dating the quaternary progress in luminescence dating of sediments abstract luminescence dating comprises a collection of numerical age techniques that are among the most significant chronological tools currently used in quaternary research this paper briefly reviews the key historical developments in luminescence dating from its roots in thermoluminescence dating of heated minerals to the development of optical dating methods for sunlight exposed sediments we describe the principles and practicalities of the various techniques commonly used in luminescence dating including multiple aliquot single aliquot and single grain procedures and we discuss some of the latest approaches to recognising and minimising potential errors in age estimation e g by means of component analysis and dose distribution methods in optical dating the overview also introduces the other papers in this special issue of quaternary science reviews which address a selection of important issues in basic research technique development and application of luminescence dating to critical questions in the geological and archaeological sciences illustrated with examples from around the world and the last million years of earth history

style and timing of glaciation in the lahul himalaya northern india a framework for reconstructing late quaternary palaeoclimatic change in the western himalayas

quaternary glaciation of the himalayan tibetan orogen glacial geological evidence from throughout the himalayan tibetan orogen is examined to determine the timing and extent of late quaternary glaciation in this region and its relation to similar changes on a global scale the evidence summarised here supports the existence of expanded ice caps and extensive valley glacier systems throughout the region during the late quaternary however it cannot yet be determined whether the timing of the extent of maximum glaciation was synchronous throughout the entire region or whether the response was more varied the lack of organic material needed for radiocarbon dating has hindered past progress in glacial reconstruction however application of optically stimulated luminescence and terrestrial cosmogenic radionuclide methods has recently expanded the number of chronologies throughout the region limits to the precision and accuracy available with these methods and more importantly geological uncertainty imposed by processes of moraine formation and alteration both conspire to limit the time resolution on which correlations can be made to milankovitch timescales several ka in order to put all studies on a common scale well dated sites have been re evaluated and all the published terrestrial cosmogenic nuclide ages for moraine boulders and glacially eroded surfaces in the himalayan tibetan orogen have been recalculated locally detailed studies indicate that there are considerable variations in the extent of glaciation from one region to the next during a glaciation glaciers throughout monsoon influenced tibet the himalaya and the transhimalaya are likely synchronous both with climate change resulting from oscillations in the south asian monsoon and with northern hemisphere cooling cycles in contrast glaciers in pamir in the far western regions of the himalayan tibet orogen advanced asynchronously relative to the other regions that are monsoon influenced regions and appear to be mainly in phase with the northern hemisphere cooling cycles broad patterns of local and regional variability based on equilibrium line altitudes have yet to be fully assessed but have the potential to help define changes in climatic gradients over time copyright 2008 john wiley sons ltd

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

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

latest pleistocene and holocene glacier fluctuations in the himalaya and tibet abstract the timing and extent of latest pleistocene and holocene alpine glacier fluctuations in the himalaya and tibet are poorly defined due to the logistical and political inaccessibility of the region and the general lack of modern studies of the glacial successions nevertheless renewed interest in the region and the aid of newly developing numerical dating techniques have provided new insights into the nature of latest pleistocene and holocene glacier oscillations these studies provide abundant evidence for significant glacial advances throughout the last glacial cycle in most high himalayan and tibetan regions glaciers reached their maximum extent early in the last glacial cycle however true last glacial maximum glacier advances were significantly less extensive notable glacier advances occurred during the lateglacial and the early holocene with minor advances in some regions during the mid holocene there is abundant evidence for multiple glacial advances throughout the latter part of the holocene although these are generally very poorly defined and were less extensive than the early holocene glacier advances the poor chronological control on latest pleistocene and holocene glacial successions makes it difficult to construct correlations across the region and with other glaciated regions in the world which in turn makes it hard to assess the relative importance of the different climatic mechanisms that force glaciation in this region the lateglacial and holocene glacial record however is particularly well preserved in several regions notably in muztag ata and kongur and the khumbu himal these successions have the potential to be examined in detail using newly developing numerical dating methods to derive a high resolution record of glaciation to help in paleoclimatic reconstruction and understanding the dynamics of climate and glaciation in the himalaya and tibet

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

reconstruction of the late quaternary glaciation of the macha khola valley gorkha himal nepal using relative and absolute 14c 10be dendrochronology dating techniques abstract late quaternary glacier fluctuations in the macha khola valley gorkha himal nepal were reconstructed using relative and absolute dating techniques our results indicate that younger moraine complexes were left by late holocene

rates of trace metal and nutrient diagenesis in an intertidal creek bank abstract carbon mineralization in marine sediments is a key process involved in the cycling of carbon nutrients and trace metals however as marine sediments are usually diffusion dominated the pace of element and nutrient cycling is slow because consumption of oxidants and or nutrients in the pore waters via microbial activity often outpaces resupply adding an advective flow component to such a system should change the biogeochemical dynamics considerably numerical simulations show that shallow coastal aquifers affected by tidal forces can establish ground water velocities of up to 7 cm h 1 driving a circulation of sea water through the sediments with subsequent discharge although known to enhance solute exchange the impact of advection on early diagenesis has not received much attention to address this issue we mapped the interstitial water chemistry down to 2 5 m sediment depth along a transect on an intertidal creek bank that is subject to a periodic advective flow additionally a recently developed hydrogeological simulation of the creek bank was applied to calculate ages of the sampled pore waters sample ages obtained were used to quantify flow path integrated production or depletion rates for trace metals nutrients and sulphate we find young sea water percolating relatively fast through sediments close to the creek showing strong signs of alteration whereas pore waters from diffusion dominated regions are less altered the increase in inorganic nutrients and some trace elements along the flow path requires high rates of turnover sulphate molybdenum and uranium are almost completely depleted after 200 days while dissolved inorganic carbon dic ammonia and manganese increase averaged production rates for dic appear to be three times higher when advection dominated the subsurface flow regime our results demonstrate that sites dominated by advection generally show signs of faster rates of diagenetic reactions

the quaternary glacial history of the lahul himalaya northern india this paper presents the first glacial chronology for the lahul himalaya northern india the oldest glaciation the chandra glacial stage is represented by glacially eroded benches at altitudes greater than 4300 m above sea level this glaciation was probably of a broad valley type the second glaciation the batal glacial stage is represented by highly weathered and dissected lateral moraines which are present along the chandra valley and some of its tributaries this was an extensive valley glaciation the third major glaciation the kulti glacial stage is represented by well preserved moraines in the main tributary valleys of the chandra valley this represents a less extensive valley glaciation two minor glacial advances the sonapani i and ii are represented by small sharp crested moraines which are within a few hundred metres or few kilometres of the present day glaciers the change in style and extent of glaciation is attributed to an increase in aridity throughout the quaternary due either to global climatic change or uplift of the pir panjal mountains to the south of lahul which restricted the northward penetration of the south asian summer monsoon 1996 john wiley sons ltd

age origin and climatic controls on vegetated linear dunes in the northwestern negev desert israel abstract the stabilized northwestern nw negev vegetated linear dunes vld of israel extend over 1300 km 2 and form the eastern end of the northern sinai nw negev erg this study aimed at identifying primary and subsequent dune incursions and episodes of dune elongation by investigating dune geomorphology stratigraphy and optically stimulated luminescence osl dating thirty five dune and interdune exposed and drilled section were studied and sampled for sedimentological analyses and osl dating enabling spatial and temporal elucidation of the nw negev dunefield evolution in a global perspective the nw negev dunefield is relatively young though sporadic sand deposition has occurred during the past 100 ka dunes began to accumulate over large portions of the dunefield area only at 23 ka three main chronostratigraphic units corresponding to three osl age clusters were found throughout most of the dunefield indicating three main dune mobilizations late to post last glacial maximum lgm at 18 11 5 ka late holocene 2 0 8 ka and modern 150 8 years the post lgm phase is the most extensive and it defined the current dunefield boundaries it involved several episodes of dune incursions and damming of drainage systems dune advancement often occurred in rapid pulses and the orientation of vld long axes indicates similar long term wind directions the late holocene episode included partial incursion of new sand reworking of late pleistocene dunes as well as limited redeposition the modern sand movement only reactivated older dunes and did not lengthen vlds this aeolian record fits well with other regional aeolian sections we suggest that sand supply and storage in sinai was initiated by the late pleistocene exposure of the nile delta sands late pleistocene winds substantially stronger than those usually prevailing since the onset of the holocene are suggested to have transported the dune sands across sinai and into the northwestern negev our results demonstrate the sensitivity of vegetated linear dunes located along the northern fringe of the sub tropical desert belt to climate change i e wind and sediment supply

