231pa 230th fractionation by ocean transport biogenic particle flux and particle type 231pa and 230th are removed from the water column by a process of reversible scavenging which quickly removes 230th to the sediment 231pa is less efficiently scavenged onto particles than 230th and is therefore more effectively transported via advection and diffusion before it reaches the ocean sediment this study combines particle fields dust opal caco3 poc derived from observations with the bern3d intermediate complexity ocean model and an equilibrium scavenging model for isotopes the equilibrium partition coefficient for particulate versus dissolved isotope activity is varied with particle type the model can explain many of the features of the global 231pa and 230th distribution the success of such a simple model at representing the global pattern of 231pa 230th activity ratio supports the use of this proxy in paleoceanographic studies we use the model to address the controversy concerning which particle types are dominant in fractionating 231pa 230th in the ocean the lithogenic dust flux is found to be unimportant for 231pa 230th fractionation the ocean fractionation of 231pa 230th is dominated by the distribution of the caco3 and opal flux we also confirm that opal is a weak scavenger of 230th

thorium 230 profiling in deep sea sediments high resolution records of flux and dissolution of carbonate in the equatorial atlantic during the last 24 000 years variations in carbonate flux and dissolution which occurred in the equatorial atlantic during the last 24 000 years have been estimated by a new approach that allows the point by point determination of paleofluxes to the seafloor an unprecedented time resolution can thus be obtained which allows sequencing of the relatively rapid events occurring during deglaciation the method is based on observations that the flux of unsupported 230th into deep sea sediments is nearly independent of the total mass flux and is close to the production rate thus excess 230th activity in sediments can be used as a reference against which fluxes of other sedimentary components can be estimated the study was conducted at two sites ceara rise western equatorial atlantic and sierra leone rise eastern equatorial atlantic in cores raised from three different depths at each site from measurements of 230th and caco3 changes in carbonate flux with time and depth were obtained a rapid increase in carbonate production starting at the onset of deglaciation was found in both areas this event may have important implications for the postglacial increase in atmospheric co2 by increasing the global carbonate carbon to organic carbon rain ratio and decreasing the alkalinity of surface waters and possibly the north atlantic deep water increased carbonate dissolution occurred in the two regions during deglaciation followed by a minimum during mid holocene and renewed intensification of dissolution in late holocene during the last 16 000 years carbonate dissolution was consistently more pronounced in the western than in the eastern basin reflecting the influence of antarctic bottom water in the west this trend was reversed during stage 2 possibly due to the accumulation of metabolic co2 below the level of the romanche fracture zone in the eastern basin

sediment redistribution and grainsize effects on 230th normalized mass accumulation rates and focusing factors in the panama basin abstract here we examine how redistribution of differing grain sizes by sediment focusing processes in panama basin sediments affects the use of 230th as a constant flux proxy we study representative sediments of holocene and last glacial maximum lgm time slices from four sediment cores from two different localities close to the ridges that bound the panama basin each locality contains paired sites that are seismically interpreted to have undergone extremes in sediment redistribution i e focused versus winnowed sites both holocene and lgm samples from sites where winnowing has occurred contain significant amounts up to 50 of the 230th within the 63 m grain size fraction which makes up 40 70 of the bulk sediment analyzed for sites where focusing has occurred holocene and lgm samples contain the greatest amounts of 230th up to 49 in the finest grain sized fraction kretschmer et al 2010 suggest a maximum change of about 30 in 230th derived mars and focusing factors at focused sites except for our most focused site which requires an approximate 70 correction in one sample our 230th corrected 232th flux results suggest that the boundary between hemipelagically and pelagically derived sediments falls between 350 and 600 km from the continental margin

the water column distributions of thorium isotopes in the western north pacific abstract four vertical profiles of 230 th and 228 th were determined using large volume water samples in the western north pacific an almost linear increase of 230 th with depth was observed for all of the profiles for which the unidirectional first order scavenging model was difficult to explain we developed a model which included a dissolved particulate transformation as well as parameters of the scavenging model application of the model to the vertical distributions of total and the geosecs particulate th isotopes 230 th and 234 th yielded the residence time of dissolved th with respect to adsorption to particles and the turnover time of particulate th to be 235 days and 57 days respectively the th isotopes appeared to be carried down the water column by fine particles with a mean settling velocity of 1 m day which continually release th into sea water as well as pick up th from the water along their journey to the bottom for 228 th a large excess over 232 th was observed throughout the water column with pronounced high concentrations in surface and bottom waters suggesting that the 228 th was derived from 228 ra diffused out of sediments the vertical distributions of 228 th seemed to be significantly influenced by lateral mixing along isopycnals

size sorting in marine muds processes pitfalls and prospects for paleoflow speed proxies the basis for and use of fine grain size parameters for inference of paleoflow speeds is reviewed here the basis resides in data on deposited sediment taken in conjunction with flow speed measurements in the field experimental data on suspended sediment transport and deposition and theoretical treatments of the generation of size distributions of deposits from suspension controlled by particle settling velocity and flow speed in the deep sea sorting events occur under resuspension deposition events in benthic storms at flow speeds below 10 15 cm s 1 size in the noncohesive sortable silt 10 63 m range is controlled by selective deposition whereas above that range removal of finer material by winnowing also plays a role the best particle size instruments to measure a flow speed related grain size employ the settling velocity method while laser diffraction sizers can yield misleading results because of particle shape effects potential problems including source effects downslope supply on continental margins spatial variability of flow over bedforms and influence of ice rafted detritus are examined a number of studies using the sortable silt flow speed proxy are reviewed and inverse modeling of grain size distributions is examined outstanding problems are that corroboration is sparse because almost no studies have yet used the full range of proxies for flow rate and water mass identification and that the sortable silt mean size is not yet properly calibrated in terms of flow speed

wolf rock lighthouse past developments and future survivability under wave loading lighthouses situated on exposed rocky outcrops warn mariners of the dangers that lurk beneath the waves they were first constructed when approaches to wave loading and structural response were rel

links between iron supply marine productivity sea surface temperature and co2 over the last 1 1 ma received 3 july 2008 revised 9 october 2008 accepted 27 october 2008 published 14 february 2009 1 paleoclimatic reconstructions have provided a unique data set to test the sensitivity of climate system to changes in atmospheric co2 concentrations however the mechanisms behind glacial interglacial g ig variations in atmospheric co2 concentrations observed in the antarctic ice cores are still not fully understood here we present a new multiproxy data set of sea surface temperatures sst dust and iron supply and marine export productivity from the marine sediment core ps2489 2 odp site 1090 located in the subantarctic atlantic that allow us to evaluate various hypotheses on the role of the southern ocean so in modulating atmospheric co2 concentrations back to 1 1 ma we show that antarctic atmospheric temperatures are closely linked to changes in so surface temperatures over the last 800 ka and use this to synchronize the timescales of our marine and the european project for ice coring in antarctica epica dome c edc records the close correlation observed between iron inputs and marine export production over the entire interval implies that the process of iron fertilization of marine biota has been a recurrent process operating in the subantarctic region over the g ig cycles of the last 1 1 ma however our data suggest that marine productivity can only explain a fraction of atmospheric co2 changes up to around 40 50 ppmv occurring at glacial maxima in each glacial stage in this sense the good correlation of our sst record to the edc temperature reconstruction suggests that the initial glacial co2 decrease as well as the change in the amplitude of the co2 cycles observed around 400 ka was most likely driven by physical processes possibly related to changes in antarctic sea ice extent surface water stratification and westerly winds position

