cosmic impact event in lake sediments from central europe postdates the laacher see eruption and marks onset of the younger dryas abstractthe younger dryas yd climate episode 12 850 11 650 calendar years before present cal bp is an event recorded widely across the northern hemisphere we conducted multiple analyses at

impact of the late glacial eruption of the laacher see volcano central rhineland germany abstract within a period of a few weeks toward the end of the allerod interstadial the major plinian eruption of the laacher see volcano produced some 20 km3 of eruptiva covering and preserving the late glacial landscape in the german central rhineland over an area of more than 1000 km2 correlation of terrestrial archives with the greenland ice core records and improved calibration of the radiocarbon timescale permit a precise accurate age determination of the laacher see event some 200 yr before the onset of the younger dryas cold episode carbonized trees and botanical macrofossils preserved by laacher see tephra permit detailed regional paleoenvironmental reconstruction and show that open woodland were typical for the cool and humid hemiboreal climatic conditions during the late allerod this woodland provided the habitat for a large variety of animal species documented at both paleontological and final paleolithic archeological sites preserved below laacher see deposits of special interest are numerous animal tracks intercalated in middle laacher see deposits at the south of the neuwied basin this knowledge may help to evaluate possible supraregional impacts of this volcanic event on northern hemispheric environment and climate during the late allerod

very high temperature impact melt products as evidence for cosmic airbursts and impacts 12 900 years ago it has been proposed that fragments of an asteroid or comet impacted earth deposited silica and iron rich microspherules and other proxies across several continents and triggered the younger dryas cooling episode 12 900 years ago although many independent groups have confirmed the impact evidence the hypothesis remains controversial because some groups have failed to do so we examined sediment sequences from 18 dated younger dryas boundary ydb sites across three continents north america europe and asia spanning 12 000 km around nearly one third of the planet all sites display abundant microspherules in the ydb with none or few above and below in addition three sites abu hureyra syria melrose pennsylvania and blackville south carolina display vesicular high temperature siliceous scoria like objects or slos that match the spherules geochemically we compared ydb objects with melt products from a known cosmic impact meteor crater arizona and from the 1945 trinity nuclear airburst in socorro new mexico and found that all of these high energy events produced material that is geochemically and morphologically comparable including i high temperature rapidly quenched microspherules and slos ii corundum mullite and suessite fe3si a rare meteoritic mineral that forms under high temperatures iii melted sio2 glass or lechatelierite with flow textures or schlieren that form at 2 200 c and iv particles with features indicative of high energy interparticle collisions these results are inconsistent with anthropogenic volcanic authigenic and cosmic materials yet consistent with cosmic ejecta supporting the hypothesis of extraterrestrial airbursts impacts 12 900 years ago the wide geographic distribution of slos is consistent with multiple impactors

bayesian chronological analyses consistent with synchronous age of 12 835 12 735 cal b p for younger dryas boundary on four continents the younger dryas impact hypothesis posits that a cosmic impact across much of the northern hemisphere deposited the younger dryas boundary ydb layer containing peak abundances in a variable assemblage of proxies including magnetic and glassy impact related spherules high temperature minerals and melt glass nanodiamonds carbon spherules aciniform carbon platinum and osmium bayesian chronological modeling was applied to 354 dates from 23 stratigraphic sections in 12 countries on four continents to establish a modeled ydb age range for this event of 12 835 12 735 cal b p at 95 probability this range overlaps that of a peak in extraterrestrial platinum in the greenland ice sheet and of the earliest age of the younger dryas climate episode in six proxy records suggesting a causal connection between the ydb impact event and the younger dryas two statistical tests indicate that both modeled and unmodeled ages in the 30 records are consistent with synchronous deposition of the ydb layer within the limits of dating uncertainty 100 y the widespread distribution of the ydb layer suggests that it may serve as a datum layer

vegetation responses to rapid warming and to minor climatic fluctuations during the late glacial interstadial gi 1 at gerzensee switzerland abstract high resolution pollen analyses made on the same samples on which the ratios of oxygen isotopes were measured that provided the time scale and a temperature proxy after correlation to northgrip 1 a primary succession the vegetation responded to the rapid rise of temperatures around 14 685 yr bp with a primary succession on a decadal to centennial time scale the succession between ca 15 600 and 13 000 yr bp included 1 1 the replacement of shrub tundra by woodland of juniperus and tree birch around 14 665 yr bp 1 2 the response of juniperus pollen to the shift in oxygen isotopes in less than 20 yr 1 3 a sequence of population increases of hippophae rhamnoides ca 14 600 yr bp salix spp ca 14 600 yr bp betula trees ca 14 480 yr bp populus cf tremula ca 14 300 yr bp and pinus cf sylvestris ca 13 830 yr bp 2 biological processes plants responded to the rapid increase of summer temperatures on all organisational levels 2 1 individuals may have produced more pollen e g juniperus 2 2 populations increased or decreased e g juniperus betula later pinus and 2 3 populations changed their biogeographical range and may show migrational lags 2 4 plant communities changed in their composition because the species pools changed through immigration and local extinction some plant communities may have been without modern analogue these mechanisms require increasing amounts of time 2 5 processes on the level of ecosystems with species interactions may involve various time scales besides competition and facilitation nitrogen fixation is discussed 3 the minor fluctuations of temperature during the late glacial interstadial which are recorded in 18o resulted in only very minor changes in pollen during the aegelsee oscillation older dryas biozone gi 1d and the gerzensee oscillation gi 1b 4 biodiversity the afforestation at the onset of bolling coincided with a gradual increase of taxonomic diversity up to the time of the major pinus expansion

