the evolution of tidal creek networks mary river northern australia tidal creek networks have in 50 years extended over 30 km inland across the coastal plains of the mary river in northern australia invading freshwater wetlands and destroying the associated vegetation the networks have grown at an exponential rate through a combination of main channel extension and tributary development with concomitant widening of the creeks a large tidal range very small elevational differences over the plains and the availability of preexisting channel lines notably in the form of palaeochannels have been major factors contributing to the rapid rate of expansion close parallels exist between these networks and terrestrial networks as regards modes of growth and planimetric properties a channel is initiated when the diffuse flow of a seepage zone becomes concentrated through localized scour subsequent development is characterized by the rapid extension of long first order channels with most tributary addition occurring later model tests suggest that branching was more likely on exterior links in the early stages but that exterior and interior link branching became more equally likely through time although the headward limits of the main creeks seem to have been reached tributary infilling will continue to progress upstream only in the most downstream parts is a stable drainage density being approached the networks not only satisfy the laws of drainage network composition and the basic postulates of the random model but also depart from topologic randomness in similar ways to terrestrial networks both topologic and length properties have changed during evolution but largely at the link rather than network scale the close correspondence with terrestrial networks may be due to the low relief and the relatively unconstrained nature of growth in which availability of space was the main determining factor

environmental context for late holocene human occupation of the south wellesley archipelago gulf of carpentaria northern australia a 2400 year record of environmental change is reported from a wetland on bentinck island in the southern gulf of carpentaria northern australia three phases of wetland development are identified with a protected coastal setting from ca 2400 to 500 years ago transitioning into an estuarine mangrove forest from ca 500 years ago to the 1940s and finally to a freshwater swamp over the past 60 years this sequence reflects the influence of falling sea levels development of a coastal dune barrier system prograding shorelines and an extreme storm cyclone event in addition there is clear evidence of the impacts that human abandonment and resettlement have on the island s fire regimes and vegetation a dramatic increase in burning and vegetation thickening was observed after the cessation of traditional indigenous kaiadilt fire management practices in the 1940s and was then reversed when people returned to the island in the 1980s in terms of the longer context for human occupation of the south wellesley archipelago it is apparent that the mangrove phase provided a stable and productive environment that was conducive for human settlement of this region over the past 1000 years

process implications of chenier dates in australia abstract chenier plains record changes in the mode of coastal progradation between periods of mudflat progradation and coarse sediment deposition there are several environmental forces responsible for these changes and these include both intrinsic and extrinsic processes in australia the causes of these changes are still not well understood the majority of australian chenier plain studies have been conducted within a relatively narrow spatial scope focussing on one or two individual plains compiling and assessing times of chenier ridge building across multiple sites can provide a broader scale perspective on chenier plain development trends potentially revealing broader scale morphodynamic relationships that may exist across a large region one such assessment was undertaken by lees and clements 1987 and since then many more chenier ridge ages have been obtained our understanding of late holocene environmental changes and computation methods have since improved a new statistical assessment of australian chenier ridge ages revealed periods of simultaneous chenier ridge building across multiple northern and southern australian coastal plains between 2400 and 1300 yr bp and possibly again in the last 1000 years previously such results were explained in terms of holocene climate changes however the spatial separation between sites in this new assessment suggests that other broad scale extrinsic processes may provide a better explanation a possible candidate for such a process is late holocene sea level changes

facies evolution of holocene estuaries and deltas a large sample statistical study from australia abstract selected geomorphic features and sedimentary facies were mapped in 283 of australia s wave and tide dominated estuaries and deltas to quantitatively evaluate established evolutionary facies models that depict the evolution of estuaries into deltas during stable sea level conditions while diagnostic facies for wave and tide dominated estuaries and deltas approximate those specified by the models statistical analyses of the data also reveal two additional insights regarding the evolution of estuaries to deltas first there is an offshore shift in the locus of sand accumulation between tide dominated estuaries and deltas associated with the onset of delta development second the mean surface area of intertidal environments i e intertidal flats mangroves melaleuca saltmarsh salt flat facies is greater in wave dominated deltas than in wave dominated estuaries tidal penetration associated with the river establishing a more direct and permanent connection to the sea during late stage development presents a natural impediment to continued formation of an alluvial plain and full development of the classic wave dominated delta morphology a notional evolutionary pathway for wave dominated estuaries is developed from the distribution of facies that predicts the rate and susceptibility of geomorphic and habitat changes the classic deltaic geomorphology may be unattainable for wave dominated systems except those with significant terrigenous sediment inputs our study is the first published example of geomorphic and sedimentary data assembled from a large number of wave and tide dominated estuaries and deltas across an entire continent

