european glacial dust deposits geochemical constraints on atmospheric dust cycle modeling for a long time global paleodust numerical simulations have greatly underestimated dust sources other than modern deserts recent modeling experiments incorporating glaciogenic sources of dust have positively improved the agreement between model and paleodust data this highlights the importance of accurately representing all areas potentially subjected to deflation during an investigated interval geochemical results obtained from european loess sequences collected along a 50 n transect combined with dust emission simulations reveal the geographical distribution of the most important european dust sources between 34 ka and 18 ka we demonstrate that most european dust traveled only a few hundred kilometers or less within the boundary layer from its source before deposition we conclude that our results encourage acquisition of similar geochemical data for other relevant areas in the world further they could provide critical constraints to benchmark atmospheric models contributing to improve their performance in simulating dust cycle and associated climate feedbacks

radiogenic and stable sr isotope ratios 87 sr 86 sr δ 88 86 sr as tracers of riverine cation sources and biogeochemical cycling in the milford sound region of fiordland new zealand this study reports radiogenic sr isotope ratios 87sr 86sr stable sr isotope ratios 88 86sr and major ion concentrations for river rock sediment soil and plant samples collected from the cleddau and hollyford catchments in the milford sound region of fiordland new zealand the catchments primarily drain gabbro but some tributaries access limestone and volcanogenic sediments the goal of the study was to understand controls on riverine 88 86sr values in a landscape with multiple factors that may influence chemical weathering including dense vegetation high rainfall and abundant freshly eroded holocene fluvio glacial and landslide debris rivers draining gabbro have higher 88 86sr values than bedrock by as much as 0 14 and the 88 86sr values strongly correlate with molar ca sr ratios r2 0 69 leaching of rocks and sediment reveals no evidence for the preferential dissolution of minerals having high 88 86sr values and ca sr ratios in stream sr isotope fractionation seems unlikely because comparison against 87sr 86sr and ca sr ratios demonstrates that riverine 88 86sr values conservatively trace water mass mixing the riverine data are best explained by the input of soil water which is distinct from potential bedrock end members i e silicates and carbonates based on 88 86sr but indistinguishable in terms of ca sr and 87sr 86sr while strontium isotope fractionation during secondary mineral formation and pedogenesis is possible clay mineral formation is minor and most soils are poorly developed instead soil water 88 86sr values more likely reflect plant uptake plant samples yielded a wide range of 88 86sr values but on average they are lower than those for bedrock consistent with the expectation that plants preferentially incorporate lighter sr isotopes mass balance constraints together with 87sr 86sr ratios indicate that soil water 88 86sr values are 0 30 higher than bedrock 88 86sr values and mixing calculations show that the plant fractionated soil water pool contributes 27 of the riverine sr for tributaries accessing limestone and volcanogenic sediments ca sr and 87sr 86sr ratios appear consistent with two component mixing between silicate and carbonate weathering but 88 86sr values reveal a third contribution from soil water inputs similar to gabbro catchments the results of this study suggest that sr isotopes behave conservatively during water mass mixing and stream transport but non conservatively in soil where plant uptake can elevate soil water 88 86sr values relative to bedrock plant uptake or related biogeochemical processes such as ion exchange on organic matter surfaces also appear to modify soil water ca sr ratios many studies use 87sr 86sr and ca sr ratios to apportion riverine solutes between silicate and carbonate weathering but ca sr ratios may be non conservative in densely vegetated areas the stable sr isotope tracer shows promise for resolving riverine cation sources as well as effects from biological cycling

the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

pedogenic carbonates forms and formation processes abstract soils comprise the largest terrestrial carbon c pool containing both organic and inorganic c soil inorganic carbon sic was frequently disregarded because 1 it is partly heritage from soil parent material 2 it undergoes slow formation processes and 3 has very slow exchange with atmospheric co2 the global importance of sic however is reflected by the fact that sic links the long term geological c cycle with the fast biotic c cycle and this linkage is ongoing in soils furthermore the importance of sic is at least as high as that of soil organic carbon soc especially in semiarid and arid climates where sic comprises the largest c pool considering the origin formation processes and morphology carbonates in soils are categorized into three groups geogenic carbonates gc biogenic carbonates bc and pedogenic carbonates pc in this review we summarize the available data and theories on forms and formation processes of pc and relate them to environmental factors after describing the general formation principles of pc we present the specific forms and formation processes for pc features and the possibilities to use them to reconstruct soil forming factors and processes the following pc are described in detail earthworm biospheroliths rhizoliths and calcified roots hypocoatings nodules clast coatings calcretes and laminar caps the second part of the review focuses on the isotopic composition of pc 13c 14c and 18o as well as clumped 13c and 18o isotopes known as 47 the isotopic signature of pc enables reconstructing the formation environment the dominating vegetation 13c temperature 18o and 47 and the age of pc formation 14c the uncertainties in reconstructional and dating studies due to pc recrystallization after formation are discussed and simple approaches to consider recrystallization are summarized finally we suggest the most important future research directions on pc including the anthropogenic effects of fertilization and soil management in conclusion pc are an important part of sic that reflect the time periods and formation processes in soils a mechanistic understanding of pc formation is a prerequisite to predict terrestrial c stocks and changes in the global c cycle and to link the long term geological with short term biological c cycles

riverine evidence for a fractionated reservoir of ca and mg on the continents implications for the oceanic ca cycle analysis of river water rock travertine and soil from the high altitude negligible vegetation setting of the southern tibetan plateau demonstrates that ca and mg isotope ratios are fractionated during weathering dissolved ca in the two rivers studied is derived primarily by limestone dissolution 44 42ca in the rivers averages 0 43 and is statistically distinct from limestone at 0 31 the range in 44 42ca in these small rivers is 0 43 equivalent to the entire range in 44 42ca recorded in marine carbonate over the last 80 ma precipitation of isotopically light travertine with a 44 42ca of 0 21 enriches solute ca in heavy isotopes the mg isotope composition of the rivers is intermediate between limestone and silicate rock averaging 1 5 silicate soil has a 26mg of 0 03 heavier than silicate rock by 0 5 these fractionations in the soil create a companion groundwater reservoir of heavy ca and light mg seasonal variations in ca and mg isotope ratios in the dissolved load are small but define an array which can be modelled as a mixture between a fractionated groundwater reservoir and surface runoff reflecting the isotopic composition of the lithology fractionation of ca during the weathering of the continents is of importance to the global cycle of ca the riverine input of ca to the oceans dominated by carbonate weathering is controlled not only by the composition of the primary continental crust but also by the size and composition of a fractionated reservoir on the continents the impact on the oceanic cycle of ca depends on the relative residence times of dissolved ca in the ocean and the storage time of fractionated ca

biogeochemistry of stable ca and radiogenic sr isotopes in a larch covered permafrost dominated watershed of central siberia stable ca and radiogenic sr isotope compositions were measured in different compartments stream water soil solutions rocks soils and soil leachates and vegetation of a small permafrost dominated watershed in the central siberian plateau the sr and ca in the area are supplied by basalt weathering and atmospheric depositions which significantly impact the sr isotopic compositions only vegetation significantly fractionates the calcium isotopes within the watershed these fractionations occur during ca uptake by roots and along the transpiration stream within the larch trees and are hypothesised to be the result of chromatographic processes and ca oxalate crystallisations during ca circulation or storage within plant organs biomass degradation significantly influences the ca isotopic compositions of soil solutions and soil leachates via the release of light ca and organic and organo mineral colloids are thought to affect the ca isotopic compositions of soil solutions by preferential scavenging of 40ca the imprint of organic matter degradation on the 44 40ca of soil solutions is much more significant for the warmer south facing slope of the watershed than for the shallow and cold soil active layer of the north facing slope as a result the available stock of biomass and the decomposition rates appear to be critical parameters that regulate the impact of vegetation on the soil water system in permafrost areas finally the obtained 44 40ca patterns contrast with those described for permafrost free environments with a much lower 44 40ca fractionation factor between soils and plants suggesting specific features of organic matter decomposition in permafrost environments the biologically induced ca isotopic fractionation observed at the soil profile scale is not pronounced at the scale of the streams and large rivers in which the 44 40ca signature may be controlled by the heterogeneity of lithological sources

