impact of subsurface rock fragments on runoff and interrill soil loss from cultivated soils field and laboratory studies have indicated that rock fragments in the topsoil may have a large impact on soil properties soil quality hydraulic hydrological and erosion processes in most studies the investigated rock fragments still remain visible at the soil surface and only properties of these visible rock fragments are used for predicting runoff and soil loss however there are indications that rock fragments completely incorporated in the topsoil could also significantly influence the percolation and water distribution in stony soils and therefore also infiltration runoff and soil loss rates therefore in this study interrill laboratory experiments with simulated rainfall during 60 min were conducted to assess the influence of subsurface rock fragments incorporated in a disturbed silt loam soil at different depths below the soil surface i e 0 001 0 01 0 05 and 0 10 m on infiltration surface runoff and interrill erosion processes for small and large rock fragment sizes i e mean largest diameter equals 0 04 and 0 20 m respectively although only small differences in infiltration rate and runoff volume are observed between the soil without rock fragments control and the one with subsurface rock fragments considerable differences in total interrill soil loss are observed between the control treatment and both contrasting rock fragments sizes this is explained by a rapid increase in soil moisture in the areas above the rock fragments and

an active deep marine strike slip basin along the north anatolian fault in turkey the tekirdag depression within the marmara sea in the mediterranean region is an active rhomb shaped strike slip basin along the north anatolian fault with a basin floor at a water depth of 1150 m new multichannel seismic reflection data and on land geological studies indicate that the basin is forming along a releasing bend of the strike slip fault and is filled with syntransform sediments of pliocene quaternary age the basin is bounded on one side by the north anatolian fault and on the other side by a subparallel normal fault which forms the steep submarine slope in cross section the basin is strongly asymmetric with the thickness of the syntransform strata increasing from a few tens of meters on the submarine slope to over 2 5 km adjacent to the north anatolian fault seismic sections also show that the slope forming normal fault connects at depth to the north anatolian fault implying that the basin is completely detached from its substratum the whole structure can be envisaged as a huge rather flat negative flower structure the releasing bend of the north anatolian fault responsible for the formation of the basin is flanked by a constraining bend along the constraining bend the syntransform strata are being underthrust implying a recent change in the direction of the regional displacement vector this thrusting is responsible for the uplift of the submarine slope to a height of 924 m possibly by a mechanism of elastic rebound regional geology suggests that most of the syntransform strata are lacustrine with only the topmost few hundred meters consisting of deep marine clays the anomalous present depth of the tekirdag depression is due to reduced quaternary sedimentation coupled with high rates of displacement along the north anatolian fault which amounts to 20 mm yr in the marmara sea region

a quasi synoptic view of the frontal circulation in the crozet basin during the antares 4 cruise abstract with the major objective of estimating the secondary vertical circulation a fine grid survey of hydrographic and current fields across the crozet basin frontal zone was made as a physical component of the multidisciplinary antares 4 cruise this frontal zone forms the boundary of the antarctic circumpolar current and the agulhas return current with the quasi permanent existence of strong eddy activity prior to any quantitative diagnosis of the vertical circulation from the fine grid data it is necessary to place the mesoscale circulation and its time variability of the survey area within the basin wide context we give a quasi synoptic view of the ambient frontal circulation during the cruise period using satellite derived chlorophyll concentrations and sea surface temperature particular emphasis is placed on evaluation of the degree of synopticity of our fine grid measurements by comparing mesoscale features on satellite images the limited survey area 1 5 latitude 2 longitude lies precisely within the southernmost and easternmost convergent zone of the two current systems cutting across mesoscale meanders having typical wavelengths of 400 km and periods of 4 months both these satellite images and topex poseidon sea surface height data indicate little temporal variability of the survey area during the 14 days of measurement although fortuitous this quasi steady state of circulation enables us to use the ensemble of fine grid data as a set of synoptic data for diagnosing the vertical circulation using quasi geostrophic dynamics preliminary analysis of the horizontal and vertical hydrographic structure of the fine grid hints at the existence of wave like cross frontal intrusions having a mean along front wavelength of about 30 km

long term seismicity of istanbul and of the marmara sea region we examine the long term seismicity of the marmara sea region in turkey over a period of twenty centuries to attempt to answer two questions 1 how well recorded in history is the earthquake activity of this region and 2 does seismicity over this long period of time differ from that over the present century we study this densely populated and fast developing region because it is one of the most tectonically active regions on the continents that appears today to be relatively quiescent

fluid flow in and around a mud volcano field seaward of the barbados accretionary wedge results from manon cruise a field of mud diapirs and mud volcanoes situated in the barbados trench at 13 50 n and extending along an old oceanic fracture zone mercurus was investigated during the manon cruise using both surface ship and nautile submersible sampling and measurements the entire zone from 13 50 n up to 14 20 n has an anomalously high heat flow which implies that fluids are drained into it from a segment of the accretionary wedge a few hundred kilometers wide two structures interpreted as diatremes atalante and cyclops expell large amounts of water and methane we propose that they were formed from the release of a light fluid when gas hydrates were dissociated in the sediment as the result of the circulation of warm fluid in the area however they expell only a small fraction of the incoming fluid implying that disperse flow is the dominant mode of expulsion in this area the chemoautotrophic communities on the surface of the structures rely mostly on sulfides submersible observations temperature measurements in the sediment and the chemistry of the pore fluid indicate that convection of seawater occurs within the first few meters of sediment through high permeability channels such as cemented carbonate conduits we propose that this convection is driven by the density difference between the pore fluid and seawater but fresh water released by the dissolution of shallow hydrates may also contribute this shallow convection may be a frequent process in cold seep environments

geochemical characteristics of iron in sediments from the sea of marmara abstract two 1000 cm long sediment cores were recovered from the sea of marmara one with the occurrence of gas hydrates in the western high and the other without hydrates in the cinarcik basin differences in mineralogical and chemical compositions have been identified between the two sediment cores based on the results of the mineralogical and geochemical analyses the main sources of the sediments are quite similar for both investigated areas but the authigenic components are different particularly iron sulfides and carbonates authigenic fe ii carbonate are much higher in core mrs cs 05 in the western high while crystalline fe iii phases are more abundant in core mrs cs 16 in the cinarcik basin notably the enrichments of greigite fe3s4 a metastable ferromagnetic iron sulfide mineral and intermediate polysulfide as well as iron carbonates are identified at 400 cmbsf with the maximum iron content in core mrs cs 05 these indicate the presence of a more reducing and acidic environment in the western high mainly due to higher organic matter content and seepage of heavy hydrocarbons in the sediments

migration of the sulphate methane reaction zone in marine sediments of the sea of marmara can this mechanism be tectonically induced abstract sulphate concentration profiles with non constant gradients are reported from porewater samples in continental margin sediments recent results on a sediment core from the ganos fault in the sea of marmara revealed a porewater pattern with two gradients comparisons with the respective methane concentrations show the position of a sulphate methane reaction zone smrz within the sediment column methane emanations from the seafloor as observed at other locations along the deeper ganos fault indicate the smrz as a transient system a computer model based on an unsteady process estimates the starting time of the methane rise between 1096 and 907 years before present within this time period one remarkable earthquake occurred in the direct vicinity of our study area in the year 1063 a d we suggest this could have opened the pathways for the ascending methane front

runoff and sediment yield from topsoils with different porosity as affected by rock fragment cover and position abstract interrill runoff and sediment yield from a topsoil having essentially textural pores and from another with structural pores were measured in the laboratory under simulated rain to investigate the effects of cover and positions of rock fragments the results reveal that the relation between the cover of rock fragments and interrill runoff or sediment yield can be negative as well as positive porosity in the soil near rock fragments determines both the type of relation and the degree to which the positions of rock fragments affect this relation rock fragments increase runoff and sediment yield when well embedded in a surface seal i e a top layer with essentially textural pore spaces a negative relation occurs either where rock fragments are partly embedded in a top layer with structural porosity or where the rock fragments rest on the surface of a soil having either textural or structural pore spaces the time at which macropores at the soil surface close is crucial for then the effect of the cover of rock fragments on the generation of runoff switches from reduction to an increase since cover can have an ambivalent effect on the hydrological and erosion response descriptions of topsoils containing rock fragments should include the type of soil porosity as well as the positions of rock fragments

internal tides and vertical mixing over the kerguelen plateau within the context of the natural iron fertilization study keops time series measurements of ctd and ladcp profiles at a site 50 6 s 72 e 528 m coinciding with an annual phytoplankton bloom over the kerguelen plateau were made during the january february 2005 keops cruise an important activity of highly nonlinear semidiurnal internal tides having peak to peak isopycnal displacements of up to 80 m is identified these internal tides appear to be a principal agent for promoting elevated vertical mixing indispensable for upward transfer of iron within the seasonal thermocline we estimate local vertical eddy diffusivities of the order of 4 10 4 m2 s 1 using a thorpe scale analysis although this estimate is higher by an order of magnitude than the canonical value o 0 1 10 4 m2 s 1 in the open ocean away from boundaries it is consistent with nonlinear internal wave wave interaction theories as verified by independent diffusivity estimates using the vertical wavenumber spectral methods for shear and strain it is also suggested that the general ocean circulation may play an important role in preconditioning the bloom in that the relatively sluggish circulation over the shallow plateau compared to the much more dynamic neighbouring deep ocean may foster the bloom s observed annual recurrence over the plateau

subantarctic mode water in the southeast pacific effect of exchange across the subantarctic front 1 this study considered cross frontal exchange as a possible mechanism for the observed along front freshening and cooling between the 27 0 and 27 3 kg m 3 isopycnals north of the subantarctic front saf in the southeast pacific ocean this isopycnal range which includes the densest subantarctic mode water samw formed in this region is mostly below the mixed layer and so experiences little direct air sea forcing data from two cruises in the southeast pacific were examined for evidence of cross frontal exchange numerous eddies and intrusions containing polar frontal zone pfz water were observed north of the saf as well as a fresh surface layer during the summer cruise that was likely due to ekman transport these features penetrated north of the saf even though the potential vorticity structure of the saf should have acted as a barrier to exchange an optimum multiparameter omp analysis incorporating a range of observed properties was used to estimate the cumulative cross frontal exchange the omp analysis revealed an along front increase in pfz water fractional content in the region north of the saf between the 27 1 and 27 3 kg m 3 isopycnals the increase was approximately 0 13 for every 15 of longitude between the 27 0 and 27 1 kg m 3 isopycnals the increase was approximately 0 15 for every 15 of longitude a simple bulk calculation revealed that this magnitude of cross frontal exchange could have caused the downstream evolution of samw temperature and salinity properties observed by argo profiling floats

