a transferable method for the automated grain sizing of river gravels 1 the spatial and temporal resolution of surface grain size characterization is constrained by the limitations of traditional measurement techniques in this paper we present an extremely rapid image processing based procedure for the measurement of exposed fluvial gravels and other coarse grained sediments defining the steps required to minimize the errors in the derived grain size distribution this procedure differs significantly from those used previously it is based around a robust object detection algorithm that produces excellent results on images exhibiting a wide range of sedimentary conditions crucially without any user intervention or site specific parameterization the procedure is tested using a data set comprising 39 images from three rivers with contrasting grain lithology shape roundness and packing configuration and representing a very wide range of textures it is shown to perform more consistently than the best existing automated method achieving a precision equivalent to that obtainable by wolman sampling but taking between one sixth and one twentieth of the time the error in area by number grain size distribution percentiles is typically less than 0 05

pleistocene molluscs from klasies river south africa reconstructing the local coastal environment abstract we explore if taxonomic analysis of archaeological mollusc assemblages can be used to reconstruct late pleistocene mis 5 3 coastal environments at klasies river in south africa to obtain a balanced reconstruction we analyse the large molluscs separately from the so called incidentals the small mollusc species based on modern mollusc habitat preferences and tolerances we identify four different eco profiles to help characterise sea surface temperatures and the character of the shore temperature profile geographical distribution substrate wave interaction we hypothesise that changes in the klasies river mollusc community eco profiles can be linked to global glacial and interglacial events and we define several testable assumptions we found that in response to global warming and cooling events the klasies river mollusc communities change slightly yet significantly other sources of marine environmental data confirm that average sea surface temperatures gradually decreased but probably remained within the modern southern east coast range of variation it appears that coastal sea surface temperatures of the warm agulhas current were not particularly depressed during the occupation sequence the character of the coastal topography does change more apparently during the occupation sequence of the sites and with it the mollusc assemblages from an interglacial rocky shore in the klasies and two mossel bay phases to a more glacial sandy environment during the howiesons poort and the msa iii in conclusion the temperature tolerance levels of many klasies river mollusc species are too broad to reflect small changes in sea surface temperatures however in conjunction with other eco profiles and environmental proxies such as substrate requirements and oxygen isotopes the temperature approximations are useful particularly when evaluating large scale sea surface temperature fluctuations for the characterisation of the shore and substrate we found the eco profile approach very useful

the downstream gradation of particle sizes in the squamish river british columbia the exponential downstream decline in particle size predicted by sternberg 1875 is examined within a highly active alpine fluvial environment the gravel bed squamish river in southwestern british columbia transect survey procedures for sampling within the coarse alluvial gravels are described in detail downstream trends for various particle size statistics plotted with distance from a major sediment source are considered according to two scenarios evaluation of overall trends indicates that the downstream expression derived by sternberg 1875 is not the most appropriate rather curves are better described by power functions this reflects a very rapid decline in particle size immediately downstream of the major sediment source secondly evaluation of downstream trends in relation to channel planform determines that exponential functions with different coefficients describe adequately relations within individual planform reaches there is insufficient evidence to suggest which of these two scenarios may be appropriate several lines of evidence suggest that the trends found are more the result of selective sediment transport phenomena than of abrasion a condition attributed to channel competence within a system dominated by sediment supply conditions

riverscape mapping and hyperscale analysis of the sediment links concept abstract longitudinal patterns in channel complexity play an important role in our understanding of fluvial systems the spatial scales over which external controls such as tributaries landslides and debris flows alter channel form and influence the broader basin wide trends in channel form channel complexity across a basin has important implications for how we conceptualize basin wide trends in channel form such as downstream hydraulic geometry and the sediment links concept this study takes a hyperscale approach to mapping channel morphology across 200 km of the rogue river in southwest oregon that is high resolution data over large spatial extents allowing analysis to be conducted simultaneously at and across multiple spatial scales using a suas and digital photosieving we measured gravels on exposed gravel bars for the study area we also measured thalweg depth in the field using a singlebeam echo sounder slope and channel width were derived using existing gis datasets we used these data to create a hyperscale view of the rogue river examining the impact of tributary and non tributary sediment links we used a statistical approach to determine if changes in channel form were truly unique in the context of larger scale channel variability our findings show inconsistent statistical significance of the identified lateral sediment sources lss between variables e g a statistically significant change in slope would not necessarily correlate with an increase in unit stream power there were many lss which triggered statistically significant changes to channel form we used hyperscale graphs to reveal the complexity and spatial trends associated with the relationships between a given sediment link and channel form the results of this study illustrate the complexity with which sediment links impact channel form and the distances below a given sediment link that a detectable signal exists if a detectable signal exists

evidence for sea level and monsoonally driven variations in terrigenous input to the northern east china sea during the last 24 3 ka geochemical and sedimentological analyses of core pc 1 recovered from the northern east china sea ecs provide insights into variations in terrigenous input associated with sea level and climate changes over the past 24 3 ka based on high resolution multiproxy records our results suggest that the competing processes of sea level and monsoonally driven precipitation determined terrigenous input to the northern ecs dominance of terrigenous material along with relatively light globigerinoides ruber 18o indicates that the last glacial maximum lgm lowstand of sea level has occurred during the period 21 5 19 6 ka not suggesting an early slow rise but supporting the conventional lgm age of 21 ka this lgm lowstand was terminated by the rapid sea level rise of 19 ka meltwater pulse mwp which is well expressed by the nearly synchronous decreases in both terrigenous detritus and mean grain size from 19 6 to 18 9 ka mwp 1a is clearly marked in our records by a sharp reduction in terrigenous input and pronounced maxima of g ruber 18o at 15 3 14 8 ka given the considerable age uncertainties of deglacial marine radiocarbon samples a slightly increasing input of terrigenous matter is noted after 13 4 ka potentially pointing to a sea level fall following the inter allerod cooling period which was seldom reported previously although mwp 1b did not leave robust signatures in terrigenous input it is explicitly captured by the heavy 18o of g ruber and decline in mean grain size at 11 5 10 9 ka mwp 1c probably occurred in a broad millennial interval with multiple peaks which are robustly marked by the abrupt variations in terrigenous input and marine organic matter at 9 7 9 3 and 9 1 ka respectively during the late holocene the effect of continuously weakening monsoon precipitation overwhelmed that of stable sea level resulting in a uniform increase in the proportion of marine derived organic matter after 5 5 ka

supply and removal of sediment in a landslide dominated mountain belt central range taiwan abstract a strong coupling between hillslope and valley systems is often inferred for mountain landscapes dominated by bedrock landsliding we reveal the nature of this link using data sets on landsliding and sediment transport from two montane catchments draining the eastern central range of taiwan here the magnitude frequency distribution of landslides can be modeled by a robust power law but this scale invariance is not mirrored in the sediment discharge at the mountain front instead downstream sediment loads reflect a complex response to both sediment supply and ambient hydraulic conditions the rivers do not transport significant amounts of sediment unless it is provided by hillslope mass wasting in the catchment removal of landslide debris is a function of the transport capacity of the stream at the site of entry thus there is a dual supply and transport control on sediment loads in bedrock floored streams over a monitoring period of 25 yr the bulk of the sediment leaving the mountain bel

sampling surficial fluvial gravels the precision of size distribution percentile sediments abstract grid by number wolman sampling is commonly used to characterize the texture of surficial fluvial sediments assessments of sampling precision have concentrated on the median grain size but adequate representation of other grain size percentiles is paramount in a number of sedimentological contexts the field effort required to construct percentile sampling distributions by replication is prohibitive and the absence of any general size distribution for fluvial sediments precludes theoretical calculation of percentile standard errors bootstrapping is used in this paper to determine percentile standard errors for large samples from two gravel bar surfaces the improvement of percentile precision with sample size follows the theoretical expectation hence improvement in percentile recision is achieved only at the expense of much greater sampling effort once sample sizes reach about 400 stones however absolute percentile standard errors differ significantly from theoretically derived values of particular interest is the stability of coarser percentile estimates in coarse skewed distributions d95 estimates may be as precise as d50 estimates for a given sample size the sensitivity of the precision of estimated percentiles to distribution shape is examined using synthetic skewed and bimodal grain size distributions the absolute precision of percentile estimates is shown to vary with the grain size distribution of a particular sediment our field results provide a reference for further work

holocene paleo climatic record from the south african namaqualand mudbelt a source to sink approach variations in the sediment input to the namaqualand mudbelt during the holocene are assessed using an integrative terrestrial to marine source to sink approach geochemical and sr and nd isotopic

beach ridge sets reflect the late holocene evolution of the st lucia estuarine lake system south africa abstract sets of sandy beach ridges and intervening swales define shoreline sections of the shallow st lucia wetland system within the isimangaliso wetland park world heritage site in northern kwazulu natal province south africa the sets comprise 3 10 beach ridges the most prominent being 80 150 m wide and rising 0 5 2 m above the adjacent swales the highest beach ridge crests elevated 3 2 4 6 m above mean sea level are furthest from the present shoreline and the lowest ridges rising about 0 5 m above the swales occur closest to the present mean lake level shoreline this investigation assesses the genesis of the sandy beach ridges on five strand plain remnants within the estuarine lake the ridges were topographically surveyed and their ages estimated using optically stimulated luminescence osl dating osl dating reveals that the oldest beach ridge formed around 6240 years ago with a sequence of beach ridges having accumulated during the period 4000 to 1500 years ago reflecting coeval accretion around the lake the present mean lake level shoreline was only reached within the past 600 years sedimentation changed from marine dominated to lacustrine deposition in the estuary during the period of beach ridge accretion the dated beach ridges supported by new radiocarbon dates of fixed biological indicators from holocene intertidal zone settings on the coast are used with published sea level curves to set the context of periodic beach ridge accretion in the marine linked estuarine lake the dated ridges suggest that episodic regression of the estuarine lake shoreline occurred after a mid holocene sea level highstand the record of sea level change is also reflected by the long term natural shrinking and shallowing of the proto st lucia lagoon estuarine lake in the context of reduced marine influences due to closure of former marine channels by progressive barrier dune accretion the sequence of coeval beach ridges reflects a pulsed lowering of relative sea level in the shallowing estuarine lake height differences between the coeval ridges at sites around the lake reflect local environmental controls including the range of wind fetch distances across shallow lake compartments wave height and wind induced seiche effects

