melting curve of mg fe sio3 perovskite to 96 gpa evidence for a structural transition in lower mantle melts the melting temperature of mg fe sio3 perovskite the dominant mineral phase of the earth s lower mantle has been measured to a pressure of 96 10 gpa below 60 gpa we find good agreement with the previous measurement of heinz and jeanloz 1987a and above 60 gpa the melting curve of silicate perovskite has a small positive slope of 19 5 5 5 k gpa the melting point of mg0 9fe0 1 sio3 perovskite is 3800 300 k at 96 gpa by extrapolation to 136 gpa it is 4500 500 k at the core mantle boundary these values provide an upper limit to the geotherm through the solid mantle and they are compatible with recent estimates of the temperature in the core being high 4500 k at the core mantle boundary our melting curve implies that the volume change on melting increases at 60 gpa from vm 0 0 0 2 cm mole to vm 0 16 0 03 cm mole we derive an equation of state for the melt from our data and find that a highly coordinated structure is required to explain the molar volume of liquid mg fe sio3 at pressures above 20 gpa

shock temperatures of sio2 and their geophysical implications the temperature of sio 2 in high pressure shock states has been measured for samples of single crystal quartz and fused quartz pressures between 60 and 140 gpa have been studied using projectile impact and optical pyrometry techniques at lawrence livermore national laboratory both data sets indicate the occurrence of a shock induced phase transformation at 70 and 50 gpa along the and fused quartz hugoniots respectively the suggested identification of this transformation is the melting of shock synthesized stishovite with the onset of melting delayed by metastable superheating of the crystalline phase some evidence for this transition in conventional shock wave equation of state data is given and when these data are combined with the shock temperature data it is possible to construct the stishovite liquid phase boundaries the melting temperature of stishovite near 70 gpa pressure is found to be 4500 k and melting in this vicinity is accompanied by a relative volume change and latent heat of fusion of 2 7 and 2 4 mj kg respectively the solid stishovite hugoniot centered on quartz is well described by the linear shock velocity particle velocity relation u s 1 822 up 1 370 km s while at pressures above the melting transition the hugoniot centered on quartz has been fit with u s 1 619 u p 2 049 km s up to a pressure of 200 gpa the melting temperature of stishovite near 100 gpa suggests an approximate limit of 3500 k for the melting temperature of sio 2 bearing solid mantle mineral assemblages all of which are believed to contain si 4 in octahedral coordination with o 2 thus 3500 k is proposed as an approximate upper limit to the melting point and the actual temperature in the earth s mantle moreover the increase of the melting point of stishovite with pressure at 70 gpa is inferred to be 11 k gpa using various adiabatic temperature gradients in the earth s mantle and assuming creep is diffusion controlled in the lower mantle the current results could preclude an increase of viscosity by more than a factor of 10 3 with depth across the mantle

the equation of state of a molten komatiite 1 shock wave compression to 36 gpa the equation of state eos of an initially molten 1550 c komatiite 27 wt mgo was determined in the 5 36 gpa pressure range via shock wave compression shock wave velocity u s and particle velocity u p kilometers second follow the linear relationship u s 3 13 0 03 1 47 0 03 u p based on a calculated density at 1550 c 0 bar of 2 745 0 005 g cm 3 this u s u p relationship gives the isentropic bulk modulus k s 27 0 0 6 gpa and its first and second isentropic pressure derivatives k s 4 9 0 1 and k s 0 109 0 003 gpa 1 the calculated liquidus compression curve agrees within error with the static compression results of agee and walker 1988 to 6 gpa but is less dense than their extrapolated values at higher pressures we determine that olivine fo 94 will be neutrally buoyant in komatiitic melt of the composition that we studied near 8 2 gpa clinopyroxene would also be neutrally buoyant near this pressure liquidus garnet majorite may be less dense than this komatiitic liquid in the 20 24 gpa interval however pyropic garnet and perovskite phases are denser than this komatiitic liquid in their respective liquidus pressure intervals to 36 gpa liquidus perovskite may be neutrally buoyant near 70 gpa at 40 gpa the density of shock compressed molten komatiite would be approximately equal to the calculated density of an equivalent mixture of dense solid oxide components this observation supports the model of rigden et al 1989 for compressibilities of liquid oxide components using their theoretical eos for liquid forsterite and fayalite we calculate the densities of a spectrum of melts from basaltic through peridotitic that are related to the experimentally studied komatiitic liquid by addition or subtraction of olivine at low pressure olivine fractionation lowers the density of basic magmas but above 13 14 gpa this trend is reversed all of these basic to ultrabasic liquids are predicted to have similar densities at 13 14 gpa and this density is approximately equal to the density of the bulk preliminary reference earth model mantle in this pressure range this suggests that melts derived from a peridotitic mantle may be inhibited from ascending from depths greater than 400 km

