geochemical characterization of the middle and late pleistocene alluvial fan dominated infill of the northern part of the weihe basin central china major reorganizations in climate and tectonic regime occurred in east asia during the pleistocene resulting in large scale environmental changes in this paper a detailed geochemical and mineralogical record of these changes is presented from a distal alluvial fan sedimentary sequence in the northern weihe basin we established that in addition to glacial interglacial variation there are three distinctly different units deposited over the past 1 m y these units are the result of variations in the overall tectonic regime in the northern weihe basin fine grained detrital minerals were predominantly delivered during colder climatic periods whereas evaporative minerals were dominantly deposited during the warmer interglacial periods probably as a result of strong seasonal contrast this compositional variation demonstrates the importance of climate control on hinterland erosion surface runoff chemical weathering and evaporation al normalized ratios of indicative major elements relative to average loess composition indicate important variations in sedimentary processes mostly related to sediment flux si enrichment is an index for past flooding events while fe enrichment just like k and ti reflects influx of clays in contrast ca and mn are strongly enriched throughout the core associated with the authigenic precipitation of carbonates especially during interglacial periods the lower 1000 690 ka and upper 330 0 ka units of the core are characterized by relative intense and frequent flooding which coincided with extensive ponding in the study area in the middle unit 690 330 ka increased salinity levels caused by evaporation as reflected in the high sr ca ratio and dolomite abundance led to increased carbonate precipitation simultaneously the increased influx of fine sediments indicates increased clay production in the source area as a result of a more intense summer monsoon strength after 600 ka 2017 elsevier b v

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

paleoclimatic significance of late quaternary lacustrine and alluvial stratigraphy animas valley new mexico lacustrine and alluvial stratigraphic sequences in the southern animas valley of new mexico allow reconstruction of late quaternary climates four separate stands of late quaternary lake cloverdale in the southern animas valley are recorded by lacustrine shoreline deposits soils and stratigraphic evidence show that three young lake highstands occurred during the holocene and that a higher lake stand occurred 18 000 to 20 00014c yr b p fluvial systems aggraded the southern animas valley during the middle to late holocene the late quaternary stratigraphy shows that several periods during the late holocene were characterized by higher effective precipitation than at any time since the last glacial maximum

age and paleoclimatic significance of late holocene lakes in the carson sink nv usa abstract new dating in the carson sink at the termini of the humboldt and carson rivers in the great basin of the western united states indicates that lakes reached elevations of 1204 and 1198 m between 915 and 652 and between 1519 and 1308 cal yr b p respectively these dates confirm morrison s original interpretation lake lahontan geology of the southern carson desert professional paper 40 u s geol survey 1964 that these shorelines are late holocene features rather than late pleistocene as interpreted by later researchers paleohydrologic modeling suggests that discharge into the carson sink must have been increased by a factor of about four and maintained for decades to account for the 1204 m lake stand the hydrologic effects of diversions of the walker river to the carson sink were probably not sufficient by themselves to account for the late holocene lake level rises the decadal long period of increased runoff represented by the 1204 m lake is also reflected in other lake records and in tree ring records from the western united states

playa lake basins on the southern high plains of texas and new mexico part i hydrologic geomorphic and geologic evidence for their development playa lake basins of the southern high plains texas and new mexico may originate wherever water periodically can collect in a surficial depression they expand however by hydrologic and geomorphic processes including 1 dissolution of lithologic carbonates by infiltrating water 2 transport downward of fine grained clastic and organic material by the infiltrating ground water leading to continuing processes of oxidation and carbonate dissolution in the subsurface and 3 eolian removal of clastic material from the floor of playa lakes which at some sites appears to have deepened playa depressions evidence for largely hydrologic processes of playa basin development on the southern high plains includes 1 a geographic occurrence restricted to relatively flat areas of the high plains surface that have poorly developed fluvial drainage and which are underlain by generally unsaturated clastic and calcrete beds 2 a tendency to occur where water collects and infiltrates as along ephemeral streams and lineations suggestive of fracture systems and 3 hydrologic geochemical petrographic and bore hole data which suggest that recharge to the high plains aquifer is principally from playa lakes that various geochemical changes including carbonate dissolution and enhancement of secondary porosity occur as water moves downward through the unsaturated zone beneath playa lakes and that calcrete beds often are missing or significantly dissolved beneath playa floors

teleconnective response of the pacific north american region atmosphere to large central equatorial pacific sst anomalies abstract a prominent year round ensemble response to a global sea surface temperature sst anomaly field fixed to that for january 1992 near the peak of a major warm el nino southern oscillation episode was observed in a 20 yr integration of the general circulation model used for operational seasonal prediction by the u s national weather service this motivated a detailed observational reassessment of the teleconnections between strong sst anomalies in the central equatorial pacific ocean and pacific north america region 700 hpa heights and u s surface temperatures and precipitation the approach used consisted of formation of monthly mean composites formed separately from cases in which the sst anomaly in a key area of the central equatorial pacific ocean was either large and positive or large and negative extensive permutation tests were conducted to test null hypotheses of no signal in these composites the results provided a substantial case for the presence of teleconnections to either the pos

paleoclimate reconstruction along the pole equator pole transect of the americas pep 1 examples are presented of inter hemispheric comparison of instrumental climate and paleoclimate proxy records from the americas for di erent temporal scales despite a certain symmetry of seasonal precipitation patterns along the pep 1 transect decadal variability of winter precipitation shows di erent characteristics in terms of amplitude and frequency in both the last 100 and last 1000 years such di erences in variability are also seen in a comparison of time series of di erent el nin8 o southern oscillation proxy records from north and south america however these di erences do not appear to a ect the spatial correlation with paci c sea surface temperature patterns local and regional di erences in response to climate change are even more pronounced for records with lower temporal resolution and inter hemispheric synchroneity may or may not be indicative of the same forcing this aspect is illustrated in an inter hemispheric comparison of the last 1000 years of glacier variability and of the full and lateglacial lake level history 1999 elsevier science ltd all rights reserved

