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

hillslope infiltration planar slopes the solution of the full nonlinear unsaturated flow equation is given for a problem of infiltration and associated subsurface flows into a planar hillslope of a homogeneous isotropic soil with uniform initial moisture content the solution uses the assumption that at some distance below the slope crest a spatial equilibrium is approached with the moisture content and other properties independent of downslope coordinate x and dependent only on the normal coordinate z and time t the analysis is found to be generally applicable beyond a small distance from the slope crest or from a point of slope change for slope angles less than 30 infiltration normal to the slope differs relatively little from infiltration from a horizontal surface interesting aspects of the solution include a time independent total horizontal flow into the slope and a time dependent downslope total flow component which behaves as t1 2 at small t and as t at large t previously hillslope flows in these directions have been discussed in terms of soil anisotropy and layering but these flows in a homogeneous isotropic soil are simple physical consequences of capillarity and gravity the analysis applies with minor modification to two simple types of hillslope anisotropy 1 anisotropy parallel to the slope and 2 horizontal anisotropy type 1 yields a complicated time dependence of the horizontal flow and type 2 affects downslope flow similarly these flow directions will commonly reverse during the course of the infiltration process

the proto earth as a significant source of lunar material geochemical evidence continues to challenge giant impact models which predict that the moon formed from both proto earth and impactor material analyses of lunar samples reveal isotopic homogeneity in titanium a highly refractory element suggesting lunar material was derived predominantly from the mantle of the proto earth

analysis of effective green ampt hydraulic parameters for vertically layered soils summary while green ampt model has been widely used in infiltration calculations through unsaturated soils upscaling this model for applications in heterogeneous formations remains difficult in this study how to upscale soil parameters in the green ampt model for vertically layered soils is examined the main idea of upscaled effective parameters is to capture infiltration behavior in layered soil formations using only one set of parameters derived from the parameters of individual layers such that the layered system can be replaced by an equivalent homogeneous medium the general p order power mean was proposed to represent the upscaling schemes of the green ampt model the optimal p value was determined by a general requirement of same total infiltration time for the layered formation and the equivalent homogeneous medium the p order power mean for the green ampt parameters can capture the infiltration rates in the layered formations well illustrating that the proposed upscaling schemes are reasonable to represent the overall behaviors of the heterogeneous layered formations the structure of layered formations can significantly influence the upscaling results however when the number of layers becomes large the layered formations tend to show homogeneity and the layer structure becomes less important the results demonstrated that the scheme based on the harmonic mean for the saturated hydraulic conductivity and the general p order power mean for the wetting front suction head can well capture the overall infiltration behaviors in both the coarse layer on top and fine layer on top formations and thus is recommended as a general upscaling scheme when using the upscaled green ampt model in layered formations

mediterranean moisture source for an early holocene humid period in the northern red sea paleosalinity and terrigenous sediment input changes reconstructed on two sediment cores from the northernmost red sea were used to infer hydrological changes at the southern margin of the mediterranean climate zone during the holocene between approximately 9 25 and 7 25 thousand years ago about 3 per thousand reduced surface water salinities and enhanced fluvial sediment input suggest substantially higher rainfall and freshwater runoff which thereafter decreased to modern values the northern red sea humid interval is best explained by enhancement and southward extension of rainfall from mediterranean sources possibly involving strengthened early holocene arctic oscillation patterns and a regional monsoon type circulation induced by increased land sea temperature contrasts we conclude that afro asian monsoonal rains did not cross the subtropical desert zone during the early to mid holocene

terrestrial magma ocean origin of the moon a conceptual framework for the origin of the moon must explain both the chemical and the mechanical characteristics of the earth moon system to be viable the classic concept of an oblique giant impact explains the large angular momentum and the lack of a large iron rich core to the moon but in this scenario it is difficult to explain the similarity in the isotopic compositions of the earth and moon without violating the angular momentum constraint here we propose that a giant solid impactor hit the proto earth while it was covered with a magma ocean under the conventional collision conditions we perform density independent smoothed particle hydrodynamic collision simulations with an equation of state appropriate for molten silicates these calculations demonstrate that because of the large difference in shock heating between silicate melts and solids rocks a substantial fraction of the ejected moon forming material is derived from the magma ocean even in a highly oblique collision we show that this model reconciles the compositional similarities and differences between the moon and earth while satisfying the angular momentum constraint moon formation by a giant impact ejecting material from a magma ocean on earth reconciles geochemical and dynamical constraints on its formation according to numerical simulations

varved sediments of lake yoa ounianga kebir chad reveal progressive drying of the sahara during the last 6100 years the sedimentological and geochemical properties of a 7 47 m long laminated sequence from hypersaline lake yoa in northern chad have been investigated representing a unique continuous 6100 year long continental record of climate and environmental change in the eastern central sahara these data were used to reconstruct the mid to late holocene history of this currently hyper arid region in order to address the question of whether the mid holocene environmental transition from a humid to a dry sahara was progressive or abrupt this study involved a suite of analyses including petrographic and scanning electron microscope examination of thin sections x ray diffraction x radiography granulometry loss on ignition and magnetic susceptibility the potential of micro x ray fluorescence core scanning was tested at very high resolution detailed microscopic investigation revealed the sedimentary processes responsible for the formation of the fine laminations identified the season during which they were formed and confirmed their annually rhythmic nature high resolution x ray fluorescence core scanning allowed the distinction of each individual lamination over the entire record opening new perspectives for the study of finely laminated sediment sequences geochemical and mineralogical data reveal that due to decreasing monsoon rainfall combined with continuous and strong evaporation the hydrologically open and fresh mid holocene lake yoa slowly evolved into the present day hypersaline brine depleted in calcium which has existed for about the past 1050 years during the oldest part of the investigated period lake yoa probably contained a permanently stratified lower water column that was nevertheless disrupted relatively frequently by mixing events deep water anoxia became more stable because of increased salinity driven density stratification in parallel the sediment grain size proxies record a progressive increase of aeolian input in the course of the last 6100 years altogether all geochemical and sedimentological indicators point to a progressive drying of the eastern central sahara strengthening previous conclusions based on palaeoecological indicators

