composition of characteristic soils on the raised atoll bellona solomon islands abstract knowledge is scarce about the composition of soils on bellona and other pacific atolls such knowledge is important as it is closely related to sustainable land use of these special soils formed on carbonatic phosphatic materials therefore the micromorphological chemical and mineralogical composition of samples from genetic horizons in three dominant bellonese soils malanga kenge ungi and kenge toaha and underlying rock tanahu were investigated tanahu mainly consists of dolomite but this mineral is absent in the three soils which are dominated by phosphate containing minerals the malanga soil is strongly dominated by ca and p with minor amounts of al f and fe present in fluorapatite hydroxyapatite and crandallite in contrast al fe and p dominate in the kenge ungi and kenge toaha soils in accordance with a mineralogy consisting of crandallite together with aluminum oxides gibbsite boehmite and iron oxides mainly goethite with minor contents of hematite the observed carbonate for phosphate substitution in the apatites and crandallite is important as it indicates an increased phosphate availability in the soils all three soil samples contain 1 si and very little k and mg total contents of essential microelements are considered adequate but the rather high contents of sr and u especially in the kenge ungi soil may be problematic although the composition of the soils suggests substantial fertility and resilience the lack of k containing weatherable minerals silicate minerals is in line with a very low k and low mg content and explains why fertilization may be needed to sustain future cultivation of these special soils due to a possible low bioavailability of fe mn and maybe other micronutrients at the circumneutral ph of these carbonatic phosphatic soils as well as the rather high contents of sr and u it may be recommended to test element availability using appropriate chemical soil tests supplemented by plant experiments to ensure safe and sustainable optimal soil use however according to the local farmers the malanga kenge toaha and kenge ungi soils are considered well suited for production of the preferred crops

strength behavior of methane hydrate bearing sand in undrained triaxial testing abstract gas hydrates represent a potential future energy source as well as a considerable geohazard in order to assess both the benefits and risks that gas hydrate bearing sediments pose fundamental information about their physical properties is required in this study the undrained shear strength of methane hydrate bearing sand was investigated the experimental program required modifications to an existing triaxial apparatus and accurate determination of the hydrate saturation lead to the use of two methods for comparison of the saturation calculations strength results indicated that the presence of gas hydrate will increase the sediment s undrained shear strength and corresponding stiffness the relative contribution of cohesion and friction angle was observed to be a function of the hydrate saturation for this particular hydrate formation methodology

mechanical properties of sand silt and clay containing tetrahydrofuran hydrate 1 the mechanical behavior of hydrate bearing sediments subjected to large strains has relevance for the stability of the seafloor and submarine slopes drilling and coring operations and the analysis of certain small strain properties of these sediments for example seismic velocities this study reports on the results of comprehensive axial compression triaxial tests conducted at up to 1 mpa confining pressure on sand crushed silt precipitated silt and clay specimens with closely controlled concentrations of synthetic hydrate the results show that the stress strain behavior of hydrate bearing sediments is a complex function of particle size confining pressure and hydrate concentration the mechanical properties of hydrate bearing sediments at low hydrate concentration probably 50 of pore space the behaviorbecomesmoreindependentofstressbecausethehydratescontrolbothstiffnessand strength and possibly the dilative tendency of sediments by effectively increasing interparticle coordination cementing particles together and filling the pore space the cementation contribution to the shear strength of hydrate bearing sediments decreases with increasing specific surface of soil minerals the lower the effective confining stress the greater the impact of hydrate formation on normalized strength

closure of the isthmus of panama the near shore marine record of costa rica and western panama the final closure of the isthmus of panama at 3 5 ma divided the american tropical ocean into two separate and different oceanographic regions consequences for the marine biota were profound but hitherto correlation of the pacific and caribbean coastal sections has not been precise enough to track biologic patterns we present here a correlation of 31 sections from the pacific and caribbean coasts of costa rica and western panama using calcareous nannofossils and planktonic foraminifera at both the tops and bottoms of each formation we estimate that the caribbean section ranges from 8 2 ma to 1 7 ma and the pacific sequence from 3 6 ma to 1 7 ma these intervals bracket postulated dates for final closure of the isthmus and provide the first well dated record of middle and late pliocene faunas from the region the caribbean and pacific sections include very different environments of deposition yet there is sufficient overlap and diversity of habitats to permit meaningful biological comparisons on the caribbean side formations tied together by the overlap of the upper pliocene markers sphenolithus abies and pseudoemiliana lacunosa 3 5 ma to 3 6 ma range from very shallow to shallow inner shelf 200 m and upper slope 200 800 m the pacific coast sections were mostly deposited in a trench slope environment which is absent on the caribbean side these sections fortuitously include abundant thick intra formational slumps containing shallow water fauna more appropriate for biological comparison with the caribbean biota similarly the 1 9 ma to 1 5 ma interval well constrained by various taxa includes middle to outer shelf and inner shelf to upper slope deposits on the caribbean side and marginal marine to inner shelf deposits on the pacific coast using our new biostratigraphic framework to correlate previously poorly constrained mollusc collections we show that evolutionary divergence of the pacific and caribbean near shore marine faunas had occurred by 3 5 ma this strongly suggests that the isthmus was effectively closed by this time

