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

an aerodynamic roughness length map derived from extended martian rock abundance data many boundary layer processes simulated within a mars general circulation model mgcm including the description of the processes controlling dust rising from the martian surface are highly sensitive to the aerodynamic roughness length z0 on the basis of rock size frequency distributions inferred from different martian landing sites and earth analog sites we have first established that lognormal modeled rock size frequency distributions are able to reproduce correctly the observed martian rock populations we have validated the hypothesis that the rock abundance of a given area could be estimated at a first order from its thermophysical properties namely its thermal inertia i and its albedo we have demonstrated the possibility of using rock abundance to estimate the roughness density on mars and to retrieve subsequently the aerodynamic roughness length by using semi empirical relationships based on terrestrial wind tunnel and field measurements by combining our methodology with remote sensing measurements of the thermal emission spectrometer aboard mars global surveyor we have derived a global map of the aeolian aerodynamic roughness length with a 1 8 1 8 resolution over the entire martian surface contrary to what is often assumed the martian aeolian aerodynamic roughness length is spatially highly heterogeneous at the fullest resolution the martian aerodynamic roughness length varies from 10 3 cm to 2 33 cm about 84 of the martian surface seems to be characterized by an aeolian aerodynamic roughness length value lower than 1 cm the spatially uniform value that most of the mgcms simulations have assumed recently since the aerodynamic roughness length z0 is a key parameter in deriving the erosion threshold wind velocities we anticipate a significant impact of our findings on the efficiencies for lifting dust in future mgcms

relationships of aeolian erosion and deposition with lidar derived landscape surface roughness following wildfire the reduction of vegetation by wildfire can subject stable soil surfaces to increased aeolian transport vegetation and associated microtopography function as surface roughness elements that influence the entrainment transport and deposition of sediment by wind in burned and unburned semiarid shrublands we examined whether surface roughness derived from lidar can explain variability in aeolian surface change following wildfire in loess soils of a cold desert shrub steppe in se idaho usa erosion bridges were installed in fall 2007 following a late summer wildfire to monitor soil surface change at sites in burned and downwind unburned areas surface elevation measurements were made when the erosion bridges were installed and again in fall 2008 surface change was determined from the difference in relative elevation between the two dates airborne lidar data were acquired in fall 2007 following erosion bridge installation surface roughness was calculated at 2 m raster resolution using the standard deviation of all lidar elevations within the 2 m cells after elevations were detrended to remove the effects of topographic slope surface change varied as a function of surface roughness among burned and unburned surfaces with net erosion occurring on the relatively smooth burned surfaces and net deposition occurring on the rough unburned surfaces site mean surface change decreased linearly as a function of the inverse of site mean surface roughness r2 0 77 p 0 00 quantile regression analysis indicated that changes in surface roughness were related to proportionally greater changes in erosion compared to deposition analysis of surface change at finer spatial scales suggested that aeolian processes occurred with strong spatial patterns on burned but not unburned surfaces future research to examine relationships between aeolian transport and fine spatial resolution topographic variability for example from ground based lidar systems is recommended

redox reactions and carbonate preservation in deep sea sediments abstract geochemical analyses of long sediment cores in turbidite sequences from two abyssal plains in the north atlantic have provided evidence for a relationship between post depositional oxic decay of organic matter and the dissolution of carbonates palaeo oxidation zones in the upper part of individual turbidites were initially identified by distinct colour changes in the sediments these zones were found to have distinctly lower amounts of organic carbon carbonate minerals and labile metals such as fe mn ni and zn as compared with the underlying unoxidized parts of the same turbidite it appears that the initial oxidation of organic matter by oxygen results in an undersaturation of the pore water with respect to carbonates while at the same time some metals are precipitated as easily reducible and soluble oxyhydroxides after burial under suboxic conditions the palaeo oxidation zones are subjected to mildly reducing pore waters that leach the oxyhydroxides resulting in a depletion in labile metal contents in the palaeo oxidized zones it is important that these characteristics be identified in the sedimentary record as the result of diagenetic processes and not as a reflection of primary production in palaeo oceans

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

metal accumulation rates in northwest atlantic pelagic sediments measurements of 230th 87sr86sr and twenty four metals were made on cores from the nares abyssal plain the sediment is characterized by slowly accumulating 0 3 0 7 g cm2 103 yr pelagic red clays and rapidly deposited grey clays transported by turbidity currents despite their colour differences and the enrichment of mn fe cu co ni zn v and to a lesser degree the rare earths in the red clays sr isotope evidence demonstrates that the clays have the same terrigenous origin the excesses of metals in the red clays have been attributed to metal removal from the water column and a comparison with the grey clays has enabled the authigenic fluxes of metals to be estimated the fluxes obtained are in the ranges 20 50 mol cm2 103 yr for mn and fe 0 1 0 4 mol cm2 103 yr for cu co ni zn v sr and ce 10 20 nmol cm2 103 yr for la and nd and 0 5 3 nmol cm2 103 yr for sm eu gd dy er and yb authigenic fluxes of y nb cr zr rb u and th were not resolvable fluxes appear to be near constant on the plain but comparison with other areas shows that they are quite variable both between and within ocean basins the chief factor controlling authigenic fluxes is the geochemical abundances of the elements but fractionation within both the transition element and rare earth series can be recognized from inter element comparisons and from differences in fluxes between atlantic and pacific red clays corresponding to the oceanic reactivities of the elements

the influence of dissolved fesi3o3 oh 08 on chemical equilibria in pore waters from deep sea sediments abstract pore water extracted from unconsolidated fine grained sediments from the southern sohm abyssal plain contain dissolved iron at concentrations greater than 100 m in glacial age sediments deeper than 2 0 m below the sea floor slightly reducing conditions pe and elevated dissolved sio 2 concentrations 300 m coincide with dissolved iron concentrations which are 2 to 4 orders of magnitude greater than would be predicted by conventional phase equilibria it is proposed that this fe exists in a fesi 3 o 3 oh 8 aq form and when its solubility is exceeded fe oh 3 or fesio 3 can be precipitated

early diagenetic processes in deep labrador sea sediments reactive and nonreactive iron and phosphorus a sequential extraction procedure was applied to separate the oxides and lithogenous phases of iron and manganese and the organic and inorganic phosphorus phases in four box cores and one piston core from the slopes and rises of the labrador sea sedimentation rate rather than the location in the basin appears as a master variable of the diagenetic transformations of fe mn and p high sedimentation rate characteristic of two of the box cores led to the creation of zones near the redox boundary of partial reprecipitation of dissolved fe mn and p released in the deeper reducing portions of the sediments in contrast surficial sediments from box cores with 10 times lower sedimentation rate only have sufficient reductive capacity to remobilize mn hydroxides while leaving the fe oxyhydroxides intact under these conditions there is evidence for a redistribution of reactive inorganic p leading to the crystallization of carbonate fluorapatite in the top 30 cm of the cores gradual transformation of bur

