early diagenesis in deep sea turbidites the imprint of paleo oxidation zones sediment cores up to 35 m long have been recovered from turbidite sequences in the madiera abyssal plain and the southern nares abyssal plain detailed geochemical analyses of these sediments si al fe mn ca organic and inorganic carbon and associate pore waters nitrate ammonia silicate fe2 mn2 and alkalinity provide representative profiles of both steady state and nonsteady state diagenetic reactions initiated by oxidation and reduction processes models demonstrate that chemical transport in the pore water system is diffusion dominated over periods of a few thousands of years to several hundreds of thousands of years mn and fe mobilized in the subsurface mildly reducing sediments are precipitated as easily reducible oxyhydroxides in the near surface oxidized sediments nonsteady state profiles show the influence of episodic and rapid turbidite deposition and the imprint of oxidation zones that developed as the result of oxygen diffusion into the upper portions of turbidites during intervals of slow pelagic deposition the time required for development of oxidation zones between turbidites ranges from 2 0 to 15 ka in the madeira abyssal plain and from 0 2 to 2 4 ka in the southern nares abyssal plain paleo oxidation zones can be recognized in old turbidites by distinct changes in color between lower and upper portions of the deposit in the basal unoxidized portion of the turbidite the sediments are characteristically dark green gray or brown in the paleo oxidized zone the sediments are pale green blue or yellowish brown these zones in both the madeira and southern nares abyssal plains contain distinctly less organic c and carbonate in the paleo oxidized zone as compared with the unoxidized sediments depletion of carbonate content in the oxidized zones in the southern nares abyssal plain is particularly significant in that as much as 80 of the initial carbonates have been lost also the relative amounts of weak acid soluble fe and mn are generally less in the paleo oxidized zones due to the initial oxidation of metal carbonate and metal hydroxide forms to easily reducible oxide forms which are then subsequently solubilized under the mildly reducing conditions at depth in the sediment column

space time description of nonstationary trapped lee waves using st radars aircraft and constant volume balloons during the pyrex experiment abstract the third intensive observation period iop3 of pyrex was a case of strong lee waves generated by a southerly wind crossing the pyrenees chain upstream radiosounds and measurements obtained by aircraft along the chain transect and by constant volume balloons launched near the crest provided spatial characteristics of the lee wave at different times and heights values ranging from 7 to 14 km for the horizontal wavelength and from 3 to 5 m s 1 for the maximum amplitude of the air vertical velocity were observed the lee wave horizontal extent measured from the crest line reached 30 to 55 km in addition two very high frequency stratosphere troposphere vhf st radars one on the mountain mean axis and another downstream in the lee wave field observed the temporal variations of the vertical profiles of the vertical velocity the analysis of those observed variations and their vertical distribution allowed the stationarity of the wave to be studied the lee wave was found to be far from stat

metal diagenesis in oxic marine sediments the metal nutrient relationships observed for nickel and cadmium in the deep ocean are continued at the interface between seawater and oxidizing pore water this continuum results in pore water concentrations of these metals which are only slightly greater than near bottom seawater levels manganese concentrations in these oxidizing pore waters are also extremely low less than three times bottom water in contrast release in the boundary layer produces a maximum of dissolved copper which is 10 40 times ambient seawater assuming these pore waters are at steady state flux estimates based on these measurements suggest that the manganese in todorokite rich nodules of the central equatorial pacific was not supplied by upward diffusion through pore waters below the interface most nodular nickel is precipitated with manganese while nodular copper is supplied by diffusion

recurrent uranium relocations in distal turbidites emplaced in pelagic conditions abstract the sediments of the madeira abyssal plain east of great meteor seamount are dominated by distal turbidite deposition while the turbidites exhibit a wide compositional range 25 80 caco3 individual examples can be correlated over a wide area and are relatively homogenous organic c oxidation by bottom water oxygen proceeds from the turbidite tops downwards after emplacement in pelagic conditions and the progress of this oxidation front is marked by a sharp colour contrast in the sediments wilson et al 1985 in turbidites with corg 0 5 redistribution of authigenic u occurs to form a concentration peak 4 9 ppm u just below the oxidation front or colour change several tens g u cm2 may be mobilised and in all examples studied 60 of the remobilised u is relocated into the peak following burial by subsequent turbidites such u concentration peaks are persistent as relict indicators of their extinct oxidation fronts for at least 2 105 years in the case of thin turbidites where labile corg is almost exhausted the u peaks may be located in underlying sedimentary units because of their relationship to the oxidation front a redox mechanism for u peak formation is suggested from these data rather than a complexation with organic matter

dissolved organic carbon doc fluxes of deep sea sediments from the arabian sea and ne atlantic abstract diffusive flux of dissolved organic carbon doc from deep sea sediments is a poorly constrained component of the global marine carbon cycle but may play an important role for doc concentrations in the oceans during six cruises between the years 1995 and 2000 we measured doc concentrations in pore waters of surface sediments and the ambient bottom waters at five stations in the deep arabian sea water depths 3190 4420 m and at two sites in the ne atlantic 4500 4800 m pore water doc concentrations were usually one order of magnitude greater than in bottom waters with maximum doc contents between 509 and 1526 mol l in the uppermost sediment interval 0 0 5 cm doc values generally decrease towards 3 cm core depth with slightly increasing concentrations in deeper layers under sub oxic to anoxic conditions calculated benthic doc effluxes into the bottom water caused by concentration gradients ranged between 59 8 and 223 9 mol m 2 d 1 in the arabian sea and 47 2 and 121 2 mol m 2 d 1 in the ne atlantic doc efflux rates were highly correlated with the annual vertical particle flux rates at the sites and thus appear to be a function of the regional productivity taking an average global oceanic doc efflux rate between 50 5 and 78 1 mol m 2 d 1 we calculated that the doc release is in the order of 70 103 1012 g c yr 1 from sediments below 2000 m water depth thus deep sea sediments have the potential to represent a significant source of doc in the oceans

depth localization of denitrification in a deep sea sediment from the madeira abyssal plain1 sediments of the madeira abyssal plain are dominated by alternate sequences of pelagic sediment and turbidites composed of relatively organic rich material transported from the continental margin after the deposition of a turbidite and resumption of pelagic sedimentation the zones of o2 and no3 respiration progress slowly into the turbidite from above the oxidation front is characterized by depletion of o2 and no3 at almost identical depths data are presented to show that no3 respiration denitrification within such a turbidite is localized in a very small depth interval at the oxidation front

the composition and diagenesis of interstitial solutions ii fluxes and diagenesis at the water sediment interface in the high latitude north and south atlantic studies of the major element composition of in situ sampled pore waters are reported for the north atlantic and southern ocean between africa and antarctica the pattern of diagenetic modification of pore water composition is similar throughout the entire atlantic enrichment of na ca2 and alkalinity and depletion of mg2 and k are nearly universal only siliceous oozes consistently provide very limited evidence of cation diagenesis the changes observed and the calculated fluxes across the seawater sediment interface are much the same as those reported previously for other areas of the atlantic and caribbean fluxes of the major cations across the interface continue to be indicated as a major factor in the geochemical cycling of these elements particularly na mg2 and k diagenetic modelling indicates that aerobic oxidation of organic matter and consequent dissolution of caco3 is a dominant reaction throughout the north atlantic the data indicate that o2 oxidation to at least 30 cm is prevalent at nearly all stations dissolution of caco3 in response to the introduction of metabolic co2 can lead to significant post depositional modification of the sediments the modelling also indicates a 1 1 stoichiometric relationship between na release and mg2 uptake by sedimentary components although dissolved silica concentrations in biogenic siliceous sediments are among the highest yet reported 700 m calculations demonstrate that solubility control cannot be through equilibria with the mineral sepiolite further the influence of cation silicate surface phases generally upon solubility is contraindicated by si oh 4 mg2 h relationships evaluation of the influence of fluid advection on pore water profiles indicates that at the stations studied in the north atlantic it is small a more general consideration of the potential contribution of fluid advection to shaping interstitial water profiles demonstrates that advection can be a dominant factor in such circumstances serious misinterpretation of the nature of diagenetic reactions may result from a lack of knowledge and consideration of fluid advection

