segmentation and differential post rift uplift at the angola margin as recorded by the transform rifted benguela and oblique to orthogonal rifted kwanza basins abstract we analyse tectonic and sedimentary field and subsurface data for the angola onshore margin together with free air gravity anomaly data for the offshore margin this enables us to characterize the mode of syn rift tectonism inherited from the precambrian and its impact on the segmentation of the angola margin we illustrate that segmentation by the progressive transition from the benguela transform rifted margin segment to the oblique rifted south kwanza and orthogonal rifted north kwanza margin segments the spatial variation in the intensity of post rift uplift is demonstrated by the study of a set of geomorphic markers detected in the post rift succession of the coastal benguela and kwanza basins upper cretaceous to cenozoic uplifted palaeodeltas erosional unconformities palaeovalleys quaternary marine terraces and perched gilbert deltas the onshore benguela transform margin has a distinctive mainly progradational stratigraphic architecture with long term sedimentary gaps and high elevation marine terraces resulting from moderate upper cretaceous cenozoic to major quaternary uplifting i e 775 1775 mm ky or m ma by contrast repeated synchronous episodes of minor cenozoic to quaternary uplift occurred along the orthogonal rifted north kwanza segment with its cenozoic aggradational architecture short term sedimentary gaps and low elevation pleistocene terraces margin style likewise governs spatial variations in the volume of offshore sediment dispersed in the associated deep sea fans along the low lying north kwanza margin sedimentation of the broad cenozoic to pleistocene kwanza submarine fan was probably governed by the width of the kwanza interior palaeodrainage basin combined with the wet tropical neogene climate along the high rising benguela margin the small size of the benguela deep sea fan is related to the interplay between moderate continental sediment dispersal from long lived small catchments and a warm very arid neogene climate however the driving forces behind the epeirogenic post rift uplift of the angola coastal bulge remain a matter of speculation

unusual radar echoes from the greenland ice sheet airborne radar images of part of the greenland ice sheet reveal icy terrain whose radar properties are unique among radar studied terrestrial surfaces but resemble those of jupiter s icy galilean satellites the 5 6 and 24 centimeter wavelength echoes from the greenland percolation zone like the 3 5 and 13 centimeter wavelength echoes from the icy satellites are extremely intense and have anomalous circular and linear polarization ratios however the detailed subsurface configurations of the galilean satellite regoliths where heterogeneities are the product of prolonged meteoroid bombardment are unlikely to resemble that within the greenland percolation zone where heterogeneities are the product of seasonal melting and refreezing

ers 1 altimetry on the greenland ice sheet preliminary investigations of annual variations the existence of an annual signal in the ers 1 35 day repeat altimetry measurements over the greenland ice sheet is investigated in this paper spectral analysis from a collinear set of long tracks indicates that the timevarying part of the elevation signal is rather constant at a level around 20 cm at frequencies higher than 1 cycle per degree at lower frequencies the presence of a stationary signal can be seen this signal can be estimated in a collinear analysis from the entire set of 35 day altimetry data over the ice sheet spanning one and a half years separation of an annual signal revealed a signal highly correlated with topography the mean amplitude is around 40 cm with amplitudes between 10 20 cm around the summit of the ice rising to between 50 80 cm approaching the ablation zone of the ice sheet

heavy metals in a contaminated australian estuary dispersion and accumulation trend very high concentrations of zn pb cu and cd occur in the muddy bottom sediments of lake macquarie a saline coastal lagoon in southeastern australia the trace metals emanate from industrial sources especially a lead zinc smelter at the northern end of the lake individual metal concentrations decrease progressively away from the source area but at differing rates zn is most mobile and cd appears to be deposited first they approach natural background levels in the southern part of the lake mn shows a reverse trend but ni co ag and fe rarely rise above background levels shallow cores in the lake bed penetrated a metal enriched surface zone 15 35 cm thick underlain by uncontaminated sediments with natural background metal concentrations sedimentation rates determined from radiocarbon ages on shells in the cores mainly range between 0 15 and 0 5 mm yr 1 over the 85 years since industrialization commenced less than 5 cm of mud has accumulated on the lake bed bioturbation is invoked to account for the depth to which the sediment has been enriched in heavy metals

