rapid bioturbation in equatorial pacific sediments evidence from excess 234th measurements in order to evaluate bioturbation in equatorial pacific sediments profiles of excess 234th were measured in cores collected during november and december 1992 at six abyssal sites along the jgofs equatorial pacific 140 w transect from 5 s to 9 n excess 234th half life 24 1 days was detected at all sites mean inventories ranged from a low of 0 25 dpm cm 2 at 9 n to a high of 2 6 dpm cm 2 at 2 n eddy diffusive models of the excess 234th profiles suggest that on 100 day timescales particle mixing is slow at 5 s and 2 s eddy diffusion coefficient db 0 4 cm2 year 1 faster at 0 and 2 n db 0 34 4 8 cm2 year 1 and fastest at 5 n db 4 7 11 cm2 year 1 at 9 n 234th is found almost entirely in the upper 5 mm of the seabed and db values are 0 1 cm2 year 1 db values generally increase as poc flux increases although the linear relationship r2 0 334 p 0 365 displays considerable scatter however if the only sites included in the regression are those where 234th profiles were measured in at least two core sets i e 0 2 n 5 n and 9 n the linear regression improves substantially r2 0 754 p 0 0012 these results suggest that measurements on a single core may not fully characterize the sediment mixing regime in a particular region and highlight the need for multiple samples from an individual site thorium 234 db values at 5 s 2 s and 9 n are in rough agreement with published db values calculated from the profiles of intermediate half life radioisotopes such as 210pb and 137cs in open ocean abyssal sediments however at 0 2 n and 5 n 234th db values are as much as an order of magnitude greater than published 210pb db values this phenomenon has been observed in other marine environments and may result from age dependent mixing non steady state mixing or a combination of the two processes particle mixing in cores collected at 5 s and 5 n appears to be best described as a largely eddy diffusive process however in cores collected at 2 s 0 2 n and 9 n non local mixing processes appear to affect 15 30 of the excess 234th inventory at these sites non local mixing appears to transport recently deposited material at least 3 4 cm below the sediment water interface within 100 days of its arrival at the seafloor the combination of rapid biodiffusive mixing and non local transport allows recently deposited reactive biogenic debris to be rapidly mixed into the seabed this may affect a wide range of diagenetic processes including oxygen consumption dissolution of biogenic debris and organic carbon remineralization models of early diagenesis in deep sea sediments may need to incorporate both non diffusive transport terms and rapid biodiffusive mixing of recently deposited particles

the variability of benthic fluxes and sedimentary remineralization rates in response to seasonally variable organic carbon rain rates in the deep sea a modeling study

biogenic sedimentation beneath the california current system for the past 30 kyr and its paleoceanographic significance a north south transect of 17 cores was constructed along the eastern boundary of the california current system from 33 to 42 n to investigate the changes in biogenic sedimentation over the past 30 kyr percentages and mass accumulation rates of caco3 corg and biogenic opal were assembled at 500 to 1000 years sample to provide relatively high resolution time space maps reveal a complex pattern of changes that do not follow a simple glacial interglacial two mode model biogenic sedimentation shows responses that are sometimes time transgressive and sometimes coeval and most of the responses show more consistency within a limited geographic area than any temporal consistency reconstructed conditions during late oxygen isotope stage 3 were more like early holocene conditions than any other time during the last 30 kyr coastal upwelling and productivity during oxygen isotope stage 3 were relatively strong along the central california margin but were weak along the northern california margin precipitation increased during the last glacial interval in the central california region and the waters of the southern california margin had relatively low productivity productivity on the southern oregon margin was relatively low at the beginning of the last glacial interval but by about 20 ka productivity in this area significantly increased this change suggests that the center of the divergence of the west wind drift shifted south at this time the end of the last glacial interval was characterized by increased productivity in the southern california margin and increased upwelling along the central california margin but upwelling remained weak along the northern california margin a sudden 300 years decrease in caco3 corg and biogenic opal occurred at 13 ka the changes suggest a major reorientation of the atmospheric circulation in the north pacific and western north america and the establishment of a strong seasonality in the central california region a carbonate preservation event occurred at 10 ka that appears to reflect the uptake of co2 by the terrestrial biosphere as the northern latitudes were reforested following retreat of the glaciers the holocene has been a period of relatively high productivity in the southern california margin relatively strong coastal upwelling along the central california margin relatively weak upwelling along the northern california margin and the northward migration of the divergence zone of the west wind drift

