developing a framework of quaternary dune accumulation in the northern rub al khali arabia located at the crossroads between africa and eurasia arabia occupies a pivotal position for human migration and dispersal during the late pleistocene deducing the timing of humid and arid phases is critical to understanding when the rub al khali desert acted as a barrier to human movement and settlement recent geological mapping in the northern part of the rub al khali has enabled the quaternary history of the region to be put into a regional stratigraphical framework in addition to the active dunes two significant palaeodune sequences have been identified dating of key sections has enabled a chronology of dune accretion and stabilisation to be determined in addition previously published optically stimulated luminescence osl dates have been put in their proper stratigraphical context from which a record of late pleistocene dune activity can be constructed the results indicate the record of dune activity in the northern rub al khali is preservation limited and is synchronous with humid events driven by the incursion of the indian ocean monsoon

the role of oceanic forcing in mid holocene northern hemisphere climatic change previous model investigations suggested that changes in orbital forcing and feedbacks associated with northward expansion of the boreal forest were both required to explain the full magnitude of enhanced high latitude northern hemisphere summer warming at 6 ka thus implying that biospheric feedbacks decreased planetary albedo associated with forest expansion may be large in the future foley et al 1994 tempo testing earth system models with paleo observations 1996 before the magnitude of past biospheric and other feedbacks can be estimated with confidence however the role of realistic high latitude oceanic forcing i e sea surface temperature sst increases and sea ice reductions should also be considered here we review existing paleoceanographic observations that suggest portions of the north atlantic were up to 4 c warmer than today at 6 ka we then combine our estimates of mid holocene north atlantic sst and sea ice conditions with new climate model simulations to suggest that a significant portion of high latitude summer warming at 6 ka in the northern hemisphere can be accounted for by altered orbital forcing ssts and sea ice relative to today our results underscore the importance of incorporating realistic boundary conditions when using paleoenvironmental data to evaluate the climate system s sensitivity to altered forcing and suggest that high latitude oceanic feedbacks were major contributors to enhanced high latitude summer warming in the northern hemisphere at 6 ka

a record of holocene climate change from lake geochemical analyses in southeastern arabia lacustrine sediments from southeastern arabia reveal variations in lake level corresponding to changes in the strength and duration of indian ocean monsoon iom summer rainfall and winter cyclonic rainfall the late glacial holocene transition of the region was characterised by the development of mega linear dunes these dunes became stabilised and vegetated during the early holocene and interdunal lakes formed in response to the incursion of the iom at approximately 8500 cal yr bp with the development of c3 dominated savanna grasslands the iom weakened ca 6000 cal yr bp with the onset of regional aridity aeolian sedimentation and dune reactivation and accretion despite this reduction in precipitation the lake was maintained by winter dominated rainfall there was a shift to drier adapted c4 grasslands across the dune field lake sediment geochemical analyses record precipitation minima at 8200 5000 and 4200 cal yr bp that coincide with bond events in the north atlantic a number of these events correspond with changes in cultural periods suggesting that climate was a key mechanism affecting human occupation and exploitation of this region

epidote in calcalkaline magmas an experimental study of stability phase relationships and the role of epidote in magmatic evolution experiments on tonalite and granodiorite were performed at conditions ranging from 2 1 to 18 kbar and 550 to 850 c to establish the magmatic stability field of epidote as a function of p t and f02 at water saturated conditions and f02 buffered by nno epidote has a wide magmatic stability field in tonalite at 13 kbar this field extends from the wet solidus at 630 to 790 0c the low pressure intersection of the magmatic epidote crystallization reaction and the h20 saturated tonalite solidus and hence the minimum pressure for magmatic epidote occurs at about 5 kbar the clapeyron slopes of epidote melting reactions are moderately positive in p t space at pressures below the intersection of the epidote melting and the gamet in reactions at 13 kbar 790 c at this intersection epidote reaches its maximal thermal stability 790 c in tonalite h20 in the presence of garnet that is above 14 kbar epidote melting reactions have steep negative clapeyron slopes in p t space at p t conditions near the low pressure intersection of the epidote melting reaction with the water saturated solidus experiments were also performed with f02 buffered by hm at these oxidizing conditions the magmatic stability field of epidote is enlarged down to a pressure of about 3 kbar in granodiorite the stability of epidote has been investigated at pressures from 7 5 to 18 kbar with respect to the tonalite the epidote out reaction is located almost at the same p t conditions at 10 kbar but the maximum thermal stability is about 50 c lower toward higher pressures although few experiments indicate that epidote stability does not increase dramatically with decreasing water activity at present state it is not possible to predict melting and crystallization behavior of epidote at waterundersaturated conditions modal abundances of epidote are low 05 vol in the presence of major 40 vol melt fractions thus epidote in calc alkaline magmatic rocks is not likely to affect major elements strongly by fractional crystallization

latest pleistocene and holocene dune construction at the north eastern edge of the rub al khali united arab emirates abstract optical dating of two dune pro les developed in linear dunes in ras alkhaimah united arab emirates has been used to establish the timing and rateof dune accretion one section at awa was over 17 m high while that at idhnwas over 40 m high the awa dune appears to have accumulated very rapidly 10 000 years ago with a vertical accumulation rate of about 3ae3mka 1 theidhn dune appears to have accumulated over the past 1000 years with 20 m ofsediment accumulating in a time period of about 270 years the awa dunemay have accumulated in response to the transgression of the persian gulf byrising sea levels in late pleistocene and holocene times the idhn dune mayhave accumulated rapidly because of intensi ed human activity a short livedclimatic event or because it may periodically be reactivated after erosion by uvial action at its base keywords linear dune optical dating rub al khali sand accumulation introductionthere remains some uncertainty surrounding thestyle and timing of deposition of large aeoliandunes with authors supporting both gradual andpunctuated models of dune development for adiscussion see thomas 1997 this divergence ofopinion results from both the general absence ofdating control within dunes in most studies anddif culties in gaining exposures within some ofthe larger dune bedforms the purpose of thispaper is to establish a chronology of dunedevelopment for two thick 10 m dune sectionsexcavated within large complex linear dunesfrom within the rub al khali near ras alkhaimah in the north of the united arabemirates fig 1 the sites were selected becauseof the availability of thick fresh sections inrecently excavated moist sand with an area of around 600 000 km

