thunderstorm genesis zones in the colorado rocky mountains as determined by traceback of geosynchronous satellite images abstract mountain thunderstorms often originate in preferred regions of the topography as shown qualitatively by pilot reports and more quantitatively by meteorological radar satellite and lightning detector studies to further investigate the phenomenon of mountain thunderstorm initiation we used time sequences of goes imagery to locate storms and to trace them back to their points of origin using three summers of data from days which started out clear we backtracked over 600 storms in the mountains of colorado and northern new mexico we plotted the origin points on a terrain map and drew contours of initiation frequency to identify regions with a high likelihood of producing thunderstorms we found that initiation sites tended to cluster into identifiable geographical locations or genesis zones consistent with findings based on the other data sources when cloud propagation effects were taken into account the locations of these genesis zones were also consistent with the locations of clusteri

sensitivity of the initiation of an isolated thunderstorm over the beijing metropolitan region to urbanization terrain morphology and cold outflows to gain insight into the processes leading to the convective initiation ci of an isolated thunderstorm near the central urban area cua of the beijing metropolitan region bmr on 9 august 2011 a series of numerical sensitivity experiments by removing or modifying the cua terrain morphology and convectively generated cold outflows is performed results show that the cua accounts for the formation of cloud condensation near the top of the mixed layer at the ci site as a result of the growing boundary layer depth through its urban heat island effects and urban induced convergence between a warm and moist southerly flow and an easterly flow on the downstream side the northerly approaching cold outflows from the mesoscale convective system mcs facilitate the generation of northerly flows through a northwestward concaved valley such that the enhanced low level convergence with the southerly and easterly flows near the cua could determine the timing of the outbreak of shallow clouds near the mixed layer top into an intense thunderstorm when the concaved valley on the northwest of the cua is eliminated little northerly flows ahead of the cold outflow boundaries into the ci site would be present the results obtained herein appear to have significant implications to understanding and forecasting the development of afternoon thunderstorms in the bmr under weak gradient environments

salinity stratification of the mediterranean sea during the messinian crisis a first model analysis abstract in the late miocene a thick and complex sequence of evaporites was deposited in the mediterranean sea during an interruption of normal marine sedimentation known as the messinian salinity crisis because the related deposits are mostly hidden from scrutiny in the deep basin correlation between onshore and offshore sediments is difficult hampering the development of a comprehensive stratigraphic model since the various facies correspond to different salinities of the basin waters it would help to have physics based understanding of the spatial distribution of salt concentration here we focus on modelling salinity as a function of depth i e on the stratification of the water column a box model is set up that includes a simple representation of a haline overturning circulation and of mixing it is forced by atlantic exchange and evaporative loss and is used to systematically explore the degree of stratification that results under a wide range of combinations of parameter values the model demonstrates counterintuitive behaviour close to the saturation of halite for parameter values that may well be realistic for the messinian we show that a significantly stratified mediterranean water column can be established in this case atlantic connectivity is limited but may be closer to modern magnitudes than previously thought in addition a slowing of mediterranean overturning and a larger deep water formation region both in comparison to the present day are required under these conditions we would expect a longer duration of halite deposition than currently considered in the msc stratigraphic consensus model

dimensions of the atlantic mediterranean connection that caused the messinian salinity crisis abstract what kind of gateway is needed to cause a salinity crisis although several reconstructions of possible atlantic mediterranean gateways are proposed for the late miocene so far the gateway that must have existed before the desiccation of the mediterranean during the messinian is unknown this study uses the theory of hydraulic control combined with the effect of bottom friction in order to find out to first order the geometrical dimensions of the connection that existed during the primary lower gypsum stage 5 97 5 61 ma of the messinian salinity crisis 5 97 5 33 ma the connecting strait is assumed to behave in a similar way as existing straits such as the strait of gibraltar or the bosphorus a salinity crisis in an enclosed basin results when its connection to the open ocean is highly restricted a strait needs to be relatively shallow narrow and or long in order to result in exchange fluxes that are of around 25 or less of the exchange at the strait of gibraltar today considering the evaporite deposits together with global sea level variations we estimate the cross section of a strait responsible of the msc to have a minimum depth of 30 45 m and a maximum width of 0 7 2 km for lengths in the range up to 500 km these dimensions are consistent with only a few of the miocene corridors identified the calculations are extended to explore the implications for sedimentary structures on the corridor floor

the gibraltar corridor watergate of the messinian salinity crisis abstract the existence and evolution of a messinian salt giant in the mediterranean sea has caused much debate in the marine science community especially the suggestion that the mediterranean was a deep desiccated basin during the messinian salinity crisis msc 5 97 5 33 ma triggered by a temporal disconnection from the global ocean made it a well known crisis beyond the scientific boundaries approximately 50 years after this provocative statement it remained unknown which mediterranean atlantic seaway delivered the 5 6 of the global ocean s salt into the mediterranean basin here we review the changes in mediterranean atlantic connectivity throughout the late miocene in order to locate date and quantify the missing messinian gateway that provided the salt water inflow during the msc we conclude that all the known pre msc gateways through southern spain and northern morocco were closed leaving the gibraltar corridor at its messinian configuration as the sole candidate we consider the possibility of longer and narrower straits existing at depth below the present gibraltar region and using strait dynamic theory we calculate its dimensions during the messinian based on the salinity changes in the mediterranean a marine messinian gateway through the gibraltar corridor is in agreement with growing evidence that atlantic waters reached the mediterranean sea during all three stages of the msc

a long lived mesoscale convective complex part i the mountain generated component abstract using data collected during colorado state university s south park area cumulus experiment in 1977 a sequence of multi scale convective events leading to the formation of a mesoscale convective complex is described in the first phase surface based cool advection in the elevated mountain basin delayed the full transition of the morning boundary layer into a deep mixed layer until well after convective instability was reached over the adjacent ridges the second phase was earmarked by the formation of convective precipitation echoes at hot spots over the high mountain terrain two groups of cells then propagated eastward across the mountain basin forming a line of discrete cells which moved across the foothills toward the high plains the cells further intensified at the foothills high plains interface and formed a still larger north south line of thunderstorms in the third phase this north south line of thunderstorms evolved into an expanding meso scale convective cluster as it contin

mixing of event and pre event water in a shallow entisol in sloping farmland based on isotopic and hydrometric measurements sw china

seasonal variability of the mixed layer depth in the mediterranean sea as derived from in situ profiles a new 0 5 resolution mediterranean climatology of the mixed layer depth based on individual profiles of temperature and salinity has been constructed the criterion selected is a threshold value of temperature from a near surface value at 10 m depth mainly derived by a method applied on the global de boyer montegut et al 2004 dbm04 with respect to dbm04 the main differences reside in the absence of spatial interpolation of the final fields and in the improved spatial resolution these changes to the method are necessary to reproduce the mediterranean mixed layer s behavior in the derived climatological maps the most relevant features of the basin surface circulation are reproduced as well as the areas prone of the deep water formation are clearly identified finally the role of density in the definition of the mixed layer s differing behaviors between the oriental and the occidental regions of the basin is presented

identifying the water source for subsurface flow with deuterium and oxygen 18 isotopes of soil water collected from tension lysimeters and cores the conventional identification of soil water with pre event water limits deep insights into the involvement of stationary and mobile soil water in subsurface hydrological processes in three tilled sloping field plots at a hilly area of southwestern china dominated by entisols soil water collected with a suction lysimeter was distinguished from the total soil water through an analysis of the stable isotopes deuterium and oxygen 18 differences in the depth profile of soil water before and after storm events were observed and used to examine how rainwater mixes with soil water and to identify the source contribution of different fractions of soil water in subsurface flow generation only water in the 0 10 cm soil layer was significantly affected by evaporation and infiltration water in the top 5 cm layer of the soil exhibited the lowest residence time because a storm can replace a substantial proportion of the pre event water soil water at the 10 20 cm depth showed the longest residence time as indicated by its high proportion of pre event water the isotopic signatures demonstrated that piston flow and preferential flow coexisted in this soil high antecedent soil water content and high rain intensity favor the formation of piston flow the water collected with the suction lysimeter represented the mobile fraction of the pre event water in the soil which effectively participates in the generation of subsurface flow newly infiltrated rainwater did not well mix with stationary pre event water in the soil the use of recent rainfall to represent mobile soil water may provide a practical solution for overcoming the negative effect of the spatial heterogeneity of the isotopic composition of soil water on hydrograph separation results bulk soil water and lysimeter water showed significant differences in isotopic composition under low soil water content or in the top soil layer stable isotopes in bulk and lysimeter soil water should be monitored synchronously to reveal the sources and pathways of soil water and their contributions to the generation of subsurface flow in the vadose zone c 2013 elsevier b v all rights reserved

the response of water column and sedimentary environments to the advent of the messinian salinity crisis insights from an onshore deep water section govone nw italy