rates of organic carbon oxidation in deep sea sediments in the eastern north atlantic from pore water profiles of o2 and the δ13c of dissolved inorganic carbon abstract the remineralization rate of sedimentary organic carbon r org and the depth integrated diffusion supplied o 2 consumption rate ioc during microbial metabolism in sediments was investigated in three deep sea sites at 1100 2000 and 3500 m water depth in the eastern north atlantic during the spring and summer 1998 in situ pore water o 2 profiles yielded an ioc of 0 45 0 07 mmol o 2 m 2 day 1 at the deepest site n 3 and ca 1 1 5 mmol o 2 m 2 day 1 at the shallowest site n 2 the r org was independently estimated at all three sites from ex situ pore water profiles of the isotopic composition of total dissolved inorganic carbon 13 c t assuming that the concentration and isotopic composition of pore water c t with depth in the sediment was controlled only by microbial oxidation of isotopically depleted sedimentary organic carbon the r org was thus estimated to be ca 0 5 0 6 mmol c m 2 day 1 at the shallowest site and ca 0 3 0 4 mmol c m 2 day 1 at the two deeper sites stoichiometric and isotopic constraints indicated that oxic remineralization of sedimentary organic matter was the dominant metabolic pathway in the sediments at 3500 m water depth similarly stoichiometric and isotopic constraints suggested that the r org estimates from the ex situ pore water 13 c t profiles from 1100 and 2000 m water depth were likely to be minimum values and provided evidence for the occurrence of post oxic remineralization processes post oxic metabolism in the sediments of these sites could be linked to or even augmented by the non diffusive mode of supply of organic matter mediated by infaunal organisms below the oxic sediment layer

recycling of organic matter in antarctic sediments a transect through the polar front in the southern ocean indian sector sediments from the polar front zone were sampled in the indian sector of the antarctic ocean as part of the french jgofs expedition antares 1 the first porewater distributions of o2 and no3 and organic carbon data in the solid phase in this part of the ocean were used to model the recycling of organic matter in sediments the data are described by a model containing two types of degradable organic matter with distinct reactivities we estimate that the reactivity of the most labile organic carbon is very close to that of fresh organic matter with an average c n ratio of 7 we estimate that particulate organic carbon fluxes deposited at the sediment water interface range between 0 2 and 0 8 mol c m l y l with two peaks near the polar front and the subantarctic front the flux 01 organic carbon deposited at the sediment water interface is unusually high and represents 10 20 of estimated primary production from these findings we conclude that production in the pelagic zone of this region is strongly linked to deposition and recycling in the sediment

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

benthic remineralization and burial of biogenic sio2 caco3 organic carbon and detrital material in the southern ocean along a transect at 170 west abstract we investigated the composition recycling and mass accumulation rates of sediments along a transect in the southern ocean located from 66 s to 57 s at 170 w this transect also corresponds to the location of a sediment trap mooring line the sediments at the seven sites studied range from largely terrigenous material to nearly pure 90 biogenic silica caco3 is a minor but persistent component at most sites mass accumulation rates have been determined on the basis of excess 230th in the sediments i e 230th normalized accumulation rates the influence of redistribution of sediments on the sea floor has been estimated from 14c analyses the recycling of material delivered to the sediments has been characterized on the basis of pore water studies that make extensive use of both in situ sampling and shipboard extractions the influence of the highly variable rates of input of particulate matter that characterize much of the southern ocean upon pore water gradients and fluxes across the sediment water interface has been considered we find only poor correspondence between bsio2 burial fraction burial particulate flux a quantifiable measure of preservation efficiency and bsio2 particulate rain along the transect however preservation does appear to be closely linked to a combination of sedimentation rate and particulate rain the burial fraction of bsio2 is small relative to benthic rain 5 19 despite the small fraction buried burial flux normalized to sedimentation rate 1 2 appears to provide a very consistent means of predicting benthic particulate rain over a large range of rain rates including data from a number of different studies and environments at sites with bsio2 rain 250 mmol m 2 yr 1 the average difference between predicted and observed rain is 25 30 such rain rates occur in many marine areas particularly the southern ocean with the result that this relationship potentially provides a means of estimating bsio2 benthic rain over prolonged periods in the past on the basis of readily measured sediment parameters at the southern most deep ocean station the particulate flux was characterized by an extremely high corg caco3 ratio 10 but this high ratio does not appear to have a substantial influence on caco3 burial caco3 is preserved in the sediments at this site despite a particulate flux with a 10 fold excess of corg above that required for complete dissolution in the sediments the unexpectedly high preservation of caco3 is due largely to the very steep corg oxidation rate profile at this site as a result a large fraction of the organic matter oxidized in the sediments does so in close proximity to the sediment water interface where most of the metabolic co2 is neutralized by co32 from the overlying water rather than by the dissolution of sedimentary caco3 diagenetic modeling indicates that at several of the stations the remineralization fluxes of carbonate species across the sediment water interface may not have been at steady state as a result of the highly pulsed nature of particulate rain in this environment we estimate that at the time of our sampling it is possible that near interface fluxes could have been a factor of 1 6 2 times the annual average at every site on the transect the burial fluxes of detrital material are substantially greater than the detrital particulate rain measured in the sediment traps by as much as a factor of 40 detrital burial is bimodal being greatest at the southern and northern extremes of the transect we postulate that the excess of burial over particulate rain in the south reflects the contribution of ice rafted debris at these high latitudes increases in the supply at the northern stations must have a different source we believe that the excess at these stations is material eroded from the sea floor to the west possibly on the campbell plateau and advected by currents to the northern portion of the transect at depths below the shallow traps