submarine channels in rupert inlet british columbia ii sediments and sedimentary structures abstract in a previous paper the morphological evolution of submarine channels in the rupert inlet mine tailing deposit was traced through a succession of three distinct periods or phases over a five year period a meandering channel phase an apron phase and a rechannelized phase the distributions of sediment properties including grain size specific gravity and cu and fe concentrations for these phases are presented here copper rich coarse grained deposits were found along channel axes and down the apron flanks sandy fining upward turbidites in cores from the levees during the meandering channel phase were characterized by higher cu and lower fe concentrations than the adjacent mud and had sharp basal contacts sometimes exhibiting flame and load pocket structures the average thickness of and fraction of the sediment column occupied by turbidites was found to increase with distance downchannel indicating a downchannel decrease in the importance of continuous as opposed to surge type flow to the channel building process deposition rates determined from the local time rates of change of tailing deposit thickness ranged from 0 1 to 4 m yr 1 at the core sites and were used together with the number of coarse grained turbidites per core to yield a minimum turbidity current surge recurrence interval of 2 5 days during the meandering channel phase

turbidity currents and submarine channel formation in rupert inlet british columbia 1 surge observations acoustic backscatter images obtained at 107 and 200 khz of surge type turbidity currents resulting from mine tailing discharge are presented excess densities in the head of the order of 100 kg m 3 are estimated from differences in acoustic backscatter intensity and in the amplitude of the bottom reflected signal these excess densities are comparable to estimates based on surge height and speed the speed being determined by assuming a universal head shape unlike gravity current surges from an impulsively started steady source the surge type turbidity flows consist of a high concentration slug of short duration followed by a longer lived wake in which sediment concentrations are lower by 2 3 orders of magnitude the profile of the high concentration slug resembles those for density slugs on small bottom slopes obtained in laboratory experiments discrete scatterers probably fish are observed to avoid the surges

hydro isostasy and the sea level isobase of 5500 b p in north queensland australia abstract previous studies of holocene sea level in north queensland have been based on a variety of sea level related deposits with interpretations of mid holocene levels ranging from near zero up to 4 m above present we report data from 8 carefully controlled new sites located from the palm group northwards and extending into the gulf of carpentaria field evidence is from coral reef flats and prograded coastal deposits the highest sea level on inner shelf islands and mainland coast occurred 5500 yrs ago the results of this and of certain previous studies are reduced to a common reference surface or isobase which varies systematically in elevation across the region the isobase correlates strongly with predicted hydro isostatic deformation caused by postglacial sea level rise

on the remote acoustic detection of suspended sediment at long wavelengths experimental results are presented which indicate a linear relation between the time averaged amplitude of the envelope of the backscattered acoustic pulse at 192 khz and the square root of suspended sediment concentration in the 10 to 103 mg 1 1 range particle sizes ranged from 2 to 140 m the measurements were made in a negatively buoyant mine tailing discharge plume in a submarine channel at depths of 60 to 90 m in rupert inlet british columbia from the theory of acoustic backscatter from a solid elastic sphere in the rayleigh region it is shown that if the pressure amplitude of the backscattered wave is rayleigh distributed then such a linear relation is to be expected expressions for the optimum acoustic frequency for the detection of dilute suspensions at a given range and for the minimum detectable concentration are obtained assuming a thermal noise background the possibility that bubbles contribute to the backscatter is considered and found to be unlikely on the basis of probable bubble lifetimes