control of sulfate pore water profiles by sedimentary events and the significance of anaerobic oxidation of methane for the burial of sulfur in marine sediments abstract gravity driven mass flow deposits proven by sedimentary and digital echosounder data are indicative for prevailing dynamic sedimentary conditions along the continental margin of the western argentine basin in this study we present geochemical data from a total of 23 gravity cores pore water so 4 is generally depleted within a few meters below the sediment surface by anaerobic oxidation of methane aom the different shapes of so 4 profiles concave kink and s type can be consistently explained by sedimentary slides possibly in combination with changes in the ch 4 flux from below thus mostly representing transient pore water conditions since slides may keep their original sedimentary signature a combined analysis and numerical modeling of geochemical physical properties and hydro acoustic data could be applied in order to reconstruct the sedimentary history we present first order estimates of the dating of sedimentary events for an area where conventional stratigraphic methods failed to this day the results of the investigated sites suggest that present day conditions are the result of events that occurred decades to thousands of years ago and promote a persisting mass transport from the shelf into the deep sea depositing high amounts of reactive compounds the high abundance of reactive iron phases in this region maintains low hydrogen sulfide levels in the sediments by a nearly quantitative precipitation of all reduced sulfate by aom for the total region we estimate a so 4 or ch 4 flux of 6 6 10 10 moles per year into the zone of aom projected to the global continental slope and rise area this may sum up to about 2 6 10 12 moles per year provided that the sulfur is completely fixed in the sediments it is about twice the global value of the recent global sulfur burial in marine sediments of 1 2 10 12 moles per year as previously estimated thus aom obviously contributes very significantly to the regulation of global sulfur reservoirs which is hitherto not sufficiently recognized this finding may have implications for global geochemical models as sulfur burial is an important control factor in the development of atmospheric oxygen levels over time

effects of rock fragments incorporated in the soil matrix on concentrated flow hydraulics and erosion rock fragments can act as a controlling factor for erosional rates and patterns in the landscape thus the objective of this study is to better understand the role that rock fragments incorporated into the soil matrix play in concentrated flow hydraulics and erosion laboratory flume experiments were conducted with soil material that was mixed with rock fragments rock fragment content ranged from 0 to 40 per cent by volume other treatments were slope 7 and 14 and flow discharge 5 7 and 11 4 l min 1 an increase in rock fragment content resulted in lower sediment yield and broader width of flow rock fragment cover at the soil surface i e surface armour increased with time in experiments with rock fragments flow energy was largely dissipated by rock fragment cover for more turbulent flow conditions when roughness elements were submerged in the flow hydraulic roughness was similar for different rock fragment contents in experiments with few or no rock fragments a narrow rill incised flow energy was dissipated by headcuts total sediment yield was much larger than for experiments with rock fragments in the soil adding just a small number of rock fragments in the soil matrix resulted in a significant reduction of sediment yield copyright 2007 john wiley sons ltd

intermediate water in the brazil malvinas confluence zone a lagrangian view the subsurface flow within the subantarctic and subtropical regions around the brazil malvinas falkland confluence zone is studied using daily hydrographic and kinematic data from four subsurface floats and a hydrographic section parallel to the south american shelf the float trajectories are mapped against sea surface flow patterns as visible in concurrent satellite sea surface temperature sst images with focus on the november 1994 and october november 1995 periods the unprecedented employment of lagrangian s diagrams enables us to trace the advection of patches of fresh antarctic intermediate water aaiw from the confluence zone into the subtropical region the fresh aaiw consists of a mixture of subtropical aaiw and malvinas current core water within the subtropical gyre these patches are discernible for extended periods and drift over long distances reaching north to 34 s and east to 40 w the cross frontal migration of quasi isobaric floats across the confluence zone from the subtropical to the subantarctic environment is observed on three occasions the reverse process float migration from a subpolar to a subtropical environment was observed once these events were located near 40 s 50 w the site of a reoccurring cold core feature subsurface float and sst data comparison reveals similarities with analogous observations made in the gulf stream rossby 1996 where cross frontal processes were observed close to meander crests the limited number of floats of this study and the complex structure of the brazil malvinas confluence zone however restricts the analysis to a description of two events

the effect of rock fragment size and position on topsoil moisture on arid and semi arid hillslopes abstract rock fragments on arid hillslopes affect rainwater redistribution and overland flow through various hydrological processes the present study focuses on the evolution of topsoil moisture content under rock fragments following rain events measurement was taken under rock fragments in various sizes large and small and positions on top of the soil surface and partially embedded within the soil surface at north and south facing hillslopes in arid and semi arid areas the main findings 1 the topsoil moisture content under rock fragments was higher over time than that of bare soil areas 2 rock fragments affect the topsoil moisture content for a longer time in semi arid areas than in arid areas and 3 large rock fragments and partially embedded ones are favorable micro environments for accepting and retaining rainwater and overland flowing water this may have eco geomorphic implications regarding the mosaic like patterns of source and sink areas on arid hillslopes

the active main marmara fault abstract this paper presents selections from and a synthesis of a high resolution bathymetric sparker and deep towed seismic reflection data set recently acquired by the french ifremer r v le suroit in an e w deep trough that forms the northern half of the sea of marmara in nw turkey it includes the first high resolution complete bathymetric map of this area a single throughgoing dextral strike slip fault system which is the western continuation of the northern branch of the north anatolian fault cuts this trough lengthwise and joins the 1999 8 17 kocaeli earthquake fault with the 1912 8 09 arkoy murefte earthquake fault both of which display strike slip offset in its eastern one fourth the structure follows closely the northern margin of the deep trough whereas in the west it hugs its southern margin the eastern one fourth of the structure has a minor component of its displacement distributed across the deep trough owing to a possible original bend in the course of the dextral structure the present course of the north anatolian fault in the sea of marmara originated some 2 105 a ago by cutting across the older basin fabric generated by a dominant nne ssw extension before it began taking up major motion in the pliocene

authigenic carbonates at cold seeps in the marmara sea turkey a lipid biomarker and stable carbon and oxygen isotope investigation abstract cold seeps along the north anatolian fault in the marmara sea turkey have been recently explored during international expeditions through submersible surveys seafloor mapping and extensive sampling of sediments biota carbonates and pore waters in this study we investigated the main mineralogy carbon and oxygen isotopic compositions and lipid biomarkers in authigenic carbonates retrieved from active seepage areas in the marmara sea abundant microbial lipid biomarkers with light 13 c values as low as 113 as well as light 13 c caco 3 values of bulk carbonate 34 to 21 provided evidence that anaerobic oxidation of methane aom mediated by methanotrophic archaea anme and their bacterial partners is the major process leading to sequestration of methane derived carbon diagnostic lipid distributions indicated that anme 2 archaea and associated sulphate reducing bacteria srb as the prevalent aom mediating microbes diverse non isoprenoid dialkyl glycerol ethers dages including tentatively identified novel compounds were identified with similar 13 c values as lipid biomarkers of srb 105 to 68 though dages are often assigned to srb other unknown bacteria closely involved in aom are likely as source organisms as well despite dominant aom related lipid biomarker patterns the stable carbon isotopic composition of bulk carbonates in two samples from south cinarcik basin and central high in combination with higher hydrocarbon signatures and environmental parameters suggested that oxidation of non methane hydrocarbons including oil may be a contributor to the dissolved inorganic carbon pool and may also be involved in carbonate authigenesis at hydrocarbon seepage settings as previously proposed in the gulf of mexico

fluid flow methane fluxes carbonate precipitation and biogeochemical turnover in gas hydrate bearing sediments at hydrate ridge cascadia margin numerical modeling and mass balances a numerical model was applied to investigate and to quantify biogeochemical processes and methane turnover in gas hydrate bearing surface sediments from a cold vent site situated at hydrate ridge an accretionary structure located in the cascadia margin subduction zone steady state simulations were carried out to obtain a comprehensive overview on the activity in these sediments which are covered with bacterial mats and are affected by strong fluid flow from below the model results underline the dominance of advective fluid flow that forces a large inflow of methane from below 869 mumol cm 2 a 1 inducing high oxidation rates in the surface layers anaerobic methane oxidation is the major process proceeding at a depth integrated rate of 870 mumol cm 2 a 1 a significant fraction 14 of bicarbonate produced by anaerobic methane oxidation is removed from the fluids by precipitation of authigenic aragonite and calcite the total rate of carbonate precipitation 120 mumol cm 2 a 1 allows for the build up of a massive carbonate layer with a thickness of i m over a period of 20 000 years aragonite is the major carbonate mineral formed by anaerobic methane oxidation if the flow velocity of methane charge fluids is high enough greater than or equal to10 cm a 1 to maintain super saturation with respect to this highly soluble carbonate phase it precipitates much faster within the studied surface sediments than previously observed in abiotic laboratory experiments suggesting microbial catalysis the investigated station is characterized by high carbon and oxygen turnover rates approximate to1000 mumol cm 2 a 1 that are well beyond the rates observed at other continental slope sites not affected by fluid venting this underlines the strong impact of fluid venting on the benthic system even though the flow velocity of 10 cm a 1 derived by the model is relative low compared to fluid flow rates found at other cold vent sites non steady state simulations using measured fluid flow velocities as forcing demonstrate a rapid respond of the sediments within a few days to changes in advective flow moreover they reveal that efficient methane oxidation in these sediments prevents methane outflow into the bottom water over a wide range of fluid flow velocities 80 cm a 1 only at flow rates exceeding approximately 100 cm a 1 does dissolved methane break through the sediment surface to induce large fluxes of up to 5000 mumol ch4 cm 2 a 1 into the overlying bottom water

fe binding dissolved organic ligands near the kerguelen archipelago in the southern ocean indian sector abstract during the ke rguelen o cean and p lateau compared s tudy keops january february 2005 cruise the area southeast of the kerguelen archipelago in the indian sector of the southern ocean was investigated to identify the mechanisms of natural iron fertilization of the kerguelen plateau in this study the organic speciation of fe is described samples were determined immediately on board using competing ligand adsorptive cathodic stripping voltammetry cl adcsv the dissolved organic ligands were always in excess of the dissolved fe concentration increasing the residence time in the water column and the potential availability for phytoplankton the concentration of the dissolved organic ligands ranged from 0 44 to 1 61 n eq of m fe complexation site for fe with an average concentration of 0 91 n eq of m fe s d 0 28 n 113 and a mean logarithm of conditional stability constant log k of 21 7 s d 0 28 n 113 a second weaker dissolved organic ligand group was detected in 32 of the samples with fe binding characteristics at the edge of the detection window of the applied method the occurrence of the highest concentrations of dissolved organic ligands in the wind mixed surface layer and near the sediment at the bottom of the water column indicated that both phytoplankton and the sediment act as sources both sources are in concert with the general conclusions from the keops research on the sources of fe where fe was regenerated organic fe binding ligands were formed in the upper layers and both fe and ligands were supplied by the sediment

