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

an 8000 year history of landscape climate and copper exploitation in the middle east the wadi faynan and the wadi dana national reserve in southern jordan abstract investigations of geomorphology geoarchaeology pollen palynofacies and charcoal indicate the comparative scales and significance of palaeoenvironmental changes throughout the holocene at the junction between the hyper arid hot wadi arabah desert and the front of the mediterranean belt mountains of edom in southern jordan through a series of climatic changes and episodes of intense mining and smelting of copper ores early holocene alluviation followed the impact of neolithic grazers but climate drove fluvial geomorphic change in the late holocene with a major arid episode corresponding chronologically with the little ice age causing widespread alluviation the harvesting of wood for charcoal may have been sufficiently intense and widespread to affect the capacity of intensively harvested tree species to respond to a period of greater precipitation deduced for the roman byzantine period a property that affects both taphonomic and biogeographical bases for the interpretation of palynological evidence from arid lands with substantial industrial histories studies of palynofacies have provided a record of human and climatic causes of soil erosion and the changing intensity of the use of fire over time the patterns of vegetational climatic change and geomorphic changes are set out for this area for the last 8000 years

milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

eolian sediment responses to late quaternary climate changes temporal and spatial patterns in the sahara abstract this paper presents a compilation of eolian based records of late quaternary climate changes in the sahara although the data are relatively sparse when viewed as a whole they reveal a general pattern of widespread eolian sediment mobilization prior to 11 000 cal years bp eolian sediment stabilization from 11 000 to 5000 cal years bp and a return to widespread eolian sediment mobilization after 5000 cal years bp furthermore an eolian based record from southern tunisia reveals the existence of millennial scale changes in eolian sediment behavior these millennial scale variations provide examples of eolian sediment responses to climate changes at a scale intermediate between seasonal and orbital milankovitch changes and they are also coincident with abrupt atmospheric and oceanic changes the general synchroneity of the eolian stratigraphic records and their coincidence with various oceanic and atmospheric changes suggest that global forcing mechanisms have influenced late quaternary eolian sediment behavior in the sahara

two high levels of continental waters in the southern tunisian chotts at about 90 and 150 ka uranium and thorium content and activity ratios were measured on 20 samples 19 molluscs and 1 calcareous concretion from the great chotts in southern tunisia results were studied by the isochron method and by age frequency histograms they suggest that two major flood episodes took place about 150 and 90 ka uranium activity ratios indicate a ground water supply of continental origin in agreement with biological indicators which show large variations in salinity from fresh to marine like conditions the existence of a lacustrine phase radiocarbon dated to 17 40 ka as previously suggested for the northern sahara is highly questionable

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

holocene climatic evolution at 22 23 n from two palaeolakes in the taoudenni area northern mali abstract in the endorheic hydrologically isolated taoudenni depression nowadays receiving 5 mm mean annual rainfall continuous sections in fossiliferous holocene deposits from two palaeolakes with different geological evolutions have been compared the following climatic sequence is determined 9000 8300 yr b p the beginning of a humid phase 8300 6700 yr b p climatic optimum from 6700 yr b p onwards a change in regime 4500 4000 yr b p end of humid phase aridification begins the data imply a 600 km northern shift of the monsoonal belt which confirms models described in the literature

processes affecting groundwater quality in arid zones the case of the bou areg coastal aquifer north morocco abstract the coastal aquifer of bou areg morocco has been studied to identify the main processes causing groundwater salinization using a multi tracer general chemistry and isotopes 2h 18o 13c 15nno3 18ono3 geochemical approach groundwater is characterized by the widespread occurrence of brackish waters tds no 3 reaching a maximum of 208 mg l 1 and cl lagoon samples represent a mixture of fresh water and sea water showing a na cl ratio in agreement with that of sea water and an excess of ca the high ca values represent the main peculiarity of the groundwater lagoon water system two types of groundwater could be identified i freshwater separated from the whole system and located at the limit of the irrigated area characterized by low tds depleted isotopic composition and relatively high quality and ii water mainly recharged by mountain runoff interacting with local recharge and acquiring salinity from different sources thus creating a complex system of dilute waters hydrochemical results confirm that the high salinity of the aquifer is caused by the coexistence of dissolution of evaporate rocks and carbonates from miocene strata water rock interaction and human impacts due to agricultural return flows the latter represents the main contribution to groundwater salinization especially in the central part of the aquifer as well as one of the main causes of the general increase in no 3 concentrations only locally in the southern part of the aquifer close to the city of kariat arkmane the high salinization observed may be attributed to the presence of lagoon water intrusion the isotopic composition of dissolved no 3 indicates manure and septic effluents especially in urban areas and in the central part of the plain and synthetic fertilizers in the agricultural zone as the main drivers for human induced pollution the study shows that agricultural return flow has significantly modified the chemistry of the system and it is a prime example of the human induced changes over coastal environments saline water intrusion from the lagoon in the shallow aquifer is negligible while discharge of polluted groundwater into the lagoon has been found to partially alter its quality

