3d seismic analysis of the coast shear zone in se alaska and western british columbia broadside analysis of accrete wide angle data abstract the multidisciplinary accrete project addresses the question of continental assemblage in southeast alaska and western british columbia by terrane accretion and magmatic addition the previous studies of this project yielded important information for understanding the structures across the coast shear zone csz and the formation of the csz and the coast mountains batholith cmb the present study extends these interpretations into pseudo 3 d by using two additional wide angle accrete seismic lines by analyzing the broadside wide angle data using a series of laterally homogeneous 2 d models we derive a lower resolution 3 d velocity model of the outboard terranes and constrain variations in crustal thickness across and along the csz models of the broadside data confirms major structural and compositional trends extend along strike to the northwest the key features are a a steep moho ramp only 15 km wide is coincident with the csz and divides thin 25 1 km crust to the west below the west vergent thrust belt wtb from thicker 31 1 km crust to the east below the cmb b low velocity mantle 7 7 7 9 km s extends beneath the entire study region indicating high crustal and upper mantle temperatures below the wtb and cmb and c the alexander terrane is characterized by strong mid crustal reflectivity and high lower crustal velocities that are consistent with gabbroic composition this study extends the earlier interpretation and implies that the ramp is indeed likely associated with transpressional tectonics and magmatic crustal addition east of the csz

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

changes in biological productivity along the northwest african margin over the past 20 000 years the intertropical convergence zone and the african monsoon system are highly sensitive to climate forcing at orbital and millennial timescales both systems influence the strength and direction of the trade winds along northwest africa and thus directly impact coastal upwelling sediment cores from the northwest african margin record upwelling related changes in biological productivity connected to changes in regional and hemispheric climate we present records of 230th normalized biogenic opal and corg fluxes using a meridional transect of four cores from 19 n 31 n along the northwest african margin to examine changes in paleoproductivity since the last glacial maximum we find large changes in biogenic fluxes synchronous with changes in eolian fluxes calculated using end member modeling suggesting that paleoproductivity and dust fluxes were strongly coupled likely linked by changes in wind strength opal and corg fluxes increase at all sites during heinrich stadial 1 and the younger dryas consistent with an overall intensification of the trade winds and changes in the meridional flux gradient indicate a southward wind shift at these times biogenic fluxes were lowest and the meridional flux gradients were weakest during the african humid period when the monsoon was invigorated due to precessional changes with greater rainfall and weaker trade winds over northwest africa these results expand the spatial coverage of previous paleoproxy studies showing similar changes and they provide support for modeling studies showing changes in wind strength and direction consistent with increased upwelling during abrupt coolings and decreased upwelling during the african humid period

millennial scale temperature variations in north america during the holocene 1 a mean continental july temperature reconstruction based on pollen records from across north america quantifies temperature variations of several timescales for the past 14 000 cal yr bp in north america temperatures increased nearly 4 c during the late glacial reaching maximum values between 6000 and 3000 cal yr bp after which mean july temperatures decreased superimposed on this orbital scale trend are millennial scale temperature variations that appear coherent in structure and frequency with highresolution ice marine and other terrestrial paleoclimate records of the holocene during the holocene climate in north america appears to have varied periodically every 1100 years rather than the 1500 year cycle found during the last glacial period coherence at frequencies between 900 and 1100 years between land ice and ocean records suggests a common forcing associated with widespread surface impacts during the holocene these results provide important insight to the global warming debate as the observed twentieth century temperature increase appears unprecedented compared to our mean north american temperature reconstruction of the past 14 000 years

the physics of wind blown loess implications for grain size proxy interpretations in quaternary paleoclimate studies abstract loess deposits are recorders of aeolian activity during past glaciations since the size distribution of loess deposits depends on distance to the dust source and environmental conditions at the source during transport and at deposition loess particle size distributions and derived statistical measures are widely used proxies in quaternary paleoenvironmental studies however the interpretation of these proxies often only considers dust transport processes to move beyond such overly simplistic proxy interpretations and toward proxy interpretations that consider the range of environmental processes that determine loess particle size distribution variations we provide a comprehensive review on the physics of dust particle mobilization and deposition furthermore using high resolution bulk loess and quartz grain size datasets from a last glacial interglacial sequence we show that because grain size distributions are affected by multiple often stochastic processes changes in these distributions over time allow multiple interpretations for the driving processes consequently simplistic interpretations of proxy variations in terms of only one factor e g wind speed are likely to be inaccurate nonetheless using loess proxies to understand temporal changes in the dust cycle and environmental parameters requires i a careful site selection to minimize the effects of topography and source distance and ii the joint use of bulk and quartz grain size proxies together with high resolution mass accumulation rate calculations if possible

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 and last interglacial cloudiness in eastern baffin island arctic canadathis article is one of a series of papers published in this special issue on the theme polar climate stability network geotop publication 2008 0027 this study presents last interglacial and holocene vegetation and climate changes at fog lake 67 11 n 63 15 w on eastern baffin island arctic canada the vegetation cover is reported as vegetat

integrated varve and pollen based temperature reconstruction from finland evidence for holocene seasonal temperature patterns at high latitudes a detailed understanding of decadal to millennial scale climate changes requires seasonal scale summer winter reconstructions of past precipitation and temperature fluctuations comparing seasonally resolved varve records with pollen based sum of growing degree days gdd reconstructions from lake nautajarvi we examined the intra annual nature of climate variability in central southern finland during the holocene the organic varve record and the gdd reconstruction show roughly comparable trends supporting the interpretation that both proxies predominantly reflect summer temperatures in the study area the records suggest low but rising early holocene 9500 to 8500 cal yr bp summer temperatures the holocene thermal maximum htm in the gdd record dates to about 7500 to 4500 cal yr bp but the organic varve record along with reconstructed changes in vegetation composition notably a peak of tilia pollen percentages indicate that during the htm there was a trend towards a more continental climate with maximum mid summer temperatures reached at 6500 to 4500 cal yr bp both records reflect the start of the post htm cooling at about 4500 cal yr bp simultaneously with an increase of the amount of catchment erosion and mineral matter influx into the lake suggesting gradually colder and or longer winters with high net accumulation of snow the organic varve record and the gdd record start to diverge at 2000 cal yr bp possibly owing to the human influence on catchment processes the reconstructed mid holocene summer temperature peak deviates from the regional climate model outputs which suggest highest summer temperatures during the early holocene

constraints on the magnitude and patterns of ocean cooling at the last glacial maximum observation based reconstructions of sea surface temperature from relatively stable periods in the past such as the last glacial maximum represent an important means of constraining climate sensitivity and evaluating model simulations1 the first quantitative global reconstruction of sea surface temperatures during the last glacial maximum was developed by the climate long range investigation mapping and prediction climap project in the 1970s and 1980s refs 2 3 since that time several shortcomings of that earlier effort have become apparent4 here we present an updated synthesis of sea surface temperatures during the last glacial maximum rigorously defined as the period between 23 and 19 thousand years before present from the multiproxy approach for the reconstruction of the glacial ocean surface margo project5 we integrate microfossil and geochemical reconstructions of surface temperatures and include assessments of the reliability of individual records our reconstruction reveals the presence of large longitudinal gradients in sea surface temperature in all of the ocean basins in contrast to the simulations of the last glacial maximum climate available at present6 7

quantitative reconstructions of annual rainfall in africa 6000 years ago model data comparison precipitation are based on 85 pollen sites 14 c dated at 6000 500 years b p and distributed over the whole of africa to improve the reliability of the pollen based climate reconstruction two methods are used the modern analogues technique mat and the plant functional types pft methods we then conduct a model data comparison for five distinct regions allowing an evaluation of model outputs the sahara sahel the eastern sahara western equatorial africa east africa and madagascar the pollen inferred reconstructions are compared with 21 mid holocene simulations yielded by atmospheric general circulation models agcms and coupled ocean atmosphere vegetation models oavgcms the large scale feature of the hydrological changes is shown to be well captured by most of the models data show that during the mid holocene the sahara was considerably wetter than today 200 to 700 mm yr the results reinforce the conclusion that the agcms significantly underestimate this precipitation increase in the sahara whereas the oavgcm simulations are in accordance with the data our results show that vegetation and ocean feedbacks do not have a strong impact in the intertropical zone and that models fail to properly reproduce the climatic conditions in east africa and madagascar the model data comparison also suggests that the lengthening of the dry season during boreal winter in the west equatorial region is a robust feature although the pollen based reconstruction shows no change or only slight drying there

