return of the coral reef hypothesis basin to shelf partitioning of caco3 and its effect on atmospheric co2 differences in the rate of coral reef carbonate deposition from the pleistocene to the holocene may account for the quaternary variation of atmospheric co sub 2 volumes of carbonate associated with holocene reefs require an average deposition rate of 2 0 times 10 sup 13 mol yr for the past 5 ka in light of combined riverine mid ocean ridge and ground water fluxes of calcium to the oceans of 2 3 times 10 sub 13 mol yr the current flux of calcium carbonate to pelagic sediments must be far below the pleistocene average of 1 2 times 10 sub 13 mol yr the authors suggest that sea level change shifts the locus of carbonate deposition from the deep sea to the shelves as the normal glacial interglacial pattern of deposition of quaternary global carbonates to assess the impact of these changes on atmospheric co sub 2 a simple numerical simulation of the global carbon cycle was developed atmospheric co sub 2 as well as calcite saturation depth and sediment responses to these carbonate deposition changes are examined atmospheric co sub 2 changes close to those observed in the vostok ice core approximately 80 ppm co sub 2 for the quaternary are observed as well as the approximate depth changes in percent carbonate of sediments measured in themore pacific ocean over the same time interval less

the role of caco3 compensation in the glacial to interglacial atmospheric co2 change the only viable explanations put forth to date for the glacial to interglacial change in atmospheric co2 content suggested from measurements of the co2 content of gas extracted from ice cores involve changes in the ocean s nutrient cycles any nutrient change capable of creating the 80 atm changes in atmosphere co2 pressure suggested by the ice core results also creates significant change in the deep ocean s co3 content evidence from deep sea sediments suggests that these co3 changes are compensated on the time scale of a few thousand years by reductions or increases in amount of caco3 accumulating in deep sea sediments this compensation process has two important consequences first it significantly increases the magnitude of the co2 change per unit of nutrient forcing second it causes a delay in the response of the atmospheric co2 change while the first of these consequences is a boon to those seeking to explain the co2 change the second may prove to be a curse the ice core co2 record shows no evidence of a significant lag between the co2 response and the polar warming in any case it is important that we improve our knowledge of the magnitude and timing of the caco3 preservation events which mark the close of episodes of glaciation and of the dissolution events which mark the onset of these episodes

origin distribution and alteration of asphalts at chapopote knoll southern gulf of mexico abstract following the discovery of asphalt volcanism in the campeche knolls a research cruise was carried out in 2006 to unravel the nature of the asphalt deposits at chapopote the novel results support the concept that the asphalt deposits at the seafloor in 3000 m of water depth originate from the seepage of heavy petroleum with a density slightly greater than water the released petroleum forms characteristic flow structures at the seafloor with surfaces that are ropy or rough similar to magmatic lava flows the surface structures indicate that the viscosity of the heavy petroleum rapidly increases after extrusion due to loss of volatiles consequently the heavy petroleum forms the observed asphalt deposit and solidifies detailed survey with a remotely operated vehicle revealed that the asphalts are subject to sequential alterations e g volume reduction leading to the formation of visible cracks in the asphalt surface followed by fragmentation of the entire deposit while relatively fresh asphalt samples were gooey and sticky older fragmented pieces were found to be brittle without residual stickiness furthermore there is evidence for petroleum seepage from below the asphalt deposits leading to local up doming and sometimes to whip shaped extrusions extensive mapping by tv guided tools of chapopote asphalt volcano indicates that the main asphalt deposits occur at the south western rim that borders a central crater like depression the most recent asphalt deposit at chapopote is the main asphalt field covering an area of 2000 m2 asphalt volcanism is distinct from oil and gas seepage previously described in the gulf of mexico and elsewhere because it is characterized by episodic intrusions of semi solid hydrocarbons that spread laterally over a substantial area and produce structures with significant vertical relief as chapopote occurs at the crest of a salt structure it is inferred that asphalt volcanism is a secondary result of salt tectonism

deglacial changes in dust flux in the eastern equatorial pacific abstract atmospheric dust levels may play important roles in feedbacks linking continental source areas tropical convection marine productivity and global climate these feedbacks appear to be particularly significant in the tropical pacific where variations in local convection and productivity have been demonstrated to have impacts on climate at higher latitudes modeling of past dust levels and related feedbacks has been limited however by a paucity of observational data in this study we present a temporal and spatial survey of dust fluxes to the eastern equatorial pacific over the past 30 kyr glacial and holocene fluxes of 232th a proxy for continental material were calculated by normalization to 230th from a north south transect of cores along 110 w between 3 s and 7 n odp sites 848 853 fluxes were 30 100 higher during the last glacial suggesting increased dustiness in both hemispheres during the glacial period in both time periods dust fluxes decrease towards the south reflecting scavenging of northern hemisphere dust by precipitation at the itcz the holocene meridional dust flux gradient between 7 n and 3 s is characterized by a steep drop in dust levels at the southern edge of the modern range of the itcz while the gradient is shallower and more nearly linear during the last glacial this change may indicate that the glacial itcz in this region was a less effective barrier to inter hemispheric dust transport most likely due to a decrease in convective intensity and precipitation during the last glacial alternatively the change in gradient may be explained by increased variability in the location of the glacial itcz our data do not appear to require a mean southerly displacement of the glacial itcz as suggested by the results of other studies

formation of fe mn crusts within a continental margin environment abstract this study examines fe mn crusts that form on seamounts along the california continental margin ccm within the united states 200 nautical mile exclusive economic zone the study area extends from approximately 30 to 38 north latitudes and from 117 to 126 west longitudes the area of study is a tectonically active northeast pacific plate boundary region and is also part of the north pacific subtropical gyre with currents dominated by the california current system upwelling of nutrient rich water results in high primary productivity that produces a pronounced oxygen minimum zone hydrogenetic fe mn crusts forming along the ccm show distinct chemical and mineral compositions compared to open ocean crusts on average ccm crusts contain more fe relative to mn than open ocean pacific crusts the continental shelf and slope release both fe and mn under low oxygen conditions silica is also enriched relative to al compared to open ocean crusts this is due to the north pacific silica plume and enrichment of si along the path of deep water circulation resulting in si enrichment in bottom and intermediate waters of the eastern pacific the ccm fe mn crusts have a higher percentage of birnessite than open ocean crusts reflecting lower dissolved seawater oxygen that results from the intense coastal upwelling and proximity to zones of continental slope pore water anoxia carbonate fluorapatite cfa is not present and ccm crusts do not show evidence of phosphatization even in the older sections the mineralogy indicates a suboxic environment under which birnessite forms but in which ph is not high enough to facilitate cfa deposition growth rates of ccm crusts generally increase with increasing water depth likely due to deep water fe sources mobilized from reduced shelf and slope sediments many elements of economic interest including mn co ni cu w and te have slightly or significantly lower concentrations in ccm crusts relative to crusts from the pacific prime crust zone and other open ocean basins however concentrations of total rare earth elements and yttrium average only slightly lower contents and in the future may be a strategic resource for the u s

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

230th and 232th distributions in mid latitudes of the north pacific ocean effect of bottom scavenging abstract vertical distributions of total 230 th and dissolved 232 th were determined in the mid latitudes of the north pacific ocean 8 n 95 w 40 n 160 e the observed 232 th concentrations are some of the lowest values reported for oceans because of low biogenic particle flux high 230 th activity is exhibited in the central gyre most vertical distributions of 230 th in the pacific ocean have been described well using the reversible scavenging model however we observed the depletion of total 230 th compared with a reversible scavenging model prediction for the deep layers in the mid latitudes of the north pacific ocean considering the time scale of the scavenging residence time of th horizontal eddy diffusion from the higher particle flux region could not have a major influence on 230 th depletion in deep waters the observed depletion is partly explained by lateral advection adopting the scavenging mixing model additionally a bottom scavenging process above the seafloor and a diffusion process are considered to explain the 230 th deficit taking into account the time scale of the scavenging residence time of th in deep waters 230 th in deep water to the upper layers

constraining oceanic dust deposition using surface ocean dissolved al we use measurements of ocean surface dissolved al a global biogeochemical elemental cycling bec ocean model and the global dust entrainment and deposition dead model to constrain dust deposition to the oceans our al database contains all available measurements with best coverage in the atlantic vertical profiles and seasonal data exist in limited regions observations show that surface dissolved al is distributed similarly to the dust deposition predicted by dead and other models there is an equatorial atlantic al maximum that decreases toward higher latitudes there are high al concentrations in the mediterranean sea and the arabian sea and low concentrations in the pacific and the southern ocean the ocean basins maintain more distinct al profiles than fe profiles in the upper ocean consistent with a weaker biological influence on al than fe the bec predicted surface dissolved al compares relatively well with observations the al distribution reflects the combined effects of al input from dust and al removal by particle scavenging and biological uptake by diatoms model observed biases suggest a southward shift of maximum dust deposition compared to current dust model predictions dead appears to overestimate deposition north of 30 n in the pacific and to underestimate deposition south of 30 n observed al concentrations and the ocean model predicted surface al lifetime provide a semi independent method to estimate oceanic dust deposition this technique indicates that dead may overestimate dust deposition to the north equatorial atlantic but underestimate in other atlantic regions the southern ocean and the arabian sea however spatial variations in aerosol al solubility may also contribute to the model observation mismatch our results have implications for all dust borne ocean nutrients including fe and demonstrate the potential of marine geochemical data to constrain atmospheric aerosol deposition fields

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

enhanced carbonate and silicate weathering accelerates recovery from fossil fuel co2 perturbations 1 increasing atmospheric co 2 and surface temperatures should increase carbonate and silicate weathering rates directly via warming and indirectly via the co 2 fertilization effect enhancing plant productivity enhanced weathering should in turn increase alkalinity input to the ocean and accelerate long term co 2 uptake we added silicate and carbonate weathering and carbonate sediments to an existing global carbon cycle and surface temperature model and subjected it to a range of long term fossil fuel emissions scenarios spanning 1100 15 000 gtc in total emissions of 7350 gtc dissolve all carbonate sediments and enhanced carbonate and silicate weathering accelerate subsequent co 2 removal from the atmosphere by up to a factor of 4 for 1100 4000 gtc emissions enhanced weathering accelerates co 2 removal by a factor of 1 5 2 5 however it takes 1 myr for silicate weathering to stabilize atmospheric co 2 if land use tends to suppress vegetation and weathering rates on this timescale then co 2 will stabilize above preindustrial levels

the isotopic composition of authigenic chromium in anoxic marine sediments a case study from the cariaco basin chromium cr isotopes are an emerging proxy for tracking redox processes at the earth s surface however there has been limited exploration of the cr isotope record of modern and recent marine sediments the basic inorganic chemistry of cr suggests that anoxic marine basins should factor prominently in the global cr cycle and that sediments deposited within anoxic basins may offer a valuable cr isotope archive throughout earth s history here we present 53 cr data from sediments of the cariaco basin venezuela a type environment for large perennially anoxic basins with a relatively strong hydrological connection to the global oceans we document a marked positive shift in bulk 53 cr values following the termination of the last glacial maximum followed by relative stasis based on a suite of independent redox proxies this transition marks a switch from oxic to persistently anoxic and sulfidic euxinic depositional conditions within the basin we find good agreement between two independent approaches toward estimating the 53 cr composition of authigenic cr in euxinic cariaco basin sediments and that these estimates are very similar to the 53 cr composition of modern open atlantic ocean seawater these data together with considerations of reaction kinetics and mass balance within the cariaco basin are consistent with the hypothesis that anoxic marine settings can serve as a chemical archive of first order trends in seawater 53 cr composition additionally the cariaco basin data suggest that there has been secular stability in the average 53 cr value of atlantic seawater over the last 15 kyr