gravity wave interactions around the jet stream 1 vhf radar measurements have been applied to study the interaction between a mountain wave and an inertia gravity wave above the jet stream in the tropopause region the mountain wave was observed to break and generate turbulence at a critical level that was induced by the inertia gravity wave this indicates that wave wave interactions can be an important source of turbulence and consequently mixing in the tropopause region

post depositional migration of elements during diagenesis in brown clay and turbidite sequences in the north east atlantic abstract two cores from a ne atlantic pelagic clay area of low accumulation rate each contain a single turbidite with different age thickness and composition diagenesis following introduction of exotic turbidite material into the pelagic clay sequence has resulted in distinctive colour changes the diagenetic process is thought to be driven by bacterially mediated organic oxidation and compositional differences in the turbidites and clays allow examination of the effects on metal concentrations of this process in one core a long turbidite section emplaced 330 000 years ago is overlain by clay organic oxidation has apparently proceeded from the turbidite top downwards and has maintained a u concentration peak below the oxidation front marked by a colour change the u source is believed to be u initially associated with the organic matter in the oxidised section of the turbidite vanadium and cu behave similarly but upward migration of the redox sensitive metals mn and ni is also seen in the second core an 8 cm turbidite section was emplaced about 170 000 years ago in a clay column in this case organic consumption now appears complete but evidence for diagenetic effects is found in a 16 cm compositional alteration halo of the underlying pelagic clay fe ii has been enriched and the hydrogenous component of mn co ni and cu removed from the pelagic clay to form the halo

biogenic budgets of particle rain benthic remineralization and sediment accumulation in the equatorial pacific abstract budgets of organic c corg cac03 and opal have been constructed for the palisades ny pacific equatorial region at 140 w between 5 n and 5 s measurements of the rain and benthic remineralization rate of biogenic materials have been adjusted and normalized to account for sampling biases sea surface temperature serves as a master variable in normalizing sediment trap and benthic remineralization data to average conditions the rain and remineralization rates for corg are nearly equal 0 40 0 05 and 0 46 0 06 mmol m 2 d 1 respectively thus only a minor fraction of this constituent is buried rain and dissolution rates for biogenic opal are similarly balanced 0 3 0 06 and 0 36 0 01 mmol m 2 d 1 and consistent with the value for opal burial 0 0 0 004 the cac03 budget appears to have changed during the holocene the best estimates of modern cac03 dissolution 0 58 0 03 mmol m 2 d 1 and rain rate 0 61 0 06 are consistent with230th normalized carbonate accumulation rates for the late holocene 0 1 mmol m 2 d 1 however the balance between dissolution and rain is not consistent with early holocene carbonate accumulation 0 3 mmol m 2 d 1 and this imbalance suggests 1 a recent increase in the rate of cac03 dissolution on the sea floor or 2 a decrease in the rain rate of carbonate particles modeling230th profiles in sediments from this region define the last 3000 years as the duration of increased dissolution or decreased particle rain 231pa 230th ratios in sediments indicate that particle rain rates have remained constant or possibly increased slightly through the holocene two potential causes for increased dissolution were investigated a change in deep water carbonate saturation or a change in co g cac03 rain ratios a model describing carbonate dissolution as a function of the degree of undersaturation and the amount of organic carbon oxidation within sediments indicates that the recent increase in dissolution is more likely due to changes in bottom water chemical composition we propose that pacific ocean bottom water carbonate ion concentration has decreased by 10 15 m over the last 3000 years

what do we learn from peaks of uranium and of manganese in deep sea sediments abstract uranium and manganese are two redox sensitive trace elements with complementary behavior under anoxic conditions u is immobile while reduced mn is dissolved in pore water of sediments uranium diffuses from sea water into reducing sediments and is enriched there the depth of the reducing layers and the sediment accumulation rate determine the enrichment of authigenic uranium on the contrary mn is dissolved in the reducing sediment sections diffuses in pore water and forms peaks of mn oxide as soon as oxygen is available thus the profiles of both mn and authigenic u record the depth of the redoxcline during periods of oxygen limitation in the sediments estimates of the depth of incorporation of uranium during the last glacial were derived for several cores at localities in the atlantic numerical modeling of the redoxcline as a function of the oxygen content of the water column and of the flux of organic matter to the sediments constrains these values during periods of extreme shallow redoxcline depths burn down of organic matter and deepening of the redoxcline during the holocene may have significantly altered the organic matter and uranium signals of glacial sediments at present day conditions sediments accumulating at rates smaller than 2 cm ky 1 may have lost the u signals peaks of manganese are then the only reliable record for a less ventilated sediment column in the past

the behaviour of manganese in atlantic carbonate sediments abstract manganese porewater and solid phase data are considered from two different atlantic carbonate sediments both with good geochemical characterisation the first case is a continuously accumulated alternating pelagic marl carbonate ooze where there is a correlation in post oxic conditions between mn ii porewater levels and an acetate leachable mn fraction of the sediment this leachable mn appears to have an association with calcite and in this example the leached residue mn content approximates to that of shale in the second case a very recent compositionally homogeneous calcareous turbidite is underlain by mn oxyhydroxide at the former sediment surface which is now acting as a source of mn ii by reduction sorption of mn by the turbidite sediment and shale like leached residue mn levels in anoxic conditions are again observed as mn ii diffuses towards present oxic conditions although no unique equilibrium is achieved similar older buried turbidites have concentration decreases in solid phase mn content preserved from bottom to top as relict evidence that this process has occurred in these turbidites 54 64 of the total mn is leachable by the acetate method and therefore presumed to be sorbed by calcite the oldest example has persisted for 125 kyr it is suggested that the slow breakdown of metastable mn oxyhydroxide and sorption of mn ii to calcite surfaces are important controls on the behaviour of mn in pelagic carbonates in mildly reducing conditions where accumulation fluctuations occur these processes act together with accumulation to limit overall mn migration and to prevent the large mn enrichments seen near the sediment surface in more reducing environments

porewater cadmium geochemistry and the porewater cadmium δ13c relationship results from two continental margin cores collected off pt sur california make possible a direct determination of the relationship between dissolved cadmium and the carbon isotopic composition of dissolved inorganic carbon in the interstitial water of suboxic marine sediments the 13c values of dissolved inorganic carbon decrease nearly 1 in the top 0 5 cm of the sediments and display a more gradual decrease through the top 20 cm of the sediments dissolved cadmium concentrations increase by 0 6 to 1 5 nmol kg in the top 0 5 cm of the sediments and then rapidly decrease to values of approximately 0 12 nmol kg between 5 and 10 cm into the sediments apparently as a result of scavenging onto iron oxide surfaces this pattern contrasts with porewater cadmium profiles previously reported for pelagic sediments which show no evidence of cadmium scavenging by the sediments however porewater cadmium concentrations are poorly correlated with porewater 13c values in both oxic and suboxic sediments these results suggest that the cadmiumcalcium ratios and 13c values of infaunal benthic foraminifera need not be tightly linked and that the relationship between these two aspects of foraminiferal shell chemistry may vary in response to changes in sediment geochemistry

