holocene thermal optimal and climate variability of east asian monsoon inferred from forest reconstruction of a subalpine pollen sequence taiwan the east asian monsoon holocene optimal period has been debated both about duration and whether conditions were a maximum in thermal conditions or in precipitation in this study we show holocene climate variability inferred by a forest reconstruction of a subalpine pollen sequence from peat bog deposits in central taiwan based on modern analogues of various altitudinal biomes in the region a warmer interval occurred between 8 and 4 ka bp calibrated 14 c years when the subtropical forests were more extensive the holocene thermal optimum is represented by an altitudinal tropical forest at 6 1 5 9 ka bp and 6 9 ka bp and only the latter was accompanied by wet conditions indicating decoupling of thermal and precipitation mechanism in the middle holocene abrupt and relative severe cold phases shown by biome changes occurred at about 11 2 11 0 ka bp 7 5 ka bp 7 2 ka bp 7 1 ka bp 5 2 ka bp 5 0 ka bp and 4 9 ka bp a spectral analysis of pollen of a relatively cold taxon salix reveals that the time series is dominated by a 1500 yr periodicity and similar to the cold cycle reported in the marine records of indian and western pacific oceans the cold warm conditions inferred by the change of forests show close relationship to solar energy in comparison with the production rate of be 10

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

variations in monsoonal rainfall over the last 21 kyr inferred from sedimentary organic matter in tung yuan pond southern taiwan abstract changes in paleorainfall intensity linked to the strength of the east asian ea summer monsoon since 21 cal kyr bp are inferred from the organic matter contents of a 15 m sediment core from tung yuan pond in southern taiwan high total organic carbon total nitrogen toc tn values in association with increased toc content suggest that more soil derived material containing terrestrial organic matter om was delivered to the lake during periods of increased runoff associated with extensive precipitation that resulted from intensified summer monsoons whereas low values indicate om possessing a dominant algal origin during weakened summer monsoons rainfall intensity in terms of the proportion of terrestrial om was high in four periods the last deglaciation 17 2 to 12 2 ka the early holocene 10 6 to 8 6 ka the middle holocene thermal optimum 7 7 to 5 ka and the late holocene 4 2 to 2 ka whereas it was low in the intervening time periods high toc tn values coincide with peak values of summer insolation and thus the strongest ea summer monsoon during the early and middle holocene small drops in these ratios correspond to increasing and decreasing solar radiation in the deglacial period and the late holocene respectively the four intervals with low toc tn ratios as well as episodic drops of the ratios during the deglaciation and the early and late holocene are concordant with the late last glacial 21 to 17 2 ka the oldest 14 8 ka the older 13 3 ka and the younger dryas 13 to 11 5 ka the 8 2 cold event 8 6 7 7 ka and a late holocene cold event 5 4 2 ka and suggest a weakened ea summer monsoon during these times moreover high frequency hydrological variability occurred during the early holocene heavy rainfall persisted during the middle holocene and precipitation intensity generally diminished after 5 ka the tung yuan pond sediment record indicates that the toc tn ratio can be used as a paleorainfall intensity proxy to trace variations in the ea summer monsoon strength in other small lakes

holocene climate change in northeastern china reconstructed from lipid biomarkers in a peat sequence from the sanjiang plain abstract lipid biomarkers extracted from a sediment peat sequence from the sanjiang plain were analyzed to assess the change in regional vegetation and climate during the last 8 ky the combination of n alkane and n alkanoic acid distributions and published pollen and plant macrofossil records for the lake sediments underlying the peat reveal that the region experienced a warmer and wetter period before ca 6 ka that corresponds to the monsoon maximum and holocene climate optimum in northeast china the climate then entered a cold and wet period from 6 to 4 ka a shift to warmer and drier conditions starting 4 ka is recorded as a transformation from a shallow lake to a peat deposit from 1 5 to 0 4 ka the region entered a cold and wet period that was followed by warm and dry conditions for the most recent 0 4 ky our lipid based paleoclimate reconstruction was compared with holocene reconstructions based on lipid records from the nearby hani peat sequence peat cellulose 13c results from the jinchuan peat sequence and pollen records from other lakes in northeast china most of the regional paleoclimate changes reconstructed from the lipid proxies in the sanjiang plain peat sequence have a strong link with sea surface temperature changes in the sea of japan that were influenced by summer solar insolation at 65 n and the east asia summer monsoon in contrast the change to the warmer and drier conditions of the last four centuries seems to be mainly a consequence of human activity

n alkan 2 one biomarkers as a proxy for palaeoclimate reconstruction in the mfabeni fen south africa abstract the sub tropical mfabeni fen is the only continuous coastal peat deposit that documents glacial and interglacial palaeoenvironmental conditions since the late pleistocene ca 47 cal kyr bp in southern africa published bulk geochemical biomarker and leaf wax 13c data along with palynology and stratigraphic studies of the mfabeni peat sequence render it an ideal record for testing new palaeoreconstruction proxies in this study we aimed to establish the proxy potential of n alkan 2 one n ket compounds by tracing their source origin and post depositional diagenetic change and if they preserve or not a robust palaeoenvironment signal that complements our understanding of palaeoclimatic variations in the mfabeni archive the most likely source for n kets is via microbial decarboxylation of n 1 alkanoic acids n fas and to a lesser degree oxidation of same chain length n alkanes n alks the n ket average chain length aclket and n c23 and c25ket precursor ratios displayed a statistical significant negative relationship with the n alk aquatic plant proxy paq suggesting the source of n kets to be submerged aquatic plants during waterlogged conditions that suppressed microbial activity during the ensuing anoxic conditions both the mid chain and long chain n ket precursor ratios displayed predominant water level fluctuation controls with temperature as a secondary regulator by comparing the n ket data with published environmental and climate reconstructions from the same core and with geomorphology and palynological studies of the mfabeni basin we conclude that the n kets show promise as a palaeoclimate proxy and can be used in conjunction with other biomarker proxies to reconstruct ancient hydrological changes in sub tropical peatlands

milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

biomarkers as proxies for plant inputs to peats an example from a sub boreal ombrotrophic bog lipid distributions in modern peat forming plants were determined and compared to biomarkers recovered from a ca 2800 year old peat deposited in a dutch ombrotrophic bog the peat section spans a well constrained shift in local hydrology and vegetation and potential molecular proxies for plant inputs were directly tested against the macrofossil record based on the analyses of modern plants low molecular weight lmw n alkanes c23 c25 and high molecular weight n alkanes c33 are proposed as potential biomarkers for sphagnum and non sphagnum inputs respectively consistent with this in the bargerveen peat core lmw n alkane abundances increase and hmw n alkane abundances decrease coincident with the shift to sphagnum dominated peat additional potential proxies include the abundances of c22 alkanedioic acid and phytenyl phytenoate as sphagnum indicators and the abundances of the triterpenoids taraxer 14 ene and taraxast 20 ene as biomarkers for ericaceae rootlets

branched gdgt based paleotemperature reconstruction of the last 30 000 years in humid monsoon region of southeast china abstract the use of bacterial branched glycerol dialkyl glycerol tetraethers brgdgts to reconstruct mean annual air temperatures maats and environmental ph from soils has sparked significant interest in the terrestrial paleoclimate community however the reconstruction of these climate proxies from peat bogs is rare in monsoonal regions of the east asia this research was carried out on a core from the shuizhuyang szy peat bog located in fujian province branched gdgt brgdgt indexes were used for reconstructing the paleoclimate of the last 30 cal ka the aim was to evaluate quantitatively the maat and ph values since the last glacial maximum lgm in the subtropical zone of china results show that the cbt mbt derived maat at mis 3 is about 15 6 c on average which is followed by a significant fall at the lgm 11 7 12 1 c the temperature difference between the lgm and the present day value is as high as 5 8 c the synchronous variation of biomarker and pollen proxies indicates that replacement of subtropical evergreen broadleaved forests by cold tolerant deciduous broadleaved forests was driven by the significant drop in air temperature our results also indicate that the younger dryas event lasted from about 12 9 to about 11 3 cal ka and cooling event at 3 2 cal ka in the late holocene was detected showing the sensitivity of peat bogs to rapid cooling our ph reconstructions indicate that the ph of the bog rose during heinrich 1 and bolling allerod periods probably due to low precipitation and were lowest in the holocene thermal maximum between 8 ka and 2 5 ka probably due to higher precipitation the decoupling of reconstructed maat and ph during particularly deglaciation and yd periods supports the hypothesis that the variations in temperature and precipitation are not always synchronous

development and refinement of proxy climate indicators from peats peat especially from acidic mires bogs is a natural archive of past environmental change reconstructions of past climate from bogs commenced in the 19th century through examination of visible peat stratigraphy and later formed the basis for a postglacial climatic scheme widely used in northwest europe nevertheless misconceptions as to how bogs grow led to a 50 year lacuna in peat climate study before the concept of cyclic regeneration in bogs was refuted in recent decades research using proxy climate indicators from bogs has burgeoned a range of proxies for past hydrological change has been developed as well as use of pollen bog oaks and pines and other data to reconstruct past temperatures most of this proxy climate research has been carried out in northern europe but peat based research in parts of asia and north america has increased particularly during the last decade while research has also been conducted in australia new zealand and south america this paper reviews developments in proxy climate reconstructions from peatlands chronicles use of a range of palaeo proxies such as visible peat stratigraphy plant macrofossils peat humification testate amoebae and non pollen palynomorphs and explains the use of wiggle match radiocarbon dating and relationship to climate shifts it details other techniques being used increasingly such as biomarkers stable isotopes inorganic geochemistry and estimation of dust flux and points to new proxies under development although explicit protocols have been developed recently for research on ombrotrophic mires it must be recognised that not all proxies and techniques have universal applicability owing to differences in species assemblages mire formation topographic controls and geochemical characteristics