measurement of adsorbed and total 232th 230th ratios from marine sediments the predictable in situ production of 230th from the decay of uranium in seawater and its subsequent removal by scavenging onto falling particles provides a valuable tool for normalizing fluxes to the seafloor we describe a new application determination of the 232th that dissolves in the water column and is removed to the seafloor 232th is supplied to the ocean in continental minerals dissolution of which leads to a measurable standing stock in the water column sedimentary adsorbed 232th 230th ratios have the potential to provide a proxy for estimating the amount of dissolved material that enters the ocean both today and in the past ten core top samples were treated with up to eight different leaching techniques in order to determine the best method for the separating adsorbed from lattice bound thorium in addition separate components of the sediments were analyzed to test whether clay dissolution was an important contribution to the final measurement there was no systematic correlation between the strength of acid used in the leach and the measured 232th 230th ratios in all cases clean foraminifera produced the same ratio as leaches on bulk sediment in three out of five samples leaches performed on non carbonate detritus in the 63 mu m size fraction were also identical without additional water column data it is not yet clear whether there is a simple one to one correlation between the expected deep water 232th 230th and that produced by leaching especially in carbonate rich sediments however higher ratios and associated high 232th adsorbed fluxes were observed in areas with high expected detrital inputs the adsorbed fraction was 35 50 of the total 232th in seven out of ten samples our 230th normalized 232th fluxes are reasonable by comparison to global estimates of detrital inputs to the ocean in nine cases out of ten the total 230th normalized 232th flux is greater than predicted from the annual dust fall at each specific location but lower than the average global detrital input from all sources

efficacy of 230 th normalization in sediments from the juan de fuca ridge northeast pacific ocean abstract 230th normalization is an indispensable method for reconstructing sedimentation rates and mass fluxes over time but the validity of this approach has generated considerable debate in the paleoceanographic community 230th systematics have been challenged with regards to grain size bias sediment composition caco3 water column advection and other processes in this study we investigate the consequences of these effects on 230th normalization from a suite of six cores on the juan de fuca ridge the proximity of these cores

greater supply of patagonian sourced detritus and transport by the acc to the atlantic sector of the southern ocean during the last glacial period reconstructing past detrital flux and provenance in the southernocean provides information about changes in source regions associated with climate variations and transport pathways we present a lastglacial maximum lgm to holocene comparison of 230th normalised fluxes combined with sediment provenance data pb nd and sr isotopes from a latitudinal core transect in the eastern atlanticsector of the southernocean odp leg 177 cores we compare the radiogenic isotopic composition ic of detritus in these cores to that of cores proximal to potential source areas we observe a well defined latitudinal holocene gradient in both detrital flux and provenance of sediment high detrital fluxes in the north are associated with terrigenous material derived from southern africa while low detrital fluxes in the south are associated with supply from southern south america west antarctica and the south sandwich islands the data suggest that this well defined holocene gradient in detrital flux and sediment provenance is controlled by the flow of the antarctic circumpolar current acc and the position of its frontal zones the lgm is characterised by 2 to 6 times higher than modern detrital fluxes at most odp leg 177 sites the lgm detrital fluxes do not show a latitudinal trend and suggest a greatersupply of glaciogenic detritussourced from southern south america glacialpatagonian outwash sediments 5 m fraction were analysed and compared to the bulk compositions of the marine sediments the pb ic of the patagonian sediments is very similar to the glacial ic of sediments in the scotia sea and at 49 s latitude in the eastern atlanticsector we propose that the glacial ic of sediments is controlled by increased delivery of patagoniandetritus initially supplied by glaciers and then transported at depth via the acc

excess sediment 230th transport along the sea floor or enhanced water column scavenging 1 the sedimentary inventory of 230th is often employed to distinguish between areas which receive excess sediment as the result of along bottom transport from those which lose sediment as a result of winnowing this process is referred to as focusing a case is made here that at least in the western equatorial pacific the excess 230th in on equator sediment is more likely scavenged from the overlying water column by the rain of organic matter than retransported along the bottom if so lateral variations in biological productivity may well contribute to the excess 230th inventories elsewhere as well

advection and scavenging controls of pa th in the northern ne atlantic over the last 2 decades significant advances have been made in reconstructing past rates of ocean circulation using sedimentary proxies for the dynamics of abyssal waters in this study we combine the use of two rate proxies sortable silt grain size and sedimentary 231pa 230th measured on a depth transect of deep sea sediment cores from the northern ne atlantic to investigate ocean circulation changes during the last deglacial we find that at two deep sites the core top 231pa 230th ratios reflect holocene circulation rates while during heinrich stadial 1 the deglacial ratios peaked as the sortable silt grain size decreased reflecting a general circulation slowdown however the peak 231pa 230th significantly exceeded the production ratio in both cores indicating that 231pa 230th was only partially controlled by ocean circulation at these sites this is supported by a record of 231pa 230th from an intermediate water depth site where values also peaked during heinrich stadial 1 but were consistently above the production ratio over the last 24 ka reflecting high scavenging below productive surface waters at our study sites we find that preserved sediment component fluxes cannot be used to distinguish between a scavenging or circulation control although they are consistent with a circulation influence since the core at intermediate depth with the highest 231pa 230th recorded the lowest particle fluxes reconstruction of advection rate using 231pa 230th in this region is complicated by high productivity but the data nevertheless contain important information on past deep ocean circulation

glacial to interglacial changes in carbonate and clay sedimentation in the atlantic ocean estimated from 230th measurements abstract the cause of the climatically controlled fluctuations in the carbonate content of deep sea sediments remains the subject of uncertainty and debate three variables are involved supply of biogenic carbonate loss by dissolution and dilution by non carbonate phases it is suggested that 230 th which is produced in the ocean at a constant rate provides a reliable reference for measuring variations in rate of sedimentation on a regional scale results of a preliminary analysis based on published data indicate that for depths at and above the lysocline the carbonate fluctuations observed in cores from the north atlantic ocean are due primarily to variations in the terrigenous clay input which was 2 5 times higher during glacials than during interglacials carbonate deposition appears to have been somewhat reduced during glacials but probably not by more than a factor of 2 from published 230 th 232 th profiles it appears that the south atlantic ocean also received increased inputs of terrigenous clay during glacial periods

late quaternary sediment dating and quantification of lateral sediment redistribution applying230thex a study from the eastern atlantic sector of the southern ocean high resolution records of the natural radionuclide230th were measured in sediments from the eastern atlantic sector of the antarctic circumpolar current to obtain a detailed reconstruction of the sedimentation history of this key area for global climate change during the late quaternary high resolution dating rests on the assumption that the230thex flux to the sediments is constant short periods of drastically increased sediment accumulation rates up to a factor of 8 were determined in the sediments of the antarctic zone during the climate optima at the beginning of the holocene and the isotope stage 5e by comparing expected and measured accumulation rate of230thex lateral sediment redistribution was quantified and vertical particle rain rates originating from the surface water above were calculated we show that lateral contributions locally were up to 6 5 times higher than the vertical particle rain rates at other locations only 15 of the expected vertical particle rain rate were deposited

productivity control of fine particle transport to equatorial pacific sediment accumulation rates of 3he from cosmic dust 230th produced in the water column barite produced in the water column during decay of organic matter and fe and ti arriving with wind borne dust all are positively correlated in an equatorial pacific core tt013 pc72 01 1 n 139 4 w water depth 4298 m these accumulation rates are also positively correlated with the accumulation rates of noncarbonate material they are not significantly correlated to the mass accumulation rate of carbonate which makes up the bulk of the sediment the fluctuations in accumulation rates of these various components from different sources thus must result from variations in some process within the oceans and not from variations in their original sources sediment focusing by oceanic bottom currents has been proposed as this process marcantonio et al 1996 we argue that the variations in the accumulation rates of all these components are dominantly linked to changes in productivity and particle scavenging 3he 230th fe ti by fresh phytoplankton detritus which delivers ba upon its decay in the equatorial pacific upwelling region we speculate that as equatorial pacific productivity is a major component of global oceanic productivity its variations over time might be reflected in variations in atmospheric levels of methanesulfonic acid an atmospheric reaction product of dimethyl sulfide which is produced by oceanic phytoplankton and recorded in antarctic ice cores