luminescence dating of loess palaeosol sequences and coversands methodological aspects and palaeoclimatic implications abstract of the terrestrial archives loess palaeosol sequences provide a most complete record of climatic change this may be compared with the marine oxygen isotope stratigraphy and may help in the reconstruction of past atmospheric circulation patterns numerical chronometry of loess palaeosol sequences has generally been based on correlation of variations in climatic proxies such as magnetic susceptibility and particle sizes with marine isotopic data such chronometric assignments involve implicit assumptions about the constancy of sedimentation rates and particle fluxes through time this review presents a brief survey of the present status methodology outstanding problems and interpretational aspects of luminescence techniques and discusses the import of luminescence ages on global land sea correlations statistical analysis of the ages suggests episodicity of loess accumulation with extended periods of quiescence recent luminescence dating studies on closely spaced samples also lead to a similar inference luminescence ages imply high variability in loess sedimentation rates this conflicts with the assumption made in some current attempts to correlate loess records with marine records of almost constant particle fluxes a review of source proximal coversand deposits of northwest europe is also presented evidence of the onset of coversand deposition at 15 ka with a peak in accretion during the younger dryas and subsequent minor reactivation episodes is discussed

the role of the indian summer monsoon and the mid latitude westerlies in himalayan glaciation review and speculative discussion new dates for late quaternary glaciations in the himalayas show that during the last glacial cycle glaciations were not synchronous throughout the region rather in some areas glaciers reached their maxima at the global glacial maximum of c 18 20 ka bp whereas in others glaciers were most extensive at c 60 30 ka bp comparison of these data with palaeoclimatic records from adjacent regions suggest that on millennial timescales himalayan glacier fluctuations are controlled by variations in both the south asian monsoon and the mid latitude westerlies

extent and spatial distribution of pleistocene glaciations in eastern tibet as a contribution to the controversial discussion regarding the nature and extent of the pleistocene glaciation on the tibetan plateau additional observations and results were obtained during several chinese german joint expeditions in the investigation area of the eastern and central tibetan plateau it will be shown that the maximum extent of the last glaciation was limited to the glaciation of isolated mountain groups or smaller plateau glaciations these glaciations are characterized by glacial erosional features such as u shaped valleys in the inner mountain massifs and cirques in the higher summit areas accumulation forms such as terminal and lateral moraines less common than basal moraines are marked by granitic and basaltic erratics using two examples from the eastern margin of the tibetan plateau nianbaoyeze shan and northern chola shan the extent of pleistocene glaciations can be mapped by the distribution of terminal and lateral moraines and erratic granite boulders on the slopes of the surrounding schists two to three main pleistocene glaciations can be separated using weathering criteria paleosols and the overlying stratum on the moraines and associated terrace sequences overlying stratum consist of aeolian sandy silt or solifluction debris the younger moraines are found to be characterized by large erratics were therefore named big boulder moraine and can be found over the investigated area the ice free areas are characterized by pleistocene terraces along the main rivers loess deposits with sand and ice wedges at higher elevations e g the basin of zoige and paleosols in the basins below 3500 m a s l e g aba basin or garze basin the hypothesis of an extensive plateau glaciation could not be verified for this region a rising snowline equilibrium line altitudes elas is revealed in two cross sections during the last glacial maximum lgm at the eastern and northern margin of the tibetan plateau snowlines migrated from about 4000 m in the east minshan to 4300 m in the nianbaoyeze and to about 4700 m in the west bayan har shan a rise was also recorded from about 3800 m in the north central qilian shan up to a range of 4300 4950 m different exposures in the kunlun shan to approximately 5200 m in the tanggula shan in the center of the tibetan plateau the general increase of modern and lgm snowlines or elas towards the plateau corresponds with a decrease of precipitation from east to west and from north to south respectively precipitation was more pronounced at the eastern margin during glacial times than compared to present

advective flow through the upper continental shelf driven by storms buoyancy and submarine groundwater discharge data from monitoring wells on the carolina usa continental shelf require a reevaluation of pore water exchange across the seafloor temperature salinity and 226ra data from 3 offshore wells require rapid and frequent pore water exchange to depths of several meters through sands and other permeable sediments the exchange is driven by tidal pumping storms buoyancy and submarine groundwater discharge tidal pumping causes semidiurnal temperature cycles in one well that can only be explained by rapid fluid flow the effect of large storms is evident in sudden temperature changes 2 4 m below the seabed in two wells these changes require considerable pore water exchange sudden cooling of the ocean may cause pore waters to become buoyant with respect to the ocean and trigger pore water convection to several meters depth as observed in one well the wells also display frequent large factor of ten changes in 226ra activity this requires a substantial input of 226ra enriched fluids to replace 226ra that is lost during exchange events these data support a fourth flow process which is groundwater seeping from the underlying limestone the pore spaces in the overlying sand provide a temporary reservoir for these fluids we conclude that pore water residence times in 2 4 m thick sands on this continental margin are on the order of a few months or less

nile behaviour and late palaeolithic humans in upper egypt during the late pleistocene abstract the reconstruction of the environment and the human population history of the nile valley during the late pleistocene have received a lot of attention in the literature thus far there seems to be a consensus that during mis2 extreme dry conditions prevailed over north eastern africa which was apparently not occupied by humans the nile valley seems to be an exception numerous field data have been collected suggesting an important population density in upper egypt during mis2 the occupation remains are often stratified in or at least related to aeolian and nile deposits at some elevation above the present day floodplain they are rich in lithics and animal bones mainly fish illustrating the exploitation of the nile valley by the late palaeolithic inhabitants the fluvial processes active during that period have traditionally been interpreted as a continuously rising highly braided river in this paper we summarize the evidence thus far available for the late pleistocene on the population densities in the nile valley and on the models of nilotic behaviour in the discussion we include data on the environmental conditions in eastern africa on the aeolian processes in the western desert of egypt derived from satellite images 14 c and osl dates in order to formulate a new model that explains the observed high remnants of aeolian and nilotic deposits and the related late palaeolithic sites this model hypothesizes that during the late pleistocene and especially the lgm dunes from the western desert invaded the nile valley at several places in upper egypt the much reduced activity of the white nile and the blue nile was unable to evacuate incoming aeolian sand and as a consequence several dams were created in the upper egyptian nile valley behind such dams the created lakes offered ideal conditions for human subsistence this model explains the occurrence of late palaeolithic hunter fisher gatherers in a very arid environment with very low nile flows even in late summer