high pressure amphibolite granulite facies metamorphism in the paleoproterozoic rudall complex central western australia abstract the rudall complex forms the basement of the paleoproterozoic to neoproterozoic paterson orogen which was deformed during at least three major orogenies the complex comprises a sequence of metamorphosed clastic and chemical sediments and basalts deposited in a marginal basin environment prior to extensive felsic intrusion deformation of the sequence during the first yapungku orogeny between 2000 and 1760 ma included extensive thrust stacking from ene to wsw the thermal peak of the associated high pressure metamorphism was late to post tectonic with respect to this deformation thermobarometry on amphibolites and mafic granulites that contain various combinations of the minerals hornblende plagioclase quartz garnet othopyroxene and clinopyroxene indicates that temperatures peaked at around 800 c while pressures reached 1200 mpa the late timing of peak temperatures together with the presence in some amphibolites of amphibole plagioclase symplectitic coronas around garnet indicates a steeply decompressive clockwise p t t path peak metamorphic pressures indicate that the crust was locally thickened by at least 40 km during an event that showed similarities to phanerozoic collisional tectonics it is suggested that this deformational and metamorphic event records the collision between the pilbara craton and a continent to the northeast the paleoproterozoic evolution of australia has previously been attributed to ensialic processes characterised by low pressure metamorphism and anti clockwise p t t paths the metamorphic history of the rudall complex is not consistent with this view and the documented high pressure metamorphism is broadly synchronous with a medium pressure metamorphic event in central australia the strangways orogeny and possibly also in northwestern australia the capricorn orogeny collisional plate tectonic processes played a significant role in the paleoproterozoic evolution of northern australia

interpreting geoproxies of late quaternary climate change in african drylands implications for understanding environmental change and early human behaviour abstract climate and environmental change in the late quaternary are widely regarded as key drivers of early human development and dispersal in africa robust records of change are required to assess the nature of potential impacts today s late quaternary palaeoenvironmental palaeoclimate reconstructions from the interior southern african basin kalahari are more spatially detailed have a stronger chronometric underpinning and span a longer time range than those of 10 20 years ago but are no less controversial reconstructions for the last 150 ka are usually interpreted in terms of changes in hydrological balance from conditions more humid or more arid than today and expressed in climatological terms as the changing latitudinal interplay between monsoon easterlies and tropical and mid latitude westerlies with more data than ever before why then is the record not yet delivering a more coherent picture of regional climate change this paper deliberately addresses current challenges and controversies including issues often ignored or neglected with the view that it is essential to do so if more robust interpretations of the past are to be generated in the future sources of palaeo data from the interior are predominantly geoproxies reconstructions not based on highly resolved organic or isotope records but on interpretation of spatially extensive geomorphological proxies of past environments despite being increasingly datable using osl their inclusion in syntheses has proved complex not least when interpretations appear to conflict with records from other sources consequently they are sometimes removed from regional syntheses of climate change these omissions are often replaced by spatially exaggerated interpretations of higher quality local records allowing more spatially coherent timeslice interpretations to be presented yet this is counter intuitive to the spatial complexity of conditions present in the palaeoenvironmental proxies or in climatic and environmental systems today in addition the quest to link regional records to master records from ice and ocean cores can force interpretation within a temporal scale that may be inappropriate for their analysis underplaying the reality of complexity within the environmental system there are not necessarily good or bad records of terrestrial palaeoenvironments in interior southern africa rather there are records that contain different suites of information about past land surface hydrological and climate conditions preserved at temporal scales which can sometimes be incomparable consideration of these factors may resolve apparent conflicts between datasets resulting in a better understanding of past environmental dynamics and revealing the nature of environmental variability which may be a key facet to which human development has responded

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

mapping the geochemistry of the northern rub al khali using multispectral remote sensing techniques spatial variations in sand sea geochemistry relate to mixing of different sediment sources and to variations in weathering due to problems of accessibility adequate spatial coverage cannot be achieved using field surveys alone however maps of geochemical composition produced from remotely sensed data can be calibrated against limited field data and the results extrapolated over large inaccessible areas this technique is applied to part of the rub al khali in the northern united arab emirates trend surface analysis of the results suggests that the sand sea at this location can be modelled as an east west mixing zone of two spectral components terrestrial reddened quartz sands and marine carbonate sands optical dating of these sediments suggests that dune emplacement occurred rapidly around 10 ka bp when sea level was rising rapidly the spatial distribution of mineralogical components suggests that this phase of dune emplacement resulted from coastal dune sands being driven inland during marine transgression thereby becoming mixed with rubified terrestrial sands copyright 2001 john wiley sons ltd

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

geoarchaeology of holocene oasis formation hydro agricultural management and climate change in masafi southeast arabia uae oases are subject to decreasing resources and changing human activities fully aware of their rich heritage the united arab emirates uae have undertaken work to preserve and revitalize these oases however there is a clear lack of understanding of the dynamic links between climate change hydraulic and agricultural management and socioeconomic activities to clarify these links our team conducted a systematic geoarchaeological geophysical spatial and chronological study of the masafi oasis uae results indicate the existence of a natural humid area as early as the late pleistocene 18 cal ka bp these conditions persist during the early mid holocene with drainage activation and soil development 12 6 3 ka during the late holocene after the emergence of the artificial oasis around 3250 cal yr bp cycles of intense management suggesting water availability 3250 2380 cal yr bp 550 cal yr bp alternate with episodes of fluvial detritism 2380 1870 cal yr bp 550 cal yr bp and scattered evidence of farming activities with complex hydroclimatic signatures 2300 550 cal yr bp these results together with regional environmental data indicate that water and soil resources were available and exploited strategically throughout the holocene despite adverse climatic conditions and the oasis of masafi could have acted as a desert refugium

geomorphological and palaeoenvironmental investigations in the southeastern arabian gulf region and the implication for the archaeology of the region abstract during the late quaternary the climate of arabia has fluctuated between periods of higher rainfall and fluvial activity dominated by the influence of the indian ocean monsoon iom and drier arid conditions under the influence of the westerlies this has left a rich legacy of landforms from which temporal and spatial patterns of environmental change are reconstructed the coastal desert region of the southeastern arabian gulf has been a focal point for human settlement since 8000 cal yr bp the region is strategically located on an important trade route between two cradles of civilization namely mesopotamia and the indus changes in the evolution and modification of this landscape under varying climatic conditions have influenced humans living in and exploiting this landscape for food and water raw materials and trade routes in this study geomorphological and palaeoenvironmental investigations are integrated to provide a framework of environmental change for the late glacial and early mid holocene periods against which the archaeology of the area can be set the late glacial and earliest holocene was characterised by intense aridity and accumulation of mega linear dunes driven by the shamal winds in the arabian gulf region this continued into the earliest part of the holocene whilst southern arabia was under the influence of the iom the monsoon rains migrated into the gulf region between 8500 6000 cal bp during this time semi nomadic herders occupied this region and grazing their animals in a landscape covered with c3 savanna grassland the neolithic peoples also practised hunting and fishing and the collection of shellfish was an important activity pottery shows links with mesopotamia at this time from 6000 cal bp the iom retreated south and rainfall was derived from winterly westerly sources under drier conditions a switch occurred to a sparser cover of c4 grasses from 4500 cal bp the climate became much drier with the development of stronger westerly summer shamal winds and the reactivation of dunes across the region an intense arid period occurred at 4100 bp which corresponds with major drought conditions in mesopotamia and the indus region which led to major changes in society this event occurs at a major transition in the arabian gulf bronze age archaeological record with a decline in population and trade the last 4000 yr has largely been characterised by arid conditions similar to those found in the region today

