ancient runoff farming and soil aggradation in terraced wadi fields negev israel obliteration of sedimentary strata by ants scorpions and humans abstract ancient terraced fields in ephemeral stream valleys in the negev desert enabled farming based on runoff water from local rainfall the runoff was captured by stone terrace walls which were built across suitable wadis in various archaeological periods runoff floods added not only water to the fields but also fine sediment however alluvial stratification is usually absent in such terraced wadi fields why we addressed this question at the rural archaeological site of horvat haluqim in the central negev highlands our geoarchaeological excavations in area 3 of terraced field 12 revealed the existence of laminar alluvial stratification but only in the upper 5 cm micromorphology showed a gradual decline in the preservation of laminae with depth radiocarbon dating showed that the upper 50 cm of the terrace soil accumulated during the past 1300 years therefore the average aggradation rate seems about 0 4 mm year similar to modern sedimentation measurements we found evidence for bioturbation particularly by ants and scorpions in the terraced wadi fields at horvat haluqim scorpions evict the soil crumbs excavated from the subsoil on one side of the crescent shaped entrance to their burrows ants on the other hand place the excavated soil crumbs all around the entrance to their underground nest besides bioturbation human soil disturbance by farming is far more destructive to alluvial stratification hoeing and ploughing tillage can erase alluvial laminae from the surface to a depth of about 10 cm in one farming season clear evidence of ancient farming activities in area 3 was found in darker soil layers from a depth of 45 cm 92 cm laminar alluvial strata have not survived in these layers micromorphology revealed fine charcoal bone and pottery fragments interpreted as kitchen household refuse added as fertilizer to the aggrading soil surface in addition non burned dung fragments and non charred spherulites were found indicating also the use of animal dung as manure darker soil layers have a lower bulk density and a high porosity with an extremely large amount of fine pores probably ancient root channels of barley or wheat though runoff flows kept adding laminated alluvial layers to the aggrading terraced wadi fields the fine laminae initial facies did not endure the tooth of time they were gradually obliterated by bioturbation and or rapidly erased by human farming activities tillage and manuring so that laminae are non existent in the ultimate facies of the aggrading sediment soil in agricultural terraced wadi fields

soil seal development under simulated rainfall structural physical and hydrological dynamics this study delivers new insights into rainfall induced seal formation through a novel approach in the use of x ray computed tomography ct up to now seal and crust thickness have been directly quantified mainly through visual examination of sealed crusted surfaces and there has been no quantitative method to estimate this important property x ray ct images were quantitatively analysed to derive formal measures of seal and crust thickness a factorial experiment was established in the laboratory using open topped microcosms packed with soil the factors investigated were soil type three soils silty clay loam zcl sandy silt loam szl sandy loam sl and rainfall duration 2 14 minutes surface seal formation was induced by applying artificial rainfall events characterised by variable duration but constant kinetic energy intensity and raindrop size distribution soil porosities derived from ct scans were used to quantify the thickness of the rainfall induced surface seals and reveal temporal seal micro morphological variations with increasing rainfall duration in addition the water repellency and infiltration dynamics of the developing seals were investigated by measuring water drop penetration time wdpt and unsaturated hydraulic conductivity kun the range of seal thicknesses detected varied from 0 6 5 4 mm soil textural characteristics and om content played a central role in the development of rainfall induced seals with coarser soil particles and lower om content resulting in thicker seals two different trends in soil porosity vs depth were identified i for sl soil porosity was lowest at the immediate soil surface it then increased constantly with depth till the median porosity of undisturbed soil was equalled ii for zcl and sl the highest reduction in porosity as compared to the median porosity of undisturbed soil was observed in a well defined zone of maximum porosity reduction c 0 24 0 48 mm below the soil surface this contrasting behaviour was related to different dynamics and processes of seal formation which depended on the soil properties the impact of rainfall induced surface sealing on the hydrological behaviour of soil as represented by wdtp and kun was rapid and substantial an average 60 reduction in kun occurred for all soils between 2 and 9 minutes rainfall and water repellent surfaces were identified for szl and zcl this highlights that the condition of the immediate surface of agricultural soils involving rainfall induced structural seals has a strong impact in the overall ability of soil to function as water reservoir

weathering rates of gneiss and depletion of exchangeable cations in soils under environmental acidification budgets of na k mg ca al and si in two forested basins in central europe indicate that the weathering rate of gneiss and the depletion of exchangeable calcium and magnesium are increased due to acidification caused by high deposition of so 2 the production of the pool of exchangeable cations is slower than its depletion there is a coincidence of a very short time necessary to deplete the topsoil of the exchangeable ca 2 and mg 2 and the die back of spruce these conclusions are derived from a new mass balance approach that enables a separation of hydrolysis of primary minerals depletion of exchangeable ions and production of the exchangeable pool of cations in soils from data on elemental budgets in small hydrological basins

a high resolution micromorphological record of changing landscapes and climates on the western loess plateau of china during oxygen isotope stage 5 abstract the micromorphological characteristics of a continuous set of block samples from 24 38 m depth in a well section on jiuzhoutai mountain lanzhou china are described the shape of the magnetic susceptibility curve together with previously published radiocarbon luminescence and geomagnetic dates indicates that this sample set encompasses the whole of the last interglacial s1 palaeosol complex and extends into the overlying and underlying loess l1 and l2 units seven pedosedimentary units are recognised on the basis of trends in the bulk properties and the key micromorphological indicators excrements textural concentrations shell fragments and calcite and gypsum features high rates of loess deposition with significant cryogenic activity gypsum precipitation and only weak bioturbation characterised oxygen isotope stage ois 6 and ois 4 at lanzhou depositional rates were moderately high in ois 5d and 5b with slightly higher bioturbation and no significant cryogenesis or gypsum precipitation ois 5e 5c and 5a were marked by low rates of accretion more extensive bioturbation and limited leaching this reconstruction reflects the pedosedimentary responses to fluctuating dominances of monsoonal controls during this period of global climatic change comparison of earlier micromorphological results from sites to west and east of lanzhou along a dry to humid climatic gradient indicate a clear regional pattern with reduced loess accumulation rates and enhanced bioturbation and leaching in the humid east tianshui and xian clay translocation occurred only in ois 5e at xian the warmest and most humid site on the transect

laboratory experiments on the influence of slope length on runoff percolation and rill development experiments to test relationships between slope length percolation and runoff were carried out in a laboratory flume under simulated rainfall at intensities from 24 2 26 mm h 1 a composite soil subject to sealing was mixed from a clay and a sand and tested on 2 39 m 7 18 m and 17 m slopes for a minimum of 200 min runoff discharge is not a simple function of rainfall excess and slope length but shows a complex pattern dominated by surface sealing rill development and headcut incision rill development by concentrated surface wash conformed to established threshold hydraulic conditions but subsequent headcut incision was necessary to breach the seal and significantly affect percolation runoff ratios headcut evolution is complex apparently reflecting hydraulic instability and possibly different stages in seal development headcut and rill incision shows a cyclic pattern interspersed with broad areas of sheetwash and colluvial deposition where percolation rates are very low

towards a field test for fracture propagation propensity in weak snowpack layers slab avalanche release requires fracture initiation and propagation in a weak snowpack layer while field tests of weak layer strength are useful for fracture initiation the challenge remains to find a verified field test for fracture propagation we introduce the two current versions of a field test for fracture propagation propensity and report results of testing conducted in the columbia mountains of british columbia canada during the winter of 2005 by extending the column of a stability test approximately 3 m in the downslope direction the test method allows for the development of a flexural wave in the slab and thereby maintains the contribution of this wave and the associated weak layer collapse to the fracture process fracture lengths collected on a day and location where the propagation propensity of the snowpack was locally high show a bimodal distribution with approximately 50 of observed fractures similar to those collected in stable snowpacks and approximately 50 with much longer fracture lengths

strontium isotopes as tracers of ecosystem processes theory and methods abstract the strontium sr isotope method can be a powerful tool in studies of chemical weathering and soil genesis cation provenance and mobility and the chronostratigraphic correlation of marine sediments it is a sensitive geochemical tracer applicable to large scale ecosystem studies as well as to centimeter scaled examination of cation mobility within a soil profile the 87sr 86sr ratios of natural materials reflect the sources of strontium available during their formation isotopically distinct inputs from precipitation dryfall soil parent material and surface or groundwater allow determination of the relative proportions of those materials entering or leaving an ecosystem the isotopic compositions of labile soil exchange complex and soil solution strontium and sr in vegetation reflect the sources of cations available to plants strontium isotopes can be used to track the biogeochemical cycling of nutrient cations such as calcium the extent of cation contributions from in situ weathering and external additions to soil from dust and rain can also be resolved with this method in this paper we review the geochemistry and isotopic systematics of strontium and discuss the use of this method as a tracer of earth surface processes

surface crusting in two alluvial soils of northen niger valentin c 1991 surface crusting in two alluvial soils of northen niger geoderma 48 201 222 surface crusting was studied in a sandy soil and a clay loam soil in northern niger in a subdesert to desert environment light microscopy electron microscopy image analysis and soil physics were used to study and explain different crusting processes in experimental plots two 1 m2 plots on each soil were subjected to rainfall simulation in the field under natural and tilled surface conditions this study demonstrates that kinetic energy of rainfall is the major crusting factor for the sandy soil waterlogging and subsequent slaking led to the formation of structural and depositional crusts in the tilled clay loam plot in this case a surface crust can be formed regardless of kinetic energy of the rainfall this was substantiated through double ring infiltrometer measurements in both soils infiltration was severely hindered by crusting the relationships of crusting to water and wind erosion were more ambiguous four types of crusts could be defined from this study in terms of structure genetic processes and properties it could also be demonstrated that crust control practices should take into account the texture of the original soil materials