the global ocean flux of particulate organic carbon areal distribution and magnitude the magnitude and distribution of the particulate organic carbon poc rain rate to the seafloor in the atlantic pacific and indian ocean basins between 61 n and 61 s has been estimated from benthic oxygen flux estimates for water depths 1000 m only the calculation utilizes the extensive data sets of sedimentary organic carbon caco3 and accumulation rate to extrapolate between individual benthic flux measurement sites using an empirically derived correlation between the seafloor oxygen flux and these parameters the poc flux through the 1000 m depth horizon was then estimated from published correlations between sediment trap determined fluxes and water depth total oxygen utilization in the deep ocean is estimated to be 1 2 1014 mol o2 yr 1 a value that agrees well with previous estimates which were based on surface water primary productivity sediment trap and depth relationships and with deep water respiration rates estimated from apparant oxygen utilization aou 14c relationships on the basis of the derived global ocean flux distribution it is concluded that 1 dissolved organic carbon doc inputs are not required to account for estimated deep water respiration rates 2 the majority of the poc input to the deep ocean occurs within 30 of the equator 3 the proportion of primary production that reaches the deep sea does not vary greatly with latitude 4 gyre and continental margin regions contribute roughly equally to the deep poc flux with a relatively minor contribution from the equatorial divergence region 5 of the estimated 7 2 1013 mol c yr 1 of poc that sinks below the 1000 m depth horizon 45 3 3 1013 mol c yr 1 reaches the seafloor where it is oxidized 6 when normalized to basin area average deep flux rates in the atlantic and pacific are similar while highest rates are observed in the indian ocean and 7 the results can be fully reconciled only if the benthic flux of doc is significantly less than the benthic o2 flux

microbial and meiofaunal abundance redox potential ph and shear strength profiles in deep sea pacific sediments vertical profiles of microbial and meiofaunal abundances and of redox potential ph water content and shear strength have been measured in sediment subcores from seven box cores collected in the southern central pacific and the findings have been related to potential effects on pelagic fluxes and sedimentation microbial and meiofaunal abundance decreased exponentially with sediment depth micro organisms were found throughout the depth of the core to 40 cm meiofauna were only present in the top 5 cm to 10 cm meiofaunal metazoans decreased more rapidly than foraminiferans redox potential was always positive decreased below the surface and often rose again deeper in the sediment ph showed no clear cut trend with depth shear strength increased with sediment depth and showed occasional anomalous fluctuations water content decreased progressively downwards with the widest scatter in the top 5 10 cm the most important implications of these results for the water column above are likely to be biologically mediated organic mineralization and nutrient regeneration into the water column and biodeposition of heavy metals and the binding of particulates at and above the sediment water interface by extracellular polymeric material which will in turn lead to differential patterns of sedimentation

biological indicators of sedimentary dynamics in the central gulf of papua seasonal and decadal perspectives 1 benthic and pelagic communities in the central gulf of papua a major deltaic clinoform located on the south coast of papua new guinea reflect the spatial and seasonal patterns in physical sedimentation conditions and the availability of food resources across this system the distribution of terrigenous and marine organic substrates the transport of riverine derived sediment and seafloor dynamics are largely controlled by two seasons and wind patterns the relatively quiescent nw monsoon and more energetic se trades the physically disturbed inner topset deposits 20 m are dominated at all times by bacterial biomass and have depressed numbers of macrofauna with evidence of periodic recolonization recorded in sedimentary structures the inner topset region also shows strong seasonality in the production and availability of labile organic matter and in bacterial activity as measured by the concentrations of photopigments and microbial biomass in the upper 2 cm of surface sediments and in the water column the comparatively quiescent nw monsoon period is associated with net delivery of reactive substrates as labile organic matter to the bottom and net growth of the benthic microbial community whereas the transition period between the nw monsoonal winds nw monsoon and se trade winds se trades and the se trades are periods of reactive substrate depletion in bottom deposits and decreased benthic bacterial and macroinfaunal biomass in contrast to the inner topset the less physically disturbed outer topset and foreset show relatively enhanced but still low abundances of large macrobenthos and possible evidence of variation related to food supply the greatest observed seasonal variation in macrofauna occurs in the umuda valley off the fly river an apparent mobile sediment conduit

