applications of organic geochemistry to paleolimnological reconstructions a summary of examples from the laurentian great lakes the organic matter content of lake sediments contains information that helps to reconstruct past environmental conditions evaluate histories of climate change and assess impacts of humans on local ecosystems the elemental isotopic and molecular compositions of organic matter buried in sediment provide evidence of the biota that have lived in a lake and its catchment area and they serve as proxies of organic matter delivery and accumulation sedimentary records from the north american great lakes provide examples of applications of organic geochemistry to paleolimnological reconstructions the records of these lakes date from retreat of the laurentide ice sheet around 12 ka include the mid holocene hypsithermal and show consequences of recent human changes low corg ntotal ratios indicate that most of the sediment organic matter in the great lakes is from algal production yet changes in biomarker molecule compositions also show that varying amounts of land plant organic matter have been delivered to the lakes elevated algal productivity that accompanies nutrient enrichments of lake waters is recorded as excursions to less negative 13c values in the organic matter of sediments that were deposited in the 1960s and 1970s increased organic carbon mass accumulation rates mirror the isotopic excursions in most parts of the great lakes accumulations of petroleum residues and pyrogenic polycyclic aromatic hydrocarbons in sediments identify fluvial and eolian delivery of organic matter components to different parts of the great lakes emerging applications of multiple and novel organic geochemical proxies to paleolimnological reconstructions are promising yet some potentially important measurements remain underutilized

organic geochemical record of increased productivity in lake naukuchiyatal kumaun himalayas india organic geochemical proxies have been studied in a 45 cm long core retrieved from lake naukuchiyatal in kumaun himalayas india increase in toc n hydrocarbons and pigments concentration from bottom to surface sediments of the core indicates increase in the lake productivity stable isotopes 13c and 15 n biomarkers tar cpi and n c15 17 19 and c n atomic between 9 and 12 suggest dominance of algal derived organic matter in these sediments decrease in organic 13c values between 27 and 31 in surface sediments indicate influence of sewage and land runoff in shifting organic 13c values whereas low between 0 23 and 2 2 15n values together with high pigment concentrations zeaxanthin and echinenone represent dominance of cyanobacteria in the lake

unexpected tunnelling volume losses in the westminster area london during construction of the running tunnels for the jubilee line extension london large variations in tunnelling volume loss were measured over about a 2 km distance between waterloo south of the thames and the area north of st james s park at the design stage a value of volume loss of 2 was adopted which was thought to be conservative in practice volume losses of greater than 3 were measured in westminster and in st james s park south of the lake north of the st james s park lake volume losses were less than 2 as expected reliable estimates of volume loss are required for the planning and approval of future tunnelling projects in london and so a detailed investigation was undertaken to establish the reasons for the observed differences two primary and interlinked causes for the large volume losses are identified first the method of tunnelling and construction control south of the lake up to 1 9 m of unsupported tunnel heading was often advanced ahead of the shield and as a result abo

characteristic patterns of variability of sea level pressure in the northern hemisphere abstract seasonal and annual mean sea level pressures for the northern hemisphere have been analyzed to determine the dominant modes of interannual and longer period variability using monthly sea level pressure analyses as revised by trenberth and paolino 1980 empirical orthogonal function eof analysis is used to reveal the modes which explain most of the variance for the period 1925 77 in winter kutzbach s 1970 eof 1 for january remains the dominant mode and a closely related pattern dominates all seasons and the annual means although there are differences in detail in each season the dominant mode is basically a high latitude zonal index type pattern with departures in pressure at high latitudes corresponding to anomalies of opposite sign in low latitudes eof 1 is linked to the north atlantic oscillation but the north south fluctuations in mass also occur in the pacific and to a lesser extent elsewhere time series associated with this pattern have highly significant spectral peaks at the

undrained stiffness anisotropy from hollow cylinder experiments on four eocene to jurassic uk stiff clays the paper describes the anisotropic undrained stiffness behaviour of four medium plasticity heavily overconsolidated uk stiff marine clays as revealed through hollow cylinder testing the experimen

sedimentary geochemical record of human induced environmental changes in the lake brunnsviken watershed sweden environmental changes in lake brunnsviken its watershed and the greater stockholm region since the middle of the nineteenth century have left interpretable geochemical imprints in the bottom sediments these humaninduced perturbations within the lake s watershed included agriculture urbanization sewage and industrial disposal and water column aeration smaller d 15 ntotal values high organic carbon mass accumulation rates low c n ratios and larger d 13 corg values identify periods of increased nutrient delivery and elevated primary productivity in the lake c s ratios that change from high to low trace the transition from an oxic hypolimnion to an anoxic one during the periods of high productivity accumulations of redox sensitive trace elements increase during the anoxic period and are further magnified during a time of industrial waste discharge into the lake a recent decrease in black carbon concentrations in sediments reflects the conversion from wood and coal to cleaner forms of energy

structure degradation and changes in the mechanical behaviour of a stiff clay due to weathering the paper discusses the results of research into the causes of weathering of stiff pleistocene clays located in the montemesola basin ta italy and on the effects of weathering on the clay s mechanical behaviour the weathered clays are yellow brown and overlie the original grey clays in the whole basin the liquidity indexes of both the yellow and the grey clays their fabric as observed by means of scanning electron microscopy as well as the yellow clay oxidation features suggest that drying has been the main weathering process in the basin this is confirmed by the results of drying wetting cycle tests carried out in the laboratory on undisturbed clay samples which show the drying wetting cycles to produce changes in the grey clay similar to those present in situ due to weathering results of oedometer stress path and triaxial tests show that weathering has caused a degradation of the clay bonding and an associated reduction in the size of the clay state boundary surface both one dimensional an

application of allochthonous organic carbon and phosphorus forms in the interpretation of past environmental conditions organic matter in sediments for instance carbon nitrogen and phosphorus can be used to reconstruct the paleoecological and pollution history of lakes and their catchment basins in this paper the contents of allochthonous organic carbon allochthonous oc and autochthonous organic carbon autochthonous oc in sediment cores taken from wuliangsuhai lake and daihai lake in northern china are quantified by using a binary model and phosphorus forms in the sediment cores from the two lakes are extracted by sequential extraction techniques the results indicate that the palaeoenvironment and paleoclimate of daihai lake and its catchment basin in the recent 250 years can be well reconstructed based on the content of allochthonous oc the climate was relatively humid and warm in the period of 1865 2005 while relatively dry and cold in the period of 1765 1865 the sedimentary information of allochthonous oc in the 22 42 cm portion of the sediment cores in daihai lake corresponds to the final cold fluctuation of the little ice age that occurred since the middle holocene the difference of phosphorus forms in the sediment cores between the two lakes indicates that phosphorus input to the lakes and the correlation between phosphorus forms and distribution and the changes of environment are influenced by the eutrophication mechanisms and environmental conditions of the two lakes

undrained triaxial strength and stress strain characteristics of a glacial till soil undrained triaxial compression tests were carried out on reconstituted and nominally undisturbed tubed samples of a lodgement till from the vale of st albans in hertfordshire england the soil is a matrix dominant chalky boulder clay of anglian age with little discernable engineering fabric electron microscope observations showed the presence of crystalline calcite in tube samples the test results were examined within the general framework of critical state soil mechanics using normalizing procedures to take account of the different states and stress histories of the samples these analyses demonstrate the practical importance of accounting for the current state and stress history in the interpretation of soil test data the present results form a self consistent pattern of behaviour differences between reconstituted and tubed samples were found only at small strain and may be attributed to cementing in tubed samples which is broken down during reconstitution and during relatively large straining in recompression and shearing

