modification and preservation of environmental signals in speleothems speleothems are primarily studied in order to generate archives of climatic change and results have led to significant advances in identifying and dating major shifts in the climate system however the climatological meaning of many speleothem records cannot be interpreted unequivocally this is particularly so for more subtle shifts and shorter time periods but the use of multiple proxies and improving understanding of formation mechanisms offers a clear way forward

tree ring δ18o in southwestern china linked to variations in regional cloud cover and tropical sea surface temperature in this paper we present the first annual oxygen isotope 8180 record 1902 to 2004 from the latewood cellulose of trees growing in a temperate moist forest in southwestern china tree ring delta o 18 ranges from 12 8 to 18 6 parts per thousand and averages 15 2 parts per thousand delta o 18 in the latewood negatively correlates with total cloud cover relative humidity and precipitation during the moist months august to october from 1951 to 2004 and to a lesser extent positively correlates with the temperature in june spatial correlation analysis revealed that tree ring latewood delta o 18 is more strongly related to variability in regional cloud cover and precipitation in autumn tree ring delta o 18 negatively correlates with the indices of the indian summer monsoon 1948 to 2004 the western north pacific monsoon 1948 to 2004 and with the east asian summer monsoon 1902 to 2000 suggesting that these monsoons strongly influence the regional climate under global warming of last century we found a strong inverse correlation between tree ring delta o 18 and the southern oscillation index in different periods indicating a complex association between the el nino southern oscillation and the regional climate which in turn affects tree ring delta o 18 correlation with the global sea surface temperature sst indicates that climatic conditions in the indian ocean might play a dominant role in modulating cloud cover and precipitation over the study region during the monsoon seasons we also found a significant correlation between tree ring delta o 18 and sst over the western north pacific ocean our results suggest strong links between tropical oceans and an enso like climate with the oxygen isotope sources and discrimination for trees in the study region c 2011 elsevier b v all rights reserved

plate tectonics lost sea floor the configurations of ancient tectonic plates are difficult to reconstruct seismic images of deep subducted plates combined with data from ancient volcanic arcs help to derive a tectonic map of the pacific ocean as it was 200 million years ago

extracting time domain green s function estimates from ambient seismic noise 1 it has been demonstrated experimentally and theoretically that an estimate of the green s function between two seismic stations can be obtained from the time derivative of the long time average cross correlation of ambient noise between these two stations this tdgf estimate from just the noise field includes all tensor components of the green s function and these green s function estimates can be used to infer earth structure we have computed cross correlations using 1 to 30 continuous days of ambient noise recorded by over 150 broadband seismic stations located in southern california the data processing yielded thousands of cross correlation pairs for receiver separations from 4 500 km which clearly exhibit coherent broadband propagating dispersive wavetrains across frequency band 0 1 2 hz

incorporating self consistently calculated mineral physics into thermochemical mantle convection simulations in a 3 d spherical shell and its influence on seismic anomalies in earth s mantle 1 phase assemblages of mantle rocks calculated from the ratios of five oxides cao feo mgo al2o3 sio2 by free energy minimization were used to calculate the material properties density thermal expansivity specific heat capacity and seismic velocity as a function of temperature pressure and composition which were incorporated into a numerical thermochemical mantle convection model in a 3 d spherical shell the advantage of using such an approach is that thermodynamic parameters are included implicitly and self consistently obviating the need for ad hoc parameterizations of phase transitions which can be complex in regions such as the transition zone particularly if compositional variations are taken into account convective planforms for isochemical and thermochemical cases are however not much different from those computed using our previous simple parameterized reference state which means that our previous results are robust in this respect the spectrum and amplitude of seismic velocity anomalies obtained using the self consistently calculated material properties are more realistic than those obtained when seismic velocity is linearly dependent on temperature and composition because elastic properties are dependent on phase relationship of mantle minerals in other words pressure and temperature in all cases the spectra are dominated by long wavelengths spherical harmonic degree 1 to 2 similar or even longer wavelength than seismic tomographic models of earth which is probably due to self consistent plate tectonics and depth dependent viscosity in conclusion this combined approach of mantle convection and self consistently calculated mineral physics is a powerful and useful technique for predicting thermal chemical phase structures in earth s mantle however because of uncertainties in various parameters there are still some shortcomings in the treatment of the postperovskite phase transition additionally transport properties such as thermal conductivity and viscosity are not calculated by this treatment and are thus subject to the usual uncertainties

model evaluation for reconstructing the oxygen isotopic composition in precipitation from tree ring cellulose over the last century the oxygen isotope composition of tree rings is controlled by many factors including temperature amount of precipitation and changes in relative humidity in this study we present a modified leaf water model from dongmann et al radiation and environmental biophysics 11 1974 41 that can be used to calculate the isotopic composition of the source water and thus of precipitation that a tree used during the growing season the calibration of the model was accomplished by comparing a previously measured oxygen isotope tree ring chronology from central switzerland with the swiss network for isotopes in the hydrologic cycle station at bern from 1971 to 1995 and integrating temperature relative humidity data and ring width in particular our efforts focused on understanding the significance of the dampening factor f which we relate to changes in humidity and its variability over both the calibration period 1971 to 1995 and the study period 1913 to 1995 our results indicate that f ranging between 0 27 to 0 49 is variable based on correlation with relative humidity average daily temperature and ring width index using this model we have constructed a record of the oxygen isotope composition of precipitation during the growing season may through september for the last century in central western europe this approach can be potentially used in other locations where isotopic and meteorological data are available to extend records of the isotopic composition of precipitation back in time beyond observational records

the effect of soil hydrology on the oxygen and hydrogen isotopic compositions of plants source water abstract many studies have demonstrated that the isotopic composition of plants source water is the main factor affecting the isotopic composition of tree rings because of soil hydrological processes soil water as the source water for plants may isotopically differ from precipitation that contains climatic information such as surface temperature this study addresses the effects of soil hydrological processes on the isotopic compositions of soil water and discusses how these effects affect interpretations of tree ring data in isotopic dendroclimatology we collected precipitation soil gas at two depths 20 and 50 cm and twigs from a maple tree acer saccharum on a biweekly basis during the growing season in 1997 1999 at hanover nh usa water was extracted from the twig samples by vacuum distillation all water samples were analyzed for both d and 18 o soil co 2 was extracted from soil gas and measured for the 18 o values and using the soil temperature and assuming isotopic equilibrium between co 2 and h 2 o we calculated the 18 o values of soil water comparisons among the isotopic time series of each type of sample indicate the following 1 the isotopic composition of soil water is much less variable than that of precipitation suggesting isotopic mixing between waters of different precipitation events 2 in early spring soil water at all depths is isotopically similar to winter precipitation but with time the surface soil water becomes progressively enriched in deuterium and 18 o due to infiltration of summer rain and enrichment through soil water evaporation 3 the influence of summer precipitation decreases with increasing depth and soil at 50 cm can only receive water from large storms 4 replacement of old soil water with new infiltrating water is dependent upon frequency and intensity of growing season precipitation and it is generally more efficient in a wet year than in a dry year 5 the tree we studied uses water mainly from near surface soil layers 6 the d 18 o relationship in twig water indicates that soil water has experienced isotopic enrichment by evaporation these results have important implications for selecting sites for paleoclimatic studies using isotopic data of tree rings

transitions in thermal convection with strongly variable viscosity one of the most important material properties influencing the style of convection in the mantles of terrestrial planets is the extreme temperature dependence of viscosity three dimensional numerical convection calculations in a wide 8 8 1 cartesian box and in a spherical shell ratio of inner to outer radius of 0 55 characteristic of terrestrial planets both display two fundamental transitions as the viscosity contrast is progressively increased from unity to a factor of 105 these transitions not only mark changes in the style of deformation in the upper boundary layer from mobile lid to sluggish lid to stagnant lid but also have dramatic effects on the style planform and horizontal length scales of convection in the entire domain vertical variations of viscosity are the most important for determining the horizontal length scales of the convective patterns while lateral viscosity variations play a role in shaping the relative structures of the upwelling and downwelling flows convection in venus appears to be represented most closely by the sluggish lid regime of convection whereas the earth with plate tectonics more closely resembles the mobile lid style of convection forcing plate like characteristics onto the convective flows in the form of imposed weak zones and prescribed surface velocities results in flow patterns dominated entirely by the form used to enforce the plate like behavior and tells us little about why the mantle exhibits long wavelength heterogeneity

oxygen isotope record of paleorainwater in authigenic carbonates of chinese loess paleosol sequences and its paleoclimatic significance abstract oxygen isotopic compositions of rhizoconcretions and land snail shells were measured to reconstruct the 18o profiles of paleorainwater 18op for well dated loess paleosols in luochuan china to assess the paleoclimatic significance of 18op factors that control the spatial and temporal 18o variations of rainwater in east asian monsoon regions were investigated modern records indicate that the spatial 18o variations of modern rainwater 18om are closely related to near surface temperature t and the amount of precipitation p in order to separate the effects of t and p on the 18om a linear relationship between 18om t and the natural logarithm of p is established by multiple regressing analyses 18 o m 1 070 0 326 t 2 041 ln p the 18o of paleorainwater over the past 130 ka in luochuan area is calculated by the modern spatial 18o t p relationship using estimated t and p from other paleoclimate records the calculated 18o match well to those reconstructed from the authigenic carbonates which implies that the spatial and temporal 18o variations of rainwater in east asian monsoon regions have similar 18o t p relationships and the authigenic carbonates in chinese loess paleosol sequences can serve as valid records of 18op as an application of the 18o t p relationship p variation in the past 130 ka in luochuan was evaluated the reconstructed p is in good agreement with other studies using different approaches our results suggest higher precipitation in marine isotope stages 1 3 and 5 reflecting intense summer monsoon influences during these periods of time

