soil mineralogy trends in california landscapes california s diverse environmental gradients serve as natural experiments for examining controls on soil mineral distribution in landscapes in this paper we use example soilscapes from throughout california to examine how lithology climate topography and duration of pedogenesis interact to produce distinctive weathering environments and characteristic suites of soil minerals seven soil geomorphic sequences were assembled from the literature to illustrate major soil mineralogical trends 1 granitic terrain of the peninsular ranges 2 granitic terrain of the central sierra nevada 3 andesitic terrain of the northern sierra nevada 4 fluvial terraces on the east side of the great valley 5 marine terraces of the central coast 6 ultramafic terrain of the klamath mountains and 7 an alluvial fan in the mojave desert results of this analysis show that kaolin is present in virtually all pedons irrespective of climate parent material age or topographic position kaolin does not form in ultramafic soils due to insufficient aluminum many secondary clay minerals reflect the state s strong climatic influence with palygorskite smectite and vermiculite in the dry hot environments hydroxy interlayered minerals gibbsite and short range ordered minerals in the cool moist environments in arid and semi arid regions the distribution of calcite gypsum and soluble salts is strongly related to patterns of eolian dust deposition and water infiltration and leaching

wind driven submesoscale subduction at the north pacific subtropical front 1 upper ocean observations from the north pacific subtropical front during late winter demonstrate the generation of submesoscale intrusions by buoyancy loss prior to generation a sharp thermohaline front was intensified by confluent flow of 1 2 10 5 s 1 relative vertical vorticity across a surface intensified along front jet on the warm side of a frontal trough was 0 5 f during the storm buoyancy loss arose due to cooling of 650 w m 2 and down front wind stress 0 5 n m 2 that generated a southward cross front ekman transport of dense water over light the resulting wind driven buoyancy flux was concentrated at the front where it exceeded that due to convection by an order of magnitude the intrusions appeared immediately following the storm both within the surface mixed layer and beneath the seasonal pycnocline they were approximately 20 m thick and horizontally elongated in the cross frontal direction the near surface intrusions had cool and fresh properties characteristic of the water underlying the seasonal pycnocline whereas the subsurface intrusions were composed of warm and saline water from the surface the apparent vertical exchange was constrained within a thin filament of 2 km zonal extent that was characterized by o 1 rossby and richardson numbers pronounced cyclonic veering in the horizontal velocity throughout the surface mixed layer and sloping isopycnals the intrusion properties background environmental context and forcing history are consistent with prior numerical modeling results for the generation of ageostrophic vertical circulations by frontogenesis intensified by buoyancy loss possibly resulting in symmetric instability

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

discrepancy between mineral residence time and soil age implications for the interpretation of chemical weathering rates virtually all soil chronosequence studies have equated the degree of mineral weather ing with the soil age which is equal to the time since the cessation of erosion or deposition the primary minerals from the parent material however enter the soil as the weathering front propagates downward and are depleted via chemical weathering the residence time of minerals is thus a function of both the rate of conversion of parent material to soil i e soil production and the minerals susceptibility to chemical weathering reactions we fi nd that mineral residence times are signifi cantly shorter than the soil age by mathematically consid ering the interactions among soil production and chemical weathering we demonstrate that traditional estimates of mineral specifi c chemical weathering rates from soil chronosequences may diverge by several orders of magnitude from the actual weathering rates

gravitational symmetric and baroclinic instability of the ocean mixed layer abstract a hierarchy of hydrodynamical instabilities controlling the transfer of buoyancy through the oceanic mixed layer is reviewed if a resting ocean of horizontally uniform stratification is subject to spatially uniform buoyancy loss at the sea surface then gravitational instability ensues in which buoyancy is drawn from depth by upright convection but if spatial inhomogeneities in the ambient stratification or the forcing are present as always exist in nature then horizontal density gradients will be induced and within a rotation period horizontal currents in thermal wind balance with those gradients will be set up within the mixed layer there are two important consequences on the convective process upright convection will become modified by the presence of the thermal wind shear fluid parcels are exchanged not along vertical paths but rather along slanting paths in symmetric instability theoretical considerations suggest that this slantwise convection sets the potential vorticity of th

evaluation of proposed early holocene advances of alpine glaciers in the north cascade range washington state usa constraints provided by palaeoenvironmental reconstructions many palaeoenvironmental reconstructions from across western north america indicate that the early to mid holocene was warmer and drier than present the wide distribution of these records suggests that relatively mild and arid conditions were regionally ubiquitous during the early holocene in contrast two recently proposed advances of alpine glaciers in the cascade range of washington state corresponding to equilibrium line altitude depressions of 350 to 450 m are placed in the early holocene the juxtaposition of the proposed major expansion of early holocene alpine glaciers with the constraint provided by a number of palaeoenvironmental reconstructions from directly adjacent areas results in palaeoclimatic gradients that are untenable the apparent diachronous behaviour of adjacent palaeoenvironmental records may be an artifact of dating errors

a mechanistic model for river incision into bedrock by saltating bed load 1 abrasion by bed load is a ubiquitous and sometimes dominant erosional mechanism for fluvial incision into bedrock here we develop a model for bedrock abrasion by saltating bed load wherein the wear rate depends linearly on the flux of impact kinetic energy normal to the bed and on the fraction of the bed that is not armored by transient deposits of alluvium we assume that the extent of alluvial bed cover depends on the ratio of coarse sediment supply to bed load transport capacity particle impact velocity and impact frequency depend on saltation trajectories which can be predicted using empirical functions of excess shear stress the model predicts a nonlinear dependence of bedrock abrasion rate on both sediment supply and transport capacity maximum wear rates occur at moderate relative supply rates due to the tradeoff between the availability of abrasive tools and the partial alluviation of the bedrock bed maximum wear rates also occur at intermediate levels of excess shear stress due to the reduction in impact frequency as grain motion approaches the threshold of suspension measurements of bedrock wear in a laboratory abrasion mill agree well with model predictions and allow calibration of the one free model parameter which relates rock strength to rock resistance to abrasive wear the model results suggest that grain size and sediment supply are fundamental controls on bedrock incision rates not only by bed load abrasion but also by all other mechanisms that require bedrock to be exposed in the channel bed

a spheroidal weathering model coupling porewater chemistry to soil thicknesses during steady state denudation abstract spheroidal weathering a common mechanism that initiates the transformation of bedrock to saprolite creates concentric fractures demarcating relatively unaltered corestones and progressively more altered rindlets in the spheroidally weathering rio blanco quartz diorite puerto rico diffusion of oxygen into corestones initiates oxidation of ferrous minerals and precipitation of ferric oxides a positive v of reaction results in the build up of elastic strain energy in the rock formation of each fracture is postulated to occur when the strain energy in a layer equals the fracture surface energy the rate of spheroidal weathering is thus a function of the concentration of reactants the reaction rate the rate of transport and the mechanical properties of the rock substitution of reasonable values for the parameters involved in the model produces results consistent with the observed thickness of rindlets in the rio icacos bedrock 2 3 cm and a time interval between fractures 200 300 a based on an assumption of steady state denudation at the measured rate of 0 01 cm a averaged over times longer than this interval the rate of advance of the bedrock saprolite interface during spheroidal weathering the weathering advance rate is constant with time assuming that the oxygen concentration at the bedrock saprolite interface varies with the thickness of soil saprolite yields predictive equations for how weathering advance rate and steady state saprolite soil thickness depend upon atmospheric oxygen levels and upon denudation rate the denudation and weathering advance rates at steady state are therefore related through a condition on the concentration of porewater oxygen at the base of the saprolite in our model for spheroidal weathering of the rio blanco quartz diorite fractures occur every 250 yr ferric oxide is fully depleted over a four rindlet set in 1000 yr and saprolitization is completed in 5000 yr in the zone containing 20 rindlets spheroidal weathering thus allows weathering to keep up with the high rate of denudation by enhancing access of bedrock to reactants by fracturing coupling of denudation and weathering advance rates can also occur for the case that weathering occurs without spheroidal fractures but for the same kinetics and transport parameters the maximum rate of saprolitization achieved would be far smaller than the rate of denudation for the rio blanco system the spheroidal weathering model provides a quantitative picture of how physical and chemical processes can be coupled explicitly during bedrock alteration to soil to explain weathering advance rates that are constant in time

