discussion of the applicability of the generalized clausius clapeyron equation and the frozen fringe process abstract based on the literature and our laboratory experiments we discuss the applicability of the generalized clausius clapeyron equation gcce for describing the phase change process between ice and water and specific applicability conditions for the gcce during soil freezing are proposed we then put forth two models a static model and a dynamic model both models include the variation tendencies of the pore water pressure ice stress effective stress and pore pressure the static model is an ideal model whereas the dynamic model is more similar to the real freezing process of soil in addition the initial conditions of ice lens are considered and developed in the models by introducing a concept of constraining force based on the dynamic model such phenomena as consolidation zoning and thickness of frozen fringe could be well explained

timing of lateglacial vegetation dynamics and respective palaeoenvironmental conditions in southern estonia evidence from the sediment record of lake nakri this paper investigates a detailed well dated lateglacial floristic colonisation in the eastern baltic area ca 14 000 9000 cal a bp using palynological macrofossil loss on ignition and 14c data during 14 000 13 400 cal a bp primarily treeless pioneer tundra vegetation existed tree birch betula sect albae macro remains and a high tree pollen accumulation rate indicate the presence of forest tundra with birch and possibly pine pinus sylvestris l trees during 13 400 12 850 cal a bp palaeobotanical data indicate that the colonisation and development of forested areas were very rapid arising within a period of less than 50 years thus far there are no indications of conifer macrofossils in estonia to support the presence of coniferous forests in the lateglacial period signs of greenland interstadial 1b cooling during 13 100 cal a bp are distinguishable biostratigraphic evidence indicates that the vegetation was again mostly treeless tundra during the final colder episode of the lateglacial period associated with greenland stadial 1 approximately 12 850 11 650 cal a bp this was followed by onset of the holocene vegetation with the expansion of boreal forests in response to rapid climatic warming copyright 2011 john wiley sons ltd

succession of arboreal taxa during the late glacial in south eastern poland climatic implications abstract this paper presents and discusses vegetation changes between ca 14 910 and 11 620 cal bp which are recorded in the deposits of a small mire located in south eastern poland particular attention is paid to arboreal taxa changes in arboreal vegetation are reconstructed on the basis of pollen analysis including pollen accumulation rate par and analysis of plant macrofossils these being supported by radiocarbon chronology before the onset of the gi 1 warming 14 910 310 14 810 280 cal bp a mosaic of pinus and betula wood patches and or isolated stands of trees along with heliophilous juniperus thickets were dispersed within patches of herb steppe and tundra communities thermal amelioration at the gs 2 gi 1 transition ca 14 810 280 14 510 200 cal bp led to the spread of salix and to a lesser extent of tree birches betula pines pinus and hippophae rhamnoides in the light of par values from ca 14 550 210 cal bp there were open pine birch woodlands there which ca 14 270 160 cal bp turned into dense forests cold oscillations such as gi 1d gi 1c2 and gi 1b dated in the profile at ca 14 190 120 13 870 140 13 740 120 13 490 80 and 13 120 12 870 60 cal bp respectively are visible as declines in the par of arboreal taxa from ca 13 770 120 cal bp picea abies whose nearest glacial refugia were located in the western carpathians probably reached the site surroundings 50 n in the younger dryas gs 1 climate deterioration caused a decline in birch population in the first phase a slight retreat of forests and the simultaneous expansion of artemisia poaceae steppe communities and juniperus thickets the par values reflect a division of the younger dryas into two distinct phases an older phase more severe for tree populations probably due to longer and cooler winters and a younger phase with milder winters which begun ca 11 960 110 cal bp

