influence of sea ice on the thermohaline circulation in the arctic north atlantic ocean a fully prognostic coupled ocean ice model is used to study the sensitivity of the overturning cell of the arctic north atlantic system to sea ice forcing the strength of the thermohaline cell will be shown to depend on the amount of sea ice transported from the arctic to the greenland sea and further to the subpolar gyre the model produces a 2 3 sv increase of the meridional circulation cell at 25n at the simulation year 15 corresponding to a decrease of 800 km in the sea ice export from the arctic previous modeling studies suggest that interannual and decadal variability in sea ice export of this magnitude is realistic implying that sea ice induced variability in the overturning cell can reach 5 6 sv from peak to peak

geochemistry of laterites stability of al goethite al hematite and fe super 3 kaolinite in bauxites and ferricretes an approach to the mechanism of concretion formation

al substituted goethite an indicator of pedogenic and other weathering environments in south africa abstract over 200 goethite containing samples from widely diverse environments along the eastern seaboard of south africa were examined and described mainly by x ray powder diffraction xrd aluminium substituted goethites ranging from 0 to about 32 mole alooh were identified mainly by xrd line shift and chemical extraction they occur in every soil zone and major soil type in one or other form from sources such as 1 non hydromorphic highly weathered strongly acid soils ferruginous bauxites saprolites and moderately weathered moderately acid soils environments 2 hydromorphic environments mottles concentrations pipe stems crusts ferricretes geodes and 3 crusts in calcareous environments these goethites formed in different climatic and weathering environments were grouped according to their amount of al substitution and crystallinity as determined by xrd line broadening al substitution in goethite formed in hydromorphic moderately acid soils and calcareous environments was generally low 0 15 mole goethite formed in non hydromorphic highly weathered environments was generally high in al substitution 15 32 mole and increased in the following order saprolites and strongly acid freely drained soils this study showed that the degree of al substitution and crystallinity of goethites may reflect the environment in which they have formed and serve as an indicator of soilforming processes

elastic thickness of the iranian lithosphere from gravity and seismic data abstract we estimate the effective elastic thickness of the iranian lithosphere and adjoining tectonic plates by using the approach that combines the vening meinesz moritz s vmm regional isostatic principle with the isostatic flexural model formulated based on solving a flexural differential equation for a thin elastic shell to model the response on a load more realistically we also consider the lithospheric density structure the resulting expression describes a functional relation that links gravity field and mechanical properties of the lithosphere the young modulus and the poisson ratio are computed from seismic velocity data in prior of estimating the lithospheric elastic thickness the presented results reveal that the estimated elastic thickness closely resembles a regional tectonic configuration associated with the extensional tectonism along the red sea gulf rift system the continental collision of the arabian and eurasian plates and the subduction along the makran subduction zone seismically and volcanically active convergent tectonic margins of the zagros and kopeh dagh fold and thrust belts further extending along the makran accretionary complex are characterised by a low lithospheric strength with the elastic thickness typically less than 30 km these small values of the elastic thickness are in a striking contrast to much larger values within most of the central iranian blocks according to our estimate local maxima there reach 70 km in the tabas micro block the elastic thickness of the turan and arabian platforms reaches maxima of 100 km these results generally support the hypothesis that tectonically active zones and orogens have a relatively low strength resulting in a significant response of the lithosphere on various tectonic loads compared to a significant strength of old cratonic formations interestingly however we observe a striking contrast between a low strength of the arabian shield compared to a high strength of the arabian platform a possible explanation of this finding could be given by a different thermal regime of the arabian lithosphere controlled mainly by a mantle upwelling and a consequent extensional tectonism along the red sea gulf rift system

winter upper ocean stability and ice ocean feedbacks in the sea ice covered southern ocean abstractin this study under ice ocean data from profiling floats instrumented seals and shipboard casts are used to assess wintertime upper ocean stability and heat availability in the sea ice c

geophysical investigation of lithosphere structure beneath sri lanka using surface and internal load variations this paper describes a method for interpreting the lateral changes in the geological structure of the lithosphere by iteratively calculating the spatial variation of a bottom to top loading ratio we use forsyth s coherence method based on multi taper spectral analysis on overlapping window areas we discuss the geological findings and their comparison with existing geological interpretations for the sri lankan region the low thickness of the elastic plate in the sri lankan region suggests a high geothermal gradient the lithospheric geological structure beneath the sri lankan region is consistent with the main crustal units of sri lanka which belong to different ancient plates together with interpretations based on metamorphic rock units our findings support the existence of thrust contact in the central highlands of sri lanka

expressions for the global gravimetric moho modeling in spectral domain we apply a newly developed numerical method to improve the moho geometry by the implementation of gravity data this method utilizes expressions for the gravimetric forward and inverse modeling derived in a frequency domain methods for a spectral analysis and synthesis of the gravity field and crust density structures are applied in the gravimetric forward modeling of the consolidated crust stripped gravity disturbances which have a maximum correlation with the a priori moho model these gravity disturbances are obtained from the earth s gravity disturbances after applying the topographic and stripping gravity corrections of major known anomalous crust density structures in the absence of a global mantle model mantle density heterogeneities are disregarded the isostatic scheme applied is based on a complete compensation of the crust relative to the upper mantle density the functional relation is established between the unknown moho depths and the complete crust stripped isostatic gravity disturbances which according to the adopted isostatic scheme have theoretically a minimum correlation with the moho geometry the system of observation equations which describes the relation between spherical functions of the isostatic gravity field and the moho geometry is defined by means of a linearized fredholm integral equation of the first kind the moho depths are determined based on solving the gravimetric inverse problem the regularization is applied to stabilize the ill posed solution this numerical procedure is utilized to determine the moho depths globally the gravimetric result is presented and compared with the seismic moho model our gravimetric result has a relatively good agreement with the crust2 0 moho model by means of the rms of differences of 3 5 km however the gravimetric solution has a systematic bias we explain this bias between the gravimetric and seismic moho models by the unmodelled mantle heterogeneities and uncertainties in the crust2 0 global crustal model

effect of upper mantle density structure on moho geometry a constant value of the moho density contrast is often assumed in the gravimetric methods used for determination of moho geometry this assumption might be sufficient in regional studies with a relatively homogenous lithospheric structure and consequently small lateral variations in moho density contrast in global studies however this assumption is not reasonable because not only the moho depth but also the moho density contrast vary substantially and are thus likely to result in systematic errors in moho geometry determined globally from gravity data in this study we address this issue by investigating the effect of variable moho density contrast on moho geometry we demonstrate that assumption of variable moho density contrast instead of a uniform model substantially improves agreement between the global gravimetric and seismic moho models by approximately 30

light toned salty soils and coexisting si rich species discovered by the mars exploration rover spirit in columbia hills 1 light toned soils were exposed through serendipitous excavations by spirit rover wheels at eight locations in the columbia hills their occurrences were grouped into four types on the basis of geomorphic settings at three major exposures the light toned soils are hydrous and sulfate rich the spatial distributions of distinct types of salty soils vary substantially with centimeter scaled heterogeneities at paso robles dead sea shredded and champagne penny a well mixed nature for light toned soils occurring near and at the summit of husband hill and relatively homogeneous distributions in the two layers at the tyrone site aeolian fumarolic and hydrothermal fluid processes are suggested to be responsible for the deposition transportation and accumulation of these light toned soils in addition a change in pancam spectra of tyrone yellowish soils was observed after being exposed to current martian surface conditions for 175 sols this change is interpreted to be caused by the dehydration of ferric sulfates on the basis of laboratory simulations and suggests a relative humidity gradient beneath the surface si rich nodules and soils were observed near the major exposures of s rich soils they possess a characteristic feature in pancam visible near infrared vis nir spectra that may be diagnostic of hydrated species and this spectral feature can be used to search for additional si rich species the exposures of hydrated salty soils within various geomorphic settings imply the potential existence of hydrous minerals in similar settings over a much wider area hydrous sulfates represent one of the candidates that may contribute the high level of water equivalent hydrogen in equatorial regions detected by the neutron spectrometer on mars odyssey

