the physics of wind blown loess implications for grain size proxy interpretations in quaternary paleoclimate studies abstract loess deposits are recorders of aeolian activity during past glaciations since the size distribution of loess deposits depends on distance to the dust source and environmental conditions at the source during transport and at deposition loess particle size distributions and derived statistical measures are widely used proxies in quaternary paleoenvironmental studies however the interpretation of these proxies often only considers dust transport processes to move beyond such overly simplistic proxy interpretations and toward proxy interpretations that consider the range of environmental processes that determine loess particle size distribution variations we provide a comprehensive review on the physics of dust particle mobilization and deposition furthermore using high resolution bulk loess and quartz grain size datasets from a last glacial interglacial sequence we show that because grain size distributions are affected by multiple often stochastic processes changes in these distributions over time allow multiple interpretations for the driving processes consequently simplistic interpretations of proxy variations in terms of only one factor e g wind speed are likely to be inaccurate nonetheless using loess proxies to understand temporal changes in the dust cycle and environmental parameters requires i a careful site selection to minimize the effects of topography and source distance and ii the joint use of bulk and quartz grain size proxies together with high resolution mass accumulation rate calculations if possible

marine os isotopic fluctuations in the early eocene greenhouse interval as recorded by metalliferous umbers from a tertiary ophiolite in japan abstract the mineoka umbers occur within the tertiary accretionary complex of central japan immediately overlying 53 7 ma tholeiitic basalts the associated tholeiitic basalts exhibit typical normal mid ocean ridge basalt n morb type geochemical signatures and are interpreted to be a remnant of tertiary oceanic crust centimeter resolution bulk rock chemical analyses were performed to cover the entire section of the 35 cm thick umber deposit there are striking similarities in major element trace element re and os contents between the umbers and modern metalliferous sediments along the east pacific rise these results demonstrate that the mineoka umbers are ancient counterparts of mor metalliferous sediments that are plume fall out ferromanganese precipitates scavenging various seawater derived elements including p v y rees and os and confirm that the umbers subaerially exposed in the accretionary complex generally preserve their primary geochemical signatures at the time of deposition the marine 187 os 188 os ratios inferred from the mineoka umbers gradually increase up section with moderate fluctuations the 187 os 188 os composition ranging from 0 47 to 0 54 is significantly higher than that of the prior period post paleocene eocene thermal maximum petm 187 os 188 os 0 38 this was probably the result of an increase in the chemical weathering rate of continental crust caused by the long duration of noticeably warm climate during the early eocene greenhouse interval several fluctuations observed in the marine 187 os 188 os record during this interval are most likely related to petm like brief hyperthermals supporting the suggestion that the intensity of continental crustal weathering controlled by climatic changes can fluctuate on timescales of 10 5 yr

detecting induced in situ erodibility of a dust producing playa in australia using a bi directional soil spectral reflectance model abstract two sites on a playa claypan in south western queensland australia were chosen to represent the variability in soil surface conditions known to control wind erosion and dust production in the region the material was very fine and comprised of large amounts and different types of salts high electrical conductivity a propensity for slaking and the presence of cyanobacteria the surfaces of 4 plots at each site were modified using in situ rainfall simulation and wind tunnel abrasion the changes in the surface conditions were recorded using digital images and multi angular spectral measurements of reflectance and inverted against a soil bi directional spectral reflectance model optimised values of the model parameters produced the single scattering albedo ssa and a description of the scattering behaviour of the soil surfaces that included an estimate of microscopic roughness the model parameters removed the effect of the measurement conditions illumination and viewing geometry on the spectral reflectance abrasion of the untreated surfaces demonstrated that the variability in the antecedent surface conditions played an important role in their response rainfall drying and subsequent abrasion appeared to reset the soil surface conditions and controlled the spatial and temporal variation in the soil surface conditions redundancy analyses conducted separately for ssa of selected wavebands model parameter values and treatments elucidated the subtle and interactive effects of the treatments and surface responses the results showed that high intensity rainfall and abrasion was associated with wavebands in the visible region and reduced roughness low intensity rainfall was associated with wavebands in the near infrared and short wave infrared regions and increased roughness the analysis was interpreted as the result of eluviation due to rainsplash impact which caused size segregation and the preferential translocation of iron oxides to the surface and the creation of a thick surface seal and caused a thin crust which enabled the movement of salts and or mineral clays to the surface because of the strong evaporation gradient a poor relationship between aerodynamic resistance and microscopic roughness suggested that features of soil surface erodibility created by natural environmental processes such as rainsplash and wind erosion required a correction for macroscopic roughness the values of the model parameters appeared to be insensitive to the directional nature of the abrasion process the findings are significant for the development of this work towards an airborne or satellite based assessment of soil surface erodibility and erosion

initial indications of abiotic formation of hydrocarbons in the rainbow ultramafic hydrothermal system mid atlantic ridge in the presence of water olivine of ultramafic rock is oxidized during the process referred to as serpentinization water in contact with the olivine is reduced to molecular hydrogen h2 with the concomitant oxidation of fe ii the molecular hydrogen formed may be used as an energy source by lithotrophic bacteria but may at high temperature also be combined with co2 for the abiotic formation of organic compounds such as hydrocarbons and fatty acids through fischer tropsch type ftt synthesis our analyses of fluids from the peridotite hosted rainbow hydrothermal field on the mid atlantic ridge indicate de novo synthesis of linear saturated hydrocarbons the chain length of the hydrocarbons is between 16 and 29 carbon atoms the discovery of ftt reactions in ultramafic hydrothermal systems on earth provides an alternative pathway for the formation of early membranes and the origin of life

dust raising in the dustiest place on earth the bodele in northern chad is the dustiest place on earth it is dusty because of the co location of strong near surface winds and a large exposure of low density friable diatomite data are reported from three kinds of observation on dust generation in the bodele a two automatic weather stations and pilot balloon tracking complemented with reanalysis data measuring and estimating wind velocities b sun photometers measuring atmospheric dust concentrations c a vacuum pump dust sampler and an array of mwac sediment samplers measuring in situ sediment transport with these data we develop four hypotheses about dust generation 1 the pulsing of dust output from the bodele depends primarily on the varying strength of a low level jet llj i e at this scale dust production is transport limited 2 the most prolific mechanism of dust production is the breakdown of saltating diatomite flakes as they collide with each other and with the surface 3 disturbance of flow around the large barchans particularly turbulence and convergence on their horns is a major contributor to dust production i e the dunes are dust mills 4 in consequence dust production is localised within the main exposure of diatomite to places where there are the most dunes as on the eastern and northern fringes of the exposure

temporal record of osmium concentrations and 187os 188os in organic rich mudrocks implications for the osmium geochemical cycle and the use of osmium as a paleoceanographic tracer the final publication is available at elsevier via https doi org 10 1016 j gca 2017 06 046 2017 this manuscript version is made available under the cc by nc nd 4 0 license http creativecommons org licenses by nc nd 4 0

search for the proverbial mantle osmium sources to the oceans hydrothermal alteration of mid ocean ridge basalt abstract we present os and sr isotopes and mg os and sr concentrations for ridge crest high temperature and diffuse hydrothermal fluids plume fluids and ridge flank warm spring fluids from the juan de fuca ridge the data are used to evaluate the extent to which 1 the high and low temperature hydrothermal alteration of mid ocean ridge basalts morbs provides os to the deep oceans and 2 hydrothermal contributions of non radiogenic os and sr to the oceans are coupled the os and sr isotopic ratios of the high temperature fluids 265 353 c are dominated by basalts 187 os 188 os 0 2 87 sr 86 sr 0 704 but the concentrations of these elements are buffered approximately at their seawater values the 187 os 188 os of the hydrothermal plume fluids collected 1 m above the orifice of hulk vent is close to the seawater value 1 05 the low temperature diffuse fluids 10 40 c associated with ridge crest high temperature hydrothermal systems on average have os 31 fmol kg 1 187 os 188 os 0 9 and sr 86 mol kg 1 87 sr 86 sr 0 709 they appear to result from mixing of a high temperature fluid and a seawater component the ridge flank warm spring fluids 10 62 c on average yield os 22 fmol kg 1 187 os 188 os 0 8 and sr 115 mol kg 1 87 sr 86 sr 0 708 the data are consistent with isotopic exchange of os and sr between basalt and circulating seawater during low temperature hydrothermal alteration the average sr concentration in these fluids appears to be similar to seawater and consistent with previous studies in comparison the average os concentration is less than seawater by more than a factor of two if these data are representative they indicate that low temperature alteration of morb does not provide adequate non radiogenic os and that another source of mantle os to the oceans must be investigated at present the magnitude of non radiogenic sr contribution via low temperature seawater alteration is not well constrained if non radiogenic sr to the oceans is predominantly from the alteration of morb our data suggest that there must be a different source of non radiogenic os and that the os and sr isotope systems in the oceans are decoupled

evaluation of a wind erosion model in a desert area of northern asia by eddy covariance for the first time vertical fluxes of mineral dust measured by eddy covariance in two desert sites of northern asia have been used to test the performances of a wind erosion model in the field soil parameters required by the model were obtained through field and laboratory determinations model predictions and direct measurements have been compared the main finding was that the direction of the horizontal wind relative to the orientation of nebkhas played a crucial role in determining the emission of particles in one of the investigated sites being unable to simulate such interaction the model generally overestimated the actual emission it provided instead reliable predictions r2 0 87 when the wind direction was suitable in detaching loose erodible elements placed on nebkhas thanks to their normal orientation copyright 2009 john wiley sons ltd

osmium isotope variations in the oceans recorded by fe mn crusts this study presents osmium os isotope data for recent growth surfaces of hydrogenetic ferromanganese fe mn crusts from the pacific atlantic and indian oceans in general these data indicate a relatively uniform os isotopic composition for modern seawater but suggest that north atlantic seawater is slightly more radiogenic than that of the pacific and indian oceans the systematic difference in the os isotopic composition between the major oceans probably reflects a greater input of old continental material with a high re os ratio in the north atlantic ocean consistent with the distribution of nd and pb isotopes this spatial variation in the os isotope composition in seawater is consistent with a residence time for os of between 2 and 60 kyr indian ocean samples show no evidence of a local source of radiogenic os which suggests that the present day riverine input from the himalaya tibet region is not a major source for os recently formed fe mn crusts from the tag hydrothermal field in the north atlantic yield an os isotopic composition close to that of modern seawater which indicates that in this area the input of unradiogenic os from the hydrothermal alteration of oceanic crust is small however some samples from the deep pacific 4 km possess a remarkably unradiogenic os isotope composition 187 os 186 os ratios as low as 4 3 the compositional control of os incorporation into the crusts and mixing relationships suggest that this unradiogenic composition is most likely due to the direct incorporation of micrometeoritic or abyssal peridotite particles rather than indicating the presence of an unradiogenic deep water mass moreover this unradiogenic signal appears to be temporary and local and has had little apparent effect on the overall evolution of seawater these results confirm that input of continental material through erosion is the dominant source of os in seawater but it is not clear whether global os variations are due to the input of mantle or meteoritic material or simply indicate that the continental source itself is not uniform 1999 elsevier science b v all rights reserved