on the dynamics of internal waves in a nonlinear weakly nonhydrostatic three layer ocean aspects of the dynamics of internal solitary waves evolving in a three layer ocean are investigated using a new numerical multilayer model that solves the nonlinear weakly nonhydrostatic boussinesq equations and uses high resolution in situ data the model applications refer to two different phenomena frequently observed in the real ocean which can be described using a three layer model rather than a two layer model in the first application the influence of the strength of a shallow seasonal thermocline superimposed on a two layer permanent stratification on the structure of internal solitary waves is studied it is found that while for small to medium wave amplitudes a decrease in the strength of the thermocline yields an increase in the simulated wavelengths for large wave amplitudes this dependence is no longer monotonic in particular in the limiting case of a vanishing thermocline first mode internal solitary wave solutions of the three layer numerical model tend to the analytical internal solitary wave solutions of the miyata equations a two layer model in which the full nonlinearity of the shallow water theory up to first order phase dispersion is retained in the second application that refers particularly to high resolution observations made north and south of the strait of messina in the eurafrican mediterranean basin the generation of internal solitary waves by the evolution of surface and subsurface water jets is investigated the analysis of the in situ data shows in fact that from very energetic surface and subsurface jet like disturbances subject to strong turbulent mixing internal solitary waves emerge as robust quasi nondissipative oceanic features idealized flow conditions aimed at approximating possible initial stages of the observed water jets are imposed to force our numerical model in general good agreement is found between characteristics of observed and simulated wave fields our investigation identifies the observed water jets as peculiar features of the complex ocean dynamics and suggests that layered numerical models can represent helpful tools in understanding fundamental processes inherent in their intricate dynamics

coastal outflow currents into a buoyant layer of arbitrary depth the long wave reduced gravity shallow water equations the semi geostrophic equations are used to study the outflow of a river into the ocean while previous models have studied dynamics driven by gradients in density the focus here is on the effects of potential vorticity anomaly pva the river water is taken to have the same density as a finite depth upper layer of oceanic fluid but the two fluids have different uniform potential vorticities under these assumptions the governing equations reduce to two first order nonlinear partial differential equations which are integrated numerically for a prescribed efflux of river water and pva results are found to depend strongly on the sign of the pva with all fluid turning downstream in the direction of kelvin wave propagation when the river water has positive pva and anticyclonic flow upstream of the river mouth when the pva is negative in all cases a nonlinear kelvin wave propagates at finite speed ahead of the river water away from the river mouth the uniformity of one set of riemann invariants allows for similarity solutions that describe the shape of the outflow as well as a theory that predicts properties of the kelvin wave a range of behaviours is observed including flows that develop shocks and flows that continue to expand offshore the qualitative behaviour of the outflow is strongly correlated with the value of a single dimensionless parameter that expresses the ratio of the speed of the flow driven by the kelvin wave to that driven by image vorticity

dynamics of the atlantic meridional overturning circulation part 1 buoyancy forced response abstract historically a hierarchy of ocean models have been used to investigate the dynamics of basin scale deep meridional overturning circulations mocs near the base of this hierarchy are idealized solutions forced only by a surface buoyancy flux our goal is to provide a complete dynamical description of such base solutions thereby placing the hierarchy on a firmer foundation for this purpose we obtain solutions to two types of models a variable density layer ocean model vlom and an ocean general circulation model coco the former allowing for nearly analytic solutions and the latter for more accurate representation of processes solutions are obtained in an idealized flat bottom basin extending 40 in longitude and from the equator to 60 n and for simplicity density depends only on temperature our standard runs are forced by a surface heating q which is spread uniformly throughout layer 1 in vlom and at depths less than hmin in coco it quickly relaxes upper ocean temperature to a prescribed t y that decreases linearly in the latitude band 30 50 n from 23 c in the south to the temperature of the deep ocean 3 c in the north at the very bottom of our hierarchy are solutions to dynamically simplified versions of the models i e no sub mixed layer entrainment or detrainment in vlom and no mixing and momentum advection in coco that adjust to a steady state without an moc initially q forms an upper layer of thickness h1 hmin and temperature t t y and there is near surface eastward flow across the basin in the latitude band where ty 0 at the eastern boundary kelvin waves cancel this current by adjusting h1 to a nearly parabolic profile he y that thickens poleward and eventually extends to the ocean bottom just south of 50 n subsequently rossby waves propagate across the basin adjusting the solution to a state in which h1 x y he y and t t y above h1 everywhere in the basin after this adjustment the only remaining flows are zonally oriented isopycnal overturning cells within the upper layer caused by thermal wind shear in the latitude band where ty 0 our standard runs which are solutions to the full models necessarily adjust to a steady state with an moc along and near the eastern boundary kelvin wave adjustments still maintain the structure he y and rossby waves begin to carry that structure offshore near 50 n however the rossby waves are strongly damped in vlom the damping is accomplished by a detrainment that prevents h1 from becoming larger than a prescribed maximum value in coco it results primarily from horizontal diffusion which thins h1 by cooling the deep ocean there because of the damping there is an across basin pressure gradient that drives northward geostrophic transport forming the surface branch of the moc furthermore the eastward flowing moc branch is located in a northern boundary layer where the damping is active because there is no wind forcing there is no steady state barotropic flow and the deep response mirrors that in the upper layer in most solutions the upper and deep circulations are closed by diffusive upwelling mostly in the interior ocean and by downwelling primarily at the eastern boundary the exceptions being for two of the extended solutions noted below a useful aspect of vlom is that it allows a closed analytic expression for m h e where m is the moc transport and he is the eastern boundary thermocline depth in the tropics for realistic parameter choices m is essentially proportional to h e 2 in agreement with prior estimates based on ad hoc principles or determined empirically from numerical solutions vlom also provides an approximation for he where is the coefficient of vertical diffusion then m h e describes the approximate dependency of m on and it varies like 2 3 again consistent with prior results in coco solutions m exhibits similar dependencies on he and a consistency traceable to he y being established in both systems by similar processes however the 2 3 relationship is not as precise because upwelling sources other than interior diffusion also contribute significantly to m we also report four solutions that extend our standard runs in straightforward and insightful ways they are solutions in which i the moc eastward branch is the surface flow of nearly isopycnal nearly closed thermal wind cells that extend to the ocean bottom a very different structure than for the northern boundary layer in the coco standard run ii t depends on both x and y and the moc downwelling branch shifts to the northern boundary iii q is weakened enough to allow upper layer temperature advection to impact the response and iv the moc upwelling branch is externally imposed by an exchange of water across the southern boundary of the basin despite the differences among these solutions and the standard runs the underlying processes that generate the moc and determine its strength remain unchanged an indication that the moc processes discussed here have general applicability

