applications of organic geochemistry to paleolimnological reconstructions a summary of examples from the laurentian great lakes the organic matter content of lake sediments contains information that helps to reconstruct past environmental conditions evaluate histories of climate change and assess impacts of humans on local ecosystems the elemental isotopic and molecular compositions of organic matter buried in sediment provide evidence of the biota that have lived in a lake and its catchment area and they serve as proxies of organic matter delivery and accumulation sedimentary records from the north american great lakes provide examples of applications of organic geochemistry to paleolimnological reconstructions the records of these lakes date from retreat of the laurentide ice sheet around 12 ka include the mid holocene hypsithermal and show consequences of recent human changes low corg ntotal ratios indicate that most of the sediment organic matter in the great lakes is from algal production yet changes in biomarker molecule compositions also show that varying amounts of land plant organic matter have been delivered to the lakes elevated algal productivity that accompanies nutrient enrichments of lake waters is recorded as excursions to less negative 13c values in the organic matter of sediments that were deposited in the 1960s and 1970s increased organic carbon mass accumulation rates mirror the isotopic excursions in most parts of the great lakes accumulations of petroleum residues and pyrogenic polycyclic aromatic hydrocarbons in sediments identify fluvial and eolian delivery of organic matter components to different parts of the great lakes emerging applications of multiple and novel organic geochemical proxies to paleolimnological reconstructions are promising yet some potentially important measurements remain underutilized

statistical behavior of the longitudinal variations of daytime electron density in the topside ionosphere at middle latitudes electron density in the topside ionosphere has significant variations with latitude longitude altitude local time season and solar cycle this paper focuses on the global and seasonal features of longitudinal structures of daytime topside electron density ne at middle latitudes and their possible causes we used in situ ne measured by demeter and f2 layer peak height hmf2 and peak density nmf2 from cosmic the longitudinal variations of the daytime topside ne show a wave number 2 type structure in the northern hemisphere whereas those in the southern hemisphere are dominated by a wave number 1 structure and are much larger than those in the northern hemisphere the patterns around december solstice ds in the northern hemisphere winter are different from other seasons whereas the patterns in the southern hemisphere are similar in each season around march equinox me june solstice js and september equinox se in the northern hemisphere and around me se and ds in the southern hemisphere the longitudinal variations of topside ne have similar patterns to hmf2 around js in the southern hemisphere winter the topside ne has similar patterns to nmf2 and hmf2 does not change much with longitude thus the topside variations may be explained intuitively in terms of hmf2 and nmf2 this approach works reasonably well in most of the situations except in the northern winter in the topside not too far from the f2 peak in this sense understanding variations in hmf2 and nmf2 becomes an important and relevant subject for this topside ionospheric study

climate instability during the penultimate glaciation evidence from two high resolution loess records china the xinzhuangyuan and lijiayuan loess sections in the northwestern part of the chinese loess plateau were studied down to paleosol unit s2 which probably formed during marine oxygen isotopic stage 7 200 000 years b p the thickness of the loess soil sequence above s2 is 63 m at xinzhuangyuan and 43 m at lijiayuan a 2 cm sample spacing yields a mean depositional resolution of 50 80 years for the last and penultimate glacial loess units l1 and l2 and 200 years for the last interglacial soil unit sl thus enabling us to reconstruct high resolution climatic changes during the last two glacial interglacial cycles the grain size records of the two sections are regarded as a proxy for changes in the monsoon desert system over northern china results show that frequent large amplitude climatic oscillations on millennial timescales occurred during the penultimate glaciation in a manner similar to that during the last glaciation suggesting that suborbital scale climatic variations may be a common feature of the climate system during glacial periods of the pleistocene the last interglacial soil s1 is composed of three individual soils and two thin intervening loess horizons in both of the sections short term variations in grain size are not prominent within the soil complex implying the absence of strong millennial scale climatic oscillations during the last interglaciation in northern china

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

a 249 kyr stack of eight loess grain size records from northern china documenting millennial scale climate variability in order to construct a stacked climatic record of millennial scale variability for northern china grain size was measured for 12 330 samples from eight thick loess sections between section correlation of these grain size records shows that although small depositional hiatuses may be present within a single section most parts of the sections display continuous dust deposition by correlating the eight records with the precisely dated chinese stalagmite 18o record a stacked 249 kyr long grain size time series was constructed termed the chilomos record which is the first high resolution stack documenting millennial scale variability in northern china this stack shows millennial scale climatic events superimposed on a prominent cooling trend during the last and penultimate glaciations consistent with the pattern of increasing global ice volume however this cooling trend is dampened in the stalagmite record and totally suppressed in the low latitude ocean record it follows that the loess plateau far from the low latitude ocean is largely influenced by the northern high latitude ice sheets while the proximal stalagmites of southern china primarily document signals from the low latitude ocean cross correlations of climatic records from high and low latitudes demonstrate that the millennial scale abrupt changes originated in the northern polar area and were propagated into east asia largely through the east asian winter monsoon the chilomos record also confirms that the driest and coldest interval of the last 249 kyr occurred in the late mis 6 and that mis 7d was extremely cold and dry similar to the stadial conditions of mis 6

