reconstructing biomes from palaeoecological data a general method and its application to european pollen data at 0 and 6 ka biome models allow the results of experiments with atmospheric general circulation models to be translated into global maps of potential natural vegetation the use of biome models as a diagnostic tool for palaeoclimate simulations can yield maps that are directly comparable with palaeoecological pollen and plant macrofossil records provided these records are biomized i e assigned to biomes in a consistent way this article describes a method for the objective biomization of pollen samples based on fuzzy logic pollen types taxa are assigned to one or more plant functional types pfts then affinity scores are calculated for each biome in turn based on its list of characteristic pfts the pollen sample is assigned to the biome to which it has the highest affinity subject to a tie breaking rule modern pollen data from surface samples reflecting present vegetation across europe are used to validate the method pollen data from dated sediment cores are then used to reconstruct european vegetation patterns for 6 ka the reconstruction shows systematic differences from present that are consistent with previous interpretations the method has proved robust with respect to human impacts on vegetation and provides a rational way to interpret combinations of pollen types that do not have present day analogs the method demands minimal prior information and is therefore equally suitable for use in other regions with richer floras and or lower densities of available modern and fossil pollen samples than europe

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

vegetation and climate dynamics during the holocene and eemian interglacials derived from lake baikal pollen records abstract the last interglacial li and holocene changes in annual precipitation p ann the mean temperature of the warmest t w and coldest t c month and the moisture index were reconstructed from continuous pollen records from lake baikal the holocene core 52 31 n 106 09 e presented in this study was recovered from a depth of 355 m in the 25 km wide underwater buguldeika saddle separating the southern sub basin of lake baikal from its central sub basin the biome reconstruction shows that tundra and steppe biomes have highest scores during ca 15 000 13 300 cal years b p and that taiga becomes a dominant vegetation type after ca 13 300 cal years b p our quantitative reconstruction indicates an onset of relatively warm and wet conditions soon after ca 10 000 cal years b p the warmest and wettest climate with t w 16 c p ann 480 mm and 0 9 1 has been reconstructed for ca 9000 7000 cal years b p in the lake baikal region this interval is characterized by the appearance and spread of hunter communities kitoi culture consistently a hiatus in the regional archaeological record 4900 4200 years b c or 6850 6150 cal years b p coincides with the interval of a major climate deterioration which followed the climatic optimum an attempt to find a relationship between the archaeological record and a spread of steppe and meadow communities in the lake baikal region demonstrates that despite a long habitation of the area the human impact on vegetation was local rather than regional and likely did not affect the pollen record from lake baikal the reconstructed peaks in the steppe biome scores during the last 9000 years are consistent with short one to five hundred year episodes of weak pacific summer monsoon supporting our interpretation that the holocene vegetation changes around lake baikal are associated with large scale circulation processes controlling regional water balance rather than with human activities thus our study proves the suitability of lake baikal pollen data for the reconstruction of natural vegetation and climate dynamics through the whole period from the onset of the li to the present comparison of the recent and the last interglacial suggests that the holocene climatic optimum was less pronounced e g lower summer and winter temperatures and annual precipitation sums than that of the li on the other hand pollen records demonstrate that the holocene forest phase already lasts some thousand years longer than that of the li the interglacial vegetation dynamics derived from the lake baikal pollen records can be satisfactorily explained by reconstructed changes in summer and winter temperatures and in available moisture the interglacial vegetation around lake baikal is dominated by the boreal forests which are associated with a generally warm and wet climate the high sea level associated with decreased ice volume appears to have had a greater impact on the siberian environments during the last and the recent interglacial than the direct effect of lower than present winter insolation reconstructed changes in the winter temperature correlate well with changes in the sea level and global ice volume while the summer temperatures derived from the lake baikal pollen records track changes in the summer insolation