mountain wave drag in the stratosphere and mesosphere inferred from observed winds and a simple mountain wave parameterization scheme abstract a daily analysis of mountain wave propagation through observed global wind and temperature fields in january and august is presented winds and temperatures are obtained from the daily 18 level nmc climate analysis center mountain wave properties are deduced from a simple gravity wave parameterization scheme in which the effects of topographic anisotropy ridge orientation are explicitly included planetary waves in the northern winter stratosphere are found to play an important role in modulating the magnitude and distribution of inferred mountain wave drag in the middle atmosphere the aleutian anticyclone is found to effectively block mountain waves generated over western north america from reaching the mesosphere by inducing local mountain wave critical levels in the stratosphere stratospheric sudden warmings have a similar effect at all longitudes so that during months with sudden warmings have a similar effect at all longitudes so that during months with sudden warmings the average in

gravity wave forcing in the stratosphere observational constraints from the upper atmosphere research satellite and implications for parameterization in global models 1 global models that include parameterized gravity wave effects have an excessively broad range of tuning parameters to choose from that allow a very broad range of gravity wave momentum forcing distributions we derive a set of constraints on gravity wave characteristics near the tropopause from databased estimates of gravity wave effects in the stratosphere we use 5 6 years of upper atmosphere research satellite data and uk met office analyzed wind and temperature fields to first derive estimates of the gravity wave mean flow forcing in the stratosphere we then compare these estimates to a suite of gravity wave model calculations to infer the constraints on the gravity wave characteristics near the tropopause these constraints apply to the portion of the gravity wave spectrum that dissipates in the stratosphere and does not include those that dissipate and drive the mesosphere we focus on equatorial and extratropical regions separately and find substantially different wave characteristics between the two we also find a seasonal variation in gravity wave characteristics in the extratropics near the equator gravity waves assist in driving the quasibiennial and semiannual oscillations and our constraints on gravity waves likely include a blend of characteristics of both ordinary gravity waves and some kelvin wave modes in the extratropics gravity wave forcing primarily assists in the annual winter to summer transition from westward to eastward winds

early diagenetic processes fluxes and reaction rates in sediments of the south atlantic abstract porewaters recovered from sediment cores gravity corers box corers and multicorers from various subrogions of the south atlantic amazon river mouth equatorial upwelling congo river mouth benguela coastal upwelling area and angola basin were investigated geochemically objectives included determination of eh ph oxygen nitrate sulfate alkalinity phosphate ammonium fluoride sulfide cal mg sr fe mn and si in order to quantify organic matter diagenesis and related mineral precipitation and dissolution processes porewater profiles from the eastern upwelling areas of the south atlantic suggest that sulfate reduction in the deeper parts of the sediment may be attributed mainly to methane oxidation whereas organic matter degradation by sulfate reduction is restricted to the near surface sediments further a prominent concentration gradient change of sulfate and related mineralization products occurred typically in the upwelling sediments at a depth of 4 to 8 m far below the zone of bioturbation or bioirrigation because other sedimentological reasons seem to fail as explanations an early diagenetic sulfide oxidation to sulfate within the anoxic environment is discussed porewater profiles from the sediments of the amazon fan area are mainly influenced by reactions with fe iii phases the remarkable linearity of the concentration gradients of sulfate supports the idea of distinct reaction layers in these sediments in contrast to the upwelling sediments the sulfate gradient develops from the sediment surface to a sulfate reduction zone at a depth of 5 3 m probably because a reoxidation of sulfide is prevented by the reaction with iron oxides and the formation of iron sulfide minerals a comparison of organic matter degradation rates from the different areas of the south atlantic show the expected relationship to primary productivity oxygen is the dominating oxidant whereas organic matter degradation by nitrate mn iv and probably also fe iii reduction is several orders of magnitude lower sulfate reduction is quantitatively of similar importance as oxygen respiration in the organic rich sediments but may also include methane oxidation reoxidation of ammonium and mn2 by oxygen or nitrate do not alter significantly the estimation of organic matter degradation in the oxic zone but may contribute to the nitrate reduction in suboxic layers

generation of the benthic foraminiferal assemblage theory and preliminary data abstract the production of benthic foraminiferal communities is filtered through taphonomic mainly destructive processes within the sediments to generate the fossil assemblage both the production and the taphonomy depend on bottom water oxygen content and flux of organic carbon to the seabed an examination of the relationships of processes generating the fossil assemblage to oxygen and organic carbon supply is made using pore water geochemical measurements to estimate carbon flux for locations in the gulf of mexico and the central california margin the locations are plotted in a three dimensional field with bottom water oxygen content organic carbon flux and sediment depth as the axes then the response of foraminiferal standing stock taphonomic processes and the developing fossil assemblage to the field is investigated variation in the vertical stratification of foraminiferal standing stock and test production species stratification taphonomic process intensity and stratification and sediment bioturbation lead to marked differences in the way the fossil assemblage is generated across the oxygen content organic carbon flux field the result is that the oxygen carbon flux field has a significant impact on the fossil assemblage through the interaction of biological and biogeochemical processes in the sediments a model of this interaction is investigated to show how its elements change across the oxygen carbon flux field and how these affect the generation of the fossil assemblage

presence of oxygen and aerobic communities from sea floor to basement in deep sea sediments the depth of oxygen penetration and microbial activity in marine sediments varies by region sediment cores from the south pacific gyre host oxygen and aerobic microbial communities to at least 75 metres below the sea floor

on the role of an anisotropic gravity wave spectrum in maintaining the circulation of the middle atmosphere the spectral parameterization of gravity wave momentum deposition proposed by medvedev and klaassen has been incorporated into the canadian middle atmosphere model numerical experiments show that an anisotropic gravity wave source significantly improves the middle atmosphere circulation compared to an isotropic source these results suggest that at least in midlatitudes the gravity waves primarily responsible for the momentum deposition at mesospheric heights are launched with observed phase velocities which are primarily in the same direction as the mean wind at tropospheric source heights

influence of slip surface geometry on earth flow deformation montaguto earth flow southern italy we investigated relations between slip surface geometry and deformational structures and hydrologic features at the montaguto earth flow in southern italy between 1954 and 2010 we used 25 boreholes 15 static cone penetration tests and 22 shallow seismic profiles to define the geometry of basal and lateral slip surfaces and 9 multitemporal maps to quantify the spatial and temporal distribution of normal faults thrust faults back tilted surfaces strike slip faults flank ridges folds ponds and springs we infer that the slip surface is a repeating series of steeply sloping surfaces risers and gently sloping surfaces treads stretching of earth flow material created normal faults at risers and shortening of earth flow material created thrust faults back tilted surfaces and ponds at treads individual pairs of risers and treads formed quasi discrete kinematic zones within the earth flow that operated in unison to transmit pulses of sediment along the length of the flow the locations of strike slip faults flank ridges and folds were not controlled by basal slip surface topography but were instead dependent on earth flow volume and lateral changes in the direction of the earth flow travel path the earth flow travel path was strongly influenced by inactive earth flow deposits and pre earth flow drainages whose positions were determined by tectonic structures the implications of our results that may be applicable to other earth flows are that structures with strikes normal to the direction of earth flow motion e g normal faults and thrust faults can be used as a guide to the geometry of basal slip surfaces but that depths to the slip surface i e the thickness of an earth flow will vary as sediment pulses are transmitted through a flow

