intracontinental subduction and palaeozoic inheritance of the lithosphere suggested by a teleseismic experiment across the chinese tien shan teleseismic tomography across the chinese tien shan shows that seismic wave speeds in the lithosphere beneath central tien shan are high and therefore the lithosphere is not weaker than that beneath the adjacent undeformed tarim and junggar basins there is evidence for significant velocity contrasts within the lithosphere that are presumably inherited from the palaeozoic collision history the high velocity thick yili block observed underneath the northern tien shan is a clue for shortening by a intracontinental subduction the observed geometry is consistent with a simple model of intracontinental subduction and suggests that during orogeny the lithosphere has remained heterogeneous and has deformed along existing planes of weakness rather than by homogeneous thickening of a particularly weak lithosphere

three dimensional thermo mechanical modeling of the cenozoic uplift of the tianshan mountains driven tectonically by the pamir and tarim abstract we develop a three dimensional thermo mechanical model as an approximate representation of the lithosphere of the tianshan orogenic belt and adjacent geological units for simulating the uplift mechanism of the tianshan mountains in the cenozoic we apply a velocity boundary condition approximating the northward push of the pamir and tarim against the tianshan block to derive lithospheric deformation of the model in particular we investigate systematically the influence of gravity induced creep deformation on mountain uplift our modeling results indicate that 1 the modeled topographic pattern coincides well with the actual topography implying that the tectonic push of the pamir and tarim can cause significant uplift of the tianshan mountains 2 the lithosphere of the tianshan mountains is mechanically weaker than that of the platforms to the south and north of the tianshan orogenic belt and 3 the gravity induced creep deformation has a significant influence on the process and elevation of mountain uplift therefore when subjected to the tectonic compression resulting from the northward push of the pamir and tarim the relatively weak lithosphere of the tianshan mountains would deform easily and hence absorb more shortening resulting in lithospheric thickening and consequent mountain uplift

shear wave splitting and subcontinental mantle deformation splitting observations are interpreted in terms of the strain induced lattice preferred orientation of mantle minerals especially olivine we consider three hypotheses concerning the origin of the continental anlsotropy 1 strain associated with absolute plate motion as in the oceanic upper mantle 2 crustal stress and 3 the past and present internal deformation of the subcontinental upper mantle by tectonic episodes it is found that the last hypothesis is the most successful namely that the most recent significant episode of internal deformation appears to be the best predictor of q for stable continental regions this is interpreted as fossil anisotropy whereas for presently active regions such as alaska the anisotropy reflects present day tectonic activity in the stable portion of north america there is a good correlation between delay time and lithospheric thickness this is consistent with the anisotropy being localized in the subcontinental lithosphere and suggests that intrinsic anisotropy is approximately constant the acceptance of this hypothesis has several implications for subcontinental mantle deformation first it argues for coherent deformation of the continental lithosphere crust and mantle during orogenies this implies that the anisotropic portion of the lithosphere was present since the deformational episode and rules out the addition of undeformed material to this layer by subsequent underplating or conductive growth of the thermal boundary layer one of the most important issues in the study of orogenies is the need to reconcile the formation of thickened lithosphere with the paradoxically high mantle temperatures often associated with orogenic episodes most efforts to date have focussed on modes of deformation whereby the cold lithospheric mantle is removed by convective instability or delamination and replaced by warm asthenosphere these models however are incompatible with the evidence for preserved coherent lithospheric deformation rather the deformed mantle appears to have been heated in place we suggest that the elevated mantle temperatures may be due to the strain heating accompanying the deformation

small scale convection in the upper mantle beneath the chinese tian shan mountains abstract small scale convection of the upper mantle beneath the chinese tian shan tien shan is investigated in terms of numerical modeling the finite element method combined with the marker in cell technique is used to describe the flow of the heterogeneous upper mantle the density model is derived from the p wave velocity structure of the crust and upper mantle along the kuche kuitun profile across the chinese tian shan which is obtained using the seismic travel time tomography technique our computational results reveal the southward counterclockwise and northward clockwise upper mantle convective cells underneath the junggar north tian shan and tarim south tian shan respectively our results also show the convective scale reaches to 500 km and the convective speed at the top of the upper mantle should not be less than 20 mm year for a normal viscosity model the northward extrusion of the tarim block plays a key role in the tian shan mountain building since the cenozoic period but it nearly does not influence the upper mantle convection the present day tectonic deformation in the chinese tian shan is related to the small scale convection of the upper mantle

a review and synthesis of glendonites pseudomorphs after ikaite with new data assessing applicability as recorders of ancient coldwater conditions abstract calcite pseudomorphs after ikaite glendonite are associated with coldwater depositional systems including glaciomarine and deepwater settings as dictated by the limited stability field of ikaite ikaite precipitation is favored by elevated alkalinity and dissolved phosphate conditions encountered commonly in association with organic rich marine sediments where methane oxidation is occurring the rapid recrystallization of ikaite to calcite during slight warming or pressure release results in considerable solid volume loss producing a highly porous crystal mesh preservation of the original ikaite crystal form requires precipitation of diagenetic calcite cement during early burial to prevent compaction and collapse of pseudomorph structures during later burial diagenesis remaining pore space may be filled with deeper burial calcite cement glendonites from the permian of the sydney basin occur in subtidal shelf facies containing glacial dropstones and a normal marine fauna stable oxygen isotope signatures of modern ikaite suggest carbonate precipitation in equilibrium with ambient seawater carbon signatures are usually strongly negative relative to normal marine carbonate consistent with derivation of carbonate from methane oxidation review of published data suggests that while holocene glendonite may provide reliable isotopic records of the conditions of ikaite precipitation precipitation of later calcite cement within the glendonite structure reduces the significance of the isotopic signature as an indicator of primary depositional conditions bulk glendonite samples from the permian sydney basin australia have a broad range of 18 o and 13c 18opdb 5 to 15 13c 8 to 16 in contrast to the narrow range for brachiopod carbonate 18opdb 1 to 5 13c 5 to 7 from the same strata handpicked separates of primary glendonite and secondary calcite also have a wide range of stable isotope values the data from sydney basin glendonites indicate that diagenetic precipitation of calcite has blurred the isotopic signature of primary ikaite replacement calcite at the scale of micosampling done in this study

active thrusting and folding along the northern tien shan and late cenozoic rotation of the tarim relative to dzungaria and kazakhstan we have studied geometries and rates of late cenozoic thrust faulting and folding along the northern piedmont of the tien shan mountain belt west of urumqi where the m 8 3 manas earthquake occurred on december 23 1906 the northern range of the tien shan rising above 5000 m overthrusts a flexural foredeep filled with up to 11 000 m of sediment of the dzungarian basement our fieldwork reveals that the active thrust reaches the surface 30 km north of the range front within a 200 km long zone of neogene quaternary anticlines fault scarps are clearest across inset terraces within narrow valleys incised through the anticlines by large rivers flowing down from the range in all the valleys the scarps offset vertically the highest terrace surface by the same amount 10 2 0 7 m inferring an early holocene age 10 2 kyr for this terrace which is continuous with the largest recent fans of the piedmont yields a rate of vertical throw of 1 0 0 3mm yr on the main active thrust at the surface a quantitative morphological analysis of the degradation of terrace edges that are offset by the thrust corroborates such a rate and yields a mass diffusivity of 5 5 2 5 m 2 kyr a rather fresh surface scarp 0 8 0 15 m high that is unlikely to result from shallow earthquakes with 6 m 7 in the last 230 years is visible at the extremities of the main fold zone we associate this scarp with the 1906 manas earthquake and infer that a structure comprising a deep basement ramp under the range gently dipping flats in the foreland and shallow ramps responsible for the formation of the active fault propagation anticlines could have been activated by that earthquake if so the return period of a 1906 type event would be 850 380 years the small size of the scarp for an earthquake of this magnitude suggests that a large fraction of the slip at depth 2 3 is taken up by incremental folding near the surface comparable earthquakes might activate flat detachments and ramp anticlines at a distance from the front of other rising quaternary ranges such as the san gabriel mountains in california or the mont blanc aar massifs in the alps we estimate the finite cenozoic shortening of the folded dzungarian sediments to be of the order of 30 km and the cenozoic shortening rate to have been 3 1 5 mm yr assuming comparable shortening along the tarim piedmont and minor additional active thrusting within the mountain belt we infer the rate of shortening across the tien shan to be at least 6 3 mm yr at the longitude of manas 85 5 e a total shortening of 125 30 km is estimated from crustal thickening assuming local airy isostatic equilibrium under the same assumption serial n s sections imply that cenozoic shortening across the belt increases westwards to 203 50 km at the longitude of kashgar 76 e as reflected by the westward increase of the width of the belt this strain gradient implies a clockwise rotation of tarim relative to dzungaria and kazakhstan of 7 2 5 around a pole located near the eastern extremity of the tien shan west of hami 96 e 43 5 n comparable to that revealed by paleomagnetism between tarim and dzungaria 8 6 8 7 a 6 mm yr rate of shortening at the longitude of manas would imply a rate of rotation of 0 45 m y and would be consistent with a shortening rate of 12 mm yr north of kashgar taking such values to be representative of late cenozoic rates would place the onset of reactivation of the tien shan by the india asia collision in the early to middle miocene 16 22 9 m y in accord with the existence of particularly thick late neogene and quaternary deposits such reactivation would thus have started much later than the collision roughly at the time of the great mid miocene changes in tectonic regimes denudation and sedimentation rates observed in southeast asia the himalayas and the bay of bengal and of the correlative rapid change in seawater sr isotopic ratio 20 to 15 ma like these other changes the rise of the tien shan might be a distant consequence of the end of indochina s escape

