resolving mass flux at high spatial and temporal resolution using grace intersatellite measurements 1 the grace mission is designed to monitor mass flux on the earth s surface at one month and high spatial resolution through the estimation of monthly gravity fields although this approach has been largely successful information at submonthly time scales can be lost or even aliased through the estimation of static monthly parameters through an analysis of the grace data residuals we show that the fundamental temporal and spatial resolution of the grace data is 10 days and 400 km we present an approach similar in concept to altimetric methods that recovers submonthly mass flux at a high spatial resolution using 4 4 blocks at 10 day intervals we estimate the mass of surplus or deficit water over a 52 60 grid centered on the amazon basin for july 2003 we demonstrate that the recovered signals are coherent and correlate well with the expected hydrological signal

tidal mixing and trapping in mangrove swamps lateral trapping in mangrove swamps is a dominant process controlling longitudinal mixing in mangrove fringed tidal rivers in the dry season the effective value of the longitudinal diffusivity is increased by the trapping effect by typically two orders of magnitude from its value in the absence of swamps in the wet season freshwater is trapped within the swamp and the adjoining boundary in the tidal river for long periods following the passage of a short lived flood this may have important ecological implications a fluid mud layer appears to be created by strong tidal currents over colloidal mangrove mud

marine transgression and dune initiation on western cape york northern australia abstract the chronostratigraphy of the coastal dunes on the western side of northern cape york differs from the general pattern of dune emplacement identified on easterly facing coasts across northern australia two episodes of dune emplacement are suggested by morphology prior to the establishment of the modern foredune tl dating and comparative soil profile development indicate the possibility of three episodes based on a small number of tl dates it is possible to associate dune emplacements at about 11 200 yrs b p 8300 yrs b p and 5200 yrs b p with shoreline disturbance and the destruction of shoreline vegetation by rising sea level stabilisation of the 11 200 yrs b p unit may be due to a short marine regression roughly around the time of the younger dryas the 8300 yrs b p unit probably stabilised due to changed environmental conditions and the 5200 yrs b p unit represents the cessation of post glacial sea level rise in northern australia

island ecosystem and biodiversity dynamics in northeastern australia during the holocene unravelling short term impacts and long term drivers vegetation changes of tropical lizard island great barrier reef world heritage area australia over the last 8000 years are derived from palaeoenvironmental analysis of a 475 cm long sediment core during early holocene sea level rise flooding of the continental shelf and thus isolation of lizard island the pollen record shows the gradual establishment of a mangrove forest paralleled by contraction of the near coastal palm and grass dominated vegetation subsequently mid holocene relative environmental stability supported a diverse rhizophora dominated mangrove and open mixed sclerophyll vegetation inland around 6000 years ago a profound disturbance of the mangrove is recorded by a siliciclastic layer and we hypothesise that this deposit documents the impact of a storm or cyclone postevent environmental conditions were strongly altered with enhanced estuarine conditions supporting a sonneratia and bruguiera dominated mangrove forest during late holocene sea level fall and stabilisation prograd

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

mid holocene palaeolimnological record of a southern hemisphere subtropical lake spanning the last 6000 years lake jennings fraser island australia the study of climate mechanisms in the southern hemisphere during the holocene remains an area of active research that lacks the spatial and temporal connectivity characteristic of northern hemisphere research the subtropical temperate climate transition zone of eastern australia provides a unique location to investigate long term environmental changes during the holocene lake jennings on fraser island was used to investigate climate change in this transition zone using palaeolimnological techniques the beginning of the lake jennings record 6000 to 3500 cal ybp is characterised by fluctuations in geochemical signals an abundance of sponge spicules and a lack of diatom species results suggest gradually increasing precipitation and water depth which affect nutrient cycling however the biological functioning of the lake is difficult to interpret due to the absence of diatoms possibly a result of turbidity dissolution and or predation by freshwater sponges during the late holocene 3500 cal

crustal dilatation observed by grace after the 2004 sumatra andaman earthquake we report the detection of an earthquake by a space based measurement the gravity recovery and climate experiment grace satellites observed a 15 microgalileo gravity change induced by the great december 2004 sumatra andaman earthquake coseismic deformation produces sudden changes in the gravity field by vertical displacement of earth s layered density structure and by changing the densities of the crust and mantle grace s sensitivity to the long spatial wavelength of gravity changes resulted in roughly equal contributions of vertical displacement and dilatation effects in the gravity measurements the grace observations provide evidence of crustal dilatation resulting from an undersea earthquake

residual ocean tide signals from satellite altimetry grace gravity fields and hydrodynamic modelling summary improvements of a global state of the art ocean tide model are identified and quantified by applying three independent approaches namely i empirical ocean tide analysis of multimission altimeter data ii evaluation of grace data and gravity field models and iii high resolution hydrodynamic modelling although these approaches have different capabilities to sense ocean tides they obtain results which are basically consistent one with each other the analysis of altimeter data clearly identifies significant residual amplitudes over shallow water for all major diurnal and semidiurnal constituents and the non linear tide m4 grace data and the time series of monthly gravity field models exhibit on a larger scale residual ocean tide signals over much the same areas the analysis of dynamic residuals of hydrodynamic modelling with data assimilation proves the validity of linear dynamics in the deep ocean and shows correlation of dynamic residuals with energy dissipation in these areas

grace measurements of mass variability in the earth system monthly gravity field estimates made by the twin gravity recovery and climate experiment grace satellites have a geoid height accuracy of 2 to 3 millimeters at a spatial resolution as small as 400 kilometers the annual cycle in the geoid variations up to 10 millimeters in some regions peaked predominantly in the spring and fall seasons geoid variations observed over south america that can be largely attributed to surface water and groundwater changes show a clear separation between the large amazon watershed and the smaller watersheds to the north such observations will help hydrologists to connect processes at traditional length scales tens of kilometers or less to those at regional and global scales

