effects of a perovskite post perovskite phase change near core mantle boundary in compressible mantle convection 1 numerical simulations of compressible isochemical mantle convection are used to investigate the effect of the perovskite to post perovskite phase transition at around 2700 km depth which has recently been discovered by high pressure experiments and ab initio calculations on the convective planform temperature and heat transport characteristics of the mantle the usual phase transitions at 410 km olivine spinel and 660 km spinel perovskite are also included the exothermic post perovskite phase change at 2700 km depth destabilizes the lower thermal boundary layer increasing the heat flow increasing interior mantle temperature and increasing the number and time dependence of upwelling plumes the resulting weak highly time dependent upwellings also have a smaller horizontal spacing than the plumes that occur in the absence of the phase transition while the influence of post perovskite phase change may be smaller than that of some other complexities such as compositional stratification it appears to have an important enough effect that it should not be ignored in dynamical studies of mantle convection

thermal energy storage in a confined aquifer second cycle during the first 6 month injection storage recovery cycle of the auburn university aquifer thermal energy storage project water pumped from an upper supply aquifer was heated to an average temperature of 55oc with an oil fired boiler and then injected into a lower storage aquifer injection and recovery temperatures flow rates and temperatures at six depths in 10 observation wells and hydraulic heads in seven wells were recorded twice daily the second cycle injection which was performed in a manner similar to the first began on september 23 1978 and continued until november 25 1978 when 58 010 m 3 of water had been pumped into the storage aquifer the major problem experienced during the first cycle a clogging injection well was reduced by regular backwashing this was done 8 times during injection and resulted in a 24 average injection rate increase compared to the first cycle a 63 day storage period ended on january 27 1979 and production of hot water began with an initial temperature of 54oc by march 23 this temperature had dropped to 33oc with 66 400 m 3 of water and 76 of the injected thermal energy recovered this compares to 66 recovery during the first cycle over the same drop in production temperature production of hot water continued until april 20 at which time 100 100 m 3 of water and 89 of the injected thermal energy was recovered at a final production temperature of 27 5 o c during the second cycle measurements were made of relative land subsidence and rebound to a precision approaching 0 1 mm the surface elevation near the injection well rose 4 mm during injection fell during storage and fell more rapidly toward its original elevation during production this movement was due to thermal expansion and contraction rather than to effects caused by head changes in the storage aquifer

the influence of post perovskite strength on the earth s mantle thermal and chemical evolution abstract we have investigated the influence of post perovskite ppv viscosity on mantle convective dynamics and stirring efficiency using numerical modeling and simple analytical theory our results show that the strength of ppv has a dramatic influence on convective dynamics the presence of a weak ppv enhances heat transfer across the bottom thermal boundary layer resulting in higher temperatures lower mantle viscosities and considerably larger convective velocities this leads to a significant increase in stirring efficiencies with decreasing the ppv strength by at least one order of magnitude in addition using a simple parameterized convection evolution that includes the influence of ppv coupled to a mixing model we show that during the long term history of the earth s mantle the presence of ppv yields systematically hotter thermal evolution and more efficient convective stirring such a strong effect of ppv strength on mantle stirring efficiency suggests that the influence of ppv phase must be considered when interpreting both geochemical and geophysical observations

effect of post perovskite rheology on the thermal evolution of the earth abstract secular cooling of the earth mantle is a complex process affected by many factors here we present the results of a modelling study focused on efficiency of cooling in the presence of rheologically distinct post perovskite we evaluate combined effects of variable thermal expansivity and diffusivity initial thermal condition and heat source model and concentrate on the effects of rheologically weak post perovskite cooling of the core is included in the model core is assumed to be an isothermal heat reservoir with temperature controlled by heat flux through core mantle boundary our 2d axisymmetric convection model has pressure temperature and phase dependent viscosity and includes the effects of an endothermic phase transition at 660 km depth and an exothermic perovskite post perovskite phase transition in the lowermost mantle in agreement with previous studies we conclude that depth dependent material parameters tend to delay secular cooling presence of the weak post perovskite on the other hand significantly enhances core cooling and its effect on core temperature is opposite and comparable in magnitude

is the long wavelength geoid sensitive to the presence of postperovskite above the core mantle boundary 1 the analysis of seismic data represents today the primary tool in the search for the presence of postperovskite in the lowermost mantle d 00 this work aims at testing whether the inversion of gravitational data can also contribute to the detection of postperovskite in d 00 w e assume that the transition from perovskite to postperovskite is accompanied by a reduction in viscosity and test the effects of such viscosity change on the prediction of the dynamic geoid with a numerical model of subducted lithosphere our results show that the long wavelength component of the geoid is very sensitive to the presence of postperovskite areas in d 00 especially if their viscosity is significantly lower than the viscosity of the surrounding perovskite and if these areas are located close to density

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr

mixing of heterogeneities in the mantle effect of viscosity differences the effect of viscosity variations associated with large scale chemical heterogeneities on mixing in the mantle is studied for a model two dimensional problem low viscosity regions are rapidly deformed develop long tendrils and are entrained towards regions of surface divergence very viscous regions are only slowly stretched thus geochemical reservoirs can persist relatively undisturbed for long periods of time if they are o 10 100 times more viscous than the surrounding mantle high viscosity ratio blobs have a tendency to aggregate leading to the formation of large scale heterogeneities from smaller ones

simultaneous volume measurements of post perovskite and perovskite in mgsio3 and their thermal equations of state abstract simultaneous volume measurements of mgsio 3 post perovskite ppv and perovskite pv were performed in a diamond anvil cell dac combined with synchrotron x rays an externally heated dac was used in addition to a laser heated dac for the volume measurement experiment at high temperatures the volume data were collected in the stability field of post perovskite from 115 to 130 gpa the temperature generated in the externally heated and the laser heated dacs for the volume measurement were up to 832 and 2330 k respectively using two different but complementary heating techniques we collected the data at a wide temperature range from 300 to 2330 k the obtained p v t data for ppv and pv were fitted to a third ordered birch murnaghan equation of state eos for a precise comparison of the volume between the two phases the eoss were constructed based on the same pressure scale of mgo the simultaneous volume measurements and the volumes calculated from the determined eoss demonstrate that the volume difference between ppv and pv of about 1 5 is almost constant with increasing temperature to 4000 k at the transition at the base of the mantle this density difference corresponds to a temperature anomaly of 1300 k without the phase transition due to the very small thermal expansivity of minerals which has a significant effect on mantle dynamics the thermal expansivity contrast between the top and the bottom of the mantle is a factor of 3 6 from a mantle convection study this value suggests that huge and hot plumes are formed at the core mantle boundary

