a geodynamic model of mantle density heterogeneity using cenozoic and mesozoic plate motion reconstructions we derive a model of present day mantle density heterogeneity under the assumption that subducted slabs sink vertically into the mantle the thermal buoyancy of these slabs is estimated from the observed thermal subsidence cooling of oceanic lithosphere slab velocities in the upper mantle are computed from the local convergence rate we assume that slabs cross the upper lower mantle interface and continue sinking into the lower mantle with a reduced velocity for a velocity reduction factor between 2 and 5 our slab heterogeneity model is as correlated with current tomographic models as these models are correlated with each other we have also computed a synthetic geoid from our density model for a viscosity increase of about a factor of 40 from the upper to lower mantle our model predicts the first 8 spherical harmonic degrees of the geoid with statistical confidence larger than 95 and explains 84 of the observed geoid assuming that the model c21 and s21 terms are absent due to a long relaxation time for earth s rotational bulge otherwise 73 of the geoid variance is explained the viscosity increase is consistent with our velocity reduction factor for slabs entering the lower mantle since downwelling velocities are expected to scale roughly as the logarithm of viscosity loge 40 3 7 these results show that the history of plate tectonics can explain the main features of the present day structure of the mantle the dynamic topography induced by this heterogeneity structure consists mainly of about 1 km amplitude lows concentrated along the active continental margins of the pacific basin our model can also be used to predict the time variation of mantle heterogeneity and the gravity field we find that the age of the geoid defined as the time in the past before which the geoid becomes uncorrelated with the present geoid is about 50 m y our model for the history of the degree 2 geoid which is equivalent to the history of the inertia tensor should give us a tool to study the variations in earth s rotation pole indicated in paleomagiietic studies

toward a boot strap hypothesis of plate tectonics feedbacks between plates the asthenosphere and the wavelength of mantle convection abstract the solid earth system is characterized by plate tectonics a low viscosity zone beneath plates the asthenosphere and long wavelength flow in the convecting mantle we use suites of numerical experiments to show 1 how long wavelength flow and the operation of plate tectonics can generate and maintain an asthenosphere and 2 how an asthenosphere can maintain long wavelength flow and plate tectonics plate subduction generates a sub adiabatic temperature gradient in the mantle which together with temperature dependent viscosity leads to a viscosity increase from the upper to the lower mantle this allows mantle flow to channelize in a low viscosity region beneath plates an asthenosphere forms dynamically flow channelization in turn stabilizes long wavelength convection the degree of dynamic viscosity variations from the upper to the lower mantle increases with the wavelength of convection and drops toward zero if the system transitions from plate tectonics to a single plate planet the plate margin strength needed to initiate that transition increases for long wavelength cells long wavelength flow allows plate tectonics to exist over a wider range of plate margin strength the coupled feedbacks allow for a linked causality between plates the asthenosphere and the wavelength of mantle flow with none being more fundamental than the others and the existence of each depending on the others under this hypothesis the asthenosphere is defined by an active process plate tectonics which maintains it and is maintained by it and plate tectonics is part of an emergent self sustaining flow system that bootstraps itself into existence

is a pyrolitic adiabatic mantle compatible with seismic data in this paper the simplest average physical model of a mantle convecting as a whole i e following an adiabatic temperature gradient with a single composition pyrolite with phase transitions is tested directly against global seismic data instead of against spherically symmetric seismic models constraints from seismic data on average velocities and lower mantle velocity gradients are hard to reconcile with an adiabatic pyrolitic mantle given the current state of knowledge of elastic and anelastic mineral parameters at high pressure and temperature this physical model generally gives a a stronger baseline offset between upper and lower mantle average travel time residuals than allowed by the data and b an insufficient decrease in velocity with depth in the lower mantle above 2500 km we tested 105 upper and 105 lower mantle models that were selected randomly within the mineral parameter uncertainties only 2 lower mantle models and 24 upper mantle models yield whole mantle seismic structures that are compatible with global isc p and s travel times and central frequencies of toroidal and spheroidal fundamental modes with angular order higher than 18 to improve the fit to the seismic data the physical model would require a a lower velocity transition zone composition than dry pyrolite at least around continents and subduction zones as well as b a gradual change in physical state of the lower mantle that decreases the velocity depth gradient e g a superadiabatic temperature gradient

