development and demise of a fringing coral reef during holocene environmental change eastern ningaloo reef western australia abstract reefs lining the western exmouth gulf located at the northern limit of the 300 km long ningaloo reef in western australia represent modern incipient coral reefs and veneers of non reef building coral algal communities on exposed pleistocene or give up holocene reef surfaces acquisition of sixteen cores alongside u series tims dates were used to confirm the nature of the pleistocene foundation and characterise holocene reef development three calcretised pleistocene units were identified as 1 the last interglacial mis 5e reef directly underlying holocene units 2 a mid pleistocene mis 7 bioclastic conglomerate unit and 3 a pleistocene alluvial fanglomerate eight holocene reef facies total thickness of 1 8 5 3 m included coral framework facies domal arborescent mixed tabulate and encrusting and detrital facies carbonate sand skeletal rubble and alluvial fan deposits holocene ages range from 7 93 to 5 8 ka bp with vertical accretion ranging from 1 46 to 9 88 mm year avg 4 11 mm year highest rates of accretion and thickest accumulation occurred in the most seaward and deepest cores composed of massive coral framestone and coralline algal crusts a six stage holocene chronology is proposed including 1 coastal inundation from 8 to 8 5 ka bp 2 initiation start up from 8 to 7 5 ka bp 3 rapid growth catch up and back step from 7 5 to 7 ka bp 4 rapid aggradational growth catch up from 7 to 6 5 ka bp 5 reef decline give up and detrital buildup from 6 5 to 5 8 ka bp and 6 detrital buildup and progradation from 5 8 ka bp to present changes in reef facies and the ultimate demise of the holocene reef probably involved a combination of increased sea level coastal flooding and erosion during the mid holocene highstand with associated increase in sedimentation turbidity and decline in water quality burial by sediment buildup during the mid holocene highstand and detrital progradation during the mid to late holocene regression and the introduction of alluvial sediment during cyclones and other severe storms to an already stressed community modern communities have thus shifted from coral dominated to bored macroalgal pavements this study shows that integration of reef development processes with response to environmental change can be used to assess future pressures on coral reef ecosystems globally

production and off bank transport of carbonate sediment black rock southwest little bahama bank abstract surficial sediments between the intertidal zone and 600 m were studied with the objectives of characterizing their source dispersal pathways and sites of accumulation bioerosion is a major source of sediment in the intertidal and shallow subtidal environments in situ enclosure experiments showed that the urchin echinometra lucunter produced 667 mg sediment cm 2 yr 1 and an associated diverse rock infauna produced an additional 183 mg cm 2 yr 1 microborers caused erosion of 25 mg cm 2 yr 1 and feeding activity by the chiton acanthopleura granulata caused additional erosion of 10 mg cm 2 yr 1 sequential weighing of tethered limestone plates showed an abrasion rate of 5 5 mg cm 2 yr 1 due chiefly to impacts on the plate edges surficial sediments between the intertidal zone and the top of the bank margin wall at 30 m are gravel sand mixtures containing 0 2 mud molluscs and halimeda plates are the main constituents of gravel fractions sand fractions are composed of bioerosion produced carbonate rock fragments 1 70 skeletal material from halimeda 3 63 forams 1 33 molluscs 6 15 and coral 0 6 gravel and sand are transported as bedload in chutes across the narrow rocky shelf chutes end at 45 m and sediment traps indicate an average flux of 5 4 kg chute 1 yr 1 equivalent to 945 kg km 1 yr 1 moving to deep water a dense population of halimeda living on the wall between 30 70 m contributes gravel and sand to sediment on wall ledges at the base of the steep wall 65 a ramp slopes into the northwest providence channel between 120 300 m the ramp 30 slope is a zone by passed by coarse and fine sediment at 300 m the slope decreases to an average of 13 and an apron shaped body of mud is accumulating the apron extends parallel to the bank margin and wall and reaches depths 600 m traps showed that sediment flux to the ramp is 0 12 kg m 2 yr 1 which is 2 of the particle flux overtopping the bank margin surficial sediment of the ramp is mostly mud 70 which is primarily of shallow water origin some form of bottom current transporting gravel and sand mostly halimeda and abraded coral heads has cut gullies into the ramp this bottom flow is probably episodic and turbulent enough to suspend and supply halimeda sand to sediment traps on the ramp at 463 m

sedimentology and the stratigraphic sequence of a tropical tidal flat north western australia abstract king sound with its semiarid tropical climate and large tides 11 5 m maximum offers an opportunity to study unique mangrove fringed tidal flats although much of the coastline is in an erosional phase there are local areas of deposition where the sedimentologic processes are active and stratigraphic sequences are developing the tidal flats are zoned into several geomorphic lithofacies units 1 low tidal sand flats are underlain by megarippled sand and shelly sand 2 mud sand slopes encompass mid to low tidal levels and are underlain by mud sand laminite and mud laminite 3 mangal mud flats occurring between msl and mhws harbour an abundant diverse biota including mangroves crustacea and molluscs bioturbated mud is accumulating on these flats 4 salt flats are the highest tidal unit and they are underlain by laminated and vesicular mud the distribution of sediment types sedimentary structures and biota across tidal flats is related ultimately to frequency of inundation and groundwater salinity physical processes dominate over biological in the frequently inundated well winnowed low tidal areas upslope sediments become finer and biogenic activity progressively becomes dominant reaching a peak in the mangal thereafter to landward infrequent wetting and hypersalinity results in decrease in biota with lateral progradation or vertical shoaling a stratigraphic sequence is generated that reflects the dynamic history of tidal flats laterally prograded sequences contain the four lithofacies in a stacked sheet like array shoaled sequences are composed of three or four lithofacies and contain abundant erosional contacts erosional products and shoal geometry bedforms within and between lithofacies regional tidal flat accretion appears to take place by an alternation of aceretion and erosion which results in laterally prograding sequences alternating with shoaling sequences

changes in meridional temperature and salinity gradients in the north atlantic ocean 30 72 n during the last interglacial period eight deep sea sediment cores from the north atlantic ocean ranging from 31 to 72 n are studied to reconstruct the meridional gradients in surface hydrographic conditions during the interval of minimum ice volume within the last interglacial period using benthic foraminiferal 18o measurements and estimates of sea surface temperature sst and sea surface salinity sss we show that summer ssts and ssss decreased gradually during the interval of minimum ice volume at high latitude sites 52 72 n whereas they were stable or increased during the same time period at low latitude sites 31 41 n this increase in meridional gradients of ssts and ssss may have been due to changes in the latitudinal distribution of summer and annual average insolation and associated oceanic and atmospheric feedbacks these trends documented for the eemian ice volume minimum period are similar to corresponding changes observed during the holocene and may have had a similar origin

