the timing and environment of tepee formation in a marinoan cap carbonate thin carbonate units capping marinoan age glacial diamictites contain atypical tepee like structures that have been interpreted as evidence of seafloor dolomite cementation at parachilna gorge in the adelaide fold thrust belt a marinoan age cap dolomite contains paired tepee and growth fault structures that demonstrate the tepees grew 3 5 7 1 m below the sediment water interface in the early diagenetic zone although generally much larger such tepees and their associated sheet veins have an external morphology and internal structure identical to that of inter tidal tepee structures formed through expansive crystallisation on the other hand cap carbonate hosted tepees lack the size chaotic internal bedding carbonate crust and concretionary morphologies and expected carbon isotope geochemistry to be cold seep structures expansive crystallisation during early diagenesis seems the most likely means of forming tepees in cap carbonates the only cement common to all cap carbonate tepees is microcrystalline dolomite the crystallisation of this mineral phase drove both tepee growth and the fluid overpressure fracturing that formed the sheet veins the same microcrystalline dolomite is the component of cap carbonates routinely selected for isotopic analysis with the resulting 13c values assumed to be representative of coeval marine bicarbonate however the parachilna gorge tepees suggest that the microcrystalline dolomite contains both primary and early diagenetic components their separation is not achieved by current analytical methods

a high resolution micromorphological record of changing landscapes and climates on the western loess plateau of china during oxygen isotope stage 5 abstract the micromorphological characteristics of a continuous set of block samples from 24 38 m depth in a well section on jiuzhoutai mountain lanzhou china are described the shape of the magnetic susceptibility curve together with previously published radiocarbon luminescence and geomagnetic dates indicates that this sample set encompasses the whole of the last interglacial s1 palaeosol complex and extends into the overlying and underlying loess l1 and l2 units seven pedosedimentary units are recognised on the basis of trends in the bulk properties and the key micromorphological indicators excrements textural concentrations shell fragments and calcite and gypsum features high rates of loess deposition with significant cryogenic activity gypsum precipitation and only weak bioturbation characterised oxygen isotope stage ois 6 and ois 4 at lanzhou depositional rates were moderately high in ois 5d and 5b with slightly higher bioturbation and no significant cryogenesis or gypsum precipitation ois 5e 5c and 5a were marked by low rates of accretion more extensive bioturbation and limited leaching this reconstruction reflects the pedosedimentary responses to fluctuating dominances of monsoonal controls during this period of global climatic change comparison of earlier micromorphological results from sites to west and east of lanzhou along a dry to humid climatic gradient indicate a clear regional pattern with reduced loess accumulation rates and enhanced bioturbation and leaching in the humid east tianshui and xian clay translocation occurred only in ois 5e at xian the warmest and most humid site on the transect

structures caused by repeated freezing and thawing in various loamy sediments a comparison of active fossil and experimental data in this paper the authors present the results of both macroscopic and microscopic investigations on structure development created by repeated ice lensing in various loamy experiments experimental data are compared with observations performed on active forms in high arctic and alpine mountain environments those observations are also compared with phenomena observed in fossil periglacial formations of western europe platy and short prismatic structure formation is bonded to the hydraulic and thermal conditions during ice segregation when a long series of alternating freezing and thawing affects platy structures the fabric evolves also being influenced by slope and drainage conditions cryoturbations frostcreep and gelifluction can appear they are characterized by specific microfabrics which are better developed with an increasing number of cycles this is clear in experiments where hydraulic and thermal parameters are better controlled vesicles are also a prominent characteristic of the surface horizon in experiments and arctic soils the genesis of vesicles is discussed on the basis of new observations and is related to the mechanical collapse of frost created aggregates under the mechanical work of soil air escape during soil saturation by water at thaw

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

early diagenesis in differing depositional environments the response of transition metals in pore water the cycling of fe mn ni co cu cr v and mo during early diagenesis was investigated in sediments from five different depositional environments in the california borderland dissolved o2 no3 no2 and so4 were also measured at each site to establish the position of redox boundaries pertinent to this study sites were chosen to allow the comparison of several parameters of potential importance to the cycling of these metals bottom water o2 concentration sediment redox conditions cycling of metal oxide carrier phases and the relative contribution of biogenic and terrigenous material to the detrital metal flux at 10 m oxygen and above the sequence of terminal electron acceptor utilization was typical of pelagic sediments differing only in scale under these conditions the recycling of mn oxides resulted in an enriched layer near the interface at bottom water 02 concentrations 5 m mn oxides are not recycled under these conditions fe oxides and so42 are important oxidants the depth of the zone of manganese oxidation with respect to the interface affects the efficiency of metal scavenging by manganese oxides trapping and recycling of ni and co with mn oxides results in remobilization from reducing sediments and enrichment in oxic sediments scavenging of these metals is favored by a deep oxic zone in the sediments in contrast cr v and mo appear to be transported to the sediments as reduced species and are released from the sediments by oxidation the source of the reduced species is assumed to be biogenic material the accumulation of these metals is favored by reducing conditions in the sediments cu is enriched in the sediments by transport with detrital biogenic material followed by adsorption onto sediment solids cu is released at the interface and rapidly removed onto the solids at all sites except the one pelagic site at the base of the slope the magnitude of cu released in the slowly accumulating pelagic sediment exceeds the cu binding capacity of the solids resulting in pore water cu concentrations in excess of 100 nm in general metal cycling associated with the early diagenesis of sediments was observed to decouple transport processes from burial processes for the transition metals measured in this study

structure and dynamics of the arizona monsoon boundary abstract the arizona monsoon boundary is defined as the boundary separating two distinctly different air masses over mexico and the adjacent pacific during the summer the structure and dynamics of this boundary are examined by cross sectional analysis using three different data sources 1 a composite cross section through the boundary constructed from the fleet numerical oceanography center fnoc analysis 2 a time height cross section constructed using radiosonde observations at the time the boundary passed through tucson in 1984 and 3 a cross section through the boundary on 22 july 1985 using high resolution fields of temperature moisture and geopotential height obtained from the vissr atmospheric sounder vas all draw cross sections showed similar structure in some respects the arizona monsoon boundary resembles a midlatitude front i e there is a distinct and relatively sharp air mass change forced almost entirely by confluence a direct ageostrophic circulation is produced by this f

micro scale biogeochemical heterogeneity in sediments a review of available technology and observed evidence the hypothesis that reducing conditions exist in localized zones of high organic matter termed microniches was first suggested over a century ago but only relatively recently have high resolution techniques been available to investigate them in any sediment containing benthic fauna bioturbation affects the distribution of a number of redox sensitive components direct faecal deposition and the death of fauna may be expected to cause particles of labile organic matter microniches to be distributed heterogeneously within the sediment this review discusses the significance and future direction of microniche studies by considering exclusively data obtained on a sub mm scale that provide significant evidence for the existence and properties of microniches microelectrodes and planar optodes have shown the significant effect of burrowing organisms on localized o2 distributions and revealed distinct depletions in o2 due to microniches localized increases in pco2 and decreases in ph measured by optodes were attributed to elevated activity at microniches diffusive gradients in thin films have shown isolated supersaturation of metals and sulphide providing evidence for possible simultaneous oxidation of organic matter by sulphate and iron oxides the stochastic nature of these data and the lack of information for the same precise location hinders interpretation in terms of sediment diagenesis if microniches are known to account for a significant proportion of organic matter degradation re examination of the current understanding of sedimentary diagenesis may be needed further investigation on the distribution and frequency of microniches is required including a wider range of analytes in order to estimate their cumulative effect on element diagenesis immobilisation remobilisation processes and ultimately pollutant fate

