crustal deformation of the eastern tibetan plateau revealed by magnetotelluric imaging the ongoing collision of the indian and asian continents has created the himalaya and tibetan plateau through a range of deformation processes these include crustal thickening detachment of the lower lithosphere from the plate delamination and flow in a weakened lower crust 1 6 debate continues as to which of these processes are most significant 7 in eastern tibet large scale motion of the surface occurs but the nature of deformation at depth remains unresolved a large scale crustal flow channel has been proposed as an explanation for regional uplift in eastern tibet 6 8 9 but existing geophysical data 10 11 do not constrain the pattern of flow magnetotellurics uses naturally occurring electromagnetic waves to image the earth s subsurface here we present magnetotelluric data that image two major zones or channels of high electrical conductivity at a depth of 20 40 km the channels extend horizontally more than 800 km from the tibetan plateau into southwest china the electrical properties of the channels imply an elevated fluid content consistent with a weak crust 12 13 that permits flow on a geological timescale these findings support the hypothesis that crustal flow can occur in orogenic belts and contribute to uplift of plateaux our results reveal the previously unknown complexities of these patterns of crustal flow many previous studies of the indiaasia

five years of florida current structure and transport from the royal caribbean cruise ship explorer of the seas 1 using ship of opportunity platform explorer of the seas five years of full depth velocity data have been collected across the florida straits at 26 n between may 2001 and may 2006 the mean transport of the florida current was 31 0 4 0 sv this compares to a mean transport of 32 4 3 2 sv inferred from cable voltages at 27 n over the same period implying an average 1 4 sv transport into the straits through the northwest providence channel the climatological core of the florida current is 170 cms 1 and is positioned at 79 8 w about 10 km east of the shelf break the largest variability in velocity occurs over the shelf and shelf break and is likely related to shelf waves a secondary maximum occurs across much of the straits over the top 100 m of the water column and may be associated with wind events the annual cycle of florida current transports has a range of 4 7 sv with a maximum in may june july and a minimum in january the difference between the summer and winter current structure appears as a first baroclinic mode with zero crossing at 150 m the maximum difference is about 15 cms 1 at the surface and is centered just offshore of the mean current core on interannual timescales low pass filtered explorer and cable transports show similar downward trends between 2002 and 2005 but diverge over the last year or so of the record

structural evolution of the yushu nangqian region and its relationship to syncollisional igneous activity east central tibet field mapping geochronological analyses and cross section construction reveal a protracted deformation history and a minimum of 61 km of cenozoic ne sw shortening in present coordinates across the yushu nangqian thrust belt in northern tibet cenozoic contraction started prior to 51 ma and was followed first by northwest striking right slip faulting and later by northwest striking left slip faulting renewed ne sw contraction is expressed by folding of neogene strata and thrusting which again was followed by northwest striking left slip faults late neogene deformation is expressed by local north striking normal faults shortening across the yushu nangqian belt appears to be accommodated by thin skinned thrusting which raises the question of how the deformation was accommodated in the lower crustal levels to resolve this problem we perform geochemical analysis of igneous rocks dated as 51 49 and 38 37 ma the rocks exhibit geochemical signatures characteristic of subduction which implies that coeval crustal thickening in northeastern tibet was most likely induced by continental subduction

cenozoic paleoaltimetry of the se margin of the tibetan plateau constraints on the tectonic evolution of the region abstract an improved understanding of the elevation history of the tibetan plateau is crucial in discriminating among the various tectonic models for the evolution of the india asia continental collision we reconstruct the paleoelevation history for three cenozoic sedimentary basins from se tibet and yunnan china to provide more constraints on the tectonic processes for raising the se margin of the tibetan plateau the results presented here together with those of previous studies indicate that 1 the plateau margin of nw yunnan was near its elevation 2 6 km by the latest middle eocene 40 ma 2 the plateau margin of se yunnan reached its current elevation 1 6 km by the middle miocene 13 ma interpretations of the tectonic processes responsible for this inferred surface uplift of the region are made in the context of well documented surface geology we conclude that high landscape 2 6 km elevation in nw yunnan may represent the remnants of the eocene tibetan plateau that originally formed in the northeastern qiangtang block by crustal thickening associated with the india asia continental collision the near modern elevation of se yunnan since 13 ma probably reflects the initiation of lower crustal flow in this area by at least that time collectively our paleoaltimetric interpretations disagree with previously proposed models of middle miocene to pliocene crustal flow acting as a sole tectonic process for raising the se margin of the plateau but support a protracted history of surface uplift that most likely involved crustal thickening during the eocene southeastward extrusion of a portion of eocene tibetan plateau during the oligocene to early miocene and lower crustal flow beneath this region since at least the early miocene

wavenumber spectrum in the gulf stream from shipboard adcp observations and comparison with altimetry measurements the wavenumber spectra for velocity and temperature in the gulf stream region are calculated from a decade 1994 2004 of shipboard acoustic doppler current profiler adcp measurements taken as part of the oleander project the velocity and temperature spectra have comparable magnitude in terms of the kinetic and potential energy and both indicate a k 23 slope in the mesoscales in contrast the corresponding velocity spectrum determined from satellite altimetry sea surface heights yields a significantly higher energy level and a k 22 slope the discrepancy between altimeter derived and directly measured velocity spectra suggests that altimetric velocity probably is contaminated by noise in sea surface height measurement also the k 23 slope which appears to be in agreement with two dimensional quasigeostrophic turbulence theory does not support the contemporary surface quasigeostrophic theory these results highlight large gaps in the current understanding of the nature of surface geostrophic turbulence

borehole to surface electrical resistivity monitoring of a salt water injection experiment a field experiment was conducted at the university of california richmond field station to demonstrate the sensitivity of borehole to surface resistivity measurements in groundwater investigations a quantity of saline water was injected into a fresh water aquifer while the resistivity was monitored using a multichannel borehole to surface system two experiments were conducted using pole pole and pole dipole receiver electrode arrays the data from the pole pole experiment were superimposed to simulate a dipole pole array and the data from the pole dipole array were superimposed to simulate a dipole dipole array this superposition of the data was done to enhance the anomaly and facilitate interpretation a numerical modeling study was performed in conjunction with the field experiment in order to interprete the results a three dimensional modeling program was used to simulate the geological setting of the field experiment and the salt water injection this modeling revealed that an asymmetric displacem

three dimensional controlled source electromagnetic modelling with a well casing as a grounded source a hybrid method of moments and finite element scheme steel well casings in or near a hydrocarbon reservoir can be used as source electrodes in time lapse monitoring using grounded line electromagnetic methods a requisite component of carrying out such monitoring is the capability to numerically model the electromagnetic response of a set of source electrodes of finite length we present a modelling algorithm using the finite element method for calculating the electromagnetic response of a three dimensional conductivity model excited using a vertical steel cased borehole as a source the method is based on a combination of the method of moments and the coulomb gauged primary secondary potential formulation using the method of moments we obtain the primary field in a half space due to an energized vertical steel casing by dividing the casing into a set of segments each assumed to carry a piecewise constant alternating current density the primary field is then substituted into the primary secondary potential finite element formulation of the three dimensional problem to obtain the secondary field to validate the algorithm we compare our numerical results with i the analytical solution for an infinite length casing in a whole space excited by a line source and ii a three layered earth model without a casing the agreement between the numerical and analytical solutions demonstrates the effectiveness of our algorithm as an illustration we also present the time lapse electromagnetic response of a synthetic model representing a gas reservoir undergoing water flooding

evaporation induced 18o and 13c enrichment in lake systems a global perspective on hydrologic balance effects growing pressure on sustainable water resource allocation in the context of global development and rapid environmental change demands rigorous knowledge of how regional water cycles change through time one of the most attractive and widely utilized approaches for gaining this knowledge is the analysis of lake carbonate stable isotopic compositions however endogenic carbonate archives are sensitive to a variety of natural processes and conditions leaving isotopic datasets largely underdetermined as a consequence isotopic researchers are often required to assume values for multiple parameters including temperature of carbonate formation or lake water delta o 18 in order to interpret changes in hydrologic conditions here we review and analyze a global compilation of 57 lacustrine dual carbon and oxygen stable isotope records with a topical focus on the effects of shifting hydrologic balance on endogenic carbonate isotopic compositions through integration of multiple large datasets we show that lake carbonate delta o 18 values and the lake waters from which they are derived are often shifted by 10 parts per thousand relative to source waters discharging into the lake the global pattern of delta o 18 and delta c 13 covariation observed in 70 of the records studied and in several evaporation experiments demonstrates that isotopic fractionations associated with lake water evaporation cause the heavy carbon and oxygen isotope enrichments observed in most lakes and lake carbonate records modeled endogenic calcite compositions in isotopic equilibrium with lake source waters further demonstrate that evaporation effects can be extreme even in lake records where delta o 18 and delta c 13 covariation is absent aridisol pedogenic carbonates show similar isotopic responses to evaporation and the relevance of evaporative modification to paleoclimatic and paleotopographic research using endogenic carbonate proxies are discussed recent advances in stable isotope research techniques present unprecedented opportunities to overcome the underdetermined nature of stable isotopic data through integration of multiple isotopic proxies including dual element c 13 excess values and clumped isotope temperature estimates we demonstrate the utility of applying these multi proxy approaches to the interpretation of paleohy droclimatic conditions in ancient lake systems understanding past present and future hydroclimatic systems is a global imperative significant progress should be expected as these modern research techniques become more widely applied and integrated with traditional stable isotopic proxies c 2015 elsevier ltd all rights reserved

