a morphological analysis of tibetan limestone pinnacles are they remnants of tropical karst towers and cones abstract limestone pinnacles on mountain slopes in tibet were measured for morphological analysis and the results were compared with those from tropical towers and cones on karst mountain slopes of shuicheng southwest china in the form analyses the symmetric products p of tibetan pinnacles present large differences between individual pinnacles the plan forms represented by long short axes ratios r l s are mostly irregular and scattered and the diameter height ratios r d h reveal that the tibetan features could belong to any three cone or tower karst types according to balaze s classification of karst towers the direction of pinnacle development seems to be primarily related to slope aspect and to geological structure the morphological structure and orientation analyses show that pinnacle development is largely controlled by lithological and stratigraphic conditions the closed water catchment structure which is a basic feature in karst areas has not been found in the limestone pinnacle areas of tibet the results of the form and structure analyses for the tibetan pinnacles differ from those for tropical and subtropical karst areas further analysis indicates that tibetan limestone pinnacles were formed by strong physical weathering under periglacial conditions four kinds of morphogenesis of the pinnacles are suggested

gcm analysis of local influences on ice core δ signals a high resolution gcm is used to examine the effect of changes in local surface climate parameters on the ice sheets that can influence the interpretation of the isotopic signal of the ice from deep cores the model suggests that the 10 c difference between the lgm surface temperature deduced from borehole thermometry and that deduced from the water isotope analysis to a great extent may be due to a modification of the precipitation seasonality in central greenland for central east antarctica the model tends to suggest a weak opposite bias

properties of modern dust accumulating in the uinta mountains utah usa and implications for the regional dust system of the rocky mountains a growing body of work is illuminating the importance of dust as a component of soil development and biogeochemical cycling in alpine environments of the rocky mountains nonetheless important questions remain about the dust system in this region due to a paucity of focused studies and direct measurements this project involved deployment of modified marble dust traps in the alpine zone of the uinta mountains of utah to trap modern atmospheric dust over a two year period results indicate that dust accumulation rates are similar to values previously reported for the wind river range of wyoming but less than values for south western colorado suggesting a south to north decrease in regional dust flux the overall mean grain size of uinta dust is similar to values reported by prior studies in colorado indicating a general uniformity in grain size distribution uinta dust is dominated by quartz plagioclase k feldspar and illite with trace amounts of kaolinite chlorite and amphibole in contrast only quartz and k feldspar are present in the uinta bedrock confirming an exotic origin for the dust arriving in the alpine zone exotic mineralogies have also been reported in dust from other mountain ranges in the western united states indicating that eolian delivery of allochthonous minerals is a widespread process geochemical analysis reveals that bi na p zn sn cu cd ba ni w sb pb and tl in uinta dust are elevated 10 to 80 times above their abundances in local bedrock these results support reports of anthropogenic elemental enrichment in lake sediments from colorado and utah patterns of elemental loading suggest that certain elements are delivered by winds arriving from different directions raising the possibility that some elements could be associated with unique source areas copyright 2014 john wiley sons ltd

the growth of siliceous sinter deposits around high temperature eruptive hot springs abstract siliceous hot spring deposits sinter are of interest as they are indicative of hydrothermal resources at depth and may provide evidence for early life on earth and possibly mars numeric models of concurrent evaporation and opal a precipitation around high temperature 73 c eruptive hot spring vents such as geysers show that silica is most efficiently precipitated by complete evaporation owing to very sluggish growth kinetics for silica precipitation from supersaturated hydrothermal water where evaporation is complete between geyser events areas of initially deeper water precipitate more silica that over time fill in topographic lows to produce a smooth surface in contrast incomplete evaporation in which water is left in low areas prior to being washed away by the next geyser event or equivalently where there is continuous surface flow in topographic low areas tends to enhance the growth of minor topographic highs and leads to an increase in surface roughness such as seen in the development of knobby geyserite sinter texture around vents

paleoclimatic forcing of magnetic susceptibility variations in alaskan loess during the late quaternary visual matches and statistical tests suggest correlations between marine isotope curves retrodictive solar insolation at lat 65 n and magnetic susceptibility profiles through late quaternary age alaskan loess sections the susceptibility changes largely appear to reflect variability in magnetite content due to climatically controlled changes in wind intensity and competence magnetic susceptibility profiles through massive loess can provide stratigraphic context for intercalated paleosols and tephras a prominent paleosol correlated with marine isotope stage 5 occurs several metres above the old crow ash in loess sections indicating that this important tephra is older than suggested by thermoluminescence dates and may have been deposited ca 215 25 ka

physico chemical and environmental controls on siliceous sinter formation at the high altitude el tatio geothermal field chile abstract el tatio geothermal field is located 4270 m above sea level in the altiplano northern chile siliceous sinter deposits from el tatio were studied to understand the influence of water chemistry and the extreme climatic conditions on their textures and mineralogy the results of this study show that the mineralogy of el tatio sinters include of opal a and accessory minerals such as halite gypsum and cahnite ca 4 b 2 as 2 o 12 4h 2 o which precipitate by full evaporation of high arsenic boron and calcium thermal waters el tatio sinters show a high degree of structural disorder probably linked to cation incorporation into the silica structure and or the occurrence of micro to nano scale accessory minerals the high content of cations in the thermal waters is strongly tied to relatively high silica precipitation rates considering silica concentration in water 147 285 mg l sio 2 precipitation rate reach 2 5 kg m 2 per year based on in situ precipitation experiments the particular environmental conditions of this high altitude geothermal area that produce high water cooling rate and high evaporation rate may also be responsible for the fast silica precipitation low environmental temperatures create freezing related sinter textures i e silica platelets and micro columns ridges silicified microbial filaments are also characteristic of el tatio sinters and they are indicative of water temperature and hydrodynamic conditions at the moment of sinter formation however sinter textural interpretation in a high altitude andean context must be done carefully as specific relationships between microbial and hydrodynamic textures are found

partly pedogenic origin of magnetic variations in chinese loess quaternary sequences of interbedded aeolian silts loess and buried soils palaeosols potentially provide one of the best terrestrial records of past climates1 5 magnetic susceptibility variations in loess and palaeosol sequences from china are strongly correlated with climate induced fluctuations of oxygen isotope ratios in deep sea sediments2 4 6 8 as an explanation of this correlation it has been suggested that the recorded variations in magnetic susceptibility depend primarily on the degree of dilution by non magnetic bulk loess constituents of a uniform magnetic assemblage derived from remote but unknown sources6 8 it has also been suggested that such a model involving changes in the accumulation rate of loess superimposed on a constant flux of magnetic particles provides a relative geological timescale through the control of loess deposition by astronomically modulated climate fluctuations7 here we report a preliminary test of this model using rock magnetic properties especially sensitive to variations in magnetic grain size our results show that palaeosols are characterized by much finer magnetic grain size assemblages than are the intervening loess units this suggests that a simple model based on constant magnetic influx and dilution by variable amounts of non magnetic loess is inadequate our magnetic measurements establish the close comparability of the fine grained magnetic minerals in the palaeosol samples to those in contemporary soils and thus point to a partially pedogenic origin for the magnetic mineral assemblages in the palaeosols

oxygen and hydrogen isotopes in the hydrologic cycle changes of the isotopic composition of water within the water cycle provide a recognizable signature relating such water to the different phases of the cycle the isotope fractionations that accompany the evaporation from the ocean and other surface waters and the reverse process of rain formation account for the most notable changes as a result meteoric waters are depleted in the heavy isotopic species of h and o relative to ocean waters whereas waters in evaporative systems such as lakes plants and soilwaters are relatively enriched during the passage through the aquifers the isotope composition of water is essentially a conservative property at ambient temperatures but at elevated temperatures interaction with the rock matrix may perturb the isotope composition these changes of the isotope composition in atmospheric waters surface water soil and groundwaters as well as in the biosphere are applied in the characterization of hydrological system as well as indicators of paleo climatological conditions in proxy materials in climatic archives such as ice lake sediments or organic materials

snow isotope diffusion rates measured in a laboratory experiment the diffusion of stable water isotopes in snow was measured in two controlled laboratory experiments two batches of snow of different isotopic composition were stacked alternately with varying layer thicknesses the stack was stored in a freezer room at constant temperature for several months and sampled at regular intervals to analyse the diffusion measured isotope profiles were fitted to a theoretical model with diffusion length as the fit parameter in the first experiment we observed a difference in diffusion rates between layers of different thicknesses which is likely caused by layers of snow not being in proper contact with each other in the second experiment we found very good agreement between measurements and model results the measured diffusivity is compared with theory in which we mainly focus on the temperature dependence of the ice vapour fractionation factors this temperature dependence is slightly different for the different isotopes of water which leads to a difference in diffusion rates we illustrate how our set up can be used to measure the ratio between ice vapour fractionation factors of oxygen 18 and deuterium which determine the relation between the difference in diffusion and the firn temperature

late quaternary aeolian sedimentation in central and south eastern tibet abstract the geomorphology and the cover sediments in the central and south eastern part of the tibetan plateau provide information about climatic change luminescence dating of aeolian and colluvial silts on top of different moraine sequences provides the first indications for the timing of these sediments during the late quaternary and holocene although there is a widespread cover of aeolian mantles in tibet only a few papers have focussed on them up to now samples from silt layers on top of pleistocene moraines or solifluction debris from central and southern tibet at elevations above 4000 m asl provide early holocene ages in most sections the aeolian silt on top of the bomi moraine in southeastern tibet situated at an elevation of about 3000 m asl provides an age of 25 ka according to geomorphological investigations the bomi moraine dates from the last ice age which can be confirmed by the luminescence data moreover one sample from a silt layer in between gravel layers xainxa is also pleistocene in age according to its sedimentary and geomorphological situation in the tibetan plateau pleistocene loess mainly occurs below 4000 m asl the holocene material a more sandy silt lying above 4000 m asl however aeolian material capping the moraines provides only minimum ages for the terminal moraines the time interval between glacier retreat and the accumulation of aeolian sediments may be several thousand years the most important fact is the trapping of dust in general lakes and a denser vegetation cover are or were the main traps for the typical loess found in the mountain areas of the tibetan plateau

isotopic characteristics of cryospheric waters in parts of western himalayas india present study has analysed stable isotopic composition 18o and 2h of cryospheric waters of ladakh and kashmir regions located in western himalayas india the samples of glacier ice 11 and melt water stream 10 collected altitude ranging between 3168 and 5465 m a s l have been analysed for 18o and 2h the measured 18o values of glacier ice varied between 16 5 and 13 8 in ladakh and between 12 8 and 9 6 in kashmir region study shows that isotopic characteristics of ice samples collected from snout of glaciers in ladakh and kashmir region are distinctly different from each other melt water samples collected from streams near the snout during september have shown good resemblance with the glacier ice melt of respective region the d excess of glaciers and melt water of kashmir region varied from 21 0 to 25 6 and from 18 0 to 21 5 respectively the d excess of glaciers of ladakh region have been found between 13 5 and 16 7 and of the melt water between 11 6 and 12 6 depleted 18o signature and low d excess value of glaciers of ladakh in comparison with that of kashmir region may be attributed to sublimation process triggered by cold arid climatic conditions the present study of kashmir and ladakh region suggest that isotopic composition of glacier ice is influenced by post depositional alteration such as sublimation during snow to glacier ice transformation