the rhine outflow plume studied by the analysis of synthetic aperture radar data and numerical simulations the dynamics of the rhine outflow plume in the proximity of the river mouth is investigated by using remote sensing data and numerical simulations the remote sensing data consist of 41 synthetic aperture radar sar images acquired by the first and second european remote sensing satellites ers 1 and ers 2 over the outflow region of the river rhine most of them show sea surface signatures of oceanic phenomena for example surface current and wind variations ship wakes and oil slicks in particular in 36 of these images pronounced frontal features are visible as narrow zones of mainly enhanced sometimes enhanced reduced radar backscatter that can be associated with the rhine surface front within the area enclosed by the frontal line large zones characterized by a lower radar backscatter than in the outer area are often visible the analysis of the ers sar images suggests that the form and the location of the frontal features are mainly linked to the semidiurnal tidal phase in the outflow region although their variability suggests also that they weakly depend on river discharge residual currents and neap spring tidal cycle in order to test this observational hypothesis the results obtained from the analysis of the ers sar images are compared with the results obtained from the numerical simulation of the hydrodynamics of the rhine outflow region carried out using a two layer frontal model which is based on the nonlinear hydrostatic shallow water equations on an f plane the model is forced by prescribing tidal and residual currents and river discharge at the open boundaries several simulations are performed by varying the values of these forcing parameters the numerical results corroborate the observational conjecture it is found that the form and the location of the simulated interface outcropping lines in the proximity of the river mouth are mainly determined by the semidiurnal tidal phase in the outflow region and that river discharge residual currents and neap spring tidal cycle contribute only secondarily to their determination inserting the simulated surface velocity field into a simple radar imaging model that relates the modulation of the backscattered radar power to the surface velocity convergence in radar look direction narrow elongated bands of enhanced radar backscatter emerge near the model frontal line while patches of low radar backscatter appear within the simulated rhine plume area the consistency of the model results with the results obtained from the analysis of the sar images enables one to infer a mean spatial and temporal evolution of the rhine outflow plume over a semidiurnal tidal cycle from the analysis of spaceborne sar images acquired during different tidal cycles over the rhine outflow area and suggests the possibility of using numerical modeling in conjunction with the analysis of spaceborne measurements for monitoring the oceanic variability in the rhine outflow area

coastal circulations driven by river outflow in a variable density 1 layer model a variable density 1 layer model is used to investigate the dynamics of the fresher water plumes generated by river outflow solutions are found in a north south channel and the transport mr and salinity sr of the outflow are specified as boundary conditions along a 25 km wide segment of the western boundary in most cases the river water discharges into a preexisting oceanic mixed layer with thickness h1 when mr is sufficiently low plumes remain coastally trapped immediately after the outflow is switched on a coastal kelvin wave is excited at the river mouth that establishes a southward current of oceanic water along the right hand coast in contrast all the river water first bends to the left as it exits the river mouth and the resulting plume advances northward along the left hand coast at the plume nose some of the fresher water reverses direction and this water together with some oceanic water flows southward on either side of the offshore density front between the fresher and salty waters two processes cause this upstream movement geostrophic adjustment generates the southward frontal current and kelvin wave propagation from the nose thins the layer within the plume thereby establishing the northward geostrophic coastal jet when mr is sufficiently high coastally trapped plumes no longer exist if the rossby number of the outflow is also large enough the river water flows directly offshore and only a portion of it recirculates to form a northward propagating coastal plume the angle at which the outflow leaves the river mouth becomes more southward as mr and sr increase and as h1 decreases the strength of the northward propagating plume is weakened as h1 decreases and sr increases when h1 0 so that there is no ambient oceanic layer there is no northward plume at all likewise the plume is weakened when the model includes entrainment a process that acts to prevent the layer thickness from thinning appreciably

mixed layer thermocline interaction in a three dimensional isopycnic coordinate model abstract the annual buildup and obliteration of the seasonal thermocline and the associated ventilation of the permanent thermocline in a wind and thermally driven ocean basin are simulated numerically the model developed for this purpose is a combination of a single layer model of the oceanic mixed layer based on a simple closure of the turbulence kinetic energy equation and a three dimensional isopycnic coordinate model of the stratified oceanic interior the joint model set in a rectangular ocean basin is forced by annually varying wind stress and radiative plus turbulent heal fluxes approximating zonnaly averaged conditions over the north atlantic special emphasis is placed on the description of the mixed layer detrainment process which requires distributing mixed layer water of continuously variable density among constant density interior layers the truncation errors associated with this process are found to be numerically tolerable the quasi lagrangian character of the model s vertical coo

