core and intact polar glycerol dialkyl glycerol tetraethers gdgts in sand pond warwick rhode island usa insights into the origin of lacustrine gdgts branched and isoprenoidal glycerol dialkyl glycerol tetraethers gdgts are abundant in lake sediments and have potential use for determining past changes in climate and limnology however emerging evidence suggests that both classes of gdgts can be associated with both allochthonous soil organic matter and in situ production potentially complicating interpretation of these compounds in lacustrine sedimentary environments here we investigate the dual source issue surrounding lacustrine gdgts with an emphasis on the branched gdgts by studying both core and intact polar gdgts within a pond and its watershed in warwick ri significant differences in both absolute concentrations of branched gdgts and the percent of branched gdgts present as ipls between the soils and shallow lake sediments suggests in situ production of these compounds within the lake environment principal components analysis of gdgt lipid concentrations and environmental parameters in sand pond sediments and soils highlights two prominent trends in the data one related to the absolute concentrations of type i branched gdgts brgdgt i ib ic and the majority of the isoprenoidal gdgts and another related to the concentration of the more methylated type iii branched gdgts brgdgt iii iiib iiic and isoprenoidal gdgt 0 the latter trend exhibits a subsurface maximum in the sediment column potentially indicating in situ production of more highly methylated branched gdgts and gdgt 0 within the lacustrine sediment column trends in the distributions of branched gdgts as reflected by the mbt and cbt indices imply mixing of two distinct sources of branched gdgts soil derived and in situ or alternatively two or more different microbial producers both possibilities present a challenge to the application of brgdgt based paleoenvironmental proxies in lakes this study highlights the importance of determining the sources of gdgts to the lacustrine environment prior to paleoenvironmental application

environmental changes since 8 4 ka reflected in the lacustrine core sediments from nam co central tibetan plateau china the tibetan plateau induces and enhances the asian monsoon that influences the plateau itself east china and even the whole of asia pursuing the changing monsoon history and its impact in this environment sensitive area is a key for understanding the climatic changes here we present the initial results from core sed iments in nam co central tibet to elucidate the holocene environment changes in this area the studied lake nam co is the second largest lake with an elevation of 4718 m water area of 2015 km 2 and catchment area of 10 610 km 2 by using echo seismic profiling and hydro echosounding we investigated the bathymetric dis tribution of the whole lake one 332 cm long piston core was successfully taken in the east part of the lake at 60 m water depth twelve ams 14 c dates from top to bottom of this core established a good time sequence toc tn n alkanes grain size clay minerals fe mn sr ba and caco3 content were analysed with sampling intervals from 1 cm to 10 cm results showed that since 8400 yr bp the environment changes in this region indicate three stages the early stage 8400 6900 yr bp was characterized by slight shifting from warm to cold with a cold dry interval at 8100 7800 yr bp the middle stage was from 6900 to 2900 yr bp during which cli mate changed from warm humid to cold dry however around 2900 yr bp the climate once was slightly cold but strongly dry the late stage from 2900 yr bp to present was characterized by a general tendency toward cold dry the first temperature decline was around 1700 1500 yr bp following which temperature increased once before decreasing again around 600 300 yr bp which might be the result of the little ice age

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

clay mineral assemblages of mesozoic pelagic and flysch sediments of the lombardian basin southern alps implications for palaeotectonics palaeoclimate and diagenesis clay mineral assemblages determined by x ray diffraction in the jurassic to lower cretaceous hemipelagic pelagic sediments and in the upper cretaceous flysch sequences of the lombardian basin southern alps record tectonic and possibly climatic changes in the source areas and to a lesser extent alterations during burial diagenesis

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

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

tropical climate at the last glacial maximum inferred from glacier mass balance modeling model derived equilibrium line altitudes elas of former tropical glaciers support arguments based on other paleoclimate data for both the magnitude and spatial pattern of terrestrial cooling in the tropics at the last glacial maximum lgm relative to the present lgm elas were maintained by air temperatures that were 3 5 to 6 6 c lower and precipitation that ranged from 63 wetter in hawaii to 25 drier on mt kenya africa our results imply the need for a 3 c cooling of lgm sea surface temperatures in the western pacific warm pool sensitivity tests suggest that lgm elas could have persisted until 16 000 years before the present in the peruvian andes and on papua new guinea

late holocene forcing of the asian winter and summer monsoon as evidenced by proxy records from the northern qinghai tibetan plateau abstract little is known about decadal to centennial scale climate variability and its associated forcing mechanisms on the qinghai tibetan plateau a decadal resolution record of total organic carbon toc and grainsize retrieved from a composite piston core from kusai lake nw china provides solid evidence for decadal to centennial scale asian monsoon variability for the northern qinghai tibetan plateau during the last 3770 yr intensified winter and summer monsoons are well correlated with respective reductions and increases in solar irradiance a number of intensified asian winter monsoon phases are potentially correlated with north atlantic climatic variations including bond events 0 to 2 and more recent subtle climate changes from the medieval warm period to the little ice age our findings indicate that asian monsoon changes during the late holocene are forced by changes in both solar output and oceanic atmospheric circulation patterns our results demonstrate that these forcing mechanisms operate not only in low latitudes but also in mid latitude regions the northern qinghai tibetan plateau

the early toarcian and cenomanian turonian anoxic events in europe comparisons and contrasts two intervals of mesozoic time are demonstrably of sufficient geological brevity to qualify readily for the term anoxic event the earlyfalciferum zone orexaratum subzone of the toarcian and thewhiteinella archaeocretacea interval zone that straddles the cenomanian turonian boundary both periods of time saw regional deposition of anomalously organic rich strata black shales accompanied by a positive 2 pdb carbon isotope excursion in coeval biogenic carbonates and significant faunal change the duration of both events was probably less than half a million years and both were preceded by regional erosion and possible upwelling coincident sea level rise and transgression is likely a european view of these events however spotlights some significant differences whereas thefalciferum zone organic matter is generally more concentrated and more hydrogen rich on the palaeo european shelf than on the tethyan continental margins the reverse holds true for the black shales formed during thewhiteinella archaeocretacea interval zone furthermore the carbon isotope composition offalciferum zone organic matter from both north european and tethyan sites is anomalously negative compared to that developed in thewhiteinella archaeocretacea interval zone differing planktonic organisms may have been involved and their possible diverse ecological requirements may go some way to explaining the nature and distribution of facies deposited during these two events

evolution of chaka salt lake in nw china in response to climatic change during the latest pleistocene holocene abstract the late pleistocene and holocene hydrologic balance of chaka salt lake in the eastern qaidam basin of nw china was studied based on the analysis of lithostratigraphy mineralogy total organic carbon and total nitrogen from a 9 0 m long sediment core an age depth model for the lake sediments is based on eight accelerator mass spectrometry ams 14 c measurements of organic matter and a 1700 year radiocarbon reservoir correction the pitzer model was used to calculate the sequence of minerals precipitated as a function of salinity assuming that the initial lake water was recharged from adjacent rivers and springs lake salinity values were derived from a good match between the calculated and observed mineral sequences our multi proxy based hydrologic reconstruction of chaka lake indicates that it was a clastic dominated freshwater lake between 17 2 and 11 4 cal ka bp which may have resulted from the input of glacial water into the lake at that time during the lateglacial and holocene a warm climatic regime predominated between 13 9 and 12 7 cal ka bp and then a cold climatic regime prevailed between 12 7 and 11 4 cal ka bp these warm and cold periods correlate with the bolling allerod and younger dryas events in the region beginning at 11 4 cal ka bp a saline or hypersaline lake developed which may have resulted from increased summer insolation and temperatures these conditions persisted throughout the holocene modeling indicates that lake salinity fluctuated between 66 and 223 ppt from 11 4 to 7 2 cal ka bp and then increased to 223 322 ppt between 7 2 and 6 0 cal ka bp when most regions of china recorded high moisture availability i e the so called mid holocene climatic optimum lake salinity decreased to 66 223 ppt during a short time period between 6 0 and 5 3 cal ka bp possibly caused by reduced evaporation subsequently salinity values rapidly increased to 223 322 ppt between 5 3 and 5 2 cal ka bp and a hypersaline lake with a salinity higher than 324 ppt similar to modern chaka salt lake became established around 5 2 cal ka bp this establishment may have been related to the weakening of asian monsoon regional comparisons of paleoclimatic records indicate that large temporal and spatial variations exist in the occurrence and intensity of drought over western china since the lateglacial

temperature responses to quasi 100 yr solar variability during the past 6000 years based on δ18o of peat cellulose in hongyuan eastern qinghai tibet plateau china abstract during the past 6000 years the temperature variation trend inferred from 18o of peat cellulose in a peat core from hongyuan eastern qinghai tibet plateau southwestern china is similar to the atmospheric 14c concentration trend and the modeled solar output trend the general trend of hongyuan 18o during the past millennium also coincides well with the atmospheric 14c concentration trend the 10be concentration trend in an ice core from the south pole the reconstructed total solar irradiance trend as well as the modeled solar output trend in addition temperature events also correspond well to solar perturbations during the past 6000 years therefore the driving force of holocene temperature variations should be properly ascribed to solar activity the spectrum analysis further illustrates that quasi 100 yr fluctuation of solar activity was probably responsible for temperature variations in northeast qinghai tibet plateau during the past 6000 years

