalysis data reveals a recurrent circumglobal teleconnection cgt pattern in the summertime midlatitude circulation of the northern hemisphere this pattern represents the second leading empirical orthogonal function of interannual variability of the uppertropospheric circulation the cgt having a zonal wavenumber 5 structure is primarily positioned within a waveguide that is associated with the westerly jet stream the spatial phases of cgt tend to lock to preferred longitudes the geographically phase locked patterns bear close similarity during june august and september but the pattern in july shows shorter wavelengths in the north pacific north america sector the cgt is accompanied by significant rainfall and surface air temperature anomalies in the continental regions of western europe european russia india east asia and north america this implies that the cgt may be a source of climate variability and predictability in the above mentioned midlatitude regions the cgt has significant correlations with the indian summer monsoon ism and el nino southern oscillation enso however in normal ism years the cgt enso correlation disappears on the other hand in the absence of el nino or la nina the cgt ism correlation remains significant it is suggested that the ism acts as a conductor connecting the cgt and enso when the interaction between the ism and enso is active enso may influence northern china via the ism and the cgt additionally the variability of the cgt has no significant association with the arctic oscillation and the variability of the western north pacific summer monsoon the circulation of the wave train shows a barotropic structure everywhere except the cell located to the northwest of india where a baroclinic circulation structure dominates two possible scenarios are proposed the abnormal ism may excite an anomalous west central asian high and downstream rossby wave train extending to the north pacific and north america on the other hand a wave train that is excited in the jet exit region of the north atlantic may affect the westcentral asian high and thus the intensity of the ism it is hypothesized that the interaction between the global wave train and the ism heat source may be instrumental in maintaining the boreal summer cgt

the reliability of uranium series mollusc dates from the western mediterranean basin abstract fossil mollusc shells from western mediterranean raised beach deposits have been dated using u series techniques sub sampling has allowed intra shell isotopic variability to be assessed although most of the calculated ages appear plausible and some internal consistency exists closer scrutiny of the data reveals that the shells have behaved as geochemically open systems and all the ages therefore must be considered suspect some previously published u series mollusc data from the same region may also contain evidence of open system behaviour and are considered equally unreliable simple modelling suggests considerable variation in isotopic uptake behaviour both within and between shells

a diverse pleistocene marsupial trackway assemblage from the victorian volcanic plains australia abstract a diverse assemblage of late pleistocene marsupial trackways on a lake bed in south western victoria provides the first information relating to the gaits and morphology of several megafaunal species and represents the most speciose and best preserved megafaunal footprint site in australia the 60 110 ka volcaniclastic lacustrine sedimentary rocks preserve trackways of the diprotodontid diprotodon optatum a macropodid probably protemnodon sp and a large vombatid perhaps ramsayia magna or phascolomys medius and possible prints of the marsupial lion thylacoleo carnifex the footprints were imprinted within a short time period demonstrating the association of the taxa present rather than the time averaged accumulations usually observed in skeletal fossil deposits individual manus and pes prints are distinguishable in some trackways and in many cases some digital pad morphology is also present several parameters traditionally used to differentiate ichnotaxa including trackway gauge and the degree of print in turning relative to the midline are shown to be subject to significant intraspecific variation in marsupials sexual dimorphism in the trackway proportions of diprotodon and its potential for occurrence in all large bodied quadrupedal marsupials is identified here for the first time

the timing of sea level high stands during marine isotope stages 7 5 and 9 constraints from the uranium series dating of fossil corals from henderson island direct dating of fossil coral reefs using the u series chronometer provides an important independent test of the milankovitch orbital forcing theory of climate change however well dated fossil corals pre dating the last interglacial period 130 thousand years ago ka are scarce due to 1 a lack of sampling localities 2 insufficient analytical precision in u series dating methods and 3 diagenesis which acts to violate the assumption of closed system u series isotopic decay in fossil corals here we present 50 new high precision u series age determinations for fossil corals from henderson island an emergent coral atoll in the central south pacific u series age determinations associated with the marine isotope stage mis 9 interglacial and mis 7 5 interstadial periods are reported the fossil corals show relatively little open system u series behaviour in comparison to other localities with fossil coral reefs formed prior to the last glacial cycle however open system u series behaviour is still evident in most of the dated corals in particular percent level shifts in the 230th 238u act composition are observed leading to conventional u series ages that are significantly younger or older than the true sample age this open system u series behaviour is not accounted for by any of the open system u series models indicating that new models should be derived the new u series ages reported here support and extend earlier findings reported in stirling et al 2001 providing evidence of prolific coral reef development on henderson island at not vert similar320 ka most likely correlated with mis 9 3 and subsequent reef development at not vert similar307 ka during mis 9 1 while relative sea level was potentially not vert similar20 m lower than during mis 9 3 the u series ages for additional well preserved fossil corals are suggestive of minor reef development on henderson island during mis 7 5 245 230 ka at 240 3 0 8 and 234 7 1 3 ka all u series observations are consistent with the milankovitch theory of climate change in terms of the timing of onset and termination of the dated interglacial and interstadial periods the best preserved samples also suggest that the oceanic 234u 238u during mis 9 and mis 7 5 was within five permil of the modern open ocean composition