moho modeling using fft technique to improve the numerical efficiency the fast fourier transform fft technique was facilitated in parker oldenburg s method for a regional gravimetric moho recovery which assumes the earth s planar approximation in this study we extend this definition for global applications while assuming a spherical approximation of the earth in particular we utilize the fft technique for a global moho recovery which is practically realized in two numerical steps the gravimetric forward modeling is first applied based on methods for a spherical harmonic analysis and synthesis of the global gravity and lithospheric structure models to compute the refined gravity field which comprises mainly the gravitational signature of the moho geometry the gravimetric inverse problem is then solved iteratively in order to determine the moho depth the application of fft technique to both numerical steps reduces the computation time to a fraction of that required without applying this fast algorithm the developed numerical producers are used to estimate the moho depth globally and the gravimetric result is validated using the global crust1 0 and regional esc seismic moho models the comparison reveals a relatively good agreement between the gravimetric and seismic models with the rms of differences of 4 5 km at the level of expected uncertainties of used input datasets while without the presence of significant systematic bias

upper mantle density and surface gravity change in fennoscandia determined from grace monthly data abstract precise gravity measurements have been repeatedly observed in fennoscandia since the 1960 ties first by relative gravimeters then by absolute gravimeters for studying the temporal change of gravity related with the on going glacial isostatic adjustment gia the results of such studies are vital for understanding gia processes and tuning gia and earth structure models this study uses monthly repeated data from the twin satellite mission grace for 164 months between 2003 and 2016 for estimating the temporal change of surface gravity its ratio f to the land uplift rate as well as the upper mantle density related with the viscous mass flow in the mantle the maximum negative change of gravity is estimated to 1 8 gal yr and f is estimated to 0 172 0 018 gal mm the solutions for f from the three independent techniques relative absolute and satellite gravity observations were found to agree statistically without significant biases and they were merged in a joint solution to 0 166 0 004 gal mm corresponding to a mean upper mantle mass flow density of 3402 5 95 kg m3 which decreases towards the uplift center

on the approximations in formulation of the vening meinesz moritz theory of isostasy different approximations are used in moho modelling based on isostatic theories the well known approximation is considering a plate shell model for isostatic equilibrium which is an oversimplifie

vertical mixing at intermediate depths in the arctic boundary current microstructure and hydrographic observations during september 2007 in the boundary current on the east siberian continental slope document upper ocean stratification and along stream water mass changes a thin warm surface layer overrides a shallow halocline characterized by a 40 m thick temperature minimum layer beginning at 30 m depth below the halocline well defined thermohaline diffusive staircases extended downwards to warm atlantic water intrusions found at 200 800 m depth observed turbulent eddy kinetic energy dissipations are extremely low epsilon 10 6 w m 3 such that double diffusive convection dominates the vertical mixing in the upper ocean the diffusive convection heat fluxes f dc h 1 w m 2 are an order of magnitude too small to account for the observed along stream cooling of the boundary current our results implicate circulation patterns and the influence of shelf waters in the evolution of the boundary current waters

determination of crustal thickness under tibet from gravity gradient data abstract we develop a novel regional inversion algorithm to determinate the moho geometry from the gravity gradient data the procedure involves two steps firstly the refined gravity gradient data which comprise mainly the gravitational signal of the moho geometry are obtained from applying the gravimetric forward modeling by using a tesseroid method secondly the refined gravity gradient data are used to find the moho depth the functional relationship between the known refined gravity gradient data and the unknown and sought moho depth is defined by means of the nonlinear fredholm integral equation of the first kind which is further linearized by means of applying a taylor series to stabilize the inverse solution of the system of observation equations the tikhonov regularization is applied the developed algorithm is tested at the study area of tibet characterized by the largest crustal thickness results of the gravimetric inversion for the uniform and variable moho density contrast models have a relatively good agreement with the seismic model crust1 0 at the level of expected uncertainties of about 5 km without the presence of a significant systematic bias

fine structure of the lowermost crust beneath the kaapvaal craton and its implications for crustal formation and evolution high quality data from a dense seismic array covering an area of approximately 60 40 km2 are used to obtain tight quantitative estimates of the fine scale velocity and density structure of the lowermost crust and the crust mantle boundary moho beneath the kaapvaal craton in the vicinity of kimberley south africa results based on a modified receiver function waveform analysis of moho conversions and crustal reverberation phases show that the crust beneath the array is thin 35 4 km with an average poisson s ratio of 0 254 the minimum s wave velocity contrast across the moho is 17 3 while the contrast in density is 15 4 the density contrast across the moho is particularly diagnostic for an assumed uppermost mantle density beneath kimberley of 3 3 gm cc as determined from mantle xenoliths the density of the lowermost crust is 2 86 gm cc indicating rocks of felsic to intermediate composition analysis of waveform broadening of the crustal reverberation phases relative to that of the direct p wave shows the thickness of the moho transition zone to be less than 0 5 km and the maximum variation in crustal thickness over the region of the array to be less than 1 km the flat and almost perfectly sharp moho together with the absence of a mafic lower crust suggests large scale crustal reworking in the period between crustal formation and the time of cratonic stabilization

submesoscale sea ice ocean interactions in marginal ice zones signatures of ocean eddies fronts and filaments are commonly observed within marginal ice zones mizs from satellite images of sea ice concentration and in situ observations via ice tethered profilers or underice gliders however localized and intermittent sea ice heating and advection by ocean eddies are currently not accounted for in climate models and may contribute to their biases and errors in sea ice forecasts here we explore mechanical sea ice interactions with underlying submesoscale ocean turbulence we demonstrate that the release of potential energy stored in meltwater fronts can lead to energetic submesoscale motions along mizs with spatial scales o 10 km and rossby numbers o 1 in low wind conditions cyclonic eddies and filaments efficiently trap the sea ice and advect it over warmer surface ocean waters where it can effectively melt the horizontal eddy diffusivity of sea ice mass and heat across the miz can reach o 200 m 2 s 1 submesoscale ocean variability also induces large vertical velocities order 10 m d 1 that can bring relatively warm subsurface waters into the mixed layer the ocean sea ice heat fluxes are localized over cyclonic eddies and filaments reaching about 100 w m 2 we speculate that these submesoscale driven intermittent fluxes of heat and sea ice can contribute to the seasonal evolution of mizs with the continuing global warming and sea ice thickness reduction in the arctic ocean submesoscale sea ice ocean processes are expected to become increasingly prominent

high resolution local moho determination using gravity inversion a case study in sri lanka the seismic data incorporated in global moho models are sparse and therefore the interpolation of global moho depths on a local area may give unrealistic results especially in regions without adequate seismic information gravity inversion is a useful tool that can be used to determine moho depths in the mentioned regions this paper describes an interactive way of local moho depth determination using the gravity inversion method constrained with available seismic data before applying inversion algorithms the bouguer gravity data is filtered in various stages that reduce the potential bias usually expected in moho depth determination using gravity methods with constant density contrast assumption a test area with reliable seismic data is used to validate the results of moho computation and subsequently the same computation procedure is applied to the sri lankan region the results of the test area are in better agreement with seismically determined moho depths than those obtained by global moho models in the sri lankan region moho determination reveals a fairly uniform thin crust of average thickness around 20 km the overall result suggests that our gravity inversion method is robust and may be suitable for local moho determination in virgin regions especially those without sufficient seismic data

comparison of gravimetric and mantle flow solutions for sub lithopsheric stress modeling and their combination based on hager and o connell s solution to mantle flow equations the stresses induced by mantle convection are determined using the density and viscosity structure in addition to topographic data