surface elevation contours of greenland and antarctic ice sheets surface elevations of the ice sheets are contoured at 50 m intervals for the region of greenland covered by seasat radar altimetry south of 72 n and at 100 m intervals for a region of east antarctica north of 72 s the surface elevations were obtained from computer retracking of the radar altimeter waveforms which were recorded at 0 1 s intervals corresponding to 662 m spacings on the surface the precision of the elevation measurements before adjustment for radial orbit errors is 1 9 m as shown by analysis of elevation differences at orbital crossover points this precision is partly determined by radial errors of approximately 1 0 m in orbit determination and partly by noise due to ice surface irregularities adjustment of the radial components of the orbits to minimize the differences in elevations at crossovers over a small relatively flat region reduces the rms difference to 0 25 m which is indicative of the optimum precision obtainable over the ice sheets however the precision degrades as the slope of the surface or amplitude of the undulations increases yielding an overall precision of 1 6 m the preliminary contour maps are not corrected for slope induced displacements a 2 m contour map in a region of highest data density illustrates the three dimensional characteristics of some surface undulations

slope induced errors in radar altimetry over continental ice sheets ranges obtained by radar altimetry from a satellite to a sloping surface on the earth are not measurements of the surface elevation at the subsatellite point instead the reflecting point is displaced upslope from the subsatellite point causing a slope induced error between the true range to the subsatellite point and the indicated range for the seasat 1 altimeter this range error is nearly 80 m for a 0 8 degree slope ice sheet surface slopes are frequently large enough to cause errors of 10 m or more in addition undulations in the surface about a mean slope cause pronounced variations in these errors altimeter measurements of ranges to modeled irregular surfaces are simulated and two correction schemes are used to reconstruct the modeled surfaces from the simulated data the results illustrate the fundamental limitations inherent in single beam radar altimetry for mapping irregular surfaces in the simpler two dimensional case for which cross track slopes are neglected a relocation scheme which constructs a surface consistent with the altimeter ranges removes 85 of the rms error the mean error along profiles of about 75 km or longer is usually reduced more than the rms error an alternate slope correction scheme which uses the local slope to calculate the expected error is less effective in the two dimensional case however over a simulated three dimensional surface where groundtracks are widely spaced and cross track slopes are significant the slope correction method must be used in at least the cross track direction the effectiveness of the three dimensional correction depends on the relative size of the errors caused by the local slope on surface undulations in comparison to the regional slope

growth of greenland ice sheet measurement measurements of ice sheet elevation change by satellite altimetry show that the greenland surface elevation south of 72 degrees north latitude is increasing the vertical velocity of the surface is 0 20 0 06 meters per year from measured changes in surface elevations at 5906 intersections between geosat paths in 1985 and seasat in 1978 and 0 28 0 02 meters per year from 256 694 intersections of geosat paths during a 548 day period of 1985 to 1986

the use of radon 222 as a tracer of sediment irrigation and mixing on the washington continental shelf abstract observations of the natural radioisotope rn 222 were used in conjunction with radiochemical biological and sedimentological techniques to investigate the irrigation and mixing of sediment at three sites about 90 m water depth along the washington continental shelf the rn 222 deficit difference between observed and predicted concentrations within the seabed was greatest near the columbia river during the summer molecular diffusion at most locations and times could account for only a portion of the deficit irrigation and mixing of the seabed explain the remainder biological mixing bioturbation and physical irrigation wave and tidal pumping have relatively little effect on the rn 222 deficit physical mixing erosion and deposition has a significant effect soon after a major erosion event storm however no such event occurred prior to the observations the conclusion is that biological irrigation and molecular diffusion are the primary causes of the rn 222 deficit and that biological irrigation is responsible for the observed spatial and temporal variations in the deficit therefore biological irrigation is greatest near the columbia river during the summer the spatial increase of irrigation near the columbia is probably due to a relatively large population of tube dwelling filter feeding polychaetes the temporal increases of irrigation during the summer is probably due to annual growth cycles of the benthic community and is not due to water temperature changes

basal melt at northgrip modeled from borehole ice core and radio echo sounder observations from temperature measurements down through the 3001 m deep borehole at the north greenland icecore project northgrip drill site it is now clear that the ice at the base 3080 m below the surface is at the pressure melting point this is supported by the measurements on the ice core where the annual layer thicknesses show there is bottom melting at the site and upstream from the borehole surface velocity measurements internal radio echo layers borehole and ice core data are used to constrain a time dependent flow model simulating flow along the north northwest trending ice ridge flow line leading to the northgrip site also time dependent melt rates along the flowline are calculated with a heat flow model the results show the geothermal heat flow varies from 50 to 200 mw m 2 along the 100km section of the modeled flowline the melt rate at the northgrip site is 0 75 cm a 1 but the deep ice in the northgrip core originated 50 km upstream and has experienced melt rates as high as 1 1 cm a 1

