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

sources and occurrence of c12c22n alkane distributions with even carbon number preference in sedimentary environments abstract the occurrence of c12 c22n alkanes with a strong even carbon number preference is reported in recent and miocene sediments encompassing marine and freshwater systems deposited under oxic and anoxic conditions it is therefore shown that these n alkanes can be found in a wider type of sedimentary environment than those previously described the occurrence in some cases of a parallel distribution of c14 c20n alk 1 enes is also illustrated a variety of biological sources including both marine and freshwater bacteria as well as fungi and yeast species is suggested to account for such distributions

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

predominance of even carbon numbered n alkanes from lacustrine sediments in linxia basin ne tibetan plateau implications for climate change this study reports the first observation of predominant even c numbered n alkanes from sediments in the continuous lacustrine sedimentary section maogou from the late miocene to the early pliocene 13 4 4 ma in the linxia basin ne tibetan plateau the n alkanes showed a bimodal distribution that is characterised by a centre at n c16 n c20 with maximum values at n c18 and n c27 n c31 as well as at n c29 the first mode shows a strong even c number predominance oep16 20 0 34 0 66 in contrast the second mode has a strong odd c number predominance oep27 31 1 20 2 45 certain types of special autochthonous bacteria are a possible source for this distribution of even c numbered n alkanes in lacustrine sediments these bacteria may have a high production rate in weak oxic anoxic and arid depositional environments in which a variety of geochemical parameters have recorded palaeoclimate change

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

marine palynological record for tropical climate variations since the late last glacial maximum in the northern south china sea the upper part 191 1439 cm of the marine sediment core md05 2906 from the northern south china sea scs was palynologically investigated the chronology suggested that it covered the record since 19 calendar kiloyears before present cal ka bp and revealed a detailed environmental change history since the late last glacial maximum lgm during the late lgm due to the lowered sea level 100 m lower and the shortened distance from the shore to the study site the pollen concentration was very high the pollen assemblages were dominated by non arboreal taxa especially artemisia pollen before 15 cal ka bp abundant subtropical and tropical pollen taxa were still important components and a south subtropical climate prevailed during the late lgm the coexistent rich artemisia pollen possibly was not derived from near shores but was derived mainly from the northern exposed continental shelf in the east china sea ecs after 15 cal ka bp with the rise in the sea level and enhanced distance from the pollen source areas to the core site pollen concentrations started to decline gradually however during the late deglaciation and early holocene the higher concentrations of many pollen taxa reoccurred which cannot be attributed to the sea level changes pinus pollen deposited in the core which is considered to be mostly water carried based on many modern pollen surveys also started to dramatically increase at the same time therefore the higher pollen concentration with more pinus and typha an aquatic plant pollen indicated a notably enhanced terrestrial runoff and precipitation during the last deglaciation holocene transition 11 3 9 4 cal ka bp we inferred that a strong summer monsoon occurred at this time during the late lgm deglaciation transition period the pollen assemblage reflected a gradually warming climate and the climate fluctuations derived from the high latitudes were not well identified this study suggests that solar insolation played a crucial role in controlling the east asian monsoon and hydrological cycle in the northern scs

increased contribution of terrigenous supply from taiwan to the northern south china sea since 3 ma seismic profiles provide evidence that there has been strong transport by deep water bottom currents and drift deposition on the northern slope of the south china sea earlier geochemical studies suggest that the drift sediments originated primarily from taiwan however the transport process history and origin of the deep water bottom deposition in the northern south china sea on both glacial interglacial and tectonic time scales remain unclear here we show new high resolution records of clay minerals grain size and mass accumulation rate mar of terrigenous materials from ocean drilling program odp site 1144 together with trace element concentrations in siliciclastic sediments from odp site 1146 combined with other published data we find that the primary source for sediments at odp sites 1144 1148 since 3 ma is from taiwan and not from pearl river as previously thought before 3 ma however sediment source to odp sites 1146 and 1148 was mainly from the pearl river increased contribution of terrigenous supply from taiwan to the northern south china sea since similar to 3 ma may be related to the formation of the taiwan orogen and strengthening of deep water bottom current transport in the northern south china sea variations in clay mineralogy and sedimentology at odp site 1144 located on a sediment drift shows strong glacial interglacial cyclicity this suggests that bottom current deposition is highly dependent on sea level fluctuations which control the terrigenous supply to the deep sea c 2010 elsevier b v all rights reserved