direct push sensing in wetland geo archaeology high resolution reconstruction of buried canal structures fossa carolina germany abstract geo archaeological trenching techniques in floodplain and wetland environments are challenging due to the impact of groundwater inflow and highly unstable trench edges alternatively classical driving core techniques often correspond with the contraction of organic layers and bias in height accuracies here we present the application of direct push sensing techniques for minimal invasive geo archaeological surveys in zones affected by a high groundwater table especially when high resolution parameterization of buried geo archaeological structures is required two of these direct push applications are electrical conductivity logging and the measurement of colorimetric proxies in unconsolidated sediments the tools provide multi proxy information about layer structure texture and organic parameters the high sensing speed allows recording a large data set with high vertical and lateral resolution in this study we exemplary provide results of a buried canal structure within a valley in sw germany we present a high resolution cross section from a zone of high groundwater table the canal is part of charlemagne s summit canal fossa carolina an early medieval hydro engineering project bridging the central european watershed we compare the direct push sensing data with driving core samples and discuss prediction and generation options of parameter transfer from multiple one dimensional logs to a two dimensional canal cross section of high resolution in this context we use in situ obtained colorimetric data and electrical conductivity as proxies for geo archaeological site characterization we model organic fills of the canal by direct push logs and robust sediment data given the cost and time effectiveness of such tools geo archaeological site information of high depth accuracy was grown rapidly compared to less densely performed drillings that require an additional high effort in laboratory analyses the carolingian excavation depth is 6 m below current surface there is evidence for multiple organic layers in the trench fills which reveal aquatic to semi terrestrial stillwater deposition and therefore evidence of multiple carolingian and post carolingian ponds we have evidence for a conceptual width of the deep buried artificial water course of at least 3 4 m this allows a passage of carolingian cargo scows with a payload of several tons in this central zone of the canal

moving multi front mmf a generalized green ampt approach for vertical unsaturated flows abstract a moving multi front mmf method is developed and tested for solving the richards equation governing unsaturated flow in vertical homogeneous porous columns the mmf model is a gridless method it can be viewed as a generalization of the green ampt piston flow approach which models flow as a single abrupt moving front separating saturated and dry regions during infiltration the mmf model further generalizes this concept using a parametrization of unsaturated water retention and conductivity pressure curves it reduces the richards pde to an ode system governing m moving front positions different tests are developed to validate this approach for 1d transient downwards upwards flows submitted to constant and time varying pressure boundary conditions they include i infiltration to deep water tables ii infiltration to shallow water tables iii capillary rise from fixed water tables iv gradual water table rise partially saturated column with evolving pressure condition at bottom the mmf results are compared favorably to finely discretized fixed grid solutions of richards pde analyses of error and accuracy show satisfactory results in terms of water content profiles and boundary fluxes e g infiltration rate

comment on effective groundwater model parameter values influence of spatial variability of hydraulic conductivity leakance and recharge by j j gomez hernandez and s m gorelick

metal silicate fractionation in the growing earth energy source for the terrestrial magma ocean based on the homogeneous accretion model of planets thermal evolution of the growing earth has been studied after the surface of the growing earth starts melting owing to the blanketing effect of the primordial atmosphere gravitational differentiation between metallic and silicate materials takes place in its upper region the differentiation would give rise to a large amount of gravitational energy release as well as layered structure inside the proto earth a part of released energy would be transported outward by convection considering the effects of gravitational fractionation and convection we have pursued numerically the evolution of the growing earth our results show that gravitational differentiation can supply energy large enough to keep the whole silicate layer in the molten state and that half of the released energy is conveyed outward by convective heat transport in the growing stage the temperature distribution in the silicate layer always lies between liquidus and solidus temperatures except in an uppermost thin zone the thermal structure obtained favors a notion of the primordial magma ocean and of chemical differentiation of mantle the structure of the growing earth which is composed of the central protocore the metallic layer and the silicate layer magma ocean would become gravitationally unstable and overturn to form a metallic core energy released by this overturn would not affect the structure of the upper magma ocean too much but undifferentiated primordial materials which come from the protocore would add to mantle materials through the overturn and this would help explain the isotopic mantle heterogeneity presently observed

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

modeling rainfall infiltration on hillslopes using flux concentration relation and time compression approximation abstract rainfall infiltration on hillslopes is an important issue in hydrology which is related to many environmental problems such as flood soil erosion and nutrient and contaminant transport this study aimed to improve the quantification of infiltration on hillslopes under both steady and unsteady rainfalls starting from darcy s law an analytical integral infiltrability equation was derived for hillslope infiltration by use of the flux concentration relation based on this equation a simple scaling relation linking the infiltration times on hillslopes and horizontal planes was obtained which is applicable for both small and large times and can be used to simplify the solution procedure of hillslope infiltration the infiltrability equation also improved the estimation of ponding time for infiltration under rainfall conditions for infiltration after ponding the time compression approximation tca was applied together with the infiltrability equation to improve the computational efficiency the analytical integral infiltrability equation was approximated with a two term power like function by nonlinear regression procedures of applying this approach to both steady and unsteady rainfall conditions were proposed to evaluate the performance of the new approach it was compared with the green ampt model for sloping surfaces by chen and young 2006 and richards equation the proposed model outperformed the sloping green ampt and both ponding time and infiltration predictions agreed well with the solutions of richards equation for various soil textures slope angles initial water contents and rainfall intensities for both steady and unsteady rainfalls