mesoscale eddies of the arctic ocean subsurface baroclinic eddies in the arctic ocean have a diameter of 10 20 km and are confined in depth between 50 and 300m during the arctic ice dynamics joint experiment aidjex in the central beaufort sea between march 1975 and may 1976 extensive information on eddy characteristics statistics and behavior was collected from four manned drifting ice camps during this 14 month period 146 eddies were encountered of which 19 were found to be repeated crossings making a total of 127 separate eddies observed during this period on the basis of the 1975 1976 aidjex data set it is concluded that eddies are 1 prevalent in the amerasia basin of the arctic ocean and in particular the beaufort sea where they may occupy up to a quarter of the available surface area 2 located in the depth range of 50 300 m although a few deeper eddies are also present 3 the second largest producers 32 of kinetic energy found within the upper 200 m of the beaufort sea and 4 predominantly anticyclonic in rotational tendency these eddies apparently originate north of point barrow alaska as a result of instability in the eastward flowing alaskan coastal current and transfer seasonally varying water properties from the chukchi sea and alaskan shelf into the arctic ocean they appear to translate in response to barotropic forcing over short time scales and over longer time periods move with the mean geostrophic field the season of formation for an eddy may be identified by the anomalous thermal properties still residing in its core

ocean heat flux under antarctic sea ice in the bellingshausen and amundsen seas two case studies we examine the role of ocean heat flux ohf in antarctic sea ice growth and melt using data from autonomous ice mass balance buoys deployed on pack ice in the bellingshausen sea and on fast ice in the amundsen sea during the spring summer october december 2007 and summer autumn february march 2009 transitions respectively ohfs are derived using two methods that examine changes in 1 sub ice ocean water properties ohf1 and 2 ice thickness ohf2 the latter only applying to thick snow covered ice i e a near zero temperature gradient near the ice bottom good agreement is found between the time averaged estimates of ohf1 and ohf2 average ohf measured was 8 2wm 2 under the pack ice and 17 2wm 2 under the landfast ice some short term ohf values ohf1 in both seas exceeded 55wm 2 the spring ohf variations in the bellingshausen sea were periodic and controlled by semi diurnal ice velocity fluctuations larger temperature fluctuations in the summer amundsen sea originating from incursions of warm deep water masses contributed to the ohf being twice as high as in the bellingshausen sea and also accounted for the irregular ohf variability there

solving vening meinesz moritz inverse problem in isostasy vening meinesz inverse problem in isostasy deals with solving for the moho depth from known bouguer gravity anomalies and normal moho depth t 0 known e g from seismic reflection data using

greater role for atlantic inflows on sea ice loss in the eurasian basin of the arctic ocean arctic sea ice loss is a leading indicator of climate change and can be attributed in large part to atmospheric forcing here we show that recent ice reductions weakening of the halocline and shoaling of the intermediate depth atlantic water layer in the eastern eurasian basin have increased winter ventilation in the ocean interior making this region structurally similar to that of the western eurasian basin the associated enhanced release of oceanic heat has reduced winter sea ice formation at a rate now comparable to losses from atmospheric thermodynamic forcing thus explaining the recent reduction in sea ice cover in the eastern eurasian basin this encroaching atlantification of the eurasian basin represents an essential step toward a new arctic climate state with a substantially greater role for atlantic inflows

ice edge eddies in the fram strait marginal ice zone five prominent ice edge eddies in fram strait on the scale of 30 to 40 kilometers were observed over deep water within 77 n to 79 n and 5 w to 3 e the use of remote sensing a satellite tracked buoy and in situ oceanographic measurements showed the presence of eddies with orbital speeds of 30 to 40 centimeters per second and lifetimes of at least 20 days ice ablation measurements made within one of these ice ocean eddies indicated that melting which proceeded at rates of 20 to 40 centimeters per day is an important process in determining the ice edge position these studies give new insight on the formation propagation and dissipation of ice edge eddies

goethite and hematite in a climosequence in southern brazil and their application in classification of kaolinitic soils abstract the goethite hematite goethite ratio of 11 profiles of oxisols ultisols and inceptisols along a 600 km e w transect in s brazil varied systematically with climatic and soil factors the ratio increased with decreasing mean annual air temperature increasing excess moisture rainfall minus evapotranspiration increasing soil organic carbon and decreasing ph this is explained in light of the current concept of goethite and hematite formation in soils higher temperatures favor hematite whereas higher excess moisture higher organic carbon and lower ph favor goethite a basis is suggested for using goethite and hematite in the mineralogical classes at the family level of soil taxonomy

non isostatic effects on crustal thickness a study using crust2 0 in fennoscandia the crustal thickness can be determined based on gravimetric isostatic and seismic models modelling crustal thickness by a gravimetric isostatic model suffers from some problems the isostatic ass

depth estimates from ratios of gravity geoid and gravity gradient anomalies the utility of combining geoid gravity and vertical gravity gradient measurements for delineation of causative mass anomalies is explained and compared with spatial and spectral methods for depth estimation depth rules for various source geometries are reviewed and new rules developed for geoid gravity and vertical gravity gradient data both spatial and frequency domain methods are discussed simple ratios of single observations of different data types e g geoid gravity or vertical gravity gradient are shown to provide information comparable to the traditional spatial and frequency analyses of one data type alone

a new fennoscandian crustal thickness model based on crust1 0 and a gravimetric isostatic approach in this paper a new gravimetric isostatic crustal thickness model vmm14 fen is estimated for fennoscandia the main motivation is to investigate the relations between geological and geophysical properties the moho depth and crust mantle density contrast at the crust mantle discontinuity for this purpose the bouguer gravity disturbance data is corrected in two main ways namely for the gravitational contributions of mass density variation due to the different layers of the earth s crust such as ice and sediments as well as for the gravitational contribution from deeper masses below the crust this second correction for non isostatic effects is necessary because in general the crust is not in complete isostatic equilibrium and the observed gravity data are not only generated by the topographic isostatic masses but also from those in the deep earth interior the correction for non isostatic effects is mainly attributed to unmodeled mantle and core boundary density heterogeneities these corrections are determined using the recent seismic crustal thickness model crust1 0 we compare our modeling results with previous studies in the area and test the fitness the comparison with the external moho model eucrust 07 shows a 3 3 km rms agreement for the moho depth in fennoscandia we also illustrate how the above corrections improve the moho depth estimation finally the signatures of geological structures and isostatic equilibrium are studied using vmm14 fen showing how main geological unit structures attribute in isostatic balance by affecting the moho geometry the main geological features are also discussed in the context of the complete and incomplete isostatic equilibrium

aleutian island arc magma production rates and primary controlling factors abstract island arc magmatism is considered a major mechanism of continental crustal growth hence the variation in island arc magma production rates and its influencing factors are of great importance the along arc strike variation in the island arc magma production rate is important for elucidating whether the subduction zone temperature is a controlling factor on arc magmatism no back arc spreading or ridge subduction is occurring in the intraoceanic subduction region of the aleutian subduction zone and the along arc temperatures vary due to differences in the subducting plate age convergence rate and slab dip therefore this is an ideal region to study the correlation between magma production rates and subduction zone temperatures however previous studies estimated the magma production rates at only a few locations due to the insufficient coverage of seismic data here we employ the gravity inversion method based on density modelling and seismic data constraints to calculate the present day arc crustal thickness and then obtain the magmatic thickness by removing the pre existing crustal thickness from the present day arc crustal thickness finally the magma production rates along the main intraoceanic subduction region of the aleutian arc are mapped by estimating the island arc magmatic thickness and the most recent subduction inception dating result in addition the subduction zone temperatures and mantle melt amounts along five profiles across the aleutian arc are calculated the magma production rate variation is highly correlated with the mantle melt amount the slab temperature controls the extent of the slab dehydration which is essential for mantle wedge melting and the mantle wedge temperature controls the size of the hydrated mantle melting region and the melting fraction therein therefore as the subduction zone temperature controls the mantle melt amount we suggest that the subduction zone temperature is the first order controlling factor on the magma production rate

