surface water vapor and momentum fluxes under unstable conditions from a rugged complex area abstract measurements were made of the profiles of mean wind velocity of temperature and of specific humidity in the unstable atmospheric boundary layer over macro rough terrain these data were obtained from radiosonde observations in a calibrated watershed of 3 2 km2 in the hilly pre alps of switzerland during the summer of 1982 the regional evaporation was reasonably well correlated r 0 7 with these profile measurements through a logarithmic height dependency between roughly 2h0 where h0 100 m is the mean height of the roughness obstacles and 0 6h where h is the height of the boundary layer above the mean valley level the shapes of the profiles appear to be essentially independent of the monin obukhov parameter z d0 l but they display a dependency on the wind shear aloft and on the value of z0 h where z0 is the roughness height over this rugged surface the relative importance of mechanical turbulence as compared to convective turbulence is larger than over terrain with smaller

cadomian subduction collision and variscan transpression in the badajoz cordoba shear belt southwest spain a discussion on the age of the main tectonometamorphic events

mobility of mo u as and sb within modern turbidites modern turbidites uranium molybdenum arsenic antimony we present and discuss porewaters and sediment data of mn fe mo u as and sb within four recent turbidites from the capbreton canyon sw france the deposition of turbidites on continental margins exerts strong influence on the fate of trace metals causing trace metal migration and or immobilization the down core distribution of the elements here depends entirely of ongoing diagenetic processes rather than the diffusion of o2 the persistence of fe mn oxides under anoxic conditions led to anoxic reoxidation of numerous species as nh4 reduced s compounds and trace metals metal oxides thus control the immobilization of mo and as in the solid phase and the remobilization of u and sb to the porewaters although the low sulphide production prevents anoxic authigenesis of mo and as reducing conditions below each horizon rich in mn fe oxides resulted in u and sb accumulation the exact mechanisms of sb immobilization are not known but it is most certainly different from that of as the profile shapes of mn and u were used to estimate the age of the turbidite deposits which cannot be determined by conventional radionuclide methods our interpretations however depend on calculations of diffusion coefficient particularly for u a simple diffusive model applied to mn suggested that the age of the latest deposit noted t1 was 22 months this date is close to the time elapsed between the core sampling and the last known turbiditic event in the capbreton canyon i e martin storm 18 months using the u data set and depending on diffusion coefficients used the estimated ages of the deeper layers were 4 7 yr for t2 and 7 5 14 yr for t3 the reliability and precision of this new approach to date sediments at short timescales is limited by the ignorance of a precise value for u diffusion coefficient reducing uncertainty on u diffusion coefficient will greatly support application of the proposed approach

review mesoscale modelling in complex terrain abstract this review focuses on those aspects of mesoscale models which require special techniques and parameterizations when modelling flow over complex terrain the basic concepts and limitations of various approaches are discussed and applications of models to specific problems are presented

early diagenetic reactions in interbedded pelagic and turbiditic sediments in the nares abyssal plain western north atlantic consequences for the composition of sediment and interstitial water abstract measured pore water concentrations of iron in interbedded pelagic and turbiditic sediments from the nares abyssal plain are in excellent agreement with sediment colour and measured redox potential the organic carbon content of these sediments appears to define the redox conditions and consequently the porewater and solid phase concentration of constituents that are involved in early diagenetic reactions in the turbiditic sediments the concentration of no 3 generally goes to zero within a sediment depth of 1 m whereas at 8 m in a pelagic core from the same area the concentration of no 3 is still higher than it is in the bottom water the pore water concentration of mn 2 in the turbiditic sediments increases sharply down to a depth of approximately 3 m and from thereon remains nearly constant due to saturation with respect to mn ca co 3 the pore water of the turbiditic sediments is also saturated with respect to calcite the few diagenetic spikes in the pore water concentration of no 3 and mn 2 and the concentration depth profile of dissolved iron h 4 sio 4 and phosphate all clearly demonstrate the inhomogeneous nature of interbedded pelagic and turbiditic sediments the simultaneous occurrence of peaks of dissolved iron silica and of sediment intervals with a relatively high organic carbon content is attributed to enhanced early diagenetic reactions associated with the decomposition of organic matter in these specific intervals linked with these reactions is the irregular pore water concentration of phosphate which is shown to originate partly from the oxidation of organic matter but mainly from the desorption of phosphate from iron oxide potential concentrations of phosphate are calculated from the stoichiometric early diagenetic reactions and compared with measured concentrations due to the unique combination of low porosity and relatively high sedimentation rates the sediments from the nares abyssal plain are an ideal basis for the study of such interbedded sequences of pelagic and turbiditic deposits

