climatic fluctuations reflected in the evolution of fluvial systems of central eastern europe 60 8 ka cal bp abstract in general the evolution of fluvial systems in central eastern europe reflects the main phases of climatic changes during the period of 60 8 ka cal bp registered in greenland ice cores and their isotopic 18 o curves the greenland isotope curve shows many more wiggles and stages than the fluvial record of the same time especially during the interpleniglacial phase in central eastern europe we observe several deviations from those climatic trends connected with different factors among which are the long distance of the region from the atlantic ocean and an increase in continentality at times this region was occupied by permafrost although the coexisting warm summers during a part of the studied period enabled the presence of a forest cover these factors together controlled the specific features of the fluvial regime and sediment load reflected in alternating trends to erosion or aggradation and from meandering to braiding the permafrost influenced snowmelt floods and tendency to braiding the dense vegetation with trees reduced the supply of sediments and stabilized the meandering channels very distinct changes occurred in the river valleys that drain the mountains where ceaseless fluctuations of vegetation vertical zones were present especially during the unstable interpleniglacial when the supply of load from the higher vegetation zones was increased this system controlled by the climate and plant vegetation was modified by other factors including tectonics wind activity during dry periods blocking of valleys by ice sheets meltwater supply and sea level fluctuations of two reservoirs

mid holocene vegetation development and herding related interferences in the carpathian region abstract the paper comprises data from 27 case studies to assess large scale human vegetation interferences in the carpathian region during the mid holocene the main focus is put on herding related vegetation changes and climate influences are addressed the publications reviewed are based on sediment sequences which provide c 14 dated pollen records charcoal and geochemical data based on a semi quantitative approach pollen of secondary indicator species and arboreal pollen values were combined in a fuzzy model to assess the intensity of herding related vegetation changes the model was applied for 20 selected case studies the data from the remaining seven sites as well as geochemical and charcoal data were used to validate the results of the standardized evaluation speleothem 18 o and 13 c records from hungary and romania were used as independent proxies to align holocene climate development the results were regionalized and trends of herding related vegetation change are presented for the southern carpathians and apuseni mountains for the eastern carpathians and for hungary mean distances between included archives and prehistoric settlement sites were calculated as indicator for the marginality of the environmental archives in all regions absolute values for herding indication are low phases of changing herding impact on the landscape can be observed for the southern carpathians and apuseni mountains as well as for hungary in the southern carpathians and apuseni mountains increased herding activities can be traced for the early chalcolithic and the late bronze age the first phase is contemporary with an intensification of the use of secondary products in hungary herding impact is in accordance with prehistoric settlement development widely increased herding indications date to the late chalcolithic and the early bronze age in the eastern carpathians interference of climate influences and human impacts occurred

methodology of the last climatic cycle reconstruction in france from pollen data abstract a numerical method has been devised to reconstruct the climate of the last climatic cycle from pollen data reliable annual reconstructions have been published recently for the two french long sequences of la grande pile and les echets covering the last 140 millennia this paper gives more details on the method used it proposes new reconstructions based on an extended modern pollen data base these reconstructions are consistent with the previous ones especially detailed information is obtained on the seasonal characteristics of climate computations of gcm on the climate variations from 125 kyr to 115 kyr b p are confirmed for western europe the insolation variations have induced at that time a decrease of seasonality accompanied by an increased cyclonic activity in winter this has been the beginning of the first ice growth after the last interglacial other glacier growth phases are detected at the end of substage 5c and particularly at the end of substage 5a

is the subtropical jet shifting poleward the tropics are expanding poleward at about 0 5 circ per decade in observations this poleward expansion of the circulation is consistently reported using hadley cell edge metrics and lower atmospheric tropical edge metrics however some upper atmospheric tropical metrics report smaller trends that are often not significant one such upper atmospheric metric is the subtropical jet latitude which has smaller trends compared to the hadley cell edge in this study we investigate the robustness of the weak trends in the subtropical jet position by introducing a new method for locating the subtropical jet and examining the trends and variability of the subtropical jet latitude we introduce the tropopause gradient method based on the peak gradient in potential temperature along the dynamic tropopause using this method we find the trends in the subtropical jet latitude are indeed much smaller than 0 5 circ per decade consistent with previous studies we also find that natural variability within the subtropical jet latitude would not prevent trends from being detected if they were similar to the hadley cell edge as trends greater than 0 24 circ per decade could reliably be detected using monthly data or 0 09 circ per decade using daily data despite the poleward expansion of the tropics there is no robust evidence to suggest the subtropical jet is shifting poleward in either hemisphere neither the current diagnostic methods nor natural variability can account for the small subtropical jet trends the most likely explanation which requires further investigation is that the subtropical jet position is not tied dynamically to the hadley cell edge

rapid vegetation change during the early holocene in the faroe islands detected in terrestrial and aquatic ecosystems high resolution pollen plant macrofossil and sedimentary analyses from early holocene lacustrine sediments on the faroe islands have detected a significant vegetation perturbation sug gesting a rapid change in climate between ca 10 380 cal yr bp and the saksunarvatn ash 10 240 60 cal yr bp this episode may be synchronous with the decline in 18 o values in the greenland ice cores it also correlates with a short cold event detected in marine cores from the north atlantic that has been ascribed to a weakening of thermohaline circulation associated with the sudden drainage of lake agassiz into the northwest atlantic or alternatively a period with dis tinctly decreased solar forcing the vegetation sequence begins at ca 10 500 cal yr bp with a succession from tundra to shrub tundra and increasing lake productivity rapid population increases of aquatic plants suggest high summer temperatures between 10 450 and 10 380 cal yr bp high pollen percentages concentra tions and influx of betula juniperus and salix together with macrofossil leaves indicate shrub growth around the site during the initial phases of vegetation colonisation unstable conditions followed ca 10 380 cal yr bp that changed both the upland vegetation and the aquatic plant communities a decrease in percentage values of shrub pollen is recorded with replacement of both aquatics and herbaceous plants by pioneer plant communities an increase in total pollen accumulation rates not seen in the concentration data suggests increased sediment delivery the catchment changes are consistent with less seasonal moister conditions subsequent climatic amelioration reinitiated a warmth driven succession and catchment stabilisation but retained high precipitation levels influ encing the composition of the post event communities copyright 2003 john wiley sons ltd

exploring the role of humans and climate over the balkan landscape 500 years of vegetational history of serbia abstract we present the first well dated high resolution record of vegetation and landscape change from serbia which spans the past 500 years biological proxies pollen spores and charcoal geochemical analysis through x ray fluorescence xrf and a detailed chronology based on ams 14c dating from a western serbian sinkhole core suggest complex woodland grassland dynamics and strong erosional signals throughout the little ice age lia an open landscape with prominent steppe vegetation e g poaceae chenopodiaceae and minor woodland exists during 1540 1720 ce early lia while the late lia 1720 1850 ce in this record shows higher tree percentages possibly due to increased moisture availability the post lia era 1850 2012 ce brings a disturbed type of vegetation with the presence of weedy genera and an increase in regional woodland anthropogenic indicators for agricultural pastoral and fire practices in the region together attest to the dominant role of humans in shaping this balkan landscape throughout the interval the changing nature of human interference potentially as a response to underlying climatic transitions is evident through large scale soil depletion resulting from grazing and land clearance during the early lia and stabilization of arable lands during the late and post lia eras

climatology of upper tropospheric lower stratospheric utls jets and tropopauses in merra abstracta global climatology 1979 2012 from the modern era retrospective analysis for research and applications merra shows distributions and seasonal evolution of upper tropospheric jets and their relationships to the stratospheric subvortex and multiple tropopauses the overall climatological patterns of upper tropospheric jets confirm those seen in previous studies indicating accurate representation of jet stream dynamics in merra the analysis shows a northern hemisphere nh upper tropospheric jet stretching nearly zonally from the mid atlantic across africa and asia in winter spring this jet splits over the eastern pacific merges again over eastern north america and then shifts poleward over the north atlantic the jets associated with tropical circulations are also captured with upper tropospheric westerlies demarking cyclonic flow downstream from the australian and asian monsoon anticyclones and associated easterly jets multiple tropopauses associated with the thermal tropopause break