the influence of climate hydrology and permafrost on holocene peat accumulation at 3500 m on the eastern qinghai tibetan plateau peatland of the eastern qinghai tibetan plateau lies at the convergence of the east asian and indian monsoon systems in eastern asia to understand the evolution of this peatland and its potential to provide new insights into the holocene evolution of the east asian monsoon a 6 m peat core was collected from the undisturbed central part of a peat deposit near hongyuan the age depth profile was determined using 16 14c ams age dates the peat analysed for a range of environmental variables including carbon nitrogen and hydrogen concentration bulk density 13c and the associated spring water analysed for hydrogen and oxygen isotopes the age depth profile of the recovered peat sequence covers the period from 9 6 to 0 3 kyr bp and is linear indicating that the conditions governing productivity and decay varied little over the holocene using changes in carbon density organic carbon content and its 13c cold dry periods of permafrost characterised by low density and impeded surface drainage were identified the low 18o and d values of the spring water emanating around the peat deposit down to 13 8 and 102 vsmow respectively with an inverse relationship between electrical conductivity and isotopic composition indicate precipitation under colder and drier conditions relative to the present day in view of the current annual mean air temperature of 1 c this suggests conditions in the past have been conducive to permafrost inferred periods of permafrost correspond to independently recognised cold periods in other holocene records from across china at 8 6 8 2 7 8 5 6 4 2 3 1 and 1 8 1 5 kyr bp the transition to a cold dry climate appears to be more rapid than the subsequent recovery and cold dry periods at hongyuan are of longer duration than equivalent cold dry periods over central and eastern china light dark banding peat on a scale of 15 30 years from 9 6 to 5 5 kyr bp may indicate a strong influence of decadal oscillations possibly the pacific decadal oscillation and a potential link between near simultaneous climatic changes in the northwest pacific enso movement of the intertropical convergence zone and the east asian monsoon

asian summer monsoonal variations during the holocene revealed by huguangyan maar lake sediment record abstract high resolution records of summer monsoonal evolution in the holocene are essential to paleoclimate reconstruction but are hard to obtain here we provide a continuous well dated high resolution record from huguangyan maar lake located in the west pacific climate regime multi proxies including chlorophyll a toc sr rb ratio and magnetic susceptibility have been used to reconstruct the monsoon variations in the holocene higher chlorophyll a values are related with stronger summer monsoon and vice versa high temporal resolution radiocarbon dating enables us to divide summer monsoon evolution stages summer monsoon in zhanjiang area was strongest in the early holocene but began to decline at 6080 yr bp and weakened substantially since about 3600 yr bp the transition around 6080 yr bp supported by our high resolution dating lags the previous estimates by 1700 years the decreasing summer solar radiation at 30 n through the holocene is probably responsible for gradually weakened summer monsoon the anti phased co variation of summer monsoon intensity and enso activity throughout the holocene suggests that they could be interlinked driven together by solar radiation at orbital scale

hydrogen isotopic ratios of plant wax n alkanes in a peat bog deposited in northeast china during the last 16 kyr abstract based on paleoclimatic reconstructions using various proxies the holocene climate optimum 10 5 6 ka has been characterized as a warmer and wetter period in most of east asia the summer monsoons associated with the east asian monsoon evidently intensified and extended further inland from the pacific ocean a source region of moisture a notable exception to this general pattern exists in northeast china where less wet conditions are recorded we determined molecular compositions of individual plant wax hydrocarbons and their hydrogen isotope compositions d values in a radiocarbon dated peat core recovered from the hani marsh in jilin province china and confirmed that the temperature dependent effective precipitation in northeast china decreased during the holocene climate optimum a combination of p aq an indicator of the relative contribution of aquatic to terrestrial plants and the difference in d between low c 23 c 25 and c 27 and high molecular weight c 31 n alkanes in the hani peat bog indicates a dramatic change in vegetation from the deglaciation to the holocene no significant differences were observed between the d values of low and high molecular weight n alkanes with relatively high d values and low p aq during the early holocene indicating that all n alkanes were produced by evapotranspiration sensitive terrestrial plants during that time however lower d values of mid chain n alkanes c 23 c 25 and c 27 relative to the long chain n alkane c 31 together with higher p aq values during the deglaciation 14 11 ka suggest an increase in the contribution of aquatic plants and a higher water level during the period the study demonstrates that northeast china was under a markedly wetter climate condition during the late deglaciation for the 16 kyr record in the hani peat sequence we infer that moisture delivery by the east asian monsoon was relatively invariable in northeast china but increased evaporation during the warmer holocene climate optimum reduced the effective precipitation defined by the balance between precipitation and evaporation

assessment for paleoclimatic utility of terrestrial biomarker records in the okhotsk sea sediments we measured terrestrial plant biomarker long chain n alkanes in the sediment cores taken from the sea of okhotsk to examine paleoclimatic utility of long chain n alkanes in marine sediments this study demonstrates that sedimentary record of n alkane in the sea has a high potential to provide important complementary paleo climate paleo environmental information molecular distributions of long chain n alkanes in marine sediments show a typical signature of terrestrial plant wax derived n alkanes with strong odd carbon number predominance from the last glacial to the present suggesting a source of long chain n alkanes in the okhotsk sea sediments has been terrestrial higher plants throughout the time the down core profiles of concentrations of c25 c35 n alkanes in xp07 c9 collected from the northwestern site revealed three events of enhanced terrestrial organic matter input during the last deglaciation the two pronounced events correspond to melt water pulse mwp events 1a 14 5 12 5 ka and 1b 11 6 5 ka these events possibly linked to increases in river discharge and erosion of submerged continental shelf due to drastic rise in sea level down core profiles of molecular distributions of n alkanes in the okhotsk sea sediments significantly vary over the last 25 kyr and are similar to that of a peat core sequence in the east russia and essentially consistent with pollen data from marine and peat core sequences

the n alkanol paleoclimate records in two peat deposits a comparative study of the northeastern margin of the tibetan plateau and northeast china a number of studies have revealed that the climate in the eastern margin of the tibetan plateau and northeast china is sensitive to postglacial changes unfortunately the link of the past climate evolution between the two regions is not well understood in this study two cores are analyzed to determine this link directly the high resolution n alkanol distribution patterns from two typical peat sequences covering the past 16 000 cal years in the northeastern margin of the tibetan plateau and northeast china respectively are closely examined by gas chromatograph mass spectrometry analysis in combination with other palaeoclimatic proxies it is proposed that the n alkanol average chain length and c22 c24 c26 c28 ratio could reflect past climate changes in the two peat sequences the n alkanol proxies reveal several climatic intervals in the period from the last deglaciation through the holocene a comparison of n alkanol records between the northeastern margin of the tibetan plateau and northeast china indicates that the start and end of the warm holocene optimum differed at the two locations the spatially asynchronous pattern of climatic change is possibly a result of different responses to change in solar radiation the evolution of the holocene paleoclimate is more consistent with changes in northern hemisphere solar radiation in northeast china than on the tibetan plateau the holocene optimum began and terminated earlier in northeast china than in the northeastern margin of the tibetan plateau thus the two n alkanol proxies provide valuable insights into the regional holocene climate and local environmental conditions

a 13 000 year climate record from western tibet although the tibetan plateau is important in influencing the atmospheric circulation of the northern hemisphere1 3 there are only a few continuous palaeoclimate records available and these are limited to the plateau s northeastern margin4 6 here we present a 13 000 yr record from sumxi co western tibet constructed from both lake core and shoreline studies which shows that conditions in the early middle holocene were warmer and wetter than at present these results confirm model predictions of an intensified monsoon over the region at 9 000 yr bp owing to an orbitally induced increase in summer insolation7 8 we also find evidence for warm humid pulses at 12 500 and 10 000 yr bp in phase with the steps of the last deglaciation and for a return to cold dry conditions at 11 10 000 yr bp none of which can be explained by orbital variations the existence of the cold episode confirms that the cooling associated with the younger dry as event occurred in continental china6 9 and provides further evidence of the global nature of this event10

paleohydrological changes in southeastern china from 13 1 to 2 5 ka based on a multi proxy peat record abstract investigating the hydrological changes in the east asian monsoon regions of china during the holocene could provide important insights into the mechanism and future variability of the east asian summer monsoon easm rainfall however existing studies have revealed large inconsistencies in the spatiotemporal pattern of the hydrological changes in east china probably due to different climatic sensitivities of various proxies the uncertainties of sedimentary chronologies and unevenness of proxy record distributions thus multi proxy records with precise dating are needed especially in southeastern china which is one of the key places to determine the spatiotemporal pattern with few hydrological records available in this study hopanoid flux humification degree the concentration of total organic carbon toc and the atomic ratio between total organic carbon and total nitrogen c n of organic matter were applied on shuizhuyang szy peat cores retrieved from southeastern china to reconstruct the paleohydrological changes spanning from 13 1 to 2 5 ka results of these proxies reveal a moderately dry period during 13 1 11 6 ka followed by an interval of increasing aridity from 11 6 to 8 6 ka the holocene optimum referred here as an effective moisture maximum occurred at 8 6 4 4 ka before the climate became drier from 4 4 to 2 5 ka the hydrological changes in szy during the holocene with a mid holocene holocene optimum are consistent with the regional climate records in southeastern china such an overall arid wet arid pattern in southeast china during the holocene closely tracked the variations in the west to east sea surface temperature sst gradient in tropical pacific we preliminarily concluded the enso state and the western pacific subtropical high wpsh position associated with variations in the thermal state of the tropical pacific were primarily responsible for the hydrological changes in southeast china during the holocene our study added new evidence to the spatiotemporal pattern of hydrological changes in eastern china during the holocene

