cirques in the sierra de guadarrama and7 somosierra mountains iberian central system shape size and controlling factors the guadarrama and somosierra mountain ranges form the eastern sector of the iberian central system and hosted numerous glaciers during the late pleistocene mis2 glaciation was of low intensity with glaciers of small sizes strongly controlled by the climatic context and the topography this study analyses the shape size distribution and location of 96 cirques existing in these mountain ranges in addition to the standard morphometric parameters and controlling factors altitude aspect and lithology used in most studies additional factors were considered here in relation to the pre glacial relief and fracture network the data were obtained and processed using arcgis 10 4 and relations between the parameters and controlling factors were evaluated using statistical methods the results indicate that most are simple cirques tending to isometry with low vertical incision capacity considerable variation in size and predominantly east facing in the context of the iberian peninsula and other european mountains these cirques are among the most isometric the lowest in height and present the least overdeepening the development of these cirques has generally been the result of random combination of various factors thus i the largest cirques are located at intermediate altitudes with the headwall located on the main divides at former torrential valley heads or at the headwalls of fracture corridor valleys and are north facing ii the longest cirques are located at former torrential valley heads on metamorphic bedrock i e schists slates and on uniform slopes finally the prevailing eastern aspects are explained by topoclimatic factors and are in agreement with previous studies which have proposed a circulation weather type cwt model throughout the iberian peninsula during the last glacial period similar to its current configuration

topography relief and trmm derived rainfall variations along the himalaya 1 along the southern himalayan topographic front the indian summer monsoon modulates erosive processes and rates to investigate the influence of topography and relief on rainfall generation and resultant erosion we processed satellite rainfall amounts for the last 8 years 1998 2005 from the tropical rainfall measurement mission trmm based upon a spatial resolution of 5 5 km for the himalaya we identify 1 the spatial distribution of rainfall and 2 the large scale relationships between topography relief and rainfall locations our results show two distinct rainfall maxima along strike in the himalaya the first outer rainfall peak occurs along the southern margin of the lesser himalaya within a narrow band of mean elevation 0 9 0 4 km and mean relief 1 2 0 2 km the second discontinuous inner band typically occurs along the southern flank of the greater himalaya elevation and relief both 2 1 0 3 km

influence of cohesion on river bed scour in the wake region of piers abstractstudies on scour in the wake region of piers in cohesive sediments containing gravel were not reported in literature to the best of our knowledge results from the laboratory experiments based study on the process of wake scour are presented here the sediment used for the experiment were of two types 1 fine gravel mixed with clay in proportions varying from 20 to 60 by weight and 2 fine gravel and fine sand in equal proportion by weight mixed with clay in proportions varying from 20 to 60 by weight the experiments revealed that the process of scour as well as depth shape and geometry of scour hole developed in such cohesive sediment were significantly different from that of cohesionless sediments proportion of clay fraction and unconfined compressive strength of cohesive sediment mixture were found to be the most significant variables controlling the depth of scour in the wake of piers on the basis of dimensional considerations relationships have been proposed for the estimation

silicate versus carbonate weathering in the himalaya a comparison of the arun and seti river watersheds abstract we studied the water chemistry of two large and geologically differing himalayan watersheds in order to maximize the contrast between silicate versus carbonate weathering effects on river chemistry our previous research involved the seti river of westernmost nepal geologically typical of many rivers in nepal in draining mixed carbonate silicate lithologies including abundant carbonate rocks of the lesser himalayan sequence for comparison the arun river was chosen for study because south of the himalayan front it drains almost exclusively greater and lesser himalayan silicate rocks despite this dominance of silicate rocks carbonate weathering probably of metamorphic calcite in great himalayan paragneisses is clearly in evidence in many arun watersheds weathering of silicate rocks exposed all along the arun south of the range front has a small impact on mainstem river chemistry the mainstems of both the seti and arun systems are dominated by weathering of carbonate rocks although the contribution of silicate weathering is more visible in arun mainstem chemistry the carbonate weathering source to the arun mainstem is probably both limestone in the tethyan sequence widely exposed in northern headwaters of the system and metamorphic calcite within the greater himalayan sequence a number of small watersheds along the arun and seti appear to be carbonate free they probably provide the best constraints to date on the ca na and mg na ratios of waters draining himalayan silicate rocks two critical parameters for calculation of co 2 consumption by silicate weathering in the himalaya the observed ca na and mg na ratios would produce slightly higher estimates of silicate weathering fluxes than previous studies the geologic contrasts between the seti and the arun produce large differences in the 87 sr 86 sr ratio of each mainstem unlike the major element chemistry the seti mainstem displays much higher 87 sr 86 sr ratios than the arun mainstem the opposite of the expected relationship since radiogenic silicate rocks of the greater and lesser himalaya are so widely exposed along the arun 87 sr 86 sr ratios of the arun mainstem never exceed 0 734 and show little downstream change as the mainstem passes through silicate rocks of the greater and lesser himalaya 87 sr 86 sr ratios of the seti mainstem increase sharply from 0 725 to 0 785 when the river enters the belt of metacarbonate rocks of the northern lesser himalayan sequence a pattern also displayed by other himalayan rivers such as the kali gandaki and bhotse khola metacarbonate rocks including those of the lesser himalaya are a major source of radiogenic sr in modern himalayan rivers and probably have been key players in elevating marine 87 sr 86 sr ratios since the early miocene

effects of aridity and vegetation on plant wax δd in modern lake sediments we analyzed the deuterium composition of individual plant waxes in lake sediments from 28 watersheds that span a range of precipitation d h vegetation types and climates the apparent isotopic fractionation ea between plant wax n alkanes and precipitation differs with watershed ecosystem type and structure and decreases with increasing regional aridity as measured by enrichment of 2 h and 18 o associated with evaporation of lake waters the most negative ea values represent signatures least affected by aridity these values were 125 5 for tropical evergreen and dry forests 130 for a temperate broadleaf

stable isotope based paleoaltimetry abstractthe quantitative estimation of paleoaltitude has become an increasing focus of earth scientists because surface elevation provides constraints on the geodynamic mechanisms operating in mountain belts as well as the influence of mountain belt growth on regional and global climate the general observation of decreasing 18o and 2h values in rainfall as elevation increases has been used in both empirical and theoretical approaches to estimate paleoelevation these studies rely on the preservation of ancient surface water compositions in authigenic minerals to reconstruct the elevation at the time the minerals were forming in this review we provide a theory behind the application of stable isotope based approaches to paleoaltimetry we apply this theory to test cases using modern precipitation and surface water isotopic compositions to demonstrate that it generally accords well with observations examples of the application of paleoaltimetry techniques to himalaya tibet and the andes are discussed

palaeoclimatic interpretation of clay minerals in marine deposits an outlook from the continental origin abstract as distribution of clay minerals in modern oceans seems to be controlled by contemporary climates marine clays in ancient deposits have been widely used to reconstruct palaeoclimates in this review we examine this question mainly from the continental origin of the clay minerals and show the difficulties of retrospective analysis of the influence of climate on common marine deposits we examine successively how soils develop and behave are reworked and palaeoweatherings are preserved focusing the review on kaolinitic soils indicative of tropical wet climates several stages intervene between the time of clay mineral development in soils and their final deposition in the basin 1 the persistence over geological times of huge amounts of kaolinitic palaeoweathering materials in the landscapes may seriously alter the palaeoclimatic signal of kaolinite in the sedimentary record although the kaolinite deposited in recent sediments of the world oceans is consistent with wet climatic zones this is mainly because the major kaolinitic and bauxitic palaeosurfaces coincide with the tropical areas where kaolinite is still developing at present 2 possible development of deep kaolinitic profiles at high latitudes and cold conditions under co 2 enriched palaeoatmospheres or even by unusual acidic weathering linked with dry climates is misleading palaeoenvironments for palaeoclimatic reconstruction 3 erosion and transport processes always cloud the signal to some extent because frequently erosion products from the bedrock and different soil horizons will be mixed and major drainage systems may include soils of different climatic zones 4 the arrival of the soil clay assemblages in the basin inevitably lags against their formation on the continent and may occur several million years after formation of the soils on the continent and climate may have considerably changed at that time it is pointed out that sedimentologists and palaeoclimatologists should consider the complexity of the relations between soil and sedimentary clay minerals soil formation rates are slow and therefore the resolution of the palaeoclimatic record in marine clay may not be closer than 1 or 2 ma at present the palaeoclimatic interpretations of marine clay assemblages are yielding at best nothing more than rather broad palaeoclimatic information this approach cannot achieve the same degree of resolution as other techniques such as isotope or microfossil studies clay mineral assemblages may provide integrated records of overall climatic impacts whereas other techniques are more likely to reveal local or temporary climates

