stepwise expansions of c4 biomass and enhanced seasonal precipitation and regional aridity during the quaternary on the southern chinese loess plateau abstract the expansion of c 4 plants is one of the most prominent vegetation changes in the global ecosystem during the cenozoic era although c 4 plant expansions in the latest miocene have been widely reported factors driving the expansions are still in debate and the details of vegetation changes during the quaternary have not been well studied here we present high resolution carbon isotope time series of both organic matter and bulk carbonates covering the past 2 58 ma derived from the loess soil successions on the southern chinese loess plateau the organic matter 13 c values indicate stepwise c 4 plant expansions initiated at 1 6 and at 0 43 ma respectively we conclude that such tectonic time scale c 4 plant expansions are controlled by enhanced seasonality of precipitation relatively more precipitation in the warm growing season as well as regional aridity and this long term fluctuation superimposes on the orbital scale variations of c 4 plants while the latter appears phase locked with cyclical changes of summer monsoon circulations

quantification of holocene asian monsoon rainfall from spatially separated cave records abstract a reconstruction of holocene rainfall is presented for southwest china an area prone to drought and flooding due to variability in the east asian monsoon the reconstruction is derived by comparing a new high resolution stalagmite 18 o record with an existing record from the same moisture transport pathway the new record is from heshang cave 30 27 n 110 25 e 294 m and shows no sign of kinetic or evaporative effects so can be reliably interpreted as a record of local rainfall composition and temperature heshang lies 600 km downwind from dongge cave which has a published high resolution 18 o record wang y j cheng h edwards r l he y q kong x g an z s wu j y kelly m j dykoski c a li x d 2005 the holocene asian monsoon links to solar changes and north atlantic climate science 308 854 857 by differencing co eval 18 o values for the two caves secondary controls on 18 o e g moisture source moisture transport non local rainfall temperature are circumvented and the resulting 18 o signal is controlled directly by the amount of rain falling between the two sites this is confirmed by comparison with rainfall data from the instrumental record which also allows a calibration of the 18 o proxy the calibrated 18 o record provides a quantitative history of rainfall in southwest china which demonstrates that rainfall was 8 higher than today during the holocene climatic optimum 6 ka but only 3 higher during the early holocene significant multi centennial variability also occurred with notable dry periods at 8 2 ka 4 8 4 1 ka 3 7 3 1 ka 1 4 1 0 ka and during the little ice age this holocene rainfall record provides a good target with which to test climate models the approach used here of combining stalagmite records from more than one location will also allow quantification of rainfall patterns for past times in other regions

a lacustrine gdgt temperature calibration from the scandinavian arctic to antarctic renewed potential for the application of gdgt paleothermometry in lakes quantitative climate reconstructions are fundamental to understand long term trends in natural climate variability and to test climate models used to predict future climate change recent advances

a 130 ka reconstruction of precipitation on the chinese loess plateau from organic carbon isotopes abstract we study the relationship between organic carbon isotopes 13ctoc in soil and mean annual precipitation map in the east asian monsoon area by combining the results of carbon isotope studies of plants c4 c3 ratios and precipitation in the modern ecosystem of the chinese loess plateau based on this relationship we estimate the amount of paleoprecipitation that has occurred in the southeastern part of the loess plateau since the last interglacial stage using the carbon isotopic compositions of the soil organic matter som the results show that the annual precipitation in that region was high during the interglacial stages with a maximum value of 850 mm and that it decreased during the last glacial stage to a minimum value of 350 mm we suggest that the use of organic carbon isotopic composition in paleosol sediments is a reliable method for reconstructing paleoprecipitation due to the clear relationships between soil 13ctoc c4 c3 abundance and precipitation in modern ecosystems

leaf wax lipids as paleovegetational and paleoenvironmental proxies for the chinese loess plateau over the last 170 kyr abstract high resolution records for long chain n alkane and n alkanol biomarkers have been obtained by extraction of sediments from the profiles of luochan 0 36 ka and xunyi 0 170 ka on the chinese loess plateau clp the two records are similar where they overlap over the last 36 ka at xunyi distributions of the n alkane and n alkanol homologues remain relatively constant over the full 170 kyr the n alkanes are characterized by high odd over even carbon number preference and predominance of the c31 n alkane whereas the n alkanols are dominated by even over odd carbon numbers and by the c28 n alkanol an alkane index a i c3l c29 c31 and an alkanol index alc i c30 c28 c30 are both positively related with magnetic susceptibility of the sediment with higher values during interglacials a lipid index l i averaging the normalized alkane and alkanol indices gives a measure of changing vegetation for palaeo environmental construction a further useful index is provided by the 13 c value of the most abundant n alkane c31 after adjustment for the calculated effect of the estimated atmospheric pco2 and precipitation the record of this index over the last 170 kyr which varies from 36 to 32 indicates that the vegetation on the clp has been mainly c3 plants and became even more so in the glacial periods especially mis 6 and 2 as the minor population of warm season grasses c4 favored in interglacial times declined when temperatures fell the lipid distributions and carbon isotope values are in general accord with the pollen and phytolith evidence recorded for the yuan areas of the clp in indicating steppe or meadow steppe vegetation with abundant cold season grasses c3 and some herbs bushes and trees especially in glacial times

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

climate variability over the last 2000 years inferred from glycerol dialkyl glycerol tetraethers gdgts in alkaline nalin lake of inner mongolia china nalin lake from western inner mongolia of china is a shallow oxbow lake with a laminated sedimentary record the distributions of glycerol dialkyl glycerol tetraethers in lacustrine sediment core collected in nalin lake in june 2011 were examined in combination with other paleoclimate proxies the cyclization index of branched tetraethers cbts inferred ph values changed primarily between 7 67 and 8 63 these changes were synchronous with those from the actual measurement and previous studies the newly proposed cbt methylation index of branched tetraethers mbts palaeothermometer was also applied to produce a mean annual air temperature record for nalin lake spanning circa the last 2000 years over much of the record temperature fluctuated from 2 76 to 7 61 c with a mean value of 4 76 c the proposed cbt mbt based temperatures revealed a strong similarity to the local records both documenting the moderate medieval warm period from 600 to 1200 a d 1400 800 cal year bp and a cooling anomaly little ice age around 16th century the cbt mbt temperature patterns seemed to follow variations in the historical and northern hemisphere records of the mean annual air temperature these suggested that the signals were produced during this period identification of high alkalinity in association with the decreased fluvial input by multiple indices was consistent with the previous observations due to the cutoff of yellow river channel therefore cbt mbt temperature records of lake sediment core can potentially be a useful tool in reconstructing past variations of alkaline lacustrine climate

paleoaltimetry potentiality of branched gdgts from southern tibet paleoaltimetric reconstructions of the southern tibetan plateau tp are crucial to understand the processes and mechanisms concomitant with the tectonic collision of the indian and eurasian continental plates we measured the branched glycerol dialkyl glycerol tetraether brgdgt indices from 88 surface soils from the southern tp and found that alkaline soils exhibited lower mbt and mbt cbt derived mat mean annual temperature while mbt cbt derived mat exhibited a strong correlation with altitude r 2 0 84 n 63 for all of the localities with neutral and acidic soils differently we found that mbt5me derived mat exhibited a strong relation with altitude even though a mixture of alkaline samples r 2 0 72 n 83 as a result two regional calibrations were developed including a neutral and acidic soil calibration based on mbt cbt mat and a calibration suitable for both acidic and alkaline soils based on mbt5me mat for the southern tp based on this new soil calibration data set and a recent global soil calibration data set founded on mbt5me we calculated paleo mat of approximate to 9 491 15 to 10 381 47 degrees c at approximate to 15 ma respectively for the namling basin applying these soil calibrations the paleoaltitudes of the namling basin can be calculated to have been between 4 360 41 km above sea level asl and 4 430 36 km asl at approximate to 15 ma respectively similar to the paleoaltitudes of approximate to 4 7 5 4 km asl at approximate to 15 ma inferred from the floral physiognomy of namling basin fossils and stable isotopes these findings would suggest the applicability of mbt cbt and or mbt5me indices as paleotopographic and paleotemperature proxies on the southern tp

