environmental perturbations caused by the impacts of asteroids and comets we review the major impact associated mechanisms proposed to cause extinctions at the cretaceous tertiary geological boundary we then discuss how the proposed extinction mechanisms may relate to the environmental consequences of asteroid and comet impacts in general our chief goal is to provide relatively simple prescriptions for evaluating the importance of impacting objects over a range of energies and compositions but we also stress that there are many uncertainties we conclude that impacts with energies less than about 10 mt are a negligible hazard for impacts with energies above 10 mt and below about 104 mt i e impact frequencies less than one in 6 104 years corresponding to comets and asteroids with diameters smaller than about 400 m and 650 m respectively blast damage earthquakes and fires should be important on a scale of 104 or 105 km which corresponds to the area damaged in many natural disasters of recent history however tsunami excited by marine impacts could be more damaging flooding a kilometer of coastal plain over entire ocean basins in the energy range of 104 105 mt intervals up to 3 105 years corresponding to comets and asteroids with diameters up to 850 m and 1 4 km respectively water vapor injections and ozone loss become significant on the global scale in our nominal model such an impact does not inject enough submicrometer dust into the stratosphere to produce major adverse effects but if a higher fraction of pulverized rock than we think likely reaches the stratosphere stratospheric dust causing global cooling would also be important in this energy range thus 105 mt is a lower limit where damage might occur beyond the experience of human history the energy range from 105 to 106 mt intervals up to 2 106 years corresponding to comets and asteroids up to 1 8 and 3 km diameter is transitional between regional and global effects stratospheric dust sulfates released from within impacting asteroids and soot from extensive wild fires sparked by thermal radiation from the impact can produce climatologically significant global optical depths of the order of 10 moreover the ejecta plumes of these impacts may produce enough no from shock heated air to destroy the ozone shield between 106 and 107 mt intervals up to 1 5 107 years corresponding to comets and asteroids up to 4 and 6 5 km diameter dust and sulfate levels would be high enough to reduce light levels below those necessary for photosynthesis ballistic ejecta reentering the atmosphere as shooting stars would set fires over regions exceeding 107 km and the resulting smoke would reduce light levels even further at energies above 107 mt blast and earthquake damage reach the regional scale 106 km tsunami cresting to 100 m and flooding 20 km inland could sweep the coastal zones of one of the world s ocean basins fires would be set globally light levels may drop so low from the smoke dust and sulfate as to make vision impossible at energies approaching 109 mt 108 years the ocean surface waters may be acidified globally by sulfur from the interiors of comets and asteroids the cretaceous tertiary impact in particular struck evaporate substrates that very likely generated a dense widespread sulfate aerosol layer with consequent climatic effects the combination of all of these physical effects would surely represent a devastating stress on the global biosphere

fireball passes and nothing burns the role of thermal radiation in the cretaceous tertiary event evidence from the charcoal record of north america high soot contents have been reported in cretaceous tertiary k t sedimentary rocks leading to the suggestion that the amount of thermal power delivered from the chicxulub impact was sufficient to have ignited wildfires soot cannot be used to indicate fire location however as soot from one large fire could spread globally sources other than biomass burning could also yield soot charcoal in nonmarine sedimentary rocks here quantified in situ in polished blocks provides a unique tool to record the distribution of wildfires and therefore assess the extent of any thermal radiation associated with the impact at chicxulub the k t and lowermost tertiary sedimentary rocks of six nonmarine sequences colorado to saskatchewan contain no charcoal or below background levels of charcoal and a significant quantity of noncharred organic materials revealing that there was no distinctive wildfire across the north american continent related to the k t event this finding indicates that the k t impact cannot have delivered a peak irradiance of 95 kw m 2 of thermal power to the atmosphere and 19 kw m 2 to the ground therefore the thermal power delivered from the impact to north america did not have the destructive potential previously predicted high amounts of thermal radiation were not responsible for the environmental perturbations or extinctions associated with the k t event

the global stratigraphy of the cretaceous tertiary boundary impact ejecta the chicxulub crater ejecta stratigraphy is reviewed in the context of the stratigraphy of underlying and overlying rock sequences the ejecta sequence is regionally grouped in a thick polymict and monomict breccia sequences inside the crater and within 300 km from the rim of the crater known from drill holes in and close to the breater and exposures near the border of yucatan and belize b gulf of mexico region 2500 m from the crater with up to 9 m thick complex tsunami wave influenced tektite bearing sequences in shallow marine 500 m deep environments and tektite bearing decimeter thick gravity flow deposits in deep water sites c an intermediate region between 2500 and 4000 km from the crater where centimeter thick tektite bearing layers occur and d a global distal region with a millimeter thin ejecta layer the distal ejecta layer is characterized by sub millimeter sized microkrystites often rich in ni rich spinels and altered clinopyroxene wherever present the ejecta layers mark exactly the sudden mass mortality horizon of the k t boundary what exactly caused the mass mortality is still uncertain but it appears the main event leading to the k t mass extinctions

constraints on the thermal energy released from the chicxulub impactor new evidence from multi method charcoal analysis it has been suggested by various workers that an extraterrestrial impact at the k t boundary delivered sufficient thermal power to ignite globally extensive wildfires numerous models have sought to predict the amount of thermal power released by the impact but none have considered the distribution of wildfire indicators in k t rocks probably the most distinctive product from combustion of biomass is charcoal the abundance of charcoal across the k t boundary at eight non marine sites in north america stretching from colorado in the south to saskatchewan in the north is recorded using three separate methods that allow quantitative analyses of microscopic to macroscopic charcoal particles this study not only provides the first extensive study of charcoals across the k t boundary but also uses the presence or absence of charred material to predict the extent and severity of the thermal pulse released by the k t impact across the area predicted to have suffered the most extreme environmental effects the k t rocks contain on average between four and eight times according to the method used less charcoal than the cretaceous rock record and non charred plant remains are abundant in the k t rocks the below background charcoal abundance and the high proportion of noncharred material in the k t and lowermost tertiary rocks across the western interior of north america suggest that there were no significant wildfires in this area associated with the k t event although soot and polyaromatic hydrocarbons pahs have been reported in the k t rocks we suggest that the soot morphology and pah types are more consistent with a source from the vaporization of hydrocarbons rather than biomass for spontaneous ignition of vegetation temperatures 545 c are necessary whereas smouldering will begin at 325 c the below background levels of charcoal in the k t rocks allow the ground temperatures following the k t impact to be constrained to between no more than 545 c at any point and not above 325 c for any significant period this implies a maximum irradiance of 2 at the ground surface and that no more than 6 kw m 2 of thermal power was delivered to the ground for more than a few hours therefore our results show that the fossil record indicates that the impact at chixculub did not generate sufficient thermal power to ignite extensive wildfires