abrupt post glacial climate events in west asia and north africa monsoon domains regions beyond the present or past penetration of the indian and african monsoons have experienced several large and abrupt climatic fluctuations over the past 13 14c kyr pollen and lake records from west asia western tibet and rajasthan east africa ethiopia and west africa western sahara sahel and subequatorial africa were selected on the basis of chronological control sensitivity of both site and environmental indicators to climate change the continuity of the record and interdisciplinary control of the palaeoclimatic interpretation conditions wetter than those of today prevailed during the early mid holocene period but major dry spells are recorded at all sites during the intervals 11 0 9 5 kyr bp 8 7 kyr bp and 3 4 kyr bp several records also suggest dry events of minor amplitude around 6 kyr bp potential boundary forcings of insolation and sea surface and tropical land surface conditions are discussed the solar radiation accounts for the general envelop of the post glacial monsoon fluctuations but explains neither the timing nor the amplitude of the short term changes in spite of apparent covariation between fluctuations in sea surface conditions in the north atlantic and the monsoon record no direct mechanism could be found relating the intensity of the oceanic thermohaline conveyor belt to the monsoon strength changes in tropical land surface conditions soil moisture negative feedback and changes in ch4 production from wetlands provide a more satisfactory hypothesis for explaining abrupt reversal events

a late pleistocene holocene lacustrine record from lake manas zunggar northern xinjiang western china information on the late quaternary palaeoclimate in the zunggar desert northern xinjiang is deduced from the study of three 5 m long cores taken from lake manas analyses including the mineralogical composition of bulk sediments stable isotope contents of carbonates organic matter pollen and diatoms were performed to help reconstruct the environmental evolution of the area the chronology is provided by 9 ams 14c dates done on carbonates or organic matter the record suggests a late pleistocene humid episode radiocarbon dated at 37 000 32 000 yr b p this episode is followed by a period of extreme aridity attributed to the last glacial maximum the early mid holocene record indicates conditions generally wetter than today as previously established for western china however our results show that the holocene period is rather complex after a minor wet warm pulse estimated to be around 12 000 yr b p the most important environmental change is recorded at 10 000 yr b p it led to the establishment of a steppic vegetation cover in the catchment and of a permanent lake which lasted 4000 years fluvial sedimentation took place between about 6000 and 4500 yr b p and it coincided with a decrease in moisture availability for vegetation growth a second lacustrine episode is recorded from about 4500 to 2500 yr b p although the pollen record and a sudden influx in detrital organic matter suggest a short term dry event around 3800 3500 yr b p the last 2500 years show climate unstability and the step wise establishment of hypersaline conditions in lake manas the major post glacial environmental changes appear to be roughly in phase with those observed in tibet

ages of quaternary pluvial episodes determined by uranium series and radiocarbon dating of lacustrine deposits of eastern sahara abstract as documented by radiocarbon dating and geoarchaeological investigations the now hyperarid northwestern sudan and southwestern egypt experienced a period of greater effective moisture during early and middle holocene time about 10 5 ka we have used the uranium series technique to date lacustrine carbonates from bir tarfawi bir sahara east wadi hussein oyo depression and the great selima sand sheet localities results indicate five paleolakeforming episodes occurred at about 320 250 240 190 155 120 90 65 and 10 5 ka four of these five pluvial episodes may be correlated with major interglacial stages 9 7 5e and 1 the 90 65 ka episode may be correlated with substage 5c or 5a our results support the contention that past pluvial episodes in north africa corresponded to the interglacial periods farther north ages of lacustrine carbonates from existing oases and from the sand sheet fail to indicate pluvial conditions between about 60 and 30 ka age results and field relationships suggest that the oldest lake and ground water deposited carbonates were much more extensive than those of the younger period and that carbonate of the latest wet periods were geographically localized within depressions and buried channels

uranium series dated authigenic carbonates and acheulian sites in southern egypt field investigations in southern egypt have yielded acheulian artifacts in situ in authigenic carbonate deposits caco 3 cemented alluvium along the edges of nowaggraded paleovalleys wadi arid and wadi safsaf uranium series dating of 25 carbonate samples from various localities as far apart as 70 kilometers indicates that widespread carbonate deposition occurred about 45 141 and 212 ka thousand years ago most of the carbonate appears to have been precipitated from groundwater which suggests that these three episodes of deposition may be related to late pleistocene humid climates that facilitated human settlement in this now hyperarid region carbonate cements from sediments containing acheulian artifacts provide a minimum age of 212 ka for early occupation of the paleovalleys