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

observations of boundary layer structure over complex terrain turbulence data collected in an area of complex terrain using a number of instrument packages attached to the tether cable of a captive balloon are presented eddy correlation measurements of the turbulent momentum flux are used to determine the magnitude of the roughness length from the drag coefficient and also to show that the roughness length is a useful concept in parametrizing the surface stress in such areas the relationship between the terrain characteristics and the roughness length is examined using a simple formula results from a numerical model and previous experimental estimates of the roughness length for complex terrain it is found that a formula based on numerical model results for separated flows gives reasonable predictions and that the measured roughness length is representative of an area of order 100 km2 non dimensionalized turbulence data are compared with similar data obtained over flat homogeneous surfaces this comparison suggests that the structure of the turbulent boundary layer over complex terrain is remarkably similar to that over flat homogeneous surfaces because of the limitations of fixed point measurements in complex terrain results from a numerical study of turbulent flow over two dimensional sinusoidal orography are shown to indicate the magnitudes of the perturbations introduced into the boundary layer flow by large undulations in the underlying surface the model results demonstrate the validity of the analysis carried out with the data

the diffusive tortuosity of fine grained unlithified sediments abstract use of fick s first law to estimate solute fluxes is arguably the most common and important calculation related to the geochemistry and environmental chemistry of fine grained unlithified sediments in such porous media the diffusion coefficient in this law must be reduced by the square of the tortuosity to account for the longer diffusive paths experimental methods to estimate tortuosity are specialized or time consuming and not routinely done an analysis of available data shows that tortuosity is accurately correlated to readily measured porosity values through the simple relation 2 1 l n 2

porewater redox species and processes in the black sea sediments during the 2003 knorr and the 2005 endeavor cruises to the black sea voltammetric solid state microelectrode data were collected for the vertical distribution of redox species in porewaters from the upper 200 to 300 mm layer of sediments with mm vertical resolution we discuss vertical distributions of dissolved sulfide manganese and iron species in sediments from the oxic suboxic anoxic sulfidic parts of the black sea results of voltammetric profiling demonstrate many processes governing the porewater chemistry of oxic shelf sediments suboxic shelf slope sediments deep anoxic sediments unit i and turbidites in deep anoxic sediments sediments from the oxic shelf areas appear to be spatially similar in their porewater chemistry revealing the same sequence of redox species as elsewhere in the ocean except for the lack of manganese this lack of manganese is explained by its diagenetic remobilization and accumulation in anoxic waters and suboxic sediments sediments from the suboxic part of the shelf slope reveal high concentrations of manganese ii and iron ii in porewaters still the flux of mn ii from these sediments comprises only a part of the mn iv that precipitates from the water column and can be diagenetically recycled in these sediments these sediments appear to be the major net sink of manganese as it is not accumulated in sediments of either the oxic or anoxic parts of the sea the porewater chemistry of deep anoxic cores showed major spatial variations in the magnitude and even direction of the flux of sulfide the sediments from the eastern central black sea show an expected unit 1 source of sulfide to the overlying water and have high sulfide content up to 1600 m in the anoxic western and near coastal cores turbidites cause significant loss of porewater sulfide down to nondetectable sulfide b0 2 m the latter can be explained by the origin and oxidized mn and fe content of turbidites 2007 elsevier b v all rights reserved

chemical mass balances in metalliferous deposits from the atlantis ii deep red sea abstract in order to assess the quantitative distribution of mineral species within the sedimentary series of the atlantis ii deep we have examined the chemical composition mineralogy and physical properties of 120 sediment samples from two cores that sampled the entire sediment sequences in the west and south west basins biostratigraphic correlations and chemical budget calculations indicate that the nonmetalliferous solid fractions i e detrital and biogenic particles in the older sedimentary unit unit 1 in the west basin represent 46 wt of the total and that they were deposited between 23 000 and 15 12 000 years bp with a mass accumulation rate between 109 and 150 kg per thousand years per square metre the muddy sediment in the upper part of the west basin core units 2 3 and 4 consists mainly of metalliferous particles which account for less than 15 wt of the mud and yield a mass accumulation rate 130 162 kg k y m 2 close to that of nonmetalliferous particles deposited simultaneously nonmetalliferous particles were probably the major source of si and a significant source of pb through dissolution in the brine system and diagenesis in the metalliferous mud the metalliferous sediments in the upper unit of the south west basin unit u 1100 cm were deposited at the same time as those of the upper unit in the west basin unit 4 335 cm the calculated mass accumulation rate is about 700 kg k y m 2 for unit u the recent sediments of the south west basin are more enriched in zn and cu and more depleted in mn relative to fe than the contemporary sediments in the west basin suggesting that the hydrothermal source has been in or near the south west basin during the last 2 250 years assuming that a salton sea like solution supplies all the fe contained in the west basin metalliferous sedimentary pile the mineralizing brine flowed at a minimum rate of 30 l s except for the period of mn oxide deposition the difference between the metal fe ratios in oxide rich and sulphide rich facies is attributed to changes in the chemical composition of the mineralizing fluid rather than to chemical processes acting in the brine system of the atlantis ii deep