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

tropical climates at the last glacial maximum a new synthesis of terrestrial palaeoclimate data i vegetation lake levels and geochemistry palaeodata in synthesis form are needed as benchmarks for the palaeoclimate modelling intercomparison project pmip advances since the last synthesis of terrestrial palaeodata from the last glacial maximum lgm call for a new evaluation especially of data from the tropics here pollen plant macrofossil lake level noble gas from groundwater and delta 18 o from speleothems data are compiled for 18 2 ka c 14 32 degrees n 33 degrees s the reliability of the data was evaluated using explicit criteria and some types of data were re analysed using consistent methods in order to derive a set of mutually consistent palaeoclimate estimates of mean temperature of the coldest month mtco mean annual temperature mat plant available moisture pam and runoff p e cold month temperature mat anomalies from plant data range from 1 to 2 k near sea level in indonesia and the s pacific through 6 to 8 k at many high elevation sites to 8 to 15k in s china and the se usa mat anomalies from groundwater or speleothems seem more uniform 4 to 6 k but the data are as yet sparse a clear divergence between mat and cold month estimates from the same region is seen only in the se usa where cold air advection is expected to have enhanced cooling in winter regression of all cold month anomalies against site elevation yielded an estimated average cooling of 2 5 to 3 k at modern sea level increasing to approximate to 6 k by 3000m how ever neotropical sites showed larger than the average sea level cooling 5 to 6 k and a non significant elevation effect whereas w and s pacific sites showed much less sea level cooling 1 k and a stronger elevation effect these findings support the inference that tropical sea surface temperatures ssts were lower than the climap estimates but they limit the plausible average tropical sea surface cooling and they support the existence of climap like geographic patterns in sst anomalies trends of pam and lake levels indicate wet lgm conditions in the w usa and at the highest elevations with generally dry conditions elsewhere these results suggest a colder than present ocean surface producing a weaker hydrological cycle more arid continents and arguably steeper than present terrestrial lapse rates such linkages are supported by recent observations on freezing level height and tropical ssts moreover simulations of greenhouse and lgm climates point to several possible feedback processes by which low level temperature anomalies might be amplified aloft

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

improving past sea surface temperature estimates based on planktonic fossil faunas a new method of past sea surface temperature sst reconstruction based on the modern analog technique prell 1985 and on the indirect approach bartlein et al 1986 has been developed the revised analog method ram applied to planktonic foraminifera this technique leads to significant improvements in modern sst reconstruction with respect to former methods our estimates are characterized by much lower residuals and a better coverage of the observed sst range moreover the error of ram estimates of past ssts is lower than that associated with former reconstructions particularly at middle and high latitudes in low latitudes cold season ssts reconstructed by ram during glacials are 1 3 c lower than previously estimated our results tend thus to reconcile paleoestimates of glacial temperatures based on planktonic microfossils and on continental data in the tropics

rapid and widespread vegetation responses to past climate change in the north atlantic region ongoing anthropogenic perturbations to the atmosphere and biosphere increase the risk of future abrupt changes in the climate system and generate concern about the ability of natural ecosystems to respond to rapid climate change study of past climatic events and biotic responses can inform us about potential future change qualitatively fast local responses of plant taxa to abrupt late glacial climate oscillations have been reported from individual records and attributed to short migration distances in areas of high topographic relief by using quantitative time series analyses we show that vegetation responses to late glacial climate change around the north atlantic were rapid and widespread and occurred in areas of differing relief cross correlation analysis of 11 high resolution lacustrine records in eastern north america and europe indicates vegetation response times consistently of 200 yr and often 100 yr despite regional differences in physiography and species composition vegetation lags of 200 yr confirm theoretical predictions and the apparently tight coupling between vegetation and atmosphere suggests that recent climatic trends may already have begun to affect plant population abundances and distributions

the climate in europe during the eemian a multi method approach using pollen data the last interglacial period the eemian offers a testbed for comparing climate evolution throughout an interglacial with the current warm period we present here results from climatic reconstructions from 17 sites distributed across the european continent allowing an assessment of trends and regional averages of climate changes during this period we use a multi method approach to allow for an improved assessment of the uncertainties involved in the reconstruction in addition the method takes into account the errors associated with the age model the resulting uncertainties are large but allow a more robust assessment of the reconstructed climatic variations than in previous studies the results show a traditional three part eemian with an early optimum followed by slight cooling and eventually a sharp drop in both temperatures and precipitation this sequence is however restricted to the north as this latter change is not observed in the south where temperatures remain stable for longer these variations led to marked variation in the latitudinal temperature gradient during the eemian the difference between the two regions is also noticeable in the magnitude of changes with greater variations in the north than the south some evidence is found for changes in lapse rates however a greater number of sites is needed to confirm this

parallel climate and vegetation responses to the early holocene collapse of the laurentide ice sheet parallel changes in lake level and pollen data show that the rapid decline of the laurentide ice sheet lis between 10 000 and 8000 cal yr bp triggered a step like change in north american climates from an ice sheet and insolation dominated climate to a climate primarily controlled by insolation maps of the lake level data from across eastern north america show a reorganization of climate patterns that the pollen data independently match raised lake levels and expanded populations of moist tolerant southern pines pinus document that summer monsoons intensified in the southeastern united states between 9000 and 8000 cal yr bp simultaneously low lake levels and an eastward expansion of the prairie illustrate an increase in mid continental aridity after the hudson bay ice dome collapsed around 8200 cal yr bp lake levels rose in new england as populations of mesic plant taxa such as beech fagus and hemlock tsuga replaced those of dry tolerant northern pines pinus available moisture increased there after a related century scale period of colder than previous conditions around 8200 cal yr bp which is also recorded in the pollen data the comparison between pollen and lake level data confirms that vegetations dynamics reflect climatic patterns on the millennial scale

vegetation and environment in eastern north america during the last glacial maximum abstract knowledge of the vegetation and environment of eastern north america during the last glacial maximum lgm is important to understanding postglacial vegetational and biogeographic dynamics assessing climate sensitivity and constraining and evaluating earth system models our understanding of lgm conditions in the region has been hampered by low site density problems of data quality particularly dating and the possibility that lgm vegetation and climate lacked modern analogs in order to generate improved reconstructions of lgm vegetation and environment we assembled pollen and plant macrofossil data from 21 and 17 well dated lgm sites respectively all sites have assemblages within the lgm timespan of 21 000 1500 calendar yr bp based on these data we prepared maps of isopolls macrofossil presence absence pollen analogs biomes inferred mean january and july temperatures and mean annual precipitation for the lgm tundra and open picea dominated forest grew along the laurentide ice sheet with tundra predominantly in the west in the east pinus dominated vegetation mainly p banksiana with local p resinosa and p strobus occurred extensively to 34 n and possibly as far south as 30 n picea glauca and a now extinct species p critchfieldii occurred locally picea dominated forest grew in the continental interior with temperate hardwoods quercus carya juglans liriodendron fagus ulmus growing locally near the lower mississippi valley at least as far north as 35 n picea critchfieldii was the dominant species in this region the florida peninsula was occupied by open vegetation with warm temperate species of pinus eastern texas was occupied by open vegetation with at least local quercus and picea extensive areas of peninsular florida and the continental interior had vegetation unmatched by any modern pollen samples the paleovegetational data indicate more extensive cooling in eastern north america at the lgm than simulated by either the ncar ccm0 or ccm1 climate models the occurrence of cool temperate conifers and hardwoods as far north as 34 35 n however indicates less severe cooling than some previous reconstructions paleoclimate inferences for the lgm are complicated by lowered atmospheric co 2 concentrations which may be responsible for the open nature and dominance of conifers in lgm vegetation

expanded response surfaces a new method to reconstruct paleoclimates from fossil pollen assemblages that lack modern analogues pollen based paleoclimatic interpretations of late glacial to early holocene climates 17 9 ka in midwestern north america are hampered by samples that lack modern analogues unresolved questions include the magnitude and direction of temperature seasonality i e were these climates more or less seasonal than present and the temporal changes in precipitation central to the no analogue problem is the truncation of modern pollen climate relationships for abundant late glacial taxa such as fraxinus here we present a new method called the expanded response surface ers method developed to reconstruct climates from no analogue pollen assemblages and applied to a high resolution late glacial pollen record from crystal lake illinois to test hypotheses about late glacial climates the key assumptions central to the ers method are 1 plant species and pollen abundances follow symmetrical unimodal distributions along climatic gradients 2 taxa with truncated distributions in modern climate space occupy a subset of their fundamental niche and 3 expansion of truncated distributions by mirroring around the distributional mode recovers the portion of the fundamental niche not realized in the modern climate space with the ers method we expanded modern pollen climate relationships by mirroring pollen abundances for each taxon around a mode defined with respect to four climate axes mean winter temperature mean summer temperature mean winter precipitation and mean summer precipitation the ers method reconstructed past temperatures and precipitation during the height of no analogue conditions 14 160 12 370 cal yr bp for 37 of the crystal lake samples where techniques that employed only modern observational data found matches for only 13 of the fossil samples the total climate space of the expanded taxa set allowed analogue matches under more seasonal than present climates with higher than present precipitation the ers climate reconstructions for the height of no analogue conditions indicated cooler than present summer and winter temperatures similar to present seasonal range in temperatures higher than present winter precipitation and similar to present summer precipitation these results thus suggest that high moisture availability helped drive the formation of the midwestern no analogue communities with high fraxinus nigra abundances but do not show higher than present temperature seasonality notwithstanding the higher than present insolation seasonality at this time during the no analogue late glacial interval picea mariana f nigra and larix stands probably grew on low lying poorly drained soils in the crystal lake region whereas abies picea glauca quercus and ostrya carpinus grew on upland positions with better soil drainage

