high resolution analysis of submarine lobes deposits seismic scale outcrops of the lauzanier area se alps france abstract the lauzanier area represents the northernmost extension of the annot sandstone series and contains deposits between 650 and 900 m thick this basin was active from upper bartonian or lower priabonian to early rupelian it is composed of two superposed units separated by a major unconformity the sediment supply is due to channelled flows coming from the south flow processes include mass flow to turbidity currents the size of the particles and the absence of fine grained sediment suggest a transport over a short distance the lower unit is made of coarse grained tabular beds interpreted as non channelled lobe deposits the upper unit is made of massive conglomerates interpreted as the channelled part of lobes these lobe deposits settle in a tectonically confined basin according to topographic compensation that occurs from bed scale to unit scale the abrupt progradation between the lower and the upper unit seems related to a major tectonic uplift in the area this uplift is also suggested by a change in the petrographic nature of the source and an abrupt coarsening of the transported clasts this field example allows providing high resolution analysis for depositional sedimentary sequences of terminal lobe deposits in a coarse grained turbidite system the outcrop analysis shows the lateral evolution of deposits and the system progradation allows a longitudinal analysis of facies evolution by superposing on the same outcrops the channelled lobe system and the non channelled lobe system these results of high resolution outcrop analysis can be extrapolated to results obtained on sedimentary lobes in recent deep sea turbidite system that are either restricted to cores or with a lesser resolution seismic

experiments on non channelized turbidity currents and their deposits abstract large scale experiments on non channelized turbidity currents show that a wide flow opening angle forms and a rapid dilution of the current with distance takes place the thickness of the deposit decreases radially away from the source resulting in tongue shaped isopachs the mean grain diameter also decreases with distance while the sorting improves with increasing distance the following succession of bedforms was observed non deposition parallel lamination ripples parallel lamination this corresponds to the b c and d division of the bouma sequence for turbidites the experiments are in good agreement with the models presented by bouma mutti and ricci lucchi and walker for classical turbidites in the depositional lobes of submarine fans

the biogeochemistry of aluminum in the pacific ocean abstract vertical distributions and horizontal surface transects of dissolved and particulate al at several locations in the pacific ocean are presented here concentrations of dissolved al in the pacific range from 0 3 to 5 nmol kg in the surface waters from 0 1 to 1 nmol kg in mid depths and from 0 5 to 2 nmol kg in the deep waters from these data and published data from other regions it is evident that al has a unique oceanic chemistry relative to that of other metals external sources and rapid particle scavenging throughout the water column are the major controls on dissolved al distributions in the oceans vertical profiles generally exhibit a surface maximum a mid depth minimum and increasing concentrations toward the sediment water interface this suggests two sources of dissolved al one to the surface waters and one to the deep waters concentrations of dissolved al in surface waters are lowest within the eutrophic low salinity california current 0 3 1 nmol kg and increase westwardly into the subtropical gyre of the north pacific 5 nmol kg values in the south pacific gyre are fivefold lower these horizontal trends indicate that the primary source of dissolved al to the surface waters of the central pacific is from eolian input dissolved al supplied by rivers to the eastern north pacific appears to be rapidly scavenged in estuaries and or the highly productive coastal region the source of dissolved al to the deep waters is not known but could be due to a flux out of the sediments or a remineralization process suspended particulate al concentrations increase with depth at all stations and decrease with distance from the ocean boundary surface values range from 1 5 nmol kg near shore to 0 3 nmol kg in the central gyres of the pacific deep water concentrations range from 22 nmol kg near shore to 4 nmol kg in the north pacific central gyre and decrease to 1 3 nmol kg in the south pacific central gyre observed distributions indicate that suspended particulate al varies with the intensity of bottom sediment resuspension and the horizontal mixing of the resulting nepheloid layer out from ocean boundary regions particle residence times estimated are consistent with other reported values

reservoir turbidity current modeling with a two dimensional layer averaged model abstracta two dimensional layer averaged model is developed and verified to simulate turbidity current characteristics and its sluicing in reservoirs the governing equations consist of mass and momentum conservation laws for the turbidity current mixture equations for the sediment transport and bed dynamics and auxiliary relations for the interactions among clear water turbidity current and bed a finite volume unstructured polygonal mesh method is adopted so that reservoirs with complex terrains may be simulated special algorithms are developed to capture the turbidity current front movement through a clear water bed and to simulate turbidity current sluicing through reservoir outlets the developed model has been tested and verified with both conservative and nonconservative turbidity currents ranging from simple to complex reservoir terrains case studies presented include a lock exchange turbidity current with large eddy simulation and direct numerical simulation results a laboratory test of

238u234u230th disequilibrium in hydrogenous oceanic femn crusts palaeoceanographic record or diagenetic alteration abstract a detailed tims study of 234uexc 238u 230th 232th and th u ratios have been performed on the outermost margin of ten hydrogenous fe mn crusts from the equatorial pacific ocean and west central indian ocean th u concentration ratios generally decrease from the crust s surface down to 0 5 1 mm depth and growth rates estimated by uranium and thorium isotope ratios are significantly different in fe mn crusts from the peru basin and the west central indian ocean fe mn crusts from the same geographical area define a single trend in plots of ln 234uexc 238u vs ln 230th 232th and th u ratios vs age of the analysed fractions results suggest that l hydrogenous fe mn crusts remain closed systems after formation and consequently 2 the discrepancy observed between the 230th and 234u chronometers in fe mn crusts and the variations of the th u ratios through the margin of femn crusts are not due to redistribution of uranium and thorium isotopes after oxyhydroxide precipitation but rather to temporal variations of both th u and initial thorium activity ratios recorded by the fe mn layers implications of these observations for determination of fe mn crust growth rates are discussed variations of both th u and initial th activity ratios in fe mn crusts might be related to changes in particle input to seawater and or changes in ocean circulation during the last 150 ka