soils of the high mountain region of eastern nepal classification distribution and soil forming processes abstract eleven soil profiles of the mt everest region dudh kosi and beni khola valley between 2 700 and 4 900 m a s l were investigated to provide information about soil classification zonal distribution and changes in the chemical and mineralogical properties with elevation and climatic conditions the soils are mainly developed from deposits of the last main glaciation which are predominated by paragneisses they were classified as entisols inceptisols and spodosols according to the u s soil taxonomy soil survey staff 1990 detailed chemical and clay mineralogical analyses indicate a strong influence of the elevation integrating several factors of climatic conditions and bioclimatic zones on soil types and soil forming processes inceptisols predominate in the hill zone and lower tropical mountain zone between 2 000 and 3 000 m a s l they are replaced by spodosols in the subalpine forest and alpine shrub zone up to 4 500 m on eroded sites and locations above 4 500 m shallow and stony soils classified as entisols are present a linear decrease in the intensity of weathering with increasing elevation is shown by the decreasing clay content of the main weathering horizon

geothermal point sources identified in a fumarolic ice cave on erebus volcano antarctica using fiber optic distributed temperature sensing 1 degassing of co2 on the flanks of the active erebus volcano is thought to occur mainly through fumarolic ice caves fic and associated fumarolic ice towers there is also minor co2 degassing from isolated areas of warm ground the mechanism supplying heat and co2 gas into the fic is poorly understood to investigate this system a fiber optic distributed temperature sensing dts system was deployed in a fic to obtain temperature measurements every meter the dts data reveal that localized gas vents gv supply heat to the fic air mass and are an important component of the fic microclimate fic temperature is anti correlated with local atmospheric pressure indicating barometric pumping of the gv these results enable the use of fic temperature as a proxy for flank degassing rate on erebus and represent the first application of dts for monitoring an active volcano

cryogenic opal a deposition from yellowstone hot springs sub zero winter temperatures on the yellowstone plateau alter the opal a precipitation pathway offluid erupting from hot springs and geysers frozen fluid often only meters from boiling pools contains abundant opal a particles comprising sheet and filamentlike aggregations of opal a microspheres which are formed by opal a precipitation in brine pockets channels and veins by natural cryogelling unconsolidated cryogenic opal a sediment accumulates in and below water ice where it is locked until spring thaw conditions sediment is then either remobilized contributing large volumes of opal a particulate to geothermally influenced wetlands or becomes adhered in situ by dehydration and cementation this strongly seasonal opal a precipitation regime has been overlooked in investigations of sinter deposition accretion rates and microbe mineral interactions natural opal a textures recorded fromyellowstonemaybereplicatedsimplybyfreezingandthawingsyntheticsilica saltsolutioninthelaboratory cryogenicprocess may have influenced mineral precipitation and sediment accumulation in many other geothermal areas particularly active terrestrial springs located at high altitude latitude fossil systems influenced by ancient glaciations plus potential astrobiological targets e g mars and europa 2007 elsevier b v all rights reserved

cryogenic silicification of microorganisms in hydrothermal fluids silica rich hydrothermal fluids that experience freezing temperatures precipitate cryogenic opal a coa within ice bound brine channels we investigated cryogenic silicification as a novel preservation pathway for chemo and photo lithotrophic bacteria and archaea we find that the co partitioning of microbial cells and silica into brine channels causes microorganisms to become fossilised in coa rod and coccoidal form bacteria and archaea produce numerous cell casts on coa particle surfaces while chloroflexus filaments are preserved inside particle interiors coa particles precipitated from natural icelandic hot spring fluids possess similar biomorphic casts including those containing intact microbial cells biomolecules and inorganic metabolic products are also captured by coa precipitation and are detectable with a combination of visible shortwave infrared reflectance ftir and raman spectroscopy we identify cryogenic silicification as a newly described mechanism by which microbial biosignatures can be preserved within silica rich hydrothermal environments this work has implications for the interpretation of biosignatures in relic hydrothermal settings and for life detection on mars and enceladus where opaline silica indicative of hydrothermal activity has been detected and freezing surface conditions predominate

pedogenic studies in aeolian deposits in the high mountain area of eastern nepal abstract pedogeochemical analyses were used to study soil development in aeolian deposits overlying moraines and landslide debris in the imja drangka valley a tributary of the dudh kosi in the khumbu himal eastern nepal particle size analysis trace element ratios iron fractionation and weathering indices based on total element contents were combined with radiocarbon analyses and morphostratigraphical features to obtain information on stratification of the solum the extent of soil weathering pre weathering and relative or absolute age of the period of deposition and soil development the results indicate several periods of deposition of loess like material at least up to 5000 m asl again indicating differences in the age and source of the aeolian deposits or different extents of weathering independent of recent soil forming processes at the study sites several paleosols have developed in these aeolian deposits during the holocene a pedogenic overprint by recent pedogenic processes can be seen beyond boundaries of beds within the aeolian deposits it may complicate the interpretation and correlation of loess paleosol sequences additional data from radiocarbon dating of buried a horizons and charcoal indicate a period of loess accumulation 3000 to 4000 years ago covering older aeolian deposits of early holocene to late pleistocene age

a magnetic investigation of a late quaternary loess palaeosol record in siberia summary a late quaternary loess palaeosol sequence at kurtak in the yenisey river valley southern siberia has been studied magnetically the 34 m section 340 samples exhibits variations in magnetic susceptibility which can be correlated with oxygen isotope stages 1 7 a detailed sampling of stage 5 a further 209 samples permits the identification of substages 5a e the susceptibility variations themselves are in the opposite sense to that found in the classic sections of the chinese loess plateau but are in agreement with the wind intensity model which has been put forward to explain similar findings in loess sequences in alaska published results for the susceptibility of magnetite imply volume fractions of 0 2 per cent in glacial stages 2 and 4 dropping to 0 05 per cent in stages 1 3 and 5 these fluctuations match the aeolian flux variations observed in core v21 146 from the north pacific even though the warmer intervals are characterized by lower susceptibilities the observed frequency dependence of susceptibility indicates that new magnetic material is produced as a result of pedogenesis during interglacial and interstadial times

paleosubarctic eolian environments along the southern margin of the north american icesheet and the southern margin of siberia during the last glacial maximum abstract based on a negative correlation of magnetic susceptibility with organic matter content and the degree of gleying documented both in north american and southern siberian eolian sequences the authors propose that reducing conditions of incipient histosol development contributed to the alteration of magnetic minerals from strongly magnetic forms of oxidized iron to weakly magnetic forms therefore the magnetic susceptibility is basically an indicator of redox cycles well vegetated conditions generally dominated the later part of the last glacial maximum lgm 15 000 8000 14 c years bp and poorly vegetated conditions the early part 21 000 15 000 14 c years bp with a rapid transition around 15 000 14 c years bp chronologically corresponding to many well documented rapid transitions around the world the magnetic susceptibility signatures indicate approximately 1000 year long cycles of environmental changes during the last glacial maximum 21 000 10 000 14 c years bp in north america the initial perturbation of these 1000 year long cycles might have started in the tropical pacific and then been promptly transferred to the north atlantic via the north american icesheet the southern siberian eolian sequence recorded approximately 1400 year cycles these 1400 year cycles might have been associated with the thermal variations in the arctic ocean that was directly linked with the thermal variations in the north atlantic ocean to sum up our research suggests that the north american eolian sequence recorded 1000 year cycles and the southern siberian eolian sequence recorded 1400 year cycles although it is not able to propose plausible mechanisms controlling the 1000 or and 1400 year cycles

isotopic features of precipitation and groundwater from the eastern alps of italy results from the mt tinisa hydrogeological system this study analyses water stable isotopes data collected from precipitation one rain gauge and groundwater outlets seven occurrences and two springs at mt tinisa in the eastern alps of italy limestones and dolostones outcrop in the mountain relief making up a single aquifer which feeds the monitored outlets with almost steady discharges lack of runoff in the streambeds throughout the whole year means that all meteoric water can be considered as recharging the aquifer sampling was undertaken during the periods 2005 2010 precipitation and 2014 2015 groundwater via monthly and two three monthly field activities respectively which allowed a total of 138 water samples to be gathered and analysed results highlighted the presence of apparent isotopic anomalies in groundwater in comparison with meteoric water the study demonstrates that the assessment of groundwater residence time and estimates of the mean monthly isotopic content in rainwater have been necessary to correctly compare the two isotopic datasets and relate the anomaly to the recharge time window occurring in the late autumn

high resolution in situ thermal imaging of microbial mats at el tatio geyser chile shows coupling between community color and temperature 1 microbial mats have spatially heterogeneous structured communities that manifest visually through vibrant color zonation often associated with environmental gradients we report the first use of high resolution thermal infrared imaging to map temperature at four hot springs within the el tatio geyser field chile thermal images with millimeter resolution show drastic variability and pronounced patterning in temperature with changes on the order of 30 c within a square decimeter paired temperature and visual images show that zones with specific coloration occur within distinct temperature ranges unlike previous studies where maximum minimum and optimal temperatures for microorganisms are based on isothermally controlled laboratory cultures thermal imaging allows for mapping thousands of temperature values in a natural setting this allows for efficiently constraining natural temperature bounds for visually distinct mat zones this approach expands current understanding of thermophilic microbial communities and opens doors for detailed analysis of biophysical controls on microbial ecology

depositional evolution of an extinct sinter mound from source to outflow el tatio chile siliceous sinter deposits from el tatio chile preserve a wide variety of depositional environments and biosignatures from high temperature 85 c vent proximal facies to distal deposits dominated by silicified microbial mats four cores were drilled into an el tatio sinter mound and associated distal apron to investigate changes in hydrothermal environments over geologic timescales sedimentary and geochemical analysis of multiple sinter cores records the initiation and accretion of diverse depositional features still observed today in el tatio facies adjacent to hydrothermal vents are dominated by laminated sinter crusts on the steep margins of a high temperature pool with sparse microbial preservation outer margins of the same pool contain extensive sinter columns up to ten centimeters in length precipitated during repeated cycles of pool overflow and subsequent evaporation low relief hydrothermal pools also form minor deposits within distal debris aprons and analogous pools are still active close to sampling locations debris aprons are dominated by palisade tufted and arborescent microbial fabrics with distinct mat textures revealing well preserved microfossils surficial deposits in all cores feature detrital rich and microbially influenced sinters overlying higher temperature facies indicating a relative decrease in hydrothermal activity over time geochemical proxies for hydrothermal fluids and de trital input match depositional interpretations based on sedimentary structures 14 c ages from core deposits extend the mound s history by 11 000 years recording at least three thousand years of sinter deposition on top of glacial sandstones 13 337 10 232 y cal bp importantly this work provides a detailed depositional model unavailable through surficial sedimentology alone

the effect of refreezing on the isotopic composition of melting snowpack the isotopic composition of solid and liquid portions of natural melting snowpack is investigated in detail by the separating of liquid water from snow grains at different depths of the snowpack the slope of the d 18o line for the liquid phase is found to be lower than for the solid phase this is proved to be due to the isotopic fractionation occurring in the melt freeze mass exchange within the snowpack melting of the snowpack has no clear impact on the d 18o line for the solid phase but the slope of the d 18o line for the liquid shows an overall slight decrease in the melting period when the snowpack is refrozen the refreezing process would inevitably cause the slope of the solid phase to decrease because of the discrepancy between the slopes of the two phases thus the slope of the solid would become lower and lower as the diurnal melt freeze episodes cycle throughout the melting season this effect is then demonstrated by looking into the isotopic composition changes of glacier firn the extent of the effect depends on the snowpack properties and environmental conditions the slope changes also result in a decreasing trend in deuterium excess copyright 2007 john wiley sons ltd