potential vorticity dynamics of coastal outflows abstracta simple quasigeostrophic model is used to examine the outflow from a river estuary or strait into a coastal ocean as shown by johnson et al these quasigeostrophic outflows are accurately described by analytical long wave solutions this paper first uses these solutions and contour dynamics simulations to discuss the behavior of coastal outflows second it extends the model and the long wave theory to consider the effects of ambient currents tides winds or a variable source flux third consideration of the momentum flux at the source is used to understand the turning of the current showing that steady solutions conserve momentum hence resolving the momentum imbalance paradox of pichevin and nof finally a new numerical scheme to compute steady outflow boundaries is developed the model focuses on the key dynamics driven by the source velocity and the generation of vorticity as the buoyant fluid adjusts the simplicity of the model and insight given by the long wave solutions enables

yangtze brackish water plume circulation and diffusion abstract a system of 3 d linearized momentum equations the continuity equation and a simplified equation of state for sea water are analytically solved the solution comprises three parts the first part is a wind driven current the second a jet like current caused by yangtze river outflow and the last a density flow the computed current velocity is obtained by solving an advection diffusion equation of salinity by a finite difference method the results show that the yangtze brackish water plume spreads as a large low salinity tongue at the surface the turning of the tongue axis is mainly controlled by wind stress yangtze run off and bottom topography near the bottom the axis changes little all the year around at about 10 15 m depth there is a sharp halocline in summer but at deeper layers the vertical distribution is almost always uniform the computed salinity distribution agrees fairly well with the observed one

buoyancy driven current during cooling periods in ise bay japan 1 the cooling effect on buoyancy driven current is studied in the coastal embayment of ise bay japan by applying knowledge derived from studies of convection in a rotating fluid this convection process is highly sensitive to the presence of inhomogeneities in the preexisting stratification and to differential buoyancy loss on freshwater input the bay water is divided into two regions that differ in their response to the cooling from the surface one region represents a river plume which in effect shields the deeper regions from the cooler surface in the other region convective mixing is active although the mixed water forms and becomes extensive in this convection region the mixed water hardly develops in the river plume region the subsequent differential deepening of the mixed water causes gravitational circulation and yields a mixed water lens which has a reversed dome shape and rotates anticyclonically in a thermal wind balance in the mixed water lends nonvanishing stratification remains because of the rotational effect the location of the mixed water lens and associated anticyclonic circulation determines the basin wide circulation during cooling periods

river forced estuarine plumes abstract the development maintenance and dissipation of river forced estuarine plumes with and without seaward sloping bottom are studied by use of a three dimensional primitive equation model inside the estuary discussion is focused on how the coriolis force induces lateral asymmetries in the circulation four physical processes dictate the transient as well as the quasi steady circulation in moderately stratified estuaries 1 upper layer convergence during the transient spinup phase 2 upward entrainment leading to the two layer steady circulation pattern 3 upward stretching of the lower layer vortex during the spindown period and 4 in the presence of a seaward bottom slope the left bounded tendency of the landward undercurrent for all phases of development deviations from the laterally averaged circulation pattern caused by these processes are discussed over the shelf various types of plumes are defined according to the visual appearance of the surface salinity field the four types of p

early evolution of the earth accretion atmosphere formation and thermal history atmospheric and thermal evolution of the earth growing by planetesimal impacts was modeled by taking into account the blanketing effect of an impact induced h2o atmosphere and the temperature dependence of h2o degassing when the water content of planetesimals is larger than 0 1 by weight and the accretion time of the earth is less than 5 107 years the surface of the accreting earth melts and thus a magma ocean forms and covers the surface the formation of a magma ocean will result in the initiation of core mantle separation and mantle differentiation during accretion once a magma ocean is formed the surface temperature the degree of melting in the magma ocean and the mass of the h2o atmosphere are nearly constant as the protoplanet grows further the final mass of the h2o atmosphere is about 1021 kg a value which is insensitive to variations in the model parameter values such as the accretion time and the water content of planetesimals that the final mass of the h2o atmosphere is close to the mass of the present oceans suggests an impact origin for the earth s hydrosphere on the other hand most of the h2o retained in planetesimals will be deposited in the solid earth free water within the proto earth may affect differentiation of the proto mantle in particular the mantle feo abundance and the incorporation of a light element in the outer core

a reduced gravity isopycnal ocean model hindcasts of el nino abstract a global isopycnal ocean model is presented for the study of interannual to interdecadal variability in the global ocean the model treats the primitive equations on a sphere with a generalized vertical coordinate this coordinate is designed to represent a turbulent well mixed surface layer and nearly isopycnal deeper layers disappearing isopycnics are treated through the quasi isopycnal technique in which the coordinate separates from the isopycnic in order to maintain a minimum layer thickness a reduced gravity treatment is made with the deepest interface at a mean depth of 2300 m coastal topography is represented but the reduced gravity treatment precludes the use of variable bottom depth the model is used for hindcast studies of el nino during the decade from 1982 through 1991 using a combination of climatological wind forcing and wind anomalies derived from various sources in order to carry out the hindcast experiments a technique is developed for constructing a mean climatological