radiochemical observations on manganese nodules from three sedimentary environments in the north pacific abstract decay series isotopes were measured on manganese nodules from three sedimentary environments characterized by substrates of red clay r siliceous ooze s and hemipelagic clay h growth rates of nodules are shown to be site dependent 1 2 mm myr at site r 3 8 mm myr at sites s and 20 50 mm myr at site h correlation between growth rate and the parameter mn fe2 suggests that regional diagenetic variations control the compositions and growth rates of the nodules the frequency of nodule turnover and the period of their growth are assessed from the top vs bottom distributions of several nuclides based on the 230th 231pa and 226ra data turnover times of 103 to 105 years are estimated and they vary with relative size and shape of the specimens at a given site the presence of unsupported 210pb and 228th in the top surfaces but not in the bottom surfaces of the surface nodules suggests active growth during the last decades or years despite their old ages the data also indicate that turnover rates are not more frequent than once every several years or decades the 230th 226ra 226ra 210pb and 232th 228th disequilibrium relationships in the nodules allow the migratory behavior of 226ra 222rn and 228ra and their fluxes to be deduced thus radium leaves the top sides but enters the bottom sides of the surface nodules at sites r and s at site r there is a net loss of radium to the sea the opposite is true at site s surface nodules at site h trap radium from both sides probably due to more intense diagenetic input of radium from sediment pore water the effective diffusivities of 226ra in nodules vary from 3 10 12 to 8 10 14 cm2 s dependent on the textural variation of the nodule material which crudely reflects the growth rate and hence sedimentary environment 222rn diffuses out of nodules from all sides with an effective diffusivity of ca 2 6 10 8 cm 2 s at all sites nodules serve as a more effective source of 222rn to sea water than their adjacent sediments the outward flux of 222rn from nodules relative to that from adjacent sediments tends to be higher in more reduced environments an effect caused by the fact that mn rich nodules from more reduced environment act as a more efficient trap for 226ra

zonal and vertical structure of the madden julian oscillation abstract a statistical study of the three dimensional structure of the madden julian oscillation mjo is carried out by projecting dynamical fields from reanalysis and radiosonde data onto space time filtered outgoing longwave radiation olr data mjo convection is generally preceded by low level convergence and upward motion in the lower troposphere while subsidence cooling and drying prevail aloft this leads to moistening of the boundary layer and the development of shallow convection followed by a gradual and then more rapid lofting of moisture into the middle troposphere at the onset of deep convection after the passage of the heaviest rainfall a westerly wind burst region is accompanied by stratiform precipitation where lower tropospheric subsidence and drying coincide with continuing upper tropospheric upward motion the evolution of the heating field leads to a temperature structure that favors the growth of the mjo the analysis also reveals distinct differences in the vertical structure

loose boundary hydraulics and fluid mechanics selected advances since 1961 s u m m a r y a maj or and acknowledged role in the advance o f sedimentological knowledge is played by the methods of physics as expressed through fluid mechanics and loose boundary hydraulics turbulence is increasingly being seen as involving orderly flow structures and these are significant for the origin of several sedimentary structures and for suspension transport recent advances in sediment transport theory are rooted in the concept of the sediment load as a downward acting force and in the notion of the flow as a transporting machine laboratory experiments are increasing our understanding of bedforms due to rivers and waves but there is a need for well framed field studies to clarify the influence of change in natural environments physical explanations are being proposed for tidal bedforms field studies in both modern environments and the stratigraphic record suggest that tidal patterns and strengths are recognizable from the internal features of cross bedded units formed by sand waves tidal patterns are complex however and a wider range of situations needs to be explored than has hitherto been the case mathematical modelling could help to define the expectable bedding patterns although successful mathematical models have been constructed of flow and sedimentation in channel bends secondary flow in real bends and the evolution of those bends are not yet well understood turbidity currents on a geologically significant scale have not been observed directly but valuable insights into their character and processes have come from laboratory experiments recent laboratory work points to the limitations of lock exchange experiments and emphasizes the various ways in which turbidity currents mix with the ambient medium these studies seem to have implications yet to be worked out for the internal features and some sole marks of turbidites

interactions between the mjo aerosols and convection over the central indian ocean abstractthis study examines covariability of boundary layer cloud condensation nuclei ccn concentrations estimated using the geos 3d chemical transport model geos chem convective clouds precipitation and lightning observed over the central equatorial indian ocean cio three distinct madden julian oscillation mjo episodes were observed during the recent dynamics of the mjo dynamo 2011 12 field campaign coherent relationships between ccn rainfall and lightning are apparent in time series from dynamo and more lightning located north of the equator is noted compared to south of the equator more polluted environments north of the equator contained deep convective clouds that had stronger radar reflectivities 2 3 db in the mixed phase region 5 10 km altitude compared to south of the equator following discussion of the mjo episodes that occurred during dynamo 22 cycles of the mjo observed during boreal cold seasons in the years 2004 11 are examined with the aid of trmm satellite obser

depositional processes of the suwolbong tuff ring cheju island korea the suwolbong pyroclastic sequence in the western part of cheju island korea comprises partly preserved rim beds of a quaternary basaltic tuff ring whose vent lies about 1 km seaward of the present shoreline the sequence consists of breccia lapillistone lapilli tuff and tuff eighteen sedimentary facies are established and organized into six lateral facies sequences lfs and seven vertical facies sequences vfs the lfs 1 4 and 5 begin with massive lapilli tuff which transforms downcurrent into either planar bedded lfs 1 undulatory bedded lfs 4 or climbing dune bedded lfs 5 lapilli tuff units they are representative of relatively dry base surge whose particle concentration decreases downcurrent with a progressive increase in both tractional processes and sorting the lfs 2 begins with disorganized and massive lapilli tuff and transforms into crudely stratified units downcurrent it results from relatively wet base surge in which sorting is poor due to the cohesion of damp ash the lfs 3 comprises well sorted lapilli tuff and stratified tuff further downcurrent suggestive of deposition from combined fall and surge of relatively dry hydroclastic eruption all seven vertical facies sequences generally comprise two facies units of coarse grained fines depleted lapilli tuff and an overlying fine grained tuff these sequences are suggestive of deposition from base surge that consists of a turbulent head and a low concentration tail depositional processes in the suwolbong tuff ring were dominated by a relatively dry base surge the base surge comprises turbulent and high concentration suspension near the vent whose deposits are generally unstratified due to the lack of tractional transport as the base surge becomes diluted downcurrent through fallout of clasts and mixing of ambient air it develops large scale turbulent eddies and is segregated into coarse grained bedload and overlying fine grained suspension forming thinly stratified units further downcurrent the base surge may be either cooled and deflated or pushed up into the air depending on its temperature the suwolbong tuff ring comprises an overall wet to dry cycle with several dry to wet cycles in it suggestive of overall decrease in abundance of external water and fluctuation in the rate of magma rise

