late glacial climatic and environmental changes in eastern central europe correlation of multiple biotic and abiotic proxies from the lake svarcenberk czech republic thick lake sediments discovered in the southern part of the czech republic provide a high resolution archive for detailed study of paleoenvironmental changes during the late pleistocene to holocene in eastern central europe until recently no similar records were available for this important region in the transition from oceanic to continental macro climatic settings using a multi proxy approach that combines sedimentological pollen analytical paleozoological chironomids geochemical and mineral magnetic methods we demonstrate that major climatic events of the late glacial can be correlated with atlantic rather than continental regimes as reported in paleoclimatic literature for the area of the interest the sensitivity of applied biological and abiological techniques to climatically driven processes allows trans regional comparisons and enables us to discuss the pattern of geographic variation in these processes we are able to establish a clear relationship between vegetation cover soil development and erosional processes a short term intra allerod cool event has been correlated with the gerzensee oscillation proxy evidence suggests that the early half of the younger dryas was rather humid whereas the latter half was dry and had significant impact on vegetation sedimentary dynamics and lake level status during the yd preboreal transition

tephrochronology and absolute centennial scale synchronisation of european and greenland records for the last glacial to interglacial transition a case study of soppensee and ngrip the tephrostratigraphy of soppensee switzerland is presented here for the first time with new geochemical data for four tephra layers derived from three volcanic centres the best available age estimates for the laacher see tephra and vedde ash layers are incorporated into a revision of the radiocarbon based bayesian age model for the last glacial to interglacial transition at soppensee which is used to explore synchronicity of climatic events between europe and the north atlantic local temperature changes recorded by biotic and abiotic proxies in soppensee appear to shift in phase with the oxygen isotope signal in greenland at the onset of the younger dryas however with the clarity of improved precision an apparent offset that likely results from a dating artefact is seen between records at the termination of the stadial event from a methodological standpoint the results clearly show that only by establishing detailed and independent chronological frameworks can abrupt climatic variability be compared between different regions with sufficiently high temporal precision to addresses the notion of hemispheric climatic synchronicity at the centennial scale in the late quaternary continuing to develop such approaches is therefore essential in order to understand how far in time and space the climate has behaved in such a way

a laacher see eruption supplement to tephrabase investigating distal tephra fallout dynamics abstract tephrabase www tephrabase org is an online data repository and research tool for tephrochronological investigations in northern europe this paper presents and discusses an update to tephrabase that contains geographic and as far as available geochemical data on 452 data points for the widespread isochronous laacher see tephra this tephra is dated to c 12 920 calendar years bp and acts as an important chronostratigraphic marker for the lateglacial gi 1a late allerod chronozone in terrestrial and lacustrine palaeoenvironmental archives as well as in archaeological stratigraphies based on these data a revised map of the total tephra distribution is presented suggesting that the north eastern fallout lobe might contain a secondary fallout thickness maximum 230 340 km distant from the eruptive centre in addition new geochemical data from a series of distal tephra deposits spanning most of the north eastern fallout lobe are used to evaluate previous suggestions regarding the distribution of fallout from distinct eruption phases the aim of the study is that future tephrochronological investigations can use this database and the revised distribution map for effectively targeting sites for analysis

late glacial sediments of the stara jimka paleolake and the first finding of laacher see tephra in the czech republic the late glacial sedimentary sequence of the stara jimka paleolake bohemian forest czech republic is characterized by the prevalence of detrital minerals with an elevated proportion of organic matter and abundant diatom valves in relatively warm periods the mineral debris originated mainly from local migmatites and mica schists or glacial and deluvial deposits derived from the same material low background contents of cao 0 20 wt and na2o 0 50 wt reflect chemical weathering correlation analysis of trace elements shows that the mineral debris concentrates rb cs ga cr zr hf light rare earth elements th u pb ba sr and weakly zn whereas mo co se as ni cu br and weakly au are allocated predominantly to sulphides and organic matter the sequence contains a continuous horizon with the laacher see tephra lst causing contrasting maxima of na ca cl and nb in bulk composition while the phonolitic tephra corresponds to the lower part of the middle lst unit it also contains phosphorus rich relicts of older sediments with small euhedral air transported volcanic crystals such sediments may have occurred in depressions at an older volcano prior to the major laacher see eruption 12 880 cal bp

