the vadose flow above soreq cave israel a tritium study of the cave waters abstract 32 tritium analyses were performed on 13 different water sources within soreq cave israel eight of the water sources were analyzed once each and the other five between 3 and 6 times each on samples collected between 1990 and 2000 the results were compared with similar analyses of a 1981 82 collection and with the tritium concentrations of the annual rainfall from 1952 to 1998 the tritium in several of the cave waters was so high up to 110 tu that they must have originated mainly in the peak tritium rain year 1964 most of the other cave waters had tritium concentrations which though somewhat lower must have originated largely from rain that fell between 1962 and 1966 the consequences of these tritium observations are that 1 it generally takes 26 36 years for rainwater to percolate from ground surface to soreq cave ceiling and 2 the type of flow undergone during this percolation is in several cases very similar to piston flow hence the annual packets of rainfall reach the cave without undergoing much mixing with either earlier or later rains in about one third of the cases tritium was too low to determine the percolation time finally the time variations of the tritium concentrations in specific cave water sources seem to indicate that the conduits which bring water to these sources may have undergone physical changes which affect the amount of time it took for rain to reach the cave ceiling

origin and morphology of limestone caves limestone caves form along ground water paths of greatest discharge and solutional aggressiveness flow routes that acquire increasing discharge accelerate in growth while others languish with negligible growth as discharge increases a maximum rate of wall retreat is approached typically about 0 01 0 1 cm yr determined by chemical kinetics but nearly unaffected by further increase in discharge the time required to reach the maximum rate is nearly independent of kinetics and varies directly with flow distance and temperature and inversely with initial fracture width discharge gradient and pco2 most caves require 104 105 yr to reach traversable size their patterns depend on the mode of ground water recharge sinkhole recharge forms branching caves with tributaries that join downstream as higher order passages maze caves form where 1 steep gradients and great undersaturation allow many alternate paths to enlarge at similar rates or 2 discharge or renewal of undersaturation is uniform along many alternate routes flood water can form angular networks in fractured rock anastomotic mazes along low angle partings or sponge work where intergranular pores are dominant diffuse recharge also forms networks and spongework often aided by mixing of chemically different waters ramiform caves with sequential outward branches are formed mainly by rising thermal or h2s rich water dissolution rates in cooling water increase with discharge co2 content temperature and thermal gradient but only at thermal gradients of more than 0 01 c m can normal ground water co2 form caves without the aid of hypogenic acids or mixing artesian flow has no inherent tendency to form maze caves geologic structure and stratigraphy influence cave orientation and extent but alone they do not determine branch work versus maze character

seismic site classifications for the st louis urban area abstract regional national earthquake hazards reduction program nehrp soil class maps have become important input parameters for seismic site characterization and hazard studies the broad range of shallow shear wave velocity v s 30 the average shear wave velocity in the upper 30 m measurements in the st louis area results in significant uncertainties between the actual spot values and the averaged values used to assign nehrp soil classes for regional seismic hazard studies in the preparation of an nehrp site classification map of the st louis urban area we analyzed 92 shear wave velocity v s measurements supplemented by 1400 standard penetration test spt profiles in areas bereft of v s measurements spt blow counts correlated to v s values based on the published correlations the data were then compiled for respective surficial geologic units and bedrock type these data suggest that the reciprocal of v s 30 exhibits a fairly linear relationship with depth to bedrock likely because v s 30 is a function of the thickness of surficial materials exhibiting relatively low v s values the v s 30 values were interpolated by summing the regressed v s 30 on the depth to bedrock and kriged values of the regression residuals the resulting nehrp site classification maps predict that upland areas of the st louis area are spatially classified as soil site classes s b to s d while the low lying floodplains are consistently classified as s d to s f

sr isotope study of vein and cave calcites from southern israel abstract the strontium isotope compositions of secondary calcites from the negev southern israel were compared to those of the marine carbonate host rocks which range in age from triassic to eocene in order to understand fluid source and migration through fracture systems in dominantly carbonate strata the sr isotopes of these calcite clusters are divided into two groups 1 calcites with 87 sr 86 sr values greater than those of the host carbonates and 2 calcites with 87 sr 86 sr values close to the values of the host carbonate 1 1 these secondary calcites were found on the main tectonic lines of the negev faults and fold axes and are enriched in 87sr 87 sr 86 sr 0 707709 0 709151 relative to the marine carbonate country rocks 87 sr 86 sr 0 707251 0 70755 with one exception these calcites are associated or crossed by thin veins filled by fe and mn oxides 2 2 secondary calcites with 87 sr 86 sr values close to those of the marine carbonate country rocks 0 7073 0 7077 are found in karstic caves and veins and are located in sites which are not on the major faults and fold axes these calcites are not crossed by fe and mn oxides the isotopic results indicate that the solutions from which the secondary minerals of the first group precipitated were not in isotopic equilibrium with the marine host rocks the possible source of the precipitating solutions can be either surface rain descending through the fault system or ascending groundwaters from the deep nubian aquifer paleozoic to early cretaceous in age in both cases there would be a limited interaction with the host sandstone rock which usually is depleted in sr the similarity of the 87 sr 86 sr values to those of the host rocks in the second group suggests that the main source of sr in these calcite crystals was from the dissolution of the marine carbonate country rocks by rain and flood waters

environmental controls of speleothem mineralogy in a karstic dolomitic terrain soreq cave israel pleistocene speleothems of the soreq cave beth shemesh israel situated within karstic cretaceous dolomitic rocks consist of two major mineralogical types 1 monomineralic low magnesium calcite lmc 0 5 and 7 5 mol mgco 3 straw stalactites stalagmites helictites and pool deposits 2 mineralogically heterogeneous deposits in the form of conical stalactites flowstones and cave corals produced from thin flowing solution films or sprays in which lmc alternates with high magnesium calcite hmc 13 to 33 mol mgco 3 dolomite 33 50 mol mgco 3 and lmc laminations a unique feature of the type 2 is the continuous 0 50 mol range of mgco 3 sem and delta 18 o studies show that all calcites and dolomites grew by direct precipitation from local groundwater solutions lmc formation represents equilibrium precipitation from dripping water solution with mg ca 2 whereas hmc and dolomite precipitation occurred from solution films enriched in mg as the result of prior clos

