preservation of extraterrestrial 3he in 480 ma old marine limestones we have measured the helium abundance and isotopic composition of a suite of lower ordovician marine limestones and associated fossil meteorites from kinnekulle sweden limestone 3he 4he ratios as high as 11 5 times the atmospheric value in fused samples and up to 23 times atmospheric in a single step heat fraction indicate the presence of extraterrestrial helium and demonstrate that at least a fraction of the extraterrestrial 3he carried by interplanetary dust particles must be retained against diffusive and diagenetic losses for up to 480 ma the carrier phase has not been identified but is not magnetic extrapolation of high temperature 3he diffusivities in these sediments is consistent with strong retention of extraterrestrial 3he under ambient earth surface conditions combination of the observed helium concentrations with sedimentation rates estimated from conodont biostratigraphy suggest that the flux of extraterrestrial 3he in the early ordovician was about 0 5 10 12 cm 3 stp cm 2 ka 1 ignoring potential post deposition helium loss this value is indistinguishable from the average 3he flux estimated for the cenozoic era in contrast previous studies of fossil meteorites ir abundances and os isotopic ratios in the limestone suggest that the total accretion rate of extraterrestrial material during the studied interval was at least an order of magnitude higher than the cenozoic average this disparity may reflect significant post depositional loss of 3he from idps within these old limestones if so the match between the ordovician flux and the cenozoic average would be fortuitous alternatively the size distribution of infalling objects during the early ordovician may have been enriched only in extraterrestrial material too large to retain 3he during atmospheric entry heating 30 m the fossil meteorites themselves also preserve extraterrestrial helium meteorite 3he concentrations of 2 to 9 10 12 cm 3 stp g 1 are several orders of magnitude lower than found in most modern meteorites suggesting very substantial helium loss probably 99 9 from these chemically altered objects the meteorites carry 3he concentrations only a factor of a few higher than the host limestones the meteorites themselves cannot be the source of the extraterrestrial 3he observed in the limestones

sources of sediment to the ionian sea and western levantine basin of the eastern mediterranean during s 1 sapropel times abstract the provenance of sediments to the ionian sea and western levantine basin during s 1 sapropel times was studied using 87 sr 86 sr isotopic ratios together with major elements measurements were made on sediment profiles from 5 box cores in the eastern mediterranean on saharan dust and on a core from the nile delta which included sediment deposited during s 1 sapropel times in the sediment profiles there was a decrease in 87 sr 86 sr ratio 1 sr ti al mg al and si al ratio starting at the upper mn peak and finishing at the base of the organic rich layer this showed that there was a major change in the nature of the detrital input during s 1 sapropel times the timing of the change in detrital input was similar to the change in surface salinity as measured by 18 o there was linear relationship between 87 sr 86 sr and 1 sr and for 87 sr 86 sr and ti al for all the sediment samples the favoured interpretation of this pattern was that the detrital input was a mixture of saharan dust similar to that being deposited today on corsica and a local riverine sediment source the data were incompatible with the riverine source to the ionian sea and western levantine basin being from the river nile the minor variations in sr isotopes and metal al ratios in the nile delta core was interpreted as due to changes in the proportion of blue nile to white nile inputs brought about by climatic variations it was calculated that the change in detrital input during s 1 time was caused by a simultaneous increase in riverine input and decrease in saharan dust input

causal links between nile floods and eastern mediterranean sapropel formation during the past 125 kyr confirmed by osl and radiocarbon dating of blue and white nile sediments abstract it has long been hypothesised that beds of highly organic mud or sapropels seen in marine sediment cores retrieved from the floor of the eastern mediterranean accumulated during times of high nile fluvial discharge our recent fieldwork in the valleys of the blue nile the white nile and the main nile has for the first time revealed a sequence of extreme flood episodes synchronous with sapropel units s5 124 kyr s4 102 kyr s3 81 kyr s2 55 kyr and s1 13 5 6 5 kyr there are more weakly defined links with nile floods and sapropel units s9 240 kyr s8 217 kyr s7 195 kyr s6 172 kyr but the dating error terms are too large to allow us to be too definite during times of extreme floods over the past 125 kyr wide distributary channels of the blue nile flowed across the gezira alluvial fan in central sudan and transported a bed load of sand and gravel into the lower white nile valley the sands were reworked by wind to form source bordering dunes all of which contain heavy minerals of ethiopian provenance these source bordering dunes were active at 115 105 kyr 60 kyr and 12 7 kyr all times of extreme blue nile floods the flood and dune sediments were dated using a combination of optically stimulated luminescence osl and radiocarbon analyses the quaternary record of nile floods discussed here shows a precessional signal and reflects episodes of stronger summer monsoon and more northerly seasonal movement of the itcz linked to times of higher insolation in northern tropical latitudes progressive aggradation of holocene nile channels in northern sudan has had a profound influence upon human settlement in the last 8 kyr

forcing mechanisms for mid cretaceous black shale formation evidence from the upper aptian and lower albian of the vocontian basin se france calcareous nannoplankton palynomorph benthic foraminifera and oxygen isotope records from the supraregionally distributed niveau paquier early albian age oceanic anoxic event 1b and regionally distributed niveau kilian late aptian age black shales in the vocontian basin se france exhibit variations that reflect paleoclimatic and paleoceanographic changes in the mid cretaceous low latitudes to quantify surface water productivity and temperature changes nutrient and temperature indices based on calcareous nannofossils were developed the nutrient index strongly varies in the precessional band whereas variations of the temperature index reflect eccentricity since polar ice caps were not present during the mid cretaceous these variations probably result from feedback mechanisms within a monsoonal climate system of the mid cretaceous low latitudes involving warm humid and cool dry cycles a model is proposed that explains the formation of mid cretaceous black shales through monsoonally driven changes in temperature and evaporation precipitation patterns the lower albian niveau paquier which has a supraregional distribution formed under extremely warm and humid conditions when monsoonal intensity was strongest bottom water ventilation in the vocontian basin was diminished probably due to increased precipitation and reduced evaporation in regions of deep water formation at low latitudes surface water productivity in the vocontian basin was controlled by the strength of monsoonal winds the upper aptian niveau kilian which has a regional distribution only formed under a less warm and humid climate than the niveau paquier low latitude deep water formation was reduced to a lesser extent and or on regional scale only the threshold for the formation of a supraregional black shale was not reached the intensity of increases in temperature and humidity controlled whether black shales developed on a regional or supraregional scale at least in the vocontian basin the increased preservation of organic matter at the sea floor was more significant in black shale formation than the role of enhanced productivity

solar forcing of nile discharge and sapropel s1 formation in the early to middle holocene eastern mediterranean we present high resolution records for oxygen isotopes of the planktic foraminifer globigerinoides ruber 18oruber and bulk sediment inorganic geochemistry for holocene age sediments from the southeast mediterranean our 18oruber record appears to be dominated by nile discharge rather than basin scale salinity temperature changes nile discharge was enhanced in the early to middle holocene relative to today the timing of the long term maximum in nile discharge during the early holocene corresponds to the timing of maximum intensity of the indian ocean influenced southwest indian summer monsoon sim this coincidence suggests a major influence of an indian ocean moisture source on nile discharge in the early to middle holocene while presently the atlantic ocean is the main moisture source nile discharge was highly variable on multicentennial time scale during the early to middle holocene being strongly influenced by variable solar activity this solar driven variability is also recorded in contemporaneous sim records however not observed in an atlantic ocean derived west african summer monsoon record from the holocene this supports the hypothesis that the indian ocean moisture source predominantly controlled nile discharge at that time solar driven variability in nile discharge also influenced paleoenvironmental conditions in the eastern mediterranean bulk sediment ba al and v al used as indicators for export productivity and redox conditions respectively varied both in response to solar forcing on multicentennial time scales we suggest that changes in nile discharge on these time scales have been concordant with nutrient inputs to and shallow ventilation of the eastern mediterranean

an open ocean region in neoproterozoic glaciations would have to be narrow to allow equatorial ice sheets 1 a major goal of understanding neoproterozoic glaciations and determining their effect on the evolution of life and earth s atmosphere is establishing whether and how much open ocean there was during them geological evidence tells us that continental ice sheets had to flow into the ocean near the equator during these glaciations here we drive the parallel ice sheet model with output from four simulations of the echam5 max planck institute ocean model atmosphere ocean general circulation model with successively narrower open ocean regions we find that extensive equatorial ice sheets form on marine margins if sea ice extends to within about 20 latitude of the equator or less jormungand like and hard snowball states but do not form if there is more open ocean than this given uncertainty in topographical reconstruction and ice sheet ablation parameterizations we perform extensive sensitivity tests to confirm the robustness of our main conclusions

climate at high obliquity abstract the question of climate at high obliquity is raised in the context of both exoplanet studies e g habitability and paleoclimates studies evidence for low latitude glaciation during the neoproterozoic and the snowball earth hypothesis states of high obliquity are distinctive in that for 54 the poles receive more solar radiation in the annual mean than the equator opposite to the present day situation in addition the seasonal cycle of insolation is extreme with the poles alternatively facing the sun and sheltering in the dark for months the novelty of our approach is to consider the role of a dynamical ocean in controlling the surface climate at high obliquity which in turn requires understanding of the surface winds patterns when temperature gradients are reversed to address these questions a coupled ocean atmosphere sea ice gcm configured on an aquaplanet is employed except for the absence of topography and modified obliquity the set up is earth like two large obliquities 54 and 90 are compared to today s earth value 23 5 three key results emerge at high obliquity 1 despite reversed temperature gradients mid latitudes surface winds are westerly and trade winds exist at the equator as for 23 5 although the westerlies are confined to the summer hemisphere 2 a habitable planet is possible with mid latitude temperatures in the range 300 280 k and 3 a stable climate state with an ice cap limited to the equatorial region is unlikely we clarify the dynamics behind these features notably by an analysis of the potential vorticity structure and conditions for baroclinic instability of the atmosphere interestingly we find that the absence of a stable partially glaciated state is critically linked to the absence of ocean heat transport during winter a feature ultimately traced back to the high seasonality of baroclinic instability conditions in the atmosphere