phytoliths as quantitative indicators for the reconstruction of past environmental conditions in china ii palaeoenvironmental reconstruction in the loess plateau abstract quantitative reconstruction of the climatic history of the chinese loess plateau is important for understanding present and past environment and climate changes in the northern hemisphere here we reconstructed mean annual temperature mat and mean annual precipitation map trends during the last 136 ka based on the analysis of phytoliths from the weinan loess section 34 24 n 109 30 e near the southern part of the loess plateau in northern china the reconstructions have been carried out using a chinese phytolith climate calibration model based on weighted averaging partial least squares regression a series of cold and dry events as indicated by the reconstructed mat and map are documented in the loess during the last glacial periods which can be temporally correlated with the north atlantic heinrich events our mat and map estimations show that the coldest and or driest period occurred at the upper part of l2 unit late mis 6 where mat dropped to ca 4 4 c and map to ca 100 mm two other prominent cold dry periods occurred at lower ll 5 ca 77 62 ka and l1 1 ca 23 10 5 ka where the mat and map decreased to about 6 1 6 5 c and 150 370 mm respectively ca 6 6 6 2 c and 400 200 mm lower than today however the highest mat average 14 6 c max 18 1 c and map average 757 mm max 1000 mm occurred at sl interval mis 5 during the interstadial of l1 4 l1 2 mis 3 and during the holocene warm wet period the mat was about 1 2 c and map 100 150 mm higher than today in the weinan region the well dated mat and map reconstructions from the chinese loess plateau presented in this paper are the first quantitatively reconstructed proxy record of climatic changes at the glacial interglacial timescale that is based on phytolith data this study also reveals a causal link between climatic instability in the atlantic ocean and climate variability in the chinese loess plateau

the importance of solar insolation on the temperature variations for the past 110 kyr on the chinese loess plateau abstract the late quaternary temperature history on the chinese loess plateau clp is little known due to the absence of suitable paleothermometers here we present a quantitative temperature record for the last 110 kyr from lantian county southern clp based on the distributions of bacterial tetraethers lantian loess temperature variations display significant correlation with the northern hemisphere insolation 35 n as well as the cave monsoon records at the precession band we attribute such correlation to both the latent heat release from the east asian summer monsoon and the direct influence of sun s sensible heat over the semi arid landscape the long term cooling during the marine isotope stage mis 3 and the modest temperature drop of 5 c from 79 to 65 ka are best explained by interactions among multiple climate forcings including insolation atmospheric co 2 concentration global ice volume and regional glacier activities the cold and modestly wet climate during mis 3 may have promoted maximum regional glacial advances whereas the minimal temperature during local lgm reduced moisture transfer and led to glacial recession the unusually early deglacial warming at 22 5 ka highlights the importance of regional climate records to decipher the complex continental climate dynamics

multiple expansions of c4 plant biomass in east asia since 7 ma coupled with strengthened monsoon circulation the expansion of plants using the c4 photosynthetic pathway is one of the most prominent changes in the global ecosystem during the cenozoic era a significant late miocene expansion is well documented however the existence and cause of subsequent expansions are still not clear owing in part to the lack of long continuous climate vegetation records here we present two high resolution carbon isotope time series covering the past 7 m y derived from eolian deposits on the chinese loess plateau the data indicate three intervals of significant c4 plant expansions within the semiarid monsoonal region of east asia ca 2 9 2 7 ma 1 3 0 9 ma and 0 6 ma present these expansions covary with strengthened east asian summer monsoon circulation we conclude that in east asia large scale late miocene c4 c3 vegetation changes in semiarid areas have been primarily driven by warm seasonal precipitation and temperature variations associated with changes in monsoon circulation

a novel proxy for terrestrial organic matter in sediments based on branched and isoprenoid tetraether lipids we propose a novel tracer for terrestrial organic carbon in sediments based on the analysis of tetraether lipids using high performance liquid chromatography mass spectrometry hplc ms analysis of terrestrial soil and peats shows that branched tetraether lipids are predominant in terrestrial environments in contrast to crenarchaeol the characteristic membrane lipid of non thermophilic crenarchaeota which is especially abundant in the marine and lacustrine environment based on these findings an index was developed the so called branched and isoprenoid tetraether bit index based on the relative abundance of terrestrially derived tetraether lipids versus crenarchaeol this bit index was applied to surface sediments from the angola basin where it was shown to trace the outflow of the congo river furthermore analyses of particulate organic matter from the north sea showed relatively higher bit indices in water column particulate organic matter near large river inputs a survey of globally distributed marine and lacustrine surface sediments shows that the bit index in these environments correlates with the relative fluvial input of terrestrial organic material making this index generally applicable the new proxy allows the rapid assessment of the fluvial input of terrestrial organic material in immature sediments up to 100 ma old

a 15 ka ph record from an alpine lake in north china derived from the cyclization ratio index of aquatic brgdgts and its paleoclimatic significance abstract a well dated sediment core from an alpine lake in north china gonghai lake was used for analysis of branched glycerol dialkyl glycerol tetraether lipids brgdgts based on the cyclization ratio index cbt of the brgdgts and using different terrestrial and lacustrine cbt ph empirical relationships the reconstructed ph records over the past ca 15 ka exhibited similar trends of variation although the absolute ph values were different in order to better understand the reconstructed ph record samples of surface soils from the dust source area and the catchment of gonghai lake as well as surface sediments from the lake were collected for instrumental ph measurements and modern brgdgt analysis the instrumental ph results demonstrated that the surface soils from the dust source area were alkaline while those from the catchment of gonghai lake were acidic in addition the instrumental ph results for the surface sediments from the lake were slightly alkaline and the corresponding ph values were intermediate between those of the two surface soil source groups this may reflect the effect of the input of material from different sources on the sedimentary ph record however the results from modern brgdgts in some of the surface soils and surface sediment samples demonstrate that brgdgts in the core sediments from gonghai lake are predominantly of aquatic origin therefore the cbt derived ph record over the past ca 15 ka from the lake can be interpreted as a record of the lake water ph history which is consistent with the carbonate content record from a parallel core from the same lake in addition using the modern lacustrine calibration the cbt derived ph values for surface sediments of gonghai lake are consistent with instrumental modern lake water ph values for the lake further comparison indicates that the lake water ph is controlled mainly by the degree of humidity of the local climate which is closely related to the intensity of the east asian summer monsoon easm therefore the ph record can be used as an indicator of easm intensity our results demonstrate that on the basis of careful analysis of its origins the cbt index of aquatic brgdgts can be used for lake water ph reconstruction and subsequent paleoclimate reconstruction and that in north china the lake water ph is controlled mainly by the degree of humidity of the local climate

environmental controls on branched tetraether lipid distributions in tropical east african lake sediments abstract quantifying past continental temperature changes is an important aspect of paleoclimate research as it allows us to constrain the amplitude of natural variability test predictive climate models and provide a proper context for changes that may arise in response to anthropogenically induced climate change the recently developed biomarker based methylation index of branched tetraethers cyclization ratio of branched tetraethers mbt cbt proxy shows potential as a new method for continental temperature reconstruction but thus far it has only been applied successfully in ocean margin sediments to assess whether this proxy is also applicable to the sedimentary record in tropical lacustrine systems we investigated the distribution of branched glycerol dialkyl glycerol tetraethers gdgts in recently deposited sediments from 46 lakes in tropical east africa these lakes span a substantial range in surface elevation 770 4500 m above sea level and thus also a wide gradient of mean annual temperature we find that saline lakes excepted branched gdgts are universally abundant in the lakes investigated and can be used to predict mean annual air temperature maat with a high degree of accuracy however the existing global mbt cbt calibration for maat based on soils predicts inaccurate temperatures when applied to our african lake dataset this observation together with the fact that surface water ph and to lesser extent lake depth appear to influence the distribution of branched gdgts among sites leads us to conclude that in situ production of branched gdgts in lakes is likely the robust relationship between branched gdgt distribution and the temperature and ph of african freshwater lakes makes these compounds suitable for paleoenvironmental reconstruction however we urge caution in using branched gdgts in lake sediments to infer past temperatures unless their exact origin can be determined

coupled thermal and hydrological evolution of tropical africa over the last deglaciation we analyzed the distribution of branched tetraether membrane lipids derived from soil bacteria in a marine sediment record that was recovered close to the congo river outflow and the results enabled us to reconstruct large scale continental temperature changes in tropical africa that span the past 25 000 years tropical african temperatures gradually increased from 21 to 25 c over the last deglaciation which is a larger warming than estimated for the tropical atlantic ocean a direct comparison with sea surface temperature estimates from the same core revealed that the land sea temperature difference was through the thermal pressure gradient an important control on central african precipitation patterns

precession driven changes in terrestrial organic matter input to the eastern mediterranean leading up to the messinian salinity crisis abstract eastern mediterranean sediments over the past 12 myr commonly show strongly developed precessional cyclicity thought to be a biogeochemical response to insolation driven freshwater input from run off the mediterranean s dominant freshwater source today and in the past is the nile which is fed by north african monsoon rain other smaller circum mediterranean rivers also contribute to mediterranean hydrology crucially run off through all of these systems appears to vary with precession but there is no direct evidence linking individual water sources to the biogeochemical response recorded in mediterranean sediments consequently it is not clear whether the north african monsoon is entirely responsible for the mediterranean s sedimentary cyclicity or whether other precessional signals such as atlantic storm precipitation drive it organic matter in sediments derives from both marine and terrestrial sources and biomarker analysis can be used to discriminate between the two thereby providing insight into sedimentary and ecological processes we analysed a wide range of lipids from the late miocene 6 6 5 9 ma pissouri section southern cyprus and reconstructed the vegetation supplied to this region by measuring the carbon isotopes of the terrestrial component to identify its geographic source bit branched isoprenoidal tetraether indices reflect changes in the relative abundance of marine vs terrestrial soil organic matter inputs and with the exception of records from the last deglaciation this work is the first application of the bit approach to the reconstruction of orbital impacts on sedimentological processes bit indices show that the organic matter supplied to cyprus changed over the course of each precession cycle and was dominantly terrestrial during insolation maxima when north african run off was enhanced the 13 c values from these intervals are compatible with tropical north african vegetation however the 13 c record indicates that during insolation minima organic material supplied to southern cyprus derives from a more arid source region this is likely to have been aeolian transported organic matter from the anatolian plateau demonstrating that even in mediterranean sedimentary systems influenced by nile run off there is more than one independent precessional organic matter contribution to the sedimentary cyclicity pissouri s organic geochemistry also illustrates a long term trend towards more saline mediterranean conditions during the 600 kyr leading up to the messinian salinity crisis