the stability and structure of primordial reservoirs in the lower mantle insights from models of thermochemical convection in three dimensional spherical geometry large scale chemical lateral heterogeneities are inferred in the earth s lowermost mantle by seismological studies we explore the model space of thermochemical convection that can maintain reservoirs of dense material for a long period of time by using similar analysis in 3 d spherical geometry in this study we focus on the parameters thought to be important in controlling the stability and structure of primordial dense reservoirs in the lower mantle including the chemical density contrast between the primordial dense material and the regular mantle material buoyancy ratio thermal and chemical viscosity contrasts volume fraction of primordial dense material and the clapeyron slope of the phase transition at 660 km depth we find that most of the findings from the 3 d cartesian study still apply to 3 d spherical cases after slight modifications varying buoyancy ratio leads to different flow patterns from rapid upwelling to stable layering and large thermal viscosity contrasts are required to generate long wavelength chemical structures in the lower mantle chemical viscosity contrasts in a reasonable range have a second order role in modifying the stability of the dense anomalies the volume fraction of the initial primordial dense material does not effect the results with large thermal viscosity contrasts but has significant effects on calculations with intermediate and small thermal viscosity contrasts the volume fraction of dense material at which the flow pattern changes from unstable to stable depends on buoyancy ratio and thermal viscosity contrast an endothermic phase transition at 660 km depth acts as a filter allowing cold slabs to penetrate while blocking most of the dense material from penetrating to the upper mantle

tropical climate at the last glacial maximum inferred from glacier mass balance modeling model derived equilibrium line altitudes elas of former tropical glaciers support arguments based on other paleoclimate data for both the magnitude and spatial pattern of terrestrial cooling in the tropics at the last glacial maximum lgm relative to the present lgm elas were maintained by air temperatures that were 3 5 to 6 6 c lower and precipitation that ranged from 63 wetter in hawaii to 25 drier on mt kenya africa our results imply the need for a 3 c cooling of lgm sea surface temperatures in the western pacific warm pool sensitivity tests suggest that lgm elas could have persisted until 16 000 years before the present in the peruvian andes and on papua new guinea

a doubling of the post perovskite phase boundary and structure of the earth s lowermost mantle a new model of the deep earth allows geophysicists to measure variations in earth s temperature near the boundary between the rocky mantle and core using a recently discovered phase change in the lowest part of the earth s mantle where atoms rearrange themselves in crystals under extreme pressure and temperature the model also explains odd features of this part of the mantle such as patchy regions that reflect seismic waves generated by large earthquakes and inferences of dense partial melting combined with observations the results imply very large variations in temperature providing further evidence for circulation of material throughout the earth s mantle the thermal structure of the earth s lowermost mantle the d layer spanning depths of 2 600 2 900 kilometres1 is key to understanding the dynamical state and history of our planet earth s temperature profile the geotherm is mostly constrained by phase transitions such as freezing at the inner core boundary or changes in crystal structure within the solid mantle that are detected as discontinuities in seismic wave speed and for which the pressure and temperature conditions can be constrained by experiment and theory a recently discovered phase transition at pressures of the d layer2 3 4 is ideally situated to reveal the thermal structure of the lowermost mantle where no phase transitions were previously known to exist here we show that a pair of seismic discontinuities observed in some regions of d can be explained by the same phase transition as the result of a double crossing of the phase boundary by the geotherm at two different depths this simple model can also explain why a seismic discontinuity is not observed in some other regions and provides new constraints for the magnitude of temperature variations within d

inferring the viscosity and the 3 d density structure of the mantle from geoid topography and plate velocities summary in a dynamic earth mantle mass heterogeneities induce gravity anomalies surface velocities and surface topography these lateral density heterogeneities can be estimated on the basis of seismic tomographic models recent papers have described a realistic circulation model that takes into account the observed plate geometry and is able to predict the rotation vectors of the present plates the relationship between the surface observables and the heterogeneities is sensitive to the viscosity stratification of the mantle here we use this model combined with a generalized least squares method in order to infer the viscosity profile of the earth from the surface observations and to get some new insight into the 3 d density structure of the mantle the computed radial viscosity profile presents a continuous increase of more than two orders of magnitude the asthenosphere has a viscosity close to 2 x lo2 pa s no sharp discontinuity is requested at the upper lower mantle interface the largest viscosity 7 x 10 pas is reached in the middle of the lower mantle at greater depth approaching the core mantle boundary the viscosity decreases by one order of magnitude the model suggests that the well known degree 2 and order 2 anomaly in the transition zone of the upper mantle is merely the signature of the slabs it also slightly increases the degree 2 and order 0 in the lower mantle and decreases it in the upper mantle in other words the inversion requests a hotter lower mantle beneath the equator and a colder upper mantle at the same latitudes

silicon self diffusion of mgsio3 perovskite by molecular dynamics and its implication for lower mantle rheology 1 the pressure effect of silicon self diffusion of mgsio3 perovskite was investigated by molecular dynamics md the viscosity variation of mgsio3 perovskite in the lower mantle was derived by the nabarro herring herring nabarro model for the md calculation the spontaneous jumping of atoms by self diffusion was reproduced without using artificial forces and the consistency of migration enthalpy hm with experimental data was improved the results showed that migration enthalpy increases monotonically with increasing pressure the viscosity of mgsio3 perovskite in the lower mantle increases monotonically with increasing depth the obtained depth profile is distinguishable from that of mgo periclase and can be utilized to determine which mineral dominates the lower mantle rheology depending upon the assumed shape of the depth profile for lower mantle viscosity we considered the dominant mineral as 1 mgsio3 perovskite for the monotonic shape case or 2 mgo periclase for the hill shape case that has the highest viscosity zone in the middle of the lower mantle

thermoelastic properties of post perovskite phase mgsio3 determined experimentally at core mantle boundary p t conditions we have performed in situ x ray diffraction measurements on mgsio3 up to 144 5 gpa and 2535 k to obtain a precise experimental determination of the elastic properties of the post perovskite polymorph of mgsio3 at high pressure and temperature the complete dataset is comprised of 24 data points at ambient temperature and an equal number at high temperature fitted physical properties are the room temperature bulk modulus the gruneisen parameter with its volume dependency the thermal expansion with its temperature dependency and the linear incompressibilities as well as thermal expansions and their temperature dependency on each axis elastic anisotropy is observed the structure being much more compressible along the b axis and less compressible along the c axis in agreement with theoretical calculations we also demonstrate with the present study that experiments can provide precise information on the elasticity of complex materials at extreme pressure and temperature conditions

equilibrium line altitudes of late quaternary glaciers in the oshtorankuh mountain iran valleys in the north flank of oshtorankuh central zagros mountain range iran are presently ice free except few relict firn basins but they were glaciated during the late quaternary the equilibrium line altitudes ela s of former glaciers were reconstructed based on the glacio geomorphological analysis of former glaciations traces in addition to the field investigations combined use of 10 m dem data satellite image interpretations and 1 25 000 topographic maps were applied to reconstruct the former elas the amount of elas during the former glaciations was evaluated based on the position of end moraines the ela reconstructions indicated that elas were about 3121 m asl during the maximum glacier extension based on the calculated value of the modern ela 4500 m a s l ela in the oshtorankuh area was depressed in the pleistocene approximately 1380 m to an elevation of 3121 m and the glaciers extended down at least as low as 2400 m a s l by comparison of the calculated ela depressions and the amount of the ela depression around the world the maximum glacier extension in oshtorankuh was correlated with the lgm last glacial maximum in the study area perfect recessional moraines are observed at elevations about 2650 3700 m a s l which can be formed in the younger glaciation phases the ela and ela depression related to youngest moraines in the study area were about 3848 m a s l and 650 m respectively the calculated ela depression with considering the leeward accumulation of wind blown snow for neo glaciation is more comparable to the latest phases of late glaciations or first phases of neo glaciations the study showed that the depression of the annual temperature during the lgm glaciations was about 9 8 c and it was about 4 6 c probably during the youngest glaciation stage