true polar wander in mantle convection models with multiple mobile continents a b s t r a c t a r t i c l e i n f o the geologic record supports numerous instances during which continents apparently moved at speeds signi cantly faster than any of today s tectonic plates while the time dependence of convective driving forces likely explains some such observations rapid motions of large continents in particular are often attributed to true polar wander tpw in order to gauge the potential for connections between continents mantle temperature anomalies and polar motion we present the rst calculations of tpw derived from models that couple mantle convection with multiple mobile continents we nd that the aggregation and dispersal of supercontinents can lead to two types of tpw driven either by a well developed hot upwelling axis that creates a stable maximum moment of inertia or by the homogenization of mantle thermal structure following continent dispersal that leads to destabilization of the principal axis and possible large magnitude polar wander these supercontinent modulated thermal heterogeneities drive model tpw events as large as 90 at rates of up to 2 5 ma 1 such magnitudes and speeds are greater than those attained in similar models lacking continents but comparable to those for episodes inferred from paleomagnetic data for some large continents in the past published by elsevier b v on behalf of international association for gondwana research

mapping spherical seismic into physical structure biases from 3 d phase transition and thermal boundary layer heterogeneity summary earth s mantle is to a very good first approximation spherically symmetric with lateral deviations in seismic velocities and density of only a few per cent this observation has led to the common assumption that average radial seismic models reflect the mantle s average physical structure we test this assumption by using a set of dynamically generated mantle structures and comparing seismic velocities for the average radial physical state with laterally averaged seismic velocities the thermal and thermochemical dynamic circulation models are earth like in terms of convective vigour thermal structure and geographical pattern of heterogeneity we find that in general averaged seismic structure is not distinguishable from the seismic structure of the physical average within the uncertainty bounds of seismic reference models an exception is near phase boundaries where phase boundary topography broadens the averaged seismic jump relative to the discontinuity at physical reference conditions in an inversion for 1 d seismic structure where narrow discontinuities are imposed these biases may map into a lower jump and substantially stronger velocity gradients above and below the interface than are actually present other small biases in averaged structure occur in thermal boundary layers including those that form above chemical piles these biases are caused by large lateral variations in temperature not compositional variability

constraints on lower mantle composition from molecular dynamics simulations of mgsio3 perovskite abstract we have carried out molecular dynamics simulations of mgsio 3 perovskite pv in order to determine its equation of state and elastic parameters under pressure and temperature conditions of the earth s lower mantle combining this information with density and elastic constants for mg fe o magnesiowustite mw and including the effects of iron on the density of perovskite we investigated possible compositional models for the lower mantle by calculating seismic velocities and densities as functions of depth and comparing them to the globally averaged seismological models ak135 f and prem the calculations were done along several possible geothermal gradients both adiabatic and non adiabatic and for a range of mg fe partitioning coeffcients k fe mg pv mw 0 10 0 35 our results indicate that the most probable compositional models for the lower mantle are pyrolitic with x mg 0 87 and x pv 0 54 for increasing temperatures at the top of the lower mantle the best fitting models increase slightly in both iron and silica content

non adiabaticity in mantle convection seismic observations indicate that earth s lower mantle is homogeneous as revealed by smooth depth variations of the bulk sound velocity and bullen s inhomogeneity parameter being close to one here we show with 3d spherical convection simulations that it should also be non adiabatic because a significant proportion of mantle heat sources is internal the computer simulations predict non adiabaticity of 100 300 degrees for the lower mantle geotherm with 1 01 implying that the temperature drop across the core mantle boundary exceeds 1000 degrees

