phosphate related artifacts in carbonate mineralization experiments abstract sedimentary deposits of calcium carbonate are ubiquitous and may preserve a record of early life on earth precipitation of carbonates and other minerals can be mediated by microorganisms a process known as organomineralization one of the many approaches for the study of organomineralization is growth of bacteria in culture although culture media commonly are based on natural conditions the levels of nutrients especially phosphate generally are much higher than in the natural systems they are meant to simulate this study demonstrates that levels of phosphate ranging from 5 8 to 0 1 mm in common laboratory media exceeding natural concentrations by 3 to 6 orders of magnitude can affect carbonate mineral morphology e g spherulites dumbells and size i e fewer larger crystals in the presence of phosphate and affect the formation of other mineral products not related to study objectives such as apatite and struvite in the microbial mats forming the modern stromatolites at highborne cay in the bahamas layers of calcium carbonate are precipitating in association with high rates of sulfate reduction sulfate reducing bacteria srb have also been implicated in the precipitation of calcium carbonate in other natural systems and in the precipitation of dolomite batch culture studies using srb from the precipitating layers of the highborne cay stromatolites produced both carbonate aragonite and unexpectedly phosphate apatite minerals although this occurrence is not a widely reported result in similar culture studies thermodynamic modeling of this medium and a range of compositions used in organomineralization investigations revealed oversaturation of apatites and of common carbonate minerals in all cases other analyses compared the effect of phosphate on other factors that can impact culture including bacterially derived extracellular polymeric substances eps sulfate and low molecular weight organic compounds lmwoc results from the eps study showed precipitated struvite a phosphate mineral indicating phosphate association with eps different phosphate levels altered calcium carbonate morphologies precipitated in the presence of sulfate and lmwoc for both the sulfate study and the lmwoc study phosphate was the dominant factor controlling mineral products these results illustrate that phosphate in culture media has a pronounced impact on carbonate mineral products and can potentially obscure or alter more subtle effects on mineral precipitation these effects might lead to misinterpretation of culture studies meant to simulate natural systems

seasonal variability in the origin of recent atmospheric mineral dust at northgrip greenland abstract isotopic sr and nd and mineralogical analyses of dust extracted from snow deposits from the last decade at the northgrip greenland ice camp 75 1 n 042 3 w confirm the eastern asian source for greenland dust and extend it to the present day the 1998 and 1999 samples which represent a 2 4 month resolution of dust deposition show that there are at least two east asian sources for the greenland dust that vary seasonally the provenance of dust during the major spring summer deposition is the takla makan desert of northwest china

the effect of extracellular polymeric substances on the adhesion of bacteria to clay minerals and goethite abstract the functions of extracellular polymeric substances eps during the adhesion of bacillus subtilis to kaolinite montmorillonite and goethite were examined by a direct comparison of the adhesion behaviors of native and eps free cells via cation exchange resin cer treatment using batch experiments attenuated total reflectance fourier transform infrared atr ftir spectroscopy and potentiometric titration the eps removal had no apparent influence on bacterial adhesion when the wet bacteria mineral mass ratio was low ofe bonds were important for adhesion to goethite in addition to electrostatic forces repulsion for clays and attraction for goethite absence of chemical interactions may also cause the relatively much weaker bacterial adhesion to clay minerals than to goethite the absence of eps did not change the interaction mode of the adhesion to clay minerals but enhanced the chemical interactions via carboxyl groups for bacteria goethite adhesion the potentiometric titration results coupled with the atr ftir spectra showed a significant increase in site concentrations of the cer treated bacteria as compared to the native cells changes in surface site concentrations and chemical interactions that were accompanied by the eps removal may reasonably explain the influences of eps on bacterial adhesion to different minerals

direct and indirect impact of the bacterial strain pseudomonas aeruginosa on the dissolution of synthetic fe iii and fe ii bearing basaltic glasses abstract this study investigates the direct and indirect bacterial contributions that influence the dissolution of basaltic glass in this regard three different types of glasses with or without fe in the reduced fe ii or oxidized fe iii states were prepared on the basis of a simplified basaltic glass composition in order to prevent the direct contact between the glasses and the model siderophore producing strain pseudomonas aeruginosa the glass samples were isolated in dialysis bags and immersed at 25 c and ph 6 5 in bacterial cultures throughout the dissolution experiments the following parameters were monitored determination of bacterial growth quantification of siderophore i e pyoverdine production microscopic observation of the glass surface and determination of dissolution kinetics isolating the glass from the bacterial suspension only triggered the biosynthesis of siderophores in the fe iii bearing glass dissolution experiments siderophores were produced in the presence of fe ii bearing and fe free glass independently on the experimental setup the siderophore production appeared to be either continuous in the absence of fe glass free control fe free glass dissolution experiments or stopped as soon as the bacteria entered their stationary phase when an fe source was present fe ii and fe iii bearing glass dissolution experiments the increase in the dissolution rates of each glass was correlated to the complex stability constants of the siderophore with the metallic cations in presence kfe2

circulation anomalies associated with tropical convection during northern winter abstract lagged cross correlations between outgoing longwave radiation olr and national meteorological center global analyses are utilized to isolate the preferred upper level and surface circulation anomalies associated with tropical convection during northern winter three intraseasonal time scales are studied 30 70 14 30 and 6 14 days in the 30 70 day band the upper level circulation signals are zonally elongated with zonal wavenumbers 0 2 dominant higher frequency signals are dominated by zonal wavenumbers 5 and 6 in the 14 30 day band convection over the eastern hemisphere is associated with upper level anticyclones in the subtropics and appears to be linked in some cases to midlatitude wave trains the strongest signals are for convection over africa australia and the eastern indian ocean only weak signals are seen for convection over indonesia in these regions of upper level easterlies olr anomalies peak prior to the maximum anomalies in wind suggesting forcing of the circulation b

microbe mineral interactions early carbonate precipitation in a hypersaline lake eleuthera island bahamas microbialites benthic microbial carbonate deposits were discovered in a hypersaline alkaline lake on eleuthera island bahamas from the edge towards the centre of the lake four main zones of precipitation could be distinguished 1 millimetre sized clumps of mg calcite on a thin microbial mat 2 thicker and continuous carbonate crusts with columnar morphologies 3 isolated patches of carbonate crust separated by a dark non calcified gelatinous mat and 4 a dark microbial mat without precipitation in thin section the precipitate displayed a micropeloidal structure characterized by micritic micropeloids strong autofluorescence surrounded by microspar and spar cement no fluorescence observations using scanning electron microscopy sem equipped with a cryotransfer system indicate that micrite nucleation is initiated within a polymer biofilm that embeds microbial communities these extracellular polymeric substances eps are progressively replaced with high mg calcite discontinuous eps calcification generates a micropeloidal structure of the micrite possibly resulting from the presence of clusters of coccoid or remnants of filamentous bacteria at high magnification the microstructure of the initial precipitate consists of 200 500 nm spheres no precipitation is observed in or on the sheaths of cyanobacteria and only a negligible amount of precipitation is directly associated with the well organized and active filamentous cyanobacteria in deeper layers of the mat indicating that carbonate precipitation is not associated with co2 uptake during photosynthesis instead the precipitation occurs at the uppermost layer of the mat which is composed of eps empty filamentous bacteria and coccoids gloeocapsa spp two dimensional mapping of sulphate reduction shows high activity in close association with the carbonate precipitate at the top of the microbial mat in combination these findings suggest that net precipitation of calcium carbonate results from a temporal and spatial decoupling of the various microbial metabolic processes responsible for caco3 precipitation and dissolution theoretically partial degradation of eps by aerobic heterotrophs or uv fuels sulphate reducing activity which increases alkalinity in microdomains inducing caco3 precipitation this degradation could also be responsible for eps decarboxylation which eliminates ca 2 binding capacity of the eps and releases ca 2 ions that were originally bound by carboxyl groups at the end of these processes the eps biofilm is calcified and exhibits a micritic micropeloidal structure the eps free precipitate subsequently serves as a substrate for physico chemical precipitation of spar cement from the alkaline water of the lake the micropeloidal structure has an intimate mixture of

association between atmospheric circulation patterns and firn ice core records from the inilchek glacierized area central tien shan asia 1 glacioclimatological research in the central tien shan was performed in the summers of 1998 and 1999 on the south inilchek glacier at 5100 5460 m a 14 36 m firn ice core and snow samples were collected and used for stratigraphic isotopic and chemical analyses the firn ice core and snow records were related to snow pit measurements at an event scale and to meteorological data and synoptic indices of atmospheric circulation at annual and seasonal scales linear relationships between the seasonal air temperature and seasonal isotopic composition in accumulated precipitation were established changes in the 18o air temperature relationship in major ion concentration and in the ratios between chemical species were used to identify different sources of moisture and investigate changes in atmospheric circulation patterns precipitation over the central tien shan is characterized by the lowest ionic content among the tien shan glaciers and indicates its mainly marine origin in seasons of minimum precipitation autumn and winter water vapor was derived from the arid and semiarid regions in central eurasia and contributed annual maximal solute content to snow accumulation in tien shan the lowest content of major ions was observed in spring and summer layers which represent maximum seasonal accumulation when moisture originates over the atlantic ocean and mediterranean and black seas

the genesis of actively growing siliceous stromatolites evidence from lake specchio di venere pantelleria island italy this study documents the attributes of siliceous stromatolites growing in the lake specchio di venere on the volcanic island of pantelleria italy in a setting characterized by very shallow cold waters and pools and by scattered hydrothermal activity which exhales mainly co2 at emission point temperatures of 34 to 58 c the saturation indexes indicate that the lake waters are saturated with respect to tridymite cristobalite chalcedony and quartz and slightly undersaturated with respect to amorphous silica common roughly laminated and poorly lithified stromatolites show scanning electron microscope sem evidence for silicified microbial mat structures including biofilms filamentous and coccoid cells and extracellular polymeric substances eps the screening of bacterial 16s rrna libraries indicates that autotrophic and heterotrophic bacterial communities colonize surface and core levels of the stromatolites locally the stromatolites show a granular non porous fabric where filaments and silica sheets are not apparent inhomogeneity in the stromatolite fabric corresponds with varying dna content and different structures of the colonizing bacterial communities non porous stromatolite levels being microbially colonized to a lesser extent based on fourier transform ft raman and ft infrared investigations the laminated stromatolite contains early diagenetic tridymite in addition to amorphous silica opal a whereas the non porous stromatolite shows an essentially amorphous character the laminated stromatolite is thought to form at relatively low rates of silica precipitation and with a possible microbial mediation in terms of microbial cells and their eps accelerating the onset of amorphous silica nucleation it is suggested that high porosity probably favoured a consistent flux of silica rich fluids that triggered the opal a to tridymite transformation thus strengthening the preservation of biosignals non porous stromatolite growth could reflect temporal or localised changes in environmental conditions that caused variations in the degree of silica saturation in the lake waters inducing abiotic silica accumulation accelerated opal a deposition could have obscured primary filamentous fabrics and limited the flux of pore fluid needed for sustaining the process of silica maturation