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

palaeoclimate reconstructions of the middle jurassic of kachchh western india an integrated approach based on palaeoecological oxygen isotopic and clay mineralogical data abstract the middle jurassic sedimentary succession of the kachchh basin shows significant changes in lithology faunal content and diversity across the bathonian callovian boundary the change in lithology from predominantly carbonates in the middle and late bathonian to siliciclastics in the callovian is accompanied by a drop in species diversity from high to moderate characteristic faunal elements of the bathonian corals sponges the bivalves eligmus and members of the opinae are absent or rare in the callovian in contrast callovian sediments contain comparatively high proportions of nuculid bivalves the clay mineral assemblage reveals prominent variations in the smectite vs kaolinite abundance especially during the bathonian to callovian transition from the bajocian to the middle bathonian smectite becomes the dominant clay mineral and is nearly exclusively present in the late bathonian towards the middle callovian its content gradually decreases and kaolinite becomes the dominant clay mineral illite generally is only a minor component throughout the middle jurassic based on these results the bajocian to middle bathonian time interval is interpreted to represent subtropical climatic conditions with seasonal droughts and a moderate supply of terrigenous clastics to the basin the late bathonian was a period with a semi arid climate hot seasonal droughts and a minor input of terrigenous clastics the increase in kaolinite contents in the callovian suggests a subtropical humid climate with less prominent seasonal droughts and a higher input of siliclastics into the basin accompanied by a higher nutrient influx oxygen isotope ratios measured on bathonian to early callovian brachiopod shells give palaeotemperatures of 19 24 c callovian to oxfordian paleotemperatures calculated from oxygen isotopes measured on belemnite rostra range from 11 to 21 c the lower palaeotemperatures estimated from the oxygen isotopic composition of belemnite calcite are explained by assuming that the belemnites spent most of their life span in colder regions of the malagassy gulf and migrated into the warmer subtropical waters of the kachchh basin combining these various lines of evidence the changes in lithology and faunal composition taking place in the kachchh basin during the middle jurassic appear to reflect largely a change towards increasing humidity rather than a distinct decrease in water temperature

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

paleosalinity determination in ancient epicontinental seas a case study of the t oae in the cleveland basin uk abstract the early jurassic toarcian oceanic anoxic event t oae was marked by deposition of organic rich sediments and a pronounced negative carbon isotope excursion across the northwest european sea nwes representing a signal that was stronger regionally than globally various models for the t oae have been proposed some focusing on general atmospheric oceanic controls to reflect its global character and others emphasizing local or regional factors to account for its strong expression in the nwes in this study we evaluate watermass dynamics of the early jurassic cleveland basin uk during the t oae using a combination of paleosalinity proxies b ga sr ba and s toc these proxies suggest that brackish conditions existed prior to onset of the t oae with a shift to nearly freshwater conditions during the t oae reflecting a large increase in terrestrial runoff due to a stronger hydrological cycle possibly combined with shallowing of the marginal sill of the cleveland basin through sea level fall following the t oae basinal salinity conditions first returned to brackish and then gradually shifted to fully marine this hydrographic history accounts for low mo concentrations in t oae sediments of the cleveland basin demonstrating control by watermass restriction and local rather than global aqueous mo drawdown these findings demonstrate the importance of local hydrographic controls on the sedimentary expression of the t oae the more general significance of this study is that it highlights the need for application of paired salinity and redox proxies in order to correctly interpret paleoenvironmental variations in marginal marine basins

1300 years of climatic history for western central asia inferred from tree rings more than 200 000 ring width measurements from 384 trees were obtained for 20 individual sites ranging from the lower to upper local timber lines in the northwest karakorum of pakistan and the southern tien shan of kirghizia samples were obtained predominantly from juniper species juniperus and were analysed to reconstruct regional climatic variation patterns in western central asia since ad 618 site distri bution represents diverse ecological conditions e g combinations of temperature and moisture stress within the karakorum and tien shan mountains permitting both intra montane and inter montane comparisons of chronologies three different types of chronologies ree ecting interannual decadal and centennial scale ring width variations were calculated a statistic skeleton plotting technique was used to identify ring width pointer years interannual a 101 year kernel e lter was used to identify decadal scale variations and for a subset of long lived trees the mean ring width of the entire single series was used to identify centennial trends after extracting and calibrating each of these three distinct wavelengths in ring width variation the results were combined into a comprehensive reconstruction ree ecting primarily temperature e uctuations in western central asia since ad 618 the nature and the temporally changing strength of the climatic signals of this reconstruction are discussed in detail a maximum latewood density record of pinus tienschanica from central tien shan was used as a predictor series to calibrate and validate tree ring width variation in so doing we link our results to the circumpolar maximum latewood density network briffa et al 1998a 1998b schweingruber and briffa 1996

duration of the early bajocian and the associated δ13c positive excursion based on cyclostratigraphy the early bajocian about 172 ma ago was a period of tectonic changes a global carbon isotope positive excursion and biological diversification of marine invertebrates e g ammonites radiolarians and coccolithophores unfortunately both the duration of the early bajocian and the associated palaeoenvironmental changes are still poorly constrained we propose here an estimate of the duration of this sub stage based on a cyclostratigraphic analysis of the carbonate content from the chaudon norante section french subalpine basin france the chaudon norante succession has been correlated with les dourbes section using greyscale variations to detect possible local hiatuses the duration estimated here for the entire early bajocian is 4 082 ma two intervals were identified in the positive 13 c excursion an increase of carbon isotope values lasting 1 36 ma and climax isotope values lasting for 2 72 ma a cooling at high latitudes and warming at low latitudes may have enhanced the earth s temperature gradient leading to an increase in humidity which in turn triggered ocean eutrophication at the origin of the 13 c positive excursion supplementary material the complete dataset presented in the paper a colour version of the figure 8 and correlation of 13 c excursions between our studied site and contemporaneous sites are available at www geolsoc org uk sup18555

continental weathering and climatic changes inferred from clay mineralogy and paired carbon isotopes across the early to middle toarcian in the paris basin abstract lower toarcian strata lower jurassic have been extensively studied with a view to understanding the oceanographic climatic and biological processes that drove the earth s system into an oceanic anoxic event oae for this time period the evolution of the european marine seaways is now relatively well constrained owing to multiple geochemical studies but investigations regarding climatic trends in the continental realm remain sparse in the present study we test the clay mineralogy as a continental climate sensitive proxy in the well documented sancerre core southern paris basin we compare variations in the kaolinite content with p co 2 fluctuations derived from paired carbon isotopes 13 c 13 c carb 13 c org taking advantage of the detailed chemostratigraphic palaeoenvironmental and sequence stratigraphy frameworks established for this core material the results indicate a substantial decrease in kaolinite abundance at the end of the pliensbachian which is compatible with a long term diminution in continental weathering and an inferred temperature decrease the early toarcian prior to the carbon cycle perturbation and deposition of black shale facies remained relatively cold with minima in both the proportion of kaolinite and reconstructed p co 2 the mineralogical and geochemical responses across the prominent negative carbon isotope excursion cie itself are not univocal the first of four steps that compose the negative limb of the cie at sancerre is associated with decreased kaolinite and p co 2 and increased carbonate oxygen isotope ratios taken together these trends are compatible with a transient cooling phase immediately preceding the onset of black shale deposition conversely the subsequent steps are marked by substantial enrichment in kaolinite that matches increased osmium isotope ratios measured in yorkshire providing compelling evidence for rapid increases in continental weathering and riverine runoff forced by intensification of greenhouse conditions during the cie relaxation in the intensity of continental weathering as suggested by resumed low kaolinite abundance is seen immediately after the cessation of co 2 input after the fourth step of the cie the interval spanning the upper portion of the early toarcian and the middle toarcian records a subsequent long term increase in the proportion of kaolinite synchronous with significant clay enrichment of the sediment continued greenhouse conditions even after the recovery from the carbon isotope perturbation and regional black shale deposition are likely related to sustained co 2 emission by karoo ferrar volcanism through the considered interval

distribution of glycerol dialkyl glycerol tetraethers in surface sediments of lake qinghai and surrounding soil abstract glycerol dialkyl glycerol tetraethers gdgts are increasingly used as proxies for paleoclimate studies of marine and lacustrine environments while gdgt based proxies have been applied to a number of lake environments globally little is known about the distribution of gdgts on the qinghai tibet plateau we have investigated the isoprenoid gdgts igdgts and branched gdgts bgdgts in lake qinghai sediments and the surrounding surface soil in order to examine their potential use as paleoclimate proxies on the qinghai tibet plateau the results show that i the values of the igdgt bgdgt ratio for surrounding soil were at the higher end among globally distributed soils and consequently bit values avg 0 71 at the lower end ii the tex86 values decreased while the mbt and cbt values increased along an onshore soil nearshore sediment offshore sediment transect iii the tex86 values for the offshore sediments were almost identical and their inferred temperatures were close to mean summer surface water temperature and iv the bgdgt inferred mean annual air temperature maat and ph for soil were consistent with measured maat and ph however the cbt inferred ph for offshore sediments seemed inconsistent with the ph of lake water or sediment our results suggest that i the higher ph may be an important factor leading to the higher igdgt bgdgt values and lower bit values in surrounding surface soil ii both igdgts and bgdgts may originate from terrestrial input and in situ production for this saline lake especially for nearshore sediments however for offshore sediments terrestrial igdgt input seems minor and tex86 may be useful for paleoclimate studies of lake qinghai

