detection of potential fields source boundaries by enhanced horizontal derivative method a high resolution method to image the horizontal boundaries of gravity and magnetic sources is presented the enhanced horizontal derivative ehd method the ehd is formed by taking the horizontal derivative of a sum of vertical derivatives of increasing order the location of ehd maxima is used to outline the source boundaries while for gravity anomalies the method can be applied immediately magnetic anomalies should be previously reduced to the pole we found that working on reduced to the pole magnetic anomalies leads to better results than those obtainable by working on magnetic anomalies in dipolar form even when the magnetization direction parameters are not well estimated this is confirmed also for other popular methods used to estimate the horizontal location of potential fields source boundaries the ehd method is highly flexible and different conditions of signal to noise ratios and depths to source can be treated by an appropriate selection of the terms of the summation a strategy to perform high order vertical derivatives is also suggested this involves both frequency and space domain transformations and gives more stable results than the usual fourier method the high resolution of the ehd method is demonstrated on a number of synthetic gravity and magnetic fields due to isolated as well as to interfering deep seated prismatic sources the resolving power of this method was tested also by comparing the results with those obtained by another high resolution method based on the analytic signal the success of the ehd method in the definition of the source boundary is due to the fact that it conveys efficiently all the different boundary information contained in any single term of the sum application to a magnetic data set of a volcanic area in southern italy helped to define the probable boundaries of a calderic collapse marked by a number of magmatic intrusions previous interpretations of gravity and magnetic fields suggested a subcircular shape for this caldera the boundaries of which are imaged with better detail using the ehd method

late glacial stage and holocene tropical ice core records from huascaran peru two ice cores from the col of huascaran in the north central andes of peru contain a paleoclimatic history extending well into the wisconsinan wurm glacial stage and include evidence of the younger dryas cool phase glacial stage conditions at high elevations in the tropics appear to have been as much as 8 to 12 c cooler than today the atmosphere contained about 200 times as much dust and the amazon basin forest cover may have been much less extensive differences in both the oxygen isotope ratio 18o 8 per mil and the deuterium excess 4 5 per mil from the late glacial stage to the holocene are comparable with polar ice core records these data imply that the tropical atlantic was possibly 5 to 6 c cooler during the late glacial stage that the climate was warmest from 8400 to 5200 years before present and that it cooled gradually culminating with the little ice age 200 to 500 years before present a strong warming has dominated the last two centuries

structural overprinting criteria determined from regional aeromagnetic data an example from the hill end trough east gondwana abstract determining overprinting relationships in the geological record has underpinned our understanding of the evolution of the earth and has provided the context in which to interpret geoscientific datasets geological overprinting relationships are generally determined from outcrop relationships when outcrop is absent or limited overprinting relationships using geological observations is often ineffective or ambiguous we show how aeromagnetic data can be used to inform superposition of geological structures using a combination of folded stratigraphy faults both high angle and low angle and plutons from the well exposed hill end trough in the phanerozoic eastern lachlan orogen overprinting relationships reveal episodic inversion of the late silurian to early devonian back arc basin succession preserved within the hill end trough occurred during superimposed shortening events the first event resulted in the development of regional folds associated with the tabberabberan orogeny and the second event resulted in the development of overprinting north south and north northwest trending faults during the early carboniferous kanimblan orogeny inversion structures are overprinted by a carboniferous granite which is overprinted by previously unrecognised northeast and northwest conjugate faults which we interpret to be related to the permo triassic hunter bowen orogeny

the influence of continental ice atmospheric co2 and land albedo on the climate of the last glacial maximum the contributions of expanded continental ice reduced atm9spheric co2 and changes in land albedo to the maintenance of the climate of the last glacial maximum lgm are examined a series of experiments is perform ed using an atmosphere mixed layer ocean model in which these changes in boundary conditions are incorporated either singly or in combination the model used has been shown to produce a reasonably reajistic simulation of the reduced temperature of the lgm manabe and broccoli 1985 by comparing the results from pairs of ex periments the effects of each of these envirornnental changes can be determined expanded continental ice and reduced atmospheric co2 are found to have a substantial impact on global mean temperature the ice sheet effect is confined almost ex clusively to the northern hemisphere while lowered co2 cools both hemispheres changes in land albedo over ice free areas have only a minor thermal effect on a global basis the reduction of co2 content in the atmosphere is the primary contributor to the cooling of the southern hemisphere the model sensitivity to both the ice sheet and co2 effects is characterized by a high latitude amplification and a late autumn and early winter maximum

stable isotope based paleoaltimetry abstractthe quantitative estimation of paleoaltitude has become an increasing focus of earth scientists because surface elevation provides constraints on the geodynamic mechanisms operating in mountain belts as well as the influence of mountain belt growth on regional and global climate the general observation of decreasing 18o and 2h values in rainfall as elevation increases has been used in both empirical and theoretical approaches to estimate paleoelevation these studies rely on the preservation of ancient surface water compositions in authigenic minerals to reconstruct the elevation at the time the minerals were forming in this review we provide a theory behind the application of stable isotope based approaches to paleoaltimetry we apply this theory to test cases using modern precipitation and surface water isotopic compositions to demonstrate that it generally accords well with observations examples of the application of paleoaltimetry techniques to himalaya tibet and the andes are discussed