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

a study of flow wetted surface area in a single fracture as a function of its hydraulic conductivity distribution the contact area between flowing water and rock the flow wetted surface fws is a main factor controlling the rock matrix diffusion and sorption of flowing solute in a rock fracture flow channeli

neolithic to copper age woodland impacts in northeast hungary evidence from the pollen and sediment chemistry records a 4 5 m sedimentary sequence collected from sirok n rjes to in northeast hungary reveals a record of environmental change from 10000 bp to the present day palaeoenvironmental analyses pollen charcoal geochemistry and physical properties of the sequence reveal an environment where parkland com posed of coniferous and broadleaved taxa existing at the start of the holocene developed rapidly into deciduous broadleaved forest from c 8200 cal bp corylus expanded rapidly and dominated the pollen assemblage until a series of fluctuations involving corylus and carpinus betulus which resulted in changes to the forest compo sition these changes occurred over timescales of 72 288 years and are attributed to neolithic and copper age forest use perhaps under a woodland management regime such as coppicing or pollarding sedimentolog ical and geochemical records for this period are stable suggesting that soil erosion was not occurring natural forest processes resumed following copper age settlement shifts bu

early to mid holocene hydroclimate trends in the western carpathians of romania abstract in this study we analyse a sequence from ic ponor ombrotrophic peat bog in the apuseni mountains of nw romania using a multi proxy approach testate amoebae pollen microcharcoal loss on ignition magnetic susceptibility radiocarbon dating lithology to reconstruct the palaeoenvironmental conditions and the hydroclimate trends that occurred between 12 700 and 6220 cal yr bp the sequence evolved from a lacustrine phase between 12 700 cal yr bp and 12 000 cal yr bp into an ombrotrophic peat bog 12 000 7600 cal yr bp accumulated in drier climate conditions with a subdued water table subsequently wetter conditions occurred with an elevated water table until 6220 cal yr bp when the peat bog was flooded and peat accumulation paused a depositional hiatus being marked by a clayey layer peat started to accumulate again ca 100 years ago under drier conditions the peat bog records the local and regional responses to rapid climate change events that occurred at 11 400 11 250 10 500 10 200 9400 9200 and 8300 8250 cal yr bp our quantitative reconstruction of hydrological changes as well as pre existing ones for this region show similar conditions to those that occurred in central eastern europe between 12 700 and 7600 cal yr bp but differ from those that occurred between 7600 and 6220 cal yr bp suggesting a distinct regional character of middle holocene climate conditions in romania

environmental changes during the holocene climatic optimum in central europe human impact and natural causes abstract the priority programme changes of the geo biosphere aimed to reconstruct the environmental history of central europe with emphasis on the time interval from 9000 to 5500 cal bp time slice ii coinciding with the holocene climatic optimum during this period the onset of human activities such as settlement agriculture and animal husbandry caused environmental changes studies of different landscape units in germany were carried out to identify these anthropogenically induced changes and to distinguish them from natural effects on the environmental system the investigated archives included laminated lake sediments fluvial sediments colluvia and soils speleothems peat and coastal sediments the different archives were examined using refined research methods including a variety of sedimentary and geochemical analyses together with pollen analysis and dating methods for the establishment of a reliable chronology the results of the various research groups are summarised and critically discussed based on these results the climatic optimum can be subdivided into three periods 1 the early atlantic from 9000 to 7500 cal bp with negligible human impact and stable environmental conditions 2 the late atlantic during early and middle neolithic from 7500 to 6300 cal bp with pollen evidence for vegetation changes but only negligible changes detectable in other proxy records and 3 the late atlantic during the younger neolithic jungneolithikum after 6300 cal bp with human impact observed in many archives and proxy records especially in the pollen record but also in lacustrine and fluvial sediments during the whole climatic optimum natural causes such as minor shifts of temperature did not induce substantial environmental changes though some changes such as temporary droughts may have facilitated and amplified the observed human impact

interannual variability of the boreal winter subtropical jet stream and teleconnections over the cordex cam domain during 1980 2010 the interannual variability of the boreal winter djf subtropical jet stream stj is analyzed over the coordinated regional downscaling experiment central america mexico and caribbean domain cordex cam during 1980 2010 we use simulations with the regional climate model regcm4 version 7 at 25 km resolution driven by era interim regera and three global models reggcms the simulations are evaluated using zonal winds at 200 hpa level from era interim and merra2 which show similar results and no significant trends in the stj despite some biases regera captures the stj variability and its relationship with several teleconnections the polarities of the principal mode of variability of the pacific and atlantic jets are significantly anti correlated they represent the longitudinal extension retraction and the poleward equatorward migration of the jet cores respectively during el nino and the pna pacific north america the north pacific jet exit region and the north atlantic jet show maximum speeds equatorward of their climatological positions during these conditions there is an extended and strong stj over the domain this pattern also tends to occur during the negative phases of the arctic and north atlantic oscillations the reggcms simulate better the principal modes of the atlantic jet variability than those of the pacific jet exit region nevertheless they reproduce the observed sign of the variations of the jet speeds and their latitudinal changes in the two basins they also partially capture the sign of the temperature and precipitation anomalies in the domain which respond to the stj polarities and their interaction with the teleconnections

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

pollen based quantitative reconstructions of holocene climate variability in nw romania abstract a modern analogue technique is applied to two high resolution pollen sequences from nw romania to provide the first quantitative evidence for winter summer and annual temperatures and for precipitation across the holocene in this region the pollen based climate reconstructions allow the identification of four main intervals i an early less stable period between 11 700 and 11 200 cal yr bp ii generally stable conditions between 11 200 and 8300 cal yr bp with winter and annual temperatures and precipitation higher than at present and summer temperatures about the same iii lower winter and annual temperatures and higher summer temperatures and precipitation between 8000 and 2400 cal yr bp iv warmer winter and annual temperatures and lower precipitation for the last 2400 years whereas summer temperatures became cooler at steregoiu and remained stable at preluca tiganului the pollen based climate reconstructions at the two sites show similar patterns in annual and winter temperatures and precipitation changes during the holocene but the trends appear to be less consistent for summer temperatures our pollen based reconstructions revealed several short term climatic oscillations during the holocene the strongest of which occur between 10 300 10 100 8300 8000 6800 6400 5100 4900 4000 3600 and 3200 3000 cal yr bp

holocene vegetation history in romanian subcarpathians abstract article history received 7 april 2008available online 5 june 2009keywords pollen analysisradiocarbon datingvegetation historyforest dynamicshuman in uencesholocenesubcarpathiansromania pollen analysis from a peat core 7 0 m in length taken from a bog near bisoca in a mid altitude area of thebuz ului subcarpathian mountains is used to reconstruct the postglacial vegetation historyof the region thevegetation record which is supported by twelve 14 c dates starts at the end of the late glacial period at thelate glacial holocene transition open vegetation was replaced by forest suggesting a fast response toclimatic warming the holocene began with the expansion of betula pinus and ulmus followed after11 000 cal yr bp by fraxinus quercus tilia and picea the rapid expansion of these taxa may be due to theirexistence in the area during the late glacial period at ca 9200 cal yr bp corylus expanded reaching amaximum after 7600 cal yr bp the establishment of carpinus occurred at ca 7200 cal yr bp with a maximumat ca 5700 cal yr bp fagus pollen is regularly recorded after 7800 cal yr bp and became dominant at ca 2000 cal yr bp the rst indications of human activities appear around 3800 cal yr bp 2009 university of washington published by elsevier inc all rights reserved

scandinavian glacial and climatic fluctuations during the holocene abstract historical documents and lichenometric studies give a detailed picture of the little ice age in scandinavia there was a large advance in norway which has been dated at a few places to 1750 small readvances during the retreat occurred around a d 1780 1810 1840 1850 1850 1870 1890 1910 and 1930 in sweden most of these advances have been recognized and in addition extensive advances are dated by lichenometry to around a d 1600 1650 and 1700 1720 soils buried beneath moraines often yield radiocarbon dates that are much too old methods dependent on these must therefore be used with care evidence for pre little ice age advances are often considered equivocal the most reliable information is probably provided by studies of lacustrine sediments combining information from all sources the most significant pre little ice age glacier advances most likely occurred in 7 5 5 1 4 5 3 2 2 8 2 2 1 9 and 1 5 1 1 radiocarbon ka bp advances that were less extensive or for which there is less evidence occurred around 6300 5600 2500 940 600 560 and 380 bp

rapid changes of glacial climate simulated in a coupled climate model abrupt changes in climate termed dansgaard oeschger and heinrich events have punctuated the last glacial period approximately 100 10 kyr ago but not the holocene the past 10 kyr here we use an intermediate complexity climate model to investigate the stability of glacial climate and we find that only one mode of atlantic ocean circulation is stable a cold mode with deep water formation in the atlantic ocean south of iceland however a warm circulation mode similar to the present day atlantic ocean is only marginally unstable and temporary transitions to this warm mode can easily be triggered this leads to abrupt warm events in the model which share many characteristics of the observed dansgaard oeschger events for a large freshwater input such as a large release of icebergs the model s deep water formation is temporarily switched off causing no strong cooling in greenland but warming in antarctica as is observed for heinrich events our stability analysis provides an explanation why glacial climate is much more variable than holocene climate

