applications of organic geochemistry to paleolimnological reconstructions a summary of examples from the laurentian great lakes the organic matter content of lake sediments contains information that helps to reconstruct past environmental conditions evaluate histories of climate change and assess impacts of humans on local ecosystems the elemental isotopic and molecular compositions of organic matter buried in sediment provide evidence of the biota that have lived in a lake and its catchment area and they serve as proxies of organic matter delivery and accumulation sedimentary records from the north american great lakes provide examples of applications of organic geochemistry to paleolimnological reconstructions the records of these lakes date from retreat of the laurentide ice sheet around 12 ka include the mid holocene hypsithermal and show consequences of recent human changes low corg ntotal ratios indicate that most of the sediment organic matter in the great lakes is from algal production yet changes in biomarker molecule compositions also show that varying amounts of land plant organic matter have been delivered to the lakes elevated algal productivity that accompanies nutrient enrichments of lake waters is recorded as excursions to less negative 13c values in the organic matter of sediments that were deposited in the 1960s and 1970s increased organic carbon mass accumulation rates mirror the isotopic excursions in most parts of the great lakes accumulations of petroleum residues and pyrogenic polycyclic aromatic hydrocarbons in sediments identify fluvial and eolian delivery of organic matter components to different parts of the great lakes emerging applications of multiple and novel organic geochemical proxies to paleolimnological reconstructions are promising yet some potentially important measurements remain underutilized

temporally and spatially uniform rates of erosion in the southern appalachian great smoky mountains we measured 1 0 be in fluvial sediment samples n 27 from eight great smoky mountain drainages 1 330 km 2 results suggest spatially homogeneous sediment generation on the 10 4 10 5 yr time scale and 100 km 2 spatial scale at 73 11 t km 2 yr 1 equivalent to 27 4 m m y of bedrock erosion this rate is consistent with rates derived from fission track long term sediment budget and sediment yield data all of which indicate that the great smoky mountains and the southern appalachians eroded during the mesozoic and cenozoic at 30 m m y in contrast unroofing rates during the paleozoic orogenic events that formed the appalachian mountains were higher 10 2 m m y erosion rates decreased after termination of tectonically driven uplift enabling the survival of this ancient mountain belt with its deep crustal root as an isostatically maintained feature in the contemporary landscape

development and refinement of proxy climate indicators from peats peat especially from acidic mires bogs is a natural archive of past environmental change reconstructions of past climate from bogs commenced in the 19th century through examination of visible peat stratigraphy and later formed the basis for a postglacial climatic scheme widely used in northwest europe nevertheless misconceptions as to how bogs grow led to a 50 year lacuna in peat climate study before the concept of cyclic regeneration in bogs was refuted in recent decades research using proxy climate indicators from bogs has burgeoned a range of proxies for past hydrological change has been developed as well as use of pollen bog oaks and pines and other data to reconstruct past temperatures most of this proxy climate research has been carried out in northern europe but peat based research in parts of asia and north america has increased particularly during the last decade while research has also been conducted in australia new zealand and south america this paper reviews developments in proxy climate reconstructions from peatlands chronicles use of a range of palaeo proxies such as visible peat stratigraphy plant macrofossils peat humification testate amoebae and non pollen palynomorphs and explains the use of wiggle match radiocarbon dating and relationship to climate shifts it details other techniques being used increasingly such as biomarkers stable isotopes inorganic geochemistry and estimation of dust flux and points to new proxies under development although explicit protocols have been developed recently for research on ombrotrophic mires it must be recognised that not all proxies and techniques have universal applicability owing to differences in species assemblages mire formation topographic controls and geochemical characteristics

compilation of non annually resolved holocene proxy climate records stacked holocene peatland palaeo water table reconstructions from northern britain abstract the number and range of holocene palaeoclimate reconstructions from various regions of the world have increased dramatically over the last decade the data density for many regions and proxies now offers the potential of robust regional scale reconstructions that avoid the problems of records from individual sites and improve communication between palaeoclimate subdisciplines and climate modellers however there are problems with chronological uncertainties and quantification of proxies which make compilation of multiple records difficult here we explore a stacking and tuning approach to the derivation of regional records from peatland climate proxies to test its applicability to non annually resolved terrestrial records twelve individual records from northern britain based on water table reconstructions from testate amoebae analysis were divided into four regions records were detrended normalised and compared within regions to identify clear correlative events the original chronologies of the records were tuned using both these events and independent age markers the stacked record for northern britain indicates pronounced changes to wet conditions at 3600 2760 and 1600 cal yr bp with more minor changes at 3060 2050 1260 860 550 and 260 cal yr bp the main wet phases are highly correlated with mid european lake highstands wider north atlantic climate change inferred from ocean and ice core records and solar variability tuning and stacking of non annual terrestrial palaeoclimate records is a new approach to the compilation and reconciliation of individual records within coherent climatic regions and provides a tool for upscaling of palaeoclimate records for climate model data comparisons

the prospectivity of a potential shale gas play an example from the southern pennine basin central england uk during the serpukhovian late mississippian stage the pennine basin now underlying much of northern england consisted of a series of interlinked sub basins that developed in response to the crustal extension north of the hercynic orogenic zone for the current study mudstone samples of the morridge formation from two sub basins located in the south eastern part of the pennine basin were collected from the carsington dam reconstruction c3 borehole widmerpool gulf sub basin and the karenight 1 borehole edale gulf sub basin detailed palynological analyses indicate that aside from the dominant often 90 or more heterogeneous amorphous organic matter aom variable abundances of homogeneous aom and phytoclasts are present to complement the palynological dataset a suite of geochemical and mineralogical techniques were applied to evaluate the prospectivity of these potentially important source rocks changes in the carbon isotope composition of the bulk organic fraction 13com suggest that the lower part biozone e2a of carsington dr c3 is markedly more influenced by terrigenous kerogen than the upper part of the core biozones e2a3 e2b1 the karenight 1 core yielded more marine kerogen in the lower part marine bands e1 e2b than the upper part marine band e2b present day rock eval total organic carbon tocpd surpasses 2 in most samples from both cores a proportion suggested by jarvie 2012 that defines prospective shale gas reservoirs however when the pyrolysable component that reflects the generative kerogen fraction is considered very few samples reach this threshold the kerogen typing permits for the first time the calculation of an original hydrogen index hio and original total organic carbon toco for carboniferous mudstones of the pennine basin the most prospective part of carsington dam reconstruction c3 marine bands e2b1 e2a3 has an average toco of 3 2 and an average hio of 465 mg g toco the most prospective part of karenight 1 242 80 251 89 m is characterized by an average toco of 9 3 and an average hio of 504 mg g toco lastly x ray diffraction xrd analysis confirms that the siliceous to argillaceous mudstones contain a highly variable carbonate content the palynological geochemical and mineralogical proxies combined indicate that marine sediments were continuously being deposited throughout the sampled intervals and were punctuated by episodic turbiditic events the terrestrial material originating from the wales brabant high to the south of the pennine basin was principally deposited in the widmerpool gulf with much less terrigenous organic matter reaching the edale gulf as a consequence the prospective intervals are relatively thin decimetre to meter scale and further high resolution characterization of these intervals is required to understand variability in prospectivitiy over these limited intervals