structure and eastward extension of the changjiang river plume in the east china sea 1 the hydrographic structure and offshore extension of freshwater plume discharged from the changjiang also known as the yangtze river in the northern east china sea were investigated by analyzing conductivity temperature depth ctd data and drifter trajectories collected during the summers of 1997 and 1998 from june to early september when southerly winds prevail the plume tends to move northeast in the chinese coastal area and then separates from the coastal zone to travel eastward over 400 km offshore across the western shelf of the northern east china sea during other seasons when northerly winds prevail the plume is confined to the chinese coast in the summer the plume in the midshelf confined to a thin surface layer 10 to 15 m thick extends eastward in the form of patches of low salinity water rather than spreading as a tongue shaped pattern from the changjiang mouth the eastward movement of patches in the western shelf is primarily due to upwelling favorable southerly winds upon reaching the vicinity of cheju do an island in the middle of northern east china sea the patches are advected to the korea tsushima strait by either the cheju warm current or a northward flowing mean current of the kuroshio branch current and then finally flow into the east japan sea

generation of komatiite magma and gravitational differentiation in the deep upper mantle abstract the densities of silicate liquids with basic picritic and ultrabasic compositions have been estimated from the melting curves of minerals at high pressures silicate liquids generated by partial melting of the upper mantle are denser than olivine and pyroxenes at pressures higher than 70 kbar and garnet is the only phase which is denser than the liquid at pressures from 70 kbar to at least 170 kbar in this pressure range garnet and some fraction of liquid separate from ascending partially molten diapirs it is therefore suggested that aluminium depleted komatiite with a high ca oal2o3 ratio may be derived from diapirs which originated in the deep upper mantle at pressures from 70 kbar to at least 140 kbar 200 400 km in depth where selective separation of pyropic garnet occurs effectively on the other hand aluminium undepleted komatiite is probably derived from diapirs originating at shallower depths

the primodial terrestrial magma ocean and its implication for stratification of the mantle fractional crystallization behaviour of a magma ocean extending to lower mantle depths was deduced from estimations of melting relations for the deep mantle and the density relationships between ultrabasic liquid and mantle minerals the accretional growth of the earth necessarily involves a molten zone magma ocean in the outer layer of the growing earth the fractionation by melting during accretion results in primary stratification composed of a molten ultrabasic upper mantle magma ocean a perovskite rich lower mantle and an iron core a certain amount of al2o3 and cao was removed from the magma ocean and retained in the lower mantle due to eclogite fractionation in the early stage of accretion and the perovskite fractionation in the later stage of accretion models of the stratification of the upper mantle arising from fractional crystallization of the magma ocean and subsequent convective disturbance were deduced on the basis of estimations of melting relations for the deep mantle and the density relationships between the ultrabasic liquid and mantle minerals the stratification of the mantle which is consistent with geophysical constraints is as follows the upper mantle is composed of two layers the upper olivine rich layer and the lower garnet rich layer with a thickness around 200 km and the lower mantle with a perovskite rich composition in this model both the 400 and 650 km discontinuities are the chemical boundaries

melting of garnet peridotite to 13 gpa and the early history of the upper mantle by analogy with the evolution of the moon it has been suggested that the earth may have had a magma ocean or liquid outer layer before 3 800 myr ago 1 its presence would have had profound implications for the primary stratification of the mantle into upper mantle transition zone and lower mantle2 3 an essential constraint on this hypothesis is a knowledge of the high pressure melting characteristics of mantle material generally assumed to be peridotite in the upper mantle we recently described4 the first melting experiments on mantle peridotite to 14 gpa using spinel iherzolite klb 1 from kilbourne hole new mexico we showed that partial melts close to the solidus at 5 7 gpa are komatiitic in composition and that the solidus and liquidus converge at high pressures here we report further melting experiments on garnet iherzolite phn1611 from thaba putsoa lesotho we confirm the convergence of the solidus and liquidus and we show a negative dt dp slope for the liquidus above 7 gpa these observations are briefly discussed in terms of their importance to the petrological evolution of the upper mantle and the presence of a magma ocean in the early archaean

the upstream spreading of bottom trapped plumes it is well known that numerical simulations of freshwater discharges produce plumes that spread in the direction opposite to that of the propagation of coastally trapped waves the upstream direction the lack of a theory explaining these motions in unforced environments deemed the numerical results suspect thus it became a common practice in numerical studies to add a downstream mean flow to arrest the development of the upstream perturbation this approach is generally unjustified and it remains a matter of interest to determine if the upstream displacement produced by models is a geophysical phenomenon or a consequence of erroneous assumptions in the model setup in this article the results of highly idealized numerical experiments are used to investigate these matters it is shown that this phenomenon is associated with the geostrophic adjustment of the discharge and that upstream motion is endemic to the baroclinic structure of bottom trapped plumes it is also shown that downstream displacements are generated by the cross shelf barotropic pressure gradient generated by the propagation of coastally trapped waves sensitivity experiments indicate that the speed of upstream propagation and the density structure of the plume are affected by bottom friction the slope of the bottom and the magnitude of the density anomaly bottom friction in particular slows down the progression of the plume and changes its density structure producing a more homogeneous downstream region and a more stratified upstream region

the role of wind on the detachment of low salinity water in the changjiang estuary in summer in july 2006 and the role of wind on detaching the lsw in particular are explored with a three dimensional numerical model the real case simulation and the sensitivity experiments results show that wind plays a crucial role in the detachment events and is highlighted in three aspects first wind is the most important dynamic factor in the two detachment processes of the lsw wind mixing wind driven northward current and wind induced upwelling are three driving forces on detaching the lsw which increase the salinity in the upper layer in the detachment region along the 30 m isobath and separate the offshore lsw from the nearshore main body of lsw the diagnostic analysis further indicates that the increase of salinity in the detachment region is mainly due to northward current which transports high salinity water from the south second a critical wind speed namely a southeasterly wind above 8 0 m s is found to be related to the timing of the detachment events a sensitivity experiment further confirms this critical wind speed and no detachment occurs when the wind speed is below 8 0 m s third the southwesterly wind plays a key role in the magnitude of the spatial size of the detached lsw before the detachment occurs a persistent southwesterly wind induces northeastward expansion of the lsw and consequently forms larger lsw offshore after detachment which is verified by another sensitivity experiment with modified wind direction

