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

flow of variably fluidized granular masses across three dimensional terrain 2 numerical predictions and experimental tests numerical solutions of the equations describing flow of variably fluidized coulomb mixtures predict key features of dry granular avalanches and water saturated debris flows measured in physical experiments these features include time dependent speeds depths and widths of flows as well as the geometry of resulting deposits three dimensional 3 d boundary surfaces strongly influence flow dynamics because transverse shearing and cross stream momentum transport occur where topography obstructs or redirects motion consequent energy dissipation can cause local deceleration and deposition even on steep slopes velocities of surge fronts and other discontinuities that develop as flows cross 3 d terrain are predicted accurately by using a riemann solution algorithm the algorithm employs a gravity wave speed that accounts for different intensities of lateral stress transfer in regions of extending and compressing flow and in regions with different degrees of fluidization field observations and experiments indicate that flows in which fluid plays a significant role typically have high friction margins with weaker interiors partly fluidized by pore pressure interaction of the strong perimeter and weak interior produces relatively steep sided flat topped deposits to simulate these effects we compute pore pressure distributions using an advection diffusion model with enhanced diffusivity near flow margins although challenges remain in evaluating pore pressure distributions in diverse geophysical flows riemann solutions of the depth averaged 3 d coulomb mixture equations provide a powerful tool for interpreting and predicting flow behavior they provide a means of modeling debris flows rock avalanches pyroclastic flows and related phenomena without invoking and calibrating rheological parameters that have questionable physical significance

holocene glacial and climatic variations on spitsbergen svalbard holocene glacial and climatic variations have been inferred from investigations of sediment cores from the proglacial lake linnevatnet western spitsbergen a low content of glacially derived coal absence of regular laminations and a slow sedimentation rate in the lower part of the lacustrine sediments indicate that the former glaciers that existed within the catchment area during the last ice age melted quickly away as a result of the younger dryas holocene warming and during the next 6000 years there were no glaciers in the valley increasing coal content incipient laminations and rising sedimentation rates indicate that the glacier linnebreen started to form 4000 5000 years ago probably as a response to the late holocene cooling the holocene maximum extent of the glacier occurred during the little ice age starting with a pronounced ice advance in the thirteenth or fourteenth century a well dated core from billefjorden which is assumed to reflect glacial fluctuations in the inner part of the i

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

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

holocene glaciation and climate evolution of baffin island arctic canada abstract lake sediment cores and cosmogenic exposure ce dates constrain the pattern of deglaciation and evolution of climate across baffin island since the last glacial maximum lgm ce dating of erratics demonstrates that the northeastern coastal lowlands became ice free ca 14 ka as the laurentide ice sheet lis receded from its lgm margin on the continental shelf coastal lakes in southeastern baffin island started to accumulate sediment at this time whereas initial lacustrine sedimentation was delayed by two millennia in the north reduced organic matter in lake sediment deposited during the younger dryas chron and the lack of a glacial readvance at that time suggest cold summers and reduced snowfall ice retreated rapidly after 11 ka but was interrupted by a widespread readvance of both the lis and local mountain glaciers 9 6 ka cockburn substage a second readvance occurred just before 8 ka during a period of unusually cold summers corresponding to the 8 2 ka cold event in the greenland ice sheet most local glaciers were behind their present margins before 7 ka and in some instances much earlier although the foxe dome of the lis continued to slowly retract toward the present day barnes ice cap throughout the holocene pollen in lake sediments is rare and dominated by exotic sources prior to 12 ka subsequently grass tundra became established followed by modern tundra vegetation ca 8 ka with subtle changes in pollen assemblages in the late holocene lake primary productivity peaked in the early holocene before terrestrial vegetation or marine surface waters reached their apparent thermal maxima lacustrine marine and glacial proxies all reflect significant late holocene cooling the onset of neoglaciation is well dated in lacustrine records at ca 6 ka with intensification after 2 5 ka the expansion of local glaciers during the little ice age represents the most extensive advance since 7 ka we suggest that the replacement of atlantic surface waters by cold low salinity arctic ocean water coupled with the steady reduction of summer insolation resulted in a significant positive sea ice feedback that produced a larger late holocene summer temperature depression over the baffin region than in the pacific sector of the arctic