weathering rates and 87sr 86sr ratios an isotopic approach the 87sr 86sr ratios of precipitation throughfall groundwater streamwater and mineral matter were analyzed precipitation strontium ratios are around 0 71 throughfall which is affected by strontium from the mineral soil has ratios of 0 72 0 73 and shallow groundwater in a drug well and runoff have ratios around 0 73 0 74 there is a tendency for this relationship to be reversed for discharge higher ratios are associated with lower discharges water from a fracture zone gave the highest value 0 78 approaching the value of the bedrock around 0 85 a calcium budget which reflects the mean conditions over a few years has been calculated this budget indicates that weathering should be of the order of 8 kg ca ha 1yr 1 to maintain the pool of exchangeable calcium at a constant level the major anion in the runoff is suphate which has entered the system in the form of acid rain sulphur deposition has been rather constant over the last two decades if acidification had an effect on weathering of silicates this would have shown up in a tendency of the strontium isotope ratios toward higher values in the soil pool and in runoff water thus its seems from the observed ratios that at least a major portion of the excess calcium export resulting from sulphur deposition is taken from the soil pool resulting in a gradual acidification of the soil

gully and tunnel erosion in the hilly loess plateau region china article i nfo article history although gully development is frequently observed to be associated with piping and tunnel erosion in many parts of the world there is a lack of detailed studies on their spatial interactions such studies not only con tribute to developing geomorphic theories on the evolution of both hillslopes and drainage networks but also are useful to design effective control measures of erosion the present study aims to examine the interactions between gully development and tunnel erosion in the hilly loess plateau region of northern china firstly gullies tunnel inlets and mass movements in the 9 1 km 2 wangjiagou watershed were mapped through ae rial photo interpretation and reconnaissance surveys secondly detailed field studies were carried out to in vestigate the interactions between gully development and tunnel formation processes in the selected gullies thirdly the physiographic variables of gullies derived from gis and field measurements were analyzed to identify differences between tunneled and untunneled gullies a total of 704 channels 967 tunnel inlets and 547 mass movements were identified in the study watershed on the basis of their location and morphology all the channels were classified into four types headwater gullies hillside gullies valleyside gullies and ephemeral river channels tunnels are associated with 79 of headwater gullies 48 of hillside gullies 3 of valleyside gullies and none of ephemeral river channels mass movements are dominated by falls in headwater gullies falls and slides in hillside gullies and soil creeps in ephemeral stream channels statistical tests indicate that there are significant differences in phys iographic variables between tunneled and untunneled gullies tunnel formation in gullies is intricately affect ed by topographic conditions land uses knickpoint distribution soil materials and mass movements published by elsevier b v

multi temporal uav data for automatic measurement of rill and interrill erosion on loess soil the fragile landscape of the north european loess belt is prone to soil erosion due to soil properties and intense land use of the fertile region exact measurement of surface changes with high temporal and spatial resolution over large areas is necessary to quantify and understand rill and interrill erosion processes high resolution aerial imagery acquired by an unmanned aerial vehicle uav is used to automatically generate precise digital surface models dsms of high spatial resolution by applying structure from motion image processing tools during an investigation period of ten months a 600 m2 field plot is observed during four field campaigns a stable reference system is established for multi temporal comparison the overall accuracy of the dsms generated from uav images is less than 1 cm verified by comparison with terrestrial laser scanner tls data furthermore a method for automatic rill extraction and rill parameter calculation is developed which enables objective rill description with cm accuracy and resolution soil surface roughness and rill development as well as volumetric quantifications are analysed for multi temporal change detection surface changes during winter season are controlled by soil consolidation crusting and sheet erosion during rainy spring season sheet erosion and rill incision occur two thunderstorms in summer season cause dominant rill erosion erosion rills are more dominantly deepening than widening from to 2 to 4 cm depth and from 17 to 23 cm width resulting in average per rill erosion values of 0 03 and 0 07 m3 respectively an orientation dependent lateral rill shift is revealed implying rill widening in eastern direction due to dominant winds from the west volumetric quantifications indicate high erosion volumes reaching up to 121 tha 1 during the summer events highest erosion volumes are due to rill erosion rather than interrill erosion copyright 2014 john wiley sons ltd

strontium isotopes as indicators of mineral weathering in catchments determination of the 87sr 86sr ratio in rain water stream water soils and rocks in two scottish catchments has provided useful information on mineral weathering over a period of 26 months the 87sr 86sr ratio in rain water had mean values of 0 7095 and 0 7098 n 12 whereas stream water had mean values of 0 7080 n 16 in catchment in devonian andesites with strontium isotope ratios of 0 7117 0 7232 in the rocks and soils and 0 7184 n 16 in catchment of cambrian metamorphic rocks with strontium isotope ratios of 0 7360 0 8218 in the rocks and soils respectively the mineralogy consists predominantly of varying proportions of quartz plagioclase feldspar and k feldspar with some mica and chlorite the fact that the 87sr 86sr ratios in the stream in the andesitic catchment are lower than for the rain water probably indicates preferential weathering of plagioclase feldspar releasing 86sr rather than k feldspar and mica which contain greater amounts of 87sr the 87sr 86sr ratio acts as a tracer for the origin of the solutes in the stream water long term monitoring of the strontium isotope ratio in stream water could be a potential means of detecting relative changes in soil weathering rates due to environmental change

soil shear strength its measurement and soil detachability abstract recent research on soil erosion mechanics has pointed out that the condition at which rill flow becomes erosive is controlled by soil surface shear strength torri et al 1987a rauws govers 1988 also splash detachment processes are strictly linked to soil shear strength as shown by nearing bradford 1985 torri et al 1987b a comparison of the proposed threshold conditions for incipient rilling immediately shows that they differ in the two quoted papers the same situation characterizes the relations proposed between splash detachment and soil shear strength those differences may depend on the different instruments used for measuring soil shear strength a geonor model g 200 laboratory cone penetration apparatus a laboratory vane tester and a pocket vane tester those instruments differ in shape pocket and laboratory vane testers or in the physics involved in their functioning vane tester and drop cone penetrometer the experimental results show that the drop cone penetrometer is characterized by a low repeatability moreover it is sensitive to small variations in soil texture the laboratory vane apparatus seems to determine a surface of shear close to that of a sphere circumscribed to the vane the pocket vane apparatus instead is characterized by a cylindrical surface of shear those results seem to explain the main differences in soil detachment in particular incipient rilling conditions are clearly reduced to a single relation between critical shear velocity and soil shear strength it can consequently be concluded that soil detachability is strictly linked to soil shear strength

snowpack tests for assessing snow slope instability information on snowpack instability is crucial for assessing avalanche risk in backcountry operations as well as for operational forecasting of the regional avalanche danger since slab avalanche release requires both fracture initiation and fracture propagation in a weak snowpack layer field observations should ideally provide reliable information on the probability or propensity of both fracture processes even simple field observations that do not require digging a snow pit can provide useful information traditional snowpack tests include the shovel shear test the shear frame test the compression test ct and the rutschblock test rb interpretation of the test results for the ct and rb has been improved by considering the appearance or type of the fracture in addition to the score more recently two tests have been developed that focus on fracture propagation rather than initiation the extended column test ect and the propagation saw test pst we compare the sensitivity specificity and unweighted average accuracy of various stability tests comparative studies indicate that the rb ect and pst have comparable accuracy for most test methods the unweighted average accuracy of a single test was 70 90 depending on the dataset test methods such as the rb ect and pst which fracture an area large enough to include fracture propagation are generally more accurate than test methods that fracture smaller areas e g the ct the threshold sum method was also less accurate even with very experienced observers for the rb ect and pst an error rate of at least about 5 10 has to be expected performing a second adjacent test on the same slope improves test reliability

experience with shear frames utilisation d une jauge a cisaillement pour des mesures in situ de la resistance au cisaillement dans l etude des stabilites des avalanches de plaques

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

strontium isotope composition as a tracer of calcium sources in two forest ecosystems in belgium the two main sources of ca in forest ecosystems are mineral weathering release and atmospheric inputs we use the 87 sr 86 sr isotopic ratio sr is used as a proxy for ca to determine the ca contribution from atmospheric deposition input in two forest ecosystems beech stands growing on soils formed from parent materials with contrasting total ca contents and isotopic ratios pleistocene loess in central belgium acid leached soil and lower devonian shales in the ardenne massif of high belgium ochreous brown earth the 87 sr 86 sr ratio and the ca and sr contents were measured in bulk precipitation in vegetation beechwood growth rings and leaves and in main soil horizons total acid extractable and labile pools the relative contributions of atmospheric input and soil mineral weathering to vegetation were calculated using mixing equations calculations based on sr isotope ratios of bulk precipitation end member 1 87 sr 86 sr close to ocean water 0 7090 0 1 m hcl extractable soil fraction end member 2 and beech wood mixing compartment indicate that about 43 central belgium and 39 ardennes of sr uptake originates from atmospheric inputs for ca the contributions of atmospheric input are 75 and 78 respectively these estimations are however very sensitive to the choice of the appropriate 87 sr 86 sr and sr ca ratios for the weathering end member the isotopic composition of the mineral source is estimated from the soil mineralogical composition and the relative weatherability of the sr bearing minerals due to soil processes mineral weathering element recycling and geomorphological events addition of allochtonous minerals to the autochtonous pool inherited from the local bedrock the distribution of minerals in both soil profiles is heterogeneous and varies from horizon to horizon which horizons are relevant and which soil pool total soil acidextractable fraction or labile pool should be selected for isotopic measurement of the weathering end member is therefore open to uncertainty the choice of the appropriate 87 sr 86 sr and sr ca ratios for the weathering end member is discussed our results emphasize the importance of the atmospheric contribution of ca for tree mineral nutrition in the studied forest stands suggesting that these ecosystems on acid soils are sensitive to chemical changes in the atmospheric environment e g acid depositions associated with decreasing input of atmospheric cations our results support therefore

runoff and interrill erosion on sandy soils under cultivation in the western paris basin mechanisms and an attempt at measurement measurements made on different scales such as rainfall simulations on 1 m2 and 20 m2 experimental plots and water sampling at the outlet of a watershed enable the analysis of the mechanisms of pluvial erosion and therefore the importance of runoffs and soil losses in the hilly and sandy parts of the western paris basin interrill erosion accounts for slow transfer of materials towards the lower part of plots and slopes the overland flow caused by restructuring of the surface tertiary and cenomanian soils erodes some 150 to 200 kg ha 1 during the month following sowing only a part of these deposits reach the river which carries away less than 50 kg ha 1 each month interrill erosion makes slopes still more uneven fills in valley bottoms and so paves the way to catastrophic erosion which scoops out rises in the ground and colluvial deposits in the lower part of slopes and valley bottoms copyright 2001 john wiley sons ltd