sr and nd isotope composition of late pleistocene sapropels and nonsapropelic sediments from the eastern mediterranean sea implications for detrital influx and climatic conditions in the source areas isotopic ratios of sr and nd from lithogenic components of three isochronous core sections recovered from an east west transect in the eastern mediterranean sea ems have been analyzed the data are used for a quantitative estimate of the temporal and spatial variation of detrital flux to the ems assuming saharan dust and aegean nile particulate matter as dominant end members it was established that the carbonate free saharan dust flux during deposition of the nonsapropel layers of marine oxygen isotope stage 5 4 mis 5 4 was similar to the present flux during the deposition of sapropels s5 and s6 however the saharan dust input was drastically reduced and was not balanced by a change in the riverine influx at this time denser vegetation cover during more humid conditions may have reduced physical erosion and sediment removal in the source area during marine oxygen isotope stage 6 2 mis 6 2 a pronounced increase of saharan dust and detrital influx from the aegean region is evident and implies more arid conditions in the southern and northern catchment areas during this period intersite variations are interpreted in terms of their geographic location relative to the seaways connecting the aegean sea and ems the width of the straits and hence the amount of sediment entering the eastern basins may have been affected by a low sea level that impeded interbasin sediment dispersal

long and short term carbon fluctuations in the eastern mediterranean during the late holocene a high resolution record of carbon isotope changes during the late holocene was obtained in core ga 112 from the easternmost mediterranean over the past 3600 yr a gradual 13 c depletion trend shown by both planktonic and benthic foraminifera corresponds to a global rise in atmospheric co 2 the global and local trends suggest that aridification and biomass destruction in the nile basin played a major role in the global co 2 rise in the late holocene superimposed on the general 13 c trend are four mirror image cycles in 13 c of planktonic and benthic foraminifera higher planktonic 13 c values reflect periods of high productivity off the coast of israel simultaneously decrease in the benthic 13 c values occurred because of degradation of higher organic matter fluxes to the sediment therefore large differences between the two records indicate periods of high productivity the eastern mediterranean productivity fluctuations respond to a periodical replenishment of nutrients to the mixed layer via nile runoff historical data of the nile flood fluctuations for the past 1400 yr show a remarkable coincidence between high and low nile floods and high and low eastern mediterranean productivity levels which are correlated with the periodic monsoonal activity over the nile headwaters

the characterisation of saharan dusts and nile particulate matter in surface sediments from the levantine basin using sr isotopes abstract the provenance of sediments within the levantine basin of the eastern mediterranean was studied using 87 sr 86 sr isotopic ratios together with major elements measurements were made on the detrital fraction of surface sediments and the two most important sources of detrital matter to the region saharan dust was characterised by an 87 sr 86 sr isotopic ratio in the range 0 7160 0 7192 there was a small systematic decrease in 87 sr 86 sr from west to east which is interpreted as due to a change in the balance of aeolian source material the nile particulate matter had a 87 sr 86 sr isotopic ratio in the range 0 7057 0 7071 87 sr 86 sr isotopic signatures together with sr concentration were used to calculate the contributions made by saharan dust and nile particulate matter to the surface sediments of the levantine basin it was shown that nile derived sediment was dispersed widely across the levantine basin enabling the area affected by retention of sediment behind the aswan dam to be determined

the kashiru pollen sequence burundi palaeoclimatic implications for the last 40 000 yr b p in tropical africa abstract a continuous pollen record from a central african highland site 3 28 s 29 34 e with 15 radio carbon dates spans at least the last 40 000 yr both modern and fossil pollen have been investigated a clear pattern of changes in vegetation and climate is suggested prior to 30 000 yr b p the occurrence of the montane conifer forest including the upper forest limit indicates climatic conditions colder and drier than now but more humid than in late glacial time between 30 000 and 15 000 yr b p grassland with afroalpine indicators expanded down to 2500 2000 m altitude as a result of dry and most probably cool climate the montane forest persisted in refuges although much reduced forest vegetation with the same floristic composition as today appeared after 13 250 200 yr b p suggesting more humid conditions the occurrence of a possible short term humid episode about 21 500 yr b p is correlated with some high lake level stages in east africa and with organic deposits in deep sea cores from the mediterranean and the atlantic ocean

mudball surface dust and snowball earth deglaciation 1 recent modeling results have raised doubts about the ability to deglaciate from a global glaciation at atmospheric carbon dioxide levels that are realistic for a neoproterozoic snowball earth here we argue that over the lifetime of a snowball event ice dynamics should lead to the development of a layer of continental and volcanic dust at the ice surface in the tropics that would significantly lower the tropical surface albedo and encourage deglaciation this idea leads to the prediction that clay drapes found on top of neoproterozoic glaciations should be thicker in tropical than extratropical regions we test this idea by running the foam general circulation model gcm with an added tropical dust layer of different sizes and albedos and find that the tropical dust layer causes snowball deglaciation at pco2 0 01 0 1 bar in a reasonable regime of these parameters we find similar though more nuanced results from a limited number of test cases using national center for atmospheric research s cam gcm

global climate instability reflected by eastern mediterranean marine records during the late holocene abstract extremely high sediment accumulation rates in the southeastern se mediterranean off israel make this region ideal for high resolution paleoceanographic reconstructions two cores were examined and foraminiferal oxygen and carbon isotope composition as well as physical and geochemical properties of the sediments were used to reconstruct the climatic and environmental changes of the se mediterranean basin during the late holocene 3 6 ka the 18o values of globigerinoides ruber suggest that the freshwater balance changed several times during this time interval humid phases took place between 3 5 3 0 ka bp and 1 7 1 0 ka bp the later was accompanied by enhanced preservation of terrestrial organic matter within the sediment ors event relatively more arid conditions prevailed in this area between 3 0 and 1 7 ka bp during the last millennia at ca 0 8 and 0 27 ka two climatic events occurred which are probably correlative to both the medieval warm period and the cooling global event known as the little ice age respectively a long term slight increase in planktonic foraminiferal 18o values occurs together with a gradual decrease in the 13c values of both g ruber and the benthic foraminifera uvigerina mediterranea this trend is associated with an increase in sedimentation rates ti al ratio magnetic susceptibility and color index of the sediments we suggest that this trend shown by various independent proxies seems to be related to the aridification process that started ca 7 0 ka in the mid low latitude desert belt and the se mediterranean region and continuous until the present the long term 13c decrease shown by surface and bottom water foraminifera reflects a gradual change in the 13c of the dissolved co2 of the entire se mediterranean water column this follows the global co2 rise in the late holocene as a result of the terrestrial biomass destruction during the aridification process moreover the gradual reduction of the vegetation cover in east africa led to an increased erratic flood related sediment flux via the nile river up to the present this is reflected by the general change in the local sediment composition at 3 6 ka the saharan eolian input reached 65 whereas at about 0 3 ka 70 of the se mediterranean sediment was composed of nile particulate matter

the osmium isotopic composition change of cenozoic sea water as inferred from a deep sea core corrected for meteoritic contributions a detailed study was made of the oceanic 187os 186os variation through the cenozoic by using a hydrogen peroxide leaching procedure on a pelagic clay core from the north pacific long lines 44 gpc3 a 6 h2o2 solution was used the range of 187os 186os obtained by this procedure was between 2 and 8 2 a milder leach 0 15 h2o2 in three out of four samples yielded a slightly higher 187os 186os value than the stronger leach implying that the stronger leach released some meteoritic os with 187os 186os of 1 using published 3he concentrations in gpc3 and cosmic dust 3he and os fluxes to deep sea sediments the extraterrestrial os concentration was estimated for each core segment and subtracted to yield corrected values of 187os 186os the results based on the milder leaching protocol and the 3he correction protocol yield similar values the corrected ocean water 187os 186os pattern for the past 25 million years is similar to that obtained by other workers and is compatible with other results for the entire cenozoic the variation with time in gpc3 uniquely provides a statigraphic signature for the paleogene

stratigraphy sedimentology and isotopic geochemistry of australian neoproterozoic postglacial cap dolostones deglaciation delta 13 c excursions and carbonate precipitation abstract thin d13c excursions in the geologic record they are interpreted to record a brief postglacial anomaly in ocean chemistry in australia the marinoan varanger equivalent 600 ma cap dolostone units exhibit many of the characteristics displayed by such deposits elsewhere around the globe including fine grained dolomitic mineralogy lateral persistenc at basinal scales thin laminae graded beds intervals with abundant marine cements crystal fans and a distinctive negative d13c isotopic signature of up to 5 pdb on the basis of these features the australian examples are interpreted here to be deeper water deposits below storm wave base resulting from an anomalous flux of inorganic carbonate to the sea floor during postglacial transgression detailed isotopic analysis of australian cap dolostones indicates d13c values ranging from 1 to 5 and gen rally becoming more depleted in 13c upsection trace element data indicate some diagenetic stabilization but textural evidence and the presence of similar profiles in different basins argue against a pervasive recrystallization event the range in d13c values between sections as well as more negative 13c values appear to correlate with greater paleobathymetry within basins this implies either 1 only partial preservation of the complete oceanic variation of d13c or 2 precipitation of this peculiar facies owes its genesis to basinal specific oceanographic processes such as proximi y of a given section to a postglacial upwelling zone in the later case d13c values would not represent whole ocean values stratigraphic constraints and paleoenvironmental interpretations suggest that much of this excursion lies within the geologically brief period of postglacial transgression this implies that the cause s of d13c variation likely operated on time scales significantly less than the residence time of carbon in the oceans 105 yr the continent wide and perhaps global nature of cap dolostones indicates that large volumes of carbonate were precipitated during the postglacial transgressive period such large scale carbonate precipitation over the hypothesized short time interval of postglacial transgression must have caused or have been the product of profound changes in the carbon cycle and global climate at tha time similar evidence for transgression and increased carbonate deposition in the holocene are attributed to the changing basin shape and ph of the oceans the coral reef hypothesis of berger 1982 cap dolostones may record a proterozoic equivalent of this process with the substitution of abiotic carbonate precipitation for skeletal precipitation by reef organisms

sediment transport of the blue nile at khartoum the blue nile supplies the nile river with the largest proportion of water and sediment nevertheless very few often contrasting data are reported in the literature about its sediment yield this paper deals with detailed field measurement of suspended sediment transport taken at khartoum during three flood seasons in the late 1960s the pattern of suspended sediment concentration discharge and grain size variation with flow is analysed and suspended sediment yield is calculated and compared with data from different sources no bedload transport measurements are reported in the literature for the blue nile the flow data measured in the field consent to select several dune geometry criteria and to adopt the dune bedforms migration method to calculate bedload transport the same procedure is applied also to the bedload data measured in four reaches of the nile river downstream of the high aswan dam with channel and sediment characteristics comparable with those of the blue nile at khartoum to ascertain which dune geometry criterion provided the most reliable results the bagnold 1980 and martin 2003 equations predict similar values of bedload transport that are compared with the very few bedload data assessed by other authors using different equations and methods finally a good relation between flow velocity and bedload transport rate is found