a progressive entrainment runout model for debris flow analysis and its application abstract a progressive entrainment model has been incorporated into an energy based runout model to calculate the kinematic characteristics of debris flow the progressive entrainment model considers both rolling and sliding motions of erodible material to study the effect of the controlling parameters in the entrainment model sensitivity analyses have been carried out by varying model parameters such as the internal friction angle of the debris the basal friction angle of the channel the turbulent flow coefficient and the mean value of the probabilistic density function pdf for the resting angle the results are evaluated by calculating the change of the maximum entrainment rate the maximum frontal velocity the final total volume the longitudinal length of deposition the maximum debris flow height and the runout distance of the debris the progressive entrainment runout model is sensitive to the characteristic particle size basal friction angle and turbulent coefficient measurements from the 1990 tsingshan debris flow hong kong china are used to validate the model velocities at different channel sections estimated using the super elevation method and entrainment depth are used to evaluate the simulation results comparing the results between simulated and observed maximum velocity and entrainment depth indicate that the progressive entrainment model together with the runout model can capture the erosion characteristics of the granular material the results are also compared with that using a dynamic entrainment model the results demonstrate that the progressive entrainment model provides a more realistic calculation of entrainment for this case compared with the dynamic entrainment model

dinoflagellate cyst distribution in high latitude marine environments and quantitative reconstruction of sea surface salinity temperature and seasonality a data base of 179 reference sites documents the relations between the assemblages of organic walled dinoflagellate cysts and sea surface temperature salinity and seasonality throughout the north atlantic adjacent subpolar basins labrador sea baffin bay irminger and iceland basins and epicontinental environments off eastern canada estuary and gulf of st lawrence hudson bay principal component analyses show close relationships between dinoflagellate cyst data and sea surface conditions the first component 71 1 of the variance correlates with the winter temperature salinity and seasonal duration of sea ice cover whereas the second component 11 3 of the variance appears mainly related to summer temperature transfer functions using the best analogue method were tested by reconstructing modern sea surface conditions on the basis of the reference dinoflagellate cyst assemblages the correlation coefficient between instrumental averages and reconstructed values ranges from 0 87 august tem

a two fluid model for avalanche and debris flows geophysical mass flows debris flows avalanches landslides can contain o 10 6 10 10 m 3 or more of material often a mixture of soil and rocks with a significant quantity of interstitial fluid these flows can be tens of meters in depth and hundreds of meters in length the range of scales and the rheology of this mixture presents significant modelling and computational challenges this paper describes a depth averaged thin layer model of geophysical mass flows containing a mixture of solid material and fluid the model is derived from a two phase or two fluid system of equations commonly used in engineering research phenomenological modelling and depth averaging combine to yield a tractable set of equations a hyperbolic system that describes the motion of the two constituent phases if the fluid inertia is small a reduced model system that is easier to solve may be derived

simmax a modern analog technique to deduce atlantic sea surface temperatures from planktonic foraminifera in deep sea sediments we present a data set of 738 planktonic foraminiferal species counts from sediment surface samples of the eastern north atlantic and the south atlantic between 87 n and 40 s 35 e and 60 w including published climate long range investigation mapping and prediction climap data these species counts are linked to levitus s 1982 modern water temperature data for the four caloric seasons four depth ranges 0 30 50 and 75 m and the combined means of those depth ranges the relation between planktonic foraminiferal assemblages and sea surface temperature sst data is estimated using the newly developed simmax technique which is an acronym for a modern analog technique mat with a similarity index based on 1 the scalar product of the normalized faunal percentages and 2 a weighting procedure of the modern analog s ssts according to the inverse geographical distances of the most similar samples compared to the classical climap transfer technique and conventional mat techniques simmax provides a more confident reconstruction of paleo ssts correlation coefficient is 0 994 for the caloric winter and 0 993 for caloric summer the standard deviation of the residuals is 0 90 c for caloric winter and 0 96 c for caloric summer at 0 m water depth the sst estimates reach optimum stability standard deviation of the residuals is 0 88 c at the average 0 to 75 m water depth our extensive database provides sst estimates over a range of 1 4 to 27 2 c for caloric winter and 0 4 to 28 6 c for caloric summer allowing sst estimates which are especially valuable for the high latitude atlantic during glacial times an electronic supplement of this material may be obtained on adiskette or anonymous ftp from kosmos agu org login toagu s ftp account using anonymous as the username and guestas the password go to the right directory by typing cd append typels to see what files are available type get and the name of the file toget it finally type exit to leave the system paper 95pa01743 simmax a modern analog technique to deduce atlantic sea surfacetemperatures from planktonic foraminifera in deep sea sediments uwepflaumann josette duprat claude pujol and laurent d labeyrie diskette may be ordered from american geophysical union 2000florida avenue n w washington dc 20009 payment mustaccompany order

