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

theory of quantitative reconstruction of vegetation i pollen from large sites reveals regional vegetation composition quantitative reconstruction of past vegetation is one of the primary goals in quaternary palynology and palaeoecology but still remains difficult this paper proposes a model reveals that estimates regional vegetation composition using pollen from large lakes that have small site to site variations of pollen assemblages even if vegetation is highly heterogeneous once these data have been used to quantify regional vegetation composition within 104 105 km2 background pollen one of the parameters crucial for vegetation reconstruction can be estimated for smaller sized sites and incorporated into the landscape reconstruction algorithm lra a multistep framework for quantitative reconstruction of vegetation in smaller areas 104 ha simulations using the pollscape modelling show that reveals can provide accurate estimates of regional vegetation composition in various landscapes and under different atmospheric conditions if pollen assemblages from lakes that are much smaller than large lakes a

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

holocene vegetation and hydroclimatic dynamics in se lithuania implications from a multi proxy study of the cepkeliai bog abstract due to the scarcity of reliable palaeoecological and climatic proxy records from the eastern baltic covering the holocene there has been increased interest for multi proxy studies in the region to detect local to regional environmental changes the cepkeliai wetland complex se lithuania provides an uninterrupted holocene sediment sequence which is used here to reconstruct palaeoenvironmental history in the southern part of the eastern baltic high resolution lithological loi magnetic susceptibility palaeobotanical pollen plant macrofossil tree rings isotopic 14c and geochemical data were employed to reconstruct the peculiarities of vegetation and hydroclimate dynamics as well as to discuss results in a local to regional context temporal lags of environmental reactions to holocene climatic warming were recorded both in lithostratigraphical and biostratigraphical data thus confirming regional significance of this phenomenon a deep meso to eutrophic basin influenced by high surface runoff and surrounded by early boreal forest existed at the site until about 11 300 cal bp thereafter immigration of thermophylous taxa such as ulmus since 10 700 10 800 cal bp corylus since 10 400 10 300 cal bp tilia and quercus after 9500 cal bp as well as changes in the limnic environment point to an amelioration of the environmental situation i e to a predominance of a warm and dry climatic regime instability of palaeobotanical and lithological records suggests that environmental anomalies of the early holocene occurred at about 11 200 11 000 cal bp 10 600 10 300 cal bp and 8200 7800 cal bp these anomalies are thus contemporaneous with the pronounced climatic shifts i e dry and cool intervals known at the continental scale an expansion of picea was facilitated by the 8200 7800 cal bp climatic shift whereas early establishment of alnus glutinosa suggests an onset of a wet interval 10 200 cal bp which was previously unknown in the area the stepwise lowering of the water table noted at about 7300 7200 and 6600 6700 cal bp with the termination of the lake phase and change to telmatic environment after 6100 cal bp proves the positive reaction of the site to the dry climatic reversals of the middle holocene following the decay of the broad leaved thermophilous forest after 4500 cal bp a cold climatic reversal favored the formation of a diverse mosaic like vegetation which was then replaced by homogenous pinus picea vegetation after 3400 cal bp the climatic and site specific factors have been playing a leading role in the development of the site whereas signals of human interference remain negligible

late glacial climatic changes in eastern france lake lautrey from pollen lake levels and chironomids high temporal resolution analyses of pollen chironomid and lake level records from lake lautrey provide multi proxy quantitative estimates of climatic change during the late glacial period in eastern france past temperature and moisture parameters were estimated using modern analogues and plant functional types transfer function methods for three pollen records obtained from different localities within the paleolake basin the comparison of these methods shows that they provide generally similar climate signals with the exception of the bolling comparison of pollen and chironomid based temperature of the warmest month reconstructions generally agree except during the bolling major abrupt changes associated with the oldest dryas bolling allerod younger dryas and the younger dryas preboreal transitions were quantified as well as other minor fluctuations related to the cold events e g preboreal oscillation the temperature of the warmest month increased by not vert similar5 c at the start of bolling and by 1 5 3 c at the onset of the holocene while it fell by ca 3 to 4 c at the beginning of younger dryas the comparative analysis of the results based on the three lautrey cores have highlighted significant differences in the climate reconstructions related to the location of each core underlining the caution that is needed when studying single cores not taken from deepest part of lake basins

the selection of sites for paleovegetational studies the judicious selection of sites for paleovegetational and paleoclimatic studies permits paleoecologists to answer specific research questions that go beyond primary descriptions of past vegetation we present a model that describes the relationship between basin size and pollen source area and predicts the proportions of local extralocal and regional pollen sampled by lake basins of different size the distinctive sampling properties of lakes peats and small hollows can be exploited to provide details of pattern in paleovegetation so long as attention is given to the limitations and problems of these types of sites combinations of site types in a single study most fully exploit the information contained in sediments