rio tinto sedimentary mineral assemblages a terrestrial perspective that suggests some formation pathways of phyllosilicates on mars abstract the presence of extensive phyllosilicate deposits from the early noachian of mars are often interpreted as having formed from neutral to subalkaline solutions in this paper we examine the rio tinto fluvial basin an early mars analog that hosts clay production and sedimentation along the entire course of the river at rio tinto phyllosilicate minerals including clays and micas are sourced by volcanosedimentary bedrock of rhyolitic and andesitic composition affected by carboniferous hydrothermal alteration pleistocene to modern acidic weathering of those materials chemically altered the volcanic and sedimentary materials to k na clay montmorillonite smectites kaolinite assemblages in paleosoils and fractures while physical weathering degrades phyllosilicates more resistant to acidic attack during the wet season phyllosilicates are eroded transported and deposited from both acidic headwaters and neutral tributaries during the dry season sulfates and nanophase oxyhydroxides co precipitate late summer storms that cause fast flooding events mix illite quartz feldspars iron oxides and other minerals in fluvial deposits where these minerals are stabilized and aggrade until the following wet season as a result chemical precipitates primary phyllosilicates and secondary clays form mineral admixtures that explain the compositional diversity of the fluvial deposits these deposits reveal the persistence of smectites whose occurrence is explained given that the reaction kinetics under acidic conditions of degradation is lowered by seasonal discharges of the river the longevity of phyllosilicate minerals within fluvial deposits depends on climatic and geochemical conditions and processes which are in turn are correlated to temperature persistence of water hydrological cycling hydrogeochemistry and composition of the source materials in the basement these parameters are universal and have to be characterized in order to understand the distribution of mineral composition on any planetary surface including mars

hydraulics of interrill overland flow on stone covered desert surfaces the hydraulics of interrill overland flow on stone covered desert surfaces depend on the resistance to flow which may be partitioned into grain resistance form resistance wave resistance and rain resistance efforts to model large scale roughness in open channels suggest that resistance to overland flow on such surfaces is a function of grain reynolds number froude number flow depth and the size shape spacing and pattern of the roughness elements the effect of flow depth on flow resistance f is often hidden in the flow reynolds number re in laboratory and field studies alike f re relations have been found to be convex upward and negatively sloping and these shapes have been explained in terms of the progressive inundation of the roughness elements where laboratory or field based models have been developed for predicting f they invariably contain percent stone cover the prominence of this variable reflects the strong influence of stone size and spacing on flow resistance a laboratory study shows that where the froude number f 0 50 wave resistance increases with stone cover and dominates resistance to flow on all surfaces with stone covers greater than 10 a field study indicates that where f 0 50 and wave resistance is inconsequential grain and form resistance typically account for about 5 and 95 of f respectively these findings have important implications for sediment transport modeling because percent grain resistance is equal to percent grain shear stress and it has recently been suggested that in overland flow as in river flow sediment transport capacity is determined by grain shear stress rather than total shear stress a laboratory study however demonstrates that this is not the case sediment transport capacity is in fact greater than predicted by grain shear stress because energy dissipated in the wakes of roughness elements in overland flow is transformed into turbulence sufficiently close to the bed to affect sediment transport

deciphering boulder mobility and erosion from cosmogenic nuclide exposure dating large boulders are prominent features in many geomorphic systems and are frequently targeted for cosmogenic exposure dating presently there are little data or theory predicting exposure age erosion rate and mobilization frequency of boulders in environments such as channels talus slopes or moraines here we explore the potential for cosmogenic isotope analysis to constrain the transport and erosion history of boulders through a series of numerical experiments we model the statistical evolution of nuclide concentrations around the surface of boulders stable boulders have distinctive radial distributions of surface concentration in comparison to those that are periodically mobile and this can be used to establish boulder stability mean nuclide accumulation rates around the surface of an eroding boulder increase when the radius is smaller than approximately 1 5 e folding lengths 1 2 m of neutron flux intensity whereupon nuclide accumulation on the underside of the boulder becomes non negligible 10 model results for cases of no cosmogenic inheritance and uniform erosion indicate the normalized standard deviation of nuclide surface concentration systematically decreases with increasing number of boulder mobilization events this may be used to constrain the minimum number of times a boulder has moved for up to approximately four events or distinguish between rarely and frequently mobilized boulders using non dimensional scaling relations between surface concentration statistics boulder size and time we propose methods to estimate the minimum age frequency of movement and erosion rate of mobile boulders with application to a range of geomorphic problems

effects of rock fragments incorporated in the soil matrix on concentrated flow hydraulics and erosion rock fragments can act as a controlling factor for erosional rates and patterns in the landscape thus the objective of this study is to better understand the role that rock fragments incorporated into the soil matrix play in concentrated flow hydraulics and erosion laboratory flume experiments were conducted with soil material that was mixed with rock fragments rock fragment content ranged from 0 to 40 per cent by volume other treatments were slope 7 and 14 and flow discharge 5 7 and 11 4 l min 1 an increase in rock fragment content resulted in lower sediment yield and broader width of flow rock fragment cover at the soil surface i e surface armour increased with time in experiments with rock fragments flow energy was largely dissipated by rock fragment cover for more turbulent flow conditions when roughness elements were submerged in the flow hydraulic roughness was similar for different rock fragment contents in experiments with few or no rock fragments a narrow rill incised flow energy was dissipated by headcuts total sediment yield was much larger than for experiments with rock fragments in the soil adding just a small number of rock fragments in the soil matrix resulted in a significant reduction of sediment yield copyright 2007 john wiley sons ltd

do gravel bed river size distributions record channel network structure 1 bed load sediment particles supplied to channels by hillslopes are reduced in size by abrasion during downstream transport the branching structure of the channel network creates a distribution of downstream travel distances to a given reach of river and thus may strongly influence the grain size distribution of the long term bed load flux through that reach here we investigate this hypothesis using mass conservation and the sternberg exponential decay equation for particle abrasion to predict bed material variability at multiple scales for both natural and artificial drainage networks we assume that over a sufficiently long timescale no net deposition occurs and that grains less than 2 mm are swept away in suspension we find that abrasion during fluvial transport has a surprisingly small effect on the bed load sediment grain size distribution for the simple case of spatially uniform supply of poorly sorted hillslope sediments this occurs because at any point in the channel network local resupply offsets the size reduction of material transported from upstream thus river bed material may essentially mirror the coarse component of the size distribution of hillslope sediment supply furthermore there is a predictable distance downstream at which the bed load grain size distribution reaches a steady state in the absence of net deposition due to selective transport large scale variability in bed material such as downstream fining must then be due primarily to spatial gradients in hillslope sediment production and transport characteristics a second key finding is that average bed load flux will tend to stabilize at a constant value independent of upstream drainage area once the rate of silt production by bed load abrasion per unit travel distance is equal to the rate of coarse sediment supply per unit channel length q bed load flux equilibrates over a distance that scales with the inverse of the fining coefficient in the abrasion rate law and can be approximated simply as q 3 thus the efficiency of particle abrasion sets a fundamental length scale shorter for weaker rocks and longer for harder rocks which controls the expression in the river bed of variability in sediment supply we explore the role of the abrasion length scale in modulating the influence of sediment supply variability in a number of channel network contexts including individual tributary junctions a sequence of tributary inputs along a main stem channel and variable basin shapes and network architecture as expressed by the width function these findings highlight the need for both data and theory that can be used to predict the grain size distributions supplied to channels by hillslopes

