the quality of sea ice velocity estimates several aspects of observed and estimated velocities for arctic sea ice are explored the long term mean ice motion field and associated variance are derived using 15 years over 85 000 observations of daily buoy motions the mean field is separated into the part due to long term currents and internal ice stress and the part due to mean winds the velocity variance is partitioned into linear and nonlinear parts the linear response has no trend over the 15 years examined for a 5 year subset of the buoy data an ice ocean model with constant air drag parameters is used to estimate daily ice velocities at the buoy locations and then the linear relationship between the modeled velocities and the geostrophic winds is examined compared with buoy velocities the modeled velocities have a larger variance and larger linear response to the winds in a parameter study the effects of seasonally varying air drag coefficients increased ice strength and different ocean currents are examined seasonally varying air drag with smaller average magnitude than the standard value significantly improves the match of total linear and nonlinear variances between observed and modeled velocities the model simulations with varying air drag also have a smaller root mean square daily velocity error comparison of daily large scale deformations shows that the day to day deformations are not modeled well but generally have means and standard deviations within 50 of the observed values no one version of the model is consistently better than the others at matching the means and standard deviations of the observed daily divergence vorticity and shear ice thickness is sensitive to the model parameters varied with 5 year average thicknesses ranging from 2 2 to 3 4 m for the various simulations

dispersion of sea ice in the bering sea the dispersion of sea ice in the bering sea is analyzed in terms of the changes in separation between pairs of ice floes the statistics of these changes depend on the separation itself and on the time interval over which the changes are measured rather than being constant as in the case of molecular or fickian diffusion the diffusivity increases according to the 1 8 power of the separation for short times the diffusivity is proportional to time for times greater than 3 days the diffusivity appears to approach a constant value for any particular separation comparison with other data shows that the ice floe diffusivity is about an order of magnitude smaller than the diffusivity at the surface of the temperate ocean and about an order greater than the diffusivity of sea ice in the beaufort sea

textural and fluid inclusion evidence for ore deposition in the pb zn deposit at laisvall sweden laisvall is a sandstone hosted lead zinc deposit on the eastern margin of the scandinavian caledonides it is part of a large ore province stretching over 1 000 km from the south of norway to north of sweden the ore occurs as interstitial filling between sand grains but textural and fluid inclusion data demonstrate that the ore was formed by open space filling of open micropores in the sandstone the textures of the cementing minerals also demonstrate that postore deformation and metamorphism are restricted to some twinning in calcite and fracturing no major recrystallization has taken place textures include growth zoning of sphalerite with systematic color changes traceable as a sphalerite stratigraphy over large areas of the deposit both sphalerite and calcite display several stages of mineral growth including dissolution breaks and etched surfaces fluid inclusion homogenization temperatures indicate that each stage was deposited in a distinct temperature interval during a generally overall temperature decrease the environment of ore deposition was characterized by a temperature of 120 degrees to 180 degrees c and a total salinity of 24 equiv wt percent nacl this resulted from mixing a hot highly saline incoming solution with a cool local ground water the principal minerals were deposited in the order calcite barite fluorite sphalerite and galena this process was repeated several times and sulfide deposition was accompanied by calcite dissolution deposition of the minerals was affected by different mechanisms during the mixing process 1 heating of ground water deposited calcite 2 cooling of brine deposited barite and 3 mixing which deposited sulfides and fluorite the mixing occurred as a result of a double diffusion process where the equalization of densities resulted from salt diffusion along an extended interface between the hot brine and the cool ground water in the porous sandstone

variability of sea ice simulations assessed with rgps kinematics 1 sea ice drift and deformation from coupled ice ocean models are compared with high resolution ice motion from the radarsat geophysical processor system rgps in contrast to buoy drift the density and extent of the rgps coverage allows a more extensive assessment and understanding of model simulations at spatial scales from 10 km to near basin scales and from days to seasonal timescales this work illustrates the strengths of the rgps data set as a basis for examining model ice drift and its gradients as it is not our intent to assess relative performance we have selected four models with a range of attributes and grid resolution model fields are examined in terms of ice drift export deformation deformation related ice production and spatial deformation patterns even though the models are capable of reproducing large scale drift patterns variability among model behavior is high when compared to the rgps kinematics the characteristics shared by the models are 1 ice drift along coastal alaska and siberia is slower 2 the skill in explaining the time series of regional divergence of the ice cover is poor and 3 the deformation related volume production is consistently lower attribution of some of these features to specific causes is beyond our current scope because of the complex interplay between model processes parameters and forcing the present work suggests that high resolution ice drift observations like those from the rgps would be essential for future model developments improvements intercomparisons and especially for evaluation of the small scale behavior of models with finer grid spacing

