iron control of past productivity in the coastal upwelling system off the atacama desert chile 1 biogenic opal and organic carbon vertical rain rates in sediment cores reveal a strong cyclicity in the productivity of the upwelling system off presently arid northern chile during the last 100 000 years changes in productivity are found to be in phase with the precessional cycle 20 000 years and with inputs of iron from the continent during austral summer insolation maxima increased precipitation and river runoff in the region appear to have brought high inputs of iron mainly from the andes to the coastal ocean enhancing primary productivity there we interpret our results as providing evidence for iron control of past productivity in this upwelling system and for a tight link between productivity and orbital forcing at midlatitudes

variability of the north atlantic thermohaline circulation during the last interglacial period studies of natural climate variability are essential for evaluating its future evolution greenland ice cores suggest that the modern warm period the holocene has been relatively stable for the past 9 000 years much less is known about other warm interglacial periods which comprise less than 10 of the climate record during the past 2 5 million years here we present high resolution ocean sediment records of surface and deep water variables from the bermuda rise spanning the last interglacial period about 118 000 127 000 years ago in general deep water chemical changes are coincident with transitions in surface climate at this site the records do not show any substantial fluctuations relative to the much higher variability observed during the preceding and subsequent cool climates the relatively stable interglacial period begins and ends with abrupt changes in deep water flow we estimate using 230 th measurements to constrain the chronology that transitions occur in less than 400 years

water column 230th systematics in the eastern equatorial pacific ocean and implications for sediment focusing 230 th and 232 th abstract in an effort to investigate the cause of higher than expected sediment inventories of 230 th in the panama basin thorium isotopes were measured in eight deep water casts within the guatemala panama and peru basins along a meridional transect at 861w between 6 51n and 8 51s dissolved 230 th concentrations increase linearly from the surface to 1000 m at each transect station below 1000 m the deep waters of the panama basin show the highest deficit 50 of 230 th assuming a reversible exchange of 230 th between dissolved and sinking particulate matter and in comparison with the globally averaged water column 230 th peru basin waters have a larger range of dissolved 230 th concentrations 7 9 16 5 fg kg than that within panama basin waters 5 7 7 1 fg kg there is a progressive decrease in average dissolved deep water 41000 m 230 th concentrations from the southernmost sites in the peru basin toward the panama basin we suggest that intense scavenging by upwelling derived productivity near the equator 7 21 and resuspension of ubiquitous mn rich particulates in panama basin sediments are the primary causes of the significant south to north lateral gradient in deep water dissolved 230 th although 230 th from peru basin waters may be transported and then scavenged and ultimately buried in the panama basin our calculations suggest that the quantity of advected 230 th is relatively small between 15 and 30 of the total 230 th being produced within water column of the panama basin itself panama basin sediment focusing factors greater than 1 3 cannot be explained by lateral export and excess scavenging of water column 230 th dissolved 232 th concentra tions in addition to being the lowest reported so far in the literature fall within a very narrow range 6 26 pg kg and are generally invariable with depth this invariability suggests the dissolution of dust in surface waters as a likely sole source of dissolved 232 th for the entire water column

the u series toolbox for paleoceanography the geochemistry of marine sediments is a major source of information about the past environment of the many measurements that provide such information those of the u series nuclides are unusual in that they inform us about the rate and timescales of processes oceanic processes such as sedimentation productivity and circulation typically occur on timescales too short to be assessed using parent daughter isotope systems such as rb sr or sm nd so the only radioactive clocks that we can turn to are those provided by cosmogenic nuclides principally 14c or the u series nuclides this makes the u series nuclides powerful allies in the quest to understand the past ocean climate system and has led to their widespread application over the last decade as in other applications of the u series those in paleoceanography rely on fractionation of the nuclides away from secular equilibrium in the oceanic setting this fractionation is generally due to differences in the solubility of the various nuclides the behavior of the u series nuclides in the ocean environment was widely researched in the middle decades of the twentieth century this work established knowledge of the concentrations of the nuclides in the various compartments of the ocean system and of their fluxes between these compartments such understanding was comprehensively summarized in the ivanovich and harmon u series volume 1992 particularly by cochran 1992 understanding of the behavior of the u series nuclides has not advanced very dramatically in the decade since that summary but a major theme of research has been the use of this geochemical understanding to develop u series tools to assess the past environment table 1 view this table table 1 summary of seawater data for u series nuclides with paleoceanographic applications s soluble i insoluble full descriptions of the paleoceanographic uses and references are provided in the text further details of the half

uranium and thorium series isotopes in recent sediments of the venezuela basin caribbean sea abstract cores from three sedimentary provinces of the venezuela basin were analyzed for uranium and thorium series isotopes carbonate free 232th activity was nearly constant with depth and location uranium activities at two sites correspond to activities found in amazon river particulates the major sediment source for the venezuela basin a third site had higher uranium concentrations possibly due to the incorporation of uraniumrich shelf sediments or in situ diagenetic processes 230th activities ranged from 1 5 to 5 dpm cm 3 these activities suggest recent sedimentation rates of 7 2 4 6 and 2 9 cm ky 1 at the turbidite hemipelagic and pelagic carbonate sites respectively these rates are in good agreement with those based on radiocarbon dating and on carbonate stratigraphy concurrent variations in the sedimentation rates at the pelagic carbonate and hemipelagic sites are shown to be due primarily to changes in the rate of caco3 delivery or preservation a large 226ra maximum was observed at the redox boundaries of the hemipelagic and turbidite cores associated with a zone rich in iron and manganese 226ra diffusion from the pelagic carbonate sediments calculated from 226ra deficits in near surface sediments is estimated to be 27 dpm m 2 yr 1 no 226ra deficiency was measured for the turbidite and hemipelagic sediments indicating 226ra migration to the metal rich layers below or scavenging of dissolved 226ra by manganese in the mixed layer 226ra transport into the deep basin on biogenic particles was estimated to be similar in magnitude to the flux from the pelagic carbonate site abyssal fluxes of 226ra and particle fluxes of 226ra from surface waters both appear to be an order of magnitude smaller than the total flux required to balance deep water removal and radioactive decay in the deep water of the basin

a 300 kyr high resolution aridity record of the north african continent new oxygen isotope data and a high resolution carbonate record of a core from the northwest african margin are presented in combination with geochemical zr rb ratio al ba organic carbon and biogenic opal fluxes and sedimentological median grain size parameters to show variations in african continental aridity wind strength and upwelling productivity the carbonate record is diluted by the supply of aeolian dust from the arid saharan region of north africa and is seen to vary with a characteristic sawtooth pattern indicating rapid increases in dust flux followed by gradual declines spectral analysis of the carbonate profile and comparison with specmap stacked oxygen isotope and etp solar radiation profiles shows that the precessional 23 kyr insolation induced african climate system is decoupled from global ice volume climate changes operating on a 100 kyr frequency detailed studies of glacial terminations i ii and iii confirm the presence of rapid short timescale climatic variations in aridity

tracing dust input to the global ocean using thorium isotopes in marine sediments thoromap continental dust input into the ocean atmosphere system has significant ramifications for biogeochemical cycles and global climate yet direct observations of dust deposition in the ocean remain scarce the long lived isotope thorium 232 232th is greatly enriched in upper continental crust compared to oceanic crust and mid ocean ridge basalt like volcanogenic material in open ocean sediments away from fluvial and ice rafted sources of continental material 232th is often assumed to be of predominantly eolian origin in conjunction with flux normalization based on the particle reactive radioisotope thorium 230 230th 232th measurements in marine sediments are a promising proxy for dust accumulation in the modern and past ocean here we present thoromap a new global data compilation of 230th normalized fluxes of 232th after careful screening we derive dust deposition estimates in the global ocean averaged for the late holocene 0 4 ka and the last glacial maximum lgm 19 23 ka thoromap is compared with dust deposition estimates derived from the community climate system model ccsm3 and ccsm4 two coupled atmosphere land ocean and sea ice models model data correlation factors are 0 63 ccsm3 and 0 59 ccsm4 in the late holocene and 0 82 ccsm3 and 0 83 ccsm4 in the lgm thoromap is the first compilation that is built on a single specific proxy for dust and that exclusively uses flux normalisation to derive dust deposition rates

authigenic 10be 9be ratios and 10be fluxes 230thxs normalized in central baffin bay sediments during the last glacial cycle paleoenvironmental implications abstract authigenic 10 be 9 be ratios and 10 be fluxes reconstructed using the 230 th xs normalization proxies of the cosmogenic radionuclide 10 be production rate in the atmosphere have been measured in a sedimentary core from baffin bay north atlantic spanning the last 136 ka bp the normalization applied on the exchangeable authigenic 10 be concentrations using the authigenic 9 be isotope and 230 th xs methods yield equivalent results strongly correlated with sedimentological parameters grain size and mineralogy lower authigenic beryllium be concentrations and 10 be 9 be ratios are associated with coarse grained carbonate rich layers while higher authigenic be values are related to fine grained felspar rich sediments this variability is due to i sediment composition control over beryllium scavenging efficiency and ii glacial history that contributed to modify the 10 be concentration in baffin bay by input and boundary scavenging condition changes most paleo denudation rates inferred from the 10 be 9 be ratio vary weakly around 220 76 tons km 2 yr 1 0 09 0 03 mm yr 1 corresponding to relatively steady weathering fluxes over the last glacial cycle except for six brief intervals characterized by sharp increases of the denudation rate these intervals are related to ice surging episodes coeval with heinrich events and the last deglaciation period an average freshwater flux of 180 6 km 3 yr 1 0 006 sv consistent with recent models has been calculated in order to sustain glacially derived 10 be inputs into baffin bay it is concluded that in such environments the authigenic 10 be measured mainly depends on climatic effects related to the glacial dynamics which masks the 10 be production variation modulated by geomagnetic field changes altogether these results challenge the simple interpretation of 10 be concentration variation as a proxy of interglacial glacial interstadial stadial cycles in arctic and sub arctic regions they rather suggest the effect of higher frequency paleoclimatic changes and local glacial dynamics on 10 be signature

a comparison of sediment accumulation chronologies by the radiocarbon and 230thexcess methods abstract four northeast atlantic cores which exhibited well correlated linear progressions of conventional radiocarbon age with depth were analysed to provide 230 th excess profiling data the current evaluation of marine radiocarbon data suggests that conventional radiocarbon ages consistently underestimate true time this deficit progressively increases from 4 to 22 ky bp as a result steady state sediment accumulation rate models based on conventional radiocarbon ages are expected to be in error by up to 17 dependent on the period over which the estimates are made when proxy timescales from the radiocarbon and 230 th excess data for the four cores are compared over periods between 0 11 5 and 0 18 2 ky bp the trend of cumulative time derived from the 230 th excess profiling data is shown to be consistent with the expected trend of conventional radiocarbon age vs the best current estimate of true time this agreement supports the use of 230 th excess as a tracer for detailed estimates of changing deep sea sediment accumulation fluxes