scour of cohesive soil by submerged circular turbulent impinging jets this paper introduces a method for estimating the scour in cohesive soils produced by a submerged vertical circular turbulent impinging jet determining scour in cohesive soils is a complex problem partly because the clay particles within the soil are held together by electrochemical forces that are not easily quantifiable as well erosion occurs in many forms such as the removal of individual particles or as large chunks of soil results of a laboratory study of scour by a circular impinging jet of a cohesive soil consisting of 40 clay 53 silt and 7 fine sand are presented analysis based on the mechanics of the impinging jets shows that the dimensions of the scour hole at an equilibrium state of scour are a function of the momentum flux from the jet the impingement height for large impingement heights the viscosity and density of the eroding fluid and the critical shear stress of the soil mass erosion was the predominant type of erosion observed

transport of terrestrial organic carbon to the oceans by rivers re estimating flux and burial rates this study re estimates one important component in the global carbon cycle the modern global fluviatile organic carbon discharge and burial rates according to these results approximately 430 1012 g of terrestrial organic carbon are transported to the ocean in modern times this amount is higher than the latest estimates but takes into account new data from oceania not previously considered in global flux studies however only the minor amount of 10 or approximately 43 1012 gc year 1 is most likely buried in marine sediments this amount is similar to the burial of marine organic carbon in the coastal ocean 55 1012 gc year 1 adding both estimates gives approximately 100 1012 gc year 1 which is the value calculated by berner 1982 for terrestrial deltaic shelf sediments however the results in this study suggest that on a global scale the organic carbon content in coastal ocean sediments is not solely of terrestrial origin but a mixture of nearly equal amounts of marine and terrestrial organic carbon the major part of the terrestrial organic carbon that enters the ocean by rivers approximately 400 1012 gc year 1 seems to be either a remineralised in the ocean whereas the mechanism by which the terrestrial organic carbon is oxidised in the ocean are unknown or b is dispersed throughout the oceans and accumulates in pelagic sediments

hydrogen isotope ratios of recent lacustrine sedimentary n alkanes record modern climate variability abstract hydrogen isotope ratios were measured on n alkanes n c12 to n c31 extracted from recent lake surface sediments along a n s european transect to test if modern climate variability is recorded in these biomarkers d values of the n alkanes are compared to d values of meteoric water from the iaea gnip database spanning a range from 119 in northern sweden to 41 in southern italy to lake water d values and to mean annual temperatures varying between 2 0 c in the north and 13 7 c in the south d values of the short chained n alkanes n c12 to n c20 excluding algal derived n c17 and n c19 are higher in the north and lower in the south the isotopic fractionation e for hydrogen between meteoric water and the short chained n alkanes is increasing from n to s by more than 100 and is significantly correlated to mean annual temperature for n c16 and n c18 this suggests that these n alkanes may originate from a different source in the northern lakes possibly due to petroleum contamination or are synthesized using a different biochemical pathway the n c17 and n c19 alkanes of algal origin the n c21 and n c23 alkanes originating from water plants and the long chain n alkanes n c25 n c27 n c29 and n c31 of terrestrial origin clearly correlate with d values of meteoric water lake water and mean annual temperature indicating that they excellently record the d value of meteoric water the mean hydrogen isotope fractionation ec17 w of 157 sd 13 between n c17 and meteoric water is fairly constant over the wide range of different climates and lake environments suggesting only minor influence of environmental factors on this biochemical fractionation this suggests that d values of n c17 are suitable to reconstruct the isotopic composition of source water the mean fractionation between the long chain n alkanes and water is 128 sd 12 the mean difference of 31 between both e values is likely due to evaporative enrichment of deuterium in the leaf water if this is the only influence on the enrichment the difference between the d values of terrestrial and aquatic compounds might be suitable to reconstruct terrestrial evapotranspiration of the lake environment

molecular and isotopic records of c4 grassland expansion in the late miocene abstract siwalik paleosol and bengal fan sediment samples were analyzed for the abundance and isotopic composition ofn alkanes in order to test for molecular evidence of the expansion of c4 grasslands on the indian subcontinent the carbon isotopic compositions of high molecular weight alkanes in both the ancient soils and sediments record a shift from low 13c values ca 30 to higher values ca 22 prior to 6 ma this shift is similar in magnitude to that recorded by paleosol carbonate and fossil teeth and is consistent with a relatively rapid transition from dominantly c3 vegetation to an ecosystem dominated by c4 plants typical of semi arid grasslands the n alkane values from our paleosol samples indicate that the isotopic change began as early as 9 ma reflecting either a growing contribution of c4 plants to a dominantly c3 biomass or a decrease in water availability to c3 plants molecular and isotopic analyses of other compounds including n alcohols and low molecular weightn alkanes indicate paleosol organic matter contains contributions from a mixture of sources including vascular plants algae and or cyanobacteria and microorganisms a range of inputs is likewise reflected in the isotopic composition of the total organic carbon from these samples in addition then alkanes from two samples show little evidence for pedegenic inputs and we suggest the compounds were derived instead from the paleosol s parent materials we suggest the record of vegetation in ancient terrestrial ecosystems is better reconstructed using isotopic signatures of molecular markers rather than bulk organic carbon this approach provides a means of expanding the spatial and temporal records of c4 plant biomass which will help to resolve possible tectonic climatic or biological controls on the rise of this important component of the terrestrial biosphere

runoff driven export of particulate organic carbon from soil in temperate forested uplands we characterise the sources pathways and export fluxes of particulate organic carbon poc in a headwater catchment in the swiss alps where suspended sediment has a mean organic carbon concentration of 1 45 0 06 by chemically fingerprinting this carbon and its potential sources using carbon and nitrogen elemental and isotopic compositions we show that it derives from binary mixing between bedrock and modern biomass with a soil like composition the hillslope and channel are strongly coupled allowing runoff to deliver recent organic carbon directly to the stream beyond a moderate discharge threshold at higher flows more biomass is mobilised and the fraction of modern carbon in the suspended load reaches 0 70 increased from 0 30 during background conditions significant amounts of non fossil organic carbon are thus transferred from the hillslope without the need for extreme events such as landsliding precipitation is key as soon as the rain stops biomass supply ceases and fossil carbon again dominates we use rating curves modelled using samples from five storm events integrated over 29 year discharge records to calculate long term export fluxes of total poc and non fossil poc from the catchment of 23 3 5 8 and 14 0 4 4 t km 2 yr 1 respectively these yields are comparable to those from active mountain belts yet the processes responsible are much more widely applicable such settings have the potential to play a significant role in the global drawdown of carbon dioxide via riverine biomass erosion and their contribution to the global flux of poc to the ocean may be more important than previously thought

the role of effective discharge in the ocean delivery of particulate organic carbon by small mountainous river systems recent research has shown that small mountainous river systems smrs account for a significant fraction of the global flux of sediment and particulate organic carbon poc to the ocean the enormous number of smrs precludes intensive studies of the sort conducted on large systems necessitating development of a conceptual framework that permits cross system comparison and scaling up herein we introduce the geomorphic concept of effective discharge to the problem of source to sink poc transport this idea recognizes that transport effectiveness is the product of discharge frequency and magnitude wherein the latter is quantified as a power law relationship between discharge and load the rating curve an analytical solution for effective discharge qe identifies two key variables the standard deviation of the natural logarithm of discharge sq and the rating exponent of constituent i bi data from selected smrs are used to show that for a given river qe poc qesediment qe for different poc constituents e g pocfossil vs pocmodern differs in predictable ways and qe for a particular constituent can vary seasonally when coupled with the idea that discharge peaks of small rivers may be coincident with specific oceanic conditions e g large waves wind from a certain direction that determine dispersal and burial these findings have potentially important implications for poc fate on continental margins future studies of poc transport in smrs should exploit the conceptual framework provided herein and seek to identify how constituent specific effective discharges vary between rivers and respond to perturbations delivery of particulate organic carbon poc from the land to the sea by rivers and its eventual burial in ocean sediments are critical processes in the global carbon cycle sequestration of poc in marine sediments is a major long