electrical resistance tomography electrical resistance tomography ert is a method that calculates the subsurface distribution of electrical resistivity from a large number of resistance measurements made from electrodes for in situ applications ert uses electrodes on the ground surface or in boreholes it is a relatively new imaging tool in geophysics the basic concept was first described by lytle and dines as a marriage of traditional electrical probing introduced by the schlumberger brothers and the new data inversion methods of tomography development of both the theory and practice of ert was confined mostly to the late 1980s and the 1990s tomographic inversion added important new capabilities as it was more general accurate and rigorous at spatial imaging of geophysical electrical resistance data than earlier pseudosection or curve fitting methods

green and ampt infiltration into soils of variable pore size with depth most expressions for infiltration rely upon the assumption of vertical uniformity in soil texture and hydraulic properties we present an extension of the results of beven 1982 1984 for infiltration and lateral flow in soils with decreasing permeability with depth unlike beven we base the derivations upon joint changes in soil properties based on an overall change in characteristic pore size via miller scaling a set of very simple expressions for the time rate of infiltration are obtained using a green and ampt approach for soils with permeability that decreases with depth following linear power law and exponential relationships

forming a moon with an earth like composition via a giant impact in the giant impact theory the moon formed from debris ejected into an earth orbiting disk by the collision of a large planet with the early earth prior impact simulations predict that much of the disk material originates from the colliding planet however earth and the moon have essentially identical oxygen isotope compositions this has been a challenge for the impact theory because the impactor s composition would have likely differed from that of earth we simulated impacts involving larger impactors than previously considered we show that these can produce a disk with the same composition as the planet s mantle consistent with earth moon compositional similarities such impacts require subsequent removal of angular momentum from the earth moon system through a resonance with the sun as recently proposed

atlantic forcing of western mediterranean winter rain minima during the last 12 000 years abstract the limited availability of high resolution continuous archives insufficient chronological control and complex hydro climatic forcing mechanisms lead to many uncertainties in palaeo hydrological reconstructions for the western mediterranean in this study we present a newly recovered 19 63 m long core from lake sidi ali in the north african middle atlas a transition zone of atlantic western mediterranean and saharan air mass trajectories with a multi proxy approach based on magnetic susceptibility carbonate and total organic c content core scanning and quantitative xrf stable isotopes of ostracod shells charcoal counts cedrus pollen abundance and a first set of diatom data we reconstruct western mediterranean hydro climatic variability seasonality and forcing mechanisms during the last 12 000 yr a robust chronological model based on ams 14 c dated pollen concentrates supports our high resolution multi proxy study long term trends reveal low lake levels at the end of the younger dryas during the mid holocene interval 6 6 to 5 4 cal ka bp and during the last 3000 years in contrast lake levels are mostly high during the early and mid holocene the record also shows sub millennial to centennial scale decreases in western mediterranean winter rain at 11 4 10 3 9 2 8 2 7 2 6 6 6 0 5 4 5 0 4 4 3 5 2 9 2 2 1 9 1 7 1 5 1 0 0 7 and 0 2 cal ka bp early holocene winter rain minima are in phase with cooling events and millennial scale meltwater discharges in the sub polar north atlantic our proxy parameters do not show so far a clear impact of saharan air masses on mediterranean hydro climate in north africa however a significant hydro climatic shift at the end of the african humid period 5 ka indicates a change in climate forcing mechanisms the late holocene climate variability in the middle atlas features a multi centennial scale nao type pattern with atlantic cooling and western mediterranean winter rain maxima generally associated with solar minima

a multi proxy analysis of the holocene humid phase from the united arab emirates and its implications for southeast arabia s neolithic populations an early to mid holocene humid phase has been identified in various arabian geo archives although significant regional heterogeneity has been reported in the onset duration and stability of this period a multi proxy lake and dune record from wahalah in the united arab emirates uae documents significant variations in hydrology biological productivity and landscape stability during the first half of the holocene these data reveal that post last glacial maximum dune emplacement continued into the earliest part of the holocene with the onset of permanent lacustrine sedimentation at the site commencing 8 5 ka cal bp a long term shift towards more arid conditions is inferred between 7 8 and 5 9 ka cal bp with intermittent flooding of the basin and distinct phases of instability throughout the catchment area this transition is linked to the southwards migration of the intertropical convergence zone itcz and associated weakening of monsoon rains a peak in landscape instability is recorded between 5 9 and 5 3 ka cal bp and is marked by a pronounced increase in regional dune emplacement these variations are considered alongside the record of human settlement raising important questions about the interactions between population demographics climate and environment in southeast arabia during the neolithic