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

a case of post depositional aerobic degradation of terrestrial organic matter in turbidite deposits from the madeira abyssal plain abstract a set of oxidized and unoxidized sediment intervals from the f turbidite identified in two piston cores from the madeira abyssal plain map was analyzed for calcium carbonate total organic carbon toc total nitrogen tn stable carbon composition of toc 13c toc total hydrolyzable amino acids thaa total neutral sugars tsug lignin phenols lig two different lipid biomarkers of marine phytoplankton origin and vascular plantwax n alkanes and n acids comparison shows changes for all properties depicting the effect of post depositional aerobic oxidation the oxidation process re mineralized approximately 80 of the toc and approximately 60 of the tn in the original deposit and left the residual organic matter depleted in 13c by 1 7 2 9 thaa and tsug account for 10 or less of the toc in all samples leaving approximately 90 of the toc chemically unidentified thaa tsug lig marine phytoplankton biomarkers and plantwax n acids were lost from the oxidized deposit to an extent as great as that for toc two non protein amino acids alanine and aminobutyric acid and plant wax n alkanes displayed much less degradation 9 37 and concentrated 3 3 4 8 times relative to toc by the oxidation process these observations show that both marine and terrestrial components contribute to the re mineralized toc fraction a binary mixing approach was used to model quantitatively the change in 13c toc and plantwax n alkane concentration results suggest that terrestrial organic carbon contributes approximately 15 to the toc content of the original turbidite its abundance increases approximately 2 4 times as a consequence of the oxidation process and approximately 40 and 90 of the terrestrial and marine component of toc in the original turbidite respectively was destroyed by the oxidation process although selective preservation of terrestrial relative to marine organic carbon is a well documented phenomenon in sedimentary processes this study represents the first attempt to assess the sensitivity of terrestrial organic matter to oxidative degradation in a sedimentary environment

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

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

indication of a diagenetically induced precipitate of an fe si mineral in sediment from the nares abyssal plain western north atlantic abstract concentration depth profiles of dissolved iron and silica in the pore waters of turbiditic sediments from the nares abyssal plain all show a maximum at the sediment depth of 1 5 2 0 m this uncommon phenomenon is attributable to alternating layers of organic rich and organic poor sediment diffusion of dissolved reduced iron and dissolved silica results in precipitation of an amorphous fe si mineral possibly with a clay mineral structure as suggested by electronmicroscopic findings

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

simple spatially distributed models for predicting flood inundation a review abstract in this paper we review recent progress in the use of reduced complexity models for predicting floodplain inundation we review the theoretical basis for modelling floodplain flow with simplified hydraulic treatments based on a dimensional analysis of the one dimensional shallow water equations we then review how such schemes can be applied in practice and consider issues of space discretization time discretization and model parameterisation before going on to consider model assessment procedures we show that a key advantage of reduced complexity codes is that they force modellers to think about the minimum process representation necessary to predict particular quantities and act as a check on any tendency to reductionism at the same time however the use compared to standard hydraulic codes of strong simplifying assumptions requires us to also address the question how simple can a model be and still be physically realistic we show that by making explicit this debate about acceptable levels of abstraction reduced complexity codes allow progress to be made in addressing a number of long standing debates in hydraulics

quantifying relationships of burning roughness and potential dust emission with laser altimetry of soil surfaces at submeter scales abstract decrease in surface roughness by the reduction of vegetation is one mechanism by which fire can promote aeolian transport in a variety of landscapes the extent to which fire might alter the roughness of the soil surface at fine spatial scales and the effect of this alteration on post fire aeolian response is not well known we examined relationships in the field between dust emissions and subcentimeter level soil surface roughness at submeter spatial scales with a terrestrial laser scanner and portable wind tunnel analog based on aeolian theory we hypothesized that observed relationships would differ from those determined in previous studies with laser altimetry at landscape scales meter kilometer length scales we examined four semiarid shrublands in southern idaho usa containing a distinct pattern of undershrub and interspace microsites including recently burned and unburned conditions mixed models were used to determine effects of burning on surface roughness and the response of dust emissions to changes in surface roughness results indicated that burned soil surfaces were rougher than unburned soil surfaces dust emissions were enhanced by increases in roughness on burned soil surfaces and in the absence of nonerodible roughness elements i e plants this finding is expectedly in contrast to previous work that demonstrated an inverse relationship between soil erosion and surface roughness determined with lidar light detection and ranging at landscape scales vegetated and unvegetated surfaces relationships of lidar derived roughness and aeolian emissions are scale dependent and vary with environmental factors of fire and vegetation these findings are integral for future research that attempts to parameterize model based predictions of aeolian emissions with lidar derived roughness

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

two step deglaciation of the southeastern barents sea marine geologic evidence from the western barents sea shelf leaves little doubt that theareawascoveredbygroundediceduringthelastglaciation butthepatternandtiming of the subsequent deglaciation were not well determined here we reconstruct the timing and mechanism of ice sheet retreat as constrained by seismic stratigraphy and lithostratigraphy and accelerator mass spectrometer 14 c dating of foraminifera and mollusc shellsinsedimentboringsfromthesoutheasternbarentssea 1000kmfromthewestern shelf edge and former ice sheet margin the deposition of ice proximal glaciomarine sediments upon till began at or shortly before 12 7 ka indicating that the ice sheet retreat whichmostlikelycommencedalongthewesternmarginofthebarentsseashelfat15 14 5 ka reached the southeastern part of the shelf in 2 ka the subsequent accumulation of glaciomarinesedimentstookplaceintwodistinctpulses 12 7 12 1kaand 10 5 9 4ka separatedbyanintervalofnondepositionlasting 1 5ka thetwopulsesofsedimentation were coeval with periods of increasing surface water and air temperatures in the northern atlanticregionandacceleratedeustaticsea levelrise suggestingthattheremainingretreat of the barents shelf ice sheet was paced by these factors