geostatistical evaluation of satellite radar altimetry for high resolution mapping of lambert glacier antarctica the potential of satellite radar altimetry for high resolution mapping of antarctic ice streams is evaluated using retracked and slope corrected data from the lambert glacier and amery ice shelf area east antarctica acquired by geosat during the exact repeat mission erm 1986 89 the map area includes lower lambert glacier north of 72 18 deg s the southern amery ice shelf and the grounded inland ice sheet on both sides the geosat erm altimetry is found to provide substantially more complete coverage than the 1978 seasat altimetry due to improved tracking variogram methods are used to estimate the noise levels in the data as a function of position throughout the map area the spatial structure in the data is quantified by constructing experimental variograms using altimetry from the area of the grounding zone of lambert glacier which is the area chiefly of interest in this topographically complex region kriging is employed to invert the along track height measurements onto a fine scale 3 km grid the unsmoothed along track geosat erm altimetry yields spatially continuous maps showing the main topographic features of lower lambert glacier upper amery ice shelf and the adjacent inland ice sheet the probable position of the grounding line of lambert glacier is identified from a break in slope at the grounded ice floating ice transition the approximate standard error of the kriged map is inferred from the data noise levels

analysis and retracking of continental ice sheet radar altimeter waveforms the seasat i radar altimeter data set acquired over both the antarctic and greenland continental ice sheets is analyzed to obtain corrected ranges to the ice surface the radar altimeter functional response over the continental ice sheets is considerably more complex than over the oceans causal factors identified in this complicated response include sloping surfaces undulating ice surfaces with characteristic wavelengths on the same spatial scale as the altimeter beam limited footprint off track reflections and dynamic lag of the altimeter tracking circuit retracking methods using the altimeter return pulse waveforms give range corrections that are typically several meters the entire set of seasat i altimetry over the continental ice sheets is being retracked by fitting a multi parameter function to each waveform many waveforms have double ramps indicating near normal reflections from two distinct portions of the ice surface within the altimeter beam two independent range measurements differing by less than 25 m are obtained from retracking the double ramp waveforms

mapping of the topography of continental ice by inversion of satellite altimeter data satellite altimeter data over ice sheets provide the best tool for mapping their topography and its possible climatic variations however these data are affected by measurement errors orbit errors and slope errors we develop here a three step inversion technique which accommodates the a priori information on the expected topography and correctly handles and propagates the data errors it estimates first a large scale reference surface then maps the residuals related to undulations and finally iteratively corrects the slope error the method is tested on overlapping small fragments of the antarctic ice sheet using a sub set of seasat data finally a topographic map of terre adelie is produced over areas of small slopes the a posteriori error should be of the order of 0 4 m using ers i data it is therefore expected that climatic variations in the ice sheet topography since the introduction of seasat will be observable

global dynamic topography observations reveal limited influence of large scale mantle flow mantle flow causes earth s surface to uplift and subside global analysis of dynamically generated topography suggests that temperature induced small scale mantle flow has a bigger influence on surface topography than large scale mantle flow

anthropogenic marker evidence for accelerated sedimentation in lake illawarra new south wales australia the chronology of near surface sediments in lake illawarra has been investigated using radiocarbon dating and anthropogenically derived substances including trace metals ash and137cs sediments at depths about 1 m below the water sediment interface ranged in age from modern to 786 calendar years bp on the basis of radiocarbon dating ofnotospisula trigonella valves multiple marker for example ash trace metals depth concentration sediment profiles yielded estimates of sedimentation rate ranging from 3 to 5 mm yr 1 at griffins bay to more than 16 mm yr 1 at macquarie rivulet sedimentation rates of approximately 10 mm yr 1 appeared to be typical of the western and southwestern portions of the lagoon rates of sediment accretion prior to catchment clearing urbanization and industrialization have been estimated at less than 1 mm yr 1 thus indicating a general tenfold increase in sediment accumulation adjacent to the western foreshore caused by catchment development accelerated sedimentation in shallow coastal lagoons constitutes significant environmental impacts including shoaling degradation of seagrass beds and increased turbidity with consequent loss of aesthetic appeal management policy should be directed at attempts to reduce the amount of sediment input by the construction of strategically placed sediment retention ponds siltation within the shallow embayments of lake illawarra could be ameliorated by a carefully planned program of dredging

