numerical reconstructions of lgm climate across the eurasian arctic abstract although limits of the eurasian ice sheet at the last glacial maximum lgm are known relatively well from geological evidence the palaeoclimate coexistent with this ice sheet has yet to be identified confidently a simple ice sheet model has been used to determine lgm climate conditions by finding the ice sheet mass balance configuration that permits model results to match with geological data relating to the extent of lgm ice cover these conditions are compared with atmospheric general circulation model agcm calculations of the climate at the lgm which reveal the meteorological conditions associated with the ice sheet mass balance the western margin of scandinavia is characterised by a maritime climate influenced by the nearby warm seasonally sea ice free ocean conditions however further east the warming effect of the north atlantic diminishes and an extreme polar desert climate dominates across the kara sea similar to east antarctica today the lgm climate that we establish is in contrast to many previous reconstructions involving snow laden warm westerly winds originating from the north atlantic affecting the entire eurasian arctic severely cold conditions across the eurasian arctic are compatible with a stable circulation cell over the kara sea that isolates the region climatically and or cold dry westerly winds from the fennoscandian ice sheet that flow across the rest of the eurasian arctic

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

the response of the coupled arctic sea ice atmosphere system to orbital forcing and ice motion at 6 kyr and 115 kyr bp abstract a coupled atmosphere mixed layer ocean gcm genesis2 is forced with altered orbital boundary conditions for paleoclimates warmer than modern 6 kyr bp and colder than modern 115 kyr bp in the high latitude northern hemisphere a pair of experiments is run for each paleoclimate one with sea ice dynamics and one without to determine the climatic effect of ice motion and to estimate the climatic changes at these times at 6 kyr bp the central arctic ice pack thins by about 0 5 m and the atmosphere warms by 0 7 k in the experiment with dynamic ice at 115 kyr bp the central arctic sea ice in the dynamical version thickens by 2 3 m accompanied by a 2 k cooling the magnitude of these mean annual simulated changes is smaller than that implied by paleoenvironmental evidence suggesting that changes in other earth system components are needed to produce realistic simulations contrary to previous simulations without atmospheric feedbacks the sign of the dynamic sea ice feedback is complicated and

origin and causes of the mammoth steppe a story of cloud cover woolly mammal tooth pits buckles and inside out beringia to account for the vastness of the northern arid steppes during glacial episodes i propose the proximate key variable was simply frequent clear skies this hitherto under emphasized point is the hub which best explains many questions low maritime cloud cover best accounts for today s tundra and in a related way the cloudy polar front accounts for the whole of the taiga even during glacial maxima the proximity of the sea to the bering isthmus created intermittent maritime cloud cover this regional cloud cover produced an ecological interruption or buckle of the arid steppe belt while this beringian mesic buckle did not serve as an intercontinental ecological barrier to most steppe adapted species it does seem to have limited the distributions of woolly rhinos camels american kiangs short faced bears badgers and some others at the beginning of the holocene this narrow refugium seems to have been a source of some mesic adapted species which colonized westward into the now tundra vegetation of northern asia and eastward into northern north america this holocene expansion from a limited and regional pleistocene refugium created our present misconceptions about beringia the mid strait mesic ecological conditions were the exception to the more extensive arid adapted communities of the mammoth steppe 2000 published by elsevier science ltd all rights reserved

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

lake sediment evidence for the date of deglaciation of the hidden lake area kenai peninsula alaska an abrupt environmental change is reflected in a core from hidden lake alaska by differences in sediment type chlorite crystallinity and content of organic carbon and water of the sediments this abrupt change in the sedimentary record occurred about 14 500 14c yr ago and probably marks the time of recession of the glacier from the hidden lake drainage basin deglaciation of the area was then underway and rock flour was being deposited in the lake after recession of the glacier from the hidden lake drainage basin rock flour was no longer introduced and organic matter content of the sediment increased by the dating of these changes in sediment type we show that retreat of glaciers in this area took place significantly earlier than previously estimated this agrees with the timing of retreat of alpine glaciers elsewhere in western north america

using the deuterium isotope composition of permafrost meltwater to constrain thermokarst lake contributions to atmospheric ch4 during the last deglaciation 1 thermokarst lakes are thought to have been an important source of methane ch4 during the last deglaciation when atmospheric ch4 concentrations increased rapidly here we demonstrate that meltwater from permafrost ice serves as an h source to ch4production in thermokarst lakes allowing for region specific reconstructions of dch4 emissions from siberian and north american lakes dch4 reflects regionally varying d values of precipitation incorporated into ground ice at the time of its formation late pleistocene aged permafrost ground ice was the dominant h source to ch4production in primary thermokarst lakes whereas holocene aged permafrost ground ice contributed h to ch4 production in later generation lakes we found that alaskan thermokarst lake dch4 was higher 334 17 than siberian lake dch4 381 18 weighted mean dch4values for beringian lakes ranged from 385 to 382 over the deglacial period bottom up estimates suggest that beringian thermokarst lakes contributed 15 4 tg ch4 yr 1 to the atmosphere during the younger dryas and 25 5 tg ch4 yr 1during the preboreal period these estimates are supported by independent top down isotope mass balance calculations based on ice core dch4 and 13cch4 records both approaches suggest that thermokarst lakes and boreal wetlands together were important sources of deglacial ch4

late quaternary vegetation of chukotka northeast russia implications for glacial and holocene environments of beringia abstract two lake records from the kankaren region of southern chukotka when combined with other palynological and macrofossil data document spatial and temporal variations in the regional vegetation history since 21 000 14c 25 400 cal yr bp full glacial environments were severely cold and arid in central and northern chukotka whereas southern sites experienced conditions that were relatively moist although still drier than present southern chukotka may represent a western extension of environments of the land bridge proper including a possible moisture barrier to intercontinental migration shrub betula tundra established earliest in southern chukotka 15 800 14 000 14c 19 000 16 700 cal yr bp 13 000 14c 15 300 cal yr bp central and north pinus pumila earliest in the north 9600 14c 11 100 cal yr bp 7600 14c 8400 cal yr bp south and shrub alnus earliest in both the south and north 12 000 11 000 14c 13 800 12 900 cal yr bp these patterns support the presence of cryptic refugia for betula and alnus in chukotka during the full glaciation in contrast p pumila probably migrated into chukotka from populations located in the northern coastal lowlands and from mountainous regions of southwestern beringia evidence for a thermal optimum 11 000 8000 14c 12 900 9000 cal yr bp is strong in northern chukotka but is absent in central and southern areas

late quaternary paleoclimate of western alaska inferred from fossil chironomids and its relation to vegetation histories abstract fossil chironomidae assemblages with a few chaoboridae and ceratopogonidae from zagoskin and burial lakes in western alaska provide quantitative reconstructions of mean july air temperatures for periods of the late middle wisconsin 39 000 34 000 cal yr b p to the present inferred temperatures are compared with previously analyzed pollen data from each site summarized here by indirect ordination paleotemperature trends reveal substantial differences in the timing of climatic warming following the late wisconsin at each site although chronological uncertainty exists zagoskin lake shows early warming beginning at about 21 000 cal yr b p whereas warming at burial lake begins 4000 years later summer climates during the last glacial maximum lgm were on average 3 5 c below the modern temperatures at each site major shifts in vegetation occurred from 19 000 to 10 000 cal yr b p at zagoskin lake and from 17 000 to 10 000 cal yr b p at burial lake vegetation shifts followed climatic warming when temperatures neared modern values both sites provide evidence of an early postglacial thermal maximum at 12 300 cal yr b p these chironomid records combined with other insect based climatic reconstructions from beringia indicate that during the lgm 1 greater continentality likely influenced regions adjacent to the bering land bridge and 2 summer climates were at times not dominated by severe cold

a 14 000yr paleoenvironmental record from windmill lake central alaska lateglacial and holocene vegetation in the alaska range abstract a 14 000 yr high resolution pollen and lake level record from windmill lake in central alaska provides new evidence for the late pleistocene and holocene paleoenvironments of this region at 14 000 14 c yr bp sparse herb tundra and low lake levels indicate a cold arid environment about 11 800 14 c yr bp the vegetation abruptly shifted to a shrub tundra and lake levels increased suggesting warmer and more mesic conditions ca 10 500 10 200 14 c yr bp herbaceous taxa increased at the expense of the shrubs suggesting a transient episode of climatic deterioration nearly contemporaneous with the younger dryas chronozone by 8000 14 c yr bp spruce was present in the watershed and alder grew locally by 6500 14 c yr bp the ams radiocarbon chronology indicates later expansions of betula picea and alnus than at most sites in central alaska which are conventionally dated