holocene climatic change in the northern midwest pollen derived estimates mapping of holocene pollen data in the midwestern united states has revealed several broadscale vegetational changes that can be interpreted in climatic terms these changes include 1 the early holocene northward movement of the spruce dominated forest and its later southward movement after 3000 yr b p and 2 the eastward movement of the prairie forest border into southwestern wisconsin by 8000 yr b p and its subsequent westward retreat after 6000 yr b p when certain basic assumptions are met multiple regression models can be derived from modern pollen and climate data and used to transform the pollen record of these vegetational changes into quantitative estimates of temperature or precipitation to maximize the reliability of the regression equations we followed a sequence of procedures that minimize violations of the assumptions that underlie regression analysis reconstructions of precipitation during the holocene indicated that from 9000 to 6000 yr b p precipitation decreased by 10 to 25 over much of the midwest while mean july temperature increased by 0 5 to 2 0 c at 6000 yr b p precipitation was less than 80 of its modern values over parts of wisconsin and minnesota after 6000 yr b p precipitation generally increased while mean july temperature decreased in the north and increased in the south the time of the maximum temperature varies within the midwest and is earlier in the north and later in the south

reconstructing millennial scale regional paleoclimates of boreal canada during the holocene abstract regional paleoclimate reconstructions for northern canada quantify holocene climate variability on orbital and millennial time scales and provide a context to better understand the current global warming the reconstructions are based on available pollen diagrams from the boreal and low arctic zones of canada and use the modern analog technique mat four regional reconstructions document the space time evolution of the climate during the holocene highest summer and winter temperatures anomalies are found in central canada during the early holocene eastern canada was relatively cool in the early holocene whereas central canada was warmest at that time labrador was relatively dry in the early to mid holocene during which time western canada was relatively moist millennial scale temperature variations especially the medieval warm period and little ice age are seen across the continent with some suggestion of time transgressive changes from west to east at the millennial scale precipitatio

the climate of north america and adjacent ocean waters ca 6 ka the climate of north america and the adjacent ocean at 6000 bp was estimated using five independent approaches using pollen data the terrestrial climate was estimated by the movement of ecozone boundaries and by the method of modern analogues both analyses indicate warmer temperatures in the western great lakes area and the northern great plains a model of sphagnum dominated peatland initiation when forced by canadian climate model 6 ka output projected a cooler and or wetter climate for continental western north america contrary to this a reconstruction of the distribution of sphagnum dominated peatlands in western canada indicates that they were located north of their modern distribution suggesting warmer and or drier conditions at 6000 bp this interpretation is strengthened by observations of lower lake levels at 6000 bp in western canada this drier climate may have been associated with warmer conditions as indicated by the quantitative climate reconstructions in general eastern north a

holocene climate of the kola peninsula evidence from the oxygen isotope record of diatom silica holocene climate variability was studied in a lake sediment record covering the last c 9000 years from lake chuna on the kola peninsula north west russia using the oxygen isotope composition of diatom silica 18odiatom the evaporation of the lake waters is likely to be minimal and thus the isotopic composition of the lake waters recorded by the 18odiatom reflects the isotopic composition of summer precipitation overall the 18odiatom signal seems to record a predominance of the polar arctic air mass bringing cold summer air temperatures immediately after the last glaciation and again after 4000 years to present time the atlantic maritime air mass is likely to have supplied warm summer rainfall especially in the mid holocene the pattern is broadly consistent with a quantitative pollen reconstruction from chuna lake which suggests higher mean july temperatures from deglaciation to 5500 years bp with a rather steep decline to lower temperatures after 4000 years bp our results support the general regional scenario of a mid holocene warm period deduced from the higher tree line vegetation changes and glacier fluctuations in fennoscandia however the 18odiatom record from the kola peninsula suggests a relatively cold early holocene with a gradual shift to warmer conditions to a maximum at around 5000 4000 years bp assuming that the modern precipitation temperature relationship has been constant throughout the holocene

quantitative estimates of glacial and holocene temperature and precipitation change in lowland amazonian bolivia quantitative estimates of temperature and precipitation change during the late pleistocene and holocene have been difficult to obtain for much of the lowland neotropics using two published lacustrine pollen records and a climate vegetation model based on the modern abundance distributions of 154 neotropical plant families we demonstrate how family level counts of fossil pollen can be used to quantitatively reconstruct tropical paleoclimate and provide needed information on historic patterns of climatic change with this family level analysis we show that one area of the lowland tropics northeastern bolivia experienced cooling 1 3 c and drying 400 mm yr relative to present during the late pleistocene 50 000 12 000 calendar years before present cal yr b p immediately prior to the last glacial maximum lgm ca 21 000 cal yr b p we observe a distinct transition from cooler temperatures and variable precipitation to a period of warmer temperatures and relative dryness that extends to the middle holocene 5000 3000 cal yr b p this prolonged reduction in precipitation occurs against the backdrop of increasing atmospheric co2 concentrations indicating that the presence of mixed savanna and dry forest communities in northeastern bolivia durng the lgm was not solely the result of low co2 levels as suggested previously but also lower precipitation the results of our analysis demonstrate the potential for using the distribution and abundance structure of modern neotropical plant families to infer paleoclimate from the fossil pollen record

two terrestrial records of rapid climatic change during the glacial holocene transition 14 000 9 000 calendar years b p from europe two independent multidisciplinary studies of climatic change during the glacial holocene transition ca 14 000 9 000 calendar yr b p from norway and switzerland have assessed organism responses to the rapid climatic changes and made quantitative temperature reconstructions with modern calibration data sets transfer functions chronology at krakenes western norway was derived from calibration of a high resolution series of 14c dates chronologies at gerzensee and leysin switzerland were derived by comparison of 18o in lake carbonates with the 18o record from the greenland ice core project both studies demonstrate the sensitivity of terrestrial and aquatic organisms to rapid temperature changes and their value for quantitative reconstruction of the magnitudes and rates of the climatic changes the rates in these two terrestrial records are comparable to those in greenland ice cores but the actual temperatures inferred apply to the terrestrial environments of the two regions

could gradual changes in holocene saharan landscape have caused the observed abrupt shift in north atlantic dust deposition abstract the abrupt change in north atlantic dust deposition found in sediment records has been associated with a rapid large scale transition of holocene saharan landscape we hypothesize that gradual changes in the landscape may have caused this abrupt shift in dust deposition either because of the non linearity in dust activation or because of the heterogeneous distribution of major dust sources to test this hypothesis we investigate the response of north atlantic dust deposition to a prescribed 1 gradual and spatially homogeneous decrease and 2 gradual southward retreat of north african vegetation and lakes during the holocene using the aerosol climate model echam ham in our simulations we do not find evidence of an abrupt increase in dust deposition as observed in marine sediment records along the northwest african margin we conclude that such gradual changes in landscape are not sufficient to explain the observed abrupt changes in dust accumulation in marine sediment records instead our results point to a rapid large scale retreat of vegetation and lakes in the area of significant dust sources