osmium isotopes in hydrothermal fluids from the juan de fuca ridge we present os data for axial high temperature and off axial low temperature hydrothermal solutions from the juan de fuca ridge the high temperature h s bearing axial fluids have unradiogenic os isotopes pointing to a nearly complete domination of osmium isotopes from the basalts during hydrothermal circulation the ridge axis fluids typically do not show large enrichment in osmium concentration over seawater although one high temperature fluid has an os concentration enhanced by a factor of 4 above seawater it appears that the os concentration of high temperature hydrothermal fluids is typically buffered at roughly the seawater concentration we suggest that subseafloor precipitation of pyrite from the high temperature hydrothermal fluids controls the osmium transportation the axial hydrothermal activity does not supply significant amounts of unradiogenic osmium to the deep oceans in contrast a low temperature off axis fluid is enriched in non radiogenic osmium over seawater by a factor of 9 showing much less precipitation of osmium at low temperature because a large fraction of the cooling of oceanic lithosphere occurs on ridge flanks os from low temperature ridge flank hydrothermal circulation may be a significant contributor to the balance of os in the oceans a detailed balance between os contributions from dissolution of cosmic dust and hydrothermal fluids is still not possible the low temperature hydrothermal sample gives os os 0 110 0 001 this extremely unradiogenic osmium can only come from a source that underwent depletion of re over 2 6 ga ago assuming no contamination during sample collection this result suggests that the convecting upper mantle contains ancient depleted material that imparted unradiogenic osmium to intruding basaltic melts

heterogeneous seawater 187os 188os during the late pleistocene glaciations abstract we report high temporal resolution osmium isotopes records of bulk sediment and sediment leachates from dsdp site 480 gulf of california over the last 30 ka from odp site 849 eastern equatorial pacific from the last 200 ka and from odp site 1002c cariaco basin across the 9 17 ka time interval in order to critically evaluate claims of a global 10 shift in the 187 os 188 os of seawater from glacial to interglacial intervals we use organic rich continental margin sites and carbonate rich pelagic sites to isolate the temporal variations of the osmium seawater isotopic composition our results reveal that variations in 187 os 188 os fail to correlate with global changes in temperature across glacials interglacials cycles as previously claimed instead these results indicate differences of a few percent in the measured 187 os 188 os between each oceanic basin we argue that these differences strongly suggest that seawater is not well homogenized with respect to its os isotope composition

fluxes to sediments underlying the rainbow hydrothermal plume at 36 14 n on the mid atlantic ridge abstract a geochemical investigation has been conducted of a suite of four sediment cores collected from directly beneath the hydrothermal plume at distances of 2 to 25 km from the rainbow hydrothermal field as well as a large biogenic component 80 caco3 these sediments record clear enrichments of the elements fe cu mn v p and as from hydrothermal plume fallout but only minor detrital background material systematic variations in the abundances of hydrothermal elements are observed at increasing distance from the vent site consistent with chemical evolution of the dispersing plume further pronounced ni and cr enrichments at specific levels within each of the two cores collected from closest to the vent site are indicative of discrete episodes of additional input of ultrabasic material at these two near field locations radiocarbon dating reveals mean holocene accumulation rates for all four cores of 2 7 to 3 7 cm kyr 1 with surface mixed layers 7 to 10 cm thick from which a history of deposition from the rainbow hydrothermal plume can be deduced deposition from the plume supplies elements to the underlying sediments that are either directly hydrothermally sourced e g fe mn cu or scavenged from seawater via the hydrothermal plume e g v p as holocene fluxes into to the cores surface mixed layers are presented which typically are an order of magnitude greater than background authigenic fluxes from the open north atlantic one core collected closest to the vent site indicates that both the concentration and flux of hydrothermally derived material increased significantly at some point between 8 and 12 14c kyr ago the preferred explanation is that this variation reflects the initiation intensification of hydrothermal venting at the rainbow hydrothermal field at this time perhaps linked to some specific tectonic event in this fault controlled hydrothermal setting

re os results from odp site 801 evidence for extensive re uptake during alteration of oceanic crust abstract re and os concentrations and os isotopic ratios were determined for composite samples prepared from volcanoclastics vcl and basaltic flows flo from jurassic oceanic crust ocean drilling program leg 185 site 801 in the western pacific with the aim of determining the effect of seafloor weathering on the re os budget a supercomposite sample prepared from a proportionate mixture of the various composite powders served to represent the average composition of the altered oceanic crust kelley k a plank t ludden j and staudigel h 2003 composition of altered oceanic crust at odp sites 801 and 1149 geochem geophys geosyst 4 6 8910 doi 10 1029 2002gc000435 re contents vary from 0 2 to 1 3 ng g 1 and from 2 2 to 3 1 ng g 1 in the vcl and flo composites respectively os contents vary from 0 005 to 0 047 ng g 1 in the vcl and from 0 008 to 0 027 ng g 1 in the flo composites the flo composites have much higher re os ratios and thus have more radiogenic os compositions 187os 188os 1 38 to 8 48 than the vcl composites 187os 188os 0 32 to 4 40 the vcl composite from the upper section of the crust shows evidence for substantial re loss and os uptake consistent with oxidative weathering processes however re uptake during weathering processes under more reducing conditions evident in the flo samples from throughout the section and to a lesser extent in the lower vcl samples more than compensates for this re loss in the upper vcl os concentrations were essentially unchanged by these reductive processes model age calculations suggest that re uptake continued for tens of millions of years after crust formation abundant secondary pyrite is found throughout the altered hole 801c crust in zones of restricted seawater flow and this may have accommodated an important part of the input re the re content of the supercomposite 2 2 ng g 1 is about 1 ng g 1 higher than would be expected on the basis of its yb content if the results from hole 801c are typical they suggest that the re concentration of at least the upper part of the oceanic crust may be nearly doubled during seafloor alteration such large extents of re uptake would have a significant effect on the oceanic re budget furthermore assuming that they survive passage through the subduction zone these elevated re contents would greatly decrease the proportion of subducted oceanic crust required in the source region to explain the radiogenic os compositions of many ocean island basalts

the emission and vertical flux of particulate matter 10 mum from a disturbed clay crusted surface arid and semi arid environments are important sources for the atmospheric loading of pm10 particulate matter 10 lm although the emission of this material is often limited by surface crusts this study investigates the emission and vertical flux of pm10 from a clay crusted playa with and without saltating grains to abrade the surface using a portable field wind tunnel it was found that despite disturbance to the surface the emission of pm10 decays rapidly without abrasion only in the presence of saltating grains was pm10 continuously liberated from the surface such that the emission rate the total amount of pm10 emitted from the surface expressed as a horizontal flux varied linearly with the saltation transport rate although the emission of pm10 was found to depend on saltation abrasion past studies have tended to focus on the relationship between the vertical flux of pm10 the amount of pm10 being transported vertically through the boundary layer and the shear velocity in this study the vertical flux of pm10 was found to vary with the shear velocity to the power of 2ae14 although the vertical pm10 flux is a proportion of the emission rate the horizontal flux no statistically significant relationship was observed between the emission rate and the shear velocity the disparity of these results is explained by the lack of a consistent relationship between the shear velocity and the saltation transport rate in this supply limited environment this suggests that the observed relationship between the vertical pm10 flux and the shear velocity is a spurious correlation resulting from the use of shear velocity to calculate the vertical dust flux it is thus concluded that shear velocity is not an appropriate variable for emission modelling in supply limited environments and that improvements in dust emission modelling will only be realized if the abrasion process is the focus of a concerted research effort

rhenium osmium and molybdenum isotope systematics of black shales from the lower cambrian niutitang formation sw china evidence of a well oxygenated ocean at ca 520 ma abstract the early cambrian was a key period in earth s history and the reconstruction of ancient ocean chemistry on spatial and temporal scales can contribute to a better understanding of events during that period new early cambrian data for re os and mo isotopic compositions and redox sensitive elements rse are reported here for the niutitang formation se chongqin sw china a re os age of 520 30 myr model 3 2 n 21 mswd 62 and a 187os 188os i ratio of 0 79 0 11 were obtained consistent with previously reported data for equivalent strata from other areas separate regression of samples with 187os 188os i of 0 72 0 79 and 0 81 0 89 produce more precise ages of 520 1 9 5 myr model1 2 n 7 mswd 1 0 and 513 10 myr model 1 2 n 8 mswd 0 96 respectively suggesting heterogeneity in the primary source of os as the dominant cause of scatter and uncertainty high initial 187os 188os of 0 79 0 11 may indicate a high os input from oxidative weathering of upper continental crust for early cambrian ocean based on rse data such as mo u v enrichment and ni co v cr v v ni moef uef re mo ratios two geochemically distinct zones upper and lower can be delineated in the sedimentary sequence as reflected in drillcore sections the upper section n 9 is characterized by low total organic carbon toc contents mean 1 8 1 5 wt low rse contents mo 0 008 0 006 10 3 g g v 0 22 0 15 10 3 g g u 0 008 0 004 10 3 g g and low v cr 2 0 1 7 ni co 5 9 3 5 moef uef 2 6 1 8 and mo toc 6 0 3 9 ratios in contrast the lower core section n 13 is characterized by high toc contents 4 4 2 2 wt high rse contents mo 0 10 0 08 10 3 g g v 1 0 1 0 10 3 g g u 0 05 0 04 10 3 g g high v cr 6 5 ni co 24 14 moef uef 6 3 2 2 and mo toc 21 9 ratios uncertainties are 1sd here significantly decreasing trends of those redox proxies from lower to upper sections suggest that the depositional conditions evolved from anoxic euxinic to oxic condition all samples display extremely low re mo ratios of 0 2 10 3 1 9 10 3 indicating the absence of intermediate reducing conditions possibly reflecting rapid ocean oxygenation the mo isotopic composition in the sedimentary succession of the yc9 core exhibits a large variation with 98 95mo values of 0 04 2 00 upper section 98 95mo values display an opposite trend to mn content and negative correlation with mo toc ratios indicating mo fractionation associated with adsorption on mn oxides or oxyhydroxides lower section 98 95mo values are positively correlated with mo toc ratios and negatively with re mo ratios suggesting incomplete conversion of molybdates to tetrathiomolybdates under weakly euxinic conditions high 98 95mo of 2 00 and high average mo toc ratios of 21 10 6 g g wt were observed in euxinic shales in the niutitang formation suggesting extensive ocean oxygenation may have taken place at ca 520 ma

