seasonal cycles of particle and solute transport processes in nearshore sediments 222rn226ra and 234th238u disequilibrium at a site in buzzards bay ma radiochemical measurements leading to the estimation of particle mixing rates and irrigation rates in the sediments of a site in buzzards bay massachusetts have been made over two nearly full seasonal cycles both particle mixing and sediment irrigation show significant seasonal variability at this site the variability is consistent with biologically driven transport mechanisms 234th238u disequilibrium measurements were used to estimate particle mixing rates based on three cores taken from december through march and four taken from june through october a cold season average mixing rate of 5 6 cm2 yr and a warm season average rate of 17 cm2 yr were found excess 234th inventories in the upper 5 cm of the sediments also varied seasonally with a cold season average value of 1 8 dpm cm2 significantly less than both the warm season value of 3 4 dpm cm2 and the predicted average value for buzzards bay 3 dpm cm2 222rn226ra disequilibrium in sediment pore waters was used to estimate sediment irrigation based on a total of seven cores three seasonal groupings of results were made 1 december through march when 222rn deficits could be explained by vertical molecular diffusion alone 2 early summer june when irrigation was important to at least 20 cm the maximum depth of the sampled region and 3 early fall when irrigation was important to about 10 cm a nonlocal exchange vertical molecular diffusion model emersonet al 1984 was used to obtain quantitative estimates of irrigation rates when the exchange parameter was allowed to vary exponentially with depth below the sediment water interface model rn deficit profiles fit measured profiles quite well

a tidal model for eastern juan de fuca strait and the southern strait of georgia a three dimensional barotropic finite element model is used to calculate the tidal flows in eastern juan de fuca strait and the southern strait of georgia the harmonics of eight constituents are computed and compared with those from previous finite difference models and those from historical tide gauge and current meter observations root mean square differences between observed and calculated sea level amplitudes are within 2 0 cm for all constituents and the phases are within 4 0 for all constituents except k2 horizontal currents from the model are found to reproduce the observed vertical variations in shear except in regions where stratification effects and internal tides exist in particular the model representation of currents at six stations in the canadian tide and current tables volume 5 is accurate the pattern of tidal residual currents has much more detail than previous coarser resolution models and numerous eddies are predicted computed energy flux fields reveal that over a 29 day period only 38 of the tidal power entering juan de fuca strait is transmitted into the southern strait of georgia and of the 39 entering haro strait 36 is dissipated within the strait itself

the seafloor as the ultimate sediment trap using sediment properties to constrain benthic pelagic exchange processes at the goban spur the benthic diagenetic model omexdia has been used to reproduce observed benthic pore water and solid phase profiles obtained during the omex study in the goban spur area n e atlantic and to dynamically model benthic profiles at site omex iii 3660 m depth with the sediment trap organic flux as external forcing the results of the dynamic modelling show that the organic flux as determined from the lowermost sediment trap 400 metres above the bottom at omex iii is insufficient to explain the organic carbon and pore water profiles the best fitting was obtained by maintaining the seasonal pattern as observed in the traps while multiplying the absolute values of the flux by a factor of 1 85 the inverse modelling of diagenetic processes resulted in estimates of total mineralisation rate and of degradability of the organic matter at the different stations these diagenetic model based estimates are used to constrain the patterns of lateral and vertical transports of organic matter using the observed degradability as a function of depth we show that the observed organic matter fluxes at the different depths are consistent with a model where at all stations along the gradient the same vertical export flux occurs at 200 m and where organic matter sinks with a constant sinking rate of around 130 m d 1 if sinking rates were higher in the order of 200 m d 1 the observations could be consistent with an off slope gradient in export production of approximately a factor of 1 5 between the shallowest and deepest sites the derived high degradability of the arriving organic matter and the consistency of the mass fluxes at the different stations exclude the possibility of a massive deposition on the margin of organic matter produced on the shelf or shelf break however other hypotheses to explain the patterns found in the sediment trap data of both omex and other continental margin study sites also suffer from different inconsistencies further close examination of the flow patterns at the margin will be needed to examine the question