late quaternary environments of the carpentaria basin australia abstract quaternary variations in the level of the sea have exposed the shallow 29 000 km2 but shallow maximum depth s 4 0 kyr the pollen assemblages closely resemble the black soil plains presently found along the southern gulf thus the biogeographic and climatic barrier across the australia papua new guinea land bridge has remained largely intact in spite of the range of environmental conditions that have occured during the last

tide model errors and grace gravimetry towards a more realistic assessment summary the manner in which errors in tide models affect monthly gravity solutions from grace satellite data is re examined we perform a complete simulation of grace gravity estimation including allowance for accelerometer calibrations and satellite state vector adjustment errors in monthly geoid estimates are for most regions of a order of 0 5 mm or roughly 1 cm of equivalent water height when smoothed over radii of 600 km in polar regions where ocean tide models are suspect errors can grow significantly larger over 2 mm in geoid height although over very localized regions errors from diurnal tides tend to cancel but they are not completely eliminated inducing geoid errors of the order of 0 3 mm the currently accepted grace total error budget is roughly an order of magnitude larger than the component arising from tide modelling errors

regional surface mass anomalies from grace kbr measurements application of l curve regularization anda priori hydrological knowledge 1 we present a method of directly estimating surface mass anomalies at regional scales using satellite to satellite k band ranging kbr data from the gravity recovery and climate experiment grace twin satellite mission geopotential differences based primarily on kbr measurement are derived using a modified energy integral method with an improved method to calibrate accelerometer measurements surface mass anomalies are computed based on a downward continuation process with optimal regularization parameters estimated using the l curve criterion method we derive the covariance functions in both space and space time domains and use them as light constraints in the regional gravity estimation process in the amazon basin study region the space time covariance function has a time correlation distance of 1 27 months which is evident that observations between neighboring months are correlated and the correlation should be taken into account however most of the current grace solutions did not consider such temporal correlations in our study the artifact in the regional gravity solution is mitigated by using the covariance functions the averaged commission errors are estimated to be only 6 86 and 5 85 for the solutions based on the space covariance function scf and the space time covariance function stcf respectively our regional gravity solution in the amazon basin study region which requires no further post processing shows enhanced regional gravity signatures reduced gravity artifacts and the gravity solution agrees with nasa gsfc s grace mascon solution to about 1 cm rms in terms of water thickness change over the amazon basin study region the regional gravity solution also retains the maximum signal energy while suppressing the short wavelength errors

currents and sediment transport in mangrove forests abstract a field study of the tidal currents cohesive sediment dynamics and transport of organic carbon in a highly vegetated mangrove swamp was carried out at middle creek cairns australia the interaction of tidal currents and the vegetation generated jets eddies and zones of stagnant waters which were numerically modelled a high value of the manning friction coefficient n 0 1 was derived by the dense vegetation about 80 of the suspended sediment brought in from coastal waters at spring flood tide was trapped in the mangroves corresponding to about 10 12 kg of sediment m 1creek length spring tide resulting in a rise of the substrate by about 0 1 cm year 1 the selective trapping of clay was caused by flocculation of the finer particles in the mangroves there was an indication of a slight inwelling of organic carbon creek water was readily differentiated from mangrove water by large differences in the molecular weight distribution of the dissolved organic carbon

the mangrove pump the tidal flushing of animal burrows in a tropical mangrove forest determined from radionuclide budgets abstract intertidal mangrove forests contribute significantly to biogeochemical solute budgets of tropical and subtropical coastlines a significant part of the biogeochemical cycling in mangrove ecosystems occurs within the subsurface of the forest floor this subsurface source and the offshore sink are linked by the tidally driven movement of water through the mangrove forest floor the tidal circulation through animal macro burrows in the coral creek mangrove forest area 3 km 2 on hinchinbrook island australia is documented by constructing mass balances of isotopes of radium and radon measured in the creek in 1997 and 2005 respectively isotope activities in burrows were found to be significantly greater than in the adjacent mangrove creek e g for 222 rn 680 1750 and 30 170 bq m 3 in burrows and creek respectively from isotope mass balances a daily water circulation flux through burrows of 30 4 4 7 l m 2 of forest floor is calculated this study quantifies the underlying physical process i e the tidal flushing of burrows that supports significant and continuous exports of soluble organic and inorganic matter from mangrove forest floors to the coastal ocean the potential significance of the circulation flux estimate is illustrated by up scaling of the forest scale estimates to the mangrove forests in the entire central great barrier reef this extrapolation indicates that the annual water flux circulated by this tidally driven mangrove pump is equivalent to as much as 20 16 22 of the total annual river discharge along the ca 400 km long coastline of this region

time variable gravity from grace first results eleven monthly grace gravity field solutions are now available for analyses we show those fields can be used to recover monthly changes in water storage both on land and in the ocean to accuracies of 1 5 cm of water thickness when smoothed over 1000 km the amplitude of the annually varying signal can be determined to 1 0 cm results are 30 better for a 1500 km smoothing radius and 40 worse for a 750 km radius we estimate the annually varying component of water storage for three large drainage basins the mississippi the amazon and a region draining into the bay of bengal to accuracies of 1 0 1 5 cm

improved estimation of terrestrial water storage changes from grace 1 the temporal variations in the earth s gravity field caused by fluctuations in terrestrial water mass can be inferred from changes in grace monthly gravity field solutions such methods have limited spatial resolution due to a necessary and possibly arbitrary truncation and smoothing of the coefficients limiting the temporal resolution to one month was necessary to solve the gravity field by a global representation our alternative method uses grace satellite to satellite tracking and accelerometer data to obtain the along track geopotential differences and directly estimate the temporal gravity variations regionally this method was tested on the estimation of hydrological mass anomaly over the amazon and orinoco river basins compared to conventional spherical harmonic methods the spatial extent of the estimated grace water height anomaly achieved finer resolution and is shown to follow more closely the boundaries of the river basins and significant systematic variation could be discerned at 15 day temporal resolutions