paleorainfall reconstructions from pedogenic magnetic susceptibility variations in the chinese loess and paleosols the rock magnetic properties of the chinese loess and paleosols constitute a unique and sensitive record of east asian paleoclimate through the quaternary period systematic variations in the concentration and grain size of the magnetic minerals in these sediments have produced systematic variations in the magnetic susceptibility signal which can be easily and rapidly measured at many sites across the loess plateau variations in many other rock magnetic properties can be used to identify the key shifts in ferrimagnetic grain size but magnetic susceptibility alone is sufficiently sensitive to record stadial and interstadial climate stages as well as glaciations and interglaciations past changes in rainfall and monsoon activity for this region are reconstructed from the susceptibility variations the susceptibility record is calibrated using the modern relationship between rainfall and pedogenic susceptibility on the loess plateau our rainfall reconstructions identify enhanced summer monsoonal activity in the chinese loess plateau region in the early holocene and the last interglaciation in the presently semiarid western area of the plateau annual precipitation in interglacial times was up to 80 higher than at present in the more humid southern and eastern areas values were up to 20 higher than today s levels during the last glaciation precipitation decreased across the entire plateau typically by 25 the relationship between pedogenic susceptibility climate and weathering age was examined over the northern hemisphere temperate zone and the observed positive correlation between rainfall and susceptibility indicates that climate rather than soil age is the predominant factor that controls pedogenic susceptibility enhancement in loess soils

is there a possibility to correct fossil n alkane data for postsedimentary alteration effects abstract the long chain n alkane composition of plant material can significantly differ between plant groups e g trees and grasses due to their relative recalcitrance they have been employed in paleoecological research as molecular proxies for different types of vegetation most of those paleoenvironmental studies rely on the assumption that characteristic molecular fingerprints of plant material are preserved in the fossil organic material without significant alteration however there exists evidence that n alkane distributions may change in the course of plant litter degradation here the authors propose and discuss a conceptual approach to the correction of n alkane patterns in paleosols and terrestrial sediments for postsedimentary alteration effects this might have potential to improve paleoenvironmental reconstructions derived from these molecular fossils in soil depth profiles typically a correlation between the oep odd over even predominance and paleoecological valuable long chain n alkane ratios lars can be found similar relationships have been also obtained from n alkane records in paleosols with the oep serving as a proxy of microbial reworking the correction procedure applies oep vs lar regression functions to correct fossil lars for degradation effects the regression functions have been derived from modern soils the application of the procedure and its significance for paleoecological interpretations is demonstrated on a case study of a loess paleosol sequence 400 700 ka in romania it is shown that changes in the c27 c31 n alkane ratio at this site are closely related to degradation effects rather than to changes in the paleovegetation e g tree vs grass abundance however it was found that the c29 c31 ratio is a more suitable paleoenvironmental proxy at the mircea voda site the results indicate that there is a future potential to correct fossil n alkane ratios via the oep lar relationship however at the moment a general straight forward application of this approach might be critical due to lack of extended and diverse n alkane records from modern soils the need of more systematic n alkane studies on soil profiles is highlighted to improve knowledge concerning dynamics and actual mechanisms of postsedimentary lar and oep changes

reconstructing in situ vegetation dynamics using carbon isotopic composition of biopolymeric residues in the central chinese loess plateau abstract carbon isotopic compositions of total organic carbon toc or leaf waxes in soils have been used to reconstruct past changes in the relative abundance of c 3 and c 4 plants however toc contains organic matter of different source organisms plants animals fungi bacteria etc and its isotopic ratios could be modified during diagenesis since different organic fractions e g carbohydrates proteins lipids etc have different isotopic ratios and degradation rates leaf waxes on the other hand are transported by wind and hence represent vegetation input from a large geographic area we report in this paper a new approach to extract in situ paleovegetation information from late quaternary paleosols by determining carbon isotopic compositions of biomarkers derived from aliphatic bio and geopolymers of plant origin we show that c 9 to c 17 n alkenes derived from aliphatic bio and geopolymers are the dominant compounds released by flash pyrolysis of insoluble organic matter isolated from the late quaternary paleosols in the chinese loess plateau because the aliphatic polymeric substances are mainly derived from plant leaves bark and roots the isotopic signatures of these alkenes determined using pyrolysis gas chromatography isotopic ratio mass spectrometry reflect in situ vegetation changes our down core 13 c data from the xifeng loess paleosol profile show significant coherence among biopolymer derived n alkenes leaf wax n alkanes and toc for the past 40 kyr however the different amplitudes of the temporal isotopic changes among these data sets are indicative of variability in in situ and regional vegetation dynamics organic sources and effect of diagenesis our data also imply that below ground biomass is a major source of soil organic matter in the central china loess sediment