complex climate induced changes in soil development as markers for the little ice age in the northern apennines italy abstract in the northern apennines the effects of the little ice age lia on the mountain landscape are poorly known a pedosedimentary sequence on the northern slope of mt cusna tuscan aemilian apennines and its geomorphological setting were investigated in order to assess the influence of the lia on the soils and the geomorphological processes the upper portion of the described sequence could be interpreted as colluvial deposits burying an old paleosurface the lia climatic effects acted on the sequence in two distinct phases in a first moment partial denudation of the surfaces allowed direct daily and seasonal freeze thaw cycles i e frost action to produce ice related relict microscopic pedofeatures in the soil horizons constituting the paleosurface and absent on modern surfaces afterwards a slope instability phase possibly caused by the change to wetter conditions promoted the widespread colluvial deposits which were later partially reworked by frost in solifluction lobes the triggering of these events seems to be influenced by the presence of pastoral communities too charcoals found on the paleosurface point to the use of fire events for clearance practices and possibly later pasture exploitation of the surfaces in this light the environmental history recorded by the mt cusna pedosedimentary sequence highlights how lia was fundamental in shaping the modern landscape of the n apennines and suggests a complex relationship between climate and human forcing on mountain environments

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

genesis of a texturally banded soil in southland new zealand abstract lamellae enriched with clay have been identified in profiles of the otama series during the course of field mapping in southland new zealand similar soils have been reported in a variety of landscapes from other parts of the world but explanations of their genesis differ considerably and do not fully account for the properties of the otama series macro and micromorphological analysis of this soil indicates a complex history in which the lamellae have formed by clay migration possibly under a seasonal freeze thaw environment as aeolian sediment was accumulating during the last glacial a cumulative mechanism of this kind may account for similar features in other aeolian landscapes limited bioturbation of lamellae occurred during the accumulation phase since establishment of a stable land surface during the holocene weathering gleying clay illuviation and bioturbation processes have been dominant with morphological features of present a and b horizons being superimposed on the uppermost lamellae and interlamellae

early holocene soil cryoturbation in northeastern usa implications for archaeological site formation abstract the study of buried soil archives in alluvial settings can be used to characterize floodplain and terrace habitats and complement other paleoenvironmental and archaeological archives this study examines the early holocene alluvial paleopedology along the delaware river valley in the northeastern usa chronological and alluvial stratigraphic data show that a widespread loam alluvial paleosol formed from 10 7 to 9 3 ka herein referred to as the jennings lane pedocomplex jlp the jlp at the jennings lane locality along the delaware river nj is a loam to silt loam soil that formed on mixed alluvium and windblown and or reworked dust likely sourced from nearby periglacial fines this finding supports previous interpretations of late quaternary dust deposition and reworking in the region fragic properties e g firm peds with brittle manner of failure and rapid slaking in water and cryogenic micromorphological features lenticular pores stone jacking and shattered grains present within the jlp suggest cryoturbation soil mass balance modeling suggests that the strain in immobile elements ti and zr show a dilation collapse profile these data indicate that organic matter and or dust addition and freeze thaw created soil dilation at the jlp paleosurface mass balance additions in fe k and mg are consistent with illuviated fe rich clay coatings present in thin section the x ray diffraction results show that these clays are illite vermiculite and kaolinite paleosol data presented here suggest that the jlp was overprinted by later pedogenic processes during the middle holocene ti na shows minimal loss throughout much of the profile although rapid thaws may have promoted downward translocation of fines the cold environment impeded base loss through either minimal release of cations from primary minerals or negligible water flux as suggested by ti na profiles and gains in ti k and ti mg this silt rich jlp pedofacies experienced minimal chemical depletion over the course of 1200 3500 years this cold climate weathering coincides with rapid temperature fluctuations 10 5 9 3 8 2 ka during the early holocene in northeastern usa this soil cryoturbation evidence has archaeological implications as well the cryoturbation in this early holocene pedocomplex suggests that vertical and lateral artifact redistribution is possible archaeologists should use caution when interpreting archaeological stratigraphy and intrasite artifact patterns at mid to high latitude archaeological sites

living in the cold geoarchaeology of sealing sites from byers peninsula livingston island antarctica few geoarchaeological studies have been conducted in the antarctic continent this paper contains the first results of the geoarchaeological research done in two sealing sites dated from the 19th century located in byers peninsula south shetland islands antarctica the research is part of a wider international project that aims at understanding the daily practices of the first anonymous occupants of antarctica and the insertion of the continent into the world system the geoarchaeological study focuses on site formation analyses to provide new data on site function use of local resources length of occupation and taphonomy with this approach data not attainable through artefact or documentary analyses is provided the studied sites are sealer 3 and sealer 4 two sealing shelters built with piled up boulders on rocky outcrops on the south beaches of livingston island two major precincts and annexes were studied by means of multi element chemical analyses micromorphology and organic petrology although local lithology and cryogenic processes are dominant in the chemical and micromorphological records respectively important distinctions could be made especially on the behavior associated with pyrotechnology and the use of local resources for survival the effects of humans on the sediments are expressed by higher p2o5 cao and total c concentrations this is related with the use of seal bones fat and herbaceous tissue as fuel for the hearths shelters with more intense occupation could be differentiated from single activity sites differences are attributed to habitation shelters vs working spaces for fat processing

soils as indicators of quaternary climatic change in mid latitude regions abstract soils result from changes to uppermost layers of the earth s crust occuring beneath stable land surfaces soil properties are determined by five factors or groups of factors climate organisms relief parent material and time quantitative climatic interpretation of soils depends upon mathematical relationships between individual soil properties and climatic factors i e climofunctions these are difficult to establish and often cannot be applied to diagenetically modified buried soils so most climatic interpretations of soils are qualitative or semi quantitative soil features formed by frost action are the most reliable climatic indicators most soils continue to develop over time however many soil dating techniques provide only a single date some time during the period of soil formation the beginning and end of a soil development period are best determined by reference to dated deposits over as large an area as possible but stratigraphical interpretation of soils is still impeded by imprecise definitions and procedures the soil chronosequences developed in the major loess deposits of europe and asia provide the best evidence for climatic change throughout the quaternary however only major glacial interglacial cycles are well expressed to obtain more detailed evidence of weaker interstadial cycles it is necessary to study chronosequences in mid latitude regions which were generally moister for much of the quaternary however these soils are less well preserved and present additional difficulties of interpretation because of greater variation in parent material relief and time as soil forming factors

calcite dissolution driven by benthic mineralization in the deep sea in situ measurements of ca 2 ph pco 2 and o 2 abstract in situ measured microprofiles of ca 2 pco 2 ph and o 2 were performed to quantify the caco 3 dissolution and organic matter mineralization in marine sediments in the eastern south atlantic a numerical model simulating the organic matter decay with oxygen was used to estimate the calcite dissolution rate from the oxygen microprofiles measured at four stations along a 1300 m isobath of the eastern african margin and one in front of the river niger at a water depth of 2200 m the diffusive oxygen uptake dou and oxygen penetration depth opd was calculated dou rates were in the range of 0 3 to 3 mmol m 2 d 1 and showed a decrease with increasing water depth corresponding to an increase in opd the calculated amount of degradated organic matter is in the range of 1 to 8 5 gc m 2 a 1 the metabolic co 2 released from mineralization of the organic matter drives calcite dissolution in these sediments overlain by calcite supersaturated water fluxes across the sediment water interface calculated from the in situ ca 2 microprofiles were 0 6 mmol m 2 d 1 for two stations at a water depth of 1300 m the ratio of calcite dissolution flux and organic c degradation is 0 53 and 0 97 respectively the microprofiles indicate that co 2 produced within the upper oxic sediment layer dissolves up to 85 of the calcite rain to the seafloor modeling our o 2 ph and ca 2 profiles from one station predicted a calcite dissolution rate constant for this calcite poor site of 1000 mol kgw 1 a 1 mol per kg water and year which equals 95 d 1 this rate constant is at the upper end of reported in situ values