modeling of riverbed evolution for bedload sediment mixtures a new computational methodology for fully coupled simulation of unsteady water and sediment movement in mobile bed alluvial rivers has been developed and tested the one dimensional approach treats bedload transport of nonuniform sediment mixtures with sorting and armoring effects considered spatial lag effects in nonequilibrium bedload transport are taken into account through innovative use of the recently developed notion of a loading law the new system of equations for water and sediment movement is solved in a fully coupled implicit manner using the preissmann finite difference scheme implemented to allow for either upstream or downstream induced mobile bed perturbations formal analysis of the coupled system sheds new light on boundary condition requirements for the multiple size class problem the fully coupled implicit solution has proven to be robust and stable and it respects the underlying volumetric conservation laws remarkably well as demonstrated in continuity analyses of computed bed e

palaeoweathering profiles developed on the iberian hercynian basement and their relationship to the oldest tertiary surface in central and western spain

burial of terrestrial organic matter in marine sediments a re assessment 1 calculations based on recent observations indicate that approximately one third of the organic matter presently being buried in marine sediments may be of terrestrial origin with the majority of this terrestrial organic matter tom burial occurring in muddy deltaic sediments these calculations further suggest that the remineralization of terrestrial organic matter in the oceans is also much less efficient than that of marine organic matter these two underappreciated observations have important implications in terms of our understanding of the controls on the global carbon cycle from a paleoceanographic perspective the results presented here also suggest that changes in tom burial on glacial interglacial timescales have the potential to impact the global carbon cycle i e atmospheric co2 levels

understanding erosion rates in the himalayan orogen a case study from the arun valley understanding the rates and pattern of erosion is a key aspect of deciphering the impacts of climate and tectonics on landscape evolution denudation rates derived from terrestrial cosmogenic nuclides tcns are commonly used to quantify erosion and bridge tectonic myr and climatic up to several kiloyears time scales however how the processes of erosion in active orogens are ultimately reflected in 10be tcn samples remains a topic of discussion we investigate this problem in the arun valley of eastern nepal with 34 new 10be derived catchment mean denudation rates the arun valley is characterized by steep north south gradients in topography and climate locally denudation rates increase northward from 0 2 mm yr 1 to 1 5 mm yr 1 in tributary samples while main stem samples appear to increase downstream from 0 2 mm yr 1 at the border with tibet to 0 91 mm yr 1 in the foreland denudation rates most strongly correlate with normalized channel steepness r2 0 67 which has been commonly interpreted to indicate tectonic activity significant downstream decrease of 10be concentration in the main stem arun suggests that upstream sediment grains are fining to the point that they are operationally excluded from the processed sample this results in 10be concentrations and denudation rates that do not uniformly represent the upstream catchment area we observe strong impacts on 10be concentrations from local nonfluvial geomorphic processes such as glaciation and landsliding coinciding with areas of peak rainfall rates pointing toward climatic modulation of predominantly tectonically driven denudation rates

fully coupled unsteady mobile boundary flow model a fully coupled one dimensional river model capable of predicting sediment transport and bed level changes under unsteady flow conditions is described the governing equations for mass and momentum balance of sediment water mixture under unsteady flow conditions in natural rivers with irregular geometries are solved simultaneously using the preissmann four point linear implicit scheme with weighting factors for space and time coordinates the resulting system of algebraic equations is solved using a solution procedure that bridges upstream and downstream boundary nodal values by successive substitutions the friction slope is expressed in a consistent form that allows the consideration of the changing alluvial roughness effect the system of governing equations is explicitly coupled by introducing the term representing the rate of change of bed level the fully coupled unsteady mobile boundary flow model fcm is applied to the classical problem of sediment deposition upstream of a dam with an arbitrar

measurements of sediment erosion and transport with the adjustable shear stress erosion and transport flume soil and sediments play an important role in water management and water quality issues such as water turbidity associated contaminants reservoir sedimentation undesirable erosion and scour and aquatic habitat are all linked to sediment properties and behaviors in situ analysis is necessary to develop an understanding of the erosion and transport of sediments sandia national laboratories has recently patented the adjustable shear stress erosion and transport asset flume that quantifies in situ erosion of a sediment core with depth while affording simultaneous examination of transport modes bedload versus suspended load of the eroded material core erosion rates and ratios of bedload to suspended load transport of quartz sediments were studied with the asset flume the erosion and transport of a fine grained natural cohesive sediment were also observed experiments using quartz sands revealed that the ratio of suspended load to bedload sediment transport is a function of grain diameter and shear

the geomorphological and geological importance of palaeosurfaces this special publication is a collection of papers which identifies describes and interprets the occurrence of palaeosurfaces in the geological record the concept of a palaeo surface is one which is generally understood across the geomorphological and geological sciences but according to discipline and application often differs in the emphasis and detail of its interpretation in order to encompass the widest range of contributions and views upon the subject of palaeosurfaces a broad remit was deliberately adopted during the preparation of this volume cations of ancient palaeosurfaces the research areas represented are geographically widespread and include examples from australia africa south america india and europe

bedload transport in gravel bed streams with unimodal sediment bedload transport in many gravel bed streams becomes highly complicated because of the nonuniformity of the grain size and the vertical stratification of channel bed material a new relation for computing bedload transport rates in gravel bed streams is proposed here in an effort to account for the variation of the makeup of the surface material within a wide range of shields stresses the relation employs a two parameter approach one related to the material in the pavement and the other to that in the subpavement layers the mode is used to represent the grain sizes of each layer available bedload transport data from gravel bed streams with unimodal sediment are used to test the accuracy of the relation a comparison with other bedload transport relations is also considered

soil n alkane δd vs altitude gradients along mount gongga china the altitude effect on the isotopic composition of precipitation and its application to paleoelevation reconstruction using authigenic or pedogenic minerals have been intensively studied however there are still no studies on variations in biomarker d along altitude transects to investigate its potential as a paleoelevation indicator although it has been observed that d of higher plant lipid may record changes in precipitation d dp here we present d values of higher plant derived c27 c29 and c31n alkanes from surface soil along the eastern slope of mount gongga china with great changes in physical variables and vegetation over a range from 1000 to 4000 m above sea level the weighted mean d values of these n alkanes dwax show significant linear correlations with predicted dp values r2 0 76 with an apparent isotopic enrichment ewax p of 137 9 indicating that soil dwax values track overall dp variation along the entire altitudinal transect leaf dwax is also highly correlated with mountain altitude by a significant quadratic relationship r2 0 80 evapotranspiration is found declining with altitude potentially lowering dwax values at higher elevations however this evapotranspiration effect is believed to be largely compensated by the opposing effect of vegetation changes resulting in less varied ewax p values over the slope transect this study therefore confirms the potential of using leaf dwax to infer paleoelevations and more generally to infer the d of precipitation

a new approach to stable isotope based paleoaltimetry implications for paleoaltimetry and paleohypsometry of the high himalaya since the late miocene the change in oxygen isotopic composition of precipitation is modeled using equilibrium fractionation during rayleigh distillation linked to the thermodynamics of atmospheric ascent and water vapor condensation the primary controllers of the vertical variation in isotopic composition with elevation are the low elevation temperature and relative humidity as these control the vertical distribution of condensation an empirical fit of precipitation versus model condensation based on alpine stations is derived this fit is represented in the model as the weighted mean composition of condensation within a 1000 m thick air parcel 1500 500 m above the ground surface and is used for all other regions comparison of model versus observed modern precipitation reveals a close fit particularly of more highly elevated sites comparison of modern waters in the himalayas and southern tibet with model predictions particularly as revealed by comparison of observed and predicted hypsometry provides additional support to the validity of the model finally application of this model to estimates of paleo waters in the himalayas and southern tibet reveals that this region had already achieved its present hypsometry by the late miocene about 10 ma ago fl 2001 published by elsevier science b v