observation of the surface horizontal thermohaline variability at mesoscale to submesoscale in the north eastern subtropical atlantic ocean the seasonal variability of the surface horizontal thermohaline structure is investigated in the north eastern atlantic surface salinity maximum ssm at length scales from five to hundreds of kilometers i e at submesoscale to mesoscale the near surface temperature and salinity data from merchant ship thermosalinograph tsg transects across the atlantic are used to compute the horizontal temperature salinity and density fluctuations and the density ratio during late winter in the north eastern ssm thermohaline compensation is observed for wavelengths from 5 km to more than 200 km in spite of large and sharp surface thermohaline fronts a weak density surface horizontal gradient is observed temperature and salinity exhibit an energetic spectra in k 2 slope scale between 20 100 km scale and a steeper slope at shorter wavelengths while density spectra exhibit lower energy level with a clear k 3 slope below 20 km consistent with interior quasigeostrophic turbulence during summer in the north eastern ssm salinity and temperature gradients are no longer compensated due to strong atmospheric heating of the upper ocean in comparison with winter the surface density spectrum is enhanced with a flatter slope between k 2 and k 1 between 5 and 20 km

sediment transport by runoff on debris mantled dryland hillslopes 1 hillslopes supply sediment to river channels and therefore impact drainage basin functioning and evolution the relationship between hillslope attributes and sediment flux forms the basis of geomorphic transport laws used to model the long term topographic evolution of drainage basins but their specific interactions during individual storm events are not well understood runoff driven erosion of coarse particles prevalent in dryland environments presents a particular set of conditions for sediment transport that is poorly resolved in current models in order to address this gap we developed a particle based force balance model for sheetwash sediment transport on coarse debris mantled hillslopes within a rainfall runoff model we use the model to examine how the interplay between hillslope attributes gradient length and grain size distribution and runoff characteristics affects sediment transport grain size changes on the hillslope and sediment supply to the slope base the relationship between sediment flux and hillslope gradient was found to transition from linear above a threshold to sigmoidal depending on hillslope length initial grain sizes and runoff characteristics grain sizes supplied to the slope base vary in a complex manner with hillslope attributes but an overall coarsening of the hillslopes is found to occur with increasing gradient corroborating previous findings from field measurements intense short duration storms result in within hillslope sediment redistribution and equifinality in sediment supply for different hillslope characteristics which explain the lack of field evidence for any systematic relationships our model findings provide insights into hillslope responses to climatic forcing and have theoretical implications for modeling hillslope evolution in dry lands

restratification at a california current upwelling front part i observations abstracta coordinated survey between a subsurface lagrangian float and a ship towed triaxus profiler obtained detailed measurements of a restratifying surface intensified front above 30 m within

spatial distribution of surface rock fragments along catenas in semiarid arizona and nevada usa improved techniques for estimating soil erosion by water have shown that soil surface cover is a major component in the estimate of soil loss erosion prediction models require the user to input slope gradient and soil profile descriptions if equations expressing the relations between slope gradient soil profile rock fragment content and surface rock fragment cover were embedded in these models then direct user input could be reduced field measurements of slope gradient soil profile rock fragment content surface rock fragment cover and vegetation type and cover were made on 12 soil slope complexes on catenas in southeastern arizona usa correlation analysis showed that both slope gradient and soil profile rock fragment content were significantly p 0 01 correlated to surface rock fragment cover additional analysis indicated that the combined effects of slope gradient and soil profile rock content were better defined by a soil slope factor ssf two equations were developed to estimate surface rock fragment cover a logarithmic relation using slope gradient as the independent variable and a hyperbolic equation using the ssf as the independent variable these equations were used to estimate surface rock fragment cover from a soil slope complex in southern nevada the ssfrfc equation gave better estimates of the measured surface rock fragment cover these relations developed for catenas in southeastern arizona may be site specific but they do show that a relation exists for this semiarid area and suggest that similar relations may exist in areas with similar geology and climate such as parts of africa asia australia and south america development of simple relations describing important erosion processes will improve erosion estimates while simultaneously decreasing time and costs associated with using erosion prediction models

restratification of the surface mixed layer with submesoscale lateral density gradients diagnosing the importance of the horizontal dimension abstract a depth cycling towed conductivity temperature depth ctd and vessel mounted acoustic doppler current profiler adcp were used to obtain four dimensional measurements of the restratification of the surface mixed layer sml at a submesoscale lateral density gradient near the subtropical front with the objective of studying the role of horizontal processes in restratification the thermohaline and velocity fields were monitored for 33 h by 16 small scale 15 km2 surveys centered on a drogued float daytime warming by insolation caused a unidirectional displacement of the initially vertical isopycnals toward increasing density across the entire sml 50 m vertical scale solar insolation accounted for 60 of observed restratification but over 10 m scales the percentage decreased with depth from 80 at 25 35 m to 25 at 55 65 m below 35 m stratification was enhanced by the vertically sheared horizontal advection of the lateral density gradient due to a near inertial wave of 100 m vertica

measuring and defining bimodal sediments problems and implications gravel bed rivers close to the transition to a sand bed often have bimodal grain size distributions these can be quantified in several ways giving wide differences in derived statistics and calculations problems associated with measuring summarizing and defining bimodality are examined using evidence from flume experiments and a simple numerical simulation of sand deposition no single index of bimodality serves all purposes alternatives are suggested measured near bed hydraulic properties relate more closely to grain size statistics calculated by area than by volume this has implications for the abrupt downstream transition often found from gravel to sand bed

spatial distribution of rock fragments in cultivated soils in northern ethiopia as affected by lateral and vertical displacement processes abstract although in semi arid environments rock fragments at the soil surface and within the topsoil play an important role in desertification control little is known about their spatial distribution therefore this study analyses spatial patterns of rock fragment cover along catenas and the vertical variations in volumetric rock fragment content in soil profiles in the highlands of tigray northern ethiopia natural and anthropogenic processes inducing these patterns are assessed volumetric rock fragment content rv was analysed in 10 soil pits all rock fragments were extracted and their volumes determined by pedo stratigraphic unit size and lithology the rock fragment cover rc was determined by the point count method using vertical photographs of the soil surface the following processes contribute to the vertical variability of rv 1 in vertisols upsqueezing as a consequence of swell shrink cycles argillipedoturbation is responsible for high rc at the soil surface 2 large rock fragments 7 5 cm are rapidly brought to the soil surface by kinetic sieving through tillage even in the case of continuous fine sediment deposition what may result in a rock fragment rich subsoil underlying a thick soil layer up to 80 cm without large rock fragments and a topsoil with a high rc at the surface 3 skeletic regosols at the foot of cliffs show no systematic vertical rock fragment distributions as to rock fragment cover along the catena some fundamental differences appear between the basalt and limestone substrate on the basalt catena with slope gradients between 0 06 and 0 42 m m 1 rc is high everywhere 57 85 and is unrelated to slope gradient vertical processes such as kinetic sieving through ploughing and argillipedoturbation determine the rock fragment distribution at the soil surface in limestone areas argillipedoturbation is less active and rc is positively correlated with slope gradient r2 0 74 n 6 p 2 cm and more kinetic sieving sensitive rock fragments lowers r2 to 0 46 n 6 n s preconditions for the present spatial distribution of rock fragments at the soil surface in the study area are the occurrence of two geomorphic processes in the past 1 mudflows depositing diamictons including much coarse debris and 2 intense water erosion which occurred after deforestation and exposed rock fragments at or near to the soil surface generally the balance between lateral and vertical movements of rock fragments now controls the spatial distribution of rc with respect to the lateral displacement processes 1 lateral transport over the soil surface by trampling tillage and concentrated runoff especially on steep slopes and 2 rockfall from the cliffs vertical supply of rock fragments to the soil surface is caused by 1 selective runoff erosion and the development of erosion pavements 2 tillage induced kinetic sieving bringing preferentially large rock fragments 7 5 cm to the soil surface and 3 argillipedoturbation in vertisol areas