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

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

palhydaf palaeohydrology in africa program objectives methods major results abstract the palhydaf program aims to reconstruct the late quaternary 130 ka b p to present environmental and hydrological changes of northwest africa and to interpret them in terms of palaeoclimate for testing coupled atmospheric ocean circulation models lacustrine sequences were obtained from closed basins which lie along two meridional transects southern tunisia southern niger and algeria mali particular attention is given to groundwater storage and periods of recharge of the aquifers the chronological framework is based on 14c dates conventional and ams methods and or the th u disequilibrium method in favourable cases e g mali correlations can be made between the chronology of surface palaeohydrology and that of aquifer recharge various environmental markers mineralogy elemental chemistry stable isotopes biological remains are used for palaeoenvironmental purposes quantitative estimates of palaeoclimatic variables e g air humidity may be attempted through the combination of geochemical and palaeobiological data the major results already obtained are summarized for the following individual sectors 1 southern tunisia 1 northern algeria 2 southern algeria 3 northern niger 3 mali 4 southern niger at the present stage of investigation the following new inferences can be drown one or several humid episode s occurred in the northern sahara between 150 and 75 ka b p several factors suggest that these humid conditions also affected lower latitudes although their southern extent cannot be given precisely at present the previously postulated existence of large lakes at 20 35 ka b p is not confirmed this time interval seems to coincide with raised water tables but not to a major humid phase in all cases the 14c chronologies obtained for the late pleistocene have to be checked by comparison with other dating methods e g th u disequilibrium after the arid period of the last glacial maximum the return of humid conditions occurred in two major steps at 12 and 9 5 9 ka b p for both the southern and the northern sahara

the rate of iron oxide enrichment in arid zone alluvial fan soils tunisian southern atlas measured by mineral magnetic techniques abstract rates of iron oxide enrichment of soils on a segmented alluvial fan in southern tunisia are examined mineral magnetic and chemical characteristics of soils developed on two dated relict segments and on contemporary alluvium suggest that the rate of fe oxide enrichment was more rapid in the holocene 2 6 10 8 g g 1 yr 1 over the last 5000 years than in the pleistocene 1 91 10 9 g g 1 yr 1 over the previous 45 000 years thus fe oxide concentration may be used to determine an ordinal chronology of some geomorphological surfaces in drylands but rates of enrichment cannot be assumed to be uniform over time

freshwater to marine like environments from holocene lakes in northern sahara continuous swamp and lacustrine sequences from the northern edge of the great western erg are dated at 9 300 3 000 yr bp diatoms ostracods molluscs and foraminifera show great changes in salinity ranging from freshwater to marine like environments the stable isotope composition of carbonates indicates that the evaporation of groundwater supplies is responsible for these fluctuations in salt contents until now evidence for the occurrence of a wet climatic phase of early and middle holocene age in the north north west sahara was based on a restricted number of 14c dates from scattered lacustrine deposits and paleosols1 8 the present study complements this knowledge and highlights the importance of local hydrological factors in interpreting palaeolimnological changes

lake level chronology on the southern bolivian altiplano 18 23 s during late glacial time and the early holocene stratigraphic analyses of outcrops shorelines and diatoms from the southern bolivian altiplano uyuni coipasa basin reveal two major lacustrine phases during the late glacial period and the early holocene based on a chronology established by radiocarbon and u th control a comparison of14c and230th 234u ages shows that during times of high lake level radiocarbon ages are valid however during low water periods 14c ages must be corrected for a reservoir effect the lacustrine tauca phase started a little before 16 00014c yr b p and the lake level reached its maximum between 13 000 and 12 00014c yr b p a dry event ticana occurred after ca 12 000 and before 950014c yr b p a moderate lacustrine oscillation coipasa event occurred between ca 9500 and 850014c yr b p using a reservoir corrected conventional14c chronology comparisons between the lake level chronology in the uyuni coipasa basin and data from other southern tropical areas of south america suggest that the lacustrine evolution may reflect large scale climatic changes

holocene environmental changes in lake bangong basin western tibet part 1 chronology and stable isotopes of carbonates of a holocene lacustrine core abstract a 12 4 m core collected from the eastern part of lake bangong is analyzed for mineralogy radiometric chronology and stable isotope contents of authigenic inorganic carbonate isotopic compositions of the modern lake waters and of its major tributaries are first presented radiocarbon activity of these waters show that equilibrium with the atmospheric co2 is not reached because of admixture of dead carbon in solution in the system a model is thus developed to correct the radiocarbon ages of fossil material of aquatic origin for this ageing the core provides a continuous holocene record changes in mineralogy of bulk sediments and in 13c and 18o contents of authigenic carbonates reveal extremely large changes in environmental conditions induced by climate changes and or local hydrological factors e g closure opening of the lake system controlled by the altitude of the outflow sill the eastern basin of lake bangong was closed before 9 6 and after 1 2 ka b p in response to aridity on the catchment wet warm conditions attributed to the monsoon influence were established suddenly at 9 6 ka b p and maintained until 6 2 ka b p although minor reversal events occurred between 8 6 and 7 7 ka b p the return towards aridity is non linear dry spells at 6 2 3 9 3 2 and 1 3 ka b p are alternated with short term periods with positive precipitation evaporation balance