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

on the problem of quaternary glaciations and the extent and patterns of pleistocene ice cover in the qinghai xizang tibet plateau abstract data accumulated during investigations since the 1960s indicate that up to four pleistocene glaciations can be recognized in the qinghai xizang tibet plateau and the adjacent himalaya mountains in order of decreasing age these are the xixabangma nyanyaxungla guxiang and baiyu glacial episodes the history of pleistocene glacial evolution in various areas throughout the plateau differs and the pattern is very complex throughout the early pleistocene the elevation of the qinghai xizang plateau was approximately 2000 m above sea level during the xixabangma glacial episode recorded at higher elevations the climate and topographical conditions on the plateau were largely unfavourable for the development of glaciers present investigations have revealed that the oldest till is only found at isolated localities on the plateau glaciofluvial or alluvial deposits such as the gongba conglomerate dating from 2 4 to 0 73 ma bp and the fluvial lacustrine deposits of the qiantang group dating from 2 4 to 1 7 ma bp are present rather than glacial till therefore the postulate of a large early pleistocene ice sheet proposed previously has been disproves during the most recent glaciation uplift of the plateau and the himalayas continued the majority of the qinghai xizang plateau reached 4000 m a s l and the great himalaya were approximately 6000 m a s l the mountains formed a barrier against the incursion of the indian monsoon so that precipitation decreased sharply on the northern flank of the himalayas and the climate to the north became cold and dry all of the glaciers on the qinghai xizang plateau underwent extensive retreat thus during the pleistocene no unified glacial cover existed over the qinghai xizang plateau similarly the source area of the hwang he yellow river did not support a local ice sheet

loess sedimentation in tibet provenance processes and link with quaternary glaciations abstract well preserved loess deposits are found on the foothills of mountains along the middle reaches of the yarlung zangbo river in southern tibet optically stimulated luminescence osl dating is used to determine loess ages by applying the single aliquot regeneration technique geochemical mineralogical and granulometric measurements were carried out to allow a comparison between loess from tibet and the chinese loess plateau our results demonstrate that i the loess deposits have a basal age of 13 11 ka suggesting they accumulated after the last deglaciation ii loess in southern tibet has a glacial origin resulting from eolian sorting of glaciofluvial outwash deposits from braided river channels or alluvial fans by local near surface winds and iii the present loess in the interior of tibet has accumulated since the last deglaciation when increased monsoonal circulation provided an increased vegetation cover that was sufficient for trapping eolian silt the lack of full glacial loess is either due to minimal vegetation cover or possibly due to the erosion of loess as glaciofluvial outwash during the beginning of each interglacial such processes would have been repeated during each glacial interglacial cycle of the quaternary

filling the gap osl data expanding 14c chronologies of late quaternary environmental change in the libyan desert several decades of geomorphological and archaeological research in the libyan desert conducted by the cologne projects b o s and acacia have yielded a wealth of radiocarbon data from archaeological sites and over the last decade also 48 osl ages mainly from aeolian deposits this paper focuses on the combination of both data sets in order to obtain a synthesis of late quaternary occupational and environmental history in this region case studies demonstrate that despite a poorer time resolution of osl chronologies compared to 14 c data osl ages can be more consistent with the archaeological context particularly if the dating of charcoals poses problems due to poor quality or re deposition comparison of data sets from the egyptian sand seas and from the wadi howar sudan shows that in both cases osl and 14 c data cover complementary time slices on the regional scale however contradictory intervals of aeolian accumulation are documented which can be explained by the different environmental histories the results accentuate that interpretation of osl data has to be done in the context of the entire environmental systems including the effective geomorphological processes r 2007 elsevier ltd and inqua all rights reserved

luminescence dating of holocene playa sediments of the egyptian plateau western desert egypt abstract this study is part of a multidisciplinary project dealing with the investigation of geoarchaeological sites on the egyptian plateau with the aim of reconstructing the palaeoecological background providing age assessment which put the various results in an age frame that is of special interest here results of one particular section have been selected because of a discrepancy in age determination based on different approaches radiocarbon ages were inconsistent with the age range provided by the archaeological context in this area the underestimation observed is inferred to be caused by poor 14 c sample quality an attempt to overcome this problem was the determination of the depositional ages of the non organic sediments by using optically stimulated luminescence osl equivalent doses of four sediment samples were estimated from osl measurements carried out on sand sized quartz grains using the single aliquot regenerative dose sar protocol dose rates were calculated from neutron activation analysis results from the osl ages obtained we conclude that the sediment sequence exposing an alternation of lacustrine and eolian layers was deposited in a short period of time during the mid holocene mean of osl ages 7 8 ka compared to the 14 c ages the luminescence ages fit better into the archaeological context confirmed by surface dating

controversy regarding the existence of a large ice sheet on the qinghai xizang tibetan plateau during the quaternary period

quaternary glaciation of mount everest abstract the quaternary glacial history of the rongbuk valley on the northern slopes of mount everest is examined using field mapping geomorphic and sedimentological methods and optically stimulated luminescence osl and 10 be terrestrial cosmogenic nuclide tcn dating six major sets of moraines are present representing significant glacier advances or still stands these date to 330 ka tingri moraine 41 ka dzakar moraine 24 27 ka jilong moraine 14 17 ka rongbuk moraine 8 2 ka samdupo moraines and 1 6 ka xarlungnama moraine and each is assigned to a distinct glacial stage named after the moraine the samdupo glacial stage is subdivided into samdupo i 6 8 7 7 ka and samdupo ii 2 4 ka comparison with osl and tcn defined ages on moraines on the southern slopes of mount everest in the khumbu himal show that glaciations across the everest massif were broadly synchronous however unlike the khumbu himal no early holocene glacier advance is recognized in the rongbuk valley this suggests that the khumbu himal may have received increased monsoon precipitation in the early holocene to help increase positive glacier mass balances while the rongbuk valley was too sheltered to receive monsoon moisture during this time and glaciers could not advance comparison of equilibrium line altitude depressions for glacial stages across mount everest reveals asymmetric patterns of glacier retreat that likely reflects greater glacier sensitivity to climate change on the northern slopes possibly due to precipitation starvation

tidally driven pore water exchange within offshore intertidal sandbanks part ii numerical simulations field measurements presented by gibbes b robinson c li l lockington d a carey h 2008 tidally driven pore water exchange within offshore intertidal sandbanks part i field measurements estuarine coastal and shelf science 79 pp 121 132 revealed a tidally driven pore water flow system within an offshore intertidal sandbank in moreton bay australia the field data suggested that this flow system might be capable of delivering nutrients and in particular bio available iron across the sediment water interface bio available iron has been implicated as a key nutrient in the growth of the toxic marine cyanobacteria lyngbya majuscula and therefore this pore water exchange process is of interest at sites where l majuscula blooms have been observed in this study two dimensional numerical simulations were used in conjunction with hydraulic data from field measurements to further investigate the tidally induced pore water flow patterns simulation results generally showed good agreement with the field data and revealed a more complex residual pore water flow system in the sandbank than shown by the field data the flow system strongly influenced by the geometry of the sandbank was characterized by two circulation cells which resulted in pore water discharge at the bank edge and also to a permanently ponded area within the sandbank interior simulated discharge volumes in these two zones were in the order of 0 813 m 3 and 0 143 m 3 per meter width along shore of sandbank per tidal cycle at the bank edge and sandbank interior respectively transit times of pore water circulating through these cells were found to range from approximate to 17 days to 60 years with an average time of 780 days the results suggest that the tidally driven flow systems might provide a mechanism for transport of bio available iron across the sediment water interface this flow could constitute a previously unrecognized source of bio available iron for l majuscula blooms in the bay c 2008 elsevier ltd all rights reserved

tidally driven groundwater flow and solute exchange in a marsh numerical simulations 1 tidal fluctuations drive groundwater flow in salt marsh sediments this flow could cause significant chemical exchange across the sediment water interface and could affect marsh ecology numerical models of a generalized tidal creek and marsh were constructed to calculate flow patterns and solute exchange between the marsh and creek the governing equation for saturated unsaturated flow was modified to account for tide related changes in total stress groundwater flow occurred primarily in the creek bank even when the marsh platform was inundated at high tide for marsh sediments with a hydraulic conductivity of 10 4 m s 1 groundwater ages in simulations lasting 60 days were on the order of days near the creek bank and increased to 50 60 days with distance into the marsh the volume of water that discharged between high and low tide was 0 22 0 31 m3 per meter length of channel which for a creek drainage density of 0 012 m 1 corresponds to 10 14 l m 2 d 1 sediment permeability and capillarity were important controls on flow and groundwater age in the marsh sediment compressibility affected groundwater age for compressible sediments representative of mud but not for sediments with lower compressibilities representative of sand simulations were relatively insensitive to dispersivity a comparison of simulation results with other estimates of groundwater exchange from the north inlet south carolina suggest that tides could drive observed exchange there only if the pleistocene sands underlying muddy marsh sediments outcrop within the tidal range

isotopic chronology of the sahara and the sahel during the late pleistocene and the early and mid holocene 15 000 6000 bp

