evidence of 550 year and 1000 year cyclicities in north atlantic circulation patterns during the holocene sedimentological colour data obtained from north atlantic deep sea sediment core neap15k pro vide a continuous climate record for the last 11500 yr with a mean sampling interval of 15 yr variations in sediment lightness a proxy for changes in north atlantic deep water nadw circulation are characterized by high frequency fluctuations with periodicities equivalent to 550 and 1000 yr as well as a 1600 yr cyclicity comparable to that reported in other studies of holocene climate cross spectral analysis suggests that the 550 yr and 1000 yr cyclical variations in nadw circulation were coherent with fluctuations in atmospheric con ditions over greenland where both these periodicities have been identified previously in the holocene gisp2 d18o record stuiver et al 1995 a similar statistical comparison provides evidence that high frequency 550 yr variability in nadw circulation patterns may have been linked to short term variations in atmospheric 14c values during the holocene in general nadw pro

widespread evidence of 1500 yr climate variability in north america during the past 14 000 yr there is debate concerning the spatial extent and magnitude of the recently identified 1500 yr climate oscillation existing evidence is largely restricted to the north atlantic and adjacent landmasses the spatial extent magnitude and effects of these climate variations within the terrestrial environment during the holocene have not been established we show that millennial scale climate variability caused changes in vegetation communities across all of north america with a periodicity of 1650 500 yr during the past 14 000 calendar years cal yr times of major transitions identified in pollen records occurred at 600 1650 2850 4030 6700 8100 10 190 12 900 and 13 800 cal yr b p consistent with ice and marine records we suggest that north atlantic millennial scale climate variability is associated with rearrangements of the atmospheric circulation with far reaching influences on the climate

major features and forcing of high latitude northern hemisphere atmospheric circulation using a 110 000 year long glaciochemical series the greenland ice sheet project 2 glaciochemical series sodium potassium ammonium calcium magnesium sulfate nitrate and chloride provides a unique view of the chemistry of the atmosphere and the history of atmospheric circulation over both the high latitudes and mid low latitudes of the northern hemisphere interpretation of this record reveals a diverse array of environmental signatures that include the documentation of anthropogenically derived pollutants volcanic and biomass burning events storminess over marine surfaces continental aridity and biogenic source strength plus information related to the controls on both high and low frequency climate events of the last 110 000 years climate forcings investigated include changes in insolation of the order of the major orbital cycles that control the long term behavior of atmospheric circulation patterns through changes in ice volume sea level events such as the heinrich events massive discharges of icebergs first identified in the marine record that are found to operate on a 6100 year cycle due largely to the lagged response of ice sheets to changes in insolation and consequent glacier dynamics and rapid climate change events massive reorganizations of atmospheric circulation that are demonstrated to operate on 1450 year cycles changes in insolation and associated positive feedbacks related to ice sheets may assist in explaining favorable time periods and controls on the amplitude of massive rapid climate change events explanation for the exact timing and global synchroneity of these events is however more complicated preliminary evidence points to possible solar variability climate associations for these events and perhaps others that are embedded in our ice core derived atmospheric circulation records

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

stochastic reservoir characterization using prestack seismic data reservoir characterization must be based on information from various sources well observations seismic reflection times and seismic amplitude versus offset avo attributes are integrated in this study to predict the distribution of the reservoir variables i e facies and fluid filling the prediction problem is cast in a bayesian setting the a priori model includes spatial coupling through markov random field assumptions and intervariable dependencies through nonlinear relations based on rock physics theory including gassmann s relation the likelihood model relating observations to reservoir variables including lithology facies and pore fluids is based on approximations to zoeppritz equations the model assumptions are summarized in a bayesian network illustrating the dependencies between the reservoir variables the posterior model for the reservoir variables conditioned on the available observations is defined by the a priori and likelihood models this posterior model is not analytically tra