solidus and liquidus profiles of chondritic mantle implication for melting of the earth across its history abstract we investigated the melting properties of a synthetic chondritic primitive mantle up to core mantle boundary cmb pressures using laser heated diamond anvil cell melting criteria are essentially based on the use of x rays provided by synchrotron radiation we report a solidus melting curve lower than previously determined using optical methods the liquidus curve is found between 300 and 600 k higher than the solidus over the entire lower mantle at cmb pressures 135 gpa the chondritic mantle solidus and liquidus reach 4150 150 k and 4725 150 k respectively we discuss that the lower mantle is unlikely to melt in the d layer except if the highest estimate of the temperature profile at the base of the mantle which is associated with a very hot core is confirmed therefore recent suggestions of partial melting in the lowermost mantle based on seismic observations of ultra low velocity zones indicate either 1 a outer core exceeding 4150 k at the cmb or 2 the presence of chemical heterogeneities with high concentration of fusible elements our observations of a high liquidus temperature as well as a large gap between solidus and liquidus temperatures have important implications for the properties of the magma ocean during accretion not only complete melting of the lower mantle would require excessively high temperatures but also below liquidus temperatures partial melting should take place over a much larger depth interval than previously thought in addition magma adiabats suggest very high surface temperatures in case of a magma ocean that would extend to more than 40 gpa as suggested by siderophile metal silicate partitioning data such high surface temperature regime where thermal blanketing is inefficient points out to a transient character of the magma ocean with a very fast cooling rate

is the mantle geotherm subadiabatic internal heating and secular cooling are expected to decrease the geothermal gradient away from an adiabat a scaling analysis that is quantified on the basis of published numerical models indicates that the interior geotherm should be nearly isothermal through the lower mantle if all heating is from within for the more realistic condition that the mantle is partly heated from within and partly from below we still expect the average thermal gradient to be significantly subadiabatic through much of the interior of the mantle values of the seismologically observable inhomogeneity parameter 1 04 to 1 07 should characterize the subadiabatic regions of the lower mantle

a mineralogical model for density and elasticity of the earth s mantle 1 we present a thermodynamic model of high pressure mineralogy that allows the evaluation of phase stability and physical properties for the earth s mantle the thermodynamic model is built from previous assessments and experiments in the five component cfmas system cao feo mgo al2o3 sio2 including mineral phases that occur close to typical chemical models of the mantle and reasonable mantle temperatures in this system we have performed a system gibbs free energy minimization including pure end member phases and a nonideal formulation for solid solutions solid solutions were subdivided into discrete pseudocompounds and treated as stoichiometric phases during computation of chemical equilibrium by the simplex method we have complemented the thermodynamic model with a model of shear wave properties to obtain a full description of aggregate elastic properties density bulk and shear moduli that provide a useful basis for the consideration of seismic and geodynamic models of the earth s mantle the thermodynamic model described here is made available for research and training purposes through a web interface http www earthmodel org we examine its validity in light of experiments from mineral physics and briefly discuss inferences for mantle structure

profiles of the bullen parameter from mantle convection modelling the state of adiabaticity in the mantle can be assessed by using the bullen parameter profile derived from seismology we have employed the extended boussinesq convection models in a cartesian 2 d domain to extract the bullen parameter as a function of depth in both base heated and internally heated configurations and for both constant and variable thermal conductivity we also studied models with depth dependent thermal expansivity our results show that the values of the bullen parameter for a rayleigh number of 10 6 lie close to one with sometimes excursions out to 0 9 and 1 1 they are sensitive to the mode of heating and the depth dependences of the thermal expansivity and changes of thermal conductivity we obtained a subadiabatic geotherm above the lower boundary layer in all the models with constant thermal expansivity but a decrease of thermal expansivity with depth can result in a subadiabatic geotherm below the upper boundary layer thus the profiles of the bullen parameter have a definite potential of being useful in constraining the physical parameters and flow structures associated with mantle convection fl 2000 elsevier science b v all rights reserved

stability of the rotation axis in high resolution mantle circulation models weak polar wander despite strong core heating 1 growing evidence points to a substantial heat flow across the core mantle boundary cmb but the rotational stability of strongly bottom heated mantle flow with prominent upwelling plumes is poorly known here we calculate polar motion for the past 100 myr induced in a new class of isochemical high resolution mantle circulation models mcms with earth like convective vigor and up to 12 tw core heat flux our mcms include internal heating and a simple three layer viscosity profile associated with the lithosphere 1023 pa s and the upper 1021 pa s and the lower mantle 1023 pa s separated at 100 and 650 km depth respectively a published mantle mineralogy model in the pyrolite composition consistent with our assumption of whole mantle flow allows us to relate thermal to density variations in a thermodynamically self consistent way all models yield modest polar motion on the order of 0 5 myr 1 or less in accordance with paleomagnetic data and agreeing with a number of studies that demonstrate the stabilizing effect of the rotational bulge although a substantially reduced lower mantle viscosity would increase this rate the good agreement between mcm and seismic mantle heterogeneity lends independent support for our viscosity profile as otherwise slabs in the mcm would rapidly sink to depth levels where they are tomographically not observed in general there is good agreement between the long wavelength geoids predicted from our mcms and recent satellite derived models of earth s geoid correlation coefficient of around 0 4 but noticeable differences at intermediate wavelengths for example in the western pacific and in africa suggest the use of gravity data to distinguish between competing plate reconstruction models

