the impact of oxic alteration on plume derived transition metals in ridge flank sediments from the east pacific rise we describe transition metal behaviour during early diagenesis in sediments collected along a transect across the eastern flank of the east pacific rise epr at 14 s overlying crust with magnetic ages of 0 36 ma to 4 6 ma the sediments are lithologically simple and consist of biogenic carbonate hydrothermal plume precipitates and minor basaltic debris sedimentation rates range from 1 cm ka in the near axis region 0 36 ma to 0 1 0 2 cm ka across the young ridge flank by 1 9 ma or within 142 km from axis redox indicators porewater mn ii aq and solid phase mo mn ratios indicate fully oxic conditions in near axis sediments changing to mildly suboxic conditions across the ridge flank sequential extraction analysis of sediments from the 0 36 ma site indicates that oxic alteration of fe oxyhydroxides is dominated by transformation of ferrihydrite to goethite implying that alteration occurs via dissolution followed by nucleation and precipitation the extent of alteration amorphous fe total plume derived fe ranges from 0 3 to 0 8 and the time to half conversion is on the order of 100 ka v associated with plume derived ferrihydrite is strongly discriminated against during alteration to goethite and the distribution coefficient dv v fe goethite v fe dissolved is in the range 0 45 0 59 cu zn and ni are delivered to the sediment in association with both fe oxyhydroxides and mn oxides where 70 of cu and zn and 10 of ni are associated with fe oxyhydroxides the fe adsorbed cu and zn are incorporated quantitatively into the lattice structure of goethite during alteration the fe associated ni most likely represents ni co precipitated as ni fe ferrihydrite and incorporated into goethite during alteration co is associated only with mn oxides the oxic alteration of hydrothermal fe oxyhydroxides therefore represents a relatively permanent sink where goethite dissolution is a prerequisite for metal release for a maximum of 70 of plume derived cu and zn 50 of v 10 of ni and 0 of co in oxic sediments the remaining plume derived metals are retained in association with amorphous fe oxyhydroxides and mn oxides although this fraction is highly susceptible to diagenetic remobilization under suboxic conditions

probabilistic formulation of avo modeling and avo attribute based facies classification using well logs we have developed a probabilistic formulation to derive the probability density function of amplitude variation with offset avo attributes given the distribution of elastic properties in the context of avo analysis of well log data the proposed probabilistic formulation includes the analytical expression of the posterior distribution and contributes to the correct propagation of the uncertainty through the avo model when this analysis is performed in each facies the resulting posterior probability density functions of avo attributes conditioned by the elastic attributes and the underlying log facies classification can be used in a bayesian inversion workflow to obtain the avo attribute based facies classification this classification is then compared with the petrophysical log facies profile and can be extended to the entire reservoir model if inverted seismic attributes are available we demonstrate the methodology on a data set from an onshore tight sand gas reservoir in texas the main results of the application are the set of probability distributions of avo properties as a function of elastic attributes in each facies and the corresponding avo based facies profile at the well location a comparison of different statistical assumptions and a sensitivity analysis on the resolution of the elastic data set are presented

can the aluminum and titanium contents of ocean sediments be used to determine the paleoproductivity of the oceans in the central equatorial pacific settling particles collected with sediment traps have al ti values greater than those of a typical crustal source the al ti values of the sediment trap material are not well correlated with either the flux of organic carbon or with total particle mass suggesting that this ratio cannot be used as a simple index of paleoproductivity however the al ti values of some trap samples are more than 3 times the ratio for typical crustal materials indicating a noncrustal source of excess al numerical analysis using linear programming indicates that the excess al is associated with opal and that this biological component carries as much as 1200 ppm of al because of the low particulate fluxes of lithogenic material in the equatorial pacific and the relatively high opal content of equatorial sediment trap material opal appears to be the predominant conveyor of al to the equatorial sediments our sediment trap al ti values are similar to ratios previously measured in equatorial sediments suggesting that measurements of this element pair in ocean sediments may be an indicator of opal rain to the seafloor the particle reactive nature of al and ti means their ratios in sediments may be relatively insensitive to opal preservation or other diagenetic processes however the al ti values of raining particles are highly sensitive to the relative proportion of opal and lithogenic material where opal lithogenic ratios are less than 20 the al ti values are indistinguishable from a crustal source ratio in addition the amount of excess al associated with opal in settling particles may be a function of the concentration of al in the water column and of the processes that fractionate dissolved al and ti these issues must be evaluated before the al ti values of ocean sediments can be used as a reliable proxy of opal flux to the seafloor

iron rich metalliferous sediments on the east pacific rise prototype of undifferentiated metalliferous sediments on divergent plate boundaries abstract sediments in a zone on the east pacific rise with an especially high spreading rate were studied chemically mineralogically and microscopically they consist of a mixture of metalliferous sediments and plankton tests the metalliferous sediments were formed by an acidic hydrothermal leaching of tholeiitic basalt with seawater and subsequent precipitation in contact with cold near bottom seawater we assume the precipitation from hydrothermal solutions in this part of the east pacific rise to be undifferentiated due to the high spreading rate and the resulting rapid flow on the water through the basalt thus these metalliferous sediments are an initial stage type that have not undergone differentiation mn mo la cu v ni fe zn co and y all of which are leachable in acidic hydrothermal solutions are enriched in the metalliferous sediments in comparison to the tholeiitic basalts zr al and ti on the other hand which under the same conditions are not easily leached are reduced in their concentrations all components of the metalliferous sediments precipitated as hydroxides or as adsorbed ions on the hydroxides of other elements this is due to the oxidizing conditions in the near bottom seawater the sedimentation rate is high the almost 3 m long cores reach only to the late pleistocene the only distinctly observable diagenetic process for this period of time is the formation of goethite from amorphous iron oxides only for na k and rb does it seem possible that a distinct enrichment in the sediments by adsorption from the seawater could have taken place ca sr pb and perhaps sc are primarily bound to the planktonic carbonate part of the sediments

chemical processes in buoyant hydrothermal plumes on the east pacific rise near 21 n hydrothermal plume water containing suspended particles of precipitated black smoke has been sampled from three hydrothermal vent fields on the east pacific rise near 21 n the samples were taken within the lower 22 m of the buoyant plumes directly above 273 350 c black smoker vents using go flo bottles mounted on the submersible alvin based on li as a conservative tracer of the high temperature endmember solution mixing ratios of 102 to 104 g seawater g vent water are achieved within the lower 22 m of the plumes the particle concentrations sampled in the lower 13 m of the plumes are much larger than predicted for these mixing ratios suggesting that the particles are settling within the lower part of the plume the major minerals in the smoke are pyrrhotite fe rich sphalerite pyrite unidentified fe s si and fe si s phases chalcopyrite amorphous silica sulfur fe oxyhydroxides including goethite and anhydrite present in trace quantities are barite isocubanite wurtzite covellite marcasite and unidentified silicates and alsilicates organic matter is common the composition of the plume solutions indicates that 35 25 of the hydrothermally injected fe remains in dissolved form i e 0 45 m within the lower 22 m of the plume in spite of a 3 to 9 fold excess of h2s in the vent solutions nearly all of the mn and si and most of the ba also remain in solution h2s by contrast has been largely 70 100 removed by precipitation as sulfides and sulfur but mainly by oxidation to dissolved species with intermediate oxidation states its early removal implies that 50 30 of the injected fe will eventually precipitate as primary oxides rather than as sulfides and that fe can be fractionated from the other chalcophile metals during sulfide precipitation compared with the vent water the particles are enriched in cu co ag cd al zn pb and ni by factors of 4 to 20 relative to fe and depleted in ba s si and mn scavenging from seawater may play a role in co and cu enrichment at the ngs field and for ag cd and ni at all three fields but is negligible for pb and zn these results indicate that two distinct metalliferous components are delivered to the distal regions of a plume as a result of reactions in the lower part of the buoyant plume 1 1 a dissolved component that includes about half the fe and all of the mn and will eventually precipitate as oxides and 2 2 a particulate component consisting of fine grained sulfide minerals that are enriched in ore metals by factors of 4 to 20

rhenium and molybdenum enrichments in sediments as indicators of oxic suboxic and sulfidic conditions of deposition abstract the trace elements re and mo both behave conservatively in seawater yet are strongly enriched in reducing sediments their potential for authigenic enrichment above crustal concentrations is greater than for many other elements due to the high ratio of metal sw metal crust we present sedimentary re and mo data from box and multi cores spanning a range of redox conditions from well oxygenated sites to locations with substantial sulfide concentrations at the oxic sites re and mo as expected accumulate at concentrations close to their crustal abundances re shows substantial enrichment in suboxic absence of o 2 and h 2 s sediments of the sea of japan in sediments within the oxygen minimum of the pakistan margin as well as in sediments underlying the sulfide bearing waters of the black sea and saanich inlet re enrichment occurs in these cores just below the depths of fe and u reduction only in the sediments underlying the sulfidic waters of the black sea and saanich inlet is there substantial authigenic mo accumulation absence of re and mo enrichments in sediment trap samples from the sulfide bearing basins suggests that the addition of both metals occurs at or below the sediment water interface the re and mo concentration profiles are modeled to hindcast the removal depth of re and mo in the sediments which along with the re mo ratio determine whether oxic suboxic or sulfidic conditions were present in the water column or in the sediments in the past using this approach historical redox conditions can be inferred even in environments such as continental margins where a substantial lithogenic component can obscure authigenic enrichments of other metals