the influence of lake morphometry on sediment focusing sediment focusing is a process whereby water turbulence moves sedimented material from shallower to deeper zones of a lake sediment focusing occurs in lakes in both the erosional coarse grained sediments and the transportational zone with the latter characterized by discontinuous sedimentation and resuspension the zone of accumulation is diefined as the zone where sedimentation is final i e no resuspension and where there is no further sediment focusing a geochemical tracer pb was used to trace sediment focusing patterns in 12 lakes of different morphomctries the area occupied by the zone of accumulation is predicted from the mean basin slope a with 86 of the variance explained only in large exposed lakes in which turbulence from waves is more severe are the resulting sediment distributions more erratic this study is the first to provide a general model of sc diment focusing patterns among lakes the study of lake bottom dynamics has received attention in the contexts of sediment contaminant and eutrophication studies the fact that sediments are major depositories for contaminants and nutrients has made them a focus for research in limnology also because sediments provide a record of past events in lakes an understanding of the manner in whllch sediments accumulate is essential for hindcasting interpretations of the historical record in sediments will be confounded if the record has been obscured by sediment resuspension the term sediment focusing was coined by likens and davis 1975 to describe the resuspension of sediments in shallower zones by waves and water currents with subsequent transport to and settling in the deeper zones of lakes much of the work

mid pacific microatolls record sea level stability over the past 5000 yr there has been geographical variation in sea level since rapid postglacial melting of polar ice ceased similar to 6 k y ago reflecting isostatic adjustments of earth and ocean surfaces to past and ongoing redistribution of ice and water loads a new data set of over 100 fossil microatolls from christmas kiritimati island provides a holocene sea level record of unparalleled continuity living reef flat corals grow up to a low tide level adjacent fossil microatolls long lived porites corals up to several meters in diameter occur at similar elevations 0 1 m and extensive fossil microatolls in the island interior are at consistent elevations within each population collectively they comprise an almost continuous sequence spanning the past 5 k y indicating that locally sea level has been within 0 25 m of its present position and precluding global sea level oscillations of one or more meters inferred from less stable locations or using other sea level indicators this mid pacific atoll is tectonically stable and far from former ice sheets the precisely surveyed and radiometrically dated microatolls indicate that sea level has not experienced significant oscillations in accordance with geophysical modeling which implies that the eustatic contribution from past ice melt and the isostatic adjustment of the ocean floor to loading largely cancel each other at this site

observations of wave transformation over a fringing coral reef and the importance of low frequency waves and offshore water levels to runup overwash and coastal flooding many low lying tropical islands are susceptible to sea level rise and often subjected to overwash and flooding during large wave events to quantify wave dynamics and wave driven water levels on fringing coral reefs a 5 month deployment of wave gauges and a current meter was conducted across two shore normal transects on roi namur island in the republic of the marshall islands these observations captured two large wave events that had waves with maximum heights greater than 6 m with peak periods of 16 s over the fore reef the larger event coincided with a peak spring tide leading to energetic highly skewed infragravity 0 04 0 004 hz and very low frequency 0 004 0 001 hz waves at the shoreline which reached heights of 1 0 and 0 7 m respectively water surface elevations combined with wave runup reached 3 7 m above the reef bed at the innermost reef flat adjacent to the toe of the beach resulting in flooding of inland areas this overwash occurred during a 3 h time window that coincided with high tide and maximum low frequency reef flat wave heights the relatively low relief characteristics of this narrow reef flat may further drive shoreline amplification of low frequency waves due to resonance modes these results 1 demonstrate how the coupling of high offshore water levels with low frequency reef flat wave energetics can lead to large impacts along fringing reef lined shorelines such as island overwash and 2 lend support to the hypothesis that predicted higher sea levels will lead to more frequent occurrences of these extreme events negatively impacting coastal resources and infrastructure

linking reef ecology to island building parrotfish identified as major producers of island building sediment in the maldives reef islands are unique landforms composed entirely of sediment produced on the surrounding coral reefs despite the fundamental importance of these ecological sedimentary links for island development and future maintenance reef island sediment production regimes remain poorly quantified using census and sedimentary data from vakkaru island maldives a sand dominated atoll interior island we quantify the major sediment generating habitats the abundance of sediment producers in these habitats and the rates and size fractions of sediment generated by different taxa the estimated annual sediment production is 685 000 kg or 370 m 3 75 of which is produced on the narrow outer reef flat despite composing only 21 of the total platform area approximately 65 of the platform acts solely as a sediment sink census data identify parrotfish as the major sediment producers generating 85 of the 5 7 kg m 2 of new sand grade sediment produced on the outer reef flat each year halimeda macroalgae produce a further 10 most as gravel grade material comparisons between production estimates and sedimentary data indicate that reef ecology and island sedimentology are tightly linked reef flat and lagoon sediments are dominated by coral and halimeda although fine to medium grained coral sand is the dominant 59 island constituent the generation of sediment suitable for maintaining this reef island is thus critically dependent on a narrow zone of high productivity reef but most especially on the maintenance of healthy parrotfish populations that can convert reef framework to sand grade sediment

understanding seismic heterogeneities in the lower mantle beneath the americas from seismic tomography and plate tectonic history we combine results from seismic tomography and plate motion history to investigate slabs of subducted lithosphere in the lower mantle beneath the americas using broadband waveform cross correlation we measured 37 000 differential p and s traveltimes 2000 pcp p and scs s times along a wide corridor from alaska to south america we invert the data simultaneously to obtain p and s wave velocity models we interpret slab structures and unravel subduction history by comparing our v s tomographic images with reconstructed plate motion from present day up to 120 myr convergence of the pacific with respect to the americas is computed using either 1 the pacific and indo atlantic hot spot reference frames or 2 the plate circuit passing through antarctica around 800 km depth four distinctive fast anomalies can be associated with subduction of the nazca cocos and juan de fuca plates beneath south central and north america respectively and of the pacific plate beneath the aleutian island arc the large fast anomalies in the lowermost mantle which are most pronounced in the s wave models can be associated with late cretaceous subduction of the farallon plate beneath the americas near 2000 km depth the images record the post 80 myr fragmentation of the proto farallon plate into the kula plate in the north and the farallon plate in the northeast near 1000 km depth we infer separate fast anomalies interpreted as the kula pacific juan de fuca and farallon slabs this interpretation is consistent with the volume and length of slabs estimated from the tomographic images and the plate history reconstruction