benthic metazoan biomass community structure and bioturbation at three contrasting deep water sites on the northwest european continental margin size structure taxonomic composition and bioturbation potential of benthic metazoan communities were examined at three contrasting sites on the northwest european continental margin as part of a wider study of biogeochemical cycling in the deep sea benthic boundary layer sampling was conducted in the hatton rockall basin 1100 m depth on the north feni ridge 1920 m and in the south rockall trough 3580 m on two cruises bracketing the expected 1998 spring phytodetrital flux density and biomass of epibenthic megafauna declined with depth and were consistent with previous data from the deep northeast atlantic aggregations of the hexactinellid sponge pheronema carpenteri occurred at 1100 m the percentage contribution of suspension feeders to megafaunal biomass at the lower slope sites was much higher than expected for these depths macrofauna sensu stricto were consistently undersampled by a box corer relative to an hydraulically damped multiple corer estimated macrofaunal densities declined with depth polychaete trophic group structure was very different at the three sites with more small carnivores at 1100 m surface deposit and interface feeders at 1920 m and a higher representation of subsurface deposit feeders at 3580 m meiofaunal densities were low in comparison with published data from comparable depths in the northeast atlantic meiofaunal numbers increased at all three sites from may to july 1998 the increase at 1920 m was statistically significant and was associated with the greatest phytodetrital accumulation observed during the study period the relative contribution of the mega macro and meiofauna to benthic metazoan biomass did not vary consistently with depth and no trend was apparent in a review of data from other studies in the north atlantic depth related patterns in community size structure recorded from previous north atlantic studies were not all replicated suggesting the importance of local hydrodynamics and other environmental factors there was no obvious link between faunal parameters and biodiffusion coefficients or mixing modes estimated from radiotracer profiles diffusion analogue 210pbexcess profiles recorded at 3580 and 1100 m resulted from a combination of macrofaunal and megafaunal sediment mixing some of it advective at 1920 m a combination of deep megafaunal subduction and near surface concentration of macrofaunal feeding activity produced subsurface radiotracer peaks the poorly known burrowing megafauna probably play a significant role in bioturbation at all three sites

evidence from early proterozoic anhydrite for sulphur isotopic partitioning in precambrian oceans relative to meteoritic sulphur sulphur in the contemporary exogenic cycle is marked by a depletion of 34s in biogenic sulphide that is balanced by excess 34s in sulphate of the oceans and evaporites1 2 the onset of this isotopic partitioning during the precambrian required sulphate in the ocean in sufficient concentration to permit significant isotopic fractionation during biogenic reduction3 4 and the evolution of sulphate reducing bacteria5 7 the conclusion that partitioning existed at 2 300 myr has been derived from strongly 34s depleted sedimentary sulphide of this age from south africa4 i report here on 34s enriched stratiform nodular anhydrite of similar age from canada which supports partitioning at this time strontium isotope data on these samples indicate that the anhydrite was derived from continental brines possibly in the inland portion of a continental sabkha this requires that the reported enrichment in 34s be considered a minimum for seawater sulphate at 2 300 myr

petrological and stable isotope studies of carbonate and sulfide minerals from the gunflint formation ontario evidence for the origin of early proterozoic iron formation abstract the 1 9 ga gunflint formation in the thunder bay district of ontario principally comprises iron formation overlain by an iron poor limestone dolostone member the upper limestone member rocks are virtually unmetamorphosed retaining primary textures except locally around diabase sills the gunflint presents an opportunity to study both unmetamorphosed and metamorphosed iron formation and to study the changes from iron rich to iron poor sedimentation of the carbonate minerals in iron rich units siderite formed at or near the sediment water interface with ankerite and calcite forming later during diagenesis and during metamorphism around sills heaviest 13c values of siderite and of dolomite in the upper limestone member are consistently near 0 throughout the stratigraphic section indicating that marine bicarbonate was the source of carbon a spread of values between 0 and 7 for unmetamorphosed rocks is the result of the incorporation of oxidized organic matter during diagenesis whereas 13c values more negative than 7 are the result of metamorphism the heaviest 18o values from unmetamorphosed rocks 5 3 pdb for siderite 6 1 for ankerite and 6 7 for calcite are considered to represent the original marine composition lighter values to 17 represent isotopic exchange reactions with pore fluids at higher temperatures and or isotopic exchange with 18o depleted meteoric water low s c ratios and a relatively narrow range of positive 34s values in pyrite throughout most of the formation are consistent with bacterial sulphate reduction of seawater containing sulphate at a significantly lower concentration than the modern ocean locally higher sulfide contents and a wider range of 34s values were the product of the introduction of sulfur after deposition it is proposed that the gunflint formation was deposited in a stratified water column with anoxic bottom water the depositional basin had restricted communication with the open ocean and was affected by distal volcanism hydrothermal activity associated with the volcanism provided a large source of dissolved iron and possibly silica which helped buffer o2 and sulphate in water to low levels low concentrations of sulphate limited the generation of h2s that would otherwise have restricted the solubility of iron during periods of increased hydrothermal activity the anoxic oxic water boundary moved upwards permitting transport of iron to the shallow shelf where it was precipitated as siderite iron hydroxides iron silicates or pyrite depending on physico chemical conditions the transition to the overlying limestone marks a decrease in hydrothermal activity with a contraction of the redox boundary