estimates of heat flow in the deep mantle based on the power requirements for the geodynamo 1 regeneration of the magnetic field by convection in the core places demands on heat flow into the base of the mantle if the heat flow is too low thermal convection is shut off and the rate of generation of compositional buoyancy by the solidification of the core becomes too low to sustain the geodynamo conversely a large heat flow causes rapid growth of the inner core so that convection prior to the appearance of the inner core must be sustained by thermal buoyancy alone the attendant requirements on primordial heat become more severe as the age of the inner core decreases we show that estimates of the present day heat flow satisfy the power requirements for the geodynamo however the resulting thermal history is incompatible with estimates of mantle temperatures prior to 3 ga this discrepancy can be resolved by accumulating radioactive isotopes in d or adding heat sources to the core

the deep earth may not be cooling down abstract the earth is a thermal engine generating the fundamental processes of geomagnetic field plate tectonics and volcanism large amounts of heat are permanently lost at the surface yielding the classic view of the deep earth continuously cooling down contrary to this conventional depiction we propose that the temperature profile in the deep earth has remained almost constant for the last 4 3 billion years the core mantle boundary cmb has reached a temperature of 4400 k in probably less than 1 million years after the moon forming impact regardless the initial core temperature this temperature corresponds to an abrupt increase in mantle viscosity atop the cmb when 60 of partial crystallization was achieved accompanied with a major decrease in heat flow at the cmb then the deep earth underwent a very slow cooling until it reached 4100 k today this temperature at or just below the mantle solidus is suggested by seismological evidence of ultra low velocity zones in the d layer such a steady thermal state of the cmb temperature excludes thermal buoyancy from being the predominant mechanism to power the geodynamo over geological time an alternative mechanism to sustain the geodynamo is mechanical forcing by tidal distortion and planetary precession motions in the outer core are generated by the conversion of gravitational and rotational energies of the earth moon sun system mechanical forcing remains efficient to drive the geodynamo even for a sub adiabatic temperature gradient in the outer core our thermal model of the deep earth is compatible with an average cmb heat flow of 3 0 to 4 7 tw furthermore the regime of core instabilities and or secular changes in the astronomical forces could have supplied the lowermost mantle with a heat source of variable intensity through geological time episodic release of large amounts of heat could have remelted the lowermost mantle thereby inducing the dramatic volcanic events that occurred during the earth s history in this scenario because the moon is a necessary ingredient to sustain the magnetic field the habitability on earth appears to require the existence of a large satellite

turbulent 3 d thermal convection in an infinite prandtl number volumetrically heated fluid implications for mantle dynamics summary the structure and time dependence of 3 d thermal convection in a volumetrically heated infinite prandtl number fluid is examined for high values of the rayleigh number the methods employed allow the numerical experiments to proceed for long enough times to derive good estimates of mean and fluctuating parts of the structure an iterative multirigid method to solve for the buoyant incompressible viscous flow at each time step of the energy equation is a novel aspect of the methodology a simple explicit time step of the energy equation is utilized that vectorizes well on serial computers and which is ideally suited to massively parallel computers numerical experiments were carried out for rayleigh numbers from 3 106 to 3 107 in a cartesian region with a prescribed temperature at the top boundary and an adiabatic bottom boundary over this complete range of rayleigh number the flow structure consists dominantly of cold nearly axisymmetric plumes that migrate horizontally sweeping off the cold thermal boundary layer that forms at the top of the convecting fluid plumes disappear by coalescing with other plumes new plumes are created by thermal boundary layer instability sheet plumes form only occasionally and do not penetrate to significant depths in the fluid plumes have sizes comparable to the thickness of the thermal boundary layer and an average spacing comparable to the fluid depth no persistent large scale motion in the fluid can be identified its absence may reflect the large subadiabatic stratification that develops beneath the thermal boundary layer as cold plumes penetrate to the bottom boundary without thermally equilibrating with surrounding fluid we consider the possible implications for convection in planetary mantles and for the existence of plate tectonics