small post perovskite patches at the base of lower mantle primordial reservoirs insights from 2 d numerical modeling and implications for ulvzs we perform numerical experiments of thermochemical mantle convection in 2 d spherical annulus geometry to investigate the distribution of post perovskite ppv with respect to the location of primordial reservoirs of dense material in the lowermost mantle high core mantle boundary temperatures lead to strong anticorrelation between the locations of ppv and large primordial reservoirs while low values lead to a ppv layer fully covering the outer core intermediate values avoid a full ppv layer but allow ppv phase change to occur within the primordial reservoirs through interactions between cold downwellings and primordial reservoirs low viscosity weak ppv leads to the formation of long lived thin tails of primordial materials extending laterally at the edges of these reservoirs small patches of ppv also form within the primordial reservoir but are short lived if primordial reservoirs are enriched in iron these patches may provide an explanation for the ultralow velocity zones

effects of low viscosity post perovskite on thermo chemical mantle convection in a 3 d spherical shell 1 numerical simulations of thermo chemical multi phase mantle convection in a 3 d spherical shell are performed to determine how a low viscosity of post perovskite affects dynamics and structures in the deep mantle low viscosity post perovskite weakens the deepest part of slabs allowing them to more effectively spread over the core mantle boundary cmb and it also results in a greater volume of basalt segregating both of which increase the size of dense chemical piles the horizontal lengthscale of regions of pooled slab material and the steepness of piles edges in composition and phase consistent with the existence of steep sharp sided edges found in seismic analyses cmb heat flux is strongly enhanced in regions of low viscosity post perovskite consistent with a theoretical prediction and both cmb and surface heat flux are increased on average by a low viscosity of post perovskite which could have important implications for the evolution of earth s core and mantle

effects of plate bending and fault strength at subduction zones on plate dynamics for subduction to occur plates must bend and slide past overriding plates along fault zones because the lithosphere is strong significant energy is required for this deformation to occur energy that could otherwise be spent deforming the mantle we have developed a finite element representation of a subduction zone in which we parameterize the bending plate and the fault zone using a viscous rheology by increasing the effective viscosity of either the plate or the fault zone we can increase the rates of energy dissipation within these regions and thus decrease the velocity of a plate driven by a given slab buoyancy we have developed a simple physical theory that predicts this slowing by estimating a convecting cell s total energy balance while taking into account the energy required by inelastic deformation of the bending slab and shearing of the fault zone the energy required to bend the slab is proportional to the slab s viscosity and to the cube of the ratio of its thickness to its radius of curvature the distribution of dissipation among the mantle lithosphere and fault zone causes the speed of a plate to depend on its horizontal length scale using the observation that earth s plate velocities are not correlated to plate size we can constrain the lithosphere viscosity to be between 50 and 200 times the mantle viscosity with higher values required if the fault zone can support shear tractions 50 mpa over 300 km these subduction zone strengths imply that the mantle fault zone and lithosphere dissipate about 30 10 and 60 of a descending slab s potential energy release if the slab is 100 km thick the lithospheric component is highly dependent on slab thickness it is smaller for thin plates but may be large enough to prevent bending in slabs that can grow thicker than 100 km ubduction zone strength should be more stable than mantle viscosity to changes in mantle temperature so the controlling influence of subduction zones could serve to stabilize plate velocities over time as the earth cools because the details of convergent plate boundaries are so important to the dynamics of plate motion numerical models of mantle flow should treat subduction zones in a realistic way

climate an exceptionally long interglacial ahead today9s comparatively warm climate has been the exception more than the rule during the last 500 000 years or more if recent warm periods or interglacials are a guide then we may soon slip into another glacial period but berger and loutre argue in their perspective that with or without human perturbations the current warm climate may last another 50 000 years the reason is a minimum in the eccentricity of earth9s orbit around the sun

40ar 39ar dating of the brunhes matuyama geomagnetic field reversal magnetostratigraphic studies are widely used in conjunction with the geomagnetic polarity time scale gpts to date events in the range 0 to 5 million years ago a critical tie point on the gpts is the potassium argon age of the most recent brunhes matuyama geomagnetic field reversal astronomical values for the forcing frequencies observed in the oxygen isotope record in ocean drilling project site 677 suggest that the age of this last reversal is 780 ka thousand years ago whereas the potassium argon based estimate is 730 ka results from 4039 ar incremental heating studies on a series of lavas from maui that straddle the brunhes matuyama reversal give an age of 783 11 ka in agreement with the astronomically derived value the astronomically based technique appears to be a viable tool for dating young sedimentary sequences

the role of solid solid phase transitions in mantle convection abstract with changing pressure and temperature conditions downwelling and upwelling crustal and mantle rocks experience several solid solid phase transitions that affect the mineral physical properties owing to structural changes in the crystal lattice and to the absorption or release of latent heat variations in density together with phase boundary deflections related to the non null reaction slope generate important buoyancy forces that add to those induced by thermal perturbations these buoyancy forces are proportional to the density contrast between reactant and product phases their volume fraction the slope and the sharpness of the reaction and affect the style of mantle convection depending on the system composition in a homogeneous pyrolitic mantle there is little tendency for layered convection with slabs that may stagnate in the transition zone because of the positive buoyancy caused by post spinel and post ilmenite reactions and hot plumes that are accelerated by phase transformations in the 600 800 km depth range by adding chemical and mineralogical heterogeneities as on earth phase transitions introduce bulk rock and volatiles filtering effects that generate a compositional gradient throughout the entire mantle with levels that are enriched or depleted in one or more of these components phase transitions often lead to mechanical softening or hardening that can be related to a different intrinsic mechanical behaviour and volatile solubility of the product phases the heating or cooling associated with latent heat and the transient grain size reduction in downwelling cold material strong variations in viscosity would enhance layered mantle convection causing slab stagnation and plume ponding at low temperatures and relatively dry conditions reactions are delayed due to the sluggish kinetics so that non equilibrium phase aggregates can persist metastably beyond the equilibrium phase boundary survival of low density metastable olivine ringwoodite pyroxene and pyrope garnet in the transition zone and uppermost lower mantle produces positive buoyancy forces that decrease the subduction velocity and may lead to slab stagnation in the transition zone the presence of deep metastable portions is still debated and should not be associated a priori with a completely dry slab as field observations suggest that heterogeneously hydrated oceanic plates could contain metastable dry portions surrounded by transformed wet rocks

quaternary glacial interglacial climate cycles in hawaii abstract the upper kilometer of the hawaiian scientific drilling program core consists of lavas that were emplaced subaerially burying paleosols these paleosols were preserved with minimal alteration and are used to construct a 330 kyr quaternary climate record within the temporal resolution of this record there appears to be a 100 kyr climate oscillation between cool dry and warm wet conditions indicating that tropical regions such as hawaii have responded to the same global climate forcings as have higher latitude areas during at least the past three glacial interglacial cycles it is also suggested that hawaiian climate may have become progressively warmer and wetter over the same period

crustal subsidence rate off hawaii determined from 234u 238u ages of drowned coral reefs a series of submerged coral reefs off northwestern hawaii was formed during largely glacial intervals when the rate of local sea level rise was less than the maximum upward growth rate of the reefs mass spectrometric sup 234 u sup 238 u ages for samples from six such reefs range from 17 to 475 ka and indicate that this part of the hawaiian ridge has been subsiding at a roughly uniform rate of 2 6 mm yr for the past 475 ka the sup 234 u sup 238 u ages are in general agreement with model ages of reef drowning based on estimates of paleo sea level stands derived from oxygen isotope ratios of deep sea sediments but there are disagreements in detail the high attainable precision plus minus 10 ka or better on samples younger than approximately 800 ka large applicable age range relative robustness against open system behavior and ease of analysis for this technique hold great promise for future applications of dating of 50 1 000 ka coral