pathways of organic carbon oxidation in three continental margin sediments we have combined several different methodologies to quantify rates of organic carbon mineralization by the various electron acceptors in sediments from the coast of denmark and norway rates of nh4 and sigma co2 liberation sediment incubations were used with o2 penetration depths to conclude that o2 respiration accounted for only between 3 6 17 4 of the total organic carbon oxidation dentrification was limited to a narrow zone just below the depth of o2 penetration and was not a major carbon oxidation pathway the processes of fe reduction mn reduction and sulfate reduction dominated organic carbon mineralization but their relative significance varied depending on the sediment where high concentrations of mn oxide were found 3 4 wt mn only mn reduction occurred with lower mn oxide concentrations more typical of coastal sediments fe reduction and sulfate reduction were most important and of a similar magnitude overall most of the measured o2 flux into the sediment was used to oxidized reduced inorganic species and not organic carbon we suspect that the importance of o2 respiration in many coastal sediments has been overestimated whereas metal oxide reduction both fe and mn reduction has probably been well underestimated

a new gravity wave drag scheme incorporating anisotropic orography and low level wave breaking impact upon the climate of the uk meteorological office unified model a new anisotropic gravity wave drag parametrization scheme which represents high drag states modelled on hydraulic jump flow blocking and internal wave reflection theory including trapped lee waves is presented the scheme is shown to represent the breaking of waves over mountains better than previous schemes by comparison with mesoscale simulations of pyrex case studies extended simulations of the meteorological office unified model at climate resolution are presented showing the impact of the new scheme and a combination of the scheme with a new orographic roughness parametrization results show a changed distribution of surface gravity wave surface stress mostly due to mountain anisotropy and a greater tendency for lower troposphere wavc drag inclusion of the orographic roughness parametrization halves the gravity wave stress the combined effect of these schemes for climate integrations being a slight improvement to the tropospheric flow

pore waters of the central pacific ocean nutrient results interstitial waters from the manop siliceous and calcareous ooze sites in the central pacific ocean were recovered by shipboard squeezing and centrifuging techniques and an in situ harpoon sampler the pore waters were analyzed for nutrients carbonate system species mn 2 ca 2 total alkaline earth metals and dissolved oxygen siliceous ooze site only in calcareous sediments the co 2 alkalinity po 4 3 and ca 2 results obtained from shipboard techniques are significantly different than those recovered in situ the other species measured as well as all of the data from the siliceous ooze site reveal no significant dependence on the method used to sample the pore water the relative changes in o 2 no 3 mn 2 alkalinity and co 2 indicate that respiration using o 2 no 3 and mno 2 as electron acceptors is the dominant reaction affecting the pore water species we develop a model which simulates the fate of pore water oxygen and nitrate and particulate organic carbon in sediments this model includes the effects of pore water diffusion oxygen and nitrate respiration sediment accumulation sediment mixing and changes in sediment porosity we observe that factor of 2 variations in the rates of sediment mixing and accumulation have only a minor effect on the pore water profiles the major factor controlling the pore water profiles is the flux of organic carbon across the sediment water interface we conclude that the large intra site variability observed in the interstitial water nitrate profiles is probably caused by small scale variations in the flux of organic material

investigation of a landslide in maskinonge quebec several first time landslides occurred in the maskinonge area quebec during the summer which is rather unusual they have been studied in detail including a site investigation the results show

phosphorus regeneration and burial in near shore marine sediments the gulf of trieste northern adriatic sea abstract according to bioassay studies and high dissolved nutrient n p ratios in the seawater column phosphorus p is thought to control marine productivity in the northern adriatic sea p in near shore marine sediments of the gulf of trieste the northernmost part of the adriatic sea was investigated using pore water p distributions and benthic p flux studies under oxic and anoxic conditions the data show that p regeneration is up to three fold more extensive in sediments overlain by oxygen depleted waters and proceeds in parallel with fe and mn enhanced benthic fluxes it appears from the incubation experiments that degradation of sedimentary organic matter is the main contribution to the flux of p at the sediment water interface while the release of phosphate adsorbed on the iron oxide surface is of minor importance it appears that about 50 of p in the gulf of trieste is retained within in the sediments probably bonded to clay minerals and carbonate grains or precipitated as fluoroapatite in these sediments total p p tot is preserved preferentially over organic c c org p regenerated from surficial sediments contributes about 1 3 of the p that is assimilated by benthic microalgae the phytoplankton p requirement should be entirely supplied from fresh water sources these results suggest that oxygen depletion in coastal areas caused by eutrophication enhances p regeneration from sediments providing the additional p necessary for increased biological productivity the development of anoxic bottom waters in coastal areas enhances the recycling of p exacerbating the nutrient requirement in the area a geochemical record of p burial in a longer sedimentary sequence revealed an increasing trend of p tot and organic p p org contents occurring approximately 50 years bp after 1950 probably due to increasing use of inorganic fertilizers and detergents in the area

denitrification in a deep sea sediment core from the eastern equatorial atlantic1 shipboard measurements of denitrification were made in sediment from the eastern equatorial atlantic using an acetylene inhibition technique undisturbed subcores were incubated for 1 9 days at 4 sup 0 c in a n sub 2 c sub 2 h sub 2 atmosphere 9 1 mixture by volume 1 atm and denitrification rates were determined from the observed accumulation of n sub 2 o in contrast to the predictions of several recent diagenetic models no denitrification activity was observed in the region directly beneath the nitrate maximum however activity was concentrated lower in the sediment at a depth coincident with an organic rich layer

investigation of a possible submarine landslide at the var delta front nice continental slope southeast france the var prodelta progrades across a straight narrow shelf less than 2 km wide with a very steep continental slope reaching locally more than 30 historically the var delta front is sadly famou

alleviation of a systematic westerly bias in general circulation and numerical weather prediction models through an orographic gravity wave drag parametrization systematic westerly biases in the northern hemisphere wintertime flow of the meteorological office 15 layer operational model and 11 layer general circulation model are described evidence that the failure to parametrize subgrid scale orographic gravity wave drag may account for such biases is presented this evidence is taken from aircraft studies surface pressure drag measurements and studies of the zonally averaged momentum budget a parametrization scheme is described in which the surface stress is proportional to the near surface wind speed and static stability and to the variance of subgrid scale orography the stress is absorbed in the vertical by considering the influence of such gravity wave activity on static stability and vertical wind shear a richardson number dependent wave breaking formulation is devised and the vertical stress profile determined by a saturation hypothesis whereby the breaking waves are maintained at marginal stability it is shown that wave breaking preferentially occurs in the boundary layer and in the lower stratosphere results from a simple zonally symmetric model show how the adjustment to thermal wind balance with a wave drag in the stratosphere warms polar regions by adiabatic descent and decelerates the mean westerlies in the troposphere the influence of the parametrization scheme on integrations of the 11 layer model is described and found to be generally beneficial in a discussion of the reasons why this problem has only recently emerged it is suggested that the satisfactory northern hemisphere winter circulations of previous coarser general circulation models were due to a compensation implied by underestimating both the surface drag and the horizontal flux of momentum by explicitly resolved large scale eddies

