sr ca and δ18o in a fast growing diploria strigosa coral evaluation of a new climate archive for the tropical atlantic this study provides the first monthly resolved 41 year record of geochemical variations 18o and sr ca in a fast growing diploria strigosa brain coral from guadeloupe caribbean sea linear regression yields a significant correlation of coral sr ca 18o with instrumental sea surface temperature sst on both monthly and mean annual scales e g r 0 59 for correlation between simple ocean data assimilation soda sst and sr ca and r 0 66 for 18o mean annual scale p 0 0001 the generated coral sr ca 18o sst calibration equations are consistent with each other and with published equations using other coral species from different regions moreover a high correlation of coral sr ca and 18o with local air temperature on a mean annual scale r 0 78 for sr ca r 0 73 for 18o p 0 0001 demonstrates the applicability of geochemical proxies measured from diploria strigosa corals as reliable recorders for interannual temperature variability both coral proxies are highly correlated with annual and seasonal mean time series of major sst indices in the northern tropical atlantic e g r 0 71 for correlation between the index of north tropical atlantic sst anomaly and sr ca and r 0 70 for 18o mean annual scale p 0 001 furthermore the coral proxies capture the impact of the el nino southern oscillation on the northern tropical atlantic during boreal spring thus fast growing diploria strigosa corals are a promising new archive for the atlantic ocean

principles of early development of karst conduits under natural and man made conditions revealed by mathematical analysis of numerical models numerical models of the enlargement of primary fissures in limestone by calcite aggressive water show a complex behavior if the lengths of the fractures are large and hydraulic heads are low as is the case in nature dissolution rates at the exit of the channel determine its development by causing a slow increase of water flow which after a long gestation time by positive feedback accelerates dramatically within a short time span mathematical analysis of simplified approximations yields an analytical expression for the breakthrough time when this happens in excellent agreement with the results of a numerical model this expression quantifies the geometrical hydraulic and chemical parameters determining such karst processes if the lengths of the enlarging channels are small but hydraulic heads are high as is the case for artificial hydraulic structures such as dams it is the widening at the entrance of the flow path which determines the enlargement of the conduit within the lifetime of the dam this can cause serious water losses this can also be explained by mathematical analysis of simplified approximations which yield an analytical threshold condition from which the safety of a dam can be judged thus in both cases the dynamic processes of karstification are revealed to gain a deeper understanding of the early development of karst systems as a further important result one finds that minimum conditions below which karstification cannot develop do not exist

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

implications for karst hydrology from 3d geological modeling using the aquifer base gradient approach we use the gradient of the aquifer base to investigate the hydrology of mature shallow karst systems we first present a 3d geological model of the gempen plateau nw switzerland that reveals the geometry of aquifers and aquitards and their displacement at faults then transfer the 3d geological model to a hydrological model the transformation is based on a conceptual karst model approximating subsurface flow in mature shallow karst systems to open surface flow on the top of the uppermost aquitard or aquifer base the gradient of this surface is expected to mainly influence regional groundwater flow patterns we use the hydrological model to delineate spring catchment areas the discharge areas and corresponding catchment areas of the model are compared with the occurrence of springs in the study area and with hydraulic links confirmed by tracer tests we also describe the way in which the hydrological model contributes to identifying flow processes the proposed aquifer base gradient approach enhances vulnerability assessment in mature shallow karst regions by 1 localizing catchment areas as a precondition of source protection strategies and 2 indicating dominant flow processes associated with individual springs

