salinity driven thermocline transients in a wind and thermohaline forced isopycnic coordinate model of the north atlantic abstract an isopycnic coordinate oceanic circulation model formulated with the aim of simulating thermodynamically and mechanically driven flow in realistic basins is presented special emphasis is placed on the handling of diabatic surface processes and on thermocline ventilation the model performance is illustrated by a 30 year spinup run with coarse horizontal resolution 2 mesh in a domain with north atlantic topography extending from 10 to 60 n latitude the vertical structure encompasses 10 isopycnic layers in steps of 0 2 units capped by a thermodynamically active mixed layer from an initially isohaline state with isopycnals prescribed by zonally averaged climatology the model is forced by seasonally varying wind stress radiative and freshwater fluxes and by a thermal relaxation process at the surface after a mechanical spinup time of about 15 years a quasi stationary pattern of mean circulation and annual variability ensues characterized by pronounced subtropical mode water formation

elasticity and lattice dynamics of enstatite at high pressure the behavior of synthetic powdered 57 fe enriched enstatite mg 0 980 fe 0 020 5 mg 0 760 fe 0 240 si 2o 6 has been explored by x ray diffraction xrd and nuclear resonant inelastic x ray scattering nrixs the pbca structured enstatite sample was compressed in fine pressure increments for our independent xrd measurements one structural transition between 10 1 and 12 2 gpa has been identified from the xrd data the xrd reflections observed for the high pressure phase are best matched with space group p2 1 c we combine density functional theory with mossbauer spectroscopy and nrixs to understand the local site symmetry of the fe atoms in our sample a third order birch murnaghan bm3 equation of state fitting gives k t0 103 5 gpa and k t0 13 2 for the pbca phase at 12 gpa a bm3 fitting gives k t12 220 10 gpa with k t12 8 4 for the p2 1 c phase nrixs measurements were performed with in situ xrd up to 17 gpa the partial phonon density of states dos was derived from the raw nrixs data and from the low energy region of the dos the debye sound velocity was determined we use the equation of state determined from xrd and debye sound velocity to compute the isotropic compressional v p and shear v s wave velocities of enstatite at different pressures our results help constrain the high pressure properties of pbca structured enstatite in the earth s upper mantle we find that candidate upper mantle phase assemblages containing pbca structured enstatite are associated with shear velocity gradients that are higher than the average earth model prem but lower than regional studies down to about 250 km depth

does stommel s mixed layer demon work abstract stommel argued that the seasonal cycle leads to a bias in the coupling between the surface mixed layer and the main thermocline of the ocean he suggested that a demon operated that effectively only allowed fluid at the end of winter to pass from the mixed layer into the main thermocline in this study stommel s hypothesis is examined using diagnostics from a time dependent coupled mixed layer primitive equation model of the north atlantic cme the influence of the seasonal cycle on the properties of the main thermocline is investigated using two methods in the first the rate and timing of subduction into the main thermocline is diagnosed using kinematic methods from the 1 resolution cme fields in the second tracer diagnostics of the cme and idealized experiments using a date tracer identifying the timing of subduction are performed over the subtropical gyre both approaches generally support stommel s hypothesis that fluid is only transferred from the mixed layer into the main therm

middle permian brachiopods from the tumenling formation in the wuchang area southern heilongjiang ne china and their palaeobiogeographical implications abstract this paper describes nine brachiopod species in eight genera from the tumenling formation in the wuchang area southern heilongjiang northeast china the tumenling fauna is constrained to a wordian capitanian guadalupian middle permian age based on the correlation of the faunas and previously published data from the same horizons in the same area this middle permian brachiopod fauna is characterized by an admixture of elements of boreal affinity kochiproductus sp yakovlevia sp stenoscisma margaritovi gypospirifer volatilis spiriferella keilhavii spiriferella lita and alispiriferella neimongolensis with palaeoequatorial forms spinomarginifera sp vediproductus sp and leptodus nobilis the wuchang fauna as a whole is comparable to several contemporaneous faunas described from inner mongolia in northern china jilin in northeast china south primorye in eastern russia and the hida gaien belt of japan in terms of its index elements and its boreal palaeoequatorial mixture during the middle permian these areas or blocks were referred to the inner mongolia japan transition zone or the northern transition zone between the palaeoequatorial and boreal realms the overwhelming majority of the boreal elements reveal that the wuchang area was probably situated in the northern subzone of this transitional zone which belongs to the southern margin of the bureya block these east and northeast asian blocks acted as migratory stepping stones bridging faunal migration between the palaeoequatorial and boreal realms during the middle permian

