cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

on the occurrence and formation of multiple layers of polar mesosphere summer echoes 1 polar mesosphere summer echoes pmse have been studied at andenes 69 n 16 e norway using vhf radar observations from 1994 1997 and since 1999 one remarkable feature of all pmse is the fact that the radar echoes often occur in the form of two or more distinct layers that can persist for periods of up to several hours until now the layering mechanism leading to these multiple structures is not well understood here we are studying the occurrence and the mean altitude distribution of these multiple layer events to discuss the processes that are potentially responsible for the creation of these multiple structures we apply a microphysical model of the generation and growth of mesospheric ice particles under the influence of temperature and wind variations caused by a long period gravity wave finally this model approach is tested with gravity wave characteristics derived from mf and vhf radar wind measurements during the pmse observations

spatial and process based modeling of soil inorganic carbon storage in an arid piedmont abstract inorganic carbon c comprises approximately a third of the total c pool in soils worldwide largely in the form of pedogenic calcite pedogenic calcite occurs in semi arid and arid regions in the form of calcareous calcic and petrocalcic horizons understanding the processes governing the storage and flux of this inorganic c pool is crucial to the development of accurate regional and global c budgets objectives of this study were to 1 develop a process based pedogenic calcite model that accounts for landscape hydrology and geomorphic position 2 calibrate model parameters with field data from a mojave desert landscape and 3 apply the model to understanding soil inorganic c response to elevated atmospheric co 2 concentrations two parameters are introduced in this study to account for surface water redistribution on the landscape the precipitation threshold and the topographic index threshold these parameters account for runoff generating rainfall events and the potential to shed or collect water at a location a one dimensional compartmentalized thermodynamic model is used to simulate calcite precipitation and dissolution geomorphic delineation sediment collected from dust traps and detailed soil descriptions including percent sand and clay and bulk density from 16 soil pits of the southern fry mountain piedmont served as inputs into the model precipitation and temperature inputs were simulated using stochastic models time steps for the sample sites used to calibrate the model were determined from optically stimulated luminescence dates incorporation of precipitation and topographic index thresholds into the model allowed more information to be extracted from carbonate depth distributions than previous pedogenic calcite models the model predicts a net loss of inorganic c from the upper 10 cm soil depth under elevated atmospheric co 2 and a consequent gain in the 10 20 cm depth the leaching of calcite from shallow depths to below 10 cm is evident in all landforms including those most susceptible to wind erosion this leads to the conclusion that increased atmospheric co 2 levels may result in a concentration of inorganic c at a depth that is protected from wind erosion creating a more geomorphically stable pool of c

the control mechanisms of erosion and weathering at basin scale from cosmogenic nuclides in river sediment the study of a sample of river sediment enables the determination of spatially averaged denudation rates that provide an exceptional perspective on erosion and weathering processes that have taken place within a landscape these measurements are done with in situ produced cosmogenic nuclides e g 10be 26al mostly in quartz from alluvial sediment cosmogenic nuclides are produced when secondary cosmic rays interact with the very uppermost layer of the earth s surface they are produced within a characteristic depth scale of about 1 m which means that the measured concentrations record an integrated denudation history while material passed through this depth interval depending on the denudation rate the resulting integration time scales are 103 to 105 years and one obtains a robust long term estimate of natural denudation that is relatively insensitive to short term changes the last 10 years have seen significant research activity using these methods and an array of fascinating tectono geomorphologic and geochemical insights are emerging amongst these is the ability to identify the physical and chemical processes with which a landscape responds to tectonic activity or climate change a compilation of world wide denudation rates in non glaciated areas that however does not yet include some of the world s most active mountain belts has resulted in the following findings some of which have been unexpected 1 no obvious relationship between precipitation or mean annual temperature and total denudation is apparent 2 topographic relief alone does not result in high rates of denudation 3 denudation rates are high in areas of landscape rejuvenation that is triggered and controlled by tectonic activity faulting escarpment formation and retreat rifting surface uplift 4 rates of weathering using a combination of cosmogenic nuclides and zirconium normalised cation loss balances co vary primarily with physical erosion rates and much less with temperature or precipitation 5 in some areas of high land use short term rates from river load gauging exceed those from cosmogenic nuclides by several orders of magnitude which serves to highlight the severity of geomorphic change caused by human action in the future the control mechanisms over denudation will be determined on all spatial scales ranging from the single soil section to entire river basins the same analysis can be done back through time on well dated terraces lake records and marine sediment cores which is possible with 10be for the past 1 2 my the rates obtained will be used to develop a quantitative understanding of tectonic geomorphologic and geochemical landscape processes which in turn is a prerequisite to design and calibrate models of the response of landscapes to tectonic climate and anthropogenic forcing

modelling weathering processes at the catchment scale the witch numerical model a numerical model of chemical weathering in soil horizons and underlying bedrock witch has been coupled to a numerical model of water and carbon cycles in forest ecosystems aspects to simulate the concentration of major species within the soil horizons and the stream of the strengbach granitic watershed located in the vosges mountains france for the first time simulations of solute concentrations in soil layers and in the catchment river have been performed on a seasonal basis the model is able to reproduce the concentrations of most major species within the soil horizons as well as catching the first order seasonal fluctuations of aqueous calcium magnesium and silica concentrations however the witch model underestimates concentrations of mg2 and silica at the spring of the catchment stream and significantly underestimates ca2 concentration the deficit in calculated calcium can be compensated for by dissolution of trace apatite disseminated in the bedrock however the resulting increased ca2 release yields important smectite precipitation in the deepest model layer in contact with the bedrock and subsequent removal of large amount of silica and magnesium from solution in contrast the model accurately accounts for the concentrations of major species ca mg and silica measured in the catchment stream when precipitation of clay minerals is not allowed the model underestimation of mg2 and h4sio4 concentrations when precipitation of well crystallized smectites is allowed strongly suggests that precipitation of well crystallized clay minerals is overestimated and that more soluble poorly crystallized and amorphous materials may be forming in agreement with observations on other watersheds draining granitic rocks this study indicates that highly soluble trace calcic phases control the aqueous calcium budget in the strengbach watershed

fluvial erosion transport equation of landscape evolution models revisited we present a mesoscale erosion deposition model which differs from previous landscape evolution models equations by taking explicitly into account a mass balance equation for the streamflow the geological and hydrological complexity is lumped into two basic fluxes erosion and deposition and two averaged parameters unit width discharge q and stream slope s the model couples the dynamics of streamflow and topography through a sediment transport length function x q which is the average travel distance of a particle in the flow before being trapped on topography this property reflects a time lag between erosion and deposition which allows the streamflow not to be instantaneously at capacity the so called x q model may reduce either to transport limited or to detachment limited erosion modes depending on x but it also may not we show in particular how it does or does not for steady state topographies long term evolution and high frequency base level perturbations apart from the unit width discharge and the settling velocity the x q function depends on a dimensionless number encompassing the way sediment is transported within the streamflow using models of concentration profile through the water column we show the dependency of this dimensionless coefficient on the rouse number we discuss how consistent the x q model framework is with bed load scaling expressions and einstein s conception of sediment motion

topographic relief driven by variations in surface rock density earth s surface topography is generated by tectonically induced variations in crustal thickness combined with erosion and to a lesser degree by vertical stresses caused by convection in the underlying mantle rock hardness and resistance to erosion are also commonly thought to influence topography because hard rocks such as granites and basalts usually form topographic highs in the landscape here we use analytical and numerical models to simulate the erosion induced isostatic rebound of rocks we find that the isostatic rebound that accompanies erosion causes denser rocks to occupy higher elevations in the landscape thereby creating topographic relief that is proportional to surface rock density differences rather than rock hardness we quantify this effect taking into account the flexural strength of the continental lithosphere we show that in a steady state erosional setting density dependent isostatic rebound can cause the densest rocks to be exhumed at double the rate of surrounding less dense rocks and has a stronger effect than typical rock hardness variations the results imply that denser rock formations should erode faster and therefore be characterized by younger thermochronological ages thermochronological data sets from the kinabalu granite in borneo and the shakhdara alichur gneiss domes in pamir confirm this counter intuitive result our findings imply that lateral variations in surface rock density have significant control on the shaping of the large scale features of earth s surface the high elevation in earth s topography of hard rocks such as granites and basalts was thought to be caused by their inherent resistance to erosion numerical modelling now demonstrates counterintuitively that erosion induced isostatic rebound of rocks which is density dependent causes granites and basalts to occupy high elevations because they are more dense than surrounding rocks

diversity of diagnostic horizons in soils of the contiguous usa a case study abstract many previous studies of pedodiversity have emphasized the lateral variability of soils in this study the vertical distribution of diagnostic horizons is examined at the soil series level unlike genetic horizons diagnostic soil horizons are based on quantitatively defined morphological and analytical properties and they form the basis of modern soil classification systems an examination of 1600 soil series in 63 representative out of 226 major land resource areas mlras in contiguous usa revealed that they contain from one to seven diagnostic soil horizons with an average of 2 6 1 2 about 20 of the soil series contain 4 or more diagnostic horizons 80 of these soil series are in seven great groups the glossudalfs haplorthods fragiorthods endoaquods epiaquods fraglossudalfs and glossaqualfs the laurentide great lakes region contains a discordant number 57 of soils with 4 or more diagnostic horizons the most common being ochric 100 albic 91 argillic 85 glossic 69 spodic 51 and a fragipan 19 several factors appear to contribute to the diversity of diagnostic horizons including proximity to the great lakes where abundant snowfall precludes soil freezing and enables water to percolate rapidly through the soil in a short interval during the spring the prevalence of stratified glacial deposits often containing a lithologic discontinuity and a fluctuating water table all of which enable specific weathering products to accumulate at different depths

the search for a topographic signature of life landscapes are shaped by the uplift deformation and breakdown of bedrock and the erosion transport and deposition of sediment life is important in all of these processes over short timescales the impact of life is quite apparent rock weathering soil formation and erosion slope stability and river dynamics are directly influenced by biotic processes that mediate chemical reactions dilate soil disrupt the ground surface and add strength with a weave of roots over geologic time biotic effects are less obvious but equally important biota affect climate and climatic conditions dictate the mechanisms and rates of erosion that control topographic evolution apart from the obvious influence of humans does the resulting landscape bear an unmistakable stamp of life the influence of life on topography is a topic that has remained largely unexplored erosion laws that explicitly include biotic effects are needed to explore how intrinsically small scale biotic processes can influence the form of entire landscapes and to determine whether these processes create a distinctive topography