tropical and high latitude forcing of enhanced megadroughts in northern china during the last four terminations abstract understanding the origin and evolutionary history of drought events is of great significance providing critical insight into future hydrological conditions under the changing climate due to the scarcity of drought proxies from northern china the occurrence and underlying mechanisms of the drought events remains enigmatic on longer timescales here we utilize microbial lipid proxies to reconstruct significant drought events over the last four ice age terminations in the southernmost section weinan section of the chinese loess plateau the abundance of archaeal isoprenoid gdgts glycerol dialkyl glycerol tetraethers relative to bacterial branched gdgts measured by ri b and bit indices is diagnostic of enhanced drought conditions the ri b and bit indices are stable and low high throughout most of the loess section spanning the last 350 thousand years but they do exhibit sharp transient peaks valleys during the intervals associated with the four ice age terminations and especially terminations ii and iv these enhanced drought events are non intuitively associated with a significant decrease in the relative abundance of c4 plants inferred by a decrease in the carbon isotope composition of bulk organic matter although the microbial records show some consistency with the weinan grain size profiles indicative of eastern asian winter monsoon variability they also show some apparent difference in fact some features of the microbial records exhibit strong similarities with marine sediment planktonic foraminiferal 13c records from the western pacific warm pool which reflect enso like changes during glacial terminations therefore enhanced droughts immediately before the interglacial warming in northern china could be explained at least in part by teleconnections in tropical ocean atmosphere circulation via shifts in the intertropical convergence zone itcz and associated jet stream over the asian continent according to our microbial biomarker data these enhanced megadroughts are apparently different both in terms of severity and causal mechanism from the more commonly discussed dry conditions observed during glacial periods

environmental fluctuation impacted the evolution of early pleistocene non human primates biomarker and geochemical evidence from mohui cave bubing guangxi southern china abstract quaternary climate variability profoundly impacting the evolution and distribution of plants and animals across the globe has been reconstructed by many sediment archives here we track past changes of temperature rainfall and plant type by using the n alkane and glycerol dialkyl glycerol tetraethers gdgts as well as weathering and pedogenesis by mineralogical and geochemical proxies from a 250 cm deep soil sediment profile from the early pleistocene deposits in mohui cave southern china indices for weathering intensity such as mineral composition quartz feldspar and calcite major element proxies ti na al na al mg ti mg ciw pia cpa cia trace element proxies ba sr and rb sr and biomarker proxies oep lsr and cpi show similar secular trends revealing a three stage historical accumulation the high long chain n alkane ratios c31 c29 and c31 c33 c27 c29 indicate that the vegetation in the region had increases in percentage of woody plants and decreases in herbs during periods of relatively lower temperature and less precipitation which evidenced from gdgts consistent with a weak weathering process influenced by summer monsoon strength further we compared the distribution of these plant types with the taxonomic variation in the vertebrate paleontological fossils excavated from the same profile in mohui cave the distribution of lufengpithecus appears in only one interval but gigantopithecus blacki appears throughout the profile despite an environment that experienced transitional stages from grassland to woodland in relatively cooler and drier conditions we infer that in face of these climatic changes lufengpithecus may have preferred to emigrate from the region while gigantopithecus blacki may have stayed given that it was limited to staying in its core area

sources and distributions of tetraether lipids in surface sediments across a large river dominated continental margin glycerol dialkyl glycerol tetraether gdgt based proxies are increasingly used in modern carbon cycling and palaeoenvironmental investigations it is therefore crucial to examine the robustness sources transport and degradation of all gdgt based proxies in continental margins where sedimentation rates and extent of carbon cycling are high we have analyzed the distributions of gdgts in surface sediments from the lower yangtze river and east china sea ecs shelf the results revealed multiple sources and complex shelf processes that govern the distributions the isoprenoid gdgt inferred sea surface temperatures ssts are robust and reflect the satellite derived annual mean ssts on the shallow ecs shelf confirming an origin from surface water column dwelling crenarchaeota the input from methanogen sourced isoprenoid gdgts is significant in the river surface sediments but they are almost absent from the ecs shelf branched gdgts are also abundant in the river sediments but ca 95 are degraded in the yangtze estuary a much greater extent than observed for other terrigenous organic matter om proxies there is also evidence for production of branched gdgts in the oxic ecs shelf water column and the anoxic sediments waters of the lower yangtze river as a result branched gdgt based proxies in the lower river and ecs surface sediments do not reflect the catchment environmental conditions the effective degradation in the estuary and widespread aquatic contributions of branched gdgts improves our understanding of how to use branched gdgt based proxies in marginal seas

major changes in glacial and holocene terrestrial temperatures and sources of organic carbon recorded in the amazon fan by tetraether lipids the amazon basin is a major component of the global carbon and hydrological cycles a significant natural source of methane and home to remarkable biodiversity and endemism reconstructing past climate changes in the amazon basin is important for a better understanding of the effect of such changes on these critical functions of the basin using a novel biomarker proxy based on the membrane lipids of soil bacteria with a new regional calibration we present a reconstruction of changes in mean annual air temperatures for the amazon catchment during the last 37 kyr b p biomarkers were extracted from ocean drilling program sediment core odp942 recovered from the amazon fan the amazon fan is a major depository for terrestrial sediments with the advantage that the terrestrial material captured reflects a regional integration of the whole river catchment the reconstructed tropical amazonian temperatures were similar to 5 degrees c cooler at the last glacial maximum similar to 21 degrees c compared to modern values similar to 26 degrees c this is in agreement with previous estimates of tropical continental temperatures in the tropical amazon basin and tropical africa during the last glacial maximum moreover we also illustrate how the soil bacterial membrane lipid record reveals major changes in basin dynamics and sediment provenance during the glacial holocene transition impacting the biomarker reconstructions from similar to 11 kyr onward

distributions of branched gdgts in soils and lake sediments from western uganda implications for a lacustrine paleothermometer bacterially produced branched glycerol dialkyl glycerol tetraethers gdgts are ubiquitous in soils and lake sediments and can potentially be used to reconstruct past temperatures in lakes however it is still unclear if these compounds are derived from eroded soils or if they are produced in situ to better understand environmental controls on the distributions of these compounds and the sources of branched gdgts to lake sediments we compare branched gdgt distributions and concentrations in lake sediments and catchment soils within a 3600 m altitudinal transect in western uganda reconstructed mean annual air temperature maat determined from the degree of methylation mbt and cyclisation cbt of branched gdgts in soils decreases with increasing altitude as is expected from the air temperature gradient in our transect however we observe significant offsets between observed and reconstructed temperatures in soils from wet high elevation soils but not in most dry low elevation soils branched gdgt distributions differ significantly between lake sediments and soils at all elevations with greater differences at low elevations than at high elevations these data support previous hypotheses that branched gdgts are produced in situ in lakes and suggest that the abundance of water in soil environments may play a role in controlling the distribution of branched gdgts while branched gdgts in lacustrine sediments can be used to reconstruct temporal temperature variations in lakes we urge caution in utilizing this proxy in lacustrine systems with high soil loadings especially if there is evidence of changing clastic fluxes through time

constraints on the application of the mbt cbt palaeothermometer at high latitude environments svalbard norway abstract branched glycerol dialkyl glycerol tetraethers gdgts are membrane lipids of unknown bacteria that are ubiquitous in soil and peat two indices based on the distribution of these lipids in soils the cyclization of branched tetraethers cbt and the methylation of branched tetraethers mbt indices have been shown to correlate with soil ph and mean annual air temperature mat and soil ph respectively and can be used to reconstruct mat in palaeoenvironments to verify the extent to which branched gdgts in marine sediments reflect the distribution pattern on land and whether these proxies are applicable for palaeoclimate reconstruction in high latitude environments with a mat of