differential weathering in ultramafic rocks of new caledonia the role of infiltration instability abstract ultramafic rocks of new caledonia present extensive pseudokarstic features undulations of the base of the weathering profile fractures enlarged by dissolution dolines possible influence of the infiltrative instability on differential weathering of ultramafic rocks in tropical climate is investigated here starting from the tiebaghi case for which a groundwater model is available infiltration instability is governed by non dimensional numbers i e the damkohler and peclet numbers and by the permeability contrasts between the bedrock and the different layers of the weathering profile these numbers are firstly estimated for the tiebaghi case and secondly a sensitivity study of the weathering style is achieved through numerical modeling computations are firstly carried out without the impervious laterite cover and then the effect of this cover is considered the characteristic time constant for weathering of peridotites is directly estimated at around 7 yrs from the thickness of the weathering front and the fluid velocity the results show that a permeability contrast of at least 100 between the most pervious layer in the weathering front and bedrock and a diffusivity of chemical species lower than 2 5 10 8 m 2 s are required to allow instability the tiebaghi case lies at the limit of instability and dissolution fingers develop in a time lapse of 1 ma however this requires the infiltration of nearly 800 mm of rainfall yearly which is not the case presently the development of dissolution fingers is promoted by any initial pervious zone such as fracture concentration around a faulted zone and the characteristic time for instability development drops to 0 1 0 3 ma extension of these results to other peridotite massifs in the tropical zone submitted to different temperatures and rainfalls is finally discussed

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

early development of karst systems 2 turbulent flow a simulation model developed to explore patterns of fracture enlargement within incipient limestone karst aquifers has been extended to turbulent flow in contrast to the highly selective passage enlargement that occurs early in cave network development under laminar flow the transition to turbulent flow results in more general passage enlargement leading to maze networks when initial fractures are large and hydraulic gradients are high these results support previously published hypotheses for the development of maze patterns including formation within structural settings that have created initially large fractures or within flow systems periodically inundated by flooding maze development is also favored under turbulent flow when passages are entirely water filled and where the groundwater flow system is long lived by contrast branched patterns are most common when passages become free surface subterranean streams because depression of the piezometric surface along main passages downcutting along main passages and possible infilling with sediment of side passages limit the sharing of discharge among interconnected fractures or bedding planes that promote maze development

assessing coral sr ca sst calibration techniques using the species diploria strigosa the coral species diploria strigosa is a promising archive for paleoclimate reconstruction in the tropical atlantic but limited work has been accomplished thus far to quantify the relationship between strontium to calcium ratios and sea surface temperatures in this species in this study we collected three modern d strigosa coral colonies from anegada british virgin islands to refine the use of this species as a paleoclimate archive three regression techniques including ordinary least squares reduced major axis and weighted least squares were used to assess how assumptions implicit in these regression methods influence the calibration our analysis demonstrated that regression slopes were strongly impacted by the assumptions about data uncertainty we recommend using the unbiased weighted least squares regression technique for calibrating the sr ca paleothermometer especially when precise local sea surface temperature data are unavailable combining our sr ca data with previously published data from this species results in a multi site multi colony temperature sensitivity of 0 046 0 001 mmol mol c for mean centered monthly data 0 059 0 001 mmol mol c for monthly anomalies and 0 063 0 004 for annual anomalies we suggest these relationships are the best available characterization of the temperature dependence of sr ca in d strigosa and can be utilized in future paleoclimate reconstructions

the role of dissolution kinetics in the development of karst aquifers in limestone a model simulation of karst evolution to model the development of karst aquifers from primary fissures in limestone rock a numerical model of solutional widening of such fractures by calcite agressive water is suggested the geological setting determines relevant geometrical parameters i e length of the fracture its initial width and the hydraulic gradient driving water from the input to the output to simulate the solutional widening as it proceeds in time the solution rates must be known as a function of concentration c of dissolved calcite they are given as a first order kinetic rate law for c leq k cdot c eq as f 1 alpha 0 c c eq for c k cdot c eq close to equilibrium a fourth order rate law becomes dominant f 4 beta cdot c c eq 4 the parameters alpha 0 beta and k depend on the chemistry of the carbonate system and rock chemistry the saturation concentration c eq with respect to calcite depends on the initial co 2 concentration of the inflowing solution

