the role of hydrogeological base level in the formation of sub horizontal caves horizons example from the dead sea basin israel this paper deals with the hydrogeological relationship between base levels of saline lakes and the formation of sub horizontal caves the mechanism presented here suggests that many horizontal cave levels in carbonate sequences are created adjacent to the saline lakes shorelines because of the converging of the groundwater flow above the fresh saline water interface the main factors that control enhanced carbonate dissolution and cave formation are high groundwater flow velocities in the shallow phreatic zone during a relative long steady state of the water table high groundwater flow velocities are evident close to the dead sea due to the convergent fast flows above the shallow interface adjacent to the shoreline the same could prevail in the case of previous paleo lakes that existed in the basin the synergetic combination of the above preconditions for enhanced cave formation seems to be responsible for the formation of elevation controlled alignment of paleo near shore cave levels in the central and southern dead sea portion of the study area these are found on the western fault escarpment and basin margin in different stratigraphic horizons of carbonate lithology many of the cave levels can be linked to late quaternary holocene lake levels obtained from dated lake sediments within the basin the most common cave s elevation was found to be around 200 m below sea level which was the elevation of the lisan lake during part of its history on the other hand the hula basin in the northern part of the dead sea basin was not occupied by saline water bodies since its formation as a base level and thus the above preconditions for enhanced cave formation did not prevail indeed this is evident by the lack of horizontal cave levels on its western carbonate margins unlike the situation in the south

path and variability of the agulhas return current the combined analysis of hydrographic kinematic and dynamic data collected during the 1997 1999 kapex cape of good hope experiments reveals a quasi stationary meandering pattern of the agulhas retroflection current east and upstream of the southwest indian ridge the current meanders between 38 s and 40 s in a spatially and temporally continuous fashion and has a core width of approximately full size image 1 k with an associated transport of full size image 1 k in the upper full size image 1 k peak surface velocities decrease from full size image 1 k near the agulhas retroflection to full size image 1 k around 32 e meander troughs northward extremes are found predominantly near 26 8 e 32 6 e and 38 9 e while crests southward extremes are located with high probability near 29 7 e 35 5 e and 42 9 e resulting in a typical wavelength of full size image 1 k cold eddies are shed along the northern boundary of the current from meander troughs into the recirculation regime between the agulhas current proper and the agulhas return current strongest cyclonic eddies are preferably shed in austral autumn the cyclonic eddies so formed propagate westward at an average phase speed of full size image 1 k with however a variability of at least the same magnitude subsequently the cyclones are absorbed by the next meander trough located upstream and to the west of the shedding trough

the flank margin model for dissolution cave development in carbonate platforms the bahama islands contain many abandoned dissolution caves at elevations between two and seven metres above current sea level the development of dissolution caves in tropical carbonate islands is dependent on the position and nature of the freshwater lens lens position is controlled by sea level which in stable carbonate platforms like the bahamas is a function of glacioeustatic sea level still stands caves in the bahamas that are currently subaerial must have developed during past higher sea levels during the late quaternary sea levels higher than present have been relatively short lived and that limits the amount of time that a freshwater lens could be situated at the elevation required for the cave formation the bahama islands are low lying landforms where only aeolian ridges extend to elevations higher than six metres above current sea level past high sea level events greatly reduced the exposed land area of the bahama islands thus also limiting both the catchment for and size of freshwater lenses caves must be younger than the rock in which they are developed most subaerial bahamian caves are found in limestones that are less than 150000 years old development of large dissolution caves under these limitations of time and lens size requires a powerful dissolutional mechanism the mixing of discharging freshwater with tide pulsed incoming marine water under the flanks of emergent dune ridges may have produced the conditions necessary bahamian caves formed by this process are phreatic chambers with complex interconnections and blind tubes their presence demonstrates that significant dissolution can occur rapidly as a result of the mixing of fresh and marine waters beneath small carbonate islands

the relationship between current and paleo groundwater base levels abstract base levels are basically divided into two categories oceanic and marine base levels and continental terminal endorheic ones the marine domain serves as the ultimate base level for both surface and groundwater drainage systems continental inland depressions very often serve as terminal endorheic base levels to both surface drainage and groundwater systems many of the current both marine and inland base levels served also in the past as paleo base levels fluctuations of base level elevations affect the adjoined groundwater system in several ways such as changes in groundwater levels location of divides depths of fresh saline water interfaces and the amount of flow to the base levels this paper provides examples from many different parts of the world that describe the relationship between current and paleo base levels the examples include marine base levels as well as inland endorheic ones both currently above and below sea level close to and distant from the sea

triassic latemar cycle tops subaerial exposure of platform carbonates under tropical arid climate the triassic latemar platform in the dolomites italy is the site of several ongoing controversies perhaps the most interesting debate focuses on apparent cyclic deposition within the latemar platform whose nature and duration are still open to debate further disagreement concerns the lack of meteoric diagenesis related isotope shifts at cycle tops that bear circumstantial petrographic evidence for subaerial emergence here an evaluation of the nature of latemar cycle tops is presented combining evidence from previous work and new field petrographic and geochemical data cycle tops are ranked according to increasing exposure duration and spatial extent type i surfaces lacking unequivocal evidence of prolonged supratidal conditions type ii dolomite caps formed in warm evaporitic intertidal lagoonal waters followed by exposure of perhaps intermediate duration type iii clastic rich red calcareous horizons with some showing platform wide extent representing prolonged supratidal conditions and type iv discontinuities in tepee belts genetically related to type ii and iii surfaces but likely representing shorter lived exposure stages petrographic and geochemical criteria indicate that most diagenesis occurred in the shallow marine and burial domain whilst an extensive meteoric overprint of cycle tops is lacking this is underlined by the scarcity of meteoric diagenetic fabrics such as gravitational cements that where present are here interpreted as marine vadose in origin the scarcity of carbon and oxygen isotope signatures commonly assigned to subaerial exposure stages is best explained in the context of mid triassic climate the low latitude tropical but arid setting of the latemar situated in the western extension of the tethys ocean its isolation from nearby continental areas and overall short term emergence episodes are in agreement with a limited degree of meteoric alteration of most cycle tops high amounts of aeolian clastic material beneath some cycle tops along with high fe and mn elemental abundances argue for intermittent subaerial conditions this study proposes an enhancement of the classical allan and matthews 1982 isotope model for subaerial exposure under strongly arid climates as the subaerial exposure nature of latemar cycle tops and therefore eustasy as the cause for cyclicity have been previously challenged due to the lack of meteoric induced isotopic signatures the outcome of this study is of significance for the ongoing latemar stratigraphic controversy

spongy like porosity in peritidal carbonates an interaction of cyclic sea level oscillations fresh water supply and sediment texture abstract this paper focuses upon the analysis of a complex paleokarstic system recorded within uppermost triassic peritidal cycles in northwestern sicily besides documenting spectacular karstification at the triassic jurassic boundary it provides an example of stratabound spongy or swiss cheese dissolution on the base of field observations microfacies analysis transmitted light and cathodoluminescence petrography and stable isotope analyses we put forward an original model for the formation of this peculiar stratabound dissolution it implies a complex interaction of several controlling factors at the interface between the marine and meteoric diagenetic realms during the relative cyclic oscillations of sea level the presence of a fresh water supply from an adjacent emerged area is the key for the periodic formation of a mixing water lens during the relative sea level lowstand that brought about the subaerial exposure of the platform the resulting dissolution pattern in the subtidal unit of a specific cycle is strongly controlled by the textural features of the sediments in the case of bioturbated wackestones the spongy or swiss cheese pattern develops while in mollusk rich beds biomoldic porosity occurs in well sorted subtidal members such as algal grainstones the dissolution originates as randomly distributed vuggy porosity during periodic flooding of the platform a new subtidal unit is formed and the dissolution stops as fully marine phreatic conditions are re established

resolving the source and mixing proportions of modern leakage to the memphis aquifer in a municipal well field using geochemical and 3h 3he data memphis tennessee usa the memphis aquifer in southwestern tennessee is a confined to semi confined unconsolidated sand aquifer and is the primary municipal water source for the memphis metropolitan area leakage of modern water from shallow unconfined aquifers through the upper claiborne confining unit locally degrades water quality in the memphis aquifer and makes the aquifer more vulnerable to contamination major solute chemistry tritium and 3h 3he data were used to investigate the source and mixing proportions of modern water in the memphis aquifer in the davis well field memphis tennessee water quality in several production wells in the davis well field has declined over the past 30 years mainly through increased total dissolved solids iron alkalinity and hardness trends in chemical data tritium and other hydrogeologic data support a source for the leakage from the mississippi river valley alluvial aquifer mixing proportions of alluvial water in production well water obtained by inverse chemical modeling with phreeqci range from 7 to 45 for two of the production wells mlgw 414 and 432 3h 3he data yield mixing ratios similar to those obtained from phreeqci in three of four cases the dissimilar ratio is likely due to a poor solution from the phreeqci inverse modeling modeling of the age distribution obtained from mlgw 414 and 432 using an exponential piston flow model epm with an inverse solution computer code yielded mixed results the epm solution obtained for mlgw 414 converged with difficulty only for a 5 year transit time in the shallow aquifer and is consistent with a source from the mississippi river valley alluvial aquifer however the modeled age of the water is greater than that observed in comparison the epm solution for mlgw 432 converged for the 5 and 7 year transit periods in the shallow aquifer and yielded model ages consistent with observed 3h 3he ages however the extent of the maximum radii for infiltration source is not consistent with a mississippi river valley alluvial aquifer source other potential sources for leakage to mlgw 432 include water from the fluvial terrace aquifer migrating along a fault east of the well field or infiltration of water from a lake south of the well field

association of tepees and palaeokarst in the ladinian calcare rosso southern alps italy the ladinian calcare rosso of the southern alps provides a rare opportunity to examine the temporal relationships between tepees and palaeokarst this unit comprises peritidal strata pervasively deformed into tepees repeatedly capped by palaeokarst surfaces mantled by terra rossa palaeokarsts characterized by a regional distribution across the southern alps occur at the base and at the top of the unit local palaeokarsts confined to this part of the platform occur within the calcare rosso and strongly affected depositional facies tepee deformation ranges from simple antiformal structures peritidal tepees to composite breccias floating in synsedimentary cements and internal sediments senile tepees peritidal tepees commonly occur at the top of one peritidal cycle in association with subaerial exposure at the cycle top while senile tepees affect several peritidal cycles and are always capped by a palaeokarst surface cements and internal sediments form up to 80 of the total rock volume of senile tepees the paragenesis of senile tepees is extremely complex and records several superimposed episodes of dissolution cement precipitation fibrous cements laminated crusts mega rays and deposition of internal sediments marine sediment and terra rossa petrographical observations and stable isotope geochemistry indicate that cements associated with senile tepees precipitated in a coastal karstic environment under frequently changing conditions ranging from marine to meteoric and were altered soon after precipitation in the presence of either meteoric or mixed marine meteoric waters stable isotope data for the cements and the host rock show the influence of meteoric water average 18o 5 8 while strontium isotopes average 87sr 86sr 0 707891 indicate that cements were precipitated and altered in the presence of marine triassic waters field relationships sedimentological associations and paragenetic sequences document that formation of senile tepees was coeval with karsting senile tepees formed in a karst dominated environment in the presence of extensive meteoric water circulation in contrast to previous interpretations that tepees formed in arid environments under the influence of vadose diagenesis tepees initiated in a peritidal setting when subaerial exposure led to the formation of sheet cracks and up buckling of strata this porosity acted as a later conduit for either meteoric or mixed marine meteoric fluids when a karst system developed in association with prolonged subaerial exposure relative sea level variations inducing changes in the water table played a key role in exposing the peritidal cycles to marine mixed marine meteoric and meteoric diagenetic environments leading to the formation of senile tepees the formation and preservation in the stratigraphic record of vertically stacked senile tepees implies that they formed during an overall period of transgression punctuated by different orders of sea level variations which allowed formation and later freezing of the cave infills

