holocene pollen spectra from oyo northwestern sudan problems of interpretation in a hyperarid environment the oyo site is in the hyperarid core of the eastern sahara a 3 4 m core of lake sediment yielded a continuous pollen record for the period 9 to 4 5 ka bp the lower regularly laminated carbonate sediments 9 6 ka show a pollen assemblage with the tropical taxa dominated by plants of sudanian and sahelian affinity and the local taxa dominated by grass and typha the upper sediments 6 4 5 ka grading from laminated carbonates to coarsely bedded and massive layers with aeolian sands have reduced frequencies of sudanian pollen taxa and increases in saharan types and sedge dominated local pollen spectra a possible vegetational reconstruction is a mosaic of savanna woodlands associated with groundwater supported lakes and marshes between 9 and 6 ka bp and sparser cover of steppe and semidesert communities between 6 and 4 5 ka bp as water tables dropped and hyperarid conditions were restored

vegetation change in equatorial west africa time slices for the last 150 ka abstract drawing on marine and terrestrial palynological data vegetation maps of equatorial west africa are presented for eleven time slices over the last 150 000 years long marine records are used as a basis for the regional picture and provide a chronology for the last glacial cycle much shorter terrestrial records help fill in the picture for the most recent periods and facilitate interpretation of regional patterns for the longer timescale temporal and spatial variation is revealed in relation to global patterns of climate change rain forest was widespread during oxygen isotope stages 1 and 5 but strongly reduced during stages 3 and 4 and especially during stages 2 and 6 when open grass rich vegetation prevailed glacial rain forest refuges are found in the southwest of the guinean mountains and along the eastern coast of the gulf of guinea miombo woodland of the zambezian vegetation zone expanded during stage 5 especially during the first half podocarpus forest had its largest expansion during substages 5d 115 to 105 ka and 5b 95 to 85 ka the last occurrence of podocarpus in the guinean mountains is during stage 5a the distribution of mangrove swamps was extremely reduced during glacial times during stage 6 savanna and open dry forest covered large areas along the northern coast of the gulf of guinea the southern saharan desert reached far to the south and the namib desert far to the north the area of rain forest was restricted mangrove swamps were strongly reduced and the area of podocarpus forest fluctuated during stage 5 large changes in the area of afromontane forest rain forest dry open forest and savanna occurred rain forest was widespread and mangroves were extensive along the coast during the last interglacial substage 5e podocarpus forest area strongly extended during substages 5d and 5b in substages 5c and 5a rain forest reclaimed areas it had lost in the previous substages 5d and 5b respectively mangrove swamps were less widespread in the later substages of stage 5 than during substage 5e during stage 4 the rain forest area was again strongly reduced and recovered only slightly during the following stage 3 also the mangrove swamp area was reduced except along the ivory coast and along the northwestern coast of the gulf of guinea podocarpus forest only occurred in angola and may be in congo during stage 4 again forest was much reduced during stage 2 and open vegetation types covered large parts of equatorial west africa mangrove swamps must have been rare at the beginning of the holocene mangrove swamps had recovered and reached their largest extension also the rain forests area increased in the early holocene and guinean and congolian rain forests were probably not separated by a savanna corridor now existing in togo and benin

a mid holocene candidate tsunami deposit from the nw cape western australia although extreme wave events are frequent along the northwestern coast of western australia and tsunamis in 1994 and 2006 induced considerable coastal flooding locally robust stratigraphical evidence of prehistoric tropical cyclones and tsunamis from this area is lacking based on the analyses of x ray computed microtomography ct of oriented sediment cores multi proxy sediment and microfaunal analyses optically stimulated luminescence osl and 14c ams dating this study presents detailed investigations on an allochthonous sand layer of marine origin found in a back barrier depression on the nw cape range peninsula the event layer consists of material from the adjacent beach and dune fines and thins inland and was traced up to 400 m onshore although a cyclone induced origin cannot entirely be ruled out the particular architecture and fabric of the sediment rip up clasts and three subunits point to deposition by a tsunami as such it represents the first stratigraphical evidence of a prehistoric mid holocene tsunami in nw western australia it was osl dated to 5400 4300 years ago thus postdating the regional mid holocene sea level highstand

quaternary forest associations in lowland tropical west africa terrestrial fossil pollen records are frequently used to reveal the response of vegetation to changes in both regional and global climate here we present a fossil pollen record from sediment cores extracted from lake bosumtwi west africa this record covers the last c 520 thousand years ka and represents the longest terrestrial pollen record from africa published to date the fossil pollen assemblages reveal dynamic vegetation change which can be broadly characterized as indicative of shifts between savannah and forest savannah formations are heavily dominated by grass poaceae pollen 55 typically associated with cyperaceae chenopodiaceae amaranthaceae and caryophyllaceae forest formations are palynologically more diverse than the savannah with the key taxa occurring in multiple forest zones being moraceae celtis uapaca macaranga and trema the fossil pollen data indicate that over the last c 520 ka the vegetation of lowland tropical west africa has mainly been savannah however six periods of forest expansion are evident which most likely correspond to global interglacial periods a comparison of the forest assemblage composition within each interglacial suggests that the holocene 11 0 ka forest occurred under the wettest climate while the forest which occurred at the time of marine isotope stage 7 probably occurred under the driest climate