the impact of humans on continental erosion and sedimentation rock uplift and erosional denudation of orogenic belts have long been the most impor tant geologic processes that serve to shape continental surfaces but the rate of geomor phic change resulting from these natural phe nomena has now been outstripped by human activities associated with agriculture con struction and mining although humans are now the most important geomorphic agent on the planet s surface natural and anthro pogenic processes serve to modify quite dif ferent parts of earth s landscape in order to better understand the impact of humans on continental erosion we have examined both long term and short term data on rates of sediment transfer in response to glacio fl u vial and anthropogenic processes phanerozoic rates of subaerial denuda tion inferred from preserved volumes of sedimentary rock require a mean conti nental erosion rate on the order of 16 m per million years m m y resulting in the accumulation of 5 gigatons of sediment per year gt yr erosion irregularly increased over the 542 m y span of phanerozoic time to a pliocene value of 53 m m y 16 gt yr current estimates of large river sediment loads are similar to this late neogene value and require net denudation of ice free land surfaces at a rate of 62 m m y 21 gt yr consideration of the variation in large river sediment loads and the geomorphology of respective river basin catchments suggests that natural erosion is primarily confi ned to drainage headwaters 83 of the global river sediment fl ux is derived from the high est 10 of earth s surface subaerial erosion as a result of human activity primarily through agricultural practices has resulted in a sharp increase in net rates of continental denudation although less well constrained than estimates based on surviving rock volumes or current river loads available data suggest that present farmland denudation is proceeding at a rate of 600 m m y 75 gt yr and is largely confi ned to the lower elevations of earth s land surface primarily along passive continental margins 83 of cropland erosion occurs over the lower 65 of earth s surface the conspicuous disparity between natu ral sediment fl uxes suggested by data on rock volumes and river loads 21 gt yr and anthropogenic fl uxes inferred from measured and modeled cropland soil losses 75 gt yr is readily resolved by data on thicknesses and ages of alluvial sediment that has been deposited immediately downslope from erod ing croplands over the history of human agriculture accumulation of postsettlement alluvium on higher order tributary channels and fl oodplains mean rate 12 600 m m y is the most important geomorphic process in terms of the erosion and deposition of sedi ment that is currently shaping the landscape of earth it far exceeds even the impact of pleistocene continental glaciers or the cur rent impact of alpine erosion by glacial and or fl uvial processes conversely available data suggest that since 1961 global cropland area has increased by 11 while the global population has approximately doubled the net effect of both changes is that per capita cropland area has decreased by 44 over this same time interval 1 per year this is 25 times the rate of soil area loss antici pated from human denudation of cropland surfaces in a context of per capita food pro duction soil loss through cropland erosion is largely insignifi cant when compared to the impact of population growth

dating sediment burial with in situ produced cosmogenic nuclides theory techniques and limitations abstract dating sediment burial over million year time scales is crucial in many areas of the earth sciences and archeology but is often difficult using traditional techniques sediment burial can be dated by the radioactive decay of cosmogenic nuclides provided that the sediment was exposed to cosmic rays prior to burial dating calculations are straightforward if sediment is buried deeply and rapidly enough to prevent cosmogenic nuclide production after burial however the analysis can be complicated by postburial production if sediment is insufficiently shielded from secondary cosmic ray nucleons and muons this paper discusses how buried sediments can be dated over timescales up to 5 myr using 26 al and 10 be in quartz

soil formation rates on silicate parent material in alpine environments different approaches different results abstract high mountain soils develop in particularly sensitive environments consequently deciphering and predicting what drives the rates of soil formation in such environments are a major challenge in terms of soil production or formation from chemical weathering the predominating perception for high mountain soils and cold environments is often that the chemical weathering portion of soil development is temperature inhibited often to the point of non occurrence several concepts exist to determine long term rates of soil formation and development we present three different approaches 1 quantification of soil formation from minimally eroded soils of known age using chronosequences known surface age and soil thickness sast 2 determination of soil residence times srt and production rates through chemical weathering using un stable isotopes e g 230 th 234 u activity ratios and 3 a steady state approach using cosmogenic isotopes e g 10 be for each method data from different climate zones and particularly from high mountains alpine environment are compared the sast and steady state approach give quite similar results for alpine environments european alps and the wind river range rocky mountains usa using the srt approach soil formation rates in mountain areas but having a temperate climate do not differ greatly from the sast and steady state approaches independent of the chosen approach the results seem moderately comparable soil formation rates in high mountain areas alpine climate range from very low to extremely high values and show a clear decreasing tendency with time very young soils have up to 3 4 orders of magnitude higher rates of development than old soils 10 5 to 10 6 yr this apparently is a result of kinetic limits on weathering in regions having young surfaces and supply limits to weathering on old surfaces due to the requirement for chemical weathering to occur soil production rates cannot be infinitely high consequently a speed limit must exist in the literature this limit has been set at about 320 to 450 t km 2 a our results from the sast approach show however that in alpine areas soil formation easily reaches rates of up to 800 2000 t km 2 a these data are consistent with previous studies in mountain regions demonstrating that particularly young soils intensively weather even under continuous seasonal snowpack and thus that the concept of temperature controlled soil development soil forming intervals in alpine regions must be reconsidered

modeling the early paleozoic long term climatic trend the early paleozoic climate has been described as warm and equable however recent data based on conodont oxygen isotopic composition reveal a large long cooling trend through the ordovician followed by an abrupt cooling during the late ordovician glaciation this long term climate change is associated with a major radiation in the earth life history nonetheless the driving mechanisms for this cooling trend remain unknown carbon dioxide consumption by the weathering of fresh rocks from volcanic arcs has recently been suggested as a possible driver for this climate change however the impact of the plate motion context has not been explored yet although it might have a major impact on atmospheric co 2 levels simulations with a climate model coupled to a biogeochemical model geoclim show that the atmospheric co 2 decreased from more than 20 pal 5600 ppmv in the furongian down to approximately 10 pal 2800 ppmv in the llandovery before rising again in the early devonian we suggest that changes in geography and exposure of fresh volcanic rocks on continents are required to explain the large co 2 drawdown that led to the onset of cooler to glacial conditions from the middle ordovician to the llandovery the weathering of fresh volcanic rocks is itself responsible for 33 of the late ordovician atmospheric co 2 decrease the rest being related to the continent motion through the intertropical convergence zone itcz mean annual continental temperature falls by 3 c in the early ordovician reaching 13 5 c during the glacial interval and rises to 16 c in the early devonian

polar mesospheric summer echoes at 78 n 16 e 2008 first results of the refurbished sounding system sousy svalbard radar 1 the second generation sounding system sousy 53 5 mhz mesosphere stratosphere troposphere mst radar at 78 n 16 e on svalbard has recently completed its inaugural summer 2008 of polar mesospheric summer echoes pmse observations here pmse observations have been assembled in order to identify dates of the earliest and latest occurrences and how the frequency of pmse occurrence correlates with dynamics and temperature which are available from the collocated nippon norway svalbard meteor 31 mhz radar nsmr we find strong correlations between preferred pmse altitude and low temperature and between equatorward flow and occurrence rate temperature drops cause increases in pmse occurrence for the height interval 82 92 km a drop of around 7 k increases the occurrence typically by 1 2 d 1 and similarly for a 1 m s 1 increase in equatorward wind a temperature drop of 5 k at 90 km altitude results in a lowering of the underlying preferred pmse altitude by 1 km this study therefore qualifies at least for 78 n 16 e and 2008 the dependence of pmse occurrence rates and preferred heights on 90 km temperature and dynamics

dense aggregations of a hexactinellid sponge pheronema carpenteri in the porcupine seabight northeast atlantic ocean and possible causes dense aggregations of the hexactinellid sponge pheronema carpenteri were encountered in the porcupine seabight at depths between about 1000 and 1300m in restricted areas within this bathymetric range the sponges attain numerical abundances of more than 1 5m 2 and an estimated biomass of up to 372g m 2 wet weight or about 10g m 2 ash free dry weight these recently acquired samples together with historical data suggest that pheronema occurs close to but not within regions of the upper continental slope where the bottom topography is expected to result in significant enhancement of the near bottom tidal current velocities it is suggested that the sponges may not be able to withstand the enhanced currents but may nevertheless be dependent upon the resuspended or undeposited organic matter carried to them from these regions of increased tidal energy

embedding reach scale fluvial dynamics within the caesar cellular automaton landscape evolution model abstract we introduce a new computational model designed to simulate and investigate reach scale alluvial dynamics within a landscape evolution model the model is based on the cellular automaton concept whereby the continued iteration of a series of local process rules governs the behaviour of the entire system the model is a modified version of the caesar landscape evolution model which applies a suite of physically based rules to simulate the entrainment transport and deposition of sediments the caesar model has been altered to improve the representation of hydraulic and geomorphic processes in an alluvial environment in channel and overbank flow sediment entrainment and deposition suspended load and bed load transport lateral erosion and bank failure have all been represented as local cellular automaton rules although these rules are relatively simple and straightforward their combined and repeatedly iterated effect is such that complex non linear geomorphological response can be simulated within the model examples of such larger scale emergent responses include channel incision and aggradation terrace formation channel migration and river meandering formation of meander cutoffs and transitions between braided and single thread channel patterns in the current study the model is illustrated on a reach of the river teifi near lampeter wales uk

does organic carbon sequestration in volcanic soils offset volcanic co2 emissions abstract volcanic soils contain the highest amounts of organic c among all mineral soil types but are they important sinks in the global terrestrial c cycle does organic c accumulation in these soils offset volcanic co 2 emissions to date no global estimates of organic c sequestration rates are available for these soils which would allow answering these questions here i combine data from available studies conducted on holocene volcanic deposits in different parts of the world to assess soil organic c accumulation i find exponentially decreasing accumulation rates with increasing soil age dropping below 10 g c m 2 yr 1 after approximately 1000 years of soil development the obtained trends are similar for soils of contrasting climate zones an estimated upper limit of global organic c sequestration in volcanic soils is 20 tg yr 1 which is at most 25 of the c degassing from terrestrial volcanoes and less than 1 of the residual land sink of c contemporary organic c sequestration in volcanic soils is less important than co 2 consumption by chemical weathering of volcanic deposits and plays a negligible role in the global terrestrial c cycle

the soil production function a brief history and its rediscovery abstract in 1877 g k gilbert reasoned that the rate at which bedrock is converted to soil reaches a maximum under an optimal soil depth that facilitates contact between bedrock and water such that freeze thaw and chemical weathering are maximised in doing so he outlined the functional dependence of soil production bedrock weathering on local soil depth however the concept of a soil production function does not appear to have been utilised until well into the following century when carson and kirkby carson m a kirkby m j 1972 hillslope form and process cambridge university press cambridge 475 pp expressed it as a notional relationship they also noted that at depths less than optimum instability exists that will either drive soil depth to the optimal weathering depth or to zero depth more recent work has also described a declining exponential soil production function in which the highest rate is at zero soil depth despite dealing with a fundamental issue in soil science viz soil formation the soil production concept has been applied mostly to landscape evolution studies the situation is ripe for its use in soil science and developments in techniques such as cosmogenic nuclides will assist this

rapid regolith formation over volcanic bedrock and implications for landscape evolution abstract the ability to quantify how fast weathering profiles develop is crucial to assessing soil resource depletion and quantifying how landscapes evolve over millennia uranium series isotopes can be used to determine the age of the weathering front throughout a profile and to infer estimates of regolith production rates because the abundance of u series isotopes in a weathering profile is a function of chemical weathering and time this technique is applied to a weathering profile in puerto rico developed over a volcaniclastic bedrock u series isotope compositions are modelled revealing that it takes 40 60 kyr to develop an 18 m thick profile this is used to estimate an average regolith production rate of 334 46 mm kyr this value is higher by a factor of up to 30 when compared to production rates estimated for weathering profiles developed over granitic or shale lithologies this quantitatively underpins the lithological control on rates of regolith production in a neighbouring watershed but over a granitic bedrock production rates are only 30 40 mm kyr moreover by comparing these results to a compilation of soil erosion rates it is clear that landscapes are controlled by the balance or imbalance between regolith production and erosion soil mantled landscapes are the result of a relative balance between production and erosion whereas in cratonic areas thicker weathering profiles are generated because erosion fails to match regolith production rates

