late oligocene early miocene birth of the taklimakan desert as the world s second largest sand sea and one of the most important dust sources to the global aerosol system the formation of the taklimakan desert marks a major environmental event in central asia during the cenozoic determining when and how the desert formed holds the key to better understanding the tectonic climatic linkage in this critical region however the age of the taklimakan remains controversial with the dominant view being from 3 4 ma to 7 ma based on magnetostratigraphy of sedimentary sequences within and along the margins of the desert in this study we applied radioisotopic methods to precisely date a volcanic tuff preserved in the stratigraphy we constrained the initial desertification to be late oligocene to early miocene between 26 7 ma and 22 6 ma we suggest that the taklimakan desert was formed as a response to a combination of widespread regional aridification and increased erosion in the surrounding mountain fronts both of which are closely linked to the tectonic uplift of the tibetan pamir plateau and tian shan which had reached a climatically sensitive threshold at this time

aeolian desertification in china s northeastern tibetan plateau understanding the present through the past abstract under a background of a significantly warming climate current aeolian desertification in china s northeastern tibetan plateau netp has been widely studied but disagreements related to its causes continue to persist in order to understand the present through the past this study determined the various phases of aeolian desertification in the netp based on the statistical analysis of 40 optically stimulated luminescence osl aeolian sand dates from 23 aeolian sections because the redistribution of aeolian sand by wind processes can reduce the number of older sand dates this research only affects exactly the past millennium following this we analyzed the relationships between aeolian desertification phases in conjunction with reconstructed climatic data results revealed three distinct aeolian desertification phases that approximately correspond to 1480 ce 1680 ce and 1800 ce respectively by comparing these dates to well established paleoclimate records we determined that these three aeolian desertification phases all occurred under a cold and dry climate background accordingly aeolian desertification in the netp today under its current warm and wet climate background can therefore be attributable to irrational human activities rather than rising temperatures accordingly we can infer that under the current warmer and wetter climate background aeolian desertification in the netp today can be reversed as long as human activities remain moderate even without the implementation of artificial revegetation initiatives

on the origin of a wedge crack within the icy crust of europa 1 we suggest that a crack that developed into a wedge shaped band within the icy crust of europa at 28 s 170 w see schenk and mckinnon 1989 figure 4 prockter et al 1999 figure 1 originated under an applied compressive stress through the operation of a frictional sliding mechanism we analyze this suggestion using a scale independent sliding crack model and obtain an estimate of the maximum compressive stress to initiate the crack that compares reasonably well with earlier estimates helfenstein and parmentier 1985 mcewen 1986 greenberg et al 1998 of europan crustal stresses that are based upon elastic deformation of a shell we then show through an application of both power law dislocation creep and diffusion creep that colder near surface europan ice appears to be capable of supporting the deduced stresses with little relaxation over a period from 104 to 105 years

evidence for enhanced aridity in the tarim basin of china since 5 3 ma abstract thick cenozoic deposits formed from the erosion of the northern evolving edge of the tibetan plateau provide opportunities to study the exhumation history and climatic changes within the region such deposits are important because they are located in an actively deforming mountain belt as well as in a rain shadow of the tibetan plateau multi proxy studies indicate that hyperarid climate has prevailed since 5 3 ma ago within the basin this information together with the geometry analysis of syntectonic deposits of the sanju anticline which indicate tectonic deformation at 5 3 ma enable us to better understand the interlay between climatic changes and tectonic uplift our results suggest that the tectonic uplift of the kunlun mountains at 5 3 ma must have been one of the significant regional tectonic events and the uplifted elevation of the kunlun mountains more effectively blocks the penetration of moisture from the indian monsoon into the tarim basin and thus enhances the rain shadow effect this can account for the increasing aridity as well as the formation of the world s second largest active sand desert the taklimakan desert in the tarim basin initiated at 5 3 ma ago

quantification of holocene asian monsoon rainfall from spatially separated cave records abstract a reconstruction of holocene rainfall is presented for southwest china an area prone to drought and flooding due to variability in the east asian monsoon the reconstruction is derived by comparing a new high resolution stalagmite 18 o record with an existing record from the same moisture transport pathway the new record is from heshang cave 30 27 n 110 25 e 294 m and shows no sign of kinetic or evaporative effects so can be reliably interpreted as a record of local rainfall composition and temperature heshang lies 600 km downwind from dongge cave which has a published high resolution 18 o record wang y j cheng h edwards r l he y q kong x g an z s wu j y kelly m j dykoski c a li x d 2005 the holocene asian monsoon links to solar changes and north atlantic climate science 308 854 857 by differencing co eval 18 o values for the two caves secondary controls on 18 o e g moisture source moisture transport non local rainfall temperature are circumvented and the resulting 18 o signal is controlled directly by the amount of rain falling between the two sites this is confirmed by comparison with rainfall data from the instrumental record which also allows a calibration of the 18 o proxy the calibrated 18 o record provides a quantitative history of rainfall in southwest china which demonstrates that rainfall was 8 higher than today during the holocene climatic optimum 6 ka but only 3 higher during the early holocene significant multi centennial variability also occurred with notable dry periods at 8 2 ka 4 8 4 1 ka 3 7 3 1 ka 1 4 1 0 ka and during the little ice age this holocene rainfall record provides a good target with which to test climate models the approach used here of combining stalagmite records from more than one location will also allow quantification of rainfall patterns for past times in other regions

inclusion of topological measurements into analytic estimates of effective permeability in fractured media we demonstrate how topology based measures of connectivity can be used to improve analytical estimates of effective permeability in 2 d fracture networks which is one of the key parameters necessary for fluid flow simulations at the reservoir scale existing methods in this field usually compute fracture connectivity using the average fracture length this approach is valid for ideally shaped randomly distributed fractures but is not immediately applicable to natural fracture networks in particular natural networks tend to be more connected than randomly positioned fractures of comparable lengths since natural fractures often terminate in each other the proposed topological connectivity measure is based on the number of intersections and fracture terminations per sampling area which for statistically stationary networks can be obtained directly from limited outcrop exposures to evaluate the method numerical permeability upscaling was performed on a large number of synthetic and natural fracture networks with varying topology and geometry the proposed method was seen to provide much more reliable permeability estimates than the length based approach across a wide range of fracture patterns we summarize our results in a single explicit formula for the effective permeability

trace element degassing and enrichment in the eruptive plume of the 2000 eruption of hekla volcano iceland during its last eruption in february 2000 hekla volcano iceland emitted a sub plinian plume that was condensed and scavenged down to the ground by heavy snowstorms offering the unique opportunity to study the chemistry of the gaseous plume released during highly explosive eruptions in this paper we present results on trace element and minor volatile species sulfates chlorides and fluorides concentrations in snow samples collected shortly after the beginning of the eruption the goal of this study is to better constrain the degassing and mobility of trace elements in gaseous emissions trace element volatility at hekla is quantified by means of enrichment factors ef relative to be well known volatile trace elements e g transition metals heavy metals and metalloids are considerably enriched in the volcanic plume of hekla their abundances are governed by the primary magmatic degassing of sulfate and or halide compounds which are gaseous at magmatic temperature their volatility is however slightly lower than in basaltic systems most likely because of the lower magma temperature and higher magma viscosity at hekla more surprisingly refractory elements e g ree th ba and y are also significantly enriched in the eruptive plume of hekla where their apparent volatility is two orders of magnitude higher than in mafic systems in addition ree patterns normalized to the hekla 2000 lava composition show a significant enrichment of hree over lree suggesting the presence of ree fluorides in the volcanic plume such enrichments in the most refractory elements and ree fractionation are difficult to reconcile with primary degassing processes since ree fluorides are not gaseous at magma temperature ree enrichments at hekla could be attributed to incongruent dissolution of tephra grains at low temperature by f rich volcanic gases and aerosols within the eruptive plume this view is supported by both leaching experiments performed on hekla tephra and thermodynamic considerations on ree mobility in hydrothermal fluids and modeling of glass dissolution in f rich aqueous solutions tephra dissolution may also explain the observed enrichments in other refractory elements e g th y and ba and could contribute to the degassing mass balance of some volatile trace elements provided they are mobile in f rich fluids it thus appears that both primary magmatic degassing and secondary tephra dissolution processes govern the chemistry of eruptive plumes released during explosive eruptions

sequential approach to joint flow seismic inversion for improved characterization of fractured media seismic interpretation of subsurface structures is traditionally performed without any account of flow behavior here we present a methodology for characterizing fractured geologic reservoirs by integrating flow and seismic data the key element of the proposed approach is the identification within the inversion of the intimate relation between fracture compliance and fracture transmissivity which determine the acoustic and flow responses of a fractured reservoir respectively owing to the strong but highly uncertain dependence of fracture transmissivity on fracture compliance the modeled flow response in a fractured reservoir is highly sensitive to the geophysical interpretation by means of synthetic models we show that by incorporating flow data well pressures and tracer breakthrough curves into the inversion workflow we can simultaneously reduce the error in the seismic interpretation and improve predictions of the reservoir flow dynamics while the inversion results are robust with respect to noise in the data for this synthetic example the applicability of the methodology remains to be tested for more complex synthetic models and field cases

chemical weathering of basalts southwest iceland effect of rock crystallinity and secondary minerals on chemical fluxes to the ocean river ground and peat water from a basaltic catchment area laxa in kjos southwest iceland were sampled and analyzed for major element concentrations to define the effect of glassy versus crystalline basalt the formation of secondary minerals and runoff on fluxes of dissolved elements to the ocean the proportions of the dissolved solids in the water samples derived from precipitation air and rock weathering were estimated the amounts of na mg ca k and s originating from precipitation were calculated from the respective solute cl marine ratios and the estimated aqueous cl originated from precipitation which was calculated using measured b content of the waters and b cl molal marine and rock ratios the rock contribution from weathering ranged from 22 to 46 percent of the total dissolved solids of the waters iron and al showed low mobility compared to na this was primarily due to consumption of these elements by ferrihydroxides allophane imogolite and clay minerals also si and to a lesser degree ca show apparent slightly lower mobility than na these results are in good agreement with these phases being dominant in the soils of the study area wada and others 1992 and the main secondary minerals of basaltic glass in iceland crovisier and others 1992 reaction progress calculations support these findings according to a model interaction of basaltic glass and meteoric water al fe and si are consumed by amorphous fe and al hydroxides and imogolite and allophane at low reaction progress with increasing reaction progress ca fe mg smectite became the primary secondary minerals limiting the mobility of ca fe mg si and al these findings suggest that the weathering in the laxa in the kjos catchment area has evolved into the beginning of the smectite weathering stage and that it is dominated by a relatively low reaction progress and a high water to rock ratio in the present study the effect of runoff and rock crystallinity was quantified for dissolved elemental fluxes temperature lithology other than rock crystallinity and rock age were similar in all of the catchment areas in this study silica ca f s al k mg and b had a very similar dependence on runoff on the other hand na fluxes were found to be less dependent on runoff and fe fluxes were found to be independent of runoff basaltic glass dissolves faster than fully crystallized basaltic rocks gislason and eugster 1987a therefore increased glass content of the primary rocks is thought to increase the leaching and elemental fluxes at constant runoff however because some of the solutes particularly al and fe were highly influenced or even controlled by the formation of secondary minerals this increasing dissolution with increasing glass content was hidden on the other hand basaltic glass was observed to enhance the fluxes of more mobile elements like na si ca f and s by a factor of 2 to 5 at a constant runoff of 200 cm yr constant vegetative cover and 0 to 100 percent glass content of the rocks the k and mg fluxes were found to be independent of rock crystallinity however runoff alone cannot explain the fluxes of these elements and it seems that vegetative cover and seasonal variations in biomass activities influence the k and mg fluxes

