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

a phase resolving cross shore sediment transport model for beach profile evolution abstract a phase resolving wave transformation module is combined with an intra wave sediment transport module to calculate the on offshore sediment transport rates the wave module is based on the boussinesq equations extended into the surf zone the vertical variation of the mean undertow and the intra wave sediment concentrations are calculated the net sediment transport rates are calculated and the equation for conservation of sediment is solved to predict the beach profile evolution the results of the present paper showed that the undertow contribution to the sediment transport rates is not dominating in all parts of the surf zone even for eroding beaches suggesting that other contributions should not be neglected the present model also showed that for the same offshore wave energy the time series of the oscillatory motion is important and that the effect of wave groups cannot be disregarded

mass flux and undertow in a surf zone abstract the mass of water carried shoreward by the breaking waves in a surf zone will in a two dimensional situation be compensated by a seaward return flow the undertow it is shown that the undertow is driven by the local difference between radiation stress and the set up pressure gradient which only balance each other in average over the depth turbulent shear stresses are required to maintain a steady situation comparison with measurements confirms the theoretical results

observations of the antarctic circumpolar current and deep boundary current in the southwest atlantic fourteen month velocity and temperature records from an array of 14 moorings north and west of the falkland plateau and supporting hydrographic and tracer data reveal a narrow boundary current that carries dense antarctic waters the current flows west along the northern flank of the falkland plateau with mean speeds of more than 10 cm s 1 at 5000 m and more than 30 cm s 1 at 2500 m the westward flow extends from the bottom to at least 1000 m but the upper portion of the current is a branch of the antarctic circumpolar current acc following the only deepwater route between the scotia sea and the argentine basin waters colder than 0 2 c are too cold to be associated with the acc at drake passage and must ultimately derive from the weddell sea as part of the deep thermohaline circulation the westward transport of water colder than 0 2 c is 8 2 106 m3 s 1 in the mean the bottom boundary current is similar to that predicted by the stommel arons model but considerable variability is introduced by the meandering of the overlying acc chlorofluorocarbon data suggest that new antarctic water from the georgia basin enters the argentine basin via the deep boundary current which passes beneath the acc some new water is also advected east after being entrained in the acc most of the water in the deep boundary current is recirculated water that has been in residence in the argentine basin for some time water colder than 0 2 c is relatively new to the basin and comprises about 2 5 106 m3 s 1 of the westward flow of the boundary current

pronounced zonation of seismic anisotropy in the western hellenic subduction zone and its geodynamic significance abstract many subduction zones exhibit significant retrograde motion of their arc and trench the observation of fast shear wave velocities parallel to the trench in such settings has been inferred to represent trench parallel mantle flow beneath a retreating slab here we investigate this process by measuring seismic anisotropy in the shallow aegean mantle we carry out shear wave splitting analysis on a dense array of seismometers across the western hellenic subduction zone and find a pronounced zonation of anisotropy at the scale of the subduction zone fast sks splitting directions subparallel to the trench retreat direction dominate the region nearest to the trench fast splitting directions abruptly transition to trench parallel above the corner of the mantle wedge and rotate back to trench normal over the back arc we argue that the trench normal anisotropy near the trench is explained by entrainment of an asthenospheric layer beneath the shallow dipping portion of the slab toward the volcanic arc this signature is overprinted by trench parallel anisotropy in the mantle wedge likely caused by a layer of strained serpentine immediately above the slab arcward steepening of the slab and horizontal divergence of mantle flow due to rollback may generate an additional component of sub slab trench parallel anisotropy in this region poloidal flow above the retreating slab is likely the dominant source of back arc trench normal anisotropy we hypothesize that trench normal anisotropy associated with significant entrainment of the asthenospheric mantle near the trench may be widespread but only observable at shallow dipping subduction zones where stations nearest the trench do not overlie the mantle wedge

differentiation conditions of a basaltic magma from santorini and its bearing on the production of andesite in arc settings santorini volcano in the aegean region greece is characterized by andesitic to silicic dominated explosive activity and caldera forming eruptions sourced from magmatic reservoirs located at various structural levels beneath the volcano there is a good understanding of the silica rich magmatism of the island whereas the andesite dominated volcanism and the petrogenesis of the parental mafic magmas are still poorly understood to fill this gap we have performed crystallization experiments on a representative basalt from santorini with the aim of determining the conditions of differentiation pressure temperature volatile fugacities and the parental magma relationship with the andesitic eruptive rocks experiments were carried out between 975 and 1040 c in the pressure range 100 400 mpa fo2 from qfm to nno 3 5 where qfm is quartz fayalite magnetite and nno is nickel nickel oxide with h2omelt contents varying from saturation to nominally dry conditions the results show that basalt phenocrysts within the basalt crystallized at around 1040 c in a magma storage reservoir located at a depth equivalent to 200 400 mpa pressure with 3 5 wt dissolved h2o and fo2 around qfm comparison with the xenocryst and phenocryst assemblages of the upper scoria 1 andesite shows that andesitic liquids are produced by fractionation of a similar basalt at 1000 c and 400 mpa following 60 80 wt crystallization of an ol cpx plag ti mag opx 6 pig ilm assemblage with melt water contents around 4 6 wt at santorini the andesitic low viscosity and water rich residual liquids produced at these depths segregate from the parent basaltic mush and feed the shallow magma reservoirs eventually erupting upon mixing with resident magma changes in prevailing oxygen fugacity may control the tholeiitic calc alkaline character of santorini magmas explaining the compositional and mineralogical differences observed between the recent thyra and old eruptive products from akrotiri