trace metal remobilization in the interstitial waters of red clay and hemipelagic marine sediments interstitial water samples from the guatemala basin and the coast of baja california have been analyzed for manganese iron copper nickel and nitrate the data provide a systematic look at changes in trace metal diagenesis proceeding from red clay to highly reducing nearshore sediments in red clay sediments the nitrate concentrations suggest that only aerobic respiration is occurring manganese and iron are below detection nickel concentrations remain the same as in bottom seawater but copper shows a pronounced maximum just at the sediment water interface proceeding to hemipelagic sediments denitrification becomes increasingly important and manganese and iron remobilization occur in the sediments the linear manganese and nitrate profiles suggest regions of production or consumption separated by zones of diffusion this differs from the conventional picture of a continuous series of reactions within the sediments manganese reduction always occurs before iron reduction the pore water nickel correlates well with manganese in these sediments suggesting that nickel is associated with mno2 in the solid phase the pore water flux ratio of manganese and nickel agrees well with the ratio in solid phase authigenic oxides copper still displays a core top concentration maximum as well as a second maximum associated with the remobilized manganese the calculated ratio of the cu c flux ratios support the argument for copper remobilization during organic carbon oxidation comparison of the upward and downward diffusive fluxes with the rate of copper buried by sedimentation shows that at least half of the copper buried must be of diagenetic origin and less than 25 of the copper reaching the sediments is buried

early diagenetic processes in coastal marine sediments disturbed by a catastrophic sedimentation event abstract following a catastrophic flash flood in july 1996 as much as 50 cm of post glacial clays were deposited in less than 2 days in the upper reaches of the saguenay fjord quebec canada disrupting the normal sedimentation and diagenetic regimes we report detailed geochemical analyses of sediments porosity eh organic and inorganic carbon fe and mn reactive solid phases and acid volatile sulfide and porewaters salinity dissolved organic carbon doc fe ii mn ii nitrate ammonium and sulfate for seven stations located in the saguenay fjord three of these sag 05 sag 09 and sag 30 were visited in 1996 and once per year thereafter to document the chemical evolution of the sediment toward a new steady state the flood deposits contain less organic carbon and more inorganic carbon than the indigenous fjord sediments the flood deposit modified the distribution patterns of reactive mn and fe as a result of the reduction of mn and fe oxides delivered with the deposit and those concentrated at the now buried former sediment water interface most of the mn ii migrated to the new sediment water interface where a mn rich layer was formed in contrast much of the fe ii was precipitated as sulfides and remained trapped at or close to the old interface a nitrate peak developed in the porewater at the old sediment water interface possibly because of the oxidation of ammonia by mn oxides the distributions of porewater doc within the flood deposit correlate with the distributions of dissolved mn ii and fe ii suggesting that adsorbed doc was released when metal oxides were reduced

the effect of paleo oceanographic changes on the sedimentary recording of hydrothermal activity in the red sea during the last 30 000 years abstract the restricted exchange of water with the indian ocean makes the red sea extremely sensitive to global oceanographic changes such as sea level variations linked with quaternary climate change the 120 m global sea level lowering during the last glacial maximum caused great reduction in water exchange with the open ocean at that time salinities reached 50 and were beyond the tolerance of planktonic foraminifera some topographic depressions located on the red sea axial zone are the centre of hydrothermal activity they are filled with hot brines and contain metalliferous sediments we studied three sediment cores in the axial part of the red sea one from the metal rich suakin deep depression and two cores sampled outside any deep at two different depths the sediment of the core located in the anoxic brine filled suakin deep contained no benthic foraminifera indicating the deep was filled by a brine pool during the recovered period of marine isotopic stages 1 2 and 3 the distribution of benthic foraminifera in the two other cores indicates that red sea waters were saltier during stage 2 and 3 than today and that at 2000 m depth red sea waters were anoxic during stage 2 and dysoxic during stage 3 profiles of fe mn and zn indicate that the sedimentary flux of metals was higher during stage 1 than during stage 2 in hydrothermal brine filled deeps in contrast the sedimentary flux of metal in cores outside the anoxic depressions was higher during stage 2 the shape of the metal profiles can be attributed to hydrological changes that induced variations of redox conditions in water column during isotopic stage 1 2 and 3 during interglacial periods metals dissolved in anoxic brines precipitated at the redox boundary that corresponded to the brine seawater interface so that metals precipitated only in the deeps during glacial period the deep water was anoxic and the redox boundary was located above the brine seawater interface therefore the hydrothermal metals could diffuse into the anoxic deep red sea water and be precipitated over a large area this interpretation suggests that the observed variations of metal concentrations are not only related to fluctuations of the hydrothermal fluid discharge but also to the varying redox conditions in the deep red sea water

benthic recycling of biogenic debris in the eastern tropical atlantic ocean abstract distributions of pore water o2 no 2 no 3 nh 4 si oh 4 po3 4 mn2 f and t a were determined at 15 stations in the eastern equatorial atlantic while overall profile characteristics are consistent with previous models of organic matter diagenesis profile shapes suggest that a deep reaction layer rich in organic c is also present at many sites while it is unlikely that the oxidation of organic c in this layer has had a major effect on the ocean c cycle pore water profile shapes are significantly altered despite exposure to seawater so2 4 concentrations for 1000 years decomposition of the organic matter in the layer appears to be restricted to oxic and suboxic processes these results suggest major differences in organic carbon decomposition and preservation under oxic suboxic and anoxic conditions present day benthic fluxes are largest adjacent to the eastern boundary coastal upwelling region and similar in magnitude to values reported for the eastern pacific preliminary estimates suggest that the benthic respiration in the eastern 1 3 of the north atlantic south of 20 n may alone account for 20 of the total deep north atlantic respiration combining these results with estimates of organic c burial and deep water column decomposition suggests that this region is a major location of organic c input into the deep sea