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

evidence from the northeastern atlantic basin for variability in the rate of the meridional overturning circulation through the last deglaciation a first study from the subtropical western atlantic using 231pa 230th ratios as a kinematic proxy for deep water circulation provided compelling evidence for a strong link between climate and the rate of meridional overturning circulation moc over the last deglaciation however these results warrant confirmation from additional locations and water depths because the interpretation of the sedimentary 231pa 230th ratio in terms of circulation vigor can be biased by variations in particle flux and composition we have measured 231pa 230th in a core from the iberian margin in the northeastern atlantic basin and have compared these new results to the data from the western atlantic basin we find that the reduction in the circulation during h1 and yd and the subsequent increases first recognized in the sediment deposited on bermuda rise are also evident in the eastern basin in a totally different sedimentary regime confirming that sedimentary 231pa 230th ratios record basin wide changes in deep water circulation however some differences between the eastern and western records are also recognized providing preliminary evidence to differentiate between renewal rates in the two north atlantic basins and between shallower and deeper overturning our results suggest the possible existence of two sources of glacial north atlantic intermediate deep water gnaiw one in the south labrador sea and another west of rockall plateau both sources contributed to the meridional overturning but the two had different sensitivity to meltwater from the laurentide and the fennoscandian ice sheets during the deglaciation these results indicate that additional information on the geometry and strength of the ventilation of the deep atlantic can be obtained by contrasting the evolution of sediment 231pa 230th in different sections of the atlantic ocean

the composition and diagenesis of interstitial solutions ii fluxes and diagenesis at the water sediment interface in the high latitude north and south atlantic studies of the major element composition of in situ sampled pore waters are reported for the north atlantic and southern ocean between africa and antarctica the pattern of diagenetic modification of pore water composition is similar throughout the entire atlantic enrichment of na ca2 and alkalinity and depletion of mg2 and k are nearly universal only siliceous oozes consistently provide very limited evidence of cation diagenesis the changes observed and the calculated fluxes across the seawater sediment interface are much the same as those reported previously for other areas of the atlantic and caribbean fluxes of the major cations across the interface continue to be indicated as a major factor in the geochemical cycling of these elements particularly na mg2 and k diagenetic modelling indicates that aerobic oxidation of organic matter and consequent dissolution of caco3 is a dominant reaction throughout the north atlantic the data indicate that o2 oxidation to at least 30 cm is prevalent at nearly all stations dissolution of caco3 in response to the introduction of metabolic co2 can lead to significant post depositional modification of the sediments the modelling also indicates a 1 1 stoichiometric relationship between na release and mg2 uptake by sedimentary components although dissolved silica concentrations in biogenic siliceous sediments are among the highest yet reported 700 m calculations demonstrate that solubility control cannot be through equilibria with the mineral sepiolite further the influence of cation silicate surface phases generally upon solubility is contraindicated by si oh 4 mg2 h relationships evaluation of the influence of fluid advection on pore water profiles indicates that at the stations studied in the north atlantic it is small a more general consideration of the potential contribution of fluid advection to shaping interstitial water profiles demonstrates that advection can be a dominant factor in such circumstances serious misinterpretation of the nature of diagenetic reactions may result from a lack of knowledge and consideration of fluid advection

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

using 230th in marine sediments to reconstruct the late quaternary history of sea level we propose a method to determine past sea levels based on the record of 230th accumulating in seafloor sediments the decay of uranium in seawater produces this nuclide which then adsorbs rapidly onto particles settling to the seafloor since the concentration of uranium is similar at all depths in the water column the flux of 230th to the seafloor at any location is proportional to water column height consequently changes in sea level must cause changes in these fluxes at shallow depths 1000 m fluctuations of sea level cause changes in the expected 230th flux that are large enough to produce measurable changes in the 230th content of the sediment we have developed two approaches to determine past sea levels from the content of 230th in sediments 1 in a single core the ratio of the past and present fluxes of 230th to a site on the seafloor is a measure of the ratio of the past and present depths of the site below sea level and 2 in two or more cores from a region where the vertical input of sediment is similar at all depths in the water column the concentrations of 230th in synchronous sediment samples are linearly related to depth and indicate past sea level as the depth where the concentrations extrapolate to zero the latter approach requires fewer assumptions and allows sea level to be estimated at discrete points in time the methodology assumptions advantages and disadvantages of the first approach is illustrated using preliminary data from a core recovered from the margin of little bahama bank

boundary scavenging in the pacific ocean a comparison of 10be and 231pa concentrations of u th 231pa and 10be were measured in holocene sediments from two cores collected off the west coast of south america two cores from the east pacific rise two from the equatorial pacific and one from the south pacific central gyre our results together with data from 5 cores reported in the literature show that boundary scavenging plays a major role in the removal of 10be from the pacific ocean deposition rates of 10be at three margin sites are more than an order of magnitude greater than at sites of red clay accumulation in the deep central pacific deposition of 231pa is 4 to 5 fold greater at the margin sites the residence time of 10be with respect to chemical scavenging defined as its inventory in the water column divided by its rate of removal to the sediments varies regionally from 1000 years at the red clay sites in the deep central pacific to 100 years at the margin sites different factors control boundary scavenging of pa and be for example scavenging of 231pa is enhanced by metal oxide coatings of particles whereas this seems to have little influence on the scavenging of 10be 1990

fluxes of 230th and 231pa to the deep sea implications for the interpretation of excess 230th and 231pa 230th profiles in sediments abstract analysis of samples obtained with deep sea moored sediment traps deployed at 15 sites representing a wide range of oceanic conditions confirms that the flux of 230 th scavenged to the seafloor remains close to its production rate from the decay of 234 u in the overlying water column and generally validates the use of 230 th as a normalizing tool for paleoflux reconstruction after correction for trapping efficiency the flux of 230 th measured in the low flux regions amounts to 90 6 of the production rate with the notable exceptions of one site near the arabian sea upwelling and one site in the weddell sea a 230 th flux equivalent to 120 of the production rate was found in panama basin similar or more extensive scavenging of 230 th may be occurring at a pacific margin site off california and south of the polar front but these estimates are obscured by large errors on our trapping efficiency estimates in contrast the flux of 231 pa and the 231 pa 230 th ratio can vary strongly with particle flux following distinct trends in different oceanic basins in the atlantic ocean 231 pa fluxes and 231 pa 230 th are low and not sensitive to particle flux this is because of the short residence time of deep water in this basin resulting from thermohaline circulation which prevents the full development of lateral concentration gradients and full expression of boundary scavenging in the pacific ocean the sensitivity of 231 pa 230 th to particle flux is highest reflecting the longer residence time of deep water in the southern ocean 231 pa 230 th ratios are invariably high even when particle fluxes are low reflecting the predominance of opal which fractionates minimally between the two radionuclides interpretation of 231 pa 230 th recorded in sediments is thus complex in the atlantic this ratio is better suited for recording past changes in the strength of thermohaline circulation in the pacific it has the best potential for providing synoptic maps of past changes in particle flux in the southern ocean retrieval of information from 231 pa 230 th is more difficult and requires a more quantitative understanding of the influence of particle composition

the african humid period and the record of marine upwelling from excess 230th in ocean drilling program hole 658c using a high resolution 230 th normalized record of sediment flux we document the deglacial and holocene history of north african aridity and coastal upwelling at ocean drilling program hole 658c at both the end of the younger dryas and after the 8 2 ka event there are significant drops in terrigenous accumulation at our site indicating an increase in the monsoon moisture flux over africa at this time at 5 5 ka there is an abrupt end to the african humid period and a return to stronger upwelling conditions for carbonate and opal fluxes the 230 th normalization completely changes the shape of each record based on percentage variations alone this site is a clear example of how variations in one sediment component can obscure changes in the others and it demonstrates the need for radionuclide measurements more generally in paleoceanography by taking our new records and a large amount of previous data from this site we conclude that increases in african moisture are tightly coupled to decreases in coastal upwelling intensity

changes in opal flux and the rain ratio during the last 50 000 years in the equatorial pacific abstract changes in the orgc caco3 ratio in particles sinking from the surface to the deep ocean have the potential to alter the atmospheric pco2 over the span of a glacial interglacial cycle recent paleoceanographic and modern observational studies suggest that silica is a key factor in the global carbon biogeochemical cycle that can influence the flux ratio especially at low latitudes through silicic acid leakage brzezinski m pride c franck m sigman d sarmiento j matsumoto k gruber n rau r coale k 2002 a switch from si oh 4 to no 3 depletion in the glacial southern ocean geophysical research letters 29 5 to test this hypothesis we reconstruct biogenic fluxes of caco3 orgc and si for three equatorial pacific cores we find evidence that a floral shift from a sio2 based community to a caco3 based occurred starting in mid marine isotope stage mis 3 24 59 cal ka and declining toward mis 2 19 24 cal ka this could reflect the connection of the peru upwelling system to the subantarctic region and we postulate that excess silica was transported from the subantarctic via the deep equatorial undercurrent to the eastern equatorial pacific in the eastern equatorial pacific only we document a significant decrease in rain ratio starting mid mis 3 toward mis 2 this decrease is concomitant with a significant decrease in silica accumulation rates at the seabed this pattern is not observed in the pacific influenced by equatorial divergence and shallow upwelling where all reconstructed fluxes caco3 orgc and opal increase during mis 2 we conclude that the overall calcium carbonate pump weakened in the eep under peru upwelling influence