decoupled warming and monsoon precipitation in east asia over the last deglaciation our understanding of the continental climate development in east asia is mainly based on loess paleosol sequences and summer monsoon precipitation reconstructions based on oxygen isotopes delta o 18 of stalagmites from several chinese caves based on these records it is thought that east asian summer monsoon easm precipitation generally follows northern hemisphere nh summer insolation however not much is known about the magnitude and timing of deglacial warming on the east asian continent in this study we reconstruct continental air temperatures for central china covering the last 34 000 yr based on the distribution of fossil branched tetraether membrane lipids of soil bacteria in a loess paleosol sequence from the mangshan loess plateau the results indicate that air temperature varied in phase with nh summer insolation and that the onset of deglacial warming at similar to 19 kyr bp is parallel in timing with other continental records from e g antarctica southern africa and south america the air temperature increased from is c at the onset of the warming to a maximum of 27 degrees c in the early holocene similar to 12 kyr bp in agreement with the temperature increase inferred from e g pollen and phytolith data and permafrost limits in central china comparison of the tetraether membrane lipid derived temperature record with loess paleosol proxy records and stalagmite 5180 records shows that the strengthening of easm precipitation lagged that of deglacial warming by ca 3 kyr moreover intense soil formation in the loess deposits caused by substantial increases in summer monsoon precipitation only started around 12 kyr bp ca 7 kyr lag our results thus show that the intensification of easm precipitation unambiguously lagged deglacial warming and nh summer insolation and may contribute to a better understanding of the mechanisms controlling ice age terminations

correlations between microbial tetraether lipids and environmental variables in chinese soils optimizing the paleo reconstructions in semi arid and arid regions the bacterial membrane lipid based continental paleothermometer the mbt cbt or mbt cbt proxy methylation index of branched tetraethers cyclization of branched tetraethers results in a large temperature deviation when applied in semiarid and arid regions here we propose new calibration models based on the investigation of 100 surface soils across a large climatic gradient with a particular focus on semiarid and arid regions of china and apply them to a loess paleosol sequence as reported elsewhere mbt values exhibit a much higher correlation with maat than with summer temperature suggesting a minimal seasonality bias however mbt is apparently insensitive to temperature 20 degrees c additional complexities are apparent in alkaline and arid soils which are characterized by different relationships to climatic parameters than those in the complete chinese or global dataset for example mbt and cbt indices exhibit a negative correlation in alkaline and arid soils in contrast to their positive correlation in acid soils moreover the cyclization ratio of bgdgts cbt previously defined as a proxy for soil ph is apparently primarily controlled by maat in these alkaline soils thus we propose 1 a local chinese calibration of the mbt cbt proxy and 2 an alternative temperature proxy for use in semiarid and arid regions based on the fractional abundances of bgdgts the latter has a markedly higher determination factor and lower root mean square error in alkaline soils than the chinese local calibration and is suggested to be preferred for paleotemperature reconstruction in chinese loess paleosol sequences these new bgdgt proxies have been applied to the weinan holocene paleosol section of the chinese loess plateau clp the fractional abundance calibration when applied in the weinan holocene paleosol produces a total holocene temperature variation of 5 2 degrees c and a temperature for the topmost sample that is consistent with the modern temperature previously we showed that the ratio of archaeal isoprenoid gdgts to bgdgts r i b increases at map 0 5 in the clp suggest the presence of enhanced aridity in the late holocene in north china in combination the high r i b ratios 0 5 and the associated low mbt values 0 4 reveal the co occurrence of dry and cold events especially in the latest holocene in the loess paleosol sequences in clp and probably also in cold and arid regions outside of clp c 2013 elsevier ltd all rights reserved

lower temperature as the main cause of c4 plant declines during the glacial periods on the chinese loess plateau abstract the distribution of c3 and c4 plants changed in regionally contrasting ways during the last glacial period c4 plant expansion in low latitude africa and america coincided with c4 plant decreases in mesoamerica and the us great plains this c4 plant expansion has been attributed to lower pco2 and increased aridity and the decline in c4 plants is believed to have been caused by increased winter precipitation and lower temperatures however it is still difficult to generalize whether pco2 temperature or aridity was mainly responsible for c3 vs c4 vegetation changes during glacial periods paleoclimate conditions on the chinese loess plateau clp offer opportunities to further evaluate the role of temperature in the c3 vs c4 competition detailed climate records have shown that the clp region was drier and colder during glacial periods with aridity favoring c4 expansion and lower temperatures favoring c3 expansion here we present two high resolution compound specific carbon isotope records of n alkanes from the clp as vegetation biomarkers to estimate the relative abundance of c4 plants during the last two glacial interglacial transitions more negative 13c values during the glacial periods from two clp sites clearly show that in contrast with low latitude sites c4 plants declined this decrease in c4 abundance was caused by lower temperature despite the lower pco2 and increased aridity on the clp during glacial time

branched and isoprenoid tetraether bit index traces water content along two marsh soil transects surrounding lake qinghai implications for paleo humidity variation abstract the bit index represents the relative abundances of branched glycerol dialkyl glycerol tetraethers bgdgts and the isoprenoid gdgt crenarchaeol while bgdgts are produced mainly by soil anaerobic bacteria crenarchaeol is known to be a biomarker for aerobic ammonia oxidation by chemolithoautotrophic thaumarchaeota particularly in the open ocean or lakes thus the index in marine and lacustrine settings has been widely used as a proxy for soil input here we have investigated gdgt distribution along two transects extending from the lake shore marsh to upland soils on the ne qinghai tibetan plateau the results show that soil water content swc correlates positively with concentration of bgdgts and negatively with concentration of crenarchaeol consequently there is a significant positive correlation between swc and the bit index our study highlights a new potential application of bit as a humidity proxy in loess soil and peat deposits

fidelity of plant wax molecular and carbon isotope ratios in a holocene paleosol sequence from the chinese loess plateau abstract loess paleosol sequences from the chinese loess plateau clp provide important archives for paleoclimate reconstruction in the quaternary lipid biomarkers from the clp have been shown to be useful as molecular paleoclimate proxies here we report a holocene record of n alkane ratios and compound specific carbon isotope compositions from the weinan section on the southern margin of the clp throughout the latest deglaciation l 1 1 and holocene s 0 layers the average chain length carbon preference index cpi relative abundance of low molecular weight to high molecular weight n alkanes and the 13 c values of n c 29 and n c 31 alkanes varied closely with the changes in paleotemperature and aridity as recorded by tetraether lipids from the same soil samples our results are consistent with the expectation that the clp c 4 c 3 plant ratio is sensitive to monsoon intensity furthermore the carbon isotope offset between n c 29 and n c 31 alkanes 13 c 29 31 correlated closely with the paleoclimate record existing data for c 4 and c 3 herb plants do not support the idea that the close relation between 13 c 29 31 and paleoclimate results from the isotopic difference between c 4 and c 3 plants instead it is likely that it arises from climate effects on vegetation dynamics although more work is required to confirm this deduction it appears that the 13 c 29 31 has potential to be considered a novel paleoclimate proxy in loess paleosol sequences and similar settings

towards an orbital time scale for chinese loess deposits abstract in this study we analyzed the grain size of the baoji loess soil sequence at 10 cm intervals results show that grain size variations are very sensitive to loess soil alternations with loess units being much coarser than soils such a change in loess soil grains is interpreted as the result of the glacial interglacial cyclic variations in the intensity of the winter monsoon winds out of siberia the grain size record is thus employed as a proxy indicator of the winter monsoon circulation and tuned to the orbital records calculated recently by berger and loutre 1991 under the control of major magnetic reversals the tuning is independent of any correlation with 18o signals in the deep sea sediments the resulting grain size time scale is tightly constrained as suggested by the following facts 1 the filtered obliquity and precession components from the grain size data on the orbital time scale closely match the theoretical orbital records 2 ages of the major magnetic reversals estimated from the grain size time scale are in good agreement with the k ar dated ages 3 there is close coherence between the baoji grain size time series and the orbital variations at the orbital frequency bands over the entire 0 2 5 ma period and 4 the grain size record on the orbital time scale shows a close similarity to the orbitally tuned dsdp site 607 and odp site 677 18o records examination of time dependent characteristics of the grain size record suggests that there are two major shifts of dominant periodicities in the long term monsoonal cycles one occurring at about 0 8 ma bp and the other around 1 7 ma bp

simulation of the last glacial maximum climate over east asia with a regional climate model nested in a general circulation model abstract the east asian climate at the last glacial maximum lgm 21 000 years b p has been simulated using a regional climate model regcm2 nested in an atmospheric general circulation model of the institute of atmospheric physics iap agcm boundary conditions for the lgm simulations are consistent with the paleoclimate modelling intercomparison project pmip the results show that the nested regional model reproduces well the colder lgm climates over east asia the simulated annual mean surface temperature is 2 c 4 c colder than the present over the east asian continent with the coldest anomaly of about 8 c in the vicinity of current coastal areas where land is exposed due to lowering sea level at the lgm the precipitation changes are complex with general features of drier conditions over eastern china and its neighborhood and wetter conditions over western china than the present compared with the driving iap agcm the regcm2 results display better agreement with geological reconstructions over east asia especially in the mideastern and southern china the simulated warming changes by the iap agcm disagree with cooling in paleodata whereas the regcm2 reproduces realistic cooler lgm climate thus the current work proves that the high resolution regcm2 can capture additional regional details in the lgm simulation produced by improved representation of topography and physics