rapid and cyclic aeolian deposition during the last glacial in european loess a high resolution record from nussloch germany abstract this paper reports the results of an investigation of the weichselian upper pleniglacial loess sequences of nussloch rhine valley germany based on stratigraphy palaeopedology sedimentology palynology malacology and geochemistry 13 c supported by radiocarbon tl and osl dating grain size and magnetic susceptibility records are taken at 5 cm intervals from the upper pleniglacial upg loess the data indicate cyclic variations in loess deposition between ca 34 and 17 ka when the sedimentation rate is especially high 1 0 1 2 m per ka for more than 10 m the grain size index gsi ratio of coarse silt versus fine silt and clay shows variations which are assumed to be an indirect measurement of wind intensity the sedimentation rate interpreted from the profiles indicates high values in loess loess events le 1 to le 7 and low or negligible values in tundra gley horizons g1 to g8 osl ages from the loess and 14 c dates from organic matter in the loess show that loess deposition was rapid but was interrupted by shorter periods of reduced aeolian sedimentation comparison between the data from nussloch and other european sequences demonstrates a progressive coarsening of the loess deposits between ca 30 and 22 ka this coarsening trend ends with a short but major grain size decrease and is followed by an increase to a new maximum at 20 2 ka w shape correlation between the loess gsi and the greenland ice core dust records suggests a global connection between north atlantic and western european global atmospheric circulation and wind regimes in addition the typical upper pleniglacial loess deposition begins at ca 30 31 ka close to heinrich event he 3 and the main period of loess sedimentation at about 25 2 ka is coeval to he 2 correlation of magnetic susceptibility and grain size records shows that the periods characterised by high gsi coincide with an increase in the amount of ferromagnetic minerals reworked from the rhine alluvial plain they suggest enhancement in the frequency of the storms from n nw these results are integrated within a palaeogeographical model of dust transport and deposition in western europe for the weichselian upper pleniglacial or late pleniglacial

origin of strontium and calcium in pedogenic needle fibre calcite nfc abstract strontium sr and calcium ca isotopic compositions and sr ca ratios have been analysed in different fractions of pedogenic needle fibre calcite nfc from the swiss jura mountains villiers neuch tel switzerland in order to determine their ca sources and to investigate the potential role of fungi in the origin of nfc 87sr 86sr ratios have been measured to trace the ca trapped within different pedogenic carbonate this ratio was compared for previously identified microscopic morphological groups of nfc the bulk soil fine earth

small scale secondary caco3 accumulations in selected sections of the european loess belt morphological forms and potential for paleoenvironmental reconstruction eighteen important quaternary loess paleosoil sites have been studied across the european loess belt they included approximately 50 buried soils the over and or underlying loess and the present day surface soils where possible from the numerous types of secondary caco3 accumulations recognized only the small scale accumulations are discussed in this paper including calcified root cells caco3 hypocoatings needle fiber calcite powdery calcite coatings earthworm biospheroliths and calcite pseudomorphs on gypsum most of the features studied are found in the rhizosphere microecosystem each of these features showed a unique relationship with organic matter micro organism and plant distribution moisture and leaching processes for example the exceptional abundance of calcified root cells is an indicator of a long stability of soil surface during favorable climatic conditions needle fiber calcite is related to biomineralization of saprophytes in soils with sufficient moisture and decomposing organic matter the presence of powdery calcite coatings covering clay and mn coatings in non calcareous soils indicates a change from leaching to non leaching soil moisture regimes earthworm biospheroids provide arguments for a relative stability of the soil surface without rapid burial processes or drastic prolonged water stress finally gypsum pseudomorphs are indicators of changes in local climatic parameters in addition to a discussion of the genesis and the dynamics of the various accumulations several examples are given to show how these accumulations can be used as indicators of a changing environment such as renewed loess deposition the extent of drought or varying intensity of leaching during the year to conclude various forms of small scale secondary caco3 accumulations are common in the loess paleosoils and each type has the potential to contribute to a better understanding of the evolution of the paleoenvironment therefore it is proposed that their individual presence or absence throughout the pedostratigraphical levels and throughout the paleo topography should be recorded at all scales of observation

introducing an improved multi proxy approach for paleoenvironmental reconstruction of loess paleosol archives applied on the late pleistocene nussloch sequence sw germany to study paleoenvironmental and paleoclimatic changes in loess paleosol sequences lps most proxies except for screening parameters have often been applied at low sampling density typically 1 2 per stratigraphic unit this might lead to results that overlook paleovegetation effects that were not only restricted to paleosols but also affected underlying loess material here a new profile was investigated in the loess paleosol sequence lps at nussloch sw germany using a high resolution multi proxy approach to improve our understanding of the late pleistocene record which serves as a standard sequence in central europe this approach included several geophysical and geochemical parameters as well as frequencies of root related features grain size distribution and osl dating enabled correlation of the new section with the nearby standard profile p4 revealing considerable variations of the thickness of stratigraphic units due to local small scale variations in depositional conditions and paleogeomorphology of longitudinal greda structures magnetic susceptibility revealed weathering of the entire lps under more humid conditions than those described for se european and chinese lps it further enabled a rough differentiation between an interval that was influenced by pedogenic processes lower pleniglacial to lower part of the upper pleniglacial and loess that was not markedly affected by soil formation color measurements confirmed these results and enabled the identification of several paleosols in the upper pleniglacial for the uppermost part of the lps low magnetic susceptibility and inorganic geochemical parameters such as low fe ti ratios indicated only weak or no pedogenic influence in contrast considerable variations e g in carbonatic carbon contents and organic carbon nitrogen c n ratio might be related to the high frequency of calcified root remains up to 200 rhizoliths m 2 and up to 12 500 microrhizoliths m 2 in certain depth intervals of the lps entailing incorporation and degradation of organic matter frequencies of biopores which are suggested to derive largely from former root growth and to a lesser extent from insect and earthworm bioturbation were related to paleosols and thus confirmed the pedostratigraphy an improved assessment of terrestrial sedimentary archives can be achieved by high resolution multi proxy analysis and three dimensional investigation of terrestrial sediments that are prone to bioturbation c 2014 elsevier b v all rights reserved

strontium isotope composition as a tracer of calcium sources in two forest ecosystems in belgium the two main sources of ca in forest ecosystems are mineral weathering release and atmospheric inputs we use the 87 sr 86 sr isotopic ratio sr is used as a proxy for ca to determine the ca contribution from atmospheric deposition input in two forest ecosystems beech stands growing on soils formed from parent materials with contrasting total ca contents and isotopic ratios pleistocene loess in central belgium acid leached soil and lower devonian shales in the ardenne massif of high belgium ochreous brown earth the 87 sr 86 sr ratio and the ca and sr contents were measured in bulk precipitation in vegetation beechwood growth rings and leaves and in main soil horizons total acid extractable and labile pools the relative contributions of atmospheric input and soil mineral weathering to vegetation were calculated using mixing equations calculations based on sr isotope ratios of bulk precipitation end member 1 87 sr 86 sr close to ocean water 0 7090 0 1 m hcl extractable soil fraction end member 2 and beech wood mixing compartment indicate that about 43 central belgium and 39 ardennes of sr uptake originates from atmospheric inputs for ca the contributions of atmospheric input are 75 and 78 respectively these estimations are however very sensitive to the choice of the appropriate 87 sr 86 sr and sr ca ratios for the weathering end member the isotopic composition of the mineral source is estimated from the soil mineralogical composition and the relative weatherability of the sr bearing minerals due to soil processes mineral weathering element recycling and geomorphological events addition of allochtonous minerals to the autochtonous pool inherited from the local bedrock the distribution of minerals in both soil profiles is heterogeneous and varies from horizon to horizon which horizons are relevant and which soil pool total soil acidextractable fraction or labile pool should be selected for isotopic measurement of the weathering end member is therefore open to uncertainty the choice of the appropriate 87 sr 86 sr and sr ca ratios for the weathering end member is discussed our results emphasize the importance of the atmospheric contribution of ca for tree mineral nutrition in the studied forest stands suggesting that these ecosystems on acid soils are sensitive to chemical changes in the atmospheric environment e g acid depositions associated with decreasing input of atmospheric cations our results support therefore