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

younger dryas and allerod summer temperatures at gerzensee switzerland inferred from fossil pollen and cladoceran assemblages linear and unimodal based inference models for mean summer temperatures partial least squares weighted averaging and weighted averaging partial least squares models were applied to a high resolution pollen and cladoceran stratigraphy from gerzensee switzerland the time window of investigation included the allerod the younger dryas and the preboreal characteristic major and minor oscillations in the oxygen isotope stratigraphy such as the gerzensee oscillation the onset and end of the younger dryas stadial and the preboreal oscillation were identified by isotope analysis of bulk sediment carbonates of the same core and were used as independent indicators for hemispheric or global scale climatic change in general the pollen inferred mean summer temperature reconstruction using all three inference models follows the oxygen isotope curve more closely than the cladoceran curve the cladoceran inferred reconstruction suggests generally warmer summers than the pollen based reconstructions which may be an effect of terrestrial vegetation not being in equilibrium with climate due to migrational lags during the late glacial and early holocene allerod summer temperatures range between 11 and 12 c based on pollen whereas the cladoceran inferred temperatures lie between 11 and 13 c pollen and cladocera inferred reconstructions both suggest a drop to 9 10 c at the beginning of the younger dryas although the allerod younger dryas transition lasted 150 160 years in the oxygen isotope stratigraphy the pollen inferred cooling took 180 190 years and the cladoceran inferred cooling lasted 250 260 years the pollen inferred summer temperature rise to 11 5 12 c at the transition from the younger dryas to the preboreal preceded the oxygen isotope signal by several decades whereas the cladoceran inferred warming lagged major discrepancies between the pollen and cladoceran inference models are observed for the preboreal where the cladoceran inference model suggests mean summer temperatures of up to 14 15 c both pollen and cladoceran inferred reconstructions suggest a cooling that may be related to the gerzensee oscillation but there is no evidence for a cooling synchronous with the preboreal oscillation as recorded in the oxygen isotope record for the gerzensee oscillation the inferred cooling was ca 1 and 0 5 c based on pollen and cladocera respectively which lies well within the inherent prediction errors of the inference models

a temperature reversal within the rapid younger dryas holocene warming in the north atlantic abstract the onset of the holocene has been generally considered rapid and uninterrupted in the circum atlantic region loss on ignition loi an index of organic carbon profiles from 18 lateglacial aged lakes in nova scotia canada together with chironomid inferred temperature reconstructions at 5 sites demonstrate that the rapid warming from the younger dryas gs 1 to the holocene was interrupted by a cooling of 1 6 6 4 c in summer surface lake water temperature the resulting inflection or reversal on the rising temperature curve has also been identified at 35 sites outside nova scotia from terrestrial and marine settings indicating that this cool step is a robust feature throughout the north atlantic and is likely the result of major oceanic and atmospheric reorganization of the holocene climate system

an analysis leading to the reduction of scattered noise on deep marine seismic records the rough and uneven basaltic basement in deep marine environments functions as a potential source of scattering the source generated noise not only interferes with the weak and deep primary reflections but often resembles primary reflections thereby confusing the seismic interpretation an analysis of the arrival time of scattered noise indicates that nmo and apparent dip of scattered noise exhibit azimuth dependence for isotropic scattering in line scattering at ranges near 0 degree azimuth and sideswipe from 90 degree azimuth should dominate the seismic section actual marine data displayed in various data gathers illustrate these characteristics of scattered noise and also correct a common misconception about the appearance of scattered noise the analysis suggests the use of cdp stacking and velocity filtering to attenuate the scattered noise the combined effect shows a total reduction of scattered noise by 21 db for the frequency bandwidth from 20 to 32 hz

coherent noise in marine seismic data three mechanisms that might produce noise patterns on stacked sections are examined direct and trapped waves that propagate outward from the seismic source cable motion caused by the tugging action of the boat and tail buoy and scattered energy from irregularities in the water bottom and sub bottom different noise patterns can be observed on shot profiles and common midpoint cmp gathers these patterns can be diagnostic of the dominant mechanism in a set of data field data suggest that the dominant noise is from waves scattered within the shallow sub bottom this type of noise is enhanced by cmp stacking moreover it can be as strong as surface wave noise on stacked land seismic data as well moveout filtering is best for suppressing the noise while preserving signal since the scattered noise does not exhibit a linear moveout pattern on cmp sorted gathers moveout filtering must be applied either to traces within shot records and common receiver gathers or to stacked traces our data example demonstrates that although it is more costly moveout filtering of the unstacked data is particularly effective because it conditions the data for the critical data dependent processing steps of predictive deconvolution and velocity analysis modified journal abstract

managing ice rich permafrost exposed during cutting excavation along qinghai tibetan railway experiences and implementation there is widespread ice rich permafrost over qinghai tibetan plateau the exposure and subsequently thawing of ice rich permafrost result in serious engineering and environmental consequences however it is often inevitable to expose ice rich permafrost during the construction of railway highway or any engineering structures in permafrost regions in this paper we described the hazards induced from ice rich permafrost exposure including slope instability thermal slumping soil erosion frost heave and thaw settlement along qinghai tibetan railway the leading factors resulting in the occurrence of hazards were reviewed various remedial measures applied during the construction of qinghai tibetan railway were introduced the operation effects on avoiding failure or minimizing the damage consequence were discussed the results show that ice rich permafrost exposure generally causes cutting failure unless proper countermeasures are applied slope instability is the most serious damage for ice rich permafrost cutting frost heaving and thaw settlement tend to damage the surface treatments and have lesser effects on railway operation experience shows that coarse grain soil replacement with insulation and drainage system are the most common measures to be applied cement concrete framework measure is more popular than turf covering and insulation covering due to its construction convenience and less cost the results indicate that the treatment of turf covering is more suitable for ice rich permafrost exposure than insulation covering due to high long term performance rating and surface deformation adaptability retaining wall is an effective remedial measure to prevent slope failure of deep cut in permafrost regions the field investigation shows that design and construction methods to deal with the exposure and thawing of ice rich permafrost along qinghai tibetan railway are efficient and these experiences are helpful for other projects in cold regions