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

geochemical and statistical evidence of recharge mixing and controls on spring discharge in an eogenetic karst aquifer summary information about sources of recharge distributions of flow paths and the extent of water rock reactions in karst aquifers commonly result from monitoring spring chemistry and discharge to investigate the relationship between spring characteristics and the complexities of karst aquifers we couple variations in surface and groundwater chemistry to physical conditions including river stage precipitation and evapotranspiration et within a sink rise system through a 6 km portion of the upper floridan aquifer ufa in north central florida principal component analysis pca of time series major element compositions suggests that at least three sources of water affect spring discharge including allogenic recharge into a swallet diffuse recharge through a thin vadose zone and water upwelling from deep within the aquifer the deep water source exerts the strongest influence on water chemistry by providing a majority of na mg2 k cl and so 4 2 to the system anomalously high temperature at one of several monitoring wells reflects vertical flow of about 1 m year mass balance calculations suggest diffuse recharge and deep water upwelling can provide up to 50 of the spring discharge however their contributions depend on head gradients between the conduit and surrounding aquifer matrix which are influenced by variations in precipitation et and river stage our results indicate that upwelling from deep flow paths may provide significant contributions of water to spring discharge and that monitoring only springs limits interpretations of karst systems by masking critical components of the aquifer such as water sources and flow paths these results also suggest the matrix in eogenetic aquifers is a major pathway for flow even in a system dominated by conduits

geochemical processes and solute transport at the seawater freshwater interface of a sandy aquifer geochemical processes occurring at a seawater freshwater interface were studied in a shallow coastal siliclastic aquifer containing minor amounts of calcite data were collected from 106 piezometers in a 120 m transect from the coastline and landward in the first 40 m from the coastline a wedge of saltwater is intruding below the freshwater aquifer the aquifer is strongly reduced with mineralization of organic matter by methanogenesis in the freshwater aquifer and sulfate reduction dominating in the most seaward part of the saline aquifer the spatial separation of cations in the aquifer indicated a slow freshening process where ca2 from freshwater displaced the marine cations na and mg2 from the exchanger complex the resulting loss of ca2 from solution decreases the saturation state for calcite and possibly causes calcite dissolution a storm flooding event was recorded where pulses of dense seawater sank through the fresh aquifer as a result the terminal electron accepting process switched from methanogenesis to sulfate reduction the pulses of sinking seawater also triggered cation exchange reactions where ca2 was expelled from the exchanger by seawater na and mg2 the released ca2 is being flushed from the aquifer by groundwater flow and this export of ca2 will in the long term cause decalcification of the sediment the water composition in the aquifer is in a transient state as the result of various processes that operate on different timescales oxidation of organic matter occurs continuously but at a rate decreasing on a geological time scale the freshening of the aquifer operates on the timescale of a few years the episodic flooding and sinking of seawater through the aquifer proceeds in the course of days to weeks but occurs irregularly with years in between

solution conduits as indicators of late quaternary sea level position abstract solution conduits or caves can provide a measure of glacio eustatic sea level position for the quaternary in high latitudes cave deposits contain artifacts fossils and sediments that reflect surface conditions with respect to climate secondary calcite deposits most notably stalagmites record growth episodes during ice minima and non growth during ice maxima they provide an indirect estimate of areal ice cover at high latitudes and are an indirect measure of sea level in low latitudes stable carbonate platforms contain caves that provide a direct measure of past sea level position solution conduits developing in a fresh water lens will record the position of the lens and therefore sea level as sea level fluctuates fresh water lens horizons and conduit development horizons will shift preserving a record of past sea level position cave wall rock and cave deposits can produce a chronology for given conduit positions secondary calcite deposits notably stalagmites record growth periods during sea level low stands or ice maxima and record growth hiatuses during flooding by sea level high stands or ice minima the inverse of high latitude stalagmites lighthouse cave san salvador island bahamas records a sea level high stand at 1 to 6 m for some time period between 85 000 and 70 000 years ago based on position and timing of conduit development and records sea level at present elevation for some time period between 49 000 and 37 000 years ago based on a stalagmite with a marine overgrowth

formation of phreatic caves in an eogenetic karst aquifer by co2 enrichment at lower water tables and subsequent flooding by sea level rise formation of extensive phreatic caves in eogenetic karst aquifers is widely believed to require mixing of fresh and saltwater extensive phreatic caves also occur however in eogenetic karst aquifers where fresh and saltwater do not mix for example in the upper floridan aquifer these caves are thought to have formed in their modern settings by dissolution from sinking streams or by convergence of groundwater flow paths on springs alternatively these caves have been hypothesized to have formed at lower water tables during sea level low stands these hypotheses have not previously been tested against one another analyzing morphological data and water chemistry from caves in the suwannee river basin in north central florida and water chemistry from wells in the central florida carbonate platform indicates that phreatic caves within the suwannee river basin most likely formed at lower water tables during lower sea levels consideration of the hydrological and geochemical constraints posed by the upper floridan aquifer leads to the conclusion that cave formation was most likely driven by dissolution of vadose co2 gas into the groundwater sea level rise and a wetter climate during the mid holocene lifted the water table above the elevation of the caves and placed the caves tens of meters below the modern water table when rising water tables reached the land surface surface streams formed incision of surface streams breached the pre existing caves to form modern springs which provide access to the phreatic caves phreatic caves in the suwannee river basin are thus relict and have no causal relationship with modern surficial drainage systems neither mixing dissolution nor sinking streams are necessary to form laterally extensive phreatic caves in eogenetic karst aquifers dissolution at water tables potentially driven by vadose co2 gas offers an underappreciated mechanism to form cavernous porosity in eogenetic carbonate rocks copyright 2012 john wiley sons ltd

regional hydrogeochemistry of a modern coastal mixing zone in west central florida groundwater samples were collected along flow paths in the unconfined upper floridan aquifer that cross the inland freshwater recharge area and the coastal discharge area a groundwater flow and solute transport model was used to evaluate groundwater flow and mixing of fresh and saline groundwater along a cross section of the unconfined upper floridan aquifer results show that between 8 and 15 of the fresh and 30 31 of the saline groundwater penetrates to the depth in the flow system where contact with and dissolution of gypsum is likely the deeply circulating fresh and saline groundwater returns to the near surface environment discharging caso4 rich water to the coastal area where it mixes with fresh cahco3 groundwater resulting in a prediction of calcite precipitation in the modern mixing zone

palaeohydrogeological control of palaeokarst macro porosity genesis during a major sea level lowstand danian of the urbasa andia plateau navarra north spain abstract an extensive palaeokarst porosity system developed during a pronounced mid paleocene third order lowstand of sea level is hosted in danian limestones of the urbasa andia plateau in north spain these limestones were deposited on a 40 50 km wide rimmed shelf with a margin characterised by coralgal buildups and coarse grained bioclastic accumulations the sea level fall that caused karstification was of approximately 80 90 m magnitude and 2 5 ma in duration during the exposure a 450 m wide belt of sub vertical margin parallel fractures developed a few hundred metres inboard of the shelf edge most fractures are 90 100 m deep average 1 m in width and are associated with large erosional features created by collapse of the reefal margin inland from the fracture belt three superimposed laterally extensive cave systems were formed over a distance of 3 5 km perpendicular to shelf edge at depths ranging from 8 31 m below the exposure surface the palaeocaves range from 0 3 to 2 m in height average 1 5 m high they show no evidence of meteoric processes and are filled with thanetian grainstones rich in reworked microcodium a lithology that also occurs infilling the fractures the caves are interpreted as due to active corrosion at the saline water fresh water mixing zone caves are missing from the shelf edge zone probably because the fractures beheaded the meteoroic lens preventing mixing zone cave development beyond the fracture zone towards the platform interior each cave system passes into a prominent horizon averaging 1 m in thickness of spongy porosity with crystal silt infills and red fe oxide coatings the spongy horizons can be traced for 5 5 km inboard from the cave zone and occur at 10 5 m 25 m and 32 m below the exposure surface in the inland zone two additional horizons with the same spongy dissolution have been recognised at depths of 50 m and 95 m all are analogous to swiss cheese mixing zone corrosion in modern carbonate aquifers and probably owe their origins to microbially mediated dissolution effects associated with a zone of reduced circulation in marine phreatic water in the most landward sections a number of collapse breccia zones are identified but their origin is unclear the palaeokarst system as a whole formed during the pulsed rise that followed the initial sea level drop with the three main cave spongy zones representing three successive sea level stillstands recorded by stacked parasequences infilling large erosional scallops along the shelf margin the geometry of the palaeo mixing zones indicates a low discharge system and together with the lack of meteoric karstic features favours a semi arid to arid climatic regime which is further supported by extensive calcrete bearing palaeosols occurring in coeval continental deposits

evolution of selenium concentrations and speciation in groundwater flow systems upper floridan florida and carrizo sand texas aquifers selenium concentrations and speciation were determined in groundwater samples collected from wells along flow paths in the upper floridan florida and the carrizo sand texas aquifers selenium concentrations in groundwaters from both aquifers are low i e nanomolal concentrations and vary both in magnitude and species i e se vi se iv se ii distributions along the flow paths redox sensitive parameters i e fe iii fe ii s ii dissolved oxygen eh are consistent with oxic and suboxic conditions in and proximal to the recharge zones where fe iii reduction buffers the redox state followed by anoxic sulfidic conditions further down gradient along the flow paths where sulfate reduction predominates evolving redox conditions in conjunction with changes in groundwater ph along the flow paths exert important controls on the distribution of se species in groundwaters from both aquifers within the upper floridan aquifer for example selenate se vi and selenite se iv predominate in oxic suboxic groundwaters from near the recharge zone whereas beyond 32 km se iv and organic selenide i e se ii are the chief dissolved forms the change in se speciation near the recharge zone coincides with the apparent initiation of fe iii reduction further down gradient along the flow path where sulfate reduction buffers the redox conditions se ii becomes locally important for the carrizo sand aquifer se iv dominates in groundwater from near the recharge zone where se vi exhibits variable concentrations and se ii is generally low and relatively constant redox conditions of groundwater from the recharge zone i e 0 to 8 km vary between oxic and suboxic however with flow beyond 8 km the aquifer becomes confined and dissolved fe ii concentrations increase dramatically suggesting the importance of fe iii reduction in the zone of fe iii reduction se iv is the dominant dissolved se species and its coincident rise in concentration with the increasing fe ii concentrations suggests se iv release to groundwaters via reductive dissolution of fe iii oxides oxyhydroxides with flow beyond 41 km sulfate reduction predominates and ph exceeds 8 these observations suggest that ph induced desorption of se vi from aquifer mineral surface sites may be important however mixing of groundwaters from multiple flow paths line and or compositional heterogeneity of aquifer sediments may also contribute overall the data are consistent with reductive dissolution of fe iii oxides oxyhydroxides adsorption desorption reactions and mixing of multiple flow lines as exerting important controls on se concentrations and speciation in groundwater flow systems

the velocity and vorticity structure of the agulhas current at 32 s the full depth velocity field of the agulhas current the western boundary current of the southwest indian ocean has been directly measured using a lowered acoustic doppler current profiler ladcp fifteen combined conductivity temperature depth ctd and ladcp stations were occupied across the current at 32 s off the east coast of south africa in february march 1995 as part of the world ocean circulation experiment indian ocean program the deep velocity structure of the agulhas current was found to be very different than previously described using geostrophic estimates in particular ladcp results reveal a v shaped pattern for the level of no motion across the agulhas current and an agulhas undercurrent is observed flowing equatorward below 800 m depth directly beneath the surface core of the poleward flowing agulhas current comparisons of direct and geostrophic velocities suggest that the velocity structure of the agulhas current is essentially geostrophic below about 200 m depth where differences are generally less than estimated errors above these depths the ladcp measured shears and geostrophic shears exhibit differences and velocities can diverge shipboard adcp data support ladcp results near the surface indicating that both instruments are measuring real signals the geostrophic and ladcp measured shears are well matched away from the surface and a depth averaged fit below 200 m between them exhibits small standard deviations the geostrophic volume transport of the agulhas current as referenced to ladcp is 73 sv and is just 3 different from the direct ladcp transport estimate the most recent full depth estimate of agulhas current transport in the literature is given by toole and warren 1993 who estimate a geostrophic volume transport of 85 sv the baroclinic velocity structures from their section and from this work are similar indicating that the difference in the transport estimates is due to the choice of geostrophic reference level and ultimately to the presence of the previously unobserved agulhas undercurrent combined ctd ladcp data are very useful for potential vorticity analysis since velocity and density measurements are simultaneous and coincident the vorticity structure of the agulhas current suggests the presence of a mixing boundary at middepths similar to features observed in the gulf stream the feature appears to be associated with a sharp upturn in isopycnals coincident with the foot of the continental slope the boundary inhibits cross stream mixing of intermediate water masses and may help explain the appearance of a discrete filament of red sea water inshore of antarctic intermediate waters in the same density layer despite intense cross stream shears

hydrogeochemistry of grand cayman british west indies implications for carbonate diagenetic studies abstract groundwater in the dolostone aquifers of the bluff group oligocene miocene on grand cayman is divided into fresh lightly and highly brackish and saline type i and ii zones according to chemical characteristics that were determined during a 3 year 1985 1988 monitoring program brackish and type i saline waters display the greatest variation in chemical properties whereas the type ii saline water has the most stable chemical characteristics most groundwaters from these dolostone aquifers are thermodynamically capable of precipitating calcite and or dolomite the saturation indices for these minerals however vary through time and space even in the context of small water lens simple mixing of fresh and sea water cannot explain the chemistry of the water found in the joint and karst controlled dolostone aquifers of grand cayman deviation from a simple mixing model is due to variations caused by tidal fluctuation the rate of rain water recharge influx of ca rich groundwater from the surrounding limestone aquifers influx of co 2 rich surface water from sinkholes and swamps and water rock interactions dissolution and precipitation of calcite and dolomite sustained groundwater abstraction from a lens can significantly alter the hydrochemistry of the water lens this suggests that hydrochemical characterization of small fresh water lenses like those on grand cayman cannot be based on spot or short term sampling interpretation of such fluids in terms of calcite dolomite precipitation and or dissolution must be treated with caution if the data base has not been derived from long term monitoring