vertical fluxes of sediment in oscillatory sheet flow time series of vertical sediment fluxes are derived from concentration time series in sheet flow under waves while the concentrations c z t vary very little with time for z 10d50 the measured vertical sediment fluxes qzs z t vary strongly with time in this vertical band and their time variation follows to some extent the variation of the grain roughness shields parameter 2 5 t thus sediment distribution models based on the pickup function boundary condition are in some qualitative agreement with the measurements however the pickup function models are only able to model the upward bursts of sediment during the accelerating phases of the flow they are so far unable to model the following strong downward sediment fluxes which are observed during the periods of flow deceleration classical pickup functions which essentially depend on the shields parameter are also incapable of modelling the secondary entrainment fluxes which sometimes occur at free stream velocity reversal the measured vertical fluxes indicate that the effective sediment settling velocity in the high 0 3 c z t 0 4 concentration area is typically only a few percent of the clear water settling velocity while the measurements of richardson and jeronimo chem eng sci 34 1979 1419 from a different physical setting lead to estimates of the order 20 the data does not support gradient diffusion as a model for sediment entrainment from the bed that is detailed modelling of the observed near bed fluxes would require diffusivities that go negative during periods of flow deceleration an observed general trend for concentration variability to increase with elevation close to the bed is also irreconcilable with diffusion models driven by a bottom boundary condition

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

a distinct source and differentiation history for kolumbo submarine volcano santorini volcanic field aegean arc this study reports the first detailed geochemical characterization of kolumbo submarine volcano in order to investigate the role of source heterogeneity in controlling geochemical variability within the santorini volcanic field in the central aegean arc kolumbo situated 15 km to the northeast of santorini last erupted in 1650 ad and is thus closely associated with the santorini volcanic system in space and time samples taken by remotely operated vehicle that were analyzed for major element trace element and sr nd hf pb isotope composition include the 1650 ad and underlying k2 rhyolitic enclave bearing pumices that are nearly identical in composition 73 wt sio2 4 2 wt k2o lava bodies exposed in the crater and enclaves are basalts to andesites 52 60 wt sio2 biotite and amphibole are common phenocryst phases in contrast with the typically anhydrous mineral assemblages of santorini the strong geochemical signature of amphibole fractionation and the assimilation of lower crustal basement in the petrogenesis of the kolumbo magmas indicates that kolumbo and santorini underwent different crustal differentiation histories and that their crustal magmatic systems are unrelated moreover the kolumbo samples are derived from a distinct more enriched mantle source that is characterized by high nb yb 3 and low 206pb 204pb 18 82 that has not been recognized in the santorini volcanic products the strong dissimilarity in both petrogenesis and inferred mantle sources between kolumbo and santorini suggests that pronounced source variations can be manifested in arc magmas that are closely associated in space and time within a single volcanic field

seismic evidence for high pore pressures in the oceanic crust implications for fluid related embrittlement 1 we estimated the p wave velocity structure of the crust of the subducting pacific plate beneath northeast japan using arrival time data of p to s converted waves the results show that the p wave velocity of the subducting crust varies along the arc and increases abruptly at a depth of 100 km from 6 5 7 0 km s in the fore arc to 7 5 8 5 km s in the back arc the p wave velocity in the fore arc is 10 lower than theoretically expected values for the metamorphosed mid ocean ridge basalt material seismicity in the subducting crust is most active at depths of 70 80 km where p wave velocities are lowest the marked reduction of p wave velocity suggests the coexistence of aqueous fluids with hydrous minerals abundant fluids elevate pore fluid pressures and reduce effective normal stress promoting intensive seismic activity in the low velocity crust our observations provide seismic evidence that earthquakes in the subducting crust are facilitated by fluid related embrittlement