airborne laser altimeter measurements of landscape topography abstract measurements of topography can provide a wealth of information on landscape properties for managing hydrologic and geologic systems and conserving natural and agricultural resources this article discusses the application of an airborne laser altimeter to measure topography and other landscape surface properties the airborne laser altimeter makes 4000 measurements per second with a vertical recording resolution of 5 cm data are collected digitally with a personal computer a video camera borehole sighted with the laser records an image for locating flight lines gps data are used to locate flight line positions on the landscape laser data were used to measure vegetation canopy topography height cover and distribution and to measure microtopography of the land surface and gullies with depths of 15 20 cm macrotopography of landscape profiles for segments up to 4 km were in agreement with available topographic maps but provided more detail larger gullies with and without vegetation and stream channel cross sections and their associated floodplains have also been measured and reported in other publications landscape segments for any length could be measured for either micro or macrotopography airborne laser altimeter measurements of landscape profiles can provide detailed information on landscape properties or specific needs that will allow better decisions on the design and location of structures i e roads pipe and power lines and for improving the management and conservation of natural and agricultural landscapes

simultaneous formation of iron rich layers at different redox boundaries in sediments of the amazon deep sea fan high resolution examinations of the solid phase have been performed on a gravity core that shows the typical amazon fan stratigraphy of the last 20 000 years the sedimentary record is characterized by two pronounced enrichments of solid phase fe the first fe peak from 0 34 to 0 37 m sediment depth consists of an indurated fe oxyhydroxide crust located close to the pleistocene holocene boundary this peak represents a widespread nonsteady state diagenetic feature on the fan the second fe peak is a pronounced enrichment of authigenic fe sulfides located between 6 15 and 6 45 m in the sediment the formation of this maximum is attributed to sulfate reduction that is mainly driven by anaerobic methane oxidation based on so42 pore water profiles and calculations of the time of formation of the fe sulfide enrichment we conclude that both fe rich layers formed more or less simultaneously the condition that caused both fe enrichments is a period of nonsteady state diagenesis induced by a pronounced decrease in sedimentation and organic carbon accumulation rates between the pleistocene and the holocene during this depositional change the redox boundaries and reaction fronts were fixed at particular sediment levels for a prolonged time thus producing higher concentrations of the authigenic minerals than possible under steady state diagenetic conditions

selective organic matter preservation in burn down turbidites on the madeira abyssal plain 1 oxidized intervals of five organic rich madeira abyssal plain map turbidites deposited during the miocene pliocene and pleistocene all displayed comparable major loss of total organic carbon toc 84 3 1 accompanied by a negative isotopic 13c shift ranging from 0 3 to 2 9 major but significantly lower loss of total nitrogen ntot 61 7 1 also occurred leading to a decrease in toc relative to ntot c ntot and a 1 3 to 2 7 ntot isotopic 15n shift compound specific isotopic measurements on plant wax n alkanes indicate the terrestrial organic component in the unoxidized deposits is 13c enriched owing to significant c4 contribution selective preservation of terrestrial relative to marine organic carbon could account for the 13c behavior of toc upon oxidation but only if a 13c depleted component of the bulk terrestrial signal is selectively preserved in the process although the c ntot decrease and positive 15n shift seems inconsistent with selective terrestrial organic preservation results from analysis of a modern eolian dust sample collected in the vicinity indicate these observations are compatible regardless of the specific explanation for these isotopic observations however our findings provide evidence that paleoreconstruction of properties such as pco2 using the 13c of toc is a goal fraught with uncertainty whether or not the marine sedimentary record considered is contaminated with significant terrestrial input nonetheless despite major and selective loss of both marine and terrestrial components as a consequence of postdepositional oxidation intensive organic geochemical proxies such as the alkenone unsaturation index u37k appear resistant to change and thereby retain their paleoceanographic promise

oxygen consumption rates in pelagic sediments from the central pacific first estimates from microelectrode profiles abstract oxygen profiles in pelagic sediments from the manganese nodule program calcareous and siliceous ooze sites manop sites c and s in the central pacific ocean were measured with microelectrodes and are used to predict oxygen consumption rates beneath the sediment water interface we explain possible artifacts which occur during sample recovery and argue that minimum estimates of 0 083 and 0 025 moles o 2 cm 2 day c and s respectively can be calculated from the data these oxygen consumption rates are in good agreement with in situ respirometer measurements previously reported for comparable sediments in the north pacific but previous estimates based on modeling of pore water nitrate profiles at both sites are two to five times smaller than our minimum fluxes the differences in oxygen fluxes calculated by the two methods are probably in part due to uncertainty in the assumptions inherent in the nitrate model however non steady state fluctuations in particulate organic matter fluxes could also be a reason for the disparity

non steady state diagenetic record in eastern equatorial atlantic sediments abstract the radiocarbon age profile of a sediment core from the eastern equatorial atlantic shows a marked decrease in both clay and carbonate accumulation rates at the end of the last glacial period with overall rates of 3 2 and 8 1 cm kyr for the holocene and late glacial respectively the transition from glacial to postglacial conditions recorded in the sediments at 39 cm is above the visual fe ii fe iii redox boundary at 48 cm which has been used in the past to identify the glacial section and even further above the increase in preserved organic carbon content at 55 cm it is concluded from the present organic carbon profile and recent observations in this area and elsewhere that organic diagenesis in these sediments is not steady state instead it is suggested that the uppermost glacial sediments lost carbon through oxic remineralisation at the change to postglacial conditions and that this process is now continued with nitrate as the electron acceptor these observations suggest that the double mno x solid phase peak which occurs in these and similar sediments is a direct consequence of an adjustment of the oxic layer depth following the decrease in carbon flux at the onset of the holocene

signature of non steady state diagenesis in continental shelf sediments the phenomenon of non steady state diagenesis is well recognized in open ocean sediments and occurs either due to the deposition of turbidites on pelagic sediments or to changes in ocean productivity however the occurrence of oxidized sediment below reducing sediments in many near shore and continental shelves indicates that non steady state diagenesis takes place even in shallow water regimes this paper shows that oxic conditions on the continental shelf result from low sedimentation rates induced by the rapid rise in sea level during the early holocene to the beginning of late holocene time whereas a comparatively high rate of sedimentation with increased burial of organic matter generating reducing conditions due to a relatively stable sea level during the late holocene is responsible for the initiation of non steady state diagenesis the lower oxidized sediments have not yet experienced a sufficient flux of reductants to mobilize base metals in contrast base metals in the upper reducing sediments have undergone mobilization and diffused out of the sedimentary column to the overlying water