early development of karst aquifers on percolation networks of fractures in limestone we have modeled flow and dissolution processes within percolation networks representing stochastic primary fracture systems in limestone at the beginning of karstification flow is evenly distributed on all fractures available as the system develops by dissolutional widening of the fractures preferred flow pathways evolve which attract more and more flow until at breakthrough the total flow rate increases dramatically these breakthrough times have been investigated with regard to their dependence on the initial fracture aperture width the dimension of the evolving karst aquifer hydraulic gradients connectivity of the percolation network and the chemical parameters such as higher order rate constants and exponents and equilibrium concentration they exhibit a behavior similar to that of breakthrough times for one dimensional conduits dreybrodt 1996 our results show that the structure of the evolving karst aquifer is determined by the initial geological setting however the final conduits are selected from competing pathways with potential breakthrough times close to each other whereby the details of the distribution of undersaturation with respect to calcite play an important role

modeling three dimensional karst aquifer evolution using different matrix flow contributions summary we have developed the program package karstaquifer which simulates flow and transport in a three dimensional transient karst aquifer consisting of fractures and matrix elements the fractures can be enlarged by chemical dissolution of calcite increasing the secondary permeability of the karst aquifer boundary conditions for our model setup are guided by published benchmark models for karst aquifer evolution in two dimensions length and width with a 100 m high hydraulic head difference across the model domain responsible for relatively fast evolution of the aquifer we are interested in the effect of the third dimension on the evolution of the karst aquifer especially the effect of matrix flow with a matrix defined either as porous medium or as fine fracture system or both we first discuss our model results using a pseudo 3d setup to be able to directly compare results to the 2d benchmark scenarios published we then discuss real 3d models with a prominent fault located in the central part of the aquifer connecting input and output regions finally we replace the prominent fault with a statistical fracture diameter distribution our results compare well with existing 2d scenarios and the additional third dimension offers new insights into the evolution of karst aquifers especially the role of matrix flow under fixed head boundary conditions in their early phases can be studied in more detail

modelling unsaturated flow in an evolving karst aquifer a two dimensional cross section of a karst aquifer in which chemical dissolution enlarges fractures with time is studied the karst aquifer is recharged by precipitation and drains towards a resurgence the initial aquifer has low conductivities both in the rock matrix and the fracture network and the initial water table is high as the enlargement of fractures by dissolution increases the fracture conductivity the water table drops until it reaches a steady state along the level of the resurgence several parameterisations are discussed for flow in the unsaturated zone above the water table it is shown that different approaches result in similar cave passage patterns with a large water table cave draining the recharge towards the resurgence however flow patterns in the unsaturated zone can be very different for the different parameterisations

cave development in the swabian alb south west germany a numerical perspective summary the formation of phreatic cave conduits in the carbonate aquifer of the swabian alb south west germany is discussed by means of numerical simulations three active cave conduit systems the blautopf cave the aachtopf cave and the wimsener cave have been partially explored by divers and exhibit a continuous conduit flow path with phreatic loops down to 50 m below the average water table these three systems drain catchments between 50 and 280 km2 and largely follow the dip of the jurassic limestone beds we use the numerical model karst karst aquifer simulation tool to explore the possibility of structural control of the conduit evolution we show that both the dip of the bedding and the frequency of major bedding partings is likely to result in numerical drainage paths which are similar to the observed cave systems

influence of aperture variability on dissolutional growth of fissures in karst formations the influence of aperture variability on dissolutional growth of fissures is investigated on the basis of two dimensional numerical simulations the logarithm of the fissure aperture before dissolution begins is modeled as a gaussian stationary isotropic random field the initial phase of dissolutional growth is studied up to the time when turbulent flow first occurs at a point within the fissure the breakthrough time the breakthrough time in variable aperture fissures is smaller than that in uniform fissures and decreases as the coefficient of variation of the aperture field increases in comparing uniform and variable aperture fissures in limestone the breakthrough time with 0 1 is about a factor of 2 smaller than that in a uniform fissure the breakthrough time is reduced by about an order of magnitude with 2 0 the mechanism leading to reduced breakthrough times is the focusing of flow into preferential flow channels which are enlarged at a faster rate than the surrounding regions of slower flow dissolution channels are narrower and more tortuous as increases investigations of the influence of reaction rate reveal that the influence of aperture variability is more pronounced in rapidly dissolving rock in uniform fissures in rapidly dissolving minerals breakthrough times are very long since water becomes saturated with respect to the mineral within a short distance of the entrance to the flow path however in variable aperture fissures breakthrough occurs rapidly because of selective growth along preferential flow channels which progressively capture larger fractions of the total flow these results partly explain why conduits develop rapidly in gypsum although previous one dimensional studies suggest that conduit growth will not occur

