sediment accumulation rates in the southern barcelona continental margin nw mediterranean sea derived from 210pb and 137cs chronology sediment cores were collected from the southern barcelona continental margin including the foix canyon in order to study sediment accumulation in this area for this purpose 210pb 137cs and to a lesser extent 239 240pu and heavy metals were determined in sediment sections using state of the art techniques 210pb concentration profiles and 137cs 239 240pu and heavy metals profile features were used to establish the sediment chronologies further information was also obtained from granulometric analyses the magnitudes studied and correlated in this work included surface activities mixing rates accumulation rates and inventories sediments on the continental shelf showed a varied degree of mixing except possibly cn 23 sedimentation rates were relatively small and the sedimentary material probably had a common origin cores from the slope showed less mixing and in cores cn 36 and eb 2 located in the foix canyon axis the 137cs signal vs depth was clear and well preserved accumulation rates and total 210pb inventories were maximum in core cn 36 at mid slope of the canyon which was considered to be an active depocenter core cn 38 collected on the open slope showed a much smaller accumulation rate therefore it was concluded that shelf material is being transported alongshore by the prevailing currents and becomes focused in the canyon which is acting as a natural trap within the canyon this material is preferentially deposited at a mid slope depocenter little extra material reaches the lower canyon area in this area core eb 2 appeared to show signs of the presence of resuspended material possibly derived from the canyon walls finally observed changes in sedimentation rates during the 1930s could not be explained on the basis of current knowledge and this is suggested to be an important subject for further research

near bed turbulence measurements stress estimates and sediment mobility at the continental shelf edge as a contribution to ocean shelf exchange studies the sediment transport and boundary layer equipment stable has been deployed west of spain near 42 40 n in 200m water depth in december and august and at three other continental shelf edge and slope locations off north west europe turbulence at 8hz and acoustic back scatter at 4hz were measured at three levels between 0 3 and 1 m above the bed typically the speed profile shows little shear the turbulence data are necessary to estimate near bed stress reynolds stress and total turbulence energy approaches give consistent results total turbulence results appear more robust but can be affected by long surface waves typical peak values of friction velocity u per tide were 10 mm s off spain and 7 18 mm s at the other locations and they were asymmetric owing to along slope flow record maxima were 30 mm s 11 48 mm s respectively sufficient to move local sediment except for a short event free record at goban spur acoustic backscatter spm showed peaks matching peaks of u or waves in the case of winter deployments off scotland and spain comparison of these stable measurement periods with contemporary current records of longer duration suggests that bed stresses in all these upper slope locations are often sufficient to move the local sediment off spain shelf sediments are re suspended and transported down current the sandy fraction settles soon but the fine fraction ws 0 1 mm s is progressively winnowed down current to the shelf edge suggesting export of the bound organic matter

oxygen diffusion in quartz diffusional oxygen exchange between quartz and water was studied by determining 18o profiles in the quartz using an ion microprobe inverse error function plots of the data are linear as required for a diffusion mechanism one natural and two synthetic samples were used and although they had different impurity concentrations oh na and al per 106 si atoms are 7 4000 35 835 and 67 127 respectively the d values were the same within experimental uncertainty diffusion parallel to c is about 2 orders of magnitude faster than that normal to c at 700 c and diffusion normal to the rhombohedron is intermediate the data indicate a change in slope on an arrhenius plot at the boundary at 100 mpa 1 kbar water pressure the preexponential factors do in square centimeters per second and activation energies q in kilojoules per mole for quartz 500 550 c are as follows do 190 and q 284 parallel to c and do 8 10 2 and q 238 normal to the rhombohedron for quartz 600 800 c do 4 10 7 and q 142 parallel to c do 9 10 7 and q 155 normal to the rhombohedron and do 1 10 4 and q 234 normal to c d increases with ph 2 o and between 25 and 350 mpa log d versus log h 2 o has a slope of approximately 1 1 these d values are all several orders of magnitude larger than previously reported values for oxygen diffusion in water free systems

quartz microstructures developed during non steady state plastic flow at rapidly decaying stress and strain rate abstract synseismic loading to very high stresses 0 5 gpa and subsequent creep during stress relaxation in the uppermost plastosphere at temperatures of ca 300 350 c near the lower tip of an inferred once seismically active crustal scale fault was proposed based on peculiar microstructures identified in rocks exposed over 100 km 2 in the sesia zone european western alps here we discuss the conspicuous and highly heterogeneous microstructural record of quartz in disseminated small scale shear zones sub basal deformation lamellae and arrays of elongate subgrains on the tem scale indicate an early stage of glide controlled deformation at high stresses distributed brittle failure is indicated by healed microcracks very fine grained recrystallised aggregates with a pronounced crystallographic preferred orientation reflect intense plastic flow by dislocation creep locally a fine grained foam microstructure indicates a final stage of static grain growth at low differential stress for the previously inferred peak stresses of about 0 5 gpa and given temperatures initial strain rates on the order of 10 10 s 1 are predicted by available flow laws for dislocation creep of quartz we emphasise the importance of short term non steady state deformation in the uppermost plastosphere underlying seismically active upper crust the related heterogeneous record of quartz is governed by the local stress history at constant temperature

experimental grain size sensitive flow of hot pressed brazilian quartz aggregates abstract grain size sensitive flow may be of particular importance in the flow of rocks in natural high strain zones hot pressed aggregates of synthetic ultrafine grained brazilian quartz of nominal grain sizes 0 4 1 3 and 4 5 m were deformed at 300 mpa confining pressure and temperatures of 1273 1473 k fully ductile flow at differential stresses below 200 mpa followed 0 4 exp 220000 r t d 2 where is strain rate s 1 is stress mpa d is grain size microns and r is the gas constant grains remained equant and mostly dislocation free without significant crystallographic fabric water pressure 25 50 mpa was estimated from water adsorbed onto grain boundaries during specimen fabrication flow was inferred to be controlled by silicon volume diffusion and to be sensitive to water fugacity at differential stresses 200 mpa non linear flow involved dislocation motion extrapolation to natural strain rates and temperatures that predict grain size sensitive flow in quartz should only be important at 800 k and very small grain sizes 1 m flow law parameters may change over the extrapolation interval e g through a transition to control by silicon grain boundary diffusion but geological evidence suggests that flow of even very fine grained quartzites commonly occurs by recrystallization accommodated dislocation creep rather than by diffusional accommodation

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

modification of fluid inclusions in quartz by deviatoric stress i experimentally induced changes in inclusion shapes and microstructures fluid inclusions in quartz are known to modify their shapes and microstructures textures during weak plastic deformation however such changes have not been experimentally demonstrated and criteria are not available to relate them to paleostress conditions to address these issues quartz crystals containing natural co2 h2o nacl fluid inclusions have been experimentally subjected to compressive deviatoric stresses of 90 250 mpa at 700 c and 600 mpa confining pressure strains of up to 1 cause the inclusions to develop irregular shapes and to generate microcracks in crystallographic planes oriented subperpendicular to the major compression axis 1 the uniform alignment of the microcracks imparts a planar fabric to the samples the microcracks heal and form swarms of tiny satellite inclusions these new inclusions lose h2o by diffusion thereby triggering plastic deformation of the surrounding quartz via h2o weakening consequently the quartz samples deform plastically only in domains originally rich in inclusions this study shows that fluid inclusions deformed by deviatoric stresses may indeed record information on paleostress orientations and that they play a key role in facilitating crystal plastic deformation of quartz

the brittle plastic transition in experimentally deformed quartz aggregates deformation experiments have been conducted to provide constraints on the processes responsible for the brittle plastic transition in quartz aggregates a correlation between mechanical behavior and distinctive microstructural characteristics indicates that the brittle plastic transition in nonporous quartzite involves at least three transitions in deformation mechanism that occur with increasing temperature and or pressure first there is a transition from cataclastic faulting to semibrittle faulting microstructural observations indicate that this transition occurs due to the activation of dislocations in addition faulting is more stable in the semibrittle faulting regime due to the blunting of the stresses at the advancing fault tip by dislocation glide second there is a transition from semibrittle faulting to semibrittle flow this transition corresponds to a change from localized to distributed deformation microstructural observations indicate that microcracks nucleate in response to stress concentrations at dislocation pileups in the semibrittle flow regime we conclude that the transition to semibrittle flow occurs when the stress intensity at crack tips is insufficient to allow propagation across grain boundaries third there is a transition from semibrittle flow to dislocation creep microstructural observations suggest that this transition occurs as a result of an increase in grain boundary mobility with increasing temperature in addition microstructural observations indicate that a transition from dominantly mode i axial to mode ii shear microcracking occurs with an increase in confining pressure from 0 4 to 0 8 gpa regardless of temperature the differential stresses supported by the experimentally deformed samples are higher than those expected under geologic conditions however a comparison of the experimentally produced microstructures to those reported from natural fault zones suggests that similar processes are operative in the laboratory and in the earth the results of this study provide further evidence to indicate that the brittle plastic transition in the continental crust occurs over a relatively wide range of conditions

a flow law for dislocation creep of quartz aggregates determined with the molten salt cell we have used the molten salt cell to conduct an experimental study on the rheology of a natural quartzite containing 0 15 wt water co axial deformation experiments were conducted at constant piston displacement rates approximating constant strain rates at low strain the strengths of our natural quartzite measured in the molten salt cell are approximately half those measured at the same conditions in solid media because unlike solid confining media molten salt does not contribute to the strength of the sample it reduces the friction on the moving piston and it allows clear identification of the hit point we have limited the experimental conditions to those required for dislocation creep and have used only steady state flow stresses measured during climb accommodated dislocation creep to calculate the flow law parameters two flow laws were determined one for samples containing minor amounts of melt 1 2 and one for melt free samples in both cases the power law stress exponent n is 4 0 0 9 which is greater than that previously reported in flow laws for dislocation creep of quartz aggregates determined in solid media the activation energy q is 137 34 kj mol 1 for samples with melt and 223 56 kj mol 1 for those without within the range of previously determined values for quartz aggregates containing 0 1 wt water the pre exponential term a is 1 1 10 4 2 mpa ns 1 for samples without melt and 1 8 10 8 2 mpa ns 1 for those with melt the lower strengths measured in the molten salt cell indicate that previous piezometer relations for quartz experimentally determined in solid media are not correct extrapolation of the flow law for melt free aggregates to natural strain rates predicts higher strengths than most previous quartz flow laws however accurate extrapolation requires determining the dependence of flow stress on fh2o and or ah