the influence of particle composition and particle flux on scavenging of th pa and be in the ocean we have examined the relative affinity of th pa and be for sorption from seawater onto particles of variable composition opal carbonate lithogenic particles and organic carbon nuclide concentrations in particles collected from time series sediment traps were normalized by the dissolved nuclide concentration in the overlying water column in order to compute partition coefficients under conditions spanning a wide range of particle flux and particle composition our results suggest that the affinity of particles for pa and be increases with their increasing opal content and decreasing carbonate content while the affinity of particles for th increases with increasing carbonate content and decreases with increasing opal content we find no correlation between the aluminosilicate content of particles and their affinity for scavenging of any of these elements extrapolating to a pure caco3 end member the partition coefficient for th 9 0 106 g g 1 is 40 times greater than for pa and roughly 100 times greater than for be whereas for a pure opal end member the partition coefficient for th 3 9 105 g g 1 is slightly less than that for pa and be partition coefficients decrease with increasing particle flux in open ocean settings but not in an ocean margin region this kinetic effect reflects the increasing contribution of unaltered surface material reaching the sediment traps as particle flux increases the degree of fractionation between pa and th and between be and th depends on the opal carbonate rain ratio these results challenge the use of sedimentary 231pa 230th and 10be 230th ratios as simple proxies of particle flux however the strong dependence of nuclide scavenging on the opal carbonate rain ratio may provide a needed tool for reconstructing past changes in planktonic community composition

sediment size fractionation and focusing in the equatorial pacific effect on 230th normalization and paleoflux measurements we use flux dissolution and excess 230th data from the joint global ocean flux study and manganese nodule project equatorial pacific study site c to assess the extent of sediment focusing in the equatorial pacific measured mass accumulation rates mar from sediment cores were compared to reconstructed mar by multiplying the particulate rain caught in sediment traps by the 230th focusing factor and subtracting measured dissolution caco3 mar is severely overestimated when the 230th focusing factor correction is large but is estimated correctly when the focusing factor is small in contrast al fluxes in the sediment fine fraction are well matched when the focusing correction is used since caco3 is primarily a coarse sediment component we propose that there is significant sorting of fine and coarse sediments during lateral sediment transport by weak currents because caco3 does not move with 230th normalization typically overcorrects the caco3 mar and because caco3 is 80 of the total sediment 230th normalization overestimates lateral sediment flux fluxes of 230th in particulate rain caught in sediment traps agree with the water column production sorption model except within 500 m of the bottom near the bottom 230th flux measurements are as much as 3 times higher than model predictions there is also evidence for lateral near bottom 230th transport in the bottom nepheloid layer since 230th fluxes caught by near bottom sediment traps are higher than predicted by resuspension of surface sediments alone resuspension and nepheloid layer transport under weak currents need to be better understood in order to use 230th within a quantitative model of lateral sediment transport

230th normalization an essential tool for interpreting sedimentary fluxes during the late quaternary there is increasing evidence indicating that syndepositional redistribution of sediment on the seafloor by bottom currents is common and can significantly affect sediment mass accumulation rates notwithstanding its common incidence this process generally referred to as sediment focusing is often difficult to recognize if redistribution is near synchronous to deposition the stratigraphy of the sediment is not disturbed and sediment focusing can easily be overlooked ignoring it however can lead to serious misinterpretations of sedimentary fluxes particularly when past changes in export flux from the overlying water are inferred in many instances this problem can be resolved at least for sediments deposited during the late quaternary by normalizing to the flux of 230th scavenged from seawater which is nearly constant and equivalent to the known rate of production of 230th from the decay of dissolved 234u we review the principle advantages and limitations of this method notwithstanding its limitations it is clear that 230th normalization does provide a means of achieving more accurate interpretations of sedimentary fluxes and eliminates the risk of serious misinterpretations of sediment mass accumulation rates

do geochemical estimates of sediment focusing pass the sediment test in the equatorial pacific 1 the paleoceanographic recording fidelity of pelagic sediments is limited by chemical diagenesis and physical mixing bioturbation and horizontal sediment transport diagenesis and bioturbation are relatively well studied but the effects of physical sedimentation have been largely ignored modeling u series isotopes e g 230th can potentially quantify horizontal sediment movement but model horizontal sediment focusing often equals or exceeds the vertical particle rain we find no evidence of this level of sediment focusing in the equatorial pacific from geophysical data or sediment core comparisons the overestimate of sediment focusing by 230th is probably caused by poor model assumptions that sediment does not fractionate does not sort according to size during transport and that 230th cannot leak from slowly accumulating sediments both assumptions are weak u series methods do hold promise to quantify sediment focusing if properly calibrated with calibration the trade offs between seeking high sedimentation rates for better time resolution and the blurring by horizontal sediment focusing can be better assessed

oceanic 231pa 230th ratio influenced by particle composition and remineralization abstract we have investigated the role of particle compositions in affecting the distribution of 231pa and 230th in the ocean by separating sediments collected by sediment traps and cores into three size fractions and analyzed for their excess 231pa 231paex excess 230th 230thex and major chemical components the samples came from stations along 140 w in the equatorial pacific and from the blake outer ridge in the north atlantic results indicate that aluminosilicates clays are the major carrier of 231pa and 230th and the ratio 231paex 230thex in marine particulates decreases with increasing 232th concentration model simulation shows that sea floor sediments and trap collected particles have similar 231paex 230thex ratios in their biogenic components which are very close to the seawater ratio but are about one order higher than the ratios in coexisting clays preferential scavenging of 230th over 231pa by clays is primarily responsible for the 231pa 230th fractionation in the ocean the fractionation factor between 230th and 231pa fth pa varies from 10 for aluminosilicates to 1 for biogenic 232th free particles changes in fth pa as a function of particle composition exert primary controls on 231paex 230thex in marine particulates and bottom sediments and on the boundary scavenging of pa remineralization of biogenic particles in the water column may result in a decrease of 231paex 230thex our observations place an important constraint on the use of sediment 231paex 230thex as a paleoproductivity proxy namely in order to use down core variations of 231paex 230thex to assess past changes in surface productivity one must either verify or assume that the lithogenic particle flux and water column particle remineralization have remained essentially constant at the core site

hydrography and sedimentation under the deep western boundary current on bjorn and gardar drifts iceland basin abstract the interaction of northern component waters overflowing the iceland scotland ridge with sediments further south in the iceland basin has been responsible for highly variable sedimentation patterns since at least the late miocene 5 million years ago and has formed both bjorn and gardar drifts presently this process is maintained by a flux of approximately 3 sv measured along the south icelandic slope of iceland scotland overflow water isow with a mean regional flow direction to the sw which affects sediment transport on bjorn drift below 1350 m depth and over most of the gardar drift coriolis deflection of isow flow causes it to move as a deep western boundary current dwbc in the iceland basin which redistributes sediments under the influence of seabed topography here hydrographic and sedimentological data are used to illustrate the effects and extent of the vigorous dwbc activity the study presents a baseline against which inferred changes in the past can be assessed north of 58 n bottom nepheloid layers with heavy suspended sediment loads are often encountered particularly under the denser and faster flowing core of isow on the eastern slope of gardar drift in this area the presence of migrating regular sedimentary waves is seen on 3 5 khz profiles this is consistent with both the near bottom flow velocity probably in excess of 10 cm s 1 estimated by the geostrophic method and the presence of well sorted foraminiferal sand on the seabed south of 58 n dilute bottom nepheloid layers associated with more tranquil conditions near the seabed inferred from photographic and sedimentological evidence show that currents on gardar drift are weak although most of the south iceland basin is mantled by both regular and irregular non migratory mudwaves the absence of migrating structures with the exception of current intensification associated with discrete basement highs indicates that more sluggish currents characterise this region throughout the region highly variable mean holocene sediment accumulation rates are inferred 2 40 cm ka 1 as a result of the dwbc interacting with the topography

