travertines associated with the alhama jaraba thermal waters ne spain genesis and geochemistry abstract freshwater carbonates are interesting archives in palaeoenvironmental reconstructions however more studies of those systems are needed to fully understand past environments in this work the actively forming travertines of the alhama jaraba thermal system were studied for the first time in order to evaluate the relationship between the geochemical and mineralogical composition and the environmental conditions during their formation with that aim a combination of petrographical mineralogical geochemical and stable isotope analyses were carried out these carbonates provide a natural laboratory for the study of the effect of different variables natural and anthropogenic on carbonate precipitation the results showed that there is a close relationship between the mineralogy of the solid precipitates and the formation temperature and only the samples formed from overheated waters 40 60 c show significant concentrations of aragonite aragonite bearing samples show higher concentrations in sr ba and u while calcitic solids are enriched in mg these differences could be attributed to mineralogy temperature or different precipitation rates the geochemical evaluation of the chemistry of both the solids and their parental waters suggests that differences in the rate of co 2 degassing and in some cases evaporation are the primary environmental controls on isotopic compositions in addition the results show that if strong evaporation and co 2 degassing are involved calcite precipitation occurs under conditions of isotopic disequilibrium with its parental water the results of our study are useful to interpret old depositional environments and palaeotemperatures

evaluating zr rb ratio from xrf scanning as an indicator of grain size variations of glaciomarine sediments in the southern ocean the ln zr rb count ratio derived from x ray fluorescence xrf core scanning holds potential as a high resolution tracer for grain size variations of glaciomarine sediments to evaluate this appro

comparison of the quaternary travertine sites in the denizli extensional basin based on their depositional and geochemical data abstract in the denizli basin turkey located in the western anatolian extensional province travertine and tufa deposition has been an ongoing process for at least 600 000 years travertine bodies which are 30 to 75 m thick and each covers areas of 1 to 34 km2 are up to 1 km3 in volume today spring waters in this area have temperatures of 19 to 57 c are of the ca mg hco3 so4 type in the pamukkale kelkaya and pinarbasi areas and the ca mg so4 hco3 type at cukurbag thermal waters along the northern margin of the basin are generally hotter than those in the east southeast and south the 18o and d values of the spring waters indicate a meteoric origin the average temperatures of the hydrothermal systems in the denizli basin appear to have decreased from pleistocene to holocene travertine which formed from the hotter water is more widespread than the tufa that formed in the cooler spring waters deposition of the travertine which formed largely on slopes in depressions and along fissure ridges mostly on northern basin margins was controlled by the interplay between various intrinsic and extrinsic parameters the travertines are formed largely of calcite with only minor amounts of aragonite in some of the vertically banded crystalline crust raft and pisoid travertines found in some of the northern sites the aragonitic samples rich in sr are typically found around the spring orifices and along the central axis of the fissure ridges the stable isotope values of the travertine found in the northwest and southeast parts of the basin are different the 13c values of the northern travertine deposits are more positive 3 7 to 11 7 vpbd than those found in the south southeast areas 4 to 5 8 vpdb in contrast the travertine and tufa in the southeastern areas have higher 18o values 15 2 to 7 8 vpdb than those of the northern areas 16 6 to 4 8 vpdb available evidence indicates that spring activity and associated travertine precipitation in the denizli basin were controlled largely by tectonic activity rather than by climatic conditions

rapid and quantitative major element analysis method for wet fine grained sediments using an xrf microscanner several types of x ray fluorescence xrf core scanners have been developed to fulfill the demands for high resolution rapid chemical analysis of wet sediment cores however their application to quantitative analysis has been hampered by the difficulty of evaluating the xrf absorption effect of water in a water film on the sediment surface and interstitial water within the sediments especially for lighter elements in this study we established a non destructive rapid high resolution and quantitative chemical analysis method for wet fine grained sediment samples using an xrf microscanner results of our experiments suggest that the degree of xrf absorption by the water film which develops on the wet sample surface covered with mylar film shows a clear positive correlation with the water content of the sediments under the measurement area a clear positive correlation also exists between the degree of xrf absorption by the interstitial water and the water content of the sediments under the measurement area we evaluated the xrf absorption by the thin water film using the relationship between the water content and thickness of the thin water film and the xrf absorption by the interstitial water using its relation with the water content the water content under the measurement area is estimated from the average transmitted x ray intensity that is measured on the same measurement area simultaneously with the measurement of xrf intensities the dry sample equivalent xrf intensities of major elements al si k ca ti and fe which are the xrf intensities of wet samples corrected for the xrf absorption by the thin water film and the interstitial water show better correlation with the major element concentrations determined by conventional xrf methods using this new method it is possible to measure the average water content and average concentrations of the 6 major elements simultaneously for a square area as small as 0 5 0 5 mm on the wet fine grained sediment within 6 min which is nearly ten times faster than the conventional xrf method

the influence of temperature ph and growth rate on the δ18o composition of inorganically precipitated calcite abstract the oxygen isotope composition of carbonate minerals varies with temperature as well as other environmental variables for carbonates that precipitate slowly under conditions that approach thermodynamic equilibrium the temperature dependence of 18 o uptake is the dominant signal and the measured 18 o content can be used as a paleotemperature proxy in the more common case where carbonate minerals grow in a regime where they are not in isotopic equilibrium with their host solution their oxygen isotope compositions are a convolution of multiple environmental variables here we present results from calcite growth experiments demonstrating the occurrence of large 2 non equilibrium oxygen isotope effects under conditions relevant to biogenic calcite growth and many natural inorganic systems we show that these non equilibrium effects vary systematically with ph and crystal growth rate an isotopic ion by ion crystal growth model quantifies the competing roles of temperature ph and growth rate and provides a general description of calcite water oxygen isotope fractionation under non equilibrium conditions the crystal growth model results show that 1 there are both equilibrium and kinetic contributions to calcite oxygen isotopes at biogenic growth rates 2 calcite does not directly inherit the oxygen isotope composition of dic even at fast growth rates 3 there is a kinetically controlled variation of about 1 per ph unit between ph 7 7 and 9 3 at constant growth rate for inorganic calcite as well as biogenic calcite and 4 extreme light isotope enrichments in calcite in alkaline environments are likely due to disequilibrium among dic species in aqueous solution the model can be extended to 13 c uptake into carbonates as well as clumped isotopes but additional data are needed to constrain the kinetic fractionation factors for carbon isotopes the experimental and model results constitute an important step in separating the relative influence of inorganic and biologic processes on isotopic fractionation and may aid the development of new paleoproxies based on non equilibrium effects