metallogenesis of an early proterozoic foreland sequence eastern hudson bay canada on the e side of hudson bay the nw margin of the archaean superior structural province is overlain by an unmetamorphosed little deformed early proterozoic supracrustal sequence the sequence is divisible into three parts possible tectosomes each characterized by a distinct style of mineralization the arkosic alluvial richmond gulf group was shed eastward from a thermal uplift and has been preserved only in a later aulacogen the richmond gulf graben it contains an apatite cemented redbed secondly a widespread post aulacogen carbonate rich w facing miogeocline blanketed the region a pyritic zone developed at its basal contact is particularly thick and hosts disseminated copper mineralization where formed on the arkose in the graben a pyritic brecciated stromatolite rich horizon within the carbonate contains galena and sphalerite thirdly widespread iron formation and a local 60 cm thick manganese carbonate bed overlying w derived basalt flows flysch and arkosic molasse all of uncertain tectonic affinity terminate the sequence

lateral dispersion over the continental shelf analysis of dye release experiments lateral dispersion over the continental shelf was examined using dye studies performed as a part of the coastal mixing and optics experiment four experiments performed at intermediate depths each lasting 2 5 5 days were examined in some cases the dye patches remained fairly homogeneous both vertically and horizontally throughout an experiment in other cases significant patchiness was observed on scales ranging from 2 to 10 m vertically and a few hundred meters to a few kilometers horizontally the observations showed that the dye distributions were significantly influenced by shearing and straining on scales of 5 10 m in the vertical and 1 10 km in the horizontal superimposed on these larger scale distortions were simultaneous increases in the horizontal second moments of the dye patches with corresponding horizontal diffusivities based on a fickian diffusion model of 0 3 4 9 m 2 s 1 analysis of the dye data in concert with shear estimates from shipboard acoustic doppler current profiler observations showed that the existing paradigms of shear dispersion and dispersion by interleaving water masses cannot account for the observed diffusive spreading of the dye patches this result suggests that some other mechanisms provided an additional diffusivity of order 0 2 4 6 m 2 s 1 an alternative mechanism dispersion by vortical motions caused by the relaxation of diapycnal mixing events may explain the observed dispersion in some cases

the role of the benthic biota in sedimentary metabolism and sediment water exchange processes in the goban spur area ne atlantic we provide an overview of the role of biological processes in the benthic boundary layer bbl and in sediments on the cycling of particulate organic material in the goban spur area northeast atlantic the benthic fauna sediment and bbl characteristics were studied along a transect ranging from 208 to 4460 m water depth in different seasons over 3 years near bottom flow velocities are high at the upper part of the slope 1000 1500 m and high numbers of filter feeding taxa are found there such that organic carbon normally passing this area during high flow conditions is probably trapped accumulated and or remineralised by the fauna overall metabolism in shelf and upper slope sediments is dominated by the macrofauna more than half of the organic matter flux is respired by macrofauna with a lower contribution of metazoan meiofauna 4 and anoxic and suboxic bacterial mineralisation 21 the remainder 23 being channelled through nanobiota and oxic bacteria by its feeding activity and movement the macrofauna intensely reworks the sediments on the shelf and upper slope mixing intensity of bulk sediment and of organic matter are of comparable magnitude the benthos of the lower slope and abyssal depth is dominated by the microbiota both in terms of total biomass 90 and carbon respiration about 80 the macrofauna 16 meiofauna 4 and megafauna 0 5 only marginally contribute to total carbon respiration at depths below 1400 m because large animals have a lower share in total metabolism mixing of organic matter within the sediments is reduced by a factor of 5 whereas mixing of bulk sediment is one to two orders of magnitude lower than on the shelf the food quality of organic matter in the sediments in the shallowest part of the goban spur transect is significantly higher than in sediments in the deeper parts the residence time of mineralisable carbon is about 120 d on the shelf and compares well with the residence time of the biota in the deepest station the mean residence time of mineralisable carbon is more than 3000 d an order of magnitude higher than that of biotic biomass

modern deep sea benthic foraminifera a brief review of their morphology based biodiversity and trophic diversity most fossil deep sea foraminifera are multichambered and have relatively robust calcareous or agglutinated shells modern assemblages on the other hand include many fragile monothalamous single chambered forms and komokiaceans a superfamily of protist currently placed within the foraminifera with soft test walls these groups are poorly known and most of the hundreds of morphospecies recognized in deep sea samples are undescribed the relative abundance of robust and fragile taxa varies with water depth and food supply calcareous and other hard shelled species tend to predominate in relatively eutrophic areas particularly on continental margins but decrease as a proportion of the entire live fauna i e including soft shelled species with increasing water depth even above the ccd carbonate compensation depth most of the species on which the foraminiferal proxies used in palaeoceanography are based live in these bathyal regions at abyssal depths and particularly below the ccd faunas are largely agglutinated and dominated by monothalamous forms these assemblages have a much lower fossilization potential than those found on continental margins in addition to carbonate dissolution these patterns probably reflect adaptations to increasingly oligotrophic conditions on the ocean floor with increasing depth and distance from land bathyal species include herbivores and opportunistic deposit feeders omnivores that consume labile organic material in addition to deep infaunal deposit feeders and must contribute significantly to carbon cycling many abyssal monothalamous foraminifera in constrast accumulate stercomata waste pellets composed of fine sediment particles and probably ingest sediment associated bacteria and more refractory organic matter some monothalamous species without stercomata may be bacteriovores although they probably process organic carbon at a slower rate than calcareous species the shear abundance of monothalamous taxa at abyssal depths suggests that they are important in carbon cycling on a global scale the loss of a substantial proportion of foraminiferal biomass and biodiversity from the fossil record should be considered when using foraminifera to reconstruct palaeoproductivity for example by using the benthic foraminiferal accummulation rate bfar different dietary preferences among calcareous species have implications for the stable carbon isotope signal preserved in their shell