diatom inferred salinity and carbonate oxygen isotopes in holocene waterbodies of the western sahara and sahel africa abstract thirteen holocene palaeolakes in the western sahara and sahel have provided diatom records with carbonate oxygen isotope profiles available from eight of them most of these palaeolakes were groundwater fed lake water chemistry is reconstructed using diatom transfer functions lake water salinity and 18 o records are assembled with some isotopic and chemical groundwater data to better understand the response of the hydrological systems to climate changes over the past 15 000 yr data are in general agreement with climate simulations using coupled atmosphere ocean vegetation models which show a mid holocene wetting over the whole of northwest africa and a rapid drying by 6 4 ka the lake record also shows that at many sites the major lake infilling lags the end of the younger dryas by 1 2 ka regional differences also appear in the timing of the lake hydrological optimum ca 10 5 8 5 and 7 5 4 5 ka in the northern sahara 10 8 5 ka in the air tenere 10 5 7 or 4 5 in the sahel and 7 5 ka in lake chad the whole of the holocene is punctuated by short term drying events changes in water isotopic composition through time are partly explained by changes in rainfall amount and air humidity during the wet holocene period however the very low values in the southern sahara also imply changes in the moisture transport pattern or rainfall mechanisms data suggest an apparent decrease in 18 o content of precipitation along the monsoon flow in contrast with modern patterns changes in water availability and quality have driven population migrations in and out of the sahara sahel but relationships between climate and cultures are complex short term dry events might have driven inventive adaptations in the sahara drying at 5 4 5 ka coincides with both the collapse of the classical neolithic civilization and the settlement of new cultures

new dates for the tata hungary archaeological site the archaeological site at tata 70 km wnw of budapest has yielded a mousterian lithic industry of small artefacts chipped from chert pebbles with affinity to the quina type1 however the two best known artefacts from the site are a churinga carved from a piece of a mammoth tooth fig 1 and an amulet with an inscribed cross made on a polished nummulite fossil marshack personal communication who examined both the churinga and nummulite observed that one or both arms of the cross engraved on the nummulite are in fact natural fractures that penetrate through the stone however the ivory plaque appears to have been carefully separated from a compound molar tooth of a mammoth shaped and bevelled and then coloured red by rubbing with ochre the age of this site was first determined by 14c analysis of charcoal from the cultural layer2 the age of 55 2 5 kyr led bordes to assign the cultural material to the middle mousterian however palaeontological data3 indicate that this site was occupied towards the end of the last interglacial also two single determinations of th u ages on travertines from the site yielded dates of 116 16 kyr ref 4 and 70 20 kyr ref 5 both of which are more consistent with present estimates of the time interval corresponding to the last interglacial 125 90 kyr we report here new uranium series dates on the travertine which show that the site was occupied at 100 kyr bp this confirms that the amulet from this site is one of the oldest decorative artefacts known and was presumably created by homo sapiens neanderthalensis

simulated climate and biomes of africa during the late quaternary comparison with pollen and lake status data new compilations of african pollen and lake data are compared with climate ccm1 ncar boulder and vegetation biome 1 2 gsg lund simulations for the last glacial maximum lgm and early to mid holocene emh the simulated lgm climate was ca 4 c colder and drier than present with maximum reduction in precipitation in semi arid regions biome simulations show lowering of montane vegetation belts and expansion of southern xerophytic associations but no change in the distribution of deserts and tropical rain forests the lakes show lgm conditions similar or drier than present throughout northern and tropical africa pollen data indicate lowering of montane vegetation belts the stability of the sahara and a reduction of rain forest the paleoenvironmental data are consistent with the simulated changes in temperature and moisture budgets although they suggest the climate model underestimates equatorial aridity emh simulations show temperatures slightly less than present and increased monsoonal precipitation in the eastern sahara and east africa biome simulations show an upward shift of montane vegetation belts fragmentation of xerophytic vegetation in southern africa and a major northward shift of the southern margin of the eastern sahara the lakes indicate conditions wetter than present across northern africa pollen data show an upward shift of the montane forests the northward shift of the southern margin of the sahara and a major extension of tropical rain forest the lake and pollen data confirm monsoon expansion in eastern africa but the climate model fails to simulate the wet conditions in western africa

1923 gleno dam break case study and numerical modeling on the morning of december 1 1923 the gleno dam located in the central italian alps suddenly collapsed a few days after the first complete reservoir filling nearly 4 5 1 0 6 m 3 of water was released the consequent inundation caused significant destruction along the downstream valley and a death toll of at least 356 lives this failure is the only historical case of dam break caused by structural deficiencies that has occurred in italy as a result it has deeply influenced the evolution of italian regulations regarding dam design and hydraulic risk evaluation however in spite of its relevance this event has never been characterized from a hydraulic standpoint this paper reports the main information obtained from the analysis of a vast amount of historical documents regarding the gleno dam break to set up a case study useful for validating dam break models in mountain settings moreover it presents the main results of one dimensional 1d modeling of the dam break wave propagation accomplished with a first order finite volume numerical scheme recently proposed in the literature for field applications the overall effectiveness and reliability of the model are evaluated for this case characterized by very irregular topography finally the practical relevance of several choices that the numerical reconstruction of this kind of event demands is tested doi 10 1061 asce hy 1943 7900 0000327 2011 american society of civil engineers ce database subject headings dam failures shallow water numerical models hydraulic models case studies italy author keywords dam failure 1d dam break modeling shallow water finite volume numerical model hydraulic hazard case study

