intergyre communication in a three layer model abstract a three layer wind driven general circulation model involving both subtropical and subpolar gyres has been developed to study intergyre exchange following some early studies the present work allows flow to baroclinically cross the intergyre boundary this model differs from past work by examining a three layer fluid solutions with both southward and northward subsurface flows are obtained the two principal objectives of this work are to clarify the structure and maintenance of the permanent thermocline and to aid in understanding the distribution of deep water masses a class of thermocline structures at the zero ekman pumping line has been constructed that permits intergyre exchange or communication the zones of exchange are called windows in this study the windows have several unique properties relative to those computed elsewhere and exhibit relatively rich structure principally the addition of an active third layer allows a new second baroclinic window to open this new window is

north atlantic potential vorticity and its relation to the general circulation abstract maps and sections of the large scale north atlantic potential vorticity q are presented here q is fd dz where f is the coriolis frequency the potential density and z the vertical coordinate they bear on the general circulation and on geostrophic waves instability and turbulence in many ways both eulerian and lagrangian mean circulations proceed along isostrophes q constant in a zero dissipation region in a resting fluid q varies simply as the sine of the latitude but we show here that the wind driven circulation reshapes the q field creating bowls and plateaus which allow the flow to cross latitude circles the implied nature of the western boundary current is very different than in classical frictional theory the maps show a region of uniform potential vorticity in the wind gyre 26 5 27 0 which fills the ocean between 15 37 n and 20 80 w such regions were prominent features of a circulation theory of rhines and young 1982a b at deeper levels and close to surface out

quantifying differential rock uplift rates via stream profile analysis despite intensive research into the coupling between tectonics and surface processes our ability to obtain quantitative information on the rates of tectonic processes from topography remains limited due primarily to a dearth of data with which to test and calibrate process rate laws here we develop a simple theory for the impact of spatially variable rock uplift rate on the concavity of bedrock river profiles application of the analysis to the siwalik hills of central nepal demonstrates that systematic differences in the concavity of channels in this region match the predictions of a stream power incision model and depend on the position and direction of the channel relative to gradients in the vertical component of deformation rate across an active fault bend fold furthermore calibration of model parameters from channel profiles argued to be in steady state with the current climatic and tectonic regime indicates that 1 the ratio of exponents on channel drainage area and slope m n is 0 46 consistent with theoretical predictions 2 the slope exponent is consistent with incision either linearly proportional to shear stress or unit stream power n 0 66 or n 1 respectively and 3 the coefficient of erosion is within the range of previously published estimates mean k 4 3 10 4 m 0 2 yr application of these model parameters to other channels in the siwalik hills yields estimates of spatially variable erosion rates that mimic expected variations in rock uplift rate across a fault bend fold thus the sensitivity of channel gradient to rock uplift rate in this landscape allows us to derive quantitative estimates of spatial variations in erosion rate directly from topographic data

the leaky thermocline a model for the vertical structure of ocean gyres is presented that extends the ideal thermocline theories of rhines and young and luyten et al to include a cross layer volume flux associated with geostrophic eddy transfer a two and one half layer model is considered that assumes that the intensity of the eddy transfer depends on the local strength of the current the ideal thermocline models emerge in the limit where the parameter characterizing the cross layer volume flux is asymptotically small inclusion of the eddy induced volume flux resolves the nonuniqueness of the sverdrup dynamics in the unventilated pool attached to the western boundary layer in the ventilated region solutions of the model equations converge to their ideal counterparts the circulation is closed explicitly by developing a western boundary layer theory based entirely on the effects of the cross isopycnal volume flux due to eddies unlike most models of western intensification the leaky boundary layer here is active and its dynamics are essential for determining the structure of the interior field