arctic ocean tides from grace satellite accelerations 1 models are routinely used to remove the effects of global ocean tides from grace data during processing to reduce temporal aliasing into monthly grace solutions these models have typically been derived using data from satellite altimeters such as topex poseidon therefore the arctic ocean components of tide models are not constrained by altimetry data potentially resulting in errors that are likely to alias into monthly grace gravity fields at all latitudes seven years of grace inter satellite accelerations are inverted to solve for corrections to the amplitude and phase of major solar and lunar ocean tides at latitudes north of 50 n using a mascon approach the tide model originally applied to our data was fes2004 truncated to maximum degree lmax 90 simulations are performed to verify that our inversion algorithm works as designed uncertainty estimates are derived from tidal solutions on land and by subtracting two independent solutions that each use 3 5 years of data features above the noise floor in the m2 k1 s2 and o1 solutions likely represent errors in fes2004 errors due to truncating the spherical harmonic expansion of fes2004 are too small and errors in the land mask model needed to transform sea surface heights into mass only affect coastal areas and do not produce similar relative amplitudes for any examined tides in the oceans north of 50 n these residuals tend to reduce the fes2004 amplitudes for m2 k1 s2 and o1 reductions in the variance of accelerations not used in our inversion suggest that our results can be used to improve grace processing

thermoluminescence dating of dune podzols at cape arnhem northern australia abstract quaternary lithostratigraphic units in coastal dunes have been dated at two locations in the dune fields near cape arnhem northern australia using coarse fraction thermoluminescence tl dating fifteen tl dates were measured five main chronostratigraphic units were identified which include a late pleistocene unit ca 19 000 yr an early holocene unit ca 9000 6500 yr a mid holocene unit ca 4000 yr and two late holocene units ca 2100 yr and ca 1000 yr these respectively have been associated with the deflation of exposed shelf sediments during the last glacial the disturbance of this material by rising sea level and climatic variations in the late holocene

late quaternary cycles of mangrove development and decline on the north australian continental shelf mangrove communities in the australian tropics presently occur as narrow belts of vegetation in estuaries and on sheltered muddy coasts palynological data from continental shelf and deep sea cores indicate a long term cyclical component of mangrove development and decline at a regional scale which can be linked to specific phases of late quaternary sealevel change extensive mangrove development relative to today occurs during periods of marine transgression whereas very diminished mangrove occurs during marine regressions and during rarer periods of relative sea level stability episodes of flourishing mangrove cannot be linked to phases of humid climate as has been suggested in studies elsewhere rather the cycle of expansion and decline of mangrove communities on a grand scale is explained in terms of contrasting physiographic settings characteristic of continental shelf coasts during transgressive and regressive phases in particular by the existence or lack of well developed tidal estuaries copyright c 1999 john wiley sons ltd

a holocene pollen record from lowland tropical australia a pollen record from a dunefield lake on groote eylandt northern australia is presented this is the first substantially complete holocene terrestrial record from the seasonally humid lowland tropics of northern australia the lake originated as a seasonal swamp prior to 10 000 bp a progressive rise in water tables occurred until a permanent lake was established at about 9000 bp from 9000 to 7500 bp the lake shows evidence of disruption in the surrounding dunefield prior to 7500 bp an open grassland covered the dunefield after 7500 bp the area was rapidly colonized by eucalyptus open forest and acacias these types remain dominant to the present the data suggest that conditions continuously ameliorated from the base of the record to the mid holocene and there is evidence of an effective precipitation maximum at about 4000 bp effective precipitation declined after 3800 bp but a recovery took place about 1000 bp

a new tide model for the antarctic ice shelves and seas we describe a new tide model for the seas surrounding antarctica including the ocean cavities under the floating ice shelves the model uses data assimilation to improve its fit to available data typical peak to peak tide ranges on ice shelves are 1 2 m but can exceed 3 m for the filchner ronne and larsen ice shelves in the weddell sea spring tidal ranges are about twice these values model performance is judged relative to the 5 10 cm accuracy that is needed to fully utilize ice shelf height data that will be collected with the geoscience laser altimeter system scheduled to be launched on the ice cloud and land elevation satellite in late 2002 the model does not yet achieve this level of accuracy except very near the few high quality tidal records that have been assimilated into the model some improvement in predictive skill is expected from increased sophistication of model physics but we also require better definition of ice shelf grounding lines and more accurate water column thickness data in shelf seas and under the ice shelves long duration tide measurements bottom pressure gauge or gps in critical data sparse areas particularly near and on the filchner ronne and ross ice shelves and pine island bay are required to improve the performance of the data assimilation model

the use of computational fluid dynamics in predicting the tidal flushing of animal burrows numerical hydrodynamic modelling has been used extensively over the last few decades to simulate flow in the ocean bays and estuaries however modelling of much smaller scale phenomena is less common in this work a commercially available computational fluid dynamics package fidap normally used for industrial applications was used to simulate tidally induced flow in multi opening animal burrows u shaped burrows of varying complexities were modelled to determine the effect of different surface characteristics and burrow geometries on surface water velocities burrow velocities and burrow flushing times the turbulent 2d model showed the slope of the surface water was proportional to the square of both the surface and burrow velocities the effect of placing a root in the surface flow was to reduce the surface water velocity however the burrow flow depended upon the root position for the root location either upstream or downstream of the burrow the burrow velocity was reduced by 50 with the root located between the burrow openings the burrow velocity increased by 200 due to the increase in pressure difference across the burrow openings a buttress root placed in the flow immediately downstream of the upstream burrow caused the burrow flushing rate to increase significantly with increasing buttress height flushing times for burrows of varying depth were determined computationally by use of a tracer for the burrow water for a burrow of depth 1 2 m the flushing times were 5 and 28 min for root location between the burrow openings and downstream of the burrow respectively animal burrows often consist of multiply connected loops a second burrow was added to the primary burrow and flushing times were found to be 15 and 38 min respectively a burrow system of four connected burrows was modelled which had corresponding flushing times up to 24 and 47 min respectively the calculated times are consistent with the hypothesis that a significant flushing of animal burrows occurs within a single tidal event this preliminary investigation indicates that cfd models may be very useful in studying small scale hydrodynamic phenomena such as flow in animal burrows