application of vertebrate trace fossils to palaeoenvironmental analysis abstract this is a review of the main uses of vertebrate trace fossils ichnofabrics and ichnofacies in the palaeoenvironmental analysis of sedimentary sequences the article accounts for the significant developments produced in the last three decades including the application of the ichnofacies concept to vertebrate trace fossils recognition of footprints in cross sectional view and their distinction from inorganic structures and burrow fills is first discussed the response of different substrates showing contrasting water content and imprinted by different animals or devices is compared in terms of the morphology of the resultant footprint trackways with sand crescents are typical of aeolian cross strata and are absent in associated flat lying to low angle deposits thick packages of highly bioturbated sandy dune and interdune sediments have been interpreted as reflecting periods of increased rainfall neoichnological observations in modern lake basins suggest that distinct zones can be recognized in the margins of fossil ponds and lakes including onshore shoreline and shallow subaqueous zones abundant flamingo like footprints and flamingo nest mounds are good indicators of alkaline and or saline lake waters hippopotamus trails are found closely associated with modern and fossil freshwater wetlands dinosaur and pterosaur swim traces from lacustrine and fluvial deposits can be used to estimate water depth turtle crocodile amphibian hippopotamus and fish swim traces allow one to infer a subaqueous substrate certain modern intertidal fish feeding traces are oriented with the predominant tidal current and can be used as palaeocurrent indicators the preferential orientation of tetrapod trackways in lacustrine and fluvial deposits is analyzed vertebrate trace fossils can help to infer discharge variability in fluvial channels the descriptions of vertebrate ichnofabrics are commonly limited to heavily bioturbated beds due to trampling by vertebrates and to a few examples of ichnofabrics with discrete trace fossils the nature and implications of the recognized vertebrate ichnofacies are still being debated and have a limited utility in palaeoenvironmental analysis the distinction of a potential vertebrate burrow ichnofacies in carbonate bearing palaeosols is proposed to represent well drained soils developed under arid or semiarid climate

the coral record of last interglacial sea levels and sea surface temperatures abstract the rise and fall of the last interglacial li sea levels and sea surface temperatures ssts are evaluated using u series dating combined with sr ca ratios in corals from both stable and tectonically uplifted sites along the stable coastal margin of western australia an extensive series of li coral reefs occur at heights of 2 3 m above present day sea level these corals have a very tight cluster of 234u 230th ages ranging from 129 1 to 119 1 ka as well as a narrow range of initial 234u values of 150 5 similar to modern seawater bahamas which is also a stable site has an essentially identical pattern of u series ages from 130 1 to 120 1 ka barbados and huon peninsula are tectonically active sites where the li terraces are found at elevations of 50 and 200 m respectively u series ages from corals exposed in the lower footwall of these uplifted reefs allow better constraints to be placed on the rate of sea level rise which initiated the li corals from the huon peninsula constrain sea level at 80 10 m at 131 2 ka and from barbados at 30 5 m at 129 1 ka combined with constraints from stable sites these observations require an exceedingly rapid rise in sea level of 30 50 m per 1000 years at 130 1 ka this indicates that large scale catastrophic melting of the once massive continental ice sheets occurred in phase with the rapidly increasing northern hemisphere nh summer insolation consistent with the orbital forcing being the main driver of glacial interglacial climate change there is also some evidence from huon peninsula although still not conclusive for a precursor oscillation in sea level during the penultimate deglaciation that may have been within 20 m of present day levels at 135 ka ssts for the li porites corals from the huon peninsula and western australia have mean annual temperatures and seasonal ranges that are remarkably similar to present day patterns the tropical site of huon peninsula has ssts of 29 1 c which is indistinguishable from the ssts given by modern corals at ningaloo reef in western australia similar mean annual 24 c and summer maximum ssts of 27 29 c are found in both li and modern corals the only significant difference is the 1 c cooler winter minimum ssts of 21 c for the li compared to present day minimums of 22 c li ssts from these southern hemisphere sh sites were thus very similar or at most only slightly cooler than today despite sea levels being up to 4 m higher this maybe indicative of asymmetric warming of the earth with the increased nh insolation during the li period being responsible for the extensive melting of the mainly nh based ice sheets and hence higher global sea levels the observation of relatively high sea levels in the li together with the rapid pulses of sea level rise indicates that the potential now exists for greenhouse warming to initiate increases in sea level of at least several metres on relatively short time scales 102 years

on the three dimensional propagation of stationary waves abstract a locally applicable nonzonally averaged conservation relation is derived for quasi geostrophic stationary waves on a zonal flow a generalization of the eliassen palm relation the flux which appears in this relation constitutes it is argued a useful diagnostic of the three dimensional propagation of stationary wave activity this is illustrated by application to a simple theoretical model of a forced rossby wave train and to a northern hemisphere winter climatology results of the latter procedure suggest that the major forcing of the stationary wave field derives from the orographic effects of the tibetan plateau and from nonorographic effects diabatic heating and or interaction with transient eddies in the western north atlantic and north pacific oceans and siberia no evidence is found in the data for wave trains of tropical origin forcing by the orographic effects of the rocky mountains seems to be of secondary importance