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 variability at the southern boundaries of the namib southwestern africa and atacama northern chile coastal deserts during the last 120 000 yr abstract in this study we present grain size distributions of the terrigenous fraction of two deep sea sediment cores from the se atlantic offshore namibia and from the se pacific offshore northern chile which we unmix into subpopulations and which are interpreted as coarse eolian dust fine eolian dust and fluvial mud the downcore ratios of the proportions of eolian dust and fluvial mud subsequently represent paleocontinental aridity records of southwestern africa and northern chile for the last 120 000 yr the two records show a relatively wet last glacial maximum lgm compared to a relatively dry holocene but different orbital variability on longer time scales generally the northern chilean aridity record shows higher frequency changes which are closely related to precessional variation in solar insolation compared to the southwestern african aridity record which shows a remarkable resemblance to the global ice volume record we relate the changes in continental aridity in southwestern africa and northern chile to changes in the latitudinal position of the moisture bearing southern westerlies potentially driven by the sea ice extent around antarctica and overprinted by tropical forcing in the equatorial pacific ocean

the global monsoon as seen through the divergent atmospheric circulation a comprehensive description is given of the global monsoon as seen through the large scale overturning in the atmosphere that changes with the seasons and it provides a basis for delimiting the monsoon regions of the world the analysis focuses on the mean annual cycle of the divergent winds and associated vertical motions as given by the monthly mean fields for 1979 93 reanalyses from the national centers for environmental prediction national center for atmospheric research ncep ncar and european centre for medium range weather forecasts ecmwf which are able to reproduce the dominant modes a complex empirical orthogonal function analysis of the divergent circulation brings out two dominant modes with essentially the same vertical structures in all months of the year the first mode which depicts the global monsoon has a simple vertical structure with a maximum in vertical motion at about 400 mb divergence in the upper troposphere that is strongest at 150 mb and decays to zero amplitude above 70 mb and convergence in the lower troposphere with a maximum at 925 mb ecmwf or 850 mb ncep however this mode has a rich three dimensional spatial structure that evolves with the seasons it accounts for 60 of the annual cycle variance of the divergent mass circulation and dominates the hadley circulation as well as three overturning transverse cells these include the pacific walker circulation an americas atlantic walker circulation both of which comprise rising motion in the west and sinking in the east and a transverse cell over asia the middle east north africa and the indian ocean that has rising motion in the east and sinking toward the west these exist year round but migrate and evolve considerably with the seasons and have about a third to half of the mass flux of the peak hadley cell the annual cycle of the two hadley cells reveals peak strength in early february and early august in both reanalyses a second monsoon mode which accounts for 20 of the variance features relatively shallow but vigorous overturning with the maximum vertical velocities near 800 mb outflow from 750 to 350 mb and inflow peaking at 925 mb it is especially strong over africa where the shallow mostly meridional overturning migrates back and forth across the equator with the seasons it influences the middle east has a signature over australia and is also an important component of the overturning in the tropical eastern pacific and atlantic and thus of the convergence zones in these regions the relationship of the global monsoon to the regional monsoons is described over six zonal sectors africa australia asia north america south america and the pacific and atlantic oceans only the two ocean areas do not undergo a seasonal reversal required for monsoons although they have direct overturning cells and they nevertheless participate in the global monsoon through the changes in large scale overturning the regional meridional cross sections highlight the importance of the shallow overturning cell in lower troposphere monsoon activity the steadiness of the overturning circulation is determined by comparing the signal of the seasonal mean vertical motions at 500 mb with the standard deviation of the transient daily variations locations where this signal exceeds 60 of the daily noise correspond closely with the regional centers of the monsoon

temperature variability and vertical vegetation belt shifts during the last 50 000 yr in the qilian mountains ne margin of the tibetan plateau china abstract a 13 94 m long sediment core collected from a medium sized lake in the qilian mountains ne tibetan plateau china was analysed palynologically at 81 horizons the interpretation of indicator taxa yielded various vertical shifts of the vegetation belts these palaeovegetation results have been checked with lake surface pollen spectra from 8 lakes representing different altitudinal vegetation belts our main findings are the following a short period of the late marine isotope stage 3 around 46 000 yr ago was characterized by interglacial temperature conditions with a tree line above its present day altitude during the lgm the vicinity of the lake was not covered by ice but by sparse alpine vegetation and alpine deserts indicating that the climate was colder by 4 7 c than today markedly higher temperatures were inferred from higher arboreal pollen frequencies between 13 000 and 7 000 yr ago with a holocene temperature optimum and a maximal picea betula mixed forest expansion between 9 000 and 7000 yr ago when temperatures exceeded the present day conditions by at least 1 2 c alpine steppes and meadows and sub alpine shrub vegetation dominated around the lake since the middle holocene suggesting that vegetation and climate conditions were exceptionally stable in comparison to previous periods

pollen derived rainfall and temperature estimates from lake tanganyika and their implication for late pleistocene water levels abstract palaeoclimatic estimates of mean annual temperature and rainfall in the southern tanganyika basin between 25 000 and 9000 yr b p have been established from two pollen sequences based on the best analogue method the results give evidence of a mean temperature decrease of about 4 2 c during the last glaciation a value consistent with that previously obtained in the catchment area on the burundi highlands this cooling was synchronous with a decrease of mean annual precipitation of about 180 mm yr postglacial climatic conditions were established by 12 700 yr b p with warming and wetness continuing to increase from this date onward these new palaeoclimatic data will be useful for hydrological reconstructions of lake tanganyika particularly during the last glacial age for which the magnitude of water level fall has been a controversial issue our rainfall estimates are more consistent with low values 250 to 300 m fall than with high ones 600 m previously proposed

paleoclimate simulations for north america over the past 21 000 years features of the simulated climate and comparisons with paleoenvironmental data maps of upper level and surface winds and of surface temperature and precipitation illustrate the results of a sequence of global paleoclimatic simulations spanning the past 21 000 years for north america we review a the large scale features of circulation temperature and precipitation that appear in the simulations from the ncar community climate model version 1 ccm 1 b the implications of the simulated climate for the past continental scale distributions of three plant taxa picea spp pseudotsuga menziesii and artemisia tridentata which are broadly representative of the vegetation across the continent and c the potential explanations in terms of atmospheric circulation or surface energy and water balance processes for mismatches between the simulations and observations most of the broad scale features of previous paleoclimatic simulations with the ncar ccm 0 for north america are present in the current simulations many of the elements of a conceptual model based on previous climate simulations that describes the controls of paleoclimatic variations across north america during the past 21 000 years are found in simulations reviewed here these include 1 displacement of the jet stream by the laurentide ice sheet to the south of its present position in both winter and summer 2 generation of a glacial anticyclone over the ice sheet at the lgm and the consequent induction of large scale sinking motions induced over eastern north america 3 changes in the strength of surface atmospheric circulation features through time including weakening of the aleutian low in winter and strengthening of the eastern pacific and bermuda high pressure systems in summer as the ice sheet decreased in size 4 development of a heat low at the surface and a strengthened ridge in the upper atmosphere over the continent at the time of the maximum summer insolation anomaly 5 increases in summer temperature earlier in regions remote from the ice sheet these increases appear earlier in the present ccm 1 simulations than in the previous ccm 0 ones however and 6 continuation of negative winter temperature anomalies into the middle holocene in general simulated surface conditions that are discordant with paleoenvironmental observations can be attributed to the simulation of particular atmospheric circulation patterns e g those that suppress precipitation or advect warm air into a region with these mismatches amplified in beringia and the southeastern united states by surface energy and water balance processes

palaeoprecipitation reconstruction by inverse modelling using the isotopic signal of loess organic matter application to the nusloch loess sequence rhine valley germany a modified version of the biome4 vegetation model for simulation of the mean 13c of plant communities is presented and used to reconstruct palaeoprecipitation we treat all fractionations by c3 and c4 plants in all coexistent plant functional types weighted by their respective net primary production we constrain the range of variation in the intracellular versus atmospheric co2 concentration by fixing a lower limit finally we replace some constant parameters by functions of external forcing to account for their responses to environmental variation the new version of biome4 was applied as an inverse model and tested on three modern data sets the fit between observations and simulations is very close to the 1 1 relationship with respective slopes of 0 90 0 02 r2 0 98 n 29 for 13c and 0 97 0 06 r2 0 90 n 29 for precipitation inverse modelling was applied using the metropolis hastings algorithm to the nusloch loess sequence over the last glaciation simulated palaeoprecipitation varies between 240 mm year 1 and 400 mm year 1 this study clearly demonstrates atmospheric teleconnections with the greenland ice sheet extension by matching dansgaard oeschger events with precipitation increase of ca 100 200 mm year 1

