preservation of extraterrestrial 3he in 480 ma old marine limestones we have measured the helium abundance and isotopic composition of a suite of lower ordovician marine limestones and associated fossil meteorites from kinnekulle sweden limestone 3he 4he ratios as high as 11 5 times the atmospheric value in fused samples and up to 23 times atmospheric in a single step heat fraction indicate the presence of extraterrestrial helium and demonstrate that at least a fraction of the extraterrestrial 3he carried by interplanetary dust particles must be retained against diffusive and diagenetic losses for up to 480 ma the carrier phase has not been identified but is not magnetic extrapolation of high temperature 3he diffusivities in these sediments is consistent with strong retention of extraterrestrial 3he under ambient earth surface conditions combination of the observed helium concentrations with sedimentation rates estimated from conodont biostratigraphy suggest that the flux of extraterrestrial 3he in the early ordovician was about 0 5 10 12 cm 3 stp cm 2 ka 1 ignoring potential post deposition helium loss this value is indistinguishable from the average 3he flux estimated for the cenozoic era in contrast previous studies of fossil meteorites ir abundances and os isotopic ratios in the limestone suggest that the total accretion rate of extraterrestrial material during the studied interval was at least an order of magnitude higher than the cenozoic average this disparity may reflect significant post depositional loss of 3he from idps within these old limestones if so the match between the ordovician flux and the cenozoic average would be fortuitous alternatively the size distribution of infalling objects during the early ordovician may have been enriched only in extraterrestrial material too large to retain 3he during atmospheric entry heating 30 m the fossil meteorites themselves also preserve extraterrestrial helium meteorite 3he concentrations of 2 to 9 10 12 cm 3 stp g 1 are several orders of magnitude lower than found in most modern meteorites suggesting very substantial helium loss probably 99 9 from these chemically altered objects the meteorites carry 3he concentrations only a factor of a few higher than the host limestones the meteorites themselves cannot be the source of the extraterrestrial 3he observed in the limestones

human resilience to lateglacial climate and environmental change in the scheldt basin nw belgium recent palaeoenvironmental analyses in the scheldt basin in nw belgium have identified significant hydrological and vegetation changes between greenland interstadial 1b gi 1b and greenland stadial 1 gs 1 younger dryas yd that enable us to develop hypotheses to explain the radical changes in land use and lithic technology observed between the federmesser and post federmesser occupation of the region the highly productive lacustrine environments of the lower scheldt basin during the allerod enabled relatively high population packing by federmesser groups exploiting the region within a residential mobility system federmesser assemblages indicate a flexible lithic technology centered on the production of unstandardized blades and flakes that were intensively backed to shape various tool forms the destabilization of these landscapes in the scheldt basin between gi 1b and gs 1 yd and the ensuing cold of the yd changed the composition of important secondary biomass from less mobile ungulate species to seasonally mobile reindeer populations human populations were resilient to these changes by developing a highly standardized micro blade technology and microlithic toolkit

a multidisciplinary approach to reconstructing late glacial and early holocene landscapes abstract understanding palaeotopographical variability forms the basis for understanding prehistoric societies alluvial and lacustrine environments in particular are key areas with both a high archaeological and palaeoecological potential however the often deep stratification of these sites the high water table and the complex sedimentological variations can hamper a detailed reconstruction of the spatial relationship between prehistoric settlement and their environment combining different remote and proximal sensing techniques and coring data can offer detailed insight into such landscapes more specifically the integration of mobile geophysical methods allows the collection of unprecedented continuous information on large scale palaeolandscape variability in this study we present a combined approach in order to map and model prehistoric landscapes and river systems in and around a late glacial palaeolake in north western belgium based on filtered and unfiltered digital elevation models a survey area of 60 ha was selected in which detailed mobile multi receiver electromagnetic induction survey was conducted the results allowed for the delineation of palaeochannels in the area and enabled modelling the depth of these features in the survey area providing insight into their flow characteristics 14c sampling enabled the dating of the evolving river system to the transition between the late glacial and the early holocene through additional coring this river system could be traced further through the palaeolake area based on these results a detailed reconstruction was made of the palaeotopography that harboured the final palaeolithic and early mesolithic occupation of the study site

a 100 kyr periodicity in the flux of extraterrestrial 3he to the sea floor most of the helium 3 in oceanic sediments comes from interplanetary dust particles idps and can therefore be used to infer the accretion rate of dust to the earth through time 3he records from slowly accumulating pelagic clays indicate that the accretion rate varies considerably over millions of years probably owing to cometary and asteroidal break up events muller and macdonald have proposed that periodic changes in this accretion rate due to a previously unrecognized 100 kyr periodicity in the earth s orbital inclination might account for the prominence of this frequency in climate records of the past million years here we report variations in the 3 he flux to the sea floor that support this idea we find that the flux recorded in rapidly accumulating quaternary sediments from the mid atlantic ridge oscillates with a period of about 100 kyr we cannot yet say however whether the 100 kyr climate cycle is a consequence of a cause of or an effect independent of these periodic changes

catastrophic meltwater discharge down the hudson valley a potential trigger for the intra allerod cold period glacial freshwater discharge to the atlantic ocean during de glaciation may have inhibited oceanic thermohaline circulation and is often postulated to have driven climatic fluctuations yet attributing meltwater discharge events to particular climate oscil lations is problematic because the location timing and amount of meltwater discharge are often poorly constrained we present ev idence from the hudson valley and the northeastern u s conti nental margin that establishes the timing of the catastrophic drain ing of glacial lake iroquois which breached the moraine dam at the narrows in new york city eroded glacial lake sediments in the hudson valley and deposited large sediment lobes on the new york and new jersey continental shelf ca 13 350 yr b p excess 14 c in cariaco basin sediments indicates a slowing in thermohaline circulation and heat transport to the north atlantic at that time and both marine and terrestrial paleoclimate proxy records around the north atlantic show a short lived 400 yr cold event intra allerod cold period that began ca 13 350 yr b p the meltwater discharge out the hudson valley may have played an important role in triggering the intra allerod cold period by diminishing thermohaline circulation

search for the origin of exotic helium in deep sea sediments merrihue1 first observed helium with a very high 3he 4he isotope ratio 10 4 here termed exotic helium in a magnetic separate of a deep ocean sediment and attributed it to input of extraterrestrial material krylov et al 2 subsequently reported the existence of exotic he in several deep sea sediments while tilles3 measured argon isotope ratios in magnetic separates of two ocean sediments observing that the 3he 4he ratio is inversely correlated with the sedimentation rate ozima et al 4 concluded that the exotic he is carried by interplanetary dust particles idps we have now examined other deep sea sediments to characterize the exotic he and to identify its carrier and have confirmed that the exotic he resides mainly in a strongly magnetic fraction stepwise degassing experiments suggest that the exotic he consists of a single component the carrier of the he is likely to be chondritic idps the higher level of exotic he in magnetic fractions of sediments can be explained by secondarily produced magnetite in idps as a result of thermal shock during atmospheric entry

low altitude aerial thermography for the archaeological investigation of arctic landscapes abstract remotely piloted aircraft rpa thermography is one of the least utilized remote sensing methods in archaeology yet it has great potential for visualizing subsurface archaeological features given the logistic constraints of remote fieldwork arctic archaeologists have much to gain from this portable and effective remote sensing application this paper presents a novel methodological approach for the collection processing and analysis of rpa thermal imagery in the canadian high arctic that accounts for the unique environmental and logistic challenges of rpa applications in polar regions the development of this approach is based on a case study of two pre inuit 4500 1000 b p archaeological sites from the foxe basin region nunavut the presented workflow demonstrates the effectiveness of rpa thermography in archaeological feature detection in an arctic tundra setting thermal detection of several previously unidentified subsurface features in foxe basin suggest that surface feature visibility is lower than previously anticipated calling attention to potential judgemental biases in pedestrian archaeological surveys in arctic contexts based on the utility of low altitude thermography for visualizing the internal structures of tuniit dwellings this paper proposes that thermography facilitates archaeological spatial analysis beyond feature prospection rpa thermography is a non destructive and economic remote sensing solution to some of the persistent logistic challenges to fieldwork in remote locations that often inhibit large scale archaeological analyses not only in the canadian arctic but remote arctic alpine regions worldwide

on the fluxes and fates of 3he accreted by the earth with extraterrestrial particles abstract the influx of extraterrestrial et matter on the earth results in appreciable fluxes of 3 he originating from several different processes we have analyzed the published data on the observed concentrations of 3 he in interplanetary dust particles idps sampled in the stratosphere in polar ice samples and in meteorites this information considered together with production of secondary fragments during the atmospheric entry of meteoroids allows us to make plausible estimates of fluxes of the extra terrestrial fluxes of the two principal 3 he types accreted along with the extraterrestrial materials i solar wind sw and solar energetic particle sep 3 he implanted in et particles and ii 3 he produced in the et matrix by interactions of galactic cosmic ray gcr particles an appreciable fraction of 3 he brought to the earth by et particles is expected to be lost from the particles during ablation and fragmentation of the particles during their transit through the atmosphere by comparing the measured 3 he fluxes in two terrestrial archives polar ice and marine sediments and based on supplementary data 3 he 4 he and 20 ne 22 ne ratios we have attempted to determine the relative fluxes of solar sw and sep and gcr 3 he that are preserved in them our analyses establish the fact that the reported 3 he concentrations in particles in relatively small size polar ice samples from greenland and antarctica are primarily due to the solar 3 he accreted via idps of 2 5 m radii scavenged in the polar ice we predict that if larger ice samples were analyzed greater contributions would be found from gcr 3 he present in fragments of meteoroids produced during their entry through the atmosphere it follows therefore that long term fluxes of idps can be estimated from studies of 3 he in relatively small samples of polar ice sheets one observes appreciable concentrations of 3 he in marine sediments extensive observational data are available for sediments in the atlantic and pacific oceans we show that besides idps there is an important source which is an important contributor to the flux of 3 he in marine sediments this is the gcr produced 3 he in meteoroids of sizes up to 1 m we compare the measured 3 he fluxes in marine sediments with those predicted from solar 3 he in idps and from gcr produced 3 he in secondary fragments of meteoroids of sizes up to 1 m produced during their transit through the atmosphere our studies allow us to reach plausible conclusions regarding the predominant source of 3 he in marine sediments