continuum sea ice rheology determined from subcontinuum mechanics 1 a method is presented to calculate the continuum scale sea ice stress as an imposed continuum scale strain rate is varied the continuum scale stress is calculated as the area average of the stresses within the floes and leads in a region the continuum element the continuum scale stress depends upon the imposed strain rate the subcontinuum scale material rheology of sea ice the chosen configuration of sea ice floes and leads and a prescribed rule for determining the motion of the floes in response to the continuum scale strain rate we calculated plastic yield curves and flow rules associated with subcontinuum scale material sea ice rheologies with elliptic linear and modified coulombic elliptic plastic yield curves and with square diamond and irregular convex polygon shaped floes for the case of a tiling of square floes only for particular orientations of the leads have the principal axes of strain rate and calculated continuum scale sea ice stress aligned and these have been investigated analytically the ensemble average of calculated sea ice stress for square floes with uniform orientation with respect to the principal axes of strain rate yielded alignment of average stress and strain rate principal axes and an isotropic continuum scale sea ice rheology we present a lemon shaped yield curve with normal flow rule derived from ensemble averages of sea ice stress suitable for direct inclusion into the current generation of sea ice models this continuum scale sea ice rheology directly relates the size strength of the continuum scale yield curve to the material compressive strength

a generalized power law approximation for fluvial incision of bedrock channels 1 sediment flux is known to influence bedrock incision rates in mountain rivers although the widely used stream power incision model lacks any explicit representation of sediment flux the model appears to work in a variety of real settings we address this apparent contradiction using numerical experiments to explore the morphology of fluvial landscapes evolved with four different incision models three of which include the influence of sediment flux on incision rate the numerical landscapes have different spatial patterns of uplift and are at steady state we analyze these landscape using the common stream power approach which views incision rates to be primarily a function of the local channel gradient s and the upstream drainage area a we find that incision rates i for these landscapes are well described by an empirical power law equation i k am sn this equation is functionally equivalent to the widely used stream power model with the important distinction that the parameters k m and n are entirely empirical these parameters take on constant values within a single landscape but can otherwise be quite different between landscapes mainly due to differences in the pattern of rock uplift within the drainage in particular the parameters m and n decrease as the rate of rock uplift becomes more focused in the upland part of a mountain belt the parameter m is particularly important in that it describes the sensitivity of a tectonically active mountain belt to changes in precipitation or tectonic accretion it also defines how incision rates will change as the discharge becomes flashier

modelling landscape evolution geomorphology is currently in a period of resurgence as we seek to explain the diversity origins and dynamics of terrain on the earth and other planets in an era of increased environmental awareness yet there is a great deal we still do not know about the physics and chemistry of the processes that weaken rock and transport mass across a planet s surface discovering and refining the relevant geomorphic transport functions requires a combination of careful field measurements lab experiments and use of longer term natural experiments to test current theory and develop new understandings landscape evolution models have an important role to play in sharpening our thinking guiding us toward the right observables and mapping out the logical consequences of transport laws both alone and in combination with other salient processes improved quantitative characterization of terrain and process and an ever improving theory that describes the continual modification of topography by the many and varied processes that shape it together with improved observation and qualitative and quantitative modelling of geology vegetation and erosion processes will provide insights into the mechanisms that control catchment form and function this paper reviews landscape theory in the form of numerical models of drainage basin evolution and the current knowledge gaps and future computing challenges that exist copyright 2010 john wiley sons ltd

