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

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

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

north atlantic ventilation of southern sourced deep water in the glacial ocean one potential mechanism for lowering atmospheric co2 during glacial times is an increase in the fraction of the global ocean ventilated by the north atlantic which produces deep water with a low concentration of unused nutrients and thus drives the ocean s biological pump to a high efficiency however the data indicate that during glacial times a water mass low in 13c 12c and 14c c occupied the deep atlantic apparently at the expense of north atlantic deep water nadw this water is commonly referred to as southern sourced because of its apparent entry into the atlantic basin from the south prompting the inference that it was ventilated at the southern ocean surface here we propose that this deep atlantic water mass actually included a large fraction of north atlantic ventilated water the chemical characteristics of which were altered by recirculation in the deep southern and indo pacific oceans in an ocean model sensitivity experiment that reduces antarctic bottom water formation and weakens its overturning circulation we find that a much greater fraction of nadw is transported into the southern ocean without contacting the surface and is entrained and mixed into the southern sourced deep water that spreads into the global abyssal ocean thus north atlantic ventilation takes over more of the ocean interior lowering atmospheric co2 and yet the abyssal atlantic is filled from the south with old water low in 13c 12c and 14c c consistent with glacial data

where are the undiscovered hydrothermal vents on oceanic spreading ridges abstract in nearly four decades since the discovery of deep sea vents one third of the length of global oceanic spreading ridges has been surveyed for hydrothermal activity active submarine vent fields are now known along the boundaries of 46 out of 52 recognized tectonic plates hydrothermal survey efforts over the most recent decade were sparked by national and commercial interests in the mineral resource potential of seafloor hydrothermal deposits as well as by academic research here we incorporate recent data for back arc spreading centers and ultraslow and slow spreading mid ocean ridges mors to revise a linear equation relating the frequency of vent fields along oceanic spreading ridges to spreading rate we apply this equation globally to predict a total number of vent fields on spreading ridges which suggests that 900 vent fields remain to be discovered almost half of these undiscovered vent fields comparable to the total of all vent fields discovered during 35 years of research are likely to occur at mors with full spreading rates less than 60 mm yr we then apply the equation regionally to predict where these hydrothermal vents may be discovered with respect to plate boundaries and national jurisdiction with the majority expected to occur outside of states exclusive economic zones we hope that these predictions will prove useful to the community in the future in helping to shape continuing ridge crest exploration

dissolved and particulate 231 pa and 230 th in the atlantic ocean constraints on intermediate deep water age boundary scavenging and 231 pa 230 th fractionation 231pa and 230th concentrations were determined in filtered seawater and suspended particulate matter collected from the labrador sea and the equatorial and south atlantic to constrain their application as tracers of intermediate deep water age and atlantic thermohaline circulation distributions of total 231pa and 230th indicate the influence of recently formed north atlantic deep water as evidenced by nearly invariant concentrations below 1000 m in the labrador sea and increasing 231pa and 230th concentrations as deep waters progress southward from northern source regions application of a scavenging mixing model to both tracer distributions indicates an intermediate deep water age of 12 yr in the labrador sea and a 30 140 yr transit time to the low latitude stations we attribute a striking increase in total 230th in the labrador sea from 1993 to 1999 to aging of intermediate waters as a consequence of the cessation of deep convection in the labrador sea since 1993 the temporal change in the 230th age of these waters is consistent with the 6 yr time interval between the observations the average particulate 231pa 230th activity ratio in the labrador sea and low latitude deep waters is 0 057 0 003 significantly below the 231pa 230th production ratio 0 093 and in agreement with excess 231pa 230th ratios in holocene sediments 0 060 0 004 and sediment trap material 0 034 0 012 from the atlantic and model simulations this observation is consistent with the southward transport of deep water strongly attenuating boundary scavenging in the atlantic a latitudinal dependence in particle fractionation of these tracers is also evident with elevated fractionation factors fth pa observed near the equator and south atlantic gyre 11 compared to low values in the labrador sea 3 and southern ocean 2 there also exists a depth dependence in fth pa characterized by low values in surface waters a broad mid depth maximum and decreasing values towards the sea floor the latitudinal and depth variations in fth pa are suggested to reflect differences in the chemical composition of marine particles