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

holocene vegetation change at treeline north of yellowknife northwest territories canada abstract two radiocarbon dated cores from small lakes located approximately 25 km north of the mapped boundary between forest tundra and tundra provide records of postglacial vegetation change at the treeline near yellowknife nwt canada basal radiocarbon dates of 6180 and 7470 yr b p were obtained from the cores the fossil pollen evidence suggests that the initial vegetation was betula tundra with a peatland component alnus became an important constituent of the pollen assemblages between 6900 and 5500 yr b p both lakes record sharp increases in picea cf mariana pollen at approximately 5000 yr b p suggesting the establishment of forest tundra by 3500 yr b p picea mariana forest tundra had withdrawn the proportion of organic to inorganic sediment in the cores was at a maximum between 5000 and 3500 yr b p tundra has dominated the region since 3500 yr b p in northwestern canada the maximum northward advance of treeline occurred between 9000 and 5000 yr b p the asynchrony in treeline advance in central and northwestern canada may reflect that glacial ice persisted in the interior nwt longer than previously believed alternatively the asynchronous history of the treeline may be a result of the geometric properties of the long wave westerly disturbance that is manifest in the median summer position of the arctic front and ultimately controls the geographic location of the treeline

late quaternary vegetation history of the fishhook bend area porcupine river alaska ped pond is a lake lying in a pleistocene scour channel of the porcupine valley the valley is considered to be a possible path of late quaternary species migrations between interior alaska and northwest canada pollen in the oldest lake sediments ca 13 000 years old indicates that shrub birch and willow probably occurred locally in a sparsely vegetated herb dominated landscape populus juniperus and typha latifolia increased about 10 000 years ago suggesting particularly warm temperatures during the early holocene picea glauca which is presently common in the surrounding forests first arrived near ped pond about 8500 years ago this arrival date together with existing evidence from other sites indicates that spruce expanded rapidly across far eastern beringia 8000 9000 years ago other boreal forest taxa picea mariana betula papyrifera and alnus spp became established locally between 7000 and 8000 years bp a date of ca 7500 years bp at ped pond suggests that the alnus rise in northeast

holocene land cover changes on the tibetan plateau information on changes in land surface features on the tibetan plateau tp during the holocene may help our understanding of the forcing of monsoonal circulation we analyse vegetation changes during the last 9000 years from pollen records of four lakes hurleg lake in the qaidam basin qinghai lake on the northeastern tp zigetang lake on the central tp and koucha lake on the eastern tp which represent different regions and vegetation types on the plateau today a set of modern pollen assemblages from 111 lake sediment samples originating from different vegetation types is used for the interpretation of the holocene pollen records four types of numerical analyses are used to infer different aspects of pollen stratigraphical and inferred vegetation changes biome reconstruction ordination to infer palynological compositional turnover rate of assemblage change analysis and a pollen lai leaf area index transfer function our results show strong regional differences in inferred vegetation change in

boreal ecosystem development in the northwestern alaska range since 11 000 yr b p abstract analyses of pollen plant macrofossils macroscopic charcoal mollusks magnetic susceptibility and geochemical content of a sediment core from farewell lake yield a 11 000 yr record of terrestrial and aquatic ecosystem changes in the northwestern foothills of the alaska range between 11 000 and 8500 yr b p the regional landscape was dominated by abetulashrub tundra in whichpopulus salixcommunities were common abundant charcoal in sediments indicates that fires were common in the lake catchment during this period and high mineral accumulation rates allogenic elemental content and magnetic susceptibility suggest intense soil erosion in addition mollusks pollen and macrofossils of aquatic macrophytes and biogenic silica provide evidence that the lake was substantially shallower and more productive 11 000 8500 yr b p than later low lake level and high aquatic productivity might have been caused by warm and dry summers associated with early postglacial insolation maximum in northern high latitudes about 8000 yr b p picea glaucaarrived within the lake catchment forming a forest tundra association until ca 6000 yr b p alnusshrub thickets established in the region ca 6500 yr b p andbetula papyriferaarrived ca 6000 yr b p closedp glaucaforests developed ca 6000 yr b p picea marianabecame important subsequently and replacedp glaucaas the dominant tree species in the region ca 4000 yr b p an increase in authigenic fe mn ratios suggests that the development of waterlogged soils accompanied this vegetation change fires increased in importance at this time and might have accelerated soil erosion the establishment ofp marianaforests probably reflected complex responses of forest ecosystems to the onset of cooler and wetter climate conditions during the late holocene

reconstruction of the grande pile eemian using inverse modeling of biomes and δ13c abstract a new method to reconstruct past climatic conditions between 130 and 100 ka bp from pollen and isotopic data is applied to a previously unanalyzed grande pile core gpxxi we applied the inverse mode to the biome4 vegetation model the method utilizes 13 c measured in parallel to the pollen samples as a constraint for the model first the biomes and the 13 c simulated by the model are compared with the biome allocation of the pollen data the 13 c to be simulated takes into account the degradation effect on the preserved organic matter this procedure allows the reconstruction of the mean annual temperature and precipitation as well as the mean temperatures of the warmest and coldest months we show that during the eemian sensu stricto the reconstructed precipitation is similar to modern values with low variability the cold stadials and the penultimate glaciation are characterized by very low precipitation amounts the temperature estimates however indicate differences with several oscillations identified the peak values are reached at about 124 125 ka bp but two other warm intervals are also identified the variations in temperature appear to be related to sea surface temperature oscillations in the north atlantic region and are also in agreement with the timing of ice sheet build up in the northern hemisphere seasonal variations are also identified in the estimated temperatures of the warmest and coldest months

variability of sea ice cover in the chukchi sea western arctic ocean during the holocene 1 dinocysts from cores collected in the chukchi sea from the shelf edge to the lower slope were used to reconstruct changes in sea surface conditions and sea ice cover using modern analogue techniques holocene sequences have been recovered in a down slope core b15 2135 m 75 44 n sedimentation rate of 1 cm kyr 1 and in a shelf core p1 201 m 73 41 n sedimentation rate of 22 cm kyr 1 the shelf record spanning about 8000 years suggests high frequency centennial oscillations of sea surface conditions and a significant reduction of the sea ice at circa 6000 and 2500 calendar cal years b p the condensed offshore record b15 reveals an early postglacial optimum with minimum sea ice cover prior to 12 000 cal years b p which corresponds to a terrestrial climate optimum in bering sea area dinocyst data indicate extensive sea ice cover 10 months yr 1 from 12 000 to 6000 cal years b p followed by a general trend of decreasing sea ice and increasing sea surface salinity conditions superimposed on large amplitude millennial scale oscillations in contrast 18o data in mesopelagic foraminifers neogloboquadrina pachyderma and benthic foraminifers cibicides wuellerstorfi reveal maximum subsurface temperature and thus maximum inflow of the north atlantic water around 8000 cal years b p followed by a trend toward cooling of the subsurface to bottom water masses sea surface to subsurface conditions estimated from dinocysts and 18o data in foraminifers thus suggest a decoupling between the surface water layer and the intermediate north atlantic water mass with the existence of a sharp halocline and a reverse thermocline especially before 6000 years b p the overall data and sea ice reconstructions from core b15 are consistent with strong sea ice convergence in the western arctic during the early holocene as suggested on the basis of climate model experiments including sea ice dynamics matching a higher inflow rate of north atlantic water