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

palynology and natural environment in the pannonian to holocene sediments of the early medieval centre pohansko near břeclav czech republic abstract pohansko czech republic is an important early medieval centre of the great moravian empire 9th century ad the locality has a settlement with archaeological findings from mesolithic to the modern times the studied sediments belong to the stream and flood deposits of the dyje river aeolian sands and buried soils the lower parts of some boreholes penetrated into the upper miocene sediments 172 samples were palynologically analysed the original forest with relative small human impact was observed on the base of holocene layers even sporadic cerealia pollen were found here a deforestation was visible in the cultural layer it is linked with existence of the great moravian agglomeration and its fortification later a partial forest reconstruction probably took place in the surroundings very abundant pollen of human exploited plants cereals herbs were discovered in the filling of archeological feature o1 the possible practical potential of rampart also as the flooding protection was indicated by the existence of marshy plants palynomorphs the existence of oxbow was proved in the excavated probe s3 the lowermost sample was dated by 14c as 7830 60 bp the findings of carpinus pollen in the layer dated as early atlantic support the earlier spreading of this genus in the czech republic i e south moravia

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

temperature trends over the past five centuries reconstructed from borehole temperatures for an accurate assessment of the relative roles of natural variability and anthropogenic influence in the earth s climate reconstructions of past temperatures from the pre industrial as well as the industrial period are essential but instrumental records are typically available for no more than the past 150 years therefore reconstructions of pre industrial climate rely principally on traditional climate proxy records each with particular strengths and limitations in representing climatic variability subsurface temperatures comprise an independent archive of past surface temperature changes that is complementary to both the instrumental record and the climate proxies here we use present day temperatures in 616 boreholes from all continents except antarctica to reconstruct century long trends in temperatures over the past 500 years at global hemispheric and continental scales the results confirm the unusual warming of the twentieth century revealed by the instrumental record but suggest that the cumulative change over the past five centuries amounts to about 1 k exceeding recent estimates from conventional climate proxies the strength of temperature reconstructions from boreholes lies in the detection of long term trends complementary to conventional climate proxies but to obtain a complete picture of past warming the differences between the approaches need to be investigated in detail

contrasting patterns of hydrological changes in europe in response to holocene climate cooling phases the quantitative reconstruction of climatic parameters from pollen and lake level data obtained at saint jorioz lake annecy eastern france gives evidence for cooler and wetter conditions during the 8 2 ka cold event a comparison of these regional data with other hydrological records reconstructed in europe for the same period suggests as a working hypothesis that mid latitudes between ca 50 and 43 underwent wetter conditions in response to the cooling whereas northern and southern europe were marked by drier climate in the latter case leading to an interruption of the sapropel 1 formation in the mediterranean a similar hydrological tri partition of europe can be observed during other holocene cooling phases associated with north atlantic ird events data indicate that the middle zone characterised by wetter climate conditions could have had a more extended latitudinal amplitude during phases of climate cooling weaker than the 8 2 ka event the differences in expansion of the wet mid european zone depending on holocene climate cooling phases could reflect variations in the strength of the atlantic westerly jet in relation with the thermal gradient between high and low latitudes

palynological evidence for climatic change and human activity during the holocene on minorca balearic islands four pollen diagrams from minorca balearic islands have been correlated with other previously studied sequences from majorca and minorca to define a holocene landscape sequence for the region from 8000 yr b p to the present the lower part of the pollen diagrams reflects a climatic phase with more rain and less marked seasonality than today significant quantities ofcorylus buxus and mesophilous taxa are found in the middle part between 5000 and 4000 yr b p a strong change is recorded in composition and structure of the vegetational landscape with vegetation appearing that was adapted to mediterranean conditions this episode coincided with the first human colonization of the island and also with a widespread climatic change in the western mediterranean region the change in taxa was complex and some sclerophyllous taxa sucholeaplayed an important role in the transformation of the landscape physiognomy from the mid holocene until the present although human activities have removed much of the mediterranean vegetation on the balearic islands it seems clear that the changes have been brought about in part by increasing dryness

modeling a 200 yr interruption of the holocene sapropel s1 an oceanic general circulation model previously used to simulate the conditions associated with the holocene sapropel s1 is used to simulate the effects of a climate deterioration represented as a cooling event on the sapropelic circulation mode the enhanced cooling 2 3 c induces deep convection in the adriatic and the gulf of lions and intermediate water formation in the aegean where in all cases there had previously been only stagnant unventilated waters the depths of ventilation to 1250 m are in agreement with core data from this period the short decadal timescales involved in modifying the sapropelic circulation suggest that such a climatic deterioration may be associated with the interruption of s1 between 7100 and 6900 14c yr b p which divided the sapropel into two subunits

late holocene history of the moldova river valley romania abstract this paper describes the results of geomorphological sedimentological and 14 c analyses of late holocene fluvial sequences in the moldova river valley of romania this river originates from the carpathians mountains and is known for the extent of its large floodplain and sediment thickness between the molid and timisesti localities river length 86 km numerous large fossil trunks of oak poplar and beech trees are exposed in the riverbanks six wood samples were selected for radiocarbon absolute dating conventional method and their ages ranged from 410 to 3200 cal yrs bp the thickness of the alluvial sediments above the sampled fossil trunks varied between 2 and 3 m and these sediments predominantly consisted of coarse gravel materials that had similar granulometry to sediments that were present in the modern riverbed additionally in the same investigated areas successive floodplain cross sections were constructed based on more than 20 hydrogeological boreholes for each cross section all data were used to calculate the local values of bed loads and these values were compared to the absolute ages of the fossil trunks and were in the range of 300 m 3 m and 5500 m 3 m based on the calculated values during the last 780 years the floodplain sedimentation rates were estimated to be in the range of 0 4 m 3 year at the molid section which was located in the mountainous area of the valley and 44 km downstream from the river headwater and during the last 410 years the sedimentation rate at the praxia section which was located 125 km downstream from the river headwater was 13 3 m 3 year in the past 100 years the fluvial processes along the moldova river were dominated by a narrowing by an average of 76 and an incision up to 2 5 m and a channel metamorphosis from braided to wandering was reported these results are discussed in the context of late holocene regional and local palaeoclimatic reconstructions as well as that of human interventions

holocene climate variability in europe evidence from δ18o textural and extension rate variations in three speleothems time series o isotope profiles for three u th dated stalagmites have revealed that for much of the holocene a site on the atlantic seaboard sw ireland exhibits first order 18o trends that are almost exactly out of phase with coupled 18o curves from two southern european sites se france and nw italy in the irish stalagmite cc3 from crag cave sw ireland low 18o at 10 000 cal yr bp reflects cool conditions by the early to mid holocene 9000 6000 cal yr bp 18o had increased reflecting the onset of warmer conditions on the atlantic seaboard this shift to higher 18o was accompanied by a marked increase in the stalagmite extension rate reinforcing our interpretation that this was a period of relative warmth except for an episode of increased extension rate about 5500 yr ago 18o in the crag stalagmite exhibits a gradual decrease accompanied by declining extension rates between 7800 and 3500 cal yr bp interpreted as a cooling trend there is evidence for increases in both 18o and stalagmite extension rate in the period from 3500 cal yr bp to the present day suggesting a return to warmer conditions on the atlantic seaboard in the stalagmite from nw italy er76 grotta di ernesto trentino province the early holocene c 9200 7800 cal yr bp is characterised by high 18o probably indicative of warm and or dry conditions exceptionally low 18o from 7800 to 6900 cal yr bp at this site reflects a well defined wet phase cerin wet phase in the last three millennia this stalagmite exhibits a shift to lower 18o interpreted as some combination of cooler and or wetter conditions unlike the irish stalagmite the italian sample does not show a correlation between 18o and extension rate instead its extension rate correlates roughly with 13c presumably reflecting a climate driven vegetation change in the early holocene 18o in the french stalagmite cl26 grotte de clamouse herault province se france was low relative to its holocene average for much of the period since c 3500 cal yr bp this stalagmite exhibits higher 18o than in the early holocene suggesting warmer conditions like the irish stalagmite the french sample exhibits a well defined correlation between 18o and extension rate had drip water availability been the dominant control on 18o at this semi arid site then higher 18o would have been accompanied by lower not higher extension rates this suggests strongly that temperature rather than rainfall amount was the dominant control at this site while conclusions regarding the patterns of climate variability on a continent scale must remain tentative because of the limited number of stalagmites studied we argue that early holocene warm conditions on the atlantic seaboard irish site coincided with relatively cool conditions at the clamouse site by c 3500 yr ago the pattern appears to have been reversed