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

size fractionated major particle composition and concentrations from the us geotraces north atlantic zonal transect the concentration and the major phase composition particulate organic matter caco3 opal lithogenic matter and iron and manganese oxyhydroxides of marine particles is thought to determine the scavenging removal of particle reactive teis particles are also the vector for transferring carbon from the atmosphere to the deep ocean via the biological carbon pump and their composition may determine the efficiency and strength of this transfer here we present the first full ocean depth section of size fractionated 1 51 m 51 m suspended particulate matter spm concentration and major phase composition from the us geotraces north atlantic zonal transect between woods hole ma and lisbon portugal conducted in 2010 and 2011 several major particle features are notable in the section intense benthic nepheloid layers were observed in the western north american margin with concentrations of spm of up to 1648 g l two to three orders of magnitude higher than surrounding waters that were dominated by lithogenic material a more moderate benthic nepheloid layer was also observed in the eastern mauritanian margin 44 g l that had a lower lithogenic content and notably significant concentrations of iron and manganese oxyhydroxides 2 5 each an intermediate nepheloid layer reaching 102 g l an order of magnitude above surrounding waters was observed associated with the mediterranean outflow finally there was a factor of two enhancement in spm at the tag hydrothermal plume due almost entirely to the addition of iron oxyhydroxides from the hydrothermal vent we observe correlations between poc and caco3 in large 51 m particles in the upper 2000 m but not deeper than 2000 m and no correlations between poc and caco3 at any depth in small 51 m particles there were also no correlations between poc and lithogenic material in large particles overall there were very large uncertainties associated with all regression coefficients for mineral ballast carrying coefficients suggesting that mineral ballast was not a strong predictor for poc in this section

numerical modeling of cosmogenic deglaciation records front range and san juan mountains colorado 1 we use cosmogenic radionuclide crn exposure ages from polished striated bedrock to constrain numerical simulations of deglaciation in the middle boulder creek valley colorado front range and the animas river valley san juan mountains colorado in both valleys the cosmogenic ages suggest initiation of deglaciation 20 ka and ongoing retreat until 12 13 ka while the first order trend in crn concentrations in each valley suggests a monotonic glacial retreat we evaluate other retreat scenarios with different implications for post last glacial maximum regional climate we use a 2 d numerical glacier simulation with a crn layer to investigate how crn based deglaciation records are affected by retreat histories that are punctuated by periods of glacier readvance the crn layer simulates both production during periods of exposure and reduction by glacial erosion during readvances we simulate glacial occupation of the valleys as they respond to equilibrium line altitude ela histories characterized by stepwise change gradual rise or a rise punctuated by short periods of lowering each scenario generates a distinct spatial pattern of concentrations in the crn layer these results and the spatial pattern of measured concentrations in bedrock constrain the range of ela histories that reproduce the crn pattern in each valley in the animas river valley the exposure ages are well explained by a linear ela rise from full glacial to deglacial conditions ages in middle boulder creek valley are best explained by a deglaciation history including a stillstand or partial readvance between 16 and 14 ka followed by rapid retreat

high resolution al and fe data from the atlantic ocean clivar co2 repeat hydrography a16n transect extensive linkages between atmospheric dust and upper ocean geochemistry 1 trace element sampling and shipboard flow injection analysis during the june august 2003 climate variability and predictability clivar co2 repeat hydrography a16n transect has produced a high resolution section of dissolved fe and al in the upper 1000 m of the atlantic ocean between 62 n and 5 s using the surface water dissolved al and the model of aluminum for dust calculation in oceanic waters madcow model we have calculated the deposition of mineral dust to the surface ocean along this transect and compare that to dissolved fe concentrations the lowest mean mineral dust depositions of 0 2 g m 2 a 1 are found to the north of 51 n a region which also exhibits characteristics of biological fe limitation through its low dissolved surface water fe 0 1 nm and residual macronutrients e g nitrate 2 m to the south of this region mean dust deposition increases by an order of magnitude reaching 3 g m 2 a 1 at 10 n underneath the saharan dust outflow surface water fe values also increase along this section to 1 nm distinct minima in fe concentrations at the depth of the chlorophyll maximum in the vertical profiles between 18 and 4 n illuminate the role that active biological uptake plays in fe cycling an extensive subsurface zone of enhanced dissolved fe concentrations 1 5 nm underlying this region is a result of the biological vertical transport and remineralization of the surface water fe and is coincident with the intermediate nutrient maximum and oxygen minimum of this region elevated concentrations of dissolved al in subsurface waters seen between 30 and 20 n coincide with the domain of the subtropical mode waters stmw which result from the sinking of surface waters in late winter in regions imprinted by dust deposition the magnitude of the al enrichment observed in this water mass implies that the predominant source to the stmw is from the more dust impacted western atlantic with only limited contributions from the stmw formation region near madeira a deeper subsurface al enrichment 30 45 n is associated with the outflow from the mediterranean another heavily dust impacted basin these two regions of al enrichment show the widespread geochemical connection between atmospheric transport processes and the north atlantic and underscore its susceptibility to imprinting by atmospherically borne materials natural as well as anthropogenic