prediction of the mechanical response of hydrate bearing sands in recent years there has been an increasing interest in production of methane gas from hydrate bearing sediments located below the permafrost in arctic regions and offshore within the continental margins in order to simulate the geomechanical response of the hydrate accumulation during gas production comprehensive evaluation of the sediments properties is imperative this paper presents an analysis of the mechanical properties of methane hydrate bearing sediments determined through numerical simulation of drained triaxial compression tests on three different sand types the adjustment of the numerical to the experimental results was performed for the entire stress strain curves and therefore enables a good understanding of the material constitutive relations new constitutive relations are suggested for the hydrate related properties an optimization process was used finding separately the soil skeleton related coefficients and the hydrate related coefficients the values of the obtained coefficients associated with the hydrate were found to have minor deviations from each other for the three examined sand types by separating the soil skeleton and the hydrate related response this paper suggests a prediction method for the mechanical response of hydrate bearing sands

an occurrence of cadmiferous phosphorite soil concretions in jamaica abstract bauxite exploration drilling revealed the presence of phosphate minerals through the chemical and xrd analysis of recovered drill hole samples at spitzbergen in manchester parish jamaica a subsequent pit led to the discovery of phosphorite concretions composed of hard competent masses of finely crystalline fluorapatite with some minor crandallite the phosphorite contains anomalously high levels of zn 5000 mg kg 1 cd 1 1 ag 20 mg kg 1 be 80 mg kg 1 and to a lesser extent u textural and geochemical evidence indicates that the phosphorite concretions were most likely formed by the replacement of limestone by secondary deposition proximal to fossil guano deposits postulated to be late miocene or pliocene sea bird colonies mechanical dispersion of the phosphorite concretions through karst weathering processes has led to their wider spatial distribution than the original guano deposits subsequent weathering of the concretions and the admixture of their decomposition products into the bauxitic and terra rossa soils is postulated to be the cause of the widespread anomalous levels of zn cd and be in these soils in central jamaica and the elevated levels of p in the bauxite

the flickering switch of late pleistocene climate change polar ice contains a unique record of past climate variations previous greenland ice cores have documented relatively warm interstadial periods during the last glaciation and short centuryscale returns to colder conditions during the glacial to interglacial warming see for example ref 1 these climate features have also been observed to varying degrees in ocean sediment cores2 4 and terrestrial pollen and insect records5 7 here we report electrical conductivity measurements from a new greenland ice core which confirm these previous observations and also reveal a hitherto unrecognized mode of rapid climate variation fluctuations in ice conductivity on the scales of 5 20 years reflect rapid oscillations in the dust content of the atmosphere this flickering between two preferred states would seem to require extremely rapid reorganizations in atmospheric circulation

coupled deformation flow analysis for methane hydrate extraction methane hydrate is estimated to be present in substantial amounts below deep sea floors particular scientific and engineering interests that encourage studies of mechanical behaviour of methane hydrate soils include submarine geohazards such as the initiation of marine landslides through hydrate dissociation wellbore stability and estimation of future gas production from wells to study these problems a formulation of a multi physics model of methane hydrate flow coupled to soil deformation is developed by assuming deformable porous media soil matrix that accommodate non movable but dissociable hydrate a two phase flow formulation of water and methane gas is suggested according to darcy s law and capillary pressure law a single phase elastic perfectly plastic constitutive model for hydrate soil sediments based on the concept of effective stress is developed to account for the effect of hydrate saturation on mechanical strength and stiffness the formulation is incorporated into the explicit sch