two paradigms of baroclinic wave life cycle behaviour two idealized baroclinic wave 6 life cycles examined here suggest a framework of opposite extremes a in which to view the behaviour of real synoptic scale disturbances in middle latitudes and b in which to interrelate the synoptic and wave theoretic viewpoints using the saturation propagation saturation sps picture of wave 6 life cycle behaviour the two life cycles dented by lc1 and lc2 are higher resolution versions of the simmons hoskins basic and anomalous cases showing strong and weak late decay of eddy kinetic energy eke they illustrate in varying degrees two extreme types of behaviour here disignated anticyclonic and cyclonic and epitomized by strongly contrasting upper air trough behaviour anticyclonic behaviour dominates the late stages of lc1 and is characterized by backward tilted thinning troughs being advected anticyclonically and equatorward as in the commoner cases of planetary scale mid stratospheric rossby wave breaking cyclonic behaviour dominates lc2 and is characterized by forward tilted broadening troughs wrapping themselves up cyclonically and poleward producing major cut off cyclones in high latitudes these morphologies are visualized by upper air maps of potential temperature on the nominal tropopause defined as a constant potential vorticity surface some atmospheric mid latitude disturbances examined here using the same visualization applied to operational analyses show the same two extreme types of trough behaviour together with intermediate cases the sps picture is re examined using eliassen palm and refractive index cross sections it is shown in particular by reference to a wave activity theorem of haynes that the late stages of lc2 can be looked upon as a remarkably clear and morphologically novel large amplitude counterpart of the nonlinear reflection scenario of rossby wave critical layer theory the late stages of lc1 by constrast look more akin to an nonlinear critical layer absorption scenario lc2 exhibits region of largely undular pv contours adjacent to a nonlinear of irreversiby deformen pv contous in the latter region pv rearrangement and hence absorption of rossby wave activity has largely ceased this accounts for the more persistent ekee in the lc2 case

strontium isotopes in trees as an indicator for calcium availability summary the increasing acidification and impoverishment of soil poses a great environmental problem today and in the future and is exemplified by the decreased availability of calcium in the soil pool unfortunately budgeting the inputs and outputs of calcium in the soil vegetation ecosystem is a very laborious task some of the fluxes are internal in the ecosystem and cannot be measured explicitely like weathering of primary minerals however since strontium and calcium exhibit similar geochemical behaviour it is possible to make an estimation of the calcium content in different media in the soil vegetation eco system using natural strontium isotopes preliminary analyses of water precipitation throughfall runoff soil water soil mineral matter and biological material trees mussel shells show that the use of the strontium isotope ratio 87 sr 86 sr is a powerful tool in estimating and understanding environmental changes

postlandfall tropical cyclone reintensification in a weakly baroclinic environment a case study of hurricane david september 1979 abstract an analysis is conducted from a potential vorticity pv perspective of the reintensification of tropical storm david over the northeastern united states in september 1979 david a major long lived hurricane originated near the cape verde islands in late august 1979 it made final landfall in georgia on 4 september 1979 and weakened rapidly thereafter the noteworthy aspect of david was its subsequent reintensification approximately 27 h after landfall as a warm core disturbance in a weakly baroclinic environment in this regard the redevelopment of david is unlike the classical extratropical transformation of a tropical storm in a strongly baroclinic environment that has been documented in the literature the authors analysis of the evolution of the dynamical tropopause subsequent to storm landfall revealed that david reintensified in response to tropopause lifting upward displacement of the dynamic tropopause ahead of a nondeepening and otherwise very weak upper tropospheric disturbance

tropical transition of hurricane chris 2012 over the north atlantic ocean a multiscale investigation of predictability abstracttropical cyclones that evolve from a nontropical origin and undergo tropical transition tt play a prominent role in cyclogenesis in the north atlantic ocean they pose a special challenge

rainwash experiments on the erodibility of loose sediments laboratory experiments using simulated rainfall splash boards and trays were conducted in order to obtain information on the erodibility of loose sediments as a time dependent phenomenon in all ten different sediments ranging from silt d50 24 m to coarse sand d50 593 m were studied the effect of three different initial states of the sediments namely the air dry state t1 the field capacity state t2 and the desiccated state t3 on the erodibility was also assessed variations in detachability during a rain erosion experiment can be explained by change in water content including liquefaction and the development of a water layer on the surface cohesion and granulometric composition of the top layer the coarsest sandy sediments almost always yielded the highest detachability when starting from an initial field capacity state t2 for the finer sediments the highest detachability was found for the homogeneous and not yet compacted initial air dry state t1 the effect of the initial desiccated state t3 on the detachability of the finer sediments was also a function of the rainfall duration the relationship between detachability and median grain size of the sediments was very similar to the relation between grain size and the susceptibility to runoff and wind erosion established by other investigators the highest detachability was found for a fine very well sorted sand with a median grain size of 96 m

a fracture arrest model for unconfined dry slab avalanches a simplified model of an unconfined dry snow slab is used to derive expressions for the rate at which elastic strain energy is released and for the fracture resistance during the propagation of the rapid brittle fractures that result in slab avalanches a relatively constant energy release rate is derived based on arguments that associate most of the released energy with the crown fracture in contrast advancing basal and crown fractures result in increasing fracture resistance by assuming fracture propagation will stop when the strain energy release rate is just greater than the fracture resistance the width of a slab avalanche is found to be proportional to an arrest parameter this parameter includes the slab thickness slab tensile strength and basal shear strength each of which can be measured prior to avalanching it is argued that compared to the three variables which can be measured the remaining variables have limited influence on the width of unconfined slab avalanches these less influen

evaluating the use of strontium isotopes in tree rings to record the isotopic signal of dust deposited on the wasatch mountains dust cycling from the great basin to the rocky mountains is an important component of ecological and hydrological processes we investigated the use of strontium sr concentrations and isotope ratios 87 sr 86 sr in tree rings as a proxy for dust deposition we report sr concentrations and isotope ratios 87 sr 86 sr from atmospherically deposited dust soil bedrock and tree rings from the wasatch mountains to investigate provenance of dust landing on the wasatch mountains and to determine if a dust sr record is preserved in tree rings trees obtained a majority of their sr from dust making them a useful record of dust source and deposition dust contributions of sr to soils were more than 94 over quartzite 63 over granodiorite and 50 over limestone dust contributions of sr to trees were more than 85 in trees growing over quartzite 55 over granodiorite and between 0 and 92 over limestone these findings demonstrate that a dust signal was preserved in some tree rings and reflects how sr from dust and bedrock mixes within the soil trees growing over quartzite were most sensitive to dust changes in sr isotope ratios for a tree growing over quartzite were interpreted as changes in dust source over time this work has laid the foundation for using tree rings as a proxy for dust deposition over time

absence of saharan dust influence on the strontium isotope ratios on modern trees from the bahamas and turks and caicos islands we report on strontium 87 sr 86 sr isotope results from 91 modern trees growing on the bahamas and turks and caicos islands the average 87 sr 86 sr ratio of 0 709169 0 000010 is consistent with the late quaternary limestone of the islands and with the modern ocean value the absence of any detectable influence of 87 sr enriched saharan dust is notable given the known contribution of this material to both past and recent soils of the caribbean our results indicate that the impact of saharan dust to the modern biosphere of the bahamian archipelago is at least an order of magnitude less than modeled in currently available strontium isoscapes for the circum caribbean we suggest that the bioavailability of sr in saharan dust may be considerably less than previously thought nevertheless further work could usefully be carried out in the bahamian archipelago on plants with different rooting depths growing on different soil types and on limestone of different ages our results have particular relevance for the refinement of existing strontium isoscapes and the archaeological provenience of artifacts animals and people in the circum caribbean

the effect of ponding depth on infiltration in a crusted surface depression over the past few decades the influence of surface sealing on infiltration has been the subject of numerous publications however very few of these experiments have considered the effect of spatial variability in seal hydraulic characteristics on infiltration field and laboratory observations have demonstrated that seal characteristics vary considerably within a range of a few cm and the changes are often related to microtopography the objective of this experiment was to investigate the influence on infiltration of a seal with varying hydraulic properties in a surface depression two soils of different aggregate stability were used in the experiment blosseville silt loam and villamblain silty clay loam soil columns 23 cm diameter by 30 cm length were packed with aggregates of 2 0 cm and a 6 cm depression was formed in the soil surface a sedimentary crust was formed in the centre of the depression and the sample was rained upon for 60 min at a rainfall intensity of 35 mm h 1 subsequently water outflow at the base of the column and pressure heads in the column were measured during two ponding periods corresponding to depths of 0 5 and 4 0 cm water outflow rates increased with ponding depth substantially more than could be attributed to the increases in ponding pressure head and submerged area for both soils the experiment demonstrated that where seal hydraulic conductivity varies with microtopography a significant increase in infiltration rate occurs as areas of greater hydraulic conductivity are submerged the increases in ponded pressure head and submerged area are negligible compared to the influence of spatial variability in seal hydraulic conductivity

the importance of sea spray to the cation budget of a coastal hawaiian soil a strontium isotope approach soil nutrients such as ca mg and k are traditionally thought to be derived primarily from rock weathering here we show that sea spray is a significant source of nutrient elements to modern and buried soils developed on 30 000 year old pahala ash deposits 50 m from the coast at south point hawaii the soil profiles evolved in a semi arid climate and have always been above sea level and the water table rhizoliths fossilized root traces and horizontal laminated carbonate sheets found in buried soils are composed of high mg calcite up to 14 mol mgco3 differences in strontium isotopic composition between marine aerosols 87sr 86sr 0 7092 and tephra parent material 0 7035 allow quantification of cation sources to the labile soil reservoir and to pedogenic carbonate mixing equations indicate that 50 80 of labile soil sr and approximately half of carbonate sr was derived from marine sources using the sr isotopic signatures and sr ca ratios of seawater and tephra as end members we determined that up to 2 3 of the ca in the labile reservoir and up to 1 3 of ca in the carbonates has a marine origin carbonate 87sr 86sr ratios are fairly constant with depth but labile 87sr 86sr ratios indicate decreasing sea spray aerosol influence with depth this trend could be due either to sequestering of aerosol derived sr in the upper part of the profile or to lower aerosol input in the past due to lower sea level the unusual occurrence of high mg pedogenic calcite probably results from high labile mg ca ratios during earlier stages of weathering coupled with rapid calcite precipitation during soil pore water evaporation