inferring the subduction rate and period over the north atlantic abstract the annual rate at which mixed layer fluid is transferred into the permanent thermocline that is the annual subduction rate sann and the effective subduction period x1d4af eff is inferred from climatological data in the north atlantic from its kinematic definition sann is obtained by summing the vertical velocity at the base of the winter mixed layer with the lateral induction of fluid through the sloping base of the winter mixed layer geostrophic velocity fields computed from the levitus climatology assuming a level of no motion at 2 5 km are used the vertical velocity at the base of the mixed layer is deduced from observed surface ekman pumping velocities and linear vorticity balance a plausible pattern of sann is obtained with subduction rates over the subtropical gyre approaching 100 m yr twice the maximum rate of ekman pumping the subduction period x1d4af eff is found by viewing subduction as a transformation process converting mixed layer fluid into stratified thermocline fluid the effective

molecular dynamics simulations of mgsio3 enstatite and seismic discontinuity in the upper mantle 1 the seismic velocities for three kinds of enstatite low clinoenstatite l cen orthoenstatite oen and high pressure clinoenstatite hp cen which is a major component in the upper mantle were estimated using molecular dynamics simulations based on the interatomic potential model the calculated seismic velocities vp and vs for oen are slower than those of l oen up to 6 gpa and 1000 k the velocities in hp cen are faster than those in oen at the transition pressure between oen and hp cen furthermore anisotropy of the seismic velocity in particular vp parallel to 100 001 010 is observed we conclude that the transitions in enstatites are related to the seismic discontinuity observed at depths less than 410 km and that enstatite is as an important a mineral as olivine for the mineralogical model and for the anisotropic propagation of seismic waves in the earth s upper mantle

indoor seismology by probing the earth s interior by using sound velocity measurements at high pressures and temperatures the adiabatic bulk ks and shear g moduli of mantle materials at high pressure and temperature can be obtained directly by measuring compressional and shear wave velocities in the laboratory with experimental techniques based on physical acoustics we present the application of the current state of the art experimental techniques by using ultrasonic interferometry in conjunction with synchrotron x radiation to study the elasticity of olivine and pyroxenes and their high pressure phases by using these updated thermoelasticity data for these phases velocity and density profiles for a pyrolite model are constructed and compared with radial seismic models we conclude that pyrolite provides an adequate explanation of the major seismic discontinuities at 410 and 660 km depths the gradient in the transition zone as well as the velocities in the lower mantle if the uncertainties in the modeling and the variations in different seismic models are considered the characteristics of the seismic scaling factors in response to thermal anomalies suggest that anticorrelations between bulk sound and shear wave velocities as well as the large positive density anomalies observed in the lower mantle cannot be explained fully without invoking chemical variations

in situ elasticity measurement for the unquenchable high pressure clinopyroxene phase implication for the upper mantle ks t 0 017 1 gpa k 1 and g t 0 015 1 gpa k 1 our results show that the elastic velocities of hp cen are not only higher than those of oen but also higher than olivine at upper mantle conditions according to these new data the elastic velocities for the depleted mantle composition with 20 vol of hp cen would result in 0 8 and 1 6 in difference for p and s waves respectively when oen data were used in previous calculations newly measured results also suggest that it is possible to distinguish undepleted and depleted composition models in the upper mantle citation kung j b li t uchida and y wang 2005 in situ elasticity measurement for the unquenchable high pressure clinopyroxene phase implication for the upper mantle geophys res lett 32 l01307 doi 10 1029 2004gl021661

on velocity anomalies beneath southeastern china an investigation combining mineral physics studies and seismic tomography observations abstract seismic tomography studies reveal distinct velocity and v p v s anomalies in the mantle transition zone mtz beneath the yangtze craton and cathaysia block in southeastern china the anomalies under the yangtze craton are characterized by high velocity both v p and v s and low v p v s ratio while those beneath the cathaysia block are characterized by low velocity especially v s and high v p v s ratio here we conduct analyses of phase relations and thermoelasticity to model the effects of thermal and chemical homogeneities in the mtz by taking advantage of recent simultaneous v p and v s seismic tomography results under southeastern china we attempt to quantify the seismic tomography results and examine the effects of temperature chemical composition and water or protonization on velocity anomalies in the deep mantle we find v p v s to be a powerful parameter in distinguishing the various effects of temperature chemical composition and protonization we conclude that an ancient stagnated oceanic slab is most likely the main cause of the observed fast velocity and low v p v s anomalies in the mtz under the yangtze craton this ancient slab material is most likely a product of paleo pacific subduction around 100 125 ma ago when the oceanic plate abruptly changed its direction of motion such an event has been shown to be closely related to the magmatic activities around eastern china the ultrahigh pressure metamorphism zone between the yangtze craton and the north china craton and the destruction of the lower crust of the north china craton the anomalies under the cathaysia block on the other hand are likely due to dehydration induced partial melting of subducted pacific slab materials here the large low v s anomaly in mtz coincides with the extensive mesozoic to cenozoic igneous features on the surface suggesting a state with lower viscosities in the upper mantle dehydration induced partial melting in mtz may have also promoted deformation of the south china fold belt our results suggest that these lithospheric processes are directly related to the tectonic interaction between the oceanic and continental plates in southeastern china and that a better understanding of past deep mantle dynamic processes may place important constraints on the evolution of the cratons in china

