mid late holocene vegetation response to climatic drivers and biotic disturbances in the banni grasslands of western india abstract tropical grasslands and savannas are globally extensive and are of significant environmental economic and ecological importance these ecosystems are anticipated to be particularly sensitive to future changes in climate and understanding how these systems have responded to climatic changes in the past can provide us with insights into their potential responses to future global change in this study the temporal dynamics of c 3 c 4 vegetation changes in response to changes in moisture availability local fire events and changing levels of herbivory in a summer rainfall region of western india are reconstructed for the past 4600 cal yr bp paleodata such as stable carbon isotope of bulk organic matter 13 c org oxygen isotope from carbonate shells 18 o shell macro charcoal and herbivore dung fungal spores are reported from the retrieved cores of two wetland sites located in the banni grasslands of western india results show that vegetation in the banni was composed mostly of c 3 vegetation from 4600 to 2500 cal yr bp after which there was a decline in c 3 vegetation from the late holocene to the present there was a mix of both c 3 and c 4 vegetation with c 4 grasses being more abundant in the ecosystem these shifts were coincident with rainfall changes from more mesic conditions during 4600 to 2500 cal yr bp to more arid conditions towards the present as indicated by 18 o shell isotope data the period of increase in c 4 vegetation also coincides with a period of increased biotic disturbances in the ecosystem particularly fire given the current scenarios of global warming recurrent drought events and increased anthropogenic use of similar ecosystems such studies can provide us insights into potential future trajectories of these ecosystems

sensitivity of carbon isotopic proxies to paleoclimatic forcing a case study from lake bosumtwi ghana over the last 32 000 years 1 analyses of carbon isotopic ratios in concomitant bulk sediment samples and fossil grass epidermal fragments from lake bosumtwi ghana demonstrate that both records reflect paleohydrologic variability however the bulk sediment signal is dominated by within lake processes whereas the fossil grass epidermal record provides the terrestrial vegetation response to changes in available moisture the direction of change is similar but the magnitude and timing of response are different during the terminal pleistocene the aquatic record shows a dramatic flip flop behavior bulk sediment 13c 4 to 32 while the terrestrial grass epidermis record is much more muted 13c shifts from 11 to 15 furthermore during the transition to the relatively moister conditions of the holocene a dominance of c4 plants persisted for at least 800 1000 years after limnological changes began on the other hand the epidermal isotopic record shows a much more dramatic response than that provided by the bulk sediment to the onset of drier more seasonally contrasted conditions during the late holocene these results emphasize the need to consider varying response times of the biogeochemical systems that control the production of proxies especially when attempting to correlate widely separated records based upon fundamentally different proxies

little ice age aridity in the north american great plains a high resolution reconstruction of salinity fluctuations from devils lake north dakota usa the little ice age was an interval between about ad 1500 and 1850 characterized by advancing glaciers in mountainous regions of europe and western north america however it is unclear whether this cool moist period was truly global in extent or how it was manifested in other regions with different climatic controls a high resolution reconstruction of salinity fluctuations in devils lake north dakota based on fossil diatoms ostracode shell geochemistry and bulk carbonate geochemistry indicates that saline conditions prevailed throughout much of the recent past these results suggest an arid climate in the northern great plains throughout the little ice age and that during this interval climatic gradients between the great plains and regions to both the east and west may have been quite steep

carbon and oxygen isotope variations among lacustrine ostracods implications for palaeoclimatic studies large ranges of 13c 12c and 18o 16o ratios are found among modem ostracods from lakes in jamaica and mexico if their calcite carapaces grew in isotopic equilibrium with the lake water then the main period of carapace formation was probably in the cooler and or wetter months differences in 13c and 18 o values between ostracods from different sites relate to spatial variations in the composition of the lake water and differences between species at the same site probably reflect differences in organic photosynthesis or decay among the micro habitats occupied by the species there nevertheless remain significant variations in both 13c and 18o among modern valves of the same species at the same site a consequence of the temporal and spatial variation in lake water and the fact that ostracods form their carapace over a short period individual valves from a 1 cm section of a sediment core show that the isotopic effects of changes in the rainfall versus evaporation status of a lake over a period of c

estimating groundwater recharge based on mass balance evaluation of unsaturated zone in a coastal catchment characterized by tropical rainforest weather conditions estimation of recharge is necessary for evaluating water resources in the north kelantan catchment of malaysia due to rapid development and consequently over drafting of available groundwater in order to determine the amount of recharge a study of natural salts i e chloride and sulfate was conducted to estimate groundwater recharge rates studies of the chloride mass balance cmb and sulfate mass balance smb were carried out in the unsaturated zone under rainforest weather conditions with a relatively shallow groundwater table ten soil profiles in different parts of the catchment representing a range of soil textures were selected for the study the cmb results showed that the mean recharge rate is 527 87 mm year the highest and lowest calculated recharge rates in the study area were 8 and 31 of local rainfall times required to accumulate chloride sulfate beneath the natural ecosystem highly depend on profile texture and the cmb age is maximized at kp94 and kt121 sites to be 15 01 and 14 15 years respectively the smb method produced lower recharge rates than those based on chloride yielding an average of 364 60 mm year with values ranging between 7 and 26 of local rainfall and the smb age is 21 01 years at kp94 site mobilization decreases with fine texture and low permeability and increases with coarse texture and high permeability in this way low permeability of surface geology not only controls the recharge rate but also causes high buffering in holding salts nevertheless higher sulfate concentration in profile may be due to different dissolution or sorption processes which are required to be studied thoroughly based on two types of scenarios representing natural water movement in unsaturated zone using hydrus 1d recharge rates were simulated to be 419 mm in profile with overlain fine texture soil and 636 mm in profile characterizing with single coarse texture for a total time of 213 days our study suggests the feasibility of using the mass balance methods in tropical rainforest weather conditions the information may improve the accuracy of prediction of possible groundwater pollution and groundwater management in the future