western north atlantic evidence for millennial scale changes in ocean circulation and climate two late quaternary series of high resolution percent carbonate data from western north atlantic sediment drifts bermuda rise and bahama outer ridge show millennial scale oscillations superimposed on the familiar longer period oscillations of orbital origin the dominant high frequency oscillation in these records has a quasi period of about 4000 years these percent caco3 changes most likely result from the influence of climate change on the flux of terrigenous material from eastern canada the resuspension of continental margin sediment by deep eddy kinetic energy and carbonate dissolution sediment is transported to the bermuda rise by deep recirculating gyres and to the bahama outer ridge by the deep western boundary current system stable isotope results on foraminifera across several of these oscillations from interstadial climate conditions and from a glacial inception display variability similar to that of percent caco3 oxygen isotope ratios of planktonic foraminifera suggest large variations in near surface temperature and or salinity and carbon isotope ratios of benthic foraminifera indicate that there were significant oscillations in the flux of north atlantic deep water nadw these data support models which couple surface ocean conditions in the north atlantic production of nadw north atlantic heat flux and evidence for temperature oscillations in ice cores

oceanic mechanisms for amplification of the 23 000 year ice volume cycle situated adjacent to the largest northern hemispher ice sheets of the ice ages the mid latitude north atlantic ocean has an important role in the earth s climate history it provides a significant local source of moisture for the atmosphere and adjacent continents forms a corridor that guides moisture bearing storms northward from low latitudes and at times makes direct contact along its shorelines with continental ice masses evidence of major ice ocean air interactions involving the north atlantic during the last 250 000 years is summarized outflow of icebergs and meltwater initially driven by summer insolation over the ice sheets affects midlatitude ocean temperatures summer heat storage winter sea ice extent and global sea level these oceanic responses in turn influence the winter moisture flux back to the ice sheets as well as ablation of land ice by calving spectral data indicate that the oceanic moisture and sea level feedbacks in part controlled by glacial melt products amplify milankovitch insolation forcing of the volumetrically dominant mid latitude ice sheets at the 23 000 year precessional cycle

a laboratory investigation into the seismic velocities of methane gas hydrate bearing sand remote seismic methods which measure the compressional wave p wave velocity vp and shear wave s wave velocity vs can be used to assess the distribution and concentration of marine gas hydrates in situ however interpreting seismic data requires an understanding of the seismic properties of hydrate bearing sediments which has proved problematic because of difficulties in recovering intact hydrate bearing sediment samples and in performing valid laboratory tests therefore a dedicated gas hydrate resonant column ghrc was developed to allow pressure and temperature conditions suitable for hydrate formation to be applied to a specimen with subsequent measurement of both vp and vs made at frequencies and strains relevant to marine seismic investigations thirteen sand specimens containing differing amounts of evenly dispersed hydrate were tested the results show a bipartite relationship between velocities and hydrate pore saturation with a marked transition between 3 and 5 hydrate pore saturation for both vp and vs this suggests that methane hydrate initially cements sand grain contacts then infills the pore space these results show in detail for the first time using a resonant column how hydrate cementation affects elastic wave properties in quartz sand this information is valuable for validating theoretical models relating seismic wave propagation in marine sediments to hydrate pore saturation

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

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

high frequency paleovariability in climate and co2 levels from vostok ice core records the high resolution of the vostok records provides a unique look at the causes of paleoclimatic variability during the last complete glacial cycle the records present strong evidence for the interaction between orbital forcing and internal physico chemical mechanisms of variability this interaction appears to account for the great wealth of spectral features found in the records

triaxial compressive properties of artificial methane hydrate bearing sediment 1 knowledge of the mechanical properties of gas hydrate bearing sediments is essential for simulating the geomechanical response to gas extraction from a gas hydrate reservoir in this study drained triaxial compression tests were conducted on artificial methane hydrate bearing sediment samples under hydrate stable temperature pressure conditions toyoura sand average particle size d50 0 230 mm number 7 silica sand d50 0 205 mm and number 8 silica sand d50 0 130 mm were used as the skeleton of each specimen axial loading was conducted at an axial strain rate of 0 1 min 1 at a constant temperature of 278 k the cell and pore pressures were kept constant during axial loading we found that the strength and stiffness of the hydrate sand specimens increased with methane hydrate saturation and with the effective confining pressure and the secant poisson s ratio decreased with the effective confining pressure the stiffness depends on the type of sand forming the skeleton of the specimens although the strength has little dependence on the type of sand according to an earlier work hydrate sand specimens are thought to contract in the early stage of axial loading before starting to expand owing to the dilatancy effect as is the case for many other geological materials the test results in this study are discussed in relation to the deformation mechanism proposed in an earlier work