eddy mean flow interaction in the gulf stream at 68 w part i eddy energetics abstract from june 1988 to august 1990 twelve tall high performance current meter moorings measured the gulf stream s velocity and temperature fields at nominal depths of 400 m 700 m 1000 m and 3500 m along three lines centered at 68 w the overall eddy variability during the 26 month experiment was dominated by six large amplitude trough formation events with each event lasting approximately one month to determine the source s of energy for this eddy variability the eddy energy budget is evaluated traditionally the baroclinic conversion of mean potential energy to eddy potential energy is defined as a downgradient heat flux however because a nondivergent heat flux can be downgradient even under conditions in which there is no barolinic conversion occurring a better more dynamically correct definition of a baroclinic conversion rate is a downgradient horizontally divergent heat flux the horizontally divergent heat flux component is estimated to be approximately half the full horizontal hea

geochemical evolution and timescale of seawater intrusion into the coastal aquifer of israel this study is an attempt to quantify the geochemical processes and the timescale of seawater intrusion into a coastal aquifer from changes in the major ionic composition of the water and the natural distribution of the cosmogenic isotopes 14c and 3h for that purpose we sampled saline and brackish groundwaters from the israeli coastal aquifer a multilayer sampler mls was used to obtain very high resolution 10 cm profiles across the fresh saline water interface fsi the chemical and stable isotope data revealed three distinct water types end members that are located in different zones on the route to the coastal aquifer 1 slightly modified mediterranean seawater sws 2 slightly diluted with up to 20 fresh groundwater saline groundwater sds and 3 fresh groundwater fgw the sws samples generally show an excess of total alkalinity and total dissolved inorganic carbon dic and a depletion of 13cdic and 14cdic with respect to normal seawater indicating that anaerobic oxidation of organic matter is the first diagenetic reaction that affects seawater during its penetration into the bottom sediments sds waters appear when sws is slightly diluted gain ca2 and sr2 and is depleted in k suggesting that the main processes that transform sws into sds are slight dilution with fresh groundwater and cation exchange at the fresh saline water interface sds generally shows conservative mixing with fgw inspection of chemical data from coastal aquifers around the world indicates that intensive ion exchange in slightly diluted saline groundwater is a globally important phenomenon of seawater intrusion most of our saline groundwater samples contain substantial amounts of 3h suggesting that penetration of mediterranean seawater and its inland travel to a distance of 50 100 m onshore occurred 15 30 yr ago this is supported by the 14cdic mass balance that explains the relatively low 14cdic activities in the sds as influenced by diagenesis and not by simple radioactive decay

variability and coherence of the agulhas undercurrent in a high resolution ocean general circulation model abstract the agulhas current system has been analyzed in a nested high resolution ocean model and compared to observations the model shows good performance in the western boundary current structure and the transports off the south african coast this includes the simulation of the northward flowing agulhas undercurrent it is demonstrated that fluctuations of the agulhas current and undercurrent around 50 70 days are due to natal pulses and mozambique eddies propagating downstream a sensitivity experiment that excludes those upstream perturbations significantly reduces the variability as well as the mean transport of the undercurrent although the model simulates undercurrents in the mozambique channel and east of madagascar there is no direct connection between those and the agulhas undercurrent virtual float releases demonstrate that topography is effectively blocking the flow toward the north

the geochemistry of carbonate diagenesis the past present and future stable carbon and oxygen isotopes 18o and 13c values and trace elements have been applied to the study of diagenesis of carbonate rocks for over 50 years as valuable as these insights have been many problems regarding the interpretation of geochemical signals within mature rocks remain for example while the 18o values of carbonate rocks are dependent both upon the temperature and the 18o value of the fluid and additional information including trace element composition aids in interpreting such signals direct evidence of either the temperature or the composition of the fluids is required such information can be obtained by analysing the 18o value of any fluid inclusions or by measuring the temperature using a method such as the clumped isotope technique such data speak directly to a large number of problems in interpreting the oxygen isotope record including the well known tendency for 18o values of carbonate rocks to decrease with increasing age unlike the 18o 13c values of carbonates are considered to be less influenced by diagenesis and more a reflection of primary changes in the global carbon cycle through time however many studies have not sufficiently emphasized the effects of diagenesis and other post depositional influences on the eventual carbon isotopic composition of the rock with the classic paradigm that the present is the key to the past being frequently ignored finally many additional proxies are poised to contribute to the interpretation of carbonate diagenesis although the study of carbonate diagenesis is at an exciting point with an explosion of new proxies and methods care should be taken to understand both old and new proxies before applying them to the ancient record

identification of indicators of groundwater quality formation process using a zoning model summary drinking water safety is a world wide focus in yinchuan plain of western china groundwater is mostly saline water and it has generated many problems for the life of local residents yinchuan plain exhibits differences from the mountain area to the plain in terrain and elevation and landforms and scales such differences resulted in hydro geological water storage structures with different water yield properties and permeabilities of the aquifers these water storage structures are the places where the groundwater moves and is retained as well as where the air water rock interaction and the migration and differentiation between substances in the water take place with the arid climate and intense irrigation in yinchuan plain the hydro chemical features of the groundwater exhibit distinct zonation to explore the formative mechanism of the groundwater quality in yinchuan plain a zoning model for the formation of groundwater quality is established in three layers the first layer shows the geological and hydrogeological conditions that express the landform and landscape geological age lithology and hydrodynamic features of the studied area the second layer indicates the zonation of the formation of groundwater quality according to the major hydro geochemical actions the plain is divided from west to east into lixiviation evaporation and evaporation mixing zones the third layer contains the hydrodynamic features that express the hydro chemical type salinity and the contents of the major ions as well as trace elements fluorine and arsenic the features of each zone are quantitatively expressed with thermodynamic hydrodynamic and hydro chemical indicators

conduit enlargement in an eogenetic karst aquifer summary most concepts of conduit development have focused on telogenetic karst aquifers where low matrix permeability focuses flow and dissolution along joints fractures and bedding planes however conduits also exist in eogenetic karst aquifers despite high matrix permeability which accounts for a significant component of flow this study investigates dissolution within a 6 km long conduit system in the eogenetic upper floridan aquifer of north central florida that begins with a continuous source of allogenic recharge at the santa fe river sink and discharges from a first magnitude spring at the santa fe river rise three sources of water to the conduit include the allogenic recharge diffuse recharge through epikarst and mineralized water upwelling from depth results of sampling and inverse modeling using phreeqc suggest that dissolution within the conduit is episodic occurring only during 30 of 16 sampling times between march 2003 and april 2007 during low flow conditions carbonate saturated water flows from the matrix to the conduit restricting contact between undersaturated allogenic water with the conduit wall when gradients reverse during high flow conditions undersaturated allogenic recharge enters the matrix during these limited periods estimates of dissolution within the conduit suggest wall retreat averages about 4 10 6 m day in agreement with upper estimates of maximum wall retreat for telogenetic karst because dissolution is episodic time averaged dissolution rates in the sink rise system results in a wall retreat rate of about 7 10 7 m day which is at the lower end of wall retreat for telogenetic karst because of the high permeability matrix conduits in eogenetic karst thus enlarge not just at the walls of fractures or pre existing conduits such as those in telogenetic karst but also may produce a friable halo surrounding the conduits that may be removed by additional mechanical processes these observations stress the importance of matrix permeability in eogenetic karst and suggest new concepts may be necessary to describe how conduits develop within these porous rocks

palaeo mixing zone karst features from palaeocene carbonates of north spain criteria for recognizing a potentially widespread but rarely documented diagenetic system abstract marine meteoric mixing zone dissolution effects are a major feature of present day karst systems in carbonate platforms yet are rarely reported in the geological record an example is described from the upper danian platform limestones of the alava province in the western pyrenees north spain this consists of several narrow zones with sponge like porosity analogous to the swiss cheese features found in present day mixing zones these zones are stained by fe oxides and overlie limestones which are irregularly dolomitized and contain disseminated pyrite these high porosity zones are interpreted as having developed in marine mixing zones where mixing corrosion and microbially mediated processes increased dissolution if collapsed ancient mixing zones could be misinterpreted as terra rossa palaeosols the main criteria to identify them as mixing zone products are their occurrence below a palaeo meteoric phreatic zone their association with stratified oxic and anoxic redox zones and petrographic evidence for highly variable calcite saturation states

adsorption and desorption of phosphate on limestone in experiments simulating seawater intrusion abstract this study investigates the potential release of po 4 3 from carbonate aquifers exposed to seawater intrusion adsorption and desorption of po 4 3 in the presence of deionized water diw and seawater were conducted on a large block of pleistocene age limestone to simulate the effects of seawater intrusion into a coastal carbonate aquifer at the laboratory scale the limestone showed strong adsorption of po 4 3 in diw while adsorption was significantly less in the presence of seawater dissolution of caco3 was found to prevent po 4 3 adsorption at salinities less than 30 psu adsorption of po 4 3 was limited at higher salinities 30 33 psu due to competition with hco 3 ions for adsorption sites at a salinity po 4 3 absorption occurred as caco3 precipitated concentrations of po 4 3 between 2 and 5 mol l were released by desorption when the limestone was exposed to seawater the results of this study suggest that as seawater intrudes into an originally freshwater coastal aquifer adsorbed po 4 3 may be released into the groundwater consequently adsorbed po 4 3 is expected to be released from coastal carbonate aquifers world wide as sea level continues to rise exposing more of the freshwater aquifer to seawater

late holocene mangrove development and onset of sedimentation in the yax chen cave system ox bel ha yucatan mexico implications for using cave sediments as a sea level indicator abstract this study examines the relationship between the flooding of cenotes and formation of coastal mangrove with holocene sea level rise and the onset of aquatic sedimentation in yax chen a cave system in quintana roo on mexico s yucatan peninsula sediment depth measurements n 180 were collected along 2 7 km of an underwater cave passage and three cores were radiocarbon dated to examine both the extent and timing of sedimentation in the cave basal radiocarbon ages 4 ka for aquatic sediments in the cave show that holocene sea level rise flooded cenotes creating sunlit open water conditions with associated mangroves on the upper karst surface these conditions initiated abundant and widespread sedimentation in the cave cenote surface area controlled the long term sediment accumulation in the cave passages through primary productivity in the sunlit open water areas of the cenotes this primary productivity was enhanced with mangrove formation which causes funneling of precipitation and nutrient rich waters into the cenotes from the mangroves accumulation histories from the radiocarbon dated sediment cores n 3 were compared with accumulation histories in previously published studies including actun ha mexico and green bay cave gbc bermuda

evidence of cryostatic desiccation processes associated with sand intraclasts within diamictons southern ontario canada shore bluffs at mohawk bay southern ontario reveal within a complex melange of glacial sediments brecciated diamicton surrounding sand block intraclasts typically each intraclast has an aureo

differential dissolution of a pleistocene reef in the ground water mixing zone of coastal yucatan mexico a geochemical explanation is provided for the extensive dissolution observed along the carbonate coast of the yucatan peninsula mexico mixing of fresh ground water with subterranean caribbean seawater generates a highly reactive geochemical zone that enhances aragonite and calcite dissolution and permits neomorphism of aragonite mixing zone dissolution caused by ground water discharge is a major geomorphic process in developing caves coves and crescent shaped beaches along the yucatan coast such dissolution has probably been a significant control on permeability and porosity distribution in carbonate rocks in the geologic record

carbonate dissolution and precipitation in coastal environments laboratory analysis and theoretical consideration 1 we have conducted laboratory experiments to examine caco3 dissolution and precipitation in saltwater freshwater mixing zones with a view to understanding and predicting porosity changes in coastal environments mixing of seawater or saline subsurface water with fresh water can be of major importance in the chemical diagenesis of carbonate rocks and sediments we used artificial seawater and nacl solutions of different concentrations under different co2 partial pressures and with different mixing ratios two dimensional flow cells filled with glass beads and crushed calcium carbonate rock were used to measure calcium carbonate precipitation and dissolution respectively an important feature of these experiments is that the results are shown to agree well with a relatively simple transport theory describing mineral precipitation dissolution that results from the nonlinear dependence of caco3 saturation upon electrolyte concentration the theory demonstrates that the rate of dissolution or precipitation depends on the curvature and sign of the solubility as a function of salinity the square of the salinity gradient and the macroscopic dispersion coefficient the theory is largely scale independent and depends upon field parameters that can be determined analysis of data from three field sites yucatan peninsula bermuda and mallorca demonstrates excellent agreement between field observations and theory