redating the onset of burning at lynch s crater north queensland implications for human settlement in australia lynch s crater preserves a continuous high resolution record of environmental changes in north queensland this record suggests a marked increase in burning that appears to be independent of any known major climatic boundaries this increase is accompanied or closely followed by the virtually complete replacement of rainforest by sclerophyll vegetation the absence of any major climatic shift associated with this increase in fire frequency therefore has been interpreted as a result of early human impact in the area the age for this increase in burning on the basis of conventional radiocarbon dating was previously thought to be approximately 38000 c 14 yr bp supporting the traditional model for human arrival in australia at 40 000 c 14 yr bp here we have applied a more rigorous pre treatment and graphitisation procedure for radiocarbon dating samples from the lynch s crater sequence these new dates suggest that the increase in fire frequency occurred at 45 000 c 14 yr bp supporting the alternative view that human occupation of australia occurred by at least 45 000 55 000 cal yr bp copyright c 2001 john wiley sons ltd

holocene diatom records of wetland development near weipa cape york australia abstract to better understand the response of tropical wetlands to holocene environmental changes two lacustrine diatom records from weipa cape york have been investigated the record from big willum bw01 commenced approx 7 9 calibrated thousand years before present k cal a bp and details stages of initial swamp development a phase of ephemeral conditions between approximately 5 7 and 2 2 k cal a bp and relative wetland stability after 2 2 k cal a bp lithological and to a lesser extent diatom assemblage changes in bw01 appear to be linked to broad scale changes in effective precipitation the record from little willum lw01 commenced around 0 9 k cal a bp and documents initial phases of swamp development until approximately 0 8 k cal a bp with subsequent relative wetland stability the uppermost 10 cm of this record approximately spanning the last 40 years coincide with mining activity in the region only minor changes in the diatom assemblage are recorded for this period implying that the overall character of the swamp probably remained unchanged both sites offer new insights into wetland dynamics in australia s dry tropics and demonstrate that changes in these lacustrine systems were probably driven by shifts in effective precipitation in particular during the late holocene

the last glacial cycle from the humid tropics of northeastern australia comparison of a terrestrial and a marine record a detailed pollen record from the ocean drilling program site 820 core located on the upper part of the continental slope off the coast of northeast queensland was constructed to compare with the existing pollen record from lynch s crater on the adjacent atherton tableland and allow the production of a regional picture of vegetation and environmental change through the last glacial cycle some broad similarities in patterns of vegetation change are revealed despite the differences between sites and their pollen catchments which can be related largely to global climate and sea level changes the original estimated time scale of the lynch s crater record is largely confirmed from comparison with the more thoroughly dated odp record conversely the lynch s crater pollen record has assisted in dating problematic parts of the odp record in contrast to lynch s crater which reveals a sharp and sustained reduction in drier araucarian forest around 38 000 yrs bp considered to have been the result of burning by aboriginal people the odp record indicates most likely a stepwise reduction dating from 140 000 yrs bp or beyond the earliest reduction shows lack of a clear connection between araucaria decline and increased burning and suggests that people may not have been involved at this stage however a further decline in araucarian forest possibly around 45 000 yrs bp which has a more substantial environmental impact and is not related to a time of major climate change is likely at least partially the result of human burning the suggestion from the odp core oxygen isotope record of a regional sea surface temperature increase of around 4 degrees c between about 400 000 and 250 000 yrs bp may have had some influence on the overall decline in araucaria and its replacement by sclerophyll vegetation c 2000 elsevier science b v all rights reserved

diatom inferred salinity and carbonate oxygen isotopes in holocene waterbodies of the western sahara and sahel africa abstract thirteen holocene palaeolakes in the western sahara and sahel have provided diatom records with carbonate oxygen isotope profiles available from eight of them most of these palaeolakes were groundwater fed lake water chemistry is reconstructed using diatom transfer functions lake water salinity and 18 o records are assembled with some isotopic and chemical groundwater data to better understand the response of the hydrological systems to climate changes over the past 15 000 yr data are in general agreement with climate simulations using coupled atmosphere ocean vegetation models which show a mid holocene wetting over the whole of northwest africa and a rapid drying by 6 4 ka the lake record also shows that at many sites the major lake infilling lags the end of the younger dryas by 1 2 ka regional differences also appear in the timing of the lake hydrological optimum ca 10 5 8 5 and 7 5 4 5 ka in the northern sahara 10 8 5 ka in the air tenere 10 5 7 or 4 5 in the sahel and 7 5 ka in lake chad the whole of the holocene is punctuated by short term drying events changes in water isotopic composition through time are partly explained by changes in rainfall amount and air humidity during the wet holocene period however the very low values in the southern sahara also imply changes in the moisture transport pattern or rainfall mechanisms data suggest an apparent decrease in 18 o content of precipitation along the monsoon flow in contrast with modern patterns changes in water availability and quality have driven population migrations in and out of the sahara sahel but relationships between climate and cultures are complex short term dry events might have driven inventive adaptations in the sahara drying at 5 4 5 ka coincides with both the collapse of the classical neolithic civilization and the settlement of new cultures

gravity recovery and climate experiment grace alias error from ocean tides 1 gravity recovery and climate experiment grace is able to observe interannual and longer period mass redistribution driven by climate changes however alias errors due to inaccurate ocean tide models may contaminate these signals to quantify this problem we estimate alias contamination due to expected errors in eight tidal constituents q1 o1 p1 k1 n2 m2 s2 and k2 for the period august 2002 to february 2006 differences between got00 2 and tpxo6 2 tide models are used as estimates of tide model errors the alias estimate is based on an approximate method employing least squares fits of spherical harmonics to potential differences between the two grace satellites results from this method are similar to previous estimates confirming this is a useful and efficient way to study the alias problem new findings are 1 the period of the m2 tide alias is about 140 d much longer than the predicted period 13 5 d because of monthly sampling of the 13 5 d period 2 there are two alias periods for k1 one about 90 d and one longer than 7 years and 3 the slow decay in the grace orbit causes tide component aliases to differ from pure frequencies as the orbit evolves we also find that aliases can contaminate in both space and time and thus may affect estimates of mass changes over land finally we compare the simulated s2 alias with the estimated s2 alias in grace data they are similar but our approximate method appears to overestimate alias error over high latitude oceans and along certain coastlines while underestimating error over low latitude oceans

