investigation of the relationship between permafrost distribution in nw europe and extensive winter sea ice cover in the north atlantic ocean during the cold phases of the last glaciation atmospheric model simulations with different extents of sea ice are compared with reconstructed european mean annual temperatures derived from permafrost indicators analysis of the results suggest that during cold phases of the last glacial the southern margin of permafrost in western europe was controlled by the latitude of the winter sea ice margin in the north atlantic ocean in this case reconstructions of permafrost extent in europe may be used to constrain past winter sea ice conditions in the north atlantic ocean accordingly extensive north atlantic sea ice cover southwards to at least 50degreesn is inferred during four phases of the last glaciation 1 early pleniglacial 74 59 cal kyr bp 2 the hasselo stadial 41 5 40 cal kyr bp 3 the lgm 23 19 cal kyr bp and 4 the younger dryas 12 7 11 5 cal kyr bp the extensive sea ice cover for the phase of maximum cold disagrees with recent studies suggesting a relatively warm north atlantic during the lgm while it agrees with the original climap reconstruction moreover the estimate for the younger dryas cooling conflicts with reconstructions based on marine proxy data c 2002 elsevier science ltd all rights reserved

climatic reconstruction of the weichselian pleniglacial in northwestern and central europe a multiproxy approach is applied to reconstructing accurately the weichselian pleniglacial climate 72 13 ka in northwestern and central europe standardised translations are used to transform proxy data into climate parameter values for six characteristic time windows quantitative reconstructions of the temperature regime are derived from periglacial coleoptera and botanical evidence while aeolian and fluvial evidence provide qualitative information on wind activity and precipitation respectively the early pleniglacial 74 59 ka the cold period between 41 38 ka and the late pleniglacial 27 13 ka are characterised by a strong north to south climatic gradient over northwestern europe during the last glacial maximum discontinuous permafrost was established in northern france whereas the continuous permafrost zone extended from the uk belgium the netherlands germany and poland to the nordic ice sheets prominent wind activity and a relatively low precipitation typify these periods in contrast an indistinct west to east climate gradient was present in the relatively more temperate intervals e g 50 41 ka seasonally frozen ground conditions prevailed in northwestern europe whereas discontinuous permafrost may be suggested for central germany it appears that the climate conditions in northwest and central europe were controlled by three major factors the scandinavian ice sheet the north atlantic surface water circulation and the russian continent 1998 john wiley sons ltd

gravel ripples on the inner scotian shelf abstract sidescan sonar and photo video surveys have revealed the presence of symmetrical gravel bedforms interpreted as wave generated ripples with wavelengths of 1 3 to 3 0 m occurring in patches and narrow ribbons in depths of 15 to 65 m on the inner scotian shelf direct observations and sediment sampling from the pisces iv submersible have been used to ground truth surface based survey dam and to quantify relationships between the bedforms and the processes responsible for their formation the ripples are formed in polymodal sandy gravels with modal sizes ranging from 0 1 to 45 mm evaluation of threshold criteria for coarse sediments together with an 11 year record from a nearby wave rider buoy suggests that existing models for wave entrainment of gravel on rippled surfaces ove estimate the critical velocity by a factor of approximately 2 and that conditions suitable for transport of the coarsest 45 mm size mode sampled in the ripple crests occur on average 43 hr yr analysis of gravel ripples on the inner scotian shelf and of other examples noted in the recent literature extends the range of empirical data for oscillation ripple wavelengths by a factor of 3 and for ripple grain size by a factor of 5 the gravel ripples display a linear scaling to wave orbital diameter similar to that reported for orbital ripples in sand use of such relations for paleoenvironmental interpretation of gravel ripples preserved in the rock record is complicated by the difficulty of selecting appropriate grain size and wave parameters conditions suitable for potential formatio of large scale symmetrical ripples in coarse sediments extend from the outer continental shelf to shallow shore face settings with possible fetch lengths as short as 20 km under intense storms

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

reaction transport modelling of a freshening aquifer tertiary ledo paniselian aquifer flanders belgium abstract the semi confined ledo paniselian eocene aquifer in flanders belgium is recharged in the areas with higher topography where it is covered by the bartonian clay initial conditions in these sediments were marine hydrogeochemical modelling of the groundwater type distribution in the aquifer with a reaction transport model considers recharge of fresh cahco3 water by downward flow through the overlying clay in the aquifer in an upstream direction progressively more freshened water types are found a typical nahco3 type occurs upstream of the brackish fresh water interface the different stages of cation exchange produce a chromatographic sequence of groundwater types which agrees well with observations cation exchange processes occurring mainly in the percolated clay result in a na increase and peaks of k nh 4 and mg2 in the aquifer which are spatially separated as a result of groundwater flow calcite equilibrium gypsum dissolution in the clay and sulphate reduction in the aquifer have also been included in the modelling