flow of variably fluidized granular masses across three dimensional terrain 1 coulomb mixture theory rock avalanches debris flows and related phenomena consist of grain fluid mixtures that move across three dimensional terrain in all these phenomena the same basic forces govern motion but differing mixture compositions initial conditions and boundary conditions yield varied dynamics and deposits to predict motion of diverse grain fluid masses from initiation to deposition we develop a depth averaged three dimensional mathematical model that accounts explicitly for solid and fluid phase forces and interactions model input consists of initial conditions path topography basal and internal friction angles of solid grains viscosity of pore fluid mixture density and a mixture diffusivity that controls pore pressure dissipation because these properties are constrained by independent measurements the model requires little or no calibration and yields readily testable predictions in the limit of vanishing coulomb friction due to persistent high fluid pressure the model equations describe motion of viscous floods and in the limit of vanishing fluid stress they describe one phase granular avalanches analysis of intermediate phenomena such as debris flows and pyroclastic flows requires use of the full mixture equations which can simulate interaction of high friction surge fronts with more fluid debris that follows special numerical methods described in the companion paper are necessary to solve the full equations but exact analytical solutions of simplified equations provide critical insight an analytical solution for translational motion of a coulomb mixture accelerating from rest and descending a uniform slope demonstrates that steady flow can occur only asymptotically a solution for the asymptotic limit of steady flow in a rectangular channel explains why shear may be concentrated in narrow marginal bands that border a plug of translating debris solutions for static equilibrium of source areas describe conditions of incipient slope instability and other static solutions show that nonuniform distributions of pore fluid pressure produce bluntly tapered vertical profiles at the margins of deposits simplified equations and solutions may apply in additional situations identified by a scaling analysis assessment of dimensionless scaling parameters also reveals that miniature laboratory experiments poorly simulate the dynamics of full scale flows in which fluid effects are significant therefore large geophysical flows can exhibit dynamics not evident at laboratory scales

latest pleistocene and holocene glaciation of baffin island arctic canada key patterns and chronologies abstract melting glaciers and ice caps on baffin island contribute roughly half of the sea level rise from all ice in arctic canada although they comprise only one fourth of the total ice in the region the uncertain future response of arctic glaciers and ice caps to climate change motivates the use of paleodata to evaluate the sensitivity of glaciers to past warm intervals and to constrain mechanisms that drive glacier change we review the key patterns and chronologies of latest pleistocene and holocene glaciation on baffin island the deglaciation by the laurentide ice sheet occurred generally slowly and steadily throughout the holocene to its present margin barnes ice cap except for two periods of rapid retreat an early interval 12 to 10 ka when outlet glaciers retreated rapidly through deep fiords and sounds and a later interval 7 ka when ice over foxe basin collapsed in coastal settings alpine glaciers were smaller during the younger dryas period than during the little ice age at least some alpine glaciers apparently survived the early holocene thermal maximum which was several degrees warmer than today although data on glacier extent during the early holocene is extremely sparse following the early holocene thermal maximum glaciers advanced during neoglaciation beginning in some places as early as 6 ka although most sites do not record near little ice age positions until 3 5 to 2 5 ka alpine glaciers reached their largest holocene extents during the little ice age when temperatures were 1 1 5 c cooler than during the late 20th century synchronous advances across baffin island throughout neoglaciation indicate sub milankovitch controls on glaciation that could involve major volcanic eruptions and solar variability future work should further elucidate the state of glaciers and ice caps during the early holocene thermal maximum and glacier response to climate forcing mechanisms

characteristics and dynamic runout analyses of 1983 saleshan landslide abstract in 1983 a catastrophic landslide occurred in saleshan dongxiang gansu china which resulted in the death of 237 people and the destruction of 585 houses saleshan landslide was a rapid moving landslide in loess area china which moved with long run out distance on a gentle sliding surface this paper reviews the characteristics of the landslide and its consequence analyzes the possible triggers and the processes of development and back calculates the kinematic characteristics of the landslide the digital elevation models dems of the study area before and after the event were used to analyze the geomorphological characteristics before and after the event the authors inferred the possible deformation and failure processes of the landslide based on available observations direct shear tests were carried out to obtain the parameters of the soil involved in the failure and post failure process which was adopted in the following simulation using an energy based runout model the velocities of moving materials at a different time stage together with the variation of runout distance and maximum flow height are presented the authors also compared the calculated results with field observations and previous simulation results sensitivity analysis was conducted to understand the effect of internal and basal friction angles on the kinematic characteristics this study indicates that the saleshan landslide was a fast moving landslide with long traveling distance the landslide lasted more than one minute with a maximum velocity of approximately 25 m s according to the calculation using the energy based runout model which was consistent with the estimations based on the observation of eyewitness this study also gives an insight on the progressive failure mechanism and explains the high mobility of saleshan landslide in details which provides a reference for hazard zonation for areas along loess platforms