osl chronology and possible forcing mechanisms of dune evolution in the horqin dunefield in northern china since the last glacial maximum the evolution processes and forcing mechanisms of the horqin dunefield in northern china are poorly understood in this study systematic osl dating of multiple sites is used together with pollen analysis of a representative section in order to reconstruct the evolution of the dunefield since the last glacial maximum lgm our results show that there was extensive dune mobilization 25 10 ka transition to stabilization 10 8 ka considerable dune stabilization 8 3 ka and multiple episodes of stabilization and mobilization after 3 ka comparison of dune evolution of the dunefields in northern china during the holocene showed that asian monsoon and resultant effective moisture have played an important role in the evolution of dunefields at the millennial time scale further analysis indicated that the dune evolution in the horqin dunefield before 3 ka was synchronous with climatic changes however increasing human activity has impacted dune evolution during the last 3 ka c 2012 university of washington published by elsevier inc all rights reserved the evolution processes and forcing mechanisms of the horqin dunefield in northern china are poorly understood in this study systematic osl dating of multiple sites is used together with pollen analysis of a representative section in order to reconstruct the evolution of the dunefield since the last glacial maximum lgm our results show that there was extensive dune mobilization 25 10 ka transition to stabilization 10 8 ka considerable dune stabilization 8 3 ka and multiple episodes of stabilization and mobilization after 3 ka comparison of dune evolution of the dunefields in northern china during the holocene showed that asian monsoon and resultant effective moisture have played an important role in the evolution of dunefields at the millennial time scale further analysis indicated that the dune evolution in the horqin dunefield before 3 ka was synchronous with climatic changes however increasing human activity has impacted dune evolution during the last 3 ka c 2012 university of washington published by elsevier inc all rights reserved

stepwise expansion of desert environment across northern china in the past 3 5 ma and implications for monsoon evolution abstract a systematic study of the last glacial cycle along three transects across the chinese loess plateau shows that sand sized particle content within loess decreases rapidly from north to south and that markedly high sand particle contents in loess horizons occur only in the northern part of the plateau this suggests that variation in the sand sized particle fraction within loess near the desert margin is closely linked to migration of the southern desert border in northern china where sand grains move mainly in saltation or modified saltation mode near the ground surface as desert margin shift is essentially controlled by the amount of monsoon precipitation the sand sized particle content within loess near desert margin is regarded as a new and readily applied proxy for variations in the strength of the east asian summer monsoon a continuous record of sand content in loess along the loess desert transitional zone shows that the mu us desert migrated southward at 2 6 1 2 0 7 and 0 2 ma suggesting a stepwise weakening of the east asian summer monsoon during the past 3 5 ma this evolutionary pattern is significantly different from that previously inferred from loess magnetic susceptibility records a widely used monsoon proxy our results further suggest that changes in global ice volume may have been an essential factor in controlling plio pleistocene monsoon evolution and that the anticipated future melting of polar ice cover may lead to a northward migration of the monsoon rainfall belt in northern china

late quaternary aeolian activity in the mu us and otindag dune fields north china and lagged response to insolation forcing 1 dune fields in parts of northern china contain important stratigraphic records of late quaternary change in the east asian monsoon in this study 33 new optically stimulated luminescence osl ages and other measurements from aeolian sediment sections are used to reconstruct the timing of wet dry climate variation in the mu us and otindag dune fields of north china the results indicate dune activity and dry climate in the last few hundred years 14 ka to about 7 8 ka and 50 ka to 60 ka the dunes were mainly stable implying a wetter climate between about 7 8 ka and 2 4 ka these results imply a lag of several thousand years between peak summer insolation at 10 11 ka and high summer monsoon rainfall after 7 8 ka in the investigated regions the monsoon climate may not respond directly to orbital forcing over millennial time scales land surface feedbacks may account for lagged dune field response

east west faults due to planetary contraction abstract contraction expansion and despinning have been common in the past evolution of solar system bodies these processes deform the lithosphere until it breaks along faults their characteristic tectonic patterns have thus been sought for on all planets and large satellites with an ancient surface while the search for despinning tectonics has not been conclusive there is good observational evidence on several bodies for the global faulting pattern associated with contraction or expansion though the pattern is seldom isotropic as predicted the cause of the non random orientation of the faults has been attributed either to regional stresses or to the combined action of contraction expansion with another deformation despinning tidal deformation reorientation another cause of the mismatch may be the neglect of the lithospheric thinning at the equator or at the poles due either to latitudinal variation in solar insolation or to localized tidal dissipation using thin elastic shells with variable thickness i show that the equatorial thinning of the lithosphere transforms the homogeneous and isotropic fault pattern caused by contraction expansion into a pattern of faults striking east west preferably formed in the equatorial region by contrast lithospheric thickness variations only weakly affect the despinning faulting pattern consisting of equatorial strike slip faults and polar normal faults if contraction is added to despinning the despinning pattern first shifts to thrust faults striking north south and then to thrust faults striking east west if the lithosphere is thinner at the poles the tectonic pattern caused by contraction expansion consists of faults striking north south i start by predicting the main characteristics of the stress pattern with symmetry arguments i further prove that the solutions for contraction and despinning are dual if the inverse elastic thickness is limited to harmonic degree two making it easy to determine fault orientation for combined contraction and despinning i give two methods for solving the equations of elasticity one numerical and the other semi analytical the latter method yields explicit formulas for stresses as expansions in legendre polynomials about the solution for constant shell thickness though i only discuss the cases of a lithosphere thinner at the equator or at the poles the method is applicable for any latitudinal variation of the lithospheric thickness on iapetus contraction or expansion on a lithosphere thinner at the equator explains the location and orientation of the equatorial ridge on mercury the combination of contraction and despinning makes possible the existence of zonal provinces of thrust faults differing in orientation north south or east west which may be relevant to the orientation of lobate scarps

seismic multiplet response triggered by melt at blood falls taylor glacier antarctica 1 meltwater input often triggers a seismic response from glaciers and ice sheets it is difficult however to measure melt production on glaciers directly while subglacial water storage is not directly observable therefore we document temporal changes in seismicity from a dry based polar glacier taylor glacier antarctica during a melt season using a synthesis of seismic observation and melt modeling we record icequakes using a dense six receiver network of three component geophones and compare this with melt input generated from a calibrated surface energy balance model in the absence of modeled surface melt we find that seismicity is well described by a diurnal signal composed of microseismic events in lake and glacial ice during melt events the diurnal signal is suppressed and seismicity is instead characterized by large glacial icequakes we perform network based correlation and clustering analyses of seismic record sections and determine that 18 of melt season icequakes are repetitive multiplets the epicentral locations for these multiplets suggest that they are triggered by meltwater produced near a brine seep known as blood falls our observations of the correspondingp wave first motions are consistent with volumetric source mechanisms we suggest that surface melt enables a persistent pathway through this cold ice to an englacial fracture system that is responsible for brine release episodes from the blood falls seep the scalar moments for these events suggest that the volumetric increase at the source region can be explained by melt input

scaling and connectivity of joint systems in sandstones from western norway abstract the scaling properties of a joint system in devonian sandstones in western norway have been investigated using seven maps covering areas from 18 to 720 m across which were generated by mapping in the field and from low level aerial photography taken from different heights each map represent a scale window on the fracture population bounded by resolution at small scales and the sample size at large scales a power law relationship between fracture trace length and critical observation height maximum height at which a trace can be identified is derived and used to create a statistical model for the resolution effects the model indicates that a continuous smooth curve without a straight line segment on a log log cumulative frequency distribution plot does not necessarily rule out a power law as the underlying population distribution together the maps indicate a powerlaw trace length distribution with an exponent of 2 1 this power law may be valid over four or more orders of magnitude with natural lower cut off of around 1 m the exponent is significantly different from 2 0 strictly selfsimilar case and is reflected in a decrease in the abundance of fractures with length comparable to map size as map scale decreases the fracture trace length distribution results in a decrease in apparent connectivity with decreasing scale high resolution large scale maps are well connected while the lowest resolution map smallest scale is unconnected fractures in the smallest scale map are however connected by small fractures below the limit of resolution represented by the largest scale map the variation in apparent connectivity with scale has implications for fluid flow when fractures are open to fluid flow the scaling properties of apparent connectivity imply that beyond a certain scale the size of fracture controlling flow will be scale independent in this fracture system this appears to occur in sample areas of around 300 m across

aeolian system responses to global change challenges of scale process and temporal integration aeolian sediment systems are extensive components of the earth s surface not just in today s active desert environments but in coastal locations and as presently stable loess and peri desert ergs all these systems are subject to potentially significant 21st century changes in dynamics due to global warming impacts on atmospheric circulation sediment moisture and vegetation cover but do we know enough in the critical areas of science to allow robust models of likely future dynamics to be developed since the establishment of modern aeolian science research has largely taken two divergent routes 1 small scale investigations of the processes of wind shear sediment entrainment and transportation and 2 landform and landscape analyses with bedform systems described and relationships to circulation explained an intermediate sedimentological route has generated attempts towards a more integrated understanding of system behaviour at a range of scales four recent developments provide the potential for more robust multiscale integrations of aeolian system behaviour these are 1 advances in empirical measurement that allow wind power and sediment flux relations to be better described 2 modelling of dune and dust dynamics and interactions with key controls 3 monitoring systems that allow high resolution observations of sediment flux variations to be recognized and aeolian deposit structures to be understood and 4 chronometric advances that permit the assessment of the frequency and drivers of dune system activity in the past we explore and analyse these methodological advances and their potential contribution to the multiscale integrations that are essential for better informed predictions of future global aeolian system dynamics considering whether the integration of these advances in reductionist and holistic elements of aeolian science represent an example of the effective application of the principles of earth system science copyright 2008 john wiley sons ltd

fluorine and boron geochemistry of an ensialic marginal basin volcano deception island bransfield strait antarctica abstract we present the initial results of a quantitative investigation of the volatile geochemistry of deception island an active volcano situated near the spreading axis of a quaternary ensialic marginal basin bransfield strait northern antarctic peninsula fluorine contents in deception island magmas 112 461 ppm are comparable with lavas from a range of tectonic environments but f k 2 o relationships most closely compare with continental flood basalts and lavas from island arcs and some marginal basins boron contents are high 4 3 16 3 ppm and the values overlap with those of arc lavas they provide strong support for the presence of a mantle source component derived from the slab subducted at the coeval trench by melting at the slab wedge interface and or during slab dehydration both f and b acted incompatibly in deception island magmas but there is significant variation in incompatible element ratios such as k f k b p f p b which strongly suggests that the magmatic system was open to some or all of these elements during differentation the variations in these ratios also provide evidence for the presence of at least two stages in the magmatic evolution of the volcano during pre caldera times mafic magma was emplaced into the upper crust where it evolved and may have reacted with the crustal envelope thus changing the contents of some or all of the elements f b k and p and their inter element ratios a later large influx of hot mafic magma into the chamber may have been responsible for a major eruption that ultimately led to the formation of the caldera k f k b etc ratios in the magma chamber were reset and subsequently continued to change possibly by further crustal interaction during melt evolution in post caldera times