seismic interpretation of pelagic sedimentation regimes in the 18 53 ma eastern equatorial pacific basin scale sedimentation and infilling of abyssal valleys understanding how pelagic sediment has been eroded transported and deposited is critical to evaluating pelagic sediment records for paleoceanography we use digital seismic reflection data from an integrated ocean drilling program site survey amat03 to investigate pelagic sedimentation across the eastern central equatorial pacific which represents the first comprehensive record published covering the 18 53 ma eastern equatorial pacific our goals are to quantify 1 basin hill scale primary deposition regimes and 2 the extent to which seafloor topography has been subdued by abyssal valley filling sediments the eastern pacific seafloor consists of a series of abyssal hills and basins with minor late stage faulting in the basement ocean crust rarely outcrops at the seafloor away from the rise crest both hills and basins are sediment covered the carbonate compensation depth is identified at 4440 m by the appearance of acoustically transparent clay intervals in the seismic data overall we recognized three different sedimentation regimes depositional high sedimentation rate transitional and minimal sedimentation low sedimentation rate regimes in all areas the sedimented seafloor mimics the underlying basement topography although the degree to which topography becomes subdued varies depositional regimes result in symmetric sedimentation within basins and subdued topography whereas minimal sedimentation regimes have more asymmetric distribution of sediments within topographic lows and higher seafloor relief regardless of sedimentation regime enhanced sediment deposition occurs within basins however we observe that basin infill is rarely more than twice as thick as sediment cover over abyssal hills if this variation is due to sediment focusing the focusing factor in the basins as measured by 230th is no more than a factor of 1 3 of the total vertical particulate rain

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

the behaviour of manganese in atlantic carbonate sediments abstract manganese porewater and solid phase data are considered from two different atlantic carbonate sediments both with good geochemical characterisation the first case is a continuously accumulated alternating pelagic marl carbonate ooze where there is a correlation in post oxic conditions between mn ii porewater levels and an acetate leachable mn fraction of the sediment this leachable mn appears to have an association with calcite and in this example the leached residue mn content approximates to that of shale in the second case a very recent compositionally homogeneous calcareous turbidite is underlain by mn oxyhydroxide at the former sediment surface which is now acting as a source of mn ii by reduction sorption of mn by the turbidite sediment and shale like leached residue mn levels in anoxic conditions are again observed as mn ii diffuses towards present oxic conditions although no unique equilibrium is achieved similar older buried turbidites have concentration decreases in solid phase mn content preserved from bottom to top as relict evidence that this process has occurred in these turbidites 54 64 of the total mn is leachable by the acetate method and therefore presumed to be sorbed by calcite the oldest example has persisted for 125 kyr it is suggested that the slow breakdown of metastable mn oxyhydroxide and sorption of mn ii to calcite surfaces are important controls on the behaviour of mn in pelagic carbonates in mildly reducing conditions where accumulation fluctuations occur these processes act together with accumulation to limit overall mn migration and to prevent the large mn enrichments seen near the sediment surface in more reducing environments

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

highly resolved beryllium 10 record from odp site 1089 a global signal abstract in this study a highly resolved beryllium 10 record from a rapidly accumulating sediment core located in the southern cape basin odp leg 177 site 1089 is presented to extract the global 10 be production signal from the sedimentary record a dedicated correction procedure is applied first sediment redistribution is quantified by applying thorium 230 normalization then lateral transport of 10 be and 230 th is assessed using simple box model calculations the model results indicate that only minor transport corrections have to be applied thus site 1089 combines the advantage of good time resolution with nearly negligible oceanic transport of 10 be leading to a favored site for the reconstruction of global 10 be production changes from marine sediments our results suggest that the transport corrected 10 be record at site 1089 reflects long term variations of the global 10 be production rate over the past 300 kyr the absolute values of the youngest holocene samples are in good agreement with the estimated recent long term averaged global 10 be production rate deduced from observations the variability of the 10 be flux over the past 300 kyr corresponds well to the expected range deduced from model calculations the comparison with other reconstructions of geomagnetic paleointensity and with records of cosmogenic nuclides further emphasizes the global character of this 10 be record therefore our results show that it is possible to quantitatively extract the global 10 be production rate from a single marine record if transport processes are corrected for since the error of a single reconstruction is large a combination of several highly resolved and transport corrected 10 be records may lead to a significantly improved reconstruction of geomagnetic variability and of global cosmic ray flux and over the past 300 kyr

biogenic budgets of particle rain benthic remineralization and sediment accumulation in the equatorial pacific abstract budgets of organic c corg cac03 and opal have been constructed for the palisades ny pacific equatorial region at 140 w between 5 n and 5 s measurements of the rain and benthic remineralization rate of biogenic materials have been adjusted and normalized to account for sampling biases sea surface temperature serves as a master variable in normalizing sediment trap and benthic remineralization data to average conditions the rain and remineralization rates for corg are nearly equal 0 40 0 05 and 0 46 0 06 mmol m 2 d 1 respectively thus only a minor fraction of this constituent is buried rain and dissolution rates for biogenic opal are similarly balanced 0 3 0 06 and 0 36 0 01 mmol m 2 d 1 and consistent with the value for opal burial 0 0 0 004 the cac03 budget appears to have changed during the holocene the best estimates of modern cac03 dissolution 0 58 0 03 mmol m 2 d 1 and rain rate 0 61 0 06 are consistent with230th normalized carbonate accumulation rates for the late holocene 0 1 mmol m 2 d 1 however the balance between dissolution and rain is not consistent with early holocene carbonate accumulation 0 3 mmol m 2 d 1 and this imbalance suggests 1 a recent increase in the rate of cac03 dissolution on the sea floor or 2 a decrease in the rain rate of carbonate particles modeling230th profiles in sediments from this region define the last 3000 years as the duration of increased dissolution or decreased particle rain 231pa 230th ratios in sediments indicate that particle rain rates have remained constant or possibly increased slightly through the holocene two potential causes for increased dissolution were investigated a change in deep water carbonate saturation or a change in co g cac03 rain ratios a model describing carbonate dissolution as a function of the degree of undersaturation and the amount of organic carbon oxidation within sediments indicates that the recent increase in dissolution is more likely due to changes in bottom water chemical composition we propose that pacific ocean bottom water carbonate ion concentration has decreased by 10 15 m over the last 3000 years

glacial to holocene changes in carbonate and clay sedimentation in the equatorial pacific ocean estimated from thorium 230 profiles uranium series nuclide concentrations have been measured on sediments from five box cores from an equatorial pacific transect 230thexcess activities show discontinuities at the holocene glacial boundary as dated by 14c the glacial sedimentation rates determined by 230th and 14c are 2 5 3 0 cm kyr the holocene rates from 230th are much lower than those dated by 14c 1 9 2 3 cm kyr because of carbonate dissolution 230th sedimentation fluxes exceed water column supply by factors of 1 2 1 8 in the holocene and 1 8 3 0 in the glacial sections a number of models have been applied to calculate carbonate dissolution rates the results show that carbonate dissolution rates in the holocene in g cm kyr equal 1 5 10 3 exp 1 4d where d is water depth in kilometers a point by point estimation of sediment fluxes through time show that clay accumulation rates in the area have been near constant at 0 1 0 2 g cm kyr over the past 20 kyr whereas carbonate accumulation rates have decreased dramatically from 0 6 1 0 g cm kyr in the glacial sections of the cores to 0 2 0 6 g cm kyr in the holocene the errors caused by the uncertainties in the age of the termination of the last glacial period have been investigated and results show that a range of 11 14 kyr leads to an error upper limit of about 30 in the estimation of caco3 dissolution rates the response time of caco3 and 230thex concentrations in the mixed layer of sediments due to an impulse of change in caco3 dissolution rate has also been discussed showing that the observed changes in carbonate dissolution may be explained in terms of a single or a continuous change depending upon the thickness of the mixed layer

late quaternary changes of western equatorial atlantic surface circulation and amazon lowland climate recorded in ceara rise deep sea sediments today the western tropical atlantic is the most important passage for cross equatorial transfer of heat in the form of warm surface water flowing from the south into the north atlantic circulation changes north of south america may thus have influenced the global thermohaline circulation system and high northern latitude climate here we reconstruct late quaternary variations of western equatorial atlantic surface circulation and amazon lowland climate obtained from a multiproxy sediment record from ceara rise variations in the illite smectite ratio suggest drier climatic conditions in the amazon basin during glacials relative to interglacials the 230thex normalized fluxes and the 13c 12c record of organic carbon indicate that sea level fluctuations shelf topography and changes of the surface circulation pattern controlled variations and amplitude of terrigenous sediment supply to the ceara rise we attribute variations in thermocline depth reconstructed from vertical planktic foraminiferal oxygen isotope gradients and abundances of the phytoplankton species florisphaera profunda to changes in southeast trade wind intensity strong trade winds during ice volume maxima are associated with a deep western tropical atlantic thermocline strengthening of the north brazil current retroflection and more vigorous eastward flow of surface waters