hydrogeochemical modeling of a thermal system and lessons learned for co2 geologic storage abstract geological storage of carbon dioxide is presently considered to be one of the main strategies to mitigate the impact of the emissions of this gas on global warming among the various alternatives considered for co 2 geological storage one of the main geological candidates for hosting injected co 2 in the long term are deep porous reservoir rock formations saturated with brackish or saline solutions although valuable information on the expected hydrogeochemical processes involved in the co 2 storage in such deep saline aquifers can be obtained in laboratory or modeling studies the only direct source of information about the long term behavior of geological storages for co 2 in deep aquifers is natural analogues in this work a classical and simple geochemical methodology is successfully applied to the study of the features and hydrogeochemical processes determining the evolution of a spanish thermal system the alhama jaraba complex which can be considered as a natural analogue for deep geological co 2 storage in carbonate rocks the geology structure depth and hydrogeochemistry of the alhama jaraba thermal system are very similar to the expected features of a potential co 2 reservoir in carbonate materials the processes determining the hydrogeochemical evolution in the alhama jaraba thermal system have been successfully identified and quantified with the assistance of ion ion plots speciation solubility calculations and mass balance calculations furthermore the feasibility of the proposed conceptual hydrogeochemical model for this system has been verified by using reaction path calculations mass balance calculation results have indicated that the observed hydrogeochemical evolution between springs is mainly due to halite dissolution and dedolomitization triggered by gypsum or anhydrite dissolution co 2 g mass transfer has been estimated to be negligible which suggests that the main processes responsible for the variation in the tic and the co 2 g pressure during deep circulation are dissolution and precipitation reactions for carbonate minerals all the processes identified in the alhama jaraba thermal system are relevant for the long term evolution of a deep co 2 storage site hosted by carbonate rocks as shown in this study the application of classical geochemical tools provides an excellent starting point for understanding the behavior of prospective storage systems moreover the existence of dedolomitization is very relevant for the hydraulic properties of carbonate aquifers potentially used for co 2 geological storage because of the effects on porosity and therefore permeability during the long term evolution of such systems furthermore dedolomitization may represent a mechanism of mineral trapping for co 2 sequestration under certain conditions

a sedimentary facies model for stepped fluvial tufa systems in the iberian range spain the quaternary piedra and mesa valleys stratigraphic and sedimentological analyses of the quaternary tufa and associated deposits in the piedra and mesa river valleys allowed a number of stages of their sedimentary evolution to be characterized and a depositional sedimentary model for this north central sector of the iberian range spain to be established the proposed sedimentary facies model may explain tufa arrangements in other medium to high gradient stepped fluvial tufa systems with narrow transverse profiles occurring in temperate semi arid areas in both recent and past scenarios there are several tufa deposits within the piedra and mesa river valleys that over a maximum thickness of about 90 m record one or more stages of tufa deposition produced following the fluvial incision of the bedrock or previous tufa deposits each depositional stage begins with coarse detrital sedimentation six fundamental vertical sequences of tufa facies with small amounts of detrital material reveal the sedimentary processes that occurred in different fluvial environments channel areas with i free flowing water ii barrages and or cascades and iii dammed water and palustrine floodplains the proposed sedimentary model involves narrow stepped fluvial valleys in which tufa cascades were common alternating intervals of bryophyte and stromatolite facies commonly formed at some cascades many of these represented barrage cascade structures that consisted of phytoclast rudstones thick phytoherms of mosses and associated stromatolites and curtain shaped phytoherms of stems upstream of these structures dammed areas with bioclastic sands and silts developed and palustrine vegetation grew the channel stretches between barrages and or cascades were loci for extensive stromatolite growth in fast flowing water the palustrine floodplain was home to pools and drainage channels the model also explains the growth of some barrages in the river piedra that surpassed the height of the divide with the diffluence of the main channel into a secondary course forming other tufa deposits in the area the distribution and abundance of certain types of tufa facies in fluvial basins may be an indicator of differences in their gradients the facies studied in this work suggest that the gradient of the ancient river piedra was steeper than that of the ancient river mesa assuming similar scenarios for climate and hydrology the depositional settings mentioned above and their dimensions would have been determined mainly by the gradient and width of the associated river valleys this sedimentary model may also be useful for inferring variations in other river basin slopes as well as accounting for the presence of tufas in areas that normally have no permanent water input

a new view of ridge segmentation and near axis volcanism at the east pacific rise 8 12 n from em300 multibeam bathymetry 1 new high resolution bathymetry for the east pacific rise between 8 n and 12 n was collected over a 6 km wide swath centered on the ridge axis using the 30 khz simrad em300 multibeam system the coverage area corresponds latitudinally to the designated ridge2000 integrated studies site iss for fast spreading ridges the em300 data gridded at 30 m latitude by 50 m longitude represent a greater than 4x improvement in horizontal resolution over previously available multibeam data and a 2x improvement in depth resolution the new bathymetry was used to update the locations and hierarchy of ridge offsets for this area among the many applications for this data it enables us to tabulate volcanoes half the size that could be previously detected the distribution of near axis volcanic cones 25 m high suggests that this population of small near axis cones results from low effusion rate eruptions of the ridge axis

geochemical evidence for airborne dust additions to soils in channel islands national park california there is an increasing awareness that dust plays important roles in climate change biogeochemical cycles nutrient supply to ecosystems and soil formation in channel islands national park california soils are clay rich vertisols or alfi sols and mollisols with vertic properties the soils are overlain by silt rich mantles that contrast sharply with the underlying clay rich horizons silt mantles contain minerals that are rare or absent in the volcanic rocks that dominate these islands immobile trace elements sc th la and ta nd cr and rare earth elements show that the basalt and andesite on the islands have a composition intermediate between upper continental crust and oceanic crust in contrast the silt fractions and to a lesser extent clay fractions of the silt mantle have compositions closer to average upper continental crust and very similar to mojave desert dust island shelves exposed during the last glacial period could have provided a source of eolian sediment for the silt mantles but this is not supported by mineralogical data we hypothesize that a more likely source for the silt rich mantles is airborne dust from mainland california and baja california either from the mojave desert or from the continental shelf during glacial low stands of sea although average winds are from the northwest in coastal california easterly winds occur numerous times of the year when santa ana conditions prevail caused by a high pressure cell centered over the great basin the eolian silt mantles constitute an important medium of plant growth and provide evidence that abundant eolian silt and clay may be delivered to the eastern pacifi c ocean from inland desert sources

sources of dissolved silica to the fjords of northern patagonia 44 48 s the importance of volcanic ash soil distribution and weathering dissolved silica dsi plays an important biogeochemical role in the fjords of northern chilean patagonia 44 48 s where it drives high biogenic productivity and promotes carbon burial it is generally believed that the dsi riverine input to lakes and coastal environments is controlled by a combination of factors including lithology climate topography vegetation and meltwater input in northern chilean patagonia several authors have proposed that the postglacial volcanic ash soils andosols may play a significant role in the high supply of dsi to the regional fjords to assess the influence of andosols on dsi concentrations in north patagonian rivers we mapped andosol thickness and compared our results with river chemistry the mineralogical and geochemical composition of three representative andosol profiles was also examined to evaluate the efficiency of weathering processes the andosol thickness map clearly demonstrates that volcanic ash was predominantly deposited on the eastern side of the regional volcanoes reflecting the influence of the prevailing westerly winds on the distribution of pyroclastic material mineralogical and geochemical results show that the andosol parent material has the typical andesitic basaltic signature of the regional volcanoes i e high amounts of amorphous material plagioclase k feldspar and pyroxene down profile variations in soil mineralogy and geochemistry indicate increased leaching of silica with depth resulting from weathering of the volcanic parent material for the five studied watersheds a highly positive correlation r2 0 98 was found between average andosol thickness and dsi concentrations suggesting that andosol thickness is the main parameter affecting dsi concentrations in north patagonian river systems on seasonal timescales increased precipitation winter and glacial meltwater summer input can significantly reduce dsi concentrations we argue that the weathering of andosols constitutes the most important source of dsi to the lakes and fjords of northern chilean patagonia explaining the particularly high regional rates of biogenic silica production copyright 2015 john wiley sons ltd

