the spatial distribution of precipitation over the west qinling region china ad 1470 2000 the west qinling mountains form part of the climatic barrier that separates southern and northern china and are located at the edge of the region dominated by the asian summer monsoon to investigate the spatial distribution of regional hydroclimatic variability in the west qinling region the annually resolved spatial field of rainy season may june july august september mjjas precipitation anomalies from ad 1470 to 2000 was reconstructed using 39 tree ring chronologies as well as 28 dryness wetness indices derived from historical documentary data the results indicate that the el nino southern oscillation enso and the tropospheric biennial oscillation tbo may jointly affect the spatial pattern of precipitation over the west qinling mountains at inter annual timescales the drought in the 1990s was found to exceed the amplitude and duration of all other periods of drought that have occurred since ad 1470 in this region the new precipitation field reconstruction assesses the spatial pattern of historical hydroclimatic variability in the west qinling region and provides an opportunity to test the performance of climate models in simulating regional precipitation variability and change

strength and water weakening of mantle minerals olivine wadsleyite and ringwoodite rheological properties of olivine and its high pressure polymorphs both dry and hydrous have been studied by monitoring x ray diffraction peak broadening as a function of pressure temperature and time the measurements were carried out up to a pressure of 10 gpa and a temperature of 600 c for olivine and wadsleyite and a pressure of 20 gpa and a temperature of 1000 c for ringwoodite the observations indicate that olivine is much weaker than the other two minerals for this range of conditions and furthermore water weakens olivine dramatically but only slightly weakens wadsleyite and ringwoodite when the temperature increases from 25 c to 400 c the yield strength in the olivine drops by 39 without water and 62 with water however there is hardly any change in strength for wet or dry wadsleyite and ringwoodite

aridity changes in the eastern qilian mountains since ad 1856 reconstructed from tree rings abstract this paper presents a drought reconstruction for the eastern qilian mountains based on a tree ring width chronology developed from three sites of the qinghai spruce picea crassifolia kom the drought reconstruction spanning the years 1856 2009 was developed by calibrating tree ring data with the regional averaged palmer drought severity index pdsi the reconstruction explains 49 9 of the actual pdsi variance during the calibration period from 1951 to 2005 the reconstruction shows droughts occurred in the 1900s the 1920s and early 1930s and at the turn of the 21st century multi taper method spectral analysis indicates the existence of some significant peaks at 2 6 4 2 and 56 9 years drought variations in the study area are significantly correlated with sea surface temperatures in eastern equatorial pacific ocean northern indian ocean eastern china sea and the atlantic ocean suggesting a possible connection with the el nino southern oscillation the asian monsoon and the westerlies

texture development and deformation mechanisms in ringwoodite ringwoodite mg2sio4 with spinel structure is an important phase in the earth s mantle transition zone controlled deformation experiments showed that ringwoodite underwent ductile deformation when compressed axially at 6 10 gpa and at room temperature in a multianvil d dia deformation apparatus texture evolution during cyclic compression has been recorded in situ using x ray transparent anvils with monochromatic synchrotron x ray diffraction and a two dimensional detector quantitative analysis of the images with the rietveld method revealed a 1 1 0 fiber texture by comparing this texture pattern with polycrystal plasticity simulations it is inferred that 111 slip is the dominant deformation mechanism in ringwoodite consistent with high temperature mechanisms observed in other spinel structured materials although strong ringwoodite textures may develop in the transition zone the contribution to bulk anisotropy is minimal due to the weak single crystal anisotropy 2005 elsevier b v all rights reserved

tree ring evidence of little ice age glacier advances in southern tibet the history of late holocene glacier fluctuations in eastern tibet was studied by determining the ages of trees growing on glacier deposits maximum tree ages yield minimum ages of ad 1760 and 1780 for moraine formation at the maximum extent of the little ice age glacier advances in two glacier forefields subsequent moraines could be dated to the beginning of the nineteenth and the beginning of the twentieth century larch trees from a third glacier forefield in southeastern tibet show evidence of glacier activity from 1580 to 1590 from the end of the eighteenth to the beginning of the nineteenth century and from 1860 to 1880 one glacier at mt gyalaperi recently advanced in both 1951 and 1987 periods of glacier advances can partly be correlated with periods of growth reductions in chronologies of total ring width and maximum latewood density derived from trees growing on slopes above the glacier valleys correlation functions with meteorological data suggest that maximum latewood density of subalpin

spatial and temporal patterns of variations in tree growth over the northeastern tibetan plateau during the period ad 1450 2001 we analyzed spatial and temporal growth variations of qilian junipers over the northeastern tibetan plateau tp during the period 1450 2001 by applying the empirical orthogonal function eof technique to seven moisture sensitive tree ring width chronologies the first three principal components together explain 78 21 of the total variance the first principal component pc1 accounts for 51 58 of the total variance and represents consistent tree growth variations in the northeastern tp the second eof mode reveals an opposite structure for the southern and northern parts of the northeastern tibetan plateau reflecting the effect of huge topography and associated atmospheric circulation on tree growth anomalies the third eof mode represents an opposite structure for the eastern and western parts of the northeastern tibetan plateau possibly indicating the influence of different branches of atmospheric circulation system in this area the eof analysis results of instrumental precipitation data resembl