climate and paleo environmental change within the mannheim formation near heidelberg upper rhine valley germany a case study based upon microsedimentological analyses abstract microsedimentological analyses were used to examine the first 56 m of a 500 m core near heidelberg germany in the upper rhine valley this core chronostratigraphically stretches from present day to 450 ka and includes proxy evidence supporting the presence of wurmian eemian and likely components of the riss and ho kirch stages the sediment in the core reflects the geomorphic biotic pedogenic and climatic processes the sediments were deposited in a fluvial environment at times within a broad floodplain in the main channel and also at other times some distance from the main river these upper sediments act as indirect proxy evidence that indicate changes in climate over time illustrative of cool periglacial tundra like conditions and of milder forested temperate environments from ho kirch to present day times within the sediments evidence can be found of an interglacial fossil soil followed later by a holocene temperate climate up to present day a strong link can be ascertained between macro and micro stratigraphic evidence the latter revealing detailed and invaluable sources of information this analysis permits the reconstruction of past climate and paleoenvironmental conditions the application of microsedimentological analyses to the mannheim formation reveals a store of data that has been largely hidden when using only macro sedimentological methods

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

microbiotic crusts in the high equatorial andes and their influence on paramo soils although microbiotic crusts are known from many lowland deserts they have apparently never been reported from alpine areas this paper describes microbiotic crusts from an equatorial high andean location paramo de piedras blancas in venezuela the main objectives are to describe the basic characteristics of the crusts to examine the properties of the soils on which they occur and to discuss their possible geomorphic significance for paramo soils properties of crusts and of the soils beneath them were compared with those of adjacent bare soils at three sites between 4360 and 4550 m altitude measurements on unconfined soil compressive strength and infiltration rates were taken in the field crust specimens were also gathered and later examined and sectioned under a microscope to ascertain micromorphological details laboratory data included soil texture organic matter content color ph water storage at field capacity and stability of soil aggregates crusts formed discontinuous garland like patches parallel to contours or covered small round soil buds produced by frost sorting microbiotic crusts contained many plants including an unclassified hepatic genus marsupella dumort a moss grimmia longirostris hook and several lichen species crusts consisted of a thin organic layer 5 35 mm overlying mineral soil and showed three parallel bands with diffuse boundaries the outer layer had green reddish brown live plant shoots and stems with few fine mineral grains the middle layer had anatomically recognizable dark brown plant material and a greater content of mineral grains the light colored basal layer had little organic matter mixed with coarse mineral particles it also contained many small orthovughs vesicles and some larger arched chambers caused mainly by frost activity soils with a microbiotic crust were darker than bare soils organic matter content in crust areas was two to three times higher than in adjacent bare soil ph dropped 0 3 units below crusts soils with crust had finer texture than bare ground the content of fines in crusts was 1 5 times higher than in bare soils but gravel in these was four times higher than below cryptogams indices of particle concentration showed that grains 0 5 1 mm were more abundant in crusts finer soils in crusts may result from a combination of a prior random texture variation b cryptogam colonization of fine soil patches sorted by frost c interception and capture of aeolian dust by cryptogams especially by mosses and d reduction of fine particle erosion by crusts as coarse grains are lost mean particle size within crusts drops geomorphic effects of crusts were also significant a infiltration rates were 70 greater in crust than in noncrust soils 67 0 vs 40 4 mm min b crust soils stored more water at field capacity 48 7 88 4 than bare areas 20 5 42 c crust soils had a higher resistance to raindrop erosion than bare areas 47 5 drops 0 1 g vs 10 2 drops 0 1 g undisturbed crust specimens were even more effective in resisting drop impact surviving up to 1100 drops 0 1 g d cryptogams increased soil compressibility more than 200 from 54 g cm2 in bare soils to 118 1 g cm2 in crust areas all these geomorphic changes should result in lower rates of soil erosion in paramo areas with dense crusts

on the dependence of sea surface roughness on wave development abstract the aerodynamic roughness of the sea surface z0 is investigated using data from lake ontario from the north sea near the dutch coast and from an exposed site in the atlantic ocean off the coast of nova scotia scaling z0 by rms wave height gives consistent results for all three datasets except where wave heights in the atlantic ocean are dominated by swell the normalized roughness depends strongly on wave age younger waves traveling slower than the wind are rougher than mature waves alternatively the roughness may be normalized using the friction velocity u of the wind stress again young waves are rougher than mature waves this contradicts some recent deductions in the literature but the contradiction arises from attempts to describe z0 in laboratory tanks and in the field with a single simple parameterization here it is demonstrated that laboratory waves are inappropriate for direct comparison with field data being much smoother than their field equivalents in the open ocea

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

niveo aeolian sedimentation of loess and sand an experimental and micromorphological approach the concept of a niveo aeolian influence on the genesis of northwest european pleistocene aeolian sand and loess deposits has been advocated in the past both to explain the presence and the absence of lamination field experiments were carried out on artificially deposited alternating layers of sand and snow and of loess and snow to investigate the role of a niveo aeolian mode of deposition on resulting sedimentary structures field observations of sand plots revealed minor changes in surface morphology typical of denivation surfaces the thin sections showed a characteristic porous structure deformations of the depositional structure and indications for erosion and redeposition were limited however the originally smooth aeolian sedimentary surface of the loess changed considerably the thin sections showed also a porous spongy structure indications were found for disturbances by frost action liquefaction during melting of the snow and ice and redeposition of loess by meltwater the experimental results strongly suggest that sand and loess deposited as niveo aeolian material are characterized both by a porous structure and that the original sedimentary structure of the sand is not affected by snowmelt whereas loess becomes non laminated thus the intercalation of snow during sedimentation of sand and loess does not in itself induce a laminated structure

wave driven porewater and solute circulation through rippled elastic sediment under highly transient forcing waves induce porewater flow and solute transport through permeable marine sediment however past studies have ignored high frequency pressure pulses under the assumption that the porewater flow field is adequately represented by a time averaged one or that the saturated sediment is incompressible we modeled porewater flow and solute transport inside ripples forced by instantaneous pressure profiles along the sediment water interface swi with 0 1 s temporal resolution the transient pressure profiles were taken from a field data driven large eddy simulation model of wave driven oscillatory flow the simulations suggest that in elastic permeable and saturated sediment a time averaged representation of the flow field may be inadequate and that this also leads to shortcomings in how transport is modeled bursts in fluid flushing occur when high frequency pressure fluctuations were considered leading to larger long term average fluid fluxes compared to a steady flow field driven by a time averaged pressure profile the pressure perturbations along the swi propagate within a few milliseconds to meter depths within the sediment leading to strongly transient porewater velocity fields this leads to enhanced dispersion of solutes and larger time averaged solute fluxes however enhanced solute flux across the swi diminished through time with increasing permeability the high frequency transient pressures and sediment elastic properties we considered have been largely ignored and unrecognized future observational and modeling studies should consider these processes especially since they mediate timing sensitive biogeochemical reactions