paleoenvironmental implications of molecular and carbon isotopic distributions of n alkanes in the hominoid bearing upper miocene sediments from the zhaotong basin southwestern china abstract it is crucial to understand the relationship between hominoid primates and their living environment located at the southeastern margin of the tibetan plateau the shuitangba stb outcrop from the zhaotong basin is famous for bearing the remains of the youngest known ape fossil in the terminal miocene 6 2 ma in this study the molecular and carbon isotope compositions of n alkanes together with the loss on ignition and the bulk carbon isotope composition of total organic matter were investigated in the stb outcrop to infer the paleoenvironmental conditions in this uppermost miocene sedimentary sequence with the emphasis on the habitat of the stb hominoid in the hominoid bearing peaty clay layer and the surrounding lignite layers the n alkane molecular and carbon isotope compositions support a primary contribution from terrestrial higher plants in contrast n alkanes in the upper shallow lake sediments are derived from multiple origins mainly from aquatic plants and bacteria both carbon preference index cpi and average chain length acl vary closely with the lithology but the cpi record shows the larger amplitude of change than the acl and varies sharply during the lithological boundary it is notable that the changes of the molecular and carbon isotope compositions of long chain n alkanes do not parallel with the abrupt increase of poaceae pollen percentage during the stb hominoid appearing stage such an inconsistency between herb pollen percentage and n alkane ratios may result from the different sources our results clearly support that these organic matter based ratios have the potential to record the paleoenvironmental changes in ancient lacustrine sediments

middle to late holocene environmental changes in the depositional system of the tropical brackish bolgoda lake coastal southwest sri lanka abstract the tropical bolgoda lake is one of the largest lagoonal estuaries in sri lanka organic constituents in this lake were investigated using 28 surface sediments three cores from the lake and four short cores from mangrove mud elemental and molecular compositions of sediments and living organic matter om were determined using cns elemental analysis and gas chromatography mass spectrometry respectively chronology of events was determined using accelerated mass spectrometry ams 14 c data for bulk oms woods and mollusk shells the history of bolgoda lake can be divided into two major chrono stratigraphic divisions namely a lower sedimentary succession from ca 7 0 cal ky b p to 2 5 cal ky b p and an upper sedimentary succession from ca 2 5 cal ky b p to the recent according to the sapropelic depositional system concentrations of the mangrove biomarker taraxone increased significantly at ca 7 0 cal ky b p the lower part of the sediment sequence had moderate productivity and was mainly deposited under marine terrestrial influence in oxygen poor anoxic conditions during mid holocene sea level highstands a drastic increase in total organic carbon toc content reaching 29 was found in one of the bolgoda cores this increase occurred because of sea level regression at about 2 5 cal ky b p this change was probably caused by development of a beach rock sandbar and the estuary system changed to a semi closed lake due to the sea level regression as a result aquatic vascular plants predominate in this depositional system after ca 2 5 cal ky b p toc content decreased slightly but relatively high toc contents were maintained in the muddy sediments in moderately sized and shallow 1 2 m tropical estuaries lagoons such as bolgoda lake drastic changes in toc contents may be the most sensitive indicator of sea level variations increase in higher plant om with higher n c 29 n c all and n c 37 n c all alkane ratios also suggest a climatic transition from wetter to somewhat drier after the middle holocene accumulations of pyrogenic polycyclic aromatic hydrocarbons pahs in the modern sediments record anthropogenic activity after european settlement in the 15th century

lipid geochemistry of sediments from upton broad a small productive lake major lipid classes isolated from 3 sections of the sediment profile of upton broad a shallow lake formed about 500 yr ago were correlated with input and with changes attributable to early diagenesis surficial sediment contains lipids characteristics of the known recent algal and microbial input preservation of chlorophyll pigments and absence of appropriate markers suggest that diagenesis is minimal older deposits from the eutrophic phase of the lake s history contain higher levels of bacterial lipids and diagenetic products the earliest sediment contains lipids characteristic of terrigenous input subjected to more extensive diagenesis than the younger sediment recognition of early diagenesis in anoxic sediment suggests that distributions of the shorter chain homologous free n alkanes alkanols and alkanoic acids result from microbial synthesis using material initially deposited at the sediment surface rather than partial preservation of the lipids of primary source organisms

multiproxy record of late pleistocene holocene climate and vegetation changes from a peat bog in patagonia abstract pollen assemblage changes and stable hydrogen isotope analysis of mosses sphagnum magellanicum and drepanocladus s l from a bog in tierra del fuego argentina provided independent proxies for reconstructing changes in effective moisture and temperature over the past 16 000 cal yr b p a deterministic model was used to reconstruct the stable hydrogen isotope composition of meteoric water from the d h ratios of bog mosses over the last 16 000 years abrupt changes in temperature as recorded in d h ratios of moss cellulose were accompanied by synchronous changes in vegetation composition during the late pleistocene and early and middle holocene when moisture levels were lower than today in contrast temperature variability during the late holocene was not accompanied by comparable vegetation changes in particular grass pollen poaceae increased during periodic cold spells between 15 000 and 11 000 cal yr b p but a cold spell of similar magnitude ca 2000 cal yr b p did not appear to affect vegetation during the late pleistocene the isotopic record from the peat core shows variations similar to the d h ratios in the antarctic taylor dome ice core however the timing of the changes in the harberton record is more in line with the timing of other southern hemisphere records

reconstruction of late glacial and holocene climate evolution in southern china from geolipids and pollen in the dingnan peat sequence we have carried out a multi proxy analysis of a radiocarbon dated peat core that records the history of paleoclimate change dating from 18 ka in the dingnan region of southern china fatty acid and hydrocarbon distributions total organic carbon toc concentrations pollen assemblages and sediment lithology reveal a succession of three major paleoclimate intervals plant waxes are the predominant origin of the n alkanoic acid and n alkane compositions of this sedimentary sequence contributions of these geolipid components vary relative to toc and with changes in lithology and help to refine a pollen based reconstruction of local paleoclimate evolution a period of cool and fairly wet climate 15 630 10 450 cal abp follows accumulation of coarse fluvial sediments under relatively dry deglacial conditions the second period 10 450 6040 cal abp experienced the warmest climate and the highest precipitation indicated by a minimum c18 1 c18 0 ratio together with the low cpi values of n alkanes and high acl values the third time interval 6040 3800 cal abp was a moderately dry and cool period the climate record of the most recent period 3800 cal abp is obscured by agricultural disturbance the younger dryas 12 900 11 600 cal abp appears in this record as a period of variable and very wet climate during the interval 10 450 6040 cal abp both temperature and the precipitation evaporation ratio maximized therefore we consider this period to represent the holocene optimum which coincides with that of the northern hemisphere moreover our results do not fit the spatially asynchronous pattern of the east asian monsoon holocene optimum in china suggested by previous studies they instead parallel the pattern of global paleoclimate change and consequently show that the evolution of holocene paleoclimate in southern china is consistent with changes in northern hemisphere solar radiation

evolution of the indian summer monsoon during the interval 32 7 11 4 cal ka bp evidence from the baoxiu peat yunnan southwest china abstract there have been few investigations of the phase relationship between the indian summer monsoon ism and the east asian summer monsoon easm during the last glacial period we present multi proxy mineralogical and geochemical records from a peat core taken from the baoxiu basin central yunnan southwest china to investigate changes in chemical weathering and climate associated with the ism in southwest china spanning the interval 32 7 11 4 ka bp the results suggest that the lgm period 23 18 ka bp was characterized by cold and dry climatic conditions a comparison of proxy data from baoxiu peat with other related proxy climate records reveals that broadly synchronous variations in the ism and easm on orbital timescales can be attributed to solar radiation forcing in the northern hemisphere in addition four synchronous weak millennial scale monsoonal events coincide well with cooling events recorded in the ngrip ice core corresponding to the younger dryas and heinrich events h1 h2 and h3 significantly the strengths of the two asian monsoons show an inverse relationship during the interval 23 19 ka bp probably resulting from el nino like conditions in the tropical pacific

effect of climate change on delivery and degradation of lipid biomarkers in a holocene peat sequence in the eastern european russian arctic lipid biomarkers from a peat plateau profile from the northeast european russian arctic were analyzed the peat originated as a wet fen ca 9 ka bp and developed into a peat bog after the onset of

a 220 ka palaeoenvironmental reconstruction of the fuentillejo maar lake record central spain using biomarker analysis abstract the sedimentary record of the volcanic lake known as the fuentillejo maar central spain offers the opportunity to determine the palaeoenvironmental evolution of the central southern part of the iberian peninsula during the middle and upper pleistocene a total of 439 samples from the upper 88 m of a ca 142 m long core spanning the last ca 355 ka were examined the interval corresponds to the last 220 ka of the record high n alkane cpi values and the presence of sulfur revealed that little diagenetic signal attenuation or modification had occurred a number of n alkane based indices e g predominant n alkane acl paq and tar hc ratios and the proportion of c 27 c 29 and c 31 n alkanes with respect to the summed c 27 c 29 c 31 alkanes showed changing conditions in the organic matter input to the maar lake over time with episodes involving a major input of terrestrial vegetation alternating with others in which algae or a mixed input of terrestrial plants aquatic macrophytes and algae occurred the proportions of c 27 c 29 and c 31 were useful for reconstructing the palaeoenvironmental evolution of the basin as they allowed assignment of several dry intervals during which grasses developed while during humid phases trees expanded at the expense of grasses in general we found good correspondence between these episodes and the climatic cycles observed in 18 o records from ices cores in greenland and antarctica as well as from marine cores thus we conclude that global palaeoclimatological changes were recorded in the maar record likewise heinrich events appeared to be reflected in the n alkane indices this was confirmed by single spectral analysis and cross spectral analysis with the insolation curve on 21 july at a latitude of 65 n the approach revealed that the cycles interpreted in the fuentillejo record 103 41 23 and 19 ka showed evidence of orbital influence related to the astronomical cycles of the eccentricity variation in the earth s orbit the earth s obliquity oscillation and the precession variation milankovitch theory