a comparison of reef protected environments in western australia the central west and ningaloo coasts variability in the regional setting and morphology of cuspate forelands on the west coast of western australia is examined in this paper in accordance with this aim principal differences in the geologic and geomorphologic setting of three prominent sites on the west coast were established and their association with historical changes and contemporary oceanographic processes was examined the cuspate forelands investigated are jurien bay winderabandi point and turquoise bay the most significant differences in geologic setting are associated with the structure and location of an extensive offshore reef system morphologically the reef alters from south to north changing from a discontinuous ridge parallel to the shore along the central west coast to a nearly continuous fringing reef at ningaloo the reefs vary in distance from the shore being farthest in the south and closest in the north and they impound a series of inshore basins or lagoons the deeper southern basins are dominated by locally generated wind waves and wind generated currents the shallower northern basins are most markedly affected by tidal currents and wave pumping across the reef flats the large cuspate foreland at jurien on the central west coast has undergone shoreline configuration change in response to changing phases of storminess as well as in response to a change in focus for sediment deposition as a result of offshore reef erosion at winderabandi point on the ningaloo coast relict pleistocene limestone has provided the focus for sedimentation and morphology has been controlled by a balance in refracted wave energy and nearshore currents driven by tidal and wave set up variability at turquoise bay where the lagoonal basin is most shallow and narrow the morphology of the foreland suggests that it may at some stage have been migratory but its present asymmetrical shape is maintained by strong northerly longshore drift and strong currents exiting the lagoon through a nearby gap in the reef crest fundamental differences between the two coastal regions include the structure of the offshore reef processes driving flow of water within the lagoons and the role of storminess in evolution of coastal landforms although many questions regarding storm surge dynamics and landform change remain unanswered this research provides a significant contribution to the understanding of the evolution of morphological systems in low wave energy protected environments copyright 2000 john wiley sons ltd

estimating the settling velocity of bioclastic sediment using common grain size analysis techniques most techniques for estimating settling velocities of natural particles have been developed primarily for siliciclastic sediments therefore to understand how these techniques apply to bioclastic environments measured settling velocities ws of bioclastic sedimentary deposits sampled from a nearshore fringing reef in western australia were compared with settling velocities calculated using results from several common grain size analysis techniques sieve laser diffraction and image analysis and established models the effects of sediment density and shape were also examined by using a range of density values and three different models of ws sediment density was found to have a significant effect on calculated ws causing a range in normalized root mean square error of up to 28 depending upon settling velocity model and grain size method accounting for particle shape improved errors in predicted ws by 3 to 6 and removed any velocity dependent bias which is particularly important for the fastest settling fractions when shape was accounted for and measured density was used normalized root mean square errors were 4 10 and 18 for laser diffraction sieve and image analysis respectively the results of this study show that established models of ws that account for particle shape can be used to estimate settling velocity of irregularly shaped sand sized bioclastic sediments from sieve laser diffraction or image analysis derived measures of grain size with a limited amount of error collectively these findings will allow for grain size data measured with different methods to be accurately converted to settling velocity for comparison this will facilitate greater understanding of the hydraulic properties of bioclastic sediment which can help to increase our general knowledge of sediment dynamics in these environments this article is protected by copyright all rights reserved

revisions of k ar ages for the hadar hominid site ethiopia conventional k ar age measurements are reported for two volcanic units from the hominid bearing hadar formation these ages represent revision of previously published ages for the bkt 2 tephra and the kadada moumou basalt bkt 2 is revised from 2 65 to 2 9 myr bp and the kadada moumou basalt is revised from 3 0 to 3 6 myr bp

the influence of coral reefs and climate change on wave driven flooding of tropical coastlines a numerical model xbeach calibrated and validated on field data collected at roi namur island on kwajalein atoll in the republic of marshall islands was used to examine the effects of different coral reef characteristics on potential coastal hazards caused by wave driven flooding and how these effects may be altered by projected climate change the results presented herein suggest that coasts fronted by relatively narrow reefs with steep fore reef slopes 1 10 and steeper and deeper smoother reef flats are expected to experience the highest wave runup wave runup increases for higher water levels sea level rise higher waves and lower bed roughness coral degradation which are all expected effects of climate change rising sea levels and climate change will therefore have a significant negative impact on the ability of coral reefs to mitigate the effects of coastal hazards in the future

incremental accretion of a sandy reef island over the past 3000 years indicated by component specific radiocarbon dating 1 low lying reef islands appear particularly threatened by anticipated sea level rise and determining how they formed and whether they are continuing to accumulate sediment is essential for their sustainable management depositional chronology of warraber island a small sand cay in torres strait australia is re examined based on ams radiocarbon dating of specific skeletal components whereas radiometric dating of bulk sand samples indicated one or more discrete phases of mid late holocene deposition component specific ams radiocarbon dating of sand grains indicates sustained incremental growth over the past 3000 years ages on gastropods that lived on the reef flat around the island indicate continuing sediment production and island progradation in contrast to bulk ages and other components produced at greater distances growth of sand cays depends on the rate and pattern of sediment supply which are functions of the local ecology of the surrounding reef and reef flat and hydrodynamic constraints

palynology stratigraphy and palaeoenvironment of a pliocene hominid site 2 9 3 3 m y at hadar ethiopia abstract the pliocene hadar formation 2 9 3 3 m y is well known for its abundant fossil fauna and hominid remains fossil pollen data obtained from 27 distinct stratigraphic layers are presented together with tectonic and sedimentary data comparison with modern pollen data from the awash basin 67 surface and fluviatile samples indicates that montane evergreen bushland presently known from above 1500 m occupied the hadar basin 500 m and was associated with a humid montane forest a downfaulting of about 1000 m presumably happened after 2 9 m y whereas a shift toward more arid grasslands occurred in the middle of the hadar formation

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

inter tidal fixed indicators of former holocene sea levels in australia a summary of sites and a review of methods and models abstract the reconstruction of mid to late holocene marine environments using the calcareous remains of inter tidal fixed biological indicators as sea level proxies is reviewed useful palaeo environmental information can be obtained from the fossil evidence of successive invasions and disappearances of tropical and temperate species within the sub fossil inter tidal biological sequences examples illustrating spatially synchronous late holocene sea level fluctuations are described from 3000 km of north south coastline along eastern australia the method uses tightly constrained species such as the tubeworm galeolaria caespitosa which allows for the precise measurement of relative sea level fluctuations by using the differential between emerged sub fossil encrustations and current distributions of the same species the error range can be defined according to the extent of preservation of the relic distributions particularly the extent that diagnostic boundaries between species limited to different inter tidal zones have been preserved the rapidity of sea level fluctuations is inferred by the preservation from erosion of emerged shell layers as well as discontinuities in the relic biological sequences and the relative preservation of fragile species this apparent rapidity of sea level fluctuations as well as evidence of near uniform synchronous sea level heights along the north south span of the entire australian coast and equally consistent variations australia wide in spencer gulf and rottnest island raises questions about the predicted poleward decline of sea level curves derived from hydro isostatic rebound modelling

