sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

contradictory correlations of paleoproterozoic glacial deposits local regional or global controls abstract there is little agreement among recently proposed correlation schemes for paleoproterozoic glaciogenic rocks scattered thinly around the globe correlations are hindered by the dearth of tight geochronological control on the ages of glacial deposits which are notoriously difficult to date most attempts at global correlation are based on comparison to the huronian supergroup in canada which contains three glaciogenic formations although the two lower glacial units were deposited in a rift setting and have a restricted distribution even in north america they have been used in attempts to effect international correlations the gowganda formation together with correlatives comprises the thickest and by far the most widespread paleoproterozoic glacial deposits in north america glacial deposits are also reported from south africa western australia and elsewhere where they appear to fall within the same time period as the huronian supergroup 2 45 2 2 ga but attempts to correlate individual diamictite bearing units to the three huronian glaciogenic formations have proved difficult none of the huronian glacial formations has been precisely dated until such geochronological data are available it is practical and prudent to recognize that during the early paleoproterozoic as in the cryogenian the earth was susceptible to glaciations that could be triggered by a variety of local events including uplift related to rifting and compressional orogeny within the 250 million years of the huronian glacial event 2 45 2 2 ga it is commonly assumed that ice sheet fluctuations were globally synchronous but this has not been demonstrated

detachment of road surface soil by flowing water abstract an agricultural watershed generally consists of two land use categories farmland and the unpaved road or path networks with different traffic frequency and size road surfaces are quite different from farmland soil in physical properties resulting in it s distinguish production transportation process hydraulic flume experiments were conducted with the flow discharges ranging from 1 to 5 l s 1 and the slope gradients ranging from 8 8 to 46 6 to simulate the soil detachment process on a road surface and to develop tools in order to calculate detachment rates occurring on that road surfaces the results illustrate that road surfaces behave characteristically in the runoff detachment and sediment delivery process due to the difference in the bulk density and functions of agricultural soils the soil detachment rate is closely related to flow depth slope gradient and other hydraulic parameters such as shear stress stream power and unit stream power multiple non linear regression analyses indicate that detachment rates for all roads can be accurately predicted by power functions of flow depth and slope gradient according to the experimental results stream power was suggested as an indicator to estimate soil detachment rate instead of shear stress in soil erosion models however considering the simplicity and availability power function of flow depth and slope gradient is also recommended to predict detachment rate on the road surfaces

has the ozone hole contributed to increased antarctic sea ice extent 1 since the 1970s sea ice extent has decreased dramatically in the northern hemisphere and increased slightly in the southern hemisphere a difference that is potentially explained by ozone depletion in the southern hemisphere stratosphere in this study we consider the impact of stratospheric ozone depletion on antarctic sea ice extent using a climate model forced with observed stratospheric ozone depletion from 1979 to 2005 contrary to expectations our model simulates a year round decrease in antarctic sea ice due to stratospheric ozone depletion the largest percentage sea ice decrease in our model occurs in the austral summer near the coast of antarctica due to a mechanism involving offshore ekman sea ice transport the largest absolute decrease is simulated in the austral winter away from the coast of antarctica in response to an ocean warming that is consistent with a poleward shift of thc large scale pattern of sea surface temperature our model results strongly suggest that processes not linked to stratospheric ozone depletion must be invoked to explain the observed increase in antarctic sea ice extent

zonal asymmetry of the antarctic oscillation 1 in this research the zonal asymmetry of the southern annular mode or the antarctic oscillation aao is studied it is indicated that apparent zonal asymmetry exists in the normalized sea level pressure differences between the middle and high latitudes during the boreal summer among different longitudes especially between the western and eastern hemispheres results show that the southern oscillation so is responsible for part of the zonal asymmetry in aao the western hemisphere and the eastern hemisphere parts of aao are correlated at 0 23 and 0 52 respectively for the period of 1959 1998 before and after the linear regressions on the southern oscillation index soi have been removed from the time series the paper also discusses the relationship between the precipitation in the east asia and the aao before and after removing the linear regressions on so index soi indicating the stable relationship between the east asian precipitation and the zonal symmetric component of aao

relationships between the interannual variability of antarctic sea ice and the southern oscillation abstract a climatology of antarctic sea ice extent based on 20 years of data 1973 1992 is presented including measures of interannual variability and extrema in the first half of the year the greatest variability is found in the western hemisphere particularly in the weddell and ross sea regions while in the second semester the variability displays a considerable degree of zonal symmetry we have used this dataset to explore the possible links between antarctic sea ice extent and the southern oscillation index soi to do this we have calculated their correlation for all pairings of calendar months as well as with the soi taken from the year before and subsequent to that of the time of the sea ice data most of the correlations assume their largest magnitude when the soi leads the anomalies in the sea ice but these differ considerably between the three ocean basins the extent of indian ocean sea ice in the months april through july is positively correlated with the soi during most of the previou

antarctic sea ice climatology variability and late twentieth century change in ccsm4 abstracta preindustrial control run and an ensemble of twentieth century integrations of the community climate system model version 4 ccsm4 are evaluated for antarctic sea ice climatology modes of variability trends and covariance with related physical variables such as surface temperature and sea level pressure compared to observations the mean ice cover is too extensive in all months this is in part related to excessively strong westerly winds over 50 60 s which drive a large equatorward meridional ice transport and enhanced ice growth near the continent and also connected with a cold bias in the southern ocean in spite of these biases in the climatology the model s sea ice variability compares well to observations the leading mode of austral winter sea ice concentration exhibits a dipole structure with anomalies of opposite sign in the atlantic and pacific sectors both the el nino southern oscillation and the southern annular mode sam project onto this mode in twentieth century inte

distribution of depth of overland flow on desert hillslopes and its implications for modeling soil erosion abstract data collected during field experiments on hillslopes in southern arizona reveal that the depth of overland flow in interrill areas can be approximated by a negative exponential distribution soil erosion over the greater part of most hillslopes is equal to detachment capacity flow detachment in interrill areas is generally modeled using a du boys type equation in which shear stress is calculated using the mean depth of flow it is shown that using the mean depth rather than the distribution of depth can result in the severe underestimation of flow detachment insofar as the exponential density is characterized by a single parameter that is the reciprocal of the mean a knowledge of the mean depth is all that is needed to specify the distribution thus utilization of the depth distribution rather than the mean depth does not require any additional information yet it yields much more accurate estimates of flow detachment and hence soil erosion in interrill areas

modelling gully erosion for a small catchment on the chinese loess plateau the rolling hills region of the chinese loess plateau is one of the areas with the highest erosion rates on earth a striking feature of this area is the occurrence of many large permanent gullies a 3 5 km2 catchment was selected to study the processes of erosion and to adapt the storm based limburg soil erosion model lisem to the conditions prevailing on the loess plateau part of this work consisted of mapping and measuring the largest gully headcuts the amount of loose soil material beneath the headcuts was also estimated observations suggest that gully headcuts are relatively stable i e do not migrate rapidly but that gullies can nevertheless produce significant amounts of sediment during overland flow events erosion of headcuts occurs mainly by soil falls in between storms the loose soil material produced by these soil falls accumulates on the gully bottom as the lisem simulates storm erosion the development of gullies over time can be ignored and only the amount of material produced by them during runoff events needs to be studied a digital elevation model dem was used to estimate the position of existing gully heads by applying an adapted form of the montgomery and dietrich science 255 1992 826 index using the assumption that headcuts are vertical it is possible to calculate headcut height from the slope angle map a simple stability model which assumes soil falls on gully headcuts to be a function of soil moisture content and headcut height was applied this daily based model can then be used to simulate the accumulation of loose soil material below the headcut the results show that while the dem is not accurate enough to allow the detection of individual headcuts this method can be used to produce a reasonable estimate of the amount of loose soil material available a map showing the amount of loose soil material accumulated can then serve as input for a storm based erosion model such as lisem

connecting antarctic sea ice to deep ocean circulation in modern and glacial climate simulations antarctic sea ice formation plays a key role in shaping the abyssal overturning circulation and stratification in all ocean basins by driving surface buoyancy loss through the associated brine rejection changes in antarctic sea ice have therefore been suggested as drivers of major glacial interglacial ocean circulation rearrangements here the relationship between antarctic sea ice buoyancy loss deep ocean stratification and overturning circulation is investigated in last glacial maximum and preindustrial simulations from the paleoclimate modelling intercomparison project pmip the simulations show substantial inter model differences in their representation of the glacial deep ocean state and circulation which is often at odds with the geological evidence we argue that these apparent inconsistencies can largely be attributed to differing and likely insufficient antarctic sea ice formation discrepancies can be further amplified by short integration times deep ocean equilibration and sea ice representation should therefore be carefully evaluated in the forthcoming pmip4 simulations

the antarctic dipole and its predictability this study investigates the nature of interan nualvariability ofantarcticseaiceanditsrelationshipwith the tropical climate we nd that the dominant interan nual variance structure in the sea ice edge and surface air temperature elds is organized as a quasi stationary wave which we call the antarctic dipole adp it is charac terized by an out of phase relationship between the ice and temperature anomalies in the central eastern pacic and atlantic sectors of the antarctic the dipole consists of a strong standing mode and a weaker propagating motion within each basin s ice eld it has the same wavelength as the antarctic circumpolar wave acw and dominates the acw variance the dipole is clearly associated with tropical enso events it can be predicted with moderate skill using linear regression involving surface temperature two to four months ahead the prediction performs better in extreme warm cold years and best in la ni na years

comparison of rill flow velocity regimes between developing and stationary rills abstract flow velocity is fundamental in calculating related parameters of physical soil erosion models it has been well known that rill flow velocity varies with developing rill form which complicates and impedes the development of soil erosion models in filed rainfall erosion frequently occurs with pre existing rills not damaged by tillage practices however the rill flow velocity in this case has received little attention in this study we investigated rill flow velocity regimes for both developing and stationary rills using 5 m length plots in the laboratory the experiments included two consecutive rainfalls which had similar runoff rate the first rainfall had an intensity of 90 mm h 1 which generated well developed rills the second had an intensity of 60 mm h 1 and did not damage the rills formed by the first rainfall the results show that for a developing rill rill flow velocity is higher in the lower slope than that in the upper slope and rill flow velocity in the lower slope fluctuates much more over time as a result of the variation of rill morphology following rill development with rill development the rill flow velocity of the lower slope decreased responding to the stabilizing rill channel and exhibited a similar trend to that in upper slope for a stationary rill the rill flow velocities at both sections varied little over time demonstrating that rill flow velocity is primarily influenced by rill morphology hence the results suggested that the strength of fluctuation in rill flow velocity could be used to characterize the instantaneous intensity of soil erosion and active level of rill development the channel of the stationary rill simply acted as transport pathways of sediment supplied by inter rill erosion the physical models of soil erosion should take into account the micro topography on land surface related to the antecedently formed rills