fluxes and distribution of tetraether lipids in an equatorial african lake constraints on the application of the tex86 palaeothermometer and bit index in lacustrine settings abstract the distribution of isoprenoid and branched glycerol dialkyl glycerol tetraether gdgt lipids was studied in material from various sources in and around lake challa a crater lake on the southeastern slope of mt kilimanjaro tanzania to examine the provenance of gdgts in lake sediments and their potential application as palaeoenvironmental and palaeoclimatic proxies the study material included samples collected at monthly intervals in a sediment trap over one complete annual cycle particles suspended in the stratified water column profundal surface sediments and soils surrounding the lake the sediment trap time series revealed that crenarchaeol and related isoprenoid gdgts were predominantly produced in january and february following the locally prominent short rain season november december the tex 86 inferred temperature derived from sedimenting particles corresponded well with lake surface water temperature at this time of largest crenarchaeol flux molecular ecological analysis showed that group 1 1a and 1 1b crenarchaeota are the most likely source organisms of these gdgts gdgt 0 in the lake sediments does not only originate from lake surface dwelling crenarchaeota but seems predominantly derived from archaea residing in the deeper anoxic part of the water column the main flux of branched gdgts to the sediment was during the short rain season and is most probably derived from eroded catchment soils in surface run off however a contribution from in situ production of branched gdgts in the lake sediment or water or in groundwater cannot be fully excluded we conclude that palaeoclimatic reconstruction based on branched gdgt distributions in lake sediments should only be performed when the origin of those branched gdgts is well constrained

temperature variations since 1750 ce inferred from an alpine lake in the southeastern margin of the tibetan plateau abstract high altitude regions are thought to be very sensitive to global climate change especially under current global warming however due to the lack of paleoclimate archives such as ice core and tree rings above the modern tree line limited paleoclimate data have been extracted to extend instrumental data over the past few centuries which will help understand the interannual to decadal scale climate variability in high altitude regions here we present a high resolution 1 6 yr quantitative temperature record from a remote alpine lake at the southeastern margin of the tibetan plateau by applying a novel proxy based on branched glycerol dialkyl glycerol tetraethers brgdgts contrary to the often documented warming trend over the past few centuries but consistent with temperature record from the northern tibetan plateau our data show a gradual decreasing trend of 0 3 c in mean annual air temperature from 1750 to 1970 ce this result suggests a gradual cooling trend in some high altitude regions over this interval which could provide a new explanation for the observed decreasing asian summer monsoon in addition our data indicate an abruptly increased interannual to decadal scale temperature variations of 0 8 2 2 c after 1970 ce in terms of both magnitude and frequency indicating that the climate system in high altitude regions would become more unstable under current global warming

crenarchaeotal membrane lipids in lake sediments a new paleotemperature proxy for continental paleoclimate reconstruction paleoclimate studies of continental environments have been hampered by the lack of an independent paleotemperature proxy a novel sea surface temperature proxy has been proposed for marine systems based on membrane lipids of marine crenarchaeota this proxy will provide an independent continental paleotemperature tool that will allow paleoclimatologists to address fundamental questions about temperature variability in continental environments and its relationship to climate change

high frequency controls on alluvial successions an integrated sedimentological and palaeopedological approach to the plio pleistocene of argentina abstract plio pleistocene palaeosol bearing alluvial strata are continuously exposed along the marine cliffs of southeastern buenos aires province argentina the study interval was deposited by a mixed predominantly suspended load fluvial system outcrops are dominated by floodplain siltstones and mudstones that exhibit a cyclic alternation between calcic and vertic palaeosols this cyclicity is represented by meter scale alluvial cycles that show as a general trend a gradual increase in the proportion of channel fill deposits up section cyclic variations in palaeosols facies and architectural elements can be related to allogenic drivers such as climate and eustasy for the lower punta san andres alloformation the stratigraphic arrangement of the recognised palaeosols and the clay mineral distribution indicate that the palaeoclimate was subhumid average mean annual precipitation map 840 mm seasonal and temperate average mean annual temperature mat 7 85 c for at least 1 ma from ca 2 9 ma to ca 1 8 ma late pliocene early pleistocene with several intervals in which conditions became drier and probably colder even though climate was a major control on palaeosol development it is suggested here that it was not the main control on high frequency cycles variations in the orbital parameters more specifically in insolation were interpreted as having controlled the sedimentation and architectural evolution of the lower punta san andres alloformation depositional systems

temperature dependency of long chain alkenone distributions in recent to fossil limnic sediments and in lake waters distribution patterns of c37 and c38 polyunsaturated long chain alkenones lcas serve as proxies for the determination of paleotemperatures for marine surface waters we studied recent subrecent and late glacial holocene sediments from germany austria russia and the u s to test for a correspondence between lca distribution and surface water temperature in limnic systems previously reports of lca occurrence were restricted to sediments of 6 wide distributed freshwater and alkaline lakes in this study 13 of 27 investigated lakes contained lcas in surface sediments with concentrations varying between 12 to 205 g g toc late glacial to holocene sediment sequences from lake steisslingen and lake wummsee germany lake pichozero russia and brush lake u s a contained abundant lcas with averaged concentrations of 33 to 7536 g g toc for the first time we observed the occurrence of lcas within in the water column of oligotrophic lake stechlin ne germany alkenones were restricted to the zone of maximum chlorophyll concentration within the water column indicating that lcas have a biosynthetic origin and can be attributed to phototrophic micro algae attempts to identify the producing organism however were not successful culture experiments allow various phytoplankton to be excluded as producers alkenone producing algae are evidently of small size hindering microscopical identification lcas commonly occur in high concentrations in late glacial sediments mainly during the cold period of the younger dryas whereas the holocene usually is devoid of polyunsaturated alkenones the episodic occurrence of lcas restricts their utility as proxies for continuous geological records furthermore lack of microscopical verification and the episodic distribution allow for different producers of unsaturated alkenones in recent and late glacial sediments an empirical relationship between lca distribution and temperature was observed in fossil sediments from lake steisslingen there is a good correspondence between uk37 and the temperature controlled 18o isotope ratio of lake chalk comparison of lca patterns obtained from the uppermost centimetres of lake sediments with averaged summer surface water temperatures of the lakes studied demonstrates a trend of covariance r2 uk 37 0 90 uk37 0 67 n 9 hence the same mechanism that causes temperature dependence of lca patterns in marine systems might be effective in limnic settings identification of alkenone producers and their culture under controlled temperature are still mandatory before lcas can be routinely applied as paleotemperature proxy in limnic systems

assessing the ratio of archaeol to caldarchaeol as a salinity proxy in highland lakes on the northeastern qinghai tibetan plateau abstract the ratio of archaeol to caldarchaeol the ace index has been proposed recently as an index for paleosalinity reconstruction and is based principally on archaeal core lipids cls from coastal salt pans turich c freeman k h 2011 archaeal lipids record paleosalinity in hypersaline systems organic geochemistry 42 1147 1157 we have examined possible relationships between salinity and ace in both cls and intact polar lipids ipls from suspended particulate matter spm and surface sediments of lakes and surrounding soils on the northeastern qinghai tibetan plateau our results showed that ace values were positively correlated with salinity in all samples however cl ace values were systematically higher than ipl ace values probably due to different degradation kinetics of intact polar ip archaeol and ip caldarchaeol on the other hand surface sediment ace values from both cls and ipls were lower than spm ace values probably due to enhanced production of caldarchaeol relative to archaeol in the sediment our results demonstrate that the ace proxy reflects changes in salinity in diverse environments on the qinghai tibetan plateau which is promising for paleosalinity reconstruction however caution should be used when applying the salinity proxy before we have a better understanding of degradation kinetics of archaeal ipls and in situ production of caldarchaeol and archaeol in sediments

deglacial and holocene archaeal lipid inferred paleohydrology and paleotemperature history of lake qinghai northeastern qinghai tibetan plateau abstract we investigate the distribution of archaeal lipids in a 5 8 m long sedimentary core recovered from lake qinghai to extract regional hydroclimate and temperature signals since the last deglaciation for this important region the paleohydrology was reconstructed from the relative abundance of thaumarchaeol thaum and the archaeol and caldarchaeol ecometric ace index the thaum inferred lake level record was extended to deglaciation showing three periods 11 9 13 0 14 1 14 7 and 15 1 17 2 cal ka bp with relatively higher lake levels than those during the early holocene the ace record demonstrates three periods 10 6 11 2 13 2 13 4 and 17 4 17 6 cal ka bp of elevated salinity when the lake was shallow filtered tex86 record based on archaeal lipid distributions corresponded to relatively higher lake levels implying that a certain lake size is required for using the tex86 paleothermometer at 1 4 cal ka bp the reconstructed temperature fluctuated significantly and correlated negatively with inferred lake level indicating that lake temperature and hydrological change might be coupled during this period we attribute this co variance to the importance of summer temperature in controlling evaporation for this arid semi arid region moreover our results indicate that archaeal lipids have potential in reconstructing paleoclimate patterns from lacustrine sedimentary cores but the data should be interpreted with care

bacterial tetraether membrane lipids in peat and coal testing the mbt cbt temperature proxy for climate reconstruction abstract peatlands are widespread and important natural archives of environmental change here we explore the potential of the recently introduced mbt cbt proxy methylation index and cyclisation ratio of branched tetraethers to estimate past annual mean air temperature mat based on the distribution of bacterially derived branched glycerol dialkyl glycerol tetraether gdgt membrane lipids in peat and coal to this end branched gdgts in an ombrotrophic peat bog from switzerland and three coal deposits of increasing maturity were analysed for the surface of the bog reconstructed annual mat is higher than both measured annual mat and measured in situ pore water temperature changes in the cbt ratio considered a proxy for ph with depth in the bog do not match with present day in situ pore water ph but coincide with a peat stratigraphic boundary this indicates that gdgts down the bog profile are predominantly fossil and not derived from extant biomass the mbt cbt derived annual mat record also shows a large drop at this stratigraphic boundary which likely relates to past change in trophic status of the bog branched gdgts are abundant in an immature lignite vitrinite reflectance r o 0 25 but occur in low amount in a slightly more mature coal r o 0 32 annual mat could be reconstructed for the lignite alone and is higher than other proxy based estimates from approximately the same time and location our results indicate potential for the application of the mbt cbt proxy in peat and immature coals but improved constraints on the effects of different types of peat on branched gdgt distributions as well as improved calibration of mat estimates are needed before the method can be confidently applied