recurring taiga forest steppe habitats in the carpathian basin in the upper weichselian many loess pro les some lake sediments and archaeological sites in di erent parts of the carpathian basin were analysed in respect of their geology sedimentology molluscs and macro charcoal remains radiocarbon dating was also carried out on charcoal remains as well as on molluscan shells the loess pro les prove to have been formed during the last glacial period between ca 70 000 and 15 000 years bp two well developed and a weakly developed charcoal layer can be found at the sites dating from that period all rest on the top of a palaeosol on the basis of palaeoecological investigations of these charcoal layers and the molluscs found within the loess it is concluded that recurring boreal forest steppe habitats characterised the carpathian basin the woodlands mostly consisting of picea trees in the north and pinus sylvestris in the south as well as six other arboreal species by reference to the subsequent charcoal layers reforestation occurred every 2000 5000 years with the same composition although their density may have varied these forests thus recur in the same places after extensive forest res how often and why these reforestation events took place and how much time was needed for the forests steppes to redevelop needs further clari cation 2001 published by elsevier science ltd

episodic build up of alluvial fan deposits during the weichselian pleniglacial in the western transylvanian basin romania and their paleoenvironmental significance abstract a weichselian pleniglacial cyclic sedimentation sequence at floresti near cluj napoca in western transylvania romania represents an alternation of slope deposits coarse fan structures and reworked loess like sediments and paleosols detailed grain size analysis together with pedological pollen and malacofaunal investigation allows the recognition of four main morphoclimatic cycles similar to those of stadial interstadial nature boreal forest steppe to periglacial steppe oscillations developed during the weichselian pleniglacial according to the u th and radiocarbon ages the period between 70 and 26 ka bp was cool and variably dry after which the climate became colder probably in response to the last glacial maximum the floresti section shows strong similarities to other central and south eastern european pedocomplexes of pleniglacial age notably the moravian section of dolni ve stonice and loess sections from vojvodina serbia

detrital events and hydroclimate variability in the romanian carpathians during the mid to late holocene the romanian carpathians are located at the confluence of three major atmospheric pressure fields the north atlantic the mediterranean and the siberian despite its importance for understanding past human impact and climate change high resolution palaeoenvironmental reconstructions of holocene hydroclimate variability and in particular records of extreme precipitation events in the area are rare here we present a 7500 year long high resolution record of past climatic change and human impact recorded in a peatbog from the southern carpathians integrating palynological geochemical and sedimentological proxies natural climate fluctuations appear to be dominant until 4500 years before present yr bp followed by increasing importance of human impact sedimentological and geochemical analyses document regular minerogenic deposition within the bog linked to periods of high precipitation such minerogenic depositional events began 4000 yr bp with increased depositional rates during the medieval warm period mwp the little ice age lia and during periods of societal upheaval e g the roman conquest of dacia the timing of minerogenic events appears to indicate a teleconnection between major shifts in north atlantic oscillation nao and hydroclimate variability in southeastern europe with increased minerogenic deposition correlating to low nao index values by linking the minerogenic deposition to precipitation variability we state that this link persists throughout the mid to late holocene

hydrologic issues associated with nuclear waste repositories significant progress in hydrology especially in subsurface flow and solute transport has been made over the last 35 years because of sustained interest in underground nuclear waste repositories the present paper provides an overview of the key hydrologic issues involved and to highlight advances in their understanding and treatment because of these efforts the focus is not on the development of radioactive waste repositories and their safety assessment but instead on the advances in hydrologic science that have emerged from such studies work and results associated with three rock types which are being considered to host the repositories are reviewed with a different emphasis for each rock type the first rock type is fractured crystalline rock for which the discussion will be mainly on flow and transport in saturated fractured rock the second rock type is unsaturated tuff for which the emphasis will be on flow from the shallow subsurface through the unsaturated zone to the repository the third rock type is clay rich formations whose permeability is very low in an undisturbed state in this case the emphasis will be on hydrologic issues that arise from mechanical and thermal disturbances i e on the relevant coupled thermo hydro mechanical processes the extensive research results especially those from multiyear large scale underground research laboratory investigations represent a rich body of information and data that can form the basis for further development in the related areas of hydrologic research

simple model representations of transport in a complex fracture and their effects on long term predictions 1 a complex fracture model for fluid flow and tracer transport that incorporates many of the important physical effects of a realistic fracture including advection through a heterogeneous fracture plane partitioning of flow into multiple subfractures in the third dimension and diffusion and sorption into fracture filling gouge small altered rock matrix blocks within the fracture zone and the unaltered semi infinite rock matrix on both sides of the fracture zone was previously developed it is common however to represent the complex fracture by much simpler models consisting of a single fracture with a uniform or heterogeneous transmissivity distribution over its plane and bounded on both sides by a homogeneous semi infinite matrix simple model properties are often inferred from the analysis of short term one to a few days site characterization sc tracer test data the question addressed in this paper is how reliable is the temporal upscaling of these simplified models are they adequate for long term calculations that cover thousands of years in this study a particle tracking approach is used to calculate tracer test breakthrough curves btcs in a complex fracture model incorporating all the features described above for both a short term sc tracer test and a 10 000 year calculation the results are considered the real world next two simple fracture models one uniform and the other heterogeneous are introduced properties for these simple models are taken either from laboratory data or found by calibration to the short term sc tracer test btcs obtained with the complex fracture model then the simple models are used to simulate tracer transport at the long term timescale results show that for the short term sc tracer test the btcs calculated using simple models with laboratory measured parameters differ significantly from the btcs obtained with the complex fracture model by adjusting model properties the simple models can be calibrated to reproduce the peak arrival time and height of the complex fracture model btcs but the overall match remains quite poor using simple models with short term sc calibrated parameters for long term calculations yields btcs with order of magnitude errors peak arrival time is 10 to 100 times too late and peak height is 50 to 300 times too small on the other hand using simple models with laboratory measured properties of unfractured rock samples for 10 000 year calculations yields btcs with peak arrivals and heights up to a factor of 50 too early and large respectively the actual magnitudes of the errors made by using the simple models depend on the parameter values assumed for the complex fracture model but in general simple models are not expected to provide reliable long term predictions the paper concludes with some suggestions on how to improve long term prediction calculations

a paleoclimate record of the last 17 600 years in stalagmites from the b7 cave sauerland germany abstract petrographical and geochemical parameters of stalagmites from the b7 cave in iserlohn letmathe northern rhenish massif nw germany record late and postglacial climate changes temperature and or precipitation fabrics and microfacies of the stalagmite profiles lead to a differentiation of four hierarchies of rhythms clastic layers in the stalagmites are caused by flooding events and are time markers twenty four tims th u age dates provide a time calibration of stalagmite growth phases one stalagmite reveals an early growth period between 17 6 and 16 7 ka bp between 9 6 and 5 5 ka bp atlantic episode of the holocene the growth rate of the stalagmites was higher than before and after this time with dominant light porous microfacial laminae and high 18 o and 13 c values representing partly kinetic fractionation effects this part of the holocene is interpreted as a mainly warm episode with frequent interruptions of dripping within the past 4 ka the profiles with predominant dark compact facies reveal low isotopic values which may be interpreted as a temperature proxy record the stalagmite records resemble records from an irish stalagmite correlation with the 14 c record from european tree rings suggests that colder periods in the north atlantic were accompanied by drier winters in central europe

on the discrepancies in tropical belt expansion between reanalyses and climate models and among tropical belt width metrics abstractthe arid subtropics are situated at the edges of the tropical belt where subsidence in the hadley cells suppresses precipitation any meridional shift in these edge latitudes could have significant impacts on surface climate recent studies have investigated past and future changes in the tropical belt width and have found discrepancies in the rates of expansion estimated with different metrics and between climate models and reanalyses here cmip5 simulations and four modern reanalyses are analyzed using an ensemble of objective tropical belt width metrics to reexamine if such inconsistencies exist the authors do not find sufficient evidence to demonstrate this discrepancy between models and reanalyses as reanalysis trends in the tropical belt width fall within the range of model trends for any given metric furthermore only metrics based on the hadley cells are found to exhibit robust historical and future expansion metrics based on the subtropical jet and the tropopause show no robust resp

observed trends in the global jet stream characteristics during the second half of the 20th century 1 in this paper we propose a new method based on the detection of jet cores with the aim to describe the climatological features of the jet streams and to estimate their trends in latitude altitude and velocity in the national centers for environmental prediction ncep national center for atmospheric research ncar and 20th century reanalysis data sets due to the fact that the detection method uses a single grid point to define the position of jet cores our results reveal a greater latitudinal definition allowing a more accurate picture of the split flow configurations and double jet structures to the best of our knowledge these results provide the first multiseasonal and global trend analysis of jet streams based on a daily resolution 3 d detection algorithm trends have been analyzed over 1958 2008 and during the post satellite period 1979 2008 we found that in general trends in jet velocities and latitudes have been faster for the southern hemisphere jets and especially for the southern polar front jet which has experienced the fastest velocity increase and poleward shift over 1979 2008 during the austral summer and autumn results presented here show an acceleration and a poleward shift of the northern and southern winter subtropical jets over 1979 2008 that occur at a faster rate and over larger zonally extended regions during this latter period than during 1958 2008