the abrasion of soil aggregate under different artificial rough beds in overland flow abstract during slope erosion the travel and abrasion of aggregate during transport may produce finer and more transportable particles causing a significant effect on the sediment transport capacity and erosion intensity little information is available on the effect of roughness on aggregate abrasion in overland flow this study investigated the potential effects of slope gradient flow discharge and roughness on aggregate abrasion and hydraulic characteristics in overland flow these factors were studied with a series of aggregate abrasion experiments in a 3 8 m long flume at four slope gradients 8 7 17 6 26 8 36 4 five discharges 0 4 l s 1 0 6 l s 1 0 8 l s 1 1 0 l s 1 1 2 l s 1 and five surfaces of artificial rough beds the results indicated that the different roughness conditions with contributions of 63 5 had obvious effects on the abrasion of aggregate compared to the slope gradient and discharge regardless of the discharge and slope gradient the abrasion degree of aggregate gradually increased as the roughness increased the changes in the abrasion degree of the aggregate were not the same at the different combinations of discharge and slope for each artificial rough bed flow depth can well explain the extent of abrasion of the aggregate for the single fixed rough bed however the abrasion degree of the aggregate had no significant variation with increases in the flow depth from all the data of the five artificial rough beds the ratio between the residual weight and initial weight of soil aggregates wr wi decreased in a power function with increase in the friction factor and shear stress from all the data of the five artificial rough beds the friction factor and shear stress should be appropriate indicators to reflect aggregate abrasion under various roughness conditions in overland flow the information of the analysis of the abrasion of soil aggregate under different artificial rough beds can be useful for the development of soil process based erosion models

soft sediment deformation structures in cambrian siliciclastic and carbonate storm deposits shandong province china differential liquefaction and fluidization triggered by storm wave loading abstract this paper focuses on soft sediment deformation structures ssds in both siliciclastic and carbonate storm deposits of the cambrian mantou and chaomidian formations shandong province china in order to understand their deformation mechanisms and possible triggers siliciclastic ssds e g sand volcanoes and pillows and carbonate ssds e g sedimentary dykes grainstone matrix breccias deformed cross beddings and marlstone matrix breccias occur exclusively in hummocky cross stratified fine sandstone and peloidal grainstone respectively the siliciclastic ssds formed in porous and permeable surface sediment whereas the carbonate ssds formed under shallow burial conditions when early marine cementation prevailed the various deformation structures resulted mainly from differences between siliciclastic and carbonate sediment conditions and resulting deformation mechanisms sand volcanoes formed by upward extrusion of over pressured fluidized sandy sediment whereas sand pillows resulted from upward injection of lower density muddy sediment into overlying liquefied sandy sediment sedimentary dykes and grainstone matrix limestone breccias formed as a result of differential liquefaction and fluidization of heterogeneously cemented carbonate sediment whereas deformed cross beddings and marlstone matrix limestone breccias developed by the thixotropic liquidization and injection of clayey sediment and further disruption of thin peloidal layers sedimentary facies analysis and analysis of the physical processes indicate that the ssds were most likely caused by cyclic loading of storm waves

the possible role of benthic microbial mats during the formation of carbonaceous shales in shallow mid proterozoic basins a considerable portion of the upper member of the mid proterozoic newland formation meagher county montana consists of carbonaceous silty shales striped shale facies this type of shale facies is common in proterozoic basins and is host to several major base metal deposits the striped shales were deposited in a subtidal setting basinward of carbonates characterized by cryptalgal laminites mudcracks and flat pebble conglomerates the carbonaceous silty shales are considered remnants of benthic microbial mats irregular internal laminae patterns of particle trapping mechanical deformation during penecontemporaneous soft sediment deformation and filamentous microbiota provide evidence for this interpretation the dolomitic clayey shale contains graded silt clay couplets and these are interpreted as storm layers modern subtidal microbial mats can only survive under special conditions but in the proterozoic it is suggested that benthic microbial mats colonized the shallow seafloor during periods of low sediment input leading to the formation of carbonaceous shales

relationships between low frequency variability in the southern hemisphere and sea surface temperature anomalies abstract long term trends and interannual variations of circulation anomalies in the southern hemisphere are examined using the national centers for environmental prediction national center for atmospheric research reanalysis from 1949 to 1998 the changes in planetary circulation regimes are linked to global sea surface temperature anomalies sstas empirical orthogonal function eof analysis was performed on 500 hpa height anomalies the leading mode eof1 shows a strong zonal symmetry with a phase reversal between height anomalies in high and midlatitudes apart from zonal symmetry a zonal wavenumber 3 is evident with three centers located in three southern oceans in the low frequency band with fluctuations longer than 60 months eof1 is associated with the second rotated eof mode of sstas with positive loadings over three southern oceans and negative loadings in the north pacific and the north atlantic the next two modes are the pacific south american psa patterns they depict wave 3 patterns in

spatial distribution of sheet flow velocity along slope under simulated rainfall conditions abstract velocity of sheet flow is an important parameter for understanding the process of inter rill erosion on a hill slope under rainfall conditions a solute centroid method was employed to measure velocity distribution of sheet flow basing on solute transport process in the flow in an 8 m long flume the flow velocity measurements were made at slope lengths of 3 5 6 and 7 m under slope gradients of 5 10 and 20 and rainfall intensities of 80 120 and 160 mm h 1 respectively the measurements clearly showed that mean flow velocity ranged from 0 050 to 0 352 m s 1 and increased with slope gradient and rainfall intensity velocity of sheet flow increased with slope length while the increase rate slowed down before approaching a steady velocity the distance for sheet flow velocity to reach its maximum became shorter under greater slope gradient and rainfall intensity water depth was

limestone pseudoconglomerates in the late cambrian gushan and chaomidian formations shandong province china soft sediment deformation induced by storm wave loading this paper focuses on the formative processes of limestone pseudoconglomerates in the gushan and chaomidian formations late cambrian of the north china platform shandong province china the gushan and chaomidian formations consist mainly of limestone and shale marlstone interlayers wackestone to packstone grainstone and microbialite as well as numerous limestone conglomerates seventy three beds of limestone pseudoconglomerate in the gushan and chaomidian formations were analysed based on clast and matrix compositions internal fabric sedimentary structures and bed geometry these pseudoconglomerates are characterized by oligomictic to polymictic limestone clasts of various shapes i e flat to undulatory disc blade and sheet marlstone and or grainstone matrix and various internal fabrics i e intact thrusted edgewise and disorganized as well as transitional boundaries limestone pseudoconglomerates formed as a result of soft sediment deformation of carbonate and argillaceous interlayers at a shallow burial depth differential early cementation of carbonate and argillaceous sediments provided the requisite conditions for the formation of pseudoconglomerates initial deformation i e burial fragmentation liquefaction and injection and subsequent mobilization and disruption of fragmented clasts are two important processes for the formation of pseudoconglomerates burial fragmentation resulted from mechanical rupture of cohesive carbonate mud whereas subsequent mobilization of fragmented clasts was due to the injection of fluid materials liquefied carbonate sand and water saturated argillaceous mud under increased stress storm wave loading was the most probable deformation mechanism as an external triggering force subsequent re orientation and rounding of clasts were probably prolonged under normal compactional stress eventually disrupted clasts along with matrix materials were transformed into pseudoconglomerates by progressive lithification soft sediment deformation is prevalent in alternate layers of limestone and mud marl stone and or grainstone regardless of their depositional environments

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

last millennium climate and its variability in ccsm4 abstractan overview of a simulation referred to as the last millennium lm simulation of the community climate system model version 4 ccsm4 is presented the ccsm4 lm simulation reproduces many large scale climate patterns suggested by historical and proxy data records with northern hemisphere nh and southern hemisphere sh surface temperatures cooling to the early 1800s common era by 0 5 c nh and 0 3 c sh followed by warming to the present high latitudes of both hemispheres show polar amplification of the cooling from the medieval climate anomaly mca to the little ice age lia associated with sea ice increases the lm simulation does not reproduce la nina like cooling in the eastern pacific ocean during the mca relative to the lia as has been suggested by proxy reconstructions still dry medieval conditions over the southwestern and central united states are simulated in agreement with proxy indicators for these regions strong global cooling is associated with large volcanic erup

determining the mean depth of overland flow in field studies of flow hydraulics in field studies of interrill overland flow conducted on runoff plots the mean depth of flow is usually obtained by averaging measurements of flow depth at regularly spaced points across the plot including points where there is no flow although this procedure may be appropriate in studies aimed at runoff prediction it is not in studies concerned with flow hydraulics in the latter studies more realistic results can be obtained by excluding those points where the depth is zero and reducing the width of flow in proportion to the number of points excluded failure to do this results in the underestimation of the actual mean flow depth reynolds number and friction factor where discharges are small or microtopography is large this underestimation is likely to be significant

twentieth century simulation of the southern hemisphere climate in coupled models part ii sea ice conditions and variability we examine the representation of the mean state and interannual variability of antarctic sea ice in six simulations of the twentieth century from coupled models participating in the intergovernmental panel on climate change fourth assessment report the simulations exhibit a largely seasonal southern hemisphere ice cover as observed there is a considerable scatter in the monthly simulated climatological ice extent among different models but no consistent bias when compared to observations the scatter in maximum winter ice extent among different models is correlated to the strength of the climatological zonal winds suggesting that wind forced ice transport is responsible for much of this scatter observations show that the leading mode of southern hemisphere ice variability exhibits a dipole structure with anomalies of one sign in the atlantic sector associated with anomalies of the opposite sign in the pacific sector the observed ice anomalies also exhibit eastward propagation with the antarctic circumpolar current as part of the documented antarctic circumpolar wave phenomenon many of the models do simulate dipole like behavior in sea ice anomalies as the leading mode of ice variability but there is a large discrepancy in the eastward propagation of these anomalies among the different models consistent with observations the simulated antarctic dipole like variations in the ice cover are led by sea level pressure anomalies in the amundsen bellingshausen sea these are associated to different degrees in different models with both the southern annular mode and the el nino southern oscillation enso there are indications that the magnitude of the influence of enso on the southern hemisphere ice cover is related to the strength of enso events simulated by the different models