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

microbial dolomite in fresh water carbonate deposits this article reports evidence for biologically mediated precipitation of dolomite in a fresh water spring in the south east of spain build ups in the spring consisted of calcite minor dolomite barite and gypsum crystals formed by the mineralisation of microbial biofilms and bryophytes a detailed microscopic study coupled with geochemical analysis of the dolomite precipitating biofilms showed that dolomite crystals occurred in association with living coccoid micro organisms providing strong evidence that micro organisms play a fundamental role in the precipitation of this mineral many of the calcite crystals observed were associated with extracellular polymeric substances moreover microbial involvement in the precipitation of calcite was further supported by the presence of living cyanobacteria within the calcite crystals two different types of build up were found in the spring soft spongy moss tufa and laminated crusts two types of crusts were identified as follows simple pink crusts and laminated crusts the latter forming in both sub aquatic and sub aerial environments sub aquatic accumulation of simple detached pink crust fragments occurred sporadically both tufa and the carbonate crusts hosted cyanobacterial dominated biofilms with different bacteria and diatoms and their extracellular polymeric substances the 13c values of calcite showed some biogenic involvement in the origin of this mineral the 18o values were similar in the tufa and carbonate crusts and corresponded to current climatological characteristics the occurrence of different groups of minerals carbonates and sulphates in close spatial association with micro organisms suggests the presence of different macro environmental and micro environmental conditions that facilitate mineral precipitation within biofilms these findings extend the known range of aerobic microbial dolomites to include springs and show that the precipitation of both dolomite and calcite carbonates occurs while organisms are alive

aeolian dust dynamics in central asia during the pleistocene driven by the long term migration seasonality and permanency of the asiatic polar front loess paleosol sequences preserve detailed archives of climate change reflecting the dynamics of aeolian dust sedimentation and the paleodust content of the atmosphere the detailed investigation of particle size distributions psds of windblown sediments is an increasingly used approach to assess the paleorecord of aeolian dust dynamics the central asian loess belt offers the potential to reconstruct pleistocene atmospheric circulation patterns along an adjacent west east transect within interior eurasia through granulometric studies in this study we present the aeolian dust record of the loess sequence at remisowka se kazakhstan which reflects a detailed signal of glacial interglacial climate and atmospheric dynamics in central asia on the basis of radiocarbon and amino acid geochronologic data long term semicontinuous trends in the aeolian dust record of the last glacial cycle are observed and interpreted to reveal their paleoclimate signal in consideration of the modern synoptical atmospheric circulation patterns and aeolian dust transport in central asia it is likely that the observed trends reflect the long term migration seasonal duration and permanency of the polar front during the late pleistocene previously published models which focused on the reciprocal glacial interglacial influence of the zonal westerlies and the asiatic high on the aeolian dust transport in central asia were overly simplified and should be modified to include the major influence of the asiatic polar front as the polar front activity is intimately connected with the development and position of the interhemispherically active high level planetary frontal zone hpfz the presented data give insight to long term aeolian dust dynamics and climate variability of interior eurasia which are linked with interhemispheric climates

erosion of biofilm bound fluvial sediments sediment grains in rivers are often bound together and stabilized by bacterial films experiments and mathematical models show that sediments bound by biofilms behave like a single elastic membrane that can rip catastrophically if the river flows fast enough

the role of bacterial extracellular polymeric substances in geomicrobiology abstract the last two decades have seen geomicrobiology evolve into a broad field encompassing a wide range of environmentally significant processes such as proton and metal adsorption onto cell surfaces and the effect of microbes on mineralisation redox cycling and contaminant transport within this sphere research groups have conducted studies using bacteria fungi diatoms and sludges all of which can play a part in geochemical processes here we review research on the role played by microbial extracellular polymeric substances eps focussing on bacterial and cyanobacterial eps we conclude by outlining future research directions in order to investigate unresolved questions in the field the effect of eps on metal adsorption is complex whereas some studies report an increase in metal adsorption when cells contain eps some report no differences yet others report a decrease these discrepancies may reflect differences in molecular and functional group composition of the eps eps provides a template for adsorption of metal cations to which carbonate ions are attracted to induce local mineral supersaturation this may be behind observed changes in both crystal polymorphism favouring formation of less stable polymorphs and crystal morphology where the presence of eps promotes the formation of rounded smoothed crystals or spheroids the role of eps in mineral dissolution bioleaching and corrosion is equivocal eps alone appears to have little effect on mineral dissolution bioleaching or biocorrosion instead it appears that eps increases rates of mineral weathering and leaching by forming complexes with metallic ions released by the mineral surface which may themselves catalyse bioleaching in the case of sulphides eps in biofilms forms effective barriers to the transport of particulate phases and exerts important controls on the transport and deposition of natural and engineered nanoparticles much less is known about the role of eps in the cycling of redox sensitive trace metals intuitively and as observed in microbial mats with sulphate reducing bacteria eps is a labile electron donor for microbial metabolism that could affect metal biogeochemistry but this remains to be conclusively demonstrated in laboratory experiments hence in this and other areas further studies are required to develop a mechanistic basis for including the effects of eps in biogeochemical models

relative rates of peoria loess accumulation and pedogenic processes implications for paleoclimatic inference abstract where it is thick enough to extend below the surface soil profile the late wisconsinan peoria loess in the midcontinent of north america has characteristics suggesting relatively little syndepositional pedogenesis in these thicker sections the peoria loess below the surface soil profile commonly displays massive macroscopic structure low organic carbon content and retention of detrital carbonate grains late wisconsinan climatic conditions provide one potential explanation for these observations this paper considers two other non climatic explanations 1 loess accumulation was more rapid than carbonate dissolution or oc accumulation and 2 post depositional diagenesis has removed evidence of syndepositional pedogenesis the approach used is comparison of potential rates for pedogenic processes and loess accumulation even when wide ranges of controlling factors precipitation evapotranspiration and soil carbon dioxide levels are considered loess accumulation was probably too rapid at many sites for carbonate mineral dissolution to keep pace on the other hand data from modern tundra and boreal forest environments suggest that soil oc accumulation could have kept pace with loess deposition in many cases low oc contents observed in the loess today probably reflect post depositional oxidation climatic factors may provide partial or local explanations for the apparent minor extent of syndepositional pedogenesis but loess accumulation rates and diagenesis are key factors as well

grain size and accumulation rate records from late cenozoic aeolian sequences in northern china implications for variations in the east asian winter monsoon and westerly atmospheric circulation we attempt to reconstruct the history of westerly and monsoonal circulations in northern china using variations in sediment grain size and accumulation rate at four loess sections in the central chinese loess plateau the initiation of aeolian accumulation at about 7 6 ma in the main part of the chinese loess plateau probably marked the onset of the monsoonal circulation both the monsoonal and westerly circulations weakened from 7 6 to 5 2 ma subsequently the monsoonal circulation strengthened progressively from 5 2 ma to the present in addition the westerly circulation strengthened from 5 2 to 0 6 ma but then weakened thereafter and especially during the last 0 6 ma comparison of our aeolian records and the deep sea sediment record suggests that the strengthening trends of the monsoonal and westerly circulations were associated with the progressive development of global ice sheets during the late cenozoic abrupt changes of both the monsoon and westerly circulations occurred at 7 6 3 4 and 1 2 0 9 ma together with a weakening trend of the westerly circulation in the last 0 6 ma and are interpreted as the consequence of the episodic uplift of the tibetan plateau spatial differences in the grain size characteristics amongst the four sections suggest that the circulation intensity and variability decreased from west to east across the loess plateau due to the topographic effect of the tibetan plateau in addition some spatial differences may have been the result of local topographic effects c 2008 elsevier b v all rights reserved

microbially mediated carbonate precipitation in a hypersaline lake big pond eleuthera bahamas microbial metabolism impacts the degree of carbonate saturation by changing the total alkalinity and calcium availability this can result in the precipitation of carbonate minerals and thus the formation of microbialites here the microbial metabolic activity the characteristics and turnover of the extracellular polymeric substances and the physicochemical conditions in the water column and sediments of a hypersaline lake big pond bahamas were determined to identify the driving forces in microbialite formation a conceptual model for organomineralization within the active part of the microbial mats that cover the lake sediments is presented geochemical modelling indicated an oversaturation with respect to carbonates including calcite aragonite and dolomite but these minerals were never observed to precipitate at the mat water interface this failure is attributed to the capacity of the water column and upper layers of the microbial mat to bind calcium a layer of high mg calcite was present 4 to 6 mm below the surface of the mat just beneath the horizons of maximum photosynthesis and aerobic respiration this carbonate layer was associated with the zone of maximum sulphate reduction it is postulated that extracellular polymeric substances and low molecular weight organic carbon produced at the surface i e the cyanobacterial layer of the mat bind calcium both aerobic and anaerobic heterotrophic microbes consume extracellular polymeric substances each process accounting for approximately half of the total consumption and low molecular weight organic carbon liberating calcium and producing inorganic carbon the combination of these geochemical changes can increase the carbonate saturation index which may result in carbonate precipitation in conclusion the formation and degradation of extracellular polymeric substances as well as sulphate reduction may play a pivotal role in the formation of microbialites both in marine and hypersaline environments