quantification of l band insar coherence over volcanic areas using lidar and in situ measurements abstract interferometric synthetic aperture radar insar is a powerful tool to monitor large scale ground deformation at active volcanoes however vegetation and pyroclastic deposits degrade the radar coherence and therefore the measurement of 3 d surface displacements in this article we explore the complementarity between alos palsar coherence images airborne lidar data and in situ measurements acquired over the piton de la fournaise volcano reunion island france to determine the sources of errors that may affect repeat pass insar measurements we investigate three types of surfaces terrains covered with vegetation lava flows a a pahoehoe or slabby pahoehoe lava flows and pyroclastic deposits lapilli to explain the loss of coherence observed over the dolomieu crater between 2008 and 2009 we first use laser altimetry data to map topographic variations the lidar intensity which depends on surface reflectance also provides ancillary information about the potential sources of coherence loss in addition surface roughness and rock dielectric properties of each terrain have been determined in situ to better understand how electromagnetic waves interact with such media rough and porous surfaces such as the a a lava flows produce a higher coherence loss than smoother surfaces such as the pahoehoe lava flows variations in dielectric properties suggest a higher penetration depth in pyroclasts than in lava flows at l band frequency decorrelation over the lapilli is hence mainly caused by volumetric effects finally a map of lai leaf area index produced using spot 5 imagery allows us to quantify the effect of vegetation density radar coherence is negatively correlated with lai and is unreliable for values higher than 7 5

glacial holocene calcium carbonate dissolution at the central equatorial pacific seafloor holocene sediments in the central equatorial pacific have lower caco3 burial rates relative to sediments deposited during the last glacial period this change could be related to shifts in the deep sea carbonate system and ultimately to the glacial interglacial atmospheric co2 cycle in this study the glacial holocene sedimentation in the central equatorial pacific is investigated using a numerical model applied to caco3 carbonate 14c and excess 230th we also employ excess 231pa to 230th ratios as proxies of past particle fluxes although the caco3 burial rates decreased by 0 7 2 0 g cm 2 kyr 1 the 231pa to 230th ratios indicate that particle and caco3 fluxes have either remained nearly constant or increased since the last glacial this suggests that the reduction in caco3 burial rates resulted from an intensification of caco3 dissolution a small to moderate decrease in bottom water carbonate concentration rather than an increase in sedimentary respiratory co2 production is the most plausible mechanism for driving the sedimentation changes

a comparative study of accumulation rates derived by he and th isotope analysis of marine sediments abstract we present a detailed down core analysis of helium isotope ratios and concentrations for bulk sediments from the central equatorial pacific that span the last two glacial interglacial cycles measured 3 he 4 he ratios range from 1 0 10 5 to 2 1 10 4 or 7 4 to 149 times the atmospheric ratio the 3he from interplanetary dust particles idps constitutes virtually all of the 3he measured within the sediment because carbonate accumulation rates are high in the equatorial pacific the measured 3he concentrations are lower than have been measured elsewhere and range from 4 7 10 13 to 3 0 10 12 cm3stp g 1 if the cosmic dust 3he flux is constant with time sediment mass accumulation rates can be determined from the 3he concentration in sediments the excess 230th technique is an entirely independent method for calculating sediment mass accumulation rates because its source is in situ decay of 234u in seawater to first order initial excess 230th activities correlate with 3he concentrations within this core based on the 230th results we estimate the 3he flux to the earth s surface as 9 6 2 0 10 16 cm3stp cm 2 a 1 if this flux has remained constant over extended periods of time it can be used to determine sediment accumulation rates beyond the 230th range 300 000 yr

strengthening of the northeast monsoon over the flores sea indonesia at the time of heinrich event 1 paleoclimate evidence from south america and asia has been interpreted to indicate that tropical rainfall migrated southward during the northern hemisphere cooling associated with heinrich stadial 1 hs1 an event of massive iceberg discharge to the north atlantic ca 18 15 ka although arid conditions associated with such a shift are well documented in southern asia as far south as borneo debate still exists regarding the precipitation response in southern indonesia and australia during hs1 this study utilizes concentrations of the long lived nuclide 232 th as a proxy for detrital riverine input and 230 th normalization to estimate the history of preserved fl uxes reaching the seafl oor in the flores sea located between southern sulawesi and the lesser sunda islands indonesia because the only source of 232 th to the ocean is continental minerals this proxy is a robust indicator of continental weathering the 230 th normalized burial fl uxes of lithogenic and biogenic matter demonstrate that both detrital and biogenic fl uxes in the flores sea were higher during hs1 than any other period in the past 22 k y high detrital fl uxes indicate enhanced precipitation runoff from surrounding landmasses during a period of maximum southward shift of the intertropical convergence zone this study further constrains the northern limit of enhanced rainfall associated with a southward shift of australian monsoon related rainfall at the time of hs1 and highlights the value of 232 th as a proxy of continental input to deep sea sediment records

removal of230th and231pa from the open ocean concentrations of230th and231pa were measured in particulate matter collected by sediment traps deployed in the sargasso sea site s2 the north equatorial atlantic site e and the north equatorial pacific site p as well as in particles collected by in situ filtration at site e concentrations of dissolved th and pa were determined by extraction onto manganese dioxide adsorbers at site p and at a second site in the sargasso sea site d dissolved230th 231pa activity ratios were 3 6 at sites p and d in contrast for all sediment trap samples from greater than 2000 m unsupported230th 231pa ratios were 22 35 average 29 7 ratios were lower in particulate matter sampled at shallower depths particles filtered at 3600 m and 5000 m at site e had ratios of 50 and 40 results show that suspended particulate matter in the open ocean preferentially scavenges th relative to pa most of the230th produced by decay of234u in the open ocean is removed by adsorption to settling particulate matter in contrast less than 50 of the231pa produced by decay of235u is removed from the water column by this mechanism mixing processes transport the remainder to other sinks

contrasting compositions of saharan dust in the eastern atlantic ocean during the last deglaciation and african humid period abstract during the african humid period ahp much of the modern hyperarid saharan desert was vegetated and covered with numerous lakes in marine sediments off northwestern africa the ahp is represented by markedly reduced siliciclastic sediment flux between 12 3 and 5 5 ka changes in the origin of this terrigenous sediment fraction can be constrained by sediment chemistry and radiogenic isotope tracers at ocean drilling program odp site 658 hole c 20 44 95 n 18 34 85 w 2263 mbsl the neodymium nd isotope composition of terrigenous detritus shows little variability throughout the last 25 kyr indicating that the contributing geological terranes have not changed appreciably since the last glacial period in contrast there were large and abrupt changes in strontium sr isotope ratios and chemical compositions associated with the ahp during which 87 sr 86 sr ratios were markedly less radiogenic and sediments show higher chemical indices of alteration we show that sediment geochemical changes during the ahp cannot be attributed to changes in the source terranes physical sorting or intensity of chemical weathering the low 87 sr 86 sr and high sr concentrations of ahp age samples also conflict with the interpretation of increased fine grained fluvially derived sediments we propose that the most significant compositional changes at odp 658c are due to the addition of an aluminosilicate component that has a highly altered major element signature but is enriched in soluble elements like sr and magnesium mg compared to aluminum al and has low 87 sr 86 sr relative to local terrigenous source areas we interpret these characteristics to reflect authigenic sediment supply from extensive north african paleolake basins that were prevalent during the ahp

barium peaks at glacial terminations in sediments of the equatorial atlantic ocean relicts of deglacial productivity pulses in sediment cores recovered from oligotrophic settings of the western and eastern north equatorial atlantic ocean ceara rise and sierra leone rise distinct peaks of excess barium were detected at glacial interglacial transitions these ba maxima are unrelated to any other potential productivity proxy e g organic carbon carbonate or opal moreover they coincide with minima in organic carbon contents despite the lack of correlation between excess barium and organic carbon we ascribe these ba spikes to pulses of productivity that occurred during glacial interglacial transitions the discrepancy between barium and organic carbon in these transitional sediment intervals is attributed to the action of downward progressing oxidation fronts during deglacial nonsteady state depositional conditions the oxidation fronts were initiated due to the overall low sedimentation rates prevailing in the study areas and an increase in bottom water oxygen concentrations at the onset of enhanced nadw production during interglacial periods the fronts led to a very efficient oxidation of the organic carbon initially present leaving peaks in solid phase barium as relicts of these short time productivity events this assumption is supported by the depth arrangement of the solid phase peaks of ba fe and mn along the 6 5 oxygen isotope stage boundary in sediments of the ceara rise which show striking similarities to the distribution of these elements in oxidized sapropel intervals in eastern mediterranean sediments it remains unclear whether productivity was proportional to the magnitude of the baexcess maxima possibly higher dissolved ba concentrations in intermediate and deep waters during glacial interglacial transitions caused the precipitation of barite to increase out of proportion of the postulated deglacial productivity pulses

glacial surface temperatures of the southeast atlantic ocean a detailed record of sea surface temperature from sediments of the cape basin in the subtropical south atlantic indicates a previously undocumented progression of marine climate change between 41 and 18 thousand years before the present ky b p during the last glacial period whereas marine records typically indicate a long term cooling into the last glacial maximum around 21 ky b p consistent with gradually increasing global ice volume the cape basin record documents an interval of substantial temperate ocean warming from 41 to 25 ky b p the pattern is similar to that expected in response to changes in insolation owing to variations in earth s tilt

active diagenetic formation of metal rich layers in n e atlantic sediments sediment cores from the porcupine abyssal plain exhibit an indurated layer 0 5 3 cm thick at depths of approximately 50 cm this is some 15 20 cm below the glacial holocene transition as interpreted by radiocarbon dating and the palaeontological criteria of ruddiman and mcintyre 1981 the layer is forming currently at the oxic post oxic boundary in the sediments as revealed by pore water data o2 and no 3 are present in solution above the layer while fe2 mn2 po3 4 and nh 4 are present in solution below and all these species show concentration gradients indicating fluxes into the layer these data are consistent with the hypothesis for the initiation and sustained formation of such layers proposed by wilsonet al 1986a b the elements mn ni co fe p v cu zn and u are all enriched to varying degrees in the vicinity of the layer some differential stratification of these elements in the vertical consistent with a redox control is observed at one site with a 0 5 cm layer with mn ni and co above fe p v and cu in the layer and u below at another site the metal rich layer has higher fe and p concentrations and is more indurated here all enrichments except co are contained within a single layer sample 3 cm thick