quantitative mineralogy of bauxite profiles in se guinea bissau abstract in the south eastern part of guinea bissau extensive highly weathered ferrallitic mantles occur within different geomorphological levels these weathered layers are usually capped by petroplinthite frequently they are of economic interest due to their enrichment in alumina they represent the remnants of a mezo cainozoic african planation surface one hundred auger drill samples from one geomorphological structure bowal were submitted to a specially developed method of quantification of the mineral phases previously detected in the representative specimens of the batch the method consisted of computing the mineralogical composition from the principal chemical component analyses al 2 o 3 sio 2 fe 2 o 3 tio 2 h 2 o combined with dta tg studies and thermodifferential x ray diffraction studies in addition the samples from available core drillings which reached the parent rocks were investigated by means of xrd and optical microscopy two groups of bauxites developed on dolerite and shale yield the same mineral paragenese the differences of mean al 2 o 3 and fe 2 o 3 content in both groups are expressed entirely by differences of concentration of gibbsite and goethite which reflect mobility of aluminium and iron in solutions circulating through the system of open large pores boehmite and hematite would tend to crystallize from oversaturated solutions in confined environment of fine pores

crustal thickness over the nw pacific and its tectonic implications abstract igneous emplacement on the nw pacific oceanic crust via mantle activity such as hot spots and mantle plumes results in perturbations of crustal thickness therefore mapping crustal thickness variations is key for understanding these mantle structures and processes improvements in resolution and accuracy of marine gravity anomalies promote the use of moho gravity inversion effects especially for large scale applications for improving the moho gravity inversion accuracy density variations of the lithospheric mantle are modelled via lithospheric age temperature density relationship since age grid with a resolution of 2 arc minutes is available and density variations of the mantle beneath lithosphere are modelled via seismic wave velocity density relationship since velocity structure with penetration to 700 km is available comparisons between the moho geometries by gravity inversion and seismic interpretation demonstrate that the mantle density modelling improves the moho inversion accuracy our crustal map shows that 1 the crustal thickness of 26 of the nw pacific region is thicker than 7 km 2 the southern end of the emperor seamounts was emplaced on the western flank of the hess rise and a part of the central hawaiian seamounts was emplaced on the eastern end of the mid pacific mountains 3 the magma production of hawaiian seamounts is greater than that of the emperor seamounts 4 the leakiness of the fracture along which the line islands formed decreases in the order of the central southern and northern segments

satellite observations of mesoscale eddy induced ekman pumping abstractthree mechanisms for self induced ekman pumping in the interiors of mesoscale ocean eddies are investigated the first arises from the surface stress that occurs because of differences between surface wind and ocean velocities resulting in ekman upwelling and downwelling in the cores of anticyclones and cyclones respectively the second mechanism arises from the interaction of the surface stress with the surface current vorticity gradient resulting in dipoles of ekman upwelling and downwelling the third mechanism arises from eddy induced spatial variability of sea surface temperature sst which generates a curl of the stress and therefore ekman pumping in regions of crosswind sst gradients the spatial structures and relative magnitudes of the three contributions to eddy induced ekman pumping are investigated by collocating satellite based measurements of sst geostrophic velocity and surface winds to the interiors of eddies identified from their sea surface height signatures on average e

vertical heat transfer in the arctic ocean the role of double diffusive mixing 1 microstructure profiles collected in the central amundsen basin are analyzed in order to quantify the role of double diffusive mixing for vertical heat transfer from the atlantic layer in the profiles a persistent but laterally incoherent thermohaline staircase structure is identified in the 200 260 m depth range the staircase contains homogeneous layers with average height of 1 3 m and thin high gradient interfaces with average temperature and salinity jumps of about 0 065 c and 0 015 respectively when inferred from a commonly used diffusive convection parameterization the average vertical heat flux within the staircase is 0 6 w m 2 this is one order of magnitude larger than the molecular diffusion alone and of the same order as the overall heat loss from the atlantic layer in the deep basins of the arctic ocean the parameterization is evaluated using observed turbulent heat fluxes and is found to overestimate diffusive convective fluxes with up to an order of magnitude especially for weak thermal forcing small temperature jumps in staircase staircases coexist with thermohaline intrusions in the vertical temperature and salinity profiles lomonosov ridge is identified as a potential region for formation of intrusions it is found that salt fingering is the dominant process during intrusion growth whereas diffusive convection is the dominant process in maintaining the intrusions at steady state in the deep basins

upper mantle density modelling for large scale moho gravity inversion case study on the atlantic ocean moho geometry is an important parameter in geodynamic understanding seismic methods can provide accurate burial depths but the coverage is low the widely used crust1 0 model under oceans is greatly restricted by a low coverage of seismic data gravity inversion can provide high coverage of moho undulations but the accuracy is relatively low observed gravity anomalies integrate gravity effects induced by 3 d density perturbations in the earth for studies of the geometry of a specific density interface based on gravity all gravity effects caused by other interfaces should be removed from the total anomaly map based on 3 d density distributions we use temperature based and velocity based methods to model the lithospheric upper mantle density two temperature calculation parameter models psm and gdh1 three thermal expansion coefficients alpha and three scaling ratio models are tested for each method psm and gdh1 result in a similar mantle gravity anomaly mga pattern but different mga average values when the alpha model is the same different alpha and scaling ratio models result in different moho inversion results and the optimal result from the temperature based method has an rms of 3 2 km with the crust1 0 model a comparison between this inversion result and the crust1 0 model shows that the temperature based method performs well in reproducing moho geometry in the main part of the atlantic ocean especially in the central basin the optimal result from the velocity based method has an rms of 4 3 km with the crust1 0 model compared with the temperature based method the velocity based method performs worse in the central basin but better in regions with low velocity and low density mantle away from the mid ocean ridge

winter sea ice melt in the canada basin arctic ocean 1 recent warming and freshening of the canada basin has led to the year round storage of solar radiation as the near surface temperature maximum nstm using year round ocean from ice tethered profilers and autonomous ocean flux buoys sea ice from ice mass balance buoys and atmosphere from ncep ncar reanalysis data from 2005 2010 we find that heat from the nstm is entrained into the surface mixed layer sml during winter entrainment can only occur when the base of the sml reaches the top of the nstm if this condition is met the surface forcing and stratification together determine whether the sml deepens into the nstm heat transfer occurs by diffusion or by the erosion of the summer halocline the average temperature of the sml warmed by as much as 0 06 c during storm events solar radiation began warming the sml about 1 month early during the winter of 2007 2008 and this can be explained by thin sea ice

aluminium mobilization in soils and waters the toxicity of dissolved aluminium to many plant and animal species is one of the major deleterious effects of the acidification of the environment al mobilization from insoluble forms in minerals and rocks is governed mainly by the ph of the solution surrounding weathering minerals to a first approximation the solubility product of gibbsite gives an indication of al concentrations expected in solution secondary silicate minerals such as kaolinite imogolite and allophane and sulphate minerals such as alunite maintain lower al concentrations in solution than does gibbsite particularly at ph 5 the cation exchange system of acid soils provides a large reserve of ionic al which can be brought into solution when soluble salts percolate through soils ligands such as fluoride and organic anions which form soluble al complexes combine with much of the al in solution when they are present in suitable concentrations and therefore maintain higher concentrations of al than might be expected from mineral solubility equilibria particularly at ph 5 7 slow reactions involving solid phases and uncertain data for possible al species present limit the rigorous application of equilibrium thermodynamics to these systems but the factors mentioned provide a reasonable understanding of the major features of aluminium mobilization