glacial hydrologic conditions in the black sea reconstructed using geochemical pore water profiles abstract chloride and 18 o compositions of interstitial water extracted from a long sediment core retrieved from the nw coast of the black sea allowed us to constrain the main hydrologic changes of the back sea during the late pleistocene and holocene prior to its reconnection with the mediterranean sea through the marmara sea at approximately 9000 calendar yr before present 9 ka cal bp the black sea has evolved as a fresh to brackish water lake at the time of reconnection hydrologic changes were drastic bottom water salinities changed from a few psu practical salinity unit to 22 psu since solutes in the interstitial water column within sediments are advected and diffused the measured concentrations do not reflect those of past bottom waters in order to reconstruct these former concentrations we used an advection diffusion model different scenarios of bottom water chloride and 18 o variations were accounted for in this model in order to simulate present day vertical profiles for concentrations of interstitial water in order to compare them to measured ones the comparison suggests that the glacial black sea was a homogeneous freshwater lake with a 18 o of 10 and a salinity of 1 psu modern hydrologic conditions would only have been reached at 2 ka cal bp concomitant with the onset of coccolith rich thin layers that characterize modern basin sediments such delayed salinization over 7000 yr in the basin may have been due to higher precipitation during the early holocene we also simulated the impact of a catastrophic reconnection and a smoother reconnection both salinity scenarios lead to undistinguishable modelled present day profiles indicating that the precise impact of the last reconnection was lost due to the advection diffusion processes

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

experimental and numerical study of the geometrical and hydraulic characteristics of a single rock fracture during shear abstract coupled shear flow tests were conducted on two artificial rock fractures with natural rock fracture characteristics under constant normal loading boundary conditions numerical simulations using the 3 d navier stokes equations taking account of the inertial effects of fluid were conducted using the void space geometry models obtained from the coupled shear flow tests the test and numerical simulation results show that the evolutions of geometrical and hydraulic characteristics of rock fracture exhibit a three stage behavior transmissivity of a certain void space geometry within a fracture is related to the reynolds number of fluid flow due to the inertial effects of fluid which can be represented by the navier stokes equations but cannot be represented by some simplified equations such as the cubic law the reynolds equation or the stokes equations the mechanical aperture is usually larger than the hydraulic aperture back calculated from measured flow rate and the difference between them is found strongly related to the geometrical characteristics of the fractures a mathematical equation is proposed to describe the relation between hydraulic aperture and mechanical aperture by means of the ratio of the standard deviation of local mechanical aperture to its mean value the standard deviation of local slope of fracture surface and reynolds number

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

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

climatic reconstruction in europe for 18 000 yr b p from pollen data an improved concept of the best analogs method is used to reconstruct the climate of the last glacial maximum from pollen data in europe in order to deal with the lack of perfect analogs of fossil assemblages and therefore to obtain a more accurate climate reconstruction we used a combination of pollen types grouped according to plant phenology and present climate constraints rather than pollen percentages for each individual taxon the distribution of pollen taxa into plant functional types pfts is aimed to reflect the vegetation in terms of biomes which have a wider distribution than a species the climatic variables are then calibrated on these pfts using an artificial neural network technique the use of pfts allowed us to deal with situations where pollen assemblages have only partial modern analogs the method is applied to the glacial steppic vegetation in europe using 15 pollen records north of the pyrenees alps line the reconstructed temperatures were lower than today 30 10 degrees c for the temperature of the coldest month t c and 12 3 degrees c far the annual mean t ann south of that line t c and t ann anomalies were respectively 15 5 degrees c and 10 5 degrees c the available moisture index and annual precipitation were also lower than present 60 20 north of mediterranean sea 800 100 mm for precipitation in italy and greece the available moisture was 20 lower with a precipitation anomaly of ca 600 200 mm southward the moisture index was close to that at present 20 and precipitation was lower 300 300 mm c 1998 university of washington

model data comparison for the 8 2 ka bp event confirmation of a forcing mechanism by catastrophic drainage of laurentide lakes abstract to improve our understanding of the mechanism behind the 8 2 ka bp cooling event we compare proxy evidence with climate model simulations in which the thermohaline ocean circulation is perturbed by a freshwater pulse into the labrador sea both the proxy data and model results show a cooling that is mainly concentrated in the north atlantic region ranging from more than 5 c cooling in the nordic seas to about 0 5 1 c over europe and less than 0 5 c over the subtropical north atlantic data and model also indicate a weakening of the summer monsoon and generally a drier circum north atlantic over the south atlantic ocean the model simulates a slight warming mostly less than 0 5 c which falls within the uncertainty of proxy data and thus could not be confirmed to examine in detail the structure of the 8 2 ka bp event we also compare the modeled climatological evolution at two locations with high quality records revealing a generally consistent picture the good model data agreement confirms the hypothesis that the 8 2 ka bp event was forced by a freshwater induced weakening of the thermohaline circulation other forcings are unlikely since they would result in an alternative geographical distribution and expression of the climate response

multicentennial scale hydrological changes in the black sea and northern red sea during the holocene and the arctic north atlantic oscillation 1 paleoenvironmental proxy data for ocean properties eolian sediment input and continental rainfall based on high resolution analyses of sediment cores from the southwestern black sea and the northernmost gulf of aqaba were used to infer hydroclimatic changes in northern anatolia and the northern red sea region during the last 7500 years pronounced and coherent multicentennial variations in these records reveal patterns that strongly resemble modern temperature and rainfall anomalies related to the arctic oscillation north atlantic oscillation ao nao these patterns suggest a prominent role of ao nao like atmospheric variability during the holocene beyond interannual to interdecadal timescales most likely originating from solar output changes

