detection of lower mantle scatterers northeast of the marianna subduction zone using short period array data short period university of washington northern california and southern california seismic array records of a sequence of deep mariana subduction zone earthquakes show unexpected clear arrivals nearly 90 and 105 s following p we measure slowness arrival time and arrival azimuth of these phases relative to p using array techniques to find where they emanate in the mantle by combining slowness and back azimuth deviations and the move out with depth of the arrivals from different earthquakes we find their most probable origin is through s to p conversion at point scatterers in the mid to lower mantle at 25 7 n 148 2 e 1590 km and 25 5 n 151 0 e 1850 km respectively separated by 300 km these features indicate elastically distinct material in the middle of the lower mantle which if fragments of subducted slabs are not related to contemporary subduction they may represent upwelling convective material from the deep mantle or d but they are not purely thermal in nature as chemically distinct bodies they may represent potential reservoirs of the isotopic and trace element components recognized geochemically

circulation mixing and production of antarctic bottom water abstract the antarctic source of bottom water to the abyssal layer of the world ocean is examined as well as its large scale flow pattern and ultimate entrainment rate into the deep water above we make use of the available high quality station data in the southern ocean to construct bottom maps of neutral density and mean property maps including chlorofluorocarbon cfc for the abyssal layer underneath a selected neutral density surface the maximum density at the sill depth of drake passage is used to distinguish between the voluminous deep water mass that is a continuous component of the antarctic circumpolar current from the relatively denser bottom water originated along the antarctic continental margins based on water density antarctic bottom water aabw is defined here generically to include all volumes of non circumpolar water of antarctic origin over the shelf regime multiple localized sources of specific aabw types contribute to the abyssal layer of the adjacent antarctic basins characteristics of these dense bottom waters reflect closely those observed on the parent shelf water mass spreading paths of newly formed deep and bottom waters over the slope regime and their subsequent oceanic circulation patterns are analyzed on the basis of global property maps for the aabw layer interior mixing and interbasin exchanges of aabw are deduced from mean characteristic curves following the southern streamline of the antarctic circumpolar current outflow and mixing of aabw from the weddell sea to the argentine basin is depicted using density and cfc distributions of two zonal hydrographic lines recirculation and mixing of deep and bottom waters within the weddell gyre are also detailed using a meridional section along the greenwich meridian the strength of all localized sources of aabw combined is estimated by two independent approaches an estimate of the total production rate of aabw is calculated based on the oceanic cfc budget for the aabw layer offshore of the 2500 m isobath the sum of all downslope inputs of well ventilated bottom water types underneath the top isopycnal must account for the measured cfc content in the bottom layer the resulting total aabw production rate is about 8 sv which is a conservative figure that neglects the loss of cfc bearing waters across the top isopycnal in recent years whereas about 9 5 sv is calculated assuming a well mixed bottom layer making use of their transient nature cfc distributions at the top of the aabw layer indicate that more direct and rapid entrainment of cfc rich bottom waters below occurs over localized areas with relatively strong upwelling rates and enhanced vertical mixing a second more ad hoc but independent oceanic mass budget of the bottom layer is also constructed a typical basin wide rate of deep upwelling of 3 10 7 m s 1 requires 10 sv 1 sv 106 m3 s 1 of newly formed aabw to sink down the slope around antarctica we have also formulated a spatial distribution of deep upwelling on the isopycnal at the top of the aabw it is expressed as a combination of wind topographic and turbulent components which in turn are functions of the isopycnal depth bottom depth and bottom layer thickness this non uniform upwelling field yields about 12 sv of aabw exported across the top isopycnal fortuitously the overall average of upward speed at the top isopycnal 3 7 10 7 m s 1 compares well with previous estimates of deep upwelling in the northern basins a series of likely sites for strong vertical entrainment of aabw are clearly identified in the modeled distribution of deep upwelling consonant with the observed cfc distributions on the top isopycnal altogether regions with relatively high upwelling rates 5 10 7 m s 1 occupy only a quarter of the total areal extent of the top isopycnal but they account for as much as 45 of the total vertical transport

flow hydrography turbulent mixing and dissipation at fieberling guyot examined with a primitive equation model 1 the extensive set of measurements previously taken at fieberling guyot provides a backdrop for model results on flow hydrography turbulent mixing and derivative variables a z level primitive equation model driven at subinertial and superinertial tidal frequencies allows the nonlinear interaction of free and topographically trapped motions to jointly determine model outcomes model residual flows mean hydrographic features topographic amplification of oscillatory currents turbulent dissipation and vertical diffusivity kv profiles are all examined in the light of the observations azimuthal residual flows are toroidal above the summit with maximum speed 20 cm s 1 diurnal flow over the summit is intensified by a factor 20 downward vertical flow as a time mean w t occurs from 150 m above the summit apex to summit rim depth with radially inward flow above the apex and radial outward flow below upward w t rings the summit at larger r the existence of the observed cold dome is shown to depend on w t in the summit circulation cell vertical current shear is concentrated in a 150 m thick cap above the summit accounting for a domed distribution of and kv with maxima of 10 7 w kg 1 and 30 cm2 s 1 respectively profiles most like the observations of kv are obtained with a subgrid scale parameterization in which the turbulent prandtl number pr depends on the shear richardson number ri

teleseismic delay times in a 3 d earth and a new look at the s discrepancy summary when the earliest measurements of the earth s normal modes became available it was soon noticed that v models satisfying this new data set were generally slower than models based on s traveltimes this s discrepancy has since then been attributed to the influence of dispersion that accompanies attenuation but it ignores a competing process that may have the same effect in a heterogeneous earth seismic rays will bend to take advantage of local high velocity anomalies this effect is difficult to quantify because of the computational problems associated with the determination of minimum traveltime paths in heterogeneous earth models in three dimensions we have developed a new method to find absolute minimum traveltimes even in very complicated earth models and applied this to a large number of rays generated in different random earth models the s discrepancy is a function of correlation length and amplitude of v heterogeneity a standard deviation u of 0 15 km sc with a correlation length of 200 km in the whole mantle would give a discrepancy even larger than observed at a 60 and must be discarded a u of 0 15 km s in the upper mantle and 0 05 km s elsewhere explains a discrepancy of 1 2 s depending on the correlation length since the total discrepancy is estimated to be about 4 s this still allows for effects of attenuation we conclude that the s wave discrepancy can be used to set limits to the heterogeneity in the lower mantle at short correlation lengths with our present day knowledge of the magnitude of the discrepancy a heterogeneity larger than 1 per cent with correlation length 200 km is unlikely

a model for planetesimal meltdown by 26al and its implications for meteorite parent bodies the melting of planetesimals heated by 26 al has been modelled using a new finite difference method that incorporates convection as an example we consider a planetesimal with a radius of 64 km which accretes instantaneously at t 0 75 myr after the formation of calcium aluminum rich inclusions from cold 250 k nebular dust with 50 porosity at t 0 9 myr t 700 k the planetesimal shrinks to a radius of 50 km due to sintering at t 1 2 myr t 1425 k the fully insulated interior deeper than a few kilometers starts to melt and at t 1 5 myr t 1725 k with 50 melting convection starts by t 2 myr the planetesimal is a globe of molten convecting slurry inside a thin residual crust from about t 2 5 myr the crust thickens rapidly as the power of 26 al fades planetesimals probably melt in this manner when they accrete before t 1 3 myr and are large enough to insulate themselves r 20 km for accretion at t 0 rising to 80 km at t 1 3 myr melting behavior will also be affected by the level of 60 fe in nebular dust by the extent of devolatilization reactions and basalt segregation during heating and by gradual accretion the model suggests that a the parent bodies of differentiated meteorites had accreted before about t 1 5 to 2 myr and before most chondritic parent bodies had formed and b that molten planetesimals may be a source for chondrule melt droplets

modeled sensitivity of the northwestern pacific upper ocean response to tropical cyclones in a fully coupled climate model with varying ocean grid resolution tropical cyclones tcs actively contribute to earth s climate but tc climate interactions are largely unexplored in fully coupled models here we analyze the upper ocean response to tcs using a highresolution earth system model in which a 0 58 atmosphere is coupled to an ocean with two different horizontal resolutions 18 and 0 18 both versions of the model produce realistic tc climatologies for the northwestern pacific region as well as the transient surface ocean response we examined the potential sensitivity of the coupled modeled responses to ocean grid resolution by analyzing tc induced sea surface cooling latent heat exchange and basin scale ocean heat convergence we find that sea surface cooling and basin scale aggregated ocean heat convergence are relatively insensitive to the horizontal ocean grid resolutions considered here but we find key differences in the poststorm restratification processes related to mesoscale ocean eddies we estimate the annual basin scale tc induced latent heat fluxes are 1 706 0 16 3 10 j and 1 436 0 16 3 10 j for the high resolution and low resolution model configurations respectively which account for roughly 45 of the total tc induced ocean heat loss from the upper ocean results suggest that coupled modeling approaches capable of capturing ocean atmosphere feedbacks are important for developing a complete understanding of the relationship between tcs and climate

transient diapycnal mixing and the meridional overturning circulation abstract an idealized three dimensional model of buoyancy forced flow in a single hemisphere is used to investigate whether transient diapycnal mixing can sustain the meridional overturning circulation in the annual mean mixing transience had little effect on the meridional overturning when mixing occurred on basin boundaries the overturning strength was found to be insensitive to mixing transience for mixing that was highly localized in space away from basin boundaries oceanic meridional mass and heat transport decreased as mixing became more transient the increased sensitivity in the highly localized case is likely due to the inhibition of surface heat flux into the thermocline the dynamic response to transient mixing featured large scale internal oscillations that increased in amplitude with the transience of mixing but were confined to the tropics and had little effect on the overturning cell through midlatitudes these results indicate that transient diapycnal mixing with a distribution sug