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

pleistocene snowlines and glaciation of the hawaiian islands abstract high volcanoes on two of the southeastern hawaiian islands experienced pleistocene ice cap glaciations drifts of three glaciations on the upper slopes of mauna kea 4206 m are interstratified with lavas during marine isotope stage mis 2 an ice cap 70 5 km2 formed when the snowline fell ca 930 m to an altitude of ca 3785 m drifts of mis 4 and 6 age largely buried by hawaiite lavas record a snowline about 100 m lower holocene lavas bury the upper slopes of mauna loa 4169 m the summit of which likely intersected the snowline during the last glaciation the reconstructed history of snowline variations and glaciation on maui s haleakala 3055 m relies on evidence of the island s growth isostatic subsidence and tilting the snowline may first have intersected haleakala about 800 000 years ago ice caps waxed and waned during the next ca 400 000 years mis 22 12 until subsidence and diminishing eruptive activity brought the summit below the snowline erosional morphology and thick diamictons indicative of subglacial eruptions are consistent with repeated summit glaciations whereas haleakala s glacial history has ended ice caps likely will regenerate on mauna kea ca 60 000 and 100 000 years in the future after which the summit will subside below the glacial age snowline

lower mantle dynamics with the post perovskite phase change radiative thermal conductivity temperature and depth dependent viscosity the new post perovskite phase near the core mantle boundary has important ramifications on lower mantle dynamics we have investigated the dynamical impact arising from the interaction of temperature and depth dependent viscosity with radiative thermal conductivity up to a lateral viscosity contrast of 10 4 on both the ascending and descending flows in the presence of both the endothermic phase change at 670 km depth and an exothermic post perovskite transition at 2650 km depth the phase boundaries are approximated as localized zones we have employed a two dimensional cartesian model using a box with an aspect ratio of 10 within the framework of the extended boussinesq approximation our results for temperature and depth dependent viscosity corroborate the previous results for depth dependent viscosity in that a sufficiently strong radiative thermal conductivity plays an important role for sustaining superplumes in the lower mantle once the post perovskite phase change is brought into play this aspect is especially emphasized when the radiative thermal conductivity is restricted only to the post perovskite phase these results revealed a greater degree of asymmetry is produced in the vertical flow structures of the mantle by the phase transitions mass and heat transfer between the upper and lower mantle will deviate substantially from the traditional whole mantle convection model streamlines revealed that an overall complete communication between the top and lower mantle is difficult to be achieved 2005 elsevier b v all rights reserved

onset of solid state mantle convection and mixing during magma ocean solidification energy sources involved in the early stages of planetary formation can cause partial or even complete melting of the mantle of terrestrial bodies leading to the formation of magma oceans upon planetary cooling solidification is expected to take place from the bottom upwards because of the steeper slope of the liquid adiabat with respect to the liquidus elkins tanton 2012 solomatov 2015 fractional solidification in particular can lead to the formation of a compositional layering that can play a fundamental role for the subsequent long term dynamics and evolution of the interior tosi et al 2013 plesa et al 2014 in order to assess to what extent primordial compositional heterogeneities generated upon magma ocean solidification can be preserved we investigate the cooling and solidification of a whole mantle magma ocean along with the conditions that allow solid state convection to start mixing the mantle before solidification has completed to this end we run 2 d numerical simulations in cylindrical geometry using the finite volume code gaia huttig et al 2013 we treat the liquid magma ocean in a parametrized fashion while we self consistently solve the conservation equations of thermochemical convection in the growing solid mantle accounting for pressure temperature and melt dependent rheology we consider two end member cases fractional crystallization where melt is instantaneously extracted into the overlying liquid leaving beneath a differentiated mantle and batch crystallization where melt remains in contact with the silicate matrix throughout solidification causing no differentiation by testing the effects of different cooling rates and rayleigh numbers we show that for a lifetime of the liquid magma ocean between 1 and 10 myr lebrun et al 2013 the onset of solid state convection prior to complete mantle crystallization is possible and that part or even all of the compositional heterogeneities generated upon fractionation can be erased by efficient mantle stirring figure 1 we discuss the consequences of our findings in relation to the early and long term evolution of compositional heterogeneities generated via fractional crystallization of magma oceans in terrestrial bodies with emphasis on mars thermochemical history

layered convection induced by phase transitions we report a systematic study on the conditions under which an endothermic phase transition can enforce layered convection two dimensional numerical calculations of convection in a domain containing a divariant phase change were performed in the framework of the extended boussinesq approximation i e considering the effects of adiabatic gradient latent heat and frictional heating in the energy equation we find that the critical value of the negative clapeyron slope which must be surpassed in order to induce layered convection decreases in magnitude with increasing rayleigh number ra in the range 104 ra 2 106 near the critical clapeyron slope vacillations between double and single layer convection or strongly leaking double layer convection are possible the breakdown into layers is influenced very little by the latent heat release but depends solely on the phase boundary deflection caused by lateral temperature differences the value of the critical clapeyron slope also seems little affected by the width of the transition zone or by its depth a possible superplastic rheology within the transition zone would tend to favor layered convection scaling the model results to the 670 km discontinuity in the earth s mantle as a possible endothermic phase boundary we estimate the critical clapeyron slope to be in the range of 4 to 8 mpa k 40 to 80 bar k the possibility that the spinel perovskite periclase transition is within this range appears to be remote but certainly cannot be neglected

a community benchmark for 2 d cartesian compressible convection in the earth s mantle benchmark comparisons are an essential tool to verify the accuracy and validity of computational approaches to mantle convection six 2 d cartesian compressible convection codes are compared for steady state constant and temperature dependent viscosity cases as well as time dependent constant viscosity cases in general we find good agreement between all codes when comparing average flow characteristics such as nusselt number and rms velocity at rayleigh numbers near 106 and dissipation numbers between 0 and 2 the results differ by approximately 1 per cent differences in discretization and use of finite volumes versus finite elements dominate the differences there is a small systematic difference between the use of the anelastic liquid approximation ala compared to that of the truncated ala in determining the onset of time dependence there was less agreement between the codes with a spread in the rayleigh number where the first bifurcation occurs ranging from 7 79 10 5 to 1 05 10 6