teleconnections between the subtropical monsoons and high latitude climates during the last deglaciation the major deglacial intensification of the southwest monsoon occurred at 11 450 150 calendar years before present synchronous with a major climate transition as recorded in greenland ice an earlier event of monsoon intensification at 16 000 150 calendar years before present occurred at the end of heinrich layer 1 in the atlantic and parallels the initial rise in global atmospheric methane concentrations and the first abrupt climate changes in the antarctic thus the evolution of the monsoonal and high latitude climates show teleconnections but hemispheric asymmetries superimposed on abrupt events the monsoonal climate shows high frequency variability of 1785 1450 and 1150 year oscillations and abrupt climate change seems to occur when at least two of these oscillations are in phase

correlation between indian ocean summer monsoon and north atlantic climate during the holocene there has been a number of investigations for the correlation between the asia monsoon and the north atlantic climate for the last glacial however little research has been done for the present interglacial the holocene here we present for the first time a high resolution composite proxy record for the indian ocean summer monsoon spanning around 12 000 years based on the 13c time series of both a single plant species carex mulieensis remains cellulose and the total plant assemblage cellulose in the hongyuan peat bog from the tibet plateau the records show that the strength of the indian ocean summer monsoon had abrupt variations during the last 12 000 years the weakest monsoon occurred in the younger dryas period following rapid strengthening from around 11 200 to 10 800 a bp the monsoon kept a generally strong level for around 5300 years from around 5500 a bp onwards the monsoon strength tended to gradual decrease in addition there are a series of abrupt variation events of the monsoon strength on centennial to millennial time scales which superimpose the general tendency of the monsoon variation in every case when the ice rafted debris events in the north atlantic occurred the summer monsoon strength decreased correspondingly these evidences show that teleconnection between the indian ocean summer monsoon and the north atlantic climate is present not only in the last glacial but also in the holocene which may be linked to abrupt reorganizations of the ocean thermohaline circulation leading to redistribution of energy changing temperature and moisture gradient over the southern subtropical indian ocean and eventually controlling the variability of the indian ocean summer monsoon

the little ice age and medieval warm period in the sargasso sea sea surface temperature sst salinity and flux of terrigenous material oscillated on millennial time scales in the pleistocene north atlantic but there are few records of holocene variability because of high rates of sediment accumulation holocene oscillations are well documented in the northern sargasso sea results from a radiocarbondated box core show that sst was approximately 1 degree c cooler than today approximately 400 years ago the little ice age and 1700 years ago and approximately 1 degree c warmer than today 1000 years ago the medieval warm period thus at least some of the warming since the little ice age appears to be part of a natural oscillation 39 refs 4 figs 1 tab

circulation in the glacial north atlantic inferred from grain size measurements records of nutrient proxies in marine sediments indicate that the nutrient distribution and hence circulation of the glacial north atlantic ocean was markedly different from that of today1 2 but these tracers are influenced by several biogeochemical factors unrelated to ocean circulation3 6 and thus do not provide a direct measure of the vigour of circulation distributions of grain size in marine sediments can provide such information owing to the sorting effects of currents7 8 if the characteristics of the input sediment flux are known here we present a record inferred from grain size measurements of variations in the relative strength of deep and intermediate currents in the eastern north atlantic over the past 25 000 years we find that glacial intermediate water flowed rapidly at depths of between 1 100 and 2 000 m in contrast deep water circulation was sluggish during the last glaciation but increased in strength shortly after the glacial maximum this would have resulted in increased heat flux to high latitudes and may have triggered sudden deglaciation deep current strengths declined again at the start of termination stage ia and during the younger dryas perhaps as a result of iceberg discharges the so called heinrich events9 10 a remarkably similar record of grain size variations has been found in the western north atlantic11 indicating that these changes in circulation are ocean wide