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

internal swell generation the spatial distribution of energy flux from the wind to mixed layer near inertial motions the energy flux from the wind to inertial mixed layer motions is computed for all oceans from 50 8 st o 508n for the years 1996 99 the wind stress t is computed from 6 h 2 58 resolution ncep ncar global reanalysis surface winds the inertial mixed layer response ui and the energy flux p5 t ui are computed using a slab model the validity of the reanalysis winds and the slab model is demonstrated by direct comparison with wind and adcp velocity records from ndbc buoys at latitudes 508 the inertial response is too fast to be resolved by the reanalysis wind 6 h output interval midlatitude storms produce the greatest fluxes resulting in broad maxima near 40 8 latitude during each hemisphere s winter concentrated in the western portion of each basin northern hemisphere fluxes exceed those in the southern hemisphere by about 50 the global mean energy flux from 1996 to 1999 and 508 st o 508n is 0 98 6 0 08 3 1023 wm 22 for a total power of 0 29 tw 1 tw 5 1012 w this total is the same order of magnitude as recent estimates of the global power input to baroclinic m2 tidal motions suggesting that windgenerated near inertial waves may play an important role in the global energy balance

near inertial ocean current response to hurricane frederic abstract hurricane frederic passed with 80 to 130 km of the u s naval oceanographic office current meter arrays in water depths ranging from 100 to 470 m near the desoto canyon region and within 150 km of an ocean thermal energy conversion otec mooring in 1050 m of water excitation of near inertial waves by the moving hurricane was observed throughout the water column along the canyon walls and at the otec site the frequencies of the waves were blue shifted between 1 to 6 above the local inertial frequency the horizontal wavelength of 250 km is consistent with an energetic first baroclinic mode response but is considerably below the linear theory prediction of 550 km the inferred vertical wavelengths of the immediate response exceeded 1000 m along the northern and eastern sides of the canyon since the currents throughout the water column increased within hours of the hurricane passage later the vertical wavelengths were about equal to the water depth the vertical group velocities associated

the role of horizontal boundaries in parameter sensitivity and decadal scale variability of coarse resolution ocean general circulation models abstract coarse resolution f plane and plane frictional geostrophic models are used to study the response to restored surface buoyancies and fixed surface buoyancy fluxes with restored surface buoyancies it is found that the overturning and meridional buoyancy transport generally follow the scaling from thermal wind and vertical advective diffusive balance when maximum midbasin rather than maximum overall streamfunction is used as the metric the sensitivity of overturning magnitude to vertical diffusivity agrees quite closely with that of a two dimensional rayleigh frictional model that follows an analogous scaling this measure of meridional overturning as well as the meridional buoyancy transport also roughly follow the predicted f 1 3 scaling and are relatively insensitive to variations in and horizontal viscosity the sensitivity experiments indicate that the coarse resolution model overturning and thermodynamic structure are well characterized by the adjustment of a uniformly rotating viscous

p wave amplitudes in a 3 d earth summary evidence is presented here that p wave amplitudes contain additional information on the earth s heterogeneity and must be considered in future tomographic interpretations we analyse the reliability and the variance of teleseismic p wave amplitudes recorded at well calibrated broadband global seismic network gsn stations from intermediate to deep earthquakes depth 46 km the dataset contains 217 earthquakes with mb between 5 6 and 7 6 from 1993 january to 2000 may using pairs of closely located events with similar focal mechanisms as well as data recorded at the closely spaced moma seismic array we demonstrate the consistency of observations we deduce that the magnification of the gsn instruments generally drifts by at most 2 per cent per year and likely much less p wave amplitudes have variations due to focusing defocusing with a standard deviation of at least 38 per cent this reduces to 19 per cent if only periods in excess of 10 s are considered tomographic p wave models with mantle velocity anomalies of the order of 1 per cent are unable to reproduce such large variations

internal tides generated on a corrugated continental slope part ii along slope barotropic forcing recent measurements in a region of continental slope characterized by ridges and valleys running up and down the slope reveal interesting high mode structure in the tidal band velocity signals with enhanced mixing above the corrugations in order to understand these observations numerical simulations of the internal tide generation in this region of topography were performed here the focus is on the response of the flow to along slope barotropic tidal forcing for small amplitude barotropic forcing internal waves are generated over the continental slope that propagate toward the ocean surface and toward shallower water when higher amplitude forcing is combined with large amplitude corrugations the flow is locally supercritical downstream of ridges and transient internal hydraulic jumps result as the flow relaxes each half tidal period these jumps are released as internal wave packets which propagate up into the thermocline the internal hydraulic jumps are a source of mixing in the valleys while the small scale shears associated with the internal waves could lead to mixing higher up the water column over the forcing range considered the response is dominated by slightly higher harmonics of the tidal forcing frequency than predicted by existing analytic theories

large scale circulation with locally enhanced vertical mixing abstract the influence of localized regions of intensified vertical mixing on the stratification and circulation in a large scale ocean model is investigated with idealized numerical experiments numerical solutions are obtained of a closed basin single hemisphere ocean model based on the planetary geostrophic equations mesoscale eddy effects are minimized and vertical mixing at the turbulent microscale is represented by a vertical diffusivity solutions with uniform are contrasted with a localized mixing solution in which increases by two orders of magnitude from its interior value 0 2 10 4 m2 s 1 in a region 500 km wide adjacent to the vertical eastern boundary when is uniform the stratification beneath the ventilated thermocline is characterized by a single vertical scale in contrast the localized vertical mixing supports a deep diffusive thermocline with two distinct vertical scales an internal boundary layer centered at the base of the ventilated thermocline roughly 1000 m

abyssal mixing where it is not abstract a parameterization based on internal wave wave interaction theory which infers turbulence production from finescale internal wave shear is applied to 114 full water depth velocity profiles in the sargasso sea an average eddy diffusivity of 0 1 10 4 m2 s 1 independent of depth is inferred this value is consistent with full water depth microstructure measurements from abyssal basins in the eastern north atlantic and eastern north pacific it is an order of magnitude smaller than the values inferred from a simple vertical advection diffusion balance or bulk budgets thus the mixing needed to close deep global water mass budgets does not appear to occur over midlatitude abyssal plains this suggests that ocean mixing is either i confined to boundary layers as in ideal thermocline theory or ii localized to hotspots such as over rough topography or restrictive passages abyssal diffusivities do not display any dependence on bottom slope for slopes less than 7 10 2 based on 5 10 km bathy

precise determination of post stishovite phase transition boundary and implications for seismic heterogeneities in the mid lower mantle abstract the phase transition boundary between stishovite and cacl2 type structure in pure sio2 was investigated at 45 75 gpa and 300 2490 k based on the in situ x ray diffraction measurements in a laser heated diamond anvil cell lhdac results show that the boundary has a positive dp dt slope of 11 1 mpa k and the transition occurs about 70 gpa at 2200 k along the typical mantle geotherm this corresponds to a depth of 1700 km somewhat shallower than the previous estimate seismic heterogeneities have been found in a wide depth range from 800 to 1850 km in the upper to middle layers of the lower mantle the post stishovite phase transition is known to be ferroelastic type which causes a considerable reduction in shear modulus leading to a large slow shear velocity anomaly the almost pure sio2 phase included in subducted crustal materials may be therefore responsible for the relatively deep mid lower mantle seismic heterogeneities the shallow lower mantle anomalies are possibly caused by the similar phase transition in sio2 phase containing al2o3 and h2o or by the phase transition in al bearing casio3 perovskite from cubic to tetragonal structure

precipitation of multiple light elements to power earth s early dynamo abstract earth has had a global magnetic field for at least 3 5 billion years but if the iron alloy in the core has high conductivity it is difficult to explain this duration with energy from cooling and inner core growth alone precipitation of light elements e g magnesium silicon and oxygen from earth s core is a potential alternative energy source to power the dynamo we develop a new framework of coupled thermo chemical evolution of the earth to consider precipitation of multiple light components from the core and their interaction with the overlying mantle layer the precipitated material accumulates in a layer at the base of the mantle which is then continuously eroded by mantle convection we allow the precipitation of three species mgo feo and sio2 including their interactions not considered by most previous studies we find that mgo sio2 and feo precipitation may each dominate entropy production depending on the choice of equilibrium constants and initial model states and that the three species together can explain the duration of earth s magnetic field across a range of plausible scenarios over the earth s history we find that the core can lose 1 2 wt silicon and oxygen suggesting that light precipitation is potentially an important process for the core compositional evolution and core mantle chemical exchange additionally our results show that precipitation does not in most cases have a systematic influence on the timing of inner core nucleation or magnitude of the resulting paleomagnetic signal with inner core nucleation typically around 550 mya however the onset of precipitation of individual species could produce additional sharp increases in paleomagnetic intensity at various points through earth s history besides the inner core nucleation event