microbioirrigation of marine sediments in dysoxic environments implications for early sediment fabric formation and diagenetic processes it is manifest in the study of dysoxic sediments from the geological record that infaunal burrowing is considered so severely limited by the lack of dissolved oxygen as to be nonexistent although the effects of megafauna and macrofauna on sedimentary and geochemical processes are well known the effects of meiofauna are largely ignored here we document abundant meiofauna in the recent severely dysoxic laminated sediments from the santa barbara basin california margin and also microcavities and microtunnels in laminated deglacial sediments from palmer deep west antarctic peninsula that we interpret to be open relict nematode burrows santa barbara basin box core subcores were sieved to quantify metazoan abundance and others were embedded with resin for examination of meiofaunal life positions using confocal microscopy metazoan densities in the surface centimeters of sediment range from 80 7 to 117 9 cm 3 and nematode populations together with their abundant burrows remain quite high to at least 3 cm scanning electron microscope analysis of fractured surfaces in palmer deep sediments revealed that the rigid diatom ooze framework aids the preservation of 50 m diameter open nematode burrows these structures were observed to at least 40 m below the seafloor surface this is the first description of a nematode produced open burrow network preserved in the geological record optical microscopy of resin embedded thin sections revealed widespread sediment redistribution without significant lamina disruption the implications of abundant nematode burrows in surface sediments and their preservation in the geological record are wide ranging for both modern and ancient dysoxic marine environments including for determining early sediment fabric production geochemical processes and diagenetic reactions in the oxic and suboxic zones

mineral assemblages in theopetra greece a framework for understanding diagenesis in a prehistoric cave abstract prehistoric cave sediments are often subjected to severe mechanical and chemical alteration making it difficult to interpret aspects of their archaeology theopetra cave offers unique opportunities to resolve aspects of this problem particularly in relation to chemical changes because it has a relatively well defined stratigraphy and its older deposits have been subjected to unusually severe diagenesis a study of the mineralogy and micromorphology of the sediments and in particular the phosphatic minerals that formed in the sediments after deposition shows that each stratigraphic unit has its own pattern of authigenic mineral distribution in some units these patterns vary sequentially in both lateral and vertical directions these variations reflect changing degrees of diagenesis and the observed patterns imply that every unit obtained its diagenetic fingerprint fairly soon after burial the prominent ash layers in the older sediments were subjected to unusually severe diagenetic alteration such that most of the relatively stable siliceous components of ash decomposed into amorphous silica an intimate association between ash minerals and the k fe phosphate mineral leucophosphite was also observed the sequential changes in authigenic mineral assemblages in theopetra are basically similar to those observed in several caves in israel raising the possibility that common processes are involved and that information obtained from these detailed studies can be applied to other caves in diverse geographic regions

a coupled atmosphere wave ocean modeling system simulation of the intensity of an idealized tropical cyclone abstract a coupled atmosphere wave ocean modeling system cawoms based on the integration of atmosphere wave atmosphere ocean and wave current interaction processes is developed the component models consist of the weather research and forecasting wrf model the simulating waves nearshore swan model and the princeton ocean model pom the coupling between the model components is implemented by using the model coupling toolkit the cawoms takes into account various wave related effects including wave state and sea spray affected sea surface roughness sea spray heat fluxes and dissipative heating in atmosphere wave coupling it also considers oceanic effects such as the feedback of sea surface temperature sst cooling and the impact of sea surface current on wind stress in atmosphere ocean coupling in addition wave current interactions including radiation stress and wave induced bottom stress are also taken into account the cawoms is applied to the simulation of an idealized tropical cyclo

landscape instability at the end of mis 3 in western central europe evidence from a multi proxy study on a loess palaeosol sequence from the eastern lower rhine embayment germany abstract the lower rhine embayment hosts important loess palaeosol sequences lps within the western european loess belt yielding valuable information on landscape evolution and palaeoclimatic dynamics the study focusses on the palaeoenvironmental development based on a lps from the eastern shoulder of the lower rhine embayment dusseldorf grafenberg the palaeoenvironmental development within the study area is presented and discussed based on high resolution grain size analyses selected environmental magnetic parameters and geochemical analyses complemented by luminescence age estimates differences in grain size distribution gsd as well as the u ratio clearly reflect main stratigraphical units within the lps in addition the centered log ratio transformation of gsd gsd clr which is sensitive to post depositional grain size variations traces units of intensified soil formation despite no magnetic enhancement can be observed within the grafenberg lps environmental magnetic parameters combined with selected geochemical analyses sr rb provide direct information on the modification of silicates and magnetic minerals in the course of pedogenesis and diagenesis overall the grafenberg lps contributes to the understanding of environmental conditions within the lower rhine embayment particularly for the late mis 3 and the transition to mis 2 the lps reflects major shifts in the geomorphic system which are compared to palaeoenvironmental records from different archives and different geographic regions in north western europe indicating a direct relation to north atlantic climate oscillations during the last glacial period it is shown that the hesbaye unconformity at the mis 3 2 boundary is bound to an erosional event which can be traced over wide areas within the northern european loess belt

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

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

a regional climate model coupled to ocean waves synoptic to multimonthly simulations the ncar regional climate model regcm is coupled to the wam ocean model using the sea state dependent roughness parameterization derived in the hexos experiment coupled model simulations are shown to give reduced wind speeds u10 compared to uncoupled simulations this is in accord with other recent studies however the wave atmosphere coupling is effected through the friction velocity field u rather than through the wind field u10 thus because the coupling gives enhanced resistive friction u10 is weakened whereas u is enhanced wave heights driven by u are also increased in our coupled model simulations compared to uncoupled model simulations coupled model outputs are shown to compare favorably with air sea observations collected during the recent labrador sea deep convection experiment in 1997 both for synoptic storm timescales and for seasonal timescales

clues to the genesis of a discontinuously distributed fragipan in the northern apennines italy abstract at about 1000 m above sea level in the vallombrosa forest northern apennines central italy a dense pan that meets the diagnostic criteria for fragipans is discontinuously distributed the unusual slope parallel digitate distribution of the pan suggests that it could have formed on water saturated soil material that moved as earthflows actually several soils in the vallombrosa forest have buried or truncated horizons indicating episodes of mass movement and deposition however the fragipan under study shows a homogeneous morphology throughout hence not providing clues about the occurrence of episodes that have contributed to the emplacement of the parent material also the physical chemical and mineralogical analyses of the fragipan do not reveal discontinuities that help to resolve distinct episodes of deposition nevertheless discontinuities in features such as the degree of alteration of biotite grains and the amount of plasma seen through the micromorphological investigation at 50 60 cm of the current depth suggest the occurrence of at least two depositional events radiocarbon dating of large size pieces of charcoal collected at three depths within the fragipan yielded three ages that may reflect different times of accumulation of the parent material during the last glacial period post depositional micromorphological features such as relatively undamaged clay coatings and a weak platy structure indicate pedogenesis with the absence of intense pedoturbation

stone heave field experiment in clayey silt we recorded movements of 24 cm large globes and cuboids made of granite concrete and wood buried at three different depths in silty soil in a cool temperate environment during four and a half years we also monitored 4 hourly soil moisture and air and ground temperature all objects heaved during freezing and fell back during thawing and some sank during the summers freeze thaw in a very shallow surface layer may result in heave of objects due partly to sediment infill in unfrozen soils beneath the objects the net result was sinking of some of the granite and concrete objects and rise of wooden ones the recorded object movements in relation to the thermal properties and specific gravity of the objects and the embedding soil show that an almost isodiametric object tends to sink or remain in place if its thermal conductivity and density exceed those of the surrounding soil and to rise if the reverse is the case c 2009 elsevier b v all rights reserved