post glacial climatic change on boothia peninsula nunavut canada abstract a high temporal resolution pollen diagram from a lake in the mid arctic region of the boothia peninsula nunavut canada documents the history of the regional vegetation and climate for the past 7200 yr major tundra pollen taxa in the core include cyperaceae and salix with cyperaceae comprising over 50 of the pollen in the early and late holocene tree pollen transported from far to the south comprised a large percentage of the pollen sum with pinus accounting for 30 of the pollen in some levels of the core pollen percentages and concentrations of taxa typical of the mid arctic were highest in the mid holocene corresponding to warm conditions decreasing pollen concentrations indicate cooling temperatures with more rapid decreases occurring around 4200 3800 3400 and 2500 cal yr bp pollen percentages of salix cyperaceae and artemisia increased in the past 35 yr in response to global warming reconstructions of july temperature using the modern analog technique showed that the mid holocene 5800 2800 cal yr bp was approximately 1 c higher than during the past 1000 yr

representation pollinique actuelle a la limite des arbres au nouveau quebec modern pollen spectra from a series of lakes in northwestern quebec reflect the major vegetation zones of the forest tundra transition from latitude 55 n to 59 n shrub tundra samples are dominated

late quaternary vegetation and climate dynamics at the northern limit of the east asian summer monsoon and its regional and global scale controls abstract a late quaternary pollen record from northern sakhalin island 51 34 n 142 14 e 15 m a s l spanning the last 43 7 ka was used to reconstruct regional climate dynamics and vegetation distribution by using the modern analogue technique mat the long term trends of the reconstructed mean annual temperature tann and precipitation pann and total tree cover are generally in line with key palaeoclimate records from the north atlantic region and the asian monsoon domain tann largely follows the fluctuations in solar summer insolation at 55 n during marine isotope stage mis 3 tann and pann were on average 0 2 c and 700 mm respectively thus very similar to late holocene modern conditions full glacial climate deterioration tann 3 3 c pann 550 mm was relatively weak as suggested by the mat inferred average climate parameters and tree cover densities however error ranges of the climate reconstructions during this interval are relatively large and the last glacial environments in northern sakhalin could be much colder and drier than suggested by the weighted average values an anti phase relationship between mean temperature of the coldest mtco and warmest mtwa month is documented during the last glacial period i e mis 2 and 3 suggesting more continental climate due to sea levels that were lower than present warmest and wettest climate conditions have prevailed since the end of the last glaciation with an optimum tann 1 5 c pann 800 mm in the middle holocene interval ca 8 7 5 2 cal ka bp this lags behind the solar insolation peak during the early holocene we propose that this is due to continuous holocene sea level transgression and regional influence of the tsushima warm current which reached maximum intensity during the middle holocene several short term climate oscillations are suggested by our reconstruction results and correspond to northern hemisphere heinrich and dansgaard oeschger events the bolling allerod and the younger dryas the most prominent fluctuation is registered during heinrich 4 event which is marked by noticeably colder and drier conditions and the spread of herbaceous taxa

out of the woods driftwood insights into holocene pan arctic sea ice dynamics the collation of 913 driftwood samples from across the western arctic with spatiotemporal distribution and available provenance data enabled the production of a high resolution proxy based reconstruction of holocene arctic ocean surface current and sea ice dynamics regionally bounded driftwood based sea ice reconstructions studies suggest spatiotemporally complex past arctic sea ice extent and movement however a large scale compilation of holocene arctic driftwood has not previously been developed sparse driftwood in the early holocene 8 2 cal ka b p deglacial period was followed by increased driftwood deposition in the warmer mid holocene 8 2 4 2 cal ka b p characterized by an enhanced transpolar drift tpd 7 cal ka b p leading to sea ice loss through the fram strait driftwood incursion peaks show spatial e w progression from the eurasian archipelagos to greenland and the canadian arctic archipelago suggesting a progressive shift in the orientation of the tpd on centennial millennial time scales and intermediate phases in the arctic oscillation late holocene cooling 4 2 cal ka b p is indicated by increased influx of probably north american picea via a strengthened beaufort gyre bg which enhanced sea ice recirculation starting in the western arctic and progressing eastward in recent millennia 2 cal ka b p a more variable driftwood record alternates between bg and tpd dominance on centennial time scales to further constrain a spatiotemporal reconstruction of variations in holocene ocean current and sea ice dynamics a more definitive determination of driftwood provenance is recommended to build upon the current framework such as through radiogenic isotope tracing and adna analysis

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

potential role of vegetation feedback in the climate sensitivity of high latitude regions a case study at 6000 years b p previous climate model simulations have shown that the configuration of the earth s orbit during the early to mid holocene approximately 10 5 kyr can account for the generally warmer than present conditions experienced by the high latitudes of the northern hemisphere new simulations for 6 kyr with two atmospheric mixed layer ocean models community climate model version 1 ccm1 and global environmental and ecological simulation of interactive systems version 2 genesis 2 are presented here and compared with results from two previous simulations with genesis 1 that were obtained with and without the albedo feedback due to climate induced poleward expansion of the boreal forest the climate model results are summarized in the form of potential vegetation maps obtained with the global biome model which facilitates visual comparisons both among models and with pollen and plant macrofossil data recording shifts of the forest tundra boundary a preliminary synthesis shows that the forest limit was shifted 100 200 km north in most sectors both ccmi and genesis 2 produced a shift of this magnitude genesis 1 however produced too small a shift except when the boreal forest albedo feedback was included the feedback in this case was estimated to have amplified forest expansion by approximately 50 the forest limit changes also show meridional patterns greatest expansion in central siberia and little or none in alaska and labrador which have yet to be reproduced by models further progress in understanding of the processes involved in the response of climate and vegetation to orbital forcing will require both the deployment of coupled atmosphere biosphere ocean models and the development of more comprehensive observational data sets

holocene paleoclimate data from the arctic testing models of global climate change to evaluate the spatial variability of arctic climate change during the present interglacial cape project members compiled well dated terrestrial marine and ice core paleoenvironmental records spanning the past 10 12 thousand years ka six tundra biomes of increasing summer temperature requirements were defined based on regionally coherent pollen assemblages using a rule based approach pollen spectra were converted to tundra forest tundra or forest biomes ranked by their average growing season requirements marine sea surface reconstructions were based on proxy data following a similar rule based approach from these data based reconstructions departures in summer temperatures from modern normals were calculated in 1 ka time slices through the holocene to test predictive models data based summer temperature reconstructions were compared with general circulation model gcm simulations for 10 ka and 6 ka ago paleodata and model results both show that warming occurred earlier across beringia and asia relative to lands adjacent to the north atlantic and that late holocene cooling was most apparent in the north atlantic region however the gcm over predicts the magnitude of mid holocene warming over northern asia and underestimates the intensification of the north atlantic drift in the early holocene strong spatial variability in environmental response during the holocene despite symmetric insolation forcing suggests that any future changes whether caused by anthropogenic or natural factors are unlikely to result in a uniform change across the arctic adding additional complexity to forecasts of global impacts

europe on fire three thousand years ago arson or climate the timing of initiation of human impacts on the global climate system is actively debated anthropogenic effects on the global climate system are evident since the industrial revolution but humans may have altered biomass burning and hence the climate system for millennia we use the specific biomarker levoglucosan to produce the first high temporal resolution hemispheric reconstruction of holocene fire emissions inferred from ice core analyses levoglucosan recorded in the greenland north greenland eemian ice core significantly increases since the last glacial resulting in a maximum around 2 5 ka and then decreasing until the present here we demonstrate that global climate drivers fail to explain late holocene biomass burning variations and that the levoglucosan maximum centered on 2 5 ka may be due to anthropogenic land clearance