spatial variability of turbulent mixing in the abyssal ocean ocean microstructure data show that turbulent mixing in the deep brazil basin of the south atlantic ocean is weak at all depths above smooth abyssal plains and the south american continental rise the diapycnal diffusivity there was estimated to be less than or approximately equal to 0 1 x 10 4 meters squared per second in contrast mixing rates are large throughout the water column above the rough mid atlantic ridge and the diffusivity deduced for the bottom most 150 meters exceeds 5 x 10 4 meters squared per second such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry

on a simple empirical parameterization of topography catalyzed diapycnal mixing in the abyssal ocean abstract the global spatial distribution of the turbulent diapycnal diffusivity in the abyssal ocean is reexamined in light of the growing body of microstructure data revealing bottom intensified turbulent mixing in regions of rough topography a direct and nontrivial implication of the observed intensification is that the diapycnal diffusivity k is depth dependent and patchily distributed horizontally across the world s oceans theoretical and observational studies show that bottom intensified mixing is dependent upon a variety of energy sources and processes whose contributions to mixing are sufficiently complex that their physical parameterization is premature only rudimentary parameterizations of tidally induced mixing have been attempted although the tides likely provide no more than half of the mechanical energy available for diapycnal mixing in the abyssal ocean here an empirical and still rudimentary parameterization of the spatially variable mean diffusivity k based on a large collection

comparison of deep ocean finescale shear at two sites along the mid atlantic ridge abstract four drifting floats were used to measure the magnitude of the vertical derivative of horizontal velocity in waters above the rough bathymetry of the mid atlantic ridge this derivative is typically the dominant component of the velocity gradient the shear two floats were at the site of the brazil basin tracer release experiment bbtre in the south atlantic and two were near the site of the guiana abyssal gyre experiment gage in the north atlantic floats operated for 1 year except for one bbtre float which operated for 100 days shear was measured over a vertical span of 9 5 m using drag elements that caused the floats to rotate slowly in response to shear for each float the first second and fourth moments of shear were elevated above levels associated with the garrett munk model internal wave spectrum three of the four floats were tracked as they moved over mountainous terrain allowing shear intensity to be measured as a function of height above the bottom a deep bbtre float showed enhancement of rms shear near the bottom floats at both areas provided measurements at 2000 m above the bottom with differing results the gage site had a lower fourth moment of shear diapycnal diffusivity proxy than the bbtre site however application of normalization factors accounting for differences between the sites in bottom roughness latitude dependent internal wave dynamics and tidal current speeds brings the results into agreement

the effect of localized mixing on the ocean circulation and time dependent climate change observations indicate that intense mixing in the ocean is localized above complex topography and near the boundaries model experiments presented here illustrate that accounting for this fact can be important in particular it is found that in the case of localized mixing the rate of overturning circulation is proportional to the net rate of generation of potential energy by the vertical mixing linked to the net downward heat diffusion rather than to the value of the mean vertical diffusivity coefficient furthermore it is shown that two climate models having the same vertical profile of diffusivity but differing in their distribution horizontally uniform versus topography boundary intensified can simulate significantly different meridional oceanic circulations vertical heat transfers and responses of simulated climate to atmospheric co2 increase this is found for relatively large o 1 0 cm 2 s 1 horizontal mean values of vertical diffusivity in the pycnocline however in cases of relatively small o 0 1 cm 2 s 1 mean diffusivity in the pycnocline the simulated integral quantities such as meridional mass and heat transports do not depend much on the details of the mixing distribution even so it is found that the deep western boundary currents are more localized near the boundaries in the case of topography boundary intensified mixing also the stratification in the deep ocean is set through the localized regions of intense vertical mixing in addition it is shown that reconciling the observed basin mean values of diffusivity in the abyssal ocean of o 10 cm 2 s 1 with realistic stratification can be problematic unless the regions of enhanced vertical mixing are localized

mixing in the main thermocline abstract a series of profiles of velocity microstructure along 152 e in the western north pacific ocean were collected in may june 1982 large averaged turbulent dissipation rates found in the main thermocline 400 to 1000 m were determined by a combination of large independent estimates of and a greater rate of occurrence of turbulent events in the main thermocline than elsewhere concurrently we find that averaged values of exhibit a positive dependence on the buoyancy frequency n and that form an is best fit by 1 when only the data below 400 m are considered of the more than 5000 m of data collected below 1000 m depth 12 showed measurable turbulence and dominated the depth averages a deep ocean estimate of an upper bound to the eddy coefficient for vertical diffusion k is 10 4 m2 s 1 and not significantly different from the value estimated by munk the inferred dependence of the mass flux with depth indicates the relative significance of vertical mixing in the main thermocli

silicon and oxygen self diffusion in stishovite implications for stability of sio2 rich seismic reflectors in the mid mantle abstract diffusion of si and o in single crystal stishovite was examined at pressures of 14 0 21 5 gpa and temperatures of 1673 2073 k self diffusion coefficients of si dsi and o d o were determined as dsi m 2 s 2 4 10 12 exp 237 kj mol 6 0 cm 3 mol p r t and d o m 2 s 7 2 10 11 exp 263 kj mol 4 8 cm 3 mol p r t respectively where p is pressure in gpa t is absolute temperature in k and r is the ideal gas constant it was revealed that diffusion of si is approximately one order of magnitude slower than that of o and thus si is the rate controlling element for plastic deformation of stishovite si diffusion in stishovite is assessed to be at least three orders of magnitude slower than that in bridgmanite under mid mantle conditions therefore it is anticipated that highly viscous sio2 rich components subducted into the lower mantle persist as the seismic reflectors for long term without mixing up with the bridgmanite dominated surrounding mantle

the wake of hurricane allen in the western gulf of mexico abstract in august 1980 hurricane allen passed over a moored array of instruments recording current temperature and conductivity in the western gulf of mexico an alongshore surge occurred during the storm passage with the horizontal current speed reaching 91 cm s 1 in the thermocline 200 m and diminishing to 15 cm s 1 32 m above the bottom 732 m a wake of near inertial frequency internal waves commenced after the storm passed the array the alongshore current oscillation reached a maximum range of 50 cm s 1 within 3 days and decayed thereafter with a time scale of about 5 days the current oscillations were clockwise polarized and slightly elliptical with a period of 22 23 h or about 85 of the local inertial period near uniform upwelling of 20 m occurred in the thermocline region 200 300 m during the most intense part of the wake depth leading phases of the horizontal current and temperature oscillations indicated downward radiation of wake energy the wake oscillations were highly coheren

magmatic crystal stratigraphy and constraints on magma chamber dynamics laser interference results on individual phenocrysts this work reports progress in current studies of zoning of magmatic crystals from basalts and andesites a simple law of normal growth is tested using zoning profiles of olivine and plagioclase crystals and is shown to be compatible with the zoning profiles of some olivines and parts of complexly zoned plagioclases using a convenient linearizing technique in which the ratio of compositional end members is plotted against volume we can identify those parts of the zoning profile which fit a simple normal growth law this technique permits easy identification of those parts of a complexly zoned crystal which require a more complex law of growth calculations used in this modeling are similar to those previously used for olivine pearce 1984c 1987 and are now extended to plagioclase it is concluded that it is both theoretically possible and practically feasible to make inferences about the liquid in the local system from which a crystal grew by examining the detailed zoning pattern of the crystal

inferences and observations of turbulent dissipation and mixing in the upper ocean at the hawaiian ridge abstract the hawaiian ridge is one of the most energetic generators of internal tides in the pelagic ocean the density and current structure of the upper ocean at the hawaiian ridge were observed using seasoar and doppler sonar during a survey extending from oahu to brooks banks and up to 200 km from the ridge peak survey observations are used to quantify spatial changes in internal wave induced turbulent dissipation and mixing the turbulent dissipation rate of kinetic energy e and diapycnal eddy diffusivity k are inferred from an established parameterization using internal wave shear as input at the kauai channel kc and french frigate shoals brooks banks sites e and k decay away from the ridge with maxima exceeding minima by 5 times at both sites average k is everywhere greater than the canonical open ocean value of 10 5 m2 s 1 along the ridge e and k vary by up to 100 times and are largest at sites of largest numerical model internal tide energy density in the eastern kc k 10 3 m2 s