precise timing of the last interglacial period from mass spectrometric determination of thorium 230 in corals the development of mass spectrometric techniques for determination of 230 th abundance has made it possible to reduce analytical errors in 238 u 234 u 230 th dating of corals even with very small samples samples of 6 x 10 8 atoms of 230 th can be measured to an accuracy of 3 percent 2 and 3 x 10 10 atoms of 230 th can be measured to an accuracy of 0 2 percent the time range over which useful age data on corals can be obtained now ranges from about 50 to about 500 000 years for young corals this approach may be preferable to 14 c dating the precision with which the age of a coral can now be determined should make it possible to critically test the milankovitch hypothesis concerning pleistocene climate fluctuations analyses of a number of corals that grew during the last interglacial period yield ages of 122 000 to 130 000 years the ages coincide with or slightly postdate the summer solar insolation high at 65 n latitude which occurred 128 000 years ago this supports the idea that changes in pleistocene climate can be the result of variations in the distribution of solar insolation caused by changes in the geometry of the earth s orbit and rotation axis

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

oscillations of lake chad over the past 50 000 years new data and new hypothesis a recent sedimentological study of the chari deltas area allowed an evaluation of the oscillations of palaeolake chad over the past 50 000 years three maximum lake levels at circa 38 000 22 000 and between 12 000 and 8000 years b p have been described the levels reached by these large lakes were never very high and there has not been any major variation over the last 8000 years the hypothesis regarding a huge palaeolake chad of 320 000 km2 reaching the 320 m level at circa 6000 years b p instead of the present 279 5 282 m and approximatively 20 000 km2 is discussed and discarded on basis of stratigraphical sedimentological geomorphological hydrological and geophysical arguments taking into account geophysical data and the deep structures of the basin a new interpretation is proposed for the perilacustrine dune ridge which was considered to run along the shoreline of the 320 m level

paleoecology of limnic ostracodes a review of some major topics abstract the paleoecology of limnic ostracodes is reviewd in the context of the evolution of their environment in order to understand why there is a rich ostracode fossil record we examine data such as the quantitative and qualitative distribution of living ostracode species and ostracode assemblages ways of describing and limitations importance of biological and physico chemical factors for the local accumulation of high numbers of ostracodes and diversified assemblages is emphasized we discuss the limits of extrapolations of information from ecology to paleocology we stress how paleontological knowledge can be applied to neontological studies the possibility of using holocene ostracodes as indicators of morphometric changes of lakes temperature salinity eutrophication and as a criterion of meromictic conditions is demonstrated relationships between ostracodes and the chemical environment and particularly the morphological response of the carapace are considered e g diversity and qualitative composition of assemblages and chemical stability types of carapace mineralization and ornamentation and chemistry of bottom waters these ideas developed from studies on recent material are tested for limnic cenozoic faunas in the mesozoic the main questions arising from the study of nonmarine ostracodes deal with the possible evaluation of paleosalinities in marginal lagoonal environments purbeck wealden and with evaluation of depth and hydrochemical and paleoclimatological regime in truly lacustrine intracratonic basins some peculiarities of paleozoic nonmarine ostracode assemblages are described the paleoecological cause of changes in diversity of several ostracode groups in the carboniferous and permian is emphasized

quaternary landforms sediments depositional environments and gastropod isotope ratios at adrar bous tenere desert of niger south central sahara

late quaternary climatic reconstruction for the maghreb north africa abstract the paleoclimatic evolution of the maghreb since 40 000 yr b p is not yet known in great detail for that purpose data from more than 35 sites have been collected although only about 11014c dates and a few prehistoric remains can be used to correlate these data however the sites are well distributed over the maghreb and the convergent results from paleosoils paleolakes alluvian or eolian deposits pollen analysis etc induce one to draw up a certain pattern in climatic evolution for the period between 40 000 and 20 000 yr b p the data are still fragmentary but are concordant in indicating wetter environments generalized as far as the northern sahara the effect of dropping temperatures on the increasing water budget and soil moisture is not yet clear but rainfall could have been more regular and more abundant as a consequence of the shifting of middle latitude cyclone paths towards the south in both summer and winter the environmental indicators show that between about 20 and 18 000 yr b p rainfall progressively became more irregular however proofs of aridity in the south maghreb and the northern sahara is evident only for the period between 12 10 000 yr b p at that time the saharan high pressure belt was reinforced and well established at higher latitudes than at present this dry climate lasted more or less until the thermal optimum after 6000 yr b p there is some evidence that the climate became wetter again but the environmental conditions were rather different from those of before 20 000 yr b p for instance the middle holocene dark humic sois are the result of a pedogenesis different from that of the late pleistocene reddish paleosoils for the last two millennia it is not easy to distinguish between a natural trend towards aridification and desertification through man s intervention