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

volcanic forcing of climate over the past 1500 years an improved ice core based index for climate models 1 understanding natural causes of climate change is vital to evaluate the relative impacts of human pollution and land surface modification on climate we have investigated one of the most important natural causes of climate change volcanic eruptions by using 54 ice core records from both the arctic and antarctica our recently collected suite of ice core data more than double the number of cores ever used before reduces errors inherent in reconstructions based on a single or small number of cores which enables us to obtain much higher accuracy in both detection of events and quantification of the radiative effects we extracted volcanic deposition signals from each ice core record by applying a high pass loess filter to the time series and examining peaks that exceed twice the 31 year running median absolute deviation we then studied the spatial pattern of volcanic sulfate deposition on greenland and antarctica and combined this knowledge with a new understanding of stratospheric transport of volcanic aerosols to produce a forcing data set as a function of month latitude and altitude for the past 1500 years we estimated the uncertainties associated with the choice of volcanic signal extraction criteria ice core sulfate deposition to stratospheric loading calibration factor and the season for the eruptions without a recorded month we forced an energy balance climate model with this new volcanic forcing data set together with solar and anthropogenic forcing to simulate the large scale temperature response the results agree well with instrumental observations for the past 150 years and with proxy records for the entire period through better characterization of the natural causes of climate change this new data set will lead to improved prediction of anthropogenic impacts on climate the new data set of stratospheric sulfate injections from volcanic eruptions for the past 1500 years as a function of latitude altitude and month is available for download in a format suitable for forcing general circulation models of the climate system

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

measurement of the sortable silt current speed proxy using the sedigraph 5100 and coulter multisizer iie precision and accuracy the weight percentage and mean size of the 10 63 m terrigenous silt fraction termed sortable silt of fine grained marine sediments have recently been argued to be proxies for near bottom palaeocurrent intensity this paper details the accuracy and precision of the sedigraph 5100 and the coulter multisizer iie in determining the weight percentage and mean size of the sortable silt at abundances characteristic of deep ocean sediments three sortable silt standards and a fine silt clay diluent were generated from natural deep sea sediment of the iceland basin these were used to produce silty clays with standard additions of sortable silt ranging from 1 to 20 of the total by weight accuracy was measured relative to the size of the pure spike measured by each instrument at sortable silt abundance 5 the sedigraph and the coulter multisizer estimate both weight percentage and mean grain size precisely and accurately while below 5 instrumental noise degrades their performance on the basis of the sedigraph results a series of percentage errors is defined which may be applied to sortable silt mean size and weight percentage estimates used in palaeoceanographic near bottom current reconstruction it is suggested that ideally palaeocurrent reconstructions should be based on sedigraph determinations of the 0 63 m grain size distribution yielding both mean and abundance or on coulter multisizer determinations of the sortable silt grain size mean the coulter multisizer may prove especially useful in regions of very depleted 5 sortable silt component

climatic events during the late pleistocene and holocene in the upper parana river correlation with ne argentina and south central brazil most quaternary studies in brazil are restricted to the atlantic coast and are mainly based on coastal morphology and sea level changes whereas research on inland areas is largely unexplored the study area lies along the parana river state of parana brazil at 22 43 s latitude and 53 10 w longitude where the river is as yet undammed paleoclimatological data were obtained from 10 vibro cores and 15 motor auger holes sedimentological and pollen analyses plus tl and 14c dating were used to establish the following evolutionary history of late pleistocene and holocene climates first drier episode 40 000 8000 bp first wetter episode 8000 3500 bp second drier episode 3500 1500 bp second present wet episode 1500 bp present full size table table options view in workspace download as csv climatic intervals are in agreement with prior studies made in southern brazil and in northeastern argentina

late holocene 1500 yr climatic periodicities and their implications fourier and nonlinear regression analysis of a 4000 yr paleoclimate proxy record in western canada shows strong periodicities of 1500 yr and several weaker century to millenial scale periodicities in conjunction with the 23 708 yr milankovitch periodicity these produce a model of climate fluctuation through the postglacial consistent with recognized paleoclimatic fluctuations of the past 15 000 yr in the northern mid latitudes these results suggest that postglacial climatic anomalies such as the little ice age and the younger dryas were at least in part periodic phenomena rather than the result of unique aperiodic events projecting these periodicities into the future suggests that even in the absence of anthropogenic climate forcing a natural warming trend will continue until ca a d 2400

