charcoal records from thermokarst deposits in central yakutia eastern siberia implications for forest fire history and thermokarst development abstract macroscopic charcoal records from a thermokarst lake deposit in central yakutia eastern siberia were used to reconstruct the history of forest fires and investigate its relationship to thermokarst initiation high accumulation rates of charcoal and pollen were coincident in the basal deposits of the thermokarst lake which suggests that both were initially deposited on the forest floor and subsequently reworked and accumulated in the thermokarst depression high charcoal and pollen accumulation rates in the basal deposits dating to 11 000 9000 cal yr bp also indicate that the thermokarst topography developed during the early holocene a lower charcoal accumulation rate after ca 9000 cal yr bp suggests that thermokarst development has been inhibited since this time it also indicates that a surface fire regime has been predominant at least since ca 9000 cal yr bp in central yakutia

assessment for paleoclimatic utility of terrestrial biomarker records in the okhotsk sea sediments we measured terrestrial plant biomarker long chain n alkanes in the sediment cores taken from the sea of okhotsk to examine paleoclimatic utility of long chain n alkanes in marine sediments this study demonstrates that sedimentary record of n alkane in the sea has a high potential to provide important complementary paleo climate paleo environmental information molecular distributions of long chain n alkanes in marine sediments show a typical signature of terrestrial plant wax derived n alkanes with strong odd carbon number predominance from the last glacial to the present suggesting a source of long chain n alkanes in the okhotsk sea sediments has been terrestrial higher plants throughout the time the down core profiles of concentrations of c25 c35 n alkanes in xp07 c9 collected from the northwestern site revealed three events of enhanced terrestrial organic matter input during the last deglaciation the two pronounced events correspond to melt water pulse mwp events 1a 14 5 12 5 ka and 1b 11 6 5 ka these events possibly linked to increases in river discharge and erosion of submerged continental shelf due to drastic rise in sea level down core profiles of molecular distributions of n alkanes in the okhotsk sea sediments significantly vary over the last 25 kyr and are similar to that of a peat core sequence in the east russia and essentially consistent with pollen data from marine and peat core sequences

post saalian transformation of dry valleys in eastern europe an example from ne poland the studies were conducted in a dry valley in ne poland they were aimed at determining the origin of this structure and tracing the processes that have shaped the dry valley in a time span of about 130 ka the research included detailed geological mapping including piercing of a number of boreholes and electrical resistivity tomography ert surveys the obtained material was pollen analysed osl dated and the grain size distribution and the morphoscopy of sand quartz grains were investigated additionally the organic matter om content was determined based on the obtained results it was concluded that the structure currently occupied by sediments of the dry valley was formed during the warta stadial of the odranian glaciation saalian mis 6 as a glacial tunnel valley small probably isolated depressions functioned in the dry valley bottom after the ice sheet retreat the sediments record a full succession of climate oscillations from the eemian interglacial mis 5e pollen zones e1 to e7 through the early vistulian mis 5a 5d to mis 4 in the early vistulian the depressions functioned as lakes or got shallower and were replaced by peat bogs depending on the climate conditions during mis 4 the bottom of the dry valley was subjected to erosion as a result of concentrated water flow this caused draining of the existing depressions and their incorporation within the flow probably during mis 3 solifluction was activated on the slopes of the dry valley during lgm permafrost aggradation occurred in the study area recorded by two generations of epigenetic sand wedges and development of aeolian processes in contrast to analogous processes within the european sand belt the latter processes acted for a short time and only locally the final record are holocene soils it seems that the analysed valley is a good example of palaeoenvironmental conditions in eastern europe

peatlands of the western siberian lowlands current knowledge on zonation carbon content and late quaternary history the western siberian lowlands wsl are the world s largest high latitude wetland and possess over 900 000 km 2 of peatlands the peatlands of the wsl are of major importance to high latitude hydrology carbon storage and environmental history analysis of the existing russian data suggests that the mean depth of peat accumulation in the wsl is 256 cm and the total amount of carbon stored there may exceed 53 836 million metric tons a synthesis of published and unpublished radiocarbon dates indicates that the peatlands first developed at the end of the last glacial with a rapid phase of initiation between 11 000 and 10 000 cal yr bp initiation slowed after 8000 cal yr bp and reached a nadir at 4000 cal yr bp there has been renewed initiation particularly south of 621n following 4000 cal yr bp the initial development of peatlands in the wsl corresponds with the warming at the close of the pleistocene cooling after 4000 cal yr bp has likely led to increased permafrost and increased peatland development particularly in central and southern regions cold and dry conditions in the far north may have inhibited peatland formation in the late holocene r 2002 elsevier science ltd all rights reserved

water and magmas thermal effects of exsolution the temperature changes caused by water exsolution from magma have been determined through calorimetric measurements performed on phonolitic and albitic compositions the enthalpies of mixing of water with these melts have been derived from hf solution calorimetry made at 323 k on glass samples containing up to 5 wt water together with heat capacity data for the same series of samples mixing between aluminosilicate melts and water appears nearly ideal at magmatic temperatures with small enthalpies of mixing that are negative for both melts at low pressures but can become positive for albite at high pressure regardless of the endothermic or exothermic nature of the process water exsolution is associated with negligible temperature changes of only a few degrees even when 5 wt h2o is degassed however thermal effects might be greater for more depolymerized melts such as basalts and related compositions

development of the palaeogeography of pangaea from late carboniferous to early permian abstract old and new well and poorly known lithofacies data of moscovian and artinskian age in the area limited by the arctic sea and central africa the atlantic ocean and the ural mountains have been plotted on present day maps the facies mapped and related environments allow the recognition of a series of different palaeogeographic palaeotectonic units including the late carboniferous to early permian deep sea to palaeo tethyan ocean west siberia kazakhstan continent and uralian kazakhstan tienshan arc uralian foredeep up to the closing arms of the uralian ocean precaspian basin russian platform donets rift basin caucasian moesian dobrogean polish oslo basinal belt syn tectonic hercynian foreland basin intramontane post hercynian basins iran anatolian hellenic dinaric carnic basin branching into the hungarian seaway apennine basin branching into the cantabrian and south portuguese basins oman iraq levantine sicily deep basin and inferred oceanic sea way south peri tethyan platform basins east arabian cratonic basin and north african intracratonic basins the subsidence sedimentation trends of these units were correlated and compared through lithostratigraphic logs bathymetric curves and uncorrected cumulative stratigraphic curves the sets of original and processed data were used to test two different palaeodynamic models a pangaea a model static from late carboniferous to triassic and a mobile pangaea b model with different dextral displacements between laurussia and gondwanaland in the same time interval the best fit for our data requires a strike slip offset of about 800 km from moscovian to artinskian time this model implies a first quasi pangaea or pangaea b assembly at the carboniferous permian transition an ephemeral pangaea b break up driven by an early permian oblique rift across the mediterranean to caribbean areas and a final pangaea a assembly in the mid to late permian the two palinspastic maps describing the model have been cross checked by comparison with an independent set of biogeographic features of late carboniferous and early permian overall floral reptile and marine benthic organism distribution is consistent with the early permian trans pangaea seaway inferred from facies and palaeodynamic analyses

epeirogenic motions of africa as inferred from cretaceous shoreline deposits epeirogenic motions can be quantified if paleodatum planes can be recognized these motions have been determined for the time interval mid cretaceous cenomanian to recent in continental africa using the vertical displacement of ancient shoreline sediments and other nearshore or low elevation deposits that are inferred to represent a cenomanian sea level datum plane the cretaceous trans saharan seaway brought shoreline sediments deep into the african continental interior and additional data suggest that most of the remaining terrestrial regions were also low lying during the cenomanian the present elevations of the sea level sediments indicate that large portions of africa have undergone epeirogenic uplift since the cenomanian the character of the motions in north africa can be described as small scale high amplitude 3 km doming separated by relatively flat lying areas of deposition the largest single epeirogenic feature is the uplift associated with red sea and east african rift development the timing of post cenomanian epeirogenic motions can be further constrained using paleontologic k ar faulting paleodrainage and sedimentary data the most likely causal mechanism for african epeirogeny may be hot spot activity reflective of the mantle convection regime underlying the african lithosphere

groundwater flow and chemistry of the oases of al wahat ne libya the quality and geochemistry of groundwater are significantly affected by the depositional environment of aquifer sediments miocene sediments in al wahat area jalu awjilah and shakherah oases in the libyan desert at the north east of the country have been deposited in fluvial marginal marine and marine environments the purposes of this paper are to describe the areal distribution of the dominant water quality constituents to identify the major hydro geochemical processes that affect the quality of water and to evaluate the relations of sedimentary depositional environments and groundwater flow to the quality and geochemistry of water in aquifer sediments of post eocene this study is the first investigation in al wahat oasis and also in the whole sahara which introduces the importance of considering the end members and the synsedimentary influence for the interpretation of the aquifer hydrochemistry the area involved in this study is within the boundaries 28 n 30 n and 21 e 23 e eighteen wells are selected in the area including eight piezometers and ten samples were analysed from wells used for domestic and agricultural purposes results show high and significant increase in total dissolved solids especially na cl so42 and no3 compared with the previous years the chemical results for the groundwater samples in al wahat are classified according to the stuyfzand groundwater classification system the water type is mostly brackish and brackish saline nacl in the downstream direction and fresh brackish nahco3 upstream these water types indicate that groundwater chemistry is changed by cation exchange reactions during flushing of the diluted saline aquifer by freshwater from the south the different stages of cation exchange produce a chromatographic sequence of groundwater types these cation exchange reactions during the freshening process occur mainly in the intercalated clay resulting in a na increase and peaks of k and mg2 in the aquifer in the north the synsedimentary marine influence on the groundwater is stronger and the abstraction for irrigation is higher upconing of deep saline water and anthropogenic pollution may contribute significantly to the aquifer water quality calcite equilibrium and gypsum dissolution are also important hydrochemical processes in the aquifer

an alternative to exotic spore or pollen addition in quantitative microfossil studies uncertainties in availability and formulation of exotic microfossils e g lycopodium spp eucalyptus spp to be added to microfossil preparations may be resolved by the use of plastic microspheres 25 0 1 0 m which are unaffected by standard pollen preparative treatments koh hcl hf acetolysis and organic solvents the microspheres are sensitive to strongly oxidizing treatments e g schulze s reagent h2o2 h2so4 reflux for diatom preparation but can be added following digestion of organic material preparation of microsphere suspensions in a suitable electrolyte e g nacl formic acid water permits calibration by coulter counter of suitable dilutions e g 5000 100 ml 1 for delivery by tipet volumetric flasks the uniformity and distinctive appearance of the microspheres not only facilitate recognition but also provide a constant reference for both size 25 m and volume 8180 m3 as well as a reference standard for computerized microfossil scanning the microspheres are inert

an integrated model of magma chamber conduit and column for the analysis of sustained explosive eruptions abstract explosive volcanic eruptions comprise a complex series of processes involving withdrawal from the magma chamber magma ascent along the conduit and eruption column dynamics numerous studies have modeled the different sub domains of a volcanic system but their interplay has seldom been analyzed to this end we developed c 3 c cubed that stands for chamber conduit and column a new integrated model that describes the dynamics of an explosive eruption as a series of steady state regimes and as a function of geometry and initial conditions of the magma reservoir we used global sensitivity analysis to quantify the role of the relevant model parameters and describe the interplay between the different volcanic sub domains in particular we analyzed the evolution of a sustained explosive eruption in order to identify the conditions for buoyant super buoyant and collapsing columns input data were based on field reconstructions of quaternary explosive eruptions in the vulsini volcanic district roman province central italy model results show that 1 the column regime although affected by complex interactions among several factors mostly depends on the conduit radius the volatile content i e supersaturation concentration at the top of the chamber and length of the conduit in decreasing level of importance 2 the amount of mass erupted is independent of the conduit radius and depends mostly on volatile supersaturation the radius of the magma chamber the length of the conduit and the overpressure at the conduit inlet 3 the mass flow rate column height and duration of the eruption are largely controlled by the conduit radius 4 the flow pressure and density at the conduit exit are mostly controlled by the conduit inlet overpressure at the onset of the eruption and by the length of the conduit at the end of the eruption 5 the exit velocity from the conduit is mostly controlled by the volatile content the length of the conduit and the inlet overpressure in this model framework and with specific reference to selected plinian events of the vulsini volcanic district simulation results show that column collapse is not achieved for reasonable eruption durations order of hours and conduit widths tens of meters this is consistent with field reconstructions suggesting that column collapse did not likely occur and that pyroclastic flows were therefore generated by independent mechanisms from ring fissures and or multiple vents concomitant to caldera collapse

holocene pollen stratigraphy indicating climatic and tree line changes derived from a peat section at ortino in the pechora lowland northern russia this study presents the results of pollen analysis and radiocarbon dates of a peat section from ortino in the pechora lowland in northern russia a pollen stratigraphy is provided for at least the last 9200 years and it provides a basis for the reconstruction of the vegetational and mire history in the northernmost part of european russia conifer stomata content was recorded as a complement to pollen studies to achieve a better resolution of tree line fluctuations the onset of holocene warming initiated a vegetation succession that started first with herb dominated tundra vegetation and later with herb shrub tundra combined pollen and stomata evidence suggests that picea accompanied by betula spp spread to ortino soon after 9000 14c yr bp trees and a climate warmer than at present persisted until c 3000 14c yr bp when forests disappeared and modern dwarf shrub tundra vegetation developed

mid holocene warming in the northwest kola peninsula russia northern pine limit movement and stable isotope evidence a set of 40 subfossil scots pines pinus sylvestris l was sampled in small lakes beyond the modernpine limit in the northwest kola peninsula russia radiocarbon dating suggests that the pine exp

the coupled moisture heat process of permafrost around a thermokarst pond in qinghai tibet plateau under global warming due to environmental disturbances such as local human activity and global warming melting of massive ground ice has resulted in thermokarst ponds which are extensively distributed in the qinghai tibet plateau qtp besides the global warming the thermokarst pond as a major heat source speeds up the moisture change and degradation of its surrounding permafrost to analyze the long term coupled moisture heat process near a representative nonpenetrative thermokarst pond in a permafrost region abundant temperature data over multiple years at different depths and horizontal distances from the center of the thermokarst pond have been collected at a field experimental station in qtp a numerical model is built to analyze this thermokarst pond the temperature and moisture processes of surrounding permafrost are simulated by this model and compared with measured temperature data our results show that if the rate of air temperature rise is 0 048 degrees c yr which refers to a 2 4 degrees c temperature rise over 50years the thawing fronts underneath the thermokarst pond move downward at a linear rate of 0 18m yr and the permafrost beneath the pond center would disappear after the year of 2281 beyond that time the impact range of the pond on the natural ground increases to about 50m in horizontal direction so a dish shape thawing zone occurs around the thermokarst pond simultaneously the moisture state is greatly changed in 2281 and becomes completely different from that in 2013 all of these would inevitably deteriorate the ecological and environmental system in qtp

climate changes in east europe and siberia at the late glacial holocene transition abstract the main climatic oscillations of the lateglacial early holocene allerod younger dryas and preboreal can be distinguished all over eastern europe and siberia distribution of the main climatic indices in the lateglacial early holocene from west to east in northern eurasia shows that variations of the mean january temperature t jan o were larger than those of july temperature t july o as at present t jan o decreased to the east while the deviations from the present day values were greater in the west during the younger dryas the seasonality of climate increased considerably especially in the western european part of the studied area the greatest negative temperature deviations from the present day values up to 14 c occurred in the northwestern part of the east european plain near the scandinavian ice sheet it can be explained by a cooling influence from the remaining large ice body accordingly with degradation of the ice sheet at the warmer intervals of the lateglacial and early holocene the regional differences in temperature deviations became smaller up to 8 c on the whole precipitation p decreased in an easterly direction though its deviations from the modern level varied for different time intervals during the younger dryas p amounted to 60 65 of the present day values in the east european plain 80 in central west siberia and only 50 in central yakutia for the entire northern eurasia p did not exceed 300 350 mm yr in yakutia it was only 100 mm yr levels typical for present day dry steppe and semidesert zones nevertheless the reconstructed changes of the main climatic indexes were proportional to the present day climatic characteristics so that the general tendencies of their contemporary distribution in the mid latitudes were preserved during the entire lateglacial early holocene interval this shows that the general circulation of the atmosphere and geographical distribution of the main highs and lows in the studied time interval were in essence similar to the present day ones boundaries of permafrost in lateglacial and early holocene migrated in response to climate changes the southern limit of permafrost during the allerod was at 60 n in east europe and 55 n in west siberia during the younger dryas it moved south to 50 52 n in east europe and parabolic sand dunes were formed

epigenetic salt accumulation and water movement in the active layer of central yakutia in eastern siberia observations of soil moisture and salt content were conducted from may to august at neleger station in eastern siberia seasonal changes of salt and soil moisture distribution in the active layer of larch forest undisturbed and a thermokarst depression known as an alas disturbed were studied electric conductivity ece of the intact forest revealed higher concentrations that increased with depth from the soil surface into the active layer and the underlying permafrost 1 ms cm 1 at 1 1 m to 2 6 ms cm 1 at 160 cm depth in the permafrost however a maximum value of 5 4 ms cm 1 at 0 6 m depth was found in the dry area of the alas the concentration of ions especially na mg2 ca2 so42 and hco3 in the upper layers of this long term disturbed site indicates the upward movement of ions together with water a higher concentration of solutes was found in profiles with deeper seasonal thawing the accumulation of salts in the alas occurs from spring through into the growing season the low concentration of salt in the surface soil layers appears to be linked to leaching of salts by rainfall there are substantial differences between water content and electric conductivity of soil in the forest and alas modern salinization of the active layer in the alas is epigenetic and it happens in summer as a result of spring water collection and high summer evaporation the gradual salt accumulation in the alas in comparison with the forest is controlled by the annual balance of water and salts in the active layer present climatic trends point to continuous permafrost degradation in eastern siberia increasing the risk of surface salinization which has already contributed to changing the landscape by hindering the growth of forest copyright 2006 john wiley sons ltd

tectonics and subsidence evolution of the sirt basin libya a backstripping analysis of 225 wells located within the sirt basin libya provides new constraints on the development of the sirt basin four tectonic phases are identified from late jurassic to present the presentation of contour maps of subsidence and crustal stretching allows spatial and temporal variations in stretching to be visualized a close match is observed with stretching phases documented for other african basins consistent with discrete phases in the opening of the tethys and atlantic rifting and reactivation appear to be primarily controlled by the orientation of the basin and the underlying basement structure with respect to stress directions the tectonic subsidence curves have also been forward modeled with an automated modeling technique to quantify the variation in timing and the magnitude of rifting the tectonic subsidence history of the sirt basin is characterized by periods of stretching alternating with periods of relative tectonic quiescence and thermal subsidence stretching started at the centers of the troughs and migrated toward the platform crests

early tertiary subsidence and sedimentary facies northern sirte basin libya the subsidence curves and subsidence rate curves for the sirte basin constructed from the stratigraphic record show that subsidence was continuous throughout late cretaceous and tertiary times reaching a maximum during the paleocene and eocene when a major reactivation of faults occurred shales and carbonates were deposited during all of the late cretaceous and tertiary abrupt lateral facies changes occur from the platform areas toward the deeper troughs along with steep downdip thickening these conditions were probably assisted by contemporaneous faulting along structurally weak hinge lines where the dominant structural elements are normal step faults the absence of upper paleozoic and lower mesozoic sediments suggests that the area was domed faulted and eroded during the late mesozoic the widespread distribution of the maastrichtian carbonate facies over much of the platform and basinal areas suggests that tectonics were relatively inactive during the maastrichtian as a result of crustal extension during the paleocene a marked lithologic and structural change occurred the heira shale succeeded the kalash limestone in the marada trough reactivation of the earlier faults accompanied by an increase in the sediment supply from the south caused these lower paleocene shales to cover the entire area with the exception of the old highs where carbonate deposition continued an intercalation of shales and carbonates provides a sensitive indicator of change of depth and sediment type commonly this intercalation has been referred to paleocene transgressive and regressive cycles the thickness of the paleocene facies corresponds closely to the structure with the thickening in the troughs and thinning on the highs

structural and tectono stratigraphic review of the sicilian orogen and new insights from analogue modeling abstract the apennines sicilian maghrebian fold and thrust belt originated from the subduction of the alpine tethys and the later collision of drifted continental blocks against the african and apulian paleomargins from north to south the sicilian fold and thrust belt sftb is divided in four main tectono stratigraphic domains 1 the calabro peloritani terrane drifted from the european margin 2 the remnants of the alpine tethys accretionary wedge atw related to the subduction of the tethys 3 the folded and thrusted platform panormide and deep water imerese sicanian series of the offscrapped african margin and 4 the african foreland hyblean unfortunately scarce quality seismic lines and outcrops of key tectono stratigraphic units make the structure and dynamic evolution of the central eastern part of the sftb controversial first this study outlines through a review of the tectono stratigraphic evolution of the central eastern sector of the sicilian orogen the major remaining issues concerning 1 the occurrence of inferred alpine tethys units far from the region where the remnants of the atw outcrop nebrodi mountains both in a forearc position above the peloritani block to the north and in an active foreland context along the present day southern front of the belt and 2 the diverging tectonic styles from stacked large scale tectonic nappes to foreland imbricated thrust systems rooted into a main basal decollement secondly new constraints are given using analogue modeling to test mechanically the hypothesized structural and tectono stratigraphic evolution of the sftb the experiment simulates the orogenic evolution of the sftb at crustal scale from the oligocene tethys subduction to the middle miocene late pliocene continental collision between the european and african paleomargins the tectono stratigraphic synthesis is used to model the first order mechanical stratigraphy of the sedimentary units involved in the sicilian belt as well as the imprint of the african margin structural inheritance the experiments succeed in reproducing the general structure and tectono stratigraphic evolution of the sftb in particular the models support field observations hypothesing a gravity driven origin of the inferred alpine tethys units intercalated within the forearc and foreland syntectonic sedimentation moreover the model testifies of the main tectonic steps that led to the sftb building first a low tapered accretionary wedge was accreted above the alpine tethys oceanic crust from the oligocene to the early miocene the following underthrusting of the stretched african continental margin and its frontal panormide platform shortened and thickened the accretionary wedge this phase provided favorable conditions for significant pulses of reworked alpine tethys units that intercalated within the forearc and foredeep successions during the middle miocene the decollement of the african meso cenozoic cover panormide platform and imerese sicanian deep water basin enhanced a deep seated deformation phase along with duplexing of the panormide platform beneath the alpine tethys wedge leading to its emersion since the late messinian activation of basement faults led to a generalized emersion of the orogenic units through large wavelength fold culminations accompanied by syn tectonic deposition at their southern limbs concurrently the prism front was partly indented to the southeast by the thick and locally already emerged hyblean platform

late weichselian valdaian and holocene vegetation and environmental history of the northern timan ridge european arctic russia abstract lake and peat deposits from the timan ridge arctic russia were pollen analysed reconstructing the vegetation history and paleoenvironment since the last glacial maximum lgm 20 18 000 years ago the sites studied are located inside the margins of a large paleolake of about 20 km 2 by us named lake timan this lake developed in the late weichselian more than 30 000 years after the deglaciation of this region and was formed due to increased precipitation and warmer summers that accelerated the melting of stagnant ice within its catchment the lake was drained during the early holocene when the outlet rivers eroded the spillways a new generation of much smaller lakes formed during the holocene when the last remnants of buried glacier ice melted away causing the exposed floor of lake timan to subside since deglaciation the following regional vegetation development has been recorded 1 during the initial stage of lake timan the dominant vegetation was discontinuous steppe tundra with patches of snow bed vegetation 2 a dwarf shrub tundra established during the late weichselian interstadial allerod probably reflecting warmer and moister conditions 3 the younger dryas cooling is recognised by a reversal to steppe tundra and snowbeds on unstable mineral soils and higher palynological richness 4 soon after the transition into the holocene a birch forest established on the timan ridge 5 a cooling starting around 8200 cal years bp initiated the deforestation of the exposed hills in the most protected sites birch trees persisted until later than 4000 years ago reflecting a gradual development into the present treeless dwarf shrub tundra

geological and geomorphological evolution of a sedimentary periglacial landscape in northeast siberia during the late quaternary a wide variety of environmental records is necessary for analysing and understanding the complex late quaternary dynamics of permafrost dominated arctic landscapes a ne siberian periglacial key region was studied in detail using sediment records remote sensing data and terrain modelling all incorporated in a geographical information system gis the study area consists of the bykovsky peninsula and the adjacent khorogor valley in the kharaulakh ridge situated a few kilometres southeast of the lena delta in this study a comprehensive cryolithological database containing information from 176 sites was compiled the information from these sites is based on the review of previously published borehole data outcrop profiles surface samples and our own field data these archives cover depositional records of three periods from pliocene to early pleistocene the late pleistocene and the holocene the main sediment sequences on the bykovsky peninsula consist of up to 50 m thick ice rich permafrost deposits ice complex that were accumulated during the late pleistocene they were formed as a result of nival processes around extensive snowfields in the kharaulakh ridge slope processes in these mountains such as in the khorogor valley and alluvial proluvial sedimentation in a flat accumulation plain dominated by polygonal tundra in the mountain foreland bykovsky peninsula during the early to middle holocene warming a general landscape transformation occurred from an extensive late pleistocene accumulation plain to a strongly thermokarst dominated relief dissected by numerous depressions thermokarst subsidence had an enormous influence on the periglacial hydrological patterns the sediment deposition and on the composition and distribution of habitats climate deterioration lake drainage and talik refreezing occurred during the middle to late holocene the investigated region was reached by the post glacial sea level rise during the middle holocene triggering thermo abrasion of ice rich coasts and the marine inundation of thermokarst depressions

mediaeval climatic warming recorded by radiocarbon dated alpine tree line shift on the kola peninsula russia studies of the tree line history in northern fennoscandia provide useful evidence about the holocene environment and the region s climatic history here we report on late holocene alpine tree line movement in the khibiny low mountains on the kola peninsula northwestern russia a highly representative collection of subfossil woods above the modern tree line was obtained and 49 pine samples were radiocarbon dated their radiocarbon ages range from c 1400 to 3000 yr bp with a distinct maximum between c 800 and 1000 yr bp about cal ad 1000 to 1300 we conclude that especially during the mediaeval climatic optimum pine forests grew at least 100 140 m above the modern pine tree line in the khibiny mountains

environmental variability in northeastern siberia during the last 13 300 yr inferred from lake diatoms and sediment geochemical parameters abstract in northeastern siberia russia a 1 2 m sediment core was retrieved and radiocarbon dated from a small and shallow lake located at the western side of the lower lena river n 69 24 e 123 50 81 m a s l the objective of this paper is to reconstruct the palaeoenvironmental variability and to infer major palaeoclimate trends that have occurred since 13 3 cal kyr bp we analysed the diatom assemblages sedimentology grain size total organic carbon toc total nitrogen tn and the elemental and mineralogical composition using x ray fluorescence xrf and x ray diffractometry xrd of the sediment core our results show parallel changes in the diatom species composition and sediment characteristics enhanced minerogenic sediment input and the occurrence of pyrite is indicative of a cold period between 12 7 and 11 6 cal kyr bp the diatom data enable a qualitative inference about the local ecological conditions to be made and reveal an oligotrophic lake system with alkaline and cold conditions during the earliest holocene moderately warmer climates are inferred for the period from 9 1 to 5 7 cal kyr bp the major shift in the diatom assemblage from dominance of small benthic fragilarioid taxa to a more complex diatom flora with an influx of several achnanthoid and naviculoid diatom species occurred after a transitional period of about 1400 yr 7 1 to 5 7 cal kyr bp at 5 7 cal kyr bp indicating a circumneutral and warmer hydrological regime during the holocene thermal maximum htm diatom valve concentrations declined starting 2 8 cal kyr bp but have been rising again since 600 cal yr bp this has occurred in parallel to the increased presence of acidophilous diatom taxa e g eunotia spp and decreased presence of small benthic fragilarioid species in the most recent sediments which is interpreted as the result of neoglacial cooling and subsequent recent climate warming our findings are compared to other lake inferred climate reconstructions along the lena river we conclude that the timing and spatial variability of the htm in the lower lena river area reveal a temporal delay from north to south

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

vesiculation in rhyolite at low h2o contents a thermodynamic model we present experimental data on the thermodynamics and kinetics of bubble nucleation and growth in weakly h2o oversaturated rhyolitic melts the high temperature 900 1100 c experiments involve heating of rhyolitic obsidian from hrafntinnuhryggur krafla iceland to above their glass transition temperature tg 690 c at 0 1 mpa for times of 0 25 24 h during experiments the rhyolite cores increase in volume as h2o vapor filled bubbles nucleate and expand the extent of vesiculation as tracked by porosity is mapped in temperature time t t space at constant temperature and for a characteristic dwell time the rhyolite cores achieve a maximum volume where the t t conditions reach thermochemical equilibrium for each t t snapshot of vesiculation we use 3 d analysis of x ray computed tomographic xct images of the quenched cores to obtain the bubble number density bnd and bubble size distribution bsd bnds for the experimental cores are insensitive to t and t indicating a single nucleation event all bsds converge to a common distribution independent of t melt viscosity or initial degree of saturation suggesting a common growth process we use these data to calibrate an empirical model for predicting the rates and amounts of vesiculation in rhyolitic melts as a function of and thermochemical affinity a two computable parameters that are dependent on t pressure and h2o content the model reproduces the experimental data set and data from the literature to within experimental error and has application to natural volcanic systems where bubble formation and growth are not diffusion limited e g lavas domes ignimbrites conduit infill

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

the massive dolomitization of platformal and basinal sequences proposed models from the paleocene northeast sirte basin libya abstract the paleocene carbonate succession in the northeast sirte basin is composed of two shallowing upward ramp cycles where each cycle is under and overlain by deeper water pelagic facies a significant proportion of each of these two cycles is dolomitized petrographic study supported by geochemical data stoichiometry stable isotopes trace elements and fluid inclusions and integrated with broader tectono sedimentary information has provided the basis for interpreting these paleocene dolomites the use of this integrated approach in the study of dolomites suggests that despite the much publicized uncertainties in interpreting geochemical analyses of ancient dolomites the results of the paleocene dolomites show that the geochemical characteristics are generally consistent with regional stratigraphic distribution and petrographic observations four distinct types of dolomite have been recognized in this part of the sirte basin based on the stratigraphic position and petrographic criteria two of these types have a platformal setting and the other two are basinal the platform varieties consist of dolomicrites and pervasive stratal dolomites the dolomicrites interpreted to be of syn sedimentary origin were probably a product of reflux of seawater with elevated salinity as suggested by palaeoenvironmental analysis and supported by geochemical evidence the average s 80 value is 0 1 pdb the average sr content is 639 ppm the pervasive dolomites were formed during the progradation of the platform sequences and probably stabilized and augmented during shallow burial a meteoric marine mixing zone is thought to have been the most likely process for the formation of these dolomites this interpretation is supported by geochemical evidence the average 18o is 2 4 pdb the average sr content is 72 ppm combined with a favourable stratigraphic position the most characteristic feature related to both mixing zone and reflux dolomitization is the basinward movement of the dolomitizing fluids which suggests that the formation of these platform dolomites was related to a lowstand system tract the two basinal varieties comprise thick over 300 m basinal dolomudstones and fracture filling sparry dolomites the stratigraphic position of the finely crystalline basinal dolomudstones within very thick shale successions as a result of being very close to the depocentre of the sirte basin combined with geochemical evidence the average 18o is 6 4 pdb suggest that the dolomitizing fluids were basin derived with mg2 released from dewatering through compaction of basinal shales the occurrence of this type of dolomite provides one of the rare examples of large scale dolomitization of thick basinal sequences late diagenetic fracture filling dolomites exhibit a structural control on their distribution geochemical evidence including fluid inclusion analysis and the lightest oxygen isotopic signature of 7 3 pdb suggests that highly saline formation brines were the solutions responsible for their formation

rapid thermokarst evolution during the mid holocene in central yakutia russia the reconstruction of holocene thermokarst landform evolution is important to understand the potential impact of current global climate change on permafrost regions a multi proxy approach was applied to analyse the sedimentological and biogeochemical characteristics as well as pollen and lacustrine microfossils of a core profile drilled in a small pingo within a large central yakutian thermokarst basin alas age depth modelling with macrofossil 14c ages reveals high thermokarst deposit sedimentation rates and a complete thermokarst sequence spanning about 900 years during the mid holocene between 6750 and 5870 cal yr bp in total three stages of thermokarst landscape evolution have been identified thermokarst processes were initiated at 6750 to 6500 cal yr bp terrestrial conditions changed quickly to lacustrine conditions and a thermokarst lake rapidly emerged and grew to an estimated size of 120 600 m diameter and 7 5 15 m depth during only 150 years between 6500 and 6350 cal yr bp the dec

the evolution of a thermokarst lake landscape late quaternary permafrost degradation and stabilization in interior alaska thermokarst processes characterize a variety of ice rich permafrost terrains and often lead to lake formation the long term evolution of thermokarst landscapes and the stability and longevity of lakes depend upon climate vegetation and ground conditions including the volume of excess ground ice and its distribution the current lake status of thermokarst lake landscapes and their future trajectories under climatewarming are better understood in the light of their long term development we studied the lake rich southern marginal upland of the yukon flats northern interior alaska using dated lake sediment cores observations of river cut exposures and remotely sensed data the region features thick up to 40 m quaternary deposits mainly loess that contain massive ground ice two of three studied lakes formed 11 000 12 000 cal yr bp through inferred thermokarst processes and fire may have played a role in initiating thermokarst development from 9000 cal yr bp all lakes exhibited steady sedimentation and pollen stratigraphies are consistentwith regional patterns the current lake expansion rates are low 0 to b7 cmyr 1 shoreline retreat compared with other regions 30 cm yr 1 or more this thermokarst lake rich region does not showevidence of extensive landscape lowering by lake drainage nor of multiple lake generations within a basin however lidar images reveal linear corrugations n5 m amplitude deep thermo erosional gullies and features resembling lake drainage channels suggesting that highly dynamic surface processes have previously shaped the landscape evidently widespread early holocene permafrost degradation and thermokarst lake initiation were followed by lake longevity and landscape stabilization the latter possibly related to establishment of dense forest cover partial or complete drainage of three lakes in 2013 reveals that there is some contemporary landscape dynamism holocene landscape evolution in the study area differs from that described from other thermokarst affected regions regional responses to future environmental change may be equally individualistic

exsolution enthalpy of water from silicate liquids abstract because water dissolves in silicate melts as at least two species h2o molecules and oh groups the exsolution evaporation enthalpy of the h2o component from a silicate melt depends on species proportions which in turn depends on h2o pressure in this short communication a formal analysis of the exsolution enthalpy of water from a silicate melt is presented taking into account of the role of speciation the exsolution enthalpy from a rhyolitic melt at 850 c is found to increase with pressure at 100 bar and this increase is mostly caused by the speciation reaction sahagian and proussevitch sahagian d l proussevitch a a 1996 thermal effects of magma degassing j volcanol geotherm res 74 19 38 also found an increase of the exsolution enthalpy with pressure up to 20 bar for an albitic melt however the rate of increase determined from this work is an order of magnitude less than that determined by sahagian and proussevitch it is concluded that the strong pressure dependence of the exsolution enthalpy at low pressures they inferred is probably an artifact of their treatment the method presented here is general and can be applied to other multi species components

intraplate stresses and the subsidence history of the sirte basin libya abstract results of quantitative analysis of subsidence data from 20 wells covering six major basement blocks from the sirte basin libya are presented following the late cretaceous onset of extension and associated collapse of the sirte arch the tectonic history post dating this event can be separated into four distinct phases 1 1 minor subsidence during the late cretaceous 2 2 differential fault tectonics and reactivation of basement faults during latest cretaceous to paleocene 3 3 regional uplift and subsidence during the eocene 4 4 minor subsidence during the early oligocene and early miocene a late cretaceous paleocene stretching phase of finite duration can explain the overall patterns of observed tectonic subsidence during the syn and post rift evolution of the sirte basin strong short term deviations from thermally induced long term subsidence observed during the eocene can be explained by intraplate compression and subsequent stress release related to changes in atlantic flowline geometry modelling of the observed tectonic subsidence for the sirte basin yields estimates of extension in excess of estimates inferred from displacements along high angle normal faults the effect of late stage intraplate compression on tectonic subsidence may cause part of the observed discrepancy between estimates of crustal extension

stratigraphic position of the cretaceous tertiary boundary in the northern sirt basin libya abstract biostratigraphic analysis reveals that the contact of the kalash limestone with the hagfa shale does not coincide with the cretaceous tertiary boundary as previously used in the subsurface geology of the sirt basin in well a1a nc29a in the northern sirt basin the cretaceous tertiary boundary lies within the uppermost part of the kalash limestone this is based on a study of the foraminiferal assemblages below and above this boundary key species of both planktonic and benthic foraminifera are used to illustrate this conclusion the local eoglobigerina minutula zone is here proposed for the earliest palaeocene biostratigraphic interval which lies between the cretaceous tertiary boundary and the subbotina pseudobulloides zone

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

thermal effects of magma degassing abstract the thermodynamics of diffusive bubble growth is dominated by latent heat of water exsolution vaporization and the work of gas expansion p dv work a numerical assessment of the effects of these on cooling of bubbly magma water in albite indicates that a magma can exsolve volatiles at equilibrium or with varying degrees of oversaturation depending on decompression history and degassing kinetics heat of water exsolution vaporization from magmatic melts has not previously been experimentally or analytically determined and we have evaluated it from others thermodynamic functions known for the albite water system heat of exsolution is small for pressures over 100 mpa but can reach 20 kj mole at 1 2 mpa 10 20 bar oversaturation degassing at 10 20 bar can cause cooling of albite by 8 k wt of exsolved water the thermal effect of equilibrium degassing depends on the starting pressure of decompression because it follows the solubility curve for a saturated melt at 100 mpa 4 wt water it can cool a magma at least by 35 k before it disrupts into spray as gas volume fraction exceeds 0 8 although we do not specifically consider the dynamics of bubble interactions in this study our results suggest that the dynamic cooling rate could be significant at the vent of an erupting magma column and under extreme eruption conditions can lead to glass formation around fast growing bubbles of magmatic foam this could cause fragmentation into fine ash by brittle failure conversely bubble wall cooling even before glass formation can serve to reduce diffusive volatile flux into bubbles decreasing the overall cooling of the system and lead to solidification of oversaturated magmas as occasionally observed in eruption products

estimating the mass flux of charcoal from sedimentary records effects of particle size morphology and orientation reconstructing past fire requires ways to compare concentration estimates obtained by different charcoal analysis methods these methods estimate concentrations from area measurements or particle counts on pollen slides on sieves and on thin sections and they do so at different magnifications depending on particle properties each method might give substantially different results image analysis of charred particles in thin sections of lake sediments is used to parameterize relationships among different concentration estimators we determined distributions of particle size shape and orientation in undisturbed sediments and assessed how those distributions affect concentration estimates particle diameter distributions were conservative across different magnifications particle shape was also conservative with major minor axis ratios near 2 5 our derived relationships among estimators could be used to improve comparability for all but the smallest particle classes which tended to be unpredictable

holocene temperature variations at a high altitude site in the eastern alps a chironomid record from schwarzsee ob solden austria few well dated quantitative holocene temperature reconstructions exist from high altitude sites in the central eastern alps here we present a chironomid based quantitative reconstruction of mean july air temperatures tjuly throughout the holocene for a remote high mountain lake schwarzsee ob solden situated above the treeline at 2796 m a s l in the austrian alps applying a chironomid temperature inference model developed from lakes of the alpine region to a high resolution chironomid record from the lake provides evidence for early holocene ca 10000 8600 cal yr bp tjuly of up to 8 5 c i e 4 c above the modern 1977 2006 mean july temperature the reconstruction reveals the so called 8 2 ka cold event centered at ca 8250 8000 cal yr bp with temperatures ca 3 c below the early holocene thermal maximum rather warm ca 6 c and productive conditions prevailed during ca 7900 4500 cal yr bp the chironomid record suggests a climate transition between ca 5200 and 4500 cal yr bp to cooler tjuly a distinct cooling trend is evident from ca 4500 until ca 2500 cal yr bp thereafter the study site experienced its coldest conditions around 4 c or less throughout the rest of the holocene with the exception of the warming trend during the late 20th century beside other factors the northern hemisphere summer insolation seems to be the major driving force for the long term trends in tjuly at high altitudes in the eastern alps due to the extreme location of the lake and the limited temperature range represented by the applied calibration data set the chironomid based temperature reconstruction fails to track phases of the late holocene climatic history with tjuly cooler than 4 c further chironomid based palaeoclimate model and down core studies are required to address this problem provide more realistic tjuly estimates from undisturbed high altitude lakes in the alps and extract a reliable regional temperature signal

vegetation pattern and sedimentation changes in the context of the lateglacial climatic events case study of staroje lake eastern belarus abstract a lake sediment core collected from the staroje lake southeastern belarus reveals significant changes of the terrestrial and limnic environmental during the lateglacial and early holocene in the periglacial zone of the late weichselian glaciation the combination of lithological loss on ignition palaeobotanical pollen non pollen palynomorphs diatoms and isotopic 18o 13c 14c proxy parameters was applied for the reconstruction of the vegetation pattern and sedimentation regime the lateglacial pre interstadial gs 2 vegetation was dominated by mineral soil pioneers with scattered occurrence of pinus and betula an interstadial gi 1 dominated by pinus forest with increasing representation of open ground species since approximately 13 500 cal bp and lateglacial stadial gs 1 with recurring opening of the vegetation pattern with scattered tree patches including those of picea presence of pinus stomata confirms the local origin of this plant since the pre interstadial starting from the holocene birch later accompanied by other deciduous species ulmus alnus quercus corylus took over in the local vegetation structure isotopic records 18o 13c obtained on bulk carbonates as well as diatom data exhibit several shifts reflecting variations both in terrestrial and limnic environment distinct negative excursion of 18o curve recorded during the first half of the gi 1 event suggests intensive groundwater discharge accompanied by active transportation of detrital carbon in to the basin limited basin productivity is also indicated by lithological and diatom records since approximately 13 700 cal bp sedimentation regime in the lake stabilised and productivity of the basin started to increase in positive correlation with loi data a considerable decrease in 18o values punctuated by a rapid jump in the middle of the interval was recorded during the gs 1 stadial and could be associated with the deterioration of the environmental regime and degradation of the soil layer increasing erosion activity alongside the rising input of detrital carbonates into the basin the water table was low as indicated by diatom data recovery of the environmental regime preceded the gs 1 holocene boundary as is seen in lithostratigraphical and isotopic data during the early holocene stable isotopes show several episodes with altered levels suggesting instability of the environmental regime most probably related with the global climatic alterations

reconciliation of experimental results on h2o speciation in rhyolitic glass using in situ and quenching techniques in order to resolve the controversy over how to interpret experimental h2o speciation results using in situ and quenching techniques we have carried out an infrared spectroscopic study to determine whether the molecular h2o 5230 cm 1 and oh 4520 cm 1 band intensity variation with measurement temperature below glass transition is owing to species interconversion or to the temperature dependence of molar absorptivities by comparing rhyolitic glasses with different total h2o content from 0 18 to 0 76 wt we show that the peak height of the 4520 cm 1 band increases by a similar relative amount about 2 if the baseline is fit with a flexicurve and 10 if the baseline is fit by a straight line from 25 to 400oc independent of the total h2o content the results show that 1 the molar absorptivities do indeed change with temperature and 2 in our experiments below the glass transition temperature species concentrations do not change noticeably with temperature and the band intensity variations are caused mainly by changes in the shape of the absorbance bands with temperature the absence of unquenchable species reaction in the glass state on our experimental time scale confirms that speciation data can be obtained using the quench technique from 400 to 600oc on the other hand the temperature dependence of the molar absorptivities must be quantified for the full potential of the in situ technique to be realised 1999 elsevier science b v all rights reserved

terrestrial heat flow in the sirt basin libya and the pattern of heat flow across northern africa we report 66 new heat flow and 24 new heat production measurements from the sirt basin a late jurassic miocene sedimentary depression in north central libya underlain by late proterozoic basement heat flow determinations were made using bottom hole temperatures from oil wells and thermal conductivity measurements from drill core and cuttings heat production measurements come from core samples of basement rock heat flow is fairly uniform throughout the basin with a mean of 72 9 s d mw m 2 it is not clear if heat flow from the sirt basin is elevated as a consequence of its origin as a late mesozoic rift the difference between the mean basin heat flow and the global mean heat flow from tectonically undisturbed late proterozoic terrains 55 17 mw m 2 is 17 mw m 2 but this difference lies within the uncertainties associated with these mean heat flow estimates if heat flow from the sirt basin is elevated it could be caused by enhanced crustal heat production and need not be attributed to thermal alteration of the lithosphere related to basin formation mean crustal heat production is 3 9 2 1 w m 3 1 2 to 3 times greater than surface heat production in other proterozoic terrains in africa from west to east the pattern of heat flow across northern africa is characterized by high 80 110 mw m 2 heat flow throughout most of northwestern africa normal to perhaps slightly elevated heat flow in the sirt basin low to normal 35 55 mw m 2 heat flow in egypt inboard of the red sea and high heat 75 100 mw m 2 flow along the red sea high heat flow near the red sea and in northwestern africa along the mediterranean coast can be readily attributed to cenozoic tectonic activity but high heat flow in the paleozoic sahara basins of southern algeria is harder to understand within the tectonic framework of northern africa a possible explanation advanced previously is that elevated heat flow in the sahara basins arises from a regional thermal anomaly within the north african lithosphere if that explanation is correct then the heat flow distribution in the sirt basin and in egypt away from the red sea suggests that the postulated lithospheric thermal anomaly does not extend beyond the sahara basins to the east

quantitative summer and winter temperature reconstructions from pollen and chironomid data between 15 and 8 ka bp in the baltic belarus area abstract new pollen based reconstructions of summer may to august and winter december to february temperatures between 15 and 8 ka bp along a s n transect in the baltic belarus bb area display trends in temporal and spatial changes in climate variability these results are completed by two chironomid based july mean temperature reconstructions the magnitude of change compared with modern temperatures was more prominent in the northern part of bb area the 4 c winter and 2 c summer warming at the start of gi 1 was delayed in the bb area and lateglacial maximum temperatures were reached at ca 13 6 ka bp being 4 c colder than the modern mean the younger dryas cooling in the area was 5 c colder than present as inferred by all proxies in addition our analyses show an early holocene divergence in winter temperature trends with modern values reaching 1 ka earlier 10 ka bp in southern bb compared to the northern part of the region 9 ka bp

formal subdivision of the holocene series epoch a discussion paper by a working group of intimate integration of ice core marine and terrestrial records and the subcommission on quaternary stratigraphy international commission on stratigraphy this discussion paper by a working group of intimate integration of ice core marine and terrestrial records and the subcommision on quaternary stratigraphy sqs of the international commission on stratigraphy ics considers the prospects for a formal subdivision of the holocene series epoch although previous attempts to subdivide the holocene have proved inconclusive recent developments in quaternary stratigraphy notably the definition of the pleistocene holocene boundary and the emergence of formal subdivisions of the pleistocene series epoch mean that it may be timely to revisit this matter the quaternary literature reveals a widespread but variable informal usage of a tripartite division of the holocene early middle or mid and late and we argue that this de facto subdivision should now be formalized to ensure consistency in stratigraphic terminology we propose an early middle holocene boundary at 8200 a bp and a middle late holocene boundary at 4200 a bp each of which is linked to a global stratotype section and point gssp should the proposal find a broad measure of support from the quaternary community a submission will be made to the international union of geological sciences iugs via the sqs and the ics for formal ratification of this subdivision of the holocene series epoch copyright 2012 john wiley sons ltd

influence of exsolved volatiles on reheating silicic magmas by recharge and consequences for eruptive style at volcan quizapu chile the two most recent eruptions of volcan quizapu southern andes chile only 86 years apart were both triggered by magma recharge and extruded the same volume about 5 km3 of the same volatile rich dacitic magma but showed a remarkable shift from effusive 1846 47 to explosive 1932 behavior we demonstrate using a newly developed model that the presence or absence of an exsolved volatile phase in the reservoir strongly influences its mechanical and thermal response to new inputs of magma we propose that prior to the 1846 47 effusive eruption gas bubbles damped the build up of excess pressure and allowed recharge of a significant volume of magma before triggering the 1846 1847 eruption the strong temperature increase that resulted enhanced syn eruptive outgassing leading to an effusive eruption in contrast during the repose period between the 1847 and 1932 eruptions new recharges found a much less compressible host reservoir as the exsolved gas phase was largely removed in response to the prior eruption yielding rapid pressurization minor reheating and comparatively less syneruptive outgassing the combination of these effects culminated in an explosive eruption

h2o in rhyolitic glasses and melts measurement speciation solubility and diffusion dissolved h2o in silicate melts and glasses plays a crucial role in volcanic eruptions on terrestrial planets and affects glass properties and magma evolution in this paper major progress on several aspects of the h2o melt or glass system is reviewed consistency among a variety of data is investigated discrepancies are evaluated and confusion is clarified on the infrared measurement of total h2o and species concentrations calibration for a variety of glasses has been carried out at room temperature the measurements for h2o in rhyolitic glasses have undergone the most scrutiny resulting in the realization that absorptivities for the near infrared bands depend on total h2o content although the variation of the absorptivities does not seem to significantly affect the determination of total h2o it does affect the determination of molecular h2o and oh species concentrations calibration of the infrared technique for h2o in rhyolitic glasses still needs much improvement especially at high total h2o furthermore it is now almost certain that the molar absorptivities also depend on the measurement temperature in in situ studies hence it will be necessary to carry out calibrations in situ at high temperatures on h2o speciation results from two experimental approaches the quench technique and the in situ technique are very different leading to controversy in our understanding of true speciation a solution is presented to reconcile this controversy it is almost certain that the quench technique does not suffer from a quench problem but interpretation of in situ results suffered from ignoring the dependence of the molar absorptivities on measurement temperature accurate calibration at high temperatures is necessary for the quantitative application of the in situ technique to h2o speciation in silicate melts and glasses on h2o solubility in silicate melts recent experimental work has significantly expanded the t p range of solubility measurements and recent solubility models fill a gap for predicting solubility for a wide range of melt compositions i present a solubility model for rhyolitic and quasi rhyolitic melts over a wide range of t and p 500 1350 c 0 8 kbar by incorporating the role of speciation the solubility model is able to recover the experimental solubility data and has extrapolative value although the partial molar volume of h2o derived from the solubility model differs from that derived from density measurements on h2o diffusion recent studies on h2o diffusion in a quasi rhyolitic melt at 800 1200 c 0 5 5 kbar and up to 7 total h2o not only provide important new diffusion data but are also challenging earlier understanding of h2o diffusion based on data in rhyolitic glasses at 400 550 c 1 bar and 0 2 1 8 total h2o a comparison between the earlier model and recent data is made the recent high temperature diffusivities at total h2o 2 can be predicted by the earlier model however at higher total h2o the earlier model fails new work is under way to understand the diffusion mechanisms at high h2o contents

holocene variations of sea surface conditions in the southeastern barents sea reconstructed from dinoflagellate cyst assemblages palynomorphs were analysed in two sediment cores from the southeastern barents sea representing the past 8 3 and 4 4 kyr high dinocyst contents and species diversity enabled the application of the best analogue method to quantitatively reconstruct sea surface salinities temperatures and ice cover using 677 modern reference sites from the north atlantic and arctic seas including new data from the barents sea reported here at the southern core site where waters are affected by the atlantic inflow sea surface conditions were relatively warm and stable between ca 8000 and 5000 calendar yr bp in contrast the past 5 kyr had periods with cooler temperatures and extended ice cover fluctuating mostly at 1 1 5 kyr frequencies at both sites most pronounced coolings occurred around 8 1 5 3 5 3 2 and 2 5 ka the northern site additionally shows younger cooling events tentatively dated to 1 4 0 3 and 0 1 ka identified variations in sea surface conditions indicate changes in atlantic water inputs to the barents sea our results generally correlate to palaeoclimatic reconstructions from northwestern eurasia exemplified by palynological records from karelia this correlation suggests that sea surface variations in the barents sea reflect large scale changes in atmospheric and oceanic interactions between the north atlantic and the arctic copyright 2001 john wiley sons ltd

sirte basin north central libya cretaceous rifting above a fixed mantle hotspot the complex pattern of horsts and grabens in the sirte basin may have developed when mesozoic drift of the african plate put north central libya over a fixed mantle hotspot in early cretaceous time 140 to 100 m y ago significant change in the motion of the plate during the prolonged residence above a hypothetical cameroon plume may have produced stress that fragmented thinned and weakened lithosphere successive uplift and subsidence along a reconstructed track of the plume as well as in the sirte basin are compatible with predicted effects of the drift of northern africa over a fixed mantle hotspot this speculation suggests a plausible alternative to the possibility that rifting throughout northern africa in early cretaceous time may have been produced along a wide zone of extension between two african plates when they were at rest relative to underlying plumes

holocene thermokarst dynamics in central yakutia a multi core and robust grain size endmember modeling approach abstract differentiating thermokarst basin sediments with respect to the involved processes and environmental conditions is an important tool to understand permafrost landscape dynamics and scenarios and future trajectories in a warming arctic and subarctic thermokarst basin deposits have complex sedimentary structures due to the variability of yedoma source sediments reworking during the late glacial to holocene climate changes and different stages of thermokarst history here we reconstruct the dynamic growth of thermokarst lakes and basins and related changes of depositional conditions preserved in sediment sequences using a combination of biogeochemical data and robust grain size endmember analysis remma this multi proxy approach is used on 10 sediment cores each 300 400 cm deep from two key thermokarst sites to distinguish four time slices that describe the holocene thermokarst lake basin evolution in central yakutia cy biogeochemical proxies and remma reveal fine grained sedimentation with rather high lake levels and or reducing conditions and coarse grained sedimentation with rather shallow lake levels and or oxidizing i e terrestrial conditions in relation to distal and proximal depositional and post sedimentary conditions statistical analysis suggests that the biogeochemical parameters are almost independent of thermokarst deposit sedimentology thus the biogeochemical parameters are considered as signals of secondary post sedimentary reworking the remma results are clearly reflecting grain size variations and depositional conditions this indicates small scale varying depositional environments frequently changing lake levels and predominantly lateral expansion at the edges of rapidly growing small thermokarst lakes and basins these small bodies finally coalesced forming the large thermokarst basins we see today in cy considering previous paleoenvironmental reconstructions in siberia we show the initiation of thaw and subsidence during the late glacial to holocene transition between about 11 and 9 cal kyrs bp intensive and extensive thermokarst activity for the holocene thermal maximum htm at about 7 to 5 cal kyrs bp severely fluctuating water levels and further lateral basin growth between 3 5 cal kyrs bp and 1 5 cal kyrs bp and the cessation of thermokarst activity and extensive frost induced processes i e permafrost aggradation after about 1 5 cal kyrs bp however gradual permafrost warming over recent decades in addition to human impacts has led to renewed high rates of subsidence and abrupt rapid cy thermokarst processes

pre eruptive magma mixing and crystal transfer revealed by phenocryst and microlite compositions in basaltic andesite from the 2008 eruption of kasatochi island volcano the august 7 8 2008 eruption of kasatochi island volcano located in the central aleutians islands alaska produced abundant compositionally heterogeneous basaltic andesite 52 55 wt sio2 that has been interpreted to result from pre eruptive magma mixing the basaltic andesite contains two populations of plagioclase phenocrysts the first volumetrically dominant population consists of oscillatory zoned phenocrysts with an overall normal zonation trend toward comparatively sodic rims an55 65 interrupted by dissolution features and spikes in calcium content up to an85 the second population consists of phenocrysts with highly calcic compositions an90 these phenocrysts contain sharp decreases in calcium content close to their rims reaching as low as an60 but are otherwise texturally and compositionally homogeneous groundmass plagioclase microlites are generally much more calcic than rims of the first phenocryst population with more than 50 of measured microlites containing an80 major minor and trace element concentrations of plagioclase microlites and phenocrysts indicate that oscillatory zoned phenocrysts derived from cooler 800 950 c more silicic mixing magma while unzoned calcic phenocrysts were associated with hotter 900 1050 c mafic magma the mixing of these magmas just prior to eruption followed by decompression during the eruption itself created high effective undercoolings in the mafic end member and lead to the nucleation of high an microlites mgo and feo concentrations of plagioclase microlites and high an phenocryst rims up to 0 4 and 1 3 wt respectively provide further evidence for high mixing and eruption induced effective undercoolings

late holocene environmental changes recorded in the deposits of paleolake of the shkotovskoe plateau sikhote alin mountains russian far east abstract new data have been obtained on the landscape evolution within basalt plateau under conditions of climatic fluctuations in the late holocene the reconstructions were based on the studies of the lacustrine swamp sequence of the larchenkovo swamp in the central part of the shkotovskoe plateau the swamp appeared in place of a paleolake the latter having passed through several stages in its evolution within the considered period the lake had the greatest area and depth about 4 48 3 9 cal ka bp under conditions of warming and increased rainfall at the final stage there were alternating intervals of the lake deepening and shallowing against the background of general waterlogging and paludification in the upper part of the peat sequence there is a volcanic ash layer b tm attributed to the baitoushan volcano eruption in ad 969 the studies permitted to identify stages in the environmental evolution and to determine the critical points in their development to analyze the natural landscape forming factors and the rate of the biotic component transformation and to make certain inferences about the geosystem stability in the past the contribution of global and regional paleoclimatic events has been estimated the intervals of warming were typically marked by increasing proportion of broadleaf species in the forests while coolings featured a higher share of korean pine and dark coniferous particularly spruce the expansion of dark coniferous forests occurred under conditions close to recent ones at about 2 63 cal ka bp while the coniferous broadleaf forests retreated towards the plateau margins role broadleaf korean pine forests increased at the medieval climate anomaly while the korean pine and spruce proportion grew at the little ice age the changes in the last 230 240 years could be related both to the natural processes such as windfalls and to forest felling larch forest persisted around the lake over the entire considered period and most probably is a relict of the last ice age

tropical salt marsh succession as sea level indicator during heinrich events abstract centennial millennial dynamics of tropical salt marsh vegetation are documented in the pollen record from marine core md03 2622 cariaco basin venezuela which spans the glacial period between 63 and 29 ka five rapid and abrupt expansions of salt marsh vegetation are linked with north atlantic heinrich events hes within each event a recurrent pattern starting with species of chenopodiaceae followed by grasses and subsequently by cyperaceae species suggests a successional process that is determined by the close relationship between sea level and community dynamics the salt tolerant chenopodiaceae at the base of each sequence indicate hypersaline intertidal environments which were most likely promoted by extremely dry atmospheric conditions rapid sea level rise characterizes the onset of he stadials causing erosion of marsh sediments and continued recruitment of pioneer species chenopodiaceae which are the only ones capable of tolerating the rapid rate of disturbance once as sea level drops or as rise decelerates marsh plants are able to trap and stabilize sediments favouring the establishment of more competitive species graminoids the increment of marsh height as a result of autochthonous sediment accumulation reduces the extent of hypersaline environments and allows the establishment of mesohaline species these results add to the scarce knowledge on tropical salt marsh ecosystems and provide independent paleoclimatic evidence on sea level changes occurring simultaneously with antarctica climate variations

thermokarst dynamics in western siberia insights from dendrochronological research abstract thermokarst dynamics and their underlying causes are investigated and reconstructed on the basis of muzhy weather station records western siberia of air temperature precipitation and snow cover and a tree ring chronology analysis of siberian stone pine pinus sibirica du tour the results indicate that the development of thermokarst over the last 50 years has depended primarily on increasing precipitation rather than increasing air temperature reconstruction of past thermokarst borderlines shows that the rate of thermokarst expansion in the second half of the 20th century increased to 7 4 cm year as compared to past rates ranging from 4 to 8 1 cm year

transient two dimensional dynamics in the upper conduit of a rhyolitic eruption a comparison of closure models for the granular stress to elucidate the role of particle collisions in redistributing momentum after fragmentation a numerical study was performed comparing the behavior of an inviscid or collision less granular material with a granular material whose viscosity and pressure were modeled using kinetic theory the granular viscosity calculation is sensitive to particle size and three particle sizes were considered 0 0002 m 0 002 m and 0 02 m a critical volume fraction of gas 0 75 identifies the onset of fragmentation dividing the region of rhyolitic magma with dispersed bubbles from the region of turbulent gas with dispersed particles the transient simulations can be divided into two dynamic regimes an initial shock followed by a transition to steady state during the initial shock phase treatment of the granular pressure and viscosity led to greater particle velocities relative to the inviscid calculation due to the development of higher gas pressure at fragmentation however as steady state is approached the viscosity slows the particle phase relative to the inviscid counterpart for particles greater than a millimeter the modeled sub millimeter particle velocity was insensitive to the treatment of the granular pressure and viscosity centimeter scale particles have a much higher granular viscosity up to 10 1 pa s and the kinetic theory calculation is thus relevant in these conditions after reaching steady state the differential velocity between gas and particles at the conduit exit correlates with particle size for both the inviscid and granular viscosity calculations negligible differential velocity develops for sub millimeter particles but centimeter scale particles exit the conduit with 5 differential velocity between phases

holocene vegetation history from the salym yugan mire area west siberia the pollen stratigraphy of an ombrotrophic patterned ridge hollow raised bog in the salym yugan mire area in boreal west siberia 60 109n 72 509e covers the entire holocene period pollen data from three parallel peat cores suggest that contrary to previous assumptions betula forests did not spread into tundra until the boreal period 9000 10000 cal bp after 9000 cal bp pinus sylvestris and picea abies forests displaced betula forests in the area and dominated until 4100 4300 cal bp when picea decreased considerably due to a climatic change and pinus sylvestris became the most abundant tree species average pollen influx estimates during the wooded period from about 9000 cal bp onwards were 5600 6350 grains cm 2 yr 1 similar to pollen trap estimates from boreal coniferous forests

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

late pleistocene and holocene vegetation and climate on the taymyr lowland northern siberia abstract pollen records from perennially frozen sequences provide vegetation and climate reconstruction for the last 48 000 14c years in the central part of taymyr peninsula open larch forest with alnus fruticosa and betula nana grew during the kargin middle weichselian interstade ca 48 000 25 000 14c yr b p the climate was generally warmer and wetter than today open steppe like communities with artemisia poaceae asteraceae and herb tundralike communities with dwarf betula and salix dominated during the sartan late weichselian stade ca 24 000 10 300 14c yr b p the statistical information method used for climate reconstruction shows that the coldest climate was ca 20 000 17 000 14c yr b p a warming allerod interstade with mean july temperature ca 1 5 c warmer than today occurred ca 12 000 14c yr b p the following cooling with temperatures about 3 4 c cooler than present and precipitation about 100 mm lower corresponds well with the younger dryas stade tundra steppe vegetation changed to betula nana alnus fruticosa shrub tundra ca 10 000 14c yr b p larch appeared in the area ca 9400 14c yr b p and disappeared after 2900 14c yr b p cooling events ca 10 500 9600 and 8200 14c yr b p characterized the first half of the holocene a significant warming occurred ca 8500 14c yr b p but the holocene temperature maximum was at about 6000 4500 14c yr b p the vegetation cover approximated modern conditions ca 2800 14c yr b p late holocene warming events occurred at ca 3500 2000 and 1000 14c yr b p a cooling little ice age took place between 500 and 200 14c yr ago

the reconstruction of boreal forest fire history from lake sediments a comparison of charcoal pollen sedimentological and geochemical indices abstract fossil charcoal fossil pollen sedimentological and geochemical analyses of lake sediments have been used previously to reconstruct a history of local fires and resulting vegetation change the rationale behind these approaches is described and the usefulness of each technique for reconstructing fire history in the boreal forest is assessed empirically historical and dendrochronological records provide regional and local fire histories for a site in wood buffalo national park alberta canada the local and regional history of fires is compared with the microscopic charcoal content macroscopic charcoal content elemental carbon content fossil pollen content sedimentology and geochemistry of annually laminated sediments from a small lake there is no significant correlation between the abundance of microscopic charcoal macroscopic charcoal and total elemental carbon content of the sediments automated measures of microscopic charcoal abundance made with an image analysis system are correlated significantly with optical counts of microscopic charcoal none of the charcoal measures provide unequivocal records of local fire activity and the abundance of microscopic charcoal appears to be influenced by variations in regional fire activity however the highest depositional rate of macrofossil charcoal occurred during the time of a fire that burned within the drainage basin variations in sedimentological measures and geochemistry do not correlate with local fire activity fossil pollen percentages and accumulation rates display a pattern of variation that is consistent with observed vegetation responses to fire in the boreal forest what is likely apparent in the pollen record are the results of a series of burns of sufficient extent and intensity to kill most of the above ground biomass of the vegetation in an area at least as great as the drainage basin the inability of evidence from lake sediments to provide detailed histories of past fire activity is not surprising given the wide range of variation in the spatial extent proximity intensity and impact of individual fires

present day variability and holocene dynamics of permafrost affected lakes in central yakutia eastern siberia inferred from diatom records thermokarst lakes are assumed to develop cyclically driven by processes that are triggered by climate and maintained by internal feedbacks that may trigger lake drainage however the duration of these cycles remains uncertain as well as whether or not they affect the stabilization of lake ecosystems in permafrost regions over millennial time scales our research has combined investigations into modern lake to lake variability with a study of the long term development of individual lakes we have investigated the physico chemical and diatom compositions of a set of 101 lakes with a variety of different origins in central yakutia eastern siberia including thermokarst lakes fluvial erosion thermokarst lakes fluvial erosion lakes and dune lakes we found a significant relationship between lake genesis and the present day variability in environmental and diatom characteristics as revealed by multi response permutation procedures indicator species analyses and redundancy analyses environmental parameters also exhibit a significant correlation with variations in the diatom data for which they may have been to a substantial extent responsible mg and so4 concentrations together with ph and water depth were identified as the most important parameters influencing the variations in the diatom data almost as much as the entire environmental parameter set we were therefore able to establish a robust mg diatom transfer function which was then applied to three holocene lake records from these reconstructions together with a general interpretation of the diatom record including e g the ratio between benthic epiphytic and planktonic taxa we have been able to infer that all three of these lakes show 1 a continuous record with no desiccation events 2 high lake water levels during the early holocene 3 centennial to millennial scale variability and 4 high levels of variability during the early holocene but rather stable conditions during the late holocene a feature that is also known from other sites around the world we therefore concluded that the development of these three lakes was mainly driven directly by the climate rather than by thaw lake cycling

abrupt increase in precipitation and weathering of soils in east siberia coincident with the end of the last glaciation 15 cal kyr bp abstract an abrupt increase in the temperature in greenland in the wake of the initiation of the bolling allerod warm phase at ca 15 cal kyr bp was followed after a few decades by a dramatic increase in the concentration of methane in the atmosphere of the earth resulting from an increase in humidity in the tropics j p severinghaus e j brook science 286 1999 930 934 analysis of a sediment core from lake baikal east siberia spanning the end of the last glacial period and the holocene revealed an abrupt stepwise 1 3 3 4 fold decrease in the concentration of several soluble elements such as na k mg ca and si in hot nitric acid extracts of small intervals 3 cm this chemical change appears to have occurred over the same time span based on similarities in the profiles of silica and diatoms found in other 14 c dated cores this suggests that the calcium rich mammoth steppe landscape r d guthrie quat sci rev 20 2001 549 573 of siberia created during the last glaciation underwent a dramatic transformation at the end of this period at the beginning of the bolling allerod warm phase due to an increase in precipitation within a time interval of less than 300 yr

constraints on cooling and degassing of pumice during plinian volcanic eruptions based on model calculations during explosive volcanic eruptions pumice clasts are transported into the atmosphere and their thermal and degassing histories determine how much volatiles are lost syneruptively this process is studied by combining a steady state eruption column model with a model for the cooling and degassing of pumice in the model we investigate the impact of various parameters e g mass eruption rate biot number eruption temperature and geometry on the cooling and degassing of pumice and find that the biot number and the eruption temperature are the most influential during typical risetimes of pumices inside eruption columns 200 300 s those smaller than 0 5 cm in diameter are found to lose little of their volatiles syneruptively and remain in thermal equilibrium with the plume in the case of larger pumices the ratio of the cooling timescale r p 2 where rp is the pumice radius and is the thermal diffusivity to the degassing timescale w 2 d 0 where w is the vesicle wall thickness and d 0 is the species diffusivity controls degassing if this ratio is larger than 50 degassing of the pumice will be nearly complete with a few percent of the original volatiles left in the outer rind of the pumice for a ratio of less than 0 1 no volatiles escape the pumice typical values for thermal and species diffusivity as well as vesicle wall thickness indicate that in the case of degassing cl and h 2 o the transition from 0 1 to 50 will be in the pumice size range of 1 10 cm here volatile concentration is a strong function of position inside the pumice suggesting that values for volatile contents measured on picked matrix glass from crushed samples may not be the best way to estimate the volatile content of matrix glass a number which is frequently used to estimate the total volatile input of volcanic eruptions this effect is even more pronounced when looking at hydrogen isotopic fractionation with larger pumices tending toward d 80

kinetics of the reaction h2o o 2oh in rhyolitic and albitic glasses preliminary results the kinetics of homogeneous reactions are important in understanding the cooling history of rocks and in understanding experimental speciation data we have experimentally studied the kinetics of the interconversion reaction between h 2o molecules and oh groups in natural rhyolitic glasses 0 5 2 3 total water and a synthetic albitic glass l total water at 400 600 c the reaction rate increases with temperature and total water content equilibrium is not always approached monotonically the speciation may first depart from equilibrium and then come back to equilibrium experimental reaction rates agree with those inferred from previous speciation data of rhyolitic glasses quenched from 850 c the experimental data are modeled successfully by considering both the reaction and the diffusion of oh that brings oh groups together to react this study shows that species concentrations in glasses quenched from 600 c reflect those at experimental temperatures unless the water content is higher than that used in the present study species concentrations in glasses with total water contents 0 8 wt and which were rapidly quenched in water from 850 c do not represent their equilibrium concentrations in the melt at 850 c but record a lower apparent equilibrium temperature that depends on water content and quench rate natural rhyolitic glasses and glass inclusions do not record preeruptive melt speciation though total water content may be conserved the experimental data are used to infer cooling rates for natural obsidian glasses pyroclastic glass fragments from the bb site of mono craters have cooling rates similar to air cooled experimental charges 3 c s different types of glasses from the mono craters have different cooling rates which cover four orders of magnitude some natural obsidians appear to have had complex cooling histories the wide range of cooling rates and thermal histories is consistent with previous inferences that some obsidian clasts at the mono craters formed as glass selvages lining volcanic conduits or dikes that were subsequently caught up in the explosive eruption which led to variable degrees of transient heating followed by rapid cooling and deposition these experimental data reveal surprisingly rich detail in water speciation in volcanic glasses and show how at least in principle quantitative constraints on thermal histories can be extracted by experimentation and application of kinetic models

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

a multiproxy study of younger dryas and early holocene climatic conditions from the grabia river paleo oxbow lake central poland abstract a multi proxy reconstruction of water depth temperature and precipitation inferred from cladocera chironomidae and pollen assemblages has been obtained from wierczyna paleo oxbow central poland during the younger dryas yd and early holocene results suggest that the yd was relatively cold and comprised two main phases the first ca 12 500 12 000 cal yrs bp is characterized by a continental climatic regime and a decrease in winter temperatures and precipitation but an increase in spring summer precipitation the second phase ca 12 000 11 500 cal yrs bp was more mild with a variable continental climate an increase in summer and winter temperature a lengthening of the growing season and increased annual precipitation the reconstructed water level generally follows changes in spring and summer precipitation and length of growing season the frequency and timing of hydroclimatic oscillations at wierczyna show strong similarities to records from other sites in europe this confirms that oxbows and valley mire ecosystems respond to rapid climate change during the yd and early holocene this study therefore brings new insights into the effects of climate changes on river environments especially during the yd we also discuss the limitations of water depth temperature and precipitation reconstructions inferred from the studied biotic assemblages

holocene paleoenvironmental implications of diatom and organic carbon records from the southeastern kara sea siberian margin diatom assemblages and organic carbon records from two sediment cores located within an estuarian bay of the inner kara sea trace changes in yenisei river runoff and postglacial depositional environments paleosalinity and sea ice reconstructions are based on modern relationships of local diatom assemblages and summer surface water salinity approximately 15 500 cal yr b p rivers and bogs characterized the study area when sea level reached the 38 to 40 m paleo isobath approximately 9300 cal yr b p the coring site was flooded from 9300 9100 cal yr b p estuarine conditions occurred proximal to the depocenter of fluvially derived material and salinity was 7 8 paleosalinity increased to 11 13 by 7500 cal yr b p following postglacial sea level rise and the southward shift of the siberian coast sharp decreases in diatom accumulation rates total sediment and organic carbon also occurred suggesting the presence of brackish conditions and greater distance between the coast and study site maximum paleosalinity up to 13 was recorded between 7500 and 6000 cal yr b p which was likely caused by the enhanced penetration of atlantic waters to the kara sea stepwise decreases to modern salinity levels happened over the last 6000 cal yr

holocene environmental history recorded in lake lyadhej to sediments polar urals russia an 1180 cm long core recovered from lake lyadhej to 68 15 n 65 45 e 150 m a s l at the nw rim of the polar urals mountains reflects the holocene environmental history from ca 11 000 cal yr bp pollen assemblages from the diamicton ca 11 000 10 700 cal yr bp are dominated by pre quaternary spores and redeposited pinaceae pollen pointing to a high terrestrial input turbid and nutrient poor conditions existed in the lake ca 10 700 10 550 cal yr bp the chironomid inferred reconstructions suggest that mean july temperature increased rapidly from 10 0 to 11 8 c during this period sparse treeless vegetation dominated on the disturbed and denuded soils in the catchment area a distinct dominance of planktonic diatoms ca 10 500 8800 cal yr bp points to the lowest lake ice coverage the longest growing season and the highest bioproductivity during the lake history birch forest with some shrub alder grew around the lake reflecting the warmest climate conditions during the holocene mean july temperature was likely 11 13 c and annual precipitation 400 500 mm the period ca 8800 5500 cal yr bp is characterized by a gradual deterioration of environmental conditions in the lake and lake catchment the pollen and chironomid inferred temperatures reflect a warm period ca 6500 6000 cal bp with a mean july temperature at least 1 2 c higher than today birch forests disappeared from the lake vicinity after 6000 cal yr bp the vegetation in the lyadhej to region became similar to the modern one shrub betula nana salix and herb tundra have dominated the lake catchment since ca 5500 cal yr bp all proxies suggest rather harsh environmental conditions diatom assemblages reflect relatively short growing seasons and a longer persistence of lake ice ca 5500 2500 cal yr bp pollen based climate reconstructions suggest significant cooling between ca 5500 and 3500 cal yr bp with a mean july temperature 8 10 c and annual precipitation 300 400 mm the bioproductivity in the lake remained low after 2500 cal yr bp but biogeochemical proxies reflect a higher terrestrial influx changes in the diatom content may indicate warmer water temperatures and a reduced ice cover on the lake however chironomid based reconstructions reflect a period with minimal temperatures during the lake history

data model comparison of the younger dryas event the younger dryas cooling event is well established in the north atlantic region through numerous climate proxy records although the climatological controls vary from site to site it is considered to have taken place between about 10 000 and 11 000 bp radiocarbon years 11 500 13 000 calendar years ago outside the north atlantic region climate proxy records and chronology commonly become problematic because of weaker signals and less dating control in addition to this evidence oceanic records reveal conflicting evidence for younger dryas forcing mechanisms and the timing of events we compare proxy evidence with the results from an ocean general circulation model coupled to the energy moisture balance atmospheric model the model results reveal a global pattern and regional magnitude which generally agree with temperature changes interpreted from paleoclimate reconstructions the model also supports the general duration of global cooling of the younger dryas although proxy data can be controversial outside of the north atlantic region the authors believe that there is enough evidence to support the younger dryas event on a global scale they also recognize however that more concrete evidence is needed before the question can be unequivocally answered

holocene development of the rogovaya river peat plateau european russian arctic in this study the holocene development of a peat plateau area in the east european russian arctic is reconstructed based on detailed macrofossil physico chemical and radiocarbon analyses from two peat sequences basal dates from these two c 2 m long peat profiles are c 9420 bp and c 9250 bp from another six peat sequences gross stratigraphic descriptions and additional radiocarbon dates are available basal dates from two short 1 m peat profiles indicate further peatland expansion at c 3635 bp and c 1285 bp the oldest macrofossils of tree birch are dated to c 9500 bp and those of conifers presumably spruce to c 8000 bp tree stands became rare in the study area after c 2800 bp but occasionally occur until present peatlands formed through terrestrialization of ponds or paludification of forested uplands between 9000 and 3100 bp the peatlands were wet rich fens beginning from c 3100 bp there are marked changes in their surface hydrology connected with climatic cooling and permafrost

the postglacial pleistocene of the northern russian mainland abstract the paper summarizes the results of recent studies of late pleistocene postglacial geological events which occurred in the flatlands of northern russia stretching from the timan ridge to the laptev sea coast the available sedimentary record includes thawed and perennially frozen subaerial sediments and in places lacustrine and fluvial formations hundreds of geochronometric measurements by radiocarbon and luminescence techniques place this record within the time span of 50 11 ka bp which confirms an early mid weichselian age of the underlying glacial complex first established by the queen programme the spectrum of proxies includes sedimentary facies pollen data plant macrofossils oxygen isotope values megafauna remains insect assemblages traces of dna paleosols and permafrost properties together they indicate a continental progressively deteriorating climate with very cold winters and warmer than present summers through the second half of the late pleistocene minor climatic fluctuations are largely due to slightly changing humidity during mis 3 these changes are more pronounced in periglacial european russia in the vicinity of the barents kara ice sheet where the mid weichselian biotic maximum contrasts with conditions in the late weichselian polar desert in siberia the periglacial environments were more stable and beneficial for biota inspite of the increased continentality the recent data accumulated by various researchers are incompatible with the conventional correlation of the karginsky interglacial strata of siberia with mis 3 or any part of the european pleniglacial

mesolithic neolithic settlements minino 2 and zamostye 5 in their geo environmental setting upper volga lowland central russia abstract the local landscapes of early mesolithic neolithic settlements within the upper volga outwash plain are reconstructed based on the investigation of the multilayer archaeological sites minino 2 and zamostye 5 moscow district russian forest zone according to former descriptions by the authors vandenberghe et al 2010 regional environments in the different stages of the holocene beginning from the preboreal are considered using pollen data while local landscapes including relief soil vegetation and water regime are reconstructed on the base of sediments fossil soils and macrofossils as preserved in a series of burial pits of different age colonization of the area by hunters fishermen followed the local proglacial lake filling and shallowing at the end of the lateglacial postglacial period about cal 12 0 12 2 ka bp drying landscape inherited sharply undulating topography where elevated dry sites were populated up to a flooding episode between cal 2 5 and 2 8 ka bp or about 850 bc water receded between 1 7 and 1 9 cal ka bp while large scale peat accumulation and wetland expansion began about 650 700 bp during the holocene depressions had been gradually filled with organic deposits reflecting change of hydrological regimes the most significant wetting occurred about cal 5 3 5 4 ka bp soil evolution has proceeded from initial calcareous alkaline soils to leached acid soils and further to peaty soils

holocene paleohydrology and paleoclimate at treeline north central russia inferred from oxygen isotope records in lake sediment cellulose lake water oxygen isotope histories for three lakes in northern russia derived from the cellulose oxygen isotope stratigraphies of sediment cores provide the basis for preliminary reconstruction of holocene paleohydrology in two regions along the boreal treeline deconvolution of shifting precipitation 18o from secondary evaporative isotopic enrichment is aided by knowledge of the distribution of isotopes in modern precipitation the isotopic composition of paleo waters preserved in frozen peat deposits as well as other supporting paleoclimatic information these data indicate that during the early holocene when the boreal treeline advanced to the current arctic coastline conditions in the lower yenisey river region were moist compared to the present whereas greater aridity prevailed to the east near the lower lena river this longitudinal moisture gradient is consistent with the suggestion that oceanic forcing increased sea surface temperatures in the nordic seas and reduced sea ice cover was a major contributor to the development of a more maritime climate in western eurasia in addition to increased summer insolation east of the taimyr peninsula large tracts of the continental shelf exposed by glacial sea level drawdown may have suppressed maritime climatic influence in what are now coastal areas in contrast during the late holocene the two regions have apparently experienced coherent shifts in effective moisture the similarity of the records may primarily reflect reduced north atlantic influence in the nordic seas and southward retreat of coastline in eastern siberia coupled with declining summer insolation