the role of mixed boundary conditions in numerical models of the ocean s climate abstract several simple numerical experiments are conducted using both single and double hemisphere ocean basins under symmetric steady forcing to study de ocean s thermohaline circulation it is shown that a stable steady state obtained under a restoring surface boundary condition on salinity becomes unstable upon a switch to a flux boundary condition the polar halocline catastrope of f bryan occurs it is shown that further integration of this collapsed state ultimately yields a steady stable one cell circulation with the approach being essentially chaotic but with significant energy at decadal period the two hemisphere ocean passes through many stages in which violent overturning occurs o 80 101 m3 a 1 these flushes occurs in both hemispheres and are of one cell structure the time period between them bushes varies from seveal hundred to about one thousand years a single 12 vertical level hemispheric basin spun up from an initial state of rest under mixed boundary conditions restoring boun

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

elasticity of diopside to 8 gpa and 1073 k and implications for the upper mantle abstract simultaneous measurements of elastic wave velocities and density have been conducted on diopside by a combined ultrasonic interferometry and x ray diffraction methods at pressure and temperature conditions relevant to the earth s upper mantle the current study not only yielded the first direct measurement of the shear modulus at high pressures but also enabled a simultaneous determination of the bulk and shear properties and their pressure and temperature derivatives from the measured density and velocities finite strain analysis of the experimental data results in ks0 116 4 7 gpa k s 0 4 9 1 ks t p 0 012 1 gpa gpa g 0 1 6 1 and g t p 0 011 1 gpa k with these results and the same finite strain equations the p and s wave velocities of diopsidic mantle clinopyroxene were calculated along a 1600 k adiabatic geotherm in comparison with other mantle minerals the seismic velocities of diopsidic clinopyroxene at upper mantle depths are 1 3 higher than those of orthopyroxene 1 2 and 6 8 lower than those of olivine and majoritic garnet respectively

distribution and circulation of labrador sea water abstract labrador sea water is the final product of the cyclonic circulation of subpolar mode water in the open northern north atlantic mccartney and talley 1982 the temperature and salinity of the convectively formed subpolar mode water decrease from 14 7 c 36 08 to 3 4 c 34 88 on account of the cumulative effects of excess precipitation and cooling the coldest mode water is labrador sea water which spreads at mid depths and is found throughout the north atlantic ocean north of 40 n and along its western boundary to 18 n a vertical minimum in potential vorticity is used as the primary tracer for labrador sea water labrador sea water is advected in three main directions out of the labrador sea 1 northeastward into the irminger sea 2 southeastward across the atlantic beneath the north atlantic current and 3 southward past newfoundland with the labrador current and thence westward into the slope water region crossing under the gulf stream off cape hatteras the labrador sea water core is

distribution and characteristics of mixed transitional mid permian late artinskian ufimian marine faunas in asia and their palaeogeographical implications abstract the permian marine biogeography of the asian region is characterised by the development of three broad realms boreal tethyan and gondwanan in the early early permian asselian to early artinskian there seems to have existed sharp biogeographical boundaries with no transitional zones between the realms presumably due to the effect of gondwanan glaciation and sharp climatic zonation the mid permian late artinskian to ufimian of the asian region is distinguished by the rise of two broad transitional zones in which mixed marine faunas flourished the northern transitional zone north and northeast china sikhote alin central and northeast japan is characterised by an admixture of both warm water cathaysian and cold temperate boreal genera the southern transitional zone arabian peninsula iran afghanistan the karakorum southeast and central pamir salt range central and northwest tibet shan thai terrane timor and western irian jaya on the other hand is distinguished by incorporating faunal elements of both gondwanan and cathaysian origin the mixed faunas of both transitional zones share several antitropically distributed genera e g monodiexodina lytvolasma and spiriferella and are succeeded by palaeotropical tethyan faunas of late permian age it has been postulated that the mixed mid permian fauna of the northern transitional zone was probably formed in an epicontinental sea which was connected to both the asian tethys and the arctic which facilitated the migration of cathaysian and boreal forms into the epicontinental sea and subsequent faunal mixing the formation of the mixed faunas of the southern transitional zone on the other hand is probably related to the breaking off of the cimmerian blocks from northern gondwana and subsequent drifting into a lower latitudinal zone with geographical proximity to both gondwana and cathaysia during the mid permian