rapid water table fluctuations within the beach face implications for swash zone sediment mobility abstract to incorporate groundwater infiltration exfiltration in the description of swash zone sediment transport it is required that the details of groundwater dynamics within the beach face be clarified field measurements of the vertical pore pressure structure within the bed identify capillarity effects as the primary mechanism driving rapid and relatively large magnitude water table fluctuations within the swash zone when the upper extent of the fully saturated capillary fringe coincides with the beach face surface wave runup produces near instantaneous increase in pore pressures across the capillary fringe corresponding to a rapid rise of the phreatic surface i e the surface where pore pressure atmospheric pressure to the sand surface therefore counter to previous conclusions in the literature the rapid rise and fall of the water table under the swash zone do not equate to regions of the beach face alternating between states that favor sediment deposition unsaturated and erosion saturated similar reports that rapid fluctuations of the water table within the beach face correspond to rapid rates of vertical flow and hence bed fluidization are also a misinterpretation field measurements and a careful consideration of saturation and pore pressure characteristics within the beach face demonstrate that rapid water table rise is associated with minute downwards swash infiltration rather than rapid upwards groundwater exfiltration the cause of the pressure fluctuations and phreatic surface oscillations is the alternating appearance and disappearance of meniscuses at the sand surface which generate pressure head fluctuations of decimeters due to the addition of millimeters of water

a mid holocene shift in arctic sea ice variability on the east greenland shelf records of iceberg rafting and palaeohydrography from two east greenland shelf cores jm96 1206 1 gc and jm96 1207 1 gc are reported benthic foraminifera stable isotopes and ird e uxes indicate a shift toward colder lower salinity polar conditions c 5 cal ka a new proxy of iceberg rafting on the east greenland shelf is the e ux of calcium carbonate tic thought to be derived from glacial erosion of cretaceous calcareous mudstones a change in the regularity and spacing of carbonate e ux peaks at c 4 7 cal ka in jm96 1207 coincides with the onset of neoglacial cooling in the renland ice core d 18 o record we propose that the carbonate e ux peaks between 4 7 and 0 4 cal ka are related to sea surface coolings associated with increased e ux of polar water and sea ice in the east greenland current these peaks are synchronous with sea surface coolings interpreted from north atlantic deep sea cores but additional peaks centred around 2 4 and 3 8 cal ka in jm96 1207 suggest that the shelf site captures higher frequency events the data indicate that severe arctic sea ice events began in the neoglacial interval and that earlier holocene cool events in deep sea records are associated with other processes such as release of meltwater from residual glacier ice and glacial lakes

south and southeast brazilian grasslands during late quaternary times a synthesis fourteen pollen records from the south s and the southeast se brazilian regions have been synthesised late glacial records from s brazilian highlands document the predominance of grassland campos where today araucaria forests occur records from se brazil show that during pre and full glacial times modern tropical semideciduous forest and cerrado savanna to dry forest were mostly replaced by grassland and some subtropical gallery forest modern montane araucaria forests and cloud forests in se brazil were mostly replaced by grassland during pre and full glacial times there is evidence that the modern tropical atlantic rainforest in s brazil was significantly reduced and replaced by cold adapted forest taxa or grassland during glacial especially during full glacial times the synthesis indicates that grasslands dominated the s and se brazilian landscape during the late pleistocene where today different forest ecosystems exist grassland extended over 750 km from s to se brazil from latitudes of about 28 27 s to at least 20 s these results indicate that climates in the region were markedly drier and 5 7 c cooler during glacial times antarctic cold fronts must have been much stronger and more frequent than today studies from s brazil show that huge areas of late pleistocene campos vegetation were still found on the s brazilian highlands during early and mid holocene times reflecting dry climatic conditions with an annual dry period of probably 3 months modern wet climatic conditions with no or only short dry periods were not established until the late holocene period when araucaria forests replaced large areas of grassland vegetation after about 3000 14c yr b p and especially after 1500 1000 14c yr b p