ocean and atmosphere storm tracks the role of eddy vorticity forcing abstract signatures of eddy variability and vorticity forcing are diagnosed in the atmosphere and ocean from weather center reanalysis and altimetric data broadly covering the same period 1992 2002 in the atmosphere there are localized regions of eddy variability referred to as storm tracks at the entrance of the storm track the eddies grow providing a downgradient heat flux and accelerating the mean flow eastward at the exit and downstream of the storm track the eddies decay and instead provide a westward acceleration in the ocean there are similar regions of enhanced eddy variability along the extension of midlatitude boundary currents and the antarctic circumpolar current within these regions of high eddy kinetic energy there are more localized signals of high eady growth rate and downgradient eddy heat fluxes as in the atmosphere there are localized regions in the southern ocean where ocean eddies provide statistically significant vorticity forcing which acts to accelerate the mean flow

biostratigraphy of the last glacial period in europe the european early weichselian early wurmian is characterized by two long and relatively warm interstadials brorup and odderade which can be traced and correlated with certainty across large parts of europe the amersfoort interstadial described earlier from the netherlands has been included in the brorup and represents the older part of it both great interstadials were forested in north west central and southern europe in the north conifer forests prevailed giving way towards the south to deciduous forests the climatic gradient was distinctly steeper mainly due to southward displacement of the gulf stream the two great interstadials are synchronous with the isotopic stages 5a and 5c in the deep sea cores subsequent to eemian brorup and odderade and from within the context of a continuous series two additional and clearly delimited interstadials have been recorded in a new standard profile from oerel nw germany these are now described as the oerel and glinde interstadials they were not forested and belong to the early pleni weichselian the lower one oerel can probably be correlated with the 3rd weichselian wurmian interstadial in southern central europe ognon ii durnten samerberg 3 while the upper one glinde has so far no known counterpart for the younger pleni glacial it is assumed that there was a long phase during which it was not too cold the formation of humic layers during this phase took place at different times partly due to local edaphic factors so that the relevant 14c dates show a wide scatter the hengelo and denekamp interstadials represent only slight ameliorations which facilitated the formation of shrub tundra and can be recorded in certain regions only

a guide to stratigraphical procedure the continuing development of stratigraphical concepts and the application of new methods has led the stratigraphy committee of the geological society of london to present a new guide to stratigraphical procedure some of the principal types of stratigraphy are outlined and guidelines and recommendations are given on procedure practice and terminological usage

paleoatmospheric pco2 fluctuations across the cretaceous tertiary boundary recorded from paleosol carbonates in ne china abstract a dramatic change in atmospheric composition has been postulated because of global carbon cycle disruption during the cretaceous k tertiary t transition following the chicxulub impact and deccan trap eruptions here pedogenic carbonates were collected from drill core of a borehole sk 1 n straddling the late cretaceous and early paleocene strata in the songliao basin northeast china to reconstruct atmospheric co 2 concentrations using a paleosol paleobarometer our estimates for atmospheric pco 2 from paleosol carbonates range between 277 115 ppmv and 837 164 ppmv between 67 8 ma and 63 1 ma one large 66 65 5 ma and several small co 2 spikes 64 7 64 2 ma during the latest maastrichtian to earliest danian are reported here and incorporated with previously published pco 2 estimates also estimated from paleosol carbonates these co 2 spikes are attributed to one million year long emplacement of the large deccan flood basalts along with the extraterrestrial impact at the k t boundary

atmospheric radiocarbon calibration to 45 000 yr b p late glacial fluctuations and cosmogenic isotope production more than 250 carbon 14 accelerator mass spectrometry dates of terrestrial macrofossils from annually laminated sediments from lake suigetsu japan provide a first atmospheric calibration for almost the total range of the radiocarbon method 45 000 years before the present the results confirm the recently revised floating german pine chronology and are consistent with data from european and marine varved sediments and combined uranium thorium and carbon 14 dating of corals up to the last glacial maximum the data during the glacial show large fluctuations in the atmospheric carbon 14 content related to changes in global environment and in cosmogenic isotope production

major ice sheet response in eastern new england to a cold north atlantic region ca 16 15 cal ka bp a large ice sheet still covered almost all of maine and eastern new england until ca 15 cal ka bp reaching south of 45 s despite rising summer insolation intensity and major ice recession elsewhere outside the north atlantic region furthermore the well studied moraine belt along eastern coastal maine including the prominent pineo ridge delta moraine complex and pond ridge moraine indicates repeated readvances and stillstands between ca 16 and 15 cal ka bp this moraine belt reflects a considerable ice sheet response over eastern north america during this time period coeval with the latter half of the european oldest dryas period moraine deposition was concurrent with reduction or elimination of north atlantic meridional overturning starting with the earlier onset of peak ird and heinrich event 1 he 1 the existing 14 c chronology suggests that the coastal moraine belt and the persistence of the ice sheet until 15 cal ka bp was a response to the severe cooling of the north atlantic region after 17 cal ka bp 2007 university of washington all rights reserved

a midge based late glacial temperature reconstruction from southwestern nova scotia we present a quantitative reconstruction of the thermal regime spanning the late glacial period of nova scotia 14 700 to 11 600 bp as inferred by analyzing fossil midges from a small lake lac a magie in southwestern nova scotia the gs 1 event equivalent to the younger dryas dating from 12 700 to 11 600 bp in maritime canada was marked by a 5 c decline in inferred mean july surface water temperatures and a 15 drop in organic content previous pollen and plant macrofossil analyses of this site demonstrate a response of vegetation to gs 1 cooling these data coupled with a midge inferred temperature reconstruction from a nearby site suggest that late glacial climate change was less pronounced in southern nova scotia than in other sites in maritime canada and adjacent eastern north america