deformation of laminated silt loam due to repeated freezing and thawing cycles the effect of repeated freezing and thawing cycles on an experimentally produced laminated silt loam was studied with the purpose of obtaining more insight into the genesis of macro and microstructures observed in the loessic formations of northwestern europe the laminated silt loam was subsequently subjected to 18 cycles of alternate freezing and thawing the minimum temperature recorded after 11 days of frost was 7 c at a depth of 5 cm and 4 c at 29 cm the underlying sediments compact loam except its upper part and sand always remained unfrozen the experiment reproduced a seasonal superficially frozen ground new structures and microfabrics in the form of vesicles platy structures shear planes and micro undulations were created by ice segregation and thawing mechanical stress and subsequent frost creep the impact of the freezing and thawing cycles is very strong all the laminae being deformed or broken judging by the abundance and the diversity of the structures created freezing is a more important process than simple drying without frost as is evidenced by the range in temperature chosen for the experiment and the low number of cycles these structures do not necessarily require severe climatic conditions to develop unlike frost cracks or ice wedge casts they could develop in winter conditions similar to those present today in the french southern alps

an investigation of periglacial slope stability in relation to soil properties based on physical modelling in the geotechnical centrifuge results are presented from eight scaled centrifuge modelling experiments designed to investigate mass movement processes on thawing ice rich slopes four pairs of simple planar slope models were constructed one in each pair being of sufficient gradient to promote slope failure during soil thaw and the second having a gradient below the threshold for instability four frost susceptible soils were used three were normally consolidated and had different clay contents 2 12 and 20 and the fourth comprised the 20 clay soil but was over consolidated prior to model testing modelling protocols included freezing from the surface downwards under an open hydraulic system and thawing from the surface downwards under an enhanced gravitational field within the geotechnical centrifuge thereby utilising scaling laws to simulate correct prototype self weight stresses during thaw slopes below the stability threshold gradient were subjected to between 2 and 4 cycles of freezing and thawing simulating annual cycles those above the stability threshold were subjected to only one cycle since they failed during the first thaw phase thermal conditions pore water pressures surface movements and profiles of displacement are reported measured pore pressures are used in slope stability analyses based on a simple planar infinite slope model profiles of solifluction shear strain and mechanisms of slope failure are both shown to be sensitive to small changes in soil properties particularly clay content and stress history in all cases pore pressures rose rapidly immediately following thaw remained below the threshold for failure in low gradient models but exceeding the threshold to trigger landslides on steeper slopes upward seepage of melt water away from the thaw front contributed to loss of shear strength mechanisms of slope failure differed between test soils ranging from mudflow in non cohesive silt to active layer detachment sliding in over consolidated silt clay during solifluction shear strain was greatest at the surface in non cohesive silt and decreased rapidly with depth but in test soils containing clay the zone of maximum shear strain was located lower in the displacement profiles

pedosedimentary reconstruction of a thick loess paleosol sequence near lanzhou in north central china abstract a 38 m well section near lanzhou at the semiarid western margin of the loess plateau china contained a continuous high resolution loess paleosol sequence spanning the last 130 000 yr depth functions of micromorphological features magnetic susceptibility calcium carbonate organic carbon and median grain size provide the basis for pedosedimentary and associated paleoenvironmental reconstructions of three paleosol complexes s1 sm and s0 each pedosedimentary stage reflects the interaction of changing intensities of controlling monsoonal forces three periods of reduced dust inputs and enhanced pedogenic activity notably bioturbation and weak leaching can be identified from within the s1 pedocomplex these soil forming intervals were separated by phases of varying land surface instability characterized by arid dust deposition semiarid accretionary pedogenesis water reworking and crust formation or even freeze thaw modification the sm pedocomplex represents an interval of relatively rapid dust accumulation with only minimal syndepositional modification and minor pedogenic alteration at ephemeral land surfaces the s0 pedocomplex is clearly more pedogenically developed although erosion reworking and mixing by water have partly homogenized the property depth functions

two dimensional ph distributions and dynamics in bioturbated marine sediments the seafloor is the site of intense biogeochemical and mineral dissolution precipitation reactions which generate strong gradients in ph near the sediment overlying water interface these gradients are usually measured in one dimension vertically with depth two dimensional ph distributions in marine sediments were examined at high resolution 65 65 m pixel and analytical precision over areas of 150 to 225 cm2 using a newly developed ph planar fluorosensor dramatic three dimensional gradients complex heterogeneity and dynamic changes of ph occur in the surficial zone of deposits inhabited by macrofauna ph can vary by 2 units horizontally as well as vertically over millimeter scales ph minima zones often form in association with redoxclines within a few millimeters of inner burrow walls and become more pronounced with time if burrows remain stable and irrigated for extended periods microenvironmental ph minima also form locally around decaying biomass and relict burrow tracks and dissipate with time 5 d h concentrations and fluxes in sandy mud show complex acid base reaction distributions with net h fluxes around burrows up to 12 nmol cm 2 d 1 and maximum net reaction rates varying between 90 consumption to 120 production m d 1 90 nmol cm 1 d 1 burrow length acid producing zones that surround irrigated burrows are largely balanced by acid titration zones along inner burrow walls and outer radial boundaries the geometry and scaling of ph microenvironments are functions of diagenetic reaction rates and three dimensional transport patterns determined by sediment properties such as diffusive tortuosity and by benthic community characteristics such as the abundance mobility and size of infauna previously undocumented biogeochemical phenomena such as low ph regions associated with in filled relict biogenic structures and burrowing tracks are readily demonstrated by two dimensional and time dependent images of ph and sedimentary structure

sedimentary processes involved in mud brick degradation in temperate environments a micromorphological approach in an ethnoarchaeological context in northern greece sun dried mud bricks are a common building material across the globe found in many archaeological sites in the old world since ca 11 000 years ago this material is known to disintegrate due to exposure to the elements mostly affected by rain yet the geomorphic and sedimentological characteristics of this disintegration process have never been studied in detail until recently here we report on mud brick degradation processes observed in an abandoned mud brick village in northern greece we demonstrate that mud bricks have unique micromorphological characteristics that differentiate them from natural soils upon degradation some of these characteristics are lost e g planar voids after fibrous vegetal temper rain initiates brick degradation at the upper parts of walls where from brick material is washed down walls and deposited at their feet forming a conical talus the talus deposits show micromorphological features indicative of a variety of flows including wet and dry grain flows debris hyperconcentrated and water flows these flows seem to operate simultaneously across small distances these talus deposits are different micromorphologically from natural soils thus their characteristics can be used to identify degraded mud brick material in archaeological sites this in turn may help identify the location of long degraded mud brick walls in the absence of stone foundations and identify the relationship between house floors and degraded infill that accumulated on floors following wall degradation a comparison between the current observations with a previous study we conducted in an abandoned mud brick house in arid southern israel illustrates the generality of these low energy slope processes in mud brick degradation which emphasizes the worldwide applicability of the processes identified in this study

the significance of cryoturbation phenomena in environmental reconstruction cryoturbation results mainly from differential heave related to 1 drainage and thermal conditions and 2 frost susceptibility loadcasting and cryostatic pressures are restricted to wet soils such as pure silt or silty sand the translocation of fine particles resulting from repeated freezing and thawing can promote frost susceptibility in a previously non susceptible material as well as a loss in stability of the surface horizons liquefaction small and metric scale cryoturbations can be explained by this process large scale deformations and injections may be related to abnormal liquefaction not necessarily associated with frost regular patterns are associated with fissure nets upturned injections in a downslope direction attest to cryoturbation and frost creep a lowering of the water table promotes the formation of drop like cryoturbations most of which can be related to seasonal frost in imperfectly to poorly drained soils they are not indicative of permafrost except in well drained situations or in the case of flat bottomed involutions

