prolonged magmatism juvenile nature and tectonic evolution of the chinese altai nw china evidence from zircon u pb and hf isotopic study of paleozoic granitoids abstract paleozoic granitoid magmatism played an important role in the tectonic evolution of the chinese altai and zircon u pb and hf isotopic compositions have been determined for samples from eleven granitic plutons batholiths the jiadengyu gneissic granitic pluton yielded a zircon u pb age of 479 ma and thus it does not represent precambrian basement as suggested previously our results and published data demonstrate that voluminous granitoids were continuously emplaced over more than 30 area of the chinese altai during the period from 447 ma to 368 ma with a climax at ca 400 ma ages for zircon overgrowth rims demonstrate additional thermal events at ca 360 and 280 ma respectively positive e hf t values 0 to 9 of normal magmatic zircons suggest that the granitoid magmas were derived from juvenile sources xenocrystic zircon cores are 543 421 ma old and also give positive e hf t values 2 5 to 12 suggesting their origin as early crystallized minerals in the magma chambers or as inherited cores from newly accreted meterials the strong magmatism at ca 400 ma significantly changed the hf isotopic composition of the magma source by substantial input of juvenile material in a relatively short period geophysical geological and geochemical data support that ridge subduction was a possible mechanism for the strong magmatism ca 400 ma and the above mentioned change of hf isotopic composition in the magma source

fossils from quaternary fluvial archives sources of biostratigraphical biogeographical and palaeoclimatic evidence fluvial sedimentary archives have the potential to preserve a wide variety of palaeontological evidence ranging from robust bones and teeth found in coarse gravel aggradations to delicate insect remains and plant macrofossils from fine grained deposits over the last decade advances in quaternary biostratigraphy based on vertebrate and invertebrate fossils primarily mammals and molluscs have been made in many parts of the world resulting in improved relative chronologies for fluviatile sequences complementary fossil groups such as insects ostracods and plant macrofossils are also increasingly used in multi proxy palaeoclimatic and palaeoenvironmental reconstructions allowing direct comparison of the climates and environments that prevailed at different times across widely separated regions this paper reviews these topics on a regional basis with an emphasis on the latest published information and represents an update to the 2007 review compiled by the flag inspired igcp 449 biostratigraphy subgroup disparities in the level of detail available for different regions can largely be attributed to varying potential for preservation of fossil material which is especially poor in areas of non calcareous bedrock but to some extent also reflect research priorities in different parts of the world recognition of the value of biostratigraphical and palaeoclimatic frameworks which have been refined over many decades in the core regions for such research particularly for the late middle and late pleistocene of nw europe has focussed attention on the need to accumulate similar palaeontological datasets in areas lacking such long research histories although the emerging datasets from these understudied regions currently allow only tentative conclusions to be drawn they represent an important stage in the development of independent biostratigraphical and palaeoenvironmental schemes which can then be compared and contrasted

a synthesis of zircon u pb ages and hf isotopic compositions of granitoids from southwest mongolia implications for crustal nature and tectonic evolution of the altai superterrane abstract granitoid magmatism is extensively developed in the altai superterrane but the timing of magmatic events is not so well determined in this study twelve granitoid intrusions from southwest mongolia were dated by the zircon u pb method and analyzed for zircon hf isotopic compositions the new age data indicated three phases of magmatic emplacement middle paleozoic 398 350 ma late paleozoic 317 289 ma and triassic ca 244 211 ma the first phase magmatism is mainly composed of hornblende bearing i type granitoids formed during a long lasting subduction process in the early to middle paleozoic the second phase magmatism was manifested by a few small intrusions primarily distributed along the erqis fault zone and probably formed in a transitional tectonic regime from subduction to post tectonic setting in the late paleozoic the third phase magmatism was represented by post tectonic granitoids emplaced in an intraplate extensional setting model ages that were calculated using the composition of new continental crust are predominantly neoproterozoic to early paleozoic indicating that the protoliths of granitoids were likely dominated by paleozoic juvenile crust with minor neoproterozoic materials the altai superterrane was a huge paleozoic tectonic collage produced by amalgamation of subduction accretion complexes in the margin of the siberian continent and the tuva mongol microcontinent

temporal variability of transformation formation and subduction rates of upper southern ocean waters 1 kinematic and thermodynamic approaches are employed to diagnose the time dependent transformation formation and subduction rates of upper southern ocean waters in a multidecadal simulation within an eddy permitting coupled climate model in the subantarctic mode water samw density class a convergence of diapycnal volume fluxes leads to the formation and inflation of mixed layer waters during winter a portion of this water is detrained into the pycnocline during early spring when surface heating restratifies the deep winter mixed layer the annually averaged subduction rate of samw shows pronounced interannual variability partly controlled by the temporal tendency of the winter mixed layer depth from one year to the next no significant correlation between the southern annular mode sam and the isopycnally integrated samw subduction rate is apparent however ekman downwelling upwelling intensities modulated by the sam influence interannual variations in the subduction rates of water masses lighter and heavier than samw with an opposing sign during positive phases of the sam more pycnocline waters are entrained into the mixed layer and transformed into lighter densities within the antarctic intermediate water density class whereas more mixed layer waters are subducted into the pycnocline within the subtropical mode water density class such distinct responses of upper southern ocean water masses to the sam are qualitatively consistent with observational constraints based on a comparison between offline kinematic and thermodynamic diagnostics we infer that diapycnal mixing within the mixed layer may contribute up to 50 of the formation rate of samw on interannual timescales

palaeoclimate in the saharan and arabian deserts during the middle palaeolithic and the potential for hominin dispersals to disperse out of sub saharan africa it was necessary for hominins to cross the deserts of either the sahara and or arabia thus understanding the palaeoclimate of the saharo arabian region is central to determining the role these deserts played in the peopling of the planet when did they act as barriers and when were they more humid opening dispersal routes across them to address these questions we have conducted a temporal and spatial evaluation of dated sites from 20 to 350 ka using combined probability density function pdf and geographical information system gis analyses of all sites dated using uranium thorium u th or optically stimulated luminescence osl methods radiocarbon dates were not considered because of contamination problems in this time range the results show that during mis 2 there is little evidence for humidity in arabia as would be expected during the height of the last glacial maximum however the sahara shows a sharp rise in probability at the beginning of mis 2 peaking near the boundary with mis 3 at 29 ka there appear to be brief periods of humidity in mis 3 and 6 though at different times in the sahara ca 37 44 138 154 and 180 ka and arabia ca 40 54 and 163 ka during mis 5 both regions show much evidence for humidity with pdf peaks corresponding to insolation maxima though not all maxima are represented in either the saharan or arabian record this situation can be explained by eccentricity modulated precession when eccentricity is strong insolation is enhanced but also more variable and the desert climate is generally more humid particularly at times of high insolation the opposite happens when eccentricity is low and deserts tend to be more arid but local factors exert more of an influence on climate affecting the timing and strength of the brief humid periods experienced so that they no longer coincide with insolation maxima the spatial distribution of humid sites is compatible with a number of different modern human dispersal theories southern arabia experienced humid periods centred on 54 ka and 125 ka and this could have facilitated dispersal from east africa to southern arabia and beyond via the bab el mandab the sahara shows considerable evidence for humidity during mis 5 and may have had dispersal across its expanse at this time

