formal definition and dating of the gssp global stratotype section and point for the base of the holocene using the greenland ngrip ice core and selected auxiliary records the greenland ice core from northgrip ngrip contains a proxy climate record across the pleistocene holocene boundary of unprecedented clarity and resolution analysis of an array of physical and chemical parameters within the ice enables the base of the holocene as reflected in the first signs of climatic warming at the end of the younger dryas greenland stadial 1 cold phase to be located with a high degree of precision this climatic event is most clearly reflected in an abrupt shift in deuterium excess values accompanied by more gradual changes in d 18 o dust concentration a range of chemical species and annual layer thickness a timescale based on multi parameter annual layer counting provides an age of 11 700 calendar yr b2 k before ad 2000 for the base of the holocene with a maximum counting error of 99 yr a proposal that an archived core from this unique sequence should constitute the global stratotype section and point gssp for the base of the holocene series epoch quaternary system period has been ratified by the international union of geological sciences five auxiliary stratotypes for the pleistocene holocene boundary have also been recognised copyright 2008 john wiley sons ltd

stable carbon and oxygen isotopes in sphagnum fuscum peat from subarctic canada implications for palaeoclimate studies stable carbon and oxygen isotope ratios in single plant components in sphagnum peat have a good potential to reveal environmental changes in peat archives two peat profiles covering the past 600

devensian lateglacial environmental changes in britain a multi proxy environmental record from llanilid south wales uk abstract a multi proxy environmental record for the devensian weichselian lateglacial and early holocene periods which includes pollen plant macrofossil coleopteran geochemical and stable isotope data is described from a site at llanilid south wales uk the geochronology of the sequence is derived from two age depth models which show a broad measure of agreement over much of the profile this data set provides the basis for a detailed reconstruction of changing environmental conditions in western britain during the transition from the last cold stage to the present holocene interglacial ca 15 000 10 000 cal yr bp two marked cooling episodes are recorded during the course of the lateglacial interstadial greenland interstadial 1 with mean july temperatures falling by more than 5 c from a maximum of around 20 c during the early interstadial and by a further 4 5 c around 13 100 cal yr bp the initial drop in temperature led to a reduction in juniperus scrub while the second and more abrupt temperature decline resulted in a significant contraction in areas of betula woodland a relatively slight and short lived warming during the later interstadial enabled tree birch to expand once again mean july temperatures of 10 11 c characterised the loch lomond younger dryas stadial greenland stadial 1 between ca 12 600 and 11 400 cal yr bp during which time a scrub tundra with betula salix and a range of open habitat taxa became established locally the onset of the holocene interglacial at ca 11 400 cal yr bp is marked by an abrupt temperature rise of the order of 9 c and by the rapid expansion of betula woodland the llanilid palaeoclimate record is similar to that from the gransmoor site in northeast england and also to the climatic sequence inferred from the grip ice core particularly during the later part of the lateglacial interstadial ca 14 000 12 600 cal yr bp during the loch lomond younger dryas stadial and in the early holocene the llanilid chronology is less secure during the early part of the lateglacial interstadial pre 14 000 cal yr bp but it is possible that warming may have begun earlier in this part of western britain than in greenland

stable carbon isotope variations in northwest europe during the last glacial interglacial transition stable carbon isotope data that span part of the last glacial interglacial transition ca 14 9 ka 14c bp ca 15 11 ka cal bp and which derive from organ specific plant macrofossils recovered from two lake sediment profiles in the uk and one in norway are compared the recorded temporal variations show similar trends which over a millennial time scale appear to parallel the main drift in 18o as determined for the grip ice core it is postulated that some smaller scale variations in the 13c profiles may reflect the shorter term oscillations in 18o values evident in the grip record although this is less certain overall however the results suggest that stable carbon isotope measurements based on organ specific terrestrial plant macrofossils may provide i a means for establishing correlations between terrestrial successions and ii additional paleoenvironmental information as the apparent shadowing of the grip record indicates a common forcing mechanism for both greenland 18o and northwest european 13c variations from the evidence available we suggest that the recorded 13c variations reflect fluctuations in air temperature and or changes in water vapour pressure in the atmosphere 1997 john wiley sons ltd

preservation of primary stable isotope signatures of peat forming plants during early decomposition observation along an altitudinal transect abstract the preservation of the primary stable isotope compositions of peat forming plants in peat was tested along a short

improved age modelling approaches as exemplified by the revised chronology for the central european varved lake soppensee abstract one of the key factors in understanding past climate change is the development of robust age models that have sufficient chronological precision for comparing different palaeoclimate archives while retaining accuracy recent developments in bayesian age modelling are applied here to the swiss varve lake soppensee we develop revised age models for this sequence using the available stratigraphic information to constrain the calibrated radiocarbon ages we begin by using stratigraphical order as the only constraint and then sequentially increase the information incorporated into the model using relative varve age sample depth and varying depositional models within this bayesian framework we develop internally robust models that significantly improve the dating precision and are applicable to both varved and non varved sequences we then compare the model output to wider chronological information such as the age of the laacher see tephra in order to test the model accuracy the results of this exercise suggest that these methods can be used to build very reliable improved age models in a variety of records