permian gondwana boreal antitropicality with special reference to brachiopod faunas in a reconstructed global permian marine biogeographic framework antitropicality is defined as a biogeographic phenomenon whereby a taxon occurs only in the boreal and gondwanan realms and is lacking completely or nearly so in the intervening palaeoequatorial realm we recognise three types of antitropical distributions bipolar high latitude generally 50 latitude in each hemisphere bitemperate approximately between 30 and 50 latitudes in each hemisphere and a combination of both evidence of permian antitropicality has been reported from almost all major marine invertebrate groups both pelagic or benthic forms and is best known at the generic level although an increasing number of antitropical species have also been recognised antitropicality appears to have occurred throughout most of the permian but its strength varied from stage to stage judging by the number of brachiopod genera shared between the two hemispheres the phenomenon manifests itself most strongly from the sakmarian to the kazanian wordian suggesting a prolonged interval of enhanced biotic interchanges between the gondwanan and boreal realms possible migration pathways and mechanisms are reviewed and discussed among a number of existing scenarios invoked to explain the origin of both modern and geological antitropicality we here present data particularly supporting 1 a south to north stepping stone migratory mechanism via island terranes scattered in the eastern palaeotethys 2 a vicariance model exemplified by the spatio temporal distribution of tomiopsis and 3 a shelf north to south migration along the western coast of the palaeotethys as suggested by sowerbina in addition we also consider dispersal along the western coast of pangea facilitated at times by upwelling systems as an additional migration pathway for intercontinental biotic exchanges during the permian although corroborating data are required at present

an isopycnic model study of the north atlantic part ii interdecadal variability of the subtropical gyre abstract in a companion paper a spinup integration of the north atlantic ocean with the miami isopycnic coordinate model was presented the wintertime mixed layer in the central north atlantic was subject to relatively little change in salinity or depth but cooled markedly most probably because of heat loss associated with a partial surface relaxation to climatological sea surface temperatures in a region in which the gulf stream was too far to the north this mixed layer cooling caused the isopycnic layers in the model ventilated subtropical gyre to rise and surprisingly to warm while the experiment was not an attempt to simulate changes in the real atlantic ocean it nevertheless appears from observations that in recent decades the mixed layer in nature has undergone a change similar to that exhibited by the model mixed layer since it is expected that changes in the ventilated subtropical gyre will be governed largely by changes in the mixed layer in the central north atlantic from where the ve

elasticity of single crystal olivine at high pressures and temperatures abstract elasticity of single crystal san carlos olivine has been derived from sound velocity and density measurements at simultaneous high pressure temperature conditions up to 20 gpa and 900 k using in situ brillouin spectroscopy and single crystal x ray diffraction in externally heated diamond anvil cells these experimental results are used to evaluate the combined effect of pressure and temperature on full elastic constants of single crystal olivine to better understand its velocity profiles and anisotropies in the deep mantle analysis of the results shows that the shear moduli display strong concave behaviors as a function of pressure at a given high temperature while the longitudinal modulus c 11 and the off diagonal moduli c 12 and c 13 exhibit greater temperature dependence at higher pressures than at relatively lower pressures using a finite strain theory and thermal equation of state modeling for a pyrolitic mantle composition along an expected mantle geotherm our results show that the magnitude of the v p and v s jumps at the 410 km depth are 6 and 6 4 respectively which are greater than that found in seismic observations suggesting a mantle olivine content of 40 50 vol which is less than what is expected for the pyrolite model our modeled velocity profiles for a metastable olivine wedge in the subduction slabs along a representative cold slab geotherm are 6 and 10 lower than those of wadsleyite and ringwoodite respectively at corresponding depths of the normal mantle our modeled results also show that metastable olivine in the cold slabs could have strong v p and v s anisotropies the maximum v p anisotropy is estimated to be 19 22 at transition zone depth whereas the maximum v s splitting is 13 23 and increases with depth as a result the presence of a metastable olivine wedge at the transition zone depth would exhibit a seismic signature of low velocity and strong seismic anisotropy which are consistent with recent seismic observations for various locations of the slabs and can be used as mineral physics constraints for future seismic detections of the metastable olivine wedges in the deep mantle

the formation of labrador sea water part i large scale processes abstract data obtained in the western labrador sea during march 1976 by hudson are analysed to show that new labrador sea water was being formed at this time on the basis of hydrographic and moored current meter data it is hypothesized that a 200 km scale cyclonic gyre forms in winter in the western labrador sea and that this gyre retains the developing deep mixed layers in this general area long enough for the transformation to labrador sea water to take place using a model it is demonstrated that water columns found along the western boundary of the labrador sea can be modified by cooling evaporation and mixing to form deep mixed layers with the properties of labrador sea water approximately 105 km3 of new labrador sea water was formed in 1976 an estimate that is consistent with earlier estimates of mean annual production rates this water 2 9 c 34 84 is some 0 6 c cooler and 0 06 fresher than that defined by lazier 1973 from his data collected in 1966 the variation of labrador sea water