stacked 2 6 ma grain size record from the chinese loess based on five sections and correlation with the deep sea δ18o record 1 this study aims to establish a stacked climate record of the quaternary period from the chinese loess sequence and to address the forcing mechanisms for the regional climate history of the loess plateau by correlating the stacked record with a composite 18o record in deep sea sediments a total of 18 352 samples were obtained from five loess sections located at baoji lingtai jingchuan puxian and pingliang in the southern and middle loess plateau these yielded high resolution grain size records between section correlation of these shows that although small depositional hiatuses are present in places within a single section most parts of the sections display near continuous dust deposition throughout the quaternary the grain size records were tuned simultaneously to the theoretical variations in obliquity and precession of the earth s orbit the grain size records plotted on their orbital timescales were then averaged to form a stacked loess grain size time series termed the chiloparts record this resolves most of the orbital timescale paleoclimate events buried in the loess soil sequences of the southern and middle loess plateau and can be used as a regional archive of the pleistocene climate history in the loess plateau comparison of the chiloparts record with a composite marine 18o record shows that for the past 1 8 ma the loess paleosol record can be correlated almost cycle by cycle with the marine record several discrepancies in the climatic events between the two records have also been identified implying that regional forcing mechanisms may have played a part in the climatic evolution of the chinese loess plateau

color reflectance of chinese loess and its implications for climate gradient changes during the last two glacial interglacial cycles 1 to examine the relationship between color changes of loess deposits and paleoclimate conditions a north south transect consisting of twelve loess sections were studied color reflectance was measured on loess paleosol samples from the loess transect which accumulated over the last two glacial interglacial cycles the redness value a shows an overall southward increase for both loess and soil units coinciding with the pattern of a southerly increase in pedogenic development and the present north south climatic gradient the redness of loess deposits is linearly correlated with latitude values implying that this parameter is an efficient proxy for the weathering intensity of loess deposits the gradient of weathering intensity is much steeper during interglacials than in glacials by comparison of color records for different time interval

late quaternary environmental changes in misiones subtropical ne argentina deduced from multi proxy geochemical analyses in a palaeosol sediment sequence abstract a 4 5 m long sediment core from a small basin in the province of misiones ne argentina was analyzed in a multi proxy geochemical approach major and minor elemental composition c org n hi oi 13 c org n alkanes and compound specific 13 c analyses of biomarkers in order to contribute to the reconstruction of the late quaternary environmental and climate history of subtropical south america the results of the elemental analyses and radiocarbon dating indicate different sediment provenances for unit a the holocene unit b the late glacial and the last glacial maximum lgm and unit c the inca huasi wet phase before 40 ka bp a sedimentary hiatus after 40 ka bp is interpreted as a pronounced pre lgm dry phase with landscape erosion deflation multi proxy geochemical characterization of the soil organic matter som shows that especially i the stable carbon isotopic composition 13 c of the grass derived alkanes n c 31 and n c 33 ii the alkane ratio n c 31 n c 27 and iii lacustrine derived short and mid chain alkanes are valuable proxies for the reconstruction of the palaeoenvironment a transition from c3 tree dominance to c4 grass dominance is recorded at the end of the inca huasi wet phase in unit b the ratio n c 31 n c 27 documents forest expansion at the beginning of a late glacial wet phase more positive 13 c values in unit a reflect the increasing contribution of c4 grasses and or cam plants to the som during the holocene and a human impact on the formation of this unit may be possible the results are in good agreement with other tropical subtropical palaeoenvironmental records and highlight the importance and temporal variability of the palaeo south american summer monsoon sasm

algal and bacterial hydrocarbons in particulate matter and interfacial sediment of the cariaco trench particulate matter samples 53 m size fractions and sediment from the sediment water interface were collected in the cariaco trench an anoxic marine basin on the continental shelf of venezuela and analyzed for hydrocarbons concentrations of hydrocarbons were highest 10 20 ng 1 in oxic surface waters 0 150 m and at the top of the anoxic zone 350 600 m and were low 3 4 ng l in the low oxygen zone above the oxic anoxic interface 150 250 m and anoxic bottom waters 600 1150 m branched c25 trienes and tetraenes dominated the hydrocarbon distributions in 53 m particles particle size and depth distributions of the hydrocarbons demonstrate the importance of algal hydrocarbons in surface waters coupled with increased abundances of bacterial hydrocarbons especially in the 53 m particles in the anoxic zone these observations illustrate the importance of oxic anoxic interfaces even in the oceanic water column as zones of intense microbial alteration of organic matter and as sources of some of the organic compounds found in sediments