lateglacial and holocene vegetation belts in the pirin mountains southwestern bulgaria pollen stratigraphy of a core 270 cm long from lake dalgoto at 2310 m in the northern pirin mountains southern bulgaria was treated by optimal partitioning and compared to a broken stick model to reveal statistically significant pollen zones the vegetational reconstructions presented here are based on pollen percentages and pollen influx on comparisons of modern and fossil pollen spectra and on macrofossil dates from other sites in the mountains during the younger dryas 11000 10200 14c yr bp an open xerophytic herb vegetation with artemisia and chenopodiaceae was widely developed around the lake deciduous trees growing at lower elevations contributed to the pollen rain deposited at the higher elevation sampling sites specifically from 10200 to 8500 yr bp quercus ulmus tilia and betula expanded rapidly at low and intermediate elevations and between 8500 and 6500 yr bp they extended to higher elevations close to the upper forest limit which was formed by betula pendula at about 1900 m coniferous species were limited in the region at this time after 6500 yr bp the expansion of conifers pinus peuce p sylvestris p mugo abies alba at high elevations forced the deciduous trees downward between 6500 and 3000 yr bp the forest limit at 2200 m was formed by p peuce and a alba had its maximum vertical range up to 1900 m later the abundance and vertical range of p peuce and a alba were reduced after 3000 yr bp picea expanded

rapid atmospheric co2 changes associated with the 8 200 years b p cooling event by applying the inverse relation between numbers of leaf stomata and atmospheric co2 concentration stomatal frequency analysis of fossil birch leaves from lake deposits in denmark reveals a century scale co2 change during the prominent holocene cooling event that occurred in the north atlantic region between 8 400 and 8 100 years b p in contrast to conventional co2 reconstructions based on ice cores from antarctica quantification of the stomatal frequency signal corroborates a distinctive temperature co2 correlation results indicate a global co2 decline of 25 ppm by volume over 300 years this reduction is in harmony with observed and modeled lowering of north atlantic sea surface temperatures associated with a short term weakening of thermohaline circulation

holocene vegetation history in the upper forest belt of the eastern romanian carpathians abstract pollen analysis supported by nine ams 14 c dates from the poiana tiol peat sequence 1540 m in the rodnei mountains eastern romanian carpathians romania is used to reconstruct the holocene vegetation history in this mountain region the results are then compared with other sequences from romania and eastern europe in order to better understand the past dynamics of the main forest constituents the vegetation record at poiana tiol starts at ca 11 000 cal yr bp with the occurrence of rather closed woodlands composed of betula pinus picea abies alnus a viridis and ulmus picea abies was the dominant tree species for almost the entire period however during the last 3000 years p abies forests were largely replaced by pinus in the area temperate tree taxa fraxinus quercus acer tilia and corylus avellana were also common but likely at lower elevation c avellana expanded around 10 300 cal yr bp and reached maximum values after 9000 cal yr bp pollen of carpinus betulus and fagus sylvatica was already recorded around 7000 cal yr bp however the spread of c betulus occurred at ca 6000 cal yr bp with maximum values between 4800 cal yr bp and 3000 cal yr bp while f sylvatica spread from ca 3200 cal yr bp and attained maximum values between 2000 and 200 cal yr bp the first indications of human activities appeared around 3200 cal yr bp and intensified within the last 200 years comparison with other sequences from romania and surrounding countries reveals both similarity and great differences related to the location of glacial refugia climate change and human impact

the climate of europe 6000 years ago palaeoclimates across europe for 6000 y bp were estimated from pollen data using the modern pollen analogue technique constrained with lake level data the constraint consists of restricting the set of modern pollen samples considered as analogues of the fossil samples to those locations where the implied change in annual precipitation minus evapotranspiration p e is consistent with the regional change in moisture balance as indicated by lakes an artificial neural network was used for the spatial interpolation of lake level changes to the pollen sites and for mapping palaeoclimate anomalies the climate variables reconstructed were mean temperature of the coldest month tc growing degree days above 5 c gdd moisture availability expressed as the ratio of actual to equilibrium evapotranspiration and p e the constraint improved the spatial coherency of the reconstructed palaeoclimate anomalies especially for p e the reconstructions indicate clear spatial and seasonal patterns of holocene climate change which can provide a quantitative benchmark for the evaluation of palaeoclimate model simulations winter temperatures tc were 1 3 k greater than present in the far n and ne of europe but 2 4 k less than present in the mediterranean region summer warmth gdd was greater than present in nw europe by 400 800 k day at the highest elevations and in the alps but 400 k day less than present at lower elevations in s europe p e was 50 250 mm less than present in nw europe and the alps but was 10 15 greater than present in s europe and p e was 50 200 mm greater than present in s and e europe

the late quaternary environmental history of batorliget n e hungary abstract a sedimentary sequence extending back into the last glacial has been obtained from batorliget marsh in n e hungary reconstruction of the environmental history of the region using the techniques of pollen analysis molluscan analysis and geochemistry has revealed an important late quaternary refugium during the last glacial a refugium for temperate flora and fauna existed within a landscape dominated by coniferous forest predominantly made up of pinus and picea the lateglacial postglacial transition at 10 000 yr b p resulted in a dramatic shift from coniferous but also including betula woodland to deciduous woodland following the lateglacial postglacial transition a highly diverse woodland became established in the early postglacial accompanied by an equally diverse molluscan assemblage this diversity remained throughout the early postglacial although the types present within the woodland changed a number of times at c 7000 yr b p anthropogenic disturbance resulted in the destruction of the mixed forest and the development of agricultural land the importance of this region as a refugial area both in the lateglacial and early postglacial is discussed and the influence that it had on the postglacial development of the fauna and flora of northeastern hungary is reviewed

origin of a boreal birch bog woodland and landscape development on a warm low mountain summit at the carpathian pannonian interface we analysed two peat cores of late glacial origin from a bog woodland in the male karpaty mts sw slovakia using plant macrofossil pollen peat chemistry and charcoal analyses to trace local successional patterns regional vegetation development and occurrence of rare species

climatic and human impact on the environment a question of scale abstract the environmental context of cultural transformation frames the central issue of this paper how were neolithic and chalcolithic landscapes in the aegean balkan and carpathian abc zones shaped and transformed by climatic and anthropogenic impacts the difficulties in interpreting proxy records for the middle transitional stage of the holocene aridification sequence falling between the early wet stage and the late arid stage have been created by the conjoint influence of two kinds of impact climatic and anthropogenic an unhelpful influence in this debate stems from willis and bennett s 1994 hypothesis of minimal human impact on the pre bronze age landscapes of south east europe in this paper two questions are posed 1 what were the effects of the claimed global changes in holocene climate at the regional and local scale in the abc zones and 2 can we recognise human impact in these proxy records prior to the bronze age of our study regions following a discussion of general long term climatic trends and rccs episodes of rapid climatic change i base a discussion of the so called 8200bp event and pre bronze age human impacts on a suite of 24 well dated proxy records mostly pollen sequences the principal findings are that there is little evidence for impact from the 8200bp event in these records while there is substantial evidence for pre bronze age human impacts on the landscapes of the aegean balkan and carpathian regions

holocene climate change and prehistoric settlement in the lower danube valley abstract an analysis of the summed probability distributions of 293 radiocarbon dates from late glacial to mid holocene sites in the danubian iron gates highlights the existence of well marked 14c discontinuities at c 9 5 9 0 ka 8 65 8 0 ka and after 7 8 ka cal bp these coincide with climate anomalies recorded in greenland ice cores and palaeoclimate archives from the danube catchment four possible explanations are considered dwindling fish resources changes in the social environment flood induced settlement relocations and taphonomic effects on present evidence the last two factors are thought to be the most likely cause of the discontinuities observed in the iron gates mesolithic early neolithic radiocarbon record

effective matrix diffusion in kilometer scale transport in fractured crystalline rock concentrations of tritium 3h and dichlorodifluoromethane cfc 12 in water samples taken from glacial drift and fractured crystalline rock over 4 km2 in central new hampshire are interpreted to identify a conceptual model of matrix diffusion and the magnitude of the diffusion coefficient dispersion and mass transfer to and from fractures has affected the 3h concentration to the extent that the peak 3h concentration of the 1960s is no longer distinguishable because of heterogeneity in the bedrock the sparsely distributed chemical data do not warrant a three dimensional transport model instead a one dimensional model of cfc 12 and 3h migration along flow lines in the glacial drift and bedrock is used to place bounds on the processes affecting kilometer scale transport arid model parameters are varied to reproduce the measured relation between 3h and cfc 12 rather than their spatial distributions a model of mass exchange to and from fractures that is dependent on the time varying concentration gradient at fracture surfaces qualitatively reproduces the measured relation between 3h and cfc 12 with an upper bound for the fracture dispersivity approximately equal to 250 m and a lower bound for the effective matrix diffusion coefficient equal to 1 m2 yr 1 the diffusion coefficient at the kilometer scale is at least 3 orders of magnitude greater than laboratory estimates of diffusion in crystalline rock the large diffusion coefficient indicates that diffusion into an immobile fluid phase rock matrix is masked at the kilometer scale by advective mass exchange between fractures with large contrasts in trarismissivity the measured transmissivity of fractures in the study area varies over more than 6 orders of magnitude advective mass exchange from high permeability fractures to low permeability fractures results in short migration distances of a chemical constituent in low permeability fractures over an extended period of time before reentering high permeability fractures viewed at the kilometer scale this process is analogous to the chemical constituent diffusing into and out of an immobile fluid phase