physical and chemical stratigraphy suggest small or absent glacioeustatic variation during formation of the paradox basin cyclothems the paradox basin cyclothems previously have been interpreted as milankovitch style glacial interglacial cycles from the late paleozoic ice age but an unambiguous test for a glacioeustatic origin has not been conducted a high resolution coupled chemical and physical stratigraphic analysis of two outcrop sections and three core segments provides new evidence that supports either minor sea level change of several meters or an autocyclic mechanism for parasequence formation high amplitude sea level change is ruled out by the scale of thin top negative isotopic meteoric diagenesis trends associated with parasequence tops and subaerial exposure fabrics isotopic gradients from shelf light to basin heavy indicate that parasequences are deposited diachronously with isotopes of more distal sections recording increased basin restriction these results support the idea that the late pennsylvanian was a prolonged period of relatively static eustasy agreeing with recent studies in the western usa the methods provide a new set of tools and context for extracting environmental information from cyclic upward shallowing carbonate parasequences

unconformities and porosity development in carbonate strata ideas from a hedberg conference the purpose of this paper is to highlight ideas from a hedberg conference concerning detection of unconformities and associated porosity in carbonate strata many types of information including cores and outcrops seismic data eustatic sea level curves wireline logs biostratigraphic data stable isotope trends cycle stacking patterns and tectonic and basin evolution models can be used to predict and or detect subaerial unconformities all methods of detecting subaerial exposure with these types of information have limits and pitfalls detailed analysis of the stratigraphy sedimentology and diagenetic history of a rock sequence from outcrop or core data is considered the most reliable means of detecting subaerial exposure though an integrated approach using all a ailable information is recommended the relationship between subaerial exposure and subsurface porosity in carbonates is not simple or easily predicted subsurface porosity is the product of many factors operating during deposition subaerial exposure and burial several concepts should be recognized when evaluating porosity associated with subaerial unconformities 1 carbonate diagenesis during subaerial exposure rearranges pore networks but usually does not increase the total porosity near surface dissolution can simply lower a topographic surface without increasing porosity within the host limestone in many cases total porosity in carbonates under unconformities is actually reduced during subaerial exposure 2 permeability is likely to change more than porosity during subaerial exposure increasing in some c ses but decreasing in others 3 pore systems evolve with time during subaerial exposure short periods of subaerial exposure 10 000 400 000 yr are often associated with greater porosity than long intervals of subaerial exposure 1 20 million yr prolonged subaerial exposure may change permeability less than porosity because high permeability karst related conduits can form quickly and persist for millions of years 4 many carbonates subjected to subaerial exposure have little or no porosity in the deep subsurface because compaction cementation and stratal collapse reduce porosity during burial 5 unconformity related diagenesis may enhance reservoir potential by creating pore systems that are resistant to compaction during deeper burial 6 vugs caverns and breccias can fo m in the deep subsurface because of dissolution by basinal fluids independent of subaerial exposure 7 lithologic changes at unconformities like shales overlying carbonates can influence the flow of subsurface fluids during end page 857 deeper burial resulting in deep burial dissolution localized along unconformities if subaerial exposure and exposure surfaces are integrated into a sequence stratigraphic paleogeographic and climatic framework systematic and hopefully predictable patterns will emerge however we do not fully understand the complex interplay between the factors critical to creating and preserving porosity in carbonates additional research is needed to quantify critical processes and products so we can reliably predict porosity associated with subaerial exposure during exploration in frontier basins and on a smaller scale during reservoir analysis

agulhas current meanders facilitate shelf slope exchange on the eastern agulhas bank large solitary meanders are arguably the dominant mode of variability in the agulhas current observational studies have shown that these large meanders are associated with strong upwelling velocities and affect the shelf circulation for over 100 days per year here 10 year time series from two ocean general circulation models are used to create a composite picture of the agulhas current and its interactions with the shelf circulation in meandering and nonmeandering modes both models show good agreement with the size propagation speed and frequency of observed meanders these composite meanders are then used to examine the response of shelf waters to the onset of large meanders with the use of model output enabling the dynamics at depth to be explored results show a composite mean warming of up to 3 c of depth averaged temperature along the shelf edge associated with an intrusion of the current jet onto the shelf driven by an intensification of the flow along the leading edge of large meanders however this intensification of flow results in cooling of bottom waters driving cold events at the shelf break of 10 c at 100 m thus the intensification of the current jet associated with large meander events appears to drive strong up and downwelling events across the inshore front of the agulhas current facilitating shelf slope exchange

frost susceptibility related to soil index properties the analysis of frost heave data on several soils confirmed that segregation potential hence frost susceptibility of saturated soils was best related to the average size of the fines fraction the specific surface area of the fines fraction and the ratio of the material s water content to its liquid limit the influence of overburden pressure can also be accounted for by an empirical relationship between the segregation potential the average size of the fines fraction and the compressibility index of the soil the segregation potential was also proportional to the relative fines content in soils where the fines do not completely fill the voids of the coarser fraction this study led to the development of a new frost susceptibility assessment methodology based on simple geotechnical routine soil index testing that was validated on a highway site on frost susceptible subgrade till key words frost heave index properties criteria soil segregation potential

island groundwater resources impacts of abstraction and a drying climate rottnest island western australia abstract coastal aquifers provide a source of water for more than one billion people with island freshwater lenses being some of the most vulnerable coastal groundwater systems due to their susceptibility to saltwater intrusion basic hydrogeological and hydrochemical knowledge regarding the recharge and salinisation processes of freshwater lenses is important to ensure sustainable utilisation especially considering possible climate change effects this paper makes an assessment of the fate of a freshwater lens in a drying climate through a comparison of current and historic hydrochemical data which to the author s knowledge is unique to this study fresh groundwater stable isotope signatures 18 o 2 h reflect local amount weighted rainfall signatures 18 o 3 8 2 h 15 1 and confirm rainfall as the origin of fresh groundwater 18 o 4 47 to 3 82 2 h 20 0 to 16 6 mixing with seawater was identified through enriched groundwater 18 o and 2 h signatures maximum values of 0 36 and 1 4 respectively compared to local rainfall and higher salinity maximum 29 267 mg l total dissolved solids tds in a number of monitoring wells around the freshwater lens enhanced seawater intrusion detected in the northern section of the lens area was identified through significantly increased tds values over the last 20 40 years with increases of up to 3000 observed between 1990 and 2014 a reduction in the extent of freshwater by approximately 1 km 2 was identified since 1977 which was found to be primarily caused by a reduction in recharge to the freshwater lens due to a 20 decline in winter rainfall in the south west western australian region since the mid 1960s groundwater abstraction was found to equate to between 5 and 9 of the estimated recharge for the island and is not a significant factor in the reduction of the lens extent compared to the observed decline in rainfall recharge interestingly seawater intrusion into the fresh water lens was found to occur by older seawater 0 03 0 09 tu in regions of the lens that were previously fresh or slightly brackish while one sample 0 67 tu suggests either modern seawater intrusion or mixing of older saline groundwaters 60 years with rainfall recharge the use of tritium dating in this island aquifer was essential in identifying older seawater that was previously unidentified until now the isotopic and hydrochemical tools used in this paper quantify the effects of groundwater abstraction and climate variability on the freshwater lens and have implications for the sustainable management of the groundwater resource on rottnest island and elsewhere

sequence stratigraphy of a late devonian ramp situated reef system in the western canada sedimentary basin dynamic responses to sea level change and regressive reef development the alexandra formation located in the northwest territories of canada is formed of a late devonian frasnian reef system that developed on a gently sloping epicontinental ramp in the western canada sedimentary basin high resolution sequence stratigraphic analysis of its deposits delineates two reef complexes that are separated by a type i sequence boundary the second reef complex developed on the outer ramp basinward of the first after sea level fell 17 m stratigraphic complexity of the second reef complex was a result of its initiation during forced regression and its development through an entire cycle of sea level rise followed by sea level fall its highstand systems tract was not characterized by high rates of carbonate production or sediment shedding rather these features took place as sea level fell after its highstand systems tract the sequence stratigraphic framework of this regressive reef system highlights a number of depositional parameters that differ from high relief shelf situated reef systems with steep narrow margins these have implications for understanding the controls on the development of ramp situated reef systems and the nature of reef systems with gently sloping profiles this study demonstrates that the development of stromatoporoid reef systems may be far more complex than generally realized and that high resolution sequence stratigraphy may provide the tools for better understanding of complex often enigmatic aspects of these systems

transport of calcium magnesium and so4 in the floridan aquifer west central florida implications to cementation rates prior hydrogeochemical studies have documented a down gradient increase in dissolved calcium magnesium and so4 in the confined upper floridan aquifer and have attributed the changes to dissolution of gypsum and dolomite and precipitation of calcite in this study hydrochemical data mol l 1 are coupled with calculated discharges 1 year 1 to calculate the down gradient changes in ion fluxes mol year 1 along two predevelopment stream tubes in west central florida evaluation of ion inflows including leakage from above and outflows to and from well to well sectors of the stream tubes enables isolation of the changes in ion fluxes due to the previously identified reactions and hence quantification of the geological work done by those reactions in the sectors over about half of the stream tubes the amount of calcite precipitation is small to non existent 0 0 25 of the bulk volume per million years which is consistent with geological evidence significant cementation rates are calculated for areas influenced by upward flow such as at the end of the stream tubes and along the peace river half of these significantly large values are impossibly large apparently reflecting an inherited signal from a flow history below the depth of the upper floridan wells similarly mass balance results that suggest significant dissolution of dolomite and gypsum probably reflect upwelling not diagenesis at the depths of the sampled wells

skeletal aragonite dissolution from hypersaline seawater a hypothesis abstract hypersaline seawater has often been invoked as a mechanism to explain the pervasive dolomitization of ancient platform carbonates but its potential in causing skeletal aragonite dissolution of these carbonates has rarely been investigated previous experimental and theoretical studies have demonstrated that hypersaline seawater is undersaturated with respect to aragonite when evaporation reaches a certain degree it is contended here that similar undersaturation could also have occurred in ancient evaporitic seas geological evidence from the miocene carbonates of se spain gulf of suez red sea and iraq suggests that this may have been the case despite differences in their geological settings these carbonates have common diagenetic features including 1 widespread dissolution of skeletal aragonite with little or no calcite cementation and 2 pervasive dolomitization dolomite occurs as both a replacement of mg calcite and mouldic pore filling cement the association of the dolomites with evaporites their relatively heavy oxygen isotopic values and widespread distribution suggest a hypersaline seawater origin of these dolomites petrographic data indicate that skeletal aragonite was dissolved during dolomitization because the aragonite fossil moulds contain dolomite cements but no pre dolomitization calcite cements implying that the dolomitizing fluids hypersaline seawater were probably undersaturated with respect to aragonite the dissolved calcium may have been subsequently incorporated into the dolomite this may help to explain the lack of calcite cementation despite the extensive skeletal aragonite dissolution

a mechanism for differential frost heave and its implications for patterned ground formation the genesis of some types of patterned ground including hummocks frost boils and sorted stone circles has been attributed to differential frost heave dfh however atheoretical modelthat adequatelydescribes dfhhasyettobe developedand validated in this paper we present a mathematical model for the initiation of dfh and discuss how variations inphysical i e soil vegetationproperties andenvironmental i e ground air temperatures properties affect its occurrence and length scale using the fowler and krantz multidimensional frost heave equations a linear stability analysis anda quasi steady statereal timeanalysisareperformed resultsindicatethatthefollow ing conditions positively affect the spontaneous initiationof dfh silty soil smallyoung s modulus small non uniform surface heat transfer or cold uniform surface temperatures and small freezing depths the initiating mechanism for dfh is multidimensional heat transfer within the freezing soil numerical integration of the linear growth rates indi catesthatexpressionof surfacepatternscanbecomeevidentonthe10 100yeartime scale

coral ba ca molar ratios as a proxy of precipitation in the northern yucatan peninsula mexico the yucatan peninsula consists of a karstic terrain that allows the aquifer to directly recharge from rainfall due to the various dissolution precipitation reactions occurring during groundwater flow the groundwater discharge in the coastal zone becomes a source of trace elements including ba the aim of this study was to use the coralline ba ca record as a proxy of precipitation under the consideration that rainfall rates vary at inter annual time scales annual ba ca ratios both the total content ba catc and the ca substitutive fraction ba cacaf were quantified in a 52 a old coral colony of montastraea annularis from the punta nizuc reef mexican caribbean average ba catc 5 90 0 56 lmol mol was 20 higher than ba cacaf 4 85 0 33 lmol mol indicating that ba is also incorporated in other fractions correlation between annual precipitation and ba catc time series is significant r 0 77 p 0 05 allowing the use of the ba catc ratio as a proxy of precipitation and hence enabling the reconstruction of precipitation patterns through time likewise the ba cacaf ratio can be used for the reconstruction of dissolved ba in coastal seawater 2012 elsevier ltd all rights reserved