the holocene vegetation history of the khibiny mountains implications for the post glacial expansion of spruce and alder on the kola peninsula northwestern russia

a late wisconsin and holocene vegetation history from the central brooks range implications for alaskan palaeoecology abstract five pollen diagrams reveal late wisconsin and holocene vegetation changes in the walker lake alatna valley region of the central brooks range approximately 100 km west of the area studied by d a livingstone 1955 ecology 36 587 600 new insights into the vegetation history of this region are provided by calculations of pollen influx and by the use of linear discriminant analysis to separate picea glauca and p mariana pollen three major pollen zones are identified 1 a basal herb zone characterized by high percentages of cyperaceae gramineae salix and artemisia and low total pollen influx 2 a shrub betula zone with increased total pollen influx and very high percentages of betula pollen predominantly in the size range of b nana and b glandulosa and 3 and alnus zone dominated by alnus pollen lakes currently within the boreal forest or near tree line show relatively high percentages of picea pollen in the alnus zone several striking vegetation changes occurred between ca 10 000 and 7000 yr b p between ca 11 000 and 10 000 yr b p populus balsamifera pollen percentages as great as 30 indicate that this species was present at low elevation sites near walker lake these populations declined abruptly ca 10 000 yr ago and have never regained prominence about 8500 yr b p picea glauca pollen reached 10 15 indicating the arrival of p glauca in or near the study area p glauca populations evidently decreased ca 8000 yr ago when picea pollen percentages and influx fell to low values about 7000 yr b p alnus pollen percentages and influx rose sharply as alder shrubs became established widely picea once more expanded ca 5000 yr ago but these populations were dominated by p mariana rather than p glauca which increased slowly at this time and may still be advancing northward some vegetation changes have been remarkably synchronous over wide areas of interior alaska and probably reflect responses of in situ vegetation to environmental changes but others may reflect the lagged responses of species migrating into new areas

holocene fluctuations in arctic sea ice cover dinocyst based reconstructions for the eastern chukchi sea cores from site hly0501 05 on the alaskan margin in the eastern chukchi sea were analyzed for their geochemical organic carbon 13corg corg n and caco3 and palynological dinocyst pollen and spores content to document oceanographic changes during the holocene the chronology of the cores was established from 210pb dating of near surface sediments and 14c dating of bivalve shells the sediments span the last 9000 years possibly more but with a gap between the base of the trigger core and top of the piston core sedimentation rates are very high 156 cm ka allowing analyses with a decadal to centennial resolution the data suggest a shift from a dominantly terrigenous to marine input from the early to late holocene dinocyst assemblages are characterized by relatively high concentrations 600 7200 cysts cm3 and high species diversity allowing the use of the modern analogue technique for the reconstruction of sea ice cover summer temperature and salinity results indicate a decrease in sea i

warm younger dryas summers and early late glacial spread of temperate deciduous trees in the pannonian basin during the last glacial termination 20 9 kyr cal bp abstract this paper focuses on the last glacial termination vegetation and climate reorganization of the eastern pannonian plain via the multi proxy paleoecological analysis of kokad mire in eastern hungary grains size sediment chemistry and magnetic susceptibility records are compared with the pollen and plant macrofossil records on the basis of which biome and quantitative summer mean temperature reconstructions are provided and discussed with other climate records of the region biome assignments indicated graminoid and forb tundra vegetation from 19 440 cal yr bp with the local presence of betula pendula b pubescens b nana and pinus sylvestris a rapid biome shift to cool coniferous forest took place at 16 200 cal yr bp and a second biome shift was identified at 14 740 cal yr bp when cool mixed forest developed and persisted into the early holocene the most prominent feature of the record was the early post last glacial maximum lgm establishment 17 700 cal yr bp and expansion 14 700 cal yr bp of elm ulmus and hazel corylus supporting the phylogeographical evidence for extra mediterranean refugia in the pannonian basin the fungal spore record indicated the presence of large grazing mammals locally after the lgm until 16 780 cal yr bp their disappearance predated the biome shift to cold coniferous forest and the final increase of forest fires pollen based summer temperature reconstruction suggested relatively warm summers 14 5 c by 19 440 cal yr bp and buffered july mean temperature fluctuations throughout the last glacial termination in this region with

electrical conductivity and partial melting of mafic rocks under pressure we demonstrate the importance of electric conductivity measurements of partially molten mafic rocks by examining of oman gabbro karelia olivinite ronda and spitzbergen peridotites the electrical conductivities of these rocks were estimated using the impedance spectroscopy at temperatures between 800 c and 1450 c and at pressures between 0 3 and 2 gpa in experiments performed in a piston cylinder apparatus at temperatures below and above melting samples were equilibrated during durations on the order of 200 h our results show that a jump in electrical conductivity can be correlated with the temperature range slightly above the solidus due to the delayed formation of an interconnected melt phase thin sections of quenched samples were used to estimate volume fractions and chemical compositions of the partial melts the increase of the electrical conductivity compares well with the connectivity of melt in partially molten samples above the solidus the electrical conductivity increases by 1 to 2 orders of magnitude in comparison with the conductivity of non melted rock below solidus when a complete melt connectivity is established the charge transport follows the network of the formed melt films at grain boundaries durations of up to 200 h are required in order to reach a steady state electrical resistance in a partially molten rock sample the experimental results were compared with the conductivity data obtained from magnetotelluric mt and electromagnetic em measurements in the northern part of the mid atlantic ridge where a series of axial magma chambers amc are presumably located there is good agreement between the measured electric conductivity of gabbroic samples with a melt fraction of 10 to 13 vol and the conductivity estimated at amc beneath the central part of reykjanes ridge as well as between the conductivity of partially molten peridotites and the source zone beneath the mid atlantic ridge at 60 km

origin of last glacial loess in the western yukon tanana upland central alaska usa loess is widespread over alaska and its accumulation has traditionally been associated with glacial periods surprisingly loess deposits securely dated to the last glacial period are rare in alaska and paleowind reconstructions for this time period are limited to inferences from dune orientations we report a rare occurrence of loess deposits dating to the last glacial period 19 ka to 12 ka in the yukon tanana upland loess in this area is very coarse grained abundant coarse silt with decreases in particle size moving south of the yukon river implying that the drainage basin of this river was the main source geochemical data show however that the tanana river valley to the south is also a likely distal source the occurrence of last glacial loess with sources to both the south and north is explained by both regional synoptic scale winds from the northeast and opposing katabatic winds that could have developed from expanded glaciers in both the brooks range to the north and the alaska range to the south based on a comparison with recent climate modeling for the last glacial period seasonality of dust transport may also have played a role in bringing about contributions from both northern and southern sources

vegetation buried under dawson tephra 25 300 14c years bp and locally diverse late pleistocene paleoenvironments of goldbottom creek yukon canada paleoecological research at goldbottom creek in the klondike region of yukon territory nw canada documents an in situ riparian grassy meadow that was buried during the winter or early spring by dawson tephra near the onset of marine isotope stage mis 2 ca 25 300 14 c years bp analyses of vascular plant macrofossils bryophytes pollen insects and paleosols from the riparian meadow contrast with evidence for well drained upland steppe tundra habitats obtained from fossil arctic ground squirrel middens within the same valley the mesic valley bottom vegetation consisted of grasses deschampsia caespitosa alopecurus sedges carex horsetail equisetum cf palustre diverse bryophytes and few forbs upland habitats with dry loessal soils along the valley slopes contained graminoids elymus festuca kobresia myosuroides sage artemisia frigida and diverse steppe and tundra forbs phlox hoodii plantago cf canescens anemone patens var multifida bistorta vivipara draba these paleoecological data highlight the effect of topographic position and moisture on substrates and their control on local scale habitat variability this study represents the first recorded in situ riparian surface from the unglaciated pleistocene refugium of beringia and provides well documented evidence for local habitat heterogeneity and ecosystem structure within the mammoth steppe biome other radiocarbon dated paleoecological data from our study sites indicate that full glacial steppe tundra habitats in west central yukon territory were established during the later stages of the mis 3 interstadial by 29 000 14 c years bp the diverse data obtained through integration of multiple paleoecological methods