local and field scale infiltration into vertically non uniform soils with spatially variable surface hydraulic conductivities we studied the problem of local and field scale infiltration over a particular class of heterogeneous soils at the local scale the soils are described as being vertically non uniform with the saturated hydraulic conductivity continuously decreasing with depth according to a power law function analogous to the green ampt model analytical expressions are first developed for local scale infiltration using a sharp front approximation and model results are compared with numerical solutions of the richards equation these results show that saturation does not occur from below in soils with such vertical non uniformity thereby allowing for the use of a sharp front approximation because of vertical non uniformity ponding conditions are achieved locally even for rainfall rates less than the surface saturated hydraulic conductivity furthermore infiltration rates asymptotically approach zero at long times to determine field scale infiltration properties the spatial variability in the surface saturated hydraulic conductivity is represented by a log normal random field using cumulative infiltration as the independent variable expressions are developed for the ensemble mean of field scale infiltration and the expected time for a given depth of water to infiltrate over the field surface horizontal heterogeneity is found to control field scale infiltration at small times whereas local vertical non uniformity exerts a strong control at long times copyright 2011 john wiley sons ltd

lunar accretion from an impact generated disk although the mechanism by which the moon was formed is currently unknown several lines of evidence point to its accretion from a circumterrestrial disk of debris generated by a giant impact on the earth theoretical simulations show that a single large moon can be produced from such a disk in less than a year and establish a direct relationship between the size of the accreted moon and the initial configuration of the debris disk

climate forcing and shifts in water management on the northwest arabian peninsula mid holocene rasif wetlands saudi arabia abstract the mid holocene climate of northwest arabia is characterised by a significant increase in aridity which gave rise to changes in water management strategies including sophisticated techniques at later stages the rasif site situated in northwest saudi arabia reveals a late neolithic society with multi roomed domestic structures 1st phase 6th millennium bce before the current era at rasif site the sediments of an endorheic basin qa show a minimum in salinity during this 1st phase the 2nd phase is characterised by a pastoral chalcolithic watering and chalcolithic burial location of the 5th millennium bce with wells complex trough systems and initial probably coexistent grave structures during this 2nd phase the qa deposits show already a slight increase in salinity we have evidence for a sub surface water rich sand layer within the qa that was exploited by shallow wells during the subsequent 3rd phase the number of pastoral chalcolithic d shaped grave structures within the qa increased probably co existing with deepened wells and complex trough systems at that time the qa is covered by an almost impermeable saline clay layer the 4th phase is characterised by a culturally yet to identify pastoral post chalcolithic watering location with single small troughs the final 5th phase represents a culturally unidentified pastoral post chalcolithic to sub recent water harvesting location with complex dam systems which were probably modified numerous times the dam systems allowed to flooding the qas for several months providing sub surface water in the nowadays northwest arabian desert

the decline of the early neolithic population center of ain ghazal and corresponding earth surface processes jordan rift valley abstract ain ghazal is among the earliest large population centers known in the middle east a total of four major stratigraphic cultural units have been identified 1 the oldest middle pre pottery neolithic b mppnb unit 10 2 to 9 5 cal ka bp clearly corresponds with the early holocene maximum dead sea levels 2 the second unit consists of late pre pottery neolithic b lppnb in situ walls and hearths 3 in the subsequent ppnc 8 9 to 8 6 cal ka bp the population density at the settlement drops dramatically which corresponds with a significant drop in the dead sea level 4 the 4th stratigraphic unit is characterized by the yarmoukian rubble layer additionally there is evidence for a previously unrecognized use of the site by chalcolithic pastoralists sedimentological analyses reveal a constant increase in dust from a remote source during the entire human occupation period which correlates well with the detectable drops in climatic humidity from the dead sea as the major focus of this study we can now rule out previous notions that the yarmoukian rubble layer could have been produced by catastrophic slope scale gravitational movements to this point it appears that the neolithic mega site was abandoned due to a climatic aridification

mid holocene climate variations revealed by high resolution speleothem records from soreq cave israel and their correlation with cultural changes mid holocene 7000 4000 yr bp paleoclimate conditions were reconstructed for the eastern mediterranean region through a high resolution 3 20 yr oxygen and carbon isotopic record in a speleothem

holocene climate and cultural evolution in late prehistoric early historic west asia abstract the precipitation climatology and the underlying climate mechanisms of the eastern mediterranean west asia and the indian subcontinent are reviewed with emphasis on upper and middle tropospheric flow in the subtropics and its steering of precipitation holocene climate change of the region is summarized from proxy records the indian monsoon weakened during the holocene over its northernmost region the ganges and indus catchments and the western arabian sea southern regions the indian peninsula do not show a reduction but an increase of summer monsoon rain across the holocene the long term trend towards drier conditions in the eastern mediterranean can be linked to a regionally complex monsoon evolution abrupt climate change events such as the widespread droughts around 8200 5200 and 4200 cal yr bp are suggested to be the result of altered subtropical upper level flow over the eastern mediterranean and asia the abrupt climate change events of the holocene radically altered precipitation fundamental for cereal agriculture across the expanse of late prehistoric early historic cultures known from the archaeological record in these regions social adaptations to reduced agro production in both dry farming and irrigation agriculture regions are visible in the archaeological record during each abrupt climate change event in west asia chronological refinement in both the paleoclimate and archaeological records and transfer functions for both precipitation and agro production are needed to understand precisely the evident causal linkages

