new geochemical support for mixing zone dolomitization at golden grove barbados dolomite occurs in the golden grove reef terrace of late pleistocene age in southeastern barbados where fore reef lithologies have been partially to completely dolomitized interpretation of the possible modes of formation of this dolomite has been a subject of disagreement for over a decade among the points of contention are the timing of deposition dolomitization and dolomite cement precipitation and the relationship of replacement dolomite with dolomite cement data from this study indicate that dolomitization occurred during a single relative sea level fall following reef development at marine oxygen isotope stage 7 3 at approximately 216 ka replacement dolomitization affected both micritic matrix and skeletal grains during or after replacement dolomitization dolomite and calcite cements filled primary and secondary pores the cement paragenesis comprises early dolomite cement complexly banded cements of alternating calcite and dolomite late dolomite cement of near stoichiometric composition and a final phase of blocky calcite cement replacement dolomitization and cement precipitation represent a continuum of processes resulting from progressive modification of diagenetic fluids stable carbon and oxygen isotope and strontium elemental compositions of replacive dolomite dolomite cements and calcite cements indicate that dolomitization occurred in a mixing zone between marine and meteoric groundwaters occupying the reef terrace shortly after deposition dolomite oxygen isotope values range from 0 18 to 3 85 pdb and become progressively more depleted throughout the paragenesis indicating a greater influence of meteoric water through time remarkably depleted carbon isotope compositions for both replacement dolomite and dolomite cement 9 53 to 23 04 pdb originated from oxidation of thermogenic methane advected from the underlying accretionary complex methane was oxidized in marine waters that subsequently mixed with meteoric waters as evidenced by a progressive enrichment in carbon isotope composition throughout the paragenesis dolomite strontium contents are substantially elevated above those expected for marine dolomitization ranging from 640 to 1650 ppm and increasing throughout the paragenesis meteoric water provided the excess strontium as aragonite to calcite transformation in the exposed reef terrace increased the fluid sr ca ratio the continuum of geochemical compositions between the replacement dolomite and dolomite cement argues for their genetic association these new data provide additional support to the mixing zone interpretation for golden grove and that the model of mixing zone dolomitization remains viable

early carbonate diagenesis in slope sequences and at their boundaries cenozoic offshore new jersey odp leg 150 this paper reports the genetic links among the depth distribution mineralogy and stable isotopic composition of diagenetic carbonates with sedimentation rates and types and preservation of organic matter in the terrigenous and biogenic sediments of oligocene and miocene age on the new jersey slope calcites formed close to the sediment surface at sequence boundaries and maximum flooding surfaces when the profile of early diagenetic reactions was stabilized in the sediment column for extended periods dolomites precipitated in the sulfate reduction zone when diagenetic profiles stabilized during truncation sequence boundary formation and the deposition of lowstand sediments that overlie the sequence boundaries most dolomites occur in distal slope sediments that were deposited before the shelf had prograded into the study area siderites formed during a later stage of burial in the methanogenic zone they are not directly genetically related to the sequence stratigraphy of the new jersey slope the diagene tic dolomites and siderites occur in widely separated depth intervals below the present sea floor the distribution of the diagenetic carbonates and their preferential occurrence in separated depth intervals resulted from different combinations of sedimentation rates and organic matter types and preservation

evaluation of slope stability with respect to snowpack spatial variability the evaluation of avalanche release conditions constitutes a great challenge for risk assessment in mountainous areas the spatial variability of snowpack properties has an important impact on snow slope stability and thus on avalanche formation since it strongly influences failure initiation and crack propagation in weak snow layers hence the determination of the link between these spatial variations and slope stability is very important in particular for avalanche public forecasting in this study a statistical mechanical model of the slab weak layer wl system relying on stochastic finite element simulations is used to investigate snowpack stability and avalanche release probability for spontaneously releasing avalanches this model accounts in particular for the spatial variations of wl shear strength and stress redistribution by elasticity of the slab we show how avalanche release probability can be computed from release depth distributions which allows us to study the influence of wl spatial variations and slab properties on slope stability the importance of smoothing effects by slab elasticity is verified and the crucial impact of spatial variation characteristics on the so called knock down effect on slope stability is revisited using this model finally critical length values are computed from the simulations as a function of the various model parameters and are compared to field data obtained with propagation saw tests