warm outbreaks of the gulf stream into the sargasso sea a warm outbreak is a large body of gulf stream water with apparent anticyclonic circulation that detaches from the gulf stream and exists as a well defined entity in the sargasso sea because warm outbreaks are warmer at the surface than sargasso sea water they are often clearly visible in satellite thermal infrared imagery from a survey of over 750 satellite images covering the sargasso sea immediately to the south of the gulf stream between 64 and 74 w and spanning a 5 year period 18 possible outbreaks have been observed all formed west of 65 w with the majority forming between 67 and 72 w five of the 18 were observed to detach completely from the gulf stream and have the following properties in common 1 they all formed in several days at or near the point of maximum cyclonic curvature of a large gulf stream meander 2 the surface expression was relatively short lived of the order of 10 to 20 days and 3 their dimensions and those of the other 13 were of the order of 100 by 200 km given the similarity between the characteristics of warm outbreaks and those of opposite vortices predicted by ikeda and apel 1981 from a two layer quasi geostrophic model of an eastward flowing jet it is suggested that the two phenomena are related further support of this hypothesis is the fact that the rate of formation of warm outbreaks between two and six per year is similar to that of anticyclonic eddies observed in expendable bathythermograph surveys of this area

a thermochronological perspective on the morphotectonic evolution of the southeastern tibetan plateau a large part of the southeastern tibetan plateau tp is characterized by low relief surfaces at high elevations 3 5 km the origin of these landscapes and their geodynamic implications with regard to evolution of the southeastern tp has been the subject of considerable debate focusing on this topic this study utilizes fission track and u th he thermochronology to reconstruct the thermal history of the late triassic daocheng granite on which a low relief high elevation landscape has developed results suggest that the plateau surface experienced widespread late jurassic to early cretaceous cooling at a rate of 1 2 c ma followed by minimal regional cooling 0 3 c ma and early miocene enhanced cooling 2 3 c ma along deep valleys at the southern edge of the landscape given the subdued late jurassic to early cretaceous crustal deformation in the study area we relate the coeval cooling to crustal refrigeration and exhumation triggered by northward subduction of the meso tethys ocean along the bangong suture subsequent late cretaceous to cenozoic minimal cooling supports arguments for the formation of a low elevation landform prior to uplift of the southeastern tp the enhanced cooling commenced at the early miocene 15 22 ma along deep valleys and heralded the onset of river incision and surface uplift of the southeastern tp this finding does not support previous proposals claiming that high elevations of the southeastern tp were formed in late miocene time resulting from lower crustal flow but rather supports a model highlighting continental subduction and extrusion along the large tanggula yushu batang red river fault system

indian continental subduction and slab break off during tertiary collision high wavespeed seismic anomalies in the transition zone and uppermost lower mantle beneath the india asia collision zone imaged by body wave seismic tomography have been interpreted as subducted fragments of continental material in this study we focus on the prominent anomaly located beneath india between depths of about 450 and 900 km by combining the location of this anomaly with palaeogeographical positions of india we constrain the timing of the subduction event probably related to this anomaly we infer that a large portion of the north western margin of india initiated subduction at 35 5 ma along a 1500 km long wnw ese striking zone and ended with a progressive slab break off process this break off started most probably around 25 ma at the western end of the slab and propagated eastwards until complete break off around 15 ma this study helps to constrain better the amount of convergence between india and asia absorbed by continental subduction

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

laboratory calibration of the calcium carbonate clumped isotope thermometer in the 25 250 c temperature range abstract many fields of earth sciences benefit from the knowledge of mineral formation temperatures for example carbonates are extensively used for reconstruction of the earth s past climatic variations by determining ocean lake and soil paleotemperatures furthermore diagenetic minerals and their formation or alteration temperature may provide information about the burial history of important geological units and can have practical applications for instance for reconstructing the geochemical and thermal histories of hydrocarbon reservoirs carbonate clumped isotope thermometry is a relatively new technique that can provide the formation temperature of carbonate minerals without requiring a priori knowledge of the isotopic composition of the initial solution it is based on the temperature dependent abundance of the rare 13c 18o bonds in carbonate minerals specified as a 47 value the clumped isotope thermometer has been calibrated experimentally from 1 c to 70 c however higher temperatures that are relevant to geological processes have so far not been directly calibrated in the laboratory in order to close this calibration gap and to provide a robust basis for the application of clumped isotopes to high temperature geological processes we precipitated caco3 mainly calcite in the laboratory between 23 and 250 c we used two different precipitation techniques first minerals were precipitated from a caco3 supersaturated solution at atmospheric pressure 23 91 c and second from a solution resulting from the mixing of cacl2 and nahco3 in a pressurized reaction vessel at a pressure of up to 80 bar 25 250 c the calibration lines of both experimental approaches overlap and agree in the slopes with theoretical estimates and with other calibration experiments in which carbonates were reacted with phosphoric acid at temperatures above 70 c our study suggests a universal 47 t calibration t in k 47 in 47 0 98 0 01 3 407 10 9 t 4 2 365 10 7 t 3 2 607 10 3 t 2 5 880 t 0 293 0 004 this new 47 t calibration given in the absolute reference frame that extends the experimentally calibrated temperature range for clumped isotopes to 250 c can be applied to carbonates that grew at intermediate temperatures 20 250 c

influence of climate change and uplift on colorado plateau paleotemperatures from carbonate clumped isotope thermometry the elevation history of earth s surface is key to understanding the geodynamic processes responsible for the rise of plateaus we investigate the timing of colorado plateau uplift by estimating depositional temperatures of tertiary lake sediments that blanket the plateau interior and adjacent lowlands using carbonate clumped isotope paleothermometry a measure of the temperature dependent enrichment of 13 c 18 o bonds in carbonates comparison of modern and ancient samples deposited near sea level provides an opportunity to quantify the influence of climate and therefore assess the contribution of changes in elevation to the variations of surface temperature on the plateau analysis of modern lake calcite from 350 to 3300 m elevation in the southwestern united states reveals a lake water carbonate temperature lct lapse rate of 4 2 0 6 c km analysis of miocene deposits from 88 to 1900 m elevation in the colorado river drainage suggests that the ancient lct lapse rate was 4 1 0 7 c km and temperatures were 7 7 2 0 c warmer at any one elevation than predicted by the modern trend the inferred cooling is plausible in light of pliocene temperature estimates off the coast of california and the consistency of lapse rates through time supports the interpretation that there has been little or no elevation change for any of the samples since 6 ma together with previous paleorelief estimates from apatite u th he data from the grand canyon our results suggest most or all of the plateau s lithospheric buoyancy was acquired 80 60 ma and do not support explanations that ascribe most plateau uplift to oligocene or younger disposal of either the farallon or north american mantle lithosphere

a double thermostad warm core ring of the gulf stream abstractan unusual double thermostad warm core ring of the gulf stream was discovered in the slope sea south of georges bank during the r v endeavor cruise 578 in may 2016 the ring s stratificat

anatomy and evolution of a cyclonic mesoscale eddy observed in the northeastern pacific tropical subtropical transition zone a cyclonic eddy in the ne pacific