propagation of kuroshio extension meanders between 143 and 149 e a two dimensional array of current and pressure recording inverted echo sounders provided synoptic measurements of the upper and deep fluctuations in the kuroshio extension between 1438 and 1498e with mesoscale resolution downstream propagating meanders with periods of 3 60 days were always present between june 2004 and september 2005 propagation speeds were estimated by two methods spectral analysis of path displacements and complex empirical orthogonal functions ceof analysis of along path anomalies the two methods produced similar results phase speeds increased smoothly from 10 km day 21 0 12 m s 21 for meanders with wavelengths and periods l t 5 420 km 40 days to 35 km day 21 0 41 m s 21 for l t 5 220 km 6 days meanders this empirically derived dispersion relationship is indistinguishable from that obtained for gulf stream meanders downstream of cape hatteras the deep ocean was populated with remotely generated upstream propagating eddies composed of a nearly depthindependent current structure upper meandersand deep eddies jointly spun up when they encountered each other with the deep eddy offset about a quarter wavelengthahead of the upper meander subsequently as the upper and deep features moved past each other and the vertical offset changed intensification ceased

electrical conductivity measurements from the gisp2 and grip greenland ice cores the direct current electrical conductivity of glacial ice depends on its acidity1 3 and can also indicate changes in climate as ice formed in cold dusty periods has a high concentration of alkaline dust1 4 5 which significantly reduces the conductivity6 7 compared to warmer less dusty periods here we present electrical conductivity records for the greenland ice sheet project 2 gisp2 and greenland ice core project grip ice cores drilled 28 km apart to enable direct comparison of the results the upper parts of both records are consistent with previous evidence from other greenland cores4 8 12 for a stable greenland climate during the holocene and a series of warm events punctuating the last glacial period however there is a significant discrepancy between the two records in the bottom 10 of the cores calling into question recent reports of climate variability in the last interglacial4 8 and the penultimate glaciation8 at this stage it is too early to say what exactly is causing the discrepancy although ice flow may have introduced some discontinuities into the records further work will be necessary to establish how much climatic information it will eventually be possible to extract from the lower parts of the two cores

the chicxulub asteroid impact and mass extinction at the cretaceous paleogene boundary the cretaceous paleogene boundary similar to 65 5 million years ago marks one of the three largest mass extinctions in the past 500 million years the extinction event coincided with a large asteroid impact at chicxulub mexico and occurred within the time of deccan flood basalt volcanism in india here we synthesize records of the global stratigraphy across this boundary to assess the proposed causes of the mass extinction notably a single ejecta rich deposit compositionally linked to the chicxulub impact is globally distributed at the cretaceous paleogene boundary the temporal match between the ejecta layer and the onset of the extinctions and the agreement of ecological patterns in the fossil record with modeled environmental perturbations for example darkness and cooling lead us to conclude that the chicxulub impact triggered the mass extinction

gulf stream meander propagation past cape hatteras the propagation and growth characteristics of gulf stream meanders past the stream s separation point at cape hatteras are analyzed using yearlong time series from a mooring program sponsored by the minerals management service which included moorings imbedded in the gulf stream cyclonic flank both upstream south and downstream north of cape hatteras in the upstream region energetic meanders of 3 8 day period 180 380 km wavelength propagate downstream along the gulf stream at speeds of 40 55 km day 21 this variability decays almost completely across the gulf stream separation with growth in lower frequency variability 30 120 day in the downstream direction wavelength and phase speed in the 3 8 day band are strong functions of frequency with increasing phase speed for increasing wavenumber phase speeds upstream from cape hatteras and across the gulf stream separation point are faster for a given wavenumber than downstream from cape hatteras in keeping with prior published estimates at the upstream end of the study site both baroclinic and barotropic mechanisms contribute to the decay of 3 8 day meanders and growth of lower frequency 30 120day variability in the downstream direction at the downstream end of the study region the reverse holds with both baroclinic and barotropic mechanisms contributing to growth of 3 8 day meanders and decay of lowerfrequency 30 120 day variability

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

k pg extinction reevaluation of the heat fire hypothesis 1 the global debris layer created by the end cretaceous impact at chicxulub contained enough soot to indicate that the entire terrestrial biosphere had burned preliminary modeling showed that the reentry of ejecta would have caused a global infrared ir pulse sufficient to ignite global fires within a few hours of the chicxulub impact this heat pulse and subsequent fires explain the terrestrial survival patterns in the earliest paleocene because all the surviving species were plausibly able to take shelter from heat and fire underground or in water however new models of the global ir heat pulse as well as the absence of charcoal and the presence of noncharred organic matter have been said to be inconsistent with the idea of global fires that could have caused the extinctions it was suggested that the soot in the debris layer originated from the impact site itself because the morphology of the soot the chain length of polycyclic aromatic hydrocarbons and the presence of carbon cenospheres were said to be inconsistent with burning the terrestrial biosphere these assertions either are incorrect or have alternate explanations that are consistent with global firestorms we show that the apparent charcoal depletion in the cretaceous paleogene layer has been misinterpreted due to the failure to correct properly for sediment deposition rates we also show that the mass of soot potentially released from the impact site is far too low to supply the observed soot however global firestorms are consistent with both data and physical modeling

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

modeling the formation of the k pg boundary layer abstract in this paper we investigate the formation of the cretaceous paleogene k pg boundary layer through numerical modeling the k pg layer is widely agreed to be composed of meteoritic material and target rock from the chicxulub impact site that has been ejected around the globe and mixed with local material during final deposition the observed composition and thickness of the k pg boundary layer changes with azimuth and distance from the impact site we have run a suite of numerical simulations to investigate whether we can replicate the observational data with a focus on the distal k pg layer and the impact glasses at proximal sites such as beloc haiti previous models of the k pg ejecta have assumed an initial velocity distribution and tracked the ejecta to its final destination here we attempt to model the entire process from impact to the arrival of the ejecta around the globe our models replicate the observed ejecta thickness at proximal sites and the modeled ejecta is composed of sediments and silicate basement rocks in agreement with observational data models that use a 45 impact angle are able to replicate the total ejecta and iridium volume at distal sites and the majority of the ejecta is composed of meteorite and target sediments sub vertical impacts generate too little iridium and oblique impacts of 30 degrees generate too much however in contrast to observations models that involve ballistic transport of ejecta lead to ejecta thickness decreasing with increasing distance and are unable to transport shocked minerals quartz and zircon from the chicxulub basement rocks around the globe we suggest that much of the k pg ejecta is transported non ballistically and that the most plausible mechanism is through re distribution from a hot expanding atmosphere the results are important for future investigations of the environmental effects of the chicxulub impact