turbidity current simulation in a diverging channel spatially varied turbidity currents with erosion and deposition of sediment occurring in slightly diverging sloping channels with a rectangular cross section are simulated the model consists of cross section integrated equations for conservation of volume and mass x momentum equation and empirical relationships for water entrainment and sediment entrainment the continuity equation for the sediment bed is coupled with the equations for the flow in order to simulate the change of bed elevation due to erosion and deposition of turbidity currents the gradually varied flow equations are solved the simulations show 1 underflows in diverging channels do not reach a normal condition 2 three different types of turbidity currents can be simulated 3 turbidity current behavior is sensitive to particle size water viscosity channel slope as well as channel diverging angle when channel aspect ratio is small

10 be profiles in seawater a knowledge of the marine geochemical cycle of 10be is basic to the use of this long lived cosmogenic radioisotope half life 1 5 myr in geochronological and geophysical studies1 3 the first attempts at measuring 10be in seawater were made only recently using nuclear accelerator spectrometry and six concentration values from four locations have been reported4 6 this data base must be expanded to include detailed water column profiles so that the behaviour of 10be in the ocean can be more fully described a parallel case in point is the recent measurement7 of a detailed oceanic profile for the stable 9be we report here two water column profiles of 10be one in the drake passage near antarctica and the other in the san nicolas basin about 100 km off the coast of southern california the san nicolas basin profile clearly demonstrates the regulation of 10be distribution by particulate cycling the data confirm the earlier suggestion4 of particle uptake of 10be in the surface ocean they also furnish evidence for regeneration of 10be across the thermocline and near the sea floor and for mid water scavenging

some new aspects of two dimensional turbidity currents a theoretical consideration of two dimensional underflows and surge type turbidity currents results in a general momentum equation a number of formulae in current use are special cases of this equation among which are the modified chezy equation and bagnold s criterion for autosuspension five dimensionless parameters are included the richardson number ri defined as the inverse square of the froude number the friction coefficient cf the slope the dimensionless settling velocity of the sediment vs u and the changes in flow height with distance dd dx the latter is mainly a measure of the dilution by entrainment of ambient water for chalk powder experiments on surge type turbidity currents and on the initial front of continuous underflows the momentum equation is shown to be correct values for ri range from about 1 5 at 0 slope to about 0 75 at 5 and are slightly to substantially lower than values from earlier authors the two types of turbidity currents investigated show close similarity a surprising attribute is their strong dilution even at very low angle slopes pelitic sedimentation is possible from the upper dilute part of the currents graded intervals found at the base of turbidites can be explained as bedload deposits from the lowermost concentrated layer of the current hydraulic jumps are expected to be rare in surge type turbidity currents and fronts of incipient underflows

flow structure of turbidity currents a two dimensional numerical model is used to describe the flow structure of turbidity currents in a vertical plane to test the accuracy of the model it is applied to historical flows in bute inlet and the grand banks flow the two dimensional spatial and temporal distributions of velocity and sediment concentration and non dimensionalized vertical profiles of velocity turbulent kinetic energy and sediment concentration are discussed for several simple computational currents the flows show a clear interaction between velocity turbulence and sediment distribution the results of the numerical tests show that flows with fine grained sediment have low vertical and high horizontal gradients of velocity and sediment concentration show little increase in flow thickness and decelerate slowly steadiness and uniformity in these flows are comparable for velocity and concentration in contrast flows with coarse grained sediment have high vertical and low horizontal velocity gradients and high horizontal concentration gradients these flows grow considerably in thickness and decelerate rapidly steadiness and uniformity in flows with coarse grained sediment are different for velocity and concentration the results show the influence of spatial and temporal flow structure on flow duration and sediment transport

the role of environmental shear and thermodynamic conditions in determining the structure and evolution of mesoscale convective systems during toga coare abstract a collection of case studies is used to elucidate the influence of environmental soundings on the structure and evolution of the convection in the mesoscale convective systems sampled by the turboprop aircraft in the tropical ocean global atmosphere toga coupled ocean atmosphere response experiment coare the soundings were constructed primarily from aircraft data below 5 6 km and primarily from radiosonde data at higher altitudes the well documented role of the vertical shear of the horizontal wind in determining the mesoscale structure of tropical convection is confirmed and extended as noted by earlier investigators nearly all convective bands occurring in environments with appreciable shear below a low level wind maximum are oriented nearly normal to the shear beneath the wind maximum and propagate in the direction of the low level shear at a speed close to the wind maximum when there is appreciable shear at middle levels 800 400 mb convective bands form parallel to the shear with

fluxes of metals to a manganese nodule radiochemical chemical structural and mineralogical studies fluxes of metals to the top and bottom surfaces of a manganese nodule were determined by combining radiochemical 230th 231pa 232th 238u 234u and detailed chemical data the top of the nodule had been growing in its collected orientation at 4 7 mm myr 1 for at least 0 5 myr and accreting mn at 200 g cm 2 kyr 1 the bottom of the nodule had been growing in its collected orientation at about 12 mm myr 1 for at least 0 3 myr and accreting mn at about 700 g cm 2 yr 1 although the top of the nodule was enriched in iron relative to the bottom the nodule had been accreting fe 50 faster on the bottom 232th was also accumulating more rapidly in the bottom despite a 20 fold enrichment of230th on the top the distribution of alpha emitting nuclides calculated from detailed radiochemical measurements matched closely the pattern revealed by 109 day exposures of alpha sensitive film to the nodule however the shape and slope of the total alpha profile with depth into the nodule was affected strongly by226ra and222rn migrations making the alpha track technique alone an inadequate method of measuring nodule growth rates diffusion of radium in the nodule may have been affected by diagenetic reactions which produce barite phillipsite and todorokite within 1 mm of the nodule surface however our sampling interval was too broad to document the effect we have not been able to resolve the importance of nodule diagenesis on the gross chemistry of the nodule