frontogenesis subduction and cross front exchange at upper ocean fronts the subduction of water at upper ocean fronts driven by internal instabilities is investigated a simple analytic model which assumes conservation of potential density and potential vorticity is used to characterize the expected structure of subducted parcels as a function of the surface layer depth and the length scale of the parcel parcels subducted from a deep surface layer will be characterized by anomalously low potential vorticity and anticyclonic circulation while shallow surface layers result in subducted parcels with high potential vorticity and cyclonic circulation a nonlinear isopycnal primitive equation model is used to demonstrate how baroclinic instability and the resulting frontogenesis force the subduction of parcels below and across the front frontogenesis generates vertical velocities of 0 30 m d and ageostrophic cross front flows of 3 to 5 cm s the subduction is achieved by the deep ageostrophic flow which carries water from the surface layer below and across the front the subducted parcels quickly develop a circulation through balanced adjustment anticyclonic for deep surface layers and cyclonic for shallow surface layers the characteristics of parcels subducted in winter conditions closely resemble a class of eddies called submesoscale coherent vortices the horizontal and vertical scales of the vortices are determined by the frontogenetic mechanism and the depth of the surface layer the total permanent subduction rate is estimated to be 20 m yr for frontal subduction driven by frontogenesis although local and temporary subduction can be much larger the subducted anticyclonic vortices are often coupled to upper ocean cyclonic vortices thus forming a baroclinic dipole that propagates at approximately 3 5 cm s and is capable of transporting the anomalous water properties far from the region of formation similarities with observations in the north atlantic subtropical convergence zone and near the gulf stream are discussed

biotite stability in peraluminous granitic melts compositional dependence and application to the generation of two mica granites in the south bohemian batholith bohemian massif czech republic abstract crystallization experiments have been conducted in the system na2o k2o mgo feo al2o3 sio2 h2o with 4 normative corundum in order to constrain the stability of biotite as a function of water activity and the mg of biotite mg mg fetotal in equilibrium with peraluminous granitic melts the temperature at which biotite breakdown starts is strongly dependent on the mg of biotite at 500 mpa the temperature of biotite breakdown to form orthopyroxene increases from 750 c to 830 c as the mg of biotite increases from 0 4 to 0 5 considering that the system investigated is relevant for ca poor peraluminous biotite bearing rocks metapelites the biotite dehydration curves obtained are used to discuss the melting reactions and the temperatures that lead to the formation of two distinct types of two mica granites found in the south bohemian batholith specifically the eisgarn and destna granites the phase relationships were determined experimentally for the composition of these two granites in order to constrain the composition of the biotite in equilibrium with the melt in the protoliths we demonstrate that eisgarn granitic melts may have been generated at temperatures in the range 830 850 c from melting reactions involving biotite with a mg up to 0 5 as a reactant in contrast destna granitic melts cannot have been generated from dehydration melting reactions involving biotite

interior water mass variability in the southern hemisphere oceans during the last decade abstractusing an argo dataset and the eccov4 reanalysis a volume budget was performed to address the main mechanisms driving the volume change of the interior water masses in the southern hemisphe

southern ocean thermocline ventilation abstract an approximate mass volume budget in the surface layer of the southern ocean is used to investigate the intensity and regional variability of the ventilation process discussed here in terms of subduction and upwelling ventilation resulting from ekman pumping is estimated from satellite winds the geostrophic mean component is assessed from a climatology strengthened with argo data and the eddy induced advection is included via the parameterization of gent and mcwilliams together with eddy mixing estimates all three components contribute significantly to ventilation finally the seasonal cycle of the upper ocean is resolved using argo data the circumpolar averaged circulation shows an upwelling in the antarctic intermediate water aaiw density classes which is carried north into a zone of dense subantarctic mode water samw subduction although no consistent net production is found in the light samw density classes a large subduction of subtropical mode water stmw is observed the s

remote sensing and gis techniques for reconstructing arabian palaeohydrology and identifying archaeological sites freshwater availability is critical for human survival and in the saharo arabian desert belt repeated fluctuations between aridity and humidity over the quaternary mean the distribution of freshwater was likely a primary control upon routes and opportunities for hominin dispersals however our knowledge of the spatio temporal distribution of palaeohydrological resources within arabia during mid late pleistocene episodes of climatic amelioration remains limited in this paper we outline a combined method for remotely mapping the location of palaeodrainage and palaeolakes in currently arid regions that were formerly subject to more humid conditions we demonstrate the potential of this approach by mapping palaeochannels across the whole arabian peninsula and palaeolakes and marshes for select regions covering c 10 of its surface our palaeodrainage mapping is based upon quantitative thresholding of hydrosheds data which applies flow routing to digital elevation model dem data while our palaeolake mapping uses an innovative method where spectral classification of landsat thematic mapper tm imagery is used to detect palaeolake deposits within endorheic closed basins before modelling maximum lake extents by flooding the basin to the level of the elevation of the highest detected deposit field survey in the nefud desert and the dawadmi and shuwaymis regions of saudi arabia indicates accuracies of 86 for palaeodrainage mapping and 96 for identifying former palaeolake basins 73 accuracy of classification of individual deposits the palaeolake mapping method has also demonstrated potential for identifying surface and stratified archaeological site locations with 76 of the surveyed palaeolake basins containing archaeological material including stratified palaeolithic archaeology initial examination of palaeodrainage in relation to archaeological sites indicates a relationship between mapped features and previously recorded palaeolithic sites an example of the application of these data for period specific regional palaeohydrological and archaeological reconstructions is presented for a region of northern saudi arabia covering the southern nefud desert and adjacent lava fields