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

transient fluvial incision in the headwaters of the yellow river northeastern tibet china 1 we utilize topographic analysis of channel profiles combined with field measurements of erosion rates to explore the distribution of channel incision in the anyemaqen shan a broad mountainous region in the northeastern tibetan plateau tributary channels to the yellow river display systematic downstream increases in channel gradient associated with convex upward longitudinal profiles steep lower reaches of channels are associated with rapid 1 m ka incision rates along the yellow river while upstream reaches are associated with relatively slow 0 05 0 1 m ka erosion of soil mantled uplands covariance between erosion rates and channel steepness indices suggest that channels are adjusted to match long wavelength differential rock uplift across the range geologic constraints indicate that rapid incision downstream of the range is associated with excavation of basin fill driven by changes in relative base level farther downstream the upstream limit of this wave of transient incision is marked by a series of knickpoints that are found at nearly the same elevation throughout the watershed consistent with knickpoint migration as a kinematic rather than diffusional wave tributary channel gradients downstream of knickpoints however display a progressive adjustment to increased incision rates that may reflect the influence of increased sediment flux comparison of observed channel profiles to a stream power model of fluvial behavior reveals that the rate of knickpoint propagation can only be explained if the erosional efficiency coefficient k increases during incision our results thus highlight the utility of channel profile analysis to reconstruct the fluvial response to both active tectonism and external changes in base level

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

rapid incision of the colorado river in glen canyon insights from channel profiles local incision rates and modeling of lithologic controls the colorado river system in southern utah and northern arizona is continuing to adjust to the baselevel fall responsible for the carving of the grand canyon estimates of bedrock incision rates in this area vary widely hinting at the transient state of the colorado and its tributaries in conjunction with these data we use longitudinal profiles of the colorado and tributaries between marble canyon and cataract canyon to investigate the incision history of the colorado in this region we find that almost all of the tributaries in this region steepen as they enter the colorado river the consistent presence of oversteepened reaches with similar elevation drops in the lower section of these channels and their coincidence within a corridor of high local relief along the colorado suggest that the tributaries are steepening in response to an episode of increased incision rate on the mainstem this analysis makes testable predictions about spatial variations in incision rates these predictions are consistent with existing rate estimates and can be used to guide further studies we also present cosmogenic nuclide data from the henry mountains of southern utah we measured in situ10be concentrations on four gravel covered strath surfaces elevated from 1 m to 110 m above trachyte creek the surfaces yield exposure ages that range from approximately 2 5 ka to 267 ka and suggest incision rates that vary between 350 and 600 m my these incision rates are similar to other rates determined within the high relief corridor available data thus support the interpretation that tributaries of the colorado river upstream of the grand canyon are responding to a recent pulse of rapid incision on the colorado numerical modeling of detachment limited bedrock incision suggests that this incision pulse is likely related to the upstream dipping lithologic boundary at the northern edge of the kaibab upwarp copyright 2009 john wiley sons ltd

on boundary value problems of the ideal fluid thermocline abstract recent developments of ideal fluid thermocline models are briefly reviewed using density coordinates boundary value problems are formulated for the ideal fluid thermocline with continuous stratification ekman pumping and surface density are specified as the upper boundary conditions no flow is permitted through the ocean s eastern boundary nor its bottom each water column is divided into three parts i e the stagnant abyssal water with specified stratification the unventilated thermocline with its potential vorticity specified and the ventilated thermocline with its potential vorticity determined by a global dynamic balance the unventilated thermocline is further divided into the shallow and deep parts potential vorticity is specified a priori for the latter however for the former potential vorticity has to be chosen in the process of calculating the solution so as to make the solution self consistent numerical integration of the ideal fluid thermocline equations is reduced to repea

a demonstration of the importance of bedload transport for fluvial bedrock erosion and knickpoint propagation we provide field evidence for the role of bedload in driving fluvial incision and knickpoint propagation using aerial photographs field surveys and hydrological data we constrain the incision history of a bedrock gorge 1200 m long and up to 20 m deep cut by da an river in western taiwan this reach of the river experienced 10 m of uplift during the 1999 chi chi earthquake for five years following the earthquake bedload was prevented from entering the uplift zone the knickpoint was static and little incision took place bedload transport across the uplift zone resumed in 2004 initiating extremely rapid incision with 620 m of knickpoint propagation and up to 20 m of downcutting by 2008 this change highlights the relative inefficiency of suspended sediment and the dominant role of bedload as a tool for fluvial erosion and knickpoint propagation once bedload tools became available knickpoint propagation was influenced by geological structure lithology and drainage organization in particular a change in dip of the sandstone beds at the site caused a decrease of knickpoint propagation velocity copyright 2012 john wiley sons ltd