longitudinally confined geomagnetic reversal paths from non dipolar transition fields it has long been thought that conditions at the boundary between the core and mantle influence the earth s magnetic field but the supporting evidence is rather indirect1 3 recent palaeomagnetic results suggesting that there are persistent preferred longitudinal paths for the virtual geomagnetic pole vgp during reversals4 would provide the first direct evidence of the solid mantle s influence on the core although their statistical significance has been disputed5 6 the results are potentially exciting because the preferred paths lie close to the pacific rim where the present geomagnetic secular variation changes character2 7 here we present a simple model based on an extension of a previous theory8 that produces reversals with vgp paths confined within relatively narrow longitude bands despite the transition field having a substantially non dipolar structure thus although longitude bias of the vgp paths is definitive evidence for core mantle interaction simple vgp paths are not evidence of near dipolar transition fields

terrigenous n alkane input in the south china sea high resolution records and surface sediments abstract molecular abundances of n nonacosane are reported for a suite of 44 surface sediments and four deep sea cores distributed throughout the south china sea scs covering the last 220 ky at different time resolutions the patterns of glacial to interglacial variability of the concentrations of this terrigenous marker are parallel for all cores taking values linearly inversely correlated to the u37k index sea surface temperatures sst with high concentrations during cold glacial intervals and low concentrations during warm interglacial periods the oscillations of this terrigenous marker likely result from the emergence and flooding of the shelves caused by sea level variations which together with scs ssts have a clear dependency on the northern hemisphere climate evolution calculation of accumulation rates for the northernmost core together with the modern distribution of n nonacosane concentrations in surface sediments evidences the complexity of sedimentation patterns in the northern scs in particular and in agreement with recent studies terrigenous materials deposited there might originate from areas different than the highly loaded pearl river for paleoceanographic purposes the noticeable general pattern of the n alkane concentration down core profiles for the four cores studied a parameter apparently unaffected by changes in sedimentation rates prompts its use as a tracer of variations in terrigenous input into this basin over glacial to interglacial times

a δ 13 c record of late quaternary climate change from tropical peats in southern india stable isotope ratios of carbon in soils or lake sediments1 3 and of oxygen and hydrogen in peats4 5 have been found to reflect past moisture variations and hence to provide valuable palaeoclimate records previous applications of the technique to peat have been restricted to temperate regions largely because tropical climate variations are less pronounced making them harder to resolve here we present a 13c record spanning the past 20 kyr from peats in the nilgiri hills southern india because the site is at high altitude 2 000 m above sea level it is possible to resolve a clear climate signal we observe the key climate shifts that are already known to have occurred during the last glacial maximum 18 kyr ago and the subsequent deglaciation in addition we observe an arid phase from 6 to 3 5 kyr ago and a short wet phase about 600 years ago the latter appears to correspond to the mediaeval warm period which previously was believed to be confined to europe and north america6 7 our results therefore suggest that this event may have extended over the entire northern hemisphere

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

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

north atlantic holocene climate evolution recorded by high resolution terrestrial and marine biomarker records abstract holocene climatic change is driven by a plethora of forcing mechanisms acting on different time scales including insolation internal ocean e g atlantic meridional overturning circulation amoc and atmospheric e g north atlantic oscillation nao variability however it is unclear how these driving mechanisms interact with each other here we present five biomarker based paleoclimate records air sea surface temperature and precipitation from a fjordic sediment core revealing north atlantic terrestrial and marine climate in unprecedented detail the early holocene 10 7 7 8 kyrs bp is characterised by relatively high air temperatures while ssts are dampened by melt water events and relatively low precipitation the middle holocene 7 8 3 2 kyrs bp is characterised by peak ssts declining air temperatures and high precipitation a pronounced marine thermal maximum occurs between 7 5 5 kyrs bp 3000 years after the terrestrial thermal maximum driven by melt water cessation and an accelerating amoc the neoglacial cooling between 5 8 and 3 2 kyrs bp leads into the late holocene we demonstrate that an observed modern link between icelandic precipitation variability during different nao phases may have existed from 7 5 kyrs bp a simultaneous decoupling of both air and sea surface temperature records from declining insolation at 3 2 kyrs bp may indicate a threshold after which internal feedback mechanisms namely the nao evolved to be the primary drivers of icelandic climate on centennial time scales