seismic attenuation beneath northeastern japan constraints on mantle dynamics and arc magmatism we apply a three step approach to estimate three dimensional 3 d p wave attenuation qp 1 structure beneath northeastern japan first corner frequencies of earthquakes are determined using the spectral ratio method for s coda waves then whole path attenuation terms t and site amplification factors are simultaneously estimated by a joint inversion the set of t is finally inverted for 3 d attenuation structure the results show that the mantle wedge has low attenuation in the fore arc and high attenuation in the back arc a depth profile of qp 1 in the back arc mantle is explained by attenuation expected for a two dimensional 2 d thermal model with qp qs 2 and grain sizes of 1 and 3 cm however an inclined high attenuation zone observed in the back arc mantle wedge which is interpreted as an upwelling flow shows higher attenuation than that calculated from the 2 d thermal model the higher seismic attenuation is probably caused by the concentration of partial melt in the upwelling flow a combined interpretation of seismic attenuation and velocity structures further suggests that the degree of partial melt in the upwelling flow varies along the arc and that volcanoes are clustered transverse to the arc below which the upwelling flow contains a higher degree of melt these observations indicate that magmatism is controlled by a mantle wedge process that depends strongly on spatial variations in the degree of partial melt in the upwelling flow our results further imply the breakdown of hydrous minerals in a hydrous layer above the pacific plate at a depth of 120 km

influence of mixtures of grain size populations on the parametric and modal characteristics of coastal sands herault mediterranean sea france abstract grain size distributions in lower beach and nearshore sands of a segment of the coast of the golfe du lion france were analyzed by a parametric method and by modal analysis the results have been considered both in a spatial framework delineating geographically distinct sedimentary compartments and cells and in a morphodynamic framework separating the dynamic components of the shoreline berm collision zone inner bar outer bar lower shoreface modal statistics indicate that a mixture of three dominant components end members contributes to the grain size distribution gsd of the sediments fine sand sedimentary type i modal value 0 195 mm i 0 35 medium and coarse sand st ii modal value 0 680 mm i 0 8 and very coarse sand and gravel st iii i modal value 2 3 mm i 1 5 quasi log normal one component gsds form a minority group and mixtures produce various apparently unimodal sands and bimodal sediments a large variation of grain size indices results from mixing a simulation of mixing of log normal populations close to the end members shows the great sensitivity of parameters sorting skewness and kurtosis to small changes in the compositional formula of the mixture the procedure followed supplies a good preliminary tool enabling rapid identification and localization of the main sand sources on a regional scale these components derive from potential sources available in the region well known from previous studies st i originates from the river rhone and provides the textural base for most of the sediments st ii and iii form a local component originating either from fluvial input aude orb and herault rivers or from the nearshore reworking of ancient quaternary sediments and late holocene beachrocks each st takes on local aspects in relation to the morphological environment but the regional scale of the study was too large to precisely reflect the local morphodynamic regime a significant change in the st i sorting of bar sands is however observed probably due to the net offshore migration reported for the bar system

focusing of upward fluid migration beneath volcanic arcs effect of mineral grain size variation in the mantle wedge we use numerical models to investigate the effects of mineral grain size variation on fluid migration in the mantle wedge at subduction zones and on the location of the volcanic arc previous coupled thermal grain size evolution t gse models predict small grain size 1 mm in the corner flow of the mantle wedge a down dip grain size increase by two orders of magnitude along the base of the mantle wedge and finer grain size in the mantle wedge for colder slab subduction zones we integrate these t gse modeling results with a fluid migration model in which permeability depends on grain size and fluid flow through a moving mantle matrix is driven by fluid buoyancy and dynamic pressure gradients induced by mantle flow our modeling results indicate that fluids introduced along the base of the mantle wedge beneath the forearc are initially dragged down dip by corner flow due to the small grain size and low permeability immediately above the slab as grain size increases with depth permeability increases resulting in upward fluid migration fluids released beneath the arc and the backarc are also initially dragged down dip but typically are not transported as far laterally before they begin to travel upward as the fluids rise through the backarc mantle wedge they become deflected towards the trench due to the effect of mantle inflow the combination of down dip migration in the forearc and trench ward migration in the backarc results in pathways that focus fluids to the arc this article is protected by copyright all rights reserved

profiling float observations of the upper ocean under sea ice off the wilkes land coast of antarctica abstractmultiyear under ice temperature and salinity data collected by profiling floats are used to study the upper ocean near the wilkes land coast of antarctica the study region is in the seasonal sea ice zone near the southern terminus of the antarctic circumpolar current the profiling floats were equipped with an ice avoidance algorithm and had a survival rate of 74 after 2 5 yr in the ocean the data show that in this part of antarctica the rate of sea ice decay exceeds the rate of sea ice growth during the sea ice growth period the water column is weakly stratified because of brine rejection and is only marginally stable the average winter mixed layer temperature is about 0 12 c above the surface freezing point providing evidence of entrainment of warmer water from the permanent pycnocline the average mixed layer salinity increases by 0 127 from june to october a one dimensional model is used to quantify evolution of the winter mixed layer under a sea ice cover the local winter entrainme