drought and dust deposition in the west african sahel a 5500 year record from kajemarum oasis northeastern nigeria a high resolution multiproxy palaeolimnological record from the manga grasslands northeastern nigeria spanning the last 5500 calendar years reveals the episodic deterioration in sahelian climate as significant biogeophysical thresholds were crossed desert dust deposition began to increase 4700 cal bp rainfall during the summer monsoon season declined permanently after 4100 cal bp a further significant change in atmospheric circulation giving rise to multidecadal to centennial scale droughts and enhanced dust deposition occurred 1500 cal bp hence the post 1968 sahel drought is not unique the prolonged arid episode that occurred around 1200 1000 cal bp in ethiopia the sahel and tropical mexico may have been linked to an abrupt cooling event in the north atlantic and to a cluster of intense el nino southern oscillation events in the eastern equatorial pacific

palaeoclimate interpretation of stable isotope data from lake sediment archives the isotope composition of authigenic and biogenic carbonates and diatom silica are commonly used as palaeoclimate proxies from lake sediments this article reviews the controls on the isotope composition of lacustrine skeletal and non skeletal deposits and illustrates how stable isotope studies contribute to an understanding of changes in temperature precipitation patterns evaporation and the carbon cycle it highlights the differences in the palaeoclimate potential of a wide range of lakes ranging from open to closed lake basins a large number of the case histories but not all are drawn from studies of temperate lakes from europe large closed lake systems in the tropics and elsewhere lose water predominantly through evaporation and contain sediments with variable and generally high 18o values fluctuations in the isotope composition of authigenic or biogenic minerals are mainly a function of long term changes in the precipitation evaporation ratio in contrast small open lakes which have a degree of through flow typically contain sediments with 18o values that vary by no more than a few these variations are generally ascribed to variations in temperature or the isotope composition of precipitation p from which either an annual or seasonally specific signal can be gained these types of lakes are common in northern europe and at high altitudes the interpretation of isotope data from a lacustrine succession requires a knowledge of the local processes that might control and modify the signal their effects need to be quantified and a robust calibration using the modern lake system is necessary to establish the relationship between the measured signal the isotopic composition of the host waters and climate

trace element variability in single ostracod valves as a proxy for hydrochemical change in nam co central tibet during the holocene ostracod shells belonging to three taxa leucocytherella sinensis huang 1982 leucocythere dorsotuberosa huang 1982 and l dorsotuberosa f postilirata sensu pang 1985 were collected from two sediment cores from lake nam co on the central tibetan plateau two variants of la icp ms laser ablation inductively coupled plasma mass spectrometry spot and line scan analyses were used to investigate trace element concentrations mg sr ba u and rare earth elements rees in single ostracod shells the results suggest that the line scan method can provide better precision than the spot analysis and is therefore preferred no significant difference in trace element composition between taxa was detected in our study fluctuations of mg ca and sr ca in the shells show good agreement with the reported lake level changes during the holocene indicating that ostracod mg and sr can be related to palaeohydrochemical processes in this area a high correlation between ba ca and sr ca was detected in our study perhaps implying that both metals were controlled by the same mechanisms a possible relationship between ostracod u ca and the past redox conditions on the lake bottom is discussed relatively low and constant la ca was observed which could be due to the ree characteristics in the lake water or ostracod biological processes or even the associated fe mn and or organic contaminants future studies on more specimens from this area especially shells from living ostracods are essential to investigate the potential of ostracod ba u and rees for use as palaeoenvironmental indicators

transition from arid to hyper arid environment in the southern levant deserts as recorded by early pleistocene cummulic aridisols abstract the time at which deserts established their current arid or hyper arid conditions remains a fundamental question regarding the history of earth cosmogenic isotope exposure ages of desert pavement and welded calcic gypsic salic reg soils that developed on relatively flat alluvial surfaces 2 ma ago in the negev desert indicate long geomorphic stability under extremely dry conditions over a short interval during their initial stage of development between 1 2 ma these cumulative soils are characterized by calcic soils reaching maximum stage iii of carbonate morphology this interval is the only period when calcic soil horizons formed on stable abandoned alluvial surfaces in the southern negev desert since 1 ma pedogenesis changed toward more arid soil environment and the formation of gypsic salic soil horizons that were later followed by dust accumulation the dichotomy of only moderately developed calcic soil stages ii iii during a relatively long time interval 105 106 years indicates an arid environment that does not support continuous development but only occasional calcic soil formation the very low 18o and relatively high 13c values of these early pedogenic carbonates support soil formation under arid climatic conditions such an environment was probably characterized by rare and relatively longer duration rainstorms which occasionally allowed deeper infiltration of rainwater and longer retention of soil moisture this in turn enabled the growth of sparse vegetation that enhanced deposition of pedogenic carbonate at 1 ma these rare events of slightly wetter conditions ceased and less atmospheric moisture reached the southern negev desert leading to deposition of soluble salts and dust deposited in the soils the combination of long term hyperaridity scarcity of vegetation and lack of bioturbation salts cementation dust accumulation and tight desert pavement cover has protected the surfaces from erosion forming one of the most remarkably stable landscapes on earth a landscape that essentially has not eroded but accumulated salt and dust for more than 106 yr

