methodology of the last climatic cycle reconstruction in france from pollen data abstract a numerical method has been devised to reconstruct the climate of the last climatic cycle from pollen data reliable annual reconstructions have been published recently for the two french long sequences of la grande pile and les echets covering the last 140 millennia this paper gives more details on the method used it proposes new reconstructions based on an extended modern pollen data base these reconstructions are consistent with the previous ones especially detailed information is obtained on the seasonal characteristics of climate computations of gcm on the climate variations from 125 kyr to 115 kyr b p are confirmed for western europe the insolation variations have induced at that time a decrease of seasonality accompanied by an increased cyclonic activity in winter this has been the beginning of the first ice growth after the last interglacial other glacier growth phases are detected at the end of substage 5c and particularly at the end of substage 5a

inverse multiparameter modeling of paleoclimate carbon cycle indices abstract a simple linear response model describing the functional relationship between ocean carbon cycle parameters and paleoclimate tracers atmospheric p co2 13c caco3 saturation was derived from a set of sensitivity experiments performed previously using a three dimensional carbon cycle model the linear model is optimally fitted to ice and marine sediment core records for the last 120 000 yr to estimate the carbon cycle parameter changes that could have caused the observed reduction of atmospheric co2 partial pressure during the last glaciation the analysis indicates that the glacial pco2 reduction was primarily caused by a strengthening of the biological poc pump and a retardation of the oceanic circulation an increase in deep sea alkalinity and a change in the advective pattern of the ocean circulation have a smaller impact on atmospheric co2 but are necessary to explain the full set of paleoclimate tracers

estimating scattering attenuation from vugs or karsts cavities in carbonate rock such as vugs or karsts cause scattering attenuation in passing waves the degree of such attenuation is often difficult to quantify because the exact scale and structure of the cavities is unknown taking the exact vug structure from x ray computerized tomography scans of two carbonate cores we use 3d finite difference modeling to determine the p wave scattering attenuation in these cores at ultrasonic frequencies the predicted scattering attenuation is quite high with q of 15 and 8 near the source frequency of 250 khz in spite of the sharp contrast in medium properties between cavity and rock and the violation of the small perturbation assumption the computed scattering attenuation is roughly comparable to that predicted by various random medium scattering theories this suggests that if the volume fraction and typical size of vugs or karsts can be estimated then a rough estimate of frequency dependent scattering attenuation can be made

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

a model for seismic velocity and attenuation in petroleum source rocks petroleum source rock is modeled as a viscoelastic transversely isotropic medium composed of illite smectite and organic matter the wave velocities and attenuation of petroleum source rocks are obtained as a function of excess pore pressure initial kerogen content and water saturation the model generalizes a previous approach based on a pure elastic formulation of backus averaging and introduces the pressure effect and the presence of fluids oil and water the model allows the simulation of different maturation levels induced by pore pressure changes caused by the conversion of kerogen to oil the higher the oil saturation the higher the maturation level assuming that the source rock has a very low permeability the excess pore pressure can be calculated as a function of the conversion factor then the bulk modulus and density of the kerogen oil mixture are obtained with the kuster and toks oz model assuming that oil is the inclusion in a kerogen matrix finally backus averaging of this mixture with the illite smectite layers gives the complex stiffnesses of the transversely isotropic and anelastic medium computed p and s velocities and quality factors parallel to bedding are higher than those normal to bedding with attenuation anisotropy higher than stiffness anisotropy in particular for the north sea kimmeridge shale and at maximum anisotropy p and s parallel velocities are approximately 0 7 km s higher than the corresponding p and s normal velocities the maximum attenuation and stiffness anisotropies are obtained for 18 and 30 volumetric kerogen content respectively both velocities and quality factors decrease with increasing kerogen content at a given pore pressure the decrease in wave velocity is 2 km s for p waves and 1 km s for s waves when kerogen increases from zero to 100 moreover anisotropy increases and velocities decrease with increasing pore pressure i e with higher kerogento oil conversion finally the presence of water affects the normal bedding velocity i e higher water saturation implies lower velocities