channel changes in badlands stripping of the vegetation and soil from a 13 hectare site in virginia underlain by coastal plain sediments created a rapidly evolving badland topography two types of channels developed 1 sand bed alluvial channels were graded to transport the bed material load supplied from slope erosion with available runoff but they also generally eroded their beds slowly and 2 steeper bedrock floored channels incised rapidly in bedrock channels the erosion rate was proportional to the 4 9ths power of drainage area and the 2 3rds power of gradient these exponents are consistent with a model in which the erosion rate is proportional to the bed shear during high flows due to rapid mass wasting and reduced runoff the alluvial channels became as much as 50 steeper during the winter than the summer with an attendant yearly cycle of winter aggradation and summer entrenchment the gradients their seasonal variability and their downstream hydraulic geometry were consistent with the predictions of total load transport formulas for sand beds and high loads the hydraulic geometry of alluvial channels in the virginia badlands were similar to that on the morrison formation in the western united states

upstream effects of the gulf stream on the structure of the mid ocean thermocline abstract attempts to resolve a paradoxical result by blandford 1965 led us to reexamine the degree of specification necessary to assure continuity of solution in a density stratified non rotating channel through which two layers move over a deep resting one we then proceeded to formulate and solve numerically a rudimentary beta plane model of an inertial boundary current fed entirely from the equator the zero potential vorticity case inspection of the numerical results indicates a simpler self similar form of the evolution of this problem leading to same results but explicitly analytical this model implies that the gulf stream exerts a control over mid ocean thermocline structure

can the western boundary layer affect the potential vorticity distribution in the sverdrup interior of a wind gyre abstract the question posed in the title of this paper is answered in the affirmative by investigating a two layer quasi geostrophic model of the wind driven circulation the two layers model the thermocline rather than the whole depth of the ocean the wind stress is balanced by interfacial and bottom drag this is perhaps the simplest baroclinic extension of stommel s 1948 barotropic circulation model it differs from an earlier model of welander 1966 in that the vortex stretching nonlinearity is of primary importance in this model the dynamics of the frictional western boundary layer determine the vertical structure of the wind driven flow in the sverdrup interior thus in a sense the boundary layer is active and cannot be appended to an arbitrary interior flow rather it partially determines the interior circulation by setting the functional relationship between the streamfunction and the potential vorticity in the lower layer in previous studies rhines and young 1982b this functional rel

knickpoint initiation and distribution within fluvial networks 236 waterfalls in the waipaoa river north island new zealand if knickpoints transmit signals of base level fall in river networks then improvements in our understanding of their retreat rate and basin wide distribution helps constrain the transient response following perturbation many studies of knickpoint retreat focus on the response of trunk streams to base level fall here we examine the response of an entire fluvial network as recorded by 236 active knickpoints distributed within the waipaoa river on the north island of new zealand base level fall within the waipaoa catchment initiated 18 000 years ago in response to a climatically triggered and tectonically exacerbated pulse of incision using observations from field work aerial photo analysis and a digital elevation model dem we study the knickpoint positions within the network we find that 70 of the knickpoints are located at drainage areas between 1 10 5 m 2 and 1 10 6 m 2 and more than half are b1 km upstream of a large change in drainage area for the knickpoints b1 km upstream of large tributary junctions we find that the retreat distances were well correlated with the tributaries drainage areas in order to determine how a pulse of incision distributes itself throughout a fluvial network we develop two simple end member models and compare their behavior to the observed knickpoint distribution in the waipaoa in the first model we propose that a knickpoint initiated at the basin outlet retreats upstream and distributes the signal throughout the network at a rate that is a power law function of drainage area in the second model we propose that knickpoints form near a threshold drainage area below which channels cannot incise with the same efficiency as possible in downstream reaches though neither model addresses the along stream variability in substrate or knickpoint form the misfit between the modeled and the observed knickpoints along stream positions are surprisingly low b1 km 1 25 of the total stream length for knickpoints with drainage areas b1 10 6 m 2 large misfits up to 3 5 km are observed for knickpoints with present day drainage areas greater than 1 10 6 m 2 the large single step in channel elevation that characterizes knickpoints presently observed in tributaries of the waipaoa river may not characterize the base level fall signal that propagated through the trunk streams evidence for progressive rather than instantaneous incision in the trunk streams the knickpoints vicinities to tributary junctions and the equivalent success of the two end member models lead us to conclude that the present positions of the 236 observed knickpoints are largely a consequence of thresholds in channel incision at low drainage areas