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

towed thermistor chain observations of fronts in the subtropical north pacific a thermistor chain was towed 1400 km through the eastern north pacific subtropical frontal zone in january 1980 the observations resolve surface layer temperature features with horizontal wavelengths of 0 2 200 km and vertical scales of 10 70 m the dominant features which have horizontal wavelengths of 10 100 km amplitudes of 0 2 1 0 c and random orientation likely arise from baroclinic instability associated with them is a plateau below 0 1 cpkm in the horizontal temperature gradient spectrum strong temperature fronts o 1 2 c 3 10 km are observed near 33 n 31 n and 27 n temperature variability is partially density compensated by salinity with the fraction of compensation increasing northward there is evidence of vertical mixing during high winds temperature at 15 m depth is roughly normally distributed around the climatological surface mean with a standard deviation of approximately 0 5 c the standard deviation would correspond to an adiabatic meridional displacement of 80 100 km in the mean gradient horizontal temperature gradient at 15 m depth has maximum values in excess of 0 25 c 100 m and kurtosis near 80 in the band 0 10 1 cpkm the 15 m gradient spectrum is inversely proportional to wave number consistent with predictions from geostrophic turbulence theory while the spectrum at 70 m depth has additional variance that is consistent with garrett munk internal wave displacements

rock fragments in top soils significance and processes this introductory paper reviews various aspects of rock fragments in top soils such information is required for various reasons and in particular for predicting the impact of climatic or landuse changes on the response of these soils particular attention is paid to the definition and measurement of rock fragment content in top soils the density of soils containing rock fragments the spatial distribution and movement of rock fragments in top soils the effects of rock fragments on some key hydrological processes thermal properties of top soils physical soil degradation soil erosion and soil productivity

parameterization of mixed layer eddies part i theory and diagnosis ageostrophic baroclinic instabilities develop within the surface mixed layer of the ocean at horizontal fronts and efficiently restratify the upper ocean in this paper a parameterization for the restratification driven by finite amplitude baroclinic instabilities of the mixed layer is proposed in terms of an overturning streamfunction that tilts isopycnals from the vertical to the horizontal the streamfunction is proportional to the product of the horizontal density gradient the mixed layer depth squared and the inertial period hence restratification proceeds faster at strong fronts in deep mixed layers with a weak latitude dependence in this paper the parameterization is theoretically motivated confirmed to perform well for a wide range of mixed layer depths rotation rates and vertical and horizontal stratifications it is shown to be superior to alternative extant parameterizations of baroclinic instability for the problem of mixed layer restratification two companion papers discuss the numerical implementation and the climate impacts of this parameterization

the role of sediment in controlling steady state bedrock channel slope implications of the saltation abrasion incision model abstract the saltation abrasion model is a mechanistic model for river incision into bedrock by saltating bedload which we have previously derived and used experimental data to constrain all parameter values here we develop a method for applying the saltation abrasion model at a landscape scale and use the model as a reference for evaluating the behavior of a wide range of alternative incision models in order to consider the implications of the saltation abrasion model as well as other models for predicting topographic steady state channel slope to determine the single valued discharge that best represents the effects of the full discharge distribution in transporting sediment and wearing bedrock we assume all runoff can be partitioned between a low flow and a high flow discharge in which all bedload sediment transport occurs during high flow we then use the gauged discharge record and measurements of channel characteristics at a reference field site and find that the optimum discharge has a moderate magnitude and frequency due to the constraints of the threshold of grain motion and bed alluviation by high relative sediment supply incision models can be classified according to which of the effects of sediment on bedrock incision are accounted for using the predictions of the saltation abrasion model as a reference we find that the threshold of motion is the most important effect that should be represented explicitly followed in order of decreasing importance by the cover effect the tools effect and the threshold of suspension effect models that lack the threshold of motion over predict incision rate for low shear stresses and under predict the steady state channel slope for low to moderate rock uplift rates and rock strengths models that lack the cover effect over predict incision rate for high sediment supply rates and fail to represent the degree of freedom in slope adjustment provided by partial bed coverage models that lack the tools effect over predict incision rate for low sediment supply rates and do not allow for the possibility that incision rate can decline for increases in shear stress above a peak value overall the saltation abrasion model predicts that steady state channel slope is most sensitive to changes in grain size such that the effect of variations in rock uplift rate and rock strength may affect slope indirectly through their possible but as yet poorly understood influence on the size distribution of sediments delivered to channel networks by hillslopes

climate controlled variations in scree production southern alps new zealand the interaction of fluvial glacial and hillslope processes controls the development of mountain belts and their response to tectonic and climatic forcing studies on the contribution of hillslope processes to mountain erosion have focused on bedrock landslides as they have a profound and readily observed impact on sediment yield and slope morphology despite the ubiquity of scree or talus mantled slopes in mountainous terrain the role of frequent low magnitude 100 m 3 rockfall events is seldom addressed in the context of landscape evolution here we quantify the contribution of rockfall erosion across an 80 by 40 km transect in the southern alps new zealand by analyzing the spatial extent of scree slopes mapped from aerial photographs and estimating long term 10 15 k y rockfall erosion rates from the accumulation of slope deposits below bedrock headwalls and in debris and alluvial fans along the rapidly uplifting high rainfall western margin where high rates of bedrock landsliding have been previously documented scree mantled slopes are sparse rainfall decreases exponentially east of the main divide and the proportion of slopes mantled by scree increases monotonically attaining a maximum value of 70 the systematic distribution of scree deposits cannot be attributed to lithologic variation seismicity or the legacy of glaciation instead climate may serve as a primary control on scree production as nearly 70 of the mapped scree deposits in our transect are confined to a narrow elevation range of 1200 1600 m above sea level masl our analysis of altitudinal controls on annual temperature variations indicates that scree production via frost cracking processes may be maximized between elevations of 1600 and 2300 masl as higher elevations are subject to persistent permafrost which obviates the frost cracking process rates of rockfall erosion near the rapidly uplifting main divide are low 0 1 mm yr whereas rates in the scree dominated eastern areas average 0 6 mm yr and may approximately balance rock uplift

thermohaline variability in the upper ocean the main goal of this exploratory study is to determine how the temperature salinity relationship changes with horizontal length scale and depth in the ocean temperature and salinity were measured on a range of scales from 4 m to 1000 km towing a seasoar along isobars and isopycnals in the subtropical gyre of the north pacific during the winter of 1997 the wavelet transform technique is used to compute the horizontal density ratio and thermohaline variability as a function of scale and location measurements along an isobar in the mixed layer show that the horizontal density ratio is 1 at all scales observed that is horizontal temperature and salinity gradients tend to cancel each other in their effect on density thermohaline variability at small scales is intermittent and clusters around large scale thermohaline anomalies below the base of the mixed layer horizontal gradients of temperature are only partially opposed by salinity and the density ratio is close to 2 in the thermocline the distribution of thermohaline variability is uniform along isobars but intermittent and colocated at different scales along isopycnals density compensated variability ubiquitous in the mixed layer is reduced along deeper isopycnals compensation of horizontal temperature and salinity gradients supports recent theoretical ideas that mixing in the winter mixed layer depends on horizontal density gradients

soil production on a retreating escarpment in southeastern australia the functional dependence of bedrock conversion to soil on the overlying soil depth the soil production function has been widely recognized as essential to understanding landscape evolution but was quantified only recently here we report soil production rates for the first time at the base of a retreating escarpment on the soil mantled hilly slopes in the upper bega valley southeastern australia concentrations of 10 be and 26 al in bedrock from the base of the soil column show that soil production rates decline exponentially with increasing soil depth these data define a soil production function with a maximum soil production rate of 53 m m y under no soil mantle and a minimum of 7 m m y under 100 cm of soil thus constraining landscape evolution rates subsequent to escarpment retreat the form of this function is supported by an inverse linear relationship between topographic curvature and soil depth that also suggests that simple creep does not adequately characterize the hillslope processes spatial variation of soil production shows a landscape out of dynamic equilibrium possibly in response to the propagation of the escarpment through the field area within the past few million years in addition we present a method that tests the assumption of locally constant soil depth and lowering rates using concentrations of 10 be and 26 al on the surfaces of emergent tors