dust deposition in the eastern indian ocean the ocean perspective from antarctica to the bay of bengal atmospheric deposition is an important but still poorly constrained source of trace micronutrients to the open ocean because of the dearth of in situ measurements of total deposition i e wet dry deposition in remote regions in this work we discuss the upper ocean distribution of dissolved fe and al in the eastern indian ocean along a 95 e meridional transect spanning the antarctic margin to the bay of bengal we use the mixed layer concentration of dissolved al in conjunction with empirical data in a simple steady state model to produce 75 estimates of total dust deposition that we compare with historical observations and atmospheric model estimates except in the northern bay of bengal where the ganges brahmaputra river plume contributes to the inventory of dissolved al the surface distribution of dissolved al along 95 e is remarkably consistent with the large scale gradients in mineral dust deposition and multiple source regions impacting the eastern indian ocean the lowest total dust deposition fluxes are calculated for the southern ocean 66 60 mg m 2 yr 1 and the highest for the northern end of the south indian subtropical gyre up to 940 mg m 2 yr 1 at 18 s and in the southern bay of bengal 2500 570 mg m 2 yr 1 our total deposition fluxes which have an uncertainty on the order of a factor of 3 5 are comparable with the composite atmospheric model data of mahowald et al 2005 except in the south indian subtropical gyre where models may underestimate total deposition using available measurements of the solubility of fe in aerosols we confirm that dust deposition is a minor source of dissolved fe to the southern ocean and show that aeolian deposition of dissolved fe in the southern bay of bengal may be comparable to that observed underneath the saharan dust plume in the atlantic ocean

distribution of dissolved and particulate230th and232th in seawater from the gulf of mexico and off cape hatteras as measured by sims we present vertical and horizontal profiles of dissolved and particulate230th and232th concentrations in seawater from shelf and slope areas of the gulf of mexico and off cape hatteras in the middle atlantic bight as measured by secondary ion mass spectrometry sims and compare the partitioning of long lived230th between particles and seawater with that of short lived234th concentrations of dissolved and particulate230th and232th in surface seawater decreased from near shore to off shore in the gulf of mexico demonstrating terrestrial input to the surface waters vertical profiles indicate that lateral transport as well as surface inputs e g fluvial and aeolian and bottom sediment resuspension could be an important source of230th and232th in ocean margin regions sea water samples collected off cape hatteras contained significantly higher dissolved and particulate230th and232th concentrations than those found in the open gulf of mexico likely the distributions of230th and232th in seawater off cape hatteras are to a large extent controlled by terrestrial particles in contrast in situ production for230th and scavenging are the major processes regulating the concentrations of dissolved230th and232th in the open gulf of mexico the observed negative correlation between log kd particle solution distribution coefficient and log cp concentration of suspended particulate matter for234th and230thxs in both study areas demonstrated a particle concentration effect down to very low cp concentrations 20 g l based on the230th inventory in situ production and the small estimated surface input the overall residence time of230th in the water column at a slope station in the gulf of mexico is calculated to be about 5 yr

variations in terrigenous dilution in western mediterranean sea pelagic sediments in response to climate change during the last glacial cycle hemipelagic intervals in four giant calypso piston cores from the balearic abyssal plain western mediterranean sea were studied in order to determine fluctuations in the supply of terrigenous sediments to the basin during the last 130 000 years and possible climatic modulation of terrigenous sediment and particle flux carbonate records from hemipelagic intervals in these cores display distinct atlantic type cycles where glacial periods show on average 20 lower calcium carbonate contents than interglacial period equivalents the decrease in calcium carbonate seen during glacials may be the result of increased dilution by terrigenous aeolian and fluvial particles derived from aeolian and or fluvial sources higher glacial aeolian particle fluxes to the western mediterranean sea may have been caused by changes in the prevailing atmospheric conditions resulting in drier and colder climatic conditions in the source areas and more frequent and intense outbreaks of dust transport the colder and drier climatic conditions in combination with a lowered sea level would allow rivers to dump their sediment load closer to the shelf edge promoting enhanced fluvial input into the basin besides significant calcium carbonate variations that correlate with glacial interglacial cycles several short term abrupt changes in the calcium carbonate content are recorded which appear coincident with enhanced magnetic susceptibility values especially the events within marine isotope stage mis 3 the timing of these short term events may be linked with cooling events in the north atlantic particularly heinrich events and cold events within mis 5 these short term trends may possibly be explained by increased terrigenous particle transport due to drier and colder climate in the mediterranean borderlands our results further show that about 90 of the sedimentary sequence of the balearic abyssal plain consists of turbidites generally these appear not to have caused significant erosion and an almost complete continuous time stratigraphy is present in the intercalated hemipelagic intervals

influence of the water content on x ray fluorescence core scanning measurements in soft marine sediments the x ray fluorescence xrf core scanner provides bulk sediment chemistry data measured nondestructively at the split core sediment surface although this method is widely accepted there is little known about the effects of physical properties such as density and water content on xrf core scanner data comparison of xrf scanner measurements from the sediment surface and dry powder samples of sediment core geob7920 indicates strongly reduced element intensities for the lighter elements al and si we relate the lower element intensities of the measurements taken at the sediment surface to the amount of water in the sample volume analyzed by the xrf core scanner the heavier elements k ca ti and fe remain relatively unaffected by the variation of any physical property within sediment core geob7920 additionally we successfully use the elemental intensity of cl as a proxy for the seawater content in the sample volume analyzed by the xrf core scanner this enables the establishment of a correction function for the elements al and si that corrects for the radiation absorption of the water content in sediment core geob7920 off cape blanc nw africa

thorium distributions in high and low dust regions and the significance for iron supply thorium and uranium isotopes 232th 230th 238u and 234u were investigated to refine their use for estimating mineral dust deposition and fe delivery to the ocean u concentrations and isotope ratios were consistent with conservative behavior and can safely be described using published u salinity relationships and global average seawater isotopic composition near barbados waters affected by the amazon outflow contained elevated 232th this signals one region where the thorium dust method is inaccurate because of a confounding continental input dissolved 232th fluxes in this region suggest that amazonian fe supply to the adjacent open ocean is much larger than local atmospheric deposition the colloidal content of dissolved th south of bermuda was found to be quite small 2 6 similar to that found north of hawaii despite the order of magnitude higher dust deposition in the atlantic this finding supports the assumption that dissolved 232th and 230th are scavenged at the same rate despite their different sources and also sheds light on the increase of dissolved 232th fluxes with integrated depth outside the region influenced by amazon river waters dissolved 232th fluxes are compared with bermudan aerosol fe deposition to estimate that fractional th solubility is around 20 in this region finally new dissolved and soluble fe mn and cr data from the subtropical north pacific support the idea that fe concentrations in the remote ocean are highly buffered whereas 232th has a larger dynamic range between high and low dust regions

the history and decay of a mediterranean salt lens subsurface coherent vortices called meddies1 are formed by the outflow of salty water from the mediterranean sea1 2 into the north atlantic in october 1984 we began a study to observe the life history and large scale changes of a meddy by identifying a specific meddy and carefully mapping it and seeding it with sofar floats3 these neutrally buoyant floats are tracked acoustically and can be located aboard ship as this meddy moved southward across the madeira abyssal plain it was resurveyed three more times during a span of two years being able to find this same lens 100km in diameter on successive surveys was itself a unique achievement that allowed us to observe the meddy evolution and to gain new insight into the importance of different mixing mechanisms that cause meddy decay we find evidence of mixing by at least three processes 1 lateral mixing by the exchange of layers of water thermohaline intrusions 4 5 2 vertical mixing at the underside of the lens by salt fingers6 and 3 mixing by turbulence together these cause the net heat and salt anomalies to decay with an e folding time of about one year despite the mixing the relative vorticity at the core remained constant for the first year and the meddy retained its coherent shape over a two year period

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

the geochemistry of redox sensitive trace metals in sediments abstract we analyzed the redox sensitive elements v mo u re and cd in surface sediments from the northwest african margin the u s northwest margin and the arabian sea to determine their response under a range of redox conditions where oxygen penetrates 1 cm or less into the sediments mo and v diffuse to the overlying water as mn is reduced and remobilized authigenic enrichments of u re and cd are evident under these redox conditions with the onset of sulfate reduction all of the metals accumulate authigenically with re being by far the most enriched general trends in authigenic metal accumulation are described by calculating authigenic fluxes for the 3 main redox regimes oxic reducing where oxygen penetrates 1 cm and anoxic conditions using a simple diagenesis model and global estimates of organic carbon rain rate and bottom water oxygen concentrations we calculate the area of sediments below 1000 m water depth in which oxygen penetration is 1 cm to be 4 of the ocean floor we conclude that sediments where oxygen penetrates 1 cm release mn v and mo to seawater at rates of 140 260 60 150 and 5 10 of their respective riverine fluxes using the authigenic metal concentrations and accumulation rates from this work and other literature these sediments are sinks for re cd and u with burial fluxes of 70 140 30 80 and 20 40 respectively of their dissolved riverine inputs we modeled the sensitivity of the response of seawater re cd and v concentrations to changes in the area of reducing sediments where oxygen penetrates 1 cm our analysis suggests a negligible change in seawater re concentration whereas seawater concentrations of cd and v could have decreased and increased respectively by 5 10 over 20 kyr if the area of reducing sediments increased by a factor of 2 and by 10 20 if the area increased by a factor of 3 the concentration variations for a factor of 2 increase in the area of reducing sediments are at about the level of uncertainty of cd ca and v ca ratios observed in foraminifera shells over the last 40 kyr this implies that the area of reducing sediments in the ocean deeper than 1000 m 4 has not been greater than twice the present value in the recent past

surficial sediments of the great australian bight facies dynamics and oceanography on a vast cool water carbonate shelf abstract the great australian bight gab the largest sector of the southern australia continental margin is a site of cool water carbonate sedimentation throughout ranging from locally warm temperate inboard to cool temperate outboard surficial sediments are a mixture of calcareous pleistocene skeletal and lithic intraclasts relict grains and holocene biofragments with minor amounts of quartz inboard the inner shelf is an area of abundant macrophytes and seagrasses active carbonate sediment production and accumulation and little relict sediment the huge middle portion is a shaved shelf with active sediment winnowing and mostly relict sediment the outer shelf and upper slope is a variably productive sediment factory characterized by prolific calcareous epibenthic growth on hard substrate subaqueous islands shedding particles into surrounding sands and muds patterns of holocene sedimentation are linked to modern oceanographic parameters in this high energy setting characterized by overall downwelling prolific rhodoliths occur on the nw inner shelf where shallow summer waters are the warmest in the gab these warm saline nutrient depleted waters then drift eastward across the shelf suppressing heterozoan carbonate production on the central and eastern mid shelf this arrested production in the eastern gab is countered locally by summer coastal upwelling along western eyre peninsula with bryozoan rich sediment extending well inboard onto the mid shelf the outer shelf and upper slope is an area of prolific bryozoan growth likely linked to upwelling except in the central gab a region of year round downwelling where the area is one of off shelf fine sediment transport and carbonate mud deposition these patterns in the central gab at least are present in the underlying holocene and pleistocene suggesting that the general modern oceanographic dynamics and resultant carbonate sedimentation have persisted throughout the quaternary