grain size effects on th 230 xs inventories in opal rich and carbonate rich marine sediments abstract excess thorium 230 230thxs as a constant flux tracer is an essential tool for paleoceanographic studies but its limitations for flux normalization are still a matter of debate in regions of rapid sediment accumulation it has been an open question if 230thxs normalized fluxes are biased by particle sorting effects during sediment redistribution in order to study the sorting effect of sediment transport on 230thxs we analyzed the specific activity of 230thxs in different particle size classes of carbonate rich sediments from the south east atlantic and of opal rich sediments from the atlantic sector of the southern ocean at both sites we compare the 230thxs distribution in neighboring high vs low accumulation settings two grain size fractionation methods are explored we find that the 230thxs distribution is strongly grain size dependent and 50 90 of the total 230thxs inventory is concentrated in fine material smaller than 10 m which is preferentially deposited at the high accumulation sites this leads to an overestimation of the focusing factor and consequently to an underestimation of the vertical flux rate at such sites the distribution of authigenic uranium indicates that fine organic rich material has also been re deposited from lateral sources if the particle sorting effect is considered in the flux calculations it reduces the estimated extent of sediment focusing in order to assess the maximum effect of particle sorting on we present an extreme scenario in which we assume a lateral sediment supply of only fine material comparing 230thxs normalized mass fluxes biased by sorting effects with uncorrected mass fluxes we suggest that 230thxs normalization is still a valid tool to correct for lateral sediment redistribution however differences in focusing factors between core locations have to be evaluated carefully taking the grain size distributions into consideration

present water mass calcium carbonate corrosiveness in the eastern south atlantic inferred from ultrastructural breakdown of globigerina bulloides in surface sediments abstract the atlantic is regarded as a huge carbonate depocenter due to an on average deep calcite lysocline however calculations and models that attribute the calcite lysocline to the critical undersaturation depth hydrographic or chemical lysocline and not to the depth at which significant calcium carbonate dissolution is observed sedimentary calcite lysocline strongly overestimate the preservation potential of calcareous deep sea sediments significant calcium carbonate dissolution is expected to begin firstly below 5000 m in the deep guinea and angola basin and below 4400 m in the cape basin our study that is based on different calcium carbonate dissolution stages of the planktic foraminifera globigerina bulloides clearly shows that it starts between 400 and 1600 m shallower depending on the different hydrographic settings of the south atlantic ocean in particular coastal areas are severely affected by increased supply of organic matter and the resultant production of metabolic co2 which seems to create microenvironments favorable for dissolution of calcite well above the hydrographic lysocline

a procedure for partitioning bulk sediments into distinct grain size fractions for geochemical analysis a method to separate sediments into discrete size fractions for geochemical analysis has been tested the procedures were chosen to minimize the destruction or formation of aggregates and involved gentle sieving and settling of wet samples freeze drying and sonication pretreatments known to influence aggregates were used for comparison freeze drying was found to increase the silt clay ratio by an average of 180 percent compared to analysis of a wet sample that had been wet sieved only sonication of a wet sample decreased the silt clay ratio by 51 percent the concentrations of metals and organic carbon in the separated fractions changed depending on the pretreatment procedures in a manner consistent with the hypothesis that aggregates consist of fine grained organic and metal rich particles the coarse silt fraction of a freeze dried sample contained 20 44 percent higher concentrations of zn cu and organic carbon than the coarse silt fraction of the wet sample sonication resulted in concentrations of these analytes that were 18 33 percent lower in the coarse silt fraction than found in the wet sample sonication increased the concentration of lead in the clay fraction by an average of 40 percent compared to an unsonicated sample understanding the magnitude of change caused by different analysis protocols is an aid in designing future studies that seek to interpret the spatial distribution of contaminated sediments and their transport mechanisms

southern ocean and glaciogenic nutrients control diatom export production on the chile margin abstract biogenic particle flux was reconstructed using 230 thorium normalization at two sites on the southern chile margin odp site 1233 at 41 s 838 m depth is at the southern limit of the peru chile upwelling system where the northern extent of the antarctic circumpolar current impinges on the south american continental margin odp site 1234 at 36 s 1014 m depth is located within the core of the coastal upwelling system near the mouths of the bio bio and itata rivers at 41 s opal lithogenic and carbonate fluxes are greatest during the last glacial interval 26 20 ka carbonate has a secondary peak during the mid holocene 8 ka and organic carbon fluxes increase slightly from 17 ka to the present at 36 s large lithogenic fluxes are observed both during the last glacial interval and the holocene and a maximum in organic carbon flux is observed during the late holocene 5 ka without an accompanying peak in opal flux these reconstructed fluxes at 36 s and 41 s fit within a larger latitudinal pattern of a poleward increase in the magnitude of opal flux during the glacial period the pattern of normalized opal flux opal mass accumulation rate and opal carbonate ratios is consistent with either i enhanced supply of si from the southern ocean as proposed by the silicic acid leakage hypothesis or ii enhanced si and fe delivery from land driven by glacial erosion the pattern of reconstructed export production supports our view that the appearance of more reducing conditions in the sediments upon deglaciation was most likely driven by decreased ventilation rather than increased local productivity

export fluxes of calcite in the eastern equatorial pacific from the last glacial maximum to present 1 the eastern equatorial pacific eep is an important center of biological productivity generating significant organic carbon and calcite fluxes to the deep ocean we reconstructed paleocalcite flux for the past 30 000 years in four cores collected beneath the equatorial upwelling and the south equatorial current sec by measuring ex230th normalized calcite accumulation rates corrected for dissolution with a newly developed proxy for fraction of calcite preserved this method produced very similar results at the four sites and revealed that the export flux of calcite was 30 50 lower during the lgm compared to the holocene the internal consistency of these results supports our interpretation which is also in agreement with emerging data indicating lower glacial productivity in the eep possibly as a result of lower nutrient supply from the southern ocean via the equatorial undercurrent however these findings contradict previous interpretations based on mass accumulation rates mar of biogenic material in the sediment of the eep which have been taken as reflecting higher glacial productivity due to stronger wind driven upwelling

the influence of particle composition on thorium scavenging in the ne atlantic ocean pomme experiment abstract 230th 232th and 234th were analyzed in sinking particles collected by moored and drifting sediment traps in the ne atlantic ocean pomme experiment in order to constrain the phase s carrying th isotopes in the water column it reveals a contrasted behaviour between 234th and 230th 234th is correlated to the particulate organic carbon suggesting that it is primarily scavenged by organic compounds in the surface waters 230thxs is correlated with mn ba and the lithogenic fraction that are enriched in small suspended particles and incorporated in the sinking particulate flux throughout the water column the lack of correlation between 230thxs and caco3 or biogenic silica bsi indicates that caco3 and bsi are not responsible for 230th scavenging in the deep waters of this oceanic region 230th is generally correlated with the lithogenic content of the trapped material but this correlation disappears in winter during strong atmospheric dust inputs suggesting that lithogenic matter is not directly responsible for 230th scavenging in the deep waters or that sufficient time is required to achieve particle solution equilibration mno2 could be the prevalent 230thxs bearing phase the narrow range of kd mno2th obtained for very contrasted oceanic environments supports a global control of 230thxs scavenging by mno2 and raises the possibility that the 230th 231pa fractionation is controlled by the amount of colloidal mno2 in seawater

holocene sediment fluxes in the northeast atlantic from 230thexcess and radiocarbon measurements radiocarbon and 230thexcess data from six ne atlantic box cores are considered the cores form a transect from the porcupine abyssal plain over the east thulean rise to the southern end of feni drift the chronology for the cores is established from bulk sediment carbonate radiocarbon data and reveals that sections exhibiting constant accumulation rates can be identified in all the cores with rates of 3 0 3 5 cm kyr 1 on the plain through the holocene and late holocene rates of 4 3 6 6 cm kyr 1 elsewhere five out of the six cores show accumulations of more 230thexcess than is produced in the overlying water column with the greatest inventories up to 225 of production in the cores from the rise and drift a size fraction comparison between two cores from the plain and rise reveals that the higher overall accumulation rates and 230thexcess inventories in the off plain cores are due to an increased fine 5 m component fraction whereas the flux of coarser material is similar to that received on the plain this suggests that the higher fluxes of materials observed are physically rather than biogeochemically driven and also that drift formation has been continuously active in the late holocene sections of all the cores where regular accumulation is defined by the radiocarbon data are modeled first by a linear radiocarbon age depth model and second by a constant rain 230thexcess 0 model prorated for the observed core inventories these modeling approaches yield historical mass accumulation rate estimates which are generally in reasonable agreement 30 but the differences observed appear to be well organized in time rather than random