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

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

bacterial tetraether lipids in ancient bones record past climate conditions at the time of disposal abstract assessing impacts of climate change on ancient human societies requires accurate reconstructions of regional climate variations however due to the scarcity of in situ climate indicators in archaeological sites climate interpretation often relies on indirect geographically distant data from geological archives such as lake or ocean sediments ice cores and speleothems because many cultural changes occurred abruptly over periods of years to decades and are regional or even local in scale correlating societal changes with climate reconstructions from geological archives induces significant uncertainties factors such as chronological dating inconsistencies and geographic heterogeneity of climate can severely undermine interpretation here we show for the first time that it is possible to determine past climate change by analyzing bacteria derived branched glycerol dialkyl glycerol tetraethers br gdgts in ancient bones from archaeological sites to the best of our knowledge this proxy has never been applied before to bones nor with the intention of developing the method for application in archaeological research we demonstrate that these compounds are likely derived from bacterial growth within bones following deposition in the ground and the potential for their distributions to reflect climate and environmental conditions during the years immediately following deposition when bacteria consume internal substrates our preliminary results show that bone samples from different climate zones display distinct br gdgt distributions well dated late pleistocene and holocene bones from alaska yield reconstructed temperatures consistent with existing climate reconstructions while further work is necessary to determine how quickly the signal stabilizes in the bones and to continue ongoing refinement of calibrations for temperature precipitation and other influences on br gdgts we propose that br gdgts from ancient bones in archaeological sites may be taken as a new in situ archive for reconstructing past climate conditions this opens new perspectives for assessing connections between climate variations and social transformations in the past

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

sensitivity of eurasian climate to surface uplift of the tibetan plateau experiments with climate models are used to illustrate how earth s climate could be expected to change if surface uplift occurred the experiments contrast two climate simulations one with all continents at sea level and one with present day mountains and plateaus the simulations in the eurasia sector show that surface uplift increased elevation produces marked increases in the intensity of summer and winter monsoons of asia with development of wetter climates to the south and east of the tibetan plateau and drier climates to the north and west of the plateau there is a general cooling in northern polar latitudes comparison of simulations from two different models shows that the magnitude of the simulated changes depends upon how the models calculate the land surface hydrology and the ocean temperature the simulated changes produced by surface uplift agree in a general way with many geologic indicators of late cenozoic climate change the results suggest that surface uplift of mountains and platea

extended megadroughts in the southwestern united states during pleistocene interglacials the potential for increased drought frequency and severity linked to anthropogenic climate change in the semi arid regions of the southwestern united states us is a serious concern1 multi year droughts during the instrumental period2 and decadal length droughts of the past two millennia1 3 were shorter and climatically different from the future permanent dust bowl like megadrought conditions lasting decades to a century that are predicted as a consequence of warming4 so far it has been unclear whether or not such megadroughts occurred in the southwestern us and if so with what regularity and intensity here we show that periods of aridity lasting centuries to millennia occurred in the southwestern us during mid pleistocene interglacials using molecular palaeotemperature proxies5 to reconstruct the mean annual temperature mat in mid pleistocene lacustrine sediment from the valles caldera new mexico we found that the driest conditions occurred during the warmest phases of interglacials when the mat was comparable to or higher than the modern mat a collapse of drought tolerant c4 plant communities during these warm dry intervals indicates a significant reduction in summer precipitation possibly in response to a poleward migration of the subtropical dry zone three mat cycles 2 c in amplitude occurred within marine isotope stage mis 11 and seem to correspond to the muted precessional cycles within this interglacial in comparison with mis 11 mis 13 experienced higher precessional cycle amplitudes larger variations in mat 4 6 c and a longer period of extended warmth suggesting that local insolation variations were important to interglacial climatic variability in the southwestern us comparison of the early mis 11 climate record with the holocene record shows many similarities and implies that in the absence of anthropogenic forcing the region should be entering a cooler and wetter phase

late cenozoic climate changes in china s western interior a review of research on lake qinghai and comparison with other records abstract we review late cenozoic climate and environment changes in the western interior of china with an emphasis on lacustrine records from lake qinghai widespread deposition of red clay in the marginal basins of the tibetan plateau indicates that the asian monsoon system was initially established by 8 ma when the plateau reached a threshold altitude subsequent strengthening of the winter monsoon along with the establishment of the northern hemisphere ice sheets reflects a long term trend of global cooling the few cores from the tibetan plateau that reach back a million years suggest that they record the mid pleistocene transition from glacial cycles dominated by 41 ka cycles to those dominated by 100 ka cycles during terminations i and ii strengthening of the summer monsoon in china s interior was delayed compared with sea level and insolation records and it did not reach the western tibetan plateau and the tarim basin lacustrine carbonate 18 o records reveal no climatic anomaly during mis3 so that high terraces interpreted as evidence for extremely high lake levels during mis3 remain an enigma following the last glacial maximum lsm several lines of evidence from lake qinghai and elsewhere point to an initial warming of regional climate about 14 500 cal yr bp which was followed by a brief cold reversal possibly corresponding to the younger dryas event in the north atlantic region maximum warming occurred about 10 000 cal yr bp accompanied by increased monsoon precipitation in the eastern tibetan plateau superimposed on this general pattern are small amplitude centennial scale oscillations during the holocene warmer than present climate conditions terminated about 4000 cal yr bp progressive lowering of the water level in lake qinghai during the last half century is mainly a result of negative precipitation evaporation balance within the context of global warming

hydrogen isotope ratios of palmitic acid in lacustrine sediments record late quaternary climate variations the rich paleoclimate information preserved in lacustrine sedimentary organic matter can be difficult to extract because of the mixed terrestrial and aquatic inputs herein we demonstrate that compound specific hydrogen isotope analysis of palmitic acid pa a ubiquitous compound in lacustrine sediments captures the d signals of lake water samples collected across a diverse range of 33 north american lakes show a strong correlation between water and dpa values at crooked pond massachusetts the dpa changes in a 14 k y sediment record parallel temperature trends inferred from fossil pollen downcore changes reveal differences between climatic trends in new england and in greenland that are consistent with important regional differences in climate controls

tertiary evolution of the intra carpathian area a model abstract the outer carpathian flysch nappes encircle an intra carpathian domain which can be divided into two megatectonic units north pannonian and tisza mostly on the basis of contrasting mesozoic and palaeogene facies development we see two major kinematic problems to be solved 1 1 the present distribution of the mesozoic and palaeogene facies is mosaic like and some belts form exotic bodies within realms of austroalpine affinity 2 2 late eocene palinspastic reconstruction of the outer carpathian flysch nappes suggest that the entire intra carpathian area must have been located several hundreds of kilometres to the south and to the west of its present position neogene extension can account for shortening in the external carpathian nappes but is unable to explain mesozoic facies anomalies and offsets of palaeogene formations we suggest that evolution of the intra carpathian area involved first late palaeogene early miocene juxtaposition of the north pannonian and tisza megatectonic units accompanied by the closure of the external carpathian flysch troughs thereafter extension of this amalgamated unit occurred which was compensated by thrusting of flysch nappes onto the european foreland and formation of molasse foredeeps eastward escape of the north pannonian unit from the alpine collisional belt involved left lateral shear along the pieniny klippen belt and right lateral shear along the mid hungarian zone parts of the late palaeogene basin and an early miocene volcanic edifice were dissected offset and elongated by several 100 kms the driving mechanism of the eastward escape of the intra carpathian area can be related to the collision of apulia and europe and the subduction of the external carpathian crust under the pannonian units the escape ceased gradually in the early miocene when oblique collision between the north pannonian unit and european continent occurred neogene extension of the pannonian region was an areal deformation the extension at locally variable rate resulted in the break up of the heterogenous floor of the neogene basin the driving mechanism of basin extension and contemporaneous compressional deformation of the external carpathians is thought to be related to ongoing subduction involving the marginal part of the attenuated european continental crust tectonic activity in the carpathians and basin subsidence and volcanism shifted in time and in unison from the west toward the east southeast

climato environmental controls on clay mineralogy of the hettangian bajocian successions of the mecsek mountains hungary an evidence for extreme continental weathering during the early toarcian oceanic anoxic event abstract clay mineralogy has been successfully used in palaeoclimatic interpretation of jurassic rocks in the mecsek zone hungary the clay mineral assemblages of the hettangian sinemurian fluvial and shallow marine coal bearing siliciclastic rocks gresten facies mecsek coal and vasas marl formations comprise predominantly illite smectite i s mixed layer minerals illite ill and kaolinite kao with the presence of berthierine and or chlorite these clay mineral suites suggest a humid subtropical climate with short term climate changes of high and low rainfall and a high supply of terrigenous clastics to the basin in the pliensbachian part of the sequence studied which is composed of predominantly hemipelagic mudstones allgau facies with intercalations of redeposited sandstone and limestone bodies the hosszuheteny calcareous marl mecseknadasd sandstone and kecskehat limestone formations are predominantly made up of illite and very little kaolinite and i s mixed layer minerals kao ill 1 suggesting a humid climate and intense continental weathering possibly related to the oceanic anoxic event in contrast rocks of the bajocian komlo calcareous marl formation contain high proportions of i s mixed layer mineral and illite with sparse occurrence of kaolinite kao ill 0 or kao ill