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

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

spatial heterogeneity of benthic biogeochemistry in two contrasted marine environments arcachon bay and bay of biscay sw france we have studied the heterogeneity of vertical profiles of biogeochemical components obtained from sediment core slicing sediment cores were collected in the intertidal zone of the arcachon bay and on the continental slope of the bay of biscay at 550 and 1000 m depth at each station of the arcachon bay five 1 m side zones were delimited at low tide in each square 3 cores were collected spatial heterogeneity on the continental slope was obtained from the study of 3 cores of multi corer while 2 or 3 multi corer deployments were used during the same oceanographic cruise similarity between profiles was determined to estimate the spatial heterogeneity at different scales in the arcachon bay results showed a spatial heterogeneity at a decimetre scale on apparently homogeneous areas despite the spatial variability all the replicated profiles in arcachon bay sediments had similar trends suggesting homogeneous benthic properties however a sampling with replicate cores handling is required for seasonal monitoring or study of biogeochemical mechanisms in coastal environments we observe that the spatial variability on the continental margin of the bay of biscay is lower than in coastal environment of the arcachon bay heterogeneity is equivalent at a decimetre scale and at a hundred meters scale which is the precision of the sampling positioning due to the drift of the boat and the tilt of the corer cable in addition our 10 year long database for the bay of biscay showed that differences in the shape of profiles obtained in sediment cores collected at the same stations throughout this long period may not be interpreted in terms of evolution with time because the observed variability is as high as the spatial heterogeneity

effect of changes in water level on sediment pore water redox geochemistry at a reservoir shoreline pore water samplers with high vertical resolution were used to evaluate the response of sediment redox geochemistry during transient hydrologic conditions at lake powell a large reservoir in utah and arizona usa samplers were deployed at two different yet proximal shoreline locations white and farley canyons before and after exposure of sediment to air and subsequent resubmersion which resulted from fluctuations in the water level of the reservoir before exposure to air an observed increase in dissolved mn concentrations and at farley canyon an observed decrease in dissolved u concentrations across and immediately below the sediment water interface indicated reducing conditions in the sub surface after exposure and resubmersion of the sediment pore water profiles at each site differed distinctly from those observed before the fluctuation in water level at white canyon an increase in u concentrations and a decrease in mn concentrations in pore water after exposure and subsequent resubmersion are suggestive of oxidative processes occurring during the period of sediment exposure data from farley canyon suggest that the same processes may be occurring but to a lesser extent depth profiles of as and pb were also examined but were relatively featureless compared to those of mn and u at both sites sediment evaluated for pore water chemistry in the second sampling was only fully resubmerged for 2 5 days prior to the second sampling event yet reducing conditions were clearly evident in the mn pore water profiles this suggests that the dynamics of the biogeochemical processes occurring in surface sediment at lake powell are responsive on the timescale defined by the fluctuating water levels in the reservoir

phosphorus diagenesis in sediment of the thau lagoon we describe the depth distribution of phosphorus in relation to the distribution of major redox species dissolved o2 n o 3 n h 4 mn and fe and particulate s organic c reactive mn and fe oxides in modern sediments of two stations in the thau lagoon sediments close to the oyster bank zone are enriched in organic carbon and are highly bioturbated while those outside the bank are less bioturbated and organic carbon levels are lower in all sites early diagenesis follows the well accepted depth sequence of redox reactions of organic matter mineralization the upper sediments of the station enriched in organic carbon contain high amounts of reactive particulate organic phosphorus that arrives at the sediment surface through biodeposition only a part of this phosphorus is released to the bottom water after mineralization since more than 50 of total p is buried as an authigenic phosphate mineral in the middle of the lagoon outside the oyster bank zone organic matter seems to be much more refractory but the distribution of the major redox compounds indicates that this organic matter is partially mineralized a portion of the phosphate and ammonium released during mineralization does not escape the sediment since the concentration gradient is close to zero between 1 and 25 cm depth below the sedimentewater interface pore water n and p are likely fixed by biological uptake the characterisation and magnitude of this process require further study 2006 elsevier ltd all rights reserved

upper quaternary deposits on the sao tome deep sea channel levee system south brazilian basin major turbidite versus contourite processes abstract this paper is an attempt to show how one may discriminate turbiditic and contouritic processes in the deposition of deep sea accumulations the case study is the sao tome deep sea channel levee system in the south brazilian basin this system is elongated parallel to the margin contour and was first interpreted as being controlled by contour current activity detailed analyses of 3 5 khz profiles and piston cores allowed to demonstrate that the upper quaternary sediments are predominantly deposited by turbidite and hemipelagic pelagic sedimentation processes on the levee and the transitional area towards the deeper rise frequent fine grained turbidites accounting for 25 45 of the entire depositional series are interbedded with the hemipelagic pelagic muds in the channel thicker and coarser turbidites 15 are associated with debris flows 20 deposit deformation in the form of slides slumps and diapir like structures largely affect the distal transitional area slight evidence of contour current activity only consists of some sediment wave fields and manganiferous rich layers or some top truncated sequences and foraminiferal sandy layers