large inert carbon pool in the terrestrial biosphere during the last glacial maximum during each of the late pleistocene glacial interglacial transitions atmospheric carbon dioxide concentrations rose by almost 100 ppm the sources of this carbon are unclear and efforts to identify them are hampered by uncertainties in the magnitude of carbon reservoirs and fluxes under glacial conditions here we use oxygen isotope measurements from air trapped in ice cores and ocean carbon cycle modelling to estimate terrestrial and oceanic gross primary productivity during the last glacial maximum we find that the rate of gross terrestrial primary production during the last glacial maximum was about 40 10 pg c yr 1 half that of the pre industrial holocene despite the low levels of photosynthesis we estimate that the late glacial terrestrial biosphere contained only 330 pg less carbon than pre industrial levels we infer that the area covered by carbon rich but unproductive biomes such as tundra and cold steppes was significantly larger during the last glacial maximum consistent with palaeoecological data our data also indicate the presence of an inert carbon pool of 2 300 pg c about 700 pg larger than the inert carbon locked in permafrost today we suggest that the disappearance of this carbon pool at the end of the last glacial maximum may have contributed to the deglacial rise in atmospheric carbon dioxide concentrations

changes in fire regimes since the last glacial maximum an assessment based on a global synthesis and analysis of charcoal data fire activity has varied globally and continuously since the last glacial maximum lgm in response to long term changes in global climate and shorter term regional changes in climate vegetation and human land use we have synthesized sedimentary charcoal records of biomass burning since the lgm and present global maps showing changes in fire activity for time slices during the past 21 000 years as differences in charcoal accumulation values compared to pre industrial there is strong broad scale coherence in fire activity after the lgm but spatial heterogeneity in the signals increases thereafter in north america europe and southern south america charcoal records indicate less than present fire activity during the deglacial period from 21 000 to 11 000 cal yr bp in contrast the tropical latitudes of south america and africa show greater than present fire activity from 19 000 to 17 000 cal yr bp and most sites from indochina and australia show greater than present fire activity from 16 000 to 13 000 cal yr bp many sites indicate greater than present or near present activity during the holocene with the exception of eastern north america and eastern asia from 8 000 to 3 000 cal yr bp indonesia and australia from 11 000 to 4 000 cal yr bp and southern south america from 6 000 to 3 000 cal yr bp where fire activity was less than present regional coherence in the patterns of change in fire activity was evident throughout the post glacial period these complex patterns can largely be explained in terms of large scale climate controls modulated by local changes in vegetation and fuel load

possible role of atmosphere biosphere interactions in triggering the last glaciation we coupled a global biome model iteratively with an atmospheric general circulation model to study the possible role of vegetation in the climate system at the time of glacial inception 115 000 years ago orbital forcing alone was not sufficient to initiate glaciation when other components of the climate system were kept as present atmospheric composition oceans biosphere and cryosphere summers were however cold enough to induce major vegetation shifts in high northern latitudes southward migration of the boreal forest tundra limit helped to create favourable conditions for continental ice sheet growth with increasing snow depth and duration in labrador arctic canada and northern western fennoscandia these results support a role for biogeophysical feedback in initiating glaciations

late quaternary vegetation history of the central mackenzie mountains northwest territories canada the sedimentary and pollen records from three lakes in the tundra forest tundra and open forest of the central mackenzie mountains of canada are described although two of the lakes lie beyond the mapped limits of late quaternary glaciation their records only extend to 12 000 yr b p the third site lies within the limits of the late wisconsin laurentide advance and a basal radiocarbon date provides a minimum date of ca 11 500 yr b p for retreat of the northwestern margin of laurentide ice artemisia and salix dominated herb tundra occurred at all elevations from at least 12 000 yr b p until ca 10 200 yr b p when shrub tundra dominated by betula glandulosa expanded throughout the region populus balsamifera was also present by this time and probably grew up to and beyond the current treeline picea arrived in the central mackenzie mountains by 8500 yr b p and expanded to the elevation of the current treeline by 8000 yr b p vegetation composition became similar to that of the present by 6000 yr b p with the expansion of alnus at all elevations pollen accumulation rates and detrended correspondence analysis suggest picea population densities in the forest tundra were greater than present between ca 8000 yr b p and 5000 yr b p and have since declined steadily at the open forest site picea population density has not declined in the late holocene but the forest composition has shifted towards a greater affinity with higher elevation sites in general the changes apparent in the treeline vegetation of the mackenzie mountains during the postglacial are consistent with predicted changes in summer insolation based on the milankovitch theory

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

integrating human dimensions of arctic palaeoenvironmental science sead the strategic environmental archaeology database environmental change has a human dimension and has had so for at least the last 10 000 years the prehistoric impact of people on the arctic landscape has occasionally left visible traces such as house and field structures more often than not however the only evidence available is at the microscopic or geochemical level such as fossil insect and seed assemblages or changes in the physical and chemical properties of soils and sediments these records are the subject of sead a multidisciplinary database and software project currently underway at umea university sweden which aims to create an online database and set of tools for investigating these traces as part of an international research infrastructure for palaeoecology and environmental archaeology

last interglacial arctic warmth confirms polar amplification of climate change the warmest millennia of at least the past 250 000 years occurred during the last interglaciation when global ice volumes were similar to or smaller than today and systematic variations in earth s orbital parameters aligned to produce a strong positive summer insolation anomaly throughout the northern hemisphere the average insolation during the key summer months m j j was ca 11 above present across the northern hemisphere between 130 000 and 127 000 years ago with a slightly greater anomaly 13 over the arctic greater summer insolation early penultimate deglaciation and intensification of the north atlantic drift combined to reduce arctic ocean sea ice allow expansion of boreal forest to the arctic ocean shore across vast regions reduce permafrost and melt almost all glaciers in the northern hemisphere insolation amplified by key boundary condition feedbacks collectively produced last interglacial summer temperature anomalies 4 5 c above present over most arctic lands significantly above the average northern hemisphere anomaly the last interglaciation demonstrates the strength of positive feedbacks on arctic warming and provides a potentially conservative analogue for anticipated future greenhouse warming

pollen representation source area and basin size toward a unified theory of pollen analysis abstract the concepts of pollen source area and of production and dispersal biases in pollen representation are quantified by means of a simple theoretical model source areas and relative pollen representation are shown to depend on basin size according to functions that describe the amount of pollen remaining airborne at increasing distances from single pollen sources the form of these functions is determined by physical processes standard formulas for elevated sources do not apply but the integrated form of sutton s equation for particle dispersal from a ground level source gives useful approximations applicable to pollen transport over a forest canopy simulations using this equation yielded source areas that increased realistically with basin size showed substantial differences between source areas for pollen grains with different deposition velocities and predicted that lighter pollen grains should become better represented with increasing basin size all of these predictions are qualitatively consistent with present knowledge of the characteristics of pollen assemblages in different depositional environments the model further allows parameters that can be estimated by statistical calibration methods to be predicted from underlying physical quantities this extension suggests procedures for testing the theory with quantitative data on surface pollen and forest composition preliminary results showed reasonable agreement between estimated and predicted values of dispersal indices for the most abundant taxa in pollen spectra from the northern midwestern united states