flow over heated terrain part ii generation of convective precipitation previous studies have shown that thunderstorms in the rocky mountain region have preferred areas in which to form there has been some indication that these areas depend on the midtropospheric wind direction a nonhydrostatic model with a terrain following horizontal grid is employed to investigate the initiation of precipitating convection over heated topography horizontally homogeneous meteorological conditions with no directional shear in the vertical wind profile are used the numerical simulations indicate that precipitating convection was more likely to be generated downwind of ridges than upwind of them initiation of these storms was more likely downwind of ridges with their long axis parallel to the wind direction than downwind of ridges with their long axis perpendicular to the wind direction in part i of this study it was shown that heating induced convergence is larger downwind of a ridge with its longer axis parallel to the wind direction for the orographic configuration of the rocky mountains total precipitation is maximized for southerly and northwesterly winds slower wind speeds are more likely and faster wind speeds are less likely to produce convective storms soundings with larger instability are more likely to produce convection the soundings with a greater temperature lapse rate produce more initiation locations and soundings with greater moisture produce greater amounts of precipitation even though a number of assumptions were made for this study the authors believe the results explain a significant amount of the observed variability in the initiation locations of precipitating convection in the rocky mountains during the summer because of the theoretical basis for this work detailed in part i of this study the authors believe it should explain convective initiation in other mountainous areas that are subject to strong solar heating

a modeling perspective on spatial and temporal variations in messinian evaporite deposits abstract during the messinian salinity crisis msc evaporite dominated sequences formed in marginal and deep basins of the mediterranean sea in the marginal basins the onset of the msc is synchronous and a single depositional framework fits all sequences in contrast msc sequences of the western and eastern deep basins appear to comprise a different number of units and differ greatly in thickness even though there exist numerous scenarios for deposition in the marginal and deep basins the link between the two settings is difficult and scenarios are rarely quantitatively supported we employ a simple box model for the messinian mediterranean to examine the causes of 1 spatial variation in thickness and 2 differences in the time of onset of deposition model results are compared with actual observations on the msc sequences the results show that a large connection between the western and eastern basin is necessary for and some degree of water column stratification is conducive to synchronous onset of the msc in the marginal basins moreover halite deposits in the deep basins are likely to be coeval and have formed in 60 ka after a further restriction of the atlantic mediterranean connection during the msc but without a significant sea level drop a difference in the net salt gain per unit volume caused the different halite deposition rates in the two basins a scenario with only a simple restriction of the atlantic mediterranean connection during the late miocene without significant changes in the mediterranean sea level the fresh water budget or the size of the strait of sicily is able to explain the synchronous onset of the msc the synchronous marginal evaporite formation and the differences in the deep basinal sequences

high frequency cyclicity in the mediterranean messinian evaporites evidence for solar lunar climate forcing abstract the deposition of varved sedimentary sequences is usually controlled by climate conditions the study of two late miocene evaporite successions one halite and the other gypsum consisting of annual varves has been carried out to reconstruct the paleoclimatic and paleoenvironmental conditions existing during the acme of the messinian salinity crisis 6 ma when thick evaporite deposits accumulated on the floor of the mediterranean basin spectral analyses of these varved evaporitic successions reveal significant periodicity peaks at around 3 5 9 11 13 20 27 and 50 100 yr a comparison with modern precipitation data in the western mediterranean shows that during the acme of the messinian salinity crisis the climate was not in a permanent evaporitic stage but in a dynamic situation where evaporite deposition was controlled by quasi periodic climate oscillations with similarity to modern analogs including quasi biennial oscillation el nino southern oscillation and decadal to secular lunar and solar induced cycles particularly we found a significant quasi decadal oscillation with a prominent 9 year peak that is commonly also found in modern temperature records and is present in the contemporary atlantic multidecadal oscillation amo index and pacific decadal oscillation pdo index these cyclicities are common to both ancient and modern climate records because they can be associated with solar and solar lunar tidal cycles during the messinian the mediterranean basin as well as the global ocean were characterized by different configurations than at present in terms of continent distribution ocean size geography hydrological connections and ice sheet volumes the recognition of modern style climate oscillations during the messinian suggests that although local geographic factors acted as pre conditioning factors turning the mediterranean sea into a giant brine pool external climate forcings regulated by solar lunar cycles and largely independent from local geographic factors modulated the deposition of the evaporites

travel times in the vadose zone variability in space and time water travel times reflect hydrological processes yet we know little about how travel times in the unsaturated zone vary with time using the soil physical model hydrus 1d we derived time variable travel time distributions for 35 study sites within the attert catchment in luxembourg while all sites experience similar climatic forcing they differ with regard to soil types 16 cambisols 12 arenosols and 7 stagnosols and the vegetation cover 29 forest and 6 grassland we estimated site specific water flow and transport parameters by fitting the model simulations to observed soil moisture time series and depth profiles of pore water stable isotopes with the calibrated model we tracked the water parcels introduced with each rainfall event over a period of several years our results show that the median travel time of water from the soil surface to depths down to 200 cm is mainly driven by the subsequent rainfall amounts the median time until precipitation is taken up by roots is governed by the seasonality of evapotranspiration rates the ratio between the amount of water that leaves the soil profile by on the one hand and evaporation and transpiration on the other hand also shows an annual cycle this time variable response due to climatic forcing is furthermore visible in the multimodal nature of the site specific master transit time distribution representing the flow averaged probability density for rainwater to become recharge the spatial variability of travel times is mainly driven by soil texture and structure with significant longer travel times for the clayey stagnosols than for the loamy to sandy cambisols and arenosols

the upper tortonian lower messinian at monte dei corvi northern apennines italy completing a mediterranean reference section for the tortonian stage abstract a high resolution integrated stratigraphy including biostratigraphy magnetostratigraphy tephrostratigraphy and cyclostratigraphy is presented for the upper tortonian and lower messinian upper miocene at monte dei corvi numerical age control comes from a combination of magnetobiostratigrapic dating and astronomical tuning while radioisotope dating of ash layers produced less reliable ages the deep marine succession is characterized by large scale non repetitive stratigraphic changes allowing the discrimination between a lower brownish rossini and euxinic shale interval the sedimentary cycles which occur superimposed on these large scale changes are related to astronomical climate forcing astronomical tuning of the sedimentary cycles provides not only absolute ages for biostratigraphic events reversal boundaries and volcanic ash layers but also for the observed non cyclic changes these can be linked to environmental and geodynamic changes in the mediterranean region preceding the messinian salinity crisis the beginning of the brownish interval marked by tripartite cycles at 8 017 ma coincides with tectonic re arrangements in the mediterranean such as compression in the betics and opening of the rifian corridor at 7 616 ma the change to the calcareous rossini interval can be linked to tectonic uplift in the northern apennines and the deepening of the rifian corridor while the betic corridor became restricted coinciding with the end of evaporite deposition in the eastern betics the change to euxinic shales at 7 168 ma reflects basin wide restriction marked by diatomite and sapropel formation in the mediterranean basin related to the severely constricted betic and rifian corridors the occurrence of a tripartite construction of cycles in the euxinic shales at 6 719 ma coincides with diatomite formation in the eastern mediterranean uplift and shallowing in the northern apennines and further constriction of the atlantic gateways we conclude that late tortonian early messinian tectonic and environmental events occur remarkably synchronously in the mediterranean basin and most likely result from a combination of geodynamic processes and eccentricity controlled climatic changes in combination with the upper serravallian and lower tortonian interval which includes the formal tortonian global stratotype section and point gssp the monte dei corvi is the only complete section in the mediterranean covering the entire tortonian stage we therefore propose the monte dei corvi section as tortonian reference section particularly for the mediterranean region in addition it may serve as a unit stratotype for the tortonian

mediterranean climate and oceanography and the periodic development of anoxic events sapropels mediterranean sapropels are layers with elevated organic carbon concentrations that contrast with surrounding sediments which are organic poor sapropels occur quasi periodically in sedimentary sequences of the last 13 5 million years and exist both in the eastern and western mediterranean sub basins they have been the subject of extensive study based on records from both short conventional and long ocean drilling program sediment cores and from a wide variety of uplifted marine sediment sequences on the basin margins and islands previous syntheses in the 1990s and 2000s have discussed how the formation of sapropels is commonly ascribed to deep sea anoxia enhanced export productivity or a combination of these effects however a wealth of new evidence and insights has emerged during the past 1 2 decades based on traditional and novel proxy data as well as modelling which has revealed intriguing new aspects and nuances to the reconstructed conditions hence it is timely to present a new synthesis of current understanding of the processes behind the formation of sapropels which have over the past decade also become a matter of commercial interest in sub salt hydrocarbon exploration in this review we present a context of modern mediterranean climate and oceanography followed by an integrated assessment of the growing understanding of climatological and ocean circulation changes that were associated with sapropel deposition we find that sapropels predominantly formed during astronomically timed episodes when climatic and oceanographic conditions and ecological responses broadly preconditioned the basin for sapropel deposition there is strong correspondence with times of monsoon intensification fuelling runoff from north africa into the mediterranean sea while preconditioning due to sea level rise and regional precipitation and runoff may have contributed as well within these broad episodes of surface buoyancy gain and resultant decline in deep water ventilation specific deposition under dysoxic anoxic or even euxinic conditions occurred within a clearly dynamic system that was characterised by complex spatial and depth dependent patterns gradients with distinct temporal variability on at least decadal to centennial millennial timescales in the final section we evaluate the implications of different modes of deep water removal from silled basins to investigate why sapropels are more frequently and often more intensely developed in the eastern mediterranean than in the western mediterranean