early development of karst systems 1 preferential flow path enlargement under laminar flow modeling of flow and solutional processes within networks of interconnected conduits in limestone aquifers indicates that enlargement occurs very selectively during the early stages of karst aquifer development under laminar flow if initial flow paths are uniform in size almost all enlargement occurs along a single set of connected conduits that lie along a direct path between recharge and discharge locations and are aligned along the hydraulic gradient with a sufficiently large variation in initial aperture widths enlargement occurs along the flow path offering the least resistance to flow but since flow rates in laminar flow are proportional to the fourth power of diameter but only linearly proportional to hydraulic gradient the preferentially enlarged set of fractures may follow an indirect path results disfavor earlier suggestions that nonselective cave patterns result from artesian flows at least under laminar flow conditions and that all passages should be competitive until the onset of turbulent flow

last interglacial temperature seasonality reconstructed from tropical atlantic corals abstract reconstructions of last interglacial lig mis 5e 127 117 ka climate offer insights into the natural response and variability of the climate system during a period partially analogous to future climate change scenarios we present well preserved fossil corals diploria strigosa recovered from the southern caribbean island of bonaire caribbean netherlands these have been precisely dated by the 230 th u method to between 130 and 120 ka ago annual banding of the coral skeleton enabled construction of time windows of monthly resolved strontium calcium sr ca temperature proxy records in conjunction with a previously published 118 ka coral record our eight records of up to 37 years in length cover a total of 105 years within the lig period from these sea surface temperature sst seasonality and variability in the tropical north atlantic ocean is reconstructed we detect similar to modern sst seasonality of 2 9 c during the early 130 ka and the late lig 120 118 ka however within the mid lig a significantly higher than modern sst seasonality of 4 9 c at 126 ka and 4 1 c at 124 ka is observed these findings are supported by climate model simulations and are consistent with the evolving amplitude of orbitally induced changes in seasonality of insolation throughout the lig irrespective of wider climatic instabilities that characterised this period the climate model simulations suggest that the sst seasonality changes documented in our lig coral sr ca records are representative of larger regions within the tropical north atlantic these simulations also suggest that the reconstructed sst seasonality increase during the mid lig is caused primarily by summer warming a 124 ka old coral documents for the first time evidence of decadal sst variability in the tropical north atlantic during the lig akin to that observed in modern instrumental records

a model of early evolution of karst conduits affected by subterranean co2 sources in investigating early karstification of one dimensional conduits by computer models so far one has assumed that the co2 content of the calcite aggressive water stems entirely from the surface subterranean sources of co2 however can rejuvenate the solutional power of water already close to equilibrium with respect to calcite and boost dissolution rates in a first scenario we have investigated the influence of a punctual source of co2 as the most simple case of release of co2 into a karstifiable fracture at some position kl from its entrance of the widening joint with length l k 1 the results show that only a small increase of the pco2 in the solution to about 0 01 atm is sufficient to reduce the breakthrough times to about 0 3 with respect to the case where no co2 is delivered other sources of co2 are due to the metabolic activity of microorganisms the existence of such diverse subterraneous microbial life in karst systems is demonstrated whether situated on the fissure surfaces or free floating in the karst water one basic product of their metabolism is co2 this contributes over the whole flow path to the pco2 of the karst water therefore in a second scenario we assumed a constant rate of co2 input along parts of the fracture as could be delivered by the activity of aerobic bacteria dwelling at its walls such a scenario also applies to an extended diffuse co2 migration from volcanic activity deep underground in this case drastic reductions of the breakthrough time by about one order of magnitude are observed these reductions are enhanced when the fracture aperture width of the initial fracture decreases the physicochemical mechanisms of enhancement of karstification are discussed in detail by considering the evolution of the fracture aperture width and of the dissolution rates in space and time