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

circulation on the western south atlantic continental shelf 1 numerical process studies on buoyancy 1 buoyancy driven currents are investigated in the western south atlantic ocean where a major river plume la plata interacts with a minor one patos lagoon a series of simulations were performed with a three dimensional free surface numerical model to better understand the processes which control both plumes evolution and their interaction the simulations are focused on the importance of turbulent mixing to the evolution of the la plata plume and its downshelf penetration toward the patos lagoon satellite observations and historical data show that the la plata plume has a tendency to expand along the river southern margin before it turns north in the direction of coastal trapped waves propagation our results on the other hand show that in the absence of the tides and the wind this plume tends to leave the estuary attached to its northern margin downstream unless the model parameters are tuned to produce unrealistically high turbulent mixing we then address the role of each parameter that controls mixing and show that by tuning the model parameters we can get plumes similar to those observed in nature however the plumes produced in the experiments with excessively high mixing parameters showed unbounded southward upstream expansion by introducing the tides we show that the plumes produced in the presence of tidal stirring and normally set mixing parameters are more realistic suggesting that tidal stirring is more effective than artificially tuned turbulent mixing on causing the plume lateral expansion

dynamics of andaman sea circulation and its role in connecting the equatorial indian ocean to the bay of bengal circulation in the bay of bengal bob is driven not only by local winds but are also strongly forced by the reflection of equatorial kelvin waves ekws from the eastern boundary of the indian ocean the equatorial influence attains its peak during the monsoon transition period when strong eastward currents force the strong ekws along the equator the andaman sea lying between the andaman and nicobar island chains to its west and indonesia thailand and myanmar to the south east and north is connected to the equatorial ocean and the bob by three primary passages the southern 6 n middle 10 n and northern 15 n channels we use ocean circulation models together with satellite altimeter data to study the pathways by which equatorial signals pass through the andaman sea to the bob and associated dynamical interactions in the process the mean coastal circulation within the andaman sea and around the islands is primarily driven by equatorial forcing with the local winds forcing a weak sea level signal on the other hand the current forced by local winds is comparable to that forced remotely from the equator our results suggest that the andaman and nicobar islands not only influence the circulation within the andaman sea but also significantly alter the circulation in the interior bay and along the east coast of india implying that they need to be represented accurately in numerical models of the indian ocean

melt segregation from partially molten source regions the importance of melt density and source region size the compressibility of basic melt at 1 atmosphere is about an order of magnitude higher than that of mantle minerals consequently the density contrast between melt and the principal residual crystals in mantle source regions is expected to decrease with increasing source region depth the increasingly olivine normative character of primary melts produced at greater depths is also expected to result in a decrease in this density contrast with increasing source region depth once vertical permeability is established by melt generated during partial melting buoyancy driven melt percolation can under some circumstances segregate melt from the residual crystals in its source region on a geologically rapid time scale limits to this process are provided by cooling of the source region freezing melt in and rigidity of the crystalline matrix mechanically trapping melt source region size influences these limits strongly consequently small partially molten diapirs km in diameter may be able to trap large melt fractions 30 but larger source regions would be unable to do so the reduction in density contrast with pressure reduces the buoyant force driving melt percolation and provides another limit to melt segregation diapirs at depth may thus stably contain large fractions of melt but may decompress and unload their melt during ascent this effect would be enhanced in small diapirs and may be relevant to the genesis of komatiitic magma melt compression may also be a factor in explaining why the very different maximum depths inferred for typical basic melt segregation from source regions on different planets 500 km on the moon 250 km on mars 100 km on earth correspond to similar pressures 25 35 kbar at greater pressures melt may no longer be capable under ordinary conditions of segregating upwards by buoyancy this may also help to explain why depleted peridotites overlie more fertile peridotites and how deep regions of the mantle are able to remain fertile over geologic time

olivine flotation in mantle melt abstract molten komatiite and peridotite have been compressed in an octahedral multi anvil device up to 10 gpa densities of the melts were measured at pressure intervals in the range 7 to 10 gpa by observing sinking and floating san carlos olivines and synthetic forsterite marker spheres the multi anvil results for komatiite when combined with piston cylinder measurements done at 4 to 6 gpa and a calculated reference density at 105 pa yield a birch murnaghan isothermal bulk modulus of k1900c 26 gpa and pressure derivativek 4 25 the pressure of neutral buoyancy for olivine in komatiite is confirmed to be near 8 gpa as predicted in earlier work olivine flotation in the experimental komatiite commences at a pressure close to where the liquidus phase changes from olivine to denser garnet leading to the possibility of density driven crystal sorting during fractionation molten peridotite klb 1 shows an isothermal compression 2000 c of 0 065 g cm 3 gpa 1 in the interval 105 pa to 8 2 gpa the olivine liquid peridotite density crossover is predicted to lie between 9 and 11 gpa indicating that olivine flotation can operate at depths of 300 500 km in a molten peridotitic mantle