climate driven changes to dune activity during the last glacial maximum and deglaciation in the mu us dune field north central china one significant change of terrestrial landscapes in response to past climate change has been the transformation between activity and stability of extensively distributed wind blown sand dunes the relations between the dynamics of the aeolian landscape and its drivers are not yet completely understood however evidence of aeolian sand deposition during the last glacial maximum lgm is scarce in many mid latitude dune fields whereas abundant evidence exists for aeolian sand accumulation during the deglaciation i e after about 15 ka whether this contrast actually reflects changes in dune activity is still unclear making paleoclimatic interpretation uncertain comprehensive field investigation and luminescence dating in the mu us dune field north central china demonstrates that aeolian sands deposited during the lgm are preserved as fills in periglacial sand wedges and beneath loess deposits near the downwind dune field margin the scarcity of lgm dune sand elsewhere in the dune field is interpreted as the result of intensive aeolian activity without substantial net sand accumulation increasing sand accumulation after 15 ka reflected by much more extensive preservation signals a change in sand supply relative to sand transportation through the dune field reduced wind strength and other environmental changes including regional permafrost degradation after 15 ka transformed the dune field state from net erosion to net accumulation the dunes however remained largely mobile as they were in the lgm similar diverging patterns of dune sand accumulation and preservation before and after 15 ka in many mid latitude dune fields imply broad climatic controls linked to the changes in high northern latitude forcing

luminescence dating of loess palaeosol sequences and coversands methodological aspects and palaeoclimatic implications abstract of the terrestrial archives loess palaeosol sequences provide a most complete record of climatic change this may be compared with the marine oxygen isotope stratigraphy and may help in the reconstruction of past atmospheric circulation patterns numerical chronometry of loess palaeosol sequences has generally been based on correlation of variations in climatic proxies such as magnetic susceptibility and particle sizes with marine isotopic data such chronometric assignments involve implicit assumptions about the constancy of sedimentation rates and particle fluxes through time this review presents a brief survey of the present status methodology outstanding problems and interpretational aspects of luminescence techniques and discusses the import of luminescence ages on global land sea correlations statistical analysis of the ages suggests episodicity of loess accumulation with extended periods of quiescence recent luminescence dating studies on closely spaced samples also lead to a similar inference luminescence ages imply high variability in loess sedimentation rates this conflicts with the assumption made in some current attempts to correlate loess records with marine records of almost constant particle fluxes a review of source proximal coversand deposits of northwest europe is also presented evidence of the onset of coversand deposition at 15 ka with a peak in accretion during the younger dryas and subsequent minor reactivation episodes is discussed

early middle holocene lake desert evolution in northern ulan buh desert china abstract located in southwestern inner mongolia in northern china the ulan buh desert ubd has evolved significantly during the holocene the northern desert is adjacent to hetao plain an important agriculture area since the han dynasty 200 b c a series of aeolian sand lacustrine sequences from the desert were measured and dated by using differential global positioning system dgps and optically stimulated luminescence osl technologies respectively these lacustrine remains with similar deposit sequences have almost identical elevations and depositional ages indicating that they belonged to a unified paleolake in addition the holocene paleolake desert evolution process in ubd is established aeolian activity prevailed before 8 3 ka and a unified ulan buh paleolake containing the modern jilantai salt lake covered the northern desert during 7 8 7 1 ka ago the paleolake shrank and broke apart after 6 5 ka ago thereafter the paleolake evolved into the modern ubd and jilantai salt lake the study of one sand lacustrine section at the southern edge of hetao plain shows that the tushenze paleolake had a similar evolution process to ulan buh paleolake though they may not be connected to each other as suggested by the elevation difference the ulan buh desert lake evolution was likely due to the climate changes in the monsoon influenced region during the early middle holocene

lateglacial and holocene dune evolution in the horqin dunefield of northeastern china based on luminescence dating abstract the horqin dunefield is located in the northern frontier of east asian monsoon eam zone and its activation and stabilization is sensitive to the ebb and flow of the eam however the activity of dunes in the horqin dunefield is still poorly understood due to limited numerical dating the purpose of the present study is to establish the chronology using luminescence dating in order to understand dune evolution of the horqin dunefield and to explore the relative role of climate and human activity eighteen samples were collected from seven sections following a southwest northeast transect through the dunefield and dated using quartz optically stimulated luminescence osl combining evidence from stratigraphy and the luminescence chronology dune evolution within the horqin dunefield since the lateglacial can be summarized as before 9 6 ka aeolian sand dunes were mobilized during the period 9 6 3 ka dunes were stabilized at around 3 ka dunes were mobilized again abruptly since 3 ka there were multiple phases of dune stabilization mobilization dune activity was dominated by climate before 3 ka however since 3 ka both climate variability and human impact have influenced dune evolution in the horqin dunefield

a statistical scaling model for fracture network geometry with validation on a multiscale mapping of a joint network hornelen basin norway 1 fracture patterns are characterized by a complex geometry which involves a large length distribution and nonhomogeneous density distributions here we address the issue of the modeling of this complex geometry over scales through a first order model providing the characterization of the number of fractures of a given length and at a given scale we propose that the simplest model is a power law in both space and fracture length with three main parameters the exponent a of a power law length distribution the fractal dimension d which fixes the scale dependence of the number of fractures and the fracture density we verify the applicability of this model on seven fracture patterns mapped from the metric scale up to almost the kilometric scale in the hornelen basin the model efficiently describes fracture network properties at all scales with a single set of parameters for the hornelen fracture networks we found a simple relationship between basic exponents a d 1 implying that the fracture network is self similar through this analysis we present different methodological developments for deriving the basic exponents a and d and for verifying the consistency of the model overall the main methodological development is about the normalization of the measurements made from different scales of observation finally we discuss both the limitations and the uses of such a model for analyzing the hydraulic and mechanical properties of fracture networks

a diverse ecosystem response to volcanic aerosols unexpectedly high aluminium concentrations beside fluoride and essential elements are released from metal salts adsorbed to volcanic ash through simulation of the mixing of pristine volcanic ash leachate with fresh water and seawater using phreeqc we found an increased potential toxicity in fresh waters through the combination of high aluminium and fluoride concentrations owing to the mixing of acid ash leachate with fresh water aluminofluoride complexes alfx 3 x persist in aqueous systems with low turnover rates and could be toxic to both plants and animals in contrast due to the well buffered and relatively high ph in seawater the speciation of the ash leachate seawater mixture shows that complexes of fluoride and aluminium i e alfx 3 x will not dominate in a well mixed marine system instead al oh x 3 x species will occur at greatest concentration consequently compared with fresh water environments the mixing of ash leachate with seawater indicates reduced toxic effects due to decreased formation of alfx 3 x complexes and the low solubility of al hydroxides in addition the deposition of volcanic aerosols may enhance biological activity in the marine environment by providing micronutrients as some oceanic phytoplankton species tolerates extreme concentrations of fluoride f

mapping permeability in heterogeneous aquifers using hydrologic and seismic data a new method is presented for identification of the permeability distribution in near surface aquifers in addition to using the usual sparsely sampled pressure and permeability data the method incorporates densely sampled seismic data as obtained from a reflection or tomography survey along with empirical relationships between seismic and hydraulic properties the procedure is to first estimate by hydrologic inversion a pressure field then the velocity permeability pressure relationship is used to map the inverted pressure and measured seismic data to multivalued estimates of the permeability of those the most probable value based on the hydrologic inversion is selected in synthetic case studies the tremendous increase in coverage offered by the seismic data leads to dramatically better results in terms of both accuracy and resolution an appealing feature is the use of relatively easy to acquire pressure data a second is the incorporation of geophysical data which can sample an entire aquifer remotely without the need for an expensive and invasive drilling program

deflated rims along the xiangshui river on the xiliaohe plain northeast china a case of active fluvial aeolian interactions abstract riverine source bordering sand dunes as a result of active fluvial aeolian interactions are a pronounced feature on the semiarid xiliaohe plain northeast china by means of satellite imagery analysis and both field survey and observation this paper presents a new type of riverine source bordering sand dunes deflated rims on the downwind margins of the xiangshui river they largely result from the deflation of escarpments on the downwind side of valley by local prevailing winds of nw direction not from the reworking of point bars on floodplain by wind in general a rim is primarily composed of three distinct zones 1 the upwind frontal escarpment zone with variable plan form shape gradient and relief which is formed by either active lateral erosion by river or significant erosion by wind and transient slope runoff 2 the deflation zone with gentle slopes of 8 18 and small scale aeolian bedforms i e ripples of fine sand ridges of coarse sand and 3 the downwind dynamic deposition zone with distinctive bedforms with variable superficial texture and slip faces the sand mass on rims derives overwhelmingly from underlying loose late quaternary sediments is sufficient and sustainable by successive retreats of the escarpment and is gradually transported downwind by pulse motions of bedforms coupled with high wind events essentially deflated rims are a starting point and the incipient phase of mature riverine dunefields the superimposed bedforms on rims are fundamentally governed by windflow dynamics sand sediments and antecedent bedform exhibiting in turn the manner and intensity of rim development consequently the upwind river valley and downwind deflated rim can jointly stimulate marked wave like motion of both windflow and aeolian bedforms at different scales especially when high wind events occur this study sheds some light on the understanding of the origin and development of riverine source bordering dunefields and offers new insights into the mechanisms of fluvial aeolian interactions on drylands worldwide

fluorine as a tool in the petrogenesis of quartz bearing magmatic associations applications of an improved f oh biotite apatite thermometer grid abstract fluorine contents of whole rock and biotites allow to discriminate quartz bearing magmatic associations through the nature of protoliths and petrogenetic processes f and rb are used to discriminate crustal and mantle derived melts with the exception of calcalkaline association in which mantle contribution may be significant the other quartz bearing associations are essentially derived from crustal melting by biotite and or amphibole vapor absent reactions based on experimental data and on an improved biotite apatite thermometer grid closure temperatures from near liquidus to near solidus conditions as well as fh2o fhf evolution during cooling are determined for the different magmatic associations it appears that the liquidus temperature and fh2o fhf decreases in the order high silica alkaline high k calcalkaline and calcalkaline associations while the solidus temperature follows an inverse order the fh2o fhf values for the peraluminous associations vary over a wide range and overlap the fh2o fhf values of the high k calcalkaline and calcalkaline associations

connectivity permeability and channeling in randomly distributed and kinematically defined discrete fracture network models a major use of dfn models for industrial applications is to evaluate permeability and flow structure in hardrock aquifers from geological observations of fracture networks the relationship between the statistical fracture density distributions and permeability has been extensively studied but there has been little interest in the spatial structure of dfn models which is generally assumed to be spatially random i e poisson in this paper we compare the predictions of poisson dfns to new dfn models where fractures result from a growth process defined by simplified kinematic rules for nucleation growth and fracture arrest davy et al 2010 2013 this so called kinematic fracture model is characterized by a large proportion of t intersections and a smaller number of intersections per fracture several kinematic models were tested and compared with poisson dfn models with the same density length and orientation distributions connectivity permeability and flow distribution were calculated for 3d networks with a self similar power law fracture length distribution for the same statistical properties in orientation and density the permeability is systematically and significantly smaller by a factor of 1 5 to 10 for kinematic than for poisson models in both cases the permeability is well described by a linear relationship with the areal density p32 but the threshold of kinematic models is 50 larger than of poisson models flow channeling is also enhanced in kinematic dfn models this analysis demonstrates the importance of choosing an appropriate dfn organization for predicting flow properties from fracture network parameters

fluorine geochemistry of basaltic rocks from continental and oceanic regions and petrogenetic application fluorine contents in about 300 samples of various types of basalts and related rocks from continental southwestern u s a zaire deccan and south africa and oceanic regions hawaii and mid atlantic ridge between 23 n and 40 n were determined by a selective ion electrode method

