forecasting cyclic coastal erosion on a multi annual to multi decadal scale southeast african coast abstract coastal erosion on the southeast african coastline shows an apparent 18 year cycle which last peaked in 2006 it is in phase with the longshore sediment transport cycle both these cycles appear to be in phase with the lunar nodal cycle lnc however the dominant tidal erosion driver on this coast appears to be the 4 4 year lunar perigean subharmonic lps we suggest that the apparent 18 year coastal erosion and longshore sediment budget cycle is a response to the 18 year mean annual precipitation cycle this cycle is 180 out of phase with the apparent coastal erosion and longshore sediment transport cycles the summer rainfall areas of southeastern africa show an 18 year map cyclicity which drives river runoff and hence controls sediment input to the coast and nearshore environment the map cycle dominates the coastal sediment budget during the lnc trough and suppresses the lps coastal erosion cycle during this time this explains why lps coastal erosion occurs close to the lnc peak thus although the lps cycle dominates the coastline it is masked during the wet portion of the 18 year map cycle it seems very likely that the lnc drives the map cycle in some way but this process is not known nevertheless these relationships can be used to predict in a general way both cyclic coastal erosion and the longshore sediment volume fluctuation this can be translated into a vital coastal planning tool which has the potential to forecast cyclic coastal erosion and hence significantly reduce the sea defense expenditure bill based on this severe cyclic coastal erosion is anticipated in 2023 and 2024

biological remains geochemistry and stable isotopes for the reconstruction of environmental and hydrological changes in the holocene lakes from north sahara abstract a detailed reconstruction of the holocene palaeoenvironments and palaeohydrology is presented for wwamp and lacustrine calcareous sediments which lie in closed depressions along the northern margin of the great western erg algeria it is based on a multidisciplinary approach using numerous techniques the chronological framework is established on the basis of 23 14 c dates on inorganic calcite and mollusc shells ranging from ca 9300 to 3000 yr b p and on an isolated 14 c age of ca 10 900 yr b p the significance of various environmental markers is discussed biological remains are abundant and diversified about 150 taxa including diatoms chrysophytes charophytes ostracods molluscs and foraminifera they provide information on the water chemistry total salinity ionic ratio ph and partial pressure of carbon dioxide and on the habitats water depth development of aquatic plants ephemerality etc emphasis is given to the total salinity individual organisms and palaeobiological assemblages are ordered as a function of their salt requirements and tolerances calibration based on modern diatom samples allows a tentative estimate of the palaeosalinities which range from fresh to marine like and even hypersaline waters attention is drawn to the possible colonization of marine organisms in continental basins without any connection with the sea stable isotope analyses have been carried out on both inorganic and biogenic mollusc and ostracod shells charophyte gyronites carbonates the 18 o contents demonstrate wide changes in the hydrological balance fluctuations in 13 c contents inform on water mixing residence time and on the importance of biological effects on total dissolved inorganic carbon geochemical analyses were performed on inorganic calcite and on ostracod shells high contents in fe and mn indicate reducing environments during stages of high salinity sr ca and mg ca are used as salinity indicators zn mg ratios suggest that the major water supply was the aquifer of the great western erg today down to about 50 m rather than surface waters from the atlas mountains salinities resulted from the balance between inputs from the water table evaporation rate leaching of pre existing salt crusts and seepage through the lake bottom a reconstruction of the evolution of the palaeosystems through time and space has been attempted with special attention to the instability of the water and ionic balances for different time scales short term fluctuations occurring during a single hydrological cycle annual or seasonal are deduced from the apparent discrepancies between the various indicators found in a given sample long term 10 2 10 3 years changes confirm the existence of a climatic phase being wetter than today from at least ca 9300 and may be from ca 10 900 yr b p to 3000 yr b p for the first time the salinity deduced from diatoms and the 18 o content of the water deduced from that of the carbonate at 25 c are used simultaneously to model the hydrological history of the basins and to estimate the relative humidity of the atmosphere during the holocene major environmental trends recorded from ca 9300 to 3000 yr b p do not show a clear synchronims between the different profiles studied therefore they cannot be interpreted in terms of palaeoclimate but instead demonstrate the importance of local hydrology in the evolution of closed basins associated with groundwater a common situation in arid and semi arid zones