nitrogen cycling in deep sea sediments of the porcupine abyssal plain ne atlantic rates of transformation recycling and burial of nitrogen and their temporal and spatial variability were investigated in deep sea sediments of the porcupine abyssal plain pap ne atlantic during eight cruises from 1996 to 2000 benthic fluxes of ammonium nh4 and nitrate no3 were measured in situ using a benthic lander fluxes of dissolved organic nitrogen don and denitrification rates were calculated from pore water profiles of don and no3 respectively burial of nitrogen was calculated from down core profiles of nitrogen in the solid phase together with 14c based sediment accumulation rates and dry bulk density average nh4 and no3 effluxes were 7 4 19 mu mol m 2 d 1 n 7 and 52 30 mu mol m 2 d 1 n 14 respectively during the period 1996 2000 during the same period the don flux was 11 5 6 mu mol m 2 d 1 n 5 and the denitrification rate was 5 1 3 0 mu mol m 2 d 1 n 22 temporal and spatial variations were only found in the benthic no3 fluxes the average burial rate was 4 6 0 9 mu mol m 2 d 1 on average over the sampling period the recycling efficiency of the pon input to the sediment was 94 and the burial efficiency hence 6 the don flux constituted 14 of the nitrogen recycled and it was of similar magnitude as the sum of burial and denitrification by assuming the pap is representative of all deep sea areas rates of denitrification burial and don efflux were extrapolated to the total area of the deep sea floor 2000 m and integrated values of denitrification and burial of 8 5 and 7 1 tg n year 1 respectively were obtained this value of total deep sea sediment denitrification corresponds to 3 12 of the global ocean benthic denitrification burial in deep sea sediments makes up at least 25 of the global ocean nitrogen burial the integrated don flux from the deep sea floor is comparable in magnitude to a reported global riverine input of don suggesting that deep sea sediments constitute an important source of don to the world ocean

dissolved organic matter in abyssal sediments core recovery artifacts we report measurements of pore water dissolved organic carbon doc dissolved organic nitrogen total dissolved carbohydrates dissolved free monosaccharides and ammonium in recovered deep sea sediments from the porcupine abyssal plain pap northeast atlantic there were distinct maxima close to the sediment water interface of these constituents at all times of the year the very high diffusive effluxes calculated from these porewater distributions were not compatible with simultaneous sediment trap measurements of particulate organic carbon nitrogen and carbohydrate fluxes toward the seafloor effluxes calculated from pore water doc distributions in recovered cores from another atlantic deep sea site showing almost identical maxima as those at pap were more than an order of magnitude greater than simultaneous in situ chamber doc flux measurements we suggest that the dissolved organic matter maxima are predominantly artifacts induced by lysis of or leakage from mainly bacterial biomass resulting from decompression and or warming during recovery of the sediment cores from the abyssal seafloor temperature elevation during core recovery from the abyss gives a n2 saturation of about 150 and the combined effect of warming and decompression results in a co2 saturation of about 135 which together plausibly are associated with bubble formation creating cell bursting previous estimates of microbial biomass in abyssal sediments may be underestimates because of the difficulty of counting lysed bacterial cells since exoenzymes are inducible previous measurements of their activities in recovered abyssal sediments may be overestimates