early diagenesis of recently deposited organic matter a 9 yr time series study of a flood deposit abstract in fall 2000 the po river italy experienced a 100 yr return period flood that resulted in a 1 25 cm thick deposit in the adjacent prodelta 10 25 m water depth in the following years numerous post depositional perturbations occurred including bioturbation reworking by waves with heights exceeding 5 m as well as periods of extremely high and low sediment supply cores collected in the central prodelta after the fall 2000 flood and over the following 9 yr allowed characterization of the event strata in their initial state and documentation of their subsequent evolution sedimentological characteristics were investigated using x radiographs and sediment texture analyses whereas the composition of sedimentary organic matter om was studied via bulk and biomarker analyses including organic carbon oc total nitrogen tn carbon stable isotope composition 13c lignin phenols cutin products p hydroxy benzenes benzoic acids dicarboxylic acids and fatty acids the 9 yr time series analysis indicated that roughly the lower half of the original event bed was preserved in the sediment record conversely the upper half of the deposit experienced significant alterations including bioturbation addition of new material as well as coarsening comparison of the recently deposited material with 9 yr old preserved strata represented a unique natural laboratory to investigate the diagenesis of sedimentary om in a non steady system bulk data indicated that oc and tn were degraded at similar rates loss 17 whereas biomarkers exhibited a broad spectrum of reactivities loss from 6 to 60 indicating selective preservation during early diagenesis given the relevance of episodic sedimentation in several margins this study has demonstrated the utility of event response and time series sampling of the seabed for understanding the early diagenesis in non steady conditions

bioavailable compounds in sinking particulate organic matter blanes canyon nw mediterranean sea effects of a large storm and sea surface biological processes abstract to ascertain whether the blanes submarine canyon functions as a conduit of labile organic compounds to the deep margin we analyzed phytopigment protein carbohydrate and lipid contents of sinking particles during a 6 months period comprised between a large storm event and the spring phytoplankton bloom four sediment traps were deployed at 300 900 1200 and 1500 m depth along the axis of the canyon from november 2008 to april 2009 fluxes of all study variables organic carbon proteins carbohydrates and lipids peaked from mid to late december afterwards organic matter fluxes in the upper canyon decreased to values comparable bc1200 or much lower bc900 than those observed at the beginning of the monitoring period the algal fraction of biopolymeric c i e the percentage contribution of phytopigments to biopolymeric c utilized here as an indicator of particles freshness ranging from 14 to about 100 was generally low median value about 32 and showed the highest values from november to early december 2008 at all stations except for the station at 1200 m which peaks in april 2009 a severe storm that occurred the 26th of december 2008 determined a strong increase in the downward transport of organic matter along the blanes canyon though associated with a decrease in its nutritional quality values of the protein to carbohydrate ratio utilized here as an indicator of particles nutritional quality ranged from 0 4 to 2 0 increasing from late winter to early spring at 900 and 1200 m depth in association with the spring phytoplankton bloom in superficial waters the material collected by sediment traps in spring had a higher nutritional value than in autumn winter at both stations according to the optimal foraging theory the results of this study suggest that following winter episodic events deep sea detritus feeders would need to ingest more detritus to fulfill their requirements for labile food than in spring when fresher material is derived from sinking particles associated with phytoplankton blooms we conclude that whilst submarine canyons like the blanes canyon act as major conduits for material exported from the continental shelf after high energy episodic events the supply of labile food to the deep sea benthic ecosystem is connected to biological processes occurring at the sea surface

tracing anthropogenic hg and pb input using stable hg and pb isotope ratios in sediments of the central portuguese margin abstract three short marine sediment cores from the cascais submarine canyon csc cores 252 32 and 252 35 and the estremadura spur core 252 16 on the central portuguese margin were analysed for hg pb al and mn concentrations and both pb and hg stable isotope compositions in order to reconstruct trends in hg and pb sources and accumulation sediment ages were determined based on 210pb measurements the studied cores reveal increasing hg and pb concentration independent of grain size variations since the middle of the 19th century towards the present concomitantly a decreasing trend of 206pb 207pb to less radiogenic values towards the surface was found indicating increasing anthropogenic inputs the lowest values of 202hg were generally observed in the older sediments characterized by low hg and pb concentrations suggesting a low input of anthropogenic metals odd mass number 199hg and 201hg hg isotopes in sediment samples from core 252 16 were characterized by positive mass independent fractionation mif while recent sediments from cores 252 32 and 252 35 did not reveal significant mif probably reflecting both the proximity to the source of anthropogenic hg contamination tagus estuary and the importance of the csc as a particle carrier the multi tracer approach based on both stable hg and pb isotopic signatures confirms anthropogenic hg and pb enrichment in recent marine sediments and also allows us to distinguish between areas dominated by detrital e g csc versus hemipelagic estremadura spur sedimentation

modification of fluid inclusions in quartz by deviatoric stress iii influence of principal stresses on inclusion density and orientation extraction of useful geochemical petrologic and structural information from deformed fluid inclusions is still a challenge in rocks displaying moderate plastic strain in order to better understand the inclusion modifications induced by deviatoric stresses six deformation experiments were performed with a griggs piston cylinder apparatus natural nacl h2o inclusions in an oriented quartz crystal were subjected to differential stresses of 250 470 mpa at 700 900 c and at 700 1 000 mpa confining pressure independently of the strain rate and of the crystallographic orientation of the quartz the inclusions became dismembered and flattened within a crystallographic cleavage plane subperpendicular to 1 the neonate newly formed inclusions that result from dismemberment have densities that tend towards equilibrium with pfluid 1 at tshearing these results permit ambiguities in earlier deformation experiments on co2 h2o nacl to be resolved the results of the two studies converge indicating that density changes in neonate inclusions are promoted by high differential stresses long periods at high p and high t and fluid compositions that maximize quartz solubility neonates spawned from large precursor inclusions show greater changes in density that those spawned from small precursors these findings support the proposal that deformed fluid inclusions can serve as monitors of both the orientation and magnitude of deviatoric stresses during low strain ductile deformation of quartz bearing rocks

earthquake faulting as a structural process abstract structural geology is concerned with the history of movement in the earth s crust and the processes by which displacements occur in the upper one third to one half of deforming continental crust displacement is accommodated largely by seismic slip increments on existing faults it follows that earthquakes and related processes are an integral part of structural geology traditionally structural geologists have been preoccupied with the complexity of the finite deformation within fault zones and with the stress states prevailing at the initiation of faults in intact crust future structural work should be directed more towards understanding the dynamic character of fault reactivation during incremental slip and related effects questions of interest include rheological and geometrical controls on the initiation perturbation and termination of ruptures directivity effects associated with rupture propagation the recognition of structures resulting from repeated stress cycling within seismogenic crust and identification of structural features diagnostic of shear stress levels during faulting structures arising from the inter relationships between slip episodes and induced fluid flow are of special importance because these dynamic fault processes appear influential in the development of much fault hosted mineralization mesothermal gold quartz lodes hosted in high angle reverse shear zones of mixed brittle ductile character form illustrative examples of structures that arguably can only be interpreted by seismo structural analysis embodying the concepts listed above

simple shear experiments on calcite rocks rheology and microfabric ideal simple shearing of carrara marble and solnhofen limestone was achieved by inserting calcite rock slices into sandstone cylinders precut at 35 the experiments covered a wide range in temperatures 25 900 c at confining pressures of 200 and 250 mpa and at strain rates between 10 3 and 10 5 s 1 shear strains of up 2 7 were achieved the stress strain data for simple shear favourably compare with predictions on the basis of existing flow laws established in coaxial testing this comparison demonstrates that the simple shear experiments covered most of the previously established flow regimes for calcite rocks at the highest temperatures carrara marble exhibited substantial work softening after high shear strains a complete texture analysis was carried out with the u stage and a texture goniometer the following four distinct microfabric regimes were found 1 twinning regime an oblique c axis maximum deflected from the pole to the flattening plane towards 1 and against the imposed sense of shear results directly from e twinning extensive twinning some grains are completely twinned rapidly rotates the c axes into near parallelism with 1 this regime was observed for carrara marble deformed at temperatures below 700 c and for solnhofen limestone at room temperature 2 intracrystalline slip regime three c axis maxima were observed in both rock types at more elevated temperatures and in the absence of twinning these c axis orientations result from an alignment of slip planes and slip directions into parallelism with the shear zone boundary and the shear direction respectively this finding supports the idea of an orientation for easy slip resulting from simple shearing in addition to r and f glide basal glide is inferred to have been operative 3 grain boundary sliding regime a great circle distribution of c axes approximately perpendicular to the direction of finite shortening is observed this texture is weaker compared to the other regimes it is interpreted to result from minor contributions of f slip towards total strain this regime is restricted to fine grained solnhofen limestone deformed at the highest temperatures 4 grain boundary migration regime only in carrara marble deformed at the highest temperatures is there substantial grain boundary migration recrystallization the texture consists of a dominant c axis maximum oriented perpendicular to the shear zone boundary this single maximum corresponds to an orientation for easy slip for basal slip grain boundary migration assists rapid lattice reorientation and leads to geometrical work softening quantitative analysis of grain boundary surface orientations gave the following results within the twinning and the intracrystalline slip regimes the characteristic grain shape is elliptical for both rock types the strain ellipses derived from this analysis closely correspond to the known finite strain at the lowest temperatures at intermediate temperatures and especially in carrara marble there is a consistent trend for the aspect ratios to indicate too little flattening and for the angles between the long axis of the strain ellipse and the shear zone boundary to be too small in the absence of grain boundary migration recrystallization this finding indicates minor translations of grains with respect to one another grain boundary sliding or translations accommodated in the mantle regions of grains at the highest temperatures where extensive grain boundary migration occurs in carrara marble grain boundary migration regime two preferred orientations of grain boundaries are observed 1 parallel to the shear zone boundary and 2 parallel to an oblique direction deflected 20 away from the normal to the shear zone boundary in the sense of the imposed shear the same pattern of grain boundary alignment is observed in solnhofen limestone deformed in the grain boundary sliding regime the geological applications of this experimental work are discussed in terms of calcite tectonites in particular and sheared rocks in general

benthic foraminifera in the nazare canyon portuguese continental margin sedimentary environments and disturbance abstract living rose bengal stained benthic foraminifera were investigated from thirteen stations ranging from 146 4976 m water depth in the nazare canyon located on the western iberian continental margin the total standing stocks tss species assemblages and in sediment distributions are compared between stations located on the highly disturbed axis of the upper 4000 m in addition the community changes were investigated in relation to water depth and bio available organic carbon overall low total standing stocks of foraminifera were found in the disturbed canyon axis which experiences frequent sediment resuspension and gravity flows at the upper canyon axis station at 1118 m a rather exceptional fauna was recovered dominated by a species of technitella that made up 75 of the tss the highest tsss were recorded in the upper canyon terrace stations where fine grained sediment and organic carbon are able to accumulate standing stocks on the terraces decreased with increasing water depths the quiescent terrace stations recorded high abundances of infaunal species including melonis barleeanum globobulimina spp and chilostomella oolina the occurrence of these species reflects the low pore water oxygen concentrations and high bio available carbon supply several tubular bathysiphon species were found in the upper canyon terrace stations instead the deepest stations of the lower canyon were dominated by another large agglutinated protozoan saccorhiza ramosa the change in the arborescent tubular foraminiferal community may reflect the increase in sediment oxygenation with increasing water depth in the canyon bathysiphon spp occurring in sediments with higher bio available carbon flux and s ramosa inhabiting more oligotrophic areas