high resolution variability of the south american summer monsoon over the last seven millennia insights from a speleothem record from the central peruvian andes stable oxygen isotope d 18 o measurements of two speleothems collected from huagapo cave in the central peruvian andes and with overlapping age from 1 1 to 1 4 ka characterize tropical south american climate variability over the last 7150 years in the study region precipitation d 18 o d 18 op is inversely correlated to rainfall amount upstream in the amazon basin and the intensity of convection associated with the south american summer monsoon sasm speleothem long axis profiles yield an average age resolution of five years and permit investigation of climate over orbital to decadal timescales variations in the isotopic composition of huagapo cave calcite d 18 oc are in good agreement with several pre

tropical boundary layer equilibrium in the last ice age a radiative convective boundary layer model is used to assess the effect of changing sea surface temperature pressure wind speed and the energy export from the tropics on the boundary layer equilibrium equivalent potential temperature it remains difficult to reconcile the observations that during the last glacial maximum 18 000 yr bp the snowline on the tropical mountains fell 950 m while the tropical sea surface temperatures fell only 1 2 k

empirical relationships between elevation and the stable isotope composition of precipitation and surface waters considerations for studies of paleoelevation change a compilation of 68 studies from throughout many of the world s mountain belts reveals an empirically consistent and linear relationship between change in elevation and change in the isotopic composition of precipitation along altitudinal transects the isotopic composition of precipitation decreases linearly with increasing elevation in most regions of the world except in the himalayas and at elevations 5000 m there are no significant differences in isotopic lapse rates from most regions of the world 0 28 permil 100 m except at the extreme latitudes where isotopic lapse rates are higher given information on past changes in the isotopic composition of precipitation preserved in pedogenic or authigenic minerals this global isotopic lapse rate can be used to place numerical constraints on the topo graphic development of some ancient mountain belts or plateaus there are many complicating factors that can confound interpretation of paleoel evation change based on stable isotopes and many of these are unique to specific mountain belts or time periods relevant to all stable isotope based paleoelevation change studies is the temperature dependent isotope fractionation between a pedo genic or authigenic mineral and the water from which it forms in cases where isotopic proxy minerals are sampled from localities where temperature will change simulta neously with elevation change the apparent change in the isotopic composition of precipitation may be dampened by several permil this suggests that samples taken from the rainshadow side of an emerging orographic barrier may be more likely to preserve isotopic changes resulting from mountain uplift than samples taken from atop a rising mountain range or plateau

edge enhancement of potential field data using normalized statistics edge enhancement in potential field data helps geologic interpretation there are many methods for enhancing edges most of which are high pass filters based on the horizontal or vertical derivatives of the field normalized standard deviation nstd a new edge detection filter is based on ratios of the windowed standard deviation of derivatives of the field nstd is demonstrated using aeromagnetic data from australia and gravity data from south africa compared with other filters the nstd filter produces more detailed results

evolution of reworked paleoproterozoic basement rocks within the ribeira belt neoproterozoic se brazil based on u pb geochronology implications for paleogeographic reconstructions of the sao francisco congo paleocontinent abstract geological geochemical and geochronological data suggest that the basement exposed in the occidental terrane of the neoproterozoic ordovician ribeira belt represents the continuation of the sao francisco paleocontinent which was amalgamated at the end of the rhyacian transamazonian orogeny the mantiqueira complex represents a cordilleran type active margin of the archean paleocontinent while the juiz de fora complex represents juvenile paleoproterozoic material probably developed within an oceanic setting primitive arc or plateau the latter unit was probably accreted to the active margin of the paleocontinent during the latest stages of the transamazonian orogeny around ca 2 05 ma causing the deformation and metamorphism of the mantiqueira complex at this time to the west and on the cratonic foreland concurrent deformation of the minas passive margin and sedimentation of the sabara basin took place subsequent to the transamazonian orogeny the basement associations were intruded by intraplate alkaline and basic rocks related to rifting events between ca 1 7 and 1 3 ga that resulted in the development of intracratonic basins the paleoproterozoic suture located between the mantiqueira and juiz de fora paleoproterozoic terranes probably controlled the neoproterozoic passive margin tectonics and also the development of a major thrust surface during the neoproterozoic cambrian brasiliano convergence

tilt depth method a simple depth estimation method using first order magnetic derivatives aeromagnetic data are routinely presented as contour or color shaded maps of the total magnetic intensity tmi an interpreter s task is to identify features anomalies contained within the map and qualitatively and or quantitatively interpret them into geologic structures at depth if the map contains anomalies that have large magnetic intensities the bodies might be considered to have large magnetizations or to be at shallow depths small amplitude anomalies superimposed on these anomalies could be masked or even missed by an interpreter thus the task of the interpreter is to use the spectral content of the anomalies to try and resolve these ambiguities part of this process is also to obtain estimates of the depth and shape of the body causing the anomalies

structural framework from gravity and magnetic data in the paleo mesoproterozoic arai rift sag basin central brazil the arai basin comprises a paleo mesoproterozoic rift sag basin inverted in a thick skinned regime during brasiliano orogeny its depth to basement geometry and lateral extension remains unknown this work aims to provide this information based on geophysical integrated to geological data to clarify its main structures and evolution understanding gravity and magnetic data allowed us to delineate the rift system its major faults and adjacent post rift sedimentary structures over its entire length the geophysical investigation included radial power spectrum analysis and euler deconvolution besides the application of edge structures enhancement filters on magnetic anomaly and matched filter grids a 2 5d forward gravity model was generated using all results with geophysical sources at depths 35 42 km 20 9 22 6 km 11 15 6 km 9 68 km 8 2 3 km and 0 37 0 54 km respectively interpreted as mohorovicic discontinuity curie surface conrad discontinuity granitic intrusions basement depths