thermal and compositional evolution of the martian mantle effects of water abstract we present numerical models of the thermochemical evolution of the mantle of mars with particular attention paid to the effects of water with a two dimensional anelastic compressible convection algorithm in combination with a parameterized model of composition and thermoelastic properties we consider how water in nominally anhydrous minerals may have influenced the melting and rheology of the martian mantle and how it may have been redistributed by melting melt extraction and convection over a period of 4 gy the strongest effect of water is found to be a marked increase in convective vigor due to the lower viscosity which leads to faster cooling of the mantle but nonetheless enhances melt production modeling results are compared with observations and independent inferences from spacecraft observations and martian meteorite analyses some models with radionuclide concentrations from wanke and dreibus 1994 but with initial mantle water concentrations between their estimate of 36 ppm by weight and 10 times this value combined with 50 degassing of crust forming material partly match observed crustal concentrations of k th and water in order to account for the observed chemical variation in crustal rocks however the formation and survival of ancient mantle heterogeneities appears to have been necessary water loss from the mantle since the end of the magma ocean stage has been minor elevated water contents notwithstanding the depth variation of viscosity in the sublithospheric mantle of a given model is likely minor depths to the curie temperature at the end of the noachian range from 40 to 60 km for magnetite and hematite in the models and present day total crustal thicknesses lie between 75 and 100 km the depth to the brittle ductile transition increases from values around 30 km in the early stages of the models to 170 240 km at present an estimate of total core entropy renders the existence of a basal perovskite ferropericlase layer unlikely the absence of stable superplumes in all of our preferred models suggests that the volcanic provinces of tharsis and elysium were formed by a succession of more short lived events such as transient plumes from specific regions at the core mantle boundary

coupled effects of phase transitions and rheology in 2 d dynamical models of subduction author s arredondo km billen mi abstract 2017 american geophysical union all rights reserved observations of seismicity and seismic tomography provide a present day constraint on the geometry of slabs within the mantle however it is challenging to directly relate the observed shape of slabs to their time evolution phase transitions modify the buoyancy forces within slabs affecting how slabs deform as they sink into the lower mantle and how forces are transmitted to the surface plates here we show that if the crustal shear zone is sufficiently weak 1020 pa s then the coupled effects of a compositionally dependent phase transition model and a stress dependent rheology lead to oscillatory plate speeds and trench motion in response to buckling and folding of the slab on average subducting plate velocity is 4 cm yr and trench motion is 0 7 cm yr however during folding subducting plate speed and trench motion increases by a factor of 3 and trench motion switches from advance to retreat in models with a higher viscosity shear zone 1021 pa s average plate speed is lower 2 cm yr and there is only trench advance stress dependent weakening due to increasing driving stresses can also cause unexpected changes in plate velocity i e decrease or no change in addition due to the added negative buoyancy from the phase transitions slab breakoff occurs in models with a yield stress 500 mpa because of the oscillatory motion of the trench long flat slabs do not form in the transition zone this suggests that other factors such as interaction of the slab with deep mantle flow may be required to create long flat slabs

flow law for ringwoodite at subduction zone conditions the plastic properties of ringwoodite a high pressure modification of olivine are experimentally determined at the pressure of 20 gpa and temperatures up to 1350 c stress relaxation experiments have been carried out on fine grained samples using a two stage t cup multiple anvil high pressure apparatus with synchrotron generated x rays we observe the presence of a significant weakening of the shear strength with a decrease from 2 5 to 0 2 gpa between 600 and 1000 c in this region the activation energy u is about 275 kj mol and it decreases with increasing stress reaching a value of about 200 kj mol when the shear stress attains 2 5 gpa we propose that the plasticity is associated with vigorous dislocation glide controlled by short range lattice resistance forces at lower temperatures the shear strength is mildly dependent on temperature reaching 3 gpa at room temperature while above 1000 c the flow may be governed by a power law relation with n about 3 5 2003 elsevier science b v all rights reserved

a 2 326 year tree ring record of climate variability on the northeastern qinghai tibetan plateau 1 high resolution climate proxy records covering the last two millennia on the qinghai tibetan plateau are scarce yet essential to evaluation of the patterns synchroneity and spatial extent of past climatic changes including those in the medieval warm period mwp and the little ice age lia here we present a 2326 year tree ring chronology of sabina przewalskii kom for dulan area of northeastern qinghai tibetan plateau we find that the annual growth rings mainly reflect variations in regional spring precipitation the greatest change in spring precipitation during the last two millennia seems to occur in the second half of the 4th century the north atlantic mwp was accompanied by notable wet springs in the study region during a d 929 1031 with the peak occurring around a d 974 three intervals of dry springs occurred in the period of lia our tree ring data will facilitate intercontinental comparisons of large scale synoptic climate variability for the last two millennia