short term climate changes during the last glacial holocene transition comparison between mediterranean records and the grip event stratigraphy this paper presents biostratigraphical and stable isotope data obtained from core cm92 43 which was recovered from the central adriatic as part of a comprehensive investigation of the palaeoenvironmental history of the basin the data span the period of the last glacial holocene lg h transition ca 18000 to 8000 grip ice core yr bp regional biozones are defined on the basis of characteristic assemblages of planktic foraminifera and these are compared with other foraminiferal biostratigraphical schemes from the southern adriatic and the tyrrhenian sea variations in relative abundance of selected planktic foraminifera and in selected pollen types are shown alongside variations in 18o and 13c obtained from globigerina bulloides and relative abundance of globigerinoides ex gr ruber the data are compared with the grip ice core record and the event stratigraphy scheme based on this record and it is concluded that the climate forcing mechanisms that controlled climate variations in the north atlantic region during the lg h transition also extended their influence into the mediterranean region over the same period copyright 1999 john wiley sons ltd

propagation of gulf stream meanders between 74 and 70 w abstract positions of the gulf stream path from 74 to 45 w were obtained from satellite infrared images for the period of april 1982 december 1989 the propagation of meanders between 74 and 70 w was studied through spectral analysis in wavenumber frequency space empirical orthogonal function analysis in time and frequency domains and direct measurements of individual meander properties progressive meanders are found to have a broad range of periods from days to years and wavelengths from about 200 to 1100 km good agreement is found between the satellite and inverted echo sounder data for short period 80 days progressive propagation retrogressive meanders with wavelengths longer than 1100 km are found to coexist with progressive ones at periods longer than 4 months the empirical dispersion relation is in qualitative agreement with the linear prediction of a recent equivalent barotropic plane thin jet model the comparison also suggests that topographic may need to be considered in order to

high resolution climate signals in the bolling allerod interstadial greenland interstadial 1 as reflected in european tree ring chronologies compared to marine varves and ice core records abstract lateglacial and holocene tree ring chronologies are unique archives which provide various information on past environments on a true annual time scale changes in ring width can be related to past climate anomalies and dendrodated wood provides an ideal source for radiocarbon calibration we present a 1051 year tree ring chronology from the late glacial built from subfossil scots pines pinus sylvestris that grew in different regions of central and southern europe through a series of high precision radiocarbon measurements we obtained a floating radiocarbon chronology which allowed accurate wiggle matching to the intcal98 calibration curve the trees show a coherent pattern in ring width variations throughout central europe and extending into the mediterranean which indicates a strong external climatic factor most probably temperature during the growing season we identified major growth events which appear synchronous with events seen in isotopic and tracer signals in the greenland ice cores and with changes in the strength of upwelling in the cariaco basin

revisiting wildfires at the k pg boundary 1 the discovery of large amounts of soot in clays deposited at the cretaceous paleogene k pg boundary and linked to the 65 ma chicxulub impact crater led to the hypothesis that major wildfires were a consequence of the asteroid impact subsequently several lines of evidence including the lack of charcoal in north american sites were used to argue against global wildfires close to the impact site fires are likely to be directly ignited by the impact fireball whereas globally they could be ignited by radiation from the reentry of hypervelocity ejecta to date models of the latter have yet to take into account that ejection and thus the emission of thermal radiation is asymmetric and dependent on impact angle here we model 1 the impact and ejection of material 2 the ballistic continuation of ejecta around a spherical earth and 3 the thermal pulse delivered to the earth s surface when ejecta reenters the atmosphere we find that thermal pulses in the downrange direction are sufficient to ignite flora several thousand kilometers from chicxulub whereas pulses at most sites in the uprange direction are too low to ignite even the most susceptible plant matter our analyses and models suggest some fires were ignited by the impact fireball and ejecta reentry but that the nonuniform distribution of thermal radiation across the surface of the earth is inconsistent with the ignition of fires globally as a direct and immediate result of the chicxulub impact instead we propose that the desiccation of flora by ejecta reentry as well as the effects of postimpact global cooling darkness left much of the terrestrial flora prone to fires and that the volume of soot in the global k pg layer is explained by a combination of syn and postimpact wildfires

geophysical characterization of the chicxulub impact crater 1 geophysical data indicate that the 65 5 million years ago chicxulub impact structure is a multi ring basin with three sets of semicontinuous arcuate ring faults and a topographic peak ring pr slump blocks define a terrace zone which steps down from the inner rim into the annular trough fault blocks underlie the pr which exhibits variable relief due to target asymmetries the central structural uplift is 10 km and the moho is displaced by 1 2 km the working hypothesis for the formation of chicxulub is a 50 km radius transient cavity lined with melt and impact breccia formed within 10 s of the impact and within minutes weakened rebounding crust rose kilometers above the surface the transient crater rim underwent localized deformation and collapsed into large slump blocks resulting in a inner rim at 70 85 km radius and outer ring faults at 70 130 km radius the overheightened structural uplift collapsed outward buried the inner slump blocks and formed the pr most of the impact melt was ultimately emplaced as a coherent 3 km thick melt sheet within the central basin that shallows within the inner regions of the pr smaller pockets of melt flowed into the annular trough subsequently slope collapse ejecta ground surge and tsunami waves infilled the annular trough and annular basin with sediments up to 3 km and 900 m thick respectively testing this working hypothesis requires direct observation of the impactites within and adjacent to the pr and central basin

low frequency variability in the midlatitude atmosphere induced by an oceanic thermal front abstract this study examines the flow induced in a highly idealized atmospheric model by an east west oriented oceanic thermal front the model has a linear marine boundary layer coupled to a quasigeostrophic equivalent barotropic free atmosphere the vertical velocity at the top of the boundary layer drives the flow in the free atmosphere and produces an eastward jet parallel to the oceanic front s isotherms a large gyre develops on either side of this jet cyclonic to the north and anticyclonic to the south of it as the jet intensifies during spinup from rest it becomes unstable the most unstable wave has a length of about 500 km it evolves into a meander and eddies detach from the eastern edge of each gyre the dependence of the atmospheric dynamics on the strength t of the oceanic front is studied the gulf stream and kuroshio fronts correspond roughly in the scaling used here to t 7 c for weak fronts t 4 c the circulation is steady and exhibits two large antisymmetric gyres sepa