late quaternary temperature record from buried soils of the north american great plains we present the first comprehensive late quaternary record of north american great plains temperature by assessing the behavior of the stable isotopic composition 13 c of buried soils after examining the relationship between the 13 c of topsoil organic matter and july temperature from 61 native prairies within a latitudinal range of 46 38 n we applied the resulting regression equation to 64 published 13 c values from buried soils of the same region to construct a temperature curve for the past 12 k y estimated temperatures from 12 to 10 ka 1 k y 1000 14 c yr b p fluctuated with a periodicity of 1 k y with two cool excursions between 4 5 and 3 5 c and two warmer excursions between 1 and 0 c relative to modern early holocene temperatures from ca 10 7 5 ka were 1 0 to 2 0 c before rising to 1 0 c in the middle holocene between 6 0 and 4 5 ka after a cool interlude from 4 2 to 2 6 ka when temperatures dropped to slightly below modern another warm interval ensued from 2 6 to 1 ka as temperatures increased to 0 5 c a final decline in temperature to below modern occurred beginning ca 0 5 ka cooler than present temperatures in the great plains indicate telecommunications with cool water episodes in the gulf of mexico and north atlantic potentially governed by a combination of glacial meltwater pulses and low solar irradiance

late holocene sedimentary environments and lake level fluctuations at walker lake nevada usa walker lake is a terminal lake located at the end of the walker river in western nevada lake level lowering of 50 m during the past 100 yr has led to deep incision by the walker river into the former lake bed this incision has exposed a sedimentary record of lake level fluctuations spanning at least the past 4000 yr fourteen new radiocarbon dates on plant material collected from diverse sedimentary environments including fluvial deltaic beach and offshore settings have led to the refinement of the late holocene lake level curve for this basin this new curve documents at least four highstands that have occurred since ca 3500 cal yr b p between elevations of 1245 and 1255 m the lake has also experienced several lowstands during this same period comparison of this outcrop based record to existing lake level curves and to an oxygen isotope curve for the past 1200 yr reveals many similarities between the records but also some differences therefore research should be conducted to integrate outcrop studies where absolute water depth and lake volume can be estimated with isotopic or other types of proxies from cored sediments that may have higher temporal resolution the extensive and nearly continuous outcrops along the lower walker river also provide valuable information on the relationships between various sedimentary features and their formative water depths in clastic dominated lacustrine systems the paleo water depth relationships deciphered here can be applied in other basins where outcrops are typically more limited to arrive at better constrained lake level records

morphology and paleoclimatic significance of pleistocene lake bonneville spits abstract pleistocene lake bonneville of western utah contains a variety of spits associated with shorelines and other features that formed between 21 000 and 12 000 14 c yr bp field studies in the low lying mountain ranges of the central portion of lake bonneville identified 17 spits of various types the spits are connected to small mountain ranges and islands vary in size from 0 02 to 0 5 km 2 and are composed of coarse grained well rounded poorly sorted sedimentary material sixteen of the 17 spits have a northeasterly to southwesterly orientation implying that winds were from the northwest to northeast approximately 180 out of phase with modern winds in the eastern great basin lake bonneville spit orientation is best explained as the result of persistent northerly winds caused by the high atmospheric pressure cell of the continental ice sheet and passage of low pressure extratropical storms south of the lake similar strong persistent winds are a common feature of modern continental ice sheets and passing low pressure systems if so the north american jet stream tracked south of lake bonneville as recently as 12 000 14 c yr bp well past the height of the last glacial maximum

characterizing formation processes of rimrock lake a late pleistocene holocene playa harney basin south eastern oregon usa using an end member mixing analysis

the impact of high tephra loading on late holocene carbon accumulation and vegetation succession in peatland communities abstract peatlands are major terrestrial stores of carbon c of importance to the global climate system recent studies have made progress in understanding the climatic controls on the c cycle however important interactions between volcanic deposition and peatland c stores remain to be addressed this study uses a 3000 year peatland record from northern japan to examine the interactions between carbon accumulation vegetation community succession and volcanic ash deposition plant macrofossil and testate amoebae records are presented alongside records of total organic carbon nitrogen and phosphorous age depth models are developed using a bayesian approach with seven ams radiocarbon dates and two identified historical tephras from baitoushan ad 969 981 cal bp and hokkaido komagatake ad 1640 310 cal bp volcanoes results show that moderate to high tephra loading can shift peatland plant communities from sphagnum to monocotyledon domination this vegetation change is associated with increased peat humification and reduced carbon accumulation where tephra deposition and reworking has occurred the apparent rate of carbon accumulation can be halved while high tephra loading of the mire surface is sustained sphagnum species vary in their tolerance to tephra deposition after each ash fall sphagnum magellanicum disappeared from the plant macrofossil record whereas sphagnum papillosum showed apparent continuity of development through the 1856 94 cal bp ko c1 tephra high rates of carbon accumulation peaking at 100 g m 2 yr 1 2 3 times faster than the average for northern peatlands were recorded in the sphagnum communities that established after the cessation of tephra deposition and reworking from the ad 969 baitoushan ash fall b tm tephra this peak in c accumulation was coincident with a radical shift in mire nutrient cycling most probably caused by the interaction of s magellanicum with leachates from the underlying tephras the phase of high c accumulation continued for over 300 years offsetting the initial negative impact of the b tm tephra on peatland c accumulation these results suggest that management for ash tolerant sphagnum species could be a highly effective strategy for minimising volcanic disruption to peatland carbon accumulation the study also shows that consideration of volcanic impacts on peatlands is essential for development of more realistic terrestrial carbon balance models in volcanically active regions