reconstruction of a subalpine grass dominated ecosystem lake rutundu mount kenya a novel multi proxy approach palaeoecological reconstructions based on a single proxy are limited but by combining pollen biogeochemistry and grass cuticle analysis ecosystem structure and function can be better understood lake rutundu is a small subalpine lake on the northeast flank of mt kenya during the last glacial pollen evidence suggests a shrub grassland dominated by afroalpine taxa and poaceae representing a dry cold open environment the 13c values of terrestrial biomarkers imply a high proportion of c4 plants grass cuticle analysis allows resolution of the different c4 subtypes and shows that the vegetation was dominated by tall c4 panicoid grasses prone to frequent fires during the holocene poaceae pollen declined while subalpine shrubs increased the 13c values of terrestrial biomarkers imply a c3 dominated vegetation together with an expansion of rainforest at lower altitudes this suggests wetter conditions more favourable to c3 plants increased percentages of c3 pooid grass cuticles confirm a reduction in moisture stress

paleohydrological changes in the eastern mediterranean region during the early to mid holocene recorded in plant wax n alkane distributions and δ13ctoc new data from tenaghi philippon ne greece abstract holocene climate dynamics have strongly influenced precipitation patterns in the eastern mediterranean region this holds particularly true for the 8 2 kyr bp climatic event arguably the strongest perturbation of early to mid holocene climate here we present a biomarker record of leaf wax derived n alkane distributions and stable isotopic composition of total organic carbon 13 c toc along with palynological data from the fen peat archive of tenaghi philippon tp ne greece spanning the interval from 8 7 to 7 5 kyr bp our record documents the response of in situ vegetation within the philippi peatland to changing hydrological conditions and addresses the applicability of organic proxies such as the aquatic index p aq average chain length acl and 13 c toc as indicators of peat surface moisture conditions at the study site the long chain n alkanes n c 27 n c 29 and n c 31 typical of vascular terrestrial plants dominated the peat sequence a period of relatively dry surface conditions indicated by low values of p aq and elevated acl values in concert with elevated 13 c toc values preceded the 8 2 kyr bp climatic event from ca 8 7 to 8 2 kyr bp slightly wetter more humid conditions suggested by an increase in p aq as well as reduced acl and 13 c toc values characterized the interval of the 8 2 kyr bp climatic event notably the increase in surface wetness as indicated by the biomarker record coincided with a marked rise in fern spore proportion as well as increasing proportion of pollen from aquatic taxa following the 8 2 kyr bp event a distinct change in paleohydrology at tp became apparent from ca 7 9 kyr bp onward an increase in the abundance of the mid chain length n alkanes n c 23 and n c 25 indicative of an increased contribution from aquatic plants to the sediment together with a steep increase in p aq and a decrease in acl as well as variation in 13 c toc imply considerably elevated surface moisture levels likely caused by the increased activity of the karstic system of the surrounding mountains collectively the biomarker proxies and pollen data reveal a concise picture of changing moisture conditions at tp in response to the 8 2 kyr bp climatic event

a case for ancient evaporite basins on mars observations indicate that a martian analog to the earth s salt pans and saline lakes of arid regions may have existed in crater basins during mars early noachian epoch terraced and channelized crater basins point to ponding of surface water as well as possible prolonged and evolving base levels in addition supportive evaporite basin analogs are offered for three other morphologic features of martian crater basins an evaporite basin model for crater basins on mars has major implications for the mechanical chemical and even biological processes that potentially have operated in mars past and represent a spectrum of potential mineral resources

proxy value of n alkan 2 ones in the hongyuan peat sequence to reconstruct holocene climate changes on the eastern margin of the tibetan plateau abstract n alkan 2 ones in the hongyuan peat core from the eastern margin of the tibetan plateau were investigated to assess the paleoclimate proxy value of variations in their compositions over the last 13 500 cal years a homologous series of these compounds that ranged from c 19 to c 31 was identified throughout the peat sequence maximizing at c 23 and showing a strong odd over even carbon chain length predominance to help evaluate the possible paleoclimatic value of the n alkan 2 ones in the hongyuan peat core we compared our molecular results with the pollen records from the same sequence results show that past changes in monsoon precipitation amounts as revealed by the ratio of abies cyperaceae firs sedges are also recorded in the n alkan 2 one c 23 c 25 c 27 c 29 c 31 ket ratio and cpi ket carbon preference index value stratigraphic variations of n alkane and n alkanoic acid ratios suggest that changes in the moisture sensitive microbial oxidation of odd chain n alkanes and decarboxylation of even chain length n alkanoic acids is recorded in the abundance of n alkan 2 ones changes in the monsoon rain intensity on millennial scales are also evident in the n alkan 2 one proxies indicating that their variations in the peat sequence are correlative with changes in microbial activity controlled by the asian monsoon

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

high resolution evidence from southern china of an early holocene optimum and a mid holocene dry event during the past 18 000 years abstract computer models suggest that the holocene optimum for east asian summer monsoon precipitation occurred at different times in different regions of china previous studies indicate that this time transgressive holocene optimum should have been experienced about 3000 yr ago in southern china in this study we describe a section which allows us to test this timing directly we have closely examined high resolution eutrophic peat mud sequences covering the past 18 000 cal yr at dahu jiangxi on the southern boundary of the mid subtropical zone in china late pleistocene successions in the dahu record indicate cooler and much wetter conditions relative to synchronous events in north central china our results indicate that the holocene optimum occurred between ca 10 000 and 6000 cal yr ago in southern china consistent with the global pattern conditions were relatively dry and cold from 6000 to 4000 cal yr ago our data also support the conclusion that the last deglaciation to early holocene in the south was much wetter resulting in the formation of dense broad leaved forests which could have acted to moderate land temperature 10 000 to 6000 cal yr ago yielding a stable early holocene climate after 6000 cal yr forest reduction led to unstable land temperatures and possibly to a northerly shift of the subtropical high pressure system whatever the mechanism these changes resulted in decreased precipitation between 6000 and 4000 cal yr b p in southern china

a 20 000 year high resolution pollen record from huguangyan maar lake in tropical subtropical south china abstract a high resolution pollen record from huguangyan maar lake near the south china sea spanning the past 20 400 yr bp has been presented aimed to provide an improved understanding of the response of the regional vegetation in tropical subtropical south china to climatic variations since the late last glacial maximum the results reveal the strong control of the asian summer monsoon asm strength on vegetation via orbitally induced variations in northern hemisphere summer solar insolation the trend of climatic evolution of the region consists of change from a warm temperate northern subtropical climate 20 400 18 700 cal yr bp to a southern subtropical climate 16 500 11 500 cal yr bp during the last deglaciation followed by a stepwise environmental shift from a tropical climate 11 500 8200 cal yr bp to a southern subtropical climate 8200 6600 cal yr bp and finally to a middle northern subtropical climate the bolling allerod warming is characterized by the highest percentages of evergreen quercus but the lowest percentages of xerophytic gramineae throughout the record suggesting intensified warm wet conditions during 15 000 13 000 cal yr bp by contrast the younger dryas is characterized by a marked decrease in subtropical evergreen broad leaved plants but a significant increase in herbaceous taxa representing a brief cold reversal during 13 000 12 000 cal yr bp the occurrence of two major cooling events at 8 2 and 6 6 kyr bp both of which are characterized by dramatic decreases in tropical evergreen broad leaved plants is supposed to be linked to a distinct weakening of the asm and southward migration of the intertropical convergence zone associated with marked declines in atlantic meridional overturning circulation the subsequent brief intervals of high herbaceous pollen percentages but low percentages of tropical taxa correspond to high el nino southern oscillation enso activity supporting a link between the weakening of solar isolation driven asm strength and a gradual intensification of enso

impacts of paleohydrological changes on n alkane biomarker compositions of a holocene peat sequence in the eastern european russian arctic coupled analyses of n alkane biomarkers and plant macrofossils from a peat plateau deposit in the northeast european russian arctic were carried out to assess the effects of past hydrology on the m

a hydrocarbon biomarker record for the last 40 kyr of plant input to lake heqing southwestern china multi proxy records relating to climate and vegetation have been obtained for a core spanning the last 40 kyr from the heqing lake basin 26 n 100 e 2200 m asl yunnan province of southwestern china compound specific carbon isotope records for the vascular plant leaf wax hydrocarbons the c23 c33 n alkanes and for the algal hydrocarbons the c23 and c25 n alkenes and a c30 cyclobotryococcatriene all show a shift of circa 3 in d 13 c values from mis 3 to the end of mis 2 followed by a rapid return to lighter values this shift from 32 to 29 for the n alkanes and n alkenes most likely derives from bicarbonate utilization by aquatic plants in the lake rather than increased c4 photosynthesis thus both pollen data and hydrocarbon data appear to reveal a rise and fall in the contributions of submerged and or floating plants during mis 2 2004 elsevier ltd all rights reserved

asian summer monsoon variability during the late glacial and holocene inferred from the stable carbon isotope record of black carbon in the sediments of muge co southeastern tibetan plateau china a sediment core from an alpine lake muge co from the southeastern margin of the tibetan plateau was analyzed for sediment grain size distribution and the carbon isotopic composition of black carb