seasonality in the madden julian oscillation abstract this study using observational data and global reanalysis products synthesizes existing knowledge on the seasonality in the madden julian oscillation mjo and discusses its possible dependence on the mean background state the seasonality in the mjo is documented in terms of its components in low level zonal wind and precipitation a single peak season boreal winter exists near the equator in the indian and western pacific oceans for the broad tropical region however the seasonality in the mjo is featured by a latitudinal migration across the equator between two peak seasons the primary peak season is in boreal winter december march during which mjo signals are mainly confined to the indian and western pacific ocean and reach their maxima in the south pacific convergence zone the secondary peak season is boreal summer june september during which the strongest mjo occurs north of the equator from the bay of bengal to the south china sea and another separated region of strong mjo

mjo initiation in the real time multivariate mjo index abstractmadden julian oscillation mjo initiation in the real time multivariate mjo rmm index is explored through an analysis of observed case studies and composite events specific examples illustrate that both the dates of mjo initiation and the existence of the mjo itself can vary substantially among several well known mjo indices depending on whether the focus is on convection or circulation composites of primary mjo initiation events in which the rmm index rapidly increases in amplitude from a non mjo state to an mjo state are presented and are supplemented by two case studies from the 1985 86 winter season results illustrate that for primary mjo initiation events in the indian ocean rmm phase 1 slowly eastward propagating 850 hpa 200 hpa easterly westerly anomalies over the indian ocean precede the amplification of the rmm index by at least 10 days while suppressed convection over the western pacific ocean precedes the amplification by 5 days these local eastern hemispheric prede

convective characteristics of the madden julian oscillation over the central indian ocean observed by shipborne radar during dynamo abstractthis study investigates the convective population and environmental conditions during three mjo events over the central indian ocean in late 2011 using measurements collected from the research vessel r v roger revelle deployed in dynamics of the mjo dynamo radar based rainfall estimates from the revelle c band radar are first placed in the context of larger scale tropical rainfall measuring mission trmm rainfall data to demonstrate that the reduced revelle radar range captured the mjo convective evolution time series analysis and mjo phase based composites of revelle measurements both support the recharge discharge mjo theory time series of echo top heights indicate that convective deepening during the mjo onset occurs over a 12 16 day period composite statistics show evident recharging discharging features in convection and the environment population of shallow isolated convective cells sst cape and the lower tropospheric moisture increase recharge substantially approximately tw

diffusion and supply rates of 10be and 230th radioisotopes in two manganese encrustations from the south china sea ages of two mn encrustations estimated by their 230th and 10be distributions are compared with k ar ages and micropaleontological datings of their nuclei to discuss possible diffusion and supply effects of the radioisotope distribution and their influence on the reliability of age determinations based on comparable results obtained by the different methods the effective diffusion coefficient of 10be can be calculated as d 1 0 10 8cm2 y this coefficient is 3 8 times smaller than the best estimates available at present in both nodules we observe lower 10be concentrations in the uppermost 2 3 mm 1 3 m y which suggests that 10be uptake has been reduced since the middle pleistocene the 2 7 fold increase of the growth rate starting 3 2 m y ago coincides with the initiation of the northern hemisphere glaciation

calcareous nannofossil biostratigraphic dating of a ferromanganese crust from schumann seamount abstract calcareous nannofossil biostratigraphy was employed to determine the age and growth rates of the different layers within ferromanganese crusts from schumann seamount 200 miles north of the island of kauai hawaii this work is part of a study to reconstruct the paleoceanographic history of crusts using various geochemical indicators the methods are based on the identification of coccolith imprints not actual coccolith remains age constraints on the time span of a particular horizon are defined either 1 by the presence of a species which was extant for only a limited geological time interval or 2 by the presence of two organisms whose time ranges overlapped age resolution is optimized by short time ranges or narrow overlaps in the crust studied there was considerable inter horizon variability in the preservation of coccolith imprints in imprint abundance and in species diversity some of the crust layers examined were narrowly constrained temporally 1 4 myr while others were less so 10 myr our results indicate that the minimum age for the interval at 27 mm depth is at least eocene this is the maximum age many believe any crust can be the position of this interval however is only about one half of the way through the crust while the data support previous estimates of average crust growth rates 0 5 mm myr the actual apparent growth rate appears to have varied by an order of magnitude 0 1 to 2 mm myr

the kinematics of turbulent suspension currents turbidity currents on inclined boundaries abstract turbulent suspension currents are investigated theoretically and experimentally for a wide density range of suspended particles it was found that suspension currents approach an equilibrium state normal state with a balance between gravity entrainment of ambient water bottom friction and the sedimentation of suspended particles for given boundary conditions the equilibrium state can be described by only four characteristic and easily measurable parameters such as a velocity a length or time scale a scale for the buoyancy and one for the buoyancy loss due to sedimentation an important dimensionless product is the sedimentation number which is proportional to the rate at which the buoyancy is lost and which remains approximately constant during an experiment other dimensionless products such as the richardson number are therefore also spatially invariant a large sedimentation number decreases the richardson number and the latter is always smaller for suspension currents which loose sediment than for density currents without buoyancy loss in the case of the geologically important suspension clouds currents fed by an instantaneous source e g a slump experimental and field data suggest an invariant number g sed u 2 which contains the thickness of the deposit the densimetric gravitational acceleration acting on the bulk of the deposit g sed and the front velocity of the current u the magnitude of the invariant number is about 0 3

non destructive alpha spectrometry and radiochemical studies of deep sea manganese nodules abstract a deep sea mn nodule handpicked from top of a 20 cm diameter north pacific tripod core was directly counted by an spectrometer with a silicon surface barrier detector a distinct 210 po peak was recorded for the nodule upper side in contact with bottom seawater based on the spectrum the 210 po supported by 210 pb with 22 year half life is thought to be confined in the top few microns of the nodule since the 210 po peak diminishes considerably for the bottom side resting on sediment nondestructive spectrometry is useful for determining the sea floor orientation of nodules this method was tested for a western north pacific dredged mn nodule and was successful in identifying the orientation and also surface loss of the nodule by dredging radiochemical analysis was also carried out for carefully scraped samples from the top and bottom of the two nodules the growth rates of the hand picked nodule based on excess 230 th and 231 pa profiles were 1 to 4 mm 10 6 y and apparently varied with time the dredged sample has grown at 2 to 6 mm 10 6 y and the growth has likely been episodic the radionuclide composition was significantly different between the top and bottom evidence was found that the radionuclide fluxes of 230 th and 231 pa into the nodules considerably changed during the growing histories the 230 th 232 th activity ratios in the nodule tops are comparable with those in bottom seawater suggesting that the top is growing with metals of seawater origin however it remains unresolved whether the nodule bottoms are growing by utilizing metals in the sediment pore water