molecular and isotopic records of c4 grassland expansion in the late miocene abstract siwalik paleosol and bengal fan sediment samples were analyzed for the abundance and isotopic composition ofn alkanes in order to test for molecular evidence of the expansion of c4 grasslands on the indian subcontinent the carbon isotopic compositions of high molecular weight alkanes in both the ancient soils and sediments record a shift from low 13c values ca 30 to higher values ca 22 prior to 6 ma this shift is similar in magnitude to that recorded by paleosol carbonate and fossil teeth and is consistent with a relatively rapid transition from dominantly c3 vegetation to an ecosystem dominated by c4 plants typical of semi arid grasslands the n alkane values from our paleosol samples indicate that the isotopic change began as early as 9 ma reflecting either a growing contribution of c4 plants to a dominantly c3 biomass or a decrease in water availability to c3 plants molecular and isotopic analyses of other compounds including n alcohols and low molecular weightn alkanes indicate paleosol organic matter contains contributions from a mixture of sources including vascular plants algae and or cyanobacteria and microorganisms a range of inputs is likewise reflected in the isotopic composition of the total organic carbon from these samples in addition then alkanes from two samples show little evidence for pedegenic inputs and we suggest the compounds were derived instead from the paleosol s parent materials we suggest the record of vegetation in ancient terrestrial ecosystems is better reconstructed using isotopic signatures of molecular markers rather than bulk organic carbon this approach provides a means of expanding the spatial and temporal records of c4 plant biomass which will help to resolve possible tectonic climatic or biological controls on the rise of this important component of the terrestrial biosphere

biogenic soil crusts and soil depth a long term case study from the central negev desert highland wind blown soil degradation is a major problem in arid regions biogenic soil crust consists of a dense growth of many small organisms covering bare desert soil surfaces in arid regions worldwide these organisms perform essential services in the ecosystem for example soil surface stabilization and carbon and nitrogen fixation a unique service provided by biogenic crusts is the incorporation of large quantities of deposited atmospheric particles leading to a significantly enhanced rate of increase in soil depth in windy and arid environments a long term study over 42 months was conducted to investigate the contribution of a biogenic crust to the accumulation of atmospheric particles in an arid zone undisturbed and treated biogenic crusts were studied for their capacity to incorporate deposited particles atmospheric particles were found to accumulate on marble dust collectors at a rate of 120 g m 2 year 1 and on sterilized crust at a rate of 208 g m 2 year 1 while the accumulation rate on live intact crusts was 277 g m 2 year 1 suggesting a soil depth accretion rate on an undisturbed biogenic crust of 10 mm every 33 years maintenance of a healthy biogenic crust in dry land environments should therefore be a major consideration for improving soil quality and increasing soil depth in arid regions

reconstruction of the late quaternary paleoenvironments of the nussloch loess paleosol sequence germany using n alkane biomarkers abstract this study contributes to the paleoenvironmental reconstruction of the loess paleosol sequence of nussloch germany by using n alkanes as plant leaf wax derived lipid biomarkers we found that n alkane patterns and concentrations in the saalian loess and the last interglacial eemian paleosol of nussloch point to very strong degradation and prevailing deciduous vegetation degradation effects in the overlying paleosols and loess layers are less pronounced and allow for the application of an end member mixing model to estimate vegetation changes semi quantitatively our findings highlight the potential for the interpretation of degradation corrected n alkane ratios n alkane modelling results for loess layers paleosols and an in filled paleochannel dated to 60 32 ka suggest that up to 50 of the n alkanes were derived from deciduous trees or shrubs this finding is in agreement with the abundant occurrence of wood fragments and indicates a highly variable and dynamic landscape dominated by tundra shrubland on the other hand deciduous trees or shrubs did not contribute significantly to the soil organic matter in the late weichselian loess layers and the intercalated gelic gleysols 32 18 ka

provenance of loess material and formation of loess deposits on the chinese loess plateau abstract results of a multiple isotopic chemical and mineralogical analysis of loess from the three northwestern inland basins the junggar basin the tarim basin and the qaidam basin and the loess plateau region of china are summarized they suggest a qualification of the conventional views that the three northwestern basins were the important source areas of the loess plateau and that the sand deserts were the primary single source of the chinese loess it is argued that the gobi stony desert in southern mongolia and the adjoining gobi and sand deserts the badain jaran desert tengger desert ulan buh desert hobq desert and mu us desert in china rather than the three inland basins are the dominant source areas of the loess plateau however although these gobi and sand deserts are regarded as the main source regions they serve as dust and silt holding areas rather than dominant producers the mountain processes including glacial grinding frost weathering salt weathering tectonic processes and some fluvial comminution in the gobi altay mts hangayn mts and the qilian mts have played an important role in producing the vast amounts of loess sized material for forming the loess plateau