remapping the thickness distribution in sea ice models in sea ice models with multiple thickness categories the ice thickness distribution evolves in time the evolution of the thickness distribution as ice grows and melts is analogous to one dimensional fluid transport and can be treated by similar numerical methods one such method remapping is applied here thickness categories are represented as lagrangian grid cells whose boundaries are projected forward in time the thickness distribution is approximated as a linear or quadratic polynomial in each displaced category and ice area and volume are transferred between categories so as to restore the original boundaries in simple test problems and in a single column model with forcing typical of the central arctic remapping performs significantly better than methods previously used in sea ice models it is less diffusive than a scheme that fixes the ice thickness in each category and behaves better numerically than a scheme that represents the thickness distribution as a set of delta functions also remapping converges faster i e with fewer thickness categories than the alternative schemes with five to seven categories the errors due to finite resolution of the thickness distribution are much smaller than the errors due to other sources linear remapping performs as well as the more complex quadratic version and is recommended for climate modeling its computational cost is minimal compared to other sea ice model components

floe formation in arctic sea ice 1 the ice pack covering northern seas is composed of a mixture of thick ridged and rafted ice undeformed ice and open water ice motions determined from satellite remote sensing data show that deformation of the pack takes place along the boundary of large floes eulerian continuum sea ice models can simulate this behavior to a degree by capturing the localization of gridded ice strength in some average sense however using a discontinuous lagrangian approach that explicitly models ice floes and the interactions between them it is possible to simulate both the fracture process that creates floe boundaries and the continued deformation along those floe boundaries we have developed a granular model of the central arctic ice pack that consists of thousands of individual grains that can freeze together fracture apart and interact through ridging accelerations produced by passing weather patterns and sustained quasi steady deformation cause the model pack to fracture apart into floes composed of one or more grains when the ice pack is nonuniformly accelerating due to passage of a weather pattern simulations show that the factors that influence the size of the floes are the tensile strength of the joints between grains the gradient of the wind field and the average size of the individual grains during sustained deformation the pack continues to deform along existing floe boundaries while stresses build and further fracture takes place in quiet areas of the basin fractures refreeze to explore the fracture process during sustained deformation we run 24 hour basin scale simulations at resolutions from 2 8 km to 14 km at the end of each simulation we construct a distribution of floe areas the cumulative distribution of floes at the large end of the distribution is approximately the same at each resolution as we increase the resolution from 14 km to 2 8 km the damage zones between large floes become more localized a log log plot of the cumulative floe size distributions obtained from the simulations appears linear over several orders of magnitude

evaluation of high resolution sea ice models on the basis of statistical and scaling properties of arctic sea ice drift and deformation sea ice drift and deformation from models are evaluated on the basis of statistical and scaling properties these properties are derived from two observation data sets the radarsat geophysical processor system rgps and buoy trajectories from the international arctic buoy program iabp two simulations obtained with the louvain la neuve ice model lim coupled to a high resolution ocean model and a simulation obtained with the los alamos sea ice model cice were analyzed model ice drift compares well with observations in terms of large scale velocity field and distributions of velocity fluctuations although a significant bias on the mean ice speed is noted on the other hand the statistical properties of ice deformation are not well simulated by the models 1 the distributions of strain rates are incorrect rgps distributions of strain rates are power law tailed i e exhibit wild randomness whereas models distributions remain in the gaussian attraction basin i e exhibit mild randomness 2 the models are unable to reproduce the spatial and temporal correlations of the deformation fields in the observations ice deformation follows spatial and temporal scaling laws that express the heterogeneity and the intermittency of deformation these relations do not appear in simulated ice deformation mean deformation in models is almost scale independent the statistical properties of ice deformation are a signature of the ice mechanical behavior the present work therefore suggests that the mechanical framework currently used by models is inappropriate a different modeling framework based on elastic interactions could improve the representation of the statistical and scaling properties of ice deformation