sediment sorting in the deposits of turbidity currents created by experimental modeling of explosive subaqueous eruptions abstract deposits of turbidity currents induced by subaqueous volcanic eruptions are increasingly recognized in settings ranging from lakes to the deep sea these eruption fed density currents have high current temperatures and low density particles which affect current dynamics and deposit features field data indicate that deposit thickness and grain size decrease downflow at a changing rate this trend is similar for deposits of noneruptive turbidity currents but with volcanic activity the deposits often exhibit a break in slope of the profile of deposit thickness and grain size distribution here we present laboratory results on density currents that address the effects of variations in grain density and water temperature on flow properties and depositional processes parallel runs were performed under identical flow conditions using quartz sand and pyroclastic sediment each grain type was used in one series of runs in which a hot density current enters a cold environment and one series in which

relay ramps as pathways for turbidity currents a study combining analogue sandbox experiments and numerical flow simulations unlike for subaerial settings the impact of subaqueous relay ramps on sediment dispersal is still poorly understood a combination of analogue laboratory experiments in a sandbox with numerical flow calculations is used to simulate relay ramp topographies on rifting continental margins and to analyse the resulting turbidity current pathways and their deposits various scenarios are investigated including inflow perpendicular and oblique to the relay ramp axis as well as flow constrained by an incised channel on the ramp and by a landward directed tilt of the ramp without channelling most sedimentation takes place on the basin floor because the bulk of the flow follows the steepest gradient down the fault and into the rift basin with a channel along the relay ramp significant flow occurs initially down the ramp axis but channel spillover and basinward ramp tilting combine to redirect much of the sediment down the fault slope into the basin when the relay ramp has a landward oriented tilt most of the current flows down the ramp and deposits its sediment load there and at the foot of the ramp however also here a considerable amount of the flow is shed over the hanging wall fault and into the basin forming a secondary depocentre while ponding redistributes thin deposits over a wider area of the basin the quantitative dependence of these results on the specific ramp geometries remains to be investigated further but may bear great importance for refined sedimentary models in subaqueous rifted settings as well as for hydrocarbon exploration therein 2009 the authors journal compilation 2009 international association of sedimentologists

evolution properties and spatial variability of mjo convection near and off the equator during dynamo abstractthis study investigates the evolution structure and spatial variability of madden julian oscillation mjo convection observed during the 2011 12 dynamics of the mjo dynamo field campaign generally the c band radars located in the near equatorial indian ocean shared mobile atmospheric research and teaching radar smart r on addu atoll gan and nasa toga on the r v roger revelle revelle observed similar trends in echo top heights stratiform rain fraction and precipitation feature size across the mjo life cycle these trends are closely related to changes in mid to upper tropospheric moisture sea surface temperature sst zonal wind and diagnosed vertical air motions however the evolution of convection moisture and vertical air motion at the r v mirai mirai located in the intertropical convergence zone itcz at 8 s exhibited a pattern nearly opposite to gan and revelle when the mjo was active over the equator convection was suppressed around mirai owing to induced subsiden

dynamic reynolds stress modeling of turbidity currents a turbidity current is idealized as a time varying one dimensional boundary layer flow a full reynolds stress model appears to give significantly better predictions than one and two equation turbulence closures model verification is obtained from stationary downslope experimental flows verification of the model is also supported by data from stratified boundary layers represented by monin obukhov relations and density interface flows

the bouma sequence 1962 and the resurgence of geological interest in the french maritime alps 1980s the influence of the gres d annot in developing ideas of turbidite systems

distribution of thorium 232 in manganese nodules and crusts paleoceanographic implications detailed depth profiles of 232th in deep sea ferromanganese nodules and encrustations often show a subsurface maximum followed by a drastic inward decrease to a certain depth before levelling out length scales of this feature vary among the profiles but are proportional to growth rates of the specimens suggesting that the profiles record changes in oceanic 232th flux with time consideration of the nodule chronology the history of eolian accumulation recorded in sediment cores and the marine geochemical behavior and budget of 232th leads us to propose that 232th in nodules crusts is of eolian origin the drastic inward decrease of 232th is a reflection of increase in the wind borne dust flux induced by the northern hemisphere glaciation beginning 2 3 ma the subsurface 232th peak may indicate the decline of eolian flux since 0 1 0 3 ma

density surges two dimensional experiments some new aspects of the development of density surges in channels are developed from recent experimental results a density surge is characterized by the flow of a finite amount of dense fluid this dense fluid may be a saline water solution a saline water solution with tracers sand in suspension or a pure suspension sand in suspension in fresh water the experimental results show in particular that 1 the velocity of the surge is effectively proportional to the square root of the initial volume 2 the velocity of the surge increases with the increase of the initial density of the heavy fluid proportionally to the square root of the ratio of density difference to the ambient fluid density 3 the speed of the surge increases again with an increase of the slope for pure suspensions the experiments show that velocities slow down much more quickly than for saline solutions with the same initial density due to loss of negative buoyancy the effects of the initial density and of the size of the grains on the distribution of sediments are described

the vertical structure of turbidity currents and a necessary condition for self maintenance a simple numerical model predicts that properties of a turbidity current can vary significantly in the vertical direction particularly when more than one sediment size is in suspension each sediment size decreases in concentration with increasing distance from the bottom boundary at a rate which depends on its settling velocity the current velocity the entrainment coefficient and the bottom slope however it is shown that the details of the vertical distribution of sediment load do not necessarily greatly influence either the vertical structure of the hydraulic properties of the flow velocity stress or the bulk properties such as the entrainment coefficient at least when only one sediment size is in suspension the ability of a turbidity current to sustain itself is strongly dependent on the sediment load and an autosuspension criterion is obtained by taking into account the vertical structure of the currents the model turbidity currents often cannot maintain their sediment in suspension even when the bottom stress is greater than the critical stress of deposition for low concentration flows when this happens the concentration near the bottom increases without limit as the turbidity current evolves with time in real turbidity currents grain grain interactions which become important at high concentrations may at times cause the current to quickly deposit its near bottom sediment load this is suggested as a possible mechanism for the formation of the poorly sorted sediments frequently found in turbidites