understanding late quaternary change at the land ocean interface a synthesis of the evolution of the wilderness coastline south africa coastal barrier systems have been widely used to understand the responses of coastal margins to fluctuating pleistocene sea levels what has become apparent particularly with the development of robust chronological frameworks is that gaps in terrestrial barrier sedimentary records are not uncommon and that they most likely reflect phases of barrier construction on the now submerged continental shelf thus understanding the land ocean interface through time is critical to fully appreciate the quaternary archives contained within the barriers and their associated back barrier deposits this study uses offshore and lakefloor back barrier seismic profiling from the south african south coast at wilderness to link the sub aerially exposed barrier stratigraphy to the currently submerged geological and sedimentological record a total of eight separate submerged aeolian units are identified at water depths of up to 130 m below mean sea level their approximate ages are constrained with reference to the eustatic sea level record and the deepest units are consistent with the estimated magnitude of sea level lowering during the last glacial maximum lgm on the south african coastline as previously assumed aeolian sedimentation tracked the shoreline onto the continental shelf during the late pleistocene during sea level regressions both the incision of fluvial channels and the deposition of back barrier systems occurred across the continental shelf during late low stand early transgression periods landward shoreface migration occurred pre existing channel incisions were infilled and pre existing barriers were truncated rapid transgression however allowed the preservation of some back barrier deposits possibly aided by protection from antecedent topography as sea level neared the present day elevation erosion of the mid shelf sediments resulted in the development of a holocene sediment wedge which was augmented by holocene fluvial sediment supply the holocene sand wedge is preserved in the back barrier lakes and was deposited during the holocene highstand inundation overlying middle to late holocene terrestrial muds reflect the deposition of river borne mud onto the shelf these results clearly demonstrate that within transgressive regressive sea level cycles accommodation space for barriers is controlled by antecedent drainage systems and gradients on the adjacent inner continental shelf

sampling techniques for gravel sized sediments the methods commonly used for sampling the coarser surface layers of gravel bed streams are reviewed it is found that while an areal sample is biased toward the coarser grains compared with a volumetric sample of the same material the conversion formula suggested by a voidless cube model overcompensates for this effect a modified version of the cube model that accounts for porosity is proposed the modified cube model and tests conducted with areal sampling using wax indicate that area by weight analyses can be converted successfully to the equivalent bulk sieve analyses the average depth of the wax samples ranged from d65 d91 increasing with median grain size the equivalence of the grid by number and bulk sieve analyses is reaffirmed

morphology and controls on the position of a gravel sand transition fraser river british columbia alluvial river channels often exhibit a relatively abrupt transition from gravel to sand bedded conditions the phenomenon is well documented but few prior studies have analyzed the spatial variability through reaches where transitions occur the downstream fining pattern observed in the fraser river is cited as a classic example of an abrupt gravel sand transition in a large alluvial channel however important questions regarding the exact location of the transition its sedimentology and morphology and what controls its location remain unanswered here we present observations of the downstream change in bed material grain size river bed topography and channel hydraulics through the reach within which the transition occurs these observations indicate that the gravel sand transition is characterized by a terminating gravel wedge but there are patches of gravel downstream of the wedge forming a diffuse extension we show that there is a dramatic decrease in shear stress at the downstream end of the wedge and a consequent cessation of general gravel mobility we argue that the patches of gravel observed beyond the wedge are the result of enhanced mobility of fine gravel over a sand bed we also find that sand in suspension declines rapidly at the downstream end of the wedge suggesting that sand is delivered to the bed completing the sedimentary conditions for a gravel sand transition we propose that the break in river slope associated with the transition is a consequential feature of the transition

bed material texture in low order streams on the queen charlotte islands british columbia low order channels comprise a large proportion of the links of every drainage basin and are often at the centre of land management concerns they exhibit hydrological and geomorphological characteristics atypical of higher order links this paper examines the nature and causes of variations in the bed material texture of two streams on the queen charlotte islands british columbia the extant functional exponential model is found to be inadequate for explaining observed changes in grain size parameters with distance downstream recurrent disruption of sediment transport by large organic debris jams and the sporadic contamination of the fluvial sediment population by colluvial inputs preclude the development of longitudinal structure rather grain size varies erratically over short distances a stochastic model best describes the observed variations and should be adopted as an alternative to the exponential model in low order links characteristic variances are controlled by the degree of hillslope channel coupling and the extent and characteristics of non alluvial storage mechanisms

coastal paleo environment and sea level change at macassa bay southern mozambique since c 6600 cal bp changes in holocene coastal paleo environment and sea level variations have been recorded in estuary sediments from macassa bay southern mozambique methods include analysis of fossil diatoms sediment stratigraphy mineral magnetic properties stable carbon and nitrogen isotope composition and carbon and nitrogen content the chronology based on six ams c 14 dates suggests a basal age of the sediment core of c 6600 cal bp calibrated years before present the multi proxy dataset implies two phases when the site was experiencing marine conditions and tentative sea level high stands 1 between c 6600 6300 cal bp which is contemporary with the last phase of the global transgression and the holocene climatic optimum and 2 between c 4700 1000 cal bp a period when sea level curves from the region suggest occasional minor sea level high stands between these phases c 6300 4700 cal bp the environment within the macassa bay estuary was less influenced by marine processes and studied proxies indicate a freshwater phase associated with relatively low sea levels after c 1000 cal bp a terrestrial environment prevailed at the site probably as a result of a combined effect of sea level lowering and high accumulation of organic peat within the estuary c 2011 elsevier ltd and inqua all rights reserved

operator bias characterizing stream substrates using wolman pebble counts with a standard measurement template this study characterizes the variability associated with using a standard measurement template to perform wolman pebble counts of coarse stream substrates four 10 count and two 12 count replicate experiments were conducted by five operators at three sample sites within gravel bed streams using a gravel template results show significant differences between different operators sampling the same location as observed in previous studies conducted without a standard sampling template as well as significant variability within each operator s replicate samples variability was highest in clast estimates larger than d50 suggesting that these metrics cannot be consistently derived from wolman pebble count samples variability was also highest in the low order study site suggesting that the sedimentary characteristics of low order streams increase the chance for operator bias in light of our findings we suggest that traditional 100 particle wolman counts be utilized with more caution than is the current norm

coarse sediment connectivity in river channel systems a conceptual framework and methodology identification of coarse sediment connectivity down river channel systems is important for understanding the linkages between river reaches the influence of sediment sources on channel morphology and the mechanisms and liability to propagation of morphological change a conceptual framework is developed in which several types and degrees of connectivity are proposed it is hypothesised that sediment connectivity varies with sediment sources and with stream competence to transport the coarse fractions a method of identifying the status of reaches is developed based on field mapping of morphology and sedimentology the analysis is exemplified by two channels one an ephemeral channel in se spain the other a perennial channel in nw england questions arise over whether reaches that lack channel stores transfer coarse sediment three scenarios are suggested 1 lack of flux due to lack of competence of the reach 2 flushing through of sediment due to high competence and 3 potential transport of coarse sediment but exhaustion or lack of availability changes in connectivity will take place over different time scales depending on the nature of exchange and time scales of storage short term variations in connectivity can be identified by repeated mapping

water worn shell and pebbles in shell middens as proxies of palaeoenvironmental reconstruction shellfish procurement and their transport a case study from the west coast of south africa abstract geoarchaeological studies today are a vital component of archaeological research the sedimentary environments of coastal settings in particular are highly dynamic and governed by a variety of factors among which changes in sea level play an important role the object of such studies often involves the study of sediments deposited by natural factors in overlapping geological and anthropogenic contexts archaeomalacological studies conducted on shell middens along the west coast of south africa in the last two decades have also identified the presence of additional natural components that became incorporated into archaeological sites through active but inadvertent human agency these sediments are relatively large particles 2 20 mm of water worn shells and water worn pebbles wwsp that became entangled among the byssus threads that rocky shore mussels use for attaching themselves to hard substrate prehistoric shellfish foraging and subsequent transport of rocky shore mussels along with their byssus contents to campsites ensured the inclusion of wwsp into archaeological middens this study shows that wwsp abundances and the proportion of their organic fraction water worn shell can be used as proxies for coastal palaeoenvironmental reconstruction and as a complement to archaeomalacological studies for inferring technologies involved in shellfish collection and transport conclusions presented here probably apply to other similarly configured shorelines and shell assemblages of comparable age from elsewhere in southern africa and beyond follow up studies from this sub region and beyond might confirm and or qualify the use of wwsp observations in other coastal settings

field evidence for rapid downstream fining of river gravels through selective transport doubts have been expressed about the ability of either abrasion or sorting to explain strong downstream fining of river gravels we describe pronounced fining over a short distance in a scottish river that has no human disturbance or lateral input of water and sediment measured abrasion rates are far too small to explain observed downstream fining but bed load trap measurements and the dispersion of magnetic tracer pebbles in six subreaches both show sorting during transport the observed downstream fining is also simulated well by a numerical sediment routing model using hydraulic and transport laws consistent with our field measurements the geomorphological cause of the strong fining is slope reduction above a local base level control in this common situation the development of downstream fining is part of the river9s tendency to minimize downstream variation in bed load transport rates and can proceed far more rapidly than the major aggradation otherwise required for equilibration