origin of the sinai negev erg egypt and israel mineralogical and geochemical evidence for the importance of the nile and sea level history abstract the sinai negev erg occupies an area of 13 000 km 2 in the deserts of egypt and israel aeolian sand of this erg has been proposed to be derived from the nile delta but empirical data supporting this view are lacking an alternative source sediment is sand from the large wadi el arish drainage system in central and northern sinai mineralogy of the negev and sinai dunes shows that they are high in quartz with much smaller amounts of k feldspar and plagioclase both nile delta sands and sinai wadi sands upstream of the dunes also have high amounts of quartz relative to k feldspar and plagioclase however sinai wadi sands have abundant calcite whereas nile delta sands have little or no calcite overall the mineralogical data suggest that the dunes are derived dominantly from the nile delta with sinai wadi sands being a minor contributor geochemical data that proxy for both the light mineral fraction sio 2 10 al 2 o 3 na 2 o k 2 o cao and heavy mineral fraction fe 2 o 3 mgo tio 2 also indicate a dominant nile delta source for the dunes thus we report here the first empirical evidence that the sinai negev dunes are derived dominantly from the nile delta linkage of the sinai negev erg to the nile delta as a source is consistent with the distribution of osl ages of negev dunes in recent studies stratigraphic studies show that during the last glacial period when dune incursions in the sinai negev erg began what is now the nile delta area was characterized by a broad sandy minimally vegetated plain with seasonally dry anastomosing channels such conditions were ideal for providing a ready source of sand for aeolian transport under what were probably much stronger glacial age winds with the post glacial rise in sea level the nile river began to aggrade post glacial sedimentation has been dominated by fine grained silts and clays thus sea level along with favorable climatic conditions emerges as a major influence on the timing of dune activity in the sinai negev erg through its control on the supply of sand from the nile delta the mineralogy of the sinai negev dunes is also consistent with a proposed hypothesis that these sediments are an important source of loess in israel

cycling of trace metals mn fe mo u v cr in deep pore waters of intertidal flat sediments trace metals mn fe mo u cr v were studied in pore waters of an intertidal flat located in the german wadden sea the study system is an example of a permeable tidal flat system where pore water exchange is affected by tidal driven pressure gradients besides diffusion permanently installed in situ samplers were used to extract pore waters down to 5 m depth throughout one year the samplers were either located close to the tidal flat margin or in central parts of the tidal flat despite dynamic sedimentological and hydrological conditions the general trends with depth in deep tidal flat pore waters are remarkably similar to those observed in deep sea environments rates of trace metal cycling must be comparably large in order to maintain the observed pore water profiles trace metals further show similar general trends with depth close to the margin and in central parts of the tidal flat seasonal sampling revealed that v and cr vary concurrent with seasonal changes in dissolved organic carbon doc concentration this effect is most notable close to the tidal flat margin where sulphate doc and nutrients vary with season down to some metres depth seasonal variations of mn fe mo and u are by contrast limited to the upper decimetres of the sediment their seasonal patterns depend on organic matter supply redox stratification and particulate matter deposited on sediment surfaces pore water sampling within one tidal cycle provides evidence for pore water advection in margin sediments during low tide pore water flow towards the creekbank is generated by a hydraulic gradient suggesting that deep pore waters may be seeping out of creekbank sediments owing to the enrichment of specific elements like mn in pore water compared to sea water seeping pore waters may have an impact on the chemistry of the open water column mass balance calculations reveal that the impact of deep pore waters on the mn budget in the open water column is below 4 mn deep pore water discharge of the whole wadden sea is estimated to be about 9 of the total dissolved riverine mn input into the southern north sea

exploring morphology layering and formation history of linear terrestrial dunes from radar observations implications for titan abstract understanding the morphology and internal layering of large aeolian dune fields through radar observations can provide unique insights into the climatic and geophysical conditions that led to their formation in this study we perform a large scale characterization of the morphology and internal layering of linear dunes in hyper arid areas on earth through utilizing multiple complementary radar datasets sir c imaging srtm interferometry derived elevations and radar sounding or ground penetrating radar gpr linear dune fields in the egyptian desert are of special interest due to their significance as planetary analogs to dunes on mars and saturn s largest moon titan satellite radar imagery and elevation data of the region show significant variance in the geomorphology of different dune fields in egypt in addition gpr probing of the first few meters suggests different inner settings in the layering of dunes of different ages in eastern and western egypt reflecting different paleo climatic regimes that led to their formation furthermore our radiometric analysis suggests that dunes with different inner layering arrangement also exhibit different radar backscatter returns as a function of their heights for relatively younger dunes with a homogeneous inner structure like the ones in eastern egypt in the qattaniya dune field we observe that sigma0 does not change as a function of the dune height for relatively older dunes in western egypt like the great sand sea northern siwa and southern dune fields we observed a linear correlation between sigma0 and the dune height thus surface properties of dunes like morphology and backscatter variation with height are related to inner characteristics like arrangement of internal layering relative ages and can be used to infer their depositional history linear dunes discovered in the equatorial regions of titan by the cassini huygens mission are morphologically very similar to these linear dune fields in the egyptian sahara hence assessing the variability of morphology and radar backscatter properties of titan s dunes as a function of their heights can help constrain the ambiguities associated with their internal structure and formation history and provide insights into titan s paleo wind regimes

implications of late pleistocene glaciation of the tibetan plateau for present day uplift rates and gravity anomalies minimal and maximal models of late pleistocene glaciation on the tibetan plateau are considered the large ice sheet models indicate that disintegration of the ice sheet could have contributed up to 7 mm yr of present vertical uplift and 2 mm yr of horizontal extension the former value can account for more than 50 of the observed uplift in central tibet the peak free air gravity anomaly arising from the deglaciation would be around 5 4 mgal in contrast the smaller ice sheet models do not contribute significantly to the signals of present uplift and gravity anomalies modern geodetic measurements therefore have the potential to constrain the late pleistocene glaciation of the tibetan plateau assuming a large ice sheet over the tibetan plateau the disintegration can contribute up to 6 m of eustatic sea level rise

uranium removal in oceanic sediments and the oceanic u balance pore water uranium data from the nw atlantic ocean cariaco trench black sea and san clemente basin are used to calculate fluxes across the sediment water interface all samples were collected in situ and show depletions in pore water u relative to the overlying water concentration the uptake rate of u derived from pore water gradients reflects the redox environment with lowest fluxes 10 g cm 2 ky in oxic su ic sediments of the nw atlantic dominated by no 3 reduction and higher fluxes 25 70 g cm 2 ky in the anoxic sulfate reducing sediments of the cariaco trench black sea and san clemente basin the anoxic fluxes compare well with previous estimates based on solid phase data calculations indicate that the areally integrated removal of u into su ic hemipelagic sediments is of greater magnitude than that into anoxic sulfate reducing sediments these fluxes are discussed in the context of the oceanic u balance the removal of u in all oceanic sediments is estimated to account for about 65 of the riverine input and this sink plus removal of u in altered oceanic crust balances the most probable value for riverine input

palaeoenvironment and holocene land use of djara western desert of egypt abstract the results of the interdisciplinary project acacia support the assumption of a more humid climate at djara on the egyptian limestone plateau which is a hyper arid desert today during the early and mid holocene the ancient plant and animal inventories give new impetus for the suggestion of an interfingering of two climatic regimes the winter rains from the north and west and the summer monsoonal rains from the south on the latitude of djara a playa sediment sequence the composition of plant and animal taxa as well as the reconstructed settlement patterns indicate a semi arid climate with alternating more humid and drier conditions the concentration of prehistoric sites in the djara depression points to locally favourable conditions in contrast to the surrounding plateau surface the widespread catchment and a distinct system of palaeochannels offered fresh water over a period of time due to the run off from the plateau surface after rain events although the ecological conditions were better during the holocene humid phase than they are today a sedentary way of life was improbable the hydrological constraints require altogether highly mobile subsistence strategies shells of the nile bivalve aspatharia sp spathopsis sp give evidence for contacts between djara and the nile valley which remains beside the egyptian oases an important retreat area with perennially available water the decrease of radiocarbon dates and related archaeological sites around 6300 bp c 5300 cal bc indicate the depopulation of the djara region as a consequence of the drying trend while the drop off of the 14 c dates can also be observed in other desert research areas of the acacia project we date the end of the holocene humid phase about 300 years earlier than previously suggested