influence of cohesion on scour under submerged circular vertical jets the results of an experimental study on scour under submerged circular vertical jets of water in cohesionless and cohesive sediments are presented the difference between scour patterns in cohesionless and cohesive sediments is identified in cohesive sediments the variations of maximum depth and volume of scour have been studied with respect to the percentage of clay content dry density antecedent moisture content etc empirical relationships have been proposed for the maximum depth and volume of scour for both nonplastic and plastic cohesive sediments the range of data for the applicability of the proposed relationships is specified

climatic and geomorphic controls on the erosion of terrestrial biomass from subtropical mountain forest 1 erosion of particulate organic carbon poc occurs at very high rates in mountain river catchments yet the proportion derived recently from atmospheric co2 in the terrestrial biosphere pocnon fossil remains poorly constrained here we examine the transport of pocnon fossil in mountain rivers of taiwan and its climatic and geomorphic controls in 11 catchments we have combined previous geochemical quantification of poc source accounting for fossil poc from bedrock with measurements of water discharge qw and suspended sediment concentration over 2 years in these catchments pocnon fossil concentration mg l 1 was positively correlated with qw with enhanced loads at high flow attributed to rainfall driven supply of pocnon fossil from forested hillslopes this climatic control on pocnon fossil transport was moderated by catchment geomorphology the gradient of a linear relation of pocnon fossil concentration and qw increased as the proportion of steep hillslopes 35 in the catchment increased the data suggest enhanced supply of pocnon fossil by erosion processes which act most efficiently on the steepest sections of forest across taiwan pocnon fossil yield was correlated with suspended sediment yield with a mean of 21 10 tc km 2 yr 1 at this rate export of pocnon fossil imparts an upper bound on the time available for biospheric growth of 800 yr over longer time periods pocnon fossil transferred with large amounts of clastic sediment can contribute to sequestration of atmospheric co2 if buried in marine sediments our results show that this carbon transfer should be enhanced in a wetter and stormier climate and the rates moderated on geological timescales by the regional tectonic setting

cohesive material erosion by unidirectional current the initiation of motion of consolidated cohesive sediments under a unidirectional flow of clear water was studied experiments were performed in a flume tunnel capable of providing a bed shear stress up to 26 pa and a velocity of 3 5 m s 3 mm above the bed samples were prepared in a specially designed press using a carefully controlled consolidation procedure critical shear stress and velocity were found to increase with compressive strength vane shear strength plasticity index clay content and consolidation pressure

estimating culvert scour in cohesive material an investigation of scour at culvert outlets in a cohesive bed material is presented twelve experiments of 1000 minutes duration were conducted using a cohesive bed material culvert 27 3 cm 10 in 35 6 cm 14 in and 45 7 cm 18 in diameters were tested with discharges ranging from 0 054 m sec 0 824 m sec 1 91 cfs to 29 13 cfs the tailwater elevation was maintained at 0 45 d n 0 05 d above the culvert invert where d is the diameter of the culvert the results yielded a series of empirical relationships expressing the depth width length and volume of scour as a function of the culvert diameter culvert outlet velocity soil plasticity index soil shear strength and fluid density general observations concerning scour hole formation growth and stabilization are reported

predicting paleoelevation of tibet and the himalaya from δ18o vs altitude gradients in meteoric water across the nepal himalaya the 18o value of meteoric water varies with elevation providing a means to reconstruct paleoelevation if the 18o values of paleowater are known in this study we determined the 18o values of water 18omw from small tributaries along the seti river and kali gandaki in the nepal himalaya we found that 18omw values decrease with increasing altitude for both transects 18omw vs altitude along the kali gandaki in west central nepal fit a second order polynomial curve consistent with increasing depletion of 18o with increasing elevation as predicted by a rayleigh type fractionation process this modern 18omw vs altitude relationship can be used to constrain paleoelevation from the 18o values of miocene pliocene carbonate 18oc deposited in the thakkhola graben in the southern tibetan plateau paleoelevations of 3800 480 m to 5900 350 are predicted for the older tetang formation and 4500 430 m to 6300 330 m for the younger thakkhola formation these paleoelevation estimates suggest that by 11 ma the southern tibetan plateau was at a similar elevation to modern

routing graded sediments in streams formulations a one dimensional numerical model is developed for simulating the movement of well graded sediments through a stream network the model is based on the physical processes governing the mechanics of sediment movement in alluvial channels it incorporates the effect of sediment gradation on the stream s potential transport capacity it also accounts for the effect of particle exchange between the sediment load and the bed while simulating aggradation degradation and armoring of the bed the applicability of the model is restricted to noncohesive materials and relatively stable channel geometries any valid water routing algorithm can be used in simulating the movement of water

hydrogen isotope ratios of lacustrine sedimentary n alkanes as proxies of tropical african hydrology insights from a calibration transect across cameroon abstract hydrogen isotope values d of sedimentary aquatic and terrestrial lipid biomarkers originating from algae bacteria and leaf wax have been used to record isotopic properties of ancient source water i e precipitation and or lake water in several mid and high latitude lacustrine environments in the tropics however where both processes associated with isotope fractionation in the hydrologic system and vegetation strongly differ from those at higher latitudes calibration studies for this proxy are not yet available to close this gap of knowledge we sampled surface sediments from 11 lakes in cameroon to identify those hydro climatological processes and physiological factors that determine the hydrogen isotopic composition of aquatic and terrestrial lipid biomarkers here we present a robust framework for the application of compound specific hydrogen isotopes in tropical africa our results show that the d values of the aquatic lipid biomarker n c17 alkane were not correlated with the d values of lake water carbon isotope measurements indicate that the n c17 alkane was derived from multiple source organisms that used different hydrogen pools for biosynthesis we demonstrate that the d values of the n c29 alkane were correlated with the d values of surface water i e river water and groundwater which on large spatial scales reflect the isotopic composition of mean annual precipitation such a relationship has been observed at higher latitudes supporting the robustness of the leaf wax lipid d proxy on a hemispheric spatial scale in contrast the d values of the n c31 alkane did not show such a relationship but instead were correlated with the evaporative lake water d values this result suggests distinct water sources for both leaf wax lipids most likely originating from two different groups of plants these new findings have important implications for the interpretation of long chain n alkane d records from ancient lake sediments in particular a robust interpretation of palaeohydrological data requires knowledge of the vegetation in the catchment area as different plants may utilise different water sources our results also suggest that the combination of carbon and hydrogen isotopes does help to differentiate between the metabolic pathway and or growth form of organisms and therefore the source of hydrogen used during lipid biosynthesis

cohesion influences on erosion and bed load transport 1 studies on erosion and transport rates of cohesive sediment mixtures containing gravel are not reported so far in the literature to the best of our knowledge results from laboratory experiments on the process of erosion of cohesive sediment mixtures by open channel flow are presented the sediment used for experimentation consisted of fine gravel mixed with clay in proportions varying from 10 to 50 and fine gravel fine sand in equal proportion by weight mixed with clay proportions again varying from 10 to 50 by weight experimental observations have revealed that the process of detachment of cohesive sediment mixtures containing gravel is significantly different from that of cohesionless sediments also it is different from the detachment process of cohesive sediment mixtures not containing coarser size material experimental data on transport rates of the bed load of the cohesive sediment mixtures are presented on the basis of dimensional considerations a computational procedure is proposed to determine the bed load transport rates generated from erosion of the different size fractions of sediment mixtures clay percentage and unconfined compressive strength of the sediment bed were the main parameters controlling bed load transport rate of such sediments in the absence of cohesion the proposed method reduces to the patel and ranga raju 1996 method for bed load transport rate computation of nonuniform cohesionless sediments