sea ice motion from satellite passive microwave imagery assessed with ers sar and buoy motions observing the motion of sea ice from space is analogous to observing wind stress over the wet oceans both provide surface forcing for modeling ocean dynamics ice motion also directly provides the advective component of the equations governing the mass balance of the sea ice cover thus its routine observation from space would be of great value to understanding ice and ocean behavior to demonstrate the feasibility of creating a global multidecadal ice motion record from satellite passive microwave imagery and to quantitatively assess the errors in the estimated ice motions we have tracked ice every 3 days in the arctic ocean and daily in the fram strait and baffin bay during the 8 winter months from october 1992 to may 1993 and daily in the weddell sea during the 8 winter months from march to october 1992 the method which has been well used previously involves finding the spatial offset that maximizes the cross correlation of the brightness temperature fields over 100 km patches in two images separated in time by from 1 to 3 days the resulting ice motions are compared with contemporaneous buoyand sar derived ice motions the uncertainties in the displacement vectors between 5 and 12 km are better than the spatial resolution of the data both 85 ghz data with 12 km spatial resolution and 37 ghz data with 25 km resolution are tracked these trials with the 37 ghz data are new and show quite surprisingly that the error is only about 1 km larger with these data than with the 12 km 85 ghz data errors are typically larger than average in areas of lower ice concentration in the most dynamic regions particularly near the ice edge in the barents and greenland seas and in zones of high shear these passive microwave ice motions show a large increase in spatial detail over motion fields optimally interpolated from buoy and wind observations especially where buoy data are virtually absent such as near coasts and in some passages between the arctic ocean and its peripheral seas the feasibility of obtaining ice motion from the 37 ghz data in addition to the 85 ghz data should allow an important record of ice motion to be established for the duration of the scanning multichannel microwave radiometer smmr special sensor microwave imager ssm i and future microwave sensors that is from 1978 into the next millenium

combined hillslope diffusion and sediment transport simulation applied to landscape dynamics modelling we present a new numerical approach for simulating geomorphic and stratigraphic processes that combines open channel flow with non uniform sediment transport law and semi empirical diffusive mass wasting it is designed to facilitate modelling of surface processes across multiple space and time scales and under a variety of environmental and tectonic conditions the physics of open channel flow is primarily based on an adapted lagrangian formulation of shallow water equations the interaction between flow and surface geology is performed by a non uniform total load sediment transport law additional hillslope processes are simulated using a semi empirical method based on a diffusion approach in the implementation the resolution of flow dynamics is made on a triangulated grid automatically mapped and adaptively remeshed over a regular orthogonal stratigraphic mesh these new methods reduce computational time while preserving stability and accuracy of the physical solutions in order to illustrate the potential of this method for landscape and sedimentary system modelling we present a set of three generic experiments focusing on assessing the influence of contrasting erodibilities on the evolution of an active bedrock landscape the modelled ridges morphometrics satisfy established relationships for drainage network geometry and slope distribution and provide quantitative information on the relative impact of hillslope and channel processes sediment discharge and alluviation our results suggest that contrasting erodibility can stimulate autogenic changes in erosion rate and influence the landscape morphology and preservation this approach offers new opportunities to investigate joint landscape and sedimentary systems response to external perturbations the possibility to define and track a large number of materials makes the implementation highly suited to model source to sink problems where material dispersion is the key question that needs to be addressed such as natural resources exploration and basin analysis copyright 2014 john wiley sons ltd

abrupt changes in the rate of andean plateau uplift from reversible jump markov chain monte carlo inversion of river profiles abstract knowledge of the rate of surface uplift of the central andean plateau provides important boundary conditions for regional geodynamic models and paleoclimate reconstructions here we present a fully nonlinear inverse method to extract the rock uplift history of the central andean plateau from the cotahuasi river and its tributaries our approach is based on an analytical solution to the stream power model that relates elevation to rock uplift history under the assumptions of constant climatic conditions in space and time and spatially invariant rock uplift we use a bayesian framework that allows us to quantify the full state of knowledge of model parameters i e uncertainties trade offs the erosional efficiency defines the landscape response time and this must be determined using independent data therefore using thermochronometric data from the cotahuasi ocona canyon which record rapid fluvial incision at 13 10 ma we calibrate our results to infer a rock uplift history for the north central andean plateau we infer a pulse of rock uplift between 25 and 10 ma at rates as high as 0 25 km my however the rock uplift rate inferred during this pulse is not as high as is predicted if the central andean plateau grew as a result of loss of unstable lithospheric mantle therefore our results are more consistent with models requiring gradual uplift of the central andean plateau