grain size characteristics of sediment transported during dust storms abstract the grain size characteristics of sediment transported by wind in creep saltation and suspension during 15 dust storms in the slims river valley yukon territory were investigated grain size analysis of the transported sediment indicated that the suspended sediment is significantly finer and better sorted than the sediment transported in either surface creep or saltation the data also show that during dust storms the mean particle size of the suspended sediment decreases as a power function of height the grain size distributions of the sediment transported in suspension and surface creep are characterized by strong positive skewness which results from the selective removal of surface particles small enough to be transported by the wind at a given velocity in contrast the grai size distribution of the saltation samples are negatively skewed which is thought to result from the selective removal of the finer particles into suspension from those particles initially lifted from the surface into the air stream thus the proportion of sediment initially entrained into the air stream which returns to the surface in saltation will lack the fine grains removed in suspension and will therefore tend to be less positively or negatively skewed

eolian suspension above the saltation layer the concentration profile abstract the acquisition of a new set of data on dust emission obtained at owens lake california was used to assess the performance of a previously published theoretical model that describes the normalized concentration profile of material in suspension above an actively emitting surface as a logarithmic function the normalized concentration profile has more commonly been modeled as a power law least squares regression was used to fit both the logarithmic and the power law model to approximately 20 hours of data on 10 minute average concentration profiles results for all these data combined and for each individual profile indicated that the logarithmic model better explains the concentration gradient profile than the power law model the predicted behavior of the model parameters including a concentration scaling parameter and a transfer coefficient for suspended particles was examined it was observed that divided by a defined reference concentration was relatively invariant during emission events as predicted by the model and had a value of 0 18 0 02 for the reference heights at which particle concentration and wind speed were measured 1 7 and 9 m the transfer coefficient for suspended particles was approximately 0 22 0 05 of the calculated momentum transfer coefficient defined here as the wind speed at the reference height divided by the friction velocity

reconstructing the marine 187os 188os record and the particulate flux of meteoritic osmium during the late cretaceous abstract paired analyses of os isotope composition and concentration of bulk sediment and leachable os in a metalliferous pelagic clay sequence from the north pacific odp site 886c are used to reconstruct the marine os isotope record and the particulate meteoritic os flux between 65 5 and 78 ma measured 187os 188os of bulk sediments ranges from approximately 0 64 to 0 32 and those of leach analyses are very similar to bulk analyses hydrogenous os dominates the sedimentary os inventory throughout most of the studied interval as a result the measured 187os 188os of leachable os approximates that of contemporaneous seawater the odp 886c record shows rising 187os 188os in the deepest portion of the core with a local maximum of 0 66 close to 74 ma the 67 72 ma portion of the record is characterized by nearly constant 187os 188os ratios close to 0 6 the structure of the marine os isotope record from odp 886c differs markedly from the seawater 87sr 86sr curve which rises monotonically throughout the time interval studied here calculated particulate meteoritic os fluxes are between 0 5 and 2 pg cm 2 kyr 1 throughout most of the studied interval two discrete intervals of the core one of which is within cretaceous tertiary boundary ktb interval are characterized by higher fluxes of meteoritic os excluding these two intervals the average background flux of particulate meteoritic os is roughly half of that estimated from analyses of cenozoic marine sediments these are the first os isotope data to provide evidence of resolvable temporal variations in the background flux of particulate meteoritic material to the earth

effects of atmospheric conditions on wind profiles and aeolian sand transport with an example from white sands national monument quantifying aeolian sand transport rates relies upon the computation of the near surface shear velocity u determined from velocity profiles of the wind while it has been recognized that various conditions such as saltation surface roughness surface slope and atmospheric conditions have an effect on the velocity profile it is commonly assumed that measurements made above the surface will be representative of the near surface shear velocity airflow and temperature data collected over a flat substrate at white sands national monument in new mexico however show the significant effects that atmospheric conditions have on velocity profiles during the day when solar insolation is heating the surface atmospheric conditions in the lowest several metres become unstable resulting in enhanced convection and vertical mixing so that the velocity gradient changes little with height as a result the shear stress in this region of vertical mixing lessens while the near surface shear stress is increased because the higher wind speeds are now nearer the surface at night the near surface atmospheric conditions are stable thereby reducing convection and vertical mixing resulting in stratified airflow and increased shear velocity away from the surface unless this atmospheric effect is accounted for estimates of sediment transport rates may be in error by as much as a factor of 15 times when wind speeds are near threshold velocity at wind speeds approaching 10 ms1 at 5m above the surface this error in computing sediment transport is reduced to a factor of only two to three times and may be within the range of measurement error

is spreading prolonged episodic or incipient in the andaman sea evidence from deepwater sedimentation abstract the central andaman basin cab is generally accepted to be a site of continuous sea floor spreading since the early pliocene 4 0 ma the adjacent alcock and sewell rises and part of the east andaman basin have been interpreted as probable miocene oceanic crust published seismic lines across the eastern half of the spreading centre show that 100 s m thickness of sediment are present right up to the central trough the central trough margins are faulted uplifted and tilted away from the central trough the youngest sediment is ponded and onlaps the tilted central trough margin while older faulted sediment lies within the trough such a configuration is incompatible with continuous spreading instead either spreading in the central basin was episodic probably comprising a late miocene early pliocene phase of spreading followed by extension accommodated in the alcock and sewell rise area by faulting and dike intrusion and then a recent quaternary return to spreading in the central trough or the central trough marks an incipient spreading centre in hyper thinned continental or possibly island arc crust to resolve these possibilities regional satellite gravity data was inverted to determine crustal type and thickness the results indicate the cab is oceanic crust however the adjacent regions of the alcock and sewell rises and the east andaman basin are extended continental crust these regions were able to undergo extension before seafloor spreading and when seafloor spreading ceased unpublished seismic reflection data across the east andaman basin supports the presence of continental crust under the basin that thins drastically westwards towards the spreading centre episodic seafloor spreading fits with gps data onshore that indicate the differential motion of india with respect to se asia is accommodated on widely distributed structures that lie between the trench and the sagaing fault

osmium in seawater vertical profiles of concentration and isotopic composition in the eastern pacific ocean os concentrations 6 6 to 9 8 pg l and isotopic compositions mean 187os 188os 1 067 0 011 2 error were measured by a new method in seawater samples collected from the eastern pacific ocean in contrast to recent work in the indian ocean measured os concentrations display a 30 depletion coincident with both the core of the oxygen minimum zone and a local minimum in light transmission whilst we cannot preclude the possibility that an oxidation resistant form of os in seawater prevented isotopic equilibration between the enriched isotope spike and naturally occurring os which would bias measured concentrations to low values we interpret these data as evidence of non conservative behaviour of os in seawater in this zone the data may be explained by two possible processes the horizontal advection of a water mass of low os concentration from the continental slope and or the in situ adsorption of os onto sinking particles to what extent each process is contributing to the os minimum is unclear from the data the os isotopic composition of these eastern pacific samples are within 2 of those recently reported from the indian ocean which indicates that the isotopic composition of seawater os in these two ocean basins is indistinguishable at this level of precision neutrally buoyant hydrothermal plume samples collected in close proximity to active vents at 9 46 n on the east pacific rise have os concentrations and isotopic compositions similar to ambient deep water this shows that the flux of os from high temperature hydrothermal vents is not large compared to the inventory of os in ambient seawater comparisons between filtered and unfiltered samples show that the majority of seawater os in these samples is in the dissolved phase

dissolved platinum in major rivers of east asia implications for the oceanic budget 1 dissolved platinum concentrations of eleven large pristine river systems in east asia 200 samples were determined to better constrain the oceanic platinum budget most samples had concentrations less than 1 4 pm relatively high concentrations up to 5 8 pm were measured in only approximately 6 of the samples the median pt concentrations of the individual river systems had only a small range from 0 18 pm duman to 0 63 pm huang he and the difference in pt yield mainly resulted from the difference in runoff the rivers draining the eastern tibetan plateau the salween mekong chang jiang yangtze hong red and huang he yellow had higher pt yield than the rivers of the russian far east the amur lena yana indigirka and kolyma if the discharge weighted mean pt concentration of our samples 0 36 pm is extrapolated globally the estimated riverine flux of dissolved pt to the ocean is 13 103 mol y 1 based on this riverine flux the estimated oceanic residence time of pt is 24 10 kyrs a 50 release and 50 uptake of pt in estuaries would modify this to 16 kyrs and 45 kyrs respectively

platinum element group variations at the permo triassic boundary in kashmir and british columbia and their significance abstract the end permian marks the greatest extinction in the geological record but there is no consensus on whether it was caused by terrestrial or extraterrestrial factors platinum group elements pge can readily separate extraterrestrial from terrestrial sources and the few studies so far from china and europe indicate terrestrial sources for the pge we report here detailed pge analyses of two expanded sections from the late permian northern and southern hemispheres that allow separate events to be distinguished and confirm a terrestrial source for the pge these sources are either contemporaneous seawater or older basaltic volcanics associated with the sections and the pge were precipitated by a possible combination of development of anoxia in the oceans and post depositional redistribution the pge content in sections at the permo triassic boundary is the result of geochemical and lithological control on metal precipitation that is found in many other black shales throughout geological time

discovery of ancient and active hydrothermal systems along the ultra slow spreading southwest indian ridge 10 16 e 1 we report the discovery of active and fossil hydrothermal systems during r v knorr cruise 162 legs vii and ix along a 400 km long segment of the ultra slow southwest indian ridge swir between 10 and 16 e where the effective spreading rate for mantle upwelling is the slowest of any ocean ridge explored to date 8 4 mm yr 1 full rate eight of forty one optical temperature profiles contain hydrothermal plume characteristics that indicate firm evidence for two active vent sites and tentative evidence for as many as three others fossil hydrothermal material was recovered in 6 of the 38 dredge hauls and includes an occurrence of partially oxidized sulfide breccias four deposits ofsepiolite and silica as well as mn oxide and nontronite cemented breccias the massive sulfide deposit likely developed during mixing of upwelling hot fluids with cold seawater within a shallow permeable fault breccia along a deep seated normal fault bounding the southern rift valley wall silica and sepiolite deposits were found mostly on the rift valley walls and likely formed during low to moderate temperature ultramafic hosted hydrothermal activity the abundance of hydrothermal material and the frequency of localized hydrothermal activity is remarkable because the mantle upwelling and magma supply rates and hence the magmatic heat input along this section of the swir are lower than on any other explored segment of the global mid ocean ridge system this observation suggests that high mantle upwelling and magma supply rates are not required to drive mid ocean ridge hydrothermal systems and that a close relationship between magmatic heat input and hydrothermal activity may not be established at the ultra slow end of the ridge spreading spectrum the frequency and distribution of hydrothermal activity in the study area may reflect a largely tectonic control on fluid circulation with hydrothermal vent sites being preferentially associated with long lived faults that provide fluid pathways our results suggest the contribution of magma starved ridge segments to the global ocean lithosphere geochemical budget is potentially much larger than previously thought