radar measurements of melt zones on the greenland ice sheet surface based microwave radar measurements were performed at a location on the western flank of the greenland ice sheet here firn metamorphosis is dominated by seasonal melt which leads to marked contrasts in the vertical structure of winter and summer firn this snow regime is also one of the brightest radar targets on earth with an average backscatter coefficient of 0 db at 5 3 ghz and an incidence angle of 25 by combining detailed observations of firn physical properties with ranging radar measurements we find that the glaciological mechanism associated with this strong electromagnetic response is summer ice lens formation within the previous winter s snow pack this observation has important implications for monitoring and understanding changes in ice sheet volume using space borne microwave sensors

a method for determining the average height of a large topographic ice sheet from observations of the echo received by a satellite altimeter ice sheet surfaces have scales of fluctuation that are similar to the diameter of the area illuminated by a satellite radar altimeter the present theory of altimetry developed to describe scattering from the ocean surface does not deal properly with the geometry of ice sheet surfaces in this paper the theory of altimetry is extended to cover this geometry a general relation for the altimeter echo from a surface of unknown geometry is developed including the effects of the penetration of the surface by the radar waves this expression is linearized using the characteristic operating geometry of satellite altimeters and the gentle nature of ice sheet gradients from this expression an integral equation is derived from whose solution the spatial average of the height of the surface relative to a spherical datum can be determined the integral equation is of a volterra type which permits the uniqueness of the solution for the average height to be investigated simply the method is extended to provide a solution for the spatial average of the height of a local region of the ice sheet provided the region remains large in comparison with the area illuminated by the altimeter and to deal with variations in the antenna boresight alignment the results have a number of implications for the collection and reduction of echoes in an experiment to determine the average height of an ice sheet the unique determination of the average height requires the echo to be known over a time interval that depends on the extrema of the surface which therefore must be known a priori the average height itself can be determined by the operation on the echo of a linear operator whose kernel is derived from the solution of the volterra type equation this marks a change from the procedures currently used in practice to reduce echoes from ice sheets

mass balance and surface movement of the greenland ice sheet at summit central greenland during the grip deep drilling in central greenland the ice sheet topography and surface movement at summit has been mapped with gps measurements of the surface velocity are presented for a strain net consisting of 13 poles at distances of 25 60 km from the grip site some results are the grip site is located approximately 2 km nw of the topographic summit the surface velocity at the gisp 2 site is 1 7 m yr in the w direction the present mass balance at summit is calculated to be 0 03 0 04 m yr i e close to steady state this result is the best now available for summit a small thinning rate might be a transient response of the greenland ice sheet due to the temperature increase at the wisconsin holocene transition

a continuous 55 million year record of transient mantle plume activity beneath iceland in the north atlantic ocean a mid ocean ridge bisects the icelandic mantle plume and provides a window into its temporal evolution1 2 3 v shaped ridges of thick oceanic crust observed south of iceland are thought to record pulses of upwelling within the plume4 5 6 7 specifically excess crust is thought to form during the quasi periodic generation of hot solitary waves triggered by thermal instabilities in the mantle8 here we use seismic reflection data to show that v shaped ridges have formed over the past 55 million years providing the longest record of plume periodicity of its kind we find evidence for minor but systematic asymmetric formation of crust due to migration of the mid ocean ridge with respect to the underlying plume we also find changes in periodicity from 55 to 35 million years ago the v shaped ridges form every 3 million years or so and reflect small fluctuations in plume temperature of about 5 10 c from 35 million years ago the periodicity changes to about 8 million years and reflects changes in mantle temperature of 25 30 c we suggest that this change in periodicity is probably caused by perturbations in the thermal state at the plume source either at the mantle transition zone or core mantle boundary

accuracy of satellite altimeter elevations over the greenland ice sheet the accuracy of geosat satellite altimetry over the greenland ice sheet is evaluated by comparing the measured heights to radar elevations from the airborne greenland aerogeophysics project at the center of the ice sheet where the ice surface is nearly level surface comparisons show a fit at the 1 to 3 m level as expected but even at moderately sloping ice regions 0 3 0 6 satellite altimetry mean errors in the range of 10 to 35 m are observed these errors are found for slope corrected and waveform retracked data so most previous accuracy estimates of current satellite altimetry ice sheet elevations in regions of sloping or undulating ice appear to be too optimistic