investigating the use of 232th 230th as a dust proxy using co located seawater and sediment samples from the low latitude north atlantic abstract the thorium isotope ratio 232 th 230 th can be measured in seawater and sediment samples and has been used as a proxy to reconstruct lithogenic fluxes to the oceans for the modern day and the pleistocene there has not yet been a systematic study testing the proxy using the 232 th 230 th ratio in seawater and the ratio recorded in the underlying sediment in this study we use co located core top sediments and seawater samples from five seamount sites spanning the tropical north atlantic to investigate the link between seawater and sediment 232 th 230 th ratios across a range of water depths our results indicate that a broad correlation exists between seawater and sedimentary 232 th 230 th ratios both seawater and sedimentary 232 th 230 th ratios record a signal consistent with decreasing lithogenic input east to west from africa to south america however calculated 232 th fluxes for the core top sediment samples indicate a strong dependence on depth with up to a factor of 4 difference from shallow 2900 m this depth dependence is likely caused by either a deficit of 230 th burial at depth compared to the production in the overlying water column through addition of 232 th or by a combination of the two by comparing seawater and sedimentary 232 th 230 th ratios we derive an apparent fractional solubility of 232 th of 29 3 in reasonable agreement with the upper end of existing estimates

near collapse of the meridional sst gradient in the eastern equatorial pacific during heinrich stadial 1 1 sea surface temperatures sst and inorganic continental input over the last 25 000 years 25 ka are reconstructed in the far eastern equatorial pacific eep based on three cores stretching from the equatorial front 0 01 n me0005 24jc into the cold tongue region 3 6 s tr163 31p and v19 30 we revisit previously published alkenone derived sst records for these sites and present a revised chronology for v19 30 inorganic continental input is quantified at all three sites based on 230th normalized fluxes of the long lived continental isotope thorium 232 and interpreted to be largely dust our data show a very weak meridional cross equatorial sst gradient during heinrich stadial 1 hs1 18 15 ka b p and high dust input along with peak export production at and north of the equator these findings are corroborated by an earth system model experiment for hs1 that simulates intensified northeasterly trade winds in the eep stronger equatorial upwelling and surface cooling furthermore the related southward shift of the intertropical convergence zone itcz during hs1 is also indicative of drier conditions in the typical source regions for dust

comment on do geochemical estimates of sediment focusing pass the sediment test in the equatorial pacific by m lyle et al accurately estimating the vertical flux of material reaching the seafloor from the overlying surface waters is essential for the paleoceanographic reconstruction of a wide variety of oceanic processes two approaches are currently being used one consists of estimating mass accumulation rates mar between dated horizons as the product of linear sedimentation rates sediment dry bulk densities and concentrations one pitfall with this approach is that sediments can be redistributed on the seafloor by bottom currents and their accumulation may not necessarily reflect the true vertical rain rate originating from the overlying water column to address this problem the method of 230th normalization was developed bacon 1984 this method is based on the assumption that the rapid scavenging of 230th produced in the water column by decay of dissolved uranium results in its flux to the seafloor always being close to its known rate of production to the extent that this assumption is correct scavenged 230th can be used as a reference to estimate the settling flux of other sedimentary constituents and to correct for sediment redistribution on the seafloor henderson and anderson 2003 francois et al 2004

reply to comment by r francois et al on do geochemical estimates of sediment focusing pass the sediment test in the equatorial pacific further explorations of 230th normalization

the response of excess 230th and extraterrestrial 3he to sediment redistribution at the blake ridge western north atlantic the constant flux proxies excess 230th 230thxs and extraterrestrial 3he 3heet are commonly used to calculate sedimentary mass accumulation rates and to quantify lateral advection of sediment at core sites in settings with significant lateral input or removal of sediment these calculations depend on the assumption that concentrations of 230thxs and 3heet are the same in both advected sediment and sediment falling through the water column above the core site sediment redistribution is known to fractionate grain sizes preferentially transporting fine grains though relatively few studies have examined the grain size distribution of 230thxs and 3heet presently available data indicate that both are concentrated in fine grains suggesting that fractionation during advection may bias accumulation rate and lateral advection estimates based on these proxies in this study we evaluate the behavior of 230thxs and 3heet in holocene and last glacial samples from two cores from the blake ridge a drift deposit in the western north atlantic at the end of the last glacial period both cores received large amounts of laterally transported sediment enriched in fine grained material we find that accumulation rates calculated by normalization to 230th and 3he are internally consistent despite large spatial and temporal differences in sediment advection our analyses of grain size fractions indicate that 70 of 3heet bearing grains are in the 20 m fraction with roughly equal amounts in the 4 and 4 20 m fractions 230thxs is concentrated in 4 m grains relative to 4 to 20 m grains by approximately a factor of 2 in holocene samples and by a much larger factor averaging a factor of 10 in glacial samples despite these enrichments of both constant flux proxies in fine particles the fidelity of 230th and 3he based accumulation rate estimates appears to be preserved even in settings with extreme sediment redistribution perhaps due to the cohesive behavior of fine particles in marine settings

sediment sorting and focusing in the eastern equatorial pacific abstract the interpretation of sedimentary records in terms of glacial interglacial changes in particle flux in the eastern equatorial pacific eep has been controversial here we analyze disaggregated inorganic grain size digs distributions of three marine sediment cores from this region focusing on the last 21 ka to investigate evidence of sediment redistribution on the sea floor grain size sorting coefficients show that sediments in the eep are moderately to well sorted indicating sediment reworking in this region due to bottom currents furthermore a systematic correlation between focusing factors and sorting coefficients at two sites shows that more focused sediments are also better sorted we conclude that grain size based sedimentary records are consistent with the 230 th based evidence of lateral sediment redistribution on the sea floor in the eep

thorium 230 normalized particle flux and sediment focusing in the panama basin region during the last 30 000 years 1 application of the 230 th normalization method to estimate sediment burial fluxes in six cores from the eastern equatorial pacific eep reveals that bulk sediment and organic carbon fluxes display a coherent regional pattern during the holocene that is consistent with modern oceanographic conditions in contrast with estimates of bulk mass accumulation rates mars derived from core chronologies two nearby sites less than 10 km apart which have different mars show nearly identical 230 th normalized bulk fluxes focusing factors derived from the 230 th data at the foot of the carnegie ridge in the panama basin are 2 in the holocene implying that lateral sediment addition is significant in this part of the basin new geochemical data and existing literature provide evidence for a hydrothermal source of sediment in the southern part of the panama basin and for downslope transport from the top of the carnegie ridge the compilation of core records suggests that sediment focusing is spatially and temporally variable in the eep during oxygen isotope stage 2 ois 2 from 13 27 ka bp focusing appears even higher compared to the holocene at most sites similar to earlier findings in the eastern and central equatorial pacific the magnitude of the glacial increase in focusing factors however is strongly dependent on the accuracy of age models we offer two possible explanations for the increase in glacial focusing compared to the holocene the first one is that the apparent increase in lateral sediment redistribution is partly or even largely an artifact of insufficient age control in the eep while the second explanation which assumes that the observed increase is real involves enhanced deep sea tidal current flow during periods of low sea level stand

periodic waves in the surf zone analysis of experimental data abstract the paper discusses observed characteristics of some basic integral parameters for regular waves essential for the determination of the energy flux the radiation stress and the energy dissipation throughout the surf zone the paper further indicates a connection to the parameters at the breaking point and hence a connection to the wave shoaling area prior to the waves breaking on a beach the variation of the integral mainly time averaged wave parameters within the surf zone is in general given as a parametric description calling for further theoretical work in this field