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

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

thorium isotopes tracing the iron cycle at the hawaii ocean time series station aloha abstract the role of iron as a limiting micronutrient motivates an effort to understand the supply and removal of lithogenic trace metals in the ocean the long lived thorium isotopes 232th and 230th in seawater can be used to quantify the input of lithogenic metals attributable to the partial dissolution of aerosol dust thus th can help in disentangling the fe cycle by providing an estimate of its ultimate supply and turnover rate here we present time series 1994 2014 data on thorium isotopes and iron concentrations in seawater from the hawaii ocean time series station aloha by comparing th based dissolved fe fluxes with measured dissolved fe inventories we derive fe residence times of 6 12 months for the surface ocean therefore fe inventories in the surface ocean are sensitive to seasonal changes in dust input ultrafiltration results further reveal that th has a much lower colloidal content than fe does despite a common source on this basis we suggest fe colloids may be predominantly organic in composition at least at station aloha in the deep ocean 2 km fe approaches a solubility limit while th surprisingly is continually leached from lithogenic particles this distinction has implications for the relevance of fe ligand availability in the deep ocean but also suggests th is not a good tracer for fe in deep waters while uncovering divergent behavior of these elements in the water column this study finds that dissolved th flux is a suitable proxy for the supply of fe from dust in the remote surface ocean

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

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

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

removal of 230th and 231pa at ocean margins abstract uranium thorium and protactinium isotopes were measured in particulate matter collected by sediment traps deployed in the panama basin and by in situ filtration of large volumes of seawater in the panama and guatemala basins concentrations of dissolved th and pa isotopes were determined by extraction onto mno 2 adsorbers placed in line behind the filters in the in situ pumping systems concentrations of dissolved 230 th and 231 pa in the panama and guatemala basins are lower than in the open ocean whereas dissolved 230 th 231 pa ratios are equal to or slightly greater than ratios in the open ocean particulate 230 th 231 pa ratios in the sediment trap samples ranged from 4 to 8 in contrast to ratios of 30 or more at the open ocean sites previously studied particles collected by filtration in the panama basin and nearest to the continental margin in the guatemala basin contained 230 th 231 pa ratios similar to the ratios in the sediment trap samples the ratios increased with distance away from the continent suspended particles near the margin show no preference for adsorption of th or pa and therefore must be chemically different from particles in the open ocean which show a strong preference for adsorption of th ocean margins as typified by the panama and guatemala basins are preferential sinks for 231 pa relative to 230 th furthermore the margins are sinks for 230 th and to a greater extent 231 pa transported by horizontal mixing from the open ocean

implications for sedimentation changes on the iberian margin over the last two glacial interglacial transitions from 230thexcess 0 systematics abstract the portuguese margin is well suited for studies of the contrasts in north atlantic circulation during glacial and interglacial times because of its rapid sediment accumulation rate this paper reports a 230thexcess 0 based study of sediment accumulation over the past 140 ky a period which includes the last two glacial interglacial transitions in two cores at 2 4 and 3 5 km water depth on a slope transect at 40 n although the independently determined mean sediment accumulation fluxes over the past 140 ky are unequivocally high with means of 13 2 and 10 5 g cm 2 ky 1 in the two cores conventional application of the 230thexcess 0 method yields consistently lower fluxes with means of 3 5 and 3 8 g cm 2 ky 1 these 230thexcess 0 estimates are interpreted as representations of the regional depositional flux through time this 230thexcess 0 regional flux is composed of a carbonate flux of