structure and dynamics of the laacher see magma chamber eifel germany from major and trace element zoning in sanidine a cathodoluminescence and electron microprobe study microtextures and zoning patterns in sanidine phenocrysts from the phonolitic laacher see tephra germany were investigated in order to constrain processes occurring in the magma chamber before eruption the laacher see tephra unit is chemically zoned and has been inferred to represent the product of eruption of an inverted layered magma chamber samples from various levels in the deposit were investigated we used a combination of textural studies optical microscopy and back scattered electron bse imaging electron microprobe emp analysis of major minor and trace elements ca na k al si ba sr fe and ti and element mapping the samples studied contain two feldspar phases and the ternary composition of the sanidine thus constrains the temperature of crystallization whereas its trace element content reflects the melt composition the large diversity in textures found in the sanidine crystals can be classified into three types composite c type pseudooscillatory po type and resorbed patchy r type trace elementpoor lamellar composite alkali feldspars c type are found in samples inferred to represent the top and the middle part of the magma chamber they grew as composite crystals from the melt at temperatures as low as 650 c in a highly differentiated and volatilerich boundary layer at the magma chamber roof or wall pseudooscillatory zoning with resorption surfaces po type is found in sanidinesfromsamplesinferredtorepresentthemiddlepartandthebase of the magma chamber repeated large an variations 1 4 mol reflect temperature variations of 100 300 ca ssociated with changes in water content variations of minor and trace elements ba sr and ti in sanidine decoupled from the pseudo oscillations of the major elements reflect chemical changes in the melt and are damped by chemicaldiffusioninthemelt bothmajorandminorelementvariations inpo typecrystalsareinterpretedastheprogressiveinfluenceofamore mafic hotter melt this may be partly explained by the settling of crystals through the thermal and chemical gradient existing in the magma chamber however the additional role of magma recharge may be required to explain the large temperature variations resorbed patchy zoned crystals r type found mainly in samples corresponding to the middle part of the magma chamber reflect early growth in a differentiated boundary layer followed by resorption and overgrowthinthemainmagmabody manyofthelaacherseesanidine crystals did not crystallize for the most part in the melt in which they were erupted in the presence of preserved major and trace element zonation in the magma this observation indicates crystal dispersion within a layered magma chamber without large scale mixing and overturn

upper ocean inertial currents forced by a strong storm part i data and comparisons with linear theory abstract a strong isolated october storm generated 0 35 0 7 m s 1 inertia frequency currents in the 40 m deep mixed layer of a 300 km 300 km region of the northeast pacific ocean the authors describe the evolution of these currents and the background flow in which they evolve for nearly a month following the storm instruments included ctd profilers 36 surface drifters an array of 7 moorings and air deployed velocity profilers the authors then test whether the theory of linear internal waves propagating in a homogeneous ocean can explain the observed evolution of the inertial frequency currents the subinertial frequency flow is weak with typical currents of 5 cm s 1 and steady over the period of interest the storm generates inertial frequency currents in and somewhat below the mixed layer with a horizontal scale much larger than the rossby radius of deformation reflecting the large scale and rapid translation speed of the storm this scale is too large for significant linear propagation of the

oceanic isopycnal mixing by coordinate rotation abstract current numerical models of oceanic circulation differentiate between the eddy diffusion and viscosity transport along the geopotential horizontal and vertical directions only in order to model the effect of anisotropic turbulence as diffusive transport along and across density surfaces the isopycnal mixing tensor has been transformed from a diagonal second rank tensor in the isopycnal coordinate system to a tensor containing off diagonal elements in the geopotential coordinate system

dipping low velocity layer in the mid lower mantle evidence for geochemical heterogeneity data from western united states short period seismic networks reveal a conversion from an s to a p wave within a low seismic velocity layer greater than or equal to the 4 percent velocity difference compared to the surrounding mantle in the mid lower mantle 1400 to 1600 kilometers deep east of the mariana and izu bonin subduction zones the low velocity layer about 8 kilometers thick dips 30 to 40 southward and is at least 500 kilometers by 300 kilometers its steep dip large velocity contrast and sharpness imply a chemical rather than a thermal origin ancient oceanic crust subducted into the lower mantle is a plausible candidate for the low velocity layer because of its broad thin extent

the analysis of zoning in magmatic crystals with emphasis on olivine many of the observed features of zoning in magmatic phenocrysts may be due to the orientation of the section rather than inherent properties of the crystals an ideal section for the studying of zoning in magmatic crystals has two characteristics it goes through the center of the crystal and is perpendicular to one or more crystal faces using a model zoned olivine crystal it is possible to construct accurate zoning profiles for different types of section centered symmetrical and skewed the probability of obtaining a random section which passes within x of the center of a crystal is shown to be p 0 0x while the probability that a random section will be within a degrees of perpendicular to a given plane is p sin a a systematic approach to the study of zoned crystals is outlined in particular it is suggested that composition be plotted against distance cubed in order to correct for the volume versus size problem a method of determining if a given section goes through or near the center of a zoned crystal is also presented the reasoning in this work applies to other types of magmatic crystals such as pyroxenes and plagioclase

vertical diffusivity of the western arctic ocean halocline a nearly year long series of upper ocean temperature conductivity and temperature microstructure profiles were collected from an ice camp drifting in the beaufort gyre as part of the 1997 1998 surface heat budget of the arctic experiment sheba geographically the record includes portions over the deep canada basin and the steep bathymetry of the chukchi borderlands region hydrographically the record includes cool pacific origin haloclines which contain a variety of subsurface temperature maxima and cold haloclines typical of the eurasian basins we present estimates of the vertical turbulent diffusivity derived from the dissipation rate of thermal variance and calculations of the associated vertical heat fluxes we find that vertical diffusion proceeds at molecular rates in the deep basins and away from topographic features while still relatively small diffusivity is enhanced by 1 order of magnitude near and above the chukchi borderlands the enhanced diffusivity is correlated to an increase in water column strain variance above the borderlands providing a linkage between bathymetry internal wave activity and turbulence the chukchi borderlands play a significant role in heat transport in the western arctic they are a pathway for horizontal heat transport and a hot spot for vertical heat transport vertical fluxes make a substantial contribution to the energy balance of the sea ice cover in this region heat fluxes between the halocline and underlying atlantic water are shown to be small and lacking vertical connection near surface waters

adiabatic temperature profile in the mantle abstract the temperature at the 410 km discontinuity is re evaluated by comparing the depth of the discontinuity with the olivine wadsleyite transition pressure obtained using in situ x ray diffraction experiments by katsura et al 2004a and equation of state eos of mgo by tange et al 2009 tange scale and matsui et al 2000 the newly estimated temperature is 1830 48 k 70 k higher than that by our previous estimation the eoses of the major mantle minerals olivine wadsleyite ringwoodite and perovskite are also recalculated using the tange scale the adiabatic temperature gradient is calculated using the thermal expansion coefficient obtained from these eoses the adiabatic temperature gradient gradually decreases with increasing depth without a phase transition and abruptly increases in association with phase transitions the adiabatic temperature gradients are found to be 04 0 5 and 0 3 k km in the upper and lower parts of the mantle respectively the temperatures at a depth of 200 km the bottom of the mantle transition zone the top of the lower mantle and a depth of 2700 km are found to be 1720 40 2010 40 1980 40 and 2730 50 k the mantle potential temperature is found to be 1610 35 k

petrogenesis of the nakhlite meteorites evidence from cumulate mineral zoning abstract a simple igneous petrogenesis for the meteorite nakhla has previously been called into question because mg fe ratios in olivine indicate substantial disequilibrium between the predominant cumulus minerals olivine and augite comparative analyses of simulated diffusive zoning and the observed cumulus mineral zoning for all three nakhlites nakhla governador valadares and lafayette show that their current compositions do not necessarily reflect parental magma compositions instead diffusion has altered primary cumulus compositions to varying degrees nakhla being the least affected and lafayette being almost completely re equilibrated only the cores of augite grains in nakhla and governador valadares appear to have preserved their original compositions mineral zoning in each meteorite is strongly concentric around mesostasis areas suggesting that reaction with intercumulus liquid has controlled the observed zoning the presence of pigeonite and orthopyroxene overgrowths in nakhla and governador valadares and of poikilitic orthopyroxene enclosing olivine relicts in lafayette indicate substantial late magmatic reactions two pyroxene geothermometry for lafayette indicates temperatures around 950 c suggesting subsolidus equilibration as well the nakhlites appear to be a series of relatively simple cumulate rocks which have undergone various amounts of late magmatic and subsolidus diffusion possibly reflecting their relative positions in a cooling cumulate pile

scale limits of free silica seismic scatterers in the lower mantle abstract lower mantle seismic scatterers are often interpreted in terms of subducted basaltic crust which should contain free silica phases that are seismically fast however free silica phases are unstable in a peridotite lower mantle as they react with ferropericlase magnesiowustite to form silicate perovskite nonetheless conservative estimates and recent measurements of diffusion coefficients in silicate perovskite suggest that free silica phases may persist as polycrystalline armored relics in lower mantle peridotite at length scales equivalent to those observed for seismic scatterers simple numerical simulations also suggest that polycrystalline silica may persist within subducted metabasalts