the quantification and application of handheld energy dispersive x ray fluorescence ed xrf in mudrock chemostratigraphy and geochemistry abstract traditionally analytical techniques such as wavelength dispersive x ray fluorescence wd xrf inductively coupled plasma icp and mass spectrometry icp ms instrumental neutron activation analysis inaa or stationary bench top energy dispersive x ray fluorescence ed xrf have been used to generate quantitative geochemical results however a more efficient means of data collection using portable ed xrf instrumentation now allows the investigator to acquire rapid non destructive quantitative measurements on drill core and clean flat rock surfaces in addition to pressed powder pellets typically used in wd xrf analysis similar to traditional xrf methods quantification using the handheld ed xrf requires a matrix specific calibration unfortunately very few internationally accepted mudrock or shale reference materials exist and their elemental ranges provide inadequate coverage for the geochemical diversity of mudrocks in order to return reliable calibrated results a unique set of reference materials has been developed that incorporates a wide range of mudrock elemental compositions the current method provides elemental calibrations for major elements heavier than sodium and the following trace elements ba v cr ni cu zn rb sr y zr nb mo th and u a comparison of handheld energy dispersive and wavelength dispersive x ray fluorescence ed xrf and wd xrf results from pressed powder pellets of mississippian age barnett shale of north central texas usa is presented in order to evaluate the reliability of the reference calibration and the quantification of unknown samples using two different instrument platforms it will be demonstrated that calibrated results from the handheld ed xrf effectively define chemostratigraphic changes in real time as a consequence quantified results can be used immediately to assess changes in bulk mineralogy paleo redox conditions and to link down core geochemical changes to stratigraphic sedimentological and paleoenvironmental observations

a redox stratified ocean 3 2 billion years ago abstract before the great oxidation event goe 2 4 2 2 billion years ago it has been traditionally thought that oceanic water columns were uniformly anoxic due to a lack of oxygen producing microorganisms recently however it has been proposed that transient oxygenation of shallow seawater occurred between 2 8 and 3 0 billion years ago here we present a novel combination of stable fe and radiogenic u th pb isotope data that demonstrate significant oxygen contents in the shallow oceans at 3 2 ga based on analysis of the manzimnyama banded iron formation bif fig tree group south africa this unit is exceptional in that proximal shallow water and distal deep water facies are preserved when compared to the distal deep water facies the proximal samples show elevated u concentrations and moderately positive 56 fe values indicating vertical stratification in dissolved oxygen contents confirmation of oxidizing conditions using u abundances is robustly constrained using samples that have been closed to u and pb mobility using u th pb geochronology although redox sensitive elements have been commonly used in ancient rocks to infer redox conditions post depositional element mobility has been rarely tested and u th pb geochronology can constrain open or closed system behavior the u abundances and 56 fe values of the manzimnyama bif suggest the proximal shallow water samples record precipitation under stronger oxidizing conditions compared to the distal deeper water facies which in turn indicates the existence of a discrete redox boundary between deep and shallow ocean waters at this time this work therefore documents the oldest known preserved marine redox gradient in the rock record the relative enrichment of o 2 in the upper water column is likely due to the existence of oxygen producing microorganisms such as cyanobacteria these results provide a new approach for identifying free oxygen in earth s ancient oceans including confirming the age of redox proxies and indicate that cyanobacteria evolved prior to 3 2 ga

quantifying lithogenic inputs to the north pacific ocean using the long lived thorium isotopes abstract dissolved 232th is added to the ocean though the partial dissolution of lithogenic materials such as aerosol dust in the same way as other lithogenically sourced and more biologically important trace metals such as fe oceanic 230th on the other hand is sourced primarily from the highly predictable decay of dissolved 234u the rate at which dissolved 232th is released by mineral dissolution can be constrained by a th removal rate derived from 230th 234u disequilibria assuming steady state calculated fluxes of dissolved 232th can in turn be used to estimate fluxes of other lithogenically sourced dissolved metals as well as the original lithogenic supplies such as aerosol dust deposition given the concentration and fractional solubility of th or other metals in the lithogenic material this method is applied to 7 water column profiles from the innovative north pacific experiment inopex cruise of 2009 and 2 sites from the subtropical north pacific the structure of shallow depth profiles suggests rapid scavenging at the surface and at least partial regeneration of dissolved 232th at 100 200 m depth this rapid cycling could involve colloidal th generated during mineral dissolution which may not be subject to the same removal rates as the more truly dissolved 230th an additional deep source of 232th was revealed in deep waters most likely dissolution of seafloor sediments and offers a constraint on dissolved trace element supply due to boundary exchange

the influence of bottom topography on baroclinic transports abstract a new and reduced set of governing equations is proposed for the modeling of baroclinic motions in a two layer system with variable bottom topography the reduction of the equations which eliminates all barotropic is based on the assumption of almost vertically compensated transports the resulting equations differ somewhat from those obtained with a rigid lid approximation the limitations are topography variability only on horizontal scales greater than the wavelength and wavelengths shorter than the barotropic radius of deformation these are not critical in many problems numerical solutions to the reduced equations are shown to be close to those obtained from the primitive equations in one and two dimensional cases in view of their relative simplicity the new governing equations have also been applied to the analytical study of coastal upwelling in the presence of variable topography it is shown then that the presence of a canyon enhances coastal upwelling the success of the reduced e

the co diagenesis of sulfur and iron in acid lake sediments of southwestern quebec reduced inorganic sulfur species constitute the major fraction of total sulfur in the recent sediments of eight acid lakes of southwestern quebec nearly all of the anthropogenically derived excess s present in the sediments has accumulated as reduced inorganic forms showing that organic s formation plays a very minor role in long term anthropogenic s retention in these lakes these results appear different from most other published studies on s fixation in acid lake sediments respectively 74 and 76 of the variance in total s and reduced inorganic s burden in the recent sediments can be explained by their fe content alone indicating that the reduced s is associated with iron and that the capacity of the sediments to retain s may be limited by available fe supply when indexes of organic c supply winter o2 deficit and sediment c are included with fe in a multiple regression analysis respectively 97 and 98 of the variance in total s and reduced inorganic s accumulation can be explained the origin of the pronounced subsurface fe maximum observed in most cores is attributed to the reduction and recent burial as iron sulfides of a surficial diagenetic fe oh 3 reserve in some sediments this fe iii reserve presently appears to be nearly or completely exhausted and the lakes may have lost their capacity to generate permanent alkalinity via so2 4 reduction the present rate of alkalinity production due to so2 4 reduction and fixation of reduced s in the sediments of one lake were estimated from several 210pb dated s profiles and averaged to 163 eq m 2 d 1 this value is comparable to those reported for other acid lakes

the removal rates of234th and228th from waters of the new york bight abstract the mean residence time of thorium with respect to non radioactive removal from water was determined as a function of location in three traverses of the new york bight using both 234 th 238 u and 228 th 228 ra correlates well with salinity increasing from about ten days near shore to 70 days at the shelf break it shows a much weaker correlation with suspended matter concentrations both because suspended matter varies in its scavenging efficiency and because salinity is a longer term integrator of scavenging potential s computed from 228 th 228 ra were often higher than those computed from 234 th 238 u either because of the detrital matter present as reflected in the 232 th concentrations or because the water parcels had recently arrived from environments of lower scavenging efficiency anomalous isotopic concentrations found in three adjacent samples can best be explained as the result of an episodic release of 228 ra from bottom sediments at a rate 200 times the normal one

impact of natural oil and higher hydrocarbons on microbial diversity distribution and activity in gulf of mexico cold seep sediments gulf of mexico cold seeps characterized by variable compositions and magnitudes of hydrocarbon seepage were sampled in order to investigate the effects of natural oils methane and non methane hydrocarbons on microbial activity diversity and distribution in seafloor sediments though some sediments were characterized by relatively high quantities of oil which may be toxic to some microorganisms high rates of sulfate reduction sr 27 9714 7 mmol m

a conceptual model for hydrocarbon accumulation and seepage processes around chapopote asphalt site southern gulf of mexico from high resolution seismic point of view 1 as part of the german r v meteor m67 2 expedition in 2006 to the southern gulf of mexico a set of 2d high resolution seismic profiles was acquired across the chapopote knoll to study seafloor asphalt occurrences on the basis of regional seismostratigraphic studies and dsdp drilling a more highly reflective coarse grained sediment unit of late miocene age is identified as a potential shallow hydrocarbon reservoir although a unit of that age would typically be buried by pliocene and pleistocene sediment cover at chapopote local salt tectonism has highly elevated the structure since the late miocene and the miocene reservoir is locally above present day regional datum the elevation resulted in a thin 100 200 m fine grained sediment cover on the crest of the knoll above the reservoir because oil and gas production can be expected at depth in jurassic cretaceous and tertiary source rocks the presence of high amplitude reflector packages within the reservoir unit is interpreted as an evidence of hydrocarbons this is variously supported by observations of crosscutting reflectors polarity reversal and drops in instantaneous frequency the thin seal above the reservoir unit facilitates leakage of trapped hydrocarbons hydrocarbons apparently invaded into the seal sediments in the wider vicinity around the crest of the knoll even extending beyond the area where seafloor asphalt is known the asphalt site thus may be a currently active spot while the rest of the crest may be temporarily sealed by solid phase hydrocarbons we propose that a shallow large reservoir with deeply sourced relatively heavy petroleum is principally responsible for the formation of asphalts on the seafloor

a comparison of different methods for determining the organic and inorganic carbon content of lake sediment from two lakes on the tibetan plateau this paper presents three parallel datasets of total organic carbon toc and total inorganic carbon tic as well as carbonate content caco3 of lake sediment from two lakes on the tibetan plateau in order to compare different methods and different machines the results indicate that two carbon analyzers a shimadzu toc vcph with solid sample module ssm 5000a and an elementar vario el ii provide very similar toc and tic content despite slightly different performance procedures and temperature controls a toc record determined by a wet oxidation method and a carbon analyzer shows consistent down core variation although it seems that the wet oxidation method may overestimate toc content due to the existence of some reduced compounds or minerals in the sediment tic content measured by a carbon analyzer and carbonate content determined by a chemical method exhibit similar fluctuation trends in both cores this suggests that tic content may be used as an environmental proxy roughly taking the place of carbonate content especially in sediment with simple carbonate compositions