water mass transformation by sea ice in the upper branch of the southern ocean overturning sea ice formation is a key factor in the lower branch of the southern ocean overturning circulation observation based data in conjunction with a water mass transformation framework reveal that sea ice plays a central role in the upper branch too

santorini volcano as a potential martian analogue the balos cove basalts the interpretation of geologic processes on mars from sparse meteorite remote sensing and rover data is influenced by knowledge gained from well characterized terrestrial analogues this calls for detailed study of candidate terrestrial analogues and comparison of their observable features to those encountered on the surface of mars we evaluated the mineralogical geochemical and physical properties of the balos cove basalts bcb from the island of santorini and compared them to martian meteorites mars rover surface measurements and other verified martian analogues obtained from the international space analogue rockstore isar twenty rock samples were collected from the balos cove area based on their freshness integrity and basaltic appearance in the field optical microscopy of bcb revealed a pilotaxitic to trachytic texture with olivine and clinopyroxenephenocrysts in a fine groundmass of olivine clinopyroxene plagioclase magnetite and devitrified glass all major minerals show normal zoning including calcic plagioclase an 78 85 at the core and an 60 76 at the rim augite en 36 48 wo 41 44 fs 11 21 and olivine fo 74 88 the dominant bands in the infrared attenuated total reflectance ir atr spectra from bcb can be assigned to olivine 875 cm 1 calcic plagioclase 1130 cm 1 and augite 970 cm 1 the whole rock chemical compositions and mineralogy of the bcb are similar to published analyses of typical olivine phyric shergottites and basalts and basaltic materials analyzed in gusev and gale craters on mars bcb porosity is in the range of 7 15 and is similar to the porosities of the isar samples although no terrestrial rock is ever a perfect match to martian compositions the differences in mineralogy and geochemistry between bcb and some classes of martian samples are relatively subtle and the basalts of santorini are as close a match as other accepted mars basalt analogues the santorini site offers excellent field logistics that together with the petrology of the outcrop makes it a valuable locality for testing and calibration deployments field training and other activities related to current and future mars exploration

analysis of bed load motion at high shear stress recent pipeline experiments performed in saskatchewan show the existence of a shear layer in which the solids concentration decreases linearly with height this finding has already been used to calculate the velocity distribution within a constant stress shear layer the analysis has now been extended to obtain the solids discharge per unit breadth of bed the result agrees with the modified meyer peter and muller equation and with the writer s sand data for larger nylon particles the solids discharge per unit breadth fell below that expected on the basis of the sand data and the new analysis shows the reason for this apparent anomaly it also shows that a shear layer several grain diameters thick will not be uncommon in open channel flow contrary to the conventional wisdom the new analysis predicts that the threshold of motion curve on the shields diagram must approach a constant value at sufficiently small abscissae a finding which appears to be in accord with recent experimental evidence

entrainment and distribution of different sand sizes under water waves abstract analysis of the bed sediment and suspended sediment collected at different elevations over wave ripples shows that for grain sizes larger than 0 5 mm the likelihood of entrainment into suspension decreases with increasing grain size whereas for the finer material diameter smaller than 0 5 mm the amount of suspended material is proportional to the amount available in the bed material the concentration profiles for individual sieve fractions very similar upwards from about 4 cm above the ripple crest so that the grain size distribution for suspended sand above this level varies very little with elevation all of this taken together indicates that the finer material that goes into suspension is not going to be sorted whereas the coarsest material will be singled out

geochemistry and evolution of the calc alkaline volcanic complex of santorini aegean sea greece abstract volcanic activity on santorini started in upper pliocene times and is still in progress the last eruption occurred in 1950 at least seven eruptive centers were active at various times and some centers were active contemporaneously the overall chemical variations displayed by lavas and pyroclastics from the volcanic complex are largely explicable in terms of fractional crystallization involving removal of the observed phenocryst phases together with variable amounts of magma mixing and assimilation comparison of the chemistry of volcanic products from different eruption centers indicates long term variations in magma chemistry progressive depletion in lil elements and enrichment in compatible elements with time that cannot be explained in terms of fractionation mixing and assimilation such variations are attributed to processes occurring within the upper mantle trace element data require that the primitive lavas erupted on santorini were derived from an upper mantle source which was relatively depleted in lil elements compared with other calc alkaline volcanics and it is proposed that the source region contained a dominant refractory component which had experienced earlier events and a component derived from the subducted slab as magmatism progressed the contribution to the source region from the slab decreased due to either 1 cessation of subduction and hence a decrease in the proportion of slab derived material in the source region 2 a rise in geothermal gradient during melting so that the earliest melts contained a higher proportion of low melting slab derived material or 3 a combination of these processes we conclude that it is possible to see through intracrustal processes and to evaluate the processes which occur in the upper mantle beneath island arcs and we also conclude that the time integrated history of the mantle wedge above the subducted slab beneath island arcs must be taken into account when constructing viable models for are magmatism