organic carbon turnover time in deep sea benthos abstract the ratio of organic carbon supply to the deep sea floor estimated with sediment traps to total benthic biomass in terms of organic carbon concentration was used to calculate average turnover or residence times for the benthic community over a broad depth interval in the western north atlantic ratios indicate that the biomass carbon turns over on average time scales of months with little predictable variation over the depth interval 70m to 5300m detrital organic carbon in sediments at the same stations turned over on scales of years to centuries the shortest detrital carbon turnover was just over 8 years in a sandy continental shelf environment versus 609 years at 5 3km depth on the hatteras abyssal plain the turnover time estimates calculated with poc fluxes were assessed by comparing poc fluxes with estimates of total community respiration at each location the poc flux rates were greater than the sediment oxygen demand flux rates in mg carbon m 2d 1 and the disparity was much greater in the deep sea than on the continental margin we suggest that this difference is primarily the result of a decline in the quality of the organic compounds in the rain of sinking poc rather than physiological responses to cold or pressure this implies that caution must be used when interpreting the relationships between the total organic carbon fluxes measured with sediment traps at great depths and rates of metabolic processes

modeling the calcite lysocline a numerical model of calcite dissolution in contact with sediment pore water is used to predict the depth and shape of the calcite lysocline in the deep sea model results are compared with lysocline data from 13 regions in the atlantic pacific and indian oceans the model lysocline shape is sensitive to the calcite dissolution rate constant the calcite organic carbon and refractory material rain rates and the rates of oxic versus anoxic organic carbon degradation in the sediment the model is able to reproduce the observed lysocline within the constraints of the sediment trap and calcite accumulation data using a calcite dissolution rate constant of 30 100 d 1 a molar ratio of organic carbon to calcite rain rates of 0 5 1 0 and an initial caco3 fraction of 90 excluding organic carbon this rate constant is consistent with microelectrode results presented by archer et al 1989 the model predicts that 30 50 of the calcite rain to the sea floor at the saturation horizon dissolves in response to organic carbon respiration consistent with previous modeling studies the range in the best fit value of the organic inorganic carbon rain rates arises from model sensitivity to uncertainty in the rate of anoxic carbon degradation in the sediment and in the rain rate of refractory material rather than from scatter in the data lysocline data from the western equatorial atlantic are anomalous to the rest of the data this anomaly may be explained by high rates of refractory material sedimentation from the amazon river

origin of the eskay creek precious metal rich volcanogenic massive sulfide deposit fluid inclusion and stable isotope evidence the eskay creek deposit is an unusual polymetallic au ag rich volcanogenic sulfide sulfosalt deposit located in the iskut river area of northwestern british columbia canada economic concentrations of precious and base metals are contained in the 21 zone which is divided into a number of subzones as of december 31 1998 total production and proven probable reserves are 1 9 million tons mt at 60 2 g t au 2 652 g t ag 3 2 percent pb 5 2 percent zn and 0 7 percent cu the 21b zone which contains the bulk of the reserves began production in 1995 the mineralization occurs mainly as well preserved stratiform clastic beds of sulfide sulfosalt debris and also as discordant footwall quartz sulfide veins the hydrothermal system that formed the eskay deposit was low temperature

late pliocene and pleistocene climatic oscillations and monsoon upwelling recorded in sediments from the owen ridge northwestern arabian sea

discussion sulphur isotope composition of the brunswick no 12 massive sulphide deposit bathurst mining camp new brunswick implications for ambient environment sulphur source and ore genesis the authors w d goodfellow and j m peter report an impressive amount of chemical data on the brunswick no 12 orebody one of the world s largest volcanic associated massive sulphide deposits they have proposed that most of the sulphur in the massive sulphide ore and the pyrites in adjoining sediments of the patrick brook formation was probably derived from an overlying anoxic seawater column in which sulphate reduction had taken place the resulting h2s having mixed with venting metal rich fluids the principal lines of evidence brought in to support this idea are 1 the sediments of the patrick brook formation underlying the footwall sedimentary and volcanic rocks of the nepisiguit falls formation which hosts the orebody have s c values and mn and fe contents that indicate anoxic conditions in the seawater during sedimentation 2 the 34s values of the sulphides in the ore types and the underlying feeder zone are similar to those of pyrites in the patrick brook formation and to coeval pyrites in the selwyn basin and 3 there is no alternative source of reduced sulphur because there would be inadequate sulphate remaining in deep circulating seawater to provide sufficient reduced sulphur for ore formation and there is little evidence for the presence of evaporite sulphate in the deep footwall sequence the significance of their major lines of evidence and also those of lentz et al 1996 is discussed below