using rock eval 6 pyrolysis for tracking fossil organic carbon in modern environments implications for the roles of erosion and weathering this work relates to the debate on the fossil organic carbon foc input in modern environments and its possible implication for the carbon cycle and suggests the use of rock eval 6 pyrolysis as a relevant tool for tracking foc in such environments considering that such a delivery is mainly due to supergene processes affecting the continental surface we studied organic matter in different reservoirs such as bedrocks alterites soils and rivers in two experimental catchments at draix alpes de haute provence france samples were subjected to geochemical rock eval 6 pyrolysis investigations and artificial bacterial degradations after comparing the geochemical fingerprint of samples geochemical markers of foc were defined and tracked in the different reservoirs our results confirm the contribution of foc in modern soils and rivers and display the various influences of weathering and erosional processes on the fate of foc during its exchange between these pools in addition the contrasting behaviour of these markers upon the supergene processes has also highlighted the refractory or labile characters of the fossil organic matter fom bedrock to river fluxes controlled by gully erosion are characterized by a qualitative and quantitative preservation of fom bedrock to alterite fluxes governed by chemical weathering are characterized by foc mineralization without qualitative changes in deeper alterites alterite to soils fluxes controlled by bio chemical weathering are characterized by strong foc mineralization and qualitative changes of fom thus weathering and erosional processes induce different fom evolution and affect the fate of foc towards the global carbon cycle in this study gully erosion would involve maintenance of an ancient sink for the global carbon cycle while bio chemical processes provide a source of co2 finally this study suggests that rock eval 6 pyrolysis can be considered as a relevant tool for tracking foc in modern environments copyright 2006 john wiley sons ltd

using chemical tracers in hillslope soils to estimate the importance of chemical denudation under conditions of downslope sediment transport 1 we present a model of hillslope soils that couples the evolution of topography soil thickness and the concentration of constituent soil phases defined as unique components of the soil with collective mass equal to the total soil mass the model includes both sediment transport and chemical denudation a simplified two phase model is developed the two phases are a chemically immobile phase which has far lower solubility than the bulk soil and is not removed through chemical weathering for example zircon grains and a chemically mobile phase that may be removed from the system through chemical weathering chemical denudation rates in hillslope soils can be measured using the concentration of immobile elements but the enrichment of these immobile elements is influenced by spatial variations in chemical denudation rates and spatial variations in the chemical composition of a soil s parent material these considerations cloud the use of elemental depletion factors and cosmogenic nuclide based total denudation rates used to identify the relationship between physical erosion and chemical weathering if these techniques do not account for downslope sediment transport on hillslopes where chemical denudation rates vary in space estimates of chemical denudation using techniques that do not account for downslope sediment transport and spatial variations in chemical denudation rates may be adequate where the chemical denudation rate is a significant fraction of the total denudation rate but are inadequate in regions where chemical weathering rates are small compared to the total denudation rate we also examine relationships between transient mechanical and chemical denudation rates soil particle residence times may affect chemical weathering rates and the relationship between total landscape lowering rates and soil particle residence times can thus be quantified

estimates of the rate of regolith production using and from an alpine hillslope abstract the production of regolith is a fundamental geomorphic process because most surface processes transport only unconsolidated material we use concentrations of the cosmogenic radionuclides crns 10 be and 26 al in regolith and bedrock to deduce the rate of production of regolith on an alpine hillslope in the wind river range wy these calculations are based on a theoretical model which we develop here this model shows that it is important to consider dissolution of regolith in regolith production and in basin averaged erosion rate studies rates of production of regolith are uniform along the hillslope and the mean rates for the entire hillslope deduced from 10 be and 26 al are 14 3 4 0 and 13 0 4 0 m ma 1 respectively rates of production of regolith deduced from 10 be concentrations in regolith mantled bedrock support the rates deduced from regolith concentrations in the alpine environment examined here the rate of production of regolith beneath 90 cm of regolith is nearly twice as fast as the average rate of production of regolith on bare rock surfaces which small et al small e e anderson r s repka j l finkel r 1997 erosion rates of alpine bedrock summit surfaces deduced from in situ 10 be and 26 al earth and planetary science letters 150 413 425 previously documented rock mantled with regolith probably weathers more rapidly than bare rock because the water required for frost weathering is limited on bare rock surfaces because the hillslope examined here is convex with constant curvature and regolith production and thickness are uniform down the slope the regolith volume flux must be proportional to the local slope of the hillside therefore our results are consistent with gilbert s gilbert g k 1909 the convexity of hilltops journal of geology 17 344 350 steady state hillslope hypothesis if tor height and the difference between rates of weathering on bare and regolith mantled rock provide a fair estimate of the age of summit flats steady state hillslope conditions have been attained in less than several million years

influence of landscape position and vegetation on long term weathering rates at the hubbard brook experimental forest new hampshire usa the spatial variability of long term chemical weathering in a small watershed was examined to determine the effect of landscape position and vegetation we sampled soils from forty five soil pits within an 11 8 hectare watershed at the hubbard brook experimental forest new hampshire the soil parent material is a relatively homogeneous glacial till deposited 14 000 years ago and is derived predominantly from granodiorite and pelitic schist conifers are abundant in the upper third of the watershed while the remaining portion is dominated by hardwoods the average long term chemical weathering rate in the watershed calculated by the loss of base cations integrated over the soil profile is 35 meq m 2 yr 1 similar to rates in other 10 to 15 ka old soils developed on granitic till in temperate climates the present day loss of base cations from the watershed calculated by watershed mass balance exceeds the long term weathering rate suggesting that the pool of exchangeable base cations in the soil is being diminished despite the homogeneity of the soil parent material in the watershed long term weathering rates decrease by a factor of two over a 260 m decrease in elevation estimated weathering rates of plagioclase potassium feldspar and apatite are greater in the upper part of the watershed where conifers are abundant and glacial till is thin the intra watershed variability across this small area demonstrates the need for extensive sampling to obtain accurate watershed wide estimates of long term weathering rates

quantification of soil production and downslope creep rates from cosmogenic 10be accumulations on a hillslope profile average soil transport rates over a period of 3500 yr on a convex soil mantled hillslope have been quantified using a mass balance model that incorporates the soil concentration of the cosmogenic isotope 10 be the 10 be model results support the assumption used in most geomorphic models that the soil creep rate is proportional to surface gradient the predicted diffusion coefficient is 360 55 cm 3 yr 1 cm 1 contour length and the average rate of soil production is 0 026 0 007 cm yr within the uncertainty of this technique the data do not reject g k gilbert9s hypothesis that some hillslopes may exist in a condition of dynamic equilibrium with a uniform soil production rate however the model does not require an assumption of dynamic equilibrium and may be an approach that uniquely allows the quantification of a local soil production rate law

the global average production rate of10be precipitation collected in continuously open containers for about a year at seven sites around the united states was analyzed for10be 90sr 210pb and238u based on these data and long term precipitation 90sr and210pb delivery patterns the stratospheric tropospheric and recycled10be components in the collections were estimated and the global10be production rate was assessed single station production rate estimates range from 0 52 106 atoms cm 2 yr 1 to 2 64 106 atoms cm 2 yr 1 the mean value is 1 21 106 atoms cm 2 yr 1 with a standard error of 0 26 106 atoms cm 2 yr 1