enhancement of the total horizontal gradient of magnetic anomalies using the tilt angle abstractmagnetic anomaly maps reflect the spatial distribution of magnetic sources which may be located at different depths and have significantly different physical and geometrical properties complicating the identification of the corresponding geologic structures filtering techniques are frequently used to balance anomalies from shallow and deep sources and to enhance certain features of interest such as the edges of the causative bodies most methods used for enhancing magnetic data are based on vertical or horizontal derivatives of the magnetic anomalies or combinations of them and the edges or centers of the sources are identified by maxima minima or null values in the transformed data normalized derivatives methods are used to equalize signals from sources buried at different depths we present an edge detector method for the enhancement of magnetic anomalies which is based on the tilt angle of the total horizontal gradient the notable features of this method are that it produces amplitud

constraints on southern hemisphere tropical climate change during the little ice age and younger dryas based on glacier modeling of the quelccaya ice cap peru 2015 the authors improving the late quaternary paleoclimate record through climate interpretations of low latitude glacier length changes advances our understanding of past climate change events and the mechanisms for past present and future climate change paleotemperature reconstructions at low latitude glaciers are uniquely fruitful because they can provide both site specific information and enhanced understanding of regional scale variations due to the structure of the tropical atmosphere we produce little ice age lia and younger dryas yd paleoclimate reconstructions for the huancane outlet glacier of the quelccaya ice cap qic and low latitude southern hemisphere regional sea surface temperatures ssts using a coupled ice flow and energy balance model we also model the effects of long term changes in the summit temperature and precipitiation rate and the effects of interannual climate variability on the huancane glacier length we find temperature to be the dominant climate driver of glacier length change also we find that interannual climate variability cannot adequately explain glacier advances inferred from the geomorphic record necessitating that these features were formed during past colder climates to constrain our lia reconstruction we incorporate the qic ice core record finding a lia air temperature cooling at the ice cap of between 0 7 c and 1 1 c and 0 4 c and regional ssts cooling of 0 6 c for the yd paleoclimate reconstructions we propose two limits on the precipitation rate since the ice core record does not extend into the pleistocene 1 the precipitation rate scales with the clausius clapeyron relationship upper limit on cooling and 2 the precipitation rate increases by 40 lower limit on cooling which is an increase about twice as great as the regional increases realized in gcm simulations for the period the first limit requires 1 6 c cooling in ice cap air temperatures and 0 9 c cooling in ssts and the second limit requires 1 0 c cooling in ice cap air temperatures and 0 5 c cooling in ssts our temperature reconstructions are in good agreement with the magnitude and trend of gcm simulations that incorporate the forcing mechanisms hypothesized to have caused these climate change events

cool tropical temperatures shift the global δ18o t relationship an explanation for the ice core δ18o borehole thermometry conflict the discrepancy between central greenland borehole temperatures and the isotopic composition of last glacial maximum ice can be explained by a shift in the 5180 t relationship for the hydrological cycle linked to cooler tropical temperatures this concept is illustrated using a simple rayleigh distillation model an estimate for o a 5180 at lgm holocene of 0 37 o oc is determined with a simple graphical technique

mechanisms of abrupt climate change of the last glacial period 1 more than a decade ago ice core records from greenland revealed that the last glacial period was characterized by abrupt climate changes that recurred on millennial time scales since their discovery there has been a large effort to determine whether these climate events were a global phenomenon or were just confined to the north atlantic region and also to reveal the mechanisms that were responsible for them in this paper we review the available paleoclimate observations of abrupt change during the last glacial period in order to place constraints on possible mechanisms three different mechanisms are then reviewed ocean thermohaline circulation sea ice feedbacks and tropical processes each mechanism is tested for its ability to explain the key features of the observations particularly with regard to the abruptness millennial recurrence and geographical extent of the observed changes it is found that each of these mechanisms has explanatory strengths and weaknesses and key areas in which progress could be made in improving the understanding of their long term behavior both from observational and modeling approaches are suggested finally it is proposed that a complete understanding of the mechanisms of abrupt change requires inclusion of processes at both low and high latitudes as well as the potential for feedbacks between them some suggestions for experimental approaches to test for such feedbacks with coupled climate models are given

holocene hydrologic balance of tropical south america from oxygen isotopes of lake sediment opal venezuelan andes precipitation in the south american andes is derived from atlantic ocean evaporation which is modified by passage over lowland south america the isotopic composition of andean precipitation reflects evaporation conditions over the atlantic ocean moisture recycling during advection across the south american lowlands and uplift to the andes records of the oxygen isotope composition of precipitation in the venezuelan andes derived from lake sediment diatom 18 o measurements show a 2 4 decrease during the past 10 000 yr a simple model of the evaporation advection and uplift processes is used to understand the cause of the isotope shift the data and model suggest that the decreasing 18 o reflects a decrease in the fraction of moisture entering south america that reaches the andes ice cores from peru and bolivia exhibit similar isotope trends indicating that the shift occurred in both hemispheres an isotopic record of amazon river discharge is consistent with the andean records indicating increasing continental runoff was associated with the decreasing export of water vapor orbital changes in solar insolation cannot explain the synchronous trends in both hemispheres changing climate in the tropical pacific is an attractive explanation for the trends because modern interannual variability in this region has similar effects in both hemispheres