extra terrestrial noble gases in deep sea sediments abstract magnetic fractions separated from four deep sea sediments from the pacific ocean were analysed for elemental abundances and isotopic ratios of noble gases by stepwise heating a 3 he 4 he ratio of 1 8 0 4 10 4 was observed in most samples in the high temperature fractions in all the samples 20 ne 22 ne ratios are constant 11 6 0 6 in most temperature fractions these ratios are different from he a ne a and he b ne b and appear to come from a unique component the 40 ar 36 ar ratios in high temperature fractions are lower than the atmospheric ratio indicating the existence of extra terrestrial ar while the 38 ar 36 ar ratios are indistinguishable from atmospheric planetary and solar ar indicating negligible spallogenic ar the isotopic ratios of kr and xe are indistinguishable from atmospheric ratios from the 20 ne 22 ne ratios and from thermal release patterns of he we conclude that the extra terrestrial noble gases are implanted solar flare particles the energy range of the solar flares is estimated from the relation between the grain size of idps interplanetary dust particles and the penetration depth of particles impinging on to a grain which gives less than 1 mev n the uniformity of isotopic ratios of he and ne can be explained by a grain size sieving effect of idps during atmospheric entry and by the subsequent diffusion loss of shallowly implanted solar wind noble gases

unusual neon isotopic composition in neoproterozoic sedimentary rocks fluorine bearing mineral contribution or trace of an impact event abstract extraterrestrial materials have he and ne isotopic compositions that are distinct from those of the earth s surface in order to track the extraterrestrial material accreted onto earth during the ediacaran period we have analyzed the he and ne isotopic composition of thirteen sedimentary rocks in the age range 550 600 ma coming from the huqf supergroup in oman for which carbon and sulfur isotopic data have been characterized previously 3he 4he ratios range between 0 006 0 003 and 0 27 0 01 ra with ra being the atmospheric ratio 3he 4he ratios show a positive relationship with 3he contents ranging between 0 6 and 31 10 13 cm3 stp g 1 the 3he contents are within the literature data for 3 to 480 myr old samples with evidence of idp 3he idp for interplanetary dust particles suggesting that extraterrestrial 3he is still retained in such old samples 20ne 22ne ratios are close to or below the modern atmospheric ratio of 9 8 with the minimum value equal to 9 05 0 03 21ne 22ne ratios show a high range of variation going from 0 0345 0 0009 to 0 0935 0 0023 the ne isotopic compositions follow a nucleogenic trend similar to that of crustal fluids from the literature and predicted continental crust however one sample 3404 shows an unusual ne isotopic composition with a lower 20ne 22ne at similar 21ne 22ne compared to the other samples two hypotheses can explain this singular ne isotopic composition first it could be the result of a particular nucleogenic trend due to the presence of f bearing minerals in this sample sem eds elemental mapping showed that although f and ca rich phases which could correspond to fluorites are present in sample 3404 however their abundance of 0 15 seems too low to explain the unusual ne isotopic composition however due to the high uncertainty of the calculations we cannot totally rule out this hypothesis alternatively the singular ne isotopic composition could be due to the presence of a ne a component a component characterizing pre solar diamonds contained in chondrites this would indicate that a major object impacted the earth at the time the sediment was forming between 600 and 550 ma which is coherent with the estimated age range of the acraman impact in australia

size fractionation reproducibility and provenance of helium isotopes in north equatorial pacific pelagic clays helium isotope compositions were measured in late quaternary pelagic clays from the north equatorial pacific where terrestrial and extra terrestrial end member components are identified and quantified in different grain size populations the results provide important constraints on the nature of interplanetary dust particles idps in sedimentary environments and on their application as constant flux proxies in paleoceanographic studies approximately 92 95 of the extra terrestrial 3 he 3 heet is concentrated in particles smaller than 20 mm within this grain size group 44 of 3 heet is concentrated in the 20 10 and 10 2 mm fractions while more than 50 of the total 3 heet is found in fine particles smaller than 2 mm the peak concentration of 3 heet in the very fine particle size population explains a consistently better reproducibility of 3 heet in sediments compared to model predictions that is related to the relatively homogenous distribution of clay size particles in sediments compared to coarser particles especially in deep sea sediments and ice cores the 3 he 4 he ratios are highest in the coarser than 20 mm fractions peaking between 63 and 38 mm 1 7871 13 10 4 compared to the bulk and the o20 mm fractions 3 2072 62 10 5 and 2 1170 88 10 5 respectively the isotopic composition of helium in each of the size fractions reflects a mixture between a pure extraterrestrial end member and a terrigenous component which is itself comprised of varying mixtures of volcanic material and eolian material associated with the fine grain size fraction of loess deposits in south east asia poor 3 heet reproducibility observed here and elsewhere inhibiting its application as a constant flux proxy stems from the presence of a small number of aliquots displaying significantly higher 3 heet contents compared to the average of their reference group these helium rich particles hrps are probably characterized by a o20 mm diameter and carry significant amounts of extraterrestrial 3 he and 4 he careful rejection of such aliquots improves the signal reproducibility by more than two fold

assessing li and other leachable geochemical proxies for paleo salinity in lake sediments from the mono basin ca usa abstract regional climate driven hydrological changes are accompanied by salinity changes in closed basin lakes we have investigated acid leachable li along with other leachable ions including mg ca and sr as geochemical proxies of salinity in lake sediments in the mono basin california all the elements in the acid leachable suite show a strong correlation with paleo lake level estimates based on physical and stratigraphic evidence the caco3 content of lake sediments which has been shown to be a reliable proxy for lake level changes in the mono basin and the adjoining owens lake basin corresponds well with our acid leachable proxy data

pleistocene holocene transition in benelux in benelux belgium the netherlands and luxembourg considerable progress in late glacial and early postglacial archaeological and environmental research has been made during the last decade a substantial part of this paper discusses new evidence on the chronology of the industries which occupied the southern part of benelux dating the occupations from the sandy north is still problematic long after the glacial maximum during which the area remained uninhabited the south of benelux was visited by magdalenian hunter gatherers while hamburgian settlements were present in the north the significance of the continental creswellian is debated during the allerod interstadial federmesser groups occupied most of the area abandoning it with the onset of the younger dryas the presence of the ahrensburgian during that stadial may have been punctuated new elements were introduced and were maintained during the development of the preboreal early mesolithic which eventually colonised the entire region throughout this sequence changes in material culture and related subsistence activities are evident in view of the major problems concerning the quality of the chrono ecological data this paper can only suggest provisional explanations in terms of human reactions to changing environmental conditions

geochemistry of great salt lake utah ii pleistocene holocene evolution sedimentologic and biostratigraphic evidence is used to develop a geochemical model for great salt lake utah extending back some 30 000 yrs b p hydrologie conditions as defined by the water budget equation are characterized by a lake initially at a low saline stage rising by about 17 000 yrs b p to fresh water basin full conditions bonneville level and then after about 15 000 yrs b p dropping rapidly to a saline stage again as exemplified by the present situation inflow composition has changed through time in response to the hydrologie history during fresh water periods high discharge inflow is dominated by calcium bicarbonate type river waters during saline stages low discharge nacl rich hydrothermal springs are significant solute sources this evolution in lake composition to nacl domination is illustrated by the massive mirabilite deposition free of halite following the rapid drawdown until about 8 000 years ago while historic droughts have yielded principally halite hydrologic history can be combined with inferred inflow composition to derive concentration curves with time for each major solute in the lake calcium concentrations before the drawdown were controlled by calcite solubility and afterwards by aragonite significant amounts of solutes are removed from the lake by diffusion into the sediments na cl and so42 are also involved in salt precipitation by including pore fluid data a surprisingly good fit has been obtained between solute input over the time period considered and the amounts actually found in lake brines pore fluids salt beds and sediments excess amounts are present for calcium carbonate and silica indicating detrital input

geochemical evolution of uraniferous soda lakes in eastern mongolia extremely high concentrations of uranium u were discovered in shallow groundwater fed hyperalkaline soda lakes in eastern mongolia a representative groundwater sample in this area is dilute and alkaline ph 7 9 with 10 mm tic and 5 mm cl in contrast a representative lake water sample is ph 10 with tic and cl each more than 1 000 mm groundwater concentrations of u range from 0 03 to 0 43 m l 1 lake water u ranges from 0 24 to 62 5 m possibly the highest naturally occurring u concentrations ever reported in surface water strontium isotopes 87sr 86sr varied in groundwaters from 0 706192 to 0 709776 and in lakes 87sr 86sr varied from 0 708702 to 0 709432 high concentrations of u na cl and k correlate to radiogenic sr in lake waters suggesting that u is sourced from local cretaceous alkaline rhyolites uranium rich groundwaters are concentrated by evaporation and u vi is chelated by co 3 2 to form the highly soluble uo2 co3 3 4 modeled evaporation of lakes suggests that a u mineral phase is likely to precipitate during evaporation

extraterrestrial 3he in seafloor sediments evidence for correlated 100 kyr periodicity in the accretion rate of interplanetary dust orbital parameters and quaternary climate we have determined the helium abundance and isotopic composition of seafloor carbonate sediments from the flanks of the ontong java plateau western equatorial pacific ocean odp site 806 these results provide a two million year record of the burial flux of extraterrestrial 3he which we believe is a proxy for the terrestrial accretion rate of interplanetary dust particles the 3he burial flux prior to 700 ka was relatively low 0 5 pcc cm 2 kyr 1 but from 700 ka to the present the burial flux gradually increased to a value of 1 0 pcc cm 2 kyr 1 100 kyr periodicity in the 3he burial flux is apparent over the last 700 kyr and correlates with the oxygen isotope record of global climate with high 3he burial fluxes associated with interglacial periods this periodicity and phase are consistent with previous 3he measurements in north atlantic sediments although 100 kyr periodicity in 3he burial flux is in agreement with recent predictions of the accretion rate of interplanetary dust based on a model of the orbital evolution of asteroidal debris the measurements and predictions differ by one half cycle in phase nevertheless our observations suggest the terrestrial accretion rate of interplanetary dust is controlled by orbital eccentricity and or inclination relative to the solar system invariable plane such control is a necessary but not sufficient condition for the hypothesis of muller and macdonald 1995 that variations in extraterrestrial dust accretion modulates terrestrial climate with a 100 kyr period we also identify several brief 25 kyr intervals of strongly enhanced 3he burial possibly related to random and transient fluctuations in the accretion rate of asteroidal or cometary dust particles