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

the isotopic composition of diatom bound nitrogen in southern ocean sediments treatment of diatom microfossils from southern ocean sediments with hot perchloric acid leaves a diatom bound n fraction which is 0 4 lower in 15n than the bulk sediment typically 3 lower in recent antarctic diatom ooze results from southern ocean surface sediments indicate that early diagenetic changes in bulk sediment n content and 15n are not reflected in diatom bound n suggesting that diatom bound n is physically protected from early diagenesis by the microfossil matrix a meridional transect of multicores from the indian sector of the southern ocean shows a northward increase in the 15n of diatom bound n suggesting that diatom bound 15n like bulk sedimentary 15n varies with nitrate utilization in the overlying surface waters the 15n of diatom bound n is 3 4 higher in glacial age antarctic sediments than in holocene sediments supporting the hypothesis previously based on bulk sediment 15n that nitrate utilization in the surface antarctic was higher during the last ice age while there are important uncertainties the inferred range of utilization changes could potentially explain the entire 80 ppm amplitude of observed glacial interglacial variations in atmospheric co2

character of seismic motion at a location of a gas hydrate bearing mud volcano on the sw barents sea margin the hakon mosby mud volcano hmmv at 1270 m water depth on the sw barents sea slope has been intensively studied since its discovery in 1989 a variety of sensors monitored morphological hydrological geochemical and biological parameters in the hmmv area an ocean bottom seismometer deployment allowed us to register seismic motion for 2 years from october 2008 to october 2010 the analysis of seismic records documents two types of seismic signals the first type are harmonic tremors with frequency peaks around 4 5 and 8 10 hz that occur in swarms their origin could be from fluid flow circulation or resonant vibrations of gas bubbles or from delayed movement of fluid rich sediments in the conduit or in a deeper pseudo mud chamber of the hmmv because swarms occur with a periodicity of 6 h tide related effects are suspected to influence the mechanism originating the tremors the second type of signals are regional earthquakes that were in 15 cases recognized in seismic records the activity of harmonic tremors was not significantly affected by earthquakes

mesoscale subduction at the antarctic polar front driven by baroclinic instability abstract a study of mesoscale subduction at the antarctic polar front pf is conducted by use of hydrographic data from a high resolution quasi synoptic survey of the front the geostrophic velocity and isopycnal potential vorticity pv fields are computed and the ageostrophic flow diagnosed from the semigeostrophic omega equation it is found that the ageostrophic circulation induced by baroclinic instability counteracts the frontogenesis and frontolysis effected by the confluence and difluence respectively of the geostrophic velocity field though the sense of the ageostrophic circulation is reversed repeatedly along the front the existence of pv gradients along isopycnals leads to a net cross front bolus transport in response to a reversal of this gradient with depth a necessary condition for the onset of baroclinic instability the bolus transport is northward at the protruding temperature minimum layer that characterizes the pf and southward above this net cross front overturning circul

methane seepage inferred from the porewater geochemistry of shallow sediments in the beikang basin of the southern south china sea abstract several tens of methane ch4 seepage sites have been discovered in the northern south china sea scs during the investigation and exploration of gas hydrates and cold seeps over the past decade however our knowledge about methane seepage in the southern scs remains scarce especially in the beikang basin on the southern slope of the scs four piston cores bh cl18 bh cl23 bh cl29 and bh cl35 were collected in the beikang basin to understand ch4 cycling in shallow sediments the extrapolated depths of the sulfate methane transition zones smtz of the four cores are between 5 3 and 8 8 mbsf by simulating the porewater profiles of so42 ch4 dic and po43 using the reaction transport model we estimated that the dissolved so42 was predominantly consumed by the anaerobic oxidation of methane aom at rates of 27 5 mmol m 2 yr 1 in bh cl18 28 1 mmol m 2 yr 1 in bh cl23 43 1 mmol m 2 yr 1 in bh cl29 and 39 4 mmol m 2 yr 1 in bh cl35 respectively due to intense aom almost all the methane sourced from subsurface sediments was depleted within the smtz resulting in negligible benthic methane fluxes the kink type depth so42 profile of bh cl23 was apparently attributable to an enhanced methane flux which was not captured by the steady state modelling furthermore highly depleted 13c values of the dissolved inorganic carbon dic in bh cl18 43 6 bh cl23 44 and bh cl29 51 2 also indicated a methane derived dic in contrast relatively higher 13c values in bh cl35 suggested a mixture of 13c enriched dic produced by methanogenesis as shown by the reversal toward more 13c enriched dic below 4 2 mbsf in bh cl29 to our knowledge this is the first quantitative study dealing with methane cycling in the shallow sediments of the southern scs and may have considerable implications for understanding the poorly investigated cold seep and gas hydrate systems on the continental slope of the southern scs

radium isotopes to investigate the water mass pathways on the kerguelen plateau southern ocean abstract natural iron fertilization promotes the phytoplankton bloom that takes place on the kerguelen plateau in the indian sector of the southern ocean we measured 228 ra t 1 2 5 75 yr and 226 ra t 1 2 1602 yr in waters above the kerguelen plateau in order to provide information on the water mass pathways which in turn could help elucidate the mechanisms controlling iron fertilization in that area 228 ra activities are extremely low in this region being in most cases 18 g kg station a3 520 m depth located on the plateau in the middle of the bloom area also displays such low values but with higher 228 ra activities and higher 228 ra 226 ra ratios in the upper 150 m such a pattern suggests the presence of a water mass that recently interacted with sediments and therefore has been advected onto the kerguelen plateau elevated 228 ra activities were found in shallow waters in the vicinity of heard island south of the kerguelen plateau contact of the water masses with the shallow lithogenic sediments likely explains these high 228 ra activities when combined with physical observations these results suggest that the water mass advected onto the plateau originates from the south of the kerguelen plateau this northward advection might represent a supply of dissolved and or particulate fe for the observed phytoplankton bloom using the 228 ra profile obtained at station a3 we could estimate the vertical eddy diffusivity k z on the kerguelen plateau our k z estimate 1 5 10 4 1 3 10 4 m 2 s compares well with that reported by park et al 2008a internal tides and vertical mixing over the kerguelen plateau deep sea research ii doi 10 1016 j dsr2 2007 12 027 based on ctd ladcp data by combining this k z estimate with the gradient of dissolved fe observed at a3 blain s sarthou g laan p 2008 distribution of dissolved iron during the natural iron fertilization experiment keops kerguelen plateau southern ocean deep sea research ii doi 10 1016 j dsr2 2007 12 028 we calculate a vertical fe flux of 1 0 14 3 nmol m 2 d

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

an authigenic calcite layer in the sediments of the sea of marmara a geochemical marker horizon with paleoceanographic significance abstract three sediment cores taken from the central sea of marmara were sedimentologically and geochemically investigated all the cores show a continuous sedimentation record according to isotopic age dating measurements two of the cores cover an age range of more than 20 000 years since the sea of marmara was an isolated lacustrine system during the last glacial maximum about 20 ka bp the two cores should include the transition from lacustrine to marine environmental conditions the third core has a very high sedimentation rate 70 cm ka and therefore does not reach the transitional section in two cores however a very calcite rich layer unit c was observed carbon isotope investigations show that this calcite is not of diagenetic or biogenic origin but may represent a direct inorganic precipitate out of a deepwater layer in order to prove this hypothesis we used a geochemical model based on thermodynamic calculations this model shows that the calcite precipitation can only be explained by mixing of anoxic deep lacustrine water with oxic marine mediterranean water the necessary aqueous conditions are also obtained the model presented thus provides an important contribution to the evolution of the sea of marmara during the transition from lacustrine to marine conditions the thickness of the unit c layer indicates that this environmental change lasted approximately 1 5 ka

surficial deep sea sediments across the polar frontal system southern ocean indian sector particulate carbon content and microphyte signatures abstract two main subjects are addressed in this study concerning a complex sub antarctic hydrological system during the antares i md75 cruise southern ocean indian sector 1 the 13 c org signature in waters fluffs and sediments and their relationships with anthropogenic effects and 2 the degree of preservation of the deep sea phytodetritus a north to south gradient was observed for the deep sea microphytes signatures with the higher concentrations in the higher latitude chaetoceros spores dominant species chaetoceros cf neglectus were abundant in the fluffy layers from the permanent open ocean zone pooz and associated with the highest chl a concentration the diatom spores were absent in the northern part of that transect the coccolith repartition and preservation also showed a latitudinal gradient the presence of coccoliths more or less intact below the lysocline may result from different sedimentation rates along this gradient undisturbed and thick fluffs in the pooz and southern polar frontal zone stations were enriched with coccoliths and chaetoceros resting spores even at 4700 m and the revival experiments demonstrated their recent origin via a possible in mass or in pulse sedimentation a latitudinal gradient clearly appeared for 13 c org poc and chloropigments with a relationship between 13 c org and chl a direct positive for the phytoplankton and indirect negative for the fluffs and sediments these observed gradients are in part attributed to the latitudinal effects and to the physical characteristic of the water bodies differences between plankton and sediment 13 c org signatures are attributed to an anthropogenic influence however diagenetic processes leading to slight 13 c org enrichment in sediments cannot be absolutely rejected at this stage a stronger deep northward advection to the north of the polar front may also in part explain these north to south bio geochemical deep sea gradients

rainwash experiments on the erodibility of loose sediments laboratory experiments using simulated rainfall splash boards and trays were conducted in order to obtain information on the erodibility of loose sediments as a time dependent phenomenon in all ten different sediments ranging from silt d50 24 m to coarse sand d50 593 m were studied the effect of three different initial states of the sediments namely the air dry state t1 the field capacity state t2 and the desiccated state t3 on the erodibility was also assessed variations in detachability during a rain erosion experiment can be explained by change in water content including liquefaction and the development of a water layer on the surface cohesion and granulometric composition of the top layer the coarsest sandy sediments almost always yielded the highest detachability when starting from an initial field capacity state t2 for the finer sediments the highest detachability was found for the homogeneous and not yet compacted initial air dry state t1 the effect of the initial desiccated state t3 on the detachability of the finer sediments was also a function of the rainfall duration the relationship between detachability and median grain size of the sediments was very similar to the relation between grain size and the susceptibility to runoff and wind erosion established by other investigators the highest detachability was found for a fine very well sorted sand with a median grain size of 96 m

effects of rock fragments on soil erosion by water at different spatial scales a review this paper reviews the various effects of rock fragments on soil erosion by water since these effects are scale dependent they are investigated at three different nested spatial scales the microplot 4 10 6 100m2 the mesoplot 10 2 102 m2 and the macroplot 101 104 m2 for each scale the corresponding process mechanisms are discussed particular attention is paid to the effects of rock fragment cover on the intensity of soil erosion processes at the mesoplot scale i e on interrill areas rock fragments at the soil surface can have negative as well as positive effects on sediment yield these ambivalent effects are conditioned by the type of fine earth porosity soil surface slope vertical position and size of rock fragments and by the occurrence of horseshoe vortex erosion at the microplot scale i e the soil surface area which is covered by a single rock fragment and at the macroplot scale i e upland areas where both interrill and rill erosion takes place rock fragments at the soil surface have a negative effect on sediment yield in these two scales rock fragments can thus be considered as natural soil surface stabilizers at the macroplot scale the mean decrease of relative interrill and rill sediment yield with rock fragment cover can be expressed by an exponential decay function the scatter of the data indicates that a given rock fragment cover can have different efficiencies in reducing interrill and rill sediment yield depending on the varying intensities of the hydrological and erosion subprocesses these findings have implications for erosion modelling and soil conservation

relation between infiltration and stone cover on a semiarid hillslope southern arizona abstract a knowledge of the spatial distribution of infiltration rates is essential to the application of realistic distributed rainfall runoff models in semiarid areas one method of determining this distribution is to develop a predictive equation based on a readily observable surface property such as stone cover previous studies of the relation between infiltration and stone cover on shrub covered semiarid hillslopes have yielded both positive and negative correlations it is suggested that positive correlations result where infiltration measurements are confined to areas between large shrubs negative correlations on the other hand reflect pronounced shrub intershrub differences in infiltration and stone cover and are found where both shrub and intershrub areas are sampled in this study of a semiarid hillslope in southern arizona both shrub and intershrub areas are sampled and a negative correlation is obtained between infiltration and stone cover this correlation arises from the fact that under shrubs fine sediments have accumulated primarily as a result of differential splash whereas between shrubs such sediments have been selectively removed by a combination of rainsplash and overland flow leaving behind a gravel lag consequently infiltration rates are higher under shrubs than between them owing to the higher percentage of sand in the surface soil the larger quantity of organic matter both within the soil and on its surface and the greater digging and burrowing by animals in addition simulated rainfall experiments imply that shrubs with moderately dense canopies are more effective than adjacent surface gravels in dissipating the kinetic energy of raindrops and thereby reducing surface sealing and promoting infiltration inasmuch as the field site is typical of gentle shrub covered piedmont hillslopes over much of the sonoran desert inverse relations between infiltration rate and stone cover are probably characteristic of such hillslopes and may be used to predict the spatial distribution of infiltration rates for inclusion in rainfall runoff models