hydraulic conditions for rill incision under simulated rainfall a laboratory experiment a series of controlled laboratory experiments were conducted in order to obtain precise data on the hydraulic and sediment transport conditions during rill formation tests were carried out using a crusting prone binary mixed soil in a 15 m long flume at an average slope of 0 087 under simulated rainfall rainfall intensities varied from 30 35 mm h 1 and developed about 70 per cent of the kinetic energy of natural rainfall of similar intensity runoff and sediment discharge measured at the downstream weir were strongly influenced by rill forming processes essentially rill incision reduced runoff discharge as a result of increased percolation in rill channels but increased sediment discharge secondary entrainment processes such as bank collapse also increased sediment discharge at the weir knickpoint bifurcation and colluvial deposition however decreased sediment discharge rills always developed through the formation of a knickpoint the critical condition for knickpoint initiation was the development of supercritical flow and waves which mould and incise the bed prior smoothing of the soil surface by entrainment and redistribution of sediment facilitated supercritical flow statistical analysis showed that hydraulic and sediment transport conditions differed significantly in rilled and unrilled flows the relationship between sediment discharge rill erosion and flow hydraulics was found to be nonlinear conforming to a standard power function in the form y axb rills were also associated with significantly increased sediment transport capacities however rill initiation was not clearly defined by any specific hydraulic threshold instead rilled and unrilled flows were separated by zones of transition within which both types of flow occur

late twentieth century simulation of arctic sea ice and ocean properties in the ccsm4 abstractto establish how well the new community climate system model version 4 ccsm4 simulates the properties of the arctic sea ice and ocean results from six ccsm4 twentieth century ensemble simulations are compared here with the available data it is found that the ccsm4 simulations capture most of the important climatological features of the arctic sea ice and ocean state well among them the sea ice thickness distribution fraction of multiyear sea ice and sea ice edge the strongest bias exists in the simulated spring to fall sea ice motion field the location of the beaufort gyre and the temperature of the deep arctic ocean below 250 m which are caused by deficiencies in the simulation of the arctic sea level pressure field and the lack of deep water formation on the arctic shelves the observed decrease in the sea ice extent and the multiyear ice cover is well captured by the ccsm4 it is important to note however that the temporal evolution of the simulated arctic sea ice cover over the

laboratory testing of a new thermal tracer for infrared based ptv technique for shallow overland flows abstract the accurate measurement of velocities of shallow overland flows normally found in the field of hydrology is essential to understand the kinematics of these flows in view of this we have tested the capability of a new thermal particle tracer cold oil droplets under controlled laboratory conditions to measure the velocity of shallow overland flows

velocity of water flow along saturated loess slopes under erosion effects abstract rainfall or snow melted water recharge easily saturates loose top soils with a less permeable underlayer such as cultivated soil slope and partially thawed top soil layer and thus may influence the velocity of water flow this study suggested a methodology and device system to supply water from the bottom soil layer at the different locations of slopes water seeps into and saturates the soil when the water level is controlled at the same height of the soil surface the structures and functions of the device the components and the operational principles are described in detail a series of laboratory experiments were conducted under slope gradients of 5 10 15 and 20 and flow rates of 2 4 and 8 l min 1 to measure the water flow velocities over eroding and non eroded loess soil slopes under saturated conditions by using electrolyte tracing results showed that flow velocities on saturated slopes were 17 to 88 greater than those on non saturated slopes flow velocity increased rapidly under high flow rates and slope gradients saturation conditions were suitable in maintaining smooth rill geomorphology and causing fast water flow the saturated soil slope had a lubricant effect on the soil surface to reduce the frictional force resulting in high flow velocity the flow velocities of eroding rills under different slope gradients and flow rates were approximately 14 to 33 lower than those of non eroded rills on saturated loess slopes compared with that on a saturated loess slope the eroding rill on a non saturated loess slope can produce headcuts to reduce the flow velocity this study helps understand the hydrodynamics of soil erosion and sediment transportation of saturated soil slopes

mechanisms forcing an antarctic dipole in simulated sea ice and surface ocean conditions abstract the mechanisms forcing variability in southern ocean sea ice and sea surface temperature from 600 years of a control climate coupled model integration are discussed as in the observations the leading mode of simulated variability exhibits a dipole pattern with positive anomalies in the pacific sector associated with negative anomalies in the atlantic it is found that in the pacific ocean circulation changes associated with variable wind forcing modify the ocean heat flux convergence and sea ice transport resulting in sea surface temperature and sea ice anomalies the pacific ice and ocean anomalies persist over a number of years due to reductions in ocean shortwave absorption reinforcing the initial anomalies in the atlantic sector no single process dominates in forcing the anomalies instead there are contributions from changing ocean and sea ice circulation and surface heat fluxes while the absorbed solar radiation in the atlantic is modified by the changing surface albedo the anomalies

flow resistance and sediment transport by concentrated overland flow in a grassland valley abstract flow resistance and sediment transport data are needed from well vegetated humid environments to evaluate surface wash erosion and channel incision by overland flow in humid environments runoff in valley floors can reach depths of several centimetres but erosion is often limited by dense grass cover intense grazing reduces grass cover but the impacts of this on sediment transport processes are poorly understood we conducted flume experiments in a grassed valley of coastal california to investigate flow resistance and sediment yield under natural conditions and with progressive clipping of grass cover flow resistance has a laminar like relationship with reynolds number but we attribute this to very low velocity beneath submerged stems and not to the state of flow the sediment transport relations provide support for the concept of a threshold shear stress below which erosion is effectively prevented by surface resistance shear stress partitioning suggests that on a densely grassed surface over 90 of flow resistance is exerted on plant stems this effectively prevents sediment transport at boundary shear stresses as high as 1000 1800 dyn cm2 complete clipping of the grass cover reduces the critical shear stress for sediment transport to 11 38 of that under natural conditions continued surface wash erosion and channel initiation are prevented however by strong soil cohesion provided by a dense root mat even with reduction of root density boundary shear stresses of at least 250 430 dyn cm2 are required for channel incision

overland flow velocity and roughness properties in peatlands overland flow is an important component of peatland hydrology hydrological models of peatlands are being developed that require estimates of flow velocity and its controls however surprisingly little is known about overland flow velocities in peatlands some peatlands have also been drained using open ditches and these need to be incorporated into flow models this paper presents field data on the velocity of overland flow and drain flow in upland peatlands the relationships between flow velocity vegetation cover slope and water depth are explored sphagnum provided a significantly greater effective hydraulic roughness to overland flow than peatland grasses in all cases a significant break in process occurred for flows with water depths of around 1 cm so that there were two components of the roughness curve this is consistent with partial submergence theory for very shallow flows where resistance increases with depth as the soil surface first becomes fully submerged while each surface cover type should be considered separately the results also suggest that a first order estimate of darcy weisbach roughness and mean velocity can be based on a single parameter for each surface cover this paper presents an empirical overland flow velocity forecasting model that can be applied to peatlands the model combines the partially submerged component for flows with water depths below 1 cm with the fully submerged component for flows with depths up to 5 cm which are representative of the depths of flows that occur across peatlands

ice atmosphere interactions during sea ice advance and retreat in the western antarctic peninsula region 1 the seasonal evolution of sea ice extent concentration and drift in the western antarctic peninsula wap region along with regional atmospheric synoptic variability are described for a winter period 1992 when sea ice advance and retreat were both anomalously early daily time series of winds opening and closing of the sea ice cover and volume fluxes in and out of the wap region indicate that synoptic variability in meridional winds determines whether the ice edge advances or retreats on daily to weekly timescales the importance of this finding is that the dynamics as opposed to the thermodynamics initiate and thereby dominate in the production of ice edge anomalies further the abrupt mid winter shift from persistently positive to negative ice edge anomalies indicates that there was a distinct change in the regional atmospheric circulation the ice atmosphere interactions in the winter of 1992 are then compared to those in the winter of 1990 when sea ice advance and retreat were both late instead of early but again the mid winter shift was abrupt the comparison highlights possible circumpolar and tropical polar atmospheric linkages in the south pacific that involve changes in the amplitude phase of the semi annual oscillation sao which in turn appear

hydraulic conditions in experimental rill confluences and scour in erodible soils 1 few studies have examined processes active within rill networks or the effect of confluence geometry on rill sediment flux and it is not clear if observations from river confluences also apply at rill scale laboratory experiments were carried out in artificial rectangular rill channels with fixed and erodible beds to identify the effects of confluence geometry on hydraulic conditions and scour patterns symmetrical and asymmetrical confluences with angles from 19 to 90 were used hydraulic changes in the confluence zone in fixed bed experiments included decreased flow velocity increased shear velocity transition from supercritical to subcritical and from transitional to turbulent flow bed scour in the confluence zone resulted generally increasing with confluence angle but a more important influence was junction symmetry or asymmetry symmetrical confluences produced a symmetrical scour pattern mirroring the original channels but in asymmetrical confluences scour was more complex evolving to a symmetrical pattern with confluence angles higher than the original system results are consistent with channel evolution to an optimally branched system controlled by minimum power criteria but validation requires testing with more precise velocity measurement

interpretation of recent antarctic sea ice variability 1 trends in the satellite derived antarctic sea ice concentrations 1979 2002 show pronounced increase decrease in the central pacific sector bellingshausen western weddell sector by 4 10 per decade confidence levels for these regional trends exceed 95 positive polarities of the antarctic oscillation aao lead to more less ice in the eastern ross amundsen sector bellingshausen northern weddell sector which are qualitatively opposite to the impacts of positive polarities of the el nino southern oscillation enso the mechanisms responsible for the covariability between the ice and the a aao and b enso are demonstrated over the last 24 years a positive aao trend and a slightly negative enso trend produce a spatial pattern of ice changes similar to the regional ice trends however the magnitude of the ice changes associated with the aao and enso is much smaller than the regional ice trends more local or less understood large scale processes should be investigated for the explanations