karst aquifer evolution in fractured rocks we study the large scale evolution and flow in a fractured karst aquifer by means of a newly developed numerical method a karst aquifer is discretized into a set of irregularly spaced nodal points which are connected to their set of natural neighbors to simulate a network of interconnected conduits in two dimensions the conduits are allowed to enlarge by solutional widening the geometric flexibility of this method along with a simplified model for the dissolution kinetics within the system water carbon dioxide calcite enables us to study both laminar and turbulent flow in a karst aquifer during its early phase of evolution a sensitivity analysis is conducted for parameters such as conduit diameter hydraulic pressure differences and recharge conditions along the surface of the aquifer and shows that passage evolution depends strongly on the recharge condition and the amount of water available under fixed hydraulic head boundary conditions an early single passage system develops under laminar conditions and is transformed into a maze like passage system after the onset of turbulence fixed recharge boundary conditions are more likely to result in a branchwork like passage system although the addition of distributed recharge may lead to a maze like system of secondary passages

looping caves versus water table caves the role of base level changes and recharge variations in cave development abstract the vertical organisation of karst conduit networks has been the focus of speleogenetic studies for more than a century the four state model of ford and ewers 1978 which still is considered as the most general relates the geometry of caves to the frequency of permeable fissures the model suggests that the water table caves are common in areas with high fissure frequency which is often the case in natural settings however in alpine karst systems water table caves are more the exception than the rule alpine speleogenesis is influenced by high uplift valley incision rates and irregular recharge to study the potential role of these processes for speleogenesis in the dimensions of length and depth we apply a simple mathematical model based on coupling of flow dissolution and transport we assume a master conduit draining the water to the spring at a base level incision of the valley triggers evolution of deeper flow pathways which are initially in a proto conduit state the master conduit evolves into a canyon following the valley incision while the deep pathways evolve towards maturity and tend to capture the water from the master conduits two outcomes are possible a deep pathways evolve fast enough to capture all the recharge leaving the master conduit dry or b the canyon reaches the level of deep pathways before these evolve to maturity we introduce the loop to canyon ratio lcr which predicts which of the two outcomes is more likely to occur in certain settings our model is extended to account for transient flow conditions in the case of an undulating master conduit floodwater is stored in troughs after the flood retreat this water seeps through sub vertical fractures soutirages connecting the master conduit with the deep pathways therefore the loops evolve also during the dry season and the lcr is considerably increased although the model is based on several approximations it leads to some important conclusions for vertical organisation of karst conduit networks and stresses the importance of base level changes and transient recharge conditions it therefore gives an explanation of speleogenesis that relies much more on the dynamic nature of water flow than on the static fracture density

karstification beneath the birs weir in basel switzerland a 3d modeling approach we present a three dimensional model describing the evolution of a gypsum karst aquifer along the birs river near basel in switzerland here a small dam site was built in 1890 to generate hydro electric power after subsidence of a nearby highway geophysical and geological field studies have been carried out and a detailed hydrogeological model has been developed these observations identified a karstified weathered zone as the reason for the subsidence to prevent any further damage remedial construction measures have been carried out we employ our numerical model karstaquifer which simulates the temporal evolution of a karst system by dissolution increasing the porosity in the aquifer we used results from geological and geophysical investigations as a priori information for implementing the initial boundary conditions into our three dimensional numerical model our model accounts for topography precipitation and geology and especially for the anisotropy of the local bedrock it can successfully reproduce the weathered zone in its current horizontal and vertical extent we cm also simulate the possible evolution of the aquifer following a remedial construction phase therefore taken together with the geophysical and geological observations and the groundwater model our three dimensional karst aquifer evolution model enhances the understanding of the development of this heterogeneous karst aquifer system c 2012 elsevier b v all rights reserved hydrogeologie der nordwestschweiz grundwasser