late quaternary humidity and aridity dynamics in the northeast rub al khali united arab emirates implications for early human dispersal and occupation of eastern arabia the major driver of palaeoclimatic dynamics over the southeast arabian region is the varying latitudinal interface between the westerly driven shamaal winds and a northward branch of the southwesterly indian ocean summer monsoon iom at present this latter system is restricted in extent to the southern coastal regions of yemen and oman monsoonal winds are widely believed to have increased in strength and penetrated much further north across southeast arabia at various intervals during the quaternary resulting in a series of humid phases which early studies suggested focussed within mis 3 and mis 1 recent speleothem studies from oman and uae have indicated humidity within mis 5 which with current debates surrounding early human dispersal and occupation could be significant for affirming the regional potential for early occupation we investigate two new geoproxy suites from al ain and tawi asmar northern uae in the presently hyper arid rub al khali sand sea that preserve evidence of multiple episodes of aeolian deposition and humidity in the form of fluvial gravels sands and silts and dune sands 35 osl ages demonstrate humid episodes occurred in mis 5e 5a and the early holocene with a major dry dune building phase in late mis 3 and the onset of dry conditions again from 6 ka the fluvial sedimentary evidence from mis 5e and 5a suggest that the present hyper arid desert landscape of the northeastern rub al khali was at those times represented by an environment experiencing significant seasonal wadi flow this provides an environmental context that supports recent studies indicating archaeological visibility in arabia dating from mis 5 and the presence of anatomically modern humans in arabia at this time

alluvial fan records from southeast arabia reveal multiple windows for human dispersal the dispersal of human populations out of africa into arabia was most likely linked to episodes of climatic amelioration when increased monsoon rainfall led to the activation of drainage systems improved freshwater availability and the development of regional vegetation here we present the first dated terrestrial record from southeast arabia that provides evidence for increased rainfall and the expansion of vegetation during both glacial and interglacial periods findings from extensive alluvial fan deposits indicate that drainage system activation occurred during marine isotope stage mis 6 ca 160 150 ka mis 5 ca 130 75 ka and during early mis 3 ca 55 ka the development of active freshwater systems during these periods corresponds with monsoon intensity increases during insolation maxima suggesting that humid periods in arabia were not confined to eccentricity paced deglaciations and providing paleoenvironmental support for multiple windows of opportunity for dispersal out of africa during the late pleistocene

reproducibility and utility of dune luminescence chronologies abstract optically stimulated luminescence osl dating of dune deposits has increasingly been used as a tool to investigate the response of aeolian systems to environmental change amalgamation of individual dune accumulation chronologies has been employed in order to distinguish regional from local geomorphic responses to change however advances in dating have produced chronologies of increasing complexity in particular questions regarding the interpretation of dune ages have been raised including over the most appropriate method to evaluate the significance of suites of osl ages when local noisy and discontinuous records are combined in this paper these issues are reviewed and the reproducibility of dune chronologies is assessed osl ages from two cores sampled from the same dune in the northeast rub al khali united arab emirates are presented and compared alongside an analysis of previously published dune ages dated to within the last 30 ka distinct periods of aeolian activity and preservation are identified which can be tied to regional climatic and environmental changes this case study is used to address fundamental questions that are persistently asked of dune dating studies including the appropriate spatial scale over which to infer environmental and climatic change based on dune chronologies whether chronological hiatuses can be interpreted how to most appropriately combine and display datasets and the relationship between geomorphic and palaeoclimatic signals chronological profiles reflect localised responses to environmental variability and climatic forcing and amalgamation of datasets with consideration of sampling resolution is required otherwise local factors are always likely to dominate using net accumulation rates to display ages may provide an informative approach of analysing and presenting dune osl chronologies less susceptible to biases resulting from insufficient sampling resolution

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

palaeoenvironmental and sea level changes during the holocene in eastern saudi arabia and their implications for neolithic populations abstract this paper presents the key findings of a multidisciplinary study investigating the nature and timing of coastal landscape evolution in eastern saudi arabia during the holocene to date most sea level reconstructions for the arabo persian gulf are based on uncalibrated 14c ages without correction for marine reservoir effects or lack precision with regard to the effects of neotectonic changes indicators of sea level used errors in elevation of sedimentary units used and the relationship with actual tides as a consequence the nature and timing of relative sea level rsl changes during the late pleistocene and holocene remain poorly understood to help address this we use sea level index points slips based on calibrated 14c ages to present a rsl curve for the central southern gulf of saudi arabia from coastal sabkha deposits near the archaeological site of dosariyah the sediments record rapid transgression during the early holocene with a mid holocene high stand immediately prior to 6880 6560 cal bp when the upper limit for the palaeo mean highest high tide water mhhw was 2 8 3 10 m above present day mean sea level transgression continued until shortly after 5575 5310 cal bp with an upper limit to the palaeo mhhw of 3 75 m above present sea levels thereafter a fall in rsl was recorded with the regression leading to the progradation of the coastal system and the development of coastal sabkhas nonetheless later transgressions are recorded in the region between 4848 4536 and 4335 3949 cal bp radiometric dating results from archaeological excavations at dosariyah one of the most important neolithic coastal sites in the gulf suggest that occupation of the site during the neolithic coincides with the mid holocene marine transgression ca 7200 6500 cal bp whilst the close proximity of the site to the sea may have facilitated maritime exchange activities occupation of the site was short lived and the phase of abandonment occurred during a period of rapid rsl rise which would have transformed the area around dosariyah into an island or certainly cut it off tidally from the mainland

luminescence dating of quaternary sediments recent advances duller geoffrey 2004 luminescence dating of quaternary sediments recent advances journal of quaternary science 19 2 pp 183 192 rae2008

late pleistocene eolian history of the liwa region arabian peninsula the liwa region of the united arab emirates is one of the most distinctive geomorphological features of the rub al khali desert of southern arabia characterized by a sharp crescentic boundary coincident with a n s elevation drop of 65 m with the transverse ridges in al q fa to the north liwa is an area of some of the world9s largest megabarchan dunes deep drilling of continuous cores has provided an opportunity to observe the internal structure and age of these two ergs subsurface stratigraphy is complex reflecting rapid facies transitions between dune and interdune sub environments most of the cored sediment is dominated by cross bedded and structureless sand units of inferred eolian transverse dune depositional origin a total of 56 optical ages for sand sized quartz grains extracted from these cores provide a chronological framework for deposition of the late quaternary ergs a marine isotope stage mis 5 erg is identified north of the liwa crescent in the al q fa region which reaches vertical thicknesses 100 m a mis 1 erg in the form of megabarchan dunes is recorded south of the liwa crescent this was deposited on a pre mis 5 land surface since ca 6 ka over a period of just a few thousand years contemporary bypassing of eolian sands via superimposed dunes in both al q fa and liwa appears to be in equilibrium with the current wind regime a consideration of a variety of factors that control the availability mobilization and preservation of eolian sediments and resulting bedforms leads us to infer that the system is not sediment supply or transport limited instead the system is preservation limited being controlled by a correlated combination of sea level and precipitation both of these factors are strongly linked to global climate variations in the eccentricity ca 100 ka band paradoxically the bulk of the preserved record of eolian activity in the southern arabian peninsula occurs within relatively humid interglacial phases rather than arid intervals evidence of eolian deposition during arid phases may not for the most part be preserved in large areas of the sand sea observed contrasts in the preserved record of eolian activity between al q fa and liwa and the wahiba sand sea may in part relate to contrasting eolian bedform morphology