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

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

a model for geotechnical analysis of flow slides and debris flows flow slides and debris flows incorporate a broad range of sediment fluid mixtures that are intermediate between dry rock avalanches and hyperconcentrated flows following a comprehensive review of some existing analytical approaches to debris flow runout analysis a new analytical model based on energy conservation has been formulated the new analytical model was developed to deepen the understanding of fundamental aspects in modeling of granular flows and to improve the geotechnical mobility analysis of flow slides and debris flows the lagrangian finite difference method was used to solve the governing equations the model and numerical scheme have been tested against analytical solutions and experiments of granular flows with simplified geometries for sliding mass and basal topography results of granular flow simulations indicate that the model based on energy conservation performs well and is robust the model can be used for geotechnical analysis of a wide range of dense granular flows such as flo

holocene boreal molluscs in greenland palaeoceanographic implications abstract boreal molluscs now extinct in greenland waters occur as subfossils in west greenland between lat 65 30 and 68 30 n a number of new localities for these warmth demanding molluscs are described and the list of species now comprises the gastropod emarqinula fissura and the bivalvalves heteranomia squamula modiolus arctica islandica panopea norvegica and zirphaea crispata during their time the molluscs formed an isolated northern outpost located in the area which as a result of the complex oceanic circulation today has greenland s highest ocean surface temperatures the occurrences are 14c dated to the interval 8400 4900 yr b p and summer surface temperatures were 1 3 c higher than now for its beginning this period coincides with similar marine optimal periods in east greenland and on the baffin island shelf whereas it took 1000 years before the beginning of warmer than present temperatures on land on the basis of this evidence it is concluded that the rise of sea surface temperatures was afforded by a decrease in inflow of cold polar water and or increase in inflow of warm atlantic water into davis strait rather than climatic change

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

first results of cosmogenic dated pre last glaciation erratics from the montoz area jura mountains switzerland the jura mountains are a perialpine chain bending from the sw to the nw of switzerland alpine ice reached only marginal areas of this chain during the last glacial maximum lgm but remaining erratic boulders of alpine origin indicate older glaciations of unknown age tentatively correlated either with the classical rissian or with the most extensive glaciation presented here are the first results of dating these pre lgm boulders by using cosmogenic radionuclides 10be and noble gases 21ne both data sets are in good agreement within 1 error with radionuclide apparent exposure ages ranging from 60 to 107 ka and noble gas apparent ages from 73 to 123 ka considering the importance of erosion on older boulders the age of the erratics corresponds most probably to marine isotope stage 6 these results are encouraging for further studies on pre lgm erratic boulders in the mid latitudes

a northern lead in the orbital band north south phasing of ice age events abstract re analysis of existing data sets shows that they are fully consistent with northern insolation control of ice age cycles and do not provide strong support for alternate models invoking tropical or southern controls the coldest time of the last 100 ka in central greenland was nearly synchronous with the minimum in summer insolation about 24 ka bp thousand years before 1950 approximately one third of the total termination i warming since then was achieved over the almost 10 ka before the abrupt warming into the bolling which some workers have interpreted as the start of the warming southern warming as recorded in the byrd station antarctica ice isotopic record lagged northern warming co2 rise was roughly synchronous with southern warming methane rise may have been delayed a little as was sea level rise and the change in the isotopic composition of atmospheric oxygen was delayed significantly the data for the extrema just before termination ii are consistent with occurrence of the same phasing as for termination i but with somewhat different progression of the two terminations once initiated perhaps because of differences in the forcing

a study of a flowslide with significant entrainment in loess areas in china flowslides are a frequent type of natural disaster in loess areas and may result in the significant loss of properties and or casualties the dagou flowslide is a typical event in a loess area and is accompanied by significant sediment entrainment to analyze the mechanisms responsible for flowslides and to obtain the parameters for a runout analysis a field investigation was conducted specimens were sampled on site to carry out laboratory tests including a triaxial test sieve analysis and chemical component analysis the parameters were used in the runout study employing an energy based runout model an analytical entrainment model was adopted to calculate the entrainment after considering physical properties and the mechanism of the entrainment process of the loess finally the entrainment model was incorporated into the runout model to simulate the post failure process of this case energy dissipation due to the deformation of slices was considered as it was thought to be important for a slide with a significant deformation the simulation results were compared with the measurements including runout distance total volume erosion depth deposition height at different sections and velocities at specific locations the results indicate that the energy based runout model together with the entrainment model can capture the kinematic characteristics of the dagou flowslide therefore it is feasible to use this model to predict the runout characteristics of flowslides in similar areas copyright c 2017 john wiley sons ltd