number and size of last glacial missoula floods in the columbia river valley between the pasco basin washington and portland oregon field evidence and radiocarbon age dating combined with hydraulic flow modeling provide new information on the magnitude frequency and chronology of late pleistocene missoula floods in the columbia river valley between the pasco basin washington and portland oregon more than 25 floods had discharges of 1 0 106 m3 s at least 15 floods had discharges of 3 0 106 m3 s at least six or seven had peak discharges of 6 5 106 m3 s and at least one flood had a peak discharge of 10 106 m3 s a value consistent with earlier results from near wallula gap but better defined because of the strong hydraulic controls imposed by critical flow at constrictions near crown and mitchell points in the columbia river gorge stratigraphy and geomorphic position combined with 25 radiocarbon ages and the widespread occurrence of the ca 13 ka radiocarbon years mount st helens set s tephra show that most if not all the missoula flood deposits exposed in the study area were emplaced after 19 ka radiocarbon years and many were emplaced after 15 ka more than 13 floods perhaps postdate ca 13 ka including at least two with discharges of 6 106 m3 s from discharge and stratigraphic relationships upstream we hypothesize that the largest flood in the study reach resulted from a missoula flood that predated blockage of the columbia river valley by the cordilleran ice sheet multiple later floods probably including the majority of floods recorded by fine and coarse grained deposits in the study area resulted from multiple releases of glacial lake missoula that spilled into a blocked and inundated columbia river valley upstream of the okanogan lobe and were shunted south across the channeled scabland

a 200 ka pollen and oxygen isotopic record from two sediment cores from the eastern arabian sea abstract we present here a pollen record from the northern indian ocean that goes back to 200 ka the boundary between marine isotopic stages mis 7 and 6 pollen oxygen isotopic composition and organic carbon have been examined for two sediment cores from the eastern arabian sea 15 02 n and 71 41 e 13 16 n and 71 00 e to reconstruct the long term palaeoclimate and palaeovegetation of the indian subcontinent oxygen isotope data suggest that glacial periods mis 2 4 and 6 are characterised by low precipitation because of a weak southwest monsoon and a strong northeast monsoon in contrast interglacial periods mis 1 3 and 5 are marked by high fresh water input resulting from a strong southwest monsoon during the last glacial interglacial cycle sea surface temperature and surface salinity changed as a result of variations in the evaporation precipitation e p balance throughout the core the dominant pollen types are poaceae and chenopodiaceae and or amaranthaceae 50 their dominance during glacial periods mis 2 4 and 6 suggests that the climate was cold and dry this dominance is also suggestive of salinity tolerant vegetation colonizing large areas near seashore due to lower sea level or high e p conditions during interglacial periods mis 1 3 and 5 when there was high precipitation the arid taxa were sparse whereas poaceae and piperaceae were abundant hence chenopodiaceae and or amaranthaceae and artemisia are suggestive of cold and arid semi arid climate and poaceae and piperaceae of warm and wet conditions mangrove pollen is not well represented in the cores

the holocene paleo tsunami history of west australia abstract west australian coastlines experienced several tsunamis in mid holocene times to expand our knowledge about holocene tsunami events in west australia the authors extended the previously studied spatial scale to include the central and south western coastlines several of the discovered events were mid and young holocene 1000 yr bp tsunami impacts on the outer coast of the cape range peninsula five hundred kilometres to the south between cape cuvier and point quobba additional tsunami evidence exists on top of steep cliffs over a coastal stretch of 30 km the sedimentary signature of two tsunamis is documented in this area by wide ridges comprised of sand shell and clasts including coral fragments at heights of 12 30 m asl and 300 500 m inland enigmatic boulders 20 100 tons appear as cliff top megaclasts up to 100 m inland here radiocarbon dating revealed a minimum of two tsunami events at 5700 yr bp with waves depositing sandy ridges far inland and at approximately 1000 yr bp with waves depositing boulders originating from the marine environment as the first dates are congruent with previously published results for the learmonth region 500 km to the north we assume that the same mid holocene tsunami hits this long coastal section as well the southwestern coast of west australia from cape naturaliste to albany also shows signs of impacts by extreme waves here huge granite boulders 80 400 tons were dislocated and transported to heights up to 10 m above sea level the most prominent dislocated boulders were positioned at merchant rock cape naturaliste national park at islet near nanarup and in cave bay close to albany

abrupt onset and termination of the african humid period rapid climate responses to gradual insolation forcing a detailed ca 100 yr resolution and well dated 18 ams 14 c dates to 23 cal ka bp record of latest pleistocene holocene variations in terrigenous eolian sediment deposition at odp site 658c off cap blanc mauritania documents very abrupt large scale changes in subtropical north african climate the terrigenous record exhibits a well defined period of low influx between 14 8 and 5 5 cal ka bp associated with the african humid period when the sahara was nearly completely vegetated and supported numerous perennial lakes an arid interval corresponding to the younger dryas chronozone punctuates this humid period the african humid period has been attributed to a strengthening of the african monsoon due to gradual orbital increases in summer season insolation however the onset and termination of this humid period were very abrupt occurring within decades to centuries both transitions occurred when summer season insolation crossed a nearly identical threshold value which was 4 2 greater than present these abrupt climate responses to gradual insolation forcing require strongly non linear feedback processes and current coupled climate model studies invoke vegetation and ocean temperature feedbacks as candidate mechanisms for the non linear climate sensitivity the african monsoon climate system is thus a low latitude corollary to the bi stable behavior of high latitude deep ocean thermohaline circulation which is similarly capable of rapid and large amplitude climate transitions

west african paleoclimates during the last climatic cycle inferred from an atlantic deep sea pollen record abstract pollen studies of marine sediments from atlantic deep sea core v22 196 13 50 n 18 57 w 3728 m water depth are used to reconstruct paleoclimates of north tropical west africa since 140 000 yr b p high concentration of pollen mainly from saharan and arid littoral zones suggests a strengthened tradewind circulation since ca 60 000 yr b p that became even stronger after 40 000 yr b p and reached a maximum 17 000 yr b p periods of eolian transport of pollen to the atlantic occurred about 94 000 and 105 000 yr b p and during termination ii conversely high relative values of pollen from sudanian and guinean zones and from mangrove and freshwater vegetation coincident with maxima of dinocyst concentration are interpreted as reflecting both strong fluvial inputs and the expansion of humid vegetation on the adjacent continent during wet periods dated between 140 000 and 118 000 105 000 and 96 000 92 000 and 73 000 52 000 and 44 000 yr b p and 12 000 yr b p and the holocene the strong correlation of these results from the eastern tropical atlantic with those from the arabian sea corroborates fluctuations of monsoon climate