atlantic subtropical storms part i diagnostic criteria and composite analysis abstract subtropical cyclones st have only recently gained attention as damaging weather systems a set of criteria for identifying and classifying these systems is introduced here and employed to identify 18 st cases forming in the 1999 2004 hurricane seasons to be classified as an st these systems must have near surface gale force winds and show hybrid structure for more than one diurnal cycle the 18 st cases are partitioned into four classes based upon their genesis environments genesis over waters with sst in excess of 25 c is observed in almost 80 of warm season cases in contrast with only 55 in an st climatology presented in a companion study the low shear magnitude constraint recognized for tropical cyclogenesis is less apparent for st formation with over 50 forming in the two partitions characterized by shear in excess of 10 m s 1 this relatively high shear environment corresponds to equatorward intrusion of upper troughs over the relatively warm sst present in the mid late hurricane s

on the fracture toughness of snow the release of a dry snow slab avalanche involves brittle fracture it is therefore essentially a non linear fracture mechanics problem traditional snow stability evaluation has mainly focused on snow strength measurements fracture toughness describes how well a material can withstand failure the fracture toughness of snow is therefore a key parameter to assess fracture propagation propensity and hence snow slope stability fracture toughness in tension kic and shear kiic was determined with notched cantilever beam experiments in a cold laboratory measurements were performed at different temperatures and with different snow types of density 100 300 kg m 3 corresponding to typical dry snow slab properties the fracture toughness in tensionkic was found to be larger by about a factor of 1 4 than in shear kiic typical values of the fracture toughness were 500 1000 pa m 1 2 for the snow types tested this suggests that snow is one of the most brittle materials known to man a power law relation of toughness kic on relative density was found with an exponent of about 2 the fracture toughness in tensionkic decreased with increasing temperature following an arrhenius relation below about 8 c with an apparent activation energy of about 0 16 ev above 6 c the fracture toughness increased with increasing temperature towards the melting point i e the ar rhenius relation broke down the key property in dry snow slab avalanche release the critical crack size under shear at failure was estimated to be about 1m

pedosedimentary reconstruction of a thick loess paleosol sequence near lanzhou in north central china abstract a 38 m well section near lanzhou at the semiarid western margin of the loess plateau china contained a continuous high resolution loess paleosol sequence spanning the last 130 000 yr depth functions of micromorphological features magnetic susceptibility calcium carbonate organic carbon and median grain size provide the basis for pedosedimentary and associated paleoenvironmental reconstructions of three paleosol complexes s1 sm and s0 each pedosedimentary stage reflects the interaction of changing intensities of controlling monsoonal forces three periods of reduced dust inputs and enhanced pedogenic activity notably bioturbation and weak leaching can be identified from within the s1 pedocomplex these soil forming intervals were separated by phases of varying land surface instability characterized by arid dust deposition semiarid accretionary pedogenesis water reworking and crust formation or even freeze thaw modification the sm pedocomplex represents an interval of relatively rapid dust accumulation with only minimal syndepositional modification and minor pedogenic alteration at ephemeral land surfaces the s0 pedocomplex is clearly more pedogenically developed although erosion reworking and mixing by water have partly homogenized the property depth functions

surface seal development under simulated rainfall on an actively eroding surface surface seals developed under controlled conditions were examined micromorphologically to obtain detailed information on the causal processes five tests were carried out using a crusting prone binary soil in a 5 m long laboratory flume at an average slope of 5 under simulated rainfall of 32 mm h 1 for 1 hour three types of surface seal were identified in thin section disruptional seals were 0 3 0 8 mm thick surface layers formed on interrills by raindrop impact due to i rapid destruction of surface aggregates by direct drop impact ii rearrangement of disrupted fragments and textural separates by splash transport and iii compaction and flattening of surface material by continued drop impact sedimentational seals developed under rill and interrill flow with their structure being dynamically dependent upon local flow conditions they were typically 1 mm often with a complex structure of 2 or more sedimentational layers afterflow seals were extremely thin 50 m skin features with strong continuous orientation of clay particles formed by fine particle deposition after rainfall cessation and not by raindrop impact mechanisms as sometimes thought

surface sealing as influenced by slope angle and position of simulated stones in the top layer of loose sediments the influence of five different slope angles and two different positions of simulated stones in the top layer of a sandy and a silty sediment on surface sealing intensity is examined in the laboratory sealing intensity is assessed by studying changes of percolation rate through a sediment layer with simulated rainfall duration and by measuring cohesion of the 5 mm thick upper sediment layer a measure of seal strength by means of a torvane slope has a negative influence on sealing intensity for a constant per cent of simulated stone cover sealing intensity is lowest in the case of stones placed on the sediment surface compared to the case of stones pushed into the surface layer explanations for these findings are given and some implications are further discussed

strontium isotope constraint on the provenance of basic cations in soil water and stream water in the kawakami volcanic watershed central japan positive correlations among the concentrations of sr ca and mg in soil water and stream water in a forested volcanic watershed at kawakami central japan indicate that the sr isotope can be used as a tool to elucidate the source and transport of the essential terrestrial ecosystem nutrients ca and mg the 87sr 86sr ratio in surface soil water varied widely along a 74 m slope it was almost identical to the 87sr 86sr ratio of exchangeable soil and existing plants with different rooting zones japanese oak and bamboo grass but differed significantly from that of soil minerals in contrast the 87sr 86sr ratios of stream water at baseflow periods were uniform regardless of location and time and were indistinguishable from those of the weathered andesite bedrock the sr isotopic and elemental data indicate that sr ca and possibly other cations e g k mg in the plant cycle efficiently with exchangeable soil through soil water and without a large supply of cations from secondary soil minerals while cations in stream water are controlled mainly by exchange reactions with bedrock derived secondary minerals occurring in the lower soil horizon to water saturated zones it is calculated that about 10 of sr and mg and 20 of ca in stream water are derived from wet precipitation while the contribution of atmospherically derived sr and ca in the exchangeable soil pool increases from 22 to 72 and from 42 to 87 respectively with increasing distance from the valley this increase of sr and ca in the exchangeable soil pool coincides with rock derived low ca materials dominating in the surface soil of the upper elevation in the slope copyright 2001 john wiley sons ltd

response of loess materials to simulated translocation by water micromorphological observations structural differences between loess material deposits produced by splash flow without splash and by rainwash i e combined splash and flow respectively were reported earlier mucher and de ploey 1977 deposits from splash alone proved to be non layered and had incurred almost no additional particle sorting deposits from flow without splash were well layered while individual laminae displayed excellent sorting rainwash produced poorly layered deposits with poorly sorted individual laminae only horizontal and subhorizontal bedding and no cross bedding were observed similar features appeared in samples from naturally layered loess deposits collected from excavations the present paper focuses on the granulometric character of the artificially created layers experiments normally involved the combined use of an erosion and a sedimentation flume slope angles of the flumes varied mainly form 0 25 to 4 degrees precipitation intensities varied from 7 to 120 mm per hour unit discharges ranged from 0 2 to 9 2 cm3 cm s flow was laminar or smooth turbulent either subcritical or supercritical froude numbers between 0 5 and 3 8 raindrop impact had little influence on the flow velocity and thickness of the surficial water film but it significantly increased transportation capacity and flow competence savat 1976 1977 undisturbed samples were collected during the experiments and impregnated with unsaturated polyester resin thin sections of 20 m thickness were studied under a polarizing microscope comparative observations were made on naturally layered loess materials during rainwash clay size particles are removed and exported whereas laminae with particles from 10 to 50 microns are more frequently produced than those with particles from 10 to 30 microns flow without splash produced relatively more laminae with grains smaller than 30 microns diameter striking in all samples is the absence of laminae composed of 30 50 m grains aggregates were only deposited by smooth turbulent flow either disturbed or undisturbed by raindrop impact in view of the experimental results the naturally formed loess deposits may be interpreted as follows the bulk of the loess from the excavation near tongrinne belgium was reworked under influence of turbulent rainwash only one sample contained laminae consisting of clay particles smaller than 10 m and of particles from 10 30 m respectively suggesting deposition from flow without splash this was taken from a gully infilling a gully fill from the excavation heverlee near leuven belgium is characterized by poorly sorted laminae dominated by the coarser silt fractions this suggests infilling under influence of turbulent rainwash

the implications of spatial variability in surface seal hydraulic resistance for infiltration in a mound and depression microtopography abstract soil surface crusting has a major impact on water infiltration and erosion in many soils considerable progress has been made in describing crusting processes and in modelling the impact of crusting on infiltration most studies however have neglected the high spatial variability in crust characteristics observed in the field the objective of this experiment was to determine the influence of runoff depth on infiltration rate in the presence of a surface seal varying in hydraulic characteristics with microtopography the blosseville silt loam has a low aggregate stability and forms crusts readily the villamblain silty clay loam has a greater aggregate stability due to its greater clay and organic matter contents and it is more resistant to aggregate breakdown processes under rainfall samples of the soils were sieved to retain aggregates less than 2 0 cm and packed in 50 50 15 cm soil trays the trays were surrounded by a 10 cm soil border to compensate for splash loss after molding the surface into a mound and depression microtopography the samples were subjected to simulated rainfall at an intensity of 22 8 mm h 1 hourly measurements of surface roughness showed that the original roughness was smoothed out due to the infilling of depressions by sediments detached from the mounds for the final hour runon was added to the top of the soil tray to increase the runoff rate and depth for both soils infiltration rate increased more than could be attributed to the increased ponding pressure head the change in infiltration rate was particularly great for villamblain the measurements of hydraulic resistance showed that structural crusts had a lower hydraulic resistance than sedimentary crusts they also showed that the crusts formed on villamblain were of a lower hydraulic resistance than those of blosseville it appears that small changes in runoff depth can significantly increase infiltration rate when structural crusts of lower hydraulic resistance are inundated the effect was less important in blosseville which formed seals of relatively high hydraulic resistance everywhere the results provide a suitable explanation for field observations of increasing infiltration rate with either increasing rainfall intensity or runoff rate the results also have implications for the relationships between surface roughness surface water storage and infiltration