quaternary stratigraphy geochronology and evolution of the magela creek catchment in the monsoon tropics of northern australia abstract magela creek a major tributary of the east alligator river in northern australia has left a detailed sedimentary record of a fluvial landscape dominated by climatic and eustatic changes associated with quaternary glacial interglacial cycles uranium series dates from young pisoliths in floodplain deposits indicate that ferruginisation is probably ongoing under present conditions while ferricretes in degraded terraces that flank the lower valley reveal a fluvial history extending back to early pleistocene or tertiary time inset within this older alluvium is a valley fill which from thermoluminescence dates was initiated about 300 kyr ago with each glacial climate change and associated fall in sea level distinct palaeochannels have been eroded into these floodplains infilling later with alluvium when climate and base level conditions were conducive to fluvial deposition radiocarbon dates show that the most recent palaeochannel beneath the modern magela creek last started to fill by downstream progradation and vertical accretion of bedload sand about 8 kyr the palaeochannel filled at an accelerating rate probably as a result of declining stream competence associated with drier conditions in the late holocene augmented by the backwater effects of sea level rise continued aggradation blocked the mouths of tributary valleys along magela creek forming alluvial dammed tributary lakes and deferred junction tributary streams from about 300 kyr cyclic episodes of channel incision and sediment evacuation in this tropical monsoon river valley have become less effective possibly because increasing aridity in the late quaternary has reduced the erosional effectiveness of australia s northern rivers reduced flow regime and rising sea level in the late holocene has resulted in the latest phase of alluvial accretion

first ever in situ observations of venus polar upper atmosphere density using the tracking data of the venus express atmospheric drag experiment vexade on its highly elliptical 24 h orbit around venus the venus express vex spacecraft briefly reaches a periapsis altitude of nominally 250 km recently however dedicated and intense radio tracking campaigns have taken place in august 2008 october 2009 february and april 2010 for which the periapsis altitude was lowered to the 186 176 km altitude range in order to be able to probe the upper atmosphere of venus above the north pole for the first time ever in situ as the spacecraft experiences atmospheric drag its trajectory is measurably perturbed during the periapsis pass allowing us to infer total atmospheric mass density at the periapsis altitude a precise orbit determination pod of the vex motion is performed through an iterative least squares fitting process to the doppler tracking data acquired by the vex radioscience experiment vera the drag acceleration is modelled using an initial atmospheric density model vts3 model hedin a e niemann h b kasprzak w t seiff a 1983 j geophys res 88 73 83 a scale factor of the drag acceleration is estimated for each periapsis pass which scales hedin s density model in order to best fit the radio tracking data reliable density scale factors have been obtained for 10 passes mainly from the second october 2009 and third april 2010 vexade campaigns which indicate a lower density by a factor of about 1 8 than hedin s model predicts these first ever in situ polar density measurements at solar minimum have allowed us to construct a diffusive equilibrium density model for venus thermosphere constrained in the lower thermosphere primarily by spicav soir measurements and above 175 km by the vexade drag measurements muller wodarg et al in preparation the preliminary results of the vexade campaigns show that it is possible to obtain with the pod technique reliable estimates of venus upper atmosphere densities at an altitude of around 175 km future vexade campaigns will benefit from the planned further lowering of vex pericenter altitude to below 170 km 2011 elsevier inc

a 30 000 year record of extreme floods in tropical australia from relict plunge pool deposits implications for future climate change relict plunge pool sedimentary sequences provide much longer paleoflood records than normally provided by slackwater deposits and other previously reported paleoflood sedimentary signatures the only two relict plunge pool sedimentary sequences so far reported lie 300 km apart in tropical northern australia and provide a record of extreme floods for the last 30 000 years each of these sequences identify the early to mid holocene and the period immediately prior to the last glacial maximum as the two periods of greatest flood magnitudes of the late quaternary flood discharges at these times were up to five times greater than any floods experienced over the last 4 000 years most climate models predict that the magnitude and frequency of storms and rainfall events will increase under a warmer greenhouse climate the plunge pool sedimentary sequences however show that periods of greatly enhanced discharge compared to present can be associated with both warm wet and cool wet phases of climate

depositional model for a chenier plain gulf of carpentaria australia the southern coast of the gulf of carpentaria northern australia consists of a broad chenier plain which is comparable in size and morphology to those reported on the coasts of surinam and south western louisiana the carpentaria chenier plain has at some locations prograded over 30 km since the middle holocene by deposition of low tide muds over subtidal muds during periods of increased sediment input by the rivers chenier ridges are formed during periods of reduced sediment flux by wave induced sorting and redistribution processes an alternation of increased and decreased sediment flux from fluvial sources has occurred several times during the upper holocene such variation in sediment supply is believed to be related to temporal fluctuations in rainfall over the drainage basin which surrounds the southern and eastern gulf