helium isotopes in ferromanganese crusts from the central pacific ocean abstract helium isotopes have been measured in samples of two ferromanganese crusts va13 2 and cd29 2 from the central pacific ocean with the exception of the deepest part of crust cd29 2 the data can be explained by a mixture of implanted solar and galactic cosmic ray produced gcr he in extraterrestrial grains and radiogenic he in wind borne continental dust grains 4he concentrations are invariant and require retention of less than 12 of the in situ he produced since crust formation loss has occurred by recoil and diffusion high 4he in cd29 2 samples older than 42 ma are correlated with phosphatization and can be explained by retention of up to 12 of the in situ produced 4he 3he 4he of va13 2 samples varies from 18 5 to 1852 ra due almost entirely to variation in the extraterrestrial he contribution the highest 3he 4he is comparable to the highest values measured in interplanetary dust particles idps and micrometeorites mms helium concentrations are orders of magnitude lower than in oceanic sediments reflecting the low trapping efficiency for in falling terrestrial and extraterrestrial grains of fe mn crusts the extraterrestrial 3he concentration of the crusts rules out whole undegassed 4 40 m diameter idps as the host instead it requires that the extraterrestrial he inventory is carried by numerous particles with significantly lower he concentrations and occasional high concentration gcr he bearing particles

repeated aeolian deflation during the allerod gi 1a c in the coversand lowland of nw belgium abstract the results of multi disciplinary research carried out on the deposits of the moerbeke driehoek site located along the northern bank of the extensive moervaart palaeolake nw belgium are presented the multi proxy study including sedimentological organic matter calcium carbonate and grain size and botanical pollen macrofossils npp analyses provided evidence of repeated aeolian deflation during the allerod our results demonstrate in combination with evidence from other soil archives within the moervaart area that the allerod period in nw europe was sedimentologically much less stable than hitherto assumed especially during the gi 1c2 event and middle allerod some of the allerod deflation events were caused by centennial abrupt climatic oscillations such as the short but pronounced cold gi 1c2 event while others were likely the result of intense forest fires or a combination of both these observations call for a revision of the existing lateglacial litho and chronostratigraphic schemes for the sand belt of northern europe

a comparative study of accumulation rates derived by he and th isotope analysis of marine sediments abstract we present a detailed down core analysis of helium isotope ratios and concentrations for bulk sediments from the central equatorial pacific that span the last two glacial interglacial cycles measured 3 he 4 he ratios range from 1 0 10 5 to 2 1 10 4 or 7 4 to 149 times the atmospheric ratio the 3he from interplanetary dust particles idps constitutes virtually all of the 3he measured within the sediment because carbonate accumulation rates are high in the equatorial pacific the measured 3he concentrations are lower than have been measured elsewhere and range from 4 7 10 13 to 3 0 10 12 cm3stp g 1 if the cosmic dust 3he flux is constant with time sediment mass accumulation rates can be determined from the 3he concentration in sediments the excess 230th technique is an entirely independent method for calculating sediment mass accumulation rates because its source is in situ decay of 234u in seawater to first order initial excess 230th activities correlate with 3he concentrations within this core based on the 230th results we estimate the 3he flux to the earth s surface as 9 6 2 0 10 16 cm3stp cm 2 a 1 if this flux has remained constant over extended periods of time it can be used to determine sediment accumulation rates beyond the 230th range 300 000 yr

multiple oscillations during the lateglacial as recorded in a multi proxy high resolution record of the moervaart palaeolake nw belgium this paper presents the results of multi disciplinary research carried out on the deposits of moervaart depression nw belgium one of the largest palaeolakes 25 km2 that existed during the lateglacial interstadial in nw europe the multi proxy study including physical organic matter and calcium carbonate magnetic susceptibility micromorphological botanical pollen macrofossils diatoms zoological ostracods molluscs chironomids and chemical analyses stable carbon and oxygen isotopes has resulted in a detailed reconstruction of the lateglacial landscape as well of the local conditions that prevailed in the lake itself a chronology of the record was provided by radiocarbon dating and comparison with radiocarbon dates of the nearby rieme site these yielded a good match with the regional biostratigraphy during the lateglacial vegetation and geomorphology of the landscape in general changed from a tundra landscape to a boreal forest the vegetation development however was interrupted by a number of cold reversals three centennial scale cold oscillations are present in the record 1 the so called older dryas corresponding to gi 1d in the greenland ice cores 2 a short and pronounced cold event during the early allerod which could be correlated to gi 1c2 and 3 a cooling event during the late allerod probably corresponding to the intra allerod cold period iacp or gi 1b the latter most likely was responsible for the disappearance of the moervaart palaeolake

extraterrestrial 3 he as a tracer of marine sediment transport and accumulation the deposition rate of deep sea sediments and their focused redeposition by deep sea currents can be evaluated from analyses of sedimentary 230th with a temporal resolution limited only by bioturbation6 7 10 11 230th is produced uniformly throughout the ocean by radioactive decay of dissolved 234u and is removed sufficiently fast by sorption onto sinking particles to act as a constant flux tracer of sedimentation rates but the half life of 230th 75 kyr limits its use for this purpose to the past 200 250 kyr here we explore the use of extraterrestrial 3he from interplanetary dust particles1 4 idps as a constant flux proxy that is free from this limitation a comparison of 3he with 230th in two cores from the equatorial pacific ocean indicates that the variability in the mean flux of idps over the past 200 kyr is less than 75 but in contrast to this relatively constant rate of supply of 3he to the deep sea the local burial rates of 3he and 230th have varied by a factor of five over the past 450 and 200 kyr respect ively we interpret this variability as reflecting sediment focusing with a temporal pattern that suggests regular cycles of climate driven reorganization of near bottom currents in the deep pacific ocean

evaluating the accretion of meteoritic debris and interplanetary dust particles in the gpc 3 sediment core using noble gas and mineralogical tracers abstract extraterrestrial et noble gases helium and neon in 35 sediment samples from central pacific core ll 44 gpc 3 demonstrate the variable flux of interplanetary dust particles idps and major meteorite impacts over the past 70 ma 21 72 ma spinel mineralogical and chemical compositions clearly distinguish major impact events from the continuous flux of idps including the well established cretaceous tertiary k t and late eocene e o impact boundaries no spinel grains with chemical or mineralogical evidence of a distinctly et origin were found in an extensive survey of background samples i e non e o or k t boundary suggesting that either the carrier grains for et noble gas occur within the fe ti oxide mineral fraction observed in this study found to include ilmenite and ulvospinel or are too small for identification by sem the presence of ilmenite and ulvospinel suggest lunar regolith is a potential source for et noble gas rich particles noble gas analysis on both the emf extractable magnetic fraction and the bulk minus emf bulk emf show that the he and ne compositions are consistent with partially degassed noble gas signatures of zero age magnetic grains z mag and stratospheric interplanetary dust particles idps conclusive evidence for a planetary ne a noble gas signature is found only in the bulk sediments at the k t boundary although all gpc 3 k t fractions bulk emf and hf digestion plot along a mixing line between planetary ne a and solar wind sw spinels from major impact boundaries k t e o exhibit dendritic texture and elevated ni consistent with previous reports in contrast to the otherwise consistent 3he signal from idps the 3he at the known impact boundaries k t and e o actually decreases these anomalously low 3he are accompanied by significantly elevated ne and significantly lower 3he 20ne solar ratios 10 lower produced by both preferentially degassing of he relative to ne at times of increased flux of larger et material degassed degassed he enriched ne profile noble gas characteristics occur in two sample intervals that do not correspond to any known impact events 47 and 71 ma explained by an influx of larger particles sem analysis of the 47 ma sample shows spinels with dendritic textures but without distinctive markers of large meteorite impacts e g elevated ni particle size increases and degassed signatures may be caused by major bolides micrometeorites comet showers or simply a flux of larger idps potentially with a different source

high 3 he 4 he ratio in ocean sediments two decades ago merrihue1 reported 3he 4he ratios of 10 4 in ferromagnetic separates from a pacific deep ocean red clay and concluded that the high ratio is due to extraterrestrial debris amounting to 1 of the sediment a decade later krylov et al 2 compiled 3he 4he isotopic data on ocean sediments measured in the soviet union and observed that the 3he 4he ratio is generally higher in pelagic sediments where the sedimentation rate is lower they suggested that the high 3he 4he ratio was attributable to extraterrestrial materials which were concentrated in slowly accumulating ocean floor however these important discoveries were almost completely neglected until we re examined the problem we have measured 39 sediments from 12 different sites 10 sites from the western to central pacific and two sites from the atlantic ocean we find 3he 4he ratios 5 10 5 for six sites well above the values generally observed in common terrestrial materials the very high 3he 4he ratio in the sediments is probably due to input of extraterrestrial materials input of stratospheric dust of 1 p p m which corresponds to a fallout rate of 2 000 tons per year can explain the observation

terrigenous helium in deep sea sediments abstract we have measured the isotope ratios of helium contained in various terrigenous materials that contribute to deep sea sediments these materials include ice rafted debris from the north atlantic chinese loess and sediment collected at or near the mouths of three large rivers the amazon the ganges and the yangtze we observe terrigenous 3he 4he ratios that vary from 1 8 10 9 to 4 6 10 7 i e values that are higher than the theoretically derived range of 10 9 to 10 8 atlantic and pacific deep sea sediment 3he 4he ratios can be explained by mixing of helium from similar extraterrestrial but different terrigenous sources terrigenous sources for north atlantic and north pacific sediments are characterized by 3he and 4he contents that are higher and 3he 4he ratios that are lower than those for central and eastern equatorial pacific sediments this is consistent with the supply to the north atlantic and north pacific oceans of older cratonic continental material that contains high amounts of in situ produced nucleogenic and radiogenic helium terrigenous material transported to central and eastern equatorial pacific sediments contains lower amounts of 3he and 4he and higher 3he 4he ratios indicative of supply from a more juvenile andean source in the equatorial atlantic core v31 135 we have used previously published 230th data to determine an extraterrestrial 3he flux of 1 16 0 15 10 12 cm3stp cm 2 ka 1 within error of that previously determined in sediments from the equatorial pacific ocean 0 78 0 29 10 13 cm3stp cm 2 ka 1 marcantonio et al 1996

hydrogeochemistry in the ngorongoro crater tanzania and implications for land use in a world heritage site the chemistry of surface and ground waters in the ngorongoro crater tanzania home to thousands of large mammals and a world heritage site is controlled by the volcanic host rock lithology evaporative concentration mineral precipitation and redissoluton and biological factors three groups of waters are informally differentiated based on their ranges of concentration 1 dilute inflow meteoric runoff and springs from short flowpaths ph 9 cl 100 mg l evaporative concentration and biological activity in swamps commonly produce strong geochemical gradients between dilute sources and peripheral concentrated ephemeral wetlands dilute inflow is found in the lerai munge and oljoro nyuki streams and several large springs near the crater wall such as ngoitokitok and seneto concentrated inflow is found in downstream reaches of the munge stream discharging from springs away from the crater wall such as engitati and mti moja and in dryseason pools brackish waters are found discharging from springs on the southern margin of lake makat in mudflats surrounding marshes in ephemeral pools and in the lake itself although few hydrologic data are available the persistence of relatively fresh water in vegetated wetlands is consistent with lower sedge dominated wetland evapotranspiration rates compared with open water this suggests that wetlands may play an important role in ensuring fresh water availability in the basin and it demonstrates the need for future hydrologic study most of the ngorongoro waters originate as rainfall outside the crater and travel into the basin as surface or ground water flow emphasizing the need for a watershed scale approach to land management