the atmospheric circulation and sea surface temperature in the north atlantic area in winter their interaction and relevance for iberian precipitation abstract the ocean surface atmosphere relationships in the north atlantic area in northern winter are empirically examined by canonical correlation analysis cca this analysis is performed from two different points of view first the connection between atmospheric circulation anomalies in terms of monthly mean sea level pressure slp and monthly standard deviation of slp slp and sea surface temperature sst anomalies of the atlantic ocean are directly examined second the air sea relationships are indirectly studied through their influence upon precipitation in an area likely to be influenced by the north atlantic the iberian peninsula the canonical correlation analysis yields two pairs of patterns that describe the coherent variations of the combined sst slp fields one pair of patterns for the sst slp fields and one pair of patterns for the slp slp fields all patterns are dominant in describing variance a lag cross correlation analysis of the time coefficients indicates that monthly mea

precise timing of the last interglacial period from mass spectrometric determination of thorium 230 in corals the development of mass spectrometric techniques for determination of 230 th abundance has made it possible to reduce analytical errors in 238 u 234 u 230 th dating of corals even with very small samples samples of 6 x 10 8 atoms of 230 th can be measured to an accuracy of 3 percent 2 and 3 x 10 10 atoms of 230 th can be measured to an accuracy of 0 2 percent the time range over which useful age data on corals can be obtained now ranges from about 50 to about 500 000 years for young corals this approach may be preferable to 14 c dating the precision with which the age of a coral can now be determined should make it possible to critically test the milankovitch hypothesis concerning pleistocene climate fluctuations analyses of a number of corals that grew during the last interglacial period yield ages of 122 000 to 130 000 years the ages coincide with or slightly postdate the summer solar insolation high at 65 n latitude which occurred 128 000 years ago this supports the idea that changes in pleistocene climate can be the result of variations in the distribution of solar insolation caused by changes in the geometry of the earth s orbit and rotation axis

crustal scale recycling in caldera complexes and rift zones along the yellowstone hotspot track o and hf isotopic evidence in diverse zircons from voluminous rhyolites of the picabo volcanic field idaho abstract rhyolites of the picabo volcanic field 10 4 6 6 ma in eastern idaho are preserved as thick ignimbrites and lavas along the margins of the snake river plain srp and within a deep 3 km borehole near the central axis of the yellowstone hotspot track in this study we present new o and hf isotope data and u pb geochronology for individual zircons o isotope data for major phenocrysts quartz plagioclase and pyroxene whole rock sr and nd isotope ratios and whole rock geochemistry for a suite of picabo rhyolites we synthesize our new datasets with published ar ar geochronology to establish the eruptive framework of the picabo volcanic field and interpret its petrogenetic history in the context of other well studied caldera complexes in the srp caldera complex evolution at picabo began with eruption of the 10 44 0 27 ma u pb tuff of arbon valley tav a chemically zoned and normal 18o 18o magma 7 9 unit with high zoned 87sr 86sri 0 71488 0 72520 and low e nd 0 18 and e hf 0 28 the tav and an associated post caldera lava flow possess the lowest end 0 23 indicating 40 60 derivation from the archean upper crust normal 18o rhyolites were followed by a series of lower 18o eruptions with more typical lower crustal sr nd hf isotope ratios and whole rock chemistry the voluminous 8 25 0 26 ma west pocatello rhyolite has the lowest 18o value 18omelt 3 3 and we correlate it to a 1 000 m thick intracaldera tuff present in the inel 1 borehole with published zircon ages 8 04 8 35 ma and similarly low 18o zircon values the significant 4 5 decrease in magmatic 18o values in picabo rhyolites is accompanied by an increase in zircon 18o heterogeneity from 1 variation in the tav to 5 variation in the late stage low 18o rhyolites a trend similar to what is characteristic of heise and yellowstone and which indicates remelting of variably hydrothermally altered tuffs followed by rapid batch assembly prior to eruption however due to the greater abundance of low 18o rhyolites at picabo the eruptive framework may reflect an intertwined history of caldera collapse and coeval basin and range rifting and hydrothermal alteration we speculate that the source rocks with pre existing low 18o alteration may be related to 1 deeply buried and unexposed older deposits of picabo age or twin falls age low 18o volcanics and or 2 regionally abundant late eocene challis volcanics which were hydrothermally altered near the surface prior to or during peak picabo magmatism basin and range extension specifically the formation of metamorphic core complexes exposed in the region could have facilitated the generation of low 18o magmas by exhuming heated rocks and creating the large water rock ratios necessary for shallow hydrothermal alteration of tectonically rift zones and volcanically calderas buried volcanic rocks these interpretations highlight the major processes by which supereruptive volumes of magma are generated in the srp mechanisms applicable to producing rhyolites worldwide that are facilitated by plume driven volcanism and extensional tectonics

the atmospheric circulation over the north atlantic as induced by the sst field spectral analyses of the sea surface temperature sst in the simple ocean data analysis soda reanalysis for the past half century identify prominent and statistically significant interannual oscillations in two regions along the gulf stream front over the north atlantic a model of the atmospheric marine boundary layer coupled to a baroclinic quasigeostrophic model of the free atmosphere is then forced with thessthistoryfromthesodareanalysis twoextremestatesarefoundintheatmosphericsimulations 1 an eastward extensionofthe westerly jetassociatedwith thefront which occurs mainly during boreal winter and 2 a quiescent state of very weak flow found predominantly in the summer this vacillation of the oceanicfront induced jet in the model is found to exhibit periodicities similar to those identified in the observed gulf stream sstfront itself in addition a close correspondence is found between interannualspectralpeaksin the observed north atlantic oscillation nao index and the soda induced oscillations in the atmospheric model in particular significant oscillatory modes with periods of 8 5 4 2 and 2 8 yr are found in both observedandsimulatedindicesandareshowntobehighlysynchronizedandofsimilarenergyinbothtimeseries theseoscillatorymodesinthesimulationsareshowntobesuppressedwheneither i thegulfstream frontor ii its interannual oscillations are omitted from the sst field moreover these modes also disappear when iii the sst front is spatially smoothed thus confirming that they are indeed induced by the oceanic front