intensive surveys of the azores front 2 inferring the geostrophic and vertical velocity fields the geostrophic and vertical velocity fields are inferred using density and horizontal velocity data from three seasoar acoustic doppler current profiler surveys of the azores front the analysis is a two step procedure consisting of 1 objective analyses to reflect the observed length scales and 2 dynamical adjustments so that the density field is statically stable and the velocity field is in geostrophic balance the vertical velocity is inferred using a version of the quasi geostrophic omega equation in which the stratification is allowed to vary in the horizontal the resulting vertical velocity peaks at 2 10 4 m s 1 at 200 300 m there is a tendency for the denser water to the north of the front to be downwelled while the warmer water to the south is upwelled the implied heat flux exceeds 10 w m 2 near 100 m depth so the upper 100 m is warmed while the lower water column is cooled tending to stratify the upper ocean ageostrophic horizontal flow is toward the dense side of the front at the surface the dominant terms in the density balance are time rate of change and horizontal advection the inferred circulation cells may be an important mechanism of subduction in the upper ocean

zircon u pb geochronology and hf isotopic composition of granitiods in russian altai mountain central asian orogenic belt the central asian orogenic belt caob consists of many tectonic terranes with distinct origin and complicated evolutionary history understanding of individual block is crucial for the reconstruction of the geodynamic history of the gigantic accetionary collage this study presents zircon u pb ages and hf isotopes for the granitoid rocks in the russian altai mountain range including gorny altai altai mongolian terrane and ctus suture zone between them in order to clarify the timing of granitic magmatism source nature continental crustal growth and tectonic evolution our dating results suggest that granitic magmatism of the russian altai mountain range occurred in three major episodes including 445 429 ma 410 360 ma and 241 ma zircons from these granitoids yield comparable positive ehf t values and neoproterozoic crustal model ages which favor the interpretation that the juvenile crustal materials produced in the early stage of the caob were probably dominant sources for the paleozoic magmatism in the region the inference is also supported by widespread occurrence of short lived juvenile materials including ophiolites seamount relics and arc assemblages in the northern caob consequently the paleozoic massive granitic rocks maybe do not represent continental crustal growth at the time when they were emplaced but rather record reworking of relatively juvenile proterozoic crustal rocks although mantle derived mafic magma was possibly involved to serve as heat engine during granitic magma generation the early triassic granitic intrusion may be a product in an intra plate environment as the case of same type rocks in the adjacent areas the positive ehf t values 1 81 7 47 and corresponding hf model ages 0 80 1 16 ga together with evidence of petrology are consistent with the interpretation that the magma source of the triassic granitic intrusion was derived from enriched mantle and melted under an usually high temperature condition likely due to basaltic magma that underplated the lower crust our data combined with evidence of the regional geology enable us to conclude that the gorny altai and altai mongolian terranes possibly have similar tectonic natures but represent two separate accretionary systems before devonian collision the accretion and amalgamation processes resulted in the paleozoic granitoid magmatism and caused the two terranes to merge as a composite tectonic domain at the siberian continental margin

inferring the subduction rate and period over the north atlantic abstract the annual rate at which mixed layer fluid is transferred into the permanent thermocline that is the annual subduction rate sann and the effective subduction period x1d4af eff is inferred from climatological data in the north atlantic from its kinematic definition sann is obtained by summing the vertical velocity at the base of the winter mixed layer with the lateral induction of fluid through the sloping base of the winter mixed layer geostrophic velocity fields computed from the levitus climatology assuming a level of no motion at 2 5 km are used the vertical velocity at the base of the mixed layer is deduced from observed surface ekman pumping velocities and linear vorticity balance a plausible pattern of sann is obtained with subduction rates over the subtropical gyre approaching 100 m yr twice the maximum rate of ekman pumping the subduction period x1d4af eff is found by viewing subduction as a transformation process converting mixed layer fluid into stratified thermocline fluid the effective

magmatic sequences in the halasu cu belt nw china trigger for the paleozoic porphyry cu mineralization in the chinese altay east junggar abstract the halasu porphyry copper belt situated in the east junggar is one of the major porphyry copper belts in xinjiang uygur autonomous region northwest china copper and molybdenum mineralization occurs as disseminated sulfides or veinlets mainly in granodiorite porphyry and diorite porphyry with the intense development of zoned alteration from potassic through sericitic to an outer zone of propylitic alteration new la icp ms zircon u pb dating reveals that magmatism in the belt can be divided into three periods during the middle devonian and early carboniferous namely the pre mineralization stage of 390 ma syn mineralization stage of 382 372 ma and post mineralization stage of 350 320 ma the syn mineralization intrusions are calc alkaline whereas pre and post mineralization intrusions are shoshonitic and high k calc alkaline the syn mineralization intrusions are enriched in highly incompatible trace elements but depleted in nb ta hf and ti relative to the pre and post mineralization intrusions zircon trace elements analyses demonstrate a negative correlation between ti in zircon temperatures and oxygen fugacity ore bearing syn mineralization granitoids are characterized by higher water content oxygen fugacity and low temperatures with higher mineralization potential than pre and post mineralization ones these characteristics together with the geochemical signature of the intrusions suggest that the ore bearing porphyries are derived from relative high h2o magma reservoir the remarkably homogeneous hf isotopic compositions ehf t 8 to 13 from syn mineralization intrusions span over 10 m y suggesting the existence of a long lived reservoir beneath halasu belt during the middle devonian all the intrusions have low initial 87sr 86sr values 0 703935 to 0 707172 high end t values 4 7 to 5 5 and young crustal model ages 650 to 750 ma combined with the mantle derived pb isotope characteristics the sr nd hf data suggest that the parental magma was probably derived from flat subduction triggered partial melting of juvenile crust generated during subduction accretionary process with no significant input of old crust whereas pre mineralization and post mineralization intrusions are supposed to emplaced in immature island arc setting and post orogenic setting respectively

fluvial deposits as an archive of early human activity progress during the 20 years of the fluvial archives group fluvial sedimentary archives are important repositories for lower and middle palaeolithic artefacts throughout the old world especially in europe where the beginning of their study coincided with the realisation that early humans were of great antiquity now that many river terrace sequences can be reliably dated and correlated with the globally valid marine isotope record potentially useful patterns can be recognized in the distribution of the find spots of the artefacts that constitute the large collections that were assembled during the years of manual gravel extraction this paper reviews the advances during the past two decades in knowledge of hominin occupation based on artefact occurrences in fluvial contexts in europe asia and africa as such it is an update of a comparable review in 2007 at the end of igcp project no 449 which had instigated the compilation of fluvial records from around the world during 2000 2004 under the auspices of the fluvial archives group an overarching finding is the confirmation of the well established view that in europe there is a demarcation between handaxe making in the west and flake core industries in the east although on a wider scale that pattern is undermined by the increased numbers of lower palaeolithic bifaces now recognized in east asia it is also apparent that although it seems to have appeared at different places and at different times in the later lower palaeolithic the arrival of levallois technology as a global phenomenon was similarly timed across the area occupied by middle pleistocene hominins at around 0 3 ma