the geographic distribution of sr isotopes from surface waters and soil extracts over the island of bornholm denmark a base for provenance studies in archaeology and agriculture abstract in this paper we report the sr isotope signatures and sr al and na concentrations of 30 surface waters lakes ponds and rivers creeks and 19 soil sample extracts from the island of bornholm denmark and present a categorized 87 sr 86 sr value distribution map that may serve as a base for provenance studies including archaeological migration and authenticity proof for particular food products the sr isotopic compositions of surface waters range from 87 sr 86 sr 0 7097 0 7281 average 0 7175 0 0049 1 whereas 0 1 m hno 3 0 05 m hno 3 and 0 01 m cacl 2 soil extracts range from 87 sr 86 sr 0 7095 0 7197 and define somewhat lower but statistically indistinguishable averages of 0 7125 0 003 1s these compositions are lower than the values expected from the precambrian granitoid basement 87 sr 86 sr 0 758 0 944 and from the overlying mainly clastic paleozoic sediments combined sr isotope composition vs sr na and al concentration relationships of soil extracts imply that lowering of the isotopic composition of leachable sr on bornholm results as a consequence of significant admixture to this fraction of sr deposited as marine salts aerosols and that rainwater only has a minor influence on the sr budget of the surface waters positively correlated al na and 1 sr vs 87 sr 86 sr relationships in soil extracts and surface waters indicate that the surface run off on bornholm is characterized by two predominant sources namely marine aerosols sea salts with high sr and low 87 sr 86 sr values and a source with lower sr delivering radiogenic sr to the surface waters which we equate with sr leached from the products of mineral weathering soils a feasibility study for using sr isotopic compositions of surface waters and soil extracts as a proxy for bioavailable sr signatures was performed with a few samples collected in the vicinity of the eleventh century ad ndr grodbygard cemetery site in sw bornholm from where sr isotope compositions of modern fauna samples and tooth enamel of humans buried in the cemetery have been reported waters and soil extracts studied herein from around this site range from 87 sr 86 sr 0 7104 0 7166 and correspond to sr compositions extracted from snail shells in this area which span a range of 87 sr 86 sr 0 7095 0 7160 some human tooth enamel is characterized by more radiogenic values 87 sr 86 sr up to 0 718 which points to a possible provenance of these humans from the granite gneiss terrain in the north of the island and or to immigration of these humans in their childhood from other places for example from mainland sweden to bornholm if the total compositional range of 87 sr 86 sr 0 709 0 718 n 44 recorded in human enamel from the ndr grodbygard site is considered representative for the variation of bioavailable sr on bornholm then our soil leachate and surface water data entirely covers this range we therefore propose that the combination of sr isotope analyses of surface waters and soil leachates are an easy fast and relatively cost efficient way to characterize a local bioavailable 87 sr 86 sr signature and consequently propose that the overall average of 87 sr 86 sr 0 7153 0 0048 1 n 50 can be taken as a band for bioavailable sr fractions suitable to discriminate between local and non local signatures in provenance studies in the field of archaeology and for food and plant authenticity control in agricultural applications

radiogenic and stable strontium isotopes in provenance studies a review and first results on archaeological wood from shipwrecks abstract different approaches are used to study wood provenance but most of them are based on tracers in wood that are generally controlled by climatic factors the strontium isotopic ratio 87 sr 86 sr in trees and soils is related to the signature of the local bedrock despite being used in diverse archaeological studies sr isotopes have rarely been used to trace the provenance of archaeological wood and especially wood from shipwrecks in addition recent analytical advances have allowed the detection of mass dependent fractionation of sr isotopes during biogeochemical processes as reflected in the variation of 88 86 sr values between different environmental materials the 88 86 sr values could be used in conjunction with the 87 sr 86 sr isotope ratio to improve constraints on the sources of sr in the archaeological materials being studied this paper discusses the potential and limitations of using both of these sr isotope ratios to trace the provenance of wood from shipwrecks we review the 87 sr 86 sr and 88 86 sr variations in rocks waters soils plants and other living organisms and discuss how to determine the local sr isotopic signature of potential sites we also compile a list of known wood post mortem modifications in seawater possible implications in terms of the modification of the original sr isotope ratios of wood during storage in seawater are illustrated through preliminary observations this paper points out some limitations and perspectives for using sr isotopes in provenancing wood from shipwrecks and suggests future research to test and apply this approach for tracing the origin of archaeological wood

nature formation and effects of soil crusts formed by water drop impact abstract research was conducted to investigate 1 the structure formation and nature of soil crusts which develop as a result of raindrop impact under controlled conditions of simulated rain and 2 the crust effect on infiltration rates scanning electron microscope sem observations performed on sandy sandy loam and clayey soil samples show the crust to be composed of two layers 1 a skin 0 1 mm thick and 2 a layer 2 3 mm thick with a higher bulk density in which aggregates have been destroyed a washing in zone described by earlier investigators could not be detected the soil beneath the crust maintains its original structure and particle orientation the chemical composition of the rain water was found to have a significant but not very large effect on the infiltration rate vs cumulative rain curve of the clayey soil material only final infiltration rate was about 20 lower when distilled water was applied compared to tap water electrical conductivity 0 6 mmho cm 1 an increase of the bulk density from 1 35 1 48 g cm 3 in undisturbed soil to 1 74 1 88 g cm 3 in crusts was found the amount of eroded material increased gradually with increase of runoff and decrease of infiltration at steady state the erosion rates were 0 45 1 25 and 0 76 g m 2 min 1 in the sandy sandy loam and clayey soil specimens respectively percentages of clay and silt in the eroded material were higher than in the bulk samples three stages to describe the changes in nature and effects of crusts during their formation are suggested 1 the rate of infiltration decreases to a point at which runoff beings 2 the initiation of runoff until infiltration and runoff rates become stabilized and 3 infiltration and runoff maintain steady rates

bulk density of surface crusts depth functions and relationships to texture abstract a range of soils from pleistocene deposits with sandy to sandy loam textures and a group of loess derived soils with predominantly silty textures were subjected to 60 mm of simulated rainfall to form structural seals after drying samples of the surface crusts were collected to determine their bulk densities at a high resolution of depth 0 15 mm using an immersion method the bulk density data obtained for each soil sample were plotted as a function of depth beneath the soil surface two models were fitted to these plots the first was an exponential decay type function as proposed by mualem et al 1990 and the second was a sigmoidal type of function assuming that maximum compaction had already progressed to some depth below the soil crust surface all of the results indicated a gradual decrease in the bulk density with depth below the surface until convergence with the initial bulk density of the undisturbed soil was attained the maximum bulk densities recorded for crust segments representing the uppermost 2 mm of the crusts ranged from 1 713 to 1 91 g cm 3 for soils with silty sand loamy sand or sandy loam textures crusts of loess derived soils showed lower values ranging from 1 44 to 1 65 g cm 3 the maximum surface bulk density was shown to be highly significantly correlated with the log of geometric mean diameter of the primary grain size distribution in most cases both models showed good to very good fits to the measured data the exponential decay function appeared to better represent the initial stages of surface compaction and the sigmoidal function the later stages of structural crust formation

quantitative strontium isotope models for weathering pedogenesis and biogeochemical cycling abstract isotopes of strontium sr are a useful tracer for weathering atmospheric fluxes cation biocycling and pedogenesis we present basic models for application of strontium isotopes to the soil vegetation atmosphere system the mathematical formulations fall into the general categories of 1 steady state models in which isotopic ratios remain constant over the time scale of interest and 2 time dependent models in which isotope ratios change through time in the steady state models fluxes of sr and other elements to the system are constant steady state models can be used to infer short term weathering rates from river and stream isotope compositions to determine fluxes to a single or multiple layer soil exchange solution system and to quantify nutrient fluxes to vegetation time dependent models involve a change in isotopic ratio from some initial value to a new value over the time period of interest in some cases the change may represent a shift from one steady state situation to a new one after a shift in one or more of the fluxes feeding the system examples of applications of time dependent models include identifying the dominant cation sources to an evolving soil exchange solution system and calculating weathering rates by measuring the isotopic compositions of primary soil minerals we use time dependent models to explain differences in the isotopic ratios of labile and carbonate sr from arid sites in hawaii with a basalt parent material isotopic signature and new mexico with an atmospheric isotopic signature these models suggest that the difference is due to a combination of low atmospheric strontium fluxes and high weathering rates in the hawaiian profile compared to the new mexico calcrete profile

diagnosis of the source of gfs medium range track errors in hurricane sandy 2012 abstractmedium range forecasts of hurricane sandy s track were characterized by widely diverging solutions with some suggesting that sandy would make landfall over the mid atlantic region of the united states while others forecast the storm to move due east to the north of bermuda here dynamical processes responsible for the eastward tracking forecasts are diagnosed using an 80 member ensemble of experimental global forecast system gfs forecasts initialized five days prior to landfall comparing the ensemble members with tracks to the east against those with tracks to the west indicates that the eastern members were characterized by a lower amplitude upper tropospheric anticyclone on the poleward side of sandy during the first 24 h of the forecast which in turn was associated with a westerly perturbation steering wind the amplification of this ridge in each set of members was modulated by differences in the advection of potential vorticity pv by the irrotational wind associated with sandy s seco

micromorphological study of slumping in a hardsetting seedbed under various wetting conditions slumping of hardsetting seedbeds upon wetting has not been extensively studied despite the likelihood that it determines the physical properties after drying slumping results from processes similar to those involved in crusting except that overburden pressure can dominate rather than rainfall kinetic energy only a few studies have dealt with the morphological description of slumping to simulate different climatic and management conditions repacked seedbeds of a hardsetting sandy loam soil were subjected to a range of wetting conditions e g capillary rise immersion and rainfall simulation slumping processes were characterized using qualitative and quantitative micromorphological observations of polished blocks and thin sections from resin impregnated samples a morphogenetical framework was proposed to help description of the complex associations of processes which can lead to structural collapse crusting and slumping on wetting three main stages were considered i e aggregate disruption or abrasion relocation of the released material and compaction in the hardsetting material studied here structural collapse under slow wetting occurred at the bottom of cores due to aggregate coalescence under overburden pressure coalescence required aggregate cohesion being reduced by microcracking therefore it differed from the coalescence previously described in unstable silty loam soils where microcracking was not necessary for aggregates to coalesce macroporosity decreased most strongly under fast wetting due to physical dispersion and aggregate breakdown under simulated rainfall compaction by raindrops could not be distinguish from aggregate breakdown the role of overburden pressure and of rainfall kinetic energy remains to be stated new data are required including measurement of total porosity in the initial wet and dry states