a 40 ka record of temperature and permafrost conditions in northwestern europe from noble gases in the ledo paniselian aquifer belgium the ledo paniselian aquifer in belgium offers unique opportunities to study periglacial groundwater recharge during the last glacial maximum lgm as it was located close to the southern boundary of the ice sheets at that time groundwater residence times determined by 14c and 4he reveal a sequence of holocene and pleistocene groundwaters and a gap between about 14 and 21 ka indicating permafrost conditions which inhibited groundwater recharge in this paper a dataset of noble gas measurements is used to study the climatic evolution of the region the derived recharge temperatures indicate that soil temperatures in the periods just before and after the recharge gap were only slightly above freezing supporting the hypothesis that permafrost caused the recharge gap the inferred glacial cooling of 9 5 c is the largest found so far by the noble gas method yet compared to other palaeoclimate reconstructions for the region recharge temperatures deduced from noble gases for the cold periods tend to be rather high most likely this is due to soil temperatures being several degrees higher than air temperatures during periods with extended snow cover thus the noble gas derived glacial cooling of 9 5 c is only a lower limit of the maximum cooling during the lgm some samples younger than the recharge gap are affected by degassing possibly related to gas production during recharge in part of the recharge area especially during times of melting permafrost the findings of this study such as the occurrence of a recharge gap and degassing related to permafrost and its melting are significant for groundwater dynamics and geochemistry in periglacial areas copyright 2010 john wiley sons ltd

the last glacial maximum climate over europe and western siberia a pmip comparison between models and data under the framework of the palaeoclimate modelling intercomparison project pmip 17 climate models 16 of which are atmospheric general circulation models have been run to simulate the climate of the last glacial maximum 21 000 years ago using the same set of boundary conditions parallel to these numerical experiments new consistent data bases have been developed on a continental scale the present work compares the range of the model responses to the large perturbation corresponding to the conditions of the last glacial maximum with consistently derived climate reconstructions from pollen records over europe and western siberia it accounts for the differences in the model results due to the models themselves and directly compares this error bar due to the models to the uncertainties in the climate reconstructions from the pollen records overall the last glacial maximum climate simulated by the models over western europe is warmer especially in winter and wetter than the one depicted by the reconstructions this is the region where the reconstructed increase in temperature precipitation and moisture index from the last glacial maximum to the present conditions is largest the same disagreement but of smaller amplitude is found over central europe and the eastern mediterranean basin while models and data are in broad agreement over western siberia the numerous modelling results allow a study of the link between the changes in atmospheric circulation and those in temperature and an interpretation of the discrepancies in precipitation in terms of those in temperature

geomorphic expression of neotectonic activity in a low relief area in an airborne laser scanning dtm a case study of the little hungarian plain pannonian basin abstract the nw corner of the little hungarian plain which lies at the junction of the eastern alps the pannonian basin and the western carpathians is a neotectonically active region linking the extrusional tectonics of the eastern alps with the partly subsiding little hungarian plain the on going deformation is verified by the earthquake activity in the region an extremely flat part of the area east of neusiedlersee the so called seewinkel has been investigated with airborne laser scanning als also known as airborne lidar techniques resulting in a digital terrain model dtm with a 1 m grid resolution and vertical precision of better than 10 cm the dtm has been compared with known and inferred neotectonic features potential neotectonic structures of the dtm have been evaluated together with geological maps regional tectono geomorphic studies geophysical data earthquake foci as well as geomorphological features and the quaternary sediment thickness values of the seewinkel and the adjacent parndorfer plateau a combined evaluation of these data allows several tectonic features with a relief of

permafrost carbon stock and decomposability of a globally significant carbon pool 1 the magnitude of future co2 induced climate warming is difficult to predict because of uncertainties in the role of ecosystems and oceans as co2 sources and sinks siberia has extensive areas 1 106 km2 of deep up to 90 m deposits of organic rich frozen loess wind blown silt that accumulated during the pleistocene but have not been considered in most global carbon c inventories similar deposits occur less extensively in alaska recent warming at high latitudes causes this permafrost permanently frozen ground to thaw raising questions about the fate of c in thawing permafrost here we show that siberian loess permafrost contains a large organic c pool 450 gt more than half the quantity in the current atmosphere that decomposes quickly when thawed and could act as a positive feedback to climate warming

climate and groundwater recharge during the last glaciation in an ice covered region a multitracer study of a small aquifer in northern switzerland indicates that the atmosphere in central europe cooled by at least 5 c during the last glacial period the relation between oxygen isotope ratios 18o and recharge temperatures reconstructed for this period is similar to the present day one if a shift in the 18o value of the oceans during the ice age is taken into account this similarity suggests that the present day 18o temperature relation can be used to reconstruct paleoclimate conditions in northern switzerland a gap in calculated groundwater age between about 17 000 and 25 000 years before the present indicates that during the last glacial maximum local groundwater recharge was prevented by overlying glaciers