palaeoenvironmental and palaeobiogeographical significance of the fossil rodent assemblages of laetoli pliocene tanzania abstract the study of the laetoli rodent assemblages and comparison with other extant and fossil communities of africa by different statistical methods provide new palaeoenvironmental and palaeobiogeographical results firstly it is demonstrated that at 3 7 myr the laetoli assemblage belonged to a southern savanna domain and that its modern equivalent is the kalahari rodent fauna namibia south west africa secondly these analyses show that the rodent faunas from laetoli hadar omo member b and f ethiopia and olduvai bed i tanzania all of which are situated in the rift valley are clearly distinct assemblages each fauna is characterized by a strong endemism and seems to have evolved independently a tentative explanation of this observation is proposed by the examination of the structure of the rift valley and its evolution during plio pleistocene times moreover the different phases of speciation and migration of the rodent faunas can also be correlated with the tectonic events related to the formation of the rift valley

response of a fringing reef coastline to the direct impact of a tropical cyclone tropical cyclones generate extreme hazards along coastlines often leading to losses of life and property although coral reefs exist in cyclone prone regions globally few studies have measured the hydrodynamic conditions and morphological responses of reef fringed coastlines to tropical cyclones here we examine the impact of tropical cyclone olwyn on a section of australia s largest fringing reef ningaloo reef using in situ wave and water level observations topographic surveys and numerical modeling despite forereef significant wave heights reaching 6 m and local winds of 140 km h 1 average beach volume change was only 3 m3 m 1 the results indicate that this erosion was due to locally generated wind waves within the lagoon rather than the offshore waves that were dissipated on the reef crest a comparison of these volume changes to observations of tropical cyclone impacts along exposed sandy beaches quantitatively demonstrates the substantial coastal protection reefs can provide against extreme storms

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

an early holocene sea level jump and delta initiation 1 early holocene sea level change controlled the evolution of clastic coastal depositional systems radiocarbon dated borehole cores obtained from three incised valley fill systems in asia changjiang song hong and kiso river record very similar depositional histories especially between about 9000 and 8500 cal bp sedimentary facies changes from estuarine sand and mud to shelf or prodelta mud suggest that the marine influence in the incised valleys increased during this period in addition large decreases in sediment accumulation rates occurred a sea level jump causes an estuarine system and its depocenter to move rapidly landward it is possible that the final collapse of the laurentide ice sheet accompanied by catastrophic drainage of glacial lakes at approximately 8500 cal bp caused such a jump the jump was followed immediately by a period of decelerated sea level rise that promoted delta initiation

parrotfish erosion underpins reef growth sand talus development and island building in the maldives abstract parrotfish play a key functional role on coral reefs as external bioerosion agents and produce large quantities of carbonate sediment as a by product of grazing on reef surfaces parrotfish are therefore an important potential source of sediment for island construction and maintenance within atoll reef environments particularly under future scenarios of sea level rise and island morphological change here we present the first field based estimates of excavating parrotfish erosion chlorurus sordidus and chlorurus strongylocephalus within the indian ocean and quantify the contribution of parrotfish to the carbonate and sediment budgets of an atoll interior reef platform in the maldives we note that parrotfish erosion rates are high 6 3 kg m 2 y 1 generating large amounts of new coral based sediment 2 6 kg m 2 y 1 that has a comparable grain size distribution to island deposits mean erosion rates by individual c strongylocephalus 405 kg individual y 1 were higher than c sordidus 55 kg individual y 1 but their contribution to erosion per unit area of reef was less due to a lower relative biomass c strongylocephalus 1 3 kg m 2 y 1 c sordidus 5 0 kg m 2 y 1 parrotfish also facilitate sediment export from reefs 0 7 kg m 2 y 1 which contributes extensively to the development of the sand talus on the fore reef slope and to the evolution of the wider atoll basin our results provide strong evidence that parrotfish erosion and sediment generation underpins island morphology on maldivian reefs and highlight the importance of larger parrotfish as producers of island grade sediment ecological processes must therefore be considered within future coastal management strategies for enhancing island stability

contemporary sedimentation in the cocos keeling islands indian ocean interpretation using settling velocity analysis abstract textural parameters of grain size distributions derived from sieve analysis and component analysis have been used to the exclusion of other methods to examine sedimentary processes in modern reef environments however because these methods do not reflect the hydraulic behaviour of bioclastic sediment this study uses settling velocity analysis accounting for grain size density and shape variability and component analysis of separated settling velocity fractions to describe and differentiate bioclastic deposits and infer transport pathways in the cocos keeling islands an indian ocean atoll principal component and cluster analysis of settling 251 samples and component 90 samples characteristics discriminated eight settling velocity and five component classes a derived settling velocity classification reflecting the hydraulic properties of the sediments describes a lagoonward gradient from those with fast settling characteristics on the outer reef flat to those with moderate settling character on sand aprons the active sediment transport system is constrained between these zones component analysis of bulk samples identifies two broad sediment types 1 those with reef derived components found throughout the active transport zone reef flat to sand aprons and 2 those characterised by greater proportions of gastropod and halimeda fragments which are produced and deposited in situ in the lagoon component analysis of settling fractions further resolves details of sediment movement in the active transport zone sediment is transported from the productive reef flat to passage entrances which form initial depositional environments slower settling material is selectively transported from the entrances through the passage conduits to passage exit environments these form the main depositional areas under mean energy conditions during moderate to high energy events sediment is flushed from the passage to sand apron zones with slower settling grains deposited in the deep lagoon sinks results show that settling velocity analysis and component analysis of settling fractions can resolve the nature of sediment transport patterns in reef environments at a much finer scale than studies in which analysis is based on grain size distributions

geology and stratigraphy of neogene deposits middle awash valley ethiopia the middle awash valley afar ethiopia contains a sedimentary sequence that is 1 km thick spans much of the neogene and contains vertebrate fossils throughout newly defined formations described here are older and younger than the hominid bearing hadar formation the awash deposystem reflects deposition in an evolving triple junction

wave driven circulation of a coastal reef lagoon system abstract the response of the circulation of a coral reef system in kaneohe bay hawaii to incident wave forcing was investigated using field data collected during a 10 month experiment results from the study revealed that wave forcing was the dominant mechanism driving the circulation over much of kaneohe bay as predicted theoretically wave setup generated near the reef crest resulting from wave breaking established a pressure gradient that drove flow over the reef and out of the two reef channels maximum reef setup was found to be roughly proportional to the offshore wave energy flux above a threshold root mean square wave height of 0 7 m at which height setup was negligible on the reef flat the wave driven currents increased approximately linearly with incident wave height however the magnitude of these currents was relatively weak typically 20 cm s 1 because of i the mild fore reef slope of kaneohe bay that reduced setup resulting from a combination of frictional wave damping and its re