stretching and mixing of viscous blobs in earth s mantle the stretching and mixing of blobs more viscous than the surrounding mantle is an important issue the subducted lithospheric material at depth might be more viscous than the surrounding mantle and its ability to mix affects its properties as a geochemical reservoir in order to study the effect of the viscosity ratio viscosity of the blob to the viscosity of the surrounding mantle on the deformation we perform three types of two dimensional numerical simulations a pure shear simulation a simulation of steady state convection and a simulation of time dependent convection in a pure shear flow the inverse of the rate of deformation of a viscous blob is to a first approximation a linear function of the ratio ar where ar is the aspect ratio of the blob for a viscous blob in a steady convection cell a periodic deformation is superimposed on the long term deformation the period corresponds to an overturn time along the streamline followed by the blob the strains of this periodic deformation obey the laws found for pure shear in a time dependent flow more representative of the mantle flow we find that the average distance a between two tracers situated within a viscous blob obeys the relationship ln a a0 at 1 2 and that it is independent of the aspect ratio of the blob these two results are well explained by a simple model of successive strains in arbitrary directions the viscosity contrast controls the mixing efficiency and it has an effect much larger than predicted by earlier studies blobs of matter more viscous than the average mantle can therefore persist unmixed in the mantle over earth s history

ages and inferred causes of late pleistocene glaciations on mauna kea hawai i glacial landforms on mauna kea hawai i show that the summit area of the volcano was covered intermittently by ice caps during the late pleistocene cosmogenic 36 cl dating of terminal moraines and other glacial landforms indicates that the last two ice caps called older makanaka and younger makanaka retreated from their maximum positions approximately 23 ka and 13 ka respectively the margins and equilibrium line altitudes of these ice caps on the remote tropical pacific island were nearly identical which would seem to imply the same mechanism for ice growth but modelling of glacier mass balance combined with palaeotemperature proxy data from the subtropical north pacific suggests that the causes of the two glacial expansions may have been different older makanaka air atop mauna kea was likely wetter than today and cold whereas younger makanaka times were slightly warmer but significantly wetter than the previous glaciation the modelled increase in precipitation rates atop mauna kea during the late pleistocene is consistent with that near sea level inferred from pollen data which suggests that the additional precipitation was due to more frequent and or intense tropical storms associated with eastward moving cold fronts these conditions were similar to modern la nina weak enso conditions but persisted for millennia rather than years increased precipitation rates and the resulting steeper temperature lapse rates created glacial conditions atop mauna kea in the absence of sufficient cooling at sea level suggesting that if similar correlations existed elsewhere in the tropics the precipitation dependent lapse rates could reconcile the apparent difference between glacial time cooling of the tropics at low and high altitudes copyright 2008 john wiley sons ltd

three dimensional structures and dynamics in the deep mantle effects of post perovskite phase change and deep mantle layering 1 three dimensional numerical simulations of thermo chemical mantle convection with multiple phase transitions olivine spinel perovskite post perovskite are used to investigate the morphology of compositional and post perovskite ppv boundary structures above the core mantle boundary cmb compositionally dense subducted morb partially segregates above the cmb forming ridge like dense piles morphologically similar to structures in previous spherical or cartesian studies in which a dense layer was inserted a priori an anti correlation is observed between regions where a thick post perovskite layer occurs and regions containing piles of dense material as in our previous two dimensional study lateral variations in the thickness or occurrence of a ppv layer cause very strong seismic shear wave velocity anomalies which may dominate thermal or composition related seismic heterogeneity in the depth range where the variable ppv boundary occurs and also generate sharp sided structures as observed seismologically both compositional and ppv effects may be necessary to simultaneously explain large scale heterogeneity and the global distribution of the discontinuity atop d

persistence of full glacial conditions in the central pacific until 15 000 years ago the magnitude of atmospheric cooling during the last glacial maximum and the timing of the transition into the current interglacial period remain poorly constrained in tropical regions partly because of a lack of suitable climate records glacial moraines provide a method of reconstructing past temperatures but they are relatively rare in the tropics here we present a reconstruction of atmospheric temperatures in the central pacific during the last deglaciation on the basis of cosmogenic 3he ages of moraines and numerical modelling of the ice cap on mauna kea volcano hawaii the only highland in the central pacific on which moraines that formed during the last glacial period are preserved our reconstruction indicates that the last glacial maximum occurred between 19 000 and 16 000 years ago in this region and that temperatures at high elevations were about 7 c lower than today during this interval glacial retreat began about 16 000 years ago but temperatures were still about 6 5 c lower than today until 15 000 years ago when combined with estimates of sea surface temperatures in the central pacific ocean our reconstruction indicates that the lapse rate during the last glacial maximum was higher than at present which is consistent with the proposal that the atmosphere was drier at that time furthermore the persistence of full glacial conditions until 15 000 years ago is consistent with the relatively late and abrupt transition to warmer temperatures in greenland5 indicating that there may have been an atmospheric teleconnection between the central pacific and north atlantic regions during the last deglaciation

field study of dispersion in a heterogeneous aquifer 3 geostatistical analysis of hydraulic conductivity observations of the spatial variability of hydraulic conductivity at a tracer test site located at columbus air force base in mississippi are presented direct measurements of hydraulic conductivity of the heterogeneous alluvial aquifer at the site were made using borehole flowmeter logging slug tests and a laboratory permeameter to test undisturbed soil cores indirect methods estimating hydraulic conductivity were also evaluated including soil grain size analyses surface geophysical surveys and mapping of sediment facies the spatial covariance of the 2187 hydraulic conductivity values obtained with the borehole flowmeter method was examined the log hydraulic conductivity variance ln2k and the horizontal and vertical correlation scales h and v of 4 5 12 8 m and 1 6 m respectively were estimated assuming second order stationarity of the conductivity field the covariance parameters are uncertain with bounding values that are 24 76 above or below the estimate covariance parameters estimated with more limited nonflowmeter data were within the same magnitude as those obtained using the extensive flowmeter data suggesting that data from a variety of methods may be used to provide approximate values of the autocovariance parameters nonstationarity of the ln k field was examined by removing three dimensional polynomial trend surfaces and calculating variograms of the residuals significantly lower estimates for ln2k h and v of 2 7 4 8 m and 0 8 m respectively were obtained from the third order log conductivity residuals after trend removal the bounding parameter values differ 15 44 from the estimated values accounting for unsteady flow and the uncertainty in the covariance parameters of the third order log conductivity residuals the calculated longitudinal and horizontal transverse macrodispersivities ranged from 1 5 m to 1 8 m and 0 3 m to 0 6 m respectively