leaf wax n alkane distributions in chinese loess since the last glacial maximum and implications for paleoclimate abstract leaf wax n alkanes have been recently introduced into loess deposits for paleovegetation and paleoclimate reconstruction however the paleoclimate significance of some n alkane parameters such as chain length ratios l h c 27 c 31 c 29 c 31 and c 27 c 29 c 31 c 33 remains to be clarified in order to evaluate the validity of those proxies in loess deposits leaf wax n alkanes were analyzed from a northwest southeast transect on the chinese loess plateau since the last glacial maximum lgm the n alkanes show a bimodal distribution between c 14 and c 33 with carbon number maxima c max at c 14 or c 16 and at c 31 or c 33 indicative of both terrestrial plant and microbial origin l h variations are in good agreement with climate changes both temporally and spatially i e the higher l h ratio the warmer and wetter climate and vice versa therefore the l h ratio in chinese loess can serve as an efficient proxy for paleoclimate by comparing long chain n alkane ratios with pollen records we suggest that the generally used woody plant proxies c 27 and c 29 and grass proxies c 31 and c 33 are not applicable to chinese loess as the chinese loess plateau was dominated by herbs in both the lgm and the holocene the long chain n alkane ratios may mainly reflect changes in the species composition of local vegetation for a better understanding of leaf wax n alkanes in chinese loess further studies are required to investigate the n alkane distributions in both the major plant species and their associated surface soils on the chinese loess plateau

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

restricted utility of δ13c of bulk organic matter as a record of paleovegetation in some loess paleosol sequences in the chinese loess plateau abstract molecular stratigraphic analyses using gas chromatograph mass spectrometry have been performed in the upper section s0 l1 s1 of the yuanbo loess paleosol sequences in northwest china with a record extending from the last interglaciation through the present interglaciation the cpi carbon preference index values of both n alkanols and n alkan 2 ones display variations between loess deposits and paleosols showing a correlation with the magnetic susceptibility record an indicator of the east asian summer monsoon the observed variations in the indexes in relation to changes in lithology paleoclimate are proposed to result from microbial degradation of higher plant lipids in the paleosols the cpi values of n alkanes n alkanols and n alkan 2 ones are negatively correlated with 13c of bulk organic matter the correlations suggest that the observed glacial interglacial variations of 13c data in the loess stratigraphy reflect the relative importance of the contribution of paleovegetation compared with microorganisms including both the degradation and the addition of organic matter and allochthonous loess soil parent materials it is thus necessary to evaluate the contributions of the latter two before the paleovegetation can be reconstructed based on the 13c analysis of bulk organic matter in some loess paleosol sequences of the chinese loess plateau

spatial patterns of vegetation and climate on the chinese loess plateau since the last glacial maximum abstract in order to identify the spatial patterns of vegetation and climate on the chinese loess plateau since the last glacial maximum lgm pollen analysis was conducted for loess deposits from seven sites which constitute two north south and west east transects across the plateau results show that steppe prevailed both in the lgm and the holocene optimum during the lgm vegetation in the northwest mainly consisted of artemisia echinops type taraxacum type and chenopodiaceae and vegetation in the southeast was characterized by the same types but with a slight increase in poaceae during the holocene optimum vegetation was more diverse with poaceae artemisia echinops type and chenopodiaceae dominant in the northwest and pinus corylus poaceae artemisia and selaginella sinensis dominant in the southeast our records also show that from the lgm to the holocene optimum the presence of echinops type and taraxacum type pollen decreased while poaceae pollen became more prevalent as it has been found that most species of poaceae prefer relatively humid conditions and abundances of echinops type and taraxacum type increase in desert vegetation a new proxy poaceae echinops type taraxacum type ratio p e t was thus developed to compare the spatial differences in climate between the lgm and the holocene optimum with high p e t values indicating relatively warm and wet conditions the p e t ratio shows an overall southward and eastward increase for both the lgm and the holocene optimum furthermore it exhibits a prominent north south and west east gradient during the holocene optimum but displays a flat one during the lgm indicating more pronounced spatial contrasts in climate during the holocene than in the lgm this phenomenon may be attributed to the unique geographic location of the loess plateau which was located in the marginal zone of the east asian summer monsoon during interglacials but was dominated by the winter monsoon during glacials due to a southward displacement of climate zones