characterisation and palaeoclimate of a loess like permafrost palaeosol sequence in ne siberia abstract we studied a 15 m high loess like permafrost palaeosol sequence the tumara palaeosol sequence tps which developed on a middle pleistocene fluvio glacial terrace of the tumara river various analytical methods were applied to characterise the tps similar to typical loess palaeosol sequences e g in china europe etc pedogenetic clay formation mineral weathering and smaller grain sizes are interpreted as representing warmer and more favourable climatic conditions interglacials or interstadials soil organic matter som however reveals an unfamiliar inverse pattern high organic carbon contents c org 1 characterise the dark grey glacial palaeosols whereas lower contents c org 0 5 are found in the brown interglacial stadial palaeosols this can be explained with permafrost and water logging having inhibited som mineralisation during cold periods d l ratios of aspartic acid and lysine proved to be useful proxies for both som aging and palaeotemperature with amino acid racemization being enhanced in interglacial stadial palaeosols on the basis of the geochemical and grain size results further palaeoclimatically relevant proxies describing the palaoewind strength u ratio the mineral weathering chemical index of alteration rb k and the changing mineral input signal ba ti zr ti al were applied to the tps in combination with numeric dating results radiocarbon and luminescence and in the context of other northern hemispheric records the simple warm cold stratigraphy as derived from the palaeoenvironment climate proxies suggests that the tps represents the last 240 000 years

superparamagnetism of two modern soils from the northeastern pampean region argentina and its paleoclimatic indications summary the magnetic susceptibility carried by pedogenic fine grained ferrimagnets has been widely used as paleoclimatic proxy to elucidate long term paleoclimatic variations for windblown terrestrial loess paleosol sequences however the magnetic properties of the lithogenic parentmaterialcanmaskthepedogenicsignals inthisstudy wesystematicallyinvestigatedthe origin of the superparamagnetism of two modern soils from the northeastern humid pampean region argentina developed on loess materials of different mineralogical composition the samples were treated with the citrate bicarbonate dithionite cbd reagent which is known to dissolve the submicron pedogenic ferrimagnets while leaving unaltered the coarse grained ones the magnetic material accounting for the frequency dependent magnetic susceptibility peak at about 50 k remained in the residuals and is independent of the pedogenic processes in addition pedogenic ferrimagnetic particles in the two soils have a magnetic signature comparable to that of the soils from the chinese loess plateau it is also suggested that the for the bulk samples does not seem to be a reliable paleoclimatic proxy for the pampean soils investigated in this study instead the cbd soluble magnetic signals could be more useful to detect paleoenvironmental variations in this region these new findings provide improved understanding of the magnetic assemblage in the pampean loess soils and make it feasible to retrieve the paleoclimatic signals carried by the pedogenic cbd soluble iron oxides after removing the effects of the lithogenic inputs

cool tropical temperatures shift the global δ18o t relationship an explanation for the ice core δ18o borehole thermometry conflict the discrepancy between central greenland borehole temperatures and the isotopic composition of last glacial maximum ice can be explained by a shift in the 5180 t relationship for the hydrological cycle linked to cooler tropical temperatures this concept is illustrated using a simple rayleigh distillation model an estimate for o a 5180 at lgm holocene of 0 37 o oc is determined with a simple graphical technique

humid glacials arid interglacials critical thoughts on pedogenesis and paleoclimate based on multi proxy analyses of the loess paleosol sequence crvenka northern serbia abstract loess paleosol sequences lps provide unique terrestrial archives for past environmental and climate changes the loess units are generally interpreted to reflect more arid conditions whereas paleosols are thought to document more humid conditions this paradigm may however deserve to be challenged in some regions because it does not take into account past changes in dust accumulation rates here we present a multi proxy sedimentological and geochemical characterization of the lps crvenka serbia spanning the last 140 ka commonly used analyses such as magnetic susceptibility organic carbon content grain size and weathering indices allow the quantification of the intensity of pedogenesis however loess accumulation rates were much higher during glacials than during interglacials so that it is not trivial to infer past rates of pedogenesis and related paleoclimate conditions novel proxies based for example on lipid biomarkers and their isotopic composition are not so directly affected by changes in loess accumulation rates and might provide interesting new insights long chain plant derived n alkanes in the lps crvenka suggest a minor but non negligible contribution of deciduous trees and shrubs c27 and c29 during mis 1 2 4 and 6 whereas grasses and herbs c31 and c33 dominate the alkane input during mis 3 and 5 this is in agreement with the notion that parts of southeast europe served as refugia for deciduous trees during glacials on the other hand edaphic conditions on the drought prone loess plateaus seem to have been more arid during mis 3 and 5 compound specific d analyses on the alkanes show only little changes on glacial interglacial timescale when compared with the isotopic enrichment of the mediterranean sea during the last glacial this likely indicates a complex combination of reduced temperatures increased rainfall reduced evapotranspiration and more advection of north atlantic moisture although disentangling these factors is difficult interpretation in terms of humid glacials and more arid interglacials seems to be supported also by other novel lipid biomarkers so called gdgts glycerol dialkyl glycerol tetraethers

holocene proglacial loess in the ranwu valley southeastern tibet and its paleoclimatic implications abstract glaciers and aeolian sediments are widespread on the tibetan plateau although glaciations have played an important role in the formation of loess in many glaciated regions in the northern hemisphere proglacial loess on the tibetan plateau is rarely reported and its origin source and paleoclimatic implications remain unclear we have found a small area of proglacial loess deposits in the ranwu valley southeastern tibet grain size geochemical and geomorphologic evidence as well as observations of local dust storms reveal that the outwash sediments of the laigu glacier 30 km long are the primary source for the local loess we also found that the glacial wind from this glacier is the main transport vector and thus speculate that the onset of the ranwu loess at ca 6 6 ka correlates with the early neoglacial advance of the laigu glacier which generated glacial winds and local dust storms in the closed and deep incised glacial valley this is supported by the basal radiocarbon ages of two ice cores and a synthesis of holocene glacial stadials on the tibetan plateau loess layers and paleoclimatic proxies indicate two drought stages at ca 6 6 6 ka and ca 2 9 ka to the present corresponding to two well documented weakened stages of the indian summer monsoon this study highlights that although local aeolian sediments always cover a small area they also have potential to record some clues of regional climate changes in some alpine regions much more detailed studies should be done to reveal their specific formation mechanisms and paleoclimatic implications

pedogenesis permafrost substrate and topography plot and landscape scale interrelations of weathering processes on the central eastern tibetan plateau article i nfo weathering indices wi and pedogenic oxidesratios por were used to describe patterns of weathering inten sities and pedogenesis along climatic gradients mainly affected by varying influences of the asian and indian monsoon these climate settings induce particular soil moisture sm conditions in turn closely related to per mafrost state substrate and topography nine sites including a total of 30 soil profiles were examined along an eastern and a western transect across the central eastern qinghai tibet plateau additionally differences between four soil groups were analysed according to our knowledge the presented study is the first attempt of a comprehensive application of different wi and por to substrates of currently permafrost affected soils it providesanevaluation ofvarious tools intermsof chemicallydescribinganddifferentiating the relatedprocesses todistinctenvironmentalsettingsinlow weatheringregions wefoundthatweatheringtrendsalongtheclimat ic gradients could be clearly outlined by wi whereas por rather account for small scale variations describing significant differences of pedogenesis between continuous and discontinuous permafrost conditions pyrophos phate soluble iron fep proved to be useful for differentiating permafrost and ground water influenced soils showing a strong correlation to total organic carbon r 0 89 the chemical index of alteration cia is the

late pleistocene and holocene ice wedge activity on the blackstone plateau central yukon canada ice wedge activity can be used to reconstruct past environmental conditions we investigated the moisture source and timing of ice wedge formation on the blackstone plateau a section of permafrost exposed ice wedges that developed at two distinct depths the first set formed syngenetically and penetrated alluvial silts from the top of permafrost the second set truncated by an erosional or thaw contact was found solely in icy muddy gravels 3 1 m depth the 18o and d excess records of the ice wedges suggest that they formed from freezing of snow meltwater whose isotopic composition evolved during meltout the 14cdoc results suggest that climate was favorable to ice wedge growth between 32 000 30 000 and 14 000 12 500 cal yr bp but there was likely a hiatus during the last glacial maximum due to climate being too dry during the early to mid holocene ice wedges were inactive as a result of warmer and wetter climate ice wedge re initiated around 6360 cal yr bp with a peak in activity between 3980 and 920 cal yr bp a period characterized by cool and moist climate overall timing of ice wedge activity was broadly consistent with the climate and vegetation evolution in the western arctic

stability of massive ground ice bodies in university valley mcmurdo dry valleys of antarctica using stable o h isotope as tracers of sublimation in hyper arid regions abstract to date studies of the stability of subsurface ice in the mcmurdo dry valleys of antarctica have been mainly based on climate based vapor diffusion models in university valley 1800 m a small glacier is found at the base of the head of the valley and adjacent to the glacier a buried body of massive ice was uncovered beneath 20 40 cm of loose cryotic sediments and sandstone boulders this study assesses the origin and stability of the buried body of massive ice by measuring the geochemistry and stable o h isotope composition of the ice and applies a sublimation and molecular diffusion model that accounts for the observed trends the results indicate that the buried massive ice body represents an extension of the adjacent glacier that was buried by a rock avalanche during a cold climate period the contrasting 18 o profiles and regression slope values between the uppermost 6 cm of the buried massive ice upward convex 18 o profile and s d 18o 5 1 and that below it progressive increase in 18 o and s d 18o 6 4 suggest independent post depositional processes affected the isotope composition of the ice the upward convex 18 o profile in the uppermost 6 cm is consistent with the ice undergoing sublimation using a sublimation and molecular diffusion model and assuming that diffusion occurred through solid ice the sublimation rate needed to fit the measured 18 o profile is 0 2 10 3 mm yr 1 a value that is more similar to net ice removal rates derived from 3 he data from cobbles in beacon valley till 7 0 10 3 mm yr 1 than sublimation rates computed based on current climate 0 1 0 2 mm yr 1 we suggest that the climate based sublimation rates are offset due to potential ice recharge mechanisms or to missing parameters particularly the nature and thermo physical properties of the overlying sediments i e temperature humidity pore structure and ice content grain size

geochemistry of metals and metalloids in siliceous sinter deposits implications for elemental partitioning into silica phases abstract sinter deposits are formed by precipitation of silica from hydrothermal fluids that have reached the surface environment they are commonly found around hot springs and represent surface expressions of underlying geothermal systems and or low sulfidation epithermal gold silver hydrothermal deposits several studies have reported ppm to weight percent concentrations of metals e g au ag cu and metalloids e g as sb b in sinters capping geothermal systems and epithermal gold silver deposits however the relation between the maturity of the siliceous sinter and its metal enrichment remains unknown here we use geochemical and mineralogical data that link the silica crystallinity degree with trace metal and metalloid contents in sinter in this paper we provide in situ trace element data in metal rich silica sinter samples from the puchuldiza geothermal field in the altiplano of northern chile that record the complete diagenetic sequence from non crystalline opal a to microcrystalline quartz combined sem xrd and la icp ms data show that the concentration of metals and metalloids in sinters from puchuldiza display a strong correspondence with silica crystallinity while arsenic and boron are predominantly enriched in the more amorphous silica phases opal a ct gold and silver show higher concentrations in the more crystalline phases opal c quartz silica structural morphological and geochemical transformations from its initial precipitation to its final maturation after diagenesis are responsible for this differential enrichment during the initial stages gold and silver are incorporated into silica microspheres as cationic species and or metal nanoparticles or colloids while arsenic and boron incorporation is controlled by as bearing accessory minerals and fe oxyhydroxides as diagenesis progresses and the crystallinity of silica increases diffusion driven processes such as ostwald ripening may progressively enrich gold and silver in the sinter while metalloids are depleted owing to the low retention of arsenic by silica these findings indicate that the diagenetic transitions of silica defined by significant structural changes that involve generation of surface defects and the creation of reactive sites may play an important role in elemental uptake by silica in near surface environments