loess depositional dynamics and paleoclimatic changes in the yili basin central asia over the past 250 ka abstract widely distributed loess deposits within the tianshan mountains are important archives for studying late quaternary climate in this central asian region however insufficient age control for these regional loess records especially over glacial interglacial cycles severely limits our understanding of loess depositional dynamics and accurate interpretation of paleoclimate conditions across central asia in this study we applied k feldspar optical dating and magnetic susceptibility grain size distribution caco3 and color to loess paleosol sections in the yili basin of the tianshan mountains to constrain loess depositional dynamics identify timing of loess paleosol formation and clarify the role of paleoclimate influence in this region since the late middle pleistocene our results demonstrate that loess deposition started as early as 350 ka in the yili basin following river down cutting associated with glacial interglacial transitions and exposure of riverbed sediments enhanced dust emission from flood plains played an important role in loess deposition very rapid loess deposition as high as 60 120 g cm 2 ka 1 on river terraces occurred during the last interglacial when loess accumulation at different locations of the site had remarkably different rates ranging from 10 to 100 g cm 2 ka 1 this heterogeneous behavior indicates that not only climatic changes influenced yili basin loess deposition and preservation but by complex interaction of local geomorphology wind velocity and changes of materials in dust origins depositional hiatuses frequently occurred during the past 250 ka likely induced by strong erosion resulting from increased wind strength and dry cold climate with poor vegetation cover in the region magnetic susceptibility grain size distribution caco3 and color analyses of the loess paleosol sequences showed that paleosols formed around 288 ka 230 191 ka 120 106 ka 92 89 ka and 84 71 ka hence a generally moist climate characterized the yili basin before marine isotope stages mis 9 mis 7 mis 5d mis 5b and the mis 5 mis 4 transition respectively this study suggests a climate pattern of moist interglacial and dry glacial periods in the tianshan mountains whereas substages of interglacials had cold moist and warm dry climate characteristics

structure and evolution of baroclinic waves as inferred from regression analysis abstract the structure of transient disturbances with periods shorter than a week is documented an the basis of one point regression maps and longitude height sections derived from the national meteorological center nmc operational analyses for nine winter seasons the reference time series for the regression coefficients is highpass filtered normalized 500 mb height at a grid point in the pacific stormtrack the field variables that were regreesed on the reference time series were not filtered the regression statistics yield quantitative estimates of the amplitudes of the high frequency fluctuations in the geopotential height temperature wind ageostrophic wind vorticity divergence vertical velocity and outgoing longwave radiation fields the observed high frequency fluctuations exhibit a vertical and meridional structure suggestive of baroclinic waves evolving through the mature phase of their life cycle most of the results are in qualitative agreement with previous studies but the ageostrop

aerobic microbial dolomite at the nanometer scale implications for the geologic record microbial experiments are the only proven approach to produce experimental dolomite under earth s surface conditions although microbial metabolisms are known to induce dolomite precipitation by favoring dolomite growth kinetics the involvement of microbes in the dolomite nucleation process is poorly understood in particular the nucleation of microbially mediated dolomite remains a matter for investigation because the metabolic diversity involved in this process has not been fully explored herein we demonstrate that halomonas meridiana and virgibacillus marismortui two moderately halophilic aerobic bacteria mediate primary precipitation of dolomite at low temperatures 25 35 c this report emphasizes the biomineralogical implications for dolomite formation at the nanometer scale we describe nucleation of dolomite on nanoglobules in intimate association with the bacterial cell surface a combination of both laboratory culture experiments and natural samples reveals that these nanoglobule structures may be 1 the initial step for dolomite nucleation 2 preserved in the geologic record and 3 used as microbial tracers through time and or as a proxy for ancient microbial dolomite as well as other carbonate minerals

luminescence dating of the zeketai loess section in the ili basin northwestern china methodological considerations abstract loess deposits in xinjiang northwestern china are ideal archives for past environmental changes in the westerlies dominated central asia among previous luminescence dating studies of loess in xinjiang few have attempted to systematically investigate the methodological aspects in this study we report results of a multiple procedure luminescence dating of the zeketai loess section in the ili basin central xinjiang optically stimulated luminescence osl and post infrared infrared stimulated luminescence pirir signals were used for quartz and polymineral grains of different sizes the pirir ages obtained with two protocols agree well with each other and constrain the loess deposition between 50 ka and 88 ka the osl ages of fine grained quartz are in stratigraphic order and range from 37 ka to 61 ka but are 30 younger than the pirir295 ages of both fine and medium grained polyminerals although the causes of the discrepancy between the ages derived from different luminescence dating protocols are still to be understood we stress that the quartz osl ages of loess in this region are likely to be underestimated especially for samples older than 40 ka the polymineral or potassium feldspar pirir signal is recommended for dating loess in the ili basin at least as an internal check

the agh band loess palaeosol sequence a terrestrial archive for climatic shifts during the last and penultimate glacial interglacial cycles in a semiarid region in northern iran abstract the northern iranian loess profiles host important information on quaternary climate and palaeoenvironmental changes in the region they build an important link between the eurasian loess belt and european and central asian archives due to a climatic gradient with decreasing precipitation from the west to the east and from the south to the north loess palaeosol sequences formed synchronously under different climatic conditions can be studied over short distance in the iranian caspian lowland the agh band profile is located in the so called iranian loess plateau a semi arid region with 200 350 mm annual precipitation the loess deposits at agh band reach a thickness of 60 m an about 50 m thick step profile was prepared and the litho pedostratigraphy was investigated samples for laser diffractometry grain size measurements were taken every 2 cm the magnetic susceptibility was measured in 4 cm intervals and the caco3 content in 8 cm intervals to establish a chronological framework a pirir290 luminescence dating approach was applied to the 4 11 m polymineral fraction the results show that the agh band profile yields a climate archive reaching from mis 7 to mis 2 several chronological hiatuses of some 10 ka show that periods of intense loess accumulation were interrupted by phases of only minor loess sedimentation and or erosion the agh band profile is subdivided by several shifts in grain size distribution the coarsening and fining up trends correlate with increasing and decreasing wind velocity respectively in the central part of the agh band loess sequence a weakly developed palaeosol is preserved which was developed at around 80 ka furthermore the loess deposits formed from about 100 ka to 60 ka ago show banded structures a pedocomplex including two well developed palaeosols consisting of bw y horizons and a cb horizon as well as intercalated loess can be found in the lower part of the sequence also evidenced by the increased values of magnetic susceptibility the corresponding luminescence age estimates indicate that the palaeosols represent a period of increased humidity and landscape stability during late mis 7 and mis 6 hence in the agh band loess various changes in the palaeo sedimentary system triggered by changes in climate can be observed this yields important information on the sensitive response of sedimentary systems and landscapes within semi arid regions to shifts in moisture and possibly temperature

bacterial extracellular polymeric substances eps mediate caco3 morphology and polymorphism abstract the effect of bacterial extracellular polymers eps on calcium carbonate morphology and polymorphism was investigated by means of free drift mineralisation experiments conducted using cells of the eps producing thermotolerant bacillus licheniformis s 86 the cells either had the eps layer intact native cells or had the eps layer removed eps free cells experiments were also undertaken in the absence of cells but with the addition of the extracted eps solution it was found that the abiotic control and eps free cell experiments contained vaterite and calcite when sampled after 12 h and 48 h whereas the native cell and eps solution experiments contained only calcite these results suggest that the presence of eps inhibits vaterite precipitation it is proposed that dissolved organic carbon doc released from the eps complexes ca 2 ions in solution reducing the calcium carbonate saturation and favouring calcite precipitation over vaterite after 7 days all experiments contained only calcite however distinct morphological differences between the calcite crystals precipitated in the four experiments were preserved after a period of 7 days suggesting that crystal morphology may indicate the biological conditions under which calcite precipitated

role of the bacterium thiobacillus in the formation of silicates in acidic mine tailings acidophilic chemolithotrophic bacteria such as thiobacillus are commonly found in sulfidic mine tailings they oxidize fe ii and reduced sulfur species from sulfide minerals left in tailings and produce acidic leachates loaded with heavy metals our study of the kam kotia mine tailings cu zn ore an abandoned mine located near timmins ontario canada showed that thiobacillus played an important role in the in situ formation of silicates transmission electron microscopic observations of ultrathin sections of tailings revealed the presence of bacteria with fine grained silica sio2 associated with their cell walls under laboratory conditions mimicking the chemistry of the pore waters of the tailings i e identical ph fe si and so4 thiobacillus promoted the rapid formation 48 h of amorphous silica at low ph values ph 2 2 2 3 while an abiotic system with the same chemical conditions did not show silica precipitation however in the presence of fe oxides silica formation was not observed because dissolved si was preferentially sorbed to the surface of the oxides in addition when the cells were grown in the presence of micas biotite and muscovite under acidic conditions mixed mg al si fe silicate precipitates were formed on the surface of thiobacillus these results indicate that si cycling and solubility in mine tailings could be strongly influenced by bacteria especially in sulfide depleted tailings like the kam kotia ones where the formation of fe oxide is negligible

influence of atlantic meridional overturning circulation on the east asian winter monsoon east asian summer monsoon precipitation varied on millennial timescales during the last glacial period sediment records and climate modelling suggest that the winter monsoon was also affected by millenial scale variability and that the abrupt changes were driven by changes in the strength of the atlantic meridional overturning circulation