cycling of trace metals mn fe mo u v cr in deep pore waters of intertidal flat sediments trace metals mn fe mo u cr v were studied in pore waters of an intertidal flat located in the german wadden sea the study system is an example of a permeable tidal flat system where pore water exchange is affected by tidal driven pressure gradients besides diffusion permanently installed in situ samplers were used to extract pore waters down to 5 m depth throughout one year the samplers were either located close to the tidal flat margin or in central parts of the tidal flat despite dynamic sedimentological and hydrological conditions the general trends with depth in deep tidal flat pore waters are remarkably similar to those observed in deep sea environments rates of trace metal cycling must be comparably large in order to maintain the observed pore water profiles trace metals further show similar general trends with depth close to the margin and in central parts of the tidal flat seasonal sampling revealed that v and cr vary concurrent with seasonal changes in dissolved organic carbon doc concentration this effect is most notable close to the tidal flat margin where sulphate doc and nutrients vary with season down to some metres depth seasonal variations of mn fe mo and u are by contrast limited to the upper decimetres of the sediment their seasonal patterns depend on organic matter supply redox stratification and particulate matter deposited on sediment surfaces pore water sampling within one tidal cycle provides evidence for pore water advection in margin sediments during low tide pore water flow towards the creekbank is generated by a hydraulic gradient suggesting that deep pore waters may be seeping out of creekbank sediments owing to the enrichment of specific elements like mn in pore water compared to sea water seeping pore waters may have an impact on the chemistry of the open water column mass balance calculations reveal that the impact of deep pore waters on the mn budget in the open water column is below 4 mn deep pore water discharge of the whole wadden sea is estimated to be about 9 of the total dissolved riverine mn input into the southern north sea

increasing arsenic mobility in the fine fraction of the dry stream sediments of the semi arid san antonio gold mining district baja california peninsula mexico the geochemical mobility of arsenic and some metals in the fine fraction of 20 alluvial sediment samples collected along the thalweg of the san antonio arroyo was assessed in the abandoned gold mining district of the semi arid southeastern baja california peninsula acid digested element concentrations were determined by treating the fine fraction of the sediments with concentrated hno3 via microwave heating a separate leaching of the diluted acid soluble as and some metals from the samples was carried out using 1 m hcl the most reactive as phase was extracted from the subsamples using an ascorbic solution of na citrate buffered at ph 8 the high abundance of sulphosalts tennantite cu12as4s13 and proustite ag3ass3 in the sediments from the head of the arroyo changes downstream to the predominance of arsenic trioxide arsenolite as2o3 and arsenate scorodite feaso4 2h2o acid digested as concentrations were always found to be high 230 270 mg kg 1 from the san antonio village until the end of the arroyo the concentration of reactive as and its relative contribution increased from low values of 2 3 mg kg 1 and 1 respectively at the upstream of the arroyo to 191 220 mg kg 1 and 75 89 in the middle and lower parts and is probably a result of as release from the mineral sulfide fraction of the tailings metallic contaminants exhibited different behavior with a peak of acid digested and diluted acid leached concentrations observed in the central part of the arroyo and an almost permanent geochemical mobility

rb sr evidence for the presence of ordovician gsranites in the deformed basement of the badajoz cordoba belt sw spain a rb sr whole rock investigation of suites of samples from two orthogneiss bodies in the almendralejo area of the oporto portalegre badajoz cordoba belt points to an ordovician age for the granitic magmatism about 470 ma for the almendralejo gneiss peralkaline metagranite and about 425 ma for the ribera del fresno gneiss leucocratic subaluminous metagranite both with high initial87sr 86sr ratios this points to a post ordovician hercynian age for the metamorphism and tectonic deformation that affected the area including the gneisses and rules out the alleged cadomian or even older age

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

the behaviour of arsenic in muddy sediments of the bay of biscay france abstract we have studied particulate and dissolved arsenic species in sediment and porewaters at sites in the bay of biscay france ranging in depths from 150 to 2 800 m at all stations major redox species oxygen nitrate ammonia total and reactive iron and manganese sulphate and sulphur reflect early diagenetic depth sequences of redox reactions comparable to other marine environments vertical distributions of dissolved and particulate as species and major redox species are related to changes in redox conditions and their major carrier phases such as fe and mn oxides arsenic diagenesis appears strongly dependent on fe cycling a subsurface maximum of dissolved as and surface enrichment of particulate as correspond to dissolution and precipitation of fe iii phases except for the shallowest and most bioturbated site flux calculations show three different vertical diffusive as fluxes two upwards and one downwards phase changes of recycled as result in local accumulations of reactive as at different redox fronts mass balance calculations indicate that the upward as flux toward the oxidized layer can explain the enrichment of hcl extractable particulate as in this layer a portion of the upward diffusing as can escape the sediment and may be fixed onto settling fe oxides by adsorption or co precipitation and contribute to reactive particulate as input i e as is recycled across the water sediment interface

control of early diagenesis processes on trace metal cu zn cd pb and u and metalloid as sb behaviors in mining and smelting impacted lacustrine environments of the bolivian altiplano abstract a combination of mineralogical sem eds empa and geochemical redox dynamics selective extractions approaches was applied to mining and smelting impacted sediments from lake uru uru and from the cala cala lagoon a non impacted reference site in the bolivian altiplano the purpose was to assess the factors controlling the post depositional redistribution mobilization sequestration of trace metals and metalloids as expected trace metals and metalloids are less reactive at the reference site than in lake uru uru in the latter trace metals and metalloids are principally hosted by fe and mn oxyhydroxides authigenic sulfides and silicate particulates post depositional redistribution is ascribed to early diagenetic processes driven by organic matter om mineralization including dissolution of trace metal bearing phases and precipitation of authigenic sulfide and carbonate phases seasonal climate variability exerts a strong influence on these processes evaporation of surface water during the dry season in the northern part of lake uru uru promotes large redox front oscillations in the sediments and therefore transient redox conditions likely leading to the weakening of anoxia in near surface sediments and to a compressed redox zonation compared to the southern part of the lake seasonal disappearance of the water column in the northern lake uru uru entails an alternation of i low trace element mobility in the dry season due to elemental precipitation and ii an increase of trace element mobility via diffusive transport during the wet season due to release from om fe and mn oxyhydroxides and carbonates upon mineralization reductive dissolution and destabilization processes respectively reoxidation of authigenic fe sulfides likely following the re instalment of the water column above the sediment at the end of the dry season and prior to the return of anoxia probably favors transport of trace elements to the water column as a consequence of this intricate web of redox and climate related processes both northern and southern sediments of lake uru uru are a source of dissolved trace elements particularly as and cd for the overlying water column via diffusive transport however much of the diffused as and cd is likely to be removed from the dissolved phase by the redox loop through fe oxyhydroxide precipitation finally it is suggested that long term sequestration of trace metals and metalloids in the sediments could be controlled by inter annual climate variability such as enso events

aspects of bulk atmospheric boundary layer similarity under free convective conditions for many hydrologic and atmospheric dynamic purposes the turbulent surface fluxes of sensible and latent or evaporative energy and of momentum must be formulated over areas covering a wide range of spatial scales these are characteristically the scales of river basins and of the grid sizes for integration in current atmospheric circulation models the bulk atmospheric boundary layer abl similarity bas approach continues to be one of the very few available formulations to describe turbulent surface fluxes over the range of scales from roughly 1 to 10 km in terms of average characteristics aloft in the upper reaches of the abl the approach is reexamined as it relates to atmospheric stability and surface characteristics under conditions of free convection since the largest gradients occur near the surface first a formulation is proposed for the monin obukhov profile functions for convective conditions that is consistent with the theoretical advances by kader and yaglom 1990 and with recent experimental data this is then combined with a slab representation of the mixed layer to derive the most plausible form of the bas functions on the basis of presently available information finally it is illustrated with available experimental data that any alternative formulation of bulk abl transport regardless of its appearance is of necessity equivalent with bas and that the same original variables are at work

bias in the paleoceanographic time series tests with a numerical model of u corg and al burial 1 we have constructed a nonsteady state numerical model of organic carbon aluminum and uranium burial to examine the dynamic response of sediments to variations on thousand years scale the three components are defined by distinct behaviors in the sedimentary system the aluminum is a conservative component the organic carbon is a nonconservative component degraded in superficial sediment and the uranium is a component affected by redox conditions by introducing a simultaneous variation of incoming fluxes of corg and al geochemical profiles of al corg and u clearly show separate distributions after burial each component record the synchronous variation of the incoming fluxes but the position in the sedimentary pile of the recording differs from a component to another we show that a minimum of u could be linked to a rapid ascent of the oxic front during an increase in corg flux