modern stable isotopic δ18o δ2h δ13c variation in terrestrial fluvial estuarine and marine waters from north central sarawak malaysian borneo stable isotope data on humid tropical hydrology are scarce and at present no such data exist for borneo delta18o 2h and 13c were analysed on 22 water samples from different parts of the sungai river niah basin rain cave drip rainforest pool tributary stream river estuary sea in north central sarawak malaysian borneo this was done to improve understanding of the modern stable isotope systematics of the sungai niah basin essential for the palaeoenvironmental interpretation of the late quaternary stable isotope proxies preserved in the great cave of niah the niah hydrology data are put into a regional context using the meteoric water line for southeast asia as derived from international atomic energy agency world meteorological organization isotopes in precipitation network data although the niah hydrological data set is relatively small spatial isotopic variability was found for the different subenvironments of the sungai niah basin a progressive enrichment occurs towards the south china sea 18o 4 6 2h 29 3 13c 4 8 from the tributary stream 18o 8 4 2h 54 7 13c 14 5 to up river 18o c 8 2h c 51 13c c 12 and down river values 18o c 7 5 2h c 45 13c c 11 this is thought to reflect differential evaporation and mixing of different components of the water cycle and a combination of depleted biogenic 13c plant respiration and decay with enriched 13c values due to photosynthesis atmospheric exchange mixing with limestone and marine waters downstream cave drip waters are relatively enriched in 13c as compared to the surface waters this may indicate rapid degassing of the cave drips as they enter the cave atmosphere copyright 2005 john wiley sons ltd

karst aquifer evolution in fractured porous rocks the evolution of flow in a fractured porous karst aquifer is studied by means of the finite element method on a two dimensional mesh of irregularly spaced nodal points flow within the karst aquifer is driven by surface recharge from the entire region simulating a precipitation pattern and is directed toward an entrenched river as a base level during the early phase of karstification both the permeable rock matrix modeled as triangular elements and fractures within the rock matrix modeled as linear elements carry the flow as the fractures are enlarged with time by chemical dissolution within the system calcite carbon dioxide water flow becomes more confined to the fractures this selective enlargement of fractures increases the fracture conductivity by several orders of magnitude during the early phase of karstification thus flow characteristics change from more homogeneous pore controlled flow to strongly heterogeneous fracture controlled flow we study several scenarios for pure limestone aquifers mixed sandstone limestone aquifers and various surface recharge conditions as well as the effect of faulting on the aquifer evolution our results are sensitive to initial fracture width faulting of the region and recharge rate

the role of the subcutaneous zone in karst hydrology abstract the subcutaneous zone is the upper weathered layer of rock beneath the soil but above the permanently saturated phreatic zone it is of particular hydrological importance in karst because of its high secondary permeability arising from the considerable chemical solution in this zone however corrosional enlargement of fissures diminishes with depth thus permeability decreases in the same direction with the result that percolation is inhibited except down widened master joints and faults storage of water consequently occurs in this zone particularly after storms the upper surface of this suspended saturated layer in the subcutaneous zone is defined by a perched water table which slopes towards points of rapid vertical percolation the potential induces lateral water movement converging on the most permeable areas such as beneath dolines leakage from the subcutaneous store sustains slow percolation in the vadose zone cross correlation of rainfall with percolation rates in caves in new mexico u s a and new zealand reveal response lags of 2 14 weeks with no apparent relationship to depth below the surface other percolation sites show no correlation with rainfall interpreted as being a consequence of considerable friction in tight fissure networks the recognition of storage and rapid as well as very slow percolation from the subcutaneous zone requires re interpretation of the components of hydrographs from karst springs and of some conceptual models of karst aquifers the importance of subcutaneous storage in sustaining baseflow discharge at some sites must be recognised as must the contribution of subcutaneous water to flood hydrographs methods of estimating the volumes of subcutaneous and phreatic components of karst spring flood hydrographs are presented the paper concludes with a discussion of the significance of subcutaneous hydrologic processes for an understanding of karst geomorphology the desirability of explaining karst landform evolution in terms of hydrologic processes is stressed

speleothem evidence for changes in indian summer monsoon precipitation over the last 2300 years speleothems from a well ventilated dolomitic cave in the pokhara valley central nepal preserve a mineralogic record of indian summer monsoon variability over the past 2300 yr annually deposited aragonite layers formed between 2300 and 1500 yr b p indicating reduced monsoon precipitation and increased cave aridity whereas alternating calcite aragonite laminae deposited after 1500 yr b p record elevated summer monsoon precipitation and increased cave humidity dense optically clear calcite layers deposited from 450 5 to 360 20 yr b p 1550 to 1640 a d indicate a less evaporative cave environment and suggest moister and or cooler conditions possibly related to climatic change associated with the onset of the little ice age

uranium series dating of the draining of an aquifer the example of wind cave black hills south dakota wind cave south dakota is a three dimensional rectilinear maze cave developed in 90 m of mississippian limestone and dolomite that is overlain by thick clastic cover strata beneath an area of 1 8 km 2 87 km of small drained phreatic passages are known exploration terminates at a water table 160 m below the highest parts of the cave as the cave was draining calcite precipitated from its waters uranium series measurements 85 were taken on fragments of broken calcite crusts collected in the lower 93 m of the cave the measurements reveal that it has been draining as a backwater for at least the past 300 000 yr 234 u 238 u ratios in the water were remarkably constant allowing estimation of ages beyond 400 ky b p after deducting glacial interglacial cyclic oscillations of 10 to 20 m amplitude the water table appears to have been lowered at a steady rate of 0 4 m per 10 3 yr since 400 ky b p most of this fall is attributed to the increase of hydraulic conductivity in the 260 m of cover strata that separates the carbonate aquifer from its spring discharge points a subaqueous calcite deposition zone extended to 70 m below the contemporary water table at all times where mean rates of deposition were 0 12 mm per 10 3 yr or less modeling of the precipitation kinetics suggests a well mixed water body with a ca 2 concentration close to the thermodynamic equilibrium value and variations of depositional rate being controlled by hydrostatic pressure

geologic conditions underlying the 2005 17th street canal levee failure in new orleans a careful program of subsurface sampling and cone penetration test soundings was employed to characterize the geologic conditions beneath the failed portion of the 17th street canal levee in new orleans where a 150 m long section of the levee and floodwall translated up to 16 m when flood waters rose to 1 2 m of the wall s crest on august 29 2005 during hurricane katrina the subsurface conditions are characterized by discrete layers of fill placed upon the historic cypress swamp which is underlain by a deeper prehistoric cypress swamp these swamp deposits were consolidated beneath the levee and in the area of the 2005 failure the swamp materials infilled a natural depression believed to be an old slough which dipped below the sheetpile tips for a distance of about 50 m which corresponds to where the breach appears to have initiated detailed examination of the recovered soils suggest that recent hurricanes periodically inundated the swamps with saline and or brackish water which cause a mass