improved age estimates for key late quaternary european tephra horizons in the reset lattice abstract the research project response of humans to abrupt environmental transitions reset used tephra layers to tie together and synchronise the chronologies of stratigraphic records at archaeological and environmental sites with the increasing importance of tephra as chronological markers in sedimentary sequences both in this project and more generally comes a requirement to have good estimates for the absolute age of these volcanic horizons this paper summarises the chronology of the key tephra in the reset tephra lattice in the time range 10 60 ka bp from the existing literature from papers produced as part of the reset project and reanalysis conducted for this paper the paper outlines the chronological approach taken to the dating of tephra within the reset project and the basis for further work as part of the intimate integrating ice core marine and terrestrial records initiative for each of the tephra layers in the lattice the existing literature is discussed and where relevant date estimates updated using the latest radiocarbon calibration curves intcal13 and marine13 and methods maps show the approximate extent of tephra finds giving a visual indication of the coverage of the lattice in different time periods

volatile composition of the phonolitic laacher see magma 12 900 yr bp implications for syn eruptive degassing of s f cl and h 2 o a volatile rich and chemically zoned phonolitic magma reservoir was tapped successively during the eruption of laacher see volcano ca 12 900 years bp and produced a tephra sequence consisting of phenocryst poor highly evolved phonolite at the base and phenocryst rich more mafic phonolite at the top the stratospheric volatile loading was estimated by comparing pre and post eruptive s f cl and h2o contents of undegassed glass inclusions and partially degassed matrix glasses glass inclusions 150 1490 ppm s and host matrix glasses 150 820 ppm s both document a strong s decrease during progressive magmatic differentiation which is interpreted to be partially caused by crystallization of hauyne the s6 stotal ratio of the pre eruptive melt increased with differentiation from 8 to 71 as indicated by s k wavelength shift measurements in glass inclusions sulfate rich highly evolved phonolitic magma was erupted during plinian and sulfide rich more mafic phonolitic magma during late phreatomagmatic phases f and cl became enriched during late stages of differentiation glass inclusions 690 4060 ppm f 1770 4400 ppm cl matrix glasses 680 3660 ppm f 2130 4330 ppm cl the most differentiated melts maximum 13 wt na2o occur only as matrix glass and are extremely f enriched 5080 8780 ppm but cl depleted 460 2820 ppm suggesting that f was retained in the melt whereas some cl was lost during pre and or syn eruptive degassing the h2o contents of glass inclusions increase irregularly with differentiation 2 5 5 7 wt matrix glasses are h2o depleted 0 2 2 8 wt compared to most glass inclusions showing that most h2o was released to the atmosphere by explosive degassing a mass balance calculation yields a syn eruptive volatile release of 1 9 tg stotal 6 6 tg cl and 403 tg h2o from the melt this is a minimum estimate since s and cl could have accumulated in a separate fluid phase as indicated by fluid inclusions in hauyne and pre eruption h2o contents close to saturation level at the likely pressure temperature conditions in the laacher see magma reservoir we estimate that at least ca 20 tg so2 were injected into the stratosphere causing a significant negative climate forcing as reflected by several paleoclimate proxies and as shown by recent modeling