near vent chemical processes in a hydrothermal plume insights from an integrated study of the endeavour segment support from onc for sample collection is gratefully acknowledge as is the analytical expertise of jody spence bruno keiffer and maureen soon who helped generate the data set reported here funding for sample analysis came from an nserc discovery grant to l a c ocean networks canada is supported through the canadian foundation for innovation all data are provided in the supporting information or through onc at http dmas uvic ca datasearch

stochastic reservoir characterization using prestack seismic data reservoir characterization must be based on information from various sources well observations seismic reflection times and seismic amplitude versus offset avo attributes are integrated in this study to predict the distribution of the reservoir variables i e facies and fluid filling the prediction problem is cast in a bayesian setting the a priori model includes spatial coupling through markov random field assumptions and intervariable dependencies through nonlinear relations based on rock physics theory including gassmann s relation the likelihood model relating observations to reservoir variables including lithology facies and pore fluids is based on approximations to zoeppritz equations the model assumptions are summarized in a bayesian network illustrating the dependencies between the reservoir variables the posterior model for the reservoir variables conditioned on the available observations is defined by the a priori and likelihood models this posterior model is not analytically tra

lithology color coded seismic sections the calibration of avo crossplotting to rock properties in the late 1960s several oil companies noticed that in environments of young clastic sediments large seismic amplitudes were associated with gas saturated sands this method of correlating lithology to normal incidence ni reflectivities was appropriately named the bright spot technique however it quickly became apparent that not all large amplitudes were necessarily associated with gas reservoirs and much to our chagrin not all gas reservoirs had large amplitudes for the next decade geophysicists tried numerous techniques to resolve the ambiguity associated with lithologic identification by means of the seismic attribute ni this met with various degrees of success finally ostrander s work on amplitude variation with offset avo led to the development of another seismic attribute s which improved our discrimination of lithologies see plane wave reflection coefficients for gas sands at nonnormal angles of incidence geophysics 1984 but proper application of this new attribute along wit

rhenium geochemical cycling insights from continental margins abstract we measured rhenium re in sediments both pore waters and solid phase from three locations on the mid atlantic bight mab from the eastern margin of the united states a northern location on the continental shelf off massachusetts oc426 75 m water depth and two southern locations off north carolina en433 1 647 m water depth and en433 2 2648 m water depth these sediments underlie high oxygen bottom waters 250 270 m but become reducing below the sediment water interface due to the relatively high organic carbon oxidation rates in sediments greater reduction intensity is reflected by shallower oxygen penetration greater ammonium concentrations at depth and shallower first appearances of mn and fe in pore waters this comparison suggests that for the three sites along the mab the reduction intensity from greatest to least is en433 1 oc426 en433 2 all of the pore water profiles show removal of re from pore waters modeled pore water re fluxes follow the trend in reducing conditions en433 1 2 0 0 2 pmol cm 2 y oc426 0 9 0 1 pmol cm 2 y and en433 2 0 60 0 03 pmol cm 2 y respectively solid phase profiles show authigenic re enrichment in sediments from all three locations and the calculated re accumulation rates also mirror the trend in reducing conditions with the values decreasing from en433 1 oc426 en433 2 1 5 0 2 pmol cm 2 y 0 29 0 09 pmol cm 2 y 0 19 0 09 pmol cm 2 y respectively controls on re accumulation are determined from the mab data and from the literature and include 1 the extent of reducing conditions with greater removal of re from pore waters with greater anoxic organic carbon oxidation as determined by the net dissolved ammonium production consistent with the expected removal of pore water re coincident with fe iii and sulfate reduction 2 irrigation which results in net removal of re to sediments augments the diffusive flux of re across the sediment water interface and is more important in shallow coastal sediments rather than locations from deeper water depths mab sites and 3 seasonal remobilization of re from surface sediments due to deepening oxygen penetration depth from 0 2 cm to 1 cm although smaller seasonal changes in oxygen penetration depth e g 0 2 cm to 0 6 cm are less conducive for remobilizing re from sediments there is an empirical relationship with larger re accumulation rates present when the oxygen penetration depth is shallow however there is a stronger correlation between organic carbon oxidation and re accumulation rates this latter relationship is more appropriate since the oxidation of labile organic matter in sediments dictates the sedimentary reducing conditions that are then conducive for re accumulation in the solid phase

hydroacoustic earthquake detection in the arctic basin with the spinnaker array eighteen arctic basin earthquakes were hydroacoustically detected during 64 days of monitoring with the spinnaker hydrophone array in the lincoln sea arctic ocean epicentral estimates were made for 12 of these events event ranges were estimated via the arrival time difference between the solid earth p wave and the hydroacoustic t wave azimuths were estimated via plane wave beamforming to the array elements in the 5 10 hz band the 12 events fall on the north american eurasian plate boundary at the extreme southern end of the gakkel ridge and along the spitsbergen fracture zone lena trough one of the events m b 5 4 11 may 1996 spitsbergen fracture zone was detected by the global seismic network gsn with an epicenter that differs from our hydroacoustic estimate by 51 km our hydroacoustic detection threshold appears to be m b 3 4 within a 1100 km radius of the spinnaker array confirming that t waves propagate efficiently in the arctic basin and that hydroacoustic techniques hold promise for seismic monitoring of the region

probabilistic approach to rock physics modeling abstractrock physics modeling aims to provide a link between rock properties such as porosity lithology and fluid saturation and elastic attributes such as velocities or impedances these models are then used in quantitative seismic interpretation and reservoir characterization however most of the geophysical measurements are uncertain therefore rock physics equations must be combined with mathematical tools to account for the uncertainty in the data we combined probability theory with rock physics modeling to make predictions of elastic properties using probability distributions rather than definite values the method provided analytical solutions of rock physics models in which the input is a random variable whose exact value is unknown but whose probability distribution is known the probability distribution derived with this approach can be used to quantify the uncertainty in rock physics model predictions and in rock property estimation from seismic attributes examples of fluid substitutio

hydrothermal scavenging at the mid atlantic ridge radionuclide distributions we have carried out a study of u series radionuclide distributions in the neutrally buoyant plume overlying the tag hydrothermal vent field at 26 n mid atlantic ridge limited uptake of u accompanies the formation of fe oxyhydroxide particulate material within the hydrothermal plume the particulate u concentrations are too small for measurable dissolved u anomalies to be produced within the water column at plume height however such uptake followed by deposition in the underlying sediments could account for 10 of the u enrichment that has been reported previously for metalliferous ridge crest sediments particulate 234th 230th and 228th activities in the tag hydrothermal plume represent 65 of total th activities typical of the deep ocean low dissolved th activities coincide with the high particulate th activities indicating that hydrothermal scavenging strongly affects th isotope distributions in the water column close to hydrothermal vents much of the scavenging occurs during the initial formation of fe rich hydrothermal precipitates but some further scavenging continues as the material is dispersed away from its source distributions of particulate 210pb and 231pa activities in the neutrally buoyant plume are also extremely high 7 12 dpm 102 l and 30 160 dpm 106 l respectively like th 210pb and231pa show evidence for scavenging within the hydrothermal plume total th activities at plume height are 50 higher than background this focusing of th into the plume is consistent with the entrainment and re emplacement at plume height of particulate material recycled from beneath the neutrally buoyant plume

oxyanions in metalliferous sediments tracers for paleoseawater metal concentrations abstract the concentration of carbon fe mn s p v cr as mo cd u and re were determined in sediment core y 71 7 53p near an active hydrothermal location on the southern east pacific rise crest 10 s the goal was to determine the usefulness of hydrothermal iron oxides as carriers of elemental tracers of seawater concentrations the sediments are 70 carbonate and about 1 3 detrital material with the remainder having a hydrothermal origin rhenium concentrations are at detrital levels suggesting little anaerobic diagenesis beyond manganese remobilization however u cd and mo concentrations all indicate alteration after deposition oxyanion fe ratios of p v and as in surface sediments are lower than the ratios in plume particles and covary with fe content downcore the probable explanation for these variations is variable efficiency of incorporation of these metals during iron oxide formation or early diagenetic processes after deposition the p fe ratio in the core sediment is about half that in the plume particles among the oxyanion ratios only the v as ratio in the sediments is relatively constant at the present plume particle ratio during the past 60 70 kyr changes in sediments older than this could reflect variability in the incorporation efficiency or changes in v as ratio in seawater this study demonstrates the difficulties of using hydrothermal sediment element enrichments as tracers of past seawater chemistry changes in this core it appears that all oxyanion ratios change for reasons other than seawater metal concentration changes with the possible exception of the v as ratio