are strongly peraluminous magmas derived from pelitic sedimentary sources igneous compositions that require the presence of a phase more aluminous than biotite are here designated as strongly peraluminous ps such compositions are common but subordinate in felsic rocks and exceedingly rare in more mafic rocks the term s type has been applied to many igneous rocks based largely or even solely upon their ps compositions neglecting or placing less emphasis on other criteria for sedimentary parentage in chappell and white s i and s type classification system the s type designation was in fact initially restricted to granites which were thought to have been derived from a chemically mature strongly weathered pelitic shaly source application of chappell s and white s criteria together with others based upon isotopic and phase equilibria considerations leads to the following conclusions about ps igneous rocks worldwide 1 very few ps rocks are derived entirely from pelitic sources 2 a majority are derived largely from intermediate to felsic crustal sources including

chronologies for late quaternary barchan dune reactivation in the southeastern arabian peninsula abstract the liwa region of the united arab emirates contains some of the largest and most areally extensive megabarchanoid sand dunes on a global scale here we present optical dating results on samples of aeolian sediment from deep drill cores extracted from the largest dune field of the liwa area optical dating of these core sediments using the single aliquot regeneration protocol indicates mid late holocene phases of rapid dune deposition the most recent period of reactivation began at ca 2 8 ka this event was preceded by a period of deposition at ca 5 ka these results suggest that the dune systems of the southeastern arabian peninsula are closely linked to changes in late quaternary global climate particularly linked to the intensity and spatial extent of palaeomonsoon rainfall since the last precessional maxima at ca 9 ka at which time a peak in monsoonal rainfall has been recognised a significant environmental transition to widespread desert conditions occurred in an apparently abrupt fashion during the initial period of aridification large quantities of sand were transported and deposited in the form of large and very large up to 160 m high scale aeolian bedforms following the initial phase of aeolian accumulation the system appears to have remained in stasis

eustatic and climatic controls on the development of the wahiba sand sea sultanate of oman aeolian sand sea accumulations can serve as valuable archives of climate change in continental environments the wahiba sand sea is situated at the northern margin of the area presently affected by indian summer monsoon circulation and it records environmental changes associated with this major climatic boundary over the last 160 000 years the internal stratigraphy and evolution of the sand sea is investigated using a combination of outcrop borehole seismic and luminescence data proximity to the indian ocean means that the sand sea succession shows the influence of sea level changes on the sedimentary architecture and composition of the dune deposits during the last two glacial periods low global sea level was associated with a high input of bioclastic grains reflecting the significance of subaerially exposed shelf areas as one of the main sources of aeolian sediment the onset of aeolian sediment transport and deposition was related to the breakdown of stabilizing vegetation during arid periods that equate with sea level lowstands the preservation of aeolian sediments by the formation of supersurfaces and associated palaeosoils took place during times of increased wetness and elevated groundwater tables this interplay of constructive and destructive periods greatly influenced the sedimentary architecture oscillations of wet and dry periods between 160 000 and 130 000 years and 120 000 105 000 years ago are attributed to the evolution of a wet aeolian system younger periods of aeolian deposition around and after the last glacial maximum were characterized by dry aeolian conditions no soil horizons developed during these times

near surface diagenesis of ophiolite derived conglomerates of the barzaman formation united arab emirates a natural analogue for permanent co2 sequestration via mineral carbonation of ultramafic rocks carbon capture and storage by mineralization is a potential method for storing anthropogenic co2 emissions and is based on the reaction between mg silicate and co2 to form mg carbonate the conglomerates of the barzaman formation exposed in the eastern united arab emirates represent an excellent natural analogue of this process these conglomerates were deposited as a series of alluvial fans along the western margin of the hajar mountains part of the oman uae ophiolite and are composed largely of ultramafic and lesser mafic clasts the clasts and matrix have been extensively altered to dolomite during diagenetic processes analysis and interpretation of rock textures provide evidence for the various factors that influenced the diagenetic processes and shed light on the silicate carbonate transformation process all the reactions have taken place in the near surface environment the silicate carbonate conversion reaction is exothermic and occurs spontaneously at near ambient pressure and temperature probably no greater than 50 c estimates of the amount of co2 stored in this way can be obtained from considerations of outcrop area formation thickness and percentage of dolomite replacement and show that c 150 billion tonnes equivalent to about 4 years of worldwide co2 emissions at current rates are stored

the utility of desert sand dunes as quaternary chronostratigraphic archives evidence from the northeast rub al khali abstract the distributions of optically stimulated luminescence osl ages from dunes are affected by palaeoenvironmental changes complex dune dynamics and sampling strategy extracting the relative importance of these factors when interpreting discontinuous osl chronologies from sand dunes has proven difficult and is particularly hindered in contexts where the internal sedimentary structures of dunes are not visible in this study samples for osl dating were taken from three major dune exposures in the rub al khali united arab emirates each showing clear internal structure with the aim of addressing these problems specific objectives were to assess how ages of individual sedimentary units represent dune accumulation as a whole and how the dune record in turn reflects known past environmental changes final ages were calculated using the oxcal software package by incorporating the known relative stratigraphy through the application of bayesian methods the results show that stratigraphy alone is not sufficient at these sites to guide osl sampling that is chrono and lithostratigraphic boundaries do not necessarily coincide where chronological hiatuses are present internal sediment stratigraphy can be a useful tool in identifying potential problems of under sampling the full dune record the implications of these findings for reconstructing quaternary climates from dune chronologies are considered

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

speleothem evidence from oman for continental pluvial events during interglacial periods growth periods and stable isotope analyses of speleothems from hoti cave in northern oman provide a record of continental pluvial periods extending back over the past four of earth s glacial interglacial cycles rapid speleothem growth occurred during the early to middle holocene 6 10 5 ka b p 78 82 ka b p 120 135 ka b p 180 200 ka b p and 300 325 ka b p the speleothem calcite deposited during each of these episodes is highly depleted in 18 o compared to modern speleothems the d 18 o values for calcite deposited within pluvial periods generally fall in the range of 24 to 28 relative to the vienna peedee belemnite standard whereas modern speleothems range from 21 to 23 the growth and isotopic records indicate that during peak interglacial periods the limit of the monsoon rainfall was shifted far north of its present location and each pluvial period was coincident with an interglacial stage of the marine oxygen isotope record the association of continental pluvial periods with peak interglacial conditions suggests that glacial boundary conditions and not changes in solar radiation are the primary control on continental wetness on glacial interglacial time scales