changes in mid and far field human landscape use following the laacher see eruption c 13 000 bp abstract around 13 000 years ago the laacher see volcano east eifel volcanic field rhenish shield erupted cataclysmically the thick tephra blanket in the eruption s near field covered and thereby preserved a large number of archaeological sites ranging from very small to some of the largest and richest sites known from the late glacial in this proximal region there is a striking contrast in the number of sites prior to the eruption and the almost complete lack of sites dating to the period after the event i e to greenland interstadial 1a the preservative function of the tephra cover itself may explain this near field pattern but it is shown here that similar stratigraphic observations can also be made in the laacher see eruption s mid field towards the west and in particular to the north east the aim of this paper is to review the stratigraphic relations of known archaeological sites outside the near field of the laacher see event with a particular focus on the german federal state of hesse and adjacent areas of lower saxony and the thuringian basin here a number of archaeological sites are known where strata of laacher see tephra cap human occupation most often these sites are not reoccupied until much later in prehistory suggesting that the eruption may have led either to a complete or a near complete abandonment of the affected regions or at the very least to a major reorganisation of landscape use

the reset tephra database and associated analytical tools abstract an open access database has been set up to support the research project studying the response of humans to abrupt environmental transitions reset the main methodology underlying this project was to use tephra layers to tie together and synchronise the chronologies of stratigraphic records at archaeological and environmental sites the database has information on occurrences and chemical compositions of glass shards from tephra and cryptotephra deposits found across europe the data includes both information from the reset project itself and from the published literature with over 12 000 major element analyses and over 3000 trace element analyses on glass shards relevant to 80 late quaternary eruptions the reset project has generated an important archive of data when added to the published information the database described here has a total of more than 22 000 major element analyses and nearly 4000 trace element analyses on glass from over 240 eruptions in addition to the database and its associated data new methods of data analysis for assessing correlations have been developed as part of the project in particular an approach using multi dimensional kernel density estimates to evaluate the likelihood of tephra compositions matching is described here and tested on data generated as part of the reset project

mineralogy at the magma hydrothermal system interface in andesite volcanoes new zealand ejecta from phreatomagmatic eruptions of ruapehu and white island andesite volcanoes in new zealand provide insight into the mineralogical reactions that occur when magma invades a vent hosted hydrothermal system at the surface and in ejected blocks from shallow depths hydrothermal alteration mineralogies are dominated by silica polymorphs anhydrite natroalunite and pyrite blocks from greater depths are composed mainly of cristobalite anhydrite halite and magnetite where altered material was heated to magmatic temperatures thermal decomposition reactions produced mullite wollastonite and indialite some ejected breccias contain osumilite cordierite sanidine and hypersthene indicative of reactions occurring near the osumilite cordierite phase boundary at 800 c and water pressure 0 2 kbar hedenbergite wollastonite andradite and magnetite are found in rare skarn fragments possibly formed by metasomatism of silica poor sulfate rich hydrothermal deposits high temperature parageneses of these types have not been reported before in shallow acidic volcano hydrothermal systems however they may be typical of the magma hydrothermal contact zone at many andesite volcanoes

large pt anomaly in the greenland ice core points to a cataclysm at the onset of younger dryas one explanation of the abrupt cooling episode known as the younger dryas yd is a cosmic impact or airburst at the yd boundary ydb that triggered cooling and resulted in other calamities including the disappearance of the clovis culture and the extinction of many large mammal species we tested the ydb impact hypothesis by analyzing ice samples from the greenland ice sheet project 2 gisp2 ice core across the bolling allerod yd boundary for major and trace elements we found a large pt anomaly at the ydb not accompanied by a prominent ir anomaly with the pt ir ratios at the pt peak exceeding those in known terrestrial and extraterrestrial materials whereas the highly fractionated pt ir ratio rules out mantle or chondritic sources of the pt anomaly it does not allow positive identification of the source circumstantial evidence such as very high superchondritic pt al ratios associated with the pt anomaly and its timing different from other major events recorded on the gisp2 ice core such as well understood sulfate spikes caused by volcanic activity and the ammonium and nitrate spike due to the biomass destruction hints for an extraterrestrial source of pt such a source could have been a highly differentiated object like an ir poor iron meteorite that is unlikely to result in an airburst or trigger wide wildfires proposed by the ydb impact hypothesis