thermal history of the enstatite chondrites from silica polymorphs here we report the results of our petrologic and mineralogical study of enstatite e chondrites in order to explore their thermal histories we studied silica phases in 20 e chondrites by laser micro raman spectroscopy to determine the silica polymorphs they contain silica phases are commonly present in e chondrites and their polymorphs reflect the physical conditions of formation the samples studied here include eh3 5 el3 6 e chondrite melt rocks and an anomalous e chondrite we identified quartz tridymite cristobalite and silica glass in the samples studied eh4 5 and eh melt rocks are divided into high and low temperature classes based on niningeritealabandite solid solutions eh3 el3 and some eh melt rocks of the high temperature class contain tridymite and cristobalite we suggest that tridymite and cristobalite crystallized in chondrules and e chondrite melts followed by rapid cooling leading to the survival of these silica polymorphs eh4 and el4 chondrites also contain tridymite and cristobalite in their chondrules indicating that these silica polymorphs survived low temperature metamorphism as estimated from opaque mineral geothermometers because of the sluggishness of the transition to a more stable polymorph tridymite and cristobalite in el6 chondrites reflect the high temperature processes experienced by these meteorites on the other hand some eh5 chondrites and eh melt rocks of the low temperature class contain quartz which may be a product of the transition from tridymite or cristobalite during a long period of low temperature metamorphism although the thermal history of e chondrites have been previously estimated from opaque minerals such compositions mainly reflect low temperature processes however we can reconstruct the primordial thermal processes and subsequent cooling histories of e chondrites from their silica polymorphs the e chondrites have complicated thermal histories which produced the observed variations among them

carbonate rhizoliths in loess and their implications for paleoenvironmental reconstruction revealed by isotopic composition δ13c 14c abstract loess paleosol sequences are important terrestrial archives for studying quaternary climate changes they often contain secondary carbonates including e g rhizoliths calcified roots these secondary carbonates are precipitated in isotopic equilibrium with root derived co2 and are therefore used to reconstruct the vegetation present during their formation based on stable carbon isotopic composition 13c usually the chronological context of secondary carbonates in general is not mentioned because it is assumed that they are formed synsedimentary with loess deposition the loess paleosol sequence at nussloch sw germany contains in its youngest part upper wurmian large carbonate rhizoliths with diameters of up to 5 cm and lengths of up to 1 m and more which have not been described in this profile so far we investigated rhizoliths as well as loess adjacent to and distant from rhizoliths for carbonatic carbon ccarb and organic carbon corg contents as well as their isotopic composition 13c radiocarbon dating to identify the rhizolith origin and the time frame of their formation considering the 13c fractionation by carbonate precipitation the 13ccarb values 10 9 0 1 revealed c3 plant origin of the rhizolith carbonate and the absence of large amounts of occluded primary loess carbonate similar 14c ages of rhizolith ccarb and corg 3788 59 years bp and 3150 59 years bp respectively argued for the absence of postsegregational alteration therefore they are suitable for the reconstruction of paleoenvironmental conditions after loess sedimentation the 14c ages clearly indicate that rhizoliths did not form synsedimentary roots penetrated the loess at nussloch after the deposition had ceased at 15 ka bp even in the loess adjacent to the rhizoliths up to a distance of 5 cm 13ccarb values indicate the presence of secondary carbonate deriving from postsedimentary organic matter of origin other than that of the reference loess material hence this postsedimentary input of younger root biomass might have masked the initial plant signal in loess paleosol sequences which could cause uncertainties for paleoenvironmental reconstructions based solely on loess organic matter

factors and processes governing the 14c content of carbonate in desert soils epsl elsevier earth and planetary science letters 125 1994 385 405 factors and processes governing the 14c content of carbonate in desert soils ronald amundson a yang wang a oliver chadwick b susan trumbore c leslie mcfadden d eric mcdonald d steven wells e michael deniro f a division of ecosystem sciences 108 hilgard university of california berkeley ca 94720 usa b earth sciences division jet propulsion laboratory pasadena ca 91109 usa c department of geosciences university of california irvine ca 92717 usa d department of earth and planetary sciences university of new mexico albuquerque nm 87131 usa e department of earth sciences university of california riverside ca 92521 usa f department of geological sciences university of california santa barbara ca 93106 usa received 1 september 1993 revision accepted 14 april 1994 abstract a model is presented describing the factors and processes which determine the measured 14c ages of soil calcium carbonate pedogenic carbonate forms in isotopic equilium with soil co 2 carbon dioxide in soils is a mixture of co 2 derived from two biological sources respiration by living plant roots and respiration of microorganisms decomposing soil humus the relative proportion of these two co z sources can greatly affect the initial 14c content of pedogenic carbonate the greater the contribution of humus derived co 2 the greater the initial 14c age of the carbonate mineral for any gwen mixture of co 2 sources the steady state co 2 distribution vs soil depth can be described by a production diffusion model as a soil ages the 14c age of soil humus increases as does the steady state 14c age of soil co 2 and the initial 14c age of any pedogenic carbonate which forms the mean 14c age of a complete pedogenic carbonate coating or nodule will underestimate the true age of the soil carbonate this discrepancy increases the older a soil becomes partial removal of outer and younger carbonate coatings greatly improves the relationship between measured 14c age and true age although the production diffusion model qualitatively explains the 14c age of pedogenic carbonate vs soil depth in many soils other factors such as climate change may contribute to the observed trends particularily in soils older than the holocene 1 introduction r a d i o c a r b o n d a t i n g o f s e d i m e n t a r y d e p o s i t s in d e s e r t s is h i n d e r e d by a lack o f o r g a n i c carbon paradoxically most o f the d e p o s i t s in t h e s e re mk gions a r e b l a n k e t e d with i n o r g a n i c c a r b o n in the f o r m o f p e d o g e n i c c a r b o n a t e since t h e early 1960s 14c ages have b e e n c a l c u l a t e d for t h e s e c a r b o n a t e s 1 fig 1 illustrates t h a t an a p p r o x i m a t e 1 1 r e l a t i o n s h i p exists b e t w e e n 14c ages of soil c a r b o n a t e a n d coexisting o r g a n i c m a t e r i a l s a n d ages d e t e r m i n e d by o t h e r m e a n s see also 2 3 t h e s e r e l a t i o n s h i p s a r e n o t perfect s o m e c a r b o n a t e is y o u n g e r t h a n i n d e p e n d e n t ages sug 0012 821x 94 07 00 1994 elsevier science b v all rights reserved ssdi 0012 821x 94 00097 i

isotope evidence of paleo el nino southern oscillation cycles in loess paleosol record in the central united states abstract the 13 c of soil carbonate in rhizoconcretions collected from aloess paleosol sequence in the central united states indicates that grow ing season c 3 c 4 plant ratio oscillated by 35 on a 900 200 yr timescale during the late wisconsinan glaciation the pattern appears inphase with advance and retreat of the southern margin of the lauren tide ice sheet suggesting influence by paleo el nino southern oscilla tion cycles the 13 c of soil organic matter indicates that the annual av erage c 3 c 4 plant ratio oscillated only by 18 with a periodicity of450 100 yr and closely matched the cyclic pattern of loess paleosollayers it suggests a periodic enhancement of the penetration of thegulf of mexico air over the region during this time keywords carbon isotope loess paleosol glacial phase paleo enso cycle introduction the el nino southern oscillation enso causes global scale climateanomalies the el nino and la nina are two counterparts of enso whichare associated with warming and cooling in surface water in the eastern trop ical pacific on the basis of modeling studies cane 1998 cane andclement 1999 and clement and cane 1999 proposed that frequency in tensity and duration of long term el nino or la nina intervals have oscil lated on a millennial time scale during the past 150 k y they proposed thatduring glacial periods these long term enso cycles might alter the globalclimate via atmospheric teleconnections in which el nino dominant inter vals may cause retreat and la nina dominant intervals may cause advanceof the southern margin of the laurentide ice sheet the enso sensitive re gions currently in north america partially overlap the area that was coveredby the laurentide ice sheet during the last glaciation fig 1 modernla nina conditions cause heavy snowfall whereas el nino conditions re duce winter precipitation in these regions http www ogp noaa gov enso it is reasonable to assume that la nina or el nino dominant intervals mighthave controlled advance and retreat of the southern margin of the laurentideice sheet if these intervals oscillate on a long term time scale in this paper we use stable isotope ratios from a loess paleosol exposure in the centralunited states to seek evidence for millennial scale paleo enso cycles