effects of lidar derived spatially distributed vegetation roughness on two dimensional hydraulics in a gravel cobble river at flows of 0 2 to 20 times bankfull abstract the spatially distributed effects of riparian vegetation on fluvial hydrodynamics during low flows to large floods are poorly documented drawing on a lidar derived meter scale resolution raster of vegetation canopy height as well as an existing algorithm to spatially distribute stage dependent channel roughness this study developed a meter scale two dimensional hydrodynamic model of 28 3 km of a gravel cobble bed river corridor for flows ranging from 0 2 to 20 times bankfull discharge with and without spatially distributed vegetation roughness results were analyzed to gain insight into stage dependent and scale dependent effects of vegetation on velocities depths and flow patterns at the floodplain filling flow of 597 49 m 3 s adding spatially distributed vegetation roughness parameters caused 8 0 and 7 4 increases in wetted area and mean depth respectively while mean velocity decreased 17 5 vegetation has a strong channelization effect on the flow increasing the difference between mid channel and bank velocities it also diverted flow away from densely vegetated areas on the floodplain vegetation stands caused high velocity preferential flow paths that were otherwise unaccounted for in the unvegetated model runs for the river as a whole as discharge increases overall roughness increases as well contrary to popular conception

calcite dissolution accompanying early diagenesis in turbiditic deep ocean sediments abstract the oxidation of marine sedimentary organic carbon c org by o 2 diffusing from bottom water produces a characteristic linked loss of c org and caco 3 a theoretical treatment is presented based on carbonate system porewater equilibrium and redfield c org stoichiometry which predicts that the molar ratio of the two losses should be 1 1 08 this ratio differs significantly from literature values which ignore porewater equilibria calcium carbonate dissolution in well constrained profiles from vertically homogenous atlantic turbiditic sediments exceeds that predicted on the basis of this simple theoretical model indicating that additional processes must also contribute to caco 3 loss possible additional diagenetic processes involving fe 2 mn 2 s no 3 and nh 4 geochemistry are evaluated to account for this discrepancy it is demonstrated that after c org respiration oxidation of trace fes 2 is the process most likely to have produced the caco 3 loss observed in addition loss of alkalinity consequent upon the oxidation of nh 4 is shown to contribute significantly to caco 3 loss this nh 4 is supplied to the progressive oxidation front from below by diffusion from a much deeper zone of so 4 2 reduction and appears quantitatively capable of accounting for the remainder of the observed caco 3 loss at a site where a progressive oxidation front is active in a turbidite in order to investigate later diagenetic effects three buried turbidite units recovered by odp drilling were also studied units sampled in the depth range 130 230 mbsf age 3 7 my still retained clear evidence of the effects of similar fossil oxidation fronts in the solid phase c org and caco 3 profiles thus the rapid oxidation front process leaves a clear signature which can survive longer term anoxic c org remineralisation processes

beyond methane towards a theory for the paleocene eocene thermal maximum abstract extreme global warmth and an abrupt negative carbon isotope excursion during the paleocene eocene thermal maximum petm have been attributed to a massive release of methane hydrate from sediments on the continental slope 1 however the magnitude of the warming 5 to 6 c 2 3 and rise in the depth of the ccd 2 km 4 indicate that the size of the carbon addition was larger than can be accounted for by the methane hydrate hypothesis additional carbon sources associated with methane hydrate release e g pore water venting and turbidite oxidation are also insufficient we find that the oxidation of at least 5000 gt c of organic carbon is the most likely explanation for the observed geochemical and climatic changes during the petm for which there are several potential mechanisms production of thermogenic ch4 and co2 during contact metamorphism associated with the intrusion of a large igneous province into organic rich sediments 5 is capable of supplying large amounts of carbon but is inconsistent with the lack of extensive carbon loss in metamorphosed sediments as well as the abrupt onset and termination of carbon release during the petm a global conflagration of paleocene peatlands 6 highlights a large terrestrial carbon source but massive carbon release by fire seems unlikely as it would require that all peatlands burn at once and then for only 10 to 30 ky in addition this hypothesis requires an order of magnitude increase in the amount of carbon stored in peat the isolation of a large epicontinental seaway by tectonic uplift associated with volcanism or continental collision followed by desiccation and bacterial respiration of the aerated organic matter is another potential mechanism for the rapid release of large amounts of co2 in addition to the oxidation of the underlying marine sediments the desiccation of a major epicontinental seaway would remove a large source of moisture for the continental interior resulting in the desiccation and bacterial oxidation of adjacent terrestrial wetlands

acquisition of detrital magnetization in four turbidites turbiditic events are mostly avoided in paleomagnetic studies and therefore their remanence and magnetic properties are poorly described turbidites are exempt of bioturbation and potentially provide pertinent information about depositional remanence we studied four quaternary turbidites of different origins in marine sediment cores upward fining of both magnetic and sedimentary fractions indicates that coarser grains reached the bottom first we observe a progressive shallowing of the magnetic inclinations between the upper and bottom layers of the turbidites that increases with the size of the events and obeys a simple linear scaling law measurements of magnetic anisotropy suggest that hydrodynamic conditions prevailing during deposition seem to be dominant for the alignment of the magnetic grains we suggest that small spherical grains are randomly oriented with zero resultant magnetization in presence of strong turbulent conditions while the alignment of elongated grains is constrained by the competition between gravity and magnetic forces a possible scenario is that under turbulent conditions they tend to rest at the bottom with their long axes parallel to the sediment surface and therefore with shallow inclinations whereas weakly turbulent conditions like during the smallest 26 cm thick event do not disturb the magnetic alignment and therefore do not generate inclination shallowing this article is protected by copyright all rights reserved

roughness dependent geographical interpolation of surface wind speed averages modele bicouche de couche limite pour le calcul regional du climat en moyenne sur une saison du vent de surface a partir des donnees de station dans la couche de surface les mesures du vent sont corrigees objectivement pour une exposition imparfaite de la station a l aide de la rugosite deduite du facteur de rafale pour chaque secteur azimutal ceci fournit a 60 m une v du vent de messechelle u m representation de blocs d etendue 5 5 km 2 le moyennage regional de u m dans la couche d eleman est effectuee par des methodes geistrophiques de similitude analyse de toutes les donnees de vent relatives aux pays bas plats a l aide d une serie de 30 ans de l indice annuel de ventosite en vue de l ajustement temporel des series non simultanees ceci conduit a une cartographie objectivement interpolee pour les vents de surface augmentee des valeurs de distribution et de v extreme extension possible de la methode a un terrain complexe