on the resolution of density within the earth roughly 30 years have passed since the last publication of a linear resolution calculation of density inside the earth since that time the data set of free oscillation degnerate frequencies has been completely re estimated taking into account the biassing effects of splitting and coupling due to 3d structure this paper presents a new resolution analysis based on the new data and focuses on two particular issues 1 the density jump at the inner core boundary which is important in discussions of the maintenance of the geodynamo and 2 a possible density excess in the lowermost mantle which might be indicative of a hot abyssal layer we find that the density jump at the inner core boundary is 0 82 0 18 mg m 3 which is significantly larger than previously thought we also find little support for an excess density in the lowermost mantle though an increase

p v t equation of state of stishovite up to mid lower mantle conditions 1 in situ p v t measurements of stishovite have been performed throughout its stability field from 17 to 54 gpa and from 300 to 1700 k by using a sintered diamond multianvil apparatus and synchrotron radiations the p v t equation of state of stishovite was precisely determined on the basis of the mie gruneisen debye model using both morse rydberg vinet and third order burch murnaghan equations for reference isotherms the new equation of state of stishovite gives the thermoelastic properties such as density adiabatic bulk modulus thermal expansivity and isobaric heat capacity without extrapolation to mid lower mantle conditions and these properties at zero pressures are consistent with those of previous measurements the present equation of state yields a lower density and larger adiabatic modulus at lower mantle conditions compared to those obtained by extrapolate on using a previous equation of state determined at upper mantle conditions our new equation of state and thermoelastic properties for stishovite at lower mantle conditions is important for quantitatively modeling the fate of subducted silica rich rocks such as morb and pelagic sediments and for interpreting seismological observations

estimates of m2 tidal energy dissipation from topex poseidon altimeter data most of the tidal energy dissipation in the ocean occurs in shallow seas as has long been recognized however recent work has suggested that a significant fraction of the dissipation perhaps 1 tw or more occurs in the deep ocean this paper builds further evidence for that conclusion more than 6 years of data from the topex poseidon satellite altimeter are used to map the tidal dissipation rate throughout the world ocean the dissipation rate is estimated as a balance between the rate of working by tidal forces and the energy flux divergence computed using currents derived by least squares fitting of the altimeter data and the shallow water equations such calculations require dynamical assumptions in particular about the nature of dissipation to assess sensitivity of dissipation estimates to input assumptions a large suite of tidal inversions based on a wide range of drag parameterizations and employing both real and synthetic altimeter data are compared these experiments and monte carlo error fields from a generalized inverse model are used to establish error uncertainties for the dissipation estimates owing to the tight constraints on tidal elevation fields provided by the altimeter area integrals of the energy balance are remarkably insensitive to required dynamical assumptions tidal energy dissipation is estimated for all major shallow seas excluding individual polar seas and compared with previous model and data based estimates dissipation in the open ocean is significantly enhanced around major bathymetric features in a manner consistent with simple theories for the generation of baroclinic tides

global abyssal mixing inferred from lowered adcp shear and ctd strain profiles abstract internal wave wave interaction theories and observations support a parameterization for the turbulent dissipation rate e and eddy diffusivity k that depends on internal wave shear vz2 and strain z2 variances its latest incarnation is applied to about 3500 lowered adcp ctd profiles from the indian pacific north atlantic and southern oceans inferred diffusivities k are functions of latitude and depth ranging from 0 03 10 4 m2 s 1 within 2 of the equator to 0 4 0 5 10 4 m2 s 1 at 50 70 diffusivities k also increase with depth in tropical and subtropical waters diffusivities below 4500 m depth exhibit a peak of 0 7 10 4 m2 s 1 between 20 and 30 latitudes where semidiurnal parametric subharmonic instability is expected to be active turbulence is highly heterogeneous though the bulk of the vertically integrated dissipation e is contributed from the main pycnocline hotspots in e show some correlation with small scale bottom roughness and near bottom flow at sites where st

mixing in the romanche fracture zone the romanche fracture zone is a major gap in the mid atlantic ridge at the equator which is deep enough to allow significant eastward flows of antarctic bottom water from the brazil basin to the sierra leone and guinea abyssal plains while flowing through the romanche fracture zone bottom water properties are strongly modified due to intense vertical mixing the diapycnal mixing coefficient in the bottom water of the romanche fracture zone is estimated by using the finestructure of ctd profiles the microstructure of high resolution profiler data and by constructing a heat budget from current meter data the finestructure of density profiles is described using the thorpe scaleslt it is shown from microstructure data taken in the bottom water that the ozmidov scale lo is related to lt by the linear relationship lo 5 0 95lt similar to other studies which allows an estimate of the diapycnal mixing coefficient using the osborn relation the thorpe scale and the diapycnal mixing coefficient estimates show enhanced mixing downstream eastward of the main sill of the romanche fracture zone in this region a mean diapycnal mixing coefficient of about 1000 3 1024 m2 s21 is found for the bottom water estimates of cross isothermal mixing coefficient derived from the heat budgets constructed downstream of the current meter arrays deployed in the romanche fracture zone and the nearby chain fracture zone are in agreement with the finestructure estimates of the diapycnal mixing coefficient within the romanche fracture zone although the two fracture zones occupy only 0 4 of the area covered by the sierra leone and guinea abyssal plains the diffusive heat fluxes across the 1 4 8c isotherm in the romanche and chain fracture zones are half that found over the abyssal plains across the 1 88c isotherm emphasizing the role of these passages for bottom water property modifications

phase transition and density of subducted morb crust in the lower mantle abstract phase relations mineral chemistry and density of a natural mid oceanic ridge basalt morb composition were investigated up to 134 gpa and 2300 k by a combination of in situ x ray diffraction measurements and chemical analyses using transmission electron microscope tem results demonstrate that the morb composition consists of mgsio 3 rich perovskite stishovite casio 3 perovskite and cafe 2 o 4 type al phase in the upper part of the lower mantle the most abundant mineral of mgsio 3 rich perovskite undergoes phase transition to a cairo 3 type post perovskite phase above 110 gpa and 2500 k post perovskite phase is similar in composition to perovskite except considerably high na 2 o content stishovite transforms to cacl 2 type sio 2 phase above 62 gpa and 2000 k and further to pbo 2 type phase above 110 gpa pbo 2 type sio 2 phase includes large amount of al 2 o 3 which significantly expands its stability relative to cacl 2 type phase phase transition of casio 3 perovskite from tetragonal to cubic was also observed with increasing temperature cafe 2 o 4 type al phase is stable to the bottom of the mantle the density of morb crust was calculated using volume data combining with measured chemical compositions and calculated mineral proportions the former morb crust is denser than the average lower mantle at all depths greater than 720 km contrary to earlier predictions the subducted basaltic crust may have accumulated at the base of the mantle

response of the deep ocean internal wave field to traveling midlatitude storms as observed in long term current measurements it has been demonstrated in a recent numerical experiment that double inertial frequency internal waves may play a crucial role in diapycnal mixing processes in the deep ocean with the energy effectively transferred across the internal wave spectrum down to small dissipation scales by nonlinear wave wave interactions hibiya et al 1998 to examine whether or not such double inertial frequency waves are actually generated in the real deep ocean current meter data from long term moorings in the northwest pacific basin are analyzed together with global sea surface wind data by incorporating the wind data into a simple damped slab model predominant inertial currents are shown to be excited in the mixed layer in the northwest pacific basin by traveling midlatitude storms during fall and winter the multiple filter analysis demonstrates that double inertial frequency waves as well as near inertial frequency waves are significantly amplified in the deep ocean internal wave field during the periods strong inertial currents are excited in the mixed layer this suggests that in addition to near inertial frequency waves double inertial frequency waves are actually excited by strong atmospheric disturbances through nonlinear effects as demonstrated in the numerical experiment by niwa and hibiya 1997 double inertial frequency waves thus excited seem to propagate over horizontal distances of the order of 1000 km from their source region while feeding their energy to the local internal wave field consistent with the theoretical prediction based on the magnitudes of group velocity and nonlinear interaction time olbers 1983

a scattering region near the core mantle boundary under the north atlantic summary we analysed pcp precursors in seven events from central america recorded at the uk array of short period stations to determine the most likely source of this signal combinations of observations of slowness traveltime and backazimuth were used to investigate the properties of the phase with the result that its source is identified as p to p scattering from an anomalous region in the lower mantle within d using a joint likelihood method the best estimate of a point source for scattering is at 44 0 n 71 5 w under nova scotia and 2720 km depth analysis of the spectrum of the scattered signal indicates that the region contains small scale heterogeneities on the order of 0 6 to 0 7 km and is 700 km in size the velocity contrast between the scattering bodies and ambient mantle is as high as 0 4 to 0 7 per cent vp and 1 4 to 6 6 per cent vs on account of their small size positive velocity anomaly and association with the reconstructed position of ancient subducted material we conclude that they represent chemical heterogeneity in the lower mantle