on the significance of the interannual relationship between the asian pacific oscillation and the north atlantic oscillation using monthly data from the european centre for medium range weather forecasts 40 year re analysis this study investigated the interannual relationship between the asian pacific oscillation apo and the north atlantic oscillation nao for the period of may to august the nao is represented by the leading empirical orthogonal function of sea level pressure anomalies over the atlantic sector the difference of upper tropospheric eddy air temperature t between asia and the north pacific is used to measure the apo results clearly show that the apo and the nao correlated very well on the interannual time scale with the positive negative phase of the apo corresponding to the strong weak nao such a relationship is well supported by the atmospheric dynamic process when the apo is in the positive phase characterized by the positive t anomaly over asia and the negative t anomaly over the north pacific in the upper troposphere the upper tropospheric geopotential height increases over asia and decreases over the north pacific accordingly anticyclonic circulation and cyclonic circulation anomalies are introduced respectively over asia and south of the north pacific and a zonal teleconnection wave train is excited from asia to the north atlantic as a consequence an anomalous anticyclonic circulation prevails in the low level of the north atlantic and an anomalous cyclonic circulation appears to its north which corresponds to the atmospheric pattern of strong nao further study proposes that the quasi stationary wave pattern emanating from the western north pacific region may serve as a bridge for this linkage

north america s largest dinosaur trackway site implications for morrison formation paleoecology little known exposures of the upper jurassic morrison formation from the purgatoire valley of southeastern colorado have yielded the world s largest continuously mapped assemblage of dinosaur trackways body fossils include plant invertebrate and vertebrate remains indicative of predominantly fresh water conditions the tracks occur in a lacustrine sequence characterized by 1 shallow water shales 2 micritic shoreface limestones with ooids intraclasts ripple marks mud cracks and 3 minor quartzose sandstone with salt crystal casts analysis of these sedimentary facies suggests that in southeastern colorado lakes were larger and longer lived than in other morrison paleoenvironments trackway orientations and footprint depth contours pinpoint the location of the paleoshoreline at successive levels in the section detailed mapping of 1 300 footprints in bed 2 has revealed more than 100 trackways which testify to the activity of both quadrupedal and bipedal dinosaurs the respective ratio based on trackway counts is 40 60 the quadrupedal tracks are attributed to sauropods and represent the first ever discovered in north america they also exhibit the first known manus claw impressions and are in need of formal description more than 90 of the bipedal tridactyl prints lack claw impressions and are tentatively therefore referred to the ornithopoda cf gypsichnites possibly a camptosaurus the small proportion with distinct claw impressions may represent allosaurus resulting estimates of species diversity 5 and predator prey ratio 1 30 are in general agreement with the estimates of other authors based on skeletal remains and they suggest that the purgatoire river tracks may accurately reflect the composition of the dinosaur fauna distinctive groupings of parallel non overlapping trackways suggest gregarious behavior among sauropods and tridactylous forms

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

introduction to u series geochemistry during the last century the earth sciences underwent two major revolutions in understanding the first was the recognition of the great antiquity of the earth and the second was the development of plate tectonic theory these leaps in knowledge moved geology from its largely descriptive origins and established the modern quantitative earth sciences for any science and particularly for the earth sciences time scales are of central importance until recently however the study of time scales in the earth sciences was largely restricted to the unraveling of the ancient history of our planet for several decades earth scientists have used a variety of isotope chronometers to unravel the long term evolution of the planet a fuller understanding of the physical and chemical processes driving this evolution often remained elusive because such processes occur on time scales 1 105 years which are simply not resolvable by most conventional chronometers the u series isotopes however do provide tools with sufficient time resolution to study these earth processes during the last decade the earth sciences have become increasingly focused on fundamental processes and u series geochemistry has witnessed a renaissance with widespread application in disciplines as diverse as modern oceanography and igneous petrology the uranium and thorium decay series contain radioactive isotopes of many elements in particular u th pa ra and rn the varied geochemical properties of these elements cause nuclides within the chain to be fractionated in different geological environments while the varied half lives of the nuclides allows investigation of processes occurring on time scales from days to 105 years u series measurements have therefore revolutionized the earth sciences by offering some of the only quantitative constraints on time scales applicable to the physical processes that take place on the earth the application of u series geochemistry to the earth sciences was thoroughly summarized in 1982

impact of the atlantic multidecadal oscillation on the asian summer monsoon 1 the impact of the atlantic multidecadal oscillation amo on the asian summer monsoon is investigated using a coupled atmosphere ocean global general circulation model by imposing the amo associated sea surface temperature anomalies in the atlantic as boundary forcing and allowing atmosphere ocean interactions outside the atlantic the positive amo phase characterized by anomalous warm north atlantic and cold south atlantic leads to strong southeast and east asian summer monsoons and late withdrawal of the indian summer monsoon these changes of monsoons are mainly through coupled atmosphere ocean feedbacks in the western pacific and indian oceans and tropospheric temperature changes over eurasia in response to the imposed forcing in the atlantic the results are in agreement with the observed climate changes in china corresponded to the amo phases they suggest a non local mechanism for the asian summer monsoon variability and provide an alternative view to understanding its interdecadal variation during the twentieth century citation lu r b dong and h ding 2006 impact of the atlantic multidecadal oscillation on the asian summer monsoon geophys res lett 33 l24701 doi 10 1029 2006gl027655