carbonate oxygen isotope paleoaltimetry evaluating the effect of diagenesis on paleoelevation estimates for the tibetan plateau carbonate oxygen isotope paleoaltimetry is based on analysis of the d 18 o value of carbonate precipitated from surface water deciphering the diagenetic history is important for establishing whether particular carbonates are accurate recorders of paleosurface waters which reflect paleoelevation this study provides examples from southern east central and northeastern tibet of approaches aimed at evaluating the diagenetic history of lacustrine micrites and pedogenic carbonates the most desirable technique for avoiding erroneous interpretations related to diagenetic overprinting is to analyze carbonates that are known to be primary such as aragonitic shell material in rocks that do not contain shell material we have compared lacustrine micrites and pedogenic carbonates to diagenetic carbonate phases to determine the effects of diagenesis on the isotopic composition of primary carbonates where the potential effects of diagenesis are subtle or ambiguous we have evaluated the fidelity of the carbonate record from systematic trends in c and o isotopes that agree with other interpretations of paleoenvironment such as high frequency covariance in c and o that corresponds with changes in the mg concentration of carbonates using these strategies we have determined that diagenesis has not affected the isotopic composition of carbonates in the late miocene pliocene thakkhola graben in southern tibet and the oligocene to pliocene linxia basin in northeastern tibet in the case of paleogene basins in east central tibet however ambiguity in data precludes the determination of diagenetic effects d 2004 elsevier b v all rights reserved

cyclonic and anticyclonic motion in the upper ocean 1 upper ocean variability is highly energetic and contributes to key processes such as heat transport and water mass formation here the distribution of ocean surface cyclonic and anticyclonic motion is computed from global drifter observations for scales from large eddies to submesoscale two zonal bands of small scale motion are recovered a known anticyclonic band at 30 40 latitude mostly wind induced and an unexpected cyclonic band at 10 20 latitude it is suggested that this is due to submesoscale processes related to salinity front instabilities these results provide a first global view of the upper ocean including these motions

stable isotopes reveal high southeast tibetan plateau margin since the paleogene abstract the evolution of the topography of eastern tibet reflects the dynamic interaction between processes at earth s surface and the lower crust reconstruction of its spatio temporal development provides constraints for our understanding of the geodynamics of continental deformation this study examines the topographic evolution of the southeast margin of the tibetan plateau throughout the cenozoic using stable isotope paleoaltimetry of pedogenic carbonates preserved in cenozoic basins extending from the northern to the southern portions of the se margin of the tibetan plateau yunnan province china paleoelevations are calculated using a monte carlo simulation of the normally distributed uncertainties in each parameter used to calculate elevations from the isotopic value of pedogenic carbonate isotope elevation relationships are determined from a modern sampling transect along the modern lancang mekong river and an estimated eocene rayleigh fractionation model that was randomly resampled calculated elevations indicate the se margin of tibet was at its present elevation as early as the late eocene with elevations of 3 3 km as far south as the northern third of china s yunnan province this result expands the extent of the eocene tibetan plateau more than 1000 km east of that previously known and precludes surface uplift via lower crustal flow in the area of sw sichuan and northern yunnan as a driver for drainage reorganization and an observed middle to late miocene pulse of rapid exhumation elevation estimates from the southern two thirds of the study area parallel to the red river fault suggest approximately 1 km of post late miocene surface uplift consistent with estimates from previous studies

rapid uplift of the altiplano revealed through 13c 18o bonds in paleosol carbonates the elevation of earth s surface is among the most difficult environmental variables to reconstruct from the geological record here we describe an approach to paleoaltimetry based on independent and simultaneous determinations of soil temperatures and the oxygen isotope compositions of soil waters constrained by measurements of abundances of 13 c 18 o bonds in soil carbonates we use this approach to show that the altiplano plateau in the bolivian andes rose at an average rate of 1 03 0 12 millimeters per year between 10 3 and 6 7 million years ago this rate is consistent with the removal of dense lower crust and or lithospheric mantle as the cause of elevation gain

stable isotope based paleoaltimetry theory and validation paleoaltimetry is the quantitative estimate of the surface height above mean sea level of ancient landforms atmospheric thermodynamic modeling of the behavior of 18o relative to 16o during condensation from water vapor establish the systematic relationship that exists between 18o p and elevation where 18o p is the difference between a low altitude preferably sea level 18o p and a potentially high elevation sample comparison of model predictions with observations suggests that the model captures the first order behavior of 18o p during condensation and precipitation in orographic settings the actual relationship between 18o p and elevation depends sensitively on climate and specifically starting temperature and to a lesser degree relative humidity thermodynamic modeling allows the 18o p and elevation relationship to be explicitly calculated for any given starting climate state this makes the theoretical approach significantly more appropriate than empirically calibrated approaches based typically on quite limited samples presently available in most orographic settings today paleoaltimetry archives derive their isotopic compositions from surface and or ground water and hence it is important to understand the systematic differences between these reservoirs and precipitation surface waters and ground waters integrate not just the change in isotopic composition with altitude but also variations in hypsometry within the drainage basin and precipitation amount as functions of elevation thus these archives should reflect the precipitation amount weighted hypsometric mean elevation of the paleo drainage basin from which they derive their waters analysis of modern data from the himalayan region supports this expectation foreland basin rivers are such integrators and it is shown using an example from the siwaliks that the rivers draining the front of the himalayas in the past had isotopic compositions comparable with modern rivers draining the himalayan front suggesting little net change in himalayan hypsometry over the past 11 million years

stirring of the northeast atlantic spring bloom a lagrangian analysis based on multisatellite data 1 the effect of the geostrophic stirring on phytoplankton variability during the northeast atlantic spring bloom is studied by analyzing satellite derived surface chlorophyll sea surface temperature and sea surface height the calculation of unstable manifolds is used as a diagnostic of the transport properties of the geostrophic velocity field calculated from the sea surface height we identify two mechanisms by which the geostrophic velocity field acts on chlorophyll patterns the first mechanism is a direct effect of the horizontal transport on already formed chlorophyll by acting as sticking transport barriers the unstable manifolds are shown to 1 modulate the fronts of already formed phytoplankton in lobular structures 2 create spiralling chlorophyll anomalies within eddies and 3 produce chlorophyll filaments the second mechanism is an indirect effect on in situ chlorophyll production mediated by nutrient upwelling supported by a recent study on the vertical velocities of the northeast atlantic legal et al 2006 we argue that the horizontal unstable manifolds also shape the filamentary vertical velocity cells and hence the patterns of in situ produced chlorophyll through submesoscale vertical nutrient injection

discrete eddies in the northern north atlantic as observed by looping rafos floats abstract rafos float trajectories near the 27 5 density level were analyzed to investigate discrete eddies in the northern north atlantic with the objective of determining their geographical distribution and characteristics floats that made two or more consecutive loops in the same direction loopers were considered to have been in an eddy overall 15 24 float years of the float data were in loopers one hundred and eight loopers were identified in 96 different eddies roughly half of the eddies were cyclonic 49 and half were anticyclonic 51 although the percentages varied in different regions a few eddies were quasi stationary for long times one for over a year in the iceland basin and many others clearly translated often in the direction of the general circulation as observed by non looping floats several floats were trapped in eddies in the vicinity of the north atlantic current just upstream west of the charlie gibbs 52 n and faraday 50 n fracture zones which seem to be preferred routes for flow crossing the mid atlantic ridge five floats looped in four anticyclones that translated southwestward away from the eastern boundary near the goban spur 47 50 n these could have been weak meddies forming from remnants of warm salty mediterranean water advected northward along the eastern boundary

carbonate clumped isotope bond reordering and geospeedometry carbonate clumped isotope thermometry is based on the preference of 13c and 18o to form bonds with each other at elevated temperatures such bond ordering is susceptible to resetting by diffusion of c and o through the solid mineral lattice this type of bond reordering has the potential to obscure primary paleoclimate information but could also provide a basis for reconstructing shallow crustal temperatures and cooling rates we determined arrhenius parameters for solid state reordering of c o bonds in two different calcites through a series of laboratory heating experiments we find that the calcites have different susceptibilities to solid state reordering reaction progress follows a first order rate law in both calcites but only after an initial period of non first order reaction that we suggest relates to annealing of nonequilibrium defects when the calcites are first heated to experimental temperature we show that the apparent equilibrium temperature equations or closure temperature equations for carbonate clumped isotope reordering are analogous dodson s equations for first order loss of daughter isotopes for each calcite the sensitivity of apparent equilibrium temperature to cooling rate is sufficiently high for inference of cooling rates within a factor of 5 or better for cooling rates ranging from tens of degrees per day to a few degrees per million years however because the calcites have different susceptibilities to reordering each calcite defines its own cooling rate apparent equilibrium temperature relationship the cooling rates of carrara marble inferred from carbonate clumped isotope geospeedometry are 10 6 10 3 degrees per annum and are in broad agreement with rates inferred from thermochronometric methods cooling rates for 13c depleted calcites from the late neoproterozoic doushantou cap carbonates in south china are on the order of 102 104 degrees per annum consistent with rapid cooling following formation of these calcites by a short lived hydrothermal event bristow et al 2011 nature v 474 p 68 71 most of the uncertainty in these estimates relates to uncertainty in arrhenius parameters for different calcites thus while the carbonate clumped isotope geospeedometer shows promise for recording cooling rates in settings and lithologies where other geospeedometers may not be applicable the uncertainty in cooling rate will be large without independent knowledge of the reordering kinetics of each study material thus the full potential of the method will only be realized if reordering kinetics can be accurately determined for each study material or predicted on the basis of mineral composition texture or other observable parameters