environmental significance and hydrochemical processes at a cold alpine basin in the qilian mountains isotope geochemistry of precipitation river water well water and spring water in the babao river basin china during different seasons showed that regional runoff was dominated by precipitation in summer and autumn and by underground water in winter and spring the 18o and d values of precipitation and spring water displayed a clear altitude effect water from the main stream and tributaries displayed a converse altitude effect in the summer wet season the isotopic composition of the various water sources was not well correlated with elevation during the winter dry season the spatial distribution of the stable isotope signals of river water demonstrated the influence of rainfall inputs evaporation and variable flow an end member mixing model used for hydrograph separation indicated that in the summer wet season the babao river water was recharged by precipitation 71 9 spring water 11 7 and well water 16 4 whereas the winter dry season recharge was sourced from spring water 28 2 and well water 71 8

hydrogeochemical and climatic interpretations of isotopic signals from precipitation to drip waters in liangfeng cave guizhou province china oxygen isotope is a commonly used proxy for paleoclimatic studies on stalagmites in order to understand the transmission of isotopic signals from precipitation to stalagmites meteorological indexes of exterior and interior cave and hydrogeochemical proxies of drip waters in liangfeng cave have been monitored from april 2011 to april 2013 samples of rain and drip waters from three drip sites designated as 1 5 and 6 are collected for hydrogen and oxygen isotopes testing results show that the amount weighted mean 18o value of rain in the first year may 9 2011 to may 1 2012 is lighter than that in the second may 30 2012 to may 2 2013 this may result from different proportions of the pacific indian ocean source moistures the arithmetic mean 18o values of 1 5 and 6 are similar to the multi year amount weighted mean 18o value of precipitation hydrogeochemical analyses of drip waters reveal that the discharge rates increase in the order of 6 1 5 and that water rock reaction fresh old water mixing and co2 degassing exert dominant controls on seepage waters in aquifers hard infiltration of rain during dry season with heavier 18o value due to its small amount may cause lower mean drip water 18o values e g 1 evaporation during the dripping and exuding processes in dry season may result in heavier mean drip water 18o values e g 6 considering calcite depositing mostly during dry season we compare the mean 18o values of drip waters during dry season between the first and second years differences exist and share the same trend with rain the results indicate that drip waters can inherit oxygen isotopic signals of rain but it is critical to have a replication test on 18o records of stalagmites from the same cave for paleoclimatic studies what s more 18o values in stalagmites feeding by drip waters that have no little annual 18o variations may be useful to paleotemperature reconstructions

age distribution estimation for karst groundwater issues of parameterization and complexity in inverse modeling by convolution summary convolution modeling is useful for investigating the temporal distribution of groundwater age based on environmental tracers the framework of a quasi transient convolution model that is applicable to twodomain flow in karst aquifers is presented the model was designed to provide an acceptable level of statistical confidence in parameter estimates when only chlorofluorocarbon cfc and tritium 3 h data are available we show how inverse modeling and uncertainty assessment can be used to constrain model parameterization to a level warranted by available data while allowing major aspects of the flow system to be examined as an example the model was applied to water from a pumped well open to the madison aquifer in central usa with input functions of cfc 11 cfc 12 cfc 113 and 3 h and was calibrated to several samples collected during a 16 year period a bimodal age distribution was modeled to represent quick and slow flow less than 50 years old the effects of pumping and hydraulic head on the relative volumetric fractions of these domains were found to be influential factors for transient flow quick flow and slow flow were estimated to be distributed mainly within the age ranges of 0 2 and 26 41 years respectively the fraction of long term flow 50 years was estimated but was not dateable the different tracers had different degrees of influence on parameter estimation and uncertainty assessments where

inverse modeling of the hydrological and the hydrochemical behavior of hydrosystems characterization of karst system functioning inverse modeling of mass transfer characterizes the dynamic processes affecting the function of karst systems and can be used to identify karst properties an inverse model is proposed to calculate unit hydrographs as well as impulse response of fluxes from rainfall runoff or rainfall flux data the purpose of which is hydrograph separation contrary to what hydrologists have been doing for years hydrograph separation is carried out by using transfer functions in their entirety which enables accurate separation of fluxes as was explained in the companion paper pinault et al this issue the unit hydrograph as well as impulse response of fluxes is decomposed into a quick and a slow component and consequently the effective rainfall is decomposed into two parts one contributing to the quick flow or flux and the other contributing to the slow flow generation this approach is applied to seven french karstic aquifers located on the larzac plateau in the grands causses area in the south of france both hydrodynamical and hydrogeochemical data have been recorded from these springs over several hydrological cycles for modeling purposes karst properties can be represented by the impulse responses of flow and flux of dissolved species the heterogeneity of aquifers is translated to time modulated flow and transport at the outlet monitoring these fluxes enables the evaluation of slow and quick components in the hydrograph the quick component refers to the flush flow effect and results from fast infiltration in the karst conduit network when connection is established between the infiltration and phreatic zones inducing an increase in water head this component reflects flood events where flow behavior is nonlinear and is described by a very short transfer function which increases and decreases according to water head the slow component consists of slow and fast infiltration underground runoff storage in annex to drain systems and discharge from the saturated zone these components can be further subdivided by measuring chemical responses at the karst outlet using such natural tracers enables the slow component of the unit hydrograph to be separated into preevent water i e water of the reservoir and event water i e water whose origin can be related to a particular rainfall event these measurements can be used to determine the rate of water renewal since the preevent water hydrograph is produced by stored water when pushed by a rainfall event and the event water hydrograph reflects rainwater transfer separating the two components can yield insights into the characteristics of karst aquifers the modes of infiltration and the mechanisms involved in karstification as well as the degree of organization of the aquifer