tracing hillslope sediment production and transport with in situ and meteoric 10be 1 we use in situ produced and meteoric 10be analyzed in soils from 28 pits on four hillcrest parallel transects along a 14 hillslope in the great smoky mountains north carolina as tracers of soil production and transport we rely upon amalgamation both to investigate and smooth spatial variability in 10be concentrations lidar indicates that the hillslope is topographically complex and that soil is moved downslope diffusively until it encounters the ephemeral channel network and is rapidly exported in situ produced 10be measured in depth profiles indicates that over millennial timescales soils are mixed above the soil saprolite boundary in contrast meteoric 10be concentrations increase with depth and are correlated to concurrent increases of dithionite extractable al and ph observations explained by similar al and be mobility in the soil the concentrations of both meteoric and in situ produced 10be increase downslope proportional to the maximum soil particle path length the data suggest virtual downslope soil velocities of 1 1 1 7 cm yr 1 in a well mixed active transport layer 60 cm thick the thickness of this transport layer is constant downslope and depends on the rooting depth and consequent root wad thickness of downed trees on the slope both of which reflect depth to the soil saprolite boundary both meteoric and in situ produced 10be suggest that soil production is balanced by surface denudation at rates between 10 and 13 m myr 1 soil residence times on the slope range from 21 to 33 kyr based on the meteoric 10be inventories major element geochemical analysis suggests little if any elemental loss during soil transport downslope

on steady states in mountain belts the dynamic system of tectonics and erosion contains important feedback mechanisms such that orogenic systems tend toward a steady state this concept is often invoked but the nature of the steady state is commonly not specified we identify four types of steady state that characterize the orogenic system and illustrate these cases by using numerical model results and natural examples these types are 1 flux steady state 2 topographic steady state 3 thermal steady state and 4 exhumational steady state they refer to the erosional flux the topography the subsurface temperature field and the spatial pattern of cooling ages respectively models suggest that the topography will reach a steady mean form at the scale of an orogenic belt but perfect topographic steady state is unlikely to be achieved at shorter length scales thermal steady state is a precondition for exhumational steady state and in the case of temperature dependent deformation topographic steady state exhumational steady state is characterized by reset age zones spatially nested according to closure temperature as illustrated in natural systems from new zealand the cascadia accretionary margin and taiwan

river response to rapid holocene environmental change evidence and explanation in british catchments macklin m g jones a f lewin j 2010 river response to rapid holocene environmental change evidence and explanation in british catchments quaternary science reviews 29 13 14 1555 1576 sponsorship welsh assembly government and the higher education funding council for wales for funding this study through its support of the centre for catchment and coastal research at aberystwyth university

modern foraminifera δ13c and bulk geochemistry of central oregon tidal marshes and their application in paleoseismology we assessed the utility of 13c and bulk geochemistry total organic content and c n to reconstruct relative sea level changes on the cascadia subduction zone through comparison with an established sea level indicator benthic foraminifera four modern transects collected from three tidal environments at siletz bay oregon usa produced three elevation dependent groups in both the foraminiferal and 13c bulk geochemistry datasets foraminiferal samples from the tidal flat and low marsh are identified by miliammina fusca abundances of 45 middle and high marsh by m fusca abundances of 25 the 13c values from the groups defined with 13c bulk geochemistry analyses decrease with an increasing elevation 24 1 1 7 in the tidal flat and low marsh 27 3 1 4 in the middle and high marsh and 29 6 0 8 in the highest marsh samples we applied the modern foraminiferal and 13c distributions to a core that contained a stratigraphic contact marking the great cascadia earthquake of ad 1700 both techniques gave similar values for coseismic subsidence across the contact 0 88 0 39 m and 0 71 0 56 m suggesting that 13c has potential for identifying amounts of relative sea level change due to tectonics

aluminum speciation and equilibria in soil solutions of a haplorthod in the adirondack mountains new york u s a abstract aluminum chemistry was evaluated in throughfall and leachates from o e and b horizons of a spodosol typic haplorthod at hardwood and conifer sites in the adirondack mountains new york organic and fluoride complexes were the dominant forms of aluminum in all soil solutions and throughfall whereas sulfate and hydroxide complexes were less prevalent aquo aluminum concentrations were extremely low in o horizon leachates 6 and 7 of total inorganic aluminum at conifer and hardwood sites respectively and increased to 28 and 26 of total inorganic aluminum in solutions from b horizons at conifer and hardwood sites respectively acid soluble aluminum was 51 and 54 of total aluminum in o horizon leachates at the conifer and hardwood sites respectively and 88 of total aluminum in throughfall like aqueous aluminum soil bound aluminum was largely associated with organic matter solutions were generally undersaturated with respect to the solubility of aluminum sulfate and aluminum hydroxide mineral phases elevated concentrations of organic and non labile aluminum in forest floor solutions suggest that biocycling by vegetation may be an important mechanism of aluminum transport in forest ecosystems

erosional equilibrium and disequilibrium in the sierra nevada inferred from cosmogenic 26al and 10be in alluvial sediment we used cosmogenic 26 al and 10 be in stream sediment to measure landscape scale erosion rates for topographically diverse catchments at seven sierra nevada sites at three sites erosion rates and hillslope gradients are strongly correlated increasing with proximity to fault scarps and river canyons which appear to have accelerated local base level lowering rates and thus increased catchment erosion rates by up to 15 fold at four other sites far from fault scarps and river canyons erosion rates are much more uniform and less sensitive to average hillslope gradient our measurements show that contrasts in landscape erosion rates cannot be inferred from hillslope gradients alone because landscapes can evolve toward a state of erosional equilibrium in which steep and gentle slopes erode at similar rates

tracking sedimentation from the historic a d 2011 mississippi river flood in the deltaic wetlands of louisiana usa management and restoration of the mississippi river deltaic plain southern united states and associated wetlands require a quantitative understanding of sediment delivery during large flood events past and present here we investigate the sedimentary fingerprint of the 2011 mississippi river flood across the louisiana coast atchafalaya delta terrebonne barataria and mississippi river delta basins to assess spatial patterns of sedimentation and to identify key indicators of sediment provenance the sediment deposited in wetlands during the 2011 flood was distinguished from earlier deposits based on biological characteristics primarily absence of plant roots and increased presence of centric planktonic diatoms indicative of riverine origin by comparison the lithological bulk density organic matter content and grain size and chemical stable carbon isotopes of bulk organic matter properties of flood sediments were nearly identical to the underlying deposit flood sediment deposition was greatest in wetlands near the atchafalaya and mississippi rivers and accounted for a substantial portion 37 to 85 of the annual accretion measured at nearby monitoring stations the amount of sediment delivered to those basins 1 1 1 6 g cm 2 was comparable to that reported previously for hurricane sedimentation along the louisiana coast 0 8 2 1 g cm 2 our findings not only provide insight into how large scale river floods influence wetland sedimentation they lay the groundwork for identifying previous flood events in the stratigraphic record

the initiation and growth of gullies in madagascar are humans to blame abstract lavaka madagascar s unusual gullies require thick lateritic regolith on smoothly convex hills and they are initiated locally by a variety of cultural and natural proximate causes such as paths roads defensive trenches around hillforts steep fields unchanneled to slightly concentrated storm run off springs mass movements etc growth continues by rain attack incision by run off earthfalls caused by wetting and drying cycles and especially basal sapping by diffuse groundwater flow above bedrock somewhat in that order lavaka are less directly permitted and promoted by 1 hardening of exposed laterite surfaces which creates a hard soft hard profile from bedrock to laterite which favors incision relative to lateral erosion 2 the superimposition of concave run off profiles onto convex hills and locally 3 re equilibration of watersheds after stream piracy and faulting run off and hardening are interrelated with devegetation because hardening results from exposure following devegetation because both hardening and devegetation increase run off relative to infiltration and because hardening rain attack and run off impede vegetation devegetation is certainly worsened by harmful human activities such as range burning forest cutting and or overgrazing but tectonism and natural climatic aridification are probably ultimately more important given that many lavaka are simply a natural part of the landscape s evolution and that some lavaka clearly predate primary uncut rain forest