hydrography and sedimentation under the deep western boundary current on bjorn and gardar drifts iceland basin abstract the interaction of northern component waters overflowing the iceland scotland ridge with sediments further south in the iceland basin has been responsible for highly variable sedimentation patterns since at least the late miocene 5 million years ago and has formed both bjorn and gardar drifts presently this process is maintained by a flux of approximately 3 sv measured along the south icelandic slope of iceland scotland overflow water isow with a mean regional flow direction to the sw which affects sediment transport on bjorn drift below 1350 m depth and over most of the gardar drift coriolis deflection of isow flow causes it to move as a deep western boundary current dwbc in the iceland basin which redistributes sediments under the influence of seabed topography here hydrographic and sedimentological data are used to illustrate the effects and extent of the vigorous dwbc activity the study presents a baseline against which inferred changes in the past can be assessed north of 58 n bottom nepheloid layers with heavy suspended sediment loads are often encountered particularly under the denser and faster flowing core of isow on the eastern slope of gardar drift in this area the presence of migrating regular sedimentary waves is seen on 3 5 khz profiles this is consistent with both the near bottom flow velocity probably in excess of 10 cm s 1 estimated by the geostrophic method and the presence of well sorted foraminiferal sand on the seabed south of 58 n dilute bottom nepheloid layers associated with more tranquil conditions near the seabed inferred from photographic and sedimentological evidence show that currents on gardar drift are weak although most of the south iceland basin is mantled by both regular and irregular non migratory mudwaves the absence of migrating structures with the exception of current intensification associated with discrete basement highs indicates that more sluggish currents characterise this region throughout the region highly variable mean holocene sediment accumulation rates are inferred 2 40 cm ka 1 as a result of the dwbc interacting with the topography

challenges involved in obtaining luminescence ages for long records of aridity examples from the arabian peninsula abstract in the last 35 years luminescence dating has provided a large database of ages for the deposition of dunes in desert environments over 380 ages have been generated for dunes from the arabian peninsula and demonstrate episodic dune deposition in the late quaternary but give a less clear pattern prior to 50 ka interpreting databases of luminescence ages faces two issues first the precision of luminescence ages in the last 50 ka is between 5 and 10 but for older ages the uncertainties may be much larger as luminescence signals reach saturation second different luminescence signals from quartz and from feldspar have been used over the last 35 years as the method has developed and expanded these different signals have different saturation limits and different rates at which they are reset by exposure to daylight at deposition approaches which focus on the most light sensitive signals e g quartz osl are better suited to dating recent events while those which show growth of the luminescence signal over the largest dose range e g the thermally transferred osl tt osl signal from quartz and the post infrared infrared stimulated luminescence pir irsl from feldspars have the potential to date much older events

holocene development of multiple dune generations in the northeast rub al khali united arab emirates it has been hypothesised that in sand seas where multiple dune generations occur each generation represents a distinct terrestrial response to contrasting palaeoatmospheric circulation conditions lancaster n kocurek g singhvi a pandey v deynoux m ghienne j f et al 2002 late pleistocene and holocene dune activity and wind regimes in the western sahara desert of mauritania geology 30 991 994 however reconstructing dunefield accumulation and preservation chronologies has often utilised a limited suite of samples because of the difficulties realised in accessing unconsolidated aeolian sands which has limited the capacity to test this hypothesis in the eastern united arab emirates artificial excavation for quarrying and construction have generated a unique opportunity to examine and sample the internal structures of dune systems and to generate data to test the hypothesis of dune generational development this paper presents new data and chronologies from a multigenerational analysis of dune

a 160 000 year record of dune development and atmospheric circulation in southern arabia aeolian deposits in the wahiba sands sultanate of oman reveal patterns of atmospheric circulation over the past 160 000 years luminescence dating indicates a correlation of dune activity with periods of low global sea level and decreased monsoon intensity evidence from dune orientation and sedimentary structures shows exclusively northbound transport of sand during times of high latitude glaciation these results are in contrast to the current paleocirculation model that assumes an increase of northwesterly winds because of a southward shift of the intertropical convergence zone our results indicate that the circulation pattern during glacial times was comparable to that of the present

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

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

coccolith evidence for instabilities in surface circulation south of iceland during holocene times abstract the coccolith based micropaleontological investigation of an exceptionally thick deep sea holocene sediment core was conducted in order to document the pattern and timing of surface circulation changes south of iceland over the gardar contour drift during the last 12 000 years fluctuations in bulk carbonate content at the core location are primarily driven by the coccolith fraction the observed overall correlation between bottom flow speed as given by the sortable silt mean size index and the bulk coccolith concentration abundance g dry sediment suggests that the accumulation of this fine carbonate fraction is as a first order controlled by processes of sediment redistribution by bottom current the down core variations in coccolith assemblage structure species indicate that changes in properties of surface waters south of iceland occurred as two distinct steps at ca 11 2 and 6 ka the onset of north atlantic drift water influence over the gardar drift after 11 2 ka was associated with excess export flux of coccolith carbonate in the vicinity of an active frontal system the period from 10 to 6 ka saw the progressive warming of the study area which culminated between 6 and 7 ka cooling of the surface waters after 6 ka as indicated changes in the relative abundances of the dominant coccolith species took place in two phases the present hydrological regime being only established after a last cooling step between 3 5 and 2 8 ka these long term reorganisations of the surface hydrology are interpreted as the response of the north atlantic to the combined force of the solar insolation and the waning laurentide ice sheet millennial scale perturbations of the surface hydrology are documented by changes in accumulation of the species emiliania huxleyi these successive decreases in the export fluxes of e huxleyi exhibit a distinct millennial pacing in phase with previously recorded holocene advection of cool ice bearing waters from the greenland iceland seas to the british islands from a clear analogy with the most recent extreme variation in global ocean climate we argue that mechanisms responsible for these observed millennial scale perturbations might be found in long term modulations of the atmospheric processes associated with the north atlantic oscillation nao

holocene itcz and indian monsoon dynamics recorded in stalagmites from oman and yemen socotra abstract high resolution oxygen isotope 18o profiles of holocene stalagmites from four caves in northern and southern oman and yemen socotra provide detailed information on fluctuations in precipitation along a latitudinal transect from 12 n to 23 n 18o values reflect the amount of precipitation which is primarily controlled by the mean latitudinal position of the itcz and dynamics of the indian summer monsoon ism during the early holocene rapidly decreasing 18o values indicate a rapid northward displacement in the mean latitudinal position of the summer itcz and the associated ism rainfall belt with decadal to centennial scale changes in monsoon precipitation correlating well with high latitude temperature variations recorded in greenland ice cores during the middle to late holocene the summer itcz continuously migrated southward and monsoon precipitation decreased gradually in response to decreasing solar insolation a trend which is also recorded in other monsoon records from the indian and east asian monsoon domains importantly there is no evidence for an abrupt middle holocene weakening in monsoon precipitation although abrupt monsoon events are apparent in all monsoon records they are short lived and clearly superimposed on the long term trend of decreasing monsoon precipitation for the late holocene there is an anti correlation between ism precipitation in oman and inter monsoon spring autumn precipitation on socotra revealing a possible long term change in the duration of the summer monsoon season since at least 4 5 ka bp together with the progressive shortening of the ism season gradual southward retreat of the mean summer itcz and weakening of the ism the total amount of precipitation decreased in those areas located at the northern fringe of the indian and asian monsoon domains but increased in areas closer to the equator