the theory of zoning patterns in magmatic minerals using olivine as an example a theory of simple zoned growth in magmatic minerals is developed using olivine as an example the law of growth in absolute feo mgo space has the form y0 ys a x0 xs k where x refers to feo y refers to mgo and the subscript s refers to the solid phase x0 and y0 are the starting amounts in the liquid a is a constant which characterizes each individual liquid line of descent and k is the distribution coefficient consideration of this equation shows that the size of the local system is the most important parameter affecting the shape of the zoning pattern the starting ratio mgo feo is the next most important magmatic parameter and k is the most tightly constrained and therefore the least important parameter affecting the pattern of zoning an empirical relationship plotting mgo feo in the crystal versus the volume of the crystal linearizes the zoning pattern allowing prediction of the fictive volume of the crystal and the diameter of the system from which the crystal grew model calculations show an error of 7 or less in determining the linear dimensions of the system on a linearized plot the starting composition of the crystal may be determined by extrapolation even if the section does not go through the center analysis of zoning profiles using this theoretical law of growth may be useful in studies of crystal growth rates nucleation mechanisms diffusion rates and viscosity of natural melts

determination of diapycnal diffusion rates in the upper thermocline in the north atlantic ocean using sulfur hexafluoride 1 the apparent diapycnal diffusivity below the wind driven surface mixed layer of the ocean was determined in an anticyclonic eddy in the eastern north atlantic using sulfur hexafluoride sf6 tracer data collected in june 1998 in this tracer experiment the downward penetration of sf6 was measured for 3 weeks following the deliberate injection of sf6 in the surface mixed layer the resulting data were used to constrain the one dimensional fickian diffusion model to estimate the diapycnal diffusivity the model also includes the lateral diffusion component so that it can more accurately represent the time evolution of the sf6 concentrations along the isopycnal surface this affects the estimation of the diapycnal diffusivity for the upper thermocline immediately below the surface mixed layer we estimated the diapycnal diffusivity for the 3 week period as 0 3 0 2 cm2 s 1 at a buoyancy frequency of 8 2 cph

olivine phenocrysts of hawaiian olivine tholeiite and oceanite olivine phenocrysts of hawaiian tholeiites display a variety of textures and a variation in composition which is due to supercooled crystallization the highest forsterite content measured is 91 and the highest magnesia content estimated for a tholeiitic liquid is 17 using the olivine geothermometer the liquid of this composition may be either a primary magma or a primitive magma it is not yet possible to specify any particular composition range for the primary hawaiian tholeiites

inferences of mantle viscosity based on ice age data sets radial structure we perform joint nonlinear inversions of glacial isostatic adjustment gia data including the following postglacial decay times in canada and scandinavia the fennoscandian relaxation spectrum frs late holocene differential sea level dsl highstands based on recent compilations of australian sea level histories and the rate of change of the degree 2 zonal harmonic of the geopotential j2 resolving power analyses demonstrate the following 1 the frs constrains mean upper mantle viscosity to be 3 1020 pa s 2 postglacial decay time data require the average viscosity in the top 1500 km of the mantle to be 1021 pa s and 3 the j2 datum constrains mean lower mantle viscosity to be 5 1021 pa s to reconcile 2 and 3 viscosity must increase to 1022 1023 pa s in the deep mantle our analysis highlights the importance of accurately correcting the j2 observation for modern glacier melting in order to robustly infer deep mantle viscosity we also perform a large series of forward calculations to investigate the compatibility of the gia data sets with a viscosity jump within the lower mantle as suggested by geodynamic and seismic studies and conclude that the gia data may accommodate a sharp jump of 1 2 orders of magnitude in viscosity across a boundary placed in a depth range of 1000 1700 km but does not require such a feature finally we find that no 1 d viscosity profile appears capable of simultaneously reconciling the dsl highstand data and suggest that this discord is likely due to laterally heterogeneous mantle viscosity an issue we explore in a companion study

satellite observations of phytoplankton enrichments around seamounts in the south west indian ocean with a special focus on the walters shoal abstract spatial anomalies associated with seamounts and islands have been detected in the south west indian ocean using a new surface chlorophyll a based enrichment index ei calculated from daily l3 4 km modis chl a data from 2003 to 2018 the ei was used to quantify recurrent seasonal surface enrichment associated with these features most notable were the shallow walters shoal 18 m and nearby deeper ws 2 seamount 480 m both located on the southern madagascar ridge which showed high ei values of 40 and 15 local enhancement tromelin island east of madagascar exhibited more moderate values of 15 local increase other shallower seamounts including la perouse 60 m and mad ridge 240 m exhibited sporadic or no measurable surface maxima regions of strong mesoscale activity such as south of madagascar where the south east madagascar current detaches from the continent also revealed high ei values a marked seasonality of the ei was observed over the walters shoal with higher values during the oligotrophic season than in the austral winter the seasonal variability of the mld in combination with the seamount bathymetry appears to induce the thermal and biological anomalies observed there possibly favoured by the presence of a taylor cap at the summit ship collected in situ measurements showed the satellite observed enrichment to be associated with shallowing of the deep chlorophyll maximum as well as a shift of phytoplankton groups towards diatoms and small flagellates no net increase of integrated chl a was measured but a potential doubling in primary productivity is expected the ei developed in this study designed to reveal sporadic small localised chl a maxima is likely applicable to other areas in the ocean where there is local enrichments

seismic evidence for small scale heterogeneity throughout the earth s mantle details in the amplitude structure of short period precursors to the seismic core phase pkp can be used to constrain the depth extent of mantle scattering the simplest model consistent with the observations invokes small 8 km weak r m s velocity perturbations of 1 random heterogeneities uniformly distributed throughout the mantle the data do not support previously proposed models that place an increase in the concentration of scattering sites near the base of the mantle and instead place an upper limit on the amplitude of any short wavelength topography at the core mantle boundary

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

subparallel dipping heterogeneities in the mid lower mantle 1 data from western u s short period seismic networks show anomalous later phases which we interpret as s to p converted waves from heterogeneities in the mid lower mantle depths of 1000 1850 km northeast of the mariana subduction zone the geometry of the objects is mapped by a two step approach 1 computing the s to p scattering likelihood with the arrival time slowness and azimuth of the later arrivals measured by array techniques relative to direct p waves and 2 by direct use of the waveforms using semblance at least three subparallel objects are detected in the lower mantle study region with the dips of 30 to 40 southward and with a lateral extent larger than 500 km by 300 km the elastic properties associated with the heterogeneous objects appear to change within several kilometers considering their high efficiency at converting short period waves wavelengths of 5 10 km previous seismic tomography studies have not predicted significant velocity anomalies around the heterogeneities this is probably because they are below the resolution limit of present methods the three major heterogeneities are separated from each other nearly 300 km vertically and significant anomalies seem absent between each object nevertheless semblance cross sections with a finer grid size 0 1 0 1 10 km of the clearest intermediate object at 1400 1600 km show a hint that the object is not a single interface but is actually composed of double interfaces nearly 50 km apart purely thermal anomalies of kilometers scale must be transient features in the mantle and thus are highly unlikely to be the cause of the heterogeneities they should rather represent either sharp chemical variations in major element composition or sharp changes in preferred orientations of anisotropic lattice of the lower mantle minerals thermal anomalies however may be superimposed on such variations because of heat generation either by concentrated radioactive nuclei or by viscous shear heating due to deformations a plausible tectonic interpretation of these dipping objects is that they represent remnants of subducted lithospheric plates which preceded the current subduction of the pacific plate although we cannot make conclusive arguments on what the mechanism of creating such heterogeneities from these observations alone we suggest that they may represent stretched thinned and duplexed rocks within chaotic mantle flows

an analysis of large scale variations in small scale mantle heterogeneity using global seismographic network recordings of precursors to pkp high frequency precursors to the core phase pkp are caused by scattering off heterogeneities in the lowermost mantle and d regions and they provide a unique window into the small scale structure of the deep earth we study lower mantle scattering by analyzing 412 high quality pkp precursor records at ranges between 120 and 137 5 as obtained from the global seismic networks during the last 10 years to examine regional variations in scattering strength we compare individual records with the globally averaged pkp precursor stack of hedlin et al 1997 we identify strong differences in apparent scattering strength among specific source receiver paths inversion of these data for scattering source regions is complicated by ambiguity between source and receiver side scattering and the sparse and uneven data coverage synthetic tests however suggest that inversions with applied smoothness constraints can resolve large scale differences in scattering strength over significant parts of the lower mantle we use a conjugate gradient method based on an approximation to rayleigh born scattering theory to image differences in the average strength of scattering within the lowermost 1000 km of the mantle our results indicate particularly strong scattering beneath central africa parts of north america and just north of india whereas weaker scattering is seen beneath south and central america eastern europe and indonesia some regions of strong scattering correlate roughly with large scale anomalies revealed by seismic tomography including the african plume and the tethys trench these correlations are tentative rather than definitive because bootstrap resampling tests show that many details in our model are not reliably resolved and the network data alone do not permit complete resolution of the source receiver ambiguity in all areas further progress in this area will require integration of available network recordings with data collected by regional networks and arrays and consideration of the phase velocity of the precursors as well as their temporal variations