pedogenesis and weathering rates of a histic andosol in iceland field and experimental soil solution study abstract it is important to study the rate determining processes of chemical weathering and soil formation in volcanic islands since a significant part of the carbon fixed by chemical weathering of silicates on earth is fixed at the surface of volcanic islands these soils are fertile and much of the river suspended matter delivered to the ocean stems from these islands this study determines the factors that drive the pedogenesis of a histic andosol in western iceland soil solutions were extracted from the profile in the field from undisturbed ex situ mesocosms and from repacked laboratory microcosms concentrations of measured and calculated inorganic species in the field and experimental soil solutions were used for thermodynamic and kinetic interpretation and to calculate the weathering rates the main primary rock constituent of the 205 cm thick soil profile was basaltic glass allophane content ranged from 2 to 22 and the soil carbon content ranged from 11 to 42 mean soil solution ph value ranged from 4 to 6 with the lowest value at 80 cm depth and highest between 150 to 205 cm the high solute concentrations in soil solutions in the beginning of the microcosm weathering experiment declined faster for anions than cations under field conditions inorganic anions were supplied by marine and anthropogenic rather than pedogenic sources and hence these anions were subsequently leached out during the experimental duration when there was a limited input of anions through experimental precipitation the factor which defined the rate at which each ion was depleted from the exchange complex of the soil decreased down the soil profile the release sequence at 50 cm depth was cl na so 4 f si the si and base cations experimental weathering rate when normalized to geographical surface area are similar to or lower than those measured from river catchments in southwestern iceland the dissolved al flux was much higher from the soil when compared to the river catchments field and experimental soil solutions were all highly undersaturated with respect to basaltic glass field and mesocosm samples were supersaturated with respect to secondary allophane and imogolite while samples from the microcosms were often undersaturated with respect to allophane and imogolite predicted dissolution rate was dictated by the soil solution a h 3 a al 3 activity ratio but slowed down by up to 20 and 30 by decreasing undersaturation in field and mesocosms respectively predicted dissolution rates according to the a h 3 a al 3 activity ratio increased up to factor of 7 30 and 37 by speciating al 3 with oxalate in field mesocosms and microcosms respectively speciation with oxalate which represents the maximum effect of the dissolved organic carbon doc on dissolution rates generally had more effect near the surface than at deep levels in the soil profile this study shows that at fixed temperature reactive surface area and composition of the volcanic glass in the soil the chemical weathering rates of andosols are dictated by 1 aeolian deposition rates and drainage which affect the saturation state and the a h 3 a al 3 activity ratio 2 the production of organic anions within the soil and 3 external supply of anions capable of complexing al 3

fluorine speciation in topsoils of three active volcanoes of sicily italy fluorine is one of the many environmental harmful elements released by volcanic activity the content of total oxalate extractable and water extractable fluorine was determined in 96 topsoils of three active volcanic systems of southern italy mt etna stromboli and vulcano total fluorine f content f tot ranges from 112 to 7 430 mg kg 1 f extracted with oxalate f ox ranges from 16 to 2 320 mg kg 1 2 93 of f tot and f extracted with distilled water f text h text 2 text o ranges from 1 7 to 159 mg kg 1 0 2 40 of f tot fluorine in the sampled topsoils derives both from the weathering of volcanic rocks and ashes and from the enhanced deposition due to volcanic gas emissions either from open conduit passive degassing mt etna and stromboli or from a fumarolic field vulcano fluorine accumulation in the studied soils does not generally present particular environmental issues except for a few anomalous sites at vulcano where measured contents could be dangerous both for vegetation and for grazing animals

the utility of desert sand dunes as quaternary chronostratigraphic archives evidence from the northeast rub al khali abstract the distributions of optically stimulated luminescence osl ages from dunes are affected by palaeoenvironmental changes complex dune dynamics and sampling strategy extracting the relative importance of these factors when interpreting discontinuous osl chronologies from sand dunes has proven difficult and is particularly hindered in contexts where the internal sedimentary structures of dunes are not visible in this study samples for osl dating were taken from three major dune exposures in the rub al khali united arab emirates each showing clear internal structure with the aim of addressing these problems specific objectives were to assess how ages of individual sedimentary units represent dune accumulation as a whole and how the dune record in turn reflects known past environmental changes final ages were calculated using the oxcal software package by incorporating the known relative stratigraphy through the application of bayesian methods the results show that stratigraphy alone is not sufficient at these sites to guide osl sampling that is chrono and lithostratigraphic boundaries do not necessarily coincide where chronological hiatuses are present internal sediment stratigraphy can be a useful tool in identifying potential problems of under sampling the full dune record the implications of these findings for reconstructing quaternary climates from dune chronologies are considered

storage of f and cl in the upper mantle geochemical implications abstract electron microprobe analyses yielded mean values of f 0 43 and cl 0 08 wt for primary textured phlogopites in coarse depleted garnet lherzolite xenoliths from kimberlites most secondary textured phlogopites have too low cl 0 01 0 08 wt to be metamorphic precursors of primary textured phlogopites marid suite phlogopites and many megacrysts in kimberlites have low cl 0 02 wt and some but not necessarily all secondary micas may result from infiltration of kimberlite into peridotite xenoliths a good correlation between p and f in some oceanic basalts and gabbros might suggest that these elements are derived mainly from f rich apatite inthe mantle and that whitlockite is not present in the source region mantle derived mica and amphibole have such low cl that it is necessary to attribute cl in oceanic basalts and gabbros either to substantial cl in the source apatite or to cl from invading solutions or both three apatites from the mantle contain 0 8 1 0 wt cl and others contain lower amounts the halogen contents of kimberlitic magmas can be explained by incorporation of cl bearing mica and f rich apatite during melting of peridotites but compositional constraints are weak

dune mobility and aridity at the desert margin of northern china at a time of peak monsoon strength wind blown sands were mobile at many sites along the desert margin in northern china during the early holocene 11 5 8 ka ago based on extensive new numerical dating this mobility implies low effective moisture at the desert margin in contrast to growing evidence for greater than modern monsoon precipitation at the same time in central and southern china dry conditions in the early holocene at the desert margin can be explained through a dynamic link between enhanced diabatic heating in the core region of the strengthened monsoon and increased subsidence in drylands to the north combined with high evapotranspiration rates due to high summer temperatures after 8 ka ago as the monsoon weakened and lower temperatures reduced evapotranspiration eolian sands were stabilized by vegetation aridity and dune mobility at the desert margin and a strengthened monsoon can both be explained as responses to high summer insolation in the early holocene

optical and radiocarbon ages of stacked paleosols and dune sands in the nebraska sand hills usa abstract optical ages for eolian sands from the nebraska sand hills indicate periods of extensive eolian activity at ca 115 25 840 70 2300 240 and 3560 340 a activity was also noted at single sampling locations at ca 6180 370 8430 510 and 13110 800 a many of these ages are similar to those noted by earlier authors optical ages from samples collected within paleosols indicate shorter and possibly less extensive periods of eolian activity at approximately 1220 150 1590 110 and possibly 1950 150 a during which the paleosol sands accumulated what was originally interpreted as a single 1 2 m thick paleosol is shown by optical dating to consist of three or more welded soils developed within eolian sands with optical ages of ca 3800 240 2740 240 1560 110 and possibly 1930 140 a each of which match eolian pulses recognized elsewhere scatter in some optical ages is attributable to intersection of sand filled rodent burrows extending in outcrop 1 5 m below the contact between paleosol and overlying topset beds a 5310 360 a optical age for one probable intersected burrow provides evidence for upward or lateral transport of older sands

late quaternary dune accumulation along the western margin of south africa distinguishing forcing mechanisms through the analysis of migratory dune forms abstract the west coast of south africa is situated at a critical location between temperate and subtropical oceanic and atmospheric circulation systems and palaeoenvironmental proxies from this region have the potential to elucidate issues concerning variations within these systems over glacial interglacical cycles while semi arid climates have hindered the preservations of organic proxies a variety of aeolian bedforms have been analysed in an effort to improve our understanding of environmental change in the region optically stimulated luminescence measurements of 51 samples from 15 reticulate dune sites along the west coast have enabled the identification of phases of aeolian activity as well as periods of relative geomorphic stability combined with data derived from previous studies of the region s sediment accumulating deposits and other palaeoenvironmental proxies periods of increased windiness are identified at 16 24 30 33 43 49 and 63 73 ka from approximately 17 12 ka decreasing transport capacity resulted in the stabilisation of the west coast s dune fields during the holocene altithermal 4 8 ka despite reduced wind strength increased aridity resulting from higher temperatures and a reduced influence of moisture bearing westerly systems appears to have trigged widespread remobilisation of the region s dune fields the combination of ages from a variety of dune forms with different development mechanisms and comparisons with a range of proxy data sources have allowed for an enhanced interpretation of the region s aeolian archives moving beyond simple correlations between dune activity and aridity

response of surface processes to climatic change in the dunefields and loess plateau of north china during the late quaternary this paper draws on recent optically stimulated luminescence osl dating to evaluate the long held assumption that dust accumulation rates in the loess plateau and the extent of active aeolian sand in the dunefields to the north have varied together over time because both are controlled by the strength of the asian monsoons and also possibly because the dunefields are proximal loess sources the results show there is little evidence that high rates of loess accumulation coincided with well dated episodes of extensive dune activity in the mu us otindag and horqin dunefields at 11 8 ka and 1 0 ka explanations for the apparent lack of coupling include local variation in the trapping of dust and post depositional preservation of the loess and dune sediments in response to varying local environmental conditions in addition a substantial portion of the loess may be transported directly from source areas where dust emission has somewhat different climatic and geomorphic controls than aeolian sand activity within the dunefields the results of this study cast doubt on the use of loess accumulation rate as a palaeoclimatic proxy at millennial timescale the dunefield and loess stratigraphic records are interpreted as primarily recording changes in effective moisture at a local scale but the timing of late quaternary dune activity along with a variety of other evidence indicates that moisture changes in many of the drylands of northern china may not be in phase with precipitation in core regions of the asian monsoons copyright 2011 john wiley sons ltd

fluorine geochemistry in volcanic rock series examples from iceland and jan mayen abstract a new analytical procedure has been established in order to determine low fluorine concentrations 30 100 ppm f in igneous rocks and the method has also proven successful for higher concentrations 100 4000 ppm f fluorine has been measured in a series of olivine tholeiites from the reykjanes peninsula a tholeiite to rhyolitic rock series from kerlingarfjoll central iceland and an alkaline rock series from jan mayen that ranges from ankaramites to trachytes fluorine is not appreciably degassed during extrusion and appears to be insensitive to slight weathering the olivine tholeiites from the reykjanes peninsula have f contents of 30 300 ppm and exhibit linear increases proportional to the incompatible elements k p and ti such incompatible behaviour for f has been confirmed for the less evolved rocks of the other series the tholeiites from kerlingarfjoll 100 2000 ppm f show a linear increase with k2o whereas the f content decreases slightly for the andesitic to rhyolitic rocks the change from a linear increase with k for the tholeiites to a moderate decrease in f for the more evolved rocks is associated with a sharp decrease in p suggesting that apatite controls the f distribution for these rocks when the activity of p is too low to allow for significant control of f by apatite the f abundances increase towards the most k rich rhyolites similar relationships between f k and p are also apparent for the alkaline jan mayen rock series but the shifts in f and p behaviour occur at higher k2o and sio2 concentrations