phoenix soil physical properties investigation 1 the phoenix lander investigated the polygonal terrain and associated soil and icy soil deposits of a high northern latitude site on mars the soil physical properties component involved the analysis of force data determined from motor currents from the robotic arm ra s trenching activity using this information and images of the landing site soil cohesion and angle of internal friction were determined dump pile slopes were used to determine the angle of internal friction of the soil 38 5 additionally an excavation model that treated walls and edges of the scoop as retaining walls was used to calculate mean soil cohesions for several trenches in the phoenix landing site workspace these cohesions were found to be consistent with the stability of steep trench slopes cohesions varied from 0 2 0 4kpa to 1 2 1 8 kpa with the exception of a subsurface platy horizon unique to a shallow trough for which cohesion will have to be determined using other methods soil on polygon mounds had the greatest cohesion 1 2 1 8 kpa this was most likely due to the presence of adsorbed water or pore ice above the shallow icy soil surface further evidence for enhanced cohesion above the ice table includes lateral increase in excavation force by over 30 n as the ra approached ice

rates and processes of periglacial solifluction an experimental approach cold room physical modelling of periglacial solifluction processes on an experimental slope of 12 is described and data on soil temperatures surface frost heave thaw consolidation downslope soil movement and porewater pressures over seven freeze thaw cycles are presented these data are analyzed in the context of laboratory determination of the rheometry of the experimental soils at high moisture contents it is concluded that the observed thaw induced solifluction represents pre failure soil shear strain and results from loss of strength due to the combined effects of raised porewater pressures during thaw consolidation and upward seepage pressures as water flows towards the surface away from the thaw front an investigation of the rheometry of thawing soils offers the prospect of an analytical model to predict rates and depths of periglacial solifluction 1997 by john wiley sons ltd

a ph plate fluorosensor optode for early diagenetic studies of marine sediments pore water ph distributions are closely coupled to early diagenetic reactions and transport processes in surficial sediments in this study an optical plate fluorosensor for rapid two dimensional detection of h 1 concentration patterns in sediment pore waters was developed the dual excitation 405 450 nm single emission 520 nm ph fluorophore hpts 8 hydroxypyrene 1 3 6 trisulfonic acid trisodium salt was immobilized onto transparent supporting sensor foils excitation emission spectra of immobilized hpts exhibited ph dependent shifts in seawater standards and fluorescence excitation ratios were used for two wavelength ratiometric detection of ph distributions in sediment and bottom water close to the sediment water interface ph 6 5 to 8 5 sensor foils were fixed to the inner sides of plastic box corers or glass plate aquaria containing sediment and overlying seawater equilibration with pore water occurred in seconds and fluorescence response excitation emission was scanned nondestructively using a monochrome integrating ccd camera the two dimensional sensor system has a vertical and horizontal resolution of 56 3 54 m m 53 5 pixels applied over an image of 34 3 26 mm reproducibility and accuracy were best when foils were prepared from solutions of similar ionic strength to samples optical sensor ph distributions correlated well with high resolution vertical distributions measured simultaneously with a minicombination ph electrode and two dimensional ph patterns demonstrated directly the transport reaction heterogeneity associated with microtopography and biogenic structures in surface deposits and overlying waters close to the sediment water interface sensor foils retained calibration characteristics for at least 50 d

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

diffusivity in surficial sediments and benthic mats determined by use of a combined n2o o2 microsensor abstract diffusional characteristics of two biologically active surface sediments were determined by use of a combined n2o o2 microsensor by analyzing changes in the n2o gradients in these sediments it was possible to determine the product ds for this species with submillimetre depth resolution where is the porosity and ds the substrate diffusion coefficient the ds value for o2 could be calculated then from ds value for n2o because the diffusivity of the two molecules were modified in the same way within the sediment both sediments exhibited fine scale horizontal and vertical variability in diffusion characteristics and this must be accounted for when analyzing microprofile data the average ds value for n2o at 20 c for an estuarine surface sediment was 0 93 10 5 cm2 s 1 at 0 4 mm depth while the value for the upper 2 mm of a stream sediment covered by a microbial mat was 1 42 10 5 cm2 s 1 biological inactivation and oxidation by exposure to an o2 atmosphere had no effect on the measured ds for the estuarine sediment however the value for the sediment covered by a microbial mat with dense populations of meiofauna decreased by 20 the method presented is ideal for measurements of diffusivity at a high spatial resolution in surficial sediments and densely packed microbial communities

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

sediment community oxygen consumption in the deep gulf of mexico sediment community oxygen consumption scoc has been measured from the continental shelf out to the sigsbee abyssal plain in the ne gulf of mexico gom scoc rates on the continental shelf were an order of magnitude higher than those on the adjacent continental slope 450 2750 m depth and two orders of magnitude higher than those on the abyssal plain at depths of 3 4 3 65 km oxygen penetration depth into the sediment was inversely correlated with scoc measured within incubation chambers but rates of scoc calculated from either the gradient of the o2 profiles or the total oxygen penetration depth were generally lower than those derived from chamber incubations scoc rates seaward of the continental shelf were lower than at equivalent depths on most continental margins where similar studies have been conducted and this is presumed to be related to the relatively low rates of pelagic production in the gom the scoc however was considerably higher than the input of organic detritus from the surface water plankton estimated from surface water pigment concentrations suggesting that a significant fraction of the organic matter nourishing the deep gom biota is imported laterally down slope from the continental margin

micromorphology of loess paleosol sequences a record of paleoenvironmental change abstract the record of paleoenvironmental change retained within thin sections from loess paleosol sequences is discussed with reference to case studies from western europe china and northwestern usa the paleoenvironmental significance of individual micromorphological features such as calcitic concentrations clay coatings and cryogenic structures are first evaluated and the value of recognising and interpreting microstratigraphic relationships of features in terms of paleoenvironmental change is illustrated recent developments have seen a greater emphasis on using micromorphology within a pedosedimentary approach whereby both pedogenic and sedimentary processes are taken into account when interpreting loess paleosol sequences this has led not only to the acquisition of important information on conditions during phases of enhanced loess accretion and periods of climatic transition but also to an increased awareness of spatial changes in processes and environmental controls during particular time periods micromorphologically based reconstructions have enabled the isolation of key stages of pedosedimentary development although absolute dating of stages is often limited by lack of age controls a novel approach aimed at addressing this limitation afforded by presence of datable tephra in microstratigraphic association with key micromorphological features is discussed

salt marsh pore water geochemistry does not correlate with microbial community structure spatial and temporal trends in pore water geochemistry and sediment microbial community structure are compared at three intertidal sites of a saltmarsh on sapelo island ga the sites include a heavily bioturbated unvegetated creek bank a levee with dense growth of spartina alterniflora and a more sparsely vegetated ponded marsh site the redox chemistry of the pore waters ranges from sulfide dominated at the ponded marsh site to suboxic at the creek bank site at the three sites the vertical redox stratification of the pore waters is more compressed in summer than in winter the trends in redox chemistry reflect opposing effects of sediment respiration and pore water irrigation intense and deep burrowing activity by fiddler crabs at the creek bank site results in the efficient oxidation of reduced byproducts of microbial metabolism and hence the persistence of suboxic conditions to depths of 50 cm below the sediment surface increased supply of labile organic substrates at the vegetated sites promotes microbial degradation processes leading to sharper redox gradients at the levee site this is partly offset by the higher density and deeper penetration of roots and macrofaunal burrows surprisingly the microbial community structure shows little correlation with the variable vertical redox zonation of the pore waters across the saltmarsh at the three sites the highest population densities of aerobic microorganisms iron plus manganese reducing bacteria and sulfate reducers coexist within the upper 10 cm of sediment the absence of a clear vertical separation of these microorganisms is ascribed to the high supply of labile organic matter and intense mixing of the topmost sediment via bioturbation