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

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

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

the reconstruction of past climates using multi proxy evidence an example of the weichselian pleniglacial in northwest and central europe abstract different lines of terrestrial biotic and abiotic evidence are used for large scale climate reconstructions to transform proxy data into climate parameter values standardisation procedures are defined and described as each type of biotic and abiotic proxy provides its own climate parameter a detailed climate reconstruction may be obtained the multi proxy database for palaeoclimate reconstruction is a specially designed computer database that facilitates data processing and management of weichselian climate proxies this paper describes the application of multi proxy evidence to reconstruct the climate across lowland northwest and central europe during the interval 41 38 bp for this period the mean temperature of the warmest month is estimated at 10 to 11 c and the mean temperature of the coldest month ranges from 27 to 20 c the annual range suggests a cold continental setting with an estimated mean annual temperature between 9 and 4 c a north to south transition from dis continuous permafrost to seasonally frozen ground is suggested by periglacial evidence

a palaeoclimatic record from the ledo paniselian aquifer in belgium indications for groundwater recharge and flow in a periglacial environment abstract understanding the mechanisms of groundwater recharge and flow in periglacial environments remains enigmatic methane releases from melting permafrost in a warming world are a hot topic in contemporary climate research noble gas analyses have been proposed to study methane driven degassing in lakes as well as in permafrost terrains the ledo paniselian aquifer is shown to provide an analogue for such processes from the last period of global warming after the lgm it is postulated that recharge from methane bubbling thermokarst lakes to groundwater took place and can be recognized by a specific signature in the groundwater the ledo paniselian aquifer offers unique opportunities to study periglacial groundwater recharge during the lgm as it was located in the permanent permafrost area to the south of the ice sheet at that time it contains holocene and pleistocene groundwaters which are separated by a recharge gap referring to permafrost during the lgm this is confirmed by noble gas temperature ngt data in the samples immediately upstream of this gap several potential indicators for the specific methanogenic recharge conditions from thawing permafrost are being put forward based on noble gases chemical and isotopic data immediately upstream of the age gap groundwaters show strikingly deviating hco3 so42 13c 18o and 2h compared to the regional trend while their 14c model ages are too young and ngts seem too high these samples are affected by degassing which is not an artefact of sampling and which according to their radiogenic helium concentrations occurred early on during recharge or shortly thereafter the origin of these samples could be explained by the conditions prevailing as the permafrost thawed and groundwater recharge could resume it is inferred that the degassed samples were infiltrated during or shortly after the lgm when recharge from methane bubbling thermokarst lakes to groundwater took place associated to the melting permafrost

a new groundwater radiocarbon correction approach accounting for palaeoclimate conditions during recharge and hydrochemical evolution the ledo paniselian aquifer belgium abstract the particular objective of the present work is the development of a new radiocarbon correction approach accounting for palaeoclimate conditions at recharge and hydrochemical evolution relevant climate conditions at recharge are atmospheric pco 2 and infiltration temperatures influencing c isotope concentrations in recharge waters the new method is applied to the ledo paniselian aquifer in belgium this is a typical freshening aquifer where recharge takes place through the semi confining cover of the bartonian clay besides cation exchange which is the major influencing process for the evolution of groundwater chemistry particularly in the bartonian clay also mixing with the original porewater solution fossil seawater occurs in the aquifer recharge temperatures were based on noble gas measurements potential infiltration water compositions for a range of possible pco 2 temperature and calcite dissolution system conditions were calculated by means of phreeqc then the sampled groundwaters were modelled starting from these infiltration waters using the computer code netpath and considering a wide range of geochemical processes fitting models were selected on the basis of correspondence of calculated 13 c with measured 13 c the 14 c modelling resulted in residence times ranging from holocene to pleistocene few hundred years to over 40 ka and yielded consistent results within the uncertainty estimation comparison was made with the 13 c and fontes and garnier correction models that do not take climate conditions at recharge into account to date these are considered as the most representative process oriented existing models yet differences in calculated residence times of mostly several thousands of years up to 19 ka are revealed with the newly calculated ages being mostly though not always younger not accounting for climate conditions at recharge pco 2 and temperature is thus producing substantial error on deduced residence times the derived 14 c model ages are correlated with he concentrations measured in the groundwater of the aquifer the obtained residence times show a gap between about 14 and 21 ka indicating possible permafrost conditions which inhibited any groundwater recharge

numerical simulation of permafrost growth and decay a series of numerical models on permafrost growth and decay are presented with special emphasis on the climatic conditions in western europe during the last glacial stage numerical modelling of growth and decay of the active layer suggests penetration depths in the range between 0 6 to 1 4 m permafrost is estimated to have grown depending on the sediment type to a thickness of 90 m to 140 m in northern germany and the netherlands within 10 000 y during the peak period of the last glacial stage permafrost continued to exist at depth for about 2000 y after the climatic improvement following the younger dryas permafrost growth under rivers and lakes is shown to be unlikely under the climatic conditions of the last glacial stage in northern germany a time period of 10 000 to 42 000 years and a massive climatic excursion of the order of 11 c is required to remove the thick permafrost layers in siberia and alaska of today 1998 john wiley sons ltd