north european last glacial interglacial transition lgit 15 9 ka tephrochronology extended limits and new events high precision correlation of palaeoclimatic and palaeoenvironmental records is crucial for testing hypotheses of synchronous change although radiocarbon is the traditional method for dating late quaternary sedimentary sequences particularly during the last glacial interglacial transition lgit 15 9 ka there are inherent problems with the method particularly during periods of climate change which are often accompanied by major perturbations in atmospheric radiocarbon content an alternative method is the use of tephras that act as time parallel marker horizons within europe numerous volcanic centres are known to have erupted during the lgit providing considerable potential for high precision correlation independent of past radiocarbon fluctuations here we report the first identification of the vedde ash and askja tephra in ireland significantly extending the known provenance of these events we have also identified two new horizons the roddans port tephras a and b and tentatively recognise an additional horizon from vallensgard mose denmark that provide crucial additional chronological control for the lgit two phases of the laacher see tephra lst are reported the lower laacher see tephra llst and probably the c2 phase of the middle laacher see tephra mlst c2 indicating a more northeasterly distribution of this fan than reported previously copyright 2006 john wiley sons ltd

low latitude dusty events vs high latitude icy heinrich events it has been proposed that tropical events could have participated in the triggering of the classic high latitude iceberg discharge heinrich events he we explore low latitude heinrich events equivalents at high resolution in a piston core recovered from the tropical north western african margin they are characterized by an increase of total dust lacustrine diatoms and fibrous lacustrine clay minerals thus low latitude events clearly reflect severe aridity events that occurred over africa at the saharan latitudes probably induced by southward shifts of the inter tropical convergence zone at a first approximation it seems that there is more likely synchronicity between the high latitude heinrich events hes and low latitude events lle rather than asynchronous behaviours

glaciation in the surroundings of prasilske lake bohemian forest czech republic abstract comprehensive geomorphological and sedimentological analyses confirmed three phases of wurm glaciation in the surroundings of prasilske lake and stara jimka in the bohemian forest sumava mountains glaciations were affected by a steep east facing slope by plateaus on the adjacent ridges and by local geological conditions a small valley glacier about 2 km long and 50 m thick occurred during the first phase in the second phase a glacier rock glacier developed probably based on remnants of the valley glacier during the last phase glacial activity was divided into stara jimka and the stepped cirque of prasilske lake a further shallow 3 m deep lake in stara jimka was dammed by slope movements after deglaciation 14 cal ka bp and survived until 4 cal ka bp the late pleistocene chronology of the bohemian forest seems to be related more closely to the alps than to northern europe in the mid mountains of central europe pleistocene glaciation decreases significantly eastward because of increasing continentality the presence of plateaus deflation areas around 1300 m altitude across the approach of westerly winds was important for the development of glaciers in the bohemian forest the termination of glaciation before the younger dryas is specific to the bohemian forest in comparison with the vosges and krkonose mountains

evidence for deposition of 10 million tonnes of impact spherules across four continents 12 800 y ago airbursts impacts by a fragmented comet or asteroid have been proposed at the younger dryas onset 12 80 0 15 ka based on identification of an assemblage of impact related proxies including microspherules nanodiamonds and iridium distributed across four continents at the younger dryas boundary ydb spherule peaks have been independently confirmed in eight studies but unconfirmed in two others resulting in continued dispute about their occurrence distribution and origin to further address this dispute and better identify ydb spherules we present results from one of the largest spherule investigations ever undertaken regarding spherule geochemistry morphologies origins and processes of formation we investigated 18 sites across north america europe and the middle east performing nearly 700 analyses on spherules using energy dispersive x ray spectroscopy for geochemical analyses and scanning electron microscopy for surface microstructural characterization twelve locations rank among the world s premier end pleistocene archaeological sites where the ydb marks a hiatus in human occupation or major changes in site use our results are consistent with melting of sediments to temperatures 2 200 c by the thermal radiation and air shocks produced by passage of an extraterrestrial object through the atmosphere they are inconsistent with volcanic cosmic anthropogenic lightning or authigenic sources we also produced spherules from wood in the laboratory at 1 730 c indicating that impact related incineration of biomass may have contributed to spherule production at 12 8 ka an estimated 10 million tonnes of spherules were distributed across 50 million square kilometers similar to well known impact strewnfields and consistent with a major cosmic impact event