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

generalization of topmodel for a power law transmissivity profile keywords hydrologie reference hydram article 1997 003doi 10 1002 sici 1099 1085 199707 11 9 3 0 co 2 uview record in web of science record created on 2005 10 11 modified on 2016 08 08

the earth moon late accretion conundrum the distribution of iron loving elements between the mantles of the moon and earth may differ from established belief suggest two studies that determine the hafnium tungsten ratio and sulfide silicate melt partitioning of elements in the lunar mantle

abrupt climate variability since the last deglaciation based on a high resolution multi proxy peat record from nw iran the hand that rocked the cradle of civilization abstract we present a high resolution sub decadal to centennial multi proxy reconstruction of aeolian input and changes in palaeohydrological conditions based on a 13000 yr record from neor lake s peripheral peat in nw iran variations in relative abundances of refractory al zr ti and si redox sensitive fe and mobile k and rb elements total organic carbon toc 13 c toc compound specific leaf wax hydrogen isotopes d carbon accumulation rates and dust fluxes presented here fill a large gap in the existing terrestrial paleoclimate records from the interior of west asia our results suggest that a transition occurred from dry and dusty conditions during the younger dryas yd to a relatively wetter period with higher carbon accumulation rates and low aeolian input during the early holocene 9000 6000 yr bp this period was followed by relatively drier and dustier conditions during middle to late holocene which is consistent with orbital changes in insolation that affected much of the northern hemisphere numerous episodes of high aeolian input spanning a few decades to millennia are prevalent during the middle to late holocene wavelet analysis of variations in ti abundances as a proxy for aeolian input revealed notable periodicities at 230 320 and 470 years with significant periodicities centered around 820 1550 and 3110 years over the last 13000 years comparison with palaeoclimate archives from west asia the north atlantic and african lakes point to a teleconnection between north atlantic climate and the interior of west asia during the last glacial termination and the holocene epoch we further assess the potential role of abrupt climate change on early human societies by comparing our record of palaeoclimate variability with historical geological and archaeological archives from this region the terrestrial record from this study confirms previous evidence from marine sediments of the arabian sea that suggested climate change influenced the termination of the akkadian empire in addition nearly all observed episodes of enhanced dust deposition during the middle to late holocene coincided with times of drought famine and power transitions across the iranian plateau mesopotamia and the eastern mediterranean region these findings indicate that while socio economic factors are traditionally considered to shape ancient human societies in this region the influence of abrupt climate change should not be underestimated

the early holocene humid period in nw saudi arabia sediments microfossils and palaeo hydrological modelling abstract an early to mid holocene humid period has been inferred from a variety of geo bio archives of the sahara and the arabian peninsula including sabkhas palaeo lakes sand dunes wadis speleothems or marine sediments on the arabian peninsula most of these records are located in the southern and southeastern part studies from the northern part are rare this paper presents the first results from palaeo environmental and hydrological investigations on the sabkha basin of the tayma oasis northwestern saudi arabia sedimentary characteristics micro and macrofauna a digital elevation model based on dgps measurements and 14 c ams data indicate the presence of a perennial lake with a minimum depth of 13 m a stored water volume of 1 16 10 7 m 3 and a surface of 18 45 km 2 between 10 000 9000 cal bp foraminiferal test malformations and the shape of sieve pores on ostracod valves were used to detect trends in palaeo salinity and ecological stress conditions the reconstructed gradual contraction of the lake at least after 8500 cal bp reflects the long term aridisation trend on the arabian peninsula after the early holocene based on the hydrological water balance equation quantitative data on minimum palaeo rainfall during the early holocene humid period were calculated input parameters for the equation are the minimum lake level lake surface and lake volume during the peak of the early holocene humid period as well as palaeo evapotranspiration groundwater infiltration and surface runoff accordingly a perennial lake in the endorheic basin of the modern sabkha with a lake level at the same elevation as the uppermost shoreline deposit would have required a minimum annual precipitation of 150 25 mm this value amounts to c 300 of recent precipitation rates

a semi analytical model for transient flow to a subsurface tile drain the goal of this paper is to develop and test a semi analytical model for event based transient flow to a subsurface tile drain a sharp front theory was used to describe redistribution of infiltrated water in the vadose zone new approximate analytical solutions in terms of fourier series were sought for the boussinesq equation describing subsurface saturated flow subject to time dependent recharge both one and two term solutions of the series approximation were compared with observed tile hydrograph data from the purdue water quality field station wqfs in west lafayette indiana in general the models were able to capture the peaks of the tile drain hydrographs as well as the times to peak and the times of initial response to rainfall events the models performed particularly well for rainfall events with single burst hyetographs and in the prediction of the first hydrograph peak from multiple burst hyetographs though subsequent peaks could not be captured as well a further comparison of results from the one term model with those from hydrus 2d suggested that the one term model is adequate for estimating transient flow to a tile drain the solution developed here holds promise for extension to larger watersheds where the hydrology is governed by tile drains

a 20 ka sediment record from the hajar mountain range in n oman and its implication for detecting arid humid periods on the southeastern arabian peninsula abstract playa like sediments from the hajar mountain range in northern oman 22 83 n 59 00 e 1050 m asl document variations of the paleoenvironmental and paleoclimate conditions over the last 20 ka based on high resolution sediment sampling and their osl dating sedimentation rates were calculated and used as a proxy for paleorainfall the results show that the glacial to lateglacial was characterized by arid conditions with a following transitional period of even less rainfall at 10 5 ka sedimentation rates increases abruptly indicating the onset of the early holocene humid period ehhp rainfall reaches its maximum at 9 8 ka ehhp 2 and a decreasing sedimentation rate after 8 ka characterizes the arid period of the middle to late holocene variations of the hydrological regime are associated with the intensity of the boreal summer indian monsoon and its related position of the itcz for the onset of the ehhp a northerly shift of the itcz is postulated thus confirming earlier results from the southern arabian peninsula