the full glacial forests of central and southeastern europe the presence of trees in central and southern europe during the last full glaciation has long been a matter of debate a low but persistent presence of fossil tree pollen in central and southern european full glacial paleoecological sequences has been interpreted either as representing long distance pollen transport from southerly refuges or as representing in situ refugial populations here we present macroscopic charcoal results from 31 sequences located throughout hungary that provide unequivocal evidence for the presence of at least seven different tree types between approximately 32 500 and 16 500 14c yr b p this evidence is presented in conjunction with molluscan and pollen analyses to indicate that during the last full glaciation trees grew as far north as hungary probably in microenvironmentally favorable sites these areas provided an important cold stage refugium for the european flora and fauna

recent widening of the tropical belt evidence from tropopause observations 1 radiosonde measurements and reanalysis data are used to examine long term changes in tropopause behavior in the subtropics tropopause heights in the subtropics exhibit a bimodal distribution with maxima in occurrence frequency above 15 km characteristic of the tropical tropopause and below 13 km typical of the extratropical tropopause both the radiosonde and reanalysis data show that the frequency of occurrence of high tropopause days in the subtropics of both hemispheres has systematically increased during the past few decades so that tropical characteristics occur more frequently in recent years this behavior is consistent with a widening of the tropical belt and the data indicate an expansion of about 5 8 latitude during 1979 2005

poleward shift of subtropical jets inferred from satellite observed lower stratospheric temperatures abstractone pronounced feature in observed latitudinal dependence of lower stratospheric temperature trends is the enhanced cooling near 30 latitude in both hemispheres the observed phenomenon has not to date been explained in the literature this study shows that the enhanced cooling is a direct response of the lower stratospheric temperature to the poleward shift of subtropical jets furthermore this enhanced lower stratospheric cooling can be used to quantify the poleward shift of subtropical jets using the lower stratospheric temperatures observed by satellite borne microwave sounding units it is shown that the subtropical jets have shifted poleward by 0 6 0 1 and 1 0 0 3 latitude in the southern and northern hemispheres respectively in last 30 years since 1979 indicating a widening of tropical belt by 1 6 0 4 latitude

the cold event 8200 years ago documented in oxygen isotope records of precipitation in europe and greenland stable oxygen isotope ratios of ostracod valves in late glacial and holocene sediments of core as 92 5 from deep lake ammersee southern germany reflect variations of mean oxygen isotope ratios in past atmospheric precipitation the record reconfirms the strong similarity of climate evolution in europe and greenland during the last deglaciation for the first time in europe we find a 200 year long negative 18o excursion which is contemporaneous with the strongest negative 18o excursion in the greenland ice around 8 2 ky before present the 8 2 ky isotopic event on both sides of the north atlantic ocean is interpreted as a cold period most probably induced by a perturbation of the north atlantic thermohaline circulation we discuss two possible triggering mechanisms 1 weak forcing as proposed by alley et al and 2 forcing by a strong and sudden freshwater pulse from the collapse of the hudson ice dome

holocene forest dynamics in northwestern romnania pollen analyses and ams radiocarbon measurements were carried out on peat deposits from the former crater lake preluca tiganului located in a mid altitude area of the gutaiului mountains nw romania in order to reconstruct the postglacial vegetation history at the lateglacial holocene transition the open vegetation was replaced by forest suggesting a fast response to climatic warming the rapid expansion of pinus betula and later picea may be due to their existence in the area during the lateglacial at approximately 11 250 cal yr bp the dense forest was composed primarily of ulmus and some picea betula and pinus a small population of ulmus might also have survived in the area during the lateglacial at 10750 cal yr bp quercus tilia and fraxinus followed by corylus at c 10200 cal yr bp expanded significantly in the forest the delay of approximately 550 years in their establishment as compared to the expansion of ulmus was probably due to their immigration from more distant localities

fine scale structure of the extratropical tropopause region 1 a vertically high resolved climatology of the thermal and wind structure of the extratropical tropopause region is presented the climatology is based on data from 80 u s radiosonde stations covering the period 1998 2002 time averages for each radiosonde station are computed using the tropopause as a common reference level for all vertical profiles within the mean a strong inversion at the tropopause in the mean vertical temperature gradient is uncovered that is temperature strongly increases with altitude within the lowermost stratosphere this tropopause inversion layer exists on average throughout the investigated extratropics about 30 n to 70 n accordingly the static stability parameter shows considerably enhanced values within the lowermost extratropical stratosphere compared to typical extratropical stratospheric values further aloft conventional averages are not able to capture the tropopause inversion layer mean profiles of the horizontal wind show behavior qualitatively corresponding to thermal wind balance winter and summer exhibit distinctly different climate states in the extratropical tropopause region an approximated potential vorticity is considered and found to be close to well mixed within the troposphere as well as within the tropopause inversion layer this suggests the view of the tropopause inversion layer as representing a dynamically active atmospheric layer some potential implications are discussed

a new approach to account for fracture aperture variability when modeling solute transport in fracture networks a simple yet effective method is presented to include the effects of fracture aperture variability into the modeling of solute transport in fracture networks with matrix diffusion and linear sorpti

on the upscaling of chemical transport in fractured rock the impact of flow heterogeneity on chemical transport from single to multiple fractures is investigated the emphasis is on the dynamic nature of the specific surface area ssa due to heterogenei

high resolution analyses of an early holocene climate event may imply decreased solar forcing as an important climate trigger early holocene lacustrine tree ring ice core and marine records reveal that the northern hemisphere underwent a short cooling event at 10 300 calendar yr b p 9100 14 c yr b p the records were compared on a common high resolution time scale and show that the event lasted less than 200 yr with a cooling peak of 50 yr and the event coincides with a distinct holocene thermohaline disturbance recognized in the north atlantic ocean in spite of wellknown freshwater forcings at the time of the event the negligible difference between the modeled d 14 c record based on the gisp2 greenland ice sheet project 2 10 be data and the measured values does not allow for detectable d 14 c changes related to global ocean ventilation we can however show that the onset of the cooling coincides with the onset of one of the largest holocene 10 be flux peaks this finding may imply that the climate system is more

seasonality and interannual variability of the westerly jet in the tibetan plateau region abstract in this study 40 yr ecmwf re analysis era 40 data are used for the description of the seasonal cycle and the interannual variability of the westerly jet in the tibetan plateau region to complement results based on the analysis of monthly mean horizontal wind speeds an occurrence based jet climatology is constructed by identifying the locations of the jet axes at 6 hourly intervals throughout 1958 2001 thus a dataset describing the highly transient and localized features of jet variability is obtained during winter and summer the westerly jet is located respectively to the south and north of the tibetan plateau during the spring and autumn seasons there are jet transitions from south to north and vice versa the median dates for these transitions are 28 april and 12 october the spring transition is associated with large interannual variations while the fall transition occurs more reliably within a 3 week period the strength of the jet exhibits a peculiar seasonal cycle during northw

isotopic climate record in a holocene stalagmite from ursilor cave romania the pu 2 stalagmite from ursilor cave provides the first dated romanian isotope record for the holocene the overall growth rate of the speleothem was 3 5 cm kyr 1 corresponding to a temporal resolution of 142 y between each isotope analysis the hendy tests indicate that isotopic equilibrium conditions occurred during the formation of pu 2 and hence that it is suitable for palaeoclimatic studies the relationship between 18 o and temperature was found to be positive this can be interpreted either as rain out with distance from the west northwest ocean source of evaporation or shifts in air mass source with changing north atlantic oscillation indices applying five u th thermal ionisation mass spectrometric tims dates to a 17 5 cm isotope profile 18 o

a 9000 year record of cyclic vegetation changes identified in a montane peatland deposit located in the eastern carpathians central eastern europe autogenic succession or regional climatic influences abstract we present a high resolution continuous plant macrofossil remains record complemented by a pollen sequence from t ul muced bog in the eastern carpathian mountains romania the record spans the last 9000 years and we test whether peatland development in the eastern carpathians is linked to climate change or to autogenic succession we find that sphagnum magellanicum was the dominant peat forming species for ca 8000 years but we also identify ten phases of increased representation of eriophorum vaginatum at approximately 8100 7550 6850 6650 5900 4650 3150 1950 1450 and 750 cal yr bp visual inspection and wavelet analysis show that the episodic increases in the relative abundances of eriophorum vaginatum were simultaneous with decreased abundances of sphagnum magellanicum and sphagnum angustifolium comparison with published palaeoclimatic records in this region suggests that these cyclical successions of s magellanicum and e vaginatum appear to be primarily a result of climate changes with e vaginatum developing mainly during dry phases and s magellanicum during wetter periods we therefore suggest that the development of this peatland was largely influenced by changing climatic conditions although the role of autogenic plant succession cannot be excluded our results show the value of ombrotrophic peat deposits as archives of past climate change