enrichment of 88 sr in continental waters due to calcium carbonate precipitation abstract 88 86sr data published over the last few years suggest that continental waters are enriched with 88sr as compared to the rocks in their drainage basins in an attempt to understand this phenomenon this study established the fractionation in the 88sr 86sr ratio during precipitation of continental carbonates i e carbonates precipitated on land from surface pedogenic or ground waters and evaluated the contribution of this process to the 88sr enrichment in rivers for this stable and radiogenic sr isotopes 88sr 87sr and 86sr were measured in calcite samples and their precipitating waters collected in various continental environments such as soil cave streams and groundwater the results indicate that continental carbonates are 88sr depleted relative to their precipitating waters placing them as one of the most 88sr depleted reservoirs on earth the average difference in 88 86sr values between waters and solid caco3 tufas or speleothems that they precipitate is carb water 0 218 0 014 1sd an even larger fractionation e carb water 0 285 0 02 was measured in groundwater with particularly high carbonate alkalinity and high carbonate precipitation rate that depleted 65 of the sr in the groundwater resulting in substantial 88sr enrichment in the residual dissolved sr sr 88 86 0 656 results also suggest that pedogenic carbonate precipitation in soil profile removes 50 85 of the sr from the recharging soil water thereby increasing the 88 86sr value of the soil water from 0 18 to 0 3 0 6 similar 88sr enrichment was observed in drip water from a karst cave a maximum removal flux of sr into continental carbonates of about 20 gmol sr y 1 is required to yield the reported 88sr enrichment in global rivers sr 88 86 0 32 relative to their rock sources when using the fractionation factor derived in this study carb water 0 218 and the published 88 86sr composition of marine carbonates of 0 16 this surprisingly large flux requires that 40 of the originally weathered sr should co precipitate with continental carbonates this calculation may suggest that caco3 precipitation is a significant mechanism in the continental sr cycle it is possible however that other mechanisms such as sr uptake by plants or incongruent weathering of silicates could also contribute to the riverine 88sr enrichment alternatively the average 88 86sr value of marine carbonate rock sections undergoing weathering is higher than suggested in current literature it is concluded that additional 88 86sr data on marine carbonate rock sections should be collected to resolve the enigma of the high value of riverine 88 86sr

branched tetraether membrane lipids associated with rhizoliths in loess rhizomicrobial overprinting of initial biomarker record abstract loess palaeosol sequences are considered important terrestrial archives for studying quaternary climate recent studies have shown that calcified roots rhizoliths can be significantly younger than surrounding terrestrial sediment loess and that loess organic matter may be contaminated with root derived carbon from post sedimentary deep rooting plants branched glycerol dialkyl glycerol tetraethers gdgts are membrane lipids produced by unknown bacteria in soil and are increasingly being used as palaeoclimate proxies the aim of this work was to examine the impact of the temporal decoupling between rhizoliths and loess on the abundance and composition of branched gdgts and consequently on the application of branched gdgts as proxies in loess deposits branched gdgts in rhizoliths and the surrounding sediment from a loess palaeosol sequence in nussloch sw germany were examined their composition varied between the rhizolith and loess which may reflect the fact that branched gdgts were biosynthesized at different times late pleistocene for loess and holocene for rhizoliths and therefore under different environmental conditions a large difference ca 7 c in branched gdgt reconstructed palaeotemperature was observed between rhizoliths and loess in addition the reconstructed temperatures were the opposite from those expected from the assumed depositional ages of branched gdgts this might be explained by the post sedimentary input of root associated microorganism derived branched gdgts to loess which might have led to an overprint of the initial branched gdgt signal in the sediment our results suggest that post sedimentary penetration of deep rooting plants in loess might entail uncertainty regarding the application of branched gdgt palaeoproxies and that caution should be exercised in interpreting temperature estimates derived from branched gdgts in loess palaeosol sequences this is of special importance for loess where rhizoliths are abundant and where non calcified root remains of different age from that of the sediment are possible in addition the gdgt concentration in rhizoliths and surrounding loess supports the hypothesis of a heterotrophic lifestyle for branched gdgt producing bacteria

abrupt millennial climatic changes from nussloch germany upper weichselian eolian records during the last glaciation abstract increasing attention has been focussed on the massive iceberg discharges in the north atlantic heinrich events during the last glaciation and their worldwide terrestrial counterparts however these events are particular episodes among more regular cyclic events named dansgaard oeschger events in ice cores or bond cycles in marine cores here we examine grain size 13c and magnetic susceptibility data from nussloch one of the most complete west european eolian sequence examined so far these indices indicate that during the 31 19 kyr interval using chronology provided by radiocarbon osl and tl dates millennial scale variations occurred affecting both precipitation and vegetation furthermore these are associated with oscillations in the wind strength matching the dust deposition rate in greenland as recorded in the grip ice core our study shows that the abrupt climatic changes the dansgaard oeschger events are also recorded in the west european loess sequences this implies an atmospheric mechanism linking dust deposition over greenland and europe which is probably connected to global climatic events during the last glaciation

evidence for holocene environmental changes in the northern fertile crescent provided by pedogenic carbonate coatings abstract holocene environmental changes in the northern fertile crescent remain poorly understood because of the scarcity of local proxy records in the region in this study we investigated pedogenic soil formed carbonate coatings on stones at the pre pottery neolithic site gobekli tepe as an indicator of local early mid holocene environmental changes the 14c ages and stable isotopic composition of carbon and oxygen in thin 0 2 0 3 mm thick pedogenic carbonate lamina indicate two main periods of coating formation the early holocene ca 10000 6000 cal yr bp and the mid holocene ca 6000 4000 cal yr bp during the first period there was an inverse relationship between 13c and 18o curves a decrease in 13c values coincide with an increase in 18o values for this period a trend towards higher temperatures is suggested in the mid holocene the mean rate of coating growth was 2 3 times higher than in the early holocene both 13c and 18o reached their maximum values during this time and the direction of changes of the 13c and 18o curves became similar the combination of data suggests that this period was the most humid in the holocene and on average warmer than the early holocene at ca 4000 cal yr bp secondary accumulation of carbonate ceased presumably reflecting a shift to a more arid climate