the provenance of vegetation and environmental signatures encoded in vascular plant biomarkers carried by the ganges brahmaputra rivers organic matter carried by rivers and deposited in continental and marine sediments contains valuable information on past environmental conditions and their impact on the terrestrial biosphere in order to use sedimentary records to reconstruct past environmental conditions on the continents such as vegetation cover and type or precipitation intensity we need to understand the provenance of the organic signatures and how they are transferred and potentially modified by fluvial transport to the sedimentary reservoir in particular we need to understand how environmental conditions are imprinted in the composition of riverine particulate organic carbon here we investigate the stable carbon and hydrogen isotopic signatures of vascular plant leaf wax biomarkers in the modern day ganges and brahmaputra river complex one of the largest fluvial systems on earth the distribution of n alkanes and n alkanoic acids in ganges brahmaputra river sediments suggests that vascular plant inputs are consistently a significant component of the organic carbon pool molecular 13c measurements reveal that c3 vegetation inputs delivered by the himalayan rivers are partly degraded and replaced by mixed c3 c4 vegetation input in the floodplain the hydrogen isotopic composition of long chain c24 n alkanoic acids in combination with their stable c isotopic composition provides constraints on the isotopic composition of the environmental water used by higher plants within the drainage basin calculated compositions compare well with the depleted d isotopic ratios of the river water during the summer monsoon suggesting that h isotopic compositions of long chain alkanoic acids are a valuable proxy for the composition of summer monsoon moisture in the ganges brahmaputra basin detailed studies of the isotopic anatomy of modern river systems are critical for informed interpretation of marine sedimentary records in river influenced continental margins

effect of precipitation regime on δ d values of soil n alkanes from elevation gradients implications for the study of paleo elevation we measured dd values of long chain n alkanes isolated from 30 surface soil samples along two elevation transects on the tibetan plateau differing in precipitation regime and water source the east asian monsoon precipitation dominates the wetter regime on the eastern slope from 1230 to 4300 m of gongga shan on the eastern tibetan plateau precipitation from the polar westerlies dominates the drier region on the slope from 1900 to 5000 m in the west kunlun shan on the northwestern tibetan plateau the decrease in dd value with elevation in the wetter region greatly exceeded that in drier region by 1 9 0 1 100 m and 1 4 1 0 100 m respectively the apparent fractionation between leaf wax and precipitation ewax p values in the wetter region ca 164 were more negative than those in drier region ca 125 above 3200 m we also measured dd values in leaves of six common living trees values from 287 to 193 from gongga shan ranging from about 2900 4200 m the abundance weighted average values of the nalkanes ddwax show a strong reverse correlation with sample source elevation r 2 0 78 for soils from 2 0 85 for soils from west kunlun shan above 3200 m suggesting that n alkane ddwax faithfully records the precipitation dd and that the isotopic altitude effect of precipitation controls ddwax altitudinal gradients in the mountains the data show a fairly strong monotonic dependency of n alkane dd values on elevation for the eastern plateau but a complex relationship between n alkane dd values and elevation for the northwestern plateau the ddwax values at sites below 3200 m from the kunlun shan area exhibit an unexpected positive correlation with elevation the study confirms the potential for using sediment ddwax values to reconstruct paleo elevation in wetter regions but suggests caution in applying the approach to dry regions our results also show it is essential to consider the intricacy of the pattern of atmospheric circulation and water sources and their influence on the lapse rate of dd values with elevation

naturally occurring arsenic in groundwater and identification of the geochemical sources in the duero cenozoic basin spain arsenic concentrations surpassing potability limit of 10 g l in the groundwater supplies of an extensive area in the duero cenozoic basin central spain have been detected and the main sources of arsenic identified arsenic in 514 samples of groundwater having mean values of 40 8 g l is natural in origin geochemical analysis of 553 rock samples assaying arsenic mean values of 23 mg kg was performed spatial coincidence between the arsenic anomaly in groundwater and the arsenic lithogeochemical distribution recorded in the middle miocene clayey organic rich zaratan facies illustrates that the rocks of this unit are the main source of arsenic in groundwater the ferricretes associated to the late cretaceous middle miocene siliciclastics also constitute a potential arsenic source mineralogical study has identified the presence of arsenic in iron oxides authigenic pyrite manganese oxides inherited titanium iron oxides phyllosilicates and organomineral compounds arsenic mobilization to groundwater corresponds to arsenic desorption from iron and manganese oxides and from organic matter

cap structures as diagnostic indicators of silcrete origin abstract cap structures within silcretes have long been used as a diagnostic indicator of pedogenic silicification however a growing number of studies of the micromorphology of non pedogenic silcretes indicate that this may no longer be appropriate this paper presents the first systematic investigation of the micro fabric geochemistry and mineralogy of cap structures in groundwater silcretes through an analysis of conglomeratic varieties puddingstones from the southern uk our results suggest that cap structures in groundwater silcretes fall within a spectrum of types related to the degree of sorting in the inter gravel host sediment at one end of this spectrum are well defined caps within otherwise well sorted overgrowth dominated silcretes these caps exhibit a grain supported fabric are cemented by micro and or cryptocrystalline silica and contain floating silt sized quartz and ti oxide grains we propose that these structures developed mainly as a result of in washing of fine sediments that were subsequently silicified at the other end of the spectrum are silcretes with caps defined by concentrations of ti oxide grains as opposed to cement type and grain size these formed mainly as a result of the remobilisation and precipitation of ti during the silicification of gravels containing interstitial clay rich sandy sediment between these end members are silcretes with cap structures formed by a combination of in washing and redistribution of fines plus some local remobilisation of ti overall the cap structures in this study exhibit a simple micromorphology lacking the alternating ti and silica rich lamellae typical of pedogenic silcrete we conclude that the presence of cap structures alone should not be considered diagnostic of pedogenic silicification unless accompanied by other indicators such as a differentiated profile and abundant complex way up structures within the micro fabric

the stability of fine grained sediments from the fraser river delta the stability and erodibility of benthic fine grained sediments on the foreshore and upper foreslope of the fraser river delta were measured using thein situbenthic flume sea carousel the erosion threshold c 0 which varied between 0 11 and 0 50 pa was inversely related to erosion rate it was also proportional to sediment wet bulk density b in the form c 0 7 10 4 b 0 47 this trend agreed with those obtained from four other sites across canada that encompassed a wide range in sediment densities 1000 b 2000 kg m 3 erosion threshold shields parameter c was positively related to grain reynolds number over the silt clay size range 0 01 re 5 c 2 86re0 58 this was similar to earlier findings for water saturated sediment this trend is also in continuity with published threshold values measured in biostabilized sand 5 re 50 copyright 1997 academic press limited three erosion types were observed type ia erosion was a surface phenomenon caused by the presence of a thin organic fluff layer it occurred at current speeds less than 0 3 m s 1 type 1b erosion asymptotically decaying with time characterized the mid portions of each erosion time series and occurred at current speeds of 0 3 0 9 m s 1 type i ii erosion transitional was largely found on the foreslope and occurred at current speeds in excess of 0 8 m s 1 the erosion process began in all cases under turbulent transitional flows the change from type i to type ii erosion corresponded to the onset of turbulent rough flows 60 re 70 this is supported by video observations which showed type i erosion to be largely the result of entrainment of small aggregates and flocs whereas type ii erosion was the result of enlargement of surface irregularities and subsequent undercutting and release of large aggregates mean erosion rate em was independent of either azimuthal current speed or bed shear stress it was largely constant throughout each deployment and varied between 1 4 and 7 4 10 4 kg m 2 s 1

silcrete and alunite genesis in alluvial palaeosols late cretaceous to early palaeocene duero basin spain abstract an extensive formation of silcretes occurs in the upper half of a late cretaceous to palaeocene siderolithic unit consisting of conglomerates sandstones and sandy mudstones along the western margin of the tertiary duero basin spain the unit is arranged in fining upward sequences that were deposited in a fluvial braided system with floodplains subject to periodic events of exposure and drying out the original mineralogy of the siderolithic unit is seen in the less altered levels where it consists of quartz illite white mica kaolinite and at the top of the unit k feldspar all coming from the palaeoalteration mantles developed on the metasediments of the variscan basement the unit is characterized by a marked development of alluvial palaeosols at the uppermost part of each sequence at field scale the pedogenic structures and features are evident from the mottled pattern burrowing cracking planes and root traces at micromorphological scale an intense development of birefringent fabrics is seen in clays micas and feldspars show evidence of alteration due to hydrolysis while the more resistant quartz grains show common corrosion gulfs and have become the only surviving elements in the most silicified beds the neoformed minerals are related to the pedodiagenetic processes developed on the floodplains the main neoformed phase is opal probably amorphous silica in origin that aged to opal ct which ranges from local cementations in pores to an almost complete replacement of the rock specially the finest components matrix kaolinite is the most abundant neoformed clay locally veinlets of alunite accompany the opalized levels all the processes described occurred in a seasonal tropical climate during dry episodes strong evaporation resulted in an increase in ph favouring the hydrolysis of the original silicates the paucity of mg2 and ca2 in the groundwater would have favoured the increase in ph in ensuing wetter periods phs fell rapidly resulting in the precipitation of kaolinite and also favouring the precipitation of opal and alunite the alunite could have formed either by oxidation of the iron sulphides developed in reducing areas of the flood plains or by evaporitic concentration of sulphate in ca2 and mg2 free groundwaters