evolution of the northern santa cruz mountains by advection of crust past a san andreas fault bend the late quaternary marine terraces near santa cruz california reflect uplift associated with the nearby restraining bend on the san andreas fault excellent correspondence of the coseismic vertical displacement field caused by the 17 october 1989 magnitude 7 1 loma prieta earthquake and the present elevations of these terraces allows calculation of maximum long term uplift rates 1 to 2 kilometers west of the san andreas fault of 0 8 millimeters per year over several million years this uplift in concert with the right lateral translation of the resulting topography and with continual attack by geomorphic processes can account for the general topography of the northern santa cruz mountains

on the relative importance of ventilation and mixing of potential vorticity in mid ocean gyres abstract an a priori estimate is given of the effect of ventilation on the process of potential vorticity homogenization since the homogenization process depends on the presence of weak mixing it is shown that only a small exposure to a zone of ventilation is required to lead to an arrest of the homogenization

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

epigenetic gorges in fluvial landscapes epigenetic gorges form when channels that have been laterally displaced during episodes of river blockage or aggradation incise down into bedrock spurs or side walls of the former valley rather than excavating unconsolidated fills and reinhabiting the buried paleovalley valley filling events that promote epigenetic gorges can be localized such as a landslide dam or an alluvial debris flow fan deposit at a tributary junction or widespread such as fluvial aggradation in response to climate change or fluctuating base level the formation of epigenetic gorges depends upon the competition between the resistance to transport strength and roughness of valley filling sediments and a river s ability to sculpt and incise bedrock the former affects the location and lateral mobility of a channel incising into valley filling deposits the latter determines rates of bedrock incision should the path of the incising channel intersect with bedrock that is not the paleovalley bottom epigenetic gorge incision by definition post dates the incision that originally cut the valley strath terraces and sculpted bedrock walls that form in relation to epigenetic gorges should not be used to directly infer river incision induced by tectonic activity or climate variability rather they are indicative of the variability of short term bedrock river incision and autogenic dynamics of actively incising fluvial landscapes the rate of bedrock incision associated with an epigenetic gorge can be very high 1 cm yr typically orders of magnitude higher than both short and long term landscape denudation rates in the context of bedrock river incision and landscape evolution epigenetic gorges force rivers to incise more bedrock slowing long term incision and delaying the adjustment of rivers to regional tectonic and climatic forcing copyright 2008 john wiley sons ltd

equilibration of a warm pumped lens on a β plane abstract the dynamics of a warm lens created by a surface buoyancy flux and ekman pumping in an initially homogeneous unbounded fluid on a plane is studied in a set of high resolution numerical experiments a simple analytical model for the equilibrium structure of the lens is developed that assumes that the input of vorticity and buoyancy from the ekman layer is balanced through transfer by baroclinic eddies that carry the warm fluid laterally away from the lens the importance of eddy induced diapycnal flux in the western intensification region is emphasized by developing a boundary layer theory based entirely on the cross frontal mass exchange due to eddies the theory is successfully tested against direct numerical eddy resolving simulations possible oceanographic implications of the study for understanding subtropical gyres and the antarctic circumpolar current are discussed

on the role of interior mixing and air sea fluxes in determining the stratification and circulation of the oceans abstract the problem of determining the eastern boundary basic stratification and the buoyancy driven circulation of the oceans is addressed a global integral constraint relating the interior stratification and the air sea heat fluxes is derived based on the condition that the total mass of water of given density is constant in a steady state ocean this constraint is then applied to two simple analytic models the first is a continuous nonlinear diffusive model of the lower mid depth and bottom circulation below the influence of the wind driven circulation it shows the tendency of the vertical density profile to look like an exponential profile in the presence of mixing the integral constraint is used to relate the stratification and circulation of the bottom and mid depth waters to the air sea heat fluxes at the surface where the deep densities outcrop the second model is a layered one of the wind driven circulation mid depth and bottom water the eastern boundary stratification of the model i