automatic detection of long period events at campi flegrei caldera italy 1 we propose a novel approach to analyze continuous seismic signal and separate the sources from background noise a specific application to the seismicity recorded at campi flegrei caldera during the 2006 ground uplift is presented the fundamental objective is to improve the standard procedures of picking the emergent onset arrivals of the seismic signals often buried in the high level ambient noise in order to obtain an appropriate catalogue for monitoring the activity of this densely populated volcanic area this is particularly useful in order to estimate the release of the seismic energy and to put constraints on the source dynamics an independent component analysis based approach for the blind source separation of convolutive mixtures is adopted to obtain a clear separation of long period events from the ambient noise the approach presents good performance and it is suitable for real time implementation in seismic monitoring its application to the continuous seismic signal recorded at campi flegrei has allowed the extraction of high quality waveforms considerably improving the detection of low energy events

role of the lithosphere in mantle convection plate geometry and kinematics generally reflect the mechanical properties of the solid lithosphere rather than those of the fluid mantle underneath and plate formation and subduction account for most of the heat transport from the earth s interior correspondingly mantle convection models must incorporate a stiff but mobile boundary layer like the lithosphere before they can reproduce the main features of mantle convection a relatively easy way to accomplish this in numerical models is to combine a temperature dependent viscosity with an imposed piecewise constant surface velocity boundary condition it is shown how surface heat flux topography gravity and geoid but not plate velocities or stresses can then be derived numerical models confirm that a lithosphere has a first order effect on the underlying flow structure for internally heated models approx imating the case of whole mantle convection the calculated surface signatures are in first order agreement with observations a level of empirical success which hitherto has not been approached by models of mantle convection companion papers exploit the observations more fully to constrain the main features of mantle convection

geodynamically consistent inferences on the uniform sampling of earth s paleomagnetic inclinations abstract paleomagnetism is a key method to reconstruct the earth s paleogeography and thus essential for understanding tectonic evolution but it assumes that the earth s magnetic field structure has always averaged to a geocentric axial dipole gad the gad hypothesis may be tested using the observed inclination frequency distribution but only if continents sampled all of the earth s latitudes uniformly which is not known here we provide new insight into the uniform sampling problem by employing a suite of 3d spherical mantle convection models that feature the self consistent evolution of mantle convection plate tectonics and continental drift over timescales of 2 gyr or more our results suggest that continents unlikely sampled latitudes uniformly during the phanerozoic consistent with previous suggestions this finding is robust for a variety of geodynamic evolutions with different mantle and lithosphere structures at least in the absence of true polar wander for longer sampling durations uniform sampling typically becomes more feasible but may only be achieved with confidence after time scales of minimum 1 3 gyr this time scale depends on the structure of the mantle and lithosphere and may be shortest when upper mantle viscosity is small such that reduced resistive drag at the cratonic base allows for faster continental drift weak plates low plastic yield strength promote more dispersed continent configurations which tends to facilitate uniform sampling if these conditions are not met the uniform sampling time scale can easily exceed several billion years even the minimum estimate of 1 3 gyr challenges the validity of using the phanerozoic inclination frequency distribution to infer the past average magnetic field structure the approach could however still be applicable using the precambrian inclination record

study on the long period source mechanism at campi flegrei italy by a multi parametric analysis abstract the source properties of the long period events that occurred at campi flegrei caldera italy during the 2004 2006 ground uplift episode are investigated by analyzing the temporal release of seismic energy amplitude distribution and inter event occurrence time moreover an entropy based decomposition method is applied to identify the simpler waveforms thought to be representative of the source mechanism of long period events on the basis of the outcomes we propose that the main part of these events is the result of a source process triggered by a mechanism of fluid charge discharge which causes pressure drop in a main branch of a dentritic network of the hydrothermal system in this model the rate of the poissonian process about 15 min which drives the occurrence of the long period events provides the average recharge time of the system up to the critical condition a partial shunting of the fluid flow away from the main conduit activates the resonance of a second branch spatially separated from the first one this is a process that occurs whenever the fluid pressure exceeds a critical value and produces less energetic long period events the mechanism of pressure variation in the two conduits generates signals with preferred amplitude scales described by a bi lognormal distribution from a dynamical point of view long period events result well described by a low dimensional dynamical system finally the time pattern of the energy release and its correlation with the diurnal solid earth tide suggest that the whole mechanism of fluid charge discharge is likely modulated by tidal stress variation

mantle convection with longest wavelength thermal heterogeneity in a 3 d spherical model degree one or two 1 the formation of longest wavelength mantle convection in the sluggish lid regime is investigated using a three dimensional spherical model the bottom rayleigh number is fixed at 107 considering temperature dependent rheology degree one dominant thermal convection occurs for both purely basal heating and mixed i e basal and internal heating modes for the purely basal heating mode degree one convection occurs when the viscosity contrast due to temperature dependent rheology is 103 104 in both boussinesq and extended boussinesq fluids however with extended boussinesq fluid degree one convection may only occur in the basal heating mode in the mixed heating mode degree one convection shifts to one with high degree modes presumably because of enhanced viscous dissipation in the highly viscous lid over up downwelling plumes the geophysically relevant degree two convection with sheet like downwellings is not observed in this study the inclusion of visco plastic rheology in the top part of the mantle breaks down degree one convection

generation of long wavelength heterogeneity in the mantle by the dynamic interaction between plates and convection lateral variations in seismic velocity through its dependence on temperature can easily be generated at the gravest harmonics including degrees one and two by the dynamic interaction between plates and convection models of thermal convection with a single non subducting plate have been formulated in a cylindrical geometry plates of width one to four times times the thickness of the convecting region strongly modulate the flow by being pushed over cold downwellings and inhibiting cooling of the fluid beneath during rapid motion off of hot regions a large scale pattern of shear is developed causing small uprising limbs to be swept into the largest upwellings both insulation and plume plume collisions pump energy into the lower wavenumber harmonics

correlation between climate events in the north atlantic and china during the last glaciation episodes of massive iceberg release heinrich events 1 3 into the north atlantic ocean during the last glaciation were associated with recurring episodes of unusually cold north atlantic surface water bond cycles 4 and cold air temperatures over greenland dansgaard oeschger events 5 6 four of the youngest of these cold events have also been reported in climate records from sites outside the north atlantic region7 but until now the entire suite has been identified only in north atlantic marine sediments greenland ice core records and tentatively in french lake sediments8 here we examine grain size data from chinese loess and intercalated accretionary palaeosols of last glacial age for evidence of similar climate signals remote from the north atlantic region we see grain size maxima with ages that match those of the last six heinrich events which we interpret as an indication of the changing strength of the east asian winter monsoon which largely controls the transport and deposition of central asian aeolian dust thus it seems that these heinrich events have left their signature in the chinese loess record this is consistent with simulations of the glacial climate9 which imply that the climates of the north atlantic and china were linked by the effect of westerly winds

internal structure and early thermal evolution of mars from mars global surveyor topography and gravity topography and gravity measured by the mars global surveyor have enabled determination of the global crust and upper mantle structure of mars the planet displays two distinct crustal zones that do not correlate globally with the geologic dichotomy a region of crust that thins progressively from south to north and encompasses much of the southern highlands and tharsis province and a region of approximately uniform crustal thickness that includes the northern lowlands and arabia terra the strength of the lithosphere beneath the ancient southern highlands suggests that the northern hemisphere was a locus of high heat flow early in martian history the thickness of the elastic lithosphere increases with time of loading in the northern plains and tharsis the northern lowlands contain structures interpreted as large buried channels that are consistent with northward transport of water and sediment to the lowlands before the end of northern hemisphere resurfacing

the space problem of caldera resurgence an example from ischia island italy a space problem can arise in a resurgent caldera when the resurgent block is non cylindrical such as for example when it is bounded by inward or outward dipping faults ischia caldera italy is an excellent case study because it is well exposed and resurgence is ongoing on the western and eastern flanks of the ischia resurgent horst uplift occurred along nnw striking normal faults with inclination from sub vertical to vertical 85 the geometry of these faults suggests negligible extension within the horst along the northern flank uplift was accomplished by ene striking normal faults that dip 60 85 outward a few bear striae which indicate almost pure dip slip the southern flank of the horst is a monocline trending ene associated with vertical faults in a nnw sse section the resulting resurgent horst has a wedge shape with an upward apex the uplift of this wedge can be accommodated by contemporaneous regional extension along ne to east west striking normal faults whose motions create space for resurgence without deformation of the caldera floor similar interaction with regional tectonics could exist in other calderas such as yellowstone usa in an extensional setting los azufres mexico in a transtensional regime and chalupas ecuador in a transpressional one at other calderas resurgence was accommodated by caldera floor arching as at valles usa or by shortening deformations between the caldera rim and the uplifting block as at latera italy