leaf wax biomarkers in transit record river catchment composition rivers carry organic molecules derived from terrestrial vegetation to sedimentary deposits in lakes and oceans storing information about past climate and erosion as well as representing a component of the carbon cycle it is anticipated that sourcing of organic matter may not be uniform across catchments with substantial environmental variability in topography vegetation zones and climate here we analyze plant leaf wax biomarkers in transit in the madre de dios river peru which drains a forested catchment across 4 5 km of elevation from the tropical montane forests of the andes down into the rainforests of amazonia we find that the hydrogen isotopic composition of leaf wax molecules specifically the c28 n alkanoic acid carried by this tropical mountain river largely records the elevation gradient defined by the isotopic composition of precipitation and this supports the general interpretation of these biomarkers as proxy recorders of catchment conditions however we also find that leaf wax isotopic composition varies with river flow regime over storm and seasonal timescales which could in some cases be quantitatively significant relative to changes in the isotopic composition of precipitation in the past our results inform on the sourcing and transport of material by a major tributary of the amazon river and contribute to the spatial interpretation of sedimentary records of past climate using the leaf wax proxy

northern hemisphere controls on tropical southeast african climate during the past 60 000 years the processes that control climate in the tropics are poorly understood we applied compound specific hydrogen isotopes d and the tex86 tetraether index of 86 carbon atoms temperature proxy to sediment cores from lake tanganyika to independently reconstruct precipitation and temperature variations during the past 60 000 years tanganyika temperatures follow northern hemisphere insolation and indicate that warming in tropical southeast africa during the last glacial termination began to increase 3000 years before atmospheric carbon dioxide concentrations d data show that this region experienced abrupt changes in hydrology coeval with orbital and millennial scale events recorded in northern hemisphere monsoonal climate records this implies that precipitation in tropical southeast africa is more strongly controlled by changes in indian ocean sea surface temperatures and the winter indian monsoon than by migration of the intertropical convergence zone

mineralogical forms of silica and their sequence of formation in silcretes the paragenesis and the sequence of formation of silica polymorphs have been studied in three examples of silicification in the regolith of the paris basin and the central massif of france the initial silica deposits are most frequently opal with varying degrees of structural organization subsequently recrystallization produced varieties of progressively better organized quartz namely fibrous quartz chalcedony and lutecite which developed from deposits of microlaminated opal and microcrystalline quartz which formed from nodular opal however even during the formation of microcrystalline quartz facies dissolution and recrystallization processes continued resulting in progressively bigger quartz crystals in the final stages of silcrete development hyaline quartz crystals grew in voids these mineral sequences are determined by the solubility of each of the component parts solubility is controlled by the purity and the degree of order of the crystalline structure the most disordered minerals are the most soluble the degree of order is controlled in part by foreign ions incorporated into the lattice but also by the degree of supersaturation of silica in solution in the system which in turn controls the rate of formation of nuclei dissolution and recrystallization processes are dependent on the percolation of dilute solutions through the silcretes the concentrations of silica and other cations in these solutions is a function of the solubility of the silica phases in the host material and of the rate of percolation thus the porosity of the host material is important rapid percolation favors dissolution but in zones with slow percolation equilibrium is attained and no transformation of existing silica phases occurs it is in the zones of intermediate porosity that progressive recrystallization of quartz occurs the effect of rate of percolation on dissolution and recrystallization explains the vertical distribution of different silica polymorphs observed in numerous silcrete duricrusts

tracing soil organic carbon in the lower amazon river and its tributaries using gdgt distributions and bulk organic matter properties abstract in order to trace the transport of soil organic carbon oc in the lower amazon basin we investigated the distributions of crenarchaeol and branched glycerol dialkyl glycerol tetraethers gdgts by analyzing riverbed sediments and river suspended particulate matter spm collected in the solimoes amazon river mainstem and its tributaries the branched and isoprenoid tetraether bit index a proxy for river transported soil oc into the ocean was determined from the distributions of these gdgts the gdgt derived parameters were compared with other bulk geochemical data i e c n ratio and stable carbon isotopic composition the gdgt derived and bulk geochemical data indicate that riverine spm and riverbed sediments in the lower amazon river and its tributaries are a mixture of c3 plant derived soil oc and aquatic derived oc the branched gdgts in the spm and riverbed sediments did not predominantly originate from the high andes soils 2500 m in altitude as was suggested previously however further constraint on the soil source area of branched gdgts was hampered due to the deficiency of soil data from the lower montane forest areas in the andes our study also revealed seasonal and interannual variation in gdgt composition as well as soil oc discharge which was closely related to the hydrological cycle by way of a simple binary mixing model using the flux weighted bit values at obidos the last gauging station in the amazon river we estimated that 70 80 of the poc pool in the river was derived of soil oc however care should be taken to use the bit index since it showed a non conservative behaviour along the river continuum due to the aquatic production of crenarchaeol further investigation using a continuous sampling strategy following the full hydrological cycle is required to fully understand how soil derived gdgt signals are transformed in large tropical river systems through their transport pathway to the ocean

bed load transport of coarse nonuniform sediment experiments involving measurements of the bed load transport rates of different fractions in a mixture are reported a conceptual model for the effect of a particular size of sediment on the transport rates of other sizes of sediment is proposed the experimental data are analyzed with the dual objectives of assessing the accuracy of existing methods of computation of bed load transport and of proposing a new method of computation

near surface geophysical analysis of the navamuno depression sierra de bejar iberian central system geometry sedimentary infill and genetic implications of tectonic and glacial footprint the geometric and genetic characterization of the navamuno depression peatland system iberian central system is presented here using results from a geophysical survey this depression is a 30 ha pseudo endorheic flat basin over granitic bedrock three geophysical techniques were used to map the subsurface geology and identify and describe the infill sequence shallow seismic refraction sr magnetic resonance sounding mrs and electrical resistivity measurements ves and ert the three main geoelectrical layers g1 g2 g3 identified in previous research have also been identified in the present work using the data obtained in this new research we have been able to analyse these three geological layers in detail and reinterpret them they can be grouped genetically into two sedimentary units an ancient sedimentary body g3 of unknown age and type beneath an upper pleistocene g2 and holocene g1 sedimentary infill the facies distribution and geometry of the upper pleistocene was examined using the sequence stratigraphy method revealing that the navamuno depression was an ice dammed in the last glacial cycle resulting in glaciolacustrine sedimentation a highly permeable sedimentary layer or regolith exists beneath the glaciolacustrine deposits below 40 m depth water content falls dramatically down to a depth of 80 m where unweathered bedrock may be present the information obtained from geophysical geological and geomorphological studies carried out in this research enabled us to consider various hypotheses as to the origin of this depression according to these data the navamuno depression may be explained as the result of a transtensional process from the puerto de navamuno strike slip fault during the reactivation of the iberian central system paleogene lower miocene alpine orogeny and can be correlated with the pull apart type basins described in these areas the neotectonic activity of this fault and the icedammed processes in these areas during the last glacial cycle mis2 were the main causes of recent sedimentary infill in this depression

erosion by submerged circular jets an experimental study on the erosion of sand beds by impinging submerged circular water jets shows similarities between air sand system and water sand system it is shown that there are significant differences between the two systems regarding the depth and radial extent of the scour hole

unified view of sediment transport by currents and waves i initiation of motion bed roughness and bed load transport attention is given to the properties of sediment beds over the full range of conditions silts to gravel in particular the effect of fine silt on the bed composition and on initiation of motion critical conditions is discussed high quality bed load transport data sets are identified and analyzed showing that the bed load transport in the sand range is related to velocity to power 2 5 the bed load transport is not much affected by particle size the prediction of bed roughness is addressed and the prediction of bed load transport in steady river flow is extended to coastal flow applying an intrawave approach simplified bed load transport formulas are presented which can be used to obtain a quick estimate of bed load transport in river and coastal flows it is shown that the sediment transport of fine silts to coarse sand can be described in a unified model framework using fairly simple expressions the proposed model is fully predictive in the sense that only the basic hydrodynamic parameters dep