timescales of lateral sediment transport in the panama basin as revealed by radiocarbon ages of alkenones total organic carbon and foraminifera abstract paired radiocarbon measurements on haptophyte biomarkers alkenones and on co occurring tests of planktic foraminifera neogloboquadrina dutertrei and globogerinoides sacculifer from late glacial to holocene sediments at core locations me0005 24jc y69 71p and mc16 from the south western and central panama basin indicate no significant addition of pre aged alkenones by lateral advection the strong temporal correspondence between alkenones foraminifera and total organic carbon toc also implies negligible contributions of aged terrigenous material considering controversial evidence for sediment redistribution in previous studies of these sites our data imply that the laterally supplied material cannot stem from remobilization of substantially aged sediments transport if any requires syn depositional nepheloid layer transport and redistribution of low density or fine grained components within decades of particle formation such rapid and local transport minimizes the potential for temporal decoupling of proxies residing in different grain size fractions and thus facilitates comparison of various proxies for paleoceanographic reconstructions in this study area anomalously old foraminiferal tests from a glacial depth interval of core y69 71p may result from episodic spillover of fast bottom currents across the carnegie ridge transporting foraminiferal sands towards the north

wave height distributions on shallow foreshores wave height distributions on shallow foreshores deviate from those in deep water due to the effects of the restricted depth to height ratio and of wave breaking laboratory data of wave heights on shallow foreshores of different slopes have been analysed to determine these effects and to derive generalised empirical parameterisations a model distribution is proposed consisting of a rayleigh distribution or a weibull distribution with exponent equal to 2 for the lower heights and a weibull with a higher exponent for the higher wave heights the parameters of this distribution have been estimated from the data and expressed in terms of local wave energy depth and bottom slope yielding a predictive model that is found to be significantly more accurate than existing expressions

fractionation of 230th 231pa and 10be induced by particle size and composition within an opal rich sediment of the atlantic southern ocean this study centers on the question how sensitive are 231pa 230th and 10be 230th to sediment composition and redistribution the natural radionuclides 231pa 230th and 10be recorded in deep sea sediments are tracers for water mass advection and particle fluxes we investigate the influence of oceanic particle composition on the element adsorption in order to improve our understanding of sedimentary isotope records we present new data on particle size specific 231pa and 10be concentrations an additional separation step based on settling velocities led to the isolation of a very opal rich phase we find that opal rich particles contain the highest 231pa and 10be concentrations and higher 231pa 230th and 10be 230th isotope ratios than opal poor particles the fractionation relative to 230th induced by the adsorption to opal rich particles is more pronounced for 231pa than for 10be we conclude that bulk 231pa 230th in southern ocean sediments is most suitable as a proxy for past opal fluxes the comparison between two neighboring cores with rapid and slow accumulation rates reveals that these isotope ratios are not influenced significantly by the intensity of sediment focusing at these two study sites however a simulation shows that particle sorting by selective removal of sediment winnowing could change the isotope ratios consequently 231pa 230th should not be used as paleocirculation proxy in cases where a strong loss of opal rich material due to bottom currents occurred

glacial interglacial changes in sediment rain rate in the sw indian sector of subantarctic waters as recorded by 230th 231pa u and δ15n high resolution records of opal carbonate and terrigenous fluxes have been obtained from a high sedimentation rate core md84 527 43 50 s 51 19 e 3269 m by normalization to 230th this method estimates paleofluxes to the seafloor on a point by point basis and distinguishes changes in sediment accumulation due to variations in vertical rain rates from those due to changes in syndepositional sediment redistribution by bottom currents we also measured sediment 15n to evaluate the changes in nitrate utilization in the overlying surface waters associated with paleoflux variations our results show that opal accumulation rates on the seafloor during the holocene and stage 3 based on 14c dating were respectively tenfold and fivefold higher than the vertical rain rates at this particular location changes in opal accumulation on the seafloor appear to be mainly controlled by sediment redistribution by bottom currents rather than variations in opal fluxes from the overlying water column correction for syndepositional sediment redistribution and the improved time resolution that can be achieved by normalization to 230th disclose important variations in opal rain rates we found relatively high but variable opal paleoflux during stage 3 with two maxima centered at 36 and 30 kyr b p low opal paleoflux during stage 2 and deglaciation and a pronounced maximum during the early holocene we interpret this record as reflecting variations in opal production rates associated with climate induced latitudinal migration of the southern ocean frontal system sediments deposited during periods of high opal paleoflux also have high authigenic u concentrations suggesting more reducing conditions in the sediment and high pa 231 th 230 ratios suggesting increased scavenging from the water column sediment 15n is circa 1 5 per mil higher during isotopic stage 2 and deglaciation the low opal rain rates recorded during that period appear to have been associated with increased nitrate depletion this suggests that opal paleofluxes do not simply reflect latitudinal migration of the frontal system but also changes in the structure of the upper water column increased stratification during isotopic stage 2 and deglaciation could have been produced by a meltwater lid leading to lower nitrate supply rates to surface waters

particle sorting during sediment redistribution processes and the effect on 230th normalized mass accumulation rates the 230th method of determining mass accumulation rates mars assumes that little to no fractionation occurs during sediment redistribution processes at the seafloor we examine 230th inventories in radiocarbon dated multicore sediments from paired winnowed and focused sites at cocos and carnegie ridges panama basin radiocarbon derived sand mars which likely represent the vertical rain of particles poorly transported by bottom currents are similar at each of the paired sites but are different using 230th normalization 230th normalized mars are about 60 lower at focused sites and likely underestimate vertical mars while the reverse is true for winnowed sites we hypothesize that size fractionation occurs most frequently at lower current velocities resulting in the coarse fraction being left behind and primarily the fine 230th rich grains being transported downslope 230th normalization works well for recording fine grained detrital and opal but not coarse grained carbonate fluxes in regions that have undergone sediment redistribution

quaternary surface water temperature estimations calibration of a diatom transfer function for the southern ocean the quantitative diatom analysis of 218 surface sediment samples recovered in the atlantic and western indian sector of the southern ocean is used to define a base of reference data for paleotemperature estimations from diatom assemblages using the imbrie and kipp transfer function method the criteria which justify the exclusion of samples and species out of the raw data set in order to define a reference database are outlined and discussed sensitivity tests with eight data sets were achieved evaluating the effects of overall dominance of single species different methods of species abundance ranking and no analog conditions e g eucampia antarctica on the estimated paleotemperatures the defined transfer functions were applied on a sediment core from the northern antarctic zone overall dominance of fragilariopsis kerguelensis in the diatom assemblages resulted in a close affinity between paleotemperature curve and relative abundance pattern of this species downcore logarithmic conversion of counting data applied with other ranking methods in order to compensate the dominance of f kerguelensis revealed the best statistical results a reliable diatom transfer function for future paleotemperature estimations is presented

increased dust deposition in the pacific southern ocean during glacial periods dust deposition in the southern ocean constitutes a critical modulator of past global climate variability but how it has varied temporally and geographically is underdetermined here we present data sets of glacial interglacial dust supply cycles from the largest southern ocean sector the polar south pacific indicating three times higher dust deposition during glacial periods than during interglacials for the past million years although the most likely dust source for the south pacific is australia and new zealand the glacial interglacial pattern and timing of lithogenic sediment deposition is similar to dust records from antarctica and the south atlantic dominated by patagonian sources these similarities imply large scale common climate forcings such as latitudinal shifts of the southern westerlies and regionally enhanced glaciogenic dust mobilization in new zealand and patagonia