liquefaction and post liquefaction assessment of lightly cemented sands post liquefaction response of lightly cemented sands during an earthquake may change and become similar to uncemented sands due to bonding breakage in the current study the effect of degree of ce

coral islands defy sea level rise over the past century records from a central pacific atoll the geological stability and existence of low lying atoll nations is threatened by sea level rise and climate change funafuti atoll in the tropical pacific ocean has experienced some of the highest rates of sea level rise 5 1 0 7 mm yr totaling 0 30 0 04 m over the past 60 yr we analyzed six time slices of shoreline position over the past 118 yr at 29 islands of funafuti atoll to determine their physical response to recent sea level rise despite the magnitude of this rise no islands have been lost the majority have enlarged and there has been a 7 3 increase in net island area over the past century a d 1897 2013 there is no evidence of heightened erosion over the past half century as sea level rise accelerated reef islands in funafuti continually adjust their size shape and position in response to variations in boundary conditions including storms sediment supply as well as sea level results suggest a more optimistic prognosis for the habitability of atoll nations and demonstrate the importance of resolving recent rates and styles of island change to inform adaptation strategies

the arid humid transition in the sahara and the sahel during the last deglaciation at the time of the last glacial maximum the sahara and sahel regions of north africa were extremely dry new records of rainfall show that during the subsequent deglaciation the transition from arid to humid conditions in these regions occurred synchronously in two main steps comparison with other records of palaeoclimate in europe and the north atlantic ocean shows that certain common factors controlled changes in ocean and atmosphere dynamics during the deglaciation

the modified bruun rule extended for landward transport article i nfo the bruun rule bruun 1954 1962 provides a relationship between sea level rise and shoreline retreat and has been widely applied by the engineering and scientific communities to interpret shoreline changes and to plan for possible future increases in sea level rise rates the bruun rule assumes that all sand removed from the upper profile is deposited offshore as sea level rises although overwash during storms and landward aeolian transport clearly indicate otherwise herein we examine processes associated with sandy beach evolution in response to relative sea level rise and propose a modified form of the bruun rule that considers the full range of parsing cross shore transport from completely seaward to completely landward depending on the prevailing storm and surge conditions and whether there is a surplus or deficit of sand in the profile with respect to the equilibrium beach profile a methodology is proposed that more appropriately represents the long term processes and beach response however an improved quantitative understanding of landward transport is required for optimal application of the proposed method published by elsevier b v

the 18 6 yr nodal cycle and its impact on tidal sedimentation abstract the 18 6 yr nodal cycle modulates tidal amplitudes and currents and consequently sedimentation in tide influenced sedimentary environments data are presented which show that such effects are obvious along the coast of the dutch barrier islands and in the sedimentary fill of abandoned channels

long term tidal cycle influences on a late holocene clay mineralogy record from the cariaco basin abstract recent analyses of coastal mudbank dynamics along northeastern south america indicate significant sediment remobilization associated with the 18 6 y lunar nodal tide over the last 20 y we present a near annually resolved record of quartz and illite illite smectite abundances spanning the last 800 y from the cariaco basin venezuela that suggests effects of the lunar nodal tide have played an important role in coastal processes over the last 8 centuries spectral analysis results of the clay and fine silt data include a statistically significant peak at 18 3 y in both the quartz and illite illite smectite records that is identified with the 18 6 y lunar nodal tide remobilization of shelf sediments by mean high water line variations driven by the lunar nodal tide is presented as the probable explanation of this signal in the cariaco basin mineral content since the period of this astronomically determined signal is constant with time it can be used to calibrate high resolution age models we modify our existing age model by tuning the 18 3 y component of the illite data to the 18 6 y period and explore its impact on the age depth relationship we suggest that the 18 6 y signal can be used to refine existing chronologies where detected