fragility of western mediterranean landscapes during holocene rapid climate changes abstract in this paper we explore the evidence for holocene rapid climate changes rccs in western mediterranean records examining similarities and differences in the timing and nature of impacts on different components of the natural environment vegetation fluvial and coastal sedimentation fire activity soil formation marine lacustrine and fluvial archives of the western mediterranean iberian peninsula and northwest africa provide evidence for both pervasive millennial scale climatic variability and abrupt decadal to centennial scale transitions we focus in particular on three rccs characterised by high latitude cooling glacier advances and north atlantic ice rafting events the mid holocene rcc interval 6 5 cal ka bp the late holocene rcc interval 3 5 2 5 cal ka bp and the historical rcc interval known as the little ice age lia 1300 1950 ad evidence from multiple records indicates wide ranging impacts of rccs in the western mediterranean region the three rcc intervals were characterised however by contrasting hydrological situations in the western mediterranean with prevailing dry conditions including marked aridification events during the rcc intervals 6 5 and 3 5 2 5 cal ka bp and prevailing or recurrent wet conditions during the lia we examine issues of proxy sensitivity in palaeoecological and geomorphological records and evaluate examples of contrasting geomorphological responses to regional climatic triggers between humid and semi arid sectors of the western mediterranean finally we consider the long term sensitivity of the region to rapid climate change the role of threshold changes and the extent to which this region represents a fragile landscape

green ampt infiltration model for sloping surfaces 1 this work quantifies and explains the direct physical effects of slope angle on infiltration and runoff generation by extending the green ampt equation onto sloping surfaces a new extended solution using identical precipitation hydrographs was compared to the original formulation and then used to calculate the infiltration and runoff generation for different slope angles but for identical horizontal projection lengths homogeneous and isotropic soil is assumed and two different boundary conditions for vertical rainfall are studied ponded infiltration and infiltration under steady rainfall infiltration under unsteady rainfall was found to be similar to cases with steady rainfall both theoretical and numerical results show that infiltration increases with increasing slope angle for cases with ponded infiltration the slope effect was generally not significant for mild to moderate slopes but the slope effect became more important for low intensity and short duration rainfall events especially as it delayed the time for ponding it was also found that the cumulative vertical infiltration depth ihp at ponding or the initial loss increases with increasing slope angle the model was compared to richards equation on horizontal and sloping surfaces and found to perform well the model s applicability for nonuniform slopes was discussed and it was found that the model is generally applicable for isotropic and mildly anisotropic soils except for some small scale topographic elements finally the occurrence of nonvertical rainfall could increase runoff with increasing slope angle when rainfall deflects a large angle to upslope

holocene climate variability and cultural evolution in the near east from the dead sea sedimentary record abstract a comprehensive record of lake level changes in the dead sea has been reconstructed using multiple well dated sediment cores recovered from the dead sea shore interpreting the lake level changes as monitors of precipitation in the dead sea drainage area and the regional eastern mediterranean palaeoclimate we document the presence of two major wet phases 10 8 6 and 5 6 3 5 cal kyr bp and multiple abrupt arid events during the holocene the arid events in the holocene dead sea appear to coincide with major breaks in the near east cultural evolution at 8 6 8 2 4 2 3 5 cal kyr bp wetter periods are marked by the enlargement of smaller settlements and growth of farming communities in desert regions suggesting a parallelism between climate and near east cultural development

magma oceans in the inner solar system theory and observations point to the occurrence of magma ponds or oceans in the early evolution of terrestrial planets and in many early accreting planetesimals the apparent ubiquity of melting during giant accretionary impacts suggests that silicate and metallic material may be processed through multiple magma oceans before reaching solidity in a planet the processes of magma ocean formation and solidification therefore strongly influence the earliest compositional differentiation and volatile content of the terrestrial planets and they form the starting point for cooling to clement habitable conditions and for the onset of thermally driven mantle convection and plate tectonics this review focuses on evidence for magma oceans on planetesimals and planets and on research concerning the processes of compositional differentiation in the silicate magma ocean distribution and degassing of volatiles and cooling

climate forcing due to the 8200 cal yr bp event observed at early neolithic sites in the eastern mediterranean we explore the hypothesis that the abrupt drainage of laurentide lakes and associated rapid switch of the north atlantic thermohaline circulation 8200 yr ago had a catastrophic influence on neolithic civilisation in large parts of southeastern europe anatolia cyprus and the near east the event at 8200 cal yr bp is observed in a large number of high resolution climate proxies in the northern hemisphere and in many cases corresponds to markedly cold and arid conditions we identify the relevant archaeological levels of major neolithic settlements in central anatolia cyprus greece and bulgaria and examine published stratigraphic architectural cultural and geoarchaeological studies for these sites the specific archaeological events and processes we observe at a number of these sites during the study interval 8400 8000 cal yr bp lead us to refine some previously established neolithisation models the introduction of farming to south east europe occurs in all study regions thrace macedonia thessaly bulgaria near 8200 cal yr bp we observe major disruptions of neolithic cultures in the levant north syria south east anatolia central anatolia and cyprus at the same time we conclude that the 8200 cal yr bp aridity event triggered the spread of early farmers by different routes out of west asia and the near east into greece and bulgaria

environmental change and archaeology lake evolution and human occupation in the eastern sahara during the holocene abstract the west nubian palaeolake is the most large scale hydrographic evidence in the eastern sahara of the early to mid holocene wet phase that affected northern africa it is the result of a significant increase in local rainfall due to the northward shift of the tropical rainfall belt a series of fieldwork based differential gps dgps measurements along several profiles across the west nubian palaeolake basin provides the first precise topographic data from this up to a 5330 km2 large palaeolake feature in combination with sedimentological geochemical and archaeological results an almost complete picture of significant palaeoclimatic changes and human occupation during the early to mid holocene for this region is presented different stages of palaeolake evolution ranging from non existence of the lake through stable freshwater conditions to its extinction were identified in the period from 9400 to 3800 14c yr bp these lake stages coincide with phases of intensive human inhabitation between ca 6300 and 3500 14c yr bp and include at least four settlement phases distinguishable by style of pottery these are known from adjacent areas of the palaeolake region emphasizing strong prehistoric cultural connections in the eastern sahara during the highstands of the palaeolake in the early to mid holocene the dotted wavy line pottery relates to the early khartoum type culture with its supra regional distribution from the nile valley to the chad and possibly with slightly different forms even to the atlantic coast later in the holocene western nubia with its large palaeolakes and migration paths along palaeowadis such as wadi howar acted as an important natural and cultural link between the nile valley and the chad basin until the region was deserted during the fourth millennium bp