pore water profiles and numerical modelling of biogeochemical processes in peru basin deep sea sediments abstract an extensive set of pore water profiles including o 2 no 3 no 2 nh 4 po 4 3 fe 2 mn 2 so 4 2 sio 4 4 ph and alkalinity as well as solid phase data on organic carbon content and porosity in 18 sediment cores obtained from five areas in the peru basin rv sonne 106 expedition in 1996 is presented the pore water profiles indicate that early diagenesis progresses through oxygen respiration denitrification and manganese iv reduction while the subsequent redox states iron iii reduction sulphate reduction and methanogenesis cannot be observed from the dissolved phase in these deep sea sediments a numerical diagenetic model was applied to the data in order to derive parameters such as the depositional flux of metabolizable organic matter or the bioturbation intensity that control the geochemical conditions in the deep sea floor and could not be obtained directly by measurements moreover the numerical simulations show that even those pore water no 3 profiles that decline non linearly to zero concentration are not compatible with a steady state assumption they can be explained only by transient downward progression of a nitrate front

in situ measurements of calcium carbonate dissolution rates in deep sea sediments benthic fluxes of alkalinity carbon dioxide and oxygen have been measured using an in situ incubation chamber at three sites manop sites c and s and pacflux site sc in the central equatorial north pacific at two carbonate rich sites c and sc a budget for oxygen alkalinity and tco2 fluxes indicate a net caco3 dissolution rate of approximately 0 4 mmol m 2 day 1 this rate is only 20 of previous estimates but is consistent with a dissolution rate constant predicted from laboratory experiments with deep sea sediments and derived from in situ flux measurements in sediments of the southern california borderland organic matter oxidation in the sediment column provides the acid for 60 100 of the calcium carbonate dissolution occurring at these sites with the remainder derived from undersaturated bottom water at a low carbonate site s no carbonate dissolution in the sediment or on the sea floor is apparent although sediment traps indicate a rain of caco3 through 3400 m the rates of remineralization relative to resuspension or erosion at this site must differ for organic carbon and calcium carbonate so that carbonate grains reaching the sea floor are physically removed by erosion or resuspension before they dissolve while organic carbon is largely oxidized before it can be physically removed

alignment of mountain wave patterns above wales a vhf radar study during 1990 1998 mountain waves must be parameterized in numerical models of the atmosphere but long term obervations of their characteristics are sparse in this study a large data set from the vhf radar at aberystwyth 52 42 n 4 00 w during the years 1990 1998 is used to investigate the relation between background wind direction local topography and the mountain wave alignment the horizontal wave vector of the mountain waves is on average found to be biased 10 anticlockwise from the wind direction in the lower troposphere near 2 km altitude and biased 20 clockwise from the wind direction near the ground this can be explained if the wave launching height where the background wind speed and direction values can be assumed responsible for generating the waves lies within the boundary layer where the wind has only partly rotated between its direction near ground level and its direction in the free troposphere above the boundary layer on average and for most background wind directions at aberystwyth the wind direction within the boundary layer is a more important influence on wave alignment than the orientation of upstream mountain ridges the relative height of the mountain peaks and the boundary layer may affect the average alignment of mountain waves and therefore the wave stress by as much as 30

simultaneous measurement of o2 mn fe i and s ii in marine pore waters with a solid state voltammetric microelectrode a solid state au hg voltammetric microelectrode was used to measure simultaneously and with millimeter spatial resolution the vertical distributions of o 2 mn 2 fe 2 hs and i in the pore water of sediments from the canadian continental shelf and slope the electrode was used shipboard to analyze undisturbed sediment cores and in a sediment mesocosm to determine the three dimensional distribution of redox species in the sediment surrounding an actively irrigated worm burrow in cores from emerald basin and cabot strait o 2 disappeared and mn 2 fe 2 and hs appeared in the vertical sequence predicted on the basis of thermodynamics in a core from the scotian slope o 2 disappeared at 14 mm depth but mn 2 was not detected over the 50 mm depth examined with the probe in all three cores i was detected in the pore water below the oxygen penetration depth in none of the cores did the distributions of o 2 and mn 2 overlap the thickness of the layer within which neither o 2 nor mn 24 could be detected ranged from 8 to 40 mm we suggest that nitrate not oxygen is used to oxidize mn 2 the upward directed mn 2 gradients of 3 5 and 10 mol m 4 in the emerald basin and cabot strait sediments respectively drive manganese fluxes that are morc than one order of magnitude lower than the o 2 fluxes which are estimated at 4 5 mmol m 2 d 1 the three dimensional distributions of solutes in the pore water in the sediment surrounding an irrigated worm burrow demonstrate that both the o 2 penetration depth and the depth where mn 2 is first detected are deeper in the vicinity of the worm burrow than away from it this is consistent with the notion that irrigation brings oxygenated water into the worm tube allowing oxygen to diffuse across the burrow wall into the sediment and react with mn 2 and other reduced porewater constituents three dimensional heterogeneity in porewater composition cannot be detected by conventional one dimensional coring and slicing techniques because these latter techniques average the porewater composition in a large volume of sediment they may indicate that the distributions of individual species overlap when in fact they do not

authigenic cadmium enrichments in suboxic sediments precipitation and postdepositional mobility the postdepositional mobility of cd and u has been investigated in north atlantic turbidites in order to validate their utility as proxies of paleo organic carbon fluxes in this region pelagic sediments are interspersed with relatively organic rich turbidites following instantaneous emplacement of turbidite units an oxidation front progressively migrated downwards into the suboxic turbidite thereby leading to redistribution of authigenic phases according to their affinity to different redox conditions authigenic cd concentrations show a large peak at the redox boundary and are significantly lower in the oxidized portion than in the deeper unoxidized part of the turbidite this distribution indicates that cd has been continuously remobilized by the oxidation front thereby suggesting high sensitivity of the cd species to the redox state and an efficient immobilization mechanism for cd under reducing conditions we propose the precipitation of cds as a plausible mechanism for removal of cd in reducing sediments rather than adsorption onto mineral surfaces this proposal is consistent with porewater data indicating diffusion of cd toward and uptake by suboxic sediments solubility calculations suggest that precipitation of cds may occur in suboxic sediments in the presence of trace levels of h2s below routine detection limits there is no evidence for release of cd or u back into seawater upon oxidation of reducing sediments the strong coupling between precipitation of authigenic cd and u and the early diagenetic degradation of organic carbon offers the potential of reconstructing paleo productivity using records of cd and u however postdepositional redistribution of authigenic cd and u may significantly alter records of authigenic cd and u thereby rendering paleo productivity reconstructions uncertain we propose that the cd u authigenic ratio may provide a qualitative indicator to assess the relative role of steady state incorporation relative to transient burn down enrichments

early diagenetic processes in the muddy sediments of the bay of biscay abstract in order to understand the early diagenesis processes occurring in continental margin environment modern sediments collected in six different sites from the bay of biscay have been studied these sites can be separated into two groups in the shallowest stations where sediments are highly bioturbated organic carbon levels are higher than 2 in the deepest stations sediments are much less bioturbated and organic carbon levels are lower in all sites the vertical distribution of redox sensitive species can be explained by the well established depth sequence of redox reactions based on the bacterially mediated oxidation of organic matter we have considered some alternative reaction pathways to explain the profiles of fe mn and n species these reactions deal with the ammonia oxidation by manganese oxide the aerobic denitrification and the oxidation of dissolved iron ii by nitrate or mn oxides vertical flux calculations with a simple diffusion model indicate that these reactions could account for the reduction of all the mn oxides and the oxidation of all the upward diffusing fe ii they may also be responsible for a significant part of the total dinitrogen production the relative importance of these pathways on early diagenetic processes and benthic fluxes has not been determined and must be examined with additional experimental works our study suggests however that the coupling between the benthic cycles of iron manganese and nitrogen could strongly influence the carbon cycling at the ocean floor