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

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

terrigenous helium in deep sea sediments abstract we have measured the isotope ratios of helium contained in various terrigenous materials that contribute to deep sea sediments these materials include ice rafted debris from the north atlantic chinese loess and sediment collected at or near the mouths of three large rivers the amazon the ganges and the yangtze we observe terrigenous 3he 4he ratios that vary from 1 8 10 9 to 4 6 10 7 i e values that are higher than the theoretically derived range of 10 9 to 10 8 atlantic and pacific deep sea sediment 3he 4he ratios can be explained by mixing of helium from similar extraterrestrial but different terrigenous sources terrigenous sources for north atlantic and north pacific sediments are characterized by 3he and 4he contents that are higher and 3he 4he ratios that are lower than those for central and eastern equatorial pacific sediments this is consistent with the supply to the north atlantic and north pacific oceans of older cratonic continental material that contains high amounts of in situ produced nucleogenic and radiogenic helium terrigenous material transported to central and eastern equatorial pacific sediments contains lower amounts of 3he and 4he and higher 3he 4he ratios indicative of supply from a more juvenile andean source in the equatorial atlantic core v31 135 we have used previously published 230th data to determine an extraterrestrial 3he flux of 1 16 0 15 10 12 cm3stp cm 2 ka 1 within error of that previously determined in sediments from the equatorial pacific ocean 0 78 0 29 10 13 cm3stp cm 2 ka 1 marcantonio et al 1996

recent terrestrial and carbonate fluxes in the pelagic eastern mediterranean a comparison between sediment trap and surface sediment a sediment trap mooring was deployed in the central eastern mediterranean from november 1991 to august 1994 at 3000 m water depth total mass al ca mg sr and 230th fluxes recovered by the sediment trap are highly seasonal with highest fluxes during early spring in 1992 and 1993 and during late spring early summer in 1994 comparison of historic annual satellite derived chlorophyll records coastal zone colour scanner with the trap flux time series indicates a lag of 4 6 months between maximum primary production in the surface ocean and maximum flux recorded by the trap only the flux of coccospheres to the trap is at a maximum 1 month after maximum pigment concentrations in surface waters a value commonly found in other areas quantification of the inorganic lithogenic flux to the trap indicates that saharan dust is likely to be the major contributor to the trap mass flux the trapping efficiency of the sediment trap as calculated from the intercepted 230th flux is only 23 and the trap al flux is similarly 4 lower than al fluxes measured in nearby uppermost sediments compared with surface sediments the trap intercepted carbonate fluxes are even lower 9 than the corresponding lithogenic fluxes this is partly due to the very low abundance of large 32 m foraminifera and pteropods found in the trap material compared to the surface sediment we speculate that the period of our sediment trap deployment was insufficiently long to recover episodical large fluxes such as may be triggered by north atlantic oscillation variations

hydrothermal deposition on the juan de fuca ridge over multiple glacial interglacial cycles abstract hydrothermal systems play an important role in modern marine chemistry but little is known about how they may have varied on 100 000 year timescales here we present high resolution records of non lithogenic metal fluxes within sediment cores covering the last 500 000 years of hydrothermal deposition on the flanks of the juan de fuca ridge six adjacent gridded cores were analyzed by x ray fluorescence for fe mn and cu concentrations corrected for lithogenic inputs with ti and normalized to excess initial 230 th to generate non lithogenic metal flux records that provide the longest orbitally resolved reconstructions of hydrothermal activity currently available fe fluxes vary with global sea level over the last two glacial cycles suggesting higher hydrothermal deposition during interglacial periods the observed negative relationship between fe and mn indicates variable sediment redox conditions and diagenetic remobilization of sedimentary mn over time thus mn fluxes may not be a reliable indicator for hydrothermal activity in the juan de fuca ridge sediment cores cu fluxes show substantial high frequency variability that may be linked to changes in vent temperature related to increased magmatic production during glacial periods deglacial hydrothermal peaks on the juan de fuca ridge are consistent with previously published records from the mid atlantic ridge and the east pacific rise moreover on the juan de fuca ridge the deglacial peaks in hydrothermal activity are followed by relatively high hydrothermal fluxes throughout the ensuing interglacial periods relative to the previous glacial period

interface dissolution control of the 14c profile in marine sediment abstract the process of carbonate dissolution at the sediment water interface has two possible endmember boundary conditions either the carbonate particles dissolve mostly before they are incorporated into the sediment by bioturbation interface dissolution or the vertical mixing is rapid relative to their extermination rate homogeneous dissolution in this study a detailed radiocarbon profile was determined in deep equatorial pacific sediment that receives a high rate of carbonate supply in addition a box model of sediment mixing was used to simulate radiocarbon carbonate content and excess thorium profiles that result from either boundary process following a dissolution increase results from homogeneous dissolution imply a strong very recent erosional event while interface dissolution suggests that moderately increased dissolution began about 10 000 years ago in order to achieve the observed mixed layer radiocarbon age increased homogeneous dissolution would concentrate a greater amount of clay and 230th than is observed while for interface dissolution the predicted concentrations are too small these results together with small discontinuities beneath the mixed layer in 230th profiles suggest a two stage increase in interface dissolution in the deep pacific the first occurring near the beginning of the holocene and the second more recently roughly 5000 years ago

accumulation rates of th 230 pa 231 and some transition metals on the bermuda rise abstract measurements of 238u 234u 230th 232th 231pa mn fe co ni cu and zn were made on 23 samples from core gpc 5 a 29 m giant piston core from a water depth of 4583 m on the northeastern bermuda rise 33 41 2 n 57 36 9 w this area is characterized by rapid deposition of sediment transported by abyssal currents unsupported 230th and 231pa are present throughout the core but because of large variations in the sedimentation rate show marked departures from exponential decay with depth the trend with depth of the 231 pa ex 230 th ex ratio is consistent with the average accumulation rate of 36 cm 1000 y reported earlier on the basis of radiocarbon dating and caco3 stratigraphy when expressed on a carbonate free basis concentrations of mn co ni cu zn 230thex and 231paex all show cyclic variations positively correlated with those of caco3 the correlations can be explained by a model in which all of these constituents including caco3 are supplied to the sediments from the water column at a constant rate concentration variations are controlled mainly by varying inputs of terrigenous detritus with low inputs occurring during interglacials and high inputs during glacials relationships between the metal and 230thex concentrations permit estimates of the rates at which the metals are removed to the sediment by scavenging from the water column the results in g cm2 1000 y are 4300 1100 for mn 46 16 for ni and 76 26 for cu these rates are somewhat larger than ocean wide averages estimated by other methods and the absolute rate of 230th accumulation in gpc 5 averages about nine times higher than production in the overlying water column this part of the bermuda rise and similar bottom current deposits may act as important accumulators of elements scavenged from seawater

authigenic uranium in atlantic sediments of the last glacial stage a diagenetic phenomenon cores from three different atlantic localities equatorial cape verde rise and porcupine abyssal plain are shown to have anomalous high u contents 5 8 ppm total in sediments laid down during the last glacial stage 12 24 ky bp radiocarbon data demonstrate that the sediments hosting the peak u levels were accumulated at rates similar to those immediately above and below all the cores exhibit maximum mn levels characteristic colour changes and maximum u levels in the same sequence with increasing depth in core on the evidence of the similarities between the cores and pore water u data from a porcupine abyssal plain site it is proposed that the authigenic u enrichments are syndiagenetic and possibly active no correlation is observed between sediment authigenic u and corg contents the source of enrichment is bottom water u which has diffused downwards into the sediments to be sorbed at a particular redox level located 10 30 cm below the oxic post oxic boundary marked by the colour change the magnitude of the enrichments is caused by the persistence of this boundary at a particular level as a result of the decrease in mean sediment accumulation rate between the last glacial stage 5 2 up to at least 19 1 cm ky 1 and the holocene 2 2 4 1 cm ky 1 similar accumulation rate contrasts are expected to be widespread in the atlantic and the implications for previous reported work particularly from the mid atlantic ridge are discussed

timescales of hydrothermal scavenging in the south pacific ocean from 234th 230th and 228th hydrothermal activity in the deep ocean generates plumes of metal rich particles capable of removing certain trace elements from seawater by adsorption and sedimentation this removal process known as scavenging can be probed using the insoluble radiogenic isotopes of thorium th which are produced at a known rate in the water column via the decay of soluble uranium 234 th 230 th and radium 228 th isotopes we present dissolved and particulate measurements of these three thorium isotopes in a hydrothermal plume observed in the southeast pacific ocean on the geotraces gp16 section since their half lives vary from days 234 th to years 228 th to tens of thousands of years 230 th the combination of their signals can be used to understand scavenging processes occurring on a wide range of timescales scavenging is a multi step process involving adsorption and desorption onto particles followed by particle aggregation sinking and eventual sedimentation we use thorium isotopes to study how hydrothermal activity affects these steps the rate constants for net adsorption of 234 th determined here are comparable to previous estimates from hydrothermal plumes in the atlantic and north pacific oceans the partitioning of 234 th and 230 th between large and small particles is more similar in the hydrothermal plume than above it indicating faster aggregation of particles within the hydrothermal plume at stations nearby the east pacific rise than in waters outside the plume in addition to rapid scavenging and aggregation near the ridge axis we also infer continuous off axis scavenging from observations and modeling of 228 th 228 ra activity ratios the degree of depletion of the three thorium isotopes increases in order of half life with total 234 th activity close to that of its parent 238 u but 230 th showing nearly 70 depletion compared to expected values from reversible scavenging by modeling the variations in depletion for the different isotopes we show that much of the 230 th removal is inherited from scavenging events happening long before the most recent hydrothermal inputs

effects of climate and the cosmic ray flux on the 10be content of marine sediments abstract 10 be from blake outer ridge bor marine sediments at leg 72 site 1061 from 35 to 160 ka b p was measured in order to obtain a record of the cosmic ray flux incident upon the earth the variations in the concentration of 10 be per gram of sediment in bor sediments and that of the oxygen isotope record of the north atlantic are strikingly similar highlighting the effects of climate on the deposition of 10 be in marine sediments in addition the long term trends of 9 be and 10 be concentrations both source dependent are shown to be inversely correlated and thus the 10 be 9 be normalization is ambiguous at best the effects of climate on 10 be deposition were best removed by normalization of 10 be to the mass of the authigenic fraction of the sediment in which it was contained the 10 be content of the sediments at site 1061 was correlated to another site on the blake outer ridge ch88 10p and to a site in the gulf of california leg 64 site 480 10 be normalized to the authigenic mass at these sites show that the 10 be concentrations within the sea fall within a range consistent with the expected secular variations of the earth s dipole field