three dimensional simulation and inversion of borehole temperatures for reconstructing past climate in complex settings 1 the majority of inversion methods used for inferring past ground surface temperatures gst from borehole temperature depth profiles rely on the assumption that heat flow is in the vertical direction only this means that accounting for certain effects caused by the local terrain of a borehole is not possible and consequently many borehole profiles cannot be used with confidence here we describe a methodology to avoid this problem by solving the heat conduction forward problem in 3 d using finite elements fe in order to make the inversion approach computationally tractable we reduce the dimensions of this fe model using proper orthogonal decomposition the inverse problem is cast in a probabilistic bayesian framework for which the posterior probability distribution of the past gsts is sampled using a reversible jump markov chain monte carlo algorithm this allows the resolution of the gst history over time to be explored by varying the parameterization of the gst model synthetic examples calculated with moderate topographies demonstrate the efficacy of the bayesian 3 d inversion method and the results are compared with those using a 1 d approach for moderate topography the latter can lead to spurious gst reconstructions a further synthetic example demonstrates that the effect of incorrectly assuming lateral geological homogeneity is negligible the inversion method is also compared with a more standard inversion method a significant advantage of the bayesian approach is that uncertainties in all of the model parameters can be accounted for leading to a more realistic interpretation of the range of gst histories supported by the data the methods presented here should allow a broader range of geothermal data to be used for paleoclimate reconstruction purposes in the future

reflection waveform inversion using local descent methods estimating attenuation and velocity over a gas sand deposit prestack seismic reflection data contain amplitudes traveltimes and moveout information waveform inversion of such data has the potential to estimate attenuation levels reflector depths and geometry and background velocities however when inverting reflection data strong nonlinearities can cause reflectors to be incorrectly imaged and can prevent background velocities from being updated to successfully recover background velocities previous authors have resorted to nonlinear global search inversion techniques we propose a two step inversion procedure using local descent methods in which we perform alternate inversions for the reflectors and the background velocities for our reflector inversion we exploit the efficiency of the back propagation method when inverting for a large parameter set for our background velocity inversion we use newton inverse methods during the background velocity inversions it is crucial to adaptively depth stretch the model to preserve the vertical traveltimes this reduces nonlinearity by largely decoupling the effects of the background velocities and reflectors on the data nonlinearity is further reduced by choosing to invert for slownesses and by inverting for a sparse parameter set which is partially defined using geological reflector picks applying our approach to shallow seismic data from the north sea collected over a gas sand deposit we demonstrate that the proposed method is able to estimate both the geometry and internal velocity of a significant velocity structure not present in the initial model over successive iterations the use of adaptive depth stretching corrects the pull down of the base of the gas sand vertical background velocity gradients are also resolved for an insignificant extra cost the acoustic attenuation parameter q is included in the inversion scheme the final attenuation tomogram contains realistic values of q for the expected lithologies and for the effect of partial fluid saturation associated with a shallow bright spot the attenuation image may also indicate the presence of fracturing

analysis of multiscale scattering and poroelastic attenuation in a real sedimentary rock sequence compressional waves in heterogeneous permeable media experience attenuation from both scattering and induced pore scale flow of the viscous saturating fluid for a real finely sampled sedimentary sequence consisting of 255 layers and covering 30 meters of depth elastic and poroelastic computer models are applied to investigate the relative importance of scattering and fluid flow attenuation the computer models incorporate the known porosity permeability and elastic properties of the sand shale sequence in a binary medium plane layered structure the modeled elastic scattering attenuation is well described by stochastic medium theory if two length scale statistics are applied to reflect the relative thickness of the shale layers when compared to the sand layers under the poroelastic biot squirt flow model fluid flow attenuation from the moderate permeability 10 14 m2 sands may be separated in the frequency domain from the attenuation due to the low permeability 5 10 17 m2 shale layers based on