chemical evolution of shallow groundwater along the northeast shore of mono lake california we attempted to quantitatively discriminate between hypothesized sources and geochemical processes responsible for the chemical evolution of shallow groundwater along the northeast shore of mono lake an alkaline saline lake located in a hydrologically closed basin in east central california shallow groundwater samples from 17 sites perpendicular and 11 sites parallel to the lakeshore were analyzed for major ions the shallow groundwater contains remnant solutes from higher lake stands which are transported toward the lake by lateral flow and surface runoff the flow system appears to be segregated into two different regions a concentrated highly saline groundwater underlying much of the northeast shore and pockets of more localized lower salinity groundwater the saturation state of the groundwater with respect to certain minerals was determined and simulations for both evaporative concentration of inflow and mixing of lake water with inflow coupled with mineral precipitation were performed solute trends in the shallow groundwater result primarily from the degree of mixing with historical lake water however evaporative concentration and redissolution cycles along with various chemical fractionation mechanisms including ca mg and na carbonate precipitation sulfate reduction ion exchange and potentially mg silicate formation are also important controls

accretion of extraterrestrial matter during the last 80 million years and its effect on the marine osmium isotope record the flux of particulate extraterrestrial et matter to the deep sea has been calculated using a four component mixing model based on osmium concentrations and isotope ratios in slowly accumulating pelagic sediments from the pacific ocean nineteen published bulk leach osmium isotope data pairs that cover the last 80 million years have been used for the calculation the calculated annual particulate flux averaged over several 100 ka by slow accumulation and bioturbation ranges from 18 000 to 67 000 tons with a mean value of 37 000 13 000 tons the data indicate no significant variability in the flux with time except at the k t boundary and are thus compatible with results based on ir accumulation in deep sea sediments the inferred constancy of the et matter flux is in contrast to recent results based on the et 3he flux that integrates only a small size fraction of the entire et matter flux 3he data indicate variability by a factor of 6 over the past 70 ma and a fivefold increase in the et flux between 3 ma and 1 ma that is not seen in the bulk et matter flux based on osmium isotope data the apparent constancy of the cosmic matter flux over the past 80 ma stands in marked contrast to the dynamic nature of the marine osmium isotope record and indicates that dissolution of cosmic matter does not drive changes in this record except at the k t boundary a comparison between osmium isotope and ir data from two pelagic sediment cores from the pacific dsdp site 596 and ll44 gpc3 indicates that the seawater soluble fraction of et os cannot exceed 36 kg a and most likely is significantly smaller the maximum value of 36 kg a can account for approximately one half of the seawater soluble et matter flux necessary to balance the radiogenic continental runoff of os without any additional unradiogenic source simple mass balance calculations indicate that an additional unradiogenic source of os to the oceans most likely alteration of oceanic crust is required to balance the present day seawater osmium isotopic composition this source is probably more important in balancing radiogenic continental runoff than is dissolution of cosmic matter in seawater

cenozoic variations in the flux of interplanetary dust recorded by 3he in a deep sea sediment helium 3 concentrations and 3he 4he ratios in modern pelagic sediments are known to be far in excess of terrestrial values as a result of micrometeorite fallout here i report that extraterrestrial helium is easily detected in a pelagic clay core dating back more than 70 myr the remarkable preservation of the extraterrestrial signature arises from high retention of 3he within interplanetary dust particles coupled with loss of radiogenic 4he from terrestrial mineral grains the core provides a continuous record of the fallout of extraterrestrial helium for the cenozoic era this record suggests that there have been significant variations in the influx of interplanetary dust through time probably related to asteroidal breakup events or the passage of comets through the inner solar system the results also show 3he to be a far more sensitive tracer of the interplanetary dust flux than is iridium

geochemical evolution of ground water in smith creek valley a hydrologically closed basin in central nevada u s a abstract smith creek valley is a hydrologically closed basin in which ground water is recharged by subsurface inflow from sorrounding mountains and infiltration of streamflow into alluvial fan deposits near the mountains ground water is discharged by evapotranspiration from shallow ground water areas in the central part of the basin dominant ions in the dilute recharge water are na ca and hco 3 dissolved solids concentration increases during flow through the basin fill sediments with na becoming increasingly dominant in the discharge area a bare soil playa sorrounded by phreatophytic vegetation ground water salinity dominated by na and cl increases markedly the main processe controlling geochemical evolution of ground water in the basin fill aquifer were identified using major ion chemistry mass balance calculations thermodynamic calculations stable isotopes and mineral identification these processes are 1 dissolution of volcanic tuff and tuff derived basin fill deposits 2 cation exchange of ca and mg in the water for na in clay minerals 3 weathering of plagioclase to montmorillonite 4 precipitation of zeolite minerals 2 concentration of dissolved constituents by evapotranspiration 6 dissolution of cl and so 4 evaporative salts 7 precipitation of calcite

hydrogeochemistry of lake turkana kenya mass balance and mineral reactions in an alkaline lake abstract lake turkana in northwestern kenya is a closed basin alkaline ph 9 2 lake of moderate salinity tds 2500 ppm principal ions are na hco 3 and ci the lake is essentially polymictic in the northern basin and little compositional variation occurs in surface waters the omo river is the principal influent providing some 80 90 of water input to the lake chloride has an apparent accumulation time of about 2500 years after accounting for burial of interstitial water the bottom sediments are predominantly detrital and fine grained yet mineral water reactions are very important for the geochcmical budget ca 2 is precipitated as calcite na is removed as an exchangeable cation on smectite mg 2 is probably incorporated into a mg silicate phase most likely poorlycrystalline smectite as it enters the lake water k may be used in illite regradation cation exchange is a very important process in the mass balance of this lake over 40 of incoming na is removed as an exchangeable cation after cation exchange and interstitial water burial na has a response time of 2650 years which compares favorably with that of chloride these processes seem to occur rapidly within the water mass of the lake other reactions may be important in regulating interstitial water compositions several changes occur in the upper 3m of sediment interstitial water ph drops to 8 3 and alkalinity increases slightly with depth so 2 4 decreases slightly and amorphous silica saturation is approached these changes are a response to organic matter oxidation and the dissolution of unstable silicates rather than a reversal of reactions occurring in the lake water high rates of sedimentation up to 1 cm per year may minimize the effects of diffusion between the interstitial waters and the lake water although burial of interstitial water assumes considerable importance

accretion rate of extraterrestrial particles determined from osmium isotope systematics of pacific pelagic clay and manganese nodules abstract pelagic clay and mn nodules from domes sites in the north pacific and a varved glacial lake deposit from connecticut were analysed for os concentration and isotopic composition by isotope dilution secondary ion mass spectrometry after treatment by nis fusion or oxalic acid leaching bulk pelagic clay from domes site c has 187 os 186 os 6 5 and os 0 14 ng g oxalic acid leaches of this same sediment and of mn nodules from domes sites a and c have more radiogenic 187 os 186 os ratios which average 8 3 bulk glacial lake hitchcock sediment has 187 os 186 os 12 5 and os 0 06 ng g the total os flux to north pacific pelagic clay is 7 to 10 ng os cm2 106 y lake hitchcock sediment provides an integrated value for the local crustal 187 os 186 os ratio the oxalic acid leaches are assumed to attack hydrogenous phases selectively a simple model in which the only sources of os to the ocean are continental crust with the isotopic composition of lake hitchcock 187 os 186 os 12 5 and extraterrestrial particles with 187 os 186 os 1 1 results in a cosmic flux of osmium to the sediment of 4 9 ngos cm2 106 y of which 20 is hydrogenous a model in which the sources of os to the ocean are continental crust with an 187os 186os ratio of 30 from the model of palmer and turekian 1986 oceanic mantle or crust with 187 os 186 os 1 04 and extraterrestrial particles with 187 os 186 os 1 1 results in a cosmic flux of os to the sediment of 5 7 ngos cm2 106 y of which none is hydrogenous these extraterrestrial os fluxes correspond to maximum c 1 chondrite accretion rates of between 4 9 104 and 5 6 104 tonnes y

temporal variation of 3he 4he ratio recorded in deep sea sediment cores he isotopic composition was measured for 72 deep sea sediments from 16 sites in the pacific and atlantic oceans and the japan sea 3he content ranges from less than 10 12 cm3 stp g to about 6 10 11 cm3 stp g and 3he 4he from about 10 8 to 1 67 10 4 the he isotopic data lie fairly well on a mixing curve in a 3he 4he 3he diagram where the end members of the mixing curve are extraterrestrial he in interplanetary dust particles idp s and terrestrial he in ocean sediments this confirms the view that there are significant amounts of extraterrestrial he in ocean sediments from global fallout of idp s into deep sea sediments 3he flux estimated for two long cores gives a value of about 1 5 1 0 10 15 cm3 stp cm2 yr over a time span of 40 m y which corresponds to an annual fallout rate of idp s size 10 m of about 400 t in one of the cores we observe a 3he spike which is associated with anomalously high ir content 1 86 0 56 ppb this may be due to meteorite debris

an alternative age model for the paleocene eocene thermal maximum using extraterrestrial 3he a continuous age model for the brief climate excursion at the paleocene eocene boundary has been constructed by assuming a constant flux of extraterrestrial 3he 3he et to the seafloor 3he et measurements from odp site 690 provide quantitative evidence for the rapid onset few kyr and short duration 120 kyr of global warming and of the associated disturbance to the earth s surficial carbon budget at this time these observations support astronomically calibrated age models indicating extremely rapid release of isotopically light carbon possibly from seafloor methane hydrate as the proximal cause of the event however the 3he et technique indicates a previously unrecognized and extreme increase in sedimentation rate coincident with the return of climate proxies to pre event values the 3he et based age model thus suggests a far more rapid recovery from the climatic perturbation than previously proposed or predicted on the basis of the modern carbon cycle and so may indicate additional or accelerated mechanisms of carbon removal from the ocean atmosphere system during this period 3he et was also measured at odp site 1051 to test the validity of the site 690 chronology comparison of these data sets seems to require removal of several tens of kyr of sediment within the climatic excursion at site 1051 an observation consistent with sediment structures and previous age modeling efforts the site 1051 age model shows a 30 kyr period in which climate proxies return toward pre event values after which they remain invariant for 80 kyr if this rise represents the recovery interval identified at site 690 then the 3he et based age models of the two sites are in good agreement however alternative interpretations are possible and work on less disrupted sites is required to evaluate the reliability of the proposed new chronology of the climate excursion regardless of these details this work shows that the 3he et technique can provide useful independent evidence for the development and testing of astronomically calibrated age models