storm graded layers on inner continental shelves examples from southern brazil and the atlantic coast of the central united states abstract size graded layers have been reported from the united states and brazilian atlantic continental shelves amid a bedform association that includes ripples megaripples sand waves and sand ridges graded layers are most apparent in the lag gravels and shell hashes that overlie an older substrate in the troughs between sand ridges but also occur as thinner isolated beds within the sand ridges at least four different models seem to be applicable to graded bed formation the stratigraphic graded model grading occurs within and immediately above the basal lag gravel of the holocene transgressive sand sheet it is a consequence of the generation of the sand sheet by erosional shoreface retreat such graded sequences are formed by landward facies displacement over thousands of years but the process is storm mediated and sequences may contain thinner storm graded layers the storm graded model calls for entrainment of sediment by storm flow and subsequent graded deposition under waning energy in the bedform migration model the migration of megaripples and sand waves may produce thin graded beds at any level within the holocene sand sheet and sand ridge migration can cause graded sequences in the basal part of the holocene sand sheet the bottom liquefaction model relies on storm wave pumping of the seafloor sands with their resultant liquefaction and settling of coarser clasts beds in which sorting is confined to coarse shell material may be of this origin these models are believed to be complementary rather than mutually exclusive

field measurement of the velocity of overland flow using dye tracing a new method of computing the mean velocity of overland flow using dye tracing is proposed in which a specified cross section is divided into zones of relatively uniform flow characteristics termed partial sections the mean surface velocity for each partial section is determined by timing the passage of injected dye and this figure is multiplied by 0 67 0 70 or 0 80 depending on whether the flow is laminar transitional or turbulent to give mean velocity the mean velocity for the entire cross section is calculated by multiplying the mean velocity of each partial section by its cross sectional area summing the products for all the partial sections and dividing by the total area of the cross section a field test shows that mean velocity derived in this manner differs from mean velocity derived by the discharge method i e by dividing discharge measured volumetrically by cross sectional area by an average of only 7 07 per cent thus the partial section technique appears to provide a reliable method of estimating mean velocity of overland flow

the tectonostatigraphic evolution of the huronian basement and the subsequent basin fill geological constraints on impact models of the sudbury event abstract whereas both meteorite impact and volcanic mechanisms have been proposed to explain the rocks and associated ore deposits within the sudbury structure 1 85 ga few models take into consideration the paleogeographic constraints implied by the history of the region before and following the sudbury event huronian depositional style south of the sudbury structure appears to have been strongly influenced by the early development of transtensional extensional basins these basins were initiated by sinistral strike slip movement along part of a paleoproterozoic continental margin which later evolved into a passive margin transition from a rifted strike slip margin to a passive margin was accompanied by major slope failure and soft sediment deformation south of the murray fault diabase dikes were intruded into unconsolidated sediments at considerable depth producing round stone breccias which are texturally similar to sudbury breccia minor compressional folding occurred prior to emplacement of the nipissing diabase suite at around 2 2 ga the abundance of diabase intrusions near the sudbury structure suggests that the area may have been a focal point for magma emplacement the post event fill of the paleoproterozoic sudbury basin reflects initial deposition in a deep water anoxic setting there is no evidence to suggest that sedimentation was influenced by the steep walls of an impact crater carbonate in the basal vermilion member is of sedimentary exhalative origin and was not derived from a shallow marine shelf turbidites in the chelmsford formation show no evidence of centripetal fill as might be expected from a restricted circular basin they appear to have been emplaced along the depositional axis of an elongate foreland basin developed in front of the rising penokean mountain chain penokean deformation continued after the sudbury event and influenced strata well into the archean craton deformation of huronian strata in paleovalleys north and west of the sudbury structure does not appear to be genetically related to the sudbury event if superfaults were generated around the sudbury structure in response to compression and crustal rebound following a meteorite impact these do not appear to have caused offset of pre existing steeply dipping contacts between the huronian and underlying archean basement a new model consistent with these observations needs to be developed

soft sediment deformation produced by tides in a meizoseismic area turnagain arm alaska turnagain arm is a semidiurnal hypertidal estuary in southeastern alaska with a recorded tidal range of 9 m contorted bedding and flow rolls preserved in tidal sediments within the estuary have previously been interpreted as resulting from the mw 9 2 great alaskan earthquake of 1964 horizons of flow rolls between undeformed beds in sediments and rock strata have been used to infer ancient earthquakes in other areas although many types of soft sediment deformation structures can be formed by earthquakes observations of sedimentation on tidal flats in the inner parts of turnagain arm in the summers of 2003 and 2004 show that a wide range of soft sediment deformation structures similar to those inferred to have been formed by earthquakes can form in macrotidal estuaries in the absence of seismic shock during sedimentation rate measurements in 2004 soft sediment deformation structures were recorded that formed during one day s tide either in response to overpressurization of tidal flats during rapid tidal drawdown or by shear stress exerted on the bed by the passage of a 1 8 m tidal bore structures consisted of flow rolls dish structures flames and small dewatering pipes in a bed 17 cm thick in the future if the flow rolls in turnagain arm were found in isolated outcrops across an area 11 km in length in an estuary known to have been influenced by large magnitude earthquakes would they be interpreted as seismites these examples show that caution is needed when using horizons of flow rolls to infer paleoseismicity in estuarine deposits because many of the mechanisms tidal flux tidal bores slumping flooding that can cause deformation in rapidly deposited unconsolidated silts and sands are orders of magnitude more common than great earthquakes

age petrogenesis and tectonic setting of the thessalon volcanic rocks huronian supergroup canada abstract the 2 5 ga huronian supergroup volcanic rocks in northern ontario represent one of the better preserved paleoproterozoic continental flood basalt sequences on earth the youngest age of huronian supergroup volcanism is refined to 2452 5 6 2 ma based on new u pb zircon analyses of the copper cliff rhyolite recent mapping and geochemical analyses of thessalon formation volcanic rocks define a well developed chemostratigraphy a lower series consisting of four geochemically distinct mafic lava sequences and an upper basalt andesite volcanic series these two mafic volcanic series are separated by felsic volcanic rocks rhyolite and dacite the mafic lavas are low ti tholeiites dominated by basalt and andesite and are characterized by enriched light rare earth element profiles and high th contents up to 12 ppm most basalt andesite sequences show some internal geochemical variation reflecting a combination of fractional crystallization and in some cases limited crustal contamination but each sequence represents a discrete magma batch derived by different degrees of partial melting in the subcontinental lithospheric mantle all magma batches display prominent negative nb ta and ti anomalies on primitive mantle normalized multi element diagrams interpreted to reflect melting of a heterogeneous and previously metasomatized garnet lherzolite that acquired some chemical characteristics of a source typical of subduction zone magmatism at least three distinct mantle source compositions are required to explain the range in the observed lava compositions the most unusual of these reservoirs has a number of geochemical features akin to upper continental crust and is characterized by high th yb 10 and low zr nb 11 this reservoir is interpreted to be peridotite modified through metasomatism and entrapment of arc magmas during northward neoarchean subduction along the southern superior craton margin

correlation of paleoproterozoic glaciations based on u pb zircon ages for tuff beds in the transvaal and huronian supergroups abstract the rise in atmospheric oxygen between 2 45 and 2 2 ga has been linked to the demise of a methane rich atmosphere and the onset of multiple glaciations culminating in a possible snowball earth the glacial deposits represent possible global marker horizons however their correlation is uncertain because key sedimentary successions are undated hampering paleoenvironmental reconstructions three potentially global glaciations have been proposed based on the correlation of glacial deposits in southern africa with those in north america however it has also been suggested that there were four glaciations and that the youngest was a snowball earth event recorded only in south african successions in situ u pb zircon ages for tuffs in southern african and north american successions establish the existence of four glaciations between 2 45 and 2 22 ga geochronological and stratigraphic data demonstrate that the three oldest glaciations predate 2 31 ga and that the final glaciation which is only recognized in south africa occurred between 2 26 and 2 22 ga the new age calibrated correlations show that a rise in atmospheric oxygen inferred from sulfur isotope data occurred between the second and third glaciations at 2 31 ga the first marine sulfate evaporites were deposited contemporaneously with 13 c enriched carbonates indicating a direct link between perturbations of the carbon and sulfur cycles and rising atmospheric oxygen the appearance of red beds and oxidized palesols after the third glaciation signals a major increase in atmospheric oxygen levels which culminated with the fourth glaciation between 2 26 and 2 22 ga after which the atmosphere remained irreversibly oxygenated

using a thermal tracer to estimate overland and rill flow velocities flow velocity is a basic hydraulic property of surface flows and its precise calculation is necessary for process based hydrological models such as soil erosion and rill development models as well as for modelling sediment and solute transport by runoff this study presents a technique based on infrared thermography to visualize very shallow flows and allow a quantitative measurement of overland flow and rill flow velocities laboratory experiments were conducted to compare the traditional dye tracer technique with this new thermal tracer technique by injecting a combined tracer heated dye into shallow flowing surface water the leading edge tracer velocities estimated by means of infrared video and by the usual real imaging video were compared the results show that thermal tracers can be used to estimate both overland and rill flow velocities since measurements are similar to those resulting from using dye tracers the main advantage of using thermography was the higher visibility of the leading edge of the injected tracer compared with the real image videos copyright 2013 john wiley sons ltd

correction factors in the determination of mean velocity of overland flow the velocity of overland flow has been conventionally measured using tracers but it is difficult to measure the mean flow velocity directly because the centroid of the tracer plume is not easily identified consequently previous investigators have measured the velocity of the leading edge of the plume and multiplied it by a correction factor to obtain an estimate of mean velocity an alternative method is to measure the velocity of the peak concentration in the tracer plume and multiply this velocity by another correction factor to estimate mean velocity to investigate the controls of and and develop predictive models for these correction factors 40 experiments were performed in a flume with a mobile sand bed multiple regression analyses reveal that both and vary inversely with slope and directly with reynolds number the derived regression equations may be used to calculate the mean velocity of other shallow overland flows at least within the range of slope and reynolds number for which the equations were developed in the experiments slope ranged from 2 7 to 10 and reynolds number from 1900 to 12 600