a new look for the southern hemisphere jet stream a new jet stream description defined as the geostrophic streamline of maximum average velocity is proposed an objective algorithm for detecting and tracking the jet has been developed tested and applied to the ncep ncar 200 hpa geopotential height in the southern hemisphere for the period 1958 2002 the results show the variability of the double character of the southern hemisphere jet with a marked seasonality during the warm season a single jet can be found around 40 s while autumn and winter are characterized by a clear double jet structure with a strong and dominant subtropical jet located around 30 s and a polar front jet progressively displaced toward southern latitudes and reaching 60 s by the end of the cold season in general a trend toward slower subtropical jets and stronger polar front jets has been detected during the study period the southern annular mode appears as a main modulator of the latitude and strength of the polar front jet influencing to a minor extent its subtropical counterpart the enso cycle strongly modifies the latitude and specially the strength of the subtropical jet affecting its preferred wavenumber as well nevertheless the effect of this oscillation seems fairly restricted in the pacific thus limiting the ability of this jet to drive the el nino teleconnections along the southern hemisphere the consistency of the results when compared with previous jet climatologies suggests that the new approach is a reliable jet tracking method thus providing a new tool to analyze climatic variability at hemispheric scales

younger dryas to mid holocene environmental history of the lowlands of nw transylvania romania pollen micro charcoal and total carbon analyses on sediments from the turbuta palaeolake in the transylvanian basin of nw romania reveal younger dryas to mid holocene environmental changes the chronostratigraphy relies on ams 14c measurements on organic matter and u th tims datings of snail shells results indicate the presence of pinus and betula open woodlands with small populations of picea ulmus alnus and salix before 12 000 cal yr bp a fairly abrupt replacement of pinus and betula by ulmus dominated woodlands at ca 11 900 cal yr bp likely represents competition effects of vegetation driven by climate warming at the onset of the holocene by 11 000 cal yr bp the woodlands were increasingly diverse and dense with the expansion of quercus fraxinus and tilia the establishment of corylus and the decline of upland herbaceous and shrubs taxa the marked expansion of quercus accompanied by tilia between 10 500 and 8000 cal yr bp could be the result of low effective moisture associated with both low elevation of the site and with regional change towards a drier climate at 10 000 cal yr bp corylus spread across the region and by 8000 cal yr bp it replaced quercus as a dominant forest constituent with only little representation of picea abies carpinus became established around 5500 cal yr bp but it was only a minor constituent in local woodlands until ca 5000 cal yr bp results from this study also indicate that the woodlands in the lowlands of turbuta were never closed

climate model biases in the width of the tropical belt abstractearth s arid subtropics are situated at the edges of the tropical belt which encircles the planet along the equator and covers half of its surface area the climate of the tropical belt is strongly influenced by the hadley cells with their subsidence and easterly trade winds both sustaining the aridity at the belt s edges the understanding of earth s past present and future climates is contingent on understanding the dynamics influencing this region an important but unanswered question is how realistically climate models reproduce the mean state of the tropical belt this study augments the existing literature by examining the mean width and seasonality of the tropical belt in climate models from phase 5 of cmip cmip5 and experiments from the second phase of the chemistry climate model validation ccmval 2 activity of the stratospheric processes and their role in climate sparc project while the models overall reproduce the structure of the tropical belt width s seasonal cycle they und

small scale moisture availability increase during the 8 2 ka climatic event inferred from biotic proxy records in the south carpathians se romania in this paper we present high resolution early holocene pollen plant macrofossil charcoal diatom biogenic silica and loss on ignition records from a mountain lake in the south carpathians in order to reveal ecosystem response to the 8 2 ka climatic oscillation we found significant changes both in terrestrial vegetation and lake diatom assemblages in the northern slope of the retezat mts between c 8300 and 8000 cal yr bp rapid changes in relative frequencies and pollen accumulation rates of the major deciduous pollen types associated with peaks in microcharcoal accumulation rates suggested that vegetation disturbance mainly took place in the mixed deciduous forest zone where woodland fires partially destroyed the populations of fraxinus excelsior quercus and corylus avellana and facilitated the establishment of carpinus betulus in the forest openings the diatom record furthermore showed the spread of a planktonic diatom species aulacoseira valida at 8150 cal yr bp coincidently with a shor

reconstruction of climatic and environmental changes in nw romania during the early part of the last deglaciation 15 000 13 600 cal yr bp high resolution pollen plant macrofossil charcoal mineral magnetic and sedimentary analyses combined with ams 14 c measurements were performed on multiple sediment sequences alonga transect through the former crater lake preluca tiganului in

a 12 000 year pollen record from lake maliq albania abstract pollen data from lake maliq the first from albania contribute new information to the discussion of the vegetational hydrological and climatological history of the balkans since 12 000 yr b p during late glacial time a perennial lake expanded at maliq it was surrounded by a complex vegetation association composed of steppe and mixed forest elements the highly diverse forest flora suggest that late glacial forest refugia were more developed here at middle altitude rather than at higher altitude as previously suggested the forest developed after 9800 yr b p while the water level remained high in the korce basin until 5000 yr b p different environmental conditions characterized by lower available moisture and warmer winters progressively took place after this date human activity in the korce basin ca 4500 yr b p was coeval with conditions characterized by an increase in winter temperatures and a decrease in summer moisture

natural variations of tropical width and recent trends the temporal evolution of the tropical width since 1979 is investigated in observations and models by using metrics based on outgoing radiation 6 7 m brightness temperature and atmospheric reanalysis the maximum 20 year widening as seen in radiation by satellites occurred during 1993 2012 and was associated with a global sea surface temperature sst change that resembles the el nino southern oscillation pacific decadal oscillation in the pacific region idealized experiments with community atmospheric model version 5 reveal that tropical pacific sst pattern largely accounts for the widening a number of coupled model intercomparison project phase 5 coupled models can simulate without any type of forcing this satellite inferred tropical widening and its associated pacific sst pattern while model simulated widenings are consistent for all metrics the two reanalysis based widenings are inconsistent internally and with the satellite based and model widenings our results reinforce suggestions that observed widenings can be explained by internal variability as captured by climate models though this depends on whether reanalysis trends are regarded as reliable

double tropopauses and the tropical belt connected to enso a detailed analysis of double tropopause dt occurrences requires vertically well resolved accurate and globally distributed information on the troposphere stratosphere transition zone here we use radio occultation observations from 2001 to 2018 with such properties we establish a connection between el nino southern oscillation enso phases and the distribution of dts by analyzing the global and seasonal dt characteristics the seasonal distribution of dts reveals several hotspot locations such as near the subtropical jet stream and over high mountain ranges where dts occur particularly often in this study we detect a higher number of dts during the cold la nina state while warmer el nino events result in lower dt rates affecting the structure of the tropopause region close to the nino 3 region this relates to a much lower first lapse rate tropopause altitude during la nina and corresponds to an apparent narrowing of the tropical belt there

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

the end of the present interglacial how and when despite the large decline in northern hemisphere summer insolation during the last 8000 years neither sea level nor polar temperatures have as yet undergone any significant downturn this behavior is consistent with the prediction by kukla and matthews 1972 that the holocene interglacial will terminate suddenly with a jump to another of the climate system s modes of operation this is what happened at the end of the last period of peak interglaciation however complicating the situation is evidence that ice sheet growth during the transition from marine stage 5e to 5d preceded the shut down of the atlantic s conveyor circulation which is thought to have brought europe s eemian to a close if so then in the natural course of events the end of the present interglaciation awaits the onset of ice cap growth however it must be kept in mind that the ongoing buildup of greenhouse gases may alter the natural course of events in particular the warming and wetting of the planet will gradually reduce the density of surface waters in the regions where deep waters form as this reduction is not likely to be symmetrical between the northern atlantic and the margin of the antarctic continent the current near balance between deep water production in the north and south may be disrupted causing an abrupt reorganization of the ocean s thermohaline circulation based on the paleoclimatic record such a reorganization would have had a profound impact on the planet s climate

flow dependence of matrix diffusion in highly heterogeneous rock fractures diffusive mass transfer in rock fractures is strongly affected by fluid flow in addition to material properties the flow dependence of matrix diffusion is quantified by a random variable transport resistance denoted as t l and computed from the flow field by following advection trajectories the numerical methodology for simulating fluid flow is mesh free using fup basis functions a generic statistical model is used for the transmissivity field featuring three correlation structures i highly connected non multi gaussian ii poorly connected or disconnected non multi gaussian and iii multi gaussian the moments of are shown to be linear with distance irrespective of the structure after approximately 10 integral scales of ln t percentiles of are found to be linear with the mean when considering all three structures taking advantage of this property a potentially useful relationship is presented between percentiles and the fracture mean water residence time that integrates all structures with high variability it can be used in discrete fracture network simulations where t statistical data on individual fractures are not available