trends of grain sizes on gravel bars in the rio chagres panama abstract we examined the trends of grain sizes along the upper 414 km 2 of the mountainous rio chagres drainage basin in panama gravel bars were sampled along 40 km of the rio chagres and five major tributary streams using a transect pebble count of median diameter lithology and clast rounding although previous investigators have found that downstream fining can be obscured by inputs of colluvial sediment and other local controls in mountain drainages we decided to examine the trends of grain sizes along a tropical mountain river where rapid weathering and high capability of transport might be capable of overriding the input effects of colluvium specifically we tested the hypotheses that downstream fining would be present as a result of selective sorting and that weak felsic particles would decrease in size preferentially to strong mafic particles because of abrasion statistical analyses reveal a weak downstream decrease of sediment size on gravel bars along the study reach of the rio chagres with a sternberg diminution coefficient for felsic and mafic grains of 0 013 and 0 017 respectively felsic clasts have thicker weathering rinds and become rounded downstream faster than mafic particles but tumbling mill tests of abrasion show no significant differences in rate of mass loss in relation to lithology and downstream decreases in grain size are similar between lithologies dividing the study reach into six sub reaches bounded by major tributary junctions we further tested the hypothesis that downstream trends in fining might be obscured at the basin scale by sediment input from tributaries but that trends in grain sizes might be more visible at the reach scale between tributaries we did not find any consistent trends in grain size between tributaries stream width appears to assert a local control on grain size coarse particles are associated with narrow channel reaches whereas smaller particles are associated with wide channel reaches

numerical simulation of downstream fining by selective transport in gravel bed rivers model development and illustration a numerical model has been developed for the routing of gravel sized sediment along a river channel which is free to adjust both its long profile and surface texture hydraulic calculations use a step backwater approach and sediment transport is predicted with the method of parker 1990a which uses a low degree of size selectivity exchange of sediment between the surface and subsurface is described using the modified exner equation of parker and sutherland 1990 the model is applied to an idealized channel based on the highly concave allt dubhaig scotland in which fining by particle wear is minor the rapid downstream fining observed in this river is closely matched by model predictions after a time equivalent to 102 years under the present flow regime of the river the evolution of the fining pattern during the model run and associated changes in sediment transport and bed aggradation are described it is concluded that strong profile concavity can force rapid downstream fining even though bed load transport is only slightly size selective this run of the model serves as a basis for testing of the sensitivity of downstream fining to alternative choices of parameter values and boundary conditions which are summarized here and will be described in a subsequent paper

late quaternary sea level change in south africa abstract a late quaternary sea level curve for south africa is presented on the basis of new and published data from a range of sea level indicators and a variety of locations available evidence suggests that sea level in south africa broadly follows that described from the caribbean but that deviations occur during sea level highstands during the last interglaciation oxygen isotope stage 5 and the late holocene coastal emergence produced higher sea levels in south africa than those identified in the caribbean during the same time intervals this is tentatively ascribed to predicted lithospheric deformation in continental margin settings

9000 years of sea level change along the southern african coastline abstract beachrocks are good indicators of sea level stillstands on microtidal coastlines and data for this sea level curve is mainly based on dating a series of holocene beachrocks and planation episodes on the southeast african coastline sea level reached its present level along the southern african coastline at ca 6500 bp sea level then rose depositing a series of beachrocks at an elevation of 2 75 m this mid holocene sea level highstand persisted for a period of 2500 years with a 3 5 m stillstand dated at 4480 bp being the highest sea level reached during the holocene in post holocene sea level optimum times a regression occurred lowering sea level to its present level at 3880 bp and down to 2 m at approximately 3000 bp subsequently sea level rose to 1 5 m at 1610 bp and attained its present level at about 900 bp the mid holocene sea level highstand appears to have resulted from a combination of isostatic emergence and the steric expansion of seawater relating to warmer ocean temperatures associated with the holocene hypsithermal event on the eastern agulhas bank

the morphology of graded gravel rivers a network perspective analytical hydraulic geometry equations are combined with a watershed model to quantify downstrem trends in equilibrium fluvial morphology in gravel streams the hydraulic geometry equations relaet fluvial morphology to discharge bedload transport rate and grain size these independent variables are in turn determined by routing gravel supplied at zero order basins through a channel network as gravel is routed downstream it decreases in size according to an empirical power law the resulting model specifies the discharge bedload transport rate grain size width depth slope and river bed elevation at every point in the drainage basin when the downstream fining law is calibrated using data from central pennsylvania dowstream hydraulic geometry exponents for the width and depth are accurately reproduced longitudinal profiles calculated from the model fit observed profiles in largerwatersheds but are inaccurate in smaller watersheds the model also reproduces hack s 1957 empirical result relating slope to the 0 6 power of a ds where a is the drainage basin area and ds is the mean grain size unfortunately the model requires an equilibrium time scale which is unreasonably long suggesting that the channels of the study area are best described as systems with multiple time scales and multiple rates of response the model probably is successful because the width and depth have relatively short relaxation times and also because downstream trends in discharge and sediment transport rate are controlled by network topology thus downstream hydraulic geometry equations do not necessarily provide strong evidence for the equilibrium of fluvial landscapes rather they reflect the constancy of network topology and the rapid response times of width and depth

holocene evolution of the anichab pan on the south west coast of namibia coastal sediment filled depressions pans are one of the few areas that contain quaternary records of sea level and palaeoenvironmental change along the western margin of southern africa anichab is a 128 km2 salt encrusted pan on the hyper arid southern coast of namibia with an emergent well preserved and in place mid holocene mollusc assemblage the molluscs are typical of subtidal sands on the sheltered side of offshore islands but include several warm water species no longer found living along this coast the holocene evolution of the pan was largely influenced by changes in sea level and supply of sand along the coast calibrated radiocarbon ages of mollusc shells indicate a maximum holocene sea level of ca 2 m above mean sea level msl from 7 0 to 6 3 ka and a return to near present day sea level by 5 3 ka the pan surface is 2 m below msl and has been emergent since 4 9 ka from the build up of sandy beaches and coastal dunes a thin 1 4 cm halite crust occurs over much of the pan surface but a layer of halite cemented sand up to 40 cm thick is restricted to the central pan gypsum occurs near the subsurface brine interface and is limited by calcium to the edges of the pan nodules of calcite cemented sand are forming in brackish relatively high alkalinity subsurface waters in the south east corner of the pan and nodules of aragonite cemented sand are forming in brines 1 m below the central pan surface although modern dolomite has been reported from coastal lagoons of brazil and australia carbonate cements are a minor feature of anichab pan and dolomite was restricted to a single reworked nodule most likely of late pleistocene age therefore anichab pan does not appear to be a modern analogue to extensive mixed water dolomite cements found in upper pleistocene sediment filled depressions on the namibian shelf

influence of the pacific decadal oscillation el nino southern oscillation and solar forcing on climate and primary productivity changes in the northeast pacific evidence of 11 year schwabe solar sunspot cycles el nino southern oscillation enso and the pacific decadal oscillation pdo were detected in an annual record of diatomaceous laminated sediments from anoxic effingham inlet vancouver island british columbia radiometric dating and counting of annual varves dates the sediments from ad 1947e1993 intact sediment slabs were x rayed for sediment structure lamina thickness and composition based on gray scale and subsamples were examined for diatom abundances and for grain size wavelet analysis reveals the presence of w2e3 w4 5 w 7a ndw9e12 year cycles in the diatom record and an w11e13 year record in the sedimentary varve thickness record these cycle lengths suggest that both enso and the sunspot cycle had an influence on primary productivity and sedimentation patterns sediment grain size could not be correlated to the sunspot cycle although a peak in the grain size data centered around the mid1970s may be related to the 1976e1977 pacific climate shift which occurred when the pdo index shifted from negative cool conditions to positive warm conditions additional evidence of the pdo regime shift is found in wavelet and cross wavelet results for skeletonema costatum a weakly silicified variant of s costatum annual precipitation and april to june precipitation higher spring april may values of the north pacific high pressure index during sunspot minima suggest that during this time increased cloud cover and concomitant suppression of the aleutian low al pressure system led to strengthened coastal upwelling and enhanced diatom production earlier in the year these results suggest that the 11 year solar cycle amplified by cloud cover and upwelling changes as well as enso exert significant influence on marine primary productivity in the northeast pacific the expression of these cyclic phenomena in the sedimentary record were in turn modulated by the phase of pdo as indicated by the change in period of enso and suppression of the solar signal in the record after the 1976e1977 regime shift

the last interglacial sea level high stand on the southern cape coastline of south africa abstract the continental margin of southern south africa exhibits an array of emergent marginal marine sediments permitting the reconstruction of long term eustatic sea level changes we report a suite of optical luminescence ages and supplementary amino acid racemization data which provide paleosea level index points for three sites on this coastline deposits in the swartvlei and groot brak estuaries display tidal inlet facies overlain by shoreface or eolian facies contemporary facies relations suggest a probable high stand 6 0 8 5 m above modern sea level amsl at cape agulhas evidence of a past sea level high stand comprises a gravel beach ca 3 8 m amsl and an overlying sandy shoreface facies up to 7 5 m amsl osl ages between 138 7 ka and 118 7 ka confirm a last interglacial age for all marginal marine facies the high stand was followed by a sea level regression that was associated with the accumulation of eolian dunes dating to between 122 7 ka and 113 6 ka these data provide the first rigorous numerical age constraints for last interglacial sea level fluctuations in this region revealing the timing and elevation of the last interglacial high stand to broadly mirror a number of other far field locations

downstream patterns of bed material grain size in a large lowland alluvial river subject to low sediment supply 1 a new data set of bimodal subaqueous channel bed sediments was analyzed for longitudinal patterns in grain size it yielded two interesting observations 1 separate fining trends in d50 exist for gravel and fines that overlap for 175 river kilometers and 2 this overlap in fining trends results in a protracted nonabrupt gravel to sand transition these suggest bed patchiness that is interpreted in the context of inherent grain size bimodality localized hydraulic sorting due to spatially heterogeneous and low sediment supply and local deviations in channel gradient the data also show that tributaries have a minor impact on main stem downstream fining due to basin shape and tectonic history in addition subaqueous channel sediments were observed to be finer than nearby sediments collected from exposed bars which may indicate a narrow active zone of transport where bars are disconnected from sediment movement this research has implications for bed material collection and theories of downstream fining