glacial interglacial circulation changes inferred from 231pa 230th sedimentary record in the north atlantic region 1 studies from the subtropical western and eastern atlantic ocean using the 231pa 230th ratio as a kinematic proxy for deep water circulation provided compelling evidence for a strong link between climate and the rate of meridional overturning circulation moc over the last deglaciation in this study we present a compilation of existing and new sedimentary 231pa 230th records from north atlantic cores between 1710 and 4550 m water depth comparing sedimentary 231pa 230th from different depths provides new insights into the evolution of the geometry and rate of deep water formation in the north atlantic during the last 20 000 years the 231pa 230th ratio measured in upper holocene sediments indicates slow water renewal above 2500 m and rapid flushing below consistent with our understanding of modern circulation in contrast during the last glacial maximum lgm glacial north atlantic intermediate water gnaiw drove a rapid overturning circulation to a depth of at least 3000 m depth below 4000 m water renewal was much slower than today at the onset of heinrich event 1 transport by the overturning circulation declined at all depths gnaiw shoaled above 3000 m and significantly weakened but did not totally shut down during the bolling allerod ba that followed water renewal rates further decreased above 2000 m but increased below our results suggest for the first time that ocean circulation during that period was quite distinct from the modern circulation mode with a comparatively higher renewal rate above 3000 m and a lower renewal rate below in a pattern similar to the lgm but less accentuated moc during the younger dryas appears very similar to ba down to 2000 m and slightly slower below

palaeocurrent reconstruction sediment and thorium focussing on the iberian margin over the last 140 ka sedimentological data in particular sediment grain size from core md95 2040 2465 m water depth and a nearby core omii 9k 1833 m water depth presently under the influence of lower north atlantic deep water and deep intermediate water respectively have been used to reconstruct changes in the vigour of near bottom water flow on the iberian margin the pattern of the palaeocurrent index indicates faster flow during the warm periods and slower in cold this also holds in the younger dryas but there is an added effect of brief collapse of the circulation in termination 1b due to meltwater input the cold periods are generally characterised by elevated clay percentage terrigenous material 2 m diameter and overall sediment accumulation fluxes in comparison warm periods of higher flow have lower depositional flux and a tendency to silt terrigenous material 2 63 m dominance consistent with the higher flow speed and suppression of clay deposition this is in contrast with a recent 230thxs based study of two cores md95 2040 and 2039 j thomson et al earth planet sci lett 165 1999 255 270 which concluded that increased glacial sediment and th focussing was caused by stronger currents the crucial factor is that the controlling speed is that of the flow at the depositional site rather than that of the erosional or transporting flow to the site high glacial maximum fluxes of carbonate 6 g cm 2 ka 1 are largely composed of fine 63 m non coccolith material suggesting a significant detrital component it is proposed that the sediment and th arrive on the lower slope via different routes sediment down slope in bottom nepheloid layers and turbidity currents th scavenged from the water column by organic matter and are rapidly mixed on the bed removal of this material from a large area and its deposition in a small one adjacent to oporto seamount together with a small amount of direct down slope supply accounts for the properties of the deposits allowance for erroneous fluxes due to possible coring expansion stretching of the upper part of md95 2040 does not invalidate these conclusions

sedimentary iron records from the cape basin abstract the iron hypothesis suggests that dust derived fe delivered to the southern ocean during glacial intervals fueled primary productivity and led to co 2 drawdown clear support for a dustier glacial atmosphere comes from ice core records of dust concentrations furthermore there is unequivocal proof from open ocean fe fertilization experiments that primary productivity in the modern day southern ocean is limited by fe however substantial hemipelagic detrital sources dilute and obscure the eolian signal here we present records of fe concentrations total and reducible and fe fluxes to highlight the importance of hemipelagic fe sources to the cape basin we illustrate that on average only 7 of the fe flux to site 1089 can be accounted for by particle settling indicating that redistribution by bottom currents accounts for an order of magnitude more fe than particulate scavenging processes distribution by surface currents or eolian deposition we also find that on average only 7 of the fe content is easily reducible furthermore we speculate that a significant source of dissolved fe to the bottom waters may come from re suspended bottom sediments

some reconciliation of glacial interglacial calcite flux reconstructions for the eastern equatorial pacific 1 carbonate production in the open ocean plays a significant role in fixing upper water column pco2 and carbonate flux from the surface transfers alkalinity to the deep sea a key region for this is in the eastern equatorial pacific eep reconstructions of calcite accumulation rates with traditional methods mass accumulation rate mar have been used to infer a large last glacial maximum lgm increase in fluxes for the eep the opposite result has been obtained using thorium normalization th norm of accumulation rates new 14c dating combined with detailed correlation among eep cores based on planktonic and benthic stable isotope records emphasizes the sensitivity of the mar approach to the age model and brings some reconciliation to the methodologies the new results lead to lgm mar based accumulation rates that are less than previously estimated and to lower lgm paleofluxes both the mar and thorium normalized methods show a flux maximum during the deglacial with the new age model although the signals show some convergence the magnitudes of mar accumulation rates appear to be between about 2 and 4 times those from th normalization for the lgm at the sites examined thus sediment focusing inferred from th normalization remains significant for the eep

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

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

refined estimation of marine and terrigenous contributions to sedimentary organic carbon molecular carbon isotopic 13c 12c ratios of a selected marine organic biomarker compound a c37 alkadienone from the pigmy basin deep sea drilling program hole 619 in the northern gulf of mexico varied by 5 3 in sychrony with the last 100 ka glacial interglacial cycle this carbon isotopic 13c variation is likely due to the effect of climatically linked variations in concentrations of co2 aq on photosynthetic fractionation of carbon isotopes by phytoplankton measurement of the 13c of the alkadienone 37 2 to reconstruct the carbon isotopic composition of total marine organic carbon permits improved estimates of the time varying 13c of preserved marine organic carbon end members with the time series record of marine end members the concentrations and net accumulation rates of terrigenous corg and marine corg are calculated and their paleoceanographic significance is considered although this method may be improved by consideration of additional biomarkers representative of diverse marine and terrigenous inputs it is the first application of molecular isotopic analysis to quantifying marine and terrigenous corg concentrations further application of such techniques will be become valuable in reconstructing regional and global budgets of marine and terrigenous corg accumulation

paleomagnetism of the upper cretaceous strata of mount tatlow evidence for 3000 km of northward displacement of the eastern coast belt british columbia this study contributes the first paleomagnetic data from dated cretaceous units of the coast belt 51 3 n 123 8 w in which paleohorizontal bedding surfaces can be identified with certainty we sampled 38 sites through a 1 5 km stratigraphic interval of cenomanian silverquick sedimentary strata and cenomanian to campanian powell creek volcanics in the tatlow syncline in the tyaughton methow basin magnetizations at 21 sites have high unblocking temperatures tub and pass the tilt test precision k 5 before untilting maximum k 48 after 100 untilting magnetic minerals of volcanics show original textures mean declinations in volcanic and sedimentary rocks are statistically identical and polarity is consistently normal the mean inclination 55 4 3 4 probability p 0 05 of this pretilting magnetization is 20 1 4 0 shallower than that expected if the rocks were deposited in their present position relative to cratonic north america field and laboratory observations rule out other causes for these anomalous shallow inclinations these rocks therefore have been displaced northward by 3000 500 km relative to cratonic north america since mid cretaceous time this displacement is almost 3 times greater than that estimated from mid cretaceous volcanics in the now adjacent intermontane belt evidently the two belts were not amalgamated until latest cretaceous or early tertiary time these results are inconsistent with all previous geologically based tectonic reconstructions of the cordillera magnetizations at eight sites in silverquick and powell creek beds have low tub and directional characteristics similar to those in three younger diorite intrusions reversed and normal polarities occur the rocks are commonly highly altered and maximum precision occurs after 40 untilting the magnetizations therefore are interpreted as overprints of latest cretaceous age acquired during folding

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

the accretion rate of extraterrestrial 3he based on oceanic 230th flux and the relation to os isotope variation over the past 200 000 years in an indian ocean core abstract in the eastern equatorial indian ocean the flux of extraterrestrial 3 he a proxy of interplanetary dust particles idps has been relatively constant over the past 200 ka the flux is equal to 1 1 0 4 10 12 cm 3 stp cm 2 ka 1 a value obtained using the xs 230 th profiling method variations in mass accumulation rates mars derived assuming a constant extraterrestrial 3 he flux have a 40 ka periodicity similar to that observed in the 18 o derived mars this frequency is similar to that of the earth s obliquity measured 187 os 188 os ratios are less radiogenic than present day seawater 0 49 0 98 reflecting the mixing of os derived from extraterrestrial terrigenous and hydrogenous sources when coupled with he data measured on the same samples os isotope data yield important information about the terrigenous component supplied to the eastern equatorial indian ocean the amount of os in the sample derived from the extraterrestrial component can be deduced with the help of the helium systematics once corrected for the extraterrestrial component of os os isotope signatures in conjunction with the 4 he concentrations suggest a supply of terrigenous material from indonesian ultramafic and himalayan crustal sources that clearly varies through time