full glacial upland tundra vegetation preserved under tephra in the beringia national park seward peninsula alaska the nature of the full glacial vegetation of beringia has been the subject of a great deal of investigation and debate here we present a reconstruction of an intact example of the full glacial upland vegetation of part of the northern seward peninsula at one point in time the area was blanketed by more than 1 m of tephra ca 18 000 14c bp ca 21 500 cal bp and the former land surface was preserved in the permafrost the discovery of the land surface provides a unique opportunity to study a fossil ecosystem preserved in situ macrofossils were used to reconstruct the vegetation growing at several sites on the buried land surface the macrofossil assemblages indicate a vegetation characterized by graminoids and forbs with the occasional occurrence of salix arctica the vegetation was dominated by kobresia myosuroides other sedges carex and grasses with a ne scale mosaic related to snow accumulation and moisture availability overall the vegetation was a closed dry herb rich tundra grassland with a continuous moss layer growing on calcareous soil that was continuously supplied with loess nutrient renewal by loess deposition was probably responsible for the relatively fertile vegetation and the occurrence of a continuous mat of acrocarpous mosses good physiognomic analogues can be suggested but no exact modern vegetational analogues have been found probably because the full glacial environment and climate with loess deposition do not occur today 2000 elsevier science ltd all rights reserved

simulation of the last glacial cycle by a coupled sectorially averaged climate ice sheet model 2 response to insolation and co2 variations a two dimensional climate model which links the northern hemisphere atmosphere ocean mixed layer sea ice and continents has been asynchronously coupled to a model of the three main northern ice sheets and their underlying bedrock the coupled model has been used to test the influence of several factors including snow surface albedo over the ice sheets in producing plausible ice age simulations using astronomically derived insolation and co2 data from the vostok ice core the impact of potentially important processes such as the water vapor transport clouds and deep sea circulation was not investigated in this study after several sensitivity experiments designed to identify the main mechanism governing surface temperature and ice accumulation the model is first run with ice sheet feedback by forcing it only with the astronomical insolation over the past 122 kyr large variations of ice volume are simulated between 122 and 55 kyr b p with a rapid latitudinal extension of the north american and eurasian ice sheets starting at 120 kyr b p the simulated last glacial maximum is at 19 kyr b p the model is able to simulate deglaciation as well the simulated evolution of the three northern ice sheets is generally in phase with geological reconstructions the major discrepancy between the simulation and paleoclimate reconstructions lies in the underestimation of temperature variations linked with an underestimation of the ice sheet extent and an excess in the prescribed co2 concentration sensitivity experiments show that ablation is more important to the ice sheet response than snow precipitation variations in the model a key mechanism in the deglaciation after the last glacial maximum appears to be the aging of snow which decreases its albedo the other factors which play an important role are in decreasing level of importance the ice sheet altitude insolation taiga cover and ice sheet extent a final set of experiments addresses the effects of co2 on the simulated climate of the last glacial maximum and on a new long term experiment covering the last 122 kyr this last experiment is made by forcing the model with both insolation and co2 variations this additional forcing improves the temperature and ice volume results despite the limitations inherent to the present modeling approach the sensitivity experiments performed can provide insight into the relative importance of possible mechanism responsible for the building and melting of huge ice sheets during the last glacial interglacial cycle

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

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

pollen stratigraphy of eaglenest lake northeastern alberta pollen analysis of a 7 65 m sediment core from eaglenest lake 57 46 n 112 06 w provides evidence of the postglacial development of vegetation in the mixedwood section of the boreal forest from the time of deglaciation approximately 12 000 11 500 years bp to 11 000 bp the area was colonized by mainly nonarboreal flora dominated by artemisia and gramineae populus the only tree taxon present grew in sheltered areas while salix and cyperaceae were common on poorly drained sites open parkland prevailed under a dry windy climate summer temperatures were rising rapidly from glacial minima in response to increased solar insolation by 11 000 bp picea initially p glauca and betula mainly tree betula migrated to the area forest prevailed but the canopy was likely more open than at present by 9000 bp peak warm and dry conditions had passed although conditions warmer and drier than at present persisted alnus migrated to the area 8450 bp pinus reached the birch mountains about 7500 bp no maj

a pollen climate transfer function from the tundra and taiga vegetation in arctic siberia and its applicability to a holocene record abstract this study aims to establish evaluate and apply a modern pollen climate transfer function from the transition zone between arctic tundra and light needled taiga in arctic siberia lacustrine samples n 96 from the northern siberian lowlands of yakutia were collected along four north to south transects crossing the arctic forest line samples span a broad temperature and precipitation gradient mean july temperature t july 7 5 18 7 c mean annual precipitation p ann 114 315 mm yr redundancy analyses are used to examine the relationship between the modern pollen signal and corresponding vegetation types and climate performance of transfer functions for t july and p ann were cross validated and tested for spatial autocorrelation effects the root mean square errors of prediction are 1 67 c for t july and 40 mm yr for p ann a climate reconstruction based on fossil pollen spectra from a siberian arctic lake sediment core spanning the holocene yielded cold conditions for the late glacial 1 2 c below present t july warm and moist conditions were reconstructed for the early to mid holocene 2 c higher t july than present and climate conditions similar to modern ones were reconstructed for the last 4000 years in conclusion our modern pollen data set fills the gap of existing regional calibration sets with regard to the underrepresented siberian tundra taiga transition zone the holocene climate reconstruction indicates that the temperature deviation from modern values was only moderate despite the assumed arctic sensitivity to present climate change

vegetation and soil feedbacks at the last glacial maximum abstract vegetation feedback at the last glacial maximum lgm about 21 000 calendar years ago remains an unresolved question a global atmospheric general circulation model agcm is asynchronously coupled with an equilibrium terrestrial biosphere model in the present study the coupled model is then used to investigate the influences of vegetation and soil feedbacks on the lgm climate it is found that the simulated geographical distribution of vegetation at the lgm differs from the present pattern dramatically and glacial vegetation cover tends to be reduced on average vegetation feedback alone leads to an annual surface temperature decrease of 0 31 c over the lgm ice free continental areas additional soil feedback reinforced vegetation induced cooling over high latitude eurasia and from the eastern middle east eastward to the indian peninsula significantly in the tropics a terrestrial annual surface cooling of 0 45 c is produced by vegetation and soil feedbacks it is shown that vegetation and soil feedbacks partly reduce data model discrepancy as produced by the agcm alone in some regions such as central africa the indian peninsula south china and north australia

a 14 000 year pollen record from sithylemenkat lake north central alaska abstract pollen analysis of a 14 000 yr old sediment core from sithylemenkat lake provides the first holocene vegetational history for the kanuti flats of north central alaska basal samples contain a curious and unusual combination of tundra and boreal taxa pollen assemblages dating from 13 500 to 9000 yr b p are more typical of southern brooks range sites and indicate the presence of betula shrub tundra with increased populus ca 10 000 to 9000 yr b p picea glauca appeared ca 9000 yr b p and alnus ca 8000 yr b p p glauca populations declined between 7800 and 5000 yr b p with a subsequent reforestation by p mariana and p glauca this pattern is seen at other sites in northeastern alaska and suggests that the holocene history of boreal forest is more complex than thought previously

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

quantitative reconstruction of the last interglacial vegetation and climate based on the pollen record from lake baikal russia changes in mean temperature of the coldest t c and warmest month t w annual precipitation p ann and moisture index were reconstructed from a continuous pollen record from lake baikal russia the pollen sequence con01 603 2 53 57 n 108 54 e was recovered from a 386 m water depth in the continent ridge and dated to ca 130 114 8 ky bp this time interval covers the complete last interglacial li corresponding to mis 5e results of pollen analysis and pollen based quantitative biome reconstruction show pronounced changes in the regional vegetation throughout the record shrubby tundra covered the area at the beginning of mis 5e ca 130 128 ky consistent with the end of the middle pleistocene glaciation the late glacial climate was characterised by low winter and summer temperatures t c 38 to 35 c and t w 11 13 c and low annual precipitation p ann 300 mm however the wide spread of tundra vegetation suggests rather moist environments associated with low temperatures and evaporation reconstructed 1 tundra was replaced by boreal conifer forest taiga by ca 128 ky bp suggesting a transition to the interglacial taiga dominant phase lasted until ca 117 4 ky bp e g about 10 ky the most favourable climate conditions occurred during the first half of the li p ann reached 500 mm soon after 128 ky bp however temperature changed more gradually maximum values of t c 20 c and t w 16 17 c are reconstructed from about 126 ky bp conditions became gradually colder after ca 121 ky bp t c dropped to 27 c and t w to 15 c by 119 5 ky bp the reconstructed increase in continentality was accompanied by a decrease in p ann to 400 420 mm however the climate was still humid enough 0 9 to support growth of boreal evergreen conifers a sharp turn towards a dry climate is reconstructed after ca 118 ky bp causing retreat of forest and spread of cool grass shrub communities cool steppe dominated the vegetation in the area between ca 117 5 ky and 114 8 ky bp suggesting the end of the interglacial and transition to the last glacial mis 5d shift to the new glaciation was characterised by cool and very dry conditions with t c 28 to 30 c t w 14 15 c p ann 250 mm and 0 5