upwind weighted advection schemes for ocean tracer transport an evaluation in a passive tracer context centered in space centered in time integration has generally been used for the advection of scalars in ocean models an assessment is made of the implications of centered leapfrog integration in the context of two dimensional passive tracer advection within a stommel 1948 gyre nonphysical ripples in the tracer field grow to alarming levels in purely advective integrations diffusive parameterizations of eddy mixing moderate these ripples but it is found that laplacian diffusion greatly reduces the peak amplitude of the tracer field while biharmonic or weaker laplacian diffusion allows ripples of large amplitude several forward in time upwind weighted schemes are found to provide better solutions smolarkiewicz s 1984 multi dimensional positive definite advection and transport algorithm mpdata scheme is slightly superior for an integration at moderate resolution within which the western boundary current is poorly resolved in typical fashion third order upwind based schemes exhibit little sensitivity to the details of multidimensional treatment for this problem of passive tracer advection with results nearly as good as for mpdata

the interaction of estuarine and shelf waters a model and applications abstract an analytical model is developed to describe the steady flow in an estuary shelf interaction region where the system is treated as a two layer density stratified flow the motion is expanded in terms of the relative thickness of the vertical ekman layer the zero order flow is geostrophic in each layer balancing of order one quantities reduces the system to two vorticity equations relating the pressure field with the displacement of the interface and the bottom topography an explicit solution is obtained for the case of linear offshore sloping bottom the flow behavior of the estuarine plume depends on the vertical structure of the flow at the river mouth the bottom slope and the ambient coastal flow under certain conditions a front exists as an offshore boundary of the plume these results are compared with observations for the changjiang river estuary in china and both the chesapeake bay and savannah river estuaries in the united states

melting temperature distribution and fractionation in the lower mantle abstract the melting curve of perovskite mgsio3 and the liquidus and solidus curves of the lower mantle were estimated from thermodynamic data and the results of experiments on phase changes and melting in silicates the initial slope of the melting curve of perovskite mgsio3 was obtained as d t m d p 77 k gpa 1 at 23 gpa the melting curve of perovskite was expressed by the kraut kennedy equation as t m k 917 1 29 6 v v 0 where tm 2900 k and p 23 gpa and by the simon equation p gpa 23 21 2 t m k 2900 1 75 1 the liquidus curve of the lower mantle was estimated as t liq 0 9 t m perovskite and this gives the liquidus temperature tliq 7000 500 k at the mantle core boundary the solidus curve of the lower mantle was also estimated by extrapolating the solidus curve of dry peridotite using the slope of the solidus curve of magnesiowustite at high pressures the solidus temperature is 5000 k at the base of the lower mantle if the temperature distribution of the mantle was 1 5 times higher than that given by the present geotherm in the early stage of the earth s history partial melting would have proceeded into the deep interior of the lower mantle estimation of the density of melts in the mgo feo sio2 system for lower mantle conditions indicates that the initial melt formed by partial fusion of the lower mantle would be denser than the residual solid because of high concentration of iron into the melt thus the melt generated in the lower mantle would tend to move downward toward the mantle core boundary this downward transportation of the melt in the lower mantle might have affected the chemistry of the lower mantle such as in the d layer and the distribution of the radioactive elements between mantle and core

high pressure equation of state of molten anorthite and diopside new hugoniot equation of state data for molten diopside at 1773 k and molten anorthite at 1923 k are reported to 38 and 35 gpa respectively the diopside data initial density 2 61 mg m 3 are described by a straight line fit to the shock velocity particle velocity results of u s 3 30 1 44 u p km s 1 and our preferred fit to the anorthite data initial density 2 55 mg m 3 is given by u s 2 68 1 42 u p km s 1 reduction of the data to a third order birch murnaghan isentrope assuming the gruneisen ratio times the density is a constant and the mie gruneisen equation of state gives k 0s 22 4 gpa and k s 6 9 for diopside for anorthite we calculate k 0s 17 9 gpa and k s 5 3 the present data for diopside are used to calculate the diopside solidus at high pressures we expect the solidus to be shallow above 10 gpa but the lack of data on the variation of either the gruneisen parameters of the liquid and crystal or the heat capacity and thermal expansion at elevated pressures makes extrapolation of fusion curves uncertain solidus temperatures of 2400 2500 k and 2560 2705 k for diopside are calculated at 10 and 20 gpa respectively the new data are combined with those of rigden et al 1988 for the di 0 64 a 0 36 eutectic composition to examine the degree to which such liquids mix ideally with respect to volume up to 25 gpa for the eutectic composition at 1400 c we calculate the volumes of the an and di mix nearly ideally to 25 gpa we find that the ratio of the partial molar volumes of the oxides in silicate melts to that of the crystal oxides at 1673 k and 1 atm is 1 0 0 1 for a wide range of oxide components for the low pressure tetrahedrally coordinated oxides e g sio 2 al 2o 3 fe 2o 3 the ratio is 1 3 with respect to oxides such as stishovite corundum and hematite in which the cations are octahedrally coordinated by oxygens if changes in coordination of al and si from tetrahedral at low pressures to octahedral at high pressures occur in melts they do so gradually over an interval of 40 gpa although 1 atm bulk moduli for a wide compositional range of silicate melts are similar the differences in integrated compression to mixed oxide like high pressure configurations are reflected mainly by variations in k t k t is found to vary inversely with fraction of network forming initially tetrahedrally coordinated cations e g al 3 si 4 thus k t which may be uncertain by 1 5 is estimated to vary from 7 for molten anorthite enstatite and diopside to 8 for molten ferrosilite to 10 for molten forsterite and to 11 for molten fayalite