land use land cover and point sources of the 15 december 2003 dust storm in southwestern north america abstract a major dust event occurred on 15 december 2003 in the chihuahuan desert region of texas and new mexico usa and chihuahua mexico and in the southern high plains region of texas and new mexico using a modis satellite image 146 individual small scale sources plumes of dust were identified these plumes merged to form the regional scale dust storm the point sources were characterized with respect to land use and land cover using a combination of field work and aerial photography fifty eight of the sources are on cropland mostly on the southern high plains forty nine are on rangeland from across the entire region thirty of the dust plumes originate within playa basins mostly in the chihuahuan desert point sources of dust only represent a small fraction of the total land surface at any given moment i e the period when the image was acquired because most of the land within the region was not subject to erosion during the event in general land use and soil characteristics of point sources matched those of adjacent areas that were not emitting dust at the time suggesting that microscale variations in erodibility or meteorological factors may dictate the actual emission points of dust during individual events

application of avhrr to monitoring a climatically sensitive playa case study chott el djerid southern tunisia the importance of monitoring changes in the levels of lakes within endorheic basins using remotely sensed data as a means of assessing changes in regional aridity is noted large salt playas are highlighted as ephemeral lakes that can display extreme sensitivity to changes in regional rainfall patterns and which commonly do not have extensively managed catchments to explore the application of high temporal frequency monitoring of salt playas using remote sensing the chott el djerid a large salt playa situated in southern tunisia was targeted a short time series of 39 advanced very high resolution radiometer avhrr resolution 1 1km at nadir images of the chott el djerid spanning 36 months between 1987 and 1990 were compiled along with climate information from a weather station at tozeur using image histogram manipulation lake areas were extracted from the time series a good level of agreement was observed between recorded rainfall events and the presence of surface water on the playa and for a limited sample of large flood events it was found that there were significant relationships between rainfall evaporation and estimated lake areas r 2 98 5 p50 001 overall these data suggest that contemporary lake formation is largely controlled by temporal changes in effective precipitation within the basin in addition it was found that the coefficient of variation of the time series and a combination of temporal reflectance profiles extracted from it could be used to give a direct indication of which sedimentary surfaces on the playa are affected by large flood events and the extent to which these events may be preserved within the recent sedimentary record at these sites copyright 1999 john wiley sons ltd

atmospheric circulation during holocene lake stands in the mojave desert evidence of regional climate change it is commonly thought that the climate conditions that supported lakes over a period of years in the mojave desert in southern california only existed before 8 000 yr bp and that the environment has been arid since1 2 here we look at a drill core in the silver lake playa at the terminus of the mojave river and find holocene lake deposits which indicate that shallow lakes existed for at least a few decades these deposits were radiocarbon dated at 3620 70 and 390 90 yr bp corresponding to the early neo glacial and the little ice age respectively3 to identify the conditions necessary to produce these holocene lake events we have examined the modern climate and hydrological patterns that produce ephemeral lakes in this usually arid watershed available data indicate that there is a link between anomalous winter atmospheric conditions over the north pacific and mojave river floods that produced ephemeral lakes in the silver lake playa and that the mojave river filters out small to medium floods and allows only the extreme floods to reach the terminal playa and leave a record of the anomalous conditions we suggest that the late holocene lakes may have resulted from persistent similar atmospheric circulation patterns and winter floods

vegetation history and the impact of tephra deposition during 7000 years based on pollen and tephra analysis of a barasantou bog sediment core eastern hokkaido northern japan abstract to estimate the impact of a volcanic eruption on vegetation we conducted a field survey and collected peaty sediments and made pollen and tephra analysis from barasantou bog in eastern hokkaido northern japan using an electron probe micro analyzer we identified five tephra layers in the core ma g 7 6 cal ka bp ma e 5 5 cal ka bp ma d 4 0 cal ka bp ta c 2 5 cal ka bp and ko c2 ad 1694 when the peat began to accumulate again after deposition of the ma g tephra the groundwater level of this area was very low and alnus poaceae thalictrum artemisia and ferns dominated gradually the groundwater level increased and the condition of this wetland approached the present conditions about 5 0 to 4 5 cal ka bp pinaceae conifers increased 2 5 cal ka bp it is presumed that picea glehnii and abiesspecies formed wetland forests myrica gale and alnus increased again and grew to the edge of the wetland at the same time quercus subgen lepidobalanus decreased and betula increased this trend might be due to the influence of human activity the wetland vegetation changed from thalictrum and artemisia to sanguisorba and then from sanguisorba to menyanthes after the deposition of ma g tephra or after 2 5 ka bp it was thought that the wetland changed from low moor to middle or high moor a tephra layer tens of cm thick is not expected to affect pollen composition and may have no clear impact on the surrounding vegetation sediment with a thickness of a few cm requires a deposition time of approximately 10 years pollen analysis results are on the scale of the average vegetation change during that period we conclude that short term vegetation changes were not detected

evidence from western north america for rapid shifts in climate during the last glacial maximum the estancia basin in southwestern united states contains evidence for strong and rapid pulsations in the supply of moisture brought into the region during the last ice age the pulses were recorded during episodes of stream discharge that spread plumes of fresh water laden with quartz sand over the saline lake the largest pulses in stream discharge lasted only a few decades were organized into cycles that were spaced approximately 200 to 250 and 2000 years apart and were of sufficient magnitude to freshen and maintain the lake at its maximum recorded elevation