high mountain region of the northern romanian carpathians responded sensitively to holocene climate and land use changes a multi proxy analysis a high altitude lake sediment sequence buh iescu mare 1918 m a s l in the subalpine zone of the rodna mountains was analysed through a multi proxy approach to determine the sensitivity of high mountain habitats to climate fire and land use changes the early holocene regional forests were dominated by pinus sylvestris and mugo and replaced by picea abies from 9800 cal yr bp after an extended hiatus in the profile c 9800 4200 cal yr bp probably because of the physical removal of sediments through avalanche or high flow events p abies abies alba and fagus sylvatica forests developed after 4200 cal yr bp the timberline and treeline reacted sensitively to past changes in climate and human impact the site was probably situated above the treeline throughout most of the investigated period however a treeline ecotone or krummholz zone may have sporadically reached the lake s elevation in the early holocene a decline in timberline and treeline elevation was noted during the last 1200 years and more evidently over the past 200 years with replacement by subalpine shrubs alnus viridis and alpine herbaceous communities because these vegetation changes were associated with an increased prevalence of pollen based anthropogenic indicators charcoal particles and abiotic indicators human induced fires and clearance and resultant erosion inputs to the lake are implied effects of current warming on the altitude range of trees are not yet visible probably because land use has more strongly contributed to changes in land cover than the climate fluctuations of the last millennium in the rodna mountains

tripartite climate reversal in central europe 5600 5300 years ago abstract the history of variations in water level of lake constance as reconstructed from sediment and pollen analysis of a sediment sequence from the archaeological site of arbon bleiche 3 shows an abrupt rise in lake level dendrochronologically dated to 5375 yr ago 5320 yr relative to ad 1950 this event paralleled by the destruction of the neolithic village by fire provoked the abandonment of this prehistoric lake shore location established in the former shallow bay of arbon bleiche and was the last of a series of three episodes of successively higher lake level the first occurring at 5600 5500 cal yr b p the dendrochronologically dated rise event was synchronous with an abrupt increase in atmospheric 14 c this supports the hypothesis of an abrupt climate change forced by varying solar activity moreover the three successive episodes of higher lake level between 5600 and 5300 cal yr b p at arbon bleiche 3 coincided with climatic cooling and or changes in moisture conditions in various regions of both hemispheres this period corresponds to the mid holocene climate transition onset of the neoglaciation and suggests inter hemispheric linkages for the climate variations recorded at arbon bleiche 3 this mid holocene climate reversal may have resulted from complex interactions between changes in orbital forcing ocean circulation and solar activity finally despite different seasonal hydrological regimes the similarities between lake level records from lake constance and from jurassian lakes over the mid holocene period point to time scale as a crucial factor in considering the possible impact of climate change on environments

a 13 600 year diatom oxygen isotope record from the south carpathians romania reflection of winter conditions and possible links with north atlantic circulation changes this study provides a continuous lateglacial and holocene record of diatom silica oxygen isotope changes 18odiat in a subalpine lake sediment sequence obtained from the retezat mts taul dintre brazi 1740 m a s l this through flow shallow high altitude lake with a surface area of only 0 4 ha has short water residence time and is predominantly fed by snowmelt and rainwater its 18odiat record principally reflects the oxygen isotope composition of the winter and spring precipitation as diatom blooms occur mainly in the spring and early summer hence changes in 18odiat are interpreted as seasonal scale changes in the amount of winter precipitation low oxygen isotope values 27 28 5 occurred during the lateglacial until 12 300 cal bp followed by a sharp increase thereafter in the holocene 18odiat values ranged from 29 to 31 until 3200 cal bp followed by generally lower values during the late holocene 27 30 short term decreases in the isotopic values were found between 10 140 9570 9000 8500 7800 7300 6300 5800 5500 5000 and at 8015 4400 4000 cal bp after 3200 cal bp a decreasing trend was visible with the lowest values between 3100 2500 and after 2100 cal bp the general trend in the record suggests that contribution of winter precipitation was generally lower between 11 680 and 3200 cal bp followed by increased contribution during the last millennia the late holocene decrease in 18odiat shows good agreement with the speleothem 18o lake level and testate amoebae records from the carpathian mountains that also display gradual 18o decrease and lake level mire water table level rise after 3200 cal bp strong positive correlation with north atlantic circulation and solar activity proxies such as the austrian and hungarian speleothem records furthermore suggested that short term increases in the isotopic ratios in the early and mid holocene are likely connectable to high solar activity phases and high frequency of positive north atlantic oscillation indexes that may have resulted in decreased winter precipitation in this region

holocene and late pleistocene climate in the sub mediterranean continental environment a speleothem record from poleva cave southern carpathians romania the pp10 stalagmite from poleva cave provides a late pleistocene and holocene isotopic record characteristic for the sw of romania a sub mediterranean climatic region the speleothem was dated by eight tims and one alpha u series dates which showed that it was precipitated between 75 ka and 2 ka with at least two hiatuses the basal sector of the stalagmite showed a slow growing regime of 0 26 cm ka while the upper one grew relatively fast with about 5 cm ka the temporal resolution for the isotopic sampling is thus 2 ka sample for the lower sector and 150 years sample for the upper one the relationship between 18 o and temperature was found positive the isotopic record of the lower sector shows two marked cold intervals during 67 and 58 ka and 40 35 ka respectively which correlate well with the villars and soreq records the upper sector record is so far the most detailed holocene isotopic record in romania and the only one available for the regions located at the exterior of the carpathians range the signal shows a gradual warming after the gs1 event punctuated by several cold events at 8 7 2 and 4 2 ka and also by warm oscillations centered at about 5 2 and 3 3 ka the results seem to indicate that if the north atlantic firstorder signals may extend well to the south eastern europe their amplitude and general trend may be diminished by the interferences with the mediterranean circulation