estuary plumes and fronts in shelf waters a layer model abstract a layer model that treats fronts as discontinuities is developed to study the steady state behavior of shallow estuary plumes on the continental shelf the complete range of earth rotation effect is evaluated from small scale or nonrotating plumes kelvin number equal zero to large scale rotating plumes kelvin number equal order one supercritical flow is assumed in the outlet channel and the method of characteristics is used to compute the flow downstream nonrotating plumes have strong boundary fronts and concentrate their greatest layer depth and mass transport offshore near the front but form no coastal current rotating plumes have boundary fronts that weaken soon after discharge form a turning region where coriolis action deflects the flow toward shore and subsequently set up a coastal current soon after its formation this coastal current is bounded offshore by a strong front called the coastal front across which the momentum balance changes from nearly inertial in the turning regi

tongue shaped frontal structure and warm water intrusion in the southern yellow sea in winter 1 in winter a thermohaline front forms at the yellow sea ys entrance where the warm and saline cheju warm current cwc water meets cold coastal water the frontal structure as well as the northwestward intrusion of the warm water was investigated by analyzing conductivity temperature depth ctd data tracks of drifting floats moored current data and satellite images the cwc water advances westward as a tongue with its tip heading westward across the ys entrance not intruding northward along the deepest part of the ys trough whereas a secondary warm water band is developed northwestward along the western flank of the trough floats in the warm tongue moved northwestward across the western frontal zone where the frontal structure was weak reflecting the northwestward intrusion along the 50 70 m isobaths through the frontal zone currents in the trough do not always meet the upwind flow theory that in an elongated basin the wind driven flow is upwind in the deep channel but rather show the predominance of the southward downwind flow model experiments show that on the western flank of the trough both the southeastward tide induced residual flow and the southeastward flow due to the nonlinear effect between tide and wind are generated at the same time thus the intermittent intrusion of the cwc across the western frontal zone may be closely associated with the predominance of the upwind flow over the southeastward nonlinear interacted flow

the equation of state of a molten komatiite 2 application to komatiite petrogenesis and the hadean mantle new experimental data for the equation of state of a komatiitic liquid were used to model adiabatic melting in a peridotitic mantle if komatiites are formed by 30 partial melting of a peridotitic mantle then komatiites generated by adiabatic melting come from source regions that began their unmelted ascent in the lower transition zone 500 670 km or the lower mantle 670 km the great depth of incipient melting implied by this model suggests that komatiitic liquids may form in a pressure regime where they are denser than their coexisting crystals possibly the bulk mantle although komatiitic magmas are thought to separate from residual crystals in the mantle at a temperature 200 c greater than modem mid ocean ridge basalts morbs their ultimate sources are predicted to be diapirs that if adiabatically decompressed from initially solid mantle were more than 700 c hotter than the sources of morbs and were derived from great depth we also studied the evolution of an initially molten mantle i e a magma ocean our model considers the thermal structure of the magma ocean density constraints on crystal segregation and approximate phase relationships for a nominally chondritic mantle crystallization will begin at the core mantle boundary perovskite buoyancy at 70 gpa may lead to a compositionally stratified lower mantle with iron enriched magnesiowustite content increasing with depth large convective velocities in the magma ocean would prohibit crystal liquid fractionation by settling or flotation until quiescent boundary layers form such boundary layers could form when the crystal content of the magma reaches a critical value near 44 vol and in the late stages of crystallization around unmelted blocks of foundered protocrust matrix compaction and diapirism could also lead to fractionation effects the upper mantle could be depleted or enriched in perovskite components relative to the bulk mantle olivine neutral buoyancy may lead to the formation of a dunite septum in the upper mantle partitioning the ocean into upper and lower reservoirs but this septum must be permeable

coastal flows driven by a local density flux a two layer model with a rigid lid and a flat bottom on an f plane is employed to study a flow field driven by a density flux through the sea surface or the coast for example freshwater discharged from a river the negative positive density flux into the upper layer is represented by the water beneath over the interface changing from the lower upper layer to the upper lower layer that is entrainment of the lower upper layer by the upper lower layer the subinertial flow pattern constrained by the coast has two components one is a baroclinic eddy nearby that matches the entrainment region and the other is a forced internal kelvin wave along the appropriate half of the coast

static compression and olivine flotation in ultrabasic silicate liquid piston cylinder techniques have been used to observe static compressions of ultrabasic silicate liquids to 6 gpa and 2000 c compressions are measured by bracketing sinking and floating of olivine crystals of known density at run conditions komatiite peridotite and their liquid mixtures with fe2sio4 all show constant density changes with pressure of 0 07 g cm3 gpa along their liquidi these results confirm shock wave studies and ultrasonic studies which show weak compositional effects on compressibility of basic to ultrabasic silicate liquid the techniques converge in supporting the conjecture of stolper et al 1981 that ultrabasic silicate liquids may be denser than their equilibrium coexisting olivines and pyroxenes at high compressions the pressure of this density inversion is 7 8 gpa for the compositions studied olivine flotation provides an important constraint upon earth evolution models that include extensive melting during early differentiation it also provides a mechanism for concentrating high mg si olivine in the upper mantle without unduly perturbing other geochemical parameters a full evaluation of the physical and geochemical consequences is required at an early date