palaeoenvironments and palaeohydrology of a tropical closed lake lake asal djibouti since 10 000 yr b p in eastern africa republic of djibouti the hypersaline lake asal occupies an exceptional geological topographical and hydrological situation at 155 m below sea level and at 12 km from the sea it lies in the youngest and the deepest basin in a chain of closed depressions of central afar decreasing in elevation from west to east and represents the hydrogeological low of the whole system presently infiltration of marine water represents the major water input to the lake due to high evaporation conditions halite precipitates halocene water level fluctuations 315 m sedimentary conditions from fresh oligosaline waters to heavy brines and palaeohydrology are reconstructed field observations are supported by 85 14c dates on inorganic carbonates mollusc shells stromatolites and hydrothermal travertines stable isotope analyses on carbonates and sulphates mineralogy geochemistry and studies of biological remains discussion of the water balance for the major stages is based on reasonable assumptions about holocene conditions of precipitation and evaporation after an arid terminal pleistocene phase marked by coarse deposits due to exceptional floods the holocene cycle begins with complex strontium rich carbonate phases aragonite high and low mg calcites and dolomite these carbonates could reflect the first underground marine supply and waters concentrated through evaporation a high lake level ca 160 m a s l from ca 8600 to 6000 yr b p corresponds to the deposition of high mg calcite precipitated in a deep fresh water lake lake asal was draining the awash river system ethiopian plateau and escarpment through groundwater circulations the terminal basin of the system was probably the present day marine gulf of ghoubbat al kharab hydrologically separated from the open ocean by a sill at 4 m below sea level possibly due to fracture opening a dramatic regression in the lake level from 160 to 150 m occurred between ca 6000 and 5000 yr b p the inputs of continental water were consequently overwhelmed by marine infiltrations the carbonate phase exhibits clear resemblance with that of the transgressive episode from 5000 yr b p lake asal experienced minor water level fluctuations aragonite rich carbonates precipitated followed by calcium sulphates and halite stable isotopes of gypsum reflect its marine origin and various diagenetic processes the holocene evolution of asal which clearly differs from that of the neighbouring closed basins is due to both its specific geological and hydrological setting and to the regional climatic changes

14 c and th u dating of pleistocene and holocene stromatolites from east african paleolakes during recent humid episodes stromatolites were built along paleolake margins some 60 m above the modern water level of lakes natron and magadi southern gregory rift valley three generations of stromatolites are observed the more recent ones frequently covering pebbles and boulders eroded from the older ones the youngest one yielded 14c ages ranging from approximately 12 000 to 10 000 yr b p their 13c values 2 6 suggest isotopic equilibrium between the paleolake total inorganic dissolved carbon and the atmospheric co2 thereby lending credence to the reliability of the 14c an initial 230th232th ratio in the detrital component was determined by thu measurements on the 14c dated stromatolites using this value a 230th234u chronology for the older stromatolites was calculated ages of 240 000 and 135 000 10 000 yr were obtained for the first and second generations respectively a humid episode apparently characterized eastern africa during each glacial interglacial transition 18o and 13c measurements on stromatolites when compared to values on modern waters and carbonates provide paleohydrological information long residence time of the paleolake waters and less seasonally contrasted regimes are inferred

the microseismic network of the ridracoli dam north italy data and interpretations the ridracoli dam has been operating since 1981 around the reservoir ismes installed and operated for 10 years a seismic network now reduced to a 3 d station earthquakes were recorded with completeness from magnitude 0 8 onwards in the same period all the parameters relevant to the dam and the environment were measured this provided a complete data base for ris studies unique in its kind in italy the main findings of the analyses performed are the following

temperature and salinity records of the tyrrhenian sea during the last 18 000 years abstract we have used the modern analogue technique to derive sea surface temperature sst records of the last 18 000 years from two well dated deep sea cores recovered in the tyrrhenian sea results show two major cooling events synchronous with the european and north atlantic oldest and younger dryas events a later cooling of lower amplitude is observed between about 8000 and 4500 yr bp tyrrhenian ssts were similar to those of the upper holocene only during the bolling allerod event and at the beginning of the holocene we compared the sst and the planktonic foraminiferal oxygen isotope records to estimate the surface salinity variations our reconstruction shows that salinity decreased in the tyrrhenian sea during the three cold events whereas high ssts correlate with high salinities during most of the last 18 000 years tyrrhenian sea salinity variations were similar to those of the north atlantic ocean near the entrance of the mediterranean sea the salinity gradient between the two basins was thus constant indicating that the western mediterranean circulation pattern and the freshwater budget were not significantly different from the modern one the case was however different during the middle holocene when the strong salinity decrease associated with the sapropel deposit in the eastern mediterranean basin had no equivalent in the north atlantic ocean this peculiar event can only be explained by a local climatic change and an increase of precipitation