scales of transient convective support beneath africa beneath sub equatorial africa there is convincing evidence for a gigantic slow velocity anomaly within the lower mantle that is inferred to be a thermochemical superplume here we define the spatial and temporal pattern of uplift across the northern edge of this putative superplume by analyzing stratal geometries and stacking velocities of neogene sedimentary rocks these marine deposits are imaged on a dense grid of seismic reflection profiles that straddle the southwest african coastal shelf inverse modeling of stacking velocity profiles demonstrates that there have been at least two significant phases of uplift a post pliocene uplift event increases from 0 to 500 m elevation over a distance of 1000 km in close agreement with geophysical estimates of the present day variation of dynamic topography an earlier phase of uplift occurred in middle oligocene time ca 30 35 ma ago we propose a two stage development of epeirogeny in which a middle oligocene phase of uplift may be related to initiation and growth of the african superplume post pliocene denudation records rapid 100 250 m ma vertical motions generated by upper mantle convection which vary on length scales of 500 1000 km our results support the existence of a convective circulation system that has operated on different temporal and spatial scales beneath the african plate

the formation of sedimentary strata in an allochthonous shelf environment the washington continental shelf nittrouer c a and sternberg r w 1981 the formation of sedimentary strata in an allochthonous shelf environment the washington continental shelf mar geol 42 201 232 models of fine scale 120 m shelf regions the inner shelf sand and mid shelf sandy silt are the predominant accretionary deposits on the shelf important sedimento logical observations obtained by boxcoring the upper 1 2 m of these deposits are a progressive decrease in grain size with distance from the columbia b downward coarsening within the seabed c loss of distinct sedimentary structure homogenization of sediment with distance from the columbia non dimensional parameters based on sediment transport and benthic biological studies can be used to relate rates of sediment mixing re working to rates of accumulation these parameters have the potential for quantitative prediction of strata formation from measurements of active processes physical and biological mixing can be assumed to remain relatively constant in an alongshelf direction on the washington shelf and accumulation rate is known from pb 210 geochronology to decrease away from the columbia together these factors tend to increase the ratio of mixing to accumulation with distance from the columbia and predict the sedimentological observations listed above

heavy metals in sediments problems concerning determination of the anthropogenic influence study in the krka river estuary eastern adriatic coast yugoslavia factors that govern heavy metal concentration in sediments were examined by a combined analytical geochemical and geological approach the constrains encountered in the determination of the anthropogenic influence are exposed the region examined was the krka river estuary located in the typical karst region of the eastern adriatic yugoslavia

evolution from estuary to delta alluvial plain morphology and sedimentary characteristics of the shoalhaven river mouth southeastern australia abstract the shoalhaven river in southern new south wales nsw drains a catchment of 7000 km2 forming a barrier estuary at its mouth with a prograded strandplain to its north previous coring and dating across the floodplain and adjacent strandplain indicate progressive infill of the estuarine basin over the past 7000 years over this time the system transitioned from a wave dominated estuary to a wave dominated delta the shoalhaven river appears to have initially discharged to the sea at crookhaven heads until it adopted a more direct route through an intermittently open mouth at shoalhaven heads construction of berrys canal in 1822 now permanently links the shoalhaven river to the adjacent smaller crookhaven river airborne lidar reveals details of topography of prominent levees and meander scroll bars that flank the lower reaches of the river and beach foredune ridges to the north sedimentological and mineralogical characteristics of modern sediment samples collected from the river channel the beach and the barrier reveal that the shoalhaven river is dominated by quartz sand along its predominantly straight course through the infilled estuarine plains this is in contrast to the tripartite classification of sedimentary depositional environments comprising sandy fluvial delta central mud basin and sandy marine barrier that characterised the initial wave dominated estuary 7000 years ago and is typical of most barrier estuaries in nsw grain size decreases downstream and sands have a higher feldspar content and angularity than is typical of marine sand that has been reworked in the nearshore this fluvially derived component is delivered to the coast intermittently by floods that re open shoalhaven heads as shown by retrospective analysis of aerial photography and satellite imagery grain size decreases with distance alongshore from the river mouth indicating that these sands are transported north by longshore drift to augment a gradual onshore delivery of sand within this coastal compartment scanning electron microscopy of selected grains implies that this fluvial sand has been contributing to incremental formation of beach ridges for much of the past 3000 years since the estuarine basin has been largely infilled with a slight detectable acceleration in the rate of progradation