central european vegetation response to abrupt climate change at 8 2 ka oxygen isotope records show a major climatic reversal at 8 2 ka in greenland and europe annually laminated sediments from two lakes in switzerland and germany were sampled contiguously to assess the response of european vegetation to climate change ca 8 2 ka with time resolution and precision comparable to those of the greenland ice cores the pollen assemblages show pronounced and immediate responses 0 20 yr of terrestrial vegetation to the climatic change at 8 2 ka a sudden collapse of corylus avellana hazel was accompanied by the rapid expansion of pinus pine betula birch and tilia linden and by the invasion of fagus silvatica beech and abies alba fir vegetational changes suggest that climatic cooling reduced drought stress allowing more drought sensitive and taller growing species to out compete corylus avellana by forming denser forest canopies climate cooling at 8 2 ka and the immediate reorganization of terrestrial ecosystems has gone unrecognized by previous pollen studies on the basis of our data we conclude that the early holocene high abundance of c avellana in europe was climatically caused and we question the conventional opinion that postglacial expansions of f silvatica and a alba were controlled by low migration rates rather than by climate the close connection between climatic change and vegetational response at a subcontinental scale implies that forecasted global warming may trigger rapid collapses expansions and invasions of tree species

seasonality of holocene hydroclimate in the eastern mediterranean reconstructed using the oxygen isotope composition of carbonates and diatoms from lake nar central turkey a positive shift in the oxygen isotope composition 18o of lake carbonates in the eastern mediterranean from the early to late holocene is usually interpreted as a change to drier reduced p e conditions however it has also been suggested that changes in the seasonality of precipitation could explain these trends here holocene records of 18o from both carbonates and diatom silica from lake nar in central turkey provide insights into palaeoseasonality we show how 18olakewater the difference between spring and summer reconstructed 18olakewater was minimal in the early holocene and for most of the last millennium but was greater at other times for example between 4 100 1 600 years bp we suggest that increased 18olakewater could have been the result of relatively more spring summer evaporation amplified by a decline in lake level in terms of change in annual mean 18o isotope mass balance modelling shows that this can be influenced by changes in seasonal p e as well as inter annual p e but lake level falls inferred from other proxies confirm there was a mid holocene transition to drier climatic conditions in central turkey

evidence of lateglacial and holocene climatic change and human impact in eastern anatolia high resolution pollen charcoal isotopic and geochemical records from the laminated sediments of lake van turkey annually laminated sediments from lake van spanning about 13000 varve years were sampled for stable isotopic geochemical pollen and charcoal analyses in order to find evidence of past regional climatic changes and human impact in the semi arid region of eastern anatolia turkey the lateglacial period was cold and dry with steppe vegetation and saline lake water during the younger dryas the lake level dropped dramatically and the vegetation turned to a semi desert geochemical and isotopic records indicate a strong increase in moisture at the onset of the holocene and artemisia chenopod steppes were partly replaced by grass steppe and pistachio scrub a delay of about 3000 years in the expansion of deciduous oak woodlands and high steppe fire frequencies suggest dry spring and summer weather during the early holocene at 8200 yr bp a shift in the regional climate regime facilitated the transport of more moisture into the interior areas of the taurus mountains and caused a change in the seasonal distribution of precipitation the steppe forests dominated by quercus advanced and reached their maximum extention at about 6200 yr bp all the proxy data indicate optimum climatic conditions low water salinity and high lake level between 6200 and 4000 yr bp after 4000 yr bp aridity increased again and the modern climatic situation was established human impact in the catchment of lake van started at 3800 yr bp and was intensified during the last 600 years

quantification of biotic responses to rapid climatic changes around the younger dryas a synthesis to assess the presence or absence of lags in biotic responses to rapid climatic changes we 1 assume that the 18o in biogenically precipitated carbonates record global or hemispheric climatic change at the beginning and at the end of the younger dryas without any lag at our two study sites of gerzensee and leysin switzerland 2 derive a time scale by correlating the 18o record from these two sites with the 18o record of the grip ice core 3 measure 18o records in ostracods and molluscs to check the record in the bulk samples and to detect possible hydrological changes 4 analyse at gerzensee and leysin as well as at two additional sites that lack carbonates and hence a 18o record pollen plant macrofossils chironomids beetles and other insects and cladocera 5 estimate our sampling resolution using the grip time scale for the isotope stratigraphies and the biostratigraphies and 6 summarise the major patterns of compositional change in the biostratigraphies by principal component analysis or correspondence analysis we conclude that at the major climatic shifts at the beginning and end of the younger dryas hardly any biotic lags occur within the sampling resolution of 8 30 years and that upland vegetation responded as fast as aquatic invertebrates we suggest that the minor climatic changes associated with the gerzensee and preboreal oscillations were weakly recorded in the biostratigraphies at the lowland site but were more distinct at higher altitudes individualistic responses of plant and animal species to climatic change may reflect processes in individuals e g productivity and phenology in populations e g population dynamics in spatial distributions e g migrations and in ecosystems e g trophic state we suggest that biotic responses may be telescoped together into relatively short periods 50 to 150 years perhaps disrupting functional interactions among species and thus destabilising ecosystems

a mid european decadal isotope climate record from 15 500 to 5000 years b p oxygen isotope ratios of precipitation delta18op inferred from deep lake ostracods from the ammersee southern germany provide a climate record with decadal resolution the record in detail shows many of the rapid climate shifts seen in central greenland ice cores between 15 000 and 5000 years before the present b p negative excursions in the estimated delta18op from both of these records likely reflect short weakenings of the thermohaline circulation caused by episodic discharges of continental freshwater into the north atlantic deviating millennial scale trends however indicate that climate gradients between europe and greenland changed systematically reflecting a gradual rearrangement of north atlantic circulation during deglaciation

first high resolution marinopalynological stratigraphy of late quaternary sediments from the central part of the bulgarian black sea area abstract spores pollen and dinoflagellate cysts of late pleistocene and holocene sediments were analyzed from giant gravity core 18 from the black sea continental slope recovered from a water depth of 971 m the investigated length of the core is 203 5 cm it includes 3 lithological units light grey clay sapropels and coccolith bearing ooze the core was sampled at 5 10 cm intervals sampling of the interval 141 5 126 cm was carried out at every cm ams radiocarbon dating of bulk organic carbon was performed on 18 selected sediment layers this chronological data allowed the first high resolution pollen stratigraphy of late quaternary sediments from the western black sea area to be presented the percentage spore pollen diagram is divided into 6 local pollen assemblage zones the trends in the vegetation dynamics and climate changes and the early history of migration of the majority of the arboreal taxa that nowadays occur in the eastern balkan range were traced out the palynological record suggests that open oak forests were spread in the eastern balkan range at the beginning of the holocene and shows early migration of the major temperate arboreal species such as quercus ulmus tilia and carpinus betulus this vegetation palaeosuccession continues with the spreading of mixed oak forests from 8950 until 2620 cal bp 8650 40 until 3120 35 14c bp followed by destructive changes due to human impact and climate deterioration a cooling of holocene climate that is well known in the north atlantic region as the 8200 yrs cold event is identified for the first time in marine records from the bulgarian black sea area the assemblages of dinoflagellate cysts and acritarchs were investigated to provide a reconstruction of surface seawater salinity and surface seawater temperature changes two main dinoflagellate cyst assemblages one dominated by fresh to brackish water species such as spiniferites cruciformis and pyxidinopsis psilata and a subsequent one that is characterized by euryhaline marine mediterranean species such as lingulodinium machaerophorum spiniferites belerius spiniferites bentorii operculodinium centrocarpum and acritarchs cymatiosphaera globulosa testified a change in sss from low salinity