depositional model of a macrotidal estuary and floodplain south alligator river northern australia the south alligator river northern territory of australia has a macrotidal estuary tidal influence spring tidal range 5 6 m at the mouth extends 105 km up the channel it is dominated by freshwater in the wet season december april with a salt wedge near the mouth but is well mixed and becomes saline throughout the dry season the tidal channel can be divided into four different channel types an estuarine funnel a sinuous meandering segment a cuspate meandering segment in which the inside of bends are pointed and an upstream tidal channel the distribution of morphologically defined land classes and morphological units within each land class on the floodplain flanking the estuary differs from one channel type to another several stratigraphic and morphostratigraphic units have been recognized from drill holes on the coastal and deltaic estuarine plains and a model of development is proposed on the basis of extensive radiocarbon chronology and palynology the coastal plain has prograded with most rapid sedimentation between 5000 and 3000 yr bp a similar pattern of progradation is identified in the estuarine funnel in the sinuous segment of the estuary the channel has migrated laterally across the floodplain previous channel positions are indicated by palaeochannels and the meander tract is occupied by laminated channel sediments within the cuspate segment there are numerous sinuous palaeochannels on the plains in the upstream segment the channel and palaeochannels have long straight reaches with irregular bends and discontinuous levees and channel avulsion is indicated mangrove mud is a widespread stratigraphic unit throughout the plains the initial phase of development is a transgressive phase 8000 6800 yr bp when mangrove forests extended landwards into a pre existing valley as sea level rose as sea level stabilized the transgressive phase was followed by a widespread mangrove phase termed the big swamp 6800 5300 yr bp the mangrove forests disappeared from most of the plains as vertical accretion continued and were replaced by grass and sedge covered floodplains during the sinuous phase about 5300 2500 yr bp the channel migrated laterally and eroded the deltaicestuarine plain and deposited lateral accretion deposits laminated channel sediments part of the channel of the south alligator river has then progressed from sinuous to cuspate in form and erosion of river banks has occurred transgressive and big swamp phases occurred under rising and stabilizing sea level respectively later morphodynamic channel adjustments occurred under conditions of stable sea level the depositional model has direct application to other estuaries in northern australia and may be applied to other areas where sea level change has been similar

late quaternary infilling of the assu river embayment and related sea level changes in ne brazil abstract a detailed geomorphological survey using light detection and ranging lidar was carried out along the western part of the assu river valley ne brazil the study was complemented by the investigation of sedimentological mineralogical and sediment benthic foraminifera indicators within the 14c geochronological framework the integration of data sets permitted the reconstruction of the main phases in the evolution of this area during the holocene the shallow embayment which is now completely infilled acquired its present form within the limits of antecedent morphology developed since the last interglacial period the main forcing factors responsible for repositioning the shoreline which ran along the strike slip afonso bezerra fault at an angle of approximately 35 to the present coast in the early mid holocene were as follows 1 tectonic activity along the strike slip afonso bezerra fault 2 fast inundation of the shallow paleo valley embayment during the last pulse of holocene transgression ca 8000 cal yr bp 3 advance of the assu river mouth through accretion of fluvial bay head delta and costal drift sediments and 4 sheltering of embayment by barrier islands which permitted a widespread development of mangrove forest during the last 3 millennia the estimated rate of progradation of the assu estuary that led to the present stage of terminal infilling is in the order of 3 4 m yr

human environment interactions in australian drylands exploratory time series analysis of archaeological records exploratory time series analysis of radiocarbon data from archaeological contexts is used to reconstruct the population history of arid australia allowing this to be read in concert with records of climatic variability over the last 20 000 years probability distribution plots of 971 radiocarbon ages from 286 sites in five dryland regions the arid west coast pilbara and murchison nullarbor arid interior and the southeastern arid zone provide a proxy record of prehistoric population fluctuations in these areas there is regional variation but the radiocarbon density plots suggest a step wise pattern of population growth and expansion with significant thresholds at 19 8 and 1 5 cal kyr bp within this the plots suggest a saw tooth pattern of rapid population growth and decline on a 1 3 kyr frequency with a marked collapse of dryland hunter gatherer populations around 3 2 5 cal kyr bp affecting most regions comparison with climate data shows broad correlations with past temperature and rainfall