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

scattering attenuation in randomly layered structures with finite lateral extent a hybrid q model since the pioneering work of o doherty and anstey 1971 much research has been devoted to understand the effect of stratigraphic filtering of seismic waves i e the problem of multiple scattering in 1d random structures e g burridge et al 1993 shapiro and hubral 1999 for many subsurface structures such as sedimentary basins the assumption of layering is reasonable as a first approximation however real geostructures do not show perfect layering but exhibit a finite lateral extent in their elastic properties this becomes particularly important when studying overburden effects in reflection seismology where amplitude information is used in subsequent data analysis for example malme et al 2003 showed that the amplitude variation with offset avo response for a vertical seismic profile vsp experiment over a north sea field is significantly distorted by nonlayered overburden inhomogeneities they demonstrated by seismic forward modeling that pointlike diffractors and large scale gas filled sand bodies can be responsible for strong amplitude fluctuations in this short note we study the transmission behavior of seismic primaries when the finite lateral extent of the inhomogeneities is accounted for physically speaking we intend to quantify the combined effects of scattering attenuation due to thin layering and random diffractions and refractions it is important to understand that our approach describes scattering attenuation of seismic primaries and not attenuation of the mean field ensemble averaged wavefield as presented in earlier works e g lerche 1986 we use the model of an anisotropic 3d random medium anisotropy in this context means that the randomly distributed inhomogeneities have three different characteristic length scales and are characterized by a spatially anisotropic correlation function we also assume that the medium is lossless so that no intrinsic wave attenuation occurs a sketch of such a structure is shown in figure 1 resembling a realization of a 2d

seismic identification of a karstified reservoir in the adriatic sea in this study an elastic prestack migration inversion m i scheme was applied to a 2 d seismic line collected in the adriatic sea the objective was to use m i images to describe a hydrocarbon reservoir consisting of karstified brine saturated limestones the m i technique offers the benefit of extracting maximum information from seismic reflection data to describe and in some cases characterize the reservoir target m i images are calibrated with well data and represent approximate changes in p and s wave impedances across the reservoir combining these two images yields a poisson s ratio image

fault distribution and timing in the central irish sea basin well data analysis and the interpretation of 2d and 3d seismic reflection data provide valuable insights into the distribution and timing of fault activity within the central irish sea basin cisb structural and stratigraphic relationships have been used to constrain the timing of fault movements and to interpret the mapped fault patterns in terms of the tectonic evolution of the area four main fault trends are identified at the top lower triassic sherwood sandstone group level i a ne sw fault trend that parallels the basin bounding faults and is believed to be of mesozoic age ii a pervasive system of north south trending faults that cross cut the earlier ne sw trending faults which manifests evidence of later mesozoic extension followed by post oligocene transpressional fault reactivation iii a nne ssw trending steeply dipping fault set iv a wnw ese trending conjugate extensional set that formed perpendicular to the nne ssw trending transpressional faults during late tertiary dextral shearing early tertiary axial centred basin inversion and regional exhumation have resulted in the elevation of the sherwood sandstone reservoir to shallow structural levels within the basin continued fault reactivation into late tertiary time has resulted in the compartmentalization of mapped structural closures and suggests that trap integrity is a major exploration risk factor in the cisb the central irish sea basin cisb is a ne sw trending graben located between the kish bank basin to the nw and the st george s channel and cardigan bay basins to the se fig la the cisb forms part of a linked system of mesozoic basins between the uk and ireland which also

scattering versus intrinsic attenuation in the vadose zone a vsp experiment abstractwe studied scattering versus intrinsic attenuation estimates in the vadose zone from a shallow vsp experiment conducted in the lawrence livermore national laboratory llnl facility using permanent downhole geophones and a vertical impact source we estimated effective attenuation of the downgoing transmitted p wave we compared theoretical scattering attenuation estimates and finite difference synthetics to the measured field q values 1 q being a measure of attenuation using a selected range of impedance profiles of variance typical for a sedimentary basin our estimates of qscattering are in the order of 20 85 given the short propagation pathlengths involved 30 m we show that attenuation due to lateral heterogeneity is not significant we analyzed additional distorting factors including near field presence local impedance effects and interference from reflections originating beneath receivers and found that they may significantly impact attenuation measurement in near surface studi

regional scale palaeoclimate modelling on soft proxy data basis an example from the upper miocene of the lower rhine embayment abstract a new method in palaeoclimatology initially proposed by mosbrugger and schilling 1992 which makes it possible to extract a maximum of information from the available proxy data is tested it possesses a capacity to produce a detailed palaeoclimate reconstruction which is consistent with both proxy data and the physics of atmospheric models since proxy data information is particularly poor on a global scale our method focuses on smaller scale regions of better proxy data coverage it consists of an iterative coupling of inverse mesoscale atmospheric modelling with proxy based palaeoclimate reconstruction using this method the palaeoclimate of the tortonian upper miocene of the lower rhine embayment northwest germany is reconstructed with a high spatial resolution the results include a physically consistent inter and extrapolation of proxy derived palaeoclimate data in space and onto variables not accessible from geological palaeontological proxies alone moreover the method delivers statistics of the large scale atmospheric flows as information on the coupling of the regional climate to global fields