a 120 year record of changes in nitrogen and carbon cycling in lake alexandrina south australia c n δ15n and δ13c in sediments variations in 15n and 13c and c n ratios of organic matter in sediment cores in lake alexandrina south australia show that there have been modifications of n and c sources due to land use changes water diversions and irrigation since european settlement of the surrounding basin in the middle 1800s 15norg and 13corg concentrations from three short sediment cores range from 1 8 to 3 9 and 26 7 to 21 1 respectively all cores showed a 2 increase in 15n over the top 100 mm with little variation below about 150 mm 13c values increased by about 3 from the base of the sediment cores to a maximum of 21 at 150 mm depth before decreasing by 5 to 27 over the top 100 mm c n mass ratios 11 suggest that organic matter preserved in the sediment is composed primarily of aquatic plant material with terrestrial plants contributing 10 excess 210pb and 137cs dating indicate a sediment accumulation rate of 3 1 mm a 1 suggesting the enrichment in 15n began in the 1950s and the 13c maxima corresponds to approximately 1940 the increase in 15n concentration over the past 30 50 a is attributed to the increasing agricultural expansion and development in the lower catchment particularly intensive grazing of cattle for dairying the authors suggest that there has been an increased flux of 15n enriched inorganic n derived from mineralized animal waste and sewage to the river and lake over the past 30 40 a which in turn is incorporated into the aquatic plants the variation in 13c reflects a change from terrestrial dominated input of inorganic c to increasingly marine dominated sources after water diversions commenced in the late 1800s once barrages were completed at the outlet of the lake in 1939 to prevent seawater intrusion the aquatic plants in the lake reverted to assimilation of dissolved inorganic c derived from oxidation of terrestrial organic matter

major and trace element geochemistry in zeekoevlei south africa a lacustrine record of present and past processes this study reports a multi parameter geochemcial investigation in water and sediments of a shallow hyper eutrophic urban freshwater coastal lake zeekoevlei in south africa zeekoevlei receives it

organic carbon and pyrite sulphur relationships as evidences of bottom water conditions of sedimentation albert formation fine grained lacustrine sediments new brunswick canada the late devonian to early carboniferous albert formation of the moncton subbasin new brunswick was deposited in a pull apart basin in a variety of subenvironments that include alluvial fans deltas shallow to deep lacustrine environments carbonate mudflats and algal swamps this study examined the role of organic carbon organic matter reactivity mineralogy iron content and sulphate availability on pyrite formation and bottom water conditions during sedimentation of the fine grained lacustrine sediments the fine grained deep lacustrine sediments have higher total organic carbon toc values 5 61 3 33 than the fine grained shallow marginal lacustrine sediments 0 97 0 82 the deep lacustrine sediments have slightly lower pyrite sulphur 0 82 0 46 than the shallow marginal lacustrine sediments 1 86 1 98 the adequate presence of reactive organic carbon in both these environments is supported by high hydrogen indices 658 181 the presence of sufficient iron for pyritization is evidenced from the association of early diagenetic siderite and pyrite least squares linear regression parameters indicate low slopes 0 03 and low positive intercepts 0 8 on the sulphur axis suggesting pyrite formation in euxinic environment the deep lacustrine sediments have higher c s ratios 6 84 0 67 than the shallow marginal lacustrine sediments 1 49 0 14 the slope and intercept of the regression equation and c s ratios suggest the existence of a sulphate gradient from the shallow marginal areas to the deep water areas of the lake 34s isotope values of pyrite 23 06 to 16 23 cdt suggest pyrite formation from bacterial reduction of sulphates of lacustrine and marine origin

remarks on the circulation over the southern hemisphere in fgge and on its relation to the phases of the southern oscillation abstract the circulation anomalies over the whole southern hemisphere in the first garp global experiment fgge were not those that one would expect in either extreme of the southern oscillation examples of the anomalies in such extremes are given the zonally averaged pressure gradients between 50 and 65 s in fgge when compared with those of several other years turned out to be abnormally strong in winter 2 5 above the mean and moderately strong in summer 1 4 above the mean the 500 mb heights were above normal in middle latitudes and below normal at high latitudes when compared with station data from series 16 29 years long as the computations are based on operational analyses they are not final although the conclusions are unlikely to be changed by the use of the complete fgge data set

shear strength anisotropy of natural london clay the paper reports the shear strength anisotropy of the natural highly overconsolidated london clay from heathrow terminal 5 as established by comprehensive hollow cylinder apparatus hca testing

the measurement of local axial strains in triaxial tests using lvdts in this technical note the author describes an experiment in the use of linear variable differential transformer lvdt to allow accurate measurement of axial displacement over the complete range of strains of interest to geotechnical engineers

the eurasia north pacific oscillation in atmospheric mass variations independent of both iho and ao and its possible impacts on winter climate using ncep ncar reanalysis we have investigated the features of migrations of atmospheric mass am between land and ocean in eurasia north pacific domain in boreal winter after having both signals of inter hemispheric oscillation and arctic oscillation removed from the physical quantities it is found that there is a eurasia north pacific oscillation enpo in surface air pressure anomalies this enpo pattern characterizes with two oppositely signed anomalous surface pressure centers over eurasia and north pacific respectively indicating strong connections between siberian high and aleutian low during period 1979 2012 the maintenance of this enpo teleconnection is significantly associated with three factors including the anomalous am flows and zonal circulation cell over eurasia north pacific domain the rossby wave energy propagations and the thermal forcing contrasts near the surface between eurasia and north pacific during boreal winter the variations of both wintertime rainfall and temperature over eurasia may be strongly affected by enpo when the enpo index is positive negative there occurs the am accumulation depletion over eurasia with simultaneous depletion accumulation over mid latitude north pacific correspondingly this anomalous surface pressure pattern along with the related circulation anomalies at different isobaric levels possibly results in winter precipitation decreases increases over siberian plain and east china whereas increases decreases over southeastern europe xinjiang of china and the west coast of sea of okhotsk on the other hand surface air temperature decreases increases over large areas of eurasia these results are helpful for our better understanding the mechanisms behind circulation and winter climate variations over eurasia north pacific region

why are they still there a model of accumulation and decay of organic prehistoric cultural deposits the circumalpine lake side settlements are a unique source of detailed information on the past nevertheless little has been published by now on why the organic matter fumier lacustre in these settlements has been preserved and how exactly this happened it is therefore necessary to closely explore the decomposition of organic matter under different conditions we present data from the literature and a decomposition model simulating the outcome of different archaeological hypotheses and comparing the result with the actual archaeological record we conclude that different scenarios of deposition should result in clearly discernible and measurable features in the archaeological record whose presence or absence allows deducing the mode of deposition the best conditions of organic preservation are to be expected under such conditions where a large organic input happens in shallow still water seasonal flooding and a later rise in lake level can also result in good preservation but imply a greater loss through mechanical erosion and in many cases clear preservation gradients within the deposits the theoretical outcomes presented here find clear analogs in the archaeological record

lakes as paleoseismic records in a seismically active low relief area rieti basin central italy abstract small lakes in low relief areas are atypical candidates for studies on paleoseismicity but their sediments can contain seismically induced event layers seismites generated through strong ground shaking sediment transport hydrological reorganization and or changes in groundwater chemistry and flow lakes lungo and ripasottile are shallow lakes