low temperature zircon growth related to hydrothermal alteration of siderite concretions in mississippian shales scotland zircon occurs in voids and cracks in phosphatic coprolites enclosed in siderite concretions in mississippian shales near edinburgh scotland the zircon formed during hydrothermal alteration of early diagenetic concretions and occurs as spherical aggregates of prismatic crystals sometimes radiating vitrinite reflectance measurements indicate temperatures of 270c for the zircon bearing concretions and the host shales molecular parameter val ues based on dibenzothiophene and phenanthrene distri bution and occurrence of di and tetra hydro products of polycyclic aromatic compounds suggest that the rocks experienced relatively high temperature aqueous condi tions related to hydrothermal fluids perhaps associated with neighboring mafic intrusions the zircon was dis solved from the concretions transported in fluids and reprecipitated in voids this is the first record of the pre cipitation of authigenic zircon in sedimentary rock as a new phase not as outgrowths

multiproxy approach for determination of nature and origin of carbonate micro particles so called micarb in pelagic sediments abstract carbonate fractions of pelagic and hemipelagic sediments may contain significant proportions of microcrystalline 6 m calcitic particles with no specific structure so called micarb depending on the authors this term is related to different descriptions and yet there is no clear consensus on their origin although micarb can dominate the sediment compositions in the pelagic realm their isolation from the other carbonate particles is not easy due to their small size the use of a granulometric separation method of the main carbonate particles allows the characterization and quantification of the compositions of the carbonate phases of the sediments and gives access to the geochemical signatures oxygen and carbon stable isotopes and mineralogical characteristics of each type of carbonate particles in the sediments this approach was applied to three sections the mid pliocene punta piccola section south sicily the upper campanian bidart section sw france and the aptian sediments from la marcouline quarry se france the quantifications showed quite important proportions up to 70 of the carbonated phases of micarb in the sections studied excepted in the mid pliocene punta piccola samples however depending on the sedimentary context it appears that those fine calcitic particles may result from fine biogenic fragmentation aptian la marcouline quarry authigenic precipitation in the water column mid pliocene punta piccola section or they may have an allochthonous origin upper campanian bidart section based on these interpretations it is then possible to estimate precisely the composition of the carbonate fractions in each studied section this work shows that except for the bidart sediments which are dominated by fine exported carbonate mud the other sections mainly consist in biogenic carbonates

pore fluid chemistry of the north anatolian fault zone in the sea of marmara a diversity of sources and processes as part of the 2007 marnaut cruise in the sea of marmara an investigation of the pore fluid chemistry of sites along the main marmara fault zone was conducted the goal was to define the spatial relationship between active faults and fluid outlets and to determine the sources and evolution of the fluids sites included basin bounding transtensional faults and strike slip faults cutting through the topographic highs the basin pore fluids are dominated by simple mixing of bottom water with a brackish low density pleistocene lake marmara end member that is advecting buoyantly and or diffusing from a relatively shallow depth this mix is overprinted by shallow redox reactions and carbonate precipitation the ridge sites are more complex with evidence for deep sourced fluids including thermogenic gas and evidence for both silicate and carbonate diagenetic processes one site on the western high displayed two mound structures that appear to be chemoherms atop a deep seated fluid conduit the fluids being expelled are brines of up to twice seawater salinity with an exotic fluid chemistry extremely high in li sr and ba oil globules were observed both at the surface and in cores and type ii gas hydrates of thermogenic origin were recovered hydrate formation near the seafloor contributes to increase brine concentration but cannot explain their chemical composition which appears to be influenced by diagenetic reactions at temperatures of 75 c 150 c hence a potential source for fluids at this site is the water associated with the reservoir from which the gas and oil is seeping which has been shown to be related to the thrace basin hydrocarbon system our work shows that submerged continental transform plate boundaries can be hydrologically active and exhibit a diversity of sources and processes

importance of submarine landslides for non steady state conditions in pore water systems lower zaire congo deep sea fan abstract most concentration profiles of sulfate in continental margin sediments show constant or continuously increasing gradients from the benthic boundary layer down to the deep sulfate reduction zone however a very marked change in this gradient has been observed several meters below the surface at many locations which has been attributed to anoxic sulfide oxidation or to non local transport mechanisms of pore waters the subject of this study is to investigate whether this feature could be better explained by non steady state conditions in the pore water system to this end data are presented from two gravity cores recovered from the zaire deep sea fan the sediments at this location can be subdivided into two sections the upper layer about 10 m thick consists of stratified pelagic deposits representing a period of continuous sedimentation over the last 190 kyr it is underlain by a turbidite sequence measuring several meters in thickness which contains large crystals of authigenic calcium carbonate ikaite caco3 6h2o ikaite 13c values are indicative of a methane carbon contribution to the co2 pool radiocarbon ages of these minerals as well as of the adjacent bulk sediments provide strong evidence that the pelagic sediments have overthrust the lower section as a coherent block therefore the emplacement of a relatively undisturbed sediment package is postulated pore water profiles show the depth of the sulfate methane transition zone within the turbiditic sediments by the adaptation of a simple transport reaction model it is shown that the change in the geochemical environmental conditions resulting from this slide emplacement and the development towards a new steady state are fully sufficient to explain all features related to the pore water profiles particularly so42 and dissolved inorganic carbon dic the model shows that the downslope transport took place about 300 yr ago

rock fragments in top soils significance and processes this introductory paper reviews various aspects of rock fragments in top soils such information is required for various reasons and in particular for predicting the impact of climatic or landuse changes on the response of these soils particular attention is paid to the definition and measurement of rock fragment content in top soils the density of soils containing rock fragments the spatial distribution and movement of rock fragments in top soils the effects of rock fragments on some key hydrological processes thermal properties of top soils physical soil degradation soil erosion and soil productivity

implications of the deep circulation and ventilation of the indian ocean on the renewal mechanism of north atlantic deep water in the indian ocean sector of the great ocean conveyor scheme the north atlantic deep water nadw replacement is realized by the transformation of the sinking circumpolar deep water cdw from the southern ocean to a prevailingly upward flow in the northern indian ocean this water mass transformation scenario has been studied by using hydrographie data including potential temperature salinity dissolved oxygen and nutrients in a water mass mixing model and by calculation of dianeutral velocity the model comprises a mixing system of three major deep water masses nadw cdw and north indian deep water this third water mass is introduced as a virtual water mass to represent the aged cdw the assumption is feasible as the artificial water mass can be eliminated on the deepest n 28 12 neutral surface characterized by isopycnal mixing the experiment is fulfilled when a conservative variable initial phosphate po40 is introduced and all conservative parameters are used in the mixing scheme the n 28 12 surface provides a major isopycnal transition path of cdw to the northern indian ocean and thus cdw is transformed to an upward flow dominant dianeutral up welling is detected on all four neutral surfaces north of 30 s showing increasingly strong dianeutral velocity toward shallower surfaces with the water mass mixing pattern and spreading path dianeutral circulation and dynamical information of the acceleration potential 10 m2 s 2 mapped on neutral surfaces a schematic of deep water circulation and ventilation of the indian ocean emerges from this study the contribution of nadw is largely limited to the southwest indian ocean the northward cdw is found mainly in two paths one in the western indian ocean apparent between 2000 and 3000 m through the western crozet and madagascar basins and farther north into the somali basin and arabian basin and another in the central indian basin apparent below 3000 m where ridge blocking becomes effective in the west and nadw salinity reaches a maximum while the major path switches from west to the central basin in the deeper layer 3000 3500 m the flow in the western indian ocean reverses southward north of the southeast indian ridge the deep path bifurcates from which point the eastern branch feeds the deep western boundary flow in the west australian basin except for part of the transformed cdw which is contributed to the upward flow in the north the return flow of cdw is found on the eastern side of these basins

cross frontal exchange of antarctic intermediate water and antarctic bottom water in the crozet basin abstract the hydrographic survey made across the antarctic circumpolar current acc in the southwestern crozet basin during the april may 1993 antares 1 cruise revealed unprecedented strong cross frontal injections of newly formed antarctic intermediate water aaiw into the subtropical zone north of the acc the acc in this area is mostly associated with the subantarctic front saf and subtropical front stf which are tightly merged into one structure bordered to the north with the eastward extension of the agulhas return current the oxygen and salinity extrema of the newly injected aaiw at a depth of 1200 m well north of the stf reach as high as 6 17 ml l 1 and 34 15 these values coincide almost exactly with those in the aaiw source found at a depth of 500 m just south of the saf but surpass considerably oxygen by 1 35 ml l 1 and salinity by 0 23 psu those values corresponding to the old aaiw at the nearby subtropical stations such spectacular cross frontal injections of new aaiw were not continuous in space and time but were found to be rather local intermittent and impulsive this was closely correlated with the highly perturbed meandering frontal zone due to the frequent passages of strong atmospheric depressions during the cruise there is also clear evidence of the northward penetration of antarctic bottom water aabw through the crozet kerguelen gap and its northward flow along the deep western boundary of the crozet basin supporting previous observations moreover our observations indicate more precisely the bottom water pathway which is concentrated against the continental rise west of 56 e following roughly the 4000 m isobath it is concluded that the crozet basin frontal zone acts as a barrier only for the upper layer water masses and that it is dynamically transparent for the cross frontal exchange of intermediate and deeper layer water masses of potential density anomalies greater than 27 1 including aaiw and aabw

the south indian ocean current in this paper the historical hydrographic database for the south indian ocean is used to investigate i the hydrographic boundary between the subtropical gyre and the antarctic circumpolar current acc the subtropical front stf and especially ii the southern current band of the gyre a current band of increased zonal speeds in the upper 1000 m is found just north of the stf in the west near south africa and at the surface stf in the open indian ocean until the waters off the coast of australia are reached as neither any other investigation of this current nor a name for it are known the flow has been called the south indian ocean current sioc this name is anologous to the same current band in the south atlantic ocean the south atlantic current the stf is located in the entire south indian ocean near 40 degrees s the associated current band of increased zonal speeds is the sioc which is found at or north of the stf east of 100 degrees e the sioc separates from the stf and continues to the northeast the zonal flow south of the stf is normally weak and serves to separate the south indian ocean and circumpolar currents near africa the sioc has a typical volume transport of 60 sv 1 sv 10 6 m3 s 1 in the upper 1000 m relative to deep potential density surfaces of sigma 4 45 87 kg m 3 2800 3500 m or sigma 2 36 94 kg m 3 1500 2500 m near western australia the sioc is reduced to about 10 sv as it turns to the northeast

slope currents around the kerguelen islands from demersal longline fishing records 1 the kerguelen plateau constitutes a natural obstacle for the eastward progress of the antarctic circumpolar current especially around the kerguelen islands however there is little quantitative knowledge of the current field around the islands due to lack of long term current measurements we performed a systematic analysis of a total of 28917 points of fishing gear drifts from setting and recovery positions of demersal longlines deployed between 2002 and 2007 for patagonian toothfish dissostichus eleginoides fisheries in kerguelen waters this enabled the construction of a realistic field of depth averaged time mean slope currents along the 1000 m isobath all around the kerguelen islands the strongest depth mean velocities of 25 cm s 1 are associated with the polar front which rounds the islands from the south and flows northward along the inner continental slope immediately east of the islands strongly supporting previous hydrographic evidence these results demonstrate the potential for hitherto unexploited historic longline drift data from demersal fishing grounds to provide valuable quantitative information on the regional circulation