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

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

stresses and pressures at the quartz to coesite phase transformation in shear deformation experiments coesite was found in quartz aggregates experimentally deformed at confining pressures of 1 0 1 5 gpa and temperatures between 600 c and 900 c the confining pressure pc and in most cases the mean stress m of the experiments were below those of the quartz to coesite phase transformation yet coesite formed when the maximum principal stress 1 was within the p t range of the coesite stability field in one sample the euhedral coesite grains were corroded indicating that coesite started to transform back to quartz it is inferred that this sample started to deform with 1 above the quartz to coesite phase transformation and with on going deformation 1 decreased to values in the quartz stability field due to strain weakening in all cases 1 triggered the quartz to coesite reaction as well as the reverse reaction suggesting that 1 is the critical parameter for the quartz to coesite transformation not pc or m with progressive deformation the coesite laths rotated towards the shear plane as more rigid particles with the sense of shear in case of back reaction new quartz grains exhibit no systematic crystallographic relationship with respect to old coesite the experiments cover different degrees of pressure overstepping different temperatures and different experimental durations at p and t and deformation always enhances the reaction kinetics the observation that 1 is critical for a pressure dependent phase transformation also for reversals poses questions for the thermodynamic treatment of such phase transformations

the recrystallized grain size piezometer for quartz an ebsd based calibration we have re analyzed samples previously used for a quartz recrystallized grain size paleopiezometer using electron backscatter diffraction ebsd recrystallized and relict grains are separated using their grain orientation spread gos which acts as a measure of intragranular lattice distortion and a proxy for dislocation density for ebsd maps made with a 1 m step size the piezometer relationship is d 103 91 0 41 1 41 0 21 for rms mean diameter values we also present a sliding resolution piezometer relationship d 104 22 0 51 1 59 0 26 that combines 1 m step size data at coarser grain sizes with 200 nm step size data at finer grain sizes the sliding resolution piezometer more accurately estimates stress in fine grained 10 m samples the two calibrations give results within 10 of each other for recrystallized grain sizes between 10 m and 100 m both piezometers match the original light optical microscopy quartz piezometer within error

sedimentary labile organic carbon and pore water redox control on species distribution of benthic foraminifera a case study from lisbon setubal canyon southern portugal abstract rose bengal stained benthic foraminifera were studied from 11 cores collected along two depth transects off southern portugal one in the lisbon setubal canyon and the other along the canyon edge the total standing stocks and distribution of foraminifera were investigated in relation to sediment and pore water geochemistry nitrate was used as a redox indicator sedimentary chlorophyll a and cpe chloroplastic pigment equivalents contents as a measure of labile organic matter and total organic carbon as a measure of bulk organic matter availability the canyon sediments were enriched in organic carbon and phytopigments at all water depths in comparison with the canyon edge water depth seemed to control sedimentary phytopigment content but not total organic carbon no significant correlation was seen between pigment and total organic carbon content the abundance of calcareous foraminifera correlated with the phytodetritus content whereas a weaker correlation was observed for the agglutinated taxa therefore calcareous foraminifera appear to require a fresher food input than agglutinated taxa the foraminiferal species composition also varied with pigment content and nitrate penetration depth in the sediment in line with the trox concept phytopigment rich surficial cpe content 20 g cm3 sediments with a shallow nitrate penetration depth 1 cm depth were inhabited by generally infaunal species such as chilostomella oolina melonis barleeanus and globobulimina spp as the nitrate penetration increased to 2 cm depth in sediment and the pigment content remained relatively high 15 g cm3 uvigerina mediterranea and uvigerina elongatastriata became dominant species with declining cpe content and increasing nitrate penetration depth the foraminiferal assemblages changed from the mesotrophic cibicides kullenbergi uvigerina peregrina assemblage to the oligotrophic abyssal assemblage mainly consisting of agglutinated taxa

orientation analysis of localized shear deformation in quartz fibres at the brittle ductile transition abstract the crystallographic preferred orientation of fibrous quartz veins deformed under subgreenschist facies conditions along a temperature gradient from 270 to 370 c has been investigated to explore the active mechanism during deformation of the quartz fibres the complete crystallographic orientation of individual recrystallized grains and subgrains was determined by using a combination of cip computer integrated polarization microscopy ebsd electron back scatter diffraction and additional specially developed image analysis techniques it was found that the quartz fibres deformed along crystallographically controlled shear bands from inverse pole figures of normals to the shear band boundaries it is evident that these bands occur along the positive and negative rhomb planes of quartz it is suggested that they are initiated as fractures along these planes inside the shear bands small grains broken off from the host grain show passive rotation of the lattice consistent with the shear sense of the shear bands continued deformation and increasing temperature lead to different recrystallization microstructures inside and outside the shear bands and to a partial obliteration of the sharp orientation relationships

slope transport of suspended particulate matter on the aquitanian margin of the bay of biscay abstract spatial and temporal characteristics of the water masses and the dispersion of the suspended particulate matter were investigated using current meter hydrographic and nephelometric observations gathered during the ecofer experiment 1989 1991 in the cap ferret canyon on the aquitanian margin of the bay of biscay while characteristics of the deep water masses were stable from one year to another large hydrographic change in the upper 500 m related to winter renewal induced by poleward advection of warm and saline water along the continental slope the slope circulation and seasonal eddy activity appear as important dynamical mechanisms that control the entrainment and the dispersion of the suspended particulate matter from the neritic domain to the deep ocean a predominantly northward along slope current with occasional reversal characterizes this circulation the nephelometric structures also showed seasonal changes in the overall suspended particulate matter content but recurrent features such as the presence of intermediate nepheloid layers at the shelf break depth and various depths along the slope 500 1000 and 2000 m were observed these nepheloid layers extended off the slope to about 10 30 km but especially laterally along the slope their presence indicated that suspended particulate matter exchanges between the shelf and the slope occurred mainly in the head of the canyon and along the southern open slope the intermediate nepheloid layers around 500 m depth detached from the slope particularly in regions where the bottom slope is close to critical for the m2 internal tide

silicon diffusion in a natural quartz aggregate constraints on solution transfer diffusion creep abstract silicon bulk diffusion rates were determined in a fine grained 1 2 m diameter natural quartz aggregate novaculite from hot springs ar the diffusion experiments were done at 600 800 c and 150 mpa confining pressure hydrothermal and at 800 1100 c and 1 atm in a stream of dry n2 the technique employed an isotopic tracer 30si and standard step scan analysis using an ion microprobe sims the temperature dependence of silicon bulk diffusion in the novaculite is described by the arrhenius parameters d0 bulk 3 7 10 10 m2 s and q 137 18 kj mol and d0 bulk 6 2 10 9 m2 s and q 178 38 kj mol for the hydrothermal and dry experiments respectively at 800 c the silicon bulk diffusion rate at 150 mpa hydrothermal is about a factor of 10 greater than at 1 atm dry for an assumed effective grain boundary width of 2 nm the silicon grain boundary diffusion rates in novaculite are a factor of two to three less than oxygen diffusion rates for similar hydrothermal conditions and more than 12 orders of magnitude greater than anhydrous silicon volume diffusion rates extrapolated to the temperature of these experiments the results of this study provide valuable constraints on the role of diffusion accommodated deformation in quartz rich rocks

bottom and suspended particle sizes implications for modern sediment transport in quinault submarine canyon abstract electronic particle size analysis of suspended particulate matter and seabed sediments collected over a two year field study of quinault canyon indicates that fine silts 5 9 m modal diameter dominate canyon sedimentation these sediments are markedly finer than the coarse silts 20 40 m modal diameter characteristic of shelf sediments at the canyon head most of the suspensate delivered to the canyon is derived from the intermediate nepheloid layer inl over the slope which in turn originates from the bottom nepheloid layer bnl on the shelf current meter data and particle sizes suggest that sediment accumulating in the upper head of the canyon m is derived directly from the mid shelf silt deposit sediment accumulating in lower portions of the canyon head and in the lower canyon 1000 m depth is apparently resuspended from the outer shelf south of the canyon transport is dominantly across canyon rather than offshore in a north northwesterly direction storms strongly influence sediment transport dramatically increasing suspensate modal sizes in the uppermost portions of the canyon head m depth and over the shelf break storms produce less significant changes in particle size distributions on the open slope m and no apparent changes in the deeper portions of the canyon 1000 m rapid settling of 30 m particles restricts sand and coarse silt accumulation primarily to the southern portion of the upper canyon head

positive feedback and momentum growth during debris flow entrainment of wet bed sediment debris flows typically occur when intense rainfall or snowmelt triggers landslides or extensive erosion on steep debris mantled slopes the flows can then grow dramatically in size and speed as they entrain material from their beds and banks but the mechanism of this growth is unclear indeed momentum conservation implies that entrainment of static material should retard the motion of the flows if friction remains unchanged here we use data from large scale experiments to assess the entrainment of bed material by debris flows we find that entrainment is accompanied by increased flow momentum and speed only if large positive pore pressures develop in wet bed sediments as the sediments are overridden by debris flows the increased pore pressure facilitates progressive scour of the bed reduces basal friction and instigates positive feedback that causes flow speed mass and momentum to increase if dryer bed sediment is entrained however the feedback becomes negative and flow momentum declines we infer that analogous feedbacks could operate in other types of gravity driven mass flow that interact with erodible beds the mechanisms by which debris flows acquire mass and momentum as they entrain material are unclear large scale experiments suggest that the pore pressure of wet bed sediment increases as the flow moves over the bed leading to reduced friction and progressive scouring of the base

modern sediment dispersal and accumulation in quinault submarine canyon a summary abstract quinault canyon off the coast of washington intersects the dispersal path of modern columbia river sediments on the continental shelf study of the dynamics dispersal and accumulation of these deposits in the canyon indicates that no systematic down canyon transport occurs rather sediment dispersal is controlled primarily by the regional flow pattern suspended particulate matter is resuspended on the shelf primarily during winter storm events and advected northward as a bottom nepheloid layer bnl over the shelf cross canyon advection produces an intermediate nepheloid layer inl over the upper slope and canyon from which the suspended particulate matter settles rapidly probably in amorphous aggregates rapid short term deposition 10 1 g cm 2 yr 1 and enhanced modern accumulation generally 10 10 2 g cm 2 yr 1 are confined to the upper canyon 1600 m where fluctuations in deposition rates and grain size are related to specific shelf sediment resuspension events in the lower canyon 1600 m accumulation is slow and temporally uniform

intensity duration threshold of rainfall triggered debris flows in the wenchuan earthquake affected area china the ms 8 0 wenchuan earthquake has greatly altered the rainfall threshold for debris flows in the affected areas this study explores the local intensity duration i d relationship based on 252 post earthquake debris flows it was found that i 525 d 0 76 accounts for more than 98 of the debris flow occurrences with rainfall duration between 1 and 135 h therefore the curve defines the threshold for debris flows in the study area this gives much lower thresholds than those proposed by the previous studies suggesting that the earthquake has greatly decreased the thresholds in the past years moreover the rainfall thresholds appear to increase annually in the period of 2008 2013 and present a logarithmic increasing tendency indicating that the thresholds will recover in the future decades c 2015 elsevier b v all rights reserved

amorphous material in experimentally deformed mafic rock and its temperature dependence implications for fault rheology during aseismic creep and seismic rupture abstract amorphous materials are frequently observed in natural and experimentally produced fault rocks their common occurrence suggests that amorphous materials are of importance to fault zone dynamics however little is known about the physico chemical impact of amorphous materials on fault rheology here we present deformation experiments on mafic fault rock where amorphous material forms due to intense mechanical wear during the experiments the experiments are run at temperatures from 300 to 600 c confining pressures of 0 5 or 1 0 gpa and at constant displacement rates of d ax 2 10 7 2 10 8 or 2 10 9 ms 1 resulting in bulk strain rates of 3 10 4 3 10 5 and 3 10 6 s 1 at these conditions the mafic rock material undergoes intense brittle deformation and cataclastic flow but sample strength significantly decreases with increasing temperatures a feature commonly attributed to viscous deformation processes microstructural analyses show that after an initial stage of homogeneous cataclastic flow strain localizes into narrow 2 10 m wide ultra cataclastic bands that evolve into amorphous shear bands with the data presented in this research paper we argue that the temperature sensitivity recorded in the mechanical data is caused by viscous deformation of the amorphous material we suggest that with the formation of amorphous materials during brittle deformation fault rheology becomes significantly temperature sensitive this has important implications for our understanding of fault strength and weakening due to the presence of amorphous materials in addition weak material along faults will lead to stress concentrations that may trigger seismic rupture