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

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

construction of the adjoint mit ocean general circulation model and application to atlantic heat transport sensitivity we first describe the principles and practical considerations behind the computer generation of the adjoint to the massachusetts institute of technology ocean general circulation model gcm using r giering s software tool tangent linear and adjoint model compiler tamc the tamc s recipe for fortran line by line generation of adjoint code is explained by interpreting an adjoint model strictly as the operator that gives the sensitivity of the output of a model to its input then the sensitivity of 1993 annual mean heat transport across 29on in the atlantic to the hydrography on january 1 1993 is calculated from a global solution of the gcm the kinematic sensitivity to initial temperature variations is isolated showing how the latter would influence heat transport if they did not affect the density and hence the flow over 1 year the heat transport at 29on is influenced kinematically from regions up to 20 o upstream in the western boundary current and up to 5 o upstream in the interior in contrast the dynamical influences of initial temperature and salinity perturbations spread from as far as the rim of the labrador sea to the 29on section along the western boundary the sensitivities calculated with the adjoint compare excellently to those from a perturbation calculation with the dynamical model perturbations in initial interior salinity influence meridional overturning and heat transport when they have propagated to the western boundary and can thus influence the integrated east west density difference our results support the notion that boundary monitoring of meridional mass and heat transports is feasible

mid holocene climates of the americas a dynamical response to changed seasonality simulations of the climatic response to mid holocene 6 ka bp orbital forcing with two coupled ocean atmosphere models foam and csm show enhancement of monsoonal precipitation in parts of the american southwest central america and northernmost south america during northern hemisphere summer the enhanced onshore flow that brings precipitation into central america is caused by a northward displacement of the inter tropical convergence zone driven by cooling of the equatorial and warming of the northern subtropical and mid latitude ocean ocean feedbacks also enhance precipitation over the american southwest although the increase in monsoon precipitation there is largely driven by increases in land surface temperature the northward shift in the equatorial precipitation band that causes enhanced precipitation in central america and the american southwest has a negative feedback effect on monsoonal precipitation in northern south america the simulations demonstrate that mid holocene aridity in the mid continent of north america is dynamically linked to the orbitally induced enhancement of the summer monsoon in the american southwest with a spatial structure wet in the southwest and dry in the mid continent similar to that found in strong monsoon years today changes in winter precipitation along the west coast of north america in central america and along the gulf coast caused by southward displacement of the westerly storm tracks indicate that changes in the northern hemisphere winter monsoon also play a role in regional climate changes during the mid holocene although the simulations with foam and csm differ in detail the general mechanisms and patterns are common to both the model results thus provide a coherent dynamical explanation for regional patterns of increased or decreased aridity shown by vegetation lake status and aeolian data from the americas

massive perturbation in terrestrial ecosystems of the eastern mediterranean region associated with the 8 2 kyr b p climatic event the climatic perturbation at ca 8 2 kyr b p is the strongest short term climate anomaly within the holocene it is generally attributed to a meltwater induced slowdown of the thermohaline circulation in the north atlantic model simulations and available proxy data suggest that it was strongest in the high to middle latitudes around the north atlantic based on new pollen data from tenaghi philippon northeastern greece we provide evidence for a massive climate induced turnover in terrestrial ecosystems of the aegean region associated with the 8 2 kyr b p event the reconstructed winter temperature decline of 4 c is much stronger than suggested by model simulations and proxy data from more northern latitudes of europe although the latter provide a direct downstream response to a north atlantic thermohaline circulation slowdown we attribute this discrepancy to mesoclimatic effects a stronger influence of the siberian high during the 8 2 kyr b p event may have enhanced the katabatic air flow from the mountains bordering the study site via a larger longer persisting snow cover our data demonstrate that high amplitude temperature anomalies and increased seasonality connected to the 8 2 kyr b p event may also have occurred in the lower mid latitudes much farther south than previously thought the magnitudes of these anomalies appear to have been strong enough to have seriously affected neolithic settlers in the northeastern mediterranean region

comparison of north american pollen based temperature and global lake status with cccma agcm2 output at 6 ka abstract we present new paleoclimate reconstructions for the time period of 6000 yr bp 6 ka that permit a quantitative comparison to corresponding mapped patterns of the newest version of the canadian cccma agcm2 climate model july temperature reconstructions were estimated using the modern analog technique employing fossil pollen records from the north american pollen database we present a new method of optimizing critical choices within the application of the mat through modern calibration the pattern of 6 ka temperature anomalies generated by the cccma agcm2 generally agree with those of the pollen based reconstruction particularly in the presence of a band of positive temperature anomalies across the continent from the yukon through the great lakes region and along the st lawrence this agreement suggests that both the model and data are reconstructing a contraction in the polar vortex over north america at 6 ka major areas of disagreement between the pollen based reconstruction and model simulation are also areas where the data are sparse and edge effects produce less reliable reconstructions the cccma agcm2 simulates drier conditions in a west east band stretching from alaska through the canadian prairies and midwest united states in agreement with low lake level observations at 6 ka simulated and reconstructed precipitation evaporation are also in agreement over the southwest united states with the exception of north central africa the cccma agcm2 fails to capture the northward and eastern extension of the afro asian monsoon belt at 6 ka general agreement between cccma agcm2 p e anomalies and lake status change is found throughout europe at 6 ka

the climate in western europe during the last glacial interglacial cycle derived from pollen and insect remains using the pollen sequence of la grande pile xx france we review problems with the application of transfer functions in paleoclimatic reconstructions one of them is to find modern analogues for the herbaceous vegetation of the cold periods we propose a method to distinguish between steppes and tundra vegetations for which the moderns are only partial analogues of the glacial periods another method to solve these problems is based on constraining by insect remains the two methods provide coherent reconstructions the results are also compared with other paleodata there is a good correlation with the six cold heinrich events between 70 and 15 ka b p a cooling event during the eemian period marked by high percentages of taxas at about 125 ka b p needs still to be correlated with high resolution ocean and ice cores

pollen plant macrofossil and charcoal records for palaeovegetation reconstruction in the mediterranean black sea corridor since the last glacial maximum new reconstructions of changing vegetation patterns in the mediterranean black sea corridor since the last glacial maximum are being produced by an improved biomisation scheme that uses both pollen and plant macrofossil data in conjunction changes in fire regimes over the same interval will also be reconstructed using both microscopic and macroscopic charcoal remains these reconstructions will allow a diagnosis of the interactions between climate fire and vegetation on millennial timescales and will also help to clarify the role of coastline and other geomorphic changes salinity and impacts of human activities in this region these new data sets are being produced as a result of collaboration between the palynology working group wg 2 within the igcp 521 project and the international palaeovegetation mapping project biome 6000 the main objective of this paper is to present the goals of this cooperation methodology including limitations and planned improvements and to show the initial results of some applications

high resolution modelling closes the gap between data and model simulations for mid holocene and present day biomes of east africa abstract east africa hosts a striking diversity of terrestrial ecosystems which vary both in space and time due to complex regional topography and a dynamic climate the structure and functioning of these ecosystems under this environmental setting can be studied with dynamic vegetation models dvms in a spatially explicit way yet regional applications of dvms to east africa are rare and a comprehensive validation of such applications is missing here we simulated the present day and mid holocene vegetation of east africa with the dvm lpj guess and we conducted an exhaustive comparison of model outputs with maps of potential modern vegetation distribution and with pollen records of local change through time overall the model was able to reproduce the observed spatial patterns of east african vegetation to see whether running the model at higher spatial resolutions 10 10 contribute to resolve the vegetation distribution better and have a better comparison scale with the observational data i e pollen data we run the model with coarser spatial resolution 0 5 0 5 for the present day as well both the area and point wise comparison showed that a higher spatial resolution allows to better describe spatial vegetation changes induced by the complex topography of east africa our analysis of the difference between modelled mid holocene and modern day vegetation showed that whether a biome shifts to another is best explained by both the amount of change in precipitation it experiences and the amount of precipitation it received originally we also confirmed that tropical forest biomes were more sensitive to a decrease in precipitation compared to woodland and savanna biomes and that holocene vegetation changes in east africa were driven not only by changes in annual precipitation but also by changes in its seasonality

simulated climate and biomes of africa during the late quaternary comparison with pollen and lake status data new compilations of african pollen and lake data are compared with climate ccm1 ncar boulder and vegetation biome 1 2 gsg lund simulations for the last glacial maximum lgm and early to mid holocene emh the simulated lgm climate was ca 4 c colder and drier than present with maximum reduction in precipitation in semi arid regions biome simulations show lowering of montane vegetation belts and expansion of southern xerophytic associations but no change in the distribution of deserts and tropical rain forests the lakes show lgm conditions similar or drier than present throughout northern and tropical africa pollen data indicate lowering of montane vegetation belts the stability of the sahara and a reduction of rain forest the paleoenvironmental data are consistent with the simulated changes in temperature and moisture budgets although they suggest the climate model underestimates equatorial aridity emh simulations show temperatures slightly less than present and increased monsoonal precipitation in the eastern sahara and east africa biome simulations show an upward shift of montane vegetation belts fragmentation of xerophytic vegetation in southern africa and a major northward shift of the southern margin of the eastern sahara the lakes indicate conditions wetter than present across northern africa pollen data show an upward shift of the montane forests the northward shift of the southern margin of the sahara and a major extension of tropical rain forest the lake and pollen data confirm monsoon expansion in eastern africa but the climate model fails to simulate the wet conditions in western africa

a 7600 yr vegetation and fire history from anthony lake northeastern oregon usa with linkages to modern synoptic climate patterns we used pollen and high resolution charcoal analysis of lake sediment to reconstruct a 7600 yr vegetation and fire history from anthony lake located in the blue mountains of northeastern oregon from 7300 to 6300 cal yr bp the forest was composed primarily of populus and fire was common indicating warm dry conditions from 6300 to 3000 cal yr bp populus declined as pinus and picea increased in abundance and fire became less frequent suggesting a shift to cooler wetter conditions from 3000 cal yr bp to present modern day forests composed of pinus and abies developed and from 1650 cal yr bp to present fires increased we utilized the modern climate analogue approach to explain the potential synoptic climatological processes associated with regional fire the results indicate that years with high fire occurrence experience positive 500 mb height anomalies centered over the great basin with anomalous southerly component of flow delivering dry air into the region and with associated sinking motions to further suppress precipitation it is possible that such conditions became more common over the last 1650 cal yr bp supporting an increase in fire despite the shift to more mesic conditions