abrupt cooling events during the early holocene and their potential impact on the environment and human behaviour along the southern north sea basin nw europe in this paper the potential impact of the 9 3k cal a bp cooling event on the environment and human occupation in the rhine meuse scheldt region of nw europe is investigated although various environmental decreased fluvial activity increased wildfires and changing vegetation and cultural changes lithic technology raw material circulation decreasing site density can be identified in the late boreal a serious problem of equifinality remains lacking a high resolution chronology for these events it is still difficult to separate the impact of gradual from punctuated climatic changes however at present it seems that some environmental and cultural changes were already ongoing before the 9 3k cal a bp event but were accelerated by the latter to gain a better understanding of these processes it is necessary to take a holistic multidisciplinary approach towards the early holocene in the southern north sea basin

laser extraction of helium isotopes from antarctic micrometeorites source of he and implications for the flux of extraterrestrial 3he to earth helium isotopes have been measured in 45 putative micrometeorites in the size range 50 to 400 m that were extracted from antarctic ice forty of the antarctic micrometeorites amms are irregular in shape and display varying degrees of partial melting whereas five are spherical and thought to represent completely melted particles of the 30 50 to 100 m suspected micrometeorites only 8 released neither 3he or 4he sixteen released 3he and 4he 0 004 3 5 10 3 cm3 stp g having 3he 4he in the range 1 5 10 4 to 4 1 10 4 six particles released only 3he yielding minimum 3he 4he of 1 6 to 10 6 10 4 5 of which fall in the range of values for amms that had measurable 3he and 4he only 2 of the 15 100 to 400 m amms released measurable 4he 4 44 10 7 cc g 1 these have 3he 4he of 6 10 4 and 20 10 4 respectively significantly higher than the majority of the ratios of 50 to 100 m amms implanted solar energetic particles are the dominant source of he in the 50 to 100 m amms with small contributions of solar wind and or spallogenic he present in 10 particles the absence of sw he is likely due to the loss of the outermost layers of the micrometeorites by ablation during atmospheric entry and abrasion during residence in ice and sampling spallation he is most important in the 100 to 400 m amms consistent with their smaller surface area to volume ratio maximum spallation 3he exposure ages of six particles are close to that predicted from poynting robertson spiral in times of asteroidal micrometeorites the two terrestrial particles identified by chemical composition and mineralogy released only 4he yielding radiogenic he isotope compositions an inverse relationship between particle sizes and solar he abundance is explained by he loss during entry helium loss is likely controlled by phyllosilicate breakdown where present and diffusion controlled bubble growth and rupture rather than melting the 50 to 100 m micrometeorites deliver 8 10 8 cm3 stp 3he g to earth this is more than 100 times less than transported by 20 m particles 2 10 5 cm3 stp 3he g but because 50 to 100 m micrometeorites deliver approximately 20 times more extraterrestrial matter to earth than 20 m particles the larger particles may contribute 5 of the total flux of extraterrestrial 3he to terrestrial sediments the mean he concentrations of the 50 to 100 m amms antarctic micrometeorites and the five spherules 2 1 10 9 cm3 stp 3he g 1 overlap those of the magnetic fraction of deep sea sediments 0 8 68 10 9 cm3 stp g a combination of this material could provide the extraterrestrial 3he measured in ancient deep sea sediments without calling upon the survival of friable 20 m chondritic interplanetary dust particles for tens of millions of years

gaylussite formation at mono lake california abstract the salinity of mono lake has steadily increased since 1941 from 50 to about 90 due to diversion of tributary streams this increase has resulted in the newly discovered precipitation of gaylussite na2ca co3 2 5h2o chemical modeling of the lake water using pitzer equations suggests that gaylussite has been forming year round since about 1970 when the salinity first exceeded 80 and that it was earlier forming intermittently at lower salinities in the winter shortly after diversion began breaking down incongruently to aragonite during summers lake water appears to remain at a constant 9 fold supersaturation with aragonite at all salinities perhaps buffered by monohydrocalcite which appears to be just at saturation for all salinities other saline lakes also appear to be buffered by monohydrocalcite

the lithium isotopic composition of waters of the mono basin california mono lake a major closed basin alkaline salt lake in eastern california derives its water from a mixture of creeks and springs with the former providing in excess of 75 of the total the li isotopic composition of lake water has not varied significantly over a 4 year meromictic period 7li 19 5 springs are isotopically distinct groundwater springs and seeps carry water enriched in isotopically heavy li whereas thermal springs supply isotopically light 7li 50 of the li to the lake 2 the li budget is sensitively balanced on small thermal spring contributions 3 of the total spring inflow and 3 the residence time of li in the lake is 28 ka other great basin closed lakes have variable li isotopic compositions 7li from 16 7 to 23 7 all of which differ significantly from those of several major lakes and seawater homogeneously 32

small headwater stream evolution in response to lateglacial and early holocene climatic changes and geomorphological features in the saint gond marshes paris basin france the study focuses on river dynamics and vegetation changes during the last glacial interglacial transition from a headwater stream located in the eastern part of the paris basin we adopt a spatial multiproxy approach combining image analyses geophysical surveys sedimentary and pollen record analyses to document the impact of lateglacial climate changes and geomorphological features on vegetation and fluvial dynamics in the small boitet catchment ca 20 km2 our results show that the sedimentary record is organized into six successive alluvial sequences reflecting changes in discharge and channel morphology in response to short phases of climate oscillations during the lateglacial and early holocene periods the boitet alluvial sequences present some similarities with other nw european rivers that are interpreted as large scale fluvial system evolution to climate changes however some local differences have also been highlighted partly related to the upstream position of the catchment among them two distinctive features of the boitet catchment are 1 the preservation of the oldest dryas deposits which have been rarely described in this area and 2 the recognition of multichannel river dynamics during the oldest dryas and younger dryas we demonstrate that the fluvial evolution is firstly triggered by climate changes and that land surface features may also influence specifically upstream areas revealing contrasting responses of the river system

hunter gatherer responses to the changing environment of the moervaart palaeolake nw belgium during the late glacial and early holocene abstract this paper presents new geo archaeological perspectives on the late glacial and early holocene human occupation around a large palaeolake the moervaart palaeolake 25 km 2 intensive fieldwork using invasive and non invasive survey techniques combined with modelling of the palaeotopography and palaeogroundwater and multi proxy palaeoecological analyses have resulted in a detailed reconstruction of the landscape during the final palaeolithic and early mesolithic occupation of the area a major shift in the occupation from the federmesser culture to the early mesolithic was contemporaneous with a sudden and drastic change in the palaeohydrology of the area between ca 13 300 and 13 000 cal bp end of allerod which coincided with a short but abrupt cooling event known as the intra allerod cold period iacp gi 1b it is assumed that this event triggered the sudden drying up of the moervaart palaeolake and surrounding ponds which until then had provided federmesser hunter gatherers with extensive and fertile grounds for hunting gathering and drinking water the population decline which followed this hydrological event was reinforced by the prevailing cold and harsh conditions of the younger dryas and probably lasted until the pre boreal hunter gatherers returned to the area in the boreal now settling along the proximal floodplain regions of a meandering channel which was connected with the southern scheldt river

a 35 myr record of helium in pelagic limestones from italy implications for interplanetary dust accretion from the early maastrichtian to the middle eocene we have determined the helium concentration and isotopic composition of a suite of early maastrichtian through middle eocene pelagic limestones in the italian apennines the results provide a 35 myr record of the implied flux of extraterrestrial 3he which is a proxy for the accretion rate of interplanetary dust particles idps our measurements show that the 3he flux was fairly constant in the maastrichtian except for possible minor increases factor of two or less from 70 5 ma to 68 ma and at 66 ma which probably reflect transient increases in the accretion rate of asteroidal and or cometary idps we find no evidence for an increase in idp accretion at or immediately before the k t boundary implying that the k t impact was not associated with enhanced solar system dustiness this observation precludes the possibility that the k t impactor was a member of a major comet shower and is more consistent with impact of a lone comet or asteroid our data suggest a 2 to 4 fold increase in idp accretion between 57 and 54 ma followed by a factor of three decrease over an 4 myr period in the early to middle eocene the duration and magnitude of this variability is inconsistent with previous observations attributed to a shower of long period comets and is more likely the result of collisions in the asteroid belt and or kuiper belt in the entire 35 myr record we find no evidence for major enhancements of the idp accretion rate of the type expected from comet showers our results in combination with earlier 3he measurements do not support models that predict recurrent comet showers with periods of 38 myrs if there is a periodicity in the cratering record that is caused by periodic modulation of the oort cloud it is not evident in the apennine sediment data along with the 3he measurements we also obtained 4he concentrations which record temporal changes in the flux or composition of terrigenous matter the most significant change in 4he occurs in the last 4 myrs of the cretaceous over which the concentration of 4he in the detrital component rises by 300 this rise tracks a strong increase in the seawater 87 sr 86 sr ratio suggesting a globally significant change in the composition of continental detritus delivered to the oceans possibly arising from increased continental weathering

the accretion rate of extraterrestrial 3he based on oceanic 230th flux and the relation to os isotope variation over the past 200 000 years in an indian ocean core abstract in the eastern equatorial indian ocean the flux of extraterrestrial 3 he a proxy of interplanetary dust particles idps has been relatively constant over the past 200 ka the flux is equal to 1 1 0 4 10 12 cm 3 stp cm 2 ka 1 a value obtained using the xs 230 th profiling method variations in mass accumulation rates mars derived assuming a constant extraterrestrial 3 he flux have a 40 ka periodicity similar to that observed in the 18 o derived mars this frequency is similar to that of the earth s obliquity measured 187 os 188 os ratios are less radiogenic than present day seawater 0 49 0 98 reflecting the mixing of os derived from extraterrestrial terrigenous and hydrogenous sources when coupled with he data measured on the same samples os isotope data yield important information about the terrigenous component supplied to the eastern equatorial indian ocean the amount of os in the sample derived from the extraterrestrial component can be deduced with the help of the helium systematics once corrected for the extraterrestrial component of os os isotope signatures in conjunction with the 4 he concentrations suggest a supply of terrigenous material from indonesian ultramafic and himalayan crustal sources that clearly varies through time