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

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

oxygen isotope and palaeotemperature records from six greenland ice core stations camp century dye 3 grip gisp2 renland and northgrip oxygen isotope variations spanning the last glacial cycle and the holocene derived from ice core records for six sites in greenland camp century dye 3 grip gisp2 renland and northgrip show strong similarities this suggests that the dominant influence on oxygen isotope variations reflected in the ice sheet records was regional climatic change differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios palaeotemperature estimates have been obtained from the records using three approaches i inferences based on the measured relationship between mean annual 18o of snow and of mean annual surface temperature over greenland ii modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile or iii by using monte carlo simulation techniques the third of these approaches was adopted to reconstruct holocene temperature variations for the dye 3 and grip temperature profiles which yields remarkably compatible results a new record of holocene isotope variations obtained from the northgrip ice core matches the grip short term isotope record and also shows similar long term trends to the dye 3 and grip inverted temperature data the northgrip isotope record reflects i a generally stronger isotopic signal than is found in the grip record ii several short lived temperature fluctuations during the first 1500 yr of the holocene iii a marked cold event at ca 8 2 ka the 8 2 ka event iv optimum temperatures for the holocene between ca 8 6 and 4 3 ka a signal that is 0 6 stronger than for the grip profile v a clear signal for the little ice age and vi a clear signal of climate warming during the last century these data suggest that the northgrip stable isotope record responded in a sensitive manner to temperature fluctuations during the holocene copyright 2001 john wiley sons ltd

unstable early holocene climatic and environmental conditions in northwestern russia derived from a multidisciplinary study of a lake sediment sequence from pichozero southeastern russian karelia unstable early holocene climate and enviromental conditions in northwestern russia derived from a multidisciplinary study of a lake sediment sequence from pichozero southeastern russia karelia

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

major δ14c excursions during the late glacial and early holocene changes in ocean ventilation or solar forcing of climate change the atmospheric 14c record during the late glacial and the early holocene shows sharp increases simultaneous with cold climatic phases these increases in the atmospheric 14c content are usually explained as the effect of reduced oceanic co2 ventilation after episodic outbursts of large meltwater reservoirs into the north atlantic in this hypothesis the stagnation of the thermohaline circulation is the cause of both climate change as well as an increase in atmospheric 14c as an alternative hypothesis we propose that changes in 14c production give an indication for the cause of the recorded climate shifts changes in solar activity cause fluctuations in the solar wind which modulate the cosmic ray intensity and related 14c production two possible mechanisms amplifying the changes in solar activity may result in climate change in the case of a temporary decline in solar activity 1 reduced solar uv intensity may cause a decline of stratospheric ozone production and cooling as a result of less absorption of sunlight this might influence atmospheric circulation patterns extension of polar cells and equatorward relocation of mid latitude storm tracks with effects on oceanic circulation and 2 increased cosmic ray intensity may stimulate cloud formation and precipitation while 14c production increases

reconciling diverse diatom based lake responses to climate change in four mountain lakes in the south carpathian mountains during the last 17 kyrs abstract climatic changes were studied using siliceous algae diatoms and chrysophyta stomatocysts analyses in four mountain lakes in the retezat mountains in the south carpathian mountains with the aim to search for synchrony in aquatic ecosystem responses according to the basal radiocarbon dating of the lake sediment cores these lakes were formed around 17 000 15 000 cal yr bp high resolution diatom analyses were carried out together with loss on ignition loi and biogenic silica bisi measurements on the lakes comparison of the proxy results suggests that despite the different slope aspect water depth and basin parameters diatom assemblage changes show clear synchrony the most remarkable changes in the aquatic ecosystems were observed around 6500 cal yr bp on the northern slope and around 6100 cal yr bp on the southern slope during the holocene evidences for sharp concomitant shifts were found between 9200 9000 and 3200 3000 cal yr bp in the siliceous algal communities on both slopes the late glacial holocene boundary was not pronounced in the shallow lakes but was significant in a deep lake the signs of a dry and bipartite younger dryas gs 1 were evident but floristic changes differed in the lakes principal component analyses explained very similar variances along the first and second axes for three lakes while the fourth lake lake bucura proved less sensitive to climate change due to the dominance of moss inhabiting diatom assemblages lake level changes have only been reconstructed on the basis of diatom life forms in one of the deep lakes lake gales high lake levels were inferred between 9300 9000 and 3000 1700 cal yr bp in addition to loi biogenic silica content bisi was measured on the sediments of the northern slope and pointed to different seasonal biological productivities increasing loi was often coupled with low bisi values