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

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

the fate of carbon in continental shelf sediments of eastern canada a case study abstract this paper discusses the effects of organic carbon oxidation on the dissolution and precipitation of calcium carbonate aragonite and calcite in fine grained continental shelf and slope sediments using data obtained during the canadian joint global ocean flux study program in the gulf of st lawrence and on the scotia shelf the oxygen penetration depth in these sediments is on the order of 10 15 mm indicating that organic carbon is mineralized aerobically within this interval below this depth organic matter degradation proceeds mostly through anoxic mineralization processes the organic carbon content of these sediments decreases smoothly with depth at all sites the bottom water is supersaturated with respect to calcite however in most cores immediately below the sediment water interface the acidity produced by the aerobic degradation of organic matter is sufficient to overcome the supersaturation of the overlying waters and induce caco 3 dissolution this is most strongly reflected by an increase in the porewater calcium concentration near the sediment water interface deeper in the cores the saturation state of the porewaters increases at depth as a result of alkalinity generation by sulfate reduction and caco 3 of precipitates unlike organic carbon the inorganic carbon content of the sediments therefore varies little or even increases with depth because what is lost through dissolution near the sediment water interface is replaced at depth by precipitation the carbon precipitated as caco 3 in the sulfate reduction zone originates in part from the organic carbon resulting in the preservation of a fraction of the original organic carbon as inorganic carbon the precipitation of caco 3 in the anoxic zone creates an additional source of co 2 to the porewaters the geochemical significance of this source is discussed

phosphorus distribution c n p ratios and δ13coc in arctic temperate and tropical coastal sediments tools for characterizing bulk sedimentary organic matter abstract onshore offshore trends in phosphorus p organic carbon oc and total nitrogen tn concentration p distribution elemental organic c n p ratios and stable carbon isotopic composition of oc 13 c oc of surficial sediments are presented from three river dominated coastal regimes the mackenzie river beaufort shelf in the canadian arctic the mississippi delta and louisiana shelf in the temperate gulf of mexico and the tropical amazon shelf these parameters measured in surficial sediments from the three sites are used to assess changes in the importance of terrestrial and marine organic matter sources to sediments as a function of distance from the locus of riverine discharge trends in elemental ratio data from the arctic transect and a portion of the gulf of mexico transects can be explained in terms of a two end member mixture of terrestrial and marine phytodetritus in the arctic transect covariation of organic c p ratios with 13 c oc is consistent with a two end member mixture of terrestrial and marine organic matter a similar relationship between c p ratios and 13 c oc is not evident in gulf of mexico or amazon shelf sediments at these sites the two end member model fails to explain the data adequately the most striking feature of the onshore offshore trends in elemental oc op and oc tn ratios is the occurrence of low ratios in sediments from deep water stations in the gulf of mexico and all stations on the amazon shelf resulting from p and n enrichments exceeding the redfield ratio for marine plankton three explanations are discussed to account for these low ratios 1 the dominance of refractory op and on compounds in the residuum of degraded organic matter 2 differential sorption of op and n compounds regardless of lability on the surfaces of the fine grained sediments characteristic of these sites and 3 a dominance of bacterial biomass or components derived from bacterial biomass elemental ratios and 13 c oc signatures indicate that differential sorption may be most important in the deep water gulf of mexico sites in contrast elemental ratios and 13 c oc on the amazon shelf are most consistent with a sedimentary organic matter pool dominated by bacterial biomass or derivative substances

regional significance of kilometric scale north east vergent recumbent folds associated with east to south east directed shear on the southern border of the central iberian zone hornachos oliva region variscan belt iberian peninsula on the southern border of the central iberian zone there are two sectors with different styles of deformation to the south west in the hornachos sector large scale recumbent folds associated with ductile shearing can be seen this shearing is characterized by a direction of movement parallel to the fold axes and can be correlated for 150 km along strike the k values of the strain ellipsoid range from 0 8 to 2 0 stretching in the x direction parallel to the recumbent fold axes is more than 100 to the north east in the oliva sector first phase folds are upright and the strain intensity is lower than in the hornachos sector metamorphic geometric and kinematic considerations lead us to conclude that the shearing in the hornachos sector is better explained as conjugate to a main shear zone along which the southern border of the central iberian zone is moved onto the ossa morena zone this main thrust is at present obliterated by a left lateral extensional shear zone that affects a high pressure exotic unit located between the central iberian and the ossa morena zones this high pressure unit constitutes a suture of the variscan belt in the iberian peninsula

the composition of phyllosilicates in precambrian low grademetamorphic clastic rocks from the southern hesperian massif spain used as an indicator to metamorphic conditions abstract in order to obtain an indication of metamorphic conditions we have studied the mineralogy of the clastic rocks in particular the phyllosilicates from three precambrian series in the central iberian and ossa morena zones of the southern hesperian massif the esquisto grauvaquico complex the so called serie negra and the azuaga formation for this purpose we have used the crystal chemical parameters obtained via x ray diffraction d 001 b 0 ratios of the basal intensity of the white micas and chlorites and the crystallinity index of the mica together with electron microprobe data from selected areas obtained via backscattered electron images the mineral assemblages commonly quartz muscovite albite chlorite biotite and the values obtained for the illite crystallinity index between 0 18 and 0 20 2 in rocks with non diagnostic mineral assemblages point to at least greenschist facies metamorphic conditons the phengite content of the mica indicates an overall pressure regime near the limits between low and intermediate pressure but some significant differences exist between the series studied the azuaga formation shows the lowest pressure about 4 kbar while the serie negra indicates a pressure of at least 1 kbar more in the esquisto grauvaquico complex when the samples are considered overall the results are similar to those of the serie negra but there is inhomogeneity in the rocks from the two sections studied the various types of chlorite both textural and optical are homogeneous in composition in each rock specimen and their chemical composition depends primarily on the composition of the host rock