pleistocene paleoenvironmental evolution at continental middle latitude inferred from carbon and oxygen stable isotope analysis of ostracodes from the guadix baza basin granada se spain abstract a representative paleoenvironmental reconstruction of continental middle latitude from ca 2 my to the upper part of middle pleistocene 279 77 ky was obtained from the carbon and oxygen stable isotopes analyzed in ostracode shells cyprideis torosa recovered in the guadix baza basin se spain an intramontaneous closed depression filled by alluvial and lacustrine sediments this study was performed along a 356 m thick composite section dated previously by paleomagnetism and the amino acid racemization method 13c and 18o profiles reflected changes in temperature the evaporation infill ratio in the water bodies and the amount of rain 13c is also affected by changes in plant biomass periods with high 13c and 18o values are associated with warm and dry regimes and with less vegetation which in some cases coincide with the development of displacive gypsum crystals whereas low 13c and 18o values correlate with cold and humid episodes which cause more vegetation biomass and therefore increasing the input of isotopically light carbon intermediate 18o values are linked to temperate dry or humid episodes when they coincide with high or low 13c values respectively 86 paleoclimatic events were distinguished in the pleistocene record from the 13c and 18o profiles from both the statistical analysis of the geochemical data and the geological observations four cold and humid long periods low 18o and four warm and dry long periods high 18o were defined this differs with respect to the paleoclimatological behavior established for the northern hemisphere where during cold periods glacial no water was available while permafrost conditions persisted whereas in warm episodes interglacial higher precipitation rates occurred good correspondences between the guadix baza basin paleoclimatic record and a marine oxygen isotope sequence two continental cores and other long mediterranean paleoenvironmental records pollen sequences from israel were found which suggested that climate changes in the guadix baza basin were in tune with global climatic changes

a late holocene palaeoenvironmental snapshot of the angamma delta lake megachad at the end of the african humid period abstract during the african humid period ahp there was a large increase in the area of lakes and wetlands lake megachad one of several huge lakes underwent dramatic fluctuations during the ahp prior to regression in the mid holocene however the timing and nature of ahp termination has been disputed we present evidence from sediments of the angamma delta from the northern end of the palaeolake for lake megachad lake level fluctuations at the end of the ahp delta slope deposits were deposited around 7000 cal bp at the height of the ahp overlying bioclastic sediments from 4300 to 4800 cal bp at an elevation of 285 290 m lie below the palaeolake highstand 339 m but close to the elevation of the bahr el ghazal sill which divided the lake s two sub basins ostracod 18o values indicate that the waters of the northern sub basin were evaporated to levels similar to modern lake chad palaeoecological evidence suggests that the lake was perennial and evaporative enrichment is attributed to restricted circulation of lake waters as the sill emerged the age and elevation of the bioclastic sediment coupled with published lake level reconstructions suggest a complex lake level history with a major regression at the end of the ahp followed by a short lived lake level rise and then a further regression this new evidence for changes in lake level provides support for other geological records and some modelling experiments that suggest rapid fluctuations in hydroclimate at the end of the ahp

anisotropic features of geometry and permeability in fractured rock masses abstract a geometric anisotropy factor a f of two dimensional natural fracture systems has been defined according to fracture spacing and orientation in a given direction geometric anisotropy of fracture systems has a major effect on the percolation threshold the critical fracture density of fracture systems below which the overall permeability is zero a two dimensional distinct element code udec has been used to calculate directional flow rates of fracture systems simulated and natural fracture patterns sampled on outcrops in the lake district england have been tested to examine the relation between geometric anisotropy and permeability anisotropy which is demonstrated to have a power law form also the differential anisotropy factor a f results in different universal exponents which govern the relation between fracture density and flow rates

integrated geoelectrical resistivity hydrochemical and soil property analysis methods to study shallow groundwater in the agriculture area machang malaysia integrated geoelectrical resistivity hydrochemical and soil property analysis methods were used to study the groundwater characteristics of sandy soils within a shallow aquifer in the agriculture area machang a pilot test investigation was done prior to the main investigation the area was divided into two sites test site 1 is non fertilized test site 2 is the former regularly fertilized site from the surface to depths of 75 cm a lower average resistivity was obtained in test site 2 around 0 37 less than in test site 1 the presence of nitrate and chloride contents in pore water reduced the resistivity values despite the low moisture content the ph values for the whole area range from 4 11 to 6 88 indicating that the groundwater is moderately to slightly acidic in the southern region concentration of nitrate is considered to be high 20 mg l while it is nearly zero in the northern region in the south the soil properties are similar however the geoelectrical model shows lower resistivity values around 18 m at the sites with relatively high nitrate concentration in the groundwater 20 mg l conversely the sites with low nitrate concentration reveal the resistivity values to be higher 35 m basement and groundwater potential maps are generated from the interpolation of an interpreted resistivity model the areas that possibly have nitrate contaminated groundwater have been mapped along with groundwater flow patterns the northern part of the area has an east to west groundwater flow pattern making it impossible for contaminated water from the southern region to enter despite the northern area having a lower elevation

magnesium content of non marine ostracod shells a new palaeosalinometer and palaeothermometer abstract ostracods are microcrustaceans with calcitic carapaces each consisting of two valves or shells that grow by moulting and regeneration of sequentially larger valves up to nine times before reaching maturity the mg content of these valves is species dependent and is a function of their growth stage and the temperature salinity mg content and mg ca ratio of their host water newly formed partly calcified valves of the non marine nektic ostracod mytilocypris henricae have high mg contents 100 000 ppm mg in caco3 at individual shell weights of 2 g this relative mg content decreases as calcification proceeds until shell weights exceed 120 g whereupon the mg content is constant and useful as an indicator of the ostracod s environment mg ca ratios in individual ostracod valves from several species of the genera mytilocypris and australocypris from culture experiments and a series of australian lakes indicate that the valve s mg content increases as a function of increasing temperature and salinity within the range 11 25 c and for waters containing 24 2325 ppm mg the molar mg ca ratio in these ostracods fully calcified valves increases by 0 0015 or 370 ppm mg in caco3 per 1 c and per change of 125 ppm mg in solution for most mainland australian lakes a change in water composition of 125 ppm mg corresponds to a change of 3 5 in salinity for a given mg content of a lake the mg ca ratio of the water may vary within the range of common lacustrine values without significantly affecting mg uptake in the ostracod valves these relationships can provide palaeosalinities and or palaeotemperatures for ostracods recovered from continental sediments for mg partitioning an increase in temperature and salinity produce increased mg content in ostracods whereas for 18o fractionation in biogenic calcite an increase in temperature produces a decrease in 18o of the ostracod and an increase in salinity leads to an increase in 18o of the ostracod thus a combination of 18o and mg measurements on non marine ostracods should enable unique resolution of palaeotemperature and palaeosalinity variations