the oxbow sedimentary subenvironment its value in palaeogeographical studies as illustrated by selected fluvial systems in the upper odra catchment southern poland research was conducted in valleys of sinuous rivers that drain medium high mountain foreland basin and upland areas where loose quaternary deposits predominate the cyclic pattern determined for deposits of the oxbow sedimentary subenvironment in the upper odra basin can be expressed as a few alternative sequences the best developed cycle occurring on a relatively high level of probability is represented by the unilateral transition from channel to overbank deposits and upwards bilateral oscillations between overbank and biochemical as well as biochemical and slope deposits in the first stage oxbow filling processes are usually determined by autocyclic factors resulting from spatial relations between abandoned channels and the active channel as a consequence overbank and or biochemical sediments usually overlie channel deposits later allocyclic processes could easily dominate autocyclic processes in these cases overbank slope and late holocene alluvial fan deposits were delivered to oxbow

the thermal structure of the venus atmosphere intercomparison of venus express and ground based observations of vertical temperature and density profiles the venus international reference atmosphere vira model contains tabulated values of temperature and number densities obtained by the experiments on the venera entry probes pioneer venus orbiter and multi probe missions in the 1980s the instruments on the recent venus express orbiter mission generated a significant amount of new observational data on the vertical and horizontal structure of the venus atmosphere from 40 km to about 180 km altitude from april 2006 to november 2014 many ground based experiments have provided data on the upper atmosphere 90 130 km temperature structure since the publication of vira in 1985 the thermal structure of the venus atmosphere team was supported by the international space studies institute issi bern switzerland from 2013 to 2015 in order to combine and compare the ground based observations and the vex observations of the thermal structure as a first step towards generating an updated vira model results of this comparison are presented in five latitude bins and three local time bins by assuming hemispheric symmetry the intercomparison of the ground based and vex results provides for the first time a consistent picture of the temperature and density structure in the 40 km 180 km altitude range the venus express observations have considerably increased our knowledge of the venus atmospheric thermal structure above 40 km and provided new information above 100 km there are however still observational gaps in latitude and local time above certain regions considerable variability in the temperatures and densities is seen above 100 km but certain features appear to be systematically present such as a succession of warm and cool layers preliminary modeling studies support the existence of such layers in agreement with a global scale circulation the intercomparison focuses on average profiles but some vex experiments provide sufficient global coverage to identify solar thermal tidal components the differences between the vex temperature profiles and the vira below 0 1 mbar 95 km are small there is however a clear discrepancy at high latitudes in the 10 30 mbar 70 80 km range the vex observations will also allow the improvement of the empirical models vts3 by hedin et al 1983 and vira by keating et al 1985 above 0 03 mbar 100 km in particular the 100 150 km region where a sufficient observational coverage was previously missing the next steps in order to define the updated vira temperature structure up to 150 km altitude are 1 define the grid on which this database may be provided 2 fill what is possible with the results of the data intercomparison and 3 fill the observational gaps an interpolation between the datasets may be performed by using available general circulation models as guidelines an improved spatial coverage of observations is still necessary at all altitudes in latitude longitude and at all local solar times for a complete description of the atmospheric thermal structure in particular on the dayside above 100 km new in situ observations in the atmosphere below 40 km are missing an altitude region that cannot be accessed by occultation experiments all these questions need to be addressed by future missions