implications for the dating of wisconsinan weichselian late glacial events of systematic radiocarbon age differences between terrestrial plant macrofossils from a site in sw ireland abstract ams radiocarbon dates were obtained from salix herbacea leaves carex seeds and bulk organic detritus from a lake sediment profile of wisconsinan weichselian lateglacial age in sw ireland there is a systematic age difference between the dated series from the two types of macrofossils with ages obtained from salix herbacea leaves being 900 to 1500 14 c years younger than those obtained from carex seeds the latter tend to be more in accord with dates from the total organic detritus in the lake sediment although the bulk organic fraction invariably registered the older ages intact survival of the fragile salix leaves indicates that they are unlikely to have been physically transferred within the sediment matrix and or otherwise reworked from the surrounding catchment hence these macrofossils are the more likely to be contemporaneous with the time of deposition however there is no significant correlation between measured 14 c age and depth in the salix values which scatter over a range of 700 14 c years in contrast the age depth relationship for carex shows a significant reversal possibly reflecting the redeposition of these macrofossils and therefore giving radiocarbon ages that are anomalously old the data have important implications for the dating of lake sediment sequences by ams radiocarbon measurement of terrestrial plant macrofossils

distal volcanic ash layers in the lateglacial interstadial gi 1 problems of stratigraphic discrimination abstract a new icelandic ash layer has been detected in mid interstadial sediments in a number of scottish lateglacial sequences and has been named the penifiler tephra it is rhyolitic in composition and possesses a chemistry which is similar to the borrobol tephra of early lateglacial interstadial age which also occurs in a number of these same sequences where the borrobol tephra has been identified in these sequences it consistently exhibits a diffuse distribution accompanied in some cases by stratigraphic bimodality a number of sedimentological and taphonomic factors are considered in order to account for this distribution one possibility is that these distributions are produced by taphonomic factors another possibility is that the borrobol tephra may not be the product of a single icelandic eruption but of two events closely spaced in time in at least two of the sequences investigated in this study basaltic shards were found in association with the penifiler and borrobol tephras suggesting either a basaltic phase associated with these eruptions or coincident eruptions from a separate basaltic volcanic centre the discovery of the new penifiler tephra makes a contribution to the regional tephrostratigraphic framework and provides an additional isochron for assessing the synchroneity of palaeoenvironmental changes during the interstadial the true stratigraphic nature and age of the borrobol tephra however remains unresolved and therefore its use as an isochron is more problematic the possible occurrence of basaltic populations may strengthen correlations with basaltic tephras recently detected in the ngrip ice core

multi component stable isotope records from late weichselian and early holocene lake sediments at imiolki poland palaeoclimatic and methodological implications late weichselian and early holocene climatic and environmental changes are inferred from stable carbon and oxygen isotope records obtained on bulk and biogenic carbonates from the sediment sequence of lake lednica western poland along with sediment and pollen stratigraphic data a wide range of carbonate components occurring in the sediments was analysed for delta c 13 and delta o 18 including shells of several gastropod species and the bivalve genus pisidium carapaces of the ostracod subfamily candoninae and oogonia of the aquatic macrophyte genus chara the development of catchment soils and the onset of authigenic carbonate production in response to the climatic amelioration during the late weichselian are clearly reflected by rising carbonate content distinct isotopic shifts in bulk carbonates and decreasing delta c 13 values of bulk organic matter in the sediments the gi 1 gs 1 the bolling allerod interstadial complex younger dryas stadial and the gs 1 preboreal transitions are marked by significant shifts in delta o 18 values of 2 3 parts per thousand as well as by distinct changes in carbonate content indicative of a decrease and a subsequent increase in mean annual temperature corresponding delta c 13 records reflect primarily changes in aquatic productivity with favourable conditions for phytoplankton and macrophytes during gi 1 and the preboreal resulting in persistent c 13 enrichment the younger dryas stadial is characterised by depletions in c 13 and o 18 with indications of a climatic tripartition consistent offsets in delta c 13 and delta o 18 between records obtained on specific carbonate components reflect vital effects in combination with seasonal characteristics and habitat preferences of the respective carbonate precipitating biota largely parallel first order variations in delta c 13 and delta o 18 of the different carbonate components demonstrate that individual isotope records may provide important palaeoclimatic information although more detailed reconstructions can be obtained from multi component analysis copyright c 2009 john wiley sons ltd

two terrestrial records of rapid climatic change during the glacial holocene transition 14 000 9 000 calendar years b p from europe two independent multidisciplinary studies of climatic change during the glacial holocene transition ca 14 000 9 000 calendar yr b p from norway and switzerland have assessed organism responses to the rapid climatic changes and made quantitative temperature reconstructions with modern calibration data sets transfer functions chronology at krakenes western norway was derived from calibration of a high resolution series of 14c dates chronologies at gerzensee and leysin switzerland were derived by comparison of 18o in lake carbonates with the 18o record from the greenland ice core project both studies demonstrate the sensitivity of terrestrial and aquatic organisms to rapid temperature changes and their value for quantitative reconstruction of the magnitudes and rates of the climatic changes the rates in these two terrestrial records are comparable to those in greenland ice cores but the actual temperatures inferred apply to the terrestrial environments of the two regions