origin and global tectonic significance of early archean cherts from the marble bar greenstone belt pilbara craton western australia abstract five sections of bedded chert in mafic ultramafic rocks of the archean warrawoona group in the marble bar greenstone belt pilbara craton were analyzed in order to understand their depositional environment and to provide some constraints on early archean tectonics the sections are divisible into two types based on their field occurrence mineralogy and geochemistry thicker ones a and b that overlie fe rich low k tholeiites and thinner ones c1 c2 and c3 overlying komatiitic basalts the thickest ferruginous section a 45 m thick is the marble bar chert of the towers formation and is interpreted to have been an in situ precipitate derived from a high t hydrothermal solution emanating from a mid oceanic ridge mor the following geochemical features are similar to those of modern hydrothermal iron rich sediments at a mor i p v zn and y are positively correlated with fe ii a positive eu anomaly normalized to chondrite decreases from 6 6 to 1 3 and the magnitude of a negative ce anomaly decreases from 0 6 to 1 0 as ree and lree hree increase the 13 m thick b section in the apex basalt dominated by sio2 and containing significant amounts of ba up to 4330 ppm originated from a low t mor hydrothermal solution this section is characterized by an association with massive black gray silica veins that were hydrothermal feeders in normal fault zones in the spreading center geochemical evidence from the greenstones underlying the b section indicates that they are of morb origin in contrast to a and b c1 c2 and c3 sections are intercalated conformably with komatiitic basalts of the apex basalt and are 3 6 m thick the geochemical signatures of these three sections suggest that they were most likely formed by low t weak hydrothermal activity that may have been associated with hot spot volcanism they show strong enrichment of cr and ni reflecting a significant contribution of komatiitic basaltic detritus during sedimentation the presence of volcaniclastic chert in their uppermost beds indicates a decrease of hydrothermal silica precipitation due to waning hydrothermal activity among the three sections the uppermost c3 exhibits greater enrichment in zr nb hf and th and higher th sc and la yb n relative to the lower c1 and c2 sections this could mean that the depositional environment of c3 was relatively closer to a continent or to island arcs composed of granitoids and or their volcanic equivalents siliceous mudstones and sandstones of the uppermost clastic rocks t section panorama formation have geochemical signatures analogous to those of felsic plutonic volcanic rocks high th sc negative eu anomalies and high ree in some siliceous mudstones from this unit imply that differentiated granitoids or volcanic equivalents were already exposed erupted at least locally in the pilbara at this time this study shows these warrawoona group cherts were deposited in a variety of environments ranging from a mid oceanic spreading center to a convergent plate boundary via a hot spot this variation was most likely due to horizontal plate motions which accordingly support the operation of plate tectonics in the early archean

glacial enrichments of authigenic cd and u in subantarctic sediments a climatic control on the elements oceanic budget we examine the possibility that glacial increase in the areal extent of reducing sediments might have changed the oceanic cd inventory thereby decoupling cd from po4 we suggest that the precipitation of cd sulfide in suboxic sediments is the single largest sink in the oceanic cd budget and that the accumulation of authigenic cd and u is tightly coupled to the organic carbon flux into the seafloor sediments from the subantarctic ocean and the cape basin south atlantic where oxic conditions currently prevail show high accumulation rates of authigenic cd and u during glacial intervals associated with increased accumulation of organic carbon these elemental enrichments attest to more reducing conditions in glacial sediments in response to an increased flux of organic carbon a third core overlain by circumpolar deep water cpdw as are the other two cores but located south of the antarctic polar front shows an approximately inverse pattern to the subantarctic record the contrasting patterns to the north and south of the antarctic polar front suggest that higher accumulation rates of cd and u in subantarctic sediments were driven primarily by increased productivity this proposal is consistent with the hypothesis of glacial stage northward migration of the antarctic polar front and its associated belt of high siliceous productivity however the increase in authigenic cd and u glacial accumulation rates is higher than expected simply from a northward shift of the polar fronts suggesting greater partitioning of organic carbon into the sediments during glacial intervals lower oxygen content of cpdw and higher organic carbon to biogenic silica rain rate ratio during glacial stages are possible causes higher glacial productivity in the cape basin record very likely reflects enhanced coastal up welling in response to increased wind speeds we suggest that higher productivity might have doubled the areal extent of suboxic sediments during the last glacial maximum however our calculations suggest low sensitivity of seawater cd concentrations to glacial doubling of the extent of reducing sediments the model suggests that during the last 250 kyr seawater cd concentrations fluctuated only slightly between high levels about 0 66 nmol kg 1 on glacial initiations and reaching lowest values about 0 57 nmol kg 1 during glacial maxima the estimated 5 lower cd content at the last glacial maximum relative to modern levels 0 60 nmol kg 1 cannot explain the discordance between cd and 13c such as observed in the southern ocean this low sensitivity is consistent with foraminiferal data suggesting minimal change in the glacial cd mean oceanic content

the nansen ridge arctic ocean some geophysical observations of the rift valley at slow spreading rate abstract we have examined continous echo soundings across the nansen rift valley and analysed the first gravity and bathymetric data available across the northern flank of the nansen ridge for comparison with other parts of the mid ocean ridge system the observed width of the inner floor 1 7 5 5 km at a total opening rate of 1 5 cm yr supports the idea of progressive narrowing of the inner floor with decreasing spreading rate for slow spreading ridges however the observed distance between the outer walls 18 22 km or rift valley width 30 33 km suggests that these parameters at least to a first approximation tend towards a minimum value with decreasing spreading rate the relation between gravity and bathymetry along the drift track of ice station fram i tentatively suggests that the sea floor topography of this part of the nansen ridge is supported by a plate with an elastic thickness less than what is observed on the mid atlantic ridge

diagenesis of oxyanions v u re and mo in pore waters and sediments from a continental margin this research tests the hypothesis that trace metals respond to the extent of reducing conditions in a predictable way we describe pore water and sediment measurements of iron fe manganese mn vanadium v uranium u rhenium re and molybdenum mo along a transect off washington state usa sediments become less reducing away from the continent and the stations have a range of oxygen penetration depths depth to unmeasurable o2 concentration varying from a few millimeters to five centi meters when oxygen penetrates 1 cm or less fe is reduced in the pore waters but reoxidized near the sediment water interface preventing a flux of fe 2 to overlying waters whereas mn oxides are reduced and mn 2 diffuses to overlying waters both re and u authigenically accumulate in sediments only at the most reducing location where the oxygen penetrates 0 3 cm below the sediment water interface does the surface 30 cm of sediments become reducing enough to authigenically accumulate mo stations in close proximity to the juan de fuca ridge crest are enriched in mn and fe from hydrothermal plume processes both v and mo clearly associate with mn cycling whereas u may be associating with either mn oxides and or fe oxyhydroxides rhenium is uncomplicated by adsorption to mn oxides and or fe oxyhydroxides and re accumulation in sediments appears to be due solely to the extent of reducing conditions therefore authigenic sediment re enrichment appears to be the best indicator for intermediate reducing conditions where oxygen penetrates less than 1 cm below the sediment water interface when coupled with negligible authigenic mo enrichment copyright 2005 elsevier ltd 1 introduction oceanic and atmospheric carbon cycles are strongly coupled with the ocean reservoir of dissolved inorganic carbon being 60 times larger than that of the atmosphere broecker and peng 1987 models that couple both ocean and atmosphere have been used to investigate why atmospheric carbon dioxide pco2 atm was reduced during the last glacial age and thus may be useful in predicting the environmental impact of future changes in pco2 atm some of these models require a large increase in organic carbon export through the more efficient use of nutrients to predict the lower pco2 atm observed during

hydrothermal sediments as a potential record of seawater nd isotope compositions the rainbow vent site 36 14 n mid atlantic ridge 1 geochemical compositions and sr and nd isotopes were measured in two cores collected 2 and 5 km from the rainbow hydrothermal vent site on the mid atlantic ridge overall the cores record enrichments in fe and other metals from hydrothermal fallout but sequential dissolution of the sediments allows discrimination between a leach phase easily leachable and a residue phase refractory the oxy anion and transition metal distribution combined with rare earth element ree patterns suggest that 1 the leach fraction is a mixture of biogenic carbonate and hydrothermal fe mn oxy hydroxide with no significant contribution from detrital material and 2 99 5 of the ree content of the leach fraction is of seawater origin in addition the leach fraction has an average 87sr 86sr ratio indistinguishable from modern seawater at 0 70916 although we lack the nd value of present day deep water at the rainbow vent site we believe that the ree budget of the leach fraction is predominantly of seawater origin we suggest therefore that the leach fraction provides a record of local seawater nd values nd isotope data from these cores span the period of 4 14 ka 14c ages and yield nd values for north east atlantic deep water neadw that are higher 9 3 to 11 1 than those observed in the nearby madeira abyssal plain from the same depth 12 4 0 9 this observation suggests that either the iceland scotland overflow water isow and lower deep water contributions to the formation of neadw are higher along the mid atlantic ridge than in the surrounding basins or that the relative proportion of isow was higher during this period than is observed today this study indicates that hydrothermal sediments have the potential to provide a higher resolution record of deep water nd values and hence deepwater circulation patterns in the oceans than is possible from other types of sediments