an abrupt decrease in southern hemisphere terrestrial temperature during the eocene oligocene transition abstract earth s climate transitioned from the greenhouse conditions of the eocene to the icehouse of the oligocene 34 million years ago global cooling was triggered by a decrease in atmospheric pco2 and is associated with the first appearance of large permanent ice sheets on antarctica the eocene oligocene transition eot is marked by a large two step increase in the 18 o of benthic foraminifera reflecting a combination of cooler global temperatures and continental ice growth we measured the hydrogen isotope composition of hydrated volcanic glasses deposited in patagonia during the eot to reconstruct stable isotope hydrology and associated changes in temperature during this critical climate transition these data show changes in stable hydrogen isotope ratios that are consistent with patagonian terrestrial mean annual temperature decreasing by 5 c during the eot before returning to 2 c below pre eot values by the early oligocene this is approximately synchronous with northern hemisphere cooling during the eot and indicates close coupling of temperature and atmospheric pco2

edge enhancement of potential field data using spectral moments abstractedge enhancement in potential field data helps geologic interpretation where the lineaments on the potential field frequently indicate subsurface faults contacts and other tectonic features therefore a variety of edge enhancement methods have been proposed for locating edges most of which are based on the horizontal or vertical derivatives of the field however these methods have several limitations including thick detected boundaries blurred response to low amplitude anomalies and sensitivity to noise we have developed the spectral moment method for detecting edges in potential field anomalies based on the second spectral moment and its statistically invariable quantities we evaluated the spectral moment method using synthetic gravity data egm 2008 gravity data and the total magnetic field reduced to the pole compared with other edge enhancing filters such as the total horizontal derivative tdx profile curvature curvature of the total horizontal gradient amplitude enhancement

glacial interglacial dynamics of the eastern equatorial pacific cold tongue intertropical convergence zone system reconstructed from oxygen isotope records record mean late holocene lh last glacial maximum lgm d 18 o amplitudes ranging between 1 0 and 1 3 we estimate that mean sea surface temperatures sst in this region during the lgm were on average 1 5 0 5 c lower than the lh larger d 18 o amplitudes are observed in sites north of the equator indicating a spatial pattern of reduced meridional sst gradient across the equator during the lgm this result is supported by comparison of mg ca sst reconstructions from two sites straddling the equator we interpret the reduction of this gradient during the lgm as evidence for a less intense cold tongue intertropical convergence zone itcz frontal system a more southerly position of the itcz and weaker southeast equatorial trades in the eep indexterms 1620 global change climate dynamics 3309 3339 meteorology and atmospheric dynamics ocean atmosphere interactions 0312 4504 3344 meteorology and atmospheric dynamics paleoclimatology 4231 oceanography general equatorial oceanography 4267 oceanography general paleoceanography keywords cold tongue itcz oxygen isotopes tropical pacific

altitudinal variation of the stable isotopes of snow in regions of high relief a major discontinuity in the variation of 18 o d with altitude in high mountains was first seen in data from mount logan yukon territory canada holdsworth and others 1991 the profile of vs altitude revealed three well defined regions 1 a lower monotonic fractionation sequence below 3 km 2 a middle layer typically 1 2 km thick within which values are nearly constant or stepped with altitude and 3 part of another fractionation sequence in the quasi geostrophic flow region above 5 3 km the middle region was inferred to be a mixed layer combining moisture from regions 1 and 3 this type of structure is now seen to occur on other high altitude mountains including cerro aconcagua argentina where observations reach almost 7 km the new observations confirm the general occurrence of a multi layered atmosphere during precipitation at high altitude glacier sites this structure is linked to synoptic scale polar cyclones where the middle layer is identified as being the signature of the warm front zone these results have implications for the common practice of using a specific spatially derived isotopic thermometer in the time domain for the paleoclimatic interpretation of high altitude ice core records

last glacial maximum equilibrium line altitude and paleo temperature reconstructions for the cordillera de merida venezuelan andes abstract the pattern and magnitude of glacier equilibrium line altitude ela lowerings in the tropics during the last glacial maximum lgm are topics of current debate in the northern tropics paleo ela data are particularly limited inhibiting the ability to make regional and large scale paleoclimatic inferences to improve these records nine paleo glaciers in the venezuelan andes were reconstructed based on field observations aerial photographs satellite imagery and high resolution digital topographic data paleo glacier equilibrium line altitudes elas were estimated using the accumulation area ratio aar and the area altitude balance ratio aabr methods during the local lgm in venezuela 22 750 to 19 960 cal yr bp elas were 850 to 1420 m lower than present local lgm temperatures were are at least 8 8 2 c cooler than today based on a combined energy and mass balance equation to account for an ela lowering this is greater than estimates using an atmospheric lapse rate calculation which yields a value of 6 4 1 c cooler the paleo glacial data from the venezuelan andes support other published records that indicate the northern tropics experienced a greater ela lowering and possibly a greater cooling than the southern hemisphere tropics during the lgm

depth estimation for magnetic gravity anomaly using model correction the tilt depth method has been widely used to determinate the source depth of a magnetic anomaly in the present study we deduce similar tilt depth methods for both magnetic and gravity data based on the contact and sphere models and obtain the same equation for a gravity anomaly as that for a magnetic anomaly the theoretical equations and the model tests show that the routine tilt depth method would result in unreliable depth estimation for deep sources this is due to that the contact model is no longer valid for causative sources under the condition in which the depths of causative sources are significantly larger than their horizontal lengths accordingly we suggest that the tilt depth derived from the contact model can be used to detect a shallow source whereas the tilt depth derived from the sphere model can be used to detect a deep source we propose a weighting method based on the estimated depths from both the contact model and the sphere model to estimate the depth for real data the model tests suggest that the determined depths from the contact model and the sphere model are shallower and deeper respectively than the real depth while the estimated depth from the proposed method is more close to the actual depth in the application to the weigang iron ore located in jiangsu province china the routine tilt depth method results in 76 relative error whereas the proposed method obtains the reliable depth estimation compared with the drill holes in addition the proposed method works well in the application for the shijiaquan iron ore located in shandong province china these results indicate that the proposed weighting equation is a general improvement