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

high resolution simulations of the last glacial maximum climate over europe a solution to discrepancies with continental palaeoclimatic reconstructions the analyses of low resolution models simulations of the last glacial maximum lgm 21 kyr bp climate have revealed a large discrepancy between all the models and pollen based palaeoclimatic reconstructions in general the models are too warm relative to the observations especially in winter where the difference is of the order of 10 c over western europe one of the causes of this discrepancy may be related to the low spatial resolution of these models to assess the impact of using high resolution models on simulated climate sensitivity we use three approaches to obtain high resolution climate simulations over europe first an atmospheric general circulation model agcm with a stretched grid over europe second a homogeneous t106 agcm high resolution everywhere on the globe and last a limited area model lam nested in a low resolution agcm with all three methods we have performed simulations of the european climate for present and lgm conditions according to the experimental design recommended by the palaeoclimate modeling intercomparison project pmip model results have been compared with updated pollen based palaeoclimatic indicators for temperature and precipitation that were initially developed in pmip for each model a low resolution global run was also performed as expected the low resolution simulations underestimate the large cooling indicated by pollen data especially in winter despite revised slightly warmer reconstructions of the temperatures of the coldest month and show results in the range of those obtained in pmip with similar models the two high resolution agcms do not improve the temperature field and cannot account for the discrepancy between model results and data especially in winter however they are able to reproduce trends in precipitation more closely than their low resolution counterparts do but the simulated climates are still not as arid as depicted by the data conversely the lam temperature results compare well with climate reconstructions in winter but the simulated hydrological cycle is not consistent with the data finally these results are discussed in regard of other possible causes for discrepancies between models and palaeoclimatic reconstructions for the lgm european climate

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

influence of insolation and glaciation on atmospheric circulation in the north atlantic sector implications of general circulation model experiments for the late quaternary climatology of europe abstract atmospheric general circulation models have been used to simulate the sensitivity of regional climates to late quaternary changes in insolation ice sheets and atmospheric co 2 model results for full glacial conditions 18 ka show the atlantic westerly jet strengthened and shifted south a corresponding southward shift of the icelandic low and a strengthening and northward shift of the subtropical anticyclone sta a glacial anticyclone developed over the european ice sheet and cold dry conditions prevailed over much of europe the full glacial climate anomaly for the north atlantic sector is explained by a combination of low atmospheric co 2 reducing global surface temperatures and circulation changes caused by the ice sheets by the early holocene 9 ka the ice sheets were much reduced while the orbital anomaly was near its maximum producing mid continental summer warming and winter cooling and a reduced latitudinal temperature gradient in the northern hemisphere in both seasons the jet and the icelandic low were displaced to north of their present position producing strong onshore flow and mild wet winters in northern europe while the sta was also shifted northwards producing offshore flow and dry summers in the same region during the late glacial transition the effects of insolation and glaciation were antagonistic for some features of the circulation and synergistic for others the model results suggest palaeoclimatic hypotheses that could be directly tested by comparison with palaeoclimatic data mapped at a synoptic scale

quantitative interpretation of fossil pollen spectra dissimilarity coefficients and the method of modern analogs abstract dissimilarity coefficients measure the difference between multivariate samples and provide a quantitative aid to the identification of modern analogs for fossil pollen samples how eight coefficients responded to differences among modern pollen samples from eastern north america was tested these coefficients represent three different classes 1 unweighted coefficients that are most strongly influenced by large valued pollen types 2 equal weight coefficients that weight all pollen types equally but can be too sensitive to variations among rare types and 3 signal0to noise coefficients that are intermediate in their weighting of pollen types the studies with modern pollen allowed definition of critical values for each coefficient which when not exceeded indicate that two pollen samples originate from the same vegetation region dissimilarity coefficients were used to compare modern and fossil pollen samples and modern samples so similar to fossil samples were found that most of three late quaternary pollen diagrams could be reconstructed by substituting modern samples for fossil samples when the coefficients indicated that the fossil spectra had no modern analogs then the reconstructed diagrams did not match all aspects of the originals no modern analogs existed for samples from before 9300 yr b p at kirchner marsh minnesota and from before 11 000 yr b p at wintergreen lake michigan but modern analogs existed for almost all holocene samples from these two sites and brandreth bog new york

quantitative estimation of bioclimatic parameters from presence absence vegetation data in north america by the modern analog technique abstract the method of modern analogs is widely used to obtain estimates of past climatic conditions from paleobiological assemblages and despite its frequent use this method involved so far untested assumptions we applied four analog approaches to a continental scale set of bioclimatic and plant distribution presence absence data for north america to assess how well this method works under near optimal modern conditions for each point on the grid we calculated the similarity between its vegetation assemblage and those of all other points on the grid excluding nearby points the climate of the points with the most similar vegetation was used to estimate the climate at the target grid point estimates based the use of the jaccard similarity coefficient had smaller errors than those based on the use of a new similarity coefficient although the latter may be more robust because it does not assume that the fossil assemblage is complete the results of these analyses indicate that presence absence vegetation assemblages provide a valid basis for estimating bioclimates on the continental scale however the accuracy of the estimates is strongly tied to the number of species in the target assemblage and the analog method is necessarily constrained to produce estimates that fall within the range of observed values we applied the four modern analog approaches and the mutual overlap or mutual climatic range method to estimate bioclimatic conditions represented by the plant macrofossil assemblage from a packrat midden of last glacial maximum age from southern nevada in general the estimation approaches produced similar results in regard to moisture conditions but there was a greater range of estimates for growing degree days despite its limitations the modern analog technique can provide paleoclimatic reconstructions that serve as the starting point to the interpretation of past climatic conditions

episodic deposition of illinois valley peoria silt in association with lake michigan lobe fluctuations during the last glacial maximum the chronology and cause of millennial depositional oscillations within last glacial loess of the central lowlands of the united states are uncertain here we present a new age model that indicates the peoria silt along the illinois river valley accumulated episodically from 28 500 to 16 000 cal yr bp as the lake michigan lobe margin fluctuated within northeastern illinois the age model indicates accelerated loess deposition coincident with regional glacial advances during the local last glacial maximum a weakly developed paleosol the jules geosol represents a period of significantly slower deposition from 23 700 to 22 000 cal yr bp a gastropod assemblage based reconstruction of mean july temperature shows temperatures 6 10 c cooler than modern during peoria silt deposition stable oxygen and carbon isotope values 18 o and 13 c of gastropod carbonate do not vary significantly across the pedostratigraphic boundary of the jules geosol suggesting slower loess accumulation was a result of reduced glacial sediment supply rather than direct climatic factors however a decrease in 18 o values occurred between 26 000 and 24 000 cal yr bp synchronous with the lake michigan lobe s southernmost advance this 18 o decrease suggests a coupling of regional summer hydroclimate and ice lobe position during the late glacial period

pollen based palaeoclimate reconstructions over long glacial interglacial timescales methodological tests based on the holocene and mis 5d c deposits at sokli northern finland palaeoclimatic reconstructions over long glacial interglacial timescales present major methodological challenges as calibration methods based on modern climate and vegetation patterns may yield biased reconstructions from non analogue palaeoclimates such as severely continental glacial periods in this work we present pollen based summer temperature reconstructions based on holocene and early weichselian marine isotope stages mis 5d c deposits at sokli northern finland we attempt to improve the robustness of reconstructions of continental palaeoclimates by using two calibration sets with one located in the region surrounding the fossil site and another in a more continental region in northwestern russia we assess the reliability of the reconstructions by estimating the compositional fit between fossil and calibration samples and by comparison with independent plant macrofossil based reconstructions we find the fossil samples to fit the extra regional high continentality calibration set better during the early holocene and mis 5d c especially in mis 5d c however even the high continentality calibration set fits the fossil samples poorly compared to the fit achieved in the mid and late holocene thus our results highlight the problem of finding applicable calibration data for pre holocene periods we finally discuss the relative strengths and vulnerabilities of different calibration methods in reconstruction of non analogue palaeoclimates copyright 2013 john wiley sons ltd