microbial controls on phosphate and lanthanide distributions during granite weathering and soil formation abstract both microbial and geochemical factors control the form distribution and abundance of lanthanides during weathering and soil formation in a profile in the bemboka granodiorite from southern new south wales australia during the initial stages of weathering hydrous ce bearing lanthanide and lanthanide aluminum phosphates including rhabdophane and florencite crystallize on etched apatite surfaces throughout the profile however their fate depends greatly on their location within the profile in rocks weathered 5 6 m below the soil zone the lower profile secondary lanthanide phosphates persist long after all apatite has been dissolved however in rocks weathered within 2 m of the soil zone the upper profile secondary phosphates are dissolved and lanthanides other than ce are removed bacteria and fungal hyphae are localized on secondary phosphate surfaces suggesting that rhabdophane and florencite are solubilized in the upper profile due to organic complexation of dissolved lanthanides and or uptake of phosphate by cells in the soils defined by loss of granitic texture secondary phosphates are replaced by ce oxides lanthanides other than ce removed in solution from the upper profile precipitate as ce poor phosphates in the lower profile when the solubility product is exceeded due to high dissolved phosphate concentrations in proximity to apatite thus the upper profile is the source of lanthanides added to the lower profile in both the lower and upper weathered granite the degree to which weight based ce abundances increase with increasing weathering is consistent with ce immobility on the centimeter scale we attribute the very high weight based ce abundances up to 12 concentrations in fresh rock to extensive leaching and compaction during transformation of weathered rock to soil

evidence from central mexico supporting the younger dryas extraterrestrial impact hypothesis we report the discovery in lake cuitzeo in central mexico of a black carbon rich lacustrine layer containing nanodiamonds microspherules and other unusual materials that date to the early younger dryas and are interpreted to result from an extraterrestrial impact these proxies were found in a 27 m long core as part of an interdisciplinary effort to extract a paleoclimate record back through the previous interglacial our attention focused early on an anomalous 10 cm thick carbon rich layer at a depth of 2 8 m that dates to 12 9 ka and coincides with a suite of anomalous coeval environmental and biotic changes independently recognized in other regional lake sequences collectively these changes have produced the most distinctive boundary layer in the late quaternary record this layer contains a diverse abundant assemblage of impact related markers including nanodiamonds carbon spherules and magnetic spherules with rapid melting quenching textures all reaching synchronous peaks immediately beneath a layer containing the largest peak of charcoal in the core analyses by multiple methods demonstrate the presence of three allotropes of nanodiamond n diamond i carbon and hexagonal nanodiamond lonsdaleite in order of estimated relative abundance this nanodiamond rich layer is consistent with the younger dryas boundary layer found at numerous sites across north america greenland and western europe we have examined multiple hypotheses to account for these observations and find the evidence cannot be explained by any known terrestrial mechanism it is however consistent with the younger dryas boundary impact hypothesis postulating a major extraterrestrial impact involving multiple airburst s and and or ground impact s at 12 9 ka

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

delayed hydrological response to greenland cooling at the onset of the younger dryas in western europe during the younger dryas cold event about 12 800 years ago environmental change in western europe seems to occur 170 years after cooling over greenland lake sediment analyses confirm this delay and suggest european hydrological and vegetation change occurred only after the build up of sea ice in the north atlantic pushed the westerly wind system south