a dated cave sediment record of pleistocene transgressions on berry head southwest england berry head a limestone headland in torbay southwest england exhibits a series of subaerial marine erosion platforms and raised beaches spanning an altitude range of 97 m solution caves on the headland show preferred horizontal development at elevations that are correlated with the marine erosion platforms and developed in a marine freshwater mixing zone whose position was controlled by high sea level still stands corbridge cave in berry head quarry lies below the raised beaches in torbay and contains evidence of three marine transgressions in the form of fine grained marine ponding deposits with a marine microfauna uranium series dating of intercalated speleothems indicates that a transgression during oxygen isotope stage 5e reached an elevation of 5 8 m od while an earlier transgression probably during stage 7 reached at least 7 2 m od these findings are used to constrain possible interpretations of the aminostratigraphy of raised beaches in southwest britain and a correlation of the unnamed stage of bowen sykes reeves miller andrews brew and hare with oxygen isotope stage 5e is proposed

karst and early fracture networks in carbonates turks and caicos islands british west indies abstract historically studies of quaternary carbonates have not adequately addressed the influence of early fracture networks on diagenesis because of this lack of detail understanding and predicting fracture related diagenetic heterogeneities and preferential fluid flow pathways in ancient carbonate successions is particularly challenging the pleistocene oolitic grainstones of the caicos platform provide an excellent opportunity to evaluate the relative importance of fractures on early diagenetic alteration styles and are a suitable analog for subsurface carbonate reservoirs detailed analyses of fractures e g orientation aperture spacing fill material from caicos outcrops combined with high resolution three dimensional ground penetrating radar 3d gpr assisted in exploring the causality and distribution of fractures and relationship to karst four models were evaluated to explain the observed distribution of dolines 1 gravitational fractured margin controlled 2 tectonic fracture controlled 3 antecedent topography controlled and 4 a hybrid model based on observations of numerous fractures n 306 on the western caicos platform early fractures are abundant and dominantly margin parallel these fracture networks are well established in limestones prior to mineralogical stabilization thereby indicating that diagenetic heterogeneities evolve very early in carbonate diagenesis the spatial distribution of dolines on providenciales is likely the result of a complex interplay between the antecedent topography margin parallel fracture systems and meteoric fluids resultant diagenetic alteration is far more complicated than simple unconfined meteoric lenses associated with topographic highs any attempts to model early diagenesis in carbonates should not dismiss the role of fractures as diagenetic facilitators and diagenetic anisotropy templates

dolomitization of the oligocene miocene bluff formation on grand cayman british west indies the oligocene miocene bluff formation on grand cayman is formed of hard white finely crystalline dolostone in which the precursor textures and fossil microstructures are commonly preserved the d

influence of overconsolidation on the freezing characteristics of a clayey silt laboratory freezing tests were performed on a saturated clayey silt at various overconsolidation ratios ocr to establish the relationship between initial void ratio and stress history and the amount of moisture transfer during freezing the frost heave tests were analysed in terms of the segregation potential as well as a function of the temperature of ice lens formation and the overall hydraulic conductivity of the frozen fringe all other factors being the same the segregation potential was found to increase with increasing values of ocr decreasing initial void ratios however the combined effects of decreasing void ratio and increasing suction at the frost line all other factors being identical in all freezing tests resulted in decreasing segregation potentials this trend was the result of a decrease in the temperature of ice lens formation and the concomitant decrease in overall hydraulic conductivity of the frozen fringe a simple model showed that the capillary unfrozen water between clay

mixing zone diagenesis in the subsurface of florida and the bahamas abstract three cores from great bahama bank and southern florida contain examples of mixing zone diagenesis where typical shallow water aragonite rich sediments were altered to low mg calcite the 40 50 m thick mixing zones are identified on the basis of downcore covariant trends from depleted meteoric 18o 3 2 0 7 13c 1 6 1 8 to enriched marine isotopic values 18o 1 0 0 3 13c 1 9 0 7 the age of the mixing zones varies from late pliocene to pleistocene so these cores provide three independent examples of mixing zone diagenesis mixing zone diagenesis produced a limestone composed of low mg calcite with petrographic fabrics including moldic porosity blocky to dogtooth calcite cementation and recrystallization of lime mud to micrite and microspar the mixing zone diagenetic model predicts alteration in only part of the mixing zone because the alteration recorded in these cores shows continuous alteration through the entire mixing zone we consider the mixing of waters itself to be largely irrelevant rather diagenesis was probably driven by the difference in solubility between aragonite and calcite with some additional dissolution of aragonite driven by the microbial oxidation of buried organic matter the mixing zone has been proposed as a likely location for dolomitization with the exception of some clearly sea floor dolomite in one core unda the mixing zones in these cores lack dolomite despite the sediment clearly having been altered in the mixing zone the lack of dolomite in these mixing zones combined with the extensive literature questioning the chemical reasoning for mixing zone dolomite supports rejection of the mixing zone dolomite model

seawater intrusion in the guanahacabibes peninsula pinar del rio province western cuba effects on karst development and water isotope composition the water resources in the guanahacabibes peninsula are distributed in two areas the northeastern area is characterized by swamps wetlands and lagoons with a low contribution of seawater whereas the area in the southwestern plain shows a considerable development of the karst structures that limits the existence of superficial waters but permits the ingression of the surrounding seawater in this latter area the groundwater showed a marked increase in salinity with the depth in particular groundwater with a seawater fraction of 0 1 had the lowest ca mg carbonates saturation indexes calculated by modeling the mixing between freshwater and seawater using different software thermodynamic databases and equations for activity coefficients generally seawater and groundwaters with an added seawater fraction above 0 60 0 65 showed similar oversaturated indexes in high mg calcites and pure ca carbonates calcite and aragonite differently in the groundwater that showed carbonates undersaturation generally with a seawater fraction between 0 02 and 0 60 the saturation indexes in high mg calcites were 0 2 lower than pure ca carbonates locally the bacterial reduction of the dissolved sulfate enhanced the dissolution of the limestone contributing to the increased development of the karst structures and the seawater intrusion finally the presence near the coastline of fresh ca and na bicarbonate waters was in accordance with the upward flow of the shallow freshwater during the formation of the saline wedge however the oxygen and hydrogen stable isotope composition of the waters showed a probable contribution to the area from a deep aquifer that is recharged in the highest reliefs of the province cordillera de guaniguanico

heterogeneous distributions of co 2 may be more important for dissolution and karstification in coastal eogenetic limestone than mixing dissolution mixing dissolution a process whereby mixtures of two waters with different chemical compositions drive undersaturation with respect to carbonate minerals is commonly considered to form cavernous macroporosity e g flank margin caves and banana holes in eogenetic karst aquifers on small islands macroporosity commonly originates when focused dissolution forms globular chambers lacking entrances to the surface suggesting that dissolution processes are decoupled from surface hydrology mixing dissolution has been thought to be the primary dissolution process because meteoric water would equilibrate rapidly with calcium carbonate as it infiltrates through matrix porosity and because pco2 was assumed to be homogeneously distributed within the phreatic zone here we report data from two abandoned well fields in an eogenetic karst aquifer on san salvador island bahamas that demonstrate pco2 in the phreatic zone is distributed heterogeneously the pco2 varied from less than log 2 0 to more than log 1 0 atm over distances of less than 30 m generating dissolution in the subsurface where water flows from regions of low to high pco2 and cementation where water flows from regions of high to low pco2 using simple geochemical models we show dissolution caused by heterogeneously distributed pco2 can dissolve 2 5 to 10 times more calcite than the maximum amount possible by mixing of freshwater and seawater dissolution resulting from spatial variability in pco2 forms isolated globular chambers lacking initial entrances to the surface a morphology that is characteristic of flank margin caves and banana holes both of which have entrances that form by erosion or collapse after cave formation our results indicate that heterogeneous pco2 rather than mixing dissolution may be the dominant mechanism for observed spatial distribution of dissolution cementation and macroporosity generation in eogenetic karst aquifers and for landscape development in these settings copyright 2015 john wiley sons ltd

groundwater geochemistry fluctuations along a fresh saltwater gradient on the carbonate islands of the lower florida keys abstract climate change will have long lasting effects on the availability of fresh water on small carbonate islands that have isolated fresh groundwater lenses particularly as sea level rises and rainfall regimes shift the carbonate islands of the florida keys provide an ideal location to study the effect of variable rainfall on the aqueous geochemistry of the islands groundwater in a rainfall driven carbonate system the expectation is that limestone dissolution will occur within the vadose zone resulting in increased ions in the groundwater however geochemical processes are also affected by the salinity of groundwater and the extent of the mixing zone between fresh and salt water we chose two islands to conduct the study of the shallow groundwater the largest island in the lower florida keys big pine key bpk and a smaller island upper sugarloaf key slk from may 2011 through april 2012 monthly groundwater samples were collected from 24 shallow 1 m deep wells located along a fresh to saline gradient on both islands groundwater chemistry was compared with rainfall amounts from a weather station on bpk saturation indices for aragonite and calcite generated with geochemical modeling in phreeqc were compared to conservative mixing between gulf of mexico water and freshwater equilibrium to supersaturated conditions with respect to carbonate minerals dominated in all of the groundwater samples saturation indices varied with rainfall with the most supersaturated samples observed after a large rain event and samples approaching equilibrium after the longest period without rainfall calcium in excess of what would be expected from conservative mixing of fresh water and seawater was observed in all groundwater samples and was elevated at near shore locations especially on bpk contrary to expectations dissolution resulting from mixing of freshwater and seawater was not supported in the shallow groundwater instead dissolution within the narrow vadose zone from rain events likely resulted in the excess calcium in the groundwater seasonal fluctuations in groundwater composition were primarily observed on the smaller island and were related to the fresh water balance changing rapidly after a heavy rain event and suggest that a size threshold has been surpassed for a stable lens rising seas will further decrease lens extent and vadose zone depth reducing the potential for future limestone dissolution

a giant underwater encrusted stalactite from the blue hole lighthouse reef belize revisited a complex history of biologically induced carbonate accretion under changing meteoric and marine conditions a late pleistocene to holocene submerged and encrusted speleothem exhibits a complex history including a meteoric phase and two marine phases a combined study using petrography mineralogy and inorganic and organic geochemistry as well as geochronology has shown that phototrophic and heterotrophic biological activity impacted carbonate precipitation during all phases of carbonate accretion the stalactite formed ca 30 m below modern sea level at a marginal overhang in the blue hole of lighthouse reef atoll unlike purely meteoric speleothems the belize example consists of a meteoric core a marine aragonite crust and a serpulid micrite rich outer crust as a result of postglacial flooding of the karst cave the core of the stalactite has a tufaceous texture containing algal or microbial remains and consists entirely of low magnesium calcite formed 19 55 10 68 kyr bp the texture suggests that the stalactite formed at the cave entrance and hence the former cave ceiling had apparently collapsed earlier during the pleistocene oxygen 18o and carbon 13c isotopes across the core suggest a trend towards drier conditions and reduced soil and plant cover after the last glacial maximum the marine aragonite crust consists of stacked botryoids in which individual crystals up to 700 lm have dark terminations enriched in high magnesium calcite this crust accreted from 10 82 to 9 95 kyr bp in warm shallow water during the early holocene thermal optimum carbonate accretion rates were considerable and averaged 125 m yr the crust has a dense laminated texture on one side and a porous shrubby texture on the other the presence of n c16 1 5 n c17 1 6 and 10me c16 fatty acids in the laminated crust suggests that sulfate reducing bacteria contributed to aragonite formation in an environment that was less open than the formation environment of the porous crust where these biomarkers are lacking n c16 1 5 n c17 1 6 or are less abundant 10me c16 enrichment of 34s and 18o in carbonate associated sulfate cas relative to seawater sulfate also suggests sulfate reduction during carbonate formation the greater contribution of heterotrophic processes to aragonite precipitation in the laminated crust is also reflected in 13c values as low as 1 3 whereas no such depletion is observed in the aragonite of the porous crust 13c values as low as 0 0 a pronounced isotopic variability and excursions to positive 13c values as high as 3 5 0 in the inner half of the laminated crust indicate an episodic local impact of photosynthesis on aragonite precipitation whereas the lack of such excursions in the porous crust 13c values as high as 1 5 0 is again best explained by a more open environment of formation after a ca 5 kyr hiatus from 4 39 kyr bp a biogenic crust of abundant serpulids and finely crystalline microbial and detrital carbonate consisting of high magnesium calcite and aragonite accreted on the outer surface of the stalactite outermost crust accretion was probably influenced by the inundation of the lighthouse reef lagoon that started to shed abundant fine grained carbonate sediment into the blue hole the stalactite broke off the cave ceiling either before or after the formation of the outermost crust likely due to seismic movements along the nearby plate boundary the study demonstrates that like speleothems from the terrestrial realm submerged stalactites may have had complex histories with great potential as paleoenvironmental archives