postglacial vegetation and climate change in the northern bristol bay region southwestern alaska pollen analysis of sediment cores from grandfather and ongivinuk lakes reveals a record of postglacial vegetation and climate change in the northern bristol bay region the chronology is based on six conventional 14c dates of bulk organic matter from the grandfather core a mesic herb tundra dominated the landscape 13 000 9800 yr b p betula shrubs probably first appeared in the region 11 300 yr b p but were restricted to favorable microhabitats until 9800 yr b p the later establishment of betula shrubs and relatively low betula pollen abundance in these records compared to other areas of eastern beringia suggest that postglacial warming in southwestern alaska was dampened by regional climatic controls possibly low sea surface temperatures of the north pacific ocean between 10 800 and 9800 yr b p diminished betula shrub cover along with decreased aquatic productivity as recorded by pediastrum cell nets and biogenic silica suggest a brief reversion to colder and drier climatic conditions possibly associated with the younger dryas event around 9800 yr b p betula shrub tundra and meadow communities expanded probably in response to increased temperature and precipitation alnus arrived and formed extensive thickets within the region ca 7400 yr b p the establishment of the modern boreal forest tundra ecotone is marked by the arrival of picea glauca at grandfather lake ca 4000 yr b p and the subsequent increase to present population densities ca 2000 yr b p the unique features of these pollen records emphasize the spatial complexity of late quaternary vegetation and climate history in eastern beringia

role of orbitally induced changes in tundra area in the onset of glaciation the link between glacial interglacial cycles and changes in insolation due to variations in the earth s orbital parameters is well established1 4 but of the attempts to simulate incipient glaciation using three dimensional general circulation models gcms driven by orbital forcing alone5 10 only one10 has been successful gcm experiments7 11 show that reduced summer insolation 115 000 years ago during an interglacial to glacial climate shift produces sufficient high latitude cooling to cause expansion of tundra at the expense of boreal forest11 which in turn can induce more cooling11 14 here we show using a global climate model that the increase in surface albedo under snow covered conditions that results from a biome model estimate11 of tundra expansion 115 000 years ago is sufficient to induce glaciation over extreme northeastern canada if the additional cooling from this estimated tundra expansion induces further expansion then widespread glaciation occurs at latitudes above 65 n these results suggest that the climate feedback from high latitude tundra expansion might have contributed to the onset of the most recent glaciation

late quaternary vegetational change in the kotzebue sound area northwestern alaska abstract two sediment cores from kaiyak and squirrel lakes in northwestern alaska yielded pollen records that date to ca 39 000 and 27 000 yr b p respectively between 39 000 and 14 000 yr b p the vegetation around these lakes was dominated by gramineae and cyperaceae with some salix and possibly betula nana glandulosa forming a local shrub component of the vegetation betula pollen percentages increased about 14 000 yr b p indicating the presence of a birchdominated shrub tundra alnus pollen appeared at both sites between 9000 and 8000yr b p and picea pollen mostly p mariana arrived at squirrel lake about 5000 yr b p the current foresttundra mosaic around squirrel lake was established at this time whereas shrub tundra existed near kaiyak lake throughout the holocene when compared to other pollen records from north western north america these cores 1 represent a meadow component of lowland beringian tundra between 39 000 and 14 000 yr b p 2 demonstrate an early holocene arrival of alnus in northwestern alaska that predates most other alnus horizons in northern alaska or northwestern canada and 3 show an east to west migration of picea across northern alaska from 9000 to 5000 yr b p

late quaternary pollen records from the kobuk and noatak river drainages northwestern alaska abstract pollen diagrams from joe and niliq lakes date to ca 28 000 and 14 000 yr b p respectively mesic shurb tundra grew near joe lake ca 28 000 to 26 000 yr b p with local populus populations prior to ca 27 000 yr b p shrub communities decreased as climate changed with the onset of itkillik ii glaciation 25 000 to 11 500 yr b p and graminoid dominated tundra characterized vegetation ca 18 500 to 13 500 yr b p herb tundra was replaced by shrub betula tundra near both sites ca 13 500 yr b p with local expansion of populus ca 11 000 to 10 000 yr b p and alnus ca 9000 yr b p mixed picea glauca p mariana woodland was established near joe lake ca 6000 yr b p these pollen records when combined with others from northern alaska and northwestern canada indicate 1 mesic tundra was more common in northwestern alaska than in northeastern alaska or northwestern canada during the duvanny yar glacial interval 25 000 to 14 000 yr b p 2 with deglaciation shrub betula expanded rapidly in northwestern alaska but slowly in areas farther east 3 an early postglacial thermal maximum occurred in northwestern alaska but had only limited effect on vegetation and 4 pollen patterns in northern alaska and northwestern canada suggest regional differences in late quaternary climates

late quaternary vegetational history of the black river region in northeastern alaska two pollen diagrams describe the previously unknown vegetational history of the black river and little black river drain ages of northeastern alaska tundra grew throughout much of the region between ca 19 800 and 15 000 years bp prior to 18 000 years bp the vegetation was dominated perhaps by xeric cyperaceae communities but apparently between ca 18 000 and 15 000 years bp a more diverse herb tundra characterized the vegetation herbaceous species continued to be important in the vegetation until ca 9700 years bp although betula nana glandulosa and salix species became more common after 15 000 years bp at ca 9700 years bp a major change in the vegetation occurred with the spread of populus probably p balsamifera b nana glandulosa and salix possibly resulting in a mosaic of shrub tundra and populus gallery forest picea glauca migrated into the black river region ca 7500 years bp followed by alnus ca 7200 years bp and picea mariana ca 6000 years bp herb zone records from the black rive

periglacial landscape dynamics in the western canadian arctic results from a thermokarst lake record on a push moraine herschel island yukon territory abstract ice rich permafrost landscapes are sensitive to climate and environmental change due to the melt out of ground ice during thermokarst development thermokarst processes in the northern yukon territory are currently not well documented lake sediments from herschel island 69 36 n 139 04 w in the western canadian arctic provide a record of thermokarst lake development since the early holocene a 727 cm long lake sediment core was analyzed for radiographic images magnetic susceptibility granulometry and biogeochemical parameters organic carbon nitrogen and stable carbon isotopes based on eight calibrated ams radiocarbon dates the sediment record covers the last 11 500 years and was divided into four lithostratigraphic units a to d reflecting different thermokarst stages thermokarst initiation at the study area began 11 5 cal ka bp from 11 5 to 10 0 cal ka bp lake sediments of unit a started to accumulate in an initial lake basin created by melt out of massive ground ice and thaw subsidence between 10 0 and 7 0 cal ka bp unit b the lake basin expanded in size and depth attributed to talik formation during the holocene thermal maximum higher than modern summer air temperatures led to increased lake productivity and widespread terrain disturbances in the lake s catchment thermokarst lake development between 7 0 and 1 8 cal ka bp unit c was characterized by a dynamic equilibrium where lake basin and talik steadily expanded into ambient ice rich terrain through shoreline erosion once lakes become deeper than the maximum winter lake ice thickness thermokarst lake sediments show a great preservation potential however site specific geomorphic factors such as episodic bank shore erosion or sudden drainage through thermo erosional valleys or coastal erosion breaching lake basins can disrupt continuous deposition a hiatus in the record from 1 8 to 0 9 cal ka bp in lake herschel likely resulted from lake drainage or allochthonous slumping due to collapsing shore lines before continuous sedimentation of unit d recommenced during the last 900 years