applying terzaghi s method of slope characterization to the recognition of holocene land slippage abstract during site investigations engineering geologists are expected to recognize landslides both active and dormant those without substantial experience evaluating the evolution of geomorphic features associated with localized mass wasting often mischaracterize site conditions karl terzaghi suggested seven steps in characterizing natural hillslopes including 1 a literature review 2 site reconnaissance 3 a program of subsurface exploration 4 preparation of sketches and diagrams illustrating the essential features 5 preparation of a preliminary geology report 6 observation and mapping of geologic structures exposed during excavation for construction and 7 development of contingency plans for anticipated variations in old landslide features based on our interpretation of terzaghi s original principles we review some of the most common interpretive problems with nomenclature of landslide features describe common mistakes in characterizing old landslides and present technical approaches that often aid in the recognition of old landslide features a wide variance in geological terms exists for describing landslides and various terms have been applied to the same features by workers in different areas which often leads to confusion some of these terms include nomenclature such as slip surfaces alluvial fans colluvium and slope creep active surficial landslides are relatively easy to recognize when they are well exposed although these features tend to become obscured with time anomalous hummocky topography often provide key recognition features of a slope s geomorphic evolution deeper seated bedrock landslides can be more difficult to recognize because their features become increasingly mollified with time these features can often be identified by anomalous geomorphic features such as isolated saddles or anomalous discontinuous benches these features are some of the best locations to excavate borings or exploratory trenches well placed trenches across headscarp grabens can provide more detailed structure of old landslides and are usually a cost effective approach additional subsurface exploration can often be employed to characterize landslides small diameter borings are usually employed for geotechnical investigations but can easily be applied to landslides depending on the mean particle size diameter d50 downhole logging of large diameter holes is the best method to evaluate complex subsurface conditions such as dormant bedrock landslides

multimodal internal waves generated over a subcritical ridge impact of the upper ocean stratification abstractinteraction of barotropic tides with subsurface topography is vital to ocean mixing yet the behavior of large amplitude nonlinear internal solitary waves isws that can cause strong mixing remains poorly understood especially that of higher mode and multimodal internal waves therefore a 2 5 dimensional nonhydrostatic model with adjustable vertical resolution was developed to investigate effects of upper ocean stratification on tidally induced multimodal internal waves and to show how they are generated by the subcritical ridge where only upward propagating internal wave beams iwbs are present the effects of the stratification on properties and characteristics of the excited iwbs and on the energy partition of the radiated mode 1 and mode 2 internal waves were investigated based on the model results higher modes of internal waves can also be effectively generated in the iwbs by the subcritical topography and the contribution to iwbs from higher modes increases with the upper ocean stra

continental oxygen isotopic record of the last 170 000 years in jerusalem abstract a long radiometrically dated oxygen isotopic record of continental climatic variations since the penultimate glaciation was obtained from a stalagmite deposited in a sealed cave in jerusalem this record shows that speleothems have the potential of assigning dates to long and short term climatic events with possible refining of milankovitch tuning of ice and marine records which themselves are not datable short term 1000 yr events are very significant in the region reaching 50 of glacial interglacial fluctuations the mediterranean sea was the most probable source of local precipitation throughout the last glacial cycle

infiltration processes and flow rates in developed karst vadose zone using tracers in cave drips the purpose of this research was to identify groundwater recharge mechanisms and measure flow velocities through the epikarst and the vadose zone in a typical site of mediterranean carbonate karst in natural rain conditions by avoiding artificial flushing more realistic travel times could be measured and the effective resultant vadose flow velocity could be inferred additionally detailed monitoring enabled better description and quantification of infiltration and percolation processes nine different cave drips were monitored and sampled for three hydrological years in fractured karst lithology on mount carmel israel at three drips discharge was measured continuously by tipping buckets rainfall and soil water content were recorded above the cave an artificial tracer experiment was conducted using uranine placed in a joint and at the soil rock interface at soil pockets both 27 m above the cave four hydrological types of drips post storm seasonal perennial and overflow were identified each demonstrating different characteristics in terms of discharge and chemistry the maximum effective flow velocities uranine dye arrival times were 41 76 cm h tracer mass flux was computed from the uranine breakthrough curves and drip hydrographs the dominant flow velocities derived from the peak of tracer mass flux were 0 35 0 41 cm h from post storm drips and 22 24 cm h from the other drips pulse through intra event piston flow was indicated by the time lags between the increase in drip rate and the time of drop in salinity and appearance of the tracer in most of the measured drips chloride concentrations were used to distinguish between old matrix water and preferential flow water in the perennial drips demonstrating a two component mixing model in 2005 2006 preferential flow water reached up to 20 25 from annual discharge of these drips this study promoted a method to compute dominant effective flow rates in the vadose zone in natural rain conditions copyright 2010 john wiley sons ltd

monitoring bunker cave nw germany a prerequisite to interpret geochemical proxy data of speleothems from this site summary monitoring cave environments is important to understand processes in karst systems if stalagmites from a specific cave are used as archives of past climate variability a quantitative understanding of the soil karst speleothem system is crucial the monitoring program performed in bunker cave nw germany which includes monthly collection of climatological data as well as air and water samples from the cave and the overlying soil since 2006 is a prerequisite for the interpretation of speleothem data from the cave in terms of climate variability the results show that bunker cave is a homogeneously ventilated cave with rather low pco2 values of 580 1200 ppmv which lacks strong seasonal variations the 18o value of cave drip water reflects the mean annual composition of the rain water and the seasonal variability is strongly attenuated indicating a well mixed karst aquifer hence stalagmites from bunker cave should be well suited to record interannual decadal climate trends seven drip sites in two cave chambers show three different types of discharge behaviour including slow seasonal drip fast seasonal drip and seepage flow the drip rate patterns of most drip sites are consistent with the main infiltration events taking into account a delay of several months an instantaneous response to precipitation i e piston flow is not observed for any drip site indicating a specific water capacity threshold in the soil karst aquifer prior calcite precipitation pcp was also identified especially during times of low discharge though pcp is not as pronounced at bunker cave as in other caves it probably has an influence on the mg ca ratios of the stalagmites

timing the transport of water through the upper vadose zone in a karstic system above a cave in israel chemical and isotopic analysis of karst water dripping over a one year period from seeps in a cave above the cenomanian aquifer in the judea hills of israel lead to several conclusions i the tritium ages and the chemical composition of water from different seeps in a karstic cave vary greatly ii the reservoirs in the upper part of the vadose zone hold water for up to several decades iii some of the cave seeps are mixtures of the old and more recent meteoric water from paths of different length iv the history of storm events can only be traced in some of the seeps v for most dripping seeps there is no immediate response of seepage discharge to the rainfall intensity and quantity i e the seepage discharge is fairly constant