a new perspective on boundary scavenging in the north pacific ocean boundary scavenging or the enhanced removal of adsorption prone elements from the ocean in areas of high particle flux is an often cited though not well quantified concept used to understand the oceanic distribution of many trace metals because 230 th and 231 pa are produced uniformly from uranium decay and removed differentially by scavenging the process of boundary scavenging can be elucidated by a more detailed knowledge of their water column distributions to this end filtered seawater was collected across the gradients in particle flux which span the subarctic pacific in the west during the innovative north pacific experiment inopex and in the east along line p lateral concentration gradients of dissolved 230 th are small throughout the subarctic pacific at 12 sites of variable particle flux this contradicts the prediction of the traditional boundary scavenging model a compilation of water column data from throughout the north pacific reveals much larger lateral concentration gradients for 230 th between the subarctic north pacific and subtropical gyre over lateral gradients in scavenging intensity similar to those found within the subarctic this reflects a biogeochemical province aspect to scavenging upper water column distributions of 231 pa and 231 pa 230 th ratio are consistent with the influence of scavenging by biogenic opal while deep waters 42 5 km reveal an additional 231 pa sink possibly related to manganese oxides produced at continental margins or ridge crests

a quasi geostrophic circulation model of the northeast pacific part i a preliminary numerical experiment abstract a limited area quasi geostrophic numerical model with mesoscale resolution is developed to study the circulation in the northeast ne pacific ocean the model domain extends from the british columbia alaska coast out to 170 w and down to 45 n and incorporates the coastline geometry and bottom topography of the region a long term integration was conducted using a steady climatological wind stress curl field to drive the circulation several statistical properties of the solution are determined and compared with observations a cyclonic circulation develops in the model basin with a meandering alaska current feeding at the head of the gulf of alaska into an intense boundary current corresponding to the alaskan stream the head of the gulf is a region where anticyclonic closed streamline features are occasionally generated with characteristics resembling those of the sitka eddy in the downstream region the boundary current separates and is subject to lateral meandering due to topographic wave

copper nickel rich amalgamated ferromanganese crust nodule deposits from shatsky rise nw pacific 1 a unique set of ferromanganese crusts and nodules collected from shatsky rise sr nw pacific were analyzed for mineralogical and chemical compositions and dated using be isotopes and cobalt chronometry the composition of these midlatitude deep water deposits is markedly different from northwest equatorial pacific pcz crusts where most studies have been conducted crusts and nodules on sr formed in close proximity and some nodule deposits were cemented and overgrown by crusts forming amalgamated deposits the deep water sr crusts are high in cu li and th and low in co te and tl concentrations compared to pcz crusts thorium concentrations ppm are especially striking with a high of 152 mean 56 compared to pcz crusts mean 11 the deep water sr crusts show a diagenetic chemical signal but not a diagenetic mineralogy which together constrain the redox conditions to early oxic diagenesis diagenetic input to crusts is rare but unequivocal in these deep water crusts copper ni and li are strongly enriched in sr deep water deposits but only in layers older than about 3 4 ma diagenetic reactions in the sediment and dissolution of biogenic calcite in the water column are the likely sources of these metals the highest concentrations of li are in crust layers that formed near the calcite compensation depth the onset of ni cu and li enrichment in the middle miocene and cessation at about 3 4 ma were accompanied by changes in the deep water environment especially composition and flow rates of water masses and location of the carbonate compensation depth

recent observations of variability in the path and vertical structure of the alaskan stream abstract current records were recently obtained from two sites on the continental slope southwest of kodiak island at the inshore site 10 month record flow mainly resembled the weak shelf break flow typical of the gulf of alaska except for two periods each of 3 months duration the offshore site 31 mouth record was in the path of the alaskan stream during the alaskan stream segments flow characteristics low eddy energy high vertical coherence and high stability were similar to those in the stream at other locations when the stream was absent from the offshore site it made a seaward excursion of 50 km as evidences by satellite tracked drifters the cause of this migration is unclear during a period of 6 months a subsurface velocity maximum was measured at 165 m flow near 1000 m was very weak for almost two years geostrophic flow estimates however suggest this is a rare situation

u and th concentrations and isotope ratios in modern carbonates and waters from the bahamas the short residence times of th and pa in seawater make them very responsive to changes in the ocean environment we use a new multi ion counting technique to make th and pa isotope measurements in seawaters from a near shore environment in which oceanic chemical tracers are not overwhelmed by terrestrial inputs the bahamas an unusual feature of the bahamas setting is the shallow depth of water residing on the bank tops these waters have significantly lower 232th 230th 10 000 than those immediately adjacent to the banks 24 000 31 000 and a 231pa 230th near the production ratio 0 1 the change in 232th 230th and 231pa 230th on the bank tops is explained by almost quantitative removal of th and pa by scavenging and their replacement with a mixture of 230th and 231pa alpha recoiled from the underlying carbonates together with th from dust dissolution analysis of a water profile in the tongue of the ocean which separates the great and little bahama banks allows us to trace the movement of bank top water to depth a distinct minimum in both 232th 230th 13 000 and 231pa 230th 0 5 is observed at 430 m and is interpreted to reflect density cascading of bank top water with entrained carbonate sediment these results suggest that th and pa can be used as water mass tracers in near shore environments uranium concentration measurements on the same waters demonstrate that u is conservative across a range in salinity of 2 psu with a concentration of 3 33 ppb at a salinity of 35 the incorporation of u and th isotopes into marine carbonates has also been assessed by analyzing carbonate samples from the same location as these bahamas waters such incorporation is critical for u th geochronology u isotope analyses demonstrate that seawater 234u averages 146 6 and does not vary by more than 2 5 o and that carbonates capture this value additional high precision measurements 1 o on modern carbonates confirm that all oceans have identical 234u modern marine carbonates are shown to have 232th 230th ratios that reflect the local seawater in which they formed

interannual variability of the equatorial pacific revisited a linear numerical model forced by monthly shipboard wind estimates used to study the interannual response of the tropical pacific ocean for 1961 1970 busalacchi and o brien 1981 is extended through december 1978 the additional 8 years include the 1972 and 1976 los ninos and the aborted event of 1975 model pycnocline variations at several locations are compared with observed sea level fluctuations el nino events are depicted as periods when the pycnocline is persistently deep along the eastern boundary remotely forced equatorial kelvin waves are responsible for this response the character of each simulated el nino is strongly dependent on the relation between zonal wind stress changes in the western and central equatorial pacific there are important differences in the location and timing of the wind changes associated with each el nino during the 1970 s the easterlies in the central equatorial pacific had more of an active role in the evolution of el nino than in the previous decade in the western tropical pacific a rapid shoaling of the pycnocline during each el nino is caused by westward propagating rossby waves interannual pycnocline displacements in the central equatorial pacific are determined by the superposition of kelvin waves excited to the west and first horizontal mode rossby waves generated to the east

dust deposition to the surface waters of the western and central north pacific inferred from surface water dissolved aluminum concentrations 1 dissolved al was determined on similar to 3500 surface water samples collected in the nw pacific during the 2002 intergovernmental oceanographic commission ioc contaminant baseline survey in addition dissolved al was determined on samples collected at 9 vertical stations occupied along the cruise track surface water al distributions when converted to annual mineral dust deposition measures and brown 1996 imply extremely low depositions mean values 0 3 g m 2 yr 1 to surface waters of the subarctic gyre despite the atmospheric transport of large amounts of mineral dust across this region from the desert regions of china the calculated deposition values are also much lower than the 1 10 g m 2 yr 1 predicted for this region by the gesamp model duce et al 1991 the lowest mineral dust depositions correspond to the high nutrient low chlorophyll hnlc region of the nw pacific which implies that the biogeochemical status of this region is the result of low atmospheric micronutrient input similar to other hnlc regions in the subtropical gyre the al derived dust deposition mean values 0 1 0 6 g m 2 yr 1 agrees well with the 1 g m 2 yr 1 predictions of the gesamp model enriched concentrations of dissolved al in the coastal waters near kauai from fluvial sources indicate the potential role of remote high islands in adding reactive trace elements to the nearby surface waters in the vertical profiles elevated dissolved al concentrations 4 8 nm were found to correspond to the potential density of the western pacific subtropical mode waters which form in the recirculation zone of the kuroshio

la icp ms analysis of rare earth elements in marine reptile bones from the middle triassic bonebed upper silesia s poland impact of long lasting diagenesis and factors controlling the uptake abstract the rare earth elements ree contained in fossil bones are widely used for provenance and palaeoenvironmental studies earlier works suggested that the ree uptake is limited to early diagenesis but more recent research provided evidence of long term open system diffusion in fossil bones we analysed thin walled reptile bones all collected from the same middle triassic 245 ma marine bonebed comprising vertebrate remains of likely different ages to check the influence of the long term diagenesis on the concentrations of ree in terms of impact of pore water the upper parts of the bones are contained in a low permeability crinoidal limestone whereas their lower parts have been affected by diagenetic fluids for a long time we measured ree and other trace element contents in 29 bones using la icp ms totally 660 spots in 45 depth profiles neither the absolute concentrations of the ree and the ree intra bone paas normalised patterns nor the inter element ratios and the la ce and eu anomalies appear useful to distinguish between the likely older and younger bones in the bonebed the mree n enrichment combined with the flat intra bone distributions of the ree lead to conclusion that ree fractionation and substitution for ca were the most important processes responsible for the selective uptake the low permeability host rock and diagenetic fluids had a significant impact on the trace element uptake and their intra bone distribution patterns the lower parts of the bones that likely had a long lasting contact with the diagenetic fluids reveal a relative enrichment in the ree and their easier diffusion into the bone centres the ability of fossil bones to incorporate trace elements over a long time span strongly limits the usage of particularly the older samples for provenance and palaeoenvironmental reconstructions additionally the presented new analyses fill the gap between the available databases of trace element concentrations in fossil bones with regard to middle triassic samples