sensitivity of sediment geochemical proxies to coring location and corer type in a large lake implications for paleolimnological reconstruction we compared a suite of geochemical proxies in sediment cores collected in 1982 1988 1991 and 2003 from sites near the depocenter of lake erie to evaluate the reliability of paleoenvironmental reconstructions derived from lacustrine sediments our proxies included the concentrations and carbon isotopic compositions of organic and inorganic carbon toc caco3 13corg and 13ccaco3 augmented by organic c to total n ratios corg ntot 15n and carbonate 18o values 18ocaco3 the three coring sites were clustered within 12 km two types of corers a box corer and a benthos gravity corer were used for the 1991 sampling campaign the variance of most proxies was accounted for not only by temporal environmental changes but also by coring locations and corer type indicating that sediment spatial heterogeneity and differences in sediment recovery due to the use of different corers also played a part in determining the geochemical compositions of these cores the toc 13corg and 13ccaco3 values showed decadal temporal patterns that were consistent between the multiple sampling campaigns in contrast the 15n corg ntot caco3 and 18ocaco3 exhibited across core differences in their temporal variations making it difficult to extract consistent environment information from different cores our findings suggest that in addition to temporal environmental changes high resolution paleolimnological reconstruction is sensitive to many factors that could include spatial sediment heterogeneity discontinuous sedimentation processes bioturbation sediment dating uncertainty and artifacts associated with analytical and coring procedures therefore multiple core sampling and analysis are important in reliably reconstructing environmental changes particularly for large heterogeneous lacustrine basins

viscoplastic constitutive approach for rate sensitive structured clays this paper extends an existing elastic viscoplastic evp constitutive model using a state dependent viscosity parameter to describe the engineering response of undisturbed structured clay the term structure refers to the effects of fabric and weak cementation bonds between clay particles the extended constitutive model is coupled with the biot consolidation theory and is formulated to describe the intrinsic or unstructured response of clay using overstress viscoplasticity an elliptical cap yield surface drucker prager failure envelope and a hardening law from critical state theory the clay structure is mathematically accounted for by assuming that the initial fluidity of structured clay at yield and failure is very low and that the fluidity increases with increasing plastic strain this process is usually referred to as destructuration the formulation is evaluated using saint jean vianney sjv clay by comparing calculated and measured behaviour during consolidated isotropically undrained triaxi

characteristics of the london clay from the terminal 5 site at heathrow airport the innovative engineering approach adopted for the new terminal 5 at heathrow airport called for an advanced investigation of the london clay strata including detailed in situ profiling and stress path laboratory testing on high quality rotary cored samples although the scope of the investigations exceeded that normally specified for conventional design questions relating to the structure and anisotropy of stiffness and strength of the clay remained that could not be answered further research was required and the deep excavations at the site provided the opportunity for a team from imperial college to take multiple block samples from three depths supplemented by two additional dedicated rotary cored boreholes intensive research was performed at imperial college on these samples as described in three companion papers by gasparre et al and nishimura et al this overview paper integrates the findings from the recent research with those from the commercial investigation and with earlier studies to e

assessment of trace elements in yercaud lake sediments southern india lake sediments are major sink for carbon and trace elements lake water and sediments need to be monitored continuously for environmental and geochemical explorations in the present study sediment characteristics source and distribution of trace metals fe mn cr cu ni co pb and zn of yercaud fresh water lake sediments south india situated at an elevation of 1515 m asl is presented twenty five surface sediments were collected covering the entire expanse of the lake in a gridded pattern detailed chemical analyses reveal the following decreasing order of elements fe cu cr mn zn ni co pb geoaccumulation index enrichment factor contamination factor and pollution load index were calculated to evaluate the ecological impacts of these trace metals in the sediments the index calculation indicates that all the trace elements were derived from natural process but there are indications of anthropogenic activities the study area was found to be highly contaminated with cu moderately contaminated with cr and co considerably contaminated with pb zn and ni and uncontaminated with mn the spatial distribution of the trace elements supports the strong association of sediment fine fraction and organic matter the statistical principal component analysis also confirms that the concentration of cr cu fe and mn was mainly derived from the natural weathering and non point agricultural sources pb and zn arise due to the confluence of sewage effluents traffic and boat activities these elements need to be further evaluated for pollution control and prohibiting further deterioration in the yercaud lake

the post yield behaviour of four eocene to jurassic uk stiff clays a detailed study is described of the post yield behaviour of four medium plasticity heavily overconsolidated uk stiff clays sub layers of the stiff to hard gault kimmeridge and oxford clays were identified sampled and tested these along with facies investigated in an earlier london clay study had broadly similar depositional histories the intention in considering a spread of similar sediments from the jurassic to the eocene was to allow any strong effects of geological age or burial depth to be identified a strongly fissured meso structure was present in three of the four clays which had a controlling influence on their effective shear strengths considering that the representative element volume is of paramount importance in measuring the strengths of such soils all four soils were brittle in shear and when sheared to sufficient displacements developed low residual shear strengths the stiff clays were investigated further through comparisons between natural and reconstituted behaviour usi

stable c and n isotope record of short term changes in water level in lakes of different morphometry lake anastazewo and lake skulskie central poland 13 ctoc d 15 n abstract we present the stable c isotope record of the changes within the past 20 yr in water level of two mor phologically different lakes in central poland the aim was to explain the relationship between lake water level and the d 13 c signature of bulk sedimentary organic matter d 13 ctoc and to assess the potential of d 13 ctoc as a paleolimnological proxy of lake level change this was done by comparison of the fossil

global fluctuations in the distribution of atmospheric mass two global data sets have been analyzed to determine the interannual variability of the zonal mean mass distribution the first is a national meteorological center nmc global data set of sea level pressures beginning in december 1977 and surface pressures beginning in april 1979 the second is an 11 year 1972 1982 hybrid set of sea level pressures from the australian southern hemisphere and u s navy northern hemisphere analyses the two sets are compared and evaluated by seeing how well they satisfy the constraint of conservation of mass anomalies in total mass due to changes in water vapor content of the atmosphere are lost in the data problems several inhomogeneities or discontinuities are found and are identified either with changes in analysis procedures in both data sets or the introduction of new orography and operational models at nmc consequently only limited periods of data are suitable for determining the dominant modes of variability nevertheless hemispheric mean anomalies in mass in one hemisphere tend to be mirrored in the other and it is clear that previously deduced fluctuations in hemispheric mean mass are mostly real predominant modes of variability of zonal means reveal systematic exchanges of mass 1 almost entirely confined within each hemisphere in isolation 2 between the extratropics of each hemisphere with little impact on the tropics as an antisymmetric mode and 3 between the tropics and extratropics in a symmetric mode the second mode played a strong role in redistributing mass during april july of 1979 during the first garp global experiment fgge and resulted in an exceptionally deep circumpolar trough over the southern hemisphere and record high pressures over the northern hemisphere the possible origin of these modes is briefly considered

the influence of structure on the behaviour of london clay an intensive investigation is described into the london clay units from heathrow terminal 5 intrinsic properties and composition were established and relating the behaviour of intact and reconsti