alexandria nile delta coast egypt update and future projection of relative sea level rise previous studies have indicated that the nile river deltaic plain is vulnerable to a number of aspects including beach erosion inundation and relatively high rates of land subsidence this issue motivates an update and analysis of new tide gauge records from which relative sea level changes can be obtained estimated rates from five tide gauges are variable in terms of magnitude and temporal trend of rising sea level analysis of historical records obtained from tide gauges at alexandria rosetta burullus damietta and port said show a continuous rise in mean sea level fluctuating between 1 8 and 4 9 mm year the smaller rate occurs at the alexandria harbor while the higher one at the rosetta promontory these uneven spatial and temporal trends of the estimated relative sea level rise rslr are interpreted with reference to local geological factors in particular holocene sediment thickness subsidence rate and tectonism are correlated with the estimated rates of relative sea level change from the relatively weak correlation between them we presume that tectonic setting and earthquakes both recent and historical ones contribute more to accelerated rslr than that of dewatering and compression dewatering of holocene mud underlying the nile delta plain as a result large areas of the coastal plain have been subsided but some sectors have been uplifted in response to tectonic activities of thick underlying older strata projection of averaged sea level rise trend reveals that not all the coastal plain of the nile delta and alexandria is vulnerable to accelerated sea level rise at the same level due to wide variability of the land topography that includes low lying areas high elevated coastal ridges and sand dunes accretionary beaches and artificially protective structures interaction of all aspects tectonic regime topography geomorphology erosion rate and rslr rate permitted to define risk areas much vulnerable to impacts of sea incursion due to accelerated sea level rise

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

pollen based continental climate reconstructions at 6 and 21 ka a global synthesis subfossil pollen and plant macrofossil data derived from 14c dated sediment profiles can provide quantitative information on glacial and interglacial climates the data allow climate variables related to growing season warmth winter cold and plant available moisture to be reconstructed continental scale reconstructions have been made for the mid holocene mh around 6 ka and last glacial maximum lgm around 21 ka allowing comparison with palaeoclimate simulations currently being carried out as part of the fifth assessment report ar5 of the intergovernmental panel on climate change the synthesis of the available mh and lgm climate reconstructions and their uncertainties obtained using modern analogue regression and model inversion techniques is presented for four temperature variables and two moisture variables reconstructions of the same variables based on surface pollen assemblages are shown to be accurate and unbiased reconstructed lgm and mh climate anomaly patterns are coherent consistent between variables and robust with respect to the choice of technique they support a conceptual model of the controls of late quaternary climate change whereby the first order effects of orbital variations and greenhouse forcing on the seasonal cycle of temperature are predictably modified by responses of the atmospheric circulation and surface energy balance

mid to late holocene climate change in north central mongolia as recorded in the sediments of lake telmen abstract a record of climatic change has been reconstructed for the past 7110 calibrated calendar cal years for lake telmen mongolia based upon sedimentologic and geomorphic evidence from the lake watershed system lake telmen is a saline presently 4 g l 1 closed basin lake and is therefore sensitive to changes in effective moisture balance between 7110 and 6260 cal yr ago conditions in the lake telmen region were hyperarid and a small saline approximately 20 g l 1 lake was present increased effective moisture balance but still arid conditions prevailed between 6260 and 4390 cal yr ago since 4390 cal yr ago generally more humid conditions prevailed in the lake telmen region as the lake deepened a hypoxic hypolimnion became established below a well developed summer thermocline resulting in varved sediment accumulation since 4390 cal yr ago between about 2710 and 1260 cal yr ago a greater than present day effective moisture balance is recorded by a series of four lake highstand terraces sedimentologic profiles from lacustrine cores suggest an increase in effective moisture during the past approximately 680 cal yr

