drilling deep into young oceanic crust hole 504b costa rica rift hole 504b is by far the deepest hole yet drilled into the oceanic crust in situ and it therefore provides the most complete ground truth now available to test our models of the structure and evolution of the upper oceanic crust cored in the eastern equatorial pacific ocean in 5 9 m y old crust that formed at the costa rica rift hole 504b now extends to a total depth of 1562 3 m below seafloor penetrating 274 5 m of sediments and 1287 8 m of basalts the site was located where the rapidly accumulating sediments impede active hydrothermal circulation in the crust as a result the conductive heat flow approaches the value of about 200 mw m predicted by plate tectonic theory and the in situ temperature at the total depth of the hole is about 165 c the igneous section was continuously cored but recovery was poor averaging about 20 the recovered core indicates that this section includes about 575 m of extrusive lavas underlain by about 200 m of transition into over 500 m of intrusive sheeted dikes the latter have been sampled in situ only in hole 504b the igneous section is composed predominantly of magnesium rich olivine tholeiites with marked depletions in incompatible trace elements nearly all of the basalts have been altered to some degree but the geochemistry of the freshest basalts is remarkably uniform throughout the hole successive stages of on axis and off axis alteration have produced three depth zones characterized by different assemblages of secondary minerals 1 the upper 310 m of extrusives characterized by oxidative seafloor weathering 2 the lower extrusive section characterized by smectite and pyrite and 3 the combined transition zone and sheeted dikes characterized by greenschist facies minerals a comprehensive suite of logs and downhole measurements generally indicate that the basalt section can be divided on the basis of lithology alteration and porosity into three zones that are analogous to layers 2a 2b and 2c described by marine seismologists on the basis of characteristic seismic velocities many of the logs and experiments suggest the presence of a 100 to 200 m thick layer 2a comprising the uppermost rubbly pillow lavas which is the only significantly permeable interval in the entire cored section layer 2b apparently corresponds to the lower section of extrusive lavas in which original porosity is partially sealed as a result of alteration nearly all of the logs and experiments showed significant changes in in situ physical properties at about 900 1000 m below seafloor within the transition between extrusives and sheeted dikes indicating that this lithostratigraphic transition corresponds closely to that between seismic layers 2b and 2c and confirming that layer 2c consists of intrusive sheeted dikes a vertical seismic profile conducted during leg 111 indicates that the next major transition deeper than the hole now extends that between the sheeted dikes of seismic layer 2c and the gabbros of seismic layer 3 which has never been sampled in situ may be within reach of the next drilling expedition to hole 504b therefore despite recent drilling problems deep in the hole current plans now include revisiting hole 504b for further drilling and experiments when the ocean drilling program returns to the eastern pacific in 1991

identifying soft sediment deformation in rocks abstract the correct identification of sedimentary folds and fabrics created during gravity driven deformation of unlithified successions from those tectonic structures formed during regional deformation is essential when interpreting geological histories preserved within the rock record this topic has become increasingly relevant over the past 40 years as improved seismic resolution and coverage have led to the realisation that significant portions of unlithified sediments along the continental margins undergo gravity driven deformation to create mass transport deposits mtd s the late pleistocene lisan formation exposed in the dead sea basin was chosen as a case study because it remains poorly lithified and structures developed within it are unequivocally related to soft sediment deformation ssd created when the succession underwent downslope directed movement this work tests various assertions previously used to deduce if structures were formed in unlithified sediments or during hard rock deformation hrd associated with subsequent tectonism within the lisan formation we describe veins developed along fractures and cleavage forming axial planar to folds that are structures previously assumed to be restricted to hrd in addition truncated folds incorporation of deformed fragile fragments into overlying sediment and cross cutting clastic dykes are all indicative of ssd the key diagnostic feature in establishing ssd is the sedimentary infill of irregular erosive surfaces that truncate underlying structures although compaction and diagenesis have not played a significant role in the case study caution should be exercised when examining structures preserved in the rock record as folds and fabrics originally created by ssd may be considerably enhanced and altered where significant overburden exists

volume imaging lidar observations of the convective structure surrounding the flight path of a flux measuring aircraft the university of wisconsin volume imaging lidar has been used to portray images of the three dimensional structure of clear air convective plumes in the atmosphere surrounding the flight path of the instrumented twin otter aircraft operated by the national aeronautical establishment nae of canada lidar images provide a context for interpretation of the aircraft measurements the position of data points within a convective element can be determined and the temporal development of the plume can be observed to time the observation with respect to the life cycle of the plume plots of the vertical flux of water vapor q w superimposed on lidar images clearly demonstrate the well known sampling difficulties encountered when attempting to measure fluxes near the top of the convective layer when loran was used to determine average aircraft velocity flight leg averaged horizontal winds measured by the aircraft and area averaged winds measured by lidar agree to within 0 2 m s 1 in speed and 1 in direction

quantitative assessment of in situ salt karstification using shear wave velocity dead sea abstract the dead sea ds coastal areas have been dramatically affected by sinkhole formation since around 1990 such sinkholes along both israeli and jordanian shores are linked to karst cavities that form through slow salt dissolution a quantitative estimate of such in situ salt karstification would be an important indicator of sinkhole hazard one of the indications of salt karstification is its increased hydraulic conductivity caused by the development of dissolution cavities forming conducting channels within the salt layer we measured the hydraulic conductivity k versus shear wave velocity vs of ds salt in situ for estimating the actual salt karstification in areas of sinkhole development these parameters were measured with the magnetic resonance sounding mrs and multichannel analysis of surface waves masw methods respectively understanding of the field relationships was augmented by similar inter relations obtained in the laboratory on samples of ds salt in situ salt velocities vs vary from 750 m s to over 1650 m s while hydraulic conductivity k in the same zones varies between about 10 4 m s to slightly over 10 8 m s both field and laboratory k and vs values fit the exponential function ln k 0 0045 vs 5 416 with a determination coefficient r2 of 0 88 a classification based on vs and k was generated for salt conditions and the corresponding degrees of sinkhole hazard which was verified in the mineral beach sinkhole development area the mapping of sinkhole sites shows that they form within highly conductive zones with k 5 5 10 5 it is suggested that this methodology with some modification can be used for evaluating the conductive properties of karstified rock and associated sinkhole hazards

mid ocean ridges fine scale tectonic volcanic and hydrothermal processes within the plate boundary zone a first order model of spreading centers as idealized linear boundaries of crustal and lithospheric generation provides only a gross understanding of global scale plate kinematics as we attempt to understand the complexity of crustal and lithospheric structure of two thirds of the earth s surface it is becoming increasingly necessary to study the tectonic volcanic and hydro thermal processes within the spreading center plate boundary zone all ocean ic crust bears the imprint of these processes this review focuses on a few selected topics concernining the fine scale tectonics and geophysics of the active axial zone of mid ocean ridges with reference to associated volcanic and hydrothermal processes it draws heavily on recent studies that use deeply towed instrument packages multi beam bathymetric mapping ocean bottom instruments and alvin e g the famous amar rise and galapagos expeditions we begin with a review of the large scale structure of spreading centers we then take a close look at the axial neovolcanic zone and progress away from the axis through the active tectonic zones next we consider the characteristics of the axial magma chamber and associated hydrothermal actvity as well as the generation of magnetic anomaly stripes and their implications for crustal generation one of our findings is that the initial two dimensional model of volcanic and tectonic zones must be expanded upon to allow for variations

a seismic refraction study of the north basin of the dead sea israel a seismic refraction experiment involving the use of 9 obs and 11 portable seismic land stations was conducted along a profile in the north basin of the dead sea the seismometers were deployed along a north south profile in the lake and the adjacent land area the interpretation of the recorded seismograms indicates the presence of two large pliocene salt diapirs in the young basin fill the basement lies at a relatively shallow depth 6 8 km under the north basin further south along the profile a major fault affecting the basement was detected the apparent sense of the faulting is down to the southeast representing the boundary of the south basin this major faulting with a downthrow of some 4 5 km has depressed the crystalline basement and the overlying cretaceous and pre cretaceous sediments the faulting was followed by the deposition of over 8 km of recent and tertiary sediments resulting in a 14 km thick sedimentary sequence in the south basin of the dead sea

convective boundary layer evolution to 4 km asl over high alpine terrain airborne lidar observations in the alps mountain ranges have important influences on the structure and composition of the convective boundary layer cbl and free troposphere ft evolution of the summer cbl measured over the european alps using airborne lidar was clearly observed to attain a near uniform height up to 4 2 km asl by early afternoon a climatology of in situ high alpine aerosol measurements suggests that such substantial growth corresponding to 0 3 of the mid latitude tropopause height often occurs during summer months subsequent nocturnal collapse of the cbl was estimated to result in the venting of 0 8 0 3 so44 gg day 1 into a ft residual layer leeward of the alps