constraints on ice sheet thickness over tibet during the last 40 000 years the late quaternary glaciation of tibet has received considerable attention in the last few decades due to its influence on the regional climate especially the asian summer monsoon recently however it has been argued that the tibetan ice sheet also might have played an important role in initiating global scale palaeoclimatic changes controversy however exists on the nature of late quaternary ice cover over tibet due largely to the subjectivity in the interpretation of the sparse and complex geomorphological evidence we have examined this problem in the light of 18o data a temperature proxy of ice cores from the dunde ice cap on the northern flank of tibet considering only the gross features in the dunde ice core isotopic data we have interpreted a temperature decrease of 4 6 c and consequent lowering of equilibrium line altitude ela in the range 700 850 m during the last glacial stage lgs this could have caused depression of the snow line below the mean altitutde of the tibetan plateau resulting in an areally extensive but marginally thick ice cover however if one also considers the possibility that precipitation on the tibetan plateau during lgs may have been significantly lower than at present the ela depression would be much less than that estimated by considering the temperature effect alone

landscape analysis of the huang he headwaters ne tibetan plateau patterns of glacial and fluvial erosion the large scale geomorphology of the huang he yellow river headwaters centered around the bayan har shan 5267 m asl in the northeastern part of the tibetan plateau is dominated by an uplifted

sensitivity of glaciation to initial snow cover co2 snow albedo and oceanic roughness in the ncar ccm we present results from numerical experiments made with a gcm the ncar ccm1 that were designed to estimate the annual balance between snow fall accumulation and ablation for geographically important land regions for a variety of conditions we also attempt to assess the reliability of these results by investigating model sensitivity to changes in prescribed physical parameters experiments were run with an initial imposition of 1 m of midwinter snowcover over all northern hemisphere land points over alaska western canada siberia and the tibetan plateau the model tended to retain this snow cover through the summer and in some cases increase its depth as well we define these regions as glaciation sensitive and note some correspondence between them and source regions for the pleistocene ice sheets an experiment with greatly reduced co2 100 ppm showed a tendency towards spontaneous glaciation i e the model remained snow covered throughout the summer over the same geographic regions noted above with 200 ppm co2 roughly equal to values at the last glacial maximum snow cover over these regions did not quite survive the summer on a consistent basis combining 200 ppm co2 and 1 m of initial northern hemisphere snow cover yielded glaciation sensitive conditions agreeing remarkably well with locations undergoing glaciation during the pleistocene to assess the reliability of these results we have determined minimal model uncertainty by varying two of the empirical coefficients in the model within physically plausible ranges in one case surface roughness of all ocean gridpoints was reduced by an order of magnitude leading to local 10 reductions in precipitation snowfall a change hard to distinguish from inherent model variability in the other case the fraction of a land grid square assumed to be occupied by snow cover for albedo purposes was varied from one half to unity large changes occurred in the degree of summer melting and in some cases the sign of the net balance changed as fractional snow cover was changed we conclude that the model may be able to reveal regions sensitive to glaciation but that it cannot yield a reliable quantitative computation of the magnitude of the net snow accumulation that can be implicitly or explicitly integrated through time

quaternary geology tectonics and distribution of palaeo and present fluvio glacio lacustrine deposits in ladakh nw indian himalaya a study based on field observations abstract the ladakh region of the northwestern indian himalaya is rich in quaternary deposits but it has not received much attention previous quaternary research in the region has focused on the glacial sequences and only some scattered data of the lacustrine deposits are available this article addresses the reconstruction of the palaeo lacustrine deposits and the present day lakes and their distribution in the ladakh region the region was under the influence of tectonic activity and cold climate during the late quaternary times tectonic activity at 50 000 years bp 35 000 years bp and 25 000 years bp has been recorded we report the presence of three major lakes in the region in the late quaternary these formed due to the damming of the indus river and its tributaries by debris avalanches initiated mainly by tectonic activity along the indus suture shyok suture and the karakoram fault these are the spituk leh palaeolake formed 50 000 years bp the lamayuru palaeolake dated to 35 000 years bp in the indus valley and the khalsar palaeolake 60 km in length in the shyok valley vast exposures of the palaeolake deposits ranging from 25 to 150 m in thickness are reported spituk section 25 m lamayuru section 110 m and khalsar 150 m and hundri 100 m and which have a wide lateral extent a glacial lake basin at bhaktpur city north of baralacha la is now completely filled the tsokar lake has been subdivided into smaller units now and the water level is lowering other lakes in the region e g pangong tso tso morari the twin kyun tso lakes are confined to the western side of the study area limited chemical weathering rapid erosion and cold climatic conditions in late quaternary times are suggested by the stable illite values in the lamayuru section four levels of palaeoseismic structures convolute structures sand dykes intraformational folds micro faulting are present in the khalsar section and at three levels in the tirit section at shyok nubra confluence palaeoseismic activity was also prevalent after 25 000 years bp as is evident from the three levels of palaeoseismic structures in the younger sediments

glacial geomorphology and paleoglaciation patterns in shaluli shan the southeastern tibetan plateau evidence for polythermal ice cap glaciation glacial geomorphological mapping from satellite imagery and field investigations provide the basis for a reconstructionof the extent and style of glaciation of the shaluli shan a mountainous area

geochemical composition and provenance of aeolian sands in the ordos deserts northern china abstract identifying the provenance of aeolian sediments in deserts is of great importance for understanding the earth surface processes in this context we conducted detailed fieldwork in the ordos deserts maowusu and kubuqi in the middle portion of the desert belt in northern china and measured the major trace and rare earth elements ree of aeolian sands and their potential source rocks and sediments our results show that aeolian sands in the eastern northeastern and western southwestern maowusu mu us sandy land exhibit different degrees of mineralogical maturity and eu eu values thus we interpret that these aeolian sands have different provenances though in the same sandy land our data suggest that the local lacustrine sediments and sandstones are the main sources of aeolian sands in the eastern province of the maowusu sandy land while aeolian sands in the western maowusu sandy land and the kubuqi desert have the same external sources the comparison of geochemical compositions of sediments in the ordos deserts with their potential sources in adjacent regions indicates that there is no genetic linkage between the helan mountains the yinshan mountains and the ordos deserts although they are not far apart the qilian orogenic belt in the northeastern margin of the tibetan plateau is however the most likely original provenance for the western maowusu mu us sandy land and the kubuqi hobq desert but with fluvial sediments in the ningxia inner mongolian section of the yellow river as the immediate source in one side our results demonstrate that dune fields that are close to each other can have significantly different source sediments on the other hand our work suggests that some dune fields and landforms that are far apart from one another e g the badain jaran desert in western inner mongolia the ordos deserts and the fluvial sediments in ningxia inner mongolian section of the yellow river can share the same ultimate sources