evolution pattern of early permian carbonate buildups with reference to the carbonate mounds in eastern inner mongolia north china abstract the sakmarian kungurian early permian carbonate mounds of the amushan formation of the deyanqimiao section in eastern inner mongolia north china comprise phylloid algae echinoderm mound fusulinid echinoderm mound and echinoderm mound they were constructed by repeating the following steps in the mid ramp and outer ramp environments 1 skeletal grains accumulated in situ or after short distance transportation 2 tubiform microbes eroded skeletal grains induced the formation of caco3 crystallites near the cell surface and trapped and bound suspended lime mud from ambient water 3 some positive topographies slightly higher than adjacent sediments were formed data from north china as well as the tropical tethyan domain and the subtropical pangean domain show a three phase development pattern of early permian carbonate buildups the first phase asselian sakmarian is marked by carbonate buildups rich in organisms such as phylloid algae palaeoaplysina shamovella sponges and bryozoans the second phase artinskian is represented by the disappearance of phylloid algae and palaeoaplysina from carbonate buildups resulted from the paleoclimatic change from an icehouse to a greenhouse the third phase kungurian is characterized by the sharp contrast between drastic decline of carbonate buildups in the subtropical pangean domain and their successful development in north china and the tropical tethyan domain

open ocean convection observations theory and models we review what is known about the convective process in the open ocean in which the properties of large volumes of water are changed by intermittent deep reaching convection triggered by winter storms observational laboratory and modeling studies reveal a fascinating and complex interplay of convective and geostrophic scales the large scale circulation of the ocean and the prevailing meteorology two aspects make ocean convection interesting from a theoretical point of view first the timescales of the convective process in the ocean are sufficiently long that it may be modified by the earth s rotation second the convective process is localized in space so that vertical buoyancy transfer by upright convection can give way to slantwise transfer by baroclinic instability moreover the convective and geostrophic scales are not very disparate from one another detailed observations of the process in the labrador greenland and mediterranean seas are described which were made possible by new observing technology when interpreted in terms of underlying dynamics and theory and the context provided by laboratory and numerical experiments of rotating convection great progress in our description and understanding of the processes at work is being made

global review of permian muir wood and cooper 1960 brachiopoda morphology palaeobiogeographical and palaeogeographical implications a global review of the stratigraphical and geographical distribution of tyloplecta reveals that the genus ranges in age from kungurian to changhsingian middle to late permian tyloplecta first evolved in south china in the kungurian late early permian the genus went through its first diversification in the guadalupian suffered a major extinction at the end of the guadalupian and re diversified in the wuchiapingian t yangtzeensis persisted into the changhsingian as the only survivor of the genus involved in the end permian mass extinction palaeogeographically south china is not only the centre of origin for the genus but also an area of diversification and evolution in addition to south china tyloplecta has also been recorded from the far east russia japan central thailand laos cambodia qiangtang terrane of tibet salt range iran armenia hungary yugoslavia and slovenia this geographic spread suggests that tyloplecta was primarily restricted to the palaeotethys and is indicative of warm water palaeoequatorial conditions its presence in some of the northeast asian terranes e g parts of japan and far east russia and in the salt range pakistan and central and north iran part of the cimmerian microcontinents demonstrate that the genus invaded the middle palaeolatitudinal regions in both hemispheres during the late middle permian in response to increased shallow marine biotic communications between cathaysia in the eastern palaeotethys and southern angaraland and between cathaysia and peri gondwanaland the invasion of tyloplecta and some other taxa into the southern shore waters of angaraland may be explained by assuming ocean surface current connections and close palaeogeographical proximities between the south china sino korea and bureya blocks in comparison the invasion of tyloplecta into the peri gondwanaland region is more likely a result of reduced palaeogeographical distance between south china and peri gondwanaland and the appearance of the cimmerian microcontinents as migratory stepping stones

multiple equilibria of the global thermohaline circulation abstract a general circulation model with a highly idealized geometry is used to investigate which fundamentally different equilibria of the global thermohaline circulation may exist the model comprises two identical basins representing the atlantic and pacific oceans which are connected by a circumpolar channel in the south the model circulation is driven in addition to wind forcing by restoring the sea surface temperature to prescribed values and specified freshwater fluxes in the surface salinity budget mixed boundary conditions the boundary conditions are symmetric with respect to the equator and identical for both oceans four fundamentally different stable steady states are found under the same set of boundary conditions two of the equilibria show both oceans in the same state with high altitude deep water formation occuring either in both northern or in both southern oceans respectively two additional equilibria exist in which the thermohaline circulations of the basins differ fundament