abrupt intensification of the sw indian ocean monsoon during the last deglaciation constraints from th pa and he isotopes abstract sediments from western arabian sea core 74kl representing the last 23 ka were analyzed for helium thorium and protactinium isotopes assuming global average fluxes of extraterrestrial 3he and 230th the average 3he derived sediment mass accumulation rate mar is a factor of 1 8 higher than the average 230th derived mar 3he and 230th derived mars converge however during the younger dryas yd and during the peak of the early holocene humid interval these features not seen anywhere else in the world probably reflect a combination of climate driven changes in the flux of 230th and 3he ratios of xs231pa xs230th proxies of paleoproductivity are lowest during the last glacial maximum lgm and increase abruptly during the bolling allerod later following a sudden decrease to near lgm values during the yd they rise abruptly to maximum values for the entire record in the early holocene we hypothesize that low xs231pa xs230th ratios reflect low productivity due to the decreased intensity of the sw monsoon whereas the opposite is true for high ratios the correlation between arabian sea productivity and monsoonal upwelling on the one hand and north atlantic climate variability on the other suggests a linkage between high and low latitude climates caused by changing patterns of atmospheric circulation

ikaite precipitation by mixing of shoreline springs and lake water mono lake california usa abstract metastable ikaite caco3 6h2o forms abundantly during winter months along the south shoreline of mono lake where shoreline springs mix with lake water ikaite precipitates because of its decreased solubility at low temperature and because of orthophosphate ion inhibition of calcite and aragonite during the spring some of the ikaite is transformed to anhydrous caco3 and is incorporated into tufa but most is dispersed by wave action into the lake where it reacts to form gaylussite na2ca co3 2 5h2o spring waters have low ph values are dominantly ca na hco3 have low radiocarbon activities and are mixtures of deep seated geothermal and cold groundwaters chemical modeling reveals that precipitation of caco3 can occur over a broad range of mixtures of spring and lake water with a maximum production occurring at 96 spring water and 4 lake water under these conditions all the ca and a significant fraction of the co3 of the precipitate is spring supplied a radiocarbon age of 19 580 years obtained on a natural ikaite sample supports this conclusion with the springs supplying a large and probably variable portion of the carbonate and with apparent 14c age of the carbonate varying from spring to spring tufa of similar actual antiquity may yield significantly different 14c dates making tufa at this location unsuitable for absolute age dating by the radiocarbon method

reconstructing a prehistoric topography using legacy point data in a depositional environment reconstruction of past topography is an essential step towards the understanding of past landscapes in terms of biophysical patterns and processes and man landscape interactions by archaeologists geomorphologists geologists and soil scientists landscape reconstructions can be based on process knowledge on data or on a combination of both in this case study we focus on a data based approach where knowledge on the geological history is used to interpret and exploit legacy data as part of a landscape reconstruction of a large area of 584 km2 a map of the elevation near 10 000 bc was produced starting from a present day grid digital elevation model gdem that was filtered for human influences we identified the thickness of accumulated sediments over the holocene mapped these and corrected the gdem to map the thickness of holocene sediments we used 72 osl and 14c dated sediment samples 731 recent profile descriptions and 3288 legacy profile descriptions protocols were formulated based on literature and local correlative studies to convert the legacy profile descriptions into estimates of the thickness of holocene sediments with an estimate of the precision the method of kriging with uncertain data was applied to obtain a map validation at 200 independent test locations with certain data showed a mean error of 6 cm and a standard deviation or error of 16 cm which was in accordance with the estimated precision of 16 cm the resulting map indicated zones with marked change that could be studied in more detail future reconstructions could employ both process knowledge and data by combining landscape genesis models with legacy data to map model errors and thus increase the quality of the reconstruction copyright 2013 john wiley sons ltd

4he as a tracer of continental dust a 1 9 million year record of aeolian flux to the west equatorial pacific ocean the mass accumulation rates mars of aeolian dust in the ocean basins provide an important record of climate in the continental source regions of atmospheric dust and of the prevailing wind patterns responsible for dust transport in the geologic past the incorporation of other terrigenous components such as volcanic ashes in seafloor sediments however often obscures the aeolian dust record we describe a new approach which uses the delivery rate of crustal 4he to seafloor sediments as a proxy for the mass accumulation rate of old continental dust which is unaffected by the addition of other terrigenous components we have determined the flux of crustal 4he delivered to the seafloor of the ontong java plateau ojp in the western equatorial pacific over the last 1 9 myrs crustal 4he fluxes vary between 7 7 and 30 ncc cm 2 kyr 1 and show excellent correlation with global climate as recorded by oxygen isotopes with high crustal 4he fluxes associated with glacial periods over the entire interval studied furthermore the onset of strong 100 kyr glacial interglacial climate cycling is clearly seen in the 4he flux record about 700 kyrs ago these data record variations in the supply of asian dust in response to climate driven changes in the aridity of the asian dust sources consistent with earlier work on asian dust flux to the northern pacific ocean however in contrast to previous studies of sites in the central and eastern equatorial pacific ocean there is no evidence that the inter tropical convergence zone an effective rainfall barrier to the southward transport of northern hemisphere dust across the equator in the central and eastern pacific has influenced the delivery of asian dust to the ojp the most likely carrier phase for crustal helium in these sediments is zircon which can reasonably account for all the 4he observed in the samples as a first order estimate these results suggest that the mass accumulation rate of asian dust on the ojp over the last 1 9 myrs varied from about 4 to 15 mg cm 2 kyr 1 in contrast previous studies show that over the same interval the total mar of terrigenous dust i e asian dust plus local volcanics on ojp varied between about 34 and 90 mg cm 2 kyr 1

pleistocene rhine thames landscapes geological background for hominin occupation of the southern north sea region this paper links research questions in quaternary geology with those in palaeolithic archaeology a detailed geological reconstruction of the netherlands south west offshore area provides a stratigraphical context for archaeological and palaeontological finds progressive environmental developments have left a strong imprint on the area s palaeolithic record we highlight aspects of landscape evolution and related taphonomical changes visualized in maps for critical periods of the pleistocene in the wider southern north sea region the middle pleistocene record is divided into two palaeogeographical stages the pre anglian elsterian stage during which a wide land bridge existed between england and belgium even during marine highstands and the anglian elsterian to saalian interglacial with a narrower land bridge lowered by proglacial erosion but not yet fully eroded the late pleistocene landscape was very different with the land bridge fully dissected by an axial rhine thames valley eroded deep enough to fully connect the english channel and the north sea during periods of highstand this tripartite staging implies great differences in i possible migration routes of herds of herbivores as well as hominins preying upon them ii the erosion base of axial and tributary rivers causing an increase in the availability of flint raw materials and iii conditions for loess accumulation in northern france and belgium and the resulting preservation of middle palaeolithic sites 2011 john wiley sons ltd

estimation of the extraterrestrial 3 he and 20 ne fluxes on earth from he and ne systematics in marine sediments abstract sediments contain interplanetary dust particles idps carrying extraterrestrial noble gases such as 3 he which have previously been used to estimate the idp accretion flux over time and the duration of past environmental events however due to its high diffusivity he can be lost by diffusion either due to frictional heating during entry in the atmosphere or once it has been incorporated in the sediments therefore the absolute values of 3 he idp fluxes cannot be known due to its lower diffusivity ne is less likely to be lost by diffusion than he and can potentially provide an absolute idp flux value here we studied the ne and he isotopic composition of 21 sediments of different ages 3 to 38 myr 56 myr and 183 myr in order to better constrain the retention of 3 he in such deposits the samples are carbonates from 2 sites of the integrated ocean drilling program iodp which previously showed evidence of detectable extraterrestrial 3 he and from the sancerre core in the paris basin the 3 he 4 he 20 ne 22 ne and 21 ne 22 ne ratios of decarbonated residues vary respectively from 0 09 10 6 to 76 5 10 6 9 54 0 08 to 11 30 0 60 and from 0 0295 0 0001 to 0 0344 0 0003 these isotopic compositions can be explained by a mixing between two terrestrial components atmosphere and radiogenic he and nucleogenic ne present in the terrigenous fractions and an extraterrestrial component the linear relationship between 20 ne 22 ne and 3 he 22 ne ratios shows that the extraterrestrial component has a unique composition and is similar to the he and ne composition of implanted solar wind this composition is different from the individual stratospheric idps for which the ne and he isotopic compositions have been measured we suggest that this difference is due to a bias in the sampling of the individual idps previously analyzed toward the largest ones that are more likely to lose he during entry in the atmosphere our data further constrains the size of the majority of the idps to be less than 10 m in diameter in addition the constant 3 he 22 ne ratio of the extraterrestrial component present in the samples which is similar to the implanted solar wind composition suggests that no diffusive loss of 3 he occurred in the atmosphere or on the seafloor thus neglecting any non fractionating he and ne loss by weathering and or alteration of the host phases on the seafloor the extraterrestrial 3 he and 20 ne fluxes between 3 to 38 myr ago are respectively 0 2 0 1 10 12 cm 3 cm 2 kyr 1 and 0 2 0 1 10 11 cm 3 cm 2 kyr 1 during the sharp increases of the late eocene and late miocene the idp 3 he and 20 ne fluxes reach values up to five times higher