correlation between fragipans and permafrost with special reference to silty weichselian deposits in belgium and northern france abstract a comparison is made between the properties of permafrost and those of fragipans the permafrost characteristics are summarized from published data on active permafrost and from personal observations on fossil permafrost the study of the fragipans mainly concerns the silty sediments of weichselian age which occur in belgium and northern france the distribution and the physical macromorphological and micromorphological properties of fragipans can all satisfactorely be explained by the growth of segregated ice during permafrost aggradation particularly striking is the relationship of both permafrost and fragipans to drainage conditions the quantity of segregated ice is highest in moist or poorly drained soil and it is at such places that the best developed fragipans are observed certain arguments that can be stated against the hypothesis of fragipan genesis by permafrost are discussed 1 the development of a platy structure by freeze thaw or by wet dry cycles 2 the discontinuous distribution of the fragipan 3 the development of the fragipan by pedogenetic weathering and migration processes it is concluded that only the permafrost hypothesis can explain the complete set of properties of the fragipan

examination of the impact of a coupled atmospheric and ocean wave system part i atmospheric aspects abstract to take into account the change of surface roughness length induced by ocean waves a coupled atmospheric and ocean wave model system is developed a two way coupling is done between a mesoscale atmospheric model mc2 and an oceanic wave model a regional version of wam cycle 4 two different approaches based on the wave age of smith et al and the wave induced stress of janssen are used to compute a coupling parameter called the charnock parameter expressed as the nondimensional surface roughness length the coupling between the two models is accomplished by the use of this parameter which is a function of sea state instead of the constant value obtained from empirical studies using the well known charnock relation the coupled atmospheric and ocean wave system was applied to four intense storms in the western atlantic to examine the impact of the two way interaction using real midlatitude storm cases in part i the atmospheric forecasts resulting from this two way coupling are discusse

micromorphology of periglacial sediments from the tayara site qikirtaq island nunavik canada abstract soil micromorphology provides an excellent resource for investigating palaeoeskimo site formation processes in the low arctic periglacial environment in this study micromorphology was used to answer questions concerning the composition structure origin and depositional agencies of the tayara site active layer s sediments as well as to distinguish between natural geogenic biopedogenic and cultural anthropogenic processes five groups of microfeatures were documented these include 1 biopedological features soil organic matter accumulation mesofaunal and fungal activities 2 transport inherited features related to depositional processes solifluction and stream sedimentation 3 frost induced microstructures and cryogenic features such as major post depositional changes ice segregation particle rearrangement frost shattering cryoturbation 4 bone preservation in the active layer at the microscopic level and 5 anthropogenic features related to palaeoeskimo activities the sediments from the three archaeological levels i ia and ii appear to have been very little influenced by anthropogenic factors cultural processes are micromorphologically observed in level ii with some evidence of feeding bone presence burning wood charcoal heated bone and possibly trampling however the effects of natural processes on the sediments are more pronounced than anthropogenic ones

microelectrode studies of organic carbon degradation and calcite dissolution at a california continental rise site fine scale porewater profiles of resistivity o2 ph and pco2 were measured in situ with microelectrodes at a site on the california continental rise they are reported here with more traditional measurements of shipboard porewater no3 alkalinity and tco2 and sediment organic c and caco3 profiles a numerical model encompassing diffusion advection and multiple reaction terms is applied to these data to characterize organic carbon degradation and caco3 dissolution processes near the sediment water interface a benthic o2 flux of 58 mol cm 2 yr 1 over the top 1 mm sediment is estimated based on one measured sub mm depth scale o2 profile the numerical model indicates that this high o2 consumption rate is related to a very labile fraction of organic c which has a degradation rate constant of approximately 4 5 10 8 s 1 1 4 yr 1 and which is not mixed downward by biological mixing seasonality in the benthic o2 consumption rate of this site may be attributed to variations in the input rate of this highly labile organic c degradation rate constants of the bulk organic c by oxygen reduction and by nitrate reduction are estimated to be about the same 1 10 9 s 1 the organic c rain rate responsible for the bulk organic c is estimated to be 53 mol cm 2 yr 1 this estimate exceeds the average rain rate determined by sediment trap collections at this site saturation state profiles calculated from the in situ ph and pco2 data and from modelling the in situ o2 and ph data both indicate that the porewater is undersaturated with respect to calcite to a depth of at least 8 cm the dissolution rate constant of calcite in this caco3 poor station is determined to be 5 10 day 1 assuming the reaction order is 4 5 which is close to the minimum estimates for environments richer in calcite a uniform calcite dissolution rate constant therefore may be adequate for representing carbonate dissolution in global scale models of ocean chemistry

manganese uptake during calcite precipitation from seawater conditions leading to the formation of a pseudokutnahorite manganoan magnesian calcite overgrowths were precipitated from artificial seawater at 25 c on pure calcite seeds using a constant disequilibrium technique the composition of the overgrowths and more specifically their mn mg na and sr content was determined as a function of the precipitation rate and mn2 concentration in the parent solution x ray diffraction patterns indicate that the overgrowths produced were one phase multicomponent solid solutions and contained up to 40 mole mnco3 the amount of mn coprecipitated with calcite decreased with increasing precipitation rate thus overgrowths are not in exchange equilibrium with the solutions from which they precipitated a kinetic model is proposed which adequately describes the composition of the overgrowths in terms of the relative precipitation rate of an 8 10 mole magnesian calcite and a pseudokutnahorite from seawater the possible existence of a pseudokutnahorite in marine sediments and its implications are discussed the concentration of mg in the overgrowths decreased with increasing mnco3 content but their mg ca ratio remained nearly constant strontium and na incorporation was strongly dependent on the number of available nonlattices sites

submillimeter life positions of bacteria protists and metazoans in laminated sediments of the santa barbara basin to provide insights into the biogeochemistry of environments where steep chemical gradients place anaerobes microaerophiles and aerobes in close proximity it might be necessary to survey biotic distributions on scales that are not possible using conventional ecological approaches to overcome such limitations we adapted sedimentological and cell biological methods to examine the life positions of microbes within sediments this fluorescently labeled embedded core flec technique was used to survey the submillimeter distributions of eukaryotic nanobiota and meiofauna plus co occurring prokaryotes inhabiting laminated sediments of the bathyal santa barbara basin sbb 34 13 n 120 02 w although sbb sediments were vertically structured on the scale of millimeters i e as laminae and microelectrode profiles suggested vertically distinct oxygenated and anoxic sulfidic layers the distributions of aerobes microaerophiles and sulfide tolerant anaerobes were not concomitantly structured unprecedented associations were observed among microorganisms for example relatively deep in the sediments where high sulfide concentrations were expected flagellates were intimately associated with beggiatoa ciliates were typically solitary whereas flagellates were often aggregated in nearly monomorphotypic swarms of 3 104 mm 3 such aggregations could significantly affect geochemical pore water processes at scales 1 l our observations indicate that a mosaic of chemically heterogeneous microhabitats exist in both vertical and horizontal dimensions suggesting that biogeochemical processes in the sbb are more complex than predictions based on standard biotic assessments and microelectrode profiling

the role of soluble fe iii in the cycling of iron and sulfur in coastal marine sediments in marine sediments fe iii is found predominantly as a solid recently however soluble species of fe3 complexed by natural organic ligands have been detected in coastal marine sediments with voltammetric microelectrodes the role of soluble fe3 complexes in diagenesis is unknown in anoxic conditions soluble fe3 can effectively oxidize fes2 and recycle iron and sulfur for use as terminal electron acceptors during natural organic matter nom degradation alternatively soluble fe3 complexes can catalyze the formation of fes and fes2 through the rapid chemical reduction of fe3 by dissolved sulfide to better understand the role of soluble fe3 in the transformation of iron and sulfur in marine sediments we incubated the first few centimeters of unvegetated salt marsh sediment in plug flow reactors microbial iron reduction seemed to prevail in suboxic conditions but sulfate reduction outcompeted microbial iron reduction in the presence of reactive organic metabolites the dominance of sulfate reduction led to the complete removal of reactive iron oxides by precipitation of fes experiments mimicking the enrichment of soluble fe3 complexes in reduced sediments show that soluble fe3 does not reoxidize fes and pyrite rather it promotes pyrite precipitation by enhancing sulfate reduction via complex bacterial interactions the rate of pyrite formation in the presence of soluble fe3 is much higher than previously reported in the literature suggesting that soluble fe3 might promote alternative pathways for microbial degradation of nom that ultimately results in the immobilization of fe and s as reduced iron sulfide minerals