orthoenstatite clinoenstatite phase transformation in mgsio3 at high pressure and high temperature determined by in situ x ray diffraction implications for nature of the x discontinuity 1 in the upper mantle the x discontinuity at the depths of 240 to 340 km is observed in many localities but its origin is under debate the phase transformation of mg fe sio3 from orthopyroxene to high pressure clinopyroxene has been proposed to cause this discontinuity in this study in situ x ray diffraction experiments were performed and the orthoenstatite high pressure clinoenstatite c2 c phase boundary in the mgsio3 system was determined all the experiments were carried out using a kawai type multianvil apparatus installed at bl04b1 in spring 8 hyogo japan two types of experiments were carried out 1 phase observation experiments at varying pressures and temperatures and 2 quench experiments at fixed pressure and temperature the phase boundary determined precisely by integrating the results of both sets of experiments was found to be p gpa 0 0035t c 3 7 using a recent mgo pressure scale the orthoenstatite high pressure clinoenstatite phase boundary at 1400 c determined here is 0 7 1 0 gpa lower than previous reports based on quench experiments the phase transformation of orthopyroxene is expected to occur at 260 km depth along a typical mantle geotherm and the shallower part of the observed x discontinuity can be explained by this phase transformation

an experimental investigation of the pyroxene garnet transformation in a pyrolite composition and its bearing on the constitution of the mantle abstract the pyroxene garnet transformation in a model pyrolite composition has been investigated over the pressure interval 4 0 to 17 5 gpa at temperatures of 1200 1400 c the transformation is largely completed in the pressure interval 14 16 gpa and a single phase aluminum deficient garnet majorite becomes stable above 16 gpa the mineral assemblages and the density and seismic velocity distributions for pyrolite are calculated as a function of depth on the basis of this and other recent experimental data density and seismic velocity profiles calculated for pyrolite are consistent with models based on seismic observations to a depth of 550 km if the existence of a high density velocity gradient between 550 km and 650 km is confirmed the presence of further phase transformations in majorite and or some degree of chemical heterogeneity in this depth interval would be indicated

elasticity of mg 0 83 fe 0 17 o ferropericlase at high pressure ultrasonic measurements in conjunction with x radiation techniques abstract the elasticity of ferropericlase with a potential mantle composition of mg 0 83 fe 0 17 o is determined using ultrasonic interferometry in conjunction with in situ x radiation techniques x ray diffraction and x radiography in a dia type cubic anvil high pressure apparatus to pressures of 9 gpa nacl pressure scale at room temperature in this study we demonstrate that it is possible to directly monitor the specimen length using an x ray image technique and show that these lengths are consistent with those derived from x ray diffraction data when no plastic deformation of the specimen occurs during the experiment by combining the ultrasonic and x ray diffraction data the adiabatic elastic bulk k s and shear g moduli and specimen volume can be measured simultaneously this enables pressure scale free measurements of the equation of state of the specimen using a parameterization such as the birch murnaghan equation of state the elastic moduli determined for mg 0 83 fe 0 17 o are k s0 165 5 12 gpa g 0 112 4 4 gpa and their pressure derivatives are k s0 4 17 20 and g 0 1 89 6 if these results are compared with those for mgo they demonstrate that k s0 and k s0 are insensitive to the addition of 17 mol feo but g 0 and g 0 are reduced by 14 and 24 respectively we calculate that the p and s wave velocities of a perovskite plus ferropericlase phase assemblage with a pyrolite composition at the top of the lower mantle 660 km depth are lowered by 0 8 and 2 3 respectively when compared with those calculated using the elastic properties of end member mgo consequently the magnitudes of the calculated wave velocity jumps across the 660 km discontinuity are reduced by about 11 for p wave and 20 for s wave if this discontinuity is considered as a phase transformation boundary only ringwoodite perovskite ferropericlase

effect of h2o on upper mantle phase transitions in mgsio3 is the depth of the seismic x discontinuity an indicator of mantle water content the mantle x discontinuity usually assigned to positive seismic velocity reflectors in the 260 330 km depth range has proved difficult to explain in terms of a single mineralogical phase transformation in part because of its depth variability the coesite to stishovite transition of sio sub 2 matches deeper x discontinuity depths but requires 5 10 free silica in the mantle to match observed impedance contrast the orthoenstatite oen to high pressure clinoenstatite hpcen transformation of mgsio sub 3 also broadly coincides with depths of the x but requires chemically depleted and orthoenstatite rich lithology at 300 km depth in order to match observed seismic impedance contrast on the basis of high pressure infrared spectroscopy x ray diffraction and raman spectroscopy we show that 1300 ppm variation of h sub 2 o content in mgsio sub 3 can displace the transition of low pressure clinoenstatite lpcen to hpcen by up to 2 gpa similar to previous quench experiments on the oen to hpcen phase transition where about 30 45 km 1 0 1 5 gpa of deflection could occur per 0 1 wt h sub 2 o if the mantle x discontinuity results from pyroxene transitions in a depleted harzburgite layer because of the strong influence of minor amounts of water on the transformation boundary the depth of the mantle x discontinuity couldmore serve as a potentially sensitive indicator of water content in the upper mantle less