a budget of carbonate framework and sediment production kailua bay oahu hawaii abstract sediments of the bay and coastal plain of kailua oahu hawaii are 90 biogenic carbonate produced by destruction of primary reef framework coral and encrusting coralline algae and by direct sedimentation through the biological activity of calcifying organisms the green alga halimeda the branching coralline alga porolithion gardineri molluscs and benthic foraminifera field measurements of benthic community structure gross carbonate production bioerosion and direct sedimentation in 17 physiographic zones in kailua bay are used to calculate modern calcareous sediment production rates in the 12 km2 fringing reef system total gross carbonate productivity by corals and encrusting coralline algae based on mapped percent cover and known growth rates occurs at an average rate of 1 22 0 36 kg m 2 y 1 over hard substrates of the reef platform corresponding to 0 8 0 2 mm y 1 using a bulk density of 1 48 g cm 3 the average of coral and coralline algae coralline algae contributes 42 of the total gross productivity bioerosion of coral and coralline algae facies at and near the reef surface estimated from slabbed reef samples occurs at average rates of 0 10 1 15 kg m 2 y 1 and releases 1 911 436 m3 of unconsolidated carbonate sediment annually mechanical erosion coral breakage likely contributes an additional 315 m3 y 1 carbonate sediment is also produced directly by the green alga halimeda branching coralline algae molluscs and benthic foraminifera at a combined rate of 1 822 200 m3 y 1 using densities specific to sediment origin the total rate of production of unconsolidated carbonate sediment in kailua bay is the sum of these sources amounting to 4 048 635 m3 y 1 normalizing gross sediment production in kg y 1 by reef habitat area in m2 generates average rates of productivity in kg m 2 y 1 that are directly comparable to each other and to the literature such rates can also be employed and tested in other reef settings in kailua bay the total production of calcareous sediment corresponds to an average normalized rate of 0 53 0 19 kg m 2 y 1 with 0 33 0 13 kg m 2 y 1 contributed through erosion of the coralgal framework and 0 20 0 06 kg m 2 y 1 contributed by direct sediment production on the reef surface applying these modern sediment production rates over the 5 000 years that kailua bay has been completely inundated by postglacial sea level rise an estimated 20 2 3 2 106 m3 of unconsolidated carbonate sediment has been produced in the system the volume of sediment stored in the various reef channels and holes in kailua bay is 3 7 0 3 106 m3 or 19 of that produced since 5 000 y bp the volume of sand in the modern beach is 1 0 0 1 106 m3 or 5 of holocene sediment production the volume of carbonate sediment stored in the coastal plain is estimated using core log data and associated radiocarbon ages to be 10 0 1 8 106 m3 or 51 of holocene sediment production the remaining 25 likely represents sediment loss due to the natural processes of dissolution attrition and transport offshore these export terms are not well understood and emphasize the need for sediment dynamics to be incorporated into reef and sediment budgets although sediment production in this reef system is prodigious the rate of new sediment supplied to the beachface is less than 2 of what moves on and off the beach seasonally

post glacial sea level changes around the australian margin a review abstract it has been known since rhodes fairbridge s first attempt to establish a global pattern of holocene sea level change by combining evidence from western australia and from sites in the northern hemisphere that the details of sea level history since the last glacial maximum vary considerably across the globe the australian region is relatively stable tectonically and is situated in the far field of former ice sheets it therefore preserves important records of post glacial sea levels that are less complicated by neotectonics or glacio isostatic adjustments accordingly the relative sea level record of this region is dominantly one of glacio eustatic ice equivalent sea level changes the broader australasian region has provided critical information on the nature of post glacial sea level including the termination of the last glacial maximum when sea level was approximately 125 m lower than present around 21 000 19 000 years bp and insights into meltwater pulse 1a between 14 600 and 14 300 cal yr bp although most parts of the australian continent reveals a high degree of tectonic stability research conducted since the 1970s has shown that the timing and elevation of a holocene highstand varies systematically around its margin this is attributed primarily to variations in the timing of the response of the ocean basins and shallow continental shelves to the increased ocean volumes following ice melt including a process known as ocean siphoning i e glacio hydro isostatic adjustment processes several seminal studies in the early 1980s produced important data sets from the australasian region that have provided a solid foundation for more recent palaeo sea level research this review revisits these key studies emphasising their continuing influence on quaternary research and incorporates relatively recent investigations to interpret the nature of post glacial sea level change around australia these include a synthesis of research from the northern territory queensland new south wales south australia and western australia a focus of these more recent studies has been the re examination of 1 the accuracy and reliability of different proxy sea level indicators 2 the rate and nature of post glacial sea level rise 3 the evidence for timing elevation and duration of mid holocene highstands and 4 the notion of mid to late holocene sea level oscillations and their basis based on this synthesis of previous research it is clear that estimates of past sea surface elevation are a function of eustatic factors as well as morphodynamics of individual sites the wide variety of proxy sea level indicators used their wide geographical range and their indicative meaning some progress has been made in understanding the variability of the accuracy of proxy indicators in relation to their contemporary sea level the inter comparison of the variety of dating techniques used and the nuances of calibration of radiocarbon ages to sidereal years these issues need to be thoroughly understood before proxy sea level indicators can be incorporated into credible reconstructions of relative sea level change at individual locations many of the issues which challenged sea level researchers in the latter part of the twentieth century remain contentious today divergent opinions remain about 1 exactly when sea level attained present levels following the most recent post glacial marine transgression pmt 2 the elevation that sea level reached during the holocene sea level highstand 3 whether sea level fell smoothly from a metre or more above its present level following the pmt 4 whether sea level remained at these highstand levels for a considerable period before falling to its present position or 5 whether it underwent a series of moderate oscillations during the holocene highstand