soils of the darror valley northeast somalia summary the darror valley is located in the arid part of northeast somalia its soils are highly influenced by their parent material which consists mainly of evaporites limestone conglomerate and alluvial deposits the most common soils in this area are calcic solonchaks gypsic solonchaks gypsic calcisols haplic calcisols eutric leptosols and calcic vertisols all soils have a neutral to weakly alkaline ph value and are very rich in carbonates often rich in gypsum often saline and their moisture content at the end of the dry season is much lower than the moisture content of the permanent wilting point most of these soils have a colour of 7 5 yr which becomes more red in the subsoil analytical data indicate that the topsoils are usually enriched in carbonate whereas the subsoils are enriched in gypsum and or salt the soil salinization is mainly due to tertiary evaporite formations

sr isotopic evidence for ion exchange buffering in tropical laterites from the parana brazil sr isotopes have been measured in laterite sequences and in associated waters from the region of ribeirao preto parana basin brasil in order to characterize the water rock interactions corresponding to the successive stages of weathering of these continental flood basalts we analyzed detailed sections of concentric rims of alteration in ball shaped spheroids developed around cores of fresh basalts waters were also analyzed on the different types of facies in this region unaltered basalts thick weathered profiles of lateritic material and surrounding sandstones the results show that a major part of the initial sr is removed from the basalt during the earliest stages of weathering within the narrow grey rims surrounding the unweathered core radiogenic sr is also leached from hydrothermal minerals located in basalt fractures or disseminated in the basalt groundmass at this early stage very high water rock ratios of at least 100 000 are calculated for this process from the sr 87 sr 86 in the related waters a general trend of increasing sr 87 sr 86 ratios is observed in the increasingly weathered facies inner yellow cortexes red kaolinitic soils and matrices and in their related waters the very high sr 87 sr 86 ratios of the red kaolinitic horizons probably result from isotopic exchange with radiogenic rainwaters or sandstone waters and also from the presence of residual or neoformed radiogenic minerals budget calculations as well as experimental leaching of kaolinite samples suggest that significant amounts of radiogenic sr can be leached from these facies during weathering thus the kaolinitic facies of tropical laterite profiles are able first to trap strontium from surficial waters then to provide radiogenic sr to the waters that weather the fresh basalts at the weathering front therefore the thick weathered horizons must be considered as a natural cation exchange layer that play an active role in the weathering process

degradation of soil structure by welding a micromorphological study abstract in 1985 a plot study was started on sloping cultivated loess soils in south limbourg the netherlands to evaluate the effects of various cropping systems of fodder maize on runoff soil loss and crop yield under natural rainfall to monitor degradation of soil structure including crust formation undisturbed vertical samples 15 7 cm for soil micromorphological analysis were taken of the top 7 cm of soil at ten dates chosen in relation to times of tillage and sowing crop stage harvest and winter frost wheel marks if present were also sampled contrary to accepted views no disintegration of structural elements by slaking or dispersion was observed freshly tilled soil exhibited a loss of its original granular structure by coalescence of the aggregates into larger units eventually leading to a structureless state of part of the top soil processes held responsible for this are mainly welding of wet aggregates and seldom fusion by silt infillings in vertical inter aggregate pores the two layer model of soil crust formation of mcintyre could not be confirmed as no important vertical translocation of fines or washed in layers were observed horizontal cracks developed in the structureless soil giving rise to a platy structure in part of the top soil transitional stages of loss of soil structure were observed characterized by the progressive reduction of compound packing voids to vughs which ultimately disappeared completely and sometimes were replaced by planar voids besides structural crusts sedimentary crusts including splash deposits were observed

land use effects on soil crusting and hydraulic response of surface crusts on a tropical alfisol soil surface crusting a common phenomenon on cultivated soils has major implications for agriculture and the environment because of its effects on soil hydrological properties erosion and crop establishment the objectives of this study were to evaluate land use controls on crust formation and the hydraulic response of soils to crust development for a patancheru series soil clayey skeletal mixed isohyperthermic udic rhodustalf in south central india soil aggregates obtained from cultivated pl and naturally vegetated fallow nv land were packed into sample trays and subjected to laboratory rain simulation to form crusts thin sections and visual observation indicated that crust development reached a more advanced stage in the pl case compared with nv following 90 min of rain at 40 80 mm h 1 intensity this was reflected in a thicker crust layer with fewer voids in the former and a less smooth surface with partially disintegrated aggregates in the latter the hydraulic response of the soil surface with the progression of crust development indicated a more permeable and less dense crust formed on nv than on pl soil the results suggested that nv soil aggregates were more stable and that crust formation is more gradual for stable aggregates compared with the less stable pl aggregates a structural crust type formed on the patancheru soil by means of parallel subprocesses involving translocation and illuviation of aggregate disruption by products and raindrop compaction and particle rearrangement copyright 1999 john wiley sons ltd

a climatology of rossby wave breaking along the subtropical tropopause ten years 1986 95 of global analyses from the european centre for medium range weather forecasts are used to investigate the temporal and spatial distributions of rossby wave breaking rwb at 350 k along the tropopause herein defined by the 61 5 potential vorticity pv unit 10 26 km 2 s21 kg21 contours though many studies acknowledge rwb as an important contributor to the complex of mixing processes in the atmosphere there exists no prior climatological study of its distribution near the tropopause as in previous studies rwb is identified in the global analyses by southward directed pv gradients at 350 k rwb along the tropopause occurs preferentially during summer over the midoceans in relative proximity to the planetary scale high pressure systems in the subtropics isentropic trajectories at 350 k show that outflow from the tops of these subtropical highs directly participates in rwb over the adjacent downstream oceanic regions two regions are highlighted in this study the north pacific during boreal summer and the south atlantic during austral summer synoptic maps of breaking rossby waves in these regions are provided to reveal the acute tropopause folding in the meridional plane which characteristically accompanies rwb the rich interaction between the tropical flow and the extratropical westerly current exhibited by these cases suggests that the subtropical highs serve as important agents in the coupling between the tropical troposphere and the extratropical stratosphere as expected from theoretical considerations the locations where rwb occurs most frequently known as surf zones are shown to coexist with regionally weak time mean wind speeds and horizontal gradients of pv at 350 k

synoptic and frontal scale influences on tropical transition events in the atlantic basin part i a six case survey abstract the process by which a baroclinic vertically sheared extratropical cyclone is transformed into a warm core vertically stacked tropical cyclone is known as tropical transition six recent tropical transitions of strong extratropical precursors in the subtropical north atlantic are compared to better understand the manner by which some of the canonical structures and dynamical processes of extratropical cyclones serve to precondition the cyclone for transition all six transitions resulted from the interaction between a surface baroclinic zone and an upper level trough during the extratropical cyclogenesis of each storm a period of intense near surface frontogenesis along a bent back warm front occurred to the northwest of each sea level pressure minimum within the resultant circulation diabatic redistribution of potential vorticity pv promoted the growth of a low level pv maximum near the western end of the warm front concurrently the upper level pv anomaly associated with each trough w

effects of crust and cracks on simulated catchment discharge and soil loss sealing crusting and cracking of crusts of the soil surface has been observed in many parts of the world in areas with sandy silty and loamy soils sealing and crust formation occurs under the influence of rain storm and drying weather with prolonged drying surface crusts might crack leading to complex situations with respect to infiltration and runoff generation cracking of crusted loamy soils appears to be a general process this study aims to measure the hydraulic properties of fully crusted and cracked crusted areas and to evaluate the effects of these measurements on catchment discharge and soil loss in a loess region of the netherlands using the lisem soil erosion model samples with minimum infiltration rates fully crusted and with maximum infiltration rates cracked crusted surfaces were taken from fields with bare soil or winter wheat and their soil hydraulic functions were measured the results of these measurements were used as input in the lisem soil erosion model simulations of discharge and soil loss were done for each of these two land uses and for two rain events additionally simulated discharge and soil loss under actual recorded land use were calculated in all cases soils with no surface cracks produced higher figures for discharge and soil loss than those where 10 of the surface crust was cracked for a good interpretation of the results for soil loss the spatial distribution of cracked crusted areas and fully crusted areas has to be investigated in detail to deal with cracked crusted and fully crusted areas in simulation modelling care has to be taken to accurately measure the soil physical functions representing the maximum and minimum infiltration rates an assignment of these functions to calculation grids has to be made as the lisem model is capable of assigning different soil physical functions to each calculation grid an improved prediction of the soil physical behaviour of the catchment can be simulated

fracture mechanical models of dry slab avalanche release experimental evidence shows that snow is a pressure sensitive dilatant strain softening material in slow constant rate shear deformation when strain softening initiates in a weak layer underneath a snow slab avalanche release is hypothesized to be possible with or without additional loading specifically two cases are discussed 1 a shear crack like disturbance can initiate after formation of a slip surface in the weak layer and traverse the layer by a self propagating progressive failure with or even without loading and 2 a self propagating shear instability can develop when a region of the weak layer is driven past peak shear strength by loading for these cases the implied fracture sequence fracture geometry time scale of release and temperature effects are discussed and shown to be consistent with the known facts of dry slab avalanche release

microgeometrical characterisation and percolation threshold evolution of a soil crust under rainfall abstract an experiment has been carried out in order to both measure the unsaturated hydraulic conductivity of a soil crust when it is developing and to characterize its macro and microstructural evolution five stages of a structural crust developing in a loamy clay soil have been identified mercury intrusion experiments and micromorphological descriptions have provided information on the structural evolution of the crust at the microscale quantitative image analysis from images of the crust microstructure has led to the definition of a particle erosion index at the microscopic scale which is the mean chord length calculated in the solid phase this index decreases from 60 to 11 m during the whole experiment the lowest value being recorded at the fourth stage specific measurements of the percolation threshold in the soil crust at different stages during its formation have given quantitative data to interpret the modifications of the unsaturated hydraulic conductivity of this crust when it develops the percolation threshold decreases from 130 m at the second stage down to 40 m at the fifth stage between the same stages the unsaturated hydraulic conductivity at 5 kpa decreases from 12 2 to 4 7 cm h both the structural information given by the chord size distribution and the functional information obtained from the percolation threshold can be related to propose a new model of soil crusting