2000 ma sulphide concretions from the productive formation of the pechenga greenstone belt nw russia genetic history based on morphological and isotopic evidence abstract two hundred and fifty nine sulphide samples from black shales of the productive formation belonging to the palaeoproterozoic 2000 ma petsamo supergroup in the kola region nw russia have been analysed for their sulphur isotope ratio the sulphide bearing black shales were formed in a non euxinic basin within an oceanic rift environment the rocks have undergone greenschist facies metamorphism the black shales are marked by very high s corg ratios and a strong positive correlation between corg and s r 0 70 with zero intercept on the sulphur axis different generations of sulphide concretions have been distinguished by means of concretional analysis individual isotope study of synsedimentary sulphide layers and sulphides from early middle and late diagenetic catagenetic sulphide concretions yields trends which suggest bacterial sulphate reduction as the concretion forming process the overall spread of 34 s from 8 3 to 24 9 indicates 34 s sulphate sulphide between 29 and 4 given a seawater sulphate at around 21 the first order trend is a progressive enrichment in 34 s with increase of burial two major populations of sulphides have been distinguished the first concretions and perhaps thin layers formed in an open system with respect to seawater sulphate and has a limited 34 s range of 2 7 to 3 8 this is coupled with extensive formation of diagenetic carbonate beds marked by 13 c of 8 7 to 12 5 the second population lenses thin layers concretions and microconcretions in carbonate nodules formed in a closed system and is characterized by a high fe2 s2 ratio and progressive development of a rayleigh distillation process which drove 34 s from 8 3 up to 24 9 the high fe2 s2 and possibly change in ph parameter resulted in pyrrhotite rather than in pyrite associated abundant carbonate nodules have 13 c in the range 8 2 to 14 1 overall low 34 s sulphate sulphide and the high s corg ratio are consistent with one stage bacterial sulphate reduction in a non euxinic basin the observed 34 s sulphate sulphide of 29 as maximum is within the pure sulphate reducing bacteria range of 4 46 advanced isotopic modification involving the oxidative part of the sulphur cycle has not been detected based on the data available one can not exclude the presence of a third population of sulphides thin massive layers with 34 s from 2 5 to 0 3 which might have inorganic origin and formed from an exhalative source

geochemical and biological recovery of the disturbed seafloor in polymetallic nodule fields of the clipperton clarion fracture zone ccfz at 5 000 m depth environmental data were obtained on the nodule fields of the clipperton clarion fracture zone at 5 000 m depth in june 2004 during the nodinaut cruise the long term effects of physical disturbance made by a dredge 26 yr ago on the sediment were investigated we focused our study on its track which is still visible on the bottom the first major consequence of the passage of this equipment was to remove 4 cm 6 0 5 cm of superficial sediment the physical and chemical properties of this disturbed sediment sampled in the track did not change significantly over time and has not shown any recovery since the disturbance however an exception was observed for depth variations of manganese concentration in the sediment which were similar in the track to those in the surrounding undisturbed sediment and can be explained by the diffusion over time of oxygen from the sea water on the other hand the biological activity measured in the track with the respirometer rap2 carried by the submersible nautile did not differ from the unperturbed site which suggests that the benthic fauna has completely recovered as have nutrient fluxes at the water sediment interface

is burial velocity a master parameter for bioturbation abstract the intensity of biological mixing in a marine sediment is widely believed to be related to the flux of labile organic matter at the same time this flux has been shown to be strongly correlated to the burial velocity one would then expect a significant correlation between biological mixing coefficient d b and burial velocity a nonlinear regression of existing data with a power law eqns 2 and 3 of the text produces a statistically significant correlation the statistical significance of the regression in no way implies causation and in fact it accounts for only about 22 of the total variance in the dataset thus reducing its physical significance a number of additional processes contribute to the large observed variance including timing of mixing events temporal and spatial heterogeneity differences in temporal scales sampling artifacts and specific particle associations with due care the d b relationship may prove useful in defining the likely range of d b values in a particular environment a similar analysis of the tracer identified surface mixed depth shows that it is essentially independent of burial velocity with a worldwide mean of 9 8 4 5 cm depth of mixing is probably more closely related to the energetic costs of deep burrowing

geologic time series from deep sea sediments time scales and distortion by bioturbation abstract in order to evaluate the time and frequency domain characteristics of geologic time series obtained from deep sea sediments two important problems must be considered first an accurate time scale must be established for the sediment records to be studied an accurate time scale is a basic requirement for such techniques as spectral and cross spectral analysis secondly the distortion of a geologic time series by sedimentation processes such as bioturbation must be considered if inferences are to be made about the mechanisms controlling climatic and oceanographic processes reflected in the geologic record recently it has been suggested that the periodic components in paleoclimatic records which can be related to variations in the earth s orbital parameters can be used as a means for providing very detailed control for late pleistocene sediment sections a time scale is estimated by tuning an individual frequency component in a climate record to an orbital parameter the tuning procedure commonly uses the technique of bandpass filtering which removes all frequency components except the one equivalent to an orbital parameter and then adjusting the geologic time scale so that the filtered record and orbital record align since bandpass filtering will produce a periodic record from any data set a question is raised as to the circularity of this tuning approach a series of numerical experiments using synthetic time series are used to determine if the tuning of a geologic record artificially induces improved correlation and increased periodic character in a climatic record these experiments indicate that the tuning does not artificially induce these effects thus it is suggested that the careful use of orbital tuning provides a powerful means of defining a geologic time scale the degree to which bioturbation distorts a paleoclimatic record is studied by comparing the spectra of oxygen isotopic records obtained from cores with sedimentation rates ranging from 1 to 12 cm 1000 yr 1 it is shown that the systematic change in the variance spectra of these records that is predicted by models of bioturbation cannot be observed for sedimentation rates greater than 2 cm 1000 yr 1 this can be explained in part if bioturbation is a function of sedimentation rates if this is the case then bioturbation must proceed to depth of tens to hundreds of centimeters however it seems likely that the degree to which bioturbation alters the climate signal preserved in deep sea sediment cores has been overestimated