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

flow laws and fabric transitions in wet quartzite abstract we investigated quartzite flow laws based on data from 21 different experimental studies on samples deformed with added water at temperatures from 700 to 1200 c two clear trends emerge one with a power law stress exponent of n 4 0 3 and the other at higher stresses and lower temperatures with a stress exponent of n 2 7 0 3 the change in stress exponent indicates a transition in the rate limiting process of dislocation creep the deformation conditions where the change in n occurs also correlate with conditions where a distinctive change in the c axis fabric is observed for samples deformed in general shear at low stresses quartz fabrics are defined by a y max where c axes align parallel to the y direction of the strain ellipse suggesting easy slip on the prism system at higher stresses quartz fabrics indicate easy slip on the basal system the correlation between the stress exponents and c axis fabrics suggests that the flow law transition results from a concomitant switch in the dominant slip system and the slip system that rate limits deformation alternatively recent studies on both experimental and natural samples provide evidence for dislocation accommodated grain boundary sliding disgbs in quartz aggregates microstructures and mechanical data acquired on samples deformed at conditions near the transition between the n 4 and n 2 7 flows laws are indicative of this process providing evidence for a rheological model similar to that proposed for ice and olivine extrapolation of these newly constrained flow laws delineates estimated deformation conditions where the y max and basal fabrics are preserved in the crust these results provide further support for the application of quartzite flow laws to investigate the rheology of the continental crust and motivate more analyses on the grain size dependence of creep in quartz aggregates

downslope volume enlargement of a debris slide debris flow in the 1999 hiroshima japan rainstorm abstract following a heavy rainstorm on 29 june 1999 hundreds of slope failures occurred in granitic mountains in hiroshima prefecture japan among these events a highly mobile landslide termed the kameyama landslide in this paper which occurred in kameyama area of hiroshima city was the most catastrophic and was investigated in detail the displaced soil mass from the source area of this landslide traveled about 300 m and deposited a volume more than 10 times as great as that in the source area the landslide originated in and traversed a valley shaped concave slope covered by pre existing colluvial debris deposits in addition a spring was visible in the source area and very shallow ground water was observed in an observation pit dug in the source area thus it is inferred that the ground water table rose quickly during the rainfall and that this rise triggered the slope failure in the source area based on a field survey along the landslide cross section a possible explanation for the mechanism of the landslide was obtained the displaced soil mass from the source area impacted the debris deposit in the path of the landslide thus triggering liquefaction failure of the saturated part of debris the original landslide and the liquefied debris then moved downslope as a single mass to examine this assumption ring shear tests were performed on samples taken from the source area undrained ring shear tests on the saturated samples showed that the sample is highly liquefiable and liquefaction failure could have been triggered in the debris deposits by a very small impact from the displaced soil mass of the initial failure in addition laboratory tests simulating the impacts on the debris deposits at natural water content i e unsaturated at the survey time 2 days after the failure showed that although shear failure could be caused by the assumed impact force the displaced soils stopped after a few centimeters displacement indicating that existence of a saturated zone in debris deposits is prerequisite for this kind of failure

catastrophic debris flows on 13 august 2010 in the qingping area southwestern china the combined effects of a strong earthquake and subsequent rainstorms in the wenchuan area in sw china an abundance of loose co seismic landslide debris was present on the slopes after the wenchuan earthquake which in later years served as source material for rainfall induced debris flows or shallow landslides slopes composed of cambrian sandstones and siltstones intercalated with slates appeared to be most susceptible to co seismic landsliding a total of 20 debris flows are described in this paper all were triggered by heavy rainfall on 13th of august 2010 field reconnaissance and measurements supported by aerial photo interpretation were conducted to identify the locations and morphological characteristics of the debris flow gullies in order to obtain information about surface area and volume of landslides and the debris flows the debris flows in the study area were initiated by two processes a run off erosion on co seismic landslide material and concentrated erosion of landslide debris in steep channels b new landslides that transform into debris flows the volume of debris flow deposits on individual fans varies by many orders of magnitude the smallest deposit has a volume of from 5760 to 3 1 million m3 a comparison of the measured volumes deposited on the fan with the volumes of debris stored in the catchment shows the huge potential for future debris flow activity whilst there is a weakly significant positive correlation between these two volumes no significant statistical correlation could be established between volumes of debris flow deposits and other morphometric parameters of the catchment a catastrophic debris flow catchment the wenjia catchment was selected as an extreme case to show in detail the mechanism of debris flow formation as a result of intensive erosion in loose material which was deposited by a rock avalanche during the 2008 earthquake event analyses of the meteorological conditions that triggered these debris flows show one day antecedent precipitation varying between 67 7 and 137 6 mm with a mean rainfall intensity of about 7 3 to 22 5 mm h a rainfall event with peak intensity of 38 7 mm h triggered the largest debris flow event rainfall data related to five debris flow events in the wenjia torrent was used to establish a primary rainfall intensity duration relationship for the triggering of debris flows which was compared to other rainfall duration thresholds from other parts of the world in the discussion emphasis is laid on the need to unravel the process mechanisms which initiated the debris flows for a better understanding and assessment of meteorological thresholds

effect of bed sediment entrainment on debris flow resistance entrainment of sediment from hillslope and channel usually has a significant influence on resistance of debris flow this effect is studied by flume experiments of debris flow over rigid and erodible beds fifty contrast flume tests show that the flow resistance over the erodible bed is significantly larger than that over the rigid bed because of higher energy consumption resulting from sediment transport a new formula of debris flow resistance involving the entrainment effect is obtained from the erodible bed data by nondimensional multiple regression analysis

accurate differential stress measurement using the molten salt cell and solid salt assemblies in the griggs apparatus with applications to strength piezometers and rheology abstract calibrations have been developed for the molten salt cell and solid salt assemblies used in tri axial griggs type piston cylinder deformation apparatus griggs apparatus that enable accurate differential stress determinations in both assemblies at high pressures and high resolution differential stress measurements in the molten salt cell elastic response of the apparatus was characterized by loading alumina and wc rods and flow strengths were measured for high purity nickel and molybdenum and a ti zr mo alloy in replicate experiments in a griggs apparatus and a heard tri axial gas apparatus gas apparatus at identical pressures temperatures and strain rates the elastic response of the griggs apparatus is nonlinear at low total loads 1 760 mpa on a 5 mm diameter sample but becomes linear at loads greater than 15 kn plastic deformation experiments on water insensitive metals indicate that differential stresses measured in the molten salt cell msc and solid salt ssa assemblies in the griggs apparatus are greater than those measured in the gas apparatus at all conditions but vary systematically and reproducibly a simple linear calibration gas apparatus 0 73 griggsmsc 10 mpa where differential stress 1 3 can be applied to the differential stresses obtained using the msc in the griggs apparatus to obtain sample flow strength a similar linear calibration gas apparatus 0 73 griggsssa 48 mpa 30 mpa can be applied to the differential stresses obtained using the griggs apparatus with a solid salt assembly to obtain accurate sample flow strength these calibrations have been tested by applying them to mechanical data for carbonates deformed in the griggs apparatus and gas apparatus the calibrations are also applied to data from previous studies performed in the griggs apparatus on clinopyroxenites and quartzites and compared to results from similar experiments using the gas apparatus when the experimental starting materials and conditions are the same the recalculated flow strengths measured in the griggs apparatus experiments agree with those measured in the gas apparatus however discrepancies in differential stress are still observed in cases where starting materials differ or water available to silicate samples varies presumably through hydrogen diffusion through sample jackets and hydrogen fugacities of the surrounding confining media

frictional slip of granite at hydrothermal conditions sliding on faults in much of the continental crust likely occurs at hydrothermal conditions i e at elevated temperature and elevated pressure of aqueous pore fluids yet there have been few relevant laboratory studies to measure the strength sliding behavior and friction constitutive properties of faults at hydrothermal conditions we slid laboratory granite faults containing a layer of granite powder simulated gouge velocity stepping experiments were performed at temperatures of 23 to 600 c pore fluid pressures ph2o of 0 dry and 100 mpa wet effective normal stress of 400 mpa and sliding velocities v of 0 01 to 1 m s 0 32 to 32 m yr conditions were similar to those in earlier tests on dry granite to 845 c by lockner et al 1986 the mechanical results define two regimes the first regime includes dry granite up to at least 845 and wet granite below 250 c in this regime the coefficient of friction is high 0 7 to 0 8 and depends only modestly on temperature slip rate and ph2o the second regime includes wet granite above 350 c in this regime friction decreases considerably with increasing temperature temperature weakening and with decreasing slip rate velocity strengthening these regimes correspond well to those identified in sliding tests on ultrafine quartz we infer that one or more fluid assisted deformation mechanisms are activated in the second hydrothermal regime and operate concurrently with cataclastic flow slip in the first cool and or dry regime is characterized by pervasive shearing and particle size reduction slip in the second hot and wet regime is localized primarily onto narrow shear bands adjacent to the gouge rock interfaces weakness of these boundary shears may result either from an abundance of phyllosilicates preferentially aligned for easy dislocation glide or from a dependence of strength on gouge particle size major features of the granite data set can be fit reasonably well by a rate and temperature dependent three regime friction constitutive model chester this issue we extrapolate the experimental data and model fit in order to estimate steady state shear strength versus depth along natural slipping faults for sliding rates as low as 31 mm yr we do this for two end member cases in the first case pore pressure is assumed hydrostatic at all depths shallow crustal strength in this case is similar to that calculated in previous work from room temperature friction data while at depths below about 9 13 km depending on slip rate strength becomes less sensitive to depth but sensitive to slip rate in the second case pore pressure is assumed to be near lithostatic at depths below 5 km strength is low at all depths in this case 20 mpa in agreement with observations of weak faults such as the san andreas the predicted depth of transition from velocity weakening to velocity strengthening lies at about 13 km depth for a slip rate of 31 mm yr in rough agreement with the seismic aseismic transition depth observed on mature continental faults these results highlight the importance of fluid assisted deformation processes active in faults at depth and the need for laboratory studies on the roles of additional factors such as fluid chemistry large displacements higher concentrations of phyllosilicates and time dependent fault healing