survival in the first hours of the cenozoic for several hours following the chicxulub impact the entire earth was bathed with intense infrared radiation from ballistically reentering ejecta the global heat pulse would have killed unsheltered organisms directly and ignited fires at places where adequate fuel was available sheltering underground within natural cavities or in water would have been a necessary but not always sufficient condition for survival survival through sheltering from an initial thermal pulse is not adequately considered in literature about cretaceous tertiary nonmarine extinctions we compare predicted intense short term thermal effects with what is known about the fossil record of nonmarine vertebrates and suggest that paleontological evidence of survival is compatible with theoretical results from bolide physics

relationship between impact crater size and severity of related extinction episodes abstract how large must an extraterrestrial impact be to cause a peak episode of increased extinctions of life impact energies 3 107 mt tnt associated with terrestrial impact craters with final diameters 100 km seem to be required to generate significant widespread climatic effects from sub micron dust and soot in the atmosphere leading to a distinct extinction episode 15 extinction of marine genera impacts creating craters smaller than 100 km in final diameter in the 106 to 107 mt tnt range are capable of mostly regional destruction with minimal impact on global climate or biota these results are supported by the fact that the ages of the four known 100 km diameter craters of the last 260 my popigai chicxulub morokweng and manicouagan are all correlative with times of documented extinction episodes whereas smaller craters are not the largest crater the 180 km diameter chicxulub crater a 108 mt tnt event is associated with the more severe major mass extinction event 45 extinction of genera at the end of the cretaceous the percent species extinctions show a significant linear relationship with final crater diameter and impact energy the very large chicxulub impact lies close to the predicted curve of percent extinction versus impact crater diameter and energy but the low angle of impact an unusual composition of the target area with thick sediments rich in carbonates sulfates and organic material and a large excavated transient crater may have led to the generation of unusually large amounts of co2 widely distributed dust soot and sulfate aerosols and a uniquely severe impact related environmental disaster chicxulub may thus be the only large body impact associated with a major mass extinction in the phanerozoic target sensitivity may apply to large impacts into ocean crust having only a thin cover of organic poor and carbonate poor pelagic sediments and thus even large oceanic impacts which are still unknown may not produce enough dust soot and aerosols to cause environmental crises leading to global extinction peaks above background levels

the preboreal oscillation around the nordic seas terrestrial and lacustrine responses the occurrence of an early preboreal climatic cooling oscillation pbo in lacustrine and glacial records from northwest europe iceland and greenland is reviewed and documented the often subtle response of the proxy records to this oscillation in combination with its short duration make it difficult to detect owing to its chronostratigraphic position between the 10 000 9900 and 9600 9500 14 c plateaux c 11 300 11 150 calendar yr bp it is also difficult to 14 c date with precision we find that the vegetation response to the pbo varies between sites and regions in contrast to the pioneer vegetation in iceland and southern sweden the expanding birch pine forest in germany denmark was more susceptible to deteriorating growing conditions the combined lacustrine tree ring and glacial records imply that the pbo was characterised by cool and humid conditions throughout northwestern and central europe this is documented by vegetation changes decreased aquatic production increased soil erosion increased 2 h and 13 c content in tree rings readvances or stillstands of the ice sheet in norway and finland and ingression of brackish water into the baltic icelandic proxy records from lake sediments and glacial moraines imply cooler conditions than during the previous preboreal period but not as extreme as during the younger dryas greenland records suggest that the early preboreal was characterised by ice readvances as an effect of cool climate and increased precipitation in relation to the younger dryas it was not until the end of the pbo that climate was warm enough to melt the land based ice sheet this preboreal oscillation found on both sides of the nordic seas is interpreted as an effect of increased freshwater forcing on the thermohaline circulation in the nordic seas which is implied by a simultaneous and distinct rise in the atmospheric 14 c 12 c ratio a slow down of the thermohaline circulation may tempor arily have pushed the polar front further south 1997 by john wiley sons ltd preboreal oscillation thermohaline circulation lacustrine records glacial records chronology

an experimental assessment of the ignition of forest fuels by the thermal pulse generated by the cretaceous palaeogene impact at chicxulub a large extraterrestrial body hit the yucatan peninsula at the end of the cretaceous period models suggest that a substantial amount of thermal radiation was delivered to the earth s surface by the impact leading to the suggestion that it was capable of igniting extensive wildfires and contributed to the end cretaceous extinctions we have reproduced in the laboratory the most intense impact induced heat fluxes estimated to have reached different points on the earth s surface using a fire propagation apparatus and investigated the ignition potential of forest fuels the experiments indicate that dry litter can ignite but live fuels typically do not suggesting that any ignition caused by impact induced thermal radiation would have been strongly regional dependent the intense but short lived pulse downrange and at proximal and intermedi ate distances from the impact is insufficient to ignite live fuel however the less intense but longer lasting thermal pulse at distal locations may have ignited areas of live fuels because plants and ecosystems are generally resistant to single localized fire events we conclude that any fires ignited by impact induced thermal radiation cannot be directly responsible for plant extinctions implying that heat stress is only part of the end cretaceous story received 3 july 2014 revised 10 october 2014 accepted 10 october 2014

a search in north greenland for a new ice core drill site a new deep ice core drilling site has been identified in north greenland at 75 12 n 42 30 w 316 km north northwest nnw of the grip drill site on the summit of the ice sheet the ice thickness here is 3085 m the surface elevation is 2919 m the north grip ngrip site is identified so that ice of eemian age 115 130 ka bp calendar years before present is located as far above bedrock as possible and so the thickness of the eemian layer is as great as possible an ice flow model similar to the one used to date the grip ice core is used to simulate the flow along the nnw trending ice ridge surface and bedrock elevations surface accumulation rate distribution and ratio echo sounding along the ridge have been used as model input the surface accumulation rate drops from 0 23 m ice equivalent year 1 at grip to 0 19 m ice equivalent year 1 50 km from grip over the following 300 km the accumulation is relatively constant before is starts decreasing again further north ice thickness up to 3250 m bring the temperature of the basal ice up to the pressure melting point 100 250 km from grip the ngrip site is located 316 km from grip in a region where the bedrock is smooth and the accumulation rate is 0 19 m ice equivalent year 1 the modeled basal ice here has always been a few degrees below the pressure melting point internal radio echo sounding horizons can be traced between the grip and ngrip sites allowing us to date the ice down to 2300 m depth 52 ka bp an ice flow model predicts that the eemian age ice will be located in the depth range 2710 2800 m which is 285 m above the bedrock this is 120 m further above the bedrock and the thickness of the eemian layer of ice is 20 m thicker than at the grip ice core site