a consistency index and rainwash mechanisms on belgian loamy soils the effects of soil crusting in belgium are particularly conspicuous on the loamy plateaus and hill regions of southern flanders brabant and hesbaye field observations made at the end of rainy winter seasons permitted the making of a simple distinction between a stable soils showing crusting on less than 50 per cent of their total surface without any evident slope wash and b unstable soils crusting over more than 50 per cent of the total surface with evident rainwash and basal colluviation the atterberg limits have been examined for both soil types it was found that the upslope part of the liquid limit curves in the range of low consistencies high water contents is steeper for stable than for unstable soils so a distinctive consistency index c2 10 was deduced from the liquid limit curves which may be used for prediction of the relative sensitivity of topsoils for crusting stable well structured clods are more hydrophobic than unstable material this was made clear by wettability tests under a rain simulator therefore more water must be added to remolded stable material to lower its consistency as is shown by the liquid limit curves crustability decreases and c5 10 values increase with increasing clay and organic matter contents as one would expect stable soils are well aggregated but rain simulator tests also showed that the detachment of this material by raindrop impact is high therefore crumbs and clods of stable soils are relatively more sensitive to splash erosion their erosion results from the ejection of stable aggregates clods of unstable topsoils are compacted and flattened by raindrop impact which causes internal liquefaction micromorphological analysis indicates that typical stable topsoils originate from well structured ap horizons and from bt horizons of grey brown podzolic soils alfisols laminated silt and mudcrust fragments characterize unstable topsoils which originate at least partly from slopewash deposits the external stability of both stable and unstable clods is increased by compaction and by surficial concentration of gravel coarse sands root and other plant fragments thin sections of unstable material show the internal collapse of structures due to liquefaction a clear distinction must be made between the structural stability and the erodability of topsoils

pedostratigraphy and chronology of the late pleistocene for the extra glacial area in the central russian upland reference section aleksandrov quarry abstract new results on stratigraphy and chronology obtained on the basis of osl and 14c dating of paleosols sediments and cryogenic deformations in the aleksandrov quarry situated at the central russian upland are discussed due to the location of the site in a paleodepression the section presents various stages of soil formation cryogenesis and sedimentation starting from the mikulino interglacial to the middle last glacial time the studied sequence is well preserved and one of the most detailed soil sedimentary terrestrial archives within eastern europe it reflects climatic variations comprising the timespan from the marine isotopic stage mis 5e to mis 3 at the base of the paleodepression the pedogenetic stages are extraordinary detailed distinct paleosols are alternating with erosion accumulative stages forming the ryshkovo pedolitocomplex during the mikulino interglacial during the early valdai time two interstadial paleosols were developed and the middle valdai section comprises two main interstadial paleosols as well in general interstadial paleosols of the late valdai time are absent in the studied quarry for the first time the chronological boundaries of the mis 5e interglacial are recorded and thus the duration of soil formation could be determined from 12 to 15 thousand years furthermore stages of periglacial conditions during the early middle and late valdai time were dated the obtained ages form the base for a chronostratigraphic framework which was correlated with those of the loess paleosol archives of eastern central and western europe

the micromorphology of unconsolidated sediments this paper aims to describe the use of thin sections micromorphology in the sedimentology of unconsolidated sediments it provides examples of the use of thin sections in a variety of sedimentary environments from fault gouge through caves and volcanics to aeolian fluviatile marine periglacial and glacial it demonstrates that in the latter three fields the use of micromorphology is relatively widespread and that in glacial sedimentology it has revolutionised our way of thinking about subglacial sediments although micromorphology has been mainly descriptive so far methods of quantification observations are demonstrated some of the important aspects of micromorphology are its use for microstratigraphy and the possibility of relating observations to documented processes thereby allowing a more robust sedimentological interpretation of modern and ancient sediments

structure and porosity of smectitic mudrocks as affected by experimental wetting drying cycles and freezing thawing cycles abstract the erosion rates in the vallcebre basin pyrenees are controlled predominantly by the physical weathering rate of bare regolith i e mudrocks to obtain information on the influence of thermic and moisture regimes on the weathering dynamics laboratory experiments were carried out to investigate how freezing thawing or wetting drying cycles under controlled conditions affect structure and porosity three different clayey mudrocks were selected to represent materials more susceptible to erosion in the studied area the three lithologies identified as ca1r ca2r carr differed mainly in mineral constituents type and quantity of the clay minerals and cation exchange capacity an automated non contact laser profile meter was used to analyse surface microtopography in order to monitor random roughness variations and to calculate bulk density porosity and pore size distribution were carried out with image analysis freezing thawing cycles were the most active in modifying soil surface and bulk structure roughness of ca1r and ca2r was more than doubled at the end of freezing thawing cycles this variation was mostly associated with the whole surface elevation related to the bulk volume increase roughness variations in carr were less pronounced and related to a modification of the microtopography micromorphological observations revealed a platy structure formation induced by repeated ice lensing also porosity was increased by freezing thawing cycles with the formation of a large number of irregular and rounded pores wetting drying cycles did not affect surface roughness and modified bulk density very little in all samples they increased porosity by the formation of large cracks and fissures overall data from wetting drying cycles showed that changes in water content alone did not produce deep structural modifications a mechanism of alteration of soil structure during freezing thawing cycles is proposed

examination of the impact of a coupled atmospheric and ocean wave system part ii ocean wave aspects a coupled atmospheric and ocean wave system has been developed to study the impact of changes of surface roughness length induced by ocean waves a two way coupling between a mesoscale atmospheric model mc2 and an oceanic wave model a regional version of wam cycle 4 was designed to ensure consistency in the treatment of the atmospheric boundary layer parameterizations between the two models two different approaches based on the wave age of smith et al and the wave induced stress of janssen are used to compute a coupling parameter called the charnock parameter expressed as the nondimensional surface roughness length the coupling between the two models is accomplished by the use of this parameter which is a function of sea state instead of the constant value obtained from empirical studies using the well known charnock relation the impacts on the atmospheric forecasts are discussed in part i in part ii the ocean wave forecasts resulting from this two way coupling are discussed for four different real cases the two approaches are evaluated by comparing ocean wave model outputs obtained from the coupled and uncoupled systems against buoy observations the coupling has some beneficial impact especially in areas of extreme sea states the significant wave heights are reduced in the coupled runs and generally show better agreement with the buoy observations the impact of the coupling also exhibits some dependence on the intensity of the cyclone development with larger changes occurring in the case of rapidly deepening storms

deformation induced microstructures in soils affected by mass movements the soil deformation produced by mass movements gives rise to specific microscopic features the study of some markers of deformation such as the orientation of rigid clasts and the morphology of fine grained intercalations indicates that in most cases mass movements can be related to simple shear the development of these features varies according mainly to the type of mass movement solifluction debris flow or earth slide different factors play a significant role in their formation intrinsic soil characteristics such as the grain size of the matrix water content and matrix element viscosity ratios and external factors such as the intensity and homogeneity of deformation a careful study of the microscopic features leads to a better understanding of the dynamics of mass deposits