response of fractured rock subject to fluid injection part ii characteristic behaviour abstract distinct element modelling has been used to investigate the mechanics of naturally fractured reservoirs subject to a constant rate of fluid injection constant stress boundary conditions were imposed with magnitudes typical of those pertaining at approximately 3 km depth in some sedimentary environments fluid leak off through fracture walls and fracture dilation during shear were modelled the progressive nature of the changes of stress and displacement occurring within the coupled fluid rock system were examined for four combinations of uniform fracture geometry and applied stress the effects of a uniform change of pore pressure on the directional nature of hydraulic conductivity in a fractured medium were characterised the influence of variation of injection rate pore fluid compressibility and leak off rate was examined effects associated with contrasts of shear stiffness between fractures and blocks and with inelastic deformation were interpreted

deciphering signals of late holocene fluvial and aeolian supply from a shelf sediment depocentre off senegal north west africa high resolution climatic records of the late holocene along the north west african continental margin are scarce here we combine sediment grain size elemental distribution and mineral assemblage data to trace dust and riverine sources at a shallow marine sediment depocentre in the vicinity of the senegal river mouth the aim is to understand how these terrigenous components reflect climate variability during the late holocene major element contents were measured and mineral identification was performed on three sub fractions of our sediment core i fluvial material 2 m ii aeolian material of 18 63 m and iii a sub fraction of dual origin material of 2 18 m results show that more than 80 of the total al and fe terrigenous bulk content is present in the fluviogenic fraction in contrast ti k and si cannot be considered as proxies for one specific source off senegal the al ca ratio recording the continental river runoff reveals two dry periods from 3010 to 2750 cal a bp and from 1900 to 1000 cal a bp and two main humid periods from 2750 to 1900 cal a bp and from 1000 to 700 cal a bp the match between i intervals of low river runoff inferred by low al ca values ii reduced river discharge inferred by integrated palynological data from offshore senegal and iii periods of enhanced dune reactivation in mali confirms this interpretation copyright 2011 john wiley sons ltd

a late quaternary palaeolimnological record from jamaica based on trace element chemistry of ostracod shells abstract the trace element chemistry of ostracod shells provides one of the most promising methods for palaeolinmological reconstruction in this paper molar sr ca and mg ca ratios in shells of the ostracod cypretta brevisaepta furtos 1934 were used to reconstruct the late quaternary palaeolimnology of wallywash great pond a small freshwater coastal lake in jamaica analyses of modern jamaican ostracods were undertaken to establish molar distribution coefficients kd d m s for this species k d sr 0 306 0 069 k d mg 0 0142 0 0088 these values were used to reconstruct past levels of sr ca water and mg ca water for a 9 23 m lake sediment core from wallywash great pond the results were coupled with previously published stable isotope 18 o and 13 c determinations on fine grained calcite to reconstruct the salinity palaeohydrology and palaeoproductivity of the lake over the last 125 ka b p 10 3 calendar years before present three major highstands with slightly elevated salinity occurred during marine isotope stage 5 under elevated sea level and a humid climate the lake dried out 93 5 ka b p as sea level felll and the climate became drier it refilled around 10 7 ka b p three separate highstands during the holocene were sustained by humid conditions and high relative sea level although there were small increases in salinity during the holocene when sea level was close to the deepest part of the lake significant saltwater intrusion appears to have been prevented by freshwater discharge from inland throughout the late quaternary the salinity of the great pond showed low absolute variations from 0 3 to 0 6 o the long term trends in lake level reflect both orbitally induced changes in insolation and eustatic sea level water level fluctuations during the holocene however reflect climatic changes on the millennial timescale rather than orbital forcing or sea level change

integrated geoelectrical resistivity and hydrogeochemical methods for delineating and mapping heavy metal zone in aquifer system a novel study on using geoelectrical resistivity soil property and hydrogeochemical analysis methods for delineating and mapping of heavy metal in aquifer system is presented in this paper a total of 47 surveys of geoelectrical resistivity with wenner configuration were conducted to determine the subsurface and the groundwater characteristics the groundwater sample from 53 existing wells and 2 new wells has been analyzed to derive their water chemical content the chemical analysis was done on the soil sample obtained from new two wells and from selected locations the water and soil chemical analysis results from the new two wells were used as calibration in resistivity interpretation the occurrence of heavy metal in aquifer system was expected to detect using the geoelectrical resistivity survey for the whole study area the result of groundwater analysis shows that the groundwater sample contains a relatively low concentration of fe 0 3 mg l elongating from the south up to the middle region while in the middle and the northwestern fe concentration is relatively high around 12 mg l chemical analysis of soil sample shows that in the lower resistivity zone 18 m al and fe concentrations are comparatively high with an average of 68 000 and 40 000 mg kg respectively starting from the middle to the northwestern zone the resistivity value appears to be low it is definitely caused by higher al and fe concentration within the soil and it is supported also by lower total anion content in the groundwater while the resistivity value of more than 40 m in aquifers is obtained in the zone which fe concentration is relatively lower in the soil but not present in the groundwater correlation fe concentration in the soil and fe concentration in the groundwater sample shows the trend of positively linear however the al concentration in soil has no correlation with al content in groundwater finally the probability of high heavy metal zone in the aquifer system is easily delineated by the distribution of geoelectrical resistivity presented in depth slice shapes which extend from the boundary range composite batholith in the north to the northwest