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

the brittle to viscous transition in polycrystalline quartz an experimental study shear experiments on quartz gouge were performed at elevated confining pressures predominantly 1 5 gpa and temperatures 500 c 1000 c at shear strain rates of 3 5 10 6 s 1 to 2 10 3 s 1 to study the brittle to viscous transition an unsystematic temperature dependence of strength at low temperatures changes towards a clear temperature weakening dependence above 650 c the transition from a pressure strengthening to a pressure weakening relationship takes place continuously between 650 c and 800 c strain rate stepping experiments reveal power law breakdown at low temperatures 650 c between 800 c and 1000 c a stress exponent of n 1 9 0 6 and an activation energy of q 170 72 kj mol indicate a combination of diffusion and dislocation creep the goetze criterion is confirmed as the upper stress limit for viscous deformation mechanisms localised deformation in the form of semibrittle shear bands with riedel geometry at low temperatures changes to homogeneous deformation with a pervasive foliation accompanied by a continuous texture evolution between 700 c and 1000 c fracturing dominates at low temperatures accompanied by increasing amounts of dissolution and precipitation in fine grained zones with increasing temperature above 650 c dislocation and diffusion creep are the dominating deformation processes with dislocation creep being favoured in larger grains while dissolution precipitation is active in the fine grained fraction

healing microstructures of experimental and natural fault gouge 1 the healing of fault gouge was studied by examining microstructures of naturally and experimentally produced granitoid fault rock we performed deformation experiments on intact granitoid rock samples at t 300 500 c pc 500 mpa and 1 2 10 4 1 3 10 7 s 1 with 0 2 wt h2o added healing experiments were carried out on deformed samples at t 200 500 c pc 500 mpa for 4 h to 14 days under hydrostatic and nonhydrostatic conditions the grain size distributions gsd of the deformed samples were quantified using the d value slope of log frequency log radius of the gsd for quartz and feldspar fault gouge healing causes a decrease in the d value from 2 0 to 1 5 the time dependence of the d decrease is described by a hydrostatic healing law of the form d d t df a e t the results of the laboratory experiments were compared to three natural fault systems 1 nojima fault zone japan 2 fault zones in the black forest germany and 3 orobic thrust italian alps natural and experimental gouges have similar d values healing is only observed in monomineralic aggregates polymineralic i e mixed fault gouges retain their high d value after extended healing times because grain growth is inhibited healing under nonhydrostatic conditions is more rapid than hydrostatic healing the low strain rates which were measured during nonhydrostatic healing are temperature dependent and suggest that diffusive mass transfer processes take place during deformation thus fault rocks at upper to midcrustal depth may deform by combined cataclasis and diffusive mass transfer

initiation conditions for debris flows generated by runoff at chalk cliffs central colorado abstract we have monitored initiation conditions for six debris flows between may 2004 and july 2006 in a 0 3 km 2 drainage basin at chalk cliffs a band of hydrothermally altered quartz monzonite in central colorado debris flows were initiated by water runoff from colluvium and bedrock that entrained sediment from rills and channels with slopes ranging from about 14 to 45 the availability of channel material is essentially unlimited because of thick channel fill and refilling following debris flows by rock fall and dry ravel processes rainfall exceeding i 6 61 d 0 77 where i is rainfall intensity mm h and d is duration h was required for the initiation of debris flows in the drainage basin the approximate minimum runoff discharge from the surface of bedrock required to initiate debris flows in the channels was 0 15 m 3 s colluvium in the basin was unsaturated immediately prior to antecedent and during debris flows antecedent volumetric moisture levels in colluvium at depths of 1 cm and 29 cm ranged from 4 9 and 4 7 respectively during debris flows peak moisture levels in colluvium at depths of 1 cm and 29 cm ranged from 10 20 and 4 12 respectively channel sediment at a depth of 45 cm was unsaturated before and during debris flows antecedent moisture ranged from 20 22 and peak moisture ranged from 24 38 although we have no measurements from shallow rill or channel sediment we infer that it was unsaturated before debris flows and saturated by surface water runoff during debris flows our results allow us to make the following general statements with regard to debris flows generated by runoff in semi arid to arid mountainous regions 1 high antecedent moisture levels in hillslope and channel sediment are not required for the initiation of debris flows by runoff 2 locations of entrainment of sediment by successive runoff events can vary within a basin as a function of variations in the thickness of existing channel fill and the rate of replenishment of channel fill by rock fall and dry ravel processes following debris flows and 3 rainfall and simulated surface water discharge thresholds can be useful in understanding and predicting debris flows generated by runoff and sediment entrainment

the role of deformation reaction interactions to localize strain in polymineralic rocks insights from experimentally deformed plagioclase pyroxene assemblages abstract in order to study the mutual effect of deformation and mineral reactions we have conducted shear experiments on fine grained plagioclase pyroxene assemblages in a griggs type solid medium deformation apparatus experiments were performed at a constant shear strain rate of 10 5 s 1 a confining pressure of 1 gpa and temperatures of 800 850 and 900 c while the peak stress of plagioclase orthopyroxene assemblages reaches values between those of the end member phases the strength of polymineralic materials strongly decreases after peak stress and reaches flow stresses that stabilize far below those of the weaker phase plagioclase this weakening correlates with the coeval development of high strain shear zones where new phases are preferentially produced including new pyroxene plagioclase and amphibole the reaction products mostly occur as intimately mixed phases within fine grained and interconnected shear bands together with different compositions with respect to the starting material this indicates that deformation significantly enhances the kinetics of mineral reactions which in turn strongly weaken the deforming sample here attributed to a switch to grain size sensitive diffusion creep through phase nucleation and grain size reduction such an interplay between deformation and mineral reactions may have strong implications for the initiation development and durability of shear zones in the lower crust

decomposition of 14c labeled organic substances in marine sediments the depth variation of total organic carbon toc organic matter composition and porewater composition in marine sediments suggests that different components of the organic matter undergo decomposition at widely different rates the decomposition of 14c labeled organic substances was followed in sediment microcosms in the laboratory the substances used were chosen to simulate a portion of material settling to the sediment water interface a marine diatom or hypothesized components of refractory sediment organic matter melanoidins and a bacterial polymer the microcosms were found to be good models of the sediment water interface in terms of how well they mimicked sediment decomposition rates and processes the decomposition of the labeled material and the natural sediment toc were monitored over 1 month the water overlying the sediment remained oxic and net consumption of nitrate was small there was no detectable sulfate reduction the algae and the bacterial polymer were decomposed on average 9 x faster than the melanoidins and 90 x faster than the natural sediment toc the soluble fraction of the algae was decomposed more rapidly than the particulate material

variation in initiation condition of debris flows in the mountain regions surrounding beijing abstract debris flows in the mountain regions surrounding beijing have been occurring for a long time and have resulted in great economic losses in this study 23 rainstorm events surficial sediments and debris flow deposits were analyzed to quantify the area s rainfall threshold and to investigate how such conditions may be used to predict debris flow in this region rainfall threshold of intensity duration i d functions after vegetation recovery was higher than before recovery and also higher than i d levels in other regions where debris flows are closely associated with runoff field investigations revealed that surficial sediments were characterized by coarse grained sediments and that debris flow deposits lacked fine particles local debris flows can be triggered by runoff however no single standard equation is used to predict the conditions that lead to runoff triggered debris flow and commonly used equations give different values here we propose an empirical function that takes into account peak discharge per width and particle diameter this model should be verified with further investigations so that it can be used as a reference to analyze the conditions that lead to debris flow in the study area finally debris flows may have been related to occasional storms in the study area which has been experiencing substantially increased temperatures and decreased annual precipitation this work provides important information about the conditions that initiated debris flow in the beijing mountain regions in the last few decades

evolution of quartz microstructure and c axis crystallographic preferred orientation within ductilely deformed granitoids arolla unit western alps abstract we have studied quartz microstructures and the c axis crystallographic preferred orientations cpos in four granitoid samples representative of increasing ductile shear deformation from a weakly deformed granitoid stage 1 to a mylonitic granitoid stage 4 the quartz c axis cpo measured in the mylonitic granitoid has been compared with the one observed in a fully recrystallized quartz mylonite from the same area all the samples belong to the austroalpine arolla unit western alps and were deformed at greenschist facies conditions the quartz c axis cpo was analyzed using a u stage and the optical orientation imaging technique the magmatic plagioclase forming more than 50 of the volume of the granitoid is extensively replaced by a mica rich aggregate even in weakly deformed samples of stage 1 these aggregates flow to form an interconnected weak matrix with increasing deformation wrapping relatively less strained quartz grains that undergo dominantly coaxial strain recrystallization of quartz ranges from less than 1 in the weakly deformed granitoid to up to 85 in the mylonitic granitoid with average grain strain of 41 and 64 respectively with increasing strain and recrystallization quartz grains in the granitoids show a sequence of transient microstructures and cpos crystal plastic deformation is initially accomplished by dislocation glide with limited recovery and at 50 grain strain it results in a cpo consistent with dominantly basal a slip at 60 grain strain recrystallization is preferentially localized along shear bands which appear to develop along former intragranular cracks and the recrystallized grains develop a strong c axis cpo with maxima orthogonal to the shear band boundaries and independent of the host grain orientation within the granitoid mylonite at an average quartz grain strain of 64 recrystallization is extensive and the c axis cpo of new grains displays maxima overlapping the host c axis orientation and therefore unrelated to the bulk sense of shear the host controlled cpo is inferred to reflect pervasive recrystallization by progressive subgrain rotation the switch from shear band control to host control on c axis cpo occurred between 40 and 70 of recrystallization in the quartz mylonite the quartz c axis cpo develops an asymmetric single girdle consistent with the bulk sense of shear and the synkinematic greenschist facies conditions this study indicates that the cpo evolution of quartz may significantly differ in cases of polymineralic vs monomineralic rocks under the same deformation conditions if quartz in the polymineralic rock behaves as a strong phase

evidence of phase nucleation during olivine diffusion creep a new perspective for mantle strain localisation for the past decades grain size reduction leading to diffusion creep in olivine is believed to be a very important process for strain localisation in the lithospheric mantle however the mechanisms of grain size reduction in this regime are still poorly understood e g platt 2015 here we show new experimental results that document grain size reduction and material weakening during wet olivine diffusion creep while occurring for both mono phase and two phase aggregates grain size reduction is coeval with strain localisation and local phase mixing in olivine pyroxene aggregates based on evidence of fluid inclusions and cracks filled with a fine grained phase mixture we conclude that grain size reduces as a result of fluid assisted nucleation that takes place in the presence of an aqueous fluid during diffusion creep cavitation induced by grain boundary sliding creep cavitation can be inferred and may play a critical role for olivine grain size reduction amongst their implications for rock rheology in general our findings highlight a key process for strain localisation in the ductile uppermost mantle