role of the westerlies in central asia climate over the cenozoic abstract there remains substantial debate concerning the relative roles of tectonics and of global climate in pacing the evolution of aridity in central asia over the cenozoic tibetan plateau uplift variable monsoonal strength paratethys retreat and reduced moisture transport from the north atlantic have all been hypothesized to drive aridity in central asia distinguishing between these mechanisms requires knowledge of moisture transport pathways to central asia through time presently central asia receives recycled high 18 o moisture that has been transported across eurasia by the westerlies while southern tibet receives low 18 o moisture distilled by passage over the himalaya here we reconstruct the spatial distribution of oxygen isotopes in precipitation since the early eocene using a compilation of 18 o data from 2750 sedimentary carbonate samples across asia the spatial distribution of paleo precipitation 18 o remains remarkably similar through time with low 18 o values in the lee of the himalaya in southern tibet constant high 18 o values in central asia and intermediate values on the central plateau despite independent evidence for substantial changes in both topography and climate through time these results suggest that a long standing topographic feature has continuously blocked southerly moisture and subsequent progressive uplift of the tibetan plateau has had little impact on central asian climate in turn southerly monsoonal moisture has never persistently extended northward of the central plateau as a result the westerlies have remained the dominant moisture source in central asia since at least the early eocene therefore sedimentary aridity indicators in central asia such as loess deposition are controlled by the trans eurasian westerly moisture flux rather than tibetan plateau uplift

lithospheric thickness of the chinese continent abstract we invert for the upper mantle temperatures of the chinese continent in the depth range of 70 240 km from a recent s velocity model the depth where temperatures intersect a mantle adiabat with a potential temperature of 1300 c is in close correspondence with the top of the seismic low velocity zone for most regions this correspondence implies that seismic lithosphere estimated from short time scale seismic information may be equivalent to the long time scale geodynamical lithosphere defining the 1300 c adiabat as coinciding with the lithospheric base we estimate the seismic thermal lithosphere thickness the estimated thickness shows obvious dependence on the tectonic settings beneath eastern china which mainly belongs to the circum pacific tectonic domain it has a thickness of 100 km and beneath the qinghai tibet plateau and south to the tarim craton which belong to the tethyan tectonic domain it has a thickness of 160 220 km the lithospheric thicknesses of the three large para platforms cratons range from 170 km for the western yangtze 140 km for tarim and 100 km for sino korean the three cratons may have been reshaped by phanerozoic tectonic activities and are thinner than most cratons in other continents

evaluation of meteoric calcite cements as a proxy material for mass 47 clumped isotope thermometry abstract meteoric diagenetic cements are ubiquitous throughout geologic history affecting most carbonate exposures worldwide they can often be difficult to interpret as it is usually difficult to separate the influences of water 18o and temperature on isotopic signals contained within the carbonate rock body despite this difficulty in interpretation meteoric phreatic cements can potentially be a useful proxy material as they form slowly in equilibrium at mean annual temperature and are not affected by any biogenic effects that can bias other proxy materials we applied the mass 47 clumped isotope paleothermometer to pleistocene and holocene carbonates from bermuda and barbados in order to investigate the effects of meteoric diagenesis on 47 signals and to determine their suitability as a paleotemperature proxy phreatic calcite cements are found to record the same temperatures as unaltered carbonate sediments while any sample exhibiting vadose characteristics is biased towards unreasonably hot apparent formation temperatures burial heating and re equilibration are not geologically viable explanations for the anomalously hot temperatures recorded in vadose cements as neither bermuda or barbados has any burial history instead it is likely that precipitation in the vadose zone occurs on timescales quicker than isotopic equilibrium can be achieved driven by a combination of co2 degassing and evaporation which have been previously shown to cause problems in speleothems and pedogenic carbonates we conclude by suggesting that meteoric phreatic calcites may be an ideal phase for paleotemperature reconstruction as they accurately record mean annual temperatures and form under equilibrium conditions while also being resistant to further mineral driven diagenesis vadose cements and any sample likely affected by processes similar to vadose diagenesis should be avoided for climate reconstructions using the mass 47 clumped isotope thermometer

remote reservoir resistivity mapping a method for surface estimation of reservoir properties wherein location of and average earth resistivities above below and horizontally adjacent to the subsurface geologic formation are first determined using geological and geophysical data in the vicinity of the subsurface geologic formation then dimensions and probing frequency for an electromagnetic source are determined to substantially maximize transmitted vertical and horizontal electric currents at the subsurface geologic formation using the location and the average earth resistivities next the electromagnetic source is activated at or near surface approximately centered above the subsurface geologic formation and a plurality of components of electromagnetic response is measured with a receiver array geometrical and electrical parameter constraints are determined using the geological and geophysical data finally the electromagnetic response is processed using the geometrical and electrical parameter constraints to produce inverted vertical and horizontal resistivity depth images optionally the inverted resistivity depth images may be combined with the geological and geophysical data to estimate the reservoir fluid and shaliness properties

efficient three dimensional data inversion soil characterization and moisture monitoring from cross well ground penetrating radar at a vermont test site we extend our methodology for three dimensional parameter structure and value estimation and apply it to a vermont test site ground penetrating radar gpr cross well travel times are inverted for estimation of heterogeneous gpr soil velocities before and after a controlled release of salt water in the unsaturated zone the method which is based on an approximation of the extended kaiman filter in conjunction with data driven zonation automatically estimates not only distributed zone values but also the number of zones zone geometry and zone covariance resultant gpr velocity estimates are shown to reduce travel time estimation errors and to be consistent with independent cone penetrometer measurements at all five walls at the site comparison of velocity estimates before and after forced injection of salt water is used to detect and visualize soil moisture patterns in three dimensions by varying the cluster tolerance criterion in the data driven zonation process the user can obtain a desired resolution of heterogeneity number of zones used in the resultant model

lithology discrimination from physical rock properties the estimation of lithology from multiple geophysical survey methods needs to be addressed to develop advanced tomographic methods an initial requirement for lithology discrimination is that lithology should be discriminable from the media properties physically related to the geophysical observations to test this condition for different combinations of the most common crustal rocks we performed several lithology discrimination exercises on rock samples under laboratory conditions the physical properties included mass density compressional velocity shear velocity electric conductivity thermal conductivity and magnetic susceptibility a categorical description of the sample lithology was followed hence the inference consisted of predicting the sample rock category lithotype membership the joint information provided by the physical properties of the rocks allowed us to discriminate the sample lithotype correctly with an overall success rate of 100 in the most favorable situation and over 85 in the least favorable situation we obtained successful classification results for a variety of common lithotypes granite gabbro limestone tuff marble basalt and gneiss using three common classification methods clustering analysis gaussian classification and discriminant analysis although discrimination was positive with each of these multivariate classification techniques discriminant analysis showed some advantages for the classification and graphic analysis of the data these results support our postulate that lithology can be estimated reliably if multiple geophysical observations are considered jointly