extreme erosion on high energy embayed beaches influence of megarips and storm grouping abstract megarips have long been recognised as an important yet poorly documented mechanism of beach erosion on high energy embayed beaches the persistence and cumulative effect of megarips during storm groups are described from three embayed beaches arrifana mt clerigo and amoreira exposed to high energy wave conditions in the mesotidal bedrock dominated southwestern coast of portugal morphological changes determined by topographic monitoring and supplemented by interpretation of digital imagery over two years revealed the development of storm induced megarips which exerted a major influence on beach erosion differences in megarip influence within and between beaches are related to embayment geometry and orientation which significantly influence the nearshore wave field rip location is topographically controlled being determined by alongshore variations in breaking wave height and obliquity along with interaction of wave driven circulation patterns and embayment nearshore topography moderate beach sand loss during individual storms was linked to the development of megarips with associated rip neck and feeder channels extreme erosion however occurred when megarips and feeder channels persisted during successive storms promoting continued erosion and seaward sediment export observations show that once initiated megarip channels persist for several months and continue to act as conduits for offshore sediment transport under non storm conditions the maintenance of such rip circulation systems driven by morphodynamic feedback reduces beach recovery ability until the rip neck and feeder channels are infilled

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

sedimentation on the narrow 8km wide oceanic current influenced continental shelf off durban kwazulu natal south africa abstract the narrow transform margin of southeast africa and its associated sedimentological and hydrodynamic setting differs to other documented continental margins the durban bluff continental shelf is extremely narrow and steep 8 km wide with a gradient ranging from 2 to 8 characterised by a wave and oceanic current dominated regime seismic sequence boundary 2 developed during the last interglacial regression spans the entire shelf separating the holocene sediment wedge seismic unit h from underlying pleistocene deposits a wave ravinement surface marks the holocene transgression comprising a pavement lag of well sorted gravels and bioclastics overlain by inshore reef derived carbonate rich sediments and offshore by quartzose mid shelf sands the shelf sands represent the transgressive holocene to modern sediment wedge forming a seaward thinning unit stacked against the pleistocene blood reef aeolianite beachrock substrate the sediment wedge is dynamic and constantly redistributed by currents associated with the durban eddy inshore of the agulhas current and bottom surge associated with high swells and marine storm events these have been instrumental in shaping large scale shoreface attached and detached sand ridges the presence of mud lenses in the vicinity of blood reef represents deposition from turbid flood waters with preservation facilitated by the morphology of the durban bluff and blood reef palynological results reflecting the local subtropical vegetation and recently introduced neophytes together with radiocarbon dates provide a very recent age for this sediment supporting a terrestrial origin and deposition from a single large flood event

apparent dynamic stability of the southeast african coast despite sea level rise the coast of southeast africa is dominated by sandy beaches that tend to be confined within log spiral or headland bound embayments investigations using serendipitous air imagery data set have been previously undertaken and conclusions drawn about the stability of the coast we show that conclusions drawn from this data with respect to the high water mark hwm position are fraught with errors which include tidal state pressure regime beach slope high swell erosion seasonal and multi annual changes we highlight and discuss these sources of error together with their magnitudes the most significant of these are the high swell seasonal and multi annual variations from case studies we show that the seasonal beach rotation and long term beach width variation are responsible for tens of metres of unaccounted hwm variation 30 to 50 m is common with maximums reaching 60 to 100 m overall the southeast african coastline appears to be in a state of long term dynamic equilibrium there is no evidence of any sea level rise forced transgression in the coastal sediment budget despite sea level rise slr if such a signal is in fact present it is lost within the beach width variation some southeast african coastal reaches are suffering chronic erosion but these are related to anthropogenic impacts the extreme difficulty of placing a hwm with any temporal validity on this coast precludes the routine use of the bruun rule although no transgressive signature is found there is evidence of a decreasing coastal sand budget as a result of anthropogenic or natural climate change or both this decrease in the coastal sand volume is likely to result in increased future erosion copyright 2016 john wiley sons ltd