100 000 years of african monsoon variability recorded in sediments of the nile margin abstract multiproxy analyses were performed on core ms27pt recovered in hemipelagic sediments deposited on the nile margin in order to reconstruct nile river palaeohydrological fluctuations during the last 100 000 years the strontium and neodymium isotope composition of the terrigenous fraction and the major element distribution reveal large and abrupt changes in source oscillating between a dominant aeolian saharan contribution during arid periods and a dominant nile river contribution during pluvial periods iron content shows a strong correlation with strontium and neodymium isotopes this allows the use of a high resolution continuous fe record as a proxy of blue nile sediment input over the last 100 000 years the detailed fe record with approximately 10 years resolution during pluvial periods is consistent with subtropical african records of well dated lake level fluctuations and thus constitutes a first continuous high resolution record of the east african monsoon regime intensity over ethiopia the detailed fe record shows the two main known pluvial periods attributed to strengthening of the african monsoon over ethiopia the nabtian period from 14 to 8 ka cal bp and the saharan period from 98 to 72 ka bp for the first time the last glacial period marine isotope stage mis 2 3 and 4 is documented with a continuous record showing large oscillations between high and low east african palaeo monsoon regimes the end of the nabtian period occurred at 8 ka in core ms27pt i e much earlier than on the east equatorial african region where it ended around 5 5 ka we interpret this as evidence that the southward shift of the rain belt occurred 3000 years earlier over the eastern ethiopian highland and propose that the gradual southward migration of the rain belt was associated with highly variable intensity and longer rainy seasons from 8 to 5 ka during the last glacial period two wet periods are present around 60 50 ka bp and 38 30 ka bp these two humid periods are in phase with the rise of atmospheric ch4 concentrations suggesting that wetland tropical african area was one of the sources of the atmospheric ch4 during the mis 3 during the last glacial maximum and mis 4 high saharan aeolian influxes in phase with records of aeolian dust deposited in east antarctica are documented this study highlights the importance of reconstructions of monsoon rainfall fluctuation at high temporal resolution to better understand the link between low and high latitude climate variability at millennial timescales

late quaternary evolution of the burullus lagoon region north central nile delta egypt abstract the evolution of late quaternary stratigraphic sequences in the burullus lagoon region of the north central nile delta egypt is determined by petrological analysis of radiocarbon dated sediment borings shallow marine lagoonal and fluvial deposits accumulated during the late pleistocene and delta plain to coastal facies during the holocene since about 7500 yrs b p the latter sequence is characterized primarily by an irregular succession of delta plain deposits i e distributary channel fill marsh and lagoon complete coarsening upward sequences formed by prodelta to coastal units and previously defined in the northeastern nile delta are not observed in this region long term sediment accumulation rates for holocene facies during the build up of the delta range from about 100 to 300 cm 1000 yrs the location and ages of three nile distributary channel systems are recognized by means of cores from east to west sebennitic saitic and bolbitine rosetta the mouth of the sebennitic which is oldest of the three was located on what is now the inner to middle shelf this would explain the absence of prodelta and delta front sequences and a presence of a belt of medium to coarse grained sands extending seaward of the coast the distribution in time and space of the holocene facies is interpreted in terms of the interplay of factors controlling sedimentation i e eustatic sea level oscillations climatic changes and land subsidence minor in this region 0 04 cm yr of the three sea level changes dominate paleogeographic maps show through a series of time slices the changing configuration of this region during the past 30 000 years maps indicate the shifting channel systems and the major displacement of associated marshes and lagoons this study suggests that without the emplacement of coastal protection barriers and containment structures an expansion of burullus lagoon may be expected in the near future

seasonal rainfall in the sinai desert during the late quaternary inferred from fluorescent bands in fossil corals skeletal bands of alternating high and low density in massive coral species have been used to record their growth history1 2 in the red sea living colonies of the genus porites deposit low density skeletal bands during summer and high density bands during winter3 additionally yellow green fluorescence can sometimes be seen in these massive corals imparted to them by the incorporation of humic material carried by coastal runoff4 annual banding of fluorescent sequences in living scleractinian corals has proved to be useful in the study of terrestrial runoff in the near shore environment5 6 here we report the finding of similar yellow green fluorescent bands in fossil porites from late quaternary reef terraces in southern sinai which are absent from living porites in the nearby fringing reefs the periodic sequences of the fluorescing humics were found to be superimposed on the low density sub bands of the fossil corals we interpret our observations as evidence that during the late quaternary reef forming peaks the climate was wetter than the extreme desert conditions now prevailing with a possible summer rainfall regime

a 6000 year geochemical record of human activities from alexandria egypt abstract recent multidisciplinary investigations of sediment cores from the ancient marine bay of alexandria egypt have documented local human activities during the iron age circa 900 1000 b c prior to alexander the great s arrival in 331 b c goiran 2001 veron et al 2006 stanley et al 2007 2010 corroborating the existence of the so called rakhotis as evoked in previous archaeological literature jondet 1916 weill 1919 chauveau 1999 baines 2003 lead pb isotopic analyses lia from alexandria bay indicate a possible anthropogenic imprint as early as circa 2300 2650 200 b c and to a lesser extent 3500 3800 170 b c veron et al 2006 here we demonstrate that lia in sediments from the nearby maryut lagoon display isotopic anomalies resulting from the release of contaminant pb into the lagoon during the egyptian early dynastic at 2897 187 b c and predynastic at 3520 145 b c periods that corroborate geochemical data from alexandria bay pb concentrations in maryut sediments show enrichments that mirror isotopic findings the absence of contaminant pb imprints within the sediments from the nearby nile canopic branch confirms that isotopic anomalies found in alexandria bay and maryut lagoon sediments are local and do not originate from long distance transport of contaminant pb associated with nile suspended material and or wind derived aerosols lia in alexandria sediment cores correspond to commonly mined pb and cu copper ores from turkey black sea region cyprus crete and the oman gulf lia substantiate the use of copper based relics in the alexandria region during the pre and early dynastic periods and provide insights into metal trading within the eastern mediterranean during the chalcolithic early bronze age transition 6000 years ago

hydroclimate variability in the nile river basin during the past 28 000 years it has long been known that extreme changes in north african hydroclimate occurred during the late pleistocene yet many discrepancies exist between sites regarding the timing duration and abruptness of events such as heinrich stadial hs 1 and the african humid period ahp the hydroclimate history of the nile river is of particular interest due to its lengthy human occupation history yet there are presently few continuous archives from the nile river corridor and pre holocene studies are rare here we present new organic and inorganic geochemical records of nile basin hydroclimate from an eastern mediterranean em sea sediment core spanning the past 28 ka bp our multi proxy records reflect the fluctuating inputs of blue nile versus white nile material to the em sea in response to gradual changes in local insolation and also capture abrupt hydroclimate events driven by remote climate forcings such as hs1 we find strong evidence for extreme aridity within the nile basin evolving in two distinct phases during hs1 from 17 5 to 16 ka bp and from 16 to 14 5 ka bp whereas peak wet conditions during the ahp are observed from 9 to 7 ka bp we find that zonal movements of the congo air boundary cab and associated shifts in the dominant moisture source atlantic versus indian ocean moisture to the nile basin likely contributed to abrupt hydroclimate variability in northern east africa during hs1 and the ahp as well as to non linear behavior of hydroclimate proxies we note that different proxies show variable gradual and abrupt responses to individual hydroclimate events and thus might have different inherent sensitivities which may be a factor contributing to the controversy surrounding the abruptness of past events such as the ahp during the late pleistocene the nile basin experienced extreme hydroclimate fluctuations which presumably impacted paleolithic cultures residing along the nile corridor

extraterrestrial 3 he as a tracer of marine sediment transport and accumulation the deposition rate of deep sea sediments and their focused redeposition by deep sea currents can be evaluated from analyses of sedimentary 230th with a temporal resolution limited only by bioturbation6 7 10 11 230th is produced uniformly throughout the ocean by radioactive decay of dissolved 234u and is removed sufficiently fast by sorption onto sinking particles to act as a constant flux tracer of sedimentation rates but the half life of 230th 75 kyr limits its use for this purpose to the past 200 250 kyr here we explore the use of extraterrestrial 3he from interplanetary dust particles1 4 idps as a constant flux proxy that is free from this limitation a comparison of 3he with 230th in two cores from the equatorial pacific ocean indicates that the variability in the mean flux of idps over the past 200 kyr is less than 75 but in contrast to this relatively constant rate of supply of 3he to the deep sea the local burial rates of 3he and 230th have varied by a factor of five over the past 450 and 200 kyr respect ively we interpret this variability as reflecting sediment focusing with a temporal pattern that suggests regular cycles of climate driven reorganization of near bottom currents in the deep pacific ocean

subsidence in the northeastern nile delta rapid rates possible causes and consequences holocene fluvial and marine deposits have accumulated in a graben like structure on the northeastern margin of the nile delta this part of the delta which includes lake manzala port said and the northern suez canal has subsided rapidly at rates of up to 0 5 centimeter per year since about 7500 years ago this subsidence has diverted at last four major distributaries of the nile river into this region the combined effects of continued subsidence and sea level rise may flood a large part of the northern delta plain by as much as 1 meter by the year 2100 the impact of continued subsidence now occurring when sediment input along the coast has been sharply reduced because of the aswan high dam is likely to be substantial particularly in the port said area and as far inland as south of lake manzala