dating silica sinter geyserite a cautionary tale abstract we describe a new effort to date hydrothermal silica sinter deposits geyserite from the upper geyser basin of yellowstone national park using 14c of co deposited organic matter u series and cosmogenic 10be methods a majority of the samples were collected from stratigraphic sections mainly at riverside giant and castle geysers ages obtained from 41 14c analyses range from modern to 12 1 cal ka bp nearly all the 14c ages show inconsistencies with their stratigraphic positions and several replicate 14c analyses from the same sample result in significantly different ages the 13c values of the organic material in the sinter range from 26 6 to 12 7 the more enriched values are attributed to microbial fixation of dissolved inorganic carbon dic which has heavier 13c values and is 14c depleted relative to atmospheric co2 leading to an apparent older age u series analyses on 4 samples yielded ages between 2 2 and 7 4 ka large 230th u age uncertainties in the sinter due to low uranium concentrations along with elevated 232th and associated initial 230th make these ages imprecise for use on holocene deposits a single cosmogenic 10be exposure age of 596 18 ka is considerably older than the age of underlying rhyolite and is thus unreliable this apparent old age results from contamination by meteoric 10be trapped in the opal that overprints the very small amount of cosmogenic 10be by presenting the problems we encountered and discussing their probable cause this paper highlights the difficulty in obtaining reliable high precision geochronological data necessary to use sinter deposits as paleoenvironmental and paleo hydrothermal archives

experimental studies on new zealand hot spring sinters rates of growth and textural development to study the rate of growth of sinters in new zealand hot springs field experiments were conducted in seven geothermal areas at wairakei fan shaped subaqueous deposits of amorphous silica grow rapidly 350 kg a 1 m 2 of drain wall and are composed of silicified filaments with subordinate bacillus and spirillium shaped organisms characterization of bacteria revealed isolates sharing 97 16s rrna gene sequence homologies affiliated with thermus meiothermus bacillus tepidomonas thermomonas porphyrobacter thermonema and hydrogenophilus spp as well as previously uncultured bacteria at rotokawa microstromatolites have a slow growth rate 0 004 mm day 1 that is attributed to low ph capillary rise and evaporation at champagne pool sinter growth 0 023 mm day 1 is dominated by wave action building alternating microbe rich and microbe poor layers silica sinter was not observed at waikite where slides developed a layer of calcite 0 026 mm day 1 sinter growth at ngatamariki 0 016 mm day 1 forms by capillary rise evaporation and diffusion and at tokaanu subaqueous growth is slow 0 002 mm day 1 and contains silicified microbes textures at orakei korako indicate similar mechanisms to ngatamariki except that growth is more rapid 0 023 mm day 1 due to a splash contribution silica and calcite saturation indices adequately explain the growth of the sinters and calcite indicating that microbes are not inducing precipitation where it should not occur the rate of precipitation is correlated with silica supersaturation but ph effects can alter this relationship the degree of preservation of microbial material is explained by the effect of ostwald ripening on silica spherules subaqueous growth allows coarsening of spherules and poor preservation of smaller microbes while subaerial nucleation is rapid ostwald ripening is inactive and better preservation can be expected

oxygen and hydrogen isotopic ratios of water in precipitation beyond paleothermometry paleoclimatologists face a dilemma no sedimentary proxy is a pure recorder of quantitative climate information yet climate modelers and policy makers increasingly seek quantitative comparisons between instrumentally documented possibly anthropogenic climate changes and those produced naturally in the past in the second edition of his influential book bradley 1999 p 6 discussed the calibration of proxy records to learn past climate changes calibration involves using modern climatic records and proxy materials to understand how and to what extent proxy materials are climate dependent it is assumed that the modern relationships observed have operated unchanged throughout the period of interest the principle of uniformitarianism in other words one relates the characteristics of sediment to climate at different places for one time or at a place for short times and then uses that relation plus characteristics of older sediments to estimate the climatic conditions that produced those sedimentary characteristics bradley 1999 then extensively discussed the difficulties in applying this methodology in a complex world with imperfect recorders nonetheless the goal of using calibrated proxies for quantitative as well as qualitative paleoclimatic reconstruction is clear a prominent recent use of calibrated paleoclimatic data is the assessment of whether the probably anthropogenic warming of the latter 20th century moved beyond the band of natural variability of the prevailing climate bradley 2000 combined recent instrumental records with several longer proxy based reconstructions of surface temperature including that of mann et al 1999 based on this composite data set bradley 2000 argued that temperatures in the late 20th century were unique in the context of the entire millennium the proxy records were primarily based on tree ring data but included isotopic and major element geochemistry of corals and occurrence of melt layers and isotopic ratios of water in ice cores however broecker 2001 questioned the basis for the reconstruction of

formation of silica oncoids around geysers and hot springs at el tatio northern chile siliceous oncoids up to 4 cm in diameter are common on the laterally extensive sinter aprons that surround the spectacular geysers and hot springs at el tatio in northern chile many of these complex oncoids developed close to geyser and spring vents that discharge boiling water internally the oncoids which are composed of precipitated amorphous silica are formed of complex arrays of spicules and concentric laminae as well as detrital volcanic grains spicular growth is dominant in most examples the formation and growth of the spicules and concentric laminae were mediated by a microbial community which included filamentous microbes mucus and possibly bacteria the microbes and mucus were silicified by replacement and encrustation in some laminae the filamentous microbes lay parallel to the growth surface in other laminae most filaments forming the thin mats were suberect amorphous silica precipitated between the filaments occluded porosity and commonly disguised the microbial fabric the oncoids grew on the proximal sinter aprons around the geyser vents and hot spring pools most growth took place subaerially with the silica delivered to the precipitation sites by splashing water from the geysers and or periodic shallow flooding of the discharge aprons unlike silica oncoids at other geothermal sites vertical growth of oncoids that formed in some rimstone pools was not limited by water depth

non climate influences on stable isotopes at taylor mouth antarctica the late holocene trends in 18 o differ significantly in two ice cores 30 km apart from the area of taylor dome antarctica it is unlikely that the trend in the core from taylor mouth the flank site is due to a standard 18 o surface temperature relationship assuming that the taylor dome near summit core records local climate variations common to both cores we assess two leading possible causes for the observed differences 1 relative to taylor dome taylor mouth may collect snow from more sources with distinct isotopic compositions 2 vapor motion during prolonged near surface exposure may cause post depositional isotope enrichment at taylor mouth where the accumulation rate is low our model of firn pore space vapor and sublimating ice grains suggests that post depositional processes can modify 18 o values by several o isotopic samples from areas with significantly different accumulation rates near taylor mouth could differentiate between possibilities 1 and 2

climate change loess and palaeosols proxy measures and resolution in north china the loess plateau of north china is a key region for the study of records of quaternary climatic change various techniques to abstract climatically sensitive data were first applied to the classic loess palaeosol site at luochuan and current views on climatic change in asia have been strongly moulded by results from this central part of the loess plateau data including the magnetic susceptibility granulometry mineralogy geochemistry micromorphology fossil content and inorganic and organic carbon content of asian loess palaeosol series have been used singly and in combination as surrogate measures of palaeoclimates to infer climatic changes with particular reference to changes in the asian monsoon some of this work is reviewed and the status of a number of parameters as climatic proxies is discussed some lithostratigraphic sequences from which proxy measures of climate have been derived are incomplete as shown by erosion surfaces water laminated zones and truncated palaeosol profiles while others provide records of relatively low resolution most descriptions of quaternary climatic changes based on studies of the loess emphasize alternations in the relative dominance of warm and moist v cool dry and dust laden monsoons some recent studies of the much higher resolution loess palaeosol successions on the western margins of the loess plateau have suggested that such changes may sometimes be out of phase with the inference that the current climate model is too simple means of testing this hypothesis are proposed

the hot spring and geyser sinters of el tatio northern chile abstract the siliceous sinter deposits of el tatio geothermal field in northern chile have been examined petrographically and mineralogically these sinters consist of amorphous silica opal a deposited around hot springs and geysers from nearly neutral silica saturated sodium chloride waters water cooling and evaporation to dryness are the main processes that control the opal a deposition in both subaqueous and subaerial settings in close spatial relation to microbial communities all fingerprints of organisms observed in the studied sinter samples represent microbes and suggest that the microbial community is moderately diverse cyanobacteria green bacteria and diatoms the most important ecological parameter is the temperature gradient which is closely related to the observed depositional settings 1 geyser setting water temperature 70 86 c boiling point at el tatio 4200 m a s l coarse laminated sinter macrostructure with rapid local variations biota comprises non photosynthetic hyperthermophilic bacteria 2 splash areas around geysers water temperature 60 75 c laminated spicule and column macrostructure locally forming cupolas

effect of accumulation rate on water stable isotopes of near surface snow in inland antarctica 1 postdepositional changes in water stable isotopes in polar firn were investigated at three sites characterized by different accumulation rates along the east antarctic ice divide near dome fuji water stable isotopes major ion concentrations and tritium contents of three 2 4 m deep pits were measured at high resolution 2 cm temporally the snow pits cover the past 50 years with snow accumulation rates in the range of 29 41 kg m 2 a 1 around dome fuji oxygen isotopic profiles in the three pits do not show annual fluctuations but instead exhibit multiyear cycles these multiyear cycles are lower in frequency at dome fuji as compared with the other two sites peaks of water stable isotopes in the multiyear cycles correspond to some ion concentration minima in the pits although such relationships are not observed in coastal regions we propose that the extremely low accumulation environment keeps the snow layer at the near surface which result in postdepositional modifications of isotopic signals by processes such as ventilation and vapor condensation sublimation we estimate that oxygen isotopic ratios could be modified by 10 and that the original seasonal cycle could be completely overprinted under the accumulation conditions at dome fuji moreover stake measurements at dome fuji suggest that the large variability in snow accumulation rate is the cause of the multiyear cycles