frontogenesis and the creation of fine scale vertical phytoplankton structure author s de verneil a franks pjs ohman md abstract 2019 american geophysical union all rights reserved fine scale spatial structuring of phytoplankton patches has significant consequences for the marine food web from altering phytoplankton exposure to surface light and limiting nutrients to influencing the foraging of zooplankton modifying carbon export and impacting patterns of diversity hence it is important to identify these fine scale features and determine what generates their variability here we present evidence of fine scale tilted interleaved layers in salinity and chlorophyll a fluorescence observed in free fall moving vessel profiler surveys across a frontal system west of point conception california the observed covariability of hydrographic and biological properties allows for decomposition of the features into different water histories our analyses suggest that recently upwelled coastal water subsequently advected and intermingled with surrounding water masses from farther offshore orientations of the fine layers found in the filament are consistent with restratification and downwelling due to an ageostrophic secondary circulation brought on by frontogenesis finite size lyapunov exponents a lagrangian diagnostic calculated from remote sensing data provide positive evidence for frontogenetic convergence occurring upstream of the feature and allow for direct comparisons with in situ data to gauge their general utility in defining dynamical boundaries these results highlight how frontal systems not only horizontally compress the biological niches represented by formerly disparate water masses but also create vertical structure and patchiness that can rapidly change over submesoscales

downstream variation in bed sediment size along the east carpathian rivers evidence of the role of sediment sources taking as an example six main rivers that drain the western flank of the eastern carpathians a conceptual model has been developed according to which fluvial bed sediment bimodality can be explained by the overlapping of two grain size distribution curves of different origins thus for carpathian tributaries of the siret coarse gravel joins an unimodal distribution presenting a right skewness with enhanced downstream fining the source of the coarse material distributions is autohtonous by abrasion and hydraulic sorting mechanisms a second distribution with a sandy mode is in general skewed to the left the source of the second distribution is allohtonous the quantity of sand that reaches the river bed through the erosion of the hillslope basin terrains the intersection of the two distributions occurs in the area of the 0 5 8 mm fractions where in fact the right skewness for gravel and left skewness for sand histogram tails meet this also explains the lack of particles in the 0 5 8 mm interval for rivers where fine sediment sources are low the 0 5 8 mm fractions have a higher proportion than the fractions under 1 mm for the siret river itself bed sediment bimodality is greatly enhanced due to the fact that the second mode is more than 25 of the full sample as opposed to its tributaries the source of the first mode of gravel is allohtonous to the siret river generated by the massive input of coarse sediment through the carpathian tributaries while the second mode of the sands is local in this case we can also observe that the two distributions of particles of different origins overlap in the 0 5 8 mm fraction domain creating the illusion of particle lack in the fluvial bed sediments copyright 2007 john wiley sons ltd

variation of rock fragment cover and size along semiarid hillslopes a case study from southeast spain abstract the spatial variation of rock fragment cover rc and rock fragment size rs along semiarid hillslopes and transects in the mediterranean is largely controlled by hillslope gradient total rock fragment cover rc 5 mm often increases in a convex upward curve with hillslope gradient while the d50 of the surface rock fragments 5 mm increases linearly with hillslope gradient on south facing slopes rc 5 mm is slightly higher than on north facing slopes lithology controls the size distribution of the stone pavement rather than its cover percentage spatial variation of rock fragment cover reflects spatial variation in past erosion and deposition rates hillslope sections that are steep south facing or have been abandoned a long time ago have undergone intense interrill and rill erosion and thus have high rock fragment covers tillage erosion leads to high rock fragment covers on convex hillslopes in intensively cultivated areas thus using information on hillslope gradient aspect lithology and landuse we have been able to describe the spatial variation of rock fragment cover and size along semiarid hillslopes in southeast spain such information is crucial for understanding and modelling the spatial variation of the hydrological and erosion response of semiarid hillslopes under environmental change especially in semiarid environments of the mediterranean where vegetation cover is predicted to decrease due to climatic or landuse changes and rock fragments at the surface become the only soil surface stabilisers

clay minerals in delta deposits and organic preservation potential on mars clay rich sedimentary deposits are often sites of organic matter preservation and have therefore been sought in mars exploration however regional deposits of hydrous minerals including phyllosilicates and sulphates are not typically associated with valley networks and layered sediments that provide geomorphic evidence of surface water transport on early mars the compact reconnaissance imaging spectrometer for mars crism has recently identified phyllosilicates within three lake basins with fans or deltas that indicate sustained sediment deposition eberswalde crater holden crater and jezero crater here we use high resolution data from the mars reconnaissance orbiter mro to identify clay rich fluvial lacustrine sediments within jezero crater which has a diameter of 45 km the crater is an open lake basin on mars with sedimentary deposits of hydrous minerals sourced from a smectite rich catchment in the nili fossae region we find that the two deltas and the lowest observed stratigraphic layer within the crater host iron magnesium smectite clay jezero crater holds sediments that record multiple episodes of aqueous activity on early mars we suggest that this depositional setting and the smectite mineralogy make these deltaic deposits well suited for the sequestration and preservation of organic material

geostrophic adjustment and restratification of a mixed layer with horizontal gradients above a stratified layer abstract the restratification of a mixed layer with horizontal density gradients above a stratified layer is considered solutions are obtained on the assumption that the width across this front is much larger than the local radius of deformation bh f based on the buoyancy change across the front b mean mixed layer depth rdh and the coriolis parameter f where b is defined as rd g 0 0 but the fractional change in the mixed layer depth is not required to be small for an initially quiescent mixed layer created by homogenizing a fluid of constant stratification to a depth that varies horizontally the isopycnals in the mixed layer tilt about their intersections with the top surface in the adjusted state and the base of the mixed layer flattens slightly in the frontal region other cases considered include mixed layer fronts with initial momentum out of geostrophic balance created by vertical mixing of a layer with horizontal gradients previously in thermal wind balance for a wide front the

mesoscale to submesoscale transition in the california current system part ii frontal processes this is the second of three papers investigating the regime transition that occurs in numerical simulations for an idealized equilibrium subtropical eastern boundary upwelling current system similar to the california current the emergent upper ocean submesoscale fronts are analyzed from phenomenological and dynamical perspectives using a combination of composite averaging and separation of distinctive subregions of the flow the initiating dynamical process for the transition is near surface frontogenesis the frontal behavior is similar to both observed meteorological surface fronts and solutions of the approximate dynamical model called surface dynamics i e uniform interior potential vorticity q and diagnostic force balance in the intensification of surface density gradients and secondary circulations in response to a mesoscale strain field however there are significant behavioral differences compared to the surface dynamics model wind stress acts on fronts through nonlinear ekman transport and creation and destruction of potential vorticity the strain induced frontogenesis is disrupted by vigorous submesoscale frontal instabilities that in turn lead to secondary frontogenesis events submesoscale vortices and excitation of even smaller scale flows intermittent submesoscale breakdown of geostrophic and gradient wind force balance occurs during the intense frontogenesis and frontal instability events

critical shear stress of natural sediments the critical shear stress of individual fractions ci in unimodal and weakly bimodal sediments shows little variation with grain size and depends only on the mean grain size bf the mixture for strongly bimodal sediments ci increases with grain size an apparent result of a lateral segregation of the finer and coarser fractions on the bed surface that causes ci to deviate from size independence in the direction of unisize shields values a quantitative definition of mixture bimodality may be used to estimate the degree of mixture bimodality beyond which a substantial size dependence of ci is observed and to predict the variation of ci with grain size in bimodal sediments because properties of sediment grain size distributions other than bimodality appear to have little influence on ci the trends presented here for 14 unimodal and bimodal sediments may be quite general