trace element cycling in a subterranean estuary part 2 geochemistry of the pore water abstract submarine groundwater discharge sgd is an important source of dissolved elements to the ocean yet little is known regarding the chemical reactions that control their flux from sandy coastal aquifers the net flux of elements from sgd to the coastal ocean is dependent on biogeochemical reactions in the groundwater seawater mixing zone recently termed the subterranean estuary this paper is the second in a two part series on the biogeochemistry of the waquoit bay coastal aquifer subterranean estuary the first paper addressed the biogeochemistry of fe mn p ba u and th from the perspective of the sediment composition of cores charette et al charette m a sholkovitz e r hansell c m 2005 trace element cycling in a subterranean estuary part 1 geochemistry of the permeable sediments geochim cosmochim acta 69 2095 2109 this paper uses pore water data from the subterranean estuary along with bay surface water data to establish a more detailed view into the estuarine chemistry and the chemical diagenesis of fe mn u ba and sr in coastal aquifers nine high resolution pore water groundwater profiles were collected from the head of the bay during july 2002 there were non conservative additions of both ba and sr in the salinity transition zone of the subterranean estuary however the extent of sr release was significantly less than that of its alkaline earth neighbor ba pore water ba concentrations approached 3000 nm compared with 25 50 nm in the surface waters of the bay the pore water sr salinity distribution suggests a 26 elevation in the amount of sr added to the subterranean estuary the release of dissolved ba to the mixing zone of surface estuaries is frequently attributed to an ion exchange process whereby seawater cations react with ba from river suspended clay mineral particles at low to intermediate salinity results presented here suggest that reductive dissolution of mn oxides in conjunction with changes in salinity may also be an important process in maintaining high concentrations of ba in the pore water of subterranean estuaries in contrast pore water u was significantly depleted in the subterranean estuary a result of sgd driven circulation of seawater through reducing permeable sediments this finding is supported by surface water concentrations of u in the bay which were significantly depleted in u compared with adjacent coastal waters using a global estimate of sgd we calculate u removal in subterranean estuaries at 20 106 mol u y 1 which is the same order of magnitude as the other major u sinks for the ocean our results suggest a need to revisit and reevaluate the oceanic budgets for elements that are likely influenced by sgd associated processes

origin and composition of organic matter in tidal flat sediments from the german wadden sea abstract two sediment cores of up to 550 cm length from an intertidal flat of the german wadden sea near the island of spiekeroog were investigated for the quantity and composition of fossil organic matter om the lowermost parts of the cores are dominated by grey mud of a salt marsh facies containing mainly terrestrial om estimated to account for 60 75 of the total om based on 13 c values and the ratio of short to long chain n alkanols the terrigenous origin of the dominant fraction is indicated among others by high proportions of c 29 sterols and long chain n alkanes typical of plant waxes coarse shell beds overlying the grey mud at 2 2 5 m depth represent a flooding and erosion event possibly related to heavy storm floods in the middle ages within the intertidal sand dominated sediments in the upper parts of the cores total organic carbon toc contents are generally low ranging from 0 1 to 0 5 and correlate well with the amount of mud fraction r 2 0 90 at the surface marine om has not undergone intense diagenetic alteration and so is the dominant fraction eroded peat particles are common throughout most of the sequence and values of the phragmites peat indicator ppi 5 indicate an origin from reed peat due to a high relative abundance of the n c 24 alkane changes in the composition of microbial communities over the depth interval investigated are documented by varying compositions of unsaturated fatty acids with 16 and 18 carbons eicosapentaenoic acid epa was detected along the entire cores and indicates the presence of epa producing bacterial strains

evaluating the life expectancy of a desert pavement abstract this paper integrates prior scholarship on desert pavements with a case study of pavements on stream terraces in the sonoran desert to analyze the processes and site conditions that facilitate the survival of ancient desert pavements this synthesis identifies vital factors key factors and site specific factors promoting pavement stability hyperaridity is the vital factor in pavements surviving for 106 years or more aided by minimal bioturbation and clast size reduction three key factors aid in pavements surviving for 104 to 105 years accumulation of allochthonous dust underneath pavement cobbles a flat topography and a lack of headward retreating swales or gullies a unified explanation for pavement longevity however did not emerge from a literature review because a variety of site specific factors can also promote pavement antiquity including resistant bedrock beneath the pavement disk shaped cobbles to promote dust accumulation and microclimatological and ecological reasons for minimal bioturbation both key and site specific explanations for pavement longevity apply well to a case study of pavements on stream terraces in the sonoran desert central arizona the buildup of cosmogenic 10be and in situ 14c optically stimulated luminescence and varnish microlamination ages reveal stable pavements range in age between 30 and 332 ka with conditions for longevity including flat surface topography pavements underlain by consolidated granitic bedrock a lack of headward retreating gullies and swales 87sr 86sr analyses indicating the infiltration of allochthonous dust floating disk shaped pavement cobbles and a quartzite lithology resistant to disintegration however 10be ages also indicate evidence for the instability of desert pavements on stream terraces underlain by unconsolidated playa clays and unconsolidated fanglomerate these weaker materials allowed the growth of headward retreating swales that in turn promoted exposure of newer gravels by surface erosion

the use of new elevation data srtm aster for the detection and morphometric quantification of pleistocene megadunes draa in the eastern sahara and the southern namib abstract new freely available digital elevation data derived from the shuttle radar topography mission srtm 3 and the advanced spaceborne thermal emission and reflection radiometer aster allow for the first time the use of area wide high resolution elevation models they are useful for various investigations especially in regions that are devoid of detailed topographic maps in this contribution the geomorphological sedimentological geochronological and archaeological results of the cologne collaborative research centre acacia are presented showing that the southern great sand sea of egypt eastern sahara is composed of a complex dune pattern of pleistocene megadunes draa and holocene dunes a conceptual model is presented suggesting draa formed by a strong unimodal trade wind regime that acted most probably as helical roll vortices the draa differ conspicuously in their dimensions and in their evolution from the smaller longitudinal dunes which arise from the recent bimodal wind regime first results of comparative investigations in the southern namib erg namibia yielded similar conditions and a synchronous landscape development based on these results the second part of the paper evaluates the elevation data for both regions with respect to their availability for the determination of draa and dunes and the morphometric quantification of the draa due to their different resolution srtm 3 90 m aster 30 m and their different sensor technology srtm 3 radar aster stereo data both models have assets and drawbacks but can complement each other with the calculation of geomorphometric parameters elevation slope the aster digital elevation model allows the location of the draa of the great sand sea of egypt the quantification of their spatial distribution size volume and consequently the holocene dune movement in conclusion the resolution of the aster elevation model is applicable for quantitative analyses of well defined morphological elements with altitudinal variations 40 50 m the volume estimation presented provides a tool for a realistic assessment of the sand mass balance of sand seas this is not possible with the srtm 3 model and generally impossible with both models if the altitudinal variation is

luminescence dating applications in geomorphological research abstract chronological control remains critical to the interpretation of environmental change and to establishing long term rates of geomorphological processes radiocarbon dating will continue to be the central technique for age assessment of carbon bearing sediments deposited in the last ca 40 ka but alternative absolute dating strategies are required for older or non carbon bearing sediments they include uranium series dating of precipitated sediments k ar and ar ar dating of primary volcanic materials and cosmogenic isotopic dating of surface exposure ages an additional family of methods collectively termed luminescence techniques is increasingly providing a basis for the age assessment of detrital sedimentary deposits these methods directly date the deposition of detrital mineral grains typically quartz and feldspar and have been demonstrated to provide accurate deposition chronologies for up to 800 ka although 150 ka is more typical in the past decade a subset of luminescence techniques which employ optical sample stimulation methods called optical dating has made it possible to date samples from a much wider range of depositional systems given that the methods directly date sedimentation they allow direct assessment of depositional dynamism in numerous terrestrial and subaqueous including marine sedimentary systems and have demonstrated particular potential in the elucidation of chronologies from aeolian dune and loess fluvial colluvial coastal and volcaniclastic environments this paper provides a summary of the principles of the luminescence especially optical dating methods and shows how recent developments specifically single aliquot dating procedures have dramatically enhanced the scope and potential of the method the luminescence techniques are increasingly being incorporated into a wide range of geomorphological studies which seek to establish the nature of landscape changes over the past interglacial glacial cycle and beyond

comparison of late pleistocene and modern glacier extents in central nepal based on digital elevation data and satellite imagery abstract late pleistocene and modern ice extents in central nepal are compared to estimate equilibrium line altitude ela depressions new techniques are used for determining the former extent of glaciers based on quantitative objective geomorphic analyses of a 90 m resolution digital elevation model dem for every link of the drainage network valley form is classified as glacial or fluvial based on cross valley shape and slope statistics down valley transitions from glacial to fluvial form indicate the former limits of glaciation in each valley landsat multispectral scanner imagery for the same region is used to map current glacier extents for both full glacial and modern cases elas are computed from the glacier limits using the dem and a toe to headwall altitude ratio of 0 5 computed ela depressions range from 100 900 m with a modal value of 650 m and a mean of 500 m values consistent with previously published estimates for the central himalaya but markedly smaller than estimates for many other regions we suggest that this reflects reduced precipitation rather than a small temperature depression consistent with other evidence for a weaker monsoon under full glacial conditions