1300 years of climatic history for western central asia inferred from tree rings more than 200 000 ring width measurements from 384 trees were obtained for 20 individual sites ranging from the lower to upper local timber lines in the northwest karakorum of pakistan and the southern tien shan of kirghizia samples were obtained predominantly from juniper species juniperus and were analysed to reconstruct regional climatic variation patterns in western central asia since ad 618 site distri bution represents diverse ecological conditions e g combinations of temperature and moisture stress within the karakorum and tien shan mountains permitting both intra montane and inter montane comparisons of chronologies three different types of chronologies ree ecting interannual decadal and centennial scale ring width variations were calculated a statistic skeleton plotting technique was used to identify ring width pointer years interannual a 101 year kernel e lter was used to identify decadal scale variations and for a subset of long lived trees the mean ring width of the entire single series was used to identify centennial trends after extracting and calibrating each of these three distinct wavelengths in ring width variation the results were combined into a comprehensive reconstruction ree ecting primarily temperature e uctuations in western central asia since ad 618 the nature and the temporally changing strength of the climatic signals of this reconstruction are discussed in detail a maximum latewood density record of pinus tienschanica from central tien shan was used as a predictor series to calibrate and validate tree ring width variation in so doing we link our results to the circumpolar maximum latewood density network briffa et al 1998a 1998b schweingruber and briffa 1996

hydrogen incorporation in stishovite at high pressure and symmetric hydrogen bonding in δ alooh first principles calculations of stishovite sio2 alooh and stishovite alooh solid solutions reveal that coupled substitutions of al3 and h for si4 provide a means for dissolving significant amounts of hydrogen in stishovite under lower mantle conditions the enthalpy of solution is positive decreasing in magnitude with increasing pressure combining our results with a model of the configurational entropy we find that the solubility of water in stishovite exceeds 0 3 wt h2o at 25 gpa and 1500 k realistic temperatures for subducting slabs and that the solubility increases with increasing pressure and temperature we predict asymmetric hydrogen bonding in the stishovite alooh solid solution that becomes increasingly symmetric with increasing pressure our results support the recently predicted symmetric hydrogen bonding in alooh and indicate that symmetric hydrogen bonding may be stable at ambient conditions in this material

modeling dislocation glide in mg2sio4 ringwoodite towards rheology under transition zone conditions abstract deformation resulting from thermally activated plastic slip is modeled in mg2sio4 ringwoodite at 20 gpa for a wide range of temperatures the model relies on the structures of the rate controlling 1 2 1 1 0 screw dislocations which have been modeled using the peierls nabarro galerkin method these calculations are parametrized by density functional theory calculations of surfaces of the 0 0 1 1 1 0 and 1 1 1 planes at finite temperatures dislocation mobility is controlled by kink pair nucleation on the thermally activated 1 4 1 1 0 partial screw dislocations as they occur in ringwoodite single slip critical resolved shear stresses crss corresponding to this mechanism are deduced from orowan s equation the results are found to be in reasonably good agreement with experimental data at 20 gpa which show high effective flow stresses under laboratory conditions finally the crss s are calculated for typical mantle strain rates of 10 16 s 1 at appropriate temperatures expected in the lower transition zone results show that dislocation glide remains difficult and that lattice friction is not yet negligible in ringwoodite under natural conditions

single crystal elasticity of wadsleyites β mg 2 sio 4 containing 0 37 1 66 wt h 2 o the presence of hydrogen can affect elastic properties and seismic velocities of minerals in the earth s upper mantle in this study the secondorder elastic constants of hydrous wadsleyites containing 0 37 0 84 and 1 66 wt h2o were determined by brillouin scattering at ambient conditions measurements were performed on at least three independent crystal planes for each composition the aggregate bulk modulus ks0 and shear modulus g0 were calculated using vrh voigt reuss hill averages the results are ks0 165 4 9 gpa g0 108 6 6 gpa for wadsleyite with 0 37 wt h2o ks0 160 3 7 gpa g0 105 3 6 gpa for 0 84 wt h2o ks0 149 2 6 gpa g0 98 6 4 gpa for 1 66 wt h2o we find that the bulk and shear moduli of hydrous wadsleyites decrease linearly with water content according to the following relations in gpa ks0 170 9 9 13 0 8 ch2o g0 111 7 6 7 8 4 ch2o where ch2o is the h2o weight percentage compared with anhydrous wadsleyite addition of 1 wt h2owillleadtoa7 6 decreaseinthebulkmodulus anda7 0 decreaseintheshearmodulus usingtheseresults weexaminethevelocitycontrast between hydrous olivine and wadsleyite at ambient conditions for an fe free system assuming an h2o partition coefficient between wadsleyite and olivine of 3 the velocity contrast in compressional and shear velocity between wadsleyite and olivine ranges from 12 13 for an h2o free system to7 8 forwadsleyitecontaining1 5wt h2o thus themagnitudeoftheseismicvelocitychangeat410 kmdepthcanbeexpectedtobesensitive

lacustrine evidence for moisture changes in the nebraska sand hills during marine isotope stage 3 abstract in the central great plains of north america loess stratigraphy suggests that climate during the late pleistocene was cold and dry however this record is discontinuous and there are few other records of late pleistocene conditions cobb basin located on the northern edge of the nebraska sand hills contains lacustrine sediments deposited during marine isotope stage 3 beginning approximately 45 000 cal yr bp and continuing for at least 10 000 yr the lake was formed by a dune dam blockage on the ancient niobrara river and its deposits contain a diatom record that indicates changes through time in lake depth driven by changes in effective moisture during the earliest stages of lake formation the climate was arid enough to mobilize dunes and emplace dune sand into a blocking position within the niobrara streambed diatom assemblages suggest that lake level was shallow at formation increased substantially during a wet interval and then became shallow again as arid conditions resumed by about 27 000 cal yr bp the lake was filled and a shallow ephemeral river occupied the basin