relationship between spring and geyser activity and the deposition and morphology of high temperature 73 c siliceous sinter yellowstone national park wyoming u s a abstract six classes of alkaline hot springs and geysers are here distinguished in yellowstone national park based on activity and eruptive style 1 non surging non boiling springs 2 gently surging non boiling springs 3 non surging to gently surging boiling springs 4 strongly surging springs 5 fountain geysers and 6 cone geysers each displays morphologically distinctive siliceous sinter deposits in the high temperature 73 c parts of the vent and outflow systems non surging and gently surging non boiling springs that do not overflow their rims develop thin digitate to lilypad like sinter rims that grow horizontally over the pool surfaces similar springs with rim overflow have rims that accrete vertically boiling springs often have nearly circular steep sided pools and rims dominated by splash and rim overflow and composed mainly of spicular and columnar sinter fountain geysers characterized by broad fountain like eruption bursts have a central vent surrounded by a zone of spicular sinter beyond which is a broad flat bottomed moat but lack steep sinter cones cone geysers have narrow vents jet like discharges that cool rapidly and fall close to the vent and steep sided spicule dominated sinter cones sinter deposition takes place within three main zones 1 fully subaqueous sides and bottoms of vent pools outflow basins and outflow channels 2 periodically wetted splash zones surrounding hot springs and geysers and 3 largely subaerial parts of the rim and outflow areas wetted mainly by overflow and surging and that dry quickly fully subaqueous surfaces are covered by fine earthy particulate siliceous sediment pss composed largely of amorphous silica spherules and spherule aggregates that appear to have precipitated around heterogeneous nuclei including microbes splash zones of hot springs and geysers are characterized by spicular sinter largely subaerial zones wetted mainly by rim overflow and surging with little or no splash show complex varieties of terraced columnar and knobby sinter the highest silica deposition rates occur where surfaces are wetted frequently and evaporate to dryness such as the tops of spicules columns and knobs associated lower areas and crevices that remain wet or moist show slow accumulation of pss most continuously wet surfaces in high temperature 73 c hot spring and geyser vent and outflow systems are probably covered by microbial biofilms although microbes may locally influence rates of silica deposition and sinter microstructure the results of this study suggest that the depositional sites morphology and macrostructuring of high temperature sinter are controlled largely by the processes of surface wetting evaporation and drying

potential forcing mechanisms of holocene lake level changes at nam co tibetan plateau inferred from the stable isotopic composition of shells of the gastropod radix the timing of lake level fluctuations on the tibetan plateau and their relationship with climatic changes is still under debate and the main reason for this is the lack of suitable archives for reconstructing the paleohydrology and paleoclimatology of the lakes here we present the results of analyses of the shell geochemistry of radix sp from an exposed terrace of nam co lake on the south central tibetan plateau optically stimulated luminescence osl dating reveals that deep water lacustrine sediments formed between ca 4 4 and 2 2 ka suggesting a high and stable lake level significantly above the present the results of sr ca 13c and 18o analyses of the fossil shells of radix sp indicate that during the mid to late holocene lake level variations in nam co were mainly controlled by variations in the indian summer monsoon a trend of decreasing evaporation also played an important role comparison with other results suggests a consistent pattern of mid to late holocene lake level changes acro

timing and spatial distribution of loess and loess like sediments in the mountain areas of the northeastern tibetan plateau abstract most studies on landscape evolution on the tibetan plateau during the late quaternary have mainly focused on using lacustrine records however mantles of sandy silt and paleosols also provide valuable archives for reconstructing holocene paleoenvironmental change yet little is known about the distribution and timing of these late quaternary aeolian sediments to enhance understanding and knowledge of aeolian sediments in tibet and to help reconstruct the nature of late glacial through mid holocene landscape development a loess paleosol sequence the suohuduo section located at the eastern margin of the tibetan plateau at about 4000 m above sea level is examined using sedimentological geochemical and geochronological methods a chronostratigraphy is established using nine optically stimulated luminescence and one radiocarbon ages sedimentation increased during the late glacial and the early holocene with an upwards fining of sediments in the lower part of the section two mid holocene paleosols that date to about 8 5 ka to 7 ka and 5 5 ka to 4 ka reflect more humid climate conditions during the mid holocene than earlier times the upper part of the section is mainly silt which reflects a more open landscape with higher aridity since 4 to 3 ka this time these data support evidence for similar climate paleoenvironmental change in adjacent regions on the tibetan plateau

an eolian deposit buried soil sequence in an alpine soil on the northern tibetan plateau implications for climate change and carbon sequestration abstract the accumulation of eolian dust plays an important role in the development of alpine soils on the northern tibetan plateau however little is known either about the nature of soil forming processes in the region or about the magnitude of soil organic and inorganic carbon soc and sic storage here we report the results of an investigation of a typical profile consisting of a series of buried soils developed within eolian deposits situated at an altitude of 4951 m in the amdo zone of the northern tibetan plateau bulk density ph soc and sic content grain size distribution magnetic susceptibility and mineralogical composition were measured at high resolution and ams 14c dating was used to provide a chronology based on all of the analytical data we conclude that this alpine accretionary soil profile contains three buried soils beneath the present surface soil layer the deepest and oldest soil is the basal paleo weathering crust ferralsol which underwent active soil formation from 5540 to 7615 yr bp or even earlier the other soils which are developed within the overlying eolian dust deposits are luvisols and they document the occurrence of two intervals of more humid conditions than the present day from 3455 to 5540 yr cal bp and from 2000 2500 yr cal bp microscopic analysis of coarse particles from the profile reveals that high values of magnetic susceptibility at the base of the profile reflect the presence of coarse magnetite grains present as inclusions within quartz grains derived from the weathering of granitic gneiss in addition the magnetic susceptibility profile reflects the effects of winnowing of the eolian fraction by wind activity and not the production of fine magnetic grains during pedogenesis soc is the dominant form of carbon in this alpine soil and the soc density and average accumulation rate values within the entire interval of eolian deposits are 19 67 kg c m 2 and 3 55 g c m 2 yr 1 respectively these remarkably high values indicate that this alpine accretionary soil is characterized by highly efficient soc burial and therefore that such soils are an important terrestrial co2 sink likewise the buried soil plays an important role in soc storage finally the characteristics of the buried soils indicate a long term climatic trend towards aridity in the study region this natural trend has promoted the processes of desertification and grassland degradation on the northern tibetan plateau and these processes may have been exacerbated by human activity

stable isotopes in surface snow along a traverse route from zhongshan station to dome a east antarctica samples of surface snow were collected for stable isotope analysis along the traverse route from zhongshan to dome a east antarctica from dec 28th 2007 to feb 8th 2008 the local relationship between d and surface temperature is established to be 6 4 0 2 per c very similar to the average for east antarctic the deuterium excess shows a pattern of high values over antarctica particularly at dome a we compare our data with an atmospheric general circulation model which includes stable water isotopes echam5 wiso the model simulation captures the right levels of d but overestimates 18o this study provides support for the ongoing deep ice core project at dome a

radiocarbon dating of silica sinter deposits in shallow drill cores from the upper geyser basin yellowstone national park abstract to explore the timing of hydrothermal activity at the upper geyser basin ugb in yellowstone national park we obtained seven new accelerator mass spectrometry ams radiocarbon 14 c ages of carbonaceous material trapped within siliceous sinter five samples came from depths of 15 152 cm within the y 1 well and two samples were from well y 7 depths of 24 cm and 122 cm these two wells at black sand and biscuit basins respectively were drilled in 1967 as part of a scientific drilling program by the u s geological survey white et al 1975 even with samples as small as 15 g we obtained sufficient carbonaceous material a mixture of thermophilic mats pollen and charcoal for the 14 c analyses apparent time of deposition ranged from 3775 25 and 2910 30 14 c years bp at the top of the cores to about 8000 years bp at the bottom the dates are consistent with variable rates of sinter formation at individual sites within the ugb over the holocene on a basin wide scale though these and other existing 14 c dates hint that hydrothermal activity at the ugb may have been continuous throughout the holocene

magnetoclimatology teleconnection between the siberian loess record and north atlantic heinrich events new environmental magnetic data from loess and paleosol successions in outcrops in the upper reaches of the ob river drainage southern siberia track the major climatic variations over the last glacial interglacial cycle profiles of magnetic susceptibility and alternating deposition of loess and soil formation events correspond to oxygen isotope stages 1 5 the magnetic susceptibility data in association with the stratigraphic succession confirm that the wind vigor magnetoclimatological model is a viable alternative to the classic pedogenic model interpretation of magnetic susceptibility data from loess paleosol successions must therefore consider eolian dynamics available source materials and transport directions in addition to pedogenic processes rapid magnetic fluctuations are also observed these are identified for the first time in siberian records as the signature of the abrupt cold pulses responsible for the heinrich layers in north atlantic marine sediments the data thus form a component of climatic teleconnections across the northern hemisphere allowing correlations to be made among 1 siberian magnetic susceptibility stratigraphy 2 data recorded from other loess paleosol successions in china european russia europe and north america 3 north atlantic ice rafted detritus and 4 sea surface temperatures derived from molecular stratigraphy of marine sediments off the northwest coast of africa

the dust provenance and transport mechanism for the chengdu clay in the sichuan basin china the chengdu clay in the sichuan basin china was named by thorp and dye in 1936 the genesis dust provenance and transport mechanism for the chengdu clay however are still debated in the present work the chengdu clay and adjacent loess from the eastern tibetan plateau the chinese loess plateau and the qinling mountains were investigated the content and grain size distribution of quartz quartz 18o sm nd isotopic system rare earth elements and other trace element concentrations for the chengdu clay and its adjacent loess were analyzed based on comparison and spatial variation analysis the results confirm that the chengdu clay is of aeolian origin the dust provenance of the chengdu clay differs from those of the adjacent loess the chengdu clay is possibly of local origin and is transported by an ancient katabatic wind over a short distance during glacial and stadial periods the alluvial sediments in the northwestern sichuan basin are possibly the major sources of the chengdu clay there is little possibility of an effective aeolian transport bringing dust from the tibetan plateau the arid area in northwestern china or inner mongolia into the sichuan basin where it may be deposited to form the chengdu clay thus long range dust transport by the east asian winter monsoon the westerly jet or the tibetan plateau winter monsoon possibly plays a minor role in controlling the magnitude of the dust flux of the chengdu clay in the sichuan basin

climate change vegetation history and landscape responses on the tibetan plateau during the holocene a comprehensive review abstract numerous studies of changes in the climate vegetation and landscape responses of the tibetan plateau tp during the holocene have been published in recent decades however several conflicting interpretations are evident within these studies and a comprehensive review of the topic is needed to reconcile them and thus to provide an improved understanding of the history and forcing mechanisms of holocene environmental changes within the region here we review the evidence for changes in climate temperature precipitation moisture vegetation and landscape attributes glacier and eolian activity on the tp during the holocene our main conclusions are as follows 1 the patterns of holocene mean annual temperature change on the tp remain controversial however an early to middle holocene summer temperature maximum is evident which coincided with high summer insolation and a strengthening of the indian summer monsoon ism this suggests that the summer land sea thermal gradient impacted by the temperature of the tp may be an important factor driving orbital scale ism changes 2 lake level records indicate an optimum in moisture conditions on the southwestern sw tp in the early holocene while on the northeastern ne tp the optimum occurred in the middle to late holocene this out of phase or anti phased relationship may be linked to the role of the ism in dominating precipitation on the sw tp while the westerlies and east asian summer monsoon dominated the precipitation on the ne tp 3 most of the lake sediment based stable isotope records 18o and leaf wax d exhibit a pattern similar to that of stalagmite 18o records from monsoonal asia reflecting the dominance of large scale patterns of atmospheric circulation rather than localized moisture changes reflected by lake level records 4 a synthesis of pollen records reveals that the extent of forest was maximal in the mid holocene while from the early holocene onwards alpine steppe shrunk and alpine meadow and desert gradually expanded 5 evidence of glacier advance increased slightly during the early holocene decreased during the mid holocene and then increased substantially after 3 ka bp 6 the integrated ages of eolian sand and loess from the ne tp reveal that eolian activity intensified during the early and late holocene site inter comparisons reveal that regional climate change played a major role in modulating changes in vegetation and other landscape attributes overall producing holocene climate reconstructions for the entire tp remains a major challenge even though much progress has been made further improvements in terms of the spatial coverage of high resolution paleoclimatic records with robust chronological control and a deeper understanding of the specific climatic significance of several climatic proxies will facilitate an improved understanding of how the monsoon and the westerlies interacted and their impacts on vegetation and landscape changes on the tp