orbital forcing of climate over south africa a 200 000 year rainfall record from the pretoria saltpan late pleistocene variations in rainfall in subtropical southern african are estimated from sediments preserved in the pretoria saltpan a 200000 year old closed basin crater lake on the interior plateau of south africa we show that south african summer rainfall covaried with changes in southern hemisphere summer insolation resulting from orbital precession as predicted by orbital precession geometry berger 1978 this south african record is out of phase with north african palaeomonsoon indices street and grove 1979 rossignol strick 1983 mcintyre et al 1989 the amplitude of the rainfall response to insolation forcing agrees with climate model estimates prell and kutzbach 1987 these results document the importance of direct orbital insolation forcing on both subtropical north and south african climate as well as the predicted antiphase sensitivity to precessional insolation forcing

evidence of atmospheric paleocirculation over the gulf of guinea since the last glacial maximum high resolution pollen and eolian input studies from core ks 84063 in the gulf of guinea record the response of the tropical atmospheric circulation to global paleoclimatic events during the last glacial interglacial transition two depositional phases centered around 15 000 and 10 300 yr b p are characterized by maximum values of pollen concentration and of eolian activity index ea1 pollen spectra record the significant presence of artemisia and ephedra of saharan origin and the scattered occurrence of podocarpus from guinean mountain forests these demonstrate the intensity of the meridional atmospheric circulation over equatorial west africa during dry periods the early holocene humid phase ca 8500 yr b p is marked by minima in pollen concentrations and eai saharan taxa are absent and in contrast podocarpus reached its highest relative values this evidence has been interpreted as reflecting a weakening in the continentocean eolian transport and the importance of monsoonal fluxes downcore variations in podocarpus percentages are used to identify the atmospheric circulation patterns over the low latitudes of west africa during extreme dry humid climatic conditions

comparison of marine and terrestrial holocene climatic reconstructions from northeastern north america quantitative climate reconstructions based on marine dinocysts and terrestrial pollen sequences are consistent through the holocene in northeastern north america principal components analysis pca indicates a large scale climate signal in the dinocysts and pollen the combined and separate analyses of marine and nearby terrestrial pollen sequences from hudson bay labrador and the st lawrence estuary differentiate tun dra boreal forest and deciduous forest assemblages in time and space these analyses indicate that the marine pollen record reflects vegetation changes of the regional terrestrial environment and allows direct correlations between the marine and terrestrial stratigraphies sea surface temperatures estimated from dinocysts and terres trial air temperatures from pollen using the method of modern analogs show that the three regions had differing climate histories associated with their location with respect to deglaciation and air mass boundaries high frequency climatic changes reconstructed

land sea comparisons during the last glacial interglacial transition pollen records from west tropical africa abstract land sea correlation off nw africa is investigated from both modern and late pleistocene holocene pollen records pollen spectra from modern soil surface samples from senegal and mauritania and from modern bottom sediment samples from the offshore eastern atlantic 21 12 n record accurately the latitudinal vegetation zonation of west tropical africa by showing the maximum percentages of the phytogeographical groups and the same characteristic taxa as the adjacent vegetation zones a strong correlation between marine core m 16017 2 near cap blanc and continental sebkha of chemchane mauritania pollen signals is also observed for the evolution of the late glacial holocene vegetation zonation at 21 n the differing sensitivities of each sedimentary environment for recording local and or subcontinental vegetation changes are discussed

paleoclimates off northwest africa 28 35 n about 18 000 yr b p based on continental eolian deposits abstract most conceptual models of atmospheric circulation deduced from bottom sediments or isopollen maps off nw africa assume the occurrence of intensified nne trade winds about 18 000 yr b p in latitudes of 28 35 n and oversimplify the glacial atmospheric circulation over africa an alternative method for reconstructing paleowinds of the last glacial maximum in these latitudes was recently put forward and uses sedimentological records from the canary islands and coastal regions of morocco the continental data do not agree with the previous models and show the prevalence of westerlies all the data from deep sea cores reduction of sea surface temperature increase of biogenic opal accumulation distribution patterns of pollen or dinoflagellate cysts and xeric conditions on the adjacent continent can be explained without increased activity of the trade winds but with a discharge current of cold meltwater from the european and north american ice sheets the model is backed up by a comparison with the present day humboldt current off subtropical south america

coherent response of arabian sea upwelling and pollen transport to late quaternary monsoonal winds the indian summer monsoon causes large seasonal changes in the environments of both eastern africa and the arabian sea here we compare time series 140 kyr long of selected pollen types and foraminiferal upwelling faunas preserved in marine sediments to identify the frequencies of their variability and the coherence and phase of the terrestrial and marine responses to monsoonal circulation during interglacial intervals the pollen and upwelling records of the western arabian sea indicate stronger monsoons and are both coherent and in phase at periodicities near the precession of the earth s rotational axis 23 kyr we conclude that the strength of the monsoonal southwesterlies accounts for this high coherence of marine and terrestrial records during interglacial intervals low correlation during glacial phases indicates weaker monsoons and some decoupling of these two records these data indicate that two distinct modes of monsoon variability may exist an interglacial mode with strong monsoons and effective coupling of terrestrial and marine records and a glacial mode with both weaker monsoons and decreased linkage between arabian sea pollen and upwelling records