diagenetic separation of cadmium and manganese in suboxic continental margin sediments abstract the vertical distribution of cd differs from that of mn in sediment cores taken from the continental margins of the arctic and atlantic oceans the oxic surface sediment is depleted in cd and enriched in mn whereas the subsurface sediment is enriched in cd and depleted in mn in some cores the distributions of solid phase and dissolved mn are offset the porewater profiles indicate that mn is being precipitated relatively deep in the sediment whereas the solid phase distributions indicate that mn has been precipitated very close to the sediment surface in the recent past at one deep site located near the base of the continental slope 3000 m the offset may be caused by a relatively recent decrease in ocean productivity a corresponding decrease in the organic carbon flux to the sediment and a subsequent migration of the redox boundary deeper into the sediment however at a site where the upper sediment layers have accumulated during the last few decades this explanation cannot account for the offset distributions we propose that a fluctuating input of organic matter to the sediment on seasonal or decadal timescales causes the position of the redox boundary to fluctuate the fluctuating redox boundary pumps dissolved mn upward and concentrates it as mn oxide in a distinct layer at the upper limit of the redox excursion at the same time it pumps cd downward and concentrates it in a distinct layer at the lower limit of the redox excursion the net result of a fluctuating redox boundary is to increase the spatial separation of cd and mn during the early diagenesis of suboxic sediments

observations and numerical model simulation of a partialy trapped lee wave over the welsh mountains abstract a large amplitude lee wave event detected in radiosonde ascents during a field experiment in the welsh mountains is described and wave characteristics are deduced the synoptic flow pattern accompanying this wave field is used to initialize the u k meteorological office s nonhydrostatic mesoscale model with a 3 km horizontal grid length in an attempt to simulate the gravity wave response over the welsh mountains after 4 h of integration time the resulting flow held is quasi study and exhibits a fairly regular wave field with a dominant wavelength at about 22 km and nearly vertical phase lines verification is achieved by comparing rate of ascent variations with model vertical velocity variations along the trajectory of a radiosonde the agreement is very good the vertical structure equation for linear gravity waves is solved using the smoothed wind and temperature fields obtained from the sondes a leaky resonance is identified at the dominant wavelength of the model simulation limited co

using ammonium pore water profiles to assess stoichiometry of deep remineralization processes in methanogenic continental margin sediments 1 in many continental margin sediments a deep reaction zone exists which is separated from remineralization processes near the sediment surface here methane diffuses upward to a depth where it is oxidized by downwardly diffusing sulfate however the methane sources that drive this anaerobic oxidation of methane aom in the sulfate methane transition zone smt may vary among sites in particular these sources can be thought of as either i internal sources from in situ methanogenesis regardless of where it occurs in the sediment column that are ultimately coupled to organic matter deposition and burial or ii external sources such as hydrocarbon reservoirs derived from ancient source rocks or deeply buried gas hydrates both of which are decoupled from contemporaneous organic carbon deposition at the sediment surface using a modeling approach we examine the relationship between different methane sources and pore water sulfate methane dissolved inorganic carbon dic and ammonium profiles we show that pore water ammonium profiles through the smt represent an independent tracer of remineralization processes occurring in deep sediments that complement information obtained from profiles of solutes directly associated with aom and carbonate precipitation i e dic methane and sulfate pore water dic profiles also show an inflection point in the smt based on the type of deep methane source and the presence absence of accompanying upward dic fluxes with these results we present a conceptual framework which illustrates how shallow pore water profiles from continental margin settings can be used to obtain important information about remineralization processes and methane sources in deep sediments

processes controlling the distribution and cycling of manganese in the oxygen minimum zone of the arabian sea abstract vertical and horizontal distributions of dissolved and particulate manganese were investigated in the arabian sea northwestern indian ocean during the 1995 spring intermonsoon period march april us jgofs process cruise 2 tn045 the region is characterized by an intense basin wide oxygen minimum zone omz that strongly influences the manganese distribution in the omz two distinct dissolved mn d mn maxima were observed at depths of 200 300 m and 600 m respectively the latter peak displayed concentration maxima of approximately 6 nanomolar and was largely confined to stations north of 19 n latitude stations n2 n7 this mid depth maximum was associated with the low oxygen core of the omz o 2 saager et al 1989 geochimica et cosmochimica acta 53 2259 2267 this signal was largely absent at stations along the southern transect likely due to oxidative scavenging of d mn to the suspended particulate phase mid depth particulate mn maxima at some southern stations stations s4 s11 appear to be remnants of this feature the upper d mn maximum 200 300 m depth was more widely distributed than the 600 m peak with d mn concentrations of 3 to as high as 8 nm at most stations east of about 62 e longitude the signal was everywhere correlated with the secondary nitrite maximum at stations within the main denitrification zone delineated by naqvi 1991 nepheloid layers presumably bacterial also were associated with this depth interval particulate mn profiles displayed corresponding concentration minima and low mn al and reactive refractory mn ratios for this same depth interval suggesting reductive dissolution of mn oxyhydroxides these observations imply that in situ microbially mediated processes may be the predominant source of d mn in the upper omz while horizontal advection is more important deeper in the water column

denitrification in continental shelf sediments has major impact on the oceanic nitrogen budget denitrification rates in sediments within the oxygen deficient waters off mexico and from the gulf of maine were investigated on the basis of interstitial nutrient profiles nitrate fluxes into the sediments were calculated from gradients across the sediment water interface and vertical molecular diffusion coefficients and averaged 0 151 mexico and 0 0920 gulf of maine pmol no 3 cm 2 s 1 these are minimum values since these gradients may have been underestimated in the gulf of maine bottom water irrigation by macrobenthos increases the nitrate supply well above this estimate in addition only 15 22 of the expected ammonium is present in gulf of maine sediments perhaps because of removal by a rapid coupling of nitrification with denitrification this large apparent loss of the regenerated ammonium appears to be ubiquitous in shelf sediments with oxygenated bottom water the global denitrification rate in continental shelf sediments was reassessed to be 50 tg n yr 1 1 tg 1012 g demonstrating that sediments are an important sink for oceanic nitrogen globally current nitrogen losses from the oceans may exceed inputs by 60 90 tg n yr 1 over the glacial interglacial cycle the global sedimentary denitrification rate probably varied commensurately with the changing continental shelf area an oscillating oceanic nitrogen budget over these time scales could occur given the sequence of 1 scouring and dumping of terrestrial nitrogen into the oceans during glacial advance 2 removal of oceanic combined nitrogen to the atmosphere by denitrification following glacial retreat and 3 reincorporation of this n into terrestrial biomass during the interglacial period

observation and interpretation of wave clouds over macquarie island images obtained from two noaa avhrr overpasses of macquarie island in october 1985 show pronounced cloud bands associated with trapped lee waves one image reveals striking evidence of an abrupt change in the propagating wave mode the structure and evolution of the waves is interpreted using a linear wave model coupled with radiosonde data obtained from the island the model successfully forecasts the mode change and accurately predicts the associated wavelengths an interpretation of the difference between the amplitudes of the two modes is also provided infrared channel measurement of the temperature of the cloud in the wave crests yields a useful constraint on the cloud height

biogenic sedimentation and surface productivity changes in the southern california borderlands during the last glacial interglacial cycle abstract a variety of geochemical evidence suggests that surface productivity in the california borderlands region was 1 5 2 times higher during the last glacial relative to the holocene high accumulation rates of opaline silica and organic carbon suggest increased glacial productivity while carbonate accumulation records and c org c co 3 ratios point toward a dominantly siliceous plankton community at that time the observed productivity changes are attributed to a southerly migration of the north pacific high pressure cell which resulted in an intensification of the california current and enhanced upwelling south of 40 n during the last glacial