quaternary paleosol stratigraphy and paleomagnetic record near dreihausen central germany summary a succession of sediments and paleosols near dreihausen in central germany records a normal magnetic remanence throughout and appears to have formed during the brunhes chron this sequence of sediments and paleosols developed in bedrock loess colluvium and residual regolith exhibits no clear evidence for secular variation swings or excursions suggesting rather slow and intermittent sedimentation rates the paleosols are primarily alfisols with pronounced argillic horizons which formed during interglacial periods when climate was presumably warmer and certainly wetter than today the distribution of higher clay in the older paleosol of eemian age supports the hypothesis of strong interglacial paleoclimates relative to the present day climate clay mineral transformations in these paleosols suggest a weathering sequence of illite illite smectite vermiculite despite minor clay mineral transformations of this type the data supports the interpretation of a mixed deciduous coniferous forest during the eemian interglaciation

lipid biomarker δ13c and plant macrofossil stratigraphy of a scottish montane peat bog over the last two millennia abstract seven horizons of a peat core covering the last 2000 years from moine mhor a blanket bog in the cairngorm mountains scotland have been examined for the carbon number distributions of the long chain hydrocarbon alcohol and acid components using gas chromatography gc and gas chromatography mass spectrometry gc ms compound specific 13 c values for individual n alkanes were obtained using gas chromatography isotope ratio mass spectrometry gc irms the lipid biomarker distributions and the 13 c values have been compared with those of eleven species of living plant dominant at the contemporary surface of the bog the observed lipid stratigraphy shows only partial agreement with that calculated using macrofossil abundance data and the lipid distributions for the living taxa a result which reflects the inherent uncertainties in both the lipid biomarker and the macrofossil approaches to palaeoenvironmental stratigraphy the carbon isotope values for the individual n alkanes of the plants 27 6 to 36 6 and of the peat layers 29 to 31 7 are as expected for the c 3 photosynthetic pathway however the n alkanes from the surface samples were more depleted by 2 in 13 c than those from the rest of the core a negative shift which may in part reflect the shift 1 2 in 13 c estimated for co 2 in a pre industrialised to an industrialised atmosphere

new age estimates and climatostratigraphic correlations for the borrobol and penifiler tephras evidence from abernethy forest scotland the emerging tephrostratigraphy of nw europe spanning the last termination ca 15 9 ka provides the potential for synchronizing marine ice core and terrestrial records but is currently compromised by stratigraphic complications geochemical ambiguity and imprecise age estimates for some layers here we present new tephrostratigraphic radiocarbon and chironomid based palaeotemperature data from abernethy forest scotland that refine the ages and stratigraphic positions of the borrobol and penifiler tephras the borrobol tephra 14 14 13 95 cal ka bp was deposited in a relatively warm period equated with greenland interstadial sub stage gi 1e the younger penifiler tephra 14 09 13 65 cal ka bp is closely associated with a cold oscillation equated with gi 1d we also present evidence for a previously undescribed tephra layer that has a major element chemical signature identical to the vedde ash it is associated with the warming trend at the end of the younger dryas and dates between 11 79 and 11 20 cal ka bp copyright 2011 john wiley sons ltd

building and testing age models for radiocarbon dates in lateglacial and early holocene sediments the growing importance of understanding past abrupt climate variability at a regional and global scale has led to the realisation that independent chronologies of past environmental change need to be compared between various archives this has in turn led to attempts at significant improvements in the required precision at which records can be dated radiocarbon dating is still the most prominent method for dating organic material from terrestrial and marine archives and as such many of the recent developments in improving precision have been aimed at this technique these include 1 selection of the most suitable datable fractions within a record 2 the development of better calibration curves and 3 more precise age modelling techniques while much attention has been focussed on the first two items testing the possibilities of the relatively new age modelling approaches has not received much attention here we test the potential for methods designed to significantly improve precision in radiocarbon based age models wiggle match dating and various forms of bayesian analyses we demonstrate that while all of the methods can perform very well in some scenarios caution must be taken when applying them it appears that an integrated approach is required in real life dating situations where more than one model is applied with strict error calculation and with the integration of radiocarbon data with sedimentological analyses of site formation processes