short paper fossil vertebrate tracks and indenter mechanics a reconnaissance study is outlined showing how an improved understanding of the formation and character of fossil vertebrate tracks in soft sediments is provided by the application of the mechanical engineer s indenter theory supported by complementary scaled laboratory experiments only the footprint at the bottom of the shaft cut by the animal9s limbs in general offers the best preservation of the shape of the underside of the foot the character of the foot is less well preserved in the deformed bedding beneath the footprint and among laminae deposited in the shaft after the passage of the animal this understanding will help to reduce errors in the use of tracks in taxonomic biostratigraphic palaeoecological behavioural and environmental studies when a limbed vertebrate traverses yielding sediment the limbs deform the substrate into tracks which vary with the nature size and gait of the animal the forcefulness of its limb movements and the sediment properties most previous geological work on tracks and trackways has emphasized their taxonomic biostratigraphical palaeocological and behavioural significance lockley 1986 leonardi 1987 but without an adequate understanding of their environmental implications lockley 1986 and in particular their genesis and preservation as trace fossils the response of an elastic plastic material to an indenter or punch both in terms of theory calladine 1969 hill 1971 johnson et al 1982 and in the light of qualitative laboratory experiments provides a general mechanical model for track formation and a basis for the assessment of track preservation in sediments the indenter represents the animal9s

extremely large variations of atmospheric 14c concentration during the last glacial period a long record of atmospheric 14c concentration from 45 to 11 thousand years ago ka was obtained from a stalagmite with thermal ionization mass spectrometric 230th and accelerator mass spectrometric 14c measurements this record reveals highly elevated 14c between 45 and 33 ka portions of which may correlate with peaks in cosmogenic 36cl and10be isotopes observed in polar ice cores superimposed on this broad peak of 14c are several rapid excursions the largest of which occurs between 44 3 and 43 3 ka between 26 and 11 ka atmospheric 14c decreased from 700 to 100 per mil modulated by numerous minor excursions carbon cycle models suggest that the major features of this record cannot be produced with solar or terrestrial magnetic field modulation alone but also require substantial fluctuations in the carbon cycle

introduction to the special issue commemorating the 30th anniversary of the royal tyrrell museum of palaeontology with a summary of the museum s early history and its research contributions located just west of drumheller in southern alberta canada the royal tyrrell museum of palaeontology rtmp is nestled among outcrops of the upper cretaceous horseshoe canyon formation exposed along the red deer river valley fig 1 since it officially opened on 25 september 19851 the museum has become one of alberta s must see tourist attractions a significant contributor to the local economy and earned an international reputation for the quality of its palaeontological collections and the research conducted by its scientists the rtmp is unique within canada in being the only government supported museum dedicated to palaeontology and it is one of the few such institutions in the world fig 1 the royal tyrrell museum of palaeontology a front of museum and main entrance circa 2010 looking westwards and with horizontal beds of the upper cretaceous horseshoe canyon formation exposed in the walls of the red deer river valley in the distance b aerial photograph oblique angle and looking to the north northeast the museum sits on top of the number 7 coal seam sensu gibson 1977 and at the base of the horsethief member of the horseshoe canyon formation d a eberth pers comm 2015 that stratigraphic position correlates with an age of about 71 5 ma i e late campanian and lies within the upper part of the edmontosaurus regalis pachyrhinosaurus canadensis dinosaur assemblage zone see eberth et al 2013 fig 6 c the iconic running theropod logo that until recently graced the exterior of the museum below a life sized tyrannosaurid sculpture by brian cooley one of many such sculptures by cooley that have been featured at the museum since its opening in 1985 and with the education wing opened in 2003 as the atco tyrrell learning centre in the background d the cretaceous alberta life sized diorama opened in 2007 an example of a rtmp exhibit that relies heavily on discoveries and interpretations by museum researchers in this case work done in the albertosaurus bonebed and at other localities throughout the horseshoe canyon formation all photographs courtesy of the royal tyrrell museum of palaeontology this special issue of the canadian journal of earth sciences presents a collection of papers commemorating the rtmp s 30th or pearl anniversary our rationale for doing a 30th anniversary volume was two fold first it is an opportunity to showcase the breadth of research conducted by current and former museum scientists as well as by some colleagues having a history of collaboration with the rtmp the 13 invited papers included in this volume are a mix of review and original research papers all thematically focused on the geology and palaeontology of alberta to varying degrees each contribution is the result of work supported by the rtmp and relies on specimens housed in the museum s collections second the 30th anniversary is an opportunity to reflect on the rtmp s history and its research program as is typical for most institutions the rtmp has done little to formally document its own history this year likely will be the last major milestone for which the original generation of museum staff are still working and available to share their recollections about the museum fieldwork and research already deaths and departures have winnowed away part of the original