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

insights into the early tibetan plateau from u th he thermochronology the central songpan ganzi belt located on the eastern margin of the tibetan plateau has a similar high elevation and low relief to parts of central tibet thermochronological studies from the central tibetan plateau reveal a history of slow exhumation rates 1 since 45ma however the exhumation history of the central songpan ganzi belt is unknown to address this we conducted an apatite and zircon u th he thermochronology study of bedrock samples collected across the central songpan ganzi belt and into central parts of the tibetan plateau zircon u th he ages range from 54 2 7 5 to 146 5 10 0ma and the majority of apatite u th he ages fall between 74 7 19 0 and 35 7 9 4ma thermal history models of these data show rapid cooling in the late mesozoic and much slower cooling diagnostic of low rates of erosion throughout most of the cenozoic the late mesozoic rapid cooling is consistent with the existence of significant topography and relief at least in some parts of the songpan ganzi belt at that time we find no evidence for a regional miocene acceleration in erosion although three samples from the headwaters of the salween and mekong rivers gave younger ahe ages between 15 and 16ma that reflect an acceleration in river incision supplementary material laser ablation inductively coupled plasma mass spectrometry zircon u pb data from central and eastern tibet are available at www geolsoc org uk sup18647

new cretaceous and early tertiary paleomagnetic results from xining lanzhou basin kunlun and qiangtang blocks china implications on the geodynamic evolution of asia we present the results of a paleomagnetic study of 360 cores drilled at three different areas from the tibetan plateau 13 sites from lower cretaceous red beds in the xining lanzhou basin around xining and lanzhou cities southwest of the qilian mountains 36 2 n 103 5 e 13 sites from cretaceous red beds in the kunlun block near maqin 34 5 n 100 1 and 9 sites from paleocene lower eocene red beds in the qiangtang block near fenghuoshan 34 5 n 92 8 e thermal demagnetization of the samples allowed us to isolate a high temperature component which passes both positive reversal and fold tests for all formations the corresponding paleopoles lie at 50 3 n 195 5 e a95 4 6 for xining lanzhou 80 1 n 281 2 e dp 7 8 dm 12 7 for maqin and 62 6 n 210 5 e dp 3 9 dm 6 8 for fenghuoshan we discuss these in the frame of a new paleogeographic reconstruction of the cretaceous paleoposition of the blocks forming the asian mosaic we conclude that the xining lanzhou area could not be part of the north china block but rather was associated with the tarim qaidam assemblage paleomagnetic data argue in favor of a qaidam kunlun tarim junggar assemblage in the cretaceous significantly to the south of its current position with respect to the asian continent siberia mongolia and north china the large n s convergence 800 500 km implied since the cretaceous appears to be far larger than could be absorbed in the altay range to the north and qilian shan to the east of the order of 300 km part of this motion could have occurred along a large left lateral strike slip fault system which may connect with the mongol okhotsk suture to the northeast verifying this hypothesis will require new geologic and paleomagnetic data from these remote regions

southern tibetan oligocene miocene adakites a record of indian slab tearing abstract oligocene miocene granitoids exposed within the 1500 km long gangdese arc of southern tibet exhibit adakitic compositions five plutonic samples from the southeastern lhasa terrane near namche barwa area were analyzed to determine their geochemical characteristics and to better understand the geodynamic evolution of the eastern himalayan syntaxis orogen the samples yielded u pb zircon ages in the range of 30 26 ma are intermediate to silicic in composition and have elevated k2o 1 5 8 9 th la ratios 0 14 1 10 low mgo

on the structure of the lofoten basin eddy 1 a small anticyclonic eddy of extraordinary intensity sits in the center of the lofoten basin near 69 40 n 3 e this paper gives a first detailed description of its kinematics and lowest order dynamic balances using a 75 khz vessel mounted acoustic doppler current profiler hydrography and six rafos floats to probe the eddy we document a solid body core with 7 8 km radius and relative vorticity very close to f where f is the local coriolis parameter maximum orbital velocities close to 0 8 ms 1 were observed at 18 km radius one float trapped in the core of the eddy for 9 months indicated undiminished strength throughout that period possibly even intensifying in winter hydrography revealed adiabatic conditions from the bottom of a shallow seasonal thermocline to 1000 m depth in early july 2010 thermal convection in winter maintains an already deep pycnostad and may also play a key role in intensifying the eddy quite possibly through penetrative convection that deepens and sharpens the underlying pycnocline heat lost to the atmosphere has to be replenished from warm anticyclonic eddies shed off the eastern branch of the norwegian atlantic current but the mechanism s by which it is added to the eddy remains to be studied examination of historical data sets suggests the eddy is a permanent feature of the lofoten basin two hydrocasts from the 1960s also show a similar adiabatic mixed layer albeit 1 c cooler than in 2010 perhaps reflecting the generally cold winter conditions that prevailed then

himalayan tectonics weathering processes and the strontium isotope record in marine limestones the time evolution of the isotopic composition of seawater strontium the ratio of strontium 87 to strontium 86 over the last 500 million years has the form of an asymmetric trough the values are highest in the cambrian and recent 0 7091 and lowest in the jurassic 0 7067 superimposed on this trend are a number of smaller oscillations consideration of the geochemical cycle of strontium and the dynamics of weathering shows that only himalayan style continental collisions can influence the isotope ratio on the scale observed the contemporary himalayan orogeny is by far the largest since the late precambrian pan african event that produced the high in the cambrian

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

temporal variations in lake water temperature paleoenvironmental implications of lake carbonate δ18o and temperature records abstract 18 o and clumped isotope measurements of lacustrine carbonates provide important records of past terrestrial climate and paleoelevation however one of the primary challenges interpreting these data is constraining the relationship between mineral formation temperature and seasonal and mean annual climate we examined surface water temperature records from 88 lakes across the globe to develop transfer functions that relate seasonal water surface temperature to mean annual air temperature these transfer functions provide a means of reconciling proxy measures of water temperature with annual climatic conditions mean annual surface water temperature is related to mean annual air temperature maat 0 0318 t water 2 2 195 t water 12 607 r 2 0 96 independent of lake size with consistently higher mean water temperatures than air n hemisphere spring april june mean lake surface temperatures maat 0 0097 t water 2 1 379 t water 8 227 r 2 0 94 are only slightly warmer than maat for lakes in all climate zones while summer water temperatures jja maat 0 0055 t water 2 1 476 t water 18 915 r 2 0 90 may be 10 20 c warmer than maat for cold climate lakes comparison of carbonate stable isotopic data from sites with different timescales of carbonate formation such as found along latitude or elevation gradients can lead to large over or underestimates of past temperature accurate paleoclimatic interpretation of isotopic proxies or use of temperature proxy constraints i e fossil leaves to estimate lake temperature and calculate water 18 o thus requires appropriate application of water temperature air temperature transfer functions particularly when considering ancient cool high elevation lake systems

middle to late cenozoic cooling and high topography in the central rocky mountains constraints from clumped isotope geochemistry abstract the timing and mechanism of the formation of the high elevations of the central rocky mountains rockies in the western interior of north america remain controversial we examine the middle and late cenozoic paleorelief between the great plains and the central rockies using clumped isotope geothermometry of carbonate cements of fluvial and eolian sandstones our petrographic observations suggest that the studied carbonate cements were formed primarily during eodiagenesis in near surface conditions and retain primary paleoclimate and paleoelevation signals carbonate clumped isotope temperatures decrease 10 c and calculated water o 18 values decrease 4 from 35 ma to 5 ma in both the central rockies and the western great plains following middle and late cenozoic global cooling trend a persistent longitudinal gradient in temperature and o 18 value existed between the central rockies and the great plains during the oligocene and miocene with temperatures 4 8 c higher and calculated water o 18 values 3 6 higher in the great plains these observations suggest the mean elevation of the central rockies was 1 km higher than the western great plains during the middle and late cenozoic similar to the present day regional relief when placed in the context of other paleoaltimetry studies and geological observations our findings support the hypothesis that the high mean topography of the rockies was developed during the late eocene possibly related to isostatic adjustment or dynamic uplift caused by foundering of lower mantle lithosphere or the farallon slab or both

anatomy and evolution of a cyclonic mesoscale eddy observed in the northeastern pacific tropical subtropical transition zone 1 in november 2005 off cabo corrientes a cyclonic eddy was sampled from i remotely sensed data of sea level anomaly near surface wind chlorophyll a concentration and sea surface temperature and ii direct observations from a lowered acoustic doppler profiler and a conductivity temperature and depth sensor the sea level anomaly data set and an automated eddy detection method showed that this vortex formed near the mexican coast and traveled westward northwestward 1000 km into the open ocean for 8 months surface winds and currents indicated that the cyclone was generated during a coastal upwelling event that occurred simultaneously with an equatorward flow located close to the coast during its growing phase the eddy extended from the surface to 750 m depth and mixed the water column in the first 100 m showing an eastward shift of the eddy axis toward the sea surface of 1 5 of longitude that generated a southward meridional heat transport in the upper layers integrated in the vertical this heat transport accounted for a total of 105 1012 w within the region of the eddy the estimation of the available heat and salt anomaly contents revealed that the eddy transported relatively cold salty and anoxic waters associated with the subtropical subsurface water mass while traveling offshore the cyclonic eddy also exhibited relatively higher chlorophyll a concentrations at the sea surface than its surroundings comparison of some surface properties estimated from satellite and in situ data showed that satellite data tend to underestimate its amplitude and orbital geostrophic velocity