late holocene upper timberline variation in the southern sierra nevada alpine timberline has been shown to be a definite tension zone between trees and climate where trees invade higher ground during favourable climatic periods and retreat during periods of deteriorating conditions1 these movements are indicative of an upper forest limit sensitively adjusted to climatic variation here i present absolutely dated dendrochronological records from living trees and standing snags and radiometric dates from relict logs of foxtail pine at cirque peak southern sierra nevada california providing the first detailed record of temperature induced mid to late holocene fluctuations in sierran timberline marked declines in timberline correspond to lichen dated cold periods and or glacial advance

vegetation and climate during the lgm and the last deglaciation on hokkaido and sakhalin islands in the northwest pacific abstract in the process of reviewing pollen data from hokkaido and sakhalin three facts were confirmed 1 the climate was revised to one colder than the last glacial maximum lgm during the last deglaciation in the last glacial period called the kenbuchi stadial which was related to the southward shift of the summer position of the kuroshio oyashio sea current boundary which affected not only northern hokkaido but also eastern hokkaido and northwestern sakhalin 2 from marine isotope stage 3 8000 cal yr bp grassland and mire that developed in hokkaido were characterized by expanded spikemoss which grows in snowpatch grassland and mire in the alpine zone of hokkaido and northern honshu today 3 during the lgm thermokarst depressions so called alas likely formed in eastern hokkaido along the sea of okhotsk based on the yield of the aquatic plants menyanthes and botryococcus in lgm sediments

global monsoons in the mid holocene and oceanic feedback the response of the six major summer monsoon systems the north american monsoon the northern africa monsoon the asia monsoon the northern australasian monsoon the south america monsoon and the southern africa monsoon to mid holocene orbital forcing has been investigated using a coupled ocean atmosphere general circulation model foam with the focus on the distinct roles of the direct insolation forcing and oceanic feedback the simulation result is also found to compare well with the ncar csm the direct effects of the change in insolation produce an enhancement of the northern hemisphere monsoons and a reduction of the southern hemisphere monsoons ocean feedbacks produce a further enhancement of the northern africa monsoon and the north american monsoon however ocean feedbacks appear to weaken the asia monsoon although the overall effect direct insolation forcing plus ocean feedback remains a strengthened monsoon the impact of ocean feedbacks on the south american and southern african monsoons is relatively small and therefore these regions especially the south america experienced a reduced monsoon regime compared to present however there is a strong ocean feedback on the northern australian monsoon that negates the direct effects of orbital changes and results in a strengthening of austral summer monsoon precipitation in this region a new synthesis is made for mid holocene paleoenvironmental records and is compared with the model simulations overall model simulations produce changes in regional climates that are generally consistent with paleoenvironmental observations

mid holocene climates of the americas a dynamical response to changed seasonality simulations of the climatic response to mid holocene 6 ka bp orbital forcing with two coupled ocean atmosphere models foam and csm show enhancement of monsoonal precipitation in parts of the american southwest central america and northernmost south america during northern hemisphere summer the enhanced onshore flow that brings precipitation into central america is caused by a northward displacement of the inter tropical convergence zone driven by cooling of the equatorial and warming of the northern subtropical and mid latitude ocean ocean feedbacks also enhance precipitation over the american southwest although the increase in monsoon precipitation there is largely driven by increases in land surface temperature the northward shift in the equatorial precipitation band that causes enhanced precipitation in central america and the american southwest has a negative feedback effect on monsoonal precipitation in northern south america the simulations demonstrate that mid holocene aridity in the mid continent of north america is dynamically linked to the orbitally induced enhancement of the summer monsoon in the american southwest with a spatial structure wet in the southwest and dry in the mid continent similar to that found in strong monsoon years today changes in winter precipitation along the west coast of north america in central america and along the gulf coast caused by southward displacement of the westerly storm tracks indicate that changes in the northern hemisphere winter monsoon also play a role in regional climate changes during the mid holocene although the simulations with foam and csm differ in detail the general mechanisms and patterns are common to both the model results thus provide a coherent dynamical explanation for regional patterns of increased or decreased aridity shown by vegetation lake status and aeolian data from the americas

monitoring playa lake inundation in the western united states modern analogues to late holocene lake level change abstract closed basin playas are among the most sensitive hydrologic systems globally and are excellent indicators of current and past climatic variability this variability can significantly impact hydrologic regimes and biotic communities and is often expressed in lake bed deposits and shoreline features we analyzed two playa basins in western north america that lie to either side of the current divide between monsoon and westerly precipitation regimes using a 23 year sequence of landsat images at a 16 day time step we determined the playa inundation response to varying precipitation inputs our results show that a strongly contrasting lake inundation response occurs in lake basins separated by only 200 km the animas lordsburg basin shows a marked lake area increase in response to winter precipitation events while the more southerly palomas basin shows a stronger response to monsoonal and el nino type events this sensitivity to different input sources over short distances may explain some of the apparent asynchronous behavior of playa response found in lake records comprehensive regional scale inundation records could be used to understand the dynamics of playa inundation events and how these events are linked to atmospheric circulation and possibly to understand the observed asynchronous behavior of lake basins during the late pleistocene and holocene

a continuous high resolution record of late pleistocene climate variability from the estancia basin new mexico lake sediments that accumulated in the estancia basin central new mexico provide a detailed record of submillennial latest pleistocene climatic oscillations sedimentologic biologic and geochemical proxies for changes in salinity and lake level were used to identify episodes of wet and dry climate that occurred between 24 and 12 k y b p as dated by 14c by means of accelerator mass spectrometry from shoreline and basin center deposits these dates determine the timing and duration of the episodes of wet and dry climate the lake expanded and contracted repeatedly during the last glacial maximum and fluctuated near its highest elevation several times during the interval ca 20 to 15 k y b p a pronounced lowstand lasting 1 k y occurred between ca 15 and 14 k y b p followed by two more highstands of the lake between ca 14 and 12 5 k y b p desiccation of the perennial lake after 12 k y b p was followed by a final poorly dated highstand at ca 10 k y b p the record of lake level fluctuations from the estancia basin provides a high resolution record of changes in water budget in a basin the comparatively simple physiography and hydrogeology of which ensured a direct response to the strong climatic fluctuations that occurred during the last glacial maximum and termination