mapping lithofacies and pore fluid probabilities in a north sea reservoir seismic inversions and statistical rock physics reliably predicting lithologic and saturation heterogeneities is one of the key problems in reservoir characterization in this study we show how statistical rock physics techniques combined with seismic information can be used to classify reservoir lithologies and pore fluids one of the innovations was to use a seismic impedance attribute related to the vp vs ratio that incorporates far offset data but at the same time can be practically obtained using normal incidence inversion algorithms the methods were applied to a north sea turbidite system we incorporated well log measurements with calibration from core data to estimate the near offset and far offset reflectivity and impedance attributes multivariate probability distributions were estimated from the data to identify the attribute clusters and their separability for different facies and fluid saturations a training data was set up using monte carlo simulations based on the well log derived probability distributions fluid substitution by ga

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

a dual origin for the hydrothermal component in a metalliferous sediment core from the mid atlantic ridge a highly metalliferous sediment core collected from tag 26 n mid atlantic ridge has been analyzed for uranium series isotopes rare earth elements ree and radiogenic isotopes two types of deposition of hydrothermal material have been identified and characterized the first is sulfide material which has been rapidly deposited and is sometimes clearly turbiditic this material exhibits high u fe and eu sm ratios and low 230th fe and ree fe ratios it is proposed that u is incorporated into the sulfides by diffusion through the oxidized coating with reductive fixation near the sulfide oxide boundary the second hydrothermal component is particulate fallout from the neutrally buoyant plume which is diluted by the background pelagic sedimentation this component exhibits u fe ratios around 2 10 5 an order of magnitude greater than reported plume particulate levels but the 230th fe ree fe and eu sm ratios are similar to plume values nd and pb isotopes have been used to differentiate the hydrothermal and pelagic end members within this sediment core

evidence of recent volcanic activity on the ultraslow spreading gakkel ridge seafloor spreading is accommodated by volcanic and tectonic processes along the global mid ocean ridge system as spreading rate decreases the influence of volcanism also decreases and it is unknown whether significant volcanism occurs at all at ultraslow spreading rates 1 5 cm yr 1 here we present three dimensional sonar maps of the gakkel ridge earth s slowest spreading mid ocean ridge located in the arctic basin under the arctic ocean ice canopy we acquired this data using hull mounted sonars attached to a nuclear powered submarine the uss hawkbill sidescan data for the ultraslow spreading approximately 1 0 cm yr 1 eastern gakkel ridge depict two young volcanoes covering approximately 720 km2 of an otherwise heavily sedimented axial valley the western volcano coincides with the average location of epicentres for more than 250 teleseismic events detected in 1999 suggesting that an axial eruption was imaged shortly after its occurrence these findings demonstrate that eruptions along the ultraslow spreading gakkel ridge are focused at discrete locations and appear to be more voluminous and occur more frequently than was previously thought

co diagenesis of iron and phosphorus in hydrothermal sediments from the southern east pacific rise implications for the evaluation of paleoseawater phosphate concentrations abstract we present a detailed study of the co diagenesis of fe and p in hydrothermal plume fallout sediments from 19 s on the southern east pacific rise three distal sediment cores from 340 1130 km from the ridge crest collected during dsdp leg 92 were analysed for solid phase fe and p associations using sequential chemical extraction techniques the sediments at all sites are enriched in hydrothermal fe oxyhydr oxides but during diagenesis a large proportion of the primary ferrihydrite precipitates are transformed to the more stable mineral form of goethite and to a lesser extent to clay minerals resulting in the release to solution of scavenged p however a significant proportion of this p is retained within the sediment by incorporation into secondary goethite by precipitation as authigenic apatite and by readsorption to fe oxyhydr oxides molar p fe ratios for these sediments are significantly lower than those measured in plume particles from more northern localities along the southern east pacific rise and show a distinct downcore decrease to a depth of 12 m molar p fe ratios are then relatively constant to a depth of 35 m the fe and p speciation data indicate that diagenetic modification of the sediments is largely complete by a depth of 2 5 m and thus depth trends in molar p fe ratios can not solely be explained by losses of p from the sediment by diffusion to the overlying water column during early diagenesis instead these sediments are likely recording changes in dissolved p concentrations off the sepr possibly as a result of redistribution of nutrients in response to changes in oceanic circulation over the last 10 million years furthermore the relatively low molar p fe ratios observed throughout these sediments are not necessarily solely due to losses of scavenged p by diffusion to the overlying water column during diagenesis but may also reflect post depositional oxidation of pyrite originating from the volatile rich vents of the southern east pacific rise this study suggests that the molar p fe ratio of oxic fe rich sediments may serve as a proxy of relative changes in paleoseawater phosphate concentrations particularly if fe sulfide minerals are not an important component during transport and deposition

ferromanganese nodules from manop sites h s and r control of mineralogical and chemical composition by multiple accretionary processes abstract the chemical composition of ferromanganese nodules from the three nodule bearing manop sites in the pacific can be accounted for in a qualitative way by variable contributions of distinct accretionary processes these accretionary modes are 1 1 hydrogenous i e direct precipitation or accumulation of colloidal metal oxides in seawater 2 2 oxic diagenesis which refers to a variety of ferromanganese accretion processes occurring in oxic sediments and 3 3 suboxic diagenesis which results from reduction of mn 4 by oxidation of organic matter in the sediments geochemical evidence suggests processes 1 and 2 occur at all three manop nodule bearing sites and process 3 occurs only at the hemipelagic site h which underlies the relatively productive waters of the eastern tropical pacific a normative model quantitatively accounts for the variability observed in nearly all elements zn and na however are not well explained by the three end member model and we suggest that an additional accretionary process results in greater variability in the abundances of these elements variable contributions from the three accretionary processes result in distinct top bottom compositional differences at the three sites nodule tops from h are enriched in ni cu and zn instead of the more typical enrichments of these elements in nodule bottoms in addition elemental correlations typical of most pelagic nodules are reversed at site h the three accretionary processes result in distinct mineralogies hydrogenous precipitation produces mno2 oxic diagenesis however produces cu ni rich todorokite and suboxic diagenesis results in an unstable todorokite which transforms to a 7 a phase birnessite upon dehydration the presence of cu and ni as charge balancing cations influence the stability of the todorokite structure in the bottoms of h nodules which accrete dominantly by suboxic diagenesis na and possibly mn 2 provide much of the charge balance for the todorokite structure limited growth rate data for h nodules suggest suboxic accretion is the fastest of the three processes with rates at least 200 mm 106 yr oxic accretion is probably 10 times slower and hydrogenous 100 times slower since these rates predict more suboxic component in bulk nodules than is calculated by the normative analysis we propose that suboxic accretion is a non steady state process variations in surface water productivity cause pulses of particulate flux to the sea floor which result in transient mn reduction in the surface sediments and reprecipitation on nodule surfaces