alpine glaciers to disappear within decades 1 past present and potential future glacier cover in the entire european alps has been assessed from an integrated approach combining in situ measurements remote sensing techniques and numerical modeling for equilibrium line altitudes alpine glaciers lost 35 of their total area from 1850 until the 1970s and almost 50 by 2000 total glacier volume around 1850 is estimated at some 200 km3 and is now close to one third of this value from the model experiment we show that a 3 c warming of summer air temperature would reduce the currently existing alpine glacier cover by some 80 or up to 10 of the glacier extent of 1850 in the event of a 5 c temperature increase the alps would become almost completely ice free annual precipitation changes of 20 would modify such estimated percentages of remaining ice by a factor of less than two

geotechnical properties of evaporite soils of the dead sea area the dead sea basin is the lowest point on earth and is tectonically subsiding during the holocene period the climate became much drier with increasing evaporation whereby initially lacustrine sediments were deposited from the non marine brines giving a multi layered stratigraphy of lime carbonate and halite sediments the lime carbonate sediments are comprised of laminated clay to silt sized clastic sediments calcite and authigenic aragonite and gypsum the halite commonly appears as rock salt chemical industries based on harvesting the salts from the dead sea have developed on both the israeli and the jordanian sides of the basin the lime carbonate soils are used for dike construction and these soils together with significant salt layers are encountered in the foundations of structures dikes and tailings dams requiring definition of their geotechnical properties use of standard soil mechanics definitions and testing approaches for the lime carbonates have been found inapplicable particularly in view of their exceptionally high saline content and it has been necessary to develop new concepts the rock salt is encountered at shallow depths with unit weights considerably lower than those usually discussed in the literature and with correspondingly different mechanical properties the geotechnical properties of these soils and approaches used to define them are discussed in the paper

the alpine mountain plain circulation airborne doppler lidar measurements and numerical simulations on summer days radiative heating of the alps produces rising air above the mountains and a resulting inflow of air from the foreland this leads to a horizontal transport of air from the foreland to the alps and a vertical transport from the boundary layer into the free troposphere above the mountains the structure and the transports of this mountain plain circulation in southern germany alpine pumping were investigated using an airborne 2 m scanning doppler lidar a wind temperature radar dropsondes rawinsondes and numerical models the measurements were part of the vertical transport and orography vertikator campaign in summer 2002 comparisons of dropsonde and lidar data proved that the lidar is capable of measuring the wind direction and wind speed of this weak flow toward the alps 1 4 ms 1 the flow was up to 1500 m deep and it extended 80 km into the alpine foreland lidar data are volume measurements horizontal resolution 5 km vertical resolution 100 m therefore they are ideal for the investigation of the flow structure and the comparison to numerical models even the vertical velocities measured by the lidar agreed with the mass budget calculations in terms of both sign and magnitude the numerical simulations with the fifth generation pennsylvania state university ncar mesoscale model mm5 mesh size 2 and 6 km and the local model lm of the german weather service mesh size 2 8 and 7 km reproduced the general flow structure and the mass fluxes toward the alps within 86 144 of the observations

mineral dust and elemental black carbon records from an alpine ice core colle gnifetti glacier over the last millennium 1 black carbon bc and mineral dust aerosols were analyzed in an ice core from the colle gnifetti glacier monte rosa swiss italian alps 45 55 n 7 52 e 4455 m above sea level using chemical and optical methods the resulting time series obtained from this summer ice record indicate that bc transport was primarily constrained by regional anthropogenic activities i e biomass and fossil fuel combustion more precisely the 13 c composition of bc suggests that wood combustion was the main source of preindustrial atmospheric bc emissions c3 c4 ratio of burnt biomass of 75 25 despite relatively high bc emissions prior to 1570 biomass burning activity and especially c 4 grassland burning abruptly dropped between 1570 and 1750 c3 c4 ratio of burnt biomass of 90 10 suggesting that agricultural practices strongly decreased in europe during this cold period of the little ice age lia on the other hand optical analysis revealed that the main source for atmospheric dust transport to the southern parts of the alps during summer months was driven by large scale atmospheric circulation control on the dust export from the northern saharan desert this southern aerosol source was probably associated with global scale hydrologic changes at least partially forced by variability in solar irradiance in fact periods of enhanced saharan dust deposition in the ice core around 1200 1300 1430 1520 1570 1690 1780 1800 and after 1870 likely reflect drier winters in north africa stronger north atlantic southwesterlies and increased spring summer precipitation in west central europe these results therefore suggest that the climatic pejorations and the resulting socioeconomic crises which occurred in europe during periods of the lia could have been indirectly triggered by large scale meridional advection of air masses and wetter summer climatic conditions

hydraulic geometry of cohesive channels undergoing base level drop abstract this study extends earlier contributions on dynamic adjustments of fluvial channels to base level changes we have investigated an in situ response of self formed cohesive channels to a base level drop conditions analogous to a gradual change in uplift and or climate empirical hydraulic geometry equations for clayey cohesive natural streams are presented using data from eight channels draining perennial brackish springs and discharge into the dead sea investigation of downstream variations in gradient and stream power relations suggests existence of three distinct reaches in which channel adjustment to base level drop is shared inequitably among hydraulic geometry variables values of the flow velocity exponent m are low 0 11 m 0 24 the mid channel reach having the lowest exponent the depth exponent f has the lowest value f 0 3 for the uppermost channel reaches the rest having higher values f 0 4 the smallest width exponent b 0 35 characterizes the upper reaches these values and their spatial distribution exhibit a regular pattern we show that the lowermost channel reach adjusts by profile steepening and channel narrowing f b the prevailing mechanism in the mid channel reaches is lateral width adjustment cross sections transiently transforming toward equilibrium the uppermost reaches have wide and shallow channel cross sections because of series of bank collapses and resultant sediment aggradation bringing rise to decreased local gradient forcing further channel widening the results of this study not only allow inference about how cohesive channels regulate their geometry but also reveal the means by which hydraulic forces overcome substrate resistance adjusting slope and channel dimensions and as such have implication for reach scale channel morphology and models of stream power

the ramesses experiment iii controlled source electromagnetic sounding of the reykjanes ridge at 57 45 n summary a controlled source electromagnetic sounding survey centred on an axial volcanic ridge avr segment of the reykjanes ridge at 57 45aen was performed as part of the ramesses experiment low frequency 0 35 11 hz electromagnetic signals were transmitted through the crust to an array of horizontal electric field recorders at the seafloor to ranges of 15 km from the source which was a 100 m long horizontal electric dipole towed at heights of 50 80 m from the seafloor coincident seismic and magnetotelluric studies were conducted during the rest of the ramesses experiment data were interpreted using a combination of 1 d forward modelling and inversion and iterative forward modelling in two dimensions on the axis of the avr the resistivity at the seafloor is 1 v m there is a steep resistivity gradient in the upper few hundred metres of the crust with the resistivity reaching approximately 10 v ma t a depth of 500 m in order to explain the low resistivities the upper layer of the crust must be heavily fractured and saturated with sea water the resistivity increases with distance from the axis as the porosity decreases with increasing crustal age the most intriguing feature in the data is the large diverence in amplitude between fields transmitted along and across the avr axis a significant zone of low resistivity material is required at approximately 2 km depth beneath the ridge crest in order to explain this diverence it is coincident with the low velocity zone required by the seismic data and has a total electrical conductance in excellent agreement with the results of the magnetotelluric study the low resistivity zone can be explained by the presence of a body of partially molten basalt in the crust taken together these results provide the first clear evidence for a crustal magma chamber at a slow spreading mid ocean ridge the data constrain the melt fraction within the body to be at least 20 per cent with a melt volume suycient to feed crustal accretion at this segment of the ridge for of the order of 20 000 years since this body would freeze in the order of 1500 years this finding lends support to the hypothesis that at slow spreading rates crustal accretion is a cyclic process accompanying periodic influxes of melt from the mantle to a crustal melt reservoir

controlled source electromagnetic sounding of the oceanic lithosphere the attenuation of ionospheric signals in the frequency range 0 06 24 hz by sea water effectively precludes using the magnetotel luric method to study the electrical structure of the upper oceanic lithosphere we have carried out a dipole dipole electromagnetic sounding in the north pacific by injecting electromagnetic signals into the ocean and sea bed the crust at the site is 25 myr old and has a thin sediment cover the technique similar to that used in earlier work1 2 involves dragging a horizontal dipole antenna along the sea floor the electric fields that propagated through the resistive basement were detected by seafloor receivers at ranges of 10 65 km as the ambient electric field is very small varying from 10 18 v2 m 2 hz 1 at 0 1 hz to 10 24 v2 m2 hz 1 above 1 hz ref 3 the controlled source signals could be easily monitored our data are consistent with a simple one dimensional earth model consisting of a 3 7 km thick crustal layer of moderate conductivity 0 001 s m 1 underlain by a thicker region of very low conductivity 2 10 5 s m 1 the results suggest an upper mantle water content of at most 0 1 by volume