dating open systems by the 238 u 234 u 230 th method application to quaternary reef terraces abstract the sedimentation conditions and diagenetic processes of biogenic and inorganic carbonates are such that the assumptions of a closed system evolution and the absence of initial th invoked in classical 238 u 234 u 230 th dating methods are very often not fulfilled for such material this problem is of interest for all studies requiring accurate dating of corals or aragonite rich sediments as in palaeoclimatology or neotectonics extending the approach of henderson and slowey nature 404 2000 61 66 we propose a consistent model that takes into account possible initial 230 th excess and where continuous selective redistribution gain or loss of 234 u 234 th and 230 th is controlled by recoil processes this model applied to quaternary marine terraces in barbados marie galante lesser antilles arc and pacific islands is able to explain the large scatter in isotopic compositions observed in the series of cogenetic corals or sediments we show that recoil processes generally tend to increase the 234 u 238 u and 230 th 234 u ratios with time leading to an overestimation of the apparent ages calculated using classical methods on the basis of simple assumptions identical marine initial 234 u 238 u 0 and 230 th 232 th 0 ratios we propose a method for calculating a best estimate of the age of cogenetic series our model offers an alternative way to date old reef terraces where corals are almost systematically altered and where classical dating methods do not apply it may also explain the apparent variations of the 234 u 238 u seawater initial ratio estimated from corals formed in the last 300 ka and the apparent uncoupling between sea level highstands and high latitude northern hemisphere summer insolation our set of equations can be applied to all weathering processes where the mobility of u series isotopes is controlled by recoil

coupled ocean atmosphere response to indian ocean warmth 1 the coupled ocean atmosphere response to indian ocean warmth is studied it is shown with atmospheric models that indian ocean warmth forces a positive polarity phase of the north atlantic oscillation nao confirming results of previous studies coupled model experiments show that this nao response forces a local air sea feedback over the north atlantic ocean which intensifies the nao response this enhancement is realized through a positive feedback between the nao atmospheric circulation anomaly and a tripolar north atlantic sst pattern consistent with other studies on north atlantic air sea interactions it is concluded that the north atlantic and european climate response to indian ocean warming may be considerably greater than hitherto judged from the analyses of atmospheric model experiments alone

dating fluvial terraces by 230th u on pedogenic carbonate wind river basin wyoming abstract reliable and precise ages of quaternary pedogenic carbonate can be obtained with 230th u dating by thermal ionization mass spectrometry applied to carefully selected milligram size samples datable carbonate can form within a few thousand years of surface stabilization allowing ages of quaternary deposits and surfaces to be closely estimated pedogenic carbonate clast rinds from gravels of glacio fluvial terraces in the wind river basin have median concentrations of 14 ppm u and 0 07 ppm 232th with median 230th 232th 270 making them well suited for 230th u dating horizons as thin as 0 5 mm were sampled from polished slabs to reduce averaging of long 105 yr and sometimes visibly discontinuous depositional histories dense translucent samples with finite 230th u ages preserve within rind stratigraphic order in all cases ages for terraces wr4 167 000 6 400 yr and wr2 55 000 8600 yr indicate a mean incision rate of 0 26 0 05 m per thousand years for the wind river over the past glacial cycle slower than inferred from cosmogenic nuclide dating terrace wr3 which formed penecontemporaneously with the final maximum glacial advance of the penultimate rocky mountain bull lake glaciation has an age of 150 000 8300 yr indicating that it is broadly synchronous with the penultimate global ice volume maximum

the timing of high sea levels over the past 200 000 years the 230 th ages and 234 u 238 u ratios were determined for barbados corals that grew during periods of high sea level within the last 200 000 years the similarity of the initial 234 u 238 u ratios of some of the corals to the modern marine value suggests that these samples are pristine and that the marine 234 u 238 u ratio 83 000 and 200 000 years ago was within 2 per mil of the modern value the accuracies of the 230 th ages are evaluated on the basis of the 234 u 238 u values and a model of the behavior of uranium and thorium isotopes during diagenesis for the last three interglacial and two intervening interstadial periods sea level peaked at or after peaks in summer insolation in the northern hemisphere this overall pattern supports the idea that glacial interglacial cycles are caused by changes in earth9s orbital geometry the sea level drop at the end of the penultimate interglacial the last interglacial and a subsequent interstadial period lagged behind the decrease in insolation by 5 000 to 10 000 years

in situ u series dating by laser ablation multi collector icpms new prospects for quaternary geochronology the capabilities and potential applications of in situ dating of quaternary materials using laser ablation mc icpms are explored 234 u 238 u and 230 th 234 u can be measured with precision sufficient for dating at a spatial resolution of 100mm or better in samples that contain as a little as 1 ppm uranium moreover u and th concentrations and u series isotope ratios can be continuously profiled to determine changes in age that occur with sample growth e g in speleothems these capabilities additionally permit the dating of bones teeth and possibly molluscs which are subject to post mortem open system behaviour of useries isotopes and can be employed to elucidate processes of u series migration during weathering and diagenesis a drawback of laser ablation mc icpms is that it cannot in general provide u series age estimates with the high precision and accuracy of conventional tims or solution mc icpms methods however sample preparation is straightforward the amount of sample consumed negligible and it can be used to rapidly characterise or screen and select samples from which more precise and accurate dates can be obtained using conventional methods given further instrumental developments and the establishment of suitable matrix matched standards for carbonates and other materials we foresee that laser ablation mc icpms will play an increasingly important role in quaternary dating research r 2005 published by elsevier ltd