robust elements of snowball earth atmospheric circulation and oases for life 1 atmospheric circulation in a snowball earth is critical for determining cloud behavior heat export from the tropics regions of bare ice and sea glacier flow these processes strongly affect snowball earth deglaciation and the ability of oases to support photosynthetic marine life throughout a snowball earth here we establish robust aspects of the snowball earth atmospheric circulation by running six general circulation models with consistent snowball earth boundary conditions the models produce qualitatively similar patterns of atmospheric circulation and precipitation minus evaporation the strength of the snowball hadley circulation is roughly double modern at low co2 and greatly increases as co2 is increased we force a 1 d axisymmetric sea glacier model with general circulation model gcm output and show that neglecting zonal asymmetry sea glaciers would limit ice thickness variations to o 10 global mean ice thickness in the 1 d sea glacier model is well approximated by a 0 d ice thickness model with global mean surface temperature as the upper boundary condition we then show that a thin ice snowball solution is possible in the axysymmetric sea glacier model when forced by output from all the gcms if we use ice optical properties that favor the thin ice solution finally we examine snowball oases for life using analytical models forced by the gcm output and find that conditions become more favorable for oases as the snowball warms so that the most critical time for the survival of life would be near the beginning of a snowball earth episode

human occupations and environmental changes in the nile valley during the holocene the case of kerma in upper nubia northern sudan abstract our article presents a detailed holocene archaeological sequence from the nile valley at kerma in upper nubia northern sudan this sequence retraces the evolution of human populations thanks to the study of several sites supported by 90 14c dates reconstruction of the environmental changes was supported by a study of dated stratigraphic sections located near the archaeological sites studied and illustrates the effects on human occupation of changes in river flow and floods which are in turn forced by climatic changes the results shed new light on the evolutionary dynamics of the holocene populations in nile valley little known due to the numerous hiatuses in occupation when compared with the situation in the sahara and the rest of the nile valley they confirm that the initial occupation took place ca 10 5 kyr bp after the start of the african humid period followed by a migration towards the banks of the nile commencing 7 3 kyr bp they also confirm the appearance of the neolithic by ca 8 0 kyr bp the kerma stratigraphic sequences show two prosperous periods 10 8 and 7 6 kyr bp and two hiatuses in the occupation of the sites 7 5 7 1 and 6 0 5 4 kyr bp resulting from increased aridity

late quaternary stratigraphy and paleogeography of the eastern nile delta egypt abstract a petrological study of numerous sediment borings identifies the late pleistocene and holocene lithofacies in the northeastern nile delta of egypt a coarsening upward sequence characterizes the major holocene depocenters located along the northern margin of the present delta stratigraphic correlation of radiocarbon dated sections and mapping of key facies such as delta front mud reveal the locations of four major holocene delta lobes related to former distributary branches of the nile river mendesian pelusiac tanitic and pre modern damietta these lobes formed primarily of marine prodelta and delta front deposits interfinger geographically but radiocarbon dating indicates that their bases are not synchronous lobes developed for the most part since 8000 years b p i e as the rate of eustatic sea level rise began to decrease climatic and sediment discharge fluctuations lateral migrations of distributaries and isostatic subsidence of land are additional factors that affected the temporal and spatial distributions of the lobes paleogeographic maps reveal the changes with time in the distributions of different lobes and deltaic plain environments marsh lagoons and concomitant displacement of the coastline holocene sediment accumulation rates to 500 cm per 1000 years are calculated this is 10 times greater than that on the nile cone and 50 times greater than on the egyptian continental shelf the delta coastal margin in the study area migrated northward by as much as 50 km during the past 5000 years an average progradational rate of up to 10 m per year the general configuration of the present delta developed during the past millennium the major changes recently induced by man in this region coupled with a series of continuing natural phenomena slow rise in sea level coastal erosion subsidence have markedly affected the evolution of the delta petrological study of the nile delta sediments provides baseline reference information to help recognize changes in the recent geological past to help identify those taking place at present and possibly to help predict those likely to occur in this region in the future

terrigenous helium in deep sea sediments abstract we have measured the isotope ratios of helium contained in various terrigenous materials that contribute to deep sea sediments these materials include ice rafted debris from the north atlantic chinese loess and sediment collected at or near the mouths of three large rivers the amazon the ganges and the yangtze we observe terrigenous 3he 4he ratios that vary from 1 8 10 9 to 4 6 10 7 i e values that are higher than the theoretically derived range of 10 9 to 10 8 atlantic and pacific deep sea sediment 3he 4he ratios can be explained by mixing of helium from similar extraterrestrial but different terrigenous sources terrigenous sources for north atlantic and north pacific sediments are characterized by 3he and 4he contents that are higher and 3he 4he ratios that are lower than those for central and eastern equatorial pacific sediments this is consistent with the supply to the north atlantic and north pacific oceans of older cratonic continental material that contains high amounts of in situ produced nucleogenic and radiogenic helium terrigenous material transported to central and eastern equatorial pacific sediments contains lower amounts of 3he and 4he and higher 3he 4he ratios indicative of supply from a more juvenile andean source in the equatorial atlantic core v31 135 we have used previously published 230th data to determine an extraterrestrial 3he flux of 1 16 0 15 10 12 cm3stp cm 2 ka 1 within error of that previously determined in sediments from the equatorial pacific ocean 0 78 0 29 10 13 cm3stp cm 2 ka 1 marcantonio et al 1996

chemostratigraphy across the cretaceous tertiary boundary and a critical assessment of the iridium anomaly the elevated concentration of iridium one of the platinum group elements pge at the cretaceous tertiary boundary is still the most generally accepted evidence that a large bolide struck the earth at the time of the end cretaceous mass extinctions new chemostratigraphic data for cross boundary sections from both hemispheres are not easily explained in terms of such an impact event for example the observation that the pge patterns show marked differences between the hemispheres the new constraints indicate that models of mantle derived pge should be seriously considered and that pge anomalies might not be as useful as previously thought as unambiguous identifiers of large impact events in the earth s history

unraveling north african riverine and eolian contributions to central mediterranean sediments during holocene sapropel s1 formation hydroclimate variability has exerted a fundamental control on the alternating deposition of organic lean marl and organic rich sapropel sediments in the eastern mediterranean sea ems however the exact mechanisms regarding the freshwater sources and related changes are still debated here sr and nd isotopes and high resolution elemental data are used to constrain different riverine and eolian supplies to the central mediterranean over the past 9 8 ka the detrital sediments in core cp10bc taken at the margin of the libyan shelf in the southwestern ionian sea can be described by a three endmember mixing system based on sr and nd isotopic compositions the same systematics can also be deduced from ti and k compositional variability the endmembers comprise saharan dust aegean nile and libyan soil representing the eolian supply from north africa the riverine inputs from the aegean nile areas as well as the riverine and shelf derived fluxes from the libyan tunisian margin respectively for the sapropel s1 period in particular we find important detrital supplies from fossil river wadi systems along the libyan tunisian margin activated by intensified african monsoon precipitation combining the temporal profiles with the consistent variability observed in the 87sr 86sr 1000 sr diagram such libyan contribution has been most prominent during the uppermost period of sapropel s1 in core cp10bc this observation is in agreement with hydroclimate reconstructions of northwestern libya comparison of the sr nd isotope data between core cp10bc and four cores taken along a west east transect throughout the ems shows that this detrital supply originated mainly from western libya tunisia and was transported as far eastward as 25 e while being diluted by an increasing nile contribution

changes in environment and provenance within the changjiang yangtze river delta during pliocene to pleistocene transition abstract this study investigates heavy mineral assemblages in sediments of the modern changjiang delta yangtze river and the quaternary pliocene q n boundary strata within the delta area with the aim of deciphering changes in sediment provenance and the depositional environment during the pliocene to pleistocene transition major heavy mineral assemblages in the modern changjiang sediments originate from their provenance rocks while the distribution of unstable amphibole ultrastable zircon tourmaline and rutile and altered minerals limonite leucoxene are closely related to the climate and the hydrodynamic environment within the catchment the ratio of a certain unstable mineral amphibole to an altered mineral limonite is considered to be a sensitive indicator of the chemical weathering intensity that is largely affected by climate conditions heavy mineral data of core sediments reveal distinctly different environments and provenances between the upper quaternary and lower pliocene sedimentary strata in the changjiang delta the pliocene sediments are characterized by abnormally high contents of limonite 42 leucoxene 8 and zircon 15 but an extremely low amphibole content 5 enrichment of zircon is indicated from the mid lower changjiang catchment where granitoid rocks are widely distributed the strong enrichment of altered minerals and the considerable great loss of unstable minerals suggest that pliocene weathering was much stronger than it is nowadays in contrast high contents of amphibole garnet and pyroxene and the low stable mineral content in the quaternary strata indicate that sediment provenances may have extended to the upper changjiang catchment which underwent weak chemical weathering these results imply that changjiang as a large river system might have drained the east china s continental margin prior to the q n transition the distinct heavy mineral assemblages found at the q n boundary in the changjiang delta are indicative of a drastic environment with provenance changes in response to intensive neotectonics it is thus inferred that sensitive heavy mineral indices can be used to indicate the q n boundary in the changjiang delta where reliable geochronological proxies have rarely reached an agreement