low viscosity mantle blobs are sampled preferentially at regions of surface divergence and stirred rapidly into the mantle the persistence of mantle heterogeneity depends on its density and viscosity and as well as the characteristics of the convecting mantle such as the vigour and possible stratification of convection low viscosity regions stretch and deform more rapidly than their high viscosity counterparts low viscosity regions are also drawn into and hence preferentially sampled at regions of surface divergence such as mid ocean ridges and plume fed hotspots low viscosity heterogeneities in the form of blobs are thus more rapidly stirred into a convecting mantle discrete blobs of primitive or enriched mantle are unlikely to persist for billions of years

near boundary mixing above the flanks of a midlatitude seamount fine scale velocity and density profile data with concurrent turbulent velocity and temperature dissipation estimates obtained above the flanks of fieberling guyot a seamount in the eastern north pacific ocean are examined for evidence of near bottom boundary mixing fine scale shear and strain spectral levels were elevated over the flanks of the seamount in a 500 m thick stratified layer above the bottom the velocity shear was horizontally isotropic clockwise and counterclockwise with depth shear spectral levels were comparable and no significant correlation between shear and strain was observed above the steepest bottom slopes near the seamount summit rim excess vertical strain relative to shear was observed as compared to the background internal wave field suggesting the presence of high frequency internal waves these signals may have been the product of wave reflections from the steep flanks of the seamount and or wave generation from tidal currents flowing over the rough bottom associated with the enhanced shears and strains were more frequent occurrences of low 10 m richardson number events increased overturning scales and larger estimated turbulent eddy diffusivity relative to observations 15 km or more from the seamount in particular turbulent diffusivity estimates increased from o 0 1 10 4 m2 s 1 in the ocean interior to 1 5 10 4 m2 s 1 within 500 m vertically 1 3 km horizontally of the seamount flank a simple geometric scaling argument suggests that boundary mixing of this intensity has relevance to the large scale circulation at abyssal depths where a large fraction of the ocean waters is in close proximity to the bottom

zagami product of a two stage magmatic history abstract large specimens of the zagami shergottite show highly varied grain sizes and mineral abundances on a cm scale and preferred alignment of pyroxene laths we document the presence of whitlockite and of melt veins and pockets of shock origin pyroxene crystals have homogeneous mg rich pigeonite and augite cores overgrown by fe rich zoned pyroxene mostly pigeonite rims amphibole bearing magmatic melt inclusions occur exclusively in the cores we conclude that zagami experienced a twostage crystallization history the first stage occurred in a deep seated slowly cooling magma chamber there the homogeneous mg rich cores of the pyroxenes crystallized during relatively slow cooling the deep seated origin of the cores is also indicated by the presence of amphibole within them which requires pressures of formation equivalent to crystallization at depths 7 5 km on mars modest abundance of homogeneous mg rich cores 15 20 indicates that crystal settling did not play a significant role in this part of the magma chamber during the second stage the mg rich pyroxenes were entrained into a magma that either intruded to the near surface and cooled in a relatively thin dike or sill or extruded to the surface and crystallized in a lava flow 10 m thick again without indications for crystal settling this scenario is suggested by estimates of cooling rates of 0 1 0 5 c h based on sizes of the plagioclase maskelynite crystals and of 0 02 c h based on the width of pyroxene exsolution lamellae brearley 1991 irregular shapes of the mg rich cores result from resorption and possible solid state diffusion and the shapes and sizes of the pyroxenes after crystallization of fe rich pigeonite rims onto the cores were strongly controlled by the shapes and sizes of the cores the finer grained areas of the rock inherited smaller and more numerous mg rich pyroxene cores from the first stage than did the coarser grained areas crystallization of both augite and pigeonite cores at depth but mostly pigeonite rims in the nearsurface environment may be the result of a phase boundary shift and expansion of the pigeonite stability field at lower pressures the estimated depth of the magma chamber for zagami of 7 5 km and thickness of the putative lava flow of 10 m are consistent with calculations and observations of volcanic constructs and flows in the tharsis region of mars

lower mantle scattering profiles and fabric below pacific subduction zones abstract the earth s mantle is compositionally evolving principally through the process of mid ocean ridge basalt production 95 by lithospheric area but also by way of arc magmatism 5 and continental growth reymer a schubert g 1984 phanerozoic addition rate to the continental crust and crustal growth tectonics 3 63 77 rowley d b 2002 rate of plate creation and destruction 180 ma to present geol soc am bull 114 927 933 convection eventually must mix these products back into the mantle but the details of the mixing process are unknown we report here new observational data documenting the location of differentiated material in the present day lower mantle and scattering power profiles with depth small scale 10 km objects which efficiently scatter short period s waves are present in the mantle lying below the pacific ocean rim at depths between 1100 and 1800 km we also observe a reduction in scattering power with depth indicating that the objects represent bodies richer in differentiated basalt than the surrounding mantle the scattering objects appear to be deformed to various degrees and usually form clusters separated from each other by a distance of 100 to 200 km the clusters probably represent folds of the order of 100 km probably corresponding to early stage of mixing process because the scattering power does not increase with depth neither does a permanent barrier to flow exist in the mid mantle nor does the intrinsic density of basalt prevent re entrainment into mantle flow from the bottom of the mantle

suspension in convective layers and style of differentiation of a terrestrial magma ocean recent physical theories for the formation of the earth suggest that about 4 5 b y ago the mantle of the earth was partially or completely molten fractional crystallization of this hypothetical magma ocean would result in a strong chemical stratification of the earth s mantle such a scenario is controversial from the geochemical point of view however it has been noted that the simple scenario of fractional crystallization could be avoidable in a convective magma ocean if crystals remain suspended in this paper the problem of suspension is developed with the help of an energetic approach convection must do some work against gravitational settling we distinguish three regimes of convective suspensions absolute or complete sedimentation occurs when the energy dissipation due to the settling exceeds the heat loss from the convective layer this is possible only in large scale systems like magma oceans and implies that cooling can proceed only together with sedimentation crystallization and a decrease in the liquidus temperature at a constant pressure a regime of partial differentiation occurs when the energy dissipation due to the settling is less than the total heat loss but larger than the power which can be spent by convection on the crystal reentrainment process the differentiation is not complete and a competition between the rate of cooling the rate of sedimentation and the rate of turbulent diffusion determines the degree of differentiation the third regime is an absolute suspension which could be sustained for an indefinitely long time in this case sedimentation starts only when the crystal fraction reaches the maximum packing value when the viscosity of the magma rapidly increases the power which can be spent by convection on reentrainment is equal to e gd cp of the total energy supply to the convective layer where e 15 gpa or 10 3 10 1 cm during crystallization of shallow layers the first regime fractional crystallization is unavoidable the estimates depend on various poorly constrained parameters and processes such as heat flux viscosity thermodynamical disequilibrium and highly variable viscosity convection for absolute suspension the crystal size must be at least e times less or 10 3 10 1 cm and 10 4 10 2 cm respectively if e 0 01 the partial differentiation occurs in a narrow one decade range between these two regimes the radius of about 1 cm must be considered as an absolute upper bound above which fractional differentiation is guaranteed these estimates for the critical crystal size are orders of magnitude lower than suggested previously and thus the problem of crystal sizes becomes a central one for magma oceans a necessary condition for reentrainment is the existence of local mechanisms the absence of such mechanisms to reentrain the particles from the bottom would mean that an absolute suspension is impossible even if the energetics allows it turbulence is considered as a possible important factor a simple model of convection predicts a strong turbulence provided the viscosity is less than 10 9 10 10 p rotation reduces this critical viscosity to 10 5 10 8 p but this is still sufficiently large and is reached only near the maximum packing crystal fraction power law or bingham rheology of partial melts can exclude any turbulence already at 20 30 of crystal fraction we also show that the energetic criterion for the absolute suspension with e 1 coincides with the condition that the particle concentration gradient suppresses the turbulence

the origin of garnets in andesitic rocks from the northland arc new zealand and their implication for sub arc processes an unusual andesitic suite from the miocene volcanic arc in northland new zealand comprises pyroxene andesite and garnetbearing hornblende pyroxene hornblende and biotite hornblende andesites garnet crystals occur as 1 10 mm single crystals or more commonly as two or more annealed crystals and as garnetite lenses the andesitic rocks also contain enclaves of high mgo pyroxenite hornblendite and pyroxene hornblende gabbro as well as highal2o3 hornblende gabbro garnet hornblende gabbro and anorthosite garnet crystals in the andesitic volcanic rocks and in the enclaves show comparable compositional ranges zoning patterns and inclusions which indicate that they share a common petrogenetic history they can be grouped into four distinct types on the basis of mode of occurrence chemical composition and zoning patterns which leads to their interpretation as antecrysts rather than orthocrysts the compositions of the garnets as well as their included mineral assemblages reflect a petrogenetic trend from high temperature pyroxene bearing high mg garnet to low temperature fe rich garnet at relatively constant pressure well preserved zoning patterns in particular those of the caand mg rich garnets reflect processes within a deep crustal arc environment later assimilation is suggested by some zoning patterns that show decreasing ca and increasing fe and mn contents the garnets are interpreted as being derived by disintegration of discrete but closely related cumulate material that formed at pressures of 8 10 kbar the host volcanic rocks and their garnet crystals together with the enclaves thus represent a consanguineous mixture of liquid and solid components that developed where subduction related magmas ponded and interacted at or near the base of the crust together they represent a rare snapshot of the processes and components that produce arc type rocks