diatom inferred lateglacial and holocene climatic variability in the south carpathian mountains romania climatic and environmental changes were studied using siliceous algae diatoms and chrysophycean cysts analyses in a mountain lake in the south carpathian mountains for the lateglacial and holocene lake brazi 1740 a s l is a small shallow lake in the retezat mountains according to the basal radiocarbon dating of the core the lake was formed around 15 750 cal bp and sediment accumulation has been continuous ever since high resolution diatom analyses were carried out together with loss on ignition and biogenic silica measurements total epilimnetic phosphorus tp concentrations and ph were reconstructed quantitatively ten statistically significant zones were distinguished six of which appeared in the lateglacial and early holocene suggesting the instability of diatom assemblages after deglaciation the uppermost zone covered six thousand years which suggests that diatom assemblages remained quite stable during the second half of the holocene high lake level occurred between 9500 and 9000 cal bp after 6300 cal bp the lake level gradually increased again until 5800 cal bp a further increase was detected at 3000 cal bp while after 1500 cal bp water level decreased although there is limited knowledge regarding the environmental constraints of several diatom taxa present in the sequence e g aulacoseira laevissima which makes the precise environmental interpretation of the diatom record more difficult the available data provide an important new insight into the environmental history of lake brazi and the carpathian mountains the most remarkable changes in the aquatic ecosystem were observed at 6000 cal bp in the holocene and 12 800 cal bp at the onset of the younger dryas marked changes were also detected at 10 500 10 300 9800 9500 9000 8900 8800 8300 6300 5800 and 3100 3000 cal bp

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

rapid vegetation response to lateglacial and early holocene climatic fluctuation in the south carpathian mountains romania abstract high resolution pollen conifer stomata and plant macrofossil analyses of two glacial lake sediments 1740 and 1990 m a s l are used to reconstruct lateglacial lg and early holocene eh vegetation and tree line changes in the retezat mountains our results show that during the lg tree line was between 1750 and 1800 m a s l formed by larix decidua pinus mugo and picea abies early lg spread to high altitudes suggests refugia of these tree species in the mountain the younger dryas cooling resulted in regional steppe tundra expansion but tree line position and composition showed little change the abundance of trees and shrubs decreased at 1740 m a s l but species richness increased with the arrival of pinus cembra our data support climate model hindcasts for only modest decrease in accumulated growing season heat at mid high altitudes regionally the pollen records suggest enhanced aridity and seasonality in the eh tree line reached 2000 m a s l higher than today by 11 100 cal yr bp p mugo p cembra p abies established around the upper lake suggesting rapid increase in summer temperatures the eh maximum of l decidua between 11 200 10 600 cal yr bp was connected to high summer insolation high altitude expansion of abies alba between 10 600 10 300 cal yr bp suggested summer mean temperatures 2 8 c higher then today in comparison with other mountain sites in europe lg interstadial tree line was at similar altitude in the s alps and 350 m higher in the pirin mountains lg tree line fluctuation had similar low amplitude in the se alps retezat and pirin mts suggesting relatively weak influence of the north atlantic thermohaline circulation changes on growing season temperatures

rapid climate change during the early holocene in western europe and greenland based on microfacies analyses of seasonally laminated varved sediments from lake holzmaar germany we report evidence of decadal to century scale climate variability during the early holocene the shifts in climate are documented in the thickness variations and changes in the composition of the varves in response to subtle shifts in limnological conditions the close similarity between the holzmaar varve record and the grip oxygen isotope record during 7 4 9 0 calendar cal ka suggests that the high frequency climatic variations in both regions were controlled by the same mechanism our more detailed studies covering the central 409 yr period 7 846 8 255 cal ka encompassing the 8 2 ka event document for the first time on a seasonal scale the changing precipitation regimes in western europe during these climate shifts we show i that winters were drier and summers shorter and cooler in western europe during colder periods in greenland ii in contrast to the present day climate in the holzmaar

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

pollen inferred palaeoclimate reconstructions in mountain areas problems and perspectives transfer functions are an efficient tool for the quantitative reconstruction of past climate from low to mid elevation pollen sites however the application of existing methods to high altitude pollen assemblages frequently leads to unrealistic results in the aim of understanding the causes of these biases the standard best modern analogue method has been applied to two high altitude pollen sequences to provide quantitative climate estimates for the lateglacial and holocene periods both pollen sequences laghi dell orgials 2130 m sw aspect and lago delle fate 2240 m e aspect are located in the subalpine belt on opposing sides of the st anna di vinadio valley italian maritime alps different results were obtained from the two sequences the largest differences occurred in palaeotemperature reconstruction with notable differences in both the values and trends at each site these biases may be attributed to 1 a lack of high elevation best modern analogues in the database of modern samples 2 the problem of pollen taxa that have multiple climatic significance 3 problems related to the complexity of mountainous ecosystems such as the phenomenon of uphill transport of tree pollen by wind possible improvements to the reconstruction process are discussed copyright 2006 john wiley sons ltd