a multi proxy analysis of the holocene humid phase from the united arab emirates and its implications for southeast arabia s neolithic populations an early to mid holocene humid phase has been identified in various arabian geo archives although significant regional heterogeneity has been reported in the onset duration and stability of this period a multi proxy lake and dune record from wahalah in the united arab emirates uae documents significant variations in hydrology biological productivity and landscape stability during the first half of the holocene these data reveal that post last glacial maximum dune emplacement continued into the earliest part of the holocene with the onset of permanent lacustrine sedimentation at the site commencing 8 5 ka cal bp a long term shift towards more arid conditions is inferred between 7 8 and 5 9 ka cal bp with intermittent flooding of the basin and distinct phases of instability throughout the catchment area this transition is linked to the southwards migration of the intertropical convergence zone itcz and associated weakening of monsoon rains a peak in landscape instability is recorded between 5 9 and 5 3 ka cal bp and is marked by a pronounced increase in regional dune emplacement these variations are considered alongside the record of human settlement raising important questions about the interactions between population demographics climate and environment in southeast arabia during the neolithic

holocene landscape evolution of the manga grasslands ne nigeria evidence from palaeolimnology and dune chronology this paper presents a synthesis of results from investigations into palaeolimnology and dune chronology in the manga grasslands and adjacent areas of ne nigeria in order to reconstruct the evolution of this semi arid landscape since the late glacial a marked wet phase gave way to a fall in lake levels during the late glacial dune emplacement was active at this time to the south of the manga grasslands but seems to have been absent from the grasslands themselves wet conditions prevailed during much of the early to mid holocene accompanied by periods of significant barchanoid dune reactivation a marked deterioration in climate and vegetation commenced around 4 1 ka bp leading to the formation of the present day semi arid landscape the data suggest that there have been major changes in humidity in this part of subsaharan west africa during the late glacial to holocene and that the relationship between changes in precipitation and aeolian activity is complex

rapid least squares inversion of apparent resistivity pseudosections by a quasi newton method1 a fast inversion technique for the interpretation of data from resistivity tomography surveys has been developed for operation on a microcomputer this technique is based on the smoothness constrained least squares method and it produces a two dimensional subsurface model from the apparent resistivity pseudosection in the first iteration a homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically for subsequent iterations a quasi newton method is used to estimate the partial derivatives which reduces the computer time and memory space required by about eight and twelve times respectively compared to the conventional least squares method tests with a variety of computer models and data from field surveys show that this technique is insensitive to random noise and converges rapidly this technique takes about one minute to invert a single data set on an 80486dx microcomputer

sample size implications of the trace element variability of ostracod shells the magnesium and strontium contents of fossil ostracod shell calcite have been used extensively in the reconstruction of water composition and temperature in lakes and to a lesser degree in marginal marine waters and in the deep ocean current instrumentation may allow single shells of these calcite microfossils to be analysed and most studies have taken advantage of this capability however there is now good evidence for large intra sample variability in the trace element content of ostracod shells both in living populations and in fossil assemblages and this has implications for any attempt to distinguish the low frequency similar to decadal or longer trends in water temperature and composition that are often the goals of palaeoenvironmental studies from higher frequency seasonal or interannual noise in this study the mg and sr contents of living and fossil populations of six species of marine marginal marine and shallow marine ostracods from 11 sites are used to investigate sources of variability and to estimate critical sample sizes for stratigraphic studies results confirm that variability amongst individual samples is generally wide and cannot be attributed to instrumental error or sample handling alone in some instances variability can be explained by fluctuations in water composition and or temperature although this has to be evaluated in each case some evidence points to non environmental control on variability in shell composition perhaps connected to genetically controlled differences in physiology that affected calcification early diagenetic alteration or the role of environmental factors other than temperature or water composition however further work is needed to verify this in some stratigraphic studies large numbers 20 of individual shells would need to be analysed in order to detect low frequency environmental changes with any degree of confidence although fewer shells may often suffice the critical sample size depends on the variability at each study site which should ideally be evaluated using pilot studies c 2008 elsevier ltd all rights reserved

numerical modeling of fault controlled fluid flow in the genesis of tin deposits of the malage ore field gejiu mining district china a distinct element finite difference model based on geologic data from the tin polymetallic hydrothermal deposits of malage is constructed to simulate the geologic processes of fault controlled fluid migration during hydrothermal ore genesis the history of hydrothermal ore genesis is strongly affected by the interaction between fault deformation and fluid flow an injected fluid induces fault slip by lowering the effective stress across a fault the subsequent movement on the fault enhances the fault aperture which provides a channelway that both facilitates and focuses fluid flow the variation of fluid injection under certain stress conditions causes cyclic movement on faults this cyclic failure gives rise to pulsating fluid flow along the faults which may be responsible in part for the precipitation zoning of mineral deposits as an important structural condition for ore formation in any fault related mineralized region like malage the linking up of fracture networks not only allows appropriate long distance channels for fluid migration but also provides the appropriate conditions for ore deposition at particular structural sites this study indicates that different fluid flow patterns i e changes in fluid flow rate or velocity with time and space can reflect the variation of structural environment for instance the flow velocity is increased gradually over time on the relatively connected faults such as the northwest southeast trending fault and the western half of the east west trending yuanlao fault in the center of the malage ore field these are the main pathways for the ore forming fluids in the smaller secondary faults the flow velocity fluctuates more rapidly with time and space in some instances causing conditions that are favorable to mineral deposition the main ore deposition sites occur on the smaller secondary faults the detailed variation of fluid and aperture conditions modeled in this complex fault array can be related to the formation and location of mineral deposits both predictively and conceptually the modeling also demonstrates that the fault deformation and fluid flow are sensitive to the principal stress orientation if the orientation of sigma 1 is changed by more than 15 degrees there are very different results for the calculated fault motion pattern hydraulic aperture and fluid flow