alluvial sequence in the north piedmont of the chinese tian shan over the past 550 kyr and its relationship to climate change abstract a new division of middle and late pleistocene alluvial sequence in the north piedmont of the chinese tian shan based on geomorphologic stratigraphic and chronologic criteria provides a framework for examining their relationship to climate change during glacial interglacial transitions over the past 550 kyr at least four major alluviation episodes occurred within the piedmont along the major river valleys in this region each episode of alluvial fan deposition morphologically correlates with a major river terrace these correlations create a regionally applicable framework for subdivision of the quaternary alluvial sequence in the study area where seven stepped river terraces are defined our new chronology of this fluvial sequence suggests that following intervals of aggradation three highest river terraces and equivalent alluvial fans were abandoned at 530 ka 300 ka and 10 ka respectively paleosols at the base of the loess sequences that directly overlie the older terraces and fans suggest that episodes of aggradation occurred late in the glacial cycles the subsequent incision that caused abandonment stabilization of these terraces and fans occurred near to glacial interglacial transitions a relatively high degree of synchrony in major river incision events across the piedmont despite disruption by several discrete structure zones with asychronous tectonic activities supports the dominant control exerted by climatic conditions on alluvial deposition and terrace creation during the quaternary across the north piedmont of the chinese tian shan

distinct mineral weathering effectiveness and metabolic activity between mineral weathering bacteria burkholderia metallica f22 and burkholderia phytofirmans g34 abstract bacteria play important roles in mineral weathering soil formation and the cycling of elements however little is known regarding the interactions between silicate minerals and burkholderia strains in this study mineral weathering bacteria burkholderia metallica f22 and b phytofirmans g34 isolated from the rhizosphere soil of a dominant grass deyeuxia arundinacea l beauv grown on mineral rich and nutrient poor soil were compared for their potash feldspar weathering and metabolic activities during the mineral weathering process although the two strains showed similar mobilization of si strain f22 demonstrated significantly higher al ranging from 41 to 143 and fe ranging from 47 to 4 8 fold mobilization from the mineral compared to strain g34 in addition strain f22 produced higher gluconic acid ranging from 68 to 24 fold and exopolysaccharides ranging from 57 to 2 2 fold than strain g34 significantly lower ph ranging from 2 61 to 3 45 and higher dehydrogenase activity ranging from 24 to 19 fold were observed in the presence of strain f22 than in the presence of strain g34 during the mineral weathering process redundancy analysis illustrated strong positive correlations between the concentrations of gluconic acid and exopolysaccharides and the dissolved al and fe these results demonstrated that the two mineral weathering burkholderia strains behaved differently with respect to mineral weathering and in their metabolic activities the results also suggested that burkholderia metallica f22 promoted potash feldspar weathering by increasing mineral weathering related metabolic activities during the weathering process

horizontal structure of 500 mb height fluctuations with long intermediate and short time scales abstract maps of standard deviations and one point correlation maps based on twice daily data subjected to a variety of temporal filters are presented in order to document the horizontal structure of 500 mb height fluctuations with different time scales the filters have been chosen to isolate fluctuations with long time scales periods much longer than 30 days intermediate time scales 10 30 day periods and short time scales 2 5 6 day periods the one point correlation maps for long time scales resemble the teleconnection patterns described by wallace and cutzler these patterns are strongly regionally dependent with meridionally oriented dipole structures in the jet exit regions over the oceans indicative of strong fluctuations in the zonal wind for intermediate time scales the dominant patterns consist of more zonally oriented wave trains which originate in the jet entrance regions and cross the jet streams as they curve southeastward into the tropics another important distinction between th

a persistent holocene wetting trend in arid central asia with wettest conditions in the late holocene revealed by multi proxy analyses of loess paleosol sequences in xinjiang china abstract there are significant differences in the interpretation of the moisture precipitation history of arid central asia aca during the holocene as inferred on one hand from speleothem oxygen isotope records and on the other from lake sediments here we present the results of measurements of climatically sensitive magnetic properties and soil color from four well dated loess paleosol sequences from the northern slopes of the tienshan mountains and the yili river valley xinjiang china in the core area of aca our results demonstrate that the characteristic holocene paleosol indicating relatively moist conditions generally formed after 6 ka 1 ka 1000 cal yr bp in the study region and that the accumulation of unweathered loess prevailed during the early holocene indicating a dry climate at that time the magnetic proxies further reveal a trend of generally increasing moisture since the last glacial maximum with the wettest climate occurring during the late holocene this trend of increasing moisture during the holocene is representative of the xinjiang region and possibly of the whole of the core area of aca and is in marked contrast both to the mid holocene moisture maximum observed in the east asian summer monsoon region and to the general decrease in the strength of the indian summer monsoon since the early holocene our findings are supported by the results of a climate simulation which indicate a trend of increasing summer and winter precipitation during the holocene in the core area of aca caused mainly by an increase in the strength of the westerlies effected by an increasing latitudinal insolation gradient and by a negative trend of the arctic oscillation ao or north atlantic oscillation nao

microbial kinetic controls on calcite morphology in supersaturated solutions recognizing microbial imprints in the morphology of calcium carbonate minerals that form in very supersaturated solutions containing a high level of dissolved inorganic carbon dic is challenging to better define criteria for this purpose we have analyzed the influence of sulfate reducing bacterium desulfovibrio desulfuricans strain g20 on the morphology of calcite in such solutions g20 does not induce large shifts of ph or alkalinity under these conditions but its uptake of millimolar sulfate and lactate decreases the number of anhedral crystals and stimulates growth of subhedral spar crystals relative to the abiotic controls in addition organic compounds associated with the basal growth medium purified exopolymeric substances produced by g20 and lypopolysaccharide stimulate the growth of anhedral crystals and crystals with rounded edges at low supersaturation index si of calcite the effect of organic compounds is reduced at higher si where rhombohedral habits dominate our results suggest that the local production and uptake of kinetic inhibitors within microbial biofilms may be an important control on calcite morphology in supersaturated solutions

differential ice volume and orbital modulation of quaternary moisture patterns between central and east asia abstract desertification is of pressing environmental concern in large parts of asia and directly affects millions of people arid central asia aca in particular is highly sensitive to desertification and environmental change climate change in aca may be driven by westerly circulation or monsoon variation however no consensus exists over their relative importance during the quaternary and this greatly restricts our understanding of how this region may be affected by future climate change here we use the most detailed luminescence dating age model yet produced for aca for three loess records in the tianshan mountains spanning the past 250 ka to show a sharp dichotomy in moisture variation between lowland and high mountain areas the lowland areas of aca are subjected to persistent aridity during past 250 ka while highland areas clearly show dry glacial and moist interglacial changes synchronous to moisture variability in monsoonal east asia and both co varying with global ice volume and greenhouse gas ghg variation in contrast moisture variability across aca within interglacials varies inversely with insolation driven precessional changes this is directly out of phase with the moisture changes of east asia which co vary with precessional insolation changes and indicates the influence of westerly circulation in aca our flexible global ocean atmosphere land system model simulations further reveal that coupled ice volume and ghg variations dominated climatic variability in both aca and east asia over glacial interglacial cycles however the out of phase relationship between the intensity of the westerly and east asian monsoon systems during interglacial periods indicates that precessional forcing is responsible for differences in moisture patterns between aca and east asia these observations indicate that moisture levels will not increase even in high altitude regions of aca over the next several millennia rather desertification is likely to worsen resulting from stabilization of the westerlies as a result of low summer insolation

stratigraphies and chronologies of late quaternary loess paleosol sequences in the core area of the central asian arid zone abstract the sporadic distribution of the quaternary loess in central asia makes it hard to establish a regional pedostratigraphy through visual tracing of marker strata the pedostratigraphic correlation presented here is thus completely based on the radiocarbon chronologies of the four studied sections the first noticeable feature is that poorly drained conditions predominated in the period between 48 000 and 30 000 14 c bp during which three entisols developed at 45 000 14 c bp 40 000 14 c bp and 35 000 14 c bp after a period of loess deposition between 30 000 and 18 000 14 c bp under poorly drained conditions an entisol at the westernmost site valikhanov south central kazakhstan developed between 18 000 and 10 000 14 c bp also under poorly drained conditions the time equivalent deposits at romantic and zeketai sections to the east do not exhibit any soil forming characteristics although poorly drained conditions are also imprinted in the time equivalent loess the holocene sequences in the central asian domain consist of an early holocene loess unit deposited between 10 000 and 5 000 14 c bp and a late holocene soil formed during the past 5000 years in comparison the climate was also wet between 48 000 and 20 000 14 c bp during which three mollisols developed under well drained conditions in the chinese loess plateau of the east asian domain the loess deposited between 23 000 and 10 000 14 c bp in the chinese loess plateau has neither observable marks of soil formation nor imprints of poorly drained conditions the holocene sequence in the east asian domain exhibits an out of phase relationship with that in the central asian domain consisting of an early holocene soil formed between 9000 and 4000 14 c bp and a late holocene loess unit deposited during the past 4000 years

the asian monsoon over the past 640 000 years and ice age terminations oxygen isotope records from chinese caves characterize changes in both the asian monsoon and global climate here using our new speleothem data we extend the chinese record to cover the full uranium thorium dating range that is the past 640 000 years the record s length and temporal precision allow us to test the idea that insolation changes caused by the earth s precession drove the terminations of each of the last seven ice ages as well as the millennia long intervals of reduced monsoon rainfall associated with each of the terminations on the basis of our record s timing the terminations are separated by four or five precession cycles supporting the idea that the 100 000 year ice age cycle is an average of discrete numbers of precession cycles furthermore the suborbital component of monsoon rainfall variability exhibits power in both the precession and obliquity bands and is nearly in anti phase with summer boreal insolation these observations indicate that insolation in part sets the pace of the occurrence of millennial scale events including those associated with terminations and unfinished terminations records of the asian monsoon have been extended to 640 000 years ago and confirm both that the 100 000 year ice age cycle results from integral numbers of precessional cycles and that insolation influences the pacing of major millennial scale climate events prior records of the asian monsoon have revealed cyclic variations over hundreds of thousands of years probably driven by variations in insolation caused by the precession of earth s orbit hai cheng and colleagues now provide a speleothem record from chinese cave samples that extends earlier records to 640 000 years ago close to the maximum age possible with uranium thorium dating this spectacular record confirms that the characteristic 100 000 year ice age cycle corresponds to an integral number four or five of precession cycles and that insolation influences millennial scale variations in monsoon strength