implications of weathering on the engineering properties of the fuller s earth formation the fuller s earth formation is an overcon solidated jointed randomly assured calcareous mudstone with some thin to medium jointed argillaceous limestone bands south of bath the formation contains the commercial montmorillonite rich fuller s earth bed this paper reviews the effect of the proportion of calcite present on the moisture content atterberg limits particle size and residual shear strength attention is drawn to the importance of appreciating that the calcite percentage and the clay mineralogy are both likely to change with time as a result of weathering processes this will affect the stability of natural slopes and man made cuttings excavations etc la formation de terre a foulon est un limon compact calcaire surconsolide jointe et fissure au hasard qui contient des bandes de chaux argillacee jointees d epaisseur faible ou moderee au sud de bath la formation comprend la couche de terre a foulon commerciale qui est riche en montmorillonite l article examine l influence de la prop

the undrained shear strength anisotropy of four jurassic to eocene stiff clays the shear strength of heavily overconsolidated stiff to hard plastic clays is crucial to their stability and also influential on the ground movements they develop in many geotechnical engineering applications this paper considers the shear strength anisotropy of the london gault kimmeridge and oxford clays through advanced hollow cylinder experiments on multiple high quality samples taken at similar depths from inland sites where the geotechnical profiles have been established by comprehensive laboratory and in situ testing suites of undrained tests are reported which loaded specimens from their in situ stress states to reach ultimate failure at pre defined final major principal stress axis orientations defined in the vertical plane while also controlling or monitoring the intermediate principal stress ratio b both stress path and simple shear tests were undertaken with the hollow cylinder apparatus which offers key advantages over conventional simple shear equipment the interpretation reveals

evaluation of the viscous behaviour of clay using generalised overstress viscoplastic theory in this paper generalised elastic viscoplastic evp theory combined with a power law is used to derive simplified equations relating undrained shear strength and preconsolidation pressure to strain rate an additional equation is derived relating the strain rate parameter in evp theory to the secondary compression index the derived equations are used to evaluate the rate sensitive and drained creep response of 20 clays reported in the literature the evaluation shows strong evidence that the rate sensitivity and time dependency of clay in compression can be described simultaneously using the generalised evp theory and power law in addition the constitutive parameter governing rate sensitivity in evp theory appears to be unique for constant rate of strain tests such as undrained triaxial compression and drained oedometer compression as well as stress controlled tests such as drained oedometer creep to conclude an approach to select the viscous parameters for clay is provided

analysis of tunnel excavation in london clay incorporating soil structure recent studies on london clay have identified a number of different units in the geological profile and have highlighted the role of soil structure in mechanical behaviour in fact structure is the dominant factor determining the differences in the mechanical response of different units in the paper numerical analyses simulating the undrained excavation of a tunnel in st james s park are presented london clay behaviour is characterised by a kinematic hardening structured soil model incorporating structure and stiffness degradation the parameters and initial conditions are based on a careful calibration that takes into account the presence of different units within the london clay formation and the different degrees of soil structure the analyses performed result in a very satisfactory reproduction of the magnitude and patterns of short term surface and subsurface displacements as well as pore pressures the paper concludes with a discussion of the results in the context of other analyses performed

influence of structure on the time dependent behaviour of a stiff sedimentary clay in this paper results from laboratory tests on london clay and artificially cemented kaolin are presented and used to develop a preliminary framework for the time dependent behaviour of soils applicable to stiff clays and other soils in the same way that the natural structure of clays has been shown to influence their monotonic behaviour it is shown that it can also alter their response to changes in strain rate the relative influence of the two main components of post sedimentation structure over consolidation and diagenesis on the time dependent behaviour of london clay was investigated in triaxial compression tests the study was carried out in two steps comparing first the behaviours of normally and overconsolidated reconstituted samples of london clay subjected to stepwise changes in strain rate and then the behaviours of overconsolidated reconstituted and undisturbed london clay samples the test results show that overconsolidation does not seem to affect the response of reconstituted london c

tectonic shear zones in the london clay formation subhorizontal shear zones observed in the london clay formation are described the physical properties of the shear zones are examined and it is demonstrated both that they are of tectonic origin the result of bedding plane slip during minor folding and that they were probably formed before there had been any significant erosion of the london clay or later overlying formations the occurrence of the shear zones is reviewed and it is shown that similar features have been recorded in other areas to the west of london and it seems likely that they will be encountered elsewhere in the london basin wherever minor folding occurs the shape of the london clay formation reading formation interface appears to give an indication of the degree of folding and hence of the possible occurrence of shear zones the displacements of the shear zones examined are believed to be small perhaps only a few centimetres and consequently the strength along the shear zones is probably slightly above the true large displace

a biostratigraphy for the london clay in london biostratigraphy enables specific layers of strata to be given a unique stratigraphic address that can be used to identify the horizons in which in situ tests are conducted and from which samples for testing are collected this is particularly valuable when working in fine grained deposits where stratigraphic position is not easily recognised by lithology alone and permits any data bank of geotechnical values and performance to be used without fear of confusing one stratigraphic layer with another construction in the london clay formation and its supporting research has necessitated an accurate and speedy method for identifying with a precision of centimetres the stratigraphic layer from which geotechnical data have been obtained the principles that enable biostratigraphy to be used for this purpose are explained and illustrated with reference to the london clay formation in london this approach can be used in most sedimentary strata an example of biostratigraphic data used in london is presented

shaft resistance and setup factors for piles jacked in clay abstractinstallation of a displacement pile often involves complex loading modes that cause substantial changes in the state of the soil surrounding the pile when a displacement pile is installed in saturated clay significant excess pore pressure develops as the excess pore pressure dissipates over time the effective stresses in the soil surrounding the pile and the pile capacity increase this paper investigates jacking of piles into clay using finite element analysis a two surface plasticity based constitutive model for clays was implemented in the finite element code solid nonlinear analysis code based on the numerical results equations are developed for quantifying the effects of undrained and residual shear strength on the shaft resistance of jacked piles in clay the gain in shaft resistance over time is assessed and setup factors are proposed that can be used to estimate the gain in shaft resistance as a function of time after installation of a jacked pile in clay good agreement was obtaine

the measurement of soil stiffness in the triaxial apparatus this paper describes a simple technique for accurately measuring the mean local axial strains of triaxial samples over a central gauge length the technique makes use of an axial displacement gauge which is a development of one devised by burland symes 1982 which makes use of electrolytic levels the device can resolve to less than 1 m over a range of 15 mm is simple to mount on the specimen and is not damaged when the sample is taken to failure the results of undrained triaxial tests are presented for a wide spectrum of soil types ranging from sands through intact reconstituted and remoulded low plasticity till undisturbed london clay to intact unweathered chalk the test results show that conventional external measurements of displacement contain errors which are frequently so large that their use in the determination of soil stiffness at working levels of stress is invalid the errors mainly result from tilting of the sample bedding at the end platens and the effects of compliance in the app

bayesian identification of soil strata in london clay identification of soil strata in the london clay formation lcf is of practical significance as it allows geotechnical property data within the same soil strata to be compared or used effectively the soil strata in lcf are generally determined based on their lithological characters and fossil contents with which geotechnical engineers are less familiar to assist geotechnical engineers in identifying the soil strata in lcf this paper aims to develop bayesian approaches to identification of soil strata in lcf using water content data equations are derived for the proposed bayesian approaches and the approaches are illustrated using a water content profile at st james s park london the proposed bayesian approaches are shown to correctly identify the soil strata in lcf in addition a sensitivity study is performed to explore the effect of data quantity i e both the measurement interval and number of measurements at the same depth in a water content profile and provide guidance on the water conten