splash detachment runoff depth and soil cohesion summary a set of laboratory experiments has been carried out in order to investigate the importance of soil cohesion and the interference due to the depth of the surface runoff on the detachment rate of soil particles and aggregates experimental data show that the soil detachment rate decreases as the runoff depth increases this indicates that the detachment power of the raindrops is partially dispersed by the water layer an inverse relationship between soil detachment and soil cohesion has been confirmed nevertheless the grain size distribution must also be used in order to define soil detachability

the geographic distribution of strontium isotopes in danish surface waters a base for provenance studies in archaeology hydrology and agriculture abstract in this paper sr isotope signatures are reported for 192 surface water lakes ponds and rivers creeks samples from within denmark and an isotope distribution map is presented that may serve as a base for provenance applications including archaeological migration studies ground water surface water seawater interaction contamination monitoring and potentially for agricultural applications including cases of authenticity proof for particular food products the sr isotopic compositions of surface waters range from 87sr 86sr 0 7078 to 0 7125 average 0 7096 0 0016 2 this average value lies above the range of 87sr 86sr values between 0 7078 and 0 7082 expected from late cretaceous to early tertiary oligocene limestones which form the dominant bedrock type in a nw se trending belt in denmark the elevated 87sr 86sr signatures 0 7095 are explained by additions to the surface waters of radiogenic sr predominantly derived from the near surface weathering and wash out of quarternary glaciogenic tills and soils deposited and formed during and after the last two ice age stages saale and weichsel the sr isotopic compositions and concentrations of the surface waters can therefore best be modeled by a two component mixing involving carbonaceous bedrock and glaciogenic cover sediments as the two predominant sr sources a feasibility study for using sr isotopic compositions of surface waters as a proxy for bio available sr signatures was conducted in a representative test area on zealand land of legends lejre where there is no use and application of commercial fertilizers it is demonstrated that the sr isotopic signatures of lake waters from within this area are slightly higher but statistically still indistinguishable from the average value defined by snail shells and soil leachates considered to characterize the true bio available sr in combination with results from other studies this is interpreted to reflect the wash out of sr with a higher 87sr 86sr signature released by weathering in the topsoils into the saturated water tables a component which is consequently not readily transferred into the shallow rooting plants and into small herbivores feeding on them since drinking water is a likely important source of sr uptake of humans and larger animals the contention is that a surface water isotopic composition can potentially characterize the bio available component relevant for human and carnivorous large animals spline functions and ordinary linear kriging were used for modeling the geographic distribution of bio available sr isotopes over territorial denmark as expected based on the two source mixing scenario the water 87sr 86sr ratio contour maps with some notable exceptions neither mirror the pre quarternary bedrock geology nor a pleistocene soil type distribution map of denmark as a conservative suggestion the use of the average 87sr 86sr ratio of 0 7096 0 0015 2 is recommended as an average for bio available sr from within denmark bornholm excluded for human and larger animals and as a confidence band for distinguishing local from non local signatures in archaeological provenance studies the study also reveals that the average 87sr 86sr ratio of 0 7088 defined from soil extracts and small herbivores lies approximately 0 15 lower than that defined by the surface waters the authors recommend using this lower value as a local non local discriminator for food and plant authenticity control in agricultural applications

physical characterization spectral response and remotely sensed mapping of mediterranean soil surface crusts abstract soil surface crusting and sealing are frequent but unfavorable processes in mediterranean areas soil crust and seals form on bare soil subject to high intensity rainfall resulting in a hard impenetrable layer that impedes infiltration and hampers the germination and establishment of plants the adverse consequences of overland flow and reduced fertility can lead to erosion and ongoing degradation therefore information on the distribution of surface crusts and their physical properties is essential to combat the undesired effects of crust formation in e g soil erosion and soil compaction we studied the occurrence of crusts in a study area in mediterranean southern france our objectives were to compare the physical and hydrological properties of the crusts and underlying soil to identify the spectral characteristics 400 to 2500 nm of the crusted and non crusted soil surfaces using high resolution field spectra and to investigate the potential of mapping crust occurrence using airborne hyperspectral hymap images the differences in some physical properties between crusted and non crusted surfaces are significant while others are only marginal crusting markedly reduces the infiltration capacity and crust strength varies between the different soil types spectral differences are small mainly in albedo values overall reflectance and in absorption band depth and shape albedo differences range from 8 to 40 differences in absorption band features in the spectra of crusts and non crusted surfaces are small sixty percent of the crusted soil surfaces showed stronger absorption features in the clay mineral absorption bands at 2200 nm than non crusted soils increased absorption is due to a relative enrichment in fines spectral feature fitting and linear spectral unmixing algorithms were applied to airborne hymap images to evaluate the possibilities of mapping surface crusts crusts could be mapped in fallow agricultural fields but the spectral response of natural badlands was too fragmented for crust mapping

baroclinically induced tropical cyclogenesis abstract the authors investigate the transition of numerous subtropical cyclones into late season tropical storms and hurricanes during the 2000 and 2001 atlantic tropical cyclone seasons in all transitioning cases 10 the 900 200 hpa wind shear was initially near or in excess of the upper limit of vertical shear deemed suitable for tropical cyclogenesis in many of these cases the vertical shear decreased markedly near or prior to the time of tropical cyclone formation in cases that did not become named tropical cyclones either the tropospheric vertical shear remained in excess of 15 20 m s 1 or the underlying sea surface temperature sst dropped below about 26 c prior to or during the weakening of the shear cases in which the shear remained large featured multiple short wave upper tropospheric troughs interacting with the developing lower tropospheric disturbance such that classical occlusion did not occur through detailed analysis and simulation of the development of hurricane michael in 2000

effects of rainfall and slope on runoff soil erosion and rill development an experimental study using two loess soils runoff generation and soil loss from slopes have been studied for decades but the relationships among runoff soil loss and rill development are still not well understood in this paper rainfall simulation experiments were conducted in two neighbouring plots scale 1m by 5m with four varying slopes 17 6 26 8 36 4 and 46 6 and two rainfall intensities 90 and 120mmh 1 using two loess soils data on rill development were extracted from the digital elevation models by means of photogrammetry the effects of rainfall intensity and slope gradient on runoff soil loss and rill development were different for the two soils the runoff and soil loss from the anthrosol surface were generally higher than those from the calcaric cambisol surface higher rainfall intensity produced less runoff and more sediment for almost each treatment with increasing slope gradient the values of cumulative runoff and soil loss peaked except for the treatments with 90mmh 1 rainfall on the slopes with anthrosol with rainfall duration runoff discharge decreased for anthrosol and increased for calcaric cambisol for almost all the treatments for both soils sediment concentration was very high at the onset of rainfall and decreased quickly almost all the sediment concentrations increased on the 17 6 and 26 8 slopes and peaked on the 36 4 and 46 6 slopes sediment concentrations were higher on the anthrosol slopes than on the calcaric cambisol slopes at 90mmh 1 rainfall intensity increasingly denser rills appeared on the anthrosol slope as the slope gradient increased while only steep slopes 36 4 and 46 6 developed rills for the calcaric cambisol soil the contributions of rill erosion ranged from 36 to 62 of the cumulative soil losses for anthrosol while the maximum contribution of rill erosion to the cumulative soil loss was only 37 9 for calcaric cambisol copyright c 2014 john wiley sons ltd

sources of strontium and calcium in desert soil and calcrete the carbon cycle significance of soil carbonate fluxes is subject to large uncertainties because it is not clear precisely how much calcium is derived from atmospheric sources compared with that from the chemical weathering of silicate minerals in the petrocalcic horizon calcrete of a pleistocene soil from the usda scs desert project area near las cruces nm approximately 1 5 g ca cm 3 has been added with an associated expansion of the profile of200 strontium isotope values for the labile cations and carbonate from the a b and k soil horizons have 87 sr 86 sr values that range from 0 7087 to 0 7093 similar to the values for easily soluble local dust and rain the parent material non calcareous camp rice alluvial sediment has a 87 sr 86 sr ratio of0 7165 mixing calculations indicate a minimum atmospheric contribution to soil carbonate calcium of 94 the more likely scenarios indicate at least 98 of the ca originated from atmospheric input the variations in 87 sr 86 sr ratios of soil silicate 0 7131 to 0 7173 are consistent with weathering of volcanogenic sediments and neoformation of clay minerals in the petrocalcic horizon moreover the sr isotope data suggest that 50 70 of silicate in the uppermost 25 cm of the profile could be atmosphere derived the isotopic composition of labile strontium in the a horizon and the mass distribution of silicon and calcium indicate that the uppermost portion of the profile is the present zone for the release of cations due to silicate weathering steady state models of the whole profile yield a sr weathering flux ranging from200 to 400 m gc m 2 ma 1 the results indicate that both the present day and long term contribution of calcium from silicate weathering is less than 2 of that supplied from the atmosphere and confirm that desert soil formation is not a significant sink for atmospheric carbon 1999 elsevier science b v all rights reserved

permanence of soil surface crusts on abandoned farmland in the central ebro basin spain abstract surface crusts are frequently found on fallow land in the semi arid ebro basin spain and are an important factor in land degradation soil surface sealing leads to a decrease in infiltration rates and a consequent increase in runoff thereby accelerating sheet wash and rill erosion thin sections were used to analyse the development and structures of the different crusts found across the ridge furrow field pattern rainfall simulations experiments and infiltration measurements show the runoff generation and the soil erosion rates on the crusts the spatial distribution of crusts was documented using large scale aerial photographs taken from a remote controlled hot air blimp splash and slaking cause structural crusts to form on the ridges while eroded material leads to a build up of sedimentary crusts in the furrows a platy structure as well as vesicles then develop in these crusts depending on the amount of time that has elapsed since ploughing and the frequency of wetting and drying cycles alluvial fan crusts develop on material accumulated at the end of erosion rills the increase in the runoff of up to 81 and the decrease in infiltration rate up to 4 6 mm h 1 on surface crusts were quantified