review the atmospheric boundary layer an overview is given of the atmospheric boundary layer abl over both continental and ocean surfaces mainly from observational and modelling perspectives much is known about abl structure over homogeneous land surfaces but relatively little so far as the following are concerned i the cloud topped abl over the sea predominantly ii the strongly nonhomogeneous and nonstationary abl iii the abl over complex terrain these three categories present exciting challenges so far as improved understanding of abl behaviour and improved representation of the abl in numerical models of the atmosphere are concerned

influence of an organic poor landslide deposit on the early diagenesis of iron and manganese in a coastal marine sediment sediments and porewaters were subsampled from two box cores collected at 135 m depth on the landward slope of the largest basin of the saguenay fjord quebec canada the saguenay fjord sediments are composed mostly of eroded glaciomarine clays surrounding the fjord area the sediments contain relatively large concentrations of organic carbon and are sulfidic a few millimeters below the sediment water interface they are characterized by anomalously high hg concentrations and acid volatile sulfide avs pyrite ratios the vertical distribution of total hg concentrations in the sediments can be correlated to the organic matter content and an anthropogenic source the high avs pyrite ratios reflect conditions conducive to preservation of fe monosulfides in 1971 a catastrophic landslide resulted in the displacement and transport of 6 9 106m3 of post wisconsinian marine clay into the saguenay fjord the landslide material was deficient in organic carbon and anthropogenic hg relative to the indigenous sediment subsequent to burial the landslide deposit influenced the migration and deposition patterns of mobilizable elements acting alternatively as a sink and a source of reduced fe and mn as the redox boundary migrated through it nonsteady state sulfate reduction rates were established due to the nonuniform distribution of organic carbon with depth iron sulfide peaks reflect this distribution and the position of the relict redox boundary manganese remobilization was apparently unaffected by the deposition of the landslide layer and reduced mn migrated freely to the redox boundary a schematic representation of the sequence of diagenetic events which led to the postdepositional remobilization of fe and mn and the migration of the oxidation front following the deposition of the landslide material is proposed

the boundary between the ossa morena and southportuguese zones southern iberian massif major suture in the european hercynian chain the ossa morena zone omz and the southportuguese zone spz represent the southernmost domains of the iberian massif european hercynian belt lithostratigraphic petrographic and structural differences exist between both zones the boundary between the omz and the spz is marked by a narrow belt of amphibolites of tholeiitic oceanic affinity bard mmunha et al 1986 and associated serpentinites flaser gabbros pillowed metabasalts castro et al 1987 which are highly sheared along their southern border these beja acebuches ophiolites op cit are exposed for over 200 km in the southernmost part of the omz and the northernmost area of the spz several zones have been distinguished on the basis of structural and lithological criteria the southernmost area of the omz which bounds the acebuches amphibolites is composed of high grade metamorphic rocks and an another important shear zone mark the omz northern boundary the boundary between the omz and the spz is considered to be a suture zone between two continental areas represented by the northern omz and the southern spz sinistral transpression associated with large scale recumbent folds are characteristic of the suture which can be tentatively correlated through the ibero armorican arc with the lizard complex sw england

microbial respiration and diffusive oxygen uptake of deep sea sediments in the southern ocean antares i cruise abstract benthic microbial respiration and diffusive oxygen uptake were measured and used to calculate rates of aerobic mineralisation of organic matter and concomitant co2 production at the sediment water interface in the abyssal region of the crozet basin this study was part of the antares i cruise on the r v marion dufresne in the permanent open ocean zone of the southern ocean on a south to north transect from 52 to 42 s in the indian ocean at all stations oxygen penetrated much deeper than 10 cm aerobic respiration was maximal in the top 1 cm 10 96 nmol cm 3 day 1 was always detectable down to 5 cm depth and at some stations even to 10 cm depth total depth integrated oxygen consumption corresponded to within 25 of the diffusive oxygen uptake across the sediment water interface the shape of the profile indicated that a diffusive downward flow of oxygen occurred below 10 cm depth thymidine incorporation experiments suggested that bacteria present at depths of between 15 cm and 1 m in the sediment were in a dormant state or growing extremely slowly however rapid dna synthesis started within 4 h after thymidine was added indicating a deep bacterial biosphere in southern ocean sediments it is proposed that the diffusive downward flux of oxygen below 10 cm depth sustains aerobic bacterial metabolism and survival at greater depths along the transect the total depth integrated oxygen uptake peaked at 48 s close to the polar front and at the subantarctic and subtropical convergence frontal zone nevertheless in general the differences were not very pronounced the average value of depth integrated microbial o2 consumption was 0 61 mmol m 2 day 1 which is equivalent to a carbon mineralisation rate of 2 3 g c m 2 year 1 these observations together with relatively high electron transport system ets values 6 6 l o2 g 1 h 1 and bacterial numbers 4 109 g 1 dry weight in the top centimeter imply that this region is less oligotrophic than previously assumed

carbon cycling in coastal sediments estimating remineralization in buzzards bay massachusetts accurately estimating rates of remineralization of organic matter in sediments early diagenesis is a prominent problem for benthic ecologists as well as organic geochemists mcnichol et al 1988 employed a novel approach to the problem by separating co sub 2 produced by respiration from caco sub 3 dissolution thus theoretically eliminating the need to measure the reduction of terminal electron acceptors in respiration o sub 2 no sub 3 so sub 4 etc pioneered by emerson et al 1980 and sayles 1981 for deep sea sediments this method employs measurements of ca sup 2 in porewater to differentiate between carbonate dissolution and respiration mcnichol et al 1988 were able to plot metabolic co sub 2 profiles over the surface 20 to 30 cm of sediment over an annual cycle at a single station in buzzards bay ma they used the carbon dioxide profiles in a vertical exchange and reaction model to estimate total organic carbon remineralization per year lower buzzards bay where mcnichol et al 1988 worked is well studied because of its proximity to the research institutions in woods hole it is the authors intention in this paper to compare the results of these older benthic metabolism studies in buzzards bay with those inferred from the modelmore of the porewater carbon dioxide profile the published data from three studies have been converted from ml o sub 2 m sup minus 2 h sup minus 1 to millimoles and plotted over a 12 month period thus illustrating the seasonal change in total benthic oxygen demand the temperature data available at the sites plotted over the year have a somewhat similar patter and as expected the oxygen demand correlates reasonably well with the temperature less

hercynian transpressional tectonics at the southern margin of the central iberian zone west spain the boundary between the central iberian and ossa morena zones in south central spain occurs within the badajoz cordoba shear zone the spatial and temporal relationships of structures across the la codosera syncline located within the central iberian zone just to the north of the shear zone demonstrate a progressive increase in strike slip shear towards the badajoz shear zone within the region of the la codosera syncline precambrian to cambrian rocks were subject to pre ordovician tilting and open folding accompanied by local faulting and veining but no cleavage these together with overlying palaeozoic rocks were subsequently affected by hercynian ductile deformation which produced steeply inclined folds cleavage and faulting intense left lateral shearing on the southern limb of the la codosera syncline produced augen shear bands sub horizontal stretching lineation boudinage variably oriented folds and steep faults whereas the northern limb of the syncline is characterized by folding and thrusting in a transpressional regime with limited net northward transport late hercynian faulting produced n s and ne sw faults which overprint the early structures and granites these rotate to a nw se trend and increase in right lateral displacement as a result of domino or bookshelf faulting which can be attributed to continued left lateral motion along the badajoz shear zone

effect of oxygen on degradation rate of refractory and labile organic matter in continental margin sediments in order to study the effect of oxygen on degradation rate of bulk sedimentary organic matter we developed a new incubation method in contrast to most previous experiments 1 all of the sediment undergoing decomposition was maintained under oxygenated or oxygen free conditions and 2 organic matter of varying lability was studied the production of co2 during incubations of sediment in glass test tubes corrected for dissolution precipitation of calcium carbonates was used as a measure of degradation rates the laboratory experiments using surficial and buried continental shelf and slope sediment from the open skagerrak northeastern north sea demonstrated that the effect of oxygen on the degradation rate of sedimentary organic matter is a function of the lability of the decomposing material fresh material was degraded with little difference in rates in the presence or absence of oxygen whereas old material was decomposed significantly up to 3 6 times faster with oxygen than without oxygen an implication of these findings is that bioturbation by exposing old buried material to oxygen may enhance integrated organic carbon oxidation in marine sediments this constitutes a previously unexplored mechanism by which faunal reworking may stimulate carbon degradation the anoxic decomposition rates of organic material buried at 20 cm depth in sediment were the lowest measured we found however that the extent of oxidation of this buried old sediment was considerably larger than that of surficial sediment under oxygenated conditions which indicated that the oxic anoxic oxic redox transitions deposition under oxic conditions burial under anoxia and reexposure to oxygen promoted degradation our results therefore also suggest that the extent of long term decomposition of sedimentary organic material is smaller under oxygenated or anoxic conditions alone than when the material is exposed to the repeated activities of both oxic and anoxic microorganisms