linkage between c4 vegetation expansion and dune stabilization in the deserts of ne china during the late quaternary abstract knowledge of the role of c4 vegetation expansion in regulating dune stabilization during the late quaternary is important for understanding the evolution of the environment and climate in the climatically sensitive margin of the east asian summer monsoon however due to the lack of both reliable vegetation records and chronological control during episodes of dune activity the relationship between c4 vegetation expansion and dune stabilization in the deserts of ne china during the late quaternary remains unclear here we present a new regional compilation of late quaternary stable carbon isotopic data from organic matter together with dated records from sub aerial sedimentary deposits in the region our compilation of vegetation development and dune activity in these deserts suggests that c4 vegetation expansion with a main contribution from chenopodiaceae and a secondary contribution from poaceae and cyperaceae may have played a critical role in dune semi stabilization with a northwestward trend from 13 to 9 ka and dune stabilization throughout the entire study region from 9 to 5 ka in addition during the late holocene intensified millet cultivation or overgrazing and or climatic deterioration at 1 5 ka likely caused an increase in c4 vegetation abundance in the deserts of ne china which is associated with a dune mobilization episode in contrast after 2 5 ka decreased vegetation cover and dune mobilization in the mu us and hobq deserts were likely caused by poor land use practices and historically documented droughts overall c4 vegetation expansion was the main cause of dune stabilization in these deserts during the late quaternary

recent volatile evolution in the magmatic system of hekla volcano iceland estimates of the volatile budgets for volcanic eruptions are often based on volatile concentrations measured in melt inclusions mis versus groundmass glass here we present new measurements and estimates of pre eruptive volatile concentrations in magma from the hekla volcano in iceland based on mis in recent basalts and basaltic icelandites from the 2000 eruption the last eruption at hekla occurred from 26 february to 8 march 2000 it began with a short sub plinian phase followed by lava effusion that produced 0 17 km 3 of basaltic icelandite volatile s cl f and h2o and major element concentrations were measured in mis trapped in olivine and plagioclase phenocrysts contained in the basaltic icelandite from the 2000 eruption and in basalt erupted in 1913 from a fissure adjacent to the hekla volcano same elements were measured in the groundmass glass from the 2000 tephra the observed compositional range of mis from the basalt mgo 7 73 to the basaltic icelandite mgo 2 51 is readily explained by fractional crystallisation allowing the prediction of the evolution of dissolved volatile concentrations within the magma plumbing system beneath hekla the incompatible behaviour of the volatile elements controls their concentrations in mis during the crystal fractionation and consequently the highest concentrations are found in the most evolved basaltic icelandite mis with the notable exception of sulphur volatile concentrations in the basaltic mis exhibit strong linear correlations with k2o and this relationship can be used to estimate the theoretical expected volatile contents in the basaltic icelandite melt just prior to eruption such an approach avoids underestimation of the pre eruptive volatile contents measured in mis and improves constraints on the volatile mass release into the atmosphere the difference of volatile contents between expected concentrations and those present in the groundmass scaled to the mass of erupted magma yields maximum atmospheric mass loading of 0 10 mt hcl 0 17 mt hf and 3 77 mt so2 during the 2000 hekla eruption whereas calculations using the measured values in the inclusions give a significant lower mass yields of 0 05 mt hcl 0 17 mt hf and 0 6 mt so2 these results are discussed and compared to the data derived from remote sensing and snow proxy of the gas phase measurements 2007 elsevier b v all rights reserved

geochemical and geomorphological evidence for the provenance of aeolian deposits in the badain jaran desert northwestern china abstract identifying provenance of aeolian deposits in the mid latitude deserts of asia is essential for understanding formation and changes of earth surface processes due to palaeoclimatic fluctuations while some earlier studies focused on the interpretation of palaeoenvironments on the basis of aeolian deposits mainly in the desert margins and inter dune lacustrine sediments research on provenance of desert sands in the vast asian mid latitude deserts is still rare in this paper we present new geochemical data which provide insight to the provenance of dune sands in the badain jaran desert northwestern china an important part of this desert belt we sampled aeolian and lacustrine sediments in various parts of the badain jaran desert and examined their major trace and rare earth elements ree in bulk samples coarse and fine fractions respectively in addition we took and analyzed samples from a rarely known dune field with red sands northeast of the badain jaran our results show that the sands from the badain jaran desert are generally different from those in the red sand dune field in terms of ree pattern and geochemical characteristics suggesting different sediment origins geochemical composition of the aeolian sand samples indicates these sediments should be mainly derived from mixed source rocks of granite granitoids and granodiorite comparing the immobile trace elements and ree ratios of the samples from the badain jaran desert red sand dune field with rocks of granite granitoids in their potential source areas we conclude that 1 the aeolian deposits in the badain jaran desert are predominantly derived from the qilian mountains northeastern tibetan plateau initially via fluvial processes 2 the altay mountains and mongolian gobi are the ultimate source areas for the red sand dune field 3 the altai mountains and mongolian gobi in the northwest that could produce massive amounts of materials via intensive deflation and alluvial process are additional sand sources of the badain jaran desert although their contribution is of secondary significance as the badain jaran desert acts as sediment sinks of sediments from the qilian mountains of northeastern tibetan plateau via fluvial processes it is likely that zircon grains of loess on the chinese loess plateau with age distributions similar to those of the northern tibetan plateau could be derived from the badain jaran desert as the wind data suggest

fault growth in brittle ductile experiments and the mechanics of continental collisions using laboratory models of continental collisions we study the mechanisms responsible for large scale deformation and the nature of the penetrative deformation localized or homogeneous and its characteristic scales and structure in order to focus the study one of the most spectacular cases of continental collisions namely the india asia collision is considered different models with varying rheologies are analyzed which attempt to respect the brittle ductile stratification corresponding to the crust and mantle structure in the earth each experiment is quantified by studying the strain field and the fault pattern as a function of the position p of the indenter within the system the strain field is characterized by 1 the second invariant of the two dimensional strain tensor and its variation with position for a fixed p the evolution of its average as a function of p 2 the evolution with p of the participation ratio s2 which quantifies the fraction of the system surface area which participates in the deformation 3 the evolution of the escape ratio calculated as the surface increase gained by the system during its eastward lateral escape divided by the surface covered by the indenter penetration qualitatively we find that the deformation first spreads out but later on undergoes localization once the fault pattern is mature the cumulative fault length does not increase anymore we observe that the strain field is essentially controlled by the kinematics of the larger faults each fault pattern is quantified by studying 1 the histograms of fault orientations 2 the capacity and barycenter fractal dimensions 3 the multifractal generalized dimensions and 4 the distribution of fault lengths the fractal dimension d is found to almost constant within experimental uncertainty d 1 7 0 1 and thus appears rather insensitive to the particular chosen rheology we find a correlation between the generalized multifractal dimensions and two exponents the barycenter fractal dimension b and the exponent a of the fault length distribution this shows that the scaling properties of fault patterns can be characterized by the knowledge of only two exponents b and a of the spatial and length distributions of faults our main results are 1 observation of the growth of self similar fault patterns 2 complete characterization of the fault patterns with two scaling exponents a and b 3 wide distribution of undeteriorated domains and large heterogeneity of the deformation field 4 maturation of the fault structure corresponding to a localization of the deformation on a few large faults in the late stage of the deformation

holocene record of eolian activity from genggahai lake northeastern qinghai tibetan plateau china the history of dust emission and eolian activity in dust source areas remains unclear due to the scarcity of geological archives grain size data from genggahai lake on the northeastern qinghai tibetan plateau show that sand sized particles in the lake sediments were transported primarily by strong winds to the lake and therefore can be used as a proxy for eolian activity eolian activity was weak from 10 3 to 6 3 ka which may be a response to increased vegetation cover due to the strengthened asian summer monsoon in contrast eolian activity occurred episodically when the summer monsoon weakened the abrupt intense sand deposition events are likely to have resulted from strong wind regimes in turn linked to cooling events in the north atlantic our results suggest that changes in atmospheric circulation patterns may have strongly affected the moisture balance and wind strength in the dust source area and hence dust emissions

palaeoclimatic evidence from sand seas abstract sand seas can be an important source of information on the quaternary history of many deserts because sand seas appear to react sensitivity to climatic changes the quality of palaeoenvironmental information obtained from them is frequently much better than that from adjacent rocky desert areas patterns of dune alignments may be used to reconstruct the wind directions that formed currently inactive or fixed dunes and thus can provide information on palaeocirculation patterns the climatic conditions under which these dunes formed can be examined using palaeoclimatic models to explore the combinations of wind velocity rainfall and evaporation rates required to reactivate them choice of appropriate values for these parameters may be hampered by the problems of dating episodes of dune activity in many sand seas the best palaeoclimatic information comes from studies of interdune lacustrine or playa deposits which may reflect increased local rainfall or higher groundwater discharge or greater penetration of the sand sea by rivers with headwaters outside the desert caution should be taken in the interpretation of such deposits for juxtaposition of aquatic and aeolian environments can occur even in modern hyperarid and seas the record of climatic changes preserved in the deposits of modern sand seas suggests that periods of dune formation may have been interrupted by long periods of stability which may also have included deposition of interdune lacustrine deposits for example within the past 40 000 years active dune formation in many sand seas appears to have been restricted to the interval between about 20 000 and 12 000 yr b p and to the late holocene approximately 1 4 to 1 3 rd of the time

the microstructure of polar ice part ii state of the art an important feature of natural ice in addition to the obvious relevance of glaciers and ice sheets for climate related issues is its ability to creep on geological time scales and low deviatoric stresses at temperatures very close to its melting point without losing its polycrystalline character this fact together with its strong mechanical anisotropy and other notable properties makes natural ice an interesting model material for studying the high temperature creep and recrystallization of rocks in earth s interior after having reviewed the major contributions of deep ice coring to the research on natural ice microstructures in part i of this work faria et al 2014 here in part ii we present an up todate view of the modern understanding of natural ice microstructures and the deformation processes that may produce them in particular we analyze a large body of evidence that reveals fundamental flaws in the widely accepted tripartite paradigm of polar ice microstructure also known as the three stage model cf part i these results prove that grain growth in ice sheets is dynamic in the sense that it occurs during deformation and is markedly affected by the stored strain energy as well as by air inclusions and other impurities the strong plastic anisotropy of the ice lattice gives rise to high internal stresses and concentrated strain heterogeneities in the polycrystal which demand large amounts of strain accommodation from the microstructural analyses of ice cores we conclude that the formation of many and diverse subgrain boundaries and the splitting of grains by rotation recrystallization are the most fundamental mechanisms of dynamic recovery and strain accommodation in polar ice additionally in fine grained high impurity ice layers e g cloudy bands strain may sometimes be accommodated by diffusional flow at low temperatures and stresses or microscopic grain boundary sliding via microshear in anisotropic ice sheared at high temperatures grain boundaries bulged by migration recrystallization and subgrain boundaries are endemic and very frequent at almost all depths in ice sheets evidence of nucleation of new grains is also observed at various depths provided that the local concentration of strain energy is high enough which is not seldom the case as a substitute for the tripartite paradigm we propose a novel dynamic recrystallization diagram in the three dimensional state space of strain rate temperature and mean grain size which summarizes the various competing recrystallization processes that contribute to the evolution of the polar ice microstructure dedicated to sepp kipfstuhl on occasion of his 60th birthday