experimental study of bedrock channel alluviation under varied sediment supply and hydraulic conditions 1 channel incision into bedrock plays a critical role in mountain landscape evolution a bed that is completely alluviated cannot undergo incision as a result incision driven by the collision of bedload grains and bedrock requires transport at below capacity conditions for example where the bed is partially covered by alluvium in a mechanistic model of bedrock incision it is important to have a formula describing the relationship between the bedload transport rate and the degree to which the bed is covered by sediment the purpose of this work is to understand the mechanisms underlying the degree of bed exposure in bedrock rivers by means of an experimental study a number of experiments with various hydraulic and morphological bed conditions were performed in order to characterize this model here we focus on planar bedrock beds with some roughness the results suggest that the sediment supply channel slope hydraulic bed roughness the degree of areal coverage and thickness of antecedent gravel in the channel as well as the presence of boulders in the channel are major factors controlling bedrock exposure for sufficiently low ratios of sediment supply to transport capacity it was found that bedrock roughness can play a role in determining the degree of bedrock exposure for higher sediment ratios on the other hand the composite roughness associated with grain roughness bars and or antidunes dominates so that the underlying bedrock roughness no longer affects the degree of exposure of the bed for lower bed slopes i e less than 0 015 based on our experimental setting bedrock exposure decreases more or less linearly with increasing values of the ratio of sediment supply rate to capacity rate for higher bed slopes i e more than 0 015 there is a range of lower values of the ratio of sediment supply rate to capacity rate where a bedrock surface becomes fully exposed without any alluvial deposit for a given bedrock roughness this range expands solely with increasing slope regardless of shear stress within the upper range of values of the ratio of sediment supply to capacity rate a linear relationship between the degree of bedrock exposure and this supply to capacity ratio still prevails the addition of model boulders can be viewed as very high hydraulic bed roughness to the channel has been found to suppress the overexposure of bedrock and so restore a linear relation between the degree of exposure and the ratio of sediment supply rate to capacity rate formulations for estimating bedrock exposure as a function of sediment supply to capacity ratio under different river channel characteristics are proposed a linear relation between the degree of alluvial cover and the ratio of sediment supply rate to capacity rate is a previously proposed model the present study expands the result for other cases including runaway alluviation some landscape evolution models assume an abrupt shift between fully exposed bedrock and complete alluviation whereas others assume the linear relation the present study shows that both formulations are valid under different settings of river characteristics

the wind driven circulation quasi geostrophic simulations and theory for nonsymmetric winds abstract simulations of the wind driven ocean circulation carded out with an eddy resolving quasi geostrophic numerical model and symmetric idealized wind forcing have a large scale structure that is predicted wen by the steady nonlinear theory of rhines and young the sharp jet and inertial recirculation am often confined weft inside the region of closed hyperbolic characteristics defined by that theory and hence do not affect the sverdrup dynamics part of the gyre the characteristics make possible simple predictions about the development of the circulation including time dependence and eddy stirring by tilting the line of vanishing ekman pumping away from the east west orientation as it is tilted in the north atlantic and less so the north pacific we explore a family of circulations as the tilt of the wind held is increased characteristics originating at the eastern boundary begin to thread through the energetic region occupied by the free jet then extensive new branches of eddy driven f

can eddies set ocean stratification abstract a simple theory is presented for the buoyancy anomaly and depth of penetration of a warm lens created by a surface buoyancy flux and ekman pumping in an initially homogeneous rotating fluid it is assumed that the overturning of isopycnals induced by pumping and differential heating balances the counteroverturning tendency of baroclinic instability baroclinic eddies not only develop on the stratified lens but also play a fundamental role in setting its stratification the theory is successfully tested against numerical and laboratory experiments in which the mechanically induced deepening of a buoyant lens is arrested by its baroclinic instability finally the possibility is discussed that the eddy transfer process studied here might play a role in setting the stratification and depth of the main thermocline in the ocean

eddy induced diapycnal fluxes and their role in the maintenance of the thermocline abstract high resolution numerical experiments are diagnosed to study the integral effects of geostrophic eddy fluxes on the large scale ocean circulation three characteristic large scale flows are considered 1 an anticyclonic single gyre 2 a double gyre and 3 an unblocked zonal flow a simple analog of the antarctic circumpolar current it is found that buoyancy and potential vorticity budgets in the presence of eddies are dominated by a balance between vertical advection into the control volume by ekman pumping and eddy transfer across the density surfaces achieved by diapycnal eddy fluxes with small scale mixing making only a minor contribution possible oceanographic implications of the results are discussed