holocene and last interglacial climate of the faroe islands from sedimentary plant wax hydrogen and carbon isotopes abstract the last interglacial period lig is earth s most recent globally warm period and is analogous in some ways to projected future global warming however questions remain regarding the state of the climate during the lig in the north atlantic a region that is extremely sensitive to changes in oceanic and atmospheric circulation here we present hydrogen and carbon isotope d and 13c records from a suite of plant wax biomarkers preserved in holocene and lig lacustrine sediments from the north atlantic faroe islands and interpret them as qualitative proxies for temperature and hydroclimate variability these data are used to directly compare lig and holocene climate using the same proxy approaches from the same terrestrial location measuring multiple isotopes on multiple types of waxes elucidates the sources of homologous plant waxes we deduce that the d values of long chain n alkanes c27 c33 and mid chain n alkanes c23 c25 in these sedimentary archives reflect leaf water and lake water d values respectively while the d values for both long chain c28 c30 and mid chain n alkanoic acids c24 c26 primarily represent lake water d values plant wax inferred d values of precipitation during the early holocene 10 100 to 8 200 cal yr bp are 35 more positive than late holocene values and decline over the holocene d inferred hydrologic change and 13c inferred plant water use efficiency both indicate that the faroe islands became drier throughout the holocene comparison with measurements from lig plant waxes indicates that late lig in the faroe islands was hydrologically similar to the early to mid holocene 8 200 to 4 000 cal yr bp with enriched precipitation isotopes and reduced evapotranspiration indicating a warmer wetter environment

a 60 000 year record of hydrologic variability in the central andes from the hydrogen isotopic composition of leaf waxes in lake titicaca sediments abstract a record of the hydrogen isotopic composition of terrestrial leaf waxes d wax in sediment cores from lake titicaca provides new insight into the precipitation history of the central andes and controls of south american summer monsoon sasm variability since the last glacial period comparison of the d wax record with a 19 kyr d record from the nearby illimani ice core supports the interpretation that precipitation d is the primary control on d wax with a lesser but significant role for local evapotranspiration and other secondary influences on d wax the titicaca d wax record confirms overall wetter conditions in the central andes during the last glacial period relative to a drier holocene during the last deglaciation abrupt d wax shifts correspond to millennial scale events observed in the high latitude north atlantic with dry conditions corresponding to the bolling allerod and early holocene periods and wetter conditions during late glacial and younger dryas intervals we observe a trend of increasing monsoonal precipitation from the early to the late holocene consistent with summer insolation forcing of the sasm but similar hydrologic variability on precessional timescales is not apparent during the last glacial period overall this study demonstrates the relative importance of high latitude versus tropical forcing as a dominant control on glacial sasm precipitation variability

magnetic data interpretation for the source edge locations in parts of the tectonically active transition zone of the narmada son lineament in central india the study has been carried out in the transition zone of the narmada son lineament nsl which is seismically active with various geological complexities upwarp movement of the mantle material into the crust through fault fractures lamination and upwelling nsl is one of the most prominent lineaments in central india after the himalaya in the indian geology the area of investigation extends from longitude 80 25 e to 81 50 e and latitude 23 50 n to 24 37 n in the central part of the indian continent different types of subsurface geological formations viz alluvial gondwana deccan traps vindhyan mahakoshal granite and gneisses groups exist in this area with varying geological ages in this study area tectonic movement and crustal variation have been taken place during the past time and which might be reason for the variation of magnetic field magnetic anomaly suggests that the area has been highly disturbed which causes the narmada son lineament trending in the ene wsw direction magnetic anomaly variation has been taken place due to the lithological variations subject to the changes in the geological contacts like thrusts and faults in this area shallow and deeper sources have been distinguished using frequency domain analysis by applying different filters to enhance the magnetic data various types of derivatives to identify the source edge locations of the causative source bodies the present study carried out the interpretation using total horizontal derivative tilt angle derivative horizontal tilt angle derivative and cos derivative map to get source edge locations the results derived from various derivatives of magnetic data have been compared with the basement depth solutions calculated from 3d euler deconvolution it is suggested that total horizontal derivative tilt angle derivative and cos derivative are the most useful tools for identifying the multiple source edge locations of the causative bodies in this tectonically active and transition zone area as this area is highly prone to hydrocarbon bearing zone hence the integrated interpretation could reliably image various thrusts and faults boundaries and the source edge locations with dip and strike orientation along with the basement lineation in encouraging exploration for better understanding of the geo scientific data