gcm simulations of the last glacial maximum surface climate of greenland and antarctica the lmdz variable grid gcm was used to simulate the last glacial maximum lgm 21 ky bp climate of greenland and antarctica at a spatial resolution of about 100 km the high spatial resolution allows to investigate the spatial variability of surface climate change signals and thus to address the question whether the sparse ice core data can be viewed as representative for the regional scale climate change this study addresses primarily surface climate parameters because these can be checked against the limited ice core record the changes are generally stronger for greenland than for antarctica as the imposed changes of the forcing boundary conditions e g sea surface temperatures are more important in the vicinity of greenland over greenland and to a limited extent also in antarctica the climate shows stronger changes in winter than in summer the model suggests that the linear relationship between the surface temperature and inversion strength is modified during the lgm the temperature dependency of the moisture holding capacity of the atmosphere alone cannot explain the strong reduction in snowfall over central greenland atmospheric circulation changes also play a crucial role changes in the high frequency variability of snowfall atmospheric pressure and temperature are investigated and possible consequences for the interpretation of ice core records are discussed using an objective cyclone tracking scheme the importance of changes of the atmospheric dynamics off the coasts of the ice sheets especially for the high frequency variability of surface climate parameters is illustrated the importance of the choice of the lgm ice sheet topography is illustrated for greenland where two different topographies have been used yielding results that differ quite strongly in certain nontrivial respects this means that the paleo topography is a significant source of uncertainty for the modelled paleoclimate the sensitivity of the greenland lgm climate to the prescribed sea surface conditions is examined by using two different lgm north atlantic data sets

geyserite in hot spring siliceous sinter window on earth s hottest terrestrial paleo environment and its extreme life siliceous hot spring deposits or sinters typically form in active terrestrial on land volcanic terrains where magmatically heated waters circulating through the shallow crust emerge at the earth s surface as silica charged geothermal fluids geyserites are sinters affiliated with the highest temperature 75 100 c natural geothermal fluid emissions comprising localized lithologically distinctive hydrothermal silica precipitates that develop around geysers spouters and spring vents they demarcate the position of hot fluid upflow zones useful for geothermal energy and epithermal mineral prospecting near vent areas also are extreme environment settings for the growth of microbial biofilms at near boiling temperatures microbial biosignatures e g characteristic silicified microbial textures carbon isotopes genetic material lipid biomarkers may be extracted from modern geyserite however because of strong taphonomic filtering and subsequent diagenesis fossils in geyserite are very rare in the pre quaternary sinter record which in and of itself is patchy in time and space back to about 400 ma only a few old examples are known such as geyserite reported from the devonian drummond basin australia devonian rhynie cherts scotland and a new example described herein from the spectacularly well preserved late jurassic 150 ma yellowstone style geothermal landscapes of patagonia argentina there geyserite is associated with fossil vent mounds and silicified hydrothermal breccias of the claudia sinter which is geologically related to the world class cerro vanguardia gold silver deposit of the deseado massif a part of the chon aike siliceous large igneous province tubular filament like micro inclusions from claudia were studied using integrated petrographic and laser micro raman analysis the results of which suggest a biological origin the putative fossils are enclosed within nodular geyserite a texture typical of subaerial near vent conditions overall this worldwide review of geyserite confirms its significance as a mineralizing geological archive reflecting the nature of earth s highest temperature habitable terrestrial sedimentary environment hot spring depositional settings also may serve as analogs for early earth paleoenvironments because of their elevated temperature of formation rapid mineralization by silica and morphologically comparable carbonaceous material sourced from prokaryotes adapted to life at high temperatures

excess ground ice of condensation diffusion origin in university valley dry valleys of antarctica evidence from isotope geochemistry and numerical modeling abstract this study investigates the origin and age of ground ice in the uppermost 1 m of permafrost in university valley one of the upper valleys in the mcmurdo dry valleys of antarctica in contrast to other regions in the mdv mean daily air and soil temperatures at the coring sites are always below 0 c which allows for unique cryogenic processes to occur in the two cores that were analyzed excess ground ice was measured throughout ranging between 23 and 85 isotope geochemical trends in the ice rich permafrost indicate that the ground in core 5 65 cm long and the uppermost 52 cm of core 7 originated from condensation diffusion of water vapor whereas the ground ice between 57 90 cm in core 7 originated from freezing of liquid water using numerical modeling we show that the excess ground ice of condensation diffusion origin formed by the long term thermal contraction expansion of the cryotic sediments which allowed for the ice content to exceed pore filling capacity absolute age estimates of the sandy loam sediments based on optically stimulated luminescence dating indicate that soils have been accreting at the site for at least the last 170 36 ka years and this places an upper limit to the age of the ground ice absolute soil ages allowed us to link the change in ground ice origin in core 7 which took place around 152 12 ka years with shifts in climate conditions since marine isotope stage 5e interglacial period our findings offer a new process of ground ice emplacement in sediments in cold dry environments and allow an alternative explanation regarding the enigmatic origin of excess ground ice identified by mars odyssey and phoenix in the northern martian plain which is that overfilled pore ice can form by vapor deposition and repeated thermal cycling without the presence of melt water

the siberian loess record and its significance for reconstruction of pleistocene climate change in north central asia abstract the siberian loess represents the most significant terrestrial proxy record of quaternary climatic history in northern asia loess is extensive in southern siberia between the irtysh basin in the west and the angara basin in the east palaeoenvironmental multi proxy data magnetic susceptibility ms grain size caco 3 toc pollen etc from high resolution loess palaeosol sections provide evidence for a strongly fluctuating climatic sequence in north central asia during the late quaternary displaying the globally diagnostic sequences found in the deep sea oxygen isotope records ms provides the most continuous and detailed record encompassing the last two interglacial glacial cycles in loess sections in the minusinsk basin yenisei area and on the northern altai plains evidence for periodic atmospheric shifts is provided by gradual changes in the main vegetation zones with parkland steppe and mixed taiga during warm interglacial interstadial stages being replaced by boreal tundra forest and arid periglacial tundra steppe during stadials climatic pulses from warm intervals to cold are recorded by incipient forest steppe tundra gleysols the occurrence of the highest sediment accumulation rates in glacial stages ois 4 and ois 2 in the southern plains and depressions indicates that the most intensive aeolian dust deposition followed the glacial maxima with the most recent interval dated to ca 19 15 ka bp because of its zonal distribution and pronounced climatic continentality the siberian loess region represents an important data source for reconstructing past climates in the northern hemisphere it provides a key to the correlation of other loess regions within the west east eurasian continental zone

borehole versus isotope temperatures on greenland seasonality does matter new simulation results obtained with the hamburg atmosphere general circulation model echam 4 under maximum glacial boundary lgm conditions confirm the paleotemperatures on greenland determined by borehole thermometry the disagreement between 18o isotope based temperatures and the borehole temperatures of the lgm is not only reproduced by the model but the simulation results provide a plausible explanation paleotemperatures inferred from 18o measurements in ice cores are biased by a substantially increased seasonality of precipitation over greenland during the lgm during the glacial winter a much more zonal circulation prevents the effective transport of moisture to the greenland ice sheet and therefore reduces the contribution of isotopically strongly depleted winter snow to the annual mean isotope signal

precipitation regime influence on oxygen triple isotope distributions in antarctic precipitation and ice cores abstract the relative abundance of 17o in meteoric precipitation is usually reported in terms of the 17o excess parameter variations of 17o excess in antarctic precipitation and ice cores have hitherto been attributed to normalised relative humidity changes at the moisture source region or to the influence of a temperature dependent supersaturation controlled kinetic isotope effect during in cloud ice formation below 20 c neither mechanism however satisfactorily explains the large range of 17o excess values reported from measurements a different approach based on the regression characteristics of 10 3 ln 1 17 o versus 10 3 ln 1 18 o is applied here to previously published isotopic data sets the analysis indicates that clear sky precipitation diamond dust which occurs widely in inland antarctica is characterised by an unusual relative abundance of 17o distinct from that associated with cloud derived synoptic snowfall furthermore this distinction appears to be largely preserved in the ice core record the respective mass contributions to snowfall accumulation on both temporal and spatial scales provides the basis of a simple first order explanation for the observed oxygen triple isotope ratio variations in antarctic precipitation surface snow and ice cores using this approach it is shown that precipitation during the last major deglaciation both in western antarctica at the west antarctic ice sheet wais divide and at vostok on the eastern antarctic plateau consisted essentially of diamond dust only despite a large temperature differential and thus different water vapour supersaturation conditions at the two locations in contrast synoptic snowfall events dominate the accumulation record throughout the holocene at both sites

paleosols of middle holocene age in the thakkhola basin central nepal and their paleoclimatic significance abstract the characteristics and climatic implication of paleosols widely distributed in the thakkhola basin upper kali gandaki central nepal were investigated the paleosols were buried in surficial deposits of eolian or colluvial origin they were composed not only of humus but also included abundant inorganic matter some of them yielded charcoal fragments pollen and phytoliths radiocarbon dating suggested that the paleosols formed between 6200 and 4500 yr b p i e during the middle holocene the paleosols are interpreted to indicate stronger summer monsoons and increased rainfall at the time of their formation the vegetation cover at that time is thought to have been relatively dense charcoal plant fossils and carbon isotope data suggest that grasslands were dominant in the northern part of the basin while trees grew in the southernmost part during the period of paleosol formation the paleosols were buried by surficial deposits under drier climatic conditions after 4500 yr b p

tracking crystallinity in siliceous hot spring deposits siliceous hot spring deposits sinters entrap paleoenvironmentally significant components and are used as extreme environment analogs in the search for early earth and extraterrestrial life however sinters undergo a series of textural and mineralogical changes during diagenesis that can modify and overprint original environmental signals for ancient hydrothermal settings including those close to the dawn of life these transformations have long since occurred so that study of diagenetic processes and effects is best undertaken in much younger deposits still undergoing change three young sinters preserve the entire diagenetic sequence of silica phases from opal a to quartz the 6000 to 11 500 years bp 70 years sinter at steamboat springs nevada the 1600 1900 160 years bp opal mound sinter at roosevelt hot springs utah and the 456 35 years bp deposit at sinter island taupo volcanic zone new zealand provide an opportunity to track crystallographic mineralogic and morphologic transitions of sinter diagenesis using standard and new analytical approaches worldwide sinter forms from cooling alkali chloride waters as noncrystalline opal a transforming first into noncrystalline opal a ct then paracrystalline opal ct moganite paracrystalline opal c and eventually to microcrystalline quartz in this study these changes were identified by the novel and combined application of electron backscatter diffraction x ray powder diffraction and scanning electron and optical microscopy techniques we show that mineralogical changes precede morphological and accompanied crystallographic transformations during this modification silica particles grow and shrink several times from the micron to nano meter scales via dissolution reprecipitation and recrystallization and diagenesis follows the ostwald step rule all deposits followed nearly identical diagenetic pathways with time as the only variable in the march toward physicochemically stable quartz crystals diagenesis alters original environmental signatures trapped within sinters after five silica phase changes filamentous microfossils are modified but still remain recognizable within sinter from the opal mound and steamboat springs deposits and during the opal a to opal ct silica phase transformations at sinter island therefore delineating diagenetic components and how they affect sinters is necessary to accurately identify biosignals from ancient hot spring deposits