quaternary environmental changes in the drylands of china a critical review abstract this paper reviews our current understanding of quaternary climate and landscape changes in the desert areas of northern china a key portion of the middle latitude drylands on earth combining earlier studies with our recent research and experience we offer a comprehensive picture of the state of chinese deserts during the quaternary and in the interest of enhancing future research identify knowledge gaps and areas of uncertainty lacustrine deposits found over an area ranging from china s western taklamakan desert to the eastern hunshandake sandy lands suggest that extensive lakes occurred in china s deserts during the pleistocene analysis of digital elevation models from srtm shuttle radar topography mission data supports this interpretation and shows the significant extent of these former lakes new estimates of mean annual evaporation of ca 1000 mm from lake surfaces and ca 100 mm from land surfaces confirms that local and regional rainfall is critical for maintenance of desert lakes in this temperate zone especially during intervals when the mean annual rainfall is more than 100 mm rapid shifts between sand seas and lakes in geologically and environmentally diverse settings suggest that the drylands of china are very sensitive ephemeral systems and not long lasting as previously thought available chronologies suggest that there were large lakes in the western taklamakan desert and the chadamu basin during mis marine isotope stage 3 at 30 ka probably related to a period of strong influence of northern hemispheric westerly winds channels and elevation models revealed by srtm data and remains of lacustrine sediments also indicate that there was a large lake in the hunshandake sandy lands in the eastern portion of the desert belt during the quaternary there is significant evidence that during the middle holocene strong summer monsoons led to a relatively large increase in moisture availability in the entire desert belt of northern china lacustrine records from the badain jaran desert in western inner mongolia suggest that it was generally dry before 10 cal ka becoming wetter from 10 to 4 cal ka and dry again afterwards study of palaeosols widely occurring in dune stratigraphy in the eastern portion of the desert belt suggests that there was a period of wet and warm climate in this region during the mid holocene optimum at a minimum between 6 ka and 4 ka but possibly lasting longer recent observations dealing with the generation and transport of dust from central asia indicate that the causal relationship between sand seas and loess sequences is not as close as previously assumed these results suggest that there is an urgent need to examine whether the frequency and amplitude of climatic variation in chinese deserts are somehow similar to that having occurred in the sahara desert of north africa deserts in northern china were also important focal regions for neolithic cultures during intervals when environmental conditions supported a denser vegetative cover there is evidence that some areas of woody vegetation to the west of badain jaran desert were deforested by humans by ca 4000 yr b p although it is still debatable whether humans have had a significant impact in other areas at that time opinions on the severity of desertification vary and are sometimes contradictory due to the lack of long term field based investigations

reversal of ice motion during the outburst of a glacier dammed lake on gornergletscher switzerland during the outburst flood of a glacier dammed lake on gornergletscher switzerland in july 2004 the drained lake water triggered anomalous glacier motion at the onset of the outburst the ice flow direction in the vicinity of the lake became closer to the central flowline when the lake discharge magnitude decreased the flow direction altered such that the ice moved back to the azimuth of the initial motion at one of the survey points where the ice flows parallel to the central flowline the ice accelerated along the pre event flow direction followed by a 1808 backward motion that lasted over 2 days these observations indicate the impact of the lake outburst on the subglacial and englacial stress conditions however the reversal in the flow direction is difficult to explain by drawing on our current understanding of glacier mechanics the timing and the timescale of the flow direction changes suggest that the elastic glacier motion and its rebound played a role under the rapidly changing stress conditions but the young s modulus of ice is too large to cause the observed ice motion other processes including basal separation and subglacial sediment deformation are discussed as possible mechanisms for the reversal of the ice motion

sulfur isotope ratios of icelandic lava incrustations and volcanic gases sulfur isotope ratios were measured in eight lava incrustations and three volcanic gas samples and their corresponding lava flows the lava incrustations of sulfate composition are from five recent eruptions and occur as thenardite or as aphtitalite thenardite mixtures with abundant trace elements the incrustations show small sulfur isotope fractionation of 1 2 compared with corresponding lavas and the volcanic gas samples the sulfate incrustations are formed through oxidation of so2 from the emitted volcanic gas and subsequent reaction with metal halides the volcanic gas samples show a distribution of decreasing 34s through time from 3 4 to 1 8 sulfate was preferentially degassed compared to sulfide the data indicate that sulfate incrustations serve as a late stage volcanic gas sample with respect to sulfur isotopes

fluorine in basalts from iceland the fluorine content of icelandic tholeiitic and alkaline basalts matches values found in similar rocks from other areas covariation between fluorine and incompatible minor elements such as potassium or phosphorus is found in evolved tholeiites and alkali basalts lack of such covariation in primitive olivine tholeiites indicates that fluorine and other incompatible minor and trace elements are not controlled by minerals such as amphibole mica or apatite in the mantle residue and that the covariation between these elements in the evolved basalts cannot be inherited from the mantle model calculations on rocks from the langjokull area show that olivine tholeiite suites are if derived by simple fractional crystallization enriched in incompatible elements much in excess of the increase due to crystal removal these observations are taken to indicate that the well documented covariation between fluorine and other incompatible elements is not established until evolution of the basaltic magma has started in crustal holding chambers the constancy of element ratios and enrichment in excess of what can be accounted for by crystal fractionation or incremental addition of new batches of primitive magmas does indicate 1 mineral control involving amphibole mica or apatite and 2 addition of fluorine potassium and phosphorous from an external source it is argued that this source is the crustal envelope of the holding chamber

large scale controls on the development of sand seas in northern china abstract although sand seas are located in arid regions given that the proportions of dune areas vary greatly from region to region they are clearly influenced by other factors as well as aridity this paper discusses the distribution pattern and major features of sand seas and large fields of stabilized dunes in northern china and demonstrates the main influences on their development it appears that the availability of onsite loose sediments not wind strength is critical to the occurrence of the sand seas on a regional scale tectonic endorheic basins or areas of alluvial fans or forelands of mountain ranges are advantageous to the accumulation of fluvial sediments and thus are ideal locations of large sand seas in an arid climate the large dune fields currently stabilized by vegetation were active sand seas during the drier periods of the late pleistocene and early holocene the distribution patterns of chinese sand seas suggest that the height or size of the dunes in the sand seas are determined more by the availability of sands than any other potential factors as the sand seas in china account for a large portion of deserts in the middle latitudes of the northern hemisphere taklamakan is the second largest sand sea on earth knowledge of these sand seas past changes is important for understanding climatic changes in the terrestrial regions of mid latitudes

strong dune activity and the forcing mechanisms of dune fields in northeastern china during the last 2 kyr abstract historical dune activity for the horqin and hulun buir dune fields of northeastern china remain poorly understood in this study we compiled a large number of aeolian sand luminescence ages from stratigraphic sections and synthesised the data to reveal periods of strong dune activity that took place in these dune fields throughout the last 2 kyr our results indicate at least four episodes of strong dune activity which occurred from 500 to 600 c e from 890 to 970 c e from 1150 to 1230 c e and since 1650 c e respectively comparisons between episodes of strong dune activity climatic change and human activity showed that the first episode was associated with a cold and dry climate the second and the third episodes can be attributed to the combined impacts of cold climate and extensive human activities the early part of the fourth episode was caused by a cold climate whereas the middle and later parts have been controlled by anthropogenic impacts

single fractures under normal stress the relation between fracture specific stiffness and fluid flow abstract fracture specific stiffness and fluid flow through a single fracture under normal stress are implicitly related through the geometry of the void space and contact area that comprise the fracture data from thirteen different rock samples each containing a single fracture show that relationships between fracture specific stiffness and fluid flow through a fracture fall into two general classes of behavior fractures either fall on a loosely defined universal curve relating fluid flow to fracture specific stiffness or else the flow is weakly dependent on fracture specific stiffness the second relationship shows that flow decreases slowly with increasing fracture specific stiffness the first relationship shows that flow decreases rapidly for increases in fracture specific stiffness to understand this behavior computer simulations on simulated single fractures were performed to calculate fluid flow fracture displacement and fracture specific stiffness as a function of normal stress simulated fractures with spatially correlated and uncorrelated aperture distributions were studied fractures with spatially uncorrelated aperture distributions tend to exhibit a weak dependence of fluid flow on fracture specific stiffness because these fractures tend to have multiple connected paths across the sample which can support flow with uniformly distributed contact area thus an increment in stress will increase the stiffness of the fracture without greatly reducing the amount of fluid flow on the other hand fractures with spatially correlated aperture distributions tend to belong to the universal relationship because correlated fractures tend to have only one or two dominant flow paths and the contact area is limited to a few regions resulting in a compliant fracture thus an increment in stress on a spatially correlated fracture will result in an increase in stiffness and rapid decrease in fluid flow these spatial correlations in fracture void geometry can be differentiated in the laboratory based on the observed fracture specific stiffness fluid flow relationship for a single fracture under normal loading

compressive shear faults within arctic sea ice fracture on scales large and small 1 we examined fracture features within arctic sea ice as revealed by landsat 7 and radarsat imagery by an aerial survey and through observations in the laboratory of specimens loaded to brittle failure under biaxial compression regardless of scale which spans the range from kilometers to millimeters the features look alike they consist mainly of narrow lineaments that traverse the field of view plus wing like and comb like secondary cracks the lineaments occasionally intersect and generally exhibit either right lateral or left lateral relative movement like strike slip faults within earth s crust we term them brittle compressive shear faults they form through the linking of en echelon arrays of deformation induced secondary cracks from an application of wing crack and comb crack mechanics we estimated the maximum compressive stress near the onset of faulting and found that our estimates compare favorably with in situ measurements by earlier investigators of ice sheet failure stresses to account for the brittle behavior of the sea ice cover we applied a recent model of the ductile to brittle transition in which the key idea is the competition between stress buildup and stress relaxation at stress concentrators in identifying the nature of sea ice fracture features we advance the view that failure occurs on many scales through highly localized as opposed to uniformly distributed deformation via the operation of scale independent mechanisms

historical settlement abandonment in the middle hexi corridor linked to human induced desertification abstract understanding past human environment interactions over a long time scale offers an analogue to predict adapt and mitigate the environmental issues caused by global change and human activities in the future the transient existence of historical cities from arid northern china can provide a valuable reference for this issue in this study we investigated a set of sand dunes which accumulated alongside the city wall of south heishuiguo ancient city shc from the middle hexi corridor in arid northern china dating these dune sands can provide the timing of both desertification and city abandonment a series of sand samples a total of 20 were collected and their ages were determined by luminescence dating of k feldspar fraction the results suggest an abrupt sand dune accumulation between 0 40 0 03 ka and 0 25 0 02 ka corresponding to 1590 1790 ce this study confirms a phase of desertification between the late 16th century and the late 18th century in the hexi corridor and the abandonment of the shc at the 17th century in order to assess the anthropogenic influences on desertification we also reconstructed the population history of the hexi corridor over the last 2000 years based on historical literature as a quantitative index of human activity intensity by comparison of the timing of onset of desertification around the shc with robust paleoclimate and historical population reconstructions we conclude that 1 the desertification of 1590 1790 ce was likely the result of considerably enhanced human activities between the late ming and the early qing dynasties as this period was dominated by a relatively moist climate and could restrain the sand deflation and 2 the desertification in turn caused abandonment of shc as the impact of environmental changes on people