woolly mammoth mammuthus primigenius blum and its environment in northern europe during the last glaciation abstract woolly mammoths were large herbivorous cold adapted mammals of the late pleistocene the diet and habitat requirements of the species set certain constraints on the palaeoenvironments it could occupy the relationship between the mammoth s shifting range and changing environments can be explored using independent data on ice sheet configuration temperature and vegetation provided the locality and age of the fossil remains can be validated here we present a comprehensive record of occurrence of the woolly mammoth in the circum baltic region of northern europe during the last glaciation based on a compilation of radiocarbon dated remains the record shows that the mammoth was widespread in northern and north eastern europe during marine isotope stage 3 mis 3 at 50 000 30 000 calibrated years ago 50 30 ka the presence of the species up to 65 n latitude supports the restriction of the scandinavian ice sheet sis during mis 3 the widest distribution range round 30 ka was followed by a decline that led to the disappearance of mammoths from the area during the maximum extent of the sis from 22 to 18 ka the woolly mammoth re colonized the baltic region and southern scandinavia after the onset of the late glacial deglaciation at 17 ka the late glacial record suggests a markedly fluctuating population changing its range in tune with the rapid environmental changes the last appearance of mammoth in our study region was in estonia during the younger dryas greenland stadial 1 gs1 at about 12 ka the two major periods of occurrence during mis 3 and the late glacial stadial suggest that mammoth had a wide tolerance of open to semi open tundra and steppe tundra habitats with intermediately cold climate whereas the 22 18 ka disappearance suggests a major southward and or eastward retreat in response to extremely cold glacial conditions near the sis margin the final regional extinction correlates with the re forestation during the rapid warming at the younger dryas holocene boundary

a stratigraphic framework for abrupt climatic changes during the last glacial period based on three synchronized greenland ice core records refining and extending the intimate event stratigraphy due to their outstanding resolution and well constrained chronologies greenland ice core records provide a master record of past climatic changes throughout the last interglacial glacial cycle in the north atlantic region as part of the intimate integration of ice core marine and terrestrial records project protocols have been proposed to ensure consistent and robust correlation between different records of past climate a key element of these protocols has been the formal definition and ordinal numbering of the sequence of greenland stadials gs and greenland interstadials gi within the most recent glacial period the gs and gi periods are the greenland expressions of the characteristic dansgaard oeschger events that represent cold and warm phases of the north atlantic region respectively we present here a more detailed and extended gs gi template for the whole of the last glacial period it is based on a synchronization of the ngrip grip and gisp2 ice core records that allows the parallel analysis of all three records on a common time scale the boundaries of the gs and gi periods are defined based on a combination of stable oxygen isotope ratios of the ice 18o reflecting mainly local temperature and calcium ion concentrations reflecting mainly atmospheric dust loading measured in the ice the data not only resolve the well known sequence of dansgaard oeschger events that were first defined and numbered in the ice core records more than two decades ago but also better resolve a number of short lived climatic oscillations some defined here for the first time using this revised scheme we propose a consistent approach for discriminating and naming all the significant abrupt climatic events of the last glacial period that are represented in the greenland ice records the final product constitutes an extended and better resolved greenland stratotype sequence against which other proxy records can be compared and correlated it also provides a more secure basis for investigating the dynamics and fundamental causes of these climatic perturbations

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

recommendations for using xrf core scanning as a tool in tephrochronology x ray fluorescence xrf core scanning is a relatively new arrangement of a classic analytical technique which allows for non destructive in situ xrf analysis of sediment cores from submillimetre

high resolution sediment and vegetation responses to younger dryas climate change in varved lake sediments from meerfelder maar germany abstract this work focuses on a 1900 year section of varved sediments from lake meerfelder maar mfm extending from the late allerod to the preboreal varve counting provides the chronological framework and determines the length of younger dryas to 1025 1090 years a strong relation between climate change environment response and depositional processes has been found in consequence varve microfacies variations are a sensitive proxy for environment changes these are reflected for example in erosion processes within the lake s catchment minerogenic input and lake productivity diatom blooms the observed varve changes have been quantified by multiproxy analyses of physical and chemical sediment parameters with a resolution of between 8 and 40 years depending on sedimentation rate in addition high resolution palynological investigations provide the biostratigraphical subdivision based on changes in the vegetation occurring during the same time interval varve observations reveal that environment changes at the beginning and the end of the younger dryas occurred within 20 50 years furthermore sediment and vegetation changes were synchronous within the actual precision of the mfm and grip chronologies divergence of only a few decades terrestrial responses in western europe occurred quasi synchronous to temperature changes in greenland