new developments of the magnetic tilt depth method to improve structural mapping of sedimentary basins this paper interprets aeromagnetic data for a deep basin section of the karroo rift in south east tanzania we use a novel integrated approach involving the application of advanced derivatives to define structure and the tilt depth method to determine and map the depth to basement in the latter case we use the result of both reduced to pole and reduced to equator data to help constrain the shape and depth of the basin we show that for a reduced to pole aeromagnetic data set the generalized form of the local phase called the tilt derivative is an effective means of providing an initial first pass mapping of a sedimentary basin in terms of its fault structure dip direction of faults and depth to basement since the amplitude of the tilt derivative does not contain information on the strength of the geomagnetic field nor magnetization other than inclination of the causative body the susceptibility contrast across faults contacts is derived from the analytic signal derivative we also investigate how effective the tilt derivative and tilt depth method are for structural and depth to basement mapping in regions close to the magnetic equator where the reduction to pole transform is often unstable this is done using the same tanzania data set transformed to the pole and the equator we find that the tilt derivative applied to the reduction to equator data cannot be used to map the structure because of the effects of magnetic anisotropy which results in the magnetic response of structures varying with strike azimuth to overcome this anisotropy problem the analytic signal and or local wavenumber derivatives which are for all practical purposes independent of inclination provide the best means of defining the major structural trends we also find that the tilt depth method provides coherent depth to basement estimates for both reduced to pole and reduced to equator data for the deep basin sections of the karroo rift there is a sparsity of tilt depth results from both the reduced to pole and reduced to equator data sets however each set of results has a different spatial coverage so when combined they provide a better spatial sampling of the long wavelength magnetic character of the basin and thus improve the constraints on the minimum curvature gridding method to map the shape and depth of the basin

is the tropical atmosphere conditionally unstable abstract we examine the mean and standard deviation of the bouyancy of lifted boundary layer parcels from a large sample of soundings from the western equatorial pacific the inclusion of condensate loading in the definition of buoyancy is emphasized as is the precise originating level of parcels in the subcloud layer we confirm the observation of betts that those parts of the tropical atmosphere experiencing deep convection are nearly neutral to adiabatic parcel ascent from the subcloud layer when adiabatic condensate loading is included in the definition of buoyancy parcels lifted from the top of the subcloud layer are more nearly neutral than those originating near the surface and atmospheres with higher levels of free convection lfcs are closer to neutral than those with low lfcs we explore possible reasons for these observations and discuss their implications for tropical meteorology

hydroclimate variability of high arctic svalbard during the holocene inferred from hydrogen isotopes of leaf waxes abstract the response of the arctic hydrologic cycle to global warming includes changes in precipitation patterns and moisture availability associated with variable sea ice extent and modes of atmospheric circulation reconstructions of past hydroclimate changes help constrain the natural range of these systems identify the manners in which they respond to different forcing mechanisms and reveal their connections to other components of the climate system all of which lead to a better understanding of present and future changes here we examine hydroclimate changes during the holocene in the high arctic archipelago of svalbard by reconstructing the isotopic composition of precipitation we measured the hydrogen isotopic composition d values of leaf wax compounds n alkanes c 25 c 31 in a sediment core from lake hakluytvatnet on the island of amsterdamoya northwest spitsbergen we interpret d values of mid chain c 25 and long chain c 29 c 31 length n alkanes to represent changes in the isotopic composition of lake water and precipitation over the last 12 9 ka after deglaciation of the catchment water supply became restricted and the lake experienced significant evaporative isotopic enrichment indicating warmer conditions from 12 8 to 7 5 ka the isotope values suggest an increase in the delivery of moisture from warmer sub polar air masses between 12 8 and 9 5 ka followed by generally warm but unstable conditions between 9 5 and 7 5 ka possibly indicating a response to meltwater forcing sedimentary evidence indicates a hiatus in deposition c 7 5 5 0 ka likely as a result of desiccation of the lake at c 5 0 ka lacustrine sedimentation resumed and over the last 5 ka there was a progressive increase in the influence of polar air masses and colder conditions which culminated in an abrupt shift to colder conditions at c 1 8 ka this late holocene cooling ended c 0 18 ka when isotopic data indicate warmer conditions and greater influence of moisture derived from lower latitudes

low latitude ice cores record pacific sea surface temperatures matic records suggested that a more conventional temperature interpretation might be more appropriate with lower isotopic values during the presumed to be cooler little ice age and increasingly enriched precipitation during the 20th century warming phase thompson 2001 3 both of these conflicting interpretations suffer from inadequate calibration of the observed isotopic record in relation to climatic conditions during periods of snow accumulation on the ice caps here we use the results of on site meteorological measurements to determine the seasonality of the ice core record and then assess how the isotopic records relate to temperature precipitation and the larger scale circulation associated with snowfall at these high elevation sites we then extend the analysis to ice core records from the asian monsoon region this empirical approach to the interpretation of the isotopic record in low latitude ice cores complements theoretical studies by broecker 1997 and pierrehumbert 1999