the relationship between p fe and v fe ratios in hydrothermal precipitates and dissolved phosphate in seawater a strong positive relationship between the molar p fe ratio in fresh hydrothermal fe ferrihydrite precipitates and seawater dissolved phosphate has been demonstrated using samples from the atlantic and pacific oceans we ascribe this relationship to scavenging of dissolved phosphate from seawater during the formation of hydrothermal fe rich particles above hydrothermal vents in contrast molar v fe ratios in hydrothermal particles are inversely correlated with dissolved phosphate these results indicate that inter ocean variations in dissolved phosphate control the p fe and v fe ratios in hydrothermal fe precipitates one of the precursors of metalliferous sediment

extreme enrichment of polymetallic ni mo pge au in lower cambrian black shales of south china an os isotope and pge geochemical investigation extreme metal enrichments occur in the lower cambrian niutitang formation a thick black shale sequence deposited on the yangtze platform of south china and form a regionally distributed conformable polymetallic ni mo pge au sulfide horizon the origin for the extreme enrichment of metals in these black shales is discussed based on a comprehensive geochemical investigation of re os isotopes and platinum group elements the black shales of the lower cambrian niutitang formation in guizhou province yielded an re os isochron age of 535 11 ma with an initial 187 os 188 os ratio of 0 80 0 04 which is similar to the initial 187 os 188 os ratio 0 78 0 19 of the ni mo sulfide ores but slightly lower than the initial 187 os 188 os ratio 1 18 0 02 of lower cambrian black shales from the lesser himalaya india a comparison of os isotope data among the chinese ni mo sulfide ores the seafloor massive sulfide deposits and contemporaneous seawater suggests a possible similar hydrothermal forming mechanism for these deposits the pge concentrations pt anomaly pt pt pt pd ir pd au pd ratios of the chinese ni mo sulfide ores are similar to those metal rich black shales of submarine volcanogenic hydrothermal origin from czech republic namibia and canada but are different from those data of the ocean floor fe mn crusts that have scavenged their pge and other metals directly from seawater it is therefore suggested that the ni mo sulfide ores from the niutitang black shale sequence in south china had a submarine hydrothermal origin the anoxic environments and abundant organic matter in the ocean basin also played a key role for the extreme metal enrichments the discharge of hydrothermal fluids into the cambrian ocean may have had a great effect on life during the cambrian explosion 2007 elsevier b v all rights reserved

effects of spatial variations in source areas upon dust concentration profiles during three wind erosion events in australia dust storms are a major contributor to soil erosion in inland australia and the simpson desert channel country region is one of the most active wind erosion regions while information is available on wind erosion rates at the land type level little is known about the influence spatial variations in the erodibility within a land type has on the resulting dust concentration profile a gaussian plume model dsis is presented along with tower based dust data to describe the influence of different spatial combinations of dust sources areas during three dust events on the diamantina river flood plain in western queensland australia

deposition of osmium and other platinum group elements beneath the ultramafic hosted rainbow hydrothermal plume osmium and other platinum group elements pges have been measured in sediments accumulating directly under the rainbow hydrothermal plume at 36 deg n on the mid atlantic ridge 187os 188os and pge concentrations in the sediments of four cores taken 2 25 km from the active vent site reveal evidence of both radiogenic os scavenged from seawater and importantly unradiogenic os released by hydrothermal venting the majority of analyses n 16 yield 187os 188os ratios that fall in a narrow range 0 99 1 06 close to that of modern seawater in these samples os concentrations correlate linearly with hydrothermal v enrichments which are also derived from seawater scavenging a smaller subset of samples characterized by unusually high concentrations of ni and cr derived from ultramafic rock fragments exhibit distinctly lower 187os 188os ratios their ir content is also higher and their pge ratios are more similar to mantle material than the pge patterns of the larger set of samples dominated by seawater scavenged os although the two most proximal cores lack evidence for any similar ultramafic detritus in their surficial sediments 187os 188os ratios in these samples are also lower than that of ambient seawater suggesting they are likely to have been influenced by unradiogenic os from vent fluid incorporated into the plume samples from the most distal core by contrast exhibit 187os 188os ratios indistinguishable from that of seawater compared with background ne atlantic sediments os is enriched four fold in the seawater dominated samples while pd pt and ir are twice the background value burial fluxes of os scavenged by hydrothermal fe in these sediments are 200 400 pg cm 2 kyr 1 up to twice that found on the epr and several times the background bg of 50 pg cm 2 kyr 1 for pt burial fluxes are 1800 3000 pg cm 2 kyr 1 bg ca 1000 pg cm 2 kyr 1 and for pd 2700 4600 pg cm 2 kyr 1 bg ca 800 pg cm 2 kyr 1

the marine osmium isotope record over the past decade the marine osmium isotope record has been developed into a new tracer in palaeoceanographic research several analytical developments particularly in the past few years have significantly increased our ability to study the behaviour of osmium in the surficial environment the 187os 188os and osmium concentration of seawater river water rain and hydrothermal vent fluids have been measured directly recently the behaviour of osmium in estuaries critical for estimating the marine residence time of osmium has been studied our knowledge of the surficial osmium cycle has thus significantly improved in addition reconstructions of past variations in the marine 187os 188os recently have been extended back into the mesozoic this review attempts to summarize our current understanding of the marine osmium system present and past the 187os 188os of seawater during the cenozoic to first order mimics the marine 87sr 86sr record it is therefore tempting to interpret both records as reflecting increased input of radiogenic osmium and strontium resulting from enhanced continental weathering regulated by climatic tectonic processes however the marine osmium isotope system differs fundamentally from the marine strontium isotope system this review emphasizes three important differences first large impacts are capable of resetting the 187os 188os to unradiogenic values without significantly affecting the marine strontium system second organic rich sediments are characterized by high 187re 188os resulting 187os 188os ingrowth trajectories are similar to the average slope of the cenozoic 187os 188os seawater record trends towards more radiogenic 187os 188os seawater therefore can be caused by weathering of organic rich sediments at a constant rate third the marine residence time of osmium is sufficiently short to capture short periodic glacial interglacial fluctuations that are inaccessible to the buffered marine strontium isotope system this offers the opportunity to discriminate between high frequency climatic and low frequency tectonic forcing

rhenium osmium isotope systematics of an early mesoproterozoic sedex polymetallic pyrite deposit in the north china craton implications for geological significance and the marine osmium isotopic record abstract the rhenium osmium re os isotopic system preserved in ancient seafloor hydrothermal sulfide deposits can be used to gain insight into the os composition of ancient seawater in particular the age of sedimentary exhalative sedex deposits can be determined by measuring re os isotopes in syn depositional pyrite a common constituent of sedex deposits here we report on the gaobanhe sediment hosted polymetallic pyrite deposit which is hosted within the gaoyuzhuang formation in the central part of the northern margin of the north china craton ncc re os isotopic data from syn depositional pyrite yield an isochron age of 1505 55 ma constraining the timing of primary mineralization as well as the minimum age of the host sediments to the mesoproterozoic analyzed pyrite grains indicate an initial 187os 188os osi value of 0 181 0 066 suggesting that the mineralizing fluids were an admixture of seawater and submarine hydrothermal fluids with the os being primarily derived from seawater the osi value is slightly higher than that of paleoproterozoic seawater 0 13 suggesting that there was a radiogenic riverine flux to the oceans and that atmospheric oxygen must have been sufficiently high at that time to drive this increased continental radiogenic os input to the oceans we propose that the re os isotopic system as recorded by these sedex deposits may provide key insights when examining changes in the os isotopic composition of seawater throughout the precambrian

accretion of extraterrestrial matter during the last 80 million years and its effect on the marine osmium isotope record the flux of particulate extraterrestrial et matter to the deep sea has been calculated using a four component mixing model based on osmium concentrations and isotope ratios in slowly accumulating pelagic sediments from the pacific ocean nineteen published bulk leach osmium isotope data pairs that cover the last 80 million years have been used for the calculation the calculated annual particulate flux averaged over several 100 ka by slow accumulation and bioturbation ranges from 18 000 to 67 000 tons with a mean value of 37 000 13 000 tons the data indicate no significant variability in the flux with time except at the k t boundary and are thus compatible with results based on ir accumulation in deep sea sediments the inferred constancy of the et matter flux is in contrast to recent results based on the et 3he flux that integrates only a small size fraction of the entire et matter flux 3he data indicate variability by a factor of 6 over the past 70 ma and a fivefold increase in the et flux between 3 ma and 1 ma that is not seen in the bulk et matter flux based on osmium isotope data the apparent constancy of the cosmic matter flux over the past 80 ma stands in marked contrast to the dynamic nature of the marine osmium isotope record and indicates that dissolution of cosmic matter does not drive changes in this record except at the k t boundary a comparison between osmium isotope and ir data from two pelagic sediment cores from the pacific dsdp site 596 and ll44 gpc3 indicates that the seawater soluble fraction of et os cannot exceed 36 kg a and most likely is significantly smaller the maximum value of 36 kg a can account for approximately one half of the seawater soluble et matter flux necessary to balance the radiogenic continental runoff of os without any additional unradiogenic source simple mass balance calculations indicate that an additional unradiogenic source of os to the oceans most likely alteration of oceanic crust is required to balance the present day seawater osmium isotopic composition this source is probably more important in balancing radiogenic continental runoff than is dissolution of cosmic matter in seawater

hydrothermal activity along the southwest indian ridge twenty years after the discovery of sea floor hot springs vast stretches of the global mid ocean ridge system remain unexplored for hydrothermal venting the southwest indian ridge is a particularly intriguing region as it is both the slowest spreading of the main ridges1 and the sole modern migration pathway between the diverse vent fauna of the atlantic and pacific oceans2 a recent model postulates that a linear relation exists between vent frequency and spreading rate3 and predicts vent fields to be scarcest along the slowest spreading ridge sections thus impeding migration and enhancing faunal diversity2 here however we report evidence of hydrothermal plumes at six locations within two 200 km long sections of the southwest indian ridge indicating a higher frequency of venting than expected these results suggest that fluxes of heat and chemicals from slow spreading ridges may be greater than previously thought and that faunal migration along the southwest indian ridge may serve as an important corridor for gene flow between pacific and atlantic hydrothermal fields

the effect of hydrothermal processes on midwater phosphorus distributions in the northeast pacific abstract the distributions of dissolved particulate and sedimentary phosphorus were measured in the region of the juan de fuca ridge to determine the impacts of hydrothermal processes on the phosphorus cycle in the oceans significant negative dissolved phosphate anomalies ranging from 0 to 60 nmol l were observed in the water column at depths between 1900 and 2300 db the largest anomalies