contrasting holocene sedimentary geologies of lower daly river northern australia and lower sepik ramu papua new guinea abstract the estuarine plain of the macrotidal daly river in monsoonal northern australia is underlain by extensive mid holocene mangrove swamp sediments which accumulated during the last stages of post glacial sea level rise sediment yield from the catchment is too low to account for the volume which accumulated during sea level rise and onshore transport is invoked this is supported by radiocarbon ages and facies analysis of the transgressive sediment tract beneath the maximum flooding surface mfs and of the tract of vertical sedimentation which extends from the mfs to the surface of estuarine fluvial transition the eft the eft occurred about 5000 to 6000 bp throughout the estuarine plain a contrasting situation exists in the lowland holocene basin of the microtidal sepik and ramu rivers in papua new guinea which derive sediment from highly tectonic catchments a tectonic basin which was a shallow brackish inland sea after post glacial transgression is separated by a low divide from a deltaic plain progradation of the deltaic plain commenced about 3500 bp after regressive sedimentation eclipsed the inland sea in the tectonic basin contrasting organic facies mangrove in the daly and freshwater swamp deposits in the sepik ramu highlight differences between facies models of the two systems differences between fluvio tidal regimes are reflected by the eft which is synchronous in the daly and diachronous in the sepik ramu and possibly by the mfs which is diachronous in the daly and may be synchronous in the sepik ramu

observation of atmospheric tides in the martian exosphere using mars reconnaissance orbiter radio tracking data 1 based on the perturbations of the trajectory of the mars reconnaissance orbiter due to atmospheric drag we estimate using precision orbit determination the density of the martian exosphere near 250 km altitude with much better temporal and therefore spatial resolution than previously possible with this method small longitudinal density variations are observed to be consistent over long time periods although they appear fixed with respect to the planet we interpret them as non migrating tides because of the sun synchronous spacecraft orbit similar tides were observed previously by mgs at much lower altitude 125 km and our results agree to first order with the mgs findings citation mazarico e m t zuber f g lemoine and d e smith 2008 observation of atmospheric tides in the martian exosphere using mars reconnaissance orbiter radio tracking data geophys res lett 35 l09202 doi 10 1029 2008gl033388

holocene development of the lower mary river plains northern territory australia extensive coastal and estuarine plains associated with several large seasonal rivers characterize the southern shore of van diemen gulf northern territory australia the mary river is unique among these rivers in that despite a catchment of 7700 km 2 it fails to reach the sea as a discrete channel but breaks up into a series of terminating multiple channels leaving much of the freshwater discharge to evaporate from the plains the extent and morphology of these plains have changed markedly during the holocene drilling radiocarbon dating and pollen analysis indicate a transgressive phase that began about 7000 years ago as the rising seas flooded the prior valley this was followed by a big swamp phase as sea level stabilized around 6000 years ago during which widespread mangrove forest development occurred rapid progradation of the coast occurred between 6000 and 4000 years bp the shoreline has prograded little since that time but has been modified by episodic chenier ridge deposition and palaeochannel abandonment infill and reoccupation the lower mary river differs from adjacent systems in that several former estuarine channels across the plains appear to have become completely blocked with sediment leaving low lying billabongs and palaeochannels which have been preferentially reinvaded by later channels several alternative explanations are examined but it remains unclear what has driven major variations in palaeochannel activity and sedimentation during the mid holocene and why these have decreased so markedly in the last 2000 years

morphological evolution of a well constrained subaerial subaqueous source to sink system wabush lake since 1964 the iron ore company of canada has deposited iron tailings resulting from mining operations into wabush lake western labrador canada this activity has resulted in a continuous hyperpycnal flow flowing over the lake floor bathymetric surveys were carried out between 1999 and 2008 as part of the overall environmental iron ore company of canada plans to maintain safe disposal strategies of tailings into the lake here this dataset is used to study the evolution of different channels present in wabush lake and their link with knickpoints found at the head of most of these channels the channels show notable evolution from one survey to the next some knickpoints and channels may be followed throughout more than one survey the evolution of these knickpoints is the process responsible for the creation of erosional channels the context in which they appear as well as the evolution of some of the subaqueous channels is analysed cyclic steps and sediment waves are also found in the lake these rhythmic bedforms also created by the passage of turbidity currents are analysed sediment waves found in wabush lake show values for both wavelength and wave height that are approximately one order of magnitude smaller than most of those found in the marine environment

holocene evolution of coastal wetlands in wet tropical northeastern australia pollen in sediments drilled from the innisfail coastal plain northeast queensland australia was examined to reconstruct the evolution of holocene wetlands in a wet tropical environment in contrast to monsoonal australia stable environmental conditions created by year round rainfall and low tidal range caused abrupt unidirectional transitions in wetland zonation as marine influence changed this has enabled a detailed reconstruction of the marine transgression and subsequent progradation mangroves colonized in response to marine transgression at c 7400 bp as riverine mangroves of low salt tolerance migrated up the mulgrave river these were replaced around 7000 bp by extensive rhizophora dominated mangroves coinciding with the development of a rhizophora dominated community in wyvuri embayment mangroves reached their greatest extent as sea level rise slowed towards 6000 bp with a stillstand indicated by a brief return to terrestrial conditions at one site high freshwater input depressed salt i