low frequency sea level fluctuations along the coasts of namibia and south africa summary sea level records at nine ports along the coasts of namibia and south africa are used to establish the existence of coastal trapped disturbances in sea level as a response to the passage of synoptic weather systems using spectral analysis the characteristics and spatial variability of the sea level fluctuations are identified the results of cross correlation analyses performed on sea level data at adjacent ports for two periods during 1982 are discussed in detail to examine the propagation of coastal trapped waves round the coast sea level records from coastal areas in southern africa exhibit extra tidal fluctuations on several different time scales associated with local or remotely forced atmospheric phenomena these scales include the synoptic or event scale of period 2 20 day the seasonal scale of period 3 6 month and the interannual or long term scale with a period of a few years the seasonal and long term components of sea level variability along the west coast of southern africa have been discussed by brundrit 1984 he concluded that there is a clear difference between the seasonal response at the northern and southern ports associated with the difference in winds affecting these two regions the long term component was found to be similar at all ports suggesting large scale non local forcing the theoretical response of sea level to pressure changes at the low frequencies associated with the passage of weather systems is that of an inverted baromei er robinson 1964 records should show a decrease in sea level of 1 01 cm for an increase in atmospheric pressure of 1 mb this assumes an ocean such that the total pressure at any fxed point on the bottom is constant in coastal areas over continental shelves this is rarely valid changes in atmospheric pressure are accompanied by changes in the velocity and direction of the wind and hence wind stress and these also contribute to fluctuations in sea level robinson

postcyclic degradation of strength and stiffness for low plasticity silt stress controlled undrained cyclic triaxial tests followed by strain controlled monotonic compressive shear tests were carried out on normally consolidated and overconsolidated reconstituted keuper marl silt to investigate the strength and stiffness degradation characteristics of a low plasticity silt special attention was paid to the changes in undrained strength and deformation modulus after undrained cyclic loading it was observed that cyclic degradation in stiffness for low plasticity silt is more marked than that of strength and this tendency increases with increasing overconsolidation ratio it was found that a previously proposed model for predicting postcyclic degradation in strength and stiffness of normally consolidated fine grained soils could be applied to that of overconsolidated silt but not however to the postcyclic degradation in young s modulus thus an attempt was made to correlate postcyclic degradation of overconsolidated silt to the equivalent cyclic shear strain instead of the normalized excess pore pressure it was concluded that cyclic shear strain was a better parameter than cyclic induced excess pore pressure for correlating the postcyclic stiffness degradation not only for normally consolidated but also for overconsolidated silt

strontium content of ostracods indicates lacustrine palaeosalinity individual non marine ostracod valves contain sr in proportion to the sr content of their host lake water two commonly coexisting large planktonic species mytilocypris praenuncia and australocypris robusta have a sr distribution coefficient kd sr ca of 0 082 which is independent of temperature in the range 10 18 c if the relationship between salinity and the sr content of a hydrologically simple lake is known palaeosalinities can be calculated from fossil ostracods we present here palaeosalinities for the past 10 000 yr for lake keilambete victoria calculated from ostracod sr ca of fossil material which are in striking agreement with independent interpretations of palaeosalinity the range of salinity spans 14 95 we also show that a reliable quantitative continuous indicator of lacustrine palaeosalinity is important for the elucidation of continental palaeoenvironments for palaeoclimatology and archaeology and ocean continent climatic correlations and interactions