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

mean july temperatures during the younger dryas in northwestern and central europe as inferred from climate indicator plant species abstract we estimated minimum mean july temperatures in northwestern and central europe during the younger dryas 10 950 10 15014c yr b p from distributions of climate indicator plant species which were reconstructed from 140 pollen and plant macrofossil diagrams paleobotanical records mainly from the central and eastern part of the study area show that the coldest conditions occurred early in the younger dryas before 10 55014c yr b p for this phase mean july temperatures at sea level of around 10 c are suggested for the northern part of the british isles and for ice free scandinavia we estimated a mean july temperature of 12 c for central england the netherlands and northern germany the 13 c mean july isotherm largely based on the modern distribution oftypha latifolia was most probably located in southern england belgium central germany and poland the reappearance of thermophilous elements in the records after 10 55014c yr b p suggests a summer warming at least temporarily of 1 to 2 c in the study area the reconstructed temperatures are comparable with temperature estimates based on beetle data however they appear rather high when compared with estimates based on glaciological evidence

multidisciplinary investigations including stable isotope studies of thick late glacial sediments from tory hill co limerick western ireland abstract multidisciplinary investigations of a 10 m long marl rich late glacial core from tory hill co limerick have enabled environmental change including estimates of summer temperature st to be reconstructed for the late glacial period the sequence opens with fine partially laminated silt clay that has varve like microstructure a cold steppic environment from the final phase of the pleniglacial is represented here it is estimated to span almost 2000 years ca 16 9 15 cal ka b p ca 14 6 12 7 ka b p substantial development of woody vegetation is limited to the early part of the late glacial interstadial cf bolling this consists mainly of juniper and birch including tree birch betula pubescens as well as herb dominated communities these developments in vegetation and also the evidence from a variety of other proxies including stable isotope records 18o and 13c show that the thermal maximum was achieved early in the interstadial but st probably did not exceeded 14 c within this relatively warm period the various biological chemical and physical proxies suggest at least one substantial but short lived climatic oscillation the later part of the bolling allerod interstadial after ca 14 cal ka b p ca 12 ka b p began with a considerable and more or less sustained fall in temperature the low temperature regime was maintained until immediately before the younger dryas when a modest but distinct amelioration is recorded by all proxies this feature referred to as a pre younger dryas warming pydw and which is seen in land ocean and greenland ice core records from the northeast atlantic region has not been previously highlighted in the literature the younger dryas stadial when st may have fallen to ca 6 c has a distinctive pollen assemblage characterised mainly by gramineae thalictrum and artemisia but for reasons not readily explainable the early part of the stadial is not well defined in the stable isotope record as in most records from the northeast atlantic region the transition to the holocene is sharp and clearly recorded the importance of juniperus in the irish late glacial record as an indicator of temperature change is discussed and also the possible role played by ephedra and secale species at tory hill the apparent absence of temperature gradients within ireland is commented on and the evidence for much lower st in ireland compared with great britain is discussed

fungus not comet or catastrophe accounts for carbonaceous spherules in the younger dryas impact layer 1 a claim attributes the onset of the younger dryas climate interval and a range of other effects 12 900 years ago to a comet airburst and or impact event one key aspect of this claim centers on the origin of carbonaceous spherules that purportedly formed during intense impact ignited wildfires samples from pleistocene holocene sedimentary sequences in the california channel islands and other sites show that carbon spherules and elongate forms are common in samples dating to before during and well after the 12 900 year time horizon including from modern samples microscopic studies show that carbon spherules have morphologies and internal structures identical to fungal sclerotia such as sclerotium and cenococcum experimental charring of fungal sclerotia shows that their reflectance increases with temperature reflectance measurements of modern and late pleistocene spherules show that the latter indicate at most low intensity burning these data cast further doubt upon the evidence suggesting a catastrophic younger dryas impact event

all age depth models are wrong but how badly the uncertainty and error associated with fitted age depth models were investigated by fitting a range of models to sets of simulated radiocarbon dates based on varved sediments and comparing the modelled relationship with the varve timescale with large numbers of dates cubic smooth splines out perform other models with few dates no model reliably provides a good fit to reality and calculated confidence intervals are over optimistic c 2003 elsevier ltd all rights reserved

characterizing carbon isotopic variability in sphagnum to understand more fully the nature of isotopic fractionation in mosses and to explore the potential of stable isotope analyses of selected peat constituents for palaeoenvironmental research we present results from a study of inter and intra plant 13c variability in sphagnum spp subdivisions of stem pendant and horizontal branch elements of modern sphagnum capillifolium plants revealed consistent and statistically significant differences in their isotopic composition sequential downstem analysis of a further cohort of four modern sphagnum capillifolium plants also reveals evidence of common forcing on the isotopic composition of sequentially formed stem and branch increments this relationship was tested further by analysis of a series of branch and stem samples manually recovered from sphagnum fuscum preserved within a late holocene ad 2003 1970 peat monolith from a european mire the high degree of isotopic coherence observed between plants supports the analysis of sphagnum in palaeoecological

a coherent high precision radiocarbon chronology for the late glacial sequence at sluggan bog co antrim northern ireland seventy five radiocarbon dates are presented from sluggan bog in co antrim northern ireland the holocene peats are underlain by late glacial sediments which also appear to have accumulated largely in a mire environment the radiocarbon dates from the late glacial and early holocene part of the profile were obtained from the humic and humin fractions of the sedimentary matrix and from plant macrofossils the last named were dated by ams and the sediment samples by radiometric beta counting methods age depth models for the three dating series show a very high level of agreement between the two fractions and the macrofossils no statistically significant difference is found between the beta counting and ams results three tephras were located in the profile the uppermost of which is in a stratigraphical position suggestive of the vedde ash but the geochemical and radiocarbon evidence do not support this interpretation the lower ashes are in the correct stratigraphical position for the laacher see and borrobol tephras attributions substantiated by the radiocarbon evidence but not by the geochemical data the sluggan sequence has generated one of the most internally consistent radiocarbon chronologies for any late glacial site in the british isles and it is suggested that in future more effort should be devoted to the search for and analysis of late glacial mire sequences rather than the limnic records that have formed the principal focus of late glacial investigations hitherto copyright 2004 john wiley sons ltd