practical determination of mechanical design parameters of intact rock considering scale effect as a rule the change in mechanical properties of rock by specimen size is regarded as scale effect a rock mass basically consists of two components intact rock and discontinuities each of which has different scale effects in order to numerically analyze the behavior of discontinuous rock masses sufficient mechanical properties must be determined not only for discontinuities but also for intact rock taking into consideration the different scale effects this paper reviews the scale effect on strength and deformation characteristics of intact rock and also discusses the possibility of using standard specimens to estimate strength and deformation characteristics of actual scale rock finally we propose an adequate method for the practical determination of mechanical design parameters based on the above discussions

the mechanics of cemented carbonate sands the behaviour of artificially cemented carbonate sand was investigated in triaxial tests at confining pressures of up to 9 mpa the results show that an important effect of cementing is a reduction in specific volume resulting from the increase in fines content this influences both the stress strain behaviour and the peak strength at strains beyond those required to fracture the cement bonding comparisons between the behaviour of cemented and uncemented soils should therefore be carried out on samples with the same gradings for cemented samples it is possible to identify a yield curve outside the state boundary surface of the uncemented soil a framework for the behaviour has been defined which depends on the relative magnitudes of the confining pressure and cement bond strength the behaviour of a natural cal carenite agreed well with this framework which is also likely to be applicable to other cemented soils le comportement d un sable carbonate artificiellement cimente a ete etudie a l aide d essa

degree of pyritization of iron as a paleoenvironmental indicator of bottom water oxygenation abstract a new method is presented for recognizing the degree of bottom water oxygenation in organic carbon bearing rock the method uses the parameter degree of pyritization dop which is the ratio of pyritic fe to pyritic fe acid soluble fe sediments with ages ranging from devonian to cretaceous have been classified on paleoecological and sedimentological criteria as having been deposited in aerobic conditions deposited in fully oxygenated bottom waters restricted marine conditions deposited in waters with low oxygen concentrations or inhospitable bottom conditions where little or no oxygen is present and h2s may be continually or intermittently present aerobic dop

spatial variability of sea level pressure and 500 mb height anomalies over the southern hemisphere abstract the spatial variability of mean sea level pressure slp and 500 mb height anomalies over the southern hemisphere during summer djf and winter jja is determined using eigenvector analysis based on daily synoptic maps from 1972 to 1979 the patterns of spatial distribution of pressure and height anomalies are further verified and examined by means of station data and the eigenvectors are compared between the seasons and to those found for the northern hemisphere the first eigenvector shows that midlatitude anomalies of slp and 500 mb height are of an opposite sign to those found over and around antarctica the pattern is highly barotropic and suggests strengthening and weakening of the zonal wind in alternating latitude belts the 500 mb height differences are calculated for five midlatitude to antarctic station pairs using data from the late 1950 s onward these latitudinal height differences are also used to describe the association between the hemispheric westerlies and the southern oscil

the stiffness of natural london clay an investigation of natural london clay is reported involving advanced triaxial hollow cylinder apparatus hca and dynamic testing techniques significant anisotropy was revealed at all scales of deformation and the framework of cross anisotropic elasticity was found to apply broadly to the initial elastic behaviour the stiffness parameters obtained by independent techniques generally exhibited good agreement with the greatest deviation being seen in the poisson s ratios which fell far from the values usually assumed in conventional foundation analysis probing tests established the limits to the elastic domain over a range of depths showing that these scaled in proportion to the mean effective stress level as did those of a second kinematic surface that surrounded the elastic domain once engaged this second surface signified a new pattern of strain increment directions faster elastic plastic stiffness decay with strain and also a greater dependence of behaviour on recent stress history howev

complex trajectories of aquatic and terrestrial ecosystem shifts caused by multiple human induced environmental stresses large shifts in the isotopic compositions of organic matter om in lake sediments over the last few hundred years are commonly interpreted as representing changes in photosynthetic productivity corresponding to eutrophication or in the input of terrestrial om due to human disturbances based on multiple proxy data c n ratio d 13 c and d 15 n of om d 13 c of calcite lithology and fossil pollen from a 700 year sediment core at white lake new jersey usa we propose a new explanation that relates these large shifts in om d 13 c and d 15 n to human induced changes in aquatic om producers combined records of geochronology fossil pollen and lithology from white lake reveal that the upland forest was cleared by european settlers for farmland beginning around 1745 a d and has gradually reforested since 1930 after the abandonment of the farmlands for the pre agricultural period om had relatively constant but extremely low d 13 cvpdb 35 8 to 34 5 and d 15 nair 3 5 to 2 5 and high atomic c n ratios 13 7 to 16 7 indicating a stable anoxic lake environment with prominent microbial producers following the human disturbance since 1745 high om mass accumulation rates and abundances of the green alga pediastrum indicate an increase in aquatic photosynthetic productivity due to enhanced nutrient input from disturbed uplands however carbonate d 13 c remains constant or even decreases during this period implying that increasing productivity did not elevate the d 13 c of dissolved inorganic carbon and thus cannot explain the observed large increase in om d 13 c 7 4 and d 15 n 5 8 over this period instead d 13 c d 15 n and c n ratios of om and differences in d 13 c between calcite and om suggest that the large increase in om d 13 c and d 15 n can be attributed to a human induced ecological shift in the predominant organic source from anaerobic bacteria to autotrophic phytoplankton during the post agricultural period mass accumulation rates of om carbonate and silicate and the d 13 c of om and calcite all decreased significantly corresponding to stabilization of the uplands however over the last 70 years an intensifying aquatic stress from the deposition of 15 n enriched industrial pollutants has resulted in a steady increase of 1 9 in d 15 n proxy records for lake d 13 c and d 15 n

holocene paleohydrology of the etzatlan magdalena basin in western central mexico and evaluation of main atmospheric forcings abstract sediments deposited in the etzatlan magdalena basin were analyzed to reconstruct the paleohydrological variations and generate a new holocene paleoclimate record for the less studied western part of central mexico concentration of ti abundance of caco 3 zr ti ratio and toc ti ratio were compared with their average values to infer variations in runoff lake water salinity transportation of clastic minerals by aeolian activity and total organic productivity in general conditions were wetter during 9 6 5 7 ka early middle holocene and 2 2 0 7 ka late holocene compared to 5 7 2 2 ka middle late holocene transportation of above average amounts of zr bearing clastic minerals from an arid watershed and deposition of the highest abundance of caco 3 at 3 5 2 8 ka occurred within the drier interval of middle late holocene except for the interval of 2 2 0 7 ka the el nino southern oscillation enso and inter tropical convergence zone itcz controlled summer precipitation forced the hydrological variations the etzatlan magdalena basin remained wet and some sites in central mexico were dry over a large part of 2 2 0 7 ka the activity of tropical cyclones and frontal systems may have increased in the northeastern pacific during this interval of enhanced enso either of them or the combination of both possibly contributed more autumn and winter precipitation to western central mexico