metalliferous mining geophysics state of the art in the last decade of the 20th century and the beginning of the new millennium the downturn in mining activity experienced during the 1990s did not preclude significant new developments in various areas of mining geophysics the methodology for acquiring and compiling data has kept pace with the latest technological developments from global positioning system navigation to raster displays and parallel computing wavelet transforms principal component analysis and fractals have begun to find successful applications in both processing and interpretation of geophysical data methods of quantitatively interpreting inverting anomalies in terms of 2 d and 3 d models of causative bodies are becoming common for the first time it is possible to make airborne gravity gradient measurements suitable for use in mineral exploration lower transmitter frequencies for airborne time domain electromagnetic em systems have enabled surveys in areas where conductive cover previously screened basement conductors the use of approximation algorithms has allowed the transformation of either time domai

late cenozoic uplift of southeastern tibet the age of surface uplift in southeastern tibet is currently unknown but the initiation of major river incision can be used as a proxy for the timing of initial uplift the topographically high eastern plateau and gently dipping southeastern plateau margin are mantled by an elevated low relief relict landscape that formed at a time of slow erosion at low elevation and low tectonic uplift rates prior to uplift of the eastern tibetan plateau thermochronology from deep river gorges that are cut into the relict landscape shows slow cooling between ca 100 and ca 10 20 ma and a change to rapid cooling after ca 13 ma with initiation of rapid river incision at 0 25 0 5 mm yr between 9 and 13 ma a rapid increase in mean elevation of eastern tibet beginning at this time supports tectonic climate models that correlate the lateral eastern expansion of high topography in tibet with the late miocene intensification of the indian and east asian monsoons

kinematics and dynamics of a mediterranean salt lens abstract two surveys of the absolute velocity field of an eddy of mediterranean water meddy in the eastern north atlantic were conducted one year apart in 1984 and 1985 two velocity regimes were revealed within the radius of maximum velocity the meddy rotated anticyclonically as a solid body with a depth dependent rotation period near 6 days at its mid depth 1000 m one year later the radius of the core had decreased by one third the rotation rate of the lens also decreased except at its mid depth where there was a small but perceptible increase there was a sharp 5 km or less transition between the core and the outer region where the velocity decayed exponentially with radius a strong potential vorticity front due to the abrupt change in sign of horizontal shear kept the core isolated from the outer region potential vorticity was nearly constant within the upper confines of the core over the study period whereas there was a notable increase in potential vorticity in the lower portion of

three dimensional massively parallel electromagnetic inversion ii analysis of a crosswell electromagnetic experiment summary a 3 d electromagnetic inversion scheme has been successfully applied to crosswell electromagnetic data collected at the richmond field station near berkeley california by comparing images of data collected before and after the injection of 50000 gallons of salt water a 3 d image of the plume has been developed which shows the location of zones of maximum permeability surrounding the injection well through which the salt water has migrated a resolution analysis has determined that the location of the plume is fairly accurate however the image of the geology will be distorted due to incomplete data coverage this latter problem is further complicated by the fact that data residuals indicate that the wells deviate from the vertical these deviations have been shown to cause artefacts within the images and thus further reduce the accuracy of the images with respect to the geology

the geological evolution of the tibetan plateau the geological evolution of the tibetan plateau is best viewed in a context broader than the india eurasia collision zone after collision about 50 million years ago crust was shortened in western and central tibet while large fragments of lithosphere moved from the collision zone toward areas of trench rollback in the western pacific and indonesia cessation of rapid pacific trench migration 15 to 20 million years ago coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern tibet the latter appear to result from rapid eastward flow of the deep crust probably within crustal channels imaged seismically beneath eastern tibet these events mark a transition to the modern structural system that currently accommodates deformation within tibet

direct measurements of the mean flow and eddy kinetic energy structure of the upper ocean circulation in the ne atlantic 1 the upper ocean circulation in the sub polar northeast atlantic has been a challenge to quantify due to strong and variable wind forcing and strong and variable deep currents that lead to large uncertainties in the use of the standard dynamical method since 1999 we have been operating an acoustical doppler current profiler on a container vessel that operates between denmark and greenland to repeatedly sample upper ocean currents across the northeast atlantic individual transects exhibit a highly energetic mesoscale variability but ensemble averaging of the sections reveals a striking organization of the mean field along the reykjanes ridge a distinct southward flow along its eastern slope and two clearly defined peaks with seasonal modulation flowing to the north along its western slope higher values of eddy kinetic energy about 150 600 cm2 s 2 are observed along the transect o 1 5 greater than surface drifter estimates

the paleoaltimetry of tibet an isotopic perspective stable isotopes provide a valuable perspective on the timing of elevation change of the tibetan plateau we begin our paper by looking in depth at isotopic patterns in modern tibet we show that the 18 o value of surface waters decreases systematically up the himalayan front in central nepal by about 2 8 km in agreement with the patterns documented and modeled by previous research on the tibetan plateau itself there is no apparent correlation between elevation and the 18 o value of flowing surface waters both surface waters and soil carbonates display a northward increase in 18 o values of about 1 5 north of the himalayan crest even though elevation increases modestly the isotopic increase with latitude reduces the isotope elevation gradient for water in the northernmost plateau to 1 to 2 km carbonates in both soils and lakes form at higher temperatures than assumed by previous studies on the plateau temperature estimates from clumped isotope 47 analyses of modern soil carbonates significantly exceed mean annual air t and modeled maximum summer soil temperatures by 15 8 2 8 and 9 7 2 5 c respectively similarly elevated temperatures best account for the 18 o values observed in modern soil and lake carbonates we recalculated paleoelevations from previous studies on the plateau using both higher formation temperatures and latitude corrected isotopic values with one notable exception our revised model produces paleoelevation estimates very close to previous estimates the exception is the reconstruction from late eocene age deposits at xoh xil for which we calculate elevations that are higher and much closer to the current elevation than previously reconstructed therefore there is no evidence for northward progression through time of tibetan elevation change instead the available but admittedly very scanty evidence suggests that much of tibet attained its modern elevation by the mid eocene a truly robust test of the various geodynamic models of uplift await expansion and replication of isotopic records all across tibet especially in the center and north and for 15 ma

the growth of northeastern tibet and its relevance to large scale continental geodynamics a review of recent studies recent studies of the northeastern part of the tibetan plateau have called attention to two emerging views of how the tibetan plateau has grown first deformation in northern tibet began essentially at the time of collision with india not 10 20 myr later as might be expected if the locus of activity migrated northward as india penetrated the rest of eurasia thus the north south dimensions of the tibetan plateau were set mainly by differences in lithospheric strength with strong lithosphere beneath india and the tarim and qaidam basins steadily encroaching on one another as the region between them the present day tibetan plateau deformed and its north south dimension became narrower second abundant evidence calls for acceleration of deformation including the formation of new faults in northeastern tibet since 15 ma and a less precisely dated change in orientation of crustal shortening since 20 ma this reorientation of crustal shortening and roughly concurrent outward growth of high terrain which swings from nne ssw in northern tibet to more ne sw and even ene wsw in the easternmost part of northeastern tibet are likely to be in part a consequence of crustal thickening within the high tibetan plateau reaching a limit and the locus of continued shortening then migrating to the northeastern and eastern flanks these changes in rates and orientation also could result from removal of some or all mantle lithosphere and increased gravitational potential energy per unit area and from a weakening of crustal material so that it could flow in response to pressure gradients set by evolving differences in elevation

geochemical evaluation of fenghuoshan group lacustrine carbonates north central tibet implications for the paleoaltimetry of the eocene tibetan plateau abstract a sedimentologic petrologic and geochemical evaluation of lacustrine carbonates from the eocene oligocene fenghuoshan group of north central tibet provides insight into the paleoenvironmental and paleolimnological setting of the hoh xil basin during the mid tertiary fenghuoshan lacustrine rocks consist primarily of carbonate mudstones and wackestones these carbonates are generally less than 3 m in thickness and are intercalated with siliciclastic lacustrine and fluvial alluvial plain deposits individual limestone beds coarsen and contain increasing amounts of siliciclastic material upward fenghuoshan carbonates also contain abundant ostracode bivalve and charaphyte fossils sedimentologic evidence suggests that carbonate deposition occurred in shallow relatively short lived lacustrine systems that were subsequently filled by alluvial deposits of coeval fluvial systems stable c and o isotopic analysis of fenghuoshan carbonates show 18o values ranging from 11 7 to 10 3 vienna pee de