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

exposure matters forest dynamics reveal an early holocene conifer refugium on a north facing slope in central europe although several studies provide a broad overview of vegetation changes in the carpathian basin during the holocene stand scale vegetation changes are lesser known because of the rarity of suitabl

prompt transgression and gradual salinisation of the black sea during the early holocene constrained by amino acid racemization and radiocarbon dating abstract the restricted environment of the black sea is particularly sensitive to climatic and oceanographic fluctuations owing to its connection with the mediterranean sea via the narrow bosphorus strait the exact mechanism and timing of the most recent connection between these water bodies is controversial with debate on the post glacial history of the black sea being dependent on radiocarbon dating for numerical ages here we present new 23 accelerator mass spectrometer ams radiocarbon ages on peat and bivalve molluscs supported by the first amino acid racemization aar dating of bivalve molluscs n 66 in the black sea these data indicate infilling of the black sea during the early holocene from an initial depth 107 m below sea level and 72 m below that of the bosphorus sill these data combined with a review of previous radiocarbon ages has enabled a unique perspective on the post glacial black sea a sea level curve based on conventional and ams radiocarbon ages on peat and ams based ages on dreissena sp shells indicate the water level in the earlier lake phase continued until the early holocene to be lower than the bosphorus sill after the younger dryas ended however the absence of ams dated mollusc ages from the shelves of this basin older than the younger dryas is suggestive of sub aerial exposure of the shelves and comparatively lower water levels when the younger dryas began thus post glacial outflow from the black sea occurred through a lowered or open bosphorus seaway basin wide radiocarbon ages on peat indicate a prompt increase in water level from that of the pre existing and unconnected palaeo lake during the earliest holocene 9600 9200 cal a bp mass colonisation of the black sea by mediterranean taxa did not occur until salinity had risen sufficiently a process which took 1000 a or more from the initial transgressive event this gradual change in salinity contrasts with the prompt transgression which would have taken 400 a to occur

environmental changes related to the 8 2 ka event and other climate fluctuations during the middle holocene evidence from two dystrophic lakes in ne poland multi proxy palaeoecological data pollen diatom cladocera about the environment during the middle holocene from suchar ii and suchar wielki dystrophic lakes in ne poland are presented fluctuations in the pollen concentration indicative of changes in pollen productivity and shifts in woodland composition document the considerable instability of the climate in ne poland between 9200 and 5750 cal yr bp the recognised colder events were dated to ca 9050 8950 8700 7800 7600 7250 7100 6600 and 6050 5900 cal yr bp all these coolings are expressed as decreases in the pollen concentration of thermophilous taxa such as corylus avellana ulmus quercus tilia cordata t and fraxinus exelsior the most pronounced was the second of these cold climatic anomalies which lasted about nine centuries and can be equated with the 8 2 ka event significant cooling at that time is confirmed by the appearance of cold water species of cladocerans and diatoms

in situ charcoal fragments as remains of natural wild fires in the upper wurm of the carpathian basin charcoal layers were found in loess layers of the younger wurm period at 11 localities around kopasz hill tokaj in the carpathian basin detailed sedimentological geochemical radiocarbon palaeontological and anthracological investigations show that picea containing taiga forest steppe habitats existed on the area between 29 000 and 21 000 years bp on the basis of radiocarbon measurements these forests fell victim to extensive fires that seem to have spread across the basin this fact is supported by the characteristic macro and microstructure of the charred remains using sem identification and thermoanalytical examination the firing temperature was 600 700 c suggesting a natural forest fire fire scars can also be observed on the remains as well as the burnt sediment forming a silhouette the so called burning court of the fallen trunks or roots thus these fragments have remained in their in situ position

the pace of holocene vegetation change testing for synchronous developments mid to high latitude forest ecosystems have undergone several major compositional changes during the holocene the temporal and spatial patterns of these vegetation changes hold potential information to their causes and triggers here we test the hypothesis that the timing of vegetation change was synchronous on a sub continental scale which implies a common trigger or a step like change in climate parameters pollen diagrams from selected european regions were statistically divided into assemblage zones and the temporal pattern of the zone boundaries analysed the results show that the temporal pattern of vegetation change was significantly different from random times of change cluster around 8 2 4 8 3 7 and 1 2 ka while times of higher than average stability were found around 2 1 and 5 1 ka compositional changes linked to the expansion of corylus avellana and alnus glutinosa centre around 10 6 and 9 5 ka respectively a climatic trigger initiating these changes may have occurred 0 5 to 1 ka earlier respectively the synchronous expansion of c avellana and a glutinosa exemplify that dispersal is not necessarily followed by population expansion the partly synchronous partly random expansion of a glutinosa in adjacent european regions exemplifies that sudden synchronous population expansions are not species specific traits but vary regionally

seasonal to multidecadal variability of the width of the tropical belt 1 an expansion of the tropical belt has been extensively reported in observations reanalyses and climate model simulations but there is a great deal of uncertainty in estimates of the rate of widening as different diagnostics give a wide range of results this study critically examines robust diagnostics for the width of the tropical belt to explore their seasonality interannual variability and multidecadal trends the width based on the latitudes of the maximum tropospheric dry bulk static stability measuring the difference in potential temperature between the tropopause and the surface is found to be closely coupled to the width based on the subtropical jet cores on all time scales in contrast the tropical belt width and northern hemisphere edge latitudes based on the latitudes at which the vertically averaged stream function vanishes a measure of the hadley circulation s poleward edges lag those of the other diagnostics by approximately 1month the tropical belt width varies by up to 10 latitude among the diagnostics with trends in the tropical belt width ranging from 0 5 to 2 0 per decade over the 1979 2012 period nevertheless in agreement with previous studies nearly all diagnostics exhibit a widening trend although the stream function diagnostic exhibits a significantly stronger widening than either the jet or dry bulk stability diagnostics finally gps radio occultation observations are used to assess the ability of the reanalyses to reproduce the tropical belt width finding that they better situate the latitudes of maximum bulk stability versus those of the subtropical jets

a novel three dimensional discrete fracture network model for investigating the role of aperture heterogeneity on fluid flow through fractured rock masses abstract effect of anisotropic aperture on the hydraulic properties of single rock fractures has been systematically investigated yet the aperture variability of individual fractures in 3d discrete fracture networks dfns is commonly negligible by using parallel plate fractures the present study proposed a 3d dfn model with fractures having heterogeneous apertures to estimate the influence of fracture variability on fluid flow in total a set of 1280 3d models with increasing fracture densities and fracture lengths are generated and the fluid flow through the models is simulated using a developed numerical code the influences of aperture heterogeneity and network topology on the flow pattern and permeability of 3d dfns are estimated the results show that the network topology provides a first order frame of geometrical connectivity and the heterogeneous aperture further allows the flow to select some most transmissive channels within these connected fractures the dfn model with identical apertures generates a large number of medium flow rate regions whereas the dfn model with fractures having heterogeneous apertures results in extremely low and high flow rate regions the permeability ratio of the two models is widely spread in terms of a small variation in the average mechanical aperture as a result of strong dependence on the aperture distribution the average permeability ratio increases significantly first and then approaches to 1 0 with increasing the average mechanical aperture this allows for the definition of a critical mechanical aperture above which the permeability can be properly predicted using the dfn model with fractures having identical apertures and below which the permeability is much altered by the aperture variability and the dfn model with fractures having heterogeneous apertures should be employed

holocene glacier fluctuations of flatebreen and winter precipitation changes in the jostedalsbreen region western norvay based on glaciolacustrine sediment records the history of holocene glacier variations of flatebreen an independent glacier close to the sw part of the jostedalsbreen ice cap has been reconstructed from lacustrine sediments in the proglacial lake jarbuvatnet the sedimentary succession shows evidence of three maini episodes of holocene glacier expansion the first is recorded in the basal part of the core up to 370 cm according to the age depth relationship in the sediment core based on 12 ams radiocarbon dates this glacier expansion episode terminated about 10200 cal yr bp the second major glacier phase lasted from 8400 to 8100 cal yr bp while the third was initiated around 4000 cal yr bp and has continued up to the present at 43 cm in the core the medium silt content increases significantly accompanied by a minor increase in the sand content this textural change is interpreted as the first time that the tenninus of flatebreen extended inlto an upstream lake at 1083 m a s l the age model suggests that this event took place around