an improved method for shallow water flow velocity measurement with practical electrolyte inputs summary the measurement of shallow water flow velocity is of interest to hill slope hydrology and soil erosion mechanics lei et al lei t xia w zhao j 2005 method for measuring velocity of shallow water flow for soil erosion with an electrolyte tracer journal of hydrology 301 139 145 proposed an electrolyte pulse method for the purpose but found that the velocity measured at short distances from the salt injector was not as well estimated as those further away from the injector though it is desirable to estimate velocity at short distances for the purpose of portable device development in this study the system was improved over the previous development an additional sensor was added at the salt injection location to register the input signal as the actual boundary condition function instead of using the pulse assumption two function forms a normal distribution function normal model and a sine function sine model were suggested to approximate the measured boundary conditions these two determined boundary models were used to fit the experimentally obtained data using the least square method to determine the model parameters of the boundary conditions the determined normal model and the sine model were both used to solve the transport processes as the convolution integrals of the pulse response and the actually determined boundary functions so as to determine the shallow water flow velocity laboratory experiments were conducted to get data to verify the proposed methods and computational procedures the experiment device included a flume 4 m long and 15 cm wide a solute injector a data logger for control and data acquisition and a computer with specially designed software for data measurement and velocity estimation the experiments involved three flow rates 12 24 and 48 l min 1 and three slope gradients 4 8 and 12 six sensors were used to measure the solute transport processes at 5 30 60 90 120 and 150 cm from the location where the salt solute was injected into the water flow the solutions of both the normal model and sine model fitted the measured data very well for all the experimental conditions the velocities at different distances from the salt solution injector and under different flow rates and slope gradients as computed by the two models were almost identical which indicated the feasibility of the method and the computational procedures as well as the two suggested models for velocity estimation the velocity values estimated by the normal and sine models agreed also with those measured by using the floating objects and the volumetric method these demonstrated the rationality of the improved methods for shallow water flow velocity measurement the results will be useful to design a practical system for the measurement of shallow water flow velocity

coupled ocean atmosphere ice response to variations in the southern annular mode abstract the coupled ocean atmosphere ice response to variations in the southern annular mode sam is examined in the national center for atmospheric research ncar community coupled climate model version 2 the model shows considerable skill in capturing the predominantly zonally symmetric sam while regional deviations between model and observation sam winds go a long way in explaining the generally small differences between simulated and observed sam responses in the ocean and sea ice systems vacillations in the position and strength of the circumpolar winds and the ensuing variations in advection of heat and moisture result in a dynamic and thermodynamic forcing of the ocean and sea ice both meridional and zonal components of ocean circulation are modified through ekman transport which in turn leads to anomalous surface convergences and divergences that strongly affect the meridional overturning circulation and potentially the pathways of intermediate water ventilation a heat budget analysis de

truncated flame structures within a deposit of the indian ocean tsunami evidence of syn sedimentary deformation this study reveals the three dimensional morphology and syn sedimentary formation processes of a deformation structure termed truncated flame structures which is found in a terrestrial tsunami deposit in southern thailand that formed during the 2004 indian ocean tsunami the structure was found at the boundary between a lower fine grained layer and an upper coarse grained layer that are related to two runup events in order to confirm the morphology of the structure the authors excavated two trenches and an opencast pit when viewed in a cross section oriented parallel to the direction of the runup current the deformed boundary has an irregularly bulging profile similar to that observed in flame structures the protruding structures are inclined towards the downstream direction of the runup current and are truncated horizontally along their upper surface by parallel laminations in the overlying layer when viewed in a cross section oriented perpendicular to the current direction it appears that parts of the upper layer descend into the lower layer as lobate masses in places these masses are completely detached from the main part of the upper layer forming circular or elliptical shapes the contact between the lower layer and the main part of the upper layer is a planar truncation surface opencast excavation of the contact surface revealed that the deformed structures have flat sinuous horseshoe crests that open in a downstream direction it is possible for the runup current to generate shear stress such that it deforms the boundary into a truncated flame structure moreover the observations made in this study indicate the syn sedimentary development of the structure deformation and truncation occurred simultaneously in association with the runup current that formed the upper layer truncated flame structures can be used as a criterion in identifying the syn sedimentary deformation of substrate the structures are indicative of unidirectional flow with sufficiently high shear velocity to deform unconsolidated substrate as in the present case the truncated flame structures may be characteristic of tsunami events that involve strong unidirectional currents on land due to the extraordinarily long wave period of tsunamis rather than other events such as storm surges or flooding

ice core evidence for antarctic sea ice decline since the 1950s the instrumental record of antarctic sea ice in recent decades does not reveal a clear signature of warming despite observational evidence from coastal antarctica here we report a significant correlation p

effect of saltating sediment load on the determination of the mean velocity of overland flow where overland flow velocity is measured using dye or salt tracing the mean velocity is often determined by multiplying the velocity of the leading edge of the tracer plume by a correction factor flume experiments show that a varies with both reynolds number and sediment load for sediment free flow over a sand covered bed is less than the theoretical value of 0 67 in laminar flow and increases rapidly with reynolds number in transitional flow and more slowly with reynolds number in turbulent flow for sediment laden flow decreases as sediment load increases in transitional and turbulent flows saltating sediment extracts momentum from the flow causing velocities near the bed to decrease and to decrease a multiple regression equation is developed which can be used to predict the value of from reynolds number and sediment load in transitional and turbulent overland flows

deriving and evaluating hydraulics and detachment models of rill erosion for some calcareous soils abstract rill erosion plays an important role in the amount of soil detachment and the transport sediment load on hillslope quantification of the soil erosion requires a more precise understanding of the processes and development of rill erosion models the objective of this study was to derive and evaluate hydraulics and detachment models of rill erosion in calcareous soils of northwestern iran rill erosion experiments were carried out at 55 locations with three replications under field conditions at each point the rill plots were created with a 0 2 m width and 4 m length on agricultural soils the inflow rates were 4 12 20 and 30 l min 1 with varying slope from 4 to 25 5 the results indicated that all conditions of flow regimes including sub and super critical laminar and turbulent were observed in created rills by overland flow the mean flow velocity and rill depth have been described well by flow rate and slope gradient while rill width and flow depth have been explained well by flow rate the prediction detachment rate by rill flow based on stream power model by non linear regression yielded the best results r2 0 545 and rmse 0 00213 kg m 2 s 1 for all combinations of slope classes however there are no significant differences between prediction accuracy of linear and non linear models when individual slope classes were considered

true to milankovitch glacial inception in the new community climate system model the equilibrium solution of a fully coupled general circulation model with present day orbital forcing is compared to the solution of the same model with the orbital forcing from 115 000 years ago the difference in snow accumulation between these two simulations has a pattern and a magnitude comparable to the ones inferred from reconstructions for the last glacial inception this is a major improvement over previous similar studies and the increased realism is attributed to the higher spatial resolution in the atmospheric model which allows for a more accurate representation of the orography of northern canada and siberia the analysis of the atmospheric heat budget reveals that as postulated by milankovitch s hypothesis the only necessary positive feedback is the snow albedo feedback which is initiated by reduced melting of snow and sea ice in the summer however this positive feedback is almost fully compensated by an increased meridionalheat transportin theatmosphereandareducedconcentrationoflow arcticclouds in contrasttosimilar previous studies the ocean heat transport remains largely unchanged this stability of the northern north atlanticcirculation is explainedby the regulatingeffect of thefreshwaterimportthroughthe naresstrait and northwest passage and the spiciness import by the north atlantic current

the influence of the large scale atmospheric circulation on antarctic sea ice during ice advance and retreat seasons antarctic sea ice a key component of the southern hemisphere climate system is influenced by several large scale modes of the atmospheric circulation antarctic sea ice variability is spatially heterogeneous and links between the atmospheric circulation modes and the sea ice variability are unclear using the observed sea ice concentration data this research isolates distinct regions of sea ice variability around antarctica and determines the advance and retreat periods for each of them the latter are then statistically linked with the observed geopotential height data to determine the atmospheric circulation pattern associated with the variability in the sea ice for each period and region the results clarify which circulation mechanism is of primary importance to sea ice variability during critical periods of the ice lifecycle in the different regions around antarctica and have potential for making estimates of past sea ice extent using the observed geopotential height data

interpretation of recent southern hemisphere climate change climate variability in the high latitude southern hemisphere sh is dominated by the sh annular mode a large scale pattern of variability characterized by fluctuations in the strength of the circumpolar vortex we present evidence that recent trends in the sh tropospheric circulation can be interpreted as a bias toward the high index polarity of this pattern with stronger westerly flow encircling the polar cap it is argued that the largest and most significant tropospheric trends can be traced to recent trends in the lower stratospheric polar vortex which are due largely to photochemical ozone losses during the summer fall season the trend toward stronger circumpolar flow has contributed substantially to the observed warming over the antarctic peninsula and patagonia and to the cooling over eastern antarctica and the antarctic plateau

method for measuring velocity of shallow water flow for soil erosion with an electrolyte tracer abstract measurement of the velocity of shallow water flow on a hill slope is of great importance in soil erosion studies electrolyte tracers have been tried to estimate mean velocity of water flow with the velocity of the leading edge of the solute propagation multiplied with a somewhat arbitrary correction factor in this study an analytical solution of solute tracer transport was formulated to serve as the mathematical foundation for measuring shallow water flow velocity to estimate the flow velocity a procedure was advanced in the procedures the analytical solution is fitted with the measured propagation curve and given the the least square estimation of velocity a detailed mathematical description is outlined for this purpose experimental results are given to show the feasibility of the method including the analytical solution and the estimation procedures this study provides the theoretical foundation for measuring the velocity of shallow water flow and for studies of overland solute transport

processes responsible for the development of soft sediment deformation structures ssds in the paleoproterozoic gordon lake formation huronian supergroup canada abstract an exposure of the paleoproterozoic gordon lake formation in the bruce mines area ontario canada contains abundant soft sediment deformation structures ssds including load casts convolute bedding pseudonodules ball and pillow structures flame structures and one dewatering pipe these features are developed in siltstone to fine grained sandstone beds and are between 1 and 120 cm in width and 3 78 cm high the primary trigger mechanism is interpreted to be storm or tsunami activity however seismic shock overloading brought about by density inversions or a combination of these processes may have influenced the formation of ssds to a lesser degree several beds also contain flat to wavy carbonaceous laminae locally with a botryoidal texture and concentrations of heavy minerals which are interpreted as relicts of microbial mats microbial mats may have played a minor role in the formation of ssds but do not appear to have been a prominent driving mechanism soft sediment deformation structures observed in the baie fine flack lake and cobalt plains regions of ontario are smaller and not as abundant as in the study area suggesting that the deposits in the study area were either affected by local events or different magnitudes of sedimentary processes in contrast to the tidal flat paleoenvironment interpreted for the gordon lake formation in the flack lake area the stratigraphically lower beds at the studied outcrop more closely resemble shallow shelf deposits