towards sub lithospheric stress determination from seismic moho topographic heights and goce data abstract sub lithospheric stresses can be estimated by analysis of gravity field measurements depending on the measured gravimetric quantity different methods can be employed to estimate those sub lithospheric stresses here we further develop the runcorn s theory for estimation of mantle stresses 1967 such that a moho model and full topographic information are used to recover the function from which the stress can be computed by taking derivatives northwards and eastwards we develop new integral equations for such a purpose and recover this function by solving those integral equations locally over the indo pak india pakistan region from 1 a gravimetric moho model computed from the srtm shuttle radar topography mission and the earth gravity model egm2008 2 srtm and the seismic moho model of crust1 0 and 3 data and measurements of the goce gravity field and steady state ocean circulation explorer mission finally we perform a joint inversion of seismic and goce data for the same purpose the numerical results show that the use of a seismic moho model recovers information about the stress field which is not seen in the results derived from a gravimetric moho model a combination of the seismic moho model srtm and goce yields a better stress field than that of either the seismic and or gravimetric data alone the magnitudes of the sub lithospheric stress are computed from the shear stress components over the area and good agreement is seen between the recovered combined stress field the regional tectonic boundaries and the seismicity of the world stress map 2008 database

distinct influence of air sea interactions mediated by mesoscale sea surface temperature and surface current in the arabian sea abstractduring the southwest monsoons the arabian sea as develops highly energetic mesoscale variability associated with the somali current sc great whirl gw and cold filaments cf the resultant high amplitude anomalies and gradients of sea surface temperature sst and surface currents modify the wind stress triggering the so called mesoscale coupled feedbacks this study uses a high resolution regional coupled model with a novel coupling procedure that separates spatial scales of the air sea coupling to show that sst and surface currents are coupled to the atmosphere at distinct spatial scales exerting distinct dynamic influences the effect of mesoscale sst wind interaction is manifested most strongly in wind work and ekman pumping over the gw primarily affecting the position of gw and the separation latitude of the sc if this effect is suppressed enhanced wind work and a weakened ekman pumping dipole cause the gw to extend northeastward delaying the sc separation by 1 current wind i

on the isostatic gravity anomaly and disturbance and their applications to vening meinesz moritz gravimetric inverse problem in this study we showthat the traditionally defined bouguer gravity anomaly needs a correction to become the no topography gravity anomaly and that the isostatic gravity anomaly is better defined by the latter anomaly plus a gravity anomaly compensation effect than by the bouguer gravity anomaly plus a gravitational compensation effect this is because only the newisostatic gravity anomaly completely removes and compensates for the topographic effect f a vening meinesz inverse problem in isostasy deals with solving for the moho depth from the known external gravity field and mean moho depth known e g from seismic reflection data by a regional isostatic compensation using a flat earth approximation h moritz generalized the problem to that of a global compensation with a spherical mean earth approximation the problem can be formulated mathematically as that of solving a non linear fredholm integral equation the solutions to these problems are based on the condition of isostatic balance of the isostatic gravity anomaly and theoretically this assumption cannot be met by the old definition of the isostatic gravity anomaly we show how the moho geometry can be solved for the gravity anomaly gravity disturbance and disturbing potential etc and from a theoretical point of view all these solutions are the same

shelf ocean exchange and hydrography west of the antarctic peninsula a review the west antarctic peninsula wap is a highly productive marine ecosystem where extended periods of change have been observed in the form of glacier retreat reduction of sea ice cover and shifts

interpretation of the lithospheric structure beneath the indian ocean from gravity gradient data abstract global geoidal undulations are often used as the constraining parameter to model the mantle convection pattern while gravity data are typically applied to interpret the lithospheric structure in more recent studies especially after launching the gravity field and steady state ocean circulation explorer goce satellite gravity gradiometry mission gravity gradient measurements have also been used in various geoscience applications the main motivation of using gravity gradients is to provide a more conclusive information about a spatial localization of investigated phenomena in geophysical studies such implications are particularly related to a probably better detection of investigated lithospheric structures such as active tectonic margins in this study we address this aspect by comparing interpretational characteristics from gravity and gravity gradient information the bouguer and mantle gravity gradients are used for this purpose to interpret the lithospheric structure beneath the indian ocean as well as the adjacent continental lithospheric structures such as the east african rift system our results confirm that gravity gradient more closely reproduces some tectonic and volcanic features such as oceanic subductions volcanic island arcs and convergent continental tectonic margins similarly mid oceanic spreading ridges are localized slightly better in the gravity gradient map our findings also indicate that the interpretational quality cannot be improved by using directly observed gravity gradients the reason is that these interpretations require applying gravimetric forward modelling techniques in order to enhance a particular lithospheric structure

trace elements and their relation to the mineral phases in the lateritic bauxites from southeast guinea bissau abstract fourteen trace elements sr ba la ca mg cu zn v ni co mn ga cr zr were determined in 120 auger and core drill samples from one bauxite plateau situated in the se part of guinea bissau following the quantitative determination of minerals identified in the samples all geochemical and mineralogical data were statistically treated the use of several statistical tools enabled us to identify two distinct populations of samples which were found to be related to the shale and dolerite parent rocks respectively the dispersion patterns of the elements mn zr la zn cu cr and ni yield strong contrasts between these two populations bauxites developed on devonian shales were found to contain more cr and ni than bauxites derived from cretaceous dolerites which were richer in cr and ni it is postulated that the difference in duration of the bauxitization processes which affected the two parent bedrocks and or the different resistance to weathering of the primary mineral host phases in the two rock types are responsible for this inversion r mode factor analysis revealed the conspicuous affinity of the mn zn ni cu co mg group and v to goethite gibbsite boehmite and anatase were found to be associated with resistate trace elements like zr and to a lesser extent cr gibbsite also reveals a certain affinity to more mobile strongly depleted elements like sr and ba the study proved the existence of numerous statistically significant correlations between the trace elements like the groups zr ti zn cu ni co mn and sr ba la

analysis of natural and beneficiated ferruginous bauxites by both x ray diffraction and x ray fluorescence abstract the quantitative determination of the main compounds al oh 3 gibbsite as al 2 o 3 and hydrated fe oxides as fe 2 o 3 in natural and beneficiated ferruginous bauxites low grade bauxites by x ray diffraction xrd is presented employing the external standard method the calibration parameters for the analysis by xrd were ascertained by using ten synthetic mixtures of the pure oxides al 2 o 3 and fe 2 o 3 which were calcined at 1200 c the concentration ranges for fe 2 o 3 were 10 70 wt and those for alumina 30 90 wt the standard deviation for the calibrations of the two oxides was 3 33 wt the results obtained by xrd for both oxides were compared with those attained by x ray fluorescence the precision of the determinations by xrd was ascertained by analysing a natural sample consecutively 5 times the accuracy was verified by the analysis of two international standard reference materials with low silica contents

global crust mantle density contrast estimated from egm2008 dtm2008 crust2 0 and ice 5g we compute globally the consolidated crust stripped gravity disturbances anomalies these refined gravity field quantities are obtained from the egm2008 gravity data after applying the topographic and crust density contrasts stripping corrections computed using the global topography bathymetry model dtm2006 0 the global continental ice thickness data ice 5g and the global crustal model crust2 0 all crust components density contrasts are defined relative to the reference crustal density of 2 670 kg m3 we demonstrate that the consolidated crust stripped gravity data have the strongest correlation with the crustal thickness therefore they are the most suitable gravity data type for the recovery of the moho density interface by means of the gravimetric modelling or inversion the consolidated crust stripped gravity data and the crust2 0 crust thickness data are used to estimate the global average value of the crust mantle density contrast this is done by minimising the correlation between these refined gravity and crust thickness data by adding the crust mantle density contrast to the original reference crustal density of 2 670 kg m3 the estimated values of 485 kg m3 for the refined gravity disturbances and 481 kg m3 for the refined gravity anomalies very closely agree with the value of the crust mantle density contrast of 480 kg m3 which is adopted in the definition of the preliminary reference earth model prem this agreement is more likely due to the fact that our results of the gravimetric forward modelling are significantly constrained by the crust2 0 model density structure and crust thickness data derived purely based on methods of seismic refraction