linearity of the atmospheric response to north atlantic sst and sea ice anomalies abstract the observations of the ocean atmosphere sea ice have recently revealed that the oceanic surfaces can have a subtle but significant impact on the atmospheric long term fluctuations low frequency variations and long term trends of the north atlantic atmospheric circulation have been partly related to particular sst and sea ice features in this work the influence of typical tripolar sst and dipolar sea ice anomalies in the north atlantic arctic on the atmosphere is investigated a large ensemble of agcm simulations forced by three different anomalous boundary conditions sst sea ice and sst sea ice are used the linearity of the simulated response in the winter season is particularly assessed in these experiments while the winter low level temperature response is mainly symmetric about the sign of the forcing the asymmetric part of the geopotential response is substantial the sea ice forcing maintains a baroclinic response with a strong temperature anomaly in the vicinity of the forcing

possible effect of the tibetan plateau on the upstream climate over west asia north africa south europe and the north atlantic we conduct several experiments using a fully coupled climate model to understand the role of tibetan plateau tp surface heating in the climate variations over west asia south europe north africa and the north atlantic during summer emphasis has been placed on the physical processes and responsible mechanisms that involve the shift of the hadley cell and the important features of rotational and divergent response of the atmosphere to the tp heating the relative importance of the tp to the asian continent is also analyzed a heating of the tp surface leads to local increases in tropospheric temperature and the thickness of the air column due to the so called air pumping effect in the upper troposphere the south asian high intensifies and extends westward to the west of tp especially in west asia south europe north africa and the north atlantic distinguished rossby wave responses to the tp heating occur with anomalous high pressure and uniform warming in the entire troposphere correspondingly descending motions intensify and precipitation decreases however the tropical sahel rainfall increases because of a northward shift of the atlantic intertropical convergence zone and the anomalous westerlies due to the weakening of the southeastern portion of the atlantic subtropical high these effects of the tp heating explain a remarkable portion of the effects by the asian continent heating in addition the impacts of different magnitudes of tp surface heating are also discussed

simulated weathering of dinosaur tracks and the implications for their characterization digital models of the tracks of bipedal theropod and ornithopod dinosaurs and the quadrupedal tracks of a sauropod were computationally eroded to investigate the effects of erosion on the shapes sizes and diagnostic details of fossil tracks narrow and or angular details such as claw marks interdigital ridges and internal ridges are removed early in erosion creating the potential for misidentification of eroded theropod tracks as those of ornithopods however with the erosion models presented here all tracks retain their basic shapes as indicated by the relative constancy of their interdigital angles and by the relative constancy of their footlength footwidth ratios surface lengths of tracks did not increase significantly with erosion so that dinosaurian hip height and speed estimates derived from trackways would not be greatly in error if based on eroded surface tracks synthetic undertracks from the surface tracks were also produced using information from published physical models of trac

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

taphonomic controls on animal tracks at saline alkaline lake bogoria kenya rift valley impact of salt efflorescence and clay mineralogy abstract the morphologies of subaerial vertebrate tracks and invertebrate traces in surficial sediments can be used in paleoenvironmental reconstructions by providing details about the initial substrate conditions e g water content and any changes experienced during trace preservation a qualitative field study was undertaken to identify the factors affecting track taphonomy in saline lake margin environments supported by experiments to isolate selected factors that modify track morphology and substrate characteristics flamingo tracks ubiquitous around saline alkaline lake bogoria in the kenya rift were the focus of field study although other vertebrate tracks and surficial invertebrate trails and tunnels were also considered a complex and interacting set of environmental factors were identified such as the effect of lake level fluctuations on substrate grain size and capillary evaporation several factors affect the early taphonomic modification destruction stabilization and or cementation of tracks and their associated substrates the laboratory experiments tested the effects of pore water salinity clay mineralogy e g swelling or non swelling clays drying method e g solar radiation or wind and wetting and drying cycles on tracks these data were supported by statistical analyses of impression depth and planimetric area the results show that track morphology in smectitic substrates is altered rapidly by wetting and drying particularly if the substrates contain saline pore waters but morphology is less affected in non swelling clays the degree of morphologic alteration and or resistance to wetting and drying varies with the rate of substrate drying and the type of the resulting salt efflorescence e g interstitial vs surficial crust these short term process related taphonomic effects help to explain the morphologic variants of tracks in lake marginal settings and provide insights into the preserved distribution patterns of subaerial ichnofossil assemblages

stalagmite from the austrian alps reveals dansgaard oeschger events during isotope stage 3 implications for the absolute chronology of greenland ice cores a mass spectrometric uranium series dated stalagmite from the central alps of austria provides unprecedented new insights into high altitude climate change during the peak of isotope stage 3 the stalagmite formed continuously between 57 and 46 kyr before present a series of hendy tests demonstrates that the outer parts of the sample show a progressive increase of both stable c and o isotope values no such covariant increase was detected within the axial zone this in conjunction with other observations suggests that the continuous stable oxygen isotope profile obtained from the axial zone of the stalagmite largely reflects the unaltered isotopic composition of the cave drip water the n 18 o record shows events of high n 18 o values that correlate remarkably with interstadials 15 a and b 14 and 12 identified in the greenland ice cores interstadial 15b started rapidly at 55 6 kyr and lasted v300 yr only interstadial 15a peaked 54 9 kyr ago and was even of shorter duration v100 yr and interstadial 14 commenced 54 2 kyr ago and lasted v3000 yr this stalagmite thus represents one of the first terrestrial archives outside the high latitudes which record precisely dated dansgaard oeschger d o events during isotope stage 3 provided that rapid d o warmings occurred synchronously in greenland and the european alps the new data provide an independent tool to improve the grip and gisp2 chronologies 2002 elsevier science b v all rights reserved