230thex flux into norwegian greenland sea sediments evidence for lateral sediment transport during the past 300 000 years 230th was determined to investigate the influence of climatic cycles on the 230thex flux into norwegian greenland sea sediments the fafp ratios i e the ratios between the measured 230thex flux fa into the sediments and the production rate of 230th in the water column fp vary considerably in the four cores investigated systematic variations in the ratios with the climatic cycles could not be observed furthermore variations in the fafp ratios cannot be correlated between individual sites it is argued that lateral sediment transport due to deglaciation of ice sheets bottom currents and or downslope sediment transport result in fafp ratios that are not equal to 1 the results suggest that both sediment winnowing and or erosion and sediment focusing have strong influences upon sediment accumulation in the norwegian greenland sea

in situ measurements of particle settling velocity in the deep sea two instruments the remote optical settling tube and the benthic autonomous settling tube have been deployed on the nova scotian continental rise at a depth of 4820 m the few results obtained suggest that optical and gravimetric methods give comparable results assumptions about particle density little affect the settling velocity distribution but do scale the total magnitude by using a distribution of declining density with increasing size indicating increasing water content the total concentration inferred from the light attenuation by using mie theory is quite close to the total found from gravimetric data the coarser end of the size distribution changes more with overall change in concentration than the fine end the settling velocity distribution shows the presence of several modes the two principal ones can be matched with modal sizes of 3 3 m and 60 m in coulter counter data allowing inference of stokes density contrasts of 1 5 and 0 061 g cm 3 respectively at concentrations of about 200 mg m 3 more than 50 of the material has a settling velocity less than 2 10 4 cm s 1 probably 3 m in size but this percentage appears to decrease with an increase in total concentration

modeling the particle flux effect on distribution of 230th in the equatorial pacific 1 the normalization of sediment accumulation rates by 230th is increasingly used to constrain particle rain rates because 230th is produced at a known rate in the water column and removed relatively quickly to the sediment several recent contributions have questioned this approach and suggested that the preferential removal of 230th in areas of high particle flux the particle flux effect introduces a systematic bias in the 230th normalization technique we use a circulation model that includes a description of particle scavenging to show that the particle flux effect cannot explain observations of high 230th accumulation in equatorial pacific sediments relative to 230th production in the water column we further consider the possible variation of particle rain rates over time we find only a minimal sensitivity in the particle flux effect due to increases in the particle rain rate at the equatorial pacific by a factor of up to 10 this situation exists because the residence time of 230th in the water column is too short to permit significant lateral transport with reasonable isopycnal mixing coefficients we conclude that the increased rates of 230th accumulation found in equatorial pacific sediments deposited during the last glacial maximum cannot have been caused by the particle flux effect

spatial and temporal offsets between proxy records in a sediment drift chronologies for late quaternary marine sediment records are usually based on radiocarbon ages of planktonic foraminifera signals carried by other sedimentary components measured in parallel can provide complementary paleoclimate information a key premise is that microfossils and other indicators within a given sediment horizon are of equal age we show here that haptophyte derived alkenones isolated from bermuda rise drift sediments are up to 7000 years older than coexisting planktonic foraminifera this temporal offset which is apparently due to lateral transport of alkenones on fine grained particles from the nova scotian margin markedly influences molecular estimates of sea surface temperatures more broadly the observation raises questions about both the temporal and the geographic fidelity of paleoenvironmental records encoded by readily transported components of sediments

barium accumulation in the atlantic sector of the southern ocean results from 190 000 year records extensive investigations of sedimentary barium were performed in the southern south atlantic in order to assess the reliability of the barium signal in antarctic sediments as a proxy for paleoproductivity maximum accumulation rates of excess barium were calculated for the antarctic zone south of the polar front where silica accumulates at high rates the correspondence between barium and opal supports the applicability of barium as a proxy for productivity within the antarctic zone north of today s average sea ice maximum interglacial vertical rain rates of excess barium are high with a maximum occurring during the last deglaciation and early holocene and during oxygen isotope chronozone 5 5 during these periods the maximum silica accumulation was supposedly located south of the polar front glacial paleoproductivity instead was low within the antarctic zone north of the polar front significantly higher barium accumulation occurs during glacial times the vertical rain rates however are as high as in the glacial antarctic zone therefore there was no evidence for an increased productivity in the glacial southern ocean

sediment focusing in the panama basin eastern equatorial pacific ocean abstract age model derived sediment mass accumulation rates mars are consistently higher than 230th normalized mars in the equatorial pacific ocean during the past 25 ka the offset being highest in the panama basin suggests a significant role for deep sea sediment redistribution i e sediment focusing in this region here we test the hypothesis that downslope transport of sediments from topographically high regions that surround the panama basin is the cause of higher than expected xs230th inventories over the past 25 ka in the deeper parts of the basin we find little difference in xs230th inventories between the highest and lowest reaches of the basin furthermore there is no correlation between xs230th derived sediment focusing factors and water depth which suggests that the topographic highs do not serve as a source of xs230th a spatial analysis suggests that there may be an enhanced scavenging effect on xs230th concentrations in sediment closest to the equator where productivity is the highest although further data is necessary to corroborate this at the equator xs230th derived focusing factors are high and range from about 1 to 5 during the holocene and about 1 to 11 during the last glacial in contrast non equatorial cores show a smaller range in variability from about 0 7 to 2 8 during the holocene and from 0 7 to 3 6 during the last glacial based on 232th flux measurements we hypothesize that the location at which eolian detrital fluxes surpass the riverine detrital fluxes is approximately 300 km from the margin while riverine fluxes from coastal margins were higher during the holocene eolian fluxes were higher during the last glacial

oroclines of the variscan orogen of iberia paleocurrent analysis and paleogeographic implications abstract coupled structural and paleomagnetic analyses have shown that the northern iberian bend of the variscan orogen referred to as the cantabrian orocline developed by vertical axis rotation of an originally linear orogen however palinspastic restoration of the orocline has proven difficult owing to 1 an unusually great orogenic width of over 700 km and 2 exposure of shallow water strata of the gondwanan margin in the northern and southern portions of the orogen we present paleocurrent data from lower ordovician shallow marine clastic sedimentary rocks across the variscan of northern and central iberia collected to constrain palinspastic restoration of the orogen paleocurrent data were collected from over 50 sites and include cross bed foresets ripple crests and casts as well as rare ball and pillow structures syn sedimentary slump folds and incised channels paleocurrent directions fan around the cantabrian orocline are consistently oriented at a high angle to structural strike and yield a consistent offshore direction outward from the oroclinal core similarly changes in structural strike and paleocurrent direction across central iberia imply the presence of a second more southerly orocline the central iberian orocline that is continuous with but convex in the opposite direction of the cantabrian orocline together the cantabrian and central iberian oroclines define an s shaped pair of continental scale buckle folds palinspastic restoration of the oroclines yields a linear continental margin 1500 km long characterized by consistent offshore paleoflow to the west defining a westerly oceanic domain presumably the rheic ocean and an easterly landward direction presumably gondwana recognition of the southern orocline explains the unusual width of the orogen the geometry of aeromagnetic anomalies attributable to variscan rocks and is consistent with available structural data paleomagnetic declination data and the distribution of correlative paleozoic and older rock sequences including shallow water strata of the gondwanan margin the s geometry of the oroclines is similar to the z geometry of the alaskan oroclines of the north america cordillera suggesting that as in the cordillera the iberian oroclines may record a significant margin parallel translation event

thorium adsorption in the ocean reversibility and distribution amongst particle sizes abstract experiments have been carried out to determine whether the adsorption of th by marine suspended particles is a reversible process the results indicate reversibility on a time scale of hours the distribution of th between the dissolved state bacon and anderson 1982 and on the settling model of tsunogai and minagawa 1978 are discussed