shallow seismic reflection mapping of the overburden bedrock interface with the engineering seismograph some simple techniques where unconsolidated overburden exceeds 20 m in thickness the reflection method may be efficiently used with a 12 channel engineering seismograph to map topography on the overburden bedrock interface as well as possible structure within the overburden the two techniques we suggest are the simplest forms of reflection profiling which can be applied with a minimum amount of equipment which we suggest is a 12 channel enhancement seismograph a 12 geophone array and a hammer source these techniques require good transmission characteristics of the overburden as well as a sharp velocity discontinuity at the overburden bedrock interface for data processing and display a microcomputer is essential

subdecadal scale vegetation responses to a previously unknown late allerod climate fluctuation and younger dryas cooling at lake meerfelder maar germany lake meerfelder maar mfm is the northernmost western european sediment record with annual laminations across the younger dryas yd and the onset of the yd in the record of mfm has previously been defined as an increase in non arboreal pollen abundance at ca 12 680 varve a bp here we present a palynological record at unprecedented subdecadal resolution for mfm covering the allerod yd transition our results show a fluctuation in pollen accumulation rates pars before the onset of the yd with lower rates between ca 12 725 and 12 685 varve a bp the fluctuation in pars occurs simultaneous with a previously undescribed short fluctuation in sediment composition and varve thickness as well as with changes in biogeochemical proxies the combined evidence indicates signs of climatic instability ca 45 years before the onset of the yd the par records of betula and pinus furthermore show earlier and more abrupt changes at the onset of the yd than the percentage records do finally heliophilous herbaceous taxa show a delayed increase following the onset of the yd of ca 145 years this paper illustrates the potential to identify previously unrecognized climate variability and vegetation change when using subdecadal resolution analyses

lake level and groundwater level changes in the lake gosciąz area poland palaeoclimatic implications lake gosci z is located in the zone of the maximum extent of the last ice sheet distinct lake terraces and deposits related to the lateglacial transgression do not exist detailed examination of annually laminated sediments and landforms revealed three phases of higher water level and storage represented by shore features by littoral deltaic and bog deposits and by higher rates of lacustrine deposition in the pelagic zone holocene lake transgressions at c 8 4 7 7 ka 2 5 2 3 ka and less distinct at 5 4 ka bp coincide with phases of higher flood frequency in poland and glacial advances in the alps because of sedimentation isolation from groundwaters encroachment by peatland and drainage of the lake lake volume during the last 12 ka diminished by as much as 70 and current water level fluctuations of about 1 2 m can change water storage by 20 25

late glacial and holocene history of former salziger see central germany and its climatic and environmental implications an 8 40 m long sediment sequence from the salziger see basin central germany was investigated by a multi disciplinary approach including chronological sedimentological geo and biogeochemical methods radiocarbon dating conducted on ten samples of aquatic and terrestrial fossil remains and the occurrence of the laacher see tephra lst reveal that the sediment sequence comprises the late glacial and holocene lake history since ca 13 800 cal year bp this onset of lacustrine sedimentation is almost 7 000 years earlier as assumed so far the geo and biogeochemical data indicate distinct variations throughout the late glacial which can be correlated with cold and warm periods such as the oldest dryas the bolling the allerod and the younger dryas during most of the holocene minor variations in the geo and biogeochemical data and a high carbonate content due to the formation and precipitation of autochthonous carbonate in the lake indicate relatively stable lacustrine conditions a slight change in the sedimentary conditions between 6 700 and 4 000 cal year bp with lower deposition of carbonate and fine material can be traced back to enhanced subrosion in the basin increased deposition of coarser sediments and a high accumulation of heavy metals document intensive human activity in the region during the past ca 1 000 years