evolutionary interpretation of holocene landscapes in eastern brazil by optimally stimulated luminescence surface coverings and climatic pulsations abstract the research seeks to explain the use of optically stimulated luminescence osl and highlight the importance of this method for the evolutionary interpretation of tropical quaternary landscapes through systematic geochronological reconstitutions of a pedogeomorphological nature to this end studies that used osl and corroborated the geochronological evolution of tropical landscapes were evidenced emphasis was given to brazilian studies conducted in the state of sao paulo in the western plateau and peripheral depression that addressed the relationship between fluvial and planation surfaces geomorphological systems and their surface coverings in addition to holocene climatic pulsations associating them with landforms and deposition processes of surface coverings such surveys showed recent erosive depositional events responsible for imposing new dynamics on pedogeomorphological systems at the same time they were able to establish regional morphoclimatic scenarios to review former geomorphological proposals based on relative dating and relatively subjective hypotheses osl was important and has undeniably contributed to the enhancement of evolutionary theories the identification of holocene climatic pulsations that lead to hot and wet periods 5 300 6 200 4 200 4 600 2 000 2 400 800 1 200 and 0 400 years b p interrupted by hot and dry periods 7 900 10 000 6 200 6 600 4 600 5 300 2 400 4 200 1 200 2 000 400 800 years b p resulting from global cooling events the building of a geochronological database ages and the innovation of geomorphological knowledge regarding surface coverings of geomorphological surfaces in tropical climates

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

structure and origin of holocene cold events abstract the present interglacial the holocene spans the period of the last 11 700 years it has sustained the growth and development of modern society the millennial scale decreasing solar insolation in the northern hemisphere summer lead to northern hemisphere cooling a southern shift of the intertropical convergence zone itcz and a weakening of the northern hemisphere summer monsoon systems on the multidecadal to multicentury scale periods of more stable and warmer climate were interrupted by several cold relapses at least in the northern hemisphere extra tropical area based on carefully selected 10 000 year long time series of temperature and humidity precipitation as well as reconstructions of glacier advances the spatiotemporal pattern of six cold relapses during the last 10 000 years was analysed and presented in form of a holocene climate atlas hoclat see http www oeschger unibe ch research projects holocene atlas a clear cyclicity was not found and the spatiotemporal variability of temperature and humidity precipitation during the six specific cold events 8200 6300 4700 2700 1550 and 550 years bp was very high different dynamical processes such as meltwater flux into the north atlantic low solar activity explosive volcanic eruptions and fluctuations of the thermohaline circulation likely played a major role in addition internal dynamics in the north atlantic and pacific area including their complex interaction were likely involved

groundwater waves in a coastal aquifer a new governing equation including vertical effects and capillarity groundwater waves that is water table fluctuations are a natural phenomenon in coastal aquifers they represent an important part of the interaction between the ocean and aquifer and affect the mass exchange between them this paper presents a new groundwater wave equation because it includes the effects of vertical flows and capillarity the new equation is applicable to both intermediate depth aquifers and high frequency waves compared with the wave equation derived by nielsen et al 1997 the present equation provides a closer representation of groundwater waves in particular it predicts high frequency water table fluctuations as observed in the field a validation of the new equation has been carried out by comparing the analytical solutions to it with predictions from direct simulations using the numerical model sutra the effects of various physical parameters and their relative importance are also discussed