downstream changes in the lithology and grain size of fluvial gravels the watarase river japan evidence of the role of abrasion in downstream fining two processes have been considered to explain downstream grain size reduction in gravel bed rivers hydraulic sorting by which finer grains are transported faster and farther than coarse grains and abrasion by which individual particles are diminished in size most studies on the cause of downstream fining in rivers emphasize hydraulic sorting as the dominant fining mechanism however broken boulders are often observed in the bed material of japanese rivers also grain size changes may be correlated with the difference in resistance to breakdown among lithologies the purpose of this study is to use the lithologic composition of bed material on the watarase river to demonstrate that some downstream fining cannot be explained by hydraulic sorting alone the study reach on the watarase river flows on a dissected alluvial fan which means that the river is no longer aggrading the study reach is influenced only slightly by input of gravel from tributaries bed gravel in the study reach consists of several lithologies andesite quartz porphyry sandstone hornfels and chert the grain size distribution and lithology of the river bed material were examined at nine sites there are two principal results 1 size distribution of the gravel is strongly related to lithology andesite boulders or large cobbles make up the framework sizes in the upstream part of the study reach while chert pebbles make up the framework sizes in the downstream part there are few andesite pebbles or chert boulders in the river bed 2 longitudinal changes in the composition of each size class show selective transportation by lithology in every gravel size because the mobility of gravel depends mainly on its size hydraulic sorting by lithology does not occur within the same size class these results indicate clearly that particle abrasion occurs in the watarase river and is responsible at least in part for the downstream decrease in particle size of bed material

surface sampling in gravel streams the accuracy of studies concerning the characteristics of gravel bed waterways is often dependent upon the techniques used to sample and quantify the material found on the channel boundary due to the vertical stratification present in the riverbed the use of sampling techniques that remove only the particles within a thin surface layer is often necessary attributes of clay and grid sampling are considered in the present work criteria for determining the minimum sample size for a desirable level of accuracy are also presented many of the current surface sampling techniques truncate either the upper or lower size range of particles truncation of part of a size distribution not only limits the available information but can also bias the rest of the distribution the present work rectifies this problem by proposing the use of a hybrid technique that can sample the entire size range of either dry or submerged bed material results of field tests that utilize this new method are described in detail

downstream fining in a network of gravel bedded rivers a network based routing model is used to determine how spatial variations in sediment supply influence rates of downstream fining in a small watershed in central pennsylvania gravel of a specified size distribution and lithology is supplied to the network at zero order basins once in transport the total sample weight and moments of the grain size distribution are modified according to empirical functions of transport distance contributions from each zero order basin are summed to determine the total population of sizes and lithologies at any location in the study area resistant quartz sandstone ridges supply sediment an order of magnitude larger than other lithologies because these ridges occur primarily in the basin headwaters spatial variations in supply strongly influence rates of downstream fining model calculations indicate that spatial variations in supply alone account for over 80 of the decrease in mean grain size along the main channel

late holocene coastal change in the southwestern cape south africa abstract radiocarbon dated elevated marine deposits and the record of anthropogenic and natural debris in archaeological deposits on the west coast of south africa indicate that significant coastal remodelling has taken place in the past 4300 years in response to sea level change geological and archaeological investigation of elevated deposits of sub fossil shell abandoned lagoons and washover bars has shown that many of these features relate to a mid holocene high stand of the sea of about 2 3 m above modern mean sea level the detailed course of local late holocene sea level change cannot be resolved from these elevated geological deposits but information from archaeological sites provides valuable indirect evidence of the effects of coastal change in response to minor fluctuations in relative sea level

self organization of river networks to threshold states numerical models in which grid cells self organize so that the shear stress in each cell equals a predetermined threshold value are remarkably successful in producing the fundamental structure of river networks such models are a reasonable approximation of networks characterized by near constant dimensionless shear stress bed shear stress7sol bed grain size with each cell s threshold value being proportional to median bed grain size previous work has shown that this is the case for channels cut into alluvium and that the characteristic narrow range of is different for gravel and sand bed channels channels in the italian apennines that are slowly incising into weak bedrock but which are covered by a veneer of gravel for most of the time are shown to be characterized by the same as alluvial gravel bed channels thus threshold models capture the fundamental behavior of many river networks even in areas of long term bedrock incision

backbeach deflation aprons morphology and sedimentology backbeach deflation aprons are heterogeneous coarse clastic deposits associated with active transverse dune fields the apron comprises variously angular rounded fractured cracked polished and ventifacted clasts of bedrock local and exotic beachrock and bioherm fragments coral and worm reef terrestrial and anthropogenic clasts from archeological sites deflated dunes flotsam and shipwrecks are also present the unit forms as a lag deposit on top of a gently sloping ca 0 008 planar sandy deflation surface and is typically only one clast thick it is up to 100 m wide and extends for tens of kilometers along the coast it is replaced landward by a steep ca 0 1 deflated soil surface armored with a layer of iron concretions backbeach deflation aprons are compound deposits that result from marine storm eolian and human activity since the mid holocene the depositional model proposed involves periodic storm deposition of coarse clasts of beachrock bedrock and biogenic origin and flotsam shipwreck and other floating debris on the backbeach or dunes some clasts are deposited directly into interdune depressions and enter the deflation plain immediately others are deposited initially on dune surfaces dune migration results in winnowing of the storm deposited coarse clasts together with rhizoliths and any other coarse material in the dune until they come to rest on the deflation surface the lag deposit is subsequently buried and uncovered multiple times by dune migration during which time it is exposed to polishing and subaerial weathering consequently the lag comprises a variety of materials that reflect both storm and eolian processes the clasts exhibit variable degrees of rounding polishing and ventification according to how long they have been in the deposit backbeach deflation aprons are characteristic of sandy beaches along approximately 475 km 10 of the total length of the south african east coast they develop in association with large scale transverse dunefields on the backbeach which in turn depend on reversing shore parallel winds and high sediment abundance the variable degree of polishing and weathering planar surface low elevation and back beach location along extensive shoreline distances distinguish backbeach deflation aprons from tsunami or marine storm deposits

origin of fluvial grain size trends in a foreland basin the pocono formation on the central appalachian basin abstract a widely recognized phenomenon of modern and ancient river systems is downstream decrease in grain size over the past two decades theoretical formulations observations of modern rivers flume studies and numerical models have significantly increased our understanding of sediment transport in mixed grain size river systems these have established that downstream fining in modern and ancient rivers can be attributed to a combination of selective sorting abrasion rate and accumulation rate however no detailed multiple grain size sediment transport model has been used to address how much subsidence rate sediment flux water discharge hydraulic geometry and the mechanics of sediment transport influence grain size distribution and facies belt development in ancient fluvial systems we have combined the results of recent empirical and theoretical studies with a multiple grain size sediment transport model midas to test the sensitivity of downstream fining trends to those controlling mechanisms our results demonstrate that subsidence and sediment feed rate are the most important mechanisms controlling downstream fining trends in a foreland basin if the evolution of hydraulic geometry is known to illustrate the application of this result we have replicated the textural trends of the mississippian upper pocono formation and burgoon sandstone of pennsylvania this methodology can be applied to constrain plausible values of accumulation and subsidence rate for ancient alluvial deposits and enhances our ability to interpret paleohydraulic conditions from such facies in a foreland basin

climate cyclicity in late holocene anoxic marine sediments from the seymour belize inlet complex british columbia abstract an 8 72 m late holocene sediment core vec02a07 obtained from alison sound in the belize seymour inlet complex of central british columbia canada was deposited between 3500 1000 yr bp under primarily anoxic marine conditions this core contains a detailed cyclic record of land sea interactions as evidenced by significant fluctuations in marine primary productivity and changes in the supply of terrigenous material that can be related to long term variation in the relative influence of the aleutian low al and north pacific high nph sedimentologically the core is characterized by alternating intervals of fine grained massive intervals 70 laminated intervals 23 turbidites 5 and graded silt clay layers 2 the laminated intervals are comprised of couplets that vary between light coloured diatom rich layers deposited primarily during the summer months and dark coloured mineral rich layers deposited during winter laminated couplets are most common in portions of the core deposited between 3150 and 2700 yr bp which corresponds to an episode of regional neoglaciation time series analysis was carried out on high resolution particle size measurements obtained from core sub samples and on sediment grey scale colour variability derived from x ray scans of the core non linear time series analyses revealed that the succession of massive and laminated sedimentation displayed characteristics of self organization following a power law relationship for core length segments of 13 cm 50 years of deposition contained evidence of sedimentary depositional cycles of 70 96 135 155 and 250 330 years that reflect changes in al and nph mediated regional precipitation patterns that can in turn be related to larger scale climate drivers such as the pacific decadal oscillation pdo or solar irradiance cyclicity

bed material size and the riffle pool sequence relationships between the bed material size distribution and riffle pool geometry of a small coarse bedload upland stream channel are described downstream sequences of bed material size are highly variable although series analysis reveals some persistence in the data over short distances cross correlation of bed material series with bed elevation series indicates riffles tend to coincide with coarser bed material sequences comparison of the bed material size distributions of individual riffles pools and bars is however more revealing mean particle size was found to be the most useful criterion for distinguishing between bed forms and in these terms bars are the most distinctive features moreover riffles and pools can be viewed as simply downstream oscillations in elevation of a single coarser grained sedimentary unit coarse sediment supply from erosion scars created where the channel meets confining bluffs in valley fill deposits does mean that the average particle size of adjacent and downstream bed forms is increased however conclusions remained unchanged after reanalysis following the identification and subtraction of immobile particle diameters plan geometry and coarse sediment supply in the upland environment are also shown to influence bed material size distributions tightly curved pools tend to have the finest pool sediments but also the least difference between bar and pool sediments size of material in pools is also negatively related to an index of cross section asymmetry