mixed layer instabilities and restratification abstract the restratification of the oceanic surface mixed layer that results from lateral gradients in the surface density field is studied the lateral gradients are shown to be unstable to ageostrophic baroclinic instabilities and slump from the horizontal to the vertical these instabilities which are referred to as mixed layer instabilities mlis differ from instabilities in the ocean interior because of the weak surface stratification spatial scales are o 1 10 km and growth time scales are on the order of a day linear stability analysis and fully nonlinear simulations are used to study mlis and their impact on mixed layer restratification the main result is that mlis are a leading order process in the ml heat budget acting to constantly restratify the surface ocean climate and regional ocean models do not resolve the scales associated with mlis and are likely to underestimate the rate of ml restratification and consequently suffer from a bias in sea surface temperatures and ml depths in a

new insights into the basement structure of the west siberian basin from forward and inverse modeling of grace satellite gravity data 1 the oil and gas rich west siberian basin is underlain by a layer of flood basalts of late permian triassic age that are coeval with the siberian traps the extent and thickness of the basalts are unknown but knowing their thickness is important for discussions on the end permian mass extinction because basalt volume constrains estimates of emitted volatiles we have used grace satellite and terrestrial gravity data to study the structure of the crust and basalt distribution published seismic sections are used to constrain the sediment isopachs and to estimate a depth density function we use published models of crustal thickness and basement depth to reduce the observed gravity field to the basement level the resulting three dimensional density model gives information on density anomalies in the lower crust and upper mantle and on the basalt thickness we identify several rift graben structures that are presumably filled with basalt the lower crust below the west siberian basin shows considerable density variations and these variations allow the region to be divided into four major blocks the eastern part of the basin toward the siberian platform shows an arch shaped density increase in the lower crust that is accompanied by a linear high density anomaly at shallower depths our work demonstrates the way in which the grace gravity field can be applied to map geological structures like buried rifts and large basins the same techniques can be used for other large remote basins such as those in cratonic south america

harmonic and statistical analyses of the gravity and topography of vesta abstract we examine the gravity and topography of the asteroid 4 vesta as recently revealed by the dawn mission the observed gravity is highly correlated with the observed topography and suggests little lateral variation in density the variance spectra of both gravity and topography follow power laws which are very similar to those seen for the moon mars venus and earth a significant way in which vesta differs from these larger silicate bodies is that both gravity and topography are significantly anisotropic with more north south variation than east west variation rapid rotation plausibly contributes to this anisotropy but only at harmonic degree two the remainder of the anisotropy appears related to the large impacts which formed the rheasilvia and veneneia basins we note that as usual gravitational inverse problems are non unique while the observed gravity and topography of vesta do not preclude existence of a metallic core they certainly do not require it

southern ocean frontal structure and sea ice formation rates revealed by elephant seals polar regions are particularly sensitive to climate change with the potential for significant feedbacks between ocean circulation sea ice and the ocean carbon cycle however the difficulty in obtaining in situ data means that our ability to detect and interpret change is very limited especially in the southern ocean where the ocean beneath the sea ice remains almost entirely unobserved and the rate of sea ice formation is poorly known here we show that southern elephant seals mirounga leonina equipped with oceanographic sensors can measure ocean structure and water mass changes in regions and seasons rarely observed with traditional oceanographic platforms in particular seals provided a 30 fold increase in hydrographic profiles from the sea ice zone allowing the major fronts to be mapped south of 60 s and sea ice formation rates to be inferred from changes in upper ocean salinity sea ice production rates peaked in early winter april may during the rapid northward expansion of the pack ice and declined by a factor of 2 to 3 between may and august in agreement with a three dimensional coupled ocean sea ice model by measuring the high latitude ocean during winter elephant seals fill a blind spot in our sampling coverage enabling the establishment of a truly global ocean observing system

a theoretical discussion on vening meinesz moritz inverse problem of isostasy the moho surface can be determined according to isostatic theories and the recent vening meinesz moritz vmm theory of isostasy has been successful for this purpose in this paper we will study t

the spherical terrain correction and its effect on the gravimetric isostatic moho determination in this study the moho depth is estimated based on the refined spherical bouguer gravity disturbance and dtm2006 topographic data using the vening meinesz moritz gravimetric isostatic hypothesis

ocean heat flux in the central weddell sea during winter abstract seasonal sea ice which plays a pivotal role in air sea interaction in the weddell sea a region of large deep water formation with potential impact on climate depends critically on heat flux from the deep ocean during the austral winter of 1994 an intensive process oriented field program named the antarctic zone flux experiment measured upper ocean turbulent fluxes during two short manned ice drift station experiments near the maud rise seamount region of the weddell sea unmanned data buoys left at the site of the first manned drift provided a season long time series of ice motion mixed layer temperature and salinity plus a truncated high resolution record of temperature within the ice column direct turbulence flux measurements made in the ocean boundary layer during the manned drift stations were extended to the ice ocean interface with a mixing length model and were used to evaluate parameters in bulk expressions for interfacial stress a rossby similarity drag law and ocean to

ocean to ice heat flux at the north pole environmental observatory 1 data from drifting buoys deployed in april 2002 as part of the north pole environmental observatory project have been analysed to estimate ocean heat flux in the time period from 1 may 2002 to 11 mar 2003 prior to late january the observatory remained in deep water but subsequently drifted directly over the yermak plateau a relatively shallow feature north of svalbard while over deep water heat flux was dominated by storage and release of solar energy in the ocean boundary layer during summer the most likely annual average value for 2002 was 2 6 w m 2 less than previous determinations in the western arctic over yermak plateau heat flux at the interface came from mixing of warmer water into the boundary layer from below when the observatory was in water with depths less than 1200 m the average heat flux was around 22 w m 2

bouguer reduction density why 2 67 one of the most widely recognized parameters in solid earth geophysics is the assumed density of the surface rocks of the continental crust 2 67 g cm 3 or 2670 kg m 3 in today9s preferred si units in the calculation of bouguer and isostatic gravity anomalies which are widely used for geological studies the gravitational effect of the earth mass between an observation site and a datum is calculated assuming an infinite flat slab of a specified density that approximates the mass the datum for most surveys is sea level or in the case of surveys of limited areas it may be the elevation of the lowest station in the survey although the choice of datum is arbitrary commonly sea level is used in an attempt to standardize anomalies from different surveys similarly a density of 2 67 g cm 3 is generally assumed for the density of the included mass in regional gravity surveys

influences of the ocean surface mixed layer and thermohaline stratification on arctic sea ice in the central canada basin 1 variations in the arctic central canada basin mixed layer properties are documented based on a subset of nearly 6500 temperature and salinity profiles acquired by ice tethered profilers during the period summer 2004 to summer 2009 and analyzed in conjunction with sea ice observations from ice mass balance buoys and atmosphere ocean heat flux estimates the july august mean mixed layer depth based on the ice tethered profiler data averaged 16 m an overestimate due to the ice tethered profiler sampling characteristics and present analysis procedures while the average winter mixed layer depth was only 24 m with individual observations rarely exceeding 40 m guidance interpreting the observations is provided by a 1 d ocean mixed layer model the analysis focuses attention on the very strong density stratification at the base of the mixed layer in the canada basin that greatly impedes surface layer deepening and thus limits the flux of deep ocean heat to the surface that could influence sea ice growth decay the observations additionally suggest that efficient lateral mixed layer restratification processes are active in the arctic also impeding mixed layer deepening

a comparison of three gravity inversion methods for crustal thickness modelling in tibet plateau crustal thickness can be determined by gravimetric methods based on different assumptions e g by isostatic hypotheses here we compare three gravimetric inversion methods to estimate the moho depth two moho models based on the vening meinesz moritz hypothesis and one by using parker oldenburg s algorithm which are investigated in tibet plateau the results are compared with crust2 0 and it will be presented that the estimated moho depths from the vening meinesz moritz model will be better than the parker oldenburg s algorithm