climate change and arctic ecosystems 1 vegetation changes north of 55 n between the last glacial maximum mid holocene and present a unified scheme to assign pollen samples to vegetation types was used to reconstruct vegetation patterns north of 55 n at the last glacial maximum lgm and mid holocene 6000 years b p the pollen data set assembled for this purpose represents a comprehensive compilation based on the work of many projects and research groups five tundra types cushion forb tundra graminoid and forb tundra prostrate dwarf shrub tundra erect dwarf shrub tundra and low and high shrub tundra were distinguished and mapped on the basis of modern pollen surface samples the tundra forest boundary and the distributions of boreal and temperate forest types today were realistically reconstructed during the mid holocene the tundra forest boundary was north of its present position in some regions but the pattern of this shift was strongly asymmetrical around the pole with the largest northward shift in central siberia 200 km little change in beringia and a southward shift in keewatin and labrador 200 km low and high shrub tundra extended farther north than today at the lgm forests were absent from high latitudes graminoid and forb tundra abutted on temperate steppe in northwestern eurasia while prostrate dwarf shrub erect dwarf shrub and graminoid and forb tundra formed a mosaic in beringia graminoid and forb tundra is restricted today and does not form a large continuous biome but the pollen data show that it was far more extensive at the lgm while low and high shrub tundra were greatly reduced illustrating the potential for climate change to dramatically alter the relative areas occupied by different vegetation types

mediterranean vegetation lake levels and palaeoclimate at the last glacial maximum the apparent conflict between pollen evidence for widespread artemisia steppe1 6 implying semi arid conditions and geomorphological evidence for high lake levels4 7 11 has produced controversy about the ice age palaeoclimate of the mediterranean region here we use a water balance model12 to predict catchment runoff and a biome model13 to predict vegetation type to reconstruct the palaeoenvironment around lake loannina a type locality for the northern mediterranean region we show that both sets of evidence are compatible with a summer dry winter wet regime with seasonal temperature anomalies similar to those predicted by atmospheric model simulations of the last glacial maximum14 18 the drying effect of the cold north atlantic ocean may have been counteracted in winter by increased storm frequency under a southward shifted jet stream as shown by several atmospheric models16 18

pollen based summer temperature reconstructions for the eastern canadian boreal forest subarctic and arctic pollen based paleoclimate reconstructions using response surface and modern analog methods reveal an 8000 year record of july temperature fluctuations for 25 eastern canadian lake sites located from the forest tundra to the high canadian arctic postglacial conditions characterized by warmer than present summer temperatures prevailed in baffin island and ne labrador beginning about 7500 and 7000 14c yr bp respectively resulting in warmer than present conditions throughout the region by 6000 14c yr bp 0 5 c to 1 c further south in quebec and w labrador july temperatures were 1 2 c colder than present until after 6000 14c yr bp and only reached modern values after all residual laurentide ice had melted increased summertime insolation and the final disappearance of laurentide ice during the middle holocene probably caused july temperatures throughout eastern canada to peak between approximately 5000 and 3500 14c yr bp mid holocene warming relative to today was more pronounced in baffin island and ne labrador 1 c to 2 c compared to the boreal and subarctic regions of quebec and w labrador 1 c over the past 4000 years decreasing summertime insolation and colder sea surface temperatures in the davis strait and labrador sea contributed to a decline in july temperatures of 1 2 c throughout baffin island and the tundra regions of n quebec and labrador the absence of similar cooling in the records from the boreal forest may support the notion that the mean position of the summertime polar front blocked the colder arctic air during the late holocene

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

late quaternary summer temperature changes in the northern european tree line region abstract we present two new quantitative july mean temperature t jul reconstructions from the arctic tree line region in the kola peninsula in north western russia the reconstructions are based on fossil pollen records and cover the younger dryas stadial and the holocene the inferred temperatures are less reliable during the younger dryas because of the poorer fit between the fossil pollen samples and the modern samples in the calibration set than during the holocene the results suggest that the younger dryas t jul in the region was 8 0 10 0 c being 2 0 3 0 c lower than at present the holocene summer temperature maximum dates to 7500 6500 cal yr bp with t jul about 1 5 c higher than at present these new records contribute to our understanding of summer temperature changes along the northern european tree line region the holocene trends are consistent in most of the independent records from the fennoscandian kola tree line region with the beginning of the holocene thermal maximum no sooner than at about 8000 cal yr bp in the few existing temperature related records farther east in the russian arctic tree line the period of highest summer temperature begins already at about 10 000 cal yr bp this difference may reflect the strong influence of the atlantic coastal current on the atmospheric circulation pattern and the thermal behaviour of the tree line region on the atlantic seaboard and the more direct influence of the summer solar insolation on summer temperature in the region east of the kola peninsula

physiological significance of low atmospheric co2 for plant climate interactions abstract methods of palaeoclimate reconstruction from pollen are built upon the assumption that plant climate interactions remain the same through time or that these interactions are independent of changes in atmospheric co 2 the latter may be problematic because air trapped in polar ice caps indicates that atmospheric co 2 has fluctuated significantly over at least the past 400 000 yr and likely the last 1 6 million yr three other points indicate potential biases for vegetation based climate proxies first c 3 plant physiological research shows that the processes that determine growth optima in plants photosynthesis mitochondrial respiration photorespiration are all highly co 2 dependent and thus were likely affected by the lower co 2 levels of the last glacial maximum second the ratio of carbon assimilation per unit transpiration called water use efficiency is sensitive to changes in atmospheric co 2 through effects on stomatal conductance and may have altered c 3 plant responses to drought third leaf gas exchange experiments indicate that the response of plants to carbon depleting environmental stresses are strengthened under low co 2 relative to today this paper reviews the scope of research addressing the consequences of low atmospheric co 2 for plant and ecosystem processes and highlights why consideration of the physiological effects of low atmospheric co 2 on plant function is recommended for any future refinements to pollen based palaeoclimatic reconstructions

dependence of creep in olivine on homologous temperature and its implications for flow in the mantle creep data for olivine when normalized by the melting temperature can be extrapolated directly to the pressure temperature and chemical environment of the upper mantle by using the appropriate solidus and geotherms the data presented here collected over a broad pressure range predict effective viscosities that are consistent with geophysical and tectonic constraints for a dry upper mantle these systematics suggest that the effective viscosity of the mantle has risen over the age of the earth as outgassing has progressively raised the solidus

climatic changes in eurasia and africa at the last glacial maximum and mid holocene reconstruction from pollen data using inverse vegetation modelling in order to improve the reliability of climate reconstruction especially the climatologies outside the modern observed climate space an improved inverse vegetation model using a recent version of biome4 has been designed to quantitatively reconstruct past climates based on pollen biome scores from the biome6000 project the method has been validated with surface pollen spectra from eurasia and africa and applied to palaeoclimate reconstruction at 6 cal ka bp calendar years the climate was generally wetter than today in southern europe and northern africa especially in the summer winter temperatures were higher 1 5 c than present in southern scandinavia northeastern europe and southern africa but cooler in southern eurasia and in tropical africa especially in mediterranean regions summer temperatures were generally higher than today in most of eurasia and africa with a significant warming from 3 to 5 c over northwestern and southern europe southern africa and eastern africa in contrast summers were 1 3 c cooler than present in the mediterranean lowlands and in a band from the eastern black sea to siberia at 21 cal ka bp a marked hydrological change can be seen in the tropical zone where annual precipitation was 200 1 000 mm year lower than today in equatorial east africa compared to the present a robust inverse relationship is shown between precipitation change and elevation in africa this relationship indicates that precipitation likely had an important role in controlling equilibrium line altitudes ela changes in the tropics during the lgm period in eurasia hydrological decreases follow a longitudinal gradient from europe to siberia winter temperatures were 10 17 c lower than today in eurasia with a more significant decrease in northern regions in africa winter temperature was 10 15 c lower than present in the south while it was only reduced by 0 3 c in the tropical zone comparison of palaeoclimate reconstructions using lgm and modern co2 concentrations reveals that the effect of co2 on pollen based lgm reconstructions differs by vegetation type reconstructions for pollen sites in steppic vegetation in europe show warmer winter temperatures under lgm co2 concentrations than under modern concentrations and reconstructions for sites in xerophytic woods scrub in tropical high altitude regions of africa are wetter for lgm co2 concentrations than for modern concentrations because our reconstructions account for decreased plant water use efficiency