hydrodynamics and sediment flux of hoa in an indian ocean atoll detailed hydrodynamic and sediment ux measurements are reported from 11 hoa shallow cross reef channels in the cocos keeling islands indian ocean all hoa exhibit unidirectional oceanside reef to lagoon uxes these currents are driven by tides wave set up and incident waves and the presence of islands that generate alongshore gradients so that currents ow toward the topographic low points of hoa entrances in the reef rim two functional groups of hoa are identi ed that extend chevalier s typology of hoa and possess different process signatures sediment limited hoa slh are ef cient conduits of sediment transport they are located close to the reef rim where incident wave energy propagates across the reef crest into the hoa and is able to entrain sediment transport limited hoa tlh are characterized by low rates of sediment transport because incident wave energy is negligible as they are located much further from the reef edge than slh in the absence of an entrainment mechanism the oceanside reef at is laden with sediment storm energy increases transport ef ciency through hoa however the net sedimentation response differs between the two hoa types proximity to the reef edge means that frequent storms ush sediment from slh increasing hoa depth and enhancing the potential for erosion of the conglomerate boundary in contrast the greater reef width fronting tlh means that sediment transport from reef ats to the lagoon is only activated during infrequent storms the contrasting process signatures account for morphological differences between sediment limited hoa lagoonward decrease in depth and increase in width and transport limited hoa lagoonward increase in depth the number and type of functional hoa are found to have signi cant implications for the rate of lagoon sedimentation in enclosed atolls in general an increase in frequency of functional hoa and increased proportion of slh will promote more rapid rates of lagoon in ll copyright 2004 john wiley sons ltd

two dimensional depth averaged model simulation of suspended sediment concentration distribution in a groyne field summary river training structures such as spur dikes are effective engineered methods used to protect banks and improve aquatic habitat this paper reports the development and application of a two dimensional depth averaged hydrodynamic model to simulate suspended sediment concentration distribution in a groyne field the governing equations of flow hydrodynamic model are depth averaged two dimensional reynold s averaged momentum equations and continuity equation in which the density of sediment laden flow varies with the concentration of suspended sediment the depth averaged two dimensional convection and diffusion equation was solved to obtain the depth averaged suspended sediment concentration the source term is the difference between suspended sediment entrainment and deposition from bed surface one laboratory experiment was chosen to verify the simulated flow field around a groyne and the other to verify the suspended sediment concentration distribution in a meandering channel then the model utility was demonstrated in a field case study focusing on the confluence of the kankakee and iroquois rivers in illinois united states to simulate the distribution of suspended sediment concentration around spur dikes results demonstrated that the depth averaged two dimensional model can approximately simulate the flow hydrodynamic field and concentration of suspended sediment spur dikes can be used to effectively relocate suspended sediment in alluvial channels

a detrital sediment budget of a maldivian reef platform abstract sediment dynamics are an important control on the morphology and development of reef systems by actively removing and redistributing excess detrital sediment this study presents quantitative data from direct point measurements of sediment transport on the platform surface and fore reef slope of vabbinfaru reef north male atoll maldives a suite of sediment traps were used to construct actual rates of platform sediment fluxes and off reef export over different spatial and temporal seasonal scales to establish key sediment transport pathways findings showed that high sediment fluxes occur on vabbinfaru platform in the absence of major storm activity up to 1905 g m 1 d 1 with 95 of annual transport occurring during the southwest monsoon as a result of increased wave energy climate driven changes in the platform process regime caused a reversal of net sediment transport pathways between each monsoon season off reef export rates were high reaching a maximum of 12 58 kg m 1 y 1 for gravel and 407 g m 1 d 1 for sand sized sediment an estimated 127 120 kg is exported from the platform annually equating to a significant loss from the reef sediment budget and contributing to the long term geomorphic development of the fore reef slope and atoll basin detrital sediment reservoirs on vabbinfaru are not purely depositional carbonate sinks but rather temporary stores that are important in the transfer of sediment between reef zones

computational modeling of fine sediment relocation within a dam reservoir by means of artificial flood generation in a reservoir cascade an edited version of this paper was published by agu copyright 2019 american geophysical union

radiocarbon evidence for the timing and rate of island development beach rock formation and phosphatization at lady elliot island queensland australia abstract lady elliot island great barrier reef is a coral cay constructed from near concentric shingle ridges composed of coral tridacna shells and bioclastic sand bound by guano derived phosphatic cement radiocarbon dating of individual tridacna samples is used to investigate the evolution of the island and place constraints on the variations in storminess of the last 3200 years a shallow platform reef existed at lady elliot since at least 6500 yrs b p shortly before 3200 yrs b p island growth by shingle progradation commenced and proceeded to the present at a rather uniform lateral rate 60 m ka 1 to leeward and 90 m ka 1 windward phosphatization may have occurred continuously or episodically at any time throughout the last 3200 years the youngest cemented ridge top is less than 770 years whereas at the base of uncemented ridges phosphatization is a modern 1950 a d process similarly low level beach rock has continued to form within the last 25 years a significant period of instability occurred less than 500 years ago during which marine erosion truncated the southwestern extremity of lady elliot island formed an eastern spit and stranded high level beach rock however the radiocarbon ages of tridacna samples from shingle ridges from lady elliot and curacoa islands are uniformly distributed kolmogorov smirnov test throughout the last 4000 years we interpret this to indicate no significant variation in ridge forming processes or fluctuation in average storminess during this interval

faunal age of the usno shungura b and hadar formations ethiopia recent work by brown1 correlating the sidi hakoma or sidiha koma2 tuff at hadar with tuffs b and u 10 of the shungura and usno formations respectively reverses a recent finding3 indicating an age of the hadar formation fauna of 2 9 to greater than 3 6 myr bp the difference in these determinations is 0 4 myr a significant period of evolutionary time we compare the faunas from shungura unit b10 usno and hadar and discuss the implications for interpretation of the early hominid fossil record

unified view of sediment transport by currents and waves i initiation of motion bed roughness and bed load transport attention is given to the properties of sediment beds over the full range of conditions silts to gravel in particular the effect of fine silt on the bed composition and on initiation of motion critical conditions is discussed high quality bed load transport data sets are identified and analyzed showing that the bed load transport in the sand range is related to velocity to power 2 5 the bed load transport is not much affected by particle size the prediction of bed roughness is addressed and the prediction of bed load transport in steady river flow is extended to coastal flow applying an intrawave approach simplified bed load transport formulas are presented which can be used to obtain a quick estimate of bed load transport in river and coastal flows it is shown that the sediment transport of fine silts to coarse sand can be described in a unified model framework using fairly simple expressions the proposed model is fully predictive in the sense that only the basic hydrodynamic parameters dep

geometry migration and evolution of wave orbital ripples at leo 15 observations of the temporal evolution of the geometric properties and migration of wave formed ripples are analyzed in terms of measured suspended sand profiles and water velocity measurements six weeks of bedform observations were taken at the sandy medium to coarse sized sand leo 15 site located on beach haven ridge during the late summer of 1995 with an autonomous rotary sidescan sonar during this period six tropical storms several of hurricane strength passed to the east of the study site ripples with wavelengths of up to 100 cm and with 15 cm amplitudes were observed the predominant ripples were found to be wave orbital scale ripples with ripple wavelengths equal to 3 4 of the wave orbital diameter although orbital diameters become larger than 130 cm during the maximum wave event it is unclear if a transition to non orbital scaling is occurring ripple migration is found to be directed primarily onshore at rates of up to 80 cm day suspended transport due to wave motions calculated by multiplying acoustic backscatter measurements of suspended sand concentrations by flow velocity measurements are unable to account for a sufficient amount of sand transport to force ripple migration and are in the opposite direction to ripple migration thus it is hypothesized that the onshore ripple migration is due to unobserved bedload transport or near bottom suspended transport bedload model calculations forced with measured wave velocities are able to predict the magnitude and direction of transport consistent with observed ripple migration rates sequences of ripple pattern temporal evolution are examined showing mechanisms for ripple directional change in response to changing wave direction as well as ripple wavelength adjustment and erosion due to changing wave orbital diameter and relative wave to current velocities