residual layer effects on the modeling of convective boundary layer growth rates with a slab model using fife data 1 the ability of slab models for the growth of the convective boundary layer cbl to work in the presence of residual layers above is analyzed in detail with a large data set from the first international satellite land surface climatology project field experiment fife 87 and fife 89 experiments we confirm that the critical element that allows the models to predict the growth as the cbl coalesces with the residual layer is the adoption of a variable lapse rate above the growing cbl this is not a new finding per se as several previous studies in the literature have adopted this strategy different parameterizations of a slab model based on the turbulence kinetic energy budget at the top of the cbl were tested and the inclusion of the storage and dissipation terms did not improve the model among the alternatives for choosing the lapse rate as the cbl grows fair results are obtained with a simple choice of two values with absolute mean errors of the order of 270 m for cases with and without a residual layer both lapse rates representative of the residual layer and the free atmosphere are obtained from the first morning sounding finally an alternative model for the cbl growth into a residual layer that assumes a zero lapse rate above the cbl did not perform well with the fife data

late holocene annual growth in three alpine stalagmites records the influence of solar activity and the north atlantic oscillation on winter climate annual growth rates and the ratio of dark to light colored calcite within single annual laminae in three contemporaneously deposited holocene speleothems from grotta di ernesto an alpine cave in northern italy respond to changes in surface temperature rather than precipitation based on monitoring of present day calcite growth and correlation with instrumental data for surface climatic conditions we interpret a higher ratio of dark to light colored calcite and the simultaneous thinning of annual laminae as indicative of colder than present winters such dark and thin laminae occur in those parts of the three stalagmites deposited from ad 1650 to 1713 and from ad 1798 to 1840 as reconstructed through lamina counting these periods correspond to the well known maunder and dalton minima of solar activity an 11 yr cyclicity in growth rate coupled with reduced calcite deposition during the historic minima of solar activity is indicative of a solar influence on lamina thickness spectral analysis of the lamina thickness data also suggests that the north atlantic oscillation variability influenced winter temperatures based on the present day controls on cave calcite formation we infer that high frequency changes in solar activity modulated the seasonal duration of soil co2 production

atmospheric warming threatens the untapped glacial archive of ortles mountain south tyrol ortles mountain 3905 m a s l south tyrol italy is the highest mountain of the eastern european alps and its upper glacier alto dell ortles presents a unique opportunity to obtain the first paleoenvironmental record from an ice core in this area to study the suitability of this glacier as a drilling site in 2009 we performed the first preliminary study of its glaciological characteristics at 3830 m a s l the maximum thickness is 75 m and lamination of the exposed ice layers is excellent down to bedrock firn and ice lenses were observed in a 10 m shallow core and the firn ice transition was below 24 m the seasonal chemical signal is clearly preserved only within the uppermost 2008 and 2009 snow firn a simple mass balance model the incipient smoothing of the chemical record and the observed ice lenses provide evidence that melting infiltration and refreezing cycles occurred within the firn layers formed before 2008 nevertheless the mass balance of the upper part of alto dell ortles was positive 800 mm a 1 during the last few years we suggest that an environmental history is likely to be well preserved only within the ice layers formed before 1980 when summer air temperature was 28c colder than today in this area clearly the continued warming trend predicted to occur over the next few decades and the consequent increase in frequency and or intensity of infiltration processes will endanger the preservation of the glacial archive conserved in the deep ice layers of ortles mountain

transient electromagnetic responses in seafloor with triaxial anisotropy summary electrical anisotropy of young oceanic crust at mid ocean ridges is detectable by observation of the rate and geometry of the diffusion of electromagnetic fields the anisotropy in electrical properties arises from the presence of conductive seawater in an interconnected network of mostly ridge parallel cracks in this paper we first justify the choice of a triaxial model to represent young oceanic crust with three distinct electrical conductivities in the vertical strike and spreading directions we then present an algorithm to calculate the transient electromagnetic responses generated by an electric dipole source over such a triaxially anisotropic seafloor we show that if the transient passages are measured with three distinct electric dipole dipole configurations it is possible to discern all three unknown conductivities independently of each other

velocity resistivity versus porosity permeability inter relations in dead sea salt samples abstract this study is intended to investigate dead sea ds salt porosity permeability hydraulic conductivity inter relations as well as their relationship to geophysical parameters such as compression and shear wave velocities vp vs respectively and specific resistivity x in laboratory and field conditions to estimate representative properties affected by porosity changes during sinkhole development some 41 salt samples were subjected to porosity measurements and 25 samples were tested to reveal hydraulic conductivity the salt of the coastal dead sea area composed of halite is revealed in 10 200 10 800 year old layers the halite commonly appears as rock salt the 7 30 m thick salt unit is located below the groundwater table at depths of 20 50 m from the surface salt layers are very conductive hydraulically and water saturated with the ds brine is of very high salinity with total dissolved solids tds of 340 380 g l two types of salt have been studied crystalline transparent salt cts distributed along the entire ds s western shore and white massive salt wms found locally along the southern ds and along the dike salt porosity measured in samples varies in the range of 5 21 whereas hydraulic conductivity varies between 10 5 to 10 9 m s density is changed in the range of 1681 2116 kg m 3 in wet samples and between 1638 and 2106 kg m 3 in dry samples during the laboratory testing of ds salt samples we have measured the following geophysical parameters vp 3700 4460 m s vs 1900 2620 m s and x 2 100 m on the other hand our previous field studies based on s wave seismic refraction surface wave prospecting swp and transient electromagnetic tem methods have shown that in in situ salt velocities vp range between 2900 and 4240 m s vs varies between limits of 750 m s to more than 1650 m s and x is of 0 8 to 2 5 m these values are considerably less than the analogous parameters measured in the salt samples the same conclusion has been made from the comparison of salt sample properties and borehole logging both studied by ultrasonic method geophysical data testify that in situ porosity calculated using relationships obtained during this study exceeds those in the laboratory samples especially in zones of heightened voidness where it is 25 hydraulic conductivities in the same zones exceed a value of 10 6 m s and even 10 5 m s we expect that in larger salt volumes these parameters can yet increase

towards radiocarbon dating of ice cores a recently developed dating method for glacier ice based on the analysis of radiocarbon in carbonaceous aerosol particles is thoroughly investigated we discuss the potential of this method to achieve a reliable dating using examples from a mid and a low latitude ice core two series of samples from colle gnifetti 4450 m a s l swiss alps and nevado illimani 6300 m a s l bolivian andes demonstrate that the 14c ages deduced from the water insoluble organic carbon fraction represent the age of the ice sample sizes ranged between 7 and 100 g carbon for validation we compare our results with those from independent dating this new method is thought to have major implications for dating non polar ice cores in the future as it provides complementary age information for time periods not accessible with common dating techniques

mechanism of heating and the boundary layer over the tibetan plateau abstract the structure of the boundary layer and the mechanism of heating over the tibetan plateau are examined using the data obtained from the first garp global atmospheric research program global experiment and the chinese qinghai xizang tibet plateau meteorological experiment from may to august 1979 the meteorological elements near the plateau surface exhibit pronounced diurnal variations there is a large ground air temperature difference during the daytime generating a thin layer of superadiabatic lapse rates near the surface the horizontal wind speed attains the minimum in the morning and the maximum in the evening a deep and well mixed layer of potential temperature is observed over the western and central plateau in the evening 1200 utc however moisture is not well mixed vertically and water vapor mixing ratio is larger in the morning 0000 utc than in the evening the mixed layer becomes shallower from the western to the central plateau and it disappears over the eastern plateau the

reasons for the extremely high ranging planetary boundary layer over the western tibetan plateau in winter abstractthe planetary boundary layer pbl over the tibetan plateau with a mean elevation about 4 km above sea level reaches an unmatched height of 9515 m above sea level the proximity of this height to the tropopause facilitates an exchange between the stratosphere and the boundary layer however the underlying mechanisms responsible for this unique pbl have remained uncertain here the authors explore these mechanisms and their relative importance using measurements of the pbl the associated surface fluxes and single column and regional numerical simulations as well as global reanalysis data results indicate that the dry conditions of both ground soil and atmosphere in late winter cannot explain the special pbl alone rather the results from a single column model demonstrate the key influence of the stability of the free atmosphere upon the growth of extremely deep pbls over the tibetan plateau simulations with the numerical weather prediction model consortium for small scale modelling cosmo