climate of east africa 6000 14c yr b p as inferred from pollen data this paper presents a spatial reconstruction of climate in east africa at 6000 14c yr b p two different approaches using pollen data have been used the standard best modern analogues method and the new plant functional type method based on groups of pollen taxa both methods have been applied to 32 fossil pollen spectra dated at 6000 14c yr b p for each site we have estimated two climatic parameters annual precipitation and mean annual temperature three bioclimatic parameters ratio of actual to potential evapotranspiration and the mean temperature of the coldest and warmest months results show that the temperature lapse rate was less steep at 6000 14c yr b p than it is today the climate was wetter north of 3 s precipitation anomalies 50 mm yr and slightly drier farther south precipitation anomalies 50 mm yr the ratio of actual to potential evapotranspiration also indicates conditions similar to or wetter than today north of 3 s anomalies 10 the climate was warmer than today by 2 c north of the equator and was cooler southward 1 c although both methods indicate similar climatic patterns the plant functional type method provides more consistent results

an assessment of the mean annual precipitation needed to sustain lake sambhar in rajasthan india during mid holocene time an application of a simple hydrological model to likely climatic conditions of lake sambhar provides tighter bounds on the range of increased precipitation seen during the early to mid holocene than those inferred from paleoclimatic proxies to examine past lake levels we developed a simple lake model based on hydrological principles of a watershed balance between precipitation evaporation and runoff from the watershed to calculate daily depth and volume calculations reveal that early to mid holocene rainfall was most likely in a range of 40 65 greater than present levels resulting in lake depths of 6 8 m this estimate incorporates all major sources of uncertainty into the lake model but it is likely that the value of mid holocene precipitation lies in the lower part of the 40 65 range additionally a 40 65 greater precipitation could have led to greater interannual variability in lake levels which may account for the lack of clear shorelines we find however that it is unlikely that lak

synoptic reorganization of atmospheric flow during the last glacial maximum a coupled global atmosphere ocean model of intermediate complexity is used to study the influence of glacial boundary conditions on the atmospheric circulation during the last glacial maximum in a systematical manner a web of atmospheric interactions is disentangled which involves changes in the meridional temperature gradient and an associated modulation of the atmospheric baroclinicity this in turn drives anomalous transient eddy momentum fluxes that feed back onto the zonal mean circulation moreover the modified transient activity weakened in the north pacific and strengthened in the north atlantic leads to a meridional reorganization of the atmospheric heat transport thereby feeding back onto the meridional temperature structure furthermore positive barotropic conversion and baroclinic production rates over the laurentide ice sheets and the far eastern north pacific have the tendency to decelerate the westerlies thereby feeding back to the stationary wave changes triggered by orographic forcing

multi proxy stalagmite records from northern california reveal dynamic patterns of regional hydroclimate over the last glacial cycle abstract despite its importance for california s water resources little is known about how precipitation has varied in far northern california beyond the historical record we present a new multi proxy paleoclimate record derived from two coeval stalagmites from lake shasta caverns lsc california that covers the end of marine isotope stage 3 through heinrich stadial 1 35 000 to 14 000 years bp at 40 8 n lsc is situated within the transition zone between regions in the northwestern and southwestern united states that demonstrate different precipitation responses to both modern and paleoclimatic drivers stable isotope and trace element proxies from lsc stalagmites indicate the region experienced wet conditions during interstadials warm periods associated with dansgaard oeschger cycles similar to proxy records from southern oregon and the northern great basin but in contrast to records from the desert southwest similar to the northern cascades and rocky mountains lsc was drier during the last glacial maximum however proxies indicate increased rainfall throughout heinrich stadial 1 similar to the great basin and southwest thus the lsc record demonstrates the non stationarity of the transition zone location and illustrates a complex pattern of precipitation response to global climate change in the western united states covariation of speleothem 18o an indicator of moisture source with 13c and trace elements indicators of moisture amount suggest a higher proportion of central pacific precipitation during the last glacial maximum despite the enhanced aridity in contrast periods characterized by increased precipitation amounts such as early heinrich 1 are associated with enhanced moisture from the northern pacific

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

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

quantitative reconstruction of holocene climate from the chuna lake pollen record kola peninsula northwest russia july mean temperatures and annual precipitation during the last 9000 years were inferred using the pollen record from chuna lake kola peninsula russia a quantitative pollen climate model was generated using the best modem analogues method from a training set of 99 surface pollen spectra from the kola peninsula northern fennoscandia and karelia according to the evidence from chuna lake the early and mid holocene c 9000 5000 cal bp was warm and dry in the central kola peninsula with july temperatures being 1 5 2c higher than at present the onset of warm and dry early to mid holocene occurred in the kola peninsula earlier than in the rest of northern fennoscandia july temperature started to decrease and annual precipitation increased from c 5000 cal yr bp and climate became cool and moist

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

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

low and high frequency climate variability in eastern beringia during the past 25 000 yearsthis article is one of a series of papers published in this special issue on the theme polar climate stability network we present new temperature and precipitation reconstructions for the past 25 000 cal years bp from across eastern beringia based on a network of pollen diagrams an updated modern pollen calibration database and an improved methodology using the modern analogue technique mat time series show july temperatures were around 4 c lower during full glacial and january temperatures were about 2 c lower than present annual temperatures rose beginning around 16 000 cal years bp reaching a maximum around 12 000 cal year bp the warming was more rapid in southern beringia annual precipitation varied by 250 mm during the past 25 000 cal years bp maps of reconstructed precipitation patterns show increasingly drier conditions since 12 000 cal years bp that vary regionally suggesting holocene atmospheric circulation changes at multiple time and space scales orbitally forced seasonality changes during the late glacial and early holocene resulted in reversed seasonal temperature reconstructions due to me

quantitative reconstruction of younger dryas to mid holocene paleoclimates at le locle swiss jura using pollen and lake level data abstract pollen and lake level data from le locle in the swiss jura were used to quantitatively reconstruct climatic parameters for the younger dryas event and the first half of the holocene period the younger dryas cold event at le locle was characterized by i a general trend toward a slight increase in summer temperature and a decrease in annual precipitation and ii a marked drying phase at ca 11 900 cal yr b p that occurred between two wetter ones further phases of major deficit in moisture occured at ca 11 500 cal yr b p younger dryas holocene transition 10 800 cal yr b p 8700 cal yr b p and 6500 cal yr b p climatic parameters reconstructed here suggest that phases of higher lake level developing at ca 12 500 12 000 11 750 11 600 11 200 10 900 synchronous with the preboreal oscillation 10 400 8900 8400 8300 possibly related to the 8200 yr event and 7800 7000 cal yr b p coincided with an increase in annual precipitation a decrease in summer temperature and a shorter growing season conversely periods of low lake level corresponded to a decrease in annual precipitation an increase in summer temperature and a longer growing season this general pattern could have resulted from alternate southward northward displacements of the atlantic westerly jet

european lakes as palaeohydrological and palaeoclimatic indicators abstract lakes in temperate regions have fluctuated in size on annual to millenial time scales changes in water level or depth can be reconstructed by applying geomorphic sedimentological and biostratigraphic methods to transects of sediment cores this systematic field based approach has been used at a number of sites in europe it is illustrated by reconstructions of water level changes in lakes from southern sweden these lakes have shown broadly synchronous changes during the holocene such synchronous changes in water levels at several sites in a region reflect climatic changes inferences about the mechanism of the climatic change depend on identifying both synchronous changes within a region and differences in the direction magnitude and timing of lake level changes between regions continental compilations of lake level data are therefore necessary detailed studies are not available from enough sites but the interpretation of already existing stratigraphic and biostratigraphic data in terms of lake level changes has greatly increased the number of sites available for a continental scale synthesis in europe this eclectic literature based approach is illustrated with examples from southern europe lakes in the mediterranean region were high around the glacial maximum and again somtime during the first half of the holocene in the western mediterranean the peak of late glacial aridity occurred at 15 000 16 000 bp and the lakes were already high again by 12 000 bp in the east maximum late glacial aridity occurred between 13 000 and 11 000 bp and there was a gradual return to wetter climates during the early holocene such that 9000 bp was more arid than 6000 bp most lakes in the mediterranean region were high at 6000 bp the transition to arid conditions after 5000 bp occurred abruptly in the west and more gradually in the east the lakes of southern sweden indicate drier climates in the early holocene ca 9000 bp more effective moisture between 8000 and 6000 bp increased aridity between 5500 and 3500 bp and increased effective moisture again during the last 3000 years the history of lake level changes in southern sweden and the mediterranean region can be partially explained in terms of changes in the direct effects of insolation and in the strength and position of the westerlies and of the subtropical high pressure cell during the late quaternary

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