development of north atlantic tropical disturbances near upper level potential vorticity streamers abstracttropical cyclone tc development near upper level potential vorticity pv streamers in the north atlantic is studied from synoptic climatology composite and case study perspectives midlatitude anticyclonic wave breaking is instrumental in driving pv streamers into subtropical and tropical latitudes in particular near the time mean midocean trough identified previously as the tropical upper tropospheric trough twelve tcs developed within one rossby radius of pv streamers in the north atlantic from june through november 2004 08 this study uses composite analysis in the disturbance relative framework to compare the structural and thermodynamic evolution for developing and nondeveloping cases the results show that incipient tropical disturbances are embedded in an environment characterized by 850 200 hpa westerly vertical wind shear and mid and upper level quasigeostrophic ascent associated with the pv streamer with minor differences between developing and nondeveloping cases the key differ

strontium and its isotopes in canadian rivers fluxes and global implications systematic sampling of the 39 largest canadian rivers shows that the weighted average 87sr86sr ratio in the dissolved load is 0 7111 similar to previous measurements on such large rivers as the amazon and mississippi consequently we believe that the above estimate is likely representative of the global average this imposes a limit of 6 5 1011g yr 1 on the amount of sr exchanged with basalts in hydrothermal cells on mid oceanic ridges evaluation of geological information suggests that sr from silicate sources is of considerable importance for all but the largest canadian rivers the latter have chemical and isotopic composition consistent with 4 1 carbonate vs silicate derivation of sr but such interpretation is not unique in terms of their water discharge the 39 canadian rivers studied account for 4 2 of the world total and their weighted average concentrations for other dissolved solutes are tds 176 ppm ca 18 ppm cl 6 8 ppm and sr 84 ppb

changing sources of strontium to soils and ecosystems across the hawaiian islands abstract strontium isotope ratios assist ecosystem scientists in constraining the sources of alkaline earth elements but their interpretation can be difficult because of complexities in mineral weathering and in the geographical and environmental controls on elemental additions and losses hawaii is a natural laboratory where a number of important biogeochemical variables have either limited ranges or vary in systematic ways providing a unique opportunity to understand the impact of time climate and atmospheric inputs on the evolution of base cation sources to ecosystems there are three major sources of strontium sr to these ecosystems each with distinct isotopic compositions basalt lava asian dust and rainfall we present sr isotope and concentration data on both bulk soil digests and nh4ac extracts from soil profiles covering a wide range of environments and substrate ages bulk soil material from dry climates and or young substrate ages with 80 g g 1 sr retain basalt like sr isotopic signatures whereas those with sr concentrations 40 by mass at elevated dust levels lava derived sr is low and dust derived sr is the dominant control of 87sr 86sr in bulk soils however 87sr 86sr of nh4ac extractable sr largely reflects atmospheric deposition of marine aerosol in these situations overall whole soil sr isotope values are controlled by complex interactions between sr provided by lava weathering but partially lost by leaching and sr provided by dust but held in more resistant minerals the isotopic composition of nh4ac extractable sr and of the biota is controlled by lava weathering and rainfall contribution of sr with only minor contributions from radiogenic dust sources

upper tropospheric precursors to the formation of subtropical cyclones that undergo tropical transition in the north atlantic basin abstractthe opportunity to examine the structure and evolution of the various upper tropospheric precursors to the formation of north atlantic natl subtropical cyclones stcs that undergo tropical transition tt motivates this study intraseasonal variability associated with the location and frequency of natl stcs forming in the presence of similar upper tropospheric features as well as similarities and differences in the various upper tropospheric precursors to the formation of natl stcs that undergo tt are examined natl stcs that undergo tt are categorized according to the upper tropospheric features associated with their formation during 1979 2010 using the 0 5 ncep climate forecast system reanalysis dataset this categorization allows for the documentation of the location and frequency of stcs forming in the presence of similar upper tropospheric features and for the construction of cyclone relative composites during the five days prior to stc formation natl stcs that undergo tt are separated

threshold conditions for rill initiation on a vertisol gunnedah n s w australia abstract the effect of soil shear strength on rill development and erosion of a strongly aggregated vertisol was studied in a flume and in a paddock sown with wheat soil strength measurements using a hand held torsional shear vane were related to threshold conditions for rill initiation in the laboratory field measurements on the same soil demonstrated the effect of increasing shear strength on rill development this simple method can be easily used in the field to assess relative susceptibility to rill erosion

morphology genesis and classification of surface crusts in loamy and sandy soils abstract in an attempt to organize the knowledge of soil crusting processes and to group soil crusts on the basis of common morphological features and physical properties we synthesized and reinterpreted information from previous publications as a result we propose a classification system for surface crusts formed by rainfall in loamy and sandy soils although this system does not aim to be comprehensive it was designed from the study of a great number of crust samples collected in the temperate and tropical zones thus corresponding to a wide range of environmental and land use conditions three main classes of crusts structural erosion and depositional were distinguished each with subclasses where possible correspondence has been made with former systems this system helps predict infiltrability in accounting not only for total porosity of surface crusts but also for pore shape and continuity since crust classes are genetically related this classification system also supplies some insight into predicting soil degradation and selecting the most suitable control techniques

penetration resistance of biological soil crusts and its dynamics after crust removal relationships with runoff and soil detachment abstract soil sealing and crusting are common widespread processes in arid and semiarid soils that strongly affect runoff and erosion in these soils biological soil crusts bscs are an essential surface component known to have an important role in water processes and are also strong erosion protection agents however these crusts are also highly vulnerable to disturbances which seriously affect their pedological and ecological roles the aims of this study were to examine whether penetration resistance pr depends on bsc developmental stage and how removal of bscs affects pr under dry and wet soil conditions and to analyse the relationship between pr and runoff and soil detachment in these soils this research was conducted in two semiarid ecosystems representative of crusting processes in se spain el cautivo and las amoladeras almeria province four pairs of plots containing the main bsc types identified at both sites were selected and two treatments were considered one in each plot in the pair i unaltered bsc and ii bsc removal by scraping two intense rainfall simulation experiments were performed one after another in these plots runoff was measured during both and water samples were collected for further determination of sediment yield pr was measured in undisturbed bsc and scalped soil on dry soil prior to rainfall on wet soil after the first and second rainfalls and on dry soil seven months after bsc removal crust pr was higher at las amoladeras 3 13 0 54 kg cm 2 than at el cautivo 1 52 0 74 kg cm 2 due to soil compaction from trampling by livestock in the former pr varied with bsc development with less developed cyanobacteria bscs showing higher resistance under dry and wet conditions than more developed lichen bscs bsc removal was followed by the formation of a new seal physical crust upon raining which however did not result in increased pr no significant relationship was found between pr and runoff but there was a weak negative relationship between pr and soil detachment because in bscs which had higher prs soil detachment rates were much lower than in recently scalped soils seven months after bsc removal pr was significantly higher in scalped soils than for undisturbed bscs our results show that pr was not a good indicator of hydrological and soil detachment response of bscs or the soil sealing during rain immediately after bsc removal but it was a good indicator of physical soil crust formation in scalped soils over time

morphological characterization of soil crust development stages on an experimental field abstract crust development on a loamy aquic hapludalf near paris was studied in an experimental field to which various fertilizers and amendments had been applied these treatments over a period of 57 years had induced a range of organic matter contents and exchangeable cation percentages the macroscopic aspects of the soil surface was closely monitored during crusting and microscopic characterization was carried out at every main crust development stage crusting followed a general pattern 1 sealing of the soil surface by a structural crust 2 development of a depositional crust even in the sodic plot where the depositional crust appeared especially early the structural crust developed first the change from the first stage to the second one mainly depended on a decrease in infiltrability due to the structural crust properties that induced micro runoff and puddling under rainfall structural crust development seemed to involve a coalescing process due to raindrop impact when moistening decreased soil cohesion this process developed much faster in the sodic than in the limed plot morphology of the depositional crust in particular microbedding and sorting could be related to the hydrodynamic behaviour of the soil surface abundance size and duration of puddles

a cyclone phase space derived from thermal wind and thermal asymmetry abstract an objectively defined three dimensional cyclone phase space is proposed and explored cyclone phase is described using the parameters of storm motion relative thickness asymmetry symmetric nonfrontal versus asymmetric frontal and vertical derivative of horizontal height gradient cold versus warm core structure via the thermal wind relationship a cyclone s life cycle can be analyzed within this phase space providing substantial insight into the cyclone structural evolution an objective classification of cyclone phase is possible unifying the basic structural description of tropical extratropical and hybrid cyclones into a continuum stereotypical symmetric warm core tropical cyclone and asymmetric cold core extratropical cyclone life cycles are illustrated using 1 navy operational global atmospheric prediction system nogaps operational analyses and 2 5 ncep ncar reanalyses the transitions between cyclone phases are clearly illustrated within the phase space including extratro

laboratory experiments on crust development and rainsplash erosion of loess soils china abstract loess soil samples obtained from wangjiagou lishi china were subjected to laboratory simulated rainfall at intensities of 72 mm h 1 for a range of durations from 1 to 30 minutes measured splash loss was found to relate to a soil strength index 1 p 20 2 in this index p 20 is defined as penetration by a standard fall cone penetrometer at a moisture content of 20 and estimated from penetration soil moisture regression equations similarly subsequent splash loss of crusted samples over a 10 minute period is significantly related to the antecedent soil strength index as a result of crust development strength of the surface soil is increased by as much as 11 times while splash loss is reduced by a maximum of 76 data on splash loss and crust stength were used to infer that crust and seal development while tending towards increasing stability as has been suggested previously appear to follow a cyclic process of crust formation and disruption this inference is supported by micromorphological observations

classification and synoptic analysis of subtropical cyclones within the northeastern atlantic ocean abstractsince more research is needed on subtropical cyclones stcs formed within the north atlantic eastern basin this survey analyzes them from a synoptic point of view on a climatological basis with the main aims of studying their common features complementing other studies of these storms in the north atlantic and aiding the forecasting community fifteen cases of stcs were identified during the period 1979 2011 by applying a set of criteria from two databases composite analysis reveals that an extratropical depression acts as a precursor when it is isolated from the westerlies and then suffers a deepening when becoming subtropical instead of decaying through occlusion this process is accompanied by an atmospheric circulation within the north atlantic whose main feature is characterized by notable departures from the climatological pattern with a statistically significant anomalous high pressure to the north of the stcs three conceptual models of synoptic pattern of subtropical cyclogenesis