channel sediment variability along a river a case study of the siret river romania the siret river has the largest drainage basin 42 274 km2 in romania it gathers all the rivers from the eastern part of the eastern carpathians a fact that causes marked asymmetry of the basin this study is principally concerned with changes in the form of the longitudinal profile and the grain size variability introduced by the carpathian tributaries channel sediment analyses considered the petrography granulometry and morphometry of the pebbles relating these to the river bed and floodplain geometry and to some properties of the drainage basin the following conclusions arise the siret river undergoes an intense regrading of its longitudinal profile with marked aggradation between transects 24 and 26 see figures 1 and 2 this reflects selective accumulation of coarse material due to the massive contribution of the carpathian tributaries this phenomenon has been continuous throughout the holocene resulting in the gravel sheet formation of the pericarpathian piedmont

mid holocene sea level and coral reef demise u th dating of subfossil corals in moreton bay australia it is increasingly apparent that sea level data e g microfossil transfer functions dated coral microatolls and direct observations from satellite and tidal gauges vary temporally and spatially at regional to local scales thus limiting our ability to model future sea level rise for many regions understanding sealevel response at far field locations at regional scales is fundamental for formulating more relevant sea level rise susceptibility models within these regions under future global change projections fossil corals and reefs in particular are valuable tools for reconstructing past sea levels and possible environmental phase shifts beyond the temporal constraints of instrumental records this study used abundant surface geochronological data based on in situ subfossil corals and precise elevation surveys to determine previous sea level in moreton bay eastern australia a far field site a total of 64 u th dates show that relative sea level was at least 1 1 m above modern lowest astronomical tide lat from at least 6600 cal yr bp furthermore a rapid synchronous demise in coral reef growth occurred in moreton bay 5800 cal yr bp coinciding with reported reef hiatus periods in other areas around the indo pacific region evaluating past reef growth patterns and phases allows for a better interpretation of anthropogenic forcing versus natural environmental climatic cycles that effect reef formation and demise at all scales and may allow better prediction of reef response to future global change

downstream channel adjustment in a low relief glacially conditioned watershed abstract river management practices are often informed by theoretical expectations of downstream channel adjustment which may not be valid in low relief glacially conditioned watersheds such as those in the lower north american great lakes region downstream trends in channel morphology and bed material size within a low relief glacially conditioned watershed are explored here and compared to a theoretical watershed model where slope and grain size are expected to decline exponentially the observed channel morphology is then tested against a theoretical concept of reach scale channel grade the downstream hydraulic geometry relations w bf q bf 0 51 s 0 02 and d bf q bf 0 32 s 0 21 were found to best describe downstream changes in channel morphology and are consistent with some prior studies bed material size varies irregularly down the channel slope controlled downstream fining trends are evident where inputs from glacial materials and tributaries are negligible but are masked by cobble boulder lag deposits where the channel is cut into these glacial deposits the asynchronous variability in slope and grain size produces downstream variations in graded and nongraded understeepened conditions separated at ex 0 graded reaches exist where ex 0 but an upper boundary with nongraded oversteepened reaches is less clear the results emphasize the geomorphic legacy of inherited slopes and sediment sources in dictating the modern downstream patterns of fluvial characteristics and morphologies in glacially conditioned and similarly complex watersheds

distribution and paleoecology of molluscan skeletal remains along an upwelling tract benguela system namibian shelf abstract this study describes and categorizes the preservable and thus predominantly molluscan component of the macrofauna death assemblages of sub environments within the northern benguela upwelling system this is especially important for assembling actualistic data that can later serve for identifying similar settings in the geological record a total of 16 samples were examined contrary to stereotypes benthic communities are present but highly variable across the high productivity tract and are characterized by distinctive community structures benguela system document a decrease in body size of chemosymbiotic bivalves lucinids and percent of chemosymbionts and deposit feeders and an overall increase in species richness and epifaunal infaunal ratio this trend is in accordance with the upwelling facies gradient from diatomaceous ooze in areas of maximum upwelling intensity outward to the aerated but food abundant carbonate oozes and spatially coexisting phosphorite concentrations differences in seafloor oxygen concentration along with variable food availability played major roles in structuring the death assemblages under the benguela upwelling system the ecologic data provide ways to distinguish between facies of low and high shell production along an increasing oxygen gradient and also between assemblages with moderate and higher species richness associated with time averaging the data support the existence of a wider range of time averaging in the formation of molluscan sand and gravel samples in the northern benguela than previously appreciated given the scarcity of information on macrobenthic ecology from modern high productivity settings these death assemblages can represent a modern analog

paleo environment and flooding of the limpopo river plain mozambique between c ad 1200 2000 multi proxy analysis was performed on a radiocarbon dated core collected from a relic oxbow lake in the limpopo river plain mozambique with the aim to reconstruct paleo environment and past flooding of the lower river system over the past c 800 years an additional objective was to evaluate and investigate the potential use of different proxies as recorders of paleo flooding events and paleo environmental variability within the floodplain the proxies applied in this study were mineral magnetic properties grain size distribution organic carbon content and diatom microfossil assemblages we found that sediment grain size and mineral magnetic properties of the minerogenic fraction were the most sensitive proxies in terms of detecting signals from high intensity river discharge events in the 800 year long sequence variations in sand content magnetic susceptibility and saturation isothermal remnant magnetization suggest at least four major flooding events at the site during the reconstructed period in the mid 1200 late 1300 mid 1500 ad and during the last century the diatom proxy reflects the development of the site from an open oxbow lake to a mainly terrestrial area the diatom assemblage indicates that open lake conditions prevailed at the site between c ad 1200 1400 with periodic inundation by marine water most likely due to late holocene sea level changes from c ad 1400 and onwards diatoms were rarely deposited at the site which indicates drier conditions this was a result of soil formation and gradual in filling of the lake a process which possibly was accentuated by a regionally dry climate situation our study shows that oxbow lakes and the proxies used here have great potential for reconstructing flooding events a knowledge that is crucial for potential prediction and mitigation of flooding events in mozambique in the future although chronological uncertainties limit comparisons to other paleo environmental records it seems that the flooding events recorded at our site occurred both during regionally wet and dry periods our data infer however that flooding was probably more clearly recorded during the lake stages than during infilled stage probably as the terrestrial environment was more exposed to erosion c 2014 elsevier b v all rights reserved less

dinoflagellate cyst based reconstructions of mid to late holocene winter sea surface temperature and productivity from an anoxic fjord in the ne pacific ocean abstract published contemporary dinoflagellate distributional data from the ne pacific margin and estuarine environments n 136 were re analyzed using canonical correspondence analysis cca and partial canonical correspondence analysis pcca these analyses illustrated the dominant controls of winter temperature and productivity on the distribution of dinoflagellate cysts in this region dinoflagellate cyst based predictive models for winter temperature and productivity were developed from the contemporary distributional data using the modern analogue technique and applied to subfossil data from two mid to late holocene 5500 calendar years before present present cores tul99b03 and tul99b11 collected from effingham inlet a 15 km long anoxic fjord located on the southwest coast of vancouver island that directly opens to the pacific ocean through barkley sound sedimentation within these basins largely comprises annually deposited laminated couplets each made up of a winter deposited terrigenous layer and spring to fall deposited diatomaceous layer the effingham inlet dinoflagellate cyst record provides evidence of a mid holocene gradual decline in winter sst ending with the initiation of neoglacial advances in the region by 3500 cal bp a reconstructed late holocene increase in winter sst was initiated by a weakening of the california current which would have resulted in a warmer central gyre and more el nino like conditions

longitudinal profiles in simple alluvial systems theoretical considerations suggest that exponential or quadratic functions are apt for describing the longitudinal profiles of aggrading alluvial systems that are unaffected by significant lateral inputs of water or sediment a new set of field data confirms this for individual sedimentary links along a wandering gravel bed river in british columbia canada each link is viewed as a simple alluvial system without major water or sediment inputs within which grain size typically fines downstream in a relatively systematic manner such homogeneous reaches are suitable for the investigation of simple profile form it is found that quadratic approximations are the most flexible descriptor for link longitudinal profiles overall the river forms an irregularly cuspate long profile structured by these fundamental length scale units both link gradients and link fining rate reflect size selective aggradation associated with the bounding lateral inputs

a fuzzy gis model to determine confluence morphological sensitivity to tributary inputs at the watershed scale abstract confluences are key nodes of river systems that have the potential of disrupting downstream longitudinal trends in the main river through inputs of water sediment wood or ice delivered from tributaries from a geomorphological perspective confluence zones are particularly active and thus susceptible to increased flooding and bed instability which in turn pose serious threats to infrastructure however not all confluences are active despite major advances in our knowledge of confluence dynamics there has been limited progress in the development of low complexity practical tools that use remotely sensed data to predict the spatial distribution of the main river s sensitivity to tributary inputs we have thus developed a novel semi automated gis model that uses a fuzzy approach to integrate key factors unit stream power valley confinement and sediment connectivity potential in order to map the distribution of the confluence morphological sensitivity cms index at the watershed scale the gis model was tested using digital elevation models of high lidar 1 m and coarser 10 m resolution in the coaticook and gaspesie watersheds quebec canada results indicate that the model is useful for detecting geomorphologically active confluences and the resulting sensitivity of the main channel and thus has potential to be used in diverse river management applications e g hazard reduction and freedom space mapping

grain size along two gravel bed rivers statistical variation spatial pattern and sedimentary links a new set of field data facilitates a detailed analysis of variations in bed material grain size within two confluent gravel bed rivers in northeastern british columbia canada a preliminary assessment of grain size variability establishes a basis for examination of the spatial pattern of grain size change standard anova techniques are inappropriate because individual samples have unequal variances and are not normally distributed alternative tests for homoscedasticity and comparison of means are therefore utilized within site between sample variability is not significant the grain size distributions that were obtained at individual sites are therefore representative of the depositional environments that were sampled in both rivers mean grain size does vary significantly between sites and there is therefore a basis for examining the data for spatial patterns such as downstream fining textural variations along the two rivers studied here are complex and show negligible overall fining in over 100 km this is the consequence of a large number of tributary inputs and non alluvial sediment sources which are the legacy of late pleistocene glaciation the identification of lateral sources like these is fundamental for understanding textural changes within rivers the sedimentary link a channel reach between significant lateral sediment inputs provides a means of isolating fluvial maturation processes abrasion and sorting from contingent lateral inputs strong fining trends are apparent in most links and classification of grain size measurements according to their location within particular links greatly improves the statistical explanation of textural variation identification of sedimentary links provides a means of applying models of fluvial fining processes so isolation of link networks will aid the development of basin scale models of textural variation 1998 john wiley sons ltd