acetic acid leachable elements in pedogenic carbonate nodules and links to the east asian summer monsoon carbonate nodules at the base of paleosols within chinese loess are products of pedogenic neoformation and thus have great potential to document the summer monsoon history here we present mineralogical and elemental compositions of carbonate nodules from a north south loess transect of northern china for the last and penultimate interglacials x ray diffraction patterns show that the nodules are composed mainly of calcite together with some silicate minerals such as quartz plagioclase orthoclase illite and kaolinite elemental composition of the acetic acid leachable fraction is characterized by extremely high ca concentration and modest k and mg content followed by al si sr mn fe p na ba pb th and u based on the mineralogical data and relationship between carbonate and the leachable element content we suggest that k mg sr ba and u mainly come from clay minerals na from highly soluble salts trapped by calcite particles and al and si from amorphous phases of pedogenic origin for both the last and penultimate interglacials the na content decreases from north to south while the al si and u concentrations show a southward increasing pattern these characteristics all suggest a southward decrease in aridity across the chinese loess plateau for both interglacials consistent with the pattern of a southerly increase in pedogenic development for the two interglacial soils and with the pattern of the present north south rainfall gradient therefore na al and na si ratios in the acetic acid extract are efficient proxies for aridity and are ultimately controlled by the summer monsoon precipitation i e high ratios indicate weakened summer monsoon intensity in addition the significant content of highly soluble na salts in carbonate nodules highlights soil dewatering as an important mechanism for the formation of pedogenic carbonate at least in the case of the northern loess plateau

lipid distributions in loess paleosol sequences from northwest china molecular stratigraphic analyses using gc ms have been performed on the top section of the jiuzhoutai loess paleosol sequences near lanzhou in northwest china with a record extending from the second last interglacial through the present interglacial the various molecular fossils identified from the second order loess and paleosol layers include c14 c35n alkanes c8 c30n alkanoic acids c12 c30n alkanols and c23 c33n alkan 2 ones the cpi carbon preference index values and the ratio of c29 c31n alkan 2 ones display alternations between loess deposits and paleosols they show a significant correlation with the loess magnetic susceptibility an indicator of the east asian summer monsoon the observed variations of the ketone indices in relation to the change of lithology are proposed to result from microbial re working of higher plant inputs in the paleosols

loess stratigraphy in central china abstract the loess deposits in central china record world wide climate changes of the last 2 5 ma numerous climatic oscillations are marked by alternating loess and soil units with continuous coverage of the matuyama and brunhes epochs magnetic susceptibility of the deposits correlates closely with the oxygen isotope record of the deep sea sediments and provides an independent measure of climate and time the key marker bed of the chinese loess sequence is the paleosol s5 the time equivalent of the mid brunhes oxygen isotope stages 13 14 and 15 it marks a prolonged interval of warm humid climate lasting from approximately 615 to 470 thousand years ago several episodes of river downcutting coincide with deposition of the exceptionally thick loess units l1 oceanic oxygen isotope stages 2 to 4 l2 stage 6 l5 stage 12 l6 stage 16 l9 stage 22 l15 stage 38 about 1 15 ma and ws4 about 2 3 ma these erosional events are interpreted as a result of episodic uplift of the loess plateau the deposition of the earliest loess layers between 2 5 and 2 3 ma ago marks a first order shift from warm and humid environments toward harsh continental steppes comparable to those of the middle and late pleistocene little if any lithologic or paleontologic changes were noted within or above the olduvai magnetozone so that the proposed plio pleistocene boundary at approximately 1 65 ma has no lithostratigraphic and biostratigraphic representation in the chinese loess series comparison with the deep sea drilling program core 552a in the north atlantic and with the santerno river section near bologna shows that the occurrence of the earliest loess in china coincides with the timing of the first significant ice rafting in the north atlantic and with the appearance of cold water foraminifers in the marine deposits of northern italy an extension of the stage system of the oxygen isotope signal extended back to the gauss matuyama boundary is proposed

summer monsoon intensity controls c4 c3 plant abundance during the last 35 ka in the chinese loess plateau carbon isotope evidence from bulk organic matter and individual leaf waxes the natural abundance of c3 and c4 plants is affected by multiple environmental factors including temperature moisture balance and atmospheric pco2 the relative importance of these factors is a subject of considerable debate and may vary in different natural ecosystems previous studies generally focus on single loess sequences in the chinese loess plateau and conflicting conclusions on c4 c3 have been reached when studying carbon isotope ratios in carbonate and organic matter in this paper we report a comprehensive carbon isotopic characterization of total organic carbon toc and individual higher plant leaf waxes from five loess sequences spanning the last 35 ka from the chinese loess plateau clp the five coring sites encompass large gradients of annual mean temperature 9 2 13 9 c and precipitation 402 673 mm allowing us to assess the controlling mechanisms on c4 c3 plant ratios glacial interglacial sequences provide carbon isotope data for comparison with other climatic and environmental proxies such as lithology and magnetic susceptibility our results demonstrate that increased c4 c3 ratios are positively correlated with higher temperature and increased summer rainfall which characterize stronger summer monsoon in all five sites we conclude c4 abundance increases from the last glacial to the holocene in response to greater monsoon activity and that the c4 expression is suppressed in the cold and drier intervals