climate correlated variations in seawater 187 os 188 os over the past 200 000 yr evidence from the cariaco basin venezuela abstract a high resolution record of seawater osmium isotopic composition 35 samples over the past 191 000 yr has been obtained from sediments from ocean drilling program odp leg 165 site 1002 in the cariaco basin venezuela strong correlations are observed between 187os 188os and both the local and global oxygen isotopic records with less radiogenic values observed during glacial intervals in conjunction with previous analyses of sediments from the east pacific rise the santa barbara basin and the japan sea the data demonstrate conclusively that there have been ocean wide changes in seawater 187os 188os over the pleistocene global seawater excursions to relatively unradiogenic 187os 188os indicating decreased continental inputs occur during cold intervals times of increased aridity and increased ice cover of old radiogenic continental masses the data thus indicate a direct climatic control on chemical weathering rates and or composition of weathering products on a glacial interglacial timescale

pge distribution in massive sulfide deposits of the iberian pyrite belt we present the first platinum group elements pge data on seven massive sulfide deposits in the iberian pyrite belt ipb one of the world largest massive sulfide provinces some of these deposits can contain significant pge values the highest pge values were identified in the cu rich stockwork ores of the aguas tenidas este pge 350 ppb and the neves corvo pge 203 ppb deposits chondrite normalized pge patterns and pd pt and pd ir ratios in the ipb massive and stockwork ores are consistent with the leaching of the pge from the underlying rock sequence

osmium isotopic variations in metalliferous sediments from the east pacific rise and the bauer basin the osmium concentration and isotopic composition of metalliferous sediments from the east pacific rise epr and bauer basin have been determined 187os186os ratios range from 7 9 to 8 6 with epr samples between 8 4 and 8 6 and bauer basin samples between 7 9 and 8 2 the osmium isotopic composition of epr samples is indistinguishable from the inferred osmium isotopic composition of seawater requiring that nearly all the osmium in these sediments is hydrogenous in origin this result is used to place broad constraints on the behavior of osmium in ridge crest hydrothermal systems while bauer basin samples also contain predominantly hydrogenous osmium an additional source of osmium with low 187os186os is required to account for the lower measured ratios calculation of total osmium burial fluxes in the bauer basin show that the background flux of cosmic osmium is adequate to produce the observed depression in bauer basin 187os186os ratios burial flux calculations also suggest that metalliferous sediment deposition is a significant sink in the marine osmium cycle

the implications for dust emission modeling of spatial and vertical variations in horizontal dust flux and particle size in the bodele depression northern chad the bodele depression has been confirmed as the single largest source of atmospheric mineral dust on earth it is a distinctive source because of its large exposure of diatomite and the presence of mega barchan dunes direct measurements of horizontal dust flux and particle size were made to investigate dust emission processes and for comparison with mechanisms of emission assumed in current dust models more than 50 masts with traps mounted on each were located across and downwind of three barchans in 56 km2 study area of the eastern bodele the size distribution of surface material is bi modal there are many fine dust modes and a mixed mineralogy with a particle density three times smaller than quartz horizontal fluxes up to 70 m above the playa of particles up to 1000 m in diameter are produced frequently from the accelerated flow over and around the barchans even in below threshold shear conditions on the diatomite playa our data on dust sizes do not conform to retrievals of dust size distributions from radiance measurements made in the same area dust emission models for the region may need to be revised to account for saltators in the bodele which are a mixture of quartz sand and diatomite flakes the great spatial and vertical variation in the abundance mass and density of dust and abraders and the patterns of surface erodibility all of these have important local effects on the vertical dust flux and its particle sizes

sediment transport by wind toward a general model a general model of eolian sediment transport by both saltation and suspension is developed saltation is analyzed through calculations of single trajectories given initial conditions of liftoff speed angle and spin profiles of particle concentration and mass flux generated by assuming that all trajectories are identical display distinct maxima at the top of the trajectory by incorporating the realistic distribution of trajectories that arises from the stochastic nature of grain impacts with a granular bed the model yields monotonic decreases in particle concentration and mass flux with height in accordance with published empirical data the analysis of suspension as the balance between downward advective flux as a result of the settling of grains and their upward diffusive flux as a result of turbulence results in concentration profiles that fall off as power laws with height also in accordance with empirical data a relation for reference level concentrations is presented for both blowing snow and dust profiles the solutions for saltation and suspension are combined to yield mass flux profiles for the entire range of grain sizes in the bed the saltation layer emerges naturally as that region where the total flux of saltating grains exceeds that of suspended grains the model points clearly to the need for further research on the stochastic grain bed interactions which control both the probability distribution of liftoff velocities in saltation and the production of fine particles in suspension

major and trace element geochemistry and os isotopic composition of metalliferous umbers from the late cretaceous japanese accretionary complex 1 metalliferous umbers and red shales occur as unique products of the kula pacific ridge forearc collision in the late cretaceous shimanto supergroup an accretionary complex in japan these umbers are closely associated with greenstones of mid ocean ridge basalt morb origin and are regarded as hydrothermal metalliferous precipitates related to mor type volcanism the umbers and red shales were deposited in the trench area where both terrigenous detritus from land and hydrothermal metalliferous particulates from a mor were supplied simultaneously besides a predominance of fe and mn the umbers exhibit remarkable enrichments in p v co ni zn y mo rare earth elements rees and os relative to continental crustal abundances the x fe x mn p v co ni zn y and rees ratios and paas normalized ree patterns of the umbers are very similar to those of modern hydrothermal plume fallout precipitates deposited on flanks of mor this indicates that the umbers preserve primary geochemical signatures of hydrothermal metalliferous sediments that scavenged seawater derived elements and thus can be used as a proxy for late cretaceous seawater the marine 187os 188os ratios reconstructed from the late maastrichtian umbers range from 0 42 to 0 56 and are very consistent with recent data obtained from the pacific and atlantic pelagic carbonates that record an abrupt decline from 0 55 to 0 4 during the period between 67 0 ma and 65 7 ma

accretion rate of extraterrestrial particles determined from osmium isotope systematics of pacific pelagic clay and manganese nodules abstract pelagic clay and mn nodules from domes sites in the north pacific and a varved glacial lake deposit from connecticut were analysed for os concentration and isotopic composition by isotope dilution secondary ion mass spectrometry after treatment by nis fusion or oxalic acid leaching bulk pelagic clay from domes site c has 187 os 186 os 6 5 and os 0 14 ng g oxalic acid leaches of this same sediment and of mn nodules from domes sites a and c have more radiogenic 187 os 186 os ratios which average 8 3 bulk glacial lake hitchcock sediment has 187 os 186 os 12 5 and os 0 06 ng g the total os flux to north pacific pelagic clay is 7 to 10 ng os cm2 106 y lake hitchcock sediment provides an integrated value for the local crustal 187 os 186 os ratio the oxalic acid leaches are assumed to attack hydrogenous phases selectively a simple model in which the only sources of os to the ocean are continental crust with the isotopic composition of lake hitchcock 187 os 186 os 12 5 and extraterrestrial particles with 187 os 186 os 1 1 results in a cosmic flux of osmium to the sediment of 4 9 ngos cm2 106 y of which 20 is hydrogenous a model in which the sources of os to the ocean are continental crust with an 187os 186os ratio of 30 from the model of palmer and turekian 1986 oceanic mantle or crust with 187 os 186 os 1 04 and extraterrestrial particles with 187 os 186 os 1 1 results in a cosmic flux of os to the sediment of 5 7 ngos cm2 106 y of which none is hydrogenous these extraterrestrial os fluxes correspond to maximum c 1 chondrite accretion rates of between 4 9 104 and 5 6 104 tonnes y

review and revision of cenozoic tropical planktonic foraminiferal biostratigraphy and calibration to the geomagnetic polarity and astronomical time scale planktonic foraminifera are widely utilized for the biostratigraphy of cretaceous and cenozoic marine sediments and are a fundamental component of cenozoic chronostratigraphy the recent enhancements in deep sea drilling recovery multiple coring and high resolution sampling both offshore and onshore has improved the planktonic foraminiferal calibrations to magnetostratigraphy and or modified species ranges this accumulated new information has allowed many of the planktonic foraminiferal bioevents of the cenozoic to be revised and the planktonic foraminiferal calibrations to be reassessed we incorporate these developments and amendments into the existing biostratigraphic zonal scheme in this paper we present an amended low latitude tropical and subtropical cenozoic planktonic foraminiferal zonation we compile 187 revised calibrations of planktonic foraminiferal bioevents from multiple sources for the cenozoic and have incorporated these recalibrations into a revised cenozoic planktonic foraminiferal biochronology we review and synthesize these calibrations to both the geomagnetic polarity time scale gpts of the cenozoic and astronomical time scale ats of the neogene and late paleogene on the whole these recalibrations are consistent with the previous work however in some cases they have led to major adjustments to the duration of biochrons recalibrations of the early middle eocene first appearance datums of globigerinatheka kugleri hantkenina singanoae guembelitrioides nuttalli and turborotalia frontosa have resulted in large changes in the durations of biochrons e7 e8 and e9 we have introduced upper oligocene zone o7 utilizing the biostratigraphic utility of paragloborotalia pseudokugleri for the neogene period major revisions are applied to the fohsellid lineage of the middle miocene and we have modified the criteria for recognition of zones m7 m8 and m9 with additional adjustments regarding the globigerinatella lineage to zones m2 and m3 the revised and recalibrated datums provide a major advance in biochronologic resolution and a template for future progress of the cenozoic time scale

the isotopic composition of leachable osmium from river sediments the 187os186os ratios of acidic hydrogen peroxide leaches of river sediments are inferred to be representative of the isotopic composition of os delivered to sea water from the continents the 187os186os values for river sediment leaches from the eastern and central u s the ganges river and the rio maipo range from 10 1 to 21 5 these results suggest that the 187os186os of the soluble river load delivered from the major continental areas to the oceans is on average more radiogenic than average currently eroding continental crust 10 5 sediment leaches from three rivers from the western u s that drain ophiolitic peridotites have distinctly lower 187os186os values 1 4 7 1 such rivers may be significant contributors to sea water of the relatively unradiogenic osmium required to yield the contemporary oceanic 187os186os of 8 6