prograded foredunes of western australia s macro tidal coast implications for holocene sea level change and high energy wave impacts the holocene evolution of the canning coast of western australia has largely been overlooked so far mainly due to its remoteness and low population density we report on new data from a sequence of foredunes inside the macro tidal admiral bay 110 km southwest of broome based on sediment cores differential global positioning system dgps based elevation transects and stratigraphical analyses on outcrops of the relict foredunes we aim at reconstructing holocene coastal changes and relative sea levels rsls as well as identifying and dating imprints of extreme wave events sedimentary analyses comprise the documentation of bedding structures foraminiferal content and macrofaunal remains grain size distribution and organic matter the chronological framework is based on 26 carbon 14 accelerator mass spectrometry 14c ams datings marine flooding of the pre holocene surface landward of the 2 5 km wide foredune barriers occurred 7400 7200 cal bp when mangroves colonized the area after only 200 400 years a high energy inter tidal environment established and prevailed until c 4000 cal bp before turning into the present supralittoral mudflat during that time coastal regression led to beach progradation and the formation of aligned foredunes drivers of progradation were a stable rsl or gradual rsl fall after the mid holocene and a positive sand budget the foredunes overlie upper beach deposits located up to 2 m above the present upper beach level and provide evidence for a higher mid holocene rsl discontinuous layers of coarse shells and sand are intercalated in the foredunes indicating massive coastal flooding events one such layer was traced over three dune ridges and dated to c 1700 1550 cal bp however it seems that most tropical cyclones induce net erosion rather than deposition at aligned foredunes and thus they are only suitable for reconstructing temporal variability if erosional features or sedimentation reliably tied to these events can be identified and dated accurately copyright 2014 john wiley sons ltd

a late quaternary marine palynological record oxygen isotope stages 1 to 7 for the humid tropics of northeastern australia based on odp site 820 a late quaternary marine palynological record from the ocean drilling program odp site 820 adjacent to the humid tropics region of northeastern australia has demonstrated marked variation in orbital scale cyclicity and also trends associated with both climate and human impact however some uncertainties in interpretation have resulted from concerns about the records chronology and continuity here we present for the first time the complete palynological data from detailed analysis of the top 67 m of sediment and examine it in relation to the marine isotope sequence from the core it is proposed that the record is relatively continuous through the last 250 000 years although the latter part of oxygen isotope stage ois 5 as well ois 4 may be missing despite the variation on orbital scales most palynological changes are not in phase with those from the marine isotope record suggesting a lack of direct milankovitch forcing on vegetation this lack of correspondence combined with major trends towards more open and sclerophyllous vegetation in association with increased burning supports a previous proposal that major control is being exercised by el nino southern oscillation variability whose influence may have been initiated by changes in oceanic circulation in the region within the mid pleistocene the lack of impact on the distribution of complex rainforest suggests that increased climate variability did not involve an overall decrease in total precipitation c 2007 elsevier b v all rights reserved

a probabilistic tsunami hazard assessment for western australia the occurrence of the indian ocean tsunami on 26 december 2004 has raised concern about the difficulty in determining appropriate tsunami mitigation measures in australia due to the lack of information on the tsunami threat a first step in the development of such measures is a tsunami hazard assessment which gives an indication of which areas of coastline are most likely to experience tsunamis and how likely such events are here we present the results of a probabilistic tsunami hazard assessment for western australia wa compared to other parts of australia the wa coastline experiences a relatively high frequency of tsunami occurrence this hazard is due to earthquakes along the sunda arc south of indonesia our work shows that large earthquakes offshore of java and sumba are likely to be a greater threat to wa than those offshore of sumatra or elsewhere in indonesia a magnitude 9 earthquake offshore of the indonesian islands of java or sumba has the potential to significantly impact a large part of the west australian coastline the level of hazard varies along the coast but is highest along the coast from carnarvon to dampier tsunamis generated by other sources e g large intra plate events volcanoes landslides and asteroids were not considered in this study

combined infragravity wave and sea swell runup over fringing reefs by super typhoon haiyan super typhoon haiyan struck the philippines on 8 november 2013 marking one of the strongest typhoons at landfall in recorded history extreme storm waves attacked the pacific coast of eastern samar where the violent typhoon first made landfall our field survey confirmed that storm overwash heights of 6 14 m above mean sea level were distributed along the southeastern coast and extensive inundation occurred in some coastal villages in spite of natural protection by wide fringing reefs a wave model based on boussinesq type equations is constructed to simulate wave transformation over shallow fringing reefs and validated against existing laboratory data wave propagation and runup on the eastern samar coast are then reproduced using offshore boundary conditions based on a wave hindcast the model results suggest that extreme waves on the shore are characterized as a superposition of the infragravity wave and sea swell components the balance of the two components is strongly affected by the reef width and beach slope through wave breaking frictional dissipation reef flat resonances and resonant runup amplification therefore flood characteristics significantly differ from site to site due to a large variation of the two topographic parameters on the hilly coast strong coupling of infragravity waves and sea swells produces extreme runup on steep beaches fronted by narrow reefs whereas the infragravity waves become dominant over wide reefs and they evolve into bores on steep beaches

eolian evidence for spatial variability of late quaternary climates in tropical africa abstract study of the eolian fraction of late quaternary sediments from the tropical atlantic reveals that two modes of long term climate variability have existed in tropical africa during the last 150 000 yr tropical northwest africa i e the southwestern sahara and sahel was driest during glaciations and stades but wetter than at present during interglaciations and interstades this may be a response to ice sheets at higher latitudes via equatorward displacement of the westerlies and the subtropical high in contrast central equatorial africa southeast of the sahara was most arid during interstades and times of ice growth and most humid during deglaciation wet periods in this area correspond to insolation maxima in northern hemisphere summer a 23 000 yr precessional rhythm is suggested supporting a direct link between african monsoon intensity and orbitally modulated insolation the late holocene is the only time observed when both areas are arid during an interglacial episode this may reflect in part anthropogenic disturbance of late holocene climates