nile river sediment fluctuations over the past 7000 yr and their key role in sapropel development the provenance pattern of nile river sediments can be used as a proxy for paleoclimatic changes in east africa the 87sr 86sr ratios are particularly appropriate for such provenance investigations because the white nile drains predominantly crystalline basement rocks whereas the blue nile and atbara flow off the ethiopian highlands which consist of tertiary volcanic rocks a high resolution profile of 87sr 86sr and ti al ratios from a well dated core in the nile delta shows a close correspondence with known changes in nile flow over the past 7000 yr at times of higher river flow there was markedly decreased input of blue nile derived and total sediment this change was caused by northward movement of the inter tropical convergence zone resulting in increased vegetative cover in the ethiopian highlands due to higher rainfall and a longer wet season this inverse relationship between nile river flow and sediment flux may have had important implications in the development of agricultural technology in ancient egypt the marked minimum in 87sr 86sr at 4200 4500 yr b p is coincident with the end of the old kingdom in egypt and provides independent evidence that demise of the old kingdom might have been associated with an extended period of catastrophic low floods during the quaternary and late neogene there was periodic deposition of organic rich sediments sapropels in the eastern mediterranean that represent important indicators of major environmental change evidence from the ti al ratio suggests that the pattern of erosion and sediment supply from the nile catchment observed in this study also occurred throughout much of the neogene and quaternary the reduced inputs of blue nile sediment during times of sapropel formation contributed to the increased primary productivity by reducing the amount of phosphate removed on particles and to the observed change to n limitation in the eastern mediterranean which are important characteristics of sapropel deposition

reconstructing precipitation changes in northeastern africa during the quaternary by clay mineralogical and geochemical investigations of nile deep sea fan sediments abstract clay mineralogy combined with high resolution element geochemistry of core md90 9064 located in the distal part of the nile deep sea fan levantine basin have been investigated to reconstruct rainfall changes in northeastern africa during the quaternary and to determine possible climatic controls clay minerals of core md90 964 are derived mainly from three sedimentary sources the sahara nile river and egyptian wadis and are characterized by contrasted mineralogical composition variations in illite content and logarithm ratios of si al and k al permit the tracking of eolian input from sahara to the mediterranean sea it is suggested that precipitation changes in the sahara are mainly dominated by glacial interglacial cycles such variations are owing to a shift of climatic conditions in the north atlantic from a nao positive like condition in glacial times to a nao negative like condition in interglacial times fe content in the levantine sediments is mostly derived from fe bearing heavy minerals brought by the nile river therefore variations of fe al ratios can be used to establish precipitation changes in the nile river basin long term variation in precipitation in the nile river basin is governed by precessional and eccentricity signals implying that the african monsoon is the most significant controlling factor for precipitation changes in this region precipitation changes in the northeastern coasts of africa are reconstructed using kaolinite contents provided by the egyptian wadis it is reported that precipitation in coastal northeastern africa is mainly of the mediterranean climate type long term variations in rainfall in this region are also affected by the nao like climatic variability and thus dominated by the glacial interglacial cycles

after the deluge mediterranean stagnation and sapropel formation in an east mediterranean marine core the upper sapropel begins soon after the start of a global event a very heavy precipitation which occurred in the equatorial latitudes during the late glacial early holocene this heavy precipitation in africa channelled by the nile river across 35 of latitude produced a low salinity surface layer in the east mediterranean in this confined basin with high bottom salinity the steep salinity gradient stratified the water column the stagnant bottom waters triggered the sapropel formation cretaceous sapropels in the tropical oceans may result from the same chain of events in warm humid climates with contrasting wet and dry seasonal rhythm

variations in eastern mediterranean hydrology during the last climatic cycle as inferred from neodymium isotopes in foraminifera abstract the nd isotopic compositions end of mixed planktonic foraminifera have been analyzed in two sediment cores collected in the nile deep sea fan in order to reconstruct past end of the eastern mediterranean deep water emdw and to assess the relative contributions of nile discharge and modified atlantic water maw inflow to the eastern mediterranean sea hydrology as well as their potential control on anoxic events over the last climatic cycle the two foraminiferal end records are similar and display an increase in end values during the african humid periods superimposed on this precession forced variability insolation received by the earth at low latitudes the record of variations in foraminiferal end indicates a 2 unit decrease in end during the interglacial marine isotope stages mis 5 and 1 compared to glacial mis6 4 3 and 2 the end results suggest that the long term glacial to interglacial changes in nd isotopic composition of emdw were not entirely induced by variations in nile river discharge and saharan dust inputs decreases in end during mis5 and mis1 interglacials indicate an increase in the contribution of unradiogenic maw to the eastern mediterranean sea related to high sea level stands and greater seawater exchange between the north atlantic and mediterranean basins in addition radiogenic seawater end values observed during african humid periods and sapropel events are associated with an intensification of nile discharge and an increase in residence time of deep water masses in the eastern mediterranean sea which induces an increase in the interaction between deep water masses and radiogenic sediments along the margin of the eastern mediterranean sea results confirm that an intensification of the hydrological exchanges between the western and eastern mediterranean basins during high sea level stand and the subsequent higher proportion of atlantic water in the levantine basin may have preconditioned the eastern mediterranean sea to sapropel depositions during the last climatic cycle

late quaternary palaeoclimatic oscillations in east africa recorded by heavy minerals in the nile delta because the nile carries a load derived from markedly different geological terrains and climatic zones it is expected that minera logical study of deposits in its delta could help define changes in palaeoclimate affecting east africa here we report measurements on heavy minerals in the nile delta which can be used as distinct markers of climatic shifts over africa during the late pleistocene to recent variations of heavy minerals in radiocarbon dated cores collected in this delta1 the nile s major depocentre2 correlate closely with oscillations in african palaeoclimate determined by other independent methods such as studies of lake levels these variations are largely a function of the characteristics of the nile it flows across nearly 35 of latitude from south of the equator to the mediterranean fig la and conditions in its drainage basin which includes central africa the ethiopian plateau and eastern sahara range from a tropical humid to a warm arid climate east african climatic belts migrated considerably during the quaternary3 5 modifying nile discharge and sediment load climatic oscillations have been recorded by changes of sediment yield and grain size along its course6 7 and by well defined depositional cycles8 including sapropels9 in the eastern mediterranean

nile floods recorded in deep mediterranean sediments clastic mud beds rich in continental organic matter are observed recurrently in the nile deep sea turbidite system they formed during flooding periods of the river similar to those that induce sapropel formation and occurred during periods of increased density stratification of the eastern mediterranean the very fine grained flood deposits are intercalated within pelagic sediments sapropels and bouma type turbidites these flood deposits form by the successive reconcentrations of surface hypopycnal plumes by convective sedimentation which in turn generate a fine grained low energy hyperpycnal flow sea level high stands seem also to favor hypopycnal plume formation and increase clastic mud bed formation consequently these muddy clastic beds provide a direct link between deep marine sedimentary records and continental climatic change through flood frequency and magnitude

eastern mediterranean surface water temperatures and d18o composition during deposition of sapropels in the late quaternary 0indices and d 18 o of planktonic foraminifer calcite d 18 ofc across late pleistocene sapropel intervals show that d 18 ofc decreased between 1 and 4 6 and sst increased between 0 7 and 6 7 c maximal d 18 oseawater depletion of eastern mediterranean surface waters at the transition is between 0 5 and 3 0 and in all but one case exceeded the depletion seen in a western mediterranean core the depletion in d 18 oseawater is most pronounced at sapropel bases in agreement with an initial sudden input of monsoon derived freshwater most sapropels coincide with warming trends of sst the density decrease by initial freshwater input and continued warming of the sea surface pooled fresh water in the surface layer and prohibited deep convection down to ageing deep water emplaced during cold and arid glacial conditions an exception to this pattern is glacial sapropel s6 its largest d 18 oseawater depletion 3 is almost matched by the depletion in the western mediterranean sea and it is accompanied by surface water cooling following an initially rapid warming phase a second period of significant isotopic depletion is in isotope stage 6 at the 150 kyr insolation maximum while not expressed as a sapropel due to cold sst it is in accord with a strengthened monsoon in the southern catchment index terms 1055 geochemistry organic geochemistry 1620 global change climate dynamics 3309 4267 oceanography general paleoceanography 9604 information related to geologic time cenozoic keywords mediterranean sea sapropels sea surface temperatures oxygen isotopes quaternary citation emeis k c et al eastern mediterranean surface water temperatures and d 18 o composition during deposition of sapropels

fast or slow melting of the marinoan snowball earth the cap dolostone record article i nfo the end of the neoproterozoic era is punctuated by two global glacial events marked by the presence of glacial deposits overlaid by cap carbonates duration of glacial intervals is now consistently constrained to 3 12 million years but the duration of the post glacial transition is more controversial due to the uncertainty in cap dolostone sedimentation rates indeed the presence of several stratabound magnetic reversals in brazilian cap dolostones recently questioned the short sedimentation duration a few thousand years at most that was initially suggested for these rocks here we present new detailed magnetostratigraphic data of the mirassol d oeste cap dolostones mato grosso brazil and bomb spike calibrated ams 14 c data of microbial mats from the lagoa vermelha rio de janeiro brazil we also compile sedimentary isotopic and microbiological data from post marinoan outcrops and or recent depositional analogues in order to discuss the deposition rate of marinoan cap dolostones and to infer an estimation of the deglaciation duration in the snowball earth aftermath taken together the various data point to a sedimentation duration in the range of a few 10 5 years

a 7500 year strontium isotope record from the northwestern nile delta maryut lagoon egypt abstract during the holocene delta evolution has been collectively mediated by relative sea level changes continental hydrology and human impacts in this paper we present a strontium isotope record from the maryut lagoon northwestern nile delta to quantify the interplay between relative sea level variations and nile flow changes during the past 7500 years 87sr 86sr stratigraphy allows five hydrological stages to be defined 1 the marine transgression of the area is dated to 7 5 ka cal bp with a clear marine 87sr 86sr signature 0 70905 0 7091 2 between 7 and 5 5 ka in the context of the so called african humid period ahp freshwater inputs became progressively predominant in the maryut s hydrology deceleration of sea level rise coupled with high nile discharge induced coastal progradation which led to the progressive closure of the maryut lagoon 3 between 5 5 and 3 8 ka the end of the ahp is translated by a progressive hydrological shift from a nile dominated to a marine dominated lagoon 87sr 86sr shifts from 0 70865 to 0 7088 to 0 70905 0 70915 4 from 2 8 to 1 7 ka 87sr 86sr ratios shift towards lower values 0 7084 although this change is not precisely resolved because of a hiatus in the maryut s sedimentary record the 87sr 86sr transition from sea like to nile dominated values is attributed to irrigation practices since the early ptolemaic period i e since 2 3 ka including the alexandria canal which played a key role in isolating the maryut from the mediterranean sea 5 the final phase of the record covers the period between 1 7 and 0 2 ka 87sr 86sr ratios indicate high freshwater inputs from 0 7080 to 0 7085 except between 1 2 and 1 1 to 0 7 ka when a maryut lowstand and seawater intrusion are attested in modern times the nile s coastal lagoons have been increasingly supplied by freshwater linked to the diversion of waters from the two nile branches into the irrigation system it is suggested that this process began in early antiquity and has engendered a reduction in the number of nile branches from seven in ancient times to just two at present