dolomite in caves recent dolomite formation in oxic non sulfate environments castanar cave spain abstract dolomite is a common mineral in the rock record but rare in recent superficial environments where it does occur it is related to anoxic sulfate rich environments and microbial activity the occurrence of some dolomite deposits in caves however indicates that dolomite formation is also possible in oxic non sulfate settings dolomite is forming at 17 c and in oxic vadose conditions on the host rocks and aragonite speleothems of the castanar cave caceres spain it appears as spheroids and dumbbells 50 300 m in diameter that internally consist of micron sized rhombic to rounded crystals initially this dolomite is ca rich non stoichiometric and poorly ordered mg rich solutions allow the precipitation of metastable mg rich carbonates such as huntite this soon transforms into this ca rich dolomite which later ages to form a more stoichiometric dolomite these dolomites show similarities to those grown under anoxic sulfate rich conditions and their presence in caves provides a different setting that may contribute to the understanding of the dolomite problem including their initial formation and later recrystallization processes

evolution of a mesoscale upper tropospheric vorticity maximum and comma cloud from a cloud free two dimensional potential vorticity anomaly a diagnostic case study is presented in which output from the limited area forecast version of the meteorological office operational unified model was used together with water vapour and cloud imagery from the meteosat satellite the case chosen for study was an archetypally simple example in which a long narrow strip of air with high potential vorticity pv in the upper troposphere strictly a tropopause depression became unstable and rolled up into fairly ling lived mesoscale vortices for much of the time the vortices were cloud free and they were dynamically pure examples of very small upper air pv anomalies moving relative to the strata beneath as such they provided a good test of theoretical deductions from the pv invertability principle and of the performance of the dynamical components of the forecast model the evolution of the mesoscale vortices as revealed in the satellite imagery was well handled by the unified model indicating that the small scales were reproduced well by the model dynamics even though they were not fully defined by the routine observations fed into the model as the vortices began to form the stretching deformation along the axis of the initial pv strip was very small and the 900 km spacing of the vortices was broadly consistent with theoretical expectations for the wavelength of instabilities growing on such a pv strip a detailed analysis of one of the mesoscale vortices throughout its 3 day lifetime showed that its maximum potential vorticity and absolute vorticity decreased with time as it travelled within the circulation of large scale anticyclonic gyre by the end of the second day when cloud first formed the vortex had become a weak upper tropospheric shear line 500 km long sandwiched between a pair of anticyclonic mesoscale vortices 900 km apart the meteosat imagery revealed a characteristic two component structure both in the water vapour channel and when the cloud eventually formed in the infrared channel too this structure which resembled that seen on other occasions is explained in terms of a particular combination of vertical motion and advection in the region of sharp humidity gradients alongside dry stratospheric air that had intruded into the upper troposphere

a computer based system simulating snowpack structures as a tool for regional avalanche forecasting this paper describes the current state of a complete automatic system of three numerical models that simulate snow cover stratigraphy and avalanche risks for operational avalanche forecasting the first model safran estimates relevant meteorological parameters affecting snowpack evolution the second crocus is a snow numerical model which simulates the physical processes inside the snowpack and its stratigraphy the last model mepra is an expert system based on an assessment of snowpack stability it deduces natural and accidental avalanche risks to describe the great variability of the snowpack and the associated avalanche risks this automatic system simulates snow cover evolution and its stability for many typical slopes elevations and aspects representative of the different french massifs to achieve this result different kinds of validations have been carried out since winter 1981 they are mainly based on comparisons with different sets of measurements and on the opinion of users although the routinely obtained results do not yet take into account all small scale effects such as wind transport they have been considered as valuable information by avalanche forecasters since 1992 93 and used operationally since then