three dimensional preservation of foot movements in triassic theropod dinosaurs dinosaur footprints have been used extensively as biostratigraphic markers environmental indicators measures of faunal diversity and evidence of group behaviour1 2 3 4 trackways have also been used to estimate locomotor posture gait and speed6 7 8 9 10 11 but most prints being shallow impressions of a foot s plantar surface provide little evidence of the details of limb excursion here we describe late triassic trackways from east greenland made by theropods walking on substrates of different consistency and sinking to variable depths that preserve three dimensional records of foot movement triassic theropod prints share many features with those of ground dwelling birds but also demonstrate significant functional differences in position of the hallux digit i foot posture and hindlimb excursion

role of the north pacific sea surface temperature in the east asian winter monsoon decadal variability in this study a possible mechanism for the decadal variability in the east asian winter monsoon eawm is proposed specifically the north pacific sea surface temperature sst may play an important role an analysis of the observations shows that the north pacific sst has a remarkable decadal pattern whose phase shifted around the mid 1980s this north pacific sst decadal pattern can weaken the east asian trough and enhance the north pacific oscillation through changing air sea interactions over the north pacific the weak east asian trough enhances the zonal circulation and weakens the meridional circulation over east asia consequently leading to a weaker southward cold surge and east asia warming around the mid 1980s the numerical experiment further confirms the pronounced physical processes in addition over the longer period of 1871 2012 the indices of the eawm and north pacific sst decadal pattern are also highly consistent on the decadal timescale which further confirms the impact of the north pacific sst decadal pattern on the eawm decadal variability

spatial patterns of atmosphere ocean interaction in the northern winter abstract the variability of monthly mean sea surface temperature sst anomalies over the extratropical north atlantic and pacific and its relation to atmospheric circulation anomalies over the northern hemisphere during wintertime is investigated by applying eigenvector analysis to a 39 year dataset and correlating the time series of the resulting expansion coefficients with the hemispheric 500 mb height and sea level pressure fields in agreement with previous studies the simultaneous correlation between the tone series of the expansion coefficient of the first empirical orthogonal function eof 1 of north pacific sea surface temperature sst and the hemispheric 500 mb height field resembles the pacific north american pattern and the corresponding pattern for atlantic sst resembles the north atlantic oscillation in the vicinity of the conters of action of thew patterns the sst fluctuations associated with these modes explain on the order of half the variance of 500 mb height and slightly less of

luminescence dating in less than ideal conditions case studies from klasies river main site and duinefontein south africa abstract luminescence dating results are reported for two south african archaeological sites where changes in the dose rate through time are apparent a subtraction procedure involving analysis of both quartz and potassium feldspar extracts is applied to detect and correct for these changes at the middle stone age site of klasies river the dose rate changes inferred from geologic evidence for shell dissolution turn out not to be significant having occurred rapidly after deposition the dates here range from 50 115 ka in broad agreement with other evidence the important howiesons poort component here appears to date somewhat later about 55 60 ka than at several other sites in south africa at the acheulian site of duinefontein the dose rate changes also thought to be caused by shell dissolution are on the other hand very significant the subtraction ages here 125 300 ka agree with independent chronological assessments

geochemical gradients within modern and fossil shells of concholepas concholepas from northern chile an insight into u th systematics and diagenetic authigenic isotopic imprints in mollusk shells abstract seriate geochemical measurements through shells of one modern one holocene and two sangamonian concholepas concholepas from marine terraces of northern chile were performed to document diagenetic vs authigenic geochemical signatures and to better interpret u series ages on such material subsamples were recovered by drilling from the outer calcitic layer to the inner aragonitic layer of each of the studied shells unfortunately this sampling procedure induces artifacts notably the convertion of up to 20 of calcite into aragonite and of up to 6 of aragonite into calcite as well as in the epimerization of a few percent of isoleucine into d alloisoleucine l isoleucine negligible sampling artifacts were noticed for stable isotope and total amino acid contents diagenetic effects on the geochemical properties of the shells are particularly pronounced in the inner aragonitic layer and more discrete in the outer calcitic layer the time dependent decay of the organic matrix of the shell is illustrated by a one order of magnitude lower total amino acid content in the sangamonian specimens by comparison with the modern shell conversely the sangamonian shells u contents increase by a similar factor and 13c 18o enrichments as high as 2 to 3 seem also to occur through the same time interval possibly due to partial replacement of aragonite by gypsum the decay of the organic matrix of the aragonitic layer of the shell is thought to play a major role with respect to u uptake processes and stable isotope shifts nevertheless asymptotic 230th ages 100 ka in the inner u rich layers of the sangamonian shells and 234u 238u ratios compatible with a marine origin for u suggest u uptake within a short diagenetic interval when marine waters were still bathing the embedding sediment thus u series ages on fossil mollusks from such a hyper arid environment should not differ much from the age of the corresponding marine unit deposition however the diagenetic enrichments in stable isotopes raise concerns about their use for paleoenvironmental reconstructions under such climate conditions

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr