mechanical interactions between rigid particles in a deforming ductile matrix analogue experiments in simple shear flow abstract the mechanical interaction between two or more particles is investigated in newtonian simple shear flow the experimental models allow observation of both the particle rotation and the deformation pattern around the particles the finite and instantaneous strain patterns around rigid particles are strongly heterogeneous and asymmetric with high finite strain zones aligned to the direction of maximum finite stretch these correspond to local flow with low vorticity number heterogeneous strain patterns around rigid particles spread over a distance of 1 2 times the particle length and this distance increases with increasing bulk strain where rigid particles are more concentrated these patterns coalesce and the overall pattern is then strongly controlled by the particles and cannot be simply related to the external boundary conditions in rocks the characteristic asymmetric strain pattern around rigid isolated particles is a reliable shear criterion which becomes unreliable with high concentrations of rigid particles particle rotation is significantly disturbed when the distance between adjacent particles of equal size is shorter than their length that is only in very concentrated suspensions of rigid particles in a composite shape fabric the development of the sub fabric corresponding to the smaller minerals will be more disturbed

organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

vegetation dynamics around lake baikal since the middle holocene reconstructed from the pollen and botanical composition analyses of peat sediments implications for paleoclimatic and archeological research the present paper summarizes the current evidence of natural changes in the forest and forest steppe areas of the lake baikal region lbr since ca 7 cal ka bp covering the period from the late neolithic to the present time to reconstruct local to small regional scale vegetation changes and their probable causes during this period pollen content and peat botanical composition were analyzed from three radiocarbon dated peat sections located near lake baikal for better understanding of the local and regional environmental history and climate variability during the middle and late holocene the results are compared with published environmental records from lacustrine and mire sediments from the lbr and from elsewhere the comparison confirms the earlier interpretations that the middle and late holocene vegetation dynamics in the lbr was primarily driven by natural forcing and likely was associated with large scale circulation processes controlling the regional water balance rather than with human activities some synchronous changes in environmental and archeological data likely point to a possible causal link between past climate changes and the cultural history of the region the kuchelga 53

modes of detachment at the inclusion matrix interface abstract with the help of a 2d theoretical model this paper analyses the modes of matrix detachment around a circular elliptical rigid inclusion under pure and simple shear bulk deformations three modes of matrix detachment are possible mode 1 the matrix is displaced normal to the inclusion boundary forming fissures at the interface mode 2 the matrix slips along the inclusion boundary without any separation mode 3 the detachment occurs by a combination of modes 1 and 2 in order to determine the onset of detachment at any point on the coherent inclusion matrix interface the tensile and shear stresses were derived at that point and compared with imposed critical values numerical simulations based on the theoretical model reveal that the three modes occur systematically along the inclusion matrix interface the geometrical dispositions of which depend on the aspect ratio r and orientation of the inclusion in the case of circular inclusions mode 1 and mode 2 domains are separated by a mode 3 domain and the disposition shows an internal symmetry on the other hand it is asymmetrical when the inclusions are elliptical and oriented oblique to the bulk extension direction in pure shear and to the shear direction in simple shear in simple shear mode 2 detachment with synthetic slip occurs dominantly when is less than 45 and greater than 135 the results obtained from numerical models are complemented with observations in physical experiments the paper also determines theoretically the critical stresses for detachment to occur as a function of r for different values revealing that for a given mechanical strength of the inclusion matrix interface a particular mode of detachment can take place only when the aspect ratio crosses a threshold value

2 d rotation behavior of a rigid ellipse in confined viscous simple shear numerical experiments using fem abstract the rotation behavior of rigid elliptical inclusions adherent to the viscous matrix in simple shear flow is investigated using a 2 d finite element numerical model several simulations were performed using different ratios s between shear zone width and inclusion s least principal axis a computational strategy was devised to calculate pressure and viscous forces exerted on the inclusion and deduce its angular velocity for large s values results agree remarkably well with theoretical predictions while for small s values results deviate significantly from theory but are in agreement with previous analogue experiments the numerical model provided detailed and coherent information about the physical parameters involved in the process e g pressure strain rate and vorticity distributions within the model

an expanded calibration model for inferring lakewater and air temperatures from fossil chironomid assemblages in northern fennoscandia chironomid temperature inference models based on an expanded data set of surface sediment and limnological data from 53 subarctic lakes in northern fennoscandia have been developed using eight different numerical techniques each based on slightly different underlying statistical models or ecological assumptions the study sites are mostly small shallow bathymetrically simple oligotrophic lakes with a ph range from 5 0 to 7 8 a total organic carbon range from 2 5 to 12 6 mg l 1 a mean july lakewater temperature ranging from 6 1 to 15 4 c and a mean july air temperature ranging from 8 5 to 14 9 c a series of redundancy analyses rda identified sediment organic content maximum lake depth and lakewater temperature as being the most important explanatory variables variance partitioning by partial rdas further suggested that each of these variables accounted for a significant fraction of variance independent from each other different cali bration models were assessed on the basis of their statisti

mantled porphyroclast gauges we investigate the behavior of the isolated mantled porphyroclast in a shear zone the method employed is a finite element model three distinct phases clast mantle and matrix are present the rheologies are power law with exponents ranging from 1 to 5 and the far field boundary condition is simple shear the effective viscosity of the mantle is assumed to be less than those of the clast and the matrix we show for which parameter sets mantled porphyroclasts reach super horizontal stabilization with respect to the shear plane and sense clasts in natural mylonites frequently exhibit similar orientations which are interpreted as stable inclinations the systematic examination of the matrix mantle clast system allows for the construction of attractor maps that can be directly used as gauges for i the effective viscosity contrast between matrix and mantle ii the production rate of mantle material around the clast as a function of the bulk shear strain and iii for the total shear strain the necessary data required to use the attractor maps are simple geometrical parameters that can be measured in the field i e clast aspect ratio clast inclination versus the shear plane mantle thickness and mantle and clast area this new method successfully reproduces the characteristics of natural porphyroclasts and is in good agreement with data from natural shear zones q 2005 elsevier ltd all rights reserved

drastic desalination of small lakes in east siberia russia in the early twentieth century inferred from sedimentological geochemical and palynological composition of small lakes reconstruction of temporal and spatial climate development on a seasonal basis during the last few centuries may help us better understand modern day interplay between natural and anthropogenic climate variability the objective of this paper is to reconstruct hydrology and landscape changes of east siberia during the termination of the little ice age and the subsequent recent warming we analysed sediment samples from the saltwater sulfatnoe lake bolshoye alginskoe and freshwater shuchie lake using high resolution x ray fluorescence spectroscopy at 1 mm scan resolution fourier transform infrared techniques and pollen analyses the depth age models of the cores were constructed by 210pb activity using the constant rate of supply model the lake sediment cover of these lakes began to form from ca 1870 three significant periods 1870 1895 1895 1925 and from 1925 to the present were defined in hydrology and chemical regime of these lakes for the past 140 years lake levels were extremely low and high saturated with salts during the final period of the little ice age lake levels began to slowly rise from 1870 to 1895 and vegetation was poor at that period intensive desalination of the lakes occurred in 1895 1925 and environment conditions were temperate and favourable for the majority of the taxa of the regional vegetation regional precipitation significantly increased and water saturation of the catchments was high from 1925 to the present the chemical precipitation of carbonate stopped completely in lake shichie and reduced considerably in lake sulfatnoe and b alginskoe strong increasing trend of weathering of the lake catchments began in 1970 and still continues

seasonal and centennial cycles of carbonate mineralisation during the past 2500 years from varved sediment in lake shira south siberia shira lake is a good representative object for detail weather climate modeling due to its local hydroclimatic information and annually laminated bottom sediments carbonate biochemical mineralization in shira lake shows not only seasonal but also centennial pulses over each 450 500 years an age depth model has been built by layer counting combined with 137cs and 14c isotopic dates thermodynamic estimation of the rock water multisystem in conformity with local conditions and source matter provides grounds for interpretation of measured geochemical parameters in sediments including environmental indicators such as temperature salinity and ph scanning x ray fluorescence for sub millimeter microstratigraphic study of varves connects geochemical oscillations of microelement content rb ti ca sr br xrd with seasonality as well as revealing centennial pulses of environmental change quantitative environmental reconstruction using multiple regression for precipitation calibrated by hydrometeorological time series year by year was carried out for the lake over the last 2500 years

reconstructing hydrological variability in lake baikal during mis 11 an application of oxygen isotope analysis of diatom silica in this paper we reconstruct hydrological variability in lake baikal during marine isotope stage 11 mis 11 427 362 ka bp from oxygen isotope analysis of diatom silica highest d 18 odiatom values are found during mis 11 3 highlighting the dominance of hydrological input from rivers flowing into the south and central basins of lake baikal especially the selenga river hydrological input from south basin rivers dominated for over 30 ka however there is evidence from both biogenic silica and d 18 odiatom records for an abrupt cooling event at ca 390 ka bp stadial conditions at this time are coincident with an iceberg discharge event into the north atlantic the decline in d 18 odiatom values suggests increasing proportion of hydrological input from rivers to the north of lake baikal due to greater influence of winter precipitation and snow melt after a period of interstadial conditions during the early stages of mis 11 1 biogenic silica and d 18 odiatom values decline mirroring the slow growth in northern hemisphere ice sheets despite rigorous cleaning procedures palaeoclimatic inferences need to be treated with caution due to contamination of the d 18 odiatom record during stadial and glacial periods contamination of the d 18 odiatom record is even more significant natural environment research council nerc copyright 2008 reproduced with the permission of nerc published by john wiley sons ltd

evidence of lateglacial and holocene climatic change and human impact in eastern anatolia high resolution pollen charcoal isotopic and geochemical records from the laminated sediments of lake van turkey annually laminated sediments from lake van spanning about 13000 varve years were sampled for stable isotopic geochemical pollen and charcoal analyses in order to find evidence of past regional climatic changes and human impact in the semi arid region of eastern anatolia turkey the lateglacial period was cold and dry with steppe vegetation and saline lake water during the younger dryas the lake level dropped dramatically and the vegetation turned to a semi desert geochemical and isotopic records indicate a strong increase in moisture at the onset of the holocene and artemisia chenopod steppes were partly replaced by grass steppe and pistachio scrub a delay of about 3000 years in the expansion of deciduous oak woodlands and high steppe fire frequencies suggest dry spring and summer weather during the early holocene at 8200 yr bp a shift in the regional climate regime facilitated the transport of more moisture into the interior areas of the taurus mountains and caused a change in the seasonal distribution of precipitation the steppe forests dominated by quercus advanced and reached their maximum extention at about 6200 yr bp all the proxy data indicate optimum climatic conditions low water salinity and high lake level between 6200 and 4000 yr bp after 4000 yr bp aridity increased again and the modern climatic situation was established human impact in the catchment of lake van started at 3800 yr bp and was intensified during the last 600 years

glacier dynamics in the southern part of east siberia russia from the final part of the lgm to the present based on from biogeochemical proxies from bottom sediments of proglacial lakes abstract in the present study we have reconstructed glacier dynamics based on the high 1 0 5 mm resolution x ray fluorescence spectrometry scanning the fourier transform infrared technique and 14c dating used in the analyses of the lake bottom sediments fluvioglacial deposits and a peat bog situated on east siberian mountains east sayan baikal barguzin and kodar ridges between 51 723 n 100 601 e and 56 885 n 117 580 e we have found what the largest glacier deposits on the baikal shoreline so called tompuda end moraine formed in two stages the first stage occurred until ca 12 cal ka bp then there was a short pause the second stage ended by 9 5 cal ka bp azarova glacier kodar ridge retreated upwards the kodar ridge by ca 11 cal ka bp it may indicate that the bolling allerod warming was very evident and it was a trigger for these deglacial events in east siberia it is most likely that remains of the late pleistocene glaciers were cardinally shrunk or fully disappeared during the holocene thermal optimum in the southern part of east siberia climate conditions were suitable for glacier formation after 3 cal ka bp however if there were new glaciers in the middle holocene their sizes were likely to be less than 1 km2 for this reason these glaciers should have completely melted during the roman and medieval warm periods it is most likely small glaciers observed at present in the south of east siberia were mainly formed during the little ice age

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

multiproxy evidence for abrupt climate change impacts on terrestrial and freshwater ecosystems in the ol khon region of lake baikal central asia abstract a palaeolimnological study of lake khall was undertaken to reconstruct impacts from five thousand years of climate change and human activity in the ol khon region of lake baikal taiga biome dominated regional landscapes although significant compositional turnover occurred due to the expansion of eurythermic and drought resistant scots pine climate during the mid holocene was wetter than the present and lake khall was fresh with abundant molluscs by 4 4 cal ka bp sedimentary geochemistry indicated a gradual change in lake water chemistry with an increase in lake salinity up to the present day most likely controlled by groundwater influences vegetation turnover rate was highest between 2 75 and 2 48 cal ka bp with the onset of drier more continental climate which resulted in an influx of aeolian particles to the lake this abrupt shift was coincident with ice rafted debris event ird 2 in north atlantic sediments and an attenuation of the east asian summer monsoon a second arid period occurred shortly afterwards 2 12 1 87 cal ka bp which resulted in the decline in ostracod numbers especially candona sp a rather more quiescent warmer period followed between 1 9 and 0 7 cal ka bp with very little change in vegetation composition and low amounts of detrital transfer from catchment to the lake peak reconstructed temperatures and low amounts of annual precipitation were concurrent with the medieval climate anomaly between 0 77 and 0 45 cal ka bp climate in the ol khon region became colder and wetter although lake khall did not become fresher cold wet conditions are seen at other sites around lake baikal and therefore represent a regional response to the period concurrent with the little ice age and ird 0 after ad 1845 the region warms and pediastrum appears in the lake in high abundances for the first time this increase is ascribed to nutrient enrichment in the lake linked to the rapid increase in regional pastoral farming

chironomid inferred air temperatures from lateglacial and holocene sites in north west europe progress and problems abstract non biting midges insecta diptera chironomidae are now widely recognised as powerful biological proxies for inferring past climatic change in this paper the response of chironomid assemblages to lateglacial and holocene climatic change from sites in scotland and norway is discussed analyses have shown that midge assemblages have responded to major and minor climatic fluctuations during the last 15 000 yr such as the aegelsee oscillation gerzensee oscillation and younger dryas in the lateglacial and the thermal optimum little ice age and cooling events at 8 2 and 2 0 cal ka bp in the holocene in an attempt to quantify these and other climatic fluctuations a chironomid mean july air temperature inference model based on a modern calibration set of 109 lakes in norway and svalbard has been developed the 3 component weighted averaging partial least squares inference model performs well with a root mean squared error of prediction of 0 90 c and a maximum bias of 0 59 c both based on leave one out cross validation which is lower than chironomid temperature inference models developed in canada switzerland and finland however while temperature inference models perform well in the lateglacial the more subtle climatic changes of the holocene are more difficult to reconstruct because the likely temperature changes are close to the limits of the prediction errors of the existing models to address this problem future work is required to refine and develop the calibration set by further improving taxonomic resolution by adding more lakes to the calibration set and by investigating the influence of other environmental variables on chironomid distributions and abundances

aquatic ecosystem responses to holocene climate change and biome development in boreal central asia boreal ecosystems are highly vulnerable to climate change and severe ecological impacts in the near future are virtually certain to occur we undertook a multiproxy study on an alpine lake esm 1 at the modern tree line in boreal southern siberia steppe and tundra biomes were extensive in eastern sayan landscapes during the early holocene boreal forest quickly expanded by 9 1 ka bp and dominated the landscape until c 0 7 ka bp when the greatest period of compositional turnover occurred at this time alpine meadow landscape expanded and picea obovata colonised new habitats along river valleys and lake shorelines because of prevailing cool moist conditions during the early holocene chironomid assemblages were dominated by cold stenotherms diatoms for much of the holocene were dominated by alkaliphilous fragilarioid taxa up until 0 2 ka bp when epiphytic species expanded indicative of increased habitat availability c n mass ratios ranged between 9 5 and 13 5 11 1 15 8 c n atomic ratios indicative of algal communities dominating organic matter contributions to bottom sediments with small persistent contributions from vascular plants however 13c values increased steadily from 34 9 during the early holocene 9 3 ka bp to 24 8 by 0 6 ka bp this large shift in magnitude may be due to a number of factors including increasing within lake productivity increasing disequilibrium between the isotopic balance of the lake with the atmosphere as the lake became isotopically mature and declining soil respiration linked to small but distinct retreat in forest biomes the influence of climatic variables on landscape vegetation was assessed using redundancy analysis rda a linear direct ordination technique changes in july insolation at 60 n significantly explained over one fifth of the variation in species composition while changes in estimates of northern hemisphere temperature and ice rafted debris events in the north atlantic were also significant but considerably less important the potential importance of climate and biome development tundra steppe cold deciduous forest and taiga on different trophic levels i e chironomid and diatom communities in lake esm 1 was also assessed using rda climate predictors had a more significant influence on holocene chironomid assemblages especially july insolation at 60 n estimates of regional precipitation and estimates of northern hemisphere temperature while only the development of the taiga biome had a significant impact on these primary consumers diatom communities also had a small but significant influence on holocene chironomid populations perhaps linked to variation in faunal feeding strategies in contrast climatic and biome predictors explained similar amounts of variation in the holocene diatom assemblage approximately 20 each while chironomids themselves as predictors explained just under 7 of diatom variation lake acidity was inferred using a diatom inference model results suggest that after deglaciation the lake did not undergo a process of gradual acidification most likely due to the presence of continuous permafrost and low levels of precipitation preventing base cations and dissolved organic carbon entering the lake except for the period between 1 7 and 0 7 ka bp we conclude that lakes in continental boreal regions undergo different models of lake ontogeny than oceanic boreal regions unlike other regions discussed climate is a more important driver of ecosystem change than catchment changes we also demonstrate that the start of the period coincident with the onset of the little ice age resulted in important thresholds crossed in catchment vegetation and aquatic communities

effect of shape and orientation on rigid particle rotation and matrix deformation in simple shear flow the rotation behaviour of rigid particles from a wide range of symmetry classes was analysed in a series of three dimensional analogue experiments in which the particles were embedded in a transparent linear viscous matrix deformed to large shear strains comparison of the measured trajectories with theoretical periodic paths for rigid ellipsoids shows that quadratic slightly orthorhombic and monoclinic particles have trajectory paths and rotation rates closest to theory orthorhombic and monoclinic particles with a minimum aspect ratio 1 5 develop non periodic trajectories the results establish that the simplified theoretical model for ellipsoidal forms is a good approximation for a wide range of natural particle shapes the relationship between the rotation of a rigid particle and deformation of the adjacent matrix was also determined in a series of experiments by placing the particle at different depths relative to an imprinted grid the results are well illustrated by the surface passing through the centre of the particle and initially parallel to the shear plane two deformed regions in the matrix are recognised in the first region the matrix rotates with the particle together forming an approximately ellipsoidal object the second region is dominated by folds of limited extent along the rotation axis and greatest extent in a direction that rotates asymptotically toward the shear direction the folds rotate more slowly than the principal direction of maximum finite stretch

a reassessment of late glacial holocene diatom oxygen isotope record from lake baikal using a geochemical mass balance approach we present a new palaeoenvironmental record of hydrological variability in lake baikal based on re modelled delta o 18 diatom values of diatom silica delta o 18 modelled where the residual contaminants are identified and compensated for using electron optical imaging and whole sample geochemistry delta o 18 modelled interpretations are based on the balance between rivers with high delta o 18 values and rivers with low delta o 18 values isotopic variability is related to latitudinal differences in precipitation which feed these rivers the delta o 18 modelled record suggests that rather moist conditions prevailed in the lake baikal region during the latter stages of the younger dryas throughout the holocene episodes of low delta o 18 modelled values are in general in good agreement with increases in percentage haematite stained grains in north atlantic sediments indicative of ice rafted debris events rivers with southerly catchments dominate fluvial input especially between c 3 3 and 2 cal ka bp concurrent with high precipitation in the lake baikal region copyright c 2011 john wiley sons ltd

holocene oxygen isotope record of diatoms from lake kotokel southern siberia russia and its palaeoclimatic implications the oxygen isotope composition of diatom silica d 18 odiatom from marine and lake sediments is helpful for the interpretation of the past climate and environments especially when complemented by other proxy records this paper presents a holocene oxygen isotope record of diatoms from lake kotokel located 2 km east of lake baikal in southern siberia russia the isotope record displays variations in d 18 odiatom from 23 7 to 30 3 from about 11 5 ka bp until today comparing the isotope composition of recent lake kotokel water mean d 18 o 12 to that of the most recent diatom sample d 18 o 27 5 an isotope fractionation in the right order of magnitude was calculated the kotokel d 18 o diatom record is controlled by changes in the isotopic composition of the lake water rather than by

evidence for deformation induced k feldspar replacement by myrmekite several examples of deformation induced myrmekite have been found in two amphibolite facies mylonites derived from granitic protoliths namely a muscovite poor s c mylonite and a single foliation muscovite poor mylonitic gneiss back scattered sem and conventional optical microscopy show that in both rock types syntectonic myrmekitic intergrowths of oligoclase and quartz formed on the two sides of k feldspar grains that faced the local inferred incremental shortening direction for the mylonite myrmekite does not occur on the two ends of the grain that faced the incremental stretching direction the replacement of k feldspar by plagioclase and quartz results in a volume decrease and is favoured on high normal stress sites around the grains we suggest that the ambient temperature pressure and chemical activities were such that the replacement reaction was favoured but the addition of extra strain energy along the high pressure sides of the grains localized the reaction at these sites this energy could arise from elastic strain or strain associated with tangled dislocations or twin boundaries the relative roles of stress and strain energy concentrations in driving the replacement reaction are not known but both were probably important

processes controlling the shrinkage of porphyroclasts in gabbroic shear zones abstract this paper presents microstructural and geochemical data on amphibole and clinopyroxene porphyroclasts collected in amphibolite facies ultramylonites of the ivrea verbano zone italy the well rounded porphyroclasts show a concentration of defects including 100 twins stacking faults free dislocations subgrains and microcracks within their rims that indicate stress concentrations localised deformation within the margins of porphyroclasts increases reaction kinetics and supports amphibole clinopyroxene replacement reactions and heterogeneous plagioclase nucleation in addition to microcracking and or subgrain rotation these metamorphic reactions lead to a marginal grain size reduction and the shrinkage of porphyroclasts in order to correlate the defect concentration at the rim of porphyroclasts with stresses a finite element inclusion matrix model is used it depends on the degree of bonding between inclusion and matrix whether strong stress concentrations within the rim of the inclusion occur for well coupled two phase systems shear stresses within the rim of the inclusion can reach a magnitude many times the magnitude of the matrix stresses marginal stress concentrations do not evolve if inclusion and matrix are decoupled this may indicate that mechanically decoupled porphyroclasts can survive to very large strains

summer temperature variations in lapland during the medieval warm period and the little ice age relative to natural instability of thermohaline circulation on multi decadal and multi centennial scales new tree ring based analysis for climate variability at a regional scale is presented for high latitudes of europe our absolutely dated temperature reconstruction seeks to characterise the summer temperatures since ad 750 the warmest and coolest reconstructed 250 year periods occurred at ad 931 1180 and ad 1601 1850 respectively these periods share significant temporal overlap with the general hemispheric climate variability due to the medieval warm period mwp and the little ice age lia further we detect a multi decadal ca 50 to 60 year rhythm attributable to instability of the north atlantic deep water in the regional climate during the mwp but not during the lia intensified formation of the north atlantic deep water further appeared coincident to the initiation and continuation of mwp the mid lia transient warmth occurring during the period ad 1391 1440 and to recent warming our results support the view that the internal climate variability i e thermohaline circulation could have played a role in the earlier start of the mwp in several proxy reconstructions compared to the externally forced model simulations copyright 2009 john wiley sons ltd

rotation of rigid elliptical cylinders in viscous simple shear flow analogue experiments we used experiments to investigate the behaviour of rigid elliptical cylinders embedded in a viscous fluid of finite thickness and for very small ratios s between shear zone width z and the shortest principal axis e2 of the ellipse that constitutes the base of the elliptical cylinder 3 5 s z e2 1 2 former theoretical and experimental work on the rotation of rigid inclusions immersed in a viscous matrix considered infinite shear zone thickness and or a very large ratio between shear zone thickness and inclusion size s 1 and concluded that inclusions rotate continuously and synthetically with the applied bulk simple shear flow except for inclusions with infinite axial ratio our results depart greatly from the analytical predictions experiments were carried out at constant shear zone thickness but variable s and degree of coupling at the inclusion matrix interface the results show that 1 confined inclusion rotation always deviates from theoretical predictions for infinite shear zone thickness even for synthetic rotation 2 the deviation in the angular velocity and or in the sense of rotation increases as s approaches 1 and antithetic rotation is possible from a position with ellipse longest axis parallel to the shear plane and 3 a slipping inclusion matrix interface greatly enhances deviation from theoretical predictions with antithetic rotations to as much as 20

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

the role of the siberian high in northern hemisphere climate variability the dominant mode of sea level pressure slp variability during the winter months in the northern hemisphere nh is characterized by a dipole with one anomaly center covering the arctic with the opposite sign anomaly stretched across the mid latitudes associated with the slp anomaly is a surface temperature anomaly induced by the anomalous circulation we will show that this anomaly pattern originates in the early fall on a much more regional scale in siberia as the season progresses this anomaly pattern propagates and amplifies to dominate much of the extratropical nh making the siberian high a dominant force in nh climate variability in winter also since the slp and surface temperature anomalies originate in a region of maximum fall snow cover variability we argue that snow cover partially forces the phase of winter variability and can potentially be used for the skillful prediction of winter climate

a 850 year record climate and vegetation changes in east siberia russia inferred from geochemical and biological proxies of lake sediments east siberia is very sensitive to moisture regimes because it is located in a margin area where moisture from the north atlantic is strongly depleted and the penetration of the east asian monsoon is weak and rare in winter months the siberian anticyclone strongly blocks and reduces the external influences on the region the high latitude of the study area at 52 n is probably sensitive to variation in insolation and solar activity we analysed a 42 cm long sediment record from lake mountain located in east siberia russia for geochemical mineralogical subfossil diatoms chironomids and pollen to provide a reconstruction of the climate history of the area for the last 850 years according to our reconstruction a clear decrease in summer temperatures occurred in east siberia after ca 1400 and we linked this temperature drop with the beginning of the little ice age the coldest summer occurred about ca 1570 1700 and 1830 1900 we assumed that the most significant changes of the lake bio productivity and the catchment area were occurred about ca 1160 1350 1350 1590 1590 1730 1730 1900 and 1940 to the present the most dramatic period with unfavorable climate conditions for lake biota was during 1590 1730

analogue modelling of the influence of shape and particle matrix interface lubrication on the rotational behaviour of rigid particles in simple shear abstract the rotational behaviour of a rigid particle embedded in a linear viscous matrix undergoing cylindrical simple shear couette flow was studied in 2d rock analogue experiments the influence of particle shape elliptical vs monoclinic aspect ratio and the nature of the matrix particle interface lubricated vs unlubricated was investigated both matrix pdms and lubricant liquid soap were linear viscous with a viscosity ratio of ca 10 4 without lubricant the rotational behaviour of all particles closely approximates the jeffery theory lubricated monoclinic particles with the long diagonal initially parallel to the shear direction show back rotation and approach a stable position lubricated elliptical particles initially parallel to the shear direction also show back rotation but only transiently stabilize weak planar zones in the matrix adjacent to unlubricated elliptical particles do not induce backward rotation in general for elliptical particles rotation rate as a function of orientation depends on axial ratio and thickness of the lubricant mantle for thick mantles initially 10 of the volume of the particle rotation rates are faster than jeffery theory for very thin mantles they are markedly slower compared with thick mantles particularly when the long axis is nearly parallel to the shear direction rotation rates are never strictly zero so true stabilization does not occur however for more elongate particles axial ratio 6 rotation rates are so slow that a very strong shape preferred orientation would develop in a lubricated elliptical particle population in experiments the volume of lubricant is constant and the thickness adjacent to the long side of the particle progressively decreases with increasing strain in natural examples of porphyroclast systems the weak mantle continually develops by recrystallization and or cataclasis of the rigid clast core and a steady state between production and thinning could be attained potentially leading to true stabilization for particles with a high axial ratio

the history and variability of the east asian paleomonsoon climate abstract changes in the east asian paleomonsoon reflect interactions between the global atmosphere ocean land and ice systems and are also an expression of their combined effect within the boundary conditions imposed by the east asian continent and solar radiation the history of the east asian monsoon is an alternation between dominance by the dry cold winter and warm humid summer monsoons high resolution eolian sequences preserved in the chinese loess plateau reveal that the east asian monsoon may have commenced at least 7 2 ma ago they also provide evidence indicating that the pulsed uplift of the tibetan plateau at about 3 4 and 7 2 ma may have played an important role in inducing climate change the palaeoclimatic records of the last glacial cycle show high frequency variability on time scales of 1000 year or even shorter and instability of the east asian paleomonsoon system the high frequency variability could be due to a non linear response to orbital forcing or a result of the coupling processes between different components of the global system cold air activity in northern high latitudes the trans equatorial air streams from the southern hemisphere and possibly enso may have played an important role in east asian monsoon variability the synchroneity of all the palaeoclimatic events along the polar equator polar pep transect is still an open question correlation of limited palaeoclimatic records for the last 30 kyr obtained from east asia and australia suggests that the trans equatorial air streams driven by the monsoon and trade winds may have had an influence on opposite hemispheres

present environment of dam lake sambe southwestern japan a geochemical study of bottom sediments geochemical analyses of lakebed and core sediments from lake sambe on the outskirts of oda city in shimane prefecture in southwestern japan were carried out in order to assess the water quality and the concentration and distribution patterns of sixteen elements the lake water showed a stratified condition with respect to dissolved o2 and as fe and mn concentrations in the bottom layers which increased in the summer the chemical composition of the sediments as measured by x ray fluorescence included major and trace elements p ca sc ti v cr fe ni cu zn as sr zr pb and th and total sulfur ts elevated values of as zn v fe p and ts were present in several layers of the upper cores from 0 to 5 cm and other surface sediments increases in the abundances of these metals in lake sediments are probably related to the reducing condition of the sediments fine grained organic rich sediments and post depositional diagenetic remobilization moreover correlations between the concentrations of trace metals and iron in the sediments suggest their adsorption onto fe oxy hydroxides whereas correlations with sulfur indicate that they were precipitated as fe sulfides the average abundances of as pb zn and cu exceeded the lowest effect level and interim sediment quality guideline values that the new york state department of environmental conservation and the canadian council of ministers of the environment determined to have moderate impact on aquatic organisms in addition concentrations of as and zn exceeded the coastal ocean sediment database threshold value indicating potentially toxic levels therefore the presence of trace metals in the lake sediments may result in adverse effects on biota health

high resolution palaeoclimatology of the last millennium a review of current status and future prospects this review of late holocene palaeoclimatology represents the results from a pages clivar intersection panel meeting that took place in june 2006 the review is in three parts the principal high resolution proxy disciplines trees corals ice cores and documentary evidence emphasizing current issues in their use for climate reconstruction the various approaches that have been adopted to combine multiple climate proxy records to provide estimates of past annual to decadal timescale northern hemisphere surface temperatures and other climate variables such as large scale circulation indices and the forcing histories used in climate model simulations of the past millennium we discuss the need to develop a framework through which current and new approaches to interpreting these proxy data may be rigorously assessed using pseudo proxies derived from climate model runs where the answer is known the article concludes with a list of recommendations first more raw proxy data are required from the diverse disciplines and from more locations as well as replication for all proxy sources of the basic raw measurements to improve absolute dating and to better distinguish the proxy climate signal from noise second more effort is required to improve the understanding of what individual proxies respond to supported by more site measurements and process studies these activities should also be mindful of the correlation structure of instrumental data indicating which adjacent proxy records ought to be in agreement and which not third large scale climate reconstructions should be attempted using a wide variety of techniques emphasizing those for which quantified errors can be estimated at specified timescales fourth a greater use of climate model simulations is needed to guide the choice of reconstruction techniques the pseudo proxy concept and possibly help determine where given limited resources future sampling should be concentrated

li ca ratios of ostracod shells at lake qinghai ne tibetan plateau china a potential temperature indicator acquiring continuous and high resolution natural records in recent 2 000 years is the hot issue in the palaeoclimate research recent studies revealed that li ca and mg li ratio of carbonate is a potential tracer of past environmental changes in the oceans and is seldom applied for palaeoclimate reconstruction in lakes to make full understanding of the potential of li ca ratios of carbonates in lakes li ca ratios of monospecific ostracod shell eucypris inflate with similar size in the lacustrine sediment core from lake qinghai ne tibetan plateau have been analysed for the first time single species can effectively avoid the interspecies effects in combination with the sedimentation rate that existed data derived from 210pb and 137cs downcore variations of li ca ratios of ostracod shells during the past 800 years in lake qinghai have been reconstructed successfully by comparing li ca ratios and temperature inferred from meteorological records and tree ring widths in dulan and qilianshan in adjacent regions li ca ratios of ostracod shells negatively correlate with temperature higher temperature corresponds with lower li ca ratios and vice versa indicating that li ca ratio of ostracod shells is an effective indicator for temperature variations therefore ongoing in depth investigation using li ca ratios of carbonates in more lakes to further reveal its palaeotemperature implications would be deserved

centennial to millennial scale holocene climate deep water linkage in the north atlantic the stability of the earth s climate is strongly linked to the steadiness of the atmospheric and oceanic transport of heat from low to high latitudes high resolution holocene sedimentary records from the subpolar north atlantic demonstrate a persistent link between centennial to millennial scale fluctuations in the flow speed of iceland scotland overflow water inferred from granulometric proxy data and both the surface north atlantic current component of the meridional overturning circulation moc and published fennoscandian atmospheric temperature variability however these data also highlight the difficulties associated with the interpretation of geochemical and sedimentological deep water circulation proxies as they do not provide a wholly consistent picture the similarity between surface and deep ocean 13c records suggests a preformed component in the deep ocean 13c signal on the other hand the sedimentological results display a strong linkage to changing conditions in the overlying surface ocean waters suggesting this proxy better reflects the activity of the moc at least during the holocene of this region the most widespread oceanic perturbation coincides with an interval of possibly global climatic deterioration around 2700 years ago these results firmly establish deep water production in the nordic seas as a key component in the assortment of variables affecting climate during the holocene

thermal infrared spectroscopy on feldspars successes limitations and their implications for remote sensing abstract minerals of the feldspar group are the most common on earth feldspars are economically important in two ways either as industrial minerals or as a vector to ore for mineral deposits in order to use feldspars for classifying rock compositions or metasomatic conditions during rock alteration events there is a need for analytical methods to identify and classify feldspars traditionally feldspar composition and structure have been investigated using methods such as optical microscopy electron microprobe analysis empa cathodoluminescence and x ray diffraction xrd analysis in this paper infrared techniques 0 7 25 m are reviewed in detail and investigated in how far some of the traditional analytical methods can be replaced by infrared spectroscopy successes as well as limitations of infrared approaches are highlighted and existing work is scrutinized in terms of its applicability to remote sensing techniques even though numerous studies on mid infrared mir spectroscopy of feldspars exist their results often cannot be directly related to remote sensing applications examples are the effects of feldspar twinning exsolution textures and structural state on infrared spectra the applicability of the results to emission remote sensing requires further research it has been shown that linear unmixing of laboratory infrared spectra of rocks works fairly well detection limits for feldspar are around 5 and plagioclase composition can be determined within error margins of 4 anorthite component infrared spectroscopy can however not detect compositional zonation or different generations of feldspars infrared spectra represent the current average plagioclase and average alkali feldspar composition in the sample with several new airborne instruments under development it is opportune to focus upcoming research efforts on developing standardized processing techniques and spectral feldspar indices for thermal infrared imagery commercially interesting products include numbers of feldspars species plagioclase and alkali feldspar composition their structural state and relative or semi quantitative abundance in the rocks

the influence of matrix rheology and vorticity on fabric development of populations of rigid objects during plane strain deformation abstract the influence of vorticity and rheology of matrix material on the development of shape preferred orientation spo of populations of rigid objects was experimentally studied experiments in plane strain monoclinic flow were performed to model the fabric development of two populations of rectangular rigid objects with object aspect ratios rob 2 and 3 the density of the rigid object populations was 14 of the total area objects were dispersed in a newtonian and a non newtonian power law matrix material with a power law exponent n of 1 2 the kinematic vorticity number wn of the plane strain monoclinic flow was 1 0 8 and 0 6 with finite simple shear strain of 4 6 3 0 and 0 9 respectively in experiments with rob 3 the spo is strongly influenced by wn and the material properties of the matrix deformation of a power law matrix material and low wn resulted in a stronger spo than deformation of a linear viscous matrix and high wn strain localization coupled with particle interaction plays a significant role in the development of a shape preferred orientation high strain simple shear zones separate trains of rigid objects that are surrounded by low strain zones with wn lower than the bulk wn in fabrics involving populations of objects with rob 2 rheology of the matrix materials does not systematically influence the intensity of the spo

time dependent formation of mantled inclusion structures for different rheologies under a simple shear abstract mantled inclusions commonly encountered in mylonites sometimes represent the only recorders of the deformation history understanding the influence of rheology on the structure of mantled inclusion is important for its interpretation and also for the retrieval of the deformation regime this paper is devoted to the 2d numerical investigation of time dependent deformation behavior of inclusion and its dependence on rheology under simple shear the numerical model is based on an iterative finite difference scheme the inclusion is taken to be deformable and having its own intrinsic rheological properties differing from those of the matrix the diffusion between the matrix and the inclusion is assumed to be insignificant in order to emulate natural mantled inclusion we imposed passive mantle around the inclusion which efficiently monitors the deformation the results of numerical modeling show that a key factor of structural appearance is the effective viscosity contrast ratio of the inclusion to matrix effective viscosities in the power law rheology even a small difference in rheological parameters may result in a high effective viscosity contrast of around 10 between matrix and inclusion the high contrast inhibits stretching of the inclusion preserving its round shape which in turn may create an illusion of the seeming rigidity of the inclusion wings or tails are developed only in the systems with a high effective viscosity contrast they are not influenced by whether the high viscosity contrast is produced by non newtonian medium or by the highly contrasting viscosity between the matrix and the inclusion in the linear rheology

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

on the long term context for late twentieth century warming 1 previous tree ring based northern hemisphere temperature reconstructions portray a varying amplitude range between the medieval warm period mwp little ice age lia and present we describe a new reconstruction developed using largely different methodologies and additional new data compared to previous efforts unlike earlier studies we quantify differences between more traditional std and regional curve standardization rcs methodologies concluding that rcs is superior for retention of low frequency trends continental north american versus eurasian rcs series developed prior to merging to the hemispheric scale cohere surprisingly well suggesting common forcing although there are notable deviations e g fifteenth to sixteenth century results indicate clear mwp warm lia cool and recent warm episodes direct interpretation of the rcs reconstruction suggests that mwp temperatures were nearly 0 7c cooler than in the late twentieth century with an amplitude difference of 1 14c from the coldest 1600 1609 to warmest 1937 1946 decades however we advise caution with this analysis although we conclude as found elsewhere that recent warming has been substantial relative to natural fluctuations of the past millennium we also note that owing to the spatially heterogeneous nature of the mwp and its different timing within different regions present palaeoclimatic methodologies will likely flatten out estimates for this period relative to twentieth century warming which expresses a more homogenous global fingerprint therefore we stress that presently available paleoclimatic reconstructions are inadequate for making specific inferences at hemispheric scales about mwp warmth relative to the present anthropogenic period and that such comparisons can only still be made at the local regional scale

how cold was the little ice age a proxy based reconstruction from finland applying modern analogues of fossil midge assemblages climate dynamics during the past ca 700 years in southern finland were reconstructed using fossil midge diptera nematocera assemblages aiming to estimate quantitatively the temperature change that has occurred from the little ice age to the present midge stratigraphies of two sediment cores from eastern and southern finland were chosen to be examined for temperature inferences utilizing the modern analogue technique the new midge based temperature inference model had a coefficient of determination of 0 901 and a prediction error of 0 498 c showing improvement over the previous finnish models the combined curve of the inferred temperatures derived from both of the cores showed a decrease towards ca 1700 ad when temperatures were approximately 1 c cooler than the past 700 years average and almost 2 c colder than present the temperatures began to increase in southern finland from 1800 ad and in eastern finland from 1900 ad onwards the highest temperatures were reached at the top of the core representing the present climate warming although there was slight overestimation in the recent inferred values the reconstructed trends were in close correspondence with the previous proxy based historical and measured data that suggests that the reconstruction was realistic and reliable

vegetation climate and lake changes over the last 7000 years at the boreal treeline in north central siberia abstract palaeoecological investigations in the larch forest tundra ecotone in northern siberia have the potential to reveal holocene environmental variations which likely have consequences for global climate change because of the strong high latitude feedback mechanisms a sediment core collected from a small lake radius 100 m was used to reconstruct the development of the lake and its catchment as well as vegetation and summer temperatures over the last 7100 calibrated years a multi proxy approach was taken including pollen and sedimentological analyses our data indicate a gradual replacement of open larch forests by tundra with scattered single trees as found today in the vicinity of the lake an overall trend of cooling summer temperature from a 2 c warmer than present mid holocene summer temperatures until the establishment of modern conditions around 3000 years ago is reconstructed based on a regional pollen climate transfer function the inference of regional vegetation changes was compared to local changes in the lake s catchment an initial small water depression occurred from 7100 to 6500 cal years bp afterwards a small lake formed and deepened probably due to thermokarst processes although the general trends of local and regional environmental change match the lake catchment changes show higher variability furthermore changes in the lake catchment slightly precede those in the regional vegetation both proxies highlight that marked environmental changes occurred in the siberian forest tundra ecotone over the course of the holocene

the development of δ clasts in non linear viscous materials a numerical approach abstract winged porphyroclasts are often used as kinematic or strain indicators in shear zones in particular it has been suggested that the geometry of clasts in mylonites can give information about the rheological behaviour of the matrix around the clast passchier et al 1993 we tested this hypothesis with a numerical finite element simulation of the flow field of a viscous matrix around a relatively rigid clast power law viscous flow properties of the matrix with stress exponents of 1 linear viscous 3 and 5 were tested as well as three different sets of approximately simple shear boundary conditions which are relevant to experimental and or natural situations the simulations show that the flow field is primarily determined by the boundary conditions the stress exponent is of secondary importance in general the different boundary conditions produce two types of flow fields about the rigid clast an eye shaped flow field and a bow tie shaped flow field the former is produced by boundary conditions that approximate simple shear applied at an infinite distance from the rigid clast and the latter is produced by boundary conditions which are equivalent to a shear box or ring shear apparatus although both the shear box and ring shear boundary conditions produce bow tie flow patterns the wing geometries which result from the flow patterns for these two cases can be significantly different the geometry of the wings that develop on a clast is a direct function of the flow field around the clast for linear and non linear rheologies only the ring shear boundary conditions produce wings that show stair stepping i e wings that are parallel but not in the same plane in natural shear zones clasts both with and without stair stepping are observed in comparing geologic observations with experimental or numerical modelling it is essential to understand which boundary conditions are appropriate

geothermal bathing and recreation centres in poland ten geothermal bathing and recreation centres have been established in poland from 2006 to 2013 the largest number of geothermal bathing and recreation centres is located in the podhale region and in the polish lowlands these structural units have the best geothermal conditions the maximum reservoir s temperatures in the main aquifer of the podhale geothermal system can reach ca 120 128 c in the deeper parts of the system the most prospective and exploited aquifers occur within the middle triassic formations and in overlaying middle eocene formations at the depth of 1 000 3 700 m at present five operating centres are located in the podhale region they use geothermal waters with the temperature of 27 82 c the lowest and the highest wellhead temperature of water from wells which are connected for recreational purposes and total dissolved solids tds of 0 4 3 g dm3 in the polish lowlands the reservoir s temperatures vary from 20 to 130 c at depths of 1 4 km the most prospective geothermal aquifers of the polish lowlands occur within the lower cretaceous and the lower jurassic formations five geothermal recreation centres are currently operating the centres use waters with the temperature of 38 72 c and a wide range tds from 0 4 to 79 g dm3 geothermal waters of the polish lowlands are generally high in na and cl concentrations the new centres will use the waters of lower jurassic aquifers the outflow temperatures of which vary from 27 to 82 c and a tds from 6 to 140 g dm3

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

experimental observations on the effect of interface slip on rotation and stabilisation of rigid particles in simple shear and a comparison with natural mylonites for axial ratios r not vert similar3 porphyroclasts from three mylonites all show a very strong spo with the long axis of the best fit ellipse at an antithetic angle of 5 10 to the shear direction this is more consistent with a stable end orientation than with the transient fabrics predicted by theory for elliptical rigid particles in simple shear the cause of this divergence is investigated in a series of high simple shear strain 15 analogue experiments performed in a ring shear machine couette flow using a linear viscous matrix pdms the rotational behaviour of elongate r not vert similar5 rigid particles with elliptical and rhomboidal shapes comparable with the natural examples is modelled for both coherent and slipping particle matrix interfaces interface slip causes a dramatic reduction in the rotation rate of the elliptical particle compared with theory when the long axis is close to the shear direction but not stabilisation interface slip does result in stabilisation of the rhomboidal particle with the long diagonal oriented at a small antithetic angle to the shear direction for monoclinic particles mirror image shapes referred to here as types 1 and 2 show different rotational behaviour for the type 1 particle with a shape comparable to porphyroclast systems and mica fish the long side rotates asymptotically into parallelism with the shear direction natural examples of type 1 particles such as hornblende and olivine porphyroclasts measured from the finero mylonites southern alps show a very strong preferred orientation for r not vert similar3 with the long side parallel or at a small 5 antithetic angle to the mylonitic foliation for type 2 particles the short side stabilises close to the shear direction or at a small synthetic angle as also observed for sillimanite porphyroclasts from the mont mary mylonites western alps in this natural case stabilisation of the short sides is against an extensional crenulation cleavage rather than the mylonitic foliation the analogue experiments establish that interface slip is one mechanism for stabilisation of elongate rhomboidal particles in natural examples decoupling from the matrix may be affected by extensional crenulation cleavage or c planes in s c fabrics

phosphorus fractions and bioavailability in relation to particle size characteristics in sediments from lake hongfeng southwest china information on the chemical composition of phosphorus p fractions in sediments is fundamental to understanding p bioavailability and eutrophication in lake ecosystems phosphorus fractions and its bioavailability in sediments cores of lake hongfeng southwest china were investigated using a chemical sequential extraction scheme relationships between p fractions p bioavailability and particle sizes were discussed p fractions concentrations were ranked in the order residual p naoh rp naoh nrp hcl p bd p nh4cl p and all of them decreased with increasing sediment depth statistical analysis showed that concentrations of bioavailable p bap which includes the nh4cl p bd p naoh rp and naoh nrp fractions ranged from 404 68 to 1 591 99 mg kg and accounted for 26 8 71 8 of the concentrations of total phosphorus tp in the top 5 cm sediments whereas in the whole sediment cores their concentrations ranged from 239 70 to 1 591 99 mg kg and accounted for 26 8 76 0 of tp the results suggested that the sediments were a large potential source of p for algae blooms in lake hongfeng phosphorus fractions and their potential bioavailability were influenced by the sediment particle sizes especially the bioavailability of the nh4cl p fraction which was strongly affected by the presence of fine particle sizes in the sediments

general characteristics of temperature variation in china during the last two millennia three alternate china wide temperature composites covering the last 2000 years were established by combining multiple paleoclimate proxy records obtained from ice cores tree rings lake sediments and historical documents five periods of temperature variation can be identified a warm stage in ad 0 240 a cold interval between ad 240 and 800 a return to warm conditions from ad 800 1400 including the medieval warm period between ad 800 1100 the cool little ice age period between 1400 1920 and the present warm stage since 1920 regional temperature variation is found during ad 800 1100 when warm conditions occurred in eastern china and in the northeastern tibetan plateau and in ad 1150 1380 when the southern tibetan plateau experienced a warm interval in contrast evidence for cool conditions during the lia is more consistent among the proxy records the temperature reconstructions for china and the northern hemisphere show good agreement over the past millennium

late pleistocene and holocene vegetation and climate records from lake kotokel central baikal region abstract climatically driven late pleistocene and holocene vegetation changes were reconstructed based on pollen records from the sediments of lake kotokel and cheremushka bog located on the eastern shore of lake baikal the described paleoenvironmental record has higher resolution than records collected from lake baikal and unites individual events identified in prior studies of bottom and onshore cores remarkable shifts in landscapes and expansions of index plants are as follows forest tundra and or forest steppe landscape with birch spruce artemisia and poaceae prevailed at ca 50 25 14 c kyr bp tundra and or steppe vegetation dominated by artemisia and poaceae was typical for the last glacial maximum the expansion of shrub birch and willow occurred at ca 15 5 14 c kyr bp two peaks of spruce expansion at ca 47 5 42 4 14 c kyr bp karginian time and at ca 14 5 13 ka bolling allerod warm intervals suggest that the condition were more humid than today a slight increase in artemisia at ca 11 10 5 14 c kyr bp 13 12 ka was indicative of the younger dryas event an expansion of birch forests with fir at ca 12 6 4 ka suggests higher humidity the currently dominant scots and siberian pine forests with birch expanded since 6 4 ka

midges and palaeotemperature reconstruction the north american experience abstract the development of midge based palaeoclimatology in north america is reviewed with a focus on lateglacial and holocene climatic change although relatively few sites have been studied midge inferred palaeotemperatures reveal detailed records of lateglacial climate oscillations and more subtle holocene temperature changes holocene climate changes are often at or near the detection limit using current palaeotemperature inference models interference from other environmental variables including water depth and oxygen concentration changes are discussed as well as the challenges inherent to developing better models the isotopic signature of chitin preserved in midge head capsules has opened new avenues for midge palaeotemperature inference through coordinated research efforts national and international collaborations will provide opportunities to reconstruct holocene palaeoclimate at continental and hemispheric scales