palaeoclimatic changes in the qinghai lake area during the last 18 000 years abstract multi proxy analysis of a sediment core from qinghai lake including pollen carbonate toc tn and 13 c of organic matter was used to document regional climatic changes during the last 18 000 years climate was very cold and dry before 16 9 cal kyr bp the warm and wet period which began at about 14 1 cal kyr bp culminated at 6 5 cal kyr bp and came to its end at about 4 5 cal kyr bp after that the climate gradually became colder and drier during the transitional period from the late glacial to the holocene the climate fluctuated frequently the short term climatic oscillations including the bolling allerod younger dryas and the cooling event at ca 8 2 cal kyr bp appear to be recorded in the qinghai lake sedimentary record the climatic evolution in the qinghai lake area during the past 18 000 years indicates that solar insolation changes on the ten thousand year scale are the likely driving force of the east asia monsoon

a review of molecular organic proxies for examining modern and ancient lacustrine environments molecular organic geochemical proxies are increasingly being utilized to reconstruct past environmental conditions as new tools continue to be discovered and developed to date organic geochemical proxies have been developed mainly for use in marine systems and are widely used in paleoceanography in contrast organic proxies have been less commonly used on lacustrine sedimentary records one reason for this is that the wide range in the physical and chemical properties of lakes complicates application of some organic geochemical proxies in lacustrine settings furthermore in comparison to marine studies presently only a small number of studies have conducted or are currently conducting fundamental research aimed at developing organic geochemical proxies for use in lacustrine settings despite this an increasing number of paleo limnological studies are currently applying organic geochemical techniques to examine present and past environmental conditions in this manuscript we review the use of a number of commonly utilized organic geochemical and isotopic proxies and discuss their potential for environmental reconstruction in quaternary lacustrine deposits

osmium isotope evidence for the regulation of atmospheric co2 by continental weathering the long term stability of earth9s climate throughout the phanerozoic stands in marked contrast to the dramatic fluctuations that have taken place on time scales as short as a few years reflecting the high efficiency of longer term climate regulation through negative feedbacks a fundamental mechanism is thought to involve control of co 2 in the ocean atmosphere system through continental weathering although unambiguous high resolution data supporting this hypothesis have hitherto not been available organic rich mud rocks from yorkshire england which were deposited during the toarcian oceanic anoxic event ca 181 ma early jurassic contain evidence of an exceptionally large excursion in the 187 os 188 os ratio of contemporaneous seawater from 0 4 to 1 0 the most likely explanation for this excursion is that it resulted from a transient increase in global continental weathering rates of 400 800 the os isotope excursion coincided with a well documented global 13 c excursion of 6 that affected all the major biospheric reservoirs of the time higher mean global temperatures caused global chemical weathering rates to increase substantially while in turn chemical weathering was very effective in reducing the elevated levels of atmospheric co 2 and the high temperatures to preexcursion levels

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

tertiary deformation history from seismic section study and fault analysis in a former european tethyan margin the mecsek villany area sw hungary abstract outcrop scale structural data and seismic section interpretation are combined to unveil a very complicated tertiary deformation history of a once tethyan margin the mecsek villany area of hungary this combination of data helped to reconstruct the possible activity of individual fault zones at least four ene wsw striking zones the northern imbricates the south mecsek zone the gorcsony mariakemend ridge and the villany mountains were confirmed as regional long lived transpressive zones with very complicated internal deformation frequently with oppositely dipping thrust faults tertiary structural history began with a roughly n s directed shortening in the south mecsek zone it was followed by a ne sw directed transpression activating practically all important wrench zones together with perpendicular transfer faults basins were created along some of these deformation zones but were also affected by major tilts due to inversion after a relatively quiescent period in the middle miocene the late sarmatian inversion followed shortly after this event was relayed by a ne sw directed extension transtension an important inversion period characterised by nw se compression occurred in late pannonian messinian when all the former wrench zones were reactivated as right lateral shear this event is responsible for the present topography of the region

alkenone based reconstruction of late holocene surface temperature and salinity changes in lake qinghai china china the alkenone temperature proxy u k 0 37 indicates up to a 1 c change in mean annual air temperature or a 2 c change in summer lake water temperature during the late holocene oscillating warm and cold periods could be related to the 20th century warm period the little ice age the medieval warm period the dark ages cold period and the roman warm period the relative importance of c37 4 alkenone to total c37 alkenone production c37 4 fluctuated between 15 45 with higher values during warm periods suggesting that lake water was also fresher during these periods the coupled late holocene surface temperature and salinity changes suggest that asian monsoons strongly influenced the climate of the lake qinghai region citation liu z a c g henderson and y huang 2006 alkenone based reconstruction of lateholocene surface temperature and salinity changes in lake qinghai china geophys res lett 33 l09707 doi 10 1029 2006gl026151

quantitative climate and vegetation trends since the late glacial on the northeastern tibetan plateau deduced from koucha lake pollen spectra quantitative information on vegetation and climate history from the late glacial holocene on the tibetan plateau is extremely rare here we present palynological results of a 4 30 m long sediment record collected from koucha lake in the bayan har mountains northeastern tibetan plateau vegetation change has been traced by biomisation ordination of pollen data and calculation of pollen ratios the application of a pollen climate calibration set from the eastern tibetan plateau to koucha lake pollen spectra yielded quantitative climate information the area was covered by alpine desert steppe characteristic of a cold and dry climate with 50 less precipitation than today between 16 700 and 14 600 cal yr bp steppe vegetation warm 1 c higher than today and wet conditions prevailed between 14 600 and 6600 cal yr bp these findings contradict evidence from other monsoon influenced areas of asia where the early holocene is thought to have been moist low effective moisture on the northeastern tibetan plateau was likely due to high temperature and evaporation even though precipitation levels may have been similar to present day values the vegetation changed to tundra around 6600 cal yr bp indicating that wet and cool climate conditions occurred on the northeastern tibetan plateau during the second half of the holocene

distribution of tetraether lipids in the 25 ka sedimentary record of lake challa extracting reliable tex86 and mbt cbt palaeotemperatures from an equatorial african lake the distribution of isoprenoid and branched glycerol dialkyl glycerol tetraether gdgt lipids was studied in the sedimentary record of lake challa a permanently stratified partly anoxic crater lake on the southeastern slope of mt kilimanjaro kenya tanzania to examine if the gdgts could be used to reconstruct past variation in regional temperature the study material comprised 230 samples from a continuous sediment sequence spanning the last 25 ka with excellent age control based on high resolution ams c 14 dating the distribution of gdgts showed large variation through time in some time intervals i e from 20 4 to 15 9 ka bp and during the younger dryas 12 9 11 7 ka bp crenarchaeol was the most abundant gdgt whereas at other times i e during the early holocene branched gdgts and gdgt 0 were the major gdgt constituents in some intervals of the sequence the relative abundance of gdgt 0 and gdgt 2 was too high to be derived exclusively from lacustrine thaumarchaeota suggesting a sizable contribution from methanogens and other archaea this severely complicated application of tex86 palaeothermometry in this lake and limited reliable reconstruction of lake water temperature to the time interval 25 13 ka bp i e the last glacial maximum and the period of post glacial warming the tex86 inferred timing of this warming is similar to that recorded previously in two of the large african rift lakes while its magnitude is slightly or much higher than that recorded at these other sites depending on which lake based tex86 calibration is used application of calibration models based on distributions of branched gdgts developed for lakes inferred temperatures of 15 18 degrees c for the last glacial maximum and 19 22 degrees c for the holocene however the mbt cbt palaeothermometer reconstructs temperatures as low as 12 degrees c for a lateglacial period centred on 15 ka bp variation in down core values of the bit index are mainly determined by the varying production rate of crenarchaeol relative to in situ produced branched gdgts the apparent relationship of the bit index with climatic moisture balance can be explained either by the direct influence of lake level and wind strength on nutrient recycling or by influx of soil nutrients promoting aquatic productivity and nitrification this study shows that gdgts can aid in obtaining climatic information from lake records but that the obtained data should be interpreted with care

distributions of branched gdgts in a tropical lake system implications for lacustrine application of the mbt cbt paleoproxy branched glycerol dialkyl glycerol tetraether gdgt lipids are abundant and ubiquitous in lake sediments potentially allowing for a paleolimnological application of the so called mbt cbt proxy methylation index of branched tetraethers cyclization ratio of branched tetraethers to investigate the origin and characteristics of these compounds in lacustrine environments we examined the distributions of gdgts in soils river sediments and lake sediments from lake towuti on the island of sulawesi indonesia we found significant differences in the degree of methylation and cyclization expressed by way of the mbt and cbt indices between the soil samples and the aquatic samples suggesting that there may be in situ production of gdgts in the aquatic environment based on these findings we urge caution in the application of the mbt cbt paleoproxy to lake sediments and encourage more rigorous study of these compounds in freshwater environments

the history and variability of the east asian paleomonsoon climate abstract changes in the east asian paleomonsoon reflect interactions between the global atmosphere ocean land and ice systems and are also an expression of their combined effect within the boundary conditions imposed by the east asian continent and solar radiation the history of the east asian monsoon is an alternation between dominance by the dry cold winter and warm humid summer monsoons high resolution eolian sequences preserved in the chinese loess plateau reveal that the east asian monsoon may have commenced at least 7 2 ma ago they also provide evidence indicating that the pulsed uplift of the tibetan plateau at about 3 4 and 7 2 ma may have played an important role in inducing climate change the palaeoclimatic records of the last glacial cycle show high frequency variability on time scales of 1000 year or even shorter and instability of the east asian paleomonsoon system the high frequency variability could be due to a non linear response to orbital forcing or a result of the coupling processes between different components of the global system cold air activity in northern high latitudes the trans equatorial air streams from the southern hemisphere and possibly enso may have played an important role in east asian monsoon variability the synchroneity of all the palaeoclimatic events along the polar equator polar pep transect is still an open question correlation of limited palaeoclimatic records for the last 30 kyr obtained from east asia and australia suggests that the trans equatorial air streams driven by the monsoon and trade winds may have had an influence on opposite hemispheres