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

flow to a well of finite diameter in a homogeneous anisotropic water table aquifer a laplace transform solution is presented for the problem of flow to a partially penetrating well of finite diameter in a slightly compressible water table aquifer the solution which allows for evaluation of both pumped well and observation piezometer data accounts for effects of well bore storage and skin and allows for the noninstantaneous release of water from the unsaturated zone for instantaneous release of water from the unsaturated zone the solution approaches the line source solution derived by neuman as the diameter of the pumped well approaches zero delayed piezometer response which is significant during times of rapidly changing hydraulic head is included in the theoretical treatment and shown to be an important factor in accurate evaluation of specific storage by means of a hypothetical field example it is demonstrated that evaluations of specific storage ss using classical line source solutions may yield values of ss that are overestimated by a factor of 100 or more depending upon the location of the observation piezometers and whether effects of delayed piezometer response are included in the analysis theoretical responses obtained with the proposed model are used to suggest methods for evaluating specific storage

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

beach water table fluctuations due to wave run up capillarity effects high frequency beach water table fluctuations due to wave run up and run down have been observed in the field waddell 1976 such fluctuations affect the infiltration exfiltration process across the beach face and the interstitial oxygenation process in the beach ecosystem accurate representation of high frequency watertable fluctuations is of importance in the modeling of 1 the interaction between seawater and groundwater more important the effects on swash sediment transport and 2 the biological activities in the beach ecosystem capillarity effects provide a mechanism for high frequency water table fluctuations previous modeling approaches adopted the assumption of saturated flow only and failed to predict the propagation of high frequency fluctuations in the aquifer in this paper we develop a modified kinematic boundary condition kbc for the water table which incorporates capillarity effects the application of this kbc in a boundary element model enables the simulation of high frequency water table fluctuations due to wave run up numerical tests were carried out for a rectangular domain with small amplitude oscillations the behavior of water table responses was found to be similar to that predicted by an analytical solution based on the one dimensional boussinesq equation the model was also applied to simulate the water table response to wave run up on a sloping beach the results showed similar features of water table fluctuations observed in the field in particular these fluctuations are standing wave like with the amplitude becoming increasingly damped inland we conclude that the modified kbc presented here is a reasonable approximation of capillarity effects on beach water table fluctuations however further model validation is necessary before the model can confidently be used to simulate high frequency water table fluctuations due to wave run up

long term coordinated changes in the convective activity of the north atlantic the north atlantic is a peculiarly convective ocean the convective renewal of intermediate and deep waters in the labrador sea and greenland iceland sea both contribute significantly to the production and export of north atlantic deep water thus helping to drive the global thermohaline circulation while the formation and spreading of 18 degree water at shallow to intermediate depths off the us eastern seaboard is a major element in the circulation and hydrographic character of the west atlantic for as long as time series of adequate precision have been available to us it has been apparent that the intensity of convection at each of these sites and the hydrographic character of their products have been subject to major interannual change as shown by aagaard 1968 clarke et al 1990 and meincke et al 1992 for the greenland sea in the ows bravo record from the labrador sea eg lazier 1980 et seq and at the panulirus hydrostation s site in the northern sargasso off bermuda eg jenkins 1982 talley and raymer 1982 this paper reviews the recent history of these changes showing that the major convective centres of the greenland and labrador seas are currently at opposite convective extrema in our postwar record with vertical exchange at the former site limited to 1000 m or so but with labrador sea convection reaching deeper than previously observed to over 2300 m as a result greenland sea deep water has become progressively warmer and more saline since the early 70 s due to increased horizontal exchange with the arctic ocean through fram strait while the labrador sea water has become progressively colder and fresher over the same period through increased vertical exchange most recently convection has become deep enough there to reach into the more saline nadw which underlies it so that cooler but now saltier and denser lsw has resulted

a monte carlo approach to the joint estimation of reservoir and elastic parameters from seismic amplitudes inversion of seismic data and quantification of reservoir properties such as porosity lithology or fluid saturation are commonly executed in two consecutive steps a geophysical inversion to estimate the elastic parameters and a petrophysical inversion to estimate the reservoir properties we combine within an integrated formulation the geophysical and petrophysical components of the problem to estimate the elastic and reservoir properties jointly we solve the inverse problem following a monte carlo sampling approach which allows us to quantify the uncertainties of the reservoir estimates accounting for the combination of geophysical data uncertainties the deviations of the elastic properties from the calibrated petrophysical transform and the nonlinearity of the geophysical and petrophysical relations we implement this method for the inference of the total porosity and the acoustic impedance in a reservoir area combining petrophysical and seismic information in our formulation the porosity and impedance are related with a statistical model based on the wyllie transform calibrated to well log data we simulate the seismic data using a convolutional model and evaluate the geophysical likelihood of the joint porosity impedance models applying the monte carlo sampling method we generate a large number of realizations that jointly explain the seismic observations and honor the petrophysical information this approach allows the calculation of marginal probabilities of the model parameters including medium porosity impedance and seismic source wavelet we show a synthetic validation of the technique and apply the method to data from an eastern venezuelan hydrocarbon reservoir satisfactorily predicting the medium stratification and adequate correlation between the seismic inversion and well log estimates for total porosity and acoustic impedance

geomorphic response to rapid climatic and hydrologic change during the late pleistocene and early holocene in the humid and sub humid tropics abstract the data base concerning late quaternary environmental change in the humid tropics is dependent on records from scattered sites the intensity and duration of wet dry oscillations remain speculative and the responses of hillslopes and river systems are based on over simplified models however available evidence indicates that prolonged aridity affected all but a few favoured core areas of equatorial climate after 20 000 bp lasting 5 7 ka dry conditions at the lgm were marked by semi arid landforms and reduced steam activity large palaeofloods occurred after 13 000 be but dry conditions returned after 11 000 bp before the early holocene pluvial led to abundant sedimentation lasting nearly 2 ka after 9500 bp in africa amazonia and australasia erosion channel cutting and flood deposition occurred at the pleistocene holocene transition followed by multiple shifts from lateral to vertical accretion fill cut episodes during the early holocene while thick overbank deposits formed during the later holocene re establishment of the lowland rainforests was delayed until after 9000 bp in africa australia and brazil and several wet dry oscillations followed in the mid holocene period hillslope activity at the lgm was marked by local sediment transfers and fan formation at the termination sediment fluxes increased rapidly but mass movement probably peaked after 10 000 bp sediment delivery to stream channels was not immediate and large sediment stores remain on the landscape today many in areas of potential sensitivity of erosion

mid to late holocene climate change an overview the last 6000 years are of particular interest to the understanding of the earth system because the boundary conditions of the climate system did not change dramatically in comparison to larger glacial interglacial changes and because abundant detailed regional palaeoclimatic proxy records cover this period we use selected proxy based reconstructions of different climate variables together with state of the art time series of natural forcings orbital variations solar activity variations large tropical volcanic eruptions land cover and greenhouse gases underpinned by results from general circulation models gcms and earth system models of intermediate complexity emics to establish a comprehensive explanatory framework for climate changes from the mid holocene mh to pre industrial time the redistribution of solar energy due to orbital forcing on a millennial timescale was the cause of a progressive southward shift of the northern hemisphere nh summer position of the intertropical convergence zone itcz this was accompanied by a pronounced weakening of the monsoon systems in africa and asia and increasing dryness and desertification on both continents the associated summertime cooling of the nh combined with changing temperature gradients in the world oceans likely led to an increasing amplitude of the el nin o southern oscillation enso and possibly increasingly negative north atlantic oscillation nao indices up to the beginning of the last millennium on decadal to multi century timescales a worldwide coincidence between solar irradiance minima tropical volcanic eruptions and decadal to multi century scale cooling events was not found however reconstructions show that widespread decadal to multi century scale cooling events accompanied by advances of mountain glaciers occurred in the nh e g in scandinavia and the european alps this occurred namely during the little ice age lia between ad w1350 and 1850 when the lower summer insolation in the nh due to orbital forcing coincided with solar activity minima and several strong tropical volcanic eruptions the role of orbital forcing in the nh cooling the southward itcz shift and the desertifi cation of the sahara are supported by numerous model simulations other simulations have suggested that the fingerprint of solar activity variations should be strongest in the tropics but there is also evidence that changes in the ocean heat transport took place during the lia at high northern latitudes with possible additional implications for climates of the southern hemisphere sh

abrupt climate events 500 000 to 340 000 years ago evidence from subpolar north atlantic sediments subpolar north atlantic proxy records document millennial scale climate variations 500 000 to 340 000 years ago the cycles have an approximately constant pacing that is similar to that documented for the last glacial cycle these findings suggest that such climate variations are inherent to the late pleistocene regardless of glacial state sea surface temperature during the warm peak of marine isotope stage 11 mis 11 varied by 0 5 to 1 c less than the 4 to 4 5 c estimated during times of ice growth and the 3 c estimated for glacial maxima coherent deep ocean circulation changes were associated with glacial oscillations in sea surface temperature

sortable silt and fine sediment size composition slicing parameters for palaeocurrent speed and palaeoceanography fine sediment size 63 ixm is best measured by a sedimentation technique which records the whole size distribution repeated size measurement with intermediate steps of removal of components by dissolution allows inference of the size distribution of the removed component as well as the residue in this way the size of the biogenic and lithogenic noncarbonate fractions can be determined observations of many size distributions suggest a minimum in grain size frequency curves at 8 to 10 ixm the dynamics of sediment erosion deposition and aggregate breakup suggest that fine sediment behavior is dominantly cohesive below 10 1xm grain size and noncohesive above that size thus silt coarser than 10 ixm displays size sorting in response to hydrodynamlc processes and its properties may be used to infer current speed silt that is f mer than 10 ixm behaves in the same way as clay 2 xm useful parameters of the distribution are the 10 63 ixm mean size and the percentage 10 63 ixm in the fine fraction we cannot use size distributions to distinguish the nature of the currents therefore to infer water mass advection speeds i e the mean kinetic energy of the flow ku regions of high eddy kinetic energy ke must be avoided at the present such abyssal regions lie under the high surface k e of major current systems gulf stream kuroshio agulhas antarctic circmpolar current and brazil falldand currents in the argenthe basin this is probably a satisfactory guide for the pleistocene with regard to the carbonate subfraction of the size spectrum size modes due to both cocco iths and foramlnlferal fragments can be recognized and analyzed with the boundary between them again at about 10 lm the flux of less than 10 lm carbonate at pelagic sites above the lysocline is another candidate for a productivity indicator

hydrography and through flow in the north eastern north atlantic ocean the nansen project abstract the circulation and hydrography of the north eastern north atlantic has been studied with an emphasis on the upper layers and the deep water types which take part in the thermohaline overturning of the oceanic conveyor belt over 900 hydrographic stations were used for this study mainly from the 1987 1991 period the hydrographic properties of subpolar mode water in the upper layer which is transported towards the norwegian sea showed large regional variation the deep water mass was dominated by the cold inflow of deep water from the norwegian sea and by a cyclonic recirculation of lower deep water with a high antarctic bottom water content at intermediate levels the dominating water type was labrador sea water with only minor influence of mediterranean sea water in the permanent pycnocline traces of antarctic intermediate water were found geostrophic transports have been estimated and these agreed in order of magnitude with the local heat budget with current measurements with data from surface drifters and with the observed water mass modification a total of 23 sv of surface water entered the region of which 20 sv originated from the north atlantic current while 3 sv entered via an eastern boundary current of this total 13 sv of surface water left the area across the reykjanes ridge and 7 sv entered the norwegian sea while 3 sv was entrained by the cold overflow across the iceland scotland ridge approximately 1 4 sv of norwegian sea deep water was involved in the overflow into the iceland basin which with about 1 1 sv of entrained water and 1 1 sv recirculating lower deep water formed a deep northern boundary current in the iceland basin at intermediate depths where labrador sea water formed the dominant water type about 2 sv of entrained surface water contributed to a saline water mass which was transported westwards along the south icelandic slope