elastic properties of hydrate bearing sediments using effective medium theory accurate and detailed models of the seismic velocity structure of gas hydrate bearing sediments may be determined by careful analysis of controlled source seismic data however interpretation of these velocities in terms of hydrate saturation of the pore space has hitherto relied on semiempirical formulas and or simple effective medium theory we develop a rigorous theoretical scheme to relate the seismic properties of a clay rich hydrate bearing sediment to its porosity mineralogy microstructural features and hydrate saturation we consider separately the two possible end members for the distribution of hydrate in the pore space 1 hydrates are unconnected and located in the pore voids without appreciable grain contact and 2 connected hydrates are forming cement binding around the grains the scheme is transversely isotropic to allow for anisotropy due to alignment of clay platelets and is based on a combination of a self consistent approximation a differential effective medium theory and a method of smoothing for crystalline aggregates we have applied the scheme to lithological and seismic velocity data from ocean drilling program site 995 on the blake ridge southeastern u s continental margin to make estimates of the hydrate saturation it was found that the hydrates are probably unconnected and their volume concentration varies between approx 0 at 100 m below the seabed and approx 9 at 400 m depth just above the bottom simulating reflector if the clay platelet orientation distribution resembles the function we have used

modelling of heat transfer with the random walk method part 1 application to thermal energy storage in porous aquifers abstract this study examines the application of the random walk method of resolution in the modelling of thermal energy storage in fractured aquifers the media under consideration have a high degree of fracturing but a low porosity the aperture of the fracture is small in relation to its overall extent the customary method of resolution developed to investigate the transport phenomenon in such fractured media is first presented briefly next the stochastic equations of the energy displacement in fractured aquifers are developed depending on the statistical location of the energy particles in the media a stochastic approach is used to determine the flow velocity field the method is applied to different configurations of fracture networks for a single well system of aquifer thermal energy storage the temperature fields corresponding to a fractured aquifer and its equivalent porous configuration are compared an equivalent porous medium is not an adequate substitute for a fractured aquifer in such modelling the effect of the porosity on the energy storage is obvious the temperature of the extracted water and the energy recovery factor increase with the fracture porosity except in a highly anisotropic medium the orientation distribution of the fractures has little effect on the heat transfer in an aquifer without regional flow in the presence of a natural hydraulic gradient the energy recovery factor tends towards zero and the production temperature towards the original ambient temperature of the aquifer in this case a charge and discharge well pair proves to be a suitable alternative to the single well system

should quaternary sea level changes be used to correct glacier elas vegetation belt altitudes and sea level temperatures for inferring climate changes abstract changes in the altitudes of glacier snowlines elas and the altitudes of montane vegetation belts vbas measure quaternary climatic change an accepted correction to such changes by deducting the amount of contemporary sea level fall is wrong since the air displaced by the ice sheets approximately fills the space left by the falling sea level and so there is no overall downward movement of the troposphere this also causes a reduced cooling at the lowered sea level relative to that at the former inter glacial sea level about 1 c at the las glacial maximum which reduces the discrepancies previously noted by others between terrestrial and marine estimates of sea level cooling the change in temperature is indicated by the product of the ela or vba lowering and the environmental lapse rate elr prior estimates of ela 900 135 m and elr 6 0 1 c km 1 would indicate a cooling of 5 4 c at interglacial sea level and 4 4 c at glacial sea level although glacial period elrs are not known reliably established ela corrections for local epeirogenic uplift or subsidence are appropriate

postperovskite phase transition and its geophysical implications 1 the stability of mg fe sio3 perovskite in the deep lower mantle has long been uncertain recently a phase transition from perovskite to postperovskite was discovered through a significant change in the x ray diffraction pattern at high pressure and high temperature conditions corresponding to the core mantle boundary region this phase transition was also confirmed by first principles calculations these suggest that mg fe sio3 postperovskite is the predominant mineral in the lowermost mantle called the d layer and phase transition from perovskite to postperovskite has significant geophysical implications for its nature and dynamics the postperovskite phase may account for the large seismic anomalies observed in the d region such as the d discontinuity s wave anisotropy and anticorrelation between the anomalies in s wave and bulk sound velocities in addition this phase transition is a strongly exothermic reaction it destabilizes the thermal boundary layer at the base of the mantle and should promote the formation of high temperature upwelling plumes

the impact of aquifer heterogeneity on the performance of aquifer thermal energy storage 1 heterogeneity in hydraulic properties of the subsurface is not accounted for in current design calculations of aquifer thermal energy storage ates however the subsurface is heterogeneous and thus affects the heat distribution around ates wells in this paper the influence of heterogeneity on the performance of a doublet well system is quantified using stochastic heat transport modeling the results show that on average thermal recovery decreases with increasing heterogeneity expressed as the lognormal standard deviation of the hydraulic conductivity field around the doublet furthermore heterogeneity at the scale of a doublet ates system introduces an uncertainty in the amount of expected thermal interference between the warm and cold storage this results in an uncertainty in thermal recovery that also increases with heterogeneity and decreases with increasing distance between ates wells the uncertainty in thermal balance due to heterogeneity can reach values near 50 percent points in case of regional groundwater flow in excess of 200 m yr to account for heterogeneity whilst using homogeneous models an attempt was made to express the effect of heterogeneity by an apparent macrodispersivity as expected apparent macrodispersivity increases with increasing heterogeneity however it also depends on well to well distance and regional groundwater velocity again the uncertainty in thermal recovery is reflected in a range in the apparent macrodispersivity values considering the increasing density of ates systems we conclude that thermal interference limits the number of ates systems that can be implemented in a specific area and the uncertainty in the hydraulic conductivity field related to heterogeneity should be accounted for when optimizing well to well distances

dynamical consequences in the lower mantle with the post perovskite phase change and strongly depth dependent thermodynamic and transport properties article i nfo we have carried out numerical simulations of large aspect ratio 2 d mantle convection with the deep phase change from perovskite pv to post perovskite ppv using the extended boussinesq approximation for a fluid with temperature and pressure dependent viscosity we have investigated the effects of various ppv phase parameters on the convective planform heat transport and mean temperature and viscosity profiles since ppv is expected to have a relatively weak rheology with respect to pv and a large thermal conductivity we have assumed that the transition from pv to ppv is accompanied by both a reduction in viscosity by 1 to 2 orders of magnitude and by an increase in thermal conductivity by a factor of 2 furthermore we have analyzed the combined effects of a strongly decreasing thermal expansivity in pv and steeply increasing thermal conductivity according to recent evidence from high pressure experiments and first principle calculations as long as the thermal expansivity and conductivity are constant ppv exerts a small but noticeable effect on mantle convection it destabilizes the d layer causes focusing of the heat flux peaks and an increase of the average mantle temperature and of the temporal and spatial frequency of upwellings when the latest depth dependent thermal expansivity and conductivity models are introduced the effects of ppv are dramatic on the one hand without ppv we obtain a very sluggish convective regime characterized by a relatively cool mantle dominated by large downwellings that tend to stagnate beneath the transition zone with ppv on the other hand we observe an extremely significant increase of the average mantle temperature due to the formation of large sized and vigorous upwellings that in some cases tend to cluster thus forming superplumes if a very large thermal conductivity at the core mantle boundary is assumed k 20 wk 1 m 1 we obtain a quasi steady state regime characterized by large and stable plumes with long lifetimes the combination of strongly depth dependent expansivity and conductivity is a viable mechanism for the formation of long wavelength long lived thermal anomalies in the deep mantle even if a low viscosity ppv atop the core mantle boundary is included