july mean temperature and annual precipitation trends during the holocene in the fennoscandian tree line area pollen based climate reconstructions july mean temperature and annual precipipation during the last 9900 cal yr bp were recon structed from pollen assemblages preserved in a sediment core from northern finland quantitative recon structions were performed using a modern pollen climate calibration model based on weighted averaging partial least squares regression the predictive ability of the model was evaluated against modern meteoro logical data using leave one out cross validation the prediction error for july mean temperature is c 1 0 c and for annual precipitation 340 mm the july mean temperatures during the earliest holocene were low c 1 1 0 c and annual precipitation was high c 600 800 mm between 8200 and 6700 cal yr bp july mean temperatures reached their maxima 12 5 13 0 c which are c 1 4 1 7 c higher than at present at the same time precipitation decreased during the late holocene july mean temperatures declined and the last 2000 years have been the coolest since the early holocene precipitation has slightly increased the spatial coherence between our results and of several other climate reconstructions from northern europe indicates that the holocene climate was strongly influenced by north atlantic oceanic and atmospheric circulation patterns we propose that the distinctly oceanic climate of the early holocene was due to enhanced westerly latitudinal airflow which was replaced at c 8200 cal yr bp by a more meridional flow pattern and by the development of predominantly anticyclonic summer conditions

late glacial and holocene paleoenvironmental records in the tatra mountains east central europe based on lake peat bog and colluvial sedimentary data a summary review abstract the tatra mountains are the highest massif in the carpathian mountain arc 2655 m and represent a typical alpine landscape developed in the course of pleistocene glaciations but are not glacierized today the glacial relief of the massif offers an abundance of topographic depressions cirque overdeepenings morainic closed depressions where sedimentary sequences may potentially reveal paleoenvironmental changes that may have occurred since the glaciers retreat from the last glacial maximum position 26 18 ka we present a review of late glacial and holocene sedimentary archives from the tatra mountains collected in the polish and non polish literature the data sets 40 sites included 21 lake 13 peat bog and 6 colluvial sediment sites the entire listed sediment sequence features radiometric datings or at the very least a chronological framework is inferred from the biostratigraphy the oldest sampled sedimentary sequences were dated back to the oldest dryas and were obtained from the deepest glacial lakes located in the subalpine zone up to 1700 m shallow lakes

vegetation responses to the 8200 cal bp cold event and to long term climatic changes in the eastern alps possible influence of solar activity and north atlantic freshwater pulses subfossil pollen from two bogs in temperature sensitive high altitude regions were analysed in order to reconstruct early to mid holocene summer temperature fluctuations in the eastern alps the p

a chironomid based holocene summer air temperature reconstruction from the swiss alps we developed a quantitative chironomid july air temperature inference model based on surface sediments from 81 swiss lakes and applied it to the holocene subfossil chironomid record of hinterburgsee a small subalpine lake in the northern swiss alps present day mean july air temperature of 11 3 c after smoothing to reduce the high between sample variability of inferred temperatures the reconstruction indicates july air temperatures of 10 4 10 9 c at the end of the younger dryas of 11 9 12 8 c during the early and mid holocene 11500 4000 cal bp and slightly lower temperatures of 11 5 12 0 c during the late holocene 3500 1000 cal bp a warming trend inferred for the past millennium is most likely an artifact of human impact on hinterburgsee s chironomid fauna rather than a genuine temperature signal the most prominent climatological events during the holocene were two periods of lower temperatures at c 10700 10500 cal bp and 8200 7700 cal bp and an abrupt shift to a cooler late holocene cl

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

evolving force balance during incipient subduction nearly half of all active subduction zones initiated during the cenozoic all subduction zones associated with active back arc extension have initiated since the eocene hinting that back arc extension may be intimately associated with an interval several tens of myr following subduction initiation that such a large proportion of subduction zones are young indicates that subduction initiation is a continuous process in which the net resisting force associated with forming a new subduction zone can be overcome during the normal evolution of plates subduction initiation is known to have occurred in a variety of tectonic settings old fracture zones transform faults and extinct spreading centers and through polarity reversal behind active subduction zones although occurring within different tectonic settings four known subduction initiation events izu bonin mariana ibm along a fracture zone tonga kermadec along an extinct subduction boundary new hebrides within a back arc and puysegur fiordland along a spreading center were typified by rapid uplift within the forearc followed by sudden subsidence other constraints corroborate the compressive nature of ibm and tonga kermadec during initiation using an explicit finite element method within a two dimensional domain we explore the evolving force balance during initiation in which elastic flexure viscous flow plastic failure and heat transport are all considered in order to tie theory with observation known tectonic settings of subduction initiation are used as initial and boundary conditions we systematically explore incipient compression of a homogeneous plate a former spreading center and a fracture zone the force balance is typified by a rapid growth in resisting force as the plate begins bending reaching a maximum value dependent on plate thickness but typically ranging from 2 to 3 1012 n m for cases that become self sustaining this is followed by a drop in stress once a shear zone extends through the plate the formation of a throughgoing fault is associated with rapid uplift on the hanging wall and subsidence on the footwall cumulative convergence not the rate of convergence is the dominant control on the force balance viscous tractions influence the force balance only if the viscosity of the asthenosphere is 1020 pa s and then only after plate failure following plate failure buoyancy of the oceanic crust leads to a linear increase with crustal thickness in the work required to initiate subduction the total work done is also influenced by the rate of lithospheric failure a self sustaining subduction zone does not form from a homogeneous plate a ridge placed under compression localizes subduction initiation but the resisting ridge push force is not nearly as large as the force required to bend the subducting plate the large initial bending resistance can be entirely eliminated in ridge models explaining the propensity for new subduction zones to form through polarity reversals a fracture zone fz placed in compression leads to subduction initiation with rapid extension of the overriding plate a fz must be underthrust by the older plate for 100 150 km before a transition from forced to self sustaining states is reached in fz models the change in force during transition is reflected by a shift from forearc uplift to subsidence subduction initiation is followed by trench retreat and back arc extension moderate resisting forces associated with modeled subduction initiation are consistent with the observed youth of pacific subduction zones the models provide an explanation for the compressive state of western pacific margins before and during subduction initiation including ibm and tonga kermadec in the eocene and the association of active back arcs with young subduction zones on the basis of our dynamic models and the relative poles of rotation between pacific and australia during the eocene we predict that the northern segment of the tonga kermadec convergent margin would have initiated earlier with a progressive southern migration of the transition between forced and self sustaining states