sediment accumulation rates west of the mid atlantic ridge 35 n abstract although carbonate curves have a long history of use for temporal correlation only limited agreement concerning the reasons for down core carbonate variations has been reached in this study these variations are examined by analyzing absolute accumulation rates of both carbonate and terrigenous sediment components carbonate content was determined in nine cores from approximately 3000 5000 m water depth down core variation in carbonate was correlated to an oxygen isotope curve to establish a down core time stratigraphy weight percent carbonate carbonate accumulation rate and terrigenous sediment accumulation rate were plotted as a function of water depth and time 0 130 000 yrs b p the weight percent carbonate plot indicates that carbonate content decreases with increasing water depth however the carbonate accumulation rate data demonstrates that this decrease in weight percent carbonate does not result from a decrease in the carbonate accumulation rate in the deeper cores the accumulation rate of carbonate actually increases in these deep cores the increase in carbonate accumulation rate is offset by a larger increase in the accumulation rate of terrigenous sediment resulting in a decrease in weight percent carbonate high accumulation rates of both carbonate and terrigenous sediment in cores below 4250 m appears to result from transport and redeposition of sediment most of the carbonate sediment deposited in these deep cores appears to be derived from shallow areas of the mid atlantic ridge mar the terrigenous sediment probably results from deposition by deep currents

role of critical state framework in understanding geomechanical behavior of methane hydrate bearing sediments a proper understanding of geomechanical behavior of methane hydrate bearing sediments is crucial for sustainable future gas production there are a number of triaxial experiments conducted over synthetic and natural methane hydrate mh bearing sediments and several soil constitutive models have been proposed to describe their behavior however the generality of a sophisticated model is questioned if it is tested only for a limited number of cases furthermore it is difficult to experimentally determine the associated parameters if their physical meanings and significance are not elucidated the objective of this paper is to demonstrate that a simple extension of the critical state framework is sufficient to capture the geomechanical behavior of mh bearing soils from various sources around the world while the significance of each parameter is quantified through variance based global sensitivity analyses our results show that the influence of hydrates can be largely represented by one hydrate dependent parameter pcd which controls the expansion of the initial yield surface this is validated through comparisons with shearing and volumetric response of mh bearing soils tested at various institutes under different confining stresses and with varying degrees of hydrate saturation our study suggests that the behavior of mh bearing soils can be reasonably predicted based on pcd and the conventional critical state parameters of the host sediments that can be obtained through typical geotechnical testing procedures

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

physical properties of hydrate bearing sediments 1 methane gas hydrates crystalline inclusion compounds formed from methane and water are found in marine continental margin and permafrost sediments worldwide this article reviews the current understanding of phenomena involved in gas hydrate formation and the physical properties of hydrate bearing sediments formation phenomena include pore scale habit solubility spatial variability and host sediment aggregate properties physical properties include thermal properties permeability electrical conductivity and permittivity small strain elastic p and s wave velocities shear strength and volume changes resulting from hydrate dissociation the magnitudes and interdependencies of these properties are critically important for predicting and quantifying macroscale responses of hydrate bearing sediments to changes in mechanical thermal or chemical boundary conditions these predictions are vital for mitigating borehole local and regional slope stability hazards optimizing recovery techniques for extracting methane from hydrate bearing sediments or sequestering carbon dioxide in gas hydrate and evaluating the role of gas hydrate in the global carbon cycle

experimental verification of a prediction model for hydrate bearing sand this paper presents an experimental verification of a prediction model for the mechanical properties of hydrate bearing sand the model is examined using experimental drained triaxial test results of three independent data sets which are associated with different hydrate formations and testing conditions for each data set an optimization process is applied based on numerical modeling of the testing conditions in order to evaluate the pure sand properties based on these properties the model forecasts the stress stain curves for different hydrate saturations based on an advanced hydrate simulator although the model does not show a fair forecast with ice seeding hydrate formation samples and for specimens tested under gas saturation it predicts the mechanical behavior of samples with partly saturated hydrate formation tested under water saturation

the presence of anomalous trace element levels in present day jamaican soils and the geochemistry of late miocene or pliocene phosphorites abstract high levels of cd and zn in jamaican soils observed in geochemical surveys are related to the presence of phosphorites of possible late miocene or pliocene age the trace element and ree geochemistry of the phosphorites together with sem studies indicate a guano origin for the phosphorites no specific host minerals for cd could be identified in the fossiliferous phosphorite which is characterized by uniquely high levels of cd zn ag be u and y however in the soil cd is present in lithiophorite and a complex history of pedological development is preserved in the aluminous goethite present in the soil the unique guano signature is preserved in the soil despite the fact that guanos themselves have either not been observed or have been destroyed by continuing karst and soil development the phosphorite geochemical signature can be traced in the data of a 1988 island wide soil geochemical survey identifying areas where the palaeo environment that supported bird rookeries existed in the late miocene or pliocene