10 be dating of a manganese crust from central north pacific and implications for ocean palaeocirculation one of the most promising applications of the new 10be detection technique using accelerator mass spectrometry is the determination of growth rates of mn nodules and crusts1 5 because the half life of cosmogenic 10be 1 5 myr is of the same order as the time needed for a few millimetres of nodule material to grow 10be is a useful tool for unravelling such evolution during the late tertiary when most nodules are assumed to have started their growth6 mass spectrometric measurement of a 10be profile across the manganese crust va 13 2 from the central pacific using a tandem van de gr a ff accelerator yields growth rates of 2 7 and 4 8 mm myr 1 for the layers of the crust accumulated between recent and 6 myr bp and between 6 and 11 myr respectively using these measurements as well as 230th dating we have been able to distinguish boundaries between zones in the crust with different structures and chemical compositions and to assign ages to them these ages are 0 12 2 9 3 4 5 7 6 7 7 9 10 12 and 13 16 myr bp all of these boundaries apparently coincide with the times reported for quaternary and late tertiary palaeoclimatic events suggesting that the crust growth has been strongly influenced by palaeoclimate

nile floods recorded in deep mediterranean sediments clastic mud beds rich in continental organic matter are observed recurrently in the nile deep sea turbidite system they formed during flooding periods of the river similar to those that induce sapropel formation and occurred during periods of increased density stratification of the eastern mediterranean the very fine grained flood deposits are intercalated within pelagic sediments sapropels and bouma type turbidites these flood deposits form by the successive reconcentrations of surface hypopycnal plumes by convective sedimentation which in turn generate a fine grained low energy hyperpycnal flow sea level high stands seem also to favor hypopycnal plume formation and increase clastic mud bed formation consequently these muddy clastic beds provide a direct link between deep marine sedimentary records and continental climatic change through flood frequency and magnitude

oscillating turbulent boundary layer with suspended sediments a dynamic boundary layer model with simultaneous interactions between constant oscillatory and turbulent flow suspended sediments and erosion is developed the model appears to be verified as well as the existing data permits in purely oscillatory flow most of the state variables appear to be associated with a turbulent kinetic energy maximum developing near the bottom and phase angle 2 and propagating upward thereafter the maximum horizontal sediment flux is approximately proportional to the third power of the maximum turbulent stress a channel flow with constant pressure gradient may be strongly reduced by the presence of waves the waves may also increase the suspended sediment concentration significantly

sedimentary indicators of atmospheric activity in the northern hemisphere during the cenozoic abstract the concentrations and accumulation rates of eolian phases and the mineralogy of sediments from a north pacific core ll44 gpc3 have been used to evaluate changes in eolian sedimentation and atmospheric activity during the cenozoic the quartz content and clay mineralogy of the sediments reflect changing source areas for eolian material whereas the accumulation rates of eolian phases reflect climatic variation and wind intensity eolian sedimentation decreased from 70 to 50 m y ago at the site as it moved north out of the equatorial pacific where it was supplied with eolian debris from north america and africa low rates of eolian sediment accumulation 50 to 25 m y ago reflect the temperate humid environment of the early tertiary and the lack of vigorous atmospheric circulation at that time from 25 to 7 m y ago eolian accumulation increased as the site moved into the influence of the westerlies from 7 to 3 m y ago there was a more rapid increase in accumulation of eolian material at the site which was not accompanied by changes in mineralogy or quartz content and was therefore related to climatic change and more vigorous atmospheric circulation about 2 5 m y ago a dramatic increase in eolian sedimentation accompanied the onset of dry northern hemisphere glaciation

modeling rotating stratified turbulent flows with application to oceanic mixed layers abstract rotational effects on turbulence structure and mixing are investigated using a second moment closure model both explicit and implicit coriolis terms are considered a general criterion for rotational effects to be small is established in terms of local turbulent rossby numbers characteristic length scales are determined for rotational effects and monin obukhov type similarity theory is developed for rotating stratified flows a one dimensional version of the closure model is then applied to simulate oceanic mixed layer evolution it is shown that the effects of rotation on mixed layer depth tend to be small because of the influence of stable stratification these findings contradict a hypothesis of garwood et al that rotational effects on turbulence are responsible for the disparity in the mixed layer depths between the eastern and western regions of the equatorial pacific ocean the model is also applied to neutrally stratified flows to demonstrate that rotation can either stabilize or destab

incorporation of be isotopes and other trace metals into marine ferromanganese deposits abstract two to threefold inward increase of 10be 9be cu and ni have been found in surface layers of marine ferromanganese deposits we interpret this phenomenon as reflecting the manner in which the be isotopes and probably other trace metals e g cu and ni are incorporated on reaching the sea floor exchangeable be is released from its carrier phase to the pore water of the ferromanganese deposits diffuses inward and gets fixed into the deposits the fixation process may be related to the mineralogical reorganizations suggested by previous studies we have modeled this concept and applied it to a mn crust on which detailed analyses of cu ni and natural decay series nuclides as well as be isotopes are made post depositional fixation of th isotopes may also occur the redistributions of be and th isotopes are confined to regions very close to the surface of the deposits for all practical purposes they will not affect growth rate determinations conventionally done using these isotopes the linearly extrapolated 10 be 9 be ratio to the surface from deep layers of a mn deposit does not necessarily represent that ratio in sea water

thorium and radium isotopic relationships in manganese nodules and sediments at manop site s abstract relationships among th and ra isotopes in nodule sediment and water phases at manop site s establish the most likely source for th in the nodules the frequency of nodule turning and the similarity of micro and macro nodules manganese nodules and bottom waters have 230 th 232 th activity ratios considerably higher than other phases at this site suggesting that sea water is the likely source of th for the nodules similar 230 th 232 th activity ratios in nodule tops and bottoms and in certain cases departure from expected 226 ra 230 th activity ratios in nodule tops and bottoms indicate that the nodules rotate every one to ten thousand years the micro nodules have diffusion coefficients of ra similar to macro nodule bottoms i suggest that they may act as a carrier phase for transporting metals through oxic sediments to nodules