interpretation of satellite imagery of a rapidly deepening cyclone model output and observational data are used to interpret in detail satellite images of a distinctive cloud system several hundred kilometres long which was observed before and during rapid cyclonic development that occurred over england conceptual models are forwarded which account for the structure of the major cloud areas and upper level moisture fields as observed by water vapour imagery immediately prior to and following the onset of vigorous cyclogenesis the cloud system corresponded to what r b weldon refers to as a baroclinic leaf cloud and was characterized by ana cold frontal ascent the baroclinic leaf lay within an area of enhanced ascent ahead of a major upper level trough a jet streak which originated upstream propagated rapidly around the base of the upper trough a tongue of dry air centred on the left flank of this jet streak lay immediately upstream of the leaf cloud and had a major influence on its subsequent development this intrusion of dry air was well represented by the meteorological office fine mesh model which showed it as a pronounced tongue of recently descended air with high potential vorticity which originated in the upper troposphere and lower stratosphere rapid cyclogenesis occurred as the dry intrusion overran low level air of high w within a warm conveyor belt at the southern tip of the leaf cloud interaction of the dry intrusion and baroclinic leaf cloud is shown to be particularly important in accounting for the detailed distribution of weather it also suggests a way of pinpointing the location and timing of vigorous cyclogenesis

large scale potential vorticity anomalies and deep convection the effect on deep convection of large scale potential vorticity pv anomalies and their associated tropospheric stable layers is complex and not well understood this article examines the meteorological events of 9 july 2007 iop7b of the convective and orographically induced precipitation study cops which was dominated by an upper level pv anomaly that stretched from the uk to southern france and as far northeast as denmark three precipitation regions were identified from the case lines of intense storms beneath the pv anomaly less intense more widespread convective precipitation to the east of the pv anomaly and in between a region of no precipitation the latter of these coincided with the high resolution measurements and model analyses from cops the extensive and varied data analyzed in this investigation show that convective available potential energy cape was present in this region the distribution of cape and convective inhibition cin is presented via an innovative pseudo 3d visualization that allows horizontal and vertical interactions to be considered however convection was capped by a complex arrangement of dry layers the base of the key layer was at 750 hpa these dry layers descended separately from the upper troposphere moving around the pv anomaly as it developed from a breaking rossby wave to the west during the seven days before the iop this case adds to other studies that show that descent of complex dry layers is an important mechanism for forming convection inhibiting atmospheric lids in western europe a simple conceptual model is developed that synthesizes the effect of large scale pv anomalies on deep convection from a series of consistent case studies this model has significant implications for storm forecasting and projections of storminess in future climates as it highlights the importance of thin structures that can advect hundreds of km before having an impact copyright 2012 royal meteorological society

methane generated lithified dolostone of holocene age eastern mediterranean abstract peritidal beachrock ledges along the south shore of bardawil lagoon a body of water located in the eastern mediterranean off the coast of the sinai peninsula consist of gypsum or gyprock and change along strike to a thoroughly cemented solid tough dolostone microprobe analysis shows that this dolostone is a non stoichiometric dolomite with mol caco3 of 65 70 except for fossils and included terrigenous particles this modern dolostone is solid rock composed entirely of dolomite under the microscope the rock is a peloidal micrite dolomicrite in which abundant fragments of solid particulate organic matter are dispersed in comparison with other kinds of beachrock this dolostone is tight the age of the dolostone is 5700 ybp the 13cpdb of dolostone samples is 39 3 and 31 2 these strongly negative 13c values suggest that the carbon of the dolomite came from methane bacterial reactions form methane when the bacteria have reduced all available sulfate i infer that bacteria were responsible for the origin of this dolomite through the methane pathway high desert temperatures may have facilitated such a dolomitization process

mesoscale analysis of a polar trough interacting with a polar front the interaction of a polar trough with a polar front can lead to a characteristic satellite cloud pattern commonly referred to as an instant occlusion the detailed structure and development of an event rather resembling an instant occlusion is analysed in this paper using routine data supplemented by additional radiosondes soundings and cloud imagery from noaa 7 and meteosat and radar network pictures the event presented differs from an instant occlusion as described by anderson and others in that a band of polar front cloud developed simultaneously with the band of cloud associated with the polar trough rather than being a pre existing feature thus we refer to it under the different name of pseudo occlusion in order to keep this distinction in mind a conceptual model of the pseudo occlusion is developed in which the key elements are i a moist relatively warm low level jet associated with the polar trough referred to as the polar trough conveyor belt and ii a major upper level jet streak associated with the polar front referred to as the polar front conveyor belt the two conveyor belts intersect almost at right angles precipitation associated with the polar front is predominantly from stratiform cloud whereas that associated with the polar trough is a mixture of stratiform and convective just on the poleward side of the upper jet the cloud top drops abruptly here dry air having recently descended beneath the tropopause fold suppresses the depth of the moist air associated with the polar trough conveyor belt this leads to a minimum in the intensity of precipitation between the rain areas associated with the trough and the front although the air overrunning the trough just on the poleward side of the polar front is dry as a result of earlier descent the air in this location is likely to have begun ascending as part of the indirect circulation in the exit region of the upper level jet streak the polar trough low level jet probably forms part of this circulation