estimating the position and variability of buried bedrock surfaces in the st louis metro area abstract the precise position of bedrock surface is the most important variable for evaluating seismic site response the subsurface data suggest that the bedrock elevations in the st louis area are proportional to ground surface elevation and bedrock depths tend to thin in dissected loess covered uplands automated contour maps of the estimated bedrock depth or elevation are commonly constructed using geographical information systems gis that employ various interpolation algorithms in deeply incised terrain interpolation techniques often make erroneous predictions because they tend to under or overestimate surfaces influenced by paleolandscapes such as incised channels that are subsequently filled or by employing single contour models across areas of differing geomorphic settings this paper compares two different models for estimating dissected and or eroded bedrock surfaces beneath the greater st louis area which varies with the geomorphic setting these models include 1 the depth to bedrock derived from ordinary kriging and 2 bedrock elevations derived from cokriging cross sections derived from the gis programs suggest that the estimated depth to bedrock tend to simplify the actual situations because they assume near constant thickness between data points ignoring natural undulations caused by previous erosion these simplified surfaces of depth to bedrock were adjusted by considering data which does not pierce the bedrock interface the estimated bedrock elevation does not conform to local topographic variations in rugged hilly terrain and tends to over smooth the natural undulations caused by stream incision in rugged deeply incised terrain the interpolation of bedrock depths yields more realistic estimates of the buried bedrock surface than those derived from bedrock elevations in the major holocene floodplains we developed a technique employing complex curve fitting of channel cross sections to produce more realistic estimations of the spatial variability of depth to bedrock within the deeply incised channels

reflecting tidal wave beams and local generation of solitary waves in the ocean thermocline it is generally accepted that ocean internal solitary waves can arise from the interaction of the barotropic tide with the continental shelf which generates an internal tide that in turn steepens and forms solitary waves as it propagates shorewards some field observations however reveal large amplitude internal solitary waves in deep water hundreds of kilometres away from the continental shelf suggesting an alternative generation mechanism tidal flow over steep topography forces a propagating beam of internal tidal wave energy which impacts the thermocline at a considerable distance from the forcing site and gives rise to internal solitary waves there motivated by this possibility a simple nonlinear long wave model is proposed for the interaction of a tidal wave beam with the thermocline and the ensuing local generation of solitary waves the thermocline is modelled as a density jump across the interface of a shallow homogeneous fluid layer on top of a deep uniformly stratified fluid and a finite amplitude propagating internal wave beam of tidal frequency in the lower fluid is assumed to be incident and reflected at the interface the induced weakly nonlinear long wave disturbance on the interface is governed in the far field by an integral differential equation which accounts for nonlinear and dispersive effects as well as energy loss owing to radiation into the lower fluid depending on the strength of the thermocline and the intensity of the incident beam nonlinear wave steepening can overcome radiation damping so a series of solitary waves may arise in the thermocline sample numerical solutions of the governing evolution equation suggest that this mechanism is quite robust for typical oceanic conditions

the hydrology of the jordan tributaries israel hydrographic and isotopic investigation abstract nahal dan nahal snir and nahal hermon are the three principal tributaries of the jordan river all three are spring fed and appear to derive their discharges from the same regional groundwater aquifer the behaviour of this aquifer is examined by hydrograph separation and multivariate time series analysis of discharge and rainfall records and by investigation of 18 o and tritium records hydrograph separation gives base flow recession constants of 11 20 months and in addition n snir and n hermon show an interflow recession of 1 month the dual reservoir system for these two tributaries is confirmed by time series analysis 18 o data distinguish the different catchments for the springs and support the idea that interflow occurs in the near surface part of the regional groundwater reservoir tritium data illustrate the inhomogeneity of the karstic reservoir assuming well mixed conditions the difference in behaviour between tritium records for rainfall and the tributaries is used to estimate the age distribution of water in the reservoir at any time 50 of the storage is less than 1 yr old and 90 is less than 3 yr old

model evaluation of the coherence of a common source water oxygen isotopic signal recorded by tree ring cellulose and speleothem calcite oxygen isotopic compositions 18o of tree rings and speleothems inherit 18o of precipitation 18oppt and are used to reconstruct past variations in the amount of precipitation or temperature integration of 18o records of both the proxies for a multiproxy climate reconstruction necessitates understanding of the extent to which the initial 18oppt is modified in both the proxies before getting preserved in them a forward modeling approach assuming both the proxies have access to a common source water 18o signal is employed to assess the expected maximum correlation between the 18o records of the two proxies on interannual time scale and the factors influencing the correlation variations in the leaf temperature relative humidity 18o of atmospheric water vapor introduce variations in 18o of tree ring cellulose while the variations in the cave temperature and oxygen isotopic equilibrium disequilibrium conditions between calcite and drip water influence 18o of speleothem calcite variation introduced by these factors in 18o of individual proxies as compared to the variation in 18oppt is crucial in deciding the correlation between 18o records of the two proxies when the former is higher than or comparable with the latter finding one to one correspondence between the 18o records of the two proxies could be challenging modeling exercise revealed a favorable climatic condition at jagdalpur 19 08 n 82 03 e a potential tropical location for tree ring and speleothem based climate reconstruction for inheriting a common source water 18o signal in both the proxies 18o records of tree ring and annually resolved speleothem from jagdalpur could be integrated for the multiproxy climate reconstruction

internal solitary waves in the mozambique channel observations and interpretation this paper presents new results showing that the sofala shelf in the mozambique channel 20 s 36 e is a previously unknown hot spot for the generation of internal tides and internal waves we investigate available envisat advanced synthetic aperture radar imagery of the region which is capable of showing the surface signatures of the internal waves this is complemented by modeling of the ray pathways of internal tidal energy propagation and of the p g baines 1982 barotropic body force which drives the generation of internal tides near the shelf break the hot spot region is localized between 20 and 21 s because of the particular nature of the bathymetry there farther north and south the forcing is reduced and insufficient to generate internal solitary waves in the synthetic aperture radar images the analysis reveals two distinct types of internal wave trains that are observed traveling oceanward away from the shelf break and we suggest that these result from direct generation at the shelf break and from local generation at about 80 km from the shelf break respectively because of the surfacing of internal tidal rays at the thermocline finally we have investigated seasonal differences in the wave patterns which penetrate more extensively into the channel during the southern summer and appear slightly farther to the south during the southern winter we also conclude that the local generation process is more likely to occur during the winter when the stratification is reduced

a review of conventional techniques for subsurface characterization of landslides naturally occurring landslides can be difficult to characterize and often exhibit anomalies in controlling geometry and consistency the characterization of landslides in engineering geology practice is usually based on program of subsurface exploration focused on identifying subsurface materials structure and stratigraphy hydrologic conditions and appropriate strength parameters on native slopes bereft of anthropogenic modification excavation geomorphic evidence of previous movement and its relative depth and scale are often discernible to the experienced eye this paper seeks to describe the various techniques that have been successfully employed in site specific subsurface investigations of prehistoric landslides these include considerations of limiting geometry for planning subsurface exploration and sampling overcoming problems with site access exploratory trenches small diameter borings downhole logging of large diameter borings and geophysical techniques these procedures can be combined to develop more realistic cross sections along the vector of maximum landslide movement so the displaced mass can be realistically analyzed the respective advantages and disadvantages of these techniques are discussed with baseline references on subsurface exploration