a simple shear construction from thomson tait 1867 abstract thomson tait treatise on natural philosophy vol 1 1867 described the kinematics of simple shear in terms of a construction this construction is redescribed in a geological context it provides a simple method of determining the orientation and amount of strain in a shear zone and is an excellent aid to teaching the geometry and equations of simple shear

finite strain in simple shear inspected with mohr circles for stretch abstract the orientation and magnitude of the finite strain built up in simple shear and the orientation and rotation of material lines eventually parallel to the long principal axis of the strain ellipse have simple relationships with the shear strain off axis mohr circles for stretch and reciprocal stretch allow convenient proof of such relationships whilst some of these are not often seen in existing structural literature in particular it is noted that the shear strain in ideal simple shear equals the difference of the principal stretches

lithium isotope geochemistry of marine pore waters insights from cold seep fluids lithium concentration and isotope data 7li are reported for pore fluids from 18 cold seep locations together with reference fluids from shallow marine environments a sediment hosted hydrothermal system and two mediterranean brine basins the new reference data and literature data of hydrothermal fluids and pore fluids from the ocean drilling program follow an empirical relationship between li concentration and 7li 7li 6 0 0 3 ln li 51 1 2 reflecting li release from sediment or rocks and or uptake of li during mineral authigenesis cold seep fluids display 7li values between 7 5 and 45 7 mostly in agreement with this general relationship ubiquitous diagenetic signals of clay dehydration in all cold seep fluids indicate that authigenic smectite illite is the major sink for light pore water li in deeply buried continental margin sediments deviations from the general relationship are attributed to the varying provenance and composition of sediments or to transport related fractionation trends pore fluids on passive margins receive disproportionally high amounts of li from intensely weathered and transported terrigenous matter by contrast on convergent margins and in other settings with strong volcanogenic input li concentrations in pore water are lower because of intense li uptake by alteration minerals and most notably adsorption of li onto smectite the latter process is not accompanied by isotope fractionation as revealed from a separate study on shallow sediments a numerical transport reaction model was applied to simulate li isotope fractionation during upwelling of pore fluids it is demonstrated that slow pore water advection order of mm a 1 suffices to convey much of the deep seated diagenetic li signal into shallow sediments if carefully applied li isotope systematics may thus provide a valuable record of fluid mineral interaction that has been inherited several hundreds or thousands of meters below the actual seafloor fluid escape structure

the osmium isotopic composition of the continental crust osmium isotopic compositions and concentrations have been determined for deltaic and continental shelf sediments from three major rivers the amazon changjiang and mississippi and for two loesses from the upper mississippi river valley the loesses have heavy mineral and clay compositions characteristic of mississippi river and delta sediment concentrations range from 15 to 120 pg os g and 187os 186os ratios range from 8 2 to 10 9 sediments which are polluted surface sediment from the changjiang estuary or which have scavenged metals from seawater gulf of mexico slope surface sediment and distal amazon shelf sediment have high osmium concentrations and less radiogenic isotopic compositions purely terrigenous sediments have 15 90 pg os g and 187os 186os 10 0 10 9 north american loess and mississippi delta sediment osmium isotopic compositions are indistinguishable we believe that 187os 186os 10 11 is a good average for currently eroding upper continental crust these sediments have neodymium isotopic compositions close to the global mean for river sediment terrigenous 187os 186os is significantly more radiogenic than seawater 187os 186os 8 6 requiring a nonriverine source of osmium to seawater terrigenous osmium is also significantly more radiogenic than bulk pelagic clay osmium we use the improved estimate of terrigenous 187os 186os to recalculate the flux of extraterrestrial osmium to pacific marine sediment if the residence age of osmium in an upper crustal region is similar to the neodymium model age of a sediment derived from that region a model dependent upper crustal 187re 186os ratio can be calculated for the model ages of the sediments analyzed in this study tdm 1 5 1 7 ga model 187re 186os ratios are 340 360 and can be used to correct for bias resulting from the preferential erosion of young crust the 187os 186os ratio of 2 2 ga crust with 187re 186os 400 is 14 2 we have also used the data from this study to estimate upper crustal osmium and rhenium concentrations of 50 pg g and 390 pg g respectively

source of nile sediments in the floodplain at saqqara inferred from mineralogical geochemical and pollen data and their palaeoclimatic and geoarchaeological significance abstract we present results of mineralogical light heavy and clay minerals geochemical and palynological investigations of floodplain sediments at saqqara our investigations provide new insights into our understanding of the source of the holocene nile sediments local palaeoclimate and palaeoenvironment of the floodplain at saqqara as well as the holocene palaeoclimatic variations at the nile headwaters we also investigate the relationship between nile floods and global climate changes and the impact of changing flood conditions on episodes of societal and central governmental collapse at the end of the egyptian old kingdom the holocene sequences recorded in two shallow drill cores saqa 21 and 22 were investigated and subdivided into six sedimentary units from underlying late pleistocene sand and gravels unit i to overlying modern soil unit viii early holocene sediments were essentially missing in the studied cores probably due to intensive erosion during the well known 8 2 kyr cal bp arid event middle holocene sediments are represented by unit ii which reflect high nile floods of equatorial african origin with less contribution from ethiopian sources the old kingdom sediments unit iii seems to be mainly of white nile sources with frequent contributions from the blue nile late holocene sediments unit iv vii show an increased contribution from blue nile river sources low nile flow episodes were recorded at 5 2 between units ii and iii 4 2 between units iii and iv 3 5 within unit iv and 2 7 kyr cal bp between units v and vi the second event corresponds to the first intermediate period fip and the third probably coincides with the second intermediate period 2nd ip periods of disorder in egypt

late holocene productivity and hydrographic variability in the eastern mediterranean inferred from benthic foraminiferal stable isotopes 1 the paleoproductivity paleo oxygenation and paleohydrographic configuration of the southeastern mediterranean during the late holocene was reconstructed on the basis of the isotopic composition of the epibenthic heterolepa floridana shallow endobenthic uvigerina mediterranea and the deeper endobenthic bulimina inflata from two high resolution cores ga 112 470 m and ga 110 670 m the 13c between h floridana and u mediterranea reveals four intervals of enhanced productivity from 3 3 2 6 2 3 1 9 1 5 1 1 and 0 8 0 4 kyr bp coinciding with increased nutrient supply by the nile river the entire basin was well aerated with oxygen consumption varying between 1 0 and 3 5 ml o2 l oxygen consumption increases toward present day probably because of higher accumulation of total organic carbon at 1 7 kyr bp coinciding with the appearance of the mesotropic benthic species the hydrographic configuration of the basin has changed during the course of the last 3 75 kyr the levantine intermediate water liw deepens below 470 m between 3 3 and 2 0 kyr and especially between 2 5 and 2 0 kyr during the last 1 5 kyr the liw becomes shallower than 470 m similar to the present day the change in the hydrographic configuration reflects changes in evaporation precipitation ratio and in temperature

stable waterbelt climates controlled by tropical ocean heat transport a nonlinear coupled climate mechanism of relevance to snowball earth ongoing controversy about neoproterozoic snowball earth events motivates a theoretical study of stability and hysteresis properties of very cold climates a coupled atmosphere ocean sea ice general circulation model gcm has four stable equilibria ranging from 0 to 100 ice cover including a waterbelt state with tropical sea ice all four states are found at present day insolation and greenhouse gas levels and with two idealized ocean basin configurations the waterbelt is stabilized against albedo feedback by intense but narrow wind driven ocean overturning cells that deliver roughly 100 w m 2 heating to the ice edges this requires three way feedback between winds ocean circulation and ice extent in which circulation is shifted equatorward following the baroclinicity at the ice margins the thermocline is much shallower and outcrops in the tropics sea ice is snow covered everywhere and has a minuscule seasonal cycle the waterbelt state spans a 46 w m 2 range in solar constant has a significant hysteresis and permits near freezing equatorial surface temperatures additional context is provided by a slab ocean gcm and a diffusive energy balance model both with prescribed ocean heat transport oht unlike the fully coupled model these support no more than one stable ice margin the position of which is slaved to regions of rapid poleward decrease in oht convergence wide ranges of different climates including the stable waterbelt are found by varying the magnitude and spatial structure of oht in both models some thermodynamic arguments for the sensitivity of climate and ice extent to oht are presented

a mohr circle construction for the opening of a pre existing fracture abstract the opening of a fracture is dependent on the fluid pressure and the local stress regime around the fracture for a fracture to open the fluid pressure must exceed the normal stress acting on the fracture the mohr circle provides a useful tool allowing the visualization of these relationships this construction determines the range of fracture orientations that are able to open as well as determining the opening direction of these fractures this is then used to produce ratios of the magma pressure and the principal stresses for some dykes from the lizard ophiolite u k

shifting sediment sources in the world s longest river a strontium isotope record for the holocene nile we have reconstructed long term shifts in catchment sediment sources by analysing for the first time the strontium sr and neodymium nd isotope composition of dated floodplain deposits in the desert nile the sediment load of the nile has been dominated by material from the ethiopian highlands for much of the holocene but tributary wadis and aeolian sediments in sudan and egypt have also made major contributions to valley floor sedimentation the importance of these sources has shifted dramatically in response to global climate changes during the african humid period before c 4 5 ka when stronger boreal summer insolation produced much higher rainfall across north africa the nile floodplain in northern sudan shows a tributary wadi input of 40 50 thousands of tributary wadis were active at this time along the full length of the saharan nile in egypt and sudan as the climate became drier after 4 5 ka the valley floor shows an abrupt fall in wadi inputs and a stronger blue nile atbara contribution in the arid new kingdom and later periods in palaeochannel fills on the margins of the valley floor aeolian sediments replace wadi inputs as the most important secondary contributor to floodplain sedimentation our sediment source data do not show a measurable contribution from the white nile to the floodplain deposits of northern sudan over the last 8500 years this can be explained by the distinctive hydrology and sediment delivery dynamics of the upper nile basin high strontium isotope ratios observed in delta and offshore records that were previously ascribed to a stronger white nile input during the african humid period may have to be at least partly reassessed our floodplain sr records also have major implications for bioarchaeologists who carry out sr isotope based investigations of ancient human remains in the nile valley because the isotopic signature of nile floodplain deposits has shifted significantly over time