sedimentology and allostratigraphy of post 240 ka to pre 26 5 ka lacustrine terraces at intracaldera lake rotorua taupo volcanic zone new zealand abstract lake rotorua partially occupies a nearly circular 20 km diameter volcano tectonic depression formed at c 240 ka by eruption of the voluminous mamaku ignimbrite three distinct lacustrine littoral terraces defined on the basis of contrasting geomorphology and field relations and separated by tephrostratigraphically dateable unconformities and basin floor disconformities fringe much of the lake basin they are here correlated with former high stands of the lake which resulted from the blockage and re establishment of a number of alternative outlets due to tectonic activity and volcanism at both the host and adjacent volcanic centres the unconformities allow division of the deposits into three allostratigraphic units each of which is then characterised by elevation and sediment provenance the

the incidence of microscopic charcoal in late glacial deposits abstract microscopic charcoal is not routinely counted by those investigating late glacial deposits it is largely the domain of those pursuing anthropogenic questions relating to the holocene interglacial 23 sites dating to the devensian late glacial ca 13 000 10 000 14c yr bp in scotland have charcoal records and seven of these can be shown to have a high charcoal content a phenomenon that has passed largely unremarked we discuss patterns of charcoal representation and explore possible explanations for high charcoal abundances especially in the loch lomond stadial including taphonomy e g secondary erosion of charcoal bearing deposits long distance transport aridity especially during the loch lomond stadial warmth and effective precipitation especially during the late glacial interstadial and humanly caused fires upper palaeolithic available data do not allow the establishment of clear relationships between vegetation types and charcoal abundance it is suggested that patterns of burning may need to be considered in the context of arid wet shifts in climate it is probable that combinations of factors are responsible for the late glacial charcoal records but the difficulty remains that too few data are routinely collected or available for study

temperature gradients in northern europe during the last glacial holocene transition 14 914c kyr bp interpreted from coleopteran assemblages late glacial and early holocene climatic conditions have been reconstructed for northern europe using the mutual climatic range mcr palaeoclimate method based on fossil coleopteran assemblages altogether beetle faunas from 77 sites have been analysed ranging from ireland in the west to poland and finland in the east and mcr estimates calculated the results are plotted on 16 maps each representative of a selected time slice covering the period from 14 5 14c kyr bp to 9 0 14c kyr bp eight of the maps show the mcr estimates of tmax mean temperature of the warmest month derived from each site for which data are available while the remainder show estimated tmax isotherms interpolated from these values it can be demonstrated that at times the thermal climate was fairly uniform throughout the study area whereas at others temperature gradients were much steeper than they are in the region today there also appears to be a distinct contrast between cold periods when contours trended nw se and warmer periods when contours trend w e or even ne sw the pattern of climatic changes that emerges is shown to be very different from the traditional view that has been used up to now as a template for classifying late glacial climatic events on a wide even global scale the suddenness and intensity of changes in the thermal climate may have been partially responsible for an apparent lack of equilibrium between the flora and fauna of the time and the physical environment in which they lived 1998 john wiley sons ltd