sortable silt and fine sediment size composition slicing parameters for palaeocurrent speed and palaeoceanography fine sediment size 63 ixm is best measured by a sedimentation technique which records the whole size distribution repeated size measurement with intermediate steps of removal of components by dissolution allows inference of the size distribution of the removed component as well as the residue in this way the size of the biogenic and lithogenic noncarbonate fractions can be determined observations of many size distributions suggest a minimum in grain size frequency curves at 8 to 10 ixm the dynamics of sediment erosion deposition and aggregate breakup suggest that fine sediment behavior is dominantly cohesive below 10 1xm grain size and noncohesive above that size thus silt coarser than 10 ixm displays size sorting in response to hydrodynamlc processes and its properties may be used to infer current speed silt that is f mer than 10 ixm behaves in the same way as clay 2 xm useful parameters of the distribution are the 10 63 ixm mean size and the percentage 10 63 ixm in the fine fraction we cannot use size distributions to distinguish the nature of the currents therefore to infer water mass advection speeds i e the mean kinetic energy of the flow ku regions of high eddy kinetic energy ke must be avoided at the present such abyssal regions lie under the high surface k e of major current systems gulf stream kuroshio agulhas antarctic circmpolar current and brazil falldand currents in the argenthe basin this is probably a satisfactory guide for the pleistocene with regard to the carbonate subfraction of the size spectrum size modes due to both cocco iths and foramlnlferal fragments can be recognized and analyzed with the boundary between them again at about 10 lm the flux of less than 10 lm carbonate at pelagic sites above the lysocline is another candidate for a productivity indicator

sediment focusing in the central equatorial pacific ocean at four sites in the central equatorial pacific ocean the flux of extraterrestrial he determined using the excess 230th profiling method is 8 10 13 cm stp cm 2 ka 1 this supply rate is constant to within 30 at these same sites however the burial rate of he determined using chronostratigraphic accumulation rates varies by more than a factor of 3 the lowest burial rates which occur north of the equator at 1 n 139 w are lower than the global average rate of supply of extraterrestrial he by 20 and indicate that sediment winnowing may have occurred the highest burial rates which are recorded at the equator and at 2 s are higher than the rate of supply of extraterrestrial he by 100 and these provide evidence for sediment focusing by analyzing several proxies measured in core pc72 sediments spanning the past 450 kyr we demonstrate that periods of maximum burial rates of 230th he 10be ti and barite with a maximum peak to trough amplitude of a factor of 6 take place systematically during glacial time however the ratio of any one proxy to another is constant to within 30 over the entire length of the records given that each proxy represents a different source 234u decay in seawater interplanetary dust upper atmosphere continental dust or upper ocean our preferred interpretation for the covariation is that the climate related changes in burial rates are driven by changes in sediment focusing

comparing different extreme wave analysis models for wave climate assessment along the italian coast abstract by utilizing various statistical models to quantify the return levels of extreme significant wave height this study seeks to achieve two objectives the updating of the state of the art concerning extreme wave analysis along the italian coast and the creation of a long term predictive model to these ends four different methods widely used in the field of metocean engineering are employed to analyze both buoy data rete ondametrica nazionale ron and wave data obtained by means of dynamical hindcasting techniques such as the forecast hindcast operational model chain in use at the university of genoa www dicca unige it meteocean return levels are estimated by the goda method the generalized extreme value gev and the generalized pareto distribution poisson point process models and the equivalent triangular storm ets algorithm all models follow the peak over threshold pot approach which require an optimal threshold implementation save for the gev analysis which is applied to model significant wave height maxima pertaining to time blocks the models exhibit different performance characteristics presented here and treated in depth in general noteworthy versatility characterizes the gpd poisson model which often recovers goda results while the gev and ets models exhibit limitations in assessment of a variety of wave fields greatly diversified in a semi closed basin such as the mediterranean sea long term estimates have been provided by means of the most appropriate model selected thus offering a complete overview of wave climate in the mediterranean basin based on wave hindcast data

radiocarbon and 230th data reveal rapid redistribution and temporal changes in sediment focussing at a north atlantic drift abstract in locations of rapid sediment accumulation receiving substantial amounts of laterally transported material the timescales of transport and accurate quantification of the transported material are at the focus of intense research here we present radiocarbon data obtained on co occurring planktic foraminifera marine haptophyte biomarkers alkenones and total organic carbon toc coupled with excess thorium 230 230thxs measurements on four sediment cores retrieved in 1649 2879 m water depth from two such high accumulation drift deposits in the northeast atlantic bjorn and gardar drifts while 230thxs inventories imply strong sediment focussing no age offsets are observed between planktic foraminifera and alkenones suggesting that redistribution of sediments is rapid and occurs soon after formation of marine organic matter or that transported material contains negligible amounts of alkenones an isotopic mass balance calculation based on radiocarbon concentrations of co occurring sediment components leads us to estimate that transported sediment components contain up to 12 of fossil organic matter that is free of or very poor in alkenones but nevertheless appears to consist of a mixture of fresh and eroded fossil material considering all available constraints to characterize transported material our results show that although focussing factors calculated from bulk sediment 230thxs inventories may allow useful approximations of bulk redeposition they do not provide a unique estimate of the amount of each laterally transported sediment component furthermore our findings provide evidence that the occurrence of lateral sediment redistribution alone does not always hinder the use of multiple proxies but that individual sediment fractions are affected to variable extents by sediment focussing

similar glacial and interglacial export bioproductivity in the atlantic sector of the southern ocean multiproxy evidence and implications for glacial atmospheric co2 we present time series of export productivity proxy data including 230thex normalized deposition rates rain rates of 10be dissolution corrected biogenic ba and biogenic opal as well as authigenic u concentrations which are complemented by rain rates of total detrital fe and sea ice indicating diatom abundances from five sediment cores across the atlantic sector of the southern ocean covering the past 150 000 years the results suggest that 10be rain rates and authigenic u concentration cannot serve as quantitative paleoproductivity proxies because they have also been influenced by detrital particle fluxes in the case of 10be and bulk sedimentation rates sediment focussing and deep water oxygenation in the case of u the combined results of the remaining productivity proxies of this study rain rates of biogenic opal and biogenic ba in those sections without authigenic u and other previously published proxy data from the southern ocean 231pa 230th and nitrogen isotopes suggest that a combination of sea ice cover shallow remineralization depth and stratification of the glacial water column south of the present position of the antarctic polar front and possibly fe fertilization north of it have been the main controlling factors of export paleoproductivity in the southern ocean over the last 150 000 years an overall glacial increase of export paleoproductivity is not supported by the data implying that bioproductivity variations in the southern ocean are unlikely to have contributed to the major glacial atmospheric co2 drawdown observed in ice cores

the influence of particle composition on thorium scavenging in the mediterranean sea abstract sediment trap data are crucial for the study of marine biochemical cycles but they need careful validation by thorium th isotopes in the present study 230th 232th uranium u aluminum al barium ba and manganese mn were analyzed in sinking particles collected by moored sediment traps in the ligurian sea dyfamed site in order to determine the collection efficiency of the traps and to constrain which particulate phase s carries th isotopes in a region with strong lithogenic inputs the 230thxs evaluation was based on the u content of each sample rather than on the 232th content of each sample and the average 238u 232th ratio of the continental crust because the latter method introduced too much uncertainty in the calculation high trapping efficiencies 187 85 at 200 m and 87 11 at 1000 m indicated no evidence of particle under collection by the traps the lack of correlation between 230thxs and the carbonate or the organic matter fraction suggests that these phases are not major 230thxs carrying phases in the deep ocean for most samples of the time series the 230thxs concentration is correlated with the lithogenic fraction and the mn concentration but pulses of particles with high lithogenic and mn content and low 230thxs concentration occur in winter assuming that 230thxs is only carried by lithogenic particles we estimate kd lithoth ranges from 0 42 0 04 107 ml g to 0 8 0 2 107 ml g assuming that 230thxs is only carried by authigenic mn oxide precipitates mno2 we estimate that kd mno2th ranges from 0 6 0 1 1010 ml g to 1 1 0 4 1010 ml g the relative variation of kd mno2th a factor 7 between different oceanic sites is significantly lower than the relative variation of kd lithoth a factor 50 suggesting that 230thxs has a tighter link with mno2 rather than with lithogenic particles and hence that 230thxs may be more likely scavenged by mno2 than by lithogenic particles the unambiguous determination of the particles carrying 230thxs remains to be done