role of mixed layer depth in surface frontogenesis the agulhas return current front air sea interaction processes that modify the sea surface temperature sst front in the agulhas return current region between 40 e and 55 e during austral summer and winter are examined using observational data and output from a high resolution ocean general circulation model while the air sea heat flux frontal variations tend to relax the sst front the frontolysis is amplified damped in summer winter when frontal variations in the mixed layer depth mld are incorporated the stronger weaker frontolysis associated with the mld variations is due to the fact that the warming cooling by the surface heat flux is amplified south of the front where the mld is shallower and is reduced north of the front where the mld is deeper this study is the first to show that the mld variations play an important role in affecting the strength of the sst front

reconstructing water level in hoyo negro quintana roo mexico implications for early paleoamerican and faunal access abstract the skeletal remains of a paleoamerican naia hn5 48 and extinct megafauna were found at 40 to 43 mbsl in a submerged dissolution chamber named hoyo negro hn in the sac actun cave system yucatan peninsula mexico the human remains were dated to between 12 and 13 ka making these remains the oldest securely dated in the yucatan twelve sediment cores were used to reconstruct the holocene flooding history of the now phreatic cave passages and cenotes ich balam oasis that connect to hn four facies were found 1 bat guano and seed sf 2 lime mud mf 3 calcite rafts crf and 4 organic matter calcite rafts om crf which were defined by their lithologic characteristics and ostracod foraminifera and testate amoebae content basal radiocarbon ages ams of aquatic sediments sf combined with cave bottom and ceiling height profiles determined the history of flooding in hn and when access was restricted for human and animal entry our results show that the bottom of hn was flooded at least by 9850 cal yr bp but likely earlier we also found that the pit became inaccessible for human and animal entry at 8100 cal yr bp when water reaching the cave ceiling effectively prevented entry water level continued to rise between 6000 and 8100 cal yr bp filling the cave passages and entry points to hn cenotes ich balam and oasis analysis of cave facies revealed that both holocene sea level rise and cave ceiling height determined the configuration of airways and the deposition of floating and bat derived om guano and seeds calcite rafts which form on the water surface are also dependent on the presence of airways but can also form in isolated air domes in the cave ceiling that affect their loci of deposition on the cave bottom these results indicated that aquatic cave sedimentation is transient in time and space necessitating extraction of multiple cores to determine a limit after which flooding occurred

cyclogenesis in the deep ocean beneath the gulf stream 1 description one of the primary scientific results of the synoptic ocean prediction synop observational program was the discovery of strong cyclones in the deep ocean beneath the large amplitude gulf stream meander troughs that routinely form at about 68 w these strong well organized cyclones extend to at least 3500 m below the sea surface and are an important component of the overall dynamical variability of the gulf stream and adjacent deep waters typically a small amplitude gulf stream meander stalls near 68 w and begins to amplify as the amplitude of troughs in the gulf stream jet increases the currents at 3500 m strengthen and turn forming a cyclonic circulation pattern during synop six well defined instances of meander trough amplification and deep cyclogenesis occurred the cyclones were characterized by strong swirl speeds up to 0 5 m s 1 and were long lived typically lasting 6 9 weeks frequent occurrences present 35 of the time during the 25 month deployment period the structure of the cyclones at 3500 m is characterized by increasing velocity from the cyclone center out to some radius of maximum velocity and decreasing velocity beyond that radius this structure was robust over the lifetime of an event and from event to event cyclone radius and the radius to maximum velocity were consistently 130 km and 55 km respectively evidence of cyclones at upper measurement levels and the low vertical shear values apparent in the deep water below the thermocline indicate that the cyclones extended throughout the entire water column from the benthic boundary layer through the thermocline and to the ocean s surface

groundwater circulation and geochemistry of a karstified bank marginal fracture system south andros island bahamas abstract on the east coast of south andros island bahamas a major bank marginal fracture system characterised by vertically extensive cavern systems blue holes is developed sub parallel to the steep sided deep water re entrant of the tongue of the ocean in addition to providing a discharge route for meteoric mixed and geochemically evolved saline groundwaters a strong local circulation occurs along the fracture system this generates enhanced vertical mixing within voids of the fracture system evidenced by the increasing mixing zone thickness and the thinning and increasing salinity of brackish lens waters from north to south along the fracture system furthermore tidally driven pumping of groundwaters occurs between the fracture and adjacent carbonate aquifer affecting a zone up to 200 m either side of the fracture the resultant mixing of groundwaters of contrasting salinity and pco2 within and along the fracture system and with the surrounding aquifer waters together with bacterial oxidation of organic matter generates significant potential for locally enhanced diagenesis undersaturation with respect to calcite within the fresh or brackish salt water mixing zone is observed in the fracture system and predicted in the adjacent aquifer while mixing between the brackish fracture lens and surrounding high pco2 fresh waters causes dissolution of aragonite but not calcite the latter gives rise to considerable secondary porosity development because active tidal pumping ensures continued renewal of dissolutional potential this is evidenced by calcium and strontium enrichment in the brackish lens which indicates porosity generation by aragonite dissolution at a maximum rate of 0 35 ka 1 up to twice the average estimated for the fresh water lens in contrast saline groundwaters are depleted in calcium relative to open ocean waters suggesting the formation of calcite cements the development of a major laterally continuous cavernous fracture zone along the margin of the carbonate platform permits enhanced groundwater flow and mixing which may result in generation of a diagenetic halo at a scale larger than that generally recognised around syn sedimentary fractures in fossil carbonates this may be characterised by increased secondary porosity where a relative fall in sea level results in exposure and formation of a meteoric groundwater system or cementation by marine calcite both below this meteoric system and where the bank surface is flooded by seawater

eddy diffusivity estimates from lagrangian trajectories simulated with ocean models and surface drifter data a case study for the greater agulhas system the lagrangian analysis of sets of particles advected with the flow fields of ocean models is used to study connectivity that is exchange pathways time scales and volume transports between distinct oceanic regions one important factor influencing the dispersion of fluid particles and hence connectivity is the lagrangian eddy diffusivity which quantifies the influence of turbulent processes on the rate of particle dispersal because of spatial and temporal discretization turbulence is not fully resolved in modeled velocities and the concept of eddy diffusivity is used to parameterize the impact of unresolved processes however the relations between observation and model based lagrangian eddy diffusivity estimates as well as eddy parameterizations are not clear this study presents an analysis of the spatially variable near surface lateral eddy diffusivity estimates obtained from lagrangian trajectories simulated with 5 day mean velocities from an eddy resolving ocean model inalt01 for the agulhas system inalt01 features diffusive regimes for dynamically different regions some of which exhibit strong suppression of eddy mixing by mean flow and it is consistent with the pattern and magnitude of drifter based eddy diffusivity estimates using monthly mean velocities decreases the estimated diffusivities less than eddy kinetic energy supporting the idea that large and persistent eddy features dominate eddy diffusivities for a noneddying ocean model orca05 lagrangian eddy diffusivities are greatly reduced particularly when the gent and mcwilliams parameterization of mesoscale eddies is employed

role of aquitards in hydrogeochemical systems a synopsis abstract aquitards exert significant influence on the hydrogeochemistry of aquifer systems this influence is manifested somewhat differently depending on the relative position of aquitards within a system in the deeper regimes they are influential in the origin and distribution of brines and the development of geopressured zones in intermediate regimes they form multi layered aquifer systems and provide a source of reactive minerals and exchangeable ions in shallow regimes aquitards can influence the topography and drainage patterns this influences the relationship between the water table and the potentiometric surface of confined aquifers controls the rates of infiltration and discharge and controls whether the geochemical system is open or closed to exchange of carbon dioxide gas in coastal areas aquitards can determine the depth of the saltwater freshwater interface its distance from the shoreline and the position of the mixing zone that causes geochemical alteration of minerals and development of porosity

the geochemistry and mixing of leakage in a semi confined aquifer at a municipal well field memphis tennessee usa abstract the memphis aquifer in southwestern tennessee is confined to a semi confined unconsolidated sand aquifer and is the primary municipal water source in the memphis metropolitan area past studies have identified regions in the metropolitan area in which the overlying upper claiborne confining unit lacks significant clay and provides a hydraulic connection between the shallow aquifer and the memphis aquifer in this study major solute chemistry 3h and 3h 3he groundwater dating are used to investigate the extent and chemical effects of leakage through the confining unit to the memphis aquifer in the vicinity of a municipal well field the 3h 3he dates and geochemical modeling of the chemical data are used to constrain mixing fractions and the timing of modern recharge tritium activities of as much as 2 8 tu are observed in shallow production wells but deeper production wells have 3h activities that approach the detection limit trends in water chemistry indicate vertical mixing in the aquifer of shallow na so4 cl rich water and deeper ca mg hco3 rich water water chemistry does not vary consistently with seasonal pumping but 3h activity generally decreases during low use periods stable o and h isotopes show little variation and are not useful groundwater tracers for this study the 3h bearing na so4 cl rich water is interpreted to reflect recharge of modern water through the upper claiborne confining unit the 3h 3he dates from 5 production wells indicate modern recharge that infiltrated 15 20 a ago is present in the shallow production wells geologic data and hydrologic boundary conditions suggest that the most likely source for continued leakage is a nearby stream nonconnah creek geochemical reaction modeling using the netpath computer code suggests that proportions of shallow aquifer water leaking into the memphis aquifer range from 6 to 32 the 3h 3he dating and netpath modeling results correlate well suggesting that these complementary analytical tools provide an effective means to evaluate proportions of modern water leaking into semi confined aquifers these results also indicate a need to carefully consider connections between surface water and semi confined groundwater resources in wellhead protection programs

the effect of a confining unit on the geochemical evolution of ground water in the upper floridan aquifer system in west central florida sections of the upper floridan aquifer system range in character from confined to leaky to unconfined the confining unit is the hawthorn formation a clay rich sequence the presence or absence of the hawthorn formation affects the geochemical evolution of the ground water in the upper floridan aquifer system mass balance and mass transfer models suggest that in unconfined areas the geochemical reactions are dolomite dissolution ion exchange mg for na k sulfate reduction calcite dissolution and co2 exchange in the areas in which the hawthorn formation is leaky the evolution of the ground water is accounted for by ion exchange sulfate reduction calcite dissolution and co2 exchange in the confined areas no ion exchange and only limited sulfate reduction occur and the chemical character of the ground water is consistent with dolomite and gypsum dissolution calcite precipitation and co2 ingassing the hawthorn formation acts both as a physical barrier to the transport of co2 and organic matter and as a source of ion exchange sites but the carbonate mineral reactions are largely unaffected by the extent of confinement of the upper floridan aquifer

palaeokarst evidence for widespread regression and subaerial exposure in the middle katian upper ordovician of baltoscandia significance for global climate we report on widespread and contemporary palaeokarst in the middle katian upper ordovician of sweden estonia and latvia the first major palaeokarst horizon to be reported from the ordovician of baltoscandia the solution features occurwithin a fewmetres of thick zone of limestone immediately belowthe widespread fjacka shale and are related to an unconformity with preserved palaeorelief in the slandrom limestone in sweden and the time equivalent saunja formation in estonia and latvia facies evidence for a karst origin comes fromseveral outcrops and core sections and includes 1 frequent karren likemorphologies interpreted as swiss cheese karst sensu baceta et al 2001 2 local occurrences of solution collapse breccia 3 presence of bladed pseudospar crystals in solution cavities and 4 carbon isotope values indicating meteoric influence to the succession these findings are herein put in context with previously reported large scale erosional channels that may cut down several tens of metres below the fjacka shale in the subsurface baltic sea area and with regional anomalous thickness variations in the slandrom limestone and saunja formation all together forming strong support for regional exposure of the baltoscandian continent in the middle katian high resolution stable isotopic data show that the regression and lowstand of sea level overlap with thewaynesville carbon isotope excursion it resulted in basin wide cessation of carbonate production near the amorphognathus superbus and a ordovicicus conodont zonal boundary the contemporary development of palaeokarst in different confacies belts of the basin suggests that this was an extraordinary sea level lowstand herein interpreted as reflecting a middle katian glaciation less

carbonate dissolution in a modern mixing zone the potential for dissolution of calcite and aragonite and precipitation of dolomite by the mixing of fresh and saline ground waters has been demonstrated theoretically1 3 although geologists have used these processes in the explanation of the diagenesis of recent4 7 and ancient8 12 carbonates there has been only limited investigation of the geochemical processes of modern mixing zones13 14 here we report the results of chemical and rock profiling through a modern mixing zone on andros island in the bahamas our results demonstrate undersaturation of the waters in the mixing zone with respect to aragonite and calcite and corresponding pervasive dissolution of the carbonate rocks at this level undersaturation is significantly enhanced by bacterial processes which are also responsible for precipitation of an iron rich crust despite chemical supersaturation precipitation of dolomite was not observed thereby casting some doubt on the mixing zone model of dolomitization