sharp decrease in long term chemical weathering rates along an altitudinal transect we used cosmogenic nuclide and geochemical mass balance methods to measure long term rates of chemical weathering and physical erosion across a steep climatic gradient in the santa rosa mountains nevada our study sites are distributed along a 2 km ridgeline transect that spans 2090 to 2750 m in altitude and encompasses marked contrasts in both vegetative cover and snow depth but is underlain by a single roughly uniform granodiorite bedrock cosmogenic nuclides in colluvial soils reveal that denudation rates vary by less than a factor of 1 4 104 144 t km2 yr along this transect bulk elemental analyses indicate that relative to the parent rock soils are less intensively weathered with increasing altitude and show little evidence of weathering related mass losses near the top of the ridge chemical weathering rates decrease rapidly with increasing altitude both in absolute terms from 24 to 0 t km2 yr and as a fraction of total denudation rates from 20 to 0 thus these results indicate an increasing dominance of physical erosion with altitude the observed decrease in chemical weathering rates is greater than one would predict from the decrease in mean annual temperature using simple weathering kinetics suggesting that weathering rates along our transect may also be affected by the progressive decline in vegetative cover and increase in snow depth with increasing altitude these results considered together with weathering rate measurements for a wide range of climates in the sierra nevada usa suggest that chemical weathering rates may be particularly sensitive to differences in climate at higher altitude sites consistent with this hypothesis chemical weathering rates fall virtually to zero at the highest sites on our transect suggesting that sparsely vegetated high altitude crystalline terrain may often be characterized by extremely slow silicate weathering rates

constitutive mass balance relations between chemical composition volume density porosity and strain in metasomatic hydrochemical systems results on weathering and pedogenesis relations characterizing the chemical physical and mechanical changes resulting from metasomatic hydrochemical processes are developed using mass balance models which formally link chemical composition to bulk density mineral density volumetric properties porosity and amount of deformation strain rigorous analysis of aqueous solute transport effects is then made possible in a variety of porous media flow environments including chemical weathering pedogenesis soil formation diagenesis ore deposition and enrichment and metamorphism application of these linear constitutive relations to chemical weathering profiles shows that immobile and locally mobile chemical elements with masses conserved on the scale of soil profiles can be accurately identified from analysis of appropriate data arrays and then used as natural geochemical tracers to infer the nature and extent of hydrochemical weathering processes and volume changes during pedogenesis assumptions commonly made in the past about the supposed immobility of certain elements e g ti and zr become unnecessary quantitative differentiation between the effects of residual and supergene fractionation is then easily made these methods are applied to ni rich laterites developed by weathering of ultramafic rocks showing that during ordinary residual enrichment ni is concentrated by as much as 4 protolith peridotite concentrations this occurs simply by silicate mineral dissolution and removal of chemical elements other than ni e g mg with a corresponding reduction in saprolite density and increase in bulk porosity without significant deformation in contrast laterites with mineable concentrations of ni which are similarly undeformed such as the nickel mountain mine in riddle oregon have experienced in addition to residual enrichment strong supergene enrichment by fractionation of ore elements between a leached zone from which ni is extracted and a complementary enriched zone positioned farther along the direction of ground water flow soil forming processes in podzol chronosequences developed on sandy beach terraces of the mendocino coast of california involved soil column collapse of 60 percent by dissolution of silicate minerals in the albic horizon of al and fe leaching and 70 percent dilation expansion in the overlying organic rich layer by root growth the amount of erosion based upon paleosurface reconstructions using the excess mass of fe al pb ga and cu in the zone of supergene enrichment spodic horizon below the ground water table indicates that subsurface erosion by dissolutional collapse is three times that of surficial erosion finally using published chemical data for ti zr and cr on major bauxite deposits in australia where erosion rates are thought to be low we infer that there may have been major amounts of dissolutional collapse to explain the upwards increase of detrital zircon and rutile in weathering profiles

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

weathering indices as climate proxies a step forward based on congo and sw african river muds abstract despite the influence of other geological and geomorphological factors chemical weathering at the earth s surface is strongly controlled by climate thus a measure of weathering intensity determined from soils or sediments should provide information about the climatic conditions associated with their formation available geochemical and mineralogical data on modern fluvial and marine muds from different regions of southern africa and its atlantic continental margin are used to review the links between sediment composition and climatic properties together with the possible causes of variance although river muds may not be generated exclusively in a single sedimentary cycle and erosion and weathering processes do not necessarily take place in a spatially homogeneous way significant relationships between mineralogical and geochemical signatures of river mud and rainfall in the corresponding catchment area were recognised our study shows that the composition of clay is strongly influenced by climatically driven weathering whilst coarser mud fractions tend to be more affected by provenance grain size hydraulic sorting and recycling in the marine environment the climatic signal may be lost even in clay because of hydraulic fractionation authigenic mineral growth and mixing with foreign particles given the ubiquitous character of fluvial muds and the easy and non expensive methods available for separating and analysing clay fractions their geochemical fingerprints represent a most precious source of information concerning climate any geochemical parameter used as a regional proxy of climate however still requires that the diversity of geological geomorphological and biological factors that affect its value are cautiously considered

imaging of polar mesosphere summer echoes with the 450 mhz poker flat advanced modular incoherent scatter radar 1 polar mesosphere summer echoes pmse occur near the mesopause during the polar summer months pmse are primarily studied at vhf however there have been some detections at higher frequencies here we report on some of the first detections of pmse with the 450 mhz 67 cm poker flat advanced modular incoherent scatter radar pfisr echoes were observed with volume reflectivities radar scattering cross section per unit volume near 2 3 10 17 m 1 on 11 june 2007 pfisr was operating in a 26 beam position mode with look directions spread over an approximately 80 by 80 km2 region at 85 km altitude with elevation angles as low as 50 the measurements showed patchy tens of kilometer irregularity regions drifting in from the north in addition to smaller more localized structures there was no evidence for strong aspect sensitivity of these uhf echoes as pmse was observed in all look directions with relatively uniform intensity the observations indicate the presence of fossilized irregularities drifting with the background wind field as well as areas of developing irregularities possibly associated with the presence of active neutral air turbulence

the marm spatially distributed soil evolution model a computationally efficient modeling framework and analysis of hillslope soil surface organization 1 hillslope surface armouring and weathering processes have received little attention in geomorphologic and hydrologic models due to their complexity and the uncertainty associated with them their importance however in a wide range of spatial processes is well recognized a physically based armouring and weathering computer model armour has previously been used to successfully simulate the effect of these processes on erosion and soil grading at a hillslope scale this model is however computationally complex and cannot realistically be applied over large areas or over long periods of time a simplified process conceptualization approach is presented named marm which uses a novel approach of modeling physical processes using transition matrices which is orders of magnitude faster we describe in detail the modeling framework we calibrate and evaluate the model against armour simulations and show it matches armour for a range of conditions the computational efficiency of marm allowed us to easily examine time and space varying relationships between erosion and physical weathering rates at the hillslope scale for erosion dominated slopes the surface coarsens over time while for weathering domination the surface fines over time when erosion and weathering are comparable in scale a slope can be weathering dominated upslope where runoff and therefore erosion is low and armouring dominated downslope in all cases for a constant gradient slope the surface armour coarsens downslope as a result of a balance between erosion and weathering thus even for weathering dominated slopes the surface grading catena is dependent on armouring through the balance between weathering and armouring we also observed that for many slopes the surface initially armours but after some period of time space and rate dependent weathering begins to dominate and the surface subsequently fines depending on the relative magnitude of armouring and weathering the final equilibrium grading of the slope may be finer or coarser than the initial conditions the results demonstrate the complexity of the evolution of surface grading and the balance between the armouring and weathering processes they also point toward inherent organization of surface grading on the hillslope driven by erosion even for extremely high weathering rates the implications for natural landforms are discussed we also plot and quantify for the first time a log log relationship between surface grading contributing area and slope for a range of weathering rates the results show that this log log relationship is robust the log log scaling is constant in space and true even for extreme weathering rates this has potentially important implications for soil geomorphology it suggests that an analytical solution can be found for soil grading catena this might allow us to more easily map soil distribution as a function of topographic characteristics

stable runoff and weathering fluxes into the oceans over quaternary climate cycles the effect of glacial interglacial cycles on surface weathering rates has been unclear a beryllium based proxy for weathering shows minimal variations in the input of silicate weathering products to the oceans for the past two million years

resolving the integral connection between pedogenesis and landscape evolution abstract soil is central in the terrestrial ecosystem linking and providing feedback responses to the other components i e water atmosphere and vegetation however the role of soil in landscape evolution is usually not well acknowledged in modeling landscape evolution soil is only treated as a residue of weathering that is transported and redistributed along the hillslope weathering is considered as a process that produces clays and generates unconsolidated materials available for erosion while pedology has been debating the form of qualitative factorial models for 75 years models for soil water heat solute gas and chemical reactions in a profile have matured as soils are distributed continuously in three dimensions across landscapes the profile models need to consider lateral fluxes this review outlines the role of soil in landscape modeling first we review the role of soil in the current landscape evolution models we then review data and models on soil weathering rates and transport processes we discuss soil profile models that simulate soil formation processes and combined soil landscape evolution models finally we discuss how the models can be tested and validated in the real world and suggest how both soil scientists and landscape modelers can work together to address the grand challenges in modeling earth surface processes

on the occurrence of polar mesosphere summer echoes polar mesospheric summer echoes pmse have become a well known characteristic of radar backscatter from the summer mesopause regions in polar regions the phenomenon has been observed at frequencies from 50 mhz to almost 1 ghz in this paper we attempt to identify a space time manifold for the occurrence of pmse the resulting manifold defined only by temperature agrees well with observations and furthermore indicates when and where we might expect to observe pmse in the future

the critical role of climate and saprolite weathering in landscape evolution landscapes evolve in response to external forces such as tectonics and climate that influence surface processes of erosion and weathering internal feedbacks between erosion and weathering also play an integral role in regulating the landscapes response our understanding of these internal and external feedbacks is limited to a handful of field based studies only a few of which have explicitly examined saprolite weathering here we report rates of erosion and weathering in saprolite and soil to quantify how climate influences denudation by focusing on an elevation transect in the western sierra nevada mountains california we use an adapted mass balance approach and couple soil production rates from the cosmogenic radionuclide crn 10be with zirconium concentrations in rock saprolite and soil our approach includes deep saprolite weathering and suggests that previous studies may have underestimated denudation rates across similar landscapes along the studied climate gradient chemical weathering rates peak at middle elevations 1200 2000 m averaging 112 3 9 7 t km 2 y 1 compared to high and low elevation sites 46 8 5 2 t km 2 y 1 measured weathering rates follow similar patterns with climate as those of predicted silica fluxes modeled using an arrhenius temperature relationship and a linear relationship between flux and precipitation furthermore chemical weathering and erosion are tightly correlated across our sites and physical erosion rates increase with both saprolite weathering rates and intensity unexpectedly saprolite and soil weathering intensities are inversely related such that more weathered saprolites are overlain by weakly weathered soils these data quantify exciting links between climate weathering and erosion and together suggest that climate controls chemical weathering via temperature and moisture control on chemical reaction rates our results also suggest that saprolite weathering reduces bedrock coherence leading to faster rates of soil transport that in turn decrease material residence times in the soil column and limit soil weathering copyright 2009 john wiley sons ltd