a dimensionless parameter approach to the thermal behavior of an aquifer thermal energy storage system to predict the performance of an aquifer thermal energy storage system an understanding of the system s hydrothermal behavior is needed one possibility is to run a detailed numerical simulation of the system however for a single well system in which fluid flow is limited to steady radial flow a characterization scheme based on a set of four dimensionless parameter groups allows production temperatures and energy recovery factors to be read from graphs the assumption of radial fluid flow is valid when buoyancy flow can be neglected and a well is fully screened in a horizontal aquifer which is confined above and below by impermeable layers criteria for little buoyancy flow include a low permeability or vertically stratified aquifer a small temperature difference between injected and ambient water and short cycle length the basic energy transport equations for the aquifer confining layer system with steady radial fluid flow in the aquifer are nondimensionalized to derive the key parameter groups next a numerical model which calculates the heat transfer in the aquifer and confining layers for an injection storage production cycle is run for a range of values of these groups the calculated production temperatures and energy recovery factors are then presented graphically as a function of the parameter groups comparisons between results of field experiments and recovery factors read from the graphs show good agreement

geochronology and paleoclimatic implications of the last deglaciation of the mauna kea ice cap hawaii we present new 3he surface exposure ages on moraines and bedrock near the summit of mauna kea hawaii which refine the age of the mauna kea ice cap during the local last glacial maximum llgm and identify a subsequent fluctuation of the ice margin the 3he ages when combined with those reported previously indicate that the local ice cap margin began to retreat from its llgm extent at 20 5 2 5 ka in agreement with the age of deglaciation determined from llgm moraines elsewhere in the tropics the ice cap margin receded to a position at least 3 km upslope for 4 5 5 0 kyr before readvancing nearly to its llgm extent the timing of this readvance at 15 4 ka corresponds to a large reduction of the atlantic meridional overturning circulation amoc following heinrich event 1 subsequent ice margin retreat began at 14 6 1 9 ka corresponding to a rapid resumption of the amoc and onset of the bolling warm interval with the ice cap melting rapidly to complete deglaciation additional 3he ages obtained from a flood deposit date the catastrophic outburst of a moraine dammed lake roughly coeval with the younger dryas cold interval suggesting a more active hydrological cycle on mauna kea at this time a coupled mass balance and ice dynamics model is used to constrain the climate required to generate ice caps of llgm and readvance sizes the depression of the llgm equilibrium line altitude requires atmospheric cooling of 4 5 1 c whereas the mass balance modeling indicates an accompanying increase in precipitation of as much as three times that of present we hypothesize 1 that the llgm temperature depression was associated with global cooling 2 that the temperature depression that contributed to the readvance occurred in response to an atmospheric teleconnection to the north atlantic and 3 that the precipitation enhancement associated with both events occurred in response to a southward shift in the position of the inter tropical convergence zone itcz such a shift in the itcz would have allowed midlatitude cyclones to reach mauna kea more frequently which would have increased precipitation at high elevations and caused additional cooling

seismostratigraphy and thermal structure of earth s core mantle boundary region we used three dimensional inverse scattering of core reflected shear waves for large scale high resolution exploration of earth9s deep interior d and detected multiple piecewise continuous interfaces in the lowermost layer d beneath central and north america with thermodynamic properties of phase transitions in mantle silicates we interpret the images and estimate in situ temperatures a widespread wave speed increase at 150 to 300 kilometers above the coremantle boundary is consistent with a transition from perovskite to postperovskite internal d stratification may be due to multiple phase boundary crossings and a deep wave speed reduction may mark the base of a postperovskite lens about 2300 kilometers wide and 250 kilometers thick the core mantle boundary temperature is estimated at 3950 200 kelvin beneath central america a site of deep subduction the d is relatively cold t 700 100 kelvin accounting for a factor of two uncertainty in thermal conductivity core heat flux is 80 to 160 milliwatts per square meter mw m 2 into the coldest d region and 35 to 70 mw m 2 away from it combined with estimates from the central pacific this suggests a global average of 50 to 100 mw m 2 and a total heat loss of 7 5 to 15 terawatts

subsidence and volcanism of the haleakala ridge hawaii abstract side looking sonar gloria mapping has revealed a series of four arcuate bands of high sonic backscatter on the crest of the haleakala ridge a major rift zone ridge extending 135 km east of the island of maui dredge recovery indicates that the shallowest of these bands is a drowned coral reef and the deeper bands are also inferred to be coral reefs the reefs occur above a prominent submarine bench 1500 2500 m deep on the ridge h terrace that marks the shoreline at the end of vigorous shield building of haleakala volcano when lava flows ceased crossing and reworking the shoreline since their growth these reefs have subsided as much as 2200 m and have tilted systematically about 20 m km southward as a result of post reef volcanic loading on the island of hawaii whose center of mass is about directly south of the haleakala ridge the 234u 238u age of the dredged coral is 750 13 ka in reasonable agreement with an age of 850 ka for the underlying h terrace previously estimated from its relationship to other dated reefs to the southwest basalt glass fragments dredged from the haleakala ridge below the h terrace are tholeiitic and contain high sulfur indicative of eruption in water deeper than 200 m basalt glass fragments associated with the reefs above the h terrace are dominantly tholeiitic and contain intermediate sulfur contents indicative of subaqueous eruption in shallow near shore conditions one alkalic glass fragment was recovered above the h terrace these relations indicate that the morphologic end of shield building as recorded by construction of the h terrace was not accompanyed by a change from tholeiitic to alkalic basalt instead tholeiite eruptions continued for some time before the erupted lava became alkalic

implications of post perovskite transport properties for core mantle dynamics abstract recent evidence on perovskite to post perovskite phase change in the lowermost mantle suggests that post perovskite piles or lens should be present in the relatively cold downwelling areas while the roots of the hot upwelling plumes consist of perovskite post perovskite is often believed to be deformed predominantly by the dislocation creep and there are some hints that the activation parameters of the dislocation creep in post perovskite induce lower viscosity than that of perovskite at the same pressure and temperature conditions that can even result in a viscosity paradox in the lowermost mantle viscosity in cold downwellings transformed to post perovskite might be lower than the viscosity of warm perovskite plumes such a viscosity structure was indeed recently suggested by the geodynamical inversions of the geoid rheologically weak areas at the base of the subducted slabs may have important consequences for the slab deformation in the d we investigate the dynamics of the cold slabs transformed to post perovskite in the lowermost mantle by means of the simulations of thermal convection in a 2d cartesian model of the lower mantle with composite rheology including diffusion creep and dislocation creep different creep parameters are used for the perovskite lower mantle and for the post perovskite lens or layer respectively while perovskite is considered to be deformed via linear diffusion creep post perovskite is modeled either as a constant viscosity material with viscosity ranging from 1020 pa s to 1023 pa s or it is deformed purely by the dislocation creep the presence of the rheologically distinct post perovskite not only strongly influences the slab deformation above the core mantle boundary cmb but also results in different dynamic regimes of the cmb region characterised by e g the different length scales of the upwelling plumes depending on the creep parameters of post perovskite further the presence of very low viscosity lens or a layer above the cmb strongly enhances the cmb heat flux in the cold slab areas according to the amount of post perovskite present in the d and the rheology of post perovskite the heat flux across the cmb can vary considerably with time which may have important implications for the core mantle coupling and the character of the earth s geomagnetic field