the role of polybaric crystallization in genesis of andesitic magmas phase equilibria simulations of the bezymianny volcanic subseries abstract using the updated comagmat model the crystallization sequences of a bezymianny volcano basaltic andesite kamchatka russia are simulated in a wide range of thermodynamic conditions p t f o 2 as a function of h 2 o concentration comparison of the modeled liquid lines of descent with petrochemical trends of the volcanic suite indicates the parental melts contain 1 5 2 wt h 2 o stored under 490 520 mpa pressure in the magma plumbing system beneath bezymianny volcano the initial magma originates as a result of the polybaric evolution of mantle derived high mg basaltic magmas of the adjacent kliuchevskoi volcano the subsequent evolution of derivative hydrous and alumina rich basaltic andesite magmas may proceed under polybaric conditions with an average decompression of 12 mpa per 1 of crystallization in the course of polybaric crystallization compositions of pyroxene bearing andesites can be numerically reproduced and the modeled liquid compositions follow the natural liquid line of descent however hornblende bearing magmas cannot be produced as a result of continued crystallization from parental basaltic andesite through the stage of pyroxene bearing andesite formation they require high water contents and high pressures of crystallization in this case liquid composition should deviate from the chemical trend defined by the whole rock compositions

lithospheric structure of the aegean obtained from p and s receiver functions combined p and s receiver functions from seismograms of teleseismic events recorded at 65 temporary and permanent stations in the aegean region are used to map the geometry of the subducted african and the overriding aegean plates we image the moho of the subducting african plate at depths ranging from 40 km beneath southern crete and the western peloponnesus to 160 km beneath the volcanic arc and 220 km beneath northern greece however the dip of the moho of the subducting african plate is shallower beneath the peloponnesus than beneath crete and rhodes and flattens out beneath the northern aegean observed p to s conversions at stations located in the forearc indicate a reversed velocity contrast at the moho boundary of the aegean plate whereas this boundary is observed as a normal velocity contrast by the s to p conversions our modeling suggests that the presence of a large amount of serpentinite more than 30 in the forearc mantle wedge which generally occurs in the subduction zones may be the reason for the reverse sign of the p to s conversion coefficient moho depths for the aegean plate show that the southern part of the aegean crustal thickness of 20 22 km has been strongly influenced by extension while the northern aegean sea which at present undergoes the highest crustal deformation shows a relatively thicker crust 25 28 km this may imply a recent initiation of the present kinematics in the aegean western greece crustal thickness of 32 40 km is unaffected by the recent extension but underwent crustal thickening during the hellenides mountains building event the depths of the aegean moho beneath the margin of the peloponnesus and crete 25 28 and 25 33 km respectively show that these areas are also likely to be affected by the aegean extension even though the cyclades crustal thickness of 26 30 km were not significantly involved in this episode the aegean lithosphere asthenosphere boundary lab mapped with s receiver functions is about 150 km deep beneath mainland greece whereas the lab of the subducted african plate dips from 100 km beneath crete and the southern aegean sea to about 225 km under the volcanic arc this implies a thickness of 60 65 km for the subducted african lithosphere suggesting that the aegean lithosphere was not significantly affected by the extensional process associated with the exhumation of metamorphic core complexes in the cyclades

conditions of melt generation beneath the taupo volcanic zone the influence of heterogeneous mantle inputs on large volume silicic systems many arc silicic igneous provinces exhibit compositional variability defined by oscillation between dry and wet rhyolites the origins of this variability are often uncertain due to the poor constraints on the compositions of the mantle derived inputs to the lower crustal hybridization zones the taupo volcanic zone tvz in new zealand the most productive of modern silicic igneous provinces exhibits variability of rhyolite compositions but small volume coeval basaltic eruptions also occur making it an ideal location to study the mantle contributions to these distinctive types of rhyolite here we present major and trace element data from 12 magmatic centers that reveal that mafic units from the northern portion of the central tvz are enriched in large ion lithophile elements lile in comparison to the southern tvz the results of models quantifying slab derived contributions to the mantle suggest that the observed heterogeneity in lile concentrations and volatile fugacities can be explained by variable amounts of subduction derived fluid within the melting region of the basalts these new data and modeling results provide the first direct evidence that the spatial diversity in the flux of mantle derived basalts and associated volatile elements into the lower crustal differentiation system of the tvz are coincident with wet to dry rhyolite compositional variability