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

holocene environmental change and its impact on sediment dynamics in the eastern mediterranean abstract investigators have studied past environmental change in the eastern mediterranean region from a number of perspectives while climate reconstructions and palynological research have focused on forces that drive the geomorphologic system many researchers have attempted to use sediment archive studies to identify periods of change in sediment dynamics due to the large variability in environmental parameters and the variety of landscapes present in the eastern mediterranean region research has focused on sediment archives ranging from small colluvial sites to deltas of large rivers on the mediterranean coast as the cultural record for the region is extremely rich the main goal of palaeo environmental research in the eastern mediterranean has been to identify the relative importance of human impact on the landscape nevertheless sediment archives have significant limitations chronological control for many palaeo environmental records is highly uncertain and rates of landscape change are oftentimes difficult to assess most palaeo environmental research has been conducted on or near archeological sites where direct human impact may obscure the indirect impact on sediment dynamics through land use changes quantification and modeling of sediment dynamics in the eastern mediterranean environment offer one solution when erosion and sediment transport rate analyses are incorporated periods of relatively important change can be identified using multiple approaches the relative importance of the main driving forces climate and land use become distinguishable since field based data from the actual sediment archives remain vital an overview of numerous studies in the eastern mediterranean is provided in order to draw a general picture for different time periods and the relative scale of regional landscape development during the holocene a comparison of sediment dynamics with the record of driving forces indicates that while climate was the main driver of the geomorphic system during the early holocene at some point human impact became widespread and began to dictate sediment dynamics to a large extent from the byzantine period onward soil properties seem to play an increasingly important role as the hillslope soil reservoir in the eastern mediterranean was progressively depleted during the late holocene

paleo environment and radiocarbon calibration as derived from lateglacial early holocene tree ring chronologies abstract we present an overview of the extended hohenheim oak chronology hoc and the dendrochronologically dated preboreal pine tree ring chronology ppc both provide an absolute annual time frame of the holocene extending into the younger dryas yd back to 11 919 bp two floating pine and larch chronologies are 14 c dated covering large parts of the lateglacial dendro ecological parameters such as ring width and stable isotope variation are used to infer past environmental conditions 14 c analyses on decadal sections provide a high precision high resolution data set for calibration of the radiocarbon time scale based on a marked change in ring width and growth pattern the yd termination is clearly identified in the german pine chronology its absolute age of 11 570 bp appears synchronous within the errors of the respective chronologies to related signals in the greenland ice cores grip gisp2 and in lacustrine varve sequences the 14 c age of the laacher see tephra lst is determined from a series of decadal tree ring samples to 11 063 12 14 c bp the calibrated range is 13 010 13 200 cal bp the climatic impact of the lst is reflected in the growth pattern of our tree ring chronologies

discordant contrasts of p and s wave speeds across the 660 km discontinuity beneath tibet a case for hydrous remnant of sub continental lithosphere abstract using high resolution triplicate shear waveforms recorded by broadband seismic arrays we show that a corresponding anomaly of high s wave speed v s is absent where an anomaly of high p wave speed v p was recently recognized in the transition zone of the mantle tz beneath central tibet a likely cause of the discrepancy between anomalies in v p and v s is a minor amount of water in nominally anhydrous polymorphs of olivine prior to thickening by continent continent collision the tibetan mantle was part of a mantle wedge which has been hydrated during past episodes of subduction hydration of the sub continental lithospheric mantle sclm provides a natural mechanism to facilitate ductile deformation so rapid thickening of the sclm which would have been hindered by advection of cold materials can take place convective instability would then lead to removal and sinking of thickened cold sclm leaving a remnant in the tz detectable only in v p this interpretation not only is consistent with previous reconstruction of the sclm in tibet based on several types of independent data but also provides a new pathway for water to enter and be stored in the tz

airstream regions of north africa and the mediterranean abstract mean monthly surface wind streamline charts for the north africa mediterranean region are extracted from a previously prepared northern hemisphere set these charts define mean airstream sources and mean confluences or fronts composite charts of airstream duration and seasonally stationary confluence positions are then extracted from the monthly streamline charts the seasonality duration and mean boundaries of the airstreams and their properties define a pattern of genetic climatic regions this pattern derived entirely from climatic data is found to match the biotic pattern quite well

shear wave splitting observations in the chinese tianshan orogenic belt 1 a linear array of 26 3 component broadband digital stations across the chinese tianshan orogenic belt ctob was deployed for 13 months to measure the shear wave splitting fast direction of teleseismic shear waves beneath the southern ctob is nww see and gradually turns into nee sww in the north delay times are 0 65 1 48s with average value of 0 97 0 15s and the maximum delay time is observed in the middle mountain and decrease in the south and the north fast directions are generally parallel to the strike of the orogenic belt indicating that more than one hundred kilometers of upper mantle is involved in collisional deformation compared to other stations change in fast direction for stations in the south and north ends of the array is probably resulted from subduction of the tarim block and the junggar block into the tianshan range respectively

dynamic support of the tien shan lithosphere based on flexural and rheological modeling abstract the tien shan is a high young and seismically active intracontinental mountain belt in central asia that has been uplifted approximately 3 km over the past 10 ma a flexural analysis using bouguer gravity and topographic data was used to determine the dynamic lithospheric mechanisms that are responsible for the topographic uplift and crustal thickening of the range bouguer gravity anomalies were used to constrain flexural models for isostatic compensation associated with the large relief of the tien shan this is explained by significant underthrusting of a continuous elastic plate below the tien shan with an effective elastic thicknesses te that gradually changes from 40 to 50 km in the tarim and junggar basins and the kazakh plate to 20 23 km beneath the tien shan horizontal shortening due to folding and thrusting of the upper middle crust causes uplift and crustal thickening of the margin of the tien shan the regional and local compensation occur at the eastern and western parts of the tien shan respectively rheological modeling using a simple geothermal structure for the tien shan reveals that the base of the strong upper crust of tibet is at a depth of 30 35 km which is consistent with the depths of 7776 earthquakes between 1970 and 2011 which serve as constraints on the brittle failure domain of the area the moho depths are used to determine the thickness of the lower crust 17 25 km and to understand the mobility of the lower crustal flow of the tien shan the tendency for the strong upper crust to flow over the weak ductile lower crust or middle lower crust depends on the thickness of the lower crust in other words its strength depends on the depths of the base of the upper crust and the moho the larger the difference the easier it is for the upper crust to flow relative to the strong upper mantle lithosphere the crustal deformation is decoupled from deformation of the upper mantle lithosphere by the weak ductile lower crust of the tien shan

a late pleistocene long pollen record from lake urmia nw iran abstract a palynological study based on two 100 m long cores from lake urmia in northwestern iran provides a vegetation record spanning 200 ka the longest pollen record for the continental interior of the near east during both penultimate and last glaciations a steppe of artemisia and poaceae dominated the upland vegetation with a high proportion of chenopodiaceae in both upland and lowland saline ecosystems while juniperus and deciduous quercus trees were extremely rare and restricted to some refugia hippophae rhamnoides constituted an important phanerophyte particularly during the late last glacial period a pronounced expansion in ephedra shrub steppe occurred at the end of the penultimate late glacial period but was followed by extreme aridity that favoured an artemisia steppe very high lake levels registered by both pollen and sedimentary markers occurred during the middle of the last glaciation and late part of the penultimate glaciation the late glacial to early holocene transition is represented by a succession of hippophae ephedra betula pistacia and finally juniperus and quercus the last interglacial period eemian slightly warmer and moister than the holocene was followed by two interstadial phases similar in pattern to those recorded in the marine isotope record and southern european pollen sequences