monsoon precipitation variation recorded by tree ring δ18o in arid northwest china since ad 1878 abstract the east asian summer monsoon easm precipitation from may to august over the helan mountains located in the northwest margin of the easm has been investigated through tree ring 18o for the last 120 years the dry and wet intervals derived from the 18o series can be verified by the tree ring width based may july precipitation reconstruction most of the time the 18o series and ring width derived precipitation reconstruction vary synchronously at low frequency high values of 18o correspond to high precipitation periods and vice versa since the 1970s the east asian summer monsoon precipitation has been increasing which was confirmed by other records and documents our results show that tree ring 18o can serve as an indicator of the strength of the east asian summer monsoon variation in the past we also found that tree ring 18o varies inversely to 13c in the study area

regional hydroclimate and precipitation δ18o revealed in tree ring cellulose δ18o from different tree species in semi arid northern china abstract oxygen isotopic ratios 18o of tree ring cellulose grown from 1954 to 2003 in semi arid northern china demonstrate a common inter annual variability despite coming from three different species in two distinct growth environments an alpine meadow and a rocky ridge the variability was significantly negative correlated with precipitation and relative humidity during the growing season this suggests that the past summer hydroclimate can be inferred from tree ring cellulose 18o from various kinds of trees growing in semi arid northern china in addition we evaluated past changes in 18o of precipitation from the tree ring cellulose 18o and relative humidity using the mechanistic model for tree ring cellulose 18o in roden et al 2000 by fixing the species dependent exchange rate of oxygen between carbohydrate and xylem water for larix principis rupprechtii and picea koraiensis we could also reconstruct the variations in precipitation 18o from the different tree species which are similar to the observed 18o of precipitation during 1985 2002 although the reconstructed 18o of precipitation does not have any significant relation to local temperature or precipitation during 1954 2003 its long term variation pattern is similar to that of the asian summer monsoon indices and 18o of stalagmite in the heshang cave 30 27 n 110 25 e fig 1 suggesting that 18o of precipitation is not controlled by local meteorology but is influenced by large scale atmospheric circulation

mid miocene c4 expansion on the chinese loess plateau under an enhanced asian summer monsoon abstract atmospheric co2 starvation aridity fire and warm season precipitation have all been proposed as major contributors to c4 plant expansion during the late miocene however the driving factors responsible for the distribution of c4 plants in the early and mid miocene still remain enigmatic here we report pedogenic carbon and oxygen isotope data 13cpedo 18opedo along with magnetic susceptibility ms results from the zhuang lang drilling core on the chinese loess plateau clp elevated 13cpedo values 5 signal a prominent c4 expansion and substantially increased 18opedo and ms values indicate enhanced asian summer monsoon asm precipitation both of these conditions are observed during the mid miocene climatic optimum mmco 14 5 17 million years ago the marked increase in c4 plants associated with warm temperatures and increased precipitation strongly suggests the control of an enhanced asm on c4 expansion on the clp during the mmco this finding contrasts with the late miocene c4 expansion associated with cooling and drying conditions observed in low latitudes and argues for regionally specific control of c4 plant distribution expansion

subsurface structure of the solfatara volcano campi flegrei caldera italy as deduced from joint seismic noise array volcanological and morphostructural analysis 1 the joint application of different seismological techniques for seismic noise analysis and the results of a volcanological and morphostructural survey have allowed us to obtain a detailed and well constrained image of the shallow crustal structure of the solfatara volcano campi flegrei caldera italy horizontal to vertical spectral ratios inversion of surface wave dispersion curves and polarization analysis provided resonance frequencies and peak amplitudes shear wave velocity profiles and polarization pattern of coherent ambient noise these results combined in a unique framework indicate that the volcanic edifice is characterized by lateral and vertical discontinuities and heterogeneities in terms of shear wave velocity lithological contrasts and structural setting the interpretation of the seismological results with the volcanological and morphostructural constraints supports the hypothesis that the volcano has been characterized by a complex and intense activity with the alternation of constructive and destructive phases during which magmatic and phreatomagmatic explosions built a complex tuff cone later reworked by atmospheric agents and altered by hydrothermal activity the differences in the velocity structure between the central and eastern parts of the crater have been interpreted as resulting from a possible eastward migration of the eruptive vent along the deformational features affecting the area and to the presence of viscous lava and lithified tuff bodies within the feeding conduits which are buried under a covering of reworked materials of variable thickness the observed fault and fracture systems partially inherited from regional structural setting and exhumed during volcanism and ground deformation episodes also seems to strongly control wave propagation affecting the noise polarization properties

annually resolved temperature reconstructions from a late pliocene early pleistocene polar forest on bylot island canada abstract here we use 18o ratios measured in tree rings of crossdated sub fossil wood to reconstruct an annually resolved record of temperature and 18o of meteoric water for an interglacial late pliocene early pleistocene fossil forest found on bylot island nunavut canada our record represents the first crossdated record of pliocene wood mean annual temperatures determined in this study average 3 4 3 8 c which is 11 4 4 4 c warmer than present day bylot island 14 8 2 2 c june july temperatures average 13 5 1 1 c approximately 12 6 1 6 c warmer than present day meteoric water 18o values average 15 5 2 9 2 6 more enriched than present values of precipitation 18o our temperatures are comparable to mid pliocene modeled temperatures for the arctic 3 5 c warmer than present suggesting that interglacial warm periods in the late pliocene early pleistocene may have been as warm as the mid pliocene warm period that both the bylot island forest deposit and the kap kobenhavn deposit represent the remains of northern tree line vegetation that lived during warm interglacial periods within the overall cool plio pleistocene suggests that forest deposits in the arctic capture a snapshot of interglacial conditions during the plio pleistocene rather than the average pliocene climate and may not be suitable records to study pliocene cooling

seismic imaging of the d and constraints on the core heat flux abstract recent seismic imaging of the deep mantle has revealed lens shaped layers near the bottom of the mantle the morphology of this layering has been attributed to the crossing of the post perovskite phase boundary by the local geotherm we have developed a technique for quantifying the relationships between the depths of the double crossings of the post perovskite transition developed in 3d spherical mantle convection as a means for testing the viability for using the clapeyron slope of the phase transition to put bounds on the heat flux from the core we have argued from the probability distribution of the local heat flow at the core mantle boundary that there are intrinsic problems in using error function from half space cooling curves for constraining the core heat flux because of the non gaussian shape of the probability distribution of the core heat flow in realistic 3d convection models in order to constrain better the core heat flux with the above arguments we need to know much better the mantle viscosity stratification and the pressure dependence of thermal conductivity in the deep mantle only then can we put together enough constraints to discuss with greater certainty about the core heat flux

climatic significance of tree ring δ18o in the qilian mountains northwestern china and its relationship to atmospheric circulation patterns it is important to understand the history and dynamics of climate in a transitional region between areas with different atmospheric circulation patterns where the vegetation and ecosystems are vulnerable to environmental change we investigated variations in the long term oxygen isotope composition delta 18 o in tree rings of qinghai spruce picea crassifolia and their relationships to climatic parameters in the and qilian mountains of northwestern china from 1870 to 2006 we found that the mean temperature from the previous november to the current february was significantly and positively correlated with the tree ring delta 18 o values the temperature effect the positive relationship between the temperature and the precipitation delta 18 o value can explain the connection between temperature and the tree ring delta 18 o values due to pooling of the earlywood and latewood into yearly tree ring samples it appears that the cellulose delta 18 o may be influenced by isotopically nonhomogeneous water sources and climatic conditions during the previous and current growing seasons subtle shifts and amplitude deviations in cellulose delta 18 o which abruptly became more positive around 1977 1978 may be attributed to the shifting climatic regime in china and to temperature variations respectively our results illustrated the potential for investigating climatic or atmospheric circulation patterns based on oxygen isotope records in tree rings in regions near the interface between different large scale synoptic circulations c 2009 elsevier b v all rights reserved

stable isotope evidence for a foggy climate on santa cruz island california at 16 600 cal yr b p abstract in this study we use stable isotope analysis to investigate the climate in southern coastal california during the last 10 000 years of the pleistocene by comparing the carbon and oxygen stable isotope ratios of preserved douglas fir pseudotsuga menziesii wood from santa cruz island to modern douglas fir wood from northern california ams age determination indicates that the preserved trees grew at about 16 600 270 cal yr b p after isolating cellulose from both the modern and pleistocene wood to remove any potential bias due to differential decomposition rates of wood components loader n j robertson i mccarroll d 2003 comparison of stable carbon isotope ratios in whole wood cellulose and lignin of oak tree rings palaeogeography palaeoclimatology palaeoecology 196 395 407 we find that the pleistocene douglas fir wood has significantly greater carbon isotope discrimination and significantly more enriched 18 o than the modern douglas fir wood which suggests that the douglas fir trees growing on santa cruz island at 16 600 cal yr b p experienced less moisture stress and used more enriched water from fog than douglas fir trees at point reyes today