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

high resolution elemental records from the south china sea and their paleoproductivity implications 1 the biogenic related elements ca sr ba p cd scavenged al and ti were analyzed by inductively coupled plasma mass spectrometry icp ms and inductively coupled plasma atomic emission spectrometry icp aes for core ns93 5 from the west slope of the south china sea terrestrial input as estimated from the accumulation of ti was higher during glacials than during interglacials carbonate accumulation rates are inversely related to those of terrestrial input suggesting higher production of calcareous phytoplankton during interglacials the accumulation patterns of authigenic sr ba p and cd match that of carbonate further indicating higher calcareous phytoplankton production during interglacials scavenged al and excess sio2 which is related to biogenic opal exhibit higher accumulation rates during glacials and correspond with changes in terrestrial input this indicates that terrestrial input driven is important to siliceous phytoplankton production but not for calcareous phytoplankton production as calcareous phytoplankton is the dominant component of the biogenic sediments in the south china sea particularly during interglacials previous inference of higher productivity in the south china sea during glacials based on only the biogenic opal proxy needs to be reconsidered

observation of mesoscale ocean features in the northeast pacific using geosat radar altimetry data in this paper geosat altimetry data from the northeast pacific are examined the data are 1 binned data on 1 latitude by 2 longitude blocks and 2 collinear track data the binned data cover the region from 20 n to 60 n from the north american coast westward to 150 w and span from december 15 1986 to june 1 1989 to examine the data for evidence of westward propagation of sea level anomalies three zonal transects 45 n 49 n and 57 n are made complex empirical orthogonal function analysis of the data transects at these latitudes reveals phase speed and amplitude information the first eigenmode at each latitude has a very strong annual signal two dimensional spectral analysis of the first eigenmode at 45 n and 57 n shows westward propagation of sea level anomalies at 45 n only the propagating features are annual in period and of order 1000 km in length at 57 n westward propagation is evident as at 45 n but there is also an eastward component to examine the variability of the coastal sea level signal collinear track data from three ascending tracks crossing the gulf of alaska are analyzed revealing mesoscale features of the order of 100 km that parallel the canadian and alaskan coast the most notable feature is the sitka eddy westward propagation of several of these features is observed the results from the analysis of both types of geosat data are compared with other observational data

non seagrass meadow sedimentary facies of the pontinian islands tyrrhenian sea a modern example of mixed carbonate siliciclastic sedimentation abstract the soft bottom of the mediterranean continental shelf is characterized by a heterozoan skeletal assemblage sensu james n p 1997 the cool water carbonate depositional realm in james n p clarke j eds cool water carbonates spec publ soc sediment geol vol 56 pp 1 20 although the contemporary presence of terrigenous and skeletal carbonate sediments has been well established tortora p 1996 depositional and erosional coastal processes during the last postglacial sea level rise an example from the central tyrrhenian continental shelf italy j sed res 66 391 405 fornos j j ahr w m 1997 temperate carbonates on a modern low energy isolated ramp the balearic platform spain journal of sedimentary research 67 364 373 fornos j j ahr w m 2006 present day temperate carbonate sedimentation on the balearic platform western mediterranean compositional and textural variation along a low energy isolated ramp in pedley h m carannante g eds 2006 cool water carbonates depositional systems and palaeoenvironmental controls geological society london special publications 255 pp 121 135 the interactions between carbonate and terrigenous siliciclastic sedimentation has not been documented well enough a total of 33 surface sediment samples from the pontinian shelf tyrrhenian sea central mediterranean have been analysed sampling stations range from 15 to 250 mwd meter water depth and are located along five transects ponzaw ponzanw ponza ne ponza e zannone plus four samples collected around palmarola island sectors colonized by seagrass meadows have not been sampled a total of 6 sedimentary facies f and 10 microfacies mf have been recognized by using component analyses grain size percentage sorting carbonate content and authigenic mineralization rate these facies and microfacies represent the pontian islands shelf sedimentation in the interval between the upper infralittoral and the epibathyal zones that represent shelf break and upper slope sedimentation the maerl facies f4a b mf4a b and the skeletal sands f2a b mf2a1 mf2a2 mf2b fall within the circalittoral zone the circalittoral zone in the water depth interval between 82 m and 112 m display relict facies f6 mf6 finally facies f5 siliciclastic sands includes subfacies f5b mf5b located in the circalittoral zone at depths of 49 to 101 mwd and restricted to the western and eastern sectors of ponza and subfacies f5a in the upper infralittoral zone 15 mwd 25 mwd where erosional processes prevail carbonate content analyses indicate that maximum carbonate production on the pontinian shelf took place in the 60 80 mwd interval facies f4 maerl represents the environment characterized by the highest carbonate production rates in the pontian area siliciclastic carbonate mixing took place in the infralittoral zone and in the lower circalittoral zone in the infralittoral zone erosional processes on the rocky shoreline produced lithoclasts and vulcanoclastic deposits that were reworked by wave induced near shore currents in the lower circalittoral zone the prolific production by photic biota red algae ends while skeletal remains of the aphotic environment mixes with planktonic sediments characterized by low carbonate values sand 63 m 2 mm is the dominant grain size class however gravel dominated facies f4 maerl are present in water depths 50 to 112 mwd which are significantly below the storm wave base glauconite mineralization appears on the pontinian shelf from 50 mwd and increases in abundance along the deeper bathymetries the compositional characteristics of relict facies f6 shows the concurrence of biota assemblages of the infralittoral and circalittoral zones likely representing the record of the last holocene transgressive event 18 ky and expressed by the overlapping of components of different environments

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

interpretation of the 231 pa 230 th paleocirculation proxy new water column measurements from the southwest indian ocean measurements of 231 pa 230 th and 232 th concentrations have been made on five water column profiles along the western margin of the madagascar and mascarene basins in the southern indian ocean these measurements help to fill a significant gap in the global coverage of water column 232 th 230 th and 231 pa data 232 th concentrations vary but generally increase with depth suggesting higher particle loading in deeper waters and the presence of a significant dissolved fraction of 232 th 230 th concentrations increase with depth and profiles are similar to the average of existing data from other regions 231 pa concentrations on the other hand show significant depth structure apparently reflecting the various water masses sampled at this location the modified remnants of north atlantic deep water are found at a depth of 62000 m and exhibit elevated 231 pa concentrations exported from the south atlantic antarctic intermediate and bottom waters have lower 231 pa probably due to scavenging onto opal particles during transit from the southern ocean the differences between water masses raises a question which water mass is important in controlling the 231 pa 230 th ratio in underlying sediments a simple one dimensional model is used to demonstrate that the 230 th and 231 pa exported to sea floor sediments last equilibrates with waters close to the seafloor within 61000 m rather than averaging the whole water column these findings suggest that 231 paxs 230 thxs in sediments provides information primarily about deep water masses in this region sedimentary records will therefore provide information about the past flow of antarctic bottom water into the indian ocean interpretation of data from other regions such as the north atlantic where this proxy has most successfully been applied requires careful consideration of regional oceanography and knowledge of the composition of the water masses being investigated d 2005 elsevier b v all rights reserved

the anticyclonic baroclinic eddy off sitka alaska in the northeast pacific ocean abstract among the many mesoscale eddies found in the northeast pacific ocean is a well developed anticyclonic baroclinic eddy situated within a few hundred kilometers of sitka alaska 57 n 138 w it has definitely been observed during spring and summer 1958 summer 1960 and summer 1961 observations made at other times show some evidence of its occurrence also the trajectories of three norpax drifting buoys for april may 1977 also indicated the probable presence of an eddy there the eddy whose diameter ranges from 200 to 300 km and whose depth extends to 100 m and probably to as much as 2000 m recurs at the same location the center of the eddy is characterized by the following features the surface water is less saline and only somewhat warmer than at its periphery at depths within and below the halocline it is warmer less saline and contains more dissolved oxygen than at the periphery and a warm core is situated within the halocline the halocline is usually depressed by less than 100 m but

magnetic properties of pelagic marine carbonates abstract pelagic carbonates are deposited far from continents usually at water depths of 3000 6000 m at rates below 10 cm kyr and are a globally important sediment type recent advances with recognition of widespread preservation of biogenic magnetite the inorganic remains of magnetotactic bacteria have fundamentally changed our understanding of the magnetic properties of pelagic carbonates we review evidence for the magnetic minerals typically preserved in pelagic carbonates the effects of magnetic mineral diagenesis on paleomagnetic and environmental magnetic records of pelagic carbonates and what magnetic properties can tell us about the open ocean environments in which pelagic carbonates are deposited we also discuss briefly late diagenetic remagnetisations recorded by some carbonates despite recent advances in our knowledge of these phenomena much remains undiscovered we are only at early stages of understanding how biogenic magnetite gives rise to paleomagnetic signals in sediments and whether it carries a poorly understood biogeochemical remanent magnetisation recently developed techniques have potential for testing how different magnetotactic bacterial species which produce different magnetite morphologies respond to changing nutrient and oxygenation conditions future work needs to test whether it is possible to develop proxies for ancient nutrient conditions from well calibrated modern magnetotactic bacterial occurrences a tantalizing link between giant magnetofossils and paleogene hyperthermal events needs to be tested much remains to be learned about the relationship between climate and the organisms that biomineralised these large and novel magnetite morphologies rather than being a well worn subject that has been studied for over 60 years the magnetic properties of pelagic carbonates hold many secrets that await discovery

distribution of 230th in the labrador sea and its relation to ventilation abstract measurements of dissolved and particulate230th and232th by thermal ionization mass spectrometry were made on samples collected from the labrador sea and the denmark strait and iceland scotland overflow waters the large scale feature of low and invariant230th evident in deep waters of the labrador sea and previously observed in the deep northern atlantic can be reproduced using a reversible scavenging model that includes the effect of ventilation advective transport also must be important in the redistribution of230th in other regions of the atlantic and for other long lived tracers such as231pa 26al and10be

natural and anthropogenic radionuclide distributions in the northwest atlantic ocean we have used in situ pumps which filter large volumes of sea water through a 1 m cartridge prefilter and two mno2 coated cartridges to obtain information on dissolved and particulate radionuclide distributions in the oceans two sites in the northwest atlantic show subsurface maxima of the fallout radionuclides137cs 239 240pu and241am although the processes of scavenging onto sinking particles and release at depth may contribute to the tracer distributions comparison of predicted and measured water column inventories suggests that at least 35 50 of the pu and241am are supplied to the deep water by advection the depth distributions of the naturally occurring radionuclides232th 228th and230th reflect their sources to the oceans 232th shows high dissolved concentrations in surface waters presumably as a result of atmospheric or riverine supply activities of232th decrease with depth to values 0 01 dpm 1000 l 228th shows high activities in near surface and near bottom water due to the distribution of its parent 228ra dissolved230th produced throughout the water column from234u decay increases with depth to 3000 m values in the deep water 3000 m are nearly constant 0 6 0 7 dpm 1000 l and the distribution of this tracer and perhaps other long lived particle reactive tracers as well may be affected by the advection inferred from pu and241am data the ratio of particulate to dissolved activity for both230th and228th is 0 15 0 20 this similarity precludes the calculation of sorption rate constants using a simple model of reversible sorption equilibrium moreover in mid depths228th tends to have a higher particulate dissolved ratio than230th suggesting uptake and release of230th and228th by different processes this could occur if228th produced in surface water were incorporated into biogenic particles formed there and released as those particles dissolved or decomposed during sinking 230th produced throughout the water column may more closely approach a sorption equilibrium at all depths 230th 241am and239 240pu are partitioned onto particles in the sequence th am pu with 15 of the230th on particles compared with 7 for am and 1 for pu distribution coefficients kd are 1 3 1 6 107 for th 5 6 106 for am and 7 10 105 for pu the lower reactivity for pu is consistent with analyses of pu oxidation states which show 85 oxidized v vi pu however thekd value for pu may be an upper limit because pu like228th may be incorporated into particles in surface waters and released at depth only by destruction of the carrier phase