middle late quaternary palaeoclimate variability from lake and wetland deposits in the nefud desert northern arabia abstract records of former lake and wetland development in present day arid hyper arid environments provide an important source of information for palaeoclimatic and palaeoenvironmental studies in arabia such records are typically confined to eccentricity modulated insolation maxima and are often spatially and temporally discontinuous here we present records from a single locality in northern arabia of wetter interludes during both global interglacial and glacial conditions providing a unique opportunity to examine the nature of these events in a common setting at jubbah in the southern nefud desert lake and wetland deposits reveal the repeated formation of a water body within a large endorheic basin over the past ca 360 kyr lake wetland formation occurred during mis 11 9 7 5 3 and the early holocene assisted by local topographic controls and spring recharge palaeoenvironmental and palaeoecological data reveal the existence of a large still water body formed during either mis 11 or 9 ca 363 ka and basin wide alluviation followed by lake formation during mis 7 ca 212 ka during mis 5e ca 130 ka a large freshwater lake occupied the basin while during mis 5a ca 80 ka the basin contained a shallow wetland and freshwater lake complex lake wetland formation also occurred during early mis 3 ca 60 ka at the terminal pleistocene holocene transition ca 12 5 ka and the early middle holocene ca 9 6 5 ka phases of lake and wetland development coincided with human occupation of the basin during the middle palaeolithic epipalaeolithic and neolithic periods highlighting the significance of the region for early demographic change

stability of phlogopite in granitic melts an experimental investigation water saturated and water undersaturated experiments ah2o 1 0 and 0 5 were performed in the temperature range 780 1040 c at 2 and 5 kbar in order to determine the upper thermal stability of phlogopite in granitic melts starting compositions were a subaluminous mixtures of 20 wt synthetic phlogopite and 80 wt synthetic anhydrous haplogranitic glass b peraluminous mixtures normative corundum 4 of 20 wt synthetic phlogopite and 80 wt synthetic anhydrous peraluminous haplogranitic glass the molar quartz albite orthoclase ratio of the glasses of the 2 kbar runs was 35 39 26 and that of the 5 kbar runs 30 42 28 in the subaluminous system phlogopite is stable up to 820 c at ah2o 1 0 and up to 780 c at ah2o 0 5 at higher temperatures it is replaced by enstatite in the peraluminous system phlogopite has a remarkably higher thermal stability up to 1000 c at 5 kbar and ah2o 1 0 and there is a temperature interval of 80 c at ah2o 1 0 and 90 100 c at ah2o 0 5 between the first appearance of enstatite and the disappearance of phlogopite in the peraluminous system phlogopite is a solid solution ss of phlogopite muscovite talc and eastonite components the crystalline product of the phlogopitess breakdown reaction is an aluminous enstatite the mgo content of the melt depends on the normative corundum content of the starting material and the run temperature it is independent of pressure in the subaluminous system the mgo content ranges between 0 05 and 0 3 wt in the temperature interval 780 880 c at both investigated water activities the mgo content of the peraluminous melts at ah2o 1 0 ranges between 0 4 and 1 7 wt and at ah2o 0 5 between 0 2 and 1 4 wt in the temperature range 780 980 c

middle and late pleistocene humid periods recorded in palaeolake deposits of the nafud desert saudi arabia present climate in the nafud desert of northern saudi arabia is hyper arid and moisture brought by north westerly winds scarcely reaches the region the existence of abundant palaeolake sediments provides evidence for a considerably wetter climate in the past however the existing chronological framework of these deposits is solely based on radiocarbon dating of questionable reliability due to potential post depositional contamination with younger 14c by using luminescence dating we show that the lake deposits were not formed between 40 and 20 ka as suggested previously but approximately ca 410 ka 320 ka 200 ka 125 ka and 100 ka ago all of these humid phases are in good agreement with those recorded in lake sediments and speleothems from southern arabia surprisingly no holocene lake deposits were identified geological characteristics of the deposits and diatom analysis suggest that a single perennial lake covered the entire south western nafud ca 320 ka ago in contrast lakes of the 200 ka 125 ka and 100 ka humid intervals were smaller and restricted to interdune depressions of a pre existing dune relief the concurrent occurrence of humid phases in the nafud southern arabia and the eastern mediterranean suggests that moisture in northern arabia originated either from the mediterranean due to more frequent frontal depression systems or from stronger indian monsoon circulation respectively however based on previously published climate model simulations and palaecolimate evidence from central arabia and the negev desert we argue that humid climate conditions in the nafud were probably caused by a stronger african monsoon and a distinct change in zonal atmospheric circulation

hydrography of the eastern south pacific ocean results from the sonne 102 cruise may june 1995 abstract full depth conductivity temperature depth hydrographic measurements were taken in may june 1995 along 28 15 35 15 and 43 15 s from the chilean coast to 86 88 w from the r v sonne sections of potential temperature salinity neutral density and oxygen are presented to illustrate the water column structure in this sparsely sampled region a more comprehensive database on all available hydrographic data from the region was compiled these data and available meteorological data are used to help in the interpretation of the sonne results a number of important features found in the sections are discussed including a shallow salinity minimum apparently ventilated from south of 37 s salt fingering as a possible mechanism to transport high salinity subtropical water into the shallow salinity minimum equatorial subsurface water subantarctic mode water and antarctic intermediate water geostrophic calculations of alongshore flow show the poleward peru chile undercurrent at each of the three sections with a poleward descending core and peak velocities of 10 cm s 1 as in earlier works a deep pacific outflow is found near the chilean coast part of a clockwise deep circulation in the chile basin

cation deficient phlogopitic mica exsolution in diopside from garnet peridotite in sulu china article i nfo deep subduction and return to the surface of sediments and other continental rocks is now well known forming terranes of ultrahigh pressure metamorphism uhpm a common constituent of these terranes is garnet peridotite mantle rock that has been brought to the surface along with the returning subducted material microstructures of these peridotites especially precipitates within their constituent minerals offer promise of providing information not only about their depth of origin but also about the subduction environment here we report exsolution lamellae of cation deficient phlogopitic mica within diopside of a drill core from the uhpm terrane of sulu china detailed analysis by transmission electron microscopy tem shows these precipitates to be phlogopitic mica that is highly complex both structurally and compositionally with a significant component of the 10 a phase a talc like phase stable only at quite high pressures several mica polytypes are present the simplest one 1m being the most cation deficient the presence of a significant 30 10 a phase component in the mica suggests a means of expanding the 10 a phase bridge for subduction of h2o to deep mantle depths published by elsevier b v