late holocene dust accumulation within the ancient town of marea coastal zone of the south mediterranean sea n egypt abstract the ruins of the marea ancient town are located on the southern shore of maryut lake ancient mareotis 45 km to the southwest of alexandria egypt marea was a very important trade religious and agricultural centre in the 5th 7th century a d the area occupied by a town in the past has diversified relief local hills are built of sandstones constituted by calcified dunes the hills are separated by flat depressions of irregular shape the uppermost layer in the depressions covering loam and sand sediments is made up of structureless aeolian dust of 0 6 1 2 m thickness the following analyses of the sediments were conducted granulometric composition the mineralogical composition of samples the loss on ignition the total organic carbon toc organic matter om and calcium carbonate caco3 clay minerals and geochemistry results of osl dating indicate that the filling of the depressions with silt deposits started probably about 2450 years ago and that it is correlated with dust deposition the rate of the dust accumulation was about 0 49 mm year however diversified humus content in the deposits suggests that it was not a permanent process the accumulation took place during intensive dust storms the sediments in the depressions are fine silt and clay with uni and bi modal particle size distribution likely caused by both the local and the regional origin of the material most dust accumulated within the ancient town of marea originated from the border between sahel and sahara local and even regional sources of material were of lower importance geochemical ratios mg ca fe mn and na k distinguished in the deposits of the depressions show that the beginning of the dust accumulation took place during environmental conditions more humid than the contemporary ones that indicates a slight increase in the humidity of climate dated to ca 10th 12th century a d followed by its significant drying initiated ca 15th 16th century a d in addition results of analysis of trace elements suggest that already in the 5th century bc the town of marea or its closest vicinity may have been the site of development of industrial activity much earlier than the age of the oldest artefacts found within the town

vegetational response to climatic changes recorded in swiss late glacial lake sediments abstract high resolution pollen analysis at five lakes on an altitudinal transect in switzerland gerzensee 603 m leysin 1230 m regenmoos 1260 m zeneggen 1510 m heremence 2290 m focused on the vegetational response to the rapid climatic changes at the end and beginning of the younger dryas and to the minor gerzensee and preboreal climatic oscillations an absolute time scale transferred from the greenland grip ice core to the gerzensee and leysin records by wiggle matching the oxygen isotope stratigraphies facilitates the estimation of pollen influx and rates of change the climatic warming at the end of the younger dryas indicated by increases in oxygen isotope values and or the beginning of organic sedimentation in the lakes was immediately reflected in the vegetation at all the sites investigated the time lags at sites situated above the timberline during the younger dryas are considered to be migrational lags at the onset of the younger dryas a time lag of several decades occurred between the oxygen isotope record of climatic cooling and the major response of the vegetation whereas minor vegetation changes occurred with or without short time lags betula reacted earlier to the new environmental conditions within about 40 50 yr at gerzensee and within less than 36 yr at leysin than pinus and artemisia about 170 yr suggesting that time lags are due to the ecological requirements of the different taxa for the gerzensee and preboreal oscillations little or no change can be observed in the pollen record from gerzensee whereas at leysin both climatic oscillations produced a statistically significant vegetational response to both climatic oscillations generally the vegetation responses to climatic changes are more pronounced near vegetation ecotones at medium and higher altitudes than in the lowlands

seasonal formation of ikaite caco3 6h2o in saline spring discharge at expedition fiord canadian high arctic assessing conditional constraints for natural crystal growth abstract spring discharge at expedition fiord pollard et al 1999 on axel heiberg island in the canadian high arctic produces a variety of travertine forms in addition to a diverse collection of mineral precipitates this paper focuses on clusters of thermally unstable crystals believed to be the mineral ikaite caco3 6h2o growing seasonally along two spring outflows at colour peak this form of calcium carbonate mineral occurs along small sections of discharge outflow as white euhedral crystals up to 0 5 cm in length difficulty in sampling storage and transport of the samples for analysis has hampered attempts to confirm the presence of ikaite by x ray diffraction however various field observations and the remarkable instability of these crystals at normal ambient temperatures strengthens our argument this paper provides a description of these particular caco3 6h2o crystals and their environmental surroundings and attempts to determine the validity of ikaite precipitation at this site by theoretical geochemical modeling these results are compared with other reported observations of ikaite to both understand their occurrence and help delineate their geochemical characteristics it is believed that the restrictive combination of spring water chemistry and long periods of low temperatures characteristic of arctic climates are necessary for ikaite growth at this site the fact that ikaite is not forming at a second group of saline springs 11 km away allows us to more specifically outline conditions controlling its presence

speleothem evidence for late holocene climate variability and floods in southern greece abstract we present stable isotope data 18o 13c from a detrital rich stalagmite from kapsia cave the peloponnese greece the cave is rich in archeological remains and there are reasons to believe that flooding of the cave has directly affected humans using the cave using a combination of u th and 14c dating to constrain a site specific correction factor for 232th 238u detrital molar ratio a linear age model was constructed the age model shows that the stalagmite grew during the period from ca 950 bc to ca ad 830 the stable oxygen record from kapsia indicates cyclical changes of close to 500 yr in precipitation amount with rapid shifts towards wetter conditions followed by slowly developing aridity superimposed on this signal wetter conditions are inferred around 850 700 500 and 400 100 bc and around ad 160 300 and ad 770 and driest conditions are inferred to have occurred around 450 bc ad 100 150 and ad 650 detrital horizons in the stalagmite indicate that three major floods took place in the cave at 500 bc 70 bc and ad 450 the stable carbon isotope record reflects changes in biological activity being a result of both climate and human activities

climate related variations in the composition of the late glacial and early holocene sediments of lake perespilno eastern poland abstract this paper presents an array of analyses of the laminated sediments of lake perespilno eastern poland covering the period between older dryas and preboreal using the varve chronologies pollen and 14 c data the laminated sequence of lake perespilno has been synchronised with that of lake go ciaz the length of the allerod and younger dryas periods derived from lake perespilno sediments agrees well with the previous estimates according to our data the climate in the allerod was relatively mild with some increase of precipitation and humidity after ca 13 2 kyr cal bp the beginning of the younger dryas is marked by drastic changes in temperature as well as humidity thinning of forests facilitated input of allochtonous material to the lake it seems that the groundwater level as well as lake level dropped significantly and the period of lowest water table was prolonged for ca 300 years surprisingly the abrupt warming at the beginning of the holocene is only slightly reflected in the sediments changes in sediment composition at that time seem to be controlled more by the development of surrounding vegetation than by the climate itself

seismic anisotropy of oceanic upper mantle shear wave splitting methodologies and observations we develop methodologies to obtain accurate measurements of shear wave splitting and apply these techniques to examine the pattern of oceanic upper mantle anisotropy to obtain high quality estimates of receiver splitting at island stations we devise a stacking method that finds the optimum splitting parameters and 95 error region for teleseismic shear wave phases from a suite of earthquake events to obtain additional measurements in oceanic regions we develop techniques to measure splitting parameters and errors for ss phases that sample upper mantle anisotropy at their bounce points however we find the data are often of low resolution and anomalous characteristics are sometimes found that make splitting difficult to interpret ten second splitting of ss is observed across the banjo seismic array but we cannot unambiguously attribute this signal to mantle anisotropy at the bounce the receiver splitting methods are used to assess the adequacy of a two anisotropic layer model for the pacific region with fast polarization azimuth in the lithosphere oriented in the fossil spreading direction and in the asthenosphere oriented in the absolute plate motion direction this model has been proposed to explain surface wave data in the pacific ocean but our splitting results demonstrate that oceanic anisotropy patterns are more heterogeneous than would be predicted while the island splitting measurements could reflect the influence of individual hotspot upwellings hotspot effects do not appear to be universally dominant we propose that splitting observations alternatively indicate broad scale differences in the underlying character of oceanic upper mantle anisotropy associated with coherant patters of lithospheric structure and asthenospheric flow in particular splitting surface wave models and regional studies all support a model where lithospheric anisotropy throughout the south pacific has been erased or reoriented toward the absolute plate motion direction whereas more limited observations in the north pacific indicate that the fossil lithospheric signature appears to be preserved