can paleoceanographic tracers constrain meridional circulation rates abstract the ability of paleoceanographic tracers to constrain rates of transport is examined using an inverse method to combine idealized observations with a geostrophic model considered are the spatial distribution accuracy and types of tracers required to constrain changes in meridional transport within an idealized single hemisphere basin measurements of density and radioactive tracers each act to constrain rates of transport conservative tracers while not of themselves able to inform regarding rates of transport improve constraints when coupled with density or radioactive observations it is found that the tracer data would require an accuracy one order of magnitude better than is presently available for paleo observations to conclusively rule out factor of 2 changes in meridional transport even when assumed available over the entire model domain when data are available only at the margins and bottom of the model radiocarbon is unable to constrain transport while density remains effective o

holocene temperature changes in northern fennoscandia reconstructed from chironomids using bayesian modelling the recently developed bayesian multinomial calibration model bummer was applied to the fossil chironomid assemblages of a lake situated at the present tree line in northern fennoscandia to reconstruct patterns in holocene climates the results are compared with inferences derived using non bayesian weighted averaging partial least squares regression the reconstruction exhibits both long term trends as well as a series of shorter term oscillations abrupt climatic excursions were particularly characteristic for the early holocene period with cooling episodes around 9200 8600 and 8200 cal yr bp the interval from ca 8000 to 5800 cal yr bp appeared to be warm and stable but was followed by a pronounced climatic cooling around 5800 cal yr bp leading to a relatively long lasting mid holocene temperature minimum between ca 5800 and 4000 cal yr bp the reconstruction during the latter part of the holocene is relatively featureless which may partly be due to gradual shallowing of the lake by sedimentation that may have affected chironomid compositions thereby masking the climate signal the major climatic patterns in our reconstruction agree well with inferences from greenland ice and marine sediments and are also in line with the previous reconstructions based on diatoms and pollen from the same core although the finer scale variations reflected by the three proxies do not always match the overall results provide evidence for climatic complexity during the holocene epoch and demonstrate that bayesian modelling is highly suitable for reconstruction purposes

constraints from paleotracer data on the north atlantic circulation during the last glacial maximum we investigate the extent to which the paleotracers 13c and 18o constrain the north atlantic ocean general circulation during the last glacial maximum lgm the distinction is made in this work between the depiction of water mass distributions and the inference of the oceanic circulation the 13c data indicate that water masses formed in the north atlantic and in the southern ocean were distributed differently during the lgm but the extent of the differences cannot be quantified because of uncertainties in the end member composition reasonable choices of values for the end members produce volumes of lower north atlantic deep water nadw significantly smaller than in the modern atlantic in agreement with previous studies to explore the range of circulations consistent with this water mass distribution a coarse resolution inverse model of the north atlantic is constrained with 13c and 18o paleodata the model shows that the glacial period tracer distribution is fully consistent with the circulation rates estimated for the modern ocean however the paleodata are also consistent with a circulation rate of one half the modern flux of nadw and indeed there are an infinite number of rates of deep water movement that are possible to remove this ambiguity the central need is for a data type capable of setting the overall rates of water movement i e a clock such as that provided by geostrophy or a well sampled radioactive tracer

quantitative palaeoclimate reconstruction as an inverse problem a bayesian inference of late holocene climate on the eastern tibetan plateau from a peat cellulose δ18o record there has been a sustained need to quantify past climate changes from proxy records to better understand the driving mechanisms and thus to improve the prediction of the future transfer function is an intuitive and frequently used method in this regard however this method is unable to provide interpretive and predictive results from proxy records because physical processes are not included the inverse proxy modelling method opened up a new avenue for quantitative palaeoclimate reconstructions through the integration of proxy records with deterministic models it is fundamentally different from the statistical approach representing a conceptual advance in quantitative palaeoclimatology here we demonstrate the potential of this method by placing a mechanistic model and a 6000 year long peat cellulose 18o record obtained from the high cold and monsoonal eastern tibetan plateau c 3500 m a s l in a bayesian paradigm in this worked example the marginal posterior probability distributions of palaeo