observation and simulation of lake air heat and water transfer processes in a high altitude shallow lake on the tibetan plateau lakes are an important part of the landscape on the tibetan plateau most of the plateau lakes area has been expanding in recent years but lake atmosphere energy and water interaction is poorly understood because of a lack of observational data and adequate modeling systems based on the eddy covariance observation over a high altitude shallow and small lake the small nam co lake during an ice free period from 10 april to 30 august 2012 this study analyzes the lake air heat and water vapor turbulent transfer processes and evaluates two popular lake air exchange models a bulk aerodynamic transfer model b model and a multilayer model m model our main results are as follows 1 observations show that the bulk transfer coefficient ce and roughness length zoq for water are higher than those for heat ch and z0h especially under low wind speed 2 both models underestimate turbulent fluxes due to inaccurate values of the charnock coefficient and the roughness reynolds number rr which are both important parameters for calculating the roughness length for momentum z0m over water 3 within a reasonable range of 0 013 0 035 for rough flow and rr for smooth flow rr 0 11 are 0 031 and 0 54 respectively by our observation the wave pattern of shorter wavelength gives a larger z0m in the small and shallow lake and 4 the b model and the m model gave consistent results and both models are more suitable for simulation of turbulent flux exchange after z0m optimization

estimates of effective aerodynamic roughness length over mountainous areas of the tibetan plateau wind profile data were measured by a wind profiler at qoms the qomolangma station for atmospheric environmental observation and research chinese academy of sciences and in separate experiments gps radiosondes were used at shiquanhe station and litang station on the tibetan plateau tp all three stations are located in the most rugged areas of the tp qoms is surrounded by the himalaya shiquanhe station by the transhimalaya and litang station is near the hengduan mountains using observational wind profile data effective aerodynamic roughness length z0meff and zero plane displacement height d0 are determined using the neutral logarithmic wind profile law the results show that the values of z0meff derived from the wind profiles can be considerably larger than the small scale aerodynamic roughness lengths of the land surface around the three stations subsequently several parametrization schemes which use land surface characteristics to estimate z0meff and d0 such as roughness obstacle height and density were assessed the result indicates that of all the methods available that proposed by grant and mason where the drag coefficient d 0 5 gives the best estimate of z0meff the interim european centre for medium range weather forecasts ecmwf re analysis era interim dataset underestimates effective aerodynamic roughness length in mountainous areas of the tp due to its use of a smaller drag coefficient of d 0 4 for estimating d0 the method of kutzbach performs well when the density of roughness obstacles is low whereas the method of raupach et al gives a more reliable estimate when is high although this analysis has some limitations it can feasibly account for form drag being exerted by an unresolved topography in the mountainous areas of the tp

accumulation of contaminant metals in marine sediments of halifax harbour nova scotia environmental factors and historical trends abstract sediments in halifax harbour have accumulated contaminant metals hg cu zn and pb as a result of discharge of untreated sewage and industrial waste leaching of land fill waste and surface drainage concentrations of contaminants in210pb dated sediment cores became significant about 1880 and rose rapidly after 1900 reaching maximum concentrations in the decades between 1950 and 1980 mean concentrations of hg increased from 0 2 g g 1 in pre 1890 sediments to 1 6 g g 1 in the 20th century similar enrichments for cu changed the concentration from 26 to 88 g g 1 for zn from 90 to 250 g g 1 and for pb the increase was from 12 to 206 g g 1 statistical factor analyses of geochemical data have been used to identify 1 primary contaminants directly associated with waste discharge these include total and organic bound forms of cu zn and pb 2 secondary contamination attributed to leaching and modification of primary contaminants include acid labile forms of zn ni and cu 3 diagenetic modification of buried sediments are identified by total and labile forms of mn 4 dispersion of contaminants from land surface drainage are characterized by fine grained aluminosilicates historical trends in the changing dominance of these environmental factors reflect changes in industrial activity urban growth and changes in the use of metals in paints domestic and industrial chemicals and in the combustion of fuels

estimation of effective aerodynamic roughness of walnut gulch watershed with laser altimeter measurements a new method to estimate the effective aerodynamic roughness of a complex landscape is presented high resolution elevation profiles measured with an airborne laser altimeter have been used to compute geometrical parameters of three landscape elements of the walnut gulch experimental watershed arizona mean crop height its standard deviation and the frequency distribution as a function of penetration depth of plant elements hit by the laser beam have been calculated for short segments 1 m measured over intervening grass between shrubs longer segments have been applied to obtain the mean height and spacing of taller shrubs and trees finally laser profiles covering the entire watershed gave the mean amplitude and wavelength of hillocks and ridges the aerodynamic roughness length of the intervening grass is estimated using the ratio of standard deviation to vegetation height corrected for instrument noise times mean height an effective roughness length which parameterizes the total stress due to grass and taller shrubs and trees is calculated first finally a watershed scale effective roughness length is calculated combining the amplitude and wavelength of hillocks and ridges with the roughness length obtained in the previous step

predicting floodplain inundation raster based modelling versus the finite element approach we compare two approaches to modelling floodplain inundation a raster based approach which uses a relatively simple process representation with channel flows being resolved separately from the floodplain using either a kinematic or diffusive wave approximation and a finite element hydraulic model aiming to solve the full two dimensional shallow water equations a flood event on a short c 4 km reach of the upper river thames in the uk is simulated the models being validated against inundation extent as determined from satellite synthetic aperture radar sar imagery the unconstrained friction parameters are found through a calibration procedure where a measure of fit between predicted and observed shorelines is maximized the raster and finite element models offer similar levels of performance both classifying approximately 84 of the model domain correctly compared with 65 for a simple planar prediction of water surface elevation further discrimination between models is not possible given the errors in the validation data the simple raster based model is shown to have considerable advantages in terms of producing a straightforward calibration process and being robust with respect to channel specification copyright 2001 john wiley sons ltd