correlation and synchronisation of lateglacial continental sequences in northern central europe based on annually laminated lacustrine sediments abstract the present study focusses on correlation and synchronisation of weichselian lateglacial varved lake sediments from western germany meerfelder maar eifel region northern germany hamelsee lower saxony central poland lake go ci a z and eastern poland lake perespilno by using varve chronology tephrochronology palynostratigraphy and stable isotopes comparison of the several independent time scales shows that biotic and abiotic parameters respond abruptly and quasi synchronously within the errors of the different chronologies during the younger dryas preboreal transition moreover there is a consensus about the length of the younger dryas cold stage of 1100 1150 varve years in the allerod the prominent laacher see tephra 12 880 varve years bp can be used to fix floating varve chronologies the relative duration of this biozone has been determined in meerfelder maar and hamelsee at between 625 and 670 varve years in the meerfelder maar a combination of continuous varve counting and biostratigraphy has been possible for the almost entire lateglacial the comparison between continental limnic sequences and greenland ice core records should be made on the basis of independent chronologies in both archives it is more practicable to develop regional stratotypes on the continental regions instead of simply using ice cores as stratotypes for the lateglacial for terrestrial european records in this respect annually laminated lacustrine sequences have a great potential

the tempo of holocene climatic change in the eastern mediterranean region new high resolution crater lake sediment data from central turkey this study presents results from a multi proxy analysis of cores taken in a crater lake sequence from eski acigol in central turkey which cover the period from pre c 16000 cal yr bp to the present the sediments comprise an upper unit of generally non laminated banded to massive silts and peats of mid to late holocene age overlying a laminated unit of late pleistocene to early mid holocene age the laminae comprising mainly aragonite amorphous silica diatom frustules and organic matter were formed in a relatively deep dilute meromictic lake pollen data indicate an abrupt replacement of artemisia chenopod steppe by grass oak terebinth parkland during the period of laminae deposition marking the start of the holocene a gradual increase in tree pollen during the early holocene came to an end c 6500 cal yr bp u series and adjusted c 14 timescale when mesic deciduous taxa declined at the same time as lake levels fell human impact on regional vegetation is inferred from a sharp decline in oak around 4500 4000 cal yr bp diatom isotopic and mineralogical data indicate that during the second half of the holocene the lake became relatively shallow and oscillated between fresh and brackish evaporated water conditions the contrast between wetter early and drier late holocene climatic conditions is matched by other eastern and central mediterranean proxy climate data while the eski acigol sequence resembles holocene hydroclimatic changes in the saharo arabian zone and was also apparently linked to orbital forcing it is unlikely to have had the same direct cause i e an expansion and subsequent retreat of monsoon rainfall

lithospheric structure and dynamic processes of the tianshan orogenic belt and the junggar basin abstract located at the center of the eurasian continent and accommodating as much as 44 of the present crustal shortening between india and siberia the tianshan orogenic belt tob is one of the youngest 7000 m orogenic belts in the world it provides a natural laboratory for examining the processes of intracontinental deformation in recent years wide angle seismic reflection refraction profiling and magnetotelluric sounding surveys have been carried out along a geoscience transect which extends northeastward from xayar at the northern margin of the tarim basin tb through the tianshan orogenic belt and the junggar basin jb to burjing at the southern piedmont of the altay mountain we have also obtained the 2d density structure of the crust and upper mantle of this area by using the bouguer anomaly data of northwestern xinjiang with these surveys we attempt to image the 2d velocity and the 2d electric structure of the crust and upper mantle beneath the tianshan orogenic belt and the junggar basin in order to obtain the small scale structure of the crust mantle transitional zone of the study area the wavelet transform method is applied to the seismic wide angle reflection refraction data combining our survey results with heat flow and other geological data we propose a model that interprets the deep processes beneath the tianshan orogenic belt and the junggar basin located between the tarim basin and the junggar basin the tianshan orogenic belt is a block with relatively low velocity low density and partially high resistivity it is tectonically a shortening zone under lateral compression a detachment exists in the upper crust at the northern margin of the tarim basin its lower part of the upper crust intruded into the lower part of the upper and the middle crust of the tianshan near the korla fault its middle crust intruded into the lower crust of the tianshan and its lower crust and lithospheric mantle subducted into the upper mantle of the tianshan in these processes the mass of the lower crust of the tarim basin was carried down to the upper mantle beneath the tianshan forming a 20 km thick complex crust mantle transitional zone composed of seven thin layers with a lower than average velocity the thrusting and folding of the sedimentary cover the intrusive layer in the upper and middle crust and the mass added by the subduction of the tarim basin into the upper mantle of the tianshan are probably responsible for the crustal thickening of the tianshan due to the important mass deficiency in the crust and the upper mantle of the tianshan buoyancy must occur and lead to rapid ascent of the tianshan the episodic tectonic uplift of the tianshan and tectonic subsidence of the junggar basin are closely related to the evolution of the paleozoic mesozoic and cenozoic tethys

complex seismic anisotropic structure beneath the central tien shan revealed by shear wave splitting analyses summary shear wave splitting parameters fast polarization directions and splitting times obtained at the permanent broad band station wushi wus which is situated in central tien shan china demonstrate systematic azimuthal variations the fast polarization directions range from 26 to 85 and the delay times range from 0 4 to 1 6 s suggesting a complex anisotropic structure that cannot be adequately explained by a single anisotropic layer with horizontal axis of symmetry the azimuthal variations have an apparent 90 periodicity and thus can be best explained by a two layer anisotropic model with horizontal symmetry axes the optimal fast direction for the upper layer is in the 60 80 range that is subparallel to the strike of the tien shan orogenic belt and can consequently be attributed to the ongoing n s directed shortening the fast direction for the lower layer ranges from 85 to 105 and can be explained by lattice preferred orientation of olivine crystals in the asthenosphere associated with present day absolute plate motion of the eurasian plate

the coupled δ13c radiocarbon systematics of three late glacial early holocene speleothems insights into soil and cave processes at climatic transitions abstract the coupled 13 c radiocarbon systematics of three european stalagmites deposited during the late glacial and early holocene were investigated to understand better how the carbon isotope systematics of speleothems respond to climate transitions the emphasis is on understanding how speleothems may record climate driven changes in the proportions of biogenic soil carbon and limestone bedrock derived carbon at two of the three sites the combined 13 c and 14 c data argue against greater inputs of limestone carbon as the sole cause of the observed shift to higher 13 c during the cold younger dryas in these stalagmites gar 01 from la garma cave n spain and so 1 from sofular cave turkey the combined changes in 13 c and initial 14 c activities suggest enhanced decomposition of old stored more recalcitrant soil carbon at the onset of the warmer early holocene alternative explanations involving gradual temporal changes between open and closed system behaviour during the late glacial are difficult to reconcile with observed changes in speleothem 13 c and the growth rates in contrast a stalagmite from pindal cave n spain indicates an abrupt change in carbon inputs linked to local hydrological and disequilibrium isotope fractionation effects rather than climate change for the first time it is shown that while the initial 14 c activities of all three stalagmites broadly follow the contemporaneous atmospheric 14 c trends the younger dryas atmospheric 14 c anomaly can be clearly discerned subtle changes in speleothem initial 14 c activities are linked to climate driven changes in soil carbon turnover at a climate transition

seismic anisotropy and mantle dynamics beneath china abstract we analyzed the shear wave splitting at 138 permanent seismograph stations to study seismic anisotropy and mantle dynamics under mainland china to obtain reliable results we used three different methods to measure the shear wave splitting parameters using core phases sks skks skiks and pks as well as the direct s waves from regional and distant earthquakes our results show that the fast orientations of the anisotropy wnw ese in eastern china are generally consistent with the absolute plate motion apm direction of the eurasian plate suggesting that the anisotropy is mainly located in the asthenosphere resulting from the lattice preferred orientation of olivine due to the shear deformation there the fast axes in western china generally agree with the strikes of the orogens and active faults while they are perpendicular to the direction of the maximum horizontal stress suggesting that the anisotropy in the lithosphere contributes significantly to the observed shear wave splitting the fast axes in western china are also consistent with the apm direction suggesting that the apm driven anisotropy in the asthenosphere is another source of the shear wave splitting there these results suggest that apm driven anisotropy commonly exists under continents similar to that under oceanic regions even though the continental lithosphere has suffered extensive deformation