a geotechnical study of evaporitic lacustrine sediments in the saline environment of the dead sea area this paper is the third by the authors relating to the geotechnical properties of the evaporitic lacustrine sediments of the saline environment in the dead sea area the earlier papers identified difficulties involved in establishing the water content of sediments in a saline environment a different approach was adopted whereby fluid content rather than water content was used to define geotechnical properties the present paper expands on the geological background presented in the previous papers and discusses additional geotechnical aspects of the materials behavior the three major sediment types encountered in the region are fluvial granular soil cohesive lime carbonate deposits and granular to massive halite sediments the granular soils composed predominantly of sand and pebbles of dolomite with minor chert and limestone have gradations which vary widely both with depth and laterally shear wave velocities are higher than those estimated from common existing correlations with standard penetration test spt blow counts while compression indices cc and cyclic shear response of the saturated lime carbonates are consistent with behavior of clay soils their effective friction angle of about 34 on average is significantly higher than that of clays the geotechnical properties of the rock salts encountered in the region are shown to be intimately related to the extent of diagenesis and burial with very significant difference between the younger more porous deposits of holocene age and the older mt sdom diapiric salt wall of upper miocene age the latter are seen to have properties consistent with those of older rock salt deposits at greater depths reported in the literature

the detection of lateral anisotropy of the ocean floor by electromagnetic methods summary in a typical marine controlled source electromagnetic csem experiment one or more self contained receivers capable of measuring small variations in the electromagnetic field are located in an array on the sea floor a remote horizontal electric dipole is towed close to the sea floor by a surface vessel variations in the current through the dipole cause correlated variations in the electric and magnetic fields at the receivers the variations contain information about the distribution of electrical conductivity of the subsurface rocks the electrical conductivity is related to such critical physical parameters as porosity temperature and fluid content published studies of the response of the sea floor to electromagnetic excitation have not included any systematic variation in the sea floor conductivity with horizontal direction a horizontally isotropic oceanic lithosphere is not an appropriate assumption particularly in the vicinity of the ridge here for example in the near surface layers basalts are extruded onto the sea floor within the very narrow fissured neo volcanic zone the fissures may be filled with sea water and sediment which are better conductors than typical basalt alternatively as time progresses they may become sealed with hydrothermal mineral deposits which can be less conductive than the host rocks in both instances the electrical conductivity of the composite material in the direction oriented along the fisures parallel to the ridge will be greater than that in the transverse direction measures of anisotropy on sea floor of varying age are an indication of the history of the tectonic activity at the ridge the electromagnetic effects of lateral anisotropy are examined through the study of the response of a simple double half space model an upper half space representing sea water is connected to a lower half space representing anisotropic crustal material a general theory describing the excitation of this model by any transient electromagnetic source is developed and the step on responses for systems composed of a horizontal electric dipole transmitter and horizontal magnetic and electric field receivers are computed the results of previous work indicate that following a change in current in the transmitter two distinct changes in horizontal electric field strength separated in time are observed at the receiver the first is caused by the diffusion of the electromagnetic field through the relatively resistive sea floor the second is caused by diffusion through the relatively conductive sea water the times at which the two events occur are robust measures of the isotropic conductivity of the sea floor and the sea water respectively the results of this study show that shape and time of the initial change in the electric field varies systematically with both the average conductivity and the anisotropy of the sea floor for some orientations of the transmitter and the receiver the effect of increasing the anisotropy is similar to the effect of increasing the average conductivity the initial event is delayed however there are orientations for which increasing the anisotropy actually results in an earlier arrival natural science and engineering research council in canada

characteristics and potential climatic significance of miniature ice caps crest and cornice type low altitude ice archives long term ice core records of alpine glaciers are usually taken from cold firn areas at high altitudes as on mont blanc and monte rosa perennial ice bodies at lower altitudes however also bear information about the past recent findings from the remains of such ice the oetztal iceman found in austria wooden bows at lotschen pass switzerland clearly indicate the hitherto little recognized fact that small more or less static perennial ice bodies which are cold and frozen to the underlying bedrock may contain very old ice and hence important palaeoclimatic information about warm periods with minimum ice extent in the alps since autumn 1998 investigations have been initiated on a crest type location or miniature ice cap at piz murtel engadine swiss alps first results from shallow drilling temperature data logging geodetic surveying visual observation finite element modelling of simplified basic two dimensional configurations and comparison to earlier measurements at similar sites provide promising perspectives concerning a little studied phenomenon with considerable scientific environmental research potential specific characteristics of the investigated site and probably of many other comparable mountain sites are cold ice about 4 c at 10 m depth no basal sliding small mass turnover striking lack of a firn zone accumulation mainly by superimposed ice and direct access to old layers centuries millennia at the ice bedrock interface

structure and evolution of a severe squall line over the arid region in northwest china abstract the structure and evolution of a long lived squall line associated with a disastrous dust storm called a black storm that occurred over the arid region in northwest china are described data used in the present study were those from routine observations in china and those acquired from surface observations of the heife river field experiment the squall line evolved within an extremely dry environment in which surface water vapor mixing ratios were less than 2 5 g kg 1 and the level of free convection lfc was very high the surface cold air outflow that emanated from the squall line propagated rapidly producing strong horizontal convergence at the leading edge of the cold pool the deep dry mixed layer that developed over the desert region owing to strong solar surface heating played a significant role in determining the squall line evolution the maximum depth of the mixed layer was estimated as more than 4 km which is often found over the desert regions of china the growth of the deep

glaciochemical dating of an ice core from upper grenzgletscher 4200 m a s l one crucial condition for the interpretation of ice core records is the establishment of an accurate time scale this task is especially difficult for glacier sites in a complex topography such as the alps due to the often irregular deposition of fresh precipitation in this work dating techniques were applied to an alpine ice core from upper grenzgletscher monte rosa massif 4200 m a s l representing about two thirds of the total glacier thickness they are based on i the radioactive decay of the isotope 210 pb ii seasonally varying signals such as the concentrations of nh 4 and the isotopic ratio 18 o and iii stratigraphic markers from saharan dust falls atmospheric nuclear weapon tests and the reactor accident in chernobyl from the combined application of these dating methods a time period of 1937 94 covered by the ice core was derived dating uncertainty is 1 year for the period 1970 94 and 2 years for the period 1937 69 the observed thinning of the annual layers as a function of depth could be well described by a simple kinematic glacier flow model

dominant control of the south asian monsoon by orographic insulation versus plateau heating heat emitted from the tibetan plateau as dry heat and water vapour has long been assumed to be the main driver of the south asian summer monsoon but new work suggests that in fact it is the neighbouring mountains that are the major influence william boos and zhiming kuang use an atmospheric model to show that flattening the tibetan plateau has little effect on the monsoon so long as the himalayas and surrounding mountain ranges remain the plateau does boost rainfall locally along its southern edge but it is the build up of hot moist air over india insulated from colder drier air by the himalayas that drives large scale monsoon circulation the elevation of the tibetan plateau is thought to cause its surface to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales here however an atmospheric model is used to show that flattening of the tibetan plateau has little effect on the monsoon provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved the tibetan plateau like any landmass emits energy into the atmosphere in the form of dry heat and water vapour but its mean surface elevation is more than 5 km above sea level this elevation is widely held to cause the plateau to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales1 2 3 4 5 observations of the present climate however do not clearly establish the tibetan plateau as the dominant thermal forcing in the region peak upper tropospheric temperatures during boreal summer are located over continental india south of the plateau here we show that although tibetan plateau heating locally enhances rainfall along its southern edge in an atmospheric model the large scale south asian summer monsoon circulation is otherwise unaffected by removal of the plateau provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved additional observational and model results suggest that these mountains produce a strong monsoon by insulating warm moist air over continental india from the cold and dry extratropics these results call for both a reinterpretation of how south asian climate may have responded to orographic uplift and a re evaluation of how this climate may respond to modified land surface and radiative forcings in coming decades

on the boundary layer structure over highly complex terrain key findings from map within map one of the scientific projects was devoted to boundary layers in complex terrain in a number of subprojects boundary layer issues were addressed and detailed high resolution multi sensor observations were combined with simulation by models allowing for adequate parametrization of turbulence processes in this contribution the projects are briefly introduced and an attempt is made to summarize their key findings and to put them into a joint perspective spatial variability is found to be large but strictly related to topography and therefore allowing for possible parametrization traditional boundary layer scaling approaches cannot simply be applied over highly complex topography but some of the map findings suggest the potential for suitable extensions of those scaling relations to cover various cases of complex terrain the mean boundary layer structure and thermally driven flows in narrow valleys are found not to be generally in line with previous results from larger valleys elsewhere furthermore local circulations are reported to contribute considerably to exchange between valley and free troposphere in particular the range of their effects on the lower atmosphere seems to be larger than just turbulent transport within the planetary boundary layer would suggest thus in larger scale numerical models where the topography is not resolved possible sub grid parametrizations for local exchange seem to be in order copyright 2007 royal meteorological society

the little ice age as recorded in the stratigraphy of the tropical quelccaya ice cap the analyses of two ice cores from a southern tropical ice cap provide a record of climatic conditions over 1000 years for a region where other proxy records are nearly absent annual variations in visible dust layers oxygen isotopes microparticle concentrations conductivity and identification of the historical a d 1600 huaynaputina ash permit accurate dating and time scale verification the fact that the little ice age about a d 1500 to 1900 stands out as a significant climatic event in the oxygen isotope and electrical conductivity records confirms the worldwide character of this event