organic carbon sources and transformations in mangrove sediments a rock eval pyrolysis approach abstract a rock eval pyrolysis study was carried out on sedimentary cores and leaf and woody tissue of vascular plant species from the mangroves of french guiana these forests develop on moving mudbanks and have a lifetime limited to few decades before being eroded our main purpose was to complete the understanding of carbon cycling in this specific environment using a method that allows monitoring the depth evolution of sources and transformation of organic matter om within a tight depth span leaf and woody tissue showed clearly distinct rock eval parameters however these parameters strongly varied with om decomposition rapidly limiting their efficiency as mangrove plant tracers the decrease in values of tps2 pyrolysis temperature corresponding to the maximum release of hydrocarbons with depth clearly showed a line between a pedogenetic layer enriched in autochthonous om and marine sediments enriched in allochthonous om this allochthonous om originated from the particulate discharge of the amazon river which is partly deflected northwestwards by the current of the guianas within the soil layer decay processes induced a strong dehydrogenation and slight oxidation of om the two processes occurring simultaneously the deeper layers were characterized by a very strong increase in oico2 quantity of pyrolysed co2 relative to total organic carbon beneath both the young and the senescent forests this trend resulted rather from an increasing content of authigenic carbonate than from increasing concentration of oxidized allochthonous debris carbonate can form as a result of the more anoxic conditions prevailing in buried layers vs the upper suboxic ones beneath the senescent mangrove a greater increase in oico2 probably reflected greater carbonate precipitation resulting from the decomposition of higher amounts of om

how well can hillslope evolution models explain topography simulating soil transport and production with high resolution topographic data the morphology of hillslopes is a direct refl ection of tectonic forcing and climatic and biologic processes that drive soil production mobilization and transport soil transport on hillslopes affects river incision by providing tools for channel abrasion and controls the distribution of sediment that infl uences aquatic habitat although numerous hillslope transport relationships have been proposed over the past 60 years a comprehensive analysis of model predictions for a real landscape has not been performed here we use high resolution topographic data obtained via airborne laser swath mapping alsm to simulate the long term evolution of oregon coast range hillslopes and test three published transport models and a new model that accounts for nonlinear depth and slopedependent transport analysis of one dimensional steady state solutions for these four models suggests that plots of gradient curvature may be diagnostic for distinguishing model predictions to evaluate two dimensional model predictions for our fi eld site we assumed local steady state erosion for a 72 000 m 2 sequence of hillslopes and valleys after calibrating each of the four models we imposed constant base level lowering for cells within the valley network simulated 500 000 yr of soil production and transport and determined which transport model best preserved morphologic patterns that describe the current landscape form models for which fl ux varies proportionally with hillslope gradient generated broadly convex hilltops inconsistent with the sharp crested steep sided slopes of our study site whereas the two nonlinear slope dependent models produced convex planar slopes consistent with current hillslope form our proposed nonlinear slope and depth dependent model accounts for how soil thickness controls the magnitude of biogenic disturbances that drive transport this model best preserved the current landscape form particularly the narrow sharply convex hilltops characteristic of the oregon coast range according to our formulation which provides an explicit linkage for relating the distribution of biota to hillslope processes the degree of hilltop convexity varies nonlinearly with the ratio of erosion rate to maximum soil production rate highlighting the profound infl uence of soil depth on hillslope evolution

derivation of lowland riparian wetland deposit architecture using geophysical image analysis and interface detection for groundwater surface water interactions to be understood in complex wetland settings the architecture of the underlying deposits requires investigation at a spatial resolution sufficient to characterize significant hydraulic pathways discrete intrusive sampling using conventional approaches provides insufficient sample density and can be difficult to deploy on soft ground here a noninvasive geophysical imaging approach combining three dimensional electrical resistivity tomography ert and the novel application of gradient and isosurface based edge detectors is considered as a means of illuminating wetland deposit architecture the performance of three edge detectors were compared and evaluated against ground truth data using a lowland riparian wetland demonstration site isosurface based methods correlated well with intrusive data and were useful for defining the geometries of key geological interfaces i e peat gravels and gravels chalk the use of gradient detectors approach was unsuccessful indicating that the assumption that the steepest resistivity gradient coincides with the associated geological interface can be incorrect these findings are relevant to the application of this approach in settings with a broadly layered geology with strata of contrasting resistivities in addition ert revealed substantial structures in the gravels related to the depositional environment i e braided fluvial system and a complex distribution of low permeability putty chalk at the bedrock surface with implications for preferential flow and variable exchange between river and groundwater systems these results demonstrate that a combined approach using ert and edge detectors can provide valuable information to support targeted monitoring and inform hydrological modeling of wetlands

revealing the temporal dynamics of subsurface temperature in a wetland using time lapse geophysics summary there is growing recognition of the need to understand the subsurface hydrological mechanisms within wetlands given their potentially significant role in the hydrological and biogeochemical function of catchments as well as their effects on the wetland habitat itself conventional subsurface hydrological sampling and monitoring techniques are often limited in such environments because of the invasive nature of such approaches and the sensitivity of the environment in this study we use ground penetrating radar gpr and electrical resistivity tomography ert to characterise the stratigraphy at a small riparian wetland site then through time lapse ert measurements over a 12 month period we demonstrate how changes in resistivity may provide additional value about localised recharge we compare direct measurements of water table depth and pore fluid electrical conductivity and temperature with subsurface resistivity derived from the ert measurements and reveal that temporal fluctuations in temperature of the subsurface dominates the change in resistivity over the monitored period from this we use the ert images of resistivity to estimate spatio temporal changes in subsurface temperature and thus infer localised zones of groundwater recharge due to suppressed seasonal variation in temperature although we focus here on one 2 d vertical profile through the wetland the results highlight the potential value of non invasive time lapse geoelectrical surveys for mapping 3 d thermal patterns within a wetland environment

erosion of an ancient mountain range the great smoky mountains north carolina and tennessee analysis of 10be and 26al in bedrock n 10 colluvium n 5 including grain size splits and alluvial sediments n 59 including grain size splits coupled with field observations and gis analysis suggest that erosion rates in the great smoky mountains are controlled by subsurface bedrock erosion and diffusive slope processes the results indicate rapid alluvial transport minimal alluvial storage and suggest that most of the cosmogenic nuclide inventory in sediments is accumulated while they are eroding from bedrock and traveling down hill slopes spatially homogeneous erosion rates of 25 30 mm ky 1 are calculated throughout the great smoky mountains using measured concentrations of cosmogenic 10be and 26al in quartz separated from alluvial sediment 10be and 26al concentrations in sediments collected from headwater tributaries that have no upstream samples n 18 are consistent with an average erosion rate of 28 8 mm ky 1 similar to that of the outlet rivers n 16 24 6 mm ky 1 which carry most of the sediment out of the mountain range grain size specific analysis of 6 alluvial sediment samples shows higher nuclide concentrations in smaller grain sizes than in larger ones the difference in concentrations arises from the large elevation distribution of the source of the smaller grains compared with the narrow and relatively low source elevation of the large grains large sandstone clasts disaggregate into sand size grains rapidly during weathering and downslope transport thus only clasts from the lower parts of slopes reach the streams 26al 10be ratios do not suggest significant burial periods for our samples however alluvial samples have lower 26al 10be ratios than bedrock and colluvial samples a trend consistent with a longer integrated cosmic ray exposure history that includes periods of burial during down slope transport the results confirm some of the basic ideas embedded in davis geographic cycle model such as the reduction of relief through slope processes and of hack s dynamic equilibrium model such as the similarity of erosion rates across different lithologies comparing cosmogenic nuclide data with other measured and calculated erosion rates for the appalachians we conclude that rates of erosion integrated over varying time periods from decades to a hundred million years are similar the result of equilibrium between erosion and isostatic uplift in the southern appalachian mountains

fluvio pedogenic processes in an ephemeral stream channel nahal yael southern negev israel abstract a detailed stratigraphic survey conducted in the alluvial fill of the channel of nahal yael a small catchment in the southern negev desert indicates the existence of a continuous compacted red colored unit at an average depth of 50 cm beneath the surficial grey non cohesive alluvium granulometric distinction between the grey and the red alluvium is evident only within the fine