multiple lines of evidence for possible human population decline settlement reorganization during the early younger dryas three approaches are used to test whether or not human populations across north america were affected by abrupt climate change and or other environmental factors associated with the onset of the younger dryas yd cooling episode at ca 12 900 cal bp they are 1 frequency analyses of paleoindian projectile points from across north america 2 time series of lithic assemblages from eleven paleoindian quarry sites in the southeastern united states and 3 summed probability analyses spa of radiocarbon dates from cultural human related sites across north america and parts of the old world the results of each analysis suggest a significant decline and or reorganization in human population during the early centuries of the yd varying in extent by region archaeological settings formerly heavily utilized such as stone quarries in the southeastern u s appear to have been largely abandoned while over large areas a substantial decline occurred in the numbers of diagnostic projectile points and cultural radiocarbon dates later in the yd beginning after about 12 600 cal bp there was an apparent resurgence in population and or settlements in many areas as indicated by increases in projectile points quarry usage and human related radiocarbon ages

tracing the laacher see tephra in the varved sediment record of the trzechowskie palaeolake in central northern poland abstract tephrochronological studies of partly varved sediments of trzechowskie palaeolake in central northern poland led to the finding of the late allerod laacher see tephra lst from the eifel volcanic field for the first time in a very distal site ca 840 km ene from its volcanic source the detection of glass shards of the lst involved a comprehensive combination of techniques i e biostratigraphical constrains high resolution xrf core scanning and areal xrf mapping of impregnated sediment slabs as well as detailed visual inspection of sediments the major element chemistry of volcanic glass confirmed the laacher see tephra composition in trzechowskie palaeolake sediments suggesting a deposition from the middle laacher see tephra mlst c or upper laacher see tephra ulst dispersal fans the finding of the lst in this palaeolake enables direct synchronisation with other high resolution archives in north central europe i e lake meerfelder maar rehwiese palaeolake to investigate regional variations of environmental responses at the onset of the younger dryas along a west east transect through north central europe

the late quaternary tephrostratigraphy of annually laminated sediments from meerfelder maar germany abstract the record of late quaternary environmental change within the sediments of meerfelder maar in the eifel region of germany is renowned for its high precision chronology which is annually laminated throughout the last glacial to interglacial transition lgit and most of the holocene two visible tephra layers are prominent within the floating varve chronology of meerfelder maar an early holocene tephra layer the ulmener maar tephra 11 000 varve years bp provides a tie line of the meerfelder maar record to the varved holocene record of nearby lake holzmaar the laacher see tephra provides another prominent time marker for the late allerod 200 varve years before the transition into the younger dryas at 12 680 varve years bp further investigation has now shown that there are also 15 cryptotephra layers within the meerfelder maar lgit holocene stratigraphy and these layers hold the potential to make direct comparisons between the meerfelder maar record and other palaeoenvironmental archives from across europe and the north atlantic most notable is the presence of the vedde ash the most widespread icelandic eruption known from the late quaternary which occurred midway through the younger dryas the vedde ash has also been found in the greenland ice cores and can be used as an isochron around which the gicc05 and meerfelder maar annual chronologies can be compared near the base of the annual laminations in meerfelder maar a cryptotephra is found that correlates to the neapolitan yellow tuff erupted from campi flegrei in southern italy 1200 km away this is the furthest north that the neapolitan yellow tuff has been found highlighting its importance in the construction of a european wide tephrostratigraphic framework the co location of cryptotephra layers from italian icelandic and eifel volcanic sources within such a precise chronological record makes meerfelder maar one of the most important tephrostratotype records for continental europe during the last glacial to interglacial transition