a coupled climate model simulation of the last glacial maximum part 2 approach to equilibrium the climate of the last glacial maximum lgm is simulated with a coupled climate model the simulated climate undergoes a rapid adjustment during the first several decades after imposition of lgm boundary conditions as described in part 1 and then evolves toward equilibrium over 900 model years the climate simulated by the coupled model at this period is compared with observationally based lgm reconstructions and with lgm results obtained with an atmosphere mixed layer slab ocean version of the model in order to investigate the role of ocean dynamics in the lgm climate global mean surface air temperature and sea surface temperature sst decrease by about 10 c and 5 6 c in the coupled model which includes ocean dynamics compared to decreases of 6 3 and 3 8 c in slab ocean case the coupled model simulates a cooling of about 6 5 c over the tropics which is larger than that of the climap reconstruction 1 7 c and larger than that of the slab ocean simulation 3 3 c but which is in reasonable agreement with some recent proxy estimates the ocean dynamics of the coupled model captures features found in the climap reconstructions such as a relative maximum of ocean cooling over the tropical pacific associated with a mean la nina like response and lead to a more realistic sst pattern than in the slab model case the reduction in global mean precipitation simulated in the coupled model is larger 15 than that simulated with the slab ocean model 10 in conjunction with the enhanced cooling some regions such as the usa and the mediterranean region experience increased precipitation in accord with proxy paleoclimate evidence the overall much drier climate over the ocean leads to higher sea surface salinity sss in most ocean basins except for the north atlantic where sss is considerably lower due to an increase in the supply of fresh water from the mississippi and amazon rivers and presumably a decrease in salt transport by the weakened north atlantic overturning circulation the north atlantic overturning stream function weakens to less than half of the control run value the overturning is limited to a shallower depth less than 1000 m and its outflow is confined to the northern hemisphere in the southern ocean convection is much stronger than in the control run leading to a stronger overturning stream function associated with enhanced antarctic bottom water formation as a result southern ocean water masses fill the entire deep ocean the antarctic circumpolar current acc transport through the drake passage increases by about 25 the acc transport despite weaker zonal winds is enhanced due to changes in bottom pressure torque the weakening of the overturning circulation in the north atlantic and the accompanying 30 decrease in the poleward ocean heat transport contrasts with the strengthening of the overturning circulation in the southern ocean and a 40 increase in heat transport as a result sea ice coverage and thickness are affected in opposite senses in the two hemispheres the lgm climate simulated by the coupled model is in reasonable agreement with paleoclimate proxy evidence the dynamical response of the ocean in the coupled model plays an important role in determining the simulated and undoubtedly the actual lgm climate

new insights into magnetic derivatives for structural mapping magnetic and gravity derivatives can be likened to seismic attributes in that they can help define estimate the physical properties of the source structure causing the anomaly this contribution looks at the tilt derivative first reported in 1994 and more recently used to derive the local wavenumber 1997 we will show that the combination of the tilt derivative and its total horizontal derivative are highly suitable for mapping shallow basement structure and mineral exploration targets and that they have distinct advantages over many conventional derivatives we provide the simple theory behind the derivatives use a range of simple 2d models to illustrate their response and apply them to mapping a mineral target in namibia

a 106ka paleoclimate record from drill core of the salar de atacama northern chile abstract a 100 m long salt core sqm 2005 from the salar de atacama northern chile 23 s 68 w a dry lake bed contains a 106 kyr paleoclimate record of hydrologic balances on the western slopes of the central andes of south america six u series disequilibrium dates range sequentially from 106 1 6 4 to 5 4 2 7 ka based on sedimentary structures and petrographic textures of salts and associated siliciclastic sediments interpretations of paleoenvironments and net hydrologic balance suggest that relatively wet periods saline lakes and expanded mudflats existed in the salar de atacama from 75 7 to 60 7 ka and from 53 4 to 15 3 ka with the wettest perennial lake interval from 26 7 to 16 5 ka short relatively wet periods also occurred in the holocene from 11 4 to 10 2 ka and from 6 2 to 3 5 ka these wet periods at salar de atacama correspond well with other late pleistocene climate records from the central andes that are a function of the net hydrologic budget the minchin tauca lake sequence from salar de uyuni bolivia is synchronous with the 53 4 15 3 ka saline lake wet period at salar de atacama the tauca phase coincided with the wettest perennial lake interval at salar de atacama from 26 7 to 16 5 ka the coipasa lake phase from uyuni was probably contemporaneous with the early holocene wet period at salar de atacama from 11 4 to 10 2 ka the early holocene wet interval at salar de atacama was also synchronous with the maximum holocene lake levels of the chilean altiplano lakes to the east and with grass rich rodent middens between 11 8 and 10 5 ka in age from the atacama basin the lake period at salar de atacama between 26 7 and 15 3 ka compares closely with low 18o values low anion concentrations and high accumulation rates from the sajama glacial ice core southwestern bolivia between 25 and 15 5 ka it is concluded that wet and dry phases were synchronous in the central andean plateau of southwestern bolivia and along the western flank of the andes of northern chile over the past 50 kyr this region which today receives its moisture from the amazon basin to the east probably also did so in the past the wet periods at salar de atacama are in phase with january insolation maxima at 15 s at 70 45 and 20 ka which suggests that past changes in summer insolation influenced precipitation patterns in the central andes however there are no major wet periods linked to the january insolation maximum at 93 ka and the present day extremely dry climate in the atacama desert is associated with a peak in summer insolation therefore there must be other important influences over precipitation in the central andes which modify the first order insolation controls

huascaran δ18o as an indicator of tropical climate during the last glacial maximum the interpretation of the isotopic composition of andes tropical mountain glaciers is reconsidered using a simple rayleigh distillation model it is shown that andes snowline depression and huascaran ice core 18o are consistent with a 3 c drop in sea surface temperature during the last glacial maximum accompanied by an increase from 40 at present to 60 during the lgm in the annual mean proportion of atmospheric water lost to continental runoff broecker s interpretation of huascaran 18o as a paleo hygrometer is discussed

ice core evidence of abrupt climate changes ice core records show that climate changes in the past have been large rapid and synchronous over broad areas extending into low latitudes with less variability over historical times these ice core records come from high mountain glaciers and the polar regions including small ice caps and the large ice sheets of greenland and antarctica