status of groundwater arsenic pollution of mirzapur district in holocene aquifers from parts of the middle ganga plain india a groundwater arsenic as distribution in mirzapur district of uttar pradesh is shown in the entrenched channels and floodplains of the ganga river a total of 45 tubewell water samples were analysed for as through flow injection hydride generation atomic absorption spectrometry fi hg aas system iron in tubewell water was analysed by 1 10 phenanthroline method by the use of uv spectrophotometer about 37 7 of tubewells in this district have as 10 g l who guideline and 15 5 of tubewells have as above 50 g l about 84 4 of tubewells have higher concentrations of iron fe beyond its permissible limit 1 mg l bis guideline the iron fe content in tubewell water samples varies from 0 1 to 7 6 mg l about 75 5 of tubewells in mirzapur district are from shallow depth 20 40 m and it is worth noticing that 37 7 of as contaminated as 10 g l tubewells are located within the depth of 25 40 m in the holocene newer alluvium aquifers most of the as contaminated villages in mirzapur district are located close to abandoned or present meander channels and floodplains of the ganga river in contrast tubewells in mirzapur and chunar towns have low concentrations of as in groundwater as 50 m in the pleistocene older alluvium aquifers would be better option for as safe groundwater the potential sources of as are mainly from the himalayas and the himalayas rivers have high content of as in suspended river sediments

new insights into the mechanics of fluvial bedrock erosion through flume experiments and theory river incision into bedrock drives the topographic evolution of mountainous terrain and may link climate tectonics and topography over geologic time scales despite its importance the mechanics of bedrock erosion are not well understood because channel form river hydraulics sediment transport and erosion mechanics coevolve over relatively long time scales that prevent direct observations and because erosive events occur intermittently and are difficult and dangerous to measure herein we synthesize how flume experiments using erodible bedrock simulants are filling these knowledge gaps by effectively accelerating the pace of landscape evolution under reduced scale in the laboratory we also build on this work by providing new theory for rock resistance to abrasion thresholds for plucking by vertical entrainment sliding and toppling and by assessing bedrock analog materials bedrock erosion experiments in the last 15 years reveal that the efficiency of rock abrasion scales inversely with the square of rock tensile strength sediment supply has a dominant control over bed roughness and abrasion rates suspended sediment is an efficient agent of erosion and feedbacks with channel form and roughness strongly influence erosion rates erodibility comparisons across rock concrete ice and foam indicate that for a given tensile strength abrasion rates are insensitive to elasticity the few experiments that have been conducted on erosion by plucking highlight the importance of block protrusion height above the river bed and the dominance of block sliding and toppling at knickpoints these observations are consistent with new theory for the threshold shields stress to initiate plucking which also suggests that erosion rates in sliding and toppling dominated rivers are likely transport limited major knowledge gaps remain in the processes of erosion via plucking of bedrock blocks where joints are not river bed parallel waterfall erosion by toppling and plunge pool erosion feedbacks between weathering and physical erosion erosional bedforms and morphodynamic feedbacks between channel form and erosion rates despite scaling challenges flume experiments continue to provide much needed tests of existing bedrock erosion theory force development of new theory and yield insight into the mechanics of landscapes

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

transport slopes sediment cover and bedrock channel incision in the henry mountains utah 1 field data from channels in the henry mountains of utah demonstrate that abundant coarse sediment can inhibit fluvial incision into bedrock by armoring channel beds the cover effect we compare several small channels that share tributary junctions and have incised into the same sedimentary bedrock unit navajo sandstone but contain differing amounts of coarse diorite clasts owing to the spatial distribution of localized sediment sources bedrock channels that contain abundant clasts diorite rich have steeper longitudinal slopes than tributaries of these channels with smaller drainage areas and less sediment diorite poor the diorite poor tributaries have incised more deeply to lower average slopes and have more reach scale slope variability which may reflect bedrock properties longitudinal sediment sorting and incision at lower sediment supply diorite rich channels have less bedrock exposed and smoother longitudinal profiles than diorite poor channels we find that 1 coarse sediment can mantle bedrock channel beds and reduce the efficiency of incision validating the hypothesized cover effect in fluvial incision models 2 the channel slope needed to transport the sediment load can be larger than that needed to erode bedrock suggesting that the slope of incising bedrock channels can become adjusted to the sediment load 3 when abundant sediment is available transport capacity rather than thresholds of motion can be dominant in setting bedrock channel slope and 4 cover effects can be important even when moderate amounts of bedrock are exposed in channel beds