the marm3d spatially distributed soil evolution model three dimensional model framework and analysis of hillslope and landform responses 1 we present a three dimensional landscape pedogenesis model marm3d matrices armour 3d which simulates soil evolution as a function of erosion and pedogenic processes the model simulates the discretized soil profile for points on a spatial grid the approach using transition matrices is computationally efficient and allows the simulation of large scale spatial coupling and long term soil evolution we study the effect of the depth dependent soil weathering rate i e the rate of soil particle breakdown and bedrock lowering rate i e the rate of conversion of bedrock to soil the difference in depth dependent weathering functions has a significant effect on the in profile soil properties through depth specifically particle size grading however the depth dependency has a relatively minor effect on the surface properties of the soil profile with all weathering functions generating very similar surface properties the surface properties were a function of the cumulative amount of weathering i e the integral of the weathering function over exhumation with finer surface grading for higher weathering rates soil thickness could be estimated without explicitly modeling soil thickness thickness was negatively correlated with surface median grain size as thickness decreases the surface grading coarsens this was driven by surface erosion where as surface grading coarsens erosion decreases and the soil deepens weathering and erosion interact to spatially organize the surface soil grading with a log log relationship between surface grading contributing area and local slope this relationship was independent of the weathering function this relationship might be useful for the spatial description of soil properties in digital soil mapping

modelling soil genesis in calcareous loess abstract the soilgen1 model was developed to simulate soil development in calcareous loess at holocene 15 000 bp present temporal extent we used the leachc model as a core and added process formulations to describe the effect of vegetation and soil macrofauna on various soil properties a limited calibration was done on the calcite solubility constant by comparing decarbonization rates in various leaching climates with values predicted by the metamodel of egli and fitze egli m and fitze p 2001 quantitative aspects of carbonate leaching of soils with differing ages and climates catena 46 35 62 soil profiles of c and ph after 15 000 years compared well with measurements in a belgian loess profile that was never under agriculture taking the composition of the c horizon as uniform parent material scenarios with and without agriculture with varying degrees of bioturbation and for documented holocene climatic and vegetation evolutions in belgium and hungary were simulated and compared results show a clear effect of bioturbation on soil development especially in the continental climate evolution of hungary indicators for the possible occurrence of clay migration and disturbance of lateglacial morphology were calculated and these also show the importance of bioturbation

hillslope soils and vegetation abstract assessing how vegetation controls hillslope soil processes is a challenging problem as few abiotic landscapes exist as observational controls here we identify five avenues to examine how actively eroding hillslope soils and processes would differ without vegetation and we explore some potential feedbacks that may result in landscape resilience on vegetated hillslopes the various approaches suggest that a plant free world would be characterized by largely soil free hillslopes that plants may control the maximum thickness of soils on slopes that vegetated landforms erode at rates about one order of magnitude faster than plant free outcrops in comparable settings and that vegetated hillslope soils generally maintain long residence times such that both n and p sufficiency for ecosystems is the norm we conclude that quantitatively parameterizing biota within process based hillslope models needs to be a priority in order to project how human activity may further impact the soil mantle

a process based model for colluvial soil depth and shallow landsliding using digital elevation data a model is proposed for predicting the spatial variation in colluvial soil depth the results of which are used in a separate model to examine the effects of root strength and vertically varying saturated conductivity on slope stability the soil depth model solves for the mass balance between soil production from underlying bedrock and the divergence of diffusive soil transport this model is applied using high resolution digital elevation data of a well studied site in northern california and the evolving soil depth is solved using a finite difference model under varying initial conditions the field data support an exponential decline of soil production with increasing soil depth and a diffusivity of about 50 cm 2 yr the predicted pattern of thick and thin colluvium corresponds well with field observations soil thickness on ridges rapidly obtain an equilibrium depth which suggests that detailed field observations relating soil depth to local topographic curvature could further test this model bedrock emerges where the curvature causes divergent transport to exceed the soil production rate hence the spatial pattern of bedrock outcrops places constraints on the production law the infinite slope stability model uses the predicted soil depth to estimate the effects of root cohesion and vertically varying saturated conductivity low cohesion soils overlying low conductivity bedrock are shown to be least stable the model may be most useful in analyses of slope instability associated with vegetation changes from either land use or climate change although practical applications may be limited by the need to assign values to several spatially varying parameters although both the soil depth and slope stability models offer local mechanistic predictions that can be applied to large areas representation of the finest scale valleys in the digital terrain model significantly influences local model predictions this argues for preserving fine scale topographic detail and using relatively fine grid sizes even in analyses of large catchments

landscape evolution models a review of their fundamental equations abstract this paper reviews the main physical laws proposed in landscape evolution models lems it discusses first the main partial differential equations involved in these models and their variants these equations govern water runoff stream incision regolith bedrock interaction hillslope evolution and sedimentation a synthesis of existing lems is proposed it proposes three models with growing complexity and with a growing number of components two equation models with only two components governing water and bedrock evolution three equation models with three components where water bedrock and sediment interact and finally models with four equations and four interacting components namely water bedrock suspended sediment and regolith this analysis is not a mere compilation of existing lems it attempts at giving the simplest and most general physically consistent set of equations coping with all requirements stated in lems and lem software three issues are in particular addressed and hopefully resolved the first one is a correct formulation of the water transport equation down slopes a general formulation for this equation is proposed coping not only with the simplest form computing the drainage area but also with a sound energy dissipation argument associated with the saint venant shallow water equations the second issue arises from the coexistence of two competing modes namely the detachment limited erosion mode on hillslopes and the transport limited sediment transport on river beds the third issue linked to the second is the fact that no conservation law is available for material in these two modes a simple solution proposed to resolve these issues is the introduction as suggested by several authors of an additional variable for suspended sediment load in water with only three variables and three equations the above mentioned contradictions seem to be eliminated several numerical experiments on real digital elevation models dems illustrate the discussion and show results of landscape evolution with the proposed synthetic models

initial observations of polar mesospheric summer echoes using the eiscat svalbard radar polar mesospheric summer echoes pmse have been observed at various frequencies from mf to uhf and at various latitudes here we report the observation of pmse over svalbard 79 n at 500 mhz although pmse have been reported earlier at such high latitude at vhf notably around 50 mhz they had hitherto not been reported at such high frequency as 500 mhz furthermore this observation represents the first one using a frequency between 224mhz and 933mhz the pmse scattering mechanism is still open to debate and is certainly frequency dependent the new observations at 500 mhz will help to identify the transition frequency between different mechanisms

erosional and climatic effects on long term chemical weathering rates in granitic landscapes spanning diverse climate regimes abstract we used cosmogenic nuclide and geochemical mass balance methods to measure long term rates of chemical weathering and total denudation in granitic landscapes in diverse climatic regimes our 42 study sites encompass widely varying climatic and erosional regimes with mean annual temperatures ranging from 2 to 25 c average precipitation ranging from 22 to 420 cm year 1 and denudation rates ranging from 23 to 755 t km 2 year 1 long term chemical weathering rates range from 0 to 173 t km 2 year 1 in several cases exceeding the highest granitic weathering rates on record from previous work chemical weathering rates are highest at the sites with rapid denudation rates consistent with strong coupling between rates of chemical weathering and mineral supply from breakdown of rock a simple empirical relationship based on temperature precipitation and long term denudation rates explains 89 95 of the variation in long term weathering rates across our network of sites our analysis shows that for a given precipitation and temperature chemical weathering rates increase proportionally with fresh material supply rates we refer to this as supply limited weathering in which fresh material is chemically depleted to roughly the same degree regardless of its rate of supply from breakdown of rock the temperature sensitivity of chemical weathering rates is two to four times smaller than what one would expect from laboratory measurements of activation energies for feldspar weathering and previous inter comparisons of catchment mass balance data from the field our results suggest that climate change feedbacks between temperature and silicate weathering rates may be weaker than previously thought at least in actively eroding unglaciated terrain similar to our study sites to the extent that chemical weathering rates are supply limited in mountainous landscapes factors that regulate rates of mineral supply from erosion such as tectonic uplift may lead to significant fluctuations in global climate over the long term

a rudimentary mechanistic model for soil production and landscape development a rudimentary mechanistic model for soil production and landscape development is proposed the continuity equation of the model assumes that the change in soil thickness over time depends on the production of soil from the weathering of bedrock and the transport of soil through natural surface erosion the parameters for the model include the weathering rate and erosive diffusivity weathering rate is expressed as an exponential decay function of soil thickness which represents mechanical weathering erosive diffusivity can be estimated from soil erosion models the model is solved numerically using the finite difference approach and is applied to a numerical example simulation is performed for a hypothetical landscape with a series of hills and valleys results show the development rate of soil initially is very large and slows down until it reaches a steady state defined by a constant change in soil thickness the model also exhibits the characteristics of a nonlinear dynamic system nonlinearity of soil thickness and curvature and initial randomness appears to cause chaos instability in the system the results show promising progress in quantitative modelling of pedogenesis the limitations and suggested improvements of the model are also presented

time evolution of the mineralogical composition of mississippi valley loess over the last 10 kyr climate and geochemical modeling abstract anthropogenic and natural climate change affect processes in the atmosphere biosphere hydrosphere and pedosphere the impact of climate on soil evolution has not been well explored largely due to slow rates and the complexity of coupled processes that must be observed and simulated the rates of mineral weathering in loess deposited 23 kyr ago and experiencing soil formation for 13 kyr are explored here using the witch model for weathering and the genesis model for climate simulation the witch model which uses rigorous kinetic parameters and laws with provision for the effect on rates of deviation from equilibrium can successfully simulate the depletion profiles in the soil for dolomite and albite if soil co2 is assumed to rise over the last 10 kyr up to about 30 40 the present atmospheric pressure and if the solubility product of the ca smectite is assumed equal to that of an fe iii rich ca montmorillonite such simulations document that dissolution behavior for silicates and carbonates are strongly coupled through ph and for ca smectite and feldspars through dissolved silica such coupling is not incorporated in simple geometric and analytical models describing mineral dissolution and therefore probably contributes to the long standing observation of discrepancies among laboratory and field mineral dissolution rates

mechanistic soil landscape modelling as an approach to developing pedogenetic classifications pedologists classify soil individuals into groups in order to communicate with each other about the properties of the soil individuals ideally the classification should be meaningful and not arbitrary some argue that it should be based on the genetics or evolutionary history of soil such that it predicts properties of newly discovered or poorly known soil individuals here we propose pedogenetic systematics which is an attempt to understand the pedogenetic interrelationships trying to interpret the way in which soil has diversified and changed over time pedogenetic systematics may be defined as the reconstruction of the pattern of events that have led to the distribution and diversity of soil this paper presents a mechanistic model for soil formation which considers the weathering of the bedrock and soil distribution by erosion using this model we simulated soil development in a landscape the simulated soil genetic properties at different times were grouped into numerical soil classes this allows us to follow the evolution of the soil classes with time starting with a single soil class thin soil soil individuals in the landscape develop into more complex and diversified soil classes this paper presents our first attempt to build a soil phylogenetic tree which allows us to begin formalising the concept of pedogenetic systematics