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

the dissolution kinetics of major sedimentary carbonate minerals abstract among the most important set of chemical reactions occurring under near earth surface conditions are those involved in the dissolution of sedimentary carbonate minerals these minerals comprise about 20 of phanerozoic sedimentary rocks calcite and to a significantly lesser extent dolomite are the major carbonate minerals in sedimentary rocks in modern sediments aragonite and high magnesian calcites dominate in shallow water environments however calcite is by far the most abundant carbonate mineral in deep sea sediments an understanding of the factors that control their dissolution rates is important for modeling of geochemical cycles and the impact of fossil fuel co 2 on climate diagenesis of sediments and sedimentary rocks it also has practical application for areas such as the behavior of carbonates in petroleum and natural gas reservoirs and the preservation of buildings and monuments constructed from limestone and marble in this paper we summarize important findings from the hundreds of papers constituting the large literature on this topic that has steadily evolved over the last half century our primary focus is the chemical kinetics controlling the rates of reaction between sedimentary carbonate minerals and solutions we will not attempt to address the many applications of these results to such topics as mass transport of carbonate components in the subsurface or the accumulation of calcium carbonate in deep sea sediments such complex topics are clearly worthy of review papers on their own merits calcite has been by far the most studied mineral over a wide range of conditions and solution compositions in recent years there has been a substantial shift in emphasis from measuring changes in solution composition to determine batch reaction rates to the direct observation of processes occurring on mineral surfaces using techniques such as atomic force microscopy afm however there remain major challenges in integrating these two very different approaches a general theory of surface dissolution mechanisms currently lacking although see lasaga and luttge science 291 2001 2400 is required to satisfactorily relate observations of mineral surfaces and the concentration of dissolved components studies of aragonite high magnesian calcites magnesite and dolomite dissolution kinetics are much more limited in number and scope than those for calcite and provide at best a rather rudimentary understanding of how these minerals are likely to behave in natural systems although the influences of a limited number of reaction inhibitors have been studied probably the greatest weakness in application of experimental results to natural systems is understanding the often profound influences of foreign ions and organic matter on the near equilibrium dissolution kinetics of carbonate minerals

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

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

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

aluminium as a tracer of the deep outflow from the mediterranean dissolved aluminium has been determined in sea water samples from the southwestern alboran sea and the gulf of cadiz partial dissolution of eolian dust is responsible for the elevated levels of dissolved al that were found in both the western mediterranean deep water wmdw 111 5 nm and levantine intermediate water liw 86 2 nm masses in the alboran sea the al concentration in the outflowing plume of mediterranean water sampled in the gulf of cadiz is also elevated 72 nm these enhanced signals and the differences between them are used in a three water mass system to calculate a maximum 10 contribution of western mediterranean deep water to the outflow plume considerably less than has been previously supposed while the synoptic nature of this study and the possibility of involvement of other water masses in the outflow plume leave scope to increase the participation of wmdw in the outflow plume these measurements indicate the potential of a nontransient tracer in elucidating the component parts of complex flow systems copyright american geophysical union 1988

230th in the eastern north atlantic the importance of water mass ventilation in the balance of230th the230th distribution in the water column on a north south transect in the eastern north atlantic was measured using thermal ionization mass spectrometry tims water samples at three locations l1 33 n 21 6 w l2 47 4 n 19 5w and l3 54 4 n 21 1 w were filtered and the dissolved and particulate fractions were analysed for their230th and232th contents in the upper water column 2000 m at l2 suggested by our model 8 25 years is probably too rapid in comparison with previous findings based on chlorofluorocarbon data enhanced scavenging of230th would be an alternative explanation for the low concentration in neadw at l2 with the scavenging mixing model we calculated an advective export flux of230th of up to 50 of the production in the water column in the eastern north atlantic advective loss of230th has to be taken into account when using the230th flux into sediments for paleoceanographic studies in ocean basins where deep water residence time is comparable to the230th scavenging residence time

the influence of the alaskan gyre on the coastal circulation in the gulf of alaska a wind driven nonlinear reduced gravity primitive equation model is used to simulate the circulation of the northeast pacific ocean including the northeast gulf of alaska the model includes the affects of bottom topography model geometry encompasses the entire gulf of alaska region from vancouver island to west of kodiak island this region is traditionally beyond the latitude limits of the reduced gravity model imposed by a weakening thermocline away from the equator the model resolution 0 025 in latitude and longitude is very fine this is the first time that a model of this type and resolution has been successfully run at these latitudes although we expected that such resolution would allow the mesoscale eddy field to develop it did not one reason may be the coarse spatial and temporal winds twenty year of comprehensive ocean atmosphere data set pseudo wind stress data used to drive the model are statistically analyzed to obtain a wind stress climatology after model spin up the monthly stresses for 1986 1989 are used to drive the model the model reproduces many of the regional oceanographic features such as the alaskan gyre the alaska current the alaska coastal current the sitka eddy and an intense cyclonic eddy that has not yet been reported in the literature northwest of the queen charlotte island in the spring in addition the model displays seasonal and interannual variability model results are validated through comparisons with national ocean service coastal sea level records and a multilayer oceanic basin scale model being run at the institute for naval oceanography

impact of atmospheric deposition on the contrasting iron biogeochemistry of the north and south atlantic ocean dissolved iron dfe distributions and atmospheric and vertical subduction fluxes of dfe were determined in the upper water column for two meridional transects of the atlantic ocean the data demonstrate the disparity between the iron biogeochemistry of the north and south atlantic ocean and show well defined gradients of size fractionated iron species in surface waters between geographic provinces the highest dfe and lowest mixed layer residence times 0 4 2 5 years were found in the northern tropical and subtropical regions in contrast the south atlantic gyre had lower dfe concentrations 5 years presumably due to lower atmospheric inputs and more efficient biological recycling of iron in this region vertical input fluxes of dfe to surface waters ranged from 20 to 170 nmol m 2 d 1 in the north atlantic and tropical provinces whereas average fluxes of 6 13 nmol m 2 d 1 were estimated for the south atlantic our estimates showed that the variable dfe distribution over the surface atlantic 50 of total vertical fe flux to surface waters rather than upwelling or vertical mixing this demonstrates the strength of the connection between land derived atmospheric fe fluxes and the biological cycling of carbon and nitrogen in the atlantic ocean

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

modern carbonate siliciclastic transitions humid and arid tropical examples climate and tectonic setting largely control characteristics of transitions between carbonate and siliciclastic sediments in depositional systems three examples selected from both humid and arid tropical settings are discussed order to illustrate details of these relationships the eastern shelf area of nicaragua is an area where siliciclastic and carbonate sediments actively interfinger under humid tropical conditions extremely high rainfall 4 5 m yr 1 in the southern part of coastal plain coupled with a correspondently high sediment flux to the nearshore shelf results in an inner shelf that is dominated by siliciclastics density gradients and persistent momentum provided by the trade winds force turbid coastal waters to the south and confine siliciclastic sediments to a coast parallel zone approximately 20 km wide the remainder of the broad shelf is characterized by carbonate sediments and reefs the mid shelf area has a coarse carbonate sediment cover composed largely of the calcareous green alga halimeda the outer shelf displays rugged topography associated with reef development skeletal carbonates containing abundant coral and coralline algal grains are characteristic of the seaward margin of the shelf significant amounts of siliciclastic sediment are confined to the nearshore part of the shelf and the transition from siliclastics to carbonates occurs over a distance of 20 km or less a second example from the humid tropics focuses on the living reefs of indonesia that are surrounded by fine grained siliciclastics a warm rainy climate results in rapid weathering of volcanic rocks from the indonesian archipelago and abundant sediment input to the shallow 40 70 m deep sunda shelf in the northern hemisphere winter monsoonally driven marine processes rrive water and sediment to the east down the axis of the java sea during summer the direction of transport is reversed this bidirectional process regime not only leaves its imprint in reef and carbonate platform morphology but also results in widespread distribution of siliciclastics from adjacent source areas isolated reefs as well as small and generally elongate reef rimmed carbonate platforms 0 5 10 km long rise 40 50 m above a sea floor composed largely of siliciclastic sediments in these cases facies transitions are very abrupt until environmental conditions curtail the carbonate producing communities of these platforms carbonate buildups and associated skeletal sediments will coexist with wider spread and more abundant siliciclastics a third example from a low latitude arid setting shows that facies transitions from carbonates to siliciclastics typically take place over short distances the lack of significant rainfall coupled with high relief along fault controlled basin margins promotes aperiodic but powerful episodes of siliciclastic that build directly into the marine environment high sloping and narrow coastal plains composed of overlapping fans result the steep seaward ends of these fans are maintained and protected from marine erosion by coral reefs and associated carbonates regionally siliciclastic to carbonate facies changes in these arid settings take place over very shor distances a few kilometers at most however on a local scale carbonates may be replaced by siliciclastics over distances as small as a few tens of meters

230th232th systematics in the central pacific ocean the sources and the fates of thorium 232 th and 230 th of unfiltered and filtered sea water samples were measured along a depth profile of the central pacific ocean using isotopic dilution and thermal ionization mass spectrometry the 232 th concentration is rather constant from below 25 m down to over 2000 m 45 60 10 6 atom cm 3 and it then increases rapidly towards the bottom 119 360 10 6 atom cm 3 at 4000 m the 230 th concentration increases linearly with depth from 3 10 3 atom cm 3 at 25 m to 110 10 3 atom cm 3 at 4000 m the reproducibility of replicate analyses and the regularity of the profiles demonstrate the reliability of the procedure however some lack of reproducibility among different samples from the same depth has to be explained by natural variability or by contamination during sample collection due to the very low 232 th concentrations and relatively high 230 th concentrations the 230 th 232 th ratios can be as high as 1 6 10 3 the ratio of the amount of th on particles 0 2 m to the amount of th in solution is significantly higher for 232 th 0 37 than for 230 th 0 18 these data are interpreted in terms of a model that specifically treats particle transport assuming local equilibrium between particles and sea water the relatively high 230 th concentrations and 230 th 232 th ratios measured at 25 m are consistent with a mixed layer of about 100 m the linear increase in 230 th with depth implies that the effect of eddy diffusion is negligible for most of the water column over the th removal time scale this profile is consistent with transport of 230 th by reversible uptake on particles settling with a constant velocity the 232 th data are inconsistent with this model and they suggest that particles carrying 232 th experience 70 of mass loss between the surface and 4000 m and must follow different transport rules this difference in the transport of 230 th and 232 th demonstrates the distinctive behavior of these isotopes during particle formation and subsequent remineralization and repackaging in the water column different speciation of 230 th and 232 th may be explained by their distinctive sources in the ocean as 230 th is produced in solution and 232 th is carried by detrital material and by their respective packaging mechanisms which are not yet known