orbital scale vegetation change in africa abstract palynological records of middle and late pleistocene marine sediments off african shores is reviewed in order to reveal long term patterns of vegetation change during climate cycles whether the transport of pollen and spores from the source areas on the continent to the ocean floor is mainly by wind or predominantly by rivers depends on the region despite the differences in transportation accumulation rates in the marine sediments decline exponentially with distance to the shore the marine sediments provide well dated records presenting the vegetation history of the main biomes of western and southern africa the extent of different biomes varied with the climate changes of the glacial interglacial cycle the mediterranean forest area expanded during interglacials the northern saharan desert during glacials and the semi desert area in between during the transitions in the sub saharan mountains ericaceous scrubland spread mainly during glacials and the mountainous forest area often increased during intermediate periods savannahs extended or shifted to lower latitudes during glacials while the representation of the tropical rain forest fluctuated with summer insolation and precession that of the subtropical biomes showed more obliquity variability or followed the pattern of glacial and interglacials

truncated flame structures within a deposit of the indian ocean tsunami evidence of syn sedimentary deformation this study reveals the three dimensional morphology and syn sedimentary formation processes of a deformation structure termed truncated flame structures which is found in a terrestrial tsunami deposit in southern thailand that formed during the 2004 indian ocean tsunami the structure was found at the boundary between a lower fine grained layer and an upper coarse grained layer that are related to two runup events in order to confirm the morphology of the structure the authors excavated two trenches and an opencast pit when viewed in a cross section oriented parallel to the direction of the runup current the deformed boundary has an irregularly bulging profile similar to that observed in flame structures the protruding structures are inclined towards the downstream direction of the runup current and are truncated horizontally along their upper surface by parallel laminations in the overlying layer when viewed in a cross section oriented perpendicular to the current direction it appears that parts of the upper layer descend into the lower layer as lobate masses in places these masses are completely detached from the main part of the upper layer forming circular or elliptical shapes the contact between the lower layer and the main part of the upper layer is a planar truncation surface opencast excavation of the contact surface revealed that the deformed structures have flat sinuous horseshoe crests that open in a downstream direction it is possible for the runup current to generate shear stress such that it deforms the boundary into a truncated flame structure moreover the observations made in this study indicate the syn sedimentary development of the structure deformation and truncation occurred simultaneously in association with the runup current that formed the upper layer truncated flame structures can be used as a criterion in identifying the syn sedimentary deformation of substrate the structures are indicative of unidirectional flow with sufficiently high shear velocity to deform unconsolidated substrate as in the present case the truncated flame structures may be characteristic of tsunami events that involve strong unidirectional currents on land due to the extraordinarily long wave period of tsunamis rather than other events such as storm surges or flooding

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

late quaternary climatic events and sea level changes recorded by turbidite activity dakar canyon nw africa the relationship of sea level changes and short term climatic changes with turbidite deposition is poorly documented although the mechanisms of gravity driven sediment transport in submarine canyons during sea level changes have been reported from many regions this study focuses on the activity of the dakar canyon off southern senegal in response to major glacial interglacial sea level shifts and variability in the nw african continental climate the sedimentary record from the canyon allows us to determine the timing of turbidite events and on the basis of xrf scanning element data we have identified the climate signal at a sub millennial time scale from the surrounding hemipelagic sediments over the late quaternary the highest frequency in turbidite activity in the dakar canyon is confined to major climatic terminations when remobilisation of sediments from the shelf was triggered by the eustatic sea level rise however episodic turbidite events coincide with the timing of heinrich events in the north atlantic during these times continental climate has changed rapidly with evidence for higher dust supply over nw africa which has fed turbidity currents increased aridity and enhanced wind strength in the southern saharan sahelian zone may have provided a source for this dust

the 2011 japan tsunami current velocity measurements from survivor videos at kesennuma bay using lidar 1 on march 11 2011 a magnitude mw 9 0 earthquake occurred off the coast of japan s tohoku region causing catastrophic damage and loss of life the tsunami flow velocity analysis focused on two survivor videos recorded from building rooftops at kesennuma bay along japan s sanriku coast a terrestrial laser scanner was deployed at the locations of the tsunami eyewitness video recordings the tsunami current velocities through the kesennuma bay are determined in a four step process the lidar point clouds are used to calibrate the camera fields of view in real world coordinates the motion of the camera during recordings was determined the video images were rectified with direct linear transformation finally a cross correlation based particle image velocimetry analysis was applied to the rectified video images to determine instantaneous tsunami flow velocity fields the measured maximum tsunami height of 9 m in the kesennuma bay narrows were followed by maximum tsunami outflow currents of 11 m s less than 10 minutes later

precipitation source inferred from stable isotopic composition of pleistocene groundwater and carbonate deposits in the western desert of egypt an atlantic source of precipitation can be inferred from stable isotopic data h and o for fossil groundwaters and uranium series dated carbonate spring deposits from oases in the western desert of egypt in the context of available stable isotopic data for fossil groundwaters throughout north africa the observed isotopic depletions delta d 72 to 81 per thousand delta sup 18 o 10 6 to 11 5 per thousand of fossil ge 32 000 yr b p groundwaters from the nubian aquifer are best explained by progressive condensation of water vapor from paleowesterly wet oceanic air masses that traveled across north africa and operated at least as far back as 450 000 yr before the present the values of delta sup 18 o 17 1 to 25 9 per thousand for 45 000 to 450 000 yr old tufas and vein filling calcite deposits from the kharga and farafra oases are consistent with deposition from groundwaters having oxygen isotopic compositions similar to those of fossil groundwaters sampled recently at these locations