geomorphic evolution of soil texture and organic matter in eroding landscapes geomorphic erosion on hillslopes creates a distribution of soil properties within the landscape that influences ecosystem erosional and hydrological processes these soil properties typically reflect topography and define a template for plant productivity and consequent soil carbon accumulation erosion also redistributes soil carbon and by burying or excavating carbon changes turnover time and may figure prominently in the global carbon budget stallard 1998 in this paper we present the changing relief and evolving ecosystems project creep a theoretical process response model that focuses on the redistribution of soil texture and soil carbon along a hillslope in response to geomorphic transport processes the creep model simulates long term ecological and geomorphic landscape evolution by simulating general soil vegetation and hillslope transport relationships in particular the model allows for the removal and downslope transport of soil carbon as well as for the burial and decomposition of carbon in the accumulation zone creep model results suggest that sandy soils are more likely to differentiate downslope with respect to soil texture than are more clay rich soils and that this redistribution will lead to disproportionately broad areas of predominantly coarse grained particles on upper slopes gridded biogeochemical models which may otherwise overlook landscape heterogeneity may use creep estimates of the areal distribution of soil texture as a basis for parametrically capturing trace gas fluxes nonlinearly related to soil texture

ecological insights into abyssal bentho pelagic fish at 4000 m depth using a multi beam echosounder on a remotely operated vehicle abstract ecological and behavioral data on mobile low density benthopelagic animals is difficult to collect in the abyssal environment however these species occupy an important position in the abyssal food chain at depth rov mounted echosounder studies provide a powerful tool to gather in situ information on abyssal benthopelagic assemblages and discern their distribution behavior and habitat associations this study presents a new perspective on mobile benthopelagic assemblages at the long term study site station m 4000 m using a seabat t20 s mbes mounted on the rov doc ricketts the targets 45 m off the seafloor are believed to be the abyssal grenadier of the species coryphaenoides armatus or c yaquinae species known to dominate the mobile benthopelagic fauna at station m the swimming behavior of the targets indicated little evidence of avoidance or attraction to the slowly moving rov and demonstrates the effectiveness of this platform to collect data on benthopelagic fish the information on targets in close

evaluating choices in multi process landscape evolution models the interest in landscape evolution models lems that simulate multiple landscape processes is growing however modelling multiple processes constitutes a new starting point for which some aspects of the set up of lems must be re evaluated the objective of this paper is to demonstrate the practical significance of and possibilities for such re evaluation we first discuss which simplifications must be made to set up lems then simplifications of particular interest to the modelling of multiple processes are identified finally case studies from new zealand belgium and croatia explore the performance of different model versions under several common choices for model and data simplifications in these case studies we illustrate methods to make the choices typically by i comparing the results of different model versions ii assessing model validity or iii indicating the sensitivity of models for different simplifications the results indicate that lem performance is strongly dependent on multi process related choices and that performance indicators can be used for ex post testing of the influence of these choices in particular we demonstrate the significance of simplifications regarding the number of processes presence of sinks and temporal resolution

new estimates of silicate weathering rates and their uncertainties in global rivers abstract this study estimated the catchment and global scale weathering rates of silicate rocks from global rivers using global compilation datasets from the gems water and hybam these datasets include both time series of chemical concentrations of major elements and synchronous discharge using these datasets we first examined the sources of uncertainties in catchment and global silicate weathering rates then we proposed future sampling strategies and geochemical analyses to estimate accurate silicate weathering rates in global rivers and to reduce uncertainties in their estimates for catchment silicate weathering rates we considered uncertainties due to sampling frequency and variability in river discharge concentration and attribution of weathering to different chemical sources our results showed that uncertainties in catchment scale silicate weathering rates were due mostly to the variations in discharge and cation fractions from silicate substrates to calculate unbiased silicate weathering rates accounting for the variations from discharge and concentrations we suggest that at least 10 and preferably 40 temporal chemical data points with synchronous discharge from each river are necessary for the global silicate weathering rate we examined uncertainties from infrequent sampling within an individual river the extrapolation from limited rivers to a global flux and the inverse model selections for source differentiation for this weathering rate we found that the main uncertainty came from the extrapolation to the global flux and the model configurations of source differentiation methods this suggests that to reduce the uncertainties in the global silicate weathering rates coverage of synchronous datasets of river chemistry and discharge to rivers from tectonically active regions and volcanic provinces must be extended and catchment specific silicate end members for those rivers must be characterized with current available synchronous datasets we suggest that the global silicate weathering rate ca mg silicate weathering flux was 2 17 2 range of 1 59 2 75 10 12 mol yr and the global co 2 consumption rates from silicate weathering was 7 85 5 78 9 93 10 12 mol yr since current synchronous datasets are not available for some rivers in tectonically active regions and highly active volcanic rocks our estimate should be considered as lower limit of estimates including the estimates from volcanic provinces from dessert et al 2003 the global co 2 consumption rates from silicates can be estimated as 11 93 9 86 14 01 10 12 mol yr which is similar to the previous estimates of gaillardet et al 1999

a threshold in soil formation at earth s arid hyperarid transition the soils of the atacama desert in northern chile have long been known to contain large quantities of unusual salts yet the processes that form these soils are not yet fully understood we examined the morphology and geochemistry of soils on post miocene fans and stream terraces along a south to north 27 to 24 s rainfall transect that spans the arid to hyperarid transition 21 to 2 mm rain y 1 landform ages are 2 my based on cosmogenic radionuclide concentrations in surface boulders and ar isotopes in interbedded volcanic ash deposits near the driest site indicate a maximum age of 2 1 my a chemical mass balance analysis that explicitly accounts for atmospheric additions was used to quantify net changes in mass and volume as a function of rainfall in the arid 21 mm rain y 1 soil total mass loss to weathering of silicate alluvium and dust 1030 kg m 2 is offset by net addition of salts 170 kg m 2 the most hyperarid soil has accumulated 830 kg m 2 of atmospheric salts including 260 kg sulfate m 2 and 90 kg chloride m 2 resulting in unusually high volumetric expansion 120 for a soil of this age the composition of both airborne particles and atmospheric deposition in passive traps indicates that the geochemistry of the driest soil reflects accumulated atmospheric influxes coupled with limited in soil chemical transformation and loss long term rates of atmospheric solute addition were derived from the ion inventories in the driest soil divided by the landform age and compared to measured contemporary rates with decreasing rainfall the soil salt inventories increase and the retained salts are both more soluble and present at shallower depths all soils generally exhibit vertical variation in their chemistry suggesting slow and stochastic downward water movement and greater climate variability over the past 2 my than is reflected in recent 100 y rainfall averages the geochemistry of these soils shows that the transition from arid to hyperarid rainfall levels marks a fundamental geochemical threshold in wetter soils the rate and character of chemical weathering results in net mass loss and associated volumetric collapse after 105 to 106 years while continuous accumulation of atmospheric solutes in hyperarid soils over similar timescales results in dramatic volumetric expansion the specific geochemistry of hyperarid soils is a function of atmospheric sources and is expected to vary accordingly at other hyperarid sites this work identifies key processes in hyperarid soil formation that are likely to be independent of location and suggests that analogous processes may occur on mars

long term observations of the arctic mesosphere with the mst radar at poker flat alaska in this report we summarize the results of 22 months of observations of arctic mesosphere echoes with the 50 mhz radar at poker flat alaska operation with a partially complete system began in february 1979 and has continued on a nearly continuous basis to the present time the altitude range of the mesospheric echoes obtained during this period shows a pronounced seasonal variation during summer months the mesospheric echoes are relatively continuous in time and extend from about 80 to 100 km with an unexpectedly strong peak in signal to noise ratio at about 85 km in contrast in nonsummer months mesospheric echoes are less intense and occur at lower altitudes in the range from 55 to 80 km these lower altitude nonsummer echoes are observed primarily during daytime hours when energetic auroral particle precipitation as determined by the poker flat 30 mhz riometer is present

weathering in three podzolized pedons on glacial deposits in northern sweden and central finland abstract chemical weathering losses were calculated for three conifer stands in relation to ongoing studies on chemical status soil solution chemistry and soil genesis weathering losses were based on elemental depletion trends in soil profiles since deglaciation and exposure to the weathering environment gradients in total geochemical composition were assumed to reflect alteration over time study sites were nyanget and heden in northern sweden and hyytiala in central finland the nyanget site is located on sandy loamy weichselian till at an altitude of 310 m a s l and the heden and hyytiala sites on water deposited coarse silt and out wash sand at an altitude of 175 and 150 m respectively volume determined samples from different soil levels were fused with lithium metaborate dissolved in hno 3 and analysed by icp aes results indicated highest cumulative weathering losses at heden and lower but similar values for nyanget and hyytiala the weathering losses for the elements are in the following order mg ca na k al fe mn si p total annual losses for ca mg k expressed in mmol c m 2 yr 1 amounted to 27 2 16 6 and 19 at heden nyanget and hyytiala respectively variations between study sites were consistent with differences in geochemistry and mineralogy the accumulated weathering losses after deglaciation were much larger in e than in b horizons for all elements studied for fe al and si this was partly due to the retention by precipitation of secondary minerals

spatial organization of soil depths using a landform evolution model 1 the evolution of soil depths is investigated by modeling the interaction between soil production and surface erosion within a landform evolution model an enhanced version of the landform evolution model siberia that incorporates a soil evolution module is used to simulate evolving landforms and soils depths over geologic timescales the spatial and temporal evolution of soil depths are examined at the hillslope scale though it is widely accepted among the geomorphology community that soil water enhances chemical physical and biological weathering processes its effect has not been explicitly included in published models of soil production the main scientific questions that we address are 1 what are the implications of incorporating soil moisture dependency in the soil production function and 2 what type of soil production dynamics is needed to generate a bedrock topography that has a different spatial pattern from that of the ground surface a range of physics for the soil production model is explored the effect of soil moisture is included using the wetness index obtained from drainage analysis of either surface elevations or the bedrock topography the results show that the various soil production functions that incorporate either a wetness index or subsurface flow depth based on the bedrock topography give rise to soils that self organize with well defined spatial patterns and bedrock elevations with spatial organization significantly different from that of the surface the model that incorporates the influence of subsurface water on soil production is able to naturally generate a soil production rate with a maximum value for a nonzero soil depth and overcomes an inconsistency of previously published humped soil production models

the ecology of the deep sea benthic and benthopelagic fish on the slopes of the rockall trough northeastern atlantic abstract a total of over 28 000 benthic and benthopelagic fish belonging to 34 families and comprising at least 85 species were collected from the hebridean terrace in the rockall trough between soundings of 500 and 2000 m commercial type trawls 20 6 m granton or 140 foot german bottom trawls fished on paired warps at 33 stations accounted for 89 of all individual caught the remainder being caught by a 16 4 m prawn trawl fished on a single warp 22 stations and a 3 m agassiz trawl 12 stations the stations sampled with a few exceptions fell into discrete bathymetric zones separated by increments of approximately 250 m and different combinations of nets were used at each of these zones the catch composition of the commercial trawls differed from those of the other nets the most obvious difference was that squalid sharks the alepocephalid alepocephalus bairdii and the black scabbard fish aphanopus carbo were important in the commercial type trawls but were absent or poorly represented in the other nets net size and towing speed were considered to be important factors influencing the catch composition net selectivity was most apparent on the upper and mid slopes but less apparent on the lower slopes relatively few families contribute to the total biomass at a given bathymetric zone and because the families squalidae and alepocephalidae contribute significantly to the biomass on the upper and mid slope it is therefore concluded that small nets must grossly underestimate the biomass at these depths the greatest biomass occurred at mid slope depths 750 1000 m