extreme snow metamorphism in the allan hills antarctica as an analogue for glacial conditions with implications for stable isotope composition understanding physical processes in near zero accumulation areas can help us to better understand polar ice core records particularly during periods when accumulation rates were lower than today we report measurements from a 5 m firn core from the allan hills antarctica which include physical properties using computer tomography stable isotope ratios d and 18 o and 210 pb activity the core shows a highly metamorphosed firn with homogeneous and stable structure but with discrete layers near the surface the observed firn structure is caused by a combination of unique depositional and post depositional processes the irregular d and 18 o signal does not follow the stratigraphic sequence and implies post depositional modification caused by microscopic pressure gradients in the firn that can result from either forced ventilation over rough surfaces in the presence of wind or alternating temperature gradients between the firn and the atmosphere our results also indicate impact snow deposition under high winds and with a high initial density and air exchange between the atmosphere and the snowpack 210 pb activity below 0 3 m falls below the detection limit implying that most of the core is more than 100 years old we conclude that the allan hills record provides a unique opportunity to investigate important processes that would have affected ice core records from glacial periods

loessic silt deposits in the western himalayas their sedimentology genesis and age abstract loess is abundant in the foreland basins of the himalayas however it is poorly developed within the intermontane basins of the western himalayas and karaloram selected sections were studied from the swat himalaya and the karakoram mountains fieldwork and sedimentological analysis including grain size mineralogy and microfabric showed that the loessic sediments have been reworked and some have undergone weak pedogeneses these silts are not true loess rather a loessic colluvium thermoluminescence tl dates from the loessic sediments in sections from the swat valley provided younger ages than earlier workers had suggested this is consistent with reworking of the loess in these areas it is concluded that care must be taken when using loessic silts for tl in similar mountainous terranes

large arctic temperature change at the wisconsin holocene glacial transition analysis of borehole temperature and greenland ice sheet project ii ice core isotopic composition reveals that the warming from average glacial conditions to the holocene in central greenland was large approximately 15 c this is at least three times the coincident temperature change in the tropics and mid latitudes the coldest periods of the last glacial were probably 21 c colder than at present over the greenland ice sheet

snow isotopic content change by sublimation we present results from cold laboratory observations of changes in isotopic d 18 o and dd content by sublimation in snow and ice samples under nearly isothermal conditions the results show large increases in observed d 18 o and dd in snow samples within several centimeters of the surface they contradict the assumption of a non changing isotopic content due to layer by layer transport mechanisms driven by sublimation desublimation processes the data also do not support the idea that isotopic changes of snow and firn are limited by the possibility that the ice matrix incorporates the atmospheric water vapor and that forced water vapor diffusion in the pore space wind pumping is a requirement for isotopic content change the observations show that sublimation from ice samples results in much lower increases in heavy isotope content in the first several millimetres near the sublimating surface over the same time period despite sublimation intensities similar to those of the snow samples the results suggest that continuous phase transitions inside snow recrystallization are the process responsible for the isotopic content change because they are the primary mass exchange mechanism between the snow mass and the surrounding environment modeling the isotopic content of the ice matrix therefore requires inclusion of a two stage process fractionation at the ice matrix surface due to repetitive phase transitions and fractionation due to preferable diffusion of light water isotopes in the pore space for interpretation of the observed natural isotopic profiles in snow the first process can be linked to the time a snow layer undergoes recrystallization while the second process is related to the total ice snow mass gain loss determined by the external environmental conditions

mineralogical characterization of silica sinters from the el tatio geothermal field chile silica sinters deposited from alkali chloride waters in the el tatio geothermal field in northern chile 22 20 s 68 01 w have been characterized by xrd sem tg dta and ftir the dominant silica phase is opal a minor contents of opal a ct and opal ct are also present together with halite nacl sylvite kcl and realgar ass accessory phases include teruggite ca4mgas2b12o22 oh 12 12 h2o sassolite h3bo3 and detrital quartz sio2 fwhm values reflect the immature nature of the studied opal a dta heating experiments of opal a show cristobalite crystallization at 1000 c whereas dta cooling experiments show the cristobalite transformation at 200 c the total weight loss is related to changes in the sinter microtextures mineral phases and organic matter contents ftir spectra show the effects of silica maturation as consequence of the loss of trapped and absorbed water attached to silanols

holocene loess deposition and soil formation as competing processes matanuska valley southern alaska although loess paleosol sequences are among the most important records of quaternary climate change and past dust deposition cycles few modern examples of such sedimentation systems have been studied stratigraphic studies and 22 new accelerator mass spectrometry radiocarbon ages from the matanuska valley in southern alaska show that loess deposition there began sometime after f6500 14 c yr b p and has continued to the present the silts are produced through grinding by the matanuska and knik glaciers deposited as outwash entrained by strong winds and redeposited as loess over a downwind distance of f40 km loess thickness sand content and sand pluscoarse silt content decrease whereas fine silt content increases loess deposition was episodic as shown by the presence of paleosols at distances 10 km from the outwash plain loess source stratigraphic complexity is at a maximum i e the greatest number of loesses and paleosols at intermediate 10 25 km distances from the loess source surface soils increase in degree of development with distance downwind from the source where sedimentation rates are lower proximal soils are entisols or inceptisols whereas distal soils are spodosols ratios of mobile cao k2o and fe2o3 to immobile tio2 show decreases in surface horizons with distance from the source thus as in china where loess deposition also takes place today eolian sedimentation and soil formation are competing processes study of loess and paleosols in southern alaska shows that particle size can vary over short distances loess deposition can be episodic over limited time intervals and soils developed in stabilized loess can show considerable variability under the same vegetation d 2004 university of washington all rights reserved

magnetic parameters reflecting pedogenesis in pleistocene loess deposits of argentina abstract quaternary loess sequences of argentina with interbedded loess and buried soils palaeosols provide terrestrial records of past climates and environmental conditions study of rock magnetic parameters measured over a large area of the pampean loess seems to indicate that the existing magnetoclimatological models cannot adequately account for the complexities of the pampean loess the chinese loess has been considered as typical where magnetic properties are largely controlled by pedogenesis on the other hand the siberian loess is an alternative magnetoclimatological model in which palaeosols appear as magnetic lows and the intercalated loess as magnetic highs argentine loess is apparently closer to the siberian model however considering the data obtained in argentina the situation seems to be more complicated the higest magnetic values sirm and susceptibiliy values in silty and sandy loess indicate a more efficient entrainment of dense iron oxides particles during stormy dry glacial intervals the parent material shows the highest susceptibility values 100 10 8 m3 kg while the waterlogged horizons show the lowest ones below 20 10 8 m3 kg pedogenesis resulting in the development of bc and b soil horizons of palaeosols in the parent loess produced decreases in susceptibility values and increases in the f factor this phenomenon occurs at some degree of humidity in which the process of gleying caused the total depletion of both susceptibility and frequency factor the magnentic data allows consideration of the relevance of major cycles arid humid separated by discontinuities as the main factor favoring one particular behavior of the magnetic parameters the b horizons of palaeosols developed during an arid cycle will not show a notable difference in the magnetic records from the parent material in contrast during humid climate condition the pristine loess can be progresively obliterated by pedogensis through to the extreme situation of gleying

continuous late quaternary proxy climate records from loess in beringia abstract loess deposits in eastern beringia contain continuous proxy records of the effects of past climatic change on terrestrial landscapes at high latitudes variations of environmental magnetism and sedimentology of high latitude loess deposits indicate that the timing and pattern of responses to local variations in wind intensity storminess and pedogenesis in eastern beringia closely resemble the pattern of global climate change during the late quaternary deduced from studies of marine and ice core records the age of paleoclimatic fluctuations permafrost features volcanic ash horizons buried forest layers and paleosols and other features of the eastern beringian loess record can be determined using a variety of quaternary dating methods tephrochronologic correlations between the loess record and the glacial history of eastern beringia indicate the delta glaciation occurred during marine isotope stage 6 several other middle and late quaternary glaciations across eastern beringia can be tephrochronologically tied to the loess record and appear to have been in phase with episodes of global cooling recorded in deep sea records

progressive glacial retreat in the southern altiplano uturuncu volcano 22 s between 65 and 14 ka constrained by cosmogenic 3he dating this work presents the first reconstruction of late pleistocene glacier fluctuations on uturuncu volcano in the southern tropical andes cosmogenic 3he dating of glacial landforms provides constraints on ancient glacier position between 65 and 14 ka despite important scatter in the exposure ages on the oldest moraines probably resulting from pre exposure these 3he data constrain the timing of the moraine deposits and subsequent glacier recessions the uturuncu glacier may have reached its maximum extent much before the global lgm maybe as early as 65 ka with an equilibrium line altitude ela at 5280 m then the glacier remained close to its maximum position with a main stillstand identified around 40 ka and another one between 35 and 17 ka followed by a limited recession at 17 ka then another glacial stillstand is identified upstream during the late glacial period probably between 16 and 14 ka with an ela standing at 5350 m this stillstand is synchronous with the paleolake tauca highstand this result indicates that this regionally wet and cold episode during the heinrich 1 event also impacted the southern altiplano the ela rose above 5450 m after 14 ka synchronously with the bolling allerod

microbial silica interactions in icelandic hot spring sinter possible analogues for some precambrian siliceous stromatolites silicified deposits such as sinters occur in several modern geothermal environments but the mechanisms of silicification and crucially the role of microorganisms in their construction are still largely unresolved detailed examination of siliceous sinter in particular sections of microstromatolites growing at the krisuvik hot spring iceland reveals that biomineralization contributes a major component to the overall structure with approximately half the sinter thickness attributed to silicified microorganisms almost all microorganisms observed under the scanning electron microscope sem are mineralized with epicellular silica ranging in thickness from 5 lm coatings on individual cells to regions where entire colonies are cemented together in an amorphous silica matrix tens of micrometres thick within the overall profile there appears to be two very distinct types of laminae that alternate repeatedly throughout the microstromatolite microbial layers are predominantly consisting of filamentous intact vertically aligned biomineralized cyanobacteria identified as calothrix and fischerella sp and weakly laminated silica layers which appear to be devoid of any microbial component the microbial layers commonly have a sharply defined base overlying the weakly laminated silica and a gradational upper surface merging into the weakly laminated silica these cyclic laminations are probably explained by variations in microbial activity active growth during spring summer allows the microorganisms to keep pace with silicification with the cell surfaces facilitating silicification while during their natural slow growth phase in the dark autumn winter months silicification exceeds the bacteria s ability to compensate i e grow upwards at this stage the microbial colony is probably not essential to microstromatolite formation with silicification presumably occurring abiogenically when conditions once again become favourable for growth recolonization of the solid silica surface by free living bacteria occurs cell motility is not responsible for the laminations we have also observed that microbial populations within the microstromatolite some several mm in depth appear viable i e they still have their pigmentation the trichomes are not collapsed cell walls are unbroken cytoplasm is still present and they proved culturable this suggests that the bulk of silicification occurred rapidly probably while the cells were still alive surprisingly however measurements of light transmittance through sections of the microstromatolite revealed that photosynthetically active light pal only transmitted through the uppermost 2 mm therefore the deeper microbial