magnesium content of non marine ostracod shells a new palaeosalinometer and palaeothermometer abstract ostracods are microcrustaceans with calcitic carapaces each consisting of two valves or shells that grow by moulting and regeneration of sequentially larger valves up to nine times before reaching maturity the mg content of these valves is species dependent and is a function of their growth stage and the temperature salinity mg content and mg ca ratio of their host water newly formed partly calcified valves of the non marine nektic ostracod mytilocypris henricae have high mg contents 100 000 ppm mg in caco3 at individual shell weights of 2 g this relative mg content decreases as calcification proceeds until shell weights exceed 120 g whereupon the mg content is constant and useful as an indicator of the ostracod s environment mg ca ratios in individual ostracod valves from several species of the genera mytilocypris and australocypris from culture experiments and a series of australian lakes indicate that the valve s mg content increases as a function of increasing temperature and salinity within the range 11 25 c and for waters containing 24 2325 ppm mg the molar mg ca ratio in these ostracods fully calcified valves increases by 0 0015 or 370 ppm mg in caco3 per 1 c and per change of 125 ppm mg in solution for most mainland australian lakes a change in water composition of 125 ppm mg corresponds to a change of 3 5 in salinity for a given mg content of a lake the mg ca ratio of the water may vary within the range of common lacustrine values without significantly affecting mg uptake in the ostracod valves these relationships can provide palaeosalinities and or palaeotemperatures for ostracods recovered from continental sediments for mg partitioning an increase in temperature and salinity produce increased mg content in ostracods whereas for 18o fractionation in biogenic calcite an increase in temperature produces a decrease in 18o of the ostracod and an increase in salinity leads to an increase in 18o of the ostracod thus a combination of 18o and mg measurements on non marine ostracods should enable unique resolution of palaeotemperature and palaeosalinity variations

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

sand bypass and updrift beach evolution after jetty construction at an ebb tidal delta abstract the evolution of an ebb tidal delta guadiana south portugal and its updrift beach after jetty construction in 1972 1974 is analysed based on 24 ortho rectified aerial photographs 1940 2012 and 13 bathymetric maps 1969 2014 the objectives are to evaluate the re establishment of the sand bypassing process and if the disruption of the historical delta may affect the updrift beach evolution post jetty progradation of the updrift beach resulted from two large accretion events the second largest event 110 m progradation in 1985 1994 was due to beach attachment of a shoal produced by the erosion of a broad shallow area relict of the historical delta the reworking of sand from this relict area also enables the individualisation of a lateral updrift bar simultaneously with the new ebb shoal proper formation both morphological features were close to volume equilibrium in 1995 indicating that most of the sand was transported towards the downdrift side of the inlet at that time this study shows that erosion of the historical delta may enhance significantly the updrift shoreline progradation and may promote the re establishment of sand bypassing after jetty construction

factors controlling shelf sediment dispersal along the southeast african continental margin abstract four major factors control sediment dispersal along the southeast african continental margin 1 morphology of the upper continental margin 2 wave regime and wind driven circulation 3 influence of the agulhas current and 4 sediment supply these factors interact on various scales to produce a unique regional sediment dispersal pattern the continental shelf is very narrow and the adjacent slope extremely steep the shelf platform is interrupted by a number of structural offsets and locally the shelf break is dissected by numerous submarine canyons the nearshore zone down to about 60 m waterdepth is dominated by a high energy swell regime and in most places is underlain by a thin wedge of sandy sediment this wedge appears to have achieved dynamic equilibrium with the prevailing energy regime and additional sediment is rapidly dispersed and fed into a sandstream situated on the central shelf where the agulhas current dominates sediment transport along some parts of the coast the sediment wedge is dammed behind a drowned coastal dune ridge within the sandstream sediment is transported alongshelf until a structural offset is reached where sediment spills over the shelf break four major localities for off shelf transport are recognized between maputo and port elizabeth most of the suspended load appears to be expelled from the system without being deposited on the shelf in the lee of each offset a clockwise gyre is developed which produces return flow currents capable of moving sediment northward thereby creating bedload partings in the vicinity of these partings depositional features are observed that are similar to those normally associated with tidal regimes e g bedforms migrating in opposite directions most of the bedload sediment entering the system is eventually deposited in well defined sinks situated in the lee of structural offsets this model applies only to inter glacial high sea level situations accompanied by strong western boundary flow of the agulhas current