rock to sediment slope to sea with 10be rates of landscape change abstract measurements of cosmogenic nuclides predominately 10be allow new insights into the ways in which and the rates at which sediment is generated transported and deposited over timescales ranging from 103 to 106 years samples from rock exposures are used to estimate erosion rates at points on the landscape whereas samples of fluvial sediment provide estimates of basin scale rates of denudation integrated over 104 km2 nuclide data show that hilltop bare rock outcrops erode more slowly than basins as a whole suggesting the potential for relief to increase over time as well drained outcrops grow higher more elaborate experiments and interpretive models provide insight into the distribution of hillslope processes including the bedrock to soil conversion rate which appears to increase under shallow soil cover and then decrease under deeper soils changes in average nuclide activity down slopes can be used to estimate grain speed over millennia suggesting for example that sediment o

testing a soil development model against southern norway soil chronosequences abstract the first results of modeling soil development in marine sediments in s norway using the model soilgen are compared to measured properties of two soil chronosequences on the western and eastern side of oslofjord respectively the aim of this work is to test how well soil development under well defined environmental conditions can be modeled such testing reveals to what degree soil forming processes are understood allowing formulation of adequate calculations reflecting these processes the model predicts particle size distribution reasonably well although clay depletion in the upper parts of the soils as a result of clay migration is overestimated the model tends to underestimate contents of organic carbon and cec in the a horizons below modeled cec matches well with measured cec base saturation is overestimated in the upper 40 cm and underestimated below apparently leaching of bases proceeds less rapidly in reality than is predicted by the model due to strong soil structure of the b horizons causing preferential flow and base leaching around the aggregates whereas bases inside the aggregates are only slightly affected by leaching difficulties and possibilities for improvements are identified some related to model input data and some to the model itself input data could be improved by determining the amounts of organic carbon in organic surface horizons and by quantifying effects of bioturbation a big challenge is the implementation of soil structure formation in the model quantitative data on the development of soil structure with time that can be included in a model are required amounts distribution and connectivity of macro pores need to be defined for each stage of soil development and zones of low and high base leaching need to be distinguished in the model for each time step the long term aim of this work is to model soil development with different sets of soil forming factors e g different climatic conditions in order to reliably predict soil development under different climate scenarios and related sets of soil forming factors the results of the first model runs and the identified possible improvements suggest that this aim is generally achievable

late quaternary erosion in southeastern australia a field example using cosmogenic nuclides late quaternary rates of apparent soil production bedrock incision and average erosion are determined for the southeastern highlands of australia using in situ produced cosmogenic nuclide concentrations of 10 be and 26 al apparent soil production rates define a steep inverse exponential function of soil depth with a maximum of 143 m ma 1 under zero soil depth there were no observed soil depths between about 25 cm and zero however such that the maximum observed rate is about 50 m ma 1 the bredbo river catchment average erosion rate is 157 1mm a 1 and is similar to the average hillslope erosion rate of 167 1mm a 1 bedrock incision rates average 9 mma 1 and suggest that the higher rates of hillslope erosion may be in response to a pulse of incision perhaps generated by knickpoint propagation bedrock erosion rates inferred froma tor profile average 3 8 mma 1 with higher rates on other more weathered tor tops an aboveground tor profile of nuclide concentrations is consistent with a simple model of rapid stripping of the surrounding saprolite supporting the view that at least one episodic period of increased denudation has affected the landscape evolution of the highlands we test this hypothesis by using a simple landscape evolution model to reasonably predict the spatial variation of soil depth as well as the emergence of tors r 2001 elsevier science ltd and inqua all rights reserved

river sediment discharge to the oceans present day controls and global budgets empirical relationships between river sediment yields and a large number of hydroclimatic biological and geomorphological parameters are investigated at the global scale for a set of 60 major world river basins the environmental characteristics were extracted from various global computer data sets and natural river sediment fluxes were taken from the literature it is found that sediment yields can be best correlated by forming the products of hydroclimatic and geomorphological factors that is runoff intensity basin slope an index characterizing rock hardness and an index characterizing rainfall variability over the year the best parameter combination varies to some extent when the rivers are grouped according to their average climatic situation but it is always a combination of the above mentioned parameters that yields the most significant models in arid climates however regression coefficients are greater than in humid climates indicating that erodibility is much greater than in arid climates when extrapolated to the total continental area on the basis of the corresponding data sets the empirical models result in a total sediment flux of about 16 gigatons discharged to the oceans every year which is in good agreement with previous estimates derived from compilations of world wide river data consequently two global maps are proposed showing the spatial distributions of river sediment yields on the continents as well as the inputs of these sediments to the oceans in a grid point scale by far most of the sediments originate from the young orogenic belts of the continents mainly due to a combination of steep morphologies and high runoff intensities

estimating the effect of tree uprooting on variation of soil horizon depth by confronting pedogenetic simulations to measurements in a belgian loess area 1 spatial patterns of soil often do not reflect those of topographic controls we attempted to identify possible causes of this by comparing observed and simulated soil horizon depths observed depths of e bt bc c1 and c2 horizons in loess derived soils in belgium showed a weak to absent relation to terrain attributes in a sloping area we applied the soil genesis model soilgen2 16 onto 108 1 1 m2 locations in a 1329 ha area to find possible causes two scenarios were simulated model 1 simulated soil development under undisturbed conditions taking slope aspect and loess thickness as the only sources of variations model 2 additionally included a stochastic submodel to generate tree uprooting events based on the exposure of trees to the wind outputs of both models were converted to depths of transitions between horizons using an algorithm calibrated to horizon depths observed in the field model 1 showed strong correlations between terrain attributes and depths for all horizons although surprisingly regression kriging was not able to model all variations model 2 showed a weak to absent correlation for the upper horizons but still a strong correlation for the deeper horizons bc c1 and c2 for the upper horizons the spatial variation strongly resembled that of the measurements this is a strong indication that bioturbation in the course of soil formation due to treefalls influences spatial patterns of horizon depths

weathering the escarpment chemical and physical rates and processes south eastern australia differences in chemical weathering extent and character are expected to exist across topographic escarpments due to spatial gradients of climatic and or tectonic forcing the passive margin escarpment of south eastern australia has a debated but generally accepted model of propagation in which it retreated within 40 ma to near its current position following rifting between australia and new zealand 85 100 ma before present we focus on this escarpment to quantify chemical weathering rates and processes and how they may provide insight into scarp evolution and retreat we compare chemical weathering extents and rates above and below the escarpment using a mass balance approach coupling major and trace element analyses with previous measurements of denudation rates using cosmogenic nuclides 10be and 26al we find a slight gradient in saprolite chemical weathering rate as a percentage of total weathering rate across the escarpment the lowlands area encompassing the region extending from the base of the escarpment to the coast experiences a greater extent of chemical weathering than the highland region above the escarpment percents of denudation attributable to saprolite weathering average 57 6 and 47 7 at low and high sites respectively furthermore the chemical index of alteration cia a ratio of immobile to mobile oxides in granitic material that increases with weathering extent have corresponding average values of 73 7 3 9 and 65 5 3 4 indicating lower extents of weathering above the escarpment finally we quantify variations in the rates and extent of chemical weathering at the hillslope scale across the escarpment to suggest new insight into how climate differences and hillslope topography help drive landscape evolution potentially overprinting longer term tectonic forcing copyright 2009 john wiley sons ltd

modelling soil landscape genesis a time split approach for hummocky agricultural landscapes abstract here we present a scheme for modelling soil landscape development in hummocky agricultural landscapes of formerly glaciated terrains soil landscape development is regarded as discontinuous over time long term progressive soil development during the holocene was replaced abruptly by an intense period of regressive pedogenesis during the last 50 years which is deduced from published 137 cs data and catchment scale mass balances consequently our primary working hypothesis is that the recent soil pattern is mainly a result of human influence during the last 50 years the paradigm behind our approach is that we have to couple geological historical information with recent dynamics of relevant processes to understand soil landscape development spatially distributed erosion and sedimentation are the most important processes during that period the intensity and extent of these processes is however also a function of the spatial pattern of soils erodibility which evolved in the progressive period therefore we developed a time split modelling approach for the progressive period relevant pedogenic processes de carbonatization silicate weathering clay translocation have to be quantified by a spatially distributed coupled water flow and solute transport model based on reconstructed initial and upper boundary conditions geomorphic units climate history relevant outputs e g topsoil textural properties are used as a spatially distributed input for the model of the regressive period for the latter we use a modified version of the dynamic physically based erosion 3d model schmidt j von werner m michael a 1996 erosion 2d 3d a computer model to simulate water erosion in german sachsische landesanstalt fur landwirtschaft dresden which allows spatially distributed modelling of water related soil erosion and deposition relevant topsoil properties are iteratively adapted to the rates of spatially distributed erosion and deposition preliminary results suggest that a coupling with tillage erosion plays an important role in our landscapes explicit analyses of the soil pattern using digital soil mapping techniques will be applied for model validation

deep sea mobile megafauna of mediterranean submarine canyons and open slopes analysis of spatial and bathymetric gradients abstract mediterranean canyons are generally characterized by complex topography and hydrographic conditions and can act as conduits for organic matter and sediments from the shelf to the deep sea which result in enhanced macro and megafaunal abundance and biodiversity here we reviewed the literature of the last 20 years and combined available information with new data from our own datasets including unpublished data on megafaunal species inhabiting submarine canyons and the adjacent slopes we analysed the data acquired using different gears from baited cameras on aluminum frames and landers and baited traps to commercial trawl gears in order to combine and complement the results in megafaunal biodiversity and assemblage structure in mediterranean canyons overall the results of our analysis on megafaunal assemblages allowed identifying 400 species including 28 species of cephalopods 64 of decapod crustaceans 25 of echinoderms 27 of elasmobranches and 127 of actinopterygii we observed significant longitudinal differences in assemblage composition with high species turnover across mediterranean sub basins our analysis also confirmed the importance of depth axis as the main factor influencing the structure of the deep sea demersal assemblages with greater diversity in the upper part of the slopes the multivariate multiple regression analysis showed that geomorphological features of the canyons i e slope dendricity sinuosity and distance from adjacent canyons contribute significantly to explain the observed variability in the taxonomic composition of megafaunal assemblages at sub basin scale the results presented here are important in global biodiversity management perspectives and confirm that canyons represent a seascape unit deserving protection at different levels modulated according to biogeographic and geomorphological features

modelling chemical depletion profiles in regolith abstract chemical or mineralogical profiles in regolith display reaction fronts that document depletion of leachable elements or minerals a generalized equation employing lumped parameters was derived to model such ubiquitously observed patterns c c 0 c 0 c x 0 c x 0 exp ini k x 1 here c cx 0 and co are the concentrations of an element at a given depth x at the top of the reaction front or in parent respectively ini is the roughness of the dissolving mineral in the parent and k is a lumped kinetic parameter this kinetic parameter is an inverse function of the porefluid advective velocity and a direct function of the dissolution rate constant times mineral surface area per unit volume regolith this model equation fits profiles of concentration versus depth for albite in seven weathering systems and is consistent with the interpretation that the surface area m2 mineral m 3 bulk regolith varies linearly with the concentration of the dissolving mineral across the front dissolution rate constants can be calculated from the lumped fit parameters for these profiles using observed values of weathering advance rate the proton driving force the geometric surface area per unit volume regolith and parent concentration of albite these calculated values of the dissolution rate constant compare favorably to literature values the model equation useful for reaction fronts in both steady state erosional and quasi stationary non erosional systems incorporates the variation of reaction affinity using ph as a master variable use of this model equation to fit depletion fronts for soils highlights the importance of buffering of ph in the soil system furthermore the equation should allow better understanding of the effects of important environmental variables on weathering rates