shear wave anisotropy beneath the tibetan plateau eleven broadband digital seismic stations were deployed across the central tibetan plateau in the first extensive passive source experiment attempted within the tibetan plateau one year of recording resulted in 186 event station pairs which we analyze to determine the characteristics of shear wave splitting in the upper mantle beneath the array measurements of the fast polarization direction and delay time t for sks and direct s arrivals reveal systematic variations along the north south oriented array in the north central region of the plateau very large delay times are observed at three stations the largest of which is budo with of t 2 4 s however at tunl which is off the northern edge of the plateau and 110 km from budo and at sites in the south central plateau t decreases by nearly a factor of 3 we also observe systematic rotation of from about 45 ne to 90 e w from south to north along the array a previously identified zone of inefficient sn propagation correlates well with our region of large t observations the large delay times suggest that a relateively high number of anisotropic crystals are preferentially alligned within the mantle lid beneath the north central portion of the tibetan plateau in most cases fast polarization directions appear to be parallel to surface geologic features suggesting as much as 200 km of the upper mantle has been involved in the collisional deformation that has produced the tibetan plateau

local holocene environmental indicators in upper mesopotamia pedogenic carbonate record vs archaeobotanical data and archaeoclimatological models abstract it has been suggested that pedogenic carbonate coatings on stones in archaeological sites can be used to reconstruct late quaternary environmental changes in the area of the fertile crescent this research compares a pedogenic carbonate record from southeastern turkey with three other local or regional sources of palaeoenvironmental information in order to evaluate the correlation of this new proxy with other independent data from the area 1 ancient plant macroremains from archaeological sites as ecological indicators 2 stable carbon isotope composition of ancient plant macroremains available in the literature and from our own investigations in six mid holocene archaeological sites and 3 modelled holocene precipitation and temperature changes in the northern fertile crescent comparison involved selected palynological and isotopic data from lacustrine sediments as well as speleothem isotopic records in near eastern locations available in the literature although the data show a certain amount of variation of proxy records on the regional scale for the northern fertile crescent upper mesopotamia they suggest three pronounced features of the holocene environmental history 1 a trend toward warmer temperatures may have affected the area during the early holocene between ca 10 000 6000 cal bp 2 increased moisture availability and relatively high temperatures in the mid holocene ca between 5000 and 4000 cal bp and 3 a significant decrease in moisture availability around 4000 cal bp further research is needed to enhance the chronological resolution of both pedogenic carbonate and plant macrofossil records this study stresses the complexity of the holocene palaeogeography of the near east and underlines the need for careful analysis of local sources of palaeonvironmental information in the region

shear wave splitting across the ailao shan red river fault zone sw china 1 a broad band seismic array was set up across the ailao shan red river asrr fault zone sw china the shear wave splitting parameters on sks and skks phases are calculated using the method of silver and chan 1991 and indicate the polarization direction of 105 6 and the delay time of 1 68 0 44 s beneath the asrr fault zone combined with previous studies the average polarization direction is 110 19 and the delay time is 1 58 0 44 s to the sw side of the fault while the values are 83 30 and 1 29 0 29 s to the ne side this result implies that the upper mantle anisotropy to two sides of the asrr fault zone are different compared with the se polarization direction observed in the p s phase and the n to s surface movement in gps data our results suggest decoupling of the crust and upper mantle beneath the study region

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

human climate interactions in the central mediterranean region during the last millennia the laminated record of lake butrint albania lake butrint 39 47 n 20 1 e is a ca 21 m deep coastal lagoon located in sw albania where finely laminated sediments have been continuously deposited during the last millennia the multi proxy analysis sedimentology high resolution elemental geochemistry and pollen of a 12 m long sediment core supported by seven ams radiocarbon dates and 137cs dating enable a precise reconstruction of the environmental change that occurred in the central mediterranean region during the last 4 5 cal kyrs bp sediments consist of triplets of authigenic carbonates organic matter and clayey laminae fluctuations in the thickness and or presence of these different types of seasonal laminae indicate variations in water salinity organic productivity and runoff in the lake s catchment as a result of the complex interplay of tectonics anthropogenic forcing and climate variability the progradation of the pavllo river delta favoured by variable human activity from the nearby ancient city of butrint led to the progressive isolation of this hydrological system from the ionian sea the system evolved from an open bay to a restricted lagoon which is consistent with archaeological data an abrupt increase in mass wasting activity between 1515 and 1450 bc likely caused by nearby seismic activity led to the accumulation of 24 homogenites up to 17 cm thick they have been deposited during the onset of finely laminated sedimentation which indicates restricted anoxic bottom water conditions and higher salinity periods of maximum water salinity biological productivity and carbonate precipitation coincide with warmer intervals such as the early roman warm period rwp 500 bc 0 ad the medieval climate anomaly mca 800 1400 ad and recent times after 1800 ad conversely lower salinity and more oxic conditions with higher clastic input were recorded during 1400 500 bc the late roman and the early medieval periods 0 800 ad and during the little ice age 1400 1800 ad hydrological fluctuations recorded in butrint are in phase with most central and western mediterranean records and correlate with nao variability in contrast opposite hydrological patterns have been recorded in the eastern balkans and the levant during the last millennium emphasizing a complex spatial variability in the region phases of maximum settlement intensity in butrint roman late antique coincide with warmer and or stable climate periods 0 800 ad and mca respectively indicating a long term influence of climatic conditions on human activities the late holocene sedimentary record of lake butrint demonstrates the complex interplay of climate variability tectonics and human impact in the recent evolution of coastal mediterranean regions

potential of ikaite to record the evolution of oceanic δ18o a challenge in the quest to understand the sensitivity of the climate system is the separation of the competing effects of ice volume or sea level salinity and temperature on foraminiferal 18o we present precipitation experiments on the mineral ikaite a hydrated form of calcium carbonate found in organic carbon rich deep marine sediments that show that the hydration waters within the ikaite crystal capture the 18o of seawater 18 osw with a fractionation factor of 1 0029 0 0002 the 18osw measures the volume of continental ice with an overprint of local salinity isolation of 18osw by analysis of the hydration waters of sedimentary ikaite preserved at temperatures 4 c could be exploited to create a record of sea level during the pleistocene preliminary data of 18osw from hydration waters of ikaite at the last glacial maximum agree with estimates from modeling of pore waters that antarctic bottom water was 1 4 0 2 heavier 2006 geological society of america

the holocene climatic optimum and pollen records of sapropel 1 in the eastern mediterranean 9000 6000 bp abstract the most recent sapropel in the deep eastern mediterranean sea has been deposited between 9 and 6 ka bp climate conditions as revealed by the pollen records of this sapropel in marine cores were most favorable for temperate deciduous trees which is in agreement with the inferences from records of peripheral land pollen sites the abundance of deciduous oak pollen is much higher than that of artemisia sage brush indicating that annual precipitation in the mid elevation borderlands was at least 550 mm without summer drought but more probably in the range 800 1300 mm the pollen of pistacia which formed a savanna at low elevations is also at its highest abundance and signals the absence of frost in winter while being capable of withstanding summer drought the early holocene therefore appears as the post glacial climatic optimum with the highest moisture and mildest winters in southwest asia this is also the time of the neolithic population explosion with incipient domestication of cereals possibly following natural selection of the tough rachis mutation in wheat and barley by the extreme aridity of the preceding younger dryas

glendonites as a paleoenvironmental tool implications for early cretaceous high latitude climates in australia glendonites calcite pseudomorphs after the metastable mineral ikaite caco3 6h2o occur in the late aptian interval of the bulldog shale in the eromanga basin australia and in other early cretaceous basins at high paleolatitudes ikaite precipitation in the marine environment requires near freezing temperatures not higher than 4 c high alkalinity increased levels of orthophosphate and high pco2 the rapid and complete transformation of ikaite to calcite at temperatures between 5 and 8 c provides an upper limit on the oxygen isotopic composition of the pore waters 2 6 w 3 4 smow if it is assumed that these pore waters are representative of the shallow eromanga basin the calculated w can be used to reassess belemnite fossil oxygen isotopic paleotemperatures temperature recorded by fauna living in the basin at the time of ikaite precipitation data previously reported as 11 to 16 c assuming w 0 0 smow yield paleotemperatures ranging from 1 to 5 c squarely in the range of ikaite stability the low w indicates hyposaline conditions most likely caused by mixing high latitude meteoric waters with seawater the 18o depleted low temperature waters suggest that the region was at least seasonally colder than previously accepted

synchronous holocene climatic oscillations recorded on the swiss plateau and at timberline in the alps eight synchronous pre roman cold phases were found at 9600 9200 8600 8150 7550 6900 6600 6200 5350 4900 4600 4400 3500 3200 and 2600 2350 radiocarbon years bp by reconstructing past climate at two sites on the swiss plateau and at timberline in the alps the cooling events during the early and mid holocene represent temperature values similar to today and apparently the onset of cooling events represents a deviation from today s mean annual temperature of about 1 c and is triggered at a 1000 year periodicity at wallisellen langachermoos 440 m a former oligotrophic lake near zurich the correlation between sum mertime lake levels and the seed production of the amphi atlantic aquatic plantnajas flexilis was used to reconstruct lake levels over a 3000 year period during the first part of the holocene at lake seedorf on the western swiss plateau 609 m the sedimentological palynological and macrofossil record revealed fluctuations of lake levels for the complete holocene from lago basso in the