groundwater flow system as an archive of palaeotemperature noble gas radiocarbon stable isotope and geochemical study in the pannonian basin hungary abstract to establish the increase in temperature and the time span of the transition between the late glacial maximum lgm and the holocene the noble gas content 18 o 2 h 13 c values 3 h and 14 c activity and chemistry were studied in a groundwater flow system in quaternary sediments in hungary the study area is a sub basin of the pannonian basin where the c isotope ratios are not influenced by carbonate reactions along the flow path because the only water rock interaction is ion exchange the 18 o and 2 h values indicate a cold infiltration period followed by warming and finally warm temperature conditions the noble gas data show that the average infiltration temperature was 3 3 c in the cold 12 9 c in the warm and intermediate in the transitional stage using the noble gas temperatures geochemical batch modelling was performed to simulate the chemical processes based on the geochemical model 13 c and 14 c 0 initial radiocarbon activity in the recharging water were calculated transport modelling was used to simulate the distribution of chemical components 18 o 2 h and 14 c 0 along the flow path it was found that the main processes determining the chemical composition of the groundwater were dissolution precipitation of calcite and dolomite during infiltration near the surface and ion exchange along the flow path in the recharge area the 13 c and 14 c 0 were controlled by dissolution and precipitation of carbonate minerals c speciation and fractionation processes all these processes were influenced by the recharge temperature ngts calculated from the dissolved noble gas concentrations showed an average of 3 3 c for cold and 12 9 c for warm infiltration i e for the lgm and for the holocene the temperature difference was thus 9 1 0 8 c which is one of the largest degree of warming detected by noble gases so far the alkalinity indicates that carbonate reactions were unimportant along the flow path owing to the temperature dependence of the equilibrium constants temperature conditions during infiltration have to be taken into consideration in radiocarbon age calculation dispersive transport along the flow path modified the chemical and isotopic composition of infiltrated water the contribution of the old pore water which was free of the 14 c isotope resulted in uncertainties in radiocarbon age determination it was concluded that determination of the radiocarbon age or mean residence time requires detailed knowledge of the hydraulic conditions of groundwater

estimating winter ebullition bubble volume in lake ice using ground penetrating radar freshwater lakes are an important source of atmospheric methane ch4 however uncertainties associated with quantifying fluxes limit the accuracy of climate warming projections among emission pathways ebullition bubbling is the principal and most challenging to account for given its spatial and temporal patchiness when lakes freeze many methane rich bubbles escaping from lake bottom sediments are temporarily trapped by downward growing lake ice as bubble position is then seasonally fixed we postulate that it should be possible to locate bubbles using a geophysical approach sensitive to perturbations in the ice water interface and ice sheet structure generated by bubbles this study utilizes ground penetrating radar gpr to non invasively quantify the amount of ebullition gas present in lake ice to do this requires an appropriate petrophysical transformation that relates radar wave velocity and volumetric gas content we utilized laboratory experiments to show that electromagnetic models and vo

surface temperature in nw europe during the younger dryas agcm simulation compared with temperature reconstructions during the younger dryas yd the climate in nw europe returned to near glacial conditions to improve our understanding of climate variability during this cold interval we compare an agcm simulation of this climate performed with the echam model with temperature reconstructions for nw europe based on geological and paleoecological records maps for the mean winter summer and annual temperature are presented the simulated winters are consistent with reconstructions in the northern part of the study area a strong deviation is noted in ireland and england where the simulation is too warm by at least 10 c it appears that the n atlantic was cooler than prescribed in the yd simulation including a southward expansion of the sea ice margin the comparison for the summer shows a too warm continental europe in the simulation supposedly these anomalously warm conditions are caused by the agcm s response to the prescribed increased summer insolation the region of maximum summer cooling is similar in both the simulation and reconstruction i e s sweden we suggest that this is due to the local cooling effect of the scandinavian ice sheet compared to the present climate a considerable increase of the annual temperature range is inferred especially for regions close to the atlantic ocean

diffraction based velocity estimates from optimum offset seismic data a graphical method is characterized for estimating seismic velocity directly from diffraction patterns observed on common offset records the nature of the resulting estimate is examined by illustrating the connection between the graphical approach and a related method used by practitioners of ground penetrating radar while the latter provides only a crude stacking velocity the graphical technique yields the generalized rms velocity for stratified media associated interval velocities can be derived from two or more diffraction events having their sources within the plane of survey where there is a lack of geological evidence to suggest that scatterers reside in plane we propose a simple strategy for locating a scatterer from its expression on two or more independent records error in the resulting location is directly related to subsurface velocity heterogeneity finally since the diffraction based velocity estimates assume that source and receiver are coincident the error stemming from nonzero off