surface based fractional transport rates mobilization thresholds and partial transport of a sand gravel sediment twenty eight coupled observations of flow transport and bed surface grain size distribution were made in a laboratory flume using a wide range of flows and a sediment with a very poorly sorted bimodal grain size distribution these observations permit the transport rates of individual size fractions to be scaled by the proportion of each size immediately available for transport on the bed surface the key to our observations is the use of a sediment in which each size fraction has been painted a different color which permits reliable repeatable and nondestructive measurement of the bed surface grain size distribution from photographs of the bed surface at a given flow the fractional transport rates may be divided into two parts a finer grained portion within which fractional transport rates are a function only of their proportion on the bed surface and total transport rate and a coarser grained portion for which fractional transport rates also depend on the proportion of individual grains within a fraction that remain essentially immobile throughout the experimental run we define the latter condition as one of partial transport and observe that the grain size separating partial and fully mobilized transport consistently increases with flow strength complete mobilization of a size fraction occurs at roughly twice the shear stress necessary for incipient motion of that fraction zones of partial and full mobility are quite distinct when fractional transport rates are scaled by the bed surface grain size distribution although a region of partial transport is evident when these data and other experimental and field observations are scaled by the bulk grain size distribution of the sediment bed critical shear stresses for the incipient motion of individual fractions in our experimental sediment vary over an order of magnitude a result strongly in contrast to many earlier observations but consistent with our observations of incipient motion in sediments with bimodal grain size distributions

modelling cross shore intensive sand transport and changes of bed grain size distribution versus field data abstract the study is focused on the cross shore transport of size graded sediment under combined wave current flow in the intensive flow regime the mathematical method for the description of hydrodynamic processes and sediment transport is adapted from the approach of kaczmarek and ostrowski coast eng 45 2002 1 for non graded sediment the theoretical model of vertical structure of sediment concentration as well as vertical mixing and sorting is presented the model of transport of graded sediment accounts for two directional cross shore sand flux the first component of this flux is directed onshore and results from wave asymmetry effects while the second one is directed seawards and is caused by undertow the vertical structure of this two directional sediment flux and its variability along a cross shore profile is a reason for segregation of grains in a horizontal direction this horizontal sorting of sand is theoretically modelled using the present approach a concept of the carpet of sorted sediments is implemented to reproduce the segregation of sediment in time and to assess the influence of grain size changes on short term evolution of the cross shore profile the results of computations are compared with the large scale laboratory data from the literature and with field measurements carried out by the authors the agreement between the model results and the experimental data is found to be very good particularly it has been theoretically shown that the observed in situ bimodal grain size distributions result from two directional sediment fluxes on the cross shore profile

geophysical source conditions for basaltic lava from santorini volcano based on geochemical modeling abstract santorini volcano sits 145 km above the aegean wadati benioff zone where the african plate subducts northward beneath eurasia there are only a few localities in the whole aegean where basaltic lavas primitive enough to constrain mantle processes beneath the aegean arc can be found in this work we analyzed one such locality a basalt lava from the southern part of santorini we apply a suite of petrological tools primacalc2 and abs5 in sequence to estimate magma chamber conditions primary magma composition mantle melting conditions and slab dehydration conditions back calculation modeling based on major element chemistry yields shallow magma chamber conditions of p 0 02 gpa fo 2 qfm 2 and 1 wt h 2 o in the primary magma the estimated major element composition of this primary magma then leads to estimated mantle melting conditions of 2 1 gpa 1353 c and f 8 whereas a more precise estimate derived from trace element modeling implies 1 7 gpa 1323 c and f 18 furthermore the trace element model implies a slab flux derived from 4 6 gpa 150 km slab depth the estimated slab depth magma segregation conditions and magma chamber depth are all consistent with seismic observations supporting slab dehydration in the seismically imaged steep slab interval and flux melting in a relatively hot mantle wedge

gradation effects in sediment transport to determine the effects of grain size and density gradation in oscillatory sheet flow experiments are conducted in an oscillating water tunnel a formal derivation of a schematised transport model shows that the transport rates per sediment fraction can be determined with and without the assumption of an active layer a technique that measures sediment composition from natural occurring radionuclides is used to determine the transport rates without that assumption of an active layer the measurements on total sediment transport rates and suspended sediment concentrations show that effects of gradation are present the effects of size gradation are mainly in the increased transport rates of the coarse fraction with respect to the uniform coarse material and the availability at the bed under similar conditions the experiments on density graded sediments indicate that total mass transport rates are larger than the mass transport rates of quartz material whilst the transport rates of the quartz fraction show that this fraction is not hindered by the availability at the bed