a model of metal silicate separation on growing planets abstract the thermal evolution of planets during their accretionary growth is strongly influenced by impact heating the temperature increase following a collision takes place mostly below the impact location in a volume a few times larger than that of the impactor impact heating depends essentially on the radius of the impacted planet when this radius exceeds 1000 km the metal phase melts and forms a shallow and dense pool that penetrates the deep mantle as a diapir to study the evolution of a metal diapir we propose a model of thermo chemical readjustment that we compare to numerical simulations in axisymmetric spherical geometry and with variable viscosity we show that the metallic phase sinks with a velocity of order of a stokes velocity the thermal energy released by the segregation of metal is smaller but comparable to the thermal energy buried during the impact however as the latter is distributed in a large undifferentiated volume and the former potentially liberated into a much smaller volume the diapir and its close surroundings a significant heating of the metal can occur raising its temperature excess by at most a factor of 2 or 3 when the viscosity of the hot differentiated material decreases the proportion of thermal energy transferred to the undifferentiated material increases and a protocore is formed at a temperature close to that of the impact zone

cracking the olivine zoning code distinguishing between crystal growth and diffusion olivine composition and zoning patterns are widely used to reconstruct the evolution of mafic magmas from source to surface and to extract time scales of magmatic processes deciphering the olivine zoning code is challenging because the contributions of growth and diffusion may overlap a detailed multielement fe mg p al and ni examination of zoning in an exceptional olivine with skeletal morphology allows unequivocal discrimination between these two processes using simple but powerful geometrical arguments olivine crystals initially grow rapidly and diagonally from corner locations whereas diffusion effectively tracks mutually perpendicular crystal lattice orientations generating the zoning patterns for our case study olivine required at least 4 5 months of diffusive reequilibration of fe mg further demonstrating that crystal morphologies produced by rapid growth can survive at magmatic temperatures for extended periods no significant major element zoning is preserved after rapid growth lending further credibility to time scales retrieved via diffusion modeling extending multielement approaches to decoding olivine zoning patterns can help determine whether the kinetic relationship between growth and diffusion induced zoning recognized herein is widely applicable such studies will improve our understanding of time scales of magma storage solidification mixing and or transit toward the surface

onset of small scale instabilities at the base of the lithosphere scaling laws and role of pre existing lithospheric structures summary numerical simulations of 2 d rayleigh benard convection are designed to study the devel opment of convection at the base of the cooling lithosphere a zero temperature is suddenly imposed at the mantle surface which has initially a homogeneous temperature the strongly temperature dependent viscosity fluid is heated from within in order to balance the internal temperature drift resulting from global fluid cooling for a while the lithosphere cools approx imatively as a conductive half space and the lithospheric isotherms depth grows as the square root of age as instabilities progressively develop at the base of the lithosphere lithospheric cooling departs from the half space model we propose two different parametrizations of the age of the first dripping instability using boundary layer marginal stability or quantifying the characteristic timescale of the instability exponential growth as a function of the rayleigh number and of the viscous temperature scale both parametrizations account very well for our numerical estimates of onset times but with a slightly better adjustment of the viscous tem perature scale dependence in the second case the absolute value of the onset time depends on the amplitude and location of initial temperature perturbations within the box and on the initial temperature structure of the thermal boundary layer tbl furthermore thermal perturba tions of finite amplitude located within the lithosphere such as the ones induced by transform faults for example strongly reduce the age of the first dripping instability however the onset time parametrization derived from transient cooling experiments well adjusts the lithospheric age of the first drip instability below a lithosphere cooling perpendicularly to the ridge axis this study emphasizes the role of the initial topography of the lithospheric isotherms on the development of instabilities

a two level wind and buoyancy driven thermocline model abstract a simple two level model is designed to simulate the thermocline equations applicable for large scale steady oceanic flow the model serves two functions first it replaces problems with the interpretation of slablike dynamics e g luyten et al 1983 by using continuously horizontally varying buoyancy but at the cost of reducing the vertical resolution drastically the equations used are geostrophy plus a small linear drag to close a stommel like western boundary layer mass conservation and buoyancy conservation with a small but necessary horizontal diffusion inclusion of vertical diffusion has little effect the ocean is driven by an ekman layer whose functions are to provide a given surface input of mass through ekman pumping and buoyancy through a specified buoyancy in the ekman layer i e to maintain the same boundary conditions as in classical thermocline studies sidewall conditions are not well understood and are almost certainly over specified in this formulation s

a basinwide estimate of vertical mixing in the upper pycnocline spreading of bomb tritium in the north pacific ocean abstract the vertical diffusivity kv in the upper half kilometer of the north pacific subtropical pycnocline is estimated from observations of the spreading rate of anthropogenic tritium the calculation is based on approximately 300 ocean tritium profiles made since tritium was introduced to the atmosphere via bomb testing in the 1960s the data coverage does not permit detailed mapping of tritium penetration especially in the sparsely sampled western pacific for this reason and to minimize advective effects the spreading rate is averaged within the closed streamlines of the subtropical gyre spanning 5 n to 40 n the result kv 1 5 0 7 10 5 m2 s 1 is consistent with inferences from microstructure and purposefully released tracer measurements in the north atlantic confirming that the spatially averaged rate of mixing in the upper pycnocline is substantially lower than the canonical munk estimate for the lower pycnocline

acoustic velocity measurements for stishovite across the post stishovite phase transition under deviatoric stress implications for the seismic features of subducting slabs in the mid mantle understanding effects of non hydrostatic pressure on phase transitions in minerals relevant to the earth s mantle is important to translate the observable seismic signals to not directly observable mineralogical models for the deep earth sio 2 can occur as a free phase in subducting slabs which contain sedimentary layers and or mid ocean ridge basalts in this study we report on the effect of deviatoric strain on the pressure induced phase transition in sio 2 and its consequences on the seismic signal the acoustic velocity in polycrystalline stishovite across the post stishovite phase transition was measured by brillouin scattering in the pure sio 2 system at room temperature under deviatoric stress high pressure synchrotron x ray diffraction data were also collected at spring 8 a linear fit to the symmetry breaking strain values and the pressure of the transverse velocity minimum indicate a transition pressure between 25 and 35 gpa which is about 20 gpa lower than that under hydrostatic conditions the transverse velocity dropped by about 3 at around 25 gpa in this study this is much smaller than the prediction from ab initio calculations that a transverse velocity reduces by 60 at around 50 gpa under hydrostatic conditions the results of the present study indicate that the deviatoric stress lowers the transition pressure and reduces the acoustic velocity change associated with the post stishovite phase transition sedimentary and mid ocean ridge basalt morb layers in a subducting slab are likely sites for finding stishovite and its high pressure polymorphs in the deep earth seismic observations of deep earthquakes occurring in subducting slabs indicate the existence of considerable stress in down going slabs this study suggests that nonhydrostatic deviatoric stress is one of the possible reasons for the absence of general seismic features that can be directly related to the post stishovite phase transition in subducting slabs at 1500 km depth the phase transition of stishovite under deviatoric stress which occurs at shallower depths can affect the local seismic scattering structures and the rheological behavior of a subducting slab in the mid lower mantle region

boundary mixing and the dynamics of three dimensional thermohaline circulations boundary mixing is implemented in an ocean general circulation model such that the vertical mixing coefficient ky is nonzero only near side boundaries and in convection regions the model is used in a highly idealized configuration with no wind forcing and very nearly fixed surface density to investigate the three dimensional dynamics of the thermohaline circulation for ky 5 20 3 1024 m2 s21 and lower the meridional overturning strength to great accuracy is proportional to meridional heat transport is proportional to the circulation 2 3 1 2 kk y y patterns resemble those from runs with uniform vertical mixing but vertical motion is entirely confined to the boundary regions near the western boundary there is upwelling everywhere near the eastern boundary there is a consistent pattern of downwelling above upwelling with downwelling reaching deeper at high latitudes this pattern is explained by convection and vertical advective diffusive balance underneath for ky 5 30 3 1024 m2 s21 and higher no steady solutions have been found the meridional overturning oscillates on a timescale of about 25 years a time averaged thermally direct overturning cell is not supported dynamically because convection extends longitudinally across the entire basin and upwelling near the western boundary does not lead to densities higher than at the eastern boundary assuming uniform upwelling in the west level isopycnals near the equator and level isopycnals along the eastern boundary south of the outcropping latitude permits the analytic determination of convection depth at the eastern wall and hence the density difference between the eastern and western walls this difference is at most one quarter the surface density difference between high and low latitudes and agrees in magnitude and latitudinal dependence with the numerical experiments scaling arguments estimate overturning strength as of the order of 10 3 106 m3 s21 and confirm the 2 3 power dependence onky the derivation also gives a dependence of overturning strength with latitude that agrees qualitatively with the numerical results the scaling for the dependence of meridional heat transport on latitude agrees well with the model results scaling for heat transport amplitude agrees less well but correctly predicts a weaker dependence on ky than maximum overturning