spatial and temporal diagenetic evolution of syntectonic sediments in a pulsatory uplifted coastal escarpment evidenced from the plio pleistocene makran subduction zone iran

snow avalanche formation 1 snow avalanches are a major natural hazard endangering human life and infrastructure in mountainous areas throughout the world in many countries with seasonally snow covered mountains avalanche forecasting services reliably warn the public by issuing occurrence probabilities for a certain region however at present a single avalanche event cannot be predicted in time and space much about the release process remains unknown mainly because of the highly variable layered character of the snowpack a highly porous material that exists close to its melting point the complex interaction between terrain snowpack and meteorological conditions leading to avalanche release is commonly described as avalanche formation it is relevant to hazard mapping and essential to short term forecasting which involves weighting many contributory factors alternatively the release process can be studied and modeled this approach relies heavily on snow mechanics and snow properties including texture while the effect of meteorological conditions or changes on the deformational behavior of snow is known in qualitative or semiquantitative manner the knowledge of the quantitative relation between snow texture and mechanical properties is limited but promising developments are under way fracture mechanical models have been applied to explain the fracture propagation and micromechanical models including the two competing processes damage and sintering have been applied to explain snow failure there are knowledge gaps between the sequence of processes that lead to the release of the snow slab snow deformation and failure damage accumulation fracture initiation and fracture propagation simultaneously the spatial variability that affects damage fracture initiation and fracture propagation has to be considered this review focuses on dry snow slab avalanches and shows that dealing with a highly porous media close to its melting point and processes covering several orders of scale from the size of a bond between snow grains to the size of a mountain slope will continue to be very challenging

statistical forecasting of regional avalanche danger using simulated snow cover data in the past numerical prediction of regional avalanche danger using statistical methods with meteorological input variables has shown insufficiently accurate results possibly due to the lack of snow stratigraphy data detailed snow cover data were rarely used because they were not readily available manual observations with the development and increasing use of snow cover models this deficiency can now be rectified and model output can be used as input for forecasting models we used the output of the physically based snow cover model snowpack combined with meteorological variables to investigate and establish a link to regional avalanche danger snow stratigraphy was simulated for the location of an automatic weather station near davos switzerland over nine winters only dry snow situations were considered a variety of selection algorithms was used to identify the most important simulated snow variables data mining and statistical methods including classification trees artificial neural networks support vector machines hidden markov models and nearest neighbour methods were trained on the forecasted regional avalanche danger european avalanche danger scale the best results were achieved with a nearest neighbour method which used the avalanche danger level of the previous day as additional input a cross validated accuracy hit rate of 73 was obtained this study suggests that modelled snow stratigraphy variables as provided by snowpack are able to improve numerical avalanche forecasting

reexamining the cold conveyor belt abstract despite the popularity of the conveyor belt model for portraying the airflow through midlatitude cyclones questions arise as to the path of the cold conveyor belt the lower tropospheric airflow poleward of and underneath the warm front some studies beginning with carlson s analysis of the eastern u s cyclone of 5 december 1977 depict the cold conveyor belt moving westward reaching the northwest quadrant of the storm turning abruptly anticyclonically rising to jet level and departing the cyclone downstream hereafter the anticyclonic path other studies depict the cold conveyor belt reaching the northwest quadrant turning cyclonically around the low center and remaining in the lower troposphere the cyclonic path to clarify the path of the cold conveyor belt the present study reexamines carlson s analysis of the cold conveyor belt using an observational and mesoscale numerical modeling study of the 5 december 1977 cyclone this reexamination raises several previously unappreciated