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

a 1 year mesoscale simulation of the northeast atlantic mixed layer heat and mass budgets during the pomme experiment 1 a simplified oceanic model is used to perform a realistic yearlong simulation to study fine scale mixed layer processes in an area of the northeast atlantic 21 15 w 38 45 n during the programme ocean multidisciplinaire meso echelle pomme experiment september 2000 october 2001 this simplified three dimensional oceanic model is obtained by degenerating the primitive equations system by prescribing continuously analysis derived geostrophic currents ug called guide into the momentum equation by the substitution of the horizontal pressure gradient the realism of the simulated mesoscale structures was validated by a comparison with in situ mesoscale and submesoscale data and results from the geostrophic adjustment to the guide with this adjustment being applied at all scales this model was able to simulate energetic small horizontal scales taking place around stirring eddies and frontal regions moreover filamentary mixed layer depth structures were simulated and correlated to intense vertical velocities confined in the mixed layer the circulation structure during pomme consisted of three quasi permanent mesoscale eddies and a front the mixed layer heat and mass budgets were thus strongly driven by the horizontal advection and the vertical transport associated with this mesoscale circulation although no effective detrainment or entrainment occurred at the domain scale three regions were found to be the site of intense detrainment around anticyclonic and cyclonic mesoscale eddies and along an axis of strong currents in which the lateral induction and the vertical velocity at the mixed layer base are the major components driving the detrainment respectively

reactivation of the pleistocene trans arabian wadi ad dawasir fluvial system saudi arabia during the holocene humid phase the wadi ad dawasir fluvial system in central saudi arabia is investigated using remote sensing and sedimentology in combination with bio proxy analyses molluscs and ostracods age control is provided by radiocarbon as well as luminescence dating using both quartz and feldspar grains it is shown that the fluvial system was active from the asir mountains across the partially sand covered interior of the arabian peninsula to the arabian gulf during the holocene humid period sedimentology and faunal analysis reveal the presence of perennial streams and a permanent freshwater lake in the distal reach of the dawasir system that are synchronous with fluvial accumulation in the headwaters of its major tributary wadi tathlith the increased runoff during the holocene led to a re activation of streams that largely followed pre existing late pleistocene courses and eroded into older sediments the absence of holocene lakes in most of the rub al khali implies that trans arabian rivers were mainly fed by precipitation in the asir mountains monsoonal rainfall was apparently stronger there as well as in the northern south eastern and southern part of the arabian peninsula southern yemen and oman but it apparently did not directly affect the interior during the holocene the palaeoenvironmental reconstruction shows a narrow trans arabian green freshwater corridor as the result of phases of sustained flow lasting up to several centuries the permanent availability of water and subsistence for wildlife provided a favourable environment for human occupation as documented by neolithic stone tools that are found all along wadi ad dawasir

palaeohydrological corridors for hominin dispersals in the middle east 250 70 000 years ago abstract the timing and extent of palaeoenvironmental connections between northeast africa the levant and the arabian peninsula during the middle and late pleistocene are critical to debates surrounding dispersals of hominins including movements of homo sapiens out of africa although there is evidence that synchronous episodes of climatic amelioration during the late middle and late pleistocene may have allowed connections to form between northern africa and western asia a number of palaeoclimate models indicate the continued existence of an arid barrier between northern arabia and the levant here we evaluate the palaeoenvironmental setting for hominin dispersals between and within northeast africa and southwest asia during marine isotope stages mis 7 5 using reconstructions of surface freshwater availability as an environmental proxy we use remotely sensed data to map palaeohydrological features lakes wetlands and rivers across the presently hyper arid areas of northern arabia and surrounding regions integrating these results with palaeoclimate models palaeoenvironmental proxy data and absolute dating to determine when these features were active our analyses suggest limited potential for dispersals during mis 7 and 6 but indicate the formation of a palaeohydrological corridor the tabuk corridor between the levant and the arabian interior during the mis 6 5e glacial interglacial transition and during mis 5e a recurrence of this corridor following a slightly different route also occurred during mis 5a these palaeohydrological and terrestrial data can be used to establish when proposed routes for hominin dispersals became viable furthermore the distribution of arabian archaeological sites with affinities to levantine assemblages some of which are associated with homo sapiens fossils and the relative density of middle palaeolithic assemblages within the tabuk corridor are consistent with it being utilised for dispersals at various times

strategies for nested and eddy permitting state estimation 1 both ocean process and prediction studies increasingly rely on state estimation i e data assimilation to provide the most complete representation of how the ocean circulates this study applies the formalism and methodology of state estimation recently developed for the global coarse resolution problem to eddy permitting state estimation in regional domains two major challenges exist for a state estimate that is nested inside a global state estimate 1 estimation of open boundary conditions consistent with information interior and exterior to the regional domain and 2 estimation with the higher resolution models of regional studies here a least squares cost function defines the problem of minimizing the misfit between a north atlantic regional general circulation model and actual observations including those of the subduction experiment a first experiment using a novel multiscale method to constrain the large scale regional circulation shows that the use of the adjoint of both an eddy permitting model and its coarse resolution twin leads to a solution of the least squares problem in a computationally practical way therefore no fundamental obstacle exists to constraining the large scale regional circulation nested within a global circulation a second experiment in the north atlantic shows that the model circulation can be constrained to the full observational signal including eddy variability as observed at selected point locations both experiments in this study produce eddy permitting state estimates which are exactly self consistent with the equations of motion as embodied by a general circulation model therefore dynamical balances can be diagnosed and easily interpreted in particular a companion paper uses the state estimates to determine eddy subduction rates in the north atlantic

epipalaeolithic occupation and palaeoenvironments of the southern nefud desert saudi arabia during the terminal pleistocene and early holocene the transition from the terminal pleistocene to the early holocene is poorly represented in the geological and archaeological records of northern arabia and the climatic conditions that prevailed in the region during that period are unclear here we present a new record from the site of al rabyah in the jubbah basin southern nefud desert saudi arabia where a sequence of fossiliferous lacustrine and palustrine deposits containing an archaeological assemblage is preserved sedimentological and palaeoenvironmental investigations both at al rabyah and elsewhere in the jubbah area indicate phases of humid conditions during which shallow lakes developed in the basin separated by drier periods at al rabyah the end of a terminal pleistocene phase of lake expansion has been dated to 12 2 ka using optically stimulated luminescence osl with a mid holocene humid phase dated to after 6 6 ka palaeoecological reconstructions based primarily on non marine molluscs and ostracods from the younger lacustrine deposits indicate a relatively shallow body of freshwater surrounded by moist well vegetated environments a lithic assemblage characterized by bladelets and geometric microliths was excavated from sediments attributed to a drier climatic phase dated to 10 1 ka the lithic artefact types exhibit similarities to epipalaeolithic industries of the levant and their occurrence well beyond the core region of such assemblages and at a significantly later date has important implications for understanding interactions between levantine and arabian populations during the terminal pleistocene early holocene we suggest that the presence of foraging populations in the southern nefud during periods of drier climate is due to the prolonged presence of a freshwater oasis in the jubbah basin during the terminal pleistocene early holocene which enabled them to subsist in the region when neighbouring areas of northern arabia and the levant were increasingly hostile