monitoring open ocean deep convection from space deep convection dc is a key process of the oceanic circulation costly to monitor in situ and under the influence of climate change our study is a first step toward monitoring dc from space we investigate the feasibility of observing its variability using improved satellite altimetry an oceanic simulation of the mediterranean circulation was performed for the 1999 2007 period dc interannual variability is realistically modelled and the sea surface elevation sse is in agreement with altimetry data numerical results show a strong correlation between the annual dc characteristics and the winter sse from that we propose a method to monitor dc interannual variability and long term evolution using altimetry data our method applied to the longest available altimetry series represents correctly the interannual variability of dc in the northwestern mediterranean between 1994 and 2007 citation herrmann m j bouffard and k beranger 2009 monitoring open ocean deep convection from space geophys res lett 36 l03606 doi 10 1029 2008gl036422

a hydraulic box model study of the mediterranean response to postglacial sea level rise 1 this paper quantifies the role of changing sea level in affecting mediterranean stratification using a new model of the strait basin system which allows for explicit time dependence during the last deglaciation fairbank s meltwater peak 1b leads to rapidly rising global sea levels and a freshening of the oceans and hence increasing influx of ever freshening atlantic water into the mediterranean basin owing to long residence times the salinity of the deep and intermediate water reservoirs would have decreased more slowly so that the basin was more stably stratified for a period with possible implications for sapropel formation our model is used to estimate the size of this reservoir effect in comparison to the freshwater influx from the opening of the black sea at the bosphorus it is found that this mechanism affects the stratification to a similar degree as the black sea opening other climatic mechanisms have also affected the freshwater budget of the mediterranean at this time but their sizes are more difficult to quantify

dense shelf water cascading and messinian canyons a new scenario for the mediterranean salinity crisis the salt giant beneath the deep mediterranean seafloor is the impressive record of the messinian salinity crisis a dramatic event that occurred about 6 ma ago following the reduction of the connections with the atlantic ocean according to the shallow water deep basin model developed for these deposits hsu and others 1973a 1973b 1978a 1978b the messinian evaporites formed in a deep but desiccated mediterranean while shelves and slopes underwent subaerial erosion due to fluvial rejuvenation triggered by a 1500 m sea level drawdown deeply incised messinian canyons in the continental slopes surrounding the mediterranean are the main argument supporting this scenario using a state of the art model and idealized but realistic numerical simulations here we demonstrate that the activation of downslope flows of hypersaline dense waters in a process similar to present day dense shelf water cascading but much more energetic may account for both slope erosion and progressive salinity rise leading to the formation of deep seated supersaturated brines our findings support a deep water deep basin model schmalz 1969 1991 de benedetti 1976 1982 dietz and woodhouse 1988 thus implying that evaporite deposition may have occurred in a non desiccated basin with strongly reduced ocean connections

the dependence of numerically simulated convective storms on vertical wind shear and buoyancy abstract the effects of vertical wind shear and buoyancy on convective storm structure and evolution are investigated with the use of a three dimensional numerical cloud model by varying the magnitude of buoyant energy and one directional vertical shear over a wide range of environmental conditions associated with severe storms the model is able to produce a spectrum of storm types qualitatively similar to those observed in nature these include short lived single cells certain types of multicells and rotating supercells the relationship between wind shear and buoyancy is expressed in terms of a nondimensional convective parameter which delineates various regimes of storm structure and in particular suggests optimal conditions for the development of supercell type storms applications of this parameter to well documented severe storm cases agree favorably with the model results suggesting both the value of the model in studying these modes of convection as well as the value of this representation i

characterizing thunderstorm gust fronts near complex terrain abstractfire safety aviation wind energy and structural engineering operations are impacted by thunderstorm outflow boundaries or gust fronts gfs particularly when they occur in mountainous te

reconciling theories of a mechanically driven meridional overturning circulation with thermohaline forcing and multiple equilibria it has recently been suggested that the structure and strength of the meridional overturning circulation in the global ocean is governed by the input of mechanical energy to the system by winds and tides however it is not clear how this suggestion relates to the existence of multiple equilibria of the meridional overturning circulation which depends on thermohaline feedbacks and is more consistent with a buoyancy driven view of the circulation both theories have been illustrated by box models in the past stommel in tellus 13 224 230 1961 gnanadesikan in science 283 2077 2079 1999 here we incorporate these two theories into a single box model in an attempt to reconcile the roles of mechanical and buoyancy forcing in driving the meridional overturning circulation the box model has two equilibrium solutions one with sinking at high northern latitudes as in the present day atlantic and one without the circulation is mechanically driven but the northern sinking can be thought of as a release valve which acts as a sink of potential energy when the surface water at high northern latitudes is dense enough to convect while the source of energy comes from mechanical forcing the presence or otherwise of multiple equilibria is therefore determined by thermohaline feedbacks in some areas of parameter space an oscillation between the model s two circulation regimes occurs reminiscent of a bipolar seesaw

seasonal variations of halite saturation in the dead sea hypersaline lakes and seas were common in the past precipitating thick evaporitic salt deposits the only modern analogue for the paleo limnology of deep salt saturated aquatic environments exists in the dead sea in this study we present new insights from the dead sea on the role of seasonal thermohaline stratification and water balance on the seasonal and depth variations of the degree of saturation of halite salt and the rate of halite growth along the water column we developed methodologies to accurately determine the empirical degree of halite saturation of the lake based on high accuracy densitometry and to quantify halite growth rate along the water column during summer the epilimnion is undersaturated and halite is dissolved whereas during winter the entire water column is supersaturated and crystallizes halite this result is not trivial because the variations in the water balance suggest the opposite summer is associated with higher loss of water by evaporation from the lake compared to the winter hence the thermal effect overcomes the hydrological balance effect and thus governs the seasonal saturation cycle the hypolimnion is supersaturated with respect to halite and crystallizes throughout the year with higher super saturation and higher crystallization rates during winter during summer simultaneous opposing environments coexist an under saturated epilimnion that dissolves halite and a supersaturated hypolimnion that crystallizes halite which results in focusing of halite deposits in the deep hypolimnetic parts of the evaporitic basins and thinning the shallow epilimnetic deposits this article is protected by copyright all rights reserved

the groundwater resources and sustainable yield of cheju volcanic island korea hydrogeologic data of 455 water wells comprising geologic logs water qualities and aquifer test results are analyzed to determine hydrogeological characteristics water quality and sustainable yield of the groundwater resources of cheju volcanic island the groundwater of the island occurs in unconsolidated pyroclastic deposits and clinkers interbedded in highly jointed basaltic and andesitic rocks as high level basal and parabasal groundwater under unconfined conditions the total storage of groundwater is estimated at about 44 billion m3 the average transmissivity and specific yield of the aquifer are at about 0 34 m2 s 1 29300 m2 day 1 and 0 12 respectively the average annual precipitation is about 3 39 billion m3 of which 1 49 billion m3 equivalent to 44 0 of the total annual precipitation is recharged into aquifers with 0 638 billion m3 year 1 of runoff and 1 26 billion m3 year 1 of evapotranspiration based on a groundwater budget analysis the sustainable yield is estimated at about 0 62 billion m3 year 1 equivalent to 41 6 of annual recharge a low permeability marine sedimentary formation sehwari formation composed of loosely cemented sandy silt was recently found to be situated at 120 68 m below mean sea level if the said marine sediment is distributed as a basal formation of the freshwater zone of the island most of its groundwater will be of parabasal type so the marine sediment is one of the most important hydrogeological boundaries and groundwater occurrences in the area

evolution of the late miocene mediterranean atlantic gateways and their impact on regional and global environmental change marine gateways play a critical role in the exchange of water heat salt and nutrients between oceans and seas as a result changes in gateway geometry can significantly alter both the pattern of global ocean circulation and associated heat transport and climate as well as having a profound impact on local environmental conditions mediterranean atlantic marine corridors that pre date the modern gibraltar strait closed during the late miocene and are now exposed on land in northern morocco and southern spain the restriction and closure of these miocene connections resulted in extreme salinity fluctuations in the mediterranean leading to the precipitation of thick evaporites this event is known as the messinian salinity crisis msc the evolution and closure of the mediterranean atlantic gateways are a critical control on the msc but at present the location geometry and age of these gateways are still highly controversial as is the impact of changing mediterranean outflow on northern hemisphere circulation here we present a comprehensive overview of the evolution of the late miocene gateways and the nature of mediterranean atlantic exchange as deduced from published studies focussed both on the sediments preserved within the fossil corridors and inferences that can be derived from data in the adjacent basins we also consider the possible impact of evolving exchange on both the mediterranean and global climate and highlight the main enduring challenges for reconstructing past mediterranean atlantic exchange