a catchment scale evaluation of the siberia and caesar landscape evolution models landscape evolution models provide a way to determine erosion rates and landscape stability over times scales from tens to thousands of years the siberia and caesar landscape evolution models both have the capability to simulate catchment wide erosion and deposition over these time scales they are both cellular operate over a digital elevation model of the landscape and represent fluvial and slope processes however they were initially developed to solve research questions at different time and space scales and subsequently the perspective detail and process representation vary considerably between the models notably caesar simulates individual events with a greater emphasis on fluvial processes whereas siberia averages erosion rates across annual time scales this paper describes how both models are applied to tin camp creek northern territory australia where soil erosion rates have been closely monitored over the last 10 years results simulating 10 000 years of erosion are similar yet also pick up subtle differences that indicate the relative strengths and weaknesses of the two models the results from both the siberia and caesar models compare well with independent field data determined for the site over different time scales representative hillslope cross sections are very similar between the models geomorphologically there was little difference between the modelled catchments after 1000 years but significant differences were revealed at longer simulation times importantly both models show that they are sensitive to input parameters and that hydrology and erosion parameter derivation has long term implications for sediment transport prediction therefore selection of input parameters is critical this study also provides a good example of how different models may be better suited to different applications or research questions copyright 2010 john wiley sons ltd and commonwealth of australia

rock weathering rates as functions of time the scarcity of documented numerical relations between rock weathering and time has led to a common assumption that rates of weathering are linear this assumption has been strengthened by studies that have calculated long term average rates however little theoretical or empirical evidence exists to support linear rates for most chemical weathering processes with the exception of congruent dissolution processes the few previous studies of rock weathering rates that contain quantitative documentation of the relation between chemical weathering and time suggest that the rates of most weathering processes decrease with time recent studies of weathering rinds on basaltic and andesitic stones in glacial deposits in the western united states also clearly demonstrate that rock weathering processes slow with time some weathering processes appear to conform to exponential functions of time such as the square root time function for hydration of volcanic glass which conforms to the theoretical predictions of diffusion kinetics however weathering of mineralogically heterogeneous rocks involves complex physical and chemical processes that generally can be expressed only empirically commonly by way of logarithmic time functions incongruent dissolution and other weathering processes produce residues which are commonly used as measures of weathering these residues appear to slow movement of water to unaltered material and impede chemical transport away from it if weathering residues impede weathering processes then rates of weathering and rates of residue production are inversely proportional to some function of the residue thickness this results in simple mathematical analogs for weathering that imply nonlinear time functions the rate of weathering becomes constant only when an equilibrium thickness of the residue is reached because weathering residues are relatively stable chemically and because physical removal of residues below the ground surface is slight many weathering features require considerable time to reach constant rates of change for weathering rinds on volcanic stones in the western united states this time is at least 0 5 my

first measurements of tidal modes in the lower thermosphere by the eiscat svalbard radar first measurements by the eiscat svalbard radar of ion velocities in the lower thermosphere show the presence of strong tidal or quasi tidal modes with periods of 24 12 and 8 hours the diurnal mode shows no variation of phase with height above 100 km in contrast the semidiurnal and terdiurnal modes show a steady variation of phase with height corresponding to vertical wavelengths of about 40 km and 30 km respectively in addition there is evidence at 93 km the lowest height measured of a planetary wave with a period of 2 3 days

a rudimentary mechanistic model for soil formation and landscape development ii a two dimensional model incorporating chemical weathering the necessity for a quantitative analysis of pedogenesis has become more compelling in the last few decades in part one of this paper we proposed a rudimentary mechanistic model that considers soil formation spatially at the catena scale this paper extends the model for soil formation in a landscape conditioned by a digital elevation model and further illustrates the application of the model in quantifying pedogenesis the current model states that the change in soil thickness over time depends on the physical weathering rate of rock the loss due to chemical weathering and the transport of soil through erosion the rate of physical weathering or lowering of the bedrock surface is represented as an exponential decline with soil thickness the chemical weathering rate is modelled as a negative exponential function of both soil thickness and time assuming uni dimensional weathering the rate of chemical weathering can be expressed as a reduction in soil thickness the movement of materials in the landscape is characterized by diffusive transport the model is solved numerically using the finite difference approach and applied to a digital elevation model the results for simulation of soil formation in a landscape after 10 000 years shows that the soil accumulates thickens in the gullies and erodes thins in the ridges the soil from the upper slope is transported down slope by the erosion processes and fills the gullies soil thickness is highly correlated with the profile curvature the effect of climate rock type and land management is illustrated by different combinations of weathering rate and erosive diffusivity to illustrate the effect of irregularity and randomness on the stability of the solution and the soil development spatially correlated normally distributed random numbers were added to the initial soil elevation the small randomness appears to cause instability chaos in the system dimensionality analysis of the soil thickness as a function of time confirms the non linear chaotic behaviour of the model rather than merely random noise a difference plot of the soil thickness time series unveiled the presence of a strange attractor alternatively these results may be a result of numerical instability

modeling the genesis of luvisols as a function of topographic position in loess parent material this article has been withdrawn at the request of the authors and editors the publisher apologizes for any inconvenience this may cause the full elsevier policy on article withdrawal can be found at http www elsevier com locate withdrawalpolicy

cosmic ray produced 10be and 26al in antarctic rocks exposure and erosion history we have measured cosmic ray produced t1 2 1 5 million years 10be and t1 2 0 705 million years 26al in purified quartz fractions of selected rock samples from antarctic mountains from these data we calculate 1 mean erosion rates for the limiting case of steady state surface exposure to cosmic rays and 2 minimum exposure ages for the limiting case of no erosion calculated mean erosion rates are very low on the order of a few times 10 5 cm yr we believe the sampling to be sufficient to generalize this result to exposed bedrock in antarctica in favorable cases it is possible to distinguish between the limiting cases steady state erosion seems a better description in such cases most samples including some taken a few meters above the present ice level seem to have been exposed for millions of years without major episodes of burial or abrasion by ice

modeling soil genesis at pedon and landscape scales achievements and problems modeling soil evolution is an important step towards understanding the complexity of the soil system and its interaction with the other systems the major challenge confronted by pedologists until now is the ability to develop models capable of describing the complete complexity of the soil system this paper presents the state of art overview of such a soil evolution model soilgen its applications and limitations in addition the paper gives an overview of how the soilgen model may be linked to landscape evolution models to model soilscape development soilgen is a mechanistic pedogenetic model in which soil forming processes such as clay migration decalcification carbon cycling bioturbation physical and chemical weathering coupled with water flow are simulated at multi millennium time scale the model has been calibrated and undergone extensive field testing giving reasonable results at both pedon and landscape scales however discrepancies between observed and simulated soil properties such as base saturation bs cation exchange capacity cec and ph have been reported these have been attributed partly to simplification of soil forming processes particularly in the weathering and chemical systems there is therefore a need to extend the description of chemical and weathering systems in the soilgen model these extensions will not only improve model performance but will also enlarge its application range in simulating the genesis of typical features of more than half of the wrb reference soil groups we also note here that although landscape evolution models have been successfully applied to model soil production and distribution simplified and or incomplete description of soil forming processes remain major limitations we therefore add to the voices in scientific literature calling for integration of pedon and landscape scale models in addition there is critical need for high quality chronosequence climosequence and toposequence profile datasets to enhance calibration and validation of soil evolution models

reconstructing ancient topography through erosion modelling one of the main aims of geomorphology is to understand how geomorphic processes change topography over long time scales over the last decades several landscape evolution models have been developed in order to study this question however evaluation of such models has often been very limited due to the lack of necessary field data in this study we present a topography based hillslope erosion and deposition model that is based on the watem sedem model structure and works on a millennial time scale soil erosion transport and deposition are calculated using slope and unit contributing area the topography is iteratively rejuvenated by taking into account modelled erosion and deposition rates thereby simulating topographic development backwards in time a first attempt has been made to spatially evaluate the model using detailed estimates for historical soil erosion and sediment deposition volumes obtained from an augering campaign in a small catchment in the belgian loess belt the results show that the model can simulate realistic soil redistribution patterns however further research is necessary in order to deal with artificial flaws that cause routing problems and significantly influence results common problems and issues related to this type of backward modelling are also discussed

first observations of summer polar mesospheric backscatter with a 224 mhz radar exceptionally strong echoes from the mesopause region have been observed with the eiscat 224 mhz radar during the summer of 1987 the echoes are so strong that they cannot be explained by incoherent scatter theory but may instead be associated with neutral air turbulence we discuss the variability of these echoes in terms of time and height distribution and outline some characteristics of vertical velocity oscillations observed at the echo height

coupling chemical weathering with soil production across soil mantled landscapes soil covered upland landscapes constitute a critical part of the habitable world our understanding of how they evolve as a function of different climatic tectonic and geological regimes is important across a wide range of disciplines and depends in part on understanding the links between chemical and physical weathering processes extensive previous work has shown that soil production rates decrease with increasing soil column thickness but chemical weathering rates were not measured here we examine a granitic soil mantled hillslope at point reyes california where soil production rates were determined using in situ produced cosmogenic nuclides 10be and 26al and we quantify the extent as well as the rates of chemical weathering of the saprolite from beneath soil from across the landscape we collected saprolite samples from the base of soil pits and analysed them for abrasion ph as well as for major and trace elements by x ray fluorescence spectroscopy and for clay mineralogy by x ray diffraction spectroscopy our results show for the first time that chemical weathering rates decrease with increasing soil thickness and account for 13 to 51 per cent of total denudation we also show that spatial variation in chemical weathering appears to be topographically controlled weathering rate decreases with slope across the divergent ridge and increases with upslope contributing area in the convergent swale furthermore to determine the best measure for the extent of saprolite weathering we compared four different chemical weathering indices the vogt ratio the chemical index of alteration cia parker s index and the silicon aluminium ratio with saprolite ph measurements of the cia were the most closely correlated with saprolite ph showing that weathering intensity decreases linearly with an increase in saprolite ph from 4 7 to almost 7 data presented here are among the first to couple directly rates of soil production and chemical weathering with how topography is likely to control weathering at a hillslope scale copyright 2006 john wiley sons ltd

coupled numerical analytical approach to landscape evolution modeling the earth s topography is shaped by surface processes that operate on various scales in particular river processes control landscape dynamics over large length scales whereas hillslope processes control the dynamics over smaller length scales this scale separation challenges numerical treatments of landscape evolution that use space discretization large grid spacing cannot account for the dynamics of water divides that control drainage area competition and erosion rate and slope distribution small grid spacing that properly accounts for divide dynamics is computationally inefficient when studying large domains here we propose a new approach for landscape evolution modeling that couples irregular grid based numerical solutions for the large scale fluvial dynamics and continuum based analytical solutions for the small scale fluvial and hillslope dynamics the new approach is implemented in the landscape evolution model dac divide and capture the geometrical and topological characteristics of dac s landscapes show compatibility with those of natural landscapes a comparative study shows that even with large grid spacing dac predictions fit well an analytical solution for divide migration in the presence of horizontal advection of topography in addition dac is used to study some outstanding problems in landscape evolution i the time to steady state is investigated and simulations show that steady state requires much more time to achieve than predicted by fixed area calculations due to divides migration and persistent reorganization of low order streams ii large scale stream captures in a strike slip environment are studied and show a distinct pattern of erosion rates that can be used to identify recent capture events iii three tectono climatic mechanisms that can lead to asymmetric mountains are studied each of the mechanisms produces a distinct morphology and erosion rate distribution application to the southern alps of new zealand suggests that tectonic advection precipitation gradients and non uniform tectonic uplift act together to shape the first order topography of this mountain range copyright 2014 john wiley sons ltd