the younger dryas impact hypothesis a requiem abstract the younger dryas yd impact hypothesis is a recent theory that suggests that a cometary or meteoritic body or bodies hit and or exploded over north america 12 900 years ago causing the yd climate episode extinction of pleistocene megafauna demise of the clovis archeological culture and a range of other effects since gaining widespread attention in 2007 substantial research has focused on testing the 12 main signatures presented as evidence of a catastrophic extraterrestrial event 12 900 years ago here we present a review of the impact hypothesis including its evolution and current variants and of efforts to test and corroborate the hypothesis the physical evidence interpreted as signatures of an impact event can be separated into two groups the first group consists of evidence that has been largely rejected by the scientific community and is no longer in widespread discussion including particle tracks in archeological chert magnetic nodules in pleistocene bones impact origin of the carolina bays and elevated concentrations of radioactivity iridium and fullerenes enriched in 3 he the second group consists of evidence that has been active in recent research and discussions carbon spheres and elongates magnetic grains and magnetic spherules byproducts of catastrophic wildfire and nanodiamonds over time however these signatures have also seen contrary evidence rather than support recent studies have shown that carbon spheres and elongates do not represent extraterrestrial carbon nor impact induced megafires but are indistinguishable from fungal sclerotia and arthropod fecal material that are a small but common component of many terrestrial deposits magnetic grains and spherules are heterogeneously distributed in sediments but reported measurements of unique peaks in concentrations at the yd onset have yet to be reproduced the magnetic grains are certainly just iron rich detrital grains whereas reported yd magnetic spherules are consistent with the diffuse non catastrophic input of micrometeorite ablation fallout probably augmented by anthropogenic and other terrestrial spherular grains results here also show considerable subjectivity in the reported sampling methods that may explain the purported yd spherule concentration peaks fire is a pervasive earth surface process and reanalyses of the original yd sites and of coeval records show episodic fire on the landscape through the latest pleistocene with no unique fire event at the onset of the yd lastly with yd impact proponents increasingly retreating to nanodiamonds cubic hexagonal lonsdaleite and the proposed n diamond as evidence of impact those data have been called into question the presence of lonsdaleite was reported as proof of impact related shock processes but the evidence presented was inconsistent with lonsdaleite and consistent instead with polycrystalline aggregates of graphene and graphane mixtures that are ubiquitous in carbon forms isolated from sediments ranging from modern to pre yd age important questions remain regarding the origins and distribution of other diamond forms e g cubic nanodiamonds in summary none of the original yd impact signatures have been subsequently corroborated by independent tests of the 12 original lines of evidence seven have so far proven to be non reproducible the remaining signatures instead seem to represent either 1 non catastrophic mechanisms and or 2 terrestrial rather than extraterrestrial or impact related sources in all of these cases sparse but ubiquitous materials seem to have been misreported and misinterpreted as singular peaks at the onset of the yd throughout the arc of this hypothesis recognized and expected impact markers were not found leading to proposed yd impactors and impact processes that were novel self contradictory rapidly changing and sometimes defying the laws of physics the yd impact hypothesis provides a cautionary tale for researchers the scientific community the press and the broader public

lateglacial vegetation and environment in ireland first results from four western sites a contribution to the north atlantic seaboard programme of igcp 253 termination of the pleistocene abstract first results of investigations that include pollen and chemical analyses of lateglacial lake sediments from four sites in western ireland are presented and the evidence for environmental change from these and previously published studies is reviewed fresh evidence is presented for a period with a cold arid continental type climate immediately after deglaciation this period is informally defined as the pre interstadial it is represented by a pinus artemisia gramineae pollen assemblage with a high proportion of long distance transported pollen recorded in highly minerogenic sediments immediately overlying outwash gravels and sands the interval between this and the younger dryas stadial informally defined as the lateglacial interstadial is characterised in the early part by maximum tall shrub development consisting mainly of juniperus tall shrub vegetation is subsequently replaced by gramineae and cyperaceae dominated open vegetation at many sites it is argued that the lateglacial interstadial is characterised by a number of climatic oscillations the most severe and sustained being responsible for this general shift in favour of herbaceous taxa at mid interstadial ca 12 ka bp prior to the onset of the younger dryas deterioration a modest expansion of juniperus at several sites and betula at some sites suggests a period of ameliorating climate the severity of climatic conditions during the younger dryas stadial is well expressed in the pollen lithological and chemical data there is some evidence to suggest that vegetation development in terrestrial environments at the transition to the holocene lagged behind developments in aquatic habitats and the thermal environment generally

oxygen isotope wiggle matching as a tool for synchronising ice core and terrestrial records over termination 1 abstract in nw europe the large number of terrestrial records that are now available from termination 1 15 10 kcal yr bp form the basis for a highly detailed picture of lateglacial environmental change nevertheless the greenland oxygen isotope records grip gisp2 are still regarded as the best high resolution climate proxy for the north atlantic region in order to evaluate spatial contrasts and leads and lags in the climate system integration of ice core marine and terrestrial records is becoming increasingly important intimate objectives however comparisons between different environments require a common time scale for the proxy climate records stable isotope analyses performed on lateglacial lacustrine calcareous deposits in the netherlands provide a terrestrial oxygen isotope record comparable to that from the greenland ice core these atmospherically controlled lacustrine oxygen isotope signals not only constitute an independent palaeoclimatic proxy but provide the basis for synchronising records from these environments as well more over this synchronisation reveals some remarkable aspects concerning the timing of the oxygen isotope and palynological events as recorded in the netherlands above all oxygen isotope wiggle matching offers a means of correlating terrestrial and ice core records

climate variations in britain during the last glacial holocene transition 15 0 11 5 cal ka bp comparison with the grip ice core record stratigraphic records from four sequences in britain that span the last glacial holocene transition c 15 0 11 5 cal ka bp are summarized and compared using a calibrated timescale palaeoclimatic changes are defined using temperature estimates based on coleopteran data at two of the sites and chironomid assemblages at the other sites an attempt is made to distingish between the timing of a climate shifts and b ecosystem responses at all four sites the british data are compared with the grip ice core record recently advocated by bjorck et al as the type sequence for the last termination in the north atlantic region there is a degree of compatibility between the british and grip palaeoclimatic records the clearest climatic signals in the british lake records are a a period of warm conditions a thermal maximum between 15 0 and 14 5 cal ka bp which equates approximately with grip zone gi le b the onset of climatic cooling which appears to have commenced during grip zone gi le at c 14 5 cal ka bp c a period of marked climatic instability from 14 4 to 12 7 cal ka bp the regional effects of which are difficult to resolve using the evidence presently available d further climatic cooling which commenced at around 13 0 cal ka bp after which the lake biota catchment soils and vegetation cover at least in some parts of britain did not recover until the onset of the holocene e continued climatic cooling with the most severe impact on lake ecosystems occurring during the period c 12 6 to 11 5 cal ka bp