environmental controls on perennial and ephemeral carbonate lakes the central palaeo andean basin of bolivia during late cretaceous to early tertiary times abstract in the central palaeo andean basin potosi basin of bolivia the up to 450 m thick el molino formation campanian maastrichtian to early tertiary includes two main carbonate lacustrine episodes each of different extent and duration these episodes are separated by an extensive development of alluvial facies floodplain deposits and limestones deposited in playa lakes or isolated ponds the el molino formation has been investigated in six different areas of the potosi basin and affords the opportunity to document climatic and tectonic controls on the development of perennial and ephemeral carbonate lacustrine systems the first lacustrine episode originated predominantly in perennial lakes with wave dominated low gradient ramp type margins outer marginal lacustrine facies include winnowed oolitic grainstones ostracod packstones and microbialite bioherms more agitated areas were characterized by nearshore oolitic bars with associated thrombolite mounds the fossil content and the lack of significant precipitation of evaporites indicate that the lake waters were of low salinity probably oligohaline during most of this period after the first lacustrine episode the widespread development of terrigenous alluvial facies floodplain deposits with interspersed playa lakes or isolated ponds in depressions on the floodplain may indicate a change in the net water budget the second lacustrine episode is dominated by dark micritic limestones and to a lesser extent microbialite bioherms which developed under semiarid climatic conditions this episode includes the deposits of ephemeral saline locally alkaline shallow lakes which were characterized by low energy low gradient ramp type margins the stable isotopic analysis of 163 carbonate samples covering the different facies and depositional settings displays a wide range of values 14 2 18 o and 12 9 13 c that is typical of nonmarine environments the distribution of the values indicates that during the deposition of the el molino formation the basin was hydrologically closed and experienced no strong hydrogeographical changes except for variations in the palaeolake level related to fluctuations in the regional p e ratio these are recorded by two main isotopic trends related to changes between perennial and ephemeral lacustrine conditions lacustrine sedimentation was controlled predominantly by climatically driven hydrological changes with repeated oscillations of the water level expansion and contraction and subsequent fluctuations in the width of lacustrine facies belts

vostok ice core climatic response to co2 and orbital forcing changes over the last climatic cycle vostok climate and co2 records suggest that co2 changes have had an important climatic role during the late pleistocene in amplifying the relatively weak orbital forcing the existence of the 100 kyr cycle and the synchronism between northern and southern hemisphere climates may have their origin in the large glacial interglacial co2 changes

marine deposits 35 000 25 000 years old in the chott el djerid southern tunisia the chott el djerid is a large salt covered depression in southern tunisia fig 1 the late nineteenth century idea that the basin had been invaded by the sea1 2 has been superseded by the view that any quaternary flooding of the chott must have resulted from climatic changes as the fossils found in its sediments are not exclusively marine and there is no indication of the fluctuations in sea level or of the crustal movements that would be required to fill and then empty the basin2 3 we report here evidence for a marine connection 35 000 25 000 years ago and show that it implies subsequent uplift by some 80 metres in an area long regarded as either stable2 or prone to subsidence throughout the quaternary4

vostok ice core a continuous isotope temperature record over the last climatic cycle 160 000 years a continuous deuterium profile along the 160 000 year vostok ice core antarctica is interpreted in terms of atmospheric temperature changes this climatic record is the awaited terrestrial complement of the deep sea records supporting the existence of a relation between the pleistocene climate and orbital forcing

a pleistocene lacustrine episode in southeastern libya fossiliferous lacustrine deposits of middle pleistocene age have been found in central fezzan libya 1 on each side of the east west depressions of the wadi shati south of the precambrian qarqaf anticline1 8 they represent the shoreline of a former brackish water lake fig 1 which some 130 000 yr bp covered an area about 100km long and 10 20 km wide at present the area may be classified as hyperarid since 1978 a collaborative study of the fossil assemblages has been undertaken it included macro and micropalaeontological determination th u dating stable isotope and chemical analyses in parallel with sedimentological and archaeological studies of the sites here we consider the th u dating and the isotopic palaeohydrology of the lacustrine episode

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

radiocarbon chronology of holocene hydrologic changes in northeastern mali abstract a detailed chronology of hydrological changes that occurred in northeastern mali during the holocene is based on approximately 30 14 c dates of molluscs which were collected from the lacustrine and paludal deposits of the ine sakane sand sea the presence of cemented paleodunes indicates that the end of the pleistocene was and arid period this was followed by an early holocene lacustrine episode ca 9500 6500 yr b p during which numerous lakes occupied depressions formed in the cretaceous limestones and between the sand ridges these lakes reflect a significant rise in the water table between ca 6500 and 5500 yr b p the lakes dried up although the water table remained close to the ground surface in several areas calcareous concretions formed at the water table fringe during this time thereby fossilizing some of the middle holocene dunes a second lacustrine episode is dated between ca 5500 and 4500 yr b p it corresponds to the establishment of numerous neolithic settlements in the area arid conditions have developed since about 4500 yr b p to attain the conditions of the present day the isotopic composition 18 o and 13 c of the fauna reflects highly variable hydrological conditions groundwaters were recharged by precipitation which was occasionally very depleted in heavy oxygen 18 o 13 evaporation induced an enrichment in 18 o high concentrations characterize some lakes the 13 c content of fossil shells reflect 1 species ecological requirements 2 isotopic composition of the total inorganic dissolved carbon tidc in groundwaters and 3 the lake metabolism