variations in the iron mineralogy of a loess section in tajikistan during the mid pleistocene and late pleistocene implications for the climatic evolution in central asia the loess sequences in tajikistan are an important archive of information about the development of climate and atmospheric circulation in central asia during the pleistocene here we present the results of an iron mineralogical study of a loess sequence in tajikistan to reconstruct paleoclimate evolution during the mid pleistocene and late pleistocene the record indicates that interglacial intervals were relatively humid and glacials were dry we propose a shift in the character of the interglacial climate of the region to more humid after beginning of mis 9 however temperature was relatively stable the location and intensity of westerlies have a close link with asian summer monsoon asm circulations from the beginning of mis 9 there was a southward movement of the westerlies circulation which corresponded to a retreat of the indian summer monsoon ism a similar relationship also existed between the east asian summer monsoon easm circulation and the westerlies which is evidenced by the formation of the most weakly developed soil unit in the easm dominated regions during mis 9 in contrast with the formation of the most strongly developed soil unit in the westerlies dominated regions as conditions in the areas of loess deposition became more humid the sedimentary basins which are the dust source areas became progressively more arid the aridification of the source areas may be the result of increased northern hemisphere ice volume and accelerated high mountains and or plateaus uplift in the surrounding regions

a composite study of the quasi periodic subtropical wind maxima over the south pacific during november 1984 april 1985 abstract a composite of 10 cases of zonal wind maxima at 200 hpa over the subtropical region stretching from australia to the central pacific is examined for the six month period november 1984 april 1985 this region is unique in that distinct westerly jets frequently form and propagate eastward at latitudes between 20 and 35 s in the summer season some statistical tests were applied and suggest that the flow patterns are quasi periodic consisting of a tendency for new jet streaks to develop over the eastern australian region approximately every one to two weeks these jets then take about 10 days to propagate across the western pacific before dissipating or perhaps moving toward higher latitudes their average propagation speed is approximately 4 m s 1 an examination of the case to case variability of the jets provides additional evidence that they are significant features a diagnosis of the trough ridge systems at 200 and 850 hpa together with calculations of the vertically integrated mean and

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

downstream development of the summertime tropical cyclone submonthly wave pattern in the extratropical north pacific abstract the impact of tropical perturbation on the extratropical wave activity in the north pacific in the submonthly time scale is demonstrated here previous studies identified a tropical cyclone tc submonthly wave pattern which propagated north northwestward in the philippine sea and recurved in the oceanic region between japan and taiwan this study found that after the arrival of the tc submonthly wave pattern at the recurving region the eastward propagating wave activity in the extratropical north pacific was significantly enhanced it is suggested that the tc submonthly wave pattern which is originated in the tropical western north pacific enhances the eastward energy propagation of rossby wave like perturbation in the extratropical north pacific and may have an impact on the long range weather predictability in the eastern north pacific and western north america

microbes produce nanobacteria like structures avoiding cell entombment microsedimentary structures referred to as nanobacteria like particles were described from modern carbonate environments where they form in close spatial association with sulfate reducing bacteria srb however the exact mechanism of their formation as well as their paleontological significance remains controversial here we report on an investigation of microbe mineral interactions in experimentally produced carbonate globules the experiments were carried out under anoxic conditions at 30 c with desulfovibrio brasiliensis a srb known to mediate dolomite formation we observed that extracellular polymeric substances eps secreted by the microbial community play a key role in the mineralization process nanobacteria like particles represent the early stage of carbonate nucleation within the eps which progressively evolve to larger globules displaying a grainy texture we excluded the possibilities that these structures are fossils of nanobacteria dissolution surfaces or artifacts created during sample preparation d brasiliensis cells are predominantly located outside of the eps aggregates where mineral growth takes place as a result they remain mobile and are rarely entombed within the mineral this self preservation behavior may not be limited to d brasiliensis other microbes may produce or may have produced during the geological past biogenic minerals through a similar process mineralization within eps explains why microbial relics are not necessarily present in biogenic carbonates

the loess record in southern tajikistan and correlation with chinese loess in the present study the chashmanigar loess soil sequence in southern tajikistan is studied this loess section has a paleomagnetic basal age of about 1 77 myr magnetic susceptibility color reflectance and grain size were systematically measured for closely spaced samples from the section paleosols consistently have a finer grain size distribution higher magnetic susceptibility redder color reflectance and lower dust sedimentation rate than loess horizons suggesting a colder drier and dustier environment during glacial periods than in interglacial periods the grain size record was tuned to variations in obliquity and precession of the earth s orbit the resulting magnetic susceptibility grain size and color reflectance time series all show well expressed astronomical periodicities during the pleistocene the mid pleistocene climate transition characterized by a shift of dominant climatic periods from 41 kyr to 100 kyr at about 1 0 0 8 myr is clearly documented in these proxy records comparison of the chashmanigar loess record with the lingtai loess section in china and the odp site 677 n 18 o record shows that during the entire pleistocene the climate cycles recorded by the central asian loess can be well correlated to the chinese loess and deep sea oxygen isotope records it is suggested that alternations of loess and soil horizons both in central asia and china could be basically forced by global ice volume variations although different wind systems have controlled the pleistocene loess transport and sedimentation in the two areas 2002 elsevier science b v all rights reserved

luminescence dating of the stratzing loess profile austria testing the potential of an elevated temperature post ir irsl protocol abstract feldspar infrared stimulated luminescence irsl signals saturate at 2000 gy i e 500 700 ka assuming a dose rate of 3 4 gy ka typical for loess and it is therefore theoretically possible to date middle pleistocene loess however the accuracy of age estimates is hampered by anomalous fading which leads to significant age underestimation fading corrections have been proposed but these corrections are reliant on inherent assumptions and in any case are inapplicable at large doses as the growth curve approaches saturation recent studies have identified a post ir irsl signal that shows less fading and is thus less dependent on accurate fading corrections this study builds upon these investigations and applies a post ir irsl sar dating protocol to polymineral fine grain samples of the loess palaeosol sequence in stratzing lower austria after a preheat at 320 c 60 s and an ir bleach at 50 c 200 s irsl was measured at 290 c for 200 s the same set of conditions were used to measure the response to a test dose recycling ratios recuperation and dose recovery tests show that this protocol is suitable for the loess under investigation although finite residual doses of up to 20 gy are observed for the oldest samples the natural signal is in or close to saturation indicating that fading is negligible in nature this observation is inconsistent with the measured laboratory fading rates of 1 1 5 decade and needs further investigation

global teleconnections in the 250 mb streamfunction field during the northern hemisphere winter abstract teleconnections of the streamfunction in the global domain based on ecmwf 250 mb winds for the 11 northern winters from 1978 79 through 1988 89 are documented in this study a zonal structure with a node near the equator indicating an out of phase relationship between the streamfunctions in the northern and southern hemisphere appears to mask the fluctuations of the asymmetric components of streamfunction after removing zonal means a global pattern emerges as the dominant structure in the low frequency band this pattern consists of several dipoles straddling either the exit region of midlatitude jets or the equator indicating the existence of teleconnections not only between the midlatitudes and the tropics but also between the northern and southern hemispheres teleconnection patterns in the intermediate frequency band are predominantly wavelike seven waveguides are identified based on the one point lag correlation maps for base points near the maximum teleconnectivity among them are thr

low temperature alteration of the upper oceanic crust and the alkalinity budget of seawater abstract while the input of river alkalinity into seawater is relatively well known the complementary acidity production is poorly understood using the major element budget of seafloor alteration of the upper 500 m of 120 ma old oceanic crust at dsdp odp sites 417a 417d and 418a in the central western atlantic we estimate the acidity flux associated with the low temperature weathering of the upper oceanic crust the acidity flux is calculated based on major element fluxes and charge balance considerations the relevant chemical fluxes from seawater to the upper crust are 4 1 0 1 1 4 1 4 2 2 0 6 and 12 2 1011 mol yr 1 for k mg na and silicate ca respectively the associated acidity flux is 3 5 3 1011 eq yr 1 relative to continental weathering these fluxes are significant for k and silicate ca but are minor for na mg and acidity thus riverine fluxes of alkalinity are not significantly balanced by acidity fluxes from low temperature upper ocean crust alteration

paleoceanographic significance of sediment color on western north atlantic drifts i origin of color reflectance spectra collected during odp leg 172 were used in concert with solid phase iron chemistry carbonate content and organic carbon content measurements to evaluate the agents responsible for setting the color in sediments factor analysis has proved a valuable and rapid technique to detect the local and regional primary factors that influence sediment color on the western north atlantic drifts sediment color is the result of primary mineralogy as well as diagenetic changes sediment lightness is controlled by the carbonate content while the hue is primarily due to the presence of hematite and fe 2 fe 3 changes in clay minerals hematite most likely derived from the permo carboniferous red beds of the canadian maritimes is differentially preserved at various sites due to differences in reductive diagenesis and dilution by other sedimentary components various intensities for diagenesis result from changes in organic carbon content sedimentation rates and h2s production via anaerobic methane oxidation iron monosulfides occur extensively at all high sedimentation sites especially in glacial periods suggesting increased high terrigenous flux and or increased reactive iron flux in glacials 7 2002 elsevier science b v all rights reserved

visualization and quantification of cd sorption to bacteria using confocal laser scanning microscopy and cd specific fluorescent probes abstract understanding metal sorption to bacteria is important for developing bioremediation strategies for determining the fate of contaminants in ground water systems and for defining controls on microbial metabolic processes in the environment x ray absorption spectroscopy xas has been the only technique available for quantifying and mapping metal sorption to bacteria on an individual cell scale but the xas approach is time consuming and expensive and quantitative mapping of the distribution of metals in complex samples is difficult with xas the development of metal specific fluorescent probes in conjunction with confocal laser scanning microscopy clsm represents a novel and more effective approach for visualizing and quantifying biosorption in this study we test and calibrate the use of a commercially available cd and pb specific probe leadmium green lg to quantify the distribution of cd in bacteria bearing systems we have developed a treatment technique that uses a combination of the stock lg molecule and a chemically de esterified form of the lg molecule delg which enables us to quantify bacterial sorbed cd in this approach we correlate the green fluorescence from lg and delg with the fluorescence at a different wavelength of syto 63 cell stain which enables us to visualize and quantify bacterial cell cd sorption on both a community and individual cell level this approach for the first time yields a means of easily quantifying and visualizing metal adsorption onto individual bacterial cells which allows us to directly measure the distribution of cd in bacteria bearing environmental systems in this study we report the results of a range of control experiments that demonstrate the efficacy of this approach we demonstrate that our chemical de esterification of lg results in 100 conversion of the lg to the delg form that is fluorescently active and that untreated lg is not fluorescently active until it enters the cell we also demonstrate that calibration curves for samples containing cells lg delg syto 63 and cd can be developed our tests also demonstrate that neither lg nor delg cause significant changes in sorption of cd to bacterial cells we present results from experiments showing that cd sorption to bacteria is highly heterogeneous between cells a result which differs from the previously held assumption of homogeneous sorption the results of this study yield new insights into metal adsorption behavior in bacteria bearing systems and our approach represents a powerful tool for quantifying the distribution of metals in complex realistic environmental samples