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

quaternary environmental changes in the drylands of china a critical review abstract this paper reviews our current understanding of quaternary climate and landscape changes in the desert areas of northern china a key portion of the middle latitude drylands on earth combining earlier studies with our recent research and experience we offer a comprehensive picture of the state of chinese deserts during the quaternary and in the interest of enhancing future research identify knowledge gaps and areas of uncertainty lacustrine deposits found over an area ranging from china s western taklamakan desert to the eastern hunshandake sandy lands suggest that extensive lakes occurred in china s deserts during the pleistocene analysis of digital elevation models from srtm shuttle radar topography mission data supports this interpretation and shows the significant extent of these former lakes new estimates of mean annual evaporation of ca 1000 mm from lake surfaces and ca 100 mm from land surfaces confirms that local and regional rainfall is critical for maintenance of desert lakes in this temperate zone especially during intervals when the mean annual rainfall is more than 100 mm rapid shifts between sand seas and lakes in geologically and environmentally diverse settings suggest that the drylands of china are very sensitive ephemeral systems and not long lasting as previously thought available chronologies suggest that there were large lakes in the western taklamakan desert and the chadamu basin during mis marine isotope stage 3 at 30 ka probably related to a period of strong influence of northern hemispheric westerly winds channels and elevation models revealed by srtm data and remains of lacustrine sediments also indicate that there was a large lake in the hunshandake sandy lands in the eastern portion of the desert belt during the quaternary there is significant evidence that during the middle holocene strong summer monsoons led to a relatively large increase in moisture availability in the entire desert belt of northern china lacustrine records from the badain jaran desert in western inner mongolia suggest that it was generally dry before 10 cal ka becoming wetter from 10 to 4 cal ka and dry again afterwards study of palaeosols widely occurring in dune stratigraphy in the eastern portion of the desert belt suggests that there was a period of wet and warm climate in this region during the mid holocene optimum at a minimum between 6 ka and 4 ka but possibly lasting longer recent observations dealing with the generation and transport of dust from central asia indicate that the causal relationship between sand seas and loess sequences is not as close as previously assumed these results suggest that there is an urgent need to examine whether the frequency and amplitude of climatic variation in chinese deserts are somehow similar to that having occurred in the sahara desert of north africa deserts in northern china were also important focal regions for neolithic cultures during intervals when environmental conditions supported a denser vegetative cover there is evidence that some areas of woody vegetation to the west of badain jaran desert were deforested by humans by ca 4000 yr b p although it is still debatable whether humans have had a significant impact in other areas at that time opinions on the severity of desertification vary and are sometimes contradictory due to the lack of long term field based investigations

geochemical and isotopic constraints on the age and origin of the nidar ophiolitic complex ladakh india implications for the neo tethyan subduction along the indus suture zone abstract the nidar ophiolite complex is exposed within the indus suture zone in eastern ladakh india the suture zone is considered to represent remnant neo tethyan ocean that closed via subduction as the indian plate moved northward with respect to the asian plate the two plates ultimately collided during the middle eocene the nidar ophiolite complex comprises a sequence of ultra mafic rocks at the base gabbroic rocks in the middle and volcano sedimentary assemblage on the top earlier studies considered the nidar ophiolite complex to represent an oceanic floor sequence based on lithological assemblage however present study based on new mineral and whole rock geochemical and isotopic data on bulk rocks and mineral separates indicate their generation and emplacement in an intra oceanic subduction environment the plutonic and volcanic rocks have nearly flat to slightly depleted rare earth element ree patterns the gabbroic rocks in particular show strong positive sr and eu anomalies in their ree and spidergram patterns probably indicating plagioclase accumulation depletion in high field strength elements hfse in the spidergram patterns may be related to stabilization of phases retaining the hfse in the subducting slab and or fractional crystallization of titano magnetite phases the high radiogenic nd and low radiogenic sr isotopic ratios for these rocks exclude any influence of continental material in their genesis implying an intra oceanic environment nine point mineral whole rock sm nd isochron corresponds to an age of 140 32 ma with an initial 143nd 144nd of 0 513835 0 000053 end t 7 4 this age is consistent with the precise early cretaceous age of hauterivian 132 2 to 127 1 6 ma to aptian 121 1 4 to 112 1 1 ma for the overlying volcano sedimentary radiolarian bearing chert sequences based on well preserved radiolarian fossils kojima s ahmad t tanaka t bagati t n mishra m kumar r islam r khanna p p 2001 early cretaceous radiolarians from the indus suture zone ladakh northern india in news of osaka micropaleontologists nom spec vol 12 257 270 and cooling ages of 110 130 ma based on 39ar 40ar for nidar spontang ophiolitic rocks maheo g berttrand h guillot s villa i m keller f capiez p 2004 the south ladakh ophiolites nw himalaya india an intra oceanic tholeiitic arc origin with implications for the closure of the neo tethys chem geol 203 273 303 as these gabbroic and volcanic rocks are interpreted to be arc related the new sm nd age data may indicate that intra ocean subduction in the neo tethyan ocean may have started much before 140 32 ma as this date is interpreted as the age of crystallization of the arc magma present and published age data on the arc magmatic rocks from the indus suture zone may collectively indicate episodic magmatism with increasing maturity of the arc from more basic during 140 32 ma when the arc was immature through intermediate andesitic granodioritic at 100 ma to more felsic rhyolitic dioritic magmatism at 50 45 ma when the indian and the asian plates collided