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

lodestone natures only permanent magnet what it is and how it gets charged magnetite and titanomagnetite exhibit magnetic properties which are attributable to the micro structures developed during oxidation and exsolution all magnetite iron ores which are lodestones contain maghemite these lodestones have hc between 10 and 30 mt sirm between 8 and 18 am kg and ri between 0 10 and 0 26 magnetite titanomagnetite and metals have rem values ratio of nrm to sirm 0 05 samples called fulgarites obtained from the smithsonian institution have rem values ranging from 0 45 to 0 92 the rem value serves as a witness parameter to the magnetic fields associated with the lightning bolt if a high rem value say 0 1 can be verified as not to be due to contamination by man and does not contain md hematite then the rock has lrm lightning remanent magnetization the magnetic field associated with lightning can be revealed from an isothermal remanent acquisition ra curve

radiocarbon simulation fails to support the temporal synchroneity requirement of the younger dryas impact hypothesis fine scale temporal processes such as the synchronous deposition of organic materials can be challenging to identify using 14 c datasets while some events such as volcanic eruptions leave clear evidence for synchronous deposition synchroneity is more difficult to establish for other types of events this has been a source of controversy regarding 14 c dates associated with a hypothesized extraterrestrial impact at the younger dryas boundary ydb to address this controversy we first aggregate 14 c measurements from northern hemisphere ydb sites we also aggregate 14 c measurements associated with a known synchronous event the laacher see volcanic eruption we then use a monte carlo simulation to evaluate the magnitude of variability expected in a 14 c dataset associated with a synchronous event the simulation accounts for measurement error calibration uncertainty old wood effects and laboratory measurement biases the laacher see 14 c dataset is consistent with expectations of synchroneity generated by the simulation however the ydb 14 c dataset is inconsistent with the simulated expectations for synchroneity these results suggest that a central requirement of the younger dryas impact hypothesis synchronous global deposition of a ydb layer is extremely unlikely calling into question the younger dryas impact hypothesis more generally

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

nanodiamonds in the younger dryas boundary sediment layer we report abundant nanodiamonds in sediments dating to 12 9 0 1 thousand calendar years before the present at multiple locations across north america selected area electron diffraction patterns reveal two diamond allotropes in this boundary layer but not above or below that interval cubic diamonds form under high temperature pressure regimes and n diamonds also require extraordinary conditions well outside the range of earth9s typical surficial processes but common to cosmic impacts n diamond concentrations range from 10 to 3700 parts per billion by weight comparable to amounts found in known impact layers these diamonds provide strong evidence for earth9s collision with a rare swarm of carbonaceous chondrites or comets at the onset of the younger dryas cool interval producing multiple airbursts and possible surface impacts with severe repercussions for plants animals and humans in north america

vertical vorticity balance in meanders downstream the agulhas retroflection abstract the agulhas current flows poleward along the western boundary of the southeastern indian ocean where at the southernmost latitude of the african continent it executes a dramatic anticyclonic turn or retroflection to the east since 1978 a large number of drifting buoys have passed through this eastward flowing agulhas return current arc or the zonal frontal boundary between subtropical and subpolar waters of the south indian ocean the spatial distribution of the ensemble averaged near surface velocity along the arc axis reveals a series of steady state meanders of 700 km wavelength and amplitudes that decrease from 170 km in the first meander to 50 km in the following four meanders here an analysis of vorticity balance of the meandering arc speed axis is presented that demonstrates a balance between the term and advection of curvature vorticity this balance implies that the arc axis or frontal region is horizontally nondivergent in agreement with the other observations of flow in t