vegetation and climate changes in the western chinese loess plateau since the last glacial maximum abstract pollen analysis was conducted for loess deposits from three sites in the western chinese loess plateau i e the loess area west of the liupan mountains results show that during the last glacial maximum lgm in situ vegetation was dominated by artemisia and some drought tolerant species such as echinops type chenopodiaceae nitraria and ephedra while coniferous forest mainly picea flourished in nearby river valleys during the holocene optimum picea almost disappeared and echinops type chenopodiaceae nitraria and ephedra decreased vegetation was characterized by artemisia taraxacum type polygonaceae and leguminosae implying the climate was warmer and wetter than during the lgm during the late holocene chenopodiaceae indicator of human managed habitats increased in the study area indicating enhanced human activity the climate was warmer and more humid in the loess areas east of the liupan mountains than in the west during both the lgm and holocene optimum likewise a significant difference in specific plant types was observed between the east and west since the lgm during the lgm pinus and some broadleaf trees emerged but no picea forest grew while in the west vegetation was characterized by desert shrub and desert steppe in situ and by dark coniferous forests mainly picea in nearby river valleys during the holocene optimum treeline advanced upward as a result of increased temperature picea thus withdrew from the western loess areas therefore temperature is the major factor controlling the growth of picea in the chinese loess plateau

environmental evolution recorded by lipid biomarkers from the tawan loess paleosol sequences on the west chinese loess plateau during the late pleistocene this study provides a reconstruction of the environmental evolution since 128 ka recorded by the lipid biomarkers of the c15 c35n alkanes the c13 c33n alkan 2 ones and the c12 c30n alkanols isolated from the tawan loess section northwest china variations in paleoenvironment are reconstructed from the values of the carbon preference index cpi the average chain length acl the l h ratio of lower molecular weight to higher molecular weight homologues the n alkane c27 c31 ratios and the n alkan 2 one c27 c31 ratio these parameters indicate the dominance of grasses over the west chinese loess plateau clp during the late pleistocene lower values of the cpi and the acl values respectively indicate stronger microbial reworking of organic matter and changes in plant species which are both indicative of a warmer wetter environment furthermore the fluctuations of environment recorded in the tawan section exhibit ten phases that show obvious cycles between warm periods and cold intervals this study reveals that changes in the biomarker proxies agree well with changes in the magnetic susceptibility and grain size and it indicates a huge potential for paleoenvironmental reconstructions by using the n alkan 2 one and n alkanol proxies

paleoclimates and monsoon variations interpreted from micromorphogenic features of the baoji paleosols china abstract a full climatic interpretation of the loess paleosol sequence in china that covers the last 2 5 ma nearly continuously has been restricted because the soils in the oldest loess unit the wucheng loess spanning about 1 2 2 5 ma are not distinct enough to ensure accurate recognition and subdivision in the field recently the authors investigated the baoji loess paleosol sequence in the southern most part of the loess plateau where 37 paleosols were clearly defined including those of the wucheng loess based on macro and micromorphological observations the major pedogenic processes involved in the formation of the baoji paleosol are believed to be carbonate eluviation and illuviation clay translocation pseudogleization and rubification the diagnostic b horizons of the 37 soils are classified into four types bw or weak bt moderate bt strong bt and very strong bt the holocene soil at baoji contains a moderately developed bt which is interpreted to have formed under steppe forest vegetation most of the soils with bt horizons to the holocene soil are interpreted to be developed under forest and or steppe forest environments primary carbonates in most of the loess beds have been leached with the loess beds acquiring weak to strong granular structures the loess is subdivided into four types massive weakly weathered moderately weathered and strongly weathered they are believed to have mainly accumulated under steppe environments variations of monsoonal rain exhibit frequent and wide oscillations over the last 2 5 ma documented by alternations of loess and paleosol units the oscillatory pattern appears to be a function of the time interval considered

reconstruction of postglacial to early holocene vegetation history in terrestrial central europe via cuticular lipid biomarkers and pollen records from lake sediments high resolution environmental reconstruction for central european terrestrial settings is commonly based on sediment records that provide the pollen spectra used for reconstruction of vegetation development alternatively complementary algal insect or zooplankton assemblages and or carbonate 18 o isotope profiles are investigated in this study vegetation development and inferred climate evolution were documented on a decadal to centennial scale by analysis of land plant cuticular lipids accumulated in lake sediments wax lipids derived from land plant leaves and blades are source diagnostic and highly resistant to degradation their aerodynamic properties favor short distance eolian transport but they are less affected by possible long distance transportation that complicates pollen analysis the late glacial to holocene sedimentary record of lake steisslingen southwestern germany was investigated by palynological and geochemical means tundra type pioneer vegetation consisting predominantly of grasses and herbs is dominated by nc31 alkanes whereas pioneer birch forest yields preferentially nc27 alkanes establishment of a pine assemblage is recognizable by elevated nc29 and nc31 leaf wax alkanes and the diversification of deciduous forests in the holocene is marked by nc29 dominance lipid geochemistry and palynology resolve decadal excursions such as the mid younger dryas event centennial climate trends with pronounced and rapid changes at the oldest dryas bolling allerod younger dryas and younger dryas preboreal transitions are consistently reflected by molecular and palynological proxy data the demonstrated suitability of an independent molecular proxy in paleoenvironmental studies provides new perspectives in high resolution climate reconstruction