practical considerations in the use of edge detectors for geologic mapping using magnetic data abstractlocating the edges of magnetized sources provides a fundamental tool in the geologic interpretation of magnetic field data much recent effort has been expended on developing improvements to existing edge detection methods resulting in purported increases in accuracy and continuity along edges reduction of noise effects and limiting the influences of variable depth to source magnetization direction and source dip these endeavors are valuable and provide interpreters with a wider range of tools to carry out geologic interpretations of aeromagnetic data nevertheless survey parameters such as flight height and line spacing impose limits on the quality of edge locations that can be achieved using model studies we quantify the effects that source size depth and interference between sources have on calculated edge locations based on the known behavior of established edge detectors we found that many of the newer approaches offer limited advantages over older methods consequently we studi

coherent isotope history of andean ice cores over the last century 1 isotope records from andean ice cores provide detailed and high resolution climate information on various time scales however the relationship between these valuable isotope records and local or regional climate remains poorly understood here we present results from two new drillings in bolivia from the illimani and the sajama ice caps all four high altitude isotope signals in the andes now available huascaran quelccaya illimani and sajama show near identical decadal variability in the 20th century comparison with general circulation model results and meteorological data suggest that the andean high altitude records are primarily controlled by precipitation variability over the amazon basin

tropical climate changes at millennial and orbital timescales on the bolivian altiplano tropical south america is one of the three main centres of the global zonal overturning circulation of the equatorial atmosphere generally termed the walker circulation1 although this area plays a key role in global climate cycles little is known about south american climate history here we describe sediment cores and down hole logging results of deep drilling in the salar de uyuni on the bolivian altiplano located in the tropical andes we demonstrate that during the past 50 000 years the altiplano underwent important changes in effective moisture at both orbital 20 000 year and millennial timescales long duration wet periods such as the last glacial maximum marked in the drill core by continuous deposition of lacustrine sediments appear to have occurred in phase with summer insolation maxima produced by the earth s precessional cycle short duration millennial events correlate well with north atlantic cold events including heinrich events 1 and 2 as well as the younger dryas episode at both millennial and orbital timescales cold sea surface temperatures in the high latitude north atlantic were coeval with wet conditions in tropical south america suggesting a common forcing

the automatic determination of the location depth and dip of contacts from aeromagnetic data abstracta simple new method termed the contact depth method for the determination of the depth location and dip of contacts from pole reduced magnetic data was evaluated the depth was obtained by computing the horizontal derivative of the tangent of the tilt angle of the magnetic field over the contact although it is based upon the tilt depth method it does not require the distance between contour lines to be measured and it additionally allows the dip of the contact to be estimated from the gradient of the depth estimates the horizontal location of the contact is that of the zero value of the tilt angle the method uses second and third order derivatives of the magnetic field to obtain the parameters of the contact so it is sensitive to noise when tested on synthetic data and on aeromagnetic data from southern africa the method gave plausible results

automatic boundary extraction from magnetic field data using triangular meshes boundary extraction is a collective term that we use for the process of extracting the locations of faults lineaments and lateral boundaries between geologic units using geophysical observations such as measurements of the magnetic field the process typically begins with a preprocessing stage where the data are transformed to enhance the visual clarity of pertinent features and hence improve the interpretability of the data the majority of the existing methods are based on raster grid enhancement techniques and the boundaries are extracted as a series of points or line segments in contrast we set out a methodology for boundary extraction from magnetic data in which we represent the transformed data as a surface in 3d using a mesh of triangular facets after initializing the mesh we modify the node locations such that the mesh smoothly represents the transformed data and that facet edges are aligned with features in the data that approximate the horizontal locations of subsurface boundaries to illustrate our boundary extraction algorithm we first apply it to a synthetic data set we then apply it to identify boundaries in a magnetic data set from the mcfaulds lake area in ontario canada the extracted boundaries are in agreement with known boundaries and several of the regions that are completely enclosed by extracted boundaries coincide with regions of known mineralization

temperature and precipitation in the southern central andes during the last glacial maximum heinrich stadial 1 and the younger dryas abstract recent developments in terrestrial cosmogenic nuclide tcn exposure dating and the reinterpretation of tcn boulder ages from moraines have improved our understanding of the glacial chronology in the central andes according to these records glacial advances throughout the region correlate with insolation driven changes in the intensity of the south american summer monsoon and millennial scale climate events such as heinrich stadials and the younger dryas quantifying the temperature and precipitation shifts during these events helps to constrain past moisture pathways and associated changes in atmospheric circulation patterns yet particularly in the southern central andes where a wealth of glacigenic landforms attests to formerly cooler and or wetter conditions the magnitudes of past temperature and precipitation changes are only loosely constrained at a few sites here we present results from tcn dated moraines combined with the reconstruction of former glaciers and paleolakes within the eastern sector of the southern central andes 24 27 s for the last glacial maximum lgm heinrich stadial 1 hs1 and the younger dryas yd we performed monte carlo simulations with 2 dimensional models of ice flow and lake hydrology that are forced by a spatially distributed surface energy balance model our results indicate that temperatures were 3 0 4 2 c 2 0 3 3 c and 1 3 2 5 c cooler during the lgm hs1 and yd respectively in agreement with previous estimates elsewhere in the central andes we find that temperature changes during the late glacial are compatible with sea surface temperature anomalies derived from the tropical atlantic precipitation was only 5 27 greater than today which contrasts with larger anomalies reconstructed for the bolivian part of the andean plateau altiplano we attribute this discrepancy to the southerly position of our study region with respect to the bolivian high supporting the hypothesis that this atmospheric pressure system played a prominent role for south american summer monsoon dynamics during glacial episodes