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

hydrothermal plumes along the east pacific rise 8 40 to 11 50 n particle distribution and composition the discovery of a volcanic eruption at the 9 45 52 n site on the east pacific rise epr led us to investigate how the composition of suspended matter in hydrothermal plumes may be used to provide a better understanding of the relative age and vent fluid characteristics of a ridge crest system during surface ship surveys during the troughs tropical ridge observations of underwater geochemical hydrothermal signals expedition we collected hydrothermal plume particles along a 350 km section extending from approximately 8 40 n to 11 50 n of the epr north and south of the clipperton transform fault over the segment south of the clipperton transform fault the sfe ratio in the particles ranged from about 0 9 to 10 with the highest values immediately over the new vent field at the 9 45 52 n site these enrichments exactly coincide with the elevated 3he heat and ch4mn ratios in the plumes over the same vent field the s rich particles are primarily organic and may be related to the bacteria blizzard associated with the eruption in addition very high cufe and znfe ratios were observed in the hydrothermal plumes south of the clipperton transform fault these high ratios are indicative of the predominance of high temperature h2s rich vents between 9 35 n and 9 50 n in contrast the samples from the segment north of clipperton transform fault had sfe ratios which ranged from 0 04 to 0 82 typical of mature fe rich hydrothermal plumes these results suggest that the gas rich vent fluids at the 9 45 52 n site produced the sulfur enriched particles in the water column gas rich plumes and sulfur enriched plume particles were also observed underneath the 1986 megaplume on the juan de fuca ridge jdfr suggesting a similar mode of formation north of the clipperton transform fault the hydrothermal particles are dominated by fe rich oxyhydroxide particles characteristic of mature high temperature vent fields the plume maximum is centered at 11 08 n the fe oxyhydroxide particles scavenge ca si p v cr and as from seawater for p and v the mean element fe ratios in the epr hydrothermal particles are intermediate between jdfr and tag hydrothermal systems for as the mean element fe ratios of all three systems are about the same new evidence for si scavenging by hydrothermal fe oxyhydroxide particles indicates that this sink for dissolved si in the oceans is small

is avo the seismic signature of lithology a case history of ship shoal south addition many times we ve heard i ve tried amplitude versus offset avo and it doesn t work in my area before casting avo aside let s look at the process one more time avo analysis is actually a two step process the first step relates the seismic response cdp gather to the rock s velocity density and poisson s ratio the second step relates these rock properties to the lithologies sand shale etc

sediment in the black smoker area of the east pacific rise 18 5 s abstract a sediment profile perpendicular to the east pacific rise epr was investigated in an area in which massive sulfides have been observed along the axis of the epr a holocene to late pleistocene age is concluded for all of the up to 3 m long cores leading to sedimentation rates of 0 3 2 6 cm 1000 a the sediments are composed of hydrothermal precipitate calcareous tests and in traces hyaloclastic material the proportion of carbonate increases with increasing distance from the spreading center the hyaloclastic material is more or less weathered and is concentrated near the spreading center the hydrothermal component is composed mainly of iron and manganese hydroxides the proportion of hydrothermal matter in the sediment is higher near the axis of the epr also near the axis the elements b p cr and v are enriched in the hydrothermal component whereas mn zn cu fe and as are depleted the core profiles show a fluctuation in the proportion of hydrothermal material periods of higher hydrothermal input correlate with periods of the best calcite preservation diagenetic alteration of the sediment increases with increasing distance from the spreading center i e with decreasing sedimentation rate mo zr co ni rb th y ba la and ree are enriched in the sediment by diagenetic processes

hydrothermal scavenging at the mid atlantic ridge modification of trace element dissolved fluxes abstract we have carried out an icp ms study of the distributions of trace elements fe ca mg al mn cu zn v as cr co pb y mo ag sn cd and be in particulate material collected from the tag hydrothermal plume 26 n mid atlantic ridge to examine the extent to which fluxes of dissolved trace elements emitted from hydrothermal vent fluids are balanced by the precipitation of associated particulate phases comparison of particulate trace element distributions with particulate fe concentrations within the neutrally buoyant plume reveals that the distribution of trace elements within the plume is controlled by the following processes i co precipitation from vent fluids ii scavenging from seawater and iii preferential settling from the plume and oxidative dissolution within the water column for y and be continuous scavenging from seawater appears to be important whereas for v as and cr it appears that conditions suitable for uptake into particles may be restricted to the buoyant portion of the hydrothermal plume from a comparison of trace element fe ratios in the particles and associated mid atlantic ridge vent fluids it appears that for many elements e g cu co ag pb al cd be and zn the flux of dissolved material from vent fluids is matched closely by the precipitation of hydrothermal particulate phases of the various elements studied here hydrothermal activity only appears to act as a significant source for dissolved ca and dissolved mn

plume dispersed hydrothermal particles a time series record of settling flux from the endeavour ridge using moored sensors abstract settling particles collected with moored sediment traps near an area of active hydrothermal venting in the northeast pacific ocean provide information about the deep sea distribution of hydrothermal material results of an 8 day near field single trap experiment and a 340 day multi instrument 5 trap deployment two kilometers from the endeavour ridge vent field show variability in the quantity and composition of the plume to sediment particle flux over time with depth and with distance from the vent field hydrothermal elemental fluxes vary by a factor of two among the four sampling intervals of the longer experiment a factor of three variation in fe s among these periods reflects temporal changes in phase composition changes in flux with depth for example a 200 fold increase in cu and zn between above and below plume traps are evidence of hydrothermal input comparison of fluxes determined in the near and far field experiments reveals the spatial influence of vent effluent near field particle flux exceeds that measured two kilometers away by a factor of 10 to 20 and is relatively enriched in fe cu and organic carbon but depleted in mn calculations of the residence time of the plume with respect to settling indicate that more than 90 percent of the particulate material is transported farther than two kilometers from the vent field interpretation of elemental mineralogical and grain size analyses suggest that chemical precipitation kinetics other physical and biological particle forming processes changes in vent output and lateral transport of hydrothermal material by abyssal currents are tenable explanations for our observations our findings suggest that these rate interdependent processes be included in realistic models of hydrothermal particle flux

environmental controls on mid ocean ridge hydrothermal fluxes abstract high temperature hydrothermal fluxes at mid ocean ridges are thought to be an important component of oceanic biogeochemical cycles however little consideration has been given to how these fluxes vary as a consequence of changing environmental conditions over earth history here we consider how changes in sea level and ocean chemistry are likely to have impacted on axis high temperature hydrothermal fluxes focusing on phanerozoic conditions changes in sea level lead to changes in hydrostatic pressure near the base of hydrothermal systems where both peak fluid rock reaction temperatures and phase separation occur in general higher global sea level will lead to higher peak temperatures of fluid rock reaction additionally phase separation at higher pressure tends to lead to formation of a more cl rich vapor that constitutes a larger mass fraction of the system these combined factors may serve to significantly modify hydrothermal fluxes even for sea level changes on the scale of 100 m changes in ocean chemistry can also affect axial hydrothermal fluxes in several ways seawater sulfate contents control the amount of anhydrite that forms which has both physical porosity filling and chemical effects the most important aspect of ocean chemistry in controlling the composition of high temperature vent fluids may be ocean salinity if evaporite formation and dissolution has changed ocean salinity substantially over the phanerozoic hydrothermal fluxes could have been greatly modified ocean chemistry also plays a large role in controlling processes operating in hydrothermal plumes and hence the net flux of elements into and out of the ocean associated with hydrothermal systems we conclude that there is a need for substantial further work to quantify the effects of sea level and ocean chemistry on high temperature hydrothermal fluxes including the development of more robust models that integrate field laboratory and theoretical observations

hypoxia in the holocene baltic sea comparing modern versus past intervals using sedimentary trace metals abstract anthropogenic nutrient input has caused a rapid expansion of bottom water hypoxia in the baltic sea over the past century two earlier intervals of widespread hypoxia coinciding with the holocene thermal maximum htmhi 8 4 ka before present bp and the medieval climate anomaly mcahi 1200 750 years bp have been identified from baltic sea sediments here we present sediment records from two sites in the baltic sea and compare the trace metal as ba cd cu mo ni pb re sb tl u v zn enrichments during all three hypoxic intervals distinct differences are observed between the intervals and the various elements highlighting the much stronger perturbation of trace metal cycles during the modern hypoxic interval both mo and u show a strong correlation with corg and very high absolute concentrations indicative of frequently euxinic bottom waters during hypoxic intervals during the modern hypoxic interval modernhi comparatively less mo is sequestered relative to corg than in earlier intervals this suggests partial drawdown of the water column mo inventory in the modern water column due to persistent euxinia and only partial replenishment of mo through north sea inflows molybdenum contents in modern sediments are likely also affected by the recent slowdown in input of mo in association with deposition of fe and mn oxides strong enrichments of u in recent sediments confirm that the modernhi is more intense than past intervals these results suggest that u is a more reliable indicator for the intensity of bottom water deoxygenation in the baltic sea than mo sedimentary re enrichment commences under mildly reducing conditions but this element is not further enriched under more reducing conditions enrichments of v are relatively minor for the mcahi and modernhi possibly due to strong reservoir effects on v in the water column indicating that v is unreliable as an indicator for the intensity of bottom water hypoxia in this setting furthermore ba profiles are strongly influenced by post depositional remobilization throughout the holocene the strong relationship between corg and ni tl and particularly cu suggests that these trace metals can be used to reconstruct the corg flux into the sediments profiles of as sb and cd and especially pb and zn are strongly influenced by anthropogenic pollution