geochemical characterization of the luochuan loess paleosol sequence china and paleoclimatic implications abstract chemical major and trace element and isotopic sr nd analyses of the luochuan loess paleosol sequence in china were performed in order to examine the following problems 1 potential source heterogeneity 2 element behavior during pedogenesis 3 paleoclimatic implications and 4 the use of loess data to determine the average composition of the upper continental crust new results clearly indicate that rb sr u and ce abundances are severely depleted in paleosols relative to their parental loess the behavior of these elements is strongly controlled by the breakdown of primary minerals such as carbonate sr or by alteration processes in highly oxidizing environments ce and u the pattern of element variations through the upper section of the luochuan sequence mimics the magnetic susceptibility signal both in position and in intensity thus reinforcing the pedogenesic origin of the enhanced magnetic susceptibility in paleosols all loess samples display highly uniform ree patterns except for ce characterized by the upper continental crust ucc ratios la yb n 10 and eu eu 0 66 the paleosol ree patterns are similar to those of the loess with the same lree hree fractionation but they also show distinct and variable negative ce anomalies nd and sr isotopic compositions are rather uniform in both loess and paleosols and do not vary with stratigraphic position nd 10 5 to 9 2 87 sr 86 sr 0 715 to 0 719 the isotopic homogeneity in the luochuan sequence strongly suggests a uniform source region during the entire period of deposition since 800 ka ago to the present several conclusions may be drawn from the present study 1 1 no geochemical distinction can be made between loess layers l1 to l7 the sources and the dust storm trajectories must have been essendally the same for the last 800 ka 2 2 some elements e g ca rb sr u ce are strongly fractionated by pedogenesis between loess and paleosols ce mobility in soils is clearly demonstrated but the process responsible for this leaching is still poorly understood 3 3 systematic variations of element abundances and ratios between loess and paleosols can be used as chemical indicators for pedogenesic intensity and so for paleoclimatic change these chemical indicators serve a function similar to that of oxygen isotopes in deep sea sediments pelagic foraminifera or that of magnetic susceptibility in loess sequences they are different recorders of paleoclimatic change 4 4 the striking uniformity of ree patterns and la th ratios in the luochuan loess and paleosols as well as in loess worldwide is an excellent starting point for estimating the average composition of the upper continental crust

geochemical evidence for the origin of late quaternary loess in central alaska loess is extensive in central alaska but there are uncertainties about its source and the direction of paleo winds that deposited it both northerly and southerly winds have been inferred the most likely sources of loess are the tanana river south the nenana river southeast and the yukon river north late quaternary loess in central alaska has immobile trace element compositions cr sc th ta th sc th u eu eu gdn ybn that indicate derivation mostly from the tanana river however other ratios as sb zr hf lan ybn and quantitative modeling indicate that the yukon river was also a source during the last glacial period there may have been a longer residence time of the siberian and canadian high pressure cells along with a strengthened aleutian low pressure cell this would have generated regional scale northeasterly winds and explains derivation of loess from the yukon river however superim posed upon this synoptic scale circulation there may have been strong southerly katabatic winds from expanded glaciers on the northern flank of the alaska range these winds could have provided eolian silt from the tanana river yukon river and tanana river sediments are highly calcareous whereas fairbanks area loess is not this suggests that carbonate leaching in loess kept ahead of sedimentation and that late quaternary loess in central alaska was deposited relatively

multi isotope approach δ44 40ca δ88 86sr and 87sr 86sr provides insights into rhizolith formation mechanisms in terrestrial sediments of nussloch germany abstract carbonates in loess paleosol sequences are considered as a valuable paleoenvironmental proxy for climate change during the quaternary period in this study we propose a new dataset of 44 40ca 88 86sr and 87sr 86sr to understand the formation of rhizoliths roots encrusted with caco3 within these kinds of sequences from nussloch region germany our results indicate that the leached fractions of rhizoliths sampled at 3 25 m 6 65 m and 8 45 m depths and leached with hcl have lower 44 40ca and 88 86sr and higher 87sr 86sr isotopic values than the leached fractions of rhizosphere and root free loess of the same stratigraphic levels this suggests different mechanisms of carbonate formation and different sources of sr and ca a three steps model of formation of rhizoliths from nussloch has been proposed first of all the roots grow in an existent stratigraphic level and the biological activity associated with roots allows for the dissolution of carbonate and non carbonate minerals a part of the available ca and sr is taken up by roots which absorb preferentially the light isotopes e g 40ca and 86sr a higher rate of water absorption by roots than nutrients in association with co2 released by biological respiration allows to reach supersaturation with respect to caco3 the precipitation of rhizolith carbonate selects preferentially the light isotopes e g 40ca and 86sr leading to lower 44 40ca and 88 86sr isotope values than the ones recorded on the closest rhizosphere and loess the higher 87sr 86sr signatures of rhizolith carbonates which is not modified by root uptake or by precipitation processes is the result of a mixture between 87sr 86sr signatures of carbonate and non carbonate minerals digested around the roots nevertheless grey zones remain in this main hypothesis about the very high contribution of residue materials to the isotopic signatures of rhizoliths in this light other mechanisms of downward transfer of ca and sr from upper stratigraphic level that could imprint the leached fractions of rhizoliths have been discussed

effect of temperature and rhizosphere processes on pedogenic carbonate recrystallization relevance for paleoenvironmental applications abstract in soils of arid and semiarid climates dissolution of primary lithogenic carbonate and recrystallization with co 2 from soil air leads to precipitation of pedogenic carbonates and formation of calcic horizons thus their carbon isotope composition represents the conditions prevailing during their formation however the widespread use of the isotopic signature 13 c 18 o 14 c of pedogenic carbonates for reconstruction of local paleovegetation paleoprecipitation and other environmental conditions lacks knowledge of the time frame of pedogenic carbonate formation which depends on climatic factors we hypothesized that temperature dependent biotic processes like plant growth and root and rhizomicrobial respiration have stronger influence on soil caco 3 recrystallization than abiotic temperature dependent solubility of co 2 and caco 3 to assess the effect of temperature on initial caco 3 recrystallization rates loess with primary caco 3 was exposed to 14 co 2 from root and rhizomicrobial respiration of plants labeled in 14 co 2 atmosphere at 10 20 or 30 c 14 c recovered in recrystallized caco 3 was quantified to calculate amounts of secondary caco 3 and corresponding recrystallization rates which were in the range of 10 6 10 4 day 1 meaning that 10 4 10 2 of total loess caco 3 were recrystallized per day increasing rates with increasing temperature showed the major role of biological activities like enhanced water uptake by roots and respiration the abiotic effect of lower solubility of co 2 in water by increasing temperature was completely overcompensated by biotic processes based on initial recrystallization rates periods necessary for complete recrystallization were estimated for different temperatures presuming that caco 3 recrystallization in soil takes place mainly during the growing season taking into account the shortening effect of increasing temperature on the length of growing season the contrast between low and high temperature was diminished yielding recrystallization periods of 5740 years 4330 years and 1060 years at 10 20 and 30 c respectively in summary increasing caco 3 recrystallization rates with increasing temperature demonstrated the important role of vegetation for pedogenic caco 3 formation and the predominantly biotic effects of growing season temperature considering the long periods of pedogenic carbonate formation lasting to some millennia we conclude that methodological resolution of paleoenvironmental studies based on isotope composition of pedogenic carbonates is limited not by instrumental precision but by the time frame of pedogenic carbonate formation and hence cannot be better than thousands of years

palaeotemperature reconstruction during the last glacial from δ18o of earthworm calcite granules from nussloch loess sequence germany abstract the nussloch loess palaeosol sequence rhine valley germany is considered to be one of the most complete records of the last glacial period in western europe due to its very high sedimentation rate and its good chronological control this sequence is therefore a good framework in which to develop new proxies for palaeoenvironmental reconstructions in this study we explore for the first time the potential of earthworm calcite granules as a new bio indicator and climatic proxy of absolute air and soil temperature in the context of last glacial loess these granules are composed of rhomboedric calcite crystals organized in a radial crystalline structure as these granules are individually generated by earthworms at a relative fast rate they are expected to record intra annual variations in the available sources of oxygen percolating waters of meteoric origin we extracted thirty earthworm calcite granules from 11 of 5 cm layers thick from tundra gley and brown soil horizons previously dated at 45 to 23 ka oxygen isotope ratios were measured on each individual granule the 18o of calcite granules and interlinked transfer functions between water cycle air and soil temperatures allowed us to estimate air temperatures ranging from 10 to 12 4 c which most likely reflect the warm periods of the year when earthworms were the most active