making riverscapes real abstract the structure and function of rivers have long been characterized either by 1 qualitative models such as the river continuum concept or serial discontinuity concept which paint broad descriptive portraits of how river habitats and communities vary or 2 quantitative models such as downstream hydraulic geometry which rely on a limited number of measurements spread widely throughout a river basin in contrast authors such as fausch et al 2002 and wiens 2002 proposed applying existing quantitative spatially comprehensive ecology and landscape ecology methods to rivers this new framework for river sciences which preserves variability and spatial relationships is called a riverine landscape or a riverscape application of this riverscape concept requires information on the spatial distribution of organism scale habitats throughout entire river systems this article examines the ways in which recent technical and methodological developments can allow us to quantitatively implement and realize the riverscape concept using 3 cm true color aerial photos and 5 m resolution elevation data from the river tromie scotland we apply the newly developed fluvial information system which integrates a suite of cutting edge high resolution remote sensing methods in a spatially explicit framework this new integrated approach allows for the extraction of primary fluvial variables such as width depth particle size and elevation from these first order variables we derive second order geomorphic and hydraulic variables including velocity stream power froude number and shear stress channel slope can be approximated from available topographic data based on these first and second order variables we produce riverscape metrics that begin to explore how geomorphic structures may influence river habitats including connectivity patchiness of habitat and habitat distributions the results show a complex interplay of geomorphic variable and habitat patchiness that is not predicted by existing fluvial theory riverscapes thus challenge the existing understanding of how rivers structure themselves and will force development of new paradigms

diatom inferred hydrological changes and holocene geomorphic transitioning of africa s largest estuarine system lake st lucia abstract the diverse lagoons and coastal lakes along the east coast of south africa occupy incised valleys that were flooded during the rise and subsequent stabilisation of relative sea level during the holocene sedimentary deposits contained within these waterbodies provide an opportunity to investigate complex hydrological and sedimentological processes and examine sea level controls governing system geomorphic evolution in this paper we combine diatom and sulfur isotope analyses from two sediment cores extracted from the northern sub basins of lake st lucia a large shallow estuarine lake that is today largely isolated from direct ocean influence behind a holocene pleistocene barrier complex analyses allow the reconstruction of hydrological changes associated with the geomorphic development of the system over the mid to late holocene the sedimentary sequences indicate that st lucia was a shallow partially enclosed estuary embayment dominated by strong tidal flows prior to 6200 cal bp infilling was initiated when sea level rise slowed and stabilised around present day levels resulting in the accumulation of fine grained sediment behind an emergent proto barrier diatom assemblages dominated by marine benthic and epiphytic species reveal a system structured by marine water influx and characterised by marsh and tidal flat habitats until 4550 cal bp a shift in the biological community at 4550 cal bp is linked to the development of a back barrier water body that supported a brackish community marine planktonics and enrichments in 34 s suggest recurrent large scale barrier inundation events during this time coincident with a mid holocene sea level highstand periodic marine incursions associated with episodes of enhanced storminess and overwash remained prevalent until 1200 cal bp when further barrier construction ultimately isolated the northern basins from the ocean this study provides the first reconstruction of the palaeohydrological environment at lake st lucia and highlights the long term geomorphic controls that have shaped the recent evolution and natural dynamics of the system unlike most coastal lake systems this system is particularly effective as an archive of geomorphological change systems driven by back barrier modifications such as lake st lucia highlight how geomorphological changes driven by sediment supply climate and sea level can be distributed unevenly over several isolated back barrier basins

river adjustment to changes in sediment load the effects of tin mining on the ringarooma river tasmania 1875 1984 the mining of alluvial tin in the ringarooma basin began in 1875 reached a peak in 1900 20 and had virtually ceased by 1982 during that time 40 million m3 of mining waste were supplied to the main river quickly replacing the natural bed material and requiring major adjustments to the channel based on estimates of sediment supply from more than 50 widely scattered mines and the frequency of flows capable of transporting the introduced load the river s transport history is reconstructed using a mass conservation model because of the lengthy time period 110 years and river distance 75 km involved the model cannot predict detailed change but it does reproduce the main pattern of sediment movement in which successive phases of aggradation and degradation progress downstream peak storage is predicted in that part of the river where braiding and anastomosis are best developed aggradation was most rapid in the upper reaches close to major supply points becoming slower and later with distance downstream channel width increased by up to 300 per cent where the valley floor was broad and braiding became relatively common bridges had frequently to be replaced while bed levels were still rising in lower reaches degradation began in upper ones notably after 1950 and by 1984 had progressed downriver over 30 km rates of incision reached 0 5 m yr 1 especially in the early 1970s when record high flows occurred as a result of degradation the bed material became gravelly through either reexposure of the original bed or lag concentration of coarser fractions also a narrower unbraided channel has developed the river is beginning to heal itself and upper reaches now have reasonably stable beds but at least another 50 years will be required for the river to cleanse its channel of mining debris

the gravel sand transition along river channels abstract this paper discusses a hitherto neglected aspect of fluvial downstream fining the transition from a gravel bed to a sand bed from the few known examples and by additional study of new sites some general features of such transitions are given these transitions are generally rapid and involve a change in bed texture from unimodal gravels through bimodal sediments to exclusively sand material and are often associated with a break in slope we propose three possible causes local base level control an excess of sand supply and abrasion breakdown of fine gravel we further argue that such transitions occur in a variety of fluvial environments and are geographically more widespread than previously supposed and on this basis we suggest they may also aid in interpreting ancient sediment showing bimodality and rapid proximal to distal changes in grain size

morphology and evolution of bars in a wandering gravel bed river lower fraser river british columbia canada a hierarchical typology for the channels and bars within aggradational wandering gravel bed rivers is developed from an examination of a 50 km reach of lower fraser river british columbia canada unit bars built by stacking of gravelly bedload sheets are the key dynamic element of the sediment transfer system linking sediment transport during individual freshets to the creation development and remoulding of compound bar platforms that have either a lateral or medial style primary and secondary unit bars are identified respectively as those that deliver sediment to compound bars from the principal channel and those that redistribute sediment across the compound bar via seasonal anabranches and smaller channels the record of bar accretion evident in ground penetrating radar sequences is consistent with the long term development of bar complexes derived from historical aerial photographs for two compound bars inter annual changes associated with individual sediment transport episodes are measured using detailed topographic surveys and longer term changes are quantified using sediment budgets derived for individual bars from periodic channel surveys annual sediment turnover on the bars is comparable with the bed material transfer rate along the channel indicating that relatively little bed material bypasses the bars bar construction and change are mainly accomplished by lateral accretion since the river has limited capacity to raise bed load onto higher surfaces styles of accretion and erosion and therefore the major bar form morphologies on fraser river are familiar and consistent with those in gravelly braided channels but the wandering style does exhibit some distinctive features for example 65 year histories reveal the potential for long sequences of uninterrupted accretion in relatively stable wandering rivers that are unlikely in braided rivers

evidence for holocene sea level change at verlorenvlei western cape south africa abstract a series of sediment cores extracted from what is today a large freshwater coastal lake verlorenvlei has been sub sampled radiocarbon dated and subjected to a range of palaeoenvironmental techniques in particular pollen analysis sedimentology and geochemistry a mid late holocene higher sea level is evident in the cores indicating the rapidity with which sea level change can occur and invoke other forms of environmental response following a hiatus in sedimentation most probably around 3800 bp the marine conditions at the site were replaced by fresh water as the dominant hydrological and ecological influence laminated organic sediments in some of the cores suggest that around 300 years ago a fresh water lake characterised verlorenvlei since then the picture revealed by high resolution palynology is one of progressive levels of human disturbance both in and around the study area sedimentological and palaeoecological analyses of additional cores from the vlei two from the distal inland and one from the proximal coastal end of the system serve further to elucidate the precise nature of sea level change in the late holocene and facilitate the construction of a refined holocene sea level curve for the region environmental changes in the late holocene are shown to be especially dynamic

rock type controls on downstream changes in clast parameters in sandur systems in southeast iceland abstract the role of rock type in controlling downstream variation in clast parameters in non jokulhlaup affected oraefi sandar in iceland was evaluated clast changes in the svinafellsa are simple but the effects of tributary sources complicate the clast parameter distance relationships in the morsardalur kjos system the behavior of individual rock types must be studied to understand the changes both selective sorting and abrasion are taking place and the relative importance of these processes is evaluated the volcanic rocks are rounding relatively rapidly with variation among individual rock types but there are no significant changes in sphericity and clast form with distance the compressive strength of the volcanic suite is variable and significant weathering changes must be takin place during transport from rock face to distal sandur the influence of such weathering changes on changes in clast parameters needs further research

coupling between hillslopes and channels in upland fluvial systems implications for landscape sensitivity illustrated from the howgill fells northwest england abstract the sensitivity of upland fluvial systems depends on the magnitude and frequency of sediment and flood producing events modified by the internal coupling characteristics of the system this paper assesses the role of hillslope channel coupling for the sensitivity of upland geomorphic systems using evidence from a 30 year monitoring programme of geomorphic change in the carlingill valley howgill fells northwest england in the hillslope zone there is little sediment supply to the stream system locally slope failures occur in response to extreme events six such events in 30 years within the ca 6 km 2 carlingill valley in the footslope coupling zone basally induced gullies are major sediment sources to the stream sediment production events occur ca 30 times per year feeding sediment to basal debris cones stream floods which can entrain these sediments occur once every ca 2 5 years stream channel morphology is adjusted to this regime downstream of gullies channels are wide and braided elsewhere they are narrow and single thread as the gullies develop however this coupling weakens and the eroding slopes eventually stabilise by revegetation over the 30 year monitoring period there has been a progressive trend towards gully stabilisation and an associated reduction in channel instability massive destabilisation may occur in response to rare extreme flood events such an event return period 100 years occurred in neighbouring langdale and bowderdale valleys in june 1982 that event destabilised the system causing slope failures fan deposition and in some places a switch in channel style to wide braided channels since 1982 there has been a progressive recovery by slope stabilisation and single thread sinuous channels have become reestablished a different style of extreme event occurred in carlingill in october 1998 in response to the wettest week in the 30 year period a slope failure fed debris flows 400 m downslope almost coupling with the channel system future climatic change could render the system prone to destabilisation through either extreme flood events or through major slope failures