long term coordinated changes in the convective activity of the north atlantic the north atlantic is a peculiarly convective ocean the convective renewal of intermediate and deep waters in the labrador sea and greenland iceland sea both contribute significantly to the production and export of north atlantic deep water thus helping to drive the global thermohaline circulation while the formation and spreading of 18 degree water at shallow to intermediate depths off the us eastern seaboard is a major element in the circulation and hydrographic character of the west atlantic for as long as time series of adequate precision have been available to us it has been apparent that the intensity of convection at each of these sites and the hydrographic character of their products have been subject to major interannual change as shown by aagaard 1968 clarke et al 1990 and meincke et al 1992 for the greenland sea in the ows bravo record from the labrador sea eg lazier 1980 et seq and at the panulirus hydrostation s site in the northern sargasso off bermuda eg jenkins 1982 talley and raymer 1982 this paper reviews the recent history of these changes showing that the major convective centres of the greenland and labrador seas are currently at opposite convective extrema in our postwar record with vertical exchange at the former site limited to 1000 m or so but with labrador sea convection reaching deeper than previously observed to over 2300 m as a result greenland sea deep water has become progressively warmer and more saline since the early 70 s due to increased horizontal exchange with the arctic ocean through fram strait while the labrador sea water has become progressively colder and fresher over the same period through increased vertical exchange most recently convection has become deep enough there to reach into the more saline nadw which underlies it so that cooler but now saltier and denser lsw has resulted

the subpolar mode water of the north atlantic ocean abstract the warm waters of the subtropical and subpolar basins of the north atlantic have tight regional temperature salinity relationships and are conventionally called the regional central waters a volumetric census of the temperature salinity characteristics of the north atlantic by wright and worthington 1970 shows that waters characterized by certain segments of the t s relationships have large volumes compared to those of other segments volumetric mode waters such mode waters appear as layers with increased vertical separation between isopycnals pycnostads the present study reports on the existence of pycnostads in the central and eastern north atlantic these subpolar mode waters are formed by deep winter convection in the subpolar north atlantic and participate in the upper water circulation of the northern north atlantic the seasonal outcropping of the pycnostads occurs within and adjacent to the north atlantic current the irminger current the east and west greenland currents and

high latitude salinity effects and interhemispheric thermohaline circulations a general circulation model for the ocean is used to investigate the interaction between the global scale thermohaline circulation and the salinity distribution it is shown that an equatorially asymmetric circulation can be maintained even under equatorially symmetric basin geometry and surface forcing multiple equilibrium solutions are obtained for the same forcing by perturbing the high latitude salinity field in an otherwise equatorially symmetric initial condition the timescale of the transition from the symmetric circulation to an asymmetric circulation depends critically on the sign of the initial salinity perturbation

coevolution of brachiopod boreal realm and pangea abstract the boreal realm originated in the early carboniferous the realm became more firmly established during the late carboniferous and early permian and peaked in the middle permian before decaying in the late permian in the early carboniferous the geographic distribution of the boreal realm was latitudinally narrow and many brachiopod genera of the realm were also common in the tethys realm the boreal realm faunas were however also characterized by many geographically and temporally restricted genera the boreal realm was well developed in the late carboniferous as represented by the continued expansion of the geographical ranges and numbers of occurrences of many permian characteristic boreal realm genera in the early permian the geographic distribution of the boreal realm expanded further as did the distribution of characteristic boreal realm genera in the middle permian the geographic distributions of the boreal realm had expanded to their greatest extent and the characteristic boreal realm genera were most abundant and diverse in the late permian the cool water characteristic genera which flourished during the carboniferous to middle permian disappeared in these areas and resulted in the decay of boreal realm the development of the boreal realm was closely related to events leading to the formation of pangea in which a variety of plates laurussian siberian etc were continuously drifting northwards some plates blocks entered middle and high latitudinal regions and were located in cool climatic environments during the evolution of pangea the siberian kazakhstan and eastern european plates were continuously located in the center of the boreal realm the barents ocean developed to the west and the paleo asian ocean developed to the east of these plates this configuration of oceans and continents differentiated the eastern central asia region and the western barents region in the paleo asian ocean tectonic domain the northern branch of the paleo asian ocean was surrounded by the siberian plate the kazakhstan plate and the jiamusi mongolia block and named the mongolia okhotsk ocean the mongolia okhotsk brachiopod fauna developed on the southern margin of the mongolia okhotsk ocean i e the northeastern margins of the siberian and kazakhstan plates and the northern margin of the jiamusi mongolia block thus forming the mongolia okhotsk province during the middle permian the xar moron ocean was enclosed by the jiamusi mongolia block and the kazakhstan tarim and south china plates on the southern margin of the xar moron ocean i e the southern margin of the jiamusi mongolia block the zhesi brachiopod fauna developed and the inner mongolia province was formed during the carboniferous permian the kolyma chukchi block siberian plate and north american plate comprised the barents ocean tectonic domain the verkhoyansk brachiopod fauna developed on the northern margin of the barents ocean i e on verkhoyansk and the southwestern margin of the siberian plate thus forming the verkhoyansk taymyr province starting in the late carboniferous a cool water brachiopod fauna developed on the southern margin of the barents ocean i e the northern margin of the north american plate and the northern margin of the eastern european plate thus forming the yukon pechora province the geographical range of which extended continuously with time