biopores and root features as new tools for improving paleoecological understanding of terrestrial sediment paleosol sequences abstract the important role of roots and rhizosphere processes is accepted for the top soil but still under debate for the deep subsoil including soil parent material especially for terrestrial sediments like loess and dune sands roots and root traces are mostly recognized in profile descriptions but not interpreted in the paleoenvironmental context further synchrony of sediment deposition and root trace formation is commonly assumed this is challenged by partially large maximum rooting depths of plants exceeding the soil depth and by frequent occurrence of secondary carbonates and biopores of potential root origin below recent soil and paleosols to improve understanding of paleoenvironmental records in terrestrial sediment paleosol sequences recent roots and root traces including calcified roots and root derived biopores were investigated in six soil loess and dune sand profiles across central and se europe visualization of small carbonate accumulations diameter 1 mm frequently called pseudomycelia by x ray microtomographic scanning and morphologic comparison with rhizoliths calcified roots diameter mostly 3 20 mm up to 100 mm possible indicate root origin of the former therefore requiring renaming to microrhizoliths quantification of roots biopores rhizoliths and microrhizoliths on horizontal levels yielded maximum frequencies of 2100 m 2 4100 m 2 196 m 2 and 12 800 m 2 respectively considering the pore volume remaining from former root growth this indicates their significant contribution to structural properties of the sediments and paleosols depth distribution of roots and root traces was frequently related to soil and paleosols respectively and mostly showed maximum frequencies within or immediately below these units root traces are therefore not necessarily of similar age like the surrounding sediment but are typically of younger age the time lag between root traces and the surrounding stratigraphic unit can vary between small time periods likely decades to centuries in case of microrhizoliths and several millenia in case of larger rhizoliths penetrating several stratigraphic units with assumed radii of former rhizosphere extension of 5 mm for microrhizoliths a frequency of 12 500 m 2 corresponded to 100 rhizosphere area in the respective depth interval these findings emphasize the meaning of root traces in sediment paleosol sequences potential temporal and spatial inhomogeneity of root growth on the one hand especially for shrub and tree vegetation and occurrence of root remains of different age and origin in identical depth intervals on the other hand hamper the assessment of the chronologic context of these with the surrounding sediment or paleosol nevertheless root traces in terrestrial archives provide valuable information with respect to paleovegetation and paleoenvironmental conditions if their chronological context is known

the long term paleomonsoon variation recorded by the loess paleosol sequence in central china abstract the loess paleosol sequence in central china during the last 2 5 ma is a good record of the asian monsoon variation which could be considered as the concrete realization of global paleoclimatic cycles the geological and biological evidence of the loess paleosol sequence indicates that the loess was mainly the dust deposits transported by the northerly wind of winter monsoons and also suffered to some extent from pedogenesis caused by weakened summer monsoons and that the paleosol accreted by the rather slow dust accumulation was closely related to strengthened summer monsoons an alternating occurrence of loess and paleosol in the luochuan section implies the variation history of warm humid climate with a summer monsoon dominance and cold dry climate with a winter monsoon dominance the magnetic susceptibility of loess and paleosol can be regarded as a proxy index of asian monsoon variation an analysis of the susceptibility curve and structure characters of luochuan section shows that the asian monsoon circulation was strengthened from early pleistocene to late pleistocene and the 500 ka bp point and 1200 ka bp point seem to be a threshold and a turning point respectively in terms of the long term paleomonsoon variation in asia

the destruction of paleoclimatic isotopic signals in pleistocene carbonate soil nodules of western australia stable carbon and oxygen isotopic analyses were conducted on small 10 mm spherical pleistocene carbonate soil nodules from 53 different levels in a 9 15 m soil auger collected in northern western australia the 13c and 18o values range from 4 to 0 and 9 to 6 pee dee belemnite standard respectively comparison of these values to the 13c values of coexisting soil organic matter som reveals marked differences between the two records the som values record an enrichment of 16 through the section whereas the carbonate values record only a 4 variability application of a diffusion production model to the data indicates isotopic disequilibrium between the two carbon records one possible interpretation of the apparent isotopic disequilibrium is that the nodules formed at depths of 1 cm but this interpretation is not supported by field observations an alternative is that the soil organic matter currently in the profile was emplaced after nodule formation such a scenario would have to have occurred numerous times during the late pleistocene as the nodules grew below different soil zones through time a third explanation is that diagenetic alteration of the carbonates in the presence of dissolved inorganic groundwater carbon has occurred this interpretation is consistent with the widely fluctuating regional groundwater table it is also supported by petrographic fabrics and heterogeneous cathodoluminescence patterns indicative of initial pedogenic development of the nodules and then at least one dissolution event multiple precipitation events prolonged nodule growth by displacive spars and microspars cementation and recrystallization of some micrite the results illustrate potential problems for 1 the use of some pedogenic carbonate isotopic records as proxies for environmental change and 2 the use of altered 18o values and unaltered 13c values as screening tools for the presence or absence of diagenesis the results highlight the necessity of understanding regional environmental conditions and diagenetic histories prior to using pedogenic carbonates in paleoreconstructions

non biological fractionation of stable ca isotopes in soils of the atacama desert chile abstract we measured ca stable isotope ratios 44 40 ca in an ancient 2 my hyperarid soil where the primary source of mobile ca is atmospheric deposition most of the ca in the upper meter of this soil 3 5 kmol m 2 is present as sulfates 2 5 kmol m 2 and to a lesser extent carbonates 0 4 kmol m 2 in aqueous extracts of variably hydrated calcium sulfate minerals 44 40 ca e values vs bulk earth increase with depth 1 4 m from a minimum of 1 91 to a maximum of 0 59 the trend in carbonate 44 40 ca in the top six horizons resembles that of sulfate 44 40 ca but with values 0 1 0 6 higher the range of observed ca isotope values in this soil is about half that of 44 40 ca values observed on earth linear correlation among 44 40 ca 34 s and 18 o values indicates either a a simultaneous change in atmospheric input values for all three elements over time or b isotopic fractionation of all three elements during downward transport we present evidence that the latter is the primary cause of the isotopic variation that we observe sulfate 34 s values are positively correlated with sulfate 18 o values r 2 0 78 and negatively correlated with sulfate 44 40 ca e values r 2 0 70 if constant fractionation and conservation of mass with downward transport are assumed these relationships indicate a 44 40 ca fractionation factor of 0 4 in caso 4 the overall depth trend in ca isotopes is reproduced by a model of isotopic fractionation during downward ca transport that considers small and infrequent but regularly recurring rainfall events near surface low ca isotope values are reproduced by a rayleigh model derived from measured ca concentrations and the ca fractionation factor predicted by the relationship with s isotopes this indicates that the primary mechanism of stable isotope fractionation in caso 4 is incremental and effectively irreversible removal of an isotopically enriched dissolved phase by downward transport during small rainfall events

strontium isotope fractionation of planktic foraminifera and inorganic calcite we have investigated the strontium isotope fractionation 88 86srcarb aq between inorganic calcite and aqueous sr2 ions by precipitation experiments at a constant temperature of 25 c and precipitation rates r ranging from 102 3 to 104 2 mol m2 h strontium isotope ratios were measured using the 87sr 84sr double spike technique it was found that strontium isotope fractionation in these calcites is strongly dependent on the precipitation rate view the mathml source the measured 88 86sr values are significantly correlated with previously measured 44 40ca and sr ca values of the same calcite samples 88 86srcarb aq 0 18 44 40cacarb aq 0 01 view the mathml source the slope of 88sr 86sr versus 44ca 40ca fractionation is 0 18 0 04 and compatible with a kinetic fractionation during dehydration of the strontium and calcium ions but not with isotope fractionation in a diffusive boundary layer using published equilibrium 44 40cacarb aq and view the mathml source values we estimate the equilibrium isotope fractionation of strontium to be very close to zero 88 86sreq carb aq 0 01 0 06 this estimate is confirmed by strontium isotope values of natural inorganic calcites that precipitated very slowly in basalts of the ocean crust the results from the inorganic calcites are used to explain strontium isotope fractionation of planktic foraminifera specimens of two warm water species globigerinoides ruber and globigerinoides sacculifer were picked from the holocene section of a caribbean sediment core we found no significant difference in 88 86sr between the two species in addition g ruber specimens from marine isotope stage 2 in the same core show 88 86sr values identical to the holocene specimens the strontium isotopes of both foraminifera species are strongly fractionated 88 86srcarb aq 0 248 0 005 when compared to published data of other major marine calcifiers applying the results from the inorganic precipitation experiments we find that the strong foraminiferal strontium isotope fractionation can be explained by calcification in a largely open system at high precipitation rates comparable in magnitude to rates known from scleractinian reef corals this interpretation is in good agreement with the kinetic calcification model for planktic foraminifera by kisakurek et al 2011 which was based on calcium isotopes and elemental sr ca ratios