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

synthesis of beryllian sapphirine in the system mgo beo al2o3 sio2 h2o and comparison with naturally occurring beryllian sapphirine and khmaralite part 1 experiments tem and xrd beryllian sapphirine mg 4 x al 4 x a1 4 x 2 y be y si 2 x y o 1 8 o 2 has been synthesized from starting compositions with y 1 at x 0 and y 0 5 at x 0 5 p 0 1 1 3 gpa t 700 1350 c electron diffraction shows the sapphirines are dominantly the 1a polytype but lamellae of a 2m phase are consistently present this is the first 2m sapphirine synthesized in the laboratory and the first known to be devoid of fe 2 no superstructure reflections corresponding to the doubled tetrahedral chain repeat of khmaralite were observed probably due to insufficient annealing time cell parameters of the synthetic sapphirine decreased strongly and linearly with be content 2 7 vol decrease from y 0 to y 1 in agreement with crystal chemical considerations experiments with starting compositions of y 1 0 resulted in additional crystalline phases either coexisting with the limiting sapphirine y 1 or without it at 900 c 1 3 2 0 gpa the saturating assemblage is surinamite chrysoberyl forsterite which is chemically equivalent to sapphirine with y 1 5 the current lack of natural khmaralite with be 0 78 cations per formula unit pfu is likely due to the bulk composition of the host rocks being too rich in sio 2 and al 2 o 3 for forsterite to be stable addition of beo to the mgo al 2 o 3 sio 2 system evidently enlarges the stability field of sapphirine forsterite relative to its restricted range in the beo free system

melting temperature of the earth s mantle and core earth s thermal structure abstract although the temperature at the top of the lower mantle is well constrained by phase equilibrium data for the transformation of transition zone minerals to the denser perovskite polymorphs the temperature distribution in the lower mantle is poorly known models depend strongly on the assumptions of the amount of internal heating and the viscosity profile new melting data on iron to pressures of the outer core 2 mbar and the observed strong decrease of eutectic melting depression in the fe feo fes system with increasing pressure however tightly constrain the temperature at the inner core boundary to slightly less than 5000 k this estimate can be reconciled with all recent static melting measurements on iron and lays within the uncertainty of shock temperature measurements the resulting temperature at the core mantle boundary of about 4000 k then requires a large temperature gradient at the bottom of the lower mantle of about 1500 k recent findings of the very high melting temperatures o

rapid south atlantic spreading changes and coeval vertical motion in surrounding continents evidence for temporal changes of pressure driven upper mantle flow the south atlantic region displays 1 a topographic gradient across the basin with africa elevated relative to south america 2 a bimodal spreading history with fast spreading rates in late cretaceous and eo oligocene and 3 episodic regional uplift events in the adjacent continents concentrated in late cretaceous and oligocene here we show that these observations can be linked by dynamic processes within earth s mantle through temporal changes in asthenosphere flow beneath the region the topographic gradient implies westward pressure driven mantle flow beneath the basin while the rapid spreading rate changes on order 10 million years require significant decoupling of regional plate motion from the large scale mantle buoyancy distribution through a mechanically weak asthenosphere andean topographic growth in late miocene can explain the most recent south atlantic spreading velocity reduction arising from increased plate boundary forcing associated with the newly elevated topography but this mechanism is unlikely to explain the late cretaceous tertiary spreading variations as changes in andean paleoelevation at the time are small we propose an unsteady pressure driven flow component in the asthenosphere beneath the south atlantic region to explain the late cretaceous tertiary spreading rate variations temporal changes in mantle flow due to temporal changes in regional mantle pressure gradients imply a correlation of horizontal and vertical motions we find that this prediction from our models agrees with geologic and geophysical observations of the south atlantic region including episodes of passive margin uplift regional basin reactivation and magmatic activity