estuarine infill and coastal progradation southern van diemen gulf northern australia abstract there are several estuaries associated with the pronouncedly seasonal rivers which drain northwards from the middle proterozoic sandstone arnhem land plateau and the tertiary koolpinyah land surface into the macrotidal van diemen gulf in the northern territory of australia the holocene development of these investigated in greatest detail for the south alligator river with an upland catchment of 10 000 km2 through drilling palynology and radiocarbon dating comprises both estuarine infill and coastal progradation three phases of estuarine infill can be recognised i a transgressive phase 8000 6800 years b p of marine incursion ii a big swamp phase 6800 5300 years b p of widespread mangrove forest development and iii a sinuous cuspate phase of floodplain development since 5300 years b p during which the tidal river has meandered and reworked earlier estuarine sediments since 6000 years b p the south alligator coastal plain has prograded at a decelerating rate with two phases of chenier ridge formation a similar pattern of estuarine infill and decelerating coastal plain progradation is demonstrated for the adelaide and mary rivers both with catchments of 6000 km2 the southern shore of van diemem gulf appears to have changed its overall position little during the last 2000 years the major source for the clay silt and fine sands which have infilled the estuary and coastal plain has been from seaward dispite the similarity of development coastal sediment build up has had different effects on the morphology of each tidal river the adelaide has undergone a major diversion and no longer flows directly into van diemen gulf but occupies a former fluvial course and the mary has been blocked entirely and its former estuarine palaeochannels have been infilled with tide transported sediment

late quaternary vegetation and climate change in the panama basin palynological evidence from marine cores odp 677b and tr 163 38 abstract the late quaternary paleoenvironmental history from pacific slopes of the western andes is reconstructed by pollen analysis of 32 samples from two marine sediment cores from the panama basin eastern equatorial pacific core odp 677b 83 44 2200 w 1 12 1440 n 3473 m water depth is 185 cm long and spans the last 39 410 years core tr 163 38 81 583 w 1 337 n 2200 m water depth is 103 cm long and covers the last 17 380 years six ecological groups were established mangrove brackish and fresh water swamps terra firma lowland forests broad range taxa andean forests and open vegetation a good correspondence was found between the changes of these ecological groups in the two cores the records evidence the continuous presence of all vegetation types during the last 39 410 years and specially the uninterrupted occurrence of tropical rain forest they record a development from 1 a cold and humid phase 39 410 28 120 yr cal bp with moderately high sea levels 2 the coldest and driest phase in the record 28 120 14 500 yr cal bp accompanied by the lowest sea levels 3 a transitional phase when sea level rose and humid conditions dominated 4 a stage 11 300 5600 yr cal bp of the highest sea levels and moisture conditions including a drier period 7000 yr bp to 5 a final period 5600 yr cal bp present when sea level reached its present height humidity persisted and indicators of disturbance expanded peaks in pollen and spore concentration associated with high river discharge periods indicate periods of higher precipitation around 33 500 28 000 and 12 000 9000 yr cal bp although main vegetation responses seem to reflect rainfall and moisture variations a good correspondence was found between 18o values and percentages of andean and lowland pollen suggesting that vegetation also responded to tempearture changes

early diagenesis of copper and molybdenum in mine tailings and natural sediments in rupert and holberg inlets british columbia the distribution and behaviour of cu and mo in interstitial waters collected from cu and mo rich mine tailings and natural sediments in rupert and holberg inlets vancouver island british columbia are discussed dissolved fe mn and h2s distributions and solid phase cu mo mn and organic carbon data are used to constrain the interpretation of cu and mo diagenesis in both tailings and natural sediment facies cu is released to solution at or near the sediment water interface in both facies either by decomposing labile organic material or as a probable result of oxidation of sulphide minerals within the tailings mo is significantly enriched up to 0 6 mol l 1 in tailings pore water probably as a result of dissolution of soluble mo oxides produced initially by oxidation of mos2 during milling of the ore in natural sediments both cu and mo are removed from solution at depth probably by precipitation as their sulphides or in solid solution with an iron sulphide phase similar reactions appear t