the long wavelength geoid from three dimensional spherical models of thermal and thermochemical mantle convection the earth s long wavelength geoid anomalies have long been used to constrain the dynamics and viscosity structure of the mantle in an isochemical whole mantle convection model however there is strong evidence that the seismically observed large low shear velocity provinces llsvps in the lower mantle underneath the pacific and africa are chemically distinct and likely denser than the ambient mantle in this study we have formulated dynamically self consistent 3 d spherical mantle convection models to investigate how chemically distinct and dense piles above the core mantle boundary may influence the geoid our dynamic models with realistic mantle viscosity structure produce dominantly spherical harmonic degree 2 convection similar to that of the present day earth the models produce two broad geoid and topography highs over two major thermochemical piles in the lower mantle consistent with the positive geoid anomalies over the pacific and african llsvps our geoid analysis showed that the bottom layer with dense chemical piles contributes negatively to the total geoid while the layer immediately above the chemical piles contributes positively to the geoid canceling out the effect of the piles thus the bottom part of the mantle as a compensation layer has zero net contribution to the total geoid and the thickness of the compensation layer is 1000 km or 2 to 3 times as thick as the chemical piles our results help constrain and interpret the large scale thermochemical structure of the mantle using surface observations of the geoid and topography as well as seismic models of the mantle

degree 1 mantle convection and the crustal dichotomy on mars the surface of mars consists of an old heavily cratered and elevated southern hemisphere and younger resurfaced and depressed northern hemisphere a feature often termed the crustal dichotomy the global crustal structure zuber et al 2000 revealed by topography and gravity data from the mars global surveyor spacecraft and the possible late formation of the boundary zone between the hemispheres mcgill and dimitriou 1990 have been proposed to indicate an endogenic origin for the dichotomy however degree 1 mantle convection that is required for any endogenic process to be viable cannot be produced with conventional mantle convection models schubert et al 1990 we have studied the role of radially stratified viscosity on mantle deformation by using rayleigh taylor instability analyses in a spherical shell geometry our analyses reveal that when mantle viscosity is stratified with a weak asthenosphere deformation at long wavelengths is more efficient than that at short wavelengths the weaker the asthenosphere the longer the wavelength at which the deformation is the most efficient a thicker asthenosphere also favors the deformation at long wavelengths both the rayleigh taylor instability analyses and numerical modeling of mantle convection show that degree 1 convection can be produced within the martian mantle provided that the mantle had a weak asthenosphere v500 km thick and v10 2 times weaker than the underlying mantle early in planetary history the degree 1 convection causes preferential heating of one hemisphere that may explain the primary features associated with the dichotomy in crustal structure fl 2001 elsevier science b v all rights reserved

effects on the long wavelength geoid anomaly of lateral viscosity variations caused by stiff subducting slabs weak plate margins and lower mantle rheology abstract instantaneous flow numerical calculations in a three dimensional spherical shell are employed to investigate the effects of lateral viscosity variations lvvs in the lithosphere and mantle on the long wavelength geoid anomaly the density anomaly model employed is a combination of seismic tomography and subducting slab models based on seismicity the global strain rate model is used to represent weak low viscosity plate margins in the lithosphere lvvs in the mantle are represented on the basis of the relation between seismic velocity and temperature i e temperature dependent rheology when highly viscous slabs in the upper mantle are considered the observed positive geoid anomaly over subduction zones can be accounted for only when the viscosity contrast between the reference upper mantle and the lower mantle is approximately 1 0 3 or lower and weak plate margins are imposed on the lithosphere lvvs in the lower mantle exert a large influence on the geoid pattern the calculated geoid anomalies over subduction zones exhibit generally positive patterns with quite high amplitudes compared with observations even when the low activation enthalpy of perovskite in the lower mantle is employed inferred weak slabs in the lower mantle may be explained in terms of recent mineral physics results highlighting the possibility of grain size reduction due to the postspinel phase transition

seismicity associated with the 2004 2006 renewed ground uplift at campi flegrei caldera italy abstract following the significant ground uplift 1 8 m of the 1982 1984 bradyseismic crisis the recent history of campi flegrei volcanic complex italy has been dominated by a subsidence phase recent geodetic data demonstrate that the subsidence has terminated and that positive ground deformation renewed in november 2004 at a low but accelerating rate leading to about 4 cm of uplift by the end of october 2006 as in previous episodes ground uplift has been accompanied by swarms of micro earthquakes m 1 4 in three distinct episodes october 2005 october 2006 and december 2006 hypocenters of these earthquakes are mainly located beneath the solfatara volcano at depths ranging between 0 5 and 4 km inversion of s wave spectra indicates source radius and stress drop on the order of 30 60 m and 104 9 105 pa respectively fault plane solutions indicate predominantly normal mechanisms accompanying the october 2006 swarm we detected intense long period lp activity for about 1 week these signals consist of weak monochromatic oscillations whose spectra exhibit a main peak at frequency 0 8 hz this peak is common to all the stations of the network and not present in the noise spectra suggesting that it is a source effect about 75 of the detected lps cluster into three groups of mutually similar events adjustment of waveforms using cross correlation allows for precise alignment and stacking which enhances signal onsets and permits accurate absolute arrival picks and thus better absolute as well as relative locations locations associated with the three different clusters are very similar and appear to delineate the se rim of the solfatara volcano at a depth of about 500 m the most likely source process for the lp events involves the resonance of a fluid filled buried cavity quality factors of the resonator cluster in a narrow interval around 4 which is consistent with the vibration of a buried cavity filled with a water vapour mixture at poor gas volume fractions we propose a conceptual model to interpret the temporal and spatial patterns of the observed seismicity

mantle dynamics in mars and venus influence of an immobile lithosphere on three dimensional mantle convection numerical calculations of fully three dimensional convection in constant viscosity compressible spherical shells are interpreted in terms of possible convective motions in the mantles of venus and mars the shells are heated both internally and from below to account for radiogenic heating secular cooling and heat flow from the core the lower boundary of each of the shells is isothermal and shear stress free as appropriate to the interface between a mantle and a liquid outer core the upper boundary of each of the shells is rigid and isothermal as appropriate to the base of a thick immobile lithosphere calculations with shear stress free upper boundaries are also carried out to assess the role of the rigid surface condition the ratio of the inner radius of each shell to its outer radius is in accordance with possible core sizes in both venus and mars a calculation is also carried out for a mars model with a small core to simulate mantle convection during early core formation different relative proportions of internal and bottom heating are investigated ranging from nearly complete heating from within to almost all heating from below the rayleigh numbers of all the cases are approximately 100 times the critical rayleigh numbers for the onset of convection cylindrical plumes are the prominent form of upwelling in the models independent of the surface boundary condition so long as sufficient heat derives from the core thus major volcanic centers on mars such as tharsis and elysium and the coronae and some equatorial highlands on venus may be the surface expressions of cylindrical mantle plumes the form of the downwelling sheets is significantly affected by the rigid boundary in that the sheets are more irregular in their horizontal structure than when the top boundary is shear stress free in the mainly heated from within models the downwelling sheets are also shorter and less temporally durable when the top boundary is rigid than when it is stress free thus the free motion of plates on the earth facilitates extensive durable convective currents that drive the plates while the stiffening of the lithospheres on mars and venus promotes a style of convection that is not particularly effective in breaking the lithosphere into plates in the rigid top cases the upper boundary layer surrounding the plumes appears to be interspersed with downwelling currents emanating radially from the plumes axes these currents may establish a stress field at the base of hotspot swells that could lead to radial fractures such as those on tharsis models with rigid upper boundaries have higher interior temperatures than do similar models with shear stress free upper boundaries on this basis venus not only has a higher surface temperature than earth but it would have a hotter mantle as well upwelling plumes are more numerous when the outer boundary is rigid as compared with shear stress free flows dominated by a few stong plumes occur when the proportion of basal heating is large thus if the martian crustal dichotomy were caused by a convective system dominated by spherical harmonic degree l 1 then the convection may have been driven strongly from below by a heating pulse accompanying core formation or from the flow of heat from an early hot core if a convective mechanism is responsible for the crustal dichotomy then the dichotomy is likely a very ancient feature however the small core models we consider consistently produce a convective pattern with a dominant l 2 signature which does not correlate with the martian crustal dichotomy a yet smaller core may be necessary to yield the l 1 pattern the small core convective pattern does correlate with the geoid and topography signatures of tharsis which have strong l 2 components and the model produces dynamic uplift comparable to the total topography of the tharsis rise models with larger cores i e with the probable inner to outer radius ratio of mars present mantle generate 4 km of uncompensated topography similar to estimates of the uncompensated tharsis topography thus the tharsis rise could have achieved its full height early in the evolution of mars by mantle plume dynamic uplift at present the uncompensated portion of the tharsis rise topography can be accounted for by dynamic uplift obviating the need for elastic support the present compensated portion of the tharsis topography could be attributed to volcanic or magmatic crustal thickening or depletion of the underlying mantle large core models appropriate to the present mars produce too many plumes to account for just two major volcanic centers i e tharsis and elysium mantle plume activity could be focussed beneath regions like tharsis if fracturing or thinning of the lithosphere in these regions has facilitated magma and heat transport across the lithosphere a similar mechanism could be responsible for clustering of coronae on venus there are no deep seated active linear upwellings in the venus models that could be associated with linear spreading centers in aphrodite if linear spreading is actually occurring in aphrodite the phenomenon is probably a shallow passive one similar to mid ocean ridges on earth