modelling karst vadose zone hydrology and its relevance for paleoclimate reconstruction abstract understanding past climatic changes allows us to better understand how our planet will evolve in the future one important source of information on paleoclimate is the analysis of speleothems that develop in karst caves and conduits due to the dissolution and precipitation of calcite however there are many uncertainties in paleoclimatic reconstruction with speleothems one of them being hydrological variability up to now only few studies have considered the impact of hydrological variability on speleothem formation and composition this review paper will provide an introduction to hydrological processes that have the potential to affect speleothem composition and the hydrological modelling approaches that are able to account for them it presents the current state of knowledge on paleoclimatic reconstruction using speleothems and shows that many important flow and transport processes have not yet been included in the interpretation of these archives mostly due to a lack of field information to parametrize them possible directions of future research efforts therefore include a better exploration of karst vadose zone processes and new approaches to incorporate this information into simulation models finally we foresee the exciting advances in reconstructing paleohydrology using karst hydrology models combined with speleothem growth rate and geochemical composition to understand how past climate changes affected the hydrological cycle and water availability

a multicoral calibration method to approximate a universal equation relating sr ca and growth rate to sea surface temperature 1 combining strontium to calcium ratios sr ca with mean annual growth rates in bermuda diploria labyrinthiformis brain corals is shown to improve sea surface temperature sst calibrations relative to instrumental data growth corrected sr ca sst calibrations based on single coral colonies over the same calibration interval however are found to be poorly suited for application to data from different coral colonies this raises concerns about the accuracy of sst reconstructions from fossil coral measurements that involve extrapolation beyond the range of values seen during the calibration period here we pursue a novel approach to this problem by incorporating data from multiple coral colonies into a single growth corrected sr ca sst calibration equation effectively expanding the range of modern values constraining the model the use of a multiple colony calibration model for reconstructing sst yields greater precision and accuracy relative to instrumental data than single colony models providing greater confidence for applications to fossil coral samples

using the continuum approach to model unsaturated flow in fractured rock the appropriateness of using the continuum approach for simulations of unsaturated flow through fractured rock is examined in a numerical study of water seepage into an underground opening a continuum model is calibrated against data generated with a high resolution model that created discrete flow and seepage behavior probabilistic predictions of injection data and seepage rates are then compared to the values from the discrete model the study shows that reasonable results can be obtained with a calibrated continuum model even for fractured systems in which the underlying flow processes are discrete calibration is a crucial step in this approach because it yields effective model related and process specific parameters the impact of discretization on the estimated parameters is discussed prediction uncertainty is evaluated by means of monte carlo simulations including both the impact of parameter uncertainties and the effect of local heterogeneity in this paper the advantages and limitations of the continuum approach are discussed from a practical perspective which includes a critical examination of project objectives data needs robustness of assumptions and prediction uncertainty

karstification of aquifers interspersed with non soluble rocks from basic principles towards case studies abstract we have developed a numerical model able to describe the karstification of aquifers in fractured rocks containing soluble limestone or gypsum and insoluble layers when water is flowing along fractures crossing the soluble layers it is able to dissolve the material there to increase the aperture width of the conduit and consequently to increase the local hydraulic conductivity depending on the thickness and the distribution of these layers the dissolution can be active only for limited periods or during the whole evolution time fractures located in insoluble layers do not change at all we are interested in the integral effect of these local processes and study four simplified scenarios of karstification along a prominent wide conduit crossing a fractured limestone block we keep the initial and the boundary conditions the same for all scenarios and vary only in the amount and the distribution of the soluble material we demonstrate that aquifers in 100 limestone without any insoluble layers develop along areas with high hydraulic conductivities and high hydraulic gradients creating channel like pathways on the other hand aquifers containing soluble layers with limited thickness develop faster and exhibit diffuse patterns determined by the chemical properties of the rock the second part of the paper is a step towards modeling of real karst systems we present the evolution of an aquifer located in the vicinity of a large hydraulic structure all initial and boundary conditions except the amount and the distribution of the soluble rock remain the same for all scenarios as a material example for the bedrock we chose gipskeuper from an aquifer along the birs river in switzerland this rock consists of soluble gypsum layers and insoluble clays and marls with typical layer thickness in the range of millimeters to centimeters the basic processes discussed in the first part of the paper remain valid we demonstrate that large insoluble zones can impair the karstification process and even completely block it while areas with thin soluble layers can provide a preferential pathway and decrease the evolution times considerably finally we show that the evolution of the leakage rates and the head distribution within the aquifer can sometimes reveal misleading information about the stage of karstification and the safeness of the dam our model can be used not only to study simplified geological settings and basic processes but also to address some of the complications arising when modeling real aquifers