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

chironomidae insecta diptera succession in żabieniec bog and its palaeo lake central poland through the late weichselian and holocene abstract subfossil chironomidae assemblages were studied in a sediment sequence from abieniec bog in central poland the climate history and habitat changes in the palaeo lake were reconstructed from these assemblages currently no chironomid based climate calibration set is available from poland and so past mean july air temperatures were inferred from chironomid climate calibration data sets from norway russia and switzerland during the late weichselian the three calibration functions from these data sets provided similar temperature inferences but there was some divergence in the reconstructions for the younger dryas and holocene in the late pleniglacial inferred summer air temperature was relatively low 8 12 c and the lake was oligotrophic at about 16 5 ka bp temperature rapidly rose to 15 c and assemblage diversity substantially increased during the interstadial temperature stayed at this level in the younger dryas july air temperature was only 1 2 c lower than in the interstadial as inferred from the norwegian calibration data set whereas the russian and swiss calibration functions did not indicate any temperature decrease from the beginning of the holocene taxa typical of meso eutrophic conditions dominated there was an increased abundance of phytophilous species and the assemblage composition was also influenced by changes in water level palaeotemperature reconstructions differed in their values from 8 0 to 8 7 ka bp inferences based on the swiss and russian data sets indicated a cold oscillation while reconstructions based on the norwegian data set did not show any temperature decrease after 2 5 ka bp assemblage diversity and head capsule concentrations decreased in the last millennium semi terrestrial taxa dominated except from late medieval to early modern times when shallow water species reappeared

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

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

eemian to early wurmian climate dynamics history and pattern of changes in central europe abstract high resolution pollen records from the northern alpine foreland are used to evaluate the patterns of climate change during the period between the late eemian interglacial marine oxygen isotope stage ois 5e about 115 ky ago and the end of the st germain ii ois 5a dansgaard oeschger interstadial d o is21 about 75 ky ago for the quantitative climate interpretation of the fossil pollen assemblages we compare two different methods a modern analogue technique and a mutual climatic range approach the results not only reveal major climatic changes at the transition to stadials and interstadials but also indicate short term oscillations which are followed by an almost full return to the preceding climate conditions and components of gradual trends resembling saw tooth structures based on the pollen data the climate reconstructions suggest that the optimum in st germain ii ois 5a d o is21 in winter temperatures was about 0 8 to 1 4 c and in summer temperatures about 0 7 to 1 2 c warmer than the optimum in st germain i ois 5c d o is22 to is24 the severe and short time montaigu cold event iceberg discharge event c23 clearly divided st germain i into two thermal periods thus st germain ia d o is24 preceding the montaigu event is slightly more favourable than the following st germain ic d o is23 since several climate oscillations occurred during these interstadials they show only limited stability with respect to the stadial periods the results reveal a coherent pattern for all records winter temperatures during melisey ii ois 5b c21 are about 1 to 4 c lower than those during melisey i ois 5d c24 as regards short term climate changes during melisey i and melisey ii consistent amelioration episodes may be distinguished during these intervals

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

low frequency and high frequency changes in temperature and effective humidity during the holocene in south central sweden implications for atmospheric and oceanic forcings of climate an integrated use of independent palaeoclimatological proxy techniques that reflect different components of the climate system provides a potential key for functional analysis of past climate changes here we report a 10 000 year quantitative record of annual mean temperature tann based on pollen climate transfer functions and pollen stratigraphical data from lake flarken south central sweden the pollen based temperature reconstruction is compared with a reconstruction of effective humidity as reflected by a 18o record obtained on stratigraphy of lacustrine carbonates from lake igelsjon c 10 km from lake flarken which gives evidence of pronounced changes in effective humidity the relatively low tann and high effective humidity as reflected by a low evaporation inflow ratio suggest a maritime early holocene climate 10 000 8 300 cal year bp seemingly incompatible with the highly seasonal solar insolation configuration we argue that the maritime climate was due to the stronger than present zonal flow enhanced by the high early holocene sea surface temperatures in the north atlantic the maritime climate mode was disrupted by the abrupt cold event at 8 200 cal year bp followed at 8 000 cal year bp by a stable holocene thermal maximum the latter was characterized by tann values about 2 5 c higher than at present and markedly dry conditions indicative of stable summer time anti cyclonic circulation possibly corresponding with modern blocking anticyclonic conditions the last 4 300 year period is characterized by an increasingly cold moist and unstable climate the results demonstrate the value of combining two independent palaeoclimatic proxies in enhancing the reliability generality and interpretability of the palaeoclimatic results further methodological refinements especially in resolving past seasonal climatic contrasts are needed to better understand the role of different forcing factors in driving millennial scale climate dynamics