late holocene climatic and environmental changes in arid central asia abstract late holocene climate and environmental changes in arid central asia were analyzed using various paleoclimate archives such as ice cores tree rings lake sediments historical documents glacial fluctuations and archeological data over the last 2000 years arid central asia witnessed three humid periods from ad 0 410 650 890 and 1500 1820s dry periods occurred in 420 660 and in 900 1510s concerning temperature the most striking features are the existence of the medieval warm period mwp and the little ice age lia the mwp was recorded in the 9 12th centuries and was accompanied by an anomalously dry climate whereas the lia extended from the 15 18th centuries and was accompanied by pluvial conditions temperature and precipitation show significantly negative correlations on annual decadal and centennial timescales temperature was generally above average when dry climate conditions predominated on decadal to centennial timescales during the last 1000 years the coldest decades of the last millennium the period 1630 1650s matched with an anomalously wet episode the combination of paleoclimatic evidence clearly suggests that the combination of cold and wet climate condition during the lia was responsible for the strong glacial advances in several mountain systems of central asia

experimental constraints on the depth of olivine metastability in subducting lithosphere the hypothesis that metastable olivine persists in some subducting slabs into the transition zone has wide implications for mantle dynamics and rheology in order to evaluate this possibility we derive new thermo kinetic subduction zone models to predict the extent of olivine metastability within the stability fields of its high pressure polymorphs wadsleyite and ringwoodite our updated models improve on previous work by incorporating experimental kinetic data on realistic mantle compositions mg fe 2sio4 rather than analogue systems furthermore latent heat due to the transformation is fed back into both the kinetics and the thermal model we also consider the effects of transformation stress on growth kinetics and the possibility of an intracrystalline transformation mechanism previously thought to be important only at high shear stresses our models predict significantly smaller wedges of metastable olivine than previous work in the case of tonga for example where high values of lithospheric age 100 140 million years and convergence rate 14 cm per year are most favorable for metastability models considering only grain boundary nucleation and interface controlled growth predict olivine metastability to 600 km depth in contrast to 660 km predicted previously by kirby et al rev geophys 34 1996 261 when intracrystalline transformation is considered the depth of metastability is further reduced by as much as 100 km due to the large increase in the density of nucleation sites inhibition of growth by transformation stress can increase the depth interval over which the transformation takes place but is unlikely to be a dominant factor especially if the intracrystalline mechanism operates these results indicate that the existence of metastable olivine at depths corresponding to those of the deepest earthquakes 680 km requires subduction of old lithosphere 100 million years and a high vertical subduction velocity 15 cm per year such conditions currently may only be achieved in the very northern part of the tonga subduction zone yet earthquakes occur at depths down to 680 km in other subduction zones in which lithospheric age and or subduction velocity are relatively low e g indonesia and the marianas therefore mechanisms other than transformational faulting in metastable olivine must operate to cause the deepest earthquakes

simple models for late holocene and present day patagonian glacier fluctuations and predictions of a geodetically detectable isostatic response summary the late holocene glacial moraine chronology in the southernmost south american andes includes four 14c dated neoglacial advances and retreats these are used as proxy information to characterize mass fluctuation of the patagonian icefields during the last 5000 years modelled ice loads force a phase lagged viscoelastic gravitational deformation of the solid earth the ancient glacier fluctuations may therefore drive present day crustal motion even in the absence of present day ice mass imbalance numerical models show that such rates of present day uplift and subsidence are larger than those driven by the viscous memory of late pleistocene deglaciation both spherical and flat earth models are employed the latter being used to study exhaustively the evects of glacial load history on the predicted vertical crustal velocity recent assessment of net mass balance from 1944 to 1985 indicates that the southern patagonian icefield has significantly deteriorated due to snout retreat and thinning volume loss rates are estimated at about 3 4 9 3 km3 yr 1 the predicted vertical isostatic response to this recession and to the modelled holocene neoglaciations is at a marginally detectable level 1m m yr 1 if the mantle asthenosphere beneath patagonia has a viscosity of about 1021 pa s however for reduced mantle viscosities the younger holocene glacial load histories predict larger signatures in fact if the viscosity is about 2 1020 pa s or lower then geodetically detectable vertical motion may be driven by a regional little ice age lia 1400 1750 ad glacier advance and subsequent 20th century retreat although this value for mantle viscosity is lower than thought typical of continental shield mantle 1021 pa s it is consistent with inversions for post seismic relaxation time constants in island arc environments and in regions with significant neogene continental tectonism in the viscosity regime of 5 1018 2 1019 pa s the predicted rates of vertical crustal motion are similar to those presently occurring in fennoscandia and hudson bay 5 10 mm yr 1 geodetic data may be sensitive to the time integrated growth and subsequent retreat of patagonian glacier ice mass over the last 600 years