computation of seismic profiles from mineral physics the importance of the non olivine components for explaining the 660 km depth discontinuity the recent increasing number of experimental works leads us to review the elastic properties and mineralogical transformations of mantle minerals the updated data set is used to compute seismic profiles for two petrological models along three adiabatic temperature profiles these profiles are chosen to stress out the influence of non olivine minerals on seismic parameters and to represent cold and horizontally averaged temperature profiles of the earth s mantle in a first part starting compositions of pyrolite and piclogite and a single layer convection are assumed the results clearly point out the importance of the non olivine part of the mineralogy two scenarios are found to explain the 660 km depth discontinuity

the impact of surface flux parameterizations on the modeling of the north atlantic ocean abstract the response of an ocean general circulation model to several distinct parameterizations of the surface heat and freshwater fluxes which differ primarily by their representation of the ocean atmosphere feedbacks is investigated in a realistic configuration for the north atlantic ocean the impact of explicitly introducing oceanic information climatological sea surface temperature into the computation of the heat flux through a haney type restoring boundary condition as opposed to the case in which the flux is based on atmosphere only climatologies and is computed with the full bulk formulation is considered the strong similarity between these two approaches is demonstrated and the sources of possible differences are discussed when restoring boundary conditions are applied to the surface salinity however an unphysical feedback mechanism is being introduced the model s response to this restoring is contrasted to the response to a flux boundary condition that prescribes the freshwater fl

the leptodus shales of central peninsular malaysia distribution age and palaeobiogeographical affinities the terms leptodus shales and leptodus beds have been used to describe a rich brachiopod bearing unit within the permian argillaceous facies of the central belt of peninsular malaysia to date there has been no formal description of this unit regarding its age spatial distribution or faunal composition a review of previous literature backed by recently collected data from our field surveys and biostratigraphical studies reveals that there is a sequence of fossiliferous assemblages within the leptodus shales which range in age from middle permian to possibly early late permian and extend geographically from southern kelantan to southern pahang peninsular malaysia these assemblages are found in argillaceous sediments which are often highly tuffaceous and in northern pahang are associated with pyroclastic volcanics of probable island arc origin the faunas are of palaeo equatorial affinity and are taxonomically close to faunas in indochina such as the sisophon fauna in cambodia typical elements include vediproductus cf punctatiformis chao transennatia gratiosa waagen t termierorum sone leman and shi uncuninellina timorensis beyrich leptodus richthofeni kayser l cf tenuis waagen leptodus nobilis waagen gubleria aff ninglangensis fang and jiang and spyridiophora gubleri termier and termier

upper mantle p velocity structure of the canadian shield waveform modeling of the phases pnl p and pp is used to determine the p wave upper mantle structure beneath the canadian shield long period recordings at world wide standard seismograph network long range seismic measurement and canadian network stations in north america are used with earthquakes within and just outside the shield as sources the p data set is incomplete due to the scarcity of large events within the shield and the inclusion of pp provides much more data using the wkbj approach to calculate the mantle response the pp waveforms can be modeled almost as well as the p the phase pnl persists to large distances in shield regions and the interference of pnl with triplication range p helps constrain the structure in the upper 400 km important features of our model which is designated s25 are 1 a thick high q high velocity lid to 165 km 2 a deep low velocity zone and 3 discontinuities of 5 at 405 km and 4 at 660 km the lid and low velocity zone create an unusual b branch arrival not seen in other regions which persists well beyond 30 only slight lateral variation is noted within the shield region the major features of the model are similar to those of grand and helmberger s s wave model for the canadian shield