australian volcanic hosted massive sulfide deposits features styles and genetic models the cambro ordovician period has yielded the major development of volcanic hosted massive sulfide vhms deposits in australia resulting in about 12 million metric tons of contained metal copper lead and zinc concentrated in the mount read volcanics tasmania and the mount windsor volcanics queensland the archean 4 million metric tons of metal and the silurian 3 5 million metric tons of metal constitute the next important episodes while the devonian and permian have produced isolated deposits the deposits range from cu type to zn cu type to zn pb cu type the zn cu type deposits are restricted to the archean and silurian whereas the cu type and zn pb cu type occur sporadically throughout the time span from early archean to permian in general terms the major vhms bearing districts are calc alkaline in character and display a thick basal pile of rhyolitic volcanics 1 3 km thick including lavas epiclastics and subvolcanic intrusions which is overlain by a polymodal sequence containing various proportions of rhyolite dacite andesite basalt and sediments the major deposits are commonly located at the top contact of the rhyolite pile or within the lower part of the overlying polymodal sequence there is a wide range in variability of styles of australian vhms deposits including mounds pipes sheets layered deposits stacked deposits stockwork and disseminated deposits distal reworked deposits and cyclic layered deposits although these various styles show a range of features there is a consistent theme across the spectrum of metal zonation alteration mineralogy alteration chemistry sulfur isotopes macrotextures microtextures and host volcanic relationships which strongly suggests that they all belong to the one genetic group of ore deposit the classic mound style deposits such as hellyer have a series of key features subsets of which are represented in the other deposit styles the mound deposits are considered to form from deposition of metal sulfides on the sea floor immediately around the hydrothermal vent growth of the mound occurs by upward replacement of sulfide assemblages stable at higher fluid temperatures leading to zone refining and lead zinc silver gold enrichment in the outer and upper parts of the mound departure from the classic mound style of deposit is related principally to three key factors the chemistry of the ore fluid salinity temperature f02 and ah2s the nature permeability and chemistry of the volcanic pile and the sea hoor environment sea hoor topography and seawater depth these factors control the aspect ratio of the deposit the extent of stringer zone development the degree of subsea floor replacement mineralization the nature and spatial development of footwall alteration and the development and style of related distal mineralization sulfur isotope studies of australian vhms deposits indicate that reduced seawater sulfate is a major source of sulfur in the deposit whereas lead and strontium isotope results are compatible with the metals being derived by seawater convection and leaching from the volcanic pile and basement rocks this conclusion is supported by the application of various leaching models which demonstrate the availability of an adequate source of both base and precious metals in the footwall volcanic sequences the input of metals directly from volcanic magma chambers is not precluded by the available data and one likely scenario involves the contribution of gold and copper from a magmatic vapor plume rising to mix with convective seawater fluids which contribute lead zinc silver and gold leached from the footwall volcanics and basement rocks the relative importance of the magmatic input compared with the seawater convective input may help to explain the spectrum of deposit styles arid their spatial relationship to volcanic centers or adjacent sedimentary basins

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

genesis of the wolverine volcanic sediment hosted massive sulfide deposit finlayson lake district yukon canada mineralogical mineral chemical fluid inclusion and sulfur isotope evidence the wolverine deposit is a high grade 6 2 mt at 12 7 zn 1 3 cu 1 6 pb 370 9 g t ag and 1 8 g t au volcanic and sedimentary rock hosted massive sulfide deposit in the finlayson lake area yukon territory the area has the potential to become an important mining camp and currently contains more than 30 million tons mt of massive sulfide ore in five deposits a succession of metamorphosed early mississippian felsic volcanic and sedimentary rocks that are interpreted to have formed on the margin of an ensialic back arc ocean basin between the yukon tanana terrane and the ancestral north american craton hosts the wolverine deposit the massive sulfide ore occurs at a single horizon that marks a significant change in the character of the volcanism from quartz and feldspar phyric rhyolite of the footwall to aphyric rhyolite and chemical sedimentary exhalative rock of the hanging wall the deposit consists of two discrete zn pb ag massive sulfide lenses situated at the same stratigraphic level connected by strata bound semimassive replacement style zn pb ag mineralization copper rich massive sulfide commonly replaces the zn pb ag massive sulfide at the base of the lenses and in the footwall replacement zones beneath the massive mineralization several zones of sulfide stringer veins and chlorite sericite carbonate alteration occur within permeable footwall volcaniclastic rocks alteration minerals preferentially associated with massive sulfide mineralization include ba rich phengitic mica biotite mg rich chlorite and siderite microthermometric measurements of fluid inclusions in the massive sulfide bodies and accompanying stringer zones indicate formation at temperatures of 235 to 353 c primary aqueous liquid rich fluid inclusions in hydrothermal quartz from quartz sulfide stringer veins contain low salinity fluids 2 1 8 5 wt nacl equiv mean 6 0 there is no evidence of fluid boiling in the inclusions and based on the average fluid salinity and temperature of homogenization mineralization took place under a minimum water depth of 1 000 m in situ analyses of 34sv cdt in sulfide minerals from massive sulfide lenses means 0 8 and sulfide stringer veins mean 12 0 display a bimodal distribution lower 34s values characterize sulfides near the top of the lenses versus higher more positive values in underlying veins may reflect different processes of reduction of seawater sulfate sulfur in sulfides from the tops of the lenses was likely derived mainly from bacterial reduction of seawater sulfate whereas sulfur in the stringer veins and at the base of the lenses was mainly from inorganic reduction of seawater sulfate sulfide minerals precipitated both on the sea floor and in the subsea floor from hydrothermal fluids that vented from multiple mounds the presence of black shales and the strongly positive sulfur isotope compositions of the sulfides provide evidence that the ambient bottom water in the basin in which the wolverine deposit formed was likely anoxic this environment may have contributed to the preservation of the sulfide mounds based on its tectonic setting host rock types local geologic setting metal grades age and source s of sulfur the wolverine deposit best exemplifies the volcanic sediment hosted massive sulfide vshms class of syngenetic massive sulfide deposits in the district