application of bacterial glycerol dialkyl glycerol tetraethers gdgts to develop modern and past temperature estimates from new zealand lakes abstract branched isoalkyl glycerol dialkyl glycerol tetraethers gdgts of bacterial origin have been found in high abundance in both modern and glacial sediments of new zealand south island freshwater lakes covering a wide range of altitude 101 2000 m like isoprenoid gdgts of archaeal origin they provide excellent potential for temperature assessment for this study their distribution patterns mbt methylation ratio and cbt cyclisation ratio of branched gdgts have been successfully used to develop an initial temperature calibration for the study area and to provide preliminary palaeo environmental interpretations mbt data from modern lake sediments correlate well with measured annual air temperature r2 0 74 enabling a regional calibration for reconstructing palaeotemperatures for fossil samples mbt derived palaeotemperatures for alpine lake calibrated against mean annual temperature were determined for the last glacial during an early cold phase between 29 000 and 26 000 years bp and for later less cold phases between 23 000 and 18 000 years bp compared with the modern temperature regime the mbt data indicate a decrease of ca 5 6 and 2 8 c respectively during this time modern and past mbt derived temperatures correlate with chironomid based temperature reconstructions in the area archaeal gdgts commonly used for the tex86 index are abundant in fossil sediments alpine lake but scarce in modern sediments hindering a new local calibration for this palaeotemperature proxy

sources of organic matter in changjiang yangtze river bed sediments preliminary insights from organic geochemical proxies insight into the content and composition of organic carbon oc in river systems contributes to our understanding of the global carbon cycle the changjiang yangtze river plays a significant role in global carbon and hydrological cycles as it is an important supplier of sediment nutrients and oc to the east china sea to provide a preliminary insight into the source of oc transported by the changjiang we analyzed bulk grain size organic carbon content 13c and molecular lignin phenols branched and isoprenoid gdgts characteristics of organic matter in bed sediments at eight locations along the river the 13c values and lignin phenol composition indicate that the oc originates from a mixture of primarily soils and plants comparison between branched gdgt br gdgt distributions in riverbed sediments and those in the different soil types in the drainage basin indicate that the br gdgt signal in the upper reaches is largely derived from soils from the qinghai tibet plateau downstream changes in br gdgt distributions can be linked to subsequent input of local soil material the observed variation in br gdgt composition along the river implies that a portion of the oc may be oxidized or replaced by the local input during transit although the relationship between 13c and lignin phenol composition indicates that the contribution of phytoplankton is limited comparison of gdgt ratios gdgt 0 crenarchaeol iso gdgts br gdgts bit index for the sediments and surrounding soils indicates that at least part of the iso gdgts has an aquatic origin overall the downstream evolution of br gdgts in the changjiang implies that their use as paleoclimate proxy in downcore applications will likely yield a local rather than a basin integrated continental climate record

applicability and calibration of the tex86 paleothermometer in lakes abstract we have conducted a global survey of archaeal glycerol dialkyl glycerol tetraether gdgt lipids in lake sediments in order to develop the tex86 paleotemperature proxy for application in continental systems surface sediments of 46 globally distributed lakes were analyzed for gdgt but isoprenoid gdgt derived from aquatic crenarchaeota were only unambiguously detected in 20 of the 46 lakes analyzed aquatic crenarchaeotal gdgt were detected mainly in sediments from large lakes 4000 km2 and hydrothermal or volcanic lakes suggesting that in some mostly smaller lakes either aquatic crenarchaeota are present at low abundance resulting in sedimentary lipids below levels of detection or they are absent branched gdgt thought to be derived primarily from soil bacteria were identified in all lake sediments analyzed correlation of the tex86 in those lakes with sufficient amounts of putative crenarchaeotal gdgt with annual mean lake temperature is reasonably good r2 0 68 n 20 in order to reduce the influence of soil derived isoprenoid gdgt on the tex86 lake temperatures we have applied a filter based on relative soil derived inputs as determined by the bit branched and isoprenoid tetraether index which results in a calibration relationship with r2 0 86 n 12 and an estimated temperature error of 3 6 c our results suggest that the tex86 should be applied only in lakes with sufficient production of gdgt by aquatic crenarchaeota relative to isoprenoid gdgt derived from soil in the watershed or other aquatic sources

calibration and application of the branched gdgt temperature proxy on east african lake sediments branched glycerol dialkyl glycerol tetraethers brgdgts are a novel proxy for mean annual air temperature maat and have the potential to be broadly applicable to climate reconstruction using lacustrine sediments several calibrations have been put forth relating brgdgt distributions to maat using a variety of linear regressions including the methylation mbt and cyclization cbt indices of brgdgts the relative abundances of the major non cyclized brgdgts mbrgdgts and best subsets regression bsr of the fractional abundances of the nine most common brgdgts however these calibrations have rarely been applied to lake sediment cores to reconstruct temperatures and test the applicability of this proxy as a paleothermometer we present an expanded east african lakes surface sediment brgdgt dataset based upon 111 lakes and examine three methods of calibrating brgdgts to maat these methods include recalculations of the east african lake mbt cbt calibration and mbrgdgts calibrations as well as a new stepwise forward selection sfs calibration that uses the four combined brgdgts that explain the most variance in temperature in our calibration set we apply these new calibrations as well as five previously published lacustrine brgdgt calibrations to the brgdgt distributions of our surface sediment dataset and a 48 kyr sediment core from sacred lake mt kenya producing the first brgdgt temperature reconstruction available from a small tropical lake we compare the reconstructed temperatures to previously published paleotemperature records from east africa to help us assess the performance of the brgdgt calibrations we find that the sfs calibration has a consistently low root mean squared error of prediction rmsep over the entire range of maat while the mbt cbt and mbrgdgt calibrations have relatively large rmseps particularly between lakes with similar temperatures but variable ph this suggests that these techniques do not properly deconvolve the temperature and ph signals recorded in the distributions of the brgdgts we further find that only the sfs calibration produces a credible reconstructed temperature history from sacred lake when compared to other last glacial maximum paleotemperature estimates from east africa thus we advocate for the use of the sfs calibration when reconstructing paleotemperatures from brgdgts in east africa

onset of long term cooling of greenland near the eocene oligocene boundary as revealed by branched tetraether lipids the eocene oligocene e o boundary interval is considered to be one of the major transitions in earth s climate witnessing the fi rst major expansion of the east antarctic ice sheet however the extent of the associated climatic cooling especially for high northern latitude continental landmasses is poorly constrained in this study we reconstruct the fi rst mean annual air temperature maat for the greenland landmass during the late eocene and early oligocene by applying a new proxy based on the distribution of branched tetraether lipids derived from soil bacteria preserved in a marine sediment core from the greenland basin the temperature estimates are compared with a composite continental temperature record based on bioclimatic analysis of pollen assemblages both proxies reveal comparable late eocene maats of 13 15 c and a gradual long term cooling of 3 5 c starting near the e o boundary these data are in agreement with other maat reconstructions from northern midlatitude continents and suggest a general cooling of the northern hemisphere during the e o transition

mineralogical and geochemical characterization of supergene cu pb zn v ores in the oriental high atlas morocco in the moroccan high atlas two sulfide deposits hosted by jurassic dolostones underwent significant weathering in the cu deposit of jbel klakh several stages of supergene mineralization are distinguished 1 the replacement of hypogene sulfides in the protolith chalcopyrite by secondary sulfides in the cementation zone bornite digenite chalcocite covellite 2 the formation of oxidized minerals in the saprolite malachite azurite brochantite where the environment becomes more oxidizing and neutral and 3 the precipitation of late carbonates calcite and iron hydr oxides in the laterite the precipitation of carbonates is related to the dissolution of dolomitic host rocks which buffers the fluid acidity due to the oxidation of sulfides in the jbel haouanit pb zn deposit the mineral assemblage is dominated by typical calamine minerals cu minerals chalcocite covellite malachite and a cu pb zn vanadate mottramite galena is successively weathered in anglesite and cerussite sphalerite is weathered in smithsonite which is rapidly replaced by hydrozincite late iron hydr oxides are mainly found at the top of both deposits laterite both deposits are thus characterized by specific mineral zoning from laterite to protolith related to variations in the mineralogy and ore grades and probably caused by varying eh ph conditions