diatom inferred salinity and carbonate oxygen isotopes in holocene waterbodies of the western sahara and sahel africa abstract thirteen holocene palaeolakes in the western sahara and sahel have provided diatom records with carbonate oxygen isotope profiles available from eight of them most of these palaeolakes were groundwater fed lake water chemistry is reconstructed using diatom transfer functions lake water salinity and 18 o records are assembled with some isotopic and chemical groundwater data to better understand the response of the hydrological systems to climate changes over the past 15 000 yr data are in general agreement with climate simulations using coupled atmosphere ocean vegetation models which show a mid holocene wetting over the whole of northwest africa and a rapid drying by 6 4 ka the lake record also shows that at many sites the major lake infilling lags the end of the younger dryas by 1 2 ka regional differences also appear in the timing of the lake hydrological optimum ca 10 5 8 5 and 7 5 4 5 ka in the northern sahara 10 8 5 ka in the air tenere 10 5 7 or 4 5 in the sahel and 7 5 ka in lake chad the whole of the holocene is punctuated by short term drying events changes in water isotopic composition through time are partly explained by changes in rainfall amount and air humidity during the wet holocene period however the very low values in the southern sahara also imply changes in the moisture transport pattern or rainfall mechanisms data suggest an apparent decrease in 18 o content of precipitation along the monsoon flow in contrast with modern patterns changes in water availability and quality have driven population migrations in and out of the sahara sahel but relationships between climate and cultures are complex short term dry events might have driven inventive adaptations in the sahara drying at 5 4 5 ka coincides with both the collapse of the classical neolithic civilization and the settlement of new cultures

holocene environmental change in the west african sahel sedimentological and mineral magnetic analyses of lake sediments from jikariya lake northeastern nigeria previous studies have demonstrated long term changes in effective moisture in sub saharan africa here we reconstruct holocene environments using a similar to 7 m lake sediment sequence recovered from the northeastern nigerian sahel and attempt to distinguish basin specific changes from regional climatic variations the sequence was analysed for sedimentological properties mineral magnetism and pollen and dated by cs 137 pb 210 excess and c 14 extremely arid conditions of the terminal pleistocene ended ca 11 500 cal bp calendar years when climate ameliorated and a lake developed until the occurrence of an arid event leading to lake desiccation at similar to 11 200 cal bp following this climate ameliorated and a water body re emerged very wet conditions predominated 11 200 5600 cal bp followed by drought between 5600 and 5500 cal bp and a return to moderate humidity from 5500 to 4000 cal bp after 4000 cal bp a marked deterioration occurred culminating in lake desiccation at ca 800 cal bp after this time the climate remained generally dry and the re emerging lake was shallow comparison of these results with other well dated sequences in the region demonstrates the importance of basin specific influences on the palaeolimnological records in addition to regional climatic controls disentangling these different controls as well as the reconstruction of holocene climate therefore requires a multiple basin approach copyright c 2008 john wiley sons ltd

response of fractured rock subject to fluid injection part i development of a numerical model abstract the selection and development of a numerical model used to investigate the response of fractured rock to injection are described the distinct element method was chosen on the basis of its ability to represent explicitly the fractures and to couple the mechanical deformation to the fluid flow the numerical model was used to simulate fluid injection from a single well into each of four basic model reservoirs the results of these simulations form the basis of the interpretation given in parts ii and iii

holocene palaeolimnology of kajemamm oasis northern nigeria an isotopic study of ostracodes bulk carbonate and organic carbon a high resolution 5500 year palaeolimnological record from kajemarum oasis a closed basin in the manga grasslands of northern nigeria provides evidence of environmental change in subsaharan africa during the holocene palaeohydrological variations mainly changes in the balance between precipitation and evaporation are recorded by stable oxygen isotope ratios in bulk carbonate and ostracod calcite and by the sr ca ratio in ostracode shells variations in the carbon isotope ratios in carbonates indicate changes in primary productivity in the lake whereas the carbon isotope composition of organic carbon reflects ecophysiological processes within the lake and its surrounding catchment results indicate that there have been marked environmental changes in the manga grasslands over the last 5500 years a more variable climate set in around 1500 cal a bp a prolonged drought between 1200 and 1000 cal a bp with reduced aquatic productivity was followed by a switch to a wetter but still unstable climate moist conditions prevailed during the little ice age the results indicate that drought has affected the sahel episodically over the last 1500 years and is not solely a twentieth century phenomenon

critical stress localization of flow associated with deformation of well fractured rock masses with implications for mineral deposits fluid flow and deformation of fractured rock masses is investigated using numerical models based on distinct element methods udec which couple mechanical and hydraulic behaviour a series of numerical experiments is presented in which diffuse flow through fracture networks changes to highly localized flow at a critical stress state slip on parts of the fracture network causes the opening up of some fractures often at fracture intersections thus a change in the stress state results in a sudden localization of deformation and fluid flow a series of plots of hydraulic conductivity v differential stress are presented for some natural fracture networks to demonstrate the influence of fracture network geometry and in situ stress on the critical phase boundary between diffuse and localized flow the onset of localized deformation and fluid flow is a critical point phenomenon resulting in fractal properties fractal and multifractal techniques are used to characterize heterogeneity of the flow in order to generalize the results of the modelling of discrete systems to a continuum based description of the flow the significance of the models and their implications for crustal behaviour are discussed in relation to hydrothermal mineralization and natural vein systems

late holocene palaeolimnology of bal lake northern nigeria a multidisciplinary study abstract a multidisciplinary study of lake sediments from bal lake a small saline lake in the sahel zone of northeastern nigeria provides evidence for changing precipitation evaporation ratios over the last 1000 cal years climatic and environmental changes over this period have been reconstructed using evidence from ostracod faunal assemblages and shell chemistry sediment properties and palynology and the sequences dated by a combination of 137 cs 210 pb and ams radiocarbon methods the results testify to major hydrological changes in the sahel over the last millennium the end of a major drought phase that is seen in other records from the manga grasslands is dated to around 950 ad this was followed by a prolonged freshwater phase of the lake from the 12th to the 16th century ad which points to wetter conditions a period of higher salinity and hence drier and more variable conditions from the 1700s to the mid 1900s was followed by a pronounced drying trend into the 20th century