the gravity recovery and climate experiment mission overview and early results 1 the grace mission is designed to track changes in the earth s gravity field for a period of five years launched in march 2002 the two grace satellites have collected nearly two years of data a span of data available during the commissioning phase was used to obtain initial gravity models the gravity models developed with this data are more than an order of magnitude better at the long and mid wavelengths than previous models the error estimates indicate a 2 cm accuracy uniformly over the land and ocean regions a consequence of the highly accurate global and homogenous nature of the grace data these early results are a strong affirmation of the grace mission concept

aridity in australia pleistocene records of palaeohydrological and palaeoecological change from the perched lake sediments of fraser island queensland australia abstract a quaternary sedimentary sequence ca 600 ka from a perched lake old lake coomboo depression on the world heritage listed coastal sandmass of fraser island has been analysed for dry bulk density carbonised particles pollen and chemistry a chronology has been constructed for the organic sediments using a combination of radiocarbon and uranium thorium disequilibrium analysis the lake basin is small ca 9 ha with a restricted groundwater catchment delimited by an aquitard and minimal surface runoff it therefore acts as a sensitive raingauge with the perched groundwater table and hence the sediment facies deposited within the lake reacting sensitively to any changes in the water budget the sequence passes through a series of glacial cycles demonstrating hydrologic and vegetation change the record indicates a long term three stage fall in the water table from lake full ca 600 ka to an ephemeral lake in the holocene paralleled by a shift in the vegetation composition from predominantly rainforest to sclerophyllous components the evidence for fire is minimal at the beginning of the record increases from 350 ka through the sequence culminating at or before the lgm is low during the lgm and is relatively high during the holocene succession fire and climatic change along with the accumulative effect of a series of 100 ka cycles are believed to have driven the hydrologic and vegetation change and a human factor is not required to explain the record within the overall long term increase in aridity recorded through about six glacial cycles there appears to be a variation in the dryness signal of glacial maxima suggesting some form of supercycle phenomenon this record complements and extends the information available from some of the oldest pollen analysed quaternary lake sequences in australasia such as lynch s crater in the atherton tableland of north queensland and lake george in the southern tablelands of new south wales and from some of the most sensitive lacustrine fluvial sedimentary records in the lake eyre basin signals for major environmental changes recorded in deep sea cores and the loess deposits of china may also be represented in the record the implications of the depression record if further corroborated are significant in relation to climatic modelling rainforest survival and faunal extinction

the tidal flushing of multiple loop animal burrows tidal flushing of animal burrows in mangrove swamps provides an effective and important mechanism for transport of salt and other soluble substances the burrows have complex morphologies consisting of multiple loops using established computational modelling techniques burrow geometries were simulated from characteristic burrow dimensions and the effect of multiple loops on flushing is studied the computational models show that flushing is enhanced in multiple loop burrows as upper loops can be completely evacuated increasing the volume of burrow water removed the models indicate that there may be a depth limit to which flushing occurs in complex burrow structures periscope loops extend further than one characteristic loop depth and are shown to affect the flushing of burrows if the surface water plume penetrates to their lower depth periscope loops with surface openings on the downstream side of the burrow relative to the tidal inundation most frequently experience this condition and thus have a great impact on burrow flushing field measurements of salinity agree with the hypothesis that there is a depth limit of flushing for complex burrows that is independent of burrow salinity and suggest a value of 30 35 cm the measurements also support the suggestion that significant flushing of burrows occurs within a single tidal event an experiment considered the movement of animals across the interface created by low salinity surface water and high salinity burrow water after a partial flushing event the motion enhances the effective diffusion coefficient of salt by a factor of at least 102 as compared with free diffusion of salt in water resulting in a more even distribution of dissolved salt in the burrow water between tidal inundations this distribution may lead to an increase in the depth to which flushing occurs during subsequent inundations

early holocene aridity in tropical northern australia thermoluminescence ages from a longitudinal dunefield in tropical northern australia suggest that complete dune activation occurred here either continuously or sporadically between approximately 8 2 ka and 5 9 ka this period in australia is normally ascribed to one of increasingly warm and wet conditions towards the holocene climatic optimum however elsewhere this time 8 ka coincides with a brief period of global climate change recognized in 18 o records from antarctica methane records of the greenland summit ice cores changes to deep sea benthic foraminferal composition and atmospheric 14 c variations in tropical africa two distinct phases of aridity have been dated at approximately 8 ka and 6 ka the coincidence of aeolian reacti vation episodes in this north australian dunefield with brief phases of early holocene climate change elsewhere suggests possible global climatic teleconnections at this time

diatom based transfer functions for inferring past hydrochemical characteristics of african lakes abstract a new dataset of 282 modern diatom samples and associated environmental information has been created by merging existing regional datasets from north and east africa and niger the relationships between diatom species distributions and hydrochemistry are examined using canonical correspondence analysis cca and partial cca variables reflecting water conductivity ph and cation and anion composition account for significant and independent components of the total variation in the diatom data predictive models transfer functions are developed using the method of weighted averaging for conductivity r 2 0 87 ph r 2 0 77 and ratios between alkali and alkaline earth metals r 2 0 81 and carbonate bicarbonate and sulphate chloride ions r 2 0 82 prediction errors are estimated using the computer intensive method of jackknifing these transfer functions enlarge the potential domain for reconstruction of past hydrochemistry from fossil diatoms preserved in lake sediments