variations of younger dryas atmospheric radiocarbon explicable without ocean circulation changes the concentration of radiocarbon 14c in the atmosphere depends on its production rate by cosmic rays and on the intensity of carbon exchange between the atmosphere and other reservoirs for example the deep oceans for the holocene the past 11 500 years it has been shown that fluctuations in atmospheric radiocarbon concentrations have been caused mostly by variations in the solar magnetic field1 2 3 recent progress in extending the radiocarbon record backwards in time4 5 6 7 8 9 10 has indicated especially high atmospheric radiocarbon concentrations in the younger dryas cold period between 12 700 and 11 500 years before the present these high concentrations have been interpreted as a result of a reduced exchange with the deep ocean reservoir caused by a drastic weakening of the deep ocean ventilation7 8 9 11 12 here we present a high resolution reconstruction of atmospheric radiocarbon concentrations derived from annually laminated sediments of two polish lakes lake go ciaz and lake perespilno these records indicate that the maximum in atmospheric radiocarbon concentrations in the early younger dryas was smaller than previously believed and might have been caused by variations in solar activity if so there is no indication that the deep ocean ventilation in the younger dryas was significantly different from today s

the global response to younger dryas boundary conditions in an agcm simulation geological evidence points to a global younger dryas yd climatic oscillation during the last glacial present interglacial transition phase a convincing mechanism to explain this global yd climatic oscillation is not yet available nevertheless a profound understanding of the mechanism behind the yd climate would lead to a better understanding of climate variability

a coupled model for liquid water water vapor and heat transport of saturated unsaturated soil in cold regions model formulation and verification in cold and arid regions vapor movement and water flow are crucial to thermal moisture dynamics of the active layer and control the soil microbial activity plant growth and engineering applications although it is widely recognized that both liquid and water vapor movement are fundamental factors in the quantification of soil mass and energy balance their computation is still rarely considered in most models or practical applications moreover previous studies on the movement of moisture migration in unsaturated frozen soil are limited this study was conducted to a implement a fully coupled numerical model that includes water migration in both the vapor and liquid phases and heat transfer by means of conduction convection latent heat of vapor diffusion and phase change effects b verify the numerical model with detailed field monitoring data c analyze the role of water flow and vapor diffusion in the heat and mass transport the result showed that the numerical model was able to fully calculate the coupled soil mass and energy budget thermal conduction dominated the heat transport in the deeper layer below 75 cm in permafrost regions while the impact of water movement on heat in summer was significant in shallow ground soil water was transported by both liquid water and water vapor and water vapor contributed more than 15 of the water flux at all depths vapor and liquid water transport play an important role in soil mass and energy transfer especially for the shallow surface it is necessary to consider the coupled liquid water water vapor and heat transport in predictions of soil water and heat dynamics in permafrost regions

late glacial early holocene environmental changes in thuringia germany stable isotope record and vegetation history abstract the 7 m thick sediment profile at plinz in northern thuringia central germany covering the time span between 10 000 and at least 8000 14 c years bp about 11 600 9000 cal bp was studied using radiocarbon stable isotopes and pollen analysis the results reflect the very fast climatic transition from the late glacial to the holocene as a change from cold and dry to warmer and wetter conditions a short climatic deterioration during the preboreal oscillation pbo at around 9800 14 c years bp is clearly reflected by a sharp drop in the pinus concentration accompanied by a considerable increase in betula salix various herbs and the distinct occurrence of aquatic plants during the preboreal stable isotopes of biogenic carbonate show several episodes with altered levels of atmospheric moisture continuous climatic improvement without any oscillations can be suggested for the period covering the end of preboreal and the boreal

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

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

mean july temperatures during the younger dryas in northwestern and central europe as inferred from climate indicator plant species abstract we estimated minimum mean july temperatures in northwestern and central europe during the younger dryas 10 950 10 15014c yr b p from distributions of climate indicator plant species which were reconstructed from 140 pollen and plant macrofossil diagrams paleobotanical records mainly from the central and eastern part of the study area show that the coldest conditions occurred early in the younger dryas before 10 55014c yr b p for this phase mean july temperatures at sea level of around 10 c are suggested for the northern part of the british isles and for ice free scandinavia we estimated a mean july temperature of 12 c for central england the netherlands and northern germany the 13 c mean july isotherm largely based on the modern distribution oftypha latifolia was most probably located in southern england belgium central germany and poland the reappearance of thermophilous elements in the records after 10 55014c yr b p suggests a summer warming at least temporarily of 1 to 2 c in the study area the reconstructed temperatures are comparable with temperature estimates based on beetle data however they appear rather high when compared with estimates based on glaciological evidence