reconstructing export production at the ne atlantic margin potential and limits of the ba proxy barium ba aluminium al and zirconium zr were measured in sediment trap material deployed at two margin settings of the ne atlantic the bay of biscaye at goban spur and the nw iberian margin the particulate organic carbon poc ba ratios of the trapped material in both margin environments are clearly higher compared to the open ocean although lateral advection of poc may partly explain these higher poc ba ratios for margin systems it is clear that the yield of authigenic particulate ba during organic matter degradation in the water column is lower in margin environments in order to assess export production in margin settings we optimised transfer functions based on trapped ba fluxes that were originally elaborated for open ocean settings calculations of export production based on trapped ba flux and poc ba ratio were compared with calculations based on trapped poc flux only export production based on ba flux show greater internal consistency amongst traps along the same mooring suggesting that this approach has advantages over the one based on poc flux only estimated export productions are of the same order of magnitude as estimates of new production but systematically fall short of the latter this systematic discrepancy needs further investigation

preparation and deformation of synthetic aggregates of quartz synthetic quartz aggregates of low porosity have been fabricated from natural quartz powder impure silica gel and high purity silicic acid by hydrothermal isostatic pressing at 300 mpa the resulting specimens have water contents comparable to those of natural quartzites and have been used for deformation tests the flow stress at 1200 1300 k was found to vary in an inverse relationship to the water pressure estimated under the assumption that the measured water content homogeneously filled the measured porosity it is questionable that the natural quartz origin specimens were fully equilibrated in respect to the activity of the water but equilibration has probably been achieved in the amorphous silica origin specimens which crystallized under the experimental conditions in the deformation of the latter materials the experimental activation energy at water pressures approaching the confining pressure was found to be about 150 kj mol 1 for both however the impure gel origin material gave a stress exponent of about 2 3 whereas the high purity silicic acid origin material gave a stress exponent of about 4 in spite of the grain sizes being about 90 m and 20 m respectively it is concluded that while the impure specimens have higher intragranular strengths there is also a significant contribution of grain boundary processes to the strain in them which is absent in the high purity specimens

deformation of granitic rocks experimental studies and natural examples crustal deformation is inherently complex because the crust is inhomogeneous and anisotropic on a wide variety of scales advances in our understanding have come from a combination of field observations laboratory experiments and theoretical models what necessarily links all these investigations is a focus on process crystal plasticity dislocation creep is one of several grain scale deformation processes or mechanisms each process is dominant over a certain range of conditions in the crust has a particular form of the flow law and produces a characteristic set of microstructures characterizing the deformation mechanisms for different minerals over a range of conditions allows one to link the mechanical behavior or flow law associated with that process to the microstructures it produces the information on microstructures can be used to help interpret the thermomechanical history of naturally deformed rocks and flow laws can be used to create more realistic models predicting crustal behavior in different tectonic settings iterations among field theoretical and experimental approaches are critical for making progress in our understanding the deformation process of crystal plasticity is the main focus of this volume crystal plastic deformation of the crust is in many ways more complex than that of the mantle because most crustal rocks are polyphase aggregates and the strengths of common crustal silicates such as quartz feldspar and mica are very different at a given set of conditions yield strength envelopes for the crust as shown schematically in figure 1 are commonly plotted using the dislocation creep flow law for quartz which inherently assumes that quartz is the controlling phase and undergoes steady state flow but is the flow law for dislocation creep of quartz a good approximation for the deformation of a granite let alone a crustal plum pudding of regions and layers of different lithologies the crust

on the incidence of debris flows from the early little ice age to a future greenhouse climate a case study from the swiss alps 1 tree ring based reconstructions of 123 debris flow events in a case study area of the swiss alps since ad 1570 show enhanced activity during the wet periods 1864 1895 following the last lia glacier advance and in the early decades of the 20th century in contrast comparably low activity can be observed since 1995 with only one event recorded from the reconstructions and based on rcm simulations there are indications that debris flow frequencies might continue to decrease in a future climate as precipitation events are projected to occur less frequently in summer but become more common in spring or fall

the triggering of debris flow due to channel bed failure in some alpine headwater basins of the dolomites analyses of critical runoff the debris deposits at the bottom of very steep natural channels and streams in high mountain areas can be mobilized by runoff triggering a water sediment mixture flow known as debris flow the routing of debris flow through human settlements can cause damage to civil structures and loss of human lives the prediction of such an event or the runoff discharge that triggers it assumes an interest in risk analyses and the planning of defence measures the object of this study is to find a method to determine the critical runoff value that triggers debris flow as a result of channel bed failure historical and rainfall data on 30 debris flows that occurred in six watersheds of the dolomites north eastern italian alps were collected from different sources field investigations at the six sites together with the hydrologic response to the rainfalls that triggered the events were performed to obtain a realistic scenario of the formation of the debris flow there occurred field observations include a survey along the channel of the triggering reach of debris flow with measurements of the channel slope and cross section and sampling of debris deposits for grain size distribution simulated runoff discharge values based on the rainfall recorded by pluviometers were then compared with values obtained through experimental criteria on the initiation and formation of debris flow by bed failure the results are discussed to provide a plausible physical based method for the prediction of the triggering of debris flow by channel bed failure copyright 2007 john wiley sons ltd

predicting the occurrence of channelized debris flow by an integrated cascading model a case study of a small debris flow prone catchment in zhejiang province china abstract excessive water in a channel is an important factor that triggers channelized debris flows floods and debris flows often occur in a cascading manner and thus calculating the amount of runoff accurately is important for predicting the occurrence of debris flows in order to explore the runoff rainfall relationship we placed two measuring facilities at the outlet of a small debris flow prone headwater catchment to explore the hydrological response of the catchment the runoff responses generally consisted of a rapid increase in runoff followed by a slower decrease the peak runoff often occurred after the rainfall ended the runoff discharge data were simulated by two different modeling approaches i e the nam model and the hydrologic engineering center hydrologic modeling system hec hms model the results showed that the nam model performed better than the hec hms model the nam model provided acceptable simulations while the hec hms model did not then we coupled the calculated results of the nam model with an empirically based debris flow initiation model to obtain a new integrated cascading disaster modeling system to provide improved disaster preparedness and hazard management in this case study we found that the coupled model could correctly predict the occurrence of debris flows furthermore we evaluated the effect of the range of input parameter values on the hydrographical shape of the runoff we also used the grey relational analysis to conduct a sensitivity analysis of the parameters of the model this study highlighted the important connections between rainfall hydrological processes and debris flow and it provides a useful prototype model system for operational forecasting of debris flows

sources of organic carbon in the portuguese continental shelf sediments during the holocene period organic c oc and total n tn concentrations and stable isotope ratios 13 c in muddy deposit sediments of the northern and southern portuguese continental shelf were used to identify sources of fine sized organic matter 63 m during the holocene period sedimentary columns off the guadiana core crida 05 tagus core md 992332 and douro core ksgx 57 estuaries are characterised by elemental and isotopic values that reflect distinct sources of organic matter oc tn and 13 c ranging respectively from 8 5 to 21 and from 22 4 to 27 intense supplies to the guadiana continental shelf of fine terrigenous particles during the younger dryas event are closely linked with higher oc tn values and lower 13 c ratios during the postglacial transgression phase an increasing contribution of marine supplies up to 80 occurred higher 13 c up to 22 4 values and low oc tn ratios down to 8 5 are found as the sea level approaches the current one the upper holocene records emphasize the return to enhanced terrestrial supplies except for the little climatic optimum between the 11th and 15th centuries ad this climatic event is especially obvious in the three cores as a return to marine production and a decrease in terrestrial sediment supply to the continental shelf the return to a cooling event the little ice age between the 15th and 19th centuries ad is mirrored by decreased terrigenous supplies in core ksgx 57 gradually increasing sedimentation in estuaries as well as formation of coastal dune fields have been hypothesized on the basis of increasing 13 c and decreasing oc tn and oc tn values

preferred orientation of anorthite deformed experimentally in newtonian creep abstract synthetic anorthite aggregates were deformed in a paterson gas deformation apparatus at confining pressures up to 400 mpa in torsion and axial compression at temperatures between 950 c and 1200 c samples deformed in torsion under newtonian creep display development of texture or crystallographic preferred orientation as documented with synchrotron x ray diffraction measurements complex diffraction patterns were deconvoluted with the rietveld method to obtain quantitative texture information torsion samples deformed up to shear strains of 4 and samples deformed in compression at higher stresses to total strains of 0 3 develop clear textures texture and shape preferred orientation spo of torsion samples display a monoclinic pattern with an asymmetry inclined against the sense of shear consistent with polycrystal plasticity simulations that assume the deformation is accomplished by dislocation glide these results show that a material deforming in linear viscous creep can develop a strong texture in striking contrast to the paradigm that the presence of a texture precludes low stress newtonian behavior our observations show that the presence or absence of crystallographic preferred orientation is not sufficient to uniquely infer the dominant rheological mechanical regime as sometimes applied for interpretation of seismic anisotropy in the earth

the processes and mechanism of failure and debris flow initiation for gravel soil with different clay content clay content can influence gravel soil mass failure and debris flow initiation significantly but quantification of the clay content influence in the published literature is lacking this paper describes the experiments carried out to explore soil mass failure and debris flow initiation with different clay contents the whole process of gravel soil mass failure and debris flow initiation can be grouped into five phases i infiltration excess runoff ii fracture extending iii initial slip iv large scale slip v debris flow triggering in the experiments when the clay content of soil mass is lower than 2 5 no soil failure and debris flow are triggered only the soil masses with moderate clay contents 5 10 show the clear processes of the five phases that need the shortest rainfall duration among different clay contents soil masses with high clay content 10 and low clay content 2 5 5 need longer rainfall duration to cover the five phases for partially triggering soil failure and debris flows clay content is closely linked with the soil failure and debris flow initiation under rainfall the key mechanism can be grouped into two reasons i the clay particles absorb the moisture and dilate to fill the soil pores and the content of the clay has a direct link with the filled pores ii the gravel soil masses with different clay content differ in their structure for the low clay content soil mass group 2 5 5 the coarse grains of the gravel soil form large pores and saturated clay particles are too few to block most soil pores as a result pore water pressure of soil mass is released easily in the raining process therefore inner friction holds strong and soil mass is hard to mobilize into slip and debris flows on the other hand for soil masses with high 10 clay contents soil failure and debris flow are triggered under the aid of surface runoff flux to reduce the cohesion of the soil whereas only for the soil masses with moderate clay contents 5 10 large scale soil failure and debris flow can be triggered within the shortest duration in this case the debris flow is of the form of soil mechanics which is triggered after soil masses slip and liquefaction the others are of the form of hydraulic mechanics the experiments provide valuable evidence for quantifying clay content impact on gravel soil failure and debris flow initiation because they were carried out in a flume the research results are applicable to the soil failure and debris flow initiation in bedrock gully situations