internal wave reflection on shelf slopes with depth varying stratification abstractreflection of internal waves from sloping topography is simple to predict for uniform stratification and linear slope gradients however depth varying stratification presents the complication that regions of the slope may be subcritical and other regions supercritical here a numerical model is used to simulate a mode 1 m2 internal tide approaching a shelf slope with both uniform and depth varying stratifications the fractions of incident internal wave energy reflected back offshore and transmitted onto the shelf are diagnosed by calculating the energy flux at the base of slope with and without topography and at the shelf break for the stratifications topographies considered in this study the fraction of energy reflected for a given slope criticality is similar for both uniform and depth varying stratifications this suggests the fraction reflected is dependent only on maximum slope criticality and independent of the depth of the pycnocline the majority of the reflected energy flux is in

use of longitudinal strain in identifying driving and resisting elements of landslides observations of deformation at the surfaces of landslides in utah and hawaii indicate that the upslope parts of the land slides have stretched and the downslope parts have shortened parallel with the direction of movement the maximum displacement of each landslide occurs in a relatively undeformed zone between the zones of shortening and stretching the pattern of deformation at the surface of these landslides may be useful in analyzing their mechanics by helping to constrain the longitudinal forces in limit equilibrium stability analysis we used earth pressure calculations to determine the range of possible longitudinal forces per unit width for active failure in the zone of stretching and for passive failure in the zone of shortening of one of the hawaiian landslides longitudinal forces computed by stability analysis assuming homogeneous strength exceeded the possible forces in much of the upslope half of the landslide consequently we assumed inhomogeneous strength and adjusted shear strength parameters at each segment of the slip surface until the longitudinal forces computed by stability analysis agreed with those computed by earth pressure theory and the factor of safety approached unity the distribution of longitudinal forces computed for inhomogeneous strength indicated that the boundary between driving and resisting elements of the landslide is near the thickest part of the slide in agreement with a simple formula for the location of the boundary

hydrochemical and hydrological processes in the different landscape zones of alpine cold region in china investigation of water sources and flow pathways is crucial to understand and evaluate the characteristics of surface water and groundwater systems this article aims to identify the hydrochemical and hydrological processes in different landscape zones based on hydrochemical analyses of various samples including samples from glacier snow frozen soil meltwater surface water groundwater and precipitation in the alpine cold region of china hydrochemical tracers indicated that chemical compositions are characterized by the ca hco3 type in the glacier snow zone the mg ca so4 type in the alpine cold desert zone the ca hco3 so4 type in the marsh meadow zone the ca mg hco3 type in the alpine shrub zone and the ca na so4 type in the mountain grassland zone an end member mixing model was used for hydrograph separation the results showed that the mafengou river in the wet season was recharged by groundwater in the alpine cold desert and alpine shrub zones 67 surface runoff in the glacier snow zone 11 surface runoff in the alpine cold desert zone 8 thawed water from frozen soil in the marsh meadow and mountain grassland zones 9 and direct precipitation on the river channel 5 this study suggests that precipitation from the whole catchment yielded little direct surface runoff precipitation was mostly transformed into groundwater or interflow and was then concentrated into the river channel this study provides a scientific basis for evaluation and management of water resources in the basin

mapping earthflows and earthflow complexes using topographic indicators abstract practical methods of mapping earthflows and earthflow complexes using topographic recognition keys are briefly profiled in this article these methods can be employed to tentatively identify earthflow features that may not be recognized on stereopair aerial photographs because of vegetation mollification of the features with age and or unfavorable sun angle on the images conventional usgs 7 5 min topographic maps 1 24 000 scale with contour intervals of 20 ft 6 1 m are not generally useful in identifying earthflows with much less than 18 to 60 m of vertical relief useful recognition keys for the topographic expression of earthflows are presented these keys include divergent contours along a slope fall line with headward cutting upslope and depositional fans downslope fans tend to widen and deepen downslope earthflows in first and second order watersheds may exhibit more dissection of their toe lobes than those in zero order basins earthflows commonly occur in large coalescing complexes with one event or lobe superceding another this forms a series of superposed lobes with the most recent lobes being easiest to discern while older lobes are increasingly mollified with time the soft cohesive clay and silt debris deposited by earthflows is most easily eroded in the headscarp area and compacted naturally in the depositional lobe this makes the recognition of earthflows increasingly difficult with age earthflow debris is often interpreted to be colluvium when deposited on slopes without appreciable shearing to form slickensided contacts discernment of earthflows using topographic recognition techniques depends on the scale and quality of the topographic maps being evaluated

carbonate geochemistry of vadose water recharging limestone aquifers abstract thrailkill j and robl t l 1981 carbonate geochemistry of vadose water recharging limestone aquifers in w back and r letolle guest editors symposium on geochemistry of groundwater 26th international geological congress j hydrol 54 195ndash 208 vadose water from lower carboniferous rocks in kentucky u s a was analyzed monthly in mammoth cave and in the caves and overlying soil at two other caves calcite saturation and equilibrium co 2 pressures of water were calculated after correcting for ion pairing and activity coefficients soil gas co 2 concentrations were determined directly both small flows of water which were usually depositing speleothems vadose seepages and larger flows vadose flows were studied some of the vadose seeps were often undersaturated with respect to calcite and showed little variation in ca content cv ca 7 while others were supersaturated and showed positive correlations between ca and soil co 2 or between ca and discharge at least some of the vadose seepages were believed to have been closed to co 2 introduction after leaving the soil zone in the soil co 2 varied with soil type moisture and season ca increased with depth but saturation with respect to calcite was not reached three types of vadose water may thus reach the aquifer undersaturated with respect to calcite 1 vadose flows which transit the vadose zone rapidly 2 low ca vadose seepage which is closed to co 2 as it transits the vadose zone and which may remain undersaturated with respect to calcite even after ventilation and 3 high ca vadose seepage which leaves the soil zone slightly undersaturated probably because of insufficient residence time

linear model describing three components of flow in karst aquifers using 18o data the stable isotope of oxygen 18o is used as a naturally occurring ground water tracer time series data for 18o are analyzed to model the distinct responses and relative proportions of the conduit intermediate and diffuse flow components in karst aquifers this analysis also describes mathematically the dynamics of the transient fluid interchange between conduits and diffusive networks conduit and intermediate flow are described by linear systems methods whereas diffuse flow is described by mass balance methods an automated optimization process estimates parameters of lognormal pearson type iii and gamma distributions which are used as transfer functions in linear systems analysis diffuse flow and mixing parameters also are estimated by these optimization methods results indicate the relative proximity of a well to a main conduit flowpath and can help to predict the movement and residence times of potential contaminants the three component linear model is applied to five wells which respond to changes in the isotopic composition of point recharge water from a sinking stream in the madison aquifer in the black hills of south dakota flow velocities as much as 540 m d and system memories of as much as 71 years are estimated by this method also the mean median and standard deviation of traveltimes time to peak response and the relative fraction of flow for each of the three components are determined for these wells this analysis infers that flow may branch apart and rejoin as a result of an anastomotic or channeled karst network

hydrological uncertainties in the modelling of cave drip water δ18o and the implications for stalagmite palaeoclimate reconstructions abstract in this paper we review our current understanding of karst drip water hydrology emphasising the extent of non linear and non stationary process dynamics that render stalagmite palaeoclimate reconstructions using a statistical pseudo proxy approach difficult to implement we outline an approach to attribute the uncertainty that arises specifically as a consequence of variable water routing through the overlying soil epikarst and karst aquifer this is based upon the development of a monthly lumped parameter karst hydrological model which we use to demonstrate the range of modelled drip water discharges possible from a single climate input refinement of the model to include precipitation 18 o enables us to determine the theoretical range in drip water and stalagmite 18 o for three sites with contrasting climates northern temperate nw scotland monsoonal ethiopia and mediterranean gibraltar for actual climate monthly mean temperature monthly total precipitation monthly mean precipitation 18 o we compare model simulations of karst groundwater storage and drip water 18 o to demonstrate our ability to model different climate regimes realistically we also investigate the 18 o variability associated with specific karst water reservoirs that differ in their capacity and drainage mechanisms 18 o variability is then compared to stalagmite 18 o record from the three regions for the last 45 years we conclude by reviewing the implications of our hydrological model for stalagmite 18 o quaternary palaeoclimate reconstructions over different timescales and sampling resolutions

an isotopic and modelling study of flow paths and storage in quaternary calcarenite sw australia implications for speleothem paleoclimate records abstract we investigated the distinctive shallow sub surface hydrology of the southwest western australia swwa dune calcarenite using observed rainfall and rainfall 18 o soil moisture cave drip rate and dripwater 18 o over a six year period august 2005 march 2012 a lumped parameter hydrological model is developed to describe water fluxes and drip 18 o comparison of observed data and model output allow us to assess the critical non climatic karst hydrological processes that modify the precipitation 18 o signal and discuss the implications for speleothem paleoclimate records from this cave and those with a similar karst setting our findings include evidence of multiple reservoirs characterised by distinct 18 o values and recharge responses low and high flow sites dripwaters exhibit 18 o variations in wet versus dry years at low flow sites receiving diffuse seepage from the epikarst with an attenuated isotopic composition that approximates mean rainfall recharge from high magnitude rain events is stored in a secondary reservoir which is associated with high flow dripwater that is 1 lower than our monitored low flow sites 18 o one drip site is characterised by mixed flow behaviour and exhibits a non linear threshold response after the cessation of drainage from a secondary reservoir following a record dry year 2006 additionally our results yield a better understanding of the vadose zone hydrology and dripwater characteristics in quaternary age dune limestones we show that flow to our monitored sites is dominated by diffuse flow with inferred transit times of less than one year diffuse flow appears to follow vertical preferential paths through the limestone reflecting differences in permeability and deep recharge into the host rock

hydrogen and oxygen isotopic records in monthly scales variations of hydrological characteristics in the different landscape zones of alpine cold regions monthly scale variations in stable isotopic composition in precipitation and various water bodies were analyzed in this study using data collected from a field station experimental observation was performed to analyze processes in the glacier snow zone alpine cold desert zone marsh meadow zone alpine shrub zone and mountain grassland zone based on the isotopic and hydrochemical analyses of glacier snow frozen soil groundwater and other water sources in the headwater catchment of the alpine cold region delta o 18 and delta d values of precipitation and various water bodies in mafengou river basin exhibited strong seasonal variations precipitation and various water bodies were rich in delta o 18 and delta d during the wet season and relatively negative in delta o 18 and delta d during the dry season the isotopic content of various water bodies in mafengou river basin was dependent on temperature elevation of the recharge area and amount of precipitation lower temperatures were typically associated with lower delta o 18 and delta d values and are believed to be mainly responsible for the seasonal patterns observed in the isotopic values of various water bodies in mafengou river basin in the alpine cold region seasonal variations were larger in streams where recent precipitation is the main source of the flow and smaller in streams where groundwater is the dominant source of water c 2013 published by elsevier b v

pleistocene paleoclimate of the arid region of israel as recorded in calcite deposits along regional transverse faults and in veins abstract the 18o and 13c values of the calcites associated with e w and ne sw transverse faults in the negev israel indicate that calcite was deposited from meteoric water a regional change in the 18o and 13c values was observed the 18o content in the calcite increases from the southwestern 18 o 17 8 to the northeastern 18 o 2 9 part of the region the 13c values show the opposite trend of the 13c content decrease from 2 in the south to 10 in the northeast these trends had to reflect changes in regional paleoclimate suggesting a change in the isotopic composition of the solution from which the calcite was deposited in different periods the variations in the 18o values reflect shifts in the 18o values of precipitation and are associated with a change in the source of moist air masses which came from the equatorial atlantic in the early pleistocene and from the mediterranean during a later period variations in 13c values reflect changes from humid to arid conditions two modes of calcite deposition are suggested 1 precipitation of calcite minerals in the unsaturated zone following the dissolution in the soil or 2 calcite deposition that occurred as co2 was lost during emergence of paleogroundwater from lower cretaceous and jurassic aquifers

climatic and environmental controls on speleothem oxygen isotope values variations in speleothem oxygen isotope values d 18 o result from a complicated interplay of environmental controls and processes in the ocean atmosphere soil zone epikarst and cave system as such the controls on speleothem d 18 o values are extremely complex an understanding of the processes that control equilibrium and kinetic fractionation of oxygen isotopes in water and carbonate species is essential for the proper interpretation of speleothem d 18 o as paleoclimate and paleoenvironmental proxies and is best complemented by study of site specific cave processes such as infiltration flow routing drip seasonality and saturation state and cave microclimate among others this review is a process based summary of the multiple controls on d 18 o in the atmosphere soil epikarst and speleothem calcite illustrated with case studies primary controls of d 18 o in the atmosphere include temperature and relative humidity through their role in the multiple isotope effects variability and modifications of water d 18 o values in the soil and epikarst zones are dominated by evaporation mixing and infiltration of source waters the isotopically effective recharge into a cave system consists of those waters that participate in precipitation of caco3 resulting in calcite deposition rates which may be biased to time periods with optimal dripwater saturation state recent modeling experimental and observational data yield insight into the significance of kinetic fractionation between dissolved carbonate phases and solid caco3 and have implications for the hendy test to assist interpretation of speleothem d 18 o time series quantitative and semi quantitative d 18 o climate calibrations are discussed with an emphasis on some of the difficulties inherent in using modern spatial and temporal isotope gradients to interpret speleothems as paleoclimate proxy records finally several case studies of globally significant speleothem paleoclimate records are discussed that show the utility of d 18 o to reconstruct past climate

climatic significance of seasonal trace element and stable isotope variations in a modern freshwater tufa abstract we present a continuous 14 yr long 1985 to 1999 high resolution record of trace element mg sr ba u and stable isotope 13c 18o variations in a modern freshwater tufa from northwestern queensland australia by utilizing the temperature dependence of the 18o signal an accurate chronology was developed for the sampled profile which allowed a comparison of the chemical records with hydrological and meteorological observations as a consequence it was possible to constrain the relevant geochemical processes relating climate variables such as temperature and precipitation to their chemical proxies in the tufa record temperatures calculated from the mg concentrations of the tufa samples provide close approximations of average annual water temperature variations furthermore we demonstrate that temporal changes in mg ca water can be estimated using an empirically derived equation relating mg ca water to the sr ba ratio measured in the tufa samples by means of this relationship it is theoretically possible to determine the mg ca ratio of paleowaters and hence to derive reliable estimates of former water temperatures from the mg concentrations of fossil tufas from the study area sympathetic variations in sr ba and 13c along the sampled profile record changes in water chemistry which are most probably caused by variable amounts of calcite precipitation within the vadose zone of the karst aquifer this process is thought to be markedly subdued whenever the amount of wet season precipitation exceeds a given threshold accordingly distinct minima in sr ba and 13c are interpreted to reflect years with above average rainfall the pronounced seasonal and annual variability of the u concentration along the profile is thought to primarily record changes in the u flux from the soil to the water table we suggest that during intensive rain events u is transported to the phreatic zone by complexing organic colloids giving rise to conspicuous u maxima in the tufa after above average wet seasons this study demonstrates the potential of freshwater tufas to provide valuable information on seasonal temperature and rainfall variations if tufa deposits turn out to be reasonably resistant to secondary processes combined investigation of speleothems and tufas from the same area could become a promising approach in future research while speleothems offer continuous records of long term paleoenvironmental changes tufas could provide high resolution time windows into selected periods of the past

hydrograph separation for karst watersheds using a two domain rainfall discharge model highly parameterized physically based models may be no more effective at simulating the relations between rainfall and outflow from karst watersheds than are simpler models here an antecedent rainfall and convolution model was used to separate a karst watershed hydrograph into two outflow components one originating from focused recharge in conduits and one originating from slow flow in a porous annex system in convolution parameters of a complex system are lumped together in the impulse response function irf which describes the response of the system to an impulse of effective precipitation two parametric functions in superposition approximate the two domain irf the outflow hydrograph can be separated into flow components by forward modeling with isolated irf components which provides an objective criterion for separation as an example the model was applied to a karst watershed in the madison aquifer south dakota usa simulation results indicate that this watershed is characterized by a flashy response to storms with a peak response time of 1 day but that 89 of the flow results from the slow flow domain with a peak response time of more than 1 year this long response time may be the result of perched areas that store water above the main water table simulation results indicated that some aspects of the system are stationary but that nonlinearities also exist

u th isotope systematics from the soreq cave israel and climatic correlations precise 230 th 234 u ages were obtained on thirty one growth laminae in speleothem samples which are self consistent with the detailed layer stratigraphy samples with low 232 th 238 u ratios give ages with analytical uncertainties of 40 years at 2 ky and 1000 years at 90 ky some growth zones with high but variable 232 th 238 u were dated by intermal isochrons this permits the determination of the initial 230 th 232 th assuming equilibrium of 232 th and 238 u series in the source of the high 232 th component this shows initial 230 th 232 th in activity units of from 1 3 to 2 9 the calculated atomic ratios of 232 th 238 u for the high 232 th component range from 1 08 to 2 4 which is well below the average crustal value speleothem materials with high 232 th 238 u are found to exhibit clear correlations of 232 th with si al and fe while 238 u correlates with sr and ba analyses of soreq cave drip waters show that the particulates in the waters have high 232 th concentrations and a 232 th 238 u ratio much lower than that found in the high 232 th component in speleothems but with 230 th 232 th 1 0 to 2 4 we infer that the trapped high th component in speleothems is from particulate matter in water with a large concentration of adsorbed u and not simply from detrital material the speleothems have only small234u excess the initial 234 u 238 u 0 show a range of 1 02 to 1 14 that was found to correlate with age over the past 25 ky the youngest samples have values in the same range as the modern drip waters there appears to be a correlation of 234 u 238 u 0 with the 18 o values there is a drop of 18 o in the time interval 20 to 15 ky which then remains relatively constant to recent times as the high 18 o values have been related to rainfall and associated climatic conditions we suggest that the 234 u 238 u in the speleothem reflects the effects of rainfall and soil weathering conditions on drip water composition and may provide a proxy for climate change

internal solitary waves induced by flow over a ridge with applications to the northern south china sea 1 the generation of internal solitary waves by barotropic tides over a ridge is studied in a nonhydrostatic numerical model under idealized oceanographic settings the experiments examine the effects of ridge width barotropic tidal strength and stratification on wave generation the barotropic tidal flow produces internal wave beams emitting from the ridge top if the slope of the ridge exceeds a critical value equal to the slope of the wave beam reflection and refraction of a wave beam in an upper ocean waveguide associated with a strong shallow thermocline produce horizontally propagating internal tides when the local froude number over a ridge is not small lee waves generated on the ridge convert enough energy from the barotropic tides to the internal tides to form tidal bores and solitary waves increasing stratification at ridge depths enhances the generation of internal waves particularly at the diurnal periods in the luzon strait the slope of the wave beam decreases in spring and summer as stratification at the ridge depths increases favoring the generation of internal tides without the presence of a strong shallow thermocline internal solitary waves are not observed east of the luzon strait in the northern south china sea internal solitary waves are likely observed from april to july when a strong shallow thermocline is present a deep mixed layer in winter suppresses the production of internal solitary waves