controlled electromagnetic sources for measuring electrical conductivity beneath the oceans 1 forward problem and model study exact closed form expressions for the electromagnetic induction fields produced by vertical and horizontal current sources in the conducting ocean overlying a one dimensional earth are derived from the maxwell equations numerical methods for the evaluation of the solutions are given including correction for the finite size of real sources simple models of the electrical conductivity structure of the ocean crust and lithosphere are deduced from geologic petrologic and laboratory data and their electromagnetic response is modeled horizontal electric dipole sources produce much larger field amplitudes than their vertical counterparts for a given frequency and range and the horizontal electric field offers superior received signal performance reflections of electromagnetic waves from the sea surface and thermocline must be considered for low enough frequencies or long ranges estimates of the ambient noise level from natural electromagnetic sources in the frequency range 0 01 10 hz are presented the ability of controlled sources to determine features of the conductivity of the ocean crust and upper mantle especially low conductivity zones is demonstrated if the mantle conductivity is low enough horizontal ranges of 50 km and conductivity estimates to over 20 km depth can be achieved

structure of the atmosphere in an urban planetary boundary layer from lidar and radiosonde observations the planetary boundary layer pbl over mexico city was probed with a scanning backscatter lidar to characterize and evaluate the multidimensional structure of the atmosphere comparisons were made between radiosonde and lidar derived pbl heights which showed the two techniques to be in close agreement the spatial properties of the free atmosphere pbl interface were found to be approximately the same size as the entrainment zone thickness below the interface the lidar observed spatially resolved structures such as thermal plumes convective eddies low level jets and entrainment into the pbl these structures were spatially correlated with the local diabatic condition and wind stress one highly unstable atmosphere contains a lidar visualized convective structure rising to a height of 0 45 the inversion base which was predicted from earlier turbulence models other features such as low level jets were found to be associated with neutral atmospheres in the mixing layer the analysis indicates that the transport of pollutants is not a continuous and gradient driven process but low frequency and spatially discontinuous the high spatial and temporal resolution afforded by the scanning lidar depicts surface atmosphere interactions which are neither spatially homogeneous nor horizontally uniform

distinguishing coeval patterns of contraction and collapse around flow lobes in mass transport deposits abstract gravity driven mass transport deposits mtds form by the downslope directed movement of sediment associated with slope failure simple models suggest that extension forms at the upslope head area contraction is focussed in the downslope toe of the slump while differential shear associated with strike slip is restricted to the lateral margins of the slump although the head and toe are considered to be dominated by layer parallel shear lps differential layer normal shear lns may be generated around the lateral margins of slumps and potentially also within mtds where flow has been separated into different lobes despite this realisation that lns must form there has been little work into the geometries and spatial relationships of resulting structures using the late pleistocene lisan formation exposed around the dead sea basin as our case study we examine detailed

distinguishing thrust sequences in gravity driven fold and thrust belts abstract piggyback or foreland propagating thrust sequences where younger thrusts develop in the footwalls of existing thrusts are generally assumed to be the typical order of thrust development in most orogenic settings however overstep or break back sequences where later thrusts develop above and in the hangingwalls of earlier thrusts may potentially form during cessation of movement in gravity driven mass transport deposits mtds in this study we provide a detailed outcrop based analysis of such an overstep thrust sequence developed in an mtd in the southern dead sea basin evidence that may be used to discriminate overstep thrusting from piggyback thrust sequences within the gravity driven fold and thrust belt includes upright folds and forethrusts that are cut by younger overlying thrusts backthrusts form ideal markers that are also clearly offset and cut by overlying younger forethrusts portions of the basal detachment to the thrust system are folded and locally imbricated in footwall synclines below forethrust ramps and these geometries also support an overstep sequence however new short cut basal detachments develop below these synclines indicating that movement continued on the basal detachment rather than it being abandoned as in classic overstep sequences further evidence for synchronous thrusting where movement on more than one thrust occurs at the same time is provided by displacement patterns on sequences of thrust ramp imbricates that systematically increases downslope towards the toe of the mtd older thrusts that initiate downslope in the broadly overstep sequence continue to move and therefore accrue greater displacements during synchronous thrusting our study provides a template to help distinguish different thrust sequences in both orogenic settings and gravity driven surficial systems with displacement patterns potentially being imaged in seismic sections across offshore mtds

electromagnetic expression of axial magma chambers the electrical conductivity of sea floor materials is a strong function of porosity pore geometry fluid content temperature and percentage of partial melt these material properties are particularly volatile near the midocean ridge tracking electromagnetic eddy currents generated on the sea floor as they diffuse across the ridge can provide images of the subaxial electrical and through interpretation the geological structure we have computed numerically in 2d the response of a crustal magma chamber located beneath the east pacific rise to excitation in two fundamental orthogonal modes rise normal te and rise parallel tm electric field a finite element representation of the electromagnetic em diffusion equations is solved in the laplace domain and the results inverted into the time domain via the gaver stehfest algorithm a sequence of snapshots for each mode for the time range 0 1 to 15 s shows the complete progression of the eddy currents into through and around the magma chamber the te and tm signals at a receiver site above the conductive magma chamber are delayed and attenuated in comparison with those expected for normal layered oceanic crust

use of gpr method for prediction of sinkholes formation along the dead sea shores israel abstract it seems the highly saline conditions of the dead sea ds coast line are not favorable for the use of ground penetrating radar gpr method for detection of underground caverns before sinkhole formation short time prediction the location of the formed caverns within the salt layer significantly more than the penetration depth of the electromagnetic waves combined with the saline ds brine groundwater covering the salt layer from above characterized by low electrical resistivity makes the application of electromagnetic waves ew impossible however our experience has shown that gpr technique in its 2d and 3d modifications can be a very efficient tool to predict sinkhole susceptibility case histories of gpr studies in the mineral beach and nahal david sites are presented the gpr study has shown that the method is effective in both urban sites and at most of sites of human activities of the dead sea coast dwellings routes agricultural areas etc but it fails in areas composed of saline mud in the subsurface some areas lower than 400 m elevation the fan areas are composed of sandy gravel sediments and the penetrating depth of the electromagnetic waves varies but is usually limited to the first meters up to 8 10 m maximum to 13 15 m but in any case not deeper than the water table depending on the dielectric constant which as a rule is 4 25 in areas covered by dead sea mud penetration depth is limited to the first meter due to the low electrical resistivity of the sediments models of sinkhole formation and principles of cavity detection in the ds area are discussed to understand the fundamentals of gpr use for the prediction of sinkhole susceptibility

electric dipole fields over an anisotropic seafloor theory and application to the structure of 40 ma pacific ocean lithosphere summary seismic anisotropy has been detected in the oceanic crust and upper mantle and likewise it is geologically reasonable to expect that a certain amount of lateral anisotropy exists in sea oor electrical properties anisotropy in earth properties can often lead to surprising eiects on geophysical responses that are not anticipated from simple isotropic theories here we investigate the eiects of lateral anisotropy on the frequency domain controlled source electromagnetic csem response of a uniaxially conducting non magnetic sea oor excited by a horizontal electric dipole whose moment is oriented obliquely with respect to the electrical strike direction a paradox of anisotropy is observed in which the sea oor electric eld strength is enhanced in the most conductive direction of the sea oor this enhancement is opposite to what one would expect based on naive isotropic theory we also show that it is possible in certain circumstances to extract the along strike electrical conductivity from marine controlled source electromagnetic data using only isotropic modelling the extraction of across strike conductivity however requires full anisotropic modelling the physical insight into electromagnetic induction in uniaxial media that is presented here should greatly assist the geological interpretation of marine csem experimental data applying our algorithm to the pegasus data set csem data collected over 40 ma paci c ocean lithosphere produces a model with conductivity in the fossil spreading direction that is seven times greater than the conductivity perpendicular to spreading strain aligned mineralogical fabric as predicted by tectonic modelling would explain our result with enhanced conductivities caused by hydrogen conduction along the olivine a axis or connected accumulations of trace conductors such as graphite or magnetite

turbulence characteristics over tropical station gadanki 13 5 n 79 2 e estimated using high resolution gps radiosonde data 1 seasonal variation of the turbulence parameters refractivity structure constant cn2 eddy dissipation rate and eddy diffusivity k is presented using 3 years april 2006 to march 2009 of high vertical resolution gps radiosonde measurements over the tropical station gadanki 13 5 n 79 2 e first a correlation analysis was done in order to study the relative contributions of temperature t and relative humidity rh to the refractive index gradient m a strong positive negative correlation between m and rh t gradients is noticed up to 10 km above 10 km a strong positive correlation between m and t gradients is seen except at altitudes near the tropopause in the present study we flag the turbulent layers using the thorpe sorting method and estimate the structure constant cn2 for the turbulent layers the probability of occurrence of cn2 is derived from the cumulative distribution at each height and is found to decrease from 10 7 to 10 17 m 2 3 with height the probability of the occurrence of cn2 conditioned to the occurrence of turbulence as a function of height is derived and it is found that only the mean and the 90th percentile profile reach an altitude of 27 km the demarcation between the boundary layer and the free atmosphere as well as between the troposphere and the stratosphere are quite clear from the turbulence profile which allows us to identify the boundary layer and tropopause heights from turbulence profiles thus the present analysis introduces an alternative approach to identify the height of the boundary layer as well as the tropopause and also to characterize the probability of turbulence and thickness of turbulent eddies in the atmosphere with a finer scale size down to 5 m for the first time from a tropical latitude