centennial to millennial scale holocene climate deep water linkage in the north atlantic the stability of the earth s climate is strongly linked to the steadiness of the atmospheric and oceanic transport of heat from low to high latitudes high resolution holocene sedimentary records from the subpolar north atlantic demonstrate a persistent link between centennial to millennial scale fluctuations in the flow speed of iceland scotland overflow water inferred from granulometric proxy data and both the surface north atlantic current component of the meridional overturning circulation moc and published fennoscandian atmospheric temperature variability however these data also highlight the difficulties associated with the interpretation of geochemical and sedimentological deep water circulation proxies as they do not provide a wholly consistent picture the similarity between surface and deep ocean 13c records suggests a preformed component in the deep ocean 13c signal on the other hand the sedimentological results display a strong linkage to changing conditions in the overlying surface ocean waters suggesting this proxy better reflects the activity of the moc at least during the holocene of this region the most widespread oceanic perturbation coincides with an interval of possibly global climatic deterioration around 2700 years ago these results firmly establish deep water production in the nordic seas as a key component in the assortment of variables affecting climate during the holocene

structure of the 8200 year cold event revealed by a speleothem trace element record abrupt first order shifts in strontium and phosphorus concentrations in stalagmite calcite deposited in western ireland during the 8200 year event the major cooling episode 8200 years before the present are interpreted as responses to a drier climate lasting about 37 years both shifts are centered on 8330 80 years before the present coinciding with a large oxygen isotope anomaly and a change in the calcite petrography in this very high resolution monthly record antipathetic second order oscillations in phosphorus and strontium reveal decreased growth rates and increased rainfall seasonality growth rate variations within the event reveal a two pronged structure consistent with recent model simulations

temporal patterns of arid humid transitions in the south eastern arabian peninsula based on optical dating abstract the rub al khali aeolian system of the arabian peninsula is the world s largest erg while the region is presently hyper arid evidence for multiple past humid periods has been documented in previous studies radiocarbon dating of lacustrine travertine and palaeogroundwater deposits suggests that the climate was humid at 10 6 and 35 25 ka these phases have been associated with summer rainfall increases occurring in tandem with an intensification and northward migration of the monsoon system during northern hemisphere precessional maxima published optical dating studies have focused on preserved sand dune and aeolianite deposits to establish ages for the intervening arid phases here we present a summary of this work and additional optical dating results for samples of aeolian sediment from a deep drill core which provides insights into the style of barchan dune accretion in the liwa region of the united arab emirates the large dune accreted rapidly during the mid late holocene the results suggest that the transitions from humid to arid conditions and resulting accumulation of aeolian sediment in the form of large bedforms occurred abruptly at around 6 ka further aeolian sedimentation has not been constant since that time with initial gradual dune growth followed by rapid vertical accretion and possible termination of accumulation around c 2 ka

reaction spaces and p t paths from amphibole eclogite to greenschist facies in the austroalpine domain oetztal complex the transition from feldspar amphibolite to eclogite is a very wide p t field that extends from some where close to 5 kbar where the garnet amphibole pair starts to appear to 10 20 kbar at albite out reaction then up to 25 30 kbar where an hydrated phase such as amphibole can be stable with pyroxene and garnet thus the assemblage garnet py amphibole tr epidote cz plagioclase ab clinopyroxene di quartz qz fluid is commonly reported in a large number of metamorphic terrains these mineral phases are complex solid solutions which adapt to variations in environmental conditions mainly by means of continuous reactions the reaction space introduced by thompson in 1982a provides a very elegant and powerful tool to approach these high variance assemblages the reactions

evaluating the use of dune sediments as a proxy for palaeo aridity a southern african case study abstract the dominance of dryland environments in the southern hemisphere makes the study of these regions of critical importance for the development of regional hemispheric and global models of environmental change unfortunately the wetting and drying cycles associated with semi hyperarid climates are not conducive to the preservation of traditional organic proxy data sources the last decade however has seen the development of a number of alternative archives including the application of luminescence dating techniques to dunes and other aeolian deposits in continental situations the existence of relict dune fields has long been thought to be evidence of drier conditions during the pleistocene and direct ages from these features have been interpreted almost exclusively as indicating phases of aridity however an increasing number of ages from a broader range of environments are calling into question the assumption that aeolian activity can be simply equated with aridity presented here is a comparison of dune ages that have been obtained from across southern africa with a range of proxies from both terrestrial and marine records taken as a whole three primary phases of activity can be identified at 60 40 35 20 and 17 4 ka the frequent discordance with other terrestrial records indicating coeval increases in humidity and the close correlation of these phases with wind strength proxies suggest that aridity is unlikely to be the sole or even primary forcing mechanism for aeolian activity in the region and the palaeoclimatic significance of these sedimentary archives needs to be reassessed

retrograde metamorphism of eclogite in the southern appalachian mountains u s a a case involving seamount subduction this work supports a growing body of evidence that the ashe metamorphic suite ams of the eastern blue ridge province in north carolina has an ensimatic origin and is part of a subduction related accretionary melange marking the taconic suture between the north american craton and the inner piedmont in a palinspastic reconstruction the thrust fault at the base of the ams appears to have intercepted the greatest depths i e highest p metamorphic rocks beneath parts of the ams now exposed adjacent to the grandfather mountain window the greatest volume of mafic rock is found in these same areas we suggest that the nascent subduction related basal thrust fault was deflected downward by an obstacle in the form of an isolated mafic volcanic edifice on the oceanic crust a sea mount pelitic and mafic rocks dominate the ams north of the grandfather mountain window retrograded eclogite occurs in the amphibolite near the base of the ams textures and mineralogy indicate that an original eclogite assemblage was subjected to the following sequence of parageneses a eclogite i facies omphacite garnet quartz b eclogite ii facies omphacite garnet epidote quartz c symplectic diopside plagioclase garnet epidote quartz d amphibolite facies diopside plagioclase garnet epidote hornblende quartz e amphibolite facies plagioclase garnet epidote hornblende quartz p t conditions estimated from geothermobarometry applied to relevant mineral compositions are c 720 c and c 16 kbar for b eclogite ii facies c 655 c and c 8 5 kbar for e amphibolite facies

late quaternary chronology of major dune ridge development in the northeast rub al khali united arab emirates the northeastern sector of the rub al khali desert in the eastern united arab emirates uae is dominated by large ne sw trending dune ridges orientated perpendicular to the currently prevailing northwesterly wind regime in this study extensive use has been made of artificially exposed sections through these major dune ridges that reveal internal sedimentary structures and allow an intensive high resolution sampling programme to be carried out here we present the optical dating results for samples from 7 sections the results indicate that dune activity and preservation occurred within the periods 7 3 ka 16 10 ka and 22 20 ka with evidence of earlier preservation during marine oxygen isotope stages mis 3 and 5 with net accumulation rates in the range 2 2 25 m ka 1 in several instances hiatuses in the preserved record of dune accumulation coincide with stratigraphic bounding surfaces visible in the exposed section profiles with associated truncation of internal sedimentary structures caution must be exercised when interpreting such gaps in the recorded accumulation chronologies of these dunes since these may simply constitute phases of low preservation potential rather than phases of low aeolian activity other factors such as sediment supply and availability in relation to sea level dynamics may be significant and are also considered