linking pattern to process in reef sediment dynamics at lady musgrave island southern great barrier reef linking surficial sediment patterns in reef environments to the processes that underlie their depositional dynamics enables predictions to be made of how environmental changes will influence reef associated sedimentary landforms such as islands and beaches geomorphic linkages between sediment deposition patterns and the biophysical processes that drive them are often poorly resolved particularly at broad landscape scales where tangible statements can be made about structural changes to landforms the present study applies geospatial techniques to link patterns in reef sediment dynamics at lady musgrave island to the underlying processes driving them in situ calcification is characterized by developing a high resolution map of the surficial calcium carbonate producing communities inhabiting the reef platform and associated sediments across the reef flat are analysed for grain size kurtosis sorting and threshold bed shear stress to explore transport pathways across the reef flat and lagoon wave energy is modelled across the entire reef platform as a potential driver of sediment dynamics and morphometric linkages are empirically defined between wave energy and grain size findings indicate that carbonate sediments are primarily sourced from calcifying communities colonizing the outer periphery of the reef platform and that sediment grain size can be reliably linked to wave energy by virtue of a linear model

reef to island sediment connections on a maldivian carbonate platform using benthic ecology and biosedimentary depositional facies to examine island building potential reef islands are low lying accumulations of unconsolidated sediment formed from the skeletal remains of carbonate producing reef organisms and are therefore perceived as highly vulnerable to environmental change however basic elements of island composition are not well described and given their high inter and intra basinal variability a better understanding of reef and island sedimentary environments and the connections between them are needed to predict future morphological response here we use detailed ecological and sedimentological datasets to delineate key sediment production zones and biosedimentary depositional facies across the surface of vabbinfaru platform maldives field measurements of platform hydrodynamics are applied to sedimentary deposits to determine the potential mobility of grains and identify transport pathways carbonate production was dominated by coral framework mean 52 within a narrow zone on the outer reef rim 22 of platform area resulting in coral rich detrital sediments reef 51 island 64 that closely resemble living assemblages the net transfer of sediment occurred lagoonward by wave driven processes leading to a decrease in grain size towards the island r2 0 502 which acts as a major control on depositional facies development within the lagoon island sediments were distinct from reefal deposits comprising a restricted suite of durable sands mean 1 34 throughout long term development our findings suggest that the production breakdown and redistribution of coral derived sediment by platform currents is fundamental to future island stability at vabbinfaru and although alterations away from current ecological states may reduce sediment supply the timescales over which island morphological response will occur depends upon phase lags between initial coral mortality and the conversion of this material into island grade sand copyright 2016 john wiley sons ltd

predicting the hydrodynamic response of a coastal reef lagoon system to a tropical cyclone using phase averaged and surfbeat resolving wave models abstract tropical cyclone tc olwyn travelled along the coast of ningaloo reef in northwestern australia as a category 3 tc during 12 13 march 2015 with sustained wind speeds of over 130 km h 1 and significant wave heights on the forereef reaching 6 m observations from tc olwyn showed that contrary to typical wave transformation patterns across a coastal reef lagoon under the tc conditions there was a substantial shoreward increase of wave height this unusual pattern was primarily due to strong local wind wave generation under the extreme wind conditions despite the lagoon itself being relatively small order 1 km wide and shallow order 1 m depth two common types of coastal numerical wave models that include either wave growth i e the phase averaged model swan or infragravity waves i e the surfbeat resolving model xbeach but not both processes were used to assess the capabilities of numerical models to predict the cyclone induced hydrodynamics model results showed that wave conditions in the lagoon and at the shoreline were dominated by locally generated wind waves with the reef efficiently dissipating the large incident waves offshore the infragravity waves in the lagoon were only of secondary importance during the tc compared to the locally generated sea swell waves although both the phase averaged swan and surfbeat resolving xbeach models were able to predict some of the local hydrodynamic responses for this specific site and storm the use of a phase averaged model yielded the most accurate predictions of the hydrodynamics given that it included wind wave growth however because the influence of infragravity waves cannot be neglected in reef environments in general these results emphasize the need for a more general modeling approach that requires the addition of wind wave growth formulations into surfbeat or fully phase resolving classes of numerical wave models and or the addition of an infragravity wave formulation in spectral wave models

interpretations of the magnetostratigraphy of the hadar hominid site ethiopia as part of an investigation to determine the age of the hominidbearing strata of the hadar formation of ethiopia we have determined the magnetostratigraphy of two separate sections of the strata two major zones of reversed polarity occur within the predominantly normally magnetized sequence one at the top and the other in the middle there are difficulties with the absolute age determinations of volcanic units within the strata which result in uncertainties in correlating the hadar magnetostratigraphy with the standard magnetic reversal time scale the age of the upper part of the section is established by the bkt 2 tuff at 2 8 myr refs 1 4 the k ar dating of the kadada moumou basalt which lies in the middle of the sequence yields variable results ranging from 3 1 to 3 6 myr refs 1 4 regional geochemical5 and bio stratigraphical6 studies suggest the younger age for the kadada moumou basalt we show here that this is also the age that results in the most consistent interpretation of the observed magneto stratigraphy of the formation which is that the hadar formation was deposited during the gauss normal epoch and that the two reversals represent the kaena and mammoth events within that epoch

timing of the last glacial maximum from observed sea level minima during the last glacial maximum ice sheets covered large areas in northern latitudes and global temperatures were significantly lower than today but few direct estimates exist of the volume of the ice sheets or the timing and rates of change during their advance and retreat here we analyze four distinct sediment facies in the shallow tectonically stable bonaparte gulf australia each of which is characteristic of a distinct range in sea level to estimate the maximum volume of land based ice during the last glaciation and the timing of the initial melting phase we use faunal assemblages and preservation status of the sediments to distinguish open marine shallow marine marginal marine and brackish conditions and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio hydroisostatic modelling our results indicate that from at least 22 000 to 19 000 calendar years before present land based ice volume was at its maximum exceeding today s grounded ice sheets by 52 5 x 10 exp 6 cu km a rapid decrease in ice volume by about 10 percent within a few hundred years terminated the last glacial maximum at 19 000 250 years