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

the dakhleh glass product of an impact airburst or cratering event in the western desert of egypt impact cratering is a ubiquitous geological process on the terrestrial planets meteorite impact craters are the most visible product of impact events but there is a growing recognition that large aerial bursts or airbursts should occur relatively frequently throughout geological time in this contribution we report on an unusual impact glass the dakhleh glass dg which is distributed over an area of 400 km 2 of the dakhleh oasis egypt this region preserves a rich history of habitation stretching back to over 400 000 years before the emergence of homo sapiens we report on observations made during recent fieldwork and subsequent analytical analyses that strengthen previous suggestions that the dg formed during an impact event the wide distribution and large size of dg specimens up to 50 cm across the chemistry e g cao and al2o3 contents up to 25 and 18 wt respectively the presence of lechatelierite and burnt sediments and the inclusion of clasts and spherules in the dg is inconsistent with known terrestrial processes of glass formation the age and other textural characteristics rule out a human origin instead we draw upon recent numerical modeling of airbursts to suggest that the properties of dg coupled with the absence of a confirmed crater can best be explained by melting of surficial sediments as a result of a large airburst event we suggest that glass produced by such events should therefore be more common in the rock record than impact craters assuming that the glass formed in a suitable preserving environment

high resolution greenland ice core data show abrupt climate change happens in few years the last two abrupt warmings at the onset of our present warm interglacial period interrupted by the younger dryas cooling event were investigated at high temporal resolution from the north greenland ice core project ice core the deuterium excess a proxy of greenland precipitation moisture source switched mode within 1 to 3 years over these transitions and initiated a more gradual change over 50 years of the greenland air temperature as recorded by stable water isotopes the onsets of both abrupt greenland warmings were slightly preceded by decreasing greenland dust deposition reflecting the wetting of asian deserts a northern shift of the intertropical convergence zone could be the trigger of these abrupt shifts of northern hemisphere atmospheric circulation resulting in changes of 2 to 4 kelvin in greenland moisture source temperature from one year to the next

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

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

environmental impact of the laacher see eruption at a large distance from the volcano integrated palaeoecological studies from vorpommern ne germany abstract in order to investigate the environmental impacts of the laacher see eruption 12 900 calendar years b p and the deposition of the laacher see tephra at a large distance from the volcano fine resolution micromorphological diatomological and palynological investigations were carried out on closely spaced areas in the reinberg basin vorpommern ne germany the lower part of the lst originates from atmospheric input whereas the upper part was washed in from the surrounding basin slopes diatom populations expanded as a consequence of the input of silica while simultaneously dissolution of dead diatoms decreased the tephra provided a favourable habitat for many epilithic and epipelic diatom taxa the diatoms show a slight acidification and an increase in specific conductivity of the water whereas no eutrophication is indicated these effects disappeared after lake sediments covered the tephra the pollen diagrams from the reinberg basin as well as many other pollen diagrams from ne germany indicate that the vegetation reacted to rising temperatures after the cooler gerzensee fluctuation to a short lived water level rise connected with higher precipitation after the volcanic eruption and to minor openings in the forest vegetation due to increased fire probably connected with severe thunderstorms

eifel maars quantitative shape characterization of juvenile ash particles eifel volcanic field germany abstract the eifel region in western central germany is the type locality for maar volcanism which is classically interpreted to be the result of explosive eruptions due to shallow interaction between magma and external water i e phreatomagmatic eruptions sedimentary structures deposit features and particle morphology found in many maar deposits of the west eifel volcanic field wevf in contrast to deposits in the east eifel volcanic field eevf lack the diagnostic criteria of typical phreatomagmatic deposits the aim of this study was to determine quantitatively the shape of wevf and eevf maar ash particles in order to infer the governing eruption style in eifel maar volcanoes the quantitative shape characterization was done by analyzing fractal dimensions of particle contours 125 250 m sieve fraction obtained from scanning electron microscopy sem and sem micro computed tomography sem micro ct images the fractal analysis dilation method and the fractal spectrum technique confirmed that the wevf and eevf maar particles have contrasting multifractal shapes whereas the low small scale dimensions of eevf particles eppelsberg green unit coincide with previously published values for phreatomagmatic particles the wevf particles meerfelder maar pulvermaar and ulmener maar have larger values indicating more complex small scale features which are characteristic for magmatic particles these quantitative results are strengthening the qualitative microscopic observations that the studied wevf maar eruptions are rather dominated by magmatic processes the different eruption styles in the two volcanic fields can be explained by the different geological and hydrological settings found in both regions and the different chemical compositions of the magmas