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

a 200 year mid european air temperature record preserved in lake sediments an extension of the δ18op air temperature relation into the past abstract a detailed history of the water oxygen isotope ratios of lake ammersee southern germany was established for the last two centuries by analyzing oxygen isotope ratios of ostracod shells from a sediment core in a three to five year resolution empirical analysis and modelling of the isotope hydrology of the lake show that the oxygen isotopic composition of the lake water is mainly controlled by the isotopic composition of local precipitation for the last 200 years the lake isotope record is strongly correlated to the air temperature record from hohenpeisenberg situated within the lake s catchment area thus the mid european relation between 18 o in precipitation and air temperature documented for the last 20 years can be extended over a longer time and a larger temperature range the results provide further support for the validity of ostracod 18 o from ammersee sediments as a quantitative proxy for mean annual air temperature probably extending back to the last glaciation

stable isotope composition of the holsteinian mis 11 freshwater snail valvata piscinalis o f muller 1774 from eastern poland and its palaeoenvironmental implications stable oxygen and carbon isotope investigations were conducted on shells of the freshwater gastropod valvata piscinalis from palaeolake deposits of holsteinian age marine isotope stage 11 from eastern poland the isotope record of this species was used for the first time as an archive of environmental conditions for selected lakes between the protocratic stage and the post optimum period of the interglacial the lowest 18o and 13c values of 8 1 and 12 1 respectively were recorded in the picea alnus zone at ortel krolewski palaeolake the sparse vegetation and low productivity of that time are reflected in the relatively low 13c values the first significant increase of temperature was recorded in the taxus zone i e an increase in 18o the higher temperature influenced the expansion of macrophytes which stimulated enhanced photosynthesis similar mean 18o values in the taxus and pinus larix zones imply no distinct temperature change v piscinalis populations from ossowka hrud and roskosz palaeolakes record variations in lake productivity during the climatic optimum of the interglacial carpinus abies zone the 18o values of that time are relatively high up to 4 5 and reveal no significant differences between the lakes decreases of the oxygen isotope values in the szymanowo lake reflect post optimum cooling

the record of hydroclimatic changes in the sediments of a kettle hole in a young glacial landscape north central poland abstract multidisciplinary research on the bottom sediments of a kettle hole at the retno site the brodnica lake district north central poland provided some information about changes in hydroclimatic conditions in the late glacial and the holocene detailed analysis sedimentological palynological macroremains geochemical and radiocarbon dating helped to identify 6 stages in the development of the depression in the village of gaj near retno lake with 11 phases of hydroclimatic conditions sediments of the retno profile with a total thickness of 6 72 m reflected individual natural stages in the development of the depression from a lake to a peat bog most of the environmental changes were gradual a sequence of late glacial and early holocene lacustrine sediments mainly gyttja occurred in the floor of the profile the upper 4 10 m consisted of paludal deposits peat of transitional and raised bogs divided at a depth of 1 56 1 54 m b g l by a thin layer of clay dated late subboreal early subatlantic the presence of this layer indicates a sudden change in the environmental conditions associated with a water level rise at that time denudation processes started within the drainage basin probably induced by human activity the important effects related to contemporary anthropopressure included desiccation of the peat bog muck formation in the uppermost 10 cm layer and elevated trophic conditions resulting in a change of the vegetation cover

the impact of cold north atlantic sea surface temperatures on climate implications for the younger dryas cooling 11 10 k the sensitivity of global climate to colder north atlantic sea surface temperatures is in vestigated with the use of the giss general circulation model north atlantic ocean temperatures 18 000 b p resembling those prevalent during the younger dryas were incorporated into the model of the present climate and also into an experiment using orbital parameters and land ice characteristic of 11 000 b p the results show that with both 11 000 b p and present conditions the colder ocean temperatures produce cooling over western and central europe in good agreement with younger dryas paleoclimatic evidence cooling also occurs over extreme eastern north america although the precise magnitude and location depends upon the specification of ocean temperature change in the western atlantic despite the presence of increased land ice and colder ocean temperatures the younger dryas summer air temperatures at northern hemisphere midlatitudes in the model are warmer than those of today due to changes in the orbital parameters chiefly precession and atmospheric subsidence at the perimeter of the ice sheets