oceanic 232th a reconnaissance and implications of global distribution from manganese nodules abstract 232 th concentrations in seawater reported in the literature since 1961 are compiled and evaluated and new data are presented in general recent data are lower than old ones by 1 to 2 orders of magnitude with nearly all post 1980 data lower than 0 1 dpm 10 3 1 and pre 1980 values higher than 0 1 dpm 10 3 1 we believe this is caused by improvements in sampling and analytical techniques reliable profiles of 232 th in coastal and open ocean waters have been measured in recent years some by the newly developed neutron activation analysis and mass spectrometry techniques the data indicate external sources of 232 th to the surface and its scavenging throughout the water column we suggest that aeolian input dominates in the open ocean but fluvial input may be more important in coastal regions if mechanisms exist for recycling th from estuarine sediments some information on the global distribution pattern and marine geochemistry of 232 th in seawater can be inferred from initial 230 th 232 th activity ratios observed on surfaces of manganese nodules and crusts the rather distinct interocean variation of the 230 th 230 th activity ratio in the central gyre region averaging 160 in the south pacific 60 in the north pacific and 17 in the atlantic may reflect higher aeolian input of materials including 232 th to the atlantic and to the northern hemisphere superimposed on the large scale global trend are some small scale variations which are indicative of the following effects 1 abrupt change of water depth and hence 230 th concentration at regions of irregular seafloor topography 2 higher 232 th input at ocean boundaries and 3 enhanced supply of 232 th from hydrothermal vents it is still unclear whether seafloor sediments act as a net source or sink of dissolved 232 th and 230 th in bottom waters pore water study should be undertaken to address this important issue this task can be accomplished by the mass spectrometric technique

cenozoic accumulation history of a pacific ferromanganese crust to investigate the growth rates and absolute time stratigraphy of marine hydrogenetic ferromanganese encrustations we performed 10be profiling and co chronometry of crustal layers as well as 87sr86sr and 18o analysis of phosphatised limestone francolite within a 9 5 cm thick ferromanganese crust from schumann seamount in the hawaiian archipelago together with microfossil stratigraphy our results indicate that some seamount crusts greatly exceed the commonly accepted miocene maximum age in this case probably approaching the cretaceous age of the seamount in addition to the unconformity at the crust substrate boundary at least eight major disconformities are indicated in the schumann seamount crust which probably represent depositional hiatuses or episodes of crust erosion three of the six upper disconformities can be placed at the plio pleistocene middle miocene and paleocene eocene based on 10be microfossil and co chronometer evidence 87sr86sr and 18o values of purified francolite from an inclusion rich layer between the depths of 44 and 49 mm suggest apparent ages that approach those of eocene late paleocene microfossils reported in overlying layers whereas francolite vein infillings in the lower part of the crust and in the basaltic substrate yield values that if interpreted as ages of phosphatization suggest a minimum oligocene age paleotracking suggests the phosphogenesis observed here and on other central pacific seamounts could not have resulted from upwelling enhanced productivity associated with equatorial divergence if the oligocene and middle miocene isotopic ages reported here and elsewhere are correct however a maximum late paleocene age for the phosphogenesis consistent with the stratigraphy would place these seamounts within 10 n of the equator paleotracking also suggests northeast tradewind transport of aluminosilicates in the cenozoic in agreement with other evidence for the antiquity of this ferromanganese crust

characteristics of tropical convection over the ocean near kwajalein radar observations have been analyzed to determine characteristics of convection over the oceanic region around kwajalein in the tropical western pacific generally the echo areas heights and durations exhibited lognormal distributions heights were greater under conditions of higher midtropospheric humidity and correlated with echo area with a wide spread of values mergers and splits often truncated echo lifetimes the most surprising result was the distribution of orientation angles of echo lines which statistically verify the shear parallel and shear normal modes of convective line organization seen elsewhere over tropical oceans the two modes typically coexisted within the area of radar coverage indicating a potential difficulty in predicting line orientation in terms of large scale variables the largest members of the echo population were mesoscale convective systems mcss which had large stratiform components they occurred in environments of increased humidity and higher midlevel buoyancy associated with westward propagating synoptic scale disturbances mcss moved with the easterlies in low to midlevels and exhibited the jump updraft overturning updraft and subsiding midlevel inflow characteristic of tropical oceanic mcss the kwajalein experiment kwajex radar echo population resembles that of the eastern tropical atlantic in terms of the shapes of the distributions of area height and lifetime the prevalence of echo mergers and splits and the tendency to form shear parallel and shear normal lines these characteristics appear to be endemic to oceanic convective populations large scale conditions appear to modulate these basic population characteristics rather than qualitatively alter them

10be and th isotopes in manganese nodules and adjacent sediments nodule growth histories and nuclide behavior abstract the concentration profiles of 9 be 10 be 230 th 232 th 231 pa via 227 th and 238 u have been measured in three manganese nodules one each from the north pacific a47 16 4 the south pacific tf 5 and the indian ocean r v vitiaz in addition the 10 be concentration in deep water from the geosecs reoccupation station 500 of the north pacific and in cores raised from the manganese nodule field in the north pacific have been measured the 10 be concentration in nodule and seawater samples was measured by the accelerator masss spectrometric technique employing the yale tandem van de graaff accelerator the concentrations of 10 be 230 th exc and 231 pa exc and ratios of 10 be 9 be and 230 th exc 232 th all decrease with depth in the nodules this decrease interpreted in terms of nodule growth yields average growth rates of a few millimeters per million years for the nodules the growth rates of the nodules exhibit temporal variations both on short time 50 000 years and long time several million years scales of the three nodules studied only in tf 5 is the short term average growth rate based on 230 th exc in the top 0 0 5 mm the same as the long term average rate based on be isotope data for the 0 5 17 mm interval for the other two nodules the recent average growth rates based on 230 th exc data differ significantly from the long term average growth rates based on be isotopes in a47 16 4 the 10 be based rate is less than the 230 th exc rate and in r v vitiaz the 10 be based rate is greater than the 230 th exc rate this observation coupled with measurable changes in growth rates even during the past few hundred thousand years suggests but does not prove that the discordant growth rates deduced from 230 th exc and 10 be profiles document changes in nodule growth rate with time rather than mixing effects on 230 th exc profiles the 10 be concentration in the geosecs north pacific deep water is 6100 1200 atoms g this value coupled with the average surface 10 be 9 be ratio of north pacific nodules predicts a 9 be concentration within the limits of measured values the inventory of 10 be and 230 th exc in the nodules is only 10 of the total the remaining being in sediments the 10 be concentrations in the upper portions of two adjacent cores studied are nearly the same but the deposition fluxes of both 10 be and 230 th based on 230 th dating vary by a factor of two this difference is attributable to local redistribution of sediment at the time of deposition prior to accumulation