middle paleolithic occupation on a marine isotope stage 5 lakeshore in the nefud desert saudi arabia major hydrological variations associated with glacial and interglacial climates in north africa and the levant have been related to middle paleolithic occupations and dispersals but suitable archaeological sites to explore such relationships are rare on the arabian peninsula here we report the discovery of middle paleolithic assemblages in the nefud desert of northern arabia associated with stratified deposits dated to 75 000 years ago the site is located in close proximity to a substantial relict lake and indicates that middle paleolithic hominins penetrated deeply into the arabian peninsula to inhabit landscapes vegetated by grasses and some trees our discovery supports the hypothesis of range expansion by middle paleolithic populations into arabia during the final humid phase of marine isotope stage 5 when environmental conditions were still favorable

human occupation of the arabian empty quarter during mis 5 evidence from mundafan al buhayrah saudi arabia the empty quarter or rub al khali of the arabian peninsula is the largest continuous sandy desert in the world it has been known for several decades that late pleistocene and holocene deposits representing phases of wetter climate are preserved there these sequences have yielded palaeontological evidence in the form of a variety of vertebrate and invertebrate fossils and have been dated using various radiometric techniques however evidence for human presence during these wetter phases has until now been ephemeral here we report on the first stratified and dated archaeology from the empty quarter recovered from the site of mundafan al buhayrah mdf 61 human occupation at the site represented by stone tools has been dated to the later part of marine isotope stage mis 5 using multiple luminescence dating techniques multigrain and single grain osl tt osl the sequence consists primarily of lacustrine and palustrine sediments from which evidence for changing local environmental conditions has been obtained through analysis of fossil assemblages phytoliths and non marine molluscs and ostracods the discovery of securely dated archaeological material at 100 to 80 ka in the empty quarter has important implications for hypotheses concerning the timing and routes of dispersal of homo sapiens out of africa which have been much debated consequently the data presented here fill a crucial gap in palaeoenvironmental and archaeological understanding of the southern arabian interior fossils of h sapiens in the levant also dated to mis 5 together with middle palaeolithic archaeological sites in arabia and india are thought to represent the earliest dispersal of our species out of africa we suggest that the widespread occurrence of similar lithic technologies across southern asia coupled with a growing body of evidence for environmental amelioration across the saharo arabian belt indicates that occupation of the levant by h sapiens during mis 5 may not have been a brief localized failed dispersal but part of a wider demographic expansion

a taxonomic and taphonomic study of pleistocene fossil deposits from the western nefud desert saudi arabia over the past decade a growing interest has developed on the archaeology palaeontology and palaeoenvironments of the arabian peninsula it is now clear that hominins repeatedly dispersed into arabia notably during pluvial interglacial periods when much of the peninsula was characterised by a semiarid grassland environment during the intervening glacial phases however grasslands were replaced with arid and hyperarid deserts these millennial scale climatic fluctuations have subjected bones and fossils to a dramatic suite of environmental conditions affecting their fossilisation and preservation yet as relatively few palaeontological assemblages have been reported from the pleistocene of arabia our understanding of the preservational pathways that skeletal elements can take in these types of environments is lacking here we report the first widespread taxonomic and taphonomic assessment of arabian fossil deposits novel fossil fauna are described and overall the fauna are consistent with a well watered semiarid grassland environment likewise the taphonomic results suggest that bones were deposited under more humid conditions than present in the region today however fossils often exhibit significant attrition obscuring and fragmenting most finds these are likely tied to wind abrasion insolation and salt weathering following fossilisation and exhumation processes particularly prevalent in desert environments

a high resolution simulation of the ocean during the pomme experiment mesoscale variability and near surface processes 1 this article is the second part of a modeling study of upper ocean mesoscale physical processes in an area of the northeast atlantic that was extensively sampled during the programme ocean multidisciplinaire meso echelle pomme experiment october 2000 september 2001 the model is a high resolution regional version of the ocean general circulation model opa integrated from february to may 2001 the mesoscale upper ocean dynamics has been carefully validated in a first paper paci et al 2005 in the present article the simulation is used to analyze the contribution of mesoscale eddies to the mixed layer processes during the period that controls the annual subduction rate and the characteristics of the subducted water mesoscale eddies account for a significant part of the mixed layer heat salt and water budgets through mesoscale and submesoscale structures acting on the horizontal advective terms they represent respectively 52 and 66 of the horizontal advection of temperature and salinity and 70 of the lateral induction they also induce an earlier and more intense restratification the domain averaged detrainment appears to be reduced by more than 15 by mesoscale eddies and reaches about 0 8 sv however these eddies increase the density of the detrained water some dense water likely to be involved in the formation of subpolar mode water is detrained by them in a way that maximizes its chance to be effectively subducted in the area

middle late quaternary paleoclimate of northern margins of the saharan arabian desert reconstruction from speleothems of negev desert israel abstract speleothems in arid and hyper arid areas of negev desert israel are used in paleoclimate reconstruction of northern margins of saharan arabian desert focused on the following objectives 1 precise u th dating of the timing of speleothem growth as an indicator of periods of humid climate i e positive effective precipitation 2 the origin of rainfall using the speleothem 18 o and changes in spatial pattern of speleothem deposition and speleothem thickness along a north south transect 3 changes of vegetation cover based on speleothem 13 c variations during the last 350 ka major humid periods referred to herein as negev humid periods nhp occurred in the central and southern negev desert at 350 310 ka nhp 4 310 290 ka nhp 3 220 190 ka nhp 2 and 142 109 ka nhp 1 nhp 4 nhp 2 and nhp 1 are interglacial events whereas nhp 3 is associated with a glacial period during nhp 1 2 and 3 the thickness and volume of the speleothems decrease from the north to the south and in the most southern part of the region only a very thin flowstone layer formed during nhp 1 with no speleothem deposition occurring during nhp 2 and 3 these data imply that the eastern mediterranean sea was the major source of the rainfall in northern and central negev more negative speleothem 18 o values relative to central parts of israel soreq cave are attributed to rayleigh distillation because of the increasing distance from the mediterranean sea speleothem deposition during the nhp 4 in the southern negev was more intensive than in most of the central negev suggesting the prominence of the tropical rain source decrease in speleothem 13 c during nhp events indicates growth of the vegetation cover nevertheless the ranges of 13 c values show that the vegetation remained semi desert c4 type throughout the nhps with an additional significant carbon fraction coming from the host rock and the atmosphere these observations together with small thickness of the speleothem layers favor that nhp events consisted of clusters of very short humid episodes interspersed with long droughts nhp events were contemporaneous with climate periods with monsoon index of 51 cal cm 2 day and with the formation of sapropel layers in the mediterranean sea such simultaneous intensification of the monsoon and atlantic mediterranean cyclones is probably related to the weakening of the high pressure cell above sub tropical atlantic ocean which enabled more rainfall to penetrate into the saharan arabian desert from the north and south the contemporaneous occurrence of the nhp events and the increased monsoon rainfall could have opened migration corridors creating climatic windows of opportunity for dispersals of hominids and animals out of the african continent