constraining velocity and density contrasts across the crust mantle boundary with receiver function amplitudes summary this paper investigates the ability of p wave receiver functions to constrain both the velocity and density contrasts across the moho expressions for receiver function amplitudes corresponding to a layer over a half space are extended to media with depth dependent properties by explicitly accounting for free surface reflection coefficients forward numerical computations show that receiver function amplitudes become frequency dependent for depth dependent structures and that for a given frequency wavelengths associated to ps converted phases are larger than wavelengths associated to multiply reverberated phases when consistent measurements of the amplitudes of ps phase and multiples can be obtained the extended expressions suffice to account for the observed amplitudes receiver function amplitudes are sensitive to both velocity and density contrasts across the moho and a two step grid search procedure is proposed to recover the contrasts from their measurement the near surface velocity is recovered in the first step from the amplitude of the direct p wave and then used in the second step to work out the relative density and s wave velocity contrast from the amplitude of the secondary phases examples from central spain pab and the indian shield hyb are discussed and demonstrate that receiver function amplitudes can constrain contrasts across the moho accurately enough to be utilized in geological interpretation

spin down of baroclinic eddies under sea ice a linear model is used to examine the spin down of a baroclinic eddy under the sea ice for anti cyclonic eddies the ice stress besides directly spinning down the azimuthal flow within the mixed layer generates an ekman divergence that raises the pycnocline near the eddy axis for eddies of the size of the baroclinic radius of deformation based on the unperturbed mixed layer depth h and the density jump across the pycnocline the doming reaches a quasi stationary state on the frictional time scale t defined as h where is the resistence coefficient at the ice water interface which generally is of the order of days upward entrainment of the fluid across the pycnocline causes a flow convergence below the mixed layer that continues to spin down the deeper flow and flatten the dome the erosion of the dome however occurs over a much longer time scale of n 1t where and n are dimensionless parameters characterizing the entrainment rate and the deep stratification using realistic parameter values for the polar eddies this time scale is of the order of a year or longer the pycnocline dome observed over the antarctic warm cells is thus likely to survive into the following freezing season and provide a preconditioning for the deep convection in the weddell sea

the minimum depth of compensation of topographic masses summary based on the recently compiled crustal thickness data it is shown that the airy heiskanen model of compensation only partly compensates the surface topographic masses to fit the external gravitational potential induced by the surface topography the pratt hayford concept of compensation has also to be considered employing the dynamical flattening of the earth the minimum depth of compensation has been estimated to be of the order of 100 150 km this means that the topographic masses are compensated throughout the earth s lithosphere at least

martian sub crustal stress from gravity and topographic models the latest martian gravity and topographic models derived from the mars orbiter laser altimeter and the mars global surveyor spacecraft tracking data are used to compute the sub crustal stress field on mars for this purpose we apply the method for a simultaneous determination of the horizontal sub crustal stress component and the crustal thickness based on solving the navier stokes problem and incorporating the vening meinesz moritz inverse problem of isostasy results reveal that most of the martian sub crustal stress is concentrated in the tharsis region with the most prominent signatures attributed to a formation of tharsis major volcanoes followed by crustal loading the stress distribution across the valles marineris rift valleys indicates extensional tectonism this finding agrees with more recent theories of a tectonic origin of valles marineris caused for instance by a crustal loading of the tharsis bulge that resulted in a regional trusting and folding aside from these features the martian stress field is relatively smooth with only a slightly enhanced pattern of major impact basins the signatures of active global tectonics and polar ice load are absent whereas the signature of the hemispheric dichotomy is also missing the long wavelength spectrum of the stress field comprises the signature of additional dichotomy attributed to the isostatically uncompensated crustal load of tharsis volcanic accumulations these results suggest a different origin of the earth s and martian sub crustal stress whereas the former is mainly related to active global tectonics the latter is generated by a crustal loading and regional tectonism associated with a volcanic evolution on mars the additional sub crustal stress around major impact basins is likely explained by a crustal extrusion after impact followed by a moho uplift

anomalous chlorofluorocarbon uptake by mesoscale eddies in the drake passage region the role of mesoscale eddies in the uptake of anthropogenic chlorofluorocarbon 11 cfc 11 gas is investigated with a 1 20 eddy resolving numerical ocean model of a region of the southern ocean with a relatively fast air sea equilibrium time scale about a month the air sea cfc 11 flux quickly responds to the changes in the mixed layer cfc 11 partial pressure pcfc 11 at the mesoscale significant correlations are observed between pcfc 11 anomaly anomalies in sea surface temperature sst net heat flux and mixed layer depth an eddy centric analysis of the simulated cfc 11 field suggests that anticyclonic warm core eddies generate negative pcfc 11 anomalies and cyclonic cold core eddies generate positive anomalies of pcfc 11 surface pcfc 11 is modulated by mixed layer dynamics in addition to cfc 11 air sea fluxes a negative cross correlation between mixed layer depth and surface pcfc 11 anomalies is linked to higher cfc 11 uptake in anticyclones and lower cfc 11 uptake in cyclones especially in winter an almost exact asymmetry in the air sea cfc 11 flux between cyclones and anticyclones is found

global maps of the crust 2 0 crustal components stripped gravity disturbances we use the crust 2 0 crustal model and the egm08 geopotential model to compile global maps of the gravity disturbances corrected for the gravitational effects attractions of the topography and of the density contrasts of the oceans sediments ice and the remaining crust down to the moho discontinuity techniques for a spherical harmonic analysis of the gravity field are used to compute both the gravity disturbances and the topographic and bathymetric corrections with a spectral resolution complete to degree 180 of the spherical harmonics the ice stripping correction is computed with a spectral resolution complete to degree 90 the sediment and consolidated crust stripping corrections are computed in spatial form by forward modeling their respective attractions all data are evaluated on a 1 1 arc degree grid at the earth s surface and provided in data sets s1 s5 in the auxiliary material for the scientific community for use in global geophysical studies the complete crust stripped gravity disturbances globally having a range of 1050 mgal contain the gravitational signal coming dominantly from the global mantle lithosphere upper mantle morphology and density composition and partially from the sublithospheric density heterogeneities large errors are expected because of uncertainties of the crust 2 0 model i e deviations of the crust 2 0 model density from the real earth s crustal density heterogeneities and the moho relief uncertainties

symmetry of the south china sea conjugate margins in a rifting drifting and collision context abstract the symmetry of conjugate rifted margins is a first order observable feature reflecting the geodynamic processes acting during and after continental rifting the symmetry of the south china sea scs rifted margins can be deduced from comprehensive geophysical datasets on a continental margin scale here we combine three key approaches 1 lateral fault distributions are delineated according to free air gravity anomalies 2 crustal stretching styles are mapped based on gravity inversion constrained by deep seismic profiles and 3 total extension of conjugate margins is estimated according to margin restorations and tectonic settings we infer a predominantly symmetric rifting style caused by pure shear extension with only narrow domains of asymmetric deformation in continent ocean transition cot regions that have undergone simple shear and where the lower crust of the highly thinned distal margin is embrittled before continental breakup however our analysis also suggests that this symmetry has been modified by post rift geodynamic processes southward lower crustal flow which occurred only on the southern margin due to the low viscosity of the lower crust and the slab pull induced by the subducting proto scs plate during seafloor spreading shifted the crustal stretching styles from symmetric to asymmetric the collision between the southern margin and borneo thickened the lower crust more than the upper crust at the southern end of the southern margin and shortened the southern margin this event had a large impact on the se margin but a small impact on the sw margin we conclude that 1 for the se and ne margins the crustal stretching styles shifted from asymmetric to approximately symmetric and the total extension shifted from symmetric to asymmetric 2 for the sw and nw margins the crustal stretching and total extension remained asymmetric and symmetric respectively

the epigenetic replacement of kaolinite by hematite in laterite petrographic evidence and the mechanisms involved abstract this paper describes the petrographical and mineralogical transformations accompanying the accumulation of iron oxides within the deep mottled layer of a laterite from burkina faso in this layer the proportions of purple red hematitic spots or nodules which form at the expense of volumes occupied by a soft microporous kaolinite plasma increase as the surface of the soil is approached the antagonism between hematite and kaolinite was observed at different levels in all cases from the border to the core of the hematitic domains kaolinite experiences corrosion soon followed by complete destruction at this later stage hemalite crystals are organized into thin lamellar structures showing clearly the shapes of former kaolinite platelets a mechanism explaining coincidence of the accumulation of hematite with the destruction of kaolinite is proposed we postulate that in the deep layers of laterites fed by fe 2 solutions the protons necessary to dissolve kaolinite are generated by a reaction similar to the oxidation hydrolysis step of ferrolysis in the mottled layer of this laterite therefore the progressive building up of a high concentration of iron appears to be the result of two closely related processes i e the precipitation of iron oxides from solution and the concommitant dissolution of kaolinite