isotopic composition of disseminated sulfur in precambrian sedimentary rocks abstract isotopic analyses of trace sulfur in precambrian carbonates and clastic sedimentary rocks support the results of previous studies which have shown that 34s measurements of archean sedimentary sulfur cluster mostly around mantle like values and that a significant overall dispersion of 34 s 32 s ratios commenced at about 2 7 ga ago the outstanding feature of the proterozoic record is the predominance of heavy 34ssulfide values mostly in excess of 0 cdm consideration of these data in combination with the sparse 534s record for proterozoic sulfates suggests that 34ssulfide sulfide may have been smaller than was the case during the phanerozoic a possible scenario that is compatible with the above data is based on a proposition that the terrestrial exogenic sulfur cycle evolved in a tripartite manner in the archean it was coupled to and controlled by the magmatic endogenic cycle the proterozoic for the most part represents a transitional stage into a phanerozoic like exogenic cycle the latter essentially decoupled from its endogenic counterpart and its redox balance maintained and mediated by the biosphere the indication that the mean combined 34s of proterozoic sulfate and sulfide may have significantly exceeded the phanerozoic mean value of 2 cdm is enigmatic and poses problems for balance considerations

the importance of relict burrow structures and burrow irrigation in controlling sedimentary solute distributions abstract some areas of the seafloor particularly the deep sea are characterized by large numbers of apparently uninhabited or relict burrow structures formed by macrobenthic organisms because of low sedimentation rates or lack of physical disturbance these structures are stable for long periods of time and could potentially influence solute diffusion patterns in surface sediments a two dimensional diffusionreaction model which allows for diffusive rather than advective transport within stagnant water filled burrows demonstrates that in the absence of advective irrigation relict burrow structures are unlikely in most cases to significantly alter average solute distributions from those predicted by one dimensional vertical models this conclusion assumes changes in diffusive transport properties alone and does not account for any effects of relict structures on reaction rates or physical ventilation of deposits by bottom currents significant changes 5 in solute distributions are generally produced only when the ratio of the halfdistance between burrows to relict burrow radii is 10 and sedimentary diffusion coefficients are 60 that in free solution because solute distributions in stagnant burrow waters are nearly that in surrounding sediment sediment water solute fluxes are also essentially unaffected by relict burrows except at extremely high abundances or fairly large differential diffusion rates between sediment and free solution in contrast even at low abundance biologically irrigated or physically ventilated burrows produce major changes in solute transport and build up patterns

on the coupling of benthic and pelagic biogeochemical models abstract mutual interaction of water column and sediment processes is either neglected or only crudely approximated in many biogeochemical models we have reviewed the approaches to couple benthic and pelagic biogeochemical models it is concluded that they can be classified into a hierarchical set consisting of five levels differing in the amount of detail given to the sediment processes the most complex approach level 4 fully couples water column processes to a vertically resolved biogeochemical sediment model first simplification is achieved by using a vertically integrated dynamic sediment model level 3 next is a reflective type of boundary level 2 where particulate material arriving at the sediment surface is instantaneously transformed into dissolved components then comes a set of models in which either the bottom water concentration of dissolved substances or the sediment water exchange is imposed level 1 finally in some biogeochemical models the bottom is plainly ignored level 0 we have tested these various approaches in a coupled physical pelagic benthic biogeochemical model for oxygen nitrogen and carbon cycling in continental shelf areas we discuss the various model approaches with respect to their impact on the pelagic system and point out some of the inconsistencies hidden in certain formulations we conclude that lower boundary types in which sediment fluxes or concentrations are imposed level 1 are especially badly designed because they fail to assure conservation of mass finally we suggest as best choice a level 3 approach in which the evolution of sedimentary particulate matter is part of the solution and where the bottom fluxes of dissolved constituents are parameterised based on mass budget considerations these simplified formulations represent the best balance between computational demand and attained accuracy