eemian tropical and subtropical african moisture transport an isotope modelling study during the last interglacial insolation maximum eemian mis 5e the tropical and subtropical african hydrological cycle was enhanced during boreal summer months the climate anomalies are examined with a general circulation model echam4 that is equipped with a module for the direct simulation of 18o and deuterium h218o and hdo respectively in all components of the hydrological cycle a mechanism is proposed to explain the physical processes that lead to the modelled anomalies differential surface heating due to anomalies in orbital insolation forcing induce a zonal flow which results in enhanced moisture advection and precipitation increased cloud cover reduces incoming short wave radiation and induces a cooling between 10 n and 20 n the isotopic composition of rainfall at these latitudes is therefore significantly altered increased amount of precipitation and stronger advection of moisture from the atlantic result in isotopically more depleted rainfall in the eemian east african subtropics compared to pre industrial climate the east west gradient of the isotopic rainfall composition reverses in the eemian simulation towards depleted values in the east compared to more depleted western african rainfall in the pre industrial simulation the modelled re distribution of 18o and d is the result of a change in the forcing of the zonal flow anomaly we conclude that the orbitally induced forcing for african monsoon maxima extends further eastward over the continent and leaves a distinct isotopic signal that can be tested against proxy archives such as lake sediment cores from the ethiopian region

an early mis 3 pluvial phase in southeast arabia climatic and archaeological implications climatic changes in arabia are of critical importance to our understanding of both monsoon variability and the dispersal of anatomically modern humans amh out of africa the timing of dispersal is associated with the occurrence of pluvial periods during marine isotope stage mis 5 ca 130 74 ka after which arid conditions between ca 74 and 10 5 ka are thought to have restricted further migration and range expansion within the arabian interior whilst a number of records indicate that this phase of aridity was punctuated by an increase in monsoon strength during mis 3 uncertainties regarding the precision of terrestrial records and suitability of marine archives as records of precipitation mean that the occurrence of this pluvial remains debated here we present evidence from a series of relict lake deposits within southeastern arabia which formed at the onset of mis 3 ca 61 58 ka at this time the incursion of monsoon rainfall into the arabian interior activated a network of channels associated with an alluvial fan system along the western flanks of the hajar mountains leading to lake formation multiproxy evidence indicates that precipitation increases intermittently recharged fluvial systems within the region leading to lake expansion in distal fan zones conversely decreased precipitation led to reduced channel flow lake contraction and a shift to saline conditions these findings are in contrast to the many other palaeoclimatic records from arabia which suggest that during mis 3 the latitudinal position of the monsoon was substantially further south and did not penetrate the peninsula additionally the occurrence of increased rainfall at this time challenges the notion that the climate of arabia following mis 5 was too harsh to permit the further range expansion of indigenous communities

middle to late pleistocene human habitation in the western nefud desert saudi arabia abstract the nefud desert is crucial for resolving debates concerning hominin demography and behaviour in the saharo arabian belt situated at the interface between the mediterranean westerlies and african monsoonal climate systems the nefud lies at the centre of the arid zone crossed by homo sapiens dispersing into eurasia and the edges of the southernmost known extent of the neanderthal range in 2013 the palaeodeserts project conducted an intensive survey of the western nefud to 1 evaluate pleistocene population dynamics in this important region of the saharo arabian belt and 2 contribute towards understanding early modern human range expansions and interactions between different hominin species thirteen lower and middle palaeolithic sites were discovered in association with palaeolake basins one of the sites t is al ghadah may feature the earliest middle palaeolithic assemblage of arabia preliminary analyses show that the lower and middle palaeolithic sites discovered display diverse technological characteristics indicating that the nefud was important for population turnovers and exchanges throughout the pleistocene periodic environmental amelioration appears to have attracted hominin incursions into the region and subsequent ephemeral occupations structured around lakes and to a lesser extent raw material sources however differences between the lower and middle palaeolithic sites are indicative of greater mobility during the later pleistocene a rarity of formal tools but strong similarities in lithic production techniques are also suggestive of demographic affinities across the nefud during the pleistocene and perhaps beyond these preliminary results support the view that the arabian peninsula was a critically important region of southwest asia during the late pleistocene in which demographic responses to climatic amelioration may have structured connectivity across the saharo arabian belt the levant and as far as india

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

first evidence for episodic flooding events in the arid interior of central saudi arabia over the last 60 ka although evidence for quaternary environmental changes in the arabian peninsula is now growing research has mostly been conducted in the united arab emirates uae and in the sultanate of oman there have been virtually no recent studies in saudi arabia especially in the central region such as around al quwaiayh in this area there are a series of outwash plains developed along the eastern edge of the arabian shield that formed in the late quaternary four sedimentary sections which are representative of the deposits that have accumulated have been studied and five luminescence ages obtained these are the first luminescence ages acquired from quaternary sediments in central saudi arabia the preserved fluvial deposits in the study area have formed during humid events at ca 54 ka ca 39 ka and ca 0 8 ka in more recent times aeolian sands have been encroaching on to the distal parts of the outwash plains copyright 2008 john wiley sons ltd

frontal dynamics in a california current system shallow front 1 frontal processes and tracer structure 1 the three dimensional dynamics in a shallow front are examined using density and current data from two surveys 100 km offshore of monterey bay california survey 1 is forced by down front winds and both surveys have considerable cross front density gradients and flow curvature the maximum rossby numbers on the dense side reached maxima of 0 60 in survey 1 and 0 45 in survey 2 downwelling occurs in regions of confluence frontogenesis associated with potential vorticity pv change and thermal wind imbalance streamers of particulate matter and pv are advected southeastward by the frontal jet and downward nonlinear ekman currents advect dense water over light water in the presence of down front winds which leads to upwelling along the front and downwelling on the light side of the front at sites of active ageostrophic secondary circulation asc induced by frontogenesis or ekman effects the observed cross front ageostrophic velocity is consistent with the diagnosed vertical velocity furthermore in survey 2 ageostrophic divergence may play an important role at the curved front presumably counteracting quasi geostrophic frontogenesis due to isopycnal confluence downward frictional vertical pv flux below the surface extracts pv from the pycnocline and reinforces the frontogenetic vertical pv flux pv destruction at the surface is inferred from a low pv anomaly below the mixed layer in survey 2 since the magnitude of the frontogenetic asc is only twice the magnitude of ekman suction external forcing may have a considerable impact on the vertical heat and pv fluxes