the messinian salinity crisis past and future of a great challenge for marine sciences forty years after the image of the mediterranean transformed into a giant salty lake was first conceived the fascinating history of the messinian salinity crisis msc still arouses great interest across a large and diverse scientific community early outcrop studies which identified severe palaeoenvironmental changes affecting the circum mediterranean at the end of the miocene were followed by investigations of the marine geology during the 1950s to 1970s these were fundamental to understanding the true scale and importance of the messinian event now after a long period of debate over several entrenched but largely untested hypotheses a unifying stratigraphic framework of msc events has been constructed this scenario is derived mainly from onshore data and observations but incorporates different perspectives for the offshore and provides hypotheses that can be tested by drilling the deep mediterranean basins the msc was an ecological crisis induced by a powerful combination of geodynamic and climatic drivers which had a great impact on the subsequent geological history of the mediterranean area and on the salinity of the global oceans these changed the mediterranean s connections with both the atlantic ocean and the freshwater paratethyan basins causing high amplitude fluctuations in the hydrology of the mediterranean the msc developed in three main stages each of them characterized by different palaeoenvironmental conditions during the first stage evaporites precipitated in shallow sub basins the msc peaked in the second stage when evaporite precipitation shifted to the deepest depocentres and the third stage was characterized by large scale environmental fluctuations in a mediterranean transformed into a brackish water lake the very high resolution timescale available for some late miocene intervals in the mediterranean makes it possible to consider environmental variability on extremely short time scales including in some places annual changes despite this fundamental questions remain some of which could be answered through new cores from the deepest mediterranean basins improvements in seismic imaging and drilling techniques over the last few decades make it possible to plan to core the entire basinal messinian succession for the first time the resulting data would allow us to decipher the causes of this extreme environmental change and its global scale consequences

deep basin evidence resolves a 50 year old debate and demonstrates synchronous onset of messinian evaporite deposition in a non desiccated mediterranean the messinian salinity crisis msc is perceived as an environmental crisis governed by climatic and tectonic controls affecting global oceans salinity and shaping the mediterranean sea s biochemical composition recently drilled offshore wells in the levant basin retrieved a sedimentary record of the deep basin mediterranean msc salt deposits and the underlying pre evaporite unit in this study we have concentrated on the pre evaporite interval and its transition into the overlying evaporites analysis of this data set changes the way these deposits have been perceived since the 1970s when they were first penetrated in their uppermost part during deep sea drilling project expeditions using sedimentology seismic interpretation biostratigraphy and astronomical tuning we show that messinian salt deposition in the eastern mediterranean began during stage 1 of the msc in contrast to the present paradigm salt was deposited synchronously with gypsum in the marginal and intermediate depth basins significantly before the 50 k y interval coined as the msc acme event 400 k y after the crisis began thus salt precipitation took place in a non desiccated deep basin having a restricted but often open connection with the atlantic ocean substantially altering our understanding of the mechanisms governing the deposition of salt giants a coeval onset of basinal halite and marginal gypsum precipitation calls for a revaluation of global scale climatic and oceanographic models of the msc taking into account a much older age for the beginning of halite deposition

characteristics of soil water movement in a grass slope in a karst peak cluster region china soil water is very important in hilly areas with thin soil layers and deep groundwater tables such as the karst peak cluster region of southwest china an investigation into soil water movement can provide insights into management of shallow water resources and soil nutrients as well as prevention of groundwater pollution in this study o 18 and h 2 tracers were used to trace soil water movement in planar soil mass type microhabitats in the middle part of a steep hillslope covered by grasses in a karst peak cluster region of china from may 2008 to july 2009 samples of precipitation and two types of soil water which had different integrated degrees of mobility and were of different depth intervals or depths were collected the hydrogeochemical characteristics were compared between precipitation and soil water and these data were applied in convolution based lumped parameter models our results indicated that vertical piston flow rather than lateral flow along the soil bedrock interface played an important role in soil water percolation at least in the upper soil layer approximately 7cm over the permeable bedrock the mixing effect and preferential flow might also play a role in soil water percolation in general the evaporation effect on soil water was weak except for the uppermost 10cm soil matrix water during winter the lower limits of mean transit time of soil matrix flow passing through 5 15 25 35 and 41 5cm depths were 4 81 7 70 16 19 21 85 and 27 44days respectively our study demonstrated the crucial functions of the soil reservoir in regulating the water cycle and could provide guidance on conservation of soil water and hydrological studies the applied method was proved to be a suitable approach for investigating soil water movement on a monthly scale

the primary lower gypsum in the mediterranean a new facies interpretation for the first stage of the messinian salinity crisis abstract the detailed facies and physical stratigraphic analysis of the primary lower gypsum in the mediterranean indicates a surprising bed by bed correlation at basin scale spain italy hellenic arc and cyprus arc that is tuned to the orbital calibration for the first stage of the messinian salinity crisis from 5 96 to 5 61 ma ago a total of 16 precessionally controlled gypsum cycles were deposited rapidly in less than 350 ka forming sequences up to 300 m thick the lack of subaerial exposure features and the common facies associations and stacking pattern for sections located thousands of kilometers apart in different geological settings indicates a modest depositional depth not extremely shallow selenite deposition occurred only at the bottom of restricted marginal basins less than 200 m deep while no gypsum could precipitate in the deeper euxinic mediterranean portions where only thin and barren shale dolostone couplets formed the lowermost selenite beds pass laterally to dolomite rich limestones interbedded with barren euxinic shales in poorly oxygenated settings indicating that the gypsum sedimentation was diachronous and did not necessarily mark the onset on the messinian salinity crisis evaporite facies sequences ef1 to 8 within individual gypsum beds show small scale subaqueous sedimentary cycles that mimic regressive transgressive cycles a initial evaporite precipitation at relatively low supersaturation produced the massive selenite facies ef3 in a relatively deep setting b continuous evaporation and drawdown by oscillating brine level formed the banded selenite ef4 at the aridity acme of the precessionally controlled cycle c general progressive brine level rise with strong brine flow led to the formation of large selenite supercones branching laterally supercones in spain and branching selenite ef5 in the rest of the mediterranean and d flooding by undersaturated continental water terminated gypsum precipitation with the deposition of argillaceous sediments ef1 northern apennines and or limestone ef2 sicily and spain during the humid phase in the precession climate cycle the stacking pattern and selenite facies associations suggest an overall shallowing upward trend with a basin wide hydrologic change starting from the 6th cycle 5 84 ma which is marked by the appearance of the branching selenite facies supercones in spain and indicates that the brines became current dominated the sr isotope stratigraphy suggests that in the northern apennines the brines were strongly modified by continental waters 87 sr 86 sr 0 708893 to 0 708998 and received direct pulses of atlantic seawater 87 sr 86 sr 0 70900 to 0 709024 only in the upper part of the section in areas away from the mainland such as sicily the continental input was by far less important

messinian salinity crisis a novel unifying shallow gypsum deep dolomite formation mechanism abstract the messinian salinity crisis is a dramatic event that took place between 5 96 and 5 33 ma and resulted not only in the desiccation and reflooding of the mediterranean but also in the deposition of 0 3 3 km thick evaporites at its seafloor there has been considerable controversy on the modes of their formation the first stage gypsum deposits are considered to have only formed at silled marginal basins whereas anoxic marls and dolostones are found at deeper settings we agree with these observations but reject the coincidental presence of similar sills as being too fortuitous to explain gypsum formation in silled basins alone alternatively we present a unifying mechanism in which gypsum precipitation takes place basin wide at all shallow water depths but its preservation is limited to silled marginal basins taking a realistic early messinian scenario including a moderate primary production rate the sulphate consumption rate in the deep water appears to exceed the sulphate supply rate as deduced from reported shallow water gypsum deposition rates the consequent lower dissolved sulphate content limits gypsum preservation but permits dolomite formation to take place in the deep water the often observed concurring anoxic environment and absence of gypsum formation is thus related to diminished dissolved sulphate content via organic matter degradation and not to oxygen free conditions as such

a box model of the blocked outflow scenario for the messinian salinity crisis abstract part of the kilometre thick messinian evaporites of the mediterranean basin is thought to have formed in a configuration of continuous inflow of water and salt from the atlantic ocean in combination with blocked return flow this mechanism is here examined for the first time quantitatively using a simple box model with parametrised exchange between sub basins and including a representation of mixing we also explore systematically the conditions under which the blocked outflow state arises the main results are 1 the rate of salinity increase is fast 2 the western and eastern sub basin evolve in concert except when exchange at the connecting strait is greatly reduced and then only when the basins are poorly stratified and 3 near complete separation from the atlantic is required to reach saturation unless mediterranean waters are strongly stratified