late pleistocene late glacial and holocene glacier advances on the tibetan plateau abstract many end moraine sequences in various mountain areas of the tibetan plateau have already been investigated in detail but a homogeneous chronostratigraphy is still lacking the ice marginal limits are commonly given local names and often the classification does not seem to be secure this is one reason for controversial discussions on the ice extent at the lgm because most organic material in tibet developed at the beginning of the holocene only a few older radiocarbon dates are available up to now late glacial terminal moraines have been found in the western kunlun shan and in the tian shan their radiocarbon ages ca 15 ka bp correspond to a glacier advance south of the qaidam basin which can be correlated with late glacial lacustrine sediments in eastern tibet different ages of peat development in different tongue like basins have been obtained even the bases of peat bogs in basins at nianbaoyeze mountains enclosed by apparent lgm end moraines gave holocene ages three main holocene intervals have been radiocarbon dated from palaeosols and basal peat layers in the area except for a younger glacier re advance at about 3000 bp and those of the little ice age the age of many last glaciation glacier advances on the tibetan plateau are constrained only on the basis of organic matter lying on top of the moraines and therefore might be of late glacial or pleistocene age

quaternary geology in zanskar nw indian himalaya evidence for restricted glaciation and preglacial topography abstract research into the quaternary geology of the nw himalaya has concentrated on the elucidation of the glacial sequence however whilst the main ranges of the himalaya have been subjected to numerous glaciations and are now an obvious alpine glaciated terrain much of the landscape in zanskar and ladakh is more equivocal and does not appear to have been glaciated during this time these landscape facets may therefore have a much older origin and relate to preglacial events in zanskar the main ice source in all glaciations was the strongly glaciated and still glacierized north slope of the main himalaya this ice then flowed generally northwards in the valleys of the zanskar river and its tributaries leaving between them a landscape supporting only a few and scattered minor local glaciers evidence of early glaciation has been found on isolated valley side remnants 200 m above the present rivers reconstruction of these preglacial valley cross profiles show them to be generally broad and shallow with gentle slopes this is in distinct contrast to the present major valley systems which can usually be divided into two parts a lower unglaciated fluvially eroded section such as the lungnak tsarap lingti chu gorge and an upper broad glacial section such as the stod doda valley down valley extent of glaciation is defined by the upper ends of unglaciated fluvial gorges laterally the glaciers were confined progressively to their valleys inevitably there is only evidence of successively smaller subsequent glaciations but the tectonic uplift of the southern ranges may have been a factor in this forming an increasing barrier to the snow bearing monsoon winds

palaeoglaciation of bayan har shan northeastern tibetan plateau glacial geology indicates maximum extents limited to ice cap and ice field scales key locations within an extensive area of the northeastern tibetan plateau centred on bayan har shan have been mapped to distinguish glacial from non glacial deposits prior work suggests palaeo

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

hydrochemical evolution of the east midlands triassic sandstone aquifer england a detailed hydrogeochemical interpretation has been made of the red bed sherwood sandstone triassic aquifer of the east midlands of england on which a radiocarbon model has been used to establish a chronology of groundwaters along the flow line groundwater evolution is dominated by carbonate and sulphate mineral solution and precipitation and by redox reactions cation exchange reactions are negligible and the hydrogeochemistry has evolved in the absence of residual saline water three distinct zones are recognised 1 i recent groundwater mainly 100 y oxidising dominated by congruent dissolution of dolomite and by inputs from atmospheric and anthropogenic sources 2 ii groundwater age 103 104 y predominantly reducing dominated by incongruent dissolution of dolomite 3 iii groundwater age 104 y reducing conditions approach to isotopic and chemical equilibrium in the carbonate system dominance of gypsum dissolution the minor and trace element variation can be interpreted in relation to the principal geochemical reactions and recharge history na cl f and b are controlled by atmospheric inputs sr2 and mn2 trends can be explained by carbonate and sulphate mineral dissolution ba2 is derived from carbonates but controlled by barite equilibrium fe so42 no3 and u are strongly influenced by redox reactions the concentrations of transition metals and other elements remain very low only li and k are considered to represent additions by reaction of silicate minerals the extent of direct anthropogenic influence is probably limited to enhanced so4 no32 and possibly cu zn and pb in zone i

reactive iron in marine sediments abstract a combined field laboratory study has been undertaken to explore the mineralogy concentrations and reactivity towards sulfide of iron in marine sediments also considered is the importance of bacterial fe liberation in regulating pore water chemistry two contrasting marine environments are included one is the relatively fe poor foam site and the other is the fe rich sediment of the subaqueous mississippi delta results show that oxide minerals are the most important fe phases in early diagenetic pyrite formation however viewed separately lepidocrocite and ferrihydrite are more reactive towards sulfide than goethite and hematite when fe oxides are present in relatively high concentrations dissolved sulfide is nearly absent from sediment pore waters with concomitant high concentrations of dissolved fe even in the presence of active sulfide production by sulfate reduction a combination of experimental results and diagenetic modelling shows that in some sediments pore water fe finds it origin in the bacterial reduction of iron oxides this seems the case even though greater amounts of fe are reduced by reaction of sulfide with iron oxides it appears that distinct microenvironments may exist in marine sediments where in one microenvironment sulfide reacts with fe oxides locally precipitating fe sulfide minerals in another fe reduced and solubilized by microorganisms migrates freely into solution

quaternary paleoenvironmental change on the tibetan plateau and adjacent areas western china and western mongolia abstract this paper summarises the nature of climatic change during the last glacial interglacial cycle on the tibetan plateau and adjacent areas the results are derived from inland glacier fluctuations lake level changes and dust loess records of central asia including tibet these are based on our field investigations from 1988 to 1998 and literature surveys the changing extents of different climatic controlled geomorphic landscapes and vegetation zones help to provide estimates of the magnitude of climatic change features such as ice wedge casts loess and palaeosols ela reconstruction s and palaeobotanical data are used to help reconstruct palaeoprecipitation and palaeotemperatures weathering characteristics the overlying strata and some luminescence dates indicate that there are two main glacial ice advances during the last glacial cycle these correspond to marine oxygen isotope stages ois 2 and 4 in some areas as the eastern or northern margin of the tibetan plateau remnants of older glaciations are preserved higher lake levels in the deserts of central asia and on the tibetan plateau are dated to 40 to 25 ka ois 3 and to late glacial early to mid holocene periods our work supports the view that in many areas of central asia cold phases during the last glacial correspond with the maximum extent of glaciers and the periglacial activity the last glaciation produced large alluvial fans alternating with periods of high lake stands on the tibetan plateau however at the northern margin of the plateau in the qaidam basin and in some particular desert areas in western china high lake levels occurred also during the pleistocene and are related with alluvial fans