34s enriched sulphate in the belcher group n w t canada evidence for dissimilatory sulphate reduction in the early proterozoic ocean sulphate molds and halite casts have been reported from a dolomite mudstone sequence near the base of the 1 9 ga belcher group bell and jackson 1974 by the in vacuo kiba technique ueda and sakai 1983 we have obtained 34s values for trace amounts of sulphate and sulphide in three samples of dolomite containing sulphate molds from the kasegalik formation for sulphate the 34s values are 26 9 to 28 9 averaging 27 8 and are independent of sulphate concentration 37 p p m to 584 p p m and the sulphide sulphate ratio the 34s values are considered to represent the composition of seawater in which the sediments were deposited this adds to the fragmentary record of the isotopic composition of early proterozoic seawater

determination of mixing parameters from tracer distributions in deep sea sediment cores abstract computer optimization and approximate analytical procedures are developed for the determination of the depth of bioturbation mixing d and the mixing coefficient d for instantaneous tracer inputs the methods have been applied to observations of microtektites volcanic ash and pumice in sixteen deep sea sediment cores the values for d are well determined generally with confidence intervals of a few centimeters or less and with an average value of d 11 cm for the sixteen cores the values for d are determined to first figure accuracy at best with values of around 10 cm 2 ka 1 or greater

lateral reynolds stress and eddy viscosity in a coastal strait abstract the lateral reynolds stress u representing the transfer of along strait momentum toward the sides of juan de fuca strait is measured with an array of adcps the contributions to the stress from a number of frequency bands are analyzed to highlight the roles of different processes motion in a frequency band that includes internal waves and doppler shifted subinertial eddies gives a reynolds stress that when scaled by the observed shear is consistent with an eddy viscosity of o 10 m2 s 1 this viscosity acts on the tides and the estuarine flow the tides can also impart a viscous stress upon the low frequency estuarine flow these tidal currents although strong are largely nondivergent within the area of the array and thus appear to be less important for the cross strait transfer of momentum the long term mean estuarine circulation can be acted upon by meanders of the estuarine flow defined as features with periods of 3 5 days these meanders are found to also have a horizontal eddy visc

the short term fate of organic carbon in marine sediments comparing the pakistan margin to other regions abstract pulse chase experiments with isotopically labelled phytodetritus conducted across the pakistan margin reveal that the impact of biological activities on benthic c cycling varies markedly among sites exhibiting different seafloor conditions in this study patterns of biological c processing across the pakistan margin oxygen minimum zone omz are compared with those observed in previous tracer studies variations in site environmental conditions are proposed to explain the considerable variations in c processing patterns among this and previous studies three categories of c processing pattern are identified 1 respiration dominated where respiration accounts for 75 of biological c processing and uptake by metazoan macrofauna foraminifera and bacteria are relatively minor processes these sites tend to show several although not necessarily all of the properties of being cold and deep and having low inputs of organic carbon to the sediment and relatively low biomass metazoan macrofaunal communities 2 active faunal uptake where respiration accounts for 2 h 1 and seem to be dominantly controlled by seafloor temperature rates of metazoan macrofaunal uptake of organic matter om on the pakistan margin are larger than those in most other studies and this is attributed to the large and active metazoan macrofaunal communities in the lower omz characteristic of omz boundaries finally biological mixing of pakistan margin sediments was reduced compared to that observed in comparable tracer studies on other margins this probably reflects faunal feeding and burrowing strategies consistent with low oxygen concentrations and a relatively abundant supply of sedimentary om

sulfur and carbon isotope records from 1700 to 800 ma carbonates of the jixian section northern china implications for secular isotope variations in proterozoic seawater and relationships to global supercontinental events abstract this study is a comprehensive stable isotope survey of the marine carbonate dominated upper paleo to lower neoproterozoic stratigraphy of jixian county china carbonate associated sulfate cas was extracted and measured for 34 s cas using the same samples analyzed for 13 c carbonate this integrated proxy approach is a step towards a more comprehensive picture of secular variation in the composition of proterozoic seawater we specifically sampled marine carbonate intervals from the lower section of the chuanlinggou formation changcheng group ca 1700 ma to the top of the jingeryu formation qingbaikou group ca 800 ma 13 c carbonate values are mostly negative in the upper paleoproterozoic changcheng group with an ascending trend from 3 to 0 we observed variation of approximately 0 1 in the mesoproterozoic jixian group and positive values of 2 2 characterize the lower neoproterozoic qingbaikou group stratigraphic variations in 34 s cas are more remarkable in their ranges and magnitudes including conspicuously high values exceeding 30 in the three intervals at ca 1700 ma 1300 1100 ma and 1000 900 ma in the changcheng group 34 s cas values are typically higher than 25 with only a few values of less than 15 in contrast most of the data spanning from the mesoproterozoic tieling formation of the jixian group to the lower neoproterozoic jingeryu formation of the qingbaikou group are highly variable between 10 and 25 with some values exceeding 25 in the late paleoproterozoic 1700 1600 ma a 10 decrease in 34 s cas and 3 increase in 13 c carbonate are coincident with and likely related to the breakup of columbia a supercontinent that predated rodinia carbon and sulfur isotope data from the mesoproterozoic when global tectonic activity was comparatively weaker fall mostly in the ranges of 15 10 and 0 1 respectively but fluctuations of 20 for 34 s cas and 3 for the 13 c carbonate at ca 1450 1400 ma may reflect subduction and large scale magmatic activity in island arcs marking the end of columbia breakup from the late mesoproterozoic ca 1300 1100 ma to the early neoproterozoic ca 800 ma the 13 c and 34 s of seawater increased gradually with increasing variability most impressive are 34 s cas values that exceed 30 in two intervals at ca 1300 1100 ma and ca 1000 900 ma which may reflect the assembly and early breakup of rodinia although gaps in the record remain and studies of even higher resolution are warranted our results suggest that changes in paleoceanographic conditions linked to global tectonics strongly influenced the biogeochemical cycles of c and s furthermore periods of the proterozoic previously noted for their isotopic invariability show clear isotopic expressions of this tectonic activity