volatiles in glasses from mauna loa volcano hawai i implications for magma degassing and contamination and growth of hawaiian volcanoes glasses from mauna loa pillow basalts recent subaerial vents and inclusions in olivine were analyzed for s cl f and major elements by electron microprobe select submarine glasses were also analyzed for h2o and co2 by infrared spectroscopy the compositional variation of these tholeiitic glasses is dominantly controlled by crystal fractionation and they indicate quenching temperatures of 1 115 1 196 c submarine rift zone glasses have higher volatile abundances except f than nearly all other submarine and subaerial glasses with the maximum concentrations increasing with water depth the overwhelming dominance of degassed glasses on the submarine flanks of mauna loa implies that much of volcano s recent submarine growth involved subaerially erupted lava that reached great water depths up to 3 1 km via lava tubes anomalously high f and cl in some submarine glasses and glass inclusions indicate contamination possibly by fumarolic deposits in ephemeral rift zone magma chambers the relatively high co2 but variable h2o k2o and s k2o in some submarine rift zone glasses indicates pre eruptive mixing between degassed and undegassed magma within mauna loa s rift system volatile compositions for mauna loa magmas are similar to other active hawaiian volcanoes in s and f but are less cl rich than l ihi glasses however cl k2o ratios are similar mauna loa and l ihi magmas have comparable but lower h2o than those from kilauea thus kilauea s source may be more h2o rich the dissimilar volatile distribution in glasses from active hawaiian volcanoes is inconsistent with predictions for a simple concentrically zoned plume model

fault size distributions are they really power law abstract power law fault size throw distributions spanning ca seven orders of magnitude are analysed using sample lines from seismic coal mine plan and outcrop data sets outcrop data sets generally have lower power law exponent values than seismic data sets consistent with a general decrease in exponent value with decrease in fault size if such a relationship does exist then probably it cannot be accounted for by sampling bias alone we suggest that either i fault size populations are not power law over a large scale range or ii they are power law but at smaller scales show a greater range of exponent values due to spatial clustering

on the relationship between dike width and magma viscosity on the basis of measurements of bulk rock and phenocryst chemical compositions phenocryst content and estimation of water content and magma temperature the magma viscosity of 44 dikes from oki dozen and tango southwest japan and ocros peruvian andes was estimated to examine a relationship between viscosity and dike width the results show that magma viscosity increases with dike width mafic magmas with viscosities of 101 102 pa s form dikes l m wide while felsic magmas with viscosities of 106 107 pa s form dikes 100 m wide this indicates that magma viscosity as well as magma driving pressure and host rock stiffness are important factors in explaining the variation of dike width because magma viscosity is a measure of internal friction the magmatic force required to widen the fracture during hydrofracturing is proportional to viscosity on the basis of the range of chemical composition of the studied samples dike widths formed by highly viscous felsic magma should be of the order of 100 m maximum furthermore the observed basaltic dike width variations from various tectonic settings indicate that the effective factor on driving pressure of dike magma may be not magma pressure but compressive stress on the other hand dikes derived from low viscosity basaltic magma and exceeding 100 m width may be formed by extremely high magma pressure associated with flood basalt volcanism this is supported by 1 the observation that a rifting event with decreased compressive stress was not always associated with the volcanism and 2 the inferred effusion rates for this type of volcanism are anomalously high suggesting increased magma pressure in addition the active magma generation and the decreased host rock stiffness by locally anomalous thermal conditions like a hotspot phenomenon may assist flood basalt volcanism or emplacement of anomalously wide mafic dikes

anisotropy and crystalline fabric of whillans ice stream west antarctica inferred from multicomponent seismic data crystal orientation fabric cof describes the intrinsic anisotropic nature of ice and is an important parameter for modeling glacier flow we present the results of three component active source seismic observations from the whillans ice stream wis a fast flowing ice stream in west antarctica surface wave dispersion analysis ray tracing and traveltime inversion of compressional p and shear s waves reveal the presence of transversely isotropic ice with a vertical axis of symmetry vti beneath approximately 65 m of isotropic firn the ice stream is characterized by weak anisotropy involving an average ice thickness of approximately 780 m the analysis indicates that about 95 of the ice mass is anisotropic and the crystalline c axes span within an average broad cone angle of 73 10 with respect to the vertical axis moreover the mean temperature t below the firn estimated from seismic data is 15 5 c these data do not show evidence of englacial seismic reflectivity which indicates the lack of abrupt changes in the cof the presence of azimuthal anisotropy due to transversely compressive flow or fractures aligned along a preferential direction is also excluded we suggest that the observed vti ice structure is typical of large ice streams in regions where basal sliding and bed deformation dominate over internal glacial deformation

holocene environmental changes in the central inner mongolia based on single aliquot quartz optical dating and multi proxy study of dune sands abstract alternating units of dune sands and paleosols in the central inner mongolia imply multiple episodes of dune building and stabilization in response to the waxing and waning of the east asian monsoon such eolian deposits were dated by using the single aliquot quartz optical dating method combined with the multi proxy study on the deposits the past environmental changes during the holocene have been reconstructed our results indicate that widespread eolian sand mobilization occurred in the studied region during the beginning of the early holocene from 11 5 ka to 9 ka the climate became warm and humid during the period between 9 ka and 5 6 ka holocene optimum after 5 6 ka the region again became arid as inferred from dune building however the environmental changes during the late holocene have been affected by both climate and human impacts and the presence of desert environment in such semiarid region is not only the result of climatic drought of the late holocene but also related to poor land use practices

chlorine and fluorine in tholeiitic and alkaline lavas of etna sicily abstract chlorine and fluorine were measured from whole rock samples from tholeiites 150 000 years old to present day hawaiites the overall range of f content is from 240 to 985 ppm with a slight decrease of f th and f cl ratios from tholeiites to hawaiites chlorine is positively correlated with th cl th 100 as well as k2o and p2o5 as the differentiation progresses and increases from 220 ppm in tholeiites to 2410 ppm in mugearites data obtained from present day hawaiites indicate that cl lost by degassing during eruption is limited however cl contents of some whole rock samples are inconsistent with previous results published for melt inclusions of phenocrysts from the same historic hawaiite samples and suggesting outgassing of cl prior to the eruption this implies that apparent correlation between cl and th can be considered as the result of superimposition of several petrogenetic processes results point out the richness of etnean tholeiites in chlorine compared to m a r basalts such a character could have been inherited from the mantle source or during the mantle source melting

tidal dissipation in enceladus uneven fractured ice shell abstract analysis of enceladus gravity topography and libration data suggests that the thickness of the ice crust significantly varies which may have important consequences for the heat transfer across and the tidal dissipation within the ice shell understanding these processes is a critical prerequisite for analyzing enceladus thermal evolution and assessing the long term stability of its subsurface ocean here we investigate the impact of ice shell thickness variations on the tidal deformation of the moon and the associated heat production using a finite element model that includes faults tiger stripes in the south polar region spr since the tidal deformation and the thermal structure of the ice shell are coupled through temperature and deviatoric stress we simultaneously solve the equations governing the anelastic deformation of ice and also equations which model conductive heat transfer in the ice shell we find that tidal heating is concentrated in a narrow low viscosity zone near the base of the ice shell and along faults outside the spr the thickness of this zone is about 1 10 of the local ice thickness and the associated volumetric heating is 1 0 6 w m 3 corresponding to less than 1 gw of dissipated power in the spr the tidal effects are enhanced by the combined action of faults and ice shell thinning although the volumetric heating in this relatively small region may be larger than 10 4 w m 3 the total heat production in this region does not exceed 1 1 gw our computations show that tidal heating in the ice shell can explain only a small fraction of enceladus heat production derived from astrometric observations implying that enceladus heat engine is powered by dissipation in the core or in the ocean

historical desertification of the mu us desert northern china a multidisciplinary study abstract the problem of historical desertification of the mu us desert northern china has been paid considerable attention during the past several decades through the analysis of stratigraphic evidence historical records and archaeological discoveries this paper studied the problem using a multidisciplinary approach the results show that two phases of serious desertification occurred during the last two millennia one is during the mid to late tang dynasty about a d 800 and the other during the late ming dynasty about a d 1500 1600 further investigation of the cause of each phase of desertification demonstrates that the former phase of desertification is closely related to abrupt climate change occurring in the mid eighth century but the latter which started during the ming dynasty and stopped at late 1980s is not consistent with climatic causation therefore we suggest that human activities contributed to the development of the latter phase of desertification

tide deflection of campbell glacier tongue antarctica analyzed by double differential sar interferometry and finite element method abstract a glacier tongue the terminus of a glacier projecting out from the coastline and floating over the ocean experiences vertical deflection due to the fluctuation of ocean tide accurate analysis of the tidal deflection of a glacier tongue is necessary to understand the elastic properties and dynamics of glacial ice we extracted the tidal deflection of campbell glacier tongue cgt one of the fast flowing glacier tongues in east antarctica by using 120 double differential interferometric sar ddinsar images from the 16 cosmo skymed one day tandem interferometric sar image pairs obtained during 2010 and 2011 a map of tide deflection ratio map defined as the ratio of the tidal deflection over tide height was generated by pixel based linear regression between the ddinsar derived tidal deflection and the tidal variation predicted by various tide models such as tpxo7 1 fes2004 cats2008a and ross inv after the inverse barometer effect correction we also generated the maps of r 2 root mean square error rmse and intercept of the linear regression model we confirmed that the horizontal flow of the campbell glacier is steady over the whole data acquisition period due to the fact that values were close to zero over the grounded part of the glacier ross inv provided the most reliable map with the highest r 2 0 97 and the smallest rmse 0 3 cm beyond the hinge zone than other tide models the spatial variation of the tidal response of the whole cgt was clearly defined from the map the grounding line retreated by 0 3 1 5 km in comparison with that in 1996 defined by rignot et al 2011a the ice thickness of cgt was estimated to be 397 71 m from icesat surface elevation data the young s modulus of cgt was found to be 0 5 1 3 gpa 0 8 gpa at an ice thickness of 397 m by simulating the in the hinge zone using a 2 dimensional finite element method

history of moisture change indicated by aeolian deposit in the horqin sandy land northeastern china since the last glacial maximum abstract the horqin sandy land located in the monsoonal boundary of northeastern china is sensitive to the vicissitudes of the asian monsoon am the aeolian sand paleosol sequences in this area especially since the last glacial maximum lgm have preserved valuable geological archives indicating the history of humidity changes in the region however existing studies on the local humidity rhythms have not been sufficient to reach a consensus in a relatively in depth study of the forcing mechanism we present the results of a systematic optically stimulated luminescence osl chronology and detailed multi proxy analyses of the grain size geochemical elements magnetic susceptibility and organic matter since the lgm the results demonstrate that the humidity gradually increased from the lgm to the middle holocene reaching optimum humidity around 9 3 ka despite intense oscillations occurring during 6 5 ka that is largely consistent with other paleoenvironmental records from ne china it is suggested that the variation in the humidity is basically controlled by the solar driven monsoonal precipitation which is the most dominant moisture source the coupled atmosphere pacific ocean system and the westerlies could have both disturbed the monsoon precipitation thus indirectly affecting the humidity of the sandy land during the late holocene human occupation also played a significant role in the re activation of dunes

late holocene dune mobilization in the horqin dunefield of northern china abstract the late holocene environmental change and its relationship with climate and human activities in the horqin dunefield of northern china are poorly understood in the current study we presented a new reconstruction of late holocene dune mobilization in the horqin dunefield based on 68 quartz osl ages from 25 dune sections and interpretations of historical documents these sections were selected from a variety of different geomorphological units across the studied region the results show that at least four phases of dune mobilization were distinguished during the last 2000 years in horqin dunefield corresponding to 400 700 ce 1200 ce 1800 ce and after 1900 ce respectively by comparison with other well dated paleoclimate records and analysis on human activity records we infer that the cold arid climate caused the dune mobilization around 400 700 ce dune mobilization around 1200 ce can be attributed to the combinative impacts of cold climate and extensive human activities increasing human activities play a dominate role in the latest two phases of dune mobilization at around 1800 ce and after 1900 ce even though the climate warming and drying in 20th century may also contribute to the last phase of dune mobilization