diagenesis of saline pan halite comparison of petrographic features of modern quaternary and permian halites abstract petrographic studies of modern saline pan halites saline valley ca salina omotepec baja california mexico and quaternary shallow buried 0 200 m halites saline valley ca bristol dry lake ca searles lake ca qarhan saline pan qaidam basin china lake uyuni bolivia show that the diagenetic modification of halite begins contemporaneously with deposition is most intense within the upper few meters of burial and is essentially complete within the first 45 m of burial halite crusts from modern saline pans that have undergone repeated episodes of flooding evaporative concentration and desiccation contain abundant syndepositional diagenetic features these mature modern halites are dominated by dissolution textures and fabrics formed during flood stages and cementati n textures formed during desiccation stages interlayered mud beds contain varying amounts of displacive halite crystals at shallow burial depths halites retain many textural features of mature modern saline pan halite halites below the first few meters are no longer susceptible to dissolution from floodwaters but continue to be cemented by clear halite within the first 10 m of burial cementation reduces the porosity of halite crusts to less than 10 the remaining pore spaces are completely filled by burial depths of approximately 45 m displacive growth of halite in muds continues at shallow burial depths and is probably limited to the first few tens of meters of burial depth the mechanisms for cementation and displacive growth of halite at shallow burial depths probably include 1 evaporative concentration of groundwater brines and 2 cooling of surface brines when they sink below the sedime t surface undeformed halites from the permian salado and rustler formations of new mexico contain delicate syndepositional textures and abundant clear halite cements that are comparable to those observed in modern saline pan halites and shallow buried halites the permian halites are interpreted to have undergone a depositional and early diagenetic history similar to the modern and quaternary analogs complete cementation of saline pan halites at shallow burial depths has important implications for the origin of saline formation waters in sedimentary basins parent evaporite brines may not be stored in the pores of halite rocks and later expelled during burial compaction if the rocks are cemented early and tightly crystallized halite rocks may also impede the downward migration of dense syndepositional brines

cold firn and ice of high altitude glaciers in the alps measurements and distribution modelling the thermal regime of high altitude accumulation areas in the swiss alps was systematically investigated on the jungfraufirn bernese alps on the breithornplateau valais alps and on grenzgletscher valais alps in 1991 1992 and 1994 temperatures were measured in a deep hole 120 m deep and in several shallow holes 14 30 m deep whereas the wide neve of the jungfraufirn at 3400 3600 m a s l and the 3800 m high breithorn plateau seems to be predominantly temperate cold firn and ice temperatures were measured throughout on grenzgletscher 3900 4450 m a s l mean firn temperatures on grenzgletscher vary strongly and range between 3 and 14 c a comparison between the measured temperature profiles and a one dimensional heat conduction calculation shows that the release of latent heat by penetrating and refreezing meltwater decisively influences the thermal pattern of the firn pack a multiple linear regression model based on measured firn temperatures from the european alps and the parameters altitude and aspect yields aspect dependent lower boundaries for the occurrence of cold firn ranging between 3400 northerly aspects and 4150 m a s l southerly aspects a total of 120 glaciers with cold firn areas are found when applying the model to glacier inventory data from the european alps

on crosswell diffusive time domain electromagnetic tomography summary we investigate the reconstruction of a conductive target using crosswell time domain electromagnetic tomography in the diffusive limit the work is a natural extension of our ongoing research in the modification of time domain methods for the rugged marine mid ocean ridge environment an environment characterized by extreme topography and pronounced variations in crustal conductivity on all scales we have proved both in theory and in practice that traveltime the time taken for an electromagnetic signal to be identified at a receiver following a change of current in the transmitter is an excellent robust estimator of average conductivity on a path between transmitter and receiver a simple estimate of the traveltime for a parallel electric dipole dipole system is the time at which the derivative of the electric field with respect to logarithmic time at the receiver reaches its maximum we have derived the fundamental relationship between the traveltime and the conductivity of the medium for a uniform whole space we have applied the concept of the traveltime inversion to the related crosswell problem and demonstrated reconstructions of finite targets based on tomographic analyses results show that the crosswell time domain electromagnetic tomography can supply useful information such as the location and shape of a conductive target

alluvial deposition and lake level fluctuations forced by late quaternary climate change the dead sea case example based on geomorphic observations we discuss lake level fluctuations alluvial deposition and river entrenchment in the dead sea wadi araba area the bulk of alluvium in the northern wadi araba was probably deposited before the lisan period of lake transgression that started at about 70 kyears b p the lake reached a maximum elevation about 150 m below sea level b s l possibly around 15 cal kyears b p as indicated by the highest preserved beach ridges cosmogenic exposure dates show that the ridge material consists mainly of remobilized pleistocene gravel indicating little sediment supply during most of the lisan period during this period a reduced sediment flux fed subaquatic fan deltas along the margin of the dead sea wetter conditions settled at the end of this period the water level rose to about 280 m b s l around 15 kyears b p and prevailed in the early holocene 10 5 7 cal kyears b p following that humid period the lake level dropped and two major episodes of fluvial aggradation occurred during periods of relative low lake level the first aggradational episode took place between about 7 0 and 6 2 cal kyears b p beach bars indicate a subsequent lake transgression between 6 2 and 4 4 kyears b p up to 350 m b s l the second aggradational episode happened between 4 4 and 2 0 cal kyears b p and was also followed by a late transgression up to 375 m b s l dated to 1960 1715 cal years b p the correlation between low lake level and fluvial aggradation is taken to reflect the synchronous change of the fluvial regime and of the lake hydrologic balance forced by climate changes rather than a base level control we also exclude large tectonic forcing on fan emplacement and river entrenchment alluviation appears in this setting as a very irregular process characterized by long periods of quiescence alternating with periods of fan build up reflecting the transient response of the water drainage system to climate change d 2003 elsevier b v all rights reserved

theoretical controlled source electromagnetic responses of fast spreading mid ocean ridge models summary new oceanic crust is being formed along active segments of the global mid ocean ridge mor system the presence of an axial magma chamber and associated zones of partial melt and hydrothermal activity located up to several kilometres beneath the seafloor is central to almost all recently proposed theories of crustal formation seismic images of the top few kilometres beneath the fast spreading east pacific rise epr have already been obtained reflection profiles place strong constraints on the geometry of the axial magma chamber but refraction data provide only coarse estimates of the subsurface temperature distribution of partial melt and porosity parameters required to distinguish between the proposed petrological models electrical conductivity is directly related to all these critical parameters and therefore electromagnetic experiments should be designed to help characterize the ridge environment we determine the magnetic field b t on the seafloor caused by a sudden change in current in a 2 d electric dipole aligned perpendicular to the strike of the ridge the finite element technique is used to solve the governing differential equation numerically in the laplace s domain the transformation to the time domain is by the gaver stehfest method we show that the extraction of two basic parameters from the response curve t can provide sufficient information to identify the more important features of the petrology the parameters are the response amplitude max which is the maximum derivative of tb t and the diffusion time t the time at which this maximum occurs the behaviour of as a function of distance from the source is analogous to that of first arrival time in refraction seismology the value of is a weighted integral of the conductivity along the most resistive path between the source and the receiver a highly conductive partially molten magma chamber beneath the ridge axis slows the rate of diffusion of electromagnetic fields across the ridge increasing but also reducing max at sites on the side of the ridge opposite the transmitter a melt lens ponding as a thin layer on top of the chamber increases max at the ridge crest and increases at sites on the far side hydrothermal fluid circulation in the uppermost 2 km of the crust reduces max everywhere across the ridge but increases only at sites within 0 3 km of the ridge crest electromagnetic energy in this case can reach the more distant points via paths which by pass the fluids inferences made from the results of 2 d modelling indicate that a practical experiment would require a 104 a m horizontal electric dipole hed transmitter located 5 km off axis and receivers with a sensitivity of at least 1 pt s 1 over a time window up to 10 s