fractal and multifractal measures of natural and synthetic fracture networks we have analyzed the fractal and multifractal nature of a series of 17 natural fracture trace maps representing a wide variety of scales geological settings and lithologies as well as a number of typical synthetic fracture networks in which fracture locations orientations and lengths are drawn from various probability distribution functions recent studies have shown that multifractal methods can be used to investigate fracture networks at greater depth since the fractal dimension represents only part of the scaling spectrum characterizing each network we find that the real and synthetic fracture maps display fractal and multifractal properties moreover the properties of the synthetic networks are very similar to those of the real networks with nontrivial fractal dimensions and multifractal spectra we suggest that different fracturing mechanisms can lead to two or more distinct subranges over which a fractal dimension can be defined while the heterogeneity of the rock and the nature of the fracturing mechanisms lead to multifractal properties we also find that the fractal dimension of a synthetic fracture network is relatively insensitive to parameters such as fracture length and orientation but can be controlled by appropriate choice of the relative fracture density

the fracture criticality of crustal rocks summary the shear wave splitting observed along almost all shear wave ray paths in the earth s crust is interpreted as the effects of stress aligned fluid filled cracks microcracks and preferentially oriented pore space once away from the free surface where open joints and fractures may lead to strong anisotropy of 10 per cent or greater intact ostensibly unfractured crustal rock exhibits a limited range of shear wave splitting from about 1 5 to 4 5 per cent differential shear wave velocity anisotropy interpreting this velocity anisotropy as normalized crack densities a factor of less than two in crack radius covers the range from the minimum 1 5 per cent anisotropy observed in intact rock to the 10 per cent observed in heavily cracked almost disaggregated near surface rocks this narrow range of crack dimensions and the pronounced effect on rock cohesion suggests that there is a state of fracture criticality at some level of anisotropy between 4 5 and 10 per cent marking the boundary between essentially intact and heavily fractured rock when the level of fracture criticality is exceeded cracking is so severe that there is a breakdown in shear strength the likelihood of progressive fracturing and the dispersal of pore fluids through enhanced permeability the range of normalized crack dimensions below fracture criticality is so small in intact rock that any modification to the crack geometry by even minor changes of conditions or minor deformation particularly in the presence of high pore fluid pressures may change rock from being essentially intact below fracture criticality to heavily fractured above fracture criticality this recognition of the essential compliance of most crustal rocks and its effect on shear wave splitting has implications for monitoring changes in any conditions affecting the rock mass these include monitoring changes in reservoir evolution during hydrocarbon production and enhanced oil recovery and in monitoring changes before and after earthquakes amongst others

an early mis 3 pluvial phase in southeast arabia climatic and archaeological implications climatic changes in arabia are of critical importance to our understanding of both monsoon variability and the dispersal of anatomically modern humans amh out of africa the timing of dispersal is associated with the occurrence of pluvial periods during marine isotope stage mis 5 ca 130 74 ka after which arid conditions between ca 74 and 10 5 ka are thought to have restricted further migration and range expansion within the arabian interior whilst a number of records indicate that this phase of aridity was punctuated by an increase in monsoon strength during mis 3 uncertainties regarding the precision of terrestrial records and suitability of marine archives as records of precipitation mean that the occurrence of this pluvial remains debated here we present evidence from a series of relict lake deposits within southeastern arabia which formed at the onset of mis 3 ca 61 58 ka at this time the incursion of monsoon rainfall into the arabian interior activated a network of channels associated with an alluvial fan system along the western flanks of the hajar mountains leading to lake formation multiproxy evidence indicates that precipitation increases intermittently recharged fluvial systems within the region leading to lake expansion in distal fan zones conversely decreased precipitation led to reduced channel flow lake contraction and a shift to saline conditions these findings are in contrast to the many other palaeoclimatic records from arabia which suggest that during mis 3 the latitudinal position of the monsoon was substantially further south and did not penetrate the peninsula additionally the occurrence of increased rainfall at this time challenges the notion that the climate of arabia following mis 5 was too harsh to permit the further range expansion of indigenous communities

ostracod calcite records the 18 o 16 o ratio of the bicarbonate and carbonate ions in water abstract the 18 o of ostracod valves is widely used to infer water 18 o and temperature however ostracod 18 o appears sensitive to other environmental variables in addition there is species dependent ostracod calcite 18 o enrichment relative to slowly precipitated inorganic calcite under the same conditions together these uncertainties complicate ostracod paleoclimate reconstructions this study presents a new understanding of the causes of ostracod 18 o variations based on a global database of published ostracod 18 o values in lake marine and coastal environments and from culture experiments the database includes associated field experiment host water parameters including temperature 1 to 32 c water 18 o 13 2 to 4 3 vsmow ph 6 9 10 4 salinity 0 72 g kg calcite saturation states 0 6 26 and dissolved inorganic carbon concentration dic 0 9 54 3 mmol kg the data show that 1 the 18 o of marine and non marine ostracods reflects the 18 o 16 o of the sum of host water co 3 2 and hco 3 ions for example at a given temperature the 18 o of non marine ostracods decreases by 4 to 6 as co 3 2 dic reaches 70 depending on the ostracod species in low co 3 2 dic settings i e high hco 3 co 3 2 ostracod 18 o 16 o is close to the 18 o 16 o of hco 3 ions which explains why on average ostracod 18 o is higher than the 18 o of inorganic calcite precipitated slowly under the same conditions 2 taxonomic offsets in ostracod 18 o vary with the host water co 3 2 dic in environments where hco 3 co 3 2 i e most freshwater lakes the 18 o 16 o of candonids is indistinguishable from the 18 o 16 o of hco 3 ions difference of 0 10 0 16 while the 18 o 16 o of cyprids is lower than the 18 o 16 o of hco 3 ions by 0 77 to 0 32 cytherids by 0 88 0 29 and limnocytherids by 1 12 0 05 3 the sensitivity of ostracod 18 o to co 3 2 dic also varies with taxonomy for each percent increase in co 3 2 dic candonids 18 o decreases by 0 098 0 024 cyprids by 0 075 0 004 cytherids by 0 057 0 012 and limnocytherids by 0 058 0 005 4 the similarity in 18 o 16 o between ostracod calcite and the sum of host water hco 3 and co 3 2 despite species specific offsets suggests rapid precipitation of a finite dic pool in the ostracod calcifying fluid we propose an ostracod 18 o model whereby the more negative the 18 o 16 o of a given species relative to the sum of co 3 2 and hco 3 the greater the isotopic equilibrium between the dic pool and h 2 o in the ostracod calcifying fluid 5 higher host water salinities and ph induce higher co 3 2 dic resulting in lower ostracod 18 o which explains the variable salinity and ph effects on ostracod 18 o our database and ostracod 18 o model shows that ostracod 18 o records from closed basin environments likely reflect high or variable co 3 2 dic rather than water temperature and 18 o alone our study reconciles contradictory observations of controls on ostracod 18 o and paves the way for improved paleo environmental interpretations and reconstructions of past water co 3 2 dic