joint seismic geodynamic and mineral physical constraints on three dimensional mantle heterogeneity implications for the relative importance of thermal versus compositional heterogeneity summary the joint interpretation of seismic and geodynamic data requires mineral physical parameters linking seismic velocity to density perturbations in the earth s mantle the most common approach is to link velocity and density through relative scaling or conversion factors r s dln dlnv s however the range of possible r s values remains large even when only considering thermal effects we directly test the validity of several proposed depthdependent conversion profiles developed from mineral physics studies for thermally varying properties of mantle materials the tests are conducted by simultaneously inverting shear wave traveltime data and a diverse suite of convection related constraints interpreted with viscous flow response functions of the mantle these geodynamic constraints are represented by surface spherical harmonic basis functions up to harmonic degree 16 and they consist of the global free air gravity field tectonic plate divergences dynamic surface topography and the excess ellipticity of the core mantle boundary cmb the tests yield an optimum 1 d thermal r s profile that is generally compatible with all considered data with the exception of the dynamic surface topography that is most sensitive to the shallow upper mantle this result is not surprising given that cratonic roots are known to be compositionally distinct from the surrounding ambient mantle moreover it is expected that the temperature dependence of the thermal r s in the upper mantle is significant due to the temperature dependence of seismic attenuation or q therefore a simple 1 d density velocity relationship is insufficient to address this problem we obtained independent estimates of the first order correction factors to the selected r s profile within the cratonic roots and in the ambient thermal upper mantle these correction factors defined as r s lnv s are highly negative within the cratons signifying considerable compositional buoyancy this result confirms that the negative buoyancy associated with the low temperatures in the cratons is significantly counteracted by the composition induced positive buoyancy resulting in near neutral buoyancy of the cratonic roots within the ambient upper mantle the correction factors are found to be positive which is consistent with the expected behaviour of the r s relationship in thermally varying upper mantle material we obtain a significantly greater reconciliation of the global gravity anomalies and dynamic surface topography when applying these laterally varying corrections compared to a simple 1 d r s relationship inversion for a fully 3 d r s relationship reveals secondary effects including additional compositional variation within the cratonic roots and the deep mantle superplume structures we estimate the relative magnitude of the thermal and compositional non thermal contributions to mantle density anomalies and conclude that thermal effects dominate shear wave and density heterogeneity throughout the non cratonic mantle we also demonstrate the potential pitfalls of scaling a purely seismically derived model to obtain density rather than performing a true joint inversion to obtain velocity and density simultaneously

are mantle plumes adiabatic abstract the issue concerning the state of adiabaticity of mantle plumes has been examined in a cartesian two dimensional box with an aspect ratio of six we have investigated in the quasi steady state regime high rayleigh number convection with both depth dependent viscosity and thermal expansivity for both the boussinesq and the extended boussinesq approximations we have also assessed the influence of various forms of thermal conductivity and internal heating we have generalized the classical bullen s parameter equation from one dimension to multidimensions for assessing the local state of adiabaticity inside plumes and in their surroundings we have extracted from the local geotherms and the local thermodynamic properties the corresponding bullen s parameter profiles and the two dimensional maps portraying the state of adiabaticity in the mantle histograms characterizing the frequency of adiabaticity are also employed for quantification purposes in general superadiabatic thermal gradients are found inside the thick plume limbs and sometimes along the central part of the plume the centers of plume heads are subadiabatic or nearly adiabatic but the edges of the plume heads are strongly subadiabatic alternating strips of subadiabaticity and adiabaticity are found in the downwellings the ambient mantle outside the plumes is generally adiabatic and is sometimes perforated with islands of marked deviations from adiabaticity

a biological origin for climate signals in corals trace element vital effects are ubiquitous in scleractinian coral skeletons 1 laser ablation icp ms was used to analyze mg sr and u at fine hundreds of microns and seasonal spatial scales in the reef coral porites and the non photosynthetic deep sea corals lophelia oculina and desmophyllum tropical corals display strong seasonal correlations between mg sr and u even when normal cycles are perturbed by unknown factors an inverse relationship between mg and u is a universal feature of all the corals but is much larger in deep corals despite stable environmental conditions this correlation originates from two aragonitic skeletal types mg rich opaque centers of calcification and u rich large translucent crystals the mg rich material probably precipitates rapidly and corresponds to materials strongly deficient in 18o and 13c compared to isotopic equilibrium combined these observations imply that varying proportions of the two skeletal types may account for most of the temperature or climate signal in tropical corals as well as anomalous vital effects