geochemistry of eastern mediterranean sediments primary sediment composition and diagenetic alterations abstract two cores recovered in the eastern mediterranean were analysed for major minor and trace elements the primary chemical composition of the sediment is different at each location probably because the lithological sources and the relative biogenic contributions differ carbonates are important for the concentration of ca mg and sr whereas aluminosilicates determine the concentration of si al k li y and be and to a lesser extent that of fe cr ti mg zn and zr in sapropels organic carbon and sulphur seem to be closely related bromine mo p fe v cu zn co ni and cr are closely associated with organic and sulphidic compounds the concentration versus depth profile for organic carbon in two sapropels points to a rapid establishment of conditions that gave rise to sapropel formation followed by a gradual transition back to normal conditions the primary composition is overprinted by diagenetic processes sulphate reducing conditions occurred during and just after sapropel deposition a progressive oxidation front mechanism which became active after sapropel deposition is responsible for additional major geochemical changes this diagenetic phenomenon has strong implications for the chemistry of fe mn ni co zn cu cr v u as and sb

selective preservation of soil organic matter in oxidized marine sediments madeira abyssal plain in ocean margin sediments both marine and terrestrial organic matter om are buried but the factors governing their relative preservation and degradation are not well understood in this study we analysed the degree of preservation of marine isoprenoidal and soil derived branched glycerol dialkyl glycerol tetraethers gdgts upon long term oxygen exposure in om rich turbidites from the madeira abyssal plain by analyzing gdgt concentrations across oxidation fronts relative to the anoxic part of the turbidites ca 7 20 of the soil derived branched gdgts were preserved in the oxidized part while only 0 2 3 of the marine isoprenoid gdgt crenarchaeol was preserved due to these different preservation factors the branched isoprenoid tetraether bit index a ratio between crenarchaeol and the major branched gdgts that is used as a tracer for soil derived organic matter substantially increases from 0 02 to 0 4 split flow thin cell splitt separation of turbidite sediments showed that the enhanced preservation of soil derived carbon was a general phenomenon across the fine particle size ranges 38 m calculations reveal that despite their relatively similar chemical structures degradation rates of crenarchaeol are 2 fold higher than those of soil derived branched gdgts suggesting preferential soil om preservation possibly due to matrix protection

fractal modeling of airborne laser altimetry data abstract airborne laser altimetry is a remote sensing technique that can provide high resolution data on the roughness of the landscape both for estimating water balance components and for distinguishing between landscapes models of the scale dependent roughness are needed to find scales most appropriate for these purposes our objectives were to apply fractal scaling to high resolution profiling laser altimetry data and to determine fractal parameters for differentiating land cover data were collected at the usda ars jornada experimental range in new mexico over grass dominated and shrub dominated sites along four transects at each site scale dependent root meansquare rms roughness and data power spectrums were computed from 100 000 data points 2 km from each transect a linearity measure and piecewise linear approximation were applied to find intervals of the fractal scaling the rms roughness data had two intervals of self affine fractal scaling on grass transects and four such intervals on shrub transects reduction in the number of data points did not lead to a decrease in roughness but caused a smoothing dependency of fractal dimension on scale ten and hundred meter scales were appropriate for distinguishing between grass and shrub transects on the basis of fractal dimensions

the geochemistry of manganese carbonate in panama basin sediments abstract the mn distribution in panama basin area sediments and interstitial waters is discussed striking surficial mn enrichments produced by a well known diagenetic recycling process characterize the sediments of the region thermodynamic solubility calculations indicate that in at least one core interstitial waters approach saturation with respect to mnco3 a mixed carbonate phase of composition mn48 ca47 mg5 co3 was recovered from an ash band in the same core the association of this material with the coarse volcaniclastic debris is thought to result from facile manganous carbonate precipitation in sediment horizons of coarser mean grain size since sulphate reduction in the upper two metres of panama basin sediments is fairly minor little increase in alkalinity is observed and it is postulated that significant production of carbonate alkalinity is not a prerequisite for manganous carbonate generation in hemipelagic sediments a more important factor appears to be the availability of mn oxides for solution during early diagenesis stable c isotopic analyses indicate that little c of organic origin is used in the precipitation reaction in either panama basin or loch fyne scotland sediments

floodplain friction parameterization in two dimensional river flood models using vegetation heights derived from airborne scanning laser altimetry two dimensional 2 d hydraulic models are currently at the forefront of research into river flood inundation prediction airborne scanning laser altimetry is an important new data source that can provide such models with spatially distributed floodplain topography together with vegetation heights for parameterization of model friction the paper investigates how vegetation height data can be used to realize the currently unexploited potential of 2 d flood models to specify a friction factor at each node of the finite element model mesh the only vegetation attribute required in the estimation of floodplain node friction factors is vegetation height different sets of flow resistance equations are used to model channel sediment short vegetation and tall and intermediate vegetation the scheme was tested in a modelling study of a flood event that occurred on the river severn uk in october 1998 a synthetic aperture radar image acquired during the flood provided an observed flood extent against which to validate the predicted extent the modelled flood extent using variable friction was found to agree with the observed extent almost everywhere within the model domain the variable friction model has the considerable advantage that it makes unnecessary the unphysical fitting of floodplain and channel friction factors required in the traditional approach to model calibration copyright 2003 john wiley sons ltd

redistribution and geochemical behaviour of redox sensitive elements around s1 the most recent eastern mediterranean sapropel the youngest eastern mediterranean sapropel s1 is generally believed to have formed 7 9 14c ky b p the distribution of redox sensitive elements above in and below the sharply defined organic rich unit reveal that s 1 has already suffered heavy diagenetic alteration its present thickness based on its dark colour is only a fraction of its original thickness in one core visual evidence of s1 with an inferred initial thickness of 6 cm has been destroyed and a similar thickness appears to have been lost from the tops of another two examples this is caused by oxidation of the upper reaches of s 1 by a progressive oxidation front which commenced 5 2 5 4 14c ky ago and still appears to be active in the three cores studied diagenetic relocation of many redox sensitive elements has occurred most elements expected to be enriched in sapropels or sulphide rich sediments already have maximum concentrations above or below rather than in the present s 1 layers similarities are observed in the geochemical behaviour of as fe and p of co cu mn ni and zn and of cd mo sb ti u and v the behaviour of ba is distinctive and its immobility as barite makes it an indicator for palaeoproductivity and the original high s1 corg content the elements se and i exhibit particularly large sharp concentration peaks and together are proposed as useful indicators of the present boundary between oxic and post oxic conditions