preliminary assessments on the modes of instability of the antalya sw turkey coastal cliffs cliff erosion and the consequent instabilities present a significant risk to antalya city sw turkey erosional processes include the chemical action of mixing zone water the mechanical action of waves salt erosion and biological degradation the rock properties lithology stratification strength etc are the controlling factors to this erosion the coastal cliffs of antalya are composed of tufa type carbonate rocks which occur in a wide range from collapsible soil to hard rock the instability problems of the cliffs of antalya tufa commonly involve rock fall cave collapse raveling washout of weakly lithified tufa shear failure and secondary toppling secondary toppling type instabilities culmann type failures and complex failures a combination of these two are widespread on the cliffs the occurrence of large failures are usually associated with heavy rainfall as heavy rainfall causes the saturation of pores increases pore water pressures and reduces the strength of the rock comparison between aerial photographs and topographic maps of different dates do not provide evidence of considerable retreat according to the historical data there has been little or no cliff retreat for 2 000 years therefore the erosion rate of the antalya tufa cliffs is said to be so very slow that retreat is valid only in a geological timescale however in an engineering timescale these cliffs are subjected to instabilities and to local failures causing local retreats

selective blackening of bioclasts via mixing zone aragonite neomorphism in late triassic limestone zlatibor mountains serbia a peculiar facies of the norian rhaetian dachstein type platform carbonates which contains large amounts of blackened bioclasts and dissolutional cavities filled by cements and internal sediments occurs in the zlatibor mountains serbia microfacies investigations revealed that the blackened bioclasts are predominantly solenoporaceae with a finely crystalline originally aragonite skeleton of fine cellular structure blackening of other bioclasts also occurs subordinately solenoporacean dominated reefs developed behind the platform margin patch reef tract were the main source of sand sized detritus the blackened and other non blackened bioclasts are incorporated in automicrite cement radiaxial fibrous calcite cements in the dissolutional cavities are also black dark grey or white reworked black pebbles were reported from many occurrences of peritidal deposits in those cases the blackening took place under pedogenic meteoric diagenetic conditions in contrast in the inner platform deposits of the ilidz ya limestone the blackening of bioclasts occurred in a marine meteoric mixing zone as indicated by petrographic features and geochemical data of the skeleton replacing calcite crystals attributes of mixingzone pore waters were controlled by mixing corrosion different solubility of carbonate minerals and microbial decomposition of organic matter in the moderate energy inner platform environment large amounts of microbial organic tissue were accumulated and subsequently decomposed triggering selective blackening in the course of early shallow burial diagenesis the d 18 o and d 13 c values of the mixing zone precipitates and replacive calcite do not produce a linear mixing trend variation mainly resulted from microbial decomposition of organic matter that occurred under mixing zone conditions the paragenetic sequence implies cyclic diagenetic conditions that were determined by marine meteoric and mixing zone pore fluids the diagenetic cycles were controlled by sea level fluctuations of moderate amplitude under a semi arid to semi humid climate

geochemical evolution of groundwater in carbonate aquifers in taiyuan northern china abstract thirty nine samples of both cold and thermal karst groundwater from taiyuan northern china were collected and analyzed with the aim of developing a better understanding of the geochemical processes that control the groundwater quality evolution in the region s carbonate aquifers the region s karst groundwater system was divided into three geologically distinct sub systems namely the xishan mountain karst groundwater subsystem xmk the dongshan mountain karst groundwater subsystem dmk and the beishan mountain karst groundwater subsystem bmk hydrochemical properties of the karst groundwaters evolve from the recharge zones towards the cold water discharge zones and further towards the thermal water discharge zones in the xmk and the dmk the hydrochemical type of the groundwater evolves from hco 3 ca mg in the recharge flow through zone to hco 3 so 4 ca mg so 4 hco 3 ca mg in the cold water discharge zone and further to so 4 ca mg in the thermal water discharge zone by contrast the water type changes from hco 3 ca mg to hco 3 so 4 ca mg in the bmk with almost invariable tds and temperatures all along from the recharge to the discharge zone the concentrations of sr si fe f and of some trace elements al b li mn mo co ni increase as groundwater temperature increases different hydrogeochemical processes occur in the three karst groundwater sub systems in the xmk and the dmk the geochemical evolution of the groundwater is jointly controlled by carbonate dissolution precipitation gypsum dissolution and dedolomitization while only calcite and dolomite dissolution precipitation occurs in the bmk without dedolomitization the hydrogeochemical data of the karst groundwaters were used to construct individual geochemical reaction models for each of the three different karst groundwater sub systems the modeling results confirm that dedolomization is the major process controlling hydrochemical changes in the xmk and the dmk in the thermal groundwaters the dissolution rates of fluorite siderite and strontianite were found to exceed those of the cold karst groundwater systems which can explain the higher concentrations of f fe and sr 2 that are found in these waters

evidence of bottom trapped currents in the kuroshio extension region as partof thekuroshioextensionsystemstudy observations fromfivecurrentmetermoorings revealthat the abyssal currents are weakly bottom intensified in the framework of linear quasigeostrophic flow the best fittedverticaltrappingdepthsrangefrom8to15 kmintheabsenceofsteeptopography butonemooringnear an isolated seamount exhibited vertical trapping that was more pronounced and energetic with a vertical trapping depth of 5 km the ratios of current speeds and geostrophic pressure streamfunctions at the sea surface compared to the bottom are 88 in the absence of steep topography 63 near an isolated seamount and overall on average 83 of their value at a reference depth of 5300 m it is hypothesized that weakly depth dependent eddies impinging upon topographic features introduce to the flow the horizontal length scales of the topography and these smaller lateral scales are subject to bottom intensification

prevalence of strong bottom currents in the greater agulhas system deep current meter data and output from two high resolution global ocean circulation models are used to determine the prevalence and location of strong bottom currents in the greater agulhas current system the two models and current meter data are remarkably consistent showing that benthic storms with bottom currents greater than 0 2 m s 1 occur throughout the agulhas retroflection region south of africa more than 20 of the time furthermore beneath the mean agulhas current core and the retroflection front bottom currents exceed 0 2 m s 1 more than 50 of the time while away from strong surface currents bottom currents rarely exceed 0 2 m s 1 implications for sediment transport are discussed and the results are compared to atmospheric storms benthic storms of this strength 0 2 m s 1 are comparable to a 9 m s 1 beaufort 5 windstorm but scaling shows that benthic storms may be less effective at lifting and transporting sediment than dust storms

reactive transport modeling of calcite dissolution in the fresh salt water mixing zone abstract dissolution of calcite in the saltwater mixing zone of coastal carbonate aquifers has been the subject of numerous studies they conclude that dissolution is driven by mixing of freshwater and saltwater which may lead to undersaturation even if both end members are saturated however as transport in the mixing zone is rather complex a fully coupled reactive transport model is needed to properly understand the interplay between transport and chemistry we perform 1 and 2d simulations to gain insight into the processes controlling dissolution rate exploring its sensitivity to the chemistry of end members and the dispersivity of the medium we conclude that the results of sanford and konikow sanford w e konikow l f 1989 simulation of calcite dissolution and porosity changes in saltwater mixing zones in coastal aquifers water resources research 25 655 667 which used a two step method solely transporting the amount of calcite dissolved are essentially correct but their solution is essentially kinetic with a rate dependent on the time increment used the 1d simulations allow us to show that maximum dissolution rates do occur neither at the location nor for the end members of maximum undersaturation for non reactive mixing in the 1d case enhanced transport at the freshwater end causes dissolution to concentrate there however in the 2d case representative of coastal aquifers maximum dissolution occurs at the saline side near the discharge zone because of a very active convection cell that develops there which enhances mixing and thus reaction rates this mechanism may explain observations at blue holes and should display a positive feedback with dissolution causing an increase in permeability that would lead to increased seawater flux and mixing thus enhancing further dissolution

the early diagenetic origin of lower carboniferous mottled limestones pseudobreccias dark mottles are a prominent and widespread feature of the regressive cyclic shallow marine limestones which form the late asbian succession in many parts of britain the colour difference which defines mottles in outcrop is caused by distinct but often subtle petrographic differences in the limestone fabric specifically mottles contain a light brown coloured opaque inclusion rich calcite spar with characteristic dull brown luminescence mottle spar outside mottle margins this calcite spar is absent with clear inequant blocky cements forming the pore filling phase mottle spar comprises a fabric of irregular crystals predominantly 5 40 m in diameter with more regular crystals up to 100 m diameter often occurring in intraparticle and large interparticle pores under cathodoluminescence mottle spar displays crystal morphologies and growth patterns which indicate that both localized neomorphism and patchy cementation contributed to mottle formation cathodoluminescence cement stratigraphy shows that mottle spar pre dates all other major pore filling cements in the local asbian succession but post dates marine micritization mottle spar sharply defines the moulds of former aragonitic allochems which are now filled by the later clear inequant spar cements this shows that aragonite dissolution occurred after the formation of mottle spar mottles in calcretes contain unaltered allochems which have been protected from the effects of subaerial micritization by mottle spar although mottles are often affected by subaerial brecciation this evidence shows that mottles formed during early diagenesis after marine micritization but before dissolution of aragonite subaerial exposure and meteoritic phreatic cementation mottles represented lithified patches of very low porosity which are interpreted to have formed in the marine freshwater mixing zone during the repeated phases of regression and emergence in the late asbian

use of tritium and helium to define groundwater flow conditions in everglades national park the concentrations of tritium 3 h and helium isotopes 3 he and 4 he were used as tracers of groundwater flow in the surficial aquifer system sas beneath everglades national park enp south florida from ages determined by 3 h 3 he dating techniques groundwater within the upper 28 m originated within the last 30 years below 28 m waters originated prior to 30 years before present with evidence of mixing at the interface interannual variation of the 3 h 3 he ages within the upper 28 m was significant throughout the 3 year investigation corresponding with varying hydrologic conditions in the region of taylor slough bridge younger groundwater was consistently detected below older groundwater in the biscayne aquifer suggesting preferential flow to the lower part of the aquifer an increase in he with depth in the sas indicated that radiogenic 4 he produced in the underlying hawthorn group migrates into the sas by diffusion higher 4 he values in brackish groundwaters compared to fresh waters from similar depths suggested a possible enhanced vertical transport of 4 he in the seawater mixing zone groundwater salinity measurements indicated the presence of a wide 6 28 km seawater mixing zone comparison of groundwater levels with surface water levels in this zone indicated the potential for brackish groundwater discharge to the overlying everglades surface water

strong bottom currents and cyclogenesis in drake passage 1 observations from 38 bottom moored current and pressure recording inverted echo sounders cpies deployed in drake passage during the 2007 2008 international polar year provide unprecedented coverage of near bottom currents and pressures spanning the entire antarctic circumpolar current year long mean currents exceed 10 cm s 1 north of the polar front and mean directions are not in general aligned with the surface fronts topographic steering is most evident at the continental margins deep eddy kinetic energy eke is maximum at about 200 cm2 s 2 between the subantarctic and polar fronts coinciding with the location but about one quarter of the value of a maximum in surface eke multiple high speed current events with peak speeds of 60 70 cm s 1 and lasting 30 to 70 days are coherent across sites separated by 45 km the observed spinup of eddies coinciding with meanders in the surface fronts is consistent with deep cyclogenesis

pleistocene speleothems of mallorca implications for palaeoclimate and carbonate diagenesis in mixing zones the pleistocene speleothems of sa bassa blanca cave mallorca are excellent indicators of palaeoclimate variations and are samples that allow evaluation of the products and processes of mixing zone diagenesis in an open water cave system integrated stratigraphic petrographic and geochemical data from a horizontal core of speleothem identified two main origins for speleothem precipitates meteoric marine mixing zone and meteoric vadose zone mixing zone precipitates formed at and just below the water air interface of cave pools during interglacial times when the cave was flooded as a result of highstand sea level mixing zone precipitates include bladed and dendritic high mg calcite microporous bladed calcite with variable mg content and acicular aragonite their presence suggests that calcium carbonate cementation is significant in the studied mixing zone system fluid inclusion salinities 13c and 18o compositions of the mixing zone precipitates suggest that mixing ratio was not the primary control on whether precipitation or dissolution occurred rather the proximity to the water table and degassing of co2 at the interface were the major controls on precipitation thus simple two end member mixing models may apply only in mixing zones well below the water table meteoric vadose speleothems include calcite and high mg calcite with columnar and bladed morphologies vadose speleothems precipitated during glacial stages when sea level was lower than present progressive increase in 13c and 18o of the vadose speleothems resulted from cooling temperatures and more positive seawater 18o associated with glacial buildup such covariation could be considered as a valid alternative to models predicting invariant 18o and highly variable 13c in meteoric calcite glacio eustatic oscillations of sea level are recorded as alternating vadose and mixing zone speleothems short term climatic variations are recorded as alternating aragonite and calcite speleothems precipitated in the mixing zone fluid inclusion and stable isotope data suggest that aragonite as opposed to calcite precipitated during times of reduced meteoric recharge