calcium and magnesium limited dolomite precipitation at deep springs lake california dolomite ca mg co3 2 precipitation from supersaturated ionic solutions at earth surface temperatures is considered kinetically inhibited because of the difficulties experienced in experimentally reproducing such a process nevertheless recent dolomite is observed to form in hypersaline and alkaline environments such recent dolomite precipitation is commonly attributed to microbial mediation because dolomite has been demonstrated to form in vitro in microbial cultures the mechanism of microbially mediated dolomite precipitation is however poorly understood and it remains unclear what role microbial mediation plays in natural environments in the study presented here simple geochemical methods were used to assess the limitations and controls of dolomite formation in deep springs lake a highly alkaline playa lake in eastern california showing ongoing dolomite authigenesis the sediments of deep springs lake consist of unlithified clay fraction dolomite ooze based on d 18 o equilibria and textural observations dolomite precipitates from oxygenated and agitated surface brine the na so4 dominated brine contains up to 500 mm dissolved inorganic carbon whereas mg 2 and ca 2 concentrations are ca 1 and 0ae 3m m respectively precipitation in the subsurface probably is not significant because of the lack of ca 2 below 0ae01 mm under such highly alkaline conditions the effect of microbial metabolism on supersaturation by ph and alkalinity increase is negligible a putative microbial effect could however support dolomite nucleation or support crystal growth by overcoming a kinetic barrier an essential limitation on crystal growth rates imposed by the low ca 2 and mg 2 concentrations could favour the thermodynamically more stable carbonate phase which is dolomite to precipitate this mode of unlithified dolomite ooze formation showing d 13 c values near to equilibrium with atmospheric co2 ca 3 contrasts the formation of isotopically light organically derived hard lithified dolomite layers in the subsurface of some less alkaline environments inferred physicochemical controls on dolomite formation under highly alkaline conditions observed in deep springs lake may shed light on conditions that favoured extensive dolomite formation in alkaline precambrian oceans as opposed to modern oceans where dolomites only form diagenetically in organic c rich sediments

crosswell electromagnetic tomography system design considerations and field results electrical conductivity is an important petroleum reservoir parameter because of its sensitivity to porosity pore fluid type and saturation although induction logs are widely used to obtain the conductivity near boreholes the poor resolution offered by surface based electrical and electromagnetic em field systems has thus far limited obtaining this information in the region between boreholes low frequency crosswell em offers the promise of providing subsurface conductivity information at a much higher resolution than was previously possible researchers at lawrence livermore national lab llnl and lawrence berkeley laboratories lbl together with an industrial consortium recently began a program to conduct low frequency crosswell em surveys and develop suitable inversion techniques for interpreting the data in developing the field instrumentation we used off the shelf components whenever possible but custom designed induction coil transmitters and receivers were built for the field experiment

tibetan and indian lithospheres in the upper mantle beneath tibet evidence from broadband surface wave dispersion broadband seismic experiments over the last two decades have produced dense data coverage across tibet yet the mechanism of the india asia lithospheric convergence beneath it remains a puzzle with even its basic features debated and with very different end member models advocated today we measured highly accurate rayleigh and love wave phase velocity curves in broad period ranges up to 5 200 s for a few tens of pairs and groups of stations across tibet combining in each case hundreds to thousands of interstation measurements made with cross correlation and waveform inversion methods robust shear velocity profiles were then determined by extensive series of nonlinear inversions of the data designed to constrain the depth dependent ranges of isotropic average shear speeds and radial anisotropy temperature anomalies in the upper mantle were estimated from shear velocities using accurate petrophysical relationships our results reveal strong heterogeneity in the upper mantle beneath tibet very large high velocity anomalies in the upper mantle are consistent with the presence of underthrust beneath southwestern tibet and subducted beneath central and eastern tibet indian lithosphere the corresponding thermal anomalies match those estimated for subducted indian lithosphere in contrast to the indian lithosphere tibetan lithosphere and asthenosphere display low to normal shear speeds tibetan lithosphere is thus warm and thin radial anisotropy in the upper mantle is weak in central and strong in northeastern tibet possibly reflecting asthenospheric flow above the subducting indian lithospheric slab

inversion of airborne tensor vlf data using integral equations the geological survey of sweden has been collecting airborne tensor very low frequency data vlf over several decades covering large parts of the country the data has been an invaluable source o

carbonate stable and clumped isotopic evidence for late eocene moderate to high elevation of the east central tibetan plateau and its geodynamic implications

a tale of two eddies diagnosing coherent eddies through acoustic remote sensing 1 a 38 khz vessel mounted acoustic doppler current profiler is used to explore in detail the dynamics of an anticyclonic and a cyclonic eddy during two transits of the cruise vessel explorer of the seas from the caribbean to new jersey in july 2007 the radial scale of the two eddies is similar but whereas the cyclone is strongly surface intensified the anticyclone has its maximum expression with near solid body rotation between 200 and 800 m depth the anticyclone has a minimum in relative vorticity very close to f at 800 m depth and the cyclone has a maximum of about 1 6 f close to the surface where f is the local coriolis parameter by integrating the momentum equation the geopotential anomaly field and hence the potential energy of the eddies can be determined quite accurately which means that the kinetic and potential energy of the eddies can be determined purely through acoustic remote sensing given a density profile just outside the eddy one can integrate the gradient wind equation to obtain an estimate of the density and hence potential vorticity fields through the two eddies the acoustic backscatter patterns in the eddies are quite distinct from the surrounding waters the backscatter intensity of the main scattering layer at 600 m depth decreases by 10 db in the core of both eddies in the cyclonic eddy three identifiable scattering layers in the main thermocline show a strong tendency for the scattering layer to track the shoaling density structure toward the center of the eddy

the tsushima warm current through tsushima straits estimated from ferryboat adcp data abstract current structures across the tsushima straits are studied using results from long term acoustic doppler current profiler adcp observations by a ferryboat between hakata and pusan conducted since february 1997 two maxima of the northeastward current are observed in the central parts of the eastern and western channels and the maximum velocity in the western channel is stronger than that of the eastern channel downstream of the tsushima islands a southwestward countercurrent is observed associated with a pair of cyclonic and anticyclonic eddies in the western channel the deep countercurrent is observed pronouncedly on the bottom slope of the korean side from summer to winter the volume transport of the tsushima warm current through the straits has strong seasonal variation with a minimum in january and two maxima from spring to autumn double peaks the spring peak of the volume transport through the eastern channel is more pronounced than the autumn peak and the autumn peak of the west

climatic and diagenetic signals in the stable isotope geochemistry of dolomitic paleosols spanning the paleocene eocene boundary abstract the precipitation of primary dolomite in soil is rare and controversial and its occurrence indicates highly unusual geochemical and climatic conditions we utilize isotopic and petrographic techniques including clumped isotope thermometry to evaluate diagenetic alteration and preservation of primary climatic signal in dolomitic paleosol nodules from a section spanning the paleocene eocene boundary in central utah isotopic measurements differentiate samples into groups that may be interpreted in terms of alteration however moderate burial depths and extreme warmth during the interval of soil formation make it difficult to reach definitive conclusions from isotope values alone with the addition of petrographic analysis including cathodoluminescence and scanning electron microscopy we are able to identify textural differences between samples suggesting differing amounts of recrystallization we conclude that while some nodules have experienced significant diagenetic alteration the original nodule mineralogy is dolomite and the majority of sampled nodules retain a primary paleoclimate signal early paleogene temperatures recorded at this site are considerably warmer than those suggested for the continental interior from alternate proxies a result that may be partially the result of the clumped isotope temperatures recording warm season soil temperatures rather than mean annual air temperature soil water isotopic composition is suggestive of heightened aridity particularly through the paleocene eocene thermal maximum petm

asian monsoons in a late eocene greenhouse world the strong present day asian monsoons are thought to have originated between 25 and 22 million years myr ago driven by tibetan himalayan uplift however the existence of older asian monsoons and their response to enhanced greenhouse conditions such as those in theeocene period 55 34myrago are unknownbecause of the paucity of well dated records here we show late eocene climate records revealing marked monsoon like patterns in rainfall and wind south and north of the tibetan himalayan orogen this is indicated by low oxygen isotope values with strong seasonality in gastropod shells and mammal teeth from myanmar and by aeolian dust deposition in northwest china our climate simulations support modern like eocene monsoonal rainfall and show that a reinforced hydrological cycle responding to enhancedgreenhouse conditions counterbalanced the negative effect of lowertibetanrelief onprecipitation these strong monsoons later weakened with the global shift to icehouse conditions 34myr ago