what have we learnt from palaeoclimate simulations there has been a gradual evolution in the way that palaeoclimate modelling and palaeoenvironmental data are used together to understand how the earth system works from an initial and largely descriptive phase through explicit hypothesis testing to diagnosis of underlying mechanisms analyses of past climate states are now regarded as integral to the evaluation of climate models and have become part of the toolkit used to assess the likely realism of future projections palaeoclimate assessment has demonstrated that changes in large scale features of climate that are governed by the energy and water balance show consistent responses to changes in forcing in different climate states and these consistent responses are reproduced by climate models however state of the art models are still largely unable to reproduce observed changes in climate at a regional scale reliably while palaeoclimate analyses of state of the art climate models suggest an urgent need for model improvement much work is also needed on extending and improving palaeoclimate reconstructions and quantifying and reducing both numerical and interpretative uncertainties

an evaluation of the simulated water balance of eurasia and northern africa at 6000 y bp using lake status data changes in the water balance of eurasia and northern africa in response to insolation forcing at 6000 y bp simulated by five atmospheric general circulation models have been compared with observations of changes in lake status all of the simulations show enhancement of the asian summer monsoon and of the high pressure cells over the pacific and central asia and the middle east causing wetter conditions in northern india and southern china and drier conditions along the chinese coast and west of the monsoon core all of the models show enhancement of the african monsoon causing wetter conditions in the zone between ca 10 20 n four of the models show conditions wetter than present in southern europe and drier than present in northern europe three of the models show conditions similar to present in the mid latitude continental interior while the remaining models show conditions somewhat drier than present the extent and location of each of the simulated changes varies between the models as does the mechanism producing these changes the lake data confirm some features of the simulations but indicate discrepancies between observed and simulated climates for example the data show 1 conditions wetter than present in central asia from india to northern china and mongolia indicating that the simulated asian monsoon expansion is too small 2 conditions wetter than present between ca 10 30 n in africa indicating that the simulated african monsoon expansion is too small 3 that northern europe was drier but the area of significantly drier conditions was more localized around the baltic than shown in the simulations 4 that southern europe was wetter than present apparently consistent with the simulations but pollen data suggest that this reflects an increase in summer rainfall whereas the models show winter precipitation and 5 that the mid latitude continental interior was generally wetter than present

climate and vegetation dynamics in the tundra and forest zone during the late glacial and holocene abstract analysis of palynological successions has enabled reconstruction of climate variations throughout the late glacial and holocene in the tundra and forest zones of northern eurasia statistical analysis allows estimation of mean annual precipitation and mean annual and july temperatures based on palynological assemblages thus the dynamic relationships between climate and vegetation changes can be established throughout the late glacial and holocene climate fluctuations were more dramatic in eastern europe than in siberia primarily as a result of the influence of westerly air masses in contrast the autochthonous climate of siberia dominated by local air masses was less prone to influence from climate changes elsewhere in the northern hemisphere and shows only an attenuated younger dryas signal mid holocene warming characterizes all of northern eurasia although the regions of siberia most influenced by continental climates show less pronounced cooling during the later holocene sharp changes between summer monsoonal and winter anti cyclonic regimes characterize the pacific maritime region