benthic denitrification and nitrogen cycling at the slope and rise of the n w european continental margin goban spur abstract the rate of benthic denitrification in slope and rise sediments of a transect across the n w european continental margin goban spur was evaluated from 31 pore water nitrate profiles obtained during six cruises between may and october all profiles had well separated zones of nitrification and denitrification high near surface nitrate concentrations prevented the influx of nitrate from the bottom water the denitrification rates obtained from steady state modelling ranged from 0 13 to 2 56 mol n cm 2 y 1 and showed an exponential increase both with decreasing water depth and with increasing rate of organic carbon degradation denitrification rates in a nearby canyon which did not follow these relationships were estimated to be much higher as a result of erosion and redistribution of organic matter denitrification at the goban spur slope and rise is much lower than previously reported for similar environments in the pacific resulting predominantly from the different oxygen and nitrate concentrations in the bottom water a weighted average for the whole slope and rise sediment system shows that 17 of the particulate organic nitrogen input 8 93 mol n cm 2 y 1 is denitrified and only 1 is buried the rest being released as nitrate although being ten times higher compared with basin sediments denitrification on the slope and rise is several times lower than on the adjacent shelf

the cycling and oxidation pathways of organic carbon in a shallow estuary along the texas gulf coast abstract the cycling and oxidation pathways of organic carbon were investigated at a single shallow water estuarine site in trinity bay texas the uppermost lobe of galveston bay during november 2000 radio isotopes were used to estimate sediment mixing and accumulation rates and benthic chamber and pore water measurements were used to determine sediment water exchange fluxes of oxygen nutrients and metals and infer carbon oxidation rates using 7 be and 234 th xs the sediment mixing coefficient d b was 4 3 1 8 cm 2 y 1 a value that lies at the lower limit for marine environments indicating that mixing was not important in these sediments at this time sediment accumulation rates s a estimated using 137 cs and 210 pb xs were 0 16 0 02 g cm 2 y 1 the supply rate of organic carbon to the sediment water interface was 30 3 9 mmol c m 2 d 1 of which 10 or 2 9 0 44 mmol c m 2 d 1 was lost from the system through burial below the 1 cm thick surface mixed layer measured fluxes of o 2 were 26 3 8 mmol m 2 d 1 and equated to a carbon oxidation rate of 20 3 3 mmol c m 2 d 1 which is an upper limit due to the potential for oxidation of additional reduced species using organic carbon gradients in the surface mixed layer carbon oxidation was estimated at 2 6 1 1 mmol c m 2 d 1 independent estimates made using pore water concentration gradients of ammonium and c n stoichiometry equaled 2 8 0 46 mmol c m 2 d 1 the flux of doc out of the sediments doc efflux was 5 6 1 3 mmol c m 2 d 1 in general while mass balance was achieved indicating the sediments were at steady state during this time changes in environmental conditions within the bay and the surrounding area mean this conclusion might not always hold these results show that the majority of carbon oxidation occurred at the sediment water interface via o 2 reduction this likely results from the high frequency of sediment resuspension events combined with the shallow sediment mixing zone leaving anaerobic oxidants responsible for only 10 15 of the carbon oxidized in these sediments