δ18o and δd of streamwaters across the himalaya and tibetan plateau implications for moisture sources and paleoelevation reconstructions abstract this study presents new 18o and d data from 191 streams across the himalaya and tibetan plateau to better constrain the spatial variability of stable isotopes in modern precipitation over this region moisture penetrating into the southeastern tibetan plateau is predominantly derived from monsoonal airmasses originating from the bay of bengal and transported into the eastern himalayan syntaxis along the brahmaputra river progressive rainout during orographic lifting and cooling results in clear relationships between 18o and d and catchment hypsometric elevation on the plateau margin however monsoonal derived moisture is progressively mixed with central asian airmasses in more western and northern parts of the tibetan plateau as a result predicted isotope elevation relationships that are based on empirical lapse rates or thermodynamic models of the isotopic evolution of an airmass produce large 1 3 km misfits between measured and predicted catchment elevations for much of the tibetan plateau including some areas directly north of the central himalayan crest this suggests that changes in the 18o or d of paleoprecipitation on the central and southwestern tibetan plateau may reflect surface uplift along moisture transport pathways or changes in the penetration of monsoonally derived moisture rather than regional surface uplift histories

tibetan plateau aridification linked to global cooling at the eocene oligocene transition the eocene oligocene transition about 33 5 million years ago was a major global climate event the end of the eocene was unusually warm with no significant ice on antarctica but the oligocene saw the arrival of a permanent antarctic ice sheet two papers this week relate to the continental effects of this global change dupont nivet et al examined sedimentary records from the tibetan plateau and find a drop in atmospheric water which caused cooling and aridification coincident with antarctic cooling previous studies attributed this phenomenon to the rapid uplift of the tibetan plateau but this new work suggests that regional tibetan climate was influenced by global events in an unrelated paper on the same climate transition zanazzi et al explore the cooling in north america at the time using stable isotope measurements from fossil teeth and bones to create a proxy temperature record they find a large drop in mean annual temperature of 8 2 c a greater fall than seen in the oceans this continental transition may explain why many cold blooded reptiles and amphibians became extinct whereas mammals able to regulate their body temperature escaped relatively unscathed precisely dated evidence details that aridification on the tibetan plateau occurred at the time of the eocene oligocene transition in the marine records this suggests a direct link between the palaeontological and palaeoenvironmental changes recorded in continental asia at the time and global climate cooling continental aridification and the intensification of the monsoons in asia are generally attributed to uplift of the tibetan plateau and to the land sea redistributions associated with the continental collision of india and asia1 2 3 whereas some studies suggest that past changes in asian environments are mainly governed by global climate4 5 6 the most dramatic climate event since the onset of the collision of india and asia is the eocene oligocene transition an abrupt cooling step associated with the onset of glaciation in antarctica 34 million years ago7 8 9 however the influence of this global event on asian environments is poorly understood here we use magnetostratigraphy and cyclostratigraphy to show that aridification which is indicated by the disappearance of playa lake deposits in the northeastern tibetan plateau occurred precisely at the time of the eocene oligocene transition our findings suggest that this global transition is linked to significant aridification and cooling in continental asia recorded by palaeontological and palaeoenvironmental changes10 11 12 and thus support the idea that global cooling is associated with the eocene oligocene transition13 14 15 we show that with sufficient age control on the sedimentary records global climate can be distinguished from tectonism and recognized as a major contributor to continental asian environments

cretaceous tertiary shortening basin development and volcanism in central tibet the geologic map pattern of the qiangtang terrane in central tibet defines a 600 km long and up to 270 km wide east plunging structural culmination it is characterized by early mesozoic blueschist bearing melange and upper paleozoic strata in the core and mainly triassic jurassic strata along the limbs in the western qiangtang terrane 84 e the culmination is unconformably overlain by weakly deformed mid cretaceous volcanic flows and tuffs along the bangong suture to the south 32 n 84 e mid cretaceous nonmarine red beds and volcanic rocks lie unconformably on jurassic suture zone rocks these relationships demonstrate that west central tibet was above sea level during the mid cretaceous and experienced significant denudation prior to mid cretaceous time growth of the qiangtang culmination is inferred to have initiated during southward emplacement of a thrust sheet of early mesozoic melange and upper paleozoic strata during the early cretaceous lhasa qiangtang collision the north south width of the inferred thrust sheet provides a minimum slip estimate of 150 km at 84 e decreasing eastward to 70 km at 87 e paleogene deformation in the qiangtang terrane is characterized by widely distributed mainly north dipping thrust faults that cut eocene oligocene red beds and volcanic rocks in their footwall along the bangong suture the north dipping shiquanhe gaize amdo thrust system cuts 64 and 43 m y old volcanic tuffs in its footwall and accommodated 40 km of post mid cretaceous shortening the tertiary south dipping gaize siling co backthrust bounds the southern margin of the bangong suture and marks the northernmost limit of mid cretaceous marine strata in central tibet cretaceous deformation and denudation in central tibet is attributed to northward underthrusting of the lhasa terrane beneath the qiangtang terrane along the bangong suture this model implies that 1 cretaceous strata along the bangong suture and in the northern lhasa terrane were deposited in a flexural foreland basin system and derived at least in part from the qiangtang terrane and 2 the central tibetan crust was thickened substantially prior to the indo asian collision although its magnitude is poorly known tertiary shortening in the qiangtang terrane is more prevalent than in the lhasa terrane this difference may be attributed to the presence of underthrust melange in the deeper central tibetan crust which would have made it weaker than the lhasa terrane during the indo asian collision

quantifying landscape differences across the tibetan plateau implications for topographic relief evolution 1 we quantify the bulk topographic characteristics of the tibet qinghai plateau with specific focus on three representative regions northern central and southeastern tibet quantitative landscape information is extracted from shuttle radar topography mission digital elevation models we find that the morphology of the tibetan plateau is nonuniform with systematic regional differences the northern and central parts of the plateau are characterized by what we suggest to call positive topography i e a topography in which elevation is positively correlated with relief and mean slope a major change from the internally drained central part of tibet to the externally drained part of eastern tibet is accompanied by a transition from low to high relief and from positive to negative topography i e a topography where there is an inverse or negative correlation between elevation and relief and between elevation and mean slope relief in eastern tibet is largest along rivers as they cross an ancient eroded plateau margin at high angle to the major strike slip faults the yalong yulong thrust belt implying strong structural control of regional topography we propose that the evolution of river systems and drainage efficiency the ability of rivers to transport sediments out of the orogen coupled with tectonic uplift is the simplest mechanism to explain systematic regional differences in tibetan landscapes basin filling due to inefficient drainage played a major role in smoothing out the tectonically generated structural relief this mode of smoothing started concurrently with tectonic construction of the relief as most clearly illustrated today in the qilian shan qaidam region of the northeastern plateau in the interior of tibet further passive filling due to internal drainage only continued to smooth the local relief millions of years after the cessation of major phases of surface uplift due to crustal shortening thus diachronous beveling at high elevation produced the low relief surface of the high plateau in southeast tibet headward retreat of external drainages brought back in the global ocean base level first disrupting then interrupting the relief reduction process it produced a transitional topography by dissecting the old remnant plateau surface which introduced younger and steeper incision of this hitherto preserved high base level this provides a unifying mechanism for the formation of the low relief plateau interior and for the origin of the high elevation low relief relict surface in southeastern tibet our analysis brings forth the importance of surface processes in particular drainage efficiency in shaping plateau morphology and landscape relief such key processes appear to have been mostly ignored in numerical models of plateau deformation our results also cast doubt on and provide a more realistic alternative to the fashionable contention that a continuous preuplift low relief surface first formed at low elevation extending all the way to the south china sea shore before being warped upward in the late miocene pliocene by lower crustal channel flow

two years in the life of a mediterranean salt lens abstract a lens of mediterranean water meddy was tracked in the eastern north atlantic for two years with sofar floats the meddy was first found between the canary islands and the azores in october 1984 it center moved in an irregular pattern at speeds of a few cm s 1 and translated 1100 km to the south in two years this meddy was surveyed four times by ctd and velocity profilers and once with the microstructure profiler epsonde when observed during the first two surveys the meddy had a core that was stably and smoothly stratified in both salinity and temperature nearly uniform in the horizontal and was saltier than the surrounding ocean by 0 65 psu the meddy was eroded from its edges top and bottom and lost salt and hat with an e folding time of about one year the salinity at the center remained at its original value during the first year and decreased during the second year evidence was seen for mixing by lateral intrusions double diffusion and turbulence the intrusions are thought to