palaeoenvironmental change in tropical australasia over the last 30 000 years a synthesis by the oz intimate group the tropics are the major source of heat and moisture for the australasian region determining the tropics response over time to changes in climate forcing mechanisms such as summer insolation and the effects of relative sea level on exposed continental shelves during the last glacial period is an ongoing process of re evaluation we present a synthesis of climate proxy data from tropical australasia spanning the last 30 000 years that incorporates deep sea core coral speleothem pollen charcoal and terrestrial sedimentary records today seasonal variability is governed largely by the annual migration of the inter tropical convergence zone itcz influencing this region most strongly during the austral summer however the position of the itcz has varied through time towards the end of marine isotope stage mis 3 conditions were far wetter throughout the region becoming drier first in the south universally cooler land and sea surface temperature sst were characteristic of the last glacial maximum with drier conditions than previously although episodic wet periods are noted in the fluvial records of northern australia the deglacial period saw warming first in the coral sea and then the indonesian seas with a pause in this trend around the time of the antarctic cold reversal c 14 5 ka coincident with the flooding of the sunda shelf wetter conditions occurred first in indonesia around 17 ka and northern australia after 14 ka the early holocene saw a peak in marine sst to the northwest and northeast of australia modern vegetation was first established on indonesia then progressively south and eastward to ne australia flores and the atherton tablelands show a dry period around 11 6 ka steadily becoming wetter through the early holocene the mid late holocene was punctuated by millennial scale variability associated with the el nino southern oscillation this is evident in the marine coral speleothem and pollen records of the region

on the equivocal fate of late pleistocene callitris vent cupressaceae woodlands in arid south australia fossil pollen assemblages suggest callitris cupressaceae dominated woodlands were prominent elements in landscapes near lake frome and lake eyre during latest pleistocene times callitris woodlands were present at lake eyre before 30 000 bp but became fragmented and disappeared in the lead up to the last glacial maximum callitris was again prominent from approximately 10 000 bp until about 5000 bp after which time it vanishes from the pollen record and presumably the region at lake frome callitris was abundant between 16 000 bp and 13 000 bp before declining to low modern levels from 11 000 bp at both sites the latest pleistocene or holocene decline in callitris occurrence and its eventual extinction in the vicinity of lake eyre broadly corresponds with archaeological indications of increasing human presence in the landscape in the absence of evidence of significant climatic changes at the times in question these observations lend tentative support to arguments that the composition and structure of modern zone vegetation has been significantly modified by aboriginal land management practices although the charcoal record is ambiguous fire is argued to be the principle agent of the changes wrought during human re colonisation of lands around lake frome and lake eyre

antarctic regional ice loss rates from grace abstract using recent improved time variable gravity solutions from the gravity recovery and climate experiment grace we estimate rates of antarctic ice mass change for the period january 2003 through september 2006 combined improvements in data and filtering techniques allow observation of ice loss in the northern antarctic peninsula ap and along the coast of the west and central amundsen sea embayment ase in west antarctica there is also evidence of ice loss along the coast near the stancomb wills sta and jutulstraumen jut glaciers in queen maud land apparent rates are adjusted for influences of limited spatial resolution filtering and estimated postglacial rebound pgr to obtain ice loss rates for the northern ap coastal ase and sta jut of 28 8 7 9 81 17 and 16 7 9 7 km3 yr respectively this is the first estimate for the northern ap from satellite gravity data the ase estimate 81 17 km3 yr is consistent with a previous value 77 14 km3 yr using an earlier grace data release these results indicate significant improvement in grace data quality increased spatial resolution and applicability of grace data to a wider class of problems than previously possible

signal and error in mass change inferences from grace the case of antarctica summary this paper examines mass changes from gravity recovery and climate experiment grace monthly spherical harmonic gravity field solutions focusing on the application to the antarctic ice sheet regional integration approaches are investigated and compared with an alternative technique of fitting predefined mass change patterns the main thrust of this new analysis is to better define error sources and error bounds on mass changes of the antarctic ice sheet toward this purpose we examine the release 4 grace products by the geoforschungszentrum potsdam although errors related to the correction for glacial isostatic adjustment are significant both leakage and grace error effects are also important in particular the details of how mass change interior to the antarctic continent is weighted and scaled is crucially linked to the end result mass trend solution accounting for error correlations in the grace monthly solutions it is shown that the corresponding errors in antarctic mass changes are about two times larger than predicted by uncorrelated error propagation our ice mass trend estimate for the grounded ice sheet in the period from 08 2002 to 01 2008 is 109 48 gt yr 1 equivalent to a mean eustatic sea level rise of 0 30 0 13 mm yr 1 w e also provide estimates for 16 individual drainage basins mass losses concentrate in the coastal regions of west antarctica and on the antarctic peninsula with together 105 35 gt yr 1 t he amundsen sea sector alone contributes 60 8 gt yr 1 although these findings agree with independent observations grace trends deduced from a short time series come with the cautioning footnote that the strength of interannual variations remains undetermined we finally discuss directions of methodological improvements

holocene palaeoenvironments and change at three quarter mile lake silver plains station cape york peninsula australia pollen and diatom analyses of organic sediments from three quarter mile lake a perched lake on cape york peninsula north queensland indicate that significant changes in vegetation and hydrology occurred during the holocene early holocene grass dominated landscapes were replaced in mid holocene times by increasingly woody vegetation comprising tropical heathlands savanna and rainforest early holocene lake levels fluctuated widely from mid holocene times lake levels stabilized and water became increasingly acidic as a mature swamp forest developed adjacent to the lake and contributed tannins to the lake water the timing and character of changes are consistent with those described from the atherton tableland in wet tropical queensland holocene dry phases described from the northern territory and the western shores of cape york cannot be identified from three quarter mile lake rainforest is currently close to its greatest holocene extent suggesting that the rainforest dependent endemic fauna of no

qualitative comparisons of global ocean tide models by analysis of intersatellite ranging data 1 four global ocean tide models are compared in terms of their contribution to gravity recovery and climate experiment grace satellite to satellite tracking residuals the residuals are computed relative to a comprehensive model of earth s time varying gravity including allowance for mass motions in the atmosphere ocean terrestrial hydrology and mantle in addition to tides for each analyzed tide model 4 years of grace range rate data are processed range and range acceleration residuals are tidally analyzed by geographic location all four global tide models are shown to be error prone in various ways leaving tidally coherent residuals especially in polar regions but also in some lower latitude regions considerable power in the solar semidiurnal s2 tide in low latitudes suggests errors in our adopted model of atmospheric tides which is based on 3 hourly european centre for medium range weather forecasts operational analyses anomalies in the 2 tidal constituent over some shallow seas suggest the presence of unmodeled nonlinear compound tides in this case 2ms2 similarly anomalies in the nonlinear m4 tide are seen if this constituent is omitted from the models errors in assumed seawater density may be contributing to some residuals