structurally controlled hydrothermal dolomite reservoir facies an overview discussion one of the issues of the aapg bulletin v 90 no 11 was concerned with hydrothermal dolomite reservoirs specifically hydrothermal dolomite fields davies and smith 2006 the term hydrothermal dolomite is confusing and meaningless machel and lonnee 2002 to study the origin of dolomite and its hydrothermal depositional setting i examined modern settings including the mediterranean sea friedman 1991 figure 1 the shallow water facies in this modern setting consists of dolomite and gypsum the rocks range from almost pure gypsum to pure tough dolostone so thoroughly cemented that sampling required hammer and chisel x ray diffraction analysis indicates the presence of minor anhydrite sporadic aragonitic gastropods occur but fossils are otherwise absent under the microscope it is a peloidal micrite dolomicrite the 13cpdb of the dolostone is 39 3 to 31 2 these strongly negative 13c values suggest that carbon of the dolomite came from methane methane forms when all sulfate has been reduced bacterial reaction was responsible for dolomite formation through the methane pathway this syngenetic dolomite is like most dolomites of hydrothermal origin but my students and i avoid this confusing bandwagon term figure 1 approximate temperatures at which holocene intertidal carbonate sediments formed calculated from isotopic signatures three classes of dolostone have been recognized which have been termed syngenetic diagenetic and epigenetic friedman and sanders 1967 the purpose of this classification has been for the orderly discussion of the subject and to facilitate descriptive study and genetic interpretation the term syngenetic has been adapted for characterizing biological and chemical origin in its

convective inhibition beneath an upper level pv anomaly upper level potential vorticity pv anomalies reduce the convective stability of the troposphere through their impact on the vertical potential temperature profile thus reducing convective inhibition cin and increasing convective available potential energy here by contrast we show the impact of a layer of stable air that was intrinsically linked with an upper level pv anomaly and that increased cin this layer descended and tracked beneath the small upper level pv anomaly which in this case was a shallow upper level trough this low humidity relatively high pv layer originated from the tropopause fold generated by a breaking rossby wave which also produced the upper level pv anomaly two days later despite conditions favourable for deep convection as demonstrated by the development of a single storm the cin produced by this dry layer or lid was largely responsible for capping convection over much of southern england at around 2 5 km during the case presented here which comes from the convective storm initiation project copyright c 2008 royal meteorological society

mesoscale dynamics of the trowal and warm frontal regions of two continental winter cyclones abstract the dynamic and thermodynamic structure and associated frontal circulations within the trowal and warm frontal regions of two extratropical winter cyclones are examined using numerical simulations in each cyclone the warm moist airstream originating in the warm sector was found to bifurcate upon reaching the warm front one branch of the flow turned anticyclonically eastward corresponding to the warm conveyor belt while the second branch turned cyclonically westward becoming the trowal airstream the dynamic forcing of vertical motion within the two airstreams was investigated using the fifth generation pennsylvania state university national center for atmospheric research mesoscale model mm5 both from an analysis of the sawyer eliassen se equation in two dimensions and from complete model solutions shearing deformation associated with the jet stream and the low level cyclonic flow dominated confluent deformation near the trowal in both cases the shearing deformation was accompanied

formation of cloud bands associated with the american subtropical jet stream and their interaction with midlatitude synoptic disturbances reaching europe abstract this study describes the evolution of very large cloud bands originating from the eastern subtropical pacific ocean and their relation to the american subtropical jet stream in many cases these cloud bands interact with polar lows and then give rise to a very large typical midlatitude cyclone the cloud pattern associated with this cyclone is very similar to that described by the norwegian cyclone model although its origin is quite different

continuous snowpack monitoring using upward looking ground penetrating radar technology snow stratigraphy and water percolation are key contributing factors to avalanche formation so far only destructive methods can provide this kind of information radar technology allows continuous non destructive scanning of the snowpack so that the temporal evolution of internal properties can be followed we installed an upward looking ground penetrating radar system upgpr at the weissfluhjoch study site davos switzerland during two winter seasons 2010 11 and 2011 12 we recorded data with the aim of quantitatively determining snowpack properties and their temporal evolution we automatically derived the snow height with an accuracy of about 5 cm tracked the settlement of internal layers 7 cm and measured the amount of new snow 10 cm using external snow height measurements we determined the bulk density with a mean error of 4 3 compared to manual measurements radar derived snow water equivalent deviated from manual measurements by 5 furthermore we tracked the location of the dry to wet transition in the snowpack until water percolated to the ground based on the transition and an independent snow height measurement it was possible to estimate the volumetric liquid water content and its temporal evolution even though we need additional information to derive some of the snow properties our results show that it is possible to quantitatively derive snow properties with upgpr