postglacial floral and climate changes in southeastern china recorded by distributions of n alkan 2 ones in the dahu sediment peat sequence abstract long chain n alkane 2 ones occur widely in lacustrine and peat depositional settings however their paleobotanical and paleoclimate implications are less understood compared with their n alkyl counterparts n alkanes n fatty acids in this study we have performed a molecular stratigraphic investigation of changes in the plant contributions and depositional conditions using n alkan 2 ones in the dahu lacustrine peat sequence spanning the last 17 kyr a series of n alkan 2 ones ranging from c23 to c33 with a maximum at c29 appears to be contributed by microbial oxidation of both n alkanes and n alkanoic acids the values of the average chain length acl and the ratios of mid to long chained n alkan 2 ones display a trend comparable with the abundance of trees relative to herbs and ferns in addition the carbon predominance index cpi of n alkan 2 ones varied in pace with lithology paleoenvironment with higher values seen in peat deposits the alternating layers represent a succession of shallow lakes and peatlands that filled the depositional basin in response to paleoclimate changes between wetter and less wet conditions the succession of paleohydrologic conditions is responsible for the variation of ketone cpi values in this peat sediment sequence

early diagenesis of organic matter in the water column and sediments microbial degradation and resynthesis of lipids in lake haruna particulate matter sediment trap and surface sediment samples collected in freshwater lake haruna were studied to understand early diageesis of organic materials in the water column and in bottom sediments the samples were analyzed for biomarkers including aliphatic and aromatic hydrocarbons fatty alcohols saturated and unsaturated fatty acids and hydroxyacids and dicar ylic acids decreases in concentrations of autochthonous saturated c12 c19 fatty acids and polyunsaturated c18 acids relative to toc occured with the settling of organic matter ot the lake bottom whereas the amounts of terrestial saturated c20 c30 acids remained almost constant conversely the concentrations of monosaturated fatty acids branched chain fatty acids and and hydroxyacids which are probably produced by microbial activity increased these results indicate that preferential degradation of algal lipids accompanies microbial resynthesis of lipids during settling however terrigenous lipids are relatively stable

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

organic geochemical evidence of late pleistocene holocene environmental changes in the lake balaton region hungary abstract this paper presents organic geochemical records and a combined interpretation of organic geochemical and palaeoecological data for a late pleistocene holocene shallow lake sequence abundance bulk chemical composition and sources of the organic matter om as well as the relative contribution of the labile and resistant bio and geo macromolecules were determined on 46 sediment samples lipids isolated from selected samples representing the lowest and highest water levels were analyzed integration of the organic geochemical and palaeoecological records suggests that climate exerted the primary control on the amount and quality of the om preserved the relative contribution of the labile fresh plant and litter and resistant lignin and cellulose bio macromolecules immature geo macromolecules humic substances and mature refractory geo macromolecules and the degree of preservation of the primary biomass calculated from mathematical deconvolution of rock eval pyrograms allowed the distinction of three and five zones related mainly to water level fluctuation within the late pleistocene and holocene sequences respectively

biomarker records of palaeoenvironmental variations in subtropical southern africa since the late pleistocene evidences from a coastal peatland abstract southern africa s unique global position has given rise to a dynamic climate influenced by large sea surface temperature gradients and seasonal fluctuations in the inter tropical convergence zone due to the semi arid climate of the region terrestrial palaeorecords are rare and our understanding of the long term sensitivity of southern african terrestrial ecosystems to climatic drivers is ambiguous a 810 cm continuous peat core was extracted from the mfabeni peatland with a 14 c basal age of c 47 thousand years calibrated before present kcal yr bp positioning it as one of the oldest known sub tropical coastal peatlands in southern africa this peat core provides an opportunity to investigate palaeoenvironmental changes in subtropical southern africa since the late pleistocene biomarker n alkane n alkanoic acid and n alkanol analysis in conjunction with previously published bulk geochemical data was employed to reconstruct organic matter om sources rates of om remineralisation and peatland hydrology our results showed that the principal om source into the peatland was emergent and terrestrial plants with exception of shallow lake conditions when submerged macrophytes dominated c 44 5 42 6 29 7 26 1 23 1 16 7 7 1 and 2 2 kcal yr bp n alkane proxies suggest that local plant assemblages were predominantly influenced by peatland hydrology by incorporating temperature sensitive n alkanoic acid and n alkanol proxies it was possible to disentangle the local temperature and precipitation changes we report large variations in precipitation intensities but subdued temperature fluctuations during the late pleistocene the holocene period was characterised by overall elevated temperatures and precipitation compared to the preceding glacial period interspersed with a millennial scale cooling event a close link between the mfabeni archive and adjacent indian ocean marine core records was observed suggesting the regional ocean surface temperatures to be the dominant climate driver in this region since the late pleistocene

lipid biomarker δ13c and plant macrofossil stratigraphy of a scottish montane peat bog over the last two millennia abstract seven horizons of a peat core covering the last 2000 years from moine mhor a blanket bog in the cairngorm mountains scotland have been examined for the carbon number distributions of the long chain hydrocarbon alcohol and acid components using gas chromatography gc and gas chromatography mass spectrometry gc ms compound specific 13 c values for individual n alkanes were obtained using gas chromatography isotope ratio mass spectrometry gc irms the lipid biomarker distributions and the 13 c values have been compared with those of eleven species of living plant dominant at the contemporary surface of the bog the observed lipid stratigraphy shows only partial agreement with that calculated using macrofossil abundance data and the lipid distributions for the living taxa a result which reflects the inherent uncertainties in both the lipid biomarker and the macrofossil approaches to palaeoenvironmental stratigraphy the carbon isotope values for the individual n alkanes of the plants 27 6 to 36 6 and of the peat layers 29 to 31 7 are as expected for the c 3 photosynthetic pathway however the n alkanes from the surface samples were more depleted by 2 in 13 c than those from the rest of the core a negative shift which may in part reflect the shift 1 2 in 13 c estimated for co 2 in a pre industrialised to an industrialised atmosphere

low latitude hydro climatic changes during the plio pleistocene evidence from high resolution alkane records in the southern south china sea abstract high resolution records of long chain n alkane biomarkers from the southern south china sea reveal tightly response of n alkane distribution to hydro climate changes over the past 5 ma with increasing longer chain n c31 alkanes indicating a correlation with drier conditions and increasing shorter chain n c27 alkanes with wetter conditions the variations of the c31 c27 ratio or the alkane chain length index imply humid conditions before 2 9 ma progressively reduced moisture since then and to bigger fluctuations between wet and dry conditions since 1 2 ma this long term hydro climate trend is superimposed by glacial dry and interglacial wet patterns over the plio pleistocene glacial cycles combined with other proxy records our results indicate that precipitation over the tropical asia pacific strengthened before the onset of the northern hemisphere glaciation and the mid pleistocene climate transition at about 1 2 ma these dramatic humidity changes over major climate transitions imply a crucial role of tropical hydrology dynamics on global climate change in the late cenozoic

lipid biomarkers in the zoige hongyuan peat deposit indicators of holocene climate changes in west china abstract lipid biomarkers extracted from a peat core obtained from the northeast edge of the tibetan plateau have provided a 13 kyr record of regional climate change a period of warmer climate corresponding to the holocene optimum between 9 ka and 5 ka is evident in greater alteration of n alkanoic acids and n alkanols and in the appearance of biomarkers indicative of greater microbial activity concomitant increases in local precipitation that raised the water level of the peat bog are recorded by increases in the proportions of c23 and c25 n alkanes that are mainly derived from submerged floating plants alternations in submergent and emergent plant n alkane proxies reveal multi decimeter scale rises and falls in the bog water level that relate to variation in precipitation on the tibetan plateau during the holocene major low water level events occurred around 12 6 11 3 10 7 9 4 8 3 6 0 4 5 3 1 2 1 and 1 0 ka these events correlate well with cold dry events recorded in same region from other climatic proxies that reflect millennial scale holocene instability in the asian monsoon system our biomarker results also indicate that peat accumulation and preservation on the tibetan plateau are more sensitive to variability in monsoonal precipitation than in annual temperature

evidence for differential degradation of alkenones under contrasting bottom water oxygen conditions implication for paleotemperature reconstruction abstract the successful reconstruction of sea surface temperatures using alkenone paleothermometry u37k has relied on the premise that there is no significant differential degradation of alkenones with different states of unsaturation during diagenetic processes to test this assumption we conducted a comparative study of contemporary sediments in oxic and anoxic bottom waters from the santa monica basin offshore california long chain alkenones were quantified and sea surface temperature were calculated using the calibrated u37k t relationship of prahl et al 1988 our results show that temperature record from the oxic sediments is higher by as much as 4 c compared to those from time equivalent anoxic sediments as a result of differential degradation of long chain unsaturated alkenones and bioturbation mixing in the oxic sediments the differential degradation of c37 3 vs c37 2 alone could account for up to 2 5 c difference between these two records this finding has significant implication in the interpretation of paleo sea surface temperature data using alkenone paleothermometry

chemical composition of n alkanes and microbially mediated n alkane degradation potential differ in the sediments of qinghai tibetan lakes with different salinity abstract n alkane based proxies are widely employed to reconstruct paleoclimate and paleoenvironment in lacustrine environments however little is known about the influence of microbially mediated alkane degradation on n alkane derived proxies in this study the chemical composition of n alkanes and microbially mediated n alkane degradation potential were investigated in the surface sediment samples collected from seven lakes with a range of salinity from freshwater to salt saturation on the northern qinghai tibetan plateau qtp the results showed that the chemical composition of n alkanes differed among the studied qtp lakes significant correlations were observed between salinity and some n alkane based paleoclimate and paleoenvironment proxies such as ratio of c21 c22 average chain length acl and carbon preference index cpi this suggested that salinity may affect the validity of some n alkane based paleoclimate and paleoenvironment proxies alkane degrading bacteria were abundant and widespread in the studied freshwater and saline hypersaline lakes but were minor or absent in salt saturation lakes the obtained alkane degrading bacterial strains showed active ability to degrade n hexadecane this suggested that the salinity influence on the n alkane distribution may be partially related to microbial degradation which awaits further in situ investigation so salinity variation should be taken into account when using n alkane based proxies for reconstructing paleoclimate and paleoenvironment in lakes