general characteristics of temperature variation in china during the last two millennia three alternate china wide temperature composites covering the last 2000 years were established by combining multiple paleoclimate proxy records obtained from ice cores tree rings lake sediments and historical documents five periods of temperature variation can be identified a warm stage in ad 0 240 a cold interval between ad 240 and 800 a return to warm conditions from ad 800 1400 including the medieval warm period between ad 800 1100 the cool little ice age period between 1400 1920 and the present warm stage since 1920 regional temperature variation is found during ad 800 1100 when warm conditions occurred in eastern china and in the northeastern tibetan plateau and in ad 1150 1380 when the southern tibetan plateau experienced a warm interval in contrast evidence for cool conditions during the lia is more consistent among the proxy records the temperature reconstructions for china and the northern hemisphere show good agreement over the past millennium

mid to late holocene climate change an overview the last 6000 years are of particular interest to the understanding of the earth system because the boundary conditions of the climate system did not change dramatically in comparison to larger glacial interglacial changes and because abundant detailed regional palaeoclimatic proxy records cover this period we use selected proxy based reconstructions of different climate variables together with state of the art time series of natural forcings orbital variations solar activity variations large tropical volcanic eruptions land cover and greenhouse gases underpinned by results from general circulation models gcms and earth system models of intermediate complexity emics to establish a comprehensive explanatory framework for climate changes from the mid holocene mh to pre industrial time the redistribution of solar energy due to orbital forcing on a millennial timescale was the cause of a progressive southward shift of the northern hemisphere nh summer position of the intertropical convergence zone itcz this was accompanied by a pronounced weakening of the monsoon systems in africa and asia and increasing dryness and desertification on both continents the associated summertime cooling of the nh combined with changing temperature gradients in the world oceans likely led to an increasing amplitude of the el nin o southern oscillation enso and possibly increasingly negative north atlantic oscillation nao indices up to the beginning of the last millennium on decadal to multi century timescales a worldwide coincidence between solar irradiance minima tropical volcanic eruptions and decadal to multi century scale cooling events was not found however reconstructions show that widespread decadal to multi century scale cooling events accompanied by advances of mountain glaciers occurred in the nh e g in scandinavia and the european alps this occurred namely during the little ice age lia between ad w1350 and 1850 when the lower summer insolation in the nh due to orbital forcing coincided with solar activity minima and several strong tropical volcanic eruptions the role of orbital forcing in the nh cooling the southward itcz shift and the desertifi cation of the sahara are supported by numerous model simulations other simulations have suggested that the fingerprint of solar activity variations should be strongest in the tropics but there is also evidence that changes in the ocean heat transport took place during the lia at high northern latitudes with possible additional implications for climates of the southern hemisphere sh

does titan s long wavelength topography contain information about subsurface ocean dynamics abstract the long wavelength topography of titan is characterized by relatively small amplitudes about 1 km peak to peak an anomalous equatorial bulge the poles are about 300 m lower than the equator and small gravity anomalies indicating a high degree of compensation in the past years the nature of titan s non hydrostatic topography has been addressed in several studies the topography has been interpreted in terms of isostatic or viscous models and discussed in connection with tidal heating in the ice shell and surface erosion here we present a model of the shape evolution of titan s ice shell driven by tidal heating in the shell and spatial variations of the heat flux from a subsurface ocean the model is obtained by solving a general set of equations coupling the viscoelastic flow of ice with the thermal evolution of the ice shell and phase transitions at the ice water interface the equations are solved in a domain with radially varying material properties and moving boundaries the motion of the boundaries is a consequence of ice flow within the shell melting and crystallization at the bottom boundary and erosion and deposition at the surface our model suggests that titan s anomalous topographic bulge can be explained by lateral variations of ocean heat flux of the order of 0 1 1 mw m 2 provided that the heat flux is stable over a period of at least 10 myr and the ice shell has a sufficiently high viscosity exceeding 1016 pa s at the base of the shell such a high value of viscosity implies that either the ice grains are coarse 10 mm or the temperature of the ocean is significantly by more than 40 k lower than the melting temperature of pure water ice the heat flux pattern predicted on top of the ocean is consistent with a flow characterized by upwelling of warm water in polar regions and downwelling of cold water at low latitudes the negative correlation between the topography and geoid at degree 3 reported in a previous study but not confirmed at higher degrees yet is shown to be compatible with erosion and deposition occurring at a rate of 0 01 0 1 mm yr 1 our results underline the importance of gravity and topography measurements for understanding titan s surface and deep interior processes

optical dating reveals that the height of earth s tallest megadunes in the badain jaran desert of nw china is increasing abstract the badain jaran desert bjd in nw china is well known for its unique landscape of megadunes coexisting with permanent lakes the megadunes are already the tallest sand dunes on earth and some of them are up to 400 m high however it is unclear whether or not the height of the megadunes is continuing to increase under present climatic and environmental conditions in order to determine the growth status of the megadunes we collected 26 samples from the windward slopes of two megadunes for optically stimulated and infrared stimulated luminescence dating the results show that the thickness of the modern eolian sand layers increases from the lower part of the windward slopes with a thickness of less than 1 m to more than 2 m in the middle and to 9 m in the upper part this indicates that the height of the megadunes is continuing to increase under modern conditions the surface sediments from the base of the windward slope and the adjacent lake basin have relatively old ages of 6 7 ka indicating that these areas are eroding the recent eolian sands of the upper part of the megadunes likely originated from the base of the dunes or from the lake basin the megadunes in the bjd are currently becoming increasingly high and steep due to the upward migration and accumulation of sand particles increased humidity and a weakened wind regime in northern china related to ongoing climatic warming are likely the main factors in maintaining the growth of the megadunes

permeability tensor for discontinuous rock masses rock masses which commonly contain a large number of discontinuities are treated as homogeneous anisotropic porous media to formulate the corresponding permeability tensor this has been successfully achieved by introducing a symmetric tensor crack tensor which depends only on the geometry of the related cracks aperture size and orientation the principal directions associated with the symmetric crack tensor are coaxial with those of the permeability tensor the first invariant of the crack tensor is proportional to the mean permeability while the deviatoric part is related to the anisotropic permeability these results are well supported by numerical experiments on the permeability of cracked media by long remer wilson and witherspoon an actual rock mass moderately jointed granite was studied to see whether the crack tensor can be determined in situ stereology based on geometrical statistics provides a sound basis for determining the crack tensor in situ the crack tensor is obtained by

dry early holocene revealed by sand dune accumulation chronology in bayanbulak basin xinjiang nw china understanding the holocene climate changes especially moisture variation and their mechanisms in the semiarid arid central asia sca is very important as water availability is crucial for sustainable developments in this area this study presents chronostratigraphy of an aeolian sedimentary sequence from bayanbulak basin xinjiang nw china aiming to infer the holocene moisture history in the sca luminescence dating technique was selected to construct the age framework of the study section since the luminescence signal intensity of quartz from the samples was too low to be detected feldspar was used as an alternative dosimeter a newly developed post infrared ir ir stimulated luminescence irsl pirir dating protocol on k feldspar was applied to determine the ages of samples a set of tests on luminescence characteristics was performed and demonstrate that this method is suitable and the resultant ages are reliable combined with the stratigraphic investigation on the sand dune palaeosol section the results imply a very dry climatic condition characterized by sand dune accumulation at similar to 9 8 kyr and a wet interval of 5 1 6 kyr when a soil layer was formed this moisture variation pattern is consistent with that inferred from many lacustrine records in the sca suggesting a widespread dry period at 11 8 kyr the present results appear to challenge a new stalagmite delta o 18 sequence located nearby to bayanbulak basin which instead suggested a humid early holocene

formation constraints on martian north polar volcanic edifices 1 this study focuses on probable volcanic features in the north polar region of mars in an effort to constrain their formation mechanisms and to estimate the thickness of a possible former ice sheet using mars orbiter laser altimeter mola high resolution imaging science experiment hirise thermal emission imaging system themis and context camera ctx data we conduct topographic analyses of 108 putative volcanic edifices in the borealis volcanic field within 69 n 81 n and 197 e 330 e as it is rarely possible to identify rock types on mars such as hyaloclastite or palagonite we are limited to the use of topographic data and images alone in our study therefore we use available data for volcanic features in iceland to predict the formational mechanisms of similar features on mars we examined 21 icelandic volcanoes of subglacial and postglacial origin using digital elevation models dems as well as limited differential gps data and suggest by analogy that many of the features in the borealis volcanic field were likely formed subglacially we use these data to estimate a minimum ice sheet thickness for the area and suggest a range of minimum ice sheet thickness that varies between 57 and 610m with an average value of 283 m

the fracture criticality of crustal rocks summary the shear wave splitting observed along almost all shear wave ray paths in the earth s crust is interpreted as the effects of stress aligned fluid filled cracks microcracks and preferentially oriented pore space once away from the free surface where open joints and fractures may lead to strong anisotropy of 10 per cent or greater intact ostensibly unfractured crustal rock exhibits a limited range of shear wave splitting from about 1 5 to 4 5 per cent differential shear wave velocity anisotropy interpreting this velocity anisotropy as normalized crack densities a factor of less than two in crack radius covers the range from the minimum 1 5 per cent anisotropy observed in intact rock to the 10 per cent observed in heavily cracked almost disaggregated near surface rocks this narrow range of crack dimensions and the pronounced effect on rock cohesion suggests that there is a state of fracture criticality at some level of anisotropy between 4 5 and 10 per cent marking the boundary between essentially intact and heavily fractured rock when the level of fracture criticality is exceeded cracking is so severe that there is a breakdown in shear strength the likelihood of progressive fracturing and the dispersal of pore fluids through enhanced permeability the range of normalized crack dimensions below fracture criticality is so small in intact rock that any modification to the crack geometry by even minor changes of conditions or minor deformation particularly in the presence of high pore fluid pressures may change rock from being essentially intact below fracture criticality to heavily fractured above fracture criticality this recognition of the essential compliance of most crustal rocks and its effect on shear wave splitting has implications for monitoring changes in any conditions affecting the rock mass these include monitoring changes in reservoir evolution during hydrocarbon production and enhanced oil recovery and in monitoring changes before and after earthquakes amongst others

a model of fracture nucleation growth and arrest and consequences for fracture density and scaling 1 in order to improve discrete fracture network dfn models which are increasingly required into groundwater and rock mechanics applications we propose a new dfn modeling based on the evolution of fracture network formation nucleation growth and arrest with simplified mechanical rules the central idea of the model relies on the mechanical role played by large fractures in stopping the growth of smaller ones the modeling framework combines in a time wise approach fracture nucleation growth and arrest it yields two main regimes below a certain critical scale the density distribution of fracture sizes is a power law with a scaling exponent directly derived from the growth law and nuclei properties above the critical scale a quasi universal self similar regime establishes with a self similar scaling the density term of the dense regime is related to the details of arrest rule and to the orientation distribution of the fractures the dfn model so defined is fully consistent with field cases former studied unlike more usual stochastic dfn models ours is based on a simplified description of fracture interactions which eventually reproduces the multiscale self similar fracture size distribution often observed and reported in the literature the model is a potential significant step forward for further applications to groundwater flow and rock mechanical issues