late pleistocene temperature history of southeast africa a tex86 temperature record from lake malawi we present a tex86 derived surface water temperature record for lake malawi that provides the first continuous continental record of temperature variability in the continental tropics spanning the past similar to 74 kyr with millennial scale resolution average temperature during marine isotope stage mis 5a was 26 5 degrees c with a range from 25 7 to 27 3 degrees c comparable to holocene temperatures mis 4 was a relatively cold period with temperatures generally decreasing from 25 5 degrees c at 68 ka to a minimum of 20 degrees cat similar to 60 ka 1 5 2 degrees c colder than the last glacial maximum lgm termination of mis 4 is characterized by a rapid increase of 3 4 degrees c in only similar to 0 5 kyr temperatures were relatively stable throughout mis 3 at the resolution of this study with an average of 23 8 degrees c and a range from 25 1 to 22 9 degrees c the lack of millennial scale temperature variability during mis 3 suggests that lake malawi s documented response to the bipolar seesaw brown et al 2007 is not reflected in its thermal history our temperature estimates for the lgm and holocene are consistent with a previously published tex86 record from lake malawi with a temperature of similar to 22 6 degrees c for the lgm similar to 25 26 degrees c in the mid holocene and similar to 25 28 for the late holocene in general the present extended tex86 record indicates that temperature variability in tropical east africa during late mis 5 and mis 4 was as great as that associated with the deglaciation and holocene a decrease in southern hemisphere insolation between 70 and 60 ka may have played an important role in forcing temperatures during mis 4 but after 60 ka other factors such as the extent of the polar ice sheets or atmospheric co2 may have forced temperature in tropical africa to a greater extent than local summer insolation

palaeoclimatic significance of changes in clay mineralogy across the jurassic cretaceous boundary in england and france abstract clay mineralogical changes across the jurassic cretaceous boundary from the northern to the southern part of western europe show similar patterns in the mudrocks exposed on the yorkshire coast the paralic sediments of the dorset wessex basin and the jura and vocontian trough of s e france this comprises a change from smectite poor sediments in the jurassic with correspondingly abundant illite and kaolinite to sediments with abundant smectite in the jurassic cretaceous boundary beds depleted in kaolinite this change occurs in the oxfordian in the south to latest volgian in the north of the study area kaolinite reappears in abundance in the late ryazanian or stratigraphic equivalent in all the locations studied comparison with other climatic indicators and other areas suggest that these variations can be ascribed to a phase of latest jurassic earliest cretaceous aridity the onset of which appears to be diachronous across w europe possible causes for the climatic change towards aridity are examined the orographic effect of mountains or plateaus to the east of the study area is considered most likely

triassic jurassic weathering and clay mineral dispersal in basement areas and sedimentary basins of southern sweden abstract the basement rocks of southern sweden were deeply weathered in late triassic through cretaceous times and possibly even earlier sub mesozoic saprolites formed presumably due to long term warmth and humidity in conjunction with decomposition of abundant organic matter and subsequent infiltration of acidic water the upper parts of the weathering profiles were subjected to intense leaching and kaolinitisation whereas the less evolved deep weathering front is enriched in smectite thus any erosion prior to full regolith development or extraordinary deep erosion released less developed smectite rich weathering material to the late triassic jurassic receiving basins mesozoic sedimentary successions in southern sweden show high detrital smectite and or kaolinite contents moderate illite contents and low chlorite contents compatible with expected mid latitude warm equable greenhouse conditions norian and older triassic haematite cemented continental arkoses and smectite dominated clays smectite kaolinite were clearly formed in arid settings from the rhaetian and throughout the jurassic humid onshore conditions sustained abundant plant and peat accumulation early diagenetic meteoric flushing and intense chemical weathering kaolinite is therefore a dominating detrital clay mineral in these sedimentary successions kaolinite illite chlorite and smectite i s minor quantitative variations in clay mineralogy within the humid climate rhaetian jurassic sedimentary successions are difficult to interpret in deltaic coal bearing successions the detrital clay mineral composition is conspicuously constant kaolinite illite chlorite possibly due to post depositional clay mineral transformation conversely in shallow marine deposits some quantitative variation is notable kaolinite illite variable smectite chlorite this may reflect that the original detrital composition was better preserved in shallow marine settings smectitic clay minerals associated with gypsum and caliche nodules ambiguously indicate increased aridity towards the end of the jurassic

clay minerals of late pleistocene sites jonzac and les cottes sw france applications of x ray diffraction analyses to local paleoclimatic and paleoenvironmental reconstructions abstract the crystal chemical properties of clay minerals are closely dependent on the physicochemical conditions prevailing at the time when they formed in soils and weathered zones the degree of alteration of primary minerals and the composition of the secondary products are clearly linked to climate and plant cover in particular changes are rapid under temperate conditions which favor the development of thick soils but slow in cold contexts favoring thin and fragile soils in this paper the mineral composition of two pleistocene clay rich deposits is investigated in order to contribute to reconstructing paleoenvironmental changes jonzac charentes sw france and les cottes vienne sw france are two rock shelters with long archaeological sequences which include faunal remains and were recently radiometrically dated the decomposition of xrd patterns at each site allows identification of the principal mineral phases and semi quantitative estimation of their relative proportions the variation of these proportions is analyzed through indexes based on the relative intensities of the decomposed bands the clay fraction of both sites mostly results from the transformation of the minerals forming the sediments in the surrounding area of the rock shelter terrace including contributions from the hillside mineralogical clay data are compared with the faunal spectrum identified at both sites in order to discuss paleoenvironmental implications at jonzac during the quina mousterian period dated to mis4 the environment was cold and dry the dominant mineralogical phases are inherited from the rocks weak pedogenesis this is consistent with the faunal analysis data typical of the mis4 during the mousterian of acheulean tradition period dated to mis3 the mineralogical composition of the clay deposits changed significantly suggesting a less wet environment the aurignacian deposits dated to the end of mis3 early mis2 are rich in mixed layer minerals mlms which are produced by the hydrolysis processes in soils the climatic conditions probably became milder however because no faunal remains were found this evolution is uncertain the les cottes deposits dated between mis3 and early mis2 are mineralogically typical of a cold environment where soil reactions are not very active however some weak variations of the indexes suggest temporary temperate conditions during the les cottes interstadial and in the aurignacian the parallelism between mineral signature and paleontological evidence in recording relatively rapid variations between contrasted climates suggests that clay mineral assemblages from rock shelter deposits can be used to assess paleoclimatic and paleoenvironmental dynamics at a local scale

the hydrothermal transformation rate of kaolinite to muscovite illite batch reactor experiments were performed to measure the rate of the reaction 1 5 kaolinite k muscovite h 1 5 water at temperatures ranging from 250 to 307 c in these experiments the rate of kaolinite conversion to muscovite illite was monitored as the rate of production of h runs were performed in small volume 50 ml titanium hydrothermal reactors charged with well crystallized georgia kaolinite indian ruby muscovite and 25 ml of kcl solution 0 5 2 0 m both solids and solutions were monitored at specific intervals throughout each experiment the determined rate law is dmh dt dmk dt amm k mk k mh where mk and mh are the concentrations of potassium ion and hydrogen ion k and k are the forward and reverse rate constants in kg m 2 sec 1 am is the total surface area of the muscovite in m2 and m is the mass of the solution in kg the initial rate method was used to find k and k was found by fitting data to an integrated rate equation temperature functions for the rate constants are in k 12 90 1 87 104 t r2 0 98 and in k 6 03 1 21 104 t r2 0 95 the activation energies ea for the forward and reverse reaction are 155 15 kj mol 1 and 101 10 kj mol 1 respectively

archaeal lipids record paleosalinity in hypersaline systems abstract we present an ecologically based biomarker method for estimating past salinity especially in hypersaline conditions the relative amounts of acyclic diether and tetraether membrane lipids synthesized by archaea correlate with salinity from 0 250 practical salinity units psu in modern settings we examined the preservation of this lipid biomarker salinity relationship in ancient sedimentary organic matter using samples from two sequences of marls and diatomites deposited just prior to the messinian salinity crisis salinity estimates were consistent with expected absolute salinity as well as the amplitude of variations leading up to the messinian salinity crisis this lipid biomarker approach to salinity reconstruction complements existing paleosalinity proxies because i archaea survive and thrive over a broad salinity range well beyond that of haptophyte algae and other plankton which form the microfossil record and ii it provides fine salinity resolution for the wide range broadly defined as hypersaline with the proxy there is the potential to provide novel insights into salinity variation within desiccating basins in climatically sensitive seas e g dead sea permian delaware basin evolution of brines timing of onset of hypersaline conditions and evaporite deposition

environmental controls on clay mineralogy of an early jurassic mudrock blue lias formation southern england we present a dataset including clay mineralogy gamma ray spectrometry organic matter content and magnetic susceptibility of the hettangian to lowest sinemurian successions of dorset and somerset southern uk blue lias formation bristol channel and wessex basins in both areas the clay assemblages comprise predominantly detrital illite kaolinite and illite smectite mixed layers clays probably originated from the erosion of the hercynian massifs the relative proportions of kaolinite and illite being modulated by arid humid climatic fluctuations the organic matter om content types ii to iv ranges up to 12 in both areas a clear stratigraphical trend in clay mineral assemblages is apparent in somerset whereas in dorset sharp contrasts between adjacent horizons and a greater dilution by carbonate mask the long term evolution correlations between both areas based on similar vertical trends in clay mineral abundance support the suggestion of a hiatus within the angulata zone of the dorset succession as expected the kaolinite illite ratio correlates with the th k ratio deduced from gamma ray spectrometry however significant departures from the correlation occur in om rich intervals suggesting that th may be partly adsorbed on to om particles surprisingly high magnetic susceptibility correlates with abundant kaolinite not with fe rich clays indicating either that kaolinite is accompanied by a soil inherited magnetisable phase possibly iron oxide or that illite rich rocks are more strongly diluted by carbonate than are kaolinite rich strata

northern hemisphere controls on tropical southeast african climate during the past 60 000 years the processes that control climate in the tropics are poorly understood we applied compound specific hydrogen isotopes d and the tex86 tetraether index of 86 carbon atoms temperature proxy to sediment cores from lake tanganyika to independently reconstruct precipitation and temperature variations during the past 60 000 years tanganyika temperatures follow northern hemisphere insolation and indicate that warming in tropical southeast africa during the last glacial termination began to increase 3000 years before atmospheric carbon dioxide concentrations d data show that this region experienced abrupt changes in hydrology coeval with orbital and millennial scale events recorded in northern hemisphere monsoonal climate records this implies that precipitation in tropical southeast africa is more strongly controlled by changes in indian ocean sea surface temperatures and the winter indian monsoon than by migration of the intertropical convergence zone