strength of mg fe 2sio4 wadsleyite determined by relaxation of transformation stress abstract the growth of a reaction rim around a crystal undergoing a polymorphic phase transformation generates elastic strain energy as a consequence of the reaction volume change the strain energy inhibits the transformation by counteracting the chemical free energy driving force for growth stress relaxation enables growth to continue at a rate controlled primarily by the mechanical properties of the rim we studied this process in high pressure experiments in order to constrain the rheology of wadsleyite one of the high pressure polymorphs of olivine single crystal spheres of san carlos olivine surrounded by a quasi hydrostatic pressure medium of nacl or au were partially transformed to wadsleyite at 1100 c and 16 17 gpa to determine the rate of growth as a function of time microstructural observations indicate that the relict olivine remains largely undeformed while the wadsleyite rims deform by dislocation creep application of an elastoplastic model to fit the observed decrease in growth rates with time constrains the yield strength of wadsleyite at these conditions to between 4 and 6 gpa a decrease in growth rates was also observed in another study in which varying amounts of water were added to the samples kubo t ohtani e kato t shinmei t fujino k 1998a experimental investigation of the transformation of san carlos olivine single crystal phys chem miner 26 1 6 kubo t ohtani e shinmei t fujino k 1998b effects of water on the transformation kinetics in san carlos olivine science 281 85 87 modeling these results gives values for the yield strength of wadsleyite between 2 and 5 gpa under various conditions a strength difference of 1 gpa is indicated by experiments at 1030 c conducted under nominally dry 200 ppm h2o and water added 500 ppm h2o conditions supporting the hypothesis that hydrolytic weakening is an important process in wadsleyite the calculated yield strengths for wadsleyite indicate that it is three to six times stronger than olivine at the same conditions based on an extrapolation of the low temperature plasticity flow law for olivine these results imply a strong increase in the strength of subducting slabs in the mantle transition zone provided that the deformation mechanism is the same as in the experiments furthermore inhibition of growth by transformation stress may be an important factor in extending the depth range over which metastable olivine transforms to its high pressure polymorphs in subducting slabs

a 1400 year high resolution record of atmospheric circulation over the north atlantic and asia major ion series developed from new subannual scale sampling of an ice core from central greenland are calibrated with instrumental series of atmospheric sea level pressure recording major marine icelandic low and terrestrial siberian high atmospheric circulation systems to provide proxy records of atmospheric circulation over the past 1400 years examination of the proxy records reveals major changes in behaviour of these systems c ad 1400 multidecadal and centennial scale periodic components characterization of mean sea level pressure anomaly fields during the little ice age and the mediaeval warm period the potential role of solar forcing coupled ocean atmosphere associations and a perspective within which the characteristics of instrumental era climate can be assessed

low frequency temperature variations from a northern tree ring density network we describe new reconstructions of northern extratropical summer temperatures for nine subcontinental scale regions and a composite series representing quasi northern hemisphere temperature change over the last 600 years these series are based on tree ring density data that have been processed using a novel statistical technique age band decomposition designed to preserve greater long timescale variability than in previous analyses we provide time dependent and timescale dependent uncertainty estimates for all of the reconstructions the new regional estimates are generally cooler in almost all precalibration periods compared to estimates obtained using earlier processing methods particularly during the 17th century one exception is the reconstruction for northern siberia where 15th century summers are now estimated to be warmer than those observed in the 20th century in producing a new northern hemisphere series we demonstrate the sensitivity of the results to the methodology used once the number of regions with data and the reliability of each regional series begins to decrease we compare our new hemisphere series to other published large regional temperature histories most of which lie within the 1 confidence band of our estimates over most of the last 600 years the 20th century is clearly shown by all of the palaeoseries composites to be the warmest during this period

high resolution palaeoclimatology of the last millennium a review of current status and future prospects this review of late holocene palaeoclimatology represents the results from a pages clivar intersection panel meeting that took place in june 2006 the review is in three parts the principal high resolution proxy disciplines trees corals ice cores and documentary evidence emphasizing current issues in their use for climate reconstruction the various approaches that have been adopted to combine multiple climate proxy records to provide estimates of past annual to decadal timescale northern hemisphere surface temperatures and other climate variables such as large scale circulation indices and the forcing histories used in climate model simulations of the past millennium we discuss the need to develop a framework through which current and new approaches to interpreting these proxy data may be rigorously assessed using pseudo proxies derived from climate model runs where the answer is known the article concludes with a list of recommendations first more raw proxy data are required from the diverse disciplines and from more locations as well as replication for all proxy sources of the basic raw measurements to improve absolute dating and to better distinguish the proxy climate signal from noise second more effort is required to improve the understanding of what individual proxies respond to supported by more site measurements and process studies these activities should also be mindful of the correlation structure of instrumental data indicating which adjacent proxy records ought to be in agreement and which not third large scale climate reconstructions should be attempted using a wide variety of techniques emphasizing those for which quantified errors can be estimated at specified timescales fourth a greater use of climate model simulations is needed to guide the choice of reconstruction techniques the pseudo proxy concept and possibly help determine where given limited resources future sampling should be concentrated

evidence for a warm humid climate in arid northwestern china during 40 30 ka bp abstract former shorelines and sedimentary records from several lake basins in northwestern china xinjiang qinghai give evidence for warm and humid climatic conditions during 40 30 ka bp further indications of this favorable climate period are derived from palaeosols from the ili loess and from cemented calcareous layers on the terraces of the keriya river at the southern margin of the tarim basin and in the badain jaran desert in inner mongolia at that time annual mean temperature in the qaidam basin was 2 c higher and in the western part of inner mongolia even 2 3 c higher than today precipitation in most parts of northwestern china was between 60 300 mm greater than today these changes were probably a consequence of an increase in ocean surface temperature and evaporation resulting from a higher radiation input at middle and low latitudes caused by changes in the earth s precessional cycle as a result of these orbital changes it is suggested that the intensified westerly circulation was responsible for increased moisture over northwestern china