altimetry of the venus cloud tops from the venus express observations 1 simultaneous observations of venus by visible and infrared thermal imaging spectrometer and venus monitoring camera onboard the venus express spacecraft are used to map the cloud top altitude and to relate it to the ultraviolet uv markings the cloud top altitude is retrieved from the depth of co2 absorption band at 1 6 m in low and middle latitudes the cloud top is located at 74 1 km it decreases poleward of 50 and reaches 63 69 km in the polar regions this depression coincides with the eye of the planetary vortex at the same latitude and hour angle cloud top can experience fast variations of about 1 km in tens of hours while larger long term variations of several kilometers have been observed only at high latitudes uv markings correlate with the cloud altimetry however the difference between adjacent uv dark and bright regions does not exceed several hundred meters surprisingly co2 absorption bands are often weaker in the dark uv features indicating that these clouds may be a few hundred meters higher or have a larger scale height than neighboring clouds ultraviolet dark spiral arms which are often seen at about 70 correspond to higher altitudes or to the regions with strong latitudinal gradient of the cloud top altitude cloud altimetry in the polar region reveals the structure that correlates with the thermal emission maps but is invisible in uv images this implies that the uv optically thick polar hood is transparent in the near ir

morphology and dynamics of the upper cloud layer of venus esa s venus express probe has been in orbit since april 2006 eight research papers in this issue present new results from the mission covering the atmosphere polar features interactions with the solar wind and the controversial matter of venusian lightning hakan svedham et al open the section with a review of the similarities and mostly differences between venus and its twin the earth andrew ingersoll considers the latest results and also how the project teams plan to make the most of the probe s remaining six years of life venus is completely covered by a thick cloud layer with the cloud tops in fast retrograde rotation global and small scale properties of these clouds and their temporal and latitudinal variations are investigated and the wind velocities are derived the southern polar region is highly variable and can change dramatically on time scales as short as one day perhaps arising from the injection of so2 into the mesosphere venus is completely covered by a thick cloud layer of which the upper part is composed of sulphuric acid and some unknown aerosols1 the cloud tops are in fast retrograde rotation super rotation but the factors responsible for this super rotation are unknown2 here we report observations of venus with the venus monitoring camera3 on board the venus express spacecraft we investigate both global and small scale properties of the clouds their temporal and latitudinal variations and derive wind velocities the southern polar region is highly variable and can change dramatically on timescales as short as one day perhaps arising from the injection of so2 into the mesosphere the convective cells in the vicinity of the subsolar point are much smaller than previously inferred4 5 6 which we interpret as indicating that they are confined to the upper cloud layer contrary to previous conclusions7 8 but consistent with more recent study9

the evolution time scale of macro tidal estuaries examples from the pacific rim the evolution of shallow macro tidal estuaries is a process that has been taking place since the last glaciation it is site specific and dependent on tides wave climate and relative fluvial dominance it is suggested that because of the increased efficiency of the tidal pumping effect with decreasing water depth these estuaries are geomorphologically unstable and may evolve much faster in the future than in the past as a result of human disturbances in the catchment principally the damming of rivers and increasing erosion from poor land use practices these estuaries may become further destabilised by a sea level rise

tidal creek extension and saltwater intrusion in northern australia low lying holocene coastal plains supporting freshwater wetlands are often close to or even below the level reached by the highest tides the vulnerability of such freshwater systems to saltwater intrusion will increase should the sea level rise as a consequence of global warming in areas with a large tidal range one of the main processes inducing a reversion to saltwater influence is likely to be the rapid extension of tidal creek systems this is demonstrated with an example from the coastal plains of the mary river in northern australia where tidal creek systems have extended more than 30 km inland in 50 years invading freshwater wetlands and destroying associated vegetation over an area of at least 17000 ha networks have grown at an exponential rate through a combination of headward extension along main channels and tributary development large tidal range very small elevational differences over the plains the presence of incompletely infilled paleochannels and uncontrolled feral buffalo have been major factors contributing to the rapid rate of expansion