short term environmental changes in the cretaceous tethyan ocean micropalaeontological evidence from the early albian oceanic anoxic event 1b to better understand the linkage between climate and ocean circulation under greenhouse conditions we have studied calcareous nannofossils palynomorphs and benthic foraminifera from the early albian oceanic anoxic event 1b black shale oae 1b in the vocontian basin se france we propose that monsoonal activity resulting from precessional forcing and modulated by eccentricity driven temperature changes represents the driving factor of oae 1b formation in low latitudes with the onset of oae 1b increasingly warm and humid conditions stronger winds and enhanced terrestrial input led to higher surface water productivity therefore increased productivity is an important factor for oae 1b formation in the vocontian basin however monsoonally forced productivity changes are a regional climate signal only the supraregional occurrence of the oae 1b is probably due to a reduction of deep water formation in the low latitudes under extremely warm and humid conditions leading to enhanced preservation of organic matter

nile sediment dispersal altered by the aswan high dam the kaolinite trace abstract proportions of kaolinite have increased substantially in lower river nile clay mineral assemblages since emplacement in 1964 of the high dam at aswan egypt monitoring this recent increase can be used to help gauge sediment load changes induced by the high dam in the lower river nile between the dam and nile delta and eventually offshore in the mediterranean s levantine basin high kaolinite values to 50 are recorded north of the new nile delta presently forming in lake nasser and are even higher below the high dam to 70 kaolinite is introduced to lake nasser from adjacent desert terrains largely from wind transported material and wave erosion of lake margins as the major clay component of the suspended sediment load in lake waters this mineral is released through the dam additional kaolinite enters the nile system just below the high dam from late pleistocene and older sections scoured by swift turbulent nile waters flowing northward of the dam during the past 31 years sediment containing higher concentrations of kaolinite 30 has migrated northward at a rate of 10 km year and presently extends to qena 350 km north of the dam this stretch defines the river nile sector most altered since closure of the high dam it is predicted that enhanced proportions of kaolinite will be recorded at cairo and the southern nile delta within 50 years and at the mediterranean coast by the end of the next century

sea glacier flow and dust transport on snowball earth 1 accumulation of dust on the surface of ice in the tropics has been proposed as a possible mechanism for the termination of neoproterozoic snowball earth episodes this mudball hypothesis relies on the assumption that sea glacier flow transports dust to the tropical ablation zone leading to the accumulation of a dust moraine there and consequent lowering of tropical albedo here we use a 1 d sea glacier flow model to simulate the ice thickness and flow on a globally glaciated earth and study the dust transport associated with the ice flow dust is entirely confined to a meteoric ice layer which does not exchange water with the ocean dust falling onto the surface of this layer is carried downward with the ice flow in extratropical regions carried equatorward by the global ice flow and re emerges on the top of the ice in the tropical ablation zone the ice flow acts as a dust conveyor belt which converges dust to tropics resulting in an amplification of effective tropical dust flux by a factor of 2 to 20 over the global average this lends support to the mudball hypothesis

accretion rates of meteorites and cosmic dust in the early ordovician abundant fossil meteorites in marine condensed lower ordovician limestones from kinnekulle sweden indicate that accretion rates of meteorites were one to two orders of magnitude higher during an interval of the early ordovician than at present osmium isotope and iridium analyses of whole rock limestone indicate a coeval enhancement of one order of magnitude in the influx rate of cosmic dust enhanced accretion of cosmic matter may be related to the disruption of the l chondrite parent body around 500 million years ago

snowball earth ice thickness on the tropical ocean 1 on the tropical oceans of a neo proterozoic snowball earth snow free ice would have existed in regions of net sublimation photosynthesis could have continued beneath this bare ice if it was sufficiently thin and sufficiently clear the steady state ice thickness is determined by the necessity to balance the upward conduction of heat with three subsurface heating rates the heat flux from the ocean to the ice base the latent heat of freezing to the ice base and the solar energy absorbed within the ice a preliminary study using a broadband model for solar radiation and assuming a large freezing rate had indicated that tropical ice might be only a few meters thick here we show that the vertical throughput of ice by surface sublimation and basal freezing would be too slow to keep the ice thin and that the broadband model had exaggerated the absorption depth of sunlight we use a spectral model for solar absorption computing radiative transfer at 60 wavelengths considering absorption by the ice and scattering by bubbles with the spectral model the computed ice thickness is much greater for a solar flux of 320 w m 2 at the equatorial surface and expected albedo of 0 5 for bare sea ice we find that surface temperatures below 12 c generate ice layers too thick for photosynthesis 100 m if the albedo were as low as 0 4 thick ice would occur only for surface temperatures below 25 c but such low temperatures would be difficult to maintain with such low albedo for surface temperatures warmer than these limits the ice becomes thin 1 m and is unlikely to represent a coherent ice layer however glacial deformation of thick floating ice from nearby oceanic regions may preclude the existence of thin or ice free patches

microfacies description linked to the magnetic and non magnetic proxy as a promising environmental tool case study from alluvial deposits of the nile river abstract alluvial deposits within the sabaloka gorge and the sixth cataract the nile river sudan represent a set of deposits with a high lithological variability this is due to the geomorphology and short time and intensive flood events resulting in aggradation and erosion of the alluvial zone human maintenance of the alluvial zone also plays a role therefore these sediments seem to be ideal for a methodological case study to show how the lithological facies differ depending on the sedimentary dynamics of the river non magnetic proxies together with toc values depend on magnetic properties characterized by magnetic susceptibility and its frequency dependence

continental weathering following a cryogenian glaciation evidence from calcium and magnesium isotopes a marked ocean acidification event and elevated atmospheric carbon dioxide concentrations following the extreme environmental conditions of the younger cryogenian glaciation have been inferred from boron isotope measurements calcium and magnesium isotope analyses offer additional insights into the processes occurring during this time data from neoproterozoic sections in namibia indicate that following the end of glaciation the continental weathering flux transitioned from being of mixed carbonate and silicate character to a silicate dominated one combined with the effects of primary dolomite formation in the cap dolostones this caused the ocean to depart from a state of acidification and return to higher ph after climatic amelioration differences in the magnitude of stratigraphic isotopic changes across the continental margin of the southern congo craton shelf point to local influences modifying and amplifying the global signal which need to be considered in order to avoid overestimation of the worldwide chemical weathering flux

evaluation of osmium isotopes and iridium as paleoflux tracers in pelagic carbonates new osmium os isotope and platinum group element pge concentration data are used in conjunction with published 3 he and th isotope data to determine the relative proportions of lithogenic extraterrestrial and hydrogenous iridium ir in a pacific pelagic carbonate sequence from the ocean drilling program odp site 806 on the ontong java plateau ojp these calculations demonstrate that lithogenic and extraterrestrial contributions to sedimentary ir budget are minor while hydrogenous ir accounts for roughly 85 of the total ir application of analogous partitioning calculations to previously reported data from a north pacific red clay sequence ll44gpc3 yields very similar results total ir burial fluxes at site 806 and ll44 gpc3 are also similar 45 and 30 pg cm 2 kyr 1 respectively average ir 3 he and ir xs 230 thinitial ratios calculated from the entire site 806 data set are similar to those reported earlier for pacific sites in general down core profiles of ir 3 he and xs 230 thinitial are not well correlated with one another however all three data sets show similar variance and yield sediment mass accumulation rate estimates that agree within a factor of two while these results indicate that ir concentration has potential as a point paleoflux tracer in pelagic carbonates ir based paleoflux estimates are likely subject to uncertainties that are similar to those associated with co based paleoflux estimates consequently local calibration of ir flux in space and time will be required to fully assess the potential of ir as a point paleoflux tracer measured 187 os 188 os of the ojp sediments are systematically lower than the inferred 187 os 188 os of contemporaneous seawater and a clear glacial interglacial 187 os 188 os variation is lacking mixing calculations suggest os contributions from lithogenic sources are insufficient to explain the observed 187 os 188 os variations the difference between the 187 os 188 os of bulk sediment and that of seawater is interpreted in terms of subtle contributions of unradiogenic os carried by particulate extraterrestrial material down core variations of 187 os 188 os with pt ir and os ir also point to contributions from extraterrestrial particles mixing calculations for each set of several triplicate analyses suggest that the unradiogenic os end member cannot be characterized by primary extraterrestrial particles of chondritic composition it is noteworthy that in efforts aimed at determining the effect of extraterrestrial contributions 187 os 188 os of pelagic carbonates has greater potential compared to abundances of pge an attempt has been made for the first time to estimate sediment mass accumulation rates based on amount of extraterrestrial os in the ojp samples and previously reported extraterrestrial os flux throughout most of the ojp record os isotope based paleoflux estimates are within a factor of two of those derived using other constant flux tracers meaningful flux estimates cannot be made during glacial maxima because the ojp sediments do not record the low 187 os 188 os reported previously we speculate that this discrepancy may be related to focusing of extraterrestrial particles at the ojp as has been suggested to explain down core 3 he variations