canyon conditions impact carbon flows in food webs of three sections of the nazare canyon submarine canyons transport large amounts of sediment and organic matter om from the continental shelf to the abyssal plain three carbon based food web models were constructed for the upper 300 750 m water depth middle 2700 3500 m and lower section 4000 5000 m of the nazare canyon eastern atlantic ocean using linear inverse modeling to examine how the food web is influenced by the characteristics of the respective canyon section the models were based on an empirical dataset consisting of biomass and carbon processing data and general physiological data constraints from the literature environmental conditions most notably organic matter om input and hydrodynamic activity differed between the canyon sections and strongly affected the benthic food web structure despite the large difference in depth the om inputs into the food webs of the upper and middle sections were of similar magnitude 7 98 0 84 and 9 30 0 71 mmol c m 2 d 1 respectively om input to the lower section was however almost 6 7 times lower 1 26 0 03 mmol c m 2 d 1 carbon processing in the upper section was dominated by prokaryotes 70 of total respiration though there was a significant meiofaunal 21 and smaller macrofaunal 9 contribution the high total faunal contribution to carbon processing resembles that found in shallower continental shelves and upper slopes although the meiofaunal contribution is surprisingly high and suggest that high current speeds and sediment resuspension in the upper canyon favor the role of the meiofauna the high om input and conditions in the accreting sediments of the middle canyon section were more beneficial for megafauna holothurians than for the other food web compartments the high megafaunal biomass 516 mmol c m 2 their large contribution to respiration 56 of total respiration and secondary production 0 08 mmol c m 2 d 1 shows that these accreting sediments in canyons are megafaunal hotspots in the deep sea conversely carbon cycling in the lower canyon section was strongly dominated by prokaryotes 86 of respiration and the food web structure therefore resembled that of lower slope and abyssal plain sediments this study shows that elevated om input in canyons may favor the faunal contribution to carbon processing and create hotspots of faunal biomass and carbon processing along the continental shelf

numerical simulations of a buoyancy driven coastal countercurrent off vancouver island abstract a three dimensional prognostic numerical model has been developed to study the ocean circulation around vancouver island british columbia in a series of simulations the model is applied to examine the role of buoyancy forcing in the dynamics of the summer coastal countercurrent found off the west coast of vancouver island the forcing is provided by the fraser river discharge into the strait of georgia an estuarine circulation establishes itself in juan de fuca strait from which a distinctive right bounded current is formed and advances along the coast sensitivity studies are conducted to determine the robustness of this current to initial conditions opposing wind enhanced vertical mixing and grid resolution finally various characteristics of the numerically modeled coastal flow are compared with observations

regional and sediment depth differences in nematode community structure greater than between habitats on the new zealand margin implications for vulnerability to anthropogenic disturbance abstract deep sea community attributes vary at a range of spatial scales however identifying the scale at which environmental factors affect variability in deep sea communities remains difficult as few studies have been designed in such a way as to allow meaningful comparisons across more than two spatial scales in the present study we investigated nematode diversity community structure and trophic structure at different spatial scales sediment depth cm habitat seamount canyon continental slope 1 100 km and geographic region 100 10000 km while accounting for the effects of water depth in two regions on new zealand s continental margin the greatest variability in community attributes was found between sediment depth layers and between regions which explained 2 4 times more variability than habitats the effect of habitat was consistently stronger in the hikurangi margin than the bay of plenty for all community attributes whereas the opposite pattern was found in the bay of plenty where effect of sediment depth was greater in bay of plenty the different patterns at each scale in each region reflect the differences in the environmental variables between regions that control nematode community attributes analyses suggest that nematode communities are mostly influenced by sediment characteristics and food availability but that disturbance fishing activity and bioturbation also accounts for some of the observed patterns the results provide new insight on the relative importance of processes operating at different spatial scales in regulating nematode communities in the deep sea and indicate potential differences in vulnerability to anthropogenic disturbance