diverse pliocene quaternary tectonics in a transform environment san francisco bay region california the san francisco bay region occupies part of the diffuse transform boundary zone between the pacific and north american plates although dextral strike slip faulting is dominant the plate motion is expressed in a variety of ways some strike slip faults are parallel with the plate boundary but some are slightly oblique the major strike slip faults are zones in which an interplay occurs between strands some of which are en echelon this interplay may be responsible for some apparent pull apart basins and presumed normal faults along the calaveras fault zone in extensive areas between strike slip fault zones there are many compressional structures folds and reverse faults that are pliocene quaternary in age hence largely coeval with the strike slip faults some of the compressional structures are oblique to and others are parallel with the major strike slip faults we have divided the san francisco bay region into domains on the basis of the types orientations and relationships of structures or in one case lack of strong deformation each domain has responded in its own way to the regional northwest southeast dextral shear imposed by the relative plate motion in an attempt to understand the origin of various structures and the interrelationships among them we compared established models with our observations some observed geometric relationships agree quite well with classical coulomb anderson and simple shear models but others require further explanation models based on fault interaction seem to apply to certain cases for example the east bay hills domain which is between the left stepping calaveras and hayward rodgers creek fault zones is under compression resulting from interaction between the two strike slip zones

modeling of knickpoint retreat on the roan plateau western colorado 1 the roan plateau in western colorado constitutes a natural experiment for studying landscape response to a drop in base level late cenozoic incision of the upper colorado river led to elevational isolation of the plateau and initiation of a wave of incision into its southern edge knickpoints oversteepened reaches that contain waterfalls 60 110 m in height mark the upstream extent of this headward propagating wave that this incision has occurred in a laterally extensive well stratified and essentially flat lying bedrock and in an area with relatively uniform climate implies that it should serve as a good test of existing knickpoint propagation models we predict the locations of knickpoints by using a stream power based celerity model in which knickpoint recession rate is a power function of drainage area and is proportional to rock susceptibility to erosion models of the parachute and roan drainages 17 and 16 knickpoints respectively show expected rapid initial knickpoint propagation rates which decline as drainage area decreases stepwise at tributary junctions the modeled positions of knickpoints match well with observed features using a single combination of parameters to model retreat in both drainage basins we compare our celerity model results with past studies and explore how longitudinal profile analysis may be used to derive independently the exponent on drainage area in the celerity model

semi adiabatic model of the deep stratification and meridional overturning abstractan analytical model of the atlantic deep stratification and meridional overturning circulation is presented that illustrates the dynamic coupling between the southern ocean and the midlatitude gyres the model expressed here in terms of the two and a half layer framework predicts the stratification and meridional transport as a function of the mechanical and thermodynamic forcing at the sea surface the approach is based on the classical elements of large scale circulation theory ideal thermocline inertial western boundary currents and eddy controlled antarctic circumpolar current acc models which are combined to produce a consistent three dimensional view of the global overturning the analytical tractability is achieved by assuming and subsequently verifying that the pattern of circulation in the model is largely controlled by adiabatic processes the time mean and eddy induced isopycnal advection of buoyancy the mean stratification of the lower thermocline is determined by the surface fo

eddy cancellation of the ekman cell in subtropical gyres abstractthe presence of large scale ekman pumping associated with the climatological wind stress curl is the textbook explanation for low biological activity in the subtropical gyres using an idealized eddy resolving model it is shown that eulerian mean ekman pumping may be opposed by an eddy driven circulation analogous to the way in which the atmospheric ferrel cell and the southern ocean deacon cell are opposed by eddy driven circulations lagrangian particle tracking potential vorticity fluxes and depth density streamfunctions are used to show that in the model the rectified effect of eddies acts to largely cancel the eulerian mean ekman downwelling to distinguish this effect from eddy compensation it is proposed that the suppression of eulerian mean downwelling by eddies be called eddy cancellation