tree ring width and density data around the northern hemisphere part 2 spatio temporal variability and associated climate patterns patterns of summer temperature over the northern hemisphere obtained from a calibration of a treering network are presented for every year from 1600 to 1877 the network of tree ring density chronologies is shown to exhibit spatially coherent modes of variability these modes closely match summer half year tempera ture variations in terms of similar spatial patterns and similar temporal evolution during the instrumental period they can therefore be considered to be proxies for the temperature patterns and time series for the eight most dominant patterns are presented back to the late seventeenth century the first pattern represents spatially coherent warming or cooling and it appears to respond to climate forcings especially volcanic erup tions most other patterns appear to be related to atmospheric pressure anomalies and they can be partially explained by heat advection associated with anomalous atmospheric circulation this provides the potential for reconstructing past variations in atmospher

sound velocities of hydrous ringwoodite to 16 gpa and 673 k article i nfo 0 026 si1 00h0 179o4 with 1 1 wt h2o using brillouin scattering combined with x ray diffraction in an externally heated diamond anvil cell up to 16 gpa and 673 k up to 12 gpa at 300 k the presence of 1 1 wt h2o lowers the elastic moduli of ringwoodite by 5 9 but does not affect the pressure derivatives of the elastic moduli compared to anhydrous ringwoodite the reduction caused by hydration is significantly enhanced when temperatures are elevated at high pressures at 12 gpa increasing temperature by t 100 k leads to a 1 3 2 4 reduction in the elastic moduli c11 c12 and c14 comparing our results with seismic observations we have evaluated the potential h2o content in the lower part of the transition zone our results indicate that the observed seismic velocity anomalies and related depth depression of the 660 km discontinuity could be attributed to thermal variations together with the presence of 0 1 wt h2o 2012 elsevier b v all rights reserved

effect of water in depleted mantle on post spinel transition and implication for 660 km seismic discontinuity abstract we have determined the post spinel transition boundary in anhydrous and hydrous mg2sio4 in a temperature range from 1173 to 2023 k at 19 3 25 4 gpa using synchrotron in situ x ray diffraction measurements the phase boundary in mg2sio4 is located at 22 gpa and 1800 k and 22 1 gpa and 1500 k which is slightly lower 0 3 0 5 gpa than that determined in the previous in situ measurements using the same pressure scale e g katsura et al 2003 post spinel transition in mg2sio4 determined by high p t in situ x ray diffractometry phys earth planet inter 136 11 24 the clapeyron slope of mg2sio4 was found to be gentle i e between 0 4 and 0 7 mpa k which is also consistent with previous in situ measurements but inconsistent with diamond anvil cell experiments and theoretical estimations the phase boundary in mg2sio4 2 wt h2o which is relevant to fe free depleted harzburgitic composition is located between 23 4 and 23 6 gpa and 1500 k which shifts the hydrous boundary to the higher pressures relative to anhydrous mg2sio4 from 1 3 to 1 0 gpa the result for hydrous mg2sio4 shows steeper clapeyron slope between 3 2 and 3 1 mpa k compared with anhydrous mg2sio4 and hydrous pyrolite system the present data suggest that water has a strong influence on 660 km discontinuity and the depressions observed at this boundary in several regions especially related to subduction zones can be explained by the presence of water in depleted harzburgite component

effect of water on melting phase relations and melt composition in the system mg2sio4mgsio3h2o up to 15 gpa melting experiments in the system mg2sio4 mgsio3 h2o up to pressures of 15 gpa show that the presence of h2o drastically changes melting temperature liquidus phases and the coexisting melt composition the system mg2sio4 h2o shows incongruent melting characterized by a high mgsi ratio of the eutectic composition exceeding 2 0 above 12 gpa whereas it exhibits congruent melting up to at least 7 7 gpa in the mgsio3 h2o system incongruent melting is observed up to 3 gpa which switches to congruent melting above 5 5 gpa and persists to at least 12 gpa the variation of the eutectic composition in the system mg2sio4 mgsio3 h2o is consistent with the variations of the melting temperatures in the systems mg2sio4 h2o and mgsio3 h2o the melting temperature solidus in the system mg2sio4 h2o decreases from 1800 c at atmospheric pressure to less than 1200 c at 10 gpa while in the system mgsio3 h2o it is reduced to a minimum value of 1250 c at approximately 5 5 gpa and then increases with pressure the composition of the initial melt in this system drastically changes at around 5 5 gpa the mgsi ratio being about 3 at 15 gpa variations of the ternary phase diagrams mgo sio2 h2o with pressure are compiled and compared with previous work on the relevant systems a modified spinel like hydrous phase is synthesized at 15 5 gpa the maximum amount of h2o accommodated in this phase is estimated to be 3 3 wt from observed chemical composition and crystal chemical considerations implying that a significant amount of h2o can be accommodated in the mantle transition zone the overall effect of h2o on ultrabasic magma genesis in the mantle is discussed a possibility is presented for the formation of komatiite magma involving the effect of h2o in the mantle of the early earth mg rich komatiite magma was possibly generated at a depth of only 200 km at temperatures much lower than that having been assumed previously

hydrogen site analysis of hydrous ringwoodite in mantle transition zone by pulsed neutron diffraction hydrogen site positions and occupancies in the crystal structure of synthetic hydrous ringwoodite have been determined for the first time by high resolution neutron powder diffraction conducted at the pulsed neutron source at japan proton accelerator research complex j parc it is demonstrated that hydrogen exchanges not only with mg or fe but also with si cations to form hydroxyl and hydrogen bonding both within the relevant octahedra or tetrahedra created by their surrounding oxygen anions the hydrated octahedra shrink whereas the hydrated tetrahedra expand the occurrence of simultaneous hydration of octahedra and tetraheda is thus unambiguously confirmed whereby the latter plays an especially unique role in reducing seismic velocity and for enhancing the electrical conductivity of ringwoodite at high pressures and temperatures these results provide distinctive implications for discussing the physical properties of hydrous ringwoodite occurring in the mantle transition zone and evaluating the actual water content in the zone