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

an event stratigraphy for the last termination in the north atlantic region based on the greenland ice core record a proposal by the intimate group it is suggested that the grip greenland ice core should constitute the stratotype for the last termination based on the oxygen isotope signal in that core a new event stratigraphy spanning the time interval from ca 22 0 to 11 5 k grip yr bp ca 19 0 10 0 k 14 c yr bp is proposed for the north atlantic region this covers the period from the last glacial maximum through termination 1 of the deep ocean record to the pleistocene holocene boundary and encompasses the last glacial late glacial of the traditional northwest european stratigraphy the isotopic record for this period is divided into two stadial episodes greenland stadials 1 gs 1 and 2 gs 2 and two interstadial events greenland interstadials 1 gi 1 and 2 gi 2 in addition gi 1 and gs 2 are further subdivided into shorter episodes the event stratigraphy is equally applicable to ice core marine and terrestrial records and is considered to be a more appropriate classificatory scheme than the terrestrially based radiocarbon dated chronostratigraphy that has been used hitherto 1998 john wiley sons ltd

holocene annual mean temperature changes in estonia and their relationship to solar insolation and atmospheric circulation patterns abstract we reconstructed annual mean temperature tann trends from three radiocarbon dated holocene pollen stratigraphies from lake sediments in estonia northern europe the reconstructions were carried out using a north european pollen climate calibration model based on weighted averaging partial least squares regression the cross validated prediction error of the model is 0 89 c and the coefficient of determination between observed modern tann values and those predicted by the model is 0 88 in the reconstruction the holocene thermal maximum htm is distinguishable at 8000 4500 cal yr b p with the expansion of thermophilous tree species and tann on average 2 5 c higher than at present the pollen stratigraphical data reflect progressively warmer and drier summers during the htm analogously with the modern decadal scale climatic variability in north europe we interpret this as an indication of increasing climatic continentality due to the intensification of anticyclonic circulation and meridional air flow post htm cooling started abruptly at around 4500 cal yr b p all three reconstructions show a transient ca 300 years cooling of 1 5 2 0 c at 8600 8000 cal yr b p we tentatively correlate this cold event with the north atlantic 8 2 ka event at 8400 8000 cal yr b p provided that the 8 2 ka event was caused by freshening of the north atlantic surface water our data provide evidence of the climatic and vegetational responsiveness of the boundary of the temperate and boreal zones to the weakening of the north atlantic thermohaline circulation and the zonal energy transport over europe no other cold events of comparable magnitude are indicated during the last 8000 years

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

holocene climate reconstructions from the fennoscandian tree line area based on pollen data from toskaljavri due to its location on the eastern north atlantic seaboard the fennoscandian tree line area is an ideal area to use biological proxies to assess the relative roles of the scandinavian ice sheet and of oceanic atmospheric and astronomic forcings on regional climate history here we report pollen based july mean temperature tjul and annual precipitation pann reconstructions from a sediment core from a high altitude tree line lake in northwestern finland the reconstructions suggest that at 9600 8300 cal yr b p tjul values were low but steadily rising while pann was high the period of warmest summers with tjul values ca 1 8 1 6 c higher than at present occurred at ca 8000 6500 cal yr b p since then climate has become gradually cooler tjul values during the medieval warm period ca 1400 1000 cal yr b p were ca 0 8 c higher that at present but decreased rapidly to the low little ice age levels at 800 cal yr b p we compare these results with an earlier pollen based climate reconstruction from the same region the reconstructions indicate a similar general holocene tjul pattern with lower values in the reconstruction from the high altitude lake however most of the small scale variations are not synchronous suggesting that they may represent noise rather than signal in our data c 2002 university of washington

insights into continental temperatures in the northwestern black sea area during the last glacial period using branched tetraether lipids abstract in the continental realm continuous quantitative temperature reconstructions spanning the last glacial are rare especially in central and eastern europe here we provide a reconstruction from the northwestern black sea catchment spanning 40 to 9 ka bp from a study of the relative distribution of branched glycerol dialkyl glycerol tetraethers brgdgts in black sea lacustrine sediments first the origins of brgdgts are discussed the comparison of geochemical proxies from the same core supports a dominant terrestrial origin for brgdgts during the last glacial and a strong decrease in the soil derived brgdgt proportion toward the holocene since the lowering of soil vs lacustrine derived brgdgts is prone to bias the temperature signal that is reconstructed using a soil calibration a correction for in situ production is applied the corrected signal is compared to independent discrete temperature records from the study area the brgdgt temperature relative evolution reconstructed in this work provides additional insight regarding millennial scale climate variability in central and eastern europe notably the imprints of heinrich event cold spells and lateglacial climatic oscillations are consistent with other regional paleorecords from the northern hemisphere