karst aquifer evolution in a changing water table environment 1 a vertical cross section through a karst aquifer is modeled by means of the finite element method to study the evolution of fractures and flow in the aquifer the karst aquifer receives a constant recharge along the top boundary by precipitation and drains toward a resurgence assumed to be the base level in a valley flow is allowed both in the permeable rock matrix and the fracture network and the fractures are enlarged with time by chemical dissolution hence during the early evolution of the karst aquifer the conductivity increases over several orders of magnitude and the initially high water table drops to a steady state base level niveau as a consequence fractures above the final water table change from phreatic to vadose flow conditions a systematic parameter study is carried out to investigate the aquifer evolution over a wide range of parameters such as recharge rate initial fracture width and density and initial calcium concentration the numerical models cover a wide range of drainage patterns from phreatic water table caves to deep bathyphreatic caves to vadose river caves the models suggest that a single theoretical approach is capable of explaining most common cave passage patterns

atlantic warm pool acting as a link between atlantic multidecadal oscillation and atlantic tropical cyclone activity 1 multidecadal variability of atlantic tropical cyclone activity is observed to relate to the atlantic multidecadal oscillation amo a mode manifesting primarily in sea surface temperature sst in the high latitudes of the north atlantic in the low latitudes of the north atlantic a large body of warm water called the atlantic warm pool awp comprises the gulf of mexico the caribbean sea and the western tropical north atlantic awp variability occurs on both interannual and multidecadal timescales as well as with a secular variation the awp multidecadal variability coincides with the signal of the amo that is the warm cool phases of the amo are characterized by repeated large small awps since the climate response to the north atlantic sst anomalies is primarily forced at the low latitudes and the awp is in the path of or a birthplace for atlantic tropical cyclones the influence of the amo on atlantic tropical cyclone activity may operate through the mechanism of the awp induced atmospheric changes the awp induced changes related to tropical cyclones that we emphasize here include a dynamical parameter of tropospheric vertical wind shear and a thermodynamical parameter of convective instability more specifically an anomalously large small awp reduces enhances the vertical wind shear in the hurricane main development region and increases decreases the moist static instability of the troposphere both of which favor disfavor atlantic tropical cyclone activity this is the most plausible way in which the amo relationship with atlantic tropical cyclones can be understood

active fault and paleoseismic studies in kangra valley evidence of surface rupture of a great himalayan 1905 kangra earthquake mw 7 8 northwest himalaya india our findings suggest that interseismic strain accumulated south of the fault ramp under the higher himalayas was not only released periodically along the himalayan frontal thrust hft during large magnitude earthquakes but also along the active faults in the hinterland the 4 april 1905 kangra earthquake m w 7 8 killed more than 20 000 people and destroyed the towns of kangra and dharamsala in northwest himalaya in spite of its large magnitude with a maximum intensity x on the rossi forel intensity scale recorded in the epicentral area no surface rupture was reported and no focal mechanism is available this article uses satellite imagery and field mapping to identify an active right lateral strike slip fault named the kangra valley fault kvf we infer that the kvf represents the surface rupture of the 1905 kangra earthquake extending west northwest east southeast and east west for 60 km it cuts through the kangra and sihunta valleys and is capable of producing m w 7 2 earthquakes existence of the kvf in the kangra re entrant is indicative of oblique convergence and slip partitioning between the main boundary thrust in the north the jawalamukhi thrust in the south and a strike slip fault in the northwest himalaya paleoseismic investigations revealed evidence of at least four earthquakes on the kvf event i oldest occurred before 900 b c or between 900 b c and 2500 b c event ii occurred between 100 b c and 80 b c penultimate event iii occurred around a d 800 and a d 1000 and the most recent event event iv occurred after a d 1620 and before a d 1940 and is likely the 1905 kangra earthquake m w 7 8 a longer recurrence along the kvf is inferred between older paleoearthquake events i and ii and a shorter interval of 1050 150 years is inferred between younger events ii iii and iv because the strain during the 1905 kangra earthquake was released along the kvf potential for large magnitude earthquakes in northwest himalaya along the hft still remains online material figures of quartz response curves growth curves and histograms of sample numbers and trench photomosaics