focal depths and mechanisms of large earthquakes on the arctic mid ocean ridge system as part of a global study of the source characteristics and tectonic implications of large earthquakes on mid ocean ridges we report on the focal depths and mechanisms of the six largest earthquakes that have occurred in the last 20 years on the arctic mid ocean ridge system for each earthquake we invert the long period p and sh waveforms to estimate the parameters of the best fitting point source including seismic moment centroid depth double couple source orientation and source time function three of the earthquakes occurred on the oceanic spreading center in the eurasian basin along ridge segments spreading at half rates of 4 6 mm yr these events have mechanisms very similar to those of ridge crest earthquakes on the mid atlantic ridge almost pure normal faulting on planes that dip at approximately 45 and strike parallel to the rift axis moments of 4 5 1024 dyn cm centroid depths of 1 2 km beneath the seafloor and water depths inferred from the predominant period of water column reverberations appropriate to epicentral locations within the median valley the remaining three earthquakes also characterized by normal faulting are associated with the continuation of the divergent plate boundary 2 3 mm yr half rate onto the continental shelf of the laptev sea where the crust becomes transitional in nature one of the largest known spreading center earthquakes august 25 1964 m0 1 1026 dyn cm occurred where the oceanic ridge intersects the outer edge of the continental slope waveform inversion for this event can resolve unilateral rupture from north to south landward along a fault at least 30 km in length the preferred centroid depth is 5 km beneath the seafloor in crustal material with an unusually low shear velocity but a centroid depth as great as 15 km cannot be ruled out two earthquakes beneath the continental shelf have significantly greater centroid depths 10 20 km than mid ocean ridge earthquakes indicating a thicker brittle regime and a cooler thermal structure than are typical of oceanic spreading centers the tectonic environment of these events is more representative of rifted continental lithosphere than of a mid ocean ridge

particle geochemistry in the rainbow hydrothermal plume mid atlantic ridge we report the analysis of 18 large volume 500 1500 l in situ filtered samples of particulate material from the largest hydrothermal plume on the mid atlantic ridge overlying the ultramafic hosted rainbow hydrothermal field at 36 deg 14 n measured particulate iron concentrations reach 614 nm high concentrations of particulate fe oxyhydroxides result from the extremely high fe concentration 24 mm and fe h2s ratio 24 of the vent fluids and persist to at least 10 km away from the vent site due to the advection of plume material with the ambient along axis flow two of the nine pairs of pump deployments appear to have intercepted the buoyant or otherwise very young portion of the hydrothermal plume these samples are characterized by anomalously compared to neutrally buoyant plume samples high concentrations of mg u and chalcophile elements and low concentrations of mn ca v y and the rare earth elements ree within the neutrally buoyant plume elemental distributions are largely consistent with previously observed behaviors preferential removal of chalcophile elements conservative behavior of oxyanions p v and u and continuous scavenging of y and the ree this consistency is particularly significant in light of the underlying differences in fluid chemistry between rainbow and other studied sites chalcophile elements are preferentially removed from the plume in the order cd zn co cu phosphorus iron and vanadium iron ratios for the neutrally buoyant plume are consistent with global trends with respect to the concentration of dissolved phosphate in ambient seawater comparison of buoyant and neutrally buoyant plume ratios with data from hydrothermal sediments underlying the rainbow plume cave et al 2002 indicates however that while p fe ratios are indeed constant v fe ratios increase progressively from early stage plume particles to sediments ree distributions in the buoyant and neutrally buoyant plume appear most consistent with a continuous scavenging process during dispersion through the water column

changes in fe oxidation rate in hydrothermal plumes as a potential driver of enhanced hydrothermal input to near ridge sediments during glacial terminations j t c and l a c were supported by the natural sciences and engineering research council of canada

uranium enrichment in metalliferous sediments from the mid atlantic ridge abstract previous studies of metal rich sediments at mid ocean ridge spreading centres have suggested that u fe ratios are relatively constant from site to site a suite of cores from the mid atlantic ridge has been analysed for u and fe content and most samples exhibit constant u fe ratios sulphide bearing parts of one core however contain excess u compared with that observed in other metalliferous sediments but apparently only during oxidative alteration of pyrite phases fission track registration has demonstrated that this excess u is intimately associated with sulphide grains in the sediment scanning electron microscope examination indicates that this u enrichment is limited to very small areas within the oxidation layer and is associated with an enhanced p concentration ion probe analyses allow semi quantitative analyses of various elements through a u rich grain the observed distribution of u coupled with its specific enrichment suggests that microbial mediation might be controlling this enrichment u fe ratios in fully oxidised tag sediments are constant and approximately an order of magnitude higher than in young plume particulates this discrepancy is attributed to a second type of post depositional u enrichment producing an homogeneous distribution of u throughout the sediment

composition and sedimentation of hydrothermal plume particles from north cleft segment juan de fuca ridge in 1990 and 1991 particles from buoyant and neutrally buoyant hydrothermal plumes above hydrothermal vents at the north cleft segment of the juan de fuca ridge were sampled to study their changing composition and fluxes away from the vent field in the rising buoyant plume 75 of the p v cr and as scavenging from seawater by hydrothermal precipitates occurs in the first 50 m above the vent cu and zn are most enriched in buoyant plume particles collected from the first few meters above the vent however the degree of enrichment decreases very rapidly with increased height above the vents due to sedimentation of the more dense cu and zn rich sulfide phases using the plume data coupled with the results of our analysis of sediment trap samples we estimated that more than 99 and 99 9 respectively of the total hydrothermal fe and mn produced at the vent field are transported beyond the vent field and dispersed in the open ocean

chemical controls on the composition of vent fluids at 13 11 n and 21 n east pacific rise six vent fields sampled at 13 11 n east pacific rise epr in may 1984 exhibit large interfield variations and a much wider range of chemical compositions than previously observed at 21 n measured ph at 25 c are acidic ranging from 3 1 to 3 7 sodium and chloride vary from 40 lower to 30 higher than seawater iron concentrations range from 2 to 10 mmol kg compared with 0 7 2 5 mmol kg at 21 n other sulfide forming metals cu zn cd and pb are generally lower at 11 13 n than at 21 n reliable temperature measurements were obtained at only two of the six vents and both were 350 5 c the vent fields at 21 n epr were resampled in august 1985 thus extending to almost 6 years the time period over which they have been monitored previous expeditions were made in november 1979 and november 1981 campbell et al this issue have shown that the chemistry of the hydrothermal fluids from these fields has been very stable over the period of repeated observation equilibrium calculations for the fluids from the fields at 13 n and 21 n using a greatly improved thermodynamic data base are described in this report they indicate that the chemistry is rock buffered and that the stability of these systems over time is a result of equilibrium control with respect to a greenschist type mineral assemblage at depth calculated high temperature ph of the fluids range from 4 1 to 4 7 with those from 13 11 n at the more acidic end of the range calculated affinities show that the fluids are close to or at saturation with respect to quartz albite muscovite smectite chlorite epidote and pyrrhotite the computations imply that lower temperature vents such as national geographic smoker ngs 273 c may have their silica concentrations controlled by equilibrium with respect to a phase other than quartz a comparison of fluid chemistry between ngs and vent 5 at 11 n suggests that the latter vent may also have a temperature 300 c while the fluid chemistry of a given field is compositionally stable the compositions themselves are unique for a particular field and cover a wide range between fields the processes controlling this variability probably include the depth of reaction i e pressure which is difficult to treat thermodynamically at present in addition increasing depth in the crust may be accompanied by decreasing permeability and hence a probable decrease in the water rock ratio it may be difficult to separate these two effects if the age differences between the fields at present unknown are of the order of decades then their temporal histories may have an important influence on their particular chemistries

distribution and composition of hydrothermal plume particles from the ashes vent field at axial volcano juan de fuca ridge in 1986 and 1987 buoyant and neutrally buoyant hydrothermal plume particles from the ashes vent field within axial volcano were sampled to study their variations in composition with height above the seafloor individual mineral phases were identified using standard x ray diffraction procedures elemental composition and particle morphologies were determined by x ray fluorescence spectrometry and scanning electron microscopy x ray energy spectrometry techniques the vent particles were primarily composed of sphalerite anhydrite pyrite pyrrhotite chalcopyrite barite hydrous iron oxides and amorphous silica grain size analyses of buoyant plume particles showed rapid particle growth in the first few centimeters above the vent orifice followed by differential sedimentation of the larger sulfide and sulfate minerals out of the buoyant plume the neutrally buoyant plume consisted of a lower plume which was highly enriched in fe s zn and cu and an upper plume which was highly enriched in fe and mn the upper plume was enriched in fe and mn oxyhydroxide particles and the lower plume was enriched in suspended sulfide particles in addition to the fe and mn oxyhydroxide particles the chemical data for the water column particles indicate that chemical scavenging and differential sedimentation processes are major factors controlling the composition of the dispersing hydrothermal particles short term sediment trap experiments indicate that the fallout from the ashes vent field is not as large as some of the other vent fields on the juan de fuca ridge