biogenic and thermogenic sulfate reduction in the sullivan pb zn ag deposit british columbia canada evidence from micro isotopic analysis of carbonate and sulfide in bedded ores abstract the layered clastic hosted sedex type proterozoic ca 1475 ma sullivan pb zn ag deposit was metamorphosed by several episodes of metamorphic recrystallization that have extensively modified or erased primary grain to grain textural relationships yet genetically significant variations of sulfur and carbon isotope ratios have been preserved at the millimeter and greater scale whereas sulfur isotope fractionations on a grain to grain scale cannot distinguish between likely formation temperatures and post peak metamorphic cooling the preserved fine scale and deposit scale stratigraphic variations of 34 s and 13 c bear on the origin and formational history of this deposit high spatial resolution documentation of accurate grain to grain and stratigraphic sulfur isotope variations in selected portions of bedded ore from the sullivan deposit was made possible by use of a cold stage during in situ laser assisted isotopic analysis pyrrhotite formed from biogenic sulfate reduction in the water column can be distinguished from sulfides e g sphalerite with higher 34 s values that formed in response to hydrothermal fluids in a brine pool isotopic analysis of carbonates in the presence of abundant sulfides was facilitated by development of a gas chromatographic carbonate extraction system with a high efficiency cryogenic trap calcite present in interlayered massive sulfide and siliciclastic layers in the bedded ore zone in trace amounts to a few weight percent records a carbon isotopic stratigraphy that suggests variable thermogenic sulfate reduction stratigraphic curves illustrating the variation in carbon and sulfur isotopes from the base of the main band to above the hu bands mine stratigraphic names in the bedded ore zone are similar in shape values of 13 c decrease abruptly at the base of the main band decrease slightly to the c band then increase to pre ore values the values of 34 s decrease from the base of the main band to the c band and then increase to pre ore values this similarity suggests some linkage between carbon and sulfur isotopic systematics and a sulfur budget dominated in the early stages of massive sulfide precipitation by hydrothermal processes involving thermogenic sulfate reduction giving way to bacteriogenic sulfate reduction in a closed then finally open marine basin

modeling vertical excursions of the redox boundary in sediments application to deep basins of the arctic ocean a diagenetic reaction transport model was used to simulate how the sediment redox boundary migrates in response to persistent or episodic changes in the deposition flux of degradable organic matter and the concentration of oxygen in the overlying bottom water the position of the redox boundary is represented by the depth of oxygen penetration the simulations reveal that the position of the redox boundary in organic poor sediments such as those in the deep basins of the arctic ocean is highly sensitive to the flux of organic matter relatively small and or brief increases in that flux can cause the redox boundary to migrate rapidly from deep within the sediment to within a few centimeters of the sediment water interface reoxidation of the sediment column after such an event can take years redox fluctuations can redistribute solid phase manganese within the sediment column and produce multiple concentration peaks in its depth profile on a decadal time scale manganese peaks observed in sediment cores from the deep basins of the arctic ocean do not necessarily correspond to the position of the redox boundary during previous climatic periods or reflect historical changes in manganese deposition rates the model supports the hypothesis that the recent decrease in the arctic ice cover has increased the flux of organic matter to the seafloor and moved the redox boundary close to the sediment water interface the presence of iron sulfides at depths significantly below the bioturbated layer suggests that either the arctic sediments have been anoxic for millennia or iron and sulfate are reduced at these depths by dissolved organic matter diffusing downward from the bioturbation zone

microelectrode studies of organic carbon degradation and calcite dissolution at a california continental rise site fine scale porewater profiles of resistivity o2 ph and pco2 were measured in situ with microelectrodes at a site on the california continental rise they are reported here with more traditional measurements of shipboard porewater no3 alkalinity and tco2 and sediment organic c and caco3 profiles a numerical model encompassing diffusion advection and multiple reaction terms is applied to these data to characterize organic carbon degradation and caco3 dissolution processes near the sediment water interface a benthic o2 flux of 58 mol cm 2 yr 1 over the top 1 mm sediment is estimated based on one measured sub mm depth scale o2 profile the numerical model indicates that this high o2 consumption rate is related to a very labile fraction of organic c which has a degradation rate constant of approximately 4 5 10 8 s 1 1 4 yr 1 and which is not mixed downward by biological mixing seasonality in the benthic o2 consumption rate of this site may be attributed to variations in the input rate of this highly labile organic c degradation rate constants of the bulk organic c by oxygen reduction and by nitrate reduction are estimated to be about the same 1 10 9 s 1 the organic c rain rate responsible for the bulk organic c is estimated to be 53 mol cm 2 yr 1 this estimate exceeds the average rain rate determined by sediment trap collections at this site saturation state profiles calculated from the in situ ph and pco2 data and from modelling the in situ o2 and ph data both indicate that the porewater is undersaturated with respect to calcite to a depth of at least 8 cm the dissolution rate constant of calcite in this caco3 poor station is determined to be 5 10 day 1 assuming the reaction order is 4 5 which is close to the minimum estimates for environments richer in calcite a uniform calcite dissolution rate constant therefore may be adequate for representing carbonate dissolution in global scale models of ocean chemistry