abrupt changes in the asian southwest monsoon during the holocene and their links to the north atlantic ocean during the last ice age the indian ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial scale climate events in the north atlantic region1 2 3 suggesting a mechanistic link in the holocene epoch which had a more stable climate the amplitude of abrupt changes in north atlantic climate was much smaller and it has been unclear whether these changes are related to monsoon variability here we present a continuous record of centennial scale monsoon variability throughout the holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic arabian sea our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the north atlantic region4 including the most recent climate changes from the medieval warm period to the little ice age and then to the present we therefore suggest that the link between north atlantic climate and the asian monsoon is a persistent aspect of global climate

wave attenuation attributes as flow unit indicators in this article we present a model based interpretation algorithm to predict attenuation signatures associated with a reservoir s structure and its intrinsic properties scattering losses are caused by multiple reflections associated with the impedance contrast between different reservoir boundaries intrinsic losses are due to the fluids in the reservoir the rock fabric and the anisotropy due to vertical fractures because amplitude data are sensitive to these reservoir characteristics we calculate the wave attenuation response of the reservoir in the frequency range of surface seismic vsp crosswell seismic and borehole sonic a model of a plane wave traveling in a poroelastic multilayer earth medium allows us to include anisotropy the multilayer part of the model simulates elastic scattering the poroelastic part of the model simulates fluid flow effects in the reservoir and the anisotropic part of the model simulates reservoir fractures

compressional wave q estimation from full waveform sonic data there is significant evidence that the anelastic loss of seismic energy is linked to petrophysical properties such as porosity permeability and clay content thus reliable estimation of anelastic attenuation from seismic data can lead to improved methods for the prediction of petrophysical properties this paper is concerned with methods for the estimation of attenuation at sonic frequencies 5 30 khz from in situ data two independent methods have been developed and tested for estimating compressional wave attenuation from full waveform sonic data a well established technique the logarithm spectral ratio lsr method is compared with a new technique the instantaneous frequency if method the lsr method uses the whole spectrum of the seismic pulse whilst the if method uses a carefully estimated value of instantaneous frequency which is representative of the centre frequency of the pulse in the former case attenuation estimation is based on the relative variation of amplitudes at different frequencies whilst in the latter case it is based on the shift of the centre frequency of the pulse to lower values during anelastic wave propagation the if method does not assume frequency independence of q which is a necessary assumption for the lsr method and it provides a stable frequency log the peak instantaneous frequency pif log which may be used as an indicator for attenuation under certain limitations the development and implementation of the two methods is aimed at minimizing the effect of secondary arrivals such as leaky modes and involved a series of parameter tests testing of the two methods using full waveform sonic data of variable quality obtained from a gas bearing sandstone reservoir showed that the if method is in general more stable and suitable for full waveform sonic data compared with the lsr method this was evident especially in data sets with high background noise levels and wave interference effects for good quality data the two methods gave results that showed good agreement whilst comparison with other log types further increased confidence in the results obtained a significant decrease approximately 5 khz in the pif values was observed in the transition from an evaporite shale sequence to the gas bearing sandstone average q values of 54 and 51 were obtained using good quality data from a test region within the gas saturated sandstone reservoir using the lsr and if methods respectively

the climate record inverted from borehole temperatures in slovenia abstract temperature profiles from nine boreholes in slovenia located mostly in the northeastern part of the country have been studied for evidence of past climatic changes the reconstruction of the ground surface temperature gst history based on 1 d theory of heat conduction was accomplished using the functional space inversion fsi method because of the paucity of quality thermal conductivity data and because the nature of heat conduction is such that information about gst changes decay with the passage of time the a priori standard deviations of the thermal conductivity model 1 w m 1 k 1 and measured temperature 0 2 k were chosen large enough so that the gst histories older than 200 years are considerably smoothed and essentially merge with the long term mean the average gst history based on consistent results from seven boreholes starts to rise at the end of the last century the amplitude of the warming is about 0 6 to 0 7 k in the past 100 years two boreholes were rejected the long term mean gsts lie between 9 4 and 11 1 c the mean annual air temperatures from the ljubljana meteorological station are in good agreement with the average gst solution the gst history of the past 20 30 thousand years ka was reconstructed from the almost 2 km deep ljutomer temperature profile the history evidences climate variations during the wurm weichselian ice age it places the glacial minimum of about 3 c at 13 14 ka ago and the postglacial maximum of 10 5 c roughly at 2 3 ka ago