a high resolution multiproxy late glacial record of climate change and intrasystem responses in northwest england a lacustrine carbonate sequence from hawes water lancashire uk has been studied using stable isotopic lithological pollen and mineral magnetic analysis the data reveal four abrupt climatic oscillations in the late glacial interstadial leading up to the onset of the loch lomond stadial the data also point to climatic warming relatively early within the stadial ca 12 500 grip yr prior to the onset of the holocene the oxygen isotope record is taken as a signature of climate forcing against which the response of the lake system can be monitored by adopting this approach it is revealed that the response of the biological system to the rapid climatic oscillations is non linear and primarily a function of the antecedent conditions a significant end devensian isotopic excursion a is matched by only minor changes in the cold adapted floras and faunas during the warmer interstadial the response of the biological ecosystem events b d is clearly influenced by thresholds major changes in the catchment vegetation associated with relatively minor oscillations in the isotopic signature the stratigraphical patterns reveal significant lag effects between the onset of climate deterioration and resulting changes in vegetation copyright 2002 john wiley sons ltd

synchronisation of palaeoenvironmental events in the north atlantic region during the last termination a revised protocol recommended by the intimate group abstract the north atlantic intimate group of the inqua palaeoclimate commission has previously recommended an event stratigraphy approach for the synchronisation of records of the last termination using the greenland grip isotopic record as the regional stratotype and intcal98 for the calibration of radiocarbon dates lowe j j hoek w intimate group 2001 inter regional correlation of palaeoclimatic records for the last glacial interglacial transition a protocol for improved precision recommended by the intimate project group quaternary science reviews 20 1175 1187 here we present a revised protocol for time stratigraphic correlation in the north atlantic region over a more extended time period 30 8 ka this employs the new ngrip isotopic record and associated greenland ice core chronology 2005 gicc05 as the regional stratotype intcal04 for the calibration of radiocarbon dates bayesian based statistical procedures for the construction of age models and tephrochronology to validate correlations between regional site records

an event stratigraphy for the last termination in the north atlantic region based on the greenland ice core record a proposal by the intimate group it is suggested that the grip greenland ice core should constitute the stratotype for the last termination based on the oxygen isotope signal in that core a new event stratigraphy spanning the time interval from ca 22 0 to 11 5 k grip yr bp ca 19 0 10 0 k 14 c yr bp is proposed for the north atlantic region this covers the period from the last glacial maximum through termination 1 of the deep ocean record to the pleistocene holocene boundary and encompasses the last glacial late glacial of the traditional northwest european stratigraphy the isotopic record for this period is divided into two stadial episodes greenland stadials 1 gs 1 and 2 gs 2 and two interstadial events greenland interstadials 1 gi 1 and 2 gi 2 in addition gi 1 and gs 2 are further subdivided into shorter episodes the event stratigraphy is equally applicable to ice core marine and terrestrial records and is considered to be a more appropriate classificatory scheme than the terrestrially based radiocarbon dated chronostratigraphy that has been used hitherto 1998 john wiley sons ltd

lateglacial and early holocene palaeoenvironmental events in sluggan bog northern ireland comparisons with the greenland ngrip gicc05 event stratigraphy a multi proxy lateglacial environmental record is described from sluggan bog in county antrim northern ireland pollen plant macrofossil charcoal sediment chemistry stable isotope and sedimentological data provide a multi faceted picture of local and regional environmental changes during the transition from the last cold stage to the beginning of the present interglacial and enable a series of distinctive palaeoenvironmental events to be identified a combination of radiometric and ams radiocarbon dates on both humic and humin sediment fractions and on charcoal fragments and plant macrofossils provides one of the most closely constrained radiocarbon timescales for any lateglacial site in the british isles the evidence suggests that an initial period of warm conditions beginning in the sluggan record around 14 2 ka b2k before ad 2000 and when open salix betula woodland was locally present was succeeded first by a heathland phase then by a re establishment of wood and scrub before this was replaced during the later part of the lateglacial woodgrange interstadial by species rich grassland in terms of timing this sequence corresponds very closely to the gi 1e gi 1d gi 1c series of events in the greenland ngrip ice core a short lived betula phase towards the end of the interstadial in the sluggan sequence may reflect the short lived climatic warming of gi 1a although the radiocarbon age model suggests that it occurred prior to that event there is a similar age discrepancy between the two sequences at the end of the interstadial with the onset of the nahanagan younger dryas stadial in sluggan appearing to predate that in ngrip by up to 200 yrs by contrast there is a very close correspondence between the date on the onset of the holocene inferred from the pollen record in sluggan 11 69 ka b2k and the age of the pleistocene holocene boundary 11 7 ka b2k in ngrip while uncertainties remain over the climatic signals in the later interstadial the evidence suggests that during the early and mid interstadial and at the onset of the holocene northern ireland and greenland appear to have been broadly phase locked in their response to hemispherical climate change