estimating uplift rate histories from river profiles using african examples 1 we describe and apply a method for estimating uplift rate histories from longitudinal river profiles our strategy is divided into three parts first we develop a forward model which calculates river profiles from uplift rate histories height variation along a river profile is controlled by uplift rate and moderated by the erosional process we assume that the erosional process can be represented by a combination of advection and diffusion which are parameterized using four erosional constants second we have posed and solved the geologically more interesting inverse problem which uplift rate history minimizes the misfit between calculated and observed river profiles the inverse algorithm has been tested on synthetic river profiles which demonstrates that uplift rate histories can be reliably retrieved our tests show that the erosional process is dominated by advection i e knickpoint retreat and that changes in lithology and discharge play a secondary role in determining the transient form of a river profile finally we have inverted river profiles from a series of african topographic swells namely the bie south african namibian hoggar and tibesti domes fits between calculated and observed river profiles are excellent calculated uplift rate histories suggest that these domes grew rapidly during the last 30 40 million years uplift rate histories vary significantly from dome to dome but cumulative uplift histories agree closely with independent geologic estimates

field calibration of sediment flux dependent river incision 1 bed erosion and sediment transport are ubiquitous and linked processes in rivers erosion can either be modeled as a detachment limited function of the shear stress exerted by the flow on the bed or as a transport limited function of the sediment flux capacity of the flow these two models predict similar channel profiles when erosion rates are constant in space in time but starkly contrasting behavior in transient settings traditionally detachment limited models have been used for bedrock rivers whereas transport limited models have been used in alluvial settings in this study we demonstrate that rivers incising into a substrate of loose but very poorly sorted relict glacial sediment behave in a detachment limited manner we then develop a methodology by which to both test the appropriate incision model and constrain its form specifically we are able to tightly constrain how incision rates vary as a function of the ratio between sediment flux and sediment transport capacity in three rivers responding to deglaciation in the ladakh himalaya northwest india this represents the first field test of the so called tools and cover effect along individual rivers

interannual extremes in new zealand precipitation linked to modes of southern hemisphere climate variability abstract interannual extremes in new zealand rainfall and their modulation by modes of southern hemisphere climate variability are examined in observations and a coupled climate model north island extreme dry wet years are characterized by locally increased reduced sea level pressure slp cold warm sea surface temperature sst anomalies in the southern tasman sea and to the north of the island and coinciding reduced enhanced evaporation upstream of the mean southwesterly airflow during extreme dry wet years in south island precipitation an enhanced reduced meridional slp gradient occurs with circumpolar strengthened weakened subpolar westerlies and an easterly westerly anomaly in zonal wind in the subtropics as a result via ekman transport anomalously cold warm sst appears under the subpolar westerlies while anomalies of the opposite sign occur farther north the phase and magnitude of the resulting sst and evaporation anomalies cannot account for the rainfall extremes over t

control of reactivated proterozoic basement structures on sandstone hosted pb zn deposits along the caledonian front sweden evidence from airborne magnetic data structural analysis and ore grade modeling strata bound nonstratiform epigenetic galena sphalerite cement mineralization in ediacaran cambrian sandstone including the previously mined deposits at laisvall and vassbo occurs along the eas

arctic ice dynamics joint experiment aidjex assumptions revisited and found inadequate 1 this paper revisits the arctic ice dynamics joint experiment aidjex assumptions about pack ice behavior with an eye to modeling sea ice dynamics the aidjex assumptions were that 1 enough leads were present in a 100 km by 100 km region to make the ice isotropic on that scale 2 the ice had no tensile strength and 3 the ice behavior could be approximated by an isotropic yield surface these assumptions were made during the development of the aidjex model in the 1970s and are now found inadequate the assumptions were made in part because of insufficient large scale 10 km deformation and stress data and in part because of computer capability limitations upon reviewing deformation and stress data it is clear that a model including deformation on discontinuities and an anisotropic failure surface with tension would better describe the behavior of pack ice a model based on these assumptions is needed to represent the deformation and stress in pack ice on scales from 10 to 100 km and would need to explicitly resolve discontinuities such a model would require a different class of metrics to validate discontinuities against observations