a 400 000 year record of vegetational and climatic changes from a volcanic basin leizhou peninsula southern china abstract the tianyang lake in leizhou peninsula is an enclosed crater formed during the early to middle pleistocene over 200 m of diatomaceous mud and clay were deposited in the last 400 000 years providing a continuous middle and late quaternary lacustrine sequence for paleoenvironmental studies the pollen record spans the last four glacial interglacial cycles equivalent to oxygen isotope stages ois 10 to 1 during most of the glacial phases fagaceous monsoon forest was replaced by altitudinal vegetation indicating a regional landscape transformation on the peninsula the montane forest reached down to the lowland by at least 600 m during the ois 6 and 8 in a cool and relatively wet condition with temperature estimated to be more than 4 c lower than present a further lowering of the montane forest belts by about 800 1000 m occurred in the ois 4 2 as implied by the appearance of many temperate elements during the last glacial maximum this mixed forest subsequently gave way to the poaceae grassland a savanna vegetation type favored by drier and cooler climatic conditions this drastic change implies a more significant drop in temperature and precipitation than the previous three glacial periods ois 10 8 and 6 it is thus inferred that the weakening of summer monsoon was more significant towards the end of the late pleistocene particularly during the last glacial maximum lgm

possible origin of n alkanes with a remarkable even to odd predominance in recent marine sediments abstract n alkane distributions with a remarkable even to odd predominance c16 c24 were found in marine surface sediments the previously proposed diagenetic reduction of the corresponding n fatty acids could not be considered as a source for these n alkane based on a comparison of compositional features of n alkane n fatty acid and n alcohol distributions carbon isotope analyses and other geochemical parameters the data indicate that the even predominant n alkanes were derived directly from marine bacteria

deep sea pollen from the south china sea pleistocene indicators of east asian monsoon abstract a high resolution pollen record sampling interval averages 820 years has been obtained from odp site 1144 water depth 2037 m northern south china sea the 504 m sequence in composition length covers the last 1 03 million years according to micropaleontological and isotopic stratigraphy the pollen assemblages are characterized by high proportions of pinus and herb pollen and by their frequent alternations based on these alternations 29 pollen zones have been recognized that are closely correlated to the marine oxygen isotope stages mis 1 29 pinus dominant pollen zones correspond to interglacial periods with lighter 18o values while herb marked ones relate to the heavier 18o stages assigned to glacials judging from the pollen data the exposed northern continental shelf of the south china sea during the glacials was covered by grassland and the extensive northern shelf has formed only since mis 6 ca 150 ka probably as a result of tectonic subsidence tree pollen influx values are indicative of winter monsoon which began to intensify 600 ka ago the summer monsoon variations can be approximated by the fern percentage within the total pollen and spore abundance and the result shows high values in general occurring at interglacials with the maxima at mis 15 5e and 1 the relatively high fern percentage with smaller amplitude in variations before 600 ka might suggest more stable humid conditions before the intensification of winter monsoon

last glacial maximum in china comparison between land and sea abstract as a result of the sea level drop at the last glacial maximum about 100 120 m in the south china sea and 130 150 m in the east china sea the size and configurations of the china seas changed greatly the east china sea with the yellow sea and bohai gulf was reduced into an elongated trough while the south china sea became a semi enclosed gulf due to the southern shift of the polar front in the north pacific and the reorganization of the surface current system the winter temperature in the south china sea was 6 10 c colder and the seasonality was much stronger than it is now the reduced sea area and thus the increased distance to the coast together with the declined sea surface temperature led to intensified aridity on the land the enhanced eolian processes related to the intensification of the winter monsoon caused an expansion of the loess deposition area reaching the southeastern part of china to the south of the yangtze river and off the modern sea coast vegetation zones greatly shifted to the southeast in north china deserts and steppes were much more extensive than they are now and the modern areas of warm temperate broad leaved forests were occupied by steppes or woodland in south china the deciduous broadleaved forests were developed in areas now covered by evergreen forests and the monsoon rain forest completely disappeared the changes in the climate on land and the configurations of seas altered the sediment supply and sedimentation rate in the china seas giving rise to the atlantic type late quaternary caco3 curve there

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

a high resolution palaeoclimatic record for the last 27 500 years in tropical west africa from the carbon and nitrogen isotopic composition of lacustrine organic matter variations in the carbon and nitrogen isotopic composition of bulk organic matter in the sediments of lake bosumtwi ghana reflect climatically induced changes to the lake and the catchment flora cores spanning the last 27 5 kyr of sedimentation in the lake show large oscillations in 13corg pdb and 15norg air the late pleistocene record is particularly detailed showing changes of ca 20 in carbon and ca 10 in nitrogen isotopic compositions these variations are of complex origin although different in magnitude major isotopic excursions in the two records are generally in phase and reveal the occurrence of two major dry intervals at and immediately following the last glacial maximum the allerod younger dryas period also seems to have been marked by generally dry conditions in this part of tropical west africa nitrogen isotopic evidence suggests that during the period 9 2 3 2 kyr the lake had an extremely stable water column probably due to the absence of a windy or cool dry season or both regular circulation of the water column recommenced during the late holocene and has persisted until the present day