physiological significance of low atmospheric co2 for plant climate interactions abstract methods of palaeoclimate reconstruction from pollen are built upon the assumption that plant climate interactions remain the same through time or that these interactions are independent of changes in atmospheric co 2 the latter may be problematic because air trapped in polar ice caps indicates that atmospheric co 2 has fluctuated significantly over at least the past 400 000 yr and likely the last 1 6 million yr three other points indicate potential biases for vegetation based climate proxies first c 3 plant physiological research shows that the processes that determine growth optima in plants photosynthesis mitochondrial respiration photorespiration are all highly co 2 dependent and thus were likely affected by the lower co 2 levels of the last glacial maximum second the ratio of carbon assimilation per unit transpiration called water use efficiency is sensitive to changes in atmospheric co 2 through effects on stomatal conductance and may have altered c 3 plant responses to drought third leaf gas exchange experiments indicate that the response of plants to carbon depleting environmental stresses are strengthened under low co 2 relative to today this paper reviews the scope of research addressing the consequences of low atmospheric co 2 for plant and ecosystem processes and highlights why consideration of the physiological effects of low atmospheric co 2 on plant function is recommended for any future refinements to pollen based palaeoclimatic reconstructions

seismic scattering in the upper crystalline crust based on evidence from sonic logs summary evidence from sonic logs indicates that velocity fluctuations in the upper crystalline crust are remarkably uniform this motivates a generic approach to classifying uppercrustal seismic heterogeneity and to studying implications for seismic wave propagation the resulting canonical model of upper crustal seismic structure is characterized by a spatially isotropic von karman autocovariance function with a z 100 m 0 15 and cj 300 m s small angle scattering theory is used to predict the transition from weak to strong scattering as well as phase fluctuations and scattering attenuation compared with exponential random media v 0 50 the high fractal dimension i e small values of v of upper crustal heterogeneity causes smaller phase fluctuations and transition from weak to strong scattering at lower frequencies and shorter path lengths acoustic finite difference modelling shows that seismic reflections from deterministic features surrounded by heterogeneities are severely degraded when they fall into the strong scattering regime conversely traveltime fluctuations of transmitted waves are found to be relatively insensitive to the transition from weak to strong scattering upper crustal scattering q is predicted to lie between 600 and 1500 which is one to two orders of magnitude higher than q values inferred from seismic data this suggests that seismic attenuation in the upper crystalline crust is dominated by anelastic effects rather than by scattering

climatic changes in eurasia and africa at the last glacial maximum and mid holocene reconstruction from pollen data using inverse vegetation modelling in order to improve the reliability of climate reconstruction especially the climatologies outside the modern observed climate space an improved inverse vegetation model using a recent version of biome4 has been designed to quantitatively reconstruct past climates based on pollen biome scores from the biome6000 project the method has been validated with surface pollen spectra from eurasia and africa and applied to palaeoclimate reconstruction at 6 cal ka bp calendar years the climate was generally wetter than today in southern europe and northern africa especially in the summer winter temperatures were higher 1 5 c than present in southern scandinavia northeastern europe and southern africa but cooler in southern eurasia and in tropical africa especially in mediterranean regions summer temperatures were generally higher than today in most of eurasia and africa with a significant warming from 3 to 5 c over northwestern and southern europe southern africa and eastern africa in contrast summers were 1 3 c cooler than present in the mediterranean lowlands and in a band from the eastern black sea to siberia at 21 cal ka bp a marked hydrological change can be seen in the tropical zone where annual precipitation was 200 1 000 mm year lower than today in equatorial east africa compared to the present a robust inverse relationship is shown between precipitation change and elevation in africa this relationship indicates that precipitation likely had an important role in controlling equilibrium line altitudes ela changes in the tropics during the lgm period in eurasia hydrological decreases follow a longitudinal gradient from europe to siberia winter temperatures were 10 17 c lower than today in eurasia with a more significant decrease in northern regions in africa winter temperature was 10 15 c lower than present in the south while it was only reduced by 0 3 c in the tropical zone comparison of palaeoclimate reconstructions using lgm and modern co2 concentrations reveals that the effect of co2 on pollen based lgm reconstructions differs by vegetation type reconstructions for pollen sites in steppic vegetation in europe show warmer winter temperatures under lgm co2 concentrations than under modern concentrations and reconstructions for sites in xerophytic woods scrub in tropical high altitude regions of africa are wetter for lgm co2 concentrations than for modern concentrations because our reconstructions account for decreased plant water use efficiency