reestablishing the circumpolar wave in sea ice around antarctica from one winter to the next remarkable correlation exists between warm water poleward winds over the ocean and low sea ice concentrations and extents over the winter sea ice pack around antarctica even to the point of continuing paterns across the ice sea boundary since the wind stress associated with poleward wind is expected to compact the ice during sea ice edge retraction we conclude that the memory of the antarctic circumpolar wave in the sea ice pack is carried from one austral winter to the next by the neighboring water temperatures since the sea ice pack retracts nearly to antarctica in austral summer

an antarctic circumpolar wave in surface pressure wind temperature and sea ice extent the southern ocean is the only oceanic domain encircling the globe it contains the strong eastward flow of the antarctic circumpolar current and is the unifying link for exchanges of water masses at all depths between the world s major ocean basins1 as these exchanges are an important control on mean global climate the southern ocean is expected to play an important role in transmitting climate anomalies around the globe interannual variability has been often observed at high southern latitudes and observations of sea ice extent suggest that such features propagate eastwards around the southern ocean2 3 here we use data from a variety of observational techniques to identify significant interannual variations in the atmospheric pressure at sea level wind stress sea surface temperature and sea ice extent over the southern ocean these anomalies propagate eastward with the circumpolar flow with a period of 4 5 years and taking 8 10 years to encircle the pole this system of coupled anomalies which we call the antarctic circumpolar wave is likely to play an important role in climate regulation and dynamics both within and beyond the southern ocean

hydraulics of interrill overland flow on a semi arid hillslope southern arizona parsons a j abrahams a d and luk s h 1990 hydraulics of interrill overland flow on a semi arid hillslope southern arizona j hydrol 117 255 273 simulated rainfall experiments were conducted on an 18 m wide by 35 m long runoff plot located in southern arizona by using a wide plot that extended from the divide to beyond the rill heads it was possible to examine the full range of lateral variability and downslope changes in interrill overland flow on a shrub covered semi arid piedmont hillslope the mean depth d mean velocity v and reynolds number re of overland flow were computed for two measured sections situated 12 5 and 21 m from the top of the plot at a section d vs re and v vs re relations show that increases in re are accomodated largely by increases in d these hydraulic relations are principally the result of resistance to flow increasing with re as overland flow spreads into new areas inasmuch as the maximum equilibrium discharge simulated in these experiments has a return period of about 7 yr increasing resistance to flow as re increases may be considered typical of most overland flow events on shrub covered piedmont hillslopes in southern arizona downslope hydraulic relations differ strikingly from at a section relations under equilibrium runoff conditions resistance to flow decreases rapidly as re increases permitting increases in re to be accomodated entirely by increases in v the decrease in resistance to flow is due to progressive downslope concentration of flow into fewer deeper threads under non equilibrium conditions downslope hydraulic relations may be quite different from those obtaining at equilibrium but resistance to flow always decreases downslope this is the result of low flows following pathways formed by higher flows that concentrate downslope analyses of overland flow hydraulics at the scale of interrill areas produce results that are quite different from those obtained from small plots a knowledge of the hydraulics at this scale is essential if models of interrill overland flow are to become more realistic and hence better predictors of runoff hydrographs and sediment yield

microbial mats implicated in the generation of intrastratal shrinkage synaeresis cracks intrastratal shrinkage often termed synaeresis cracks are commonly employed as diagnostic environmental indicators for ancient salinity stressed transitional fluvial marine or marginal marine depositional environments despite their abundance and use in facies interpretations the mechanism of synaeresis crack formation remains controversial and widely accepted explanations for their formation have hitherto been lacking sedimentological ichnological petrographic and geochemical study of shallow marine mudstone beds from the ordovician beach formation of bell island newfoundland has revealed that crack development cf synaeresis cracks on the upper surface of mudstone beds is correlated with specific organic geochemical and sedimentological parameters contorted sinuous sand filled cracks are common at contacts between unbioturbated mudstone and overlying sandstone beds cracks are absent in highly bioturbated mudstone and are considered to pre date firmground assemblages of trace fossils that include planolites and trichophycus the tops of cracked mudstone beds contain up to 2 1 wt total organic carbon relative to underlying mudstone beds that contain around 0 5 wt total organic carbon high resolution carbon isotope analyses reveal low 13corg values 27 6 on bed tops compared with sandy intervals lacking cracks 24 4 to 24 9 cracked mudstone facies show evidence for microbial matgrounds including microbially induced sedimentary structures on bedding planes and carbonaceous laminae and tubular carbonaceous microfossils in thin section non cracked mudstone lacks evidence for development of microbial mats microbial mat development is proposed as an important prerequisite for intrastratal shrinkage crack formation both microbial mats and intrastratal shrinkage cracks have broad palaeoenvironmental distributions in the precambrian and early phanerozoic in later phanerozoic strata matgrounds are restricted to depositional environments that are inhospitable to burrowing and surface grazing macrofauna unless evidence of synaeresis i e contraction of clay mineral lattices in response to salinity change can be independently demonstrated the general term intrastratal shrinkage crack is proposed to describe sinuous and tapering cracks in mudstone beds

synchronous variability in the southern hemisphere atmosphere sea ice and ocean resulting from the annular mode zonally symmetric fluctuations of the midlatitude westerly winds characterize the primary mode of atmospheric variability in the southern hemisphere during all seasons this is true not only in observations but also in an unforced 15 000 yr integration of a coarse resolution r15 coupled ocean atmosphere model here it is documented how this mode of atmospheric variability known as the southern annular mode sam generates ocean circulation and sea ice variations in the model integration on interannual to centennial timescales that are tightly in phase with the sam the positive phase of the sam is associated with an intensification of the surface westerlies over the circumpolar ocean around 608s and a weakening of the surface westerlies farther north this induces ekman drift to the north at all longitudes of the circumpolar ocean and ekman drift to the south at around 308s through mass continuity the ekman drift generates anomalous upwelling along the margins of the antarctic continent and downwelling around 458s the anomalous flow diverging from the antarctic continent also increases the vertical tilt of the isopycnals in the southern ocean so that a more intense circumpolar current is also closely associated with positive sam in addition the anomalous divergent flow advects sea ice farther north resulting in an increase in sea ice coverage finally positive sam drives increases in poleward heat transport at about 308s while decreases occur in the circumpolar region ocean and sea ice anomalies of the opposite sign occur when the sam is negative the ocean and sea ice fluctuations associated with the sam constitute a significant fraction of simulated ocean variability poleward of 308s year round the robustness of the mechanisms relating the sam to oceanic variability suggests that the sam is likely an important source of large scale variability in the real southern hemisphere ocean

slow oceanic teleconnections linking the antarctic circumpolar wave with the tropical el nino southern oscillation a case study for the period 1982 1994 shows that a major source for the antarctic circumpolar wave is in the western subtropical south pacific where interannual anomalies in sea surface temperature sst and precipitable water prwat form once established these interannual anomalies in tandem with anomalies in sea level pressure slp move south toward the southern ocean the system then migrates east around the globe through a combination of oceanic advection with the antarctic circumpolar current and ocean atmosphere coupling the coincidence of interannual anomalies in sst slp and prwat indicates the extratropical ocean and atmosphere are tightly linked on these timescales large portions of the interannual sst anomalies branch advectively northward into the south atlantic and indian oceans ultimately reaching the tropics in each basin some 6 8 years after appearing in the low latitude pacific this constitutes a slow oceanic teleconnection that is unique in climate dynamics made possible by the continuity of earth s oceans via the southern ocean in the tropical indian ocean these interannual anomalies move east and arrive at the indo pacific transition in advance of the trans pacific propagation of the respective el nino southern oscillation enso phases the interannual sst and prwat anomalies that appear in the subtropical south pacific are directly linked with the enso cycle on the equator through anomalous vertical convection and a regional overturning cell in the troposphere the same cell that initiates fast planetary waves in the atmosphere that carry enso signals around the southern hemisphere on much shorter timescales

terrestrial laser scanning soil surfaces a field methodology to examine soil surface roughness and overland flow hydraulics smith m w cox n j bracken l j 2011 terrestrial laser scanning soil surfaces a field methodology to examine soil surface roughness and overland flow hydraulics hydrological processes 25 6 842 860

aseismic controls on in situ soft sediment deformation processes and products in submarine slope deposits of the karoo basin south africa intervals of soft sediment deformation features including vertical fluid escape and load structures are common and well exposed in permian lower slope deposits of the tanqua depocentre karoo basin the structures mainly comprise elongated flames and load structures associated with ruptured sandstones and structureless siltstones observed over a range of scales the presence of an upper structureless siltstone layer linked to the flames interpreted as a product of the debouching of fine grained material transported through the flame onto the palaeo seabed together with the drag and upward folding of lower sandstone layers is evidence that the flames were formed in situ by upward movement of sediment rich fluids flames are oriented parallel to the deep water palaeoslope in lateral splay deposits between two major slope channel complexes statistical correlation and regression analyses of 180 flame structures from seven stratigraphic intervals suggest a common mechanism for the deformation and indicate the importance of fluidization as a deformation mechanism importantly deformation occurred in an instantaneous and synchronous manner liquefaction and fluidization were triggered by incremental movement of sediment over steeper local gradients that were generated by deposition of a lateral splay on an inherited local north west facing slope seismic activity is not invoked as a trigger mechanism because of the restricted spatial occurrence of these features and the lack of indications of earthquakes during the time of deposition of the deep water succession the driving mechanisms that resulted in the final configuration of the soft sediment deformation structures involved a combination of vertical shear stress caused by fluidization development of an inverse density gradient and a downslope component of force associated with the local slope ground penetrating radar profiles confirm the overall north east orientation of the flame structures and provide a basis for recognition of potential larger scale examples of flames in seismic reflection data sets