early wisconsinan mis 4 arctic ground squirrel middens and a squirrel eye view of the mammoth steppe abstract fossil arctic ground squirrel spermophilus parryii middens were recovered from ice rich loess sediments in association with sheep creek klondike and dominion creek tephras ca 80 ka exposed in west central yukon these middens provide plant and insect macrofossil evidence for a steppe tundra ecosystem during the early wisconsinan mis 4 glacial interval midden plant and insect macrofossil data are compared with those previously published for late wisconsinan middens dating to 25 2914c ka bp mis 3 2 from the region although multivariate statistical comparisons suggest differences between the relative abundances of plant macrofossils the co occurrence of steppe tundra plants and insects e g elymus trachycaulus kobresia myosuroides artemisia frigida phlox hoodii connatichela artemisiae provides evidence for successive reestablishment of the zonal steppe tundra habitats during cold stages of the late pleistocene arctic ground squirrels were well adapted to the cold arid climates steppe tundra vegetation and well drained loessal soils that characterize cold stages of late pleistocene beringia these glacial conditions enabled arctic ground squirrel populations to expand their range to the interior regions of alaska and yukon including the klondike where they are absent today arctic ground squirrels have endured numerous quaternary climate oscillations by retracting populations to disjunct interglacial refugia during warm interglacial periods e g south facing steppe slopes well drained arctic and alpine tundra areas and expanding their distribution across the mammoth steppe biome during cold arid glacial intervals

late quaternary lacustrine pollen records from southwestern beringia sediment cores from three lakes in the upper kolyma region northeast russia provide the first well dated continuous record of late quaternary vegetation change from far southwestern beringia the oldest pollen zone tentatively assigned to the karginsk mid wisconsinan interstade indicates an artemisia shrub tundra with pinus pumila betula and alnus at mid to low elevations with the onset of the sartan late wisconsinan stade pinus disappeared probably indicating severely cold dry winters and cool summers as conditions deteriorated further an artemisia gramineae tundra developed selaginella rupestris and minor herb taxa indicate the presence of poor soils and disturbed ground this herb tundra was replaced by a short lived 1000 yr betula alnus shrub tundra followed by the rapid establishment of a larix dahurica forest with a betula exilis ericales lichen understory populus suaveolens and chosenia may have formed limited hardwood gallery forests at this time modern vegetation associations probably developed during the early holocene with the arrival of pinus pumila ca 9000 yr b p this shrub became important in the forest understory and with b exilis formed a belt of shrub tundra beyond altitudinal treeline comparison of the upper kolyma and alaskan pollen records indicates that important differences in vegetation types and timing of vegetation change occurred across beringia during the late quaternary

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

could a 1755 like tsunami reach the french atlantic coastline constraints from twentieth century observations and numerical modeling the tsunami generated by the 1 november 1755 earthquake off the coast of portugal affected mainly the coastlines of the iberian peninsula and northwest morocco but was also observed in some places along the north atlantic coasts to determine whether the event could have effected the french coastline we conducted a study to search for signs of the tsunami in historical records from all tide gauge stations off the french atlantic coast during the twentieth century specifically for the 28 february 1969 and the 26 may 1975 tsunamis that were recorded by the portuguese tide gauge network because many recordings are available in la rochelle located on the southwest coast of france we focused our study on this harbor the analysis of the tide gauge data shows no evidence for tsunamis in la rochelle neither in 1969 nor in 1975 to confirm this lack of tsunami signals we used nonlinear shallow water equations to compute the tsunami propagation to the french atlantic coastline for both 1969 and 1975 events results obtained from these simulations confirm otherwise unnoticeable wave amplitudes at la rochelle harbor in a second step tsunamis from three different scenarios for the 1755 earthquake were modeled to estimate the impact of such a tsunami on the french atlantic coast with a focus on la rochelle harbor a comparison of the functions of tide configuration was made in order to analyse the difference in impact the results show that while the harbor is poorly impacted several areas western part of the island of re and northern coast of the island of oleron may have experienced a moderate impact from 0 5 to 1 m especially since the tide was high at the time of arrival possibly causing local inundations in lowland areas

modern and holocene pollen assemblages from some small arctic lakes on somerset island nwt canada abstract modern pollen samples from 15 lakes along a north south transect on western somerset island nwt canada show a decrease in pollen concentrations from the high arctic to the mid arctic zone but there are few differences in the pollen percentages between these sites long distance transport accounts for up to 50 of the pollen in these lake sediments cores from two lakes show few changes in the percentages of important pollen types except for an initial period before 6000 yr b p of increased salix the pollen concentration of lake rs36 from the mid arctic is twice that of lake rs29 from the high arctic and at both sites the concentrations decreased during the past 6000 yr b p this suggests a climatic deterioration during the past 6000 yr which has caused a decrease in the abundance of plants on the landscape

transient simulations of holocene atmospheric carbon dioxide and terrestrial carbon since the last glacial maximum 1 conflicting hypotheses are investigated for the observed atmospheric co2 increase of 20 ppm between 8 ka bp and pre industrial time the carbon component of the bern carbon cycle climate bern cc model which couples the lund potsdam jena dynamic global vegetation model to an atmosphere ocean sediment component is driven by climate fields from time slice simulations of the past 21 ka with the hadley centre unified model or the ncar climate system model the entire holocene ice core record of co2 is matched within a few ppm for the standard model setup and results are broadly consistent with proxy data of atmospheric 13 co2 mean ocean d 13 c and pollen data within their uncertainties our analysis suggests that a range of mechanisms including calcite compensation in response to earlier terrestrial uptake terrestrial carbon uptake and release sst changes and coral reef buildup contributed to the 20 ppm rise the deep sea d 13 c record constrains the contribution of the calcite compensation mechanism to 4 10 ppm terrestrial carbon inventory changes related to climate and co2 forcing the greening of the sahara peat buildup and land use have probably influenced atmospheric co2 by a few ppm only the early holocene co2 decrease is quantitatively explained by terrestrial uptake and calcite compensation in response to terrestrial uptake during the glacial interglacial transition the recent hypothesis by ruddiman 2003 that anthropogenic land use caused a 40 ppm co2 anomaly over the past 8 ka preventing the climate system from entering a new glacial would imply an anthropogenic emission of 700 gtc and a decrease in atmospheric d 13 co f 0 6 permil this is not compatible with the ice core d 13 c record and would require an upward revision of land use emission estimates by a factor of 3 to 4 index terms 0322 atmospheric composition and structure constituent sources and sinks 0315 atmospheric composition and structure biosphere atmosphere interactions 1615 global change biogeochemical processes 4805 1610 global change atmosphere 0315 0325 keywords carbon cycle modeling carbon dioxide holocene

holocene treeline history and climate change across northern eurasia radiocarbon dated macrofossils are used to document holocene treeline history across northern russia including siberia boreal forest development in this region commenced by 10 000 yr b p over most of russia forest advanced to or near the current arctic coastline between 9000 and 7000 yr b p and retreated to its present position by between 4000 and 3000 yr b p forest establishment and retreat was roughly synchronous across most of northern russia treeline advance on the kola peninsula however appears to have occurred later than in other regions during the period of maximum forest extension the mean july temperatures along the northern coastline of russia may have been 2 5 to 7 0 c warmer than modern the development of forest and expansion of treeline likely reflects a number of complimentary environmental conditions including heightened summer insolation the demise of eurasian ice sheets reduced sea ice cover greater continentality with eustatically lower sea level and extreme arctic penetration of warm north atlantic waters the late holocene retreat of eurasian treeline coincides with declining summer insolation cooling arctic waters and neoglaciation