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

temperature and salinity variations of mediterranean sea surface waters over the last 16 000 years from records of planktonic stable oxygen isotopes and alkenone unsaturation ratios alkenone unsaturation ratios and planktonic d18o records from sediment cores of the alboran ionian and levantine basins in the mediterranean sea show pronounced variations in paleo temperatures and salinities of surface waters over the last 16 000 years average sea surface temperatures ssts are low during the last glacial averages prior to 13 000 years 11 15 c vary rapidly at the beginning of the holocene and increase to 17 18 ca t all sites during s1 formation dated between 9500 and 6600 calendar years the modern temperature gradient 2 3 c between the mediterranean sub basins is maintained during formation of sapropel s1 in the eastern mediterranean sea after s1 ssts have remained uniform in the alboran sea at 18 c and have fluctuated around 20 c in the ionian and levantine basin sites the d18o of planktonic foraminifer calcite decreases by 2 from the late glacial to s1 sediments in the ionian basin and by 2 8 in the levantine basin in the alboran sea the decrease is 1 7 of the 2 8 decrease in the levantine basin the evect of global ice volume accounts for a maximum of 1 05 and the temperature increase explains only a maximum of 1 3 the remainder is attributed to salinity changes we use the temperature and salinity estimates to calculate seawater density changes they indicate that a reversal of water mass circulation is not a likely explanation for increased carbon burial during s1 time instead it appears that intermediate and deep water formation may have shifted to the ionian sea approximately 2000 years before onset of s1 deposition because surface waters were as cold but saltier than surface water in the levantine basin during the younger dryas sapropel s1 began to form at the same time when a significant density decrease also occurred in the ionian sea 2000 elsevier science b v all rights reserved

ikaite tufa towers in ikka fjord southwest greenland their formation by mixing of seawater and alkaline spring water abstract ikka fjord in southwest greenland is the type locality for ikaite a metastable hexahydrate of calcium carbonate here ikaite forms submarine tufa columns rising up to 18 m above the fjord bottom the columns are spectacular examples of abiogenic carbonate precipitation in a cold seawater environment and so far represent the only known formation of ikaite in seawater we have analyzed the 2h 13c 14c 18o and 87sr contents and major element and minor element compositions of ikaite and of the different water types in and around ikka fjord in order to understand the formation of the ikka columns water from inside the columns is fresh but alkaline rich in ions of sodium bicarbonate and carbonate and has a stable isotope composition identical to precipitation falling on the nearby gronnedal ika igneous complex and we conclude that the tufa columns form over submarine springs issuing from the bottom of ikka fjord dissolution of unidentified sodium carbonate minerals in carbonatites in the igneous complex probably accounts for the peculiar chemistry of the springs ikaite supersaturation and precipitation is controlled by mixing of spring water and seawater at the cold 6 c fjord bottom and precipitation is accelerated by the formation of hydrated caco3o aq ion pairs while phosphate ions in the spring water act as inhibitor for precipitation of anhydrous carbonates we propose that the spring water seeps in ikka fjord literally create their own conduits in the form of the vertical chimney like columns with ikaite forming continuously at the tops of the columns the only limits to upward growth are winter ice and the fresh water layer capping the fjord during summer

el nino suppresses antarctic warming here we present new isotope records derived from snow samples from the mcmurdo dry valleys antarctica and re analysis data of the european centre for medium range weather forecasts era 40 to explain the connection between the warming of the pacific sector of the southern ocean jacka and budd 1998 jacobs et al 2002 and the current cooling of the terrestrial ross sea region doran et al 2002a our analysis confirms previous findings that the warming is linked to the el nino southern oscillation enso kwok and comiso 2002a 2002b carleton 2003 ribera and mann 2003 turner 2004 and provides new evidence that the terrestrial cooling is caused by a simultaneous enso driven change in atmospheric circulation sourced in the amundsen sea and west antarctica

oxygen isotopes of lake marl at gerzensee and leysin switzerland covering the younger dryas and two minor oscillations and their correlation to the grip ice core the ratio of oxygen isotopes is a temperature proxy both in precipitation and in the calcite of lacustrine sediments the very similar oxygen isotope records from greenland ice cores and european lake sediments during the last glacial termination suggest that the drastic climatic changes occurred quasi simultaneously on an extra regional probably hemispheric scale in order to study temporal relations of the different parameters recorded in lake sediments for example biotic response times to rapid climatic changes a precise chronology is required in unlaminated lake sediments there is not yet available a method to provide a high resolution chronology especially for periods with radiocarbon plateaux alternatively an indirect time scale can be constructed by linking the lake stratigraphy with other well dated climate records new oxygen isotope records from gerzensee and leysin with an estimated sampling resolution of between 15 and 40 years match the greenlandic isotope record in many details under the assumption that the main variations in temperature and thus in oxygen isotopes occurred about simultaneously in greenland and switzerland we have assigned a time scale to the lake sediments of gerzensee and leysin by wiggle matching their stable isotope records with those of greenland ice cores which are among the best dated climatic archives we estimate a precision of 20 to 100 years during the last glacial termination

the eastern mediterranean paleoclimate as a reflection of regional events soreq cave israel the climate of the eastern mediterranean region of the last 60 ky was determined by a high resolution study of the oxygen and carbon isotopic composition 1500 measurement pairs of speleothems from the soreq cave israel with chronology provided by 53 precise 230 th 234 u tims ages the high precision of the speleothem tims ages permits us to determine the timing of regional climatic events in the eastern mediterranean region and to see if they correlate with global events during the period from 60 to 17 ky the 18 o and 13 c values were generally 2 2 5 higher than during the period from 17 ky to present this is consistent with the climatic transition from glacial to interglacial within the 60 to 17 ky period the soreq cave stable isotope profile includes four cold peaks at 46 35 25 and 19 ky and 2 warm peaks at 54 and 36 ky in addition the period 17 ky has two more cold peaks at 16 5 and from 13 2 to 11 4 ky the ages of four of the six cold peaks correlate well with the ages of three heinrich events h1 h2 h5 and with the age of the younger dryas however the other two heinrich events are not reflected in the soreq cave record several other isotope peaks which appear during the last 7 ky are contemporaneous with regional climatic events in the middle east and north africa in addition to the drop in 18 o and 13 c observed between the last glacial and the holocene sharp simultaneous drops in 234 u 238 u 0 ratios sr concentrations and in 87 sr 86 sr are also observed suggesting that the latter are climate related these variations are interpreted in terms of major changes in the temperature the mean annual rainfall and its isotopic composition the isotopic composition of the mediterranean vapor source the soil moisture conditions and in the mixing proportions of sources with different 87 sr 86 sr ratios sea spray dust particles and dolomitic host rock

upper mantle tomography of the western junggar implications for its geodynamic evolution abstract a high resolution 3 d p wave velocity model of the upper mantle beneath the western junggar is determined by inverting a large number of relative travel time residuals of teleseismic events our results reveal a prominent high velocity high v anomaly beneath the western junggar basin and a low velocity low v anomaly beneath the darbut belt the ne sw striking high v anomaly at depths of 50 200 km beneath the western junggar basin dips toward the northwest which represents a fossil oceanic slab the low v anomaly may reflect an intraoceanic arc related terrain that has experienced strong metasomatism by hot upwelling asthenosphere in the late paleozoic resulting in adakitic intrusions and concentration of porphyry cu au deposits in the darbut belt these results shed new light on the geodynamic evolution of the western junggar and formation mechanisms of the adakites and porphyry cu au deposits