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

persist or take advantage of global warming a development of early holocene riparian forest and oxbow lake ecosystems in central europe abstract in this study we focus on the environmental changes recorded in the san river valley stubno naklo site south eastern poland at the beginning of the holocene this multi proxy study for the first time in the region of the northern foreland of the western carpathians included quantitative thermal reconstruction based on chironomidae and high stratigraphic resolution of 14c ams dating we hypothesised that i climate events during the early holocene contributed to ecosystem turnovers via stimulating disturbances related to the river s fluvial activity and ii woodland and oxbow lake ecosystems became more resilient to flood disturbances along with the advance of forest succession on the floodplain the results revealed that the response of ecosystems on the early holocene warming was strongly linked with the decrease in fluvial activity of the river the reconstruction of the mean july temperature based on chironomidae revealed the exceptionally high rate of warming during the period of ca 11 490 11 460 cal bp at least 1 c per decade up to values 2 c than modern ones during this period the lake trophy and productivity started to increase with a simultaneous spread of betula woodlands on the alluvial plain the preboreal oscillation cooling was dated at ca 11 450 11 250 cal bp at that time an increased climate instability led to a higher rate of extremal events such as flood at ca 11 400 11 330 cal bp which probably led to the disruption of the betula population the development of riparian woodlands initiated by the expansion of ulmus from ca 11 100 cal bp and further spread of quercus and fraxinus excelsior on the alluvial plain and lower river terraces increased plant transpiration and therefore limited the river runoff and its fluvial activity this together with the expansion of reed belt communities probably limited the impact of floods on the oxbow lake however ca 10 010 9880 cal bp traces of higher fluvial activity but of lower impact were recorded

experimental study on unfrozen water content and soil matric potential of qinghai tibetan silty clay a new soil moisture content sensor coupled with a new matric potential sensor that can operate in the subfreezing environment was used to measure the moisture content and soil matric potential dynamics of qinghai tibetan silty clay combined with nuclear magnetic resonance nmr technique and thermal resistor temperature probe the characteristics of unfrozen water content and soil matric potential and their relationships with temperature were analyzed the results show that initial water content has an impact on the freezing point and unfrozen water content the decrease in the initial water content results in a depression in the freezing point the qinghai tibetan silty clay has more similar unfrozen water content characteristic to clay than to silt there is approximately 3 of unfrozen water content retained when the soil temperature drops to 15 c the change of soil matric potential with temperature is similar to that of the unfrozen water content the matric potential value of the saturated silty clay is approximately 200 kpa when the soil temperature drops to 20 c the measured matric potentials are significantly lower than the calculated theoretical values based on the freezing point depression moisture migration experiment indicates that soil matric potential controls the direction of moisture movement and moisture redistribution including ice and liquid water during the soil freezing

the kettle hole mire as archives of postglacial changes in biogenic sedimentation tuchola forest north central poland abstract kettle holes are a circular shape product of ice decay and thus are strongly linked with young glacial landscapes once glaciation terminates these holes transform either into wetland and lakes or occasionally into kettle hole mires since an entire sediment sequence preserve in the kettle holes these provide an excellent settings to exploit any sensitive paleoenvironmental changes here the kettle hole mire located onto the brda river outwash plain tuchola forest is explored towards a better understanding of local and global environmental trends in the late glacial present day time frame to fulfill this multi proxy study as geochemical palynological and macrofossils analyses along with the radiocarbon dating are used therefore this study allows to distinguish five phases of steep environmental gradients in the investigated mire as follows 1 paludification after glaciation when dead ice melted and long term permafrost was degraded 2 lake started to disappear in the late glacial followed by a rich vegetation in the first part of the holocene 3 vegetation encroachment onto the lake in the first part of the holocene which consequently turned into an peat bog 4 the late holocene peat bog with a limited human influence and finally 5 the peat bog with a major human impact along with acidification as related to sandy underlying sediments leaching of calcium carbonate recharge from precipitation and pine monoculture as additionally apparent from this small ecosystem both local character of substrate sediments morphology of the area rate of permafrost melting climate conditions and human activity and regional climate changes and human activity are detectable nevertheless the record of these changes is sometimes unclear

capillary bundle model of hydraulic conductivity for frozen soil 1 we developed a capillary bundle model to describe water flow in frozen soil we assume that the soil can be represented as a bundle of cylindrical capillaries we consider that the freezing point in the capillaries is depressed according to the gibbs thomson effect and that when stable ice forms in a capillary the ice forms in the center of the capillaries leaving a circular annulus open for liquid water flow we use the model to demonstrate how the hydraulic conductivity changes as a function of temperature for both saturated and unsaturated soils using a sand and two silt loam soils as examples as temperature decreases more and more ice forms and the water flux consequently decreases in frozen soil near 0 c water predominantly flows through ice free capillaries so that the hydraulic conductivity of frozen soil is similar to that of an unfrozen soil with a water content equal to the unfrozen water content of the frozen soil at low temperatures however ice forms in almost all capillaries and the hydraulic conductivity of frozen soil is greater than that of unfrozen soil with the same water potential