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

holocene variations in the asian monsoon inferred from the geochemistry of lake sediments in central tibet we present a record of monsoon variations for the early and middle holocene that is inferred from the geochemistry of sediment cores from ahung co a lake in central tibet the resolution of this record is better than 50 yr and the age model is derived from radiocarbon ages of terrestrial charcoal which eliminates errors associated with the lake hard water effect we made down core geochemical measurements of carbonate organic carbon c n and 13c of bulk organic matter 13c and 18o of carbonate and dolomite proxy calibration and modern water balance reconstruction show that these are proxies for lake depth and the amount of monsoon precipitation we find that lake level and monsoon precipitation have been decreasing at ahung co since the early holocene 7500 cal yr b p superimposed on this trend are rapid declines in monsoon rainfall at 7000 7500 and 4700 cal yr b p and seven century scale wet dry oscillations the cores do not contain sediment from the last 4000 yr surface sediments from the lake accumulated during the 20th century however from this we argue that lake levels have risen again recently following a late holocene dry period

comparison of clay mineral stratigraphy to other proxy palaeoclimate indicators in the mesozoic of nw europe this paper reviews the opportunities and pitfalls associated with using clay mineralogical analysis in palaeoclimatic reconstructions following this conjunctive methods of improving the reliability of clay mineralogical analysis are reviewed the mesozoic succession of nw europe is employed as a case study this demonstrates the relationship between clay mineralogy and palaeoclimate proxy analyses may be integrated with clay mineralogical analysis to provide an assessment of aridity humidity contrasts in the hinterland climate as an example the abundance of kaolinite through the mesozoic shows that while interpretations may be difficult the mesozoic climate of nw europe was subject to great changes in rates of continental precipitation we may compare sedimentological facies mineralogy geochemistry indicators of palaeoprecipitation with palaeotemperature estimates the integration of clay mineralogical analyses with other sedimentological proxy indicators of palaeoclimate allows differentiation of palaeoclimatic effects from those of sea level and tectonic change we may also observe how widespread palaeoclimate changes were whether they were diachronous or synchronous how climate sea level and tectonics interact to control sedimentary facies and what palaeoclimate indicators are reliable

deciphering processes controlling mid jurassic coccolith turnover the middle jurassic is characterized by major changes within the fossil coccolithophorid community with a transition from lotharingius dominated to watznaueria dominated assemblages concomitant with a significant increase in the pelagic carbonate production the mechanisms that triggered this overturn remain poorly understood here we present a compilation new and previously published data of lotharingius and watznaueria abundances through the early middle jurassic transition alongside this trends in newly acquired and literature derived carbon and oxygen isotope data were used to represent paleoceanographic indicators such as nutrient and temperature changes the nannofossil data show a rapid around 1 5 myr turnover around the aalenian bajocian transition across the aalenian bajocian boundary assemblages dominated by lotharingius spp give way to assemblages dominated by watznaueria spp coinciding with a peak in a particular morphological group of watznaueria species with a cross in the central area the proliferation of this morphogroup occurred during a time of oceanic opening and rearrangement of ocean circulation this led on to the evolution of pioneering coccolithophorid taxa but also to extinctions in several marine groups in the early bajocian the proliferation of two other morphogroups watznaueria without a central area structure and watznaueria with a bar corresponds to the major diversification of watznaueria and the beginning of its meso zoic dominance the watznaueria diversification and dominance are associated with radiation in other marine groups and these biotic changes occurred during a time of putative enhanced oceanic fertility and relatively low temperatures this study suggests that restructuring of fossil coccolithophorid communities may be favored during short turnover intervals related to major paleoceanographic change

continental humid and arid zones during the jurassic and cretaceous abstract the global distribution of climatically significant criteria is surveyed for six successive time intervals hettangian toarcian aalenian callovian oxfordian tithonian berriasian barremian aptian cenomanian and turonian maastrichtian the criteria are primarily mineralogical evaporites coals bauxites ironstones and kaolinite but include sedimentological and palaeontological aspects of facies e g aeolian sands fossil ferns and xerophytes fresh water invertebrates in early and mid jurassic times an arid zone can be distinguished in low to mid latitudes in western pangaea with humid zones elsewhere in the late jurassic this arid zone spread northwards to embrace much of southern eurasia there followed in the early cretaceous a sharp reversal to more humid conditions over a large area extending from the eastern margin of north america to the middle east a major consequence of which was the widespread replacement of carbonates by coarse siliciclastic facies by late cretaceous times humid conditions were well established also in north america and the south atlantic margins and the tropical arid zone had contracted to a minimum the 87 sr 86 sr ratio of marine carbonates provides an independent monitor of continental runoff which is related to a area and b extent of aridity changes in the ratio confirm that taking sea level stand into account the late cretaceous was appreciably more humid than the late jurassic these climatic changes are related primarily to the progressive breakup of pangaea in the late jurassic and cretaceous which together with sea level rise in the mid to late cretaceous caused a significant increase in maritime influence this implies that monsoonal winds probably had a major role in promoting higher precipitation rates a puzzle remains as to why there was a spread of aridity in the late jurassic finally some implications for terrestrial plant evolution are noted

holocene temperature and precipitation variability on the central tibetan plateau revealed by multiple palaeo climatic proxy records from an alpine wetland sequence this study has reconstructed the holocene environmental history of central tibetan plateau a transitional area between monsoon dominated asia and westerlies dominated asia to examine the interplay between the two circulation systems and effects of other potential mechanisms on the temporal variability of holocene climatic conditions in the study area specifically this study has produced a twin record of palaeo hydrology and palaeo temperature from an alpine wetland sediment sequence using two sets of lipid based biomarker indices n alkanes and branched glycerol dialkyl glycerol tetraethers bgdgts the results show that 1 the asian summer monsoon has supplied moisture that helped initiate the wetland habitat around 8000 cal yr bp about 2000 years later than locations along the southeastern edge of the plateau 2 a significant decline in moisture supply is evident since the medieval warm period 3 the westerlies have transmitted variability of the north atlantic climate to the study area resulting in periodic increases in evaporation and causing short term expansion or contraction of the wetland and 4 the palaeo air temperature change follows closely that of global sea level and sea surface temperature implying a link to global ice volume change throughout the holocene this study concludes that the holocene climate history of central tibetan plateau is a result of monsoonal moisture supply interacted with the westerlies variability while the palaeo temperature has followed changes in global ice volume during the present warm interglacial

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

palaeoclimatic changes deduced from 13c 12c and c n ratios of karewa lake sediments india most long palaeoclimatic records based on isotope studies have come from deep sea cores however in order to obtain information on regional climatic variations it is essential to study continental deposits the chief limitation has been the lack of well preserved datable geological records with the exception of cave formations we report here values for the stable carbon isotope ratio 13c 12c and the elemental carbon to nitrogen c n ratio of the organic fraction of the palaeomagnetically and radiometrically dated pleistocene karewa lake sediments from kashmir india together the two ratios which are anticorrelated provide an excellent marker of the source of organic matter in the lake the karewa sediments indicate at least three major episodes of shallower than normal levels these episodes of shallow lake levels and hence a cold dry climatic regime are broadly correctable with deep sea records

sound velocity and density measurements of liquid iron up to 800 gpa a universal relation between birch s law coefficients for solid and liquid metals abstract we performed compressional sound velocity and density measurements on liquid iron at pressures up to 800 gpa with a newly refined shock compression method using a high power laser we found that sound velocity as a function of density can be fitted to a linear relation following birch s law for hot dense liquid as well as for the solid phase of iron with a slope ratio between the solid and liquid of approximately 1 5 a comparison of birch s law for solid and liquid metals indicates that the sound velocity in the liquid phase is about 10 lower than that in the solid phase at melting point density which is about 1 5 times larger than the initial density we suggest that these relations between birch s law coefficients for solid and liquid phases along the hugoniot are universal for metals

late holocene temperature fluctuations on the tibetan plateau abstract proxy data of palaeoclimate like ice cores tree rings and lake sediments document aspects of climate changes on the tibetan plateau during the last 2000 years the results show that the tibetan plateau experienced climatic episodes such as the warm intervals during ad 800 1100 and 1150 1400 the little ice age between ad 1400 and 1900 and an earlier cold period between the 4th and 6th centuries in addition temperatures varied from region to region across the plateau a warm period from ad 800 to 1100 in the northeastern tibetan plateau was contemporaneous with cooling in the southern tibetan plateau which experienced warming between ad 1150 and 1400 large scale trends in the temperature history from the northeastern tibetan plateau resemble those in eastern china more than the trends from the southern plateau the most notable similarities between the temperature variations of the tibetan plateau and eastern china are cold phases during ad 1100 1150 1500 1550 1650 1700 and 1800 1850