spatial discontinuity and temporal evolution of channel morphology along a mixed bedrock alluvial river upper drome river southeast france contingent responses to external and internal controls abstract the rehabilitation of degraded river channels is often guided by assumptions of continuity yet in response to spatial and temporal variations in controlling conditions rivers typically display discontinuous response in space and time this study examines the development of a 5 km reach of the drome river s e france characterised by alternating alluvial and bedrock zones that are separated by abrupt downstream transitions this reach is representative of the drome river as a whole and other rivers in the european alps where braided channel planforms have been replaced by more complex discontinuous morphologies the primary aims are to understand how this spatial complexity has developed on the drome evaluate how temporal channel changes have been affected by local factors particularly bedrock exposures and by long term catchment scale changes in sediment supply and the flood activity and consider the implications of this discontinuous geomorphology for reach management the development of geomorphological zonation is examined by documenting sequential changes in channel planform between seven periods using aerial photography 1948 2006 and by analysing change in bed elevation from profiles surveyed in 1928 2003 and 2005 between 1948 and 2001 bedrock exposed in the channel bed and along the floodplain margins defined discontinuities in sediment connectivity that were largely responsible for the configuration of channel zones the impact of floods on this system was not proportional to flood magnitude a modest flood in 1978 was an important event that by incision and avulsion at key locations defined a pattern of zonation that persisted until the end of the study in 2006 during the final 5 years of the study alluvial zones that previously responded to large floods by widening underwent narrowing despite the occurrence of a large flood and led to an overall reduction in width variance this resulted from progressive incision beneath and disconnection from formerly active channel areas in response to long term catchment scale reductions in sediment supply and flood frequency in 2006 the pattern of zonation remains distinct disguising this recent change in channel response and underlining the need for long term and sequential perspectives of channel development to fully understand the processes in operation contemporary snapshots of channel form may be misleading understanding interactions between inherent channel complexity and prevailing flow and sediment conditions and how this shapes channel response to individual floods is essential when interpreting future trajectories of channel change and likely response to management intervention

selective sorting and abrasion of river gravel i theory most gravel rivers show a tendency for characteristic grain size to decrease in the downstream direction over scales of tens or hundreds of kilometers it has been surmised that this downstream fining is due to some combination of selective sorting by which finer grains are preferentially transported downstream and abrasion by which individual particles are reduced in size here a framework for the simultaneous treatment of both phenomena is developed the analysis is restricted to bed load transport of gravel only abrasion due to binary collisions between moving bed load and stationary bed particles is considered the formulation includes the possibility of differential basin uplift and subsidence due to tectonism and mixtures of rock types with differing coefficients of abrasion the formulation of selective sorting is based on the concept of hiding as applied to a surface based bed load transport relation abrasion is first treated in terms of a lagrangian formulation for individual grains and t

new evidence for far field holocene sea level oscillations and links to global climate records abstract rising sea level in the coming century is of significant concern yet predicting relative sea level change in response to eustatic sea level variability is complex potential analogues are provided by the recent geological past but until recently many sea level reconstructions have been limited to millennial scale interpretations due to age uncertainties and paucity in proxy derived records here we present a sea level history for the tectonically stable far field great barrier reef australia derived from 94 high precision uranium thorium dates of sub fossil coral microatolls our results provide evidence for at least two periods of relative sea level instability during the holocene these sea level oscillations are broadly synchronous with indo pacific negative sea surface temperature anomalies rapid global cooling events and glacial advances we propose that the pace and magnitude of these oscillations are suggestive of eustatic thermosteric processes operating in conjunction with regional climatic controls

the mid holocene sea level highstand at bogenfels pan on the southwest coast of namibia the radiocarbon ages of mollusc shells from the bogenfels pan on the hyper arid southern coast of namibia provide constraints on the holocene evolution of sea level and in particular the mid holocene highstand the bogenfels pan was flooded to depths of 3 m above mean sea level amsl to form a large subtidal lagoon from 7300 to 6500 calibrated radiocarbon years before present cal yr bp the mollusc assemblage of the wave sheltered lagoon includes nassarius plicatellus lutraria lutraria and the bivalves solen capensis and gastrana matadoa both of which no longer live along the wave dominated southern namibian coast the radiocarbon ages of mollusc shell from a gravely beach deposit exposed in a diamond exploration trench indicate that sea level fell to near or 1 m below its present day position between 6500 and 4900 cal yr bp the rapid emergence of the pan between 6500 and 4900 cal yr bp exceeds that predicted by glacio isostatic models and may indicate a 3 m eustatic lowering of sea level the beach deposits at bogenfels indicate that sea level rose to 1 m amsl between 4800 and 4600 cal yr bp and then fell briefly between 4600 and 4200 cal yr bp before returning to 1 m amsl since 4200 cal yr bp sea level has remained within one meter of the present day level and the beach at bogenfels has prograded seaward from the delayed arrival of sand by longshore drift from the orange river a 6200 cal yr bp coastal midden and a 600 cal yr bp midden 1 7 km from the coast indicate sporadic human utilization of the area the results of this study are consistent with previous studies and help to refine the holocene sea level record for southern africa

refining the eustatic sea level curve since the last glacial maximum using far and intermediate field sites the eustatic component of relative sea level change provides a measure of the amount of ice transferred between the continents and oceans during glacial cycles this has been quantified for the period since the last glacial maximum by correcting observed sea level change for the glacio hydro isostatic contributions using realistic ice distribution and earth models during the last glacial maximum lgm the eustatic sea level was 125 5 m lower than the present day equivalent to a land based ice volume of 4 6 4 9 107 km3 evidence for a non uniform rise in eustatic sea level from the lgm to the end of the deglaciation is examined the initial rate of rise from ca 21 to 17 ka was relatively slow with an average rate of ca 6 m ka 1 followed by an average rate of ca 10 m ka 1 for the next 10 ka significant departures from these average rates may have occurred at the time of the younger dryas and possibly also around 14 ka most of the decay of the large ice sheets was completed by 7 ka but 3 5 m of water has been added to the oceans since that time

pleistocene sea level fluctuations and human evolution on the southern coastal plain of south africa abstract humans evolved in africa but where and how remain unclear here it is proposed that the southern coastal plain scp of south africa may have served as a geographical point of origin through periodic expansion and contraction isolation in response to glacial interglacial changes in sea level and climate during pleistocene interglacial highstands when sea level was above 75 m human populations were isolated for periods of 360 3400 25 yr generations on the scp by the rugged mountains of the cape fold belt climate and vegetation barriers the scp expands five fold as sea level falls from 75 to 120 m during glacial maxima to form a continuous unobstructed coastal plain accessible to the interior an expanded and wet glacial scp may have served as a refuge to humans and large migratory herds and resulted in the mixing of previously isolated groups the expansive glacial scp habitat abruptly contracts by as much as one third in 300 yr during the rapid rise in sea level associated with glacial terminations rapid flooding may have increased population density and competition on the scp to select for humans who expanded their diet to include marine resources or hunted large animals successful adaptations developed on an isolated scp are predicted to widely disperse during glacial terminations when the scp rapidly contracts or during the initial opening of the scp in the transition to glacial maxima the hypothesis that periodic expansion and contraction of the scp as well as the coastal plain of north africa contributed to the stepwise origin of our species over the last 800 thousand years kyr is evaluated by comparing the archeological dna and sea level records these records generally support the hypothesis but more complete and well dated records are required to resolve the extent to which sea level fluctuations influenced the complex history of human evolution

predicting natural channel patterns based on landscape and geomorphic controls in the columbia river basin usa 1 based on known relationships of slope discharge valley confinement sediment supply and sediment caliber in controlling channel patterns we developed multivariate models to predict natural channel patterns across the 674 500 km2 columbia river basin usa we used readily available geospatial data sets to calculate reach slopes 2 year flood discharge and valley confinement as well as to develop hypothesized landscape level surrogates for sediment load and caliber relative slope percent of drainage area in alpine terrain and percent of drainage area in erosive fine grained lithologies using a support vector machine svm classifier we found that the four channel patterns were best distinguished by a model including all variables except valley confinement 82 overall accuracy we then used that model to predict channel pattern for the entire basin and found that the spatial distribution of straight meandering anabranching and braided patterns were consistent with regional topography and geology a simple slope discharge model distinguished meandering channels from all other channel patterns but did not clearly distinguish braided from straight channels 68 overall accuracy addition of one or more of the hypothesized sediment supply surrogates improved prediction accuracy by 4 14 over slope and discharge alone braided and straight channels were most clearly distinguished on an axis of relative slope whereas braided and anabranching channels were most clearly distinguished by adding percent alpine area to the model

holocene geoarchaeology of the sixteen mile beach barrier dunes in the western cape south africa holocene evolution and human occupation of the sixteen mile beach barrier dunes on the southwest coast of south africa between yzerfontein and saldanha bay are inferred from the radiocarbon ages of calcareous dune sand limpet shell patella spp manuports and gull dropped white mussel shells donax serra a series of coast parallel dunes have prograded seaward in response to an overall marine regression since the mid holocene with dated shell from relict foredunes indicating periods of shoreline progradation that correspond to drops in sea level at around 5900 4500 and 2400 calibrated years before the present cal yr b p however the active foredune extensively covered by a layer of gull dropped shell has migrated 500 m inland by the recycling of eroded dune sand in response to an approximate 1 m sea level rise over the last 700 yr manuported limpet shells from relict blowouts on landward vegetated dunes indicate human occupation of coastal dune sites at 6200 and 6000 cal yr b p and help to fill the mid holocene gap in the regional archaeological record coastal midden shells associated with small hearth sites exposed in blowouts on the active foredune are contemporaneous 1600 500 cal yr b p with large midden sites on the western margin of langebaan lagoon and suggest an increase in marine resource utilisation associated with the arrival of pastoralism in the western cape