climate of the last 500 years high resolution ice core records precipitation accumulating on the earth s ice sheets and ice caps records a variety of physical and chemical information about the atmosphere and in some cases provides unique insight to both the history and the mechanics of the earth s environmental system high resolution well dated dust records from both polar ice sheets suggest a linkage between increased atmospheric dust and cooler temperatures over antarctica but a similar relationship is not observed in ice cores from either greenland or china net accumulation histories for the last 490 years reveal no discemible global pattern although interesting regional differences and similarities exist excess non sea salt sulfate profiles provide

late holocene temperature fluctuations on the tibetan plateau abstract proxy data of palaeoclimate like ice cores tree rings and lake sediments document aspects of climate changes on the tibetan plateau during the last 2000 years the results show that the tibetan plateau experienced climatic episodes such as the warm intervals during ad 800 1100 and 1150 1400 the little ice age between ad 1400 and 1900 and an earlier cold period between the 4th and 6th centuries in addition temperatures varied from region to region across the plateau a warm period from ad 800 to 1100 in the northeastern tibetan plateau was contemporaneous with cooling in the southern tibetan plateau which experienced warming between ad 1150 and 1400 large scale trends in the temperature history from the northeastern tibetan plateau resemble those in eastern china more than the trends from the southern plateau the most notable similarities between the temperature variations of the tibetan plateau and eastern china are cold phases during ad 1100 1150 1500 1550 1650 1700 and 1800 1850

a dislocation model of seismic wave attenuation and micro creep in the earth harold jeffreys and the rheology of the solid earth a microphysical model of seismic wave attenuation is developed to provide a physical basis to interpret temperature and frequency dependence of seismic wave attenuation the model is based on the dynamics of dislocation motion in minerals with a high peierls stress it is proposed that most of seismic wave attenuation occurs through the migration of geometrical kinks micro glide and or nucleation migration of an isolated pair of kinks bordoni peak whereas the long term plastic deformation involves the continuing nucleation and migration of kinks macro glide kink migration is much easier than kink nucleation and this provides a natural explanation for the vast difference in dislocation mobility between seismic and geological time scales the frequency and temperature dependences of attenuation depend on the geometry and dynamics of dislocation motion both of which affect the distribution of relaxation times the distribution of relaxation times is largely controlled by the distribution in distance between pinning points of dislocations l and the observed frequency dependence of q q w is shown to require a distribution function of p l l m with m 4 2 the activation energy of q 1 in minerals with a high peierls stress corresponds to that for kink nucleation and is similar to that of long term creep the observed large lateral variation in q 1 strongly suggests that the q 1 in the mantle is frequency dependent micro deformation with high dislocation mobility will temporarily cease when all the geometrical kinks are exhausted for a typical dislocation density of 108 m 2 transient creep with small viscosity related to seismic wave attenuation will persist up to the strain of 10 6 thus even a small strain 10 6 10 4 process such as post glacial rebound is only marginally affected by this type of anelastic relaxation at longer time scales continuing nucleation of kinks becomes important and enables indefinitely large strain steady state creep causing viscous behavior

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

deformation of peridotite at high pressure in a new molten salt cell comparison of traditional and homologous temperature treatments abstract we have conducted a series of constant strain rate experiments on a synthetic peridotite composed of isostatically hot pressed olivine and orthopyroxene over a pressure range of 700 2200 mpa and a temperature range of 1250 1700 k by using a sample assembly in which specimens are surrounded by molten salt the data are of much higher quality than previously obtained in solid pressure medium apparatus we find that both the temperature and pressure dependence of creep in our experiments can be combined quantitatively as the homologous temperature dependence of creep this quantitative relationship between creep and melting greatly simplifies the thermodynamic treatment of creep and provides a simple model for the extrapolation of laboratory creep data for peridotite to conditions throughout the earth s upper mantle

investigation of the martensitic like transformation from mg2geo4 olivine to its spinel structure polymorph a coherent mechanism for the transformation of olivine to its spinel structure polymorph has been investigated in mg 2 geo 4 olivine at conditions ranging from 6 gpa to 18 gpa at 300 to 1250 c using a multi anvil apparatus this transformation mechanism which produces plates of spinel lying parallel to the 100 planes in olivine becomes increasingly important above 10 gpa at temperatures between 300 and 400 c the primary effect of temperature above 400 c is to increase the length of the lamellae the primary effect of pressure is to increase the number of lamellae that have nucleated the distribution of transformation is very inhomogeneous lamellae first appear in patches associated with grain edges and corners as the degree of transformation increases patches become more extensive and more heavily populated until the majority if not all grains contain large numbers of lamellae that span large portions of their host grains the mechanism that produces the lamellae requires three factors high pressure overstep of the equilibrium boundary some level of differential stress either microscopic or macroscopic and high enough temperature to facilitate rearrangement of the cations it is most consistent with a martensitic like transformation mechanism the results of this study suggest that olivine may exhibit similar behavior in cold rapidly subducting lithospheric slabs if conditions are too cold for olivine to transform by reconstructive nucleation and growth it could instead progressively transform by the martensitic like mechanism as conditions deviate further and further from the equilibrium phase boundary