sediment transport in oscillatory boundary layers in cases of rippled beds and sheet flow an experimental study was focused on the process of sediment transport in unsteady flow conditions due to wave action wave induced oscillatory flow conditions near the seabed were simulated at full scale 1 1 in a new large oscillating water tunnel two sets of experiments series a and b were carried out during series a bed forms and wave cycle averaged suspended sediment concentrations were measured under sinusoidal waves series b focused on measurement of the wave cycle averaged sediment transport rates under regular and random asymmetric oscillatory flows upper shoreface conditions and was aimed at the verification of quasi steady formulas for the description of cross shore sediment transport bedform dimensions appeared to decrease considerably under the influence of wave asymmetry and wave randomness only the measured ripple dimensions under asymmetric waves series b showed good agreement with nielsen s 1979 relations for most of the series b experiments the bed was plane sheet flow the net sediment transport was directed onshore and the measured transport rates showed a strong correlation with the velocity moment an empirical quasi steady transport model is proposed which is based on the new tunnel data and other existing data sets the limitations of the quasi steady model approach became clear in the rippled bed regime and through the presence of a consistent influence of the wave period in plane bed conditions in rippled bed conditions the suspended concentration profiles followed a negative exponential distribution for most of the experiments the measured concentration decay length showed a linear relation with the ripple height in plane bed sheet flow conditions the measured suspended concentration profiles followed a negative power function the power or concentration decay parameter was constant 2 1 for a wide range of velocity conditions it is suggested that the mobile bed sheet flow layer has a strong damping effect on the mixing of suspended sediments turbulence damping

on why gravel bed streams are paved bedload transport in poorly sorted gravel bed streams downstream of dams is considered bedload and typical bed material subpavement size distributions are observed to be similar it follows that the coarse half of the subpavement moves through a reach at a rate near that of the fine half since coarser grains are intrinsically less mobile than fine grains it follows that some mechanism must act to nearly equalize mobility it is hypothesized that the pavement seen in gravel bed streams at low flow is in fact in place during typical transport events capable of moving all available sizes this pavement can provide the equalizing mechanism by exposing proportionally more coarse grains to the flow field data are used to quantify this concept and to develop a predictive relation for river pavement the model indicates that pavement should be absent in most sand bed streams in agreement with observation

southern ocean sea ice driven shallow overturning conversion of antarctic circumpolar upwelling waters to less dense water has mainly been attributed to surface heat fluxes an analysis of water mass transformation shows that the dominant process is the formation of sea ice near antarctica and its melt offshore

the geometry of the wadati benioff zone and lithospheric kinematics in the hellenic arc abstract accurate locations of 961 shallow and intermediate depth earthquakes which occurred between 1956 and 1995 in the hellenic arc 34 39 n 19 28 e are used to define the plate boundaries in this area reliable fault plane solutions for 77 shallow and intermediate depth earthquakes are also used in order to define the interaction between the different plates in the arc an ocean continent type of interaction occurs on a curved surface which is defined by the shallow branch 20 100 km of the wadati benioff zone the intersection of this zone with the earth s surface is a curve which follows the convex outer side of the sedimentary arc western peloponnese west of cythera south coast of crete east coast of rhodes and dips at low angle 30 to the aegean sea coupling between the subducted oceanic crust and the overriding of the aegean lithospheric plate takes place on this surface the deep branch 100 180 km of the wadati benioff zone is dipping freely without coupling at a high angle 45 beneath the south aegean trough and the volcanic arc the high shallow seismicity h 20 km which is observed in the southwestern convex outer side of the arc ionian sea is attributed to the fast southwestward motion of the aegean plate location of strong deep earthquakes h 100 km in the fore arc area of the southwestern part of the hellenic arc west of cythera indicates that oceanic crust is destroyed in this part of the hellenic trench due to roll back of the descending lithospheric slab

comparisons between sediment transport models and observations made in wave and current flows above plane beds as a part of the mast2 g8 m coastal morphodynamics project the predictions of four sediment transport models have been compared with detailed laboratory data sets obtained in the bottom boundary layer beneath regular waves asymmetrical waves and regular waves superimposed co linearly on a current each data set was obtained in plane bed sheet flow conditions and each of the four untuned numerical models has provided a one dimensional vertical 1dv time varying representation of the various experimental situations comparisons have been made between the model predictions and measurements of both time dependent sediment concentration and also wave averaged horizontal velocity and concentration for the asymmetrical waves and for the combined wave current flows comparisons have been made with vertical profiles of the cycle averaged sediment flux and also with the vertically integrated net sediment transport rate each of the turbulence diffusion models gives an accurate estimate of the net transport rate invariably well within a factor of 2 of the measured value in contrast none of the models provides a good detailed description of the time dependent suspended sediment concentration due mainly to the inability of conventional turbulence diffusion schemes to represent the entrainment of sediment into suspension by convective events at flow reversal however in the cases considered here this has not seriously affected the model predictions of the net sediment flux due to the dominance of the near bed transport the comparisons in this paper are aimed not only at testing the predictive capability of existing sediment transport modelling schemes but also at highlighting some of their deficiencies