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

high resolution late glacial chronology for the gerzensee lake record switzerland δ18o correlation between a gerzensee stack and ngrip oxygen isotope variations were analyzed on bulk samples of shallow water lake marl from gerzensee switzerland in order to evaluate major and minor climatic oscillations during the late glacial to highlight the overall signature of the gerzensee 18o record 18o records of four parallel sediment cores were first correlated by synchronizing major isotope shifts and pollen abundances then the records were stacked with a weighting depending on the differing sampling resolution to develop a precise chronology the 18o stack was then correlated with the ngrip 18o record applying a monte carlo simulation relying on the assumption that the shifts in 18o were climate driven and synchronous in both archives the established chronology on the gicc05 time scale is the basis for 1 comparing the 18o changes recorded in gerzensee with observed climatic and environmental fluctuations over the whole north atlantic region and 2 comparing sedimentological and biological changes during the rapid warming with smaller climatic variations during the bolling allerod period the 18o record of gerzensee is characterized by two major isotope shifts at the onset and at the termination of the bolling allerod warm period as well as four intervening negative shifts labeled gi 1e2 d c2 and b which show a shift of one third to one fourth of the major 18o shifts at the beginning and end of the bolling allerod despite some inconsistency in terminology these oscillations can be observed in various climatic proxies over wide regions in the north atlantic region especially in reconstructed colder temperatures and they seem to be caused by hemispheric climatic variations

size limits for rounding of volcanic ash particles heated by lightning volcanic ash particles can be remelted by the high temperatures induced in volcanic lightning discharges the molten particles can round under surface tension then quench to produce glass spheres melting and rounding timescales for volcanic materials are strongly dependent on heating duration and peak temperature and are shorter for small particles than for large particles therefore the size distribution of glass spheres recovered from ash deposits potentially record the short duration high temperature conditions of volcanic lightning discharges which are hard to measure directly we use a 1 d numerical solution to the heat equation to determine the timescales of heating and cooling of volcanic particles during and after rapid heating and compare these with the capillary timescale for rounding an angular particle we define dimensionless parameters capillary fourier stark biot and peclet numbers to characterize the competition between heat transfer within the particle heat transfer at the particle rim and capillary motion for particles of different sizes we apply this framework to the lightning case and constrain a maximum size for ash particles susceptible to surface tension driven rounding as a function of lightning temperature and duration and ash properties the size limit agrees well with maximum sizes of glass spheres found in volcanic ash that has been subjected to lightning or experimental discharges demonstrating that the approach that we develop can be used to obtain a first order estimate of lightning conditions in volcanic plumes

gradual onset of anoxia across the permian triassic boundary in svalbard norway the permian triassic extinction event is considered to be the most devastating environmental crisis of the phanerozoic with many coinciding factors involved the role of marine anoxia during the extinction is still poorly understood in this study a boreal permian triassic boundary ptb section from svalbard norway has been investigated with the aim of better understanding the timing and nature of local marine anoxia onset and extinction events across the ptb the section comprises the kapp starostin and vikinghogda formations 13corg values indicate the ptb is located within the lower part of the vikinghogda formation lag deposits at the top of the kapp starostin formation indicate a marine hiatus and ensuing transgression during the late permian shortly before the extinction event implying concurrence of major ecological changes and sea level rise pyrite framboid size distributions and total organic carbon toc were used to evaluate bottom water oxygen conditions and show that changes in bottom water redox conditions and extinction are clearly linked oxic to dysoxic bottom water conditions prevailed during deposition of kapp starostin formation sediments and changed to anoxic to euxinic conditions above the formation boundary the onset of anoxia is not abrupt but rather shows a gradual increase within the kapp starostin formation during the late permian the tipping point where bottom waters reach a long term state of anoxia to euxinia coincides with the final extinction event though changes in biotic assemblages at the top of the kapp starostin formation indicate a marine ecosystem crisis prior to this oxygen depletion in the boreal region as seen in our study section and correlating to greenland and arctic canada seems to be consistently more severe than in lower latitude settings

the impact of regional uplift of the tibetan plateau on the asian monsoon climate abstract the climatic effect of tibetan plateau tp uplift is a hot topic in paleoclimate research in this paper the results of a set of numerical simulations are reported to analyze the impact of regional tp uplift on the asian monsoon climate the focus is on the impact of the regional uplift in the west and east parts on south asian summer monsoon as well as the impact of regional uplift on east asian winter monsoon the results show that the uplifts of the himalaya and the central southern tp have little effect on summer precipitation increasing over south asia whereas the further uplifts of the tp in the west and east parts including the uplifts of both the eastern and western tp have important effects on the strengthening of the south asian summer monsoon the uplift of the eastern tp leads to low level cyclonic circulation anomalies appearing in the bay of bengal accompanied by anomalous upward movement and in turn precipitation markedly increases in the bay of bengal whereas the uplift of the western tp produces low level cyclonic circulation anomalies around the uplifted region and intensifies the moisture transport from the tropical ocean and thus precipitation further increases in south asia especially in the northern arabian sea the strengthened summer monsoon in south asia is coupled with the intensification in diabatic heating and moisture convergence for the east asian winter monsoon the intensification of winter monsoon winds is related more to the regional uplifts than the uplift of the whole tp the uplifts of the central southern tp the northern tp and other northern topography have greater effects on the strengthening of the winter monsoon winds

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

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