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

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

controls on seawater 231pa 230th and 232th concentrations along the flow paths of deep waters in the southwest atlantic measurements of dissolved th 230 pa 231 and th 232 were made for twelve full depth profiles along a southwest atlantic section during geotraces cruise ga02s sampling captures all the main atlantic deep water masses along their meridional flow paths and allows insight into the control on th and pa in a setting where waters are flowing in opposing directions with direct relevance to understanding the use of pa 231 th 230 as an ocean circulation proxy water column th 230 increases linearly with depth in line with expected reversible scavenging models pa 231 increases from the surface to similar to 1200 1500 m but is invariant or decreases with greater depth deviating from the behavior expected for reversible scavenging dissolved pa 231 th 230 ratios display a mid water column maximum at similar to 1000 2000 m which is broadly coincident with upper circumpolar deep water below 2000 m nuclide distributions and ratios exhibit no dependence on water mass nor any indication of progressive change within a water mass challenging the use of pa 231 th 230 as a past circulation tracer in the south atlantic calculation of horizontal transport of th 230 and pa 231 by ocean circulation indicates a net southward export out of the atlantic of 19 of the pa 231 and 3 of the th 230 produced in that ocean this removal is all from the north atlantic while in the south atlantic removal to sediment equals production simple one dimensional modeling can simulate th 230 profiles but not the mid water column maximum observed in pa 231 profiles suggesting an additional source of pa 231 perhaps lateral transport from the margin or removal at depth due to bottom scavenging near seafloor minima in concentrations indicates bottom scavenging of th 230 and 231 pa which is enhanced in the presence of nepheloid layers particularly for 231pa this additional scavenging fractionates th 230 and pa 231 and in the presence of nepheloid layers may lead to an increase in sedimentary pa 231 th 230 ratios th 232 concentrations were paired with th 230 derived residence times in the upper 250 m of the water column to test the application of th as a tracer of dust deposition maxima in th 232 indicate high dust input from the african and possibly south american continents

composition age and provenance of organic matter in nw african dust over the atlantic ocean 1 eolian dust deposited on a meteorology buoy over the boreal winter and spring of 1992 1993 in the northeast atlantic off northwest africa 18 n 22 w afforded sufficient material for detailed assessment of its biogeochemical characteristics and provenance the sample was subjected to microscopic examination and bulk elemental isotopic black carbon and molecular lignin lipid analyses the bulk elemental composition and organic carbon oc content 1 02 dry weight establishes the dust s origin as continental upper crust and is typical of dusts that emanate from west africa these data are in accord with the extensive satellite imagery documenting the transit of dust clouds from the sahara and sahel regions e g nasa toms aerosol index microscopic examination reveals that charcoal like particles from vegetation fires black carbon bc are the most abundant morphologically distinct organic components accelerator mass spectrometry ams 14c analysis yields conventional 14c ages for bulk oc of 1260 40 years and bc of 2070 35 years taken together with corresponding stable carbon isotopic compositions 13c 18 9 and 15 1 respectively these results suggest the presence of biomass and burning residues derived from predominantly c4 vegetation that accumulated in soils over the late holocene molecular level measurements are also consistent with this scenario for example lignin derived phenols in the dustfall sample indicate a significant contribution of angiosperm grass type tissue the altered nature of the lignin suggests storage as residues in soils solvent extractable lipid constituents include a marked leaf wax type component with a molecular and stable carbon isotopic composition similar to those observed in surface marine sediments in this region the hydrocarbon fraction contained some diesel type contamination but the n alkanes c23 c33 retained a prominent odd even distribution with 13c ranging from 26 7 to 28 5 the suite of even carbon numbered n alkanols c22 c32 is 14c dated at 647 150 years with 13c values ranging from 23 9 to 30 4 the long chain n alkanoic acids c22 c32 exhibited 13c values ranging from 22 6 to 27 4 these waxes are evidently a mixed signal derived from contemporary c3 and c4 vegetation and from ablated soils and desiccated lake sediments of middle to late holocene age this molecular approach shows promise as a tool for continental paleoenvironmental assessment particularly with respect to past vegetation cover regional aridity and wind systems