upper mantle structure beneath central eurasia using a source array of nuclear explosions and waveforms at regional distances we have observed very consistent broadband regional three component p waveforms from a set of 11 explosions that occurred at the former soviet test site in kazakhstan during 1988 and 1989 and have modeled most of the prominent features in these waveforms to determine upper mantle structure beneath central eurasia using a subset of events as a source array we have identified four consistent arrivals during the first 15 s of p waves recorded at the soviet incorporated research institutions for seismology iris stations arti aru d 1500 km and garm gar d 1380 km these arrivals show consistent variations in frequency content relative timing and amplitudes from event to event despite a range in source magnitude mb between 4 9 and 6 1 we have also identified consistent features in p waveforms of these events recorded at obninsk obn d 2880 km we argue that most of the prominent features in these waveforms can be explained by reflections at or refractions near discontinuities or large velocity gradients in the upper mantle we show that a model with discontinuities of approximately 3 0 and 6 5 near 200 km and 400 km respectively produces a better fit to the broadband data at aru and gar than previous models for this region this model also produces a good match to waveforms recorded at obn and noress however this model is not unique for example we show that it is also possible to produce similar waveforms by replacing the 200 km discontinuity with a large notch shaped low velocity zone between approximately 100 and 140 km based on reflectivity synthetics we suggest that additional data especially from distances less than 1000 km should indicate which of these models is more accurate although our models are not unique our observations do constrain the following features 1 there must be reflectors between about 140 and 200 km and near 400 km depth in the upper mantle to explain the large secondary arrivals at both aru and gar 2 based on the relative size of some of the secondary arrivals at aru and gar the discontinuity near 400 km must be large however it cannot be much greater than about 6 5 because there is no evidence in our data of a reflection from 400 km at obn 3 the relatively small amplitude of the first arrivals at both aru and gar suggests that either the gradient in the uppermost mantle is very small or that a shallow low velocity zone is present comparison of our results with other upper mantle studies shows that the central eurasian upper mantle is similar to the upper mantle of the central and eastern united states

over representation of picea pollen induced by water transport in arid regions picea pollen plays an important role for reconstructing a cold humid climate or palaeo elevations however research has not yet taken into account the pollen transportation pathways within rivers in arid regions a sporopollen study of surface the uppermost river sediments and surface soils from the heihe and shiyang rivers originating in the qilian mountains suggests that significant differences exist between picea pollen percentages within these two different sediment types in surface soils the picea pollen fractions are low representing transportation by wind however percentages of picea pollen reach up to 15 9 of total pollen counts in surface river sediments as far as about 120 km away from the lower spruce forest line this result together with the demonstrated enrichment of picea pollen in water bodies that lie along those observed rivers indicate an over representation within fluvial and lacustrine sediments knowledge about these relationships provides fundamental information for the reconstruction of palaeo vegetation palaeo climate or palaeo elevations

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

heterogeneous vegetation sensitivity at local and regional scales implications for pollen based climate reconstruction abstract vegetation climate relationships are often different at varying spatial scales which is seldom taken into account in reconstructing past climate changes from fossil pollen spectra represent more local vegetation composition but using regional or extra regional modern pollen climate calibration set in this paper we employ 2620 surface pollen spectra and six pollen sequences from continental east asia to reconstruct holocene climate with modern analogue technique a novel data set of vegetation sensitivity index vsi is introduced to examine vegetation climate relationships in 0 5 search windows around the fossil sites local and in the tailored calibration sets regional then we compare them to the explanatory abilities of reconstructed climate variables on explaining the pollen variance in calibration sets and in the fossil pollen data sets using constrained ordination cross validation and significance test by this procedure that we called local regional fossil comparison we can better determine which variable reconstruction is valid and useful in our cases moisture variable reconstructions in temperate forest steppe ecotone at the east asian summer monsoon margin are reliable consistent holocene moisture variations with a strong monsoon influence during 8 6 4 0 cal ka bp which can help us to better interpret human adaptations along the great wall however quantitative climate reconstructions at some sites are less reliable due to highly heterogeneous vegetation sensitivities surrounding the site particularly for areas with complicated topographical contexts we stress that vegetation sensitivities at local and regional scales both need to be investigated before conducting quantitative climate reconstruction