a dynamic origin for the global asymmetry of lunar mare basalts we propose that the hemispheric asymmetry fig 1 of mare basalts may be explained as a result of hydrodynamic instabilities associated with a layer of mixed ilmenite rich cumulates ic and olivine orthopyroxene opx overlying a metallic core this mixed layer mic should form shortly after the solidification of the magma ocean p c hess and e m parmentier earth planet sci lett 134 1995 501 514 because of gravitational differentiation of chemically dense ic material that is expected to form below the anorthositic crust in the final stages of magma ocean crystallization a e ringwood and s e kesson proc lunar planet sci conf 7 1976 1697 1722 ic material is rich in heat producing elements and thermal expansion due to radiogenic heating causes the mic layer to become less dense than overlying mantle the time required for the mic layer to become thermally buoyant may explain a delay of mare volcanism until about 500 ma after solidification of the magma ocean our analyses of the resulting rayleigh taylor instability and numerical modeling of thermo chemical convection show that the instabilities produce spherical harmonic degree 1 thermal and compositional structure if a lunar metallic core is sufficiently small less than 250 km in radius fl 2000 elsevier science b v all rights reserved

effects of multiple phase transitions in a three dimensional spherical model of convection in earth s mantle numerical models of mantle convection that incorporate the major mantle phase changes of the transition zone reveal an inherently three dimensional flow pattern with cylindrical features and linear features that behave differently in their ability to penetrate the 670 km discontinuity the dynamics are dominated by accumulation of cold linear downwellings into rounded pools above the endothermic phase change at 670 km depth resulting in frequent avalanches of upper mantle material into the lower mantle the effect of the exothermic phase transition at 400 km depth is to reduce the overall degree of layering by pushing material through the 670 km phase change resulting in smaller and more frequent avalanches and a wider range of morphologies large quantities of avalanched cold material accumulate above the coremantle boundary cmb resulting in a region of strongly depressed mean temperature at the base of the mantle the 670 km phase change has a strong effect on the temperature field with three distinct regions being visible 1 the upper mantle containing linear downwellings and pools of cold material in the transition zone and characterized by a high amplitude long wavelength spectrum 2 the midmantle containing quasi cylindrical avalanche conduits and characterized by a low amplitude broad spectrum and 3 the deep mantle containing large pools of cold avalanched material and characterized by a high amplitude ultra red i e long wavelength spectrum the effect on the velocity field is very different flow penetration across the 670 km phase change is strongly wavelength dependent with easy penetration at long wavelengths but strong inhibition at short wavelengths thus when comparing numerical models with long wavelength seismic tomography diagnostics based on the density field such as the radial correlation function are much more sensitive to the effects of phase transitions than those based on the velocity field the amplitude of the geoid is not significantly affected by the partial layering because the contribution from the strong heterogeneity in the transition zone is almost perfectly balanced by the contribution from deflection of the 670 km discontinuity avalanches are associated with geoid lows however a more complex viscosity structure is required to correctly match the sign of the geoid over slabs in earth

the history and variability of the east asian paleomonsoon climate abstract changes in the east asian paleomonsoon reflect interactions between the global atmosphere ocean land and ice systems and are also an expression of their combined effect within the boundary conditions imposed by the east asian continent and solar radiation the history of the east asian monsoon is an alternation between dominance by the dry cold winter and warm humid summer monsoons high resolution eolian sequences preserved in the chinese loess plateau reveal that the east asian monsoon may have commenced at least 7 2 ma ago they also provide evidence indicating that the pulsed uplift of the tibetan plateau at about 3 4 and 7 2 ma may have played an important role in inducing climate change the palaeoclimatic records of the last glacial cycle show high frequency variability on time scales of 1000 year or even shorter and instability of the east asian paleomonsoon system the high frequency variability could be due to a non linear response to orbital forcing or a result of the coupling processes between different components of the global system cold air activity in northern high latitudes the trans equatorial air streams from the southern hemisphere and possibly enso may have played an important role in east asian monsoon variability the synchroneity of all the palaeoclimatic events along the polar equator polar pep transect is still an open question correlation of limited palaeoclimatic records for the last 30 kyr obtained from east asia and australia suggests that the trans equatorial air streams driven by the monsoon and trade winds may have had an influence on opposite hemispheres

long wavelength convection poiseuille couette flow in the low viscosity asthenosphere and the strength of plate margins summary mixed heated 3 d mantle convection simulations with a low viscosity asthenosphere reveal relatively short and long wavelength regimes with different scalings in terms of surface velocity and surface heat flux and show that mantle flow in the lithosphere asthenosphere region is a poiseuille couette flow the poiseuille couette velocity magnitude ratio d u allows us to characterize solid state flow in the asthenosphere and to predict the regime transition the transition from dominantly pressure driven poiseuille flow at shorter wavelengths to dominantly shear driven couette flow at long wavelengths depends on the relative strength of lithosphere and asthenosphere and is associated with a switch in the dominant resistance to convective motion in the poiseuille regime significant resistance is provided by plate bending whereas in the couette regime most resistance is due to vertical shear in the bulk mantle the couette case corresponds to classical scaling ideas for mantle convection whereas the poiseuille case with asthenospheric velocities exceeding surface velocities is an example of a sluggish lid mode of mantle convection that has more recently been invoked for thermal history models of the earth our simulations show that both modes can exist for the same level of convective vigour i e rayleigh number but at different convective wavelengths additional simulations with temperature and yield stress dependent viscosity show consistent behaviour and suggest an association of the regime crossover with the relative strength of plate margins our simulations establish a connection between the strength of plate margins solid state flow in the asthenosphere and the wavelength of mantle convection this connection suggests that plate tectonics in the sluggish lid mode is wavelength dependent and potentially more robust than previously envisioned

dynamic feedback between a continentlike raft and thermal convection seismic observations of the mantle which include long wavelength structure a k 1 dependence of heterogeneity on harmonic k and a heterogeneous upper boundary layer and supercontinent kinematics may be explained by the dynamic interaction between a continent like raft and thermal convection we have formulated finite element models of convection with rafts simulating continental plates in a cylindrical geometry the azimuthal interconnectivity of this geometry is vital to resolve the two way dynamics between rafts and convection computations show that 1 raft motion is periodic 2 long wavelength thermal structure is significant within both thermal boundary layers and the fluid interior and 3 the large scale thermal structure with a wavelength longer than the width of raft is responsible for raft motion these three results which are observed for a range of rayleigh numbers internal heating rates and raft sizes are a direct consequence of the dynamic interaction between the raft and convection the physical processes for a model with a rayleigh number of 10 5 are representative when the raft is stationary due to the less efficient heat transfer through the raft and instabilities from the bottom boundary layer heat accumulates beneath the raft and results in long wavelength thermal anomalies the long wavelength thermal anomalies enhance raft motion accompanying the enhanced raft movement the long wavelength thermal anomalies diminish and the raft velocity decreases or the raft comes to rest since convection models without rafts generate less long wavelength heterogeneity compared to the models with rafts or continental plates we suspect that continental plates may play a crucial role in mantle dynamics interestingly raft motion with a period of about 10 transit times is usually significant 10 transit times is about 600 m y if scaled to the earth this is close to the observed 300 500 m y period of supercontinent aggregation and dispersal

quantitative models of hydrothermal fluid mineral reaction the ischia case abstract the intricate pathways of fluid mineral reactions occurring underneath active hydrothermal systems are explored in this study by applying reaction path modelling to the ischia case study ischia island in southern italy hosts a well developed and structurally complex hydrothermal system which because of its heterogeneity in chemical and physical properties is an ideal test sites for evaluating potentialities limitations of quantitative geochemical models of hydrothermal reactions we used the eq3 6 software package version 7 2b to model reaction of infiltrating waters mixtures of meteoric water and seawater in variable proportions with ischia s reservoir rocks the mount epomeo green tuff units megt the mineral assemblage and composition of such megt units were initially characterised by ad hoc designed optical microscopy and electron microprobe analysis showing that phenocrysts dominantly alkali feldspars and plagioclase are set in a pervasively altered with abundant clay minerals and zeolites groundmass reaction of infiltrating waters with megt minerals was simulated over a range of realistic for ischia temperatures 95 260 c and co 2 fugacities 10 0 2 to 10 0 5 bar during the model runs a set of secondary minerals selected based on independent information from alteration minerals studies was allowed to precipitate from model solutions when saturation was achieved the compositional evolution of model solutions obtained in the 95 260 c runs were finally compared with compositions of ischia s thermal groundwaters demonstrating an overall agreement our simulations in particular well reproduce the mg depleting maturation path of hydrothermal solutions and have end of run model solutions whose na k mg compositions well reflect attainment of full equilibrium conditions at run temperature high temperature 180 260 c model runs are those best matching the na k mg compositions of ischia s most chemically mature water samples supporting quenching of deep reservoir conditions for these surface manifestations whilst fe sio 2 and to a lesser extent so 4 contents of natural samples are better reproduced in low temperature 95 c runs suggesting that these species reflect conditions of water rock interaction in the shallow hydrothermal environment the ability of model runs to reproduce the compositional features of ischia s thermal manifestations demonstrated here adds supplementary confidence on reaction path modelling as a realistic and insightful representation of mineral fluid hydrothermal reactions our results in particular demonstrate the significant impact of host rock minerals assemblage in governing the paths and trends of hydrothermal fluids maturation