abrupt changes in the asian southwest monsoon during the holocene and their links to the north atlantic ocean during the last ice age the indian ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial scale climate events in the north atlantic region1 2 3 suggesting a mechanistic link in the holocene epoch which had a more stable climate the amplitude of abrupt changes in north atlantic climate was much smaller and it has been unclear whether these changes are related to monsoon variability here we present a continuous record of centennial scale monsoon variability throughout the holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic arabian sea our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the north atlantic region4 including the most recent climate changes from the medieval warm period to the little ice age and then to the present we therefore suggest that the link between north atlantic climate and the asian monsoon is a persistent aspect of global climate

the temporal variability of centimeter scale surface roughness in a playa dust source synthetic aperture radar investigation of playa surface dynamics abstract emission of mineral dust aerosols is highly dynamic in part due to variability in surface erodibility investigation of the variations of surfaces within dust source regions has the potential to elucidate the processes that control erodibility and to improve model representations of dust emission in this study we investigate surface temporal variability in the black rock playa nevada usa using synthetic aperture radar sar satellite data from between 2004 and 2010 the sar backscatter 0 observations of the playa surface are compared to weather station observations and temporally resolved measurements of water inundation derived from multi spectral modis satellite data the data illustrate that centimeter scale surface roughness on the playa is surprisingly heterogeneous over multi meter length scales and evolves dynamically on annual time scales interannual changes in surface roughness on the playa are quite large compared to the variability of surface roughness during the summer months july september suggesting that summer anthropogenic and aeolian processes are substantially less important than water related processes for controlling the evolution of the playa surface playa median 0 is relatively low in years with high annual precipitation 140 mm suggesting that surface water controls centimeter scale surface roughness and potentially erodibility spatially there is a relationship between 0 and the time of year at which a surface dries areas drying in july have significantly higher 0 than surfaces that dry earlier in the year suggesting that spatial heterogeneity in 0 is controlled by cycles of wetting and drying at the edge of the playa lake the implications in the black rock playa and potentially more broadly are that water is a critical factor controlling playa surface evolution and the annual time scale is crucial for investigations of playa erodibility

chronology of expansion and contraction of four great basin lake systems during the past 35 000 years abstract during the past 35 000 years lake bonneville lake russell and lake searles underwent a major period of lake level change the lakes were at moderate levels or dry at the beginning of the period and seem to have achieved highstands between about 15 000 and 13 500 yr b p the rise of lake lahontan was gradual but not continuous in part because of topographic constraints intrabasin spill lake lahontan also had an oscillation in lake level at 15 500 yr b p radiocarbon age estimations for materials that were deposited in the lake basins indicate that lake bonneville rose more or less gradually from 32 000 yr b p and had major oscillations in level between 23 000 and 21 000 yr b p and between 15 250 and 14 500 yr b p lake russell and lake searles had several major oscillations in lake level between 35 000 and 14 000 yr b p the timing and exact magnitude of the oscillations are difficult to decipher but both lakes may have achieved multiple highstand states all four lakes may have had nearly synchronous recessions between about 14 000 and 13 500 yr b p after the recessions the lakes seem to have temporarily stabilized or experienced a minor increase in size between about 11 500 and 10 000 yr b p these data provide circumstantial evidence that the younger dryas event affected climate on at least a hemispheric scale during the holocene the four lakes remained at low levels and small oscillations in lake level occurred an important aspect of the lake level data is the accompanying expansion of lake surface area at the time of the last highstand lake bonneville and lake lahontan had surface areas about 10 times larger than their mean historical reconstructed areas whereas lake russell and lake searles had surface areas about 5 times larger than their mean historical reconstructed areas differences in the records of effective wetness may have been due to the locations of the basins relative to the position of the jetstream or they may have resulted from lake atmosphere feedback processes

the southwest indian monsoon over the last 18 000 years previously published results suggest that the strength of the sw indian monsoon can vary significantly on century to millenium time scales an observation that has important implications for assessments of future climate and hydrologic change over densely populated portions of asia we present new well dated multi proxy records of past monsoon variation from three separate arabian sea sediment cores that span the last glacial maximum to late holocene to a large extent these records confirm earlier published suggestions that the monsoon strengthened in a series of abrupt events over the last deglaciation however our data provide a somewhat refined picture of when these events took place and suggest the primacy of two abrupt increases in monsoon intensity one between 13 and 12 5 ka and the other between 10 and 9 5 ka this conclusion is supported by the comparisons between our new marine data and published paleoclimatic records throughout the african asian monsoon region the comparison of data sets further supports the assertion that maximum monsoon intensity lagged peak insolation forcing by about 3000 years and extended from about 9 5 to 5 5 ka the episodes of rapid monsoon intensification coincided with major shifts in north atlantic european surface temperatures and ice sheet extent this coincidence coupled with new climate model experiments suggests that the large land sea thermal gradient needed to drive strong monsoons developed only after glacial conditions upstream of and on the tibetan plateau receded cold north atlantic sea surface temperatures european ice sheets and extensive asian snow cover it is likely that abrupt changes in seasonal soil hydrology were as important to past monsoon forcing as were abrupt snow related changes in regional albedo our analysis suggests that the monsoon responded more linearly to insolation forcing after the disappearance of glacial boundary conditions decreasing gradually after about 6 ka our data also support the possibility that significant century scale decreases in monsoon intensity took place during the early to mid holocene period of enhanced monsoon strength further highlighting the need to understand paleomonsoon dynamics before accurate assessments of future monsoon strength can be made