the greening of arabia multiple opportunities for human occupation of the arabian peninsula during the late pleistocene inferred from an ensemble of climate model simulations climate models are potentially useful tools for addressing human dispersals and demographic change the arabian peninsula is becoming increasingly significant in the story of human dispersals out of africa during the late pleistocene although characterised largely by arid environments today emerging climate records indicate that the peninsula was wetter many times in the past suggesting that the region may have been inhabited considerably more than hitherto thought explaining the origins and spatial distribution of increased rainfall is challenging because palaeoenvironmental research in the region is in an early developmental stage we address environmental oscillations by assembling and analysing an ensemble of five global climate models ccsm3 cosmos hadcm3 kcm and noresm we focus on precipitation as the variable is key for the development of lakes rivers and savannas the climate models generated here were compared with published palaeoenvironmental data such as palaeolakes speleothems and alluvial fan records as a means of validation all five models showed to varying degrees that the arabia peninsula was significantly wetter than today during the last interglacial 130 ka and 126 125 ka timeslices and that the main source of increased rainfall was from the north african summer monsoon rather than the indian ocean monsoon or from mediterranean climate patterns where available 104 ka mis 5c 56 ka early mis 3 and 21 ka lgm timeslices showed rainfall was present but not as extensive as during the last interglacial the results favour the hypothesis that humans potentially moved out of africa and into arabia on multiple occasions during pluvial phases of the late pleistocene

continuity and change in the lithic industries of the jurreru valley india before and after the toba eruption lithic assemblage variability is synthesized and discussed for seven open sites and one rockshelter from the jurreru valley in the kurnool district of southern india the sites span the last c 77 000 years and provide an invaluable record of cultural change spanning the toba super eruption 74 thousand years ago ka as well as the transition to the microlithic lithic evidence documents long term continuities before and after the eruption that indicates the toba eruption had a minimal impact on the underlying system of flake production in the valley the analysis also indicates that many cores from above and below the toba ash are technologically extremely similar to those from early modern human sites in sub saharan africa southeast asia and australia suggesting modern humans may have entered india before the toba eruption as part of an early eastward dispersal from africa

effects of mesoscale eddies on subduction and distribution of subtropical mode water in an eddy resolving ogcm of the western north pacific abstract the effects of mesoscale eddies on the subduction and distribution of the north pacific subtropical mode water stmw are investigated using an eddy resolving ocean general circulation model ogcm first the subduction rate is calculated and the contribution of eddies to the subduction of stmw is estimated it is found that eddy subduction significantly contributes to the total subduction of stmw second eddy thickness transport and diapycnal flux are directly diagnosed to investigate the large scale eddy induced transport process of stmw the large southward eddy thickness transport in the stmw core density is consistent with eddy subduction the eddy transport on the isopycnal surface of stmw is directed down the thickness gradient and traverses the mean flow the meridional eddy transport streamfunction indicates two eddy circulation cells south of 30 n associated with the circulation of stmw these cells flatten density surfaces similar to the effect of the gent and mcwilliams gm schem

human occupation of the northern arabian interior during early marine isotope stage 3 the early part of marine isotope stage mis 3 ca 60 50 ka is a crucial period for studying human demography and behaviour in south west asia and how these relate to climatic changes however the archaeological and palaeoenvironmental records for mis 3 in critical areas such as the arabian peninsula remain poorly developed here we present findings from the al marrat basin in the nefud desert which provides the first clear evidence for both increased humidity and human occupation of the interior of northern arabia during early mis 3 a middle palaeolithic assemblage dated by optically stimulated luminescence to ca 55 ka was found stratified within a sequence of relict palustrine deposits indicative of shallow water body formation in the al marrat basin hominin presence in northern arabia at this time coincides with the intensification and northward displacement of monsoon rainfall systems during a period of maximum insolation these findings add to a growing corpus of palaeoenvironmental evidence which indicates that the arabian interior was neither arid nor unpopulated during early mis 3 and that hydrodynamic responses to enhanced moisture availability facilitated demographic expansions into the arabian interior

subduction on the northern and southern flanks of the gulf stream abstract sections of temperature salinity dissolved oxygen and velocity were made crossing the gulf stream in late january 2006 to investigate the role of frontal processes in the formation of eighteen degree water edw the subtropical mode water of the north atlantic the sections were nominally perpendicular to the stream and measured in a lagrangian frame by following a floating spar buoy drifting in the gulf stream s warm core during the survey edw was isolated from the mixed layer by the stratified seasonal pycnocline suggesting that edw was not yet actively being formed at this time in the season and at the longitudes over which the survey was conducted 64 70 w however in two of the sections the seasonal pycnocline in the core of the gulf stream was broken by an intrusion of cold fresh weakly stratified water nearly saturated in oxygen that appears to have been subducted from the surface mixed layer north of the stream the intrusion was identified in three of the sections in profi

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

on the role of the azores current in the ventilation of the north atlantic ocean three high resolution ocean circulation models of the north atlantic differing chiefly in their description of the vertical coordinate are used to examine the ventilation of the north atlantic subtropical gyre all the models produce mode waters of realistic densities in the sargasso sea and the european basin but have azores currents of differing strengths which are categorised as strong of realistic transport intermediate and weak these differences have a critical impact upon the ventilation of the gyre most importantly the strong azores current forms an effective barrier to the southward ventilation of eastern north atlantic water from the northern european basin initially driving it southwestwards into the central gyre before turning it back eastwards again in a general cyclonic circulation north of the current the intermediate and weak azores currents instead allow the southward ventilation of this water mass near the european and african coasts the situation in nature appears to be intermediate between these two cases with the azores current acting as a partial block the study also raises the possibility of the azores current forming an advective connection between the sargasso sea mode waters in the western basin and modes of similar densities found in the eastern basin on the southern side of the current although there are high levels of variability in the extent of these lighter modes in the eastern basin in nature this postulate is supported by a number of observational studies in addition the present study also provides some support for the local production of madeira mode water in the eastern basin associated with retroflecting current branches on the southern side of the azores current overall the azores current is therefore likely to have a critical impact upon the ventilation of the subtropical gyre over a large area rather than just locally affecting the potential vorticity and density structure of the upper ocean between subtropical latitudes and the northern european basin the study also contributes to an ongoing community effort to assess the realism of our current generation of ocean models