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

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

nonfluvial control of bimodal grain size distributions in river bed gravels abstract conventional explanations for bimodal grain size distributions with a gap somewhere in the 1 10 mm range as found in some river deposits have commonly invoked processes which occur within the channel itself such as abrasion or selective transport field data from two lithologically distinct watersheds suggest that the size distribution of the input material may be largely responsible for the size distribution of the channel deposits data from a small second order basin of sandstone indicate that the gap is present in the most headward channel deposits as well as in material at the base of the hillslopes along the channel it is not present in samples taken at the ridge crests which mark the boundary of the watershed data from a slightly larger second order basin of basalt exhibi ed no gap in the stream deposits

mars surface diversity as revealed by the omega mars express observations the observatoire pour la mineralogie l eau les glaces et l activite omega investigation on board the european space agency mars express mission is mapping the surface composition of mars at a 0 3 to 5 kilometer resolution by means of visible near infrared hyperspectral reflectance imagery the data acquired during the first 9 months of the mission already reveal a diverse and complex surface mineralogy offering key insights into the evolution of mars omega has identified and mapped mafic iron bearing silicates of both the northern and southern crust localized concentrations of hydrated phyllosilicates and sulfates but no carbonates and ices and frosts with a water ice composition of the north polar perennial cap as for the south cap covered by a thin carbon dioxide ice veneer

monsoonal hillslope processes determine grain size specific suspended sediment fluxes in a trans himalayan river sediments in rivers record the dynamics of erosion processes while bulk sediment fluxes are easily and routinely obtained sediment caliber remains underexplored when inferring erosion mechanisms yet sediment grain size distributions may be the key to discriminating their origin we have studied grain size specific suspended sediment fluxes in the kali gandaki a major trans himalayan river two strategically located gauging stations enable tracing of sediment caliber on either side of the himalayan orographic barrier the data show that fine sediment input into the northern headwaters is persistent while coarse sediment comes from the high himalayas during the summer monsoon a temporally matching landslide inventory similarly indicates the prominence of monsoon driven hillslope mass wasting thus mechanisms of sediment supply can leave strong traces in the fluvial caliber which could project well beyond the mountain front and add to the variability of the sedimentary record of orogen erosion

arrested development erosional equilibrium in the southern sierra nevada california maintained by feedbacks between channel incision and hillslope sediment production tributary creeks of the southern sierra nevada have pronounced knickpoints that separate the landscape into an alternating sequence of gently sloped treads and steeply sloped risers these knickpoints and the surrounding stepped topography suggest that the landscape is still responding to pleistocene changes in base level on main stem rivers we tested this hypothesis using cosmogenic nuclides and uranium isotopes measured in stream sediment from widely distributed locations catchment scale erosion rates from the cosmogenic nuclides suggest that the treads are relict surfaces that have adjusted to a previous base level nevertheless erosion rates of relict interfluves are similar to canyon incision rates implying that relief is unchanging in the lower kings and san joaquin rivers in addition our results suggest that much of the southern sierra nevada is in a state of arrested development the landscape is not fully adjusted to and moreover is not responding to changes in base level lowering in the canyons we propose that this can be explained by a paucity of coarse sediment supply which fails to provide sufficient tools for bedrock channel incision at knickpoints we hypothesize that the lack of coarse sediment in channels is driven by intense weathering of the local granitic bedrock which reduces the size of sediment supplied from hillslopes to the channels our analysis highlights a feedback in which sediment size reduction due to weathering on hillslopes and transport in channels is both a key response to and control of bedrock channel incision and landscape adjustment to base level change

soil development along an elevational transect in the western sierra nevada california soil development along an elevational transect on the western slopes of the the central sierra nevada was investigated to assess the effects of climate on soil properties and processes the transect of seven soils formed in granitic residuum spans elevations from 198 to 2865 m with mean annual temperature and precipitation differences of 13 c 3 9 16 7 and 94 cm 33 127 respectively soil ph decreased by about two units and base saturation decreased from 90 to 10 with increasing elevation concentrations of organic c in the solum increased with elevation with the largest single increase occurring between the oak woodland 5 6 kg c m2 and mixed conifer sites 10 15 kg c m2 clay mineralogy showed a general trend of desilication and hydroxy al interlayering of 2 1 layer silicates with increasing elevation the degree of chemical weathering based on clay and secondary fe oxide concentration in the solum showed a maximum clay 536 kg m2 and fe oxides 24 kg m2 at mid elevations having intermediate levels of precipitation and temperature while some soil properties show a continuous progression e g organic carbon base saturation clay mineralogy with elevation other properties e g ph soil color clay and secondary fe oxide concentrations show a pronounced change threshold type step over a short distance at about 1600 m the explanation for the abrupt nature of this shift is not known however it coincides with the approximate elevation of the present day average effective winter snow line

sub mesoscale lateral density structure in the oceanic surface mixed layer 1 we investigate the horizontal scales of density variability in the surface mixed layer sml in the north pacific subtropical front stf during a period of highly variable atmospheric forcing wavelet analysis shows that horizontal density variability is not restricted to scales l 10 km as previously suggested but extends to l 2 km the limiting l varies strongly with location and corresponds to a local internal rossby radius that accounts for transient stratification above the seasonal thermocline density compensation in the sml achieved when temperature and salinity effects cancel in their effect on density occurs at 30 n at the climatological front associated with the northern boundary of the stf where large thermohaline gradients are observed at 28 n however temperature gradients within the sml are not compensated by salinity and horizontal density gradients result in 2 l 10 km our observations suggest dynamic processes restratify the sml at scales rarely resolved by numerical models of the sml

in situ evidence for an ancient aqueous environment at meridiani planum mars sedimentary rocks at eagle crater in meridiani planum are composed of fine grained siliciclastic materials derived from weathering of basaltic rocks sulfate minerals including magnesium sulfate and jarosite that constitute several tens of percent of the rock by weight and hematite cross stratification observed in rock outcrops indicates eolian and aqueous transport diagenetic features include hematite rich concretions and crystal mold vugs we interpret the rocks to be a mixture of chemical and siliciclastic sediments with a complex diagenetic history the environmental conditions that they record include episodic inundation by shallow surface water evaporation and desiccation the geologic record at meridiani planum suggests that conditions were suitable for biological activity for a period of time in martian history

influence of lithology on hillslope morphology and response to tectonic forcing in the northern sierra nevada of california 1 many geomorphic studies assume that bedrock geology is not a first order control on landscape form in order to isolate drivers of geomorphic change e g climate or tectonics yet underlying geology may influence the efficacy of soil production and sediment transport on hillslopes we performed quantitative analysis of lidar digital terrain models to examine the topographic form of hillslopes in two distinct lithologies in the feather river catchment in northern california a granodiorite pluton and metamorphosed volcanics the two sites separated by 2 km and spanning similar elevations were assumed to have similar climatic histories and are experiencing a transience in landscape evolution characterized by a propagating incision wave in response to accelerated surface uplift c 5 ma responding to increased incision rates hillslopes in granodiorite tend to have morphology similar to model predictions for steady state hillslopes suggesting that they adjust rapidly to keep pace with the incision wave by contrast hillslopes in metavolcanics exhibit high gradients but lower hilltop curvature indicative of ongoing transient adjustment to incision we used existing erosion rate data and the curvature of hilltops proximal to the main channels where hillslopes have most likely adjusted to accelerated erosion rates to demonstrate that the sediment transport coefficient is higher in granodiorite 8 8 m2 ka 1 than in metavolcanics 4 8 m2 ka 1 hillslopes in both lithologies get shorter i e drainage density increases with increasing erosion rates

rapid changes in mixed layer stratification driven by submesoscale instabilities and winds 1 submesoscale eddies generated by baroclinic instability of upper ocean fronts lead to rapid restratification of the mixed layer on a time scale of days this restratification can be opposed by a down front wind stress acting in the direction of the geostrophic velocity that drives a surface ekman flow from the dense side to the light side of the front to arrest the slumping of isopycnals a scaling diagnostic is suggested to determine whether the effect of eddies or wind dominates under different conditions using a numerical model we investigate the juxtaposition of submesoscale eddies and down front winds acting on the mixed layer by estimating the eddy induced overturning stream function in the mixed layer we separate the along and cross isopycnal fluxes of buoyancy associated with submesoscale mixed layer eddies and demonstrate the need for parameterization of the advective along isopycnal flux though the cross front transport of buoyancy induced by the down front component of the wind opposes restratification by mixed layer eddies it becomes diminished as the eddies and growth of the frontal instability disrupt alignment between the wind and frontal axis