numerical modelling of erosion processes in the himalayas of nepal effects of spatial variations of rock strength and precipitation the interplay between tectonics and erosion has a predominant control on the evolution of the morphology of mountain belts here we investigate the modalities of deformation in central nepal on a c 100 ka time scale in response to tectonic and external forcings through the use of a finite element thermomechanical model coupled with an integrative denudation formulation that accounts for fluvial incision and hillslope landsliding we study the complex coupling existing between tectonics and erosion with special emphasis on the influences of rock strength and rainfall distributions our results underline the key role played by lithologic variations in the elevation of both rivers and mean topography we show that the location of the main frontal thrust is mainly controlled by the low erodability of the unconsolidated sandstone in the siwaliks hills as previously suspected burbank et al 2003 our simulations demonstrate that the pattern of uplift in nepal is mainly dependent on both erodability and fault geometry rather than on rainfall distribution

global analysis of the stream power law parameters based on worldwide 10be denudation rates abstract the stream power law expressed as e kamsn where e is erosion rate lt 1 k is an erodibility coefficient t 1l 1 2m a is drainage area l 2 s is channel gradient l l and m and n are constants is the most widely used model for bedrock channel incision despite its simplicity and limitations the model has proved useful for topographic evolution knickpoint migration palaeotopography reconstruction and the determination of rock uplift patterns and rates however the unknown parameters k m and n are often fixed arbitrarily or are based on assumptions about the physics of the erosion processes that are not always valid which considerably limits the use and interpretation of the model in this study we compile a unique global data set of published basin averaged erosion rates that use detrital cosmogenic 10be these data n 1457 enable values for fundamental river properties to be empirically constrained often for the first time such as the concavity of the river profile m n ratio or concavity index the link between channel slope and erosion rate slope exponent n and substrate erodibility k these three parameters are calculated for 59 geographic areas using the integral method of channel profile analysis and allow for a global scale analysis in terms of climatic tectonic and environmental settings in order to compare multiple sites we also normalize n and k using a reference concavity index m n 0 5 a multiple regression analysis demonstrates that intuitive or previously demonstrated local scale trends such as the correlation between k and precipitation rates do not appear at a global scale our results suggest that the slope exponent is generally 1 meaning that the relationship between erosion rate and the channel gradient is nonlinear and thus support the hypothesis that incision is a threshold controlled process this result questions the validity of many regional interpretations of climate and or tectonics where the unity of n is routinely assumed

rock uplift and erosion rate history of the bergell intrusion from the inversion of low temperature thermochronometric data the bergell intrusion european alps was one of the first locations where thermochronometry was used to resolve changes in erosion rate yet relating these changes to variations in climate or in local tectonics remains challenging one approach that enables changes in erosion rate to be related to changes in climate or rock uplift rate is to utilize landscape evolution models as topographic response to these forcing parameters is unique furthermore low temperature thermochronometric systems have the potential to resolve topography through time and thus topographic response we present new u th he data for samples collected across 2 km of relief from the bergell the ages range from 2 to 16 ma and define an age elevation with an apparent exhumation rate of 0 1 km myr in order to infer erosion rates we use a thermokinematic model to solve the heat equation in the crust track material points through time and predict thermochronometric data paleo topography and erosion rate are parameterized using the stream power model we find that rock uplift rates were 0 4 km myr from 25 to 20 ma and subsequently decreased to 0 05 km myr this results in a gradual decrease in erosion rate from rates of 0 4 to 0 1 km myr a recent increase in rock uplift rate at 4 ma to 0 6 km myr is required to explain the youngest ages and high topographic relief

opening and closing of sea ice leads digital measurements from synthetic aperture radar the coming opportunity to extract quantitative sea ice data from routine synthetic aperture radar imagery requires the development of automated image processing techniques an algorithm is described for measuring the opening and the closing of leads by comparing two sequential synthetic aperture radar sar digital images the pair of images is classified into leads and ice correcting for variation in brightness with range displacements are determined automatically on a regular 2 km grid on a 100 km square scene by cross correlation an algorithm groups together cells which cover a lead event the lead area change is estimated for each cell group by counting lead pixels before and after deformation all positive changes are summed to obtain the amount of opening and all negative changes give closing errors are estimated by comparison with area changes determined from manually digitized lead boundaries and are about 0 2 of the area of the scene for comparison the measured opening and closing are in the range of 1 to 3 of the scene area in ice models the openings and closings of leads are parameterized in terms of the large scale deformation sar allows us to study these parametric relations by giving us access both to direct observations of opening and closing and to detailed kinematic data from which to estimate the mean deformation in this image pair for which the deformation is nearly pure shear we find relatively small amounts of opening and closing consistent with previous observations and with parameterizations in most models the large values of opening and closing predicted by the poisson gauss kinematic model are not in evidence