reconstruction of climate and vegetation changes of lake bayanchagan inner mongolia holocene variability of the east asian monsoon a high resolution pollen and pediastrum record spanning 12 500 yr is presented for lake bayanchagan 115 21 e 41 65 n and 1355 m a s l southern inner mongolia individual pollen taxa pt mat and the pft affinity scores pft mat were used for quantitative climatic reconstruction from pollen and algal data both techniques indicate that a cold and dry climate similar to that of today prevailed before 10 500 cal yr b p the wettest climate occurred between 10 500 and 6500 cal yr b p at which time annual precipitation was up to 30 60 higher than today the early holocene increases in temperature and precipitation occurred simultaneously but mid holocene cooling started at approximately 8000 cal yr b p 1500 yr earlier than the drying vegetation reconstruction was based on the objective assignment of pollen taxa to the plant functional type the results suggest that this region was dominated by steppe vegetation throughout the holocene except for the period 9200 to 6700 cal yr b p when forest patches were relatively common inner mongolia is situated at the limit of the present east asian monsoon and patterns of vegetation and climate changes in that region during the holocene probably reflect fluctuations in the monsoon s response to solar insolation variations the early to middle holocene monsoon undoubtedly extended to more northern latitudes than at present

holocene climate conditions in central yakutia eastern siberia inferred from sediment composition and fossil chironomids of lake temje abstract a 380 cm long sediment core from lake temje central yakutia eastern siberia was studied to infer holocene palaeoenvironmental change in the extreme periglacial setting of eastern siberia during the last 10 000 years data on sediment composition were used to characterize changes in the depositional environment during the ontogenetic development of the lake temje the analysis of fossil chironomid remains and statistical treatment of chironomid data by the application of a newly developed regional russian transfer functions provided inferences of mean july air temperatures tjuly and water depths wd reconstructed wds show minor changes throughout the core and range between 80 and 120 cm all the fluctuations in reconstructed water depth lie within the mean error of prediction of the inference model rmsep 0 35 so it is not possible to draw conclusions from the reconstructions a qualitative and quantitative reconstruction of holocene climate in central yakutia recognized three stages of palaeoenvironmental changes the early holocene between 10 and 8 ka bp was characterized by colder than today and moist summer conditions cryotextures in the lake sediments document full freezing of the lake water during the winter time a general warming trend started around 8 0 ka bp in concert with enhanced biological productivity reconstructed mean tjuly were equal or up to 1 5 c higher than today between 6 0 ka and 5 0 ka bp during the entire late holocene after 4 8 ka bp reconstructed mean tjuly remained below modern value limnological conditions did not change significantly the inference of a mid holocene climate optimum supports scenarios of holocene climatic changes in the subpolar part of eastern siberia and indicates climate teleconnections to the north atlantic realm

a 94 10 ka pollen record of vegetation change in qaidam basin northeastern tibetan plateau drill core isl1a was obtained from the qarhan salt lake in central eastern qaidam basin northeastern tibetan plateau ne tp fossil pollen and the lithology of the core sediment were analyzed in conjunction with ams c 14 and th 230 dating the results indicated that artemisia and chenopodiaceae dominated the steppe desert steppe vegetation developed around the lake between 94 and 51 2 ka corresponding with the organic rich silty clay deposited in the core sediments pediastrum continuously appeared in the core sediments between 94 and 51 2 ka indicating freshwater to oligohaline conditions of the paleo qarhan lake during the late marine isotope stage mis 5 mis 4 and early mis 3 during the 51 2 to 32 5 ka period ephedra dominated shrub desert vegetation expanded in the basin while pediastrum disappeared in the core sediments the core sediments consisted of interbedded layers of halite silt and clay rich halite between 51 2 and 32 5 ka signifying a shift toward drier hydrologic conditions thus the paleo qarhan lake experienced periods of desiccation and shallow water levels artemisia and chenopodiaceae dominated steppe desert steppe vegetation appeared again from 32 5 to 253 ka with clay rich sediments in the core thereby suggesting an increase of runoff from the lake under relatively wetter climatic conditions since 253 ka however pollen concentrations declined corresponding with the amount of halite deposited in the core sediment and suggesting a cold dry climatic condition during mis2 our findings have important implications for understanding complex regional vegetation and climatic responses to large scale forcings in the qaidam basin c 2015 elsevier b v all rights reserved