weakening of calcium iridate during its transformation from perovskite to post perovskite magnesium silicate perovskite the dominant mineral in the lower mantle is thought to transform into a post perovskite phase in the mantle s lowermost region laboratory experiments suggest substantial weakening could occur during the transformation from perovskite to post perovskite which could explain the anomalous physical properties of the lowermost mantle

grain size variations in the earth s mantle and the evolution of primordial chemical heterogeneities 1 chemical heterogeneities with relatively high viscosity are known to be poorly mixed by mantle convection one of the factors which can cause viscosity variations is the grain size analysis of various physical processes in the earth s mantle suggests that variation in the grain size can be extremely large even outside of subducting slabs the largest grains are formed in the early molten earth where ostwald ripening is controlled by liquid state diffusion the smallest grains are formed due to recrystallization by the spinel perovskite phase transformation in downwelling flow and subsequent ostwald ripening the viscosity contrast between primordial large grain size material and recrystallized material is likely to be many orders of magnitude preliminary numerical simulations show that strongly time dependent mantle convection can process primordial large grain size heterogeneities through the spinel perovskite phase boundary only after a few overturns this reduces the viscosity contrasts and leads to rapid mixing by mantle convection a more steady flow in the lower mantle may lead to the formation of stagnant poorly mixed regions which may never have had a chance to cross the 660 km discontinuity and be recrystallized by the spinel perovskite phase transformation heterogeneities can also avoid grain size reduction and mixing if their density is slightly larger than the surrounding mantle in this case they accumulate at the core mantle boundary

radiative conductivity and abundance of post perovskite in the lowermost mantle abstract thermal conductivity of the lowermost mantle governs the heat flow out of the core energizing planetary scale geological processes yet there are no direct experimental measurements of thermal conductivity at relevant pressure temperature conditions of earth s core mantle boundary here we determine the radiative conductivity of post perovskite at near core mantle boundary conditions by optical absorption measurements in a laser heated diamond anvil cell our results show that the radiative conductivity of mg0 9fe0 1sio3 post perovskite 1 1 w m k is almost two times smaller than that of bridgmanite 2 0 w m k at the base of the mantle by combining this result with the present day core mantle heat flow and available estimations on the lattice thermal conductivity we conclude that post perovskite is at least as abundant as bridgmanite in the lowermost mantle which has profound implications for the dynamics of the deep earth

effects of low viscosity post perovskite on the stability and structure of primordial reservoirs in the lower mantle we performed numerical experiments of thermochemical convection in 3 d spherical geometry to investigate the effects of a low viscosity of post perovskite ppv on the stability and structure of primordial reservoirs of dense material in the lower mantle of the earth our results show that weak ppv 1000 viscosity reduction in regions containing ppv strongly increases the core mantle boundary cmb heat flux the volume averaged mantle temperature with weak ppv is slightly higher than that with regular ppv except in the lowermost mantle this is because weak ppv weakens the base of the cold downwellings allowing cold slabs to spread more easily and broadly along the cmb the stability and size of the dense reservoirs is not substantially altered by weak ppv in the weak ppv case slabs spreading along the cmb slightly decreases the stability of dense reservoirs i e the amount of dense material entrained upward is slightly larger than in the regular ppv case i e viscosity of ppv identical to that of perovskite furthermore the topography and steepness of these reservoirs slightly increase however as in the regular ppv case the dense reservoirs are maintained over periods of time comparable to the age of the earth

regular vs chaotic mantle mixing abstract most quantitative models of mantle mixing have been based on simulations of tracer advection by 2 d flows the present work shows that the mixing properties of 3 d time independent flows cannot be understood or extrapolated from previous 2 d models steady convective flows appropriate to simulate a uniform fluid with large viscosity are restricted to poloidal components they seem to have regular streamlines however the existence of plates on the earth s surface imposes the existence of a strong toroidal field flows where both poloidal and toroidal components are present can yield chaotic pathlines which are very efficient in mixing the mantle within areas of turbulent mixing where the stretching increases exponentially with time regular islands of laminar stretching persist in which unmixed material can survive our findings indicate that the intrinsic three dimensionality of convection coupled with plates as much as its time dependence must be included in numerical models to understand the mixing properties of the mantle as the viscosity is significantly larger in the lower mantle than in the upper mantle the toroidal component of the flow is confined to the upper mantle where a more thorough mixing should take place

development of in aquifer heat testing for high resolution subsurface thermal storage capability characterisation the ongoing transition from fossil fuels to alternative energy source provision has resulted in increased geothermal uses as well as storage of the shallow subsurface existing approaches for exploration of shallow subsurface geothermal energy storage often lack the ability to provide information concerning the spatial variability of thermal storage parameters however parameter distributions have to be known to ensure that sustainable geothermal use of the shallow subsurface can take place especially when it is subject to intensive usage in this paper we test a temperature decay time approach to obtain in situ direct qualitative spatial high resolution information about the distribution of thermal storage capabilities of the shallow subsurface to achieve this temperature data from a high resolution fibre optic distributed temperature sensing device as well as data from conventional pt100 temperature sensors were collected during a heat injection test the latter test was used to measure the decay time of temperature signal dissipation of the subsurface signal generation was provided by in aquifer heating with a temperature self regulating electric heating cable heating was carried out for 4 5 days after this a cooling period of 1 5 weeks was observed temperature dissipation data was also compared to direct push derived high resolution hydro geological data the results show that besides hydraulic properties also the bedding and compaction state of the sediment have an impact on the thermal storage capability of the saturated subsurface the temperature decay time approach is therefore a reliable method for obtaining information regarding the qualitative heat storage capability of heterogeneous aquifers for the use with closed loop system geothermal storage systems furthermore this approach is advantageous over other commonly used methods e g soil sampling and laboratory analysis as even small changes in hydro geological properties lead to strong variances in observed heat storage capabilities at the investigated case study site by using fibre optic thermometers nearly every requested spatial resolution can be achieved and easily be adjusted to the needs of actual test sites for shallow geothermal storage exploration

sensible energy storage in aquifers 2 field experiments and comparison with theoretical results ten successive in situ experimental investigations of hot water storage by a single well and a pair of wells doublet were conducted in 1976 1977 at bonnaud jura in a confined aquifer 2 5 m thick the injected volumes ranged from 500 1700 m3 temperature profiles were measured daily in 12 boreholes distributed along two perpendicular axes within 13 m of the injection well individual temperatures were measured by ten thermistors placed in the caprock the results are discussed and used to calibrate two mathematical models an axisymmetric model allows the calibration of average values of the parameters while a three dimensional model is used to determine their spatial variation in the horizontal plane the latter model leads to the identification of a nonhomogeneous transmissibility field which fully accounts for both hydraulic and thermal contour curves the models which were matched against particular experiments proved accurate when simulating other periods evidence is given of the importance to the recovery ratio of thermal dispersion in the aquifer and of the water content of the caprock in a final section experimental results of single well storage at bonnaud campuget and auburn are compared with general type curves derived in the companion paper they prove to yield adequate predictions of water temperature during the production phases