variability of the large scale general circulation of the mediterranean sea from observations and modelling a review abstract in this paper we present an overview of the most recent findings about the mediterranean sea present day circulation structure both historical observations and numerical model simulations are presented outlining the differences and agreement the model simulations are presented for both an eddy resolving and a coarse resolution numerical model and the results are intercompared the importance of the mesoscales in modifying the large scale flow field is elucidated the critical point is the discovery of the large amplitude interannual variability of the circulation and water mass structure associated with the anomalies of atmospheric forcing over the basin the seasonal variability can be strictly related to changes in heat and momentum fluxes while the interannual variability has a component which is related to the mesoscale field the latter is very intense in the algerian current region and levantine basin but different in structure in the two regions results are shown which confirm the importance of wind driving in establishing the kinetic energy of the flow field by comparing the current transport at the strait of corsica with observations in conclusion the essential characteristics of the present day circulation are associated with the atmospheric forcing and the basin topographic structure results from palaeoceanographic simulations for the last 20 000 years show that changing the atmospheric forcing can cause large changes in the circulation structure which may have affected sapropel formation

the mediterranean hydrologic budget from a late miocene global climate simulation during the late miocene the mediterranean experienced a period of extreme salinity fluctuations known as the messinian salinity crisis msc the causes of these high amplitude changes in salinity are not fully understood but are thought to be the result of restriction of flow between the mediterranean and atlantic eustatic sea level change and climate results from a new atmospheric general circulation model agcm simulation of late miocene climate for the mediterranean and adjacent regions are presented here the model hadam3 was forced by a late miocene global palaeogeography higher co2 concentrations and prescribed sea surface temperatures the results show that fluvial freshwater fluxes to the mediterranean in the late miocene were around 3 times greater than for the present day most of this water was derived from north african rivers which fed the eastern mediterranean this increase in runoff arises from a northward shift in the intertropical convergence zone caused by a reduced latitudinal gradient in global sea surface temperatures the northwards drainage of the late miocene chad basin also contributes numerical models designed to explore late miocene salt precipitation regimes in the mediterranean which typically make use of river discharge fluxes within a few tens of percent of present day values may therefore be grossly underestimating these fluxes although the agcm simulated late miocene river discharge is high the model predicts a smaller net hydrologic budget river discharge plus precipitation minus evaporation than for present day we discuss a possible mechanism by which this change in the hydrologic budget coupled with a reduced connection between the mediterranean and the global ocean could cause the salinity fluctuations of the msc

the demise of a salt giant driven by uplift and thermal dissolution abstract the development of giant salt basins and eventual cessation of rapid salt deposition is founded on a delicate balance of salinity and heat fluxes within the water body governed by tectonic climatic and eustatic change the onset of salt deposition in such basins is widely accepted to be initiated by basin restriction however the processes that lead to the termination of salt deposition are comparatively unclear here we use an array of 2d and 3d seismic surveys to reveal that the truncation surface at the top of a thick salt sequence in the eastern mediterranean is far more extensive than previously thought we show that uplift of the salt driven by deformation and thermal dissolution initiated the demise of the salt giant even prior to the final dilution and emplacement of brackish lago mare and fluvial deposits progressive uplift of the salt through the thermocline and into the under saturated epilimnion led to dissolution we argue that dissolved salt was recycled and re precipitation from the hypolimnion in the deepest sections of the basin contemporaneous with dissolution of halite from the shallower epilimnion these findings explain how rapid basinwide salt deposition was brought to an end in the eastern mediterranean and present a novel process for sculpting the final architecture of a salt giant

convective episodes in the east central united states nine years of composited radar data are investigated to assess the presence of organized convective episodes in the east central united states in the eastern united states the afternoon maximum in thunderstorms is ubiquitous over land however after removing this principal diurnal peak from the radar data the presence and motion of organized convective systems becomes apparent in both temporally averaged fields and in the statistics of convective episodes identified by an objective algorithm convective echoes are diurnally maximized over the appalachian chain and are repeatedly observed to move toward the east partly as a result of this the daily maximum in storms is delayed over the piedmont and coastal plain relative to the appalachian mountains and the atlantic coast during the 9 yr studied the objective algorithm identified 2128 total convective episodes 236 yr 1 with several recurring behaviors many systems developed over the elevated terrain during the afternoon and moved eastward often to the coastline and even offshore in addition numerous systems formed to the west of the appalachian mountains and moved into and across the eastern u s study domain in particular many nocturnal convective systems from the central united states entered the western side of the study domain frequently arriving at the eastern mountains around the next day s afternoon maximum in storm frequency a fraction of such well timed systems succeeded in crossing the appalachians and continuing across the piedmont and coastal plain convective episodes were most frequent during the high instability low shear months of summer which dominate the year round statistics even so an important result is that the episodes still occurred almost exclusively in above average vertical wind shear despite the overall dominance of the diurnal cycle the data show that adequate shear in the region frequently leads to long lived convective episodes with mesoscale organization

using h and o isotopic data for estimating the relative contributions of rainy and dry season precipitation to groundwater example from cheju island korea abstract a comparison of deuterium excess or d values of precipitation and groundwater at cheju island korea indicates that unlike in many temperate climates precipitation during the whole year contributes to groundwater recharge this in turn suggests that evapotranspiration effects are minimal consistent with the fact that the island contains highly permeable volcanic rocks overlain by thin soils this hypothesis is contrary to current water budget models that ascribe a significant role to evapotranspiration processes three coastal springs and several streams and ponds throughout the island have enriched 18 o and d values that plot off the local meteoric water line and have relatively high cl concentrations this relationship is suggestive of seawater mixing for the coastal springs and evaporation for the streams and ponds this database thus provides a useful means for evaluation of groundwater resources of the island

an x ray spectroscopic perspective on messinian evaporite from sicily sedimentary fabrics element distributions and chemical environments of s and mg the messinian salinity crisis is a dramatic hydrological and biological crisis that occurred in the mediterranean basin at 5 97 5 33 ma the interpretation of the facies and stratigraphic associations of the messinian salt deposits is still the object of active research because of the absence of modern depositional analogues of comparable scale in this study the spatial distributions of na mg s o si and al in a potassic magnesian salt and a halite layers of messinian evaporites from the realmonte mine on sicily were determined using synchrotron based micro x ray fluorescence the dominant molecular host site of mg and s obtained by x ray absorption near edge structure xanes is applied to specify the hydrochemistry of hypersaline brines and the presence of diagenetic minerals thus shedding light on evaporative concentration processes in the caltanissetta basin of sicily mg and s k edge xanes spectra revealed the presence of highly soluble mg bearing sulfates the massive halite layer unit c contains less soluble minerals thus did not exceed the stage of halite crystallization we infer that as evaporative concentration increased the density of the brine at the shallow margin of the basin increased as salinity increased to concentrations over 70 times the starting values creating brines that were oversaturated with mg sulfate density stratification of the deep basin caused heavy brines to sink to the bottom and become overlain by more dilute brines we propose lateral advection of dense mg sulfate brines that certainly affected marine biota

orbitally controlled oscillations in planktic communities and cyclic changes in western mediterranean hydrography during the messinian we use quantitative analyses of the planktic foraminiferal assemblages and stable isotope analyses of the sorbas section in the western mediterranean to reconstruct the cyclical changes in surface and deep water hydrographic conditions during the late miocene prior to the messinian salinity crisis oscillations in winter and summer temperatures linked to cyclical fluctuations in the hydrographic conditions and nutrient availability were the main mechanisms driving the cyclical changes in the planktic foraminiferal assemblages during the messinian the winter intensification and southward expansion of the northern cool and dry winds during precession maxima lowered sea surface temperatures below 14 15 c favoring water convection and the upward mixing of nutrients with the consequent increase in the proportion of cold eutrophic water foraminifera the low summer temperatures below 24 c inhibited the growth of warm oligotrophic water foraminifera as occurs today in the mediterranean by contrast at times of precession minima the low influence of the high latitude air masses caused winter temperatures to remain relatively high which combined with the lower surface salinities led to the formation of a permanent pycnocline winter conditions prevented the growth of cold eutrophic water foraminifera while high summer temperatures and the formation of a permanent pycnocline stimulated the growth of warm oligotrophic water foraminifera the prevalence of stable water stratification during winter due to the large density gradient between the surface and intermediate waters prevented deep water formation and slowed down the rates of oxygen supply to the bottom resulting in the formation of the sapropels a sharp decrease in 13c of benthic and planktic foraminifera that occurred between 6 8 and 6 7 myr is related to an increase in the residence time of mediterranean waters because similar changes have been observed in other regions of the mediterranean we conclude that this change records a significant reduction in the atlantic mediterranean water exchange at that time mediterranean climatic amplification increased throughout the messinian as the atlantic mediterranean water exchange was progressively more limited and oscillations in the ratio of planktic benthic foraminifera and of warm oligotrophic cold eutrophic species are good records of this increasing amplification which culminated at 5 95 myr with the deposition of gypsum pelitic layers that mark the onset of the messinian salinity crisis