very fast environmental changes at the pleistocene holocene boundary recorded in laminated sediments of lake gościz poland abstract this paper presents a reconstruction of the climatic changes at the pleistocene holocene transition recorded in the annually laminated sediments of lake go ci a z poland this reconstruction is based on pollen stable isotope mineralogical and chemical analyses of sediments made with a time resolution of 1 4 yr it reveals a sequence of abrupt climatic changes which preceded and followed the major warming around 11 500 cal bp our data show that the warming period was preceded by a 30 yr long phase of increased winter and decreased summer precipitation 11 550 11 520 cal bp about 11 520 cal bp a very brief period of wetter conditions occurred simultaneously with the beginning of the major warming however most of the first phase of the major warming 11 520 11 500 cal bp was characterised by a generally dry climate presumably due to lowered winter precipitation our records suggest that in this phase the warming concerned winter seasons mostly in the second phase 11 500 11 460 cal bp the warming also concerned summer seasons also a distinct increase of humidity is noted in this period which caused moistening of soils and despite enhanced evaporation and evapotranspiration inhibited the process of lake level drop the following 70 years 11 460 11 390 cal bp were rather dry which caused a distinct lowering of the lake and probably also of groundwater level in this period maximum biological productivity per unit area in the lake is noted the whole sequence of phases of rather different climates was completed within a time interval 160 years spanning two human lifes only one should stress that the transitions between the consecutive phases were rather abrupt lasting no longer than 10 years

oxygen isotope geothermometers in lacustrine sediments new insights through combined δ18o analyses of aquatic cellulose authigenic calcite and biogenic silica in lake gościąz central poland abstract two water based oxygen isotope geothermometers calcite cellulose and silica cellulose were tested using well dated intervals of laminated sediment retrieved from lake go ci z a small hardwater lake in central poland five sections spanning ca 90 200 years of deposition were selected and subsampled at approximately decadal resolution to characterize relatively stable climatic and hydrologic conditions during the middle of the younger dryas cold period the rapid environmental changes that occurred at the younger dryas preboreal yd pb boundary and three subsequent periods of relative stability during the early middle and late holocene the two geothermometers are based on the premise that aquatic cellulose 18 o serves as a direct proxy for lakewater 18 o thereby allowing resolution of temperature signals in 18 o records obtained from co existing authigenic calcite or diatom silica qualitatively consistent results from the calcite cellulose geothermometer were obtained for all five intervals clearly showing the expected low epilimnion water temperatures in the mid yd rapid warming during the yd bp transition and maximum temperatures during the early holocene followed by slightly lower temperatures during the middle and late holocene results from the silica cellulose geothermometer also showed lower temperatures during the yd than the late holocene although insufficient diatom silica for analysis was present in the intervening intervals the calcite cellulose geothermometer yielded consistently higher estimates of epilimnion temperatures than the silica cellulose thermometer in the yd and late holocene intervals and unrealistically high values throughout the holocene we speculate that the calcite cellulose geothermometer is influenced by kinetic effects during rapid carbonate precipitation which offsets temperature dependent fractionation and thus leads to high temperature estimates in contrast the silica cellulose geothermometer may be affected by the production of diatom silica early in the spring prior to seasonal warming and isotopic enrichment of the epilimnion thus generating low temperature estimates

evolution of permafrost on the qinghai xizang tibet plateau since the end of the late pleistocene 1 the present distribution of permafrost on the qinghai xizang tibet plateau qtp is largely a relict of the permafrost formed during the late pleistocene it has been degrading and shrinking in areal extent under the fluctuating climates with a general trend of warming during the holocene the major criteria for the occurrence of relict permafrost include the remnants of ancient buried permafrost relict permafrost tables thawed sandwiches taliks thick layered ground ice and periglacial phenomena such as pingo scars cryoturbations primary sand and clayey silt wedges ice wedge casts aeolian sand dunes and loesses thick layers of peat and humic soils on the basis of 14c dating of soils comprehensive analyses and comparisons of the spatiotemporal distribution of relict and modern permafrost and periglacial phenomena the evolution of permafrost and periglacial environments since the late pleistocene was divided into seven stages 1 the cold period at the end of the late pleistocene 35 000 to 10 800 years b p 2 the period of significant climatic change during the early holocene 10 800 to 8500 7000 years b p 3 the megathermal period in the middle holocene 8500 7000 to 4000 3000 years b p 4 the cold period in the late holocene 4000 3000 to 1000 years b p 5 the warm period in the later holocene 1000 to 500 years b p 6 the little ice age 500 to 100 years b p and 7 the recent warming period 100 years b p to present the conditions for permafrost development distribution and the paleoclimates and paleoenvironments are discussed for each stage