glacial interglacial dust and export production records from the southern indian ocean abstract we present 230th normalized dust and export production fluxes for two contrasted marine sediment cores spanning the antarctic polar front close to the kerguelen plateau in the southern indian ocean covering the last glacial cycle we report glacial lithogenic fluxes comparable to the south atlantic and higher than in the south pacific sectors of the southern ocean structural and temporal discrepancies with dust reconstructions from antarctic ice cores and the atlantic and pacific sectors of the subantarctic zone saz point towards southern africa and or the kerguelen plateau as an additional source of lithogenic material to the southern indian ocean during the last ice age in the saz export production proxies respond to iron fe fertilization with total organic carbon toc fluxes as high as those previously reported from the atlantic sector of the southern ocean however the correlation between export production and dust proxies is weaker than in the other sectors and shows a muted response of export production during peak glacials we hypothesize that this muted response may be related to macronutrient co limitation imposed on phytoplankton growth possibly induced by a northward displacement of wind driven upwelling and or the polar frontal system during peak glacials the antarctic zone az record depicts the typical pattern of enhanced export production during interglacials and comparatively low productivity during glacials suggesting a decrease in the supply of macronutrients to the az surface during ice ages compared to warm periods as previously proposed however a muted response of opal fluxes during marine isotope stage mis 5e argues for a southward migration of the frontal system during warmer mis 5e possibly causing silicic acid co limitation at this site these results illustrate the important role of fe fertilization and changes in wind driven upwelling intensities in modulating the strength and efficiency of the biological carbon pump in the southern ocean but also highlight the potential role of frontal movements in explaining export production variability at sites located close to the antarctic circumpolar current acc fronts overall our new datasets provide new insights on the regional differences in dust and export production patterns that need to be considered in order to evaluate the efficiency of carbon sequestration in the different sectors of the southern ocean during ice ages

a geochemical approach to reconstruct modern dust fluxes and sources to the south pacific abstract we present the first comprehensive dust provenance and lithogenic flux data set extracted from surface sediments distributed across the polar and subpolar south pacific the dataset comprises 230th normalized lithogenic fluxes combined with rare earth elements strontium neodymium and lead isotope data to determine lithogenic fluxes spatial distribution and sources of dust

multiple late quaternary episodes of exceptional diatom production in the gulf of alaska abstract hole 887b of the ocean drilling program odp comprises a 44 m 750 kyr long continuous section recovered from the patton murray rise an elevated plateau that is largely isolated from turbidite deposition the patton murray area is centered under the alaska gyre a region characterized by the domal upwelling of nutrient rich waters marked increases in productivity and rapid settling of biogenic matter are suggested throughout the section by the episodic accumulation of diatomaceous oozes up to 1 m thick that are accompanied by barium enrichments significant 13corg maxima in the major diatomaceous bands suggest that mixed layer co2 aq may have been drawn down significantly during some of the productivity events the episodes of enhanced productivity at site 887 occur synchronously with short lived minima in planktonic foram 18o suggesting a direct link to low salinity or less likely warming events in the gulf of alaska there is no obvious explanation for the events but they may be related to seasonal incursions of meltwater from alaska we speculate that episodic input of meltwater or dust borne iron from asian or alaskan sources may have promoted the extraordinary diatom production events recorded in the sedimentary record

bioturbation and holocene sediment accumulation fluxes in the north east atlantic ocean benthic boundary layer experiment sites bioturbation and holocene sediment accumulation are quantified in the three experimental areas of the benthic boundary layer benbo programme by means of the natural radionuclides 14c and 210pb and the artificial radionuclides 137cs and 241am the holocene accumulation rates determined by the radiocarbon method are 4 4 and 6 5 cm kyr 1 at sites b rockall plateau 1100 m water depth and c feni drift 1925 m water depth respectively accumulation at site a situated between feni drift and porcupine bank at 3570 m water depth was interrupted by an erosional event in the mid holocene which removed 0 25 m or more of the uppermost sediment present at that time the estimated accumulation rate since that event is 2 1 cm kyr 1 different estimates of surficial bioturbation mixing depths at site b are returned by the 210pbexcess and 14c methods with the former indicating 10 cm and the latter unusually deep at 17 cm at site c 210pbexcess and the fallout radionuclides 137cs and 241am are present in two distinctly separated depth zones with the deepest mixing down to 15 cm similar to the 14c mixed layer depth this is ascribed to deep burrowing by sipunculid or echiuran worms at site c and similar deep mixing is inferred to be necessary at site b to produce the differences in mixed layer depths derived from the longer and shorter lived radionuclide profiles although the deep burrowing episodes must be rare 1 event per 102 yr the greater accumulation rate at site c compared with site b is produced by an enhanced flux of current driven clay and silt sized material this fine material both dilutes the caco3 content of the site c sediment and is responsible for the higher corg content observed at site c compared with site b unlike the site b and c sediments which are fine grained the coarse 63 125 m size fraction is the most abundant size class in the late holocene sediments at site a suggesting that the sediments at this location are winnowed

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

glacial interglacial variability in the delivery of dust to the central equatorial pacific ocean abstract fluxes of continental mineral aerosols dust were greater during glacial periods than during interglacials throughout most regions of the earth the equatorial pacific ocean was a possible exception to this pattern in that previous studies have reported either greater dust fluxes during interglacials or no consistent glacial interglacial pattern of dust flux we have applied the 230th normalization technique to derive five new records of dust flux from central equatorial pacific ocean sediments in contrast to previous studies which relied on stratigraphic accumulation rates the 230th normalization technique produces internally consistent results revealing fluxes to this region of continental lithogenic material that were positively correlated with global ice volume throughout the past 300 000 yr maximum glacial fluxes of continental mineral aerosols exceed minimum interglacial fluxes by about a factor of 2 similar to changes found elsewhere at low and mid latitudes this amplitude of variability is substantially smaller than that seen in some recent models and these observations provide a calibration point for future model development

alkenones as paleoceanographic proxies 1 alkenone derived estimates of temperature and co2 are contributing to our understanding of earth s climate history in order to increase confidence in alkenone based climate proxies we recommend the following actions first the sedimentary component or fraction containing alkenones should be identified in order to assess the impact of horizontal advection and vertical mixing on alkenone derived temperature and co2 estimates second differential mixing rates of alkenone containing particles and sand sized foraminifera should be quantified by independent dating of the two phases until that is accomplished apparent temporal offsets of climate proxies in the two phases should be interpreted cautiously third the stability of the unsaturation ratio and carbon isotopic compositions of alkenones during all phases of diagenesis should be confirmed both field and laboratory observations are required fourth future alkenone investigations should be coupled with other paleoclimate proxy measurements at high deposition rate sites in a variety of oceanographic settings in upwelling regions and in the vicinity of river plumes salinity and nutrient proxies should be measured since changes in these parameters may affect alkenone biosynthesis

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

the laschamp geomagnetic dipole low expressed as a cosmogenic 10 be atmospheric overproduction at 41 ka authigenic 10be 9be ratiomeasurementswere performed at high resolution along a portuguese margin deep sea core 37 48 n 10 09w spanning the 20 50 ka time interval in order to reconstruct variations in atmospheric cosmogenic 10be production rates and derive the related geomagnetic dipole moment modulation a complementary approach consisting in 230thxs normalized 10be deposition rate determination on selected samples confirmed the reliability of the authigenic 10be 9be record this study constitutes the first successful comparison of the two widely used normalization techniques of 10be concentrations for both methods the presented results herein evidence a factor of 2 cosmogenic nuclide overproduction linked to a minimum dipole moment associated with the laschamp excursion the latter is stratigraphically constrained beneath heinrich event 4 its age is estimated at 41 ka on the basis of direct correlation between the series of rapid paleoclimatic events recorded in the portuguese margin sediments and in the greenland ice sheet and is confirmed by calibrated radiocarbon dating carried out on the same sediments the remarkable agreement between the authigenic 10be 9be and the greenland ice cores 10be deposition rate records attests to their global significance this new authigenic 10be 9be record has been combined with that previously obtained at the same site to produce a stacked record that is calibrated using absolute values of virtual dipole moment determined on lava flows this provides a reconstruction of dipole geomagnetic moment variations over the 20 50 ka interval independent frompaleomagnetically constrainedmethods that documents the laschamp dipole low but fails to express any dipole low related to t e mono lake excursion this high resolution record responds to the necessity of supplementing the knowledge of the atmospheric 14c variations in the 30 45 ka interval during which the 14c calibration curve suffers from a lack of accurate data and during which a discrepancy of about 5500 yr between the 14c and u th ages is due to the laschamp geomagnetic dipole low such new high resolution datasets from records obtained from different latitudes will be required to make significant advances in understanding the causes of atmospheric 14c variations

holocene sediment deposition on a ne atlantic transect including feni drift quantified by radiocarbon and 230thexcess methods radiocarbon and 230thexcess measurements were undertaken on the sediments from fifteen box cores recovered between 48 58 n and 12 22 w at water depths of 1100 4500 m in the northeast atlantic eight of the cores were from feni drift in the rockall trough at depths of 1700 2500 m and the remaining seven formed an approximate north south transect at various water depths from the abyssal plain north on to rockall plateau mean holocene sediment accumulation fluxes for all cores were established from profiles of bulk sediment radiocarbon age against depth to be in the range 3 7 cm ky 1 off the drift and 4 23 cm ky 1 on the drift when compared with these radiocarbon based sediment accumulation rates precision measurements of 230th reveal that the 230thexcess levels present in the sediments match or slightly exceed the potential supply from the vertically overlying water column in a majority of the cores one core from the open abyssal plain that had the lowest radiocarbon based accumulation rate in the entire set also had a close balance between predicted and measured 230thexcess values with the assumption that only 230thexcess produced in the overlying water column is supplied to the sediments the 230thexcess values in this core and the other six containing carbonate ooze sediments all imply a rather constant regionally averaged sedimentation flux of 2 0 0 2 1 n 7 min 1 8 max 2 3 g cm 2 ky 1 rather than matching the 230thexcess fluxes implied by the radiocarbon data this singular value is similar to the mean holocene flux reported for the northeast atlantic by previous work that utilized the 230thexcess method although it is somewhat lower than estimates for the holocene based on oxygen isotope stratigraphy or radiocarbon methods the current transport processes that result in the high sediment accumulation rates on feni drift have also resulted in a compositional fractionation of the sediments all sediments from feni drift have lower caco3 contents than the remainder of the sediments studied and these are accompanied by lower 230thexcess specific activities than are found at comparable water column depths elsewhere on the transect consistently higher and more variable regional sediment accumulation fluxes are therefore calculated from the feni drift 230thexcess data with the constant flux assumption average 2 8 0 4 g cm 2 ky 1 n 8 min 2 3 max 3 3 some 40 higher than the constant value measured in the other cores it seems likely that the mean sediment accumulation flux at feni drift inside rockall trough is consistently higher than on the open ocean margin of the basin so that the regionally averaged sedimentation fluxes indicated for the drift by the measured 230thexcess data are also consistently higher than the singular value measured elsewhere in the northeast atlantic