10be analysis of a quaternary weathering profile in the virginia piedmont samples from a residual weathering profile in the virginia piedmont have been analyzed for cosmogenic 10be concentrations are highest in clay rich soil and decrease exponentially to a depth of about 15 m despite uncertainties about the processes by which 10be may be intercepted before entering the solum and eroded after incorporation a minimum age may be calculated for the regolith this calculation is based on the delivery rate of 10be and its decay rate and suggests that this residual profile developed during a period no shorter than 8 105 yr the calculated minimum age may be within a factor of 2 of maximum age estimates based on surface lowering by erosion and on the rate of rock weathering to saprolite the vertical distribution of 10be in the profile could result from a steady state balance of deposition weathering radioactive decay and erosion

modelling the effects of climate change and its uncertainty on uk chalk groundwater resources from an ensemble of global climate model projections projections of climate for the 2080s from an ensemble of global climate models gcms run under a medium high a2 emissions scenario are used to simulate changes in groundwater resources of a chalk aquifer in central southern england few studies that have investigated the impacts of climate change on groundwater resources have addressed uncertainty in this paper the uncertainty associated with use of a suite of gcm outputs in catchment scale impact studies is quantified a range of predictions is obtained by applying precipitation and temperature change factors derived from thirteen gcms to a distributed recharge model and a groundwater flow model of the chalk aquifer of the marlborough and berkshire downs and south west chilterns in the uk the ensemble average suggests there will be a 4 9 reduction in annual potential groundwater recharge across the study area although this is not statistically significant at the 95 confidence level the spread of results for simulated changes in annual potential groundwater recharge range from a 26 decrease to a 31 increase by the 2080s with ten predicting a decrease and three an increase whilst annual recharge is not found to change significantly the multi model results suggest that the seasonal variation in the groundwater resource will be greater with higher recharge rates during a reduced period of time in winter the spread of predictions for changes in river baseflow at the bottom of the largest river sub catchment is from 16 to 33 in march and from 68 to 56 in october the effects of climate change are shown to depend significantly on the type of land use it is concluded that further research is required to quantify the effect of different vegetation types on chalk covered by different thicknesses of soil and their response to a changing climate

cosmogenic nuclides topography and the spatial variation of soil depth abstract if the rate of bedrock conversion to a mobile layer of soil depends on the local thickness of soil then hillslopes on uniform bedrock in a landscape approaching dynamic equilibrium should be mantled by a uniform thickness of soil conversely if the depth of soil varies across an actively eroding landscape then rates of soil production will also vary and consequently the landscape will not be in morphologic equilibrium the slow evolution of hillslopes relative to the tempo of climatic variations and tectonic adjustments would suggest that local morphologic disequilibrium may be expected in many landscapes here we explore this issue of equilibrium landscapes through a previously developed model that predicts the spatial variation in thickness of soil as a consequence of the local balance between soil production and erosion first we confirm the assumption in the model that soil production varies inversely with the thickness of soil using two independent methods one method uses the theoretical prediction that at local steady state soil production equals removal the depth of soil should vary inversely with hillslope curvature the second method relies on direct measurements of in situ produced concentrations of cosmogenic 10 be and 26 al in bedrock at the base of the soil column for our study site in northern california the two methods agree and yield the expression that the rate of soil production declines exponentially with the thickness of soil from 0 077 mm year with no soil mantle to 0 0077 mm year under 1 m of soil we then use this function of soil production in a coupled production and diffusive model of sediment transport to explore the controls on the spatial variation of the depth of soil on four separate spur ridges noses where we measured the data for the function of soil production model predictions are sensitive to boundary conditions grid scale and run time nonetheless we found good agreement between predicted and observed depths of soil as long as we used the observed function of soil production the four noses each have spatially varying curvature and consequently have varying depths of soil implying morphologic disequilibrium we suggest that our study site has been subjected to a wave of incision and varying intensities of erosion because of tectonic and climatic oscillations that have a frequency shorter than the morphologic response time of the landscape

integration of geochemical mass balance with sediment transport to calculate rates of soil chemical weathering and transport on hillslopes 1 we developed a process oriented hillslope soil mass balance model that integrates chemical and physical processes within hillslope soils the model explicitly factors that soil chemical weathering at any hillslope position is related to the flux of soil eroded from upslope as well as soil production from underlying bedrock the model was merged with measurements of soil elemental chemistry and cosmogenic radionuclide based saprolite to soil conversion rates along a 50 m transect of a semiarid granodiorite hillslope in the southeastern australian highlands inverse modeling results in the simultaneous quantification of the rates of soil chemical weathering and soil transport as a function of hillslope position soil chemical weathering rates per land surface area systematically varied along the transect from losses of 0 035 kg m 2 yr 1 on the ridge to gains of 0 035 kg m 2 yr 1 at the lowest slope position the mass loss via soil chemical weathering would have been overestimated by 40 if the impact of soil transport on soil chemistry was ignored the chemical mobility of elements combined with biological nutrient demand controlled the spatial redistribution of individual elements p and ca were preferentially retained relative to si al and fe within the hillslope base the calculated soil transport rate is linearly related to the product of soil thickness and slope gradient instead of slope alone soil residence time was determined by calculating the time length for a 3 dimensional box volume 1 m2 surface area soil thickness to be entirely removed by mass flux of soil transport 4 ka on the ridge to 0 9 ka at the hillslope base these soil residence times combined with soil chemical weathering rates indicate that a 1 m2 area of soil loses 1 800 kg via chemical weathering while passing through the upslope portion of the hillslope but that it regains 90 kg probably via clay precipitation and biological retention of cations during its passage through the lower segments of the transect this study provides a previously unrecognized linkage between physical soil transport and soil chemical weathering that have implications for hillslope evolution as well as biogeochemistry

a mississippian black shale record of redox oscillation in the craven basin uk early diagenetic redox oscillation processes have been rarely recognised in the ancient rock record but potentially exert an important control on mineral authigenesis hydrocarbon prospectivity and supply of metals and or reduced s as part of associated mineral systems the upper unit of the mississippian bowland shale formation is a candidate record of diagenetic redox oscillation processes because it was deposited under a relatively high sediment accumulation rate linked to a large delta system and under dominantly anoxic and intermittently sulphidic bottom water conditions in order to characterise the syngenetic and early diagenetic processes sedimentological and geochemical data were integrated through the upper bowland shale at three sites in the craven basin lancashire uk organic matter om comprises a mixture of type ii ii s ii iii and iii om redox zones are defined by patterns of fe speciation and redox sensitive trace element enrichment and split into two groups sulphidic zones eux an iii an i and an it represent sediments deposited under conditions of at least intermittently active sulphate reduction in bottom waters non sulphidic zones ox rx ox f and ox represent sediments deposited under non sulphidic oxic to ferruginous anoxic bottom waters operation of a shelf to basin reactive fe fehr shuttle moderated by sea level fluctuation and delta proximity controlled the position and stability of redoxclines between zones of fe and sulphate reduction and methanogenesis early diagenetic redoxclines were capable of migration through the shallow sediment column relatively quickly in response to sea level fluctuation preservation of syngenetic and early diagenetic geochemical signals shows redoxclines between fe and sulphate reduction and the upper boundary of sulphate methane transition zone were positioned within decimetres i e 10 s cm of seabed falling sea level and increasing fehr supply is recognised as a switch from zones eux high sea level an iii and ultimately an i and an it low sea level zone an i defines the operation of redox oscillation between zones of fe and sulphate reduction in shallow porewaters associated with enhanced degradation of om and complete dissolution of primary carbonate preservation of om and carbonate in this system was a function of changing bottom and pore water redox processes redox oscillation operated in a siliciclastic prodeltaic environment associated with a relatively high sediment accumulation rate and high loadings of labile organic matter and metal oxides these findings are important for understanding late palaeozoic black shales in the context of hydrocarbon and mineral systems

an isotopic biogeochemical assessment of shifts in organic matter input to holocene sediments from mud lake florida abstract a molecular and isotopic study of sediment cores from a sinkhole lake mud lake florida usa was performed in order to relate documented changes in the regional terrestrial vegetation and water table over the last 5500 years to molecular and isotopic proxies for biological sources of organic matter to the lake sediments temporal shifts in the source of organic matter to the sediment as determined by the stable carbon isotope composition of bulk organic matter and biomarkers correspond with previously defined regional scale transitions in forest ecosystems quercus to pinus at 5500 14 c yr bp and taxodium expansion at 2500 14 c yr bp and coincident increases in the floridan water table the 13 c values for total sedimentary organic carbon showed a shift from terrestrial and aquatic macrophyte sources 27 8 in sediments dated at 5400 14 c yr bp within the basal peat to a cyanobacterial dominated sapropel 18 1 at the surface a comparison of the 13 c values of bulk sediment and biomarkers representative of cyanobacterial and algal input e g 7 and 8 methylheptadecane and the n alkane c 17 indicates that the present shallow lake was fully developed by 2400 14 c yr bp differences among the 13 c values of specific biomarkers derived from vascular plants c 29 and c 31 n alkanes and cuo lignin oxidation products and from cyanobacteria and algae are nearly equivalent in magnitude to the shift recorded in 13 c of toc indicating their effective use as source proxies in this system

tepexpan palaeoindian site basin of mexico multi proxy evidence for environmental change during the late pleistocene late holocene the tepexpan palaeoindian skeleton was discovered in 1947 close to the former lake texcoco margin in the basin of mexico the find has been the object of considerable interest and discussion over the last 60 years regarding its real age and archaeological interpretation here we report new ams radiocarbon dates associated with the sedimentary succession at tepexpan with ages between 19 110 90 and 612 22 14c years bp and a new uranium series date for the skeleton with an age of 4700 200 years bp that indicates a mid holocene age the sedimentary succession was studied in detail using stable isotopes diatoms organic geochemistry and tephrochronology the multi proxy evidence suggests large changes around the margins of lake texcoco in terms of the balance between aquatic and terrestrial plants c3 and c4 plants saline alkaline and freshwater conditions volcanic activity marginal reworking of lake sediments and input from the drainage basin through the late pleistocene late holocene these changes had large impacts on the prehistoric human populations living by the lake shores since the late pleistocene in the basin of mexico

hydrodynamics of floodplain wetlands in a chalk catchment the river lambourn uk variations in floodplain channel water levels and valley floor groundwater levels measured in piezometers and boreholes are examined at selected points along the course of the river lambourn a chalk river in southern england a local alluvial gravel aquifer in the valley bottom is associated with numerous small wetlands that extend over much of the river s perennial profile variations in hydraulic gradient between local borehole levels and or floodplain channel water levels are described for three sites in the seasonal section of the channel at bockhampton east garston and west shefford the results indicate that observed groundwater levels are closely associated with flows from discrete springs at the margins of the channel and floodplain however as the floodplain widens and the alluvial gravel aquifer increases in size the gravel aquifer accounts for a substantial down valley component of groundwater flow with a diffuse vertical water flux in the lower catchment the exchange of flows between the gravel aquifer and the river enables some attenuation of floodplain water table variability providing a stable hydrological regime for valley bottom wetlands catchment controls upon the local valley bottom wetland regime are demonstrated with the application of a simple groundwater model developed using modflow the model is used to simulate groundwater discharge to the river in the upper and lower catchment in addition to the water level regime at selected points in the valley bottom in the lower catchment the results demonstrate the importance of taking catchment scale water flow into account when managing isolated wetlands in a permeable catchment

denudation rates determined from the accumulation of in situ produced 10be in the luquillo experimental forest puerto rico we present a simple method for estimation of long term mean denudation rates using in situ produced cosmogenic 10be in fluvial sediments procedures are discussed to account for the effects of soil bioturbation mass wasting and attenuation of cosmic rays by biomass and by local topography our analyses of 10be in quartz from bedrock outcrops soils mass wasting sites and riverine sediment from the icacos river basin in the luquillo experimental forest puerto rico are used to characterize denudation for major landform elements in that basin the 10be concentration of a discharge weighted average of size classes of river sediment corresponds to a long term average denudation of 43 m ma 1 consistent with mass balance results

soil transport driven by biological processes over millennial time scales downslope soil transport in the absence of overland flow has been attributed to numerous mechanisms including particle by particle creep and disturbances associated with biological activity process stochasticity and difficulties associated with field measurement have obscured the characterization of relevant long term soil transport rates and mechanisms in a series of incised fluvial terraces along the charwell river south island new zealand we documented vertical profiles of tephra concentration and topographic derivatives along a hillslope transect to quantify soil transport processes along the undissected hilltop we observed a thin primary tephra layer ca 22 6 ka within loess deposits 80 cm below the landscape surface in the downslope direction the depth to the highly concentrated tephra layer decreases coincident with an increase in hillslope convexity which is proportional to landscape lowering rate if soil flux varies linearly with hillslope gradient exhumation of the tephra layer results from landscape lowering due to disturbance driven soil transport approximately 20 m downslope of the interfluve the depth to the tephra layer declines to 40 50 cm peak tephra concentrations decrease by a factor of 4 and tephra is distributed uniformly within the upper 40 cm of soil the transition from a thin highly concentrated tephra layer at depth to less concentrated widely distributed tephra in the upper soil may result from soil mixing and transport by biological disturbances along our transect the depth to this transition is 50 cm coincident with the rooting depth of podocarp and nothofagus trees that populated the region during much of the holocene our observations can be used to calibrate the linear transport model but more important they suggest that over geomorphic time scales stochastic bioturbation may generate a well mixed and mobile soil layer the depth of which is primarily determined by flora characteristics