luminescence dating of the pasado core 5022 1d from laguna potrok aike argentina using irsl signals from feldspar in this paper we develop and test a luminescence chronology for the pasado core 5022 1d taken in the laguna potrok aike maar lake because of unsuitable quartz osl characteristics sand sized k feldspar extracts were chosen as a dosimeter and the dose was measured using a recently developed post ir irsl pirir290 measurement protocol using this approach we were able to access a stable signal and thus avoid the ubiquitous problem of signal instability in feldspar dating extensive laboratory tests show that the chosen pirir290 protocol is applicable to these samples we also develop a new criterion based on the known relative bleaching rates of the conventional irsl signal ir50 and the pirir290 signals and the relationship between the resulting equivalent doses this is used to identify and reject poorly bleached samples fourteen samples out of 35 were rejected based on this criterion the resulting age depth profile is self consistent increases smoothly with depth and is in agreement with the independent age control reclus mt burney and hudson tephras at the top of the core our new luminescence chronology suggests the 5022 1d core reaches back to 65 ka at 96 m below lake floor

the australian subtropical jet during the second observing period of the global weather experiment abstract the upper level circulation of the southern hemisphere winter is characterized by two distinct zonal wind maxima a subtropical jet found in the vicinity of australia and the western pacific ocean and a polar jet which maximizes in the indian ocean in the 45 55 s latitudinal belt this paper describes the global characteristics of the atmosphere for cases with strong subtropical jets during the 1979 northern hemisphere summer such cases are shown to co exist with episodes of strong release of latent heat in the northern hemisphere at similar longitudes gridded analyses of the global weather experiment produced by the geophysical fluid dynamics laboratory of the national oceanic and atmospheric administration are used to obtain composites of atmospheric motions prior to the onset and during active episodes of the asian monsoon projections of these motions into the normal modes of a linearized primitive equation model about a basic state at rest are presented to isolate observed global flow ch

hells bells unique speleothems from the yucatan peninsula mexico generated under highly specific subaquatic conditions abstract we here report on a type of meter sized pendant speleothem growing under water in the submerged el zapote sinkhole cenote west of puerto morelos on the mexican yucatan peninsula these conical mantle shaped downward expanding and diverging calcareous structures here termed as hells bells are yet unreported in the scientific literature they are characterized by bell or trumpet shaped longitudinal and circular elliptical or horse shoe like horizontal cross sections hells bells grow downward based on the downward divergence of the structures and the horizontally laminated internal texture of both blade shaped spar calcite and microspar laminae age dating confirms that hells bells are young

paleoenvironmental changes recorded in a luminescence dated loess paleosol sequence from the tianshan mountains arid central asia since the penultimate glaciation abstract mid latitude arid central asia aca is one of the driest regions in the world and is a key source area of global atmospheric dust loess records of paleoclimatic changes in aca are complex and interpretations are problematic due primarily to the lack of robust chronologies quartz osl and k feldspar pirir dating methods were employed to date 8 quartz and 30 k feldspar samples from a 30 m loess sequence byh10 section on the northern slope of the tianshan mountains central aca northwest china the reliability of quartz and k feldspar ages was monitored by internal checks of luminescence characteristics and by comparison of the quartz and k feldspar ages the section lithology proxy indexes of grain size and magnetic susceptibility and the high resolution osl chronology together indicate 1 quartz osl dating can be used to date aca loess samples less than 40 ka while k feldspar pirir dating is reliable for loess samples at least as old as 150 ka from aca 2 aeolian loess began to be deposited on the northern slope of tianshan mountains beginning at least 145 ka ago and was deposited primarily during the penultimate and last glaciation periods 3 rapid loess deposition occurred during mis 6 mis 4 to early mid mis 3 and mis 2 but little or no loess deposition occurred during mis 5 mis 3a and mis 1 4 this loess depositional sequence is comparable to previously published stalagmite growth records in the region on glacial interglacial cycles rapid dust deposition and lack of stalagmite growth during glacials and lack of loess deposition and stalagmite growth during interglacials indicate a climatic pattern of wet warm interglacial and dry cold glacial climatic regimes on orbital cycles in aca 5 variation in the loess deposition rates in aca was much larger than in the central loess plateau during the last glaciation 6 depositional hiatuses of 50 kyr occur in aca loess sequences and high resolution chronologies are needed when reconstructing past climatic changes

a tianshan mountains loess paleosol sequence indicates anti phase climatic variations in arid central asia and in east asia abstract paleoclimatic changes in arid central asia aca one of the largest arid regions in the world are complex and the nature of these changes on orbital cycles remains unclear widely distributed loess records in aca potentially provide records of paleoclimatic variation but these records are difficult to interpret due to a lack of robust high resolution chronologies k feldspar pirir dating was employed to date 37 samples from a 13 m loess paleosol sequence section ks15 in an intermontane basin of the tianshan mountains central aca nw china the reliability of the pirir ages was determined by using internal checks of luminescence characteristics of the pir50ir290 and pir200ir290 signals and by comparing pir50ir290 and pir200ir290 ages a high resolution chronology for the loess paleosol sequence spanning 130 45 ka was established using bacon age depth modeling in combination with climate proxy indexes of magnetic susceptibility total organic material and 13 c of organic remains from the sequence our results suggest 1 the pirir ages utilizing pir50ir290 and pir200ir290 signals are consistent for loess samples

nucleation of calcium carbonate on bacterial nanoglobules nucleation of calcium carbonate on microbial cell material may have been the dominant mode of microbial carbonate formation during most of earth s history current knowledge predicts that nucleation takes place on the cell surface or on extracellular polymeric substances however the initial nucleation steps have not been described in detail and the process remains elusive here we describe the bacterial nucleation of calcium carbonate at the nanometer scale in our precipitation experiment with sulfate reducing bacteria srb the bulk of calcium carbonate precipitates on hundreds of individual globules 60 200 nm in diameter globules originate from the srb cell surface but calcify significantly only when released to the culture medium similar globules have been observed albeit at a much larger scale in other bacterial precipitation experiments and in many natural microbial carbonates suggesting that the process we describe could be an important step in microbial calcification

short term planetary scale interactions over the tropics and midlatitudes during northern winter part i contrasts between active and inactive periods abstract objectively analyzed 200 mb winds of four winters are used to study the short term several days teleconnections between planetary scale circulation components over the monsoon region the composited structures suggest that during very active northeasterly monsoon surge periods the midlatitude and tropical circulation components vary in a coherent way the jet streak and local hadley circulation over east asia the divergent flow over the maritime continent and the equatorial walker circulations over the pacific and indian oceans all strengthen steadily while the secondary jet streak over west asia weakens during inactive break periods the midlatitude circulation components all exhibit reversed changes while the variations in the tropics are less coherent although still showing reversed tendencies the results basically verify the short term teleconnection model proposed by chang and lau 1980 but more complex processes in the acceleration of the midlatitude jet streaks are indicated

time variation of 500 mb height fluctuations with long intermediate and short time scales as deduced from lag correlation statistics abstract the time variation of northern hemisphere wintertime 500 mb height fluctuations with short intermediate and long time scales is investigated using lag correlation patterns derived from time filtered data fluctuations with short 2 5 6 day periods time scales propagate eastward at a rate consistent with the notion of a steering level around 700 mb which supports an interpretation in terms of baroclinic waves the mobile teleconnection patterns associated with the intermediate 10 30 day periods time scales exhibit a pattern of time variation suggestive a rossby wave dispersion with a predominance of southward dispersion from middle latitudes into the tropics the geographically fixed teleconnection patterns characteristic of the longer time scales do not show a well defined pattern of time variation but their horizontal structure resembles that of the fastest growing normal mode associated with barotropic instability of the climatological mean wintertime flow

asian provenance of glacial dust stage 2 in the greenland ice sheet project 2 ice core summit greenland samples of dust from the greenland ice sheet project 2 gisp2 ice core summit greenland dated within marine isotope stage 2 between 23 340 and 26 180 calendar years b p around the time of the coldest local last glacial temperatures have been analyzed to determine their provenance to accomplish this we have compared them with approximately coeval aeolian sediments mostly loesses sampled in possible source areas psas from around the northern hemisphere the 5 m grain size fraction of these samples was analyzed on the basis that it corresponds to the atmospheric dust component of that time and locale which was sufficiently fine grained to be transported over long distances on the basis of comparison of the clay mineralogy and sr nd and pb isotope composition with ice dust and psas and assuming that we have sampled the most important psas we have determined that the probable source area of these gisp2 dusts was in eastern asia the dust was not derived from either the midcontinental united states or the sahara two more proximal areas that have been suggested as potential sources based on atmospheric circulation modeling except for a brief period during an interstadial when dust transport was exceptionally low for glacial times and had a mineralogical composition indicative of a slightly more southern provenance the source area of the dust did not change significantly during times of variably higher fluxes of dust with larger mean grain size or lower fluxes of dust with smaller mean grain size this includes the high dust period that correlates with the heinrich 2 period of major iceberg discharge into the north atlantic variable wind strengths must therefore be invoked to account for these abrupt and significant changes in dust flux and grain size