modelling intensive near bed sand transport under wave current flow versus laboratory and field data abstract the present study is focused on sand transport in combined wave current flow at any angle between them in the intensive flow regime the present model is based on the 1dv approximation the mathematical method for the continuous description of processes from the immobile bed to the formation of sheet flow and suspended load is presented the way of modelling of sediment flow interaction is proposed in which the near bed flow is divided into three layers as done previously by kaczmarek and ostrowski kaczmarek l m ostrowski r 1998 modelling of a three layer sediment transport system in oscillatory flow proc 26th icce asce 2559 2572 for pure oscillatory flow measured by katopodi et al katopodi i ribberink j s ruol p lodahl c 1994 sediment transport measurements in combined wave current flows proc coastal dynamics 94 asce 837 851 and dohmen janssen dohmen janssen m 1999 grain size influence on sediment transport in oscillatory flow febodruk bv isbn 90 9012929 4 enschede the netherlands the time averaged velocity profiles are compared with results provided by the present model for the respective conditions the laboratory data of combined wave current flow were further used to compare the model results for instantaneous and time averaged concentration in the bedload pick up layer and the contact load upper sheet flow layer as well as for net sediment transport rate in the case of unidirectional 0 wave current interaction the model cases for non zero wave current angle were tested in the context of longshore sediment transport rate against field radio isotopic tracer data of lubiatowo poland by pruszak and zeidler pruszak z zeidler r b 1994 sediment transport in various time scales proc 24th icce asce 2513 2526 and field luminescent tracer data of ancao peninsula portugal by balouin and howa balouin y howa h 2000 correspondence contact with university of bordeaux generally the agreement between the model results and the experimental data was found satisfactory in the context of the apparent roughness and time averaged velocity profiles above the bed boundary layer further the anti phase behaviour of measured bedload concentration with respect to sediment concentration in the contact load layer and the asymmetric effects resulting from wave current interaction are well represented by the model consequently the present theoretical approach provides a useful tool for predictions of sand transport under wave current flow within an accuracy factor of 1 5 either way

the stratification and water masses at drake passage the waters at drake passage are known to be separated horizontally into four distinct zones of relatively small geostrophic shear by three fronts in which the shear and eastward flow are large the two northern fronts subantarctic front and polar front that bound the polar frontal zone comprise most of the transport of the antarctic circumpolar current vertical sections of closely spaced 50 km oceanographic stations made across drake passage in the summers of 1975 and 1976 produced quality measurements of temperature salinity oxygen silicate nitrate and phosphate based on these data a traditional description of characteristic distributions is presented good sampling resolution in the vertical allows maxima in hydrostatic stability to be traced laterally approximately along isopycnals between individual stations eleven strata of maximum stability are identified most vertically separate distinct water masses the most pronounced stability stratum is associated with the seasonal pycnocline north of the polar front it separates the subantarctic surface waters from subantarctic mode water to the south of the polar front the seasonal pycnocline is found slightly above the temperature minimum characteristic of the antarctic surface waters in austral summer this stability stratum extends northward near the base of the subantarctic mode water another stability stratum extending across the entire passage forms the upper boundary for the circumpolar deep water south of the polar front this stratum is at the base of the antarctic surface water to the north it is the lower boundary of the antarctic intermediate water although subantarctic mode water and antarctic intermediate water are separated by a stability stratum north of the polar front there is no such separation between antarctic intermediate water and the temperature minimum of the antarctic surface water south of the front this suggests that subantarctic mode water and antarctic intermediate water are distinct and that the latter derives from the surface waters south of the polar front at greater depths a horizontally discontinuous stratum is found between the upper and lower circumpolar deep water two horizontally continuous stability strata are found near the base of the circumpolar deep water marking the transition to a high silicate variety of denser deep water from the southeast pacific basin the densest water mass found is weddell sea deep water which flows through a gap in the south scotia ridge and along the southern scotia sea to fill the trough in the southern drake passage it is overlain by a laterally continuous stratum of relative maximum stability

modeling the influence of moho topography on receiver functions a case study from the central hellenic subduction zone 1 pseudospectral 2d modeling of wave propagation provides a fresh look at receiver function data from the hellenic subduction zone it is shown that distinct moho topography which is suggested for this complex subduction environment from various geophysical data sets can provide a conclusive explanation for previously observed inverted moho phases in the forearc as well as for a complex sequence of apparently dipping conversions in the volcanic arc prominent effects of strongly dipping discontinuities include the change of sign in ps phases refracted past the vertical and multiple p reflections that cannot be separated from ps conversions during receiver function processing unambiguous identification of these phenomena can be hampered by poor azimuthal coverage of the data still in regions where discontinuity topography can reasonably be expected its effects should be considered when interpreting receiver functions as results might be spurious otherwise