osmium isotope geochemistry of a tropical estuary abstract fundamental aspects of the estuarine geochemistry of os were investigated by analysis of the os isotope composition and concentration variations in filtered water samples from a salinity transect taken in the estuary of the tropical fly river of new guinea 187os 188os of the waters in the salinity transect increase with salinity from 0 6165 in the river endmember 0 1 salinity to a maximum of 0 913 in the most saline water 33 these values are distinctly lower than the 187os 188os of 1 06 reported for open ocean waters from the indian and pacific oceans sharma et al 1997 levasseur et al 1998 woodhouse et al 1999 the os concentrations in the waters range from a minimum of 4 59 pg os g in the river to a maximum of 5 66 pg os kg at 12 salinity these concentrations are all significantly lower than the open ocean range of 6 6 to 10 86 pg os kg levasseur et al 1998 woodhouse et al 1999 the isotopic results indicate that the rivers draining the new guinea landmass provide unradiogenic dissolved os to the oceans and led to a lowering of the 187os 188os of the local seawater the os concentration salinity relationship indicates that the mixing process is not conservative and that removal of os from the dissolved state has taken place the proportion of os lost from solution increases with salinity resulting in removal of a large proportion of seawater os in the estuary high concentrations of os in marine sediments within the gulf of papua were previously interpreted to be due to incorporation of seawater derived os into organic matter martin et al 2000 earth planet sci lett 183 261 274 and are the likely complement to the processes observed in the dissolved state enhanced removal of seawater os in estuaries could help to resolve the differences in estimates of os residence time made on the basis of oceanic deposits versus those based on measured river water concentrations

the osmium riverine flux and the oceanic mass balance of osmium the osmium concentration os and isotopic composition were determined in a set of 17 of the largest rivers of the world os varies between 4 6 and 52 1 pg kg and the 187os 188os ratio varies between 0 64 and 2 94 measurement of rainwater samples shows that there is no input of oceanic os to the continent through rain assuming a negligible anthropogenic os input in the dissolved load the natural average river water has an os concentration of 7 9 pg kg and a mean 187os 188os ratio of 1 54 the total riverine flux of os to the ocean is estimated to be 295 kg yr the dissolved os flux from island arcs and oceanic islands represents less than 5 of the total riverine flux and is not further considered the continental os flux to the ocean is then represented by the riverine flux as dissolved os from eolian dust and glacial sediments is negligible assuming steady state it is possible to estimate a maximum unradiogenic flux to the ocean of 126 kg yr cosmic dust or mantle derived and an oceanic residence time between 2 5 104 and 5 4 104 with a mean of 3 5 104 year the estimation of the flux of dissolved cosmic particles shows that their contribution to the seawater os would be 14 of the contribution of the unradiogenic component which means that the mantle derived flux should contribute a major part the first results on water from high temperature axial hydrothermal systems indicate that their input is probably negligible which would necessitate that dominant contribution from the low temperature alteration of the oceanic crust and or of the ultramafic exposures contributes dominantly to the input of unradiogenic os to the seawater we show that it would be necessary to leach 1 3 of the os contained in the volume of ultramafic exposures accessible to seawater to account for all of the unradiogenic component contribution another simpler but less likely possibility is that the dissolved cosmic dust represents the only source of dissolved unradiogenic os to the ocean in which case the riverine input represents 94 of the total dissolved flux to the ocean instead of 70 the modern global dissolved os flux to the ocean would then have a 187os 188os ratio of 1 44 instead of 1 06 and the system would be far from steady state

scavenging of 234th and phosphorus removal from the hydrothermal effluent plume over the north cleft segment of the juan de fuca ridge dissolved and total 234th t1 2 24 1 days profiles were measured over the hydrothermal field located within the north cleft segment of the juan de fuca ridge above the hydrothermal effluent plume which rose approximately 200 m from the seafloor 90 of the 234th was dissolved and the total 234th activity was in equilibrium with its parent uranium this is typical of deep water for which the residence time of dissolved 234th with respect to particle uptake is greater than 200 days within the effluent plume however as little as 30 of the 234th was in the dissolved state and the residence time of dissolved 234th with respect to particle uptake was then of the order of only a few weeks the flux jth of dissolved 234th to the particle phase was about 300 disintegrations per minute dpm cm 2 yr 1 the total 234th was still approximately in equilibrium with u indicating that the residence time of the 234th bearing particles with respect to sinking was greater than 100 days particulate p v and as while insignificant above the plume attained concentrations as high as 60 0 65 and 0 45 nmol l within the plume the particulate p 234th ratio and the 234th flux jth are used to calculate a removal flux of p resulting from hydrothermal scavenging of 50 g cm 2 yr 1 or approximately 5 0 106 g p yr 1 per kilometer of active ridge crest similarly 1 0 105 g km 1 of v and as are removed per year from the water column by hydrothermal scavenging over this region extrapolation to a global scale suggests that ridge crest scavenging removes 10 of these elements from the ocean

wind tunnel and field calibration of five aeolian sand traps the efficiency of five aeolian sand samplers was tested via wind tunnel experiments and field measurements the samplers were the big spring number eight bsne sampler the modified wilson and cooke mwac sampler the suspended sediment trap sustra the pollet catcher polca and the saltiphone in the wind tunnel the samplers were calibrated against an isokinetic sampler a modified sartorius sm 16711 sampler with adjustable flow rate and this for three sand types median diameter 132 194 and 287 m and five wind speeds ranging from 6 6 to 14 4 m s 1 in the field seven calibration tests of two weeks each were conducted the absolute efficiencies of the bsne mwac and polca are more or less comparable and vary between 70 and 120 depending on sediment size and wind speed for the sustra the efficiency is somewhat lower for fine sands and for wind speeds above 11 m s 1 finally the saltiphone can accurately detect the periods of saltation transport but in its current version the instrument is not accurate when measuring the absolute saltation flux the most recommendable sampler in the test is the mwac not only because of its high efficiency but also because its efficiency is independent of wind speed

threshold friction velocities and rupture moduli for crusted desert soils for the input of soil particles into the air desert soils having clay crusts mostly from the mojave desert were tested for threshold friction velocity the friction velocity at which soil erosion begins with an open bottomed wind tunnel the soils were also tested for content of clay water soluble material calcium carbonate organic material mineralogy of clay and of salts soil moisture modulus of rupture and crust thickness if no loose material existed on the soil surface crusts having modulus of rupture greater than 0 7 bar and crust thickness of 0 7 cm to 0 3 cm were effective in protecting against wind erosion disturbed clay crusts having modulus of rupture before disturbance greater than 2 bar with thickness less than 1 9 cm did not experience significant wind erosion modulus of rupture was related to composition of soil but was shown to depend mostly on clay content soil composition is related to modulus of rupture in an empirical equation

deep sea sediments in the eastern equatorial atlantic off the african coast and meteorological flow patterns over the sahel deep sea mineral dust deposits are a powerful tool allowing to deduct atmospheric flow patterns here deep sea sediments from the eastern tropical atlantic were used to derive climatic conditions over the african continent where in summer the dust is lifted in the transition zone of the sahara and the sahel the meteorological process causing this aeolian dust injection are the squall lines the rain bearing disturbances of the sahel they produce a high surface wind velocity area in their northern vicinity the deep sea deposits of sediments and their spatial patterns allowed to conclude that the dust raising mechanism connected with the squall lines were similar for present day conditions and for the time of the last glacial maximum the saharan trades and the african monsoon had about the same extension in either time slice coupled with an identical travel belt of the squall lines however the intensity and the frequency of the squall lines were lower in glacial times

kinky profiles effects of soil surface heating upon vertical dust concentration profiles in the channel country of western queensland australia 1 in rangelands unlike cultivated fields soil surface conditions and vegetation cover are far from uniform field measurements taken within rangeland environments show that the shape of vertical dust concentration profiles can vary significantly between wind erosion events regression fits used to analyze vertical dust concentration profiles are therefore better for some events than others such variability has usually been explained as experimental error or noise or as a result of the nonuniformity of surface conditions a computer simulation model dsism is used to examine this variability in terms of wind erosion processes analysis of these simulation results together with field observations shows that nonuniformity in surface conditions alone cannot explain variations observed in the vertical dust concentration profiles these same simulations suggest that much of the variability in vertical dust concentration profiles is the result of thermal heating of the soil surface

an osmium based method for assessing the source of dissolved rhenium and molybdenum to archean seawater abstract authigenic enrichments of re and mo in 2 7 2 5 ga organic rich mudrocks orm indicate that dissolved re and mo were present in late archean seawater however it can be difficult to determine if the dissolved re and mo were sourced from oxidative crustal weathering or magmatic hydrothermal extraterrestrial mhe inputs comparison of re mo and 192 os non radiogenic os isotope concentrations and initial 187 os 188 os isotope compositions from re os isochron regressions of orm can shed insight on the source of re and mo to archean seawater seawater 187 os 188 os reflects the relative contributions of radiogenic crustal versus unradiogenic mhe os inputs to seawater during the phanerozoic transient increases in magmatic hydrothermal activity marked by unradiogenic 187 os 188 os excursions and higher 192 os concentrations in orm are accompanied in some cases by higher re concentrations these unradiogenic os sources could thus have played a greater role in the archean marine re and possibly mo budget given that the riverine re and mo flux at that time was likely smaller than the phanerozoic flux hence a positive correlation between re mo and 192 os concentrations in archean orm that yields unradiogenic initial 187 os 188 os may reflect a mhe origin for dissolved re and mo in the overlying paleo seawater local oxidative weathering in the presence of photosynthetic o 2 of mafic ultramafic rocks and crustal sulfide minerals with low re os ratios is an alternative explanation but the two scenarios cannot be readily distinguished on the basis of initial 187 os 188 os by contrast an initial 187 os 188 os from archean orm that is statistically higher than the mhe baseline of 0 10 0 11 points to oxidative mobilization of re os and mo from crustal sulfide minerals rhenium and mo concentrations that are negatively correlated with 192 os concentrations in archean orm yielding unradiogenic initial 187 os 188 os suggests that some re and mo were derived from oxidative weathering such negative correlations may reflect an increased marine os sink adsorption to oxide minerals during a mild increase in local environmental o 2 levels these concepts may help trace the onset of photosynthetic o 2 production and accumulation along archean ocean margins

osmium in marine sediments osmium is enriched in ferromanganese minerals and its concentrations follow those of other pt group metals except pd oxidative capture during solid formation is the probable mechanism for uptake in some sediments forming under reducing conditions phosphorites and anoxic coastal deposits there is also an enrichment this may relate to reductive capture although deposits also formed under reducing conditions from hydrothermal areas are depleted in osmium

discovery of abundant hydrothermal venting on the ultraslow spreading gakkel ridge in the arctic ocean submarine hydrothermal venting along mid ocean ridges is an important contributor to ridge thermal structure and the global distribution of such vents has implications for heat and mass fluxes from the earth s crust and mantle and for the biogeography of vent endemic organisms previous studies have predicted that the incidence of hydrothermal venting would be extremely low on ultraslow spreading ridges ridges with full spreading rates 2 cm yr 1 which make up 25 per cent of the global ridge length and that such vent systems would be hosted in ultramafic in addition to volcanic rocks here we present evidence for active hydrothermal venting on the gakkel ridge which is the slowest spreading 0 6 1 3 cm yr 1 and least explored mid ocean ridge on the basis of water column profiles of light scattering temperature and manganese concentration along 1 100 km of the rift valley we identify hydrothermal plumes dispersing from at least nine to twelve discrete vent sites our discovery of such abundant venting and its apparent localization near volcanic centres requires a reassessment of the geologic conditions that control hydrothermal circulation on ultraslow spreading ridges