influences of high and low latitude processes on african terrestrial climate pleistocene eolian records from equatorial atlantic ocean drilling program site 663 high and low latitude forcing of terrestrial african paleoclimate variability is demonstrated using 900 ka eolian and biogenic component records from ocean drilling program site 663 in the eastern equatorial atlantic terrigenous eolian dust and phytolith savannah grass cuticle accumulation rate records vary predominantly at 100 and 41 kyr periodicities and spectral phase estimates implicate high latitude forcing the abundance of freshwater diatoms melosira transported from dry african lake beds varies coherently at 23 19 kyr orbital periodicities and at a phasing which implicates low latitude precessional monsoon forcing modeling studies demonstrate that african climate is sensitive to both high and low latitude boundary conditions african monsoon intensity is modulated by direct insolation variations due to orbital precession whereas remote high latitude forcing can be related to cool north atlantic sea surface temperatures ssts which promote african aridity and enhance dust transporting wind speeds the site 663 terrigenous and phytolith records covary with north atlantic sst variability at 41 n site 607 we suggest that pleistocene african climate has responded to both high latitude north atlantic sst variability as well as low latitude precessional monsoon forcing the high latitude influence dominates the sedimentary record prior to circa 2 4 ma terrigenous variations occurred primarily at precessional periodicities 23 19 kyr indicating that african climate was largely controlled by low latitude insolation variations prior to the onset of high amplitude glacial interglacial climate change

the last interglacial ocean the final effort of the climap project was a study of the last interglaciation a time of minimum ice volume some 122 000 yr ago coincident with the substage 5e oxygen isotopic minimum based on detailed oxygen isotope analyses and biotic census counts in 52 cores across the world ocean last interglacial sea surface temperatures sst were compared with those today there are small sst departures in the mid latitude north atlantic warmer and the gulf of mexico cooler the eastern boundary currents of the south atlantic and pacific oceans are marked by large sst anomalies in individual cores but their interpretations are precluded by no analog problems and by discordancies among estimates from different biotic groups in general the last interglacial ocean was not significantly different from the modern ocean the relative sequencing of ice decay versus oceanic warming on the stage 6 5 oxygen isotopic transition and of ice growth versus oceanic cooling on the stage 5e 5d transition was also studied in most of the southern hemisphere the oceanic response marked by the biotic census counts preceded led the global ice volume response marked by the oxygen isotope signal by several thousand years the reverse pattern is evident in the north atlantic ocean and the gulf of mexico where the oceanic response lagged that of global ice volume by several thousand years as a result the very warm temperatures associated with the last interglaciation were regionally diachronous by several thousand years these regional lead lag relationships agree with those observed on other transitions and in long term phase relationships they cannot be explained simply as artifacts of bioturbational translations of the original signals

african monsoons an immediate climate response to orbital insolation the croll milankovitch astronomical theory of climate1 3 has received strong support from the evidence of a linear climatic forcing by obliquity and precession although nonlinearity had to be assumed for eccentricity4 5 moreover interglacials have appeared to be controlled by the orbital insolation6 although a phase shift of 6 000 5 000 yr is seen between an astronomical climate index and terrestrial climate indicators dominated by the northern ice sheet dynamics climate proxy data of low latitudes are less directly dependent on the ice sheets here it is shown that during the past 464 000 yr african monsoons signalled by the east mediterranean sapropels were heaviest always and only when a northern summer monsoon index computed from the orbital variation of insolation reached maximum values this occurred during all the interglacials but also twice during glacial periods thus tropical aridity is not the single climatic pattern of glacial periods an immediate terrestrial climate response to orbital variations of insolation is established

traces of historical tropical cyclones and tsunamis in the ashburton delta north west australia although the north western coast of western australia is highly vulnerable to tropical cyclones and tsunamis little is known about the geological imprint of historic and prehistoric extreme wave events in this particular area despite a number of site specific difficulties such as post depositional changes and the preservation potential of event deposits both tropical cyclones and tsunamis may be inferred from the geomorphology and the stratigraphy of beach ridge sequences washover fans and coastal lagoons or marshes a further challenge is the differentiation between tsunami and storm deposits in the geological record particularly where modern deposits and or historical reports on the event are not available this study presents a high resolution sedimentary record of washover events from the ashburton river delta western australia spanning approximately the last 150 years a detailed characterization of event deposits is provided and a robust chronostratigraphy for the investigated washover sequence is established based on multi proxy sediment analyses and optically stimulated luminescence dating combining sedimentological geochemical and high resolution optically stimulated luminescence data event layers are assigned to known historical events and tropical cyclone deposits are separated from tsunami deposits for the first time the 1883 krakatoa and 1977 sumba tsunamis are inferred from sedimentary records of the north western part of western australia it is demonstrated that optically stimulated luminescence applied in coastal sedimentary archives with favourable luminescence characteristics can provide accurate chronostratigraphies even on a decadal timescale the results contribute to the data pool of tropical cyclone and tsunami deposits in holocene stratigraphies however they also demonstrate how short lived sediment archives may be in dynamic sedimentary environments

isopollen maps for 18 000 years b p of the atlantic offshore of northwest africa evidence for paleowind circulation distribution patterns of the most important pollen types from southern european and northwest african source areas for the 18 000 years b p time slice are reconstructed from pollen records of 14 well dated deep sea cores located between 37 and 9 n and compared with the modern pollen distribution in this area it is concluded that the belt with maximum african easterly jet transport did not shift latitudinally during the last glacial interglacial transition but remained at about 20 n furthermore it is substantiated that the trade winds did not shift latitudinally during the last glacial interglacial transition this evidence is not compatible with an atmospheric circulation model that assumes a zone of surface westerlies in the northern part of northwest africa trade winds during glacial episodes did however intensify especially from about 36 to 24 n