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

decreasing overflow from the nordic seas into the atlantic ocean through the faroe bank channel since 1950 the overflow of cold dense water from the nordic seas across the greenland scotland ridge and into the atlantic ocean is the main source for the deep water of the north atlantic ocean this flow also helps drive the inflow of warm saline surface water into the nordic seas the faroe bank channel is the deepest path across the ridge and the deep flow through this channel accounts for about one third of the total overflow previous work has demonstrated that the overflow has become warmer and less saline over time here we show using direct measurements and historical hydrographic data that the volume flux of the faroe bank channel overflow has also decreased estimating the volume flux conservatively we find a decrease by at least 20 per cent relative to 1950 if this reduction in deep flow from the nordic seas is not compensated by increased flow from other sources it implies a weakened global thermohaline circulation and reduced inflow of atlantic water to the nordic seas

holocene vegetation dynamics in the northeastern rub al khali desert arabian peninsula a phytolith pollen and carbon isotope study the holocene vegetation history of the arabian peninsula is poorly understood with few palaeobotanical studies to date at awafi ras al khaimah uae a 3 3 m lake sediment sequence records the vegetation development for the period 8500 cal yr bp to 3000 cal yr bp 13 c isotope pollen and phytolith analyses indicate that c3 pooid grassland with a strong woody element existed during the early holocene between 8500 and 6000 cal yr bp and became replaced by mixed c3 and c4 grasses with a strong c4 panicoid tall grass element between 5900 and 5400 cal yr bp an intense arid event occurred at 4100 cal yr bp when the lake desiccated and was infilled by aeolian sand from 4100 cal yr bp the vegetation was dominated by c4 chloridoid types and cyperaceae suggesting an incomplete vegetation cover and aeolian dune reactivation owing to increased regio nal aridity these data outline the ecosystem dynamics and carbon cycling in response to palaeomon soon and north westerly variability during the holocene copyright 2004 john wiley sons ltd

humid periods in southern arabia windows of opportunity for modern human dispersal arabia is a key area for the dispersal of anatomically modern humans amh homo sapiens out of africa given its modern hostile environment the question of the timing of dispersal is also a question of climatic conditions fresh water and food were crucial factors facilitating amh expansions into arabia by dating relict lake deposits four periods of lake formation were identified one during the early holocene and three during the late pleistocene centered ca 80 ca 100 and ca 125 ka favorable environmental conditions during these periods allowed amh to migrate across southern arabia between ca 75 and 10 5 ka arid conditions prevailed and turned southern arabia into a natural barrier for human dispersal thus expansion of amh through the southern corridor into asia must have taken place before 75 ka possibly in multiple dispersals

low latitude holocene hydroclimate derived from lake sediment flux and geochemistry this study investigates hydrological responses to climatic shifts using sediment flux data derived from two dated palaeolake records in south east arabia flux values are generally low during the early holocene humid period ehhp 9 0 6 4k cal a bp although several short lived pulses of increased detrital input are recorded the most prominent of which is dated between 8 3 and 7 9k cal a bp the ehhp is separated from the mid holocene humid period mhhp 5 0 4 3k cal a bp by a phase of increased sediment flux and aridity which began between 6 4 and 5 9k cal a bp and peaked between 5 2 and 5 0k cal a bp the termination of the mhhp is marked by a phase of high detrital sediment flux between 4 3 and 3 9k cal a bp while long term shifts in climate are most likely linked to changes in the summer position of the intertropical convergence zone and associated indian and african monsoon systems it is noted that the abrupt short term phases of aridity observed in both records are coeval with intervals of rapid climate change globally which triggered non linear widespread landscape reconfigurations throughout south east arabia

a high resolution study of holocene paleoclimatic and paleoceanographic changes in the nordic seas 1 high resolution records from images core md95 2011 in the eastern norwegian sea provide evidence for relatively large and small scale high latitude climate variability throughout the holocene during the early and mid holocene a situation possibly driven by consistent stronger westerlies increased the eastward influence of arctic intermediate and near surface waters for the late holocene a relaxation of the atmospheric forcing resulted in increased influence of atlantic water the main changes in holocene climate show no obvious connection to changing solar irradiance and spectral analysis reveals no consistent signature for any periodic behavior of holocene climate at millennial or centennial timescales there are however indications of consistent multidecadal variability

late pleistocene palaeolake in the interior of oman a potential key area for the dispersal of anatomically modern humans out of africa relict fluvial and lacustrine deposits in the interior of oman near saiwan consist of waterlain breccias with pebble imbrications and current ripples covered by algal laminites containing calcified reeds and charcoal pieces geomorphological evidence suggests that the palaeolake covered a maximum surface of 1400 km2 and had a maximum depth of about 25 m optically stimulated luminescence osl and thermally transferred osl dating indicate that this palaeolake existed sometime between 132 and 104 ka the rich archaeological evidence in the area suggests substantial human occupation possibly at the time when palaeolake saiwan existed interestingly the lithic traditions of the archaeological material show no clear relation to coeval findings from neighbouring areas putting a question mark on the origin of the culture found at saiwan this finding raises questions concerning the origin of the population inhabiting saiwan as the site lies along one possible route for the dispersal of anatomically modern humans out of africa copyright 2011 john wiley sons ltd

cumulative probability functions and their role in evaluating the chronology of geomorphological events during the holocene cumulative probability functions cpfs for large numbers of radiocarbon age determinations are increasingly being used by scientists as a methodology to discern environmental histories while the recent compilation of regional databases of the radiocarbon dating control for fluvial sediment sequences has been beneficial for identifying gaps in knowledge and stimulating new research there are a number of problems that critically undermine the use of these cpfs as sensitive hydroclimatic proxies i the cpf method is underpinned by the assumption that each radiocarbon measurement is a true age estimate for a point in time whereas each measured age in fact forms a scatter around the true age of the sample ii calibration of radiocarbon ages is responsible for much of the structure in cpfs and compounds the problem of scatter and smears the chronological control iii the databases incorporate multiple types of environmental changes differing chronological relationships between the 14c measurements and the dated events with pre dating dating or post dating chronological control each displaying variable length temporal lags all mixed together in the same analysis and iv the radiocarbon ages from individual case studies need to be more robustly tested before being incorporated into regional databases all these factors negate the value of cpfs as sensitive proxies of environmental change because peaks in probability for individual radiocarbon measurements are likely to be an incorrect estimate for the age of a geomorphological event and this problem is compounded by combining probabilities for multiple unrelated events in this paper we present a critical analysis of cpfs and their interpretation before suggesting alternative approaches to analysing radiocarbon geochronologies of geomorphic events which include i bayesian age modelling of river terrace development ii developing regional databases that test specific geomorphic hypotheses iii bayesian age modelling of palaeoflood records and iv analysis of sedimentation rates copyright 2011 john wiley sons ltd