composition of inland waters with marine like fauna and inferences for a miocene lake in spain abstract knowledge of the ionic composition of athalassic non marine waters where marine like organisms currently live allows to evaluate their ionic and total dissolved solid tds tolerance ranges together with other ecological data these chemical parameters can be used to interpret hydrological and hydrochemical conditions in ancient lake basins where analogous faunas have been recorded an example of such a utilization of the biological record is presented for miocene clastic dominated lacustrine deposits of the tertiary ebro basin of ne spain which contain marine like fossils comparison of the deduced chemical parameters for the miocene lake waters with the chemical composition of recent groundwaters and saline springs in the same area allows us to infer a similar mode of solute acquisition this implies that there were important cl so 4 saline inflows to the miocene lakes

mechanical behavior of compacted composite clays composite clay is a mixture of clay as the main body and aggregates which are floating within the clayey matrix the undrained behavior of composite clay in its natural or compacted state e g

effective stress response of clay to undrained cyclic loading the effective stress response of a natural marine clay to slow undrained symmetrical cyclic reversal in shear stress is presented the effects of cyclic principal stress difference amplitude cyclic principal effective stress ratio amplitude initial direction of loading and step increase in cyclic stress level on the clay stress strain response are studied under stress conditions of the triaxial test characteristic behaviour patterns are identified in terms of effective stresses key words clay cyclic loading effective stress hysteretic work loading direction step loading

pre and post cyclic behavior of mixed clayey soils soil structures are often comprised or supported by soils that are mixtures of cohesive and granular geomaterials these soils are termed as intermediate or mixed soils and are widely found in natu

effect of initial consolidation condition on postcyclic undrained monotonic shear behavior of mississippi river valley silt abstractthe postcyclic undrained monotonic shear behavior of mississippi river valley mrv silt is investigated by carrying out triaxial tests under various initial consolidation conditions results show that the variation of cyclic shear strength of mrv silt against initial overconsolidation ratio ocr and mean effective consolidation pressure c was consistent with previous studies i e it increased with both increase in ocr and decrease in c the cyclic stress ratio csr had no apparent effect on postcyclic shear behavior for mrv silt at higher ocrs the postcyclic reconsolidation behavior was more similar to recompression unlike the specimens not previously subjected to cyclic loading the initial ocr did not influence effective stress path of the postcyclic reconsolidated specimens at the early stages of shearing the normalized undrained shear strength su oc su nc of mrv silt reconsolidated after cyclic loading increased with ocr stress strain curves of mrv silt reconsolidated after c

contrasting styles of swell driven coastal erosion examples from kwazulu natal south africa during 2006 2007 the kwazulu natal coast of south africa was exposed to several large swell events ho 3 m near the peak of the lunar nodal cycle causing shoreline recession the largest swell hs 8 5 m struck the coast on the march equinox 18th 20th and generated a strong storm return flow observations made before during and after record dramatic coastal erosion shoreline recession of up to 40 m and substantial property damage this swell event removed the semi continuous nearshore bar system and conditioned the coast such that lesser subsequent swell events accomplished much greater amounts of coastal erosion than expected up to 100 m at certain erosion hotspots because waves reached the coast without significant energy dissipation subsequent bar generation rebuilt the inshore bars within six months the styles of erosion during the march 07 event and other 2007 swells were markedly different lesser swells are focused by headlands and result in megarip development and activation of erosion hotspots the march 07 event still water level was raised equinoctial spring high tide and a storm surge of 0 33 0 45 m to a level that rendered most headlands and erosion hotspots ineffective and resulted in laterally extensive erosion of soft shorelines results record cumulative effects of successive swell events on coastal behaviour that proved to be critical in enabling erosion to proceed at rapid rates after the coast had been initially destabilized unlike hurricanes and tsunamis surges associated with swell events are relatively minor and therefore extensive erosion is linked with high lunar tides there is circumstantial evidence that swell induced erosion follows the broad 18 6 yr lunar nodal tidal cycle when the chances of large swells coinciding with high water levels are increased