pge fractionation in seafloor hydrothermal systems examples from mafic and ultramafic hosted hydrothermal fields at the slow spreading mid atlantic ridge the distribution of platinum group elements pges in massive sulfides and hematite magnetite pyrite assemblages from the recently discovered basalt hosted turtle pits hydrothermal field and in massive sulfides from the ultramafic hosted logatchev vent field both on the mid atlantic ridge was studied and compared to that from selected ancient volcanic hosted massive sulfide vhms deposits cu rich samples from black smoker chimneys of both vent fields are enriched in pd and rh pd up to 227 ppb and rh up to 149 ppb when compared to hematite magnetite rich samples from turtle pits pd up to 10 ppb rh up to 1 9 ppb a significant positive correlation was established between cu and rh in sulfide samples from turtle pits pge chondrite normalized patterns with a positive rh anomaly and pd and au enrichment pd pt and pd au ratios close to global morb and high values of pd ir and pt ir ratios indicate mafic source rock and seawater involvement in the hydrothermal system at turtle pits similarly shaped pge chondrite normalized patterns and high values of pd pt and pd ir ratios in cu rich sulfides at logatchev likely reflect a similar mechanism of pge enrichment but with involvement of ultramafic source rocks

re os and mo isotope systematics of black shales from the middle proterozoic velkerri and wollogorang formations mcarthur basin northern australia joint application of the mo isotope paleoredox proxy and re os deposition age geochronometer to euxinic black shales has potential for tracing the evolution of ocean redox chemistry over geological time here we report new re os and mo isotope data for the mesoproterozoic velkerri formation roper group and paleoproterozoic wollogorang formation tawallah group mcarthur basin northern australia new re os ages of 1361 21 ma 2 n 14 mean square of weighted deviates mswd 1 3 model 1 and 1417 29 ma 2 n 12 mswd 1 3 model 1 constrain the depositional age of the velkerri formation and its contained biomarkers as well as acritarchs and microfossils from the roper group black shales from the upper velkerri formation have high mo abundances 105 119 ppm and degree of pyritization dop values 0 90 0 92 implying quantitative conversion of molybdate moo42 to thiomolybdate mos42 in overlying bottom waters the average 97 95mo 0 72 0 10 2 n 6 of these shales is consistent with previous data but represents a significantly more precise determination for global seawater 97 95mo at 1 4 ga this value is lighter than present day seawater by 0 85 and reflects expanded strongly euxinic deep ocean conditions h2s aq 11 m relative to oxic suboxic and weakly intermittently euxinic h2s aq 11 m marine deposition in the 1 4 ga oceans mass balance modelling suggests mo removal into strongly euxinic and oxic sediments may have comprised 30 70 and less than 15 respectively of the oceanic mo sink at 1 4 ga as opposed to 5 and 35 today respectively the re os radioisotope system in organic rich shales serves as a test for post depositional alteration that could affect the usefulness of paleoredox tracers such as mo stable isotopes re os isotope data for the wollogorang formation black shales are scattered and yield a highly imprecise date of 1359 150 ma 2 n 21 mswd 85 model 3 this age is younger than u pb zircon ages from interbedded tuffs that constrain the age of deposition at ca 1730 ma in conjunction with previous petrological geochemical and paleomagnetic data the re os isotope data suggest hydrothermal fluid flow through the wollogorang formation possibly associated with formation of the ca 1640 ma mcarthur river pb zn ag sedimentary exhalative deposit resulted in post depositional mobilization of re and os based on the degree of deviation of the re os data from a 1730 ma reference line open system behavior of re and os was greatest near the base of the black shale unit wollogorang formation black shales are enriched in mo 41 58 ppm but are characterized by variable 97 95mo 0 3 0 8 and dop 0 57 0 92 the lightest 97 95mo values occur near the base of the black shale unit based on the re os systematics hydrothermal fluids have probably overprinted the authigenic 97 95mo signature in those shales however the heaviest 97 95mo values in the wollogorang formation come from stratigraphically higher shales and are similar to those observed for the velkerri formation and thus may reflect seawater 97 95mo at 1 73 ga

sources of osmium isotopes in manganese nodules abstract we have measured the 187 os 186 os and os concentrations of ferromanganese crusts forming on serpentinized peridotites from the atlantic ocean and also report major element data for these samples and six manganese nodules previously analyzed for os variations in the 187 os 186 os ratios of manganese nodules are the result of two processes operating on different spatial scales the large scale variations result from the impression of intense local os inputs from continental and oceanic sources on a generally homogeneous oceanic 187 os 186 os ratio fine scale variations may be understood as the result of the mixing of a constant fine grained debris flux of meteoritic os imposed on varying amounts of os precipitated from seawater

os isotopes as tracers in seafloor hydrothermal systems metalliferous deposits from the tag hydrothermal area 26 n mid atlantic ridge abstract os isotopic analyses of a suite of samples from the tag hydrothermal area 26 n on the mid atlantic ridge reveal evidence of release of ocean crust derived os to seawater and removal of seawater derived os to the seafloor 187 os 186 os ratios of sulfide samples from the active tag mound vary between 8 7 and 1 3 the highest ratios are indistinguishable from the inferred 187 os 186 os ratio of seawater the incorporation of seawater derived os in these samples is interpreted as evidence of both entrainment of seawater into hydrothermal fluids and the addition of seawater os to samples during sulfide oxidation several sulfide samples from the active tag mound have 187 os 186 os ratios lower than the inferred seawater value with the lowest ratio approaching values expected for pristine oceanic crust these low 187 os 186 os ratios indicate that os derived from alteration of the oceanic crust is released to seawater in association with venting of high temperature hydrothermal fluids precipitates from low temperature hydrothermal fluids fe and mn oxide deposits from the east wall of the axial rift valley also have low 187 os 186 os ratios 4 2 6 8 relative to seawater these data suggest os isotopes may be sensitive tracers of low temperature hydrothermal circulation on the seafloor and that supply of ocean crust derived os to seawater is not strictly limited to high temperature hydrothermal vents the os concentration and isotopic composition of metalliferous sediment samples from a push core collected 125 m from the base of the active tag mound are also reported in this core metalliferous sediment horizons derived from mass wasting of altered sulfides exhibit variable 187 os 186 os ratios 4 8 8 7 reflecting mixing of seawater derived and ocean crust derived os in contrast sediments in which the metalliferous component is derived from fall out of hydrothermal material from the neutrally buoyant hydrothermal plume have 187 os 186 os ratios which vary over a narrow range 8 6 8 7 and appear to accurately record the os isotopic composition of seawater

pge distribution in massive sulfides from the pacmanus hydrothermal field eastern manus basin papua new guinea implications for pge enrichment in some ancient volcanogenic massive sulfide deposits the distribution of platinum group elements pge in cu and zn rich samples from the roman ruins and satanic mills vent sites in the pacmanus hydrothermal field papua new guinea was studied and compared to that from selected ancient volcanogenic massive sulfide vms deposits samples from the satanic mills site are enriched in pd and rh when compared to samples from roman ruins and reach highest values in active and inactive cu rich black smoker chimneys and chalcopyrite cemented dacite breccias up to 356 ppb pd and up to 145 ppb rh a significant positive correlation was established between cu and pd and rh in samples from both vent sites comparisons of chondrite normalized patterns and values of pd pt and pd ir ratios in cu rich sulfides and probable source rocks felsic volcanic rocks morb along with the evidence for a magmatic component in the pacmanus hydrothermal system indicate that leaching of back arc volcanic rocks together with addition of magmatic volatiles to the convecting hydrothermal system was the most important factor for pge enrichment at pacmanus and likely at some pge enriched ancient vms deposits

hydrography and high temperature heat flux of the rainbow hydrothermal site 36 14 n mid atlantic ridge on the basis of an extensive set of conductivity temperature depth lowered acoustic doppler current profiler ladcp and nephelometry profiles and tow yos the hydrography flow field and particle plume of the rainbow hydrothermal site on the mid atlantic ridge are analyzed in the rift valley the water column is less dense and stratified than both eastern and western off ridge water with t s characteristics consistent with inflow across a sill from the east the buoyant hydrothermal plumes rise into a strong boundary current flowing along the slope of a topographic high which partially blocks the rift valley below 1950 m the bulk of the neutrally buoyant plume is advected across a sill which forms both the narrowest and the shallowest part of the valley and acts as a hydraulic control point for the flow below 2000 m large amplitude internal waves consistent with tidal forcing are observed near the sill but ladcp measurements suggest that the tidal signal is not strong enough to lead to flow reversal at plume depth above 2000 m the mean current across the topography generates lee waves which radiate energy upward and downstream density averaged light scattering profiles show the hydrothermal particle plume to be gaussian in depth even in the near field where many of the individual profiles are characterized by multiple peaks and the horizontal variability is highest the temperature anomalies associated with the mean near source particle plume are of order 5 10 3 c that is the plume is cold fresh as expected from the background hydrography of the deep atlantic using the flow field light scattering and hydrographic anomaly observations the heat flux associated with the hydrothermal particle plume at rainbow is estimated to lie between 1 and 5 gw

evaluation of osmium isotopes and iridium as paleoflux tracers in pelagic carbonates new osmium os isotope and platinum group element pge concentration data are used in conjunction with published 3 he and th isotope data to determine the relative proportions of lithogenic extraterrestrial and hydrogenous iridium ir in a pacific pelagic carbonate sequence from the ocean drilling program odp site 806 on the ontong java plateau ojp these calculations demonstrate that lithogenic and extraterrestrial contributions to sedimentary ir budget are minor while hydrogenous ir accounts for roughly 85 of the total ir application of analogous partitioning calculations to previously reported data from a north pacific red clay sequence ll44gpc3 yields very similar results total ir burial fluxes at site 806 and ll44 gpc3 are also similar 45 and 30 pg cm 2 kyr 1 respectively average ir 3 he and ir xs 230 thinitial ratios calculated from the entire site 806 data set are similar to those reported earlier for pacific sites in general down core profiles of ir 3 he and xs 230 thinitial are not well correlated with one another however all three data sets show similar variance and yield sediment mass accumulation rate estimates that agree within a factor of two while these results indicate that ir concentration has potential as a point paleoflux tracer in pelagic carbonates ir based paleoflux estimates are likely subject to uncertainties that are similar to those associated with co based paleoflux estimates consequently local calibration of ir flux in space and time will be required to fully assess the potential of ir as a point paleoflux tracer measured 187 os 188 os of the ojp sediments are systematically lower than the inferred 187 os 188 os of contemporaneous seawater and a clear glacial interglacial 187 os 188 os variation is lacking mixing calculations suggest os contributions from lithogenic sources are insufficient to explain the observed 187 os 188 os variations the difference between the 187 os 188 os of bulk sediment and that of seawater is interpreted in terms of subtle contributions of unradiogenic os carried by particulate extraterrestrial material down core variations of 187 os 188 os with pt ir and os ir also point to contributions from extraterrestrial particles mixing calculations for each set of several triplicate analyses suggest that the unradiogenic os end member cannot be characterized by primary extraterrestrial particles of chondritic composition it is noteworthy that in efforts aimed at determining the effect of extraterrestrial contributions 187 os 188 os of pelagic carbonates has greater potential compared to abundances of pge an attempt has been made for the first time to estimate sediment mass accumulation rates based on amount of extraterrestrial os in the ojp samples and previously reported extraterrestrial os flux throughout most of the ojp record os isotope based paleoflux estimates are within a factor of two of those derived using other constant flux tracers meaningful flux estimates cannot be made during glacial maxima because the ojp sediments do not record the low 187 os 188 os reported previously we speculate that this discrepancy may be related to focusing of extraterrestrial particles at the ojp as has been suggested to explain down core 3 he variations