on sharp spectral lines in the climate record and the millennial peak the existence of a narrow spectral line in the internal oscillations of the climate system would be a physical discovery of the first order thus the appearance of such a spectral peak with a q 20 near 1500 years period in the physical properties of the greenland ice core is intriguing bandwidth less than two cycles in 110 000 years apparently similar phenomena exist in some deep sea cores it is shown however that the peak appears at precisely the period predicted as a simple alias of the seasonal cycle inadequately under the nyquist criterion sampled at integer multiples of the common year if this peak is therefore discounted climate variability appears as expected to be a continuum process in the millennial band more generally however aliasing of high frequencies must be a concern in any core analysis

calcareous dunes of the united arab emirates and noah s flood the postglacial reflooding of the persian arabian gulf abstract aeolian dunes cover most of the united arab emirates and a large part of the eastern arabian peninsula although these sands as well as older aeolianites are largely composed of quartz there is a high percentage of detrital carbonate in them south of the persian arabian gulf for more than 40 km this percentage decreases inland these carbonate grains consist mainly of marine bioclastic fragments and calcareous ooids and were derived from the floor of the persian gulf which was exposed during low sea level of the last glacial period the postglacial rise in sea level rapidly reflooded the floor of the persian gulf cutting off the source for these aeolian sediments between 12 and 6 ka the sea transgressed more than 1000 km inundating the extended route of the tigris euphrates river and forcing people living on the exposed floor of the gulf to abandon their settlements because of the varying rate of eustatic sea level rise these waters at times flooded across the flat floor of the persian gulf at more than a kilometer per year we proposed that the stories of a great flood recorded in the bible as noah s flood and in babylonian history on clay tablets excavated in the tigris euphrates delta as the epic of gilgamesh are a record of this rapid postglacial flooding of the floor of the persian gulf

sortable silt and fine sediment size composition slicing parameters for palaeocurrent speed and palaeoceanography fine sediment size 63 ixm is best measured by a sedimentation technique which records the whole size distribution repeated size measurement with intermediate steps of removal of components by dissolution allows inference of the size distribution of the removed component as well as the residue in this way the size of the biogenic and lithogenic noncarbonate fractions can be determined observations of many size distributions suggest a minimum in grain size frequency curves at 8 to 10 ixm the dynamics of sediment erosion deposition and aggregate breakup suggest that fine sediment behavior is dominantly cohesive below 10 1xm grain size and noncohesive above that size thus silt coarser than 10 ixm displays size sorting in response to hydrodynamlc processes and its properties may be used to infer current speed silt that is f mer than 10 ixm behaves in the same way as clay 2 xm useful parameters of the distribution are the 10 63 ixm mean size and the percentage 10 63 ixm in the fine fraction we cannot use size distributions to distinguish the nature of the currents therefore to infer water mass advection speeds i e the mean kinetic energy of the flow ku regions of high eddy kinetic energy ke must be avoided at the present such abyssal regions lie under the high surface k e of major current systems gulf stream kuroshio agulhas antarctic circmpolar current and brazil falldand currents in the argenthe basin this is probably a satisfactory guide for the pleistocene with regard to the carbonate subfraction of the size spectrum size modes due to both cocco iths and foramlnlferal fragments can be recognized and analyzed with the boundary between them again at about 10 lm the flux of less than 10 lm carbonate at pelagic sites above the lysocline is another candidate for a productivity indicator

palaeo oceanography deepwater variability in the holocene epoch the conversion of surface water to deep water in the north atlantic results in the release of heat from the ocean to the atmosphere which may have amplified millennial scale climate variability during glacial times1 and could even have contributed to the past 11 700 years of relatively mild climate known as the holocene epoch 2 3 4 here we investigate changes in the carbon isotope composition of benthic foraminifera throughout the holocene and find that deep water production varied on a centennial millennial timescale these variations may be linked to surface and atmospheric events that hint at a contribution to climate change over this period

hydrography and through flow in the north eastern north atlantic ocean the nansen project abstract the circulation and hydrography of the north eastern north atlantic has been studied with an emphasis on the upper layers and the deep water types which take part in the thermohaline overturning of the oceanic conveyor belt over 900 hydrographic stations were used for this study mainly from the 1987 1991 period the hydrographic properties of subpolar mode water in the upper layer which is transported towards the norwegian sea showed large regional variation the deep water mass was dominated by the cold inflow of deep water from the norwegian sea and by a cyclonic recirculation of lower deep water with a high antarctic bottom water content at intermediate levels the dominating water type was labrador sea water with only minor influence of mediterranean sea water in the permanent pycnocline traces of antarctic intermediate water were found geostrophic transports have been estimated and these agreed in order of magnitude with the local heat budget with current measurements with data from surface drifters and with the observed water mass modification a total of 23 sv of surface water entered the region of which 20 sv originated from the north atlantic current while 3 sv entered via an eastern boundary current of this total 13 sv of surface water left the area across the reykjanes ridge and 7 sv entered the norwegian sea while 3 sv was entrained by the cold overflow across the iceland scotland ridge approximately 1 4 sv of norwegian sea deep water was involved in the overflow into the iceland basin which with about 1 1 sv of entrained water and 1 1 sv recirculating lower deep water formed a deep northern boundary current in the iceland basin at intermediate depths where labrador sea water formed the dominant water type about 2 sv of entrained surface water contributed to a saline water mass which was transported westwards along the south icelandic slope

orbital insolation forcing of the indian monsoon a motor for global climate changes abstract both modern and ancient indian summer monsoons are driven by transequatorial pressure differences directly coupled with the insolation difference between the northern and southern subtropical hemispheres a high resolution record of upwelling and dust flux from the western arabian sea resembles an insolation based indian summer monsoon index this index and the observed monsoonal climate variations share major elements on the orbital obliquity and precessional band with the specmap marine oxygen isotope record representing global ice volume the long term evolution of the index mirrors almost exactly the insolation changes at 65 n showing that the forcing of low latitude climate variability has a structure similar to that of the insolation forcing in the high northern latitudes moreover insolation forcing in the low latitudes directly controls atmospheric processes in the african indian and asian monsoon being responsible for a huge amount of transequatorial water vapour and therefore latent heat transport millennial scale variability of the monsoonal climate is concentrated at periodicities near 1100 1450 1750 and 2300 years these cycles are not strictly periodic but occur in bands with specific activity phases and amplitude increases during warm stages and interstadials for the 1100 and 1750 yr cycles whereas the 1450 yr cycle dominates the cold intervals