chronology with a pinch of salt integrated stratigraphy of messinian evaporites in the deep eastern mediterranean reveals long lasting halite deposition during atlantic connectivity abstract the messinian salinity crisis msc 5 97 5 33 ma is considered an extreme environmental event driven by changes in climate and tectonics which affected global ocean salinity and shaped the biogeochemical composition of the mediterranean sea yet after more than 50 years of research msc stratigraphy remains controversial recent studies agree that the transition from the underlying pre evaporite sediments to thick halite deposits is conformal in the deep eastern mediterranean basin however the age of the base and the duration of halite deposition are still unclear also disputed is the nature of the intermediate and upper msc units which are characterized as periods of increased clastic deposition into the eastern mediterranean based on marginal outcrops and seismic data we provide a multidisciplinary study of sedimentary geochemical and geophysical data from industrial offshore wells in the levant basin which recovered a sedimentary record of deep basin mediterranean evaporites deposited during the msc in combination with previous observations of the msc throughout the mediterranean basin our results promote the need for a new chronological model remarkably the one kilometer thick lower part of the evaporitic unit is composed of essentially pure halite except for a thin transitional anhydrite layer at its base the halite is undisturbed and homogeneous lacking diverse features apparent in more proximal sections indicating a deep sea depositional environment we find that distinct meters thick non evaporitic intervals interbedded with the halite previously thought to be clastic layers are diatomites while xrd analysis confirms an increase in clastic components in these sediments they are composed primarily of well preserved marine and freshwater planktonic diatoms the occurrence of marine planktonic diatoms in these intervals indicates the input of atlantic waters into the mediterranean basin during the deposition of the massive halite unit seismic stratigraphy and well log cyclostratigraphy further support deep basin halite deposition which started about 300 kyr earlier than widely assumed 5 97 ma we propose that halite deposition in the deep mediterranean took place during stage 1 of the msc rather than being limited to the short 50 kyr msc acme when sea level was presumably at its lowest thus brine formation salt precipitation and faunal extinction occurred at least in part in a deep non desiccated basin with a restricted yet open mediterranean atlantic connection that allowed inflow of oceanic water we observe an increase in heavy minerals and reworked fauna within the clastic evaporitic interbedded evaporites of the basinal msc section and argue that these settings correspond in the deep basins with a significant sea level drawdown during stage 2 of the msc as observed in the marginal sections this correlation is corroborated by astrochronology and chemostratigraphic markers such as the distribution of n alkanes and biomarker based thermal maturity indices the levant deposits indicate that high sea level and partial connectivity with global oceans promoted the deposition of deep basin deep water halite while sea level drawdown promoted deposition of reworked and transported material from the margins into deep mediterranean basins this study modifies the current understanding of the mechanisms governing salt deposition throughout the msc with implications for other evaporitic events in the geologic record

a quantitative analysis of the desiccation and re filling of the mediterranean during the messinian salinity crisis abstract notwithstanding the great deal of attention that the messinian evaporites of the mediterranean region have received from an observational point of view there is to date no consensus as to their mechanism of formation we aim to contribute to the investigation through a quantitative analysis of the processes of desiccation and re filling these processes are thought to have played a role in particular during the deposition of the upper part of the evaporite sequence we calculate the evolution of sea level and average salinity based on both the present day geometry and a paleogeographic reconstruction and assess the sensitivity to variations in the freshwater budget our results support previous inferences that desiccation and re filling are fast desiccation occurs on a time scale of 3 8 kyr re filling probably even faster equilibrium sea levels imply that most water has gone from the western basin while a significant water column remains in the eastern basin whether or not the eastern basin reaches the level of halite saturation depends critically on in particular the freshwater budget the fast rate of desiccation and re filling imply that temporal differences in the onset of salt precipitation between western and eastern basin and between marginal basins and basin centres are below the resolution of astronomical dating also when atlantic sea level periodically varied from below to above the level of the intervening sill the mediterranean basin will have responded with repeated desiccation and re filling fast re filling is found to require only a small connection to the atlantic ocean this in combination with the previous results suggests the mediterranean is unlikely to attain stable intermediate water levels

quantifying the mediterranean freshwater budget throughout the late miocene new implications for sapropel formation and the messinian salinity crisis the cyclic sedimentary record of the late miocene mediterranean shows a clear transition from open marine to restricted conditions and finally to evaporitic environments associated with the messinian salinity crisis this evolution has been attributed to changes in mediterranean atlantic connectivity and regional climate which has a strong precessional pulse 31 coupled climate simulations with different orbital configurations have been combined in a regression model that estimates the evolution of the freshwater budget of the mediterranean throughout the late miocene the study suggests that wetter conditions occur at precession minima and are enhanced at eccentricity maxima we use the wetter peaks to predict synthetic sapropel records using these to retune two mediterranean sediment successions indicates that the overall net freshwater budget is the most likely mechanism driving sapropel formation in the late miocene our sapropel timing is offset from precession minima and boreal summer insolation maxima during low eccentricity if the present day drainage configuration across north africa is used this phase offset is removed if at least 50 more water drained into the mediterranean during the late miocene capturing additional north african monsoon precipitation for example via the chad eosahabi catchment in libya in contrast with the clear expression of precession and eccentricity in the model results obliquity which is visible in the sapropel record during minimum eccentricity does not have a strong signal in our model by exploring the freshwater evolution curve in a box model that also includes mediterranean atlantic exchange we are able for the first time to estimate the mediterranean s salinity evolution which is quantitatively consistent with precessional control additionally we separate and quantify the distinct contributions regional climate and tectonic restriction make to the lithological changes associated with the messinian salinity crisis the novel methodology and results of this study have numerous potential applications to other regions and geological scenarios as well as to astronomical tuning

synchronous onset of the messinian evaporite precipitation first mediterranean offshore evidence the messinian salinity crisis msc was a major ecological crisis affecting shallow and deep water settings over the entire mediterranean basin however the evolution of the msc and its ecological impacts have mainly been explained on the basis of sediments from onshore outcrops lack of complete and physically connected records from onshore and offshore settings has inhibited comprehensive understanding of basin behaviour during the msc herein we present a continuous record from an intermediate depth basin on the balearic promontory that comprises late tortonian messinian marls and evaporitic beds from the first msc phase i e primary lower gypsum plg stage well log and biostratigraphic data allow us establishing a large scale calibration to the astronomical solutions and to correlate pre msc sediments with classical rhythmic successions outcropping onshore thickness and characteristic sedimentary patterns observed in the offshore evaporitic records resemble those from marginal plg sequences furthermore seismic reflectors from a bedded unit bu which corresponds to an evaporitic interval according to well to seismic ties are correlated with the onshore plg sequences this correlation constitutes the first attempt to link well known marginal sequences with intermediate depth offshore settings which have previously only been studied through seismic imaging our time calibration provides direct evidence supporting a synchronous onset of the plg phase between onshore and offshore settings along the southwestern balearic promontory margin those bu reflectors which were positively correlated to the plg were likely precipitated offshore the continental shelf at messinian times these results suggest that gypsum precipitation and or preservation was not always limited to 200 m water depths and could occur in non silled basins finally we only found a major erosion at the top of the plg sequences implying that the msc drawdown occurred after the precipitation of the onshore lower evaporites studied sequences provide new insights into the plg precipitation preservation settings as well as into the land sea correlations of msc units and thus could potentially help refine current msc models

analysis of water movement through an unsaturated soil zone in jeju island korea using stable oxygen and hydrogen isotopes summary in order to analyze water movement through an unsaturated soil zone in jeju island korea temporal variations in the oxygen 18 and deuterium isotopes of precipitation and soil waters at three different depths were monitored for about one year the stable oxygen and hydrogen isotopic compositions of the soil waters are plotted between or near the two local meteoric water lines for summer and winter precipitation indicating that the soil waters were recharged from the year around precipitation and evaporation was negligible even during hot summer season in the study area mean residence times of the soil waters were then estimated from the 18o d and deuterium excess or d values of the precipitation and soil waters using two well mixed or exponential models em and one exponential piston flow model epm the regression results show that the combination of the exponential piston flow model and the d values of the precipitation and soil waters gives the most reasonable estimation of the mean residence times of the soil waters in the study area it suggests that the deuterium excess or d values can be used as a better parameter than the 18o or d values alone for estimating mean residence times of subsurface waters not only in korea but also in other northeast asian countries the estimated low moisture contents and hydraulic diffusivities of the soils at the three different depths also indicate that the boundary between the upper fine grained soil and the lower coarse grained soil may act as a capillary barrier and the soil waters probably flow slowly through micropores rather than rapidly through macropores in the unsaturated soil zone