comparative in situ x ray diffraction study of san carlos olivine influence of water on the 410 km seismic velocity jump in earth s mantle a comparative study of the equation of states of hydrous 0 4 wt h2o and anhydrous san carlos olivine 30 ppm h2o was conducted using synchrotron x rays up to 11 gpa in a diamond anvil cell dac at ambient temperature both samples were loaded in the same high pressure chamber of the dac to eliminate the possible pressure difference in different experiments the obtained compression data were fitted to the third order birch murnaghan equation of state yielding a bulk modulus k 123 3 gpa for hydrous olivine and k 130 4 gpa for anhydrous olivine as k is fixed at 4 6 therefore 0 4 wt h2o in olivine results in a 5 reduction in bulk modulus previous studies reported bulk modulus reduction by water in olivine s high pressure polymorph wadsleyite to which the transformation from olivine gives rise to the seismic discontinuity at 410 km depth the new data results in a reduction in the magnitude of the discontinuity by 50 in v p and 30 in v s for 1 5 water partitioning between olivine and wadsleyite with respect to anhydrous mantle previous knowledge of the influence of water on this phase transition has been in opposition to a large amount of water e g 200 ppm by wood 1995 existing at 410 km depth calculation of the seismic velocities based on newly available elasticity data of the hydrous phases indicates that the presence of water is favorable for the mineral composition model pyrolite and seismic observations in terms of the magnitude of the 410 km discontinuity

deformation of olivine at subduction zone conditions determined from in situ measurements with synchrotron radiation abstract we report measurements of the deformation stress for san carlos olivine at pressures of 3 5 gpa temperatures of 25 1150 c and strain rates of 10 7 10 5 s 1 we determine a deformation stress of approximately 2 5 gpa that is relatively temperature and strain rate independent in the temperature range of 400 900 c the deformation experiments have been carried out on a deformation dia d dia apparatus sam85 at x17b2 nsls powder samples are used in these experiments enstatite mgsio 3 3 5 total quality of sample is used as the buffer to control the activity of silica ni foil is used in some experiments to buffer the oxygen fugacity water content is confirmed by ir spectra of the recovered samples samples are compressed at room temperature and are then annealed at 1200 c for at least 2 h before deformation the total plastic and elastic strains macroscopic are derived from the direct measurements of the images taken by x ray radiograph technique the differential stresses are derived from the diffraction determined elastic strains in the regime of 25 400 c there is a small decrease of stress at steady state as temperature increases in the regime of 400 c to the transition temperature the differential stress at steady state 2 5 gpa is relatively insensitive to the changes of temperature and strain rate however it drastically decreases to about 1 gpa and becomes temperature dependent above the transition temperature and thereafter the transition temperature is near 900 c above the transition temperature the flow agrees with power law creep measurements of previous investigations the anisotropy of differential stress in individual planes indicates that the deformation of olivine at low temperature is dominated by 0 0 1 1 0 0 accounting to a slower strain rate in the natural system the transition temperature for the olivine in the slab is most likely in the range of 570 660 c

hydrometeorological reconstructions for northeastern mongolia derived from tree rings 1651 1995 reconstructions of annual prior august current july precipitation and streamflow 345 yr in length 1651 1995 are presented for northeastern mongolia based on tree ring width data these precipitation and streamflow reconstructions account for 54 and 48 of the respective variance in instrumental data over the past 50 years variations in instrumental precipitation and streamflow are within the range of those reconstructed over the length of tree ring records however there appear to be more frequent extended wet periods during the twentieth century multitaper spectral analysis revealed statistically significant peaks at 10 8 and 12 8 yr for the precipitation reconstruction and at 12 8 and 20 3 23 8 yr for the streamflow reconstruction similarly singular spectrum analysis identified spectral modes of variation at 12 and 21 yr for both series these spectra resemble those found for tree ring based precipitation reconstructions in central china as well as the western united states and may reflect solar influences on the climate of mongolia

new developments in deformation experiments at high pressure although the importance of rheological properties in controlling the dynamics and evolution of the whole mantle of earth is well recognized experimental studies of rheological properties and deformation induced microstructures have mostly been limited to low pressure conditions this is mainly a result of technical limitations in conducting quantitative rheological experiments under high pressure conditions a combination of factors is changing this situation increased resolution of composition and configuration of earth s interior has created a greater demand for well resolved laboratory measurement of the effects of pressure on the behavior of materials higher strength materials have become readily available for containing high pressure research devices and new analytical capabilities in particular very bright synchrotron x ray sources are now readily available to high pressure researchers one of the biggest issues in global geodynamics is the style of mantle convection and the nature of chemical differentiation associated with convectional mass transport although evidence for deep mantle circulation has recently been found through seismic tomography e g van der hilst et al 1997 complications in convection style have also been noted they include 1 significant modifications of flow geometry across the mantle transition zone as seen from high resolution tomographic studies fukao et al 1992 masters et al 2000 van der hilst et al 1991 and 2 complicated patterns of flow in the deep lower mantle 1500 2500 km perhaps caused by chemical heterogeneity kellogg et al 1999 van der hilst and karason 1999 these studies indicate that while large scale circulation involving the whole mantle no doubt occurs significant deviations from simple flow geometry are also present two mineral properties have strong influence on convection 1 density and 2 viscosity rheology contrasts in the past the effects of density contrast have been emphasized honda et al 1993 kellogg et al 1999 tackley et al 1993 and the influence of