global climate variations connected with sea surface temperature anomalies in the eastern equatorial pacific ocean for the 1958 73 period abstract the sea surface temperature anomalies in the eastern equatorial pacific ocean are shown to demarcate a key region new 130 w for observed variations in the global general circulation various techniques are used to describe global conditions during warm and cold sea surface conditions in the key region based on a global 15 year set of surface and upper air analyses earlier work is confirmed that during warm episodes 1 the westerly jets in both hemispheres are strengthened and 2 some of the semi permanent circulation features such as the intertropical convergence zone the subtropical high over the western and central pacific and the aleutian low increase in strength and vice versa for cold episodes the time series of monthly mean atmospheric temperature averaged over the entire man of the northern hemisphere is found to be highly correlated with the sea surface temperature anomalies in the key region the highest correlation of r 0 65 is found when the atmosphere lags the ocean by 6 m

the shear stiffness characteristics of four eocene to jurassic uk stiff clays a large proportion of the southern uk is underlain by stiff clays improving their geotechnical characterisation is important for many current and future infrastructure projects this paper presents an integrated study of the complex stiffness behaviour of four key medium plasticity highly overconsolidated strata the gault kimmeridge oxford and london clays the latter were deposited between the jurassic and the eocene under broadly similar marine conditions coordinated programmes of advanced static and dynamic laboratory measurements have been undertaken on high quality samples concentrating on samples taken from similar depths at inland sites and including triaxial and hollow cylinder stress path experiments employing high resolution local strain multi axial bender element and resonant column techniques a new approach was employed to interpret the hollow cylinder experiments and the laboratory measurements are examined in combination with independent field shear wave data the clays stiffness c

experimental investigation of the evolution of elastic stiffness anisotropy in a clayey soil the paper presents the main results of a research study into the very small strain shear stiffness of a clayey soil as measured in vertical and horizontal directions ghv and ghh respectively by means of t shaped horizontal bender elements fitted in a stress controlled triaxial system the testing programme was designed to investigate the evolution of the anisotropy ratio ghh ghv along isotropic 0 and anisotropic 0 virgin radial paths in particular a reconstituted clay has been chosen as tested material in order to unequivocally relate the observed evolution of its stiffness anisotropy to the specific stress strain histories imposed in laboratory the results show that the small strain stiffness anisotropy smoothly adapts itself to the imposed strain history achieving different constant values ranging from 1 to 1 2 for ranging from 0 to 0 8 the experiments show that the complete modification of the directional elastic properties of the soil requires the virgin radial compression path

geochemical records of palaeoenvironmental controls on peat forming processes in the mfabeni peatland kwazulu natal south africa since the late pleistocene the mfabeni peatland is the only known sub tropical coastal fen that transcends the last glacial maximum lgm this ca 10 m thick peat sequence provides a continuous sedimentation record spanning from the late pleistocene to present basal age c 47 kcal yr bp we investigated the paleaeoenvironmental controls on peat formation and organic matter source input at the mfabeni fen by 1 exploring geochemical records mass accumulation rate total organic carbon carbon accumulation rate delta c 13 delta n 15 and c n ratio to delineate primary production organic matter source input preservation and diagenetic processes and 2 employ these geochemical signatures to reconstruct the palaeoenvironmental conditions and prevailing climate that drove carbon accumulation in the peatland we established that the mfabeni peat sediments have undergone minimal diagenetic alteration the peat sequence was divided into 5 linear sedimentation rate lsr stages indicating distinct changes in climate and hydrological conditions isr stage 1 c 47 to c 32 2 kcal yr bp predominantly cool and wet climate with c4 plant assemblages interrupted by two short warming events lsr stage 2 c 32 2 to c 27 6 kcal yr bp dry and windy climate followed by a brief warm and wet period with increased c4 sedge swamp vegetation lsr stage 3 c 27 6 to c 20 3 kcal yr bp initial cool and wet period with prevailing c4 sedge plant assemblage until c 23 kcal yr bp then an abrupt change to dry and cool glacial conditions and steady increases in c3 grasses lsr stage 4 c 203 to c 10 4 kcal yr bp continuation of cool and dry conditions and strong 0 grassland signature until c 15 kcal yr bp after which precipitation increases lsr stage 5 c 10 4 kcal yr bp to present characterised by extreme fluctuations between pervasive wet and warm to cool interglacial conditions with intermittent abrupt millennial scale cooling drying events and oscillations between c3 and c4 plant assemblages in this study we reconstructed a high resolution record of local hydrology bulk plant assemblage and inferred climate since the late pleistocene which suggest an anti phase link between southern african and the northern hemisphere most notably during heinrich 5 to 2 and younger dryas events

intraseasonal variations in the southern hemisphere circulation abstract intraseasonal variations in the southern hemisphere atmospheric circulation have been examined through the application of a 10 50 day bandpass filter to daily ecmwf analyses for 1980 88 variations on this time scale contribute more than 40 of the daily variance in 500 hpa geopotential over much of the middle and high latitudes of the southern hemisphere eof analysis of the unnormalized variance for all seasons shows that 49 of this variance can be explained by zonal wave trains centered on the south pacific and southern atlantic indian oceans a high latitude mode of global extent and a wavenumber 3 pattern at midlatitudes these modes are essentially equivalent barotropic but slope westward with height so that the patterns at 100 hpa typically lag those at 1000 hpa by around 1o longitude there appears to be little interaction with the low latitude circulation all of the leading modes propagate eastward but the most consistent movement is shown by the south pacific wave train represented

the effects of weathering on the physical and mechanical properties of a granitic saprolite less research has been carried out on the changes induced by weathering to the mechanical properties of reconstituted and intact soils that originate from chemical decomposition of rocks saprolite

a multi proxy reconstruction of the late holocene climate evolution in lake bolgoda sri lanka abstract palaeoclimate investigations in sri lanka have been rarely attempted despite being located directly in the path of the inter tropical convergence zone in this study a 4 1 m undisturbed sediment core was retrieved from the bolgoda lake situated in the western coast of sri lanka and influenced by the strong southwest monsoons mollusc shells in the core were dated and the age depth model indicated a depositional history extending from 2941 cal yr bp to the present grain size major and trace elements total organic c and n content and stable c and n isotopes were analysed in freeze dried sediments to reconstruct the palaeoclimate changes the multi proxy records in the core revealed four distinct zones that show distinct variations in physical and chemical conditions in the lake associated with climate change zone 1 2941 to 2390 cal yr bp 385 252 cm indicated the climate to be warm and humid with intense precipitation the resulting high lake level helped in organic matter preservation in bottom sediments zone 2 2390 to 1782 cal yr bp 252 140 cm indicated an unstable dry period associated with weak precipitation consequently low lake level and intense degradation of organic matter occurred in this zone zone 3 1782 to 1299 cal yr bp 140 60 cm indicated a resurgence of intense monsoon along with warm and humid conditions zone 4 1299 cal yr bp to present 60 0 cm indicated dry conditions with less intense monsoon low lake level and extensive degradation of organic matter vascular plants were the predominant organic matter source into the lake during the late holocene in contrast algal input was significant between 2390 cal yr bp and 2153 cal yr bp the palaeoclimate evidences in this study showed an overall weakening trend of sw monsoon during the late holocene and this was consistent with changes happening in other locations as in southern and western india