a fossil coral perspective on western tropical pacific climate 350 ka 1 the nature of tropical climate variability 350 ka is addressed using 18o and sr ca records from a modern and a fossil coral from vanuatu southwestern tropical pacific ocean modern el nino events at vanuatu produce positive coral 18o and sr ca anomalies similar anomalies observed in the fossil coral records suggest that el nino was operative 350 kyr ago seasonal variations in coral sr ca a sea surface temperature sst proxy have the same amplitude in both corals whereas seasonal 18o variations are smaller in the fossil coral than in the modern coral this is consistent with displacement of the south pacific convergence zone toward the southwest during the boreal summer 350 ka mathematical modeling results preclude warmer sst and higher sss at vanuatu during this time but permit the surface ocean to be 2 c cooler and 0 2 psu fresher than today assessing the potential of variations in late quaternary seawater sr ca remains the largest obstacle to accurately reconstructing tropical sst using pristine fossil corals

minimum hydrochemical conditions allowing limestone cave development early theoretical investigations into initiation of limestone cave development suggested that water entering small fractures approaches saturation within a short distance and thus appeared to be unable to produce much further enlargement of these fractures the answer to this problem seems to be white s 1977 kinetic trigger idea emphasizing the precipitous drop in dissolution rates as equilibrium is approached however minimum conditions of flow rate passage geometry and initial co2 concentration may exist below which the waters will so nearly achieve saturation that caves will be unable to develop modeling results indicate that under geologically reasonable pco2 and head gradient values the minimum initial aperture widths in which caves will develop is of the order of 100 m initial apertures wider than about 500 m will form passages very easily even under low head gradients there will thus be strong differential selection among initial flow paths with regard to cavern passage development

a model of the early evolution of karst aquifers in limestone in the dimensions of length and depth a new model of the early evolution of limestone karst aquifers in the dimensions of length and depth is presented in its initial state the aquifer consists of a rock massive with evenly spaced fractures of about 50 mm aperture widths with an hydraulic conductivity of 10 27 ms 21 in addition to this a coarser network of prominent fractures with aperture widths of several 100 mm is also present boundary conditions of constant recharge 450 mm year or constant head from the input of allogenic streams are imposed first the position of the water table in the aquifer is calculated then dissolutional widening during a time step in all the fractures below the water table is found by use of the well known nonlinear dissolution kinetics of limestone this is iterated and the position of the water table as well as the fracture widths are found as a function of time in the case of constant recharge to a karst plateau the water table in any case drops to base level and conduits there propagate from the spring headwards if constant head conditions are valid the position of the water table remains almost stable and conduits propagate along the water table from the input towards the spring there is competition between conduit evolution along prominent fractures and along tight fissures close to the water table in any case under constant head conditions one of these pathways wins and early karst evolution is terminated by a breakthrough event with an explosive increase of the flow through the aquifer until constant head conditions break down depending on the boundary conditions of constant head or constant recharge or a combination of both it is possible to describe models of cave genesis which have been derived from field evidence such as the water table models of swinnerton geol soc am bull 34 1932 662 and rhoades and sinacori j geol 49 1941 785 as well as the four state model by ford and ewers can j earth sci 15 1978 1783 q 2001 elsevier science b v all rights reserved