holocene palynology of whitehaven swamp whitsunday island queensland and implications for the regional archaeological record palynological study of whitehaven swamp whitsunday island provides the first holocene palaeoenvironmental record for the whitsunday region on the central queensland coast sediment stratigraphy and radiocarbon dating indicate continuous freshwater swamp conditions since around 7000 radiocarbon years before present bp pollen and charcoal analyses provide local and regional vegetation and fire histories for the site and surrounding area varying representation of swamp elements particularly leptocarpus and cyperaceae provides evidence for phases of permanent and ephemeral swamp conditions the regional vegetation record is dominated by rainforest sclerophyll and beach strand elements strongest rainforest representation occurs around the mid holocene while sclerophyll elements increase from the late holocene to present charcoal analyses indicate that fire has been a constant component of the whitsunday environment throughout the period represented negative correlation between high charcoal and leptocarpus pollen concentrations suggests a strong local component to the charcoal record and a history of on site burning during ephemeral swamp phases the vegetation reconstruction suggests moister than present conditions at whitehaven between approximately 7000 to 4500 bp this complies with claims for a mid holocene climatic optimum based on pollen records from the atherton tableland to the north but contrasts with suggested mid holocene aridity based on a surrogate lake water level record from fraser island to the south comparisons with the regional archaeological record provide no evidence for direct links between major environmental change and archaeologically identified cultural change in particular claims for late holocene population intensification are not matched by changes in the charcoal record this may suggest that widespread vegetation burning was not a predominant feature of hunter gatherer strategies that were focused towards marine resources and or that human induced fire regimes were already well entrenched prior to intensification

pleistocene vegetation of the humid tropics of northeastern queensland australia abstract the humid tropics area of northeastern queensland has provided a substantial and detailed history of rainforest and rainforest savanna interactions from the pollen analysis of a number of sites on the volcanic atherton tableland through the latter part of the quaternary period a recent extension of the record to close to the base of the quaternary from examination of an offshore core provides a broad regional and temporal context for evaluation of the true significance of late quaternary changes it is apparent that the major sustained change in the vegetation of the region occurred relatively recently probably within the last 140 000 yr and that this change was time transgressive it involved the replacement of extensive moist rainforest by open eucalypt woodland and is considered to have been most likely caused by the burning activities of aboriginal people some aspects of the record from this region can contribute to the history of rainforest on a global scale but other features of it re inforce the unique nature of the development of australian vegetation patterns

reconnaissance thermoluminescence dating of northern australian coastal dune systems abstract quaternary lithostratigraphic units in coastal dunes have been dated at three locations in northern australia cobourg peninsula shelburne bay and cape flattery by both radiocarbon dating of shell and organic carbon and thermoluminescence tl sediment dating both coarse fraction and fine fraction tl methods were used seventeen tl dates were measured none of the tl dates contradict the ages given by radiocarbon where multiple tl dates were taken from a unit they overlap within 2 standard deviation giving added confidence in the results a phase of dune emplacement during the late holocene ca 2700 1800 yr b p was identified in two of the dune fields an early holocene phase of dune emplacement ca 8600 7500 yr b p in two of the dune fields and a late pleistocene episode ca 24 000 17 000 yr b p in both the cape york dunefields three older units gave dates of about 29 000 81 000 and 171 000 yr b p but these must be treated with caution

low degree gravity changes from grace earth rotation geophysical models and satellite laser ranging 1 several independent time series of variations c 21 s 21 and c 20 in earth s gravity field are compared for the period april 2002 to may 2007 we examine estimates from the gravity recovery and climate experiment grace earth rotation variations climate models and satellite laser ranging slr recently released grace solutions show significant improvement relative to earlier results especially for c 21 and s 21 at the annual period all estimates agree remarkably well and good correlation is found among time series at intraseasonal periods in general earth rotation values for c 21 and s 21 and slr values for c 20 agree best with grace estimates grace c 20 time series are contaminated by aliased ocean tide model errors slr c 21 and s 21 time series have been reported without an ocean pole tide opt correction and with an older solid earth pole tide sept model after correcting for opt and sept deficiencies slr c 21 and s 21 time series show improved agreement with other estimates

reef parameterisation schemes with applications to tidal modelling a variety of analytical models is used to investigate the effects on tidal propagation of a barrier reef system these models specify reef geometry by two parameters they can accommodate cases where water flows over reefs as well as through inter reef gaps and also incorporate quadratic bottom friction although based on a one dimensional approach adaptations of a solution by huthnance are used to account for the additional blockage effects associated with two dimensional flow patterns near reef barriers the present work adopts the philosophy that only a numerical approach can cope with the wide variations in reef geometry that are encountered in areas such as the great barrier reef gbr region of australia moreover since typical model grids cannot resolve inter reef gaps and other features with sufficient accuracy a parameterised approach is needed to accommodate the conflicting demands of reef geometry and an economically feasible model resolution the formulation of the analytical models is such that they can be applied immediately to standard numerical algorithms numerical experiments for flow in a channel with a reef barrier across its centre are used to test the parameterisation schemes comparison of the results for parameterised reefs with those obtained using extremely fine grids shows convincing evidence of the success of the schemes a separate method for automatically generating reef parameters has simplified the task of applying the methodology to real reefal systems a tidal model of the southern gbr a region which exhibits unusual tidal behaviour but which also has ample field data available for model testing is used to demonstrate the accuracy that can be attained with the parameterised approach although tides are considered specifically in the present work the formulation should be applicable with equal ease to the many other significant classes of low frequency motions in the gbr