holocene environmental changes in northern mongolia inferred from diatom and pollen records of peat sediment abstract the holocene paleoenvironment in nur sphagnum bog northern mongolia was reconstructed by diatom pollen analysis and measurement of chemical properties on a 3 7 m long peat boring sample development processes of peatland are well reflected in these multiproxy records showing that peat accumulation started as early as 9 ka cal bp and the present acidic peat bog was established no later than 6 ka cal bp synchronous trends in diatom and pollen assemblages revealed wetter climate in the early holocene and extensive drought in the mid late holocene centered at 5900 2800 cal bp as a result of temperature increase and low precipitation periods of shifts in proxy data were potentially correlated with other studies in not only mongolia and siberia but also the north atlantic ocean and the climatic periods at 8 4 and 2 8 ka cal bp were highly significant however responses to climate changes seem regionally varied in time and strength demonstrating that local differences in vegetation and orography greatly influence the balance of precipitation and evapotranspiration climate changes that coincided in time with the medieval climate anomaly and little ice age were observed as wetter 1200 980 cal bp and drier 370 240 cal bp conditions probably caused by meridional shifts of westerlies

reconstructing palaeoclimatic variables from fossil pollen using boosted regression trees comparison and synthesis with other quantitative reconstruction methods abstract we test and analyse a new calibration method boosted regression trees brts in palaeoclimatic reconstructions based on fossil pollen assemblages we apply brts to multiple holocene and lateglacial pollen sequences from northern europe and compare their performance with two commonly used calibration methods weighted averaging regression wa and the modern analogue technique mat using these calibration methods and fossil pollen data we present synthetic reconstructions of holocene summer temperature winter temperature and water balance changes in northern europe highly consistent trends are found for summer temperature with a distinct holocene thermal maximum at ca 8000 4000 cal a bp with a mean t jja anomaly of ca 0 7 c at 6 ka compared to 0 5 ka we were unable to reconstruct reliably winter temperature or water balance due to the confounding effects of summer temperature and the great between reconstruction variability we find brts to be a promising tool for quantitative reconstructions from palaeoenvironmental proxy data brts show good performance in cross validations compared with wa and mat can model a variety of taxon response types find relevant predictors and incorporate interactions between predictors and show some robustness with non analogue fossil assemblages

last glacial maximum climate of the former soviet union and mongolia reconstructed from pollen and plant macrofossil data an improved concept of the best analogues method was used to reconstruct the last glacial maximum lgm climate from a set of botanical records from the former soviet union and mongolia terrestrial pollen and macrofossil taxa were grouped into broad classes plant functional types pfts defined by the ecological and climatic parameters used in the biome1 model pft scores were then calibrated in terms of modern climate using 1245 surface pollen spectra from eurasia and north america in contrast to individual taxa which exhibit great variability and may not be present in the palaeoassemblages even in suitable climates pfts are more characteristic of the vegetation types the modified method thus allows climate reconstruction at time intervals with partial direct analogues of modern vegetation e g the lgm at 18 kbp mean temperatures were 20 29 degrees c colder than today in winter and 5 11 degrees c colder in summer in european russia and ukraine sites from western georgia show negative but moderate temperature anomalies compared to today 8 11 degrees c in january and 5 7 degrees c in july lgm winters were 7 15 degrees c colder and summers were 1 7 degrees c colder in siberia and mongolia annual precipitation sums were 50 750 mm lower than today across northern eurasia suggesting a weakening of the atlantic and pacific influences reconstructed drought index shows much drier lgm conditions in northern and mid latitude russia but similar to or slightly wetter than today around the black sea and in mongolia suggesting compensation of precipitation losses by lower than present evaporation