on the ages of humid holocene and late pleistocene phases in north africa remarks on late quaternary climatic reconstruction for the maghreb north africa by p rognon discussion sur l article de rognon p paru en 1987 dans palaeogeogr palaeoclimatol palaeoecol vol 58 p 11 34

changes in east atlantic deepwater circulation over the last 30 000 years eight time slice reconstructions using 95 epibenthic 13c records eight time slices were reconstructed to trace the distribution of east atlantic deepwater and intermediate water masses over the last 30 000 years our results show that there have been three distinct modes of deepwater circulation near the stage 3 2 boundary the origin of north atlantic deep water nadw was similar to today mode 1 however after late stage 3 the source region of the nadw end member shifted from the norwegian greenland sea to areas south of iceland mode 2 a reduced nadw flow persisted during the last glacial maximum with constant preformed 13c values the nutrient content of nadw increased markedly near the azores fracture zone from north to south probably because of the mixing of upwelled antarctic bottom water aabw from below which then advected with much higher flux rates into the northeast atlantic later the spread of glacial meltwater over the north atlantic led to a marked short term ventilation minimum below 1800 m about 13 500 14c years ago mode 3 the formation of nadw recommenced abruptly north of iceland 12 800 12 500 years ago and reached a volume approaching that of the holocene in the younger dryas 10 800 10 350 years b p another short term shutdown of deepwater formation followed between 10 200 and 9 600 years b p linked to a further major meltwater pulse into the atlantic each renewal of deepwater formation led to a marked release of fossil co2 from the ocean the likely cause of the contemporaneous 14c plateaus over the last 9000 years deepwater circulation varied little from today apart from a slight increase in aabw about 7000 14c years ago it is also shown that the oxygenated mediterranean outflow varied largely independent of the variations in deepwater circulation over the last 30 000 years

retreat velocity of the north atlantic polar front during the last deglaciation determined by 14 c accelerator mass spectrometry the glacial oscillations which dominate the quaternary global climate are closely related to changes in incoming solar radiation but the details of palaeoclimatic spectra suggest that other parameters usually referred to as feedback have significantly increased the climatic response to extraterrestrial forcing1 the last deglaciation appears to be one of the more characteristic examples of nonlinearity because its abruptness strongly contrasts with the smooth shape of the associated solar radiation maximum dated at 11 000 yr bp in addition the presence of the younger dryas cold event concomitant with the solar radiation maximum could be interpreted as a transitory phenomenon caused by the rapid meltwater influx linked to the first phase of the ice sheet s disintegration2 3 here using accelerator mass spectrometry we date precisely the movements of the polar front during the whole period of glacial retreat 15 000 8 000 yr bp our results show that the polar front has moved between 35 n and 55 n in 1 000 yr for the earliest retreat 12 500 12 000 bp and moved almost instantaneously that is 400 yr during the two abrupt climatic changes associated with the younger dry as cold event

sahara and sahel vulnerability to climate changes lessons from holocene hydrological data abstract the examination of more than 1500 paleohydrological dated records collected between 10 and 28 n during the last 50 years have been used to improve our knowledge and understanding of the sahara and sahel vulnerability to the atlantic monsoon changes in the long term we have analyzed the distribution of water bodies mainly lakes and wetlands over time and space the central saharan massifs played a major role in favoring water supply to the lowlands throughout the whole african humid period in addition distinct east west dynamics is recorded with humidity starting and stopping several millennia earlier to the east than to the west of the sahara a series of time lags are discussed 1 between the maximum of deep fresh water lake formation during the early holocene and the maximum of water body extensions during the mid holocene which highlight the primary role of aquifer water level in lake response to climate change 2 between the hydrological history of the sahara and the sahel and the forcings mainly insolation changes during the early and mid holocene which involves complex interactions between remnant ice sheet in the northern hemisphere open water bodies in the sahara and sahel and the atlantic monsoon system

mediterranean pluvial periods and sapropel formation over the last 200 000 years abstract three mediterranean deep sea cores have been studied to reconstruct the hydrological conditions at the time of deposition of interglacial and glacial sapropels during the time interval 200 60 kyr bp the isotopic and sea surface temperature records of planktonic foraminifera were used to estimate the oxygen isotopic composition of surface water w in the tyrrhenian sea and levantine basin our results show a strong w salinity decrease in both basins associated with each sapropel these w decreases reflect a drastic change in the local freshwater budget and were comparable to that observed during the last sapropel s 1 centred at ca 8 kyr bp a strong precipitation increase transformed the whole mediterranean sea into a non concentration basin the low surface salinity was responsible for the water column stratification while nutrients brought in by the runoff enhanced productivity it resulted in a significant reduction in the rate of deep water oxygenation and sapropel formation in the eastern basin in addition the mediterranean sea 18 o record is very similar to that of the bay of bengal as the latter is very sensitive to the summer monsoon rain this similarity suggests that both glacial and interglacial sapropels result from enhanced monsoon like precipitation due to an increase in summer insolation driven by precession variations