chemical hydrogeology in natural and contaminated environments abstract chemical hydrogeology including organic and inorganic aspects has contributed to an increased understanding of groundwater flow systems geologic processes and stressed environments most of the basic principles of inorganic chemical hydrogeology were first established by investigations of organic free regional scale systems for which simplifying assumptions could be made the problems of groundwater contamination are causing a shift of emphasis to microscale systems that are dominated by organic chemical reactions and that are providing an impetus for the study of naturally occurring and manmade organic material along with the decrease in scale physical and chemical heterogeneity become major controls current investigations and those selected from the literature demonstrate that heterogeneity increases in importance as the study site decreases from regional scale to macroscale to microscale increased understanding of regional scale flow systems is demonstrated by selection of investigations of carbonate and volcanic aquifers to show how application of present day concepts and techniques can identify controlling chemical reactions and determine their rates identify groundwater flow paths and determine flow velocity and determine aquifer characteristics the role of chemical hydrogeology in understanding geologic processes of macroscale systems is exemplified by selection of investigations in coastal aquifers phenomena associated with the mixing zone generated by encroaching sea water include an increase in heterogeneity of permeability diagenesis of minerals and formation of geomorphic features such as caves lagoons and bays ore deposits of manganese and uranium along with a simulation model of ore forming fluids demonstrate the influence of heterogeneity and of organic compounds on geochemical reactions associated with genesis of mineral deposits in microscale environments importance of heterogeneity and consequences of organic reactions in determining the distributions and concentrations cf constituents are provided by several studies including infiltration of sewage effluent and migration of creosote in coastal plain aquifers these studies show that heterogeneity and the dominance of organically controlled reactions greatly increase the complexity of investigations

deep inflow into the mozambique basin more than 200 conductivity temperature depth ctd stations were worked around the southwest indian ridge and del cano rise as part of the world ocean circulation experiment a selection of these data provides information about the inflow of bottom water into the mozambique basin the basin is closed below 3000 m yet the inflow is significantly large of order 1 sv 1 sv 106 m3 s 1 estimates of the basin scale upwelling at 4000 m suggest that the vertical velocity is also large 10 10 5 cm s 1 or more an order of magnitude greater than global ocean estimates examination of the characteristics of the bottom water in the mozambique and agulhas basins and the prince edward fracture zone shows that bottom water enters the mozambique basin from the agulhas basin and also directly from the enderby basin most of the transport enters the mozambique basin via the agulhas basin where two regions of northward flow below 4000 m are found the major flow on the eastern flank of the mozambique ridge is through and above the deep extending 5900 m trench that connects the agulhas and mozambique basins the second weaker flow enters the transkei basin along the deep eastern flank of the agulhas plateau then turning east into the mozambique basin the only source of bottom water to the agulhas basin is the enderby basin but a more direct route between the enderby and mozambique basins exists via the prince edward fracture which extends deeper than 4000 m throughout its length and links the two basins directly across the southwest indian ridge full depth ctd stations trace the changing characteristics of the deep and bottom water in the fracture and moored current meter data show the strength and persistence of the throughflow strong mixing with the overlying deep water elevates the salt content of the bottom water by comparison with the other water in the mozambique basin thus two distinct bottom waters of the mozambique basin originate in the same place the enderby basin and their different characteristics are solely a function of the routes they have taken and the processes encountered along the different pathways

geochemical modeling of the madison aquifer in parts of montana wyoming and south dakota stable isotope data for dissolved carbonate sulfate and sulfide are combined with water compo sition data to construct geochemical reaction models along eight flow paths in the madison aquifer in parts of wyoming montana and south dakota the sulfur isotope data are treated as an isotope dilution problem whereas the carbon isotope data are treated as rayleigh distillations all reaction models reproduce the observed chemical and carbon and sulfur isotopic composition of the final waters and are partially validated by predicting the observed carbon and sulfur isotopic compositions of dolomite and anhydrite from the madison limestone the geochemical reaction models indicate that the dominant groundwater reaction in the madison aquifer is dedolomitization calcite precipita tion and dolomite dissolution driven by anhydrite dissolution sulfate reduction ca mg2 ina cation exchange and halite dissolution are locally important particularly in central montana the groundwater system is treated as closed to c02 gas from external sources such as the soil zone or cross formational leakage but open to c02 from oxidation of organic matter coupled with sulfate reduction and other redox processes occurring within the aquifer the computed mineral mass transfers and modeled sulfur isotopic composition of madison anhydrites are mapped throughout the study area carbon 14 groundwater ages adjusted for the modeled carbon mass transfer range from modem to about 23 000 years b p and indicate flow velocities of 7 7 ftlyr 2 1 26 5 rnlyr most horizontal hydraulic conductivities calculated from darcy s law using the average 14 c flow velocities are within a factor of 5 of those based on digital simulation the calculated mineral mass transfer and adjusted 14 c groundwater ages permit determination of apparent rates of reaction in the aquifer the apparent rate of organic matter oxidation is typically 0 12 jlidol uyr sulfate and to a lesser extent ferric iron are the predominant electron acceptors the kinetic biochemical fractionation of 34 s between sulfate and hydrogen sulfide is approximately 44 o at 25 c with a temperature variation of

dissolution in a variably confined carbonate platform effects of allogenic runoff hydraulic damming of groundwater inputs and surface groundwater exchange at the basin scale in variably confined carbonate platforms impermeable confining units collect rainfall over large areas and deliver runoff to rivers or conduits in unconfined portions of platforms runoff can increase river stage or conduit heads in unconfined portions of platforms faster than local infiltration of rainfall can increase groundwater heads causing hydraulic gradients between rivers conduits and the aquifer to reverse gradient reversals cause flood waters to flow from rivers and conduits into the aquifer where they can dissolve limestone previous work on impacts of gradient reversals on dissolution has primarily emphasized individual caves and little research has been conducted at basin scales to address this gap in knowledge we used legacy data to assess how a gradient of aquifer confinement across the suwannee river basin north central florida affected locations magnitudes and processes of dissolution during 2005 2007 a period with extreme ranges of discharge during intense rain events runoff from the confining unit increased river stage above groundwater heads in unconfined portions of the platform hydraulically damming inputs of groundwater along a 200 km reach of river hydraulic damming allowed allogenic runoff with sical 4 to fill the entire river channel and flow into the aquifer via reversing springs storage of runoff in the aquifer decreased peak river discharges downstream and contributed to dissolution within the aquifer temporary storage of allogenic runoff in karst aquifers represents hyporheic exchange at a scale that is larger than found in streams flowing over non karst aquifers because conduits in karst aquifers extend the area available for exchange beyond river beds deep into aquifers post depositional porosity in variably confined carbonate platforms should thus be enhanced along rivers that originate on confining units this distribution should be considered in models of porosity distribution used to manage water and hydrocarbon resources in carbonate rocks copyright 2013 john wiley sons ltd

the origin and isotopic composition of dissolved sulfide in groundwater from carbonate aquifers in florida and texas the 34s values of dissolved sulfide and the sulfur isotope fractionations between dissolved sulfide and sulfate species in floridan ground water generally correlate with dissolved sulfate concentrations which are related to flow patterns and residence time within the aquifer the dissolved sulfide derives from the slow in situ biogenic reduction of sulfate dissolved from sedimentary gypsum in the aquifer in areas where the water is oldest the dissolved sulfide has apparently attained isotopic equilibrium with the dissolved sulfate 34s 65 per mil at the temperature 28 c of the system this approach to equilibrium reflects an extremely slow reduction rate of the dissolved sulfate by bacteria this slow rate probably results from very low concentrations of organic matter in the aquifer in the reducing part of the edwards aquifer texas there is a general down gradient increase in both dissolved sulfide and sulfate concentrations but neither the 34s values of sulfide nor the sulfide sulfate isotope fractionation correlates with the ground water flow pattern the dissolved sulfide species appear to be derived primarily from biogenic reduction of sulfate ions whose source is gypsum dissolution although upgradient diffusion of h2s gas from deeper oil field brines may be important in places the sulfur isotope fractionation for sulfide sulfate about 38 per mil is similar to that observed for modern oceanic sediments and probably reflects moderate sulfate reduction in the reducing part of the aquifer owing to the higher temperature and significant amount of organic matter present contributions of isotopically heavy h2s from oil field brines are also possible

field observations of frost action in intact and weathered champlain sea clay this paper presents the results of a field study on frost action in sensitive saint alban clay both in an intact state never subjected to any freeze thaw cycles and in its weathered state corres

heterogeneity induced mixing and reaction hot spots facilitate karst propagation in coastal aquifers the data provided in the included folders are results directly taken from simulations originating from comsol multiphysics all data are provided as text files each text file includes coordinate data and the raw values for the variable of interest presented in the manuscript and supporting information the files provided are separated into folders for homogeneous equivalent cases and heterogeneous cases for each of these folders the data is further subdivided by the variance of the hydraulic conductivity field finally the data is organiyed according to the output variable of interest

influence of partial confinement and holocene river formation on groundwater flow and dissolution in the florida carbonate platform much of what is known about groundwater circulation and geochemical evolution in carbonate platforms is based on platforms that are fully confined or unconfined much less is known about groundwater flow paths and geochemical evolution in partially confined platforms particularly those supporting surface water in north central florida sea level rise and a transition to a wetter climate during the holocene formed rivers in unconfined portions of the florida carbonate platform focusing on data from the santa fe river basin we show river formation has led to important differences in the hydrological and geochemical evolution of the santa fe river basin relative to fully confined or unconfined platforms runoff from the siliciclastic confining layer drove river incision and created topographic relief reorienting the termination of local and regional groundwater flow paths from the coast to the rivers in unconfined portions of the platform the most chemically evolved groundwater occurs at the end of the longest and deepest flow paths which discharge near the center of the platform because of incision of the santa fe river at the edge of the confining unit this pattern of discharge of mineralized water differs from fully confined or unconfined platforms where discharge of the most mineralized water occurs at the coast mineralized water flowing into the santa fe river is diluted by less evolved water derived from shorter shallower flow paths that discharge to the river downstream formation of rivers shortens flow path lengths thereby decreasing groundwater residence times and allowing freshwater to discharge more quickly to the oceans in the newly formed rivers than in platforms that lack rivers similar dynamic changes to groundwater systems should be expected to occur in the future as climate change and sea level rise develop surface water on other carbonate platforms and low lying coastal aquifer systems copyright 2012 john wiley sons ltd

steady state freshwater seawater mixing zone in stratified coastal aquifers summary the mixing zone between freshwater and intruding seawater which controls regional groundwater flow dynamics and reactive transport processes is the most important component in coastal aquifers laboratory experiments and numerical simulations were conducted to investigate the effects of aquifer stratification on the thickness of a steady state freshwater seawater mixing zone a series of experiments were implemented in a laboratory tank packed with three layers of coastal sands and manipulated by two flow cells for maintaining constant head boundary conditions packed aquifers included a homogenous aquifer a high hydraulic conductivity k low k high k stratified aquifer and a low k high k low k stratified aquifer both tank scale and field scale density dependent models were developed to simulate the laboratory experiments and to systematically investigate aquifer stratification effects on the thickness of a steady mixing zone with varying layer configurations results showed that when an aquifer layer with a low k overlies a layer with a relatively high k slanting upward flow of diluted saltwater and re circulated seawater flow are refracted at the interface between the two layers resulting in streamline separation and a broad mixing zone in the low k layer by contrast the mixing zone in a high k layer is slightly narrowed when it overlies a layer with a relatively low k because flow refraction squeezes the streamlines within the mixing zone the mixing zone profile in head controlled systems is a function of k contrast but independent of the magnitude of k our results demonstrated the significant impact of aquifer stratification on controlling groundwater flow and solute transport in coastal subsurface environments and would have significant implications for studying physical chemical and biological processes in coastal subsurface environments as aquifer stratification is naturally prevalent

a new seismic stratigraphy in the indian atlantic ocean gateway resembles major paleo oceanographic changes of the last 7 ma the exchange of water masses between the indian ocean and the atlantic constitutes an integral interocean link in the global thermohaline circulation long term changes in deep water flow have been studied using seismic reflection profiles but the seismic stratigraphy was poorly constrained and not resolved for the time period from the late miocene onward here we present results from international ocean discovery program site u1475 agulhas plateau located over a sediment drift proximal to the entrance of north atlantic deep water into the southern ocean and south indian ocean site u1475 comprises a complete carbonate rich stratigraphic section of the last 7 ma that provides an archive of climate induced variations in ocean circulation six marker reflectors occurring in the upper 300 m of the drift are identified here for the first time the formation of these reflectors is mainly due to density changes that are mostly caused by changes in biogenic versus terrigenous sediment deposition synthetic seismograms allow age assignments for the horizons based on biostratigraphy and magnetostratigraphy prominent reflectors are related to late pleistocene glacial interglacial variability the middle and early pleistocene transitions and the onset of the northern hemisphere glaciation a peculiar early pliocene interval 5 3 4 0 ma bounded by two reflectors is characterized by fourfold elevated sedimentation rates 10 cm kyr and the occurrence of sediment waves we argue that this enhanced sediment transport to the agulhas plateau was caused by a reorganization of the bottom current circulation pattern due to maximized inflow of north atlantic deep water