quantitative analysis of detrital modes statistically rigorous confidence regions in ternary diagrams and their use in sedimentary petrology abstract detrital modes are the basic type of quantitative data used in sedimentary petrology they represent estimates of the petrographic framework composition of sand or sandstone obtained by point counting of thin sections at present geological inferences from analysis of these numerical data are semi quantitative only because many of the data processing methods employed in sedimentary petrology lack a firm theoretical basis a review of existing methods reveals a number of fundamental statistical problems associated with the use of univariate statistics and the construction of so called hexagonal fields of compositional variation it is shown that these problems can be overcome by using multivariate methods that honour the non negativity and unit sum constraints on compositional data and incorporate the covariance structure spread in compositional data can be modelled on two levels 1 by regarding the grain as unit of observation and the total point count as a sample from a multinomial distribution 2 by regarding the total count as unit of observation and a set of counts as a sample from an additive logistic normal distribution numerical methods are presented for constructing statistically rigorous confidence regions in ternary diagrams by inversion of significance tests for these two distributions statistical analyses of the framework composition and heavy mineral assemblages of modern beach and river sands illustrate their use the case histories are followed by a brief overview of popular multivariate methods for reconstructing sediment provenance

late holocene covariability of the southern westerlies and sea surface temperature in northern chilean patagonia abstract the climate of chilean patagonia is strongly influenced by the southern westerlies which control the amount and latitudinal distribution of precipitation in the southern andes in austral summer the southern westerly wind belt swwb is restricted to the high latitudes it expands northward in winter which results in a strong precipitation seasonality between 35 and 45 s here we present a new precipitation seasonality proxy record from quitralco fjord 46 s where relatively small latitudinal shifts of the swwb result in large changes in precipitation seasonality our 1400 yr record is based on sedimentological and geochemical data obtained on a sediment core collected in front of a small river that drains the patagonian andes which makes this site particularly sensitive to changes in river discharge our results indicate fe al and ti al values that are low between 600 and 1200 ce increasing at 1200 1500 ce and high between 1500 and 1950 ce increasing fe al and ti al values reflect a decrease in mean sediment grain size from 30 to 20 m which is interpreted as a decrease in seasonal floods resulting from an equatorward shift of the swwb our results suggest that compared to present day conditions the swwb was located in a more poleward position before 1200 ce it gradually shifted towards the equator in 1200 1500 ce where it remained in a sustained position until 1950 ce this pattern is consistent with most precipitation records from central and southern chile the comparison of our record with published regional sea surface temperature sst reconstructions for the late holocene shows that equatorward shifts of the swwb are systematically coeval with decreasing ssts and vice versa which resembles fluctuations over glacial interglacial timescales we argue that the synchronicity between sst and swwb changes during the last 1400 years represents the response of the swwb to temperature changes in the southern hemisphere

circulation in the glacial north atlantic inferred from grain size measurements records of nutrient proxies in marine sediments indicate that the nutrient distribution and hence circulation of the glacial north atlantic ocean was markedly different from that of today1 2 but these tracers are influenced by several biogeochemical factors unrelated to ocean circulation3 6 and thus do not provide a direct measure of the vigour of circulation distributions of grain size in marine sediments can provide such information owing to the sorting effects of currents7 8 if the characteristics of the input sediment flux are known here we present a record inferred from grain size measurements of variations in the relative strength of deep and intermediate currents in the eastern north atlantic over the past 25 000 years we find that glacial intermediate water flowed rapidly at depths of between 1 100 and 2 000 m in contrast deep water circulation was sluggish during the last glaciation but increased in strength shortly after the glacial maximum this would have resulted in increased heat flux to high latitudes and may have triggered sudden deglaciation deep current strengths declined again at the start of termination stage ia and during the younger dryas perhaps as a result of iceberg discharges the so called heinrich events9 10 a remarkably similar record of grain size variations has been found in the western north atlantic11 indicating that these changes in circulation are ocean wide

effects of chemical weathering and sorting on the petrogenesis of siliciclastic sediments with implications for provenance studies the bulk chemical compositions mineralogy and mineral proportions of sands and muds of the mallacoota basin in southeastern australia reflect the composition of weathering profiles mantling source rocks rather than bedrock muds contain abundant clay minerals that are virtually absent from the source rocks but abundant in the weathering profiles sands are strongly enriched in quartz relative to source rocks even in the headwaters of the fluvial system demonstrating that feldspar destruction occurs by in situ chemical weathering within profiles and before detritus enters the fluvial system k feldspar is proportionally more abundant in fluvial sands than in source rocks because plagioclase is more rapidly destroyed than either quartz or k feldspar in weathering profiles subsequent erosion and sorting produce sands enriched in quartz with high k feldspar plagioclase ratios relative to source rocks the composition of plagioclase incorporated into the fluvial sands is also controlled by chemical weat

the sedimentary record of glacial retreat marinelli fjord patagonia regional correlations and climate ties abstract the inland passage of chile comprises the most continuous latitudinal transect of ice fields ice caps and alpine glaciers in the southern hemisphere providing an excellent natural laboratory for the study of glacial response to climate change during the holocene here we report results from a marine geological investigation of marinelli fjord tierra del fuego 54 25 s 69 35 w and ainsworth fjord which merges with marinelli fjord data acquired during july 2005 onboard the rv ib nathaniel b palmer include high resolution seismic data multibeam swath bathymetry data and sediment cores post cruise analyses include detailed seismic facies and lithofacies analysis and radiocarbon dating the results indicate that a major transition in the glacimarine record from ice proximal facies to ice distal facies occurred in the outer basins of the fjord at 15 5 kyr to 12 5 kyr the ice proximal facies consists of pebbly mud with abundant laminations and is characterized by high average sedimentation rates 28 mm yr in contrast an ice distal facies is dominantly bioturbated mud with low average sedimentation rates 0 56 mm yr this transition marks the retreat of marinelli glacier from the outer basins with no evidence for glacial re advance subsequently during the mid to late holocene ainsworth glacier retreated and exposed ainsworth fjord our results are consistent with the climatic trends for southern south america where the final deglaciation of the region ended at 12 5 ka during the holocene stable ice conditions persisted until the mid 1960s when marinelli glacier began rapidly retreating to its modern day position

partitioning of strontium between calcite and fluid the sr ca ratio of biogenic carbonate is widely used as a proxy for paleotemperature this application is supported by empirical calibrations of sr ca as a function of temperature but it is also known that sr uptake in calcite gauged by kdsr is affected by other variables including bulk precipitation rate kdsr increases with increasing precipitation rate there are no data from controlled experiments specifically addressing the effect of radial growth rate of individual crystals on kdsr for this reason we conducted two series of experiments to explore sr partitioning at varying growth rates 1 growth from a cacl2 nh4cl srcl2 solution by diffusion of co2 from an ammonium carbonate source drift experiments and 2 drip precipitation of calcite on a substrate using a steady flow of cacl2 srcl2 and na2co3 solutions mixed just before passage through a tube and dripped onto a glass slide precoated with calcite cave type experiments the growth rates of individual crystals were determined by periodic monitoring of crystal size through time or roughly by comparison of the final size with the duration of the experiment electron microprobe analyses across sectioned crystals grown in the drift experiments show that the concentration of sr is high in the center where radial growth rates are highest and decreases systematically toward the edge the center to edge drop in sr concentration is a consequence of the slowing radial growth rate as individual crystals become larger in general high crystal growth rate v enhances sr uptake in calcite due to a type of kinetic disequilibrium we refer to as growth entrapment the apparent kdsr ranges from 0 12 to 0 35 as v increases from 0 01 nm s to 1 m s at 25 c