changes in sediment redox conditions following the bp dwh blowout event abstract following the blowout of the macondo well a pulse in sedimentation resulted in changes in sedimentary redox conditions this is demonstrated by downcore and temporal changes in the concentration of redox sensitive metals mn re and cd sediment cores collected in the ne gulf of mexico gom reveal increased sedimentation after the deepwater horizon dwh blowout the formation of mucous rich marine snow in surface waters and subsequent rapid deposition to underlying sediments is the likely cause respiration of this material resulted in decreased pore water oxygen concentration and a shoaled redoxcline resulting in two distinct mn peaks in sediments following the event one typically in the top 10 mm with the other at 20 30 mm most cores near the wellhead reveal this non steady state behavior for up to two years after the event associated with the mn minimum between the two mn peaks a modest 15 30 enrichment of re consistent with reducing sediments typically exists a three year time series of three stations following the event reveal that sediment re increased 3 4 times compared to the pre impact baseline value for two years indicating sediments are increasingly more reducing for two years in the third year re concentration decreased suggesting a return towards pre impact conditions in select sites where the density of benthic foraminifera was determined an assemblage wide decrease occurred coincident with reducing conditions as determined by redox sensitive metals demonstrating the important consequences of changing redox conditions on benthic ecosystems determination of redox sensitive metals will continue to constrain the temporal evolution of reducing conditions which will serve to document the long term effects of the spill and the possible return to pre event conditions

the scavenging of u 230th and 231pa during pulsed hydrothermal activity at 20 s east pacific rise abstract uranium th and pa isotopes were measured in eight box cores from two transects to the west of the east pacific rise at 10 s and 20 s sediment geochemistry al ca fe mn and water column paniculates mn suggest that highly metalliferous plumes rich in fe and mn are emanating from the rise crest at 19 s measurements of 230thxs and 231paxs indicate decreasing sediment accumulation rates from the rise flank 0 4 cm ky 1 to the tiki basin 0 23 cm ky 1 over this geographical area al is found to have a constant flux of 3 6 10 4 g cm 2 ky 1 application of an al constant flux model to ridge crest metalliferous sediment reveals two 1 000 year pulses of hydrothermal activity during the holoccne since 11 000 y bp these hydrothermal pulses are characterised by hydrothermal fe mn ratios 3 5 1 enhanced 230th and 231pa scavenging and low 230thxs 231paxs ratios 3 4 the similarity of the 230thxs and 231paxs ratio to the dissolved seawaterrauo suggests that in fracuonation of the isotopes occurs during scavenging supplementary supply of dissolved 230th and 231pa in a westwards moving water mass is suggested

dispersal patterns for hydrothermal plumes in the south pacific using manganese as a tracer abstract manganese profiles over the spreading axis of the east pacific rise epr between 22 15 s and 19 25 s disclose a series of plumes which are formed by buoyant emanations of hot hydrothermal vent fluids the plume ceilings or anomaly maxima can occur several hundred meters above the sea floor these plumes are dispersed laterally and are detectable as mid depth manganese anomalies 2000 km from the spreading axis along this section the plumes are dispersed mainly westward but at 30 s the plumes are advected eastward the asymmetrical dispersal pattern inferred from these data is coincident with the asymmetrical distribution of metalliferous sediments about the epr which suggests that plumes generated by high temperature venting play a dominant role in the formation of these sediments

sedimentary and crustal velocities in the norwegian greenland sea refraction and wide angle reflection velocities from the oceanic crust and the overlying sediments in the norwegian greenland sea have been analyzed there is a relatively rapid increase in velocity with depth in the uppermost sediments whereas a low constant gradient is representative of the main sediment sequence two regions the northeastern greenland sea and the oldest parts of the basins have particularly high velocity gradients 0 71 and 0 85 s 1 respectively the high gradient in the northeastern greenland sea is associated with the shear rifted margin off svalbard relatively high sea floor sediment sound velocities are typical of the norwegian greenland sea the crustal velocities fit the houtz ewing model which divides layer 2 into layers 2a 2b and 2c average velocities in the norwegian greenland sea are 3 88 2a 5 18 2b 6 05 2c 6 66 3 and 7 80 4 km s layer 2a is age dependent and has not been observed on crust older than 36 m y the model is not representative of the uppermost crust near the active spreading axis where one has to introduce additional layers or assume continuous velocity changes with depth

vanadium in foraminiferal calcite as a tracer for changes in the areal extent of reducing sediments we have used the vanadium concentration in cleaned foraminiferal calcite as a tracer of seawater v changes in the past since the benthic flux of vanadium is sensitive to the redox po tential of sediments changes in the vanadium concentration of seawater should be a reflection of changes that control the redox state of sediments v ca in g sacculifer from an eastern equatorial atlantic core eno66 17ggc is 21 6 2 8 nmol v mol ca this value does not change over 35 kyr indicating that there was no measurable change in seawater vanadium levels over this period potential artifacts from partial dissolution are not significant based on low constant values for foraminiferal fragmentation 6 7 in the top 50 cm of the core a minor correction to account for vanadium associated with mn carbonate overgrowths estimated from two caribbean cores where this mixed phase dominates the deeper v ca values has been applied changes in the areal extent of anoxic and suboxic sediments are thus constrained by this constant value and the standard deviation of the measurement 12 based on a mass balance for vanadium where suboxic sedi ments are a source and anoxic sediments are a sink to the ocean suboxic sediments are predicted to have changed by no more than 0 5 1 5 times the current value assuming no changein the areal extent of anoxic sediments this correspondsto 1 3 3 5 of total ocean sediments given a con stant area of suboxic sediments the areal extentof anoxic sediments didonot increase by more than fivefold or 1 5 of the ocean floor over th e past 35 kyr the significant reductions in deep water oxygen levels and consequent changes in sedimen t redox conditions required by polar nutrient de pletion scenarios are not reflected in the foraminiferal vanadium data over the past 35 kyr this suggests that models which call on less or no changes in deep water oxygen are more likely alternatives

history and geochemistry of a metalliferous sediment core from the mid atlantic ridge at 26 n fourteen thousand years of hydrothermal deposition are recorded in a metalliferous sediment core recovered from the trans atlantic geotraverse tag hydrothermal field on the mid atlantic ridge at 26 n an estimated 26 to 96 of the sediment at this core site is hydrothermally derived as determined from the caco3 al and fe data layers of essentially pure vent precipitates contain 3 caco3 and 0 5 al with high concentrations of fe 43 cu 4 1 zn 1 2 mn 1 1 v 480 ppm pb 175 ppm cd 32 ppm and hg 3 8 ppm sediment accumulation rates vary from 1 to 30 g cm2 1000 y throughout the core a function of the intensity of hydrothermal inputs distinct hydrothermal events are recorded at 6000 and 8500 y b p in layers containing 90 vent derived material vertical metal profiles and interelement relationships in the core result from variable deposition of oxides and sulfides oxidation and dissolution of sulfide phases and scavenging of metals from seawater

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

tracing low temperature fluid flow on ridge flanks with sedimentary uranium distribution the uranium content of sediments and pore fluids along a ridge axis to ridge flank transect perpendicular to the southern east pacific rise is used to assess the impact of low temperature fluid flow on u distribution two distinct regions are identified 1 a young crustal site 0 36 ma crust where significant solid phase u enrichments occur and 2 the ridge flank 1 9 4 6 ma crust with uniform u association with hydrothermal fe oxide phases in the solid phases upward advection and diffusion of cool u depleted basement fluids occurs at many coring sites at the 0 36 ma site the oxic basal fluids strip the plume derived sediment of the excess u effectively migrating the u upwards through the sediment into the overlying water column at the ridge flank sites the pore fluid advection rates are highest at bathymetric basement highs and advection velocities of up to 7 5 mm yr 1 are inferred from the pore fluid profiles these estimates are consistent with previous calculations based on fluoride pore fluid distributions the basal fluid u depletions are in the range 10 70 relative to seawater depending on temperature and redox state low temperature uptake of u during basalt alteration is a significant sink from seawater in the global seawater u budget 6 7 29 mmol yr 1 pore fluid u content is a sensitive tracer of extremely low temperature advection through ridge flank systems and the basal sediment u fe ratio is potentially a useful proxy for basement alteration history where low ratios indicate extensive oxic alteration of basal sediments during fluid flow