comparison of rill flow velocity over frozen and thawed slopes with electrolyte tracer method summary freeze thaw erosion is the primary soil water erosion form in high altitude and or high latitude regions the water flow velocity along an eroding rill over frozen and thawed slopes is vital to understanding of rill erosion hydrodynamics this study experimentally measured rill flow velocity over frozen and thawed slopes using electrolyte trace method under pulse boundary model the experiments used three flow rates of 1 2 and 4 l min 1 three slope gradients of 5 10 and 15 the temperature of the rill flow water was supplied at 0 c as controlled with ice water mixture seven sensors were used to measure flow velocity by tracing the solute transport process at 10 110 210 310 410 510 and 610 cm distances from the electrolyte injection position the measured velocity became steady at a distance of about 3 m from the electrolyte injection location where the effect of the pulse boundary condition on the analytic solution to the partial differential equation becomes negligible results showed that flow velocity increased with slope gradient and flow rate on frozen slopes a significant effect was observed on the steepest slope or at the highest flow rate over the thawed slope which changed slightly on the gentle slopes and low flow rates flow velocity was about 25 30 and 40 higher on the frozen soil than on the thawed slope at 5 10 and 15 slopes and about 30 higher over the frozen slope at all flow rates this study demonstrates that water over a frozen slope flows much faster than over a thawed slope this study helps in the study and further understanding of the hydrodynamics of soil erosion and sediment transport behaviors of frozen and thawed slopes

sea surface temperature induced cyclogenesis in the antarctic circumpolar wave 1 an antarctic circumpolar wave acw of 3 to 4 year period propagated eastward around the southern ocean in covarying sea surface temperature sst and sea level pressure slp anomalies from 1983 through 1992 composed of two wavelengths that circled most of the global ocean along the midlatitude storm track near 40 s in this acw positive sst anomalies drove upward latent heat flux positive precipitation pcp and mid to upper level diabatic heating anomalies in the troposphere the latter balanced principally by the cooling tendency from deep convection white and chen 2002 one hypothesis has the anomalous pcp and deep convection in this acw arising from that in more frequent and or stronger extratropical cyclones in the synoptic storm aggregate here we verify this hypothesis finding negative slp anomalies in this acw collocated with positive extratropical cyclone intensity eci and extratropical cyclone density ecd anomalies in the annual synoptic storm aggregate because individual extratropical cyclones are 3 to 4 times smaller than slp anomalies in the acw their density and intensity appear to be modulated by anomalous zonal sst gradients in the acw these results are corroborated by finding greater interannual pcp anomalies over southeast australia collocated with positive sst anomalies occurring on the eastern side of covarying negative slp and positive eci and ecd anomalies in the acw along the mid latitude storm track because positive interannual pcp anomalies over southeast australia derive from the integral of rainfall from more dense and or intense extratropical cyclones in the aggregate the same is true for the acw propagating eastward along the midlatitude storm track over the remainder of the southern ocean

wind driven ocean dynamics impact on the contrasting sea ice trends around west antarctica since late 1978 antarctic sea ice extent in the east pacific has retreated persistently over the amundsen and bellingshausen seas in warm seasons but expanded over the ross and amundsen seas in cold seasons while almost opposite seasonal trends have occurred in the atlantic over the weddell sea by using a surface forced ocean and sea ice coupled model we show that regional wind driven ocean dynamics played a key role in driving these trends in the east pacific the strengthening southern hemisphere sh westerlies in the region enhanced the ekman upwelling of warm upper circumpolar deep water and increased the northward ekman transport of cold antarctic surface water the associated surface ocean warming south of 68 s and the cooling north of 68 s directly contributed to the retreat of sea ice in warm seasons and the expansion in cold seasons respectively in the atlantic the poleward shifting sh westerlies in the region strengthened the northern branch of the weddell gyre which in turn increased the meridional thermal gradient across it as constrained by the thermal wind balance ocean heat budget analysis further suggests that the strengthened northern branch of the weddell gyre acted as a barrier against the poleward ocean heat transport and thus produced anomalous heat divergence within the weddell gyre and anomalous heat convergence north of the gyre the associated cooling within the weddell gyre and the warming north of the gyre contributed to the expansion of sea ice in warm seasons and the retreat in cold seasons respectively

flow resistance in concentrated overland flow on rough slope surfaces field experiments have been done on simulated flows over different rough pre rill and rill bed surfaces the purpose of the experiments was to evaluate the hydraulic roughness properties of these bed surfaces conventional equations describing the relation of the resistance coefficient to the reynolds number for flow in closed conduits or open channels can also be applied to shallow flows provided the boundary values of the reynolds number which discriminate between the various flow regimes are adapted when the reynolds number is less than 100 the flow regime is laminar above this figure the flow is either transitional or turbulent depending on the roughness of the bed surface the degree of turbulence can be deduced from a morphological description of the pre rill and rill bed surface roughness

relationship between discharge velocity and flow area for rills eroding loose non layered materials a relationship between discharge flow velocity and flow area in rills is established using data from four field and laboratory studies the proposed relationship is shown to predict successfully flow velocities measured in six other studies although slopes range from 0 035 to 0 45 and soil materials range from stony sands over silt loams to vertisols mean flow velocity can be well predicted from discharge alone thus there is no important influence of slope and or soil material characteristics on flow velocities in rills the proposed relationship may be used to improve performance of deterministic flow routing models when applied to rilled catchments furthermore it allows the calculation of unit stream power which has been shown to be related to the transporting capacity of overland flow in terms of slope and discharge

long term variation of the antarctic circumpolar wave 1 during the period 1968 1999 the character of circum antarctic anomalies in sea level pressure sea ice edge and sea surface temperature changed substantially an antarctic circumpolar wave acw is only clearly visible in the period 1985 1994 before and perhaps after this the signal particularly in sea level pressure is quite different with no clear sign of precession accompanying the change from precessional to nonprecessional modes is a change in the spatial pattern of variability and a change in the predictability of atmospheric anomalies from oceanic forcing evidence from general circulation model integration suggests that during the precessional mode of the acw there is enhanced predictability as would be required to support a coupled ocean atmosphere interaction

velocity measurement of water flow within gravel layer with electrolyte tracer method under virtual boundary condition summary the measurement velocity of water flow along gravel rich hill slope is of great interest for hydrological simulation and prediction in alpine watersheds the alpine terrain is often covered by rock debris of different origin size and type here summarized as gravel for the sake of simplicity to do this water flow velocity within a gravel layer was measured using the electrolyte tracer method under virtual boundary conditions an improved method over pulse electrolyte tracer method models employing two virtual boundary conditions a sine function and a normal distribution function are suggested as preferable for determining flow velocity by simulating the transport processes of electrolytes along a gravel covered flume at different flow rates 3 6 and 12 l min 1 and slope gradients 4 8 and 12 flow velocities as well as determination coefficients and mean square errors were calculated at five measurement locations 0 3 0 6 0 9 1 2 and 1 5 m using model simulation the feasibility and accuracy of velocity measurements for water flow within gravel layers are justified to the extent that the two models fit well with the experimental data the velocity values predicted by the two models are almost identical and finally the relations between velocity and discharge and between velocity and slope gradient are rationally explained the estimated velocity results also agree well with those previously measured by commonly used methods such as the pulse boundary method and the conventional dye tracer method our results show that the virtual boundary conditions method when used to measure water flow velocity within a gravel layer predicts the flow velocity more rationally than the pulse boundary and dye tracer methods and with greater precision this study suggests that this method is not only readily applicable for obtaining water flow velocity measurements within gravel layers but also for understanding hydrodynamics in typical watershed

consistent past half century trends in the atmosphere the sea ice and the ocean at high southern latitudes simulations performed with the climate model loveclim aided with a simple data assimilation technique that forces a close matching of simulated and observed surface temperature variations are able to reasonably reproduce the observed changes in the lower atmosphere sea ice and ocean during the second half of the twentieth century although the simulated ice area slightly increases over the period 1980 2000 in agreement with observations it decreases by 0 5 106 km2 between early 1960s and early 1980s no direct and reliable sea ice observations are available to firmly confirm this simulated decrease but it is consistent with the data used to constrain model evolution as well as with additional independent data in both the atmosphere and the ocean the simulated reduction of the ice area between the early 1960s and early 1980s is similar to the one simulated over that period as a response to the increase in greenhouse gas concentrations in the atmosphere while the increase in ice area over the last decades of the twentieth century is likely due to changes in atmospheric circulation however the exact contribution of external forcing and internal variability in the recent changes cannot be precisely estimated from our results our simulations also reproduce the observed oceanic subsurface warming north of the continental shelf of the ross sea and the salinity decrease on the ross sea continental shelf parts of those changes are likely related to the response of the system to the external forcing modifications in the wind pattern influencing the ice production melting rates also play a role in the simulated surface salinity decrease

the effect of spatial variability in overland flow on the downslope pattern of soil loss on a semiarid hillslope southern arizona summary in this study we investigate the relation between soil loss and slope length in an interrill portion of a gentle plan planar semiarid hillslope in southern arizona simulated rainfall experiments were conducted on an 18 m wide by 35 m long runoff plot the upper end of which coincided with the hillslope divide sediment loads were measured at two cross sections s1 and s2 located 12 5 and 21 m respectively downslope from the divide from these data section soil losses under equilibrium runoff conditions were computed average section soil loss was found to increase from the divide to s1 and to decrease from s1 to s2 to explain this downslope pattern of soil loss a simulation model was developed for soil detachment by raindrop impact and sediment removal by overland flow at a cross section input data for the model consist of overland flow depths and velocities measured at closely spaced points along a cross section the model was applied to three cross sections located at 3 3 12 5 and 21 m downslope from the divide and predicted a downslope pattern of soil loss similar to that observed the success of the model suggests that in the interrill portions of a wide range of gentle arid and semiarid hillslopes downslope patterns of soil loss are controlled in large part by downslope changes in across slope distributions of overland flow depth and velocity

partial least squares regression for linking aggregate pore characteristics to the detachment of undisturbed soil by simulating concentrated flow in ultisols subtropical china soil pores are known as an effective medium for water air and chemical movement however quantifying pore structures and their relationship to the detachment of undisturbed soil by concentrated flow is not fully understood the objectives of this study were to quantify 3d aggregate microstructures using synchrotron based high resolution x ray micro computed tomography sr mu ct under wetting and drying cycles and to investigate the effects of pore characteristics on the detachment of undisturbed soil by simulating concentrated flow the detachment rates d r of undisturbed topsoil samples which were subjected to a pretreatment of zero to eleven wetting and drying cycles were measured in a 3 8 m long 0 2 m wide hydraulic flume under unitary flow shear stresses tau 14 49 pa 3 5 mm aggregates were collected from the pretreatment soils which were subjected to zero five and eleven wetting and drying cycles and were scanned at a 3 7 mu m voxel resolution for reconstructing three dimensional microtomography images the relationships among pore characteristics and d r were analyzed using partial least squares regression plsr the results indicated that d r and the aggregate microstructure changed significantly after the wetting and drying cycles dr was closely associated with the pore characteristics the pore characteristics such as a 100 mu m porosity total porosity fraction of regular pores 30 75 mu m porosity fraction of elongated pores and fraction of irregular pores were identified as the primary parameters that control the d r the pore characteristics and clay content could account for as much as 68 2 of the variation in d r d r was significantly and positively related to a 100 mu m porosity total porosity and fraction of elongated pores thus soil fragmentation depended on microcracks that formed during the wetting and drying cycles and on the geometrical characteristics of the pores or cracks the results from this study provide a quantitative evaluation of the relationships between pore characteristics and the detachment of undisturbed soil by simulated concentrated flow a further understanding of the effect of topsoil microstructure on water erosion and quantitative information for assessing and modeling erosion processes was obtained c 2015 elsevier b v all rights reserved