localization and backscattering spectrum of seismic waves in stratified lithology using four sonic well logs from diverse geological environments we analyze the statistics of lithological layers relevant to seismic wave propagation the autocorrelation functions are found to be well approximated by exponentials with correlation lengths generally in the 1 5 to 3 m range we use localization theory to calculate the apparent attenuation caused by random scattering as a function of frequency this attenuation has a peak at 50 to 150 hz with a corresponding localization length of 1 6 to 4 8 km 1 to 3 mi and an apparent q of 120 to 450 at seismic frequencies 20 hz the attenuation is smaller with localization lengths in the 16 to 32 km 10 to 20 mi range and an apparent q of 300 to 700 these values of apparent q are consistent with observations of previous authors who used well log calculations using finite differences we compute synthetic traces for a 20 hz pulse with multiple backscattering from the lithology given by each of the well logs the power spectral density of the trace

seismic study of the low permeability volume in southern france karst systems locating groundwater in deep seated karst aquifers is inherently difficult with seismic methods we studied the upper epikarst and the underneath low permeability volume lpv of several karst systems located in the southern quercy and larzac regions of france and found that refraction tomography was effective only in the epikarst and not in the lpv we evaluated a 3d case study using a combination of surface records and downhole receivers to overcome this limitation this 3d approach unveiled a set of elongated furrows at the base of the epikarst and identified heterogeneities deep inside the lpv that may represent high permeability preferred pathways for water inside the karst to achieve the same result when no borehole was available we studied seismic amplitudes of the wavefield recognizing that wave induced fluid flow in low permeability carbonates is a driving mechanism of seismic attenuation we developed a workflow describing the heterogeneity of the lpv with spectral attributes derived from surface consistent decomposition principles and we validated its effectiveness at benchmark locations we applied this workflow to the 3d study and found a low amplitude signal area at depth we interpreted this anomaly as a water saturated body perched above the aquifer

quantifying uncertainties in attenuation estimation at methane hydrate bearing zones using sonic waveform logs abstractapplication of seismic attenuation estimation using sonic waveform data is limited because the estimation methods have not yet been fully developed although the median frequency shift method is considered to be effective and robust compared to the conventional spectral ratio method we demonstrated that the median frequency shift methods strongly depend on reference data under lower signal to noise ratios we modified an existing median frequency shift method not to depend on arbitrarily choosing a reference value and to quantify the uncertainties in attenuation estimation furthermore we implied the optimum selection of receiver pairs used for more stable attenuation analysis our numerical experiments supported the advantage of the proposed method although our main findings by applying the proposed methods in methane hydrate bearing sediments are almost consistent with past field sonic logging measurements we find some differences in the magnitude of attenuation values compared to existing s

p and s wave attenuation logs from monopole sonic data in this paper a modification of an existing method for estimating relative p wave attenuation is proposed by generating synthetic waveforms without attenuation the variation of geometrical spreading related to changes in formation properties with depth can be accounted for with the modified method reliable p and s wave attenuation logs can be extracted from monopole array acoustic waveform log data synthetic tests show that the p and s wave attenuation values estimated from synthetic waveforms agree well with their respective model values in situ p and s wave attenuation profiles provide valuable information about reservoir rock properties field data processing results show that this method gives robust estimates of intrinsic attenuation the attenuation profiles calculated independently from each waveform of an eight receiver array are consistent with one another in fast formations where s wave velocity exceeds the borehole fluid velocity both p wave attenuation qp 1 and s wave attenuation