low degree mantle convection with strongly temperature and depth dependent viscosity in a three dimensional spherical shell 1 a series of numerical simulations of thermal convection of boussinesq fluid with infinite prandtl number with rayleigh number 10 7 and with the strongly temperature and depth dependent viscosity in a three dimensional spherical shell is carried out to study the mantle convection of single plate terrestrial planets like venus or mars without an earth like plate tectonics the strongly temperature dependent viscosity the viscosity contrast across the shell is 10 5 makes the convection under stagnant lid short wavelength structures numerous cylindrical upwelling plumes are developed because of the secondary downwelling plumes arising from the bottom of lid this convection pattern is inconsistent with that inferred from the geodesic observation of the venus or mars additional effect of the stratified viscosity at the upper lower mantle the viscosity contrast is varied from 30 to 300 are investigated it is found that the combination of the strongly temperature and depth dependent viscosity causes long wavelength structures of convection in which the spherical harmonic degree l is dominant at 1 4 the geoid anomaly calculated by the simulated convections shows a long wavelength structure which is compared with observations the degree one l 1 convection like the martian mantle is realized in the wide range of viscosity contrast from 30 to 100 when the viscosity is continuously increased with depth at the lower mantle

inferences on the source of long period seismicity at campi flegrei from polarization analysis and reconstruction of the asymptotic dynamics in the present paper we analyse long period lp events and seismic noise recorded at campi flegrei during the uplift episode of 2004 2006 the results of a detailed polarization analysis indicate that the large number of lps detected during the seismic crisis were accompanied by a sustained activity consisting of very low energy volcanic signals these weak volcanic signals which are usually absent in ambient noise recorded in the studied area and lp events have similar properties namely they are radially polarized towards the same lp source the large dataset analysed allows us to study the statistics of the polarization leading to the extraction of the average properties of the volcanic signals an estimate of the complexity of the system can be provided by the degrees of freedom necessary to describe the asymptotic dynamics in a reconstructed phase space this analysis shows that both lps and low energy signals can be described by a low dimensional dynamical system while ambient noise unrelated to volcanic activity is higher dimensional based on these observations we interpret the phenomena observed during the seismic crisis in the framework of the theory of self oscillating systems in which lps and low energy signals represent self oscillations generated by a persistent hydrothermal source

grain size of quartz as an indicator of winter monsoon strength on the loess plateau of central china during the last 130 000 yr the chinese loess paleosol sequence constitutes an important record of variations in asian monsoon climate over the past 2 4 myr magnetic susceptibility of loess and paleosols has been used as a proxy for summer monsoon intensity while median grain size has been regarded as a measure of the strength of winter monsoon winds that were responsible for most of the dust transport however median grain size is only an approximate index of winter monsoon strength because both paleosols and loess have been modified to various degrees by weathering processes that have produced pedogenic clay the quartz component of loess and paleosols is largely unaffected by weathering processes and therefore constitutes a more reliable proxy index of monsoon wind strength median grain size qmd and maximum grain size qmax values of monomineralic quartz isolated from the loess paleosol section at luochuan in the central loess plateau are characterized by two main intervals during the last ca 130 000 yr when these parameters were significantly greater than 9 and 85 m respectively and three main intervals when they were lower the data imply that the winter monsoon weakened during the intervals with low qmd and qmax values which coincide with marine oxygen isotope stages 5 3 and 1 and was strongest ca 67 000 and 20 000 yr ago during isotope stages 4 and 2 however both quartz grainsize records display second order high frequency high amplitude variations which are lacking in the magnetic susceptibility record that imply rapid and significant changes in atmospheric conditions that affect dust transport and deposition

tidal heating and the long term stability of a subsurface ocean on enceladus abstract tidal dissipation has been suggested as the heat source for the south polar thermal anomaly on enceladus we find that under present day conditions and assuming maxwellian behavior tidal dissipation is negligible in the silicate core dissipation may be significant in the ice shell if the shell is decoupled from the silicate core by a subsurface ocean we have run a series of self consistent convection and conduction models in 2d axisymmetric and 3d spherical geometry in which we include the spatially variable tidal heat production we find that in all cases the shell removes more heat from the interior than can be produced in the core by radioactive decay resulting in cooling of the interior and the freezing of any ocean under likely conditions a 40 km thick ocean made of pure water would freeze solid on a 30 ma timescale an ocean containing other chemical components will have a lower freezing point but even a water ammonia eutectic composition will only prolong the freezing not prevent it if the eccentricity of enceladus were higher e 0 015 in the past the increased dissipation in the ice shell may have been sufficient to maintain a liquid layer we cannot therefore rule out the presence of a transient ocean as a relic of an earlier era of greater heating if the eccentricity is periodically pumped up the ocean may have thickened and thinned on a similar timescale as the orbital evolution provided the ocean never froze completely we conclude that the current heat flux of enceladus and any possible subsurface ocean is not in steady state and is the remnant of an epoch of higher eccentricity and tidal dissipation

degree one mantle convection dependence on internal heating and temperature dependent rheology 1 geophysical and geological observations suggest that a degree one mantle flow pattern consisting of one upwelling and one downwelling may have existed at some time in the mantles of mars the moon and perhaps even for the earth during times of supercontinent formation simple fluid experiments utilizing isoviscous rheologies predict shorter wavelength flow patterns and it is therefore important to determine fluid dynamical parameter sets which lead to larger wavelength flow patterns consistent with observations we perform a series of numerical fluid dynamics calculations in a spherical 3 d geometry in which we vary rayleigh number rheological activation parameter and the degree of internal heating in order to define which parameter choices can lead to degree one mantle convection we find that increasing the degree of internal heating increases the interior temperature of the mantle which leads to a larger viscosity contrast across the top thermal boundary layer and that degree one mantle flow occurs only in cases which exhibit internal heating utilize activation coefficients which lead to 103 or higher viscosity contrasts across the mantle and have viscosity contrasts across the top thermal boundary layer within the range of 200 3000

δ18o values of tree rings as a proxy of monsoon precipitation in arid northwest china abstract it is important to understand the history and dynamics of east asian monsoon system which is the key control of environmental conditions in china this work investigates the relationship between precipitation amount and oxygen isotopic compositions recorded in tree ring cellulose as a potential tool for reconstruction of summer monsoon strength in arid northwest china we found a significant positive correlation between the total annual precipitation and the 18o value of tree rings this correlation results from the fact that summer monsoon precipitation in the study area is relatively more enriched in 18o than winter precipitation and the total amount of annual precipitation predominantly varies with the amount of summer precipitation brought by summer monsoons the amount effect the negative relationship between the precipitation amount and the precipitation 18o is often used to explain the seasonal isotopic distribution in meteoric water of china this study presents a case where the 18o value of tree rings and precipitation is positive associated we point out that the amount effect which was originally used for tropical convective storms should not be simplistically considered as a mechanism for determining isotopic variations in china particularly at high latitude 30 n and or inland locations

self consistent generation of single plume state for enceladus using non newtonian rheology the thermal dichotomy of enceladus suggests an asymmetrical structure in its global heat transfer so far most of the models proposed that obtained such a distribution have prescribed an a priori asymmetry i e some anomaly in or below the south polar ice shell we present here the first set of numerical models of convection that yield a stable single plume state for enceladus without prescribed mechanical asymmetry using the convection code stagyy in a 2 d spherical annulus geometry we show that a non newtonian ice rheology is sufficient to create a localized single hot plume surrounded by a conductive ice mantle we obtain a self sustained state in which a region of small angular extent has a sufficiently low viscosity to allow subcritical to weak convection to occur due to the stress dependent part of the rheological law we find that the single plume state is very unlikely to remain stable if the rheology is newtonian confirming what has been found by previous studies in a second set of numerical simulations we also investigate the first order effect of tidal heating on the stability of the single plume state tidal heating reinforces the stability of the single plume state if it is generated in the plume itself lastly we show that the likelihood of a stable single plume state does not depend on the thickness of the ice shell

characterization of gps time series at the neapolitan volcanic area by statistical analysis 1 the gps time series recorded at the neapolitan volcanic area reveals a very peculiar behavior when a clear deformation is observed the amplitude distribution evolves from a super gaussian to a broader distribution this behavior can be characterized by evaluating the kurtosis spurious periodic components were evidenced by independent component analysis and then removed by filtering the original signal the time series for all stations was modeled with a fifth order polynomial fit which represents the deformation history at that place indeed when this polynomial is subtracted from the time series the distributions again become super gaussian a simulation of the deformation time evolution was performed by superposing a laplacian noise and a synthetic deformation history the kurtosis of the obtained signals decreases as the superposition increases enlightening the insurgence of the deformation the presented approach represents a contribution aimed at adding further information to the studies about the deformation at the neapolitan volcanic area by revealing geologically relevant data