reconstructing spatio temporal patterns of debris flow activity using dendrogeomorphological methods debris flows are a major threat in many parts of the alps where they repeatedly cause severe damage to infrastructure and transportation corridors or even loss of life nonetheless the spatial behavior of past debris flow activity and the analysis of areas affected during particular events have been widely neglected in reconstructions so far it was therefore the purpose of this study to reconstruct spatio temporal patterns of past debris flows on a forested cone in the swiss alps bruchji torrent blatten valais the analysis of past events was based on a detailed geomorphic map 1 1000 of all forms related to debris flows as well as on tree ring series from 401 heavily affected trees larix decidua mill and picea abies l karst growing in or next to deposits the samples were analyzed and growth disturbances related to debris flow activity assessed such as tangential rows of traumatic resin ducts the onset of reaction wood or abrupt growth suppression or release in total 960 growth disturbances were identified in the samples belonging to 40 different event years between a d 1867 and 2005 in addition the coupling of tree ring data with the geomorphic map allowed reconstruction of eleven formerly active channels and spatial representation of individual events based on our results we believe that before 1935 debris flows preferentially used those channels located in the western part of the cone whereas the eastern part of the cone remained widely unaffected the spatial representation of the 40 events also allowed identification of five different spatial patterns for debris flows at the study site 2006 elsevier b v all rights reserved

evolution of c axis pole figures and grain size during dynamic recrystallization results from experimentally sheared quartzite 1 quartzite samples experimentally sheared at conditions where subgrain rotation and grain boundary migration recrystallization are active show a striking change in the c axis crystallographic preferred orientation cpo with increasing shear strain up to 8 and degree of recrystallization up to 100 we used optical methods to determine the c axis cpo for the bulk samples and for porphyroclasts and recrystallized grains separately and to track the strengths of the cpos in five different orientation domains with increasing the c axis pole figure evolves from a broad peripheral maximum indicative of basal a slip to an inclined single girdle with two maxima indicative of rhomb a slip and finally an elongate single maximum at the girdle center indicative of prism a slip throughout this sequence the fabric skeleton rotates with the sense of shear the bulk preferred c axis orientation results from growth and shrinkage of differently oriented crystallographic domains grain boundary density analysis indicates that the size of prism a recrystallized grains is 1 5 times that of average and 2 times that of rhomb grains indicating that prism a slip is significantly easier at our experimental conditions this inference is supported by autocorrelation function analysis of the various orientation domains and how they evolve with strain similar progressive changes in c axis cpo are observed in quartzites naturally sheared at conditions where grain boundary migration recrystallization operates these results indicate that achievement of microstructural and mechanical steady state requires high strain and complete recrystallization

lateral and vertical distributions of living benthic foraminifera off the douro river western iberian margin impact of the organic matter quality abstract in this study we assess the impact of the quantity and quality of the organic matter on the distribution of live benthic foraminifera on a cross margin transect off the douro river western iberian margin surface sediments from five stations ranging from 50 to 2000 m water depth were collected in march 2011 at the end of the period of maximal river runoff in order to better evaluate the importance of terrestrial input living stained benthic foraminiferal assemblages 150 m and environmental parameters grain size total organic carbon toc total nitrogen tn c n ratio 13 c toc pigments and amino acids were investigated organic matter amounts follow the sediment grain size pattern with higher concentration in fine sediments and seem to control faunal density except at the shallowest station where toc is low and faunal density high at this coastal site a massive sandy deposit is identified and associated with very low faunal diversity labile organic matter is richest at the shelf stations where benthic foraminifera standing stocks are high this is particularly evident on the douro mud patch where both density and diversity are high foraminiferal faunas living at the shelf stations are dominated by species e g nonion scaphum ammonia beccari i bulimina aculeata and eggerella scabra characteristic of the rich trophic conditions with organic matter of mixed estuarine and marine origin very low total standing stocks on the upper slope are associated with coarse sediments probably resulting from intense bottom currents at this depth resulting in poor trophic conditions deeper environments are characterized by species e g hoeglundina elegans uvigerina mediterranea and reophax scorpiurus indicative of fairly abundant but low quality organic matter finally the faunal differences between the shelf stations may reflect different successional stages an early stage at 50 m water depth where unstable conditions are observed with faunas dominated by opportunistic species and a more mature fauna in the mud patch where more stable conditions prevail

compositional changes of minerals associated with dynamic recrystallizatin the rate of compositional and isotopic exchange between minerals may be enhanced significantly if the rock is deformed simultaneously the enhanced exchange rate may result from a reduction in grain size shorter distance for volume diffusion dissolution and growth of grains by diffusion creep pressure solution or the movement of high angle grain boundaries through strained grains during recrystallization in the dislocation creep regime the migration of high angle grain boundaries provides high diffusivity paths for the rapid exchange of components during recrystallization the operation of the latter process has been demonstrated by deforming aggregates consisting of two plagioclases an1 and an79 at 900 c 1 gpa confining pressure and a strain rate of 2x10 6s 1 the polygonal recrystallized grains were analyzed using an analytical transmission electron microscope and have a variable but often intermediate composition at the conditions of these experiments the volume interdiffusion rate of nasi caal is too slow to produce any observable chemical change and microstructural chemical relations indicate that the contribution from diffusion creep was insignificant except for initially fine grained 2 10 m aggregates these results indicate that strain induced recrystallization can be an effective mechanism for enhancing the kinetics of metamorphic reactions and for resetting the isotope systematics of minerals such as feldspars pyroxenes and amphiboles

measurements of diffusivity near the sediment water interface with a fine scale resistivity probe fine scale profiles of the sedimentary formation factor f were obtained from measurements of resistivity at millimetre intervals in marine sediments these profiles demonstrated that rapid decreases in diffusivity occurred in the upper few centimeters of both compact intertidal sands and fine silty muds in the compact sands a 70 decrease in the formation factor was observed within 2 cm of the interface close correlations were found between the formation factor and sediment porosity for both sediment types profiles of 1f predicted from these correlations and porosity profiles were very similar to those obtained from measurements of resistivity these correlations also suggested that 3 is a better approximation of the formation factor in fine muds than the archie relation 2 in both sediments the interfacial value of the diffusion coefficient was estimated to be between 74 and 87 of its value in free solution a value much higher than is normally assumed

macrofaunal assemblages in canyon and adjacent slope of the nw and central mediterranean systems abstract macrofaunal assemblages were studied along bathymetric transects in six canyons and four adjacent open slopes of the mediterranean sea the different areas investigated were located approximately along a longitudinal gradient at similar latitudes three regions were investigated the catalan from 334 to 1887 m depth the ligurian from 222 to 2005 m depth and the south adriatic margins from 196 to 908 m depth the analysis of the meso scale distribution of assemblage structure and biomass showed significant differences among regions which resulted in high values of diversity clear differences in trophic composition were also observed and a decreasing pattern in the individual body size of macrofaunal organisms moving eastward these patterns were apparently linked to changes in food supply whereas macrofaunal abundance and number of taxa showed a decrease pattern with increasing water depth when the assemblage structure was compared between canyons and adjacent open slope a very high diversity was observed indicating that the bottom topography exerted a strong effect on the assemblage characteristics

semi brittle deformation of granitoid gouges in shear experiments at elevated pressures and temperatures abstract the physical and chemical processes acting in the brittle to plastic transition are of great interest for a better understanding of fault rheology we performed a series of experiments on granitoid gouge material under high confining pressures pc 500 1500 mpa temperatures t 300 c and 500 c and fast shear strain rates 1 8 10 4 s 1 where the material deforms by semi brittle flow samples deformed at 500 c are systematically weaker than samples deformed at 300 c over the whole examined confining pressure range indicating a non frictional component of the deformation all samples develop an s c fabrics and deformation localizes in slip zones containing amorphous feldspar material with an intermediate composition na ca and k rich further we observe changes in composition of feldspars enrichment in the albite component in the highly fragmented but crystalline regions with increasing finite shear strain our results indicate that mass transfer processes keep pace with frictional deformation even at high strain rates and together with viscous flow of the amorphous material are responsible for the observed strength difference

deposition rates mixing intensity and organic content in two contrasting submarine canyons the hydrographically different conditions characterising the western iberian margin ne atlantic and the gulf of lions mediterranean may play an important role in determining the biogeochemical characteristics of the sediments to investigate this we compared the nazare and cap de creus canyons and their respective adjacent open slopes in terms of the organic carbon corg contents chlorophyll a chl a concentrations c n and chl a phaeopigment ratios and also in terms of modelled mixing intensities chl a and 210pb deposition and background concentrations in sediments chlorophyll a and 210pb profiles were fitted simultaneously with a reactive transport model to estimate mixing intensity deposition and background concentrations further to account for the possibility that the decay of chl a may be lower in the deep sea than in shallow areas we estimated the model parameters with two models in one approach model 1 the temperature dependent decay rate of chl a as given by sun et al sun m y lee c aller r c 1993 laboratory studies of oxic and anoxic degradation of chlorophyll a in long island sound sediments geochimica et cosmochimica acta 57 147 157 for estuaries was used in the other approach model 2 an extra parameter was estimated to derive the chlorophyll a degradation rate an f test taking into account the different number of parameters in the models was used to single out the model that significantly fitted the data best in most cases the model parameters were best explained with model 1 indicating the empirical relationship by sun et al 1993 is a valid means to estimate the chlorophyll a degradation rate in deep sea sediments to assess the robustness with which the model parameters were estimated we provide a first application of bayesian analysis in the modelling of tracers in sediments bayesian analysis allows calculating the mean and standard deviation for each model parameter and correlations among parameters the model parameters for stations for which 210pb and chlorophyll a profiles were available were robustly fitted as evidenced by an average coefficient of variation of 0 22 corg contents chl a concentrations chl a phaeo ratios mixing intensities depositions and background concentrations of chl a and 210pb indicated that the cap de creus canyon and adjacent slope were less active in terms of organic matter accumulation and burial than the nazare canyon and respective open slope

on the oxidation and burial of organic carbon in sediments of the iberian margin and nazare canyon ne atlantic abstract as a contribution to the ec omex ii program sediment carbon and nitrogen budgets are presented for the iberian margin northeastern atlantic the budgets for degradable organic carbon and associated nitrogen were calculated from sediment and pore water properties using a steady state version of a numerical coupled diagenetic model omexdia data were collected throughout the major upwelling period along five transects four of which were located on the open margin and one positioned in a major submarine canyon the nazare canyon a comparison of in situ oxygen profiles measured with monocathodic microelectrodes and with clark type microelectrodes showed that monocathodic electrodes overestimate the oxygen concentration gradient near the sediment water interface this artifact probably results from the loss in sensitivity of the monocathodic microelectrode during profiling shipboard time course measurements with clark type electrodes demonstrated transient conditions upon sediment retrieval on deck and indicated enhanced rates of oxygen consumption in the surface sediment presumably as a result of lysis or exudation of oxidisable substrates by infauna as a result oxygen fluxes calculated from shipboard oxygen profiles overestimated in situ fluxes by up to a factor of 5 for water depths 1000 m the sediments from the canyon and from a depositional area on the shelf were enriched in organic carbon 3 4 5 wt relative to the open margin stations 0 5 2 wt and showed c n ratios exceeding redfield stoichiometry for marine organic matter indicating there was deposition of organic carbon of terrestrial origin in these areas the oxidation of organic carbon on the open margin declined from 11 gcm 2 y 1 on the shelf to 2 gcm 2 y 1 at 5000 m water depth and was dominated by aerobic oxidation the reactivity of the degradable organic carbon at the time of deposition was 1 on the shelf and declined to 1 offshore the burial of refractory organic carbon at the stations along the open margin transects also declined with increasing water depth from 5 gcm 2 y 1 on the shelf to 2 y 1 at 2000 m depth whereas the burial of particulate inorganic carbon declined from 20 gcm 2 y 1 to 2 y 1 a comparison of the estimated total organic carbon deposition and predicted delivery for the shelf suggest that 58 to 165 gcm 2 y 1 is oxidized in the water column laterally advected or focused into one of the canyons anaerobic oxidation denitrification and therefore total oxidation of organic carbon was enhanced within the canyon relative to the open margin total organic carbon oxidation decreased with water depth from 22 gcm 2 y 1 at the head of the canyon to 3 gcm 2 y 1 over its fan the reactivity of the organic carbon deposited in the canyon was lower than those of the shelf stations suggesting that the canyon is being enriched in older laterally advected organic matter the burial of refractory organic carbon in sediments from the nazare canyon was considerably higher than in the sediments from the open margin it also decreased with depth from 20 gcm 2 y 1 at 343 m to 2 5 gcm 2 y 1 at 4298 m water depth the burial of particulate inorganic carbon was slightly lower than that of refractory organic carbon the burial of refractory organic carbon and the deposition of degradable organic carbon were both positively correlated with the sedimentation rates for the iberian margin and indicated burial efficiencies were 0 6 to 48 a single trend for burial efficiency versus sedimentation rate for both the canyon and the open margin indicates that the sedimentation rate was the master variable for the geographical distribution of organic carbon oxidation and carbon preservation on the nw iberian margin