carbon sulfur iron relationships and δ13c of organic matter for late albian sedimentary rocks from the north atlantic ocean paleoceanographic implications abstract cores from six deep sea drilling project sites 367 369 137 386 387 and 603 of the late albian north atlantic ocean were investigated for organic carbon content 13c values of the kerogens maceral composition of the organic matter c s ratios fe toc s relationships and framboidal pyrite size distribution in order to evaluate processes that led to the accumulation of organic matter rich black shale deposits the results show a clear separation of the albian north atlantic into an anoxic eastern part and a mostly oxic western part the eastern north atlantic is dominated by organic matter rich deposits sulfate reduction occurred in an oxygen free water column and resulted in characteristic c s ratios fe toc s relationships and framboidal pyrite size distribution patterns elevated productivity anoxia and high sedimentation rates supported the formation of black shale deposits for most of the western and central parts organic matter sedimentation took place through an oxygenated water column the accumulated organic matter is dominantly of terrigenous origin the deposition of marine derived organic matter was most likely controlled by productivity paleobathymetry and low sedimentation rates

black carbon in soils and sediments analysis distribution implications and current challenges this review highlights the ubiquity of black carbon bc produced by incomplete combustion of plant material and fossil fuels in peats soils and lacustrine and marine sediments we examine various definitions and analytical approaches and seek to provide a common language bc represents a continuum from partly charred material to graphite and soot particles with no general agreement on clear cut boundaries formation of bc can occur in two fundamentally different ways volatiles recondense to highly graphitized soot bc whereas the solid residues form char bc both forms of bc are relatively inert and are distributed globally by water and wind via fluvial and atmospheric transport we summarize chronologically the ubiquity of bc in soils and sediments since devonian times differentiating between bc from vegetation fires and from fossil fuel combustion bc has important implications for various biological geochemical and environmental processes as examples bc may represent a significant sink in the global carbon cycle affect the earth s radiative heat balance be a useful tracer for earth s fire history build up a significant fraction of carbon buried in soils and sediments and carry organic pollutants on land bc seems to be abundant in dark colored soils affected by frequent vegetation burning and fossil fuel combustion thus probably contributing to the highly stable aromatic components of soil organic matter we discuss challenges for future research despite the great importance of bc only limited progress has been made in calibrating analytical techniques progress in the quantification of bc is likely to come from systematic intercomparison using bcs from different sources and in different natural matrices bc identification could benefit from isotopic and spectroscopic techniques applied at the bulk and molecular levels the key to estimating bc stocks in soils and sediments is an understanding of the processes involved in bc degradation on a molecular level a promising approach would be the combination of short term laboratory experiments and long term field trials

the general and congruent effects of structure in natural soils and weak rocks the engineering properties of naturally occurring sedimentary and residual deposits which are usually treated in geotechnical engineering as soils are reviewed and it is shown that usually they have characteristics due to bonded structure which are similar to those of porous weak rock while this structure can arise from many causes its effects follow a simple general pattern that involves stiff behaviour followed by yield this yield can be described in a similar way to that occurring due to overconsolidation although it is a separate phenomenon the effects of structure are as important in determining engineering behaviour as are the effects of initial porosity and stress history which are the basic concepts of soil mechanics as it can be described in a general way it is concluded that structure and its effects should be treated as a further basic concept of equal importance l article passe en revue les proprietes des depots sedimentaires et residuels naturels qui sont nor malement traites comm

holocene history of the baltic sea as recorded in a sediment core from the gotland deep a 4 m long sediment core from the gotland deep baltic sea was investigated by means of biostratigraphical and chemical parameters and c 14 datings this multidisciplinary approach allows us to ev

the reddest atmospheric modes and the forcings of the spectra of these modes abstract the reddest atmospheric modes are studied using a 500 yr integration performed with the coupled echam1 lsg general circulation model by fitting a first order autoregressive process to the considered time series a simple measure of the spectral shape is obtained that allows an objective intercomparison of the spectra and the time series two modes the tropical and the southern hemisphere modes are identified as the reddest modes of the model atmosphere both are strongly anisotropic the southern hemisphere mode characterized by a dipole of zonal wind anomalies at southern hemispheric mid and high latitudes is related to a mass redistribution and a well defined meridional circulation whereas no significant anomalies of surface pressure and meridional velocity are found for the tropical mode which is characterized by a maximum of zonal wind anomalies in the upper tropical troposphere on timescales longer than a month the two modes make relative to other motions the largest contribution

regional contributions to the atmospheric excitation of rapid polar motions daily fields of surface pressure produced by the national meteorological center during 1981 1985 are used to identify the sectors of the globe over which changes in atmospheric mass contribute most importantly to the excitation of intraseasonal variations in the earth s polar axis maxima in the excitation function are found over the extratropical south pacific north pacific and north atlantic consistent with previous studies that have identified maxima in surface pressure variations in these regions because these centers are located over the ocean the manner in which the ocean responds to changes in the atmospheric mass above it becomes of central importance in fully understanding the causes of rapid polar motions

numerical assessment of the effects of end restraints and a pre existing fissure on the interpretation of triaxial tests on stiff clays conventional laboratory triaxial tests apply axisymmetric boundary conditions to a cylindrical sample which has an axisymmetric geometry for a homogeneous sample this implies that the deformed sha

the use of kinematic hardening models for predicting tunnelling induced ground movements in london clay the use of a kinematic hardening soil model for predicting short and long term ground movements due to tunnelling in london clay is investigated the model is calibrated against oedometer and triaxial tests on intact samples from different units of the london clay the calibrated model is then used in finite element analysis to simulate the field response at st james s park during excavation of the jubilee line extension tunnels the finite element predictions compare well with the available field monitoring data the importance of using consistent initial conditions for this complex boundary value problem in conjunction with the model parameters selected is highlighted the stiffness response of different regions of the finite element mesh indicates that the rate at which the stiffness degrades and the stiffness response further away from the tunnel boundary affect the short term predictions significantly the long term predictions confirm that the compression characteristics of the soil control the mag

production sedimentation and isotopic composition of organic matter in lake ontario organic matter and its carbon and nitrogen isotopic composition were measured in sequential sediment trap and core samples from the rochester basin of lake ontario to evaluate their usefulness in reconstructing historic changes in lake productivity the greatest flux of organic matter from the epilimnion occurred during late summer and coincided with whiting events indicating that calcite precipitation is an effective mechanism for sedimenting organic matter carbon isotopes of organic matter were low prior to the onset of stratification increased to maximum values in late summer and then decreased following fall overturn this pattern is controlled mainly by the timing of stratification and primary productivity which preferentially removes 12co2 from the epilimnion the physiological effect of decreased carbon isotopic fractionation with decreasing supplies of co2 aq may have also contributed to increased 13corgc nitrogen isotopes showed a seasonal pattern opposite to that of carbon whereby 15n values were low during the summer stratified period and high for the remainder of the year seasonal variability in 15norgn probably reflects changes in the source of sedimented organic particles which is dominated by isotopically depleted phytodetritus during the stratified period and isotopically enriched organic matter from heterotrophic or detrital sources during the mixed period a comparison of organic carbon accumulation rates and 13corgc between sediment cores collected in 1987 and 1993 1994 confirms earlier predictions that diagenetic processes reduce the mass accumulation of organic carbon in the zone of oxic pore waters but will not change the 13corgc values all cores analyzed for 13corgc display the reproducible pattern of a progressive increase in the 19oos peaking in the early to mid 1970s and then decreasing to the present this pattern matches the historical trends of phosphorus loading to the basin suggesting that 13c of organic carbon is a reliable proxy for paleoproductivity and responds to spring phosphorus supplies in the water column the 15n of sedimentary organic matter increased linearly from 1840 to 1960 at a rate of 0 3ppt per decade and remained relatively constant thereafter except for an increase in the upper few centimeters of sediment the increase in 15norgn reflects a combination of factors including early forest clearance by europeans increased sewering by municipalities after 1940 and increased nitrate utilization as productivity increased in the lower great lakes increased rates of denitrification in the central basin of upstream lake erie from the 1930s to the early 1970s may have also contributed to the rise in 15norgn values