paleoclimate variability in central taiwan during the past 30 kyrs reflected by pollen δ13ctoc and n alkane δd records in a peat sequence from toushe basin abstract a total of 233 samples from the upper 16 m of the toushe peat core retrieved in central taiwan were measured for toc and 13ctoc values from these samples 17 selected samples with large 13ctoc fluctuations were analyzed for n alkane and d of the c27 and c29 n alkanes combining with the detailed high resolution pollen and geochemical records this study reveals more detailed climatic variations in terms of temperature and precipitation as well as abrupt climatic events during the past 30 kyrs before the last glacial maximum lgm climate was cold and damp with predominantly woodland vegetation in toushe basin and turned to cold and dry after 25 kyr bp climatic conditions there were the worst during lgm over the past 30 kyrs especially around 23 and 18 kyr bp when the woodland was diminished and c4 grass was dominated although short durations of relatively wet conditions could be found at 17 16 and 14 kyr bp cold and dry climates were prevailing during 29 5 28 24 22 17 15 and 13 11 5 kyr bp corresponding to heinrich h events 3 2 1 and younger dryas yd respectively during the early holocene dry climate occurred at 11 10 9 7 9 2 and 8 kyr bp whereas wet condition appeared at 10 3 9 8 9 7 5 kyr bp in the middle holocene climate kept warm and moderate wet in the first half period but many dry events existed in the second half following a cold and dry event at 6 kyr bp after a sharply warm peak at 5 2 kyr bp the climate in toushe turned to cold quickly and tree shrub vegetation disappeared completely with the replacement of c3 grasses in the late holocene climate was relatively wetter with predominant c3 grasses in the basin our climatic interpretations based on the peat records agree well with the greenland ice core and chinese speleothem records on millennium time scales during the last glacial period dry climates corresponding to weakening of the east asian summer monsoon easm during the heinrich events and younger dryas in central taiwan and eastern china demonstrate the climatic forcing on such long time scales in concert with regional monsoon climate however the discrepancies exist between our peat record and the dongge hulu stalagmite record on 1 the age of h2 2 climate intensities of lgm and h1 and 3 wetness condition during holocene these observations call for further study on high resolution climatic changes especially on moisture budget in the east asian monsoonal region

the biogeochemistry of ellesmere lake u k i source correlation of leaf wax inputs to the sedimentary lipid record abstract analyses of the free lipid distributions from ellesmere lake sediments taken from two depths and comparison with leaf wax lipid distributions from six deciduous tree species around the lake were made in order to assess lipid sources close correlations of aliphatic lipid distributions in the carbon number range c 20 c 50 were seen c 28 and c 29 sterols were observed in both sediment and leaf waxes but c 27 sterols were only present in the sediments and were thus assigned a nonleaf wax source unsaturated steroidal ketones were observed both in the sediment and in certain leaf waxes and were assigned specific sources alkan 2 ones were not present in the leaf waxes but were present in the sediment samples with an almost identical distribution to the sediment n alkanes indicating a microbially mediated source c 20 c 30 n aldehydes which have not previously been widely reported in free lipid distributions of freshwater lacustrine sediments were prominent in the surface sediment and in the leaf waxes examined

holocene tephrostratigraphic framework and monsoon evolution of east asia key tephra beds for synchronising palaeoclimate records abstract in east asia our understanding of holocene climate change forcing mechanisms and propagation require the precise chronological control of palaeoclimate records to allow robust integration of data sets the existing chronologies predominantly based on 14c method however are not sufficient to constrain key questions about abrupt climate shifts that occur within a century in the transitions between states widely dispersed tephra layers allow precise dating and synchronisation of sedimentary archives providing a chronological framework for integrating records especially where the visible tephra record is complemented by the addition of cryptotephra non visible ash despite significant tephra studies in this region however a comprehensive holocene tephra framework is not available to address this issue we carry out a thorough review on holocene tephra investigations undertaken in japan using widespread tephra beds we present an integrated tephra framework and suggest the way forward for establishing this as a wider approach for east asia the framework is based on twenty two ash layers that are mainly from japan and to a lesser extent china n korea s korea and russia each tephra is assessed in terms of chronology geochemistry and distribution the framework is compared with high resolution palaeoclimate records from east asia using this we demonstrate regional variations in monsoon evolution and more importantly the potential of tephra isochrons in constraining such variations given the scarce identification of tephra layers in those well resolved palaeoclimate records we advocate a more systematic employment of the cryptotephra method which would potentially lead to a significant advance in east asian tephrochronology and the correlation of palaeoclimate archives in the region

pollen records from southern taiwan implications for east asian summer monsoon variation during the holocene pollen records from two cores retrieved from a valley basin in southern taiwan show major changes in vegetation and climate occurring during the holocene between 11 400 and 8200 cal yr bp the up

asynchronous holocene optimum of the east asian monsoon abstract the spatial and temporal distribution of summer monsoon precipitation or effective moisture during the holocene has been reconstructed on the basis of geological data including lake levels pollen profiles and loess paleosol records in addition the summer july precipitation increment effective precipitation and monsoon strength index have been obtained from numerical modeling experiments both geological data and numerical modeling indicate that the holocene optimum as defined by peak east asian summer monsoon precipitation was asynchronous in central and eastern china reaching a maximum at different times in different regions e g ca 10 000 8000 yr ago in northeastern china 10 000 7000 yr ago in north central and northern east central china ca 7000 5000 yr ago in the middle and lower reaches of the yangtze river and ca 3000 yr ago in southern china in southwestern china the maximum appeared ca 11 000 yr ago but probably was related to the maximum landward extension of the indian summer monsoon the regional shift in the maximum precipitation belt from northwest to southeast over the past 10 000 yr is interpreted as a response to changing seasonality related to orbital forcing of the climate the southeastward shift of the east asian summer monsoon maximum is consistent with the progressive weakening of the summer monsoon as the summer solar radiation anomaly decreased progressively through the holocene and the east asian monsoon index declined while the early maximum in southwestern china matches the maximum of the indian monsoon index

a preliminary reconstruction of the paleoecological and paleoclimatic history of the chinese loess plateau from the application of biomarkers abstract this study provides a preliminary reconstruction of paleoecological and paleoclimatic history over the central chinese loess plateau clp during the last 8 1 ma based on biomarker records from the earliest of the chaona stratigraphic section throughout the section we found variations in n alkane and n alkan 2 one distributions and dramatic changes in six other biomarker proxies 1 n alkanes c27 c29 c31 c33 ratios 2 n alkanes c27 c31 ratios 3 cpi carbon preference index values for cpi h alk 4 values for cpi h ket 5 n alkane mean chain lengths acl alk and 6 n alkan 2 ones c29 c31 ratios the c29 n alkanes dominate the red clay sediments with little variability indicating that trees dominated the clp and that the climate was relatively stable and less variable during the 8 1 2 6 ma period in contrast the c31 n alkanes dominate the loess paleosol sediments and biomarkers vary with relatively greater amplitude and higher frequency indicating that grasses dominated the clp and the climate was more arid and variable these biomarker records chronicle a drying and cooling trend on the clp since 4 ma these records can be further divided into four stages with boundaries around 5 6 3 8 and 2 6 ma indicating that the clp vegetation and climate experienced four evolutionary phases broadly consistent with those inferred from other available proxy data

effects of sample disturbance and consolidation procedures on measured shear strength of soft marine norwegian clays after many decades of research the issue of sample disturbance is still important as regards to determining reliable and representative soil parameters for foundation design in soft clays parallel laboratory tests have been carried out on high quality block samples and ordinary piston tube samples from 12 deposits of soft norwegian marine clays undrained triaxial and direct simple shear dss tests on samples reconsolidated to the in situ effective stresses show that sample disturbance has a significant effect on the measured stress strain strength behaviour the more disturbed the sample the lower the shear stress at small strains and the higher the shear stress at large strains breakdown of the clay structure including cementation bonds is the assumed cause of lower shear resistance at small strains whereas at large strains the shear resistance is governed mainly by the water content which for soft clay samples reconsolidated to the in situ effective stresses will be lower and the strength t

variations in organic matter composition in sediments from lake huguang maar huguangyan south china during the last 68 ka implications for environmental and climatic change abstract this study presents a continuous and long term palaeoenvironmental and palaeoclimatic record from a lacustrine sediment core lake huguang maar at the northern coast of the south china sea extending back to about 68 cal ka bp we provide a comprehensive ecosystem analysis from the opportunity to combine organic geochemical and palynological data several climatically induced changes to the flora and fauna have been recognised from 68 to 58 and 48 to 40 5 cal ka bp relatively depleted 13 c toc 31 3 to 25 0 and 13 c values of mid and long chain n alkanes 34 3 to 30 2 as well as high percentages of tropical pollen indicate a vegetation dominated by subtropical tropical forest c 3 plants an expansion of a mixed c 3 c 4 open grassland between 58 and 48 and particularly after 40 5 cal ka bp mirrors drier climatic conditions in conjunction with a lowering of atmospheric co 2 concentrations 13 c toc 24 1 to 16 8 and 13 c values of n alkyl lipids 28 9 to 24 1 are heavier higher percentages of non arboreal pollen were observed and the wood grass lignin index wgli from open pyrolysis py gc indicates a higher input of grass lignin abundant oxidised terrigenous particles that resulted from increased fire activity and or greater erosion rates are a further hint of enhanced dryness the clear drop in moisture availability suggests that this site is sensitive in fluctuations of the summer and winter monsoon activity in accordance with other proxy records in south east asia the response of the aquatic ecosystem is documented by an extremely large 13 c shift of algal derived botryococcenes from 35 4 to 6 2 which records a change towards a bicarbonate carbon source at low dissolved co 2 concentrations