statistical properties of episodes of enhanced 2 3 day convection in the indian and pacific oceans abstract using 9 yr of ir brightness temperature values as a proxy for tropical convection the climatology and statistics of the 2 3 day convective oscillation signal are examined these higher frequency oscillations are shown to have a very different spatial distribution than the signal associated with the 25 70 day intraseasonal oscillation making it quite unlikely that these oscillations simply represent a form of noise in the time series the characteristics of the oscillations are shown to be strong functions of latitude season and strength of the oscillation itself only the strongest of the 2 3 day oscillations prove to be in good agreement with the properties shown in previous studies which were based on smaller spatial and temporal domains these strong oscillations manifest a strong association with the intraseasonal oscillation and westerly wind bursts particularly in the deep tropics weaker oscillations on the other hand are found to be more stochastic and less dependent on larger sca

bacterially induced mineralization of calcium carbonate in terrestrial environments the role of exopolysaccharides and amino acids this study stresses the role of specific bacterial outer structures such as glycocalix and parietal polymers on calcium carbonate crystallization in terrestrial environments the aim is to compare calcium carbonate crystals obtained in bacterial cultures with those obtained during abiotically mediated synthesis to show implications of exopolysaccharides and amino acids in the mineralogy and morphology of calcium carbonate crystals produced by living bacteria this is done using various amounts of purified exopolysaccharide xanthan eps and l amino acids with a range of acidities amino acids and increasing xanthan content enhance sphere formation in calcite and vaterite regarding calcite the morphology of crystals evolves from rhombohedral to needle shape this evolution is characterized by stretching along the c axis as the amino acid changes from glutamine to aspartic acid and as the medium is progressively enriched in eps regarding vaterite the spherulitic habit is preserved throughout the morphological sequence and starts with spheres formed by the agglomeration of short needles which are produced in a xanthan free medium with glutamine monocrystals forming spheres increase in size as xanthan is added and the acidity of amino acids glutamic and aspartic acids is increased at high xanthan concentrations amino acids and mainly aspartic and glutamic acids induce vaterite precipitation the role of the carboxyl group is also probably critical because bacterial outer structures associated with peptidoglycan commonly contain carboxyl groups this role combined with the results presented here clearly demonstrate the influence of bacterial outer structure composition on the morphology and mineralogy of bacterially induced calcium carbonate this point should not be neglected in the interpretation of calcite cements and carbonate accumulations in terrestrial environments

coupling of fe ii oxidation in illite with nitrate reduction and its role in clay mineral transformation abstract in pedogenic and diagenetic processes clay minerals transform from pre existing phases to other clay minerals via intermediate interstratified clays temperature pressure chemical composition of fluids and time are traditionally considered to be the important geological variables for clay mineral transformations nearly ten years ago the role of microbes was recognized for the first time where microbial reduction of structural fe iii in smectite resulted in formation of illite under ambient conditions within two weeks however the opposite process the oxidation of structural fe ii in illite has not been studied and it remains unclear whether or not this process would result in the back reaction e g from illite to smectite the overall objective of this study was to investigate biological oxidation of structural fe ii in illite coupled with nitrate reduction and the effect of this process on clay mineral transformation laboratory incubations were set up where structural fe ii in illite served as electron donor nitrate as electron acceptor and pseudogulbenkiania sp strain 2002 as mediator solution chemistry and gas composition were monitored over time mineralogical transformation resulting from bio oxidation was characterized with x ray diffraction and scanning and transmission electron microscopy our results demonstrated that strain 2002 was able to couple oxidation of structural fe ii in illite with reduction of nitrate to n 2 with nitrite as a transient intermediate this oxidation reaction resulted in transformation of illite to smectite and ultimately to kaolinite illite smectite kaolinite transformations this study illustrates the importance of fe redox process in mediating the smectite illite mineral cycle with important implications for fe redox cycling and mineral evolution in surficial earth environments

distribution and composition of loess sediments in the ili basin central asia loess deposits in central asia provide an important record of regional climate and environmental change however in contrast to the intensively investigated loess deposits on the chinese loess plateau clp loess sediments in the ili basin of eastern central asia are poorly understood based on field investigation and existing literature this paper presents a preliminary study of the distribution strata and composition of the ili loess the distribution of the ili loess is clearly controlled by topographic and geomorphic conditions mainly in the river terraces low uplands and slopes of the tianshan mountains the thickness of the loess varies from several meters to over two hundred meters to characterize the ili loess composition the authors analyzed its grain size geochemistry x ray diffraction pattern and heavy mineral assemblage grain size analyses reveal that the ili loess consists predominantly of silt 4 63 mu m with a minor proportion of sand which is coarser than the loess of the clp and suggests a nearby provenance the bulk mineral components of the ili loess are dominated by quartz and feldspar with minor amounts of calcite chlorite mica dolomite and hornblende more than 20 types of heavy minerals were observed with major components of amphibole magnetite and epidote the major elements of the ili loess are characterized by high abundance of sio2 al2o3 and cao and minor amounts of fe2o3 mgo na2o and k2o compared to the clp loess the ili loess is relatively rich in na2o and displays higher na2o al2o3 ratios suggesting weak weathering the distribution patterns of rees indicate that both the ili loess and clp loess are of typical upper crustal composition with enrichment in lree negative eu anomalies and depletion of hree both the heavy mineral assemblage and geochemistry indicate that the local bedrock of the ili basin may have contributed only a little to the loess sediments c 2014 elsevier ltd and inqua all rights reserved

holocene east asian monsoonal precipitation pattern revealed by grain size distribution of core sediments of daihai lake in inner mongolia of north central china abstract two sediment cores recovered in the central part of daihai lake in north central china were analysed at 2 to 4 cm intervals for grain size distribution grain size distributions of the lake sediments are inferred to be a proxy for past changes in east asian monsoon precipitation such that greater silt size percentage and higher median grain size reflect increased monsoonal precipitation rates the grain size record of daihai lake sediments spanning the last ca 10 000 yr indicates that the monsoonal precipitation in the lake region can be divided into three stages the early middle and late holocene during the early holocene before ca 7900 cal yr bp the median grain size md and the silt fraction content were relatively low and constant suggesting relatively low precipitation over the lake region the middle holocene between ca 7900 and 3100 cal yr bp was marked by intensified and highly variable monsoonal precipitation as indicated by high and variable md values and silt contents of the lake sediments during this period average precipitation rate gradually increased from ca 7900 to 6900 cal yr bp displayed intense oscillations between ca 6900 and 4400 cal yr bp and exhibited a decreasing trend while fluctuating from ca 4400 to 3100 cal yr bp although generally high during the middle holocene both the md and the silt content assumed distinctly low values at the short intervals of ca 6500 6400 6000 5900 5700 5600 4400 4200 cal yr bp implying that monsoonal precipitation might have been significantly reduced during these intervals during the late holocene since ca 3100 cal yr bp grain size values suggest that precipitation decreased however during the late holocene relatively higher md values and silt contents occurring between ca 1700 to 1000 cal yr bp may denote an intensification of hydrological cycles in the lake area changes in the east asian monsoonal precipitation were not only directly linked with the changing seasonality of solar insolation resulting from progressive changes in the earth s orbital parameters but also may have been closely related to variations in the temperature and size of the western pacific warm pool in the intensity of the el nino southern oscillation and in the path and strength of the north equatorial current in the western pacific

palaeoclimatic records of the loess palaeosol sequences of the chinese loess plateau whether during past climate stages or into a progressively warming world changes in precipitation constitute a key component of climatic change quantitative proxies for palaeo precipitation are relatively rare the magnetic properties of the windblown loess units and interbedded palaeosols of the famous chinese loess plateau provide key palaeo precipitation data for this populous monsoon dominated region the loess palaeosol sediments record rainfall totals directly complementing the oxygen isotope records of chinese speleothems these isotopic records predominantly reflect moisture source and hence large scale atmospheric circulation changes the two major asian monsoon systems appear to display antiphase behaviour dominance of the indian summer monsoon system seems associated with minimum precession maximum northern hemisphere summer heating dominance of the east asian summer monsoons with maximum precession at 2 8 ma more intense development of the east asian winter monsoon initiated major increases in dust deposition rates and formation of relatively unweathered loess layers glacial stage loess units then interleaved with interglacial interstadial stage palaeosols throughout the quaternary period decoupling of the loess palaeosol rainfall records from the chinese cave records of moisture source shows that the indian and east asian monsoon winds were continuously driven by precessional forcing while summer monsoonal rainfall was greatly suppressed during cool glacial stages the timing of these east asian climatic transitions the subsequent intensification of northern hemisphere glaciations and the association between monsoon circulation changes and north atlantic temperatures indicates a possibly leading global role for these monsoonal changes via alterations in the poleward distribution of heat and moisture

a pole to pole west pacific atmospheric teleconnection during august 1 an observational analysis is presented that reveals an august teleconnection involving both the northern hemisphere nh and the southern hemisphere sh the teleconnection includes three primary anomalies in the monthly average surface pressure field 1 a high southern latitude component including wilkes land antarctica the nearby southern ocean and the ross sea 2 a sh midlatitude component near australia and new zealand and 3 a nh subtropical component over the extreme western pacific ocean surface pressure for the sh high latitude anomaly is negatively correlated to the other two primary anomalies the sh midlatitude and nh subtropical component are positively correlated furthermore the teleconnection is correlated to surface pressure near the aleutian islands the teleconnection anomalies result from tropical convection on intraseasonal timescales monsoon rainfall over east asia during august is correlated to the teleconnection furthermore august precipitation at several other locations in the nh and sh is modulated by the teleconnection two different sets of numerical experiments with the national center for atmospheric research ncar community climate model version 2 ccm2 show a similar appearing teleconnection during late boreal summer the modeled teleconnection however is forced from high southern latitudes