no evidence of extraterrestrial noble metal and helium anomalies at marinoan glacial termination abstract high concentrations of extraterrestrial iridium have been reported in terminal sturtian and marinoan glacial marine sediments and are used to argue for long likely 3 12 myr durations of these cryogenian glaciations reanalysis of the marinoan sedimentary rocks used in the original study supplemented by sedimentary rocks from additional terminal marinoan sections however does not confirm the initial report new platinum group element concentrations and 187os 188os and 3he 4he signatures are consistent with crustal origin and minimal extraterrestrial contributions the discrepancy is likely caused by different sample masses used in the two studies with this study being based on much larger samples that better capture the stochastic distribution of extraterrestrial particles in marine sediments strong enrichment of redox sensitive elements particularly rhenium up section in the basal postglacial cap carbonates may indicate a return to more fully oxygenated seawater in the aftermath of the marinoan snowball earth sections dominated by hydrogenous osmium indicate increasing submarine hydrothermal sources and or continental inputs that are increasingly dominated by young mantle derived rocks after deglaciation sedimentation rate estimates for the basal cap carbonates yield surprisingly slow rates of a few centimeters per thousand years this study highlights the importance of using sedimentary rock samples that represent sufficiently large area time products to properly sample extraterrestrial particles representatively and demonstrates the value of using multiple tracers of extraterrestrial matter

provenance of lithogenic surface sediments and pathways of riverine suspended matter in the eastern mediterranean sea evidence from 143nd 144nd and 87sr 86sr ratios in order to characterize the provenance of lithogenic surface sediments from the eastern mediterranean sea ems residual leached fraction of 34 surface samples have been analysed for their 143 nd 144 nd and 87 sr 86 sr isotope ratios the sample locations bracket all important entrances of riverine suspended matter into the ems as well as all sub basins of the ems the combined analyses of these two isotope ratios provide a precise characterization of the lithogenic fraction of surface sediments and record their dilution towards the central sub basins we reconstruct provenance and possible pathways of riverine dispersal and current redistribution assuming more or less homogenous isotopic signatures and flux rates of the eolian fraction over the ems lithogenic sediments entering the ionian sea from the calabrian arc and the adriatic sea are characterized by high 87 sr 86 sr isotope ratios and low end 0 values average 87 sr 86 sr 0 718005 and end 0 11 06 n 5 aegean sea terrigenous sediments show an average ratio of 87 sr 86 sr 0 713089 n 5 and values of end 0 7 89 n 5 the aegean isotopic signature is traceable up to the southwest south and southeast of crete the sediment loads entering the ems via the aegean sea are low and spread out mainly through the strait of casos east of crete surface sediments from the eastern levantine basin are marked by the highest end 0 values 3 3 n 6 and lowest 87 sr 86 sr isotope ratios average 0 709541 n 6 reflecting the predominant input of the nile sediment the influence of the nile sediment is traceable up to the ne trending eastern flank of the mediterranean ridge the characterization of the modern riverine dispersal and eolian flux based on isotope data may serve as a tool to reconstruct climate coupled variations of lithogenic sediment input into the ems d 2002 elsevier science b v all rights reserved

timing and stepwise transitions of the african humid period from geochemical proxies in the nile deep sea fan sediments large fluvial systems such as the nile river allow a basin scale integrated view of climatological and environmental changes in this study we reconstructed the nile discharge history for the last 20 ka using molecular ratios of glycerol dialkyl glycerol tetraethers gdgts and neodymium nd radiogenic isotopes by characterizing both the organic and inorganic fractions we assessed the relevance of the gdgt based proxies in deltaic environments as tracers of terrigenous origin a large increase in nile discharge is documented from 14 8 to 8 4 ka bp reflecting enhanced physical erosion and transport processes from the ethiopian traps we confirmed the primary control of insolation on precipitation on north east africa through the last 20 ka the centennial time resolution reached on the sedimentary sequence revealed a step wise onset and termination of the african humid period ahp starting at 14 8 ka and ending at 8 4 ka bp respectively our centennial millennial records allowed furthermore pinpointing the abrupt periods of arid conditions corresponding to the younger dryas these data illustrate the linkage between low and high latitude hydrological variability

the use of mohr circles to describe non coaxial progressive deformation abstract mohr circles are useful in strain analysis but are also potentially powerful tools to translate geological fabric data into tensors describing the deformation and to reconstruct flow parameters this paper shows how mohr circles can be used to visualize the effects of variable flow parameters such as stretching rate volume change rate and vorticity number on parameters of cumulative deformation as described by the position gradient tensor a mean vorticity number is introduced as a deformation parameter besides finite cumulative strain and volume change

late quaternary nile flows as recorded in the levantine basin the palynological evidence abstract this study aims to trace changes in the river nile flows over the late quaternary and is based on palynomorphs which were embedded in the sea floor of the levantine basin the palynomorphs were extracted from two marine sediment cores which cover the last 86 ka and are located at the two ends of the levantine basin md 9509 at the southern part of the levantine basin and md 9501 at its northern part core md 9509 was taken from the nile cone and is characterized by high sedimentation rates and a good state of palynomorph preservation the assemblages included palynomorphs which were transported via the nile headwaters and therefore enabled the reconstruction of the river nile flows the results demonstrate that the last glacial period 75 16 ka was characterized by a decrease in nile water discharge and an increase in sediment influx while opposite trends were observed prior to the last glacial period as well as during the deglaciation and the holocene based on the study of the spores it is suggested that during the last glacial the main contributors of freshwater and sediment load to the eastern mediterranean sea were the blue nile and the atbara and only during interglacials was there a more significant contribution of the white nile within the northern core md 9501 pollen was preserved only during the formation of sapropels s3 and s1 the comparison of the sapropelic palynological spectra in both core sites clearly indicates that during sapropel deposition climate conditions were more humid in the northern levant reflecting the north south regional mediterranean climatic moisture gradient sapropel formation was a result of the intensification of the monsoonal climate system which was most probably related to the maximum insolation values at 65 n while currently the atlantic is the main influencing climate system in the region one of the most interesting observations in this study is that during heinrich events h2 h6 which originated in the north atlantic and were identified in md 9509 based on minimum arboreal pollen percentages pollen originating from tropical regions was not embedded in the levantine basin these results lend support to the view that episodes of dryness in tropical sub tropical eastern africa were associated not only with low latitude climate controls but also with high latitude glacial stress

mechanisms forcing abrupt fluctuations of the indian ocean summer monsoon during the last deglaciation abstract a piston core from the somali upwelling area has been studied at high resolution for its dinoflagellate cyst content variations in cyst association are inferred to reflect changes in indian ocean summer monsoon intensity several abrupt fluctuations in monsoon intensity are detected for the interval between 20 and 10 ka bp comparison of these fluctuations with changes in contrast between 30 n and 30 s july insolation and the 18 o grip ice core values suggests that different mechanisms influenced monsoon intensity at different time intervals a general trend in monsoon intensity follows variations in insolation contrast lagging minimum contrast by 7 5 ka and maximum contrast by 4 ka this phase lag difference can be explained by assuming the existence of an ice snow cover over central asia tibet during glacial times between 18 7 and 12 5 ka bp fluctuations in sw monsoon intensity may be forced by variations in the thermohaline ocean circulation a rapid transition towards strong sw monsoons at 12 5 ka bp is possibly the result of variations in atmospheric circulation and melting of the snow ice fields in central asia tibet variations in glacial interglacial boundary conditions related to temperature change at northern latitudes are likely to have influenced sw monsoon intensity between 12 5 and 10 ka bp whereas after 10 ka bp variations in tropical land surface boundary conditions may be the dominant forcing factor 0 1997 elsevier science ltd all rights reserved

riverine supply to the eastern mediterranean during last interglacial sapropel s5 formation a basin wide perspective abstract organic rich sapropel sediments were repeatedly deposited in the eastern mediterranean sea ems in response to insolation driven freshwater forcing however the exact freshwater sources and causal associated paleoclimate related processes remain unresolved sapropel s5 formed during the insolation maximum of the last interglacial is one of the most intensely developed sapropels of the late quaternary here detrital sediments of sapropel s5 obtained from 8 cores together with 13 ems surface samples are analyzed for major elements rare earth elements ree and sr and nd isotopes this permits a basin wide investigation of the source and distribution of river borne material to the ems for sapropel s5 and its comparison to the present day and the holocene sapropel s1 period during the sapropel s5 there was minor saharan dust input the marked east west geochemical gradient in s5 detrital sediments across the ems is therefore attributed to mixing between fluvial contributions being nile discharge aegean adriatic riverine inputs and libyan tunisian paleodrainage fluxes the offshore distribution of nile sediments during sapropel s5 was comparable to those during s1 and the present the nile sediment contribution appears to be only dominant for the levantine basin decreasing to negligible values south of crete this rather limited sediment delivery despite inferred increased runoff during s5 is related to denser vegetation cover on the ethiopian highlands by contrast small rivers around the aegean and adriatic sea brought large amounts of detrital material into the ems this is particularly noticeable around crete and the northern ionian sea the enhanced riverine input is probably due to strong precipitation seasonality over the northern ems borderlands particularly for the early phase of the last interglacial maximum furthermore there are substantial fluvial contributions from the libyan tunisian margin to the ionian sea sediments in particular during the last part of sapropel s5 the inferred river borne material was transported via paleodrainage systems reactivated by intensified monsoon precipitation and derived from central saharan mountains compared to sapropel s1 these s5 related paleodrainage fluxes were not only stronger but also had a more predominant provenance from eastern rather than western libya in addition a similar averaged endmember of saharan dust sources is revealed by ree signatures

nile delta vegetation response to holocene climate variability a 7000 yr palynologic record from burullus lagoon nile delta egypt is assessed to investigate changes in terrestrial vegetation in response to nile flow previous studies in this region have shown that sea level rise in the early to mid holocene and markedly increased human land use during the past several centuries altered vegetation in and around the lagoon the pollen record from this study documents changes in delta vegetation that likely reflect variations in nile flow we suggest that cyperaceae pollen is a sensitive marker of precipitation over the nile headwaters and the resultant nile flow decreases in cyperaceae pollen interpreted as a marker for diminished nile flow as well as the increase in relative abundance of microscopic charcoal occurred at ca 6000 5500 ca 5000 ca 4200 and ca 3000 cal yr b p calibrated years before present these correspond to extreme regional and global aridity events associated with a more southerly mean position of the intertropical convergence zone these changes also recorded by other proxy studies indicate that several marked regional drought events affected the nile delta region and impacted ancient egyptian and middle eastern civilizations