stable isotope δ13c and δ15n based interpretation of organic matter source and paleoenvironmental conditions in al azraq basin jordan abstract this study examines the stable isotopes of carbon and nitrogen from cored lacustrine sediments of the al azraq an arid lake basin on the jordan plateau lacustrine sediments contain valuable records of paleoenvironmental conditions recording local and regional responses to environmental change previous paleo reconstructions on the jordan plateau are based on archaeology pollen mineralogy and stratigraphy the application of organic geochemistry analyses to these lake sediments identifies multiple sources of organic matter biological production and contributes to understanding the paleoenvironments of the al azraq basin during the mid pleistocene period organic carbon concentration corg provides an overview of the organic matter distribution carbon isotopic composition 13corg and nitrogen isotopic composition 15n are indicators of organic matter sources and paleoproductivity magnetic susceptibility mgsus measured the concentration of ferromagnetic minerals and indicated aeolian inputs organic geochemistry differentiated five paleoenvironmental zones with specific sources of organic matter both aquatic and terrestrial it identified a long period of climate wetter than the present punctuated by a short intense period of aridity diagenesis plays an important role in the decomposition of organic matter and studies indicate this degradation can alter the isotopic signals of organic matter analyses of the isotopic signals and statistical analyses demonstrate diagenesis is not a factor in the al azraq sediments in all but zone 4 of the paleoenvironmental zones this zone is defined by less negative carbon isotopic composition and the presence of thick primary gypsum layers in addition to the influx of high peaks of aeolian sediment as reflected in the magnetic susceptibility data stable isotope geochemistry provides detailed information on the paleoenvironments of lake sediments and is applicable to typically challenging arid basin sediments

210pb derived chronology and the fluxes of 210pb and 137cs isotopes into continental shelf sediments east chukchi sea alaskan arctic abstract eleven sediment cores and eight sediment trap samples from the continental shelf of the eastern chukchi sea were analyzed for 210pb cs and 2226ra in selected samples the organic carbon content and stable carbon isotope ratios were also determined the excess 210pb 210pbxs concentrations in the 1 cm core tops are generally lower than those of surficial sediments of subarctic shelves and arctic lakes the sediment inventory derived depositional fluxes of 210ph vary between 0 09 and 0 38 dpm cm 2y 1 with a mean of 0 18 dpm cm 2 y 1 the apparent mass sediment accumulation rates which vary between 31 and 324 mg cm 2 y 1 with a mean value of 133 mg cm 2 y 1 are about an order of magnitude lower than the yearly particle flux obtained from the sediment trap experiments this difference between the relatively long term and short term yearly accumulation rates is likely due to the occasional resuspension of fine particles in the continental shelf areas and their advective transport to sites other than their initial deposition the sediment inventory of 137cs varied between 0 64 and 4 09 dpm cm 2 with a mean of 2 18 dpm cm 2 a comparison of this inventory with the expected fallout inventory of 137cs suggests that there had been no detectable input of 137cs to the study area from the former ussr nuclear dump sites

the selborne cutting stability experiment the paper describes a field experiment in which a 9 m deep cut slope in gault clay was brought to failure by pore pressure recharge the geology of the site is described and the procedures used to

the southern oscillation part i global associations with pressure and temperature in northern winter abstract we describe the global correlations between a measure of the southern oscillation and sea level pressure and surface air temperature in the northern winter the stability of these correlations were tested on the northern hemisphere for an 80 year period and it turned out that most stable correlation coefficients were found over india the north pacific ocean the rocky mountains and the central and western north atlantic ocean on the southern hemisphere most records are too short for a similar test but the following may tentatively be said about the southern oscillation in middle and high southern latitudes when pressure is low in lower latitudes over the south pacific ocean it tends to be high at higher latitudes of that ocean high over east antarctica and low in the belt of westerlies in the indian and south atlantic oceans in the zonal average on both hemispheres the pressure gradients in this extreme of the oscillation tend to be steeper at lower latitudes and flatter at higher latitud

a simple piezometer probe for the routine measurement of pore pressure in triaxial tests on saturated soils a technique has been evolved for installing a piezometer probe on samples down to a diameter of 38 mm the probe is based on a miniature silicon diaphragm pressure transducer mounted at mid height to cause minimum interference between the sample and probe and to provide a rapid response for the piezometer soil system considerable savings can be made in testing times by using the probe at mid height and by using effective lubricated end platens measurements can also be made in cyclic loading tests on clays and are viable in quick undrained tests even at shearing rates used in commercial laboratories examples are given of measurements made in undrained compression extension triaxial tests in cromer fill and medium dense ham river sand the probe provides a more accurate method of measuring pore pressures in unconsolidated undrained triaxial tests and can be effectively used to maintain an acceptably low gradient of pore pressure in the sample when following a drained stress path trrl

large scale redistributions of atmospheric mass abstract seven years of daily global surface pressure ps analyses derived from european centre for medium range forecasts ecmwf data are examined to describe more fully interhemispheric mass exchanges and intraseasonal variability extreme events in hemispheric mean ps are determined and composited grid point differences show that hemispheric anomalies are mainly determined by pressures in the north pacific western north atlantic northern asia and the southern hemisphere sh circumpolar trough seasonal differences in the composites indicate that the regional anomalies occur farther poleward in the winter hemisphere and the tropical anomalies tend to have the same sign as that of the summer hemispheric mean anomaly long lasting localized extreme ps anomalies are identified in 18 significant events of hemispheric mass imbalance and are found to be highly favored when the hemispheric mean departs significantly from normal the result implies that regionally persistent anomalies are related to

geochemical evidence of the anthropogenic alteration of element composition in lacustrine sediments from wuliangsu lake north china abstract wuliangsu lake is located in the upper reaches of the yellow river and its catchment is found in the hetao basin one of the three largest irrigation districts in china a 56 cm length sediment core was collected from the south side of the lake geochronology radiometric methods using 137 cs and 210 pb were subsequently used to date the short sediment core the concentrations of elements al fe ca mg na k ti co v cr be ba sr cu pb zn mn ni and p were studied in the solid phase at each 1 cm section based on correlation analysis and principal component analysis four groups of elements were identified the first group included total p cu and mn which indicate anthropogenic activities such as agriculture industry and sewage effluents the second group included co pb and zn that were influenced by both anthropogenic and natural factors the third group consisted of ca and sr the concentration profiles of ca and sr displayed a negative correlation with the remaining elements al k fe mg be etc which comprised the fourth group that were mainly terrigenous in addition the enrichment factors efs for all elements used as a means of identifying and quantifying human interference was evaluated the efs for cu mn pb zn co and p showed significant variation finally with constrained clustering analysis of efs for cu mn pb zn co and p the stages of regional environment were orderly and objectively divided before the 1960s efs for heavy metals displayed relatively constant values suggesting a little human influence the increasing severity of heavy metal accumulation evidenced by enhancement of efs for heavy metals began to appear in the 1960s which corresponded to local environmental development and therefore reflects strengthened human impacts the efs of total phosphorus and heavy metals then increased rapidly especially at the beginning of the 21st century