rapid mantle driven uplift along the angolan margin in the late quaternary mantle flow can warp earth s surface reconstructions of surface deformation in angola over the past 45 000 years reveal rapid uplift of about 2 mm per year implying that mantle induced uplift may occur in quick pulses

selenium contamination redistribution and remobilisation in sediments of lake macquarie nsw this paper examines the history of selenium pollution in lake macquarie nsw australia and three factors that may aaect the redistribution and remobilisation of particle bound selenium changes in redox state bioturbation and bioaccumulation by macrobenthos and bacteria sediment cores were taken from nords wharf a relatively unpolluted area and from mannering bay near the vales point coal fired power station the age profile at the unpolluted site seems to indicate that mild selenium pollution has been occurring for over 100 years however some mixing of the sediments has occurred at the polluted site the age profile indicated that major contamination has occurred in the last 30 years due to a fly ash dam associated with nearby electric power generation facilities the contamination chronology suggests that remobilisation and reduction processes have aaected the selenium profile changing the redox state of lake macquarie sediment results in a release of selenium under oxidising conditions and immobilisation under reducing conditions the sediment bound selenium was associated with the operationally defined organic sulfide fraction under reducing conditions and as the redox potential increases this moves into the exchangeable and iron manganese oxyhydroxide phases to a limited extent bioturbation by the animals marphysa sanguinea and spisula trigonella caused increases in the redox potential and pore water selenium concentrations in surficial sediments relative to unbioturbated controls both animals accumulated significantly more selenium when exposed to contaminated sediment than when exposed to uncontaminated control sediments selenium concentrations in molluscs from mannering bay were all significantly higher than those collected from nords wharf most of the selenium in the mollusc tissues was found to be associated with the protein fraction selenium isolated from hydrolysed muscle tissue was not present as selenate or selenite but as selenomethionine and an unidentified compound seven types of bacteria were isolated from lake macquarie sediment all seven isolates were able to transform selenite quantitatively to elemental selenium as evidenced by a red precipitate and identified by x ray diaraction six isolates grew on media containing selenate but no elemental selenium was formed mass balances showed that for three isolates total selenium was conserved selenate decreased and selenium 0 ii increased indicating the production of non volatile organic selenium compounds for two isolates both total selenium and selenate decreased with no increase in selenium 0 ii therefore loss of selenium occurred from the media

global ice volume during mis 3 inferred from a sea level analysis of sedimentary core records in the yellow river delta abstract estimates of global ice volume during the glacial phase of the most recent ice age cycle are characterized by significant uncertainty reflecting the relative paucity of geological constraints on sea level relevant to this time interval for example during the middle stages of marine isotope stage 3 published estimates of peak global mean sea level gmsl relative to the present range from 25 m to 87 m the large uncertainty in gmsl at mis 3 has significant implications for estimates of the rate of ice growth in the period leading to the last glacial maximum 26 ka we refine estimates of global ice volume during mis 3 by employing sediment cores in the bohai and yellow sea that record a migration of the paleoshoreline at 50 37 ka through a transition from marine to brackish conditions in particular we correct relative sea level at these sites for contamination due to glacial isostatic adjustment using a sea level calculation that includes a gravitationally self consistent treatment of sediment redistribution and compaction and estimate a peak global mean sea level of 38 7 m during the interval 50 37 ka with suitable sedimentary core records the approach described herein can be extended to refine existing constraints on global ice volume across the entire glacial period

airborne measurement of absolute sea surface heights topographic profiles may be measured from an aircraft by differencing precise radar or laser altitudes with ellipsoidal heights obtained by means of kinematic interferometric mode gps over the ocean the difference between the two altitudes is the geoid height plus dynamic oceanographic effects such as tides currents eddies etc aircraft might provide on a local scale altimetry measurements similar to those from geosat and ers 1 such airborne measurements could be applied to the determination of a local high resolution geoid or for oceanographic studies several long over water altimetry profiles were obtained during the 1991 field campaign of the greenland aerogeophysics project gap91 kinematic interferometric gps between multiple short or zero baseline airborne receivers and several sets of stationary gps receivers on the ground provided precise three dimensional positioning for airborne gravity magnetic and topographic profiling sensor systems mounted aboard a p 3 orion aircraft the logistics of surveying a large region long gps baselines and poor satellite coverage limit the accuracy of the gps positioning but the geoid signal is clearly visible in the over water profiles in spite of gps baseline lengths of up to 1000 km differences between modeled geoid heights and measured sea surface heights ranged from about 1 2 meters r m s although the differences are primarily due to errors in the gps positions some portion is due to errors in the model geoid uncompensated tides sea ice contamination of the radar data and other errors in the radar we believe that this represents the first airborne measurement of absolute sea surface heights