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

thorium isotopes in the western mediterranean sea an insight into the marine particle dynamics we present a detailed view of the 230 th 232 th systematics in the western mediterranean sea in order to constrain water and particle fluxes the conclusions obtained at the regional scale are also relevant at a more global scale although they may be more difficult to establish in the open ocean 230 th and 232 th were analyzed in size fractionated seawater and marine particle samples collected in the ligurian alboran and ionian seas the 230 thxs 230 th produced by the radioactive decay of 234 u in seawater profiles at dyfamed and in the alboran sea site are not linear due to the formation of deep waters the difference of 230 thxs concentration between these two sites is related to the aging of the water masses and to different scavenging conditions the 230 th 232 th ratio is used as a tracer during mixing processes to provide information on the pathways followed by the matter in the water column at dyfamed filtered 6 0 2 wm and ultrafiltered 6 1 kda solutions have similar 230 th 232 th ratios suggesting that an equilibrium exists between truly dissolved and colloidal th the change of the th flux and of the 230 th 232 th ratio of trapped particles observed in august between 200 m and 1000 m is best explained by aggregation of filtered large particles on the trapped particles the residence time of filtered large particles with respect to aggregation on trapped particles is of the order of 8 80 days the combined budget of 230 th and 232 th inputs to the western mediterranean sea requires the dissolution of 3 5 of the th associated with all the continental particulate inputs including particles sequestered in margins suggesting that eolian inputs are not the only source of refractory elements to the mediterranean sea and may be to the whole ocean fl 2002 elsevier science b v all rights reserved

massive siliciclastic discharge to slopes of the great barrier reef platform during sea level transgression constraints from sediment cores between 15 s and 16 s latitude and possible explanations abstract the northeast australian continental margin including the great barrier reef gbr platform provides an outstanding modern analogue for understanding sedimentation in tropical mixed siliciclastic carbonate depositional systems previous studies of cores from this margin have suggested that in contrast to widely accepted models maximum siliciclastic fluxes to slopes over the last 30 ky occurred when sea level transgressed the shelf ca 11 7 ka rather than when sea level was at a lowstand before 18 ka however climate and bathymetry can affect regional sediment deposition significantly and the cores examined to date have come from the southern queensland trough where the margin has a wet tropical climate and a broad shelf 50 km with gradual slopes in this study we examine the abundance and accumulation of siliciclastic material in four cores from lower slopes of the northern queensland trough where rivers drain a drier region and debouche onto a narrow shelf with steep incised slopes similar to previously examined cores all cores contain a dark greyish brown horizon within the upper few meters this horizon represents a low in carbonate content and corresponding high in siliciclastic material primarily clay and oxygen isotope stratigraphy shows that it was deposited during late transgression nominally between 11 and 7 ka moreover mass accumulation rate calculations demonstrate that this horizon reflects a significant rise in siliciclastic fluxes when combined with the previous work to the south it appears that slopes all along a large portion of the northeast australian continental margin received greatly enhanced inputs of siliciclastic material during late transgression independent of proximal climate and bathymetry two general explanations are offered for this observation 1 climate change induced highly variable riverine discharge over the past 30 ky with a prominent maximum coincident with late transgression or 2 the shelf stores large quantities of siliciclastic sediment during lowstand and releases this material to the slope during late transgression in either case siliciclastic accumulation on the northeast australia continental margin behaves completely opposite to predictions from conventional models

238u234u and232th230th in the baltic sea and in river water the concentration c of dissolved238u 234u 232th and230th in fresh and brackish waters from the baltic sea were determined using tims the brackish waters range in salinity from that of sea water sw to 2 5 c238u in oxygen saturated surface waters is well correlated with salinity and shows quasi conservative behavior as does sr samples from the redox water interface show depletion in c238u demonstrating that dissolved u is being removed by femn oxyhydroxides from a simple mixing relationship for the brackish water 234u 1000 was calculated for the fresh water source in the northern baltic a study of the kalixalven river over an annual cycle yields high 234u during spring and summer discharge and lower values during fall and winter showing that different sources contribute to the u load in the river during different seasons c232th and c230th in river water are governed by the discharge reflecting the importance of the increased abundance of small particles 0 45 m for the232th230th load at high discharge 232th 238u in river water is about 40 times less than in detrital material in the brackish water c232th drops 2 orders of magnitude in the low salinity region 5 reaching a value close to that of sea water at a salinity of 7 5 almost all of the riverine232th must be deposited in the low salinity regions of the estuary the230th 232th in river waters is about twice the equilibrium value for232th 238u 3 8 in the brackish waters 230th 232th is greater by a factor of 10 100 than both river water and sw the big increase in230th 232th in the baltic sea waters over the riverine input indicates that the th isotopes enter the estuary as a mixture of two carrier phases we infer that about 96 of232th in river water is carried by detrital particles whereas the other phase solution colloidal has a much higher232th 232th entering the estuary the detrital particles sediment out rapidly whereas the non detrital phase is removed more slowly causing a marked increase in230th 232th in the brackish water in sw 230th 232th is closer to river input and detrital material than in brackish water we conclude that in the deep sea 232th is almost exclusively dominated by windblown dust and can be used to monitor dust flux the230th excess in baltic rivers is produced in u rich 232th poor peatlands and trapped in authigenic particles and transported with the particles time scales for producing the230th excess are 2000 8000 yr this is younger than but comparable to the time of the latest deglaciation which ended some 9000 yr ago when the mires were forming these results have implications for the possible mobility of actinides stored in repositories

tracking eolian dust with helium and thorium impacts of grain size and provenance reconstructions of the deposition rate of windblown mineral dust in ocean sediments offer an important means of tracking past climate changes and of assessing the radiative and biogeochemical impacts of dust in past climates dust flux estimates in ocean sediments have commonly been based on the operationally defined lithogenic fraction of sediment samples more recently dust fluxes have been estimated from measurements of helium and thorium as rare isotopes of these elements he 3 and th 230 allow estimates of sediment flux and the dominant isotopes he 4 and th 232 are uniquely associated with the lithogenic fraction of marine sediments in order to improve the fidelity of dust flux reconstructions based on he and th we present a survey of he and th concentrations in sediments from dust source areas in east asia australia and south america our data show systematic relationships between he and th concentrations and grain size with he concentrations decreasing and th concentrations increasing with decreasing grain size we find consistent he and th concentrations in the fine fraction 5 m of samples from east asia australia and central south america puna central west argentina with th concentrations averaging 14 g g and he concentrations averaging 2 cc stp g we recommend use of these values for estimating dust fluxes in sediments where dust is dominantly fine grained and suggest that previous studies may have systematically overestimated th based dust fluxes by 30 source areas in patagonia appear to have lower he and th contents than other regions as fine fraction concentrations average 0 8 cc stp g and 9 g g for 4he and 232th respectively the impact of grain size on lithogenic he and th concentrations should be taken into account in sediments proximal to dust sources where dust grain size may vary considerably our data also have important implications for the hosts of he in long traveled dust and for the 3he 4he ratio used for terrigenous he in studies of extraterrestrial he in sediments and ice we also investigate the use of he th ratios as a provenance tracer our results suggest differences in fine fraction he th ratios between east asia australia central south america and patagonia with ratios showing a positive relationship with the geological age of source rocks he th ratios may thus provide useful provenance information for example allowing separation of patagonian sources from puna central west argentina or australian dust sources he th ratios in open ocean marine sediments are similar to ratios in the fine fraction of upwind dust source areas he th ratios in mid latitude south atlantic sediments suggest that dust in this region primarily derives from the puna central west argentina region 23 32 s rather than patagonia 38 s in the equatorial pacific he th ratios are much lower than in extratropical pacific sediments or potential source areas measured as a part of this study east asia south america australia for reasons that are at present unclear complicating their use as provenance tracers in this region

tracing euxinia by molybdenum concentrations in sediments using handheld x ray fluorescence spectroscopy hhxrf abstract elevated molybdenum mo contents in organic rich sediments are indicative of deposition from an anoxic and sulfide rich euxinic water column this can be used for tracing past euxinic conditions in ancient oceans from sedimentary archives conventional analytical detection of elevated molybdenum levels is however expensive and cannot be directly performed in the field here we show that handheld x ray absorption spectroscopy hhxrf on both rock powders and rock surfaces provides a powerful tool for laboratory or field based geochemical characterization of mo content and the tracing of euxinic depositional conditions we further present a sedimentary mo database compiled from over 300 globally distributed modern marine sites to show that modern euxinic marine basins are characterized by molybdenum enrichment 25 ppm relative to average crust 1 5 ppm and river suspended matter 3 ppm only mn oxide rich deposits from oxygenated deep sea settings match such high mo enrichments but these are easily distinguished from mo rich sediments from the continental shelves hence past and present organic rich sediments enriched in mo are indicative of at least intermittent water column euxinia we analyzed the molybdenum content of powdered and homogenized samples of holocene miocene triassic jurassic ordovician and cambrian age by hhxrf and inductively coupled plasma mass spectrometry icpms we further analyzed 2 certified nist standard references nist 2781 with mo 47 ppm and nist 2702 with mo 10 ppm for analytical control analytical precision 1 after 30 120 and 300 seconds of measuring time was 4 2 and 1 ppm with a respective detection limit of 11 5 3 ppm 3 noise level the data were accurate to within the given precision 1 after a daily calibration to samples covering a range of mo concentrations from 0 to 30 ppm hand held xrf equipment also allows mo measurements directly on fresh rock surfaces both in the field and under laboratory conditions rock samples from a cambrian drill core closely match icpms obtained mo concentrations from homogenous powders of the same rocks collectively our data show that hhxrf as a quick and reliable method for the precise and accurate quantification of molybdenum concentrations in both rock powders and at fresh rock surfaces the non destructive nature of the hhxrf measurements is combined with low per sample analytical costs minor sample preparation and easy applicability in the field

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

mixing of siliciclastic and carbonate sediments in shallow shelf environments the inhibiting effect that siliciclastic material has on carbonate secreting organisms has lead to the generalization that sediments composed of mixtures of carbonate and siliciclastic material should rarely form however many modern and ancient shelf deposits contain a spectrum of sediments that are of mixed composition the processes responsible for this mixing can be grouped into four categories 1 punctuated mixing where sporadic storms and other extreme periodic events transfer sediments from one depositional environment to another 2 facies mixing where sediments are mixed along the diffuse boundaries between contrasting facies 3 in situ mixing where the carbonate fraction consists of the autochthonous or parautochthonous death assemblages of calcareous organisms that accumulated on or within siliciclastic substrates and 4 source mixing where admixtures are formed by the uplift and erosion of nearby carbonate source terranes the allochemical constituents of mixed sediments are both coralgal and foram mollusc in composition the foram mollusc assemblage is the most common because of the effects of increased turbidity unstable substrates and the clogging of filter feeding mechanisms associated with a siliciclastic influx