dissolved and particulate 230 th 232 th in the central equatorial pacific ocean evidence for far field transport of the east pacific rise hydrothermal plume we assess the distribution of 230th and 232th along a latitudinal gradient in the central equatorial pacific ocean 155 w 159 w at two sites 8 n and the equator the dissolved 230th concentration profile at 8 n increases nearly linearly from the surface to 2000 m exhibiting behavior consistent with thermodynamic reversible scavenging however from 2000 m to 3000 m the dissolved 230th concentrations exhibit little change before increasing slightly from 3000 m to the bottom at this site dissolved 230th concentrations range from 1 1 fg kg at 100 m to 55 2 fg kg at 4600 m at the equator dissolved 230th concentrations are slightly lower and range from undetectable at 25 m to 19 1 fg kg at 3038 m the pattern in the dissolved 230th concentration profile at the equator is indistinguishable from that at 8 n the mid depth water deviation from equilibrium reversible scavenging between 2 and 3 km in the 230th profiles lower concentrations than expected at both sites occurs in the interval of the water column that is consistent with an interval that has high concentrations of 3he and dissolved fe at other nearby sites this 3he and fe rich signal has been traced to hydrothermal plumes from the east pacific rise thousands of kilometers away we hypothesize that the lower concentrations of 230th in mid depth waters of the central equatorial pacific are a result of a 5000 km transit of waters that have had their 230th scavenged by fe mn particulates close to the epr oceanic residence times of thorium combined with dissolved 232th concentrations suggest dust fluxes of about 0 5 0 6 gm 2yr 1 to the sea surface these fluxes are in agreement with other empirical studies in the pacific but are higher than those suggested by global atmospheric circulation models

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

analysis and modelling of gravity and piston coring based on soil mechanics the effects of gravity and piston corers on the dimensional accuracy of marine sediment cores is analysed using principles of soil mechanics a model for the coring process is built around the feedback that arises and develops between the core barrel and the sampled sediment this model for sediment response is applied to different hypothetical coring scenarios which are then compared to real examples providing insights into the specific effects of each sampling method and the development of these effects down core four cores from a single location on the iberian margin are found to contain stratigraphically intact successions that differ in length by a factor of up to 2 7 due solely to the different effects of each coring method these dimensional discrepancies are attributed to the combined effects of over sampling in the upper portions of the piston cores due to cable rebound causing upward piston acceleration and under sampling dominant in the basal portions of the open barrel gravity type cores it is suggested that heavier piston corers deployed on longer lighter cables are prone to greater over sampling ratios over longer stratigraphic intervals due to the increased likelihood and extent of cable rebound cable rebound may also give rise to double penetration of gravity corers resulting in repeated stratigraphic intervals knowledge of the dimensional accuracy of marine sediment cores is essential to an evaluation of past sedimentation rates and hence interpretations of past depositional processes it is therefore essential that we recognise the sampling effects of each coring method and their variability down core lest coring artefacts be interpreted as sedimentary signals different core types may be more suited to different palaeoceanographic investigations hence failing the development of a practical cable deployed recoilless piston corer a combination of a variety of core types will permit the best acquisition of the in situ stratigraphic truth our results suggest that a large diameter dc 20 30 cm square barrel gravity corer for the top 10 12 m combined with a cylindrical piston corer below 10 m may provide the least deformed material

opal burial in the equatorial atlantic ocean over the last 30 ka implications for glacial interglacial changes in the ocean silicon cycle 1 the silicic acid leakage hypothesis salh suggests that during glacial periods excess silicic acid was transported from the southern ocean to lower latitudes which favored diatom production over coccolithophorid production and caused a drawdown of atmospheric co2 downcore records of 230th normalized opal fluxes and 231pa 230th ratios from seven equatorial atlantic cores were used to reconstruct diatom productivity over the past 30 ka where a is years and to test the salh downcore records of 231pa 230th ratios and opal fluxes are highly correlated suggesting that they constitute a production based record of opal flux opal flux records support the salh in that glacial opal burial exceeded holocene burial by 1 8 gt opal ka in the area 0 40 w and 5 n 5 s earlier results from the eastern equatorial pacific ocean showed the opposite trend with greater holocene than glacial opal burial but approximately the same magnitude of difference between glacial and interglacial opal burial we suggest four nonexclusive scenarios to explain the data from both basins 1 increased upwelling in the equatorial atlantic and el nino like conditions suppressing upwelling in the eastern equatorial pacific altered the overall nutrient supply to both basins 2 si leaked from the southern ocean because of fe fertilization but was prevented from upwelling in the equatorial pacific because of el nino like conditions during the lgm 3 si leaked from the southern ocean because diatom productivity was limited by increased sea ice extent and was again prevented from upwelling in the equatorial pacific or 4 changes in ocean circulation related to the decreased input of agulhas water to the glacial south atlantic provided excess dissolved si to the equatorial atlantic ocean a deglacial opal pulse is seen in both the atlantic and pacific oceans all four scenarios and the presence of the common deglacial opal pulse suggest a common driver in the southern ocean

geological effects of the gulf stream system on the northern bermuda rise abstract the gulf stream system contains a clockwise rotating set of bottom currents which influence the sea bed in the northern north american basin it is possible to interpret the present day and historical record of current activity in this basin in terms of the deep flow of the gulf stream this interpretation provides a much more satisfactory and consistent explanation of the geologic record than previous interpretations based strictly on the influence of the classic abyssal circulation the present day circulation of the gulf stream actively resuspends large quantities of sediment on and near the northern bermuda rise and it is suggested that this resuspension may be due to the eddy field which is embedded in the westward flowing return flow during the late cenozoic the gulf stream system was responsible for depositing and shaping the major acoustic sedimentological units on the relatively smooth surface of the horizon a complex fine grained mont morillionite rich sediments derived from the chemically weathered saprolites of the hudson and st lawrence drainage basins were injected into the deep ocean basins by turbidity currents during the late paleogene and the neogene fine grained turbidites from the st lawrence spread southward down the southeastern sohm abyssal plain across the eastward flowing gulf stream and its westward flowing return flows portions of these fine grained sediments were entrained by the main and return flows and deposited downstream as acoustically non laminated accumulations on the corner and bermuda rises respectively the hudson river input was injected into the deep basin through the hudson canyon system the interaction of these fine grained turbidites with the northward flowing deep flow of the gulf stream system led to the formation of the gulf stream outer ridge here defined for the first time during the late neogene or early pleistocene the gulf stream outer ridge was partially eroded by the gulf stream system and portions subsequently covered by coarse grained pleistocene turbidites the coarse grained illite rich turbidites that flowed across the southeastern sohm abyssal plain also crossed the main and return flows of the gulf stream system the finer portions of these sediments were entrained and deposited as pleistocene acoustically laminated sediments on the plateaus of the bermuda and corner rises

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

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

clay sediment accumulation rates on the monsoon dominated western continental shelf and slope region of india abstract clay accumulation rates shown in sediment cores from the nearshore to outer continental shelf and slope regions in water depths of 10 1246 m on the western continental margins of india were determined by the 210 pb dating technique the 210 pb excess concentration encountered in these regions is about 3 5 dpm g and is independent of water depth the range of clay accumulation rates is from 1 8 to 19 mm yr for the shelf region and decreases southward from the tapti and narbada river confluence in the gulf of cambay this pattern indicates sediment dispersal in the coastal region regulated by southwest monsoon dominated littoral currents the same trend is encountered all along the southwestern traverse this suggests that suspended matter transport across the shelf is minimal since clay accumulation rates on the outer shelf are only 1 8 2 5 mm yr the clay accumulation rate in the slope region is 3 8 mm yr the high accumulation rates encountered on the upper continental slope may be attributed to the terrigenous influx of indus river sediment

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

fidelity of alkenone paleotemperatures in southern cape basin sediment drifts 0 in two drift cores tn057 21 and ocean drilling program site 1089 are nearly identical during the interval of overlapping analyses mis 4 5c ssts in a nearby nondrift core tn057 6 covary with those in core tn057 21 throughout mis 1 5c while climatological ssts overlying tn057 21 and tn057 6 are similar and consistent with reconstructed holocene ssts in the nondrift core surface waters overlying tn057 21 are 6 c colder than holocene alkenone ssts in the drift core temperatures remain 6 c warmer in tn057 21 relative to tn057 6 during the 100 kyr duration of the records we hypothesize that alkenone derived ssts in tn057 21 are higher than climatological ssts in the overlying surface water and those in tn057 6 as a result of the winnowing and focusing of sedimentary alkenones produced in warmer waters to the north climatological ssts in the central and northern cape basin are 16 20 c a 1 5 offset of fine fraction d 18 o values relative to planktonic foraminifera in tn057 21 supports this hypothesis temporal changes in sediment focusing were evaluated directly using uranium series radioisotopes while higher sediment focusing factors would be expected to result in higher alkenone derived ssts if sediment advection were the primary control on down core changes in alkenone derived ssts 230 th derived focusing factors indicate no such correlation exists we conclude that alkenone paleotemperature reconstructions from southern cape basin drifts reliably record regional sst variations in the cape basin index terms 4267 oceanography general paleoceanography 1055 geochemistry organic geochemistry 1040 geochemistry isotopic composition chemistry 3022 marine geology and geophysics marine sediments processes and transport keywords alkenones cape basin thorium