implications of sedimentological studies for environmental pollution assessment and management examples from fluvial systems in north queensland and western australia abstract sedimentology is of increasing importance in environmental research particularly environmental pollution studies where past trends in environmental processes need to be combined with data on present conditions to predict likely future changes the past and present as a key to the future two examples are used to illustrate the role of sedimentology in assessing the influence of major processes on the transport accumulation deposition and modification of contaminants in fluvial estuarine systems and in developing environmental management plans example 1 shows that when assessing nutrient behaviour in fluvial estuarine depositional settings it is important to examine the partitioning of phosphorus between grain size fractions to evaluate the sedimentological processes which control the dispersion and trapping of these contaminants example 2 shows that in studies of anthropogenic metal inputs to modern depositional settings lateral and stratigraphic trends in sediment texture and mineralogy should be examined in addition to trends in metal loads and evaluation of the prevailing physical chemical and biological processes that may influence metal mobility and dispersion clearly basic sedimentological data should form part of any assessment of potentially contaminated sites and part of investigations into the dispersion and trapping of contaminants in fluvial systems these data are also required for rational environmental management to ensure that planning decisions are compatible with natural environmental constraints

geodynamics surface sculpting by hidden agents tectonic plate interiors are often regarded as relatively inactive yet reconstructions of marine terrace uplift in angola suggest that underlying mantle flow can rapidly warp earth s surface far from obviously active plate boundaries

the great west african tertiary coastal uplift fact or fiction a perspective from the angolan divergent margin 1 we explore exhumation in the coastal kwanza basin by combining analyses of tertiary hiatuses and apatite fission tracks planktonic biozones show five major hiatuses in the oligo miocene and plio pleistocene between gaps oligo miocene strata accumulated under marine conditions a marine setting refutes the idea of a massively raised coastal plateau in the mid tertiary marine conditions continued until 5 ma fission track data suggest three thermal events 150 ma during rifting and volcanism 100 70 ma during shortening and volcanism and 20 10 ma during exhumation tertiary uplift was spatially highly variable for the kwanza basin we infer that tertiary uplift on the west african margin is indeed a fact but that estimates of uplift timing and size are unreliable when extrapolated to adjoining areas massive uplift 2000 4000 m of the precambrian craton had little structural effect in the outer basin instead minor uplifts on the shelf drove late tertiary deformation on the slope

optically stimulated luminescence dating of young sediments a review optically stimulated luminescence osl dating of young 1000 years sediments is used increasingly in a wide variety of late holocene studies as a mean of establishing contemporary sedimentation rates or the timing of sediment deposition this paper provides a summary of the basic principles of osl dating outlines the problems specific to the dating of young material and then uses recent applications to young sediments to illustrate the greatly increased scope and potential of the method in geomorphology and the geology of recent deposits the overall reliability of this new generation of osl ages is examined by comparing where possible osl ages with independent age control it is concluded that the osl ages are accurate in that there is no evidence for systematic over or under estimation it is our conclusion that osl dating should be regarded as a reliable chronological tool for determining the time of deposition of water lain sediments from the coastal zone and aeolian deposits from both coastal and inland environments our conclusion is supported by the growing popularity of osl dating in geomorphology and geology

balance velocities of the greenland ice sheet we present a map of balance velocities for the greenland ice sheet the resolution of the underlying dem which was derived primarily from radar altimetery data yields far greater detail than earlier balance velocity estimates for greenland the velocity contours reveal in striking detail the location of an ice stream in northeastern greenland which was only recently discovered using satellite imagery enhanced flow associated with all of the major outlets is clearly visible although small errors in the source data result in less accurate estimates of the absolute flow speeds nevertheless the balance map is useful for ice sheet modelling mass balance studies and field planning