paleohydrologie isotopique de l oued el akarit sud tunisie au pleistocene superieur et a l holocene previous data from gobert and howe coque and page on the upper quaternary deposits from wadi el akarit are expanded through radiocarbon and stable isotope measurements 18c and 13c from carbonates 18o and 34s from sulphates these new results report on detailed stratigraphic profiles and indicate fluviatile and palustrine environments during the late pleistocene vegetal dams linked to spring activity caused water stagnation fine grained sediments were deposited with appreciable amounts of organic matter which locally developed into some peaty levels in the upper part of the typical cross section located on the left bank about 100 m upstream of the railway bridge pleistocene deposits show a palustrine carbonate crust this formation is attributed to the drainage induced by the major marine regression at glacial maximum during the holocene stagnation periods still occurred interrupted by flood episodes marked by bottom transport and coarse deposits in the typical cross section deposits are well drained and oxidized however downstream a stagnation episode takes place with a rich malacofauna dominated by cerastoderma cardium the uneven distribution of rainfall is documented by the alternation of fine and coarse deposits and it is accentuated by the climatic evolution toward aridity which results in the formation of a gypsum crust after 4000 yr bp later exceptional floods removed sediments from the wadi channel cutting the upper quaternary deposits for about 13 m along the central course of the wadi radiocarbon ages on carbonates are discussed according to various possible origins of total dissolved carbon atmospheric co2 organic activity in the basins and aquifer supply a simple exchange mixing model between aquifer bicarbonate and atmospheric co2 is used for calculations of initial carbonate activities chemical isotopic and hydraulic steady states are assumed in this treatment present day 14c and 13c contents of aquifer bicarbonate are thus adopted for past values the model leads to acceptable corrected ages for pleistocene carbonate samples corrected ages are younger than apparent ages by a few thousands of years and become consistent with ages given by organic matter from nearby levels however holocene samples appear overcorrected their crystallization appears to be controlled by modern organogenic co2 holocene 14c ages are probably correct 18o contents of carbonate indicate a continental origin for environmental water nodules and carbonate concretions crystallized in bottom sediments through upward leakage of confined aquifers they show 18o contents compatible with present day stable isotope compositions of artesian springs this supports the concept of a good time constancy in stable isotope contents shell carbonate values indicate a variable evaporation rate from the same initial waters 18o and 34s contents of gypsums are also compatible with aqueous sulphates from springs the data set falls within the range of permo triassic sulphate and suggests deep hydraulic connections within aquifer systems the entire formation appears to be of continental origin the occurence of cardium rich basins can only be attributed to the initial salinity of springs waters 7 9 g 1 1 sightly increased by evaporation this signifies that one can not deduce any tectonic uplift from their location with respect to sea level

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

wave influences in contemporary and mesoarchaean stromatolites abstract contemporary shore platform stromatolites sps are becoming well known we describe the physical environment and macrostructures from contemporary shore platform stromatolites sps on the wave dominated southeast african coast this was then compared with mesoarchaean 2 97 ga stromatolites from white umfolozi 100 km inland we use the tinley manor sps occurrence as the basis for physical environmental comparison but where necessary draw on evidence from other sps environments sps and mesoarchean umfolozi stromatolites contain similar stromatolitic structures and wave deposits the sps environment is wave dominated and the occurrence of similar sedimentary structures associated with the mesoarchean umfolozi stromatolites indicates a paleoenvironment associated with waves the contemporary tinley manor sps wave climate is robust and from this locality we have identified broad limits in which sps can develop and be preserved applying this knowledge to the mesoarchaean white umfolozi stromatolites suggests that they formed in a protected wave climate where wave incursions were less frequent both these wave influenced settings are were subject to very low siliciclastic input the frequency of marine sediment input appears to be a limiting factor on microbialite growth in both the contemporary sps and archaean examples