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

spatial and temporal reconstructions of changes in the asian palaeomonsoon a new mineral magnetic approach abstract a new quantitative approach is proposed for estimating palaeoprecipitation across the chinese loess plateau at present there is a strong rainfall gradient across the plateau from 300 mm yr in the near desert conditions in the northwest to over 750 mm yr in the southeast just 700 km distant we find that the concentration of ferrimagnetic iron oxide minerals in nine modern soil types represented by 37 individual soil profiles is strongly correlated with this contemporary rainfall gradient the ferrimagnetic concentration rises along this gradient from 0 01 in the northwest to over 0 2 in the southeast the nine modern soil types have been used in the construction of a rainfall vs magnetic susceptibility least squares regression climofunction past variations of loess soil iron oxide content are easily established through magnetic susceptibility measurements and so can be used to reconstruct the rainfall of former interglacial and glacial periods the physical and pedological basis of the rainfall vs susceptibility relationship is discussed and potential limitations of our rainfall reconstruction method are explored our palaeoclimate reconstructions indicate dramatic changes in rainfall due to variations in the structure of the asian monsoon the rainfall variations are about four times greater than has been suggested for this region by atmospheric general circulation modelling our data indicate increased rainfall throughout central china both in interglacial periods and in the early holocene the increases in monsoonal rain were particularly pronounced at our westernmost sites adjacent to the northeastern edge of the tibetan plateau in contrast for glacial periods a reduction in rainfall is found across the whole loess area with the greatest decreases in the southeast

chinese loess and the paleomonsoon abstract this paper presents a general review of the recent research advances of the east asian paleomonsoon based mainly on studies of the loess soil sequences in the chinese loess plateau in the last 2 6 million years the paleomonsoonal history may be divided into about 166 events on a time scale of the earth s orbital variations during the last glacial period millenial scale oscillations of the monsoon system were prominent which can be fairly well correlated with the dansgaard oeschger cycles recognized in the greenland ice cores the monsoonal rainfall belt has experienced a wide repeated advance retreat change during the glacial interglacial cycles of the pleistocene both temporal and spatial changes of the monsoon system in the quaternary could have been linked closely to global ice volume variations

synchronous change of temperature and moisture over the past 50 ka in subtropical southwest china as indicated by biomarker records in a crater lake abstract over the past few decades studies on the indian summer monsoon ism have been mainly based on paleo marine records whilst the sparsity of land records limits our understanding of the ism evolutionary process over continental landscapes here we provide paleoclimate reconstructions based on n alkanes and branched glycerol dialkyl glycerol tetraethers brgdgts from a 50 ka lacustrine sediment core collected from lake tengchong qinghai in southwestern subtropical china our results reveal that the botanical sources of sedimentary n alkanes in this lake are mainly from aquatic macrophytes and terrestrial plants the lake level evolution from the mis 3 to the holocene can be divided into four stages high in the mis 3 low in the lgm high in last deglacial and low in mid and late holocene our brgdgts based climate reconstructions indicate that the mean air temperature differences between the present day and the lgm were up to about 3 4 c from mis 3 to holocene there was a broadly and consistently synchronous trend between precipitation and air temperature in this ism region this is different from the asynchronous temperature and precipitation variations in the east asian summer monsoon easm regions in the period of last glacial termination our study shows that the climate in ism regions was primarily driven by changes in june summer solar insolation at 30 n and those glacial boundary conditions such as ice volume and sea surface temperature might also have affected the ism

paleoclimatic reconstruction and the response of carbonate minerals during the past 8000 years over the northeast tibetan plateau abstract the climatic significance of the carbonate content and composition of lake sediments remains unclear in this study we analyzed the glycerol dialkyl glycerol tetraethers and mineral contents of alake lake sediments to reconstruct temperature and moisture changes over the northeast tibetan plateau since 8000 cal yr bp we identified warm cold and wet dry conditions during the roman warm period and holocene climate optimum early neoglacial cooling period accompanied by a dominance of aragonite monohydrocalcite based on our results and previous laboratory experiments we suggest that monohydrocalcite is predominantly deposited in colder drier and higher mg ca conditions relative to that of aragonite the carbonate mineral composition should therefore be fully considered when sediment carbonate contents are used to reconstruct paleotemperature moisture changes

variation in 6 methyl branched glycerol dialkyl glycerol tetraethers in lantian loess paleosol sequence and effect on paleotemperature reconstruction abstract the distribution of branched glycerol dialkyl glycerol tetraethers brgdgts has been increasingly used as a proxy in paleoclimate studies of marine lacustrine and loess environments a paleothermometer was subsequently quantified using a combination of the methylation and cyclization index of branched tetraethers mbt cbt on the basis that mbt was related to mean annual air temperature and to a lesser extent soil ph whereas cbt correlated only with soil ph as newly described 6 methyl brgdgts seemed to introduce a dependence on soil ph of this temperature proxy we investigated the effect of the 6 methyl brgdgts on an existing paleotemperature reconstruction we describe the evolution in temperature and ph recorded in the lantian loess paleosol sequence for the last 120 kyr using a new analytical method the results show that 6 methyl brgdgts were abundant comprising on average 26 of the total amount of brgdgts in the sequence the fractional abundance of 6 methyl brgdgts generally tracked the change in soil ph at the same soil section a considerable delay up to ca 7 kyr in the variation in fractional abundance of 6 methyl brgdgts vs that of 5 methyl brgdgts was observed possibly resulting from the different environmental factors to which they respond we also found that variation in the reconstructed mat values using different calibrations could be up to 7 c possibly due to soil moisture variation since soil moisture may have a significant impact on the distribution of brgdgts our results further indicate that early warming occurred on the southern chinese loess plateau relative to a monsoonal precipitation increase as reported elsewhere

microbial lipid records of highly alkaline deposits and enhanced aridity associated with significant uplift of the tibetan plateau in the late miocene saline alkaline sediments and soils are widespread in arid and semiarid regions but their occurrence in ancient dry periods remains unknown due to the lack of a suitable proxy on the basis of investigations of modern chinese soils with a wide ph range of 3 5 9 1 we suggest that the microbial lipid ratio r i b i e the abundance ratio of archaeal isoprenoid gdgts glycerol dialkyl glycerol tetraethers to bacterial branched gdgts indicates the presence of drought induced alkaline deposits in terrestrial settings the r i b is invariant in modern soils with ph 600 mm but it increases sharply at higher ph values and lower mean annual precipitation i b ratio in a fluviolacustrine section in the zhada basin of the southwestern tibetan plateau covering the time period 9 2 2 6 m y ago the r i b ratio remains relatively stable in most intervals but exhibits maxima in some horizons indicative of the occurrence of severe drought and alkaline deposits in the basin catchment these occur in fluvial sediments deposited 9 m y ago a critical time with respect to the intensification of the east asian and indian monsoons and the significant uplift of the plateau that has previously been associated with enhanced aridity in central asia

mineral magnetic variation of the jingbian loess paleosol sequence in the northern loess plateau of china implications for quaternary development of asian aridification and cooling a high resolution mineral magnetic investigation has been carried out on the jingbian loess paleosol sequence at the northern extremity of the chinese loess plateau results show that the magnetic assemblage is dominated by large pseudo single domain and multidomain like magnetite with associated maghemite and hematite variations in the ratios of sirm100mt sirm sirm100mt sirm30mt and sirm100mt sirm60mt sirm is the saturation isothermal remanent magnetization sirmnmt represents the residual sirm after an n mt alternating field demagnetization have been used to document regional paleoclimate change in the asian interior by correlating the mineral magnetic record with the composite 18o record in deep sea sediments the long term up section decreasing trend in those ratios in both loess and paleosol units has been attributed to a long term decrease in the relative contributions of eolian hematite during glacial extrema and of pedogenic hematite during interglacial extrema respectively which reveals a long term decreasing trend in chemical weathering intensity in both glacial stage source region the gobi and deserts in northwestern china and interglacial stage depositional area the loess plateau region we further relate this long timescale variation to long term increasing aridification and cooling during both glacial extrema in the dust source region and interglacial extrema in the depositional area over the quaternary period changes in those ratios are most likely due to quaternary aridification and cooling driven by ongoing global cooling expansion of the arctic ice sheet and progressive uplift of the himalayan tibetan complex during this period

post cranial remains of coelurosaurs dinosauria theropoda from the late jurassic of tanzania small theropod post cranial material from tendaguru tanzania the only known late jurassic theropod locality in the southern hemisphere is reviewed material originally described as coelurosaurs includes at least one taxon of basal tetanuran and one taxon of small abelisauroid together with the abelisauroid elaphrosaurus and the presence of a larger ceratosaur in tendaguru this material indicates that ceratosaurs were an important faunal element of late jurassic east african theropod faunas one bone furthermore shares derived characters with the holotype of the poorly known middle jurassic australian theropod ozraptor and allows the identification of the latter as the oldest known abelisauroid thus indicating an early divergence of ceratosaurids and abelisauroids within ceratosaurs abelisauroids might have originated in gondwana and represent important faunal elements of cretaceous gondwanan theropod faunas in general