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

sources and flux of natural gases from mono lake california abstract the ability to identify a formation mechanism for natural gas in a particular environment requires consideration of several geochemical factors when there are multiple sources present four primary sources of methane have been identified in mono lake two of these sources were associated with numerous natural gas seeps which occur at various locations in the lake and extend beyond its present boundary the two other gas sources result from current microbiological processes in the natural gas seeps we observed flow rates as high as 160 moles ch4 day 1 and estimate total lakewide annual seep flux to be 2 1 106 moles ch4 geochemical parameters 13ch4 dch4 ch4 c2h6 c3h8 and 14ch4measurements revealed that most of the seeps originate from a paleo biogenic 13ch4 about 70 natural gas deposit of pleistocene age which underlies the current and former lakebed gas seeps in the vicinity of hot springs had in combination with the biogenic gas a prominent thermogenic gas component resulting from hydrothermal alteration of buried organic matter current microbiological processes responsible for sources of natural gas in the lake included pelagic meth anogenesis and decomposition of terrestrial grasses in the littoral zone methanogenesis in the pelagic sediments resulted in methane saturation 2 3 mm at 50 cm 13ch4 about 85 interstitial sulfate decreased from 133 mm at the surface to 35 mm by 110 cm depth indicating that sulfate reduction and methanogenesis operated concurrently methane diffused out of the sediments resulting in concentrations of about 50 m in the anoxic bottom waters methane oxidation in the oxic anoxic boundry lowered the concentration by 98 but values in surface waters 0 1 1 3 m were supersaturated with respect to the atmosphere the 13ch4 range 21 8 to 71 8 of this unoxidized residual methane was enriched in 13c relative to methane in the bottom water and sediments average outward flux of this methane was 2 77 107 moles yr 1 a fourth but minor source of methane 13ch4 55 2 was associated with the decomposition of terrestrial grasses taking place in the lake s recently expanded littoral zone

growing spherulitic calcite grains in saline hyperalkaline lakes experimental evaluation of the effects of mg clays and organic acids the origin of spherical radial calcite bodies spherulites in sublacustrine hyperalkaline and saline systems is unclear and therefore their palaeoenvironmental significance as allochems is disputed here we experimentally investigate two hypotheses concerning the origin of spherulites the first is that spherulites precipitate from solutions super saturated with respect to magnesium silicate clays such as stevensite the second is that spherulite precipitation happens in the presence of dissolved organic acid molecules in both cases experiments were performed under sterile conditions using large batches of a synthetic and cell free solution replicating waters found in hyperalkaline saline lakes such as mono lake california our experimental results show that a highly alkaline and highly saline solution supersaturated with respect to calcite control solution will precipitate euhedral to subhedral rhombic and trigonal bladed calcite crystals the same solution supersaturated with respect to stevensite precipitates sheet like stevensite crystals rather than a gel and calcite precipitation is reduced by 50 compared to the control solution producing a mixture of patchy prismatic subhedral to euhedral and minor needle like calcite crystals enhanced magnesium concentration in solution is the likely the cause of decreased volumes of calcite precipitation as this raised equilibrium ion activity ratio in the solution on the other hand when alginic acid was present then the result was widespread development of micron size calcium carbonate spherulite bodies with further growth time but falling supersaturation these spherules fused into botryoidal topped crusts made of micron size fibro radial calcite crystals we conclude that the simplest tested mechanism to deposit significant spherical radial calcite bodies is to begin with a strongly supersaturated solution that contains specific but environmentally common organic acids furthermore we found that this morphology is not a universal consequence of having organic acids dissolved in the solution but rather spherulite development requires specific binding behaviour finally we found that the location of calcite precipitation was altered from the air water interface to the surface of the glassware when organic acids were present implying that attached calcite precipitates reflect precipitation via metal organic intermediaries rather than direct forcing via gas exchange

reconstructing palaeochannel morphology with a mobile multicoil electromagnetic induction sensor abstract field methods to map and reconstruct the morphology of buried river systems are highly dependent on spatial interpolation conventional methods such as standard borehole survey allow a detailed vertical reconstruction of the shallow subsurface but leave lateral connections between sample locations open to interpretation geophysical survey techniques have recently introduced more detail mobile electromagnetic induction emi survey combines high density sampling with full lateral coverage but fails to produce detailed information about vertical facies changes recently multicoil emi survey added vertical discrimination potential to this lateral continuity in this study we present an integrated approach for reconstructing the morphology of a known palaeochannel segment by modelling the depth to the sandy substrate in addition a calibration method based on a limited number of auger data is proposed in a first phase the modelling procedure was evaluated along two transects on a test site showing palaeochannel depths ranging from 1 to 4 m beneath the surface in a second phase the morphology of the entire site was reconstructed these three resulting depth models were then compared with auger observations and electrical resistivity tomography ert data the high correlation coefficients 0 9 between observed and modelled depths showed that even in complex pedological environments palaeochannel morphology could be predicted precisely using multicoil emi data therefore we concluded that a multicoil emi survey proves to be an efficient and reliable solution for mapping and reconstructing the morphology of the shallow subsurface

a sealed flint knapping site from the younger dryas in the scheldt valley belgium bridging the gap in human occupation at the pleistocene holocene transition in w europe based on the evidence of a recently excavated sealed site situated at ruien rosalinde in the belgian scheldt valley the response of hunter gatherers to changing climate at the transition from the temperate allerod to the cold younger dryas is discussed radiocarbon dated to the end of the allerod or the very beginning of the younger dryas the site of ruien provides the earliest evidence of a refined lithic technology characterized by the use of a soft stone hammer and the production of straight and regular blade let s from intensively prepared cores with two opposite platforms and sharp striking angles in the course of the younger dryas and early pre boreal this knapping method will become standard all over europe from the tanged point technocomplex in the north to the epi laborian in the south it contrasts sharply with the knapping style of previous lithic traditions such as the late federmesser azilian and bromme technocomplexes which was much less elaborated and mainly oriented towards the knapping of short irregular blades with a hard stone hammer this apparently abrupt technological change was also accompanied by increased raw material procurement networks extending over up to 250 km and a marked microlithisation of the hunting equipment finally the site of ruien is also important as it demonstrates the limited archaeological visibility of younger dryas sites explaining the scarcity of such sites within western europe

preboreal climate oscillations in europe wiggle match dating and synthesis of dutch high resolution multi proxy records abstract in order to compare environmental and inferred climatic change during the preboreal in the netherlands five terrestrial records were analysed detailed multi proxy analyses including microfossils e g pollen spores algae and fungal spores macroremains e g seeds fruits wood mosses etc and loss on ignition measurements were carried out with high temporal resolution to link the five preboreal records accurate chronologies were produced by ams 14c wiggle match dating the dutch records show that following the lateglacial holocene climate warming birch woodlands expanded between 11 530 and 11 500 cal bp during the friesland phase of the preboreal after the friesland phase two distinct climatic shifts could be inferred 1 around 11 430 11 350 cal bp the expansion of birch forests was interrupted by a dry continental phase with open grassland vegetation the rammelbeek phase this phase was coeval with the coldest part of the preboreal oscillation pbo as observed in the 18o record of the greenland ice core records and has been attributed to a large meltwater flux that resulted in a temporary decrease of the thermohaline circulation in the north atlantic 2 at the start of the late preboreal between 11 270 and 11 210 cal bp a sudden shift to a more humid climate occurred and birch forests expanded again a simultaneous increase in the cosmogenic nuclides 14c and 10be suggests that these changes in climate and vegetation were forced by a sudden decline in solar activity expansion of pine occurred during the later part of the late preboreal at the onset of the boreal between 10 770 and 10 700 cal bp dense woodlands with hazel oak elm and pine started to develop in the netherlands

reviewing the lateglacial holocene transition in nw iberia a palaeoecological approach based on the comparison between dissimilar regions isotopic records from greenland ice cores have revealed a number of centennial to millennial scale climatic fluctuations affecting the eastern north atlantic during the lateglacial holocene transition most of them appear directly correlated with quantitative temperature changes reconstructed for a very climate sensitive locality in nw iberia laguna de la roya lr the chironomid inferred lr temperature record was used as a reference to update the chronologies and improve the interpretations of 16 different key pollen sites from nw iberia botanical and zoological macroremains from archaeological sites and natural deposits were also reviewed in order to check if they support the changing environments predicted by pollen data pollen evidence corresponding to the less intense lateglacial and early holocene cold phases identified in lr was found at all sites nevertheless only minor vegetation changes occurred during the older dryas la roya i 13 600 13 350 cal bp la roya ii 13 300 12 900 cal bp the 11 4 ka and the 9 3 ka event at very sensitive sites located close to ecotonal situations we conclude that the lr chironomid inferred temperature curve is able to explain the main tree line oscillations and also the major local regional vegetation changes that occurred over the whole of nw iberia during the lateglacial and early holocene during this period the most relevant landscape modifications occurred at the onset of the lateglacial at the transition to the yd and at the onset of the holocene however noticeable changes also occurred during the 8 2 ka event which mostly affected the hyperoceanic coastal mountain ranges and some continental depressions inland the rapid succession of changes registered during the early holocene affected the different co existing biocoenoses in an unequal way and resulted in a diversity of plant and animal resources available for human populations this may explain that the hunter gatherer groups even persisted in some areas of nw iberia until the mid holocene

synchronisation of palaeoenvironmental records over the last 60 000 years and an extended intimate event stratigraphy to 48 000 b2k the intimate protocol for the correlation of marine ice core and terrestrial records is here updated reflecting recent developments in palaeoclimate research originally focussed on last glacial to interglacial transition lgit 22 000 11 500 years b p the intimate group has now extended its study period back to 60 000 years as a first step the intimate event stratigraphy has now been extended to include 8000 48 000 b2k based on a combined ngrip and grip isotope profile against a gicc05 chronology and key tephra horizons from iceland and continental european volcanic sources in this lead article of this intimate special issue we introduce some of the recent achievements of the intimate community and discuss the challenges associated with extending the intimate approach back in time focussing in particular on the chronological problems inherent in comparing different proxy records the intimate approach has thus far been limited predominantly to the north atlantic and australasian regions and we also discuss the potential to extend the intimate protocol beyond these regions

a late miocene dust shower from the break up of an asteroid in the main belt throughout the history of the solar system earth has been bombarded by interplanetary dust particles idps which are asteroid and comet fragments of diameter approximately 1 1 000 microm the idp flux is believed to be in quasi steady state particles created by episodic main belt collisions or cometary fragmentation replace those removed by comminution dynamical ejection and planetary or solar impact because idps are rich in 3he seafloor sediment 3he concentrations provide a unique means of probing the major events that have affected the idp flux and its source bodies over geological timescales here we report that collisional disruption of the 150 km diameter asteroid that created the veritas family 8 3 0 5 myr ago also produced a transient increase in the flux of interplanetary dust derived 3he the increase began at 8 2 0 1 myr ago reached a maximum of approximately 4 times pre event levels and dissipated over approximately 1 5 myr the terrestrial idp accretion rate was overwhelmingly dominated by veritas family fragments during the late miocene no other event of this magnitude over the past approximately 10 8 yr has been deduced from main belt asteroid orbits one remarkably similar event is present in the 3he record 35 myr ago but its origin by comet shower or asteroid collision remains uncertain