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

230th u dating of last interglacial brain corals from bonaire southern caribbean using bulk and theca wall material abstract we compared the suitability of two skeletal materials of the atlantic brain coral diploria strigosa for 230th u dating the commonly used bulk material comprising all skeletal elements and the denser theca wall material eight fossil corals of presumably last interglacial age from bonaire southern caribbean sea were investigated and several sub samples were dated from each coral for four corals both the ages and the activity ratios of the bulk material and theca wall agree within uncertainty three corals show significantly older ages for their bulk material than for their theca wall material as well as substantially elevated 232th content and 230th 238u ratios the bulk material samples of another coral show younger ages and lower 230th 238u ratios than the corresponding theca wall samples this coral also contains a considerable amount of 232th the application of the available open system models developed to account for post depositional diagenetic effects in corals shows that none of the models can successfully be applied to the bonaire corals the most likely explanation for this observation is that the assumptions of the models are not fulfilled by our data set comparison of the theca wall and bulk material data enables us to obtain information about the open system processes that affected the corals the corals showing apparently older ages for their bulk material were probably affected by contamination with a secondary detrital phase the most likely source of the detrital material is carbonate sand the higher 230th 232th ratio of this material implies that detrital contamination would have a much stronger impact on the ages than a contaminant with a bulk earth 230th 232th ratio and that the threshold for the commonly applied 232th reliability criterion would be much lower than the generally used value of 1 ng g 1 the coral showing apparently younger ages for its bulk material was probably influenced by more than one diagenetic process a potential scenario is a combination of detrital contamination and u addition by secondary pore infillings our results show that the dense theca wall material of d strigosa is generally less affected by post depositional open system behaviour and better suited for 230th u dating than the bulk material this is also obvious from the fact that all ages of theca wall material reflect a last interglacial origin 125 ka whereas the bulk material samples are either substantially older or younger however for some corals the 230th u ages and activity ratios of the bulk material and the theca wall samples are similar this shows that strictly reliable 230th u ages can also be obtained from bulk material samples of exceptionally well preserved corals however the bulk material samples more frequently show elevated activity ratios and ages than the corresponding theca wall samples our findings should be generally applicable to brain corals mussidae that are found in tropical oceans worldwide and may enable reliable 230th u dating of fossil corals with similar skeletal architecture even if their bulk skeleton is altered by diagenesis the 230th u ages we consider reliable 120 130 ka along with a recently published age of 118 ka provide the first comprehensive dating of the elevated lower reef terrace at bonaire 118 130 ka which is in agreement in timing and duration with other last interglacial records

the northeast pacific ocean response to the 1982 1983 el nino the ocean s response to atmospheric forcing and to forcing along the coast by kelvin waves is examined in light of nearshore seasonal variability and the major 1982 1983 el nino in addition to driving the northeast pacific gyre and local currents the wind modifies the depth to the main thermocline changing the apparent westward phase speed of rossby waves excited by passing kelvin waves the amplitude of the passing kelvin wave determines whether the rossby wave depresses or raises the thermocline while propagating westward along the northeast pacific coast from oregon to washington model results suggest that the wind raises the main thermocline during the 1982 1983 el nino generally the coastal response off oregon and washington appears to be strongly driven by the large scale atmosphere while along the california coast and south to the equator the dominant el nino signal has an oceanic origin that signal with periods between 2 and 5 years originates in the western equatorial pacific ocean and is tracked eastward through the equatorial waveguide and then poleward along the coast to 50 n using data from two reduced gravity primitive equation models coupled at 18 n at shorter seasonal time scales the acceleration of the wind appears to be an important mechanism in driving coastal currents

silicate weathering in anoxic marine sediments two sediment cores retrieved at the northern slope of sakhalin island sea of okhotsk were analyzed for biogenic opal organic carbon carbonate sulfur major element concentrations mineral contents and dissolved substances including nutrients sulfate methane major cations humic substances and total alkalinity down core trends in mineral abundance suggest that plagioclase feldspars and other reactive silicate phases olivine pyroxene volcanic ash are transformed into smectite in the methanogenic sediment sections the element ratios na al mg al and ca al in the solid phase decrease with sediment depth indicating a loss of mobile cations with depth and producing a significant down core increase in the chemical index of alteration pore waters separated from the sediment cores are highly enriched in dissolved magnesium total alkalinity humic substances and boron the high contents of dissolved organic carbon in the deeper methanogenic sediment sections 50 150 mg dm 3 may promote the dissolution of silicate phases through complexation of al3 and other structure building cations a non steady state transport reaction model was developed and applied to evaluate the down core trends observed in the solid and dissolved phases dissolved mg and total alkalinity were used to track the in situ rates of marine silicate weathering since thermodynamic equilibrium calculations showed that these tracers are not affected by ion exchange processes with sediment surfaces the modeling showed that silicate weathering is limited to the deeper methanogenic sediment section whereas reverse weathering was the dominant process in the overlying surface sediments depth integrated rates of marine silicate weathering in methanogenic sediments derived from the model 81 4 99 2 mmol co2 m 2 year 1 are lower than the marine weathering rates calculated from the solid phase data 198 245 mmol co2 m 2 year 1 suggesting a decrease in marine weathering over time the production of co2 through reverse weathering in surface sediments 4 22 15 0 mmol co2 m 2 year 1 is about one order of magnitude smaller than the weathering induced co2 consumption in the underlying sediments the evaluation of pore water data from other continental margin sites shows that silicate weathering is a common process in methanogenic sediments the global rate of co2 consumption through marine silicate weathering estimated here as 5 20 tmol co2 year 1 is as high as the global rate of continental silicate weathering

the role of the global carbonate cycle in the regulation and evolution of the earth system we review one of the most ancient of all the global biogeochemical cycles and one which reflects the profound geochemical and biological changes that have occurred as the earth system has evolved through time that of calcium carbonate caco3 in particular we highlight a mid mesozoic revolution in the nature and location of carbonate deposition in the marine environment driven by the ecological success of calcareous plankton this drove the creation of a responsive deep sea sedimentary sink of caco3 the result is that biologically driven carbonate deposition provides a significant buffering of ocean chemistry and of atmospheric co2 in the modern system however the same calcifying organisms that under pin the deep sea carbonate sink are now threatened by the continued atmospheric release of fossil fuel co2 and increasing acidity of the surface ocean we are not yet in a position to predict what the impact on caco3 production will be or how the uptake of fossil fuel co2 by the ocean will be affected this uncertainty in the future trajectory of atmospheric co2 that comes from incomplete understanding of the marine carbonate cycle is cause for concern

a novel method to measure calcium carbonate with portable x ray fluorescence instrumentation and its application to gulf of mexico surficial sediments abstract a novel rapid low cost non destructive and reliable technique was developed to simultaneously measure calcium carbonate caco3 and trace element concentrations in sediments with a portable x ray fluorescence pxrf analyzer and applied to 27 samples of surficial sediments collected from the yucatan continental shelf 1200 m water depth of the gulf of mexico this technique is based on calculation of authigenic calcium caauth from the total ca measured with the pxrf results obtained with the pxrf showed a very high and highly significant correlation r 0 99 p

efficient representation of the north atlantic hydrographic and chemical distributions abstract the large scale temperature salinity oxygen and nutrient distributions of the north atlantic ocean are explored with the aim of identifying the minimum data set necessary to describe the general circulation and to identify the dominant physical characteristics a form of empirical onthogonal function principal component analysis based upon the singular value decomposition is used six modes are capable of describing 92 of the variance of the full hydrographic fields a second singular value decomposition applied to the horizontal property modes shows that there are only two independent tracers among the six used the modal reconstruction satisfactorily reproduces the large scale transport properties of the original data a clear physical interpretation of the modes has not been found but they are obviously connected to the large scale water mass characteristics of the ocean much remains to be learned about how to use such descriptions

asphalt volcanism and chemosynthetic life in the campeche knolls gulf of mexico in the campeche knolls in the southern gulf of mexico lava like flows of solidified asphalt cover more than 1 square kilometer of the rim of a dissected salt dome at a depth of 3000 meters below sea level chemosynthetic tubeworms and bivalves colonize the sea floor near the asphalt which chilled and contracted after discharge the site also includes oil seeps gas hydrate deposits locally anoxic sediments and slabs of authigenic carbonate asphalt volcanism creates a habitat for chemosynthetic life that may be widespread at great depth in the gulf of mexico

organic matter budget in the southeast atlantic continental margin close to the congo canyon in situ measurements of sediment oxygen consumption abstract a study of organic carbon mineralization from the congo continental shelf to the abyssal plain through the congo submarine channel and angola margin was undertaken using in situ measurements of sediment oxygen demand as a tracer of benthic carbon recycling two measurement techniques were coupled on a single autonomous platform in situ benthic chambers and microelectrodes which provided total and diffusive oxygen uptake as well as oxygen microdistributions in porewaters in addition sediment trap fluxes sediment composition org c tot n caco3 porosity and radionuclide profiles provided measurements of respectively input fluxes and burial rate of organic and inorganic compounds the in situ results show that the oxygen consumption on this margin close to the congo river is high with values of total oxygen uptake tou of 4 0 6 3 6 0 5 mmol m 2 d 1 at 1300 and 3100 m depth respectively and between 1 9 0 3 and 2 4 0 2 mmol m 2 d 1 at 4000 m depth diffusive oxygen uptakes dou were 2 8 1 1 2 3 0 8 0 8 0 3 and 1 2 0 1 mmol m 2 d 1 respectively at the same depths the magnitude of the oxygen demands on the slope is correlated with water depth but is not correlated with the proximity of the submarine channel levee system which indicates that cross slope transport processes are active over the entire margin comparison of the vertical flux of organic carbon with its mineralization and burial reveal that this lateral input is very important since the sum of recycling and burial in the sediments is 5 8 times larger than the vertical flux recorded in traps transfer of material from the congo river occurs through turbidity currents channelled in the congo valley which are subsequently deposited in the lobe zone in the congo fan below 4800 m ship board measurements of oxygen profiles indicate large mineralization rates of organic carbon in this zone which agrees with the high organic carbon content 3 and the large sedimentation rate 19 mm y 1 found on this site the lobe region could receive as high as 19 mol c m 2 y 1 1 3 being mineralized and 2 3 being buried and could constitute the largest depocenter of organic carbon in the south atlantic

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

atmospheric forcing of interannual variability in the northeast pacific ocean connections with el nino the nature and causes of the observed interannual variability of oceanic conditions in the northeast pacific were investigated using a variety of meteorological and oceanographic data sets an examination of a long series of seasonal mean atmospheric sea level pressure slp charts showed that when the winter average slp pattern in the north pacific varies significantly from climatology it tends to do this in one of two characteristic ways in particular in some winters there is an anomalously strong circulation which differs from climatology mainly in having an intensified aleutian low in other winters there is an anomalously weak atmospheric circulation this is almost invariably associated with the westward displacement of the aleutian low and the production of a separate but much weaker low in the gulf of alaska the north pacific winter slp appears to have some relation to the southern oscillation so and oceanic temperatures in the tropics in particular el nino southern oscillation enso episodes are generally coincident with strong north pacific slp patterns and often follow winters with weak slp patterns however this relationship is far from being perfectly regular and predictable interannual variations in the intensity of the north pacific atmospheric surface circulation were found to be strongly correlated with the anomalies of both sea surface temperature sst and sea level height slh at stations along the british columbia coast an intense aleutian low is invariably associated with warm coastal waters and high coastal sea levels by comparing a large number of pacific slp and sst maps it was possible to verify that the relation between north pacific slp and oceanic surface temperature actually applies to the sst over much of the northeast pacific at least as far west as 150 w the relationship of north pacific slp with the so together with the relationship between north pacific slp and oceanic conditions in the northeast pacific can account for the observed general tendency for sst and slh along the west coast of north america to be anomalously high during tropical enso episodes on the other hand the lack of a truly predictable relation between the southern oscillation and north pacific slp explains the fact that not all enso events are associated with wanning of the northeast pacific

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

topographically induced baroclinic eddies near a coastline with application to he northeast pacific abstract a mathematical model is developed to describe the interaction between variable bottom topography and a steady horizontally sheared baroclinic coastal current the topography modeled in this study consists of an offshore seamount and a seaward protrusion of the continental slope the fluid motions are assumed to conserve potential vorticity on the f plane and expressions for the pressure density velocity and mass transport fields are obtained using a normal mode analysis and the appropriate green s function for the horizontal problem the theory is applied to the northeast pacific ocean in an attempt to model the anticyclonic eddy which has been observed by tabata west of sitka alaska the numerical calculations of the model and the observed location dimensions velocities and transports of the sitka eddy are in good agreement the axial velocities and dimensions of the calculated eddy field are largest for upstream surface and bottom currents of approximately 5 7 and 1 2 cm s 1 respectivel