eddy mixing of potential vorticity versus thickness in an isopycnic ocean model abstract parameterizations of the eddy induced velocity that advects tracers in addition to the eulerian mean flow are traditionally expressed as a downgradient fickian diffusion of either isopycnal layer thickness or large scale potential vorticity pv there is an ongoing debate on which of the two closures is better and how the spatial dependence of the eddy diffusivity should look like to increase the physical reasoning on which these closures are based the authors present a systematic assessment of eddy fluxes of thickness and pv and their relation to mean flow gradients in an isopycnic eddy resolving model of an idealized double gyre circulation in a flat bottom closed basin the simulated flow features strong nonlinearities such as tight inertial recirculations a meandering midlatitude jet pools of homogenized pv and regions of weak flow where h dominates the pv gradient it is found that the zonally averaged eddy flux of thickness scales better with the zonally averaged meridional thickn

field evidence for the control of grain size and sediment supply on steady state bedrock river channel slopes in a tectonically active setting we exploit a natural experiment in boulder creek a 30 km2 drainage in the santa cruz mountains ca usa to explore how an abrupt increase in the caliber of bedload sediment along a bedrock channel influences channel morphology in an actively uplifting landscape boulder creek s bedrock channel which is entirely developed on weak sedimentary rock has a high flow stress that is about 3 5 times greater where it transports coarse 22 cm d50 diorite in the lower reaches in comparison to the upstream section of the creek that transports only relatively finer bedload 2 cm d50 derived from weak sedimentary rocks in addition boulder creek s channel abruptly widens and shallows downstream and transitions from partial to nearly continuous alluvial cover where it begins transporting coarse diorite boulder creek s tributary channels are also about three times steeper where they transport diorite bedload and within the santa cruz mountains channels in sedimentary bedrock are systematically steeper when 50 of their catchment area is within crystalline basement rocks despite this clear control of coarse sediment size on channel slopes the threshold of motion stress for bedload alone does not appear to control channel profile slopes here upper boulder creek which is starved of coarse sediment maintains high flow shear stresses well in excess of the threshold for motion in contrast lower boulder creek with a greater coarse sediment supply exerts high flow stresses much closer to the threshold for motion we speculate that upper boulder creek has evolved to sustain partial alluvial cover and transfer greater energy to the bed via bedload impacts to compensate for its low coarse sediment supply thus bedload supply bedrock erosion efficiency and grain size all appear to influence channel slopes here

a model of wind and buoyancy driven ocean circulation abstract a layered model of steady geostrophic ocean circulation driven by wind stress and buoyancy flux at the surface is derived potential vorticity or thickness of the two near surface layers is driven by ekman pumping and buoyancy pumping the latter is represented as a flow of mass proportional to the modified buoyancy flux across the first submerged layer interface this mass flux is modified by the advection of buoyancy in the wind driven ekman layer though diffusive diapycnal buoyancy flux across deeper layers is neglected at lowest order it is essential for the global balance of the buoyancy budget the global buoyancy balance requirement determines such parameters as the midocean outcrop latitudes of layers that outcrop in the subtropical gyre and the depths of interfaces at the eastern boundary of layers that do not these parameters control the mean thicknesses of the layers and with the diapycnal diffusivity the mean diffusive flux of buoyancy through each active layer in this way t

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

argon as a tracer of cross isopycnal mixing in the thermocline abstract noble gases such as argon are unaffected by chemical reactions in the ocean interior but a number of physical mechanisms can lead to measurable sea level atmospheric disequilibrium in subsurface waters of the ocean one such mechanism is the mixing of waters of different temperatures which can lead to supersaturation in the ocean interior the authors simulate the supersaturation mixing signature in the thermocline in a global ocean general circulation model parallel ocean program model version 1 4 pop 1 4 in contrast to existing mixing diagnostics such as dye tracers or microstructure measurements which yield the local recent rate of diabatic mixing argon disequilibrium traces an integrated lifetime history of subsurface mixing a theoretical model of the subtropical atlantic ocean gyre is built based on the competing time scales of horizontal and vertical mixing that agrees well with the full general circulation model argon supersaturation gradient in the thermocline these results