quantifying the role of biosphere atmosphere feedbacks in climate change coupled model simulations for 6000 years bp and comparison with palaeodata for northern eurasia and northern africa the lmd agcm was iteratively coupled to the global biome1 model in order to explore the role of vegetation climate interactions in response to mid holocene 6000 y bp orbital forcing the sea surface temperature and sea ice distribution used were present day and co2 concentration was pre industrial the land surface was initially prescribed with present day vegetation initial climate anomalies differences between agcm results for 6000 y bp and control were used to drive biome1 the simulated vegetation was provided to a further agcm run and so on results after five iterations were compared to the initial results in order to identify vegetation feedbacks these were centred on regions showing strong initial responses the orbitally induced high latitude summer warming and the intensification and extension of northern hemisphere tropical monsoons were both amplified by vegetation feedbacks vegetation feedbacks were smaller than the initial orbital effects for most regions and seasons but in west africa the summer precipitation increase more than doubled in response to changes in vegetation in the last iteration global tundra area was reduced by 25 and the southern limit of the sahara desert was shifted 2 5 n north to 18 n relative to today these results were compared with 6000 y bp observational data recording forest tundra boundary changes in northern eurasia and savana desert boundary changes in northern africa although the inclusion of vegetation feedbacks improved the qualitative agreement between the model results and the data the simulated changes were still insufficient perhaps due to the lack of ocean surface feedbacks

late quaternary lake level record from northern eurasia lake records from northern eurasia show regionally coherent patterns of changes during the late quaternary lakes peripheral to the scandinavian ice sheet were lower than those today but lakes in the mediterranean zone were high at the glacial maximum reflecting the dominance of glacial anticyclonic conditions in northern europe and a southward shift of the westerlies the influence of the glacial anticyclonic circulation attenuated through the late glacial period and the westerlies gradually shifted northward such that drier conditions south of the ice sheet were confined to a progressively narrower zone and the mediterranean became drier the early holocene shows a gradual shift to conditions wetter than present in central asia associated with the expanded asian monsoon and in the mediterranean in response to local monsoon type circulation there is no evidence of mid continental aridity in northern eurasia during the mid holocene in contrast the circum baltic region was drier reflecting the increased incidence of blocking anticyclones centered on scandinavia in summer there is a gradual transition to modern conditions after ca 5000 yr b p although these broad scale patterns are interrupted by shorter term fluctuations the long term trends in lake behavior show a clear response to changes in insolation and glaciation

intercomparison of simulated global vegetation distributions in response to 6 kyr bp orbital forcing abstract the response of ten atmospheric general circulation models to orbital forcing at 6 kyr bp has been investigated using the biome model which predicts equilibrium vegetation distribution as a diagnostic several common features emerge a reduced tropical rain forest as a consequence of increased aridity in the equatorial zone b expansion of moisture demanding vegetation in the old world subtropics as a consequence of the expansion of the afro asian monsoon c an increase in warm grass shrub in the northern hemisphere continental interiors in response to warming and enhanced aridity and d a northward shift in the tundra forest boundary in response to a warmer growing season at high northern latitudes these broadscale features are consistent from model to model but there are differences in their expression at a regional scale vegetation changes associated with monsoon enhancement and high latitude summer warming are consistent with palaeoenvironmental observations but the simulated sh

late glacial to middle holocene climate and environmental changes as recorded in lake dood sediments darhad basin northern mongolia abstract the paper presents new data on climatic lake level and environmental changes in the darhad basin northern mongolia during the late glacial and early to middle holocene two cores dn1 and dn2 from lake dood were investigated using the following proxies grain size total carbon tc total inorganic carbon tic total organic carbon toc total nitrogen tn total sulfur ts 13c 18o and diatom our reconstructions indicate that dramatic climatic and environmental changes occurred several times since ca 14 ka cal bp a cold and dry climate of the late glacial changed to a relatively cold and wet climate starting around 9 5 ka cal bp in response to an early holocene humidization a generally warm and humid climate prevailed in the region at ca 7 8 5 8 ka cal bp later on after 5 8 ka cal bp the climate became cooler and drier the darhad paleolake the predecessor of lake dood disappeared during the late glacial to early holocene times and started to reappear since ca 9 5 ka cal bp lake dood fluctuated considerably in response to changes in precipitation or and in ground ice melting between 9 5 and 5 8 ka cal bp and started to decrease at 5 8 ka cal bp