δd values of individual n alkanes from terrestrial plants along a climatic gradient implications for the sedimentary biomarker record abstract the compound specific hydrogen isotope composition d of sedimentary n alkanes is increasingly used as a palaeoclimate proxy to explore the origin of the hydrogen isotope signal of n alkanes from higher terrestrial plant biomass in sedimentary organic matter of small lakes we have analysed the n alkane composition and d values of 31 plant biomass samples birch betula beech fagus oak quercus alder alnus hornbeam carpinus and myrtle myrtus as well as non stomata containing sphagnum cladonia and moss from 14 sites along a climatic gradient from northern finland to southern italy eleven of the sites were previously investigated for the n alkane d values in adjacent lake sediments and are compared to the leaf wax n alkane d values the distribution of terrestrial n alkanes in lake sediments was not found to be characteristic of the dominant vegetation around the lake evidently n alkane distributions within the same species at different sites were found to be variable these findings complicate the use of certain n alkane distributions in sediments as a palaeoenvironmental indicator d values of plant biomass n alkanes show a significant positive correlation with the precipitation d values biomass n alkane d values are in general less negative than the associated sedimentary n alkanes of terrestrial origin possibly due to the stronger evapotranspiration during the summer when sampling took place this suggests that n alkanes in leaves show seasonal variations and the sedimentary organic matter receives the lighter isotope signal of the autumn when most leaves are incorporated into the sediment the variability of the d values from non stomata containing plants is much higher than for broadleaf trees since stomata can regulate water loss through evapotranspiration the average chain length acl of n alkanes from deciduous tree leaves increases from north to south with increasing acl the hydrogen isotopic fractionation e between source water and n alkanes also increases our results prove that terrestrial n alkane d values record the d value of precipitation modified by the amount of isotope enrichment in the leaf water due to plant anatomy stomata vs no stomata and site specific meteorological conditions such as evapotranspiration relative humidity and soil moisture therefore terrestrial n alkanes in lake sediments can deliver information on changes in these parameters over geological timescales in lake sediments where aquatic n alkanes such as n c 17 record the lake water d value the isotopic difference between terrestrial and aquatic n alkanes could therefore be used to reconstruct changes in evapotranspiration

disentangling marine soil and plant organic carbon contributions to continental margin sediments a multi proxy approach in a 20 000 year sediment record from the congo deep sea fan abstract a 20 kyr long sediment sequence from the congo deep sea fan core geob 6518 1 one of the world s largest deep sea river fans has been analysed for bulk and molecular proxies in order to reconstruct the marine soil and plant organic carbon oc contributions to these sediments since the last glacial maximum the bulk proxies applied c n ratio and 13 c org ranged from 10 to 12 5 and from 24 5 to 21 vpdb respectively as molecular proxies concentrations of marine derived alkenones and terrestrial derived odd numbered n alkanes were used which varied between 0 2 and 4 g g dry weight sediment in addition the branched vs isoprenoid tetraether bit index a proxy for soil organic matter input was used which varied from 0 3 to 0 5 in this core application of binary mixing models based on the different individual proxies showed estimates for terrestrial oc input varying by up to 50 due to the heterogeneous nature of the oc application of a three end member mixing model using the 13 c org content the c n ratio and the bit index enabled the distinction of soil and plant organic matter as separate contributors to the sedimentary oc pool the results show that marine oc accounts for 20 to 40 of the total oc present in the deep sea fan sediments over the last 20 kyr and that soil oc accounts for about half 45 on average of the oc present this suggests that soil oc represents the majority of the terrestrial oc delivered to the fan sediments accumulation rates of the plant and soil oc fractions over the last 20 kyr varied by a factor of up to 5 and are strongly related to sediment accumulation rates they showed an increase starting at ca 17 kyr bp a decline during the younger dryas peak values during the early holocene and lower values in the late holocene this pattern matches with reconstructions of past central african humidity and congo river discharge from the same core and revealed that central african precipitation patterns exert a dominant control on terrestrial oc deposition in the congo deep sea fan marine oc accumulation rates are only weakly related to sediment accumulation rates and vary only little over time compared to the terrigenous fractions these variations are likely a result of enhanced preservation during times of higher sedimentation rates and of relative small fluctuations in primary production due to wind driven upwelling

pre aged soil organic carbon as a major component of the yellow river suspended load regional significance and global relevance abstract large rivers connect the continents and the oceans and corresponding material fluxes have a global impact on marine biogeochemistry the yellow river transports vast quantities of suspended sediments to the ocean yet the nature of the particulate organic carbon poc carried by this system is not well known the focus of this study is to characterize the sources composition and age of suspended poc collected near the terminus of this river system focusing on the abundance and carbon isotopic composition 13c and 14c of specific biomarkers the concentrations of vascular plant wax lipids long chain c24 n alkanes n fatty acids and poc co varied with total suspended solid tss concentrations indicating that both were controlled by the overall terrestrial sediment flux poc exhibited relatively uniform 13c values 23 8 to 24 2 and old radiocarbon ages 4000 4640 yr however different biomarkers exhibited a wide range of 14c ages short chain c16 c18 fatty acid 14c ages were variable but generally the youngest organic components from 502 yr to modern suggesting they reflect recently biosynthesized material lignin phenol 14c ages were also variable and relatively young 1070 yr to modern suggesting rapid export of carbon from terrestrial primary production in contrast long chain plant wax lipids display relatively uniform and significantly older 14c ages 1500 1800 yr likely reflecting inputs of pre aged mineral associated soil oc from the yellow river drainage basin even carbon numbered n alkanes yielded the oldest 14c ages up to 26 000 yr revealing the presence of fossil petrogenic oc two isotopic mass balance approaches were explored to quantitively apportion different oc sources in yellow river suspended sediments results indicate that the dominant component of poc 53 57 is substantially pre aged 1510 1770 yr and likely sourced from the extensive loess paleosol deposits outcropping within the drainage basin of the remaining poc between 10 and 31 is fossil in origin 26 000 yr resulting from the physical erosion of ancient sedimentary rock and input of fossil fuel residues from anthropogenic activity and 16 33 is modern carbon derived from terrestrial and aquatic productivity these findings have implications both regarding the provenance and vintage of organic matter signatures emanating from the yellow river basin and similar catchments containing extensive paleosol sequences as well as for the reactivity and fate of this poc upon supply to adjacent marginal seas

orogen parallel extension and exhumation enhanced by denudation in the trans himalayan arun river gorge ama drime massif tibet nepal focused denudation and mid crustal flow are coupled in many active tectonic settings including the himalaya where exhumation of mid crustal rocks accommodated by thrust faults and low angle detachment systems during crustal shortening is well documented new structural and u th he apatite data from the mount everest region demonstrate that the trans himalayan ama drime massif has been exhumed at a minimum rate of 1 mm yr between 1 5 and 3 0 ma during orogen parallel extension the ama drime massif offsets the south tibetan detachment system and therefore the south tibetan detachment system is no longer capable of accommodating south directed mid crustal flow or coupling it with focused denudation previous investigations interpreted the nne ssw striking shear zone on the west side of the ama drime massif as the main central thrust zone however our data show that the ama drime massif is bounded on either side by 100 300 m thick normal sense shear zone and detachment systems that are kinematically linked to young brittle faults that offset quaternary deposits and record active orogen parallel extension when combined with existing data these results suggest that the ama drime massif was exhumed during orogen parallel extension that was enhanced by or potentially coupled with denudation in the trans himalayan arun river gorge this model provides important insights into the mechanisms that exhumed trans himalayan antiformal structures during orogen parallel extension along the southern margin of the tibetan plateau