on gravity inversion by no topography and rigorous isostatic gravity anomalies we discuss some theoretical aspects and practical consequences of using traditional versus new rigorous formulations of the bouguer and isostatic gravity anomalies disturbances in principle the differences between these two concepts are in the definition of the so called secondary indirect topographic effect site on the gravity data although we follow the tradition to call this effect site we show that it is formally a direct topographic effect dite needed to remove all topographic signal but in practice not regarded as such consequently there is a need for a no topography gravity anomaly which removes all topographic effects leaving the below crust earth transparent for gravity inversion similarly a rigorous isostatic gravity anomaly includes also a compensation effect for the site by using a simple topographic model we confirm a theoretically found ratio of 2 n 1 between the magnitudes of the site and dite by wavelength spherical harmonic degree n both for the bouguer and isostatic gravity anomalies finally global gravity inversions are applied by utilizing the vening meinesz moritz isostatic model to determine the moho geometry using the bouguer gravity disturbances anomalies and the no topography gravity anomalies and the results are compared the numerical results confirm our theoretical findings that the bouguer gravity disturbances and the no topography gravity anomalies provide very similar results a comparison of these gravimetrically computed moho depths with the crust1 0 seismic model shows rms agreements of 4 3 and 4 5 km respectively this is a significant improvement when compared to the moho result obtained by using the bouguer gravity anomalies yielding the rms difference of 7 3 km for the crust1 0 model these results confirm a theoretical deficiency of the classical definition of the bouguer and isostatic gravity anomalies which do not take into consideration the site effects on the topography and its compensation

a numerical model of mesoscale physical biological interactions in the fram strait marginal ice zone a numerical model of marginal ice zones is presented which includes ice atmosphere ocean interactions and couples biological processes to the physical dynamics of the ice edge we have used initial conditions from the fram strait in spring when stratification is increasing nutrient concentrations are high and solar radiation is increasing conditions which are found prior to an ice edge phytoplankton bloom we present three sets of experiments 1 a standard case and variations resulting from different initial conditions with oceanic and ice melt stratification but no winds or eddies 2 one with wind forcing and ice cover but no eddies and 3 cases with cyclonic and anticyclonic eddies under ice cover in general stratification within the upper layers accelerates the growth and accumulation of phytoplankton when the stratification is due to ice melt only the bloom is horizontally constrained between the ice and the ice edge frontal structure maximum primary productivity occurs 7 to 10 days after the introduction of stratification and chlorophyll reaches a maximum approximately 3 days later the bloom s biomass is eventually limited by nutrients wind driven ice edge upwelling alone was ineffective in stimulating phytoplankton growth however any wind induced horizontal movement of ice either uncovers nutrient rich water or advects nutrients into open water which stimulates phytoplankton growth when a cyclonic eddy rotates under the ice a surface divergence results causing the ice to open in the center while upwelling at the eddy core injects nutrients into the euphotic zone anticyclonic eddies induce downwelling at the eddy s core and upwelling and surface divergence at the outer edges with the increased irradiance and high nutrient concentrations phytoplankton biomass within the eddy increases rapidly

evolution of the southern ocean winter mixed layer and sea ice open ocean deepwater formation and ventilation an analytical model has been developed to describe the nature of the winter ocean sea ice interaction in the southern ocean to determine the principal processes responsible for maintaining stability in this marginally stable region and to predict the response to changes in the external forcing and initial conditions the model accurately describes the sparse winter observations and the general temporal evolution of the ice mixed layer depth and salinity for the period following the elimination of the seasonal pycnocline by rapid fall ice growth a scale analysis and sensitivity study reveal the system parameter dependence this indicates that the magnitude of entrainment is proportional to fst h0 s where fs is the external salt flux h0 the depth of the winter mixed layer and s the salinity gradient through the pycnocline thermodynamic ice growth reflects predominantly the competition between the oceanic diffusive heat gain across the base of the mixed layer and the loss to the atmosphere through the ice and leads a strong thermal gradient across the pycnocline leads to a significant diffusive flux which balances most of the heat lost to the atmosphere this limits the amount of ice growth possible and plays the principal role in maintaining the system stability since the ice growth is required for destabilization through haline rejection during the growth process the system is also sensitive to the large ratio of heat to salt in the pycnocline this introduces a negative feedback where increasing ice growth induces entrainment by the associated salt flux which in turn drives an entrainment heat flux which compensates for heat lost to the atmosphere this moderates the ability to grow ice and drive further entrainment the absolute strength of the salinity gradient on the other hand dictates the effectiveness which a same magnitude external salt flux will have in driving entrainment the effectiveness with which changes in these parameters as well as several other external parameters can influence the southern ocean stability is explicitly evaluated through the sensitivity study and analysis

isostatic goce moho model for iran abstract one of the major issues associated with a regional moho recovery from the gravity or gravity gradient data is the optimal choice of the mean compensation depth i e the mean moho depth for a certain area of study typically for orogens characterised by large moho depth variations in case of selecting a small value of the mean compensation depth the pattern of deep moho structure might not be reproduced realistically moreover the definition of the mean compensation depth in existing isostatic models affects only low degrees of the moho spectrum to overcome this problem in this study we reformulate the sjoberg and jeffrey s methods of solving the vening meinesz isostatic problem so that the mean compensation depth contributes to the whole moho spectrum both solutions are then defined for the vertical gravity gradient allowing estimating the moho depth from the goce satellite gravity gradiometry data moreover gravimetric solutions provide realistic results only when a priori information on the crust and upper mantle structure is known usually from seismic surveys with a relatively good accuracy to investigate this aspect we formulate our gravimetric solutions for a variable moho density contrast to account for variable density of the uppermost mantle below the moho interface while taking into consideration also density variations within the sediments and consolidated crust down to the moho interface the developed theoretical models are applied to estimate the moho depth from goce data at the regional study area of the iranian tectonic block including also parts of surrounding tectonic features our results indicate that the regional moho depth differences between sjoberg and jeffrey s solutions reaching up to about 3 km are caused by a smoothing effect of sjoberg s method the validation of our results further shows a relatively good agreement with regional seismic studies over most of the continental crust but large discrepancies are detected under the oman sea and the makran subduction zone we explain these discrepancies by a low quality of seismic data offshore

a new analytical solution estimating the flexural rigidity in the central andes summary we present a new 2 d analytical solution of the fourth order differential equation which describes the flexure of a thin elastic plate the new analytical solution allows the differential equation for an elastic plate to be solved for any irregular shaped topography with a high spatial resolution we apply the new method to the central andes the flexural rigidity distribution calculated by this technique correlates well with tectonic units and the location of fault zones for example the central andean gravity high correlates with the presence of a rigid high density body

an eddy permitting southern ocean state estimate abstract an eddy permitting general circulation model of the southern ocean is fit by constrained least squares to a large observational dataset during 2005 06 data used include argo float profiles ctd synoptic sections southern elephant seals as oceanographic samplers seaos instrument mounted seal profiles xbts altimetric observations envisat geosat jason 1 and ocean topography experiment topex poseidon and infrared and microwave radiometer observed sea surface temperature an adjoint model is used to determine descent directions in minimizing a misfit function each of whose elements has been weighted by an estimate of the observational plus model error the model is brought into near agreement with the data by adjusting its control vector here consisting of initial and meteorological boundary conditions although total consistency has not yet been achieved the existing solution is in good agreement with the great majority of the 2005 and 2006 southern ocean observations and better repr