2004 indian ocean tsunami flow velocity measurements from survivor videos 1 the tsunami of 26th december 2004 severely affected banda aceh along the north tip of sumatra indonesia at a distance of 250 km from the epicenter of the magnitude 9 0 earthquake this tsunami flow velocity analysis focused on two survivor videos recorded within banda aceh more than 3 km from the open ocean the exact locations of the tsunami eyewitness video recordings were revisited by the survey team between february 22 and 25 2005 to record camera calibration ground control points the motion of the camera during the recordings was determined the individual video images were rectified with a direct linear transformation dlt assuming a planar water surface at the level finally a cross correlation based particle image velocimetry piv analysis was applied to the rectified video images to determine instantaneous tsunami flow velocity fields the measured tsunami flow velocities were within the range of 2 to 5 m s

sediment and pollen evidence for an early to mid holocene humid period in the eastern sahara a major problem in the study of holocene palaeoenvironments of the arid and wind deflated sahara is the low preservation potential of sediments from which a record of past climatic change can be established several indirect and imprecisely dated pieces of evidence have suggested humid episodes in the holocene that may have supported more productive ecosystems and denser human populations than today searches for reliable proxy data on past climates however have failed to yield satisfactory results we report here the discovery of buried lake muds in north west sudan in the hyperarid core of the eastern sahara which yield sedimentological and palynological data clearly interpretable as recording an early to mid holocene humid episode that supported a relatively deep stratified lake surrounded by tropical savanna woodland vegetation

changes in the vegetation and trade winds in equatorial northwest africa 140 000 70 000 yr b p as deduced from two marine pollen records abstract the deep sea cores m 16415 2 and m 16416 2 at about 9 n off sierra leone were analysed palynologically for the time interval 140 000 70 000 yr b p results were presented in absolute pollen concentration and pollen influx and relative diagrams pollen percentage in a previous study it was evidenced that in northwest africa pollen is mainly transported to the atlantic by wind so that the efficiency of aeolian pollen transport pollen flux could be used to evaluate changes in the intensity of the northeast trade winds the glacial episodes represented by the oxygen isotope stages 6 and 4 are characterized by strong northeast trade winds whereas the last interglacial stage 5 is characterized by weak trace winds the pollen influx diagram shows that the intensity of the trade winds increased slightly during the relatively cool intervals of stage 5 viz 5 4 and 5 2 tropical forest had maximally expanded around 124 000 yr b p stage 5 5 around 98 000 yr b p transition of stage 5 3 to 5 2 and around 70 000 yr b p first part of stage 4 an increasing delay of the response of tropical forest to global intervals with maximum temperature is apparent during the last interglacial as tropical forests need continuous humidity the record of tropical forest monitors changes in climatic humidity south of the sahara during the last interglacial the southern boundary of the sahara shifted only little expansions and contractions of the tropical forest area are correlated with contra oscillations of the grass dominated savanna zone great latitudinal shifts of the desert savanna boundary on the contrary occurred during the penultimate glacial interglacial transition around 128 000 yr b p to the north and during the last interglacial glacial transition around 65 000 yr b p to the south

petrology of organic matter in modern and late quaternary deposits of the equatorial atlantic climatic and oceanographic links abstract organic petrologic and geochemical analyses were performed on modern and quaternary organic carbon poor deep sea sediments from the equatorial atlantic the study area covers depositional settings from the west african margin odp site 959 through the equatorial divergence odp site 663 to the pelagic equatorial atlantic response of organic matter om deposition to quaternary climatic cycles is discussed for odp sites 959 and 663 the results are finally compared to a concept established for fossil deep sea environments littke r sachsenhofer r f 1994 organic petrology of deep sea sediments a compilation of results from the ocean drilling program and the deep sea drilling project energy and fuels 8 1498 1512 organic geochemical results obtained from equatorial atlantic deep sea deposits provide new aspects on the distribution of sedimentary om in response to continental distance atmospheric and oceanographic circulation and depositional processes controlling sedimentation under modern and past glacial interglacial conditions the inventory of macerals in deep sea deposits is limited due to mechanical breakdown of particles degree of oxidation and selective remineralization of labile mostly marine om nevertheless organic petrology has a great potential for paleoenvironmental studies especially as a proxy to assess quantitative information on the relative abundance of marine vs terrigenous om discrepancies between quantitative data obtained from microscopic and isotopic 13 c org analyses were observed depending on the stratigraphic level and depositional setting strongest offset between both records was found close to the continent and during glacial periods suggesting a coupling with wind born terrigenous om from central africa since african dust source areas are covered by c4 grass plants supply of isotopically heavy om is assumed to have caused the difference between microscopic and isotopic records