measurement of the sortable silt current speed proxy using the sedigraph 5100 and coulter multisizer iie precision and accuracy the weight percentage and mean size of the 10 63 m terrigenous silt fraction termed sortable silt of fine grained marine sediments have recently been argued to be proxies for near bottom palaeocurrent intensity this paper details the accuracy and precision of the sedigraph 5100 and the coulter multisizer iie in determining the weight percentage and mean size of the sortable silt at abundances characteristic of deep ocean sediments three sortable silt standards and a fine silt clay diluent were generated from natural deep sea sediment of the iceland basin these were used to produce silty clays with standard additions of sortable silt ranging from 1 to 20 of the total by weight accuracy was measured relative to the size of the pure spike measured by each instrument at sortable silt abundance 5 the sedigraph and the coulter multisizer estimate both weight percentage and mean grain size precisely and accurately while below 5 instrumental noise degrades their performance on the basis of the sedigraph results a series of percentage errors is defined which may be applied to sortable silt mean size and weight percentage estimates used in palaeoceanographic near bottom current reconstruction it is suggested that ideally palaeocurrent reconstructions should be based on sedigraph determinations of the 0 63 m grain size distribution yielding both mean and abundance or on coulter multisizer determinations of the sortable silt grain size mean the coulter multisizer may prove especially useful in regions of very depleted 5 sortable silt component

an empirical method to predict sediment grain size from inorganic geochemical measurements grain size is one of the most fundamental properties of sediments it is frequently used in paleoclimate paleoceanographic and paleoenvironmental research as a proxy for river discharge current and wind strength and to identify mass flow deposits measuring grain size is however time consuming and destructive given the strong influence of grain size on sediment inorganic geochemistry single element variations measured by for example x ray fluorescence core scanning are increasingly used to estimate grain size variations at high resolution in sediment cores this approach is however limited to a narrow grain size range since individual elements only monotonically relate to grain size over a narrow size range here we present a simple code free multielement method based on partial least squares regression to predict sediment mean grain size from inorganic geochemical data over the range of sizes commonly encountered in sedimentary basins clay to sand the method was first tested using river sediment samples separated in 11 grain size fractions and it was later successfully applied to two sediment cores from the chilean fjords our method only requires measuring grain size on a limited number around 10 of selected training samples and it allows to predict mean grain size at x ray fluorescence core scanner resolution this method has the potential to be applied to any lake or marine sediment core provided sediment provenance weathering and diagenesis remain relatively stable through time and we anticipate that it will result in a significant increase in the resolution of sediment proxy records of climate and environmental change plain language summary sediment grain size is one of the best indicators of past transport conditions here we present a method to predict mean sediment grain size from inorganic geochemical measurements this method can be applied to geochemical measurements obtained by x ray fluorescence core scanning to generate grain size profiles quickly and at high resolution and we anticipate that it will result in much improved paleoclimate and paleoenvironmental reconstructions

a 550 ka record of aeolian activity near north west cape australia inferences from grain size distributions and bulk chemistry of se indian ocean deep sea sediments abstract the terrigenous fraction of sediments from a deep sea sediment core recovered from the northwestern western australian continental slope offshore north west cape se indian ocean reveals a history of western australian climate throughout the last 550 ka end member modelling of a data set of grain size distributions n 438 of the terrigenous sediment fraction allows to interpret the record in terms of aeolian and fluvial sediment deposition both related to palaeo environmental conditions in the north west cape area the data set can be best described by two aeolian end members and one fluvial one changes in the ratio of the two aeolian end members over the fluvial one are interpreted as aridity variations in northwestern western australia these grain size data are compared with bulk geochemical data obtained by xrf scans of the core log ratios of the elements zr fe and ti ca which indicate a terrigenous origin corroborate the grain size data we postulate that the mid to late quaternary near north west cape climate was relatively arid during the glacial and relatively humid during the interglacial stages owing to meridional shifts in the atmospheric circulation system opposite to published palaeo environmental records from the same latitude 20 s offshore chile and offshore namibia the australian aridity record does not show the typical southern hemisphere climate variability of humid glacials and dry interglacials which we interpret to be the result of the relatively large land mass of the australian continent which emphasises a strong monsoonal climatic system

late quaternary aeolian dust input variability on the chinese loess plateau inferences from unmixing of loess grain size records abstract the grain size distributions gsds of loess paleosol sequences may provide valuable information on provenance transport and paleoclimate variability and consequently a wide range of methods to extract genetic information from loess gsds has been proposed here it is shown that a genetically meaningful decomposition of a series of late quaternary loess grain size records extending across the chinese loess plateau can be accomplished with the end member modelling algorithm emma the unmixing results in conjunction with loess accumulation rate estimates reveal that two contrasting dust supply patterns were active over the loess plateau during the last glacial interglacial cycle i a background sedimentation pattern that was dominant during interglacial periods especially over the central and southern parts of the loess plateau is reflected by the constant flux of the fine grained loess component ii an episodic highly variable dust input pattern that was dominant during glacial periods throughout the loess plateau and noticeable during interglacial periods mainly over the northern loess plateau and almost disappearing over the southern loess plateau is reflected in the admixture of two coarse grained loess components a genetic interpretation and the paleoclimatic significance of the mixing model are provided by comparison of the modelled end members with modern dust samples in terms of their gsd and flux rates

wet dry seasonal and spatial variations in the δ13c and δ18o values of the modern endogenic travertine at baishuitai yunnan sw china and their paleoclimatic and paleoenvironmental implications abstract seasonal and spatial variations in the 13 c and 18 o values of the modern endogenic thermogene travertine deposited in a calcite depositing canal at baishuitai yunnan sw china were examined to understand their potential for paleoclimatic and paleoenvironmental implications the sampling sites were set in the upstream middle reach and downstream of the canal and the modern endogenic travertine samples were collected semimonthly to measure their 13 c and 18 o values it was found that both 13 c and 18 o values of the endogenic travertine were low in the warm rainy season and high in the cold dry season and correlated with each other the low 18 o values in warm rainy season were mainly related to the higher water temperature and the lower 18 o values of rainwater and the low 13 c values are caused by the dilution effect of overland flow with low 13 c values in the warm rainy season and the reduced co 2 degassing of canal water caused by the dilution effect of the overland flow the linear negative correlation between the travertine 18 o or 13 c values and rainfall amount may be used for paleo rainfall reconstruction if one knows the 18 o or 13 c values of the fossil endogenic travertine at baishuitai though the reconstruction was not straightforward it was also found that there was a progressive downstream increase of the 18 o and 13 c values of the travertine along the canal the former being mainly due to the preferential evaporation of h 2 16 o to the atmosphere and the latter to the preferential release of 12 co 2 to the atmosphere during co 2 degassing however the downstream increase of the travertine 18 o and 13 c values was less intensive in rainy season because of the reduced evaporation and co 2 degassing during the rainy season to conclude the downstream travertine sites could be more favorable for the paleo rainfall reconstruction while the upstream travertine sites are more favorable for the paleo temperature reconstruction so this study demonstrates that endogenic travertine like epigenic meteogene tufa could also be a good candidate for high resolution paleoclimatic and paleoenvironmental reconstruction

first evidence of a mid holocene earthquake triggered megaturbidite south of the chile triple junction abstract megaturbidites have been the focus of many paleoseismic and paleoenvironmental studies because they can provide evidence for catastrophic and or hazardous events with potentially major environmental implications during a recent research cruise in baker fjord chile 47 54 s 74 30 w a megaturbidite was described between the northern and southern patagonian icefields here we aim to determine the depositional processes of the megaturbidite and identify its origin based on the turbidite s location a possible origin was the early holocene drainage of paleo lake general carrera which was recently proposed in the literature as having produced a glacial lake outburst flood glof that drained through baker fjord due to the fjord s location in a subduction zone and close to the chile triple junction however seismic activity must also be considered as a potential triggering mechanism to achieve our goals we undertook a multi proxy analysis of sediment core md07 3121 including sedimentology grain size loss on ignition foraminifera counts magnetic properties bulk organic geochemistry and radiocarbon dating and we analysed bathymetric maps and sub bottom profiles our grain size results display a diagnostic fining upward trend and show evidence of seiching in the 733 cm thick megaturbidite the age of the event 5513 5211 cal yr bp contradicts the hypothesis of an early holocene glof origin bulk organic geochemical results indicate that the sediments that compose the turbidite are clearly of marine origin which further goes against a glof origin in addition the megaturbidite is underlain by a 1136 cm thick mass transport deposit mtd also composed of marine sediments according to the sub bottom profiles the mtd and the megaturbidite originate from the reworking of thick packages of sediment previously deposited on nearby sills and on the fjord s flanks furthermore similar coeval deposits are found in an adjacent sub basin we therefore interpret these deposits to be triggered by an earthquake during the late mid holocene while megathrust and intraslab earthquakes are possible in the region we argue that a crustal earthquake is the most likely seismic trigger in the study area this study reveals the first earthquake triggered megaturbidite south of the chile triple junction

an extended and revised lake suigetsu varve chronology from 50 to 10 ka bp based on detailed sediment micro facies analyses abstract lake suigetsu japan is a key site for radiocarbon 14c calibration and palaeo environmental reconstruction in east asia here we present a description of the sediment micro facies which in combination with a new approach to varve interpolation allows construction of a revised varve based chronology that extends the previous 2012 varve based chronology by 10 ka back to 50 ka bp challenges in varve counting and interpolation which were previously discussed in detail only for the last glacial interglacial transition are described here back to 50 ka bp furthermore the relative merits of varve counting by xrf scanning and by thin section microscopy are discussed facies analysis reveals four facies zones their transitions driven by both local and climatic controls the lamination quality of the sediment is highly variable and varve interpolation reveals that in the analysed time interval on average only 50 of the annual cycles are represented by seasonal layers in the remaining years seasonal layers are indistinguishable i e either did not form or were not preserved for varve interpolation an advanced version of the varve interpolation program was used which enabled the construction of the longest purely varve dated chronology published despite long intervals of poor lamination quality the calculated interpolation uncertainty is 8 9 and 4 6 which is well within expectations considering the high degree of interpolation and the length of the record

the avaatech xrf core scanner technical description and applications to ne atlantic sediments abstract x ray fluorescence xrf core scanning provides rapid high resolution down to 1 mm records of chemical composition on split sediment cores the measurements are non destructive and require very limited sample preparation the new avaatech xrf core scanner operational since 2002 covers the atomic mass range from al to u instrument parameters especially tube voltage can be adjusted to provide optimum settings for selected elements or sets thereof owing to the nature of the surface of split sediment cores particularly effects resulting from sample inhomogeneity and surface roughness results are semiquantitative yet provide reliable records of the relative variability in elemental composition downcore selected case studies from diverse sedimentary settings in the ne atlantic ocean illustrate a range of applications of xrf logging data these include preliminary stratigraphic interpretations glacial interglacial cycles provenance studies of the terrigenous sediment fraction lithological characterization early diagenetic processes and distinction between carbonate phases aragonite v calcite

controls on trace element partitioning in cave analogue calcite abstract we report trace element data from a series of carbonate growth experiments in cave analogue conditions in the laboratory with the goal of better understanding environmental controls on trace element incorporation in stalagmites the experimental setup closely mimics natural processes e g precipitation driven by co2 degassing low ionic strength solution thin solution film but with a tight control on growth conditions temperature pco2 drip rate calcite saturation index and the composition of the initial solution calcite is dissolved in deionized water in a 20 000 ppmv pco2 environment with trace elements li na mg co sr cd ba u at appropriate concentrations to mimic natural cave drip waters this solution is dripped onto glass plates coated with seed calcite in a lower pco2 environment at 7 15 25 and 35 c and drip rates of 2 6 and 10 drips per minute d sr was shown to be statistically invariant over the full range of temperature and growth rate studied no relationship between sr ca and growth rate is therefore expected in stalagmite samples over comparable growth rates d mg has a relationship with temperature defined by d mg 0 01e0 02 0 006 t but temperature is not expected to be the dominant control on mg ca in cave calcite due to the larger impact of calcite precipitation on mg ca over short timescales in conditions where temperature is well buffered the fraction of calcium remaining in solution f is likely to be the dominant control on mg ca and other trace element ratios but differences in the response of trace elements to f and t may allow their combined use to assess past cave conditions high cd castalagmite is particularly indicative of low amounts of prior calcite precipitation and cd ca would be a useful addition to trace element studies of natural stalagmites significant scatter is observed in trace element ratios during the laboratory experiments which cannot be explained by simple rayleigh distillation this scatter is well explained by solution mixing and by the mixing of calcite with different fractions of calcite growth accounting for the effects of mixing on trace element concentrations or ratios may help to achieve more robust interpretations of stalagmite chemistry as part of a multi proxy approach to assessment of past environments

calibration of xrf core scanners for quantitative geochemical logging of sediment cores theory and application abstract on line analysis of split sediment cores by xrf core scanners has become increasingly popular in the past decade because it allows nondestructive extraction of near continuous records of element intensities from sediment cores with a minimum of analytical effort a disadvantage of xrf core scanning relative to conventional geochemical analysis is the problematic conversion of core scanner output to element concentrations the main reason for this long standing problem is the poorly constrained measurement geometry attributable to inhomogeneity of the specimens e g variable water content and grain size distribution irregularities of the split core surface and in some setups spatial variations in thickness of an adhesive pore water film which forms directly below a protective foil covering the core surface we propose a log ratio calibration model for xrf core scanners derived from a combination of xrf spectrometry theory principles of compositional data analysis and empirical evidence the log ratio calibration model provides accurate and precise predictions of sediment composition element concentrations from xrf core scanner output with a limited number of parameters namely 2 d 1 where d equals the number of chemical elements whose concentrations are to be estimated the model can accommodate the inherent non linearity of the relation between relative intensities and concentrations which is apparent from the fact that it provides unbiased estimates an immediate corollary of our results is that log ratios of element intensities which are related to log ratios of element abundances by a simple linear transformation provide the most easily interpretable signals of relative changes in chemical composition consistent use of log ratios of element intensities or concentrations should minimise the risk of drawing erroneous conclusions from geochemical proxies the relative standard deviation precision of predicted element concentrations in core geob7920 is less than 2 stochastic simulations indicate that this level of precision can be attained with 40 randomly selected calibration specimens improved control over input errors and development of robust goodness of fit statistics allows xrf core scanning to be developed into a rigorous quantitative measurement technology the log ratio calibration equation derived in this study may be adapted to inter laboratory and inter instrument calibration as well

modelling the joint variability of grain size and chemical composition in sediments abstract the geochemical composition of siliciclastic sediments correlates strongly with grain size hence geochemical composition may serve as a grain size proxy in the absence of grain size variations geochemical data of siliciclastic sediments may be used to characterise size independent processes i e sediment provenance weathering mixing shape density sorting and diagenesis in general however geochemical data sets contain both types of information in order to formalise interpretation of geochemical data we propose a mathematical method to decompose the total geochemical variability of a series of genetically related specimens into a grain size dependent the shared signal and a grain size independent part the residual signal the former may serve as a proxy for grain size whereas the latter represents geochemical variability that would have been observed if all sediments would have had the same grain size distribution the two data sets are jointly decomposed by means of partial least squares pls and orthogonal projection subsequently the presence of significant grain size independent geochemical variability in the residual signal is determined in a statistically rigorous manner using a 2 test using a synthetic example we show that the residual record effectively reveals an imposed provenance signal which could not have been resolved from the geochemical or grain size data sets individually we analysed the relation between grain size and geochemical composition in three quaternary marine sediment cores located offshore west africa and south america geob7920 2 geob9508 5 and geob7139 2 both sites are characterised by biogenic sediment input in addition to fluvial and aeolian sediment input from the continent it was found that all cores show a strong but different correlation between the mean grain size and the bulk geochemical composition these results demonstrate that geochemical grain size proxies are empirical and site specific it was also found that the geochemical and grain size data in cores geob7920 2 and geob7139 2 do not contain unique information whereas in core geob9508 5 ti varies independently from the grain size this residual ti signal correlates with the transport mechanism as demonstrated by statistically different values of aeolian and fluvial dominated sediments however a unique interpretation of this residual signal in terms of the postulated grain size independent mechanisms could not be provided without additional information we conclude that the proposed model facilitates identification and validation of different element ratios as grain size proxies and more importantly as proxies for size independent processes for this reason the model paves the way for rigorous analysis of multi proxy data which are widely used in palaeoceanographic and palaeoclimatic research

correcting for the influence of ice rafted detritus on grain size based paleocurrent speed estimates the grain size of deep sea sediments provides an apparently simple proxy for current speed however grain size based proxies may be ambiguous when the size distribution reflects a combination of processes with current sorting only one of them in particular such sediment mixing hinders reconstruction of deep circulation changes associated with ice rafting events in the glacial north atlantic because variable ice rafted detritus ird input may falsely suggest current speed changes inverse modelling has been suggested as a way to overcome this problem however this approach requires high precision size measurements that register small changes in the size distribution here we show that such data can be obtained using electro sensing and laser diffraction techniques despite issues previously raised on the low precision of electro sensing methods and potential grain shape effects on laser diffraction down core size patterns obtained from a sediment core from the north atlantic are similar for both techniques reinforcing the conclusion that both techniques yield comparable results however ird input leads to a coarsening that spuriously suggests faster current speed we show that this ird influence can be accounted for using inverse modelling as long as wide size spectra are taken into account this yields current speed variations that are in agreement with other proxies our experiments thus show that for current speed reconstruction the choice of instrument is subordinate to a proper recognition of the various processes that determine the size distribution and that by using inverse modelling meaningful current speed reconstructions can be obtained from mixed sediments

rare earth elements in marine sediments and geochemical standards abstract a comparison was made of sediment dissolution methods used for analysis of rare earth elements ree and major elements fe al ti zr p dissolution by hf and lithium metaborate fusion were compared in seven geochemical standards and twenty marine sediments using hf dissolution of shelf and slope sediments this author previously observed that these marine sediments were significantly depleted in heavy ree hree relative to the crustal abundance i e shale this observation plus published ree compositions of river particles lead to the conclusion that the riverine input of particles to the oceans cannot be assumed to have the crustal abundance for ree comparisons of fusion total to hf dissolutions for marine sediments show that the latter method misses between 20 and 100 of the hree i e dy er yb lu and large percentages of zr in contrast fusion and hf dissolution yield similar concentrations for the light la ce nd and middle eu gd ree and other major elements the fusion data show that the marine sediments are more similar in ree composition to shales than previously reported by this author who underestimated the contribution of hf insoluble residues to the concentration of hree the heavy mineral zircon is the most likely cause of this observation zircons known to be enriched in hree were identified by x ray diffraction as a major component of the hf insoluble residues geochemical standards also have a significant but usually smaller fraction of their hree associated with hf insoluble phases these compositional differences have significance with respect to interpreting river inputs oceanic abundances and diagenesis of ree

carbon mass balance modelling and carbon isotope exchange processes in dynamic caves abstract diverse interpretations have been made of carbon isotope time series in speleothems reflecting multiple potential controls here we study the dynamics of 13 c and 12 c cycling in a particularly well constrained site to improve our understanding of processes affecting speleothem 13 c values the small tubular grotta di ernesto cave ne italy hosts annually laminated speleothem archives of climatic and environmental changes temperature air pressure pco 2 dissolved inorganic carbon dic and their c isotopic compositions were monitored for up to five years in soil water and gas cave dripwater and cave air mass balance models were constructed for co 2 concentrations and tested against the carbon isotope data air advection forces winter pco 2 to drop in the cave air to ca 500 ppm from a summer peak of ca 1500 ppm with a rate of air exchange between cave and free atmosphere of approximately 0 4 days the process of cave ventilation forces degassing of co 2 from the dripwater prior to any calcite precipitation onto the stalagmites this phase of degassing causes kinetic isotope fractionation i e 13 c enrichment of dripwater whose 13 c dic values are already higher by about 1 than those of soil water due to dissolution of the carbonate rock a subsequent systematic shift to even higher 13 c values from 11 5 in the cave drips to about 8 calculated for the solution film on top of stalagmites is related to degassing on the stalagmite top and equilibration with the cave air mass balance modelling of c fluxes reveals that a very small percentage of isotopically depleted cave air co 2 evolves from the first phase of dripwater degassing and shifts the winter cave air composition toward slightly more depleted values than those calculated for equilibrium the systematic 13 c enrichment from the soil to the stalagmites at grotta di ernesto is independent of drip rate and forced by the difference in pco 2 between cave water and cave air this implies that speleothem 13 c values may not be simply interpreted either in terms of hydrology or soil processes

palaeo climate reconstruction from stable isotope variations in speleothems a review abstract speleothems are now regarded as valuable archives of climatic conditions on the continents offering a number of advantages relative to other continental climate proxy recorders such as lake sediments and peat cores they are ideal materials for precise u series dating yielding ages in calendar years thereby circumventing the radiocarbon calibration problems associated with most other continental records stable isotope studies in speleothems have shifted away from attempting to provide palaeo temperature reconstructions to the attainable goal of providing precise estimates for the timing and duration of major o isotope defined climatic events characterised by high signal to noise ratios e g glacial interglacial transitions dansgaard oeschger oscillations the 8200 year event unlike the marine records speleothem data sets are not tuned and their independent chronology offers opportunities to critically assess leads and lags in the climate system that in turn can provide important insights into forcing and feedback mechanisms improved procedures for the extraction and measurement of stable isotope ratios in fluid inclusions trapped in speleothems are likely to provide in the near future a much enhanced basis for the quantitative interpretation of o isotope ratios in speleothem calcite the latter developments open up once again the tantalising prospect of palaeo temperature estimates but more importantly perhaps provide a direct test for a new generation of general circulation models whose hydrological cycles will incorporate the water isotopes the literature is reviewed briefly to provide for the reader a sense of the current state of the art and to provide some pointers for future research directions

cortex a shipboard xrf scanner for element analyses in split sediment cores abstract the cortex corescanner texel is a non destructive xrf system for the logging of split sediment cores it is a seaworthy instrument that remains active during heavy weather conditions the scanner produces reliable counts for k to sr highly correlated with concentrations measured with atomic absorption spectrometry aas the option to scan al si and elements heavier than sr is in preparation a core section of 1 m can be scanned at 2 cm intervals within an hour a maximum resolution of 1 mm can be achieved at present each region and sedimentary environment requires separate calibration in the nearby future the generator settings will be standardized which may result in the development of a standard calibration procedure because of the high resolution of its semi quantitative records the cortex is a useful tool for detailed time series analysis inter core correlation and shipboard analysis

quantitative models of sediment generation and provenance state of the art and future developments abstract an overview of quantitative approaches to analysis and modelling of sediment generation and provenance is presented with an emphasis on major framework components as determined by means of petrographic techniques conceptual models of sediment provenance are shown to be consistent with two classes of numerical statistical models i e linear mixing models and compositional linear models these cannot be placed within a common mathematical framework because the former requires that sediment composition is expressed in terms of proportions whereas the latter requires that sediment composition is expressed in terms of log ratios of proportions additivity of proportions a fundamental assumption in linear mixing models cannot be readily expressed in log ratio terms linear mixing models may be used to describe compositional variability in terms of physical and conceptual un mixing models of physical un mixing are appropriate for describing compositional variation within transport invariant subpopulations of grains as a result of varying rates of supply of detritus from multiple sources conceptual un mixing governs the relations among chemical mineralogical and petrographic characteristics of sediments which represent different descriptive levels within a compositional hierarchy compositional linear process models may be used to describe compositional and or textural evolution resulting from selective modifications induced by sediment transport as well as chemical and mechanical weathering current approaches to modelling of surface processes treat the coupled evolution of source areas and sedimentary basins in terms of bulk mass transfer only and do not take into account compositional and textural sediment properties moving from the inverse modelling approach embodied in provenance research to process based forward models of sediment generation which provide detailed predictions of sediment properties meets with considerable albeit not insurmountable problems strategies for developing more advanced parameterizations of sediment properties and for simulating their evolution are proposed and expansion of current data acquisition protocols is discussed in the light of data requirements for such advanced sediment generation models inclusion of sediment generation modules in models of landscape evolution and basin filling will mark a significant step towards full fledged source to sink simulations of earth surface processes

postglacial fluctuations of cordillera darwin glaciers southernmost patagonia reconstructed from almirantazgo fjord sediments abstract most outlet glaciers of the cordillera darwin icefield cdi patagonia 54 s are currently transitioning from calving to land based conditions whether this situation is unique to the modern climate or also occurred during the holocene is entirely unknown here we investigate the holocene fluctuations of outlet glaciers from the northern flank of the cdi using a multi proxy sedimentological and geochemical analysis of a 13 5 m long sediment core from almirantazgo fjord our results demonstrate that sedimentation in almirantazgo fjord started prior to 14 300 cal yr bp with glacier proximal deposits occurring until 13 500 cal yr bp after 12 300 cal yr bp most glaciers had retreated to land locked locations and by 9800 cal yr bp almirantazgo fjord was a predominantly marine fjord environment with oceanographic conditions resembling the present day setting our sediment record shows that during the first part of the holocene cdi glaciers were almost entirely land based with a possible re advance at 7300 5700 cal yr bp this is in clear contrast with the neoglaciation during which cdi glaciers rapidly re advanced and shrank back several times mostly in phase with the eastern outlet glaciers of the southern patagonian icefield spi two significant meltwater events indicative of rapid glacier retreat were identified at 3250 2700 and 2000 1200 cal yr bp based on an increase in grain size mode and related inorganic geochemical parameters this interpretation is additionally supported by concomitant decreases in organic carbon of marine origin and in cl counts salinity reflecting higher terrestrial input to the fjord and freshening of the fjord waters overall our record suggests that cdi outlet glaciers advanced in phase with eastern spi glaciers during the neoglaciation and retreated far enough into their valleys twice to form large outwash plains our results also highlight the potential of fjord sediments to reconstruct glacier variability at high resolution on multi millennial timescales

devils hole paleotemperatures and implications for oxygen isotope equilibrium fractionation subaqueous calcite in devils hole nevada was growing continuously from slightly super saturated groundwater providing a 570 kyr long o18 paleoclimate record due to its very slow growth it has been assumed to have grown under conditions of isotopic equilibrium however its holocene o18 value is 1 5 higher than predicted by laboratory precipitation based oxygen isotope thermometer calibrations the suggestion that devils hole calcite anchors the isotope thermometer to more 18o enriched values has stirred a debate as to which paleothermometer calibration is relevant for paleoclimate and casts doubt on the validity of o18 based paleotemperatures we used clumped isotopes to test the assumptions of the devils hole alternative 18o thermometer carbonate clumped isotopes are a temperature proxy that measures the abundance of 13c18o bonds in caco3 this proxy is independent of the water composition and therefore gives independent estimates of temperatures when calcite forms at thermodynamic and isotopic equilibrium we find that devils hole water paleotemperatures were constant at 30 6 2 6 c between 27 and 180 ka similarly to the modern groundwater temperature of 32 8 34 3 c the proximity of the devils hole clumped isotope data to values expected based on modern groundwater temperatures supports the notion that devils hole calcite grew under equilibrium conditions therefore the commonly used laboratory based o18 temperature calibrations should be reconsidered the constant water temperature over the glacial interglacial cycles indicates that the long devils hole o18 record reflects only variations in the groundwater o18 values and as such represents a valuable archive of paleoclimate and isotope paleohydrology

climatic change recorded by stable isotopes and trace elements in a british holocene tufa combined stable isotope d18o and d13c and trace element mg sr geochemistry from bulk tufa calcite and ostracod shell calcite from an early holocene british tufa reveal clear records of holocene palaeoclimatic change variation in d18o is caused principally by change in the isotopic composition of holocene rainfall recharge itself caused mainly by change in air temperature the d13c variability through much of the deposit reflects increasing influence of soil zone co2 owing to progressive woodland soil development bulk tufa mg ca and sr ca are controlled by their concentrations in the spring water importantly mg ca ratios are not related to d18o values and thus show no temperature dependence first order sympathetic relationships between d13c values and mg ca and sr ca are controlled by aquifer processes residence times co2 degassing and calcite dissolution reprecipitation and probably record intensity of palaeorainfall recharge effects stable isotope records from ostracod shells show evidence of vital effects relative to bulk tufa data the ostracod isotopic records are markedly spiky because the ostracods record snapshots of relatively short duration years whereas the bulk tufa samples record averages of longer time periods probably decades the d18o record appears to show early holocene warming a thermal maximum at ca 8900 cal yr bp and the global 8200 yr bp cold event combined d13c mg ca and sr ca data suggest that early holocene warming was accompanied by decreasing rainfall intensity the mg ca data suggest that the 8200 yr bp cold event was also dry warmer and wetter conditions were re established after the 8200 yr bp cold event until the top of the preserved tufa sequence at ca 7100 cal yr bp

travertines depositional morphology and the bacterially constructed constituents abstract investigation of travertine accumulations throughout central italy and the west central u s has shown that the carbonate is precipitated in response to both inorganic and organic processes individual deposits range up to 85 m thick and hundreds of square kilometers in areal extent all of the carbonate is low magnesian calcite water chemistry temperature and morphology of the accumulation greatly influence the constituents comprising these deposits harsh environmental situations favor inorganic deposits while increasingly more moderate conditions result in the formation of a greater abundance of organically precipitated material morphological variations of travertine deposits recognized include 1 waterfall or cascade 2 lake fill 3 sloping mound fan or cone 4 terraced ound and 5 fissure ridge gross morphology internal stratification and constituents comprising these deposits vary systematically depending upon the type of accumulation and chemistry of the waters bacterially precipitated calcite forms a large percentage of the carbonate in many travertine accumulations exceeding 90 of the framework grains comprising some of the lake fill deposits bacteria are among the first taxa to inhabit and reproduce in harsh spring environments and produce a variety of fascinating constituents the bacteria are primarily rods generally 0 2 m in diameter and less than 1 0 m in length the rods readily decay resulting in calcite crystals loaded with micropores the basic building block of bacterially constructed travertine is a clump of bacteria averaging 20 m in diameter enclosed in a single crystal of calcite aggregates of these crystals produce a variety of deposits including 1 crudely laminated carbonate mud 2 finely laminat d layers of mud 3 intraclasts 4 foam rock and 5 shrubs the shrubs are most striking commonly forming layers 1 3 cm thick but also producing bacterial pisoids at some locales bacterial stromatolites composed of layers of shrubs alternating with finely laminated layers of bacterial mud comprise essentially the entire deposit the shrub layers are the result of flourishing summer growth of bacteria and furthermore show remarkable daily laminae 0 1 0 5 mm thick the importance of bacteria in the formation of travertine and their universally recognized abundance in modern sediments provides an impetus for a reexamination of the role of bacteria in the origin of other types of ancient deposits

muddled or mixed inferring palaeoclimate from size distributions of deep sea clastics abstract one of the outstanding problems of palaeoclimate reconstruction from physico chemical properties of terrigenous deep sea sediments stems from the fact that most basin fills are mixtures of sediment populations derived from different sources and transported to the site of deposition by different mechanisms conventional approaches to palaeoclimate reconstruction from deep sea sediments do not distinguish between provenance and dispersal related variations and therefore often fail to recognise the true significance of variations in sediment properties we formulate a set of requirements that each proposed palaeo environmental indicator should fulfil and focus on the intrinsic coupling between grain size and chemical composition a critical review of past achievements in grain size analysis serves to introduce a conceptual model of spatio temporal grain size variation based on dynamic populations each dynamic population results from a characteristic combination of production and transport mechanisms that corresponds to a distinct subpopulation in the data analysed the mathematical statistical representation of the conceptual model can be obtained by means of the end member modelling algorithm emma applications of the model to several ocean basins are discussed as well as methods to examine the validity of grain size based palaeoclimate reconstructions palaeoclimate reconstructions of a high and low latitude basin illustrate the common degree of complexity of deep sea grain size records

geochemistry of surface sediments from the fjords of northern chilean patagonia 44 47 s spatial variability and implications for paleoclimate reconstructions abstract the patagonian fjords have a clear potential to provide high resolution sedimentary and geochemical records of past climate and environmental change in the southern andes to improve our ability to interpret these proxy records we investigated the processes that control fjord sediment inorganic geochemistry through a geochemical mineralogical and sedimentological analysis of surface sediment samples from the fjords of northern chilean patagonia a simple terrestrial index based on measurements of salinity and fraction of terrestrial carbon was used to estimate the terrestrial input river discharge at each site our results demonstrate that under the cold climate conditions of patagonia chemical weathering is weak and the inorganic geochemical composition of the fjord sediments is primarily controlled by hydrodynamic mineralogical sorting i e the intensity of river discharge our results suggest that the distribution of fe ti and zr in surface sediments is controlled by their association with heavy and or coarse minerals whereas al is independent of hydrodynamic processes the elemental ratios fe al ti al and zr al are therefore well suited for estimating changes in the energy of terrestrial sediment supply into the fjords through time zr al is particularly sensitive in proximal environments while fe al is most useful in the outer fjords and on the continental margin in the most proximal environments however fe al is inversely related to hydrodynamic conditions caution should therefore be exercised when interpreting fe al ratios in terms of past river discharge the application of these proxies to long sediment cores from quitralco fjord and golfo elefantes validates our interpretations our results also emphasize the need to measure al based elemental ratios at high precision which can be achieved using simultaneous acquisition icp aes technology this study therefore constitutes a strong basis for the interpretation of sedimentary records from the chilean fjords

c and o stable isotope variability in recent freshwater carbonates river krka croatia three types of recent carbonate precipitates from the river krka croatia were analysed 1 bulk tufa from four main cascades in a 34 km long section of the river flow through the krka national park 2 a laminar stromatolite like incrustation formed in the tunnel of a hydroelectric power plant close to the lowest cascade and 3 recent precipitates collected on artificial substrates during winter spring and summer periods stable isotope compositions of carbon d 13 c and oxygen d 18 o in the carbonate and organic carbon d 13 corg were determined and compared with d 18 o of water and d 13 c of dissolved inorganic carbon dic the source of dic which provides c for tufa precipitation was determined from the slope of the line dic dic0 1 vs d 13 c dic dic dic0 sayles curry 1988 the d 13 c value of added dic was 13ae6 corresponding to the dissolution of co2 with d 13 c between 19ae5 and 23ae0 vienna pee dee belemnite vpdb the observed difference between the measured and calculated equilibrium temperature of precipitation of bulk tufa barriers indicates that the higher the water temperature the larger the error in the estimated temperature of precipitation this implies that the climatic signals may be valid only in tufas precipitated at lower and relatively stable temperatures the laminar crust comprising a continuous record of the last 40 years of precipitation shows a consistent trend of increasing d 13 c and decreasing d 18 o the lack of covariation between d 13 c and d 18 o indicates that precipitation of calcite was not kinetically controlled for either of the elements d 13 c and d 18 o of precipitates collected on different artificial substrates show that surface characteristics both of substrates and colonizing biota play an important role in c and o isotope fractionation during carbonate precipitation

african monsoon enhancement during the penultimate glacial period mis 6 5 170 ka and its atmospheric impact 1 a reconstruction of northwest african summer monsoon strength during the cold marine isotopic stage mis 6 indicates a link to the seasonal migration of the intertropical convergence zone itcz high resolution studies of eolian dust supply and sea surface temperature recorded in marine core md03 2705 on the mauritanian margin provide a better understanding about the penultimate glacial history of northwestern african aridity humidity and upwelling coastal activity today site md03 2705 experiences increased upwelling and dust flux during the winter months when the itcz is in a southerly position analyses of foraminifera isotopic composition suggest that during mis 6 5 180 168 ka the average position of the itcz migrated north marked by an increase in the strength of the summer monsoon which decreased eolian dust transport and the coastal upwelling activity the northward migration is in phase with a specific orbital combination of a low precessional index with a high obliquity signal high resolution analysis of stable isotopes 18o and 13c and microscale resolution geochemical ti al and quartz grain counts determinations reveal that the transition between monsoonal humid mis 6 5 and dry mis 6 4 conditions has occurred in less than 1 3 ka such rapid changes suggest a nonlinear link between the african monsoonal rainfall system and environmental changes over the continent this study provides new insights about the influence of vegetation and oceanic temperature feedbacks on the onset of african summer monsoon and demonstrates that during the penultimate glacial period changes in tropical dynamics had regional and global impacts