applying plant functional types to construct biome maps from eastern north american pollen data comparisons with model results abstract global biome models like biome1 convert climate model simulations of past climates into biome distributions and thus facilitate comparison of both climate and biome model results with biomes estimate from paleoecological data we adapted a biomization method recently developed for european pollen data for use with pollen data in eastern north america and then compared its estimated biomes with those derived from applying biome1 to the climate simulations from the ncar ccm1 national center for atmospheric research community climate model version 1 for 6000 years ago 6 ka we first tested the biomization method by seeing how well the biomes inferred from modern pollen data match observed biomes we found that modifications to the method were necessary in part to account for physiological differences between north american and european taxa and in part to cope with our choice of using just 23 major pollen taxa our modifications significantly improved the match between observed modern biomes and pollen derived biomes as measured by the kappa statistic we tested our tuning of the biomization method by matching its inferred 6 ka biomes to biomes estimated from pollen data using the modern analog technique the degree of agreement at 6 ka is close to that for today showing that 1 the biomization method and modern analog technique when applied to the same pollen data produce consistent results and 2 the modifications made to the biomization method are robust back to 6 ka we then used the results of the biomization method to test the biome maps simulated by biome1 which derives biome distributions from observed climate values for today and from the climatic simulations of the ccm1 for 6 ka only a fair agreement is seen and significant offsets exist in the placement of biomes by biome1 for today biome1 simulates the boundary between the temperate deciduous and cool mixed forests to be too far south and the steppe forest boundary to be too far west these model biases are also evident in the simulations at 6 ka despite the fact that ccm1 simulates warmer than present temperatures in the central united states to the north however biome1 correctly simulates the cool mixed forest and taiga boundary at 6 ka as more northwestward than at present

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

how well can we simulate past climates evaluating the models using global palaeoenvironmental datasets abstract global syntheses of palaeoenvironmental data are required to test climate models under conditions different from the present data sets for this purpose contain data from spatially extensive networks of sites the data are either directly comparable to model output or readily interpretable in terms of modelled climate variables data sets must contain sufficient documentation to distinguish between raw primary and interpreted secondary tertiary data to evaluate the assumptions involved in interpretation of the data to exercise quality control and to select data appropriate for specific goals four data bases for the late quaternary documenting changes in lake levels since 30 14 c kyr bp the global lake status data base vegetation distribution at 18 14 c kyr and 6 14 c kyr bp biome 6000 aeolian accumulation rates during the last glacial interglacial cycle dirtmap and tropical terrestrial climates at the last glacial maximum the lgm tropical terrestrial data synthesis are summarised each has been used to evaluate simulations of last glacial maximum lgm 21 calendar kyr bp and or mid holocene 6 cal kyr bp environments comparisons have demonstrated that changes in radiative forcing and orography due to orbital and ice sheet variations explain the first order broad scale in space and time features of global climate change since the lgm however atmospheric models forced by 6 cal kyr bp orbital changes with unchanged surface conditions fail to capture quantitative aspects of the observed climate including the greatly increased magnitude and northward shift of the african monsoon during the early to mid holocene similarly comparisons with palaeoenvironmental datasets show that atmospheric models have underestimated the magnitude of cooling and drying of much of the land surface at the lgm the inclusion of feedbacks due to changes in ocean and land surface conditions at both times and atmospheric dust loading at the lgm appears to be required in order to produce a better simulation of these past climates the development of earth system models incorporating the dynamic interactions among ocean atmosphere and vegetation is therefore mandated by quaternary science results as well as climatological principles for greatest scientific benefit this development must be paralleled by continued advances in palaeodata analysis and synthesis which in turn will help to define questions that call for new focused data collection efforts

a model for the runout analysis of rapid flow slides debris flows and avalanches runout analyses are used for risk assessment and design of remedial measures against rapid landslides such as debris flows debris avalanches rockslide avalanches large scale liquefaction failure

environmental change in eastern greenland during the last 1300 years evidence from foraminifera and lithofacies in nansen fjord 68 n lithofacies and benthic foraminiferal analyses of two sediment cores bs1191 k13b and k14 from nansen fjord eastern greenland show evidence of changing oceanographic and sea ice conditions from

holocene glacier and climate fluctuations on franz josef land arctic russia 80 n fluctuations in glacier extent provide the first comprehensive record of holocene paleoclimate for franz josef land glacier fluctuations were constrained using 45 14c ages from 16 glacier margins many glaciers were behind present margins before 9 4 kyr possibly as early as 10 3 kyr and probably remained so until at least 4 4 kyr where kyr 14c yr b p 1000 subsequently glaciers expanded probably reaching present margins before 3 2 kyr but certainly by 2 kyr a prominent neoglacial advance occurred ca 1 kyr and was followed by little ice age advances including one in the middle 1600s a d glaciers were larger than present at the turn of the century followed by widespread retreat soon after the holocene glacier record closely mimics that of svalbard 500 to 1000 km to the west suggesting similar glacier mass balance changes over a broad region of the eurasian arctia independent paleoclimate evidence from svalbard indicates higher than present summer air temperatures during the early to middle holocene when glaciers were behind present margins followed by generally cooler summer conditions and intermittent glacier advances and retreats holocene glacier variations were probably more influenced by summer temperature than winter precipitation