holocene forcing of the indian monsoon recorded in a stalagmite from southern oman a high resolution oxygen isotope record from a thorium uranium dated stalagmite from southern oman reflects variations in the amount of monsoon precipitation for the periods from 10 3 to 2 7 and 1 4 to 0 4 thousand years before the present ky b p between 10 3 and 8 ky b p decadal to centennial variations in monsoon precipitation are in phase with temperature fluctuations recorded in greenland ice cores indicating that early holocene monsoon intensity is largely controlled by glacial boundary conditions after approximately 8 ky b p monsoon precipitation decreases gradually in response to changing northern hemisphere summer solar insolation with decadal to multidecadal variations in monsoon precipitation being linked to solar activity

element partitioning between transition zone minerals and ultramafic melt under hydrous conditions 1 element partitioning between wadsleyite garnet and hydrous ultramafic melt has been determined at 16 gpa and 1600 c using a kawai type multi anvil high pressure apparatus element partitioning between olivine and hydrous ultramafic melt was also studied at 5 gpa and 1500 c in order to compare element partitioning behavior between wadsleyite and olivine major and trace elements analyses of the quenched melt and coexisting wadsleyite garnet and olivine were made with an epma and la icp ms respectively the experimental results demonstrate that lil rb sr ba and hfs ti zr nb hf ta th u elements are preferably incorporated into wadsleyite relative to olivine suggesting that the concentration of these elements in the hydrous transition zone could be greater than that in upper mantle our results contribute to understand magmatism and chemical differentiation in the earth s interior

high resolution x ray fluorescence core scanning analysis of les echets france sedimentary sequence new insights from chemical proxies the les echets sediment sequence has recently been the subject of a high resolution multi proxy study which revealed shifts in lake productivity linked to greenland stadials and interstadials over the last 40 ka wohlfarth et al 2008 rapid ecosystem response to abrupt climate changes during the last glacial period in western europe 40 16 ka geology 36 407 410 here we present new elemental data for this sequence as acquired using an x ray fluorescence core scanning system which provides in situ high resolution continuous multi element analyses it was found that the strength of associations between the studied elements ti rb k zr si ca sr mn and fe varied over time with changes in lake status which are ultimately driven by changes in climate increases in fine grained detrital input as indicated by ti rb k and zr rb overlap with independently established periods of lower lake productivity and are interpreted to represent more arid conditions several of these arid periods are coincident with low diatom concentrations and the timing of heinrich events h4 h3 and h2 the duration of the environmental impacts linked to the h events varied by proxy with elemental data ti and zr rb estimating shorter events than the diatom data periods of lower detrital input and coarser grain sizes agreed in time with periods of higher lake productivity the elemental data provide new insights into hydrological changes and related sediment processes within the catchment and highlight the need for multi element and multi proxy approaches when reconstructing climate change using lacustrine sediment sequences copyright 2011 john wiley sons ltd

when the desert was green grassland expansion during the early holocene in northwestern arabia abstract an early to mid holocene lake in the north of the oasis of tayma northwestern saudi arabia proved to be an excellent palynological archive a shallow probably brackish water body formed at about 9200 cal bp with the dominance of goosefoot throughout the sequence indicating the persistence of desert vegetation however distinct vegetation changes are recorded during the early holocene grasslands spread soon after 9000 cal bp and reached their maximal expansion ca 8600 8000 cal bp at about 8000 cal bp these grasslands retreated abruptly and were replaced by more drought resistant dwarf shrublands similar to the present day ecosystems the recorded early holocene grassland expansion furnishes for the first time evidence of an additional and more favourable grazing resource and thereby improved conditions for herders hunters during the early holocene in northwestern arabia which retreated abruptly due to aridification at about 8000 cal bp

reconstructing hydraulic conductivity field for hydrogeological modeling in an urban environment abstract hydrogeological analysis of flow is largely based on the concept of hydraulic conductivity in numerical hydrogeological modeling a value of hydraulic conductivity must be assigned at each element of mesh in heterogeneous geological formations this value governs the average behavior of groundwater flow within an aquifer the goals of this study are twofold 1 development of a methodology to transform the description of lithological units into local hydraulic conductivity values and 2 development of a methodology for reconstruction of hydraulic conductivity fields on a 83 km2 of the bordeaux urban area two approaches a 2d approach and a 3d approach based on geostatistical analysis are explained in details and compared for both approaches variographical analysis and ordinary kriging are carried out on the logarithmic of hydraulic conductivity and composite hydraulic conductivity is calculated using thickness weighting to get horizontal and vertical hydraulic conductivities the comparison of both approaches and the assessment of their potential and limitations suggest that the 2d approach is more appropriate than the 3d approach

a hit and run giant impact scenario abstract the formation of the moon from the debris of a slow and grazing giant impact of a mars sized impactor on the proto earth cameron and ward 1976 lunar planet sci conf canup and asphaug 2001 nature 412 708 is widely accepted today we present an alternative scenario with a hit and run collision asphaug 2010 chem erde 70 199 with a fractionally increased impact velocity and a steeper impact angle