strontium 87 strontium 86 as a tracer of mineral weathering reactions and calcium sources in an alpine subalpine watershed loch vale colorado sr isotopic ratios of atmospheric deposition surface and subsurface water and geologic materials were measured in an alpine subalpine watershed to characterize weathering reactions and identify sources of dissolved ca in stream water previous studies have noted an excess of ca in stream water above that expected from stoichiometric weathering of the dominant bedrock minerals mixing calculations based on 87 sr 86 sr indicate that on an annual basis 26 67 of ca export in streams is atmospherically derived 23 61 is from weathering of plagioclase and the remainder is from weathering of calcite present in trace amounts in the bedrock a potential source of error when applying sr isotopes in catchment studies is determination of the 87 sr 86 sr of sr released by mineral weathering which is complicated by the wide range of mineral isotopic compositions particularly in older rocks and the variable rates at which the minerals weather in this study base flow stream chemistry was used to represent the 87 sr 86 sr of sr derived from mineral weathering because it effectively integrates the potentially variable isotopic composition of sr released by weathering in the alpine environment

high resolution record of the last interglacial glacial cycle in the nussloch loess palaeosol sequences upper rhine area germany the nussloch loess sequences were sampled at close intervals 10 cm and documented in respect of their stratigraphy palaeopedology sedimentology palynology malacology and geochemistry and were dated using radiocarbon and osl methods for each stratigraphic unit the results of both the eld studies and the analytical and geochronological data obtained cast light upon the response of the loessic environment to global climatic variations during the last cycle the basal soil complex underwent a pedosedimentary evolution similar to those of the bordering area complex luvisol greyzem steppe soila which re ects the classic progression towards increased continentality of the environment between the end of the eemian 5d and the beginning of the full glacial stage pleniglacial the lower pleniglacial corresponds to an initially very arid phase dominated by the accumulation of loess followed by the deposition of strati ed niveo eolian sands the middle pleniglacial complex ca 55 30 is clearly characterised by the inhibited loessic sedimentation it is primarily marked by two phases of stabilisation recorded in the form of weathered horizons cambisols which are separated by a rather thin layer corresponding to loessic sedimentation with tundra gleys this intermediate phase brings together organic silt deposits which record an interstadial dated at 32 33 ka c bp the thick loessic accumulations of the upper pleniglacial 10 m which clearly began to accumulate before the oxygen isotope stage ois 3 2 boundary show evidence of vulnerability to considerable uctuations in response to variations in wind dynamics and the intensity of de ation in the rhine valley finally a proposed correlation of loess palaeosol stratigraphies from germany belgium and france spanning the entire last interglacial glacial cycle is presented 2001 elsevier science ltd and inqua all rights reserved

rhizoliths in loess evidence for post sedimentary incorporation of root derived organic matter in terrestrial sediments as assessed from molecular proxies abstract loess palaeosol sequences are important terrestrial archives for studying quaternary climate change a major assumption for palaeoenvironmental reconstruction based on loess organic matter om is that it represents the signal of syn sedimentary incorporated plant biomass i e predominantly grass vegetation however recent studies on rhizoliths roots encrusted by secondary carbonate formed in loess reveal the possibility of post sedimentary penetration of loess palaeosol sequences by deeply rooting plants this likely led to incorporation of younger root derived om into surrounding loess potentially causing an overprinting of the initial plant derived signal of loess om to obtain information on the source vegetation of rhizoliths and surrounding loess om we examined rhizoliths and loess from nussloch sw germany using alkane and fatty acid fa molecular proxies moreover the lipid composition was compared in transects from rhizoliths via rhizosphere loess towards root free loess for a preliminary assessment towards quantifying the post sedimentary input of root derived om in loess loess om gave a combined signal from shoot and root biomass from grass vegetation confirming the assumption of deposition during glacial periods with scarce grass vegetation cover in contrast the lipid composition of rhizolith om reflected roots of woody vegetation indicating the post sedimentary character of rhizoliths stronger degradation of om together with a large content of microorganism derived fas in the former rhizosphere indicated rhizodeposition associated with high microbial activity in loess adjacent to rhizoliths at least up to a distance of 5 cm rhizosphere loess and reference loess at a distance of 50 70 cm showed a significantly different om composition thereby revealing the incorporation of considerable portions of root derived om into loess in the vicinity of roots further studies are necessary for an exact quantification of this potential overprint of the syn sedimentary loess om which might cause uncertainty in palaeoenvironmental studies

entrainment into mixed layers part ii a new closure abstract a new entrainment closure for convectively mixed boundary layers particularly those topped by stratocumulus clouds is developed and calibrated against results of large eddy simulations carried out by c h moeng the closure differs principally in two ways from those developed by j w deardorff s nicholls and others the prediction of interface buoyancy flux from its vertical integral is modified by a height weighting term this accounts for the greater entrainment produced by buoyancy flux near the cloud top as compared to that generated by surface heating the relationship between buoyancy flux at the top of a cloud layer and entrainment is reconsidered entrainment increases with the wetness of the cloud top which is evidently a function of cloud top liquid water content and the cloud top jumps in potential temperature and total water content this result is related to findings by s nicholls and j d turton though using a somewhat different approach and with different interpretatio

isotope fractionation during ca exchange on clay minerals in a marine environment abstract in order to interpret marine porewater profiles it is mandatory to understand the behavior of calcium ca and its isotopes during cation exchange in marine sediments it has been proposed that the exchange of adsorbed ca 2 for ammonium which is a product of organic matter decomposition results in the releases of light ca from clay minerals into the porewater teichert et al 2009 in order to investigate the effect of ammonium on ca isotope fractionation experiments with clay mineral separates illites montmorillonite kaolinite and natural marine sediments from the north atlantic integrated ocean drilling project site u1306a in artificial seawater were carried out at different temperatures 4 14 21 c and ammonium concentrations 100 140 180 mm the results of the adsorption experiments carried out in artificial seawater show that during adsorption of ca 2 the light ca isotopes are favored over the heavier ca isotopes this effect is most prominent for the illite samples 1000ln 0 82 to 1 15 and kaolinite sample 1000ln 1 23 to 2 76 whereas montmorillonite and the natural marine sediments show smaller degrees of fractionation from the fluid in the range of 0 46 to 0 06 determination of the desorbed ca 2 is based on the adsorbed ca 2 left on the exchanger and reveals that the desorbed ca 2 has a significantly different isotopic signature from the surrounding fluid in general the degree of ca isotope fractionation is dependent on the ammonium concentration and does not show significant influence of temperature modeling the ca 2 desorption induced by ammonium adsorption demonstrates that according to the prevailing mineralogy and porewater sediment ratio desorbed ca 2 has the potential to shift the porewater isotopy by up to 2 5 and needs to be considered when interpreting ca isotope porewater profiles