the influence of sea level rise and changes in fringing reef morphology on gradients in alongshore sediment transport 1 climate change induced alterations to coral reef ecosystems in combination with sea level rise have the potential to significantly alter wave dissipation across reefs leading to shifts in alongshore sediment transport gradients and alterations to tropical coastlines we used delft3d to model schematized profiles of two reef flat widths based on the south molokai hawaii coast simulated anthropogenic modifications include incremental degradation of the reef structure as well as sea level rise our findings indicate that sea level rise has a greater relative effect on wave energy flux and alongshore sediment transport over a wide flat whereas both reef degradation and sea level rise exert similar influence over a narrow flat these results suggest reefs that vary in width alongshore are more likely to experience changes in alongshore sediment transport gradients and therefore shifts in shoreline erosion and accretion patterns than more uniform reef systems

late quaternary structure and development of the northern ningaloo reef australia ningaloo reef situated on the central west coast is australia s largest fringing reef system extending southward from 22 s for over 200 km its narrow lagoon is backed by a coastal plain which is largely composed of an emergent last interglacial reef on the flank of folded tertiary limestones the west facing reef is exposed to strong oceanic swells across a narrow 8 km continental shelf climatic aridity cyclones tsunamis and the poleward flowing leeuwin current all influence the reef system seismic profiling and a coring and dating program along a transect through a reef pass indicate two periods of reef development in the northern part of the reef holocene and last interglacial seaward of the crest the holocene reef forms either a prominent 500 m wide bulge with 10 m of relief and an abrupt seaward slope or a series of discrete patch reefs holocene reef development is limited to depths of less than 30 m and reaches a maximum thickness of ca 10 15 m below the reef crest u th tims dates from distal parts of the last interglacial section between 18 and 36 m give ages toward the end of the high stand 120 115 ka last interglacial reef growth was more extensive of the two filling much of the available accommodation space perhaps as a result of a stronger leeuwin current this substrate subsequently provided an antecedent foundation for holocene reef development

megaripple migration in a natural surf zone migrating megaripples are bedforms that appear in the surf zone of sandy coasts1 with heights of 0 1 0 5 m and wavelengths of 1 5 m they are similar in size and shape to small dunes large ripples or sand waves such sedimentary bedforms have been studied in subaerial2 steady flow3 and intertidal4 environments as well as in laboratory flume experiments5 they affect overlying currents by introducing hydraulic roughness4 6 and may provide a mechanism for sediment transport7 8 as well as forming sedimentary structures in preserved facies9 10 the formation orientation and migration of such bedforms is not understood well11 12 dunes for example can be aligned with their crests perpendicular to steady unidirectional winds13 but in more complex wind fields their orientation becomes difficult to predict14 15 16 17 similarly it is not known how sea floor megaripples become aligned and migrate in the complex flows of the surf zone here we present observations in the surf zone of a natural beach which indicate that megaripples do not migrate in the direction of the vector sum of the currents but are aligned so that the sediment transport normal to the bedform crest is maximized17 this may need to be taken into account in modelling morphology change and interpreting existing and fossil morphologic patterns

mid late holocene sea level variability in eastern australia a re analysis of sea level data from eastern australia based on 115 calibrated c 14 ages is used to constrain the origin timing and magnitude of sea level change over the last 7000 years we demonstrate that the holocene sea level highstand of 1 0 1 5 m was reached 7000 cal yr bp and fell to its present position after 2000 yr bp these findings are in contrast to most previous studies that relied on smaller datasets and did not include the now common conversion of conventional c 14 ages to calendar years during this 5000 year period of high sea level growth hiatuses in oyster beds and tubeworms and lower elevations of coral microatolls are interpreted to represent short lived oscillations in sea level of up to 1 m during two intervals beginning c 4800 and 3000 cal yr bp the rates of sea level rise and fall 1 2 mm yr 1 during these centennial scale oscillations are comparable with current rates of sea level rise the origin of the oscillations is enigmatic but most likely the result of oceanographic and climatic changes including wind strengths ice ablation and melt water contributions of both greenland and antarctic ice sheets

holocene emergence and evolution of the mcarthur river delta southwestern gulf of carpentaria australia abstract the mcarthur river drains from a semiarid sandstone catchment into a shallow embayment behind the sir edward pellew group of islands in the southwestern gulf of carpentaria it has built a broad holocene delta presently with two active distributaries and several abandoned mangrove lined former distributaries augering indicates that much of the delta is underlain by shelly sands which contain distinct shell beds in their position of growth these are interpreted as delta front deposits and the elevation of the landwardmost beds above high tide level implies emergence of 1 2 m over the last 4000 years this relative sea level fall appears to have been a major cause of rapid mid holocene delta progradation the eastern margin of the delta has undergone little net progradation over the last 2000 years though there has been accretion of small mangrove covered islands to the northwest of the delta distributaries have migrated across the upper deltaic plain by lateral migration leaving nested sequences of fluvial ridges in the lower deltaic plain channel migration appears to have occurred mainly by avulsion former distributaries have been infilled with fluvial sands and are now tidally dominated

understanding the history of extreme wave events in the tuamotu archipelago of french polynesia from large carbonate boulders on makemo atoll with implications for future threats in the central south pacific abstract numerous large carbonate boulders up to 164 tonnes in mass were investigated on the reef flat and beaches of makemo atoll in the tuamotu archipelago of french polynesia to reveal the past occurrence and to anticipate the future potential threat of extreme wave events possibly generated by tropical cyclones and tsunamis the modern reef edge and emerged mid holocene coastal landforms were identified as sources of boulders mobilized during extreme wave events in the past the minimum flow velocities produced by extreme wave events were estimated to exceed 5 4 15 7 m s at the reef edge on different parts of the atoll comparison of uranium thorium ages of boulder coral fabric with written historical records indicates that two large boulders 77 and 68 tonnes were possibly emplaced on the reef flat by a powerful cyclone in february 1878 although most boulder dates are older than the earliest historical cyclone and tsunami records in french polynesia their ages concur with the following a periods of storminess i e increased cyclone activity compared to today in the central south pacific over the last millennium and b periods of high sea surface temperature sst at the great barrier reef possibly associated with higher than normal ssts pacific wide that facilitated the generation of cyclones affecting the central south pacific ocean none of the boulders on makemo were dated younger than ce1900 implying that the last century has not experienced extreme waves of similar magnitude in the past nevertheless the findings suggest that waves of comparable magnitudes to those that have transported large boulders on makemo may recur in the tuamotus and threaten island coasts across the central south pacific in the future