glacial interglacial environmental changes inferred from molecular and compound specific δ13c analyses of sediments from sacred lake mt kenya abstract molecular stratigraphic analyses including lipid distributions and compound specific 13c measurements have been performed at 15 levels in a sediment core from sacred lake mt kenya a high altitude 2350 m a s l freshwater lake with a record extending from the last glacial 40 000 cal yr bp through the present interglacial terrestrial and aquatic organic matter sources were independently assessed using source specific biomarkers 13c values of long chain n alkyl lipids from terrestrial higher plants exhibit large glacial to interglacial shifts those from the last glacial maximum lgm 20 to 18 indicate a terrestrial vegetation dominated by c4 grasses or sedges whereas those from the early holocene 34 to 27 reflect recolonization of the catchment area by c3 plants consistent with a rapid rise in the upper treeline specific algal biomarkers including five unsaturated hydrocarbons of novel structure ascribed to the microalga botryococcus braunii were abundant as confirmed by scanning electronic microscopy sem an extreme 13c shift of over 25 is displayed by the algal biomarkers an elevated value of 5 1 at the last glacial maximum lgm contrasting with a minimum value of 30 3 at the beginning of the holocene a major change in the molecular distributions of the algal biomarkers parallels this large 13c shift with acyclic isoprenoid hydrocarbons dominating the last glacial and cyclic isoprenoid hydrocarbons the holocene the low atmospheric partial pressure of co2 pco2 at the lgm would favour photosynthetic organisms possessing co2 concentrating mechanisms including terrestrial c4 grasses and freshwater green algae hence glacial interglacial changes in pco2 and in the co2 o2 ratio in particular had a significant impact on both terrestrial and aquatic ecosystems on mt kenya in addition to the effects of climate and local environmental factors

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

abrupt climate variability since the last deglaciation based on a high resolution multi proxy peat record from nw iran the hand that rocked the cradle of civilization abstract we present a high resolution sub decadal to centennial multi proxy reconstruction of aeolian input and changes in palaeohydrological conditions based on a 13000 yr record from neor lake s peripheral peat in nw iran variations in relative abundances of refractory al zr ti and si redox sensitive fe and mobile k and rb elements total organic carbon toc 13 c toc compound specific leaf wax hydrogen isotopes d carbon accumulation rates and dust fluxes presented here fill a large gap in the existing terrestrial paleoclimate records from the interior of west asia our results suggest that a transition occurred from dry and dusty conditions during the younger dryas yd to a relatively wetter period with higher carbon accumulation rates and low aeolian input during the early holocene 9000 6000 yr bp this period was followed by relatively drier and dustier conditions during middle to late holocene which is consistent with orbital changes in insolation that affected much of the northern hemisphere numerous episodes of high aeolian input spanning a few decades to millennia are prevalent during the middle to late holocene wavelet analysis of variations in ti abundances as a proxy for aeolian input revealed notable periodicities at 230 320 and 470 years with significant periodicities centered around 820 1550 and 3110 years over the last 13000 years comparison with palaeoclimate archives from west asia the north atlantic and african lakes point to a teleconnection between north atlantic climate and the interior of west asia during the last glacial termination and the holocene epoch we further assess the potential role of abrupt climate change on early human societies by comparing our record of palaeoclimate variability with historical geological and archaeological archives from this region the terrestrial record from this study confirms previous evidence from marine sediments of the arabian sea that suggested climate change influenced the termination of the akkadian empire in addition nearly all observed episodes of enhanced dust deposition during the middle to late holocene coincided with times of drought famine and power transitions across the iranian plateau mesopotamia and the eastern mediterranean region these findings indicate that while socio economic factors are traditionally considered to shape ancient human societies in this region the influence of abrupt climate change should not be underestimated

the importance of atmospheric input of terrestrial organic material to deep sea sediments the concentrations of lipids were determined in atmospheric particle gas and rain samples collected from the tropical north pacific to assess lipid sources transport mechanisms and fluxes to the ocean surface four lipid compound classes aliphatic hydrocarbons fatty alcohols fatty acid esters and salts all unequivocally show a terrestrial vascular plant source these aerosol lipids originate from wind erosion of asian and american soils and direct emission from vegetation the major fluxes result from rain rather than dry deposition these fluxes are large enough to have a major potential impact on the inventory of terrestrially derived lipid material found in deep sea sediments this has been showm for n alkanes fatty alcohols fatty acids total lipids and for organic carbon by comparing atmospheric and sediment trap fluxes with sediment accumulation rates it is suggested that some biogenic terrestrial material is more protected from degradation than marine derived material

organic geochemistry of agacbasi yayla peat deposits koprubasi trabzon ne turkey abstract peat deposits which outcrop in the southern agacbasi region in trabzon northern turkey were studied by using chemical organic geochemical petrographic and palynological characteristics of peats palynological data indicate that the peats were deposited in terrestrial or lacustrine environments comprising organic matter with an average composition of 70 woody 19 3 herbaceous and 10 7 amorphous material the peats are holocene recent in age the peat organic matter that has been interpreted as immature based on the sci spore color index analyses suggests that the peat organic matter was immature rock eval analyses show that the average total organic carbon toc content of the peat is 42 and the average hi value is 315 mghc gtoc which is very high for peat the high oi values avg 134 mgco 2 gtoc point that the depositional environment of peats were deposits under oxic or suboxic conditions the selected sample aby 13 with the highest extractable yield has tar terrigenous aquatic ratio and cpi carbon preference index index values of 2 4 and 3 4 respectively these values reflect high levels of n alkanes supporting a terrestrial organic matter input the p aq aquatic plant n alkane proxy ratio 0 6 indicates that there was a contribution from mixtures of submerged floating emergent and terrestrial plant mixtures the p wax vascular plant n alkane proxy ratio 0 6 is a sign of moist and wetter conditions the toc acl q wood grass c 27 c 31 q wood plant c 27 c 29 c 27 c 29 c 31 and q grass plant c 31 c 27 c 29 c 31 values indicate that woody plants were the dominant vegetation in the peat mire was woody plants and the climate was relatively wet and cold according to the m z 191 and m z 217 fragments tracking from gc ms chromatogram data obtained using biomarker analyses the lack of c 34 and c 35 homohopanes was interpreted as that organic matter was deposited under oxic or suboxic conditions moretane hopane tm ts and tm c 30 pentacyclic triterpane ratios also point indicate oxic and acidic conditions during the formation of the peat the absence of 17 h 28 30 bisnorhopane from the m z 191 chromatograms support the interpretation that the agacbasi yayla peat was deposited in a terrestrial or lacustrine environment under oxic or suboxic conditions the dominance of c 29 steranes indicates significant terrestrial organic matter input using sterane carbon number distributions the extract of the peat sample plots in the terrigenous region additionally c 30 steranes which imply marine environments were not detected the ts ts tm ratios also suggest that the peat contained immature organic matter

n alkanes as indicators of climate and vegetation variations since the last glacial period recorded in a sediment core from the northeastern south china sea scs abstract variations in n alkanes proxies l h c31 c27 and acl molecular abundances of n alkanes and stable carbon isotopic compositions of n alkanes 13calk from the core std235 20 21 15 n 118 22 56 e have been used to trace characterize the climatic changes that occurred in the northern south china sea scs during the last glacial period the ratio of low to high molecular weight n alkanes l h and the concentration of n alkanes indicated that organic matters in the sediments were derived from the mixture of both marine and terrestrial sources but dominated by marine autochthonous input over the past 20 ka total n alkanes were higher during the last glacial stage relative to the interglacial stage implying the low sea level and the strengthened east asian winter monsoon eawm during the glacial time the 13calk data indicated that the terrestrial plants on the adjacent continent of the present study area were dominated by c3 plants during the holocene and experienced the expansion of c4 plants during the last glacial period this similar result can be proved by the chain length parameter of n alkanes c31 c27 acl and the content of the herb pollen in addition n alkanes distributions and c4 vegetation proportion calculated by 13c of long chain n alkanes in the core std235 recorded a short arid duration paralleled by the heinrich event 1 thereby we deduced that the occurrence of the dry event and the variation of regional vegetation community at the adjacent lands of the northern scs were likely under the influence of the climate change emanated from the boreal high latitudes

lipids of aquatic organisms as potential contributors to lacustrine sediments ii abstract the relationship between the lipid composition of organisms in the water column of an eutrophic lake and the lipid composition of underlying sediments previously examined for n alkanols and steroids is now reported for hydrocarbons ketones and carboxylic acids the n c7 alkane and alkenoic acids from two primary sources are rapidly metabolized in the water column and surficial sediment bacterial biomarkers including hopenes and i ai branched fatty acids were detected in the photosynthetic bacterial layer occurring just above the sediment water interface within the sediment the apparent conversion of free n alkanes alkan 2 ones and hydroxy acids to the corresponding bound form is noted microbiological oxidation of n alkanes to alkan 2 ones is supported by the detection of the intermediate alkan 2 ols with a distribution similar to that of the ketones the geochemistry of sediment deposited c 1900 prior to biological study of the site was interpreted from stable biomarkers and the diagenetic changes recognised in the study of contemporary deposition a qualitative difference in algal input to the older sediment is inferred from the low 7 sterol content and presence of 2 6 10 trimethyl 7 3 methylbutyl dodecane however there was still significant dinoflagellate input as indicated by the presence of 4 methylsterols a difference in higher plant input to the older sediment indicated from the n alkane alkene and triterpenoid ketone distributions is consistent with the recent development of tree cover