multivariate analysis and quantitative paleoecology of benthic foraminifera in surface and late quaternary shelf sediments northern canada abstract benthic foraminifera in surface sediments from northeastern canada and the beaufort shelf were studied to determine the quantitative relationship between recent assemblage distributions and modern water depth temperature and salinity factor analysis shows that 7 factor assemblages account for 92 of the variance between samples multiple linear regression shows that different factors are significantly related to water depth august bottom water temperature or salinity multiple correlation coefficients for depth temperature and salinity are 0 94 0 72 and 0 92 respectively labrador fjords contain arenaceous faunas dominated by eithersaccammina atlantica andreophax fusiformis or byeggerella advena regression analysis shows that thesaccammina reophax factor is most strongly related to salinity theeggerella factor is related to depth and temperature a fauna dominated bytrochammina nana andbuliminella elegantissima is correlated with warm deep water in davis strait calcareous assemblages dominated byelphidium excavatum orcassidulina reniforme are found in arctic bays and shelf areas these factor assemblages are strongly related to temperature and depth cassidulina is also related to salinity anislandiella helenae fauna on the inner labrador shelf is strongly correlated with depth and salinity anonionellina labradorica fauna in deep shelf basins is closely related to salinity the multiple regression model for the sea bed data estimates water depth august bottom water temperature and salinity within confidence limits of 67 m 1 3 c and 1 0 paleoecological transfer functions were used to quantify environmental changes recorded by the foraminifera in two piston cores on a transect across the labrador shelf paleo depth estimates obtained from the core data produce relative sea level curves which are similar in shape to theoretical curves for this region paleo salinity and temperature estimates for offshore core 12 show that the change from a postglacialnonionellina fauna to a late glaciale excavatum fauna is accompanied by a decrease of about 2 in salinity and 4 c in temperature paleoecological estimates for fjord core 111 show that the change from a modernsaccammina reophax fauna to a mid holocenei helenae fauna corresponds to a salinity increase of 3 5 and temperature increase of 1 2 c

holocene temperature trends in the extratropical northern hemisphere based on inter model comparisons large uncertainties exist in holocene climate estimates especially for the early holocene when large scale reorganization occurred in the climate system to improve our understanding of these uncertainties we compare four holocene simulations performed with the loveclim ccsm3 hadcm3 and famous climate models the simulations are generally consistent for the large scale northern hemisphere extratropics while the multi simulation consistencies are heterogeneous on the sub continental scale consistently simulated temperature trends are found in greenland northern canada north eastern and north western europe and central west siberia these holocene temperatures show a pattern of an early holocene warming mid holocene warmth and gradual decrease towards the pre industrial in winter and the extent of early holocene warming varies spatially with 9 c warming in northern canada compared with 3 c warming in central west siberia in contrast mismatched temperatures are detected in alaska the warm early holocene winter in loveclim primarily results from strongly enhanced southerly winds induced by the ice sheets in eastern siberia the intense early holocene summer warmth anomaly in ccsm3 is caused by large negative albedo anomalies due to overestimated snow cover at 0 ka in the arctic cool winter conditons in famous can be attributed to extensive sea ice coverage probably due to simplified sea ice representations thus the holocene temperature trends in these regions remain inconclusive

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

geophysical granular and particle laden flows review of the field an introduction is given to the title theme in general and the specific topics treated in detail in the articles of this theme issue of the philosophical transactions they fit into the following broader subjects i dense dry and wet granular flows as avalanche and debris flow events ii air borne particle laden turbulent flows in air over a granular base as exemplified in gravity currents aeolian transport of sand dust and snow and iii transport of a granular mass on a two dimensional surface in ripple formations of estuaries and rivers and the motion of sea ice

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

holocene thermal maximum in the western arctic 0 180 w the spatio temporal pattern of peak holocene warmth holocene thermal maximum htm is traced over 140 sites across the western hemisphere of the arctic 0 180 w north of 60 n paleoclimate inferences based on a wide variety of proxy indicators provide clear evidence for warmer than present conditions at 120 of these sites at the 16 terrestrial sites where quantitative estimates have been obtained local htm temperatures primarily summer estimates were on average 1 6 0 8 c higher than present approximate average of the 20th century but the warming was time transgressive across the western arctic as the precession driven summer insolation anomaly peaked 12 10 ka thousands of calendar years ago warming was concentrated in northwest north america while cool conditions lingered in the northeast alaska and northwest canada experienced the htm between ca 11 and 9 ka about 4000 yr prior to the htm in northeast canada the delayed warming in quebec and labrador was linked to the residual laurentide ice sheet which chilled the region through its impact on surface energy balance and ocean circulation the lingering ice also attests to the inherent asymmetry of atmospheric and oceanic circulation that predisposes the region to glaciation and modulates the pattern of climatic change the spatial asymmetry of warming during the htm resembles the pattern of warming observed in the arctic over the last several decades although the two warmings are described at different temporal scales and the htm was additionally affected by the residual laurentide ice the similarities suggest there might be a preferred mode of variability in the atmospheric circulation that generates a recurrent pattern of warming under positive radiative forcing unlike the htm however future warming will not be counterbalanced by the cooling effect of a residual north american ice sheet