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

field and laboratory studies of metal uptake and release by hydrothermal precipitates data for suspended particles from hydrothermal plumes on the mid atlantic ridge mar support uptake of dissolved v and as during formation of fe oxides and release of cu and cd during alteration of sulfides to complement these field observations we carried out laboratory time series experiments to determine the stability of v as cu and cd in precipitates from hydrothermal plumes on the mar and juan de fuca ridge for v and as the metal fe ratio in plume particles remained uniform after sampling in contrast to v and as particulate cu and cd values decreased relative to fe over time in laboratory studies using both plume particles and mound derived sulfides the combined field and laboratory results show that scavenging is an important removal mechanism for seawater v and as whereas oxidative dissolution of hydrothermal precipitates in seawater adds cu and cd to the ocean

hydrothermal plume particles and dissolved phosphate over the superfast spreading southern east pacific rise abstract the distribution and elemental composition of hydrothermal plume particles were mapped along the superfast spreading southern east pacific rise from the garret transform fault to 19 s hydrographic and optical data were obtained using a series of seven tow yos and thirty vertical casts employing a rosette sampler with 19 l pvc bottles for collecting discrete samples of various dissolved and particulate hydrothermal species the extent of hydrothermal plume coverage over the southern east pacific rise between 13 33 and 18 40 s is significantly greater than in other ridgecrest systems the region south of 17 20 s is characterized by significant enrichments of volatile gases resulting from magmatic input of fresh lava at the seafloor between 17 20 and 18 40 s the ratio of s fe in the plume particles is highly correlated with the dissolved gases in the neutrally buoyant hydrothermal plumes plume inventories of fe and s over this portion of the southern east pacific rise are 6 150 times higher than what has been observed over other vent fields because the total abundance of plumes is much greater in addition significant depletions 100 nmol l of dissolved phosphate over the ridge axis were observed at the depth of the hydrothermal plumes these results provide clear evidence that this section of the southern east pacific rise maintains the most extensive complex of hydrothermal plumes observed thus far on the global ridgecrest system

hydrothermal sediments record changes in deep water oxygen content in the se pacific the distribution of redox sensitive metals in sediments is potentially a proxy for past ocean ventilation and productivity but deconvolving these two major controls has proved difficult to date here we present a 740 kyr long record of trace element concentrations from an archived sediment core collected at 15 s on the western flank of the east pacific rise epr on 1 1 myr old crust and underlying the largest known hydrothermal plume in the world ocean the downcore trace element distribution is controlled by a variable diagenetic overprint of the inferred primary hydrothermal plume input two main diagenetic processes are operating at this site redox cycling of transition metals and ferrihydrite to goethite transition during aging the depth of oxidation in these sediments is controlled by fluctuations in the relative balance of bottom water oxygen and electron donor input organic matter and hydrothermal sulfides these fluctuations induce apparent variations in the accumulation of redox sensitive species with time subsurface u and p peaks in glacial age sediments in this and other published data sets along the southern epr indicate that basin wide changes in deep ocean ventilation in particular at glacial interglacial terminations ii iii iv and v alter the depth of the oxidation front in the sediments these basin wide changes in the deep pacific have significant implications for carbon partitioning in the ocean atmosphere system and the distribution of redox sensitive metals in ridge crest sediment can be used to reconstruct past ocean conditions at abyssal depths in the absence of alternative proxy records

hydrothermal scavenging on the juan de fuca ridge 23othxs 10be and rees in ridge flank sediments abstract we have investigated the geochemistry of a hydrothermally enriched sediment core recovered from the western flank of the n cleft segment juan de fuca ridge 8km west of the megaplume area previously identified near 45 n the core contains varying biogenic lithogenic and hydrothermal components as reflected in caco3 al and fe contents respectively horizons of pronounced hydrothermal input in core top sediments and at depth exhibit increased concentrations of fe cu zn and pb and shifts in pb isotopic compositions toward nonradiogenic morb hydrothermal values ree concentrations co vary with hydrothermal fe down core and shale normalised ree distribution patterns exhibit both negative ce anomalies and positive eu anomalies indicative of input from plume particle fall out unsupported 230thxs activities down core are consistent with continuous slow sediment accumulation rates of 0 54 cm ky for 200 ky since the deposition of the deeper fe rich horizon 10be 0 and 9be isotope concentrations also co vary with hydrothermal fe down core and exhibit 10 be o 9 be ratios which approach that of pacific ocean deep water indicative of a seawater scavenging source 10 be 0 230 oth xs 0 ratios throughout most of core gc88 6 are greater than mean pacific ocean values indicating that hydrothermal scavenging can lead to significant net removal of dissolved 10be into ridge flank sediments

spinifex basalts with komatiite tholeiite trend from the nansen gakkel ridge arctic ocean abstract during cruise ark iv 3 with rv polarstern 1987 volcanic rocks were recovered from the nansen gakkel ridge ngr a slow spreading half rate approximately 0 5 cm ridge with an axial depth of more than 5000 m the ngr is one of the slowest and deepest mid ocean ridges so far known and calculations based on the distance of sampling location from the axial valley yielded ages of approximately 600 ka for the rocks investigated here according to petrographic and geochemical results i e spinifex textures mg 70 and mgo 9 wt the volcanics are termed komatiitic basalts dark spherical droplets of basanitic composition within the komatiitic basalts are believed to be relicts of an incomplete magma mixing whose basanitic end member could well account for the enriched character of the ngr basalts in terms of rare earth elements ti and incompatible trace elements based on nd isotope as well as high sm nd ratios mantle metasomatism i e veined mantle model could be responsible for the enrichment of incompatible trace elements in the source region of komatiitic basalts of the ngr

sensitivity of the phosphate cadmium carbon isotope relation in the ocean to cadmium removal by suboxic sediments reconstructions of past deep ocean nutrient concentrations rely largely on the carbon isotopic composition and cadmium content of shells of benthic foraminifera when comparing records of these two paleonutrient tracers a relation similar to the phosphate cadmium carbon isotope relation in the water column today is generally assumed we present new water column sediment and pore water data from the california continental margin which demonstrate that cd accumulation is enhanced in suboxic sediments these results suggest that the oceanic cd inventory is sensitive to changes in the areal extent and redox intensity of suboxic sediments and thus that the phosphate cadmium relation in the ocean could have been different in the past the magnitude of this effect and its evolution through time is presently hard to quantify because the oceanic cd budget is poorly constrained

the geochemical cycle of rhenium a reconnaissance rhenium re is one of a suite of elements including uranium and molybdenum that display conservative behavior in seawater and are enriched in anoxic sediments the decay of187re to187os provides a geochronometer in ancient sedimentary rocks and gives rise to os isotopic variations in nature in order to better characterize its sources to seawater re was measured in three major rivers amazon orinoco ganges brahmaputra and some of their tributaries re concentrations span four orders of magnitude from 0 02 to 400 pmol kg with the highest concentrations found in rivers draining black shales in the venezuelan andes mainstream re levels in the three rivers are between 1 and 10 pmol kg with a flux weighted average of 2 3 pmol kg the residence time for re in the oceans is estimated to be 750 000 yr with respect to river inputs re profiles from the atlantic and pacific oceans confirm that re behaves conservatively in seawater with no significant uptake onto particles and or recycling within the water column this is also true in the anoxic water column of the black sea re removal into anoxic sediments occurs at or below the sediment water interface as demonstrated in sediment pore waters from chesapeake bay in oxic sediments re is not cycled with manganese oxides and it is not enriched in very slowly accumulating pelagic sediments with a large hydrogenous iron and manganese component or in manganese nodules burial of re in anoxic sediments which accumulate on 0 3 of the ocean floor removes approximately 50 of the riverine re flux to the oceans hence oceanic re concentrations may be very sensitive to changes in the area of anoxic sedimentation

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

chemical transport to the seafloor of the equatorial pacific ocean across a latitudinal transect at 135 w tracking sedimentary major trace and rare earth element fluxes at the equator and the intertropical convergence zone we have analyzed the major trace and rare earth element composition of surface sediments collected from a transect across the equator at 135 w longitude in the pacific ocean comparing the behavior of this suite of elements to the caco3 opal and corg fluxes which record sharp maxima at the equator previously documented at the same sampling stations enables us to assess the relative significance of the various pathways by which trace elements are transported to the equatorial pacific seafloor the 1 1 high biogenic source at the equator associated with equatorial divergence of surface water and upwelling of nutrient rich water and 2 2 high aluminosilicate flux at 4 n associated with increased terrigenous input from elevated rainfall at the intertropical convergence zone itcz of the tradewinds are the two most important fluxes with which elemental transport is affiliated the biogenic flux at the equator transports ca and sr structurally bound to carbonate tests and mn primarily as an adsorbed component trace elements such as cr as pb and the rees are also influenced by the biogenic flux at the equator although this affiliation is not regionally dominant normative calculations suggest that extremely large fluxes of ba and p at the equator are carried by only small proportions of barite and apatite phases the high terrigenous flux at the itcz has a profound effect on chemical transport to the seafloor with elemental fluxes increasing tremendously and in parallel with ti normative calculations however indicate that these fluxes are far in excess of what can be supplied by lattice bound terrigenous phases the accumulation of ba is greater than is affiliated with biogenic transport at the equator while the p flux at the itcz is only 10 less than at the equator this challenges the common view that ba and p are essentially exclusively associated with biogenic fluxes many other elements including mn pb as and rees also record greater accumulation beneath the itcz than at the equator thus adsorptive scavenging by terrigenous paniculate matter or phases intimately associated with them appears to be an extremely important process regulating elemental transport to the equatorial pacific seafloor these findings emphasize the role of vertical transport to the sediment and provide additional constraints on the paleochemical use of trace elements to track biogenic and terrigenous fluxes