a high resolution record of mire development and climatic change spanning the late glacial holocene boundary at church moss davenham cheshire england excavations of deposits filling a closed basin within glacial drift at church moss davenham near northwich cheshire england revealed a sequence of late glacial and early holocene sediments analyses of pollen and plant and invertebrate macrofossils were undertaken together with loss on ignition analyses and a programme of ams radiocarbon dating to provide a record of changing biostratigraphy and climatic and ecological regimes the infilling of features identified as frost cracks in the till flooring the basin gave remains that reflected conditions of extreme cold towards the end of the devensian the pollen record from a 3 5 m sequence of peat towards the deepest part of the basin supported by radiocarbon dates shows that organic deposition was initiated during the late glacial interstadial and continued into the early part of the holocene there was some evidence for a cool episode during the interstadial with amelioration prior to the rapid onset of the tundra conditions of the loch lomond stadial following the stadial amelioration was rapid there was evidence from both central and marginal sequences for a mosaic of fen dominated by sedges and often also mosses with short lived small pools through much of the succession change to terrestrial conditions proceeded intermittently probably as a result of subsidence caused by solution of underlying salt bearing strata

integrating the intimate records using tephrochronology rising to the challenge little has challenged our understanding of climate change more so than the abruptness with which large scale shifts in temperature occurred during the late quaternary the causal mechanisms driving

the irish quaternary fauna project abstract much of ireland s pleistocene and early holocene mammalian faunas are derived from a series of late 19th early 20th century cave excavations in many instances it would appear that the deposits containing these faunal remains were disturbed this project assessed the chronological range of the mammalian species present in the caves using 14 c dating in particular accelerator mass spectrometry ams the research has shown that 1 a wide range of mammals colonised ireland in the period between at least 45 ka and 20 ka with some elements surviving until close to the last glacial maximum 2 a more restricted range of species re colonised ireland during the lateglacial period with evidence for a slightly more temperature fauna being replaced by an arctic fauna at about 11 ka 3 certain elements of ireland s holocene fauna may have survived through from the lateglacial into the holocene 4 there is a lack of evidence for red deer cervus elaphus being present in the early holocene in ireland and 5 horse is only documented in the irish holocene from 4 ka the paper also discusses the implications of the quaternary fauna project for the late pleistocene of ireland the mechanism and period of colonisation of ireland as well as the introduction of domesticates in the mid holocene

the biosphere a homogeniser of pb isotope signals abstract rock soil and plant terrestrial moss european mountain ash leaves mountain birch leaves bark and wood and spruce needles and wood samples collected at 3 km intervals along a 120 km long transect 40 sites cutting the city of oslo norway were analysed for their pb concentration and pb isotope ratios a general decrease in 206 pb 207 pb 208 pb 207 pb and 206 pb 208 pb ratios with a characteristic low variability in all plant materials and the plant derived o horizon of soil profiles compared to rocks and mineral soils is observed along the transect it is demonstrated that minerogenic and biogenic sample materials belong to two different spheres the lithosphere and biosphere and that geochemical processes determining their chemical and isotopic compositions differ widely background variation for both sample materials needs to be established and documented at the continental and global scale before the anthropogenic influence on the geochemistry of the earth s surface can be reliably estimated

a 750 year fire history based on lake sediment records in central yellowstone national park usa a 750 year fire history was reconstructed for the central plateau of yellowstone national park from the deep water sediments of five lakes the charcoal record from a large lake provided a chronology of regional fires data from four small lakes were used to study local and extralocal fires the co occurrence of abundant charcoal and high magnetic susceptibility values at the same stratigraphic level was used as evidence of a local catchment fire and a charcoal peak without high magnetic susceptibility was ascribed to an extralocal fire or a local fire without a related erosion event the fire history was compared with the dendrochronologic fire record for the last 450 years and the close agreement provided the justification to extend the chronology back in time large areas of the region burned in ad 1988 c 1700 c 1560 and c 1440 from c 1220 to 1440 and c 1700 to 1987 intermediate to small areas burned the near absence of fires in the twentieth century prior to the large fires of 1988 is evi

deposition models for chronological records abstract long term sedimentary sequences provide a wealth of useful information for research into the palaeo environment especially in relation to past climate change shorter records provide similar information in many archaeological contexts however if such records are to be used to provide precise timing of events and more critically the relative timing between different records methods are needed to provide accurate and precise age depth models for these sequences given the imprecision of individual calibrated radiocarbon determinations it is necessary to use the information we have about the deposition process to refine our chronologies and also to provide interpolation between dated levels in any sequence even with layer counted chronologies the uncertainties are sometimes hard to quantify this paper outlines a range of bayesian models for deposition which have been implemented in the computer programme oxcal these models can be used to combine information from the sediments themselves with radiocarbon or other direct dating information such models have the potential to integrate information between different records and provide a coherent chronology on which to base environmental or archaeological research