the early toarcian jurassic anoxic event stratigraphic sedimentary and geochemical evidence detailed paleogeographic studies in the southern alps suggest that an oxygen minimum model is appropriate for interpreting conditions on tethyan continental margins advection of manganese in this low oxygen layer may explain the local occurrence of carbonate ores of this element carbon sulfur and iron sulfur ratios although showing considerable scatter suggest that bottom waters at this time were locally euxinic containing free hydrogen sulfide this oceanic anoxic event was preceded by significant faunal turnover of ammonites in tethys and accompanied by widespread extinction of benthos in northern europe in response to the lateral spread of anoxic bottom waters during transgression similar changes may be recognized in other parts of the world other anoxic events may have taken place during the jurassic but documentation is as yet meagre furthermore models for such phenomena remain largely speculative although upwelling and increased planktonic productivity commencing in pre toarcian time are favored for the falciferum zone event documented here from author

a change from warm humid to cold dry climate conditions recorded in lower barremian clay dominated continental successions from the se iberian chain ne spain abstract a combined facies and clay mineralogy analysis of the continental succession recorded in the lower part of the blesa formation early barremian oliete subbasin ne spain allowed us to specify the palaeoclimatic and palaeoenvironmental conditions under which this sedimentary record originated six outcrops including clays clays marls and dm thick interbedded palustrine lacustrine limestone levels were logged and sampled for x ray diffraction and optical and electron microscopy analysis the lower levels consist of red clays with abundant ferruginous pisoids 1 5 mm in size and macropisoids 5 mm whereas the intermediate and upper levels are ochre and violet clays marls with few or no pisoids the pisoids normally consist of a nucleus and a cortex made up of several layers some pisoids have a fragment of a previous pisoid acting as a nucleus indicating local re working processes both the nucleus and the cortex are formed by hematite goethite variable contents of kaolinite and minor proportions of ilmenite their texture and mineralogy show an in situ growth interbedded limestone beds within the clay and clay marl dominated levels are formed by micrite microsparite and sparite these limestones are cemented by kaolinite and they also have pisoids indicating the occurrence of edaphic processes the red clays have the lowest calcite content and the highest hematite anatase diaspore goethite and kaolinite content by contrast the ochre and violet clays marls have higher illite content smectite is only detected in the ochre clays marls this mineral association is characteristic of lateritic palaeosols formed under warm and humid conditions kaolinite and smectite textures indicate that they are authigenic whereas illite may be of detrital origin the upward decrease in kaolinite hematite anatase diaspore and goethite content along with the increase in quartz content and the presence of smectite and illite reflect a change from warm and humid conditions to drier and colder conditions during the early barremian in the studied area

branched glycerol dialkyl glycerol tetraethers in lake sediments can they be used as temperature and ph proxies a series of surface sediments from 82 lakes of variable water depth and size was analyzed for glycerol dialkyl glycerol tetraethers gdgts in order to investigate the potential of the mbt cbt methylation ratio cyclization ratio of branched tetraethers as a continental palaeothermometer in lacustrine environments branched gdgts dominated in most sediments as indicated by the high branched vs isoprenoid tetraether bit values we observed that cbt and mbt varied substantially mean annual air temperature maat reconstructed and ph values were calculated using the cbt and mbt values and the calibration from the global soil data set the mbt cbt inferred temperatures were considerably lower than measured values nevertheless there was a significant correlation between maat reconstructed and maat observed on site although there was still considerable scatter r2 0 47 lacustrine sediments integrate organic remains of organisms in a lake and its drainage basin thereby offering a unique opportunity for calibrating mbt and cbt as small scale variability is averaged out since the source of the branched gdgts in the lake sediments is ambiguous it is not clear whether only temperature and ph in the catchment area are the driving factors therefore even in lake sediments with high concentrations of branched gdgts the straightforward application of mbt cbt as palaeoproxies may be difficult given the uncertainties regarding their source and origin

illite in aridic soils desert dusts and desert loess abstract in some desert loess deposits notably those of central asia illite dominates the clay fraction in others such as in the near east and north africa illite is a minor component the interaction between desert loess deposits and aridic desert soils via desert dusts is used to explain the difference in illite contents vertical profile distribution of illite as well as vertical distributions of soluble and exchangeable potassium are taken to indicate that illite forms pedogenetically in the surface horizon of aridic soils once formed it is stable and accumulates it is postulated that the potassium required for the illitazation process is introduced by aeolian dusts the process is facilitated by wetting and drying cycles dusts originating in deserts where they are presently produced by desert weathering of various rocks are defined as primary or juvenile dusts they have low illite contents such are the dusts that are carried from the eastern sahara and sinai peninsula northeast towards the middle east where they form local loess deposits the central asian dusts on the other hand have been subjected to numerous cycles of deflation and deposition resulting in relatively long residence times in the pedogenic environment of aridic soils this results in the enrichment of these dusts with illite the central asian desert loess deposits that interact with these dusts are consequently enriched with illite similar processes of illite enrichment may have operated in other areas such as australia

comparison of instrumental and gdgt based estimates of sea surface and air temperatures from the skagerrak sea surface temperatures ssts and annual mean air temperatures mats are estimated for the last 200 years from glycerol dialkyl glycerol tetraethers gdgts proxies in a marine sediment core from the skagerrak off southern norway the reconstructed values compare well with annual ssts and summer air temperatures obtained from composite regional instrumental records the results provide further confidence in the application of proxies based on gdgts to estimate past temperatures

carbonate to biosilica transition at the norian rhaetian boundary controlled by rift related subsidence in the western tethyan lagonegro basin southern italy abstract the lagonegro basin located in the southern apennines italy records a transition from carbonate sediments of the calcari con selce fm cherty limestone to biosiliceous sediments of the scisti silicei fm siliceous shale around the norian rhaetian boundary nrb upper triassic sedimentologic and chemostratigraphic analysis of three sections pignola abriola monte volturino and madonna del sirino representing a proximal to distal transect across the basin document marine productivity redox and chemical weathering conditions the basin was characterized by low to moderate productivity and mainly oxic deep waters with no systematic secular variation throughout the 10 myr long study interval a weathering proxy the chemical index of alteration cia shifts toward higher values from 0 70 to 0 80 in all three study sections suggesting development of warmer and or more humid conditions just before the nrb the lack of evidence for changes in marine productivity or redox conditions and the time transgressive nature of the carbonate biosilica transition suggests that the latter was caused not by changes in planktonic communities but rather by a rise in the ccd the most likely cause of which was seafloor subsidence within the actively rifting ionian ocean i e the westernmost branch of the tethys ocean the tectonically active character of the lagonegro basin is also reflected in evidence of synsedimentary paleoseismic activity e g numerous debris flows around the basin margins the present study thus documents sedimentologic changes within a marginal basin in a geologically young ocean

deuterium excess record in a southern tibetan ice core and its potential climatic implications a 55 m long ice core drilled close to bedrock from mt noijin kangsang on the southern tibetan plateau in summer 2007 was annually dated covering the period of 1864 2006 ad the stable isotope ratios 18o and d of the ice core were measured and thereby the deuterium excess d was calculated by d d 8 18o for the individual ice samples results show that the d values of the ice samples were predominantly controlled by the moisture sources the significant increasing trend of annual mean d values along the ice core is mainly related to the rapid warming of the tropical indian ocean although the tendency is subjected to the modulation by the western derived moisture the decreasing indian monsoon precipitation on the southern tibetan plateau physically linked with the increasing tropical indian ocean sst reduced the share of monsoon precipitation in the annual total accumulation making an additional contribution to the significant increase of annual mean d in the noijin kangsang ice core with high values during the past 143 years

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

evaluation of glycerol dialkyl glycerol tetraether proxies for reconstruction of the paleo environment on the qinghai tibetan plateau the uplift of the qinghai tibetan plateau has a great effect on local and global climate changes here we report the late holocene climate change in the northern plateau by using a 3490 year sediment core record from kusai lake glycerol dialkyl glycerol tetraethers gdgts collected from the core were examined in combination with other paleo environmental proxies the reconstructed mean annual air temperatures maat using branched gdgt membrane lipids of certain bacteria proxies are higher than the measured maat but much closer to measured summer air temperatures suggesting a possibility of a bias of the reconstructed maat towards summer temperatures the ph values derived from a branched gdgt proxy show a negative correlation with toc a lake productivity indicator in arid regions furthermore both cbt ph and toc show temporal cyclic changes which suggest that the branched gdgt derived ph index may be useful in reconstructing paleo ph values in a lacustrine system lastly the composition of isoprenoid gdgts membrane lipids of archaea shows a major shift around 1400 bp which is in line with a large increase in sediment soluble salts at this time but lags behind the onset of salt mineral precipitation by 600 yr suggesting that change in archaeal community composition and salt mineral precipitation may require different threshold values of salinity the results of this study demonstrate that useful paleo climatic and paleo environmental information can be extracted from the gdgts preserved in lake sediments

glacial interglacial indian summer monsoon dynamics the modern indian summer monsoon ism is characterized by exceptionally strong interhemispheric transport indicating the importance of both northern and southern hemisphere processes driving monsoon variability here we present a high resolution continental record from southwestern china that demonstrates the importance of interhemispheric forcing in driving ism variability at the glacial interglacial time scale as well interglacial ism maxima are dominated by an enhanced indian low associated with global ice volume minima in contrast the glacial ism reaches a minimum and actually begins to increase before global ice volume reaches a maximum we attribute this early strengthening to an increased cross equatorial pressure gradient derived from southern hemisphere high latitude cooling this mechanism explains much of the nonorbital scale variance in the pleistocene ism record