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

the temperature of europe during the holocene reconstructed from pollen data we present the first area average time series reconstructions of warmest month coldest month and mean annual surface air temperatures across europe during the last 12 000 years these series are based on quantitative pollen climate reconstructions from over 500 pollen sites assimilated using an innovative four dimensional gridding procedure this approach combines three dimensional spatial gridding with a fourth dimension represented by time allowing data from irregular time series to be focussed onto a regular time step we provide six regional reconstructed temperature time series as well as summary time series for the whole of europe the results suggest major spatial and seasonal differences in holocene temperature trends within a remarkably balanced regional and annual energy budget the traditional mid holocene thermal maximum is observed only over northern europe and principally during the summer this warming was balanced by a mid holocene cooling over southern europe whilst central europe occupied an intermediary position changes in annual mean temperatures for europe as a whole suggest an almost linear increase in thermal budget up to 7800 bp followed by stable conditions for the remainder of the holocene this early holocene warming and later equilibrium has been mainly modulated by increasing winter temperatures in the west which have continued to rise at a progressively decreasing rate up to the present day

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

carbon sources in arc volcanism with implications for the carbon cycle new co2 3 he data from the east sunda arc indonesia confirm earlier observations that arc volcanic gases have higher co2 3 he ratios than mor environments on average 80 of arc volcanic co2 is recycled exogene carbon addition of a few percent of carbonate bearing sediments to the mantle wedge explains much of the carbon abundance andcarbon isotopic data of arc gases but can not explain the he isotope observations the co2 3he in arc volcanoes is not strongly dependent on the composition of modem trough sediments e g deep sea clays vs carbonate rich sequences and calcite veins in the hydrothermally altered subducted slab may provide a contribution to the recycled carbon flux of arcs the sum of globally deep subducted sediment and slab carbon exceeds the estimated arc co2 flux and approximately 3 5 teramole of carbon may return annually to the mantle in convergent zones the modem combined processes of mor volcanism slab alteration and subduction volcanism do not produce a substantial carbon flux into the exosphere and rate changes in ocean floor spreading are unlikely to cause major changes in atmospheric co2 as a result of changes in the volcanic co2 fluxes intense pulses of flood basalt volcanism however may alter the co2 contents of the atmosphere over the course of a millenium or so and influence global climate

the pleistocene reindeer of the north sea initial palaeontological data and archaeological remarks abstract the interdisciplinary north sea project aims at investigating the biotic history of the pleistocene in the southern bight of the north sea humans were part of these biotopes too as palaeolithic flint artefacts prove based on a large fossil record and radiocarbon dating it becomes clear that reindeer was part of the late pleistocene mammoth fauna upper palaeolithic hunters often are described as reindeer hunters despite a large fossil reindeer record and collection of palaeolithic flint artefacts no evidence was found for co existence of humans and reindeer or for reindeer hunting

interplanetary dust in the transmission electron microscope diverse materials from the early solar system abstract an analytical electron microscope study of dispersed interplanetary dust aggregates collected in the earth s stratosphere shows that in spite of their similarities the aggregates exhibit significant differences in composition internal morphology and mineralogy of 11 chondritic particles examined two consist mostly of a noncrystalline chondritic material with atomic s fe 2 in places one consists of submicron metal and reduced silicate microchondrules and sulfide grains embedded in a carbonaceous matrix and another consists of submicron magnetite decorated unequilibrated silicate and sulfide grains with thick low z coatings although the particles are unmetamorphosed by criteria commonly applied for chondritic meteorites the presence of reduced chemistries and the ubiquity of mafic instead of hydrated silicates confirm that they are not simply c1 or c2 chondrite matrix material the observations indicate that portions of some particles have not been significantly altered by thermal or radiation processes since their assembly and that the particles probably contain fine debris from diverse processes in the early solar system

noble gases in ocean waters and sediments noble gases are widely used in studies of the basic properties and dynamics of natural systems including the ocean this chapter describes some of the more extensive applications of noble gases mainly helium isotopes to studies of oceanographic problems they include the modern oceanic circulation paleo oceanography hydrothermal and cold brine systems in the deep ocean and ocean atmosphere gas exchange originally oceanic noble gas studies were focused on geochemical problems such as the question of the existence of excess helium in seawater derived from radioactive decay of the elements of the uranium and thorium series in ocean sediments suess and wanke 1965 bieri et al 1966 after the discovery of mantle primordial helium during the 1960s clarke et al 1969 craig and weiss 1971 craig et al 1975 and 3he derived from decay of tritium in the near surface waters of the ocean jenkins and clarke 1976 large programs were developed to exploit helium isotopes frequently in combination with tritium for studies of water mass formation circulation and variability e g jenkins 1987 schlosser et al 1991 more recent studies started to explore the use of helium isotopes to paleoceanographic objectives these studies build upon the discovery of extraterrestrial helium in deep sea sediments in the early 1960s merrihue 1964 this signal is now being systematically examined for its potential as a tool for investigations of sediment accumulation rates on very long time scales millions of years and their correlation with changes in paleoceanography e g farley 1995 farley and patterson 1995 marcantonio et al 1995 1996 2001 soon after the discovery of mantle helium in seawater noble gases were applied to studies of hydrothermal systems originally these studies were focused on the source of the fluids emanating from hydrothermal vents as well as

3he4he ratio noble gas abundance and k ar dating of diamonds an attempt to search for the records of early terrestrial history the 3he4he ratios measured in 27 southern africa diamond stones four from premier mine and the rest of unidentified origin range from 4 2 10 8 to 3 2 10 4 with three stones above 1 10 4 we conclude that the initial helium isotopic ratio 3he4he 0 in the earth was significantly higher than that of the planetary helium a 3he4he 1 42 10 4 but close to the solar helium 3he4he 4 10 4 the apparent k ar ages for the twelve diamonds of unidentified origin show enormously old age indicating excess argon 40 3he4he evolution in diamonds suggests that the diamonds with the high 3he4he ratio 2 10 4 may be as old as the earth noble gas elemental abundance in the diamonds relative to the air noble gas abundance shows monotonie decrease with a decreasing mass number this paper discusses the implications of these observations on the early solar system and the origin of diamonds

extraterrestrial accretion from the gisp2 ice core the rate of extraterrestrial accretion for particles in the size range 0 45 m to 20 m was determined from dust concentrates extracted from greenland ice sheet project 2 gisp2 ice core samples using instrumental neutron activation analysis inaa we determined the iridium ir content of the dust following a core specific correction for terrestrial ir and assuming a chondritic ir abundance of 500 ppb we measure an average accretion rate for 0 45 m to 20 m particles over the entire earth of 0 22 0 11 109 g yr kton yr for 317 years of ice through the interval 6 to 20 ka this is consistent with the interplanetary dust accretion rate of 0 17 0 08 x 109 g yr that we derive from published 3he data for the gisp2 core accounting for particles that are larger and smaller than those detected by or experiment our best estimate of the total accretion rate including particle sizes up to about 4 cm in diameter is 2 5 109 g yr the uncertainty in this estimate is dominated by statistical fluctuations in the number of particles expected to end up in the ice core and not by measurement error based on monte carlo simulations we estimate the upper limit for total extraterrestrial accretion to earth of 6 25 109 g yr 95 confidence level this accretion rate is consistent with some estimates from micrometeorite concentrations in polar ice estimates from ground based radar studies and with accretion estimates of 3he bearing interplanetary dust particles assuming that 3he is correlated with particle surface area it is however lower than estimates based on platinum group element studies of marine sediments the conflict may indicate systematic errors with either the marine or the non marine samples departures from the assumed particle spectrum of grun and coauthors or time variable accretion rates with the early holocene period being characterized by low levels of accretion

a record of the extraterrestrial 3he flux through the late cretaceous abstract late cretaceous 100 73 ma pelagic limestones were measured for helium concentration and isotopic composition to characterize the interplanetary dust flux using 3he as a tracer in the bottaccione section near gubbio italy three intervals of elevated 3he concentration were detected k1 in the campanian stage at 79 ma k2 in the santonian stage at 85 ma and k3 in the turonian stage at 91 ma all three of these episodes are associated with high 3he 4he and 3he non carbonate ratios consistent with their derivation from an enhanced extraterrestrial 3he flux rather than decreased carbonate sedimentation or dissolution while k2 is modest in magnitude and duration and thus is of limited significance k1 and k3 are each identified by a few myr interval with an 4 fold enhancement in mean 3he flux compared with pre event levels samples from odp hole 762c in the indian ocean spanning both k2 and k3 93 83 ma confirm the presence of a peak in the turonian stage suggesting that k3 is a global event the k1 and k3 3he events are similar in most respects to the two peaks previously detected in the cenozoic suggesting a similar origin these have been attributed to a major asteroid collision in the late miocene and to a shower of either comets or asteroids in the late eocene based on the age and temporal evolution of k1 we suggest that it most likely records the collision which produced the baptistina asteroid family independently dated at 80 ma the k3 event is less easily explained it is characterized by an unusually spiky and erratic temporal progression suggesting an unusual abundance of very 3he rich particles not previously seen in the sedimentary 3he record we suggest this episode arises either from a comet shower or from an asteroid shower possibly associated with dust producing lunar impacts

geochemistry of great salt lake utah i hydrochemistry since 1850 abstract the hydrochemistry of great salt lake utah has been defined for the historic period 1850 through 1982 from published data combined with new observations the water balance depends largely on river inflow atmospheric precipitation onto the lake surface and evaporation input of the major solutes can best be accounted for by mixing dilute calcium bicarbonate type river waters with nacl dominated hydrothermal springs prior to 1930 lake concentrations fluctuated inversely with lake volume in response to small climatic variations since then salt precipitation and dissolution have significantly modified lake brine compositions and have led to density stratification and the formation of brine pockets of differing composition brine mixing has become an important component of brine evolution we have used calculated evaporation curves with mineral precipitation and dissolution to clarify these processes pore fluids represent important storage for solutes solute profiles can be modeled by simple one dimensional diffusion calculations short term historic variations in lake composition affect shallow pore fluids in the upper 2 metres of sediment

hydrological and geochemical processes controlling variations in na mg2 cl so42 groundwater brines south eastern australia abstract evaporative discharge of regional groundwater from more than 50 playa lakes at the 400 km 2 raak plain groundwater discharge complex forms a very large reservoir of hypersaline na mg 2 cl so 4 2 type subsurface brine but very little salt precipitates the main processes controlling the formation and evolution of brine compositions are a evapo concentration of the regional groundwater b mixing between the high and low tds end members and c subsurface gypsum precipitation uniformity in these processes across the entire groundwater discharge complex coupled with the chemical similarity between the regional groundwater and local recharge sources has led to remarkably similar brine chemistries and evaporite compositions across raak plain the similarity between the source waters and the ultimate brine compositions indicates that solutes are generally conserved within the system the greatest variation in groundwater chemistry at raak plain was found to occur within the playa lakes particularly within the top 1 2 m of the subsurface brine body rather than amongst the different lakes this small scale variability is a result of 1 advective and diffusive mixing between the hypersaline shallow 20 kyr