self shielding of thermal radiation by chicxulub impact ejecta firestorm or fizzle as hypervelocity ejecta from the chicxulub yucatan mexico impact fell back to earth the surface may have received a deadly dose of thermal radiation sufficient to ignite global wildfires using a two phase fluid flow code which includes ejecta and air opacities in a radiative transfer calculation we modeled the atmospheric reentry of spherules arriving at distal sites the models predict a pulse of thermal radiation at the surface peaking at 5 15 kw m 2 analogous to an oven set on broil 260 c previous calculations which ignored spherule opacity yielded 10 kw m 2 sustained over 20 min and such an extended pulse is thought to be required for wood ignition however the new modeling suggests that fluxes only exceed the solar norm for 30 min and are only 5 kw m 2 for a few minutes previous models failed to consider the self shielding effect of settling spherules which block an increasing proportion of downward thermal radiation emitted by the later arriving spherules such self shielding may have prevented widespread wildfire ignition although the thermal pulse may have been sufficient to ignite localized fires and kill fauna lacking temporary shelter an opaque cap of submicron dust in the upper atmosphere could however override the self shielding effect

the δ18o record along the greenland ice core project deep ice core and the problem of possible eemian climatic instability over 70 000 samples from the 3029 m long greenland ice core project grip ice core drilled on the top of the greenland ice sheet summit have been analyzed for 8o a highly detailed and continuous 8o profile has thus been obtained and is discussed in terms of past temperatures in greenland we also discuss a three core stacked annual 8o profile for the past 917 years the short term 50 years variability of the annual 8o signal is found to be 1 in the holocene and estimates for the coldest parts of the last glacial are 3 or higher these data also provide insights into possible disturbances of the stratigraphic layering in the core which seems to be sound down to the onset of the eemian spectral analysis of highly detailed sequences of the profile helps determine the smoothing of the 8o signal which for the holocene ice is found to be considerably stronger than expected we suggest this is due to a process involving diffusion of water molecules along crystal boundaries in the recrystallizing ice matrix deconvolution techniques were employed for restoring with great confidence the highly attenuated annual 8o signal in the holocene we confirm earlier findings of dramatic temperature changes in greenland during the last glacial cycle abrupt and strong climatic shifts are also found within the eem sangamon interglaciation which is normally recorded as a period of warm and stable climate in lower latitudes the stratigraphic continuity of the eemian layers is consequently discussed in section 3 of this paper in terms of all pertinent data which we are not able to reconcile

impact ejecta emplacement on terrestrial planets abstract impact cratering is one of the most fundamental processes responsible for shaping the surfaces of solid planetary bodies one of the principal characteristics of impact events is the formation and emplacement of ejecta deposits an understanding of which is critical for planetary exploration current models of ejecta emplacement however do not account for several important observations of ejecta deposits on the terrestrial planets in particular the presence of more than one layer of ejecta furthermore there is also no universal model for the origin and emplacement of ejecta on different planetary bodies we present a unifying working hypothesis for the origin and emplacement of ejecta on the terrestrial planets in which the ejecta are emplaced in a multi stage process the generation of the continuous ejecta blanket occurs during the excavation stage of cratering via the conventional ballistic sedimentation and radial flow model this is followed by the emplacement of more melt rich ground hugging flows the surface melt flow phase during the terminal stages of crater excavation and the modification stage of crater formation minor fallback occurs during the final stages of crater formation several factors will affect the final morphology and character of ejecta deposits the volatile content and cohesiveness of the uppermost target rocks will significantly affect the runout distance of the ballistically emplaced continuous ejecta blanket with impact angle also influencing the overall geometry of the deposits e g the production of the characteristic butterfly pattern seen in very oblique impacts ejecta deposited during the surface melt flow stage is influenced by several factors most importantly planetary gravity surface temperature and the physical properties of the target rocks topography and angle of impact play important roles in determining the final distribution of surface melt flow ejecta deposits with respect to the source crater this working hypothesis of ballistic sedimentation and surface melt flow provides a framework in which observations of ejecta at impact craters can be compared and placed in the context of the respective terrestrial planets

a regional 8200 cal yr bp cooling event in northwest europe induced by final stages of the laurentide ice sheet deglaciation the most notable change in 18o in greenland ice cores during the holocene occurs at 8200 cal yr bp here we present a new high resolution marine record from the northern north sea along with tree ring data from germany which contain evidence of a pronounced temperature drop 2 c contemporaneous with that of the greenland ice core records the synchronous timing of the cooling event in the greenland ice cores marine record and tree ring data from northwest europe reflects a regional influence on the north atlantic ocean atmospheric system suggesting a prominent role of the north atlantic thermohaline circulation the operation of the north atlantic ocean circulation is sensitive to variation in the freshwater budget implying that any change in freshwater flux is capable of altering the north atlantic circulation system we hypothesise minor but long term freshwater fluxes in the final stages of the deglaciation of the laurentide ice sheet as a forcing mechanism 1998 john wiley sons ltd