paleoclimate changes of the past 30 cal ka bp inferred from lipid biomarkers and geochemical records from qionghai lake southwest china abstract multi proxy records of paleoclimate changes spanning the past 30 cal ka bp were obtained from qionghai lake sediment core sichuan province southwest china where southwest summer monsoon prevails the core was studied for molecular compositions of n alkanes stable carbon isotope ratios 13c of organic matter om total organic carbon toc total nitrogen tn and trace elements evidence from n alkanes cross chart of c n 13c values and trace elements indicated the organic matter derived from a mixed source composed of autochthonous aquatic organisms and allochthonous terrestrial plants and the sediments mainly deposited in reducing conditions which is in favor of preservation and accumulation of om variations of n alkanes biomarker proxies 13c of organic matter and mo concentrations reflected three stages of paleoclimate evolution during the past 30 cal ka bp a relatively warm and humid climate between 29 1 and 22 9 cal ka bp corresponding to a strong southwest summer monsoon climate shifted towards cold and dry condition during the period of 22 9 15 7 cal ka bp in response to the reduced insolation and weakened southwest summer monsoon temperature and humidity gradually increased in the holocene with fluctuations broadly track the strengthening trend of southwest summer monsoon our findings further confirm that variations in solar activity may primarily affect the strength of southwest summer monsoon resulting in the shifts of paleoclimate conditions further studies are needed to better constrain the detailed forcing drivers which may amplify the intensity of southwest summer monsoon particularly in the holocene period

multi proxy study of soil organic matter dynamics in permafrost peat deposits reveal vulnerability to climate change in the european russian arctic soil organic carbon soc in permafrost terrain is vulnerable to climate change perennially frozen peat deposits store large amounts of soc but we know little about its chemical composition and l

southern hemisphere westerly wind influence on southern new zealand hydrology during the lateglacial and holocene southern hemisphere westerly wind influence on new zealand hydrology

molecular stratigraphy a new tool for climatic assessment variations in sea surface temperatures over the past 500 000 years are inferred from the relative abundance behaviour of two organic compounds c37 alkenones over the upper 8 metres of a sediment core from the eastern equatorial atlantic this molecular record ascribed to contributions from prymnesiophyte algae correlates well with the variations in the 18 signal for the calcareous skeletons of certain planktonic foraminifera thus providing the first demonstration of a new stratigraphical technique which may be especially valuable where methods based on carbonate 18 fail

lipid stratigraphy of a flandrian peat bed northumberland uk comparison with the pollen record a flandrian peat bed near low hauxley northumberland uk was studied both optically and geochemically to compare the pollen and lipid records of changing plant input during its accumulation a pr

a new approach for reconstruction of the holocene climate in the mongolian altai the high resolution δ13c records of toc and pollen complexes in hoton nur lake sediments abstract 13 c of total organic carbon toc and pollen grain toc c n ratio and 15 n of total organic nitrogen ton in a 2 57 m long core from hoton nur lake in mongolian altai have been measured for reconstruction of the holocene climates the 13 c values of toc and pollen carbon have similar average values but different ranges pollen 13 c has negative correlation with ap arboreal taxa pollen and positive correlation with nap herbaceous pollen and spores that are connected with conditions of humidity in the area taiga biome has lighter 13 c than steppe biome hence pollen 13 c composition is more sensitive to changes of humidity in the analogous spectra than palynotaxonomical structure and 13 c of toc based on our results the holocene climates in mongolian altai are 1 dry conditions prior to 11 5 kyr bp 2 wet conditions between 11 5 and 6 0 kyr bp 3 a relatively dry cool episode during 6 4 kyr bp 4 stable cool and semiarid conditions with moderately effective moisture during the past 4000 years two abrupt climatic changes occurred at 7 45 kyr bp and 11 5 kyr bp might be related to glacial activities the holocene climatic trend in mongolian altai which is controlled by the westerlies is similar to the trend of monsoonal climate shown by the chinese speleothem records as well as the lake sand dune evidence in the deserts of nw china the contact of the two climatic systems and shift of the monsoonal boundary during the past need to be further studied

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

molecular and isotopic stratigraphy in an ombrotrophic mire for paleoclimate reconstruction a 40 cm deep sphagnum dominated peat monolith from bolton fell moss in northern england was systematically investigated by lipid molecular stratigraphy and compound specific 13c and d analysis using gas chromatography gc gc mass spectrometry gc ms gc combustion isotope ratio ms gc c irms and gc thermal conversion irms gc tc irms techniques 210pb dating showed the monolith accumulated during the last ca 220 yr a period encompassing the second part of little ice age while the distributions of lipids including n alkan 1 ols n alkan 2 ones wax esters sterols n alkanoic acids alkandioic acids and hydroxy acids display relatively minor changes with depth the cooler climate event was recorded in the concentrations of n alkanes and organic carbon cpi values of n alkanes and n alkanoic acids and the ratio of 5 n alkylresorcinols sterols superimposed on the fossil fuel effect the relatively cooler climate event was also recorded by 13c values of individual hydrocarbons especially the c23n alkane a major compound in certain sphagnum spp the d values of the c29 and c33n alkanes correlated mainly with plant composition and were relatively insensitive to climatic change in contrast the c23n alkane displayed variation that correlated strongly with recorded temperature for the period represented by the monolith agreeing with previously reported deuterium records in tree ring cellulose spanning the same period in scotland germany and the usa with more negative values occurring during the second part of little ice age these biomarker characteristics including the compound specific 13c and d records provide a new set of proxies of climatic change potentially independent of preserved macrofossils which will be of value in deeper sections of the bog where the documentary records of climate are unavailable and humification is well advanced

postglacial climate change record in biomarker lipid compositions of the hani peat sequence northeastern china abstract the peat sequence at hani in northeastern china accumulated over the past 16 cal kyr in a percolation mire in which rain water and ground water seeped through the peat system the molecular compositions of n alkanes n alkanols and n alkanoic acids extracted from the hani peat sequence reveal different responses to the progressive evolution of climate and changes in the nature of the peat forming vegetation long chain length components that originate from the waxy coatings of subaerial vascular plants dominate the n alkane distributions throughout the hani peat sequence the paleoclimate integrity of these biomarker molecules appears to be well preserved most of the n alkanol distributions are similarly dominated by long chain components that indicate their origins from subaerial plants in contrast n alkanoic acid distributions are dominated by secondary components that record the importance of post depositional microbial activity in this peat sequence which evidently can be extensive in a percolation mire elevated n alkane paq values and c23 c29 ratios which are both molecular proxies for water loving plants record an especially moist local climate in the bolling allerod 14 5 to 12 9 ka younger dryas 12 9 to 11 5 ka and pre boreal 11 5 to 10 5 ka portions of the hani peat sequence depressed paq values and c23 c29 ratios and larger n alkane average chain length values indicate that the holocene climatic optimum 10 5 to 6 ka was a period of warmer climate with lower effective precipitation which contrasts with evidence of wetter climates in most of east asia

different patterns of changes in the asian summer and winter monsoons on the eastern tibetan plateau during the holocene previous sedimentological studies on peat sequences from the eastern tibetan plateau showed that there have been eolian dust inputs to the wetlands on the eastern tibetan plateau thereby providing an opportunity to reconstruct the history of the asian winter monsoon at a higher temporal resolution here the dust flux and the content of trace metallic elements ti ni and v in a peat sequence from the hongyuan swamp 32 46 7 n 102 31 0 e are used to reconstruct variations in the intensity of the asian winter monsoon during the holocene this record when compared with the summer monsoon proxy can help elucidate the phase relationship between these two systems our proxy based reconstructions show different patterns of changes in the asian winter and summer monsoons before and after 5 5 cal ka bp generally the two monsoons varied reciprocally before 5 5 cal ka bp however after 5 5 cal ka bp these two systems exhibit synchronous changes moreover both the frequency and amplitude of the variations in these two monsoons are different before and after 5 5 cal ka bp the rate of changes in the solar insolation during the holocene matches well with these monsoon records implying that the mid holocene climate transition may have resulted from orbital forcing

palaeoclimate records in compound specific δd values of a lipid biomarker in ombrotrophic peat compound specific d values recorded by means of gas chromatography thermal conversion isotope ratio mass spectrometry gc tc irms of the biomarker n alkane n tricosane n c23 representative of the dominant sphagnum species in a 40 cm peat profile from bolton fell moss cumbria uk correlate with vegetation changes in the past 200 years age depth model based on 210pb dating the bog vegetation is sensitive to climate change correlating with the global scale cooler period of the later 19th and early 20th centuries the correlation with meteorological records suggests compound specific d values of lipid biomarkers have potential for use as a new climate proxy

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

holocene monsoonal climate changes tracked by multiproxy approach from a lacustrine sediment core of the subalpine retreat lake in taiwan abstract the aim of this study is to improve the understanding of environmental changes and the linkages with the dynamics of the east asian monsoon eam during the holocene in the western north pacific we analyzed the pollen diatom and weak acid leachable fractions associated with extracted organic compounds of lacustrine sediments retrieved from the subalpine retreat lake in northwestern taiwan during the early holocene 10 100 8600 cal bp cool climate was inferred by the dominance of grass pollen with poor preservation of diatom valves in the record at that time derived biomarkers were also dominated by long chain alkanes originating from herbs the following holocene optimum 8600 6400 cal bp was characterized by a remarkable increase of tree pollen indicating the warmer and humid climate and a stronger summer eam the possible enhanced monsoon driven precipitation resulted in higher contents of total organic carbon buried in sediments however the climate and precipitation of the alpine area in taiwan might have been unstable the high variability of wetland pollen and diatom abundance reveals weak periods of eam during the late holocene optimum 6400 4500 cal bp the hiatus in the deposit during 4500 2100 cal bp suggests the continuously decline of the eam during the last 2100 years dominated wetland plant pollen accompanying stable diatom abundance indicated humid climatic conditions and a stable increase of the eam the climatic condition of study area was similar with modern situation during this late holocene