use of anisotropy of magnetic susceptibility ams in the study of tsunami deposits application to the 2004 deposits on the eastern coast of banda aceh north sumatra indonesia abstract we studied emplacement dynamics of the december 26 2004 tsunami deposits in artificial shallow ponds and in shallow lagoons along the northern coast of sumatra in banda aceh area successive tsunami waves inundated topographic lows which acted as sediment traps and favored preservation of deposits individual waves led to the deposition of fining upwards sedimentary sequences this multiple normal grading deposit with a thickness ranging from 2 to 80 cm constitutes a site of major interest for the study of the deposits emplaced by a tsunami wave train the main interest lies in the characteristics of the deposits that can be correlated to the behavior of the waves attested by numerous testimonies in this setting we aimed at testing the applicability of the ams anisotropy of magnetic susceptibility technique as a proxy of unconsolidated sediment fabric the combination of this proxy and traditional sedimentary analysis helped reconstructing the hydrodynamic conditions particularly the flow direction prevailing during sedimentation we applied the ams technique on eight sections stretching inland from 1 5 km to 2 2 km from the pre tsunami coastline grain size and ams data from these deposits provide similar and partially complementary information traction dominates in the basal parts of the deposits and occurs mainly for the basal layers of the sequences whereas settling dominates for the upper layers of these sequences the vertical evolution of the ams parameters within the deposits is related to the arrival of the successive waves with variations in the traction and decantation processes during deposition variations of current strength during sedimentation are related to the wave s momentum and to the progressive infill of topographic depressions the vertical change of the fifth coarsest percentile vs the median grain sizes of the deposits suggests strong variations of the energy of the currents and confirms the evolution of the ams parameters in the present study the fabric of the deposits which developed exclusively during the uprush phase of the cycle also allows the reconstruction of flood directions that are both normal and parallel to the shoreline with variations related to flow dynamics mean grain size and local topographic control due to the absence of backwash in between the waves and low velocity of the final backwash information about the sedimentation conditions of the tsunami deposits appears to be better preserved in topographic depressions in areas located remote from the seashore the ams proxy appears to be a promising tool for further studies of recent and paleo tsunami deposits

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

freshwater diatom influx in intertropical atlantic relationships with continental records from africa diatom assemblages from modern west african rivers and from lacustrine sediments subjected to deflation represent the present day sources of continental diatoms to the sea diatom productivity in large rivers is high especially for the genus melosira windblown diatoms derive mainly from the central and northern sahara summer dust plume where saline chloride water assemblages are widespread or from the southern edge of the sahara winter dust plume where melosira rich assemblages of dilute water predominate freshwater diatom peaks in atlantic cores may reflect 1 phases of increased river influx correlated with humid episodes on the continent or 2 phases of enhanced deflation and wind transport during arid episodes the single hypothesis for fine sediments from mid ocean sites genus melosira dominates the freshwater assemblages of many modern and fossil marine samples whatever the transport agent is therefore it is not an accurate paleoclimate indicator by itself but associated taxa may provide information on the environmental and geographical origin of the displaced diatoms this tentative approach shows that freshwater diatoms in atlantic cores may be a good tool for reconstructing paleoclimates and for establishing continent ocean correlations if species analyses are made and if the continental distribution of the taxa encountered is considered

sedimentary deposits from the 17 july 2006 western java tsunami indonesia use of grain size analyses to assess tsunami flow depth speed and traction carpet characteristics the 2006 western java tsunami deposited a discontinuous sheet of sand up to 20 cm thick flooded coastal southern java to a depth of at least 8 m and inundated up to 1 km inland in most places the primarily heavy mineral sand sheet is normally graded and in some it contains complex internal stratigraphy structures within the sand sheet probably record the passage of up to two individual waves a point noted in eyewitness accounts we studied the 2006 tsunami deposits in detail along a flow parallel transect about 750 m long 15 km east of cilacap the tsunami deposit first becomes discernable from the underlying sediment 70 m from the shoreline from 75 to 300 m inland the deposit has been laid down in rice paddies and maintains a thickness of 10 20 cm landward of 300 m the deposit thins dramatically reaching 1 mm by 450 m inland from 450 m to the edge of deposition around 700 m inland the deposit remains 1 mm thick deposition generally attended inundation along the transect the tsunami deposited sand to within about 40 m of the inundation limit the thicker part of the deposit contains primarily sand indistinguishable from that found on the beach 3 weeks after the event but after about 450 m and roughly coinciding with the decrease in thickness the tsunami sediment shifts to become more like the underlying paddy soil than the beach sand grain sizes within the deposit tend to fine upward and landward although overall upward fining takes place in two discrete pulses with an initial section of inverse grading followed by a section of normal grading the two inversely graded sections are also density graded with denser grains at the base and less dense grains at the top the two normally graded sections show no trends in density the inversely graded sections show high density sediment to the base and become less dense upward and represents traction carpet flows at the base of the tsunami these are suggestive of high shear rates in the flow because of the grain sorting in the traction carpet the landward fining trends usually seen in tsunami deposits are masked although lateral changes of mean sediment grain size along the transect do show overall landward fining with more variation as the deposit tapers off the deposit is also thicker in the more seaward portions than would be produced by tsunamis lacking traction carpets

holocene climatic optimum in southwest africa evidence from the marine clay mineral record abstract sediment composition grain size and clay mineral record of a high resolution sediment core from the continental slope off namibia was investigated to gain information on the deposition of terrigenous matter in this part of the southwest african continental margin during the last 18 k y the depositional processes involved are fluvial input by the kunene river and eolian input from the namib and kalahari deserts each supplying characteristic mineral suites during low sea level erosion of the exposed shelf yields additional material the amount of eolian or fluvial matter depends on the strength of the transport process which is a function of aridity or humidity of the source area thus allowing paleoclimatic interpretations arid conditions prevailed during a low sea level from 18 to 15 ka and unconsolidated shelf sediment was mobilized and supplied to the slope by short distance transport by southerly winds a dramatic increase in the accumulation of terrigenous sediment is recorded from 15 to 10 ka without major changes in sediment composition which is attributed to increased runoff of the kunene river and fluvial erosion of shelf sediments this period coincides with a strengthening of the monsoonal system during a precessional minimum which is observed in numerous sites in central africa and indicates an intensified influence of the monsoon at the kunene headwaters a distinct shift in clay mineralogy towards river derived material marks a second period of increased river runoff during high sea level from 9 to 5 ka indicating maximum humidity in the source area from 6 to 5 ka this corresponds to the holocene climatic optimum observed in the arid belts of northern africa the present balance between fluvial and eolian input was reached approximately at 4 ka

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr