sediment transport resuspension and accumulation rates in the northeastern skagerrak results of watercolumn light transmission measurements in the skagerrak and of 210pb excess and 137cs determinations in boxcore sediments of the eastern skagerrak are combined to study regional sediment transport resuspension and sedimentation patterns and rates in the upper water layer a 20 m thick surface nepheloid layer formed by concentration of particles at the thermocline and pycnocline is best developed in the eastern skagerrak and less well in the southwestern skagerrak off the danish coast bottom nepheloid layers are extensively developed in the southeastern skagerrak and indicate additional sediment input via resuspension in shallow water areas and near bottom sediment transport in suspension following the prevailing current regime locally the transmission in the bnl is reduced by more than 50 compared to clear water transmission values between 85 and 90 210pb and 137cs derived sedimentation rates are highest in the eastern and northeastern skagerrak and least in the central deep basin there is generally a good agreement between 137cs and 210pb data indicating that sediment accumulation on the short 30 year and longer 100 year time scale is of comparable magnitude

patterns rates and possible causes of saltmarsh erosion in the greater thames area uk the estuary dominated coast of the greater thames in england has experienced rapid lateral erosion and internal dissection of saltmarshes this paper provides an overview of saltmarsh development in this area and re examines the role of environmental and human forcing factors it draws on documentary evidence including historical maps survey data and time series data of forcing factors lateral marsh retreat began in the 19th century in the medway and blackwater estuaries followed by other estuaries in the greater thames region at the beginning of the 20th century the outer estuaries and the wider parts of the inner estuaries especially have experienced erosion erosion has been modest in wave sheltered areas e g the colne and the inner crouch in the 1960s and more widely the 1970s a phase of rapid erosion took place with erosion rates of up to ca 16 ha year 1 per site notably along the open coast of dengie and foulness and in the blackwater and thames estuaries at all sites vertical sediment accretion was well able to keep up with sea level rise over the past century evidence indicates that there may have been several causes for the erosion of saltmarshes these are notably land claim and embankment construction increasing the tidal range and current velocities and a continuous rise of especially high and extreme water levels the latest episode of rapid erosion in the 1970s is largely attributed to changes in the wind wave climate for example erosion at wave exposed sites coincided with a peak in high magnitude waves combined with a high incidence of southeasterly waves the study shows that many factors including natural forcing factors and human activities have to be taken into account when explaining saltmarsh development

dispersal concentration and deposition of suspended matter in the north sea suspended matter comes into the north sea from the atlantic ocean from the channel rivers seafloor erosion coastal erosion the atmosphere and from primary production the contribution of the last source is temporarily large when phytoplankton growth is abundant but is soon decomposed mineralized or consumed so that over the year the net effect is small accumulation and deposition of suspended matter occurs predominantly in only a few areas the waddensea the german bight the skagerrak norwegian channel the remainder of the north sea floor consists of pleistocene and early holocene relict deposits and of reworked sands and gravels the mechanisms resulting in accumulation and deposition are discussed there are strong indications that the amount of suspended matter flowing out from the north sea into the norwegian sea along the norwegian coast is only little more or the same as the amount coming in from the north atlantic although its composition may be different

transport of clay minerals and anthropogenic compounds into the german bight and the provenance of fine grained sediments se of helgoland a large mud body 500 km 2 and up to 21 m thick se of helgoland has been investigated using geochemical mineralogical and sedimentological methods the analysis of 27 sediment cores from this area revealed that overlying older fine grained sediments there is a 9cake9 of muddy polluted sediments up to 3 m thick which has accumulated over the last 100 years it is assumed that human activities like dredging and dumping are responsible for this rapid rate of deposition generally it has been estimated that all of this mud has been supplied by rivers entering this part of the north sea but analyses of sediments from the ems weser and the elbe rivers show that under normal conditions the river sediments do not enter the open sea but are trapped in the estuaries it may therefore be concluded that much of the underlying unpolluted sediments of the mud area were derived from elsewhere or were laid down during an earlier period one possibility is that the lower sediments were deposited when the german bight was a sheltered area protected by a barrier of morainic sediments in the north between helgoland and schleswig holstein this barrier must have been breached more than 2000 years ago

large mammal fossil occurrences and associated archaeological evidence in pleistocene contexts of peninsular india and sri lanka the indian subcontinent represents a rich source of diverse paleoanthropological data in the form of pollen assemblages various isotopic records vertebrate and invertebrate fossil assemblages and prehistoric stone tools in a range of palaeoecological contexts most of the quaternary fossil evidence including hominin specimens comes from the fluvial sediments of the narmada and other similar rivers although abundant and well preserved vertebrate fossil assemblages are known from the siwalik hills and karewa deposits in the north similar evidence is less well known from peninsular india and sri lanka to the south with the exception of two occurrences in gujarat and bihar there is an almost complete absence of neogene fossil evidence older than the middle pleistocene in peninsular india and late middle pleistocene in sri lanka the richest non fluvial sources of vertebrate fossils are represented by the kurnool cave complex in southern india and numerous cave and open air deposits in sri lanka the majority of which are upper pleistocene age this unique faunal record of peninsular india and sri lanka probably played a critical role in influencing the dispersal settlement and subsistence behaviors of pleistocene hominins this paper summarizes the known pleistocene megafauna fossil occurrences from peninsular india and sri lanka and includes key lithic associations with these assemblages

event stratigraphy paleoenvironment and chronology of se arabian deserts the geological record of the se arabian desert is exhibited in a variety of geomorphic features and their characteristic sediments ranging from alluvial fans to inland and coastal dunes and sabkhas together they suggest a large range of environmental and climatic variability between periods of relative aridity and humidity sedimentary events in the emirates appear to correlate broadly with high latitude glaciations which affected both the shamal winds and the extent of exposure of the arabian gulf in general the aeolian sands in the rub al khali responded to glacial events as a consequence of exposure of the floor of the arabian gulf during glacials when global sea level was low quartz sands from across the exposed floor of the arabian gulf were transported by the shamal winds south eastwards to the emirates and then south to the rub al khali the supply of shamal transported sand from the floor of the arabian gulf was cut off by high stands of sea level during interglacial periods the new coastal dunes miliolite rich in foraminifera and other cement assisting calcareous shell fragments were deflated down to the water table as their sand was transported further to the south leading to the creation of coastal sabkhas studies on aeolianites and the lacustrine deposits provide evidence of phases of enhanced humidity prior to the last glacial maximum and during the holocene in contrast the bedding attitudes of miliolites in se oman suggest that the wahiba sands were transported from south to north by a branch of the sw monsoon the depositional ages of these dunes indicate a close connection between the winds and coeval fluctuations of the sw monsoon the interdunal lakes and underlying dune sands reflect an active sw monsoon during the holocene this is also indicated by the aeolian and lacustrine records of the thar desert in india which likewise are controlled by the sw monsoon south and west of the oman mountains is a broad alluvial fan bajada that is mostly inactive today the oldest fluvial sediments are undated but preliminary age estimates suggest that some correlate with more humid earlier interglacials

sediment transport pathways in the skagerrak and kattegat as indicated by sediment chernobyl radioactivity and heavy metal concentrations abstract the concentration of the heavy metals hg cu pb and zn as well as chernobyl cs 137 radioactivity was determined in surface sediments from the skagerrak and kattegat sediment samples from adjacent swedish fjords were analysed as well the sampling was carried out between spring 1988 and autumn 1990 highest concentrations of heavy metals and largest cs 137 activities occur in fine grained organic rich 62 2 c org sediment from swedish inshore waters and locally also in the kattegat regional trends of relative enrichment of the various heavy metals and chernobyl cs 137 with respect to organic carbon was used to determine transport patterns of material enriched with respective elements it can be proven that deposition of fine grained material transported from the southern north sea by the jutland current is the main mechanism determining the regional accumulation of lead and chernobyl derived cs 137 this mechanism principally controlls the areal distribution of mercury enriched material as well but it is regionally of less importance as far as the accumulation of cu and zn concerns the chernobyl cs 137 data show that a large proportion of the fine grained material transported by the jutland current originally is river borne suspension load from central western europe the areal enrichment pattern of copper and on a smaller scale those of mercury and zinc too points to westerly directed suspension load transport across the kattegat material enriched with these elements apparently is being discharged from swedish industrial and urban centers in particular the goteborg area

lead in sediments and suspended particulate matter of the german bight natural versus anthropogenic origin sediments 568 and suspended particulate matter spm 302 samples of the southern german bight and the adjacent tidal flat areas were analysed for selected major elements al fe k trace metals mn pb and 206pb 207pb ratios using xrf icp oes icp ms for selected samples a leaching procedure with 1 m hcl was used to estimate the pb fraction associated with labile phases e g mn fe oxihydroxide coatings in contrast to the resistant mineral matrix enrichment factors versus average shale efs reveal elevated pb contents for all investigated sediments and spm in the following order holocene tidal flat sediments htf human unaffected 5 mg l 1 offhore spm 5 mg l 1 besides pollution rtf contain elevated amounts of natural pb rich materials k feldspars and heavy minerals due to a man made high energy environment dike building in comparison to htf 206pb 207pb ratios of rtf 1 192 0 019 are similar to the local geogenic background determined from htf 1 207 0 008 in contrast pb isotope ratios of nearshore spm 1 172 0 007 and offshore spm 1 166 0 012 show a distinct shift towards the anthropogenic atmospheric signal of 1 11 1 14 this difference between rtf and spm supports the assumption of low deposition rates of fine material in the intertidal systems as the 206pb 207pb ratios of spm do not reach the pure anthropogenic signal the adsorbed pb fraction was examined leaching however the leachates also contained large amounts of geogenic pb spm 40 recent sediments 60 the authors assume that the uptake of natural pb occurs in nearshore waters presumably in the turbid intertidal systems possible sources for dissolved pb are mobilisation during weathering geogenic signal and dissolution of oxihydroxide coatings with subsequent release from porewaters and unspecific riverine input comparatively small parts of spm leave the coastal water mass and reach the open north sea this process therefore leads to a decontamination of the tidal flat sediments due to more pronounced atmospheric input the offshore spm becomes enriched in anthropogenic pb as indicated by decreasing 206pb 207pb ratios with increasing distance from the coast

links between climate and sea levels for the past three million years the oscillations between glacial and interglacial climate conditions over the past three million years have been characterized by a transfer of immense amounts of water between two of its largest reservoirs on earth the ice sheets and the oceans since the latest of these oscillations the last glacial maximum between about 30 000 and 19 000 years ago approximately 50 million cubic kilometres of ice has melted from the land based ice sheets raising global sea level by approximately 130 metres such rapid changes in sea level are part of a complex pattern of interactions between the atmosphere oceans ice sheets and solid earth all of which have different response timescales the trigger for the sea level fluctuations most probably lies with changes in insolation caused by astronomical forcing but internal feedback cycles complicate the simple model of causes and effects

indications of long term episodic suspension transport of sand across the norfolk banks north sea abstract predicted 50 year maximum storm surge currents and the currents resulting from their combination with strong tidal currents are veered and amplified as they pass over the norfolk banks they therefore drive sand off the crest of well bank in a wide arc of directions between north east and south southwest this arc corresponds to that seen in the cross bedding dip directions known from the lee slope of well bank and to the northeasterly growth of the well bank the strength of these currents is such that some sand may even pass from bank to bank in the series this is facilitated by the proximity of the upper part of the sand banks to the sea surface such that their crests act as stepping stones where sand suspensions originate during storm surge episodes it is postulated that this new sand transport path oblique to the path of the peak tidal currents probably commences at the coast of east anglia and provides a route for transporting sand for up to about 100 km seaward

hominin responses to pleistocene environmental change in arabia and south asia palaeoanthropologists typically outline human evolution within a framework of pleistocene environmental change environmental change occurring across the early middle pleistocene transition is examined relative to patterns of hominin dispersal ecological adaptations cognitive advances and behavioural flexibility although climatic information has been used as the backdrop to human evolution major lacunae exist in our understanding of the ecological settings where hominins evolved data from investigations conducted in the arabian peninsula and the indian subcontinent are reviewed indicating the nature of palaeolithic localities and their physical settings although much information remains to be obtained from these terrestrial records significant changes are recognized in the environmental and archaeological record the early middle pleistocene transition shows some conservative trends in hominin adaptations and technology yet it is also an interval that evidences an increasing ability to transcend environmental controls through a greater level of behavioural flexibility and innovation

late holocene coastal hydrographic and climate changes in the eastern north sea we present a high resolution palaeoenvironmental reconstruction covering the late holocene from the skagerrak and other sites in the north sea area the data which are based on the analyses of marine sediment cores reveal a marked environmental shift that took place between ad 700 and ad 1100 with the most pronounced changes occurring at ad 900 both surface and bottom waters in the skagerrak were subject to major circulation and productivity changes at this time due to an enhanced advection of atlantic waters to the north sea marking the beginning of the mediaeval warm period mwp the observed increase in bottom current strength is especially remarkable as there is hardly any comparable signal in the older part of the record going back to 1000 bc at the transition to the little ice age lia the bottom current strength remains at a high level now probably forced by atmospheric circulation thus despite opposite temperature forcing these two consecutive climate scenarios are apparently able to generate distinctly stronger bottom currents in the skagerrak than observed in the preceding 2000 years and demonstrate the significance of climatic forcing in shaping the marine environment indeed both the mwp and the lia are reported as strong climatic signals in northwest europe being the warmest except the late twentieth century and coldest periods respectively during at least the last 2000 years

rare earth element fractionation by selective sediment dispersal in surface sediments the skagerrak abstract neutron activation analysis was carried out to study the abundance distribution and fractionation of ree rare earth elements in surface sediment samples of 28 box cores collected along transects across the skagerrak results show that the clays have 3 5 times higher contents of k sc cr fe co rb k cs ta and th lree la and ce and mree sm eu and tb compared to sands and silts the hree yb and lu are only up to two times enriched in the clays and silts compared with the values measured in sands shale normalized ree patterns vary from flat for the sands towards enrichment 1 3 1 5 times of lree relative to hree in the clays this is consistent with published ree data for oceanic and riverine sediments and evidences fractionation hf and zr are up to thee times enriched in sands and silts compared to clays samples with highest contents of hf show hree enrichment in shale normalized ree patterns simple model calculations show that on the average zircon grains in skagerrak silts and sands contain 800 1200 ppm yb assuming that this value is also valid for the zircon grains in the shales this indicates that lower hree contents observed in atlantic ocean shelf and oceanic sediments compared to shales cannot be related to a greater abundance of zircon in shales

holocene and pleistocene pluvial periods in yemen southern arabia arabia is an important potential pathway for the dispersal of homo sapiens out of africa yet because of its arid to hyper arid climate humans could only migrate across southern arabia during pluvial periods when environmental conditions were favorable however knowledge on the timing of arabian pluvial periods prior to the holocene is mainly based on a single and possibly incomplete speleothem record from hoti cave in northern oman additional terrestrial records from the arabian peninsula are needed to confirm the hoti cave record here we present a new speleothem record from mukalla cave in southern yemen the mukalla cave and hoti cave records clearly reveal that speleothems growth occurred solely during peak interglacial periods corresponding to marine isotope stages mis 1 early to mid holocene 5 1 5 3 5 5 eemian 7 1 7 5 and 9 of these humid periods highest precipitation occurred during mis 5 5 and lowest during early to middle holocene

bioerosion and carbonate mud production on high latitude shelves low latitude carbonate muds often are composed either of entire units of skeletons e g algal muds or of precipitates whereas high latitude carbonate muds are bioerosional or result from maceration bioerosion at high latitudes is most intense in the photic zone particularly down to 25 m depth shelly substrata may be crushed bitten drilled bored or scraped clionid sponges endolithic algae acmaeid gastropods and regular echinoids are the most significant agents clionids produce distinctive facetted carbonate silt chips when boring which have been described from both high and low latitudes faecal pellets break down to yield mud sized carbonate particles that are more irregular than those produced by maceration exhumed infaunal bivalves are often preferred to epifaunal organisms as substrata bioerosion occurs very rapidly shells may be totally infested with boring algae in three months a moth eaten appearance therefore does not denote a relict grain reliable rates of fine sediment production are not yet available the mud fraction of northwest european shelf sediment generally contains 10 20 caco3 though an inshore and offshore belt with higher values may be identified some holocene supratidal mud flats exceed 50 caco3 much of the shelf represents a modern day equivalent of the calcareous shale facies common in the geological record instances of synsedimentary cementation are not uncommon particularly in association with heavily burrowed muds

holocene sedimentation in the skagerrak interpreted from chirp sonar and core data high resolution chirp sonar profiling in the northeastern skagerrak shows acoustically stratified sediments draping a rough surfaced substratum a 32 metre long sediment core retrieved from the survey area encompasses the entire holocene and latest pleistocene the uppermost seismo acoustic units in the chirp profiles represent holocene marine sediments the lowermost unit is interpreted as ice proximal glacial marine sediments rapidly deposited during the last deglaciation the end of ice proximal sedimentation is marked by a strong reflector interpreted to have been formed during latest pleistocene time as a consequence of rapid ice retreat and drastically lowered sedimentation rate the subsequent distal glacial marine sediments were deposited with initially high sedimentation rates caused by an isostatic rebound associated sea level fall based on correlation between the core and the chirp sonar profiles using measured sediment physical properties and ams 14 c dating we propose a revised position for the pleistocene holocene boundary in the seismo acoustic stratigraphy of the investigated area copyright 2005 john wiley sons ltd

benthic organic matter supply and metabolism at depositional and non depositional areas in the north sea in 1994 four stations in the southern north sea the german bight and the skagerrak were visited with the aim to get insight into spatial and temporal variation in the supply of fresh organic matter to the benthos and its subsequent metabolic reaction stations were chosen on the basis of differences in sediment type depth and depositional regime sediments were sampled sliced and analysed for phytopigments fatty acids and nucleic acids on deck sediment core incubations provided the sediment oxygen demand sod fatty acids as well as chlorophyll a indicated a seasonal variation of phytodetritus sedimentation with highest values in may reflecting the spring bloom sedimentation the two stations in the depositional areas german bight and skagerrak had the highest input of algal detritus into the sediment these stations also contained higher concentrations of bacterial and long chain fatty acids probably related to the relatively higher proportion of fine particles in the sediment and to the input of terrestrial organic matter and or refractory marine organic matter respectively the metabolic indices viz the sod and the rna concentrations reflected the benthic metabolic reaction to the labile organic matter supply the three stations in the southern and south eastern north sea had a sod congruent with the phytodetrital inventories with highest sod measured at the german bight surprisingly the skagerrak sediment did not have a high oxygen demand although it contained the highest inventory of labile organic matter and high rna concentrations the fluxes of carbon to the sediment at station sk calculated from the chlorophyll a inventory were about four times higher than the sediment oxygen demand we hypothesise two mechanisms for this discrepancy one is the decreased mineralisation rate of labile organic matter due to sorption to clayey sediment particles the other is advection of labile organic matter from the shallower coastal waters of northern denmark to and subsequent removal from the deeper skagerrak sediments by periodically occurring high near bottom water currents

multi scale acheulean landscape survey in the arabian desert abstract the interpretation of acheulean landscape use through the analysis of artefact distributions over a range of environmental settings is vital for understanding early hominin behaviour such approaches have been successfully applied in areas such as east africa and south africa where long term and sustained archaeological research has led to the development of robust environmental frameworks within which to analyse hominin land use patterns much less is known about acheulean hominin behaviour in the arabian peninsula which is increasingly being recognised as an important area for studying early hominin dispersals and adaptations to new environments to address this lacuna we have undertaken the first multi scale systematic survey of acheulean occupation evidence at dawadmi in the centre of the arabian peninsula specifically we carried out systematic transect surveys over a large andesite dyke at saffaqah on which the majority of 26 known acheulean sites are associated as well as across narrow drainage channels desert pavements and hills located within 5 km of the dyke survey transects also crossed neighbouring dykes and adjacent landscape units with a 25 20 km area our surveys at saffaqah have led to the discovery of 14 new acheulean sites initial lithic analyses reveal differences between sites in terms of typology but further work on the assemblages is required to determine if these differences are behavioural or a product of post depositional processes a broad regional survey was undertaken to identify the full extent of acheulean activity around dawadmi this led to the discovery of a further 22 sites there is a strong correspondence between acheulean sites and fine grained andesite dykes which were major lithic raw material sources no acheulean sites in the study area were found away from dykes or their adjacent landscape units based on dyke distributions the geographic range of acheulean activity is estimated to be 100 55 km making dawadmi one of the largest acheulean landscapes in the world

insights from carnivore community composition on the paleoecology of early pleistocene eurasian sites implications for the dispersal of hominins out of africa abstract understanding the forces that led to the early pleistocene dispersal of hominins from africa into eurasia is an extremely important question in paleoanthropology hypotheses can be roughly divided into intrinsic and environmental consistency hypotheses the former suggest that characters unique to hominins provided the push for dispersal while the latter hypothesis suggest that environmental factors and specifically the presence of open savanna habitats may have provided the pull for hominins into eurasia here i present the application of a paleoecological proxy which uses carnivore community composition to determine paleoenvironment in five eurasian early pleistocene sites carnivore community composition i e number of species per family can distinguish between the main koppen geiger habitats and between two main biomes grassland shrubland and forest woodland based on comparisons to modern carnivore assemblages we can identify three groups of early eurasian pleistocene sites the first group includes stratum b of the site of dmanisi early matuyama chron which was classified as an arid shrubland grassland environment while the second group includes sites dated to matuyama chron ubeidiya venta micena and akhalkalaki which were classified as temperate forest woodland environments the third group includes another site dated to the matuyama chron as well pirro nord which was classified as temperate shrubland grassland while dispersal during in the olduvai matuyama boundary 1 78 ma may have preferentially targeted arid and semi arid environments compatible with the environmental consistency hypothesis matuyama chron dispersals 1 78 0 78 ma may have occupied a wider range of environments consistent with the intrinsic hypothesis

northern north sea benthic ostracoda modern distribution and palaeoenvironmental significance the ostracod faunas of the northern north sea exhibit a depth related distribution that is controlled by substrate and hydrographic conditions four biofacies are defined on the basis of total live dead counts sandy substrates shallower than 110 m are characterized by robertsonites tuberculatus and cytheropteron latissimum these species are replaced by acanthocythereis dunelmensis and palmenella limicola on sandy muds in the fladen ground 110 150 m muellerina abyssicola dominates from 175 250 m in the norwegian channel giving way to krithe praetexta at greater depths on soft bottom substrates the results are compared with data from the skagerrak and the western european shelf area temperature ranges for the commonest taxa show that north sea faunas contain endemic western european species temperature range on average 2 20 c some southern species 5 26 c and taxa that range to high latitudes 2 to 14 c southern species are confined to the southern and western margins of the north sea

organic facies of surface sediments in the north sea abstract surface sediments of the north sea were investigated by organic geochemical and sedimentological methods including organic carbon and nitrogen determination rock eval pyrolysis protokerogen microscopy gas chromatography of aliphatic hydrocarbons grain size fractionation and clay mineral analysis the total organic matter was found to be a mixture of mostly reworked or oxidized marine and terrestrial constituents with a generally strong influence of the latter throughout the platform locally improved hydrodynamic conditions yielded an incorporation of more freshly produced marine organic matter differences in water current velocities and turbulence also appeared to determine whether this supplement is incorporated into the fine or coarse fractions of the sediments a general constancy of the organic carbon contents within the individual size fractions was recognized independently of sediment type and age i e in recent and pre recent deposits this suggested that the latter have been effectively overprinted by the shelf processes operating at present or that these processes have been of comparable intensity since about the beginning of the holocene transgression the major factors controlling the spatial variations in the organic facies are the sediment grain size and the present day hydraulic regime

recent sediment accumulation organic carbon burial and transport in the northeastern north sea abstract organic carbon and nitrogen and sedimentation rate determinations were made of boxcores from the norwegian channel north sea the geographical distribution of recent sedimentation areas were defined by analysis of published data and 3 5 khz penetrating echo sounder data the annual dry bulk sediment accumulation in the northeastern north sea is established at 74 10 6 tons as the average organic carbon content for the norwegian channel and skagerrak kattegat sediments is 0 6 and 1 8 respectively the organic carbon accumulation rate in the northeastern north sea could be calculated the total organic carbon accumulation in the norwegian channel and skagerrak northern kattegat is 0 17 10 6 tons yr 1 and 0 83 10 6 tons yr 1 respectively less than 10 of this is accounted for by local primary production this means that more than 90 of the organic carbon buried in the sediments of the northeastern north sea must have been supplied from different sources terrigenous sources supply 20 of the organic carbon the remainder is marine organic matter produced elsewhere in the north sea or imported from the atlantic ocean norwegian sea and the baltic sea storm wave and current induced near bottom nepheloid layers are the main likely mechanism to transport fine grained sediments and associated organic matter from the north sea plateau into the kattegat skagerrak and norwegian channel

early to middle pleistocene homo dispersals from africa to eurasia geological climatic and environmental constraints abstract although the pleistocene human dispersal is one of the most intriguing issues of paleoanthropology large sectors along possible migratory pathways are ill defined or poorly documented this paper examines the geological geomorphological climatic and environmental conditions that could have determined hominin transit from their motherland in the east africa rift valley toward the circummediterranean regions or arabian peninsula for their choice between these two alternatives the danakil depression afar rift immediately north of the ethiopian rift valley was a strategic area they could reach the mediterranean sea through a northern route along the nile river valley the trans sahara megalake or riverine belts or else navigate an eastern route into the arabian peninsula after crossing the bab el mandeb straits it is assumed all of these pathways were possible during convenient geological climatic and or sea level conditions hominins had three additional choices once they arrived at the mediterranean sea shores with eurasia as their final destination the levant corridor was the easiest because walkable and almost always under favorable conditions two other possibilities were the sicily channel and the strait of gibraltar these sea arms are located in two extremely active settings of the mediterranean sea and were at their embryonic stage during the early pleistocene because large scale deformations of the sea floor were associated to prolonged sea level lowstands these two sea arms could have been passable similar considerations apply to the bab el mandeb straits region for the trans mediterranean and the trans red sea routes of dispersal the environmental conditions and the submarine and terrestrial topographical features that could have made sea transit possible even without land bridges are underscored to track the dispersal relations between northern africa and eurasia three schematic maps are presented to show the distribution of the archeological and paleoanthropological sites currently regarded as reliably dated they document three groups of dates between 2 0 and 1 5 ma 1 4 and 0 7 ma and 0 6 and 0 1 ma their distribution is matched with coeval paleoclimatic proxies such as marine oxygen isotope stages aeolian dust in the atlantic ocean and sapropels levels and dust fluxes in the eastern mediterranean dispersal was temporally arranged into cycles of four major exodus waves 2 0 1 6 ma 1 4 1 2 ma 1 0 0 8 ma and 0 6 0 1 ma controlled by climatic and environmental changes

postglacial palaeoceanography in the skagerrak crucial periods of change in the latest glacial to early holocene palaeogeographic and palaeoceanographic evolution in the skagerrak region are portrayed in four time slice maps on a calibrated age scale at 14 0 kyr 11 2 kyr 10 2 kyr and 8 1 kyr the course of palaeoenvironmental events is set in a high resolution chronological framework using images core md99 2286 and a grid of chirp sonar profiles these maps visualize the complex rapid palaeogeographic and palaeoceanographic changes during the glacialinterglacial transition which is characterized by major changes in circulation sediment sources and depositional processes

nonstationary phase of the plio pleistocene asian monsoon paleoclimate records indicate that the strength of the asian summer monsoon is sensitive to orbital forcing at the obliquity and precession periods 41 000 and 23 000 years respectively and the extent of northern hemisphere glaciation over the past 2 6 million years the timing phase of strong monsoons has changed by 83 degrees in the precession and 124 degrees in the obliquity bands relative to the phase of maximum global ice volume inferred from the marine oxygen isotope record these results suggest that one or both of these systems is nonstationary relative to orbital forcing

petrology of quaternary fluvial low magnesian calcite coated grains from central texas abstract coated grains formed and accumulated as fluvial deposits 4 to 5 m thick and up to 16 km wide parallel to contemporary streams in central texas grain size and sedimentary structure data indicate deposition by bedload ephemeral streams the source of the calcium carbonate was spring water from the edwards aquifer which today has a mg ca ratio of 0 5 and is supersaturated with respect to calcite ooids are most common in medium to very coarse grained sands and range in size from 0 21 mm to 1 5 cm cortices consist of alternating fine and coarse grained laminae fine grained laminae are 0 5 to 20 m thick consist of clay minerals and organic matter and extend into the interstices of radially oriented calcite crystals of the coarse grained laminae coarse grained laminae are 4 to 100 m thick and consist of radially oriented elongate crystals of low magnesian calcite 2 to 3 m wide and 10 to 20 m long rhombohedral terminations of individual crystals occur on ooid outer surfaces and in cortical interiors between coarse and fine grained laminae a primary low magnesian calcite mineralogy is indicated by the presence of rhombohedral terminations and he absence of replacement fabrics the stout nature of the original crystals was responsible for the development and preservation of the radial cortical structure pisoids most commonly occur in gravels and range in size from 0 67 mm to 12 cm nuclei are most commonly terrigenous pebbles and show evidence of boring in the form of dark irregular filaments approximately 7 m in diameter which contain organic matter cortices are biogenic in origin and consist of porous zones and zones of dense laminae dense laminae are a few tenths of a millimeter thick and are composed of aphanocrystalline low magnesian calcite porous zones are a few tenths of a millimeter to several centimeters thick and consist of domed accretionary bodies accretionary bodies range from a millimeter to several centimeters in area and consist of radially oriented branched filaments 10 to 20 m in diameter transecting alternating laminae of finely to very finely crystalline calcite

seismic stratigraphy and quaternary sedimentation in the skagerrak northeastern north sea abstract ice movement sea level fluctuations and currents are the controlling factors of the late pleistocene and holocene sedimentation processes in the skagerrak the erosional truncation at the top of a mesozoic depositional sequence defines the extent of the norwegian channel and functions as the initial depositional surface for quaternary sedimentation on this surface in shallow waters off the danish coast weichselian glacial sediments are deposited an end morain ridge marks a temporary stillstand of the retreating ice front at the beginning of ice free conditions some 15 000 yrs ago when the sea was about 70 m below the present level the skagerrak was a fjord like forebasin of the northern atlantic and constituted a favorable outlet for rivers draining the subaerial glacial deposits of the southern skagerrak and the present southern north sea fluvial erosion released large amounts of detrital material which was laid down in the form of a progradational delta prodelta complex slumping and mass flow processes led to high sedimentation rates and a rapid infilling of the norwegian channel in front of the delta complex with the rapid transgression of the southern north sea at the beginning of the holocene a dramatic change in the depoenvironment of the skagerrak took place the modern current pattern became established whereby sediment transport and redeposition became the rule along the danish coast sandwaves and megaripples with an apparent northeasterly migration direction were formed as a result of the wind forced jutland current fine suspended particles bypass the coastal zones to settle out in the deep norwegian channel

late glacial and holocene paleoceanography in the skagerrak from high resolution grain size records abstract high resolution grain size analyses of the ams 14c dated 32 m long core md99 2286 from the northeastern skagerrak were performed in order to study late glacial and holocene paleoceanographic and sedimentary changes all ages in this study are given in calibrated thousand years before present ad 1950 abbreviated kyr unless otherwise noted the distinct ending of ird ice rafted debris in core md99 2286 which was retrieved from a location down current from the final calving ice margin in the region indicates that iceberg calving in the skagerrak ended between 10 6 and 10 2 kyr a clay rich sequence in core md99 2286 deposited between 11 3 and 10 3 kyr is attributed to outflow from the baltic basin across south central sweden the sequence is correlated to similar units from cores along the swedish west coast the onset of this clay rich deposition occurs progressively later in cores further south along the coast supporting a previous hypothesis that differential glacio isostatic uplift caused a southward migration of the baltic outflow from the otteid stenselva to the gota alv outlet a distinct coarsening towards younger sediments in core md99 2286 indicates a hydrographic shift at 8 5 kyr which is correlated to a shift previously reported in the skagerrak kattegat and the norwegian channel this shift reflects the establishment of the modern circulation system in the eastern north sea as a consequence of the opening of the english channel and the danish straits and increased atlantic water inflow and the subsequent development of the south jutland current a general trend of coarsening poorer sorting and increasing variability from 8 5 kyr until the present indicates increasing strength and influence of the variable south jutland current a series of changes from ca 6 3 to ca 3 8 kyr in core md99 2286 reflects strengthening of the jutland current towards the present day sedimentation system in the skagerrak kattegat these changes are correlated to previously reported hydrographic shifts at 5 5 14c years bp in the skagerrak and at 4 0 14c years bp in the kattegat it is suggested that these shifts were separate features of a transitional period related to strengthening of the current system the resulting changes are differently manifested in different parts of the skagerrak kattegat due to the complex circulation system the last 800 years are characterised by poorly sorted sediments with a relatively high and variable proportion of coarse material reflecting a circulation system significantly modified by regional climatic conditions especially the general wind directions and storm frequency over the southern north sea

early diagnesis of carbohydrates in the marine environment ii composition and origin of carbohydrates in skagerrak sediments abstract the distribution and composition of carbohydrates were determined for the upper 15 cm of four cores from the southern slope of the skagerrak high concentrations were found in the upper bioturbated layers rapidly decreasing at sediment depths 3 cm total contents appear to be controlled by bioturbation application of various biomarker criteria suggests that carbohydrates originated from terrestrial macroalgal and planktonic sources input from these sources might be by episodic events rather than by continuous sedimentation as can be hypothesised from the irregular occurrence of marine and terrestrial signals

the dynamics of oceanic fronts part ii shelf water structure due to freshwater discharge abstract in part i of this series a framework was introduced for the study of oceanic frontal dynamics the dynamics was studied by posing an initial value problem starting with a near surface discharge of buoyant water with a prescribed density deficit into an ambient stationary fluid of uniform density an essential aspect of the framework was the identification of the proper length scales an inertial length scale l0 a buoyancy length scale h0 and a diffusive length scale hv in part i the horizontal and vertical dimensions were scaled by l0 and h0 respectively and two dimensionless parameters were formed viz ro l0 h0 and e hv h0 2 it was shown in part i that under this scaling the normalized equations depended on e only for ro sufficiently large the solution for e small i e for the almost inviscid case was given in part i and the equilibrium state was discussed in a frame of reference in which the front was stationary in this paper we present the solution for large e it will b

recent sediments and foraminiferal distribution in the skagerrak northeastern north sea abstract a number of bottom sediment samples from the skagerrak have been studied the surface sediment samples reflect the presence of three main sediment types with a fourth which occurs more scattered a selection of 50 samples was used for the study of the foraminifers of the 125 m fraction benthic foraminifers dominate the assemblages using factor analysis and the computer program cabfac the benthic foraminiferal data were reduced to five factors eight species have proven to be significant the factors benthic foraminiferal assemblages are dominated by bolivina cf b robusta elphidium excavatum cassidulina laevigata bulimina marginata melanis barleeanum globobulimina turgida and hyalines balthica respectively the first factors are clearly related to known hydrographic and bottom conditions

sediment deposition in offshore deeps of the western north sea questions for models a three dimensional hydrodynamic model is used to investigate the potential for offshore bathymetric deeps in the north sea to act as fine sediment traps simple conditions are established representative of the observed conditions and the response of the model investigated two deeps are considered here inner silver pit and sole pit the model study suggests that in inner silver pit deposition of fine sediment is only possible under weak tidal neap flows under all other conditions the flow is too energetic to allow deposition a transport path for fine sediment across inner silver pit is established but does not significantly modify the sediment dynamics in the pit experiments including wave action show that 50 year return period waves induce bed shear velocities sufficiently large to remove coarse sediment for sole pit a cycle of deposition followed by erosion at spring tides will inhibit deposition in the pit long term accretion of fine sediment does not seem possible in either pit

accumulation of barium in recent skagerrak sediments sources and distribution controls abstract geochemical and mineralogical methods have been applied to document the ba and barite distributions in the skagerrak sediments barite released in the central north sea during hydrocarbon drilling as a component of the drilling mud is a principal carrier of ba in the recent skagerrak sediments the systematic pattern of the surface ba contents displaying a generally decreasing trend from south to north is consistent with the barite transport from the north sea towards the skagerrak the predominant barite grain size ranges between 10 and 20 m the sub surface ba distribution is characterised by the elevated contents within the top 5 10 cm which downward is followed by uniformly low contents considering the sedimentation rate the start of sub surface ba enrichment generally corresponds to the late 1960s coinciding with the beginning of off shore drilling in the north sea in addition to the primary depositional factors controlling the shallow stratigraphic ba distribution the influence of diagenetic processes is suggested by the dissolution features on the barite grain surfaces and the profile relationships to the interpreted diagenetic zones

magnetic polarity stratigraphy of upper siwalik sub group soan valley pakistan implications for early human occupance of asia abstract the results of a detailed paleomagnetic study of a 68 m section of upper siwalik sediments in the soan syncline northern pakistan are presented a palaeolithic artefact and other pieces of struck quartzite were found in situ in a gritstone conglomerate horizon near the base of the section incremental thermal demagnetization was used to remove later magnetic overprints in these sediments since alternating field demagnetization was shown to be inappropriate with the exception of the lowest stratigraphic level the upper siwalik sediments examined in the riwat section show reverse polarity magnetization the declination values are consistent with a 16 4 counterclockwise rotation of the soan syncline tectonic block since deposition of the sediments on the basis of the palaeomagnetic analyses and the tectonic and stratigraphic context of the section our current best estimate of the age of the artefact bearing horizon is 2 0 0 2ma

biomarkers in upper holocene eastern north sea and wadden sea sediments total extracts of sediment cores from five different stations in the north sea and wadden sea were analysed for their biomarker composition only sediments of the skagerrak contained significant amounts of marine biomarkers mainly alkenones other sites contained predominantly terrestrial biomarkers bioturbation in the skagerrak is however far too high to determine sea surface temperature sst changes within short time intervals these results indicate that biomarkers contained in these sediments are not useful to reconstruct climate fluctuations during the upper holocene high amounts of and hydroxy fatty acids as well as small amounts of dihydroxy fatty acids were released from the insoluble organic material of the sediments from the wadden sea station indicating a significant input of the eelgrass zostera marina this was confirmed by microscopic observations this is the first time the dihydroxy fatty acids have been found in a sediment core and they have proven to be potential biomarkers for these seagrass species

diagnostic criteria for reconstruction of tidal continental shelf regimes changing the paradigm abstract a biogeochemical flux paradigm is presented which provides a conceptual and numerical framework for reconstructing the dynamical and biogeochemical regimes of ancient tide driven continental shelves the paradigm links turbulence primary production and suspended particulate matter flux in the water column to microbiological and isotopic proxies in the sediment record and identifies the diagnostic signatures of sediments deposited in stratified frontal and mixed dynamic regimes of tidal shelves the critical governing processes in the water column and at the sediment water interface are temperature particulate organic carbon supply and benthic oxygen consumption which exhibit strong gradients across tidal mixing fronts the diagnostic proxies in the sediment record are microplanktonic e g dinoflagellate cysts and microbenthic e g foraminifera and their associated stable isotopic properties advanced numerical models are available which incorporate biophysical coupling in the water column and benthic boundary layer and which simulate biogeochemical and ecological processes and organic fluxes to the seabed these models offer potential advances for interpreting microbiological and isotopic proxies of biogeochemical regime preserved in the fine sediment record quaternary shelf deposits provide the best potential validation of the biogeochemical flux paradigm since most quaternary species are living today but the paradigm is applicable to ancient tidal shelf deposits the paradigm is particularly applicable to the fine sediment record which potentially preserves the most complete history of shelf evolution