frontal structure water masses and circulation in the crozet basin due to topographic steering by the crozet and kerguelen plateaus the antarctic circumpolar current acc core in the crozet basin area is shifted to its northernmost position in the southern ocean along the southern limb of the south indian subtropical gyre here the jet like current is embedded within a narrow band 26 5 kg m3 in the western half of the basin and heavier mode 26 7 kg m3 in its eastern half these different varieties of crozet basin mode water are closely correlated with the degree of exchange and mixing between subtropical and subantarctic waters along the dynamically active frontal zone the area north of the kerguelen plateau appears to be an important source of water mass modification antarctic intermediate water advected from the west also undergoes there significant modification by intrusions across the frontal zone of fresher oxygen richer colder subantarctic water energetic eddy activities observed along the frontal zone likely enhance such cross frontal exchange of water masses equatorward spreading of the modified thermocline water masses mode water antarctic intermediate water occurs as part of the anticyclonic circulation in the south indian subtropical gyre which is centered within the basin strong injection of north indian deep water into the acc south of amsterdam island is clearly evidenced for the first time this deep oxygen minimum water centered at about 3000 m can be traced to the east of madagascar from where it spreads southward through the eastern part of the crozet basin due to the influence of this water mass north atlantic deep water characteristics of the circumpolar deep water are significantly altered in kerguelen amsterdam passage our results indicate a cyclonic deep level circulation pattern in the crozet basin with a northward flow 9 sv of circumpolar deep water antarctic bottom water as a deep western boundary current and a partially compensating southward flow 3 sv of north indian deep water through the eastern part of the basin it is concluded that the crozet basin constitutes an important passage for the exchange of water masses between the southern ocean and the indian ocean

surface sealing as influenced by slope angle and position of simulated stones in the top layer of loose sediments the influence of five different slope angles and two different positions of simulated stones in the top layer of a sandy and a silty sediment on surface sealing intensity is examined in the laboratory sealing intensity is assessed by studying changes of percolation rate through a sediment layer with simulated rainfall duration and by measuring cohesion of the 5 mm thick upper sediment layer a measure of seal strength by means of a torvane slope has a negative influence on sealing intensity for a constant per cent of simulated stone cover sealing intensity is lowest in the case of stones placed on the sediment surface compared to the case of stones pushed into the surface layer explanations for these findings are given and some implications are further discussed

microevents produced by gas migration and expulsion at the seabed a study based on sea bottom recordings from the sea of marmara summary different types of 4 component ocean bottom seismometers obs were deployed for variable durations ranging from 1 week to about 4 months in 2007 over soft sediments covering the seafloor of the tekirdag basin western part of the sea of marmara turkey non seismic microevents were recorded by the geophones but generally not by the hydrophones except when the hydrophone is located less than a few tens of centimetres above the seafloor the microevents are characterized by short durations of less than 0 8 s by frequencies ranging between 4 and 30 hz and by highly variable amplitudes in addition no correlation between obss was observed except for two obss located 10 m apart interestingly a swarm of 400 very similar microevents based on principal component analysis was recorded in less than one day by an obs located in the close vicinity of an active gas prone fault cutting through the upper sedimentary layers the presence of gas in superficial sediments together with analogies with laboratory experiments suggest that gas migration followed by the collapse of fluid filled cavities or conduits could be the source of the observed microevents this work shows that obss may provide valuable information to improve our understanding of natural degassing processes from the seafloor

geochemical and geological constraints on the composition of marine sediment pore fluid possible link to gas hydrate deposits abstract pore water sulfate consumption in marine sediments is controlled by microbially driven sulfate reduction via organo clastic and methane oxidation processes in this work we present sediment pore fluid compositions of 10 long sediment cores and high resolution seismic data from the krishna godavari k g basin bay of bengal our results show occurrence of transient s and kink types and steady state quasi linear sulfate concentration profiles which are attributed partly to the anaerobic oxidation of methane 13 c ch 4 84 8 to 100 1 vpdb and organo clastic sulfate reduction influence of aom on alkalinity is evident from the presence of authigenic carbonate layers with highly depleted carbon isotope ratios in core md161 8 the authigenic carbonates represent the paleo smtzs and suggest marked fluctuation in vertical methane flux our geophysical data show the acoustic signatures of upward fluid migration from shallow sub surface whereas coring during nghp expedition 01 confirms the presence of sub surface gas hydrate deposits in k g basin which can be linked to deep methane sources the geochemical analysis suggests that shallow methane source can be attributed to high burial flux of labile organic matter due to high sedimentation rate sampling sites with high methane flux from the shallow gas source are characterized by quasi linear sulfate concentration profile and a shallow sulfate methane transition zone smtz and may not be necessarily linked to deeper gas hydrate deposits in contrast the deep methane source results in a transient kink type sulfate profile and a deeper smtz we have observed a close link between the occurrence of gas hydrate and the s kink type sulfate profile we interpret the short lived kink in the sulfate profiles as a result of recent enhancement in vertical methane flux possibly driven by reactivation of fault fractures systems which provide the conduits for fluid flow

variation of rock fragment cover and size along semiarid hillslopes a case study from southeast spain abstract the spatial variation of rock fragment cover rc and rock fragment size rs along semiarid hillslopes and transects in the mediterranean is largely controlled by hillslope gradient total rock fragment cover rc 5 mm often increases in a convex upward curve with hillslope gradient while the d50 of the surface rock fragments 5 mm increases linearly with hillslope gradient on south facing slopes rc 5 mm is slightly higher than on north facing slopes lithology controls the size distribution of the stone pavement rather than its cover percentage spatial variation of rock fragment cover reflects spatial variation in past erosion and deposition rates hillslope sections that are steep south facing or have been abandoned a long time ago have undergone intense interrill and rill erosion and thus have high rock fragment covers tillage erosion leads to high rock fragment covers on convex hillslopes in intensively cultivated areas thus using information on hillslope gradient aspect lithology and landuse we have been able to describe the spatial variation of rock fragment cover and size along semiarid hillslopes in southeast spain such information is crucial for understanding and modelling the spatial variation of the hydrological and erosion response of semiarid hillslopes under environmental change especially in semiarid environments of the mediterranean where vegetation cover is predicted to decrease due to climatic or landuse changes and rock fragments at the surface become the only soil surface stabilisers

linking foraging behaviour to physical oceanographic structures southern elephant seals and mesoscale eddies east of kerguelen islands in the southern ocean mesoscale features such as fronts and eddies have been shown to have a significant impact in structuring and enhancing primary productivity they are therefore likely to influence the spatial structure of prey fields and play a key role in the creation of preferred foraging regions for oceanic top predators optimal foraging theory predicts that predators should adjust their movement behaviour in relation to prey density while crossing areas with sufficient prey density we expect predators would change their behaviour by for instance decreasing their speed and increasing their turning frequency diving predators would as well increase the useful part of their dive i e increase bottom time thereby increasing the fraction of time spent capturing prey southern elephant seals from the kerguelen population have several foraging areas in antarctic waters on the kerguelen plateau and in the interfrontal zone between the subtropical and polar fronts this study investigated how the movement and diving behaviour of 22 seals equipped with satellite relayed data loggers changed in relation to mesoscale structures typical of the interfrontal zone we studied the links between oceanographic variables including temperature and sea level anomalies and diving and movement behaviour such as displacement speed diving duration and bottom time correlation coefficients between each of the time series were calculated and their significance tested with a parametric bootstrap we focused on oceanographic changes both temporal and spatial occurring during behavioural transitions in order to clarify the connections between the behaviour and the marine environment of the animals we showed that a majority of seals displayed a specific foraging behaviour related to the presence of both cyclonic and anticyclonic eddies we characterized mesoscale oceanographic zones as either favourable or unfavourable based on the intensity of foraging activity as identified by the behavioural variables our findings highlight the importance of mesoscale features for top predators behaviour and introduce a new approach for evaluating the importance to the seals of the origin and intensity of these features

sedimentary earthquake records in the izmit gulf sea of marmara turkey abstract sedimentary earthquake records of the last 2400 a including that of the devastating 17 august 1999 izmit earthquake mw 7 4 were studied in cores from the 210 m deep central karamursel basin of the izmit gulf in the eastern sea of marmara using laser grain size physical properties stable o and c isotopes and xrf core scanner analyses and dated by radionuclide and radiocarbon methods the earthquake records are represented by turbidite homogenite mass flow units thu that commonly contain a basal coarse layer a middle laminated silt layer and an overlying homogeneous mud layer the coarse basal part has a sharp and sometimes scoured lower boundary and includes multiple coarse sand silt layers or laminae showing normal size grading multiple coarse layers and occasional bi directional cross bedding suggest deposition from a bed load during water column oscillations or seiche effect the grain size characteristics of the overlaying laminated silt and the homogeneous mud units indicate deposition from weak oscillating currents and homogeneous suspension respectively high mn value just below the base of thus suggests diagenetic enrichment at oxic anoxic redox boundary before the mass flow event sharp decrease in mn with very low values within the thus suggests transient redox conditions following the mass flow variable geochemical compositions of the basal coarse layers indicate different sediment sources for different thus eight sedimentary earthquake records observed in the last 2400 a in the izmit gulf can be confidently correlated with the historical earthquakes of 1999 1509 ad ms 7 2 1296 ad i vii 865 ad i viii 740 ad i viii 268 ad i viii 358 ad i ix and 427 bc this gives an earthquake recurrence time of ca 300 a with the interval between consecutive events ranging from 90 to 695 a

living stained deep sea foraminifera from the sea of marmara a preliminary study abstract in this preliminary study we investigate living stained foraminifera from the sea of marmara we focus on the faunal composition and geochemical signatures trace elements carbon and oxygen stable isotopes in foraminiferal tests at two deep sea sites 329 and 1240 m depth respectively documented by rov observations and sampling both study areas are heterogeneous including bacterial mats and carbonate concretions proximal to cold seeps and consist of dysoxic bottom water o2

evidence and age estimation of mass wasting at the distal lobe of the congo deep sea fan on continental margins sulfate reduction occurs within the sedimentary column it is coupled with the degradation of organic matter and the anaerobic oxidation of methane these processes may be significantly disturbed by sedimentary events leading to transient state profiles for the involved chemical species yet little is known about the impact of turbidity currents and mass wasting on the migration of chemical species and the redox reactions in which they are involved due to its connection to the river the congo deep sea fan continuously receives huge amount of organic matter rich sediments primarily transported by turbidity currents which impact on the development of the associated ecosystems rabouille et al 2016 thus it is well suited to better understand causal relationships between sedimentary events and fluid flow path with consequences on the zonation of early diagenesis sequences here we combined sedimentological observations with geochemical analyses of pore water and sediment samples to explore how sedimentary instabilities affected the migration of methane and the distribution of organic matter within the sedimentary column the results unveiled mass wasting processes affecting recent turbiditic and pelagic deposits and are interpreted as being slides slumps and debrites two slides were responsible for the exhumation of an organic matter rich sedimentary block of more than 5 m thick and the movement of a methane rich sedimentary block while turbidity currents enable the intercalation of sandy intervals within a pelagic clay layer the youngest slide promoted the development of two sulfate methane transition zones smtz and may have possibly triggered a lateral migration of methane numerical simulation of the sulfate profile indicates that the youngest sedimentary event has occurred around a century ago our study emphasizes that turbidity currents and sedimentary instabilities can significantly affect the transport paths and the distribution of both methane and organic matter in the terminal lobe complex with consequences on geochemical zonation of the sequential early diagenetic processes within the sedimentary column

determination of the surface geostrophic velocity field from satellite altimetry 1 presently available marine geoid models are not accurate enough to extract the mean surface circulation directly from satellite altimetry a novel method for estimating the mean velocity field of major ocean current systems is derived from the free surface boundary condition with a given quasi geostrophic balance for the horizontal surface flow a scaling analysis of this boundary condition indicates that although the vertical velocity w is mostly balanced by the local change of the free surface t useful information on the mean current is contained in a small ageostrophic departure t w our method consists in the development of a simple algebraic equation with two unknowns and an adjustable parameter associated with t assuming that the latter is proportional to t w most interestingly t and all other coefficients of the equation can be determined from altimetry the altimeter data used is combined topex poseidon ers gridded data and the solution is obtained by least squares minimizing the contribution from the time variable part of the parameter and prescribing the zonal direction of the mean current the method which is found to be particularly useful for quasi zonal high energy current systems has been validated against direct observations in the gulf stream and southern ocean comparisons with direct observations and monte carlo experiments suggest an overall solution error of about 10 cm s 1 once calibrated against regional velocity statistics this method will be able to determine from altimetry the mean or instantaneous surface velocity field down to the frontal scale with a realism that has been inaccessible because of the geoid constraint

holocene sedimentation in the tectonically active tekirdag basin western marmara sea turkey abstract the effects of various depositional conditions and active tectonics on the late holocene sedimentation in the tekirdag basin west of the marmara sea were investigated in 11 gravity cores and on 3 seismic profiles representing shelf to slope to deep basin floor environments except for the two coarser grained avg 60 sand and gravel and calcareous avg 25 caco 3 shelf cores sediments in the slope and basin floor cores constitute low calcareous avg 12 caco 3 and terrigenous mud 90 silt and clay the occurrences of relatively higher total organic carbon contents in sediments from the southern slope 1 14 1 38 compared to that from the northern slope 0 37 1 2 indicate significant input from the southern rivers the presence of silty sandy laminations within the mud matrix of the cores and chaotic and mounded reflection configurations on the seismic profiles from the slope and basin floor environments all suggest the effects of gravity mass movements of sediments slides slumps turbidites most likely due to seismotectonic events earthquakes however it was difficult to establish a basin wide correlation between the historical earthquake events in the region and the positions of silty sandy laminations in dated deep sea sediment cores due to complicated other events such as repeated river run off and floods increased sediment load and slope failure the water contents of sediments from the basin floor avg 10 30 are significantly lower than those from the slope sediments avg 32 46 the former can be explained by the influences of synsedimentation with tectonics and compaction between the north and south boundary sub faults of the naf system whereas the latter shows fluidization of slope sediments during sliding and slumping radiocarbon dated base sections from three cores revealed that sediment deposition at these sites commenced about 4700 bp when the late holocene depositional conditions changed from the formation of upper sapropels to the present state the increases of organic carbon contents at or near the base sections of the cores support this contention

seafloor authigenic carbonate crusts along the submerged part of the north anatolian fault in the sea of marmara mineralogy geochemistry textures and genesis abstract extensive seafloor authigenic carbonate crusts occur as pavements mounds and chimneys along the north anatolian fault system nafs in the sea of marmara they are often covered or surrounded by patches of black fe sulphide rich sediments and associated with hydrocarbon rich gas and brackish water emissions in the 1250 m deep deep basins and with deep saline formation waters and hydrocarbons emissions from mud volcanoes and anticlines on the 350 650 m deep compressional highs the authigenic carbonate crusts are commonly porous with sinter like botryoidal and sugary granular textures and constructed from cementation of framework elements consisting mainly of bivalve shells and shell fragments serpulid tubes fibrous microbial organic matter and rarely pebbles the authigenic cements consist mainly of aragonite in most sites but high mg calcite occurs as a major carbonate cement at some basinal sites where the brackish former marmara lake waters emerge the buoyant emission of brackish waters in the deep marmara basins and deeply sourced fluids from the tertiary thrace basin at the compressional highs are supported by relatively low 18o values 0 5 to 3 8 v pdb average 2 1 v pdb n 24 of carbonates in the former and high values 2 6 to 3 4 v pdb average 3 0 n 9 in the latter areas low 13c values 47 6 to 13 7 v pdb average 34 9 v pdb n 33 and close association with black reduced sediments indicate that the seafloor authigenic carbonates are formed by the anaerobic oxidation of methane aom at or near the seafloor as result of high methane flux possibly during periods of high seismic activity authigenic carbonates from the western and central highs are relatively less depleted in 13c than those of the deep basin sites suggesting both microbial and thermogenic methane source for the deep basins carbonates and mainly thermogenic hydrocarbon with some contribution from the biodegradation of heavy hydrocarbons and gas hydrate dissociation for carbonates from the compressional highs u th ages of the authigenic carbonates range from less than 1 ka bp to 9 6 ka bp the age distribution together with the geochemical and mineralogical data suggests that different processes such as seismo tectonics and gas hydrates destabilization might have played important role in the authigenic carbonate formation in the sea of marmara over the last 10 ka

deep sulfate reduction completely mediated by anaerobic methane oxidation in sediments of the upwelling area off namibia abstract porewater concentrations of sulfate methane and other relevant constituents were determined on four sediment cores from the high productivity upwelling area off namibia which were recovered from the continental slope at water depths of 1300 and 2000 m at all four stations a distinct sulfate methane transition zone was observed several meters below the seafloor in which both sulfate and methane are consumed nutrient porewater concentration profiles do not show gradient slope changes at the depths of the transition zones flux calculations carried out on the basis of the determined porewater profiles revealed that anaerobic methane oxidation accounts for 100 of deep sulfate reduction within the sulfate methane transition zone and consumes the total net diffusive sulfate flux a significant contribution of organic carbon oxidation to the reduction of sulfate at these depths could therefore be excluded we state that porewater profiles of sulfate with constant gradients above the transition zones are indicative for anaerobic methane oxidation controlling sulfate reduction

geochemical paleogradient in pore waters controlled by aom recorded in an oligocene laminated limestone from the outer carpathians abstract a 20 cm thick laminated limestone of oligocene age from the outer carpathians is composed mainly of coccoliths and authigenic calcite 13 c values unequivocally indicate that the authigenic calcite precipitated as a result of methane oxidation the 13 c and 18 o values change gradually from the base to the top of the bed from 38 0 to 17 6 and from 1 1 to 5 7 respectively this trend reflects a geochemical gradient which developed in the zone of anaerobic oxidation of methane aom due to the consumption of sulfate by methane this gradient was related to an inverse relationship between the concentrations of both compounds in the pore waters of the aom zone methane was the source of isotopically light carbon it was accompanied by heavy oxygen containing water liberated from decomposition of gas hydrates the methane bearing fluids migrated upwards to the base of the sulfate reduction sr zone where methane was oxidized ch 4 so 4 2 hco 3 hs h 2 o and the aom zone developed the bicarbonate produced in this reaction was significantly depleted in 13 c and 16 o in the sr zone organic matter was oxidized by sulfate 2ch 2 o so 4 2 h 2 s 2hco 3 the bicarbonate released in that reaction was the source of isotopically heavier c and lighter o the proportion of bicarbonate produced by oxidation of methane to bicarbonate produced by oxidation of organic matter decreased upwards the resultant isotopic composition of bicarbonate dissolved in the pore waters changed upwards towards higher 13 c and lower 18 o values and has been recorded in the limestone s isotopic composition

concentrated flow erosion rates as affected by rock fragment cover and initial soil moisture content abstract concentrated flow experiments using a small hydraulic flume and a constant flow discharge and bed slope have been conducted in order to investigate the effects of rock fragment cover rc on sediment yield for an initially wet and an initially air dry loamy topsoil the experimental results indicate that rc reduces concentrated flow erosion rates e in an exponential way i e e e brc which is similar to previously reported relations for other water erosion processes such as interrill erosion and sheet rill erosion measured on runoff plots the decay rate b of this exponential relationship increased throughout the experiments because of scour hole development and bed armouring the concentrated flow erosion rates and b values also depend on the initial moisture content of the topsoil depending on rc mean concentrated flow erosion rates were 20 to 65 less on initially wet compared to initially air dry topsoils the mean value for b was 0 032 for the initially wet but only 0 017 for the initially air dry topsoil indicating that a rock fragment cover is less efficient in reducing concentrated flow erosion rates when the topsoil is initially air dry than when it is initially wet the results help explain the data scatter in reported relationships between rc and interrill rill erosion rates they also indicate that a given surface rock fragment cover will offer more protection to wet topsoils than to dry topsoils which are very common in mediterranean environments event based water erosion models should incorporate effects of antecedent soil moisture content as well as those of rc on concentrated flow erosion rates

bacterial proteolytic activity in sediments of the subantarctic indian ocean sector abstract organic material entering the oceanic benthic zone can be permanently buried or recycled to co2 in the sediment therefore it is important to know the carbon flux across the sediment water interface to determine the initial and rate limiting step in carbon oxidation a bacterial enzymatic activity bacterial density and ectoproteolytic activity determined using a fluorogenic substrate analog l leucine 7 amino 4 methyl coumarin leu mca were investigated in the water column and in sediments during the antares 1 jgofs cruise in the indian sector of the southern ocean a strong decrease in ectoproteolytic activity was observed with increasing water depth peak activity in surface water was three orders of magnitude less than in surface sediment analysis of experimental data revealed for most sediment bacterial communities the existence of a biphasic mechanism with different velocities for organic matter degradation and different affinities of enzymatic systems for substrates to explain this we hypothesize a strategy of bacterial communities that use the episodic supplies of organic matter reaching the sediment microbial ectoproteolytic activities were highest in surface sediment horizons and decreased progressively with depth as benthic microbial activities reflect the quantity and quality of organic matter reaching the sea floor high potential ectoproteolytic activities pea measured in the sediment of the polar front zone could indicate a direct and rapid coupling of relatively high surface productivity and deep ocean water by sinking particle fluxes lower values of pea were found in sediment in the northern study area where lateral processes associated with ocean circulation antarctic circumpolar current have an important influence on settling particles the lowest sediment pea values were measured at 52 s a region in which low primary production provides a poor supply of organic matter for the sea floor

pore fluid compositions and inferred fluid flow patterns at the haima cold seeps of the south china sea abstract fluid flow patterns at cold seeps provide insights into the mechanism and influence of methane emission into the ocean which is critical in its environmental impact assessment here we report pore fluid compositions of three 8 m long piston cores qdn 14a qdn 14b and r1 collected from the newly discovered active haima cold seeps on the northwestern slope of the south china sea reaction transport models were further applied to quantify related biogeochemical processes and to reveal the patterns of fluid flow extremely low 13c values

effects of grass roots on the erodibility of topsoils during concentrated flow abstract traditional vegetative techniques to control gully development rely mainly on the effects of above ground biomass whereas little attention has been given to the role of below ground biomass yet in a context where above ground biomass may temporarily or spatially disappear e g due to fire or grazing roots can play an important role in protecting soil against erosion few studies have investigated the impacts of roots of natural vegetation such as grass on the resistance of topsoils in concentrated flow erosion zones although grasses grow in many environments therefore the objective of this study is to investigate the impact of root density and root length density of grass on the erodibility of root permeated saturated topsoils three plots were established on a sandy loam their treatments were 1 bare 2 low density drilled grass and 3 high density drilled grass simulating different root densities after one month topsoil samples were taken and subjected to concentrated flow using a hydraulic flume in the laboratory slope flow discharge mean velocity water temperature and sediment concentration were measured root density and root length density values were assessed relative soil detachment rates and mean flow shear stresses were calculated the results indicate a negative exponential relation between the relative soil detachment rate and root density as well as root length density independent of the applied flow shear stresses however the best relationship fitting the data is the hill curve indicating that relative soil detachment rates decrease to very low values 0 05 with an increase in root density from 0 to 4 kg m 3 or root length density from 0 to 400 km m 3 a comparison between the effects of vegetation cover on sheet and rill erosion rates and those of the root area ratio of grass roots on relative soil detachment rates reveals that grass roots are very effective in reducing soil detachment rates the equations obtained can be used to predict the effect of grass roots on soil erosion rates during concentrated runoff and to evaluate the ability of roots to increase topsoil resistance against erosion by concentrated flow calculations of relative erosion rates using the equations from the rusle and wepp models indicate that the observed trend is better predicted with the rusle model and the wepp model for croplands than with the wepp model for rangelands

sulfate reduction and methane oxidation in continental margin sediments influenced by irrigation south east atlantic off namibia abstract sulfate reduction rates srr and concentrations of so 4 2 h 2 s pyrite sulfur total sulfur ch 4 and organic carbon were measured with high depth resolution through the entire length of the so 4 2 zone and well into the ch 4 zone at two continental slope stations in the eastern south atlantic benguela upwelling area the sediments were characterized by a high organic carbon content of approx 7 5 at geob 3703 and 3 7 at geob 3714 at geob 3703 so 4 2 concentrations decreased linearly with depth to about 40 m at the sulfate methane transition zone smt at 3 5 m while at geob 3714 so 4 2 remained at sea water concentration in the top 2 m of the sediment and then decreased linearly to about 70 m at the smt at 6 m direct rate measurements of srr 35 so 4 2 showed that the highest srr occurred within the surface 3 5 cm with peak rates of up to 20 and 7 nmol so 4 2 cm 3 day 1 at geob 3703 and geob 3714 respectively srr decreased quasi exponentially with depth at geob 3703 and the cumulative srr over the length of the so 4 2 zone resulted in an areal srr srr area of 1114 3493 mol m 2 day 1 median value 2221 mol m 2 day 1 at geob 3703 with more than 80 of the total sulfate reduction proceeding in the top 30 cm sediment at geob 3714 srr exhibited more scatter with a cumulative srr area of 398 1983 mol m 2 day 1 median value 1251 mol m 2 day 1 and with 60 of the total sulfate reduction occurring below a depth of 30 cm due partially to a deeply buried zone of sulfate reduction located between 3 and 5 m depths srr peaks were also observed in smt of both cores ostensibly associated with methane oxidation but with rates about 10 times lower than at the surface modeled srr balanced both methane oxidation rates and measured srr within the smt but severely underestimated by up to 89 the total srr area that were obtained from direct measurements modeled and measured srr were reconciled by including solute transport by irrigation described by a non local pore water exchange function which had values of up to 0 3 year 1 in the top sediment and decreased exponentially to zero i e no irrigation at 2 3 meters i e above smt these results suggested that co existing sulfate reduction processes and linear so 4 2 gradients can be maintained by a non local transport mechanism such as irrigation by which pore water in tubes or burrows is exchanged with bottom waters by activities of tube dwelling animals or some similar physical transport phenomenon i e bubble ebullition further support for an irrigation mechanism was found in the observations of open tubes of up to 8 mm id at depths down to 6 m which also contained fecal pellets indicating that these tubes were or had been inhabited

surface sealing as affected by various rock fragment covers in west africa field studies on the influence of rock fragments on surface sealing hence infiltration remain scarce and contradictory to document this issue rainfall simulation experiments were carried out on 37 undisturbed 1 m2 plots located along a pedo climatic transect across west africa an important part of the variability of infiltration coefficient r2 0 71 could be explained by a simple model based on the position of rock fragments in the top layer and accounting for the areal percentages of three types of soil surface 1 bare surface 2 soil surface covered with rock fragments embedded in the soil surface and 3 surface with rock fragments resting on top of the soil surface an even higher determination coefficient r2 0 76 was gained when rock fragment size were accounted for in combination with vesicular porosity furthermore a positive linear relationship was obtained between infiltration coefficient and mean annual rainfall suggesting that additional factors related to climate might be involved including organic matter content and clay mineralogy two main regions could thus be differentiated in the arid and semi arid zones coarse gravel and cobbles embedded in a seal are predominant and generate high runoff conversely fine and medium gravel mainly free at soil surface are dominant in the wetter zone favouring therefore higher infiltration rate

diatoms preserved in surface sediments of the northeastern kerguelen plateau abstract an island mass effect was observed from the sedimentary distribution of diatoms on the northeastern kerguelen plateau five new samples placed in context to species distributions previously reported from the permanently open ocean zone pooz revealed a plateau community dominated by three species taxa fragilariopsis kerguelensis thalassionema nitzschioides f nitzschioides and chaetoceros hyalochaete resting spores intermediate abundances of thalassiosira antarctica were unique to the plateau sediment signature as were increased abundances of eucampia antarctica v antarctica the off plateau sediment sample contained typical pooz sediment distributions dominated by f kerguelensis thalassiosira lentiginosa and thalassiothrix antarctica the role of deposition from the surface waters to the sediments was investigated by comparison to the diatom thanatocoenose observed in surface waters these results suggest that the use of sediment abundances of c hyalochaete resting spores and f kerguelensis to determine past productivity events such as wind sourced iron enrichment of the southern ocean at the last glacial maximum is not straightforward the elevated abundance of t nitzschioides f nitzschioides on the plateau did not indicate an iron deplete regime but the converse for the evaluation of paleo productivity hypotheses for the open southern ocean we suggest caution in the use of subantarctic and kerguelen plateau sediment signatures and emphasize that there is a need to also study antarctic coastal and especially sea ice melt water stimulated blooms

subsurface methane sources and migration pathways within a gas hydrate mound system gulf of mexico 1 geochemical profiles were coupled with seismic information to examine subsurface hydrocarbon source migration and fate at a gulf of mexico carbonate gas hydrate mound woolsey mound three seafloor features were investigated in detail 1 major faults resulting from a rising salt body 2 an acoustic backscatter anomaly and 3 a pockmark associated with a major fault we analyzed sulfate chloride dissolved inorganic carbon and hydrocarbon concentrations and carbon isotopes in pore water extracted from 20 m piston cores to characterize gas source and calculate methane flux dissolved biogenic methane dominated the off fault sites while the contribution of thermogenic methane increased near a major fault where thermogenic gas hydrates were recovered within the pockmark methane concentrations were low and isotopes indicated a biogenic source since pockmarks are typically formed from expulsive fluid flow this suggests that either the pockmark is the legacy of a conduit that has become plugged or that the expulsed fluid is confined within the fault walls at the acoustic anomaly nonsteady state sulfate profiles suggested temporal variability in methane flux estimates from 75 gravity cores collected across woolsey mound since 2002 were mapped to display the spatial variability in methane flux relative to the faults methane flux to the seafloor was generally low but increased several fold near the faults suggesting that the faults may provide conduits for hydrocarbons to bypass the microbial biofilter and cross the sediment water interface

diagenetic pyritisation under eastern mediterranean sapropels caused by downward sulphide diffusion recurrent organic rich layers sapropels in eastern mediterranean sediments are enriched in corg fe and s sulphur and fe are enriched in a zone immediately below the sapropels whereas corg is not 34s values of bulk sediments and simple mass balance calculations indicate that so42 reduction has taken place in an open system with all hs formed at or close to the sediment surface formation of pyrite in the sapropel was fe limited and consequently excess hs was able to migrate downwards downward sulphidisation this resulted in the formation of pyrite below the sapropel by reaction of this hs with solid phase ferric iron and fe2 diffusing upwards from underlying sediments the fe2 source probably includes fe hydr oxide layers formed at former oxidation fronts above previously deposited and buried sapropels this downward sulphidisation mechanism allows accumulation of twice as much s in alternating organic rich anoxic organic poor suboxic sediments compared to what is preserved in organic rich anoxic sediments

structure and transport of the antarctic circumpolar current and agulhas return current at 40 e hydrographic data are presented from a near meridional section across the agulhas return current the subtropical front and the antarctic circumpolar current acc in the southwest indian sector of the southern ocean the location and characteristics of the fronts are examined and the water masses are defined the agulhas return current emerges as a strong current as far east as 40 e which forms a marked front that is separate from the subtropical front and can be distinguished by a separate water mass comparisons are made with a similar hydrographic section at the greenwich meridian and several notable differences are found the subantarctic front at the greenwich meridian is a pronounced feature carrying a large proportion of the geostrophic transport of the acc on the southwest indian section however the subantarctic front is merged with the polar front at 48 s where the flow associated with the acc is concentrated geostrophic calculations show a large volume transport 84 to 103 sverdrup 1 sv 106 m3 s 1 associated with the agulhas return current at 40 s this is quite separate from the transport of the acc which totals 138 sv south of the subantarctic zone and the crozet plateau or 150 sv including flow in the subantarctic zone the transport of the acc out of the south atlantic sector appears to be higher than the transport into the south atlantic sector at drake passage with the extra transport most probably carried by upper layer and intermediate waters eddies are seen to be an important feature of the subantarctic zone where they help to modify the water masses antarctic intermediate water appears in two forms a saline 34 4 indian ocean variety and a fresh 34 2 atlantic ocean variety the atlantic variety is freshest at the polar front and occupies the southern half of the subantarctic zone within the eddies in the central subantarctic zone there is interleaving between these two forms of antarctic intermediate water north atlantic deep water is unable to cross the southwest indian ridge but can pass south of the crozet plateau in the form of circumpolar deep water which is slightly more saline 34 75 than at drake passage 34 73

large scale circulation over and around the northern kerguelen plateau abstract the kerguelen plateau is known to constitute a major barrier to the eastward flowing antarctic circumpolar current however there is limited knowledge on the regional circulation due to sparse observations especially in the northern kerguelen plateau between the fawn trough and the kerguelen islands as part of the physical component of the multidisciplinary keops cruise systematic ctd measurements along three sw ne oriented sections were made on the latter plateau cutting through the annual phytoplankton bloom across the eastern flank of the plateau into deep water major hydrographic features and geostrophic velocities perpendicular to the sections were first documented from these in situ observations in order to interpret the results within the general circulation context and to trace the upstream pathways of the observed water masses we established a synthetic picture of the large scale circulation over and around the entire northern kerguelen plateau using the combination of new data from keops with historical hydrographic data together with all available information on mid depth and near surface velocities derived from autonomous floats surface drifting buoys and satellite altimetry this synthesis shows that the time mean geostrophic flow over the shallow platform is sluggish of the order of 3 5 cm s 1 with a general anticyclonic circulation roughly following the local bathymetry this weak flow is bordered to the east by relatively strong up to 18 cm s 1 northwestward flow along the eastern flank of the northern kerguelen plateau due to a northward bifurcation of cold antarctic waters of eastern enderby basin origin carried by the powerful fawn trough current we have shown the utmost importance of the general circulation for the spatial distribution of primary productivity in that the sluggish circulation over the complex shallow topography of the northern kerguelen plateau may precondition the recurrence of annual blooms in contrast to neighboring strong advective regimes without blooming in deep water

paleomagnetic and geochemical record from cores from the sea of marmara turkey age constraints and implications of sapropelic deposition on early diagenesis abstract we present results of a multi proxy analysis of two sediment cores from the marmara sea the cores were analyzed using paleomagnetic and geochemical measurements two sapropels are documented in the last 11 kyr and are recorded in several locations across the marmara sea these two sapropels have contrasting magnetic properties the magnetic record is affected by intense early diagenesis the most recent upper sapropelic layer has low remanence and susceptibility values a record of paleomagnetic inclinations could still be isolated above the diagenesis front and is compared with secular variation models the lower sapropel is identified in the deep part of the oldest studied core klg07 and has distinct magnetic properties characterized by high remanence and susceptibility values using the magnetic properties it is possible to constrain bottom water ventilation and reconnection episodes between the marmara sea and the black sea following the sea level rise during the last glacial to inter glacial transition

the hydrological response of soil surfaces to rainfall as affected by cover and position of rock fragments in the top layer rainfall experiments have been conducted in the laboratory in order to assess the hydrological response of top soils very susceptible to surface sealing and containing rock fragments in different positions with respect to the soil surface for a given cover level rock fragment position in the top soil has an ambivalent effect on water intake and runoff generation compared to a bare soil surface rock fragments increase water intake rates as well as time of runoff concentration and decrease runoff volume if they rest on the soil surface for the same cover level rock fragments reduce infiltration rate and enhance runoff generation if they are well embedded in the top layer the effects of rock fragment position on infiltration rate and runoff generation are proportional to cover percentage micromorphological analysis and measurements of the saturated hydraulic conductivity of bare top soils and of the top layer underneath rock fragments resting on the soil surface reveal significant differences supporting the mechanism proposed by poesen 1986 i e runoff generated as rock flow or as horton overland flow can partly infiltrate into the unsealed soil surface under the rock fragments provided that they are not completely embedded in the top layer hence rock fragment position beside other rock fragment properties should be taken into account when assessing the hydrological response of soils susceptible to surface sealing and containing rock fragments in their surface layers a simple model based on the proportions of bare soil surface soil surface occupied by embedded rock fragments and soil surface covered with rock fragments resting on the soil surface describes the runoff coefficient data relatively well

water mass and biogeochemical variability in the kerguelen sector of the southern ocean a machine learning approach for a mixing hot spot author s rosso isabella mazloff matthew r talley lynne d purkey sarah g freeman natalie m maze guillaume

multiple mechanisms of remagnetization involving sedimentary greigite fe3s4 sedimentary greigite fe3s4 is being increasingly implicated as the carrier of late diagenetic remagnetizations in fine grained marine and terrestrial sediments we have conducted detailed scanning electron microscope observations on polished sections from such sediments coupled with elemental microanalysis to identify greigite and to characterize the mode of occurrence and the relationships between the observed greigite and other authigenic and detrital mineral phases this detailed observational work in conjunction with recently published work has enabled identification of several mechanisms for remagnetization involving greigite 1 neoformation of greigite on the surfaces of early diagenetic framboidal and nodular pyrite 2 greigite growth within cleavages of detrital sheet silicate grains 3 neoformation of greigite on the surfaces of authigenic clays smectite illite 4 greigite nucleation on the surfaces of siderite 5 greigite growth on the surface of gypsum that resulted from earlier oxidation of nodular pyrite many other mechanisms for greigite neoformation are conceivable the key variables are appropriate redox conditions for generation of sulphide and availability of iron from the dissolution of a wide range of possible reactive detrital and authigenic iron bearing minerals documentation of a wide range of mechanisms for neoformation of greigite provides compelling evidence that sediments containing greigite should be routinely suspected of remagnetization which will complicate or compromise studies of environmental magnetism and geomagnetic field behaviour

subduction zone earthquake as potential trigger of submarine hydrocarbon seepage methane is abundant in marine sediments analysis of sediment cores and seismic images of marine sediments obtained off the coast of pakistan show fracturing of gas hydrates and an increase in upward methane flux in the decades following a large earthquake in the arabian sea in 1945 suggesting that quakes can trigger hydrocarbon seepage

on the origins of deep and bottom waters of the indian ocean the characteristics of the deep and bottom waters of the indian ocean when illustrated on potential density anomaly surfaces indicate that the waters enter from both the atlantic and pacific oceans the paths of spreading are constrained by the complex topography and characteristics are seen to be altered by exchange with the overlying and underlying water and with the sediments especially in the northern indian ocean the weddell sea contributes to the densest waters found in the western basins and the ross sea and adelie coast to the densest waters found in the eastern basins both dense water varieties are altered by and incorporated in the less dense water above initially water carried by the circumpolar current then water from the north atlantic and finally by deep water whose characteristics are derived in the northern indian ocean contact with the sediments increases the silica content of the bottom water in the southern ocean in the northern indian ocean the sediments alter the silica of the water at the bottom and together with enhanced salinity from diffusion of saline overflows from the marginal seas above imprint unique markers to the deep water that flows back to the south at middepths the series of ridges between madagascar and australia confine the flow to a series of gyres that carry characteristics from the circumpolar current equatorward and the northern indian ocean characteristics southward within the circumpolar current low oxygen deep water from the pacific is carried across the atlantic and into the indian ocean south of africa part flows around the cyclonic weddell sea gyre and part extends across the southern ocean water from another pacific source can be seen near 2000 m extending westward from the tasman sea south of aus tralia and across the indian ocean and perhaps to the aghulas current region southeast of africa in this study we show some maps of deep and bottom water characteristics of the indian ocean which may be used in a qualitative sense to infer pathways of spreading of water below a depth of about 2000 m the indian ocean has numerous ridges and basins figure 1 that severely restrict possible pathways of deep and bottom wa ter flow in the following we will begin by looking at char acteristics at the bottom of the ocean to reveal the path ways of spreading of the densest bottom waters from basin to basin then a series of six potential density anomaly surfaces at progressively shallower depths from about 4000 m up to about 2000 m will be shown to see what character istics influence the deep waters and how pathways of flow are constrained by the bathymetry of the indian ocean the choice of the specific density levels table 1 was based primarily on various property extrema shown by the 18os atlantis ii cruise 93 colored sections that accompany warren s 1981 detailed discussion of the major features of the central indian ocean between madagascar and aus tralia the sections approximately midway between antarctica and the northern indian ocean boundaries are well positioned to show features originating from both the north and the south as well as some brought into the indi an ocean by the antarctic circumpolar current the full ocean area isopycnal maps provide essential evidence on the origins and fates of features seen in the sections and

factors affecting the diagenesis of quaternary sediments at odp leg 172 sites in western north atlantic evidence from pore water and sediment geochemistry abstract pore waters and quaternary sediments at odp leg 172 sites on the carolina slope cs site 1054 blake outer ridge bor sites 1057 and 1060 bahama outer ridge baor 1062 and bermuda rise br site 1063 were studied the sediments are mainly clayey and silty mud with intercalations of nannofossil rich and lutite rich beds towards the top sedimentation rate ranges from 4 2 cm ky at site 1054 to 23 cm ky at site 1060 average total organic carbon toc contents of the upper sediment units range from 0 40 to 0 58 at sites 1057 1060 1062 and 1063 and from 0 86 to 1 25 at site 1054 the organic matter at all the sites is mostly degraded except at site 1054 sediments at sites 1062 and 1063 have lower total sulfur ts 0 00 0 62 average 0 06 than those at the other sites site 1054 has the highest ts 0 8 1 4 and the lowest reactive iron 0 003 0 074 contents among all the sites the deep water sites 1062 and 1063 have concave down pore water sulfate concentration depth profiles relatively deep sulfate methane interfaces smis 65 and 38 meters below sea floor mbsf respectively and steep methane gradients at the base of the smi whereas the shallow water sites 1054 1057 and 1060 have near linear sulfate and relatively shallow methane gradients the near linear sulfate depth profiles and shallow smis 17 and 14 mbsf respectively at sites 1057 and 1060 are primarily due to high sulfate consumption by anaerobic methane oxidation amo at the smi concave down profiles and deep smis at sites 1062 and 1063 are the result of low rates of sulfate consumption through organic matter degradation due to a limitation of metabolizable organic matter site 1054 is unusual in having an 8 m thick oxic suboxic zone a 48 m deep smi and a linear sulfate depth profile despite the high organic matter content of sediments at this site the thick oxic suboxic zone is mainly due to intense bioturbation while the linear sulfate depth profile and the deep smi are likely caused by low sedimentation rate and by reactive iron limitation pore water magnesium calcium and strontium profiles indicate that carbonate precipitation has occurred near the smi this is confirmed by the presence of authigenic dolomite rhombs and nodules especially at and below smi at all sites

antares i a biogeochemical study of the indian sector of the southern ocean abstract the first expedition of the antares program the french contribution to southern jgofs investigated the biology and the chemistry of the benthic environment and the water column in a region located between 60 s 72 e and 39 s 55 e in this special issue we present a detailed description of the transports of water masses across the polar front zone which are corroborated by chemical and microbial tracer studies a description of the sediment water interface bridging biological chemical and microbial studies and new insights into the diagenesis of biogenic silica

pore water geochemistry at two seismogenic areas in the sea of marmara within the sea of marmara the highly active north anatolian fault naf is responsible for major earthquakes mw 7 and acts as a pathway for fluid migration from deep sources to the seafloor this work reports on pore water geochemistry from three sediment cores collected in the gulfs of izmit and gemlik along the northern and the middle strands of the naf respectively the resulting data set shows that anaerobic oxidation of methane aom is the major process responsible for sulfate depletion in the shallow sediment in the gulf of gemlik depth concentration profiles of both sulfate and alkalinity exhibit a kink type profile the sulfate methane transition zone smtz is located at moderate depth in the area in the gulf of izmit the low concentrations observed near the seawater sediment interface for sulfate calcium strontium and magnesium result from rapid geochemical processes aom and carbonate precipitation occurring in the uppermost part of the sedimentary column and sustained by free methane accumulation barite dissolution and carbonate recrystallization have also been identified at deeper depth at the easternmost basin of the gulf of izmit this is supported by the profile of the strontium isotope ratios 87sr 86sr as a function of depth which exhibits negative anomalies compared to the modern seawater value the strontium isotopic signature also shows that these carbonates had precipitated during the reconnection of the sea of marmara with the mediterranean sea finally a first attempt to interpret the sulfate profiles observed in the light of the seismic activity at both sites is presented we propose the hypothesis that seismic activity in the areas is responsible for the transient sulfate profile and that the very shallow smtz depths observed in the gulf of izmit is likely due to episodic release of significant amount of methane

influence of rock fragments on the water retention and water percolation in a calcareous soil abstract the water retention properties of a calcareous soil containing rock fragments have been determined in the laboratory thanks to pressure plate measurements done on both the fine earth and the rock fragments from the soil the available water content awc has been calculated from these data we have shown that when the rock fragments are neglected the awc can be overestimated by 39 when we do not neglect their volume but when their hydraulic properties are not considered the awc can be underestimated by 34 by using a reservoir model we have also calculated the effect of rock fragments on water percolation to groundwater depending of the climatic characteristics of the year the underestimation of percolation when we neglect the rock fragments can reach up to 14 9 and the overestimation when we neglect their hydraulic properties can be equal to 15 8 these findings emphasise the role of the rock fragments on the water supply in stony soils