rates and time scales of clay mineral formation by weathering in saprolitic regoliths of the southern appalachians from geochemical mass balance rates of clay formation in three watersheds located at the coweeta hydrologic laboratory western north carolina have been determined from solute flux based mass balance methods a system of mass balance equations with enough equations and unknowns to allow calculation of secondary mineral formation rates as well as the more commonly determined primary mineral dissolution rates was achieved by including rare earth elements ree in the mass balance rates of clay mineral formation determined by mass balance methods have been used to calculate the time needed for a 5 50 g kg 1 change in relative clay abundance in the saprolite at coweeta this corresponds to the response time of the clay mineral to for example a change in climate the 5 change in relative clay abundance is the smallest change that can generally be detected using x ray diffraction xrd response times range from tens of thousands to hundreds of thousands of years extrapolating the coweeta clay formation rates to other southern appalachian regoliths the time required to form measured clay abundances production times in eastern blue ridge and inner piedmont regolith have been calculated the production times of clay mineral assemblages range from 2 k y to 2 m y with mean values ranging from 50 k y to 1 m y the results of this study are consistent with the arguments of thiry 2000 1 that the best resolution of the paleoclimatic record in marine clay rich sediments and mudrocks is 1 or 2 m y 1 ref 107

erosional dynamics flexural isostasy and long lived escarpments a numerical modeling study erosional escarpments are common features of high elevation rifted continents fission track data suggest that these escarpments form by base level lowering and or marginal uplift during rifting followed by lateral retreat of an erosion front across tens to hundreds of kilometers previous modeling studies have shown that this characteristic pattern of denudation can have a profound impact upon marginal isostatic uplift and the evolution of offshore sedimentary basins yet at present there is only a rudimentary understanding of the geomorphic mechanisms capable of driving such prolonged escarpment retreat in this study we present a nonlinear two dimensional landscape evolution model that is used to assess the necessary and sufficient conditions for long term retreat of a rift generated escarpment the model represents topography as a grid of cells with drainage networks evolving as water flows across the grid in the direction of steepest descent the model accounts for sediment production by weathering fluvial sediment transport bedrock channel erosion and hillslope sediment transport by diffusive mechanisms and by mass failure numerical experiments presented explore the effects of different combinations of erosion processes and of dynamic coupling between denudation and flexural isostatic uplift model results suggest that the necessary and sufficient conditions for long term escarpment retreat are 1 incising bedrock channels in which the erosion rate increases with increasing drainage area so that the channels steepen and propagate headward 2 a low rate of sediment production relative to sediment transport efficiency which promotes relief generating processes over diffusive ones 3 high continental elevation which allows greater freedom for fluvial dissection and 4 any process including flexural isostatic uplift that helps to maintain a drainage divide near an escarpment crest flexural isostatic uplift also facilitates escarpment retreat by elevating topography in the vicinity of an eroding escarpment thereby increasing channel gradients and accelerating erosion which in turn generates additional isostatic uplift of all the above conditions high continental elevation is common to most rift margin escarpments and may ultimately be the most important factor

scaling factors for the rates of production of cosmogenic nuclides for geometric shielding and attenuation at depth on sloped surfaces abstract the decrease in rates of production of cosmogenic nuclides occurs because of shielding of cosmic rays by mountains sloped surfaces and local rock formations that block them when a large part of the sky is blocked this correction is large and requires detailed model calculations this paper considers three geometries a rectangular obstruction a triangular obstruction and a sloped surface other geometries can be considered as a combination of these the results are presented in terms of formulas and graphs so that the reader can easily apply them to common field situations any use of cosmogenic nuclides in the study of geomorphic processes or forms must consider factors that introduce variations in the production of nuclides

impact of hillslope derived sediment supply on drainage basin development in small watersheds at the northern border of the central alps of switzerland abstract this paper explores the effects of hillslope mobility on the evolution of a 10 km 2 drainage basin located at the northern border of the swiss alps it uses geomorphologic maps and the results of numerical models that are based on the shear stress formulation for fluvial erosion and linear diffusion for hillslope processes the geomorphic data suggest the presence of landscapes with specific cross sectional geometries reflecting variations in the relationships between processes in channels and on hillslopes in the headwaters the landscape displays parabolic cross sectional geometries indicating that mass delivered to channels by hillslope processes is efficiently removed in the trunk stream portion the landscape is i v shaped if the downslope flux of mass is balanced by erosion in channels i e if mass delivered to channels by hillslope processes is efficiently removed and ii u shaped if in channel accumulation of hillslope derived material occurs this latter situation indicates a non balanced mass flux between processes in channels and on hillslopes information about the spatial pattern of the postglacial depth of erosion allows comparative estimates to be made about the erosional efficiency for the various landscapes that were mapped in the study area the data suggest that the erosional potential and sediment discharge are reduced for the situation of a non balanced mass flux between processes in channels and on hillslopes these findings are also supported by the numerical model indeed the model results show that high hillslope mobility tends to reduce the hillslope relief and to inhibit dissection and formation of channels in contrast stable hillslopes tend to promote fluvial incision and the hillslope relief increases the model results also show that very low erosional resistance of bedrock promotes backward erosion and steepening of channel profiles in headwaters beyond that the model reveals that sediment discharge generally increases with decreasing erosional resistance of bedrock but that this increase decays exponentially with increasing magnitudes of fluvial and hillslope mobilities very high hillslope diffusivities even tend to reduce the erosional potential of the whole watershed it appears that besides rates of base level lowering factors limiting sediment discharge might be the nonlinear relationships between processes in channels and on hillslopes

the cause of particle size distribution in soil profiles derived from crystalline rocks france abstract particle size distributions of horizons of 600 profiles derived from crystalline rocks were plotted on right angled texture triangles points representing horizons within the same profile were connected and the resulting curves called particle displacement paths demonstrate that only a small number of types of such paths are common and distinctive the types are related for the most part to kinds of soils although source rocks also affect particle size distribution computer models constructed on the basis of the evolution of particle size distribution indicate that fragmentation and dissolution probably play an important role in the textural differentiation of the profiles

comparing landscape evolution models with quantitative field data at the millennial time scale in the belgian loess belt this study compares three landscape evolution models and their ability to correctly simulate measured 2500 year landscape evolution in two small catchments in the belgian loess belt watem lt and lapsus both model tillage and water erosion and deposition and have detachment limited descriptions for water erosion and deposition equations in lapsus are more mechanistic than those in watem lt watem ltt resembles watem lt but is a transport limited model all three models are dem based calibration and validation simulations were performed forward in time on 1d transects for four spatial resolutions and backward in time for 2d catchments at 20 m resolution for transects model outputs were compared with discretized observations of transect shape for catchments outputs were compared with point observations of palaeo altitude averaged over landscape element classes for transects the three models performed well resulting in model efficiency factors of 0 92 to 0 99 for calibration and 0 62 to 0 96 for validation however for catchments simulations showed that the transport limited watem ltt model could not realistically simulate long term landscape evolution performance of watem lt and lapsus at catchment scale was similar to that on transects although lapsus has problems with backward calculation tests demonstrate that a transport limited approach cannot be used to model long term landscape evolution in the belgian loess belt which is in agreement with theoretical and empirical understanding of soil erosion processes in this environment the difference in performance between transport limited and detachment limited models is clear only when the models are evaluated in a 2d catchment the lack of such distinction when models were applied in a 1d transect highlights the importance of evaluating landscape evolution models in a 2d setting so that effects of flow convergence divergence can be accounted for copyright 2011 john wiley sons ltd

spatio temporal modeling of soil characteristics for soilscape reconstruction abstract full coverage maps for several specific soil characteristics were produced at particular time intervals over a time span of 12 716 years for a 584 km 2 large study area located in belgium the pedogenetic process model soilgen2 was used to reconstruct the evolution of several soil variables at specific depths in the soil profile at various point locations 96 in total the time span covered by the simulations encompassed the final part of the younger dryas and the holocene up till the present time series on climate organisms and groundwater table were reconstructed and supplied to the model as boundary conditions model quality optimization was performed by calibrating the solubility constant of calcite by a comparison of the simulated time necessary for decarbonization with literature values and evaluating the calibrated value over a wide range of precipitation surpluses representative for the regarded time period the simulated final state was evaluated against measurements collected in a database representing the historic state of the soil at 1950 the simulated specific soil characteristics at the point locations were then used to produce full coverage maps at the particular time intervals by regression kriging such maps are believed to provide useful information for geoarcheological studies and archeological land evaluations

the impact of climate on the biogeochemical functioning of volcanic soils abstract rainfall and the amount of water available to leach ions from soil are among the most important features determining mineral weathering secondary mineral synthesis and soil chemical properties along an arid to humid climosequence on kohala mountain hawaii we sampled 16 soil profiles and found that weathering and soil properties change in a nonlinear fashion with increased rainfall the lavas are influenced by a strong rain shadow with mean annual precipitation map averaging 160 mm near the coast and rising to 3000 mm near the summit a temperature decline from 24 to 15 c with increasing elevation is matched by lower potential evapotranspiration et a water balance model monthly precipitation minus monthly et defines three broad climate zones along the sampling transect an arid zone with moisture deficit in every month an intermediate zone with moisture deficit during low rainfall summer months and moisture surplus during high rainfall winter months and a humid zone with moisture surplus during every month the annualized water balance can be ratioed with the integrated porosity of the top meter of soil to provide a leaching index the index reaches 1 total filling of the pore space on an annual basis at about 1400 mm map index values 1 imply intense leaching conditions because of pore water replacement in these 170 ka soils leaching losses of soluble base cations and si are nearly complete at index values 1 whereas only 60 of al has been lost at index values 1400 mm soil buffering capacity has been totally exhausted leading to low ph and low ecec the nonlinear decline in ecec is irreversible under natural conditions base cation depleted soils will remain so even if the climate shifts to drier conditions in contrast a climate shift to wetter conditions can drastically modify surface chemical properties existing in the drier soils as weathering depletes primary minerals elements are lost to leaching and surface chemistry is modified there is a time dimension implied in climate gradient studies soils forming in recently rejuvenated landscapes contain more primary minerals and should experience loss of buffering capacity at higher rainfall loss of buffering capacity means that biological acidity will move more deeply into the vadose zone or into the aquatic system the details of this transfer depend on present and past climate and the age and erosional stability of landscapes

how fast does soil grow abstract quantifying the rate of soil formation has become important in response to the consideration of soil as a renewable resource the availability of new sophisticated laboratory techniques has opened up the possibility of addressing the demand of quantifying processes of soil landscape evolution in the critical zone here we investigated the rate of soil formation of world soils based on published results of tcn derived terrestrial cosmogenic nuclides 10 be soil production rates spr the compilation of published tcn derived spr for different climatic zones and lithologic conditions showed exponentially decreasing spr with increasing soil thickness for the majority of the discussed studies this implies that the presence of a soil mantle protects the bedrock from further weathering we found that rates of soil production in australia appear to be similar in range when compared with other parts of the world we concluded that we can formulate an average quantitative estimate of global soil production based on tcn soil production rate mm kyr 1 114 11 exp 2 05 soil thickness in mm such a rate is useful for global modelling of soil formation to better understand the role of soils in landscape evolution

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