holocene moisture evolution across the mongolian plateau and its surrounding areas a synthesis of climatic records abstract based on the review of 26 high standard holocene climatic reconstructions mainly pollen based from the mongolian plateau and its surrounding areas temporal and spatial patterns of the holocene moisture evolution are synthesized the regionally averaged moisture history from the summer monsoon influenced semiarid belt in china i e region a demonstrates that the moisture index curve is broadly in agreement with the synthesized east asian monsoon strength curve both following the general trend of the west tropical pacific sst that is in turn the delayed response to the northern hemispheric summer solar insolation the regionally averaged moisture indices from the winter monsoon dominated southern siberia including lake baikal area and the altai mountains i e region b exhibit a general declining trends since 10 6 9 6 cal kyr bp being largely consistent with the trends of the annual precipitation and the warm season temperature in the russian plain the consistency might be attributable to the holocene declining trend of the warm season temperature in north atlantic region the predominant feature of the regionally averaged moisture index from the westerlies affected northern xinjiang i e region c is a persistent increasing trend since 8 cal kyr bp the wetting trend of northern xinjiang during the past 8000 years might be attributable to the increasing trend of winter insolation and to the associated increasing trend of cold season temperature in northwestern europe the chronological correspondences between dry phases and warm intervals in the arid areas of the mongolian plateau i e northern mongolian plateau within mongolia and southern mongolian plateau within china region d lend a support to the proposal that the mid holocene dry phase was most likely the result of mid holocene high warm season temperature

climate in northern eurasia 6000 years ago reconstructed from pollen data using a climatic calibration based on the scores of the plant functional types pfts calculated for 1245 surface pollen spectra the climate at 6 ka bp has been reconstructed for a set of 116 pollen spectra from the former soviet union and mongolia the results are presented as maps of climatic anomalies and maps of probability classes showing the significance of these differences from the modern climate the reconstructed patterns are spatially coherent but have confidence levels that vary from region to region due to the often large error ranges at 6 ka the winters were more than 2oc warmer than today north of 50on with a high significance east of the urals summers were also more than 2oc warmer than today with a high level of confidence north of the polar circle and in central mongolia in the mid latitudes of siberia in northern kazakhstan and around the black and the caspian seas 6 ka summers were significantly cooler than today the reconstructed moisture availability ratio of actual to equilibrium evapotranspiration was more than 10 higher than today in the ukraine southern russia and northern mongolia and more than 10 lower than today in central mongolia this pattern corresponds partly with that of the water budget annual precipitation minus evaporation reconstructed from lake level records 1999 elsevier science b v all rights reserved

quantitative pollen based climate reconstruction in central japan application to surface and late quaternary spectra abstract climate reconstruction in japan by the best modern analogues method was tested with 285 surface pollen spectra and then applied to the 47 000 years pollen profile from lake mikata central japan both pollen taxa percentages and plant functional type affinity scores were used in the reconstruction of six climate variables the reconstructed values were compared with the estimated modern climate at each surface pollen site in order to evaluate the accuracy of the pollen based reconstruction the reconstruction of thermal parameters is very reliable correlation coefficient r between 0 86 and 0 89 the reconstruction of annual precipitation is less accurate r 0 7 we also proposed a new technique to calibrate reconstructed values into both probability distribution and or confidence regions of observed values the specialized programs for this calibration polcalib and polhist are available at qsr website http www elsevier nl locate quascirev the reconstruction of the late quaternary climate changes around lake mikata shows that the summer and winter temperatures were 5 c lower than present around 40 uncal kyr bp reached a minimum around 20 uncal kyr bp 10 c lower than present and became similar to present day at 8 uncal kyr bp the estimates for annual precipitation show that it was driest around 20 uncal kyr bp