calcium isotopic fractionation during travertine deposition under different hydrodynamic conditions examples from baishuitai yunnan sw china abstract revealing the potential of ca isotopes in the research of travertine formation processes is the principal goal of this study to achieve this the hydrochemistry travertine precipitation rates and variations in ca isotopic compositions 44 40 ca of present day endogenic thermogenic travertine in two different hydrodynamic systems canal and pool are studied at baishuitai yunnan sw china in the canal where the travertine precipitation is faster 44 40 ca values of both solution and travertine show a downstream increase with ca isotopic fractionation 44 40 ca caco3 aq equal to 1 6 compared to the canal ca isotopic fractionation between travertine and aqueous ca 2 is smaller 44 40 ca caco3 aq 1 2 in the pools where travertine precipitation rates are lower the spatial variations in 44 40 ca values of solution and travertine are related to the amount of ca removed from the solution when 44 40 ca values of spring water remain stable in addition the results confirm the control of precipitation rates on ca isotopic fractionation between calcite and parent aqueous ca 2 using natural samples the observed negative correlation between 44 40 ca caco3 aq and travertine precipitation rates can be explained by the steady state kinetic surface reaction model proposed by depaolo 2011 with equilibrium and kinetic fractionation factors of eq 1 0000 0 0001 and f 0 9983 0 0002 respectively an important consequence of this study is that ca isotopes in travertine systems are good tools to have access to variations of 44 40 ca aq which are directly linked to the amount of precipitated ca this could then be useful for reconstructing past hydrodynamic conditions when applied to travertine core data

evidence for mass dependent isotopic fractionation of strontium in a glaciated granitic watershed abstract the stable isotope composition of strontium expressed as 88 86sr may provide important constraints on the global exogenic strontium cycle here we present 88 86sr values and 87sr 86sr ratios for granitoid rocks a 150 yr soil chronosequence formed from these rocks surface waters and plants in a small glaciated watershed in the central swiss alps incipient chemical weathering in this young system whether of inorganic or biological origin has no resolvable effect on the 87sr 86sr ratios and 88 86sr values of bulk soils which remain indistinguishable from bedrock in terms of sr isotopic composition although due in part to the chemical heterogeneity of the forefield the lack of a resolvable difference between soil and bedrock isotopic composition indicates that these soils have thus far witnessed minimal net loss of sr a low degree of chemical weathering is also implied by bulk soil chemistry the isotopic composition of sr in streamwater is more radiogenic than median soil reflecting the preferential weathering of biotite in the catchment streamwater 88 86sr values however are indistinguishable from bulk soil 88 86sr values implying that no resolvable fractionation of sr isotopes takes place during release to the weathering flux in the damma forefield analyses of plant tissue reveal that plants rhododendron and vaccinium preferentially assimilate the lighter isotopes of sr such that their 88 86sr values are significantly lower than those of the soils in which they grow additionally 88 86sr values of foliar and floral tissues are lower than those of roots contrary to observations for ca for which sr is often used as an analogue in weathering studies we suggest that processes that discriminate against sr in favour of ca due to the different nutritional requirement of plants for these two elements are responsible for the observed contrast

seasonal changes in the radiogenic and stable strontium isotopic composition of xijiang river water implications for chemical weathering seasonal changes in strontium sr isotopic systematics in large rivers can effectively track temporal variations in regional chemical weathering and help to better constrain the sr isotopic budget of global oceans however such records are scarce here we present a year long time series of both radiogenic and stable sr isotope measurements 87sr 86sr and 88sr from river water at guiping in the middle reaches of the xijiang river south china temporal changes in chemical weathering in the drainage basin were investigated by recording seasonal changes in the composition of both sr isotopes and major ions in the river water river water 87sr 86sr values range from 0 708487 to 0 710336 with most values being 0 7092 are generally accompanied by high rb sr ratios and low ph and 13c of dissolved inorganic carbo dic and occur during periods of large river flux this indicates that the contribution to the chemistry of river water from the weathering of silicate rocks is enhanced during rainy seasons seasonal variation in river water 88sr is large from 0 147 to 0 661 with higher 88sr values generally corresponding to higher 87sr 86sr values again low 88sr values 0 3 suggest a dominant contribution from the weathering of carbonate rocks whereas the high 88sr values may represent a contribution from intensive weathering of silicate rocks using the time series data we estimated the flux weighted averages of sr concentration 87sr 86sr and 88sr for the xijiang river to be 1 00 mol l 0 70960 and 0 38 respectively the sr concentration and 87sr 86sr results are close to previous estimates while the 88sr value is amongst the highest recorded for the large rivers of the world and is close to that of seawater our results indicate that large rivers draining through tropical sub tropical regions could play an important role in regulating the stable sr isotopic budget of global oceans

link between european and north atlantic abrupt climate changes over the last glaciation 1 sub millennial timescale climate variations correlated with those in the north atlantic area are identified in the loess sequence from nussloch germany exceptionally developed over the interval between about 38 000 and 18 000 years ago the dansgaard oeschger do events 8 to 2 as well as some less pronounced warming episodes recorded in the greenland ice have their counterpart in the nussloch loess stratigraphy and in the variations of the loess grain size index gsi the north atlantic heinrich events 3 and 2 are expressed at nussloch as maxima of the gsi record the similarity of the fine variations in the nussloch loess and the greenland ice records points to an intimate link of climate changes in western europe with those in the north atlantic

lateral and depth variation of loess organic matter overprint related to rhizoliths revealed by lipid molecular proxies and x ray tomography abstract terrestrial sediments like loess are well known for their paleoenvironmental significance although organic carbon contents are commonly very low loess and organic matter lom thereof is regarded as important terrestrial archive for vegetation and climate during deposition however the lom signal is prone to contamination by om of other age and origin than the synsedimentary vegetation e g by postsedimentary deep rooting plants we hypothesized that the influence of rhizosphere effects related to deep rooting plants varies with depth in quality quantity and distance to the former root the 13 m thick late pleistocene loess paleosol sequence at nussloch sw germany contains rhizoliths calcified roots of holocene age with the carbonatic encrustation leading to preservation of former root deposits rhizoliths allow for assessment of rhizosphere processes that occurred during the root s lifetime several horizontal transects comprising rhizoliths surrounding loess rhizoloess up to a distance of 11 cm from rhizoliths and root free reference loess from different depth intervals were analyzed for their carbon c alkane and fatty acid fa composition alkane proxies like carbon preference index cpi average chain length acl as well as n c27 n c31 and n c29 n c31 ratios indicated grass vegetation as origin of lom while rhizoliths derived from woody vegetation several lipid molecular proxies e g short chain long chain alkanes long chain alkane composition and long chain very long chain fa indicated the incorporation of considerable amounts of root and rhizomicrobial om the rhizosphere effect i e postsedimentary overprint of initial lom in the vicinity of roots was not restricted to few mm around the former root but notable to distances of at least 5 cm and possibly more this was confirmed by x ray tomography analyses enabling identification of small calcified root remains and non calcified root channels in the former rhizosphere which could not be identified under field conditions in depth intervals with high rhizolith frequency this entailed lateral overprint of large parts of loess which in depths of 1 95 and 3 2 m below present surface can cover the whole loess due to extension of the former rhizosphere of 5 cm regarding the high rhizolith frequency maximizing at 200 m 2 at 2 6 m depth at nussloch these findings raise the importance of deep rooting plants as potential source for significant postsedimentary overprint of loess paleosol sequences

reconstructing the response of c3 and c4 plants to decadal scale climate change during the late pleistocene in southern illinois using isotopic analyses of calcified rootlets abstract the 13c and 18o values of well preserved carbonate rhizoliths crs provide detailed insights into changes in the abundance of c3 and c4 plants in response to approximately decadal scale changes in growing season climate we performed stable isotope analyses on 35 40 crs sampled at 1 cm intervals from an 18 cm thick paleosol formed in southern illinois during wisconsin interstadial 2 minimum 13c values show little variation with depth whereas maximum values vary dramatically and average values show noticeable variability maximum 18o values vary less than the minimum 18o values these findings indicate that a diverse and stable c3 flora with a limited number of c4 grass species prevailed during this interval and suggest that the maximum growing season temperatures were relatively stable but minimum growing season temperatures varied considerably two general patterns characterize the relationships between the 13c and 18o values obtained from the 1 cm samples in some cases low 13c values correspond to low 18o values and high 13c values correspond to high 18o values suggesting that cooler growing season temperatures favored c3 and warmer growing season temperatures favored c4 plants in other cases low 13c values correspond to high 18o values likely suggesting that wetter growing season conditions were favorable to c3 plants the high density of well preserved crs in this paleosol provides a unique opportunity to study detailed ecological responses to high resolution variability in growing season climate