influence of mantle flow on the drainage of eastern australia since the jurassic period recent studies of the past eastern australian landscape from present day longitudinal river profiles and from mantle flow models suggest that the interaction of plate motion with mantle convection accounts for the two phases of large scale uplift of the region since 120 ma we coupled the dynamic topography predicted from one of these mantle flow models to a surface process model to study the evolution of the eastern australian landscape since the jurassic period we varied the rainfall regime erodibility sea level variations dynamic topography magnitude and elastic thickness across a series of experiments the approach accounts for erosion and sedimentation and simulates catchment dynamics despite the relative simplicity of our model the results provide insights on the fundamental links between dynamic topography and continental scale drainage evolution based on temporal and spatial changes in longitudinal river profiles as well as erosion and deposition maps we show that the motion of the australian plate over the convecting mantle has resulted in significant reorganization of the eastern australian drainage the model predicts that the murray river drained eastward between 150 and 120 ma and switched to westward draining due to the tilting of the australian plate from 120 ma first order comparisons of eight modeled river profiles and of the catchment shape of modeled murray darling basin are in agreement with present day observations the predicted denudation of the eastern highlands is compatible with thermochronology data and sedimentation rates along the southern australian margin are consistent with cumulative sediment thickness

geologic constraints on bedrock river incision using the stream power law denudation rate in unextended terranes is limited by the rate of bedrock channel incision often modeled as work rate on the channel bed by water and sediment or stream power the latter can be generalized as ka m s n where k represents the channel bed s resistance to lowenng whose variation with lithology is unknown a is drainage area a surrogate for discharge s is local slope and m and n are exponents whose values are debated we address these uncertainties by simulating the lowering of ancient river profiles using the finite difference method we vary m n and k to match the evolved profile as closely as possible to the corresponding modern river profile over a time period constrained by the age of the mapped paleoprofiles we find at least two end member incision laws ka 0 3 0 5 s for australian rivers with stable base levels and k f a 0 1 0 2 s n for rivers in kauai subject to abrupt base level change the long term lowering rate on the latter expression is a function of the frequency and magnitude of knickpoint erosion characterized by k f incision patterns from japan and california could follow either expression if they follow the first expression with m 0 4 k varies from 10 7 10 6 m 0 2 yr for granite and metamorphic rocks to 10 5 10 4 m 0 2 yr for volcaniclastic rocks and 10 4 10 2 m 0 2 yr for mudstones this potentially large variation in k with lithology could drive strong variability in the rate of long term landscape change including denudation rate and sediment yield

discussion a refined genetic model for the laisvall and vassbo mississippi valley type sandstone hosted deposits sweden constraints from paragenetic studies organic geochemistry and s c n and sr isotope data

sea ice rheology from in situ satellite and laboratory observations fracture and friction on the basis of an analysis of in situ ice stresses and of satellite derived ice strain rates as well as of a comparison between field and laboratory behaviour we describe an alternative viewpoint for modelling sea ice deformation during winter we propose that fracture and frictional sliding govern inelastic deformation over all spatial and temporal scales even under small stresses consequently winter and or perennial sea ice does not behave as a viscous material even at large scales the normal flow rule is not obeyed as observed during laboratory tests on sea ice samples harvested from the field and stresses are highly intermittent and poorly correlated spatially