comparison of thermal salt and dye tracing to estimate shallow flow velocities novel triple tracer approach abstract the accurate measurement of shallow flow velocities is crucial to understand and model the dynamics of sediment and pollutant transport by overland flow in this study a novel triple tracer approach was used to re evaluate and compare the traditional and well established dye and salt tracer techniques with the more recent thermal tracer technique in estimating shallow flow velocities for this purpose a triple tracer i e dyed salted heated water was used optical and infrared video cameras and an electrical conductivity sensor were used to detect the tracers in the flow leading edge and centroid velocities of the tracers were measured and the correction factors used to determine the actual mean flow velocities from tracer measured velocities were compared and investigated experiments were carried out for different flow discharges 32 1813 ml s 1 on smooth acrylic sand stones and synthetic grass bed surfaces with 0 8 4 4 and 13 2 slopes the results showed that thermal tracers can be used to estimate shallow flow velocities since the three techniques yielded very similar results without significant differences between them the main advantages of the thermal tracer were that the movement of the tracer along the measuring section was more easily visible than it was in the real image videos and that it was possible to measure space averaged flow velocities instead of only one velocity value with the salt tracer the correction factors used to determine the actual mean velocity of overland flow varied directly with reynolds and froude numbers flow velocity and slope and inversely with flow depth and bed roughness in shallow flows velocity estimation using tracers entails considerable uncertainty and caution must be taken with these measurements especially in field studies where these variables vary appreciably in space and time

forcing of the antarctic circumpolar wave by el nino southern oscillation teleconnections we address several issues regarding the antarctic circumpolar wave acw these include the extent to which the acw is related to el nino southern oscillation enso cycles and the need to reconcile differences between the observed zonal wavenumber 2 pattern and the wavenumber 3 pattern found in coupled ocean atmosphere models in the present study we revisit the sea surface temperature sst signal of the observed acw we find that the associated sst variations may be decomposed into several empirical orthogonal functions eofs that are linearly independent the first four eofs describe 84 of the total variance on timescales of 3 7 years and superposition of sst signals of the four eofs reproduces sst signals of the observed acw given that eof analysis can only describe standing oscillations we then employ complex eof ceof analysis suitable for studying propagating waves the first two ceofs denoted ceofsst1 and 2 account for 70 of the total variance and the sst variability reconstructed from them again reproduces the observed acw the real part of ceofsst1 44 of the total variance is similar to the first real eof eofsst1 both eofsst1 and ceofsst1 may be identified with enso and have a wavenumber 2 zonal pattern in the southern middle to high latitudes ceofsst1 is the major constituent of the acw in the period of 1981 1997 the associated atmospheric circulation displays a pacific south america psa pattern statistical analyses demonstrate that the psa pattern teleconnected to enso is the major mechanism that forces this principal constituent of the acw ceofsst2 26 of the total variance has a zonal wavenumber 3 pattern in the same latitude band similar to that simulated by several coupled models we suggest that if enso is not adequately resolved in coupled models but structures with zonal wavenumber 3 pattern are then the modeled acw would appear to have a zonal wavenumber 3 pattern

quartz arenites review and interpretation abstract quartz arenites orthoquartzites are exceptional sands pettijohn et al 1972 that in the past have formed extensive and commonly thick formations they are somewhat enigmatic in that they do not appear to be forming at the present time this paper examines the origin of quartz rich sands documents the range of environments in which they are found and suggests a model for their genesis quartz sand is most commonly formed by tropical weathering of coarse grained quartz bearing rocks such as granite it may be deposited as texturally immature fluvial sandstones generally under a humid climate with drying of the climate quartz rich bauxitic soils and sandy alluvium can be a substantial source of poorly rounded dune sands for major deserts quartz sand when transported into shallow marine environments becomes very well rounded through reworking by tidal currents such sand may spill into deep oceanic environments and by sedimentary or tectonic transport may come to rest in both stable and active tectonic settings quartz rich sandstones can also be formed by diagenetic destruction of labile framework grains of immature sandstones precambrian orthoquartzites are commonly thick and widespread when compared to younger examples the thinness of post silurian quartz arenites may be largely due to the trapping effect of land vegetation and solution of quartz by organic acids in weathering profiles there is an abundance of shallow marine and fluvial quartz arenites in the early paleozoic and the cretaceous this is due to widespread continental flooding and a humid world climate following the disintegration of supercontinents the shallow marine examples are commonly associated with bituminous sometimes phosphatic shale glauconite and possibly chamositic ironstone there is an abundance of eolian quartz arenites in the permo triassic this is related to a widespread dry continental climate during assembly of the pangean supercontinent

regional cross section of the southern province adjacent to lake huron ontario implications for the tectonic significance of the murray fault zone the southern province in the lake huron area of ontario and the penokean fold belt of minnesota wisconsin and michigan have the earmarks of a collisional orogen the huronian supergroup a southerly facing passive margin sequence was deposited during early aphebian early proterozoic crustal stretching and ocean basin formation along the southern margin of the superior province archean craton it accumulated as four unconformity bounded northerly tapering onlapping clastic wedges megacycles the thickness and facies variations reflect syndepositional down to the basin south normal faulting that controlled the accumulation and preservation of the lower three huronian megacycles these are overlapped northward by the youngest megacycle an extensive sheet of clastic sediments recording post stretching regional subsidence of the cratonic margin due to cooling and thermal contraction soft sediment folds in the rocks of the youngest megaycycle to the extreme south probably indicate southward slu

sea ice transports in the weddell sea time series of sea ice draft in the weddell sea are evaluated together with hydrographic observations satellite passive microwave data and ice drift for estimation of the freshwater fluxes into and out of the weddell sea ice draft is measured with moored upward looking sonars since 1990 along two transects across the weddell gyre one transect extending from the tip of the antarctic peninsula to kapp norvegia was sampled between 1990 and 1994 and covers the flow into and out of the southern weddell sea the other transect sampled since 1996 and extending from the antarctic continent northward along the greenwich meridian covers the exchange of water masses between the eastern and the western weddell sea in order to relate results obtained during the different time periods empirical relationships are established between the length of the sea ice season derived from the satellite passive microwave data and defined as the number of days per year with the sea ice concentration exceeding 15 and 1 the annual mean ice draft and 2 the annual mean ice volume transport by using these empirical relationships estimates of annual mean ice drafts and ice volume transports are derived at all mooring sites for the period february 1979 through february 1999 wind and current force a westward ice transport in the coastal areas of the eastern weddell sea and a northward ice transport in the west during the 2 year period 1991 1992 the mean ice volume export from the weddell sea is 50 19 103 m3 s 1 this freshwater export is representative for a longer term 20 year mean and exceeds the average amount of freshwater gained by precipitation and ice shelf melt by about 19 103 m3 s 1 yielding an upper bound for the formation rate of newly ventilated bottom water in the weddell sea of 2 6 sv

estimating manning s n for steep slopes abstract hydrological and soil erosion models require calculations of flow velocity for which either the darcy weisbach or the manning equation is generally used a series of field experiments was carried out in a small catchment on the chinese loess plateau to obtain reliable values of manning s n the soils are typically erodible loess soils the experiments were conducted for a range of land uses as well as for different slope angles 6 64 measurements were performed on a 2 5 0 4 m plot on which flow was allowed to find its own path water was evenly applied to the top of the plot and discharge surface velocity flow width and slope were measured the results show that manning s n can just like darcy weisbach f be estimated from reynolds number furthermore for croplands there is an apparent linear increase in manning s n and f with increasing slope angle r2 0 70 as manning s n is usually assumed to be constant this must mean that either velocity increases with slope or hydraulic radius decreases the measurements showed virtually no increase in velocity and a minor increase in hydraulic radius with slope as flow was more concentrated on steeper slopes possible explanations for this lack of increase in velocity include increased roughness water resour res 37 2001 791 decreased effective slope angle because of the development of vertical head cuts and a shift in energy use all three hypotheses only apply to situations involving erosion the trend of manning s n with slope implies that in soil erosion models using manning s equation or darcy weisbach the value of n or f should be a function of the slope for erodible soils for non erodible soil as in woodland no increase in manning s n with slope was observed

anthropogenic co2 in the southern ocean distribution and inventory at the indian atlantic boundary world ocean circulation experiment line i6 1 the southern ocean where various water masses are formed mode intermediate deep and bottom waters has a high potential to absorb anthropogenic co2 cant however most data based and model estimates indicate low cant inventories south of 50 s in order to investigate this paradox the distribution of cant is estimated between south africa and antarctica world ocean circulation experiment woce line i6 based on a back calculation technique previously used in the north atlantic kortzinger et al 1998 and adapted here for application in the southern ocean at midlatitudes 30 50 s formation and spreading of mode and intermediate waters results in a deep penetration of cant down to 2000 m south of 50 s significant concentrations of cant were estimated in circumpolar deep water 10 mol kg and antarctic bottom water aabw 20 25 mol kg higher concentrations are detected along the continental slope in aabw presumably formed in prydz bay compared to aabw of weddell sea origin the distribution of cant obtained north of 50 s compares well with previous data based and model estimates but large disagreements are found in the south however although transient tracers are not used in the back calculation technique employed here the distribution of cant is remarkably well correlated with cfcs we reevaluated the column inventories of cant for the southern ocean and found higher values at high latitudes 70 90 mol m2 compared to the subtropical subantarctic region 40 80 mol m2 these results support the idea that deep and bottom water formation in the southern ocean is a key process in the natural sequestration of anthropogenic co2