tsunami backwash deposits with chicxulub impact ejecta and dinosaur remains from the cretaceous palaeogene boundary in the la popa basin mexico the la popa basin in north eastern mexico features outstanding continuous three dimensional exposures of the cretaceous palaeogene boundary event deposit in shallow shelf environments pierced by salt stocks in the area to the south east of the el papalote diapir the cretaceous palaeogene deposit consists of two superimposed sedimentary units and erosively overlies upper maastrichtian sand siltstones with soft sediment deformation and liquefaction structures the basal unit 1 is an up to 8 m thick chaotic carbonate rich bed that discontinuously fills incised gutters and channels besides abundant silicic and carbonate ejecta spherules from the chicxulub impact unit 1 includes large sandstone boulders and abundant shallow water debris for example mud clasts algae bivalve shells gastropod shells and vertebrate remains unit 1 is conformably overlain by unit 2 distal to the diapir unit 2 consists of a centimetre to decimetre thick conglomeratic coarse bioclast and spherule bearing sandstone bed closer to the diapir unit 2 becomes a metre thick series of four to eight conglomeratic to fine grained graded sandstone beds rich in shell debris and ejecta spherules unit 2 is conformably overlain by structureless to parallel laminated sandstone beds that may mark the return to the pre event depositional regime the sedimentary characteristics of the cretaceous palaeogene deposit including its erosive base its sheet like geometry the presence of multiple graded beds evidence for upper flow regime conditions and the absence of bioturbation support an origin by a short term multiphase depositional event the occurrence of soft sediment deformation structures for example liquefaction below the cretaceous palaeogene deposit suggests that earthquakes were the first to occur at la popa then shelf collapse and strong backflow from the first tsunami waves may have triggered erosion and deposition by violent ejecta rich hyperconcentrated density flows unit 1 subsequently a series of concentrated density flows resulting from tsunami backwash surges may have deposited the multiple graded bedding structures of unit 2 the specific depositional sequence and the fe mg rich as well as si k rich composition of the ejecta spherules both provide a critical link to the well known deep marine cretaceous palaeogene boundary sites in the adjacent burgos basin in north eastern mexico moreover the pulse like input of chicxulub ejecta material at the base of the event deposit allows for correlation with other cretaceous palaeogene boundary sites in the gulf of mexico and the atlantic as well as in central and northern america the presence of diverse dinosaur and mosasur bones and teeth in the event deposit is the first observation of such remains together with chicxulub ejecta material these findings indicate that dinosaurs lived in the area during the latest maastrichtian and suggest that the tsunami waves not only eroded deltas and estuaries but the coastal plain as well

severity of ocean acidification following the end cretaceous asteroid impact ammonites went extinct at the time of the end cretaceous asteroid impact as did more than 90 of species of calcium carbonate shelled plankton coccolithophores and foraminifera comparable groups not possessing calcium carbonate shells were less severely affected raising the possibility that ocean acidification as a side effect of the collision might have been responsible for the apparent selectivity of the extinctions we investigated whether ocean acidification could have caused the disappearance of the calcifying organisms in a first detailed modelling study we simulated several possible mechanisms from impact to seawater acidification our results suggest that acidification was most probably not the cause of the extinctions

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

vegetation and climate during the weichselian early glacial and pleniglacial in the niederlausitz eastern germany macrofossil and pollen evidence cryoturbated organic beds and channel fills intercalated with sandy and gravelly fluvial units have been studied in an opencast brown coal mine near nochten niederlausitz eastern germany the fluvial aeolian sequence covers parts of the early pleni and late glacial the detailed chronology is based on 11 radiocarbon and 12 osl dates covering the period between ca 100 kyr and 11 kyr bp basal peat deposits are correlated with an early weichselian interstadial during this period boreal forests were present and minimum mean summer temperatures were 13 c early pleniglacial deposits are absent the middle and late pleniglacial environments were treeless and different types of tundra vegetation can be recognised minimum mean summer temperatures varied between 10 and 15 c vegetation and climate is reconstructed in detail for the periods around 34 38 kyr bp and 24 25 kyr bp around 34 38 ka a mixture between a low shrub tundra and a cottongrass tussock subshrub tundra was present the botanical and sedimentological data suggest that from the middle to the late pleniglacial the climate became more continental aridity and wind strength increased and the role of a protecting winter snow cover decreased a sedge grass moss tundra dominated around 24 and 25 kyr bp copyright 2001 john wiley sons ltd

decadal shifts of the kuroshio extension jet application of thin jet theory abstractmeridional shifts of the kuroshio extension ke jet on decadal time scales are examined using a 1960 2004 hindcast simulation of an eddy resolving ocean general circulation model for the earth simulator ofes the leading mode of the simulated ke represents the meridional shifts of the jet on decadal time scales with the largest southward shift in the early 1980s associated with the climate regime shift in 1976 77 a result confirmed with subsurface temperature observations the meridional shifts originate east of the date line and propagate westward along the mean jet axis a trajectory inconsistent with the traditionally used linear long rossby waves linearized in cartesian coordinates although the phase speed is comparable to that in the traditional framework the zonal scale of these westward propagation signals is about 4000 km and much larger than their meridional scale to understand the mechanism for the westward propagation of the ke jet shifts the authors consider the limit of a thin

saturn s northern hemisphere ribbon simulations and comparison with the meandering gulf stream voyager observations of saturn in 1980 81 discovered a wavy feature engirdling the planet at 47 n planetographic latitude its latitude coincides with that of an eastward jet stream which is the second fastest on saturn after the equatorial jet the 47 n jet s wavy morphology is unique among the known atmospheric jets on the gas giant planets since the voyagers it has been seen in every high resolution image of this latitude for over 25 years and has been termed the ribbon the ribbon has been interpreted as a dynamic instability in the jet stream this study tests this interpretation and uses forward modeling to explore the observed zonal wind profile s stability properties unforced initial value numerical experiments are performed to examine the nonlinear evolution of the jet stream parameter variations show that an instability occurs when the 47 n jet causes reversals in the potential vorticity pv gradient which constitutes a violation of the charney stern stability criterion after the initial instability development the simulations demonstrate that the instability s amplitude nonlinearly saturates to a constant when the eddy generation by the instability is balanced by the destruction of the eddies when the instability saturates the zonal wind profile approaches neutral stability according to arnol d s second criterion and the jet s path meanders in a ribbon like manner it is demonstrated that the meandering of the 47 n jet occurs over a range of tropospheric static stability and background wind speed the results here show that a nonlinearly saturated shear instability in the 47 n jet is a viable mechanism to produce the ribbon morphology observations do not yet have the temporal coverage to confirm the creation and destruction of eddies but these simulations predict that this is actively occurring in the ribbon region similarities exist between the behaviors found in this model and the dynamics of pv fronts studied in the context of meandering western boundary currents in earth s oceans in addition the simulations capture the nonlinear aspects of a new feature discovered by the cassini visual and infrared mapping spectrometer vims the string of pearls which resides in the equatorward tip of the 47 n jet the explicit planetary isentropic coordinate epic model is used herein