radiocarbon dating of mangrove sediments to constrain holocene relative sea level change on zanzibar in the southwest indian ocean mangrove sedimentary deposits are sensitive to changes in sea level and can be used to reconstruct mid to late holocene sea level fluctuations in intermediate and far field locations distant to t

rapid sea level fall and deep ocean temperature change since the last interglacial period we have dated huon peninsula papua new guinea and barbados corals that formed at times since the last interglacial period applying both 230 th and 231 pa dating techniques as a test of age accuracy we show that marine isotope stage mis 5e ended prior to 113 1 8 0 7 kyr when sea level was 319 m during mis 5b sea level was 357 m at 92 6 8 0 5 kyr having dropped about 40 m in approximately 10 kyr during the mis 5c 5b transition sea level then rose more than 40 m during the mis 5b 5a transition also in about 10 kyr mis 5a lasted until at least 76 2 8 0 4 kyr at a level of 324 m at that time combined with earlier data that places mis 4 sea level at 381 m at 70 8 kyr our late mis 5a data indicate that sea level fell almost 60 m in less than 6 kyr 10 6 m kyr during the mis 5 4 transition the magnitude of the drop is half that of the glacial interglacial amplitude and approximatelyequivalent to the volume of the present dayantarctic ice sheet during this interval the minimum average rate of net continental ice accumulation was 18 cm yr likely facilitated by efficient moisture transport from lower latitudes at three specific times 60 6 8 0 3 50 8 8 0 3 and 36 8 0 2 kyr during mis 3 sea level was between 385 and 374 m sea level then dropped to 3107 m at 23 7 8 0 1 kyr early in mis 2 before dropping further to last glacial maximum lgm values and then rising to present values during the last deglaciation times of rapid sea level drop correspond to times of high winter insolation at low northern latitudes and high winter latitudinal gradients in northern hemisphere insolation supporting the idea that these factors mayhave resulted in high water vapor pressure in moisture sources and efficient moisture transport to high latitude glaciers therebycontributing to glacial buildup we combined our sea level results with deep sea n 18 o records as a means of estimating the temperature and ice volume components in the marine n 18 o record this analysis confirms large deep ocean temperature shifts following mis 5e and during termination i deep ocean temperatures changed bymuch smaller amounts between mis 5c and 2 maximum temperature shift in the deep pacific is about 2 whereas the shift at a site in the atlantic is 4 under glacial conditions temperatures at both sites are near the freezing point the shift in the atlantic is likelycaused bya combination of changing proportions of northern and southern source waters as well as changing temperature at the sites where these deep waters form

holocene sea level fluctuations inferred from the evolution of depositional environments of the southern langebaan lagoon salt marsh south africa a holocene sea level curve is constructed from the facies distribution and radiocarbon ages of sediment recovered from the distal southern salt marsh of langebaan lagoon on the southwest coast of south africa calibrated radiocarbon analyses of an oyster rich bioclastic gravel indicate that the flandrian transgression flooded the lagoon to 0 3 m above present day levels by 6750 years ago 6 8 ka organic matter and shell material dated in distal lagoonal sediments indicate that sea level returned to present day levels by 4 9 ka and have since remained within 61 m of present day levels bleached shell and a hiatus in sedimentation suggest an approximate 1 m sea level lowstand between 2 5 and 1 8 ka changes in the macrobenthos assemblage since 1 5 ka that include the loss of the oysterostrea atherstonei razor clamsolen capensis brown musselarcuatula capensis and periwinkleoxystele variegata reflect loss of hard substrate decreased tidal flow velocities as reworked sands prograded into the southern la

breakup and reestablishment of the armour layer in a large gravel bed river below dams the lower ebro changes in armour layer during floods under supply limited conditions are little known this paper describes the breakup and the reestablishment of the bed armour layer in the regulated gravel bed ebro river during a flooding period the study was conducted over a 28 km study reach from 2002 to 2004 the surface subsurface and bed load grain size distribution constitute the bases for the analysis of bed armouring dynamics the results indicate that the magnitude of floods controlled the degree of armouring of the river bed the initial mean armouring ratio was 2 3 with maximum values reaching 4 4 floods in the winter of 2002 2003 q8 caused the breakup of the armour layer in several sections this resulted in the erratic bed load pattern observed during the december 2002 flushing flow and in the increase in bed load transport during successive events most grain size classes were entrained and transported causing river bed incision the mean armouring ratio decreased to 1 9 in contrast during low magnitude floods in 2003 2004 q2 the coarsest fractions 64 mm did not take part in the bed load while finer particles were winnowed thus surface deposits coarsened as a result the armour layer was reestablished i e the mean armouring ratio increased to 2 3 and the supply of subsurface sediment decreased the supply and transport of bed material appear to be in balance in the river reach immediately below the dam in contrast the transport of medium and finer size classes in the downstream reaches was higher than their supply from upstream a phenomenon that progressively reduced their availability in the river bed surface hence the armour layer reworking

timing and magnitude of holocene sea level changes along the middle and south patagonian atlantic coast derived from beach ridge systems littoral terraces and valley mouth terraces abstract geomorphologic and chronostratigraphic investigations in various coastal localities along the middle and south patagonian atlantic coast from bahia vera 44 s in the north to san julian 49 s in the south confirm a rich sequence of holocene beach ridge systems and littoral and valley mouth terraces beach ridges are present up to 10 m above current highest tide level htw and date to the early mid holocene transgression maximum beach ridge deposits represent high energy wave dominated coastal environments whereas valley mouth terraces and littoral terraces elevations of 5 5 6 5 m above htw developed in wave protected coastal environments the surface elevation of these littoral forms suggest that the middle and south patagonian atlantic coast is likely undergoing a slow glacio isostatic uplift on the order of 0 3 0 4 mm a since the mid holocene the early holocene sea level rise reached the modern coastline by 8100 14 c years ago c 8600 cal bp at the latest sea level at that time was most likely near its present position the holocene transgression maximum lasted from 6900 to at least 6200 14 c bp c 7400 to 6600 cal bp raising relative sea level to about 2 m to a maximum of 3 m above the present level after which sea level declined to the present level two significant sea level falls of at most 1 m occurred a between 6200 and 6000 14 c bp c 6600 to 6400 cal bp and b between 2600 and 2400 14 c bp c 2300 to 2050 cal bp we assume that both significant sea level falls were predominantly driven by eustatic changes of ocean volume whereas both thermo steric changes and changes of tides may also have contributed to these relatively strong sea level drops gravitational changes driven by greenland ice growth sensu mitrovica et al 2001 may also have amplified any eustatic portion of sea level fall the trend of a general sea level decline since the mid holocene transgression maximum seems to be predominantly glacio isostatically driven

palynological evidence for holocene climatic and oceanographic changes off western south africa abstract atmospheric and oceanographic interactions between the atlantic and indian oceans influence upwelling in the southern benguela upwelling system in order to obtain a better knowledge of paleoceanographic and paleoenvironmental changes in the southern benguela region during the holocene 12 marine surface sediment samples and one gravity core geob8331 4 from the namaqualand mudbelt off the west coast of south africa have been studied for organic walled dinoflagellate cysts in high temporal resolution the results are compared with pollen and geochemical records from the same samples our study emphasizes significantly distinct histories in upwelling intensity as well as the influence of fluvial input during the holocene three main phases were identified for the holocene high percentages of cysts produced by autotrophic taxa like operculodinium centrocarpum and spiniferites spp indicate warmer and stratified conditions during the early holocene 9900 8400 cal yr bp suggesting reduced upwelling likely due to a northward shift of the southern westerlies in contrast the middle holocene 8400 3100 cal yr bp is characterized by a strong increase in heterotrophic taxa in particular lejeunecysta paratenella and echinidinium spp at the expense of autotrophic taxa this indicates cool and nutrient rich waters with active upwelling probably caused by a southward shift of the southern westerlies during the late holocene 3100 cal yr bp to modern brigantedinium spp and other abundant taxa interpreted to indicate fluvial nutrient input such as cyst of protoperidinium americanum and lejeunecysta oliva imply strong river discharge with high nutrient supply between 3100 and 640 cal yr bp

lateral sediment sources and knickzones as controls on spatio temporal variations of sediment transport in an alpine river modern mixed alluvial bedrock channels in mountainous areas provide natural laboratories for understanding the time scales at which coarse grained material has been entrained and transported from their sources to the adjacent sedimentary sink where these deposits are preserved as conglomerates this article assesses the shear stress conditions needed for the entrainment of the coarse bed particles in the glogn river that drains the 400 km2 val lumnezia basin eastern swiss alps in addition quantitative data are presented on sediment transport patterns in this stream the longitudinal stream profile of this river is characterized by three ca 500 m long knickzones where channel gradients range from 0 02 to 0 2 m m 1 and where the valley bottom confined into a 10 m wide gorge downstream of these knickzones the stream is flat with gradients 0 01 m m 1 and widths 30 m measurements of the grain size distribution along the trunk stream yield a mean d84 value of ca 270 mm whereas the mean d50 is ca 100 mm the consequences of the channel morphology and the grain size distribution for the time scales of sediment transport were explored by using a one dimensional step backwater hydraulic model hydrologic engineering centre river analysis system the results reveal that along the entire trunk stream a two to 10 year return period flood event is capable of mobilizing both the d50 and d84 fractions where the shields stress exceeds the critical shields stress for the initiation of particle motion these return periods however varied substantially depending on the channel geometry and the pebble boulder size distribution of the supplied material accordingly the stream exhibits a highly dynamic boulder cover behaviour it is likely that these time scales might also have been at work when coarse grained conglomerates were constructed in the geological past