geochemical investigation of the south wellesley island wetlands insight into wetland development during the holocene in tropical northern australia the south wellesley islands in the gulf of carpentaria northern australia were the recent focus of a palynological investigation which found vegetation change during the holocene was driven by coastal progradation and regional climate here we present new elemental data from x ray fluorescence core scanning which provides non destructive continuous and high resolution analysis from three wetlands across bentinck island the largest of the south wellesley islands elemental data and grain size analyses are combined with lead 210 210pb and accelerator mass spectrometry ams carbon 14 14c dates an open coastal environment was present 1250 cal a bp on the south east coast of bentinck island with sediment supply incorporating fluvial deposition and detrital input of titanium and iron from eroding lateritic bedrock prograding shorelines dune development and river diversion formed a series of swales parallel to the coast by 800 cal a bp forming the marralda wetlands wetlands developed at sites

sea level and environmental changes since the last interglacial in the gulf of carpentaria australia an overview abstract the gulf of carpentaria is an epicontinental sea maximum depth 70 m between australia and new guinea bordered to the east by torres strait currently 12 m deep and to the west by the arafura sill 53 m below present sea level throughout the quaternary during times of low sea level the gulf was separated from the open waters of the indian and pacific oceans forming lake carpentaria an isolation basin perched above contemporaneous sea level with outlet channels to the arafura sea a preliminary interpretation is presented of the palaeoenvironments recorded in six sediment cores collected by the images program in the gulf of carpentaria the longest core approx 15 m spans the past 130 ka and includes a record of sea level lake level changes with particular complexity between 80 and 40 ka when sea level repeatedly breached and withdrew from gulf lake carpentaria evidence from biotic remains foraminifers ostracods pollen sedimentology and geochemistry clearly identifies a final marine transgression at about 9 7 ka radiocarbon years before this transgression lake carpentaria was surrounded by grassland was near full and may have had a surface area approaching 600 km 300 km and a depth of about 15 m the earlier rise in sea level which accompanied the marine isotopic stage 6 5 transgression at about 130 ka is constrained by sedimentological and biotic evidence and dated by optical and thermoluminescence and amino acid racemisation methods

patagonia icefield melting observed by gravity recovery and climate experiment grace 1 using recently released reprocessed gravity solutions from the gravity recovery and climate experiment grace we estimate the ice loss rate for the patagonia icefield pif of south america for the period april 2002 through december 2006 after postglacial rebound and hydrological effects are corrected the estimated rate is 27 9 11 km 3 year equivalent to an average loss of 1 6 m year ice thickness change if evenly distributed over the entire pif area the estimated contribution to global sea level rise is 0 078 0 031 mm year this is an independent confirmation of relatively large melting rate estimates from earlier studies employing topographic and cartographic data

grace observations of m2 and s2 ocean tides underneath the filchner ronne and larsen ice shelves antarctica 1 by processing the grace satellite to satellite tracking data and estimating the temporal gravity fields regionally over the southern polar region with a 5 day interval we observed m2 and s2 ocean tides underneath the filchner ronne and larsen ice shelves antarctica based on the predicted aliased periods we extracted the m2 and s2 signals from the time series of 5 daily mean grace regional gravity estimates the grace observations agreed well with the predicted tides from the fes2004 and cats02 01 models after smoothing the models to the commensurate spatial resolution as grace overall the grace and the models agreed within 10 20 difference in the tidal amplitude and 20 in phase for both m2 and s2 our results suggest that grace provides valuable observations of ocean tides with a spatial resolution as short as 300 km over the remote area lacking of quality observations such as the antarctica ice shelves

ocean tides in the weddell sea new observations on the filchner ronne and larsen c ice shelves and model validation 1 ocean tides under the large weddell sea ice shelves are among the least well observed on earth here we present new spatially extensive observations of the vertical tidal motion of the filchner ronne and larsen c ice shelves using global positioning system gps data spanning a few weeks to years we pay particular attention to the major tidal constituents m2 s2 o1 k1 as well as important grace aliasing periods k2 and s1 we compare the estimated constituents with recent global and regional tide models and find that no single model is the most accurate across all constituents or ice shelves the root sum square errors are 7 8 cm cats2008a and tpxo7 2 and 11 12 cm got4 7 and fes2004 with the energetic m2 rmse 4 8 cm and s2 4 5 cm generally dominating these statistics the fes2004 k1 is particularly inaccurate near the larsen c ice shelf with errors approaching 20 cm meaning that grace release 4 estimates of mass change in the northern antarctic peninsula will be biased we find tidal energy at 3 4 5 6 and weakly at 7 cycles per day at all of our sites the largest amplitudes within these bands are at m4 mo3 and sp3 and approach 30 mm although significant spatial variations exist we show that they generally do not appear to originate in areas of reduced water column in ice shelf grounding zones comparing model estimates with our m4 ms4 and mn4 values shows that models do not accurately represent these terms

validation of ocean tide models around antarctica using onshore gps and gravity data 1 ocean tide models around antarctica are presently only sparsely tested against independent data ocean tide modeling errors along with subsequent ocean tide loading otl displacement modeling errors alias into altimetry and time variable gravity e g gravity recovery and climate experiment grace time series for example to validate various ocean tide models around antarctica gps data from 15 sites have been used to derive three dimensional displacement estimates at eight diurnal and semidiurnal tidal frequencies using hundreds of days of gps data harmonic parameters were estimated on a daily basis then combined these were then compared with otl displacement estimates derived from global and regional ocean tide models in east antarctica where the tides are well defined submillimeter differences are demonstrated in each coordinate component with the lunar n2 and q1 constituents in closest agreement as found in other studies k1 and especially k2 agree less well the spatial variation in the misfits for these two constituents indicates a site dependency with the k2 errors also suggesting an interaction with satellite dependent effects in west antarctica where sites are nearer the largest ice shelves agreement with the older models csr3 and tpxo 2 and nao 99b is poor for all constituents modeled tidal gravity variations were also compared with gravity measurements at the south pole overall the gps and gravity data agree best with newer tide models namely tpxo 6 cada00 10 fes99 and cats02 01 however validation data are lacking at the southern extents of the large ice shelves and hence some uncertainty still exists in all ocean tide models in these regions