the holocene younger dryas transition recorded at summit greenland analysis of ice from dye 3 greenland has demonstrated that the transition between the younger dryas and holocene climate periods occurred over a 40 year period a near annually resolved multiparameter record of the transition recorded in the gisp2 core from summit greenland shows that most of the transition occurred in a series of steps with durations of about 5 years some climate proxies associated with mid latitude sources appear to have changed about 15 years before climate proxies associated with more northern regions changes in atmospheric water vapor are likely to have played a large role in the climate transition

isotopic events in the grip ice core a stratotype for the late pleistocene an event stratigraphy for the last termination based on the stratotype of the grip ice core record has been outlined for the north atlantic region it is suggested that such an approach to stratigraphic subdivision may o er a more satisfactory alternative to conventional stratigraphical procedures for those parts of the recent quaternary record that are characterised by rapid and or short term climatic uctuations 1999 elsevier science ltd all rights reserved

physics of crustal fracturing and chert dike formation triggered by asteroid impact 3 26 ga barberton greenstone belt south africa archean asteroid impacts reflected in the presence of spherule beds in the 3 2 3 5 ga barberton greenstone belt bgb south africa generated extreme seismic waves spherule bed s2 provides a field example it locally lies at the contact between the onverwacht and fig tree groups in the bgb which formed as a result of the impact of asteroid possibly 50 km diameter scaling calculations indicate that very strong seismic waves traveled several crater diameters from the impact site where they widely damaged onverwacht rocks over much of the bgb lithified sediments near the top of the onverwacht group failed with opening mode fractures the underlying volcanic sequence then failed with normal faults and opening mode fractures surficial unlithified sediments liquefied and behaved as a fluid these liquefied sediments and some impact produced spherules filled near surface fractures today represented by swarms of chert dikes strong impact related tsunamis then swept the seafloor p waves and rayleigh waves from the impact greatly exceeded the amplitudes of typical earthquake waves the duration of extreme shaking was also far longer probably hundreds of seconds than that from strong earthquakes dynamic strains of 10 3 occurred from the surface and downward throughout the lithosphere shaking weakened the onverwacht volcanic edifice and the surface layers locally moved downhill from gravity accommodated by faults and open mode fractures coast parallel opening mode fractures on the fore arc coast of chile formed as a result of megathrust events are the closest modern analogs it is even conceivable that dynamic stresses throughout the lithosphere initiated subduction beneath the onverwacht rocks

energetics of eddy mean flow interactions in the gulf stream region a detailed energetics analysis of the gulf stream gs and associated eddies is performed using a highresolution multidecadal regional ocean model simulation the energy equations for the time mean and timevaryingflowsarederivedasatheoreticalframeworkfortheanalysis theeddy meanflowenergycomponents and their conversions show complex spatial distributions in the along coast region the cross stream and cross bump variations are seen in the eddy mean flow energy conversions whereas in the off coast region a mixed positive negative conversion pattern is observed the local variations of the eddy mean flow interaction are influenced by the varying bottom topography when considering the domain averaged energetics theeddy meanflowinteractionshowssignificantalong streamvariability upstreamofcapehatteras the energy is mainly transferred from the mean flow to the eddy field through barotropic and baroclinic instabilities upon separating from the coast the gs becomes highly unstable and both energy conversions intensify when the gs flows into the off coast region an inverse conversion from the eddy field to the mean flow dominates the power transfer for the entire gs region the mean current is intrinsically unstable and transfers 28 26gw of kinetic energy and 26 80gw of available potential energy to the eddy field the mesoscaleeddykineticenergyisgeneratedbymixedbarotropicandbaroclinicinstabilities contributing28 26 and 9 15gw respectively beyond directly supplying the barotropic pathway mean kinetic energy also provides 11 55gw of power to mean available potential energy and subsequently facilitates the baroclinic instability pathway

the last climatic cycle at la grande pile vosges france a new pollen profile a new pollen diagram has been made from an old unanalyzed core from la grande pile gp xx correlations with the previous work of woillard 1975 1978 leads to the following conclusions the end of the eemian was marked by a minor climatic change prior to the melisey i stadial the ognon ii and ognon iii interstadials are not consistent and correspond to the level of reworking of mesophilous taxa during the last pleniglacial the limitations of the botanical interpretation of pollen spectra from the last pleniglacial are underlined lastly bruckenthalia and larix are identified for the first time at la grande pile the respective roles of these taxa following the eemian are additional arguments for correlating the st germain i and ii with the early weichsel interstadials in the north of middle europe

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

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

combustion of fossil organic matter at the cretaceous paleogene k p boundary recognition of elevated concentrations of aciniform soot in cretaceous paleogene k p boundary sediments worldwide led to the hypothesis that global scale forest wildfires could have been generated by the k p boundary bolide impact and might have contributed directly to the extinction event the wildfires are estimated to have injected 10 13 t of co 2 into the atmosphere resulting in an interval of greenhouse warming yet minimal amounts of charred plant remains and abundant noncharred material occur in various k p boundary locations across north america this refutes the inference that wildfires occurred on a global scale and requires an alternative explanation for the aciniform soot here we describe significant concentrations of carbon cenospheres in k p boundary sediments from new zealand denmark and canada carbon cenospheres are thought to derive solely from incomplete combustion of pulverized coal or fuel oil droplets which suggests that the impact may have combusted organic rich target crust the chicxulub impact crater is located adjacent to the cantarell oil reservoir one of the most productive oil fields on earth this indicates that abundance of organic carbon in the chicxulub target crust was likely to have been above global mean values but even if we discount chicxulub9s organic rich locality the global mean crustal abundance for fossil organic matter is more than adequate to account for observed concentrations of both carbon cenospheres and aciniform soot therefore making the global wildfire hypothesis unnecessary

regression coefficients of thermal gradients in northwestern europe during the last glacial holocene transition using beetle mcr data palaeotemperature estimates obtained from 74 sites in northern europe and collectively spanning approximately the last 45 000 yr radiocarbon time scale have been compiled as a major component o

global fire at the cretaceous tertiary boundary cretaceous tertiary k t boundary clays from five sites in europe and new zealand are 102 104 fold enriched in elemental c mainly soot which is isotopically uniform and apparently comes from a single global fire the soot layer coincides with the ir layer suggesting that the fire was triggered by meteorite impact and began before the ejecta had settled