disentangling marine soil and plant organic carbon contributions to continental margin sediments a multi proxy approach in a 20 000 year sediment record from the congo deep sea fan abstract a 20 kyr long sediment sequence from the congo deep sea fan core geob 6518 1 one of the world s largest deep sea river fans has been analysed for bulk and molecular proxies in order to reconstruct the marine soil and plant organic carbon oc contributions to these sediments since the last glacial maximum the bulk proxies applied c n ratio and 13 c org ranged from 10 to 12 5 and from 24 5 to 21 vpdb respectively as molecular proxies concentrations of marine derived alkenones and terrestrial derived odd numbered n alkanes were used which varied between 0 2 and 4 g g dry weight sediment in addition the branched vs isoprenoid tetraether bit index a proxy for soil organic matter input was used which varied from 0 3 to 0 5 in this core application of binary mixing models based on the different individual proxies showed estimates for terrestrial oc input varying by up to 50 due to the heterogeneous nature of the oc application of a three end member mixing model using the 13 c org content the c n ratio and the bit index enabled the distinction of soil and plant organic matter as separate contributors to the sedimentary oc pool the results show that marine oc accounts for 20 to 40 of the total oc present in the deep sea fan sediments over the last 20 kyr and that soil oc accounts for about half 45 on average of the oc present this suggests that soil oc represents the majority of the terrestrial oc delivered to the fan sediments accumulation rates of the plant and soil oc fractions over the last 20 kyr varied by a factor of up to 5 and are strongly related to sediment accumulation rates they showed an increase starting at ca 17 kyr bp a decline during the younger dryas peak values during the early holocene and lower values in the late holocene this pattern matches with reconstructions of past central african humidity and congo river discharge from the same core and revealed that central african precipitation patterns exert a dominant control on terrestrial oc deposition in the congo deep sea fan marine oc accumulation rates are only weakly related to sediment accumulation rates and vary only little over time compared to the terrigenous fractions these variations are likely a result of enhanced preservation during times of higher sedimentation rates and of relative small fluctuations in primary production due to wind driven upwelling

occurrence of tetraether lipids in stalagmites implications for sources and gdgt based proxies lipid biomarkers in stalagmites have potential in palaeoenvironmental reconstruction but glycerol dialkyl glycerol tetraethers gdgts in stalagmites have rarely been investigated we report the occurrence of archaeal isoprenoid gdgts and bacterial branched gdgts in heshang cave stalagmites in central china the archaeal component crenarchaeol dominated bacterial branched gdgts in the stalagmites and on the weathered parent rock surface collected inside the cave in contrast the distribution of gdgts in the overlying soil shows that branched gdgts dominated archaeal gdgts hence the majority of archaeal gdgts in stalagmites may be produced by crenarchaeota inhabiting the cave rather than being inherited from the overlying soil bacterial branched gdgt distributions expressed as mbt and cbt indices showed remarkable differences between stalagmite and soil samples implying that most branched gdgts may also be produced in situ in the cave the tex86 or tex86 values were found to increase with more depleted 18o values representing much stronger monsoon and therefore usually higher temperatures in the study region however the mbt cbt index in stalagmites may be influenced by a variety of factors besides palaeotemperature

temperature changes reconstructed from branched gdgts on the central loess plateau during the past 130 5 ka abstract this study investigated the glycerol dialkyl glycerol tetraethers gdgts in a loess paleosol sequence lps to quantitatively reconstruct the mean annual air temperature mat on the central chinese loess plateau clp during the past 130 5 ka the results show that 1 mat variations reconstructed by global mbt methylation index of branched tetraethers and cbt cyclisation ratio of branched tetraethers transfer functions at xifeng range from 7 3 c to 28 4 c the mat variation on the central clp xifeng site is between the previously reported mat variations on the western yuanbao site and eastern clp mangshan site in agreement with the pattern that temperature increases from the northwestern clp to the southeastern clp 2 mat variations estimated by transfer functions of global mbt cbt global mbt cbt and chinese mbt cbt for lps are nearly all higher than the modern mat at xifeng indicating that the reconstructed mat values are probably overestimated 3 the maximum value of magnetic susceptibility at xifeng lagged that of the mat derived by mbt cbt proxy during the last interglacial 9 ka lag and since the last deglacial 6 ka lag

branched glycerol dialkyl glycerol tetraethers in pleistocene loess paleosol sequences three case studies abstract branched glycerol dialkyl glycerol tetraethers branched gdgts are membrane lipids presumably derived from anaerobic heterotrophic soil bacteria empirical studies have shown that the composition of branched gdgts in topsoils varies in degree of cyclization and methylation expressed as cbt and mbt i e cyclization and methylation index of branched tetraethers depending on soil ph and mean annual air temperature mat here we present results from three case studies namely three well studied loess paleosol sequences lpss in which we measured the branched gdgts in order to test the applicability of these biomarkers for paleoclimate reconstruction the results show that major disagreements exist between expectations based on available stratigraphic pedological and geochemical data on the one hand and gdgt derived reconstructions on the other hand caution is therefore advised when interpreting the respective indices in lps studies we discuss several potential directions for future research i some of the target peaks in the hplc chromatograms consist of multiple unidentified compounds this needs to be addressed by way of improved component separation identification and new calibration studies ii factors other than mat and soil ph that could affect membrane composition should be further investigated e g nutrient availability and redox conditions as well as seasonality and changes in bacterial communities iii gdgts may be produced in non negligible amounts at depth and thus overprint the original in situ signal a concern that could be termed growth depth effect iv gdgts should also be analyzed in dust source regions and contemporaneous eolian sediments in order to address a potential redeposition effect

distributional variations in marine crenarchaeotal membrane lipids a new tool for reconstructing ancient sea water temperatures it has recently been shown that membrane lipids of marine crenarchaeota a ubiquitous and abundant component of plankton occur in relatively high concentrations in recent and ancient sediments in this study we investigated the environmental controls on the relative distribution of these lipids in surface sediments we especially focussed on temperature as it is known from the thermophilic genetic relatives of marine crenarchaetoa that the composition of their membrane strongly depends on growth temperature indeed a significant linear correlation r2 0 92 is found between the number of cyclopentane rings in sedimentary membrane lipids derived from marine crenarchaeota and the annual mean sea surface temperatures this suggests that the mechanism of physical adaptation of their membrane compositions to temperature is identical to that of their thermophilic relatives in turn archaeal lipid distributions in sediments may thus allow the reconstruction of sea water temperatures of ancient marine environments

distribution of glycerol dialkyl glycerol tetraethers in soils from two environmental transects in the usa abstract glycerol dialkyl glycerol tetraethers gdgts of both archaeal and bacterial origin form the basis of new temperature proxies applicable to soil and lake and marine sediments in soil branched gdgts are prevalent and their abundance of methyl or cyclic groups has been calibrated to mean annual temperature mat using mbt and cbt indices however soil ph is also known to be an important variable controlling the distribution of branched gdgts precipitation amount helps control soil moisture as well as ph and soil moisture is a leading variable affecting microbial diversity and activity in soil we have evaluated the distribution of gdgts from two soil transects in the usa a dry western transect covering six western states and a wet east coast transect from maine to georgia in order to assess the effect of precipitation on the distribution of soil gdgts our results show distinctly different gdgt distributions across climatic regions with dry western soils characterized predominantly by thaumarchaeotal isoprenoid iso gdgts and as a consequence low bit index values 0 2 0 6 and moist temperate east coast transect soils expressing mostly branched br gdgts and higher bit values 0 9 1 the predominance of iso gdgts in the western soils is related to the degree of aeration which in turn is related to precipitation amount and also to soil ph we also observed a substantial increase in the offset between measured mat and mbt cbt based mat below an annual precipitation of 700 800 mm yr 1 implying an impact of precipitation amount on mbt cbt based temperature reconstruction the data suggest that while soil tetraethers work well as a temperature proxy in moist temperate regimes they do not produce reliable measurements of temperature in sediments sourced from areas with 1 precipitation moreover erosion of soils with low bit values into lacustrine or marginal marine environments will not be detected via the bit index which can potentially affect paleotemperature reconstruction from sediments and so provide erroneous estimates of soil carbon delivery bit index values also show a correlation with precipitation amount the abundance of iso gdgts in western transect soils allowed calculation of tex 86 values but no correlation was found between tex 86 calculated temperature and mean annual temperature