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

palaeoclimate and the formation of sapropel s1 inferences from late quaternary lacustrine and marine sequences in the central mediterranean region abstract synchronous responses to climatic changes during the late pleistocene holocene transition are inferred from marine and lacustrine stratigraphic records in the central mediterranean region new stratigraphic data are presented from well dated sequences in the meso adriatic depression mad two crater lakes in the lazio region and in the tyrrhenian sea the sequences all span the last termination and the holocene but we focus here on the evidence in each record for the time period during which sapropel s1 formed in the mediterranean ca 9 0 to 6 8 cal kyr b p the new records provide evidence of palaeoenvironmental changes on land and sea that can be reconstructed at a high temporal resolution and which throw some light on the processes which led to the formation of s1 the collective evidence indicates that i organic rich sediments occurred in both the marine and the crater lake sites during the time of formation of the s1 sapropel ii there is evidence of increased stratification and anoxia in the sea water column during the period of s1 formation iii the s1 period in the study area is divisible into two sub phases s1a and s1b which reflect short term variations in oceanographic conditions stratification and anoxia iv changes in stratification in the marine column were contemporaneous with regional climate variations that are inferred from the terrestrial records we conclude that the key factor that initiated the formation of s1 was increased discharge of freshwater into the mediterranean following a change post 9 0 cal kyr b p to a warmer and wetter climate furthermore the period of s1 formation was interrupted by a short lived episode ca 500 years of comparatively cooler and drier conditions during the early middle holocene transition emht

sea land correlation of pollen records in the eastern mediterranean for the glacial interglacial transition biostratigraphy versus radiometric time scale abstract pollen diagrams based on marine cores from the eastern mediterranean and arabian seas and land cores from greece turkey the levant and western iran during the last deglaciation reveal a similar succession of conspicuous pollen abundance maxima an early phase with chenopodiaceae signaling the highest aridity a late phase with pistacia and gramineae in the mediterranean domain and tropical humid taxa in the arabian sea domain indicating conditions of mildest winter and wettest summer between these two phases the record for deciduous oak in the mediterranean and near east shows a continuous increase that points to rising moisture the chronology of this succession and its exact relationship with the marine isotopic record of global climate are established using marine cores the marine records dated by the ams 14 c method show that the chenopodiaceae phase correlates with the younger dryas chronozone globally dated 11 000 to 10 000 bp during which the climate reversed to quasi glacial conditions at least in the northern hemisphere they also show that the pistacia phase during which the mediterranean climate reached its seasonal optimum occurred from 9000 to 6000 14 c years bp boreal and early atlantic chronozones defined in nw europe in the first half of the holocene the oak pollen abundance increases rapidly from 10 000 to 9000 bp preboreal chronozone thus in terms of climate the younger dryas chronozone is regionally expressed by wide spread desert conditions as a cold and arid period during the pistacia phase the climate was most favourable both for plants that require frost free winters such as the mediterranean pistacia and those that need spring summer moisture such as gramineae at low annual moisture level seasonally 300 mm and deciduous oak at higher levels 600 mm all year without summer drought during the brief intermediary phase the climate changed drastically through an increase of winter temperature and of spring summer moisture the chronologies of the land cores however based on few 14 c dates show significant discrepancies with the marine based time frame these discrepancies imply a lack of coherence in the climate history of this mediterranean irano turanian region we propose using the chronology derived from the marine records for the entire region the local 14 c dates generally appear too old perhaps because of geological contamination of the material by older carbon

teleseismic p wave tomography and the upper mantle structure of the central tien shan orogenic belt abstract in this study an updated version of the teleseismic tomographic method is applied to 7176 high quality first p wave arrivals from four combined seismic networks to determine the detailed deep structure under the central tien shan our high resolution tomographic model not only displays the general features contained in the previous models but also reveals some new features a much narrower tilted columnar high velocity anomaly with a diameter of about 60 km below 150 200 km depth under the tien shan extends down to the mantle transition zone suggesting the breaking and dropping off of the collided portions of the southward underthrusting kazakh shield and the northward underthrusting tarim basin prominent low velocity low v anomalies above 150 200 km depth beneath the tien shan may be related to two branches of ascending hot anomalies one rises upward from the lower mantle beneath the tarim basin while the other rises up from the top of the mantle transition zone beneath the western kazakh shield these results suggest that the underthrusting of the tarim basin and kazakh shield and the upwelling of hot anomalies indeed play an important role in the mountain building of the central tien shan these dynamic processes might be related to the collision of the indian plate with eurasian plate

seismic anisotropy beneath the continents probing the depths of geology seismic anisotropy beneath continents is analyzed from shear wave splitting recorded at more than 300 continental seismic stations anisotropy is found to be a ubiquitous property that is due to mantle deformation from past and present orogenic activity the observed coherence with crustal deformation implies that the mantle plays a major if not dominant role in orogenies no evidence is found for a continental asthenospheric decoupling zone suggesting that continents are coupled to general mantle circulation

injection of mantle type helium into lake van turkey the clue for quantifying deep water renewal helium neon and tritium concentrations have been measured to study long term vertical mixing and deep water renewal in lake van eastern turkey the largest soda lake on earth helium excesses were found in the water column of lake van although neon concentrations were close to air saturation the excesses of both isotopes are strictly correlated and increase with depth in the bottom water 4he supersaturation is about 20 and the corresponding 3he concentration is 2 5 times the air saturation value the mean excess 3he 4he ratio of 1 1 2 10 5 is slightly higher than the morb ratio found in lake nemrut a neighbouring volcanic crater lake in which a large input of mantle helium was detected mantle helium accounts for the majority of the helium excesses in lake van although part of the 3he excess is attributed to the presence of tritium a one dimensional lake model was used which describes tritium input vertical mixing and gas exchange to reconstruct the evolution of the helium isotopes and the tritium as a conclusion the model based on the measured 3he and 4he profiles shows that 1 the vertical exchange of deep water occurs within 1 2 yr 2 the flux of mantle helium into the lake averaged over the total cross section of lake van is 0 23 0 35 cm3 stp m 2 yr 1 2 3 1011 atoms m 2 s 1 the present estimate of the global mantle helium flux averaged over the total surface area of the earth is 3 9 109 atoms m 2 s 1 the flux into lake van would account for at least 0 04 0 06 of this

climate change and the collapse of the akkadian empire evidence from the deep sea the akkadian empire ruled mesopotamia from the headwaters of the tigris euphrates rivers to the persian gulf during the late third millennium b c archeological evidence has shown that this highly developed civilization collapsed abruptly near 4170 150 calendar yr b p perhaps related to a shift to more arid conditions detailed paleoclimate records to test this assertion from mesopotamia are rare but changes in regional aridity are preserved in adjacent ocean basins we document holocene changes in regional aridity using mineralogic and geochemical analyses of a marine sediment core from the gulf of oman which is directly downwind of mesopotamian dust source areas and archeological sites our results document a very abrupt increase in eolian dust and mesopotamian aridity accelerator mass spectrometer radiocarbon dated to 4025 125 calendar yr b p which persisted for 300 yr radiogenic nd and sr isotope analyses confirm that the observed increase in mineral dust was derived from mesopotamian source areas geochemical correlation of volcanic ash shards between the archeological site and marine sediment record establishes a direct temporal link between mesopotamian aridification and social collapse implicating a sudden shift to more arid conditions as a key factor contributing to the collapse of the akkadian empire

a high resolution late holocene landscape ecological history inferred from an intramontane basin in the western taurus mountains turkey abstract late holocene vegetation and geomorphological history is reconstructed from a 800 cm long high resolution palynological and sedimentological record sampled from bereket a 6 3 km 2 semi arid to sub humid intramontane basin in the western taurus mountains southwest turkey the well dated bereket record provides from cal 360 bc to cal ad 400 a unique record of biennial to decadal landscape changes caused primarily by intensive human impacts against a background of global climate variations during this period land clearance with multiple fire episodes intensive agricultural practices and grazing pressure profoundly altered the pre existing warm mixed forest increasing moisture availability since cal 280 bc has acted as a trigger to crop cultivation and mountain adapted arboriculture starting with juglans regia during the beysehir occupation phase pollen from olive groves have been recorded above 1400 m a s l only at cal 23 bc and have disappeared definitively at cal ad 294 during this phase the sediment accumulation rate was extremely high reflecting landscape instability from cal ad 450 to recent times the area has mainly recorded pasture and minor cultivation activities reflected in stable soils and thin colluvial depths