estimates of ocean macroturbulence structure function and spectral slope from argo profiling floats abstractthe argo profiling float network has repeatedly sampled much of the world ocean this study uses argo temperature and salinity data to form the tracer structure function of ocean variability at the macroscale 10 1000 km mesoscale and above here second order temperature and salinity structure functions over horizontal separations are calculated along either pressure or potential density surfaces which allows analysis of both active and passive tracer structure functions using argo data a map of global variance is created from the climatological average and each datum when turbulence is homogeneous the structure function slope from argo can be related to the wavenumber spectrum slope in ocean temperature or salinity variability this first application of structure function techniques to argo data gives physically meaningful results based on bootstrapped confidence intervals showing geographical dependence of the structure functions with slopes near on average independent of depth

evidence for persistent flow and aqueous sedimentation on early mars landforms representative of sedimentary processes and environments that occurred early in martian history have been recognized in mars global surveyor mars orbiter camera and mars odyssey thermal emission imaging system images evidence of distributary channelized flow in particular flow that lasted long enough to foster meandering and the resulting deposition of a fan shaped apron of debris indicate persistent flow conditions and formation of at least some large intracrater layered sedimentary sequences within fluvial and potentially lacustrine environments

three dimensional structure and temporal evolution of submesoscale thermohaline intrusions in the north pacific subtropical frontal zone abstract four instances of persistent intrusive deformation of the north pacific subtropical front were tagged individually by a lagrangian float and tracked for several days each feature was mapped in three dimensions using repeat towed observations referenced to the float isohaline surface deformations in the frontal zone included sheetlike folds elongated in the alongfront direction and narrow tongues extending across the front all deformations appeared as protrusions of relatively cold and fresh water across the front no corresponding features of the opposite sign or isolated lenslike structures were observed the sheets were o 10 m thick protruded about 10 km into the warm saline side of the front and were coherent for 10 30 km along the front having about the same thickness and cross frontal extent as the sheets tongues extended less than 5 km along the front all of the intrusions persisted as long as they were followed several days to one week their structures evolved on both inertial

stream incision tectonics uplift and evolution of topography of the sierra nevada california abstract stream incision faulting thermochronologic and geobarometric data suggest that sierra nevada topography is a consequence of two periods of uplift stream incision of up to 1 km has occurred since 5 ma maximum eocene miocene incision was 150 m uplift of the sierra nevada westward tilting stream incision and east down normal and dextral faulting along the present eastern escarpment of the range began at 5 ma estimates of late cenozoic crestal rock uplift for different areas in the sierra nevada range from 1440 to 2150 m low summit erosion rates suggest that the rock uplift approximates the surface uplift of crestal summits tertiary stream gradients were lower than modern ones suggesting that the bottoms of the canyons have been uplifted in the late cenozoic and that the mean elevation of the sierra nevada has increased the elevation of pre cenozoic basement rocks above the base of tertiary paleochannels ranges from 1000 m in the south and

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

late quaternary snowline reconstructions for the southern and central sierra nevada california and a reassessment of the recess peak glaciation abstract in the sierra nevada the recess peak glaciation has been previously defined on the basis of deposits exhibiting relative age characteristics intermediate between those of the little ice age deposits and those of early holocene or older moraines in the absence of reliable chronological control the recess peak deposits were assigned an early neoglacial age although numerous moraines in the central and southern sierra have been attributed to this interval regional snowline gradients reconstructed from these deposits lack internal consistency and appear to represent several distinctly different episodes of glacier advance as a basis for comparison with the recess peak data modern and late pleistocene regional snowlines were reconstructed using accumulation area ratios and cirque floor altitudes these reconstructions display regionally consistent gradients rising gradually southward and more steeply eastward based on these data the full glacial late pleistocene snowline depression is estimated to have been 800 m estimates of recess peak snowline depression vary widely ranging from 140 to 500 m and a reconstructed regional gradient rises northward in opposition to the late pleistocene and modern snowlines limited radiocarbon dating and the irregular pattern derived from the recess peak snowline data suggest that even in the type area these deposits resulted from both pre and post hypsithermal glacier advances

rock fragment distributions and regolith evolution in the ouachita mountains arkansas usa rock fragments in the regolith are a persistent property that reflects the combined influences of geologic controls erosion deposition bioturbation and weathering the distribution of rock fragments in regoliths of the ouachita mountains arkansas shows that sandstone fragments are common in all layers even if sandstone is absent in parent material shale and sandstone fragments are produced at the bedrock weathering front but the shale weathers rapidly and intact fragments are rare in the solum sandstone is weathered from ridgetop outcrops and transported downslope some of these fragments are moved downward by faunalturbation and by transport into pits associated with rotting tree stumps upward movement by treethrow is common resulting in a net concentration of rocks near the surface however the highest fragment concentrations are in the lower regolith indicating active production at the weathering front the regolith is a dynamic feature reflecting the influences of vertical and horizontal processes of active weathering at the bedrock interface and of surficial sediment movements the role of trees in redistributing rock fragments suggests that significant regolith mixing occurs over time scales associated with forest vegetation communities and that forest soils have likely been extensively mixed within holocene and historic time copyright 2005 john wiley sons ltd

horizontal density structure and restratification of the arctic ocean surface layer ice tethered profiler itp measurements from the arctic ocean s canada basin indicate an ocean surface layer beneath sea ice with significant horizontal density structure on scales of hundreds of kilometers to the order 1 km submesoscale the observed horizontal gradients in density are dynamically important in that they are associated with restratification of the surface ocean when dense water flows under light water such restratification is prevalent in wintertime and competes with convective mixing upon buoyancy forcing e g ice growth and brine rejection and shear driven mixing when the ice moves relative to the ocean frontal structure and estimates of the balanced richardson number point to the likelihood of dynamical restratification by isopycnal tilt and submesoscale baroclinic instability based on the evidence here it is likely that submesoscale processes play an important role in setting surface layer properties and lateral density variability in the arctic ocean

parameterization of mixed layer eddies part ii prognosis and impact abstract the authors propose a parameterization for restratification by mixed layer eddies that develop from baroclinic instabilities of ocean fronts the parameterization is cast as an overturning streamfunction that is proportional to the product of horizontal buoyancy gradient mixed layer depth and inertial period the parameterization has remarkable skill for an extremely wide range of mixed layer depths rotation rates and vertical and horizontal stratifications in this paper a coarse resolution prognostic model of the parameterization is compared with submesoscale mixed layer eddy resolving simulations the parameterization proves accurate in predicting changes to the buoyancy the climate implications of the proposed parameterization are estimated by applying the restratification scaling to observations the mixed layer depth is estimated from climatology and the buoyancy gradients are from satellite altimetry the vertical fluxes are comparable to monthly mean air sea fluxes in large areas of

mining soil databases for landscape scale patterns in the abundance and size distribution of hillslope rock fragments landscape scale variation in rock fragments on soil mantled hillslopes is poorly understood despite the potential importance of rock fragments in soil weathering and coarse sediment supply to river networks we explored the utility of soil survey databases for data mining with the goals of identifying landscape scale patterns in the abundance and size distribution of rock fragments diameter d 2 mm and potential controls on grain size production we focus on data from three regions the hawaiian islands and the sierra nevada and cascade mountains where elevation transects span a range of environmental conditions we selected pedons from pits dug on hillslopes with active soil production and transport for the 27 pedons selected we constructed depth averaged grain size distributions and calculated the mass fraction of rock fragments frf and the median rock fragment grain size d50rf we also categorized as bimodal size distributions with a clear breakpoint between fine and coarse modes several strong patterns emerge from the data we find rock fragments in 85 of the pedons primarily in distinct coarse modes within bimodal size distributions values of frf and d50rf are strongly correlated although the best fit power law scaling between frf and d50rf differs between the warmer hawaiian and colder sierra nevada and cascade mountain sites we also find a regional contrast in the variation in frf with elevation frf declines with elevation in hawaii but increases in the mainland sites although this contrast could be an artifact of variable lithology precipitation may influence many patterns in the data lower mean annual precipitation correlates with higher frf dominantly bimodal distributions and surface enrichment in the vertical distribution of rock fragments these observations may be useful in refining models of coarse sediment supply to rivers and suggest opportunities for future work to test mechanistic hypotheses for rock fragment production on soil mantled hillslopes copyright 2011 john wiley sons ltd