three dimensional strain produced by 50 my of episodic extension horse prairie basin area sw montana u s a abstract the horse prairie basin of southwestern montana is a complex east dipping half graben that contains three angular unconformity bounded sequences of tertiary sedimentary rocks overlying middle eocene volcanic rocks new mapping of the basin and its hanging wall indicate that five temporally and geometrically distinct phases of normal faulting and at least three generations of fault related extensional folding affected the area during the late mesozoic to cenozoic all of these phases of extension are evident over regional or cordilleran scale domains the extension direction has rotated 90 four times in the horse prairie area resulting in a complex three dimensional strain field with 60 east west and 25 north south bulk extension extensional folds with axes at high angles to the associated normal fault record most of the three dimensional strain during individual phases of extension phases 3a 3b and 4 cross cutting relationships between normal faults and tertiary volcanic and sedimentary rocks constrain the ages of each distinct phase of deformation and show that extension continued episodically for more than 50 my gravitational collapse of the sevier fold and thrust belt was the ultimate cause of most of the extension

late quaternary vegetation history of southeast africa the molecular isotopic record from lake malawi abstract accurate reconstructions of past hydrological variability are essential for understanding the climate history of the tropics in tropical africa the relative proportion of vegetation utilizing the c3 vs c4 photosynthetic pathway is mainly controlled by precipitation and thus past hydrological changes can be inferred from the vegetation record in this study biomarkers of terrestrial plants lignin phenols and plant leaf wax carbon isotopes are examined from a well dated sedimentary record from lake malawi to provide a vegetation aridity record of the past 23 cal ka from southeast africa we suggest that the ratio of cinammyl to vanillyl c v lignin phenols in lake malawi sediments mainly reflects inputs of c3 trees woody tissue vs c4 grasses non woody tissue and find that changes in the c v ratio generally support variability noted in the n alkane carbon isotope record together these records provide evidence for increased c4 vegetation grasses surrounding lake malawi during last glacial maximum lgm the younger dryas in the early holocene and from 2 cal ka to the present suggesting drier conditions at these times elevated inputs of c3 vegetation are noted in the intervals from 17 13 6 cal ka and 7 7 2 cal ka indicating wet conditions in southeast africa a relationship is noted between the n alkane average chain length acl and temperature with longer acls associated with higher temperatures higher n alkane carbon preference index cpi values correlate with higher mass accumulation rates of biogenic silica and may result from periodic increased northerly winds over lake malawi which enhance upwelling and diatom productivity while simultaneously increasing erosion and transport of plant leaf waxes to the lake the molecular data produced in this study suggest that the carbon isotopic signature of bulk sediment 13ctoc in lake malawi is primarily a reflection of terrestrial inputs c3 vs c4 vegetation and may not mainly reflect changes in algal productivity as previously thought

organic geochemistry of recent marine sediments from the nansha sea china recent marine sediments from two cores collected on the continental slope of the nansha sea china have been analyzed for organic matter content n alkane and isoprenoid hydrocarbons fatty acids n alkanols and sterols the organic carbon contents of the two sediment cores average 0 7 and 0 53 respectively and are higher than those of other sedimentary environments in this region the distributions of various lipid compounds indicate that most of the sedimentary organic matter in the two cores is derived from marine plankton and bacteria with land derived organic matter present in relatively small amounts the decrease in relative abundances of shorter chain lipids n alkanes n fatty acids and n alkanols with depth is evident as is the biochemical conversion of stenols to stanols in some samples the low pristane phytane ratios may result primarily from microbial activity and reflect the occurrence of significant diagenetic alteration of organic matter in the two cores

plio pleistocene climatic transition and the lifting of the teton range wyoming abstract fine grained lacustrine riverine and ash fall sediments of the shooting iron formation whose late pliocene age is established by blancan gastropods and vertebrates yield a pollen flora that is essentially similar in composition to the modern pollen rain in the jackson hole area the pliocene assemblage suggests a climate like that of the jackson valley and foothills today these spectra also resemble a pliocene pollen flora from yellowstone park dated at 2 02 ma however the underlying miocene teewinot sediments differ by containing pollen of four exotic deciduous hardwoods tertiary relicts that suggest a summer moist climate unlike that of today the shooting iron sediments lie with an angular unconformity on and above the miocene lake sediments of the teewinot formation both of these deposits probably preceded the main uplift of the teton range based on the absence of precambrian clasts in the tertiary valley deposits because the pliocene floras were modern in aspect a plio pleistocene transition would be floristically imperceptible here the sequence denotes a protracted period of relative stability of climate during teewinot time and a shift in vegetational state summer wet trees drop out sometime between the latest miocene and latest pliocene the pliocene spectra suggest a dry cooler climate toward the end of shooting iron time