importance of biological loess crusts for loess formation in semi arid environments the essential abiotic components for loess formation are material dust atmospheric circulation wind suitable surface conditions for the trapping of aeolian material and for the subsequent development of typical loess sedimentary structures in spite of the world wide distribution of loess deposits knowledge of the processes of dust accumulation and its transformation to mature loess sediment is still inadequate loess accumulation appears greatest during the most arid periods and in semi arid regions biological crusted surfaces bcs are of potentially great importance in loess formation especially in semi arid regions bcs are highly specialized extremophile communities and apparently play an important role in atmospheric dust trapping and erosion prevention results indicate that cyanobacterial strains isolated from current carpathian basin loess exhibit specific morphological and eco physiological characteristics that play a key role in loess formation warranting adoption of the new term biological loess crusts blc a model of the influence of cyanobacterial blc life strategies on loess formation explains trapping accumulation and preservation as well as loess texture and structure this potential significance of blc in the accumulation and preservation of loess sediments may be considered as a model suitable model database for recognition of bioorganic modification of geological strata mycosporine and scytonemin pigments can serve as blc biomarkers elucidating their role in soil evolution and in aiding paleoclimatic paleoenvironmental and paleovegetation reconstructions

molecular proxies for paleoclimatology we summarize the applications of molecular proxies in paleoclimatology marine molecular records especially are proving to be of value but certain environmentally persistent compounds can also be measured in lake sediments loess deposits and ice cores the fundamentals of this approach are the molecular parameters the compound abundances and carbon hydrogen nitrogen and oxygen isotopic contents which can be derived by the analysis of sediment extracts these afford proxy measures which can be interpreted in terms of the conditions which control climate and also reflect its operation we discuss two types of proxy those of terrigenous and those of aquatic origin and exemplify their application in the study of marine sediments through the medium of ten case studies based in the atlantic mediterranean and pacific oceans and in antarctica the studies are mainly for periods in the present the holocene and particularly the last glacial interglacial but they also include one study from the cretaceous the terrigenous proxies which are measures of continental vegetation are based on higher plant leaf wax compounds i e long chain circa c30 hydrocarbons alcohols and acids they register the relative contributions of c3 vs c4 type plants to the vegetation in the source areas the two marine proxies are measures of sea surface temperatures sst the longer established one u37k is based on the relative abundances of c37 alkenones photosynthesized by unicellular algae members of the haptophyta the newest proxy tex86 is based on c86 glycerol tetraethers gdgts synthesized in the water column by some of the archaeal microbiota the crenarchaeota

variations in loess and palaeosol properties as indicators of palaeoclimatic gradients across the loess plateau of north china abstract new data are presented on micromorphology magnetic susceptibility and particle size characteristics of three soil sediment units at four locations along a wnw ese transect across the loess plateau of north china differences and spatial trends are used to assess the sensitivity of such data as proxies of regional palaeoclimatic gradients the steepest climatic gradient suggested by the magnetic susceptibility for the s1 palaeosol is at the eastern humid end of the traverse micromorphology and particle size analysis show that the loess units in the east are richer in clay than the best developed palaeosols in the semi arid west and that particle size in the west appears to provide a more sensitive record of climatically driven changes than magnetic susceptibility the use of surface and near surface soils as a datum for inferring palaeoprecipitation values is reviewed in the light of recent evidence of substantial degradation of such soils micromorphological and particle size analysis of closely spaced samples from loess palaeosol sequences is a sensitive addition to magnetic susceptibility stratigraphy and correlation

a new osl chronology for dust accumulation in the last 130 000 yr for the chinese loess plateau abstract a sensitivity corrected multiple aliquot regenerative dose protocol has been developed for fine grained quartz osl dating of chinese loess its reliability has been assessed on the basis of the methodology and by dating reference samples of known age close to the transition from the last interglacial paleosol s 1 to the last glacial loess l 1 which corresponds to the marine oxygen isotope stage mis 5 4 transition on the basis of the fine grained quartz osl age estimates for 33 loess samples from the upper part of the luochuan profile a detailed chronostratigraphy of continuous dust accumulation in the past 130 ka has been proposed changes in the accumulation rate occurred during the last glacial period mis 4 to mis 2 unexpectedly high accumulation rates were found in the weakly developed l 1 2 s paleosol of the last interstadial mis 3 rather than in the classic l 1 1 and l 1 3 loess of the cold dry glacial condition mis 2 and 4 the osl ages show some disagreement with the previous numerical chronology for the loess paleosol sequence based on correlation of variations in grain size with sedimentation rate the latter method resulted in an almost constant accumulation rate from 72 to 12 ka

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