tectonics from fluvial topography using formal linear inversion theory and applications to the inyo mountains california tectonic activity generates topography and the variability of tectonic forcing is responsible for topographic patterns and variability of relief in fluvial landscapes despite this basic relation the inverse problem by which features of the topography are used for inferring tectonic uplift rates has proven challenging here we develop formal linear inversion schemes to infer a record of the rate of relative uplift as a function of space and time from the long profiles of rivers the relative uplift rate is the difference between the rates of rock uplift and of the base level change the inversion schemes are based on a closed form analytic solution to the transient linear stream power model and to increase model resolution they make use of the multiplicity of information made available by multiple rivers and their tributaries the distribution of the fluvial response time to tectonic perturbations is a key component of the inversion scheme as this determines which tectonic events are preserved in the topography we develop two inversion parameterizations that differ in their assumptions about the tectonic forcing space invariant and time space variability with an assumed spatial distribution the inversion schemes are applied to the inyo mountains an uplifted block along the western boundary of the basin and range province in california inversion results indicate that the range has been experiencing an acceleration of the relative uplift in the past 2 3 ma we use the inversion results to constrain the paleotopography and paleo erosion rate along the range and to recover the throw rate history along the fault that bounds the inyo range

implications of sediment flux dependent river incision models for landscape evolution 1 developing a quantitative understanding of the factors that control the rate of river incision into bedrock is critical to studies of landscape evolution and the linkages between climate erosion and tectonics current models of long term river network incision differ significantly in their treatment of the role of sediment flux we analyze the implications of various sediment flux dependent incision models for large scale topography in an attempt 1 to identify quantifiable and diagnostic differences between models that could be detected from topographic data or from the transient responses of perturbed systems and 2 to explain the apparent ubiquity of mixed bedrock alluvial channels in active orogens although certain forms of the various models can be discarded as inconsistent with morphological data we find that the relative intrinsic concavity indices of detachment and transport limited systems defined herein largely dictate whether the various models can be tied to distinctive steady state morphologies preliminary data suggest that no such diagnostic differences may exist and other methods must be developed to test models accordingly we develop and explore differences in the scaling behavior of topographic relief and the extent of detachment versus transport limited channels as a function of rock uplift rate that may allow discrimination among various models further we explore potentially diagnostic differences in the rates and patterns of transient channel response to changes in rock uplift rate in addition to general differences between detachment and transport limited systems our analysis identifies an interesting hysteresis in landscape evolution hybrid channels at the threshold between detachment and transport limited conditions are expected to act as detachment limited systems in response to an increase in rock uplift rate or base level fall and as transport limited systems in response to a decrease in rock uplift rate especially during postorogenic topographic decline the analyses presented set the stage for field studies designed to test quantitatively the various river incision models that have been proposed

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

bayesian inference gibbs sampler and uncertainty estimation in geophysical inversion the posterior probability density function ppd m d obs of earth model m where d obs are the measured data describes the solution of a geophysical inverse problem when a bayesian inference model is used to describe the problem in many applications the ppd is neither analytically tractable nor easily approximated and simple analytic expressions for the mean and variance of the ppd are not available since the complete description of the ppd is impossible in the highly multi dimensional model space of many geophysical applications several measures such as the highest posterior density regions marginal ppd and several orders of moments are often used to describe the solutions calculation of such quantities requires evaluation of multidimensional integrals a faster alternative to enumeration and blind monte carlo integration is importance sampling which may be useful in several applications thus how to draw samples of m from the ppd becomes an important aspect of geophysical inversion such that importance sampling can be used in the evaluation of these multi dimensional integrals importance sampling can be carried out most efficiently by a gibbs sampler gs we also introduce a method which we called parallel gibbs sampler pgs based on genetic algorithms ga and show numerically that the results from the two samplers are nearly identical we first investigate the performance of enumeration and several sampling based techniques such as a gs pgs and several multiple maximum a posteriori map algorithms for a simple geophysical problem of inversion of resistivity sounding data several non linear optimization methods based on simulated annealing sa ga and some of their variants can be devised which can be made to reach very close to the maximum of the ppd such map estimation algorithms also sample different points in the model space by repeating these map inversions several times it is possible to sample adequately the most significant portion s of the ppd and all these models can be used to construct the marginal ppd mean covariance etc we observe that the gs and pgs results are identical and indistinguishable from the enumeration scheme multiple map algorithms slightly underestimate the posterior variances although the correlation values obtained by all the methods agree very well multiple map estimation required 0 3 of the computational effort of enumeration and 40 of the effort of a gs or pgs for this problem next we apply gs to the inversion of a marine seismic data set to quantify uncertainties in the derived model given the prior distribution determined from several common midpoint gathers