a model for ischia hydrothermal system evidences from the chemistry of thermal groundwaters abstract ischia volcano in central italy has long been known for its copious surface hydrothermal manifestations signs of a pervasive circulation of hot fluids in the subsurface because of the significant chemical heterogeneity of fumarolic gas discharges and hot spring discharges evidences of a complex hydrothermal setting a definite model of fluid circulation at depth is currently unavailable in spite of the several previous efforts here we report on the chemical and isotopic composition of 120 groundwater samples collected during several sampling surveys from 2002 to 2007 the acquired data suggest that the composition of surface manifestations reflect contributions from meteoric water sea water and thermal fluids rising from two distinct hydrothermal reservoir with equilibrium temperatures of respectively 150 c and 270 c and depths of 150 300 m and 300 m but possibly 1000 m we also make use of an isotopic characterization of the dissolved gas phase in thermal waters to demonstrate that the ischia hydrothermal system is currently supplied by a deep rising gas component dgc characterized by co2 97 7 1 2 vol on a water free basis 13cco2 3 51 0 9 and helium isotopic ratio of about 3 5 ra 3he 4he ratio normalized to the air ratio ra likely magmatic in origin an assessment of the thermal budget for ischia hydrothermal system is also presented in the attempt to derive a first estimate of the size and rate of degassing of the magmatic reservoir feeding the gas emissions we calculate that a heat flow of about 153 222 mw presently drives hydrothermal circulation on the island which we suggest is supplied in convective form e g by the ascent of a high t magmatic vapour phase by complete degassing of 2 2 3 3 107 m3 yr 1 of trachytic magma with 2 1 wt dissolved h2o content if extrapolated to entire period of quiescence lasting since the arso eruption in 1302 a d this volume corresponds to 1 6 2 3 1010 m3 of magma degassed in about 700 years of quiescent activity

mantle convection and the dynamic geoid of mars this study compares different 3d spherical models of thermal convection in the martian mantle the best fit to the tharsis bulge is obtained if the endothermic phase transition to perovskite occurs closely above the core mantle boundary in this case a large scale flow develops and the associated geoid anomaly explains approximately half of the observed long wavelength geoid the shallower exothermic phase transitions have little influence on the planform of the flow and on the shape of the geoid previous studies that included exothermic transitions were biased by effects of a soft lithosphere which introduces a large scale mantle flow even without a deep endothermic phase transition however such models predict a continous resurfacing and a dominant geoid low which is in conflict with observations

constraints on mantle viscosity structure from continental drift histories in spherical mantle convection models abstract earth s continents drift in response to the force balance between mantle flow and plate tectonics and actively change the plate mantle coupling thus the patterns of continental drift provide relevant information on the coupled evolution of surface tectonics mantle structure and dynamics here we investigate rheological controls on such evolutions and use surface tectonic patterns to derive inferences on mantle viscosity structure on earth we employ global spherical models of mantle convection featuring self consistently generated plate tectonics which are used to compute time evolving continental configurations for different mantle and lithosphere structures our results highlight the importance of the wavelength of mantle flow for continental configuration evolution too strong short wavelength components complicate the aggregation of large continental clusters while too stable very long wavelength flow tends to enforce compact supercontinent clustering without reasonable dispersal frequencies earth like continental drift with episodic collisions and dispersals thus requires a viscosity structure that supports long wavelength flow but also allows for shorter wavelength contributions such a criterion alone is a rather permissive constraint on internal structure but it can be improved by considering continental oceanic plate speed ratios and the toroidal poloidal partitioning of plate motions the best approximation of earth s recent tectonic evolution is then achieved with an intermediate lithospheric yield stress and a viscosity structure in which oceanic plates are 103 more viscous than the characteristic upper mantle which itself is 100 200 less viscous than the lowermost mantle such a structure causes continents to move on average 2 2 1 0 slower than oceanic plates consistent with estimates from present day and from plate reconstructions this does not require a low viscosity asthenosphere globally extending below continental roots however this plate speed ratio may undergo strong fluctuations on timescales of several 100 myr that may be linked to periods of enhanced continental collisions and are not yet captured by current tectonic reconstructions

three dimensional models of martian mantle convection with phase transitions we have employed a three dimensional compressible convection model to study the dynamics of phase transitions in the martian mantle a large core model with two exothermic phase transitions the olivine to spinel and the to spinel transition and a small core model including also the endothermic spinel to perovskite transition have been considered the two exothermic transitions create thermal barriers for small upwellings due to the latent heat consumption from the phase change upwelling plumes lose part or all of their buoyancy which causes the formation of one stable area full of plumes this tendency for the merging of plumes increases with internal heating this type of convective planform is consistent with the relatively few large volcanic centers the presence of a 175 km thick perovskite layer above the core mantle boundary cmb yields a similar flow pattern albeit with an even smaller number of plumes however the excess temperatures of the plumes and the mantle flow velocities in the lower mantle are smaller than those found in models without perovskite layer the phase transitions cause an increase of temperature near the cmb which prevents the lower mantle and the core from extensive cooling a model with a perovskite layer decreasing in thickness with time can account for a peak in volcanic and magnetic activity early in the martian history

paleoprecipitation record from coral sr ca and δ18o during the mid holocene in the northern south china sea coupled high resolution sr ca and delta o 18 records of a modern and a mid holocene coral from sanya in the southern hainan island northern south china sea scs were reported and the residual delta o 18 delta delta o 18 were calculated to indicate precipitation change in this region unlike other paleoclimate studies this study focused on changes of precipitation time rather than precipitation amount as negative delta delta o 18 peaks in coral generally correspond to peak precipitations or rainy seasons in the surrounding region the time offsets between negative delta delta o 18 peaks and other seasonal indicators such as sea surface temperature sst can well indicate the time of rainy seasons and the precise time offsets can be estimated by the method of cross spectral analysis the results of the modern coral indicate that the variation of the coral delta delta o 18 lags that of the instrumental measured precipitation by about 2 months and about 3 months to the sst derived from coral sr ca ratios this agrees well with the modern observation that the salinity change in the southern coastal regions generally lags that of the precipitation in hianan island by about 2 months and the precipitation change lags about 1 month behind the sst in this region thus coral delta delta o 18 records can be a reliable proxy for the change of rainy seasons in this region the results of the mid holocene coral show about 2 5 months leading of the delta delta o 18 variation ahead of the sst by compensating the approximate 3 months lag of the delta delta o 18 variation behind the sst in modern time the occurrence of rainy seasons during the mid holocene may have advanced about 5 6 months in detail it may start around december and end around april to may with maximum occurring around february therefore rainy seasons mainly occur in winter through early spring during the mid holocene compared with that from may through october in modern times such precipitation patterns appear to agree with the mid holocene pollen records in this region variations of large scale circulation may possibly result in such a different precipitation pattern further studies in particular climate model studies collaborated with meteorologists are required for a better understanding of the mechanism

degree 1 convection in the martian mantle and the origin of the hemispheric dichotomy 1 the surface of mars appears dramatically different between the northern and southern hemispheres any endogenic origin for this hemispheric dichotomy must involve a pattern of mantle convection that reflects the shape of the dichotomy primarily spherical harmonic degree 1 we investigated two mechanisms by which degree 1 convection may be initiated in the martian mantle 1 an endothermic phase change near the cmb and 2 viscosity layering in the mid mantle using two dimensional 2 d and 3 d spherical finite element convection models we explored the conditions under which each mechanism can produce degree 1 structures the phase transition is only effective at generating degree 1 structures when the mantle viscosity is constant or weakly temperature dependent activation energy 100 kj mol but the degree 1 pattern requires several billion years to develop increasing convective vigor in phase change models leads to reduced wavelengths for convective structures degree 1 convection can also develop in a layered viscosity mantle with temperature and depth dependent viscosity an overall sublithospheric radial viscosity variation of a factor of 100 including a factor of 8 25 jump in the midmantle can lead to formation of degree 1 structure in a timescale ranging from 100 my to several hundred my consistent with the timescale for the formation of the dichotomy neither convective vigor nor the internal heating rate greatly affects the formation of degree 1 structures we propose that degree 1 mantle convection induced by a layered viscosity structure may be responsible for the formation of the crustal dichotomy