monsoon climate of the early holocene climate experiment with the earth s orbital parameters for 9000 years ago values for the precession and obliquity of the earth 9000 years ago indicate that the global average solar radiation for july 9000 years ago was 7 percent greater than at present when the estimated solar radiation values are used in a low resulation climate model the model simulates an intensified continent scale monsoon circulation this result agrees with paleoclimatic evidence from africa arabia and india that monsoon rains were stronger between 10 000 and 5000 years ago than they are today

stratigraphy distribution and petrographic properties of holocene tephras in hokkaido northern japan abstract thirty one widespread visible holocene tephras in hokkaido northern japan were identified and their stratigraphic relationships were examined among these three tephras from komagatake volcano ko c1 ko c2 and ko g three from tarumae volcano ta a ta b and ta c us 1663 from usu volcano ma b from mashu volcano and b tm from baegdusan volcano on the boundary between north korea and china cover a large area of southern and eastern hokkaido and are thus useful tephras for correlating sedimentary records and holocene phenomena all tephras were identified on the basis of their mineral composition and the refractive indices and major elements of their glass shards the volcanic glass samples were dehydrated before refractive index measurement by heating at 400 c for 12 h most holocene tephras in hokkaido can be easily identified on the basis of the refractive indices and major element compositions of volcanic glass

an improved bathymetric model for the modern and palaeo lake eyre abstract here we demonstrate the applicability of using altimetry data and landsat imagery to provide the most accurate digital elevation model dem of australia s largest playa lake lake eyre we demonstrate through the use of geospatial techniques a robust assessment of lake area and volume of recent lake filling episodes whilst also providing the most accurate estimates of area and volume for larger lake filling episodes that occurred throughout the last glacial cycle we highlight that at a depth of 25 m lake mega eyre would merge with the adjacent lake mega frome to form an immense waterbody with a combined area of almost 35 000 km2 and a combined volume of 520 km3 this would represent a vast water body in what is now the arid interior of the australian continent the improved dem is more reliable from a geomorphological and hydrological perspective and allows a more accurate assessment of water balance under the modern hydrological regime the results presented using glas icesat data suggest that earlier historical soundings were correct and the actual lowest topographic point in australia is 15 6 m below sea level the results also contrast nicely the different basin characteristics of two adjacent lake systems lake eyre and lake frome

timing and distribution of alluvial fan sedimentation in response to strengthening of late holocene enso variability in the sonoran desert southwestern arizona usa abstract the integration of geomorphic mapping soil stratigraphy and radiocarbon dating of alluvial deposits offers insight to the timing magnitude and paleoclimatic context of holocene fan sedimentation near yuma arizona mapping of 3400 km2 indicates about 10 of the area aggraded in the late holocene and formed regionally extensive alluvial fan and alluvial plain cut and fill terraces fan deposits have weakly developed gravelly soils and yielded a date of 3200 2950 cal yr bp from carbonized wood alluvial plain deposits have weakly developed buried sandy soils and provided a date of 2460 2300 cal yr bp from a terrestrial snail shell precipitation records were analyzed to form historical analogues to the late holocene aggradation and to consider the role of climatic variability and extreme hydrologic events as drivers of the sedimentation the historical precipitation record indicates numerous above average events correlated to the southern oscillation index soi in the region but lacks any significant reactivation of alluvial fan surfaces the timing of aggradation from 3200 to 2300 cal yr bp correlates well with other paleoclimatic proxy records in the southwestern u s and eastern pacific region which indicate an intensification of the el nino southern oscillation enso climatic pattern and rapid climate change during this period

record of the north american southwest monsoon from gulf of mexico sediment cores summer monsoonal rains the southwest monsoon are an important source of moisture for parts of the southwestern united states and northern mexico improved documentation of the variability in the southwest monsoon is needed because changes in the amount and seasonal distribution of precipitation in this semiarid region of north america influence overall water supply and fire severity comparison of abundance variations in the planktic foraminifer globigerinoides sacculifer in marine cores from the western and northern gulf of mexico with terrestrial proxy records of precipitation tree ring width and packrat midden occurrences from the southwestern united states indicate that g sacculifer abundance is a proxy for the southwest monsoon on millennial and submillennial time scales the marine record confirms the presence of a severe multicentury drought centered ca 1600 calendar cal yr b p as well as several multidecadal droughts that have been identified in a long tree ring record spanning the past 2000 cal yr from west central new mexico the marine record further suggests that monsoon circulation and thus summer rainfall was enhanced in the middle holocene ca 6500 4500 14 c yr b p ca 6980 4710 cal yr b p the marine proxy provides the potential for constructing a highly resolved well dated and continuous history of the southwest monsoon for the entire holocene

lake bonneville fluctuations and global climate change lake bonneville the largest late pleistocene closed basin lake in the north american great basin fluctuated widely in response to changes in climate the geochemistry and mineralogy of endogenic calcium carbonate deposited in deep water and stratigraphic studies of shore zone deposits provide evidence of millennial scale lake level fluctuations that had amplitudes of about 50 m between 30 and 10 ka falling lake events occurred at 21 18 5 19 17 5 16 15 5 14 13 and 10 ka radiocarbon years synchronously with the terminations of heinrich events h1 and h2 and other smaller scale iceberg rafting events a b c and younger dryas in the north atlantic ocean the lake bonneville results thus support other climate records that suggest that late pleistocene millennial scale climate change was global in extent the size and shape of the northern hemisphere ice sheets which determined the mean positions of storm tracks may have been the primary control on late pleistocene water budgets of great basin lakes

palaeolimnological records of climate change in mexico frustrating past promising future central and northern mexico contain numerous closed basin lakes that may preserve valuable palaeoclimatic records in their sediments research has however focused on the basins of the trans mexican volcanic belt tmvb in particular the basin of mexico results from the zacapu basin michoacan are used to illustrate both the potential benefits and problems of palaeoclimatic studies in such basins three diatom sequences provide a discontinuous record spanning 30 000 years the presence of a deep lake before 28 000 bp is indicated there are no sediments covering the pleistocene holocene transition during the holocene only minor changes in lake level are indicated with drying about 5000 bp and most importantly about 1100 years bp difficulties in reconstructing past climates in this basin and in many others in central mexico include discontinuous sedimentation obtaining a reliable chronology the possible impacts of tectonism and the effects of long term human disturbance in spite of these problems the records from zacapu and other basins in the region provide a basis for preliminary palaeoclimatic interpretation there is a clear need for long records for high resolution studies to investigate the detailed nature of climate and for more work outside the tmvb

large holocene lakes and climate change in the chihuahuan desert lake level variations preserved as beach ridges in the laguna el fresnal and laguna santa maria subbasins northern mexico record millennially spaced episodes of increased precipitation during the holocene epoch we find that the early middle and late holocene were punctuated by periods wet enough to establish large pluvial lakes in currently dry basins in the chihuahuan desert the largest dated pluvial lake covered 5650 km2 during the early holocene constructional beach ridges in these subbasins are 221 33 14c yr b p little ice age equivalent 3815 52 to 4251 59 14c yr b p early neoglacial 6110 80 to 6721 68 14c yr b p mid holocene and 8269 64 to 8456 97 14c yr b p early holocene dates that correlate with other millennially spaced wet or cold events in the northern hemisphere we attribute these wet episodes to increased precipitation cooler temperatures and reduced evaporation following southward shifts in winter storm tracks which are related to long term el nino southern oscillation variability during the holocene

late pleistocene and late holocene lake highstands in the pyramid lake subbasin of lake lahontan nevada usa shoreline geomorphology shoreline stratigraphy and radiocarbon dates of organic material incorporated in constructional beach ridges record large lakes during the late pleistocene and late holocene in the pyramid lake subbasin of lake lahontan nevada usa during the late holocene a transgression began at or after 3595 35 14 c yr b p and continued perhaps in pulses through 2635 40 14 c yr b p resulting in a lake as high as 1199 m during the latest pleistocene and overlapping with the earliest part of the younger dryas interval a lake stood at approximately 1212 m at 10 820 35 14 c yr b p and a geomorphically and stratigraphically distinct suite of constructional shorelines associated with this lake can be traced to 1230 m these two lake highstands correspond to periods of elevated regional wetness in the western basin and range that are not clearly represented in existing northern sierra nevada climate proxy records

an enhanced role for the tropical pacific on the humid pleistocene holocene transition in southwestern north america abstract climate effects on landscape evolution during the late pleistocene holocene transition 14 6 8 ka in southwestern north america traditionally are linked to the activity of the north american monsoon and to vegetation change related to a decrease in winter precipitation acting in response to orbital cyclicity we performed an integrated analysis of regional alluvial fan lacustrine and paleobotanical records for the area comparing them with hemispheric and regional paleoclimate proxies our focus was on the potential role the tropical pacific has as a synoptic pattern modulator and moisture source for hydrogeomorphic activity in the region our analysis indicates that the onset of alluvial fan aggradation in most of the region at 13 5 ka could have been a response to semi permanent el nino like conditions in the tropical pacific which enhanced the frequency of winter frontal storms as well as increased penetration of tropical cyclones in the region the north american monsoon was restricted in extent and intensity until 7 ka and probably was not a major factor in alluvial fan aggradation a second stage of alluvial fan aggradation from 11 5 to 9 ka was dominated by hyper concentrated flows and sheet flood sedimentation along with deposition in fluvial settings storms were probably were linked to landfall of enhanced water vapor bands in the leading edge of winter extra tropical cyclones with moisture advected directly from the tropical pacific at 8 ka favorable conditions for the occurrence of these storms waned and storm tracks shifted northward analysis of modern analogs for storm types described above as prevalent during this period indicates that changes in circulation patterns across the tropical pacific can affect storm properties enough to explain the observed geomorphic effects regardless of other factors traditionally considered of large impact like vegetation change our results suggest that the tropical pacific plays a larger role than currently thought in landscape evolution of the region

millennial and centennial scale vegetation and climate changes during the late pleistocene and holocene from northern new mexico usa abstract high resolution pollen and magnetic susceptibility ms data from a sediment core from an alpine bog 3100 m in the sangre de cristo mountains new mexico record variations in treeline elevation and in sedimentation for the last 14 ka cal yr bp strong correspondence between the paleovegetation and the ms profile suggests that both records can be used to reconstruct past climatic conditions the coldest conditions in this area occurred at the end of the late pleistocene during the pinedale glaciation and the younger dryas chron a general warming trend took place during the early holocene lasting until 5 6 ka when the warmest conditions occurred a progressive climate cooling is then observed until today millennial and centennial scale changes are also observed throughout the vegetation and ms records the higher amplitude millennial scale cold events appear to correlate with the timing and duration of episodes of enhanced sea ice drift in the north atlantic and the lower amplitude centennial scale cold events may correlate with periods of lower solar activity a solar climate connection is suggested from these records by a prominent ca 200 yr cycle in tree pollen abundance which may correlate with the 208 yr suess solar cycle this study shows an immediate response of the vegetation treeline to climate change at millennial and centennial scales probably related to variations in summer insolation and solar activity during the late pleistocene and holocene such high resolution studies are very important in order to predict future climate change and particularly in very arid areas where human activity and economies are strongly influenced by climate