dirtmap the geological record of dust atmospheric dust is an important feedback in the climate system potentially affecting the radiative balance and chemical composition of the atmosphere and providing nutrients to terrestrial and marine ecosystems yet the potential impact of dust on the climate system both in the anthropogenically disturbed future and the naturally varying past remains to be quantified the geologic record of dust provides the opportunity to test earth system models designed to simulate dust records of dust can be obtained from ice cores marine sediments and terrestrial loess deposits although rarely unequivocal these records document a variety of processes source transport and deposition in the dust cycle stored in each archive as changes in clay mineralogy isotopes grain size and concentration of terrigenous materials although the extraction of information from each type of archive is slightly different the basic controls on these dust indicators are the same changes in the dust flux and particle size might be controlled by a combination of a source area extent b dust emission efficiency wind speed and atmospheric transport c atmospheric residence time of dust and or d relative contributions of dry settling and rainout of dust similarly changes in mineralogy reflect a source area mineralogy and weathering and b shifts in atmospheric transport the combination of these geological data with process based forward modelling schemes in global earth system models provides an excellent means of achieving a comprehensive picture of the global pattern of dust accumulation rates their controlling mechanisms and how those mechanisms may vary regionally the dust indicators and records of terrestrial and marine palaeoenvironments dirtmap data base has been established to provide a global palaeoenvironmental data set that can be used to validate earth system model simulations of the dust cycle over the past 150 000 years

combining seawater 232th and 230th concentrations to determine dust fluxes to the surface ocean abstract aeolian dust is a significant source of iron and other nutrients to the surface ocean but constraining the size of this flux is difficult chemical tracers such as al are useful but are limited by lack of information about their rate of removal from surface seawater in this study we test the use of th isotopes as an improved tracer of dust input by measuring 232 th and 230 th concentrations of upper ocean seawater at six stations along a meridional atlantic section that spans the saharan dust plume open ocean 232 th like al is dominantly derived from dust dissolution while 230 th is produced in seawater by u decay and provides an assessment of th removal rates the highest 232 th concentrations and 232 th 230 th ratios particularly in the surface waters are observed at stations expected to be influenced by input of saharan dust the pattern of 232 th concentration is in agreement with dissolved al distributions and seawifs aerosol imagery supporting the use of 232 th as a proxy for short term dust addition deeper in the water column 232 th concentration may also reflect longer term dust inputs in addition lateral input of 232 th from mediterranean outflow water is detected at 1000 m in the north atlantic surface water residence times are calculated separately from 230 th and 234 th using a simple scavenging model and values from the two isotopes are generally consistent with one another th 230 residence times appear to reflect the longer term value however rather than exhibiting the strong seasonal influence seen for 234 th these th residence times allow dust flux to the surface ocean to be calculated using the known concentration of th in dust and assumed values for the solubility of dust th in seawater resulting dust fluxes show good agreements with models of dust deposition if th solubility is 1 to 5 in the north atlantic yielding fluxes of 0 4 19 2 g m 2 yr 1 and 5 to 10 in the south atlantic fluxes of 0 2 0 7 g m 2 yr 1 despite the need for better constraints on the fractional solubility of dust th this study demonstrates the power of combining th isotope measurements to constrain dust fluxes to the surface ocean

synchronous centennial abrupt events in the ocean and atmosphere during the last deglaciation antarctic ice core data reveal that the atmosphere experienced abrupt centennial increases in co2 concentration during the last deglaciation 18 thousand to 11 thousand years ago establishing the role of ocean circulation in these changes requires high resolution accurately dated marine records here we report radiocarbon data from uranium thorium dated deep sea corals in the equatorial atlantic and drake passage over the past 25 000 years two major deglacial radiocarbon shifts occurred in phase with centennial atmospheric co2 rises at 14 8 thousand and 11 7 thousand years ago we interpret these radiocarbon enriched signals to represent two short lived less than 500 years overshoot events with atlantic meridional overturning stronger than that of the modern era these results provide compelling evidence for a close coupling of ocean circulation and centennial climate events during the last deglaciation

transient stratification as the cause of the north pacific productivity spike during deglaciation during the last deglaciation the north pacific ocean was characterized by a spike in primary productivity which has been attributed to iron input marine sediment analyses suggest that instead the productivity may have been fuelled by deep convection and subsequent stratification