global estimates of lateral springtime restratification abstractsubmesoscale frontal dynamics are thought to be of leading order importance for stratifying the upper ocean by slumping horizontal density gradients to produce vertical stratification presented here is an investigation of submesoscale instabilities in the mixed layer mixed layer eddies mles as a potential mechanism of frontal slumping that stratifies the upper ocean during the transition from winter to spring when wintertime forcings weaken but prior to the onset of net solar warming observations from the global argo float program are compared to predictions from a one dimensional mixed layer model to assess where in the world s oceans lateral processes influence mixed layer evolution the model underestimates spring stratification for 75 25 of the world s oceans relationships between vertical and horizontal temperature and salinity gradients are used to suggest that in 30 20 of the oceans this excess stratification can be attributed to the slumping of horizontal density fronts fin

submesoscale fronts in the antarctic marginal ice zone and their response to wind forcing submesoscale flows in the ocean are energetic motions o 1 10 km that influence stratification and the distributions of properties such as heat and carbon they are believed to play an important role in sea ice impacted oceans by modulating air sea ice fluxes and sea ice extent the intensity of these flows and their response to wind forcing are unobserved in the sea ice regions of the southern ocean we present the first submesoscale resolving observations in the antarctic marginal ice zone miz collected by surface and underwater autonomous vehicles for 3 months in austral summer we observe salinity dominated lateral density fronts occurring at sub kilometer scales surface winds are shown to modify the magnitude of the mixed layer density fronts revealing strongly coupled atmosphere ocean processes we posture that these wind front interactions occur as a continuous interplay between front slumping and vertical mixing which leads to the dispersion of submesoscale fronts such processes are expected to be ubiquitous in the southern ocean miz

organic burial site on mars the nili fossae region on mars is one of the places earmarked for the search of evidence for life a combination of geomorphological and mineralogical data from the area suggest ideal conditions for the burial of organic matter

modulation of erosion on steep granitic slopes by boulder armoring as revealed by cosmogenic 26al and 10be cosmogenic 26 al and 10 be in quartz from boulders bedrock and sandy sediment from 21 small watersheds in the diamond mountains batholith ca usa and two small watersheds from the nearby fort sage mountains confirm that exposed granitic bedrock and boulders erode more slowly than the catchments in which they are found exposed bedrock and boulders are more abundant on steep slopes and may play an important role in regulating mountain erosion rates rapid transport of fine sediment on steep slopes exhumes resistant corestones which accumulate on the surface the resulting boulder lag apparently shields the underlying soil and bedrock from erosion even when the bedrock is deeply weathered and friable where steep slopes have an abundant boulder lag they erode as slowly as gentler slopes nearby in contrast steep slopes lacking a boulder lag erode much more quickly than gentle slopes boulder armoring can modulate hillslope erosion such that erosion rates of summits steep mountain flanks and gentle footslopes are indistinguishable thus permitting local relief and steep mountain slopes to persist for long periods of time fl 2001 elsevier science b v all rights reserved

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

a one dimensional model for simulating armouring and erosion on hillslopes 2 long term erosion and armouring predictions for two contrasting mine spoils this paper investigates the dynamics of soil armouring as a result of fluvial erosion for a non cohesive sandy gravel spoil from the ranger mine australia and a cohesive silt loam spoil from the northparkes mine australia using a model for hillslope soil armouring these long term predictions concentrate on the temporal and spatial changes of the spoil grading and erosion over 100 200 years for the flat cap regions 1 2 and steep batter edges 10 30 typically encountered on waste rock dumps the existence of a significant rock fragment fraction in the ranger spoil means that it armours readily while northparkes does not for ranger the waste rock showed reductions in 1 cumulative erosion of up to 81 from that obtained by extrapolating the initial erosion rate out 100 years and 2 the erosion year by more than 10 fold for northparkes reductions were less marked with the maximum reduction in erosion year being 37 after 200 years for ranger the reductions were greatest and fastest for intermediate gradient hillslopes for the steepest hillslopes the armouring decreased because the flow shear stresses were large enough to mobilize all material in the armour layer model uncertainty was assessed with probabilistic confidence limits demonstrating that these erodibility reductions were statistically significant a commonly used hillslope erosion model sediment flux 1 discharge m1 slope n1 was fitted to these predictions the erodibility 1 and m1 decreased with time which was consistent with our physical intuition about armouring at ranger the parameter m1 asymptoted to 1 5 1 6 while at northparkes it asymptoted to 1 2 1 3 at ranger transient spatial trends in armouring led to a short term 50 200 years in the future reduction in n1 to below zero under certain circumstances recovering to an asymptote of about 0 5 1 at northparkes n1 asymptoted to about 0 6 with no negative transients predicted the m1 and n1 parameters predicted for ranger were shown to be consistent with field data from a 10 year old armoured hillslope and consistent with published relationships between erodibility and rock content for natural hillslopes copyright 2007 john wiley sons ltd

grain size distribution function of polymodal sediments in hydraulic and aeolian environments and numerical partitioning of the sedimentary components most continental sediments are polymodal composed of overlapping components of which the grain size generally obeys some type of natural distribution the grain size components and their function types can be determined from frequency and cumulative curve plots in order to define the function formula of the grain size distribution the function parameters can be estimated by fitting a defined function formula to the measured grain size data of the sample which simultaneously achieves numerical partitioning of the sedimentary components genetic analysis of grain size components of hydraulic and aeolian sediments demonstrates the following environmental implications fluvial sediment is composed of isolated saltation and suspension components the sediments in closed lake basins are dominated by a suspension silt clay component with a small proportion of saltation sand the fine sand component makes up the majority of desert sand overlapping with a small proportion of fine dust aeolian loess is composed of two overlapping components a short suspension time silt component and a long suspension time fine component aeolian material in the north pacific deep sea sediments is dominated by long suspension time fine dust the fine component in aeolian sediments shows a consistent grain size distribution and genetic connection from the desert sand loess of northern china to the north pacific ocean which is mainly transported by westerly winds and is dispersed in the atmosphere forming a background dust c 2002 elsevier science b v all rights reserved

lithological controls on hillslope sediment supply insights from landslide activity and grain size distributions the volumes rates and grain size distributions of sediment supplied from hillslopes represent the initial input of sediment delivered from upland areas and propagated through sediment routing systems moreover hillslope sediment supply has a significant impact on landscape response time to tectonic and climatic perturbations however there are very few detailed field studies characterising hillslope sediment supply as a function of lithology and delivery process here we present new empirical data from tectonically active areas in southern italy that quantifies how lithology and rock strength control the landslide fluxes and grain size distributions supplied from hillslopes landslides are the major source of hillslope sediment supply in this area and our inventory of 2800 landslides reveals that landslide sediment flux is dominated by small shallow landslides we find that lithology and rock strength modulate the abundance of steep slopes and landslides and the distribution of landslide sizes outcrop scale rock strength also controls the grain sizes supplied by bedrock weathering and influences the degree of coarsening of landslide supply with respect to weathering supply finally we show that hillslope sediment supply largely determines the grain sizes of fluvial export from catchments and that catchments with greater long term landslide rates deliver coarser material therefore our results demonstrate a dual control of lithology on hillslope sediment supply by modulating both the sediment fluxes from landslides and the grain sizes supplied by hillslopes to the fluvial system

grain size effects on energy delivery to the streambed and links to bedrock erosion fluvial bedrock erosion rates are thought to be proportional to the energy delivered to the channel bed by impacting bed load particles combining methods for field measurements of impact energy and for automatic sensing of grain size distributions in the instrumented channel of the erlenbach we show that the larger a bed load grain is the more efficient it is in transferring energy to the streambed on average the largest grain size class contributes only 9 to the total bed load mass but is responsible for more than 40 of the energy delivery this effect may help to explain the predominance of extreme floods when large grains are mobile in driving long term erosion while the mechanistic saltation abrasion model accounts for hydraulic forcing of energy delivery the observed grain size effect is not captured we suggest that the discrepancy arises from differing transport modes rolling sliding and saltation not currently captured in modeling