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

temporal evolution of the stress state in a supercontinent during mantle reorganization summary previous numerical simulation models of isoviscous mantle convection in both 2 d and 3 d geometries have revealed that the presence of a supercontinental lid produces large scale horizontal mantle flow thereby reorganizing the thermal structure of the mantle interior large scale upwelling plumes arising from the core mantle boundary cmb beneath the supercontinent are observed in some models these upwelling plumes have been hypothesized to produce tensional stresses in the supercontinent and to be responsible for the subsequent continental lifting and breakup in this study numerical simulations using a 3 d spherical shell model are conducted in order to elucidate temporal changes in stress state in an idealized supercontinent during mantle reorganization the model supercontinent is assumed to be an undeformable highly viscous supercontinental lid hvsl with respect to the mantle the mantle is heated from the base and from within the hvsl is imposed abruptly on well developed convection systems and remains fixed during the simulations i first consider the scenario in which the hvsl is imposed on isoviscous or weakly temperature dependent viscosity convection exhibiting short wavelength thermal structures the simulation results reveal that a tensional stress regime rapidly predominates throughout the hvsl within 50 100 myr in model time in response to the horizontal mantle flow beneath the hvsl the subsequent large scale plumes upwelling from the cmb also induce tensional stresses in the supercontinent but the effects of these stresses on the overall stress state appear to be secondary for most of the models investigated herein the maximum deviatoric tensional stress generated in the hvsl once convection is re established is 30 90 mpa which is probably comparable to the minimum stress magnitude required to break up the supercontinent to investigate the effects of the hvsl on other convection regimes i next consider the scenario in which an hvsl having a viscosity contrast of 10 is imposed on much longer wavelength i e degree one or degree two dominant convection systems with moderately temperaturedependent viscosity the patterns of such low degree dominant convection are affected little by the imposition of the hvsl and notable mantle reorganization does not occur on the other hand when a reasonable yielding stress is imposed at the continental margins newly formed weak upwelling plumes develop due to enhanced downwelling at the margins rather than large scale mantle reorganization however the newly upwelling plumes do not seem to produce a visible tensional stress regime in the hvsl interior and the spatial distributions of the stress regime and stress magnitude in the hvsl depend on the spatial relationship between the hvsl and the convection pattern since the series l models of the present study do not include the yield stress in the oceanic part of the lithosphere plate like behaviour and subducting plates are not actualized the results for series s models in which the oceanic lithosphere freely sinks and the convection pattern is easily organized imply that the broadly tensional regime prevailing in the supercontinent may support the penetration of mantle plumes into the supercontinent the emergence of hotspots and subsequent continental uplift and break up

diapir induced reorientation of saturn s moon enceladus the recent discovery of active water venting from the surface of saturn s icy moon enceladus has caused a ripple of excitement as it suggests the possibility of subsurface liquid water geologically enceladus poses problems one the reason why the hotspot of geological activity is centred precisely on the south pole has been tackled by francis nimmo and robert t pappalardo they identify reorientation of enceladus s rotation axis as the likely cause and an upwelling of low density material to the surface as the cause of that reorientation comparison of the distribution of impact craters on the leading and trailing hemispheres will be a good test of the reorientation part of the theory enceladus is a small icy satellite of saturn its south polar region consists of young tectonically deformed terrain and has an anomalously high heat flux1 2 this heat flux is probably due to localized tidal dissipation within either the ice shell3 or the underlying silicate core4 the surface deformation is plausibly due to upwelling of low density material diapirism5 as a result of this tidal heating here we show that the current polar location of the hotspot can be explained by reorientation of the satellite s rotation axis because of the presence of a low density diapir if the diapir is in the ice shell then the shell must be relatively thick and maintain significant rigidity elastic thickness greater than 0 5 km if the diapir is in the silicate core then enceladus cannot possess a global subsurface ocean because the core must be coupled to the overlying ice for reorientation to occur the reorientation generates large 10 mpa tectonic stress patterns6 that are compatible with the observed deformation of the south polar region2 we predict that the distribution of impact craters on the surface will not show the usual leading hemisphere trailing hemisphere asymmetry a low density diapir also yields a potentially observable negative gravity anomaly

δ18o of tree ring cellulose in two species spruce and oak as proxies of precipitation amount and relative humidity in northern japan abstract relationships between climatic factors and 18o values of tree rings in two species with different root systems were investigated in the northern area in hokkaido island northern japan this region has a heavy snow cover in winter and has a humid climate throughout the year in the case of spruce picea jezoensis which has shallow roots the 18o values are negatively correlated with precipitation in july and august probably due to higher relative humidity in summer and lower 18o of summer precipitation in a year of higher summer precipitation which is governed by the precipitation amount effect thus the 18o value of tree ring cellulose in spruce must be valuable as a proxy of summer precipitation in this area on the other hand the 18o value in oak quercus crispula which has deeper roots than spruce is not very sensitive to summer precipitation but is negatively correlated mainly with relative humidity in july and august this can be attributed to the smaller 18o enrichment in leaf water in the summer of higher relative humidity our results indicate that 18o values of tree rings in two species with different root systems from the same forest have the potential to reconstruct the two different climate factors

the whisper of the hydrothermal seismic noise at ischia island abstract this work is devoted to the study of the background seismic noise at ischia island we highlight two persistent independent signals with dominant frequency peaks in the range 1 2 hz and 3 4 hz respectively the first signal is the most energetic and persistent and its polarization properties are well defined revealing a shallow propagation likely controlled by both tectonic volcanic structures and morphological features this signal is well correlated at all the stations in the casamicciola area and its group velocity is estimated as 500 600 m s the second signal shows similar polarization properties but the temporal pattern of its amplitude is strongly affected by anthropogenic noise revealing a modulation on a diurnal scale on the investigated spatial scales any clearly correlated signal is not evidenced we interpret the 1 2 hz correlated wave packets as the persistent whisper of the shallow circulation of fluids which are a mixing of sea and meteoric water and thermal fluids of the hydrothermal reservoir in the conceptual scheme of the self sustained musical instruments we hypothesize that the solid structure of the shallow hydrothermal system of ischia is formed by a network of channels continuously excited by the circulating hydrothermal fluids which produce a whispered sound i e the seismic noise this mechanism is able to produce persistent self sustained oscillations that we observe as the 1 2 hz seismic signal and eventually higher modes

seismicity at old faithful geyser an isolated source of geothermal noise and possible analogue of volcanic seismicity abstract old faithful geyser in yellowstone national park u s a is a relatively isolated source of seismic noise and exhibits seismic behavior similar to that observed at many volcanoes including bubblequakes that resemble b type earthquakes harmonic tremor before and during eruptions and periods of seismic quiet prior to eruptions although old faithful differs from volcanoes in that the conduit is continuously open that rock fracturing is not a process responsible for seismicity and that the erupting fluid is inviscid h2o rather than viscous magma there are also remarkable similarities in the problems of heat and mass recharge to the system in the eruption dynamics and in the seismicity water rises irregularly into the immediate reservoir of old faithful as recharge occurs a fact that suggests that there are two enlarged storage regions one between 18 and 22 m the base of the immediate reservoir and one between about 10 and 12 m depth transport of heat from hot water or steam entering at the base of the recharging water column into cooler overlying water occurs by migration of steam bubbles upward and their collapse in the cooler water and by episodes of convective overturn an eruption occurs when the temperature of the near surface water exceeds the boiling point if the entire water column is sufficiently close to the boiling curve that the propagation of pressure release waves rarefactions down the column can bring the liquid water onto the boiling curve the process of conversion of the liquid water in the conduit at the onset of an eruption into a two phase liquid vapor mixture takes on the order of 30 s the seismicity is directly related to the sequence of filling and heating during the recharge cycle and to the fluid mechanics of the eruption short 0 2 0 3 s monochromatic high frequency events 20 60 hz resembling unsustained harmonic tremor and in some instances b type volcanic earthquakes occur when exploding or imploding bubbles of steam cause transient vibrations of the fluid column the frequency of the events is determined by the length of the water column and the speed of sound of the fluid in the conduit when these events occur damping is controlled by the characteristic and hydraulic impedances which depend on the above parameters as well as on the recharge rate of the fluid two periods of reduced seismicity of a few tens of seconds to nearly a minute in duration occur during the recharge cycle apparently when the water rises rapidly through the narrow regions of the conduit causing a sudden pressure increase that temporarily suppresses steam bubble formation a period of decreased seismicity also precedes preplay or an eruption this appears to be the time when rising steam bubbles move into a zone of boiling that is acoustically decoupled from the wall of the conduit because of the acoustic impedance mismatch between boiling water c 10 3 g cm 2 s 1 and rock c 3 10 5 g cm 2 s 1 sustained harmonic tremor occurs during the first one to one and a half minutes of an eruption of old faithful but is not detectable in the succeeding minutes of the eruption the eruption tremor is caused by hydraulic transients propagating within a sublayer of unvesiculated water that underlies the erupting two phase liquid vapor mixture the resonant frequencies of the fluid column decrease to about 1 hz when all of the water in the conduit has been converted to a water steam mixture surges are observed in the flow at this frequency but the resonance has not been detected seismically possibly because the two phase erupting fluid is seismically decoupled from the rock on which seismometers are placed if old faithful is an analogue for volcanic seismicity this study shows that because the frequency of tremor depends on the acoustic properties of the fluid and on conduit dimensions both properties must be considered in analysis of tremor in volcanic regions because magma sound speed can vary over nearly two orders of magnitude as it changes from an undersaturated liquid into a saturated two phase mixture tremor frequency might vary by this magnitude and very broad band seismographs may be required if tremor is to be monitored as magma goes from an undersaturated liquid to a vesiculated froth cessation of fluid induced seismicity may indicate that the processes that drive the transients cease but it is also possible that the processes that drive the transients continue but the fluid properties change so that the fluid becomes acoustically decoupled from the rock on which seismometers are placed