climatology of extreme rainfall and flooding from orographic thunderstorm systems in the upper arkansas river basin 1 analyses of the spatial and temporal distribution of extreme rainfall in the arkansas river basin above pueblo colorado are based on volume scan reflectivity observations from the pueblo wsr 88d radar during the period 1995 2003 a storm catalog of 66 rainfall events during the 9 year period has been developed climatological analyses of extreme rainfall are carried out both from an eulerian perspective in which distributional aspects of rainfall at fixed locations are examined and from a lagrangian perspective in which distributional aspects of rainfall are based on storm tracking algorithms of particular interest is the spatial heterogeneity of extreme rainfall in the complex terrain of the upper arkansas river basin lagrangian analyses are used to characterize the spatially varying distribution of storm initiation storm motion and storm structure climatological analyses indicate that convective rainfall in the arkansas river basin above canon city drainage area of 8070 km2 does not contribute to the extreme flood response of the arkansas river at pueblo drainage area of 12 140 km2 there is pronounced diurnal variation in warm season rainfall in the arkansas river basin and this feature of extreme rainfall is a key element of flood response in the upper arkansas river basin climatological analyses of extreme rainfall in the upper arkansas river basin are examined relative to the spatial and temporal properties of rainfall for extreme flood events that have occurred in the basin including major flood episodes in june 1921 and june 1965

mean recharge times and chemical modelling transfers from shallow groundwater to mineralized thermal waters at montrond les bains eastern massif central france summary a re appraisal of interactions between basinal waters and hydrothermal fluids within the silici clastic series of the intracontinental cenozoic forez basin is proposed using major element and isotope geochemistry together with thermodynamic models recharge processes and shallow sedimentary units in the forez basin were compared using major elements and isotopic data 87 sr 86 sr 18 o 2 h 13 c tritium and 14 c for waters sedimentary carbonates and hercynian basement rocks waters derived from late pleistocene to early holocene surface recharge followed by mixing and chemical evolution through percolation into deep groundwater horizons are investigated isotopic ratios and chemical speciation computed for deeper waters from 0 to 200 m depth indicate that mineralised waters were produced by initial surficial dissolution of calcite in calcareous mudstone providing its sr isotopic signature at about 200 m depth na h 3 o cation exchange with clayey sand rich levels provides additional ca na and oh contents for carbonate saturated water na h 3 o cation exchange can not contribute large na hco 3 concentrations geochemical changes such as increasing 13 c dic values observed from 200 to 500 m depth were modelled by addition of thermal water and geogenic co 2 in increasing proportions with depth 500 mbs thermodynamic calculations of mineral proportions indicate water rock interactions with primary minerals in the metamorphic basement and secondary minerals observed in the basin water temperature and its meteoric origin suggest a basin wide recharge system with water rock interaction driven by heat flow rather than through deep crustal fractures

pliocene climate variability northern annular mode in models and tree ring data the northern annular mode nam and its regional expression the north atlantic oscillation nao are the primary interannual oscillatory systems in the northern hemisphere in the modern climate nam has been linked with a number of weather extremes including large terrestrial temperature increases and extreme snowfalls its connection to climate is more controversial although a change in its behaviour between 1970 and 2000 coincided with rapid temperature increases in the northern hemisphere the north atlantic and nordic seas are a key component in pliocene climate showing the largest increases from modern sea surface temperature to understand these changes and the ability of climate models to reproduce them we must consider simulations of the nam here we show that existing mid pliocene simulations exhibit large changes to the mean state and variability in the north atlantic and a significant dampening of the nao through sensitivity experiments this change is primarily attributed to the impact of the lowering of the rocky mountains as the timing of rocky mountains uplift is still disputed simulations of the north atlantic region contain significant uncertainty particularly relating to interannual variability and its climate feedbacks new high temporal resolution climate proxy data is required to test these model reconstructions here we report new annual resolution data and an analysis of climate variability from fossil tree rings these fossils from sites in the canadian arctic provide support for a strong north atlantic oscillation during the pliocene

how entraining density currents influence the stratification in a one dimensional ocean basin abstract the sensitivity of ocean stratification to the vertical distribution of plume entrainment is analyzed a large ocean basin supplied by dense water from an adjoining marginal sea is considered the dense water flows into the ocean basin as an entraining density current and interleaves at the bottom or at the level of neutral density where it deposits a mixture of marginal sea and basin water as the basin water i e old plume water is entrained and re circulated in the plume a stratification develops in the basin the mixture deposited at the bottom hence contains an increasing fraction of marginal sea water and the basin density increases with depth as well as with time a stationary solution in which diffusion of buoyancy from above is important is approached asymptotically in time non diffusive solutions to the initial transient adjustment as well as the diffusive asymptotic state have been studied in four different parameterizations of plume entrainment it is shown that in the transient regime the basin stratification and plume density are highly sensitive to how mixing is parameterized the stationary diffusive solution that is approached asymptotically in time is less sensitive to parameterization but depends strongly on basin topography source water density and buoyancy flux at the surface

seasonal 18o variations and groundwater recharge for three landscape types in central pennsylvania usa seasonal 18 o variations in precipitation soil water snowmelt spring flow and stream baseflow were analyzed to characterize seasonal dynamics of groundwater recharge in three central pennsylvania catchments the catchments represented three common landscape types valley and ridge shale mahantango creek valley and ridge carbonate buffalo run and appalachian plateau sandstone benner run samples were collected on a biweekly basis from may 18 1999 to may 9 2000 precipitation soil water and baseflow isotopic composition data indicated that a seasonal recharge bias existed for these catchments most recharge occurred in the fall winter and spring months an altitude effect of k0 16 to k0 32 100 m change in elevation was discernible in precipitation soil water and stream baseflow isotopic compositions soils effectively damped seasonal variations of recharge 18 o composition after depths of 1 62 2 85 m the greatest damping of the annual isotopic composition signal occurred in the shallow soil layers 0 15 cm in these and similar landscapes with thick soils the annual isotopic composition signal may be completely damped prior to reaching the stream as baseflow isotopic variations measured in stream baseflow are more likely to be caused by the shallow flowpath water relatively close to the streams baseflow stable isotope variations found on the basins studied suggested that residence times for subsurface waters to reach channels were much longer than the annual seasonal cycle of 18 o in precipitation damping depths were similar for the three different catchments but it is not certain how spatially variable damping depths were within each catchment this information would be useful in determining areas within catchments that contribute to short term isotopic composition fluctuations within streams new water predictive models that determine isotopic damping depth from meteorological soil and vegetation land use data can help develop a better understanding of the variability of recharge and attenuation of contaminants across the landscape q 2004 elsevier b v all rights reserved

impact of the spatial distribution of the atmospheric forcing on water mass formation in the mediterranean sea the impact of the atmospheric forcing on the winter ocean convection in the mediterranean sea was studied with a high resolution ocean general circulation model the major areas of focus are the levantine basin the aegean cretan sea the adriatic sea and the gulf of lion two companion simulations differing by the horizontal resolution of the atmospheric forcing were compared the first simulation med16 era40 was forced by air sea fields from era40 which is the ecmwf reanalysis the second simulation med16 ecmwf was forced by the ecmwf analyzed surface fields that have a horizontal resolution twice as high as those of era40 the analysis of the standard deviations of the atmospheric fields shows that increasing the resolution of the atmospheric forcing leads in all regions to a better channeling of the winds by mountains and to the generation of atmospheric mesoscale patterns comparing the companion ocean simulation results with available observations in the adriatic sea and in the gulf of lion shows that med16 ecmwf is more realistic than med16 era40 in the eastern mediterranean although deep water formation occurs in the two experiments the depth reached by the convection is deeper in med16 ecmwf in the gulf of lion deep water formation occurs only in med16 ecmwf this larger sensitivity of the western mediterranean convection to the forcing resolution is investigated by running a set of sensitivity experiments to analyze the impact of different time space resolutions of the forcing on the intense winter convection event in winter 1998 1999 the sensitivity to the forcing appears to be mainly related to the effect of wind channeling by the land orography which can only be reproduced in atmospheric models of sufficient resolution thus well positioned patterns of enhanced wind stress and ocean surface heat loss are able to maintain a vigorous gyre circulation favoring efficient preconditioning of the area at the beginning of winter and to drive realistic buoyancy loss and mixing responsible for strong convection at the end of winter

the generation of a mesoscale convective system from mountain convection a mesoscale convective system mcs that formed just to the east of denver is investigated with a nonhydrostatic numerical model to determine which processes were important in its initiation the mcs developed from outflow from previous convective activity in the rocky mountains to the west model results indicate that this outflow was necessary for the development of the mcs even though a convergence line was already present in the area where the mcs developed a simulation with a 3 km grid spacing more fully resolves the convective activity in the mountains but the development of the mcs can be simulated with a 6 67 km grid cloud effects on solar radiation and ice sedimentation both influence the strength of the outflow from the mountain convection but only the ice sedimentation makes a significant impact on the development of the mcs after its initiation the frequent convective activity in the rocky mountains during the warm season provides outflow that would make mcs generation favorable in this region thus there is a close connection between mountain convective activity and mcs generation the implications of such a connection are discussed and possible directions of future research are indicated