vhf radar measurements and model simulations of mountain waves over wales very high frequency vhf radar measurements of mountain waves over aberystwyth wales during 29 november 1997 are presented and compared with the predictions made by a three dimensional numerical model which is based on the linearized equations of motion the radar height time plot of vertical velocity reveals a wave field in the troposphere and lower stratosphere which changes significantly throughout the day four separate radiosonde soundings taken during the day are used to represent the steady background flow in the numerical model in this case the steady state model wave fields are shown to compare qualitatively well with the radar measurements and the three dimensional information provided by the model is used to help explain the changes in the wave field observed by the radar throughout the day the radiosonde profiles are interpolated in time to provide approximate basic state data at two hour intervals model steady state vertical velocity fields based on each of these 13 approximate basic state profiles are used to generate a model time height vertical velocity plot which is qualitatively similar to that obtained from the radar measurements indicating that to a reasonable approximation the evolving wave field can be regarded as a sequence of independent steady states this is generally true if the basic state flow remains steady over the time taken for wave packets to propagate over several wavelengths group velocity arguments are used to show that for typical mountain waves in the troposphere such time scales are generally less than one hour model simulations in which the basic state flow is allowed to vary in time continually based on either the interpolated radiosonde soundings or the radar horizontal wind measurements are conducted in this case the simulated wave fields are always unsteady the waves show a tendency to drift in response to changes in the basic state wind field for example during instances when the wind speed at a given level decreases whilst the wind direction remains the same the waves show an upwind phase propagation with a typical phase speed of the order of 1 m s 1 the consequence of this unsteadiness for the propagation of the waves is discussed copyright 2002 royal meteorological society

denitrification in sediments of the laurentian trough st lawrence estuary quebec canada abstract the isotope pairing technique was used to obtain the first sedimentary denitrification rates for the st lawrence estuary gulf system quebec canada denitrification rates were measured on intact sediment cores collected at three stations down the slope of the laurentian trough at 103 200 and 320 m depth for samples collected in june 1997 total denitrification rates ranged from 1 8 to 3 3 mol n m 2 h 1 among the three stations only 3 5 of the no 3 consumed by the sediments was subsequently denitrified nitrification was the major source of no 3 for denitrification representing 56 79 of total denitrification rates sediment consumption of water column o 2 102 187 mol o 2 m 2 h 1 and no 3 13 9 25 5 no 3 m 2 h 1 increased significantly downslope as did total denitrification rates denitrification made a negligible

a theoretical study of diagenetic concentration fields near manganese nodules at the sediment water interface the effects of manganese nodules on concentration fields in adjacent pore waters and sediments are investigated theoretically with a three dimensional axisymmetric diffusion reaction model the nodules are idealized as impermeable and poorly permeable disks and hemispheres the first part of this paper examines the organic matter and coupled pore water oxygen fields in order to evaluate the local redox conditions under an isolated nodule oxygen is allowed to disappear on a free surface that is calculated as an output of the model in sediments that become suboxic like those at manop site c the model predicts that pore waters neighboring a nodule are markedly more depleted in oxygen than in its absence although these reduced conditions may remobilize metals that would be available for nodule growth these same conditions would appear to favor nodule dissolution typically the presence of a nodule raises the local position of the zero oxygen surface but it is deeper than expected for large nodules on sediments containing only highly reactive organic matter the redox changes calculated for an isolated nodule on a hypothetical but representative oxidized abyssal red clay appear inadequate to raise the redox boundaries enough to facilitate metal transport from reduced regions deeper in the sediment in the later part of the paper the model is used to evaluate the influence of a nodule field on the outward flux of dissolved silica from a siliceous ooze although the flux attenuation is generally modest some dense packings observed in the pacific should produce substantial reductions 35 which should promote opal preservation

climatic control of turbidite deposition on the madeira abyssal plain studies of sedimentation in the southwestern part of the madeira abyssal plain have revealed sequences of turbidites correlatable over thousands of square kilometres turbidites are sediments transported by turbidity currents and represent rapidly accumulated sedimentary units1 in this case in the distal part of the flow they are very fine grained and homogeneous occasionally with silty bases individual turbidites are separated by thin pelagic units which alternate from oozes to pelagic clays a stratigraphy for these pelagic units has been produced from combining coccolith distributions and lithological changes which enables comparison to cores containing only pelagic sediments from outside the turbidite province these comparisons show that turbidity currents cause no significant erosion in the area the major turbidites occur between lithological alternations which reflect global climate changes associated with glaciations and related eustatic sea level fluctuations turbidites have been linked with eustacy on previous occasions but only with low stands of sea level2 3 our work shows that turbidites are more likely to occur during regressions and transgressions rather than in the quiet periods between

detection of shear zones in a natural clay slope using the cone penetration test and continuous dynamic sampling the detection of shear zones along which a mass of soil is moving is essential for understanding the state of stability of natural slopes weaker zones in clay soils can be identified from low values of cone penetration test cpt tip resistance measured during penetration this paper presents a case history illustrating the identification of softened shear zones in clay soils using the cpt and the observation of shear surfaces using continuous dynamic sampling cds the analysis and interpretation of the cpt data are discussed in relation to the detection of shear surfaces using the cds at a site with a history of slope instability difficulties encountered in identifying shear zones and detecting shear surfaces are discussed key words cone penetration testing slope stability in situ testing case history shear zone

early organic diagenesis the significance of progressive subsurface oxidation fronts in pelagic sediments abstract porewater and solid phase geochemical data at two contrasting ne atlantic stations are reported station 10552 on the cape verde abyssal plain is a site of slow pelagic accumulation ca 0 4 cm kyr 1 molecular oxygen is present in the sediment column to at least 2 m and probably much deeper labile organic carbon is almost totally consumed in the upper few centimetres of the sediment by contrast at station 10554 on the madeira abyssal plain the pelagic sequence has been interrupted by the occasional deposition of organic rich turbidites porewater oxygen and nitrate profiles show that subsurface organic metabolism of the organic carbon associated with the uppermost turbidite layer is a significant fraction of the overall metabolism in the sediment column this metabolism occurs at a relatively thin reaction front which progresses deeper into the turbidite with time this phenomenon exerts a controlling influence on the present nutrient profile and redox succession in a less extreme form substrate distributions of this latter type are not uncommon in atlantic sediments a model has been developed which is controlled by both oxygen and nitrate data this model permits a vertical profile of metabolic activity to be derived and also gives estimates of the reaction rate constants and solid phase mixing rates at these two contrasting stations about 30 of the total activity at station 10554 is located within the turbidite at the deepening reaction front this is a non steady state condition in fact it is found that the integrated metabolic activity at the two stations is not dissimilar ca 1 2 10 13 moles cm 2 sec 1 the striking differences in redox profile are therefore primarily attributable to differences in the distribution of metabolic activity within the column