using champ radio occultation data to determine the top altitude of the planetary boundary layer 1 a simple approach to derive the planetary boundary layer pbl top altitude from champ challenging minisatellite payload radio occultation ro data is presented our ro processing cuts off at an altitude typically 4 km below which the gps signals are affected by tracking errors this lowest processed altitude lpa is assumed to coincide with the pbl top we average lpas for the years 2001 to 2004 over 5 degree latitude longitude boxes and compare them to ecmwf analysis data the ecmwf pbl top was calculated from the relative humidity gradient with respect to altitude agreement between the data sets is good in terms of mean pbl height especially over sea the champ data shows the major features of pbl height with a realistic transition from stratocumulus regions to shallow and deep cumulus areas champ also shows a substantial amount of pbl height variability that may prove useful to study pbl dynamics

airborne lidar and in situ aerosol observations of an elevated layer leeward of the european alps and apennines 1 an elevated layer was observed during airborne lidar and in situ aerosol measurements leeward of the european alps and apennine mountains the layer was encountered during the mesoscale alpine program map in autumn 1999 and extended 200 km at an altitude 4100 m asl over the northern adriatic sea detailed meteorological analysis suggested that mountain venting followed by advection was responsible for formation of the layer evidence for particle nucleation was found in six profiles and was associated with regions of cloud outflow despite determination of the average aerosol mass concentration within the layer 1 8 so4 g m 3 an estimate of export to the free troposphere was complicated by the complex structure of the planetary boundary layer

late holocene climates of the near east deduced from dead sea level variations and modern regional winter rainfall the dead sea is a terminal lake of one of the largest hydrological systems in the levant and may thus be viewed as a large rain gauge for the region variations of its level are indicative of the climate variations in the region here we present the decadal to centennialresolution holocene lake level curve of the dead sea then we determine the regional hydroclimatology that affected level variations to achieve this goal we compare modern natural lake level variations and instrumental rainfall records and quantify the hydrology relative to lake level rise fall or stability to quantify that relationship under natural conditions rainfall data pre dating the artificial dead sea level drop since the 1960s are used in this respect jerusalem station offers the longest uninterrupted pre 1960s rainfall record and jerusalem rains serve as an adequate proxy for the dead sea headwaters rainfall principal component analysis indicates that temporal variations of annual precipitation in all stations in israel north of the current 200 mm yr 1 average isohyet during 1940 1990 are largely synchronous and in phase 70 of the total variance explained by pc1 this station also represents well northern jordan and the area all the way to beirut lebanon especially during extreme drought and wet spells we a determine the modern and propose the past regional hydrology and eastern mediterranean em climatology that affected the severity and length of droughts wet spells associated with multiyear episodes of dead sea level falls rises and b determine that em cyclone tracks were different in average number and latitude in wet and dry years in jerusalem the mean composite sea level pressure and 500 mb height anomalies indicate that the potential causes for wet and dry episodes span the entire em and are rooted in the larger scale northern hemisphere atmospheric circulation we also identified remarkably close association within radiocarbon resolution between climatic changes in the levant reflected by level changes and culture shifts in this region

boundary layer effects above a himalayan valley near mount everest 1 periodical wind profiler and radio acoustic sounding system observations have been commenced at the himalayas northern slope nearby mount everest in september 2005 primarily data sets obtained 25 km remote from the glacier edge are utilized for a preliminary discussion of planetary boundary layer circulation resembling high alpine mountainous regions substantial findings include the detection of two wind shears and the phenomenon of glacier wind at a distance of 25 km from the glaciers the latter lead to a reversed compensatory flow in a vertical scale of up to 2000 m above ground level pointing at supra regional impact

a novel radiocarbon dating technique applied to an ice core from the alps indicating late pleistocene ages ice cores retrieved from high altitude glaciers are important archives of past climatic and atmospheric conditions in midlatitude and tropical regions because of the specific flow behavior of ice their age depth relationship is nonlinear preventing the application of common dating methods such as annual layer counting in the deepest and oldest part here we present a new approach and technique allowing dating of any such ice core at arbitrary depth for the age range between 500 years b p and the late pleistocene this new complementary dating tool has great potential for numerous ice core related paleoclimate studies since it allows improvement and extension of existing and future chronologies using small to ultrasmall sample size 100 g carbon content 5 g accelerator mass spectrometry we take advantage of the ice included water insoluble organic carbon fraction of carbonaceous aerosols for radiocarbon 14c dating analysis and dating of the bottom ice of the colle gnifetti glacier swiss italian alps 45 55 50 n 7 52 33 e 4455 m asl has been successful in a first application and the results revealed the core to cover most of the holocene at the least with indication for late pleistocene ice present at the very bottom

boundary layer evolution and regional scale diurnal circulations over the and mexican plateau data collected in a measurement campaign in february and march 1997 showed that the mexico basin also called the valley of mexico located atop the mexican plateau fails to develop the strong nocturnal inversions usually associated with basins and does not exhibit diurnally reversing valley wind systems data analyses two and three dimensional numerical simulations with the regional atmospheric modeling system rams and a lagrangian particle dispersion model are used to interpret these observations and to examine the effects of topography and regional diurnal circulations on boundary layer evolution over the mexico basin and its surroundings during fair weather periods in the winter dry season we show that the boundary layer evolution in and above the basin is driven primarily by regional diurnal circulations that develop between the air above the mexican plateau and the generally cooler surrounding coastal areas a convective boundary layer cbl grows explosively over the plateau in the late morning to reach elevations of 2250 m agl 4500 m msl by noon and a strong baroclinic zone forms on the edges of the plateau separating the warm cbl air from its cooler surroundings in early afternoon the rates of heating and cbl growth are slowed as cool air leaks onto the plateau and into the basin through passes and over low lying plateau edges the flow onto the plateau is retarded however by the strongly rising branch of a plain plateau circulation at the plateau edges especially where mountains or steep slopes are present an unusually rapid and deep cooling of the air above the plateau begins in late afternoon and early evening when the surface energy budget reverses the cbl decays and air accelerates onto the plateau through the baroclinic zone flow convergence near the basin floor and the associated rising motions over the basin and plateau produce cooling in 3 hours that is equivalent to half the daytime heating while the air that converges onto the plateau comes from elevations at and above the plateau it is air that was modified earlier in the day by a cool moist coastal inflow carried up the plateau slopes by the plain plateau circulation

the temperature of europe during the holocene reconstructed from pollen data we present the first area average time series reconstructions of warmest month coldest month and mean annual surface air temperatures across europe during the last 12 000 years these series are based on quantitative pollen climate reconstructions from over 500 pollen sites assimilated using an innovative four dimensional gridding procedure this approach combines three dimensional spatial gridding with a fourth dimension represented by time allowing data from irregular time series to be focussed onto a regular time step we provide six regional reconstructed temperature time series as well as summary time series for the whole of europe the results suggest major spatial and seasonal differences in holocene temperature trends within a remarkably balanced regional and annual energy budget the traditional mid holocene thermal maximum is observed only over northern europe and principally during the summer this warming was balanced by a mid holocene cooling over southern europe whilst central europe occupied an intermediary position changes in annual mean temperatures for europe as a whole suggest an almost linear increase in thermal budget up to 7800 bp followed by stable conditions for the remainder of the holocene this early holocene warming and later equilibrium has been mainly modulated by increasing winter temperatures in the west which have continued to rise at a progressively decreasing rate up to the present day

the alpine iceman and holocene climatic change abstract the finding of a prehistoric mummified corpse at the upper edge of the accumulation area of an alpine glacier together with its unique set of artifacts provided new information on glacier dimensions during the little known phases of major glacier shrinkage that characterized the warmest parts of the holocene the sudden burial of the corpse in a permanent snow cover occurred 5300 5050 cal yr b p indicating a significant climatic change that induced glacier expansion at the beginning of neoglaciation new geomorphologic data and two ams14c ages from buried soils suggest that the present glacier size following over 100 yr of shrinkage is comparable to that immediately preceding neoglaciation therefore we can deduce that the current global climatic warming may have interrupted the environmental conditions prevailing in the alps during neoglacial time restoring characteristics similar to those prevailing during theclimatic optimumthat were never achieved during the second half of the holocene

internal accumulation in firn and its significance for the mass balance of storglaciaren sweden the discussion on global change has led to increased interest in glacier mass balance since glaciers can be used as climatic indicators to meet the need for high quality mass balance data requires critical examination of traditional mass balance methods and their possible errors one issue regarding mass balance measurements that has received little attention is internal accumulation our study shows that internal accumulation in the firn layer of storglaciaren sweden significantly affects the mass balance of the glacier this occurs because the winter cold wave penetrates below the previous year s summer surface and into underlying firn we estimated internal accumulation from measurements of temperature and water content in firn the depth of the 0 c isotherm correlated with snow depth and air temperature so that low snow depth and low air temperature separately cause a deeper 0 c isotherm we determined irreducible gravimetric water content in firn to 2 3 which corresponds to an irreducible water saturation of 6 8 our value for firn is relatively high compared with that for snow probably due to trapped water in isolated firn pores refreezing of percolating meltwater in spring accounted for 30 of annual internal accumulation the remaining 70 was due to refreezing of retained capillary water in firn pores during winter disregarding internal accumulation would lead to underestimation of annual net mass balance by 0 04 0 06 m w e corresponding to 3 5 of annual accumulation of the entire glacier in an average year hence internal accumulation potentially becomes a source for systematic error if not accounted in mass balance measurements