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

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

the diagenetic formation of metal rich layers in sapropel containing sediments in the eastern mediterranean two cores recovered from different locations in the eastern mediterranean contain intercalations of organic rich sapropels in organic poor hemipelagic sediments in both cores enrichments of mn and fe were found in the oxidised section of the sediment above the sapropel s1 the sediments followed a diagenetic cycle which began after the sapropel formation finished about 7000 years ago first during a non steady state diagenetic phase metal rich layers were formed at a downward moving oxidation front the front decelerated at the top of the sapropel as a consequence of increasing amounts of corg and sulphides that had to be oxidised during the second part of this non steady state phase the oxidation front starts moving upwards with respect to the sapropel manganese is remobilised in preference to iron due to thermodynamics reinforced by kinetics when the upward movement of the oxidation front becomes equal to the sedimentation rate steady state is established with respect to the new organic poor sedimentary circumstances at location 31g1 the system is at or close to steady state at location 9g1 however this steady state phase has never been reached between 1900 and 1350 years bp the organic carbon accumulation rate probably increased suddenly inducing a retreat of the oxidation front and the non steady state formation of double peaks

effects of turbidity flows on organic matter accumulation sulfate reduction and methane generation in deep sea sediments on the iberia abyssal plain non steady state sedimentation has affected preservation of organic matter in a pliocene pleistocene turbidite sequence sampled by the ocean drilling program at four closely spaced drill sites on the iberia abyssal plain organic carbon concentrations average ca 0 7 in sediments from sites 897 and 898 and ca 0 4 at sites 899 and 900 headspace concentrations of interstitial methane exceed 100 000 ppm in sediments from sites 897 and 898 but are essentially zero in those from sites 899 and 900 methane concentrations do not rise until interstitial sulfate concentrations are virtually depleted suggesting the presence of deep in situ methanogenic bacterial activity at sites 897 and 898 and its absence at sites 899 and 900 two factors associated with the turbidity flows that created the sedimentary sequence evidently influenced post depositional diagenesis at these sites the principal factor is that the rapidly deposited turbidite sequences at sites 897 and 898 protected organic matter from early oxic degradation and thereby permitted subsequent anoxic degradation to proceed in contrast organic matter in the more slowly deposited turbidites at sites 899 and 900 was oxidized soon after deposition and was therefore not available for later microbial utilization a lesser factor is that the turbidity flows may have obtained their entrained organic matter from different environments and consequently delivered organic matter with different characteristics both factors contributed to heterogeneity of the types and amounts of organic matter that accumulated in these deep sea sediments and this variability has influenced subsequent sulfate reduction and methanogenesis

internal structure of the wenchuan earthquake fault zone revealed by surface outcrop and wfsd 1 drilling core investigation abstract fault zones record a series of faulting events that have occurred under different physical conditions during their evolution therefore it is essential to understand the internal structures of fault zones in order to better understand the mechanical behavior of faults the internal structure of the wenchuan earthquake fault zone that prevailed at the bajiaomiao outcrop and in the wfsd 1drilling cores located along the southern segment of the yingxiu beichuan surface rupture in the hongkou area is described in details in this paper based on field surveys x ray diffraction analysis microstructure and analysis of the drilling cores an 240 m wide fault zone was confirmed as the yingxiu beichuan fault zone ybf at the bajiaomiao outcrop corresponding to the 100 m fault zone in the wfsd 1 drilling cores fault rocks including fault breccia fault gouge and cataclasite were identified in both the outcrop and drilling cores while pseudotachylyte was only present at the outcrop two different types of gouge veins formed by thermal pressurization and fluidization respectively are observed in this area the ybf possesses the characteristics of a multiple core model and consists of 5 different fault rock units from top to bottom these are cataclasite zone black fault gouge breccia zone gray fault breccia zone dark gray fault breccia zone and black fault gouge breccia zone outcrop investigation and drilling core research show that the slip zone of the wenchuan earthquake does not completely follow the ancient fault slip zone the wenchuan earthquake fault is a high angle thrust fault which crosses the ybf obliquely the multi layered fault rocks displayed in the research area might indicate that the ybf comes from the long term fault activity and evolution over the last 15 10 ma

geochemical evidence of pore water advection along a fault in plastic sediments from the southern nares abyssal plain western north atlantic abstract four small fractures in unconsolidated sediments were sampled at depths between 17 and 25 m below the sea floor in the southern nares abyssal plain all of the fractures occurred in oxidized brown clays but two fractures had pale brown halos around the slip plane these fractures appear to be associated with a compaction fault identified in seismic reflection profiles of the sediments in this area detailed analyses of fe mn cu zn and ni in the sediments around the fractures by a selective chemical leaching technique revealed that the sediments in the halo around one of the fractures had been chemically altered apparently by a reducing pore fluid this reduction decreased the labile oxidized metal content by 52 79 for the metals fe mn and cu it is proposed that this alteration took place as a result of upward advection of pore fluids along the fracture plane this process may have important significance in estimating the vertical flux of metals through deep sea sediments

early diagenesis of marine organic matter alteration of the carbon isotopic composition in two distal carbonate turbidites labelled a and e from the madeira abyssal plain oxidation of organic matter om has been accompanied by a reduction in hydrogen index hi and change in the isotopic composition of carbon since the emplacement of turbidite 0 5 ka ago 35 of the om in the upper part has been oxidised by oxygen and nitrate diffusing from sea water into the sediment there is an accompanying decrease of 0 3 in 13c om and a decrease of 25 in hi turbidite e was emplaced about 73 ka and was exposed to bottom water for 12 3 ka before being buried beneath later turbidites during exposure oxygen and nitrate diffused into its upper part and oxidised 50 of the toc without an accompanying change in isotopic composition further oxidation of the more refactory organic components decreased toc by a further 25 and decreased 13c by 2 5 oxidation also reduced hi by 50 from originally low values unless corrected for the isotopic changes accompanying extended oxic and suboxic degradation of organic matter in sediments will give rise to erroneous estimates of marine terrestrial om ratios