volcanism and human prehistory in arabia abstract the cenozoic harrats lavafields of western arabia constitute one of the major volcanic areas of the world recent precise chronometric dating of volcanic rocks in harrat rahat makes it possible to outline a detailed chronology of volcanic activity likewise recent advances in archaeology have demonstrated that early humans repeatedly occupied the arabian peninsula in the pleistocene most archaeological sites in arabia correlate with phases of increased rainfall such as interglacials however we should be cautious about reducing the prehistory of arabia to simply the story of rainfall fluctuation this paper explores the impacts of volcanism on human populations in arabia as a case study of causality and scale in human environment interactions periodic environmental windows of opportunity allowed early human groups to expand into western arabia however the western highlands are also home to volcanically active areas that saw repeated eruptions in the holocene a major eruption occurred in western arabia around every 300 years and the emerging evidence for pleistocene volcanism demonstrates repeated major eruptions at the same times as early humans were occupying the area as well as offering a review of human volcanism interactions in arabian prehistory a model is proposed in which volcanic activity in western arabia may have facilitated further population dispersal as well as negative health impacts as a push factor a balanced perspective on the impacts of volcanism and associated phenomena such as earthquakes emphasises possibly positive impacts in terms of factors such as water availability and the formation of fertile volcanic soils these positive impacts may have offered pull factors and facilitated regional occupation longer than would be predicted based on climatic variables alone this framework offers not only an explanation for some of the characteristics of the arabian archaeological record but potentially offers part of the explanation for how early human populations were able to pass through the saharo arabian arid belt from our african birthplace to populate the rest of the world

climatic forcing of eastern mediterranean deep water formation and benthic ecosystems during the past 22 000 years abstract lateglacial and holocene faunal and stable isotope records from benthic foraminifers in the eastern mediterranean sea ems suggest a high spatiotemporal variability of deep water oxygenation and biogeochemical processes at the sea floor during that time changes in the oxygenation and food availability of the deep sea ecosystems are closely linked to the hydrology of the ems borderlands they reflect orbital and suborbital climate variations of the high northern latitudes and the african monsoon system during the last glacial maximum cool surface waters and high evaporation resulted in maximum convection and oxic deep waters in all sub basins strong wind induced mixing fostered surface water production with seasonal phytodetritus fluxes during the glacial termination and the holocene oxygenation and food availability of deep sea benthic ecosystems were characterized by a pronounced regional differentiation local deep water formation and trophic conditions were particularly variable in the northern aegean sea as a response to changes in riverine runoff and black sea outflow during the interval of sapropel s1 formation in the early holocene average oxygen levels decreased exponentially with increasing water depth suggesting a basin wide shallowing of vertical convection superimposed by local signals in the northernmost aegean sea deep water ventilation persisted during the early period of s1 formation owing to temperature driven local convection and the absence of low salinity black sea outflow at the same time severe temporary anoxia occurred in the eastern levantine basin at water depths as shallow as 900 m this area was likely influenced by enhanced nutrient input of the nile river that resulted in high organic matter fluxes and related high oxygen consumption rates in the water column in the southern aegean and levantine seas we observe a gradual increase in deep water residence times preceding s1 formation by approximately 1 1 5 kyr once oxygen levels fell below a critical threshold the benthic ecosystems collapsed almost synchronously with the onset of s1 deposition the recovery of benthic ecosystems during the terminal phase of s1 formation is controlled by subsequently deeper convection and re ventilation over a period of approximately 1500 years after the re ventilation of the various sub basins had been completed during the middle and late holocene deep water renewal was more or less similar to recent rates during that time deep sea ecosystem variability was driven by short term changes in food quantity and quality as well as in seasonality all of which are linked to millennial scale changes in riverine runoff and associated nutrient input

depositional history and archaeology of the central lake mungo lunette willandra lakes southeast australia abstract lake mungo presently a dry lake in the semi arid zone of southeastern australia preserves a unique record of human settlement and past environmental change within the transverse lunette that built up on its downwind margin the lunette is 30 km long and the variable morphology along its length suggests spatial variability in deposition over time consequently this presents differential potential for the preservation of past activity traces of different ages along the lunette earlier work at lake mungo focused primarily on the southern section of the lunette where two ritual burials of considerable antiquity were found here we describe the depositional history of the central section of the lake mungo lunette together with the first single grain optically stimulated luminescence osl chronology of the full stratigraphic sequence and of three hearths we thereby lay the foundation for systematic investigation of the distribution of archaeological traces through the sedimentary record the older depositional units lower and upper mungo were deposited ca 50 40 ka and 34 ka respectively and are substantially thinner in the central section of the lunette compared with the south by contrast the overlying unit of interbedded sands and clayey sands arumpo zanci units deposited ca 25 14 ka is markedly thicker and dominates the stratigraphic sequence in the central portion of the lunette although the sequence broadly reflects previous models of the lunette s depositional history and changing hydrological conditions our results indicate spatially variable deposition of sediments possibly as a result of changes in prevailing wind regimes archaeological traces are exposed in all stratigraphic units deposited after ca 50 ka including sediments deposited after the final lake drying ca 15 ka indicating human occupation of the area under a range of palaeoenvironmental conditions dating and stratigraphical examination of individual hearth features demonstrates that even within individual stratigraphic units human occupation persisted under variable conditions mid holocene occupation of the area following the final lake retreat took place during a period of relatively humid climate