temperature dependent variation in the distribution of tetraether membrane lipids of marine crenarchaeota implications for tex86 paleothermometry 1 recently a new geochemical temperature proxy the tex86 was introduced this proxy is based on the number of cyclopentane moieties in the glycerol dialkyl glycerol tetraethers gdgts of the membrane lipids of marine crenarchaeota which changes as a response to temperature however until now only sediment data have been used to establish this proxy and experimental work is missing we performed mesocosm studies with marine crenarchaeota incubated at temperatures ranging from 5 to 35 c and salinities of 27 and 35 to test the validity of the tex86 proxy growth of marine crenarchaeota in these mesocosms was evident from the substantial increase in the concentration of marine crenarchaeotal membrane lipids with amounts up to 3400 ng l with increasing temperature an increase in the number of cyclopentane moieties in the crenarchaeotal membrane lipids was observed different salinities did not show any effect on the gdgt distribution the tex86 showed a significant linear correlation to incubation temperature tex86 0 015 t 0 10 r2 0 79 this equation has a similar slope to the correlation obtained from core tops but differs in the intersection tex86 0 015 t 0 28 r2 0 92 this difference is mainly determined by the smaller amount of the regioisomer of crenarchaeol in the incubation series compared to core top samples these incubation experiments indicates that water temperature is indeed the major controlling factor for the membrane distribution of marine crenarchaeota and confirms that the tex86 proxy depends on a physiological response to regulate membrane fluidity

high frequency pulses of east asian monsoon climate in the last two glaciations link with the north atlantic three loess sections in the loess plateau of china have been studied to characterize the variations of the east asian monsoon climate in the late quaternary period paleo weathering profiles based on two weathering indices reveal a series of spatially correlative intervals of lower weathering intensity lw in the last glacial and late penultimate glacial loess indicating significantly cooler or and drier conditions most of them are identified at or near the transitional boundaries between loess and soil units suggesting that climatic conditions favorable for lw events tended to occur at or near major climatic boundaries twenty eight radiocarbon and thermoluminescence measurements combined with kukla s magnetic susceptibility age model date these events at 14 21 29 38 52 71 135 and 145 ka bp with 5 10 ka frequency inlaid within the orbitally induced 20 ka periodicity the ages of the first six events in the last glacial period are therefore close to those of the coarse grained heinrich layers in the north atlantic ocean which resulted from massive discharges of icebergs the results indicate that the climate in the area affected by the east asian monsoon has experienced high frequency changes more or less synchronous with the heinrich events these high frequency changes have been reported by porter and an based on the grain size time series from the luochuan loess section our data also reveal that similar events also occurred during the penultimate glaciation the mechanisms linking the heinrich events and the east asian monsoon climate may be similar to that driving the younger dryas event which has been identified in a large number of records in china and in the surrounding oceans

transition from a warm and dry to a cold and wet climate in ne china across the holocene abstract northeast ne china lies in the northernmost part of the east asian summer monsoon easm region although a series of holocene climatic records have been obtained from lakes and peats in this region the holocene hydrological history and its controls remain unclear more specifically it is currently debated whether ne china experienced a dry or wet climate during the early holocene here we reconstruct changes in mean annual air temperature and peat soil moisture across the last 13 000 year bp using samples from the gushantun and hani peat located in ne china our approach is based on the distribution of bacterial branched glycerol dialkyl glycerol tetraethers brgdgts and the abundance of the archaeal isoprenoidal iso gdgt crenarchaeol using the recently developed peat specific maatpeat temperature calibration we find that ne china experienced a relatively warm early holocene 5 7 c warmer than today followed by a cooling trend towards modern day values during the mid and late holocene moreover crenarchaeol concentrations brgdgt based ph values and the distribution of 6 methyl brgdgts all indicate an increase in soil moisture content from the early to late holocene in both peats which is largely consistent with other data from ne china this trend towards increasing soil moisture wetter conditions across the holocene in ne china records contrasts with the trends observed in other parts of the easm region which exhibit an early and or mid holocene moisture precipitation maximum however the holocene soil moisture variations and temperature moisture relationships warm dry and cold wet observed in ne china are similar to those observed in the core area of arid central asia which is dominated by the westerlies we therefore propose that an increase in the intensity of the westerlies across the holocene driven by increasing winter insolation expanding arctic sea ice extent and the enhanced okhotsk high caused an increase in moisture during the late holocene in ne china

distributions and temperature dependence of branched glycerol dialkyl glycerol tetraethers in recent lacustrine sediments from china and nepal 1 glycerol dialkyl glycerol tetraether gdgt membrane lipids in surface sediments from 24 lakes in china and nepal were analyzed the result shows that branched gdgt lipids occur widely in the studied lake sediments the different distribution of branched gdgts between the chinese soils from weijers et al 2007b and the chinese lake sediments indicates that the branched gdgts in the lacustrine sediment are the mixture of allochthonous and autochthonous branched gdgts our result supports the suggestion that temperature is the principal factor affecting the distribution of gdgts seasonality sources and precipitation increase the uncertainty of the correlation between the methylation index of branched tetraethers mbt cyclization ratio of branched tetraethers cbt proxy and the temperature the correlations of the mbt cbt index with mean annual air temperature t for the global lakes are t 6 803 7 062 cbt 37 090 mbt n 139 p 0 0001 r2 0 62 and rmse 5 24 c for the global lakes with ph 8 5 t 3 949 5 593 cbt 38 213 mbt n 100 p 0 0001 r2 0 73 and rmse 4 27 c the significant correlation suggests that the mbt cbt proxy might be used as a potential paleotemperature proxy in the limnic environment the mbt cbt proxy provides an independent way to evaluate and verify the sensitivities of the different proxies for paleotemperature reconstruction from lacustrine sediments

plant wax hydrogen isotopic evidence for postglacial variations in delivery of precipitation in the monsoon domain of china the asian monsoon is a key component of the earth s climate system that directly affects the livelihood of 60 of the world population reliable reconstruction of changes in monsoon precipitation during the holocene is required to better understand the present climate conditions and to predict future climate processes in the asian monsoon domain reconstruction of changes in holocene monsoon precipitation has been done in various regions of this domain using a variety of paleoclimate proxies however different proxies have yielded different paleoclimate records of long term monsoon rainfall variability we apply compound specific stable hydrogen isotope compositions of the plant wax n alkanes isolated from the hongyuan peat sequence in eastern tibet to reevaluate the regional carbonate oxygen isotopic and lake level records the d h ratios of the n alkanes resolve the apparent discrepancy among the different paleoclimate proxies our result indicates that lake level fluctuation is a reliable recorder of changes in the amount of summer monsoonal precipitation while long term isotope records largely reflect large scale changes in the source of water vapor rather than a local precipitation signal combining lake level biomarker and carbonate isotopic records we conclude that the early holocene monsoon precipitation in southwest china has been greatly influenced by the indian monsoon

compound specific d h ratios and molecular distributions of higher plant leaf waxes as novel paleoenvironmental indicators in the chinese loess plateau abstract we measured d h ratios of individual long chain leaf wax n alkanes isolated from a loess profile spanning the last 130 ka from xifeng china the d values show large variation 140 to 200 for the past 130 ka and are highly correlated with changes in magnetic susceptibility ms an accepted proxy for past monsoon circulation in the chinese loess plateau peaks in high d values 140 to 160 coincide with low ms values for loess sections formed under relatively dry conditions marine isotope stages miss 2 and 4 whereas peaks in low d values 190 to 200 coincide with high ms values for paleosol sections formed under relatively wet conditions miss 1 3 and 5 we attribute the isotopic variations to the combined effects of varying aridity which controls the soil and leaf water evaporation and temperature and monsoon intensity which alter the d h ratios of precipitation we also discovered a strong negative correlation between the molecular distributions ratios of c31 c29 and c31 c27 n alkanes and the d values of n alkanes based on studies of modern plants and the xifeng loess sequence the complex relationship between ms and monsoon circulation has been difficult to understand mechanistically however the climatic controls on the d h ratios of individual long chain n alkanes and c31 c29 n alkane ratios can be readily demonstrated and calibrated from modern plants and surface soils therefore these new molecular and isotopic proxies have potential as quantitative proxies for paleoenvironmental reconstruction in the chinese loess plateau

source settling and degradation of branched glycerol dialkyl glycerol tetraethers in the marine water column abstract branched glycerol dialkyl glycerol tetraethers branched gdgts are commonly found in distal marine sediments however their presence in the water column source and delivery process are not fully understood in this study we examined seasonal and depth variation in the flux of branched gdgts in sinking particles and underlying sediment at 39 n 147 e in the mid latitude nw pacific from november 1997 to august 1999 branched gdgts showed synchronous variation in their sinking flux at different depths and the variation was similar to that of lithogenic material of eolian dust origin their degrees of cyclization and methylation were nearly constant and bear some resemblance to those of alkaline soils this suggests that westerly winds transport branched gdgts to the study site via the atmosphere from continental asia the sinking flux of branched gdgts was higher in 1999 than in 1998 presumably reflecting changes in the migration path of asian dust in response to the el nino southern oscillation synchronous variation in branched gdgt concentrations at different depths implies rapid vertical transport of branched gdgts to deep water with a sinking velocity exceeding 260 m d 1 the sinking flux of the branched gdgts decreased with increasing depth but the rate of decrease was much smaller than those of other compounds the preservation efficiency of branched gdgts was 3 5 6 4 of surface inputs at the water sediment interface which is much higher than those of isoprenoid gdgts 1 0 1 3 and other compounds the branched and isoprenoid tetraether bit index values were extremely low i e