recurrence pattern of holocene earthquakes along the dead sea transform revealed by varve counting and radiocarbon dating of lacustrine sediments abstract a high resolution holocene seismic history of the dead sea transform dst is established from laminated sedimentary cores recovered at the shores of the dead sea radiocarbon dating and annual laminae counting yield excellent agreement between disturbed sedimentary structures identified as seismites and the historical earthquake record all recent and historical strong events of the area were identified including the major earthquakes of a d 1927 1837 1212 1033 749 and 31 b c the total of 53 seismites recognized along the entire holocene profile indicate varying recurrence intervals of seismic activity between a few and 1000 years with a conspicuous minimum rate at 2100 31 b c and a noticeable maximum during the past six to eight centuries most of the epicenters of the correlated earthquakes are situated very close to the dead sea within 150 km or up to 400 km north of it along the dst between 1000 b c and a d 1063 and from a d 1600 to recent time the epicenters are all located on the northern segment of the dst whereas prior to 1000 b c and between a d 1000 and 1600 they appear to scatter along several segments of the dst we establish how the local intensity exerts a control on the formation of seismites at historically estimated intensities greater than vii all well documented earthquakes are correlated whereas at intensities smaller than vi none are matching the periods with enhanced earthquake rate along the dst correlate with those along the north anatolian fault as opposed to the intervening east anatolian fault this may indicate some elastic coupling on plate boundary scale that may also underlie escape and extrusion tectonics typical of continental collision

bed parallel slip identifying missing displacement in mass transport deposits abstract bed parallel slip bps where neighbouring beds slide past one another along bedding planes is notoriously difficult to identify without reference to pre existing features such as steep faults or dykes that act as markers to record bps offset while bps is intuitively thought to operate during downslope sliding of mass transport deposits mtds in sedimentary basins there is a conspicuous lack of supporting outcrop or seismic data to corroborate this and bps displacement may therefore have remained unaccounted for this study addresses this gap in knowledge by investigating late pleistocene mtds developed around the dead sea basin and provides the first detailed analysis of bps that pervades a gravity driven setting in particular we examine the role of bps that crosscuts earlier normal and reverse faults that act as markers to allow metre scale patterns of horizontal displacement to be identified in mtds the studied bps always forms with a consistent top to the east sense of offset that corresponds with gravity driven downslope movement towards the depo centre of the basin bps frequently develops adjacent to competent detrital rich beds and forms discrete glide planes with little or no visible deformation in sediments on either margin although detachment folds are occasionally developed above the slip plane and confirm directions of easterly movement early downslope dipping normal faults that are cut by later bps planes results in older over younger stratigraphic relationships across the bps surface together with sawtooth patterns where multiple bps planes have developed conversely early upslope dipping normal faults that are cut by bps create younger over older stratigraphic relationships combined with missing section and staircase patterns where multiple bps planes exist as bps in sub horizontal sequences does not have a vertical component of displacement it may be examined in terms of horizontal heave bps increases heave in upslope dipping normal faults whereas it reduces heave in downslope dipping normal faults and may even become negative where sections are repeated across sawtooth profiles in addition bps increases heave in upslope dipping reverse thrust faults and reduces heave across downslope dipping backthrusts although individual bps planes may have limited displacement the net consequence of multiple planes of bps that form in the shallow subsurface is to distort patterns and estimates of extension and contraction across fault zones in mtds

the effects of meltwater percolation on the seasonal isotopic signals in an arctic snowpack we investigate the evolution of snow temperature water content density and stable water isotopes of 18 o at four arctic snow pit sites during early season melt in order to understand the effects of melt on snowpack stratigraphies and seasonal isotopic signals we relate isotopic changes observed at these sites to temperature reconstructions derived from a 33 year firn core record drilled on the same icefield decreases in seasonal isotopic amplitudes observed at all but one snow pit site coincide with the percolation of more enriched meltwater into the snowpack suggesting that meltwater percolation is the dominant process causing isotopic redistribution in arctic snowpacks during the melt season the decrease in isotopic range was accompanied by increases in mean 18 o values at all snow pit sites positive degree day pdd calculations are used to relate the amount of melt observed at the low elevation snow pit sites to the firn core site results based on pdd values suggest an average overestimation of 1 1 c in average annual temperature reconstructions from the firn core site from 1967 to 2006 with the possibility of errors in excess of 3 c during high melt years

on the theory of sea floor conductivity mapping using transient electromagnetic systems the electrical conductivity of the sea floor is usually much less than that of the seawater above it a theoretical study of the transient step on responses of some common controlled source electromagnetic systems to adjoining conductive half spaces shows that two systems the horizontal in line electric dipole dipole and horizontal coaxial magnetic dipole dipole are capable of accurately measuring the relatively low conductivity of the sea floor in the presence of seawater for these systems the position in time of the initial transient is indicative of the conductivity of the sea floor while at distinctly later times a second characteristic of the transient is a measure of the seawater conductivity the diagnostic separation in time between the two parts of the transient response does not occur for many other systems including several systems commonly used for exploration on land a change in the conductivity of the sea floor produces a minor perturbation in what is essentially a seawater response some transient responses which could be observed with a practical deep towed coaxial magnetic dipole dipole system located near the sea floor are those for the half space the layer over a conductive or resistive basement and the half space with an intermediate resistive zone the system response to two adjoining half spaces representing seawater and sea floor respectively is derived analytically the solution is valid for all time provided the conductivity ratio is greater than about ten or less than about one tenth the analytic theory confirms the validity of numerical evaluations of closed form solutions to these layered earth models a lateral conductor such as a vertical infinite conductive dike outcropping at the sea floor delays the arrival of the initial crustal transient response the delay varies linearly with the conductance of the dike this suggests that time delay could be inverted directly to give a measure of the anomalous integrated conductance of the sea floor both between and in the vicinity of the transmitter and the receiver dipoles

detection of near surface horizontal anisotropy in a weathered metamorphic schist at llano uplift texas by transient electromagnetic induction abstract the use of transient controlled source electromagnetic prospecting to detect buried steeply dipping foliation in metamorphic rocks is illustrated with data acquired over the precambrian packsaddle schist in the llano uplift of central texas the azimuthal variation of the transient voltage at a given transmitter receiver separation about a fixed central point is consistent with the forward model response of a homogeneous halfspace exhibiting horizontal electrical anisotropy the loop loop exploration configuration is ideally suited to probe horizontal anisotropy a quantitative match of the forward response to the observed data produces reasonable electrical conductivity values and coefficient of anisotropy for resistive crystalline geological materials the most conductive direction consistently lies within a few degrees of the geologically mapped foliation strike direction the electrical anisotropy is strongest below the near surface weathered layer within the more competent bedrock the agent responsible for generating the anistropy cannot be definitively determined because it is likely to be a combination of geological factors such as weathering compositional banding and microcracking all of which enhance electrical conductivity parallel to the plane of foliation the transient electromagnetics is supplemented by dc resistivity and seismic surveys the elastic anisotropy is evident in the near surface weathered layer but it may not persist very deep into the underlying competent schist the exposure of foliated schist at the surface is not sufficient to rule out a possible role for systematically aligned macrofracture sets as a secondary cause of the observed anisotropy

sinkholes subsidence and subrosion on the eastern shore of the dead sea as revealed by a close range photogrammetric survey abstract ground subsidence and sinkhole collapse are phenomena affecting regions of karst geology worldwide the rapid development of such phenomena around the dead sea in the last four decades poses a major geological hazard to the local population agriculture and industry nonetheless many aspects of this hazard are still incompletely described and understood especially on the eastern dead sea shore in this work we present a first low altitude our analysis reveals a kilometer scale sinuous depression bound partly by flexure and partly by non tectonic faults the estimated minimum volume loss of this subsided zone is 1 83 106 m3 with an average subsidence rate of 0 21 m yr 1 over the last 25 years sinkholes in the surveyed area are localized mainly within this depression the sinkholes are commonly elliptically shaped mean eccentricity 1 31 and clustered nearest neighbor ratio 0 69 their morphologies and orientations depend on the type of sediment they form in in mud sinkholes have a low depth to diameter ratio 0 14 and a long axis azimuth of nne ne in alluvium sinkholes have a higher ratio 0 4 and are orientated nnw n from field work we identify actively evolving artesian springs and channelized sediment laden groundwater flows that appear locally in the main depression consequently subrosion i e subsurface mechanical erosion is identified as a key physical process in addition to dissolution behind the subsidence and sinkhole hazard furthermore satellite image analysis links the development of the sinuous depression and sinkhole formation at ghor al haditha to preferential groundwater flow paths along ancient and current wadi riverbeds