numerical modeling of benthic processes in the deep arabian sea abstract aerobic and anaerobic degradation of particulate organic carbon poc and carbonate equilibria in deep sea surface sediments were studied at five stations located in the western wast northern nast eastern east central cast and southern sast arabian sea in situ oxygen fluxes porewater profiles of dissolved oxygen nitrate and mn ph profiles and solid phase profiles of particulate organic carbon mn and fe were measured at each station an early diagenesis model was applied to simulate the degradation and dissolution processes and to determine the benthic fluxes of poc oxygen nitrate phosphate co2 hco3 and co32 the benthic data sets were evaluated to constrain the poc input and the kinetics of organic matter degradation used in the model the modeling showed that the poc rain rate to the seafloor is high at the western and northern stations and decreases towards the southeast at stations located in the vicinity of continental margins wast nast east 5 7 of the primary production sinks to the deep sea floor this unusually high poc rain is either caused by dust particles that accelerate and amplify the particle export from the euphotic zone or by rapid lateral transport processes at the more remote stations cast sast that receive lower dust inputs the rain efficiency decreases to 1 4 in the model organic matter was separated into three fractions 3 g model that differ considerably in reactivity at stations wast nast east and cast the bulk of organic matter is composed of extremely labile organic matter with a first order degradation constant k of 15 30 yr 1 the moderately labile fraction with a kinetic constant of 0 2 0 6 yr 1 dominates the poc input at the oligotrophic station in the southern arabian sea sast the third fraction that has a very low reactivity k 2 5 10 4 yr 1 is only a minor component of the poc rain at all investigated stations more than 95 of the organic matter is consumed in aerobic degradation processes denitrification and metal oxide reduction only contribute 1 2 to the total poc degradation at the western station wast a non negligible portion 2 of organic matter is consumed via sulfate reduction the modeling demonstrates that carbonate dissolution is a major process in the deep arabian sea 52 83 of the carbonate rain to the seafloor is dissolved within the surface sediments in the western arabian sea the monsoon systems produce a strong seasonality in the primary production non steady state modeling indicates that the benthic oxygen nutrient and inorganic carbon fluxes closely follow the seasonal dynamics in primary and export production this very close benthic pelagic coupling is established by the extremely labile organic matter fraction that dominates the poc rain to the seafloor the metabolically released co2 induces a seasonal change in carbonate dissolution and carbonate alkalinity fluxes

pore water distribution and quantification of diffusive benthic fluxes of silicic acid nitrate and phosphate in surface sediments of the deep arabian sea benthic fluxes and pore water compositions of silicic acid nitrate and phosphate were investigated for surface sediments of the abyssal arabian sea during four cruises 1995 1998 five sites located in the northern nast western wast central cast eastern east and southern sast arabian sea were revisited during intermonsoonal periods after the ne and sw monsoon at these sites benthic fluxes of remineralized nutrients from the sediment to the bottom water of 36 106 102 350 and 4 16 mmol m 2 yr 1 were measured for nitrate silicic acid and phosphate respectively the benthic fluxes and pore water compositions showed a distinct regional pattern highest fluxes were observed in the western and northern region of the arabian sea whereas decreasing fluxes were derived towards the southeast at wast the general temporal pattern of primary production related to the ne and sw monsoon is reflected by benthic fluxes in contrast at sites nast sast cast and east a temporal pattern of fluxes in response to the monsoon is not obvious our results reveal a clear coupling between the general regional pattern of production in surface waters and the response of the benthic environment as indicated by the flux of remineralized nutrients though a spatially differing degree of decoupling during transport and remineralization of particulate organic matter and biogenic opal was observed this has to be taken into account regarding budget calculations and paleoceanographic topics

a late glacial holocene pollen record from the eastern andes of northern peru abstract a pollen and sediment record of a core 4 2 m long from laguna baja 7 42 s 77 32 w 3575 m in the cordillera oriental of northern peru suggests several episodes of major vegetational and climatic change over the past 13 000 yr the oldest pollen assemblage consists of a mixture of paramo elements tropical alpine vegetation including high percentages of poaceae 40 that decline upward moist montane forest compositae and polylepis and wet montane forest e g hedyosmum and podocarpaceae organic carbon content range from 60 with high percentages of jamesonia a fern characteristic of paramo and decreasing values of plantago tubulosa and the wet montane forest elements hedyosmum and podocarpaceae charcoal percentages are at a maximum during this period magnetic susceptibility and sand percentages are high and percentages of organic matter are low several explanations for these changes are possible including a reduction in temperature and moisture more frequent periods of aridity with increased fires or natural succession the holocene record begins with pronounced increases in organic carbon and pollen of wet montane forest primarily hedyosmum podacarpaceae and urticales high values of podocarpaceae pollen 35 and a decline in charcoal suggest temperature and moisture levels above modern day values wet montane forest pollen remain high and charcoal values are low from about 10 000 to 6000 yr b p suggesting that warm and moist conditions prevailed for about 4000 yr subsequently podocarpaceae and urticales decline and for a brief time alnus is prominent in the pollen record following the alnus maximum at about 5000 yr b p poaceae ambrosia and chenopodiaceae amaranthaceae become frequent increased paramo and disturbance indicator pollen suggest increased anthropogenic activities in this region from the middle holocene to the present