hydrographic changes in the lincoln sea in the arctic ocean with focus on an upper ocean freshwater anomaly between 2007 and 2010 hydrographic data from the arctic ocean show that freshwater content in the lincoln sea north of greenland increased significantly from 2007 to 2010 slightly lagging changes in the eastern and central arctic the anomaly was primarily caused by a decrease in the upper ocean salinity in 2011 upper ocean salinities in the lincoln sea returned to values similar to those prior to 2007 throughout 2008 2010 the freshest surface waters in the western lincoln sea show water mass properties similar to fresh canada basin waters north of the canadian arctic archipelago in the northeastern lincoln sea fresh surface waters showed a strong link with those observed in the makarov basin near the north pole the freshening in the lincoln sea was associated with a return of a subsurface pacific water temperature signal although this was not as strong as observed in the early 1990s comparison of repeat stations from the 2000s with the data from the 1990s at inline image showed an increase of the atlantic temperature maximum which was associated with the arrival of warmer atlantic water from the eurasian basin satellite derived dynamic ocean topography of winter 2009 showed a ridge extending parallel to the canadian archipelago shelf as far as the lincoln sea causing a strong flow toward nares strait and likely fram strait the total volume of anomalous freshwater observed in the lincoln sea and exported by 2011 was close to inline image approximately 13 of the total estimated fw increase in the arctic in 2008

radon in chalk streams spatial and temporal variation of groundwater sources in the pang and lambourn catchments uk summary variations in dissolved 222 rn radon concentrations in rivers and groundwater are observed in the cretaceous chalk catchments of the pang and lambourn stream radon concentrations and flow data were used to model radon inputs to rivers from groundwater with the modelled radon input concentrations c i varying between 0 2 bq l 1 and 3 8 bq l 1 consistent with measured groundwater values groundwater in both catchments was found to have higher and more variable radon concentrations 2 12 bq l 1 in the near surface weathered horizons compared to a consistent 1 bq l 1 from the solid chalk the variations in c i can be related to flow generation pathways and hydrological events in the lambourn the radon budget is controlled by diffuse groundwater inputs supporting the hypothesis that the alluvial aquifer plays a greater role during periods of high accretion the pang is more complex than the lambourn having a combination of diffuse and point source inputs with spring inputs dominating both flow and radon signatures in the lower part of the catchment significant temporal and spatial variations were determined for c i in both catchments reflecting their differing geologies and flow regimes one use of radon in hydrology is the determination of groundwater discharges to rivers but the observed variations in c i mean this approach may not be appropriate to all situations and that changes in source need further evaluation nonetheless radon is shown to be a useful tracer of flow paths and processes within these catchments

long term holocene groundwater fluctuations in a chalk catchment evidence from rock eval pyrolysis of riparian peats he depositional history of peat dominated wetlands can be used to understand palaeoclimate and palaeohydrology and also constrain the impacts of future climate change however in chalkland valleys seasonal water table fluctuations and a high alkalinity have diminished key environment indicators such as pollen and there is a need for alternative investigative techniques the method of rock eval pyrolysis can track changes in organic matter source and degradation potentially relating to historic changes in vegetation cover this is the first rock eval on cores from a groundwater dependent riparian chalk valley wetland combined with radiocarbon dating the dating showed that the cores represented approximately 4000 years of depositional history changes in hydrocarbon chemistry including normal alkane composition of the peat indicated shifts of around 500 to 1000 years between terrestrial and more aquatic species relating to periods of climate wetness these climatic shifts are broadly consistent with other evidence from ombrotrophic peatland and lacustrine sediments across northwest europe however the connection between climate wetness and groundwater dependent chalkland wetlands is complicated by external anthropogenically driven factors relating to land use and vegetation cover changes in the catchment nonetheless this study suggests that rock eval pyrolysis is a useful and cost effective tool that can provide evidence for long term holocene groundwater fluctuations

regional climate change from peat stratigraphy for the mid to late holocene in central ireland at the millennial scale bog surface wetness bsw records show a clear holocene climate event stratigraphy with major phases comparable with other regional climate proxies such as chironomid inferred temperature records moving towards the centennial scale however and towards the limits of chronological certainty within the records regional differences are apparent which likely reflect the more heterogeneous precipitation patterns which occur on shorter timescales the bsw data presented in this paper are reconstructed from testate amoebae assemblages from central ireland and are compared with other regional records the results suggest that this region is in phase with the north of ireland in terms of timings and durations of climate change but the comparisons are less clear with a stacked and tuned record from northern britain that shows an apparent offset compared to the irish records this may reflect variations in past regional precipitation or be a function of the tuning and stacking process the broad phases of comparison between the irish records and the extension of the central irish record back to 6000 cal bp allow comparisons with low frequency temperature reconstructions from chironomids which also show a broad level of correlation with cooler temperatures relating to wetter bsw at centennial to millennial timescales

stochastic processes of soil production and transport erosion rates topographic variation and cosmogenic nuclides in the oregon coast range landscapes in areas of active uplift and erosion can only remain soil mantled if the local production of soil equals or exceeds the local erosion rate the soil production rate varies with soil depth hence local variation in soil depth may provide clues about spatial variation in erosion rates if uplift and the consequent erosion rates are sufficiently uniform in space and time then there will be tendency toward equilibrium landforms shaped by the erosional processes soil mantle thickness would adjust such that soil production matched the erosion previous work in the oregon coast range suggested that there may be a tendency locally toward equilibrium between hillslope erosion and sediment yield here results from a new methodology based on cosmogenic radionuclide accumulation in bedrock minerals at the base of the soil column are reported we quantify how soil production varies with soil thickness in the southern oregon coast range and explore further the issue of landscape equilibrium apparent soil production is determined to be an inverse exponential function of soil depth with a maximum inferred production rate of 268 m ma 1 occurring under zero soil depth this rate depends however on the degree of weathering of the underlying bedrock the stochastic and large scale nature of soil production by biogenic processes leads to large temporal and spatial variations in soil depth the spatial variation of soil depth neither supports nor rejects equilibrium morphology our observed catchment averaged erosion rate of 117 m ma 1 is however similar to that estimated for the region by others and to soil production rates under thin and intermediate soils typical for the steep ridges we suggest that portions of the oregon coast range may be eroding at roughly the same rate but that local competition between drainage networks and episodic erosional events leads to landforms that are out of equilibrium locally and have a spatially varying soil mantle copyright 2001 john wiley sons ltd

10be concentrations and the long term fate of particle reactive nuclides in five soil profiles from california concentration depth profiles of cosmic ray produced 10 be t 1 2 1 5m y have been measured by accelerator mass spectrometry in five soil profiles these measurements were made in an effort 1 to understand the retentivity of soil surfaces for particle reactive tracers depositing from the atmosphere on time scales of 10 4 10 6 years and 2 to explore the application of 10 be as a chronometer of geomorphic surface age the profiles sampled are from two wave cut terraces located near mendocino california a table mountain top and an alluvial fan both located near friant california the ages of the mendocino terraces are inferred to be 1 5 10 5 years based on amino stratigraphic correlations and models of terrace evolution those of the table mountain top and alluvial fan are 9 5 10 6 years and 6 0 10 5 years respectively based on k ar analyses all the surfaces sampled are nearly flat and exhibit few erosional features in addition to 10 be we measured 210 pb 239 240 pu and 7 be to ascertain the retentivity of the soils for particle reactive nuclides and to assess the present day delivery rate of nuclides from the atmosphere the 7 be inventory is 4 0 dpm cm 2 similar to those observed at nearby locations the inventories of 210 pb and pu isotopes conform to those predicted from model calculations and suggest that the soil surfaces sampled retain the entire burden of particle reactive nuclides delivered to them over short time scales 100 years the 10 be concentrations in the sample range between 0 2 and 7 10 8 atoms g soil and show strong correlations with leachable fe and or al the inventory of 10 be in the soil domain sampled is 1 2 orders of magnitude lower than that expected from the geological age of the surface and an average delivery rate of 10 be from the atmosphere 5 2 10 5 atoms cm 2 yr the low inventory of 10 be is attributed to its loss from the soil domain sampled by solution transport based on a simple model type calculation with a first order removal process for 10 be the residence time of 10 be in the soil domains sampled is determined to be of the order of 10 4 years the low residence time of 10 be in the soil domains sampled requires that it be found either deeper in the regolith or in ground waters in either case the application of 10 be as a chronometer of geomorphic surface age is severely constrained however the study of 10 be in soils provides the only entry into the long term 10 4 10 6 years behavior of particle reactive nuclides in soils and hence could be important for understanding the behavior of analogous nuclides introduced into soils by natural and anthropogenic processes