benthic fluxes and pore water studies from sediments of the central equatorial north pacific nutrient diagenesis benthic exchange rates of radon 222 oxygen nitrate ammonia and silica were determined using an in situ benthic flux chamber and by modeling pore water profiles at three sites in the central equatorial north pacific a comparison of these results reveals several artifacts of pore water collection and processing whole core squeezer wcs silica profiles are influenced by adsorption during squeezing and yield calculated fluxes that are too large pore water ammonia profiles show near surface maxima that appear to be an artifact of core recovery near surface nitrate measurements may also be suspect due to oxidation of the ammonia released causing anomalously large nitrate gradients that yield overestimates of benthic exchange rates fluxes of radon oxygen and nitrate calculated from wcs profiles agree with chamber fluxes to better than 40 at all sites fluxes of silica and nitrate calculated from pore water data collected at coarser scales 1 cm intervals agree within 50 with chamber measurements previous flux estimates from pore water and solid phase models established at two of these sites using data collected 6 years prior to this work differ from these chamber measurements in some cases by up to a factor of 5 due to modeling uncertainties and temporal variabilities in the delivery of organic matter to a site the benthic oxygen consumption rates measured at these sites are similar they average 0 36 0 03 mmol m 2 day 1 and are consistent with a trend of oxygen uptake vs water depth previously established by others on a transect through the oligotrophic north pacific gyre

mapping the fluid flow of the mariana mounds ridge flank hydrothermal system pore water chemical tracers we present a conceptual model of fluid circulation in a ridge flank hydrothermal system the mariana mounds the model is based on chemical data from pore waters extracted from piston cores and from push cores collected by deep sea research vessel alvin in small meter sized mounds situated on a local topographic high these mounds are located within a region of heat flow exceeding that calculated from a conductive model and are zones of strong pore water upflow we have interpreted the chemical data with time dependent transport reaction models to estimate pore water velocities in the mounds themselves pore water velocities reach several meters per year to kilometers per year within about 100 m from these zones of focused upflow velocities decrease to several centimeters per year up to tens of centimeters per year a larger area of low heat flow surrounds these heat flow and topographic highs with upwelling pore water velocities less than 2 cm yr in some nearby cores downwelling of bottom seawater is evident but at speeds less than 2 cm yr downwelling through the sediments appears to be a minor source of seawater recharge to the basaltic basement we conclude that the principal source of seawater recharge to basement is where basement outcrops exist most likely a scarp about 2 4 km to the east and southeast of the study area

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

stable carbon isotopes in marine porewaters abstract we present centimeter scale porewater 13 c profiles from four sites in the central equatorial pacific ocean which reveal steep porewater 13 c gradients up to 1 0 cm 1 at the deep sea sediment water interface we describe the processes controlling porewater carbon isotopic composition and incorporate them into a model of the deep sea benthic carbon cycle our measured 13 c profiles are then used to estimate carbon rain rates at two of these sites manop sites c and s the 13 c data yield organic carbon rain rates of 10 mol c cm 2 yr 1 at site c and 3 mol c cm 2 yr 1 at site s these carbon rain rates agree with recent carbon rain estimates based on sediment trap data and porewater nitrate profiles but are a factor of 2 lower than estimates based on millimeter scale porewater oxygen profiles our model results indicate that changes of the same magnitude in organic carbon rain rate and bottom water composition o 2 co 2 and 13 c have comparable effects on the carbon isotopic composition of surficial porewaters this suggests the need to consider the effects of benthic carbon cycling on the stable carbon isotope record preserved in deep sea benthic foraminifera tests

al to oxide and ti to organic linkages in biogenic sediment relationships to paleo export production and bulk al ti abstract to increase our understanding of the mechanisms that control the distribution of al and ti within marine sediment we performed sequential extractions targeting the chemical signatures of the loosely bound exchangeable carbonate oxide organic opal and residual fraction of sediment from a carbonate dominated regime equatorial pacific and from a mixed opal terrigenous regime west antarctic peninsula we observe a systematic partitioning of al and ti between sediment phases that is related to bulk al ti we show that where we can quantify an alexcess component the dissolved al is preferentially affiliated with the oxide fraction resulting in al ti molar ratios of 500 3000 this is interpreted as the result of surface complexation in the water column of dissolved al onto oxyhydroxides we also observe a previously undetected tiexcess with as much as 80 of the total ti in the organic fraction which is most likely a function of metal organic colloidal removal from the water column in samples where the excess metals are obscured by the detrital load the al and ti are almost exclusively found in the residual phase this argues for the paired removal of al preferentially by the oxide component and ti preferentially by the organic component from the water column by settling particulate matter this research builds upon earlier work that shows changes in the bulk ratio of al to ti in carbonate sediment from the central equatorial pacific that coincide with changes in the sedimentary bulk accumulation rate bar the ratios that are observed are as much as three times higher than typical shale values and were interpreted as the result of scavenging of dissolved al onto particles settling in the water column because this non terrigenous alexcess accounts for up to 50 of the total sedimentary al inventory and correlates best with bar the bulk al ti may be a sensitive tracer of particle flux and therefore export production because we show that the excess metals are the result of scavenging processes the bulk al ti may be considered a sensitive proxy for this region

simulation of early diagenetic processes in continental slope sediments off southwest africa the computer model cotam tested abstract pore water of marine sediments recovered from two stations of the continental slope off southwest africa were investigated we present computer simulations of in situ and laboratory concentration profiles of oxygen as well as laboratory concentration profiles of nitrate calcium ph and alkalinity the simulations were carried out with help of a numerical model cotam to describe the transport and the reaction of dissolved species in sediments cotam is based on an operator splitting approach comprising the independent calculation of transport and chemical reaction the consumption rates of oxygen and nitrate were determined by optimal fits to the measured pore water profiles of these species it could be shown that measured concentrations of nitrate in pore water correspond to a decomposition of organic matter with c n ratios between 3 and 3 7 however artificially increased subsurface nitrate concentrations due to core recovery cannot be excluded but our results show much greater deviations from expected concentrations assuming redfield stoichiometry than previously reported from comparative studies i e martin and sayles 1996 oxygen consumption in situ was shown to be distinctively lower than measured in multicorer cores after recovery simulations with varying denitrification rates indicate reduced diffusive nitrate release into the bottom water by up to 50 compared to shipboard results effects of nitrification and denitrification on pore water ph carbonate alkalinity and calcium concentrations were simulated by recalculating concentrations of these species with regard to calcite equilibrium for these calculations we used the standard software phreeqe as a subroutine of cotam calcium and carbonate alkalinity increase due to solid phase calcite dissolution ph was calculated to be an order of magnitude lower within the zone of oxygen depletion than indicated by shipboard results this difference is mainly related to non equilibrium conditions during ph measurements

chemical evidence for advection of hydrothermal solutions in the sediments of the galapagos mounds hydrothermal field pore water profiles of ca mg f po4 3 and mn in the galapagos mounds hydrothermal field are believed to reflect in part upwelling of hydrothermal solutions through the sediments concentration depth profiles in a low heat flow area just north of the mounds field display diagenetic changes typical of those found in pore waters underlying highly productive surface waters consistent with the inference of no water flow or very slow downwelling w 5 cm yr of bottom water through these sediments rates of upward advection calculated from mounds field pore water profiles of ca mg and f profiles agree well with each other averaging about 1 cm yr in the pelagic sediments near the mounds and 15 30 cm yr within the hydrothermal mounds themselves the upward advection also modifies the shape of po4 3 and mn profiles advection rates inferred from the pore water data are generally in reasonable agreement with those made from heat flow data the higher ca and lower mg f po4 3 and mn concentrations in mounds field pore waters compared with those of the low heat flow area suggest chemical exchange between the solution and basalt prior to upwelling li k rb sr and so4 concentrations are indistinguishable from bottom water this suggests very high effective water rock ratios during the reactions which produced the upwelling solutions perhaps due to extensive prior alteration of basalt adjacent to the flow path of water through the crust inferred reaction temperatures are between 70 150 c