controls on messinian lower evaporite cycles in the mediterranean the messinian salinity crisis in the mediterranean 5 96 5 33 million years ago ma represents the most recent case of massive evaporite deposition throughout an ocean basin here we quantitatively investigate the nature of the gypsum marl cycles within its first phase known as lower evaporites le or primary lower gypsum plg 5 96 5 59 ma we conclude that to precondition the basin for deposition of the le plg sequence its connection with the open atlantic must have been reduced to about 3 of the cross sectional area of the modern strait of gibraltar using the modern strait morphology for scale this would imply a connection with a depth of about 50 m and a width of several kilometres we find that the le plg evaporite marl cycles may then have resulted from sea level fluctuations of the order of 5 to 10 m and or fluctuations in the mediterranean s hydrological deficit of the order of 20 previous work has argued that sea level control may be excluded because there are too many cycles to agree with orbital obliquity related timing however we argue from analogy with quaternary sea level records that sub orbital sea level fluctuations may easily reach the required magnitudes so that sea level control remains plausible

numerical study of an observed orogenic mesoscale convective system part 1 simulated genesis and comparison with observations abstract the interaction of topographically induced thermally and mechanically driven diurnal flow regimes in the lee of the rockies is shown to lead to the growth of a mesoscale convective system mcs an organic mcs observed during the 1977 combined south park area cumulus experiment and high plains experiment is numerically simulated with a two dimensional nonhydrostatic cloud model covering spatial scales of 1000 km in this numerical investigation meso meso and meso scales of motion are represented simultaneously as a result interesting features of cloud mesoscale interaction are predicted that cannot be represented in cloud parameterization frameworks based on the results of this simulation a six stage conceptual model of orogenic development is given

meso β scale characteristics of an episode of meso α scale convective complexes abstract a variety of meso scale 20 200 km 6 h convective complex mcc are described the analysis is based on a typical episode of mccs in the central united states thunderstorms in the mcc are generally well organized into meso scale convective features the larger mccs are typically preceded by several of these meso convective clusters or bands which tend to be aligned along linear meso scale features such as the eastern slope of the rockies or thermodynamic discontinuities evident in hourly surface or satellite data the intense development of these larger systems involves the growth merger and interaction of those meso convective feature located nearest the intersection of the meso axes along which they are aligned throughout the mature phase of the mcc multiple meso convective components may persist within the more uniform meso cloud shield as expanding regions of str

a modeling study and scaling analysis of orographic effects on boundary layer shallow convection effects of orography on boundary layer shallow convection under various background winds are studied using a two dimensional model together with scaling analysis under a motionless background state the flow response over a heated hill is a vortex pair with one horizontal vortex over each slope additional lifting of the inversion by this vortex pair is estimated by wt n with wt being the intensity of the terrain induced thermal circulation and n the brunt vaisalafrequency for which a simple expression is given based on heat engine framework modification of the cbl top by terrain induced waves is quantified using linear gravity wave theory in a two layer atmosphere configuration these simple estimates of the cbl top perturbation are found to be consistent with the model results when waves and convection dominate the flow pattern a convective core is found to occur over high hills when the winds are light developing in the late afternoon when the cbl depth is high a scaling is proposed to determine the existence of the convective core in terms of hill slope background winds boundary layer depth and tropospheric stability the downstream modification of convection by terrain related processes is also examined under light wind conditions the reversed thermal circulation in the lee and corresponding downward motions may suppress thermal eddies in the vicinity of the lee of a hill

mesoscale convective systems in weakly forced large scale environments part i observations abstract during a 24 h period beginning 1200 utc 11 may 1982 a series of five mesoscale convective systems mcss developed within a weakly forced large scale environment analyses indicate that the large scale flow created a broad region of potential buoyant energy but owing to a restraining inversion and weak large scale upward motion convection was initiated only where lifting associated with mesoscale features was able to eliminate the inversion the series of mcss developed sequentially and moved eastward across the moist axis two of these systems had a large component of motion against the mean tropospheric flow and propagated in a direction nearly opposite to that of the traveling upper level disturbances each system produced an outflow of cold downdraft air that spread progressively farther south than that from the preceding system this description of the development and evolution of convection is very different from traditional ones wherein convection develops and moves more or less in pha

lithology and characteristics of the messinian evaporite sequence of the deep levant basin eastern mediterranean abstract as the lithological composition of the messinian salt sequence of the levant basin is still controversial and unconstrained we reveal for the first time the lithology of the entire evaporite sequence from deep basin depth migrated seismic and borehole data the data presented here shows that the seismic transparent layers are composed of pure and uniform halite while the reflective layers are bundles of thin clay layers interbedded in the halite background the thin clay layers inside the deep basin evaporites have a cumulative thickness of 25 40 m high amplitude fan structures are observed on the deepest internal reflector which may suggest clay transportation among all the internal reflectors the upper units are more deformed while the deeper units are more coherent and flat two sets of folds faults are shown on the shallower intra units folds with nne ssw trending axes and thrust faults strike nw se on a regional scale the top salt reflector is generally horizontal while the other internal reflectors dip toward the nw the shallowest intra unit is the only one that has a wedge shape thickening to the nw while the other intra units generally have uniform thicknesses

hydraulic theory of sea straits applied to the onset of the messinian salinity crisis abstract theory for the dynamics of flow in sea straits holds promise to provide in addition to geological evidence insight into the configuration of the connection between the mediterranean sea and the atlantic ocean at the onset of the messinian salinity crisis this paper for the first time systematically explores the application of hydraulic control theory to the question of how about 6 ma ago mediterranean salinity could have risen to values associated with gypsum saturation the theory is based on the notion that it is the greatest constriction of the flow between basin and ocean that acts to limit the exchange the response of basin salinity to strait depth strait width and relative thickness of the outflow layer proves to be highly nonlinear for strait width on the order of kilometres an asymptotic rise in basin salinity occurs when the strait depth is on the order of a few tens of metres completely blocked outflow takes place when the depth is reduced to metres the nonlinear nature of the system implies that even a slow gradual reduction in the sill depth leads to an event like rise in basin salinity for values of basin salinity approaching gypsum saturation the response of the basin to changes in the strait depth is significantly delayed

a stable isotope study of recharge processes in the english chalk the 2h and 18o values of water contained in unsaturated chalk have been measured in drillcore profiles taken over a period of 28 months on arable land in cambridgeshire eastern england the isotopic composition of rainfall and lysimeter drainage on the same site has also been monitored over a period of four years the distribution of isotope values in the upper few metres of soil and unsaturated chalk shows that the mechanism of infiltration is not simple piston like downward displacement since the scale of vertical fluctuations is incompatible with estimated annual infiltration and the apparent rates of movement of matrix water derived from thermonuclear tritium studies lysimeter drainage is not isotopically identical to matrix water at the same depth suggesting that different routes to water table are associated with consistently different isotopic content although there is an apparent difference between matrix water beneath arable and permanent grassland these differences appear to cancel out in the composition of bulk recharge beneath these land types the regional aquifer has a uniform isotopic composition similar in value to weighted average rainfall and lysimeter drainage suggesting that the recharge abstraction system has been in isotopic equilibrium for many years despite changes in pumping rates and land use two other chalk sites in southern england have been investigated in less detail but indicate clear difference in infiltration behaviour from that seen in cambridgeshire this seems to be related to a higher matrix conductivity and annual rainfall amount

understanding groundwater systems and their functioning through the study of stable water isotopes in a hard rock aquifer maheshwaram watershed india summary groundwater degradation through abstraction contamination etc shows a world wide increase and has been of growing concern for the past decades in this light the stable isotopes of the water molecule 18 o and 2 h from a hard rock aquifer in the maheshwaram watershed andhra pradesh india were studied this small watershed 53 km 2 underlain by granite is endorheic and representative of agricultural land use in india with more than 700 bore wells in use in such a watershed the effect of overpumping can be severe and the environmental effects of water abstraction and contamination are of vital importance a detailed and dynamic understanding of groundwater sources and flow paths in this watershed thus is a major issue for both researchers and water managers especially with regards to water quality as well as the delimitation of resources and long term sustainability to this end the input from monsoon precipitation was monitored over two cycles as well as measuring spatial and temporal variations in 18 o and 2 h in the groundwater and in precipitation individual recharge from the two monsoon periods was identified leading to identification of periods during which evaporation affects groundwater quality through a higher concentration of salts and stable isotopes in the return flow such evaporation is further affected by land use rice paddies having the strongest evapotranspiration