study of paleoweathering on the spanish hercynian basement montes de toledo central spain summary the hercynian basement of the iberian peninsula consists of a series of late hercynian blocks that were unleveled by the alpine orogeny the montes de toledo range is found in one of the elevated blocks of the central zone and shows ancient alterations affecting different rocks which are fossilized by sediments of different ages two of these weathering profiles under the plio pleistocene sediments of rana formations are studied one is developed on granodiorite with some intercalated metamorphic rocks and the other on a slaty series in both profiles smectite is formed in a first weathering process a second weathering process yielding kaolinite and affecting rana sediments is superimposed on older one both processes seem to be widely spread in the western part of the iberian peninsula

climatic and geomorphic drivers of plant organic matter transport in the arun river e nepal fixation of atmospheric co2 in terrestrial vegetation and subsequent export and deposition of terrestrial plant organic matter in marine sediments is an important component of the global carbon cycle yet it is difficult to quantify this is partly due to the lack of understanding of relevant processes and mechanisms responsible for organic matter transport throughout a landscape here we present a new approach to identify terrestrial plant organic matter source areas quantify contributions and ascertain the role of ecologic climatic and geomorphic controls on plant wax export in the arun river catchment spanning the world s largest elevation gradient from 205 to 8848 m asl in eastern nepal our approach takes advantage of the distinct stable hydrogen isotopic composition expressed as d d values of plant wax n alkanes produced along this gradient transported in river waters and deposited in flood deposits alongside the arun river and its tributaries in mainstem flood deposits we found that plant wax n alkanes were mostly derived from the lower elevations constituting only a small fraction 15 of the catchment informed by remote sensing data we tested four differently weighted isotopic mixing models that quantify sourcing of tributary plant derived organic matter along the arun and compare it to our field observations the weighting parameters included catchment area net primary productivity npp and annual rainfall amount as well as catchment relief as erosion proxy when weighted by catchment area the isotopic mixing model could not explain field observations on plant wax d d values along the arun which is not surprising because the large arid tibetan plateau is not expected to be a major source weighting areal contributions by annual rainfall and npp captured field observations within model prediction errors suggesting that plant productivity may influence source strength however weighting by a combination of rainfall and catchment relief also captured the observed d d value pattern suggesting dominantly erosive control we conclude that tributaries at the southern himalayan front with high rainfall high productivity high relief and high erosion rates dominate plant wax exports from the catchment

hydraulics of submerged jet subject to change in cohesive bed geometry the results of an experimental investigation of the time variation of scour hole and the flow characteristics of the quasi equilibrium state of scour of a cohesive bed downstream of an apron due to a submerged horizontal jet issuing from a sluice opening are presented experiments were carried out with natural cohesive sediment for various sluice openings jet velocities and lengths of apron attempts are made to explain the similarity existing either in the process of scour or in the scour profiles that the scour holes follow downstream of an apron the scour profiles at different times follow a particular geometrical similarity and can be expressed by a polynomial using relevant parameters the characteristic parameters affecting the time variation of scour depth are identified based on the physical reasoning and dimensional analysis an equation for time variation of maximum scour depth is obtained empirically the diffusion characteristics of the submerged jet growth of boundary layer thickness velocity distribution within the boundary layer and shear stress at the quasi equilibrium state of scour are also investigated the expression of shear stress is obtained from the solution of the von karman momentum integral equation

erosion surfaces and neogene landscape evolution in the ne duero basin north central spain abstract we present a chronological model of erosion surface development in the iberian and cantabrian ranges of north central spain we map four erosion surfaces and interpret these to be related to duero basin continental sediments and tectonic activity from upper oligocene to plio pleistocene the oldest erosion surface se1 formed across upper oligocene lower miocene synorogenic deposits while surface se2 was contemporaneous with the middle miocene alluvial systems ending with an uplift stage in the astaracian the two most recent erosion surfaces se3 and se4 developed during extensional tectonic episodes and are associated with the deposition of upper paramo sedimentary units at the end of the miocene upper turolian and alluvial fan deposits known as ranas plio pleistocene with the exception of se1 which seems to be associated with a relatively wet climate the surfaces formed during periods of marked aridity and generally warm temperatures through geostatistical reconstruction of the best preserved surface se2 applying ordinary kriging method to the topography dem of the erosion surface and its correlating sedimentary plains we identify the deformation processes which occurred on this surface after its formation

new views on old carbon in the amazon river insight from the source of organic carbon eroded from the peruvian andes 1 mountain rivers play a key role in the delivery of particulate organic carbon poc to large river systems and the ocean due to the extent of its drainage area and runoff the amazon river is one of earth s most important biogeochemical systems however the source of poc eroded from the humid region of the eastern andes and the input of fossil poc from sedimentary rocks pocfossil remains poorly constrained here we collected suspended sediments from the kosnipata river during flood events to better characterize andean poc measuring the nitrogen to organic carbon ratio n c stable carbon isotopes 13corg and radiocarbon 14corg 14corg values ranged from 711 to 15 and significant linear trends between 14corg n c and 13corg suggested that this reflects the mixing of pocfossil with very young organic matter 14corg 50 from the terrestrial biosphere pocnon fossil using n c and 14corg in an end member mixing analysis we quantify the fraction of pocfossil to within 0 1 and find that it contributes a constant proportion of the suspended sediment mass 0 37 0 03 and up to 80 of total poc in contrast the relative contribution of pocnon fossil was variable being most important during the rising limb and peak discharges of flood events the new data shed light on published measurements of old poc low 14corg in andean fed tributaries of the amazon river with their 14corg and 13corg values consistent with variable addition of pocfossil the findings suggest a greater persistence of andean poc in the lowland amazon than previously recognized

δ18o and δd of streamwaters across the himalaya and tibetan plateau implications for moisture sources and paleoelevation reconstructions abstract this study presents new 18o and d data from 191 streams across the himalaya and tibetan plateau to better constrain the spatial variability of stable isotopes in modern precipitation over this region moisture penetrating into the southeastern tibetan plateau is predominantly derived from monsoonal airmasses originating from the bay of bengal and transported into the eastern himalayan syntaxis along the brahmaputra river progressive rainout during orographic lifting and cooling results in clear relationships between 18o and d and catchment hypsometric elevation on the plateau margin however monsoonal derived moisture is progressively mixed with central asian airmasses in more western and northern parts of the tibetan plateau as a result predicted isotope elevation relationships that are based on empirical lapse rates or thermodynamic models of the isotopic evolution of an airmass produce large 1 3 km misfits between measured and predicted catchment elevations for much of the tibetan plateau including some areas directly north of the central himalayan crest this suggests that changes in the 18o or d of paleoprecipitation on the central and southwestern tibetan plateau may reflect surface uplift along moisture transport pathways or changes in the penetration of monsoonally derived moisture rather than regional surface uplift histories

influence of cohesion on the incipient motion condition of sediment mixtures 1 previous investigations on initiation of motion and erosion of cohesive sediment mixtures have not included gravel within the mixtures experimental results on the incipient motion characteristics of cohesive sediment mixtures containing gravel are presented in this paper the sediment used consisted of fine gravel mixed with clay in proportions varying from 10 to 50 by weight and fine gravel with fine sand mixed in equal proportion with clay proportions again varying from 10 to 50 by weight the stages of the incipient condition of motion were visually identified three modes of initiation of motion of cohesive sediment mixtures were noticed namely pothole erosion line erosion and mass erosion the modes of initiation of motion changed mainly with clay percentages in the mixture its antecedent moisture characteristics and the applied shear stress analysis of the experimental data from the present study and the literature revealed that depending upon the flow and sediment characteristics the critical shear stress of the incipient motion condition in cohesive sediment mixtures can be up to 50 times larger than the critical shear stress of cohesionless sediments having similar arithmetic mean size as the cohesive sediments on the basis of dimensional considerations a relationship is proposed for the determination of critical shear stress of the incipient motion condition in cohesive sediment mixtures also containing gravel the variables namely clay percentage void ratio and unconfined compressive strength of the sediment bed are noticed to be the main parameters controlling the incipient motion condition of the cohesive sediments in the absence of cohesion the proposed relationship reduces to the critical shear stress for the incipient motion condition of the cohesionless sediment mixture having the same arithmetic mean size the condition for the threshold of erosion of cohesive sediment mixtures by the flow is thus parameterized in the present study