floodplain environmental change during the younger dryas and holocene in northwest europe insights from the lower kennet valley south central england abstract many lowland rivers across northwest europe exhibit broadly similar behavioural responses to glacial interglacial transitions and landscape development difficulties exist in assessing these largely because the evidence from many rivers remains limited and fragmentary here we address this issue in the context of the river kennet a tributary of the thames since c 13 000 cal bp some similarities with other rivers are present suggesting that regional climatic shifts are important controls the kennet differs from the regional pattern in a number of ways the rate of response to sudden climatic change particularly at the start of the holocene and also mid holocene forest clearance appears very high this may reflect abrupt shifts between two catchment scale hydrological states arising from contemporary climates land use change and geology stadial hydrology is dominated by nival regimes with limited winter infiltration and high spring and summer runoff under an interglacial climate infiltration is more significant the probable absence of permafrost in the catchment means that a lag between the two states due to its gradual decay is unlikely palaeoecology supported by radiocarbon dates suggests that at the very start of the holocene a dramatic episode of fine sediment deposition across most of the valley floor occurred lasting 500 1000 years a phase of peat accumulation followed as mineral sediment supply declined a further shift led to tufa deposition initially in small pools then across the whole floodplain area with the river flowing through channels cut in tufa and experiencing repeated avulsion major floods leaving large gravel bars that still form positive relief features on the floodplain followed mid holocene floodplain stability prehistoric deforestation is likely to be the cause of this flooding inducing a major environmental shift with significantly increased surface runoff since the bronze age predominantly fine sediments were deposited along the valley with apparently stable channels and vertical floodplain accretion associated with soil erosion and less catastrophic flooding the kennet demonstrates that while a general pattern of river behaviour over time within a region may be identifiable individual rivers are likely to diverge from this consequently it is essential to understand catchment controls particularly the relative significance of surface and subsurface hydrology

a high resolution late glacial to holocene record of environmental change in the mediterranean from lake ohrid macedonia albania lake ohrid macedonia albania is the oldest extant lake in europe and exhibits an outstanding degree of endemic biodiversity here we provide new high resolution stable isotope and geochemical data from a 10 m core co1262 through the late glacial to holocene and discuss past climate and lake hydrology tic 13ccalcite 18ocalcite as well as the terrestrial and aquatic vegetation response to climate toc toc n 13corganic rock eval pyrolysis the data identifies 3 main zones 1 the late glacial holocene transition represented by low tic and toc contents 2 the early to mid holocene characterised by high toc and increasing toc n and 3 the late holocene present which shows a marked decrease in tic and toc in general an overall trend of increasing 18ocalcite from 9 ka to present suggests progressive aridification through the holocene consistent with previous records from lake ohrid and the wider mediterranean region several proxies show commensurate excursions that imply the impact of short term climate oscillations such as the 8 2 ka event and the little ice age this is the best dated and highest resolution archive of past late glacial and holocene climate from lake ohrid and confirms the overriding influence of the north atlantic in the north eastern mediterranean the data presented set the context for the international continental scientific drilling program scientific collaboration on past speciation conditions in lake ohrid project cores recovered in spring summer 2013 potentially dating back into the lower pleistocene and will act as a recent calibration to reconstruct climate and hydrology over the entire lake history

quantification of chemical weathering rates across an actively eroding hillslope abstract chemical weathering rates for landscapes are difficult to quantify because the timescales over which weathering occurs are often unknown in this study we use timescales defined by prior cosmogenic nuclide analyses and a suite of geochemical measurements to calculate weathering rates in saprolite and soil and to determine how these rates vary across an eroding hillslope we also estimate the relative contributions of solute and erosional mass loss to landscape lowering analyses were conducted on a soil mantled hillslope developed on a granodiorite pluton in southern nsw australia mass loss in solution accounts for 35 to 55 of the total mass loss from the hillslope saprolite close to the soil saprolite boundary is less weathered at the ridge than at distance from the ridge the calculated flux of silica from the saprolite is 5 tons km 2 yr 1 and does not vary with distance from the ridge or overlying soil thickness the assumption of steady state but spatially variable erosion rates with a temporally constant thickness of soil and saprolite allows us to calculate the downslope variation in the rate of solute losses soil silica weathering rates initially increase from 12 tons km 2 yr 1 at the ridge crest to 20 tons km 2 yr 1 on the convex region of the hillslope and then decrease to 13 tons km 2 yr 1 by the time soils have been transported 45 50 m soils closer to the surface are more weathered than deeper soils this geochemical stratification suggests that the soil column does not become thoroughly vertically mixed as soils move down slope dependence of solute loss on transport distance may explain the previously noted discrepancy between the observed soil thickness and that predicted based on curvature variation of solute loss with transport distance may also contribute to the linear dependence of soil thickness on distance from the ridge

testing the use of microfossils to reconstruct great earthquakes at cascadia coastal stratigraphy from the pacific northwest of the united states contains evidence of sudden subsidence during ruptures of the cascadia subduction zone transfer functions empirical relationships between assemblages and elevation can convert microfossil data into coastal subsidence estimates coseismic deformation models use the subsidence values to constrain earthquake magnitudes to test the response of foraminifera the accuracy of the transfer function method and the presence of a pre seismic signal we simulated a great earthquake near coos bay oregon by transplanting a bed of modern high salt marsh sediment into the tidal flat an elevation change that mimics a coseismic subsidence of 0 64 m the transplanted bed was quickly buried by mud after 12 mo and 5 yr we sampled it for foraminifera reconstruction of the simulated coseismic subsidence using our transfer function was 0 61 m nearly identical to the actual elevation change our transplant experiment and additional analyses spanning the a d 1700 earthquake contact at the nearby coquille river 15 km to the south show that sediment mixing may explain assemblage changes previously interpreted as evidence of pre seismic land level change in cascadia and elsewhere

the illusion of diffusion field evidence for depth dependent sediment transport soil covered upland landscapes are common in much of the habitable world and our understanding of their evolution as a function of different climatic tectonic and geologic regimes is important across a wide range of disciplines erosion laws direct quantitative study of the processes shaping earth s surface and form the basis of landscape evolution modeling but are based on limited field data here we use in situ produced cosmogenic 1 0 be and 2 6 al concentrations from granitic saprolite to quantify an exponential decline in soil production with increasing soil thickness for a new field site in point reyes california results are similar to soil production functions from two different previously studied field sites and are used with extensive measurements of soil thickness to quantify depth integrated sediment transport flux plots of calculated sediment fluxes against the product of soil depth and hillslope gradient provide the first field based evidence that soil transport is a nonlinear depth dependent function data from all sites suggest that the widely used linear diffusion equation is only appropriate for shallow gradient convex up regions while the depth dependent transport law is more broadly applicable quantifying both the mobile soil thickness and landscape morphology is therefore critical to understanding how landscapes evolve