storm rainfall conditions for floods and debris flows from recently burned areas in southwestern colorado and southern california abstract debris flows generated during rain storms on recently burned areas have destroyed lives and property throughout the western u s field evidence indicate that unlike landslide triggered debris flows these events have no identifiable initiation source and can occur with little or no antecedent moisture using rain gage and response data from five fires in colorado and southern california we document the rainfall conditions that have triggered post fire debris flows and develop empirical rainfall intensity duration thresholds for the occurrence of debris flows and floods following wildfires in these settings this information can provide guidance for warning systems and planning for emergency response in similar settings debris flows were produced from 25 recently burned basins in colorado in response to 13 short duration high intensity convective storms debris flows were triggered after as little as six to 10 min of storm rainfall about 80 of the storms that generated debris flows lasted less than 3 h with most of the rain falling in less than 1 h the storms triggering debris flows ranged in average intensity between 1 0 and 32 0 mm h and had recurrence intervals of two years or less threshold rainfall conditions for floods and debris flows sufficiently large to pose threats to life and property from recently burned areas in south central and southwestern colorado are defined by i 6 5 d 0 7 and i 9 5 d 0 7 respectively where i rainfall intensity in mm h and d duration in hours debris flows were generated from 68 recently burned areas in southern california in response to long duration frontal storms the flows occurred after as little as two hours and up to 16 h of low intensity 2 10 mm h rainfall the storms lasted between 5 5 and 33 h with average intensities between 1 3 and 20 4 mm h and had recurrence intervals of two years or less threshold rainfall conditions for life and property threatening floods and debris flows during the first winter season following fires in ventura county and in the san bernardino san gabriel and san jacinto mountains of southern california are defined by i 12 5 d 0 4 and i 7 2 d 0 4 respectively a threshold defined for flood and debris flow conditions following a year of vegetative recovery and sediment removal for the san bernardino san gabriel and san jacinto mountains of i 14 0 d 0 5 is approximately 25 mm h higher than that developed for the first year following fires the thresholds defined here are significantly lower than most identified for unburned settings perhaps because of the difference between extremely rapid runoff dominated processes acting in burned areas and longer term infiltration dominated processes on unburned hillslopes

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

suspended particle movement in and around quinault submarine canyon abstract time and space dependent light transmission temperature salinity and velocity data obtained during two winter experiments in the vicinity of quinault submarine canyon are used to examine processes controlling subtidal cpd fluctuations in suspended particulate concentration in the region in particular local resuspension of particles by waves and currents horizontal advection and vertical advection data include time series from four to eight mooring locations as many as 16 current meters and 10 transmissometers on the shelf over the open slope and in the canyon during each experiment spatial distributions from five ctd transmission surveys and gravity wave information particle concentration in the bottom boundary layer at the shelf edge was dominated by resuspension events the mechanism for resuspension had a large inter annual variation in the first year wave induced resuspension dominated whereas in the second year current induced resuspension dominated the cut off depth for storm related resuspension was generally m subtidal advection across isobaths upwelling downwelling accounted for 20 of the variance in concentration fluctuations at the shelf edge in the bottom boundary layer horizontal advection of material suspended in the bottom nepheloid layer on the shelf resulted in the formation of shelf break depth intermediate nepheloid layers over the canyon in regions where the flow crosses isobaths the existence strength onshore offshore extent and vertical structure of such nepheloid layers at a given time in this asymmetrical canyon appear to be a function of the direction of flow over the outer shelf and over the upper slope in the canyon whether active resuspension is occurring over the shelf and the maximum resuspension depth and magnitude of the active resuspension event the frequency timing and magnitude of previous resuspension events spatial and temporal continuity magnitude and direction of flow over the open slope north and south of the canyon vertical settling and upwelling or downwelling related to the along isobath flow over the upper slope fluctuations in particle concentration below the shelf break depth over the canyon slope were controlled by vertical rather than horizontal advection vertical excursions by the water mass of 100 m occurred both as a result of isopycnal adjustment to the quasi geostrophic along isobath flow and as a result of semidiurnal tidal oscillations when an overhead nepheloid layer was present such water mass excursions produced concentration fluctuations at depths below the maximum depth of storm related local resuspension in open slope regions where strong inls intermediate depth nepheloid layers were absent the portion of concentration variance that could be explained by advective models with constant spatial gradients was almost negligible only one resuspension event was documented in the bottom boundary layer within the deep canyon bottom depth 1000 m suggesting that advection must account for the observed variance in particle concentration however the large scale gradients at these depths are sufficiently weak cf the smaller scale gradients or noise that advective control could only be demonstrated during the second winter experiment when velocities along the canyon axis were relatively large finally the data demonstrate that subtidal concentration fluctuations within 50 m of the canyon floor are correlated to those at the shelf edge this correlation reflects a correlation in the velocity field rather than a transfer of particles as might occur with a turbidity current

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

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

grain boundary sliding in san carlos olivine flow law parameters and crystallographic preferred orientation 1 we performed triaxial compressive creep experiments on aggregates of san carlos olivine to develop a flow law and to examine microstructural development in the dislocation accommodated grain boundary sliding regime gbs each experiment included load and temperature steps to determine both the stress exponent and the activation energy grain boundary maps created with electron backscatter diffraction data were used to quantify grain size distributions for each sample inversion of the resulting data produced the following flow law for gbs gbs 104 8 0 8 2 9 0 3 d0 7 0 1 exp 445 20 kj mol 1 rt with d and gbs in units of mpa m and s 1 respectively although relatively weak crystallographic preferred orientations cpos have 010 maxima parallel to the compression direction along with 100 and 001 girdles perpendicular to the compression direction cpos and subgrain boundary misorientation axes suggest that the 010 100 slip system contributes significantly to deformation we propose that these experimental results are best modeled by a deformation mechanism in which strain is accomplished primarily through grain boundary sliding accommodated by the motion of dislocations extrapolation of our flow laws to mantle conditions suggests that gbs is likely to be the dominant deformation mechanism in both lithospheric shear zones and asthenospheric flow and therefore strong upper mantle seismic anisotropy can not be attributed solely to the dominance of dislocation creep

experimental intracrystalline plastic flow in hot pressed synthetic quartzite prepared from brazilian quartz crystals samples of synthetic ultrafine grained quartzite were prepared by hot pressing aggregates of crushed clear brazilian quartz of mean grain size 0 4 m at 300 mpa and 1373 and 1473 k the samples displayed rapid grain growth to ca 12 20 m with 2 porosity at 1473 k facilitated by the 0 6 wt of water adsorbed onto the grain boundaries during sample preparation this water could be driven off by preheating thereby preventing grain growth sufficient water was incorporated during growth into the coarsened samples to render them weak and ductile these were deformed experimentally in the quartz field using an argon gas medium apparatus at 300 mpa confining pressure at temperatures mainly between t 1273 and 1473 k ductile flow was described by the flow law 10 4 9 3 2 9 7 f h 2 o exp 242000 rt with stress a in mpa and grain size d in microns and strain rate in s 1 r is the gas constant and f h 2 o is water fugacity based on observation of grain flattening optical strain features shapes and densities of dislocation arrays and flow law parameters samples deformed dominantly by dislocation creep with some contribution from grain boundary sliding bearing in mind possible changes in the flow law parameters over the extrapolation interval and possible effects of the phase transition extrapolation to natural strain rates and temperatures predicts plastic flow at higher flow stresses at the same water fugacity at greenschist facies temperatures than previously published flow laws

dynamic recrystallization of quartz correlation between natural and experimental conditions quartz veins in the eastern tonale mylonite zone italian alps were deformed in strike slip shear due to the synkinematic emplacement of the adamello pluton a temperature gradient between 280 c and 700 c was effected across this fault zone the resulting dynamic recrystallization microstructures are characteristic of bulging recrystallization subgrain rotation recrystallization and grain boundary migration recrystallization the transitions in recrystallization mechanisms are marked by discrete changes of grain size dependence on temperature differential stresses are calculated from the recrystallized grain size data using paleopiezometric relationships deformation temperatures are obtained from metamorphic reactions in the deformed host rock flow stresses and deformation temperatures are used to determine the strain rate of the tonale mylonites through integration with several published flow laws yielding an average rate of approximately 10 14s 1 to 10 12s 1 the deformation conditions of the natural fault rocks are compared and correlated with three experimental dislocation creep regimes of quartz of hirth tullis linking the microstructures of the naturally and experimentally deformed quartz rocks a recrystallization mechanism map is presented this map permits the derivation of temperature and strain rate for mylonitic fault rocks once the recrystallization mechanism is known

dislocation creep regimes in quartz aggregates abstract using optical and tem microscopy we have determined that three regimes of dislocation creep occur in experimentally deformed quartz aggregates depending on the relative rates of grain boundary migration dislocation climb and dislocation production within each regime a distinctive microstructure is produced due primarily to the operation of different mechanisms of dynamic recrystallization at lower temperatures and faster strain rates the rate of dislocation production is too great for diffusion controlled dislocation climb to be an effective recovery mechanism in this regime recovery is accommodated by strain induced grain boundary migration recrystallization with an increase in temperature or decrease in strain rate the rate of dislocation climb becomes sufficiently rapid to accommodate recovery in this regime dynamic recrystallization occurs by progressive subgrain rotation with a further increase in temperature or decrease in strain rate dislocation climb remains sufficiently rapid to accommodate recovery however in this regime grain boundary migration is rapid thus recrystallization occurs by both grain boundary migration and progressive subgrain rotation the identification of the three regimes of dislocation creep may have important implications for the determination of flow law parameters and the calibration of recrystallized grain size piezometers in addition the identification of a particular dislocation creep regime could be useful in helping to constrain the conditions at which a given natural deformation has occurred