distribution and behavior of dissolved hydrogen sulfide in hydrothermal plumes through the deep ocean hydrothermal plumes disperse high concentrations of key chemical tracers including he 3 ch4 mn fe h2s etc this paper focuses on the distribution and behavior of total dissolved sulfide sulfide hereafter in hydrothermal plumes to show that its plume concentration decreases to subnanomolar a few kilometers from the vents we also report on sulfide removal rates determined at in situ conditions we observe that they are two orders of magnitude greater than for open ocean seawater consistent with sulfide being detected only in the vicinity of hydrothermal vents from our observations we infer that the sole presence of sulfide in hydrothermal plumes locates active venting at thekilometer scale

highly metalliferous carbonaceous shale and early cambrian seawater comment and reply comment lehmann et al 2007 1 reported trace rare earth element ree and mo isotope data from the ni mo sulfide layer and host black shale of the lower cambrian niutitang formation in southern china they argue that the metals in the sulfidic rocks originated purely from early cambrian seawater

the rainbow vent fluids 36 14 n mar the influence of ultramafic rocks and phase separation on trace metal content in mid atlantic ridge hydrothermal fluids fluids were collected from the rainbow vent field 36 14 n on the mid atlantic ridge mar during the 1997 diving flores cruise this vent field in ultramafic rocks at a depth of 2300 m is composed of 10 black smokers emitting acidic ph 2 8 fluids at 365 c the low ph of the hot temperature rainbow fluids likely results from seawater ultramafic rock interaction that releases h ions into reducing hydrothermal fluids fluid chemistry is strongly influenced by phase separation generating cl rich brines clem 750 mm strongly enriched with mn fe co ni cu zn ag cd cs pb y and rare earth elements ree ree and transition metal abundance particularly fe and mn in the rainbow fluids is dramatically higher than in other mar fluids the abundance of trace element and ree enrichment is due to the greater solubility of these elements that is strongly favored by cl complexation at low ph and high temperature conditions chondrite normalized ree patterns show strong lree enrichment with evidence of the typical eu anomaly this ree partitioning suggests that either 1 ultramafic rocks represent only a part of rocks leached during hydrothermal alteration and or 2 that the unique rainbow fluid temperature ph and redox state issued from the ultramafic character of leached substratum can produce unique ree partitioning

the marine187os 186os record of the past 80 million years we report new187os 186os data and re and os concentrations in metalliferous sediments from the pacific to construct a composite os isotope seawater evolution curve over the past 80 m y analyses of four samples of upper cretaceous age yield187os 186os values of between 3 and 6 5 and187re 186os values below 55 mass balance calculations indicate that the pronounced minimum of about 2 in the os isotope ratio of seawater at the k t boundary probably reflects the enormous input of cosmogenic material into the oceans by the k t impactor s following a rapid recovery to187os 186os of 3 5 at 63 ma data for the early and middle part of the cenozoic show an increase in187os 186os to about 6 at 15 ma variations in the isotopic composition of leachable os from slowly accumulating metalliferous sediments show large fluctuations over short time spans in contrast analyses of rapidly accumulating metalliferous carbonates do not exhibit the large oscillations observed in the pelagic clay leach data these results together with sediment leaching experiments indicate that dissolution of non hydrogenous os can occur during the hydrogen peroxide leach and demonstrate that os data from pelagic clay leachates do not always reflect the os isotopic composition of seawater new data for the late cenozoic further substantiate the rapid increase in the187os 186os of seawater during the past 15 ma we interpret the correlation between the marine sr and os isotope records during this time period as evidence that weathering within the drainage basin of the ganges brahmaputra river system is responsible for driving seawater sr and os toward more radiogenic isotopic compositions the positive correlation between87sr 86sr and u concentration the covariation of u and re concentrations and the high dissolved re u and sr concentrations found in the ganges brahmaputra river waters supports this interpretation accelerating uplift of many orogens worldwide over the past 15 ma especially during the last 5 ma could have contributed to the rapid increase in187os 186os from 6 to 8 5 over the past 15 ma prior to 15 ma the marine sr and os record are not tightly coupled the heterogeneous distribution of different lithologies within eroding terrains may play an important role in decoupling the supplies of radiogenic os and sr to the oceans and account for the periods of decoupling of the marine sr and os isotope records

topographic control of a dispersing hydrothermal plume deep sea hydrothermal vents represent a major source of heat and chemicals to the oceans and support endemic chemosynthetic biological communities to fully understand the impact of hydrothermal activity upon the oceans however requires investigation of both the physical and the biogeochemical processes which are active in hydrothermal plumes and which serve to determine the net hydrothermal flux to the oceans we have recently conducted a detailed multidisciplinary study of the lateral dispersion of the hydrothermal plume emitted from the rainbow vent site near 36 15 n mid atlantic ridge combining velocity measurements from a lowered adcp optical back scatter measurements from a deep tow ctd and methane measurements from bottle samples we are able for the first time in the atlantic to trace a neutrally buoyant plume for a distance of over 50 km the path of the plume is seen to be heavily controlled by the local topography with a general northeast movement of water both particle and methane concentrations decrease downstream over the length of the observed plume the dataset provides an excellent opportunity to study the mixing and biogeochemical processes active in a hydrothermal plume and estimate fluxes of biogeochemical constituents

187os 186os in marine manganese nodules and the constraints on the crustal geochemistries of rhenium and osmium during their formation marine manganese or more properly ferromanganese oxide nodules include and commonly concentrate elements dissolved in seawater this attribute makes them especially valuable recorders of the isotopic composition of elements supplied to the oceans having radiogenic isotopes for these can be used in exploring crustal composition and evolution1 5 from measurements of 187os 186os ratios in marine manganese nodules and comparison with the 143nd 144nd ratios of the same nodules we have calculated the os isotopic composition and the osmium and rhenium concentrations of the weatherable portion of the continental crust together with the proportions of ultra mafic and granitic rock that constitute this crustal mass

quantifying dust emissions from desert landforms eastern mojave desert usa abstract the measurement of natural dust emissions from desert landforms is crucial in environmental hazard assessment and field checking the accuracy of global dust models more than 500 individual dust measurements from eight common desert landforms in southern california were collected using the pi swerl portable in situ wind erosion lab the largest emitters of dust are dry washes 13 787 to 0 007 mg m 2 s 1 dunes playa margins distal alluvial fans and lacustrine beaches low emitters include salt crusted playas 0 692 to 0 002 mg m 2 s 1 silt clay crusted playas and desert pavements high emissions are a function of saltating sand that bombards the surface liberating dust sized particles for entrainment low dust emissions are primarily a function of surface crusting gravel armoring and vegetation density pi swerl measurements reveal that emission rates can vary by at least three orders of magnitude reflecting local variability in soil texture and continuity of surface crusts shear stress partitioning models can be applied to dust data measured by the pi swerl to account for large surface roughness features such as vegetation the results presented here give an approximation of the contributions to atmospheric dust loading by landforms in the mojave desert and can potentially be used to improve atmospheric dust models

dust emission and transport in mali west africa vertical dust fluxes were measured in the inland delta region of the niger river mali west africa during april june 1989 and 1990 measurements of dust flux represent for the most part non dust storm conditions or dust haze periods the observed concentration versus height relationships are similar to data presented by other investigators the relationship between wind shear velocity u m s 1 and vertical dust flux f g m 2 s 1 can be described by a relationship in which f is proportional to u 4 however there is considerable scatter within the data set which is attributable to textural controls and surface conditions the vertical dust fluxes measured in mali are compared to dust fluxes measured in texas usa and yukon territories canada the significantly different values for the constant of proportionality a in the f a u 4 relationship for these geographically diverse areas is a function of surficial controls on the release of sediments to the air stream dust concentrations measured in mali were found to be uniformly high and in general exceed who health standards for acceptable total suspended particulate loadings as a result background dust may be considered a long term stress on health for the people of this region of mali

a possible link between the seawater osmium isotope record and weathering of ancient sedimentary organic matter the os isotopic composition of leachable os from a north pacific pelagic clay sequence pegram et al 1992 and bulk sediment samples of metalliferous carbonates deposited near the east pacific rise ravizza 1993 display similar patterns of temporal variation fig 1 this similarity indicates that the composite record of t87os 186os ratio variations reflects changes in the os isotopic composition of seawater temporal changes in the sr isotopic composition of seawater record changes in the relative rates of continental weathering and oceanic crustal alteration the os isotopic composition of seawater should be influenced by similar processes in both the rb sr and re os systems the continental crust is characterized by large time integrated parent daughter ratios compared to the deep earth imparting relatively radiogenic sr and os signatures to continental material however the seawater sr and os records are decoupled from one another over the past 27 ma from 27 to 15 ma 87sr 86sr increased rapidly while the 18vos 186os ratio of seawater remained nearly constant at 15 ma the 87os ts6os ratio of seawater began to increase rapidly but the rate

partitioned transtensional cenozoic stratigraphic development of north sumatra abstract the cenozoic sedimentary history of north sumatra is reviewed and a new account of basin development is proposed that accommodates contrasting stratigraphic histories across the region especially times of sudden facies change micropalaeontology and geohistory techniques have been used to estimate the magnitude of stratigraphic change and together with the timing of events this indicates that north sumatra developed in a dynamic transtensional tectonic setting as has been proposed in regional structural models and not the back arc setting usually assumed by oil industry workers this style of basin development has direct control on the nature and areal distribution of the petroleum systems elements new definitions of common formation terms are suggested based on a well constrained sequence stratigraphic model which has been assigned a new nomenclature of ns10 to ns50 megasequences it is noted that the stratigraphic and geographic position and extent of the source rock for the arun nso a nso j and south lho sukon giant gas and condensate fields is still not known