an improved landslide mobility model a relatively simple and versatile numerical model known as dan developed by oldrich hungr for the assessment of landslide mobility has been enhanced to incorporate the consideration of a trapezoidal shaped flow channel for more realistic modelling purposes this enhanced debris mobility model dmm has been programmed to run on a spreadsheet and has been calibrated against detailed landslide data in hong kong in contrast to previous work the enhanced dmm eliminates the limitations inherited from the assumption of a rectangular flow channel with frictionless side boundaries when using dmm no predefined width of landslide is needed the dmm simulates landslide mobility with the flow resistance on the whole wetted perimeter of the channel calculates the surface width of the landslide based on the cross sectional geometry of the channel and is capable of predicting a lobe shaped debris deposition area this technical note presents details of the enhancement to the dan formulation key words landslides

holocene temperature history of northern iceland inferred from subfossil midges abstract the holocene temperature history of iceland is not well known despite iceland s climatically strategic location at the intersection of major surface currents in the high latitude north atlantic existing terrestrial records reveal spatially heterogeneous changes in iceland s glacier extent vegetation cover and climate over the holocene but these records are temporally discontinuous and mostly qualitative this paper presents the first quantitative estimates of temperatures throughout the entire holocene on iceland mean july temperatures are inferred based upon subfossil midge chironomidae assemblages from three coastal lakes in northern iceland midge data from each of the three lakes indicate broadly similar temperature trends and suggest that the north icelandic coast experienced relatively cool early holocene summers and gradual warming throughout the holocene until after 3 ka this contrasts with many sites on iceland and around the high latitude northern hemisphere that experienced an early to mid holocene thermal maximum in response to enhanced summer insolation forcing our results suggest a heightened temperature gradient across iceland in the early holocene with suppressed terrestrial temperatures along the northern coastal fringe possibly as a result of sea surface conditions on the north iceland shelf

contrasting rainfall patterns over north america during the holocene and last interglacial as recorded by sediments of the northern gulf of mexico 1 the comparison of geochemical and mineralogical characteristics of terrigenous sediments deposited in the northern gulf of mexico gom during the holocene and last interglacial lig is used to document the impact of slight differences in insolation and ice sheet retreat rates on moisture transfer and precipitation patterns over central north america the records indicate distinct sedimentological signatures over the two time periods which likely reflect a modification of the main detrital provenance during the lig compared to the holocene here we postulate that the observed differences in the terrigenous supply during the lig relative to the holocene reflect a northeast migration of the main precipitation belt over the mississippi river watershed likely in response to deglaciation of the laurentide ice sheet prior to the peak in boreal summer insolation and the overall greater increase in boreal summer insolation relative to the holocene these combined effects allowed more northward migration of the jet stream atlantic warm pool and intertropical convergence zone than during the holocene which may have also forced the bermuda high farther to the northeast of its present position thereby pumping more moisture from the gom and the caribbean region into both the upper mississippi river and northeast great lakes area

channelized free surface flow of cohesionless granular avalanches in a chute with shallow lateral curvature received 29 november 1997 and in revised form 15 february 1999 a series of laboratory experiments and numerical simulations have been performed to investigate the rapid fluid like flow of a nite mass of granular material down a chute with partial lateral connement the chute consists of a section inclined at 40 to the horizontal which is connected to a plane run out zone by a smooth transition the flow is conned on the inclined section by a shallow parabolic cross slope prole photogrammetric techniques have been used to determine the position of the evolving boundary during the flow and the free surface height of the stationary granular deposit in the run out zone the results of three experiments with dierent granular materials are presented and shown to be in very good agreement with numerical simulations based on the savage hutter theory for granular avalanches the basal topography over which the avalanche flows has a strong channelizing eect on the inclined section of the chute as the avalanche reaches the run out zone where the lateral connement ceases the head spreads out to give the avalanche a characteristic tadpole shape sharp gradients in the avalanche thickness and velocity began to develop at the interface between the nose and tail of the avalanche as it came to rest indicating that a shock wave develops close to the end of the experiments