lakes groundwater and palaeohydrology in the sahel of ne nigeria evidence from hydrogeochemistry the geochemistry of natural waters from rain soil the unsaturated zone shallow aquifers lakes and the stratified aquifer system of the chad basin sediments has been investigated to interpret modern hydrological processes and to reconstruct the palaeohydrology of ne nigeria a type region of the southern sahel recharge to the confined middle and lower aquifers recorded in ne nigeria occurred between 24 and 18 6 ka bp prior to the last glacial maximum the mean annual temperature at this time derived from dissolved noble gas ratios was at least 6 c cooler than at the present day this groundwater is not coupled to the active modern recharge cycle and was not reactivated during the holocene wet phases as elsewhere in the saharan region a reflection of changing lake levels and or of changing climatic regimes the absence of groundwater recharge at the time of the last glacial maximum supports other evidence for aridity at this time present day direct recharge rates in the manga grasslands are high mean 44 mm a 1 however regional recharge in ne nigeria at the present day is even higher 60 mm a 1 emphasizing the importance of infiltration from surface runoff as input to groundwater the present study confirms that the shallow aquifer in the region contains significant renewable groundwater resources however the confined aquifer of the chad basin clearly contains palaeowater and this declining artesian basin will need careful conservation prior to a return to traditional water use methods via improved management of the renewable waters in the shallow phreatic aquifers

6000 years of environmental changes recorded in blue lake south australia based on ostracod ecology and valve chemistry abstract a 4 m long core taken from the freshwater blue lake crater near the township of mount gambier in southeastern south australia provided a high resolution palaeoclimatic record for the last six millennia accelerator mass spectrometry ams radiocarbon 14 c dates were obtained from organic plant fibres and biogenic carbonates from the laminated sequence of the core and from a modern water sample large discrepancies between the radiocarbon ages determined from plant fibres and biogenic carbonates indicate the presence of a time variable lacustrine reservoir which is consistent with what is known of the lake s hydrology ostracod assemblages associated with stable isotope 13 c 18 o analyses and in combination with mg ca sr ca and na ca analyses done on ostracod valves infer salinity temperature and water level changes in blue lake over the last 6 millenia the influence of local aquifers through time has also been determined from the na ca of ostracod valves approximately 900 year cycles are evident in the 13 c record from 5 4 ka to 1 8 ka the history of blue lake records an initial period of high hydrological variability around 6 ka becoming increasingly deeper as groundwater flowed into the basin by 4 ka the lake had reached steady state with the lake level fluctuating by as much as 9 m although significant geochemical variations represent temperature fluctuations until european settlement near the lake in 1839

effects of stress on the two dimensional permeability tensor of natural fracture networks the effects of stress on the 2 d permeability tensor of natural fracture networks were studied using a numerical method universal distinct element code on the basis of three natural fracture networks sampled around dounreay scotland numerical modelling was carried out to examine the fluid flow in relation to the variations in burial depth differential stress and loading direction it was demonstrated that the permeability of all the networks decreased with depth due to the closure of aperture the permeability approached the minimum value at some depth below which little further variation occurred also differential stress had a significant effect on both the magnitude and direction of permeability the permeability generally decreased with increasing major horizontal stress for a fixed minor horizontal stress but the various networks considered showed different behaviours a factor termed the average deviation angle of maximum permeability am was defined to describe quantitatively the deviation degree of the direction of the major permeability component from the applied major stress direction for networks whose behaviour is controlled by set s of systematic fractures am is significantly greater than zero whereas those comprised of non systematic fractures have am close to zero in general fractured rock masses especially those with one or more sets of systematic fractures cannot be treated as equivalent porous media specification of the geometry of the network is a necessary but not sufficient condition for models of fluid flow knowledge of the in situ stress and the deformation it induces is necessary to predict the behaviour of the rock mass

a sediment based reconstruction of caribbean effective precipitation during the little ice age from freshwater pond barbuda contemporary climate dynamics of the circum caribbean region are characterised by significant precipitation variability on interannual and interdecadal timescales controlled primarily by el nino southern oscillation enso and the atlantic multidecadal oscillation amo however our understanding of pre industrial climate variability in the region is hampered by the sparse geographic distribution of palaeoclimate archives here we present a high resolution reconstruction of effective precipitation for barbuda since the mid 16th century based on biostratigraphic and stable isotope analyses of fossil ostracods and gastropods recovered from lake sediment cores from freshwater pond the only freshwater lake on the island we interpret episodic fluctuations in shell accumulation in the sediment record to represent changes in the balance between precipitation and evaporation during the little ice age lia 1400 1850 ce and industrial 1850 present periods comparisons between indices of reconstructed enso and amo variability the abundance of the freshwater gastropod pyrgophorus parvulus and the 18o records from ostracod calcite suggest that the relative influence of enso and amo on long term rainfall patterns in barbuda has changed over the last 400 years our findings are in agreement with other high resolution palaeoclimate studies that suggest that long term changes in effective precipitation during the lia were much more variable temporally and spatially than previously suggested