loess accumulation in the tian shan piedmont implications for palaeoenvironmental change in arid central asia whilst correlations have been made between the loess of europe and china deposits in central asia have remained largely overlooked by scientific investigation the nature of the relationship between loess accumulation and palaeoclimate at the core of the eurasian loess belt is particularly poorly understood here we reconstruct palaeoenvironmental change in central asia over the last 40 ky based on data from the remizovka loess profile in the northern foothills of the tian shan in southern kazakhstan our interpretations are based on synthesis of chronostratigraphic colour and magnetic susceptibility data supported by chronostratigraphies from two additional sites nearby maibulak and valikhanova all three sites record substantially increased loess accumulation during late mis 3 into the global last glacial maximum glgm at remizovka increased loess flux occurred in two pulses at c 38 25 ka and 22 18 ka with the intervening period involving incipient pedogenesis at maibulak two loess pulses at c 40 30 ka and c 28 22 ka are separated by a weakly developed paleosol which may date to the same time as pedogenesis at remizovka there is additional possible periglacial influence at maibulak from c 40 33 5 ka at valikhanova there is some age overlap between paleosol and loess samples but overall loess accumulation appears to have increased at c 42 35 ka c 30 ka and the glgm with pedogenesis occurring 40 ka and c 32 ka at all three sites holocene loess accumulation is minimal this period is characterised by pedogenesis the chronostratigraphic variability between our sites highlights a need to interrogate climate driven models for loess formation in piedmont environments we interpret our data in the context of regional palaeoenvironmental archives to indicate that loess accumulation increased coeval with mis 3 glacial advance in the tian shan which was facilitated by northward expansion of the asian monsoon and associated increase in precipitation we hypothesise that increased ice volume impeded teleconnections with the temperate zone westerlies to the north these were compressed against the piedmont resulting in increased wind strength and facilitating increased loess flux peak loess accumulation during the glgm occurred under colder drier climatic conditions with reduced but sustained glacial ice volume and persistent influence of the westerlies in the arid central asian piedmont loess belt in the absence of more widespread reliably dated palaeoenvironmental records from the region our data become of critical importance for understanding past environmental conditions in central asia relative to elsewhere in eurasia and globally

behavior of one to two week summertime subtropical wind maxima over the south pacific during an enso cycle abstract the behavior of subtropical jet streaks over the australian south pacific region is investigated for four consecutive 6 month summer seasons november to april during the period 1985 89 the study is an extension of a recent one by ko and vincent hereafter referred to as kv in which jet streaks during the summer season of 1984 85 were examined ko and vincent found that the upper tropospheric zonal wind behaved in a quasi periodic manner with maxima recurring over the western south pacific at intervals between one and two weeks in the present study wind maxima are found to exhibit a 1 2 week periodic oscillation over the south pacific in all four years thus substantiating the finding by kv in addition a second set of jet streaks with a similar periodicity is found over the southern australian region it is also seen that the mean summertime position of the south pacific jet and its accompanying jet streaks are much farther cast during the el nino event of 1986 87 than they are in the

geomicrobiology of carbonate silicate microbialites from hawaiian basaltic sea caves abstract modern microbial mats and microbialites are described from basaltic sea caves on the island of kauai hi the mats grow on the ceilings and walls in the photic zone of several open caves where fresh water seeps out of the rock scanning sem and transmission electron microscopy tem showed that the active mats are dominated by filamentous and nonfilamentous cyanobacteria in the surface layers and heterotrophic bacteria in deeper layers energy dispersive x ray analysis revealed that copious amounts of extracellular polymeric substances eps are rich in mg si o and ca likely concentrated from solution petrographic microscopy and electron microprobe analysis of the mineralized microbialites showed textures reminiscent of stromatolitic laminations consisting mainly of alternating calcium carbonate calcite and aragonite and magnesium rich silicate kerolite thin coatings rich in magnesite hydromagnesite and monohydrocalcite surround the microbialites on the rock surfaces and are likely inorganic in origin within the mats minerals tend to form and concentrate within or around dense matrices of eps microenvironments with geochemical conditions favorable for mineral crystallization likely develop in the mats as a result of the mucilaginous extracellular material and the development of bacterial microcolonies in addition copious amounts of extracellular polymers bind ions from solution and provide nucleation sites for mineral crystallization and growth this combination of biological and inorganic processes can explain the occurrence of the secondary minerals in these caves as well as the stromatolitic textures of the microbialites

phosphate stromatolites from condensed cephalopod limestones upper jurassic southern spain upper jurassic phosphate stromatolites of the almola sierra southern spain encrust macrofossils and hardgrounds and form oncoids included within pelagic condensed fossiliferous limestones their accretion was determined by bacterially mediated precipitation of phosphate by the trapping and binding of fine siliciclastics and pelagic biomicrite and by the encrustation of benthonic foraminifera phosphorous trace elements and rare earth elements were concentrated from degraded organic matter and seawater by stromatolite building communities which mediated the formation of phosphate rich and fe al si rich organic gels under oxic conditions favouring the precipitation of amorphous mineral precursors acp and fe al si oxyhydroxides the observed ce enrichment for some stromatolites is explained by oxidative scavenging of ce4 from seawater by fe mn oxyhydroxides the bacterially mediated gels were able to migrate and fill the voids of the stromatolite structure and later changed to carbonate fluorapatite haematite and poorly crystalline fe rich clays under postoxic conditions phosphatization of trapped carbonate particles also occurred the phosphate stromatolites formed on a sediment starved pelagic swell during periods of no carbonate sedimentation and hardground development stromatolite lamination provides evidence for rhythmic alternation between bacterially mediated phosphogenesis sedimentation and erosion suggesting episodic changes in the sedimentary environment although some of the parameters that controlled phosphate precipitation associated with the stromatolites local high organic productivity sediment starvation moderate depth of deposition and physicochemical conditions were similar to those found in modern and ancient phosphogenic settings the palaeogeographical framework and the intensity of sedimentary processes were different to those of the world s major phosphorite deposits

subaerial freshwater phosphatic stromatolites in deer cave sarawak a unique geobiological cave formation abstract a suite of distinctive freshwater subaerial phosphatic stromatolites is developed close to the northeastern entrance of deer cave gunung mulu national park sarawak borneo in conditions of very low light but ample supply of nutrients from guano these stromatolites are not particulate they are composed of alternating layers of more porous and more dense amorphous hydroxylapatite this biomineralization occurs as moulds of coccoid the majority and filamentous less abundant cyanobacteria mineralization occurs at a ph of 7 0 in the extracellular sheaths and in micro domains of varying carbonate content in the surrounding mucus of the biofilm the most recent surfaces that are not yet strongly mineralized show still living filamentous coccoid and rod shaped forms trace element composition shows enrichment in metal ions especially mn and zn the stromatolites are present as horizontal shelves arranged in series on a steep rock face that is vertically under a guano laden shelf the rock face undergoes active dissolution from acidic guano drainage water e g ph of 2 43 and from aggressive rainwater from an overhead discharge however the rock surface under the stromatolite is protected while the rest of the cliff face is backcut creating a hoodoo like effect the stromatolites are 15 20 cm deep 4 7 cm thick and of variable width generally 50 cm eventually guano and biological detritus in the descending water film lodge in the lee of the stromatolite lip causing local acidification and erosion of stromatolite and rock on the underside of the ledge a dynamic equilibrium is established between upward accretion of the fresh surface and destruction at the base such that the base of the stromatolite does not reflect the date of its inception and the stromatolite climbs up the wall

holocene vegetation history and sea level changes in the se corner of the caspian sea relevance to sw asia climate the palynological investigation of core tm 27 7 m long taken in a dried out lagoon reveals both holocene vegetation history in the north eastern foothills of the alborz mountains and past water level changes of the caspian sea cs the delay in woodland expansion at the beginning of the holocene which is typical of eastern turkey the iranian plateau and recorded in the cs south basin is only weakly felt as the region is close to glacial refugia of trees the succession of the main trees out of their refugia has been established as deciduous quercus carpinus betulus parrotia persica and fagus orientalis pterocarya fraxinifolia presenting therefore close affinities to south european interglacials of the early pleistocene this suggests a similarity in climate a pterocarya decline is observed after ad 495 the studied region is close to the easternmost tree distribution this could explain why it has been affected earlier than elsewhere in the northern alborz and the caucasus in addition human activities during the sasanian empire and the subsequent drying of the climate contributed to weakening the spread of this tree a maximal sea level occurs in the first part of the holocene from 10 6 to 7 2 cal ka it is suggested that the cs levels were significantly influenced by the monsoon precipitations over the western himalayas via the uzboy inflow this is followed by low levels from 7 2 to 3 5 cal ka with a minimum at 3 9 cal ka the neocaspian period should be considered a biozone rather than a chronozone as the environmental conditions reconstructed from dinocyst assemblages are different in shallow shelf waters and in the deep basins

loess chronology of the middle and upper pleistocene in tadjikistan the loess paleosol sequences of central asia are continuous terrestrial records of the quaternary period and enable detailed comparison with paleoclimatic archives such as marine and ice core records in order to reconstruct regional and global paleoclimatic and paleoecological development during the past 130 000 years thermoluminescence tl and infrared stimulated luminescence irsl dating methods are applied to the extensively studied loess paleosol sequence of the section at darai kalon chashmanigar tadjikistan in order to determine a more accurate chronological framework and climatostratigraphic reconstruction for the last interglacial glacial cycle luminescence dating suggests that the loess above the first pedocomplex from the top pc1 accumulated during the last glacial period a high accumulation rate of up to 1 20 m per 1000 years was determined for the last glacial loess especially for the uppermost 5 8 m pc1 formed during the last interglacial period oxygen isotope stage 5 the loess between pc1 and pc2 is designated to be of penultimate glacial deposition age infrared stimulated luminescence and tl age estimates are in agreement to 80 000 years before present bp indicating a long distance transport of the aeolian dust prior to deposition the upper numerical age limit range is between 300 000 and 450 000 years however reliable dating of the loess older than 130 000 years is not possible due to age scatter between samples and an inadequate increase of paleodose with depth this high resolution dating study underlines the importance of the section at darai kalon and indicates that it is one of the most continuous loess paleosol records of the northern hemisphere the chronological results are particularly important for the reconstruction of the human evolution in central asia suggesting much older age estimates than previously obtained for most of the archeological key sites associated with pc5 and pc4 in tadjikistan