abrupt onset of the little ice age triggered by volcanism and sustained by sea ice ocean feedbacks 1 northern hemisphere summer temperatures over the past 8000 years have been paced by the slow decrease in summer insolation resulting from the precession of the equinoxes however the causes of superposed century scale cold summer anomalies of which the little ice age lia is the most extreme remain debated largely because the natural forcings are either weak or in the case of volcanism short lived here we present precisely dated records of ice cap growth from arctic canada and iceland showing that lia summer cold and ice growth began abruptly between 1275 and 1300 ad followed by a substantial intensification 1430 1455 ad intervals of sudden ice growth coincide with two of the most volcanically perturbed half centuries of the past millennium a transient climate model simulation shows that explosive volcanism produces abrupt summer cooling at these times and that cold summers can be maintained by sea ice ocean feedbacks long after volcanic aerosols are removed our results suggest that the onset of the lia can be linked to an unusual 50 year long episode with four large sulfur rich explosive eruptions each with global sulfate loading 60 tg the persistence of cold summers is best explained by consequent sea ice ocean feedbacks during a hemispheric summer insolation minimum large changes in solar irradiance are not required

a sliding consolidation model for flow slides a model is proposed for the behaviour of flow slides in loose cohesionless materials in which the debris spreads out as a uniform sheet excess pore fluid pressures are assumed to be generated for example by undrained loading arising from the collapse of metastable structure in the source area of the flow slide under the influence of these the leading element of the debris moves downslope by basal sliding consolidating as it does so by single upward drainage as a result the pore pressure at the base of the element eventually decays to a value that brings the element to rest hence defining the run out of the flow slide the model is applicable in principle to subaqueous and subaerial flow slides and to pore fluids consisting of water gas or both of these the predictions of the model are tested against the observed behaviour and measured properties of the 1966 flow slide at aberfan south wales the results show that a sliding consolidation model provides a possible mechanism for that event

some features of the holocene insect faunas of northeastern siberia the composition of fossil insect faunas from northeastern siberia changed significantly during the pleistocene holocene transition the late pleistocene insect fauna reflects tundra steppe environments and was dominated by xerophilic species this fauna persisted regionally until ca 12 000 yr bp a radical transformation of the environment occurred between 12 000 and 10 000 yr bp marked by the permafrost degradation and invasion of tall shrubs and later trees into the higher latitudes the early holocene insect assemblages are dominated by mesophilic tundra species but also include small number of more thermophilic species which are currently restricted to the taiga zone tree dependent species however were virtually absent this early holocene fauna has no modern analogue the faunal assemblages indicate that the early holocene climate was more humid than that of the late pleistocene and warmer than today post glacial sea level rise was in progress at that time but the shoreline was still much further north and the new siberian islands were still a part of the mainland during the second half of the holocene sea level continued to rise and trees and tall shrubs retreated to the south regional ecosystems including insect faunas approached their modern compositions and boundaries

a sliding block model for the runout prediction of high speed landslides a sliding block model is developed for predicting the runout of high speed slide like landslides based on the analysis of the dynamic mechanism of high speed landslides this model adopts the limit equilibrium analysis approach and incorporates mass dynamics and soil deformation into the calculation of soil movements the critical state is considered as the initial stress state and the interslice forces are obtained considering the equivalence of deformation energy it is possible applying this model to simulate the whole travel process of the soil mass from the onset of the landslide and to predict the travel speed of the soil mass and the hazard area of the landslide application of the model to the sale mountain landslide and the tianshui forging machine factory landslide in china gives reasonable results in comparison to the field observations the calculated results illustrate that i the fundamental causes of the high speed are the decline of the resultant friction force during sliding and the

paleoceanographic reconstructions of surface ocean conditions in the greenland iceland and norwegian seas through the last 14 ka based on diatoms prior reconstructions of the last glacial maximum and the holocene did not include detailed paleoclimate data from the greenland iceland and norwegian gin seas which cover sensitive areas for oceanographic boundaries sea ice distribution and deep water formation in order to fill this gap we studied nine well dated sediment cores from this area and reconstructed the paleoceanographic conditions of the surface gin seas at 2000 year intervals since 13 400 bp based on the diatom record results show that a n s extending sea ice free corridor had opened along norway already at 13 400 bp indicating a northward flow of a branch of the north atlantic drift possibly caused by a change in the jet stream flow due to the decreased height of the north american ice sheet a major change of climatic conditions occurred over the gin seas as the insolation anomaly reached its maximum around 9000 bp when the sea ice cover and the oceanic fronts retreated to a northwesterly position along greenland and the ocean temperatures rose the first half of the holocene is recorded as the warmest period during the last 13 400 bp in the gin seas the duration of this climatic optimum decreased both toward the north and toward the margins of the area the second half of the holocene is characterized by a cooling trend in step with the decreasing insolation these results support the proposal of imbrie et al 1992 that the gin seas region acts as an initial responder to insolation changes

hydrogeology of a complex champlain sea deposit quebec canada implications for slope stability the thick sequences of marine clayey deposits which blanket the st lawrence lowlands in south eastern canada are highly susceptible to landslides with 89 of the population of the province of que