late quaternary landscape evolution in the kunlun mountains and qaidam basin northern tibet a framework for examining the links between glaciation lake level changes and alluvial fan formation abstract the qaidam basin in northern tibet is one of the largest hyper arid intermontane basins on earth alluvial fans pediment surfaces shorelines and a thick succession of sediments within the basin coupled with moraines and associated landforms in the adjacent high mountain catchments of the kunlun mountains record a complex history of late quaternary paleoenvironmental change and landscape evolution the region provides an ideal natural laboratory to examine the interaction between tectonics and climate within a continent continent collision zone and to quantify rates of landscape evolution as controlled by climate and the associated glacial and hydrological changes in hyper arid and adjacent high altitude environments geomorphic mapping analysis of landforms and sediments and terrestrial cosmogenic radionuclide surface exposure and optically stimulated luminescence dating serve to define the timing of formation of late quaternary landforms along the southern and northwestern margins of the qaidam basin and in the burhan budai shan of the kunlun mountains adjacent to the basin on the south these dates provide a framework that suggests links between climatic amelioration deglaciation lake desiccation and alluvial fan evolution at least three glacial advances are defined in the burham budai shan of the kunlun mountains on the northern side of this range these occurred in the penultimate glacial cycle or early in the last glacial cycle during the last glacial maximum lgm lateglacial and during the holocene on the south side of the range advances occurred during the penultimate glacial cycle mis 3 and possibly the lgm lateglacial or holocene several distinct phases of alluvial fan sedimentation are likewise defined alluvial fans formed on the southern side of the kunlun mountains prior to 200 ka ice contact alluvial fans formed during the penultimate glacial and during mis 3 extensive incised alluvial fans that form the main valley fills north of the burham budai and extend into the qaidam basin are dated to 30 ka these ages suggest that there was a period of alluvial fan aggradation and valley filling that persisted until desiccation of the large lakes in the qaidam basin post 30 ka led to base level lowering and active incision of streams into the valley fills the continued lateglacial and holocene desiccation likely led to further degradation of the valley fills ice wedge casts in the qaidam basin date to 15 ka indicating significant lateglacial climatic amelioration while holocene loess deposits north of the burham bdudai suggest that aridity has increased in the region since the early holocene from these observations we infer that the major landscape changes within high glaciated mountains and their adjacent hyper arid intermontane basins such as the kunlun mountains and qaidam basin occur rapidly over millennial timescales during periods of climatic instability

dune ages in the sand deserts of the southern sahara and sahel in this paper we aim to document the history of aeolian processes within the southern sahara as part of the inqua dune atlas we review available luminescence ages for sand dunes across the southern sahara to develop an improved understanding of the dune chronology on a regional basis and attempt to correlate periods of sand accumulation this was achieved by analysing dune age by country as well as by latitude and longitude the results show a very patchy spatial distribution of dune ages with large gaps that encompass some of the largest sand seas despite these gaps some related patterns in dune morphology and stratigraphy appear to be consistent between northern nigeria and southern mali where older linear dunes are distinct from younger late holocene transverse and barchanoid dunes elsewhere in mauretania linear dunes with different orientations appear to have accumulated at different times most likely in response to changes in atmospheric circulation regional climatic changes are identified where dunes are transgressed by lake deposits within endorehic basins we identify four locations where dune accumulation is terminated by lacustrine transgressions two of which in lake chad and the bodele depression occur shortly after the last glacial maximum lgm the third example at gobiero in niger occurred later in the early holocene around 8 4 ka and a fourth marks a later transgression of palaeolake megachad after 4 7 ka larger scale latitudinal and longitudinal distributions in dune ages across the southern sahara do not show any consistent patterns though this may be due to the small sample size relative to the study area in addition local variations in external controls such as wind regime rainfall vegetation and sand supply need to be considered sometimes on a site by site basis limiting the analysis to dune ages determined using the single aliquot regenerative dose sar protocol indicates a lack of dune preservation during the lgm and the younger dryas times associated with increased dust input to the oceans which is assumed to indicate increased aeolian activity the sar dune dates suggest that preservation of dunes at the onset of succeeding humid intervals is an important component of the dune record the most striking examples of this phenomenon occur where dunes are preserved within endorehic basins by lacustrine transgressions

mid to late holocene climate response from the triloknath palaeolake lahaul himalaya based on multiproxy data abstract a 2 13 m thick palaeolake sequence deposited between the right lateral moraine and the valley wall of triloknath glacier has been studied at high resolution to understand the past climatic changes in lahaul himalaya the osl and ams 14c chronology suggests that the lake building activity was initiated post cooling phase since 6484 cal ybp the combination of sedimentological geochemical and environmental magnetic parameters helped to infer five first order climatic zones the influx of magnetic minerals along with a notable increase in antiferromagnetic mineralogy appearance of hematite and higher chemical index of alteration cia values during 5925 cal ybp to 5676 cal ybp suggests warm and wet conditions owing to enhanced indian summer monsoon ism precipitation corresponding to the mid holocene warming further reduction in the magnetic mineral concentration with few peaks of antiferromagnetic mineralogy and higher cia values suggests warmer episodes within an overall cold climate and the finer ferrimagnetic grain size suggests intermittent low energy and ponding conditions during 3904 cal ybp to 2365 cal ybp this was followed by fluctuating cold arid conditions in response to reduced ism precipitation during 2365 cal ybp and 1758 cal ybp further between 1758 cal ybp to the present episodic warming pedogenic enhancement and increased monsoon precipitation have been recorded a major warm episode medieval warm period as depicted from enhanced antiferromagnetic mineralogy and higher cia values has been recorded between 742 cal yrs bp and 593 cal ybp the sudden drop in the magnetic mineral concentration as well as the cia value around 300 cal ybp 1650 ce is likely because of colder conditions prevailing during the little ice age lia the study illustrates high sensitivity of the lake sediment sequence to witness the climatic episodes experienced in the glaciated regime of the triloknath glacier

recent environmental change and prehistoric human activity in egypt and northern sudan abstract this paper reviews the various late quaternary records that are available from western egypt and northern sudan which includes more than 500 published radiocarbon dates and various sedimentary archives from local landscape components including palaeolakes soils drainages wadis and archaeological sites this palaeoenvironmental compilation frames the spatial and temporal context of local cultural activities when the region was most hospitable 9000 6000 bp at this time monsoonal weather influenced the portion of the african continental interior creating enough convective rainfall for occasional surface water storage in this part of the modern sahara rapid hydroclimatic changes play a key role in geomorphic evolution and resource availability as watering holes formed and dried up in the early to middle holocene neolithic people developed various subsistence strategies including opportunistic hunting of small animals e g gazelle and hare and food related e g wild sorghum millet and legumes activities gathering plant cultivation and livestock rearing during its wettest phases during the monsoonal maximum the area was drought prone sustaining a meager steppe shrub desert flora further desertification and aeolian deflation during the middle and late holocene fostered technological innovation migration and settlement as well as the further development of agrarian communities and complex culture

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

tidally induced groundwater circulation in an unconfined coastal aquifer modeled with a hele shaw cell we use a scaled hele shaw cell to mimic tidally induced nearshore groundwater motion in an unconfined aquifer the low slope angle of sandy beaches contributes to a strongly asymmetric pattern of fluid exchange across the water sediment interface during tidal cycles this asymmetry leads to a time averaged groundwater circulation centered beneath the low tide level horizontal and vertical components of motion are of the same order horizontal seaward flow extends a significant depth beneath the interface consonant with a time averaged water table that is elevated above mean sea level providing the hydraulic gradient necessary to drive this deeper export of mass equal to the time averaged inflow by infiltration this tidally forced flow behavior likely contributes to observed fluctuations in submarine seepage rates moreover the circulation largely involves a subsurface cycling of seawater that infiltrates during the rising tide measurements of submarine seepage near the tidal zone therefore likely involve this cycled seawater as well as freshwater flows

relative dating of quaternary moraines rongbuk valley mount everest tibet implications for an ice sheet on the tibetan plateau abstract relative dating studies applied to high altitude moraines 5000 5500 m in the rongbuk valley on the northern flank of mt everest reveal strong contrasts in the weathering characteristics of the boulders exposed along moraine crests these differences serve to define three intervals of major pleistocene glaciation that on the basis of the degree of weathering are interpreted to extend back to at least the penultimate glaciation and probably encompass at least one still older glaciation either interpretation indicates that some of these moraines are considerably older than their previously assigned ages the magnitude of equilibrium line lowering during neoglacial and late pleistocene times is calculated to be ca 50 100 and 350 450 m respectively the data described here are incompatible with the recently proposed model kuhle 1987 for large scale ice sheet development on the tibetan plateau the reconstructed equilibrium line lowering in the everest region is only 30 of that cited in the ice sheet model moreover the flow patterns and geometry of the former rongbuk glaciers are in opposition to those proposed by the model based on the data from the everest region it appears that valley glaciation rather than ice sheet growth characterized the southern margin of the tibetan plateau during the middle and late pleistocene glaciations