ice core age dating and paleothermometer calibration based on isotope and temperature profiles from deep boreholes at vostok station east antarctica an interpretation of the deuterium profile measured along the vostok east antarctica ice core down to 2755 m has been attempted on the basis of the borehole temperature analysis an inverse problem is solved to infer a local geophysical metronome the orbital signal in the surface temperature oscillations expressed as a sum of harmonics of milankovich periods by correlating the smoothed isotopic temperature record to the metronome a chronostratigraphy of the vostok ice core is derived with an accuracy of 3 0 4 5 kyr the developed timescale predicts an age of 241 kyr at a depth of 2760 m the ratio 13d 13t i between deuterium content and cloud temperature fluctuations at the top of the inversion layer is examined by fitting simulated and measured borehole temperature profiles the conventional estimate of the deuterium temperature slope corresponding to the present day spatial ratio 9 per mil oc is confirmed in general however the mismatch between modeled and measured borehole temperatures decreases noticeably if we allow surface temperature responsible for the thermal state of the ice sheet to undergo more intensive precession oscillations than those of the inversion temperature traced by isotope record with this assumption we obtain the long term temporal deuterium temperature slope to be 5 8 6 5 per mil oc which implies that the glacial interglacial temperature increase over central antarctica was about 15oc in the surface temperature and 10oc in the inversion temperature past variations of the accumulation rate and the corresponding changes in the ice sheet surface elevation are simultaneously simulated

depositional facies and diagenetic alteration in a relict siliceous hot spring accumulation examples from yellowstone national park u s a abstract siliceous precipitates from portions of an 11 m long core drilled through a relict yellowstone hot spring deposit provide valuable insights into the diagenetic facies in this hydrothermal environment most of the core consists of relatively low temperature siliceous sinter containing abundant plant diatom and microbial fossilized remains derived from the distal debris apron and discharge channel flowpath of the hot spring a few intervals contain stromatolitic horizons analogous to modern siliceous pool margin and discharge channel flowpath facies despite the abundance of silicified microbial remains e g silicified stromatolitic horizons as well as individual filamentous microbes diatoms distinctive organic biomarkers are not preserved in the core the apparent lack of distinctive organic biomarkers is attributable to pervasive diagenetic alteration in the presence of high temperature chemically reactive fluids numerous diagenetic features have been superimposed on the siliceous sinter especially considering the relatively shallow depths of burial the uppermost interval 0 to 1 2 m consists of highly porous siliceous sinter opal a and interbedded travertine amorphous manganese oxides and sparry calcite cements are present and are irregularly distributed throughout this interval below is a diagenetic facies 4 8 to 5 3 m that consists of opal ct and minor chalcedony the most pervasive diagenetic alteration in the core is the 6 8 to 11 2 m depth interval where abundant zeolites mordenite heulandite bladed cristobalite lepispheres chalcedony cements and calcite veins are present judging by the assemblage of plant and diatom remains most of this pervasive alteration is superimposed on relatively low temperature siliceous sinters and is likely the result of migration of hot waters through this interval the paragenesis of all these intervals is very complex involving numerous episodes of mineral precipitation and dissolution this diagenetic alteration is facilitated by the porous nature of the siliceous sinter thermal convection of superheated fluids or steam strongly oxidizing spring waters and fluctuating hydrochemical regimes rapid dissolution and or replacement of organic matter indicates that standard morphological means e g petrographic identification of body fossils may be the best method by which to identify that organisms were previously present in ancient hot spring accumulations

foraminiferal faunal estimates of paleotemperature circumventing the no analog problem yields cool ice age tropics the sensitivity of the tropics to climate change particularly the amplitude of glacial to interglacial changes in sea surface temperature sst is one of the great controversies in paleoclimatology here we reassess faunal estimates of ice age ssts focusing on the problem of no analog planktonic foraminiferal assemblages in the equatorial oceans that confounds both classical transfer function and modern analog methods a new calibration strategy developed here which uses past variability of species to define robust faunal assemblages solves the no analog problem and reveals ice age cooling of 5 o to 6oc in the equatorial current systems of the atlantic and eastern pacific oceans classical transfer functions underestimated temperature changes in some areas of the tropical oceans because core top assemblages misrepresented the ice age faunal assemblages our finding is consistent with some geochemical estimates and model predictions of greater ice age cooling in the tropics than was inferred by climate long range investigation mapping and prediction climap 1981 and thus may help to resolve a long standing controversy our new foraminiferal transfer function suggests that such cooling was limited to the equatorial current systems however and supports climap s inference of stability of the subtropical gyre centers

influence of summer sublimation on δd δ18o and δ17o in precipitation east antarctica and implications for climate reconstruction from ice cores

the geomorphology sediment distribution soil formation nexus on the northeastern qinghai tibetan plateau implications for landscape evolution abstract the interactions between geomorphology sediment distribution and soil development in alpine regions are poorly understood in this study we analyzed the spatial variations of different sediment types and corresponding soils in 15 pedosedimentary profiles across three major geomorphic units in an alpine ridge valley basin of the qilian mountains northeastern qinghai tibetan plateau particle size distribution was used to trace the sediment types inorganic and organic carbon concentrations were included as metrics of soil processes aeolian silts from both distant and proximal sources cover floodplains hillslopes and some positions on alluvial fans while the distribution of fluvial sediments and periglacial slope deposits are much more limited due to the coverage of loess the soils vary in response to sediment types and climatic conditions under the influence of their geomorphic settings the vertical distribution patterns of carbonates in soil profiles show considerable differences among different geomorphic units reflecting their contrasting water balance and migration pathways soil organic carbon accumulates most extensively in aeolian silts with sufficient water supply a special pedogenic soil horizon the mattic epipedon is formed primarily in loessial sediments in kobresia ecosystems the complex entanglement of fine earths and massive grassroots make the mattic epipedon extremely resilient which helps to preserve the soils and to shape the landscapes by integrating geomorphology sedimentology ecology and pedology the outcomes of this study promote the understanding of the evolution of typical landscapes and ecosystems of the northeastern qinghai tibetan plateau and many other periglacial settings

aeolian dust contribution to the formation of alpine soils at amdo northern tibetan plateau abstract the tibetan plateau has one of the largest distributions of alpine meadow in the world due to the cold climate and dominance of physical weathering conditions coarse or massive debris prevails thus pedogenesis is controlled by both the temperature and parent material in this study the alpine soils gelic cambisol at altitudes of 4768 4980 m in the amdo zone of the northern tibetan plateau were investigated we found that the parent materials throughout the alpine soil profiles were rich in clayey and silty minerals here we focused on the origin of the soil forming materials of alpine meadows we examined the grain size distribution mineral compositions trace element concentrations and sr nd isotopic compositions of the alpine soils and their potential source materials in various grain size fractions based on a comparison of many fingerprints our results indicated that a red clay rich bed at the bottom of the alpine soil profile is a residual paleo weathering crust nevertheless the parent materials in the alpine soils did not have a clear inherited relationship with the weathering products of the in situ bedrock correspondingly we confirmed that the parent materials in the alpine soils have an aeolian origin the alluvial sediments and widespread beach and lacustrine delta sediments in the amdo zone are the main source of alpine soil materials however it was not clear whether sediments are the main source of aeolian dust aeolian dust with a short transport distance is one of the main components 300 m of alpine soils had a local origin i e from adjacent bedrock outcrops in contrast long range transport of dust had a minor role in the formation of alpine soils in the region investigated the aeolian dust began accumulating in the middle holocene on the tibetan plateau one positive effect of aeolian processes is that the aeolian dust accretion is a source of parent materials and nutrients for alpine soils

how old is the human footprint in the world s largest alpine ecosystem a review of multiproxy records from the tibetan plateau from the ecologists viewpoint the age at which a human environment was made is strongly debated in quaternary science the perception of the human footprint requires an understanding of the contrast between the present cultural environment and the natural vegetation this is especially true for high altitude ecosystems such as the world s largest alpine ecosystem the 450 000 km 2 of golf course like pastures dominating the southeastern tibetan plateau this ecosystem is widely considered to be natural but only because of the unawareness of the effects of grazing management and the incorrect assessment of human signals in palaeo proxies here we posit the hypothesis that this ecosystem is a human induced replacement to test our hypothesis against defined a priori criteria we 1 monitored vegetation in grazing exclosures 2 produced floristically complete vegetation records 3 compared the vegetation records with data of the nearest climate stations 4 surveyed forest and experimental reforestation trials with endemic tree species 5 analyzed pollen and re evaluated published pollen diagrams and 6 integrated these results with palaeopedological and anthracological results of previous studies the results of long term grazing exclosure experiments the prevalence of grazing adapted plant functional types the occurrence of isolated vigorous forests in alpine pastures and the successful reforestation trials in presently treeless pastures together suggest that dominant pastures replaced forests in the montane belt and tall grassland in the alpine belt the spatial and temporal coincidence of palaeosols and archaeological sites with tree species charcoal the decline in forest pollen during the mid holocene climatic optimum and the first appearance of human indicator pollen are most parsimoniously explained by the early presence of foragers and pastoralists the onset of pastoralism in the tibetan highlands is presumed to date from the 8th millennium bp c 2013 elsevier ltd all rights reserved

validity of the isotopic thermometer in central antarctica limited impact of glacial precipitation seasonality and moisture origin the classical interpretation of water stable isotopes deuterium or oxygen 18 retrieved from ice cores into past local temperature relies on the use of the spatial isotope temperature slope as a surrogate of the temporal slope whereas this assumption has been challenged by independent methods in central greenland it is still considered as valid in central antarctica we use an atmospheric general circulation model gcm to study two parameters highlighted by previous studies as being among the most important with respect to this assumption we show that in the gcm between present day and last glacial maximum the change in precipitation seasonality and the cooling of the moisture sources have limited and opposite effects on the isotopic record of the antarctic local temperature this conclusion strengthens the validity of the classical interpretation of isotope records in central antarctica

seasonal changes in silica deposition in hot spring systems abstract monthly monitoring of water chemistry at octopus spring yellowstone national park reveals no changes in the chemical composition over this eight month study differences in silica deposition are attributed to flow dynamics and seasonal air temperatures colder air temperatures in winter promote visible accumulation of siliceous sinter probably as a result of decreased solubility periodic drying promotes accumulation and subsequent dehydration of the silica this combination of intermittent supply and periodic dehydration may account for the laminated siliceous deposits observed in the geological record the processes described herein are important in the siliceous preservation of microbial fossils but the following observations underscore the difficulty in preserving microbial fabrics in the geological record pools populated by cyanobacteria are bounded by margins built of silicified microbial mats silicification of the pool margins occurs through an evaporative process called wicking silica rich water is transported upward through the microbial mats by capillary action depositing silica at the surface of the mat as water evaporates the upper surface of such wicking deposits is extremely resistant to brecciation but the underlying support is highly friable and would be difficult to preserve intact in winter months temporary isolation of some pools from active flow causes fragile silica deposition around biological and other debris film coated gas bubbles on the surfaces of microbial mats are observed during all seasons and probably are filled with oxygen released during photosynthesis although this has not been confirmed they become coated with silica during winter months presumably because of increased cooling possibly forming thin discontinuous silica sheets as observed in the geological record