stratification and particle segregation in flowing polydisperse suspensions with applications to the transport and sedimentation of pyroclastic density currents abstract pyroclastic density currents pdcs are particle laden gravity driven flows of volcanic origin they typically contain solid particles with a wide range of sizes and densities resulting in complicated segregation effects during transport and sedimentation this paper describes experimental high density aqueous suspension flows scaled approximately to turbulent pyroclastic density currents it provides information on the development of concentration and particle size gradients in such flows and their relationships to vertical and stream wise grading in the resulting deposit the currents were generated by lock exchange release of initially homogeneous suspensions of highly polydispersed particles with concentrations of 13 8 23 0 vol size distributions were chosen to encompass a wide range of rouse pn numbers from particles that were fully supported by turbulence in the currents pn 2 5 to those whose motion was essentially decoupled from turbulent eddies pn 2 5 as in many pyroclastic density currents experimental currents of two different particle populations were studied one containing particles of a single density and another with particles of two different densities in each case the current head was sampled at different locations along the flume in order to study the evolution of vertical gradients in particle size concentration and density distribution in the propagating flow these gradients were then related to grading observed in the resulting deposits differential settling resulted in rapid segregation of particles of different sizes and densities in the currents and the development of both vertical and longitudinal gradients in particle concentrations sizes and proportions longitudinal gradients developed as vertical gradients were pulled out longitudinally by the vertical velocity profile in the fluid gradient development involved principally large particles capable of moving independently of turbulent eddies in the fluid the segregation behaviour of large light particles equivalent to pumice in the natural system in the bidensity currents was strongly influenced by buoyancy forces in the dense initial suspension sedimentation of large light particles was delayed and reverse vertical and longitudinal grading of these particles was generated in the resulting deposit reverse grading in the deposit was not caused by flotation of the large light particles which were normally stratified in the current during transport deposition of large light particles was probably delayed by a thin boundary layer of sufficiently high bulk density at the base of the rapidly evolving density stratified current vertical or longitudinal reverse grading of large pumices in pyroclastic density current deposits does not necessarily imply flotation during transport

turbidity current with erosion and deposition the equations which govern the movement of two dimensional gradually varied turbidity currents in reservoirs and over beaches are derived and solved numerically turbidity currents are sediment laden gravity currents that exchange sediment with the bed by erosion or deposition as the flow travels over the downslope turbidity currents derive this driving force from the sediment in suspension they experience a resisting shear force on the bed and entrain water from above turbidity currents can be eroding or depositive accelerating or decelerating dependent on the combination of initial conditions bed slope and size of sediment particles they can be controlled from upstream supercritical or downstream subcritical gravity currents with and without erosion and deposition are examined in order to understand the effects of sediment exchange on the flow

late pleistocene paleoclimatology of the central equatorial pacific a quantitative record of eolian and carbonate deposition detailed records of vso 6i3c percentage and mass accumulation rate of caco and eolian percentage mass accumulation rate and grainsize generated for core rcl l 210 from the equatorial pacific reveal the timing of paleoclimatic events over the past 950 000 yr the caco percentage record shows the standard pacific correlation of high caco content with glacial periods but displays a marked change of character about 490 000 yr ago with older stages showing much less variability the carbonate mass flux record however does not show such a noticeable change sedimentation rates vary from about 0 5 to 3 0 cm l000 yr and during the past 490 000 yr sections with enhanced sedimentation rates correspond to periods of high caco percentage eolian mass accumulation rates an indication of the aridity of the source region are usually higher during glacial times eolian grainsize an indication of the intensity of atmospheric circulation generally fluctuates at a higher frequency than the loo ooo yr glacial cycle the mid brunhes climatic event centered at 300 000 yr ago appears as a 50 000 yr interval of low intensity and reduced variability of atmospheric circulation furthermore the nature of this entire record changes then with the younger portion indicating less variation in wind intensity than the older part of the record the late matuyama increase in amplitude of paleoclimatic signals begins 875 000 yr ago in the eolian record 25 000 yr before the 6i80 and caco percentage amplitude increases about

a 420 000 year record of cyclicity in oceanic and atmospheric processes from the eastern equatorial pacific samples from the upper portion of a cyclic pelagic carbonate sediment sequence in deep sea drilling project dsdp hole 503b 4 0 n 95 6 w are the first group to be analyzed for paleoceanographic and paleoclimatic proxy indicators of ice volume deep ocean and surface water circulation and atmospheric circulation in order to resolve the complex origin of the cyclicity temporal resolution is taken from the 18o time scale most other parameters are calculated in terms of their mass flux to the seafloor caco3 percent in the sediments fluctuates in the well known pacific pattern and is higher during glacial times the fluxes of opal and organic carbon have patterns similar to each other and show a variability of a factor of 2 5 to 4 the longer organic carbon record shows flux maxima during both glacial and interglacial times the accumulation patterns of both opal and organic carbon suggest that the variability in surface water productivity and or seafloor preservation of those materials is not simply correlated to glacial or interglacial periods eolian dust fluxes are greater during interglacial periods by factors of 2 to 5 indicating that eolian source regions in central and northern south america were more arid during interglacial periods the record of eolian grain size provides a semiquantitative estimation of the intensity of the